WO2025039376A1 - 正极材料及其制备方法、正极片与二次电池 - Google Patents

正极材料及其制备方法、正极片与二次电池 Download PDF

Info

Publication number
WO2025039376A1
WO2025039376A1 PCT/CN2023/129924 CN2023129924W WO2025039376A1 WO 2025039376 A1 WO2025039376 A1 WO 2025039376A1 CN 2023129924 W CN2023129924 W CN 2023129924W WO 2025039376 A1 WO2025039376 A1 WO 2025039376A1
Authority
WO
WIPO (PCT)
Prior art keywords
carbon
layer
positive electrode
electrode material
source
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/CN2023/129924
Other languages
English (en)
French (fr)
Inventor
徐荣益
曾绍洪
孔令涌
李意能
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Shenzhen Dynanonic Co Ltd
Original Assignee
Shenzhen Dynanonic Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from CN202311049485.9A external-priority patent/CN117080387A/zh
Priority claimed from CN202311049489.7A external-priority patent/CN117080388A/zh
Application filed by Shenzhen Dynanonic Co Ltd filed Critical Shenzhen Dynanonic Co Ltd
Priority to EP23923210.1A priority Critical patent/EP4535462A4/en
Priority to JP2024557963A priority patent/JP2025530949A/ja
Priority to US18/843,575 priority patent/US20260109604A1/en
Publication of WO2025039376A1 publication Critical patent/WO2025039376A1/zh
Anticipated expiration legal-status Critical
Pending legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/08—Intercalated structures, i.e. with atoms or molecules intercalated in their structure
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/82—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by IR- or Raman-data
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/14—Pore volume
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/16—Pore diameter
    • C01P2006/17—Pore diameter distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the technical field of positive electrode materials for lithium-ion batteries, and more specifically, to positive electrode materials and preparation methods thereof, positive electrode sheets and secondary batteries.
  • Lithium-ion batteries have the advantages of high energy density, good safety, no memory effect, and long cycle life. In recent years, they have become the mainstream of the global new energy power vehicle market.
  • the positive electrode material is one of the key materials that determine the performance of lithium-ion batteries.
  • the lithium manganese iron phosphate positive electrode material can increase the energy density by about 20%, and has better low-temperature performance. Compared with ternary positive electrode materials, it is low in cost and safer.
  • similar to lithium iron phosphate it has the defect of low electronic conductivity.
  • the current optimization synthesis method is mostly used, and the post-synthesis modification, such as nano-sizing and carbon coating, is used to improve the performance of lithium manganese iron phosphate.
  • the electronic conductivity of lithium iron manganese phosphate is lower than that of lithium iron phosphate, it needs to be prepared into finer nanoparticles to fully exert its performance.
  • the in-situ carbon coating layer itself is loose and porous. Therefore, the nano lithium iron manganese phosphate particles prepared in the process have a higher specific surface area.
  • the aforementioned nano lithium iron manganese phosphate particles are more difficult to process in full-electric pulping, mainly because the slurry is prone to produce more bubbles. After the slurry is screened, large bubbles are easy to break, but during the coating process, there are many small bubbles attached to the pole piece.
  • the bubbles on the pole piece will break and leave pits or form cavitation nuclei, which makes the pole piece uneven in thickness, further leading to a large number of fine cracks, peeling, powder loss and other phenomena on the pole piece, affecting the yield rate of the pole piece, and ultimately causing the battery capacity, internal resistance, cycle life and safety to deteriorate, seriously affecting the full-electric performance evaluation of lithium iron manganese phosphate.
  • defoaming is performed by increasing the amount of binder and solvent, reducing the viscosity by reducing the solid content, or prolonging the vacuum low-speed stirring time, the defoaming effect is not ideal and leads to increased economic and time costs.
  • the purpose of this application is to overcome the above-mentioned deficiencies of the prior art, to provide a positive electrode material and a preparation method thereof, a positive electrode sheet and a secondary battery, so as to solve the technical problem in the prior art that the existing nano-manganese iron phosphate lithium particles are difficult to process in full electric pulping, resulting in deterioration of the battery's capacity, internal resistance, cycle life and safety.
  • a positive electrode material including an inner core and a first carbon layer, wherein the first carbon layer is a multi-carbon intercalated layer, and the multi-carbon intercalated layer includes main skeleton carbon and modified carbon, wherein the main skeleton carbon is bonded to the surface of the inner core, and the modified carbon is intercalated and grown in the main skeleton carbon.
  • the carbon in the main skeleton carbon is in the form of stacked carbon sheets bonded to the surface of the inner core; and/or,
  • the carbon of the modified carbon is in the form of carbon flakes embedded in the main skeleton carbon; and/or,
  • the mass content of the main skeleton carbon in the multi-carbon intercalation layer is 80%-90%, and the mass content of the modified carbon in the multi-carbon intercalation layer is 10%-20%.
  • the length of the carbon sheet in the main skeleton carbon is greater than the length of the carbon sheet in the modified carbon, and the length of the carbon sheet in the modified carbon is less than 2 nm; and/or,
  • the pore volume of the multi-carbon mosaic layer is less than 0.070 cm 3 /g; and/or,
  • the thickness of the multi-carbon mosaic layer is less than 10 nm; and/or
  • the IG / ID value of the first carbon layer is 0.75-1.5.
  • the multi-carbon mosaic layer includes a carbon element and a first non-carbon element
  • the first non-carbon element includes at least one of N, S, P, and Li; and/or,
  • the mass content of the carbon element in the first carbon layer is 97%-98.5%, and the mass content of the first non-carbon element in the first carbon layer is 1.5%-3%.
  • the positive electrode material further includes a second carbon layer, which is an outer carbon layer, and the outer carbon layer is coated on the outer surface of the multi-carbon intercalated layer.
  • the pore volume of the outer carbon layer is less than 0.020 cm 3 /g; and/or,
  • the thickness of the outer carbon coating layer is less than 1.5 nm, and the thickness of the outer carbon coating layer is smaller than the thickness of the multi-carbon intercalated layer.
  • the graphitization degree of the second carbon layer is higher than that of the first carbon layer.
  • the long-range disorder degree of the carbon structure in the first carbon layer is higher than the long-range disorder degree of the carbon structure in the second carbon layer.
  • most of the carbon structures of the first carbon layer are longer carbon sheet structures, which are deposited on the surface of the inner core; most of the carbon structures of the second carbon layer are shorter carbon sheet structures, which are deposited on the surface of the first carbon layer in a non-continuous and directionally anisotropic manner; the size of the longer carbon sheet structure is larger than that of the shorter carbon sheet structure.
  • the second carbon layer includes a carbon element and a second non-carbon element
  • the second non-carbon element includes at least one of N, P, and Li; and/or,
  • the mass content of the carbon element in the second carbon layer is 98%-99%, and the mass content of the second non-carbon element in the second carbon layer is 1%-2%.
  • the IG / ID value of the second carbon layer is 1.0-1.9.
  • the inner core contains phosphorus element, and part of the phosphorus in the inner core forms C-P bonds and/or C-O-P bonds with part of the carbon in the multi-carbon intercalated layer.
  • the bonding ratio of C-P bond and C-O-P bond is 0.5%-1.15%.
  • the core is a lithium-phosphate-based positive electrode active material core; and/or,
  • the particle size of the core is less than 400nm.
  • the total pore volume of the positive electrode material is 0.04 cm 3 /g-0.10 cm 3 /g; and/or,
  • the specific surface area of the positive electrode material is 12.0 m 2 /g to 17.0 m 2 /g; and/or,
  • the IG / ID value of the positive electrode material is 0.8-1.25.
  • a method for preparing a positive electrode material which is used to prepare the positive electrode material, and the preparation method comprises the following steps:
  • the core is mixed with the first carbon source and the carbon source solvent to obtain a mixed material
  • the mixed material is sintered for a second time under an inert atmosphere, and an atomized second carbon source is introduced during the second sintering process.
  • the first carbon source is cracked in situ to form a main skeleton carbon that is accumulated on the surface of the inner core.
  • the second carbon source is cracked in situ and/or vapor deposited to form modified carbon.
  • the modified carbon is interwoven and embedded in the main skeleton carbon to form a first carbon layer, which is a multi-carbon embedded layer, to obtain a positive electrode material.
  • the core precursor material is a lithium iron manganese phosphate precursor
  • the preparation method of the lithium iron manganese phosphate precursor comprises the following steps:
  • the lithium source, iron source, phosphorus source, manganese source, precursor solvent and co-solvent are mixed and reacted in proportion to obtain a lithium manganese iron phosphate precursor.
  • the pH of the mixed solution obtained by mixing the lithium source, the iron source, the phosphorus source, the manganese source, the precursor solvent and the co-solvent is 5.0 to 7.5.
  • the first carbon source includes at least one of hydroxypropyl distarch phosphate, glucose, fructose, sucrose, lactose, stevioside, xylose, maltose, starch, cellulose, chitin, D-glucosamine, glucosamine sulfate, fructose phosphate, glucose-6-phosphate, N-acetylglucosamine, peptidoglycan, polyacrylate, polyethylene glycol, citric acid, malic acid, propylene, polypropylene glycol, polypropylene, polyacrylamide, lithium polyacrylate, polyvinyl alcohol, cyclodextrin, polyvinyl butyral, polystyrene, and graphite; and/or,
  • the second carbon source includes at least two of methanol, ethanol, ethyl acetate, polyethylene glycol, acetone, butanone, ether, acetic acid, oxalic acid, polypropylene glycol, aniline, benzylamine, para-diazine, ammonium citrate, ammonium formate, ammonium acetate, formamide, acetamide, propionamide, butyramide, monoisopropanolamine, N,N-dimethylethanolamine, dimethylethanolamine, and triethylenediamine.
  • At least one of the first carbon source and the second carbon source includes a carbon element and a first non-carbon element
  • the first non-carbon element includes at least one of N, S, P, and Li elements
  • the mass content of the carbon element in the total mass of the first carbon source and the second carbon source is 97%-98.5%
  • the mass content of the first non-carbon element in the total mass of the first carbon source and the second carbon source is 1.5%-3%.
  • the positive electrode material further includes a second carbon layer, which is an outer carbon layer.
  • a second carbon layer which is an outer carbon layer.
  • the atomized second carbon source is continuously introduced, and the second carbon source forms an outer carbon layer on the surface of the multi-carbon mosaic layer through in-situ cracking and/or vapor deposition.
  • the preparation method satisfies at least one of the following conditions (1)-(4):
  • the temperature of the first sintering is 350°C-660°C;
  • the temperature of the second sintering is 650°C-855°C;
  • the gas flow rate of the second carbon source atomizing gas is 10 mL/min-120 mL/min;
  • the second carbon source includes carbon and a second non-carbon element, the second non-carbon element includes at least one of N, P, and Li, the mass content of carbon in the second carbon source is 98%-99%, and the mass content of the second non-carbon element in the second carbon source is 1%-2%.
  • a positive electrode sheet is provided, which is made of the positive electrode material mentioned above or the positive electrode material prepared by the method for preparing the positive electrode material mentioned above.
  • a secondary battery comprising the above-mentioned positive electrode sheet.
  • the positive electrode material provided in the present application uses a multi-carbon intercalation layer to coat the positive electrode active material core, and the multi-carbon intercalation layer includes a main skeleton carbon and a modified Carbon, the main skeleton carbon is combined with the surface of the inner core, and the modified carbon is embedded in the main skeleton carbon, which can reduce the generation of pores and make the porosity of the multi-carbon embedded layer lower than the porosity of the existing in-situ carbon coating layer; the pore structure of the multi-carbon embedded layer is reduced, so that the time for the solvent to infiltrate the pores during the slurry making process is shortened, and the volume of the solvent required to infiltrate the pores is also reduced, which is conducive to reducing the generation of slurry bubbles, and it is easy to prepare a slurry with good rheology and good uniformity, thereby reducing a series of problems caused by bubbles and improving the energy density of a unit electrode;
  • the preparation method of the positive electrode material provided in the present application is to perform a second high-temperature sintering and introduce an atomized second carbon source, so that the first carbon source is in-situ cracked at high temperature to form a main skeleton carbon, and the second carbon source is in-situ cracked and/or vapor deposited to form modified carbon, and the modified carbon is interwoven and embedded in the main skeleton carbon to form a multi-carbon embedded layer, which effectively reduces pore generation and obtains a multi-carbon embedded layer with low porosity, which helps to improve the electronic conductivity of the positive electrode material;
  • the positive electrode sheet provided in the present application is made of the above-mentioned positive electrode material.
  • the positive electrode material includes a core and a multi-carbon interlayer.
  • the multi-carbon interlayer has a low porosity, so bubbles are not easily generated during the slurry making process, thereby avoiding the problem of bubbles generated during the slurry screening, electrode coating and electrode drying processes, and preventing the uneven thickness of the electrode sheet, cracks, peeling and powder loss of the electrode sheet caused by pits or cavitation nuclei generated by bubble rupture, thereby effectively improving the yield rate of the positive electrode sheet;
  • the secondary battery provided in the present application includes the above-mentioned positive electrode sheet, which effectively improves the problems of uneven thickness, cracks, peeling and powder loss, and improves the capacity, internal resistance, cycle life and safety of the secondary battery.
  • FIG1 is a flow chart of a method for preparing a positive electrode material according to an embodiment of the present application
  • FIG2 is a flow chart of a method for preparing a positive electrode material according to Example 1 of the present application.
  • FIG3 is a schematic diagram showing the structures of the positive electrode material of Example 1 of the present application and the positive electrode material of Comparative Example 1;
  • FIG4 is a TEM image of the positive electrode material of Example 1 of the present application.
  • FIG5 is a SEM image of the positive electrode material of Example 1 of the present application.
  • FIG6 is a pore size distribution diagram of the positive electrode material of Example 1 of the present application and the positive electrode material of Comparative Example 1;
  • FIG7 is a schematic diagram of the structure of the positive electrode material of an embodiment of the present application.
  • FIG8 is a TEM photo of the positive electrode material of Example 7 of the present application.
  • FIG9 is a SEM photograph of the positive electrode material of Example 7 of the present application.
  • FIG10 is a Raman spectrum fitting analysis diagram of the positive electrode material of Example 7 of the present application.
  • FIG3 11, the inner core of Example 1; 12, the multi-carbon mosaic layer of Example 1; 13, the outer carbon layer; 21, the inner core of Comparative Example 1; 22, the carbon coating layer of Comparative Example 1;
  • FIG. 7 10 , positive electrode material; 11 , inner core; 12 , first carbon layer; 13 , second carbon layer.
  • An embodiment of the present application provides a positive electrode material, including an inner core and a first carbon layer, wherein the first carbon layer is a multi-carbon intercalated layer, which includes a main skeleton carbon and modified carbon, wherein the main skeleton carbon is bonded to the surface of the inner core, and the modified carbon is intercalated and grown in the main skeleton carbon.
  • the first carbon layer is a multi-carbon intercalated layer, which includes a main skeleton carbon and modified carbon, wherein the main skeleton carbon is bonded to the surface of the inner core, and the modified carbon is intercalated and grown in the main skeleton carbon.
  • the positive electrode material provided in the embodiment of the present application adopts a multi-carbon intercalation layer (first carbon layer) to coat the inner core, and the multi-carbon intercalation layer includes a main skeleton carbon and a modified carbon, the main skeleton carbon is bonded to the surface of the inner core, and the modified carbon is intercalated and grown in the main skeleton carbon, which can reduce the generation of pores and make the porosity of the multi-carbon intercalation layer lower than the porosity of the existing in-situ carbon coating layer.
  • first carbon layer first carbon layer
  • the pore structure of the multi-carbon intercalation layer is reduced, so that the time for the solvent to infiltrate the pores during the slurrying process is shortened, and the volume of the solvent required to infiltrate the pores is also reduced, which is conducive to reducing the generation of slurry bubbles, and it is easy to prepare a slurry with good rheology and good uniformity, thereby reducing a series of problems caused by bubbles and improving the energy density of a unit electrode.
  • the main skeleton carbon is formed by high-temperature in-situ pyrolysis of a first carbon source, and the carbon in the main skeleton carbon is in the form of stacked carbon sheets bonded to the surface of the inner core, and the modified carbon is formed by in-situ pyrolysis and/or vapor deposition of a second carbon source, and the modified carbon is interwoven and embedded in the main skeleton carbon, and the carbon in the modified carbon is in the form of carbon sheets, the first carbon source is different from the second carbon source, and the carbon chain of the first carbon source is longer than the carbon chain of the second carbon source.
  • the first carbon source and the second carbon source are pyrolyzed and interwoven at the same time, and the second carbon source is pyrolyzed and/or vapor deposited to form the overall pore structure of the multi-carbon interlayer less than that of only in-situ carbon coating.
  • the carbon structure of the modified carbon is arranged randomly, and is mostly deposited in a non-continuous and directional manner.
  • the carbon sheet produced by the high-temperature in-situ pyrolysis of the first carbon source is longer and flatter.
  • the modified carbon is deposited on the surface of the inner core, which plays a role of introducing and supporting the modified carbon, so that the modified carbon formed by in situ pyrolysis and/or vapor deposition can be better coated on the surface of the inner core through the main skeleton carbon.
  • the multi-carbon mosaic layer formed by interweaving can completely coat the inner core to obtain a carbon coating layer with uniform thickness, and the surface of the multi-carbon mosaic layer tends to be smooth, reducing the generation of pores.
  • the carbon sheet length of the main skeleton carbon is greater than that of the modified carbon, which is conducive to forming a support structure and covering the core, and the carbon sheet length of the modified carbon is shorter, which is conducive to forming an interlaced mosaic. In some embodiments, the carbon sheet length of the modified carbon is less than 2nm.
  • the pore volume of the multi-carbon intercalated layer can reach ⁇ 0.07 cm 3 /g, with a typical value of 0.04 cm 3 /g-0.06 cm 3 /g, which is much smaller than the pore volume of the existing in-situ carbon coating layer of 0.12-0.20 cm 3 /g.
  • the specific surface area is smaller than the existing in-situ carbon coating layer, which can shorten the time for the solvent to infiltrate the pores.
  • the typical value of the embodiments of the present application refers to the average value or normal value of a certain performance of the product, which is a representative parameter that can characterize the characteristics of a group (or the characteristics of a certain subgroup).
  • the mass content of the main skeleton carbon in the multi-carbon interlayer is 80%-90%, and the mass content of the modified carbon in the multi-carbon interlayer is 10%-20%, or in some embodiments, the mass content of the main skeleton carbon in the multi-carbon interlayer is 82%-91%, and the mass content of the modified carbon in the multi-carbon interlayer is 9%-18%.
  • a small proportion of short structure modified carbon can have an effect similar to particle grading, which is conducive to a tighter stacking of the multi-carbon interlayer.
  • the main thickness of the multi-carbon interlayer is contributed by the main skeleton carbon, and the modified carbon serves as an auxiliary modification.
  • the main skeleton carbon of the multi-carbon intercalated layer is seamlessly and parallelly deposited on the surface of the inner core to form a seamless coating, thereby reducing the probability of shedding and increasing the stability of the positive electrode material.
  • the multi-carbon intercalated layer includes carbon elements and intercalated non-carbon elements (first non-carbon elements), the intercalated non-carbon elements include at least one of N, S, P, and Li, the mass content of carbon elements in the multi-carbon intercalated layer is 97%-98.5%, and the mass content of intercalated non-carbon elements in the multi-carbon intercalated layer is 1.5%-3%.
  • a small amount of non-carbon elements are uniformly distributed in the multi-carbon intercalated layer.
  • the introduction of a small amount of non-carbon elements in the multi-carbon intercalated layer can improve the graphitization degree of the residual carbon layer to a certain extent, and the increase of sp2 carbon is beneficial to improve the electronic conductivity of the positive electrode material.
  • the inner core of the positive electrode active material is a lithium phosphate-containing inner core
  • part of the carbon in the multi-carbon intercalated layer forms C-P bonds and C-O-P bonds with part of the phosphorus in the inner core
  • the multi-carbon intercalated layer and the inner core are in surface contact, forming a gapless coating
  • the binding energy of C-P bonds and C-O-P bonds is stronger than the van der Waals bonds generated on the contact surface, and their formation is conducive to improving the bonding strength and stability between the multi-carbon intercalated layer and the inner core, and reducing the probability of peeling off of the multi-carbon intercalated layer and the outer carbon layer during processing and pulping and battery recycling.
  • the multi-carbon interlocking layer is formed by the main skeleton carbon formed by the high-temperature in-situ pyrolysis of the first carbon source and the modified carbon formed by the high-temperature in-situ pyrolysis and/or vapor deposition of the second carbon source, the two are interwoven and interlocked, the probability of forming C-P bonds and C-O-P bonds between the carbon in the multi-carbon interlocking layer and the phosphorus in the inner core can reach 0.5%-1.15%, the multi-carbon interlocking layer has a strong bonding force and high stability with the inner core, and is not easy to peel off.
  • the degree of peeling of the multi-carbon interlayer is as low as 0.8%.
  • bonding probability in the embodiments of the present application means that in the process of preparing precursors such as lithium manganese iron phosphate, the C-H bond or C-O bond in the solvent carbon source may undergo a coupling reaction with the P-H bond or P-O-H bond in the phosphorus source under the action of a catalyst to form a C-P bond or C-O-P bond, and still exist after sintering.
  • the lithium phosphate-containing core is, for example, a lithium manganese phosphate core, a lithium iron phosphate core or a lithium iron manganese phosphate core.
  • the core is a lithium iron manganese phosphate core with an olivine structure
  • the positive electrode material is a carbon-coated lithium iron manganese phosphate positive electrode material.
  • the particle size of the core is less than 400nm, the particle size of most cores is 80nm-300nm, and the cores with a particle size of 80nm-300nm account for 70%-80% of the total number of core particles.
  • the particle size of the core is less than 400nm, the particle size of most cores is 50nm-300nm, and the cores with a particle size of 50nm-300nm account for 70%-80% of the total number of core particles, and nano-scale lithium manganese iron phosphate positive electrode materials can be prepared.
  • the positive electrode material also includes a second carbon layer, which is an outer carbon layer.
  • the outer carbon layer is coated on the outer surface of the multi-carbon interlayer.
  • the outer carbon layer and the multi-carbon interlayer can cooperate to improve the electronic conductivity of the positive electrode material.
  • the inner core contains manganese, it can also inhibit the dissolution of manganese in the inner core, thereby improving the cycle life of the positive electrode material.
  • the outer carbon layer (second carbon layer) is formed on the outer surface of the multi-carbon interlayer by high-temperature in-situ cracking and/or vapor deposition using a second carbon source. From the inner core to the outside, it is the second layer in the carbon coating layer of the positive electrode material, and there is no macroscopic gap between the outer carbon layer and the multi-carbon interlayer.
  • the multi-carbon interlayer contains carbon formed by high-temperature cracking of both the first carbon source and the second carbon source
  • the carbon sheet structure in the single carbon layer is in point contact or line contact with the carbon sheet structure formed by cracking the first carbon source in the multi-carbon interlayer
  • the two are connected by a C-C chemical bond
  • the carbon sheet structure in the outer carbon layer is in surface contact with the carbon sheet structure formed by cracking the first carbon source in the multi-carbon interlayer, the two are connected by a van der Waals bond.
  • the homologous carbon in the outer carbon layer and the multi-carbon interlayer is connected by a C-C chemical bond, and a "pinning structure" is formed at the same time, which enhances the bonding force between the multi-carbon interlayer and the outer carbon layer.
  • the thickness of the multi-carbon mosaic layer is less than 10 nm, with a typical value of 3 nm-6 nm, a typical value of 2.8 nm-5.8 nm, etc.;
  • the thickness of the carbon coating is less than 1.5nm, with a typical value of 0.65nm-1.0nm, and the thickness of the outer carbon coating is less than or equal to the thickness of the multi-carbon intercalation layer.
  • the outer carbon coating is a thin carbon layer in the carbon coating, similar to a "membrane structure".
  • the thicker multi-carbon intercalation layer is beneficial to the stability of the overall carbon skeleton and is not easily damaged during processing stress or battery recycling.
  • the thinner outer carbon coating layer can minimize the increase in the thickness of the overall carbon layer while ensuring that it can fill and modify the multi-carbon intercalation layer, which is beneficial to shortening the Li + transmission path.
  • the overall thickness of the outer carbon layer is thin, and the small molecular carbon structure cracked by the second carbon source is continuously accumulated, so that the pore volume of the outer carbon layer can be ⁇ 0.020cm3 /g, and the typical value is 0.010-0.014cm3 /g.
  • the reduction of the pore volume of the outer carbon layer is conducive to the reduction of the specific surface area of the positive electrode material, and the reduction of bubble nuclei generated by the solvent infiltration of the positive electrode material during pulping; at the same time, the reduction of the pore structure is conducive to reducing the contact between the positive electrode material and the electrolyte, weakening the interface reaction between the positive electrode material and the electrolyte, and reducing the erosion of the electrolyte on the positive electrode material.
  • the pore volume of the outer carbon layer is smaller than the pore volume of the multi-carbon interlayer, and the two ends of the pores of the outer carbon layer are respectively connected to the pores of the multi-carbon interlayer and the outside of the outer carbon layer.
  • the air in the pores of the multi-carbon interlayer has a certain resistance to the infiltration of the solution, which increases the resistance of the solution entering the pores of the outer carbon layer, further reducing the possibility of bubbles generated due to solvent infiltration of the positive electrode material during pulping processing.
  • the total pore volume of the positive electrode material is 0.04 cm 3 /g-0.10 cm 3 /g.
  • the carbon structures in the outer carbon layer are mostly short carbon sheets. Due to the randomness of in-situ pyrolysis and/or vapor deposition, the arrangement of the carbon structures in the outer carbon layer also has a certain randomness. The carbon structures are mostly stacked in a non-continuous and directional manner.
  • the electron conduction rate can be further increased and the electrochemical performance of the positive electrode material can be improved.
  • the pore volume of the positive electrode material is lower than the pore volume of the existing in-situ carbon coating layer, and the specific surface area of the positive electrode material will also be lower than the specific surface area of the existing in-situ carbon coating layer.
  • the specific surface area of the positive electrode material is 12m2 /g- 17.0m2 /g.
  • the specific surface area of the positive electrode material is too small, for example, less than 12m2 /g, the carbon content is too small, which may cause uneven carbon coating; if the specific surface area of the positive electrode material is too large, for example, higher than 17m2 /g, the dispersion of the slurry during the slurrying process is more difficult, and agglomeration problems may occur, thereby affecting the electrical performance. Therefore, when the specific surface area is in the range of 12m2 / g- 17.0m2 /g, the agglomeration of the particles is reduced, which is conducive to the dispersion of the active material and the uniform coating of the conductive agent during processing.
  • the specific surface area in the embodiments of the present application refers to the total area per unit mass of a material, and the unit is m2 / m3 or m2 /g, and generally refers to the specific surface area of solid materials, such as powders, fibers, particles, flakes, blocks, etc.
  • the calculation method is area/volume, or area/mass.
  • the graphitization degree of the second carbon layer 13 is higher than the graphitization degree of the first carbon layer 12 .
  • the carbon-coated positive electrode material 10 provided in the embodiment of the present application adopts the second carbon layer 13 and the first carbon layer 12 to cooperate in transmitting electrons.
  • the degree of graphitization of the second carbon layer 13 is higher than that of the first carbon layer 12.
  • the electron migration resistance of the second carbon layer 13 is less than that of the first carbon layer 12, which is beneficial to the transfer of electrons from the inner core 11 to the outside, increases the conduction rate of electrons, and thereby improves the electrical properties of the positive electrode material 10.
  • the multilayer carbon structure helps to inhibit the dissolution of manganese in the inner core and improve the cycle life of the positive electrode material.
  • most of the carbon structures in the second carbon layer are short carbon sheets.
  • the arrangement of the carbon structures in the second carbon layer also has a certain randomness due to the randomness of in-situ pyrolysis and/or vapor deposition, and the carbon structures are mostly stacked in a non-continuous and directionally heterogeneous manner.
  • the long-range disorder degree of the carbon structure in the second carbon layer is lower than that in the first carbon layer, vapor deposition belongs to gaseous mass transfer in the atomic category, which makes the short-range order degree of the carbon structure in the second carbon layer higher, that is, the degree of graphitization is higher.
  • the IG / ID value of the second carbon layer is 1.0-1.9, and the typical value is 1.2-1.6. In some embodiments, the IG / ID value of the positive electrode material is 0.8-1.25.
  • the degree of graphitization of the first carbon layer is higher than that of in-situ carbon coating using only the first carbon source. If the degree of graphitization of the first carbon layer is characterized by IG to ID , the degree of graphitization of the first carbon layer can reach 0.75-1.5, and the typical value is 0.8-1.1.
  • the IG / ID value of the second carbon layer is greater than the IG / ID value of the first carbon layer.
  • the increase in the degree of graphitization of the first carbon layer is conducive to the transfer of electrons from the inner core to the outside, while the increase in the degree of graphitization of the second carbon layer is conducive to increasing the conduction rate of electrons between the particles of the carbon-coated positive electrode material, so that the electrons of the inner core migrate from the inner core through the first carbon layer to the second carbon layer, which are all conducive to improving the electrochemical performance of the carbon-coated positive electrode material.
  • most of the carbon structure of the first carbon layer is a longer carbon sheet structure, and the longer carbon sheet structure is accumulated and bonded to the surface of the inner core; most of the carbon structure of the second carbon layer is a shorter carbon sheet structure, and is accumulated and coated on the surface of the first carbon layer in a non-continuous and directionally anisotropic manner; the size of the longer carbon sheet structure is larger than the size of the shorter carbon sheet structure.
  • the organic carbon chain of the first carbon source is longer than the organic carbon chain of the second carbon source
  • the size of the carbon sheet of the carbon structure of the first carbon layer is larger than the size of the carbon sheet of the second carbon layer, which is conducive to the uniform coverage of the first carbon layer. It covers the outer surface of the inner core and provides a growth structural basis for the carbon structure of the second carbon layer, thereby supporting the carbon structure of the second carbon layer.
  • the second carbon layer includes carbon and a second non-carbon element (external non-carbon element), the mass content of carbon in the second carbon layer is 98%-99%, the second non-carbon element includes at least one of N, P, and Li elements, and N element can be selected, and the mass content of the second non-carbon element in the second carbon layer is 1%-2%.
  • the introduction of a small amount of non-carbon elements in the second carbon layer can improve the graphitization degree of the residual carbon layer to a certain extent, and the increase of sp2 carbon is beneficial to improve the electronic conductivity of the carbon-coated positive electrode material.
  • the first carbon layer can be a single carbon layer or formed by a variety of carbon sources through a suitable process.
  • the main thing is that there is a difference in the degree of graphitization between the first carbon layer and the second carbon layer, and the degree of graphitization of the second carbon layer is higher than that of the first carbon layer, so that the electrons in the inner core have a tendency to transfer outward.
  • the present application also provides a method for preparing a positive electrode material, which can be used to prepare the positive electrode material.
  • the preparation method comprises the following steps:
  • the core is obtained through high-temperature sintering to prepare materials for the next step.
  • the core precursor material in order to obtain core particles with suitable particle size and clean surface, is crushed and ball-milled before the first sintering.
  • the core precursor material can be shaped into particles using a drum vacuum ball mill, and the shaping time can be 15 minutes to 60 minutes, so that the multi-carbon intercalation layer can tightly cover the core and is suitable for preparing positive electrode materials and positive electrode sheets.
  • the protective atmosphere of the vacuum ball mill can be at least one of hydrogen, nitrogen, and argon.
  • the inert atmosphere during the first sintering is any one of nitrogen and argon.
  • the temperature of the first sintering is 350° C.-650° C.
  • the sintering time can be selected according to actual conditions, for example, it can be selected to be 2 h-10 h.
  • the temperature of the first sintering is 355° C.-660° C.
  • the sintering time can be selected according to actual conditions, for example, it can be selected as 2h-8h.
  • the core is a lithium iron manganese phosphate core
  • the corresponding core precursor material is a lithium iron manganese phosphate precursor
  • the method for preparing the lithium manganese iron phosphate precursor comprises the following steps:
  • the lithium source, iron source, manganese source, phosphorus source, precursor solvent and co-solvent are mixed and reacted in proportion to obtain a lithium manganese iron phosphate precursor.
  • the lithium source, iron source, manganese source, and phosphorus source are configured according to the element molar ratio of Li:(Fe+Mn):P (0.90-1.10):(0.90-1.10), wherein the molar ratio of Fe:Mn in the iron source and the manganese source is 1:(0-10), for example, it can be 1:0, 1:0.1, 1:0.5, 1:0.75, 1:1, 1:2, 1:3, 1:5, 1:7, 1:8, 1:10.
  • the proportion of the precursor solvent and the co-solvent is added according to the mass ratio of the total mass of the lithium source, the iron source, the manganese source, and the phosphoric acid, and the proportion of the precursor solvent can be 150%-500%; the mass proportion of the co-solvent does not exceed 5%, or in some embodiments, the proportion of the precursor solvent can be 200%-600%; the mass proportion of the co-solvent does not exceed 6%.
  • the lithium source includes at least one of lithium carbonate, lithium sulfate, lithium phosphate, and lithium dihydrogen phosphate.
  • the manganese source includes at least one of manganese sulfate, manganese carbonate, manganese acetate, manganese nitrate, manganese chloride, manganese oxide, and manganese hydroxide.
  • the iron source includes at least one of ferric chloride, ferric carbonate, ferric acetate, ferrous acetate, and ferric phosphate.
  • the phosphorus source includes at least one of diammonium phosphate, monoammonium phosphate, ferric phosphate, red phosphorus, white phosphorus, phosphorus pentoxide, phosphorus trioxide, ammonium phosphate, and ferric phosphate.
  • the precursor solvent includes at least one of water, methanol, ethanol, ethylene glycol, glycerol, polyethylene glycol, dimethyl sulfoxide, hexadecyltrimethylammonium salicylate, and the like.
  • the cosolvent may be at least one of nitric acid, phosphoric acid, ammonium dihydrogen phosphate, acetic acid, oxalic acid, citric acid, ascorbic acid (catalyst), and polyvinyl pyrrolidone (anti-agglomeration agent).
  • the function of the cosolvent is to promote the dissolution of each component material, disperse the mixed slurry, catalyze the reaction process, regulate the pH of the reaction system, and participate in the formation of at least one of the precursors of the lithium manganese iron phosphate material.
  • the pH of the mixed solution of lithium source, iron source, phosphorus source, manganese source, precursor solvent and co-solvent is 5.0-7.5, which is used to regulate the morphology of the core precursor material and the residual alkali amount of the core precursor material after sintering, so as to prevent the pH value from being too high and causing gel problems during processing, affecting the processing performance evaluation of the positive electrode material.
  • the reaction of the lithium source, the iron source, the phosphorus source, the manganese source, the precursor solvent and the auxiliary solvent includes any one of a liquid phase hydrothermal reaction, a coprecipitation reaction and a sol-gel reaction.
  • the first carbon source infiltrates the surface of the inner core.
  • the carbon structure generated by its high-temperature in-situ cracking can adhere to the inner core surface, and even part of the carbon structure is chemically bonded to the phosphorus element of the inner core.
  • the mass ratio of the core to the first carbon source can be 1:(4-16), and the mass ratio of the core to the carbon source solvent can be 1:(0.5-10). Alternatively, the mass ratio of the core to the first carbon source can be 1:(4-18), and the mass ratio of the core to the carbon source solvent can be 1:(0.4-12).
  • the carbon source solvent is mainly used to dissolve and/or disperse the first carbon source, form a mixed liquid with the first carbon source, and provide a solution environment for the core, so that the mixed liquid can evenly infiltrate the surface of the core, and prepare the foundation for forming a first carbon layer of uniform thickness on the core.
  • the first carbon source includes at least one of hydroxypropyl distarch phosphate, glucose, fructose, sucrose, lactose, stevioside, xylose, maltose, starch, cellulose, chitin, D-glucosamine, glucosamine sulfate, fructose phosphate, glucose-6-phosphate, N-acetylglucosamine, peptidoglycan, polyacrylate, polyethylene glycol, citric acid, malic acid, propylene, polypropylene glycol, polypropylene, polyacrylamide, lithium polyacrylate, polyvinyl alcohol, cyclodextrin, polyvinyl butyral, polystyrene, and graphite.
  • the inner core contains phosphorus, and part of the phosphorus in the inner core forms C-P bonds and/or C-O-P bonds with part of the carbon in the multi-carbon interlayer, and the first carbon source includes a carbohydrate compound, and the carbohydrate compound includes, for example, at least one of glucose, fructose, and sucrose.
  • the first carbon source includes a carbon element and a first non-carbon element
  • the first non-carbon element includes at least one of N, S, P, and Li elements
  • the mass content of the carbon element in the first carbon source is 96%-98%
  • the mass content of the first non-carbon element in the first carbon source is 2%-4%.
  • the carbon source solvent includes at least one of water, glycerol, ethanol, ethylene glycol, isopropanol, polyethylene glycol, ethyl acetate, and ethyl acetate.
  • the mixed material is sintered for a second time under an inert atmosphere, and an atomized second carbon source is introduced during the sintering process.
  • the first carbon source is cracked in situ to form a main skeleton carbon that is accumulated on the surface of the inner core material.
  • the second carbon source is cracked in situ and/or vapor deposited to form modified carbon.
  • the modified carbon is interwoven and embedded in the main skeleton carbon to form a multi-carbon embedded layer to obtain a positive electrode material.
  • the first carbon source and the second carbon source are simultaneously cracked at high temperature, wherein the carbon structure generated after the cracking of the first carbon source is stacked in parallel on the surface of the inner core to form a main skeleton carbon, and the carbon structure generated after the cracking of the second carbon source is formed into modified carbon through in situ cracking and/or vapor deposition, and the modified carbon is interwoven and embedded in the main skeleton carbon, and the main skeleton carbon and the modified carbon together form a multi-carbon embedded layer.
  • the first carbon source is a macromolecular organic matter
  • the second carbon source is a small molecule organic matter, or the carbon chain of the first carbon source is longer than the carbon chain of the second carbon source.
  • the carbon sheets of the main skeleton carbon formed are longer and can be stacked parallel to the surface of the inner core, and the carbon sheets of the modified carbon are shorter, for example, the maximum size of the carbon sheets of the modified carbon is less than 2nm, and can be interwoven and embedded in the main skeleton carbon.
  • the second carbon source includes carbon and a first non-carbon element
  • the first non-carbon element includes at least one of N, S, P, and Li elements
  • N element is optional.
  • the first non-carbon element in the first carbon source and the first non-carbon element in the second carbon source can be independently at least one of N, S, P, and Li elements, that is, in the embodiment, the first non-carbon element in the first carbon source is not limited to be the same or different from the first non-carbon element in the second carbon source.
  • At least one of the first carbon source and the second carbon source includes a carbon element and a first non-carbon element
  • the first non-carbon element includes at least one of N, S, P, and Li elements
  • the mass content of the carbon element in the total mass of the first carbon source and the second carbon source is 97%-98.5%
  • the mass content of the first non-carbon element in the total mass of the first carbon source and the second carbon source is 1.5%-3%.
  • the inert atmosphere of the second sintering includes at least one of hydrogen, nitrogen, and argon.
  • the temperature of the second sintering can be 660° C.-855° C., and the sintering time can be selected according to actual conditions, for example, it can be selected as 4h-12h.
  • the preparation method of the positive electrode material provided in the embodiment of the present application comprises the following steps: a second high-temperature sintering and introduction of an atomized second carbon source to make the first carbon source high
  • the main skeleton carbon is formed by in-situ pyrolysis at low temperature
  • the second carbon source is formed by in-situ pyrolysis and/or vapor deposition to form modified carbon.
  • the modified carbon is interwoven and embedded in the main skeleton carbon to form a first carbon layer.
  • the first carbon layer is a multi-carbon embedded layer, which effectively reduces pore generation and obtains a multi-carbon embedded layer with low porosity.
  • the multi-carbon embedded layer has a high degree of graphitization, which helps to improve the electronic conductivity of the positive electrode material.
  • the second carbon layer is an outer carbon layer, after forming the multi-carbon intercalated layer, as shown in FIG1 , the following step S4 is further included:
  • the multi-carbon interlayer is basically formed, and the atomized second carbon source continues to be introduced while maintaining the temperature of the second sintering.
  • the second carbon source is accumulated on the surface of the multi-carbon interlayer through in-situ cracking and/or vapor deposition to form an outer carbon layer.
  • the generated outer carbon layer has a high degree of graphitization, which can improve the electronic conductivity of the positive electrode material.
  • the second carbon source used in the first carbon layer is the same as the second carbon source used in the second carbon layer.
  • the second carbon source can be continuously introduced during the preparation process, thereby avoiding the complicated operation of repeatedly replacing the atomized second carbon source, simplifying the process and improving process efficiency.
  • the atomized second carbon source continued to be introduced in step S4 can be the same as or different from the atomized second carbon source in step S3, that is, in some embodiments, the atomized second carbon source continued to be introduced in step S4 includes at least two of methanol, ethanol, ethyl acetate, polyethylene glycol, acetone, butanone, ether, acetic acid, oxalic acid, polypropylene glycol, aniline, benzylamine, para-diazine, ammonium citrate, ammonium formate, ammonium acetate, formamide, acetamide, propionamide, butyramide, monoisopropanolamine, N,N-dimethylethanolamine, dimethylethanolamine, and triethylenediamine.
  • the temperature in step S4 can be the same as or different from the temperature of the second sintering in step S3. That is, in some embodiments, the temperature of continuing to introduce the atomized second carbon source for in-situ cracking and/or vapor deposition in step S4 can include the above-mentioned second sintering temperature of 650°C-855°C.
  • the reaction time of step S4 can be estimated according to the input amount of the second carbon source, and the thickness of the outer carbon layer can be controlled by controlling the flow rate and time of continuing to introduce the atomized second carbon source.
  • step S4 the amount of the second carbon source added is controlled by the introduction time and gas flow rate of the atomizing gas, which can be 4h-12h, such as 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, etc.
  • the gas flow rate of the second carbon source atomizing gas can be 10mL/min-110mL/min of the gas flow rate of the second carbon source atomizing gas in the above step S3, or, it can be 15mL/min-120mL/min, such as 15mL/min, 30mL/min, 45mL/min, 60mL/min, 80mL/min, 85mL/min, 90mL/min, 100mL/min or 120mL/min, etc., optionally, 45-90mL/min.
  • the introduced atomized second carbon source includes a carbon element and a second non-carbon element
  • the second non-carbon element includes at least one of N, P, and Li elements
  • the mass content of the carbon element in the second carbon source is 98%-99%
  • the mass content of the second non-carbon element in the second carbon source is 1%-2%.
  • the second carbon source forms a second carbon layer on the surface of the first carbon layer through in-situ pyrolysis and/or vapor deposition, forming two different carbon layer structures.
  • vapor deposition belongs to gaseous mass transfer in the atomic category, which makes the carbon structure in the second carbon layer have a higher degree of short-range order, that is, a higher degree of graphitization.
  • a graphitization degree step is generated between the first carbon layer and the second carbon layer, which guides the direction of electron transfer in the inner core, and can improve the electronic conduction rate of the positive electrode material.
  • the preparation method is simple and controllable, and has good industrial application prospects.
  • the embodiment of the present application also provides a positive electrode sheet, which is made of the above-mentioned positive electrode material.
  • the positive electrode material includes an inner core, a multi-carbon interlayer and an outer carbon layer.
  • the multi-carbon interlayer and the outer carbon layer have low porosity, so no bubbles or very few bubbles are generated during the slurry making process, thereby avoiding the problems of bubbles generated during slurry screening, electrode coating and electrode drying, and eliminating the problems of uneven electrode thickness, cracks, peeling and powder loss on the electrode sheet caused by pits or cavitation nuclei caused by bubble rupture, thereby effectively improving the yield rate of the positive electrode sheet.
  • the embodiment of the present application also provides a secondary battery, including the above-mentioned positive electrode sheet, which does not have the problems of uneven thickness, cracks, peeling and powder loss, thereby improving the capacity, internal resistance, cycle life and safety of the secondary battery.
  • the positive electrode material of this embodiment includes an inner core 11, a multi-carbon intercalated layer 12 and an outer carbon layer 13.
  • the multi-carbon intercalated layer 12 includes a main skeleton carbon and modified carbon.
  • the main skeleton carbon is deposited on the surface of the inner core 11, and the modified carbon is intercalated and grown in the main skeleton carbon; the outer carbon layer 13 is coated on the surface of the multi-carbon intercalated layer 12.
  • the mass content of the main skeleton carbon in the multi-carbon intercalation layer 12 is 85%, and the mass content of the modified carbon in the multi-carbon intercalation layer is 15%;
  • the pore volume of the multi-carbon intercalation layer 12 is 0.0495 cm 3 /g, the pore volume of the outer carbon layer 13 is 0.0122 cm 3 /g, and the total pore volume is 0.0472 cm 3 /g;
  • the thickness of the multi-carbon intercalation layer 12 is 3.14 nm, and the thickness of the outer carbon layer 13 is 0.86 nm;
  • the particle size of the core 11 is 52 nm-368 nm;
  • the specific surface area of the positive electrode material is 14.16 m 2 /g;
  • the method for preparing the positive electrode material of this embodiment includes the following steps:
  • the core precursor material is subjected to a first sintering at 400° C. in a nitrogen atmosphere for 6 hours to obtain a core.
  • S3 Mix the kernel with glucose and fructose phosphate (first carbon source) and water (carbon source solvent) to obtain a mixed material.
  • the mass ratio of the kernel to the first carbon source is 1:10, and the mass ratio of the kernel to water is 1:4.
  • the mass ratio of fructose phosphate in the first carbon source is 4%, and the non-carbon element in the first carbon source is P.
  • the mixed material is sintered for a second time at 700°C for 6 hours, and atomized ethanol, polyethylene glycol and N,N-dimethylethanolamine (the second carbon source) are introduced in a mass ratio of 3:6:1.
  • the non-carbon element in the second carbon source is N.
  • the gas flow rate of the atomized second carbon source is 60 mL/min.
  • the introduction time is 6 hours to form a multi-carbon mosaic layer on the surface of the inner core.
  • S5 Maintain the temperature of the second sintering, and introduce atomized ethanol, polyethylene glycol and N,N-dimethylethanolamine (the second carbon source).
  • the gas flow rate of the atomized second carbon source is 60 mL/min, and the introduction time is 2 h.
  • An outer carbon layer is formed on the surface of the multi-carbon interlayer to obtain a positive electrode material.
  • FIG. 4 which is a transmission electron microscope (TEM) image of the obtained positive electrode material, the thickness of the multi-carbon intercalated layer and the outer carbon layer is uniform.
  • TEM transmission electron microscope
  • the positive electrode material particles are relatively round and have a relatively low specific surface area, which is conducive to processing.
  • the positive electrode material of this embodiment has the same material structure as that of Embodiment 1, except that: the mass content of the main skeleton carbon in the multi-carbon intercalation layer is 90%, and the mass content of the modified carbon in the multi-carbon intercalation layer is 10%; the pore volume of the multi-carbon intercalation layer is 0.0687 cm 3 /g, the pore volume of the outer carbon layer is 0.0184 cm 3 /g, and the total pore volume is 0.0725 cm 3 /g; the thickness of the multi-carbon intercalation layer is 4.28 nm, and the thickness of the outer carbon layer is 0.98 nm; the particle size of the inner core is 43 nm-322 nm; and the specific surface area of the positive electrode material is 16.35 m 2 /g.
  • the core precursor material is subjected to a first sintering at 400° C. in a nitrogen atmosphere for 6 hours to obtain a core.
  • S3 Mixing the kernel with sucrose and chitosan (first carbon source) and water to obtain a mixed material.
  • the mass ratio of the kernel to the first carbon source is 1:14
  • the mass ratio of the kernel to water is 1:4
  • the mass ratio of chitosan in the first carbon source is 4%
  • the non-carbon element in the first carbon source is N.
  • the mixed material is sintered for a second time at 750°C for 6 hours, and atomized acetic acid, polypropylene glycol and benzylamine (second carbon source) are introduced in a mass ratio of 3:6:1.
  • the non-carbon element in the second carbon source is N.
  • the gas flow rate of the atomized second carbon source is 80 mL/min.
  • the introduction time is 6 hours to form a multi-carbon mosaic layer on the surface of the inner core.
  • S5 Maintain the temperature of the second sintering, and introduce atomized acetic acid, polypropylene glycol and benzylamine (the second carbon source).
  • the gas flow rate of the atomized second carbon source is 70 mL/min, and the introduction time is 2 h.
  • An outer carbon layer is formed on the surface of the multi-carbon interlayer to obtain a positive electrode material.
  • the positive electrode material of this embodiment has the same material structure as that of Embodiment 1, except that: the mass content of the main skeleton carbon in the multi-carbon intercalation layer is 90%, and the mass content of the modified carbon in the multi-carbon intercalation layer is 10%; the pore volume of the multi-carbon intercalation layer is 0.0724 cm 3 /g, the pore volume of the outer carbon layer is 0.0125 cm 3 /g, and the total pore volume is 0.0681 cm 3 /g; the thickness of the multi-carbon intercalation layer is 3.65 nm, and the thickness of the outer carbon layer is 0.8 nm; the particle size of the inner core is 45 nm-316 nm; and the specific surface area of the positive electrode material is 15.87 m 2 /g.
  • the lithium manganese iron phosphate material precursor is subjected to a first sintering at 400° C. in a nitrogen atmosphere for 6 hours to obtain a core.
  • S3 Mixing the kernel with glucose and fructose phosphate (the first carbon source) and water to obtain a mixed material.
  • the mass ratio of the kernel to the first carbon source is 1:14, the mass ratio of the kernel to water is 1:4, the mass ratio of fructose phosphate in the first carbon source is 4%, and the non-carbon element in the first carbon source is P.
  • the mixed material is sintered for a second time at 750°C for 6 hours, and atomized ethanol, polyethylene glycol and N,N-dimethylethanolamine (the second carbon source) are introduced in a mass ratio of 3:6:1.
  • the non-carbon element in the second carbon source is N.
  • the gas flow rate of the atomized second carbon source is 60 mL/min.
  • the introduction time is 6 hours to form a multi-carbon mosaic layer on the surface of the inner core.
  • S5 Maintain the temperature of the second sintering, and introduce atomized ethanol, polyethylene glycol and N,N-dimethylethanolamine (the second carbon source).
  • the gas flow rate of the atomized second carbon source is 80 mL/min, and the introduction time is 2 h.
  • An outer carbon layer is formed on the surface of the multi-carbon interlayer to obtain a positive electrode material.
  • the positive electrode material of this embodiment has the same material structure as that of Embodiment 1, except that: the mass content of the main skeleton carbon in the multi-carbon intercalation layer is 85%, and the mass content of the modified carbon in the multi-carbon intercalation layer is 15%; the pore volume of the multi-carbon intercalation layer is 0.0513 cm 3 /g, the pore volume of the outer carbon layer is 0.0267 cm 3 /g, and the total pore volume is 0.0604 cm 3 /g; the thickness of the multi-carbon intercalation layer is 3.22 nm, and the thickness of the outer carbon layer is 1.26 nm; the particle size of the inner core is 60 nm-350 nm; and the specific surface area of the positive electrode material is 15.28 m 2 /g.
  • the core precursor material is subjected to a first sintering at 400° C. in a nitrogen atmosphere for 6 hours to obtain a core.
  • S3 Mixing the kernel with glucose and fructose phosphate (first carbon source) and water to obtain a mixed material.
  • the mass ratio of the kernel to the first carbon source is 1:10
  • the mass ratio of the kernel to water is 1:4
  • the mass ratio of fructose phosphate in the first carbon source is 4%
  • the non-carbon element in the first carbon source is P.
  • the positive electrode material of this embodiment has the same material structure as that of embodiment 1, except that: the mass content of the main skeleton carbon in the multi-carbon intercalation layer is 85%, and the mass content of the modified carbon in the multi-carbon intercalation layer is 15%; the pore volume of the multi-carbon intercalation layer is 0.0506cm 3 /g, the pore volume of the outer carbon layer is 0.0131cm 3 /g, and the total pore volume is 0.0490cm 3 /g; the thickness of the multi-carbon intercalation layer is 3.20nm, and the thickness of the outer carbon layer is 0.90nm; the particle size of the inner core is 54nm-355nm; the specific surface area of the positive electrode material is 14.52m 2 /g;
  • S3 Mixing the kernel with glucose (the first carbon source) and water to obtain a mixed material.
  • the mass ratio of the kernel to the first carbon source is 1:10, and the mass ratio of the kernel to water is 1:4.
  • the mixed material is sintered for a second time at 700°C for 6 hours, and atomized ethanol and polyethylene glycol (the second carbon source) are introduced in a mass ratio of 3:7.
  • the gas flow rate of the atomized second carbon source is 60 mL/min and the introduction time is 6 hours to form a multi-carbon mosaic layer on the surface of the inner core.
  • the positive electrode material of this embodiment has the same material structure as that of Embodiment 1, except that: the mass content of the main skeleton carbon in the multi-carbon intercalation layer is 85%, and the mass content of the modified carbon in the multi-carbon intercalation layer is 15%; the pore volume of the multi-carbon intercalation layer is 0.0498 cm 3 /g, and the total pore volume is 0.0498 cm 3 /g; the thickness of the multi-carbon intercalation layer is 3.06 nm, and there is no outer carbon layer; the particle size of the inner core is 62 nm-384 nm; and the specific surface area of the positive electrode material is 14.76 m 2 /g.
  • the core precursor material is subjected to a first sintering at 400° C. in a nitrogen atmosphere for 6 hours to obtain a core.
  • S3 Mixing the kernel with glucose and fructose phosphate (first carbon source) and water to obtain a mixed material.
  • the mass ratio of the kernel to the first carbon source is 1:10
  • the mass ratio of the kernel to water is 1:4
  • the mass ratio of fructose phosphate in the first carbon source is 4%
  • the non-carbon element in the first carbon source is P.
  • the mixed material is sintered for a second time at 700°C for 8 hours, and atomized ethanol, polyethylene glycol and N,N-dimethylethanolamine (the second carbon source) are introduced in a mass ratio of 3:6:1.
  • the non-carbon element in the second carbon source is N.
  • the gas flow rate of the atomized second carbon source is 60 mL/min.
  • the introduction time is 6 hours to form a multi-carbon mosaic layer on the surface of the inner core.
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at 420° C. for 5.5 h to obtain a core;
  • S3 Mix the core with the first carbon source lactose and hydroxypropyl distarch phosphate and carbon source solvent water to obtain a mixed material.
  • the mass ratio of the core to the first carbon source is 1:12, and the mass ratio of the core to the carbon source solvent is 1:5.
  • the mass ratio of hydroxypropyl distarch phosphate in the first carbon source is 5%, and the non-carbon element in the first carbon source is P;
  • S4 The mixed material is sintered for the second time at 720°C for 7 hours, and atomized second carbon sources of butanone, polyethylene glycol and ammonium formate are introduced in a mass ratio of 3.2:5.8:1, the non-carbon element in the second carbon source is N, the gas flow rate of the atomized second carbon source is 65 mL/min, and the introduction time is 7 hours, forming a first carbon layer on the surface of the core;
  • S5 Maintain the temperature of the second sintering, and introduce atomized second carbon sources such as butanone, polyethylene glycol and ammonium formate.
  • the gas flow rate of the atomized second carbon source is 65 mL/min, and the introduction time is 2.5 h.
  • a second carbon layer is formed on the surface of the first carbon layer to obtain a positive electrode material.
  • the positive electrode material of this embodiment includes a core (i.e., an inner core), a first carbon layer, and a second carbon layer.
  • the first carbon layer is bonded to the surface of the core, and the second carbon layer is coated on the surface of the first carbon layer.
  • the degree of graphitization of the second carbon layer is higher than that of the first carbon layer.
  • the thickness of the first carbon layer is 4.12nm
  • the thickness of the second carbon layer is 0.97nm
  • the particle size of the core is 40nm-342nm
  • the IG / ID value of the first carbon layer is 0.90
  • the IG / ID value of the second carbon layer is 1.12
  • the degree of graphitization of the positive electrode material is 0.97.
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at 420° C. for 5.5 h to obtain a core;
  • S3 Mix the core with the first carbon source fructose and D-glucosamine, and carbon source solvent water to obtain a mixed material.
  • the mass ratio of the core to the first carbon source is 1:16, and the mass ratio of the core to the carbon source solvent is 1:5.
  • the mass ratio of D-glucosamine in the first carbon source is 5%, and the non-carbon element in the first carbon source is N;
  • S4 The mixed material is sintered for a second time at 670°C for 7 hours, and atomized second carbon sources of methanol, polypropylene glycol and aniline are introduced in a mass ratio of 3.2:5.8:1, the non-carbon element in the second carbon source is N, the gas flow rate of the atomized second carbon source is 95 mL/min, and the introduction time is 7 hours, forming a first carbon layer on the surface of the core;
  • the positive electrode material of this embodiment includes a core (i.e., an inner core), a first carbon layer, and a second carbon layer.
  • the first carbon layer is bonded to the surface of the core, and the second carbon layer is coated on the surface of the first carbon layer.
  • the degree of graphitization of the second carbon layer is higher than that of the first carbon layer.
  • the thickness of the first carbon layer is 3.42nm
  • the thickness of the second carbon layer is 0.86nm
  • the particle size of the core is 78nm-546nm
  • the IG / ID value of the first carbon layer is 1.10
  • the IG / ID value of the second carbon layer is 1.38.
  • the first carbon layer includes carbon element and a first non-carbon element, the first non-carbon element includes P element, and the mass content of carbon element in the first carbon layer is 98.48%, and the mass content of the first non-carbon element in the first carbon layer is 1.52.
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at 420° C. for 5.5 h to obtain a core;
  • S3 Mix the core with the first carbon source lactose and hydroxypropyl distarch phosphate and carbon source solvent water to obtain a mixed material.
  • the mass ratio of the core to the first carbon source is 1:16, and the mass ratio of the core to the carbon source solvent is 1:5.
  • the mass ratio of hydroxypropyl distarch phosphate in the first carbon source is 5%, and the non-carbon element in the first carbon source is P;
  • S4 The mixed material is sintered for a second time at 800°C for 7 hours, and atomized second carbon sources of butanone, polyethylene glycol and ammonium formate are introduced in a mass ratio of 3.2:5.8:1, the non-carbon element in the second carbon source is N, the gas flow rate of the atomized second carbon source is 95 mL/min, and the introduction time is 7 hours, forming a first carbon layer on the surface of the core;
  • S5 Maintain the temperature of the second sintering, and introduce atomized second carbon sources such as butanone, polyethylene glycol and ammonium formate.
  • the gas flow rate of the atomized second carbon source is 95 mL/min, and the introduction time is 2.5 h.
  • a second carbon layer is formed on the surface of the first carbon layer to obtain a positive electrode material.
  • the positive electrode material of this embodiment includes a core (i.e., an inner core), a first carbon layer and a second carbon layer, wherein the thickness of the first carbon layer is 3.08 nm, and the thickness of the second carbon layer is 0.77 nm; the particle size of the core is 60 nm-454 nm; the IG / ID value of the first carbon layer is 0.94, the IG / ID value of the second carbon layer is 1.14, and the degree of graphitization of the positive electrode material is 1.02.
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at 420° C. for 5.5 h to obtain a core;
  • S3 Mix the core with the first carbon source lactose and hydroxypropyl distarch phosphate and carbon source solvent water to obtain a mixed material.
  • the mass ratio of the core to the first carbon source is 1:8, and the mass ratio of the core to the carbon source solvent is 1:5.
  • the mass ratio of hydroxypropyl distarch phosphate in the first carbon source is 5%, and the non-carbon element in the first carbon source is P;
  • S4 The mixed material is sintered for the second time at 670°C for 7 hours, and atomized second carbon sources of butanone, polyethylene glycol and ammonium formate are introduced in a mass ratio of 3.2:5.8:1, the non-carbon element in the second carbon source is N, the gas flow rate of the atomized second carbon source is 35 mL/min, and the introduction time is 7 hours, forming a first carbon layer on the surface of the core;
  • S5 Maintain the temperature of the second sintering, and introduce atomized second carbon sources such as butanone, polyethylene glycol and ammonium formate.
  • the gas flow rate of the atomized second carbon source is 35 mL/min, and the introduction time is 2.5 h.
  • a second carbon layer is formed on the surface of the first carbon layer to obtain a positive electrode material.
  • the positive electrode material of this embodiment includes a core (i.e., an inner core), a first carbon layer, and a second carbon layer, wherein the second carbon layer is coated on the surface of the first carbon layer, and the degree of graphitization of the second carbon layer is higher than that of the first carbon layer.
  • the thickness of the first carbon layer is 3.32nm
  • the thickness of the second carbon layer is 0.92nm
  • the particle size of the core is 58nm-365nm
  • the IG / ID value of the first carbon layer is 1.01
  • the IG / ID value of the second carbon layer is 1.23
  • the degree of graphitization of the positive electrode material is 1.08.
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at 420° C. for 5.5 h to obtain a core;
  • the mixed material is sintered for the second time at 720°C for 7 hours, and atomized second carbon sources of butanone and polyethylene glycol are introduced in a mass ratio of 3.2:6.8.
  • the gas flow rate of the atomized second carbon source is 65 mL/min and the introduction time is 7 hours to form a first carbon layer on the surface of the core;
  • the positive electrode material of this embodiment includes an inner core (core), a multi-carbon intercalation layer (first carbon layer) and an outer carbon layer (second carbon layer), the first carbon layer includes a main skeleton carbon and a modified carbon, the main skeleton carbon is deposited on the surface of the inner core, and the modified carbon is intercalated and grown in the main skeleton carbon; the second carbon layer is coated on the surface of the first carbon layer, and the degree of graphitization of the second carbon layer is higher than that of the first carbon layer.
  • the thickness of the first carbon layer is 3.20nm
  • the thickness of the second carbon layer is 0.90nm
  • the particle size of the inner core is 50nm-372nm
  • the IG / ID value of the first carbon layer is 1.06
  • the IG / ID value of the second carbon layer is 1.32
  • the IG / ID value of the positive electrode material is 1.13.
  • the core precursor material is subjected to a first sintering at 400° C. in a nitrogen atmosphere for 6 hours to obtain a core.
  • S3 Mix the kernel with glucose and fructose phosphate (first carbon source) and water (carbon source solvent) to obtain a mixed material.
  • the mass ratio of the kernel to the first carbon source is 1:10, and the mass ratio of the kernel to water is 1:4.
  • the mass ratio of fructose phosphate in the first carbon source is 4%, and the non-carbon element in the first carbon source is P.
  • S4 The mixed material is sintered for the second time at 720°C for 7 hours, and atomized second carbon sources of butanone, polyethylene glycol and ammonium formate are introduced in a mass ratio of 3.2:5.8:1, the non-carbon element in the second carbon source is N, the gas flow rate of the atomized second carbon source is 65 mL/min, and the introduction time is 7 hours, forming a first carbon layer on the surface of the core;
  • S5 Maintain the temperature of the second sintering, and introduce atomized second carbon sources such as butanone, polyethylene glycol and ammonium formate.
  • the gas flow rate of the atomized second carbon source is 65 mL/min, and the introduction time is 2.5 h.
  • a second carbon layer is formed on the surface of the first carbon layer to obtain a positive electrode material.
  • the positive electrode material of this comparative example includes a core 21 and a carbon coating layer 22 coated on the surface of the core 21 .
  • the total pore volume of the carbon coating layer 22 is 0.137 cm 3 /g and the thickness is 3.10 nm.
  • the particle size of the core 21 is 64 nm-395 nm.
  • the specific surface area of the positive electrode material is 17.85 m 2 /g.
  • the preparation method of the positive electrode material of this comparative example comprises the following steps:
  • the core precursor material is subjected to a first sintering at 400° C. in a nitrogen atmosphere for 6 hours to obtain a core.
  • S3 Mix the kernel with glucose and fructose phosphate (the first carbon source) and water to obtain a mixed material.
  • the mass ratio of the first carbon source is 1:10, and the mass ratio of the core to water is 1:4.
  • the mass ratio of fructose phosphate in the first carbon source is 4%, and the non-carbon element in the first carbon source is P.
  • the positive electrode material of this comparative example includes a core and a first carbon layer, wherein the first carbon layer is deposited on the surface of the core, wherein the thickness of the first carbon layer is 3.25 nm, the particle size of the core is 62 nm-408 nm, the IG / ID value of the first carbon layer is 1.05, and the IG / ID value of the positive electrode material is 1.04.
  • the preparation method of the positive electrode material of this comparative example comprises the following steps:
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at 420° C. for 5.5 h to obtain a core;
  • the mixed material is sintered for the second time at 720°C for 9.5 hours, and atomized second carbon sources of butanone, polyethylene glycol and ammonium formate are introduced in a mass ratio of 3.2:5.8:1.
  • the non-carbon element in the second carbon source is N.
  • the gas flow rate of the atomized second carbon source is 65 mL/min.
  • the introduction time is 7 hours to form a first carbon layer on the surface of the core.
  • This comparative example provides a positive electrode material, including a core, a first carbon layer and a second carbon layer, wherein the first carbon layer is deposited on the surface of the core, the second carbon layer is coated on the surface of the first carbon layer, and the graphitization degree of the second carbon layer is higher than the graphitization degree of the first carbon layer.
  • the thickness of the first carbon layer is 3.12 nm; the particle size of the core is 65 nm-465 nm; and the IG / ID value of the positive electrode material is 0.69.
  • the preparation method of the positive electrode material of this comparative example comprises the following steps:
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at a temperature of 420° C. for 5.5 h to obtain a core;
  • This comparative example provides a positive electrode material, including a core, a first carbon layer and a second carbon layer, wherein the first carbon layer is deposited on the surface of the core, the second carbon layer is coated on the surface of the first carbon layer, and the graphitization degree of the second carbon layer is higher than the graphitization degree of the first carbon layer.
  • the thickness of the first carbon layer is 3.17 nm
  • the thickness of the second carbon layer is 1.05 nm
  • the particle size of the core is 52 nm-403 nm
  • the IG / ID value of the first carbon layer is 1.08
  • the IG / ID value of the second carbon layer is 1.02
  • the IG / ID value of the positive electrode material is 1.05.
  • the preparation method of the positive electrode material of this comparative example comprises the following steps:
  • the core precursor material is sintered for the first time in a nitrogen atmosphere at 420° C. for 5.5 h to obtain a core;
  • S3 Mix the core with the first carbon source lactose and hydroxypropyl distarch phosphate and carbon source solvent water to obtain a mixed material.
  • the mass ratio of the core to the first carbon source is 1:12, and the mass ratio of the core to the carbon source solvent is 1:5.
  • the mass ratio of hydroxypropyl distarch phosphate in the first carbon source is 5%, and the non-carbon element in the first carbon source is P;
  • the mixed material is sintered for the second time at 720°C for 7 hours, and the second carbon source butanone, polyethylene glycol and ammonium formate, with a mass ratio of 3.2:5.8:1, the non-carbon element in the second carbon source is N, the gas flow rate of the atomized second carbon source is 65 mL/min, the introduction time is 7 h, and a first carbon layer is formed on the surface of the core;
  • Carbon layer thickness A transmission electron microscope (TEM) was used to photograph the carbon layer of the positive electrode material, and Image J software was used to calculate the thickness of the carbon layer.
  • the test results of the carbon layer thickness of Examples 1-6 and Comparative Example 1 are shown in Table 1, and the test results of the carbon layer thickness of Examples 7-12 and Comparative Examples 2-4 are shown in Table 2.
  • the TEM photograph of the positive electrode material of Example 7 is shown in Figure 8.
  • Core particle size The carbon layer of the positive electrode material was photographed using a scanning electron microscope (SEM), and the primary particle size of the particles was calculated using Image J software.
  • SEM scanning electron microscope
  • Table 1 The results of Examples 1-6 and Comparative Example 1 are shown in Table 1, and the results of Examples 7-12 and Comparative Examples 2-4 are shown in Table 2.
  • Table 9 The SEM photograph of the core (kernel) of Example 7 is shown in Figure 9.
  • Carbon layer pore volume The pore volume of the carbon layer of the positive electrode material is tested by a static nitrogen adsorption method. 2-3g of sample is placed in a U-shaped sample tube, heated and degassed under vacuum, and then placed in liquid nitrogen. The powder surface adsorbs nitrogen, and the adsorption pressure and the volume of gas adsorbed on the surface of the substance are measured to obtain data such as pore volume and pore size distribution.
  • the pore volume and pore size distribution diagrams of the positive electrode material of Example 1 and the positive electrode material of Comparative Example 1 are shown in Figure 6. Specifically, the pore volume and pore size test results of the positive electrode materials of Examples 1-6 and Comparative Example 1 are shown in Table 1.
  • Powder resistivity The powder resistivity of the positive electrode material was tested using an automatic planning powder resistivity tester, with a sample mass of 0.5000-0.5050 g, a test pressure of 8 MPa, and a holding time of 5 s.
  • the powder resistivity can reflect the external conductivity of the material, and can also reflect the electron transmission capacity and coating uniformity of the carbon coating layer of the positive electrode material from the side.
  • the test results of Examples 7-12 and Comparative Examples 2-4 are shown in Table 2.
  • Carbon content The carbon content of the positive electrode material was tested using a carbon-sulfur analyzer. The sample mass was about 0.1 g and the co-solvent was 1.5 g. The test results of Examples 7-12 and Comparative Examples 2-4 are shown in Table 2.
  • Graphitization degree Raman spectrometer (Raman) is used to test the carbon spectrum of the positive electrode material carbon layer (including the first carbon layer and the total carbon layer of the positive electrode material, and the second carbon layer is collected separately by a ceramic sheet for testing), with a scanning range of 3500cm ⁇ 1 ⁇ 100cm ⁇ 1 and a laser wavelength of 532nm. Since Raman scattering is very sensitive to the offset symmetry reaction in the carbon structure, the carbon material with graphite structure will show two characteristic peaks, D (Defect) peak and G (Graphite) peak, in its Raman spectrum.
  • the position of D peak is near 1350cm ⁇ 1 , representing a defective graphite layer structure; G peak is near 1580cm ⁇ 1 , representing a complete graphite layer structure, and both D peak and G peak belong to sp 2 hybridized carbon.
  • the sp2 hybridized carbon peak and the sp3 hybridized carbon peak of the disordered structure can be separated, and IG / ID is used to characterize the degree of graphitization of the carbon material. The larger the value, the higher the degree of graphitization.
  • the Raman spectrum fitting analysis graph of the core of Example 7 is shown in Figure 10, and the Raman spectrum fitting analysis results of the positive electrode materials of Examples 7-12 and Comparative Examples 2-4 are shown in Table 2.
  • Positive electrode sheet The positive electrode slurry was prepared by mixing NMP: lithium manganese iron phosphate positive electrode material: Super P: PVDF in a mass ratio of 100:93:2:3. The mixing method was ball milling for 120 min. The rotation speed was set to 30 Hz. After homogenization-coating-drying-cutting operations, positive electrode sheets were prepared respectively. The positive electrode sheets were baked in a vacuum oven at 100°C for 12 h to constant weight.
  • Negative electrode metallic lithium sheet.
  • Diaphragm Use polyethylene (PE) diaphragm.
  • Electrolyte is a 1 mol/L LiPF 6 solution, and the solvent is composed of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1.
  • Assembly of secondary batteries flatten the lithium sheet, diaphragm, positive electrode sheet, gasket, spring and positive electrode shell in turn at the center of the negative electrode shell, and drip an appropriate amount of electrolyte on the diaphragm to moisten it. After assembly, use a button battery packaging machine to package the battery to obtain a button battery. After standing for 12 hours, put it on the shelf and conduct corresponding electrochemical performance tests.
  • Test method for positive electrode slurry The battery is tested at a temperature of 25°C ⁇ 2°C and a humidity of ⁇ 2% RH according to the operating procedures of the battery charge and discharge tester to obtain the 0.1C discharge capacity data of the simulated battery. The results are shown in Tables 1 and 2.
  • the phosphate positive electrode material prepared in Example 1 of the present application has the lowest specific surface area and total pore volume while ensuring the most excellent 0.1C charge and discharge capacity.
  • the positive electrode slurry prepared further has no bubbles, which is due to the modified filling effect of the modified carbon obtained by in-situ cracking and/or vapor deposition of small pore volume.
  • the prepared positive electrode material After changing the type, amount and sintering conditions of the first carbon source and the second carbon source, the prepared positive electrode material has an increased specific surface area and pore volume, a decreased electrical performance, and a small amount of bubbles appear in the further prepared positive electrode slurry compared with Example 1.
  • the dosage of the first carbon source in step S3 and the second carbon source in step S5 are changed respectively to prepare the positive electrode materials of Examples 3 and 4, the thicknesses of the multi-carbon intercalated layer and the outer carbon layer increase accordingly, the specific surface area and the total pore volume both increase, and the electrical properties decrease slightly.
  • the slurry prepared from the positive electrode material of Example 3 has bubbles, while there are no bubbles in Example 4.
  • the particle geometric properties and electrical properties of the positive electrode material of Example 4 are better than those of Example 3, which indicates that the modified carbon formed by the second carbon source by in-situ pyrolysis and/or vapor deposition has less pore structure and better electronic conductivity.
  • the multi-carbon intercalated layer and the outer carbon layer of the positive electrode material of Example 5 do not contain non-carbon elements, and their pore volume and specific surface area are slightly larger than those of Example 1, but the electrical properties are slightly worse, indicating that the introduction of non-carbon elements into the carbon layer can make the carbon layer denser and improve the electronic conductivity of the positive electrode material, which may be related to its ability to increase the degree of graphitization of the carbon layer.
  • the carbon layer of the positive electrode material in Example 6 only includes a multi-carbon intercalated layer, and the total pore volume is small.
  • the prepared slurry also does not contain bubbles, but the electrical properties are poor, indicating that the outer carbon layer has the effect of enhancing the electronic conductivity of the positive electrode material, which is related to its high degree of graphitization and further modification of the surface of the particle multi-carbon intercalated layer.
  • the positive electrode material of Comparative Example 1 was only in-situ carbon coated, and its comprehensive performance was the worst, and the prepared positive electrode slurry also had a large number of bubbles.
  • the comparison results of the particle geometry characteristics, electrical properties, and slurry bubble conditions of the positive electrode materials of the embodiment and the comparative example show that the positive electrode material with a multi-carbon intercalated intermediate layer and an outer carbon layer prepared in the embodiment of the present application can reduce the porosity in the carbon layer, effectively reduce the specific surface area of the material, and at the same time improve the electrical properties of the material, and ultimately eliminate or improve the bubbles in the slurry.
  • Table 2 shows the physicochemical parameters and carbon layer graphitization degree of the positive electrode materials of Examples 7-12 and Comparative Examples 2-4. It can be seen from Table 2 combined with the data in Table 1 that the phosphate positive electrode material prepared in Example 7 of the present application has a moderate carbon content, the first carbon layer, the second carbon layer and the total carbon coating layer of the positive electrode material all have a high degree of graphitization, a low resistivity, a small range of primary particle size, the highest 0.1C charge and discharge capacity per gram, and the best overall performance.
  • Example 7 the physical and chemical indicators, graphitization degree and electrical performance changes of the positive electrode materials of other examples are compared and analyzed, and it can be concluded that:
  • Example 8 After changing the types of the first carbon source and the second carbon source from step S3 to step S5, increasing the amount of the carbon source, and reducing the second sintering temperature, the carbon content of the positive electrode material increased, the graphitization degree of the carbon layer decreased, the resistivity increased, the primary particle size was the smallest, but the electrical performance decreased, indicating that the excessively high carbon content and the excessively thick carbon layer made it more difficult for lithium ions in the positive electrode material to be deintercalated, and the reduced graphitization degree of the carbon layer after the sintering temperature was reduced was not conducive to the conduction of electrons between the carbon layers;
  • step S3 to step S5 When the amounts of the first carbon source and the second carbon source in step S3 to step S5 are increased and the second sintering temperature is raised to prepare the positive electrode material of Example 9, the carbon content increases, the graphitization degree of the carbon layer is the highest, the resistivity is the lowest, but the electrical performance is the worst. This is mainly attributed to the significant increase in the primary particle size of the positive electrode material after the sintering temperature is increased, which increases the diffusion distance of lithium ions in the crystal and deteriorates the material kinetics.
  • step S3 to step S5 When the amount of the first carbon source and the second carbon source in step S3 to step S5 is reduced, and the second sintering temperature is reduced to prepare the positive electrode material of Example 10, the carbon content is reduced, the thickness of the carbon layer is thinned, the degree of graphitization is reduced, the resistivity is increased, and the electrical performance is reduced, indicating that it is difficult to form a good carbon-coated conductive network when the amount of carbon source is too small, and it is also difficult to make the carbon layer form more graphite layer structures when the temperature is reduced, which leads to a decrease in electrical performance;
  • the first carbon layer and the second carbon layer of the positive electrode material of Example 11 do not contain non-carbon elements, and the carbon content and the carbon layer thickness are similar to those of Example 7, but the degree of graphitization of the two carbon layers is reduced, the resistivity is correspondingly increased, and the electrical performance is reduced, which indicates that the non-carbon elements contained in the first carbon source and the second carbon source are conducive to the carbon layer forming a more complete graphite layer structure;
  • the carbon content of the positive electrode material is reduced, the carbon layer thickness is thinned, the degree of graphitization is slightly reduced, and the resistivity is increased, but they are all similar to Example 7, and the electrical properties are relatively good, indicating that when the carbon source amount and the sintering temperature are close to the conditions in Example 7, even if the carbon source type is changed, the positive electrode material with good electrical properties can be obtained.
  • the core (kernel) of the positive electrode material of Comparative Example 2 has only the first carbon layer outside and no second carbon layer, and its carbon content and carbon layer thickness are correspondingly reduced.
  • the degree of graphitization of the carbon layer decreases, the resistivity increases, and the electrical properties decrease, indicating that the second carbon layer, as a carbon layer with a higher degree of graphitization, can effectively improve the overall electronic conductivity of the positive electrode material, and can inhibit the growth of crystals to a certain extent during the sintering process, thereby improving the kinetic properties of the positive electrode material.
  • Comparative Example 3 the positive electrode material was only coated in situ, and the graphitization degree and electrical properties of its carbon layer were the worst.
  • Comparative Example 4 the proportion of the second carbon source was adjusted and the sintering temperature was lowered when coating the second carbon layer.
  • the second carbon layer contained no non-carbon elements, which made the graphitization degree of the second carbon layer lower than that of the first carbon layer.
  • the electrical properties of the positive electrode material were lower than those of Example 7 and similar to those of Comparative Example 2. This shows that if the graphitization degree of the carbon layer forms a spatial distribution trend with a gradient increase from the first carbon layer to the second carbon layer (from inside to outside), it is beneficial to achieve the best external electronic conductivity of the positive electrode material particles.
  • the graphitization degree forms a spatial distribution trend with a gradient increase from outside to inside, it is similar to having a low-conductivity carbon layer coated on a high-conductivity carbon layer. This will hinder the surface electron transport of the positive electrode material and lead to a decrease in electrical performance.
  • the positive electrode material prepared in the embodiment of the present application includes a core (inner core), a first carbon layer and a second carbon layer.
  • the first carbon layer is bonded to the surface of the core, and the second carbon layer is coated on the surface of the first carbon layer.
  • the degree of graphitization of the second carbon layer is higher than that of the first carbon layer, which is beneficial to improving the surface electron transmission capacity of the positive electrode material, reducing the resistivity between powders, and improving the electrical properties of the positive electrode material.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Composite Materials (AREA)
  • Materials Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

提供一种正极材料及其制备方法、正极片与二次电池，正极材料包括内核以及第一碳层，第一碳层为多碳嵌合层，多碳嵌合层包括主体骨架碳以及修饰碳，主体骨架碳结合于内核的表面，修饰碳嵌合生长于主体骨架碳中。修饰碳嵌合生长于主体骨架碳中，可减少孔隙的生成，使多碳嵌合层的孔隙率低于原位碳包覆层的孔隙率；多碳嵌合层的孔隙结构减少，使得在制浆过程中溶剂浸润孔隙的时间缩短，需要浸润孔隙的溶剂体积也减少，有利于减少浆料气泡的产生，容易制得流变性佳、均一性好的浆料，进而减少气泡带来的一系列问题，提高单位极片的能量密度。

Description

正极材料及其制备方法、正极片与二次电池
本申请要求于2023年08月18日提交中国专利局，申请号为202311049485.9，申请名称为“正极材料及其制备方法、正极片与二次电池”的中国专利申请的优先权，
本申请还要求2023年08月18日提交中国专利局，申请号为202311049489.7，申请名称为“碳包覆正极材料及其制备方法、正极片与二次电池”的中国专利申请的优先权，
其全部内容通过引用结合在本申请中。
技术领域
本申请属于锂离子电池正极材料技术领域，更具体地说，是涉及正极材料及其制备方法、正极片与二次电池。
背景技术
在全球环境污染逐渐加重、能源愈发匮乏的大环境下，寻求可再生新能源转型已迫在眉睫。锂离子电池具有能量密度高、安全性好、无记忆效应、循环寿命长等优势，近年来已成为全球新能源动力汽车市场的主流。正极材料是决定锂离子电池性能的关键材料之一，磷酸锰铁锂正极材料作为磷酸铁锂的升级版，能量密度可提高约20％，低温性能更优异，相较于三元正极材料成本低且更安全。但和磷酸铁锂类似，存在电子电导率低的缺陷。面对这一问题，目前多采用优化合成方法，合成后改性，如纳米化、碳包覆等方法改善磷酸锰铁锂的性能。
由于磷酸锰铁锂的电子电导率比磷酸铁锂更低，需制备成更细的纳米颗粒才能充分发挥性能，再加上原位碳包覆层本身疏松多孔，因此，工艺上制备出的纳米磷酸锰铁锂颗粒比表面积更高。但是，在碳含量、pH相近的情况下，前述纳米磷酸锰铁锂颗粒在全电制浆加工时更困难，主要表现为浆料容易产生较多气泡，浆料过筛后大气泡易破裂，但涂布的过程中存在较多小气泡附着于极片上，极片上的气泡烘干后会破裂留下凹坑或形成空泡核，这使极片厚度不均，进一步导致极片出现大量细小裂纹、剥落、掉粉等现象，影响极片的良品率，并最终导致电池的容量、内阻、循环寿命及安全性等变差，严重影响磷酸锰铁锂的全电性能评估。若通过增大粘结剂和溶剂的量，降低固含的方式降低黏度或者延长真空低速搅拌的时长来进行除泡，除泡效果并不理想，而且导致经济成本和时间成本增加。
技术问题
本申请的目的在于克服现有技术的上述不足，提供正极材料及其制备方法、正极片与二次电池，以解决现有技术中存在的现有纳米磷酸锰铁锂颗粒在全电制浆加工困难而导致电池的容量、内阻、循环寿命及安全性等变差的技术问题。
技术解决方案
为实现上述目的，本申请采用的技术方案是：
第一方面，提供了一种正极材料，包括内核以及第一碳层，第一碳层为多碳嵌合层，多碳嵌合层包括主体骨架碳以及修饰碳，主体骨架碳结合于内核的表面，修饰碳嵌合生长于主体骨架碳中。
可选地，主体骨架碳中的碳呈碳片堆叠状结合于内核的表面；和/或，
修饰碳的碳呈碳片状嵌合于主体骨架碳中；和/或，
主体骨架碳在多碳嵌合层中的质量含量为80％-90％，修饰碳在多碳嵌合层中的质量含量为10％-20％。
可选地，主体骨架碳中的碳片长度大于修饰碳的碳片长度，修饰碳中的碳片长度＜2nm；和/或，
多碳嵌合层的孔容＜0.070cm3/g；和/或，
多碳嵌合层的厚度＜10nm；和/或
第一碳层的IG/ID值为0.75-1.5。
可选地，多碳嵌合层包括碳元素和第一非碳元素；
其中，第一非碳元素包括N、S、P、Li中的至少一种；和/或，
碳元素在第一碳层中的质量含量为97％-98.5％，第一非碳元素在第一碳层中的质量含量为1.5％-3％。
可选地，正极材料还包括第二碳层，第二碳层为外包碳层，外包碳层包覆于多碳嵌合层的外表面。
可选地，外包碳层的孔容＜0.020cm3/g；和/或，
外包碳层的厚度＜1.5nm，并且外包碳层的厚度小于多碳嵌合层的厚度。
可选地，第二碳层的石墨化程度高于第一碳层的石墨化程度。
可选地，第一碳层中的碳结构长程无序化程度高于第二碳层中的碳结构长程无序化程度。
可选地，第一碳层的大部分碳结构为较长碳片结构，较长碳片结构堆积于内核的表面；第二碳层的大部分碳结构为较短碳片结构，并以非连续的、方向各异性的方式堆积于第一碳层的表面；较长碳片结构的尺寸大于较短碳片结构的尺寸。
可选地，第二碳层包括碳元素和第二非碳元素；
其中，第二非碳元素包括N、P、Li元素中的至少一种；和/或，
碳元素在第二碳层的质量含量为98％-99％，第二非碳元素在第二碳层的质量含量为1％-2％。
可选地，第二碳层的IG/ID值为1.0-1.9。
可选地，内核含有磷元素，并且内核的部分磷与多碳嵌合层的部分碳形成C-P键和/或C-O-P键。
可选地，C-P键和C-O-P键的成键率为0.5％-1.15％。
可选地，内核为含锂磷酸盐系正极活性材料内核；和/或，
内核的粒径＜400nm。
可选地，正极材料的总孔容为0.04cm3/g-0.10cm3/g；和/或，
正极材料的比表面积为12.0m2/g-17.0m2/g；和/或，
正极材料的IG/ID值为0.8-1.25。
第二方面，提供了一种正极材料的制备方法，用于制备上述正极材料，制备方法包括以下步骤：
提供内核前驱体材料，将内核前驱体材料在惰性气氛下进行第一次烧结，得到内核；
将内核与第一碳源、碳源溶剂进行混合处理，得到混合物料；
将混合物料在惰性气氛下进行第二次烧结，并且第二次烧结过程中通入雾化第二碳源，第一碳源原位裂解形成主体骨架碳堆积于内核的表面，第二碳源原位裂解和/或气相沉积形成修饰碳，修饰碳交织嵌合于主体骨架碳中，形成第一碳层，为多碳嵌合层，得到正极材料。
可选地，内核前驱体材料为磷酸锰铁锂前驱体，磷酸锰铁锂前驱体的制备方法包括以下步骤：
将锂源、铁源、磷源、锰源、前驱体溶剂和助溶剂按比例进行混合并反应，得到磷酸锰铁锂前驱体。
可选地，锂源、铁源、磷源、锰源、前驱体溶剂和助溶剂混合后得到的混合溶液的pH为5.0至7.5。
可选地，第一碳源包括羟丙基二淀粉磷酸酯、葡萄糖、果糖、蔗糖、乳糖、甜菊糖、木糖、麦芽糖、淀粉、纤维素、壳多糖、D-氨基葡萄糖、硫酸氨基葡萄糖、果糖磷酸酯、葡萄糖-6-磷酸、N-乙酰氨基葡萄糖、肽聚糖、聚丙烯酸酯、聚乙二醇、柠檬酸、苹果酸、丙烯、聚丙二醇、聚丙烯、聚丙烯酰胺、聚丙烯酸锂、聚乙烯醇、环糊精、聚乙烯醇缩丁醛、聚苯乙烯、石墨中的至少一种；和/或，
第二碳源包括甲醇、乙醇、乙酸乙酯、聚乙二醇、丙酮、丁酮、乙醚、乙酸、乙二酸、聚丙二醇、苯胺、苯甲胺、对二氮杂苯、柠檬酸铵、甲酸铵、乙酸铵、甲酰胺、乙酰胺、丙酰胺、丁酰胺、一异丙醇胺、N,N-二甲基乙醇胺、二甲基乙醇胺、三乙烯二胺中的至少两种。
可选地，第一碳源和第二碳源中的至少一碳源包括碳元素和第一非碳元素，第一非碳元素包括N、S、P、Li元素中的至少一种，碳元素在第一碳源和第二碳源总质量中的质量含量为97％-98.5％，第一非碳元素在第一碳源和第二碳源总质量中的质量含量为1.5％-3％。
可选地，正极材料还包括第二碳层，第二碳层为外包碳层，在形成多碳嵌合层之后，还包括以下步骤：
第二碳源裂解完全，继续通入雾化第二碳源，第二碳源通过原位裂解和/或气相沉积在多碳嵌合层的表面形成外包碳层。
可选地，制备方法满足以下(1)-(4)中的至少一个条件：
(1)第一次烧结的温度为350℃-660℃；
(2)第二次烧结的温度为650℃-855℃；
(3)第二碳源雾化气体的气流量为10mL/min-120mL/min；
(4)第二碳源包括碳元素和第二非碳元素，第二非碳元素包括N、P、Li元素中的至少一种，碳元素在第二碳源中的质量含量为98％-99％，第二非碳元素在第二碳源中的质量含量为1％-2％。
第三方面，提供了一种正极片，采用上述正极材料或上述正极材料的制备方法制备的正极材料制成。
第四方面，提供了一种二次电池，包括上述正极片。
本申请的有益效果在于：
本申请提供的正极材料采用多碳嵌合层包覆正极活性材料内核，多碳嵌合层包括主体骨架碳和修饰 碳，主体骨架碳结合于内核的表面，修饰碳嵌合生长于主体骨架碳中，可减少孔隙的生成，使多碳嵌合层的孔隙率低于现有原位碳包覆层的孔隙率；多碳嵌合层的孔隙结构减少，使得在制浆过程中溶剂浸润孔隙的时间缩短，需要浸润孔隙的溶剂体积也减少，有利于减少浆料气泡的产生，容易制得流变性佳、均一性好的浆料，进而减少气泡带来的一系列问题，提高单位极片的能量密度；
本申请提供的正极材料的制备方法通过第二次高温烧结和通入雾化第二碳源，使第一碳源高温原位裂解形成主体骨架碳，第二碳源原位裂解和/或气相沉积形成修饰碳，修饰碳交织嵌合于主体骨架碳中，形成多碳嵌合层，有效减小孔隙生成，得到孔隙率低的多碳嵌合层，有助于提高正极材料的电子电导率；
本申请提供的正极片采用上述正极材料制成，正极材料包括内核、多碳嵌合层，多碳嵌合层孔隙率低，所以制浆过程不易产生气泡，避免了气泡在浆料过筛、涂布极片和极片烘干工序中产生的问题，以及防止了气泡破裂产生的凹坑或空泡核带来的极片厚度不均、极片出现裂纹、剥落和掉粉的问题，有效提高正极片的良品率；
本申请提供的二次电池包括上述正极片，正极片有效改善了厚度不均、裂纹、剥落和掉粉的问题，提高了二次电池的容量、内阻、循环寿命和安全性。
附图说明
下面结合附图及实施例对本发明作进一步说明，附图中：
图1为本申请实施例的正极材料的制备方法的流程图；
图2为本申请实施例1的正极材料的制备方法的流程图；
图3为本申请实施例1正极材料和对比例1正极材料的结构对照示意图；
图4为本申请实施例1的正极材料的TEM图；
图5为本申请实施例1的正极材料的SEM图；
图6为本申请实施例1的正极材料和对比例1的正极材料的孔径分布图；
图7为本申请实施例的正极材料的结构示意图；
图8为本申请实施例7的正极材料的TEM照片；
图9为本申请实施例7的正极材料的SEM照片；
图10为本申请实施例7的正极材料的拉曼光谱拟合分析图；
附图标记说明：
图3中：11、实施例1的内核；12、实施例1的多碳嵌合层；13、外包碳层；21、对比例1的内核；22、对比例1的碳包覆层；
图7中：10、正极材料；11、内核；12、第一碳层；13、第二碳层。
本发明的实施方式
为了使本申请所要解决的技术问题、技术方案及有益效果更加清楚明白，以下结合附图及实施例，对本申请进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本申请，并不用于限定本申请。
本申请实施例提供了一种正极材料，包括内核以及第一碳层，第一碳层为多碳嵌合层，多碳嵌合层包括主体骨架碳以及修饰碳，主体骨架碳结合于内核的表面，修饰碳嵌合生长于主体骨架碳中。
本申请实施例提供的正极材料采用多碳嵌合层(第一碳层)包覆内核，多碳嵌合层包括主体骨架碳和修饰碳，主体骨架碳结合于内核的表面，修饰碳嵌合生长于主体骨架碳中，可减少孔隙的生成，使多碳嵌合层的孔隙率低于现有原位碳包覆层的孔隙率。多碳嵌合层的孔隙结构减少，使得在制浆过程中溶剂浸润孔隙的时间缩短，需要浸润孔隙的溶剂体积也减少，有利于减少浆料气泡的产生，容易制得流变性佳、均一性好的浆料，进而减少气泡带来的一系列问题，提高单位极片的能量密度。
一些实施例中，主体骨架碳采用第一碳源通过高温原位裂解形成，主体骨架碳中的碳呈碳片堆叠状结合于内核的表面，修饰碳采用第二碳源通过原位裂解和/或气相沉积形成修饰碳，修饰碳交织嵌合于主体骨架碳中，并且修饰碳中的碳呈碳片状，第一碳源与第二碳源相异，并且第一碳源的碳链长于第二碳源的碳链。第一碳源和第二碳源同时裂解相互交织，第二碳源通过原位裂解和/或气相沉积的绕镀性，使多碳嵌合层的整体孔隙结构相比于只进行原位碳包覆而言更少。
由于原位裂解和/或气相沉积具有随机性，使修饰碳的碳结构排列具有一定随机性，多以非连续的、方向各异性的方式进行堆积。主体骨架碳中的碳结构，第一碳源高温原位裂解产生的碳片长度较长，平 行堆积于内核的表面，对修饰碳起到引进和支撑的作用，使原位裂解和/或气相沉积形成的修饰碳能够通过主体骨架碳更好地包覆于内核表面，最终交织形成的多碳嵌合层能够完全包覆内核，得到厚度均匀的碳包覆层，并使多碳嵌合层的表面趋于光滑，减少孔隙的产生。
可以理解地，主体骨架碳的碳片长度大于修饰碳的碳片长度，利于形成支撑结构，并包覆内核，修饰碳的碳片长度较短，利于形成交织嵌合。一些实施例中，修饰碳的碳片长度＜2nm。
在本申请实施例中，多碳嵌合层的孔容可达＜0.07cm3/g，典型值为0.04cm3/g-0.06cm3/g，远小于现有原位碳包覆层的孔容0.12-0.20cm3/g，比表面积小于现有原位碳包覆层，可缩短溶剂浸润孔隙的时间。
本申请实施例的典型值是指产品某性能的平均值或正常值，具有代表性的、能表征群体特性的(或某一亚群特点的)参数。
一些实施例中，主体骨架碳在多碳嵌合层中的质量含量为80％-90％，修饰碳在多碳嵌合层中的质量含量为10％-20％，或一些实施例中，主体骨架碳在多碳嵌合层中的质量含量为82％-91％，修饰碳在多碳嵌合层中的质量含量为9％-18％。小占比的短结构修饰碳可以起到类似颗粒级配的效果，利于使多碳嵌合层实现更紧密的堆积。多碳嵌合层的主要厚度由主体骨架碳贡献，修饰碳作为辅助修饰。
一些实施例中，多碳嵌合层的主体骨架碳无间隙平行堆积于内核的表面，形成无间隙包覆，减少脱落概率，增加正极材料的稳定性。
一些实施例中，多碳嵌合层包括碳元素和嵌合非碳元素(第一非碳元素)，嵌合非碳元素包括N、S、P、Li中的至少一种，碳元素在多碳嵌合层中的质量含量为97％-98.5％，嵌合非碳元素在多碳嵌合层中的质量含量为1.5％-3％。较优地，少量的非碳元素在多碳嵌合层中均匀分布。多碳嵌合层中少量非碳元素的引入在一定程度上能够提高残碳层的石墨化程度，sp2碳的增加有利于提高正极材料的电子电导率。
一些实施例中，正极活性材料内核为含锂磷酸盐系内核，多碳嵌合层的部分碳与内核中的部分磷形成C-P键和C-O-P键，多碳嵌合层与内核之间为面接触，形成无间隙包覆，C-P键和C-O-P键的结合能比接触面产生的范德华键更强，其形成有利于提高多碳嵌合层与内核的结合力和稳定性，降低在加工制浆以及电池循环使用过程中多碳嵌合层和外包碳层的剥落脱离概率。
当多碳嵌合层由第一碳源高温原位裂解形成的主体骨架碳、第二碳源高温原位裂解和/或气相沉积形成的修饰碳，两者交织嵌合形成，多碳嵌合层的碳与内核中的磷形成C-P键和C-O-P键的成键概率可达0.5％-1.15％，多碳嵌合层与内核的结合力强和稳定性高，不易剥离脱落。
由于多碳嵌合层与内核的强结合力，一些实施例中，多碳嵌合层的剥离程度低至0.8％。
本申请实施例中的成键概率的定义是指在制备磷酸锰铁锂等前驱体的过程中，溶剂碳源中的C-H键或者C-O键有可能与磷源中的P-H键或者P-O-H键在催化剂的作用下发生偶联反应形成C-P键或者C-O-P键，并在烧结后仍存在。
含锂磷酸盐系内核例如磷酸锰锂内核、磷酸铁锂内核或磷酸锰铁锂内核等，一些实施例中，内核选为橄榄石结构的磷酸锰铁锂内核，则正极材料为碳包覆磷酸锰铁锂正极材料。
一些实施例中，内核的粒径＜400nm，大部分内核的粒径为80nm-300nm，粒径为80nm-300nm的内核占内核颗粒总数的70％-80％。或一些实施例中，内核的粒径＜400nm，大部分内核的粒径为50nm-300nm，粒径为50nm-300nm的内核占内核颗粒总数的70％-80％，可制备纳米级的磷酸锰铁锂正极材料。
一些实施例中，正极材料还包括第二碳层，第二碳层为外包碳层，外包碳层包覆于多碳嵌合层的外表面，外包碳层与多碳嵌合层配合可提高正极材料的电子电导率，当内核中含有锰时，还能抑制内核中的锰溶出，提高正极材料的循环寿命。
一些实施例中，外包碳层(第二碳层)采用第二碳源通过高温原位裂解和/或气相沉积形成于多碳嵌合层的外表面，自内核向外，是正极材料的碳包覆层中的第二层，外包碳层与多碳嵌合层之间无宏观间隙。
若多碳嵌合层中同时包含第一碳源和第二碳源高温裂解形成的碳，一方面，当单碳层中的碳片结构与多碳嵌合层中采用第一碳源裂解形成的碳片结构以点接触或线接触时，两者形成C-C化学键连接；当外包碳层中的碳片结构与多碳嵌合层中采用第一碳源裂解形成的碳片结构以面接触时，两者形成范德华键连接。另一方面，外包碳层与多碳嵌合层中的同源碳以C-C化学键连接，同时形成“钉扎结构”，提升了多碳嵌合层与外包碳层之间的结合力。
一些实施例中，多碳嵌合层的厚度＜10nm，典型值为3nm-6nm、典型值为2.8nm-5.8nm等范围；外 包碳层的厚度＜1.5nm，典型值为0.65nm-1.0nm，并且外包碳层的厚度小于等于多碳嵌合层的厚度，外包碳层是碳包覆层中的薄碳层，类似“膜层结构”。较厚的多碳嵌合层有利于整体碳骨架的稳定性，不易在加工受力或者电池循环使用的过程中受到破坏，较薄的外包碳层在保证能对多碳嵌合层起到填充修饰作用的前提下，最小程度的增加整体碳层的厚度，这利于缩短Li+传输路径。
外包碳层的整体厚度薄，由第二碳源裂解出来的小分子碳结构不断堆积，使该外包碳层的孔容可以<0.020cm3/g，典型值为0.010-0.014cm3/g。外包碳层的孔容降低有利于正极材料比表面积的降低，减少制浆加工时因溶剂浸润正极材料所产生的气泡核；同时，孔隙结构的减少有利于减少正极材料与电解液的接触，削弱正极材料与电解液的界面反应，降低电解液对正极材料的侵蚀。
一些实施例中，外包碳层的孔容小于多碳嵌合层的孔容，外包碳层孔隙的两端分别连通多碳嵌合层的孔隙与外包碳层的外部，多碳嵌合层孔隙中的空气对溶液的浸润具有一定阻力，增大了溶液进入外包碳层孔隙的阻力，进一步减少制浆加工时因溶剂浸润正极材料产生气泡的可能。
一些实施例中，正极材料的总孔容为0.04cm3/g-0.10cm3/g。
外包碳层中的碳结构多为短小碳片，由于原位裂解和/或气相沉积具有随机性，使外包碳层中的碳结构排列也具有一定随机性，碳结构多以非连续的、方向各异性的方式进行堆积。
当多碳嵌合层无间隙堆积于内核的表面时，例如内核与多碳嵌合层的紧密度，多碳嵌合层与外包碳层之间的紧密度均一性；或者多碳嵌合层的部分碳与内核的部分磷形成C-P键和C-O-P键，以及多碳嵌合层的碳片结构与外包碳层的碳片结构形成C-C化学键连接和/或范德华键连接等，可进一步增大电子传导速率，提高正极材料的电化学性能。
可以理解地，正极材料的孔容比现有原位碳包覆层的孔容更低，正极材料的比表面积也将比现有原位碳包覆层的比表面积更低。本申请的一些实施例中，正极材料的比表面积为12m2/g-17.0m2/g，若正极材料的比表面积过小，例如低于12m2/g，碳含量过小，可能会导致碳包覆不均匀；若正极材料的比表面积过大，例如高于17m2/g，制浆过程中浆料的分散较困难，可能会产生团聚的问题，从而影响电性能。所以比表面积在12m2/g-17.0m2/g范围时，颗粒的团聚性降低，利于加工时活性物质的分散及导电剂的均匀包裹。
本申请实施例的比表面积是指单位质量物料所具有的总面积，单位是m2/m3或者m2/g，通常指固体材料的比表面积,例如粉末,纤维,颗粒,片状,块状等材料。计算方式为面积/体积，或者面积/质量。
一些实施例中，如图7所示，第二碳层13的石墨化程度高于第一碳层12的石墨化程度。
本申请实施例提供的碳包覆正极材料10采用第二碳层13与第一碳层12配合传输电子，第二碳层13的石墨化程度高于第一碳层12的石墨化程度，则第二碳层13的电子迁移阻力小于第一碳层12的电子迁移阻力，有利于内核11向外转移电子，增加电子的传导速率，进而提高正极材料10的电学性能。
当内核中含有锰时，多层碳结构利于抑制内核中的锰溶出，提高正极材料的循环寿命。
一些实施例中，第二碳层中的大部分碳结构为短小碳片，当采用原位裂解和/或气相沉积形成第二碳层，由于原位裂解和/或气相沉积具有随机性，使第二碳层中的碳结构排列也具有一定随机性，碳结构多以非连续的、方向各异性的方式进行堆积。虽然第二碳层中的碳结构长程无序化程度比第一碳层中的碳结构更低，但气相沉积属于原子范畴的气态传质，这使第二碳层中的碳结构短程有序化程度更高，即石墨化程度更高。若以IG/ID表征石墨化程度，一些实施例中，第二碳层的IG/ID值为1.0-1.9，典型值为1.2-1.6。一些实施例中，正极材料的IG/ID值为0.8-1.25。
正因此，第一碳层的石墨化程度比仅采用第一碳源进行原位碳包覆的更高，若以IG比ID表征第一碳层的石墨化程度，第一碳层的石墨化程度可以达到0.75-1.5，典型值为0.8-1.1。第二碳层的IG/ID值大于第一碳层的IG/ID值。第一碳层的石墨化程度提高有利于内核向外转移电子，而第二碳层石墨化程度的提高有利于增大碳包覆正极材料颗粒之间电子的传导速率，使内核的电子自内核经过第一碳层向第二碳层迁移，皆有利于提高碳包覆正极材料的电化学性能。
一些实施例中，第一碳层的大部分碳结构为较长碳片结构，较长碳片结构堆积结合于内核的表面；第二碳层的大部分碳结构为较短碳片结构，并以非连续的、方向各异性的方式堆积包覆于第一碳层的表面；较长碳片结构的尺寸大于较短碳片结构的尺寸。实施例中，当第一碳层通过第一碳源高温原位裂解形成，第二碳层通过原位裂解和/或气相沉积形成时，一般地，第一碳源的有机物碳链比第二碳源的有机物碳链长，得到的第一碳层的碳结构碳片尺寸比第二碳层的碳结构碳片尺寸，这有利于第一碳层均匀包 覆内核的外表面，并为第二碳层的碳结构提供生长结构基础，对第二碳层的碳结构具有支撑的作用。
一些实施例中，第二碳层包括碳元素和第二非碳元素(外包非碳元素)，碳元素在第二碳层的质量含量为98％-99％，第二非碳元素包括N、P、Li元素中的至少一种，可选为N元素，第二非碳元素在第二碳层的质量含量为1％-2％。第二碳层少量非碳元素的引入在一定程度上能够提高残碳层的石墨化程度，sp2碳的增加有利于提高碳包覆正极材料的电子电导率。
可以理解地，第一碳层可以为单碳层或者由多种碳源通过合适的工艺形成，主要是第一碳层与第二碳层的石墨化程度具有差值，并且第二碳层的石墨化程度高于第一碳层的石墨化程度，便可以使内核的电子具有向外转移的趋势。
本申请实施例还提供了一种正极材料的制备方法，可用于制备上述正极材料，该制备方法包括以下步骤：
S1：提供内核前驱体材料，将内核前驱体材料在惰性气氛下进行第一次烧结，得到内核。
通过高温烧结得到内核，为下一步工序做材料准备。
一些实施例中，为了得到合适粒度和表面干净的内核颗粒，在第一次烧结之前，还对内核前驱体材料进行破碎、球磨整形。
一些实施例中，内核前驱体材料可采用滚筒式真空球磨机进行颗粒整形，整形时间可以为15min-60min，使多碳嵌合层能够紧密的包覆内核，并适用于制备正极材料以及正极片。真空球磨机的保护气氛可以为氢气、氮气、氩气中的至少一种。
一些实施例中，第一次烧结时的惰性气氛为氮气、氩气中的任意一种。
一些实施例中，第一次烧结的温度为350℃-650℃，烧结时间可以根据实际情况进行选择，例如可以选为2h-10h。
或一些实施例中，第一次烧结的温度为355℃-660℃，烧结时间可以根据实际情况进行选择，例如可以选为2h-8h。
一些实施例中，内核为磷酸锰铁锂内核，则对应的内核前驱体材料为磷酸锰铁锂前驱体。
一些实施例中，磷酸锰铁锂前驱体的制备方法包括以下步骤：
将锂源、铁源、锰源、磷源、前驱体溶剂和助溶剂按比例进行混合并反应，得到磷酸锰铁锂前驱体。
一些实施例中，锂源、铁源、锰源、磷源按照Li:(Fe+Mn):P为(0.90-1.10)：(0.90-1.10)：(0.90-1.10)的元素摩尔比配置，其中铁源和锰源中Fe:Mn的摩尔比为1：(0-10),例如可以是1:0、1:0.1、1:0.5、1:0.75、1:1、1:2、1:3、1:5、1:7、1:8、1:10。前驱体溶剂和助溶剂比例按照锂源、铁源、锰源和磷酸总质量的质量比加入，前驱体溶剂的占比可以是150％-500％；助溶剂的质量比例不超过5％，或一些实施例中，前驱体溶剂的占比可以是200％-600％；助溶剂的质量比例不超过6％。
一些实施例中，锂源包括碳酸锂、硫酸锂、磷酸锂、磷酸二氢锂中的至少一种。
一些实施例中，锰源包括硫酸锰、碳酸锰、乙酸锰、硝酸锰、氯化锰、氧化锰、氢氧化锰中的至少一种。
一些实施例中，铁源包括氯化铁、碳酸铁、乙酸铁、乙酸亚铁、磷酸铁中的至少一种。
一些实施例中，磷源包括磷酸氢二铵、磷酸二氢铵、磷酸铁、红磷、白磷、五氧化二磷、三氧化二磷、磷酸铵、磷酸铁中的至少一种。
一些实施例中，前驱体溶剂包括水、甲醇、乙醇、乙二醇、丙三醇、聚乙二醇、二甲基亚砜、水杨酸十六烷基三甲基溴化铵等其中的至少一种。
一些实施例中，助溶剂可以是硝酸、磷酸、磷酸二氢铵、乙酸、乙二酸、柠檬酸、抗坏血酸(催化剂)、聚乙烯吡咯烷酮(防团聚剂)其中的至少一种。助溶剂的作用为促进各组分材料的溶解，分散混合浆料、催化反应进程，调控反应体系的pH，参与形成磷酸锰铁锂材料前驱体中的至少一种。
一些实施例中，锂源、铁源、磷源、锰源、前驱体溶剂和助溶剂的混合液的pH为5.0-7.5，用于调控内核前驱体材料的形貌和内核前驱体材料烧结后的残碱量，以防止pH值过高导致加工时出现凝胶问题，影响正极材料的加工性能评估。
锂源、铁源、磷源、锰源、前驱体溶剂和助溶剂的反应包括液相水热法反应、共沉淀反应、溶胶凝胶反应中的任意一种。
S2：将内核与第一碳源、碳源溶剂进行混合处理，得到混合物料。
内核与第一碳源、碳源溶剂混合后，第一碳源浸润于内核的表面，在第二次烧结时，其高温原位裂解产生的碳结构即可附着于内核表面，甚至部分碳结构与内核的磷元素产生化学键连接。
内核与第一碳源的质量比例可以是1:(4-16)，内核与碳源溶剂的质量比例可以是1:(0.5-10)。或者，内核与第一碳源的质量比例可以是1：(4-18)，内核与碳源溶剂的质量比例可以是1：(0.4-12)。碳源溶剂主要用于溶解和/或分散第一碳源，与第一碳源形成混合液体，并为内核提供溶液环境，使混合液体能够均匀浸润内核表面，为在内核形成均匀厚度的第一碳层做好基础准备。
一些实施例中，第一碳源包括羟丙基二淀粉磷酸酯、葡萄糖、果糖、蔗糖、乳糖、甜菊糖、木糖、麦芽糖、淀粉、纤维素、壳多糖、D-氨基葡萄糖、硫酸氨基葡萄糖、果糖磷酸酯、葡萄糖-6-磷酸、N-乙酰氨基葡萄糖、肽聚糖、聚丙烯酸酯、聚乙二醇、柠檬酸、苹果酸、丙烯、聚丙二醇、聚丙烯、聚丙烯酰胺、聚丙烯酸锂、聚乙烯醇、环糊精、聚乙烯醇缩丁醛、聚苯乙烯、石墨中的至少一种。
一些实施例中，内核含有磷元素，并且内核的部分磷与多碳嵌合层的部分碳形成C-P键和/或C-O-P键，第一碳源包括糖类化合物，糖类化合物例如包括葡萄糖、果糖、蔗糖中的至少一种。
一些实施例中，第一碳源包括碳元素和第一非碳元素，第一非碳元素包括N、S、P、Li元素中的至少一种，碳元素在第一碳源中的质量含量为96％-98％，第一非碳元素在第一碳源中的质量含量为2％-4％。
一些实施例中，碳源溶剂包括水、丙三醇、乙醇、乙二醇、异丙醇、聚乙二醇、醋酸乙酯、乙酸乙酯中的至少一种。
S3：将混合物料在惰性气氛下进行第二次烧结，并且烧结过程中通入雾化第二碳源，第一碳源原位裂解形成主体骨架碳堆积于内核材料的表面，第二碳源原位裂解和/或气相沉积形成修饰碳，该修饰碳交织嵌合于主体骨架碳中，形成多碳嵌合层，得到正极材料。
在第二次烧结过程中，第一碳源和第二碳源同时高温裂解，其中，第一碳源裂解后生成的碳结构平行堆积于内核的表面，形成主体骨架碳，第二碳源裂解后生成的碳结构通过原位裂解和/或气相沉积形成修饰碳，修饰碳交织嵌合于主体骨架碳中，主体骨架碳与修饰碳共同形成多碳嵌合层。
第二碳源包括甲醇、乙醇、乙酸乙酯、聚乙二醇、丙酮、丁酮、乙醚、乙酸、乙二酸、聚丙二醇、苯胺、苯甲胺、对二氮杂苯、柠檬酸铵、甲酸铵、乙酸铵、甲酰胺、乙酰胺、丙酰胺、丁酰胺、一异丙醇胺、N,N-二甲基乙醇胺、二甲基乙醇胺、三乙烯二胺中的至少两种。
一般地，第一碳源选大分子有机物，第二碳源选小分子有机物，或者，第一碳源的碳链长于第二碳源的碳链，如此，形成的主体骨架碳的碳片长度较长，能够平行堆积于内核的表面，修饰碳的碳片长度较短，例如修饰碳的碳片长度最大尺寸＜2nm，能够交织嵌合到主体骨架碳中。
一些实施例中，第二碳源包括碳元素和第一非碳元素，第一非碳元素包括N、S、P、Li元素中的至少一种，可选的是N元素，在实施例中，第一碳源中的第一非碳元素与第二碳源中的第一非碳元素可以独立的为N、S、P、Li元素中的至少一种，也即是，实施例中，不限制第一碳源中的第一非碳元素与第二碳源中的第一非碳元素相同或不同。第一非碳元素N元素可以由苯胺、苯甲胺、对二氮杂苯、柠檬酸铵、甲酸铵、乙酸铵、甲酰胺、乙酰胺、丙酰胺、丁酰胺、一异丙醇胺、N,N-二甲基乙醇胺、二甲基乙醇胺、三乙烯二胺中的至少一种引入。碳元素在第二碳源中的质量含量为98％-99％，第一非碳元素在第二碳源中的质量含量为1％-2％。
一些实施例中，上述第一碳源和第二碳源中的至少一碳源包括碳元素和第一非碳元素，第一非碳元素包括N、S、P、Li元素中的至少一种，碳元素在第一碳源和第二碳源总质量中的质量含量为97％-98.5％，第一非碳元素在第一碳源和第二碳源总质量中的质量含量为1.5％-3％。
一些实施例中，第二次烧结的惰性气氛包括氢气、氮气、氩气中的至少一种。
一些实施例中，第二次烧结的温度可以为650℃-850℃，烧结时间可以根据实际情况进行选择，例如可以选为4h-10h。
或一些实施例中，第二次烧结的温度可以为660℃-855℃，烧结时间可以根据实际情况进行选择，例如可以选为4h-12h。
第二碳源的添加量通过雾化气体的通入时间和气流量控制，可以为4h-10h，例如4h、5h、6h、7h、8h、9h或10h等。第二碳源雾化气体的气流量可以为10mL/min-110mL/min，可选地，为40mL/min-80mL/min。
本申请实施例提供的正极材料的制备方法通过第二次高温烧结和通入雾化第二碳源，使第一碳源高 温原位裂解形成主体骨架碳、第二碳源原位裂解和/或气相沉积形成修饰碳，修饰碳交织嵌合于主体骨架碳中，形成第一碳层，第一碳层为多碳嵌合层，有效减小孔隙生成，得到孔隙率低的多碳嵌合层，且多碳嵌合层的石墨化程度高，有助于提高正极材料的电子电导率。
一些实施例中，当正极材料还包括第二碳层，第二碳层为外包碳层，在形成多碳嵌合层之后，如图1所示，还包括以下步骤S4：
S4：第二碳源裂解完全，继续通入雾化第二碳源，第二碳源通过原位裂解和/或气相沉积在多碳嵌合层的表面形成外包碳层(第二碳层)，得到正极材料。
一些实施例中，第二碳源裂解完成后，多碳嵌合层基本形成，保持在第二次烧结的温度中继续通入雾化第二碳源，第二碳源通过原位裂解和/或气相沉积在多碳嵌合层的表面堆积生成外包碳层，生成的外包碳层石墨化程度高，可提高正极材料的电子电导率。
一些实施例中，当第一碳层采用第一碳源高温原位裂解、第二碳源原位裂解和/或气相沉积形成时，第一碳层所采用的第二碳源与第二碳层采用的第二碳源相同，在制备过程中可持续通入第二碳源，避免多次更换雾化第二碳源的繁复操作，简化工艺，提高工艺效率。
在一具体实施例中，步骤S4中继续通入的雾化第二碳源与步骤S3中的雾化第二碳源可以保持相同，也可以不同，也即是，一些实施例中，步骤S4中继续通入的雾化第二碳源包括甲醇、乙醇、乙酸乙酯、聚乙二醇、丙酮、丁酮、乙醚、乙酸、乙二酸、聚丙二醇、苯胺、苯甲胺、对二氮杂苯、柠檬酸铵、甲酸铵、乙酸铵、甲酰胺、乙酰胺、丙酰胺、丁酰胺、一异丙醇胺、N,N-二甲基乙醇胺、二甲基乙醇胺、三乙烯二胺中的至少两种。
在一具体实施例中，步骤S4中的温度与步骤S3中的第二次烧结的温度可以保持相同，也可以不同，也即是，一些实施例中，步骤S4中继续通入雾化第二碳源进行原位裂解和/或气相沉积的温度可以包括上述第二次烧结的温度650℃-855℃。
步骤S4的反应时间可根据第二碳源的投入量估算反应时间，并通过控制继续通入雾化第二碳源的流量以及通入时间来控制外包碳层的厚度。
步骤S4中，第二碳源的添加量通过雾化气体的通入时间和气流量控制，可以为4h-12h，例如5h、5.5h、6h、6.5h、7h、7.5h、8h、8.5h、9h、9.5h、10h、10.5h、11h、11.5h或12h等。第二碳源雾化气体的气流量可以为上述步骤S3中第二碳源雾化气体的气流量10mL/min-110mL/min，或者，可以为15mL/min-120mL/min，例如15mL/min、30mL/min、45mL/min、60mL/min、80mL/min、85mL/min、90mL/min、100mL/min或120mL/min等，可选地，为45-90mL/min。
一些实施例中，步骤S4中，通入的雾化第二碳源包括碳元素和第二非碳元素，第二非碳元素包括N、P、Li元素中的至少一种，碳元素在第二碳源中的质量含量为98％-99％，第二非碳元素在第二碳源中的质量含量为1％-2％。
第二碳源通过原位裂解和/或气相沉积在第一碳层的表面形成第二碳层，形成两种不同的碳层结构，其中，气相沉积属于原子范畴的气态传质，使得第二碳层中的碳结构短程有序化程度更高，即石墨化程度更高，第一碳层与第二碳层之间产生石墨化程度阶梯，引导内核转移电子的方向，可以提高正极材料的电子传导速率，制备方法操作简单、可控，具有良好的工业应用前景。
本申请实施例还提供了一种正极片，采用上述正极材料制成，正极材料包括内核、多碳嵌合层和外包碳层，多碳嵌合层和外包碳层孔隙率低，所以制浆过程不产生气泡或者产生很少气泡，避免了气泡在浆料过筛、涂布极片和极片烘干产生的问题，免去了气泡破裂产生的凹坑或空泡核带来的极片厚度不均、极片出现裂纹、剥落和掉粉的问题，有效提高正极片的良品率。
本申请实施例还提供了一种二次电池，包括上述正极片，正极片没有厚度不均、裂纹、剥落和掉粉的问题，提高了二次电池的容量、内阻、循环寿命和安全性。
以下通过多个实施例来举例说明。
实施例1
如图3所示，本实施例的正极材料包括内核11、多碳嵌合层12以及外包碳层13，多碳嵌合层12包括主体骨架碳以及修饰碳，主体骨架碳堆积于内核11的表面，修饰碳嵌合生长于主体骨架碳中；外包碳层13包覆于多碳嵌合层12的表面。
其中，主体骨架碳在多碳嵌合层12中的质量含量为85％，修饰碳在多碳嵌合层中的质量含量为15％； 多碳嵌合层12的孔容为0.0495cm3/g，外包碳层13的孔容0.0122cm3/g，总孔容为0.0472cm3/g；多碳嵌合层12的厚度3.14nm，外包碳层13的厚度0.86nm；内核11的粒径52nm-368nm；正极材料的比表面积为14.16m2/g；
如图2所示，本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水(前驱体溶剂)和乙二酸(助溶剂)分别按前述原料总质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将内核前驱体材料在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与葡萄糖和果糖磷酸酯(第一碳源)、水(碳源溶剂)进行混合处理，得到混合物料。内核与第一碳源的质量比为1：10，内核与水的质量比例为1：4。第一碳源中果糖磷酸酯的质量比为4％，第一碳源中的非碳元素为P。
S4：将混合物料在700℃进行第二次烧结，烧结时间为6h，并通入雾化乙醇、聚乙二醇和N,N-二甲基乙醇胺(第二碳源)，质量比例为3：6：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为60mL/min，通入时间为6h，在内核的表面形成多碳嵌合层。
S5：保持第二次烧结的温度，以及通入雾化乙醇、聚乙二醇和N,N-二甲基乙醇胺(第二碳源)，雾化第二碳源的气流量为60mL/min，通入时间为2h，在多碳嵌合层的表面形成外包碳层，得到正极材料。
如图4所示，为所得正极材料的投射电镜(TEM)图，多碳嵌合层以及外包碳层的厚度均匀。
如图5所示，为所得正极材料的扫描电镜(SEM)图，正极材料颗粒比较圆，比表面积会比较低，有利于加工。
实施例2
本实施例的正极材料与实施例1的材料结构大部分相同，不同之处在于：主体骨架碳在多碳嵌合层中的质量含量为90％，修饰碳在多碳嵌合层中的质量含量为10％；多碳嵌合层的孔容为0.0687cm3/g，外包碳层的孔容为0.0184cm3/g，总孔容为0.0725cm3/g；多碳嵌合层的厚度4.28nm，外包碳层的厚度0.98nm；内核的粒径43nm-322nm；正极材料的比表面积为16.35m2/g。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水和乙二酸分别按前述原料总质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将内核前驱体材料在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与蔗糖和壳多糖(第一碳源)、水进行混合处理，得到混合物料。内核与第一碳源的质量比为1：14，内核与水的质量比例为1：4，第一碳源中壳多糖的质量比为4％，第一碳源中的非碳元素为N。
S4：将混合物料在750℃进行第二次烧结，烧结时间为6h，并通入雾化乙酸、聚丙二醇和苯甲胺(第二碳源)，质量比例为3：6：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为80mL/min，通入时间为6h，在内核的表面形成多碳嵌合层。
S5：保持第二次烧结的温度，以及通入雾化乙酸、聚丙二醇和苯甲胺(第二碳源)，雾化第二碳源的气流量为70mL/min，通入时间为2h，在多碳嵌合层的表面形成外包碳层，得到正极材料。
实施例3
本实施例的正极材料与实施例1的材料结构大部分相同，不同之处在于：主体骨架碳在多碳嵌合层中的质量含量为90％，修饰碳在多碳嵌合层中的质量含量为10％；多碳嵌合层的孔容为0.0724cm3/g，外包碳层的孔容为0.0125cm3/g，总孔容为0.0681cm3/g；多碳嵌合层的厚度3.65nm，外包碳层的厚度0.8nm；内核的粒径45nm-316nm；正极材料的比表面积为15.87m2/g。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中，乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水和乙二酸分别按前述 原料总质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将磷酸锰铁锂材料前驱体在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与葡萄糖和果糖磷酸酯(第一碳源)、水进行混合处理，得到混合物料。内核与第一碳源的质量比为1：14，内核与水的质量比例为1：4，第一碳源中果糖磷酸酯的质量比为4％，第一碳源中的非碳元素为P。
S4：将混合物料在750℃进行第二次烧结，烧结时间为6h，并通入雾化乙醇、聚乙二醇和N,N-二甲基乙醇胺(第二碳源)，质量比例为3：6：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为60mL/min，通入时间为6h，在内核的表面形成多碳嵌合层。
S5：保持第二次烧结的温度，以及通入雾化乙醇、聚乙二醇和N,N-二甲基乙醇胺(第二碳源)，雾化第二碳源的气流量为80mL/min，通入时间为2h，在多碳嵌合层的表面形成外包碳层，得到正极材料。
实施例4
本实施例的正极材料与实施例1的材料结构大部分相同，不同之处在于：主体骨架碳在多碳嵌合层中的质量含量为85％，修饰碳在多碳嵌合层中的质量含量为15％；多碳嵌合层的孔容为0.0513cm3/g，外包碳层的孔容0.0267cm3/g，总孔容为0.0604cm3/g；多碳嵌合层的厚度3.22nm，外包碳层的厚度1.26nm；内核的粒径60nm-350nm；正极材料的比表面积为15.28m2/g。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水和乙二酸分别按前述原料质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将内核前驱体材料在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与葡萄糖和果糖磷酸酯(第一碳源)、水进行混合处理，得到混合物料。内核与第一碳源的质量比为1：10，内核与水的质量比例为1：4，第一碳源中果糖磷酸酯的质量比为4％，第一碳源中的非碳元素为P。
S4：将混合物料在750℃进行第二次烧结，烧结时间为6h，并通入雾化乙醇、聚乙二醇和N,N-二甲基乙醇胺(第二碳源)，质量比例为3：6：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为60mL/min，通入时间为6h，在内核的表面形成多碳嵌合层。
S5：保持第二次烧结的温度，以及通入雾化乙醇、聚乙二醇和N,N-二甲基乙醇胺(第二碳源)，雾化第二碳源的气流量为80mL/min，通入时间为2h，在多碳嵌合层的表面形成外包碳层，得到正极材料。
实施例5
本实施例的正极材料与实施例1的材料结构大部分相同，不同之处在于：主体骨架碳在多碳嵌合层中的质量含量为85％，修饰碳在多碳嵌合层中的质量含量为15％；多碳嵌合层的孔容为0.0506cm3/g，外包碳层的孔容为0.0131cm3/g，总孔容为0.0490cm3/g；多碳嵌合层的厚度3.20nm，外包碳层的厚度0.90nm；内核的粒径54nm-355nm；正极材料的比表面积为14.52m2/g；
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水和乙二酸分别按前述原料总质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将内核前驱体材料在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与葡萄糖(第一碳源)、水进行混合处理，得到混合物料。内核与第一碳源的质量比为1：10，内核与水的质量比例为1：4。
S4：将混合物料在700℃进行第二次烧结，烧结时间为6h，并通入雾化乙醇和聚乙二醇(第二碳源)，质量比例为3：7，雾化第二碳源的气流量为60mL/min，通入时间为6h，在内核的表面形成多碳嵌合层。
S5：保持第二次烧结的温度，以及通入雾化乙醇和聚乙二醇(第二碳源)，雾化第二碳源的气流量 为60mL/min，通入时间为2h，在多碳嵌合层的表面形成外包碳层，得到正极材料。
实施例6
本实施例的正极材料与实施例1的材料结构大部分相同，不同之处在于：主体骨架碳在多碳嵌合层中的质量含量为85％，修饰碳在多碳嵌合层中的质量含量为15％；多碳嵌合层的孔容为0.0498cm3/g，总孔容为0.0498cm3/g；多碳嵌合层的厚度3.06nm，无外包碳层；内核的粒径62nm-384nm；正极材料的比表面积为14.76m2/g。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水和乙二酸分别按前述原料总质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将内核前驱体材料在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与葡萄糖和果糖磷酸酯(第一碳源)、水进行混合处理，得到混合物料。内核与第一碳源的质量比为1：10，内核与水的质量比例为1：4，第一碳源中果糖磷酸酯的质量比为4％，第一碳源中的非碳元素为P。
S4：将混合物料在700℃进行第二次烧结，烧结时间为8h，并通入雾化乙醇、聚乙二醇和N,N-二甲基乙醇胺(第二碳源)，质量比例为3：6：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为60mL/min，通入时间为6h，在内核的表面形成多碳嵌合层。
实施例7
本实施例的正极材料包括芯部(即内核)、第一碳层和第二碳层，第一碳层结合于芯部的表面，第二碳层包覆于第一碳层的表面，第二碳层的石墨化程度高于第一碳层的石墨化程度。其中，第一碳层的厚度3.26nm，第二碳层的厚度0.90nm；芯部的粒径54nm-376nm；第一碳层的IG/ID值为1.05第二碳层的IG/ID值为1.32，正极材料的IG/ID值为1.14。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源乳糖和羟丙基二淀粉磷酸酯、碳源溶剂水进行混合处理，得到混合物料。芯部与第一碳源的质量比为1：12，芯部与碳源溶剂的质量比例为1：5。第一碳源中羟丙基二淀粉磷酸酯的质量比为5％，第一碳源中的非碳元素为P；
S4：将混合物料在720℃进行第二次烧结，烧结时间为7h，并通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，质量比例为3.2：5.8：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为65mL/min，通入时间为7h，在芯部的表面形成第一碳层；
S5：保持第二次烧结的温度，以及通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，雾化第二碳源的气流量为65mL/min，通入时间为2.5h，在第一碳层的表面形成第二碳层，得到正极材料。
实施例8
本实施例的正极材料包括芯部(即内核)、第一碳层和第二碳层，第一碳层结合于芯部的表面，第二碳层包覆于第一碳层的表面，第二碳层的石墨化程度高于第一碳层的石墨化程度。其中，第一碳层的厚度4.12nm，第二碳层的厚度0.97nm；芯部的粒径40nm-342nm；第一碳层的IG/ID值为0.90，第二碳层的IG/ID值为1.12，正极材料的石墨化程度为0.97。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源果糖和D-氨基葡萄糖、碳源溶剂水进行混合处理，得到混合物料。芯部与第一碳源的质量比为1：16，芯部与碳源溶剂的质量比例为1：5。第一碳源中D-氨基葡萄糖的质量比为5％，第一碳源中的非碳元素为N；
S4：将混合物料在670℃进行第二次烧结，烧结时间为7h，并通入雾化第二碳源甲醇、聚丙二醇和苯胺，质量比例为3.2：5.8：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为95mL/min，通入时间为7h，在芯部的表面形成第一碳层；
S5：保持第二次烧结的温度，以及通入雾化第二碳源甲醇、聚丙二醇和苯胺，雾化第二碳源的气流量为95mL/min，通入时间为2.5h，在第一碳层的表面形成第二碳层，得到正极材料。
实施例9
本实施例的正极材料包括芯部(即内核)、第一碳层和第二碳层，第一碳层结合于芯部的表面，第二碳层包覆于第一碳层的表面，第二碳层的石墨化程度高于第一碳层的石墨化程度。其中，第一碳层的厚度3.42nm，第二碳层的厚度0.86nm；芯部的粒径78nm-546nm；第一碳层的IG/ID值为1.10，第二碳层的IG/ID值为1.38。第一碳层包括碳元素和第一非碳元素，第一非碳元素包括P素，且碳元素在第一碳层中的质量含量为98.48％，第一非碳元素在第一碳层中的质量含量为1.52。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源乳糖和羟丙基二淀粉磷酸酯、碳源溶剂水进行混合处理，得到混合物料。芯部与第一碳源的质量比为1：16，芯部与碳源溶剂的质量比例为1：5。第一碳源中羟丙基二淀粉磷酸酯的质量比为5％，第一碳源中的非碳元素为P；
S4：将混合物料在800℃进行第二次烧结，烧结时间为7h，并通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，质量比例为3.2：5.8：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为95mL/min，通入时间为7h，在芯部的表面形成第一碳层；
S5：保持第二次烧结的温度，以及通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，雾化第二碳源的气流量为95mL/min，通入时间为2.5h，在第一碳层的表面形成第二碳层，得到正极材料。
实施例10
本实施例的正极材料包括芯部(即内核)、第一碳层和第二碳层，其中，第一碳层的厚度3.08nm，第二碳层的厚度0.77nm；芯部的粒径60nm-454nm；第一碳层的IG/ID值为0.94，第二碳层的IG/ID值为1.14，正极材料的石墨化程度为1.02。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源乳糖和羟丙基二淀粉磷酸酯、碳源溶剂水进行混合处理，得到混合物料。芯部与第一碳源的质量比为1：8，芯部与碳源溶剂的质量比例为1：5。第一碳源中羟丙基二淀粉磷酸酯的质量比为5％，第一碳源中的非碳元素为P；
S4：将混合物料在670℃进行第二次烧结，烧结时间为7h，并通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，质量比例为3.2：5.8：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为35mL/min，通入时间为7h，在芯部的表面形成第一碳层；
S5：保持第二次烧结的温度，以及通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，雾化第二碳源的气流量为35mL/min，通入时间为2.5h，在第一碳层的表面形成第二碳层，得到正极材料。
实施例11
本实施例的正极材料包括芯部(即内核)、第一碳层和第二碳层，第二碳层包覆于第一碳层的表面，第二碳层的石墨化程度高于第一碳层的石墨化程度。其中，第一碳层的厚度3.32nm，第二碳层的厚度0.92nm；芯部的粒径58nm-365nm；第一碳层的IG/ID值为1.01，第二碳层的IG/ID值为1.23，正极材料的石墨化程度为1.08。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源乳糖、碳源溶剂水进行混合处理，得到混合物料。芯部与第一碳源的质量比为1：12，芯部与碳源溶剂的质量比例为1：5；
S4：将混合物料在720℃进行第二次烧结，烧结时间为7h，并通入雾化第二碳源丁酮和聚乙二醇，质量比例为3.2：6.8，雾化第二碳源的气流量为65mL/min，通入时间为7h，在芯部的表面形成第一碳层；
S5：保持第二次烧结的温度，以及通入雾化第二碳源丁酮和聚乙二醇，雾化第二碳源的气流量为65mL/min，通入时间为2.5h，在第一碳层的表面形成第二碳层，得到正极材料。
实施例12
本实施例的正极材料包括内核(芯部)、多碳嵌合层(第一碳层)以及外包碳层(第二碳层)，第一碳层包括主体骨架碳以及修饰碳，主体骨架碳堆积于内核的表面，修饰碳嵌合生长于主体骨架碳中；第二碳层包覆于第一碳层的表面，且第二碳层的石墨化程度高于第一碳层的石墨化程度。其中，第一碳层的厚度3.20nm，第二碳层的厚度0.90nm；内核的粒径50nm-372nm；第一碳层的IG/ID值为1.06，第二碳层的IG/ID值为1.32，正极材料的IG/ID值为1.13。
本实施例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水(前驱体溶剂)和乙二酸(助溶剂)分别按前述原料总质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将内核前驱体材料在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与葡萄糖和果糖磷酸酯(第一碳源)、水(碳源溶剂)进行混合处理，得到混合物料。内核与第一碳源的质量比为1：10，内核与水的质量比例为1：4。第一碳源中果糖磷酸酯的质量比为4％，第一碳源中的非碳元素为P。
S4：将混合物料在720℃进行第二次烧结，烧结时间为7h，并通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，质量比例为3.2：5.8：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为65mL/min，通入时间为7h，在芯部的表面形成第一碳层；
S5：保持第二次烧结的温度，以及通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，雾化第二碳源的气流量为65mL/min，通入时间为2.5h，在第一碳层的表面形成第二碳层，得到正极材料。
对比例1
如图3所示，本对比例的正极材料包括内核21以及包覆于内核21表面的碳包覆层22，碳包覆层22的总孔容为0.137cm3/g，厚度为3.10nm；内核21的粒径64nm-395nm；正极材料的比表面积为17.85m2/g。
本对比例的正极材料的制备方法包括以下步骤：
S1：将碳酸锂、乙酸亚铁、磷酸二氢铵、碳酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中乙酸亚铁和碳酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，水和乙二酸分别按前述原料总质量比的350％、2.5％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体。
S2：将内核前驱体材料在氮气气氛中，在400℃温度下进行第一次烧结，烧结时间6h，得到内核。
S3：将内核与葡萄糖和果糖磷酸酯(第一碳源)、水进行混合处理，得到混合物料。内核与第一碳 源的质量比为1：10，内核与水的质量比例为1：4。第一碳源中果糖磷酸酯的质量比为4％，第一碳源中的非碳元素为P。
S4：将混合物料在700℃进行第二次烧结，烧结时间为6h，得到正极材料。
对比例2
本对比例的正极材料包括芯部、第一碳层，第一碳层堆积于芯部的表面。其中，第一碳层的厚度3.25nm；芯部的粒径62nm-408nm；第一碳层的IG/ID值为1.05，正极材料的IG/ID值为1.04。
本对比例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源乳糖和羟丙基二淀粉磷酸酯、碳源溶剂水进行混合处理，得到混合物料，芯部与第一碳源的质量比为1：12，芯部与碳源溶剂的质量比例为1：5，第一碳源中羟丙基二淀粉磷酸酯的质量比为5％，第一碳源中的非碳元素为P；
S4：将混合物料在720℃进行第二次烧结，烧结时间为9.5h，并通入雾化第二碳源丁酮、聚乙二醇和甲酸铵，质量比例为3.2：5.8：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为65mL/min，通入时间为7h，在芯部的表面形成第一碳层。
对比例3
本对比例提供一种正极材料，包括芯部、第一碳层和第二碳层，第一碳层堆积于芯部的表面，第二碳层包覆于第一碳层的表面，第二碳层的石墨化程度高于第一碳层的石墨化程度。其中，第一碳层的厚度3.12nm；芯部的粒径65nm-465nm；正极材料的IG/ID值为0.69。
本对比例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源乳糖和羟丙基二淀粉磷酸酯、碳源溶剂水进行混合处理，得到混合物料，芯部与第一碳源的质量比为1：15，芯部与碳源溶剂的质量比例为1：5，第一碳源中羟丙基二淀粉磷酸酯的质量比为5％，第一碳源中的非碳元素为P；
S4：将混合物料在720℃进行第二次烧结，烧结时间为9.5h，得到正极材料。
对比例4
本对比例提供一种正极材料，包括芯部、第一碳层和第二碳层，第一碳层堆积于芯部的表面，第二碳层包覆于第一碳层的表面，第二碳层的石墨化程度高于第一碳层的石墨化程度。其中，第一碳层的厚度3.17nm，第二碳层的厚度为1.05nm；芯部的粒径52nm-403nm；第一碳层的IG/ID值为1.08，第二碳层的IG/ID值为1.02，正极材料的IG/ID值为1.05。
本对比例正极材料的制备方法包括以下步骤：
S1：将碳酸锂、磷酸铁、磷酸二氢铵、乙酸锰按照Li:(Fe+Mn):P＝1：1：1的元素摩尔比进行配置并混合，其中磷酸铁和乙酸锰按照Fe：Mn＝1：1.5的元素摩尔比进行配置，前驱体溶剂水和助溶剂柠檬酸分别按前述原料质量比的400％、3.0％进行掺入并混合，混合后的溶液pH为6.0，进行反应后，得到磷酸锰铁锂材料前驱体；
S2：将芯部前驱体材料在氮气气氛中，420℃温度下进行第一次烧结，烧结时间5.5h，得到芯部；
S3：将芯部与第一碳源乳糖和羟丙基二淀粉磷酸酯、碳源溶剂水进行混合处理，得到混合物料。芯部与第一碳源的质量比为1：12，芯部与碳源溶剂的质量比例为1：5。第一碳源中羟丙基二淀粉磷酸酯的质量比为5％，第一碳源中的非碳元素为P；
S4：将混合物料在720℃进行第二次烧结，烧结时间为7h，并通入雾化第二碳源丁酮、聚乙二醇和 甲酸铵，质量比例为3.2：5.8：1，第二碳源中的非碳元素为N，雾化第二碳源的气流量为65mL/min，通入时间为7h，在芯部的表面形成第一碳层；
S5：降低第二次烧结温度至670℃，通入雾化第二碳源丁酮和聚乙二醇，质量比例为6：4，雾化第二碳源的气流量为65mL/min，通入时间为4h，在第一碳层的表面形成第二碳层，得到正极材料。
性能测试实验
正极材料的测试方法：
1.碳层厚度：采用透射电子显微镜(TEM)拍摄正极材料的碳层，采用Image J软件统计碳层的厚度，其中，实施例1-6，对比例1的碳层厚度测试结果见表1，实施例7-12，对比例2-4的碳层厚度测试结果见表2，实施例7正极材料的TEM照片如图8所示。
2.内核粒径：采用扫描电子显微镜(SEM)拍摄正极材料的碳层，采用Image J软件统计颗粒的一次粒径，其中，实施例1-6，对比例1的结果见表1，实施例7-12，对比例2-4的结果见表2，实施例7的芯部(内核)的SEM照片如图9所示。
3.碳层孔容：正极材料碳层孔容采用静态氮气吸附法进行测试，取2-3g样品装在U型的样品管内，在真空下加热脱气后置于液氮中，粉体表面对氮气产生吸附，测量吸附压力和物质表面吸附的气体体积即可得到孔容、孔径分布等数据，其中，实施例1正极材料的和对比例1正极材料的孔容、孔径分布图如图6所示，具体地，实施例1-6、对比例1的正极材料的孔容、孔径测试结果见表1。
4.比表面积：采用态氮气吸附法进行测试，取2-3g样品装在U型的样品管内，在真空下加热脱气后置于液氮中，粉体表面对氮气产生吸附，测量吸附压力和物质表面吸附的气体体积即可求出样品的比表面积，实施例1-6、对比例1的正极材料的测试结果见表1。
5.粉末电阻率：采用自动规划粉末电阻率测试仪测试正极材料的粉末电阻率，样品质量0.5000-0.5050g，测试压力8Mpa，保压时间5s。粉末电阻率可以反映材料的外部导电性，可从侧面反映出正极材料的碳包覆层的电子传输能力及包覆均匀程度，实施例7-12、对比例2-4的测试结果见表2。
6.碳含量：采用碳硫分析仪测试正极材料的碳含量，样品质量约0.1g，助溶剂1.5g，实施例7-12、对比例2-4的测试结果见表2。
7.石墨化程度：采用拉曼光谱仪(Raman)测试正极材料碳层(包括第一碳层和正极材料总碳层，第二碳层采用陶瓷片单独收集后进行测试)的碳谱，扫描范围为3500cm□1□100cm□1，激光波长为532nm。由于拉曼散射对碳结构中的偏移对称性反应非常敏感，具有石墨结构的碳材料在其拉曼光谱上会呈现出D(Defect)峰和G(Graphite)峰这两个特征峰，其中，D峰的位置在1350cm□1附近，代表具有缺陷的石墨层结构；G峰在1580cm□1附近，代表完整的石墨层结构，D峰和G峰均属于sp2杂化碳。采用PeakFit软件对测试的正极材料拉曼光谱进行分峰拟合后，可将sp2杂化碳峰和无序化结构的sp3杂化碳峰分离，用IG/ID表征碳材料的石墨化程度，值越大，表示石墨化程度越高，其中，实施例7的芯部的拉曼光谱拟合分析图如图10所示，实施例7-12、对比例2-4正极材料的拉曼光谱拟合分析结果见表2。
二次电池的组装和充放电容量测试方法：
1.正极片：按照NMP：磷酸锰铁锂正极材料：Super P：PVDF的质量比为100:93:2:3的比例混合配置正极浆料，混合方式为球磨，球磨时间为120min；转速设置为30Hz；经过匀浆-涂布-烘干-裁片操作，分别制备成正极片，正极片在100℃真空烘箱中烘烤12h至恒重。
2.负极片：金属锂片。
3.隔膜：使用聚乙烯(PE)隔膜。
4.电解液：电解液为1mol/L的LiPF6溶液，溶剂由EC(碳酸乙烯酯)和DEC(碳酸二乙酯)按体积比1:1组成。
5.二次电池的组装：在负极壳中心的位置处依次压平锂片、隔膜、正极片、垫片、弹片和正极壳，其中隔膜上滴加适量的电解液润湿，组装完成后利用纽扣电池封装机封装电池得到扣式电池，静置12h后上架，进行相应的电化学性能测试。
6.正极浆料的测试方法：电池在温度25℃±2℃，湿度<2％RH条件下，按照电池充放电测试仪操作规程测试出模拟电池的0.1C放电比容量数据，结果见表1和表2。
全电正极浆料的制备方法浆料气泡的观察：采用真空搅拌器在进行正极浆料的制备，匀浆方式为湿法，制浆结束后采用图像拍照法记录浆料中的气泡情况，结果见表1。表1包括各实施例正极材料的物化 参数、充放电容量及制浆产气泡情况。
表1
从表1中的数据可以看出，本申请实施例1制备的磷酸盐正极材料在确保重0.1C充放电容量最为优异的情况下，同时具有最低的比表面积和总孔容，进一步制备出的正极浆料无气泡，这得益于小孔容的原位裂解和/或气相沉积得到修饰碳的修饰填充作用。实施例2改变第一碳源和第二碳源种类、用量及烧结条件后，制备出的正极材料较实施例1而言，比表面积、孔容增加，电性能下降，进一步制备出的正极浆料出现了少量气泡。
当分别改变步骤S3第一碳源和步骤S5第二碳源的用量，制备出实施例3、实施例4正极材料时，多碳嵌合层和外包碳层的厚度对应增加，比表面积、总孔容均增大，电性能稍有降低，但仅实施例3正极材料制备出的浆料出现了气泡，实施例4的无气泡，且实施例4正极材料的颗粒几何特性、电性能比实施例3的更好，这表明第二碳源采用原位裂解和/或气相沉积的方式形成的修饰碳具有更少的孔结构和更优良的电子传导性。
实施例5正极材料的多碳嵌合层和外包碳层中不含非碳元素，其孔容和比表面均比实施例1略大，但电性能略差，表明碳层中引入非碳元素能够使碳层更加致密且改善正极材料的电子传导性，这可能与其能增大碳层的石墨化程度相关。
实施例6正极材料的碳层仅包括多碳嵌合层，总孔容较小，制备的浆料同样不含气泡，但电性能较差，说明外包碳层具有增强正极材料电子传导性的作用，这与其石墨化程度较高和对颗粒多碳嵌合层表面的进一步修饰作用相关。
对比例1正极材料仅进行了原位碳包覆，其综合性能最差，制备的正极浆料也出现了较多的气泡。实施例与对比例正极材料的颗粒几何特性、电性能、浆料气泡情况对比结果表明，本申请实施例制备的具有多碳嵌合中间层和外包碳层的正极材料能减少碳层中的孔隙率，有效降低材料的比表面积，同时提升材料电性能，并最终使浆料中的气泡得到消除或改善。
表2
表2为实施例7-12、对比例2-4正极材料的物化参数、碳层石墨化程度，由表2结合表1中的数据可见，本申请实施例7制备的磷酸盐正极材料碳含量适中，第一碳层、第二碳层以及正极材料总碳包覆层均具有较高的石墨化程度，电阻率较低，一次颗粒粒径范围较小，0.1C充放电克容量最高，综合性能最佳。
以实施例7为参照，对比分析其它实施例正极材料的物化指标、石墨化程度和电性能变化，可得出：
实施例8改变步骤S3至步骤S5第一碳源和第二碳源种类、增加碳源用量、降低第二次烧结温度后，正极材料的碳含量增加，碳层石墨化程度下降，电阻率增大，一次颗粒粒径最小，但电性能反而下降，表明碳含量过高、碳层过厚使正极材料中的锂离子脱嵌更难，烧结温度降低后使碳层石墨化程度降低也不利于碳层间电子的传导；
当增大步骤S3至步骤S5第一碳源和第二碳源用量，升高第二次烧结温度制备出实施例9正极材料，其碳含量增加，碳层石墨化程度最高，电阻率最低，但电性能表现最差，这主要归因于烧结温度升高后正极材料的一次颗粒粒径明显增大，这使晶体内锂离子的扩散距离增长，材料动力学变差；
当降低步骤S3至步骤S5第一碳源和第二碳源用量，降低第二次烧结温度制备出实施例10正极材料，其碳含量降低，碳层厚度减薄，石墨化程度降低，电阻率增大，电性能下降，表明碳源用量过少难以形成良好的碳包覆导电网络，温度降低时也难以使碳层形成更多的石墨层结构，这均导致电性能下降；
实施例11正极材料的第一碳层和第二碳层均不含非碳元素，碳含量和碳层厚度与实施例7相近，但两种碳层的石墨化程度均降低，电阻率相应升高，电性能下降，这表明第一碳源和第二碳源中含有的非碳元素有利于碳层形成更完整的石墨层结构；
实施例12改变步骤S1至步骤S3的第一碳源种类、降低第一碳源用量、降低第一次烧结温度后，正极材料的碳含量降低，碳层厚度减薄，石墨化程度略微降低，电阻率升高，但均与实施例7较为相近，电性能表现较良好，表明当碳源用量和烧结温度接近于实施例7中条件时，即使改变碳源种类，同样可获得电性能较好的正极材料。
对比例2正极材料的芯部(内核)外仅有第一碳层，无第二碳层，其碳含量、碳层厚度相应减小， 碳层石墨化程度降低、电阻率增大，电性能下降，表明第二碳层作为石墨化程度更高的碳层，能有效改善正极材料整体的电子传导性，且在烧结过程中能一定程度上抑制晶体的生长，改善正极材料的动力学性能。
对比例3正极材料仅进行了原位包覆，其碳层的石墨化程度及电性能最差；对比例4正极材料在包覆第二碳层时调整了第二碳源比例、降低了烧结温度，第二碳层无非碳元素，这使第二碳层的石墨化程度比第一碳层更低，正极材料的电性能比实施例7更低、与对比例2相近，这表明碳层石墨化程度若形成由第一碳层至第二碳层(由内至外)梯度增大的空间分布趋势有利于使正极材料颗粒的外部电子导电性达到最佳效果，若石墨化程度形成由外至内的梯度增大的空间分布趋势，类似于有一层低导电性的碳层包覆于高导电性的碳层，这会对正极材料的表面电子传输造成阻碍，导致电性能下降。
综上所述，本申请实施例制备的正极材料包含芯部(内核)、第一碳层和第二碳层，第一碳层结合于芯部的表面，第二碳层包覆于第一碳层的表面，第二碳层的石墨化程度高于第一碳层的石墨化程度，这有利于提高正极材料的表面电子传输能力，降低粉末间电阻率，提升正极材料的电性能。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本申请的保护范围之内。

Claims (24)

  1. 一种正极材料，其特征在于：包括内核以及第一碳层，所述第一碳层为多碳嵌合层，所述多碳嵌合层包括主体骨架碳以及修饰碳，所述主体骨架碳结合于所述内核的表面，所述修饰碳嵌合生长于所述主体骨架碳中。
  2. 根据权利要求1所述的正极材料，其特征在于：所述主体骨架碳中的碳呈碳片堆叠状结合于所述内核的表面；和/或，
    所述修饰碳的碳呈碳片状嵌合于所述主体骨架碳中；和/或，
    所述主体骨架碳在所述多碳嵌合层中的质量含量为80％-90％，所述修饰碳在所述多碳嵌合层中的质量含量为10％-20％。
  3. 根据权利要求1或2所述的正极材料，其特征在于：所述主体骨架碳中的碳片长度大于所述修饰碳的碳片长度，所述修饰碳中的碳片长度＜2nm；和/或，
    所述多碳嵌合层的孔容＜0.070cm3/g；和/或，
    所述多碳嵌合层的厚度＜10nm；和/或
    所述第一碳层的IG/ID值为0.75-1.5。
  4. 根据权利要求1-3任一所述的正极材料，其特征在于：所述多碳嵌合层包括碳元素和第一非碳元素；
    其中，所述第一非碳元素包括N、S、P、Li中的至少一种；和/或，
    所述碳元素在所述第一碳层中的质量含量为97％-98.5％，所述第一非碳元素在所述第一碳层中的质量含量为1.5％-3％。
  5. 根据权利要求1-4任一所述的正极材料，其特征在于：所述正极材料还包括第二碳层，所述第二碳层为外包碳层，所述外包碳层包覆于所述多碳嵌合层的外表面。
  6. 根据权利要求5所述的正极材料，其特征在于：所述外包碳层的孔容＜0.020cm3/g；和/或，
    所述外包碳层的厚度＜1.5nm，并且所述外包碳层的厚度小于所述多碳嵌合层的厚度。
  7. 根据权利要求5或6所述的正极材料，其特征在于：所述第二碳层的石墨化程度高于所述第一碳层的石墨化程度。
  8. 根据权利要求5-7任一所述的正极材料，其特征在于：所述第一碳层中的碳结构长程无序化程度高于所述第二碳层中的碳结构长程无序化程度。
  9. 根据权利要求5-8任一所述的正极材料，其特征在于：所述第一碳层的大部分碳结构为较长碳片结构，所述较长碳片结构堆积于所述内核的表面；所述第二碳层的大部分碳结构为较短碳片结构，并以非连续的、方向各异性的方式堆积于所述第一碳层的表面；所述较长碳片结构的尺寸大于所述较短碳片结构的尺寸。
  10. 根据权利要求5-9任一所述的正极材料，其特征在于：所述第二碳层包括碳元素和第二非碳元素；
    其中，所述第二非碳元素包括N、P、Li元素中的至少一种；和/或，
    所述碳元素在所述第二碳层的质量含量为98％-99％，所述第二非碳元素在所述第二碳层的质量含量为1％-2％。
  11. 根据权利要求5-10任一所述的正极材料，其特征在于：所述第二碳层的IG/ID值为1.0-1.9。
  12. 根据权利要求1-11任一所述的正极材料，其特征在于：所述内核含有磷元素，并且所述内核的部分磷与所述多碳嵌合层的部分碳形成C-P键和/或C-O-P键。
  13. 根据权利要求12所述的正极材料，其特征在于：所述C-P键和C-O-P键的成键率为0.5％-1.15％。
  14. 根据权利要求1-13任一所述的正极材料，其特征在于：所述内核为含锂磷酸盐系正极活性材料内核；和/或，
    所述内核的粒径＜400nm。
  15. 根据权利要求1-14任一所述的正极材料，其特征在于：所述正极材料的总孔容为0.04cm3/g-0.10cm3/g；和/或，
    所述正极材料的比表面积为12.0m2/g-17.0m2/g；和/或，
    所述正极材料的IG/ID值为0.8-1.25。
  16. 一种正极材料的制备方法，用于制备如权利要求1至15任一所述的正极材料，其特征在于，所述制备方法包括以下步骤：
    提供内核前驱体材料，将所述内核前驱体材料在惰性气氛下进行第一次烧结，得到内核；
    将所述内核与第一碳源、碳源溶剂进行混合处理，得到混合物料；
    将所述混合物料在惰性气氛下进行第二次烧结，并且第二次烧结过程中通入雾化第二碳源，所述第一碳源原位裂解形成主体骨架碳堆积于所述内核的表面，所述第二碳源原位裂解和/或气相沉积形成修饰碳，所述修饰碳交织嵌合于所述主体骨架碳中，形成第一碳层，所述第一碳层为多碳嵌合层，得到所述正极材料。
  17. 根据权利要求16所述的正极材料的制备方法，其特征在于：所述内核前驱体材料为磷酸锰铁锂前驱体，所述磷酸锰铁锂前驱体的制备方法包括以下步骤：
    将锂源、铁源、磷源、锰源、前驱体溶剂和助溶剂按比例进行混合并反应，得到磷酸锰铁锂前驱体。
  18. 根据权利要求17所述的正极材料的制备方法，其特征在于：所述锂源、铁源、磷源、锰源、前驱体溶剂和助溶剂混合后得到的混合溶液的pH为5.0至7.5。
  19. 根据权利要求16-18任一所述的正极材料的制备方法，其特征在于：所述第一碳源包括羟丙基二淀粉磷酸酯、葡萄糖、果糖、蔗糖、乳糖、甜菊糖、木糖、麦芽糖、淀粉、纤维素、壳多糖、D-氨基葡萄糖、硫酸氨基葡萄糖、果糖磷酸酯、葡萄糖-6-磷酸、N-乙酰氨基葡萄糖、肽聚糖、聚丙烯酸酯、聚乙二醇、柠檬酸、苹果酸、丙烯、聚丙二醇、聚丙烯、聚丙烯酰胺、聚丙烯酸锂、聚乙烯醇、环糊精、聚乙烯醇缩丁醛、聚苯乙烯、石墨中的至少一种；和/或，
    所述第二碳源包括甲醇、乙醇、乙酸乙酯、聚乙二醇、丙酮、丁酮、乙醚、乙酸、乙二酸、聚丙二醇、苯胺、苯甲胺、对二氮杂苯、柠檬酸铵、甲酸铵、乙酸铵、甲酰胺、乙酰胺、丙酰胺、丁酰胺、一异丙醇胺、N,N-二甲基乙醇胺、二甲基乙醇胺、三乙烯二胺中的至少两种。
  20. 根据权利要求16-19任一所述的正极材料的制备方法，其特征在于：所述第一碳源和所述第二碳源中的至少一碳源包括碳元素和第一非碳元素，所述第一非碳元素包括N、S、P、Li元素中的至少一种，碳元素在所述第一碳源和所述第二碳源总质量中的质量含量为97％-98.5％，所述第一非碳元素在所述第一碳源和所述第二碳源总质量中的质量含量为1.5％-3％。
  21. 根据权利要求16-20任一所述的正极材料的制备方法，其特征在于：所述正极材料还包括第二碳层，第二碳层为外包碳层，在形成所述多碳嵌合层之后，还包括以下步骤：
    所述第二碳源裂解完全，继续通入雾化所述第二碳源，所述第二碳源通过原位裂解和/或气相沉积在多碳嵌合层的表面形成外包碳层。
  22. 根据权利要求16-21任一所述的正极材料的制备方法，其特征在于：所述制备方法满足以下(1)-(4)中的至少一个条件：
    (1)所述第一次烧结的温度为350℃-660℃；
    (2)所述第二次烧结的温度为650℃-855℃；
    (3)所述第二碳源雾化气体的气流量为10mL/min-120mL/min；
    (4)所述第二碳源包括碳元素和第二非碳元素，所述第二非碳元素包括N、P、Li元素中的至少一种，碳元素在所述第二碳源中的质量含量为98％-99％，所述第二非碳元素在所述第二碳源中的质量含量为1％-2％。
  23. 一种正极片，其特征在于：采用权利要求1至16任一所述的正极材料或由权利要求17至22任一所述正极材料的制备方法制备的正极材料制成。
  24. 一种二次电池，其特征在于：包括如权利要求23所述的正极片。
PCT/CN2023/129924 2023-08-18 2023-11-06 正极材料及其制备方法、正极片与二次电池 Pending WO2025039376A1 (zh)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP23923210.1A EP4535462A4 (en) 2023-08-18 2023-11-06 POSITIVE ELECTRODE MATERIAL AND ITS PREPARATION PROCESS, POSITIVE ELECTRODE SHEET AND SECONDARY BATTERY
JP2024557963A JP2025530949A (ja) 2023-08-18 2023-11-06 正極材料及びその製造方法、正極板並びに二次電池
US18/843,575 US20260109604A1 (en) 2023-08-18 2023-11-06 Cathode material, preparation method thereof, cathode plate, and secondary battery

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
CN202311049485.9 2023-08-18
CN202311049489.7 2023-08-18
CN202311049485.9A CN117080387A (zh) 2023-08-18 2023-08-18 正极材料及其制备方法、正极片与二次电池
CN202311049489.7A CN117080388A (zh) 2023-08-18 2023-08-18 碳包覆正极材料及其制备方法、正极片与二次电池

Publications (1)

Publication Number Publication Date
WO2025039376A1 true WO2025039376A1 (zh) 2025-02-27

Family

ID=94731268

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2023/129924 Pending WO2025039376A1 (zh) 2023-08-18 2023-11-06 正极材料及其制备方法、正极片与二次电池

Country Status (4)

Country Link
US (1) US20260109604A1 (zh)
EP (1) EP4535462A4 (zh)
JP (1) JP2025530949A (zh)
WO (1) WO2025039376A1 (zh)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN120208305A (zh) * 2025-05-21 2025-06-27 南通金通储能动力新材料有限公司 一种金属氧化物前驱体及其制备方法和应用

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102522546A (zh) * 2011-12-27 2012-06-27 江苏中电长迅能源材料有限公司 纳米锂离子电池级正极材料磷酸亚铁锂的制备方法
JP2016157684A (ja) * 2015-02-24 2016-09-01 東レ株式会社 炭素被覆ポリアニオン系正極活物質粒子の製造方法および炭素被覆ポリアニオン系正極活物質粒子の製造のための中間体粒子
CN109244462A (zh) * 2018-11-20 2019-01-18 浙江瑞邦科技有限公司 一种高电导率磷酸铁锂材料的制备方法
CN112897491A (zh) * 2021-01-21 2021-06-04 广东邦普循环科技有限公司 磷酸铁锂正极材料的制备方法和应用
WO2023273917A1 (zh) * 2021-06-30 2023-01-05 清华大学 正极材料及其制备方法和锂离子电池

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103443972B (zh) * 2011-01-17 2016-08-17 昭荣化学工业株式会社 锂离子二次电池用正极材料及其制造方法
JP2015118874A (ja) * 2013-12-19 2015-06-25 トヨタ自動車株式会社 リチウム電池用正極材料及びその製造方法
TWI801064B (zh) * 2021-12-27 2023-05-01 台灣立凱電能科技股份有限公司 碳包覆正極材料及其製備方法
KR20250088624A (ko) * 2023-02-07 2025-06-17 컨템포러리 엠퍼렉스 테크놀로지 (홍콩) 리미티드 양극 활물질 및 이의 제조 방법, 양극편, 배터리 및 전기 장치

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102522546A (zh) * 2011-12-27 2012-06-27 江苏中电长迅能源材料有限公司 纳米锂离子电池级正极材料磷酸亚铁锂的制备方法
JP2016157684A (ja) * 2015-02-24 2016-09-01 東レ株式会社 炭素被覆ポリアニオン系正極活物質粒子の製造方法および炭素被覆ポリアニオン系正極活物質粒子の製造のための中間体粒子
CN109244462A (zh) * 2018-11-20 2019-01-18 浙江瑞邦科技有限公司 一种高电导率磷酸铁锂材料的制备方法
CN112897491A (zh) * 2021-01-21 2021-06-04 广东邦普循环科技有限公司 磷酸铁锂正极材料的制备方法和应用
WO2023273917A1 (zh) * 2021-06-30 2023-01-05 清华大学 正极材料及其制备方法和锂离子电池

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP4535462A4

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN120208305A (zh) * 2025-05-21 2025-06-27 南通金通储能动力新材料有限公司 一种金属氧化物前驱体及其制备方法和应用

Also Published As

Publication number Publication date
EP4535462A4 (en) 2025-12-31
US20260109604A1 (en) 2026-04-23
EP4535462A1 (en) 2025-04-09
JP2025530949A (ja) 2025-09-19

Similar Documents

Publication Publication Date Title
EP3309873B1 (en) Anode active material for lithium secondary battery, preparation method therefor, and lithium secondary battery containing same
WO2023093893A1 (zh) 纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置
WO2024050756A1 (zh) 硅碳负极材料及其制备方法、二次电池和用电装置
JP2014216240A (ja) 電極活物質と電極材料及び電極、リチウムイオン電池並びに電極材料の製造方法
CN115101739A (zh) 多功能碳化硅碳负极材料制备方法及硅碳负极材料
CN117080388A (zh) 碳包覆正极材料及其制备方法、正极片与二次电池
CN116525776A (zh) 纳米硅氧碳复合材料及其制备方法和应用
CN117457882A (zh) 一种硅基负极材料及其制备方法、电池、应用
CN115863574A (zh) 一种负极材料及包括该负极材料的负极片和电池
WO2024001581A1 (zh) 负极材料及其制备方法、电池
EP4614588A2 (en) Negative electrode material, and preparation method and use thereof
WO2024061099A1 (zh) 复合负极材料及其制备方法和应用
US20250239598A1 (en) Negative electrode material and preparation method thereof, secondary battery, and power-consuming device
CN116598491A (zh) 补锂材料及其制备方法、正极片和二次电池
CN117080387A (zh) 正极材料及其制备方法、正极片与二次电池
CN118748241A (zh) 一种自支撑高强度硅碳负极及其制备方法
WO2025039376A1 (zh) 正极材料及其制备方法、正极片与二次电池
CN115954476B (zh) 快充负极材料、其制备方法及锂离子电池
CN118511347A (zh) 负极活性材料、负极极片、二次电池、用电装置和制备方法
CN120221626A (zh) 一种硅基复合材料、负极极片与二次电池
CN118919673A (zh) 一种硅碳负极材料及其制备方法与应用
CN118738336A (zh) 一种磷酸盐系正极材料及其制备方法和应用
CN118507685A (zh) 一种硅碳复合负极材料及其制备方法和应用
CN118315560A (zh) 一种复合正极材料及其制备方法和应用
Wang et al. Simple fabrication of Ni nanodots decorated Ni/Ketjen black composite for sulfur host in lithium‐sulfur battery

Legal Events

Date Code Title Description
WWE Wipo information: entry into national phase

Ref document number: 18843575

Country of ref document: US

ENP Entry into the national phase

Ref document number: 2023923210

Country of ref document: EP

Effective date: 20240829

ENP Entry into the national phase

Ref document number: 2024557963

Country of ref document: JP

Kind code of ref document: A

WWE Wipo information: entry into national phase

Ref document number: 2024557963

Country of ref document: JP

WWP Wipo information: published in national office

Ref document number: 2023923210

Country of ref document: EP

NENP Non-entry into the national phase

Ref country code: DE