WO2023046048A1 - 电池正极材料及其制备方法和应用 - Google Patents

电池正极材料及其制备方法和应用 Download PDF

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WO2023046048A1
WO2023046048A1 PCT/CN2022/120748 CN2022120748W WO2023046048A1 WO 2023046048 A1 WO2023046048 A1 WO 2023046048A1 CN 2022120748 W CN2022120748 W CN 2022120748W WO 2023046048 A1 WO2023046048 A1 WO 2023046048A1
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positive electrode
battery
lithium
electrode material
limn
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French (fr)
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程斌
潘仪
庄明昊
叶钰珍
邓若燚
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BYD Co Ltd
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BYD Co Ltd
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Priority to EP22872092.6A priority Critical patent/EP4343888A4/en
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Priority to JP2023579123A priority patent/JP7734218B2/ja
Publication of WO2023046048A1 publication Critical patent/WO2023046048A1/zh
Priority to US18/394,462 priority patent/US20240186490A1/en
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Definitions

  • the present application relates to the field of lithium ion batteries, in particular to a battery cathode material and its preparation method and application.
  • LiFePO 4 Polyanionic lithium iron phosphate LiFePO 4 is recognized as the safest cathode material for lithium-ion batteries, but its theoretical energy density is low (586Wh/kg), which largely limits its wide application. Lithium manganese phosphate LiMnPO 4 has a similar structure to lithium iron phosphate, and has a higher theoretical energy density (701Wh/kg), which has great application prospects.
  • lithium manganese phosphate ⁇ 10 -10 S/cm and 10 -15 cm 2 /s, respectively
  • lithium iron phosphate 10 -9 S/cm and 10 -14 cm 2 /s
  • there is a problem of dissolving divalent Mn which makes it difficult for lithium manganese phosphate to obtain excellent electrochemical performance.
  • a more feasible solution is to partially replace Mn with Fe to form LiMn x Fe 1-x PO 4 (0 ⁇ x ⁇ 1), which is a compromise between energy density and kinetic properties, and on this basis, the material Make necessary modifications to obtain materials with excellent properties.
  • the first aspect of the present application provides a battery positive electrode material, including an inner core and a first shell layer disposed on the inner core, the inner core includes LiMn x Fe 1-x PO 4 , and the first shell layer includes LiMn y Fe 1-y PO 4 , where 0 ⁇ x ⁇ 0.4, 0.6 ⁇ y ⁇ 0.9.
  • the mass ratio of the inner core to the first shell is 1:(1.5-9).
  • the diameter of the inner core is 0.5 ⁇ m-5 ⁇ m.
  • the thickness of the first shell layer is 0.09 ⁇ m-2.7 ⁇ m.
  • the molar ratio of Fe element to Mn element is 1:(1-9).
  • a second shell layer is further provided on the surface of the first shell layer, and the second shell layer includes LiFePO 4 and carbon.
  • the thickness of the second shell layer is 20 nm-600 nm.
  • the mass percentage of the inner core is 10%-40%; the mass percentage of the first shell layer is 45%-80%; the The mass percentage of the second shell layer is 10%-20%.
  • the positive electrode material of the battery further includes a doping element
  • the doping element includes one of Ti, V, Co, Ni, Cu, Zn, Mg, Al, Ca, Mo, W or more; the doping element accounts for 0.1%-0.5% by mass of the positive electrode material of the battery.
  • the first shell layer includes the doping element.
  • the carbon accounts for 1%-3% by mass of the positive electrode material of the battery.
  • the second aspect of the present application provides a method for preparing a battery positive electrode material, including:
  • Lithium source, iron source, manganese source, phosphorus source and solvent are placed in the reactor for the first reaction to obtain the inner core, the inner core includes LiMn x Fe 1-x PO 4 , where 0 ⁇ x ⁇ 0.4; the second The temperature of the first reaction is 375°C-500°C, and the pressure of the first reaction is greater than or equal to 23Mpa;
  • the first shell layer includes LiMny Fe 1-y PO 4 , where 0.6 ⁇ y ⁇ 0.9; the temperature of the second reaction is 375°C-500°C, and the pressure of the second reaction is greater than or equal to 23Mpa;
  • the inner core provided with the first shell layer is calcined at 500° C. to 800° C. to obtain the positive electrode material of the battery.
  • the inner core provided with the first shell further includes: placing a lithium source, an iron source, a phosphorus source, a carbon source, a solvent and the inner core provided with the first shell Carry out the third reaction in the reactor, coat the second shell layer on the surface of the first shell layer, the second shell layer includes LiFePO 4 and carbon; the temperature of the third reaction is 375°C-500°C, The pressure of the third reaction is greater than or equal to 23Mpa.
  • the lithium source includes inorganic lithium salts and organic lithium salts;
  • the inorganic lithium salts include lithium carbonate, lithium bicarbonate, lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium phosphate, lithium nitrate, One or more of lithium sulfate, lithium chromate, and lithium hydroxide;
  • the organic lithium salt includes one or more of lithium oxalate, lithium acetate, lithium benzoate, lithium citrate, and lithium benzoate.
  • the iron source includes one or more of iron oxide, ferrous carbonate, ferrous oxalate, ferrous sulfate, ferrous chloride and ferrous acetate.
  • the manganese source includes one of manganese monoxide, manganese dioxide, manganese hydroxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese nitrate, manganese sulfate, manganese chloride and manganese acetate or more.
  • the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, and lithium dihydrogen phosphate.
  • the carbon source includes one or more of glucose, sucrose, polyvinyl alcohol, starch, and citric acid.
  • the calcination is performed under an inert atmosphere, and the inert atmosphere includes one or more of nitrogen, argon, helium, neon, krypton, xenon, and radon.
  • the third aspect of the present application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, the positive electrode includes a positive electrode sheet, and the positive electrode sheet includes a current collector and a positive electrode material disposed on the current collector layer, the positive electrode material layer includes the battery positive electrode material as described in the first aspect.
  • Fig. 1 is a battery cathode material according to an embodiment of the present application
  • Fig. 2 is the structural representation of the positive electrode material of the battery of structure A;
  • Fig. 3 is the structural representation of the positive electrode material of structure B;
  • FIG. 4 is a method for preparing a battery positive electrode material according to an embodiment of the present application.
  • Fig. 5 is a method for preparing a battery anode material according to another embodiment of the present application.
  • lithium manganese phosphate LiMnPO 4 has a higher theoretical energy density than lithium iron phosphate, its electronic conductivity and lithium ion diffusion rate are lower than those of lithium iron phosphate, which is not conducive to its capacity. Moreover, in the positive electrode material of the battery, the ions and electrons inside the material have a long distance to travel outward, and the transport of ions and electrons is relatively difficult, which further limits the capacity of the lithium manganese phosphate positive electrode material.
  • this battery positive electrode material will LiMn x Fe 1-x PO 4 (0.6 ⁇ The x ⁇ 1) part is placed in the outer layer, and the LiMn x Fe 1-x PO 4 (0 ⁇ x ⁇ 0.4) part with low manganese content and better electronic and ionic conductivity is placed in the inner layer, thereby effectively shortening the electron.
  • the distance between the ion transport difficult part (the difficult transport part refers to the part in which the transport is relatively difficult), improves the electrochemical performance of the positive electrode material.
  • FIG. 1 is a battery anode material according to an embodiment of the present application.
  • the battery anode material of the present application includes an inner core 10 and a first shell layer 20 disposed on the surface of the inner core 10 , and the first shell layer 20 completely covers the inner core 10 .
  • the inner core 10 includes the lithium manganese iron phosphate compound shown in formula I
  • the first shell layer 20 includes the lithium manganese iron phosphate compound shown in formula II.
  • LiMn x Fe 1-x PO 4 formula I, where 0 ⁇ x ⁇ 0.4.
  • LiMn y Fe 1-y PO 4 formula II, wherein, 0.6 ⁇ y ⁇ 0.9.
  • ions and electrons have a longer diffusion path from the inner core of the material, which is not conducive to the transport of ions and electrons.
  • doping Fe elements in LiMnPO 4 can improve the conductivity of the positive electrode material.
  • the proportion of iron element can increase the diffusion rate of ions and electrons, thereby improving the electrochemical performance of the positive electrode material.
  • the first shell layer has a relatively high proportion of manganese element, thereby ensuring that the positive electrode material of the battery has a high energy density.
  • the value of x in LiMn x Fe 1-x PO 4 may be, but not limited to, 0.1, 0.2, 0.3 or 0.4, and in LiMn y Fe 1-y PO 4 , the value of y may be, but not limited to Limited to 0.6, 0.7, 0.8 or 0.9. Controlling x to be less than or equal to 0.4 can ensure high electrical conductivity of the inner layer, and controlling y to be greater than or equal to 0.6 can ensure high energy density of the material as a whole. In some embodiments of the present application, the value of x is 0.2-0.3, and the value of y is 0.8-0.9.
  • the mass percentage content of the iron element in the inner core is higher than the mass percentage content of the iron element in the first shell layer, and the higher proportion of iron in the inner core can make the inner core have better conductivity and improve
  • the transmission speed of ions and electrons at the core position promotes the transmission of ions and electrons inside the positive electrode material of the battery;
  • the first shell layer has a high proportion of manganese content, thereby ensuring that the positive electrode material of the battery has a high energy density as a whole.
  • the positive electrode material with the structure B is used as a comparison below to illustrate that the positive electrode material with the structure of the present application can improve the electrochemical performance of the material.
  • the anode material of this application takes structure A as an example, the composition of the battery anode material of structure A from inside to outside is LiMn 0.2 Fe 0.8 PO 4 (40%)/LiMn 0.8 Fe 0.2 PO 4 (60%), wherein, LiMn 0.2 Fe 0.8 PO 4 accounts for 40% by mass of the positive electrode material of the battery, and LiMn 0.8 Fe 0.2 PO 4 accounts for 60% by mass of the positive electrode material of the battery.
  • composition of the positive electrode material of structure B from the inside to the outside is LiMn 0.8 Fe 0.2 PO 4 (60%)/LiMn 0.2 Fe 0.8 PO 4 (40%), please refer to Figure 2 and Figure 3,
  • Figure 2 is the battery positive electrode of structure A Schematic diagram of the structure of the material
  • FIG. 3 is a schematic diagram of the structure of the positive electrode material of structure B.
  • the arrangement positions of the two layers of materials in structure A and structure B are opposite, that is, LiMn 0.8 Fe 0.2 PO 4 as the shell layer in structure A is the core in structure B, and LiMn 0.8 Fe 0.2 PO 4 in structure A and structure B 4 and LiMn 0.2 Fe 0.8 PO 4 with a mass ratio of 3:2, that is, the energy density of the positive electrode material of the structure A and the positive electrode material of the structure B are the same, and because LiMn 0.8 Fe 0.2 PO 4 and LiMn 0.2 The material density of Fe 0.8 PO 4 is almost equal, and although structure A and structure B are arranged differently, the overall particle size is similar.
  • the content of manganese in the inner core LiMn 0.8 Fe 0.2 PO 4 is relatively high and the content of iron is low, so the transport of electrons and ions in the inner core is more difficult, that is, the inner core is a difficult transport layer.
  • the maximum distance for the ion and electron transport in the transport difficult layer is 0.843R. The calculation of the transmission distance is as follows: Assuming that the radius of the positive electrode material is R, the radius of the inner core is R 1 , since the inner core LiMn 0.8 Fe 0.2 PO 4 accounts for 60% of the mass percentage of the positive electrode material, there is the following relationship between R and R 1 :
  • R 1 0.843R, that is, for the positive electrode material of structure B, the maximum transmission distance of ions and electrons in the transport-difficult layer is 0.843R.
  • the shell layer is the difficult transport layer, assuming that the radius of the positive electrode material of the battery is R, and the radius of the inner core is R 2 , the maximum transmission distance of ions and electrons in the difficult transport layer of the positive electrode material of the battery of structure A is RR 2 , its calculation is as follows:
  • the structure distribution of the present application can effectively shorten the transmission distance of ions and electrons in the battery positive electrode material that are difficult to transport, thereby improving the electrochemical performance of the battery positive electrode material. Performance, so that the battery cathode material can effectively improve the rate performance of the battery.
  • the mass proportion of the first shell layer in the positive electrode material of the battery is greater than that of the inner core. Further, the mass ratio of the inner core to the first shell layer is 1:(1.5-9).
  • the mass ratio of the inner core to the first shell may specifically be, but not limited to, 1:1.5, 1:2, 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9. Controlling the mass ratio of the first shell layer within the above range can ensure that the positive electrode material of the battery has a high energy density, and the inside of the material can also have high conductivity.
  • the core-shell distribution structure has a good adjustment effect on the cathode material, which can effectively improve the electrochemical performance of the cathode material.
  • the diameter of the inner core is 0.5 ⁇ m-5 ⁇ m, specifically, but not limited to, the diameter of the inner core may be 0.5 ⁇ m, 0.8 ⁇ m, 1 ⁇ m, 2 ⁇ m, 4 ⁇ m or 5 ⁇ m.
  • the thickness of the first shell layer is 0.09 ⁇ m-2.7 ⁇ m. Specifically, the thickness of the first shell layer may be, but not limited to, 0.09 ⁇ m, 0.1 ⁇ m, 0.5 ⁇ m, 1 ⁇ m, 2 ⁇ m or 2.7 ⁇ m.
  • the molar ratio of Fe element to Mn element in the positive electrode material of the battery is 1:(1-9).
  • the molar ratio of Fe element to Mn element in the positive electrode material of the battery may be, but not limited to, 1:1, 1:3, 1:5 or 1:9.
  • the composition of the battery positive electrode material from the inside to the outside is LiMn 0.2 Fe 0.8 PO 4 (20%)/LiMn 0.8 Fe 0.2 PO 4 (80%)
  • the molar ratio of Fe element to Mn element is 1:2.125. Controlling the molar ratio of Fe element to Mn element in the positive electrode material of the battery within the above range can ensure that the battery has a higher energy density.
  • the positive electrode material of the battery further includes doping elements, and the doping elements include one or more of Ti, V, Co, Ni, Cu, Zn, Mg, Al, and Ca, and the doping elements can improve Ionic and electronic conductivities of battery cathode materials.
  • both the inner core and the first shell layer of the positive electrode material of the battery can be doped with elements to improve conductivity.
  • the doping elements are located in the first shell layer of the positive electrode material of the battery.
  • the dopant element accounts for 0.1%-0.5% by mass of the positive electrode material of the battery. The mass percentage content of the doping element in the positive electrode material of the battery can be, but not limited to, 0.1%, 0.3%, 0.4% or 0.5%.
  • the surface of the first shell layer of the positive electrode material of the battery is further provided with a second shell layer, and the second shell layer includes LiFePO 4 and carbon. Since Mn will dissolve in the electrolyte and deposit at the interface between the electrode and the electrolyte to form a high-resistance layer, increase the internal resistance of the battery, and reduce the rate performance and cycle performance of the battery. Therefore, the surface of the first shell layer is coated with LiFePO 4 The first shell layer can be isolated from the electrolyte, thereby suppressing the dissolution of Mn. In some embodiments of the present application, LiFePO 4 accounts for 10%-20% by mass of the positive electrode material of the battery.
  • the mass percentage of LiFePO 4 in the positive electrode material of the battery may be, but not limited to, 10%, 13%, 15% or 20%.
  • the carbon in the second shell layer can improve the conductivity of the positive electrode material of the battery, and realize charging and discharging at a higher rate.
  • carbon accounts for 1%-5% by mass of the positive electrode material of the battery.
  • the mass percentage of carbon in the positive electrode material of the battery may specifically be, but not limited to, 1%, 3%, 4% or 5%.
  • the thickness of the second shell layer is 20nm-600nm.
  • the thickness of the second shell layer may be, but not limited to, 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm or 600 nm. In some embodiments of the present application, the thickness of the second shell layer is 25nm-400nm.
  • the battery positive electrode material provided by this application not only has a higher energy density, but also has good electrical conductivity, and can achieve a higher rate of charging and discharging. Its application in the battery can effectively improve the battery cycle performance and rate performance.
  • FIG. 4 is a method for preparing a positive electrode material for a battery according to an embodiment of the present application. Please refer to FIG. 4 , the method includes:
  • Step 100 Put the lithium source, the iron source, the manganese source, the phosphorus source and the solvent in the reactor for the first reaction to obtain the inner core, the inner core includes LiMn x Fe 1-x PO 4 , where 0 ⁇ x ⁇ 0.4; the first The temperature of the reaction is 375°C-500°C, and the pressure of the first reaction is greater than or equal to 23Mpa;
  • Step 200 Put the lithium source, iron source, manganese source, phosphorus source, solvent and inner core in the reactor for the second reaction, coat the inner core with the first shell layer, and obtain the inner core with the first shell layer;
  • the second A shell layer includes LiMn y Fe 1-y PO 4 , where 0.6 ⁇ y ⁇ 0.9; the temperature of the second reaction is 375°C-500°C, and the pressure of the second reaction is greater than or equal to 23Mpa;
  • Step 300 calcining the inner core provided with the first shell layer at 500° C.-800° C. to obtain the positive electrode material of the battery.
  • the solvent includes water.
  • the lithium source includes inorganic lithium salts and organic lithium salts, wherein the inorganic lithium salts include lithium carbonate, lithium bicarbonate, lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium phosphate, lithium nitrate, lithium sulfate, One or more of lithium chromate and lithium hydroxide, and organic lithium salts include one or more of lithium oxalate, lithium acetate, lithium benzoate, lithium citrate, and lithium benzoate.
  • the iron source includes one or more of iron oxide, ferrous carbonate, ferrous oxalate, ferrous sulfate, ferrous chloride and ferrous acetate.
  • the manganese source includes one or more of manganese monoxide, manganese dioxide, manganese hydroxide, manganese carbonate, manganese oxalate, manganese sulfate, manganese nitrate, manganese sulfate, manganese chloride and manganese acetate .
  • the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, and lithium dihydrogen phosphate.
  • the temperature of the first reaction is 375°C-500°C
  • the pressure of the first reaction is 23MPa-60Mpa
  • the reaction time of the first reaction is 0.5h-10h.
  • the reaction time of the first reaction is 0.5h-3h
  • a structurally stable inner core can be formed within a reaction time of 0.5h-3h.
  • the reaction time of the first reaction can be specifically but not limited to 0.5h, 1h, 2h, 3h, 5h or 10h.
  • the temperature of the second reaction is 375°C-500°C
  • the pressure of the second reaction is 23MPa-60Mpa
  • the reaction time of the second reaction is 0.5h-10h.
  • the reaction time of the second reaction is 0.5h-3h, and the structurally stable first shell layer can be formed within the reaction time of 0.5h-3h.
  • the first reaction and the second reaction are carried out in an inert atmosphere, and the inert atmosphere includes one or more of nitrogen, argon, helium, neon, krypton, xenon, and radon.
  • the calcination temperature is 500°C-800°C, and the calcination time is 2h-10h.
  • the calcination temperature may be, but not limited to, 500°C, 600°C, 700°C or 800°C, and the calcination time may be, but not limited to, 2h, 4h, 6h or 10h.
  • This application adopts the supercritical fluid method to prepare the inner core and the first shell.
  • the reaction temperature is greater than or equal to 375°C and the pressure is greater than or equal to 23Mpa
  • the solvent in the reactor is in a state of supercritical fluid, which can greatly improve the activity of the reaction, and It is conducive to the formation of a dense crystal structure, and the method is easy to operate, and the positive electrode material of the battery can be obtained through one-time sintering, which greatly shortens the reaction time.
  • the method for preparing the positive electrode material of the battery further includes preparing a second shell layer.
  • FIG. 5 is a method for preparing the positive electrode material of the battery according to another embodiment of the present application. Please refer to FIG. 5 , the method includes:
  • Step 100 Put the lithium source, the iron source, the manganese source, the phosphorus source and the solvent in the reactor for the first reaction to obtain the inner core, the inner core includes LiMn x Fe 1-x PO 4 , where 0 ⁇ x ⁇ 0.4; the first The temperature of the reaction is 375°C-500°C, and the pressure of the first reaction is greater than or equal to 23Mpa;
  • Step 200 Put the lithium source, iron source, manganese source, phosphorus source, solvent and inner core in the reactor for the second reaction, coat the inner core with the first shell layer, and obtain the inner core with the first shell layer;
  • the second A shell layer includes LiMn y Fe 1-y PO 4 , where 0.6 ⁇ y ⁇ 0.9; the temperature of the second reaction is 375°C-500°C, and the pressure of the second reaction is greater than or equal to 23Mpa;
  • Step 300 Put the lithium source, iron source, phosphorus source, carbon source, solvent and the inner core provided with the first shell layer in the reactor to carry out the third reaction, coat the second shell layer on the surface of the first shell layer, and the second shell layer
  • the second shell layer includes LiFePO 4 and carbon; the temperature of the third reaction is 375°C-500°C, and the pressure of the third reaction is greater than or equal to 23Mpa;
  • Step 400 calcining the inner core provided with the first and second shell layers at 500° C.-800° C. to obtain the positive electrode material of the battery.
  • the carbon source includes one or more of glucose, sucrose, polyvinyl alcohol, starch, and citric acid.
  • the temperature of the third reaction is 375°C-500°C
  • the pressure of the third reaction is 23MPa-60Mpa
  • the reaction time of the third reaction is 0.5h-10h.
  • the supercritical fluid method is conducive to the formation of a dense second shell, thereby more effectively inhibiting the dissolution of Mn.
  • the third reaction is performed in an inert atmosphere.
  • the preparation method of the battery positive electrode material provided by the application is simple and operable, and the battery positive electrode material with excellent rate performance and cycle performance can be prepared.
  • the present application also provides a positive electrode sheet, which includes a current collector and a positive electrode material layer disposed on the current collector, wherein the positive electrode material layer includes the battery positive electrode material of the present application.
  • the positive electrode material layer can be prepared by mixing the battery positive electrode material, conductive agent, binder and solvent to form a positive electrode slurry, and coating and drying the positive electrode slurry to obtain the positive electrode material layer.
  • the binder and the solvent can be mixed first, and then the conductive agent is added after being fully stirred, and then the positive electrode material of the battery is added after stirring, and the positive electrode slurry is obtained by sieving after stirring.
  • the binder may be selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide ( PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethylcellulose (CMC) and sodium alginate.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PVA polyvinyl alcohol
  • SBR styrene-butadiene rubber
  • PAN polyacrylonitrile
  • PAN polyimide
  • PAA polyacrylic acid
  • polyacrylate polyolefin
  • CMC sodium carboxymethylcellulose
  • the conductive agent may be selected from one or more of carbon nanotubes, carbon black and graphene.
  • the present application also provides a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode, wherein the positive electrode includes the positive electrode sheet provided in the present application.
  • the negative electrode of the secondary battery may be any negative electrode known in the art.
  • the negative electrode may include one or more of carbon-based negative electrodes, silicon-based negative electrodes, tin-based negative electrodes, and lithium negative electrodes.
  • the carbon-based negative electrode can include graphite, hard carbon, soft carbon, graphene, etc.
  • the silicon-based negative electrode can include silicon, silicon carbon, silicon oxygen, silicon metal compounds, etc.
  • the tin-based negative electrode can include tin, tin carbon, tin oxide, tin Metal compound
  • lithium negative electrode may include metal lithium or lithium alloy.
  • the lithium alloy may be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy and lithium-indium alloy.
  • the current collector of the negative electrode is copper foil
  • the negative electrode active material includes natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon, silicon oxide, One or more of tin and antimony
  • the binder contains one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC) and styrene-butadiene latex (SBR)
  • the conductive agent includes one or more of acetylene black, Ketjen black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon and graphene.
  • the preparation method of the negative electrode can adopt any method known in the art.
  • the separator of the secondary battery can be any separator known to those skilled in the art, for example, the separator can be polyolefin microporous membrane, polyethylene terephthalate, polyethylene felt, glass fiber felt or ultrafine One or more of glass fiber paper.
  • the electrolyte solution of the secondary battery includes a solution formed of an electrolyte lithium salt in a non-aqueous solvent.
  • the electrolyte lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium hexafluorosilicate (LiSiF 6 ), lithium tetraphenylborate (LiB(C 6 H5) 4 ), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl 4 ), lithium fluorocarbonate (LiC(SO 2 CF 3 ) 3 ), LiCH 3 SO 3 , LiN(SO 2 CF 3 ) 2 and LiN(SO 2 C 2 F 5 ) 2 or more.
  • the non-aqueous solvent includes one or more of chain acid esters and cyclic acid esters.
  • chain esters include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and dipropyl carbonate (DPC) ) in one or more.
  • the chain esters include chain organic esters containing fluorine, sulfur or unsaturated bonds.
  • the cyclic acid ester includes ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), ⁇ -butyrolactone ( ⁇ -BL) and sultone one or more.
  • the cyclic ester includes cyclic organic esters containing fluorine, sulfur or unsaturated bonds.
  • the non-aqueous solvent includes one or more of chain ether and cyclic ether solutions.
  • the cyclic ethers include tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL) and 4-methyl-1,3-dioxo One or more of cyclopentane (4-MeDOL).
  • the cyclic ether includes cyclic organic ethers containing fluorine, sulfur or unsaturated bonds.
  • chain ethers include dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP) and diethylene glycol One or more of dimethyl ether (DG).
  • the chain ethers include chain organic ethers containing fluorine, sulfur or unsaturated bonds.
  • the concentration of the electrolyte lithium salt in the electrolyte is 0.1 mol/L-15 mol/L. In some embodiments of the present application, the concentration of the electrolyte lithium salt is 1 mol/L-10 mol/L.
  • any one of lamination process or winding process may be used for the preparation of the battery.
  • a stacking process is used to prepare batteries.
  • the secondary battery provided by the present application has good cycle performance and safety performance due to the use of the battery positive electrode sheet of the present application.
  • a method for preparing a positive electrode material for a battery is LiMn 0.2 Fe 0.8 PO 4 (30%)/LiMn 0.8 Fe 0.2 PO 4 (60%)/LiFePO 4 (10%)/ C, whose composition formula is LiMn 0.54 Fe 0.46 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • LiMn 0.2 Fe 0.8 PO 4 (30%) means that LiMn 0.2 Fe 0.8 PO 4 accounts for 30% by mass of the positive electrode active material of the battery
  • LiFePO 4 (10%) means that LiFePO 4 accounts for 30% by mass of the positive active material of the battery.
  • Min content is 10%.
  • the solids content of the slurry was 50%. Coat the slurry on the surface of the aluminum foil, cut it into 61mm*72mm positive pole pieces after drying, and assemble the positive pole pieces with the diaphragm and the graphite negative pole to obtain the battery.
  • Example 2 The difference between Example 2 and Example 1 is that the mass ratio of the inner core to the first shell layer is different.
  • the structure of the positive electrode material of the battery in Example 2 is LiMn 0.2 Fe 0.8 PO 4 (10%)/LiMn 0.8 Fe 0.2 PO 4 (80% )/LiFePO 4 (10%)/C, whose composition formula is LiMn 0.66 Fe 0.34 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • LiMn 0.2 Fe 0.8 PO 4 accounts for 10% by mass of the positive active material of the battery
  • LiMn 0.8 Fe 0.2 PO 4 accounts for 80% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Example 3 The difference between Example 3 and Example 1 is that the mass ratio of the inner core to the first shell layer is different.
  • the structure of the positive electrode material of the battery in Example 3 is LiMn 0.2 Fe 0.8 PO 4 (40%)/LiMn 0.8 Fe 0.2 PO 4 (45% )/LiFePO 4 (15%)/C, whose composition formula is LiMn 0.44 Fe 0.56 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • LiMn 0.2 Fe 0.8 PO 4 accounts for 40% by mass of the positive active material of the battery
  • LiMn 0.8 Fe 0.2 PO 4 accounts for 45% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Example 4 The difference between Example 4 and Example 1 is that the mass ratio of the inner core to the first shell layer is different.
  • the structure of the positive electrode material of the battery in Example 4 is LiMn 0.2 Fe 0.8 PO 4 (10%)/LiMn 0.8 Fe 0.2 PO 4 (75% )/LiFePO 4 (15%)/C, whose composition formula is LiMn 0.62 Fe 0.38 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • LiMn 0.2 Fe 0.8 PO 4 accounts for 10% by mass of the positive active material of the battery
  • LiMn 0.8 Fe 0.2 PO 4 accounts for 75% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Example 5 The difference between Example 5 and Example 1 is that the mass ratio of the inner core to the first shell layer is different.
  • the structure of the positive electrode material of the battery in Example 5 is LiMn 0.2 Fe 0.8 PO 4 (20%)/LiMn 0.8 Fe 0.2 PO 4 (70% )/LiFePO 4 (10%)/C, whose composition formula is LiMn 0.6 Fe 0.4 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • LiMn 0.2 Fe 0.8 PO 4 accounts for 20% by mass of the positive active material of the battery
  • LiMn 0.8 Fe 0.2 PO 4 accounts for 70% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Example 6 The difference between Example 6 and Example 5 is that the composition of the inner core is different.
  • the structure of the positive electrode material of the battery in Example 6 is LiMn 0.4 Fe 0.6 PO 4 (20%)/LiMn 0.8 Fe 0.2 PO 4 (70%)/LiFePO 4 ( 10%)/C, and its composition formula is LiMn 0.64 Fe 0.36 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.4 Fe 0.6 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • LiMn 0.4 Fe 0.6 PO 4 accounts for 20% by mass of the positive active material of the battery
  • LiMn 0.8 Fe 0.2 PO 4 accounts for 70% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Example 7 The difference between Example 7 and Example 5 is that the composition of the first shell layer is different.
  • the structure of the positive electrode material of the battery in Example 7 is LiMn 0.2 Fe 0.8 PO 4 (20%)/LiMn 0.9 Fe 0.1 PO 4 (70%)/ LiFePO 4 (10%)/C, its general composition formula is LiMn 0.67 Fe 0.33 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.9 Fe 0.1 PO 4 and LiFePO 4 . Wherein, LiMn 0.2 Fe 0.8 PO 4 accounts for 20% by mass of the positive active material of the battery, and LiMn 0.9 Fe 0.1 PO 4 accounts for 70% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Example 8 The difference between Example 8 and Example 5 is that the composition of the first shell layer is different.
  • the structure of the positive electrode material of the battery in Example 8 is LiMn 0.2 Fe 0.8 PO 4 (20%)/LiMn 0.6 Fe 0.4 PO 4 (70%)/ LiFePO 4 (10%)/C, its composition formula is LiMn 0.56 Fe 0.44 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.6 Fe 0.4 PO 4 and LiFePO 4 . Wherein, LiMn 0.2 Fe 0.8 PO 4 accounts for 20% by mass of the positive active material of the battery, and LiMn 0.6 Fe 0.4 PO 4 accounts for 70% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Example 9 The difference between Example 9 and Example 5 is that the components of the inner core and the first shell layer are different.
  • the inner core and the first shell layer of the battery positive electrode material in Example 9 are doped with Co, and the structure of the battery positive electrode material is sequentially arranged from the inside to the outside. It is LiMn 0.19 Fe 0.8 Co 0.01 PO 4 (20%)/LiMn 0.79 Fe 0.2 Co 0.01 PO 4 (70%)/LiFePO 4 (10%)/C, and its composition formula is LiMn 0.591 Fe 0.40 Co 0.009 PO 4 / c.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.19 Fe 0.8 Co 0.01 PO 4 , LiMn 0.79 Fe 0.2 Co 0.01 PO 4 and LiFePO 4 .
  • Example 9 The preparation method of battery cathode material comprises:
  • the second shell layer and battery were prepared by the same method as in Example 5.
  • Example 10 The difference between Example 10 and Example 5 is that the second shell layer does not contain LiFePO 4 , and the structure of the positive electrode material of the battery in Example 10 is LiMn 0.2 Fe 0.8 PO 4 (25%)/LiMn 0.8 Fe 0.2 PO 4 (75%)/ C, whose composition formula is LiMn 0.65 Fe 0.35 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 and LiMn 0.8 Fe 0.2 PO 4 .
  • the battery was prepared by the same method as in Example 1.
  • Example 11 The difference between Example 11 and Example 5 is that the mass ratio of each layer is different.
  • the structure of the positive electrode material of the battery in Example 11 is LiMn 0.2 Fe 0.8 PO 4 (20%)/LiMn 0.8 Fe 0.2 PO 4 (75%)/LiFePO 4 (5%)/C, and its composition formula is LiMn 0.64 Fe 0.36 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • the battery was prepared by the same method as in Example 1.
  • Example 12 The difference between Example 12 and Example 1 is that the mass ratio of the inner core to the first shell layer is different, and the positive electrode material structure of Example 12 is LiMn 0.2 Fe 0.8 PO 4 (60%)/LiMn 0.8 Fe 0.2 PO 4 (30%) /LiFePO 4 (10%)/C, whose composition formula is LiMn 0.36 Fe 0.64 PO 4 /C.
  • the battery positive electrode active materials in the battery positive electrode material are LiMn 0.2 Fe 0.8 PO 4 , LiMn 0.8 Fe 0.2 PO 4 and LiFePO 4 .
  • LiMn 0.2 Fe 0.8 PO 4 accounts for 60% by mass of the positive active material of the battery
  • LiMn 0.8 Fe 0.2 PO 4 accounts for 30% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 1.
  • Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the structure of the positive electrode material is different.
  • the positive electrode material structure of Comparative Example 1 is LiMn 0.8 Fe 0.2 PO 4 (70%)/LiMn 0.2 Fe 0.8 PO 4 (20%)/LiFePO 4 (10 %)/C, and its composition formula is LiMn 0.6 Fe 0.3 PO 4 /C.
  • the battery was prepared by the same method as in Example 1.
  • Comparative Example 2 is prepared by a hydrothermal method, and the preparation method of the positive electrode material of Comparative Example 2 is:
  • Comparative Example 3 The difference between Comparative Example 3 and Example 5 is that the composition of the first shell layer is different, and the positive electrode material structure of Comparative Example 3 is LiMn 0.2 Fe 0.8 PO 4 (20%)/LiMn 0.5 Fe 0.5 PO 4 (70%)/ LiFePO 4 (10%)/C, its general composition formula is LiMn 0.39 Fe 0.61 PO 4 /C.
  • LiMn 0.2 Fe 0.8 PO 4 accounts for 20% by mass of the positive active material of the battery
  • LiMn 0.5 Fe 0.5 PO 4 accounts for 70% by mass of the positive active material of the battery.
  • the battery was prepared by the same method as in Example 5.
  • the present application also provides effect examples.
  • the first shell layer is LiMn 0.8 Fe 0.2 PO 4
  • the mass proportion of LiMn 0.8 Fe 0.2 PO 4 in the positive electrode material of the battery is 60%
  • the mass proportion of LiMn 0.2 Fe 0.8 PO 4 is 30%. %
  • this structural distribution makes the positive electrode material of the battery have higher electrical conductivity, so that the battery has good rate performance.
  • the mass proportion of LiMn 0.8 Fe 0.2 PO 4 in the positive electrode material of the battery is 80%, so that the battery has a higher energy density, but also because the LiMn 0.8 Fe 0.2 PO 4 layer is more dense than that of Example 1 Thick, so its rate performance is slightly poor.
  • Example 3 the mass proportion of LiMn 0.8 Fe 0.2 PO 4 in the positive electrode material of the battery is 45%, so that the battery has a higher energy density, but its rate performance is better than that of Example 1.
  • Example 4 the mass proportion of the second shell layer in the positive electrode material of the battery is 15%, and the mass proportion of LiMn 0.8 Fe 0.2 PO 4 is 75%.
  • the overall material has a higher energy density.
  • the mass proportion of LiMn 0.8 Fe 0.2 PO 4 in Example 5 is 70%, and its rate performance is similar to that of Example 1.
  • the composition of the inner core in Example 6 is LiMn 0.4 Fe 0.6 PO 4 . Compared with Example 5, Example 6 has a higher energy density, but its rate performance is relatively poor.
  • the first shell layer of Example 7 is LiMn 0.9 Fe 0.1 PO 4 , the higher manganese content makes the battery have higher energy density, but its rate performance is poor.
  • the first shell layer of Example 8 is LiMn 0.6 Fe 0.4 PO 4 , and its manganese content is lower than that of Example 5, so the rate performance is better and the energy density is lower.
  • the positive electrode material of the battery in Example 9 is doped with Co element, and compared with the battery in Example 5 and Example 9, it has better rate performance.
  • the second shell layer of Example 10 does not contain LiFePO 4 , the content of the first shell layer is higher so it has a higher energy density, and the content of the second shell layer is lower so that the effect of suppressing the dissolution of manganese is poor, so the cycle of the battery Performance is poor.
  • the second shell layer of Example 11 contains a certain amount of LiFePO 4 , and compared with the battery of Example 10, the battery has better cycle performance.
  • the mass proportion of LiMn 0.8 Fe 0.2 PO 4 in the positive electrode material of the battery is 30%, and the energy density of the battery is relatively low.
  • LiMn 0.8 Fe 0.2 PO 4 is the material core, and its general composition formula is similar to that of Example 5, but its rate performance is much lower than that of Example 5.
  • the positive electrode material was prepared by the hydrothermal method. Since the crystallinity of the material prepared by the hydrothermal method was poor, the shell and the inner core interpenetrated to form a transition structure during the subsequent sintering process, and the delamination in the material was not obvious. The expected design structure cannot be realized, and the conduction of electrons and ions in the material is not significantly improved.
  • the first shell layer is LiMn 0.5 Fe 0.5 PO 4 , the manganese content of which is low, and the energy density of the battery is low.

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Abstract

一种电池正极材料，包括内核和设置在内核上的第一壳层，内核包括LiMnxFe1-xPO4，第一壳层包括LiMnyFe1-yPO4，其中，0＜x≤0.4，0.6≤y≤0.9。该电池正极材料具有多层的分布结构。还提供了上述电池正极材料的制备方法及其应用。

Description

电池正极材料及其制备方法和应用
本申请要求于2021年9月24日提交中国专利局、申请号为202111125874.6、发明名称为“一种电池正极材料及其制备方法和应用”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
本申请涉及锂离子电池领域，具体涉及一种电池正极材料及其制备方法和应用。
背景技术
聚阴离子型磷酸铁锂LiFePO 4是公认的最安全的锂离子电池正极材料，但其理论能量密度较低(586Wh/kg)，很大程度限制了其广泛应用。磷酸锰锂LiMnPO 4与磷酸铁锂具有相似的结构，且具有更高的理论能量密度(701Wh/kg)，具有很大的应用前景。但是，磷酸锰锂的电子电导率和锂离子扩散速率(分别为＜10 -10S/cm和10 -15cm 2/s)比磷酸铁锂(10 -9S/cm和10 -14cm 2/s)更低，且存在二价Mn溶解的问题，使得磷酸锰锂很难获得优异的电化学性能。目前较为可行的方案是Mn被Fe部分取代形成LiMn xFe 1-xPO 4(0＜x＜1)，在能量密度和动力学性能上取一个折中的方案，在此基础上再对材料进行必要的改性，获得性能优异的材料。
发明内容
本申请第一方面提供了一种电池正极材料，包括内核和设置在所述内核上的第一壳层，所述内核包括LiMn xFe 1-xPO 4，所述第一壳层包括LiMn yFe 1-yPO 4，其中，0＜x≤0.4，0.6≤y≤0.9。
在本申请一实施例中，所述内核与所述第一壳层的质量比为1:(1.5-9)。
在本申请一实施例中，所述内核的直径为0.5μm-5μm。
在本申请一实施例中，所述第一壳层的厚度为0.09μm-2.7μm。
在本申请一实施例中，所述电池正极材料中，Fe元素与Mn元素的摩尔比为1:(1-9)。
在本申请一实施例中，所述第一壳层表面还设置有第二壳层，所述第二壳层包括LiFePO 4和碳。
在本申请一实施例中，所述第二壳层的厚度为20nm-600nm。
在本申请一实施例中，所述电池正极材料中，所述内核的质量百分含量为10％-40％；所述第一壳层的质量百分含量为45％-80％；所述第二壳层的质量百分含量为10％-20％。
在本申请一实施例中，所述电池正极材料还包括掺杂元素，所述掺杂元素包括Ti、V、Co、Ni、Cu、Zn、Mg、Al、Ca、Mo、W中的一种或多种；所述掺杂元素占所述电池正极材料的质量百分含量为0.1％-0.5％。
在本申请一实施例中，所述第一壳层包括所述掺杂元素。
在本申请一实施例中，所述碳占所述电池正极材料的质量百分含量为1％-3％。
本申请第二方面提供了一种电池正极材料的制备方法，包括：
将锂源、铁源、锰源、磷源和溶剂置于反应釜中进行第一反应得到内核，所述内核包括 LiMn xFe 1-xPO 4，其中，0＜x≤0.4；所述第一反应的温度为375℃-500℃，所述第一反应的压力大于或等于23Mpa；
将锂源、铁源、锰源、磷源、溶剂和所述内核置于反应釜中进行第二反应，在所述内核表面包覆第一壳层，得到设置有第一壳层的内核；所述第一壳层包括LiMn yFe 1-yPO 4，其中，0.6≤y≤0.9；所述第二反应的温度为375℃-500℃，所述第二反应的压力大于或等于23Mpa；
将所述设置有第一壳层的内核在500℃-800℃下煅烧，得到电池正极材料。
在本申请一实施例中，所述设置有第一壳层的内核在煅烧之前还包括：将锂源、铁源、磷源、碳源、溶剂和所述设置有第一壳层的内核置于反应釜中进行第三反应，在所述第一壳层表面包覆第二壳层，所述第二壳层包括LiFePO 4和碳；所述第三反应的温度为375℃-500℃，所述第三反应的压力大于或等于23Mpa。
在本申请一实施例中，所述锂源包括无机锂盐和有机锂盐；所述无机锂盐包括碳酸锂、碳酸氢锂、磷酸二氢锂、磷酸一氢锂、磷酸锂、硝酸锂、硫酸锂、铬酸锂和氢氧化锂中的一种或多种；所述有机锂盐包括草酸锂、乙酸锂、苯甲酸锂、柠檬酸锂、苯甲酸锂中的一种或者多种。
在本申请一实施例中，所述铁源包括氧化铁、碳酸亚铁、草酸亚铁、硫酸亚铁、氯化亚铁和醋酸亚铁中的一种或多种。
在本申请一实施例中，所述锰源包括一氧化锰、二氧化锰、氢氧化锰、碳酸锰、草酸锰、硫酸锰、硝酸锰、硫酸锰、氯化锰和乙酸锰中的一种或多种。
在本申请一实施例中，所述磷源包括磷酸、磷酸二氢铵、磷酸一氢铵、磷酸二氢锂中的一种或多种。
在本申请一实施例中，所述碳源包括葡萄糖、蔗糖、聚乙烯醇、淀粉、柠檬酸中的一种或多种。
在本申请一实施例中，所述煅烧在惰性气氛下进行，所述惰性气氛包括氮气、氩气、氦气、氖气、氪气、氙气、氡气中的一种或多种。
本申请第三方面提供了一种二次电池，包括正极、负极、隔膜和电解液，所述正极包括正极极片，所述正极极片包括集流体和设置在所述集流体上的正极材料层，所述正极材料层包括如第一方面所述的电池正极材料。
附图说明
图1为根据本申请一实施方式的电池正极材料；
图2为结构A的电池正极材料的结构示意图；
图3为结构B的正极材料的结构示意图；
图4为根据本申请一实施方式的电池正极材料的制备方法；
图5为根据本申请另一实施方式的电池正极材料的制备方法。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
磷酸锰锂LiMnPO 4相比于磷酸铁锂尽管具有更高的理论能量密度，但其电子电导率和锂离子扩散速率比磷酸铁锂低，不利于其容量的发挥。并且在电池正极材料中，材料内部的离子和电子向外传输的距离长，离子和电子传输较为困难，进一步限制了磷酸锰锂正极材料容量的发挥。为改善磷酸锰锂正极材料的电化学性能，本申请提供了一种电池正极材料，该电池正极材料将锰含量高、电子和离子电导率较差的LiMn xFe 1-xPO 4(0.6≤x≤1)部分放在较外层，将锰含量低、电子和离子电导率较好的LiMn xFe 1-xPO 4(0＜x≤0.4)部分放在内层，从而有效地缩短电子和离子传输困难部分(传输困难部分为在其中进行传输较为困难的部分)中的距离，提高正极材料的电化学性能。
请参阅图1，图1为根据本申请一实施方式的电池正极材料。如图1所示，本申请的电池正极材料包括内核10和设置在内核10表面的第一壳层20，第一壳层20完全包覆内核10。其中，内核10包括如式Ⅰ所示的磷酸锰铁锂化合物，第一壳层20包括如式Ⅱ所示的磷酸锰铁锂化合物。
LiMn xFe 1-xPO 4，式Ⅰ，其中，0＜x≤0.4。
LiMn yFe 1-yPO 4，式Ⅱ，其中，0.6≤y≤0.9。
在电池正极材料中，离子和电子由材料内核向外扩散路径较长，不利于离子和电子的传输，本申请在LiMnPO 4中掺杂Fe元素可以提高正极材料的导电性，材料内核中较高占比的铁元素可以提高离子和电子的扩散速率，进而改善正极材料的电化学性能，第一壳层具有较高占比的锰元素，从而保证电池正极材料具有较高的能量密度，通过该结构设置可以使电池正极材料在具有较高能量密度的同时具有较好的导电性，将其应用在电池时可以使电池具有较高的充放电容量。
本申请一些实施方式中，LiMn xFe 1-xPO 4中x的值具体可以但不限于为0.1、0.2、0.3或0.4，LiMn yFe 1-yPO 4中，y的值具体可以但不限于为0.6、0.7、0.8或0.9。控制x小于或等于0.4可保证内层具有较高的电导率，控制y大于或等于0.6可保证材料整体具有较高的能量密度。本申请一些实施方式中，x的值为0.2～0.3，y的值为0.8～0.9。本申请电池正极材料中，内核中的铁元素的质量百分含量高于第一壳层中铁元素的质量百分含量，内核中较高占比的铁可以使内核具有较好的导电性，提高内核位置处离子和电子的传输速度，促进电池正极材料内部离子和电子的传输；第一壳层具有较高占比的锰含量，从而保证电池正极材料整体具有较高的能量密度。
下面以具有结构B的正极材料作为对比，说明本申请结构的正极材料能够改善材料电化学性能。本申请的正极材料以结构A为例，结构A的电池正极材料由内向外的组成依次是LiMn 0.2Fe 0.8PO 4(40％)/LiMn 0.8Fe 0.2PO 4(60％)，其中，LiMn 0.2Fe 0.8PO 4占电池正极材料的质量百分含量为40％，LiMn 0.8Fe 0.2PO 4占电池正极材料的质量百分含量为60％。结构B的正极材料由内向外的组成依次是LiMn 0.8Fe 0.2PO 4(60％)/LiMn 0.2Fe 0.8PO 4(40％)，请参阅图2和图3，图2为结构A的电池正极材料的结构示意图，图3为结构B的正极材料的结构示意图。结构A与结构B中两层材料的排布位置是相反的，即结构A中作为壳层的LiMn 0.8Fe 0.2PO 4在结构B中为内核，并且结构A和结构B中LiMn 0.8Fe 0.2PO 4与LiMn 0.2F e0.8PO 4的质量比均为3:2，即结构A的电池正极材料和结构B的正极材料的能量密度是相同的，又因为LiMn 0.8Fe 0.2PO 4与LiMn 0.2Fe 0.8PO 4的材料密度几乎相等，结构A和结构B尽管结构排布不同，其颗粒整体的尺寸是相近的。
对于结构B的正极材料，其内核LiMn 0.8Fe 0.2PO 4中锰的含量较高且铁的含量较低，电子和离子在内核的传输较为困难，即内核为传输困难层。对于结构B的正极材料，其传输困难 层中的离子、电子传输的最大距离为0.843R。该传输距离的计算如下：假设正极材料的半径为R，内核的半径为R 1，由于内核LiMn 0.8Fe 0.2PO 4占正极材料的质量百分含量为60％，故R和R 1存在以下关系：
Figure PCTCN2022120748-appb-000001
Figure PCTCN2022120748-appb-000002
由上述公式可以得到R 1＝0.843R，即对于结构B的正极材料，其传输困难层中离子和电子的最大传输距离为0.843R。
对于结构A的电池正极材料，其壳层为传输困难层，假设电池正极材料的半径为R，内核的半径为R 2，结构A的电池正极材料传输困难层中离子和电子的最大传输距离为R-R 2，其计算具体如下：
Figure PCTCN2022120748-appb-000003
Figure PCTCN2022120748-appb-000004
由上述公式可以得到R 2＝0.737R，则对于结构A的电池正极材料，其传输困难层中离子和电子的最大传输距离为0.263R。因此，相比于结构B将LiMn 0.8Fe 0.2PO 4置于内核的正极材料，结构A的电池正极材料中其传输困难层中离子的电子的传输距离更短，其距离缩短比例为69％，其中，距离缩短比例的计算为：(0.843R-0.263R)/0.843R。
同样地，当LiMn 0.8Fe 0.2PO 4占正极材料的质量百分含量为70％时，对于结构A的电池正极材料，其困难层的传输距离为0.331R，对于结构B的电池正极材料，其困难层的传输距离为0.888R。即相比于结构B将LiMn 0.8Fe 0.2PO 4置于内核的分布结构，结构A的电池正极材料中其传输困难层中离子的电子的传输距离更短，其距离缩短比例为63％。本申请还列举了其他含量组成的正极材料传输距离对比，请参阅表1，表1为不同含量的LiMn 0.8Fe 0.2PO 4正极材料的传输距离对比表。
表1不同含量的LiMn 0.8Fe 0.2PO 4正极材料的传输距离对比表
编号 LiMn 0.8Fe 0.2PO 4含量 结构A 结构B 距离缩短比例
1 60％ 0.263R 0.843R 69％
2 70％ 0.331R 0.888R 63％
3 80％ 0.415R 0.928R 55％
4 90％ 0.536R 0.965R 44％
由上述计算可以明显地看出，在具有相同能量密度的前提下，本申请的结构分布可以有效地缩短电池正极材料中传输困难层的离子和电子的传输距离，从而改善电池正极材料的电化学性能，使电池正极材料能够有效地提高电池的倍率性能。
本申请一些实施方式中，第一壳层在电池正极材料中的质量占比大于内核的质量占比，进一步地，内核与第一壳层的质量比为1:(1.5-9)。内核与第一壳层的质量比具体可以但不限于为1:1.5、1:2、1:4、1:5、1:6、1:7、1:8或1:9。控制第一壳层的质量比在上述范围可以保证电池正极材料具有较高的能量密度，并且材料内部也能具有较高的导电性，当第一壳层的质量占比在上述范围内时，核壳分布结构对正极材料的调节效果较好，能够有效改善正极材料的电化学性能。
本申请一些实施方式中，内核的直径为0.5μm-5μm，内核的直径具体可以但不限于为0.5μm、0.8μm、1μm、2μm、4μm或5μm。本申请一些实施方式中，第一壳层的厚度为0.09μm-2.7μm。第一壳层的厚度具体可以但不限于为0.09μm、0.1μm、0.5μm、1μm、2μm或2.7μm。
本申请一些实施方式中，电池正极材料中Fe元素与Mn元素的摩尔比为1:(1-9)。电池正极材料中Fe元素与Mn元素的摩尔比具体可以但不限于为1:1、1:3、1:5或1:9。例如，当电池正极材料由内向外的组成为LiMn 0.2Fe 0.8PO 4(20％)/LiMn 0.8Fe 0.2PO 4(80％)时，Fe元素与Mn元素的摩尔比为1:2.125。控制电池正极材料中Fe元素与Mn元素的摩尔比在上述范围可以保证电池具有较高的能量密度。
本申请一些实施方式中，电池正极材料还包括掺杂元素，掺杂元素包括Ti、V、Co、Ni、Cu、Zn、Mg、Al、Ca中的一种或多种，掺杂元素可以改善电池正极材料离子和电子电导。本申请中，电池正极材料的内核和第一壳层均可进行元素的掺杂以提高导电性，本申请一些实施方式中，掺杂元素位于电池正极材料的第一壳层。本申请一些实施方式中，掺杂元素占电池正极材料的质量百分含量为0.1％-0.5％。掺杂元素占电池正极材料的质量百分含量具体可以但不限于为0.1％、0.3％、0.4％或0.5％。
本申请一些实施方式中，电池正极材料的第一壳层表面还设置有第二壳层，第二壳层包括LiFePO 4和碳。由于Mn在电解液中会发生溶出并在电极与电解液的界面沉积形成高电阻层，增大电池内阻，降低电池的倍率性能和循环性能，因此，在第一壳层表面包覆LiFePO 4可以将第一壳层与电解液隔离，从而抑制Mn的溶出。本申请一些实施方式中，LiFePO 4占电池正极材料的质量百分含量为10％-20％。LiFePO 4占电池正极材料的质量百分含量具体可以但不限于为10％、13％、15％或20％。本申请中，第二壳层中的碳能够提高电池正极材料的导电性，实现较大倍率的充电和放电。本申请一些实施方式中，碳占电池正极材料的质量百分含量为1％-5％。碳占电池正极材料的质量百分含量具体可以但不限于为1％、3％、4％或5％。本申请一些实施方式中，第二壳层的厚度为20nm-600nm。第二壳层的厚度具体可以但不限于为20nm、50nm、100nm、200nm、300nm、400nm、500nm或600nm。本申请一些实施方式中，第二壳层的厚度为25nm-400nm。
本申请提供的电池正极材料不仅具有较高的能量密度，且电池正极材料具有良好的导电性，能够实现较大倍率的充电和放电，将其应用在电池中可以有效地改善电池的循环性能和倍率性能。
本申请还提供了一种电池正极材料的制备方法，图4为根据本申请一实施方式的电池正极材料的制备方法，请参阅图4，该方法包括：
步骤100：将锂源、铁源、锰源、磷源和溶剂置于反应釜中进行第一反应得到内核，内核包括LiMn xFe 1-xPO 4，其中，0＜x≤0.4；第一反应的温度为375℃-500℃，第一反应的压力大于或等于23Mpa；
步骤200：将锂源、铁源、锰源、磷源、溶剂和内核置于反应釜中进行第二反应，在内 核表面包覆第一壳层，得到设置有第一壳层的内核；第一壳层包括LiMn yFe 1-yPO 4，其中，0.6≤y≤0.9；第二反应的温度为375℃-500℃，第二反应的压力大于或等于23Mpa；
步骤300：将设置有第一壳层的内核在500℃-800℃下煅烧，得到电池正极材料。
本申请一些实施方式中，溶剂包括水。本申请一些实施方式中，锂源包括无机锂盐和有机锂盐，其中，无机锂盐包括碳酸锂、碳酸氢锂、磷酸二氢锂、磷酸一氢锂、磷酸锂、硝酸锂、硫酸锂、铬酸锂和氢氧化锂中的一种或多种，有机锂盐包括草酸锂、乙酸锂、苯甲酸锂、柠檬酸锂、苯甲酸锂中的一种或者多种。本申请一些实施方式中，铁源包括氧化铁、碳酸亚铁、草酸亚铁、硫酸亚铁、氯化亚铁和醋酸亚铁中的一种或多种。本申请一些实施方式中，锰源包括一氧化锰、二氧化锰、氢氧化锰、碳酸锰、草酸锰、硫酸锰、硝酸锰、硫酸锰、氯化锰和乙酸锰中的一种或多种。本申请一些实施方式中，磷源包括磷酸、磷酸二氢铵、磷酸一氢铵、磷酸二氢锂中的一种或多种。
本申请一些实施方式中，第一反应的温度为375℃-500℃，第一反应的压力为23MPa-60Mpa，第一反应的反应时间为0.5h-10h。本申请一些实施方式中，第一反应的反应时间为0.5h-3h，在0.5h-3h的反应时间下即可形成结构稳定的内核。第一反应的反应时间具体可以但不限于为0.5h、1h、2h、3h、5h或10h。本申请一些实施方式中，第二反应的温度为375℃-500℃，第二反应的压力为23MPa-60Mpa，第二反应的反应时间为0.5h-10h。本申请一些实施方式中，第二反应的反应时间为0.5h-3h，在0.5h-3h的反应时间下即可形成结构稳定的第一壳层。本申请实施方式，第一反应和第二反应是在惰性气氛中进行反应的，惰性气氛包括氮气、氩气、氦气、氖气、氪气、氙气、氡气中的一种或多种。
本申请一些实施方式中，煅烧的温度为500℃-800℃，煅烧的时间为2h-10h。煅烧的温度具体可以但不限于为500℃、600℃、700℃或800℃，煅烧的时间具体可以但不限于为2h、4h、6h或10h。
本申请采用超临界流体法制备内核和第一壳层，反应的温度大于或等于375℃且压力大于或等于23Mpa时，反应釜内的溶剂处于超临界流体状态，能够大大提高反应的活性，并且有利于形成的致密的晶体结构，并且该方法操作简便，通过一次烧结即可得到电池正极材料，大大缩短了反应时间。
本申请一些实施方式中，电池正极材料的制备方法还包括制备第二壳层，图5为根据本申请另一实施方式的电池正极材料的制备方法，请参阅图5，该方法包括：
步骤100：将锂源、铁源、锰源、磷源和溶剂置于反应釜中进行第一反应得到内核，内核包括LiMn xFe 1-xPO 4，其中，0＜x≤0.4；第一反应的温度为375℃-500℃，第一反应的压力大于或等于23Mpa；
步骤200：将锂源、铁源、锰源、磷源、溶剂和内核置于反应釜中进行第二反应，在内核表面包覆第一壳层，得到设置有第一壳层的内核；第一壳层包括LiMn yFe 1-yPO 4，其中，0.6≤y≤0.9；第二反应的温度为375℃-500℃，第二反应的压力大于或等于23Mpa；
步骤300：将锂源、铁源、磷源、碳源、溶剂和设置有第一壳层的内核置于反应釜中进行第三反应，在第一壳层表面包覆第二壳层，第二壳层包括LiFePO 4和碳；第三反应的温度为375℃-500℃，第三反应的压力大于或等于23Mpa；
步骤400：将设置有第一和第二壳层的内核在500℃-800℃下煅烧，得到电池正极材料。
本申请一些实施方式中，碳源包括葡萄糖、蔗糖、聚乙烯醇、淀粉、柠檬酸中的一种或多种。第三反应的温度为375℃-500℃，第三反应的压力为23MPa-60Mpa，第三反应的反应时间为0.5h-10h。采用超临界流体法有利于形成致密的第二壳层，从而更加有效地抑制Mn 的溶出。本申请一些实施方式中，第三反应是在惰性气氛中进行的。
本申请提供的电池正极材料的制备方法简单，可操作性强，可制得具有优异倍率性能和循环性能的电池正极材料。
本申请还提供了一种正极极片，该正极极片包括集流体和设置在集流体上的正极材料层，其中，正极材料层包括本申请的电池正极材料。本申请一些实施方式中，正极材料层的制备可以是将电池正极材料、导电剂、粘结剂和溶剂混合形成正极浆料，将正极浆料经涂覆、干燥后得到正极材料层。在配制正极浆料时，可以先将粘结剂与溶剂混合，充分搅拌后，再加入导电剂，经搅拌后再加入电池正极材料，搅拌后过筛得到正极浆料。其中，导电剂、粘结剂和溶剂为电池领域的常规选择。例如，粘结剂可以选自聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇(PVA)、丁苯橡胶(SBR)、聚丙烯腈(PAN)、聚酰亚胺(PI)、聚丙烯酸(PAA)、聚丙烯酸酯、聚烯烃、羧甲基纤维素钠(CMC)和海藻酸钠中的一种或多种。导电剂可以选自碳纳米管、炭黑以及石墨烯中的一种或多种。
本申请还提供了一种二次电池，该二次电池包括正极、负极、电解液以及位于正极与负极之间的隔膜，其中，正极包括本申请提供的正极极片。
本申请中，二次电池的负极可以是本领域公知的任意负极。本申请一些实施方式中，负极可包括碳基负极、硅基负极、锡基负极和锂负极中的一种或多种。其中碳基负极可包括石墨、硬碳、软碳、石墨烯等；硅基负极可包括硅、硅碳、硅氧、硅金属化合物等；锡基负极可包括锡、锡碳、锡氧、锡金属化合物；锂负极可包括金属锂或锂合金。锂合金具体可以是锂硅合金、锂钠合金、锂钾合金、锂铝合金、锂锡合金和锂铟合金中的至少一种。本申请一些实施例中，负极的集流体为铜箔，负极活性材料包括天然石墨、人造石墨、硬碳、软碳、钛酸锂、氧化铁、磷酸钛锂、二氧化钛、硅、氧化亚硅、锡和锑中的一种或多种；粘结剂包含聚丙烯酸(PAA)、聚偏氟乙烯(PVDF)、羧甲基纤维素(CMC)和丁苯乳胶(SBR)中的一种或多种；导电剂包括乙炔黑、科琴碳黑、Super-P、碳纳米管、碳纳米纤维、活性炭和石墨烯中的一种或多种。本申请中，负极的制备方法可以采用本领域公知的任意方法。
本申请中，二次电池的隔膜可以是本领域技术人员公知的任意隔膜，例如隔膜可以是聚烯烃微多孔膜、聚对苯二甲酸乙二醇酯、聚乙烯毡、玻璃纤维毡或超细玻璃纤维纸中的一种或多种。
本申请中，二次电池的电解液包括电解质锂盐在非水溶剂中形成的溶液。本申请一些实施方式中，电解质锂盐包括六氟磷酸锂(LiPF 6)、高氯酸锂(LiClO 4)、四氟硼酸锂(LiBF 4)、六氟砷酸锂(LiAsF 6)、六氟硅酸锂(LiSiF 6)、四苯基硼酸锂(LiB(C 6H5) 4)、氯化锂(LiCl)、溴化锂(LiBr)、氯铝酸锂(LiAlCl 4)、氟烃基磺酸锂(LiC(SO 2CF 3) 3)、LiCH 3SO 3、LiN(SO 2CF 3) 2和LiN(SO 2C 2F 5) 2中的一种或多种。本申请一些实施方式中，非水溶剂包括链状酸酯和环状酸酯中的一种或多种。本申请一些实施方式中，链状酸酯包括碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸甲丙酯(MPC)和碳酸二丙酯(DPC)中的一种或多种。本申请一些实施方式中，链状酸酯包括含氟、含硫或含不饱和键的链状有机酯类。本申请一些实施方式中，环状酸酯包括碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸亚乙烯酯(VC)、γ-丁内酯(γ-BL)和磺内酯中的一种或多种。本申请一些实施方式中，环状酸酯包括含氟、含硫或含不饱和键的环状有机酯。本申请一些实施方式中，非水溶剂包括链状醚和环状醚溶液中的一种或多种。本申请一些实施方式中，环状醚包括四氢呋喃(THF)、2-甲基四氢呋喃(2-MeTHF)、1,3-二氧戊烷(DOL)和4-甲基-1,3-二氧环戊烷(4-MeDOL)中的一种或多种。本申请一些实施方式中，环状醚包括含氟、含硫或含不饱和键的环状有机醚。本申请一些实 施方式中，链状醚包括二甲氧基甲烷(DMM)、1,2-二甲氧基乙烷(DME)、1,2-二甲氧基丙烷(DMP)和二甘醇二甲醚(DG)中的一种或多种。本申请一些实施方式中，链状醚包括含氟、含硫或含不饱和键的链状有机醚。本申请一些实施方式中，电解液中电解质锂盐的浓度为0.1mol/L-15mol/L。本申请一些实施方式中，电解质锂盐的浓度为1mol/L-10mol/L。
本申请一些实施方式中，电池的制备可以采用叠片工艺或卷绕工艺中的任意一种。本申请一些实施例中，采用叠片工艺制备电池。
本申请提供的二次电池由于采用本申请的电池正极片故具有良好的循环性能和安全性能。
下面分多个实施例对本申请技术方案进行进一步的说明。
实施例1
一种电池正极材料的制备方法，该电池正极材料的结构由内至外依次为LiMn 0.2Fe 0.8PO 4(30％)/LiMn 0.8Fe 0.2PO 4(60％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.54Fe 0.46PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.8Fe 0.2PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4(30％)表示LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为30％，LiFePO 4(10％)表示LiFePO 4占电池正极活性物质的质量百分含量为10％。
1)制备LiMn 0.2Fe 0.8PO 4内核
按照化学计量比称量碳酸锂、乙酸铁、乙酸锰和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至高压反应釜中，向高压反应釜通入氩气保持惰性气氛，在搅拌状态下升温至380℃，反应釜的压力为24Mpa，反应1h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后得到LiMn 0.2Fe 0.8PO 4内核。
2)制备LiMn 0.8Fe 0.2PO 4第一壳层
按照化学计量比称量碳酸锂、乙酸铁、乙酸锰和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至高压反应釜中并加入LiMn 0.2Fe 0.8PO 4内核，向高压反应釜通入氩气保持惰性气氛，在搅拌状态下升温至380℃，反应釜的压力为24Mpa，反应1h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后得到核壳结构的LiMn 0.2Fe 0.8PO 4/LiMn 0.8Fe 0.2PO 4。
3)制备第二壳层
按照化学计量比称量碳酸锂、乙酸铁、葡萄糖和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至高压反应釜中并加入核壳结构的LiMn 0.2Fe 0.8PO 4/LiMn 0.8Fe 0.2PO 4，向高压反应釜通入氩气保持惰性气氛，在搅拌状态下升温至380℃，反应釜的压力为24Mpa，反应1h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后，将产物在700℃下煅烧5h得到电池正极材料LiMn 0.2Fe 0.8PO 4(30％)/LiMn 0.8Fe 0.2PO 4(60％)/LiFePO 4(10％)/C。
4)制备二次电池
将制备得到的电池正极材料与导电剂、粘结剂按照90：5：5的质量比分散于N-甲基吡咯烷酮中，其中，导电剂为炭黑和碳纳米管，粘结剂为PVDF5130，浆料的固含量为50％。将浆料涂覆在铝箔表面，烘干后裁切为61mm*72mm的正极极片，将正极极片与隔膜和石墨负极组装得到电池。
实施例2
实施例2与实施例1的区别在于内核与第一壳层的质量比不同，实施例2的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(10％)/LiMn 0.8Fe 0.2PO 4(80％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.66Fe 0.34PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、 LiMn 0.8Fe 0.2PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为10％，LiMn 0.8Fe 0.2PO 4占电池正极活性物质的质量百分含量为80％。采用与实施例1相同的方法制备得到电池。
实施例3
实施例3与实施例1的区别在于内核与第一壳层的质量比不同，实施例3的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(40％)/LiMn 0.8Fe 0.2PO 4(45％)/LiFePO 4(15％)/C，其组成通式为LiMn 0.44Fe 0.56PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.8Fe 0.2PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为40％，LiMn 0.8Fe 0.2PO 4占电池正极活性物质的质量百分含量为45％。采用与实施例1相同的方法制备得到电池。
实施例4
实施例4与实施例1的区别在于内核与第一壳层的质量比不同，实施例4的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(10％)/LiMn 0.8Fe 0.2PO 4(75％)/LiFePO 4(15％)/C，其组成通式为LiMn 0.62Fe 0.38PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.8Fe 0.2PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为10％，LiMn 0.8Fe 0.2PO 4占电池正极活性物质的质量百分含量为75％。采用与实施例1相同的方法制备得到电池。
实施例5
实施例5与实施例1的区别在于内核与第一壳层的质量比不同，实施例5的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(20％)/LiMn 0.8Fe 0.2PO 4(70％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.6Fe 0.4PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.8Fe 0.2PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为20％，LiMn 0.8Fe 0.2PO 4占电池正极活性物质的质量百分含量为70％。采用与实施例1相同的方法制备得到电池。
实施例6
实施例6与实施例5的区别在于内核的组分不同，实施例6的电池正极材料结构为LiMn 0.4Fe 0.6PO 4(20％)/LiMn 0.8Fe 0.2PO 4(70％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.64Fe 0.36PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.4Fe 0.6PO 4、LiMn 0.8Fe 0.2PO 4和LiFePO 4。其中，LiMn 0.4Fe 0.6PO 4占电池正极活性物质的质量百分含量为20％，LiMn 0.8Fe 0.2PO 4占电池正极活性物质的质量百分含量为70％。采用与实施例1相同的方法制备得到电池。
实施例7
实施例7与实施例5的区别在于第一壳层的组分不同，实施例7的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(20％)/LiMn 0.9Fe 0.1PO 4(70％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.67Fe 0.33PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.9Fe 0.1PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为20％，LiMn 0.9Fe 0.1PO 4占电池正极活性物质的质量百分含量为70％。采用与实施例1相同的方法制备得到电池。
实施例8
实施例8与实施例5的区别在于第一壳层的组分不同，实施例8的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(20％)/LiMn 0.6Fe 0.4PO 4(70％)/LiFePO 4(10％)/C，其组成通式为 LiMn 0.56Fe 0.44PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.6Fe 0.4PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为20％，LiMn 0.6Fe 0.4PO 4占电池正极活性物质的质量百分含量为70％。采用与实施例1相同的方法制备得到电池。
实施例9
实施例9与实施例5的区别在于内核与第一壳层的组分不同，实施例9的电池正极材料的内核和第一壳层掺杂有Co，电池正极材料的结构由内至外依次为LiMn 0.19Fe 0.8Co 0.01PO 4(20％)/LiMn 0.79Fe 0.2Co 0.01PO 4(70％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.591Fe 0.40Co 0.009PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.19Fe 0.8Co 0.01PO 4、LiMn 0.79Fe 0.2Co 0.01PO 4和LiFePO 4。
实施例9电池正极材料的制备方法包括：
1)制备LiMn 0.19Fe 0.8Co 0.01PO 4内核
按照化学计量比称量碳酸锂、乙酸铁、乙酸锰、乙酸钴和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至高压反应釜中，向高压反应釜通入氩气保持惰性气氛，在搅拌状态下升温至380℃，反应釜的压力为24Mpa，反应1h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后得到LiMn 0.19Fe 0.8Co 0.01PO 4内核。
2)制备LiMn 0.79Fe 0.2Co 0.01PO 4第一壳层
按照化学计量比称量碳酸锂、乙酸铁、乙酸锰、乙酸钴和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至高压反应釜中并加入LiMn 0.19Fe 0.8Co 0.01PO 4内核，向高压反应釜通入氩气保持惰性气氛，在搅拌状态下升温至380℃，反应釜的压力为24Mpa，反应1h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后得到核壳结构的LiMn 0.19Fe 0.8Co 0.01PO 4/LiMn 0.79Fe 0.2Co 0.01PO 4。
采用与实施例5相同的方法制备第二壳层和电池。
实施例10
实施例10与实施例5的区别在于第二壳层不含有LiFePO 4，实施例10的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(25％)/LiMn 0.8Fe 0.2PO 4(75％)/C，其组成通式为LiMn 0.65Fe 0.35PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4和LiMn 0.8Fe 0.2PO 4。采用与实施例1相同的方法制备得到电池。
实施例11
实施例11与实施例5的区别在于各层的质量占比不同，实施例11的电池正极材料结构为LiMn 0.2Fe 0.8PO 4(20％)/LiMn 0.8Fe 0.2PO 4(75％)/LiFePO 4(5％)/C，其组成通式为LiMn 0.64Fe 0.36PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.8Fe 0.2PO 4和LiFePO 4。采用与实施例1相同的方法制备得到电池。
实施例12
实施例12与实施例1的区别在于内核与第一壳层的质量比不同，实施例12的正极材料结构为LiMn 0.2Fe 0.8PO 4(60％)/LiMn 0.8Fe 0.2PO 4(30％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.36Fe 0.64PO 4/C。该电池正极材料中的电池正极活性物质为LiMn 0.2Fe 0.8PO 4、LiMn 0.8Fe 0.2PO 4和LiFePO 4。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为60％，LiMn 0.8Fe 0.2PO 4占电池正极活性物质的质量百分含量为30％。采用与实施例1相同的方法制备得到电池。
对比例1
对比例1与实施例1的区别在于正极材料的结构不同，对比例1的正极材料结构为LiMn 0.8Fe 0.2PO 4(70％)/LiMn 0.2Fe 0.8PO 4(20％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.6Fe 0.3PO 4/C。采用与实施例1相同的方法制备得到电池。
对比例2
对比例2与实施例1的区别在于对比例2是通过水热法进行制备，对比例2的正极材料制备方法为：
按照化学计量比称量碳酸锂、乙酸铁、乙酸锰和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至水热反应釜中，向水热反应釜通入氩气保持惰性气氛，在搅拌状态下升温至175℃，反应8h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后得到LiMn 0.2Fe 0.8PO 4内核。
按照化学计量比称量碳酸锂、乙酸铁、乙酸锰和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至水热反应釜中并加入LiMn 0.2Fe 0.8PO 4内核，向水热反应釜通入氩气保持惰性气氛，在搅拌状态下升温至175℃，反应8h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后得到核壳结构的LiMn 0.2Fe 0.8PO 4/LiMn 0.8Fe 0.2PO 4。
按照化学计量比称量碳酸锂、乙酸铁、葡萄糖和磷酸并将其溶解于水中得到混合溶液，将混合溶液转移至水热反应釜中并加入核壳结构的LiMn 0.2Fe 0.8PO 4/LiMn 0.8Fe 0.2PO 4，向水热反应釜通入氩气保持惰性气氛，在搅拌状态下升温至175℃，反应6.5h后收集沉淀，将沉淀采用水和乙醇洗涤并干燥后，将产物在720℃下煅烧7h得到电池正极材料LiMn 0.2Fe 0.8PO 4(30％)/LiMn 0.8Fe 0.2PO 4(60％)/LiFePO 4(10％)/C，虽然对比例2制备的材料中的元素和总含量与实施例1相同，但是制备出的壳层与内核之间相互渗透形成过渡结构，无法实现预期的设计结构，电子和离子在材料中的传导提升不明显。采用与实施例1相同的方法制备得到电池。
对比例3
对比例3与实施例5的区别在于第一壳层的组分不相同，对比例3的正极材料结构为LiMn 0.2Fe 0.8PO 4(20％)/LiMn 0.5Fe 0.5PO 4(70％)/LiFePO 4(10％)/C，其组成通式为LiMn 0.39Fe 0.61PO 4/C。其中，LiMn 0.2Fe 0.8PO 4占电池正极活性物质的质量百分含量为20％，LiMn 0.5Fe 0.5PO 4占电池正极活性物质的质量百分含量为70％。采用与实施例5相同的方法制备得到电池。
效果实施例
为验证本申请制得的电池正极材料的性能，本申请还提供了效果实施例。
1)对实施例1-12和对比例1-3的电池进行电化学性能测试，将实施例1-12和对比例1-3的电池在25℃，2.8-4.3V的电压测试区间内，以0.1C恒流恒压充电，截止电流为0.02C，0.1C恒流放电，记录首次充电容量和放电容量，根据以下公式计算电池的参数：放电比容量＝电池首次放电容量(毫安时)/正极材料重量(克)，能量密度＝放电比容量(mAh/g)*平均放电电压(V)，测试结果请参阅表2。
表2实施例1-12和对比例1-3电池的电化学性能参数表
Figure PCTCN2022120748-appb-000005
Figure PCTCN2022120748-appb-000006
本申请实施例1中第一壳层为LiMn 0.8Fe 0.2PO 4，并且LiMn 0.8Fe 0.2PO 4在电池正极材料中的质量占比为60％，LiMn 0.2Fe 0.8PO 4的质量占比为30％，该结构分布使得电池正极材料具有较高的电导率，从而使电池具有良好的倍率性能。实施例2中LiMn 0.8Fe 0.2PO 4在电池正极材料中的质量占比为80％，从而使电池具有较高的能量密度，但也由于LiMn 0.8Fe 0.2PO 4层相比于实施例1更厚，故其倍率性能稍差。实施例3中LiMn 0.8Fe 0.2PO 4在电池正极材料中的质量占比为45％，从而使电池具有较高的能量密度，但其倍率性能较实施例1更好。实施例4中第二壳层在电池正极材料中的质量占比为15％，且LiMn 0.8Fe 0.2PO 4的质量占比为75％，材料整体较实施例1具有较高的能量密度。实施例5中LiMn 0.8Fe 0.2PO 4的质量占比为70％，其倍率性能与实施例1相近。实施例6中内核的组分为LiMn 0.4Fe 0.6PO 4，相比于实施例5，实施例6具有更高的能量密度，但其倍率性能也相对较差。实施例7的第一壳层为LiMn 0.9Fe 0.1PO 4，较高的锰含量使电池具有更高的能量密度，但其倍率性能较差。实施例8的第一壳层为LiMn 0.6Fe 0.4PO 4，其锰含量相对实施例5较低，故其倍率性能较好，能量密度较低。实施例9的电池正极材料掺杂有Co元素，相比于实施例5实施例9的电池具有较好的倍率性能。实施例10的第二壳层不含有LiFePO 4，第一壳层的含量较高故具有较高的能量密度，第二壳层含量较低其抑制锰溶解问题的效果较差，故电池的循环性能较差。实施例11第二壳层含有一定的LiFePO 4，相比于实施例10的电池具有更好的循环性能。实施例12中LiMn 0.8Fe 0.2PO 4在电池正极材料中的质量占比为30％，其电池的能量密度相对较低。
对比例1中LiMn 0.8Fe 0.2PO 4为材料内核，其组成通式与实施例5相近，但其倍率性能远低于实施例5。对比例2是采用水热法制备正极材料，由于水热法制备的材料结晶性较差，故在后续烧结过程中壳层与内核之间相互渗透形成过渡结构，材料中的分层不明显，无法实现预期的设计结构，电子和离子在材料中的传导提升不明显。对比例3中第一壳层为LiMn 0.5Fe 0.5PO 4，其锰含量较低，电池的能量密度低。
以上所述是本申请的实施方式，但并不能因此而理解为对本申请范围的限制。应当指出，对于本技术领域的普通技术人员来说，在不脱离本申请原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也视为本申请的保护范围。

Claims (20)

  1. 一种电池正极材料，其特征在于，包括内核(10)和设置在所述内核(10)表面的第一壳层(20)，所述内核(10)包括LiMn xFe 1-xPO 4，所述第一壳层(20)包括LiMn yFe 1-yPO 4，其中，0＜x≤0.4，0.6≤y≤0.9。
  2. 如权利要求1所述的电池正极材料，其特征在于，所述内核(10)与所述第一壳层(20)的质量比为1:(1.5-9)。
  3. 如权利要求1或2所述的电池正极材料，其特征在于，所述内核(10)的直径为0.5μm-5μm。
  4. 如权利要求1-3任一项所述的电池正极材料，其特征在于，所述第一壳层(20)的厚度为0.09μm-2.7μm。
  5. 如权利要求1-4任一项所述的电池正极材料，其特征在于，所述电池正极材料中，Fe元素与Mn元素的摩尔比为1:(1-9)。
  6. 如权利要求1-5任一项所述的电池正极材料，其特征在于，所述第一壳层(20)表面还设置有第二壳层，所述第二壳层包括LiFePO 4和碳。
  7. 如权利要求6所述的电池正极材料，其特征在于，所述第二壳层的厚度为20nm-600nm。
  8. 如权利要求6或7所述的电池正极材料，其特征在于，所述电池正极材料中，所述内核(10)的质量百分含量为10％-40％；所述第一壳层(20)的质量百分含量为45％-80％；所述第二壳层的质量百分含量为10％-20％。
  9. 如权利要求1-8任一项所述的电池正极材料，其特征在于，所述电池正极材料还包括掺杂元素，所述掺杂元素包括Ti、V、Co、Ni、Cu、Zn、Mg、Al、Ca、Mo、W中的一种或多种；所述掺杂元素占所述电池正极材料的质量百分含量为0.1％-0.5％。
  10. 如权利要求9所述的电池正极材料，其特征在于，所述第一壳层(20)包括所述掺杂元素。
  11. 如权利要求6所述的电池正极材料，其特征在于，所述碳占该电池正极材料的质量百分含量为1％-3％。
  12. 一种电池正极材料的制备方法，其特征在于，包括：
    将锂源、铁源、锰源、磷源和溶剂置于反应釜中进行第一反应得到内核(10)，所述内核(10)包括LiMn xFe 1-xPO 4，其中，0＜x≤0.4；所述第一反应的温度为375℃-500℃，所述第一反应的压力大于或等于23Mpa；
    将锂源、铁源、锰源、磷源、溶剂和所述内核(10)置于反应釜中进行第二反应，在所述内核(10)表面包覆第一壳层(20)，得到设置有第一壳层(20)的内核(10)；所述第一壳层(20)包括LiMn yFe 1-yPO 4，其中，0.6≤y≤0.9；所述第二反应的温度为375℃-500℃，所述第二反应的压力大于或等于23Mpa；
    将所述设置有第一壳层(20)的内核(10)在500℃-800℃下煅烧，得到所述电池正极材料。
  13. 如权利要求12所述的制备方法，其特征在于，所述设置有第一壳层(20)的内核(10)在煅烧之前还包括：将锂源、铁源、磷源、碳源、溶剂和所述设置有第一壳层(20)的内核(10)置于反应釜中进行第三反应，在所述第一壳层(20)表面包覆第二壳层，所述第二壳 层包括LiFePO 4和碳；所述第三反应的温度为375℃-500℃，所述第三反应的压力大于或等于23Mpa。
  14. 如权利要求12或13所述的制备方法，其特征在于，所述锂源包括无机锂盐和有机锂盐；所述无机锂盐包括碳酸锂、碳酸氢锂、磷酸二氢锂、磷酸一氢锂、磷酸锂、硝酸锂、硫酸锂、铬酸锂和氢氧化锂中的一种或多种；所述有机锂盐包括草酸锂、乙酸锂、苯甲酸锂、柠檬酸锂、苯甲酸锂中的一种或者多种。
  15. 如权利要求12或13所述的制备方法，其特征在于，可选地，所述铁源包括氧化铁、碳酸亚铁、草酸亚铁、硫酸亚铁、氯化亚铁和醋酸亚铁中的一种或多种。
  16. 如权利要求12所述的制备方法，其特征在于，所述锰源包括一氧化锰、二氧化锰、氢氧化锰、碳酸锰、草酸锰、硫酸锰、硝酸锰、硫酸锰、氯化锰和乙酸锰中的一种或多种。
  17. 如权利要求12或13所述的制备方法，其特征在于，所述磷源包括磷酸、磷酸二氢铵、磷酸一氢铵、磷酸二氢锂中的一种或多种。
  18. 如权利要求13所述的制备方法，其特征在于，所述碳源包括葡萄糖、蔗糖、聚乙烯醇、淀粉、柠檬酸中的一种或多种。
  19. 如权利要求12或13所述的制备方法，其特征在于，所述煅烧在惰性气氛下进行，所述惰性气氛包括氮气、氩气、氦气、氖气、氪气、氙气、氡气中的一种或多种。
  20. 一种二次电池，其特征在于，包括正极、负极、隔膜和电解液，所述正极包括正极极片，所述正极极片包括集流体和设置在所述集流体上的正极材料层，所述正极材料层包括如权利要求1-11任一项所述的电池正极材料。
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