WO2023138577A1 - 正极补锂添加剂及其制备方法和应用 - Google Patents

正极补锂添加剂及其制备方法和应用 Download PDF

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Publication number
WO2023138577A1
WO2023138577A1 PCT/CN2023/072609 CN2023072609W WO2023138577A1 WO 2023138577 A1 WO2023138577 A1 WO 2023138577A1 CN 2023072609 W CN2023072609 W CN 2023072609W WO 2023138577 A1 WO2023138577 A1 WO 2023138577A1
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positive electrode
lithium
polymer
electrode lithium
segments
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English (en)
French (fr)
Inventor
王敏
万远鑫
孔令涌
余永龙
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Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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Priority to US18/729,600 priority Critical patent/US20250096273A1/en
Priority to EP23742892.5A priority patent/EP4468408A4/en
Publication of WO2023138577A1 publication Critical patent/WO2023138577A1/zh
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    • 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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/22—Compounds of iron
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C3/00—Treatment in general of inorganic materials, other than fibrous fillers, to enhance their pigmenting or filling properties
    • C09C3/10—Treatment with macromolecular organic compounds
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
    • C09D133/04—Homopolymers or copolymers of esters
    • C09D133/14—Homopolymers or copolymers of esters of esters containing halogen, nitrogen, sulfur or oxygen atoms in addition to the carboxy oxygen
    • 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
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • 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
    • 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
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • 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
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 application belongs to the field of secondary batteries, and specifically relates to a positive electrode lithium supplement additive and its preparation method and application.
  • Lithium-ion batteries are considered to be one of the most promising energy sources because of their high operating voltage and energy density, relatively small self-discharge level, no memory effect, no pollution from heavy metal elements such as lead and cadmium, and long cycle life. Lithium-ion batteries are widely used in many aspects such as electric vehicles, power tools, mobile consumer electronics, and energy storage.
  • lithium-ion batteries have many advantages, during the first charging process of lithium-ion batteries, the surface of the negative electrode is usually accompanied by the formation of a solid electrolyte film SEI film. This process consumes a large amount of Li + , which means that the Li + part released from the positive electrode material is irreversibly consumed, and the reversible specific capacity of the corresponding battery cell is reduced.
  • Anode materials will further consume Li + , resulting in loss of lithium in cathode materials, reducing the first Coulombic efficiency and capacity of lithium-ion batteries. For example, in a lithium-ion battery system using a graphite negative electrode, about 10% of the lithium source will be consumed for the first charge.
  • anode materials with high specific capacity such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide), and amorphous carbon anodes, the consumption of lithium sources in the cathode will be further aggravated.
  • the researchers developed related lithium-rich compounds as additives to solve the problem of irreversible loss of lithium ions during the first charge and discharge.
  • the methods used include adding acid anhydride compounds, cyclic esters such as ⁇ -butyrolactone, and polynitrile compounds as additives to the electrolyte to form positive and negative protective films to suppress gas production.
  • these measures often have problems such as poor ion conductivity of the protective film, increased impedance, and instability of the positive and negative protective films. Therefore, how to effectively improve the gas production problem caused by the use of lithium-supplementing additives without affecting other performances of lithium-ion batteries is an urgent problem to be solved at present, which has a significant impact on the improvement of the performance of lithium-ion batteries.
  • the purpose of the present application is to overcome the above-mentioned deficiencies in the prior art, and provide a positive electrode lithium supplement additive and a preparation method thereof, so as to solve the technical problem that the existing positive electrode lithium supplement additive causes the gas production of lithium-ion batteries to increase.
  • Another object of the present application is to provide a positive electrode sheet and a secondary battery containing the electrode sheet, so as to solve the technical problem that the first coulombic efficiency of the existing secondary battery is improved but the gas production is increased.
  • the first aspect of the present application provides a positive electrode lithium supplement additive.
  • the positive electrode lithium supplement additive of this application has a core-shell structure.
  • the core body of the core-shell structure includes a positive electrode lithium supplement material, and the coating layer covering the core body contains a polymer represented by the following molecular structure formula I:
  • X 1 , X 2 , X 3 , and X 4 are independently any one of a hydrogen atom and an alkyl group with 1 to 3 carbon atoms, and R is a polymer segment.
  • alkyl group includes any one of methyl, ethyl, propyl, and isopropyl.
  • the polymer segment includes at least one segment of a carbon chain polymer chain, a heterochain polymer chain, and a non-carbon chain polymer chain.
  • piperidine group contained in the general formula I is a branched or terminal group.
  • the mass content of the polymer in the positive electrode lithium supplement additive is 0.1%-5%.
  • R includes one or more of polyolefin segments, polyacrylate segments, polymethacrylate segments, polyester segments, polyamide segments, polyurethane segments, polyether segments, polysilane segments, and polysiloxane segments.
  • X 1 , X 2 , X 3 , and X 4 are all methyl groups, and R is one or more of polyolefin, polyacrylate, polymethacrylate, polyester, polyamide, polyurethane, polyether, polysilane, and polysiloxane.
  • the polymer includes one or more of the following molecular structural formulas I 1 to I 6 :
  • the coating layer includes a polymer coating layer, and the polymer contained in the polymer coating layer includes a polymer.
  • the positive electrode lithium supplement material includes the positive electrode lithium supplement material containing oxygen atoms.
  • the coating layer further includes a hydrophobic encapsulation layer, and the hydrophobic encapsulation layer covers the core body, and the polymer coating layer covers the surface of the hydrophobic encapsulation layer away from the core body.
  • the hydrophobic encapsulation layer includes at least one of an ion conductor encapsulation layer and an electronic conductor encapsulation layer.
  • the material of the ion conductor encapsulation layer includes at least one of perovskite type, NASICON type and garnet type.
  • the material of the electronic conductor packaging layer includes at least one of carbon materials, conductive oxides, and conductive organics.
  • hydrophobic encapsulation layer contains a polymer represented by general formula I in molecular structure.
  • the thickness of the hydrophobic encapsulation layer is 1-100 nm.
  • the second aspect of the present application provides a preparation method of the positive electrode lithium supplement additive of the present application.
  • the preparation method of the positive electrode lithium supplement additive of the present application comprises the following steps:
  • the mixture is dried, so that the polymer is dispersed on the surface of the positive electrode lithium supplement material particles to obtain the positive electrode lithium supplement additive;
  • X 1 , X 2 , X 3 , and X 4 in the general formula I are independently any one of a hydrogen atom and an alkyl group with 1 to 3 carbon atoms, and R is a polymer chain segment.
  • the polymer forms a polymer coating layer covering the positive electrode lithium supplement material particles.
  • the positive electrode lithium supplement material particle raw material includes a core body containing the positive electrode lithium supplement material and a hydrophobic encapsulation layer covering the core body.
  • the mass concentration of the polymer represented by the general molecular structure formula I in the solution is 2%-20%.
  • the solvent of the solution includes at least one of methanol, ethanol, n-hexane, cyclohexane, ethyl acetate, toluene, xylene, tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide and the like.
  • a positive electrode sheet in a third aspect of the present application, includes a positive electrode current collector and a positive electrode active layer bonded to the surface of the positive electrode current collector, wherein the positive electrode active layer contains the positive electrode lithium supplementary additive of the present application or the positive electrode lithium supplementary additive prepared by the preparation method of the positive electrode lithium supplementary additive of the present application.
  • a secondary battery in a fourth aspect of the present application, includes a positive electrode sheet and a negative electrode sheet, and the positive electrode sheet is the positive electrode sheet of this application.
  • the capacity retention rate of the secondary battery is higher than 87% after 300 cycles at normal temperature.
  • the capacity retention rate of the secondary battery is higher than 80% after 300 cycles at 45°C.
  • the battery thickness change rate of the secondary battery after 300 cycles at 45° C. is less than 15%.
  • the polymer represented by the general formula I contained in the coating layer of the positive electrode lithium supplement additive of the present application can effectively inhibit the generation of active oxygen inside the lithium supplement material on the one hand; And it can effectively capture the free radicals generated during the charging and discharging process of lithium-ion batteries to form stabilized products.
  • the polymer represented by the general formula I in the molecular structure of the positive electrode lithium supplement additive of the present application endows the coating layer with the function of inhibiting active oxygen and capturing the free radicals generated by the charge and discharge of the lithium ion battery, so that the gas production of the lithium ion battery during charge and discharge is significantly reduced, and the volume expansion of the lithium ion battery is reduced, thereby effectively improving the stability and safety of the charge and discharge of the lithium ion battery, and at the same time improving its lithium supplementation effect.
  • the preparation method of the positive electrode lithium-replenishing additive of the present application can effectively disperse the polymer represented by the general formula I on the surface of the positive electrode lithium-replenishing material particles, so that the prepared positive electrode lithium-replenishing additive has the functions of inhibiting active oxygen and capturing free radicals generated by charging and discharging of lithium-ion batteries, so that the gas production of lithium-ion batteries during charging and discharging is significantly reduced.
  • the preparation method of the positive electrode lithium supplement additive can ensure that the prepared positive electrode lithium supplement additive is stable in structure and electrochemical performance, has high efficiency, and saves production costs.
  • the positive electrode sheet of the present application contains the positive electrode lithium-replenishing additive of the present application
  • the positive electrode lithium-replenishing additive contained in the positive electrode sheet of the present application can exert a lithium-replenishing effect during the first cycle of charging, and can effectively capture and consume lithium-ion batteries during charging and discharging.
  • the secondary battery of the present application produces little gas during circulation, can effectively reduce or avoid volume expansion and the like, has high cycle performance, thus has high safety performance, long working life, high initial coulombic efficiency and secondary battery capacity, and stable electrochemical performance.
  • Fig. 1 is a kind of structural representation of positive electrode lithium supplement additive of the embodiment of the present application
  • Fig. 2 is a schematic diagram of another structure of the positive electrode lithium-supplementing additive according to the embodiment of the present application.
  • the term "and/or” describes the relationship between related objects, and means that there may be three relationships.
  • a and/or B may mean: A exists alone, A and B exist simultaneously, and B exists alone. Among them, A and B can be singular or plural.
  • the character "/" generally indicates that the contextual objects are an "or" relationship.
  • At least one means one or more, and “multiple” means two or more.
  • At least one of the following (pieces)” or similar expressions refer to any combination of these items, including any combination of a single item (pieces) or a plurality of items (pieces).
  • “at least one item (pieces) of a, b, or c”, or “at least one item (pieces) of a, b, and c” can mean: a, b, c, ab (ie, a and b), ac, bc, or abc, where a, b, and c can be single or multiple.
  • serial numbers of the above-mentioned processes do not mean the sequence of execution, some or all steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
  • the weight of the relevant components mentioned in the description of the embodiment of the present application can not only refer to the specific content of each component, but also can represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components in the description of the embodiment of the application is scaled up or down, it is within the scope of the disclosure of the description of the embodiment of the application.
  • the mass described in the description of the embodiments of the present application may be ⁇ g, mg, g, kg and other well-known mass units in the chemical industry.
  • first and second are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features.
  • first XX can also be called the second XX
  • second XX can also be called the first XX.
  • a feature defined as “first” and “second” may explicitly or implicitly include one or more of these features.
  • the embodiment of the present application provides a positive electrode lithium supplement additive.
  • the positive electrode lithium supplement additive in the embodiment of the present application has a core-shell structure, as shown in FIG. 1 , including a core body 01 and a coating layer 02 covering the core body 01 .
  • the core body 01 includes a positive electrode lithium supplement material.
  • the core body 01 is rich in lithium, thereby ensuring that the positive electrode lithium supplement additive in the embodiment of the present application can provide abundant lithium.
  • the positive electrode lithium supplement additive After it is added to the positive electrode as the positive electrode lithium supplement additive, it can be used as a "sacrifice agent" during the first cycle of charging. Release all the lithium ions contained in the positive electrode lithium supplement additive as much as possible at one time to supplement the irreversible lithium ions consumed by the formation of the SEI film on the negative electrode, thereby improving the first coulombic efficiency of the lithium ion battery.
  • the positive electrode lithium supplement material contained in the core body 01 can be a commonly used positive electrode lithium supplement material, or a positive electrode lithium supplement material modified or modified based on a common positive electrode lithium supplement material, or a newly developed positive electrode lithium supplement material.
  • gas positive electrode lithium supplement materials such as positive electrode lithium supplement materials containing oxygen atoms.
  • the above-mentioned oxygen-atom-containing positive electrode lithium-supplementing material may include at least one of L x My N z O q and Li w O.
  • L in the molecular formula of L x My N z O q is Li or/and a mixed alkali metal element of Li and at least one of K and Na not exceeding 30%
  • M includes at least one of Fe, Co, Ni, Mn, V, Fe-Co, Cu, Mo, Al, Ti, Mg
  • N includes at least one of Fe, Co, Mn, Ni, Si, Al or other equivalent or different-valent metal elements
  • O is oxygen
  • x is 4-6
  • y is 0.7-1 .0
  • z is 0-0.3, q is 4-5.
  • the lithium-replenishing material can be at least one of iron-based lithium-replenishing material, manganese-based lithium-replenishing material, nickel-based lithium-replenishing material and the like.
  • the L x My N z O q can be a doped or non-doped positive electrode lithium supplement material.
  • M is Fe and N is Al.
  • the lithium-rich lithium supplementary material represented by L x My N z O q may be Li 5 Fe 0.98 Al 0.02 O 4 .
  • O in the molecular formula of Li w O is oxygen element; w is 1.5-3.5.
  • These lithium-supplementing materials are rich in lithium, and can release lithium ions during the first cycle of charging to effectively supplement lithium.
  • the lithium-replenishing material has an inverse fluorite structure, it can also improve the unidirectional capacity characteristics of the lithium-replenishing material, thereby ensuring the lithium-replenishing effect of the positive electrode lithium-replenishing additive of the present application.
  • the core body 01 can contain other lithium-replenishing materials in addition to the positive electrode lithium-replenishing additive containing oxygen atoms. More importantly, on the basis of giving full play to the lithium supplementing effect of these positive electrode lithium supplement materials containing oxygen atoms, under the action of the coating layer 02 below, they can effectively inhibit the generation of active oxygen in the lithium supplement materials, further effectively inhibit the gas production phenomenon, and further improve the lithium supplement effect of the positive electrode lithium supplement additives.
  • the core body 01 may be at least one of primary particles and secondary particles, specifically, at least one of primary particles and secondary particles formed by the positive electrode lithium-supplementing additive contained in the core body 01 .
  • the particle size of the primary particle that is, the particle size distribution of the nucleus 01 is 0.01 ⁇ m-5.0 ⁇ m
  • the particle size of the secondary particle that is, the particle size distribution of the nucleus 01 is 0.02 ⁇ m-20 ⁇ m.
  • secondary particles refer to agglomerated particles formed by aggregating more than one primary particle.
  • the overall particle size of the positive electrode lithium-replenishing additive in the embodiment of the present application can be controlled and the lithium-replenishing effect of the positive electrode lithium-replenishing additive can be adjusted.
  • the coating layer 02 contained in the positive electrode lithium-replenishing additive in the embodiment of the present application contains a polymer represented by the general formula I of the following molecular structure:
  • X 1 , X 2 , X 3 , and X 4 are independently any one of a hydrogen atom and an alkyl group with 1 to 3 carbon atoms, and R is a polymer chain segment. Since the coating layer 02 of the positive electrode lithium-replenishing additive in the embodiment of the present application contains the polymer represented by the general formula I, the coating layer 02 is endowed with the effect of effectively inhibiting the generation of active oxygen, thereby effectively inhibiting gas production and improving the lithium-replenishing effect of the positive electrode lithium-replenishing additive.
  • lithium-ion batteries are prone to generate harmful free radicals during charging and discharging, such as CH 3 free radicals, acyl free radicals , and CH 3 O free radicals
  • the presence of the polymer shown in general formula I can effectively inhibit the generation of free radicals in the process of charging and discharging lithium-ion batteries, and can effectively capture free radicals generated in lithium-ion batteries during charging and discharging to form stabilized products, such as RN-O free radicals contained in the polymer shown in general formula I. Coupling occurs to form relatively stable chemical bonds to consume CH 3 ⁇ free radicals, acyl free radicals, and CH 3 O ⁇ free radicals.
  • the polymer represented by the above molecular structure formula I endows the coating layer 02 with the function of inhibiting active oxygen and capturing the free radicals generated by the charging and discharging of the lithium-ion battery, so that the gas production of the lithium-ion battery during charging and discharging is significantly reduced, and the volume expansion of the lithium-ion battery is reduced, thereby effectively improving the stability and safety of the charging and discharging of the lithium-ion battery, and at the same time improving its lithium supplementation effect.
  • the mass content of the polymer represented by the general formula I in the positive electrode lithium supplement additive of the present application is 0.1%-5%, specifically 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. Typical but non-limiting content.
  • the effect of the polymer is fully exerted, such as improving the effect of the coating layer 02 to suppress active oxygen and capture the free radicals generated by the charging and discharging of the lithium-ion battery, so that the gas production of the lithium-ion battery during charging and discharging is significantly reduced, and the volume expansion of the lithium-ion battery is reduced.
  • X 1 , X 2 , X 3 , and X 4 contained in the polymer represented by general formula I can stabilize the nitroxide radical contained in the polymer represented by general formula I through steric hindrance effect.
  • the alkyl group may be any of methyl, ethyl, propyl, isopropyl, and the like. These groups can improve the steric hindrance effect and further improve the stability of the nitroxide free radical.
  • the piperidine group contained in the general formula I specifically the piperidine group substituted with X 1 , X 2 , X 3 , X 4 and nitrogen-oxygen free radicals may be a branched chain or a terminal group, all of which can exert the above-mentioned effects of the above-mentioned polymer.
  • the polymer segment R contained in the polymer represented by the general formula I can form a film and improve the adhesion between the coating layer 02 and the core body 01.
  • the polymer segment R may be at least one segment including a carbon chain polymer chain (a carbon chain polymer chain means that the main molecular chain contains only carbon atoms), a heterochain polymer chain (a heterochain polymer chain means that the molecular main chain contains carbon and other atoms (such as O, N, S, etc.)), and a non-carbon chain polymer chain (a non-carbon chain polymer chain means that the molecular main chain does not contain carbon atoms).
  • a carbon chain polymer chain means that the main molecular chain contains only carbon atoms
  • a heterochain polymer chain a heterochain polymer chain means that the molecular main chain contains carbon and other atoms (such as O, N, S, etc.)
  • a non-carbon chain polymer chain a non-carbon chain polymer chain means that the molecular main chain does not
  • the polymer segment R may comprise at least one segment of a polyolefin segment, a polyacrylate segment, a polymethacrylate segment, a polyester segment, a polyamide segment, a polyurethane segment, a polyether segment, a polysilane segment, and a polysiloxane segment.
  • These polymer segments can further improve the properties such as film-forming properties of the polymer represented by the general formula I.
  • the polymer represented by the general formula I in the example can be at least the polymer represented by the following molecular structure formulas I 1 to I 6 :
  • R in I 1 includes a polyacrylate segment
  • R in I 2 includes a polymethacrylate segment
  • R in I 3 includes a polyallyloxy segment
  • R in I 4 includes a polystyrene segment
  • R in I 5 includes a polyester segment
  • R in I 6 includes a polyamide segment.
  • n in the polymer structures shown in I 1 to I 6 is the degree of polymerization of each polymer, and the value of n can be the usual value of the degree of polymerization of the polymer, and the value of n can be adjusted according to actual performance needs.
  • the polymer represented by the above general formula I can be prepared according to existing preparation methods (such as free radical polymerization, condensation polymerization, esterification and other methods).
  • the preparation method includes: using a monomer to obtain a polymer segment through free radical polymerization or condensation polymerization; using the polymer segment to perform an esterification reaction or amidation reaction with a small molecule containing a piperidine group, and The piperidine structure is connected to the polymer segment to obtain the polymer represented by the general formula I in each embodiment.
  • the coating layer 02 includes a polymer coating layer, and the polymer coating layer includes the polymer shown in the above general formula I.
  • the polymer coating layer can be formed from the polymer shown in the above general formula I alone, or can be formed from a mixture of other polymers and the above general formula I.
  • the polymer coating layer can also be formed from the polymer shown in the above general formula I to form the first polymer coating layer alone and other polymers to form a composite polymer coating layer.
  • the polymer represented by the above general formula I is dispersed in the polymer coating layer or formed into a polymer coating layer covering the core body 01, thereby improving the function of the above coating layer 02 to inhibit active oxygen and capture free radicals generated by charging and discharging of lithium-ion batteries.
  • the coating layer 02 contained in the positive electrode lithium-replenishing additive of the embodiment of the present application contains the above-mentioned polymer coating layer
  • the coating layer 02 contained in the positive electrode lithium-replenishing additive of the embodiment of the present application also includes a hydrophobic encapsulation layer. As shown in FIG. 2 , the hydrophobic encapsulation layer 21 contained in the cladding layer 02 covers the core body 01 , and the polymer coating layer 22 covers the surface of the hydrophobic encapsulation layer 21 away from the core body 01 .
  • the material of the hydrophobic encapsulation layer 21 may be a material capable of forming a dense hydrophobic coating layer and effectively ensuring the stability of the positive electrode lithium supplement material contained in the core body 01.
  • the material of the hydrophobic encapsulation layer 21 can also be an ionic conductor encapsulation layer that can facilitate ion conduction, or an electronic conductor encapsulation layer that can improve conductivity, and of course it can also be a composite layer structure of an ion conductor encapsulation layer and an electronic conductor encapsulation layer.
  • the hydrophobic encapsulation layer 21 is a composite layer structure of an ionic conductor encapsulation layer and an electronic conductor encapsulation layer
  • either layer of the ionic conductor encapsulation layer or the electronic conductor encapsulation layer can be directly coated on the surface of the above granular lithium-supplementing material with lithium fluoride bound to its surface.
  • the ionic conductor encapsulation layer can improve the intercalation and extraction effect of lithium ions on lithium ions and the ionic conductivity of lithium ions.
  • the electronic conductor encapsulation layer can improve the electronic conductivity of the lithium supplement material, improve its electrical conductivity, stimulate the gram capacity of the positive electrode lithium supplement additive, and realize efficient lithium supplement in the true sense.
  • the material of the ion conductor encapsulation layer can be a material that is beneficial to improve the ion conductivity, such as but not only including at least one of perovskite type, NASICON type, and garnet type.
  • LLTO lalogox La 2/3-x TiO 3
  • LLTO lalogox La 2/3-x TiO 3
  • ⁇ Li 0.5 La 0.5 TiO 3 ⁇ Li 0.33 La 0.57 TiO 3 ⁇ Li 0.29 La 0.57 TiO 3 ⁇ Li 0.33 Ba 0.25 La 0.39 TiO 3 ⁇ (Li 0.33 La 0.56 ) 1.005 Ti 0.99 Al 0.01 O 3 ⁇ Li 0.5 La 0.5 Ti 0.95 Zr 0.05 O 3 ⁇ ,NASICON ⁇ Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP), ⁇ Li 7 La 3 Zr 2 O 12 (LLZO) ⁇ Li
  • the electronic conductor encapsulation layer 21 can enhance the electronic conductivity of the hydrophobic encapsulation layer, thereby enhancing the electronic conductivity of the positive lithium supplement additive, which is beneficial to reduce the internal impedance of the electrode.
  • the electronic conductor encapsulation layer can also be used for secondary use, and it plays an auxiliary role as a conductive agent inside the positive electrode.
  • the electronic conductor encapsulation layer or the ionic conductor encapsulation layer can further enhance the compactness of the hydrophobic encapsulation layer, thereby improving the lithium supplementation stability and lithium supplementation effect of the positive electrode lithium supplementation additive.
  • the electronic conductor packaging layer can be fully covered or partially covered.
  • the material of the electronic conductor encapsulation layer includes at least one of carbon materials, conductive oxides, and conductive organics.
  • the carbon material includes at least one of amorphous carbon, carbon nanotubes, graphite, carbon black, graphene, and the like.
  • the conductive oxide when the electronic conductor encapsulation layer is made of conductive oxide, the conductive oxide may include at least one of In 2 O 3 , ZnO, and SnO 2 .
  • the conductive organic substance may be a conductive polymer or the like.
  • the thickness of the hydrophobic encapsulation layer 21 as shown in FIG. 2 may be 1-100 nm.
  • it can be adjusted by controlling the thickness of the ionic conductor encapsulation layer and the electronic conductor encapsulation layer included in the above hydrophobic encapsulation layer. Controlling the thickness of the hydrophobic encapsulation layer within this range can improve the compactness of the hydrophobic encapsulation layer, further improve the storage stability and processing stability of the positive electrode lithium supplement additive, and simultaneously improve the ion and/or electronic conductivity of the positive electrode lithium supplement additive.
  • hydrophobic encapsulation layer may also include other functional layers as required, and the types of other functional layers may be flexibly selected as required.
  • the above-mentioned hydrophobic encapsulation layer 21 also contains the polymer represented by the general molecular structure formula I above.
  • the polymer and the hydrophobic encapsulation layer 21 have a hydrophobic isolation effect, such as enhancing its isolation from water vapor in the production process and the environment, improving the storage and processing performance of the positive electrode lithium supplement additive, and further reducing the gas production of the battery to improve safety performance.
  • the embodiment of the present application also provides a preparation method of the above positive electrode lithium supplement additive.
  • the preparation method of the positive electrode lithium supplement additive in the embodiment of the present application comprises the following steps:
  • the positive electrode lithium supplement material particle raw material in step S01 is the core body 01 material containing the positive electrode lithium supplement material that forms the positive electrode lithium supplement additive in the above application example. Then the type and particle size of the positive electrode lithium supplement material particle raw material are the same as the positive electrode lithium supplement material contained in the core body 01 of the positive electrode lithium supplement additive in the application example above.
  • the polymer represented by the general formula I is also the above positive electrode lithium supplement
  • the polymer contained in the coating layer 02 of the additive has a molecular structure represented by the general formula I. Therefore, in order to save space, the raw materials of the positive electrode lithium supplementing material particles will not be described in detail here.
  • the positive electrode lithium supplement material particle raw material in step S01 includes the hydrophobic encapsulation layer 21 containing the core body 01 contained in the positive electrode lithium supplement additive and the coating core body 01 in the above application example.
  • the hydrophobic encapsulation layer 21 may be a composite layer comprising the ionic conductor encapsulation layer or the electronic conductor encapsulation layer or the composite layer of the ionic conductor encapsulation layer and the electronic conductor encapsulation layer.
  • the method of forming the hydrophobic encapsulation layer can be formed by selecting a corresponding or suitable method according to the structure and material of the hydrophobic encapsulation layer 21 .
  • step S01 after the positive electrode lithium supplement material particle raw material is mixed with the solution containing the polymer represented by the general formula I, the solution is uniformly mixed with the positive electrode lithium supplement material particle raw material, so that the solution containing the polymer represented by the general formula I can form a film layer on the surface of the positive electrode lithium supplement material particle raw material, and at least the polymer represented by the general formula I can be dispersed on the surface of the positive electrode lithium supplement material particle. Therefore, as long as the mixing method is any mixing method that can make the positive electrode lithium-supplementing material particle raw material and the solution evenly mixed, it is within the scope disclosed in the description of the embodiments of the present application, such as stirring or ball milling.
  • the mixing ratio of the positive electrode lithium-replenishing material particle raw material and the solution can ensure that the content of the polymer represented by general formula I in the positive electrode lithium-replenishing additive prepared in step S02 is 0.1%-5%.
  • the polymer represented by the general formula I forms a polymer coating layer on the surface of the positive electrode lithium-replenishing material particle raw material, that is, the surface of the positive electrode lithium-replenishing additive prepared in step S02 is formed with a polymer coating layer formed by the polymer represented by the general formula I.
  • the mass concentration of the polymer represented by the general formula I contained in the solution in step S01 may be 2%-20%.
  • the solvent contained in the solution may be a solvent capable of dispersing the positive electrode lithium-supplementing material particle raw material and the polymer shown in general formula I and ensuring their stable performance, such as methanol, ethanol, n-hexane, cyclohexane, ethyl acetate, toluene, xylene, tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, etc. At least one organic solvent.
  • the drying treatment in step S02 is to remove the solvent contained in the wet film in step S01. Therefore, on the basis of ensuring the stability of the positive electrode lithium-replenishing material particle raw material and the polymer shown in the general formula I, any drying treatment method is within the scope disclosed in the description of the embodiment of the present application, such as drying at elevated temperature, drying at reduced pressure, or natural drying.
  • the protective atmosphere is formed by continuously feeding a chemically inert gas.
  • the chemically inert gas may be a conventional chemically inert gas, such as at least one of Ar, N 2 , He, and the like.
  • the preparation method of the above-mentioned positive electrode lithium supplement additive can effectively disperse the polymer represented by the general formula I on the surface of the positive electrode lithium supplement material particles, so that the prepared positive electrode lithium supplement additive has the structural characteristics and corresponding electrochemical properties of the positive electrode lithium supplement additive of the above text application, such as endowing the prepared positive electrode lithium supplement additive with the full play of the above text application positive electrode lithium supplement additive
  • the preparation method of the positive electrode lithium supplement additive can ensure that the prepared positive electrode lithium supplement additive is stable in structure and electrochemical performance, has high efficiency, and saves production costs.
  • the embodiment of the present application also provides a positive electrode sheet.
  • the positive electrode sheet in the embodiment of the present application includes an electrode positive electrode collector and a positive electrode active layer bonded to the surface of the positive electrode collector.
  • the positive electrode active layer contains the positive electrode lithium replenishing additive in the above application example.
  • the positive electrode sheet of the embodiment of the present application contains the above-mentioned positive electrode lithium-replenishing additive of the embodiment of the present application
  • the positive electrode lithium-replenishing additive contained in the positive electrode sheet plays the above-mentioned role, and can be used as a lithium source in the first cycle of charging as a "sacrifice agent" and is first consumed to replenish the irreversible lithium ions consumed by the formation of the SEI film on the negative electrode, thereby maintaining the abundance of lithium ions in the lithium-ion battery system and improving the first effect and overall electrochemical performance of the lithium-ion battery.
  • the quality of the electrode sheet is stable and the yield rate is high.
  • the mass content of the positive electrode lithium-supplementing additive contained in the positive electrode active layer of the above application example may be 0.1wt%-10wt%; preferably, 0.5wt%-5wt%.
  • the positive active layer includes, in addition to the positive lithium supplement additive, a positive active material, a binder and a conductive agent, wherein the binder can be a commonly used electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.
  • the binder can be a commonly used electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl
  • the conductive agent may be a commonly used conductive agent, such as one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes.
  • the positive electrode active material may be one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadium phosphate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate.
  • the preparation process of the positive electrode sheet can be as follows: the positive electrode active material, the positive electrode lithium supplement additive, the conductive agent and the binder are mixed to obtain the electrode slurry, the positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet is prepared by drying, rolling, die-cutting and other steps.
  • the embodiment of the present application further provides a secondary battery.
  • the secondary battery of the embodiment of the present application includes necessary components such as a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, and of course other necessary or auxiliary components.
  • the positive electrode sheet is the above-mentioned positive electrode sheet in the embodiment of the present application.
  • the secondary battery of the embodiment of the present application contains the positive electrode lithium-replenishing additive of the above-mentioned application embodiment, the secondary battery of the embodiment of the present application produces little gas during the cycle, can effectively reduce or avoid volume expansion, etc., and has high cycle performance, thereby having high safety performance, long working life, and the first Coulombic efficiency and lithium-ion battery capacity are high, and the electrochemical performance is stable. If it is tested, the capacity retention rate of the secondary battery can still be higher than 87% after 300 cycles at room temperature, which is further high. at 91%. After cycling at high temperature, such as 300 cycles at 45°C, the capacity retention rate can still be higher than 80%, further higher than 85%. At this time, the battery thickness change rate is less than 15%, further less than 9%. It has excellent cycle performance and high safety.
  • the present embodiment A1 to embodiment A6 respectively provide positive electrode lithium supplement additives, and the components contained in each positive electrode lithium supplement additive are as shown in the following table 1.
  • the positive electrode lithium supplement additive in embodiment A1 contains a coating layer formed by the polymer represented by structural formula I1
  • embodiment A2 contains a coating layer formed by the polymer represented by structural formula I2 , and so on.
  • the content of each component contained in the positive electrode lithium-replenishing additive in the lithium-replenishing additive is shown in Table 1 respectively.
  • This comparative example A1 provides a positive electrode lithium supplement additive. Compared with the positive lithium supplementary additive in Example A1 in this comparative example, the positive lithium supplementary material (Li 5 FeO 4 ) particle raw material is not mixed with the polymer represented by the general molecular structure formula I 1 to I 6 , and everything else is identical.
  • the present embodiment B1 to embodiment B6 and comparative example B1 respectively provide a lithium ion battery.
  • Each lithium-ion battery is assembled as a component lithium-ion battery according to the following method:
  • the positive electrode lithium supplement additives provided in Example A1 to Example A6 and Comparative Example A1 are respectively used as the positive electrode lithium supplement additives of lithium ion battery embodiment B1 to embodiment B6 and comparative example B1.
  • LiFePO positive electrode lithium supplement additive: Super P : PVDF
  • the mass ratio of the five is 100:93:2:2:3
  • the mixing method is ball milling, and the ball milling time is 60min; the rotation speed is set to 30Hz; Slurry-coating-drying-cutting operations to prepare positive electrode sheets, which are baked in a vacuum oven at 100°C to remove traces of water.
  • Negative electrode sheet Mix the negative active material graphite, conductive agent Super P, thickener carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in deionized water to make negative electrode slurry.
  • the mass ratio of graphite: Super P: CMC: SBR is 95:2:0.5:2.5.
  • the negative electrode slurry is coated on the copper foil of the current collector, and after drying-rolling-secondary drying process, the negative electrode sheet is made.
  • Diaphragm Polyethylene (PE) diaphragm is used.
  • Electrolyte is a 1mol/L LiPF 6 solution, and the solvent is composed of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1.
  • the above-mentioned positive electrode sheet, negative electrode sheet, electrolyte and diaphragm are assembled into a lithium ion soft pack battery according to the lithium ion battery assembly requirements.
  • the lithium-ion battery of each embodiment assembled in section 5) and comparative example is carried out following performance test:
  • Normal temperature cycle test the battery is left at 25°C, and the charge and discharge voltage range is 3.0 to 4.4V.
  • the charge and discharge cycle is carried out with a current of 1C.
  • the initial thickness is recorded as T 0 and the initial capacity is Q 0 .
  • the thickness after 300 cycles is T 1 and the capacity is Q 1 .
  • High-temperature cycle test Under the condition of high temperature 45°C, use 1C current to carry out charge-discharge cycle in the charge-discharge voltage range of 3.0-4.4V, record the initial thickness as T 2 and the initial capacity as Q 2 , and the thickness after cycling to 300 cycles as T 3 and capacity as Q 3 , and calculate the thickness change rate and capacity retention rate of the battery at a high temperature (45°C) cycle for 300 cycles by the following formula:
  • the thickness change rate of the lithium-ion battery at room temperature is significantly smaller than that of the comparative example B1 without the polymer coating layer, indicating that the gas production is significantly reduced, and the capacity retention rate of the 300 cycles of the embodiment cycle is significantly higher than that of the comparative example; at the same time, a similar rule is also observed for the high temperature (45%) cycle of 300 cycles.
  • the use of the electrolyte additive of the present application can suppress the gas production of the lithium-ion battery during charging and discharging, and its cycle performance is good, so it has high safety performance and long working life.

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Abstract

本申请公开了一种正极补锂添加剂及其制备方法和应用。本申请正极补锂添加剂为核壳结构，核壳结构的核体包括正极补锂材料，包覆核体的包覆层包括含哌啶基团的聚合物。本申请正极补锂添加剂所用聚合物赋予包覆层抑制活性氧的作用和捕捉锂离子电池充放电产生的自由基的作用，使得锂离子电池在充放电过程中产气量明显减少，降低锂离子电池体积膨胀，从而有效提高锂离子电池充放电的稳定性和安全性，同时提高其补锂效果，正极补锂添加剂的制备方法能够保证制备的正极补锂添加剂结构和电化学性能稳定，而且效率高，节约生产成本。其可以在正极片和二次电池中应用。

Description

正极补锂添加剂及其制备方法和应用
本申请要求于2022年01月20日提交中国专利局，申请号为202210070564.7，申请名称为“正极补锂添加剂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
本申请属于二次电池领域，具体涉及一种正极补锂添加剂及其制备方法和应用。
背景技术
20世纪60、70年代的石油能源危机问题迫使人们去寻找新的可替代的新能源，随着人们对环境保护和能源危机意识的增强。锂离子电池因其具备较高的工作电压与能量密度、相对较小的自放电水平、无记忆效应、无铅镉等重金属元素污染、超长的循环寿命等优点，被认为是最具应用前景的能源之一。锂离子电池被广泛应用于电动车、电动工具、可移动电子消费品以及储能等诸多方面。
目前最常用的锂离子电池正极材料主要有磷酸铁锂、镍钴锰(铝)酸锂三元材料(俗称三元材料)、钴酸锂、锰酸锂等，负极应用最多的是碳基石墨材料以及硅基负极材料等。虽然锂离子电池有很多优点，但是锂离子电池在首次充电过程中，负极表面通常伴随着固态电解质膜SEI膜的形成，这个过程会消耗大量的Li+，意味着从正极材料脱出的Li+部分被不可逆消耗，对应电芯的可逆比容量降低。负极材料特别是硅基负极材料则会进一步消耗Li+，造成正极材料的锂损失，降低锂离子电池的首次库伦效率和锂离子电池容量。如在使用石墨负极的锂离子电池体系中，首次充电会消耗约10％的锂源。当采用高比容量的负极材料，例如合金类(硅、锡等)、氧化物类(氧化硅、氧化锡)和无定形碳负极时，正极锂源的消耗将进一步加剧。
为改善由于负极不可逆损耗引起的低库伦效率问题，研究者开发出了相关富锂化合物，作为添加剂来解决首次充放电锂离子不可逆损耗的问题。
然而，在研究和实际应用中发现，现有补锂添加剂的使用也导致了锂离子电池在化成阶段的产气量增大的问题，会导致密闭电池系统内部发生胀气现象，引发电池体积膨胀以及安全性问题。
目前，正极补锂添加剂的研究尚处于初始阶段，尚未形成稳定、成熟的产品，关于补锂添加剂产气机理仍未有明确的、系统的研究成果。而对于传统的锂离子电池，SEI膜分解、电解液分解、负极活性物质与粘结剂的反应等反应容易导致气体的产生，并且这些反应往往并非独立进行的，很可能同时存在多种反应的发生。为解决上述锂离子电池产气问题，目前 使用的方法有使用酸酐类化合物、γ-丁内酯等环状酯、多腈基化合物等作为添加剂加入至电解液中，形成正负极保护膜从而抑制产气，但这些措施往往存在保护膜离子传导性差、阻抗增大、正负极保护膜不稳定等问题。因此，如何有效改善由补锂添加剂的使用带来的产气问题而不影响锂离子电池的其他性能是目前亟需解决的问题，对锂离子电池性能的提升具有重大影响。
技术问题
本申请的目的在于克服现有技术的上述不足，提供一种正极补锂添加剂及其制备方法，以解决现有正极补锂添加剂导致锂离子电池产气量增加的技术问题。
本申请的另一目的在于提供一种正极片和含有该电极片的二次电池，以解决现有二次电池首次库伦效率得到改善但是产气量增加的技术问题。
技术解决方案
为了实现上述申请目的，本申请的第一方面，提供了一种正极补锂添加剂。本申请正极补锂添加剂为核壳结构，核壳结构的核体包括正极补锂材料，包覆核体的包覆层中含有如下分子结构通式Ⅰ所示的聚合物：
通式Ⅰ中，X1、X2、X3、X4独立为氢原子、碳原子数1～3的烷基中的任一种，R为高分子链段。
进一步地，烷基包括甲基、乙基、丙基、异丙基中的任一种。
进一步地，高分子链段包括碳链高分子链、杂链高分子链、非碳链高分子链中的至少一种链段。
进一步地，通式Ⅰ所含的哌啶基团为支链或末端基团。
进一步地，聚合物在正极补锂添加剂中的质量含量为0.1％-5％。
进一步地，R包括聚烯烃链段、聚丙烯酸酯链段、聚甲基丙烯酸酯链段、聚酯链段、聚酰胺链段、聚氨酯链段、聚醚链段、聚硅烷链段、聚硅氧烷链段中的一种或多种。
进一步地，X1、X2、X3、X4均为甲基，R为聚烯烃、聚丙烯酸酯、聚甲基丙烯酸酯、聚酯、聚酰胺、聚氨酯、聚醚、聚硅烷、聚硅氧烷中的一种或多种。
具体地，聚合物包括如下分子结构式I1～I6中的一种或多种：
进一步地，包覆层包括聚合物包覆层，且聚合物包覆层所含聚合物包括聚合物。
进一步地，正极补锂材料包括含氧原子的正极补锂材料。
更进一步地，包覆层还包括疏水封装层，且疏水封装层包覆核体，聚合物包覆层包覆在疏水封装层的背离核体的表面。
更进一步地，疏水封装层包括离子导体封装层、电子导体封装层中的至少一层。
具体地，离子导体封装层的材料包括钙钛矿型、NASICON型、石榴石型中的至少一种。
具体地，电子导体封装层的材料包括碳材料、导电氧化物、导电有机物中的至少一种。
更进一步地，疏水封装层中含有分子结构通式Ⅰ所示的聚合物。
更进一步地，疏水封装层的厚度为1-100nm。
本申请的第二方面，提供了本申请正极补锂添加剂的制备方法。本申请正极补锂添加剂的制备方法包括如下步骤：
将正极补锂材料颗粒原料与包括如下分子结构通式Ⅰ所示聚合物的溶液进行混合处理，形成混合物料；
在保护气氛中，将混合物进行干燥处理，使得聚合物分散在正极补锂材料颗粒的表面上，得到正极补锂添加剂；
其中，通式Ⅰ中的X1、X2、X3、X4独立为氢原子、碳原子数1～3的烷基中的任一种，R为高分子链段。
进一步地，聚合物形成聚合物包覆层，包覆正极补锂材料颗粒。
进一步地，正极补锂材料颗粒原料包括含有正极补锂材料的核体和包覆核体的疏水封装层。
进一步地，分子结构通式Ⅰ所示聚合物在所述溶液中的质量浓度为2％-20％。
进一步地，溶液的溶剂包括甲醇、乙醇、正己烷、环己烷、乙酸乙酯、甲苯、二甲苯、四氢呋喃、N-甲基吡咯烷酮、N,N-二甲基甲酰胺等中的至少一种。
本申请的第三方面，提供了一种正极片。本申请正极片包括正极集流体和结合在正极集流体表面的正极活性层，其中，正极活性层中含有本申请正极补锂添加剂或由本申请正极补锂添加剂制备方法制备的正极补锂添加剂。
本申请的第四方面，提供了一种二次电池。本申请包括正极片和负极片，正极片为本申请正极片。
进一步地，二次电池在常温下经300次循环后容量保持率高于87％。
进一步地，二次电池在45℃下经300次循环后容量保持率高于80％。
进一步地，二次电池在45℃下经300次循环后的电池厚度变化率小于15％。
与现有技术相比，本申请具有以下的技术效果：
本申请正极补锂添加剂的包覆层所含的通式Ⅰ所示聚合物，一方面能够有效抑制补锂材料内部活性氧的产生；另一方面，能够有效抑制锂离子电池在充放电过程中自由基的产生， 并能够有效捕捉锂离子电池充放电过程中产生的自由基而形成稳定化物。因此，本申请正极补锂添加剂所含分子结构通式Ⅰ所示的聚合物赋予包覆层抑制活性氧的作用和捕捉锂离子电池充放电产生的自由基的作用，使得锂离子电池在充放电中产气量明显减少，降低锂离子电池体积膨胀，从而有效提高锂离子电池充放电的稳定性和安全性，同时提高其补锂效果。
本申请正极补锂添加剂制备方法能够有效在正极补锂材料颗粒表面分散通式Ⅰ所示聚合物，使得赋予制备的正极补锂添加剂具有上文本申请正极补锂添加剂在充分发挥补锂作用的基础上，同时具有抑制活性氧和捕捉锂离子电池充放电产生的自由基的作用，使得锂离子电池在充放电中产气量明显减少。另外，正极补锂添加剂的制备方法能够保证制备的正极补锂添加剂结构和电化学性能稳定，而且效率高，节约生产成本。
本申请正极片由于含有本申请正极补锂添加剂，因此，本申请正极片所含的正极补锂添加剂能够在首圈充电过程发挥补锂作用，同时能够有效捕捉和消耗锂离子电池在充放电过程中产生的有害基团，有效降低锂离子电池在充放电中的产气现象，从而有效提高锂离子电池充放电的稳定性和安全性。
本申请二次电池在循环中产气小，能够有效降低或避免体积膨胀等现象，其循环性能高，从而具有高的安全性能，工作寿命长，而且首次库伦效率和二次电池容量高，电化学性能稳定。
附图说明
为了更清楚地说明本申请具体实施方式或现有技术中的技术方案，下面将对具体实施方式或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本申请实施例正极补锂添加剂的一种结构示意图；
图2为本申请实施例正极补锂添加剂的另一种结构示意图。
本发明的实施方式
为了使本申请要解决的技术问题、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。
本申请中，术语“和/或”，描述关联对象的关联关系，表示可以存在三种关系，例如，A和/或B，可以表示：单独存在A，同时存在A和B，单独存在B的情况。其中A，B可以是单数或者复数。字符“/”一般表示前后关联对象是一种“或”的关系。
本申请中，“至少一个”是指一个或者多个，“多个”是指两个或两个以上。“以下至少一项 (个)”或其类似表达，是指的这些项中的任意组合，包括单项(个)或复数项(个)的任意组合。例如，“a,b,或c中的至少一项(个)”，或，“a,b,和c中的至少一项(个)”，均可以表示：a,b,c,a-b(即a和b),a-c,b-c,或a-b-c，其中a,b,c分别可以是单个，也可以是多个。
应理解，在本申请的各种实施例中，上述各过程的序号的大小并不意味着执行顺序的先后，部分或全部步骤可以并行执行或先后执行，各过程的执行顺序应以其功能和内在逻辑确定，而不应对本申请实施例的实施过程构成任何限定。
在本申请实施例中使用的术语是仅仅出于描述特定实施例的目的，而非旨在限制本申请。在本申请实施例和所附权利要求书中所使用的单数形式的“一种”、“所述”和“该”也旨在包括多数形式，除非上下文清楚地表示其他含义。
本申请实施例说明书中所提到的相关成分的重量不仅仅可以指代各组分的具体含量，也可以表示各组分间重量的比例关系，因此，只要是按照本申请实施例说明书相关组分的含量按比例放大或缩小均在本申请实施例说明书公开的范围之内。具体地，本申请实施例说明书中所述的质量可以是μg、mg、g、kg等化工领域公知的质量单位。
术语“第一”、“第二”仅用于描述目的，用来将目的如物质彼此区分开，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。例如，在不脱离本申请实施例范围的情况下，第一XX也可以被称为第二XX，类似地，第二XX也可以被称为第一XX。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括一个或者更多个该特征。
大量研究表明，锂离子电池在形成SEI膜的过程中以及在充放电过程中，SEI膜分解、电解液分解、负极活性物质与粘结剂等反应往往伴随着多种自由基的形成，这些自由基可以互相结合或进一步引发其他连锁反应而最终产生气体。当锂离子电池含有补锂添加剂时，在首次充电过程中也会导致产气量增大。
为了解决该问题，第一方面，本申请实施例提供了一种正极补锂添加剂。本申请实施例正极补锂添加剂为核壳结构，其结构如图1所示，包括核体01和包覆核体01的包覆层02。
其中，核体01包括正极补锂材料。这样，该核体01富含锂，从而保证本申请实施例正极补锂添加剂能够提供丰富的锂，其作为正极补锂添加剂加入正极中后，使得在首圈充电过程中作为“牺牲剂”，尽可能一次性将该正极补锂添加剂所含的全部锂离子释放出来，用以补充负极形成SEI膜而消耗掉的不可逆的锂离子，从而提高锂离子电池的首次库伦效率。
核体01所含的正极补锂材料可以是常用的正极补锂材料，也可以是基于常用正极补锂材料进行修饰或改性的正极补锂材料，当然还可以是新研发的正极补锂材料。在本申请实施例中，结合下文中包覆层02中的特性，相对是易产气的正极补锂材料，如含氧原子的正极补锂材料。
如实施例中，上述含氧原子的正极补锂材料可以包括LxMyNzOq、LiwO中的至少一种。其中，LxMyNzOq分子式中的L为Li或/和Li与不超过30％的K、Na中至少一种的混合碱金属元素；M包括Fe、Co、Ni、Mn、V、Fe-Co、Cu、Mo、Al、Ti、Mg其中的至少一种；N包括Fe、Co、Mn、Ni、Si、Al或其他等价或者异价的金属元素中的至少一种；O为氧元素；x为4-6，y为0.7-1.0，z为0-0.3，q为4-5。因此，根据M所示元素种类，补锂材料可以是铁系补锂材料、锰系补锂材料、镍系锂材料等中的至少一种。当z零时，该LxMyNzOq可以是掺杂或非掺杂的正极补锂材料。在具体实施例中，LxMyNzOq中M为Fe的同时N为Al。此时，LxMyNzOq所示的富锂补锂材料可以是Li5Fe0.98Al0.02O4。还可以但不仅仅为Li2NiO2、Li5FeO4、LiCoO2、Li2MnO2、LiMn2O4、LiFePO4等。LiwO分子式中的O为氧元素；w为1.5-3.5。该些补锂材料富含锂，能够在首圈充电过程中释放锂离子起到有效的补锂作用。当该补锂材料为反萤石结构时，还能够提高补锂材料单向容量特性，从而保证本申请正极补锂添加剂补锂效果。当补锂材料含有铝元素掺杂时，Al原子以替代铁原子晶格的形式存在，这种形式存在的Al原子可以拓宽锂离子的传输通道，并能够提高锂离子的脱出速率。当然，核体01除了可以含氧原子的正极补锂添加剂，还可以含有其他补锂材料。更重要的是，该些含氧原子的正极补锂材料在充分发挥其补锂作用的基础上，在下文包覆层02的作用下，能够有效抑制补锂材料中活性氧的产生，进一步有效抑制产气现象，并进一步提高正极补锂添加剂的补锂效果。
实施例中，核体01可以是一次颗粒、二次颗粒中的至少一种，具体是核体01所含正极补锂添加剂形成的一次颗粒、二次颗粒中的至少一种。如当核体01为一次颗粒时，一次颗粒粒径也即是核体01的粒径分布为0.01μm-5.0μm；当核体01为二次颗粒时，二次颗粒粒径也即是核体01的粒径分布为0.02μm-20μm。其中，二次颗粒是指由一颗以上的一次颗粒聚集而成的团聚颗粒。通过对核体01形态和粒径控制，可以控制本申请实施例正极补锂添加剂的整体粒径和调节正极补锂添加剂的补锂效果。
本申请实施例正极补锂添加剂所含的包覆层02中含有如下分子结构通式Ⅰ所示的聚合物：
其中，通式Ⅰ中，X1、X2、X3、X4独立为氢原子、碳原子数1～3的烷基中的任一种，R为高分子链段。由于本申请实施例正极补锂添加剂的包覆层02中含有通式Ⅰ所示聚合物，赋予包覆层02有效抑制活性氧产生的作用，从而有效抑制产气现象，并提高正极补锂添加剂的补锂效果。
由于锂离子电池在充放电过程中易产生有害自由基，如生成包括CH3·自由基、酰基自由基、CH3O·自由基反应，因此，通式Ⅰ所示聚合物的存在能够有效抑制锂离子电池在充放电过程中自由基的产生，并能够有效捕捉锂离子电池在充放电过程中产生的自由基而形成稳定化物，如通式Ⅰ所示聚合物所含的RN-O·自由基与CH3·自由基、酰基自由基、CH3O·自由基发生耦合，形成较为稳定的化学键而起到消耗CH3·自由基、酰基自由基、CH3O·自由基的作用。因此，上述分子结构通式Ⅰ所示的聚合物赋予包覆层02抑制活性氧的作用和捕捉锂离子电池充放电产生的自由基的作用，使得锂离子电池在充放电中产气量明显减少，降低锂离子电池体积膨胀，从而有效提高锂离子电池充放电的稳定性和安全性，同时提高其补锂效果。
实施例中，通式Ⅰ所示聚合物在本申请正极补锂添加剂中的质量含量为0.1％-5％，具体可以是0.1％、0.5％、1％、1.5％、2％、2.5％、3％、3.5％、4％、4.5％、5％等典型但非限制性含量。通过对该聚合物在本申请实施例正极补锂添加剂中的含量，充分发挥该聚合物的作用，如提高包覆层02抑制活性氧的作用和捕捉锂离子电池充放电产生的自由基的作用，使得锂离子电池在充放电中产气量明显减少，降低锂离子电池体积膨胀等作用。
其中，通式Ⅰ所示聚合物所含的X1、X2、X3、X4通过位阻效应可以起到使通式I所示通式Ⅰ所示聚合物所含的氮氧自由基稳定存在的作用。实施例中，当X1、X2、X3、X4独立为碳原子数1～3的烷基时，该烷基可以是包括甲基、乙基、丙基、异丙基等中的任一种。该些基团能够提高位阻效应，进一步提高氮氧自由基的稳定性。
在具体实施例中，通式Ⅰ所含的哌啶基团，具体是取代有X1、X2、X3、X4和含氮氧自由基的哌啶基团可以是支链或末端基团，均能够发挥该上文聚合物的上文所述作用。
通式Ⅰ所示聚合物所含的高分子链段R能够起到成膜、提高包覆层02与核体01之间的附着性作用。实施例中，该高分子链段R可以是包括碳链高分子链(碳链高分子链是指分子主链只含碳原子)、杂链高分子链(杂链高分子链是指分子主链含有碳和其他原子(如O、N、S等))、非碳链高分子链(非碳链高分子链是指分子主链不含碳原子)中的至少一种链段。进一步实施例中，该高分子链段R可以是包括聚烯烃链段、聚丙烯酸酯链段、聚甲基丙烯酸酯链段、聚酯链段、聚酰胺链段、聚氨酯链段、聚醚链段、聚硅烷链段、聚硅氧烷链段中的至少一种链段。该些高分子链段能够进一步提高通式Ⅰ所示聚合物的成膜性等性能。
基于上文通式Ⅰ中X1、X2、X3、X4、R所示的基团种类，在具体实施例中，上述各实施 例中通式Ⅰ所示聚合物具体至少可以是如下分子结构式Ⅰ1至Ⅰ6所示聚合物：
其中，Ⅰ1中的R包括聚丙烯酸酯链段；Ⅰ2中的R包括聚甲基丙烯酸酯链段；Ⅰ3中的R包括聚烯丙氧基链段；Ⅰ4中的R包括聚苯乙烯链段；Ⅰ5中的R包括聚酯链段；Ⅰ6中的R包括聚酰胺链段。而且Ⅰ1至Ⅰ6所示聚合物结构中的n是各聚合物的聚合度，该n的数值可以是聚合物通常的聚合度数值，具体可以根据实际的性能需要调节该n数值。
均能够发挥聚合物的上文作用，起到抑制活性氧的作用和捕捉锂离子电池充放电产生的自由基的作用，使得锂离子电池在充放电中产气量明显减少，降低锂离子电池体积膨胀。
另外，上述通式Ⅰ所示聚合物可以按照现有制备方法(如按照自由基聚合、缩合聚合、酯化反应等方法)制备获得。如实施例中，制备方法包括：利用单体通过自由基聚合或缩合聚合得到高分子链段；用高分子链段与含哌啶基团的小分子进行酯化反应或酰胺化反应，将 哌啶结构接在高分子链段上，得到各实施例中通式Ⅰ所示聚合物。
基于上文各实施例基础上，包覆层02包括聚合物包覆层，且该聚合物包覆层包括上述通式Ⅰ所示聚合物，如可以是由上文通式Ⅰ所示聚合物单独形成该聚合物包覆层，也可以与其它聚合物与上文通式Ⅰ所示聚合物的混合物形成的聚合物包覆层，还可以是由上文通式Ⅰ所示聚合物单独形成第一聚合物包覆层和其它聚合物形成的第二聚合物包覆层形成的复合聚合物包覆层。将上文通式Ⅰ所示聚合物分散在聚合物包覆层中或形成聚合物包覆层包覆核体01，从而提高上文包覆层02抑制活性氧的作用和捕捉锂离子电池充放电产生的自由基的作用。
在本申请实施例正极补锂添加剂所含包覆层02含有上述聚合物包覆层的基础上，在进一步实施例中，本申请实施例正极补锂添加剂所含的包覆层02还包括疏水封装层。如图2所示，包覆层02所含的疏水封装层21包覆核体01，聚合物包覆层22包覆在疏水封装层21的背离核体01的表面。在包覆层02中增设疏水封装层21，使得包覆层02在充分发挥上通式Ⅰ所示聚合物的作用基础上，能够起到隔绝层的作用，保护核体01所含的正极补锂材料与存储环境隔绝，如避免与环境中的水汽和二氧化碳等不利因素接触，从而提高正极补锂材料的补锂稳定性，从而赋予核体01高补锂的稳定性和补锂效果以及本申请实施例正极补锂添加剂的储存性能和加工性能。基于疏水封装层21的作用，疏水封装层21的材料可以是能够形成致密疏水包覆层而有效保证核体01所含正极补锂材料稳定性的材料。如该疏水封装层21的材料还可以是能够利于离子传导的离子导体封装层，也可以是利于提高导电性的电子导体封装层，当然也可以是离子导体封装层与电子导体封装层的复合层结构。当疏水封装层21为离子导体封装层与电子导体封装层的复合层结构时，该离子导体封装层或电子导体封装层任一层可以直接包覆在表面结合有氟化锂的上文颗粒状补锂材料的表面。其中，离子导体封装层能够改善补锂材料对锂离子的嵌脱效果和锂离子的离子导率。电子导体封装层能够改善补锂材料的电子导率，提高其导电性能，激发正极补锂添加剂的克容量发挥，实现真正意义上的高效补锂。
当疏水封装层21包括离子导体封装层时，其起到提高锂离子导率作用。因此，该离子导体封装层的材料可以是有利于离子导率提高的材料，如可以但不仅仅包括钙钛矿型、NASICON型、石榴石型中的至少一种。具体实施例中，钙钛矿型包括Li3xLa2/3-xTiO3(LLTO)，具体如Li0.5La0.5TiO3、Li0.33La0.57TiO3、Li0.29La0.57TiO3、Li0.33Ba0.25La0.39TiO3、(Li0.33La0.56)1.005Ti0.99Al0.01O3、Li0.5La0.5Ti0.95Zr0.05O3等中的至少一种，NASICON型如但不仅仅为Li1.4Al0.4Ti1.6(PO4)3(LATP)，石榴石型包括Li7La3Zr2O12(LLZO)、Li6.4La3Zr1.4Ta0.6O12，Li6.5La3Zr1.5Ta0.5O12中的至少一种。通过对离子导体封装层材料选择，能够进一步提高离子导体封装层离子电导率。
当疏水封装层21包括电子导体封装层时，该电子导体封装层能够增强疏水封装层的电子电导率，从而增强正极补锂添加剂的电子电导率，有利于减小电极内部的阻抗。同时，在上述颗粒状补锂材料作为“牺牲品”释放过程中和释放完毕之后，电子导体封装层还可以进行二次利用，在正极内部起到导电剂的辅助作用。而且该电子导体封装层或进一步与离子导体封装层起到致密性的增效作用，提高疏水封装层的致密性，从而提高正极补锂添加剂的补锂稳定性和补锂效果。基于电子导体封装层的作用，可以是电子导体封装层全包覆，也可以是部分包覆。实施例中，电子导体封装层的材料包括碳材料、导电氧化物、导电有机物中的至少一种。具体实施例中，电子导体封装层的材料为碳材料时，碳材料包括无定形碳、碳纳米管、石墨、炭黑、石墨烯等中的至少一种。另些具体实施例中，电子导体封装层的材料为导电氧化物时，导电氧化物可以包括In2O3、ZnO、SnO2中的至少一种。导电有机物可以是导电聚合物等。通过调节电子导体封装层的含量和材料，能够进一步提高其电子电导率。
进一步实施例中，如图2所示的疏水封装层21的厚度可以为1-100nm。如可以通过控制上文疏水封装层所含的离子导体封装层、电子导体封装层的厚度进行调节。将疏水封装层厚度的控制在该范围，能够提高疏水封装层的致密性，进一步提高正极补锂添加剂的存储稳定性和加工稳定性，同时提高正极补锂添加剂的离子和/或电子导率。
另外，疏水封装层还可以根据需要包括其他功能层，其他功能层的种类可以根据需要进行灵活选择。
在进一步实施例中，上述疏水封装层21中还含有上文分子结构通式Ⅰ所示的聚合物。通过在疏水封装层21中进一步增设该聚合物，从而使得该聚合物与疏水封装层21起到疏水隔绝作用，如增强其与生产加工中与环境中水汽等隔绝作用，提高正极补锂添加剂的存储和加工性能，进一步降低电池的产气现象提高安全性能。
第二方面，本申请实施例还提供了上文正极补锂添加剂的制备方法。本申请实施例正极补锂添加剂的制备方法包括以下步骤：
S01：将正极补锂材料颗粒原料与包括上文分子结构通式Ⅰ所示聚合物的溶液进行混合处理，形成混合物料；
S02：在保护气氛中，将混合物进行干燥处理，使得聚合物分散在正极补锂材料颗粒的表面上，得到正极补锂添加剂。
其中，步骤S01中的正极补锂材料颗粒原料是形成上文本申请实施例正极补锂添加剂的含正极补锂材料的核体01材料。那么该正极补锂材料颗粒原料的种类和粒径均如上文本申请实施例正极补锂添加剂的核体01所含正极补锂材料。通式Ⅰ所示聚合物也为上文正极补锂 添加剂的包覆层02所含的分子结构通式Ⅰ所示聚合物。因此，为了节约篇幅，在此不再对该正极补锂材料颗粒原料进行赘述。
实施例中，当上文正极补锂添加剂所含包覆层02含有如图2所示的疏水封装层21时，那么步骤S01中的正极补锂材料颗粒原料包括含上文本申请实施例正极补锂添加剂所含核体01和包覆核体01的疏水封装层21。具体实施例中，疏水封装层21可以是含上文所述离子导体封装层或电子导体封装层或离子导体封装层与电子导体封装层的复合层。另外，形成疏水封装层的方法可以根据疏水封装层21的结构和材料选取对应或适合方法形成。
步骤S01中，将正极补锂材料颗粒原料与含通式Ⅰ所示聚合物的溶液混合处理后，使得溶液与正极补锂材料颗粒原料混合均匀，使得含通式Ⅰ所示聚合物的溶液能够在正极补锂材料颗粒原料表面形成膜层，至少使得通式Ⅰ所示聚合物能够分散在正极补锂材料颗粒的表面上。因此，混合处理的方式只要是能够使得正极补锂材料颗粒原料和该溶液混合均匀的任何混合方式均在本申请实施例说明书公开的范围，如可以但不仅仅是搅拌或球磨等混合处理。
实施例中，正极补锂材料颗粒原料与溶液的混合比例可以保证通式Ⅰ所示聚合物在步骤S02中制备正极补锂添加剂中的含量为0.1％-5％。进一步实施例中，通过控制正极补锂材料颗粒原料与溶液的混合比例，使得通式Ⅰ所示聚合物在正极补锂材料颗粒原料表面形成聚合物包覆层，也即是使得在步骤S02中制备的正极补锂添加剂表面形成有由通式Ⅰ所示聚合物形成的聚合物包覆层。
进一步实施例中，步骤S01中溶液所含的通式Ⅰ所示聚合物质量浓度可以是2％-20％，通过控制通式Ⅰ所示聚合物在溶液中的浓度，能够提高溶液在正极补锂材料颗粒原料表面形成湿膜的完整性和均匀性，如形成完整和均匀的湿膜。其中，溶液所含的溶剂可以是能够分散正极补锂材料颗粒原料和通式Ⅰ所示聚合物并保证它们性能稳定的溶剂，如可以是甲醇、乙醇、正己烷、环己烷、乙酸乙酯、甲苯、二甲苯、四氢呋喃、N-甲基吡咯烷酮、N,N-二甲基甲酰胺等中的至少一种有机溶剂。
步骤S02中的干燥处理是为了除去步骤S01中湿膜所含溶剂，因此，在保证正极补锂材料颗粒原料和通式Ⅰ所示聚合物稳定的基础上，任何干燥处理方式均在本申请实施例说明书公开的范围，如可以是升温干燥、减压干燥或自然晾干等方式。
实施例中，保护气氛是通过持续通入化学惰性气体形成。具体实施例中，该化学惰性气体可以是常规的化学惰性气体，如Ar、N2、He等中的至少一种。
因此，上述正极补锂添加剂的制备方法能够有效在正极补锂材料颗粒表面分散通式Ⅰ所示聚合物，从而使得制备的正极补锂添加剂具有上文本申请正极补锂添加剂的结构特征和相应的电化学性能，如赋予制备的正极补锂添加剂具有上文本申请正极补锂添加剂在充分发挥 补锂作用的基础上，具有抑制活性氧的作用和捕捉锂离子电池充放电产生的自由基的作用，使得锂离子电池在充放电中产气量明显减少。另外，正极补锂添加剂的制备方法能够保证制备的正极补锂添加剂结构和电化学性能稳定，而且效率高，节约生产成本。
第三方面，本申请实施例还提供了一种正极片。本申请实施例正极片包括电极正极集流体和结合在正极集流体表面的正极活性层。其中，正极活性层中含有上文本申请实施例正极补锂添加剂。由于本申请实施例正极片含有上述本申请实施例电极正极补锂添加剂，因此，在充放电中过程中，正极片所含的正极补锂添加剂发挥上文作用，能够作为锂源在首圈充电过程中作为“牺牲剂”首先被消耗，用以补充负极形成SEI膜而消耗掉的不可逆的锂离子，从而保持锂离子电池体系内锂离子的充裕，提高锂离子电池首效和整体电化学性能。而且电极片质量稳定且良品率高。于此同时，还能够有效捕捉和消耗锂离子电池在充放电过程中产生的有害基团，有效降低锂离子电池在充放电中的产气现象，从而有效提高锂离子电池充放电的稳定性和安全性。
在一实施例中，正极活性层中所含上文本申请实施例正极补锂添加剂的质量含量可以为0.1wt％-10wt％；优选地，0.5wt％-5wt％。正极活性层包括除了该正极补锂添加剂之外，还包括正极活性材料、粘结剂和导电剂，其中，粘结剂可以是常用的电极粘结剂，如包括聚偏氯乙烯、可溶性聚四氟乙烯、丁苯橡胶、羟丙基甲基纤维素、甲基纤维素、羧甲基纤维素、聚乙烯醇、丙烯腈共聚物、海藻酸钠、壳聚糖和壳聚糖衍生物中的一种或多种。本申请实施方式中，导电剂可以是常用的导电剂，如包括石墨、碳黑、乙炔黑、石墨烯、碳纤维、C60和碳纳米管中的一种或多种。正极活性材料可以是包括钴酸锂、锰酸锂、磷酸铁锂、磷酸锰铁锂、磷酸钒锂，磷酸钒氧锂、氟代磷酸钒锂、钛酸锂、镍钴锰酸锂、镍钴铝酸锂中的一种或多种。
实施例中，正极片制备过程可以为：将正极活性材料、正极补锂添加剂、导电剂与粘结剂混合得到电极浆料，将正极浆料涂布在正极集流体上，经干燥、辊压、模切等步骤制备得到正极片。
第四方面，本申请实施例还提供了一种二次电池。本申请实施例二次电池包括正极片、负极片、隔膜和电解质等必要的部件，当然还包括其他必要或辅助的部件。其中，正极片为上述本申请实施例正极片。
由于本申请实施例二次电池中含有上文本申请实施例正极补锂添加剂，因此，本申请实施例二次电池在循环中产气小，能够有效降低或避免体积膨胀等现象，其循环性能高，从而具有高的安全性能，工作寿命长，而且首次库伦效率和锂离子电池容量高，电化学性能稳定。如经检测，该二次电池在常温下经300次循环后容量保持率依然能够高于87％，进一步是高 于91％。在高温下循环如在45℃下经300次循环后容量保持率依然能够高于80％，进一步高于85％，此时，电池厚度变化率小于15％，进一步小于9％。其循环性能优异，安全性高。
以下通过多个具体实施例来举例说明本申请实施例正极补锂添加剂及其制备方法和应用等。
1.正极补锂添加剂及其制备方法实施例：
实施例A1至实施例A6
本实施例A1至实施例A6分别提供了正极补锂添加剂，各正极补锂添加剂所含组分如下述表1中所示，具体的，实施例A1正极补锂添加剂含由结构式I1所示的聚合物形成的包覆层，实施例A2含由结构式I2所示的聚合物形成的包覆层，依次类推。其中，正极补锂添加剂所含的各组分在补锂添加剂中的含量分别如表1中所示。
各实施例正极补锂添加剂的制备方法，包括如下步骤：
S1：将正极补锂材料(Li5FeO4)颗粒原料分别与包括分子结构通式I1～I6所示聚合物的溶液进行混合处理，形成混合物料；
S2：在保护气氛中，将混合物进行干燥处理，使得聚合物分散在正极补锂材料颗粒的表面上，得到正极补锂添加剂。
对比例A1
本对比例A1提供一种正极补锂添加剂。本对比例正极补锂添加剂与实施例A1中正极补锂添加剂相比，正极补锂材料(Li5FeO4)颗粒原料不与分子结构通式Ⅰ1～I6所示聚合物进行混合处理，其他完全相同。
表1 各实施例及对比例正极补锂添加剂组成
2.锂离子电池实施例：
本实施例B1至实施例B6和对比例B1分别提供一种锂离子电池。各锂离子电池分别按照如下方法组装成分锂离子电池：
1)正极片：
分别以实施例A1至实施例A6和对比例A1提供的正极补锂添加剂作为锂离子电池实施例B1至实施例B6和对比例B1的正极补锂添加剂，在相同条件下，按照NMP：LiFePO4：正极补锂添加剂：Super P：PVDF，五者质量比为100:93:2:2:3的比例混合，混合方式为球磨，球磨时间为60min；转速设置为30Hz；经过匀浆-涂布-烘干-裁片操作，制备成正极片，正极片在100℃真空烘箱中烘烤，除去痕量水。
2)负极片：将负极活性物质石墨、导电剂Super P，增稠剂羧甲基纤维素(CMC)、粘结剂丁苯橡胶(SBR)在去离子水中混合均匀制成负极浆料，其中石墨：Super P：CMC：SBR的质量比为95:2:0.5:2.5。将负极浆料涂布在集流体铜箔上，经过烘干-辊压-二次烘干工序后，制成负极极片。
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：
将上述正极片、负极片、电解液和隔膜按照锂离子电池组装要求组装成锂离子软包电池。
3.锂离子电池相关性能测试：
将第5)节中组装的各实施例和对比例的锂离子电池进行如下性能测试：
常温循环测试：电池搁置在25℃条件下，在3.0～4.4V的充放电压区间下使用1C电流进行充放电循环，记录初始厚度为T0和初始容量为Q0，循环至300cycles的厚度为T1和容量为Q1，由如下公式计算电池常温循环300cycles的厚度变化率和容量保持率：
常温循环300cycles厚度变化率(％)＝(T1-T0)/T0×100％；
常温循环300cycles容量保持率(％)＝Q1/Q0×100％。
高温循环测试：在高温45℃条件下，在3.0～4.4V的充放电压区间下使用1C电流进行充放电循环，记录初始厚度为T2和初始容量为Q2，循环至300cycles的厚度为T3和容量为Q3，由如下公式计算电池高温(45℃)循环300cycles的厚度变化率和容量保持率：
高温(45℃)循环300cycles厚度变化率(％)＝(T3-T2)/T2×100％；
高温(45℃)循环300cycles容量保持率(％)＝Q3/Q2×100％。
相关性能测试结果如下表2中所示：
表2 性能测试结果
从表2测试结果可以看出：在实施例B1～B6制备的锂离子电池中，使用具有结构式I1～I6聚合物作为包覆层的补锂添加剂后，锂离子电池在室温下的厚度变化率明显小于不含聚合物包覆层的对比例B1，说明产气量明显减少，而且实施例循环300cycles的容量保持率明显高于对比例；同时，高温(45％)循环300cycles也观察到相似的规律。综上，使用本申请电解液添加剂可以抑制锂离子电池在充放电过程中的产气现象，而且其循环性能好，从而具有高的安全性能和工作寿命长。
以上实施例仅表达了本申请的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对本申请专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请专利的保护范围应以所附权利要求为准。

Claims (15)

  1. 一种正极补锂添加剂，为核壳结构，所述核壳结构的核体包括正极补锂材料，其特征在于，包覆所述核体的包覆层中含有如下分子结构通式Ⅰ所示的聚合物：
    所述通式Ⅰ中，X1、X2、X3、X4独立为氢原子、碳原子数1～3的烷基中的任一种，R为高分子链段。
  2. 根据权利要求1所述的正极补锂添加剂，其特征在于：所述烷基包括甲基、乙基、丙基、异丙基中的任一种；和/或
    所述高分子链段包括碳链高分子链、杂链高分子链、非碳链高分子链中的至少一种链段；和/或
    所述通式Ⅰ所含的哌啶基团为支链或末端基团；和/或
    所述聚合物在所述正极补锂添加剂中的质量含量为0.1％-5％。
  3. 根据权利要求1或2所述的正极补锂添加剂，其特征在于：所述R包括聚烯烃链段、聚丙烯酸酯链段、聚甲基丙烯酸酯链段、聚酯链段、聚酰胺链段、聚氨酯链段、聚醚链段、聚硅烷链段、聚硅氧烷链段中的一种或多种。
  4. 根据权利要求1～3任一项所述的正极补锂添加剂，其特征在于：所述X1、X2、X3、X4均为甲基，R包括聚烯烃链段、聚丙烯酸酯链段、聚甲基丙烯酸酯链段、聚酯链段、聚酰胺链段、聚氨酯链段、聚醚链段、聚硅烷链段、聚硅氧烷链段中的一种或多种。
  5. 根据权利要求1～4任一项所述的正极补锂添加剂，其特征在于，所述聚合物包括如下分子结构式I1～I6中的一种或多种：
  6. 根据权利要求1～5任一项所述的正极补锂添加剂，其特征在于：所述包覆层包括聚合物包覆层，且所述聚合物包覆层所含聚合物包括所述聚合物；和/或
    所述正极补锂材料包括含氧原子的正极补锂材料。
  7. 根据权利要求6所述的正极补锂添加剂，其特征在于：所述包覆层还包括疏水封装层，且所述疏水封装层包覆所述核体，所述聚合物包覆层包覆在所述疏水封装层的背离所述核体的表面。
  8. 根据权利要求7所述的正极补锂添加剂，其特征在于：所述疏水封装层包括离子导体封装层、电子导体封装层中的至少一层；和/或
    所述疏水封装层中含有所述分子结构通式Ⅰ所示的聚合物；和/或
    所述疏水封装层的厚度为1-100nm。
  9. 根据权利要求8所述的正极补锂添加剂，其特征在于：所述离子导体封装层的材料包 括钙钛矿型、NASICON型、石榴石型中的至少一种；
    所述电子导体封装层的材料包括碳材料、导电氧化物、导电有机物中的至少一种。
  10. 一种正极补锂添加剂的制备方法，其特征在于，包括如下步骤：
    将正极补锂材料颗粒原料与包括如下分子结构通式Ⅰ所示聚合物的溶液进行混合处理，形成混合物料；
    在保护气氛中，将所述混合物进行干燥处理，使得所述聚合物分散在所述正极补锂材料颗粒的表面上，得到正极补锂添加剂；
    其中，所述通式Ⅰ中的X1、X2、X3、X4独立为氢原子、碳原子数1～3的烷基中的任一种，R为高分子链段。
  11. 根据权利要求10所述的制备方法，其特征在于：所述聚合物形成聚合物包覆层，包覆所述正极补锂材料颗粒；和/或
    所述正极补锂材料颗粒原料包括含有正极补锂材料的核体和包覆所述核体的疏水封装层。
  12. 根据权利要求10或11所述的制备方法，其特征在于：所述分子结构通式Ⅰ所示聚合物在所述溶液中的质量浓度为2％-20％；和/或
    所述溶液的溶剂包括甲醇、乙醇、正己烷、环己烷、乙酸乙酯、甲苯、二甲苯、四氢呋喃、N-甲基吡咯烷酮、N,N-二甲基甲酰胺中的至少一种。
  13. 一种正极片，包括正极集流体和结合在正极集流体表面的正极活性层，其特征在于：所述正极活性层中含有权利要求1-9任一项所述的正极补锂添加剂或由权利要求10-12任一项所述的制备方法制备的正极补锂添加剂。
  14. 一种二次电池，包括正极片和负极片，其特征在于：所述正极片为权利要求13所述的正极片。
  15. 根据权利要求14所述的二次电池，其特征在于：所述二次电池在常温下经300次循环后容量保持率高于87％；和/或
    所述二次电池在45℃下经300次循环后容量保持率高于80％；和/或
    所述二次电池在45℃下经300次循环后的电池厚度变化率小于15％。
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