Positive electrode lithium supplementing additive, preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a positive electrode lithium supplementing additive as well as a preparation method and application thereof, wherein the positive electrode lithium supplementing additive comprises a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, the material of the coating layer is selected from a conductive hydrophobic polymer with a surface modification hydrophobic reinforcing agent; the coating layer can compensate for the poor electronic conductivity of the lithium-containing compound, improve the electronic conductivity, and act as a conductive agent in the electrode sheet, thereby reducing the addition amount of the conductive agent in the electrode sheet; on the other hand, the polymer surface is modified with the hydrophobic reinforcing agent to provide a hydrophobic group and further set up a hydrophobic barrier, effectively improve the stability of the lithium-containing core in the air, effectively block the contact reaction of moisture and carbon dioxide in the air with the lithium supplementing material, prevent the lithium-containing compound from reacting with water and losing effectiveness, and protect the stability of the lithium supplementing material.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium-ion batteries, and in particular relates to a positive electrode lithium supplement additive and a preparation method and application thereof. Background Art

[0002] During the first charging process of lithium-ion batteries, a solid electrolyte membrane (SEI membrane) will form at the interface between the negative electrode and the electrolyte. Although the formation of this irreversible SEI membrane can improve the interface stability of the negative electrode material, it also consumes a large amount of Li2O3 released from the electrolyte and the positive electrode material. + , resulting in a huge capacity loss and a decrease in the first coulombic efficiency.

[0003] To solve the above problems, researchers use lithium replenishment technology to compensate for the active lithium consumption caused by the formation of SEI film. Common lithium replenishment technologies include positive electrode lithium replenishment and negative electrode lithium replenishment. Negative electrode lithium replenishment technology mostly uses lithium foil, lithium powder, Li-organic complex solution, lithiated negative electrode materials and other materials for lithium replenishment, but these lithiated reagents have poor chemical stability, are incompatible with air and polar solvents, have extremely high requirements for the production and use environment, and have safety hazards. Positive electrode lithium replenishment technology is to remove Li from lithium-rich compounds. + To supplement the consumption of active lithium in the positive electrode by the formation of the negative electrode SEI film during the first charge, reduce capacity loss, and improve the first coulombic efficiency. Currently reported positive electrode lithium supplement additives include Li3N, Li2S, Li2O, Li2O2, Li2NiO2, Li5FeO4, etc., which can be mixed with traditional positive electrode materials such as LiCoO2, LiMn2O4, LiFePO4, etc. to form a common positive electrode, thereby improving the first coulombic efficiency and reversible capacity. However, most of these lithium supplement additives themselves have disadvantages such as poor electronic conductivity and reaction with moisture, which affect the electrical performance of lithium-ion batteries during use. In addition, the storage and use conditions are relatively high, which is not conducive to widespread use. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode lithium replenishing additive and its preparation method and application, aiming to solve the problems in the prior art that positive electrode lithium replenishing additives are sensitive to air and moisture and have poor electronic conductivity.

[0005] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0006] In a first aspect, the present application provides a positive electrode lithium replenishing additive, which includes a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, wherein the material of the coating layer is selected from a conductive hydrophobic polymer with a surface-modified hydrophobic enhancer.

[0007] In a second aspect, the present application provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0008] The positive electrode lithium supplement additive is prepared by the method.

[0009] The conductive hydrophobic polymer and the hydrophobic reinforcing agent are mixed in a first organic solvent to obtain a conductive hydrophobic polymer with surface-modified hydrophobic reinforcing agent.

[0010] The conductive hydrophobic polymer with surface-modified hydrophobic reinforcing agent and the lithium-containing material as the core are mixed in a second organic solvent to obtain a positive electrode lithium supplement additive mixture.

[0011] The positive electrode lithium supplement additive mixture is post-processed in an inert atmosphere to obtain the positive electrode lithium supplement additive.

[0012] In a third aspect, the present application provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a binder, a conductive agent and a positive electrode lithium supplement additive.

[0013] In a fourth aspect, the present application provides a secondary battery, which comprises the positive electrode tab.

[0014] Compared with the prior art, the present application has the following technical effects:

[0015] The positive electrode lithium supplement additive provided in the first aspect of the present application forms a coating layer on the surface of the lithium-containing core, and the positive electrode lithium supplement additive is prepared in a core-shell structure by coating. The coating layer of the outer shell is a conductive hydrophobic polymer coating with surface-modified hydrophobic reinforcing agent. On the one hand, it can compensate for the poor electronic conductivity of the lithium-containing compound and improve the electronic conductivity. At the same time, it can act as a conductive agent in the electrode tab, reducing the amount of conductive agent added in the electrode tab. On the other hand, the polymer surface is modified with hydrophobic reinforcing agent to provide hydrophobic groups and further set up a hydrophobic barrier to effectively improve the stability of the lithium-containing core in the air, effectively block the contact reaction of moisture and carbon dioxide in the air with the core lithium supplement material, prevent the lithium-containing compound from reacting with water and losing effectiveness, and protect the stability of the lithium supplement material. The positive electrode lithium supplement additive can be used in lithium ion batteries to compensate for the loss of active lithium of the electrode active material during the first charge and discharge process, improve the reversible capacity and the first coulombic efficiency, and improve the electronic conductivity and electrochemical performance of the battery.

[0016] The preparation method of the positive electrode lithium supplement additive provided in the second aspect of the present application is to mix and process the lithium-containing material as the core and the conductive hydrophobic polymer of the surface modification hydrophobic enhancer to obtain a positive electrode lithium supplement additive mixture, and then perform post-processing to obtain the positive electrode lithium supplement additive. The prepared positive electrode lithium supplement additive has a core-shell structure. The conductive hydrophobic polymer coating layer of the surface modification hydrophobic enhancer can effectively block the contact reaction of moisture and carbon dioxide in the air with the inner core lithium supplement material, and has a certain protective effect on the lithium-containing inner core. At the same time, the conductive hydrophobic polymer coating layer of the surface modification hydrophobic enhancer can improve the electronic conductivity, which is conducive to the full play of the electrochemical performance of the electrode active material. Moreover, the preparation method is simple in process and does not require expensive equipment, and is suitable for wide application.

[0017] The positive electrode tab provided in the third aspect of the present application adds the positive electrode lithium supplement additive to the positive electrode tab material. Since the lithium-containing inner core of the positive electrode lithium supplement additive contains abundant lithium, lithium ions can be released during the use of the positive electrode tab packaged into a battery, to compensate for the active lithium lost by the electrode active material during the first charge and discharge process, improve the reversible capacity and the first coulombic efficiency, improve the lithium supplement effect, and is suitable for industrial production.

[0018] The secondary battery provided in the fourth aspect of the present application contains a positive electrode tab, and the positive electrode tab contains a positive electrode lithium supplement additive. The obtained secondary battery has high first coulombic efficiency and good cycle stability, and improves the electronic conductivity and overall electrochemical performance of the battery, which is conducive to wide use. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0020] Figure 1 is a structural schematic diagram of the positive electrode lithium supplement additive provided in the embodiments of the present application.

[0021] Figure 2 is an infrared spectrum diagram of the conductive hydrophobic polymer, lithium supplement inner core and the obtained positive electrode lithium supplement additive after coating provided in the embodiment A2 of the present application. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application more clear and explicit, the following will further describe the present application with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0023] In this application, the term "and / or", describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the following three cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0024] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0025] It should be understood that in various embodiments of the present application, the size of the sequence number of the above-mentioned processes does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence. The execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0026] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0027] The weight of the related components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the weight ratio relationship between each component. Therefore, as long as the content of the related components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass in the specification of the embodiments of the present application can be μg, mg, g, kg, etc. Mass units commonly known in the chemical field.

[0028] The terms "first", "second" are only used for description purposes, to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Therefore, the features limited by "first" and "second" can explicitly or implicitly include one or more of the features.

[0029] The first aspect of the embodiments of the present application provides a positive electrode lithium supplement additive, as shown in the accompanying drawings Figure 1 The positive electrode lithium supplement additive includes a lithium-containing core 1 and a coating layer 2 formed on the surface of the lithium-containing core 1, wherein the material of the coating layer 2 is selected from a surface-modified hydrophobic reinforcing agent conductive hydrophobic polymer.

[0030] The positive electrode lithium supplement additive provided by the first aspect of the embodiments of the present application forms a coating layer on the surface of the lithium-containing core, and the positive electrode lithium supplement additive is made into a core-shell structure in a coating manner. The coating layer of the shell is a surface-modified hydrophobic reinforcing agent conductive hydrophobic polymer coating layer, which can compensate for the poor electronic conductivity of the lithium-containing compound itself, improve the electronic conductivity, and at the same time act as a conductive agent in the electrode sheet to reduce the amount of conductive agent added in the electrode sheet. On the other hand, the polymer is surface-modified with a hydrophobic reinforcing agent to provide a hydrophobic group and further set up a hydrophobic barrier to effectively improve the stability of the lithium-containing core in the air, effectively block the contact reaction of moisture and carbon dioxide in the air with the lithium supplement material in the core, prevent the lithium-containing compound from reacting with water and losing effectiveness, and protect the stability of the lithium supplement material. The positive electrode lithium supplement additive can be used in lithium ion batteries to compensate for the loss of active lithium of the electrode active material in the first charge-discharge process, improve the reversible capacity and the first coulombic efficiency, and improve the electronic conductivity and electrochemical performance of the battery.

[0031] In some embodiments, the coverage of the coating layer on the surface of the lithium-containing core is 80% or more. Since the material of the coating layer is a surface-modified hydrophobic reinforcing agent conductive hydrophobic polymer, coupling can occur between the surface-modified hydrophobic reinforcing agents, the mutual connection between the polymers forms a grid structure, the coverage of the coating layer on the surface of the lithium-containing core is 80% or more, and most of the moisture and carbon dioxide in the air can be effectively blocked from contacting the lithium supplement material in the core, preventing the lithium-containing compound from reacting with water and losing effectiveness, and protecting the stability of the lithium supplement material.

[0032] In some embodiments, the material of the coating layer 2 includes a surface-modified hydrophobic reinforcing agent conductive hydrophobic polymer, wherein the hydrophobic reinforcing agent is selected from a fluorine-containing silane coupling agent containing a "Si-O" bond and a "F" group. The fluorine-containing silane coupling agent can form a coupling network through self-crosslinking, and the fluorine-containing group is connected as a branch to further enhance the hydrophobic effect, so that the lithium-containing core is not affected by the moisture and carbon dioxide in the air.

[0033] In some embodiments, the fluorine-containing silane coupling agent includes one or more of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, dodecafluoroheptylpropylmethyldimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane, 3,3,3-trifluoropropylmethyldimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane, 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane.

[0034] In some embodiments, the coating layer includes an inner layer containing a conductive polymer main chain structure and a protective outer layer containing F branched chains self-polymerized on the surface of the conductive polymer inner layer to form a Si-O-Si network structure and adsorbed on the main chain structure on the surface of the conductive polymer. Since the material of the coating layer is selected from the surface-modified hydrophobicity-enhancing conductive hydrophobic polymer, in the formed coating layer, the conductive hydrophobic polymer serves as the inner layer, and the "Si-O" bond in the fluorine-containing silane coupling agent used to modify the conductive hydrophobic polymer can undergo cross-linking reaction to generate "Si-O-Si" bond to polymerize and form a coupling network, which is attached to and wrapped around the surface of the conductive hydrophobic polymer. The "fluorine-containing" group branched chains of the fluorine-containing silane coupling agent form a protective outer layer, further forming a hydrophobic protective outer layer, enhancing the effect of hydrophobicity, and preventing the lithium-containing inner core from being affected by water vapor and carbon dioxide in the air.

[0035] In some embodiments, the conductive hydrophobic polymer includes one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, polyphenylene, poly(p-phenylenevinylene), and derivatives thereof. The conductive hydrophobic polymer is used as the main material of the coating layer, which can effectively improve the stability of the lithium-containing inner core in the air, effectively block the contact reaction between moisture and carbon dioxide in the air and the lithium supplement material, prevent the lithium-containing compound from reacting with water and losing effectiveness, and protect the stability of the lithium supplement material. On the other hand, since the conductive hydrophobic polymer material has good electrical conductivity, it can be used as a shell material for the positive electrode lithium supplement additive, which can improve the electronic conductivity and electrochemical performance of the battery.

[0036] In some specific embodiments, the material of the coating layer 2 of the positive electrode lithium supplement additive is selected from polyacetylene, which is a polymer material with a structural unit of (CH=CH) n During use as the material of the coating layer 2, the polyacetylene forms a grid structure after heat treatment, and under the action of the fluorine-containing silane coupling agent, the compactness of the grid structure is improved, forming a dense coating layer that can densely coat the lithium-containing inner core 1, effectively isolating the lithium-containing inner layer from water vapor and carbon dioxide in the air, and improving the stability of the lithium-containing inner core 1. At the same time, polyacetylene has a certain electrical conductivity, which can improve the electrochemical performance of the battery.

[0037] In some embodiments, the material of the coating layer 2 of the positive electrode lithium supplement additive is selected from polyaniline, which forms a dense film layer covering the surface of the lithium-containing core 1 during heat treatment, and under the action of the fluorine-containing silane coupling agent, the fluorine-containing silane coupling agent forms a protective outer layer containing F branched on the conductive polymer main chain structure, further isolating water vapor and carbon dioxide in the air, in addition, the electrical activity of polyaniline is derived from the P electron conjugated structure in the molecular chain, and with the expansion of the P electron system in the molecular chain, the P bonding state and the P* antibonding state form the valence band and the conduction band respectively, thereby showing high electrical conductivity.

[0038] In some embodiments, the material of the coating layer 2 of the positive electrode lithium supplement additive is selected from polyaniline, which forms a dense film layer covering the surface of the lithium-containing core 1 during heat treatment, and under the action of the fluorine-containing silane coupling agent, the fluorine-containing silane coupling agent forms a protective outer layer containing F branched on the conductive polymer main chain structure, further isolating water vapor and carbon dioxide in the air, in addition, the electrical activity of polyaniline is derived from the P electron conjugated structure in the molecular chain, and with the expansion of the P electron system in the molecular chain, the P bonding state and the P* antibonding state form the valence band and the conduction band respectively, thereby showing high electrical conductivity. 2 S / cm, and good stability; it is beneficial to effectively supplement lithium and improve the electronic conductivity of the battery.

[0039] In some embodiments, the thickness of the coating layer 2 is 1-100 nm, and controlling the thickness of the coating layer 2 to be moderate is beneficial to better isolate the lithium-containing core 1 from water vapor or carbon dioxide in the air, while ensuring that the battery has high charge and discharge performance. If the thickness of the coating layer 2 is <1 nm, it is difficult to isolate air and moisture, which can cause the lithium-containing core 1 to have poor stability and easily fail, and thus cannot play a good protective role. If the thickness of the coating layer 2 is >100 nm, the positive electrode lithium supplement additive particles obtained after being coated will be large, which can reduce the charge and discharge performance of the lithium ion battery made by using the lithium supplement additive.

[0040] In some embodiments, the thickness of the coating layer 2 is selected from 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, and 100 nm.

[0041] In some embodiments, the positive electrode lithium supplement additive includes a lithium-containing core 1, and the material of the lithium-containing core includes Li x M y O z , Li wAt least one of A, wherein 0 < x≤ 6, 0 < y≤ 3, 0 < z≤ 4, 0 < w≤ 5, and M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, Zr, and A includes at least one of C, N, O, P, S, F, B, Se. The lithium-containing core provided can provide lithium ions for the positive electrode material, achieving the effect of positive electrode lithium supplementation, so that the positive electrode lithium supplementation additive is used in a lithium ion battery, can compensate for the active lithium lost by the electrode active material during the first charge and discharge process, improve the reversible capacity and the first coulombic efficiency.

[0042] In some embodiments, the particle size of the lithium-containing core 1 is 0.01-10 μm; controlling the particle size of the lithium-containing core 1 to be moderate is conducive to obtaining a positive electrode lithium supplementation additive that can be well dispersed and can better perform the lithium supplementation function and improve the rate of the battery. If the particle size of the lithium-containing core 1 is <0.01 μm, not only is it easy to agglomerate and not uniformly dispersed, but also the compaction density of the pole piece is reduced; if the particle size of the lithium-containing core 1 is >10 μm, the rate performance is reduced.

[0043] In some specific embodiments, the particle size of the lithium-containing core 1 is selected from 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, and 10 μm.

[0044] On the basis of the above embodiments of the core 1 and the coating layer 2, in some embodiments, the mass ratio of the lithium-containing core 1 and the coating layer 2 is 90-99.9:0.1-10. If the mass of the coating layer 2 is too small, the coating is not complete or the thickness of the coating layer 2 is too small, which easily leads to the lithium-containing core 1 contacting water vapor or carbon dioxide in the air, affecting the stability of the lithium-containing core 1; if the mass of the coating layer 2 is too large, the thickness of the coating layer 2 is too large, which increases the lithium ion release path and reduces the lithium supplementation effect, making the charge and discharge performance of the lithium ion battery made using the lithium supplementation additive low.

[0045] The second aspect of the embodiments of the present application provides a preparation method of a positive electrode lithium supplementation additive, including the following steps:

[0046] S01. providing a lithium-containing material as a core, a hydrophobic reinforcing agent, and a conductive hydrophobic polymer as the positive electrode lithium supplementation additive;

[0047] S02. performing first mixing treatment of the conductive hydrophobic polymer and the hydrophobic reinforcing agent in a first organic solvent to obtain a conductive hydrophobic polymer with a surface-modified hydrophobic reinforcing agent;

[0048] S03. The conductive hydrophobic polymer of the surface-modified hydrophobic enhancer and the lithium-containing material as the core are subjected to a second mixing treatment in a second organic solvent to obtain a positive electrode lithium supplement additive mixture;

[0049] S04. The positive electrode lithium supplement additive mixture is subjected to a post-treatment under an inert atmosphere to obtain a positive electrode lithium supplement additive.

[0050] The preparation method of the positive electrode lithium supplement additive provided in the second aspect of the embodiments of the present application is to mix the lithium-containing material as the core and the conductive hydrophobic polymer of the surface-modified hydrophobic enhancer to obtain a positive electrode lithium supplement additive mixture, and then to perform a post-treatment to obtain a positive electrode lithium supplement additive. The prepared positive electrode lithium supplement additive is of a core-shell structure. The conductive hydrophobic polymer coating layer of the surface-modified hydrophobic enhancer of the shell can effectively block the contact reaction of moisture and carbon dioxide in the air with the inner core lithium supplement material, and has a certain protective effect on the lithium-containing inner core. Meanwhile, the conductive hydrophobic polymer coating layer of the surface-modified hydrophobic enhancer can improve the electronic conductivity, which is conducive to the full play of the electrochemical performance of the electrode active material. Moreover, the preparation method is simple in process and does not require expensive equipment, and is suitable for wide application.

[0051] In step S01, the lithium-containing material as the core of the positive electrode lithium supplement additive, the hydrophobic enhancer and the conductive hydrophobic polymer are provided.

[0052] In some embodiments, the material of the lithium-containing inner core includes Li x M y O z , Li w A, wherein 0 < x ≤ 6, 0 < y ≤ 3, 0 < z ≤ 4, 0 < w ≤ 5, and M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, Zr, and A includes at least one of C, N, O, P, S, F, B and Se.

[0053] In some embodiments, the hydrophobic enhancer is a fluorine-containing silane coupling agent. The fluorine-containing silane coupling agent includes one or more of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, dodecafluoroheptylpropylmethyldimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane, 3, 3, 3-trifluoropropylmethyldimethoxysilane, 3, 3, 3-trifluoropropyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane, and 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane.

[0054] In some embodiments, the conductive hydrophobic polymer includes one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, polyphenylene, poly-p-phenylenevinylene, and derivatives thereof.

[0055] In step S02, the electrically conductive hydrophobic polymer and the hydrophobic reinforcing agent are mixed in a first organic solvent to obtain the electrically conductive hydrophobic polymer with surface modification of the hydrophobic reinforcing agent.

[0056] In some embodiments, in the step of mixing the electrically conductive hydrophobic polymer and the hydrophobic reinforcing agent in the first organic solvent, the mixing is performed at 25-80°C for 30-120 minutes, followed by drying at 80-120°C for 3-10 hours.

[0057] In some embodiments, the first organic solvent is selected from an alcohol solvent or an alcohol-water mixed solvent.

[0058] In some embodiments, the mass ratio of the electrically conductive hydrophobic polymer, the hydrophobic reinforcing agent, and the first organic solvent is 100:0.2-2:100-1000.

[0059] In step S03, the electrically conductive hydrophobic polymer with surface modification of the hydrophobic reinforcing agent and the lithium-containing material as the core are mixed in a second organic solvent to obtain the positive electrode lithium supplement additive mixture.

[0060] In some embodiments, in the step of mixing the electrically conductive hydrophobic polymer with surface modification of the hydrophobic reinforcing agent and the lithium-containing material as the core in the second organic solvent, the electrically conductive hydrophobic polymer with surface modification of the hydrophobic reinforcing agent is mixed with the second organic solvent to obtain a polymer mixture, and then the polymer mixture is mixed with the lithium-containing material as the core.

[0061] In some embodiments, in the step of the third mixing, the third mixing is performed by one or more of heating dissolution, stirring, ultrasonic, and ball milling; and in the step of the fourth mixing, the second mixing is performed by heating and stirring, wherein the heating temperature is 50-150°C, the stirring speed is 100-1000 rpm, and the heating and stirring time is 1-6 hours.

[0062] In some embodiments, the second organic solvent is selected from one or more of benzene, toluene, xylene, tetrahydrofuran, 2-methyltetrahydrofuran, cyclohexane, and n-hexane.

[0063] In some embodiments, the mass ratio of the electrically conductive hydrophobic polymer with surface modification of the hydrophobic reinforcing agent, the lithium-containing material as the core, and the second organic solvent is 1:9-1000:50-1000. Controlling the mass ratio of the electrically conductive hydrophobic polymer with surface modification of the hydrophobic reinforcing agent and the organic solvent ensures that the electrically conductive hydrophobic polymer can form a true solution or a uniform and stable dispersion in the solvent.

[0064] In some embodiments, the mass ratio of the lithium-containing core and the coating layer is 90-99.9:0.1-10. If the mass of the coating layer is too small, the coating is incomplete or the thickness of the coating layer is too small, which easily leads to the lithium-containing core contacting water vapor or carbon dioxide in the air, affecting the stability of the lithium-containing core; if the mass of the coating layer is too large, the thickness of the coating layer is too large, which will make the charge-discharge performance of the lithium ion battery prepared by using the lithium supplement additive low.

[0065] In step S04, the positive electrode lithium supplement additive mixture is post-treated under an inert atmosphere to obtain the positive electrode lithium supplement additive.

[0066] In some embodiments, the step of heat treatment comprises: performing heat treatment, wherein the temperature of the heat treatment is 200-400°C, and the heat treatment time is 3-10 h. Through the heat treatment, on the one hand, the organic solvent added in the pre-treatment is completely removed, and on the other hand, the coating layer material is partially melted through the action of the heat treatment, which is conducive to improving the compactness of the coating layer material, and the positive electrode lithium supplement additive with uniform size and complete morphology is obtained.

[0067] The third aspect of the embodiments of the present application provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a binder, a conductive agent and a positive electrode lithium supplement additive. The positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additive or is prepared by the preparation method of the positive electrode lithium supplement additive.

[0068] The positive electrode tab provided by the third aspect of the embodiments of the present application adds the positive electrode lithium supplement additive in the positive electrode tab material. Since the lithium-containing core of the positive electrode lithium supplement additive contains abundant lithium, lithium ions can be released in the process of packaging the positive electrode tab into a battery for use, so as to compensate for the active lithium lost by the electrode active material in the first charge-discharge process, improve the reversible capacity and the first coulombic efficiency, improve the lithium supplement effect, and be suitable for industrial production.

[0069] In some embodiments, the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 1-15%. Since the lithium supplement additive provides a large amount of Li, and most of the Li cannot be cycled, if the amount of the positive electrode lithium supplement additive added in the positive electrode active material layer is too large, too much Li will cause lithium ions to be precipitated on the surface of the negative electrode during the charging process, generating lithium dendrites; if the amount is too small, the first efficiency of the battery will be reduced, affecting the use.

[0070] In some specific embodiments, the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is selected from 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0071] The fourth aspect of the embodiments of the present application provides a secondary battery, which comprises a positive electrode sheet.

[0072] The secondary battery provided by the fourth aspect of the embodiments of the present application comprises a positive electrode sheet, and the positive electrode sheet comprises a positive electrode lithium supplement additive, so that the obtained secondary battery has higher initial efficiency and better cycle stability, and the electronic conductivity and overall electrochemical performance of the battery are improved, which is conducive to wide use.

[0073] The following will be described in conjunction with specific embodiments.

[0074] Embodiment A1

[0075] Positive electrode lithium supplement additive and preparation method thereof

[0076] The positive electrode lithium supplement additive comprises a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, wherein the material of the coating layer comprises a conductive hydrophobic polymer with a surface-modified hydrophobic enhancer, the hydrophobic enhancer is selected from 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, the conductive hydrophobic polymer is selected from polyacetylene, and the lithium-containing core is selected from Li5FeO4, and the average particle size of the lithium-containing core is about 200 nm, and the average thickness of the coating layer is about 10 nm.

[0077] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0078] The lithium-containing material, the hydrophobic enhancer and the conductive hydrophobic polymer are provided as the core according to the positive electrode lithium supplement additive of Embodiment A1;

[0079] The conductive hydrophobic polymer and the hydrophobic enhancer are mixed and treated in a first organic solvent at 25°C for 30 minutes, and then dried at 80°C for 3 hours to obtain the conductive hydrophobic polymer with a surface-modified hydrophobic enhancer, wherein the mass ratio of the conductive hydrophobic polymer, the hydrophobic enhancer and the first organic solvent is 100:0.2:100, and the first organic solvent is selected from methanol;

[0080] The conductive hydrophobic polymer with a surface-modified hydrophobic enhancer is ultrasonically mixed with a second organic solvent to obtain a polymer mixture, wherein the mass ratio of the conductive hydrophobic polymer and the second organic solvent is 1:100, and the second organic solvent is selected from n-hexane;

[0081] The polymer mixture and the lithium-containing material as the core are further mixed, wherein the mass ratio of the lithium-containing core and the coating layer is 90:10; in the mixing step, the mixing is performed by heating and stirring, wherein the heating temperature is 70°C, the stirring speed is 200 rpm, and the heating and stirring time is 2 hours;

[0082] The positive electrode lithium supplement additive mixture is heat treated under an inert atmosphere to obtain the positive electrode lithium supplement additive, wherein the temperature of the heat treatment is 200°C and the heat treatment time is 3h.

[0083] Example A2

[0084] Positive electrode lithium supplement additive and preparation method thereof

[0085] The positive electrode lithium supplement additive comprises a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, wherein the material of the coating layer comprises a surface-modified hydrophobicity-enhancing agent and a conductive hydrophobic polymer, the hydrophobicity-enhancing agent is selected from dodecafluoroheptylpropylmethyldimethoxysilane, the conductive hydrophobic polymer is selected from polyaniline, the lithium-containing core is selected from Li2CuO2, the particle size of the lithium-containing core is about 1 μm, and the thickness of the coating layer is about 20 nm.

[0086] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0087] The positive electrode lithium supplement additive according to Example A2 provides a lithium-containing material as a core, a hydrophobicity-enhancing agent and a conductive hydrophobic polymer;

[0088] The conductive hydrophobic polymer and the hydrophobicity-enhancing agent are mixed at 40°C for 60 minutes in a first organic solvent, and then dried at 90°C for 4 hours to obtain the surface-modified hydrophobicity-enhancing agent and the conductive hydrophobic polymer, wherein the mass ratio of the conductive hydrophobic polymer, the hydrophobicity-enhancing agent and the first organic solvent is 100:0.5:200, and the first organic solvent is selected from ethanol.

[0089] The surface-modified hydrophobicity-enhancing agent and the conductive hydrophobic polymer are ultrasonically mixed with an organic solvent to obtain a polymer mixture, wherein the mass ratio of the conductive hydrophobic polymer and the organic solvent is 1:500, and the organic solvent is selected from xylene.

[0090] The polymer mixture and the lithium-containing material as the core are further mixed, wherein the mass ratio of the lithium-containing core and the coating layer is 92:8; in the mixing step, the mixing is performed by heating and stirring, wherein the heating temperature is 120°C, the stirring speed is 300 rpm, and the heating and stirring time is 1.5 hours.

[0091] The positive electrode lithium supplement additive mixture is heat treated under an inert atmosphere to obtain the positive electrode lithium supplement additive, wherein the temperature of the heat treatment is 400°C and the heat treatment time is 3.5h.

[0092] Example A3

[0093] Positive electrode lithium supplement additive and preparation method thereof

[0094] A positive electrode lithium supplement additive includes a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, wherein the material of the coating layer includes a conductive hydrophobic polymer surface-modified with a hydrophobic enhancer selected from dodecafluoroheptylpropyltrimethoxysilane, the conductive hydrophobic polymer is selected from polypyrrole, the lithium-containing core is selected from Li6MnO4, the particle size of the lithium-containing core is about 3 μm, and the thickness of the coating layer is about 40 nm.

[0095] A method for preparing a positive electrode lithium supplement additive includes the following steps:

[0096] The positive electrode lithium supplement additive according to Embodiment A3 provides a lithium-containing material as a core, a hydrophobic enhancer, and a conductive hydrophobic polymer;

[0097] The conductive hydrophobic polymer and the hydrophobic enhancer are mixed in a first organic solvent at 50°C for 90 minutes, and then dried at 100°C for 6 hours to obtain a conductive hydrophobic polymer surface-modified with a hydrophobic enhancer, wherein the mass ratio of the conductive hydrophobic polymer, the hydrophobic enhancer, and the first organic solvent is 100:1:400, and the first organic solvent is selected from isopropyl alcohol.

[0098] The conductive hydrophobic polymer surface-modified with a hydrophobic enhancer is ultrasonically mixed with an organic solvent to obtain a polymer mixture, wherein the mass ratio of the conductive hydrophobic polymer and the organic solvent is 1:300, and the organic solvent is selected from tetrahydrofuran.

[0099] The polymer mixture is mixed with a lithium-containing material as a core, wherein the mass ratio of the lithium-containing core and the coating layer is 95:5; in the mixing step, the mixing is performed by heating and stirring, wherein the heating temperature is 100°C, the stirring speed is 400 rpm, and the heating and stirring time is 2 hours.

[0100] The positive electrode lithium supplement additive mixture is heat-treated under an inert atmosphere to obtain a positive electrode lithium supplement additive, wherein the heat-treatment temperature is 250°C, and the heat-treatment time is 5h.

[0101] Embodiment A4

[0102] A positive electrode lithium supplement additive and a method for preparing the same

[0103] A positive electrode lithium supplement additive includes a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, wherein the material of the coating layer includes a conductive hydrophobic polymer surface-modified with a hydrophobic enhancer selected from 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, the conductive hydrophobic polymer is selected from polythiophene, the lithium-containing core is selected from Li2MnO2, the particle size of the lithium-containing core is about 5 μm, and the thickness of the coating layer is about 65 nm.

[0104] A method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0105] The positive electrode lithium supplement additive according to embodiment A4 provides the lithium-containing material as the core, the hydrophobic enhancer, and the conductive hydrophobic polymer;

[0106] The conductive hydrophobic polymer and the hydrophobic enhancer are mixed at 50°C for 90 minutes in a first organic solvent, and then dried at 120°C for 10 hours to obtain the conductive hydrophobic polymer with the surface-modified hydrophobic enhancer, wherein the mass ratio of the conductive hydrophobic polymer, the hydrophobic enhancer, and the first organic solvent is 100:1:500, and the first organic solvent is selected from n-butanol;

[0107] The conductive hydrophobic polymer with the surface-modified hydrophobic enhancer is ultrasonically mixed with an organic solvent to obtain a polymer mixture, wherein the mass ratio of the conductive hydrophobic polymer and the organic solvent is 1:300, and the organic solvent is selected from cyclohexane;

[0108] The polymer mixture is further mixed with the lithium-containing material as the core, wherein the mass ratio of the lithium-containing core and the coating layer is 97:3; in the mixing step, the mixing is performed by heating and stirring, wherein the heating temperature is 110°C, the stirring speed is 450 rpm, and the heating and stirring time is 4 hours;

[0109] The positive electrode lithium supplement additive mixture is heat-treated under an inert atmosphere to obtain the positive electrode lithium supplement additive, wherein the heat-treatment temperature is 350°C, and the heat-treatment time is 5h.

[0110] Embodiment A5

[0111] A positive electrode lithium supplement additive and a method for preparing the same

[0112] The positive electrode lithium supplement additive comprises a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, wherein the material of the coating layer comprises a conductive hydrophobic polymer with a surface-modified hydrophobic enhancer, the hydrophobic enhancer is selected from 3,3,3-trifluoropropyl methyl dimethoxy silane, the conductive hydrophobic polymer is selected from polyphenylene, the lithium-containing core is selected from Li2NiO2, the particle size of the lithium-containing core is about 8μm, and the thickness of the coating layer is about 80nm.

[0113] A method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0114] The positive electrode lithium supplement additive according to embodiment A4 provides the lithium-containing material as the core, the hydrophobic enhancer, and the conductive hydrophobic polymer;

[0115] The conductive hydrophobic polymer and the hydrophobic reinforcing agent are mixed in a first organic solvent at 50°C for 120 minutes, and then dried at 80°C for 6 hours to obtain the conductive hydrophobic polymer surface-modified with the hydrophobic reinforcing agent, wherein the mass ratio of the conductive hydrophobic polymer, the hydrophobic reinforcing agent and the first organic solvent is 100:2:500, and the first organic solvent is selected from ethanol;

[0116] The conductive hydrophobic polymer surface-modified with the hydrophobic reinforcing agent is mixed with an organic solvent by ultrasonic mixing to obtain a polymer mixture, wherein the mass ratio of the conductive hydrophobic polymer and the organic solvent is 1:450, and the organic solvent is selected from xylene;

[0117] The polymer mixture is further mixed with the lithium-containing material as the core body in a second mixing process, wherein the mass ratio of the lithium-containing core body and the coating layer is 98:2; in the mixing process, the mixing is performed by heating and stirring, wherein the heating temperature is 130°C, the stirring speed is 800 rpm, and the heating and stirring time is 5 hours;

[0118] The positive electrode lithium supplement additive mixture is heat-treated under an inert atmosphere to obtain the positive electrode lithium supplement additive, wherein the heat-treatment temperature is 400°C, and the heat-treatment time is 7h.

[0119] Example A6

[0120] Positive electrode lithium supplement additive and preparation method thereof

[0121] The positive electrode lithium supplement additive comprises a lithium-containing core body and a coating layer formed on the surface of the lithium-containing core body, wherein the material of the coating layer comprises a conductive hydrophobic polymer surface-modified with a hydrophobic reinforcing agent, the hydrophobic reinforcing agent is selected from 3,3,3-trifluoropropyltrimethoxysilane, the conductive hydrophobic polymer is selected from poly-p-phenylenevinylene, the lithium-containing core body is selected from Li5FeO4, the particle size of the lithium-containing core body is about 10μm, and the thickness of the coating layer is about 100nm.

[0122] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0123] The positive electrode lithium supplement additive according to Example A6 comprises a lithium-containing material as the core body, a hydrophobic reinforcing agent and a conductive hydrophobic polymer;

[0124] The conductive hydrophobic polymer and the hydrophobic reinforcing agent are mixed in a first organic solvent at 50°C for 100 minutes, and then dried at 80°C for 6 hours to obtain the conductive hydrophobic polymer surface-modified with the hydrophobic reinforcing agent, wherein the mass ratio of the conductive hydrophobic polymer, the hydrophobic reinforcing agent and the first organic solvent is 100:1:400, and the first organic solvent is selected from ethanol;

[0125] The conductive hydrophobic polymer with surface modified hydrophobic reinforcing agent is mixed with an organic solvent under ultrasonic treatment to obtain a polymer mixture, wherein the mass ratio of the conductive hydrophobic polymer and the organic solvent is 1:1000, and the organic solvent is selected from dimethylbenzene;

[0126] The polymer mixture is mixed with the lithium-containing material as the core, and the mass ratio of the lithium-containing core and the coating layer is 99:1; in the mixing step, a second mixing treatment is performed by heating and stirring, wherein the heating temperature is 150°C, the stirring speed is 1000 rpm, and the heating and stirring time is 6 hours;

[0127] The positive electrode lithium supplement additive mixture is heat treated under an inert atmosphere to obtain a positive electrode lithium supplement additive, wherein the heat treatment temperature is 400°C, and the heat treatment time is 10h.

[0128] Example B1

[0129] Positive electrode sheet

[0130] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material LiFePO4, a binder PVDF, a conductive agent SP and a positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additive provided in Example A1, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 1%.

[0131] Example B2

[0132] Positive electrode sheet

[0133] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material LiFePO4, a binder PVDF, a conductive agent SP and a positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additive provided in Example A2, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 3%.

[0134] Example B3

[0135] Positive electrode sheet

[0136] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material LiFePO4, a binder PVDF, a conductive agent SP and a positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additive provided in Example A3, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 5%.

[0137] Example B4

[0138] Positive electrode tab

[0139] The positive electrode tab comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the positive electrode active material layer comprises positive electrode active material LiFePO4, binder PVDF, conductive agent SP and positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additives provided in Example A4, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 7%.

[0140] Example B5

[0141] Positive electrode tab

[0142] The positive electrode tab comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the positive electrode active material layer comprises positive electrode active material LiFePO4, binder PVDF, conductive agent SP and positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additives provided in Example A5, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 15%.

[0143] Example B6

[0144] Positive electrode tab

[0145] The positive electrode tab comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the positive electrode active material layer comprises positive electrode active material LiFePO4, binder PVDF, conductive agent SP and positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additives provided in Example A6, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 10%.

[0146] Comparative Example A1

[0147] Positive electrode lithium supplement additive and preparation method thereof

[0148] The positive electrode lithium supplement additive comprises a lithium-containing core and an outer conductive layer formed on the surface of the lithium-containing core, wherein the lithium-containing core is selected from Li5FeO4, the material of the outer conductive layer is selected from a conductive hydrophobic polymer, the conductive hydrophobic polymer is selected from polyacetylene, the particle size of the lithium-containing core is about 200 nm, and the thickness of the outer conductive layer is about 10 nm.

[0149] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0150] The lithium-containing material and the conductive hydrophobic polymer are provided as the core according to the positive electrode lithium supplement additive of Comparative Example A1;

[0151] The conductive hydrophobic polymer is mixed with an organic solvent by ultrasonic treatment to obtain a polymer mixture, wherein the mass ratio of the conductive hydrophobic polymer and the organic solvent is 1:100, and the organic solvent is selected from n-hexane;

[0152] The polymer mixture is mixed with the lithium-containing material as the core by mixing treatment, wherein the mass ratio of the lithium-containing core and the coating layer is 90:10; in the mixing treatment step, the mixing treatment is performed by heating and stirring, wherein the heating temperature is 70°C, the stirring speed is 200 rpm, and the heating and stirring time is 2 hours;

[0153] The positive electrode lithium supplement additive mixture is heat treated under an inert atmosphere to obtain a positive electrode lithium supplement additive, wherein the heat treatment temperature is 200°C, and the heat treatment time is 3h.

[0154] Comparative Example A2

[0155] Positive electrode lithium supplement additive and preparation method thereof

[0156] The positive electrode lithium supplement additive comprises a lithium-containing core and an outer conductive layer formed on the surface of the lithium-containing core, wherein the lithium-containing core is selected from Li5FeO4, the material of the outer conductive layer is selected from a carbon layer, and the particle size of the lithium-containing core is about 8μm, and the thickness of the outer conductive layer is about 80nm.

[0157] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0158] The lithium-containing material as the core and the outer conductive layer are provided according to the positive electrode lithium supplement additive of Comparative Example A1.

[0159] The positive electrode lithium supplement additive is ball milled with citric acid as a carbon source to obtain a positive electrode lithium supplement additive mixture, wherein the mass ratio of the positive electrode lithium supplement additive and the citric acid is 90:10; and the positive electrode lithium supplement additive mixture is heat treated under an inert atmosphere to obtain a positive electrode lithium supplement additive coated with a conductive carbon layer, wherein the heat treatment temperature is 500°C, and the heat treatment time is 5h.

[0160] Comparative Example A3

[0161] Positive electrode lithium supplement additive and preparation method thereof

[0162] The positive electrode lithium supplement additive comprises a lithium-containing core, an intermediate hydrophobic layer formed on the surface of the lithium-containing core, and an outer conductive layer arranged on the surface of the intermediate hydrophobic layer, wherein the lithium-containing core is selected from Li5FeO4, the material of the intermediate hydrophobic layer is selected from polyimide powder (PI powder), and the material of the outer conductive layer is selected from a carbon layer, and the particle size of the lithium-containing core is about 10μm, the thickness of the intermediate hydrophobic layer is about 50nm, and the thickness of the outer conductive layer is about 50nm.

[0163] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0164] The positive electrode lithium supplement additive according to the comparative example A2 provides a lithium-containing material and a hydrophobic polymer as the core;

[0165] The positive electrode lithium supplement additive is ball-milled with the hydrophobic polymer to obtain a first mixture, wherein the mass ratio of the positive electrode lithium supplement additive and the hydrophobic polymer is 99:1; the first mixture is heat-treated under an inert atmosphere to obtain the positive electrode lithium supplement additive coated with the hydrophobic layer, wherein the temperature of the heat treatment is 400 DEG C, and the heat treatment time is 10 h.

[0166] The positive electrode lithium supplement additive coated with the hydrophobic layer is further ball-milled with citric acid as a carbon source to obtain a second mixture, wherein the mass ratio of the positive electrode lithium supplement additive coated with the hydrophobic layer and the citric acid is 90:10; the second mixture is heat-treated under an inert atmosphere to obtain the positive electrode lithium supplement additive with the carbon layer as the outer layer and the hydrophobic layer as the intermediate layer, wherein the temperature of the heat treatment is 500 DEG C, and the heat treatment time is 5 h.

[0167] Comparative example B1

[0168] Positive electrode tab

[0169] The positive electrode tab comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material LiFePO4, a binder PVDF, a conductive agent SP and a positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additive provided in the comparative example A1, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 15%.

[0170] Comparative example B2

[0171] Positive electrode tab

[0172] The positive electrode tab comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material LiFePO4, a binder PVDF, a conductive agent SP and a positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive is selected from the positive electrode lithium supplement additive provided in the comparative example A2, and the mass percentage of the positive electrode lithium supplement additive in the positive electrode active material layer is 15%.

[0173] Comparative example B3

[0174] Positive electrode tab

[0175] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material LiFePO4, a binder PVDF, a conductive agent SP and a positive electrode lithium replenishing additive, wherein the positive electrode lithium replenishing additive is selected from the positive electrode lithium replenishing additive provided in Comparative Example A3, and the mass percentage of the positive electrode lithium replenishing additive in the positive electrode active material layer is 10%.

[0176] Performance testing and result analysis

[0177] (1) The conductive hydrophobic polymer, the lithium-supplementing core and the positive electrode lithium-supplementing additive obtained after coating provided in Example A2 were subjected to infrared spectroscopy analysis. Figure 2 Comparing the infrared spectra of the lithium-supplementing core and the lithium-supplementing additive obtained after coating, it can be seen that before coating, the lithium-supplementing core has no absorption peak at the dotted line; after coating, the lithium-supplementing additive exhibits a more obvious absorption peak at the dotted line. Comparing with the infrared spectrum of the conductive hydrophobic polymer, it can be seen that these three absorption peaks correspond to the absorption peaks of the conductive hydrophobic polymer, indicating that the preparation method of the lithium-supplementing additive successfully coats the conductive hydrophobic polymer on the surface of the lithium-supplementing core while still maintaining the original chemical structure of the conductive hydrophobic polymer without changing its chemical composition.

[0178] (II) The positive and negative electrode sheets obtained in Examples B1 to B6 and Comparative Examples B1 to B3 were assembled with separators and electrolytes to produce batteries, wherein the negative electrode sheet was a lithium metal sheet, the separator was a polypropylene microporous membrane, and the electrolyte was a 1 mol / L LiPF6 solution (a solvent containing a mixture of ethylene carbonate and diethyl carbonate in a 1:1 volume ratio). The charge and discharge performance of the resulting batteries was measured. The results are listed in Table 1.

[0179] Table 1

[0180]

[0181]

[0182] As can be seen from the results of Table 1, the batteries formed by assembling the positive electrode sheets of Examples B1-B6 have a first charge specific capacity of 168.4-198.5 mAh / g, a first discharge specific capacity of 161.6-193.1 mAh / g, and a first coulombic efficiency of 97.06-97.62%; the second cycle charge specific capacity is 160.0-191.2 mAh / g, the second cycle discharge specific capacity is 158.3-189.7 mAh / g, and the second cycle coulombic efficiency is 99.01-99.22%. In contrast, the batteries formed by assembling the positive electrode sheets of Comparative Examples B1-B3 have a first coulombic efficiency of only 93.42-94.04% and a second cycle coulombic efficiency of only 97.67-97.83%. In particular, a comparison of Example B1 with Comparative Example B1, Example B5 with Comparative Example B2, and Example B6 with Comparative Example B3 shows that the charge and discharge specific capacities of the examples are significantly higher than those of the comparative examples. In summary, the lithium supplementing additive provided herein can be used in electrode materials to improve the reversible capacity and the first coulombic efficiency.

[0183] The above description is merely the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall fall within the protection scope of the present application.

Claims

1. A positive electrode lithium supplementing additive, characterized by, The positive electrode lithium supplement additive comprises a lithium-containing core and a coating layer formed on the surface of the lithium-containing core, wherein the material of the coating layer is selected from a conductive hydrophobic polymer of a surface modification hydrophobic reinforcing agent selected from a fluorine-containing silane coupling agent, the coating layer comprises an inner layer containing a conductive polymer main chain structure and a protective outer layer containing F branched chains self-assembled on the surface of the conductive polymer inner layer to form a Si-O-Si network structure so as to be adsorbed on the surface of the conductive polymer, and the material of the lithium-containing core comprises Li x M y O z , Li w at least one of A, wherein 0 < x ≤ 6, 0 < y ≤ 3, 0 < z ≤ 4, 0 < w ≤ 5, and M comprises at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, Zr, and A comprises at least one of C, N, O, P, S, F, B, and Se.

2. The positive-electrode lithium supplementing additive according to claim 1, characterized by The coverage of the coating layer on the surface of the lithium-containing core is 80% or more.

3. The positive-electrode lithium supplementing additive according to claim 1, characterized by The fluorine-containing silane coupling agent includes one or more of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, dodecafluoroheptylpropylmethyldimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane, 3, 3, 3-trifluoropropylmethyldimethoxysilane, 3, 3, 3-trifluoropropyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane, and 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane.

4. The positive-electrode lithium supplementing additive according to any one of claims 1 to 3, characterized by The conductive hydrophobic polymer includes one or more of polyacetylene, polyaniline, polypyrrole, polythiophene, polyphenylene, poly(p-phenylenevinylene), and derivatives thereof.

5. The positive-electrode lithium supplementing additive according to any one of claims 1 to 3, characterized by The particle size of the lithium-containing core is 0.01-10 μm; and / or, The thickness of the coating layer is 1-100 nm.

6. The positive-electrode lithium supplementing additive according to any one of claims 1 to 3, characterized by The mass ratio of the lithium-containing core and the coating layer is 90-99.9:0.1-10.

7. A method for preparing a positive electrode lithium supplementing additive, characterized by, The method includes the following steps: The positive electrode lithium supplement additive according to claim 1 provides a lithium-containing material as a core, a hydrophobic reinforcing agent, and a conductive hydrophobic polymer; The conductive hydrophobic polymer and the hydrophobic reinforcing agent are mixed in a first organic solvent to obtain a conductive hydrophobic polymer with a surface-modified hydrophobic reinforcing agent; The conductive hydrophobic polymer with a surface-modified hydrophobic reinforcing agent and the lithium-containing material as a core are mixed in a second organic solvent to obtain a positive electrode lithium supplement additive mixture; The positive electrode lithium supplement additive mixture is post-treated under an inert atmosphere to obtain a positive electrode lithium supplement additive.

8. The method of claim 7, wherein the lithium supplementing additive for a positive electrode is prepared by the steps of: (a) preparing a mixture of a lithium metal and a lithium compound; (b) mixing the mixture with a solvent; and (c) drying the mixture. The first organic solvent is selected from an alcohol solvent or an alcohol-water mixed solvent; and / or, The second organic solvent is selected from one or more of benzene, toluene, xylene, tetrahydrofuran, 2-methyltetrahydrofuran, cyclohexane, and n-hexane; and / or, The mass ratio of the conductive hydrophobic polymer, the hydrophobic reinforcing agent, and the first organic solvent is 100:0.2-2:100-1000; and / or, The mass ratio of the conductive hydrophobic polymer with a surface-modified hydrophobic reinforcing agent, the lithium-containing material as a core, and the second organic solvent is 1:9-1000:50-1000.

9. The method of claim 7, wherein the lithium supplementing additive for a positive electrode is prepared by the steps of: (a) preparing a mixture of a lithium metal and a lithium compound; (b) mixing the mixture with a solvent; and (c) drying the mixture. In the step of mixing the conductive hydrophobic polymer and the hydrophobic reinforcing agent in a first organic solvent, the conductive hydrophobic polymer and the hydrophobic reinforcing agent are mixed in the first organic solvent at 25-80°C for 30-120 minutes, and then dried at 80-120°C for 3-10 hours; and / or, In the step of mixing the conductive hydrophobic polymer with a surface-modified hydrophobic reinforcing agent and the lithium-containing material as a core in a second organic solvent, the conductive hydrophobic polymer with a surface-modified hydrophobic reinforcing agent is mixed with the second organic solvent to obtain a polymer mixture, and then the polymer mixture is mixed with the lithium-containing material as a core; In the third mixing process, the third mixing process is selected from one or more of heating dissolution, stirring, ultrasonic, and ball milling; in the fourth mixing process, the second mixing process is performed by heating and stirring, wherein the heating temperature is 50-150 DEG C, the stirring speed is 100-1000 rpm, and the heating and stirring time is 1-6 hours; and / or, In the post-processing, heat treatment is performed, wherein the heat treatment temperature is 200-400 DEG C, and the heat treatment time is 3-10 h.

10. A positive electrode sheet characterized by comprising: The positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a binder, a conductive agent, and a positive electrode lithium supplementing additive, wherein the positive electrode lithium supplementing additive is selected from the positive electrode lithium supplementing additive according to any one of claims 1-6 or prepared by the preparation method of the positive electrode lithium supplementing additive according to any one of claims 7-9.

11. A secondary battery characterized by comprising: The secondary battery comprises the positive electrode plate according to claim 10.

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