Positive electrode lithium supplement additive and its preparation method and application

Abstract

The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode lithium supplement additive and its preparation method and application, wherein the positive electrode lithium supplement additive includes a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, the encapsulation layer has pores and / or cracks, and a sealing agent is distributed at least in the pores and / or cracks to seal the pores and / or cracks; wherein the material of the sealing agent includes an organic hydrophobic material. The provided sealing agent including the organic hydrophobic material can be embedded in the pores of the encapsulation material, further filling the gaps of the sealing material to form a dense film layer, which can effectively isolate water vapor and carbon dioxide in the air, and can also prevent the metal elements in the lithium-containing core from being reduced during the reaction process, protect the stability of the lithium-containing core, improve the lithium supplement effect, and make the obtained battery material have the characteristics of high capacity and long cycle.

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] The oil crisis of the 1960s and 1970s forced people to search for new alternative energy sources. Lithium-ion batteries are considered one of the most promising energy sources due to their high operating voltage and energy density, relatively low self-discharge, no memory effect, no contamination from heavy metals such as lead and cadmium, and extremely long cycle life.

[0003] During the first charge of a lithium-ion battery, the surface of the negative electrode is usually accompanied by the formation of a solid electrolyte membrane SEI film. This process consumes a large amount of Li+, which means that the Li+ released from the positive electrode material is irreversibly consumed, and the reversible specific capacity of the corresponding battery cell is reduced. The negative electrode material, especially the silicon-based negative electrode material, will further consume Li+. + , resulting in the first time low Coulomb efficiency.

[0004] In order to improve the low coulombic efficiency problem caused by irreversible loss of the negative electrode, in addition to pre-lithiation of the negative electrode material and the electrode, lithium supplementation of the positive electrode can also achieve the requirements of high energy density. The theoretical capacity of lithium-rich iron-based materials is as high as 867mAh / g, the operating voltage window is consistent with that of conventional lithium-ion batteries, and they basically do not participate in the electrochemical process in the later stage. They are lithium supplement additives with broad prospects. CN109301242A discloses a method for preparing lithium-ion positive electrode lithium supplement material Li5FeO4 using a sol-gel method. This material has the characteristics of large charging capacity and small discharge capacity when used as a lithium-ion battery positive electrode lithium supplement material. However, this material has harsh environmental adaptability, and the residual alkali on the surface is large and difficult to process; CN 110459748 discloses a carbon-coated lithium ferrite material and its preparation method. By using a carbon source for gas-phase coating to isolate the external environment, the contact between lithium ferrite and water in the air is alleviated, thereby improving the stability of the material; despite this, it is always difficult to completely isolate the coating layer from contact with water in the air, resulting in material deterioration and failure.

[0005] Research has shown that the primary challenges in developing lithium-replenishing materials lie in obtaining high-purity active materials and controlling the large amount of residual alkali on the surface. In a moderately humid atmosphere, the residual alkali easily converts into products such as lithium hydroxide, complicating subsequent slurry processing and affecting the lithium-replenishing effect in batteries. Summary of the Invention

[0006] The purpose of this application is to provide a positive electrode lithium replenishing additive and its preparation method and application, aiming to solve the problem in the prior art that even if the lithium-rich material is wrapped with an encapsulation layer, the encapsulation layer still has a large number of pores, which makes the material susceptible to water vapor, resulting in a large amount of residual alkali on the surface of the material, which is difficult to process and has a poor lithium replenishing effect during use.

[0007] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0008] In a first aspect, the present application provides a positive electrode lithium replenishing additive, which includes a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, the encapsulation layer having pores and / or cracks, and a sealing agent is distributed at least in the pores and / or cracks to seal the pores and / or cracks; wherein the material of the sealing agent includes an organic hydrophobic material.

[0009] In a second aspect, the present application provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0010] According to the positive electrode lithium supplement additive, lithium-containing core material particles, encapsulation layer material precursor and sealing agent material precursor are provided respectively;

[0011] In an inert atmosphere, a coating layer is formed by using a packaging layer raw material precursor and a sealing agent material precursor, and the coating layer is coated on the lithium-containing core material particles to prepare a precursor;

[0012] In an inert atmosphere, the precursor is post-processed so that the coating layer forms an encapsulation layer, and the sealing agent is distributed at least in the pores and / or cracks of the encapsulation layer to seal the pores and / or cracks, thereby obtaining a positive electrode lithium supplement additive.

[0013] In a third aspect, the present application provides a positive electrode plate, wherein the lithium core-containing positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer located on the lithium core-containing positive electrode current collector, and the lithium core-containing positive electrode active material layer comprises a positive electrode active material, a binder, a conductive agent and a positive electrode lithium replenishing additive, wherein the lithium core-containing positive electrode lithium replenishing additive is selected from a positive electrode lithium replenishing additive or is prepared by a preparation method of a positive electrode lithium replenishing additive.

[0014] In a fourth aspect, the present application provides a secondary battery, wherein the lithium core-containing secondary battery comprises a positive electrode plate containing a lithium core.

[0015] Compared with the existing technology, this application has the following technical effects:

[0016] The first aspect of the present application provides a positive electrode lithium replenishing additive, which has an encapsulation layer provided on the surface of a lithium-containing core, the encapsulation layer having pores and / or cracks, and a sealing agent distributed at least at the pores and / or cracks for plugging the pores and / or cracks; wherein the material of the sealing agent includes an organic hydrophobic material; the provided sealing agent including the organic hydrophobic material can be embedded in the pores of the encapsulation material, further filling the gaps of the sealing material to form a dense film layer, which can effectively isolate water vapor and carbon dioxide in the air, and can also organize the metal elements in the lithium-containing core to be reduced during the reaction process, thereby protecting the stability of the lithium-containing core; and, during the process of being added to the secondary battery for use, it can stimulate the release of lithium ions from the lithium-containing core material, thereby achieving truly efficient lithium replenishment and improving the overall conductivity of the material; therefore, the encapsulation layer effectively ensures the storage stability and processing stability of the lithium-containing material, and the encapsulation layer has a high density, which solves the problems of difficult processing and reduced performance caused by insufficient density of traditional encapsulation layers, ensures easy processing, and the resulting battery material has the characteristics of high capacity and long cycle life.

[0017] The second aspect of the present application provides a method for preparing a positive electrode lithium replenishing additive. The preparation method is simple to operate and only requires providing lithium-containing core material particles, an encapsulation layer material precursor, and a sealing agent material precursor; the encapsulation layer raw material precursor and the sealing agent material precursor are used to form a coating layer to prepare a precursor, and then post-processing is performed to obtain the positive electrode lithium replenishing additive. In the positive electrode lithium replenishing additive obtained by this preparation method, the sealing agent is distributed at least in the pores and / or cracks of the encapsulation layer, and is used to seal the pores and / or cracks, and can form a dense film layer. On the one hand, it isolates the lithium-containing core from water vapor or carbon dioxide in the air, ensuring the stability of the lithium-containing core; on the other hand, it has good conductivity, which can improve the application of the material in secondary batteries and ensure that the obtained battery material has the characteristics of high capacity and long cycle.

[0018] The third aspect of the present application provides a positive electrode plate, which 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 the provided positive electrode lithium replenishing additive. The provided positive electrode lithium replenishing additive can help replenish lithium, so that the obtained positive electrode material has good cycle stability, further improving the performance of the lithium-ion battery.

[0019] The fourth aspect of the present application provides a secondary battery, which includes a positive electrode plate, and the positive electrode plate includes a positive electrode lithium supplement additive, so that the obtained secondary battery has the characteristics of high capacity and long cycle, improves the overall electrochemical performance of the battery, and is conducive to wide use. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 Schematic diagram of the positive electrode lithium supplement additive provided in the embodiment of the present application.

[0022] Figure 2 This is a scanning electron microscope image of the positive electrode lithium supplement additive provided in Example A1 of the present application.

[0023] Figure 3 This is a scanning electron microscope image of the positive electrode lithium supplement additive provided in Example A2 of the present application.

[0024] Figure 4 This is a scanning electron microscope image of the positive electrode lithium supplement additive provided in Comparative Example A1 of this application.

[0025] Figure 5 This is the X-ray diffraction pattern of the positive electrode lithium supplement additive provided in Example A1 of the present application.

[0026] Figure 6 This is the X-ray diffraction pattern of the positive electrode lithium supplement additive provided in Example A5 of the present application. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0028] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0029] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0030] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0031] 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", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0032] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass of the lithium-containing core in the examples of this application may be μg, mg, g, kg, etc., which are mass units known in the chemical industry.

[0033] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features being referred to. For example, a first XX could also be referred to as a second XX, and similarly, a second XX could also be referred to as a first XX, without departing from the scope of the embodiments of this application. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0034] The first aspect of the present application provides a positive electrode lithium supplement additive, as shown in the attached Figure 1 As shown, the positive electrode lithium supplement additive includes a lithium-containing core 1 and an encapsulation layer 2 coated on the surface of the lithium-containing core 1, the encapsulation layer 2 has pores and / or cracks, and a sealing agent is distributed at least in the pores and / or cracks to seal the pores and / or cracks; wherein the material of the sealing agent includes an organic hydrophobic material.

[0035] The first aspect of the present application provides a positive electrode lithium replenishing additive, which has an encapsulation layer provided on the surface of a lithium-containing core, the encapsulation layer having pores and / or cracks, and a sealing agent distributed at least at the pores and / or cracks for plugging the pores and / or cracks; wherein the material of the sealing agent includes an organic hydrophobic material; the provided sealing agent including the organic hydrophobic material can be embedded in the pores of the encapsulation material, further filling the gaps of the sealing material to form a dense film layer, which can effectively isolate water vapor and carbon dioxide in the air, and can also organize the metal elements in the lithium-containing core to be reduced during the reaction process, thereby protecting the stability of the lithium-containing core; and, during the process of being added to the secondary battery for use, it can stimulate the release of lithium ions from the lithium-containing core material, thereby achieving truly efficient lithium replenishment and improving the overall conductivity of the material; therefore, the encapsulation layer effectively ensures the storage stability and processing stability of the lithium-containing material, and the encapsulation layer has a high density, which solves the problems of difficult processing and reduced performance caused by insufficient density of traditional encapsulation layers, ensures easy processing, and the resulting battery material has the characteristics of high capacity and long cycle life.

[0036] In some embodiments, the positive electrode lithium supplement additive includes a lithium-containing core, wherein the material of the lithium-containing core includes Li x M y O z , wherein 0<x≤6, 0<y≤3, 0<z≤4, and M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, and Zr.

[0037] In some embodiments, the positive electrode lithium supplement additive includes a lithium-containing core, wherein the material of the lithium-containing core is selected from a lithium-rich iron composite material, and the lithium-rich iron composite material includes aLiFeO2·bLi2O·cN x O y Wherein, a+b ≥ 0.98, c ≤ 0.02, 1.8 ≤ b / a ≤ 2.1, a, b, and c are molar numbers; 1 ≤ y / x ≤ 2.5; and N comprises at least one of Ni, Co, Mn, T, Al, Cu, V, and Zr. Based on the fact that lithium-rich iron-based materials have a theoretical capacity of up to 867 mAh / g, an operating voltage window consistent with conventional lithium-ion batteries, and essentially no participation in the electrochemical process in the later stages, a lithium-rich iron-based composite material is provided as a lithium-containing core material for a positive electrode lithium supplementation additive.

[0038] In some embodiments, the lithium-containing core satisfies: 1 μm ≤ D 50 ≤10μm, D 10 / D 50 ≥0.3, D 90 / D 50≤2; By controlling the particle size of the lithium-containing core, the resulting material can be ensured to be highly stable and well-balanced in size. If the median particle size of the lithium-containing core is too large, lithium ion resistance will be greater during lithium ion release, hindering complete release and lithium replenishment. If the median particle size of the lithium-containing core is too small, the resulting particles will have an excessively large specific surface area and are prone to agglomeration, resulting in material instability, material failure, and inability to achieve a good lithium replenishment effect.

[0039] In some embodiments, the specific surface area of ​​the lithium-containing core is 0.5 to 20 m 2 / g, controlling the specific surface area of ​​the lithium-containing core to be moderate, ensuring that the obtained lithium-containing core particle size is moderate, which is conducive to better dispersion and can achieve the effect of efficient lithium replenishment during use.

[0040] Furthermore, the positive electrode lithium supplement additive includes: an encapsulation layer coated on the surface of the lithium-containing core, the encapsulation layer having pores and / or cracks, and a sealing agent distributed at least at the pores and / or cracks for sealing the pores and / or cracks; wherein the material of the sealing agent includes an organic hydrophobic material. The provided sealing agent including the organic hydrophobic material can be embedded in the pores of the encapsulation material, further filling the gaps of the sealing material to form a dense film layer, which can effectively isolate water vapor and carbon dioxide in the air, and can also organize the metal elements in the lithium-containing core to be reduced during the reaction process, thereby protecting the stability of the lithium-containing core; and, when added to the secondary battery for use, it can stimulate the release of lithium ions from the lithium-containing core material, achieve truly efficient lithium supplementation, and improve the overall conductivity of the material; therefore, the encapsulation layer effectively ensures the storage stability and processing stability of the lithium-containing material, and the encapsulation layer has a high density, which solves the problem of difficult processing and reduced performance caused by insufficient density of the traditional encapsulation layer, ensures easy processing, and the resulting battery material has the characteristics of high capacity and long cycle life.

[0041] In some embodiments, during use of the positive electrode lithium replenishment additive, at least a portion of the sealing agent escapes from the pores and / or cracks of the encapsulation layer. Because the battery generates gas during charge and discharge during use of the positive electrode lithium replenishment additive, the gas dislodges at least a portion of the sealing agent from the pores and / or cracks of the encapsulation layer, reopening the pores and / or cracks of the encapsulation layer. This facilitates the release of lithium ions from the positive electrode lithium replenishment additive, achieving truly efficient lithium replenishment and improving the overall conductivity of the material.

[0042] In some embodiments, the organic hydrophobic material includes at least one of tar, polyethylene, and polypropylene.

[0043] In some embodiments, tar is used as a sealing agent, which can be embedded in the pores of the packaging material, further filling the gaps of the sealing material to form a dense film layer. Tar is mainly composed of high molecular weight components such as aromatic hydrocarbons produced during the thermal decomposition of organic carbon sources, and tar is a hydrophobic material that can effectively isolate water vapor and carbon dioxide in the air. At the same time, it can organize the metal elements in the lithium-containing core to be reduced during the reaction process, thereby protecting the stability of the lithium-containing core.

[0044] In some embodiments, the tar includes at least one of xylene, phenanthrene, anthracene, pyrene, benzopyrene, and benzopyrene.

[0045] In other embodiments, polyethylene is used as a sealing agent. Polyethylene is obtained by the polymerization reaction of multiple C2H4 monomers. Polyethylene can be well embedded in the pores of the packaging material, filling the gaps of the sealing material, and forming a dense protective film with the sealing material. Polyethylene has excellent acid and alkali resistance, good chemical stability, and is not easy to absorb water. As a sealing material, it can effectively protect the lithium-containing core and effectively isolate water vapor and carbon dioxide in the air.

[0046] In some other embodiments, polypropylene is used as a sealing agent. Polypropylene is obtained by the polymerization reaction of multiple C3H6 monomers. It has a low density and can form a dense film layer with the packaging material to ensure low product quality, which is conducive to use. It is also resistant to corrosion by acids, alkalis, salt solutions and various organic solvents, which is conducive to better protecting the lithium-containing core from the influence of water vapor and carbon dioxide in the air, thereby improving the stability of the lithium-containing core.

[0047] In some embodiments, the encapsulation layer comprises a conductive hydrophobic material. Providing a conductive hydrophobic material allows it to be evenly mixed with the organic hydrophobic material to form a dense film layer, ensuring close bonding with the organic hydrophobic material. Furthermore, ensuring that the conductive hydrophobic material has a certain degree of conductivity ensures that the resulting positive electrode lithium replenishment additive has good conductivity and can stimulate the release of lithium ions from the lithium-containing core material, achieving truly efficient lithium replenishment.

[0048] In some embodiments, the conductive hydrophobic material includes a conductive carbon material. Providing the conductive carbon material can, on the one hand, effectively isolate water vapor and carbon dioxide in the air. On the other hand, it has a certain conductivity, which can make the obtained positive electrode lithium replenishing additive have good conductivity and can stimulate the release of lithium ions from the lithium-containing core material, thereby realizing truly efficient lithium replenishment.

[0049] In some embodiments, the mass ratio of the lithium-containing core to the encapsulation layer is 95-99:1-5. If the mass of the encapsulation layer is too small, the lithium-containing core cannot be completely and evenly coated, and the coating effect is poor. During use, the lithium-containing core will be susceptible to the influence of water vapor and carbon dioxide in the air, which is not conducive to processing and has low performance; if the mass of the encapsulation layer is too large, the thickness of the obtained encapsulation layer will be too thick, which will affect the migration of lithium ions and is not conducive to achieving efficient lithium replenishment.

[0050] In some embodiments, the mass content of the sealing agent in the encapsulation layer is 100 to 6000 ppm; the mass content of the sealing agent is controlled to be moderate so that it can be well mixed with the encapsulation material; if the content of the sealing agent is too high, it will affect the stability of the material; if the content of the sealing agent is too low, the stability of the transition metal containing the lithium core cannot be guaranteed under high temperature conditions, which will cause the transition metal containing the lithium core to be easily reduced, thereby affecting the release of lithium ions, which is not conducive to achieving efficient lithium replenishment.

[0051] In some embodiments, the thickness of the encapsulation layer is 5 to 100 nm. If the encapsulation layer is too thin, the lithium-containing core cannot be evenly and completely coated; if the encapsulation layer is too thick, the migration of lithium ions will be affected, and the weight of the additive will be increased, affecting its use.

[0052] In some specific embodiments, the thickness of the encapsulation layer is 10 to 50 nm, ensuring that the obtained encapsulation layer can evenly and completely encapsulate the lithium-containing core and is suitable for the migration of lithium ions to achieve a better lithium replenishment effect.

[0053] In some embodiments, the powder resistivity of the positive electrode lithium supplement additive is 1.0 to 500 Ω / cm. Controlling the powder resistivity of the positive electrode lithium supplement additive to ensure good conductivity is beneficial to improving battery performance.

[0054] A second aspect of the present invention provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0055] S01. According to the positive electrode lithium supplement additive, lithium-containing core material particles, encapsulation layer material precursor and sealing agent material precursor are provided;

[0056] S02 in an inert atmosphere, the use of a raw material precursor and a sealing agent material precursor to form a coating layer, coated on the lithium-containing core material particles, to prepare a precursor;

[0057] S03. In an inert atmosphere, post-process the precursor so that the coating layer forms an encapsulation layer, and the sealing agent is distributed at least in the pores and / or cracks of the encapsulation layer to seal the pores and / or cracks, thereby obtaining a positive electrode lithium supplement additive.

[0058] The second aspect of the present application provides a method for preparing a positive electrode lithium replenishing additive. The preparation method is simple to operate and only requires providing lithium-containing core material particles, an encapsulation layer material precursor, and a sealing agent material precursor; the encapsulation layer raw material precursor and the sealing agent material precursor are used to form a coating layer to prepare a precursor, and then post-processing is performed to obtain the positive electrode lithium replenishing additive. In the positive electrode lithium replenishing additive obtained by this preparation method, the sealing agent is distributed at least in the pores and / or cracks of the encapsulation layer, and is used to seal the pores and / or cracks, and can form a dense film layer. On the one hand, it isolates the lithium-containing core from water vapor or carbon dioxide in the air, ensuring the stability of the lithium-containing core; on the other hand, it has good conductivity, which can improve the application of the material in secondary batteries and ensure that the obtained battery material has the characteristics of high capacity and long cycle.

[0059] In step S01 , lithium-containing core material particles, an encapsulation layer material precursor, and a sealing agent material precursor are provided respectively according to the positive electrode lithium supplement additive.

[0060] In some embodiments, the lithium core material includes Li x M y O z , wherein 0<x≤6, 0<y≤3, 0<z≤4, and M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, and Zr.

[0061] In some specific embodiments, since the material containing the lithium core is selected from the lithium-rich iron composite material, the lithium core-containing lithium-rich iron composite material includes aLiFeO2·bLi2O·cN x O y , wherein a+b≥0.98, c≤0.02, 1.8≤b / a≤2.1, a, b, c are molar numbers; 1≤y / x≤2.5; and N includes at least one of Ni, Co, Mn, T, Al, Cu, V, and Zr.

[0062] In some embodiments, the preparation method of lithium-containing core material particles includes: providing a lithium source and an M metal source, uniformly mixing the lithium source and the M metal source according to a molar ratio according to the lithium core material particles contained therein, and then drying and crushing them to obtain lithium-containing core material particles.

[0063] In some embodiments, the lithium-containing core Li source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium oxide.

[0064] In some embodiments, the lithium-containing core M metal source includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, and Zr.

[0065] In some specific embodiments, the lithium-containing core material particles are selected from lithium-rich iron-based composite materials, and the preparation method includes: providing an iron source, a lithium source, and an M metal source, and uniformly mixing the iron source, lithium source, and N metal source according to a molar ratio according to the lithium core material particles contained, and then drying and crushing them to obtain lithium-containing core material particles.

[0066] In some embodiments, the iron source includes at least one of iron oxide, iron nitrate, iron chloride, iron hydroxide, iron acetate, and iron hydroxide.

[0067] In some embodiments, the lithium-containing core Li source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium oxide.

[0068] In some embodiments, the lithium-containing core N metal source includes at least one of Cu, Co, Al, Ti, Fe, V, and Zr.

[0069] In some embodiments, the sealant material precursor includes at least one of C1-C4 alcohols, ethers, ketones, and hydrocarbon compounds.

[0070] In some embodiments, the encapsulation layer material precursor includes at least one of C1-C4 alcohols, ethers, ketones, and hydrocarbon compounds.

[0071] In some specific embodiments, when the encapsulation layer material is selected from a conductive carbon material, the provided sealer material precursor and the encapsulation layer material precursor are consistent.

[0072] In step S02, in an inert atmosphere, a coating layer is formed by using a packaging layer raw material precursor and a sealing agent material precursor, and the coating layer is coated on the lithium-containing core material particles to prepare a precursor.

[0073] In some embodiments, the inert atmosphere is selected from at least one of Ar atmosphere, N2 atmosphere, and He atmosphere.

[0074] In some embodiments, the step of preparing the precursor includes: in an inert atmosphere, mixing the lithium-containing core material particles, the encapsulation layer material precursor and the sealing agent material precursor, and then performing in-situ composite coating, using the encapsulation layer raw material precursor and the sealing agent material precursor to form a coating layer, which is coated on the lithium-containing core material particles.

[0075] In other embodiments, the step of preparing the precursor includes: providing an encapsulation layer material precursor and a sealing agent material precursor, placing lithium-containing core material particles in an inert atmosphere, and using the encapsulation layer material precursor and the sealing agent material precursor to coat the lithium-containing core material by chemical vapor deposition to form a coating layer, which is coated on the lithium-containing core material particles.

[0076] In some embodiments, in the step of preparing the precursor, the preparation conditions are: heating to 600-1000° C. at a heating rate of 10-500° C. / h, and reacting for 4-48 hours.

[0077] In some specific embodiments, the encapsulation layer material precursor and the sealing agent material precursor are both selected from carbon materials. The steps of preparing the precursor include: placing the lithium-containing core raw material in an inert atmosphere, heating it to 450°C to 900°C at 100-500°C / h, passing a carbon source and then keeping it warm for 0.5-10h for coating, forming an encapsulation layer on the surface of the lithium-containing core raw material, and preparing the precursor.

[0078] In step S03, the precursor is post-processed in an inert atmosphere so that the coating layer forms an encapsulation layer, and the sealing agent is distributed at least in the pores and / or cracks of the encapsulation layer to seal the pores and / or cracks, thereby obtaining a positive electrode lithium supplement additive.

[0079] In some embodiments, the post-treatment step of the precursor comprises heating the precursor to 600-1000° C. at a heating rate of 0-500° C. / h for 0.5-20 hours. By performing the heat treatment under these conditions, a sealing agent can be formed in the encapsulation layer.

[0080] In some embodiments, the sealing agent precursor is selected from a carbon source, and the precursor is post-treated to form tar in the encapsulation layer to obtain a positive electrode lithium supplement additive.

[0081] In some specific embodiments, the step of forming tar in the encapsulation layer includes: heating the precursor to 500°C at a heating rate of 200°C / h and keeping it at that temperature for 1 hour, cooling it to room temperature, and forming tar in the encapsulation layer of the precursor, so that the sealing agent is distributed at least in the pores and / or cracks of the encapsulation layer to seal the pores and / or cracks, thereby obtaining a positive electrode lithium supplement additive.

[0082] In other specific embodiments, the step of forming tar in the encapsulation layer includes: placing the precursor in an inert atmosphere, heating it to 700°C at a heating rate of 200°C / h, introducing 1 L / min of carbon source, keeping it warm for 0.5 h, cooling it to room temperature, forming tar in the encapsulation layer of the precursor, and obtaining a positive electrode lithium supplement additive.

[0083] In some embodiments, the preparation method of the positive electrode lithium supplement additive is carried out in a high-temperature calcination device, wherein the high-temperature calcination equipment is selected from at least one of a roller kiln, a push plate kiln, a rotary kiln, a rotary kiln, and a fluidized bed.

[0084] A third aspect of an embodiment of the present application provides a positive electrode plate, wherein the lithium-core-containing positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer located on the lithium-core-containing positive electrode current collector, wherein the lithium-core-containing positive electrode active material layer comprises a positive electrode active material, a binder, a conductive agent and a positive electrode lithium replenishing additive, wherein the lithium-core-containing positive electrode lithium replenishing additive is selected from a positive electrode lithium replenishing additive or is prepared by a preparation method of a positive electrode lithium replenishing additive.

[0085] The third aspect of the present application provides a positive electrode plate, which 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 the provided positive electrode lithium replenishing additive. The provided positive electrode lithium replenishing additive can help replenish lithium, so that the obtained positive electrode material has good cycle stability, further improving the performance of the lithium-ion battery.

[0086] In some embodiments, the lithium core-containing positive electrode lithium replenishing additive comprises 60-99 wt% of the lithium core-containing positive electrode active material layer. Because the lithium replenishing additive provides a large amount of lithium, and most of the lithium cannot be recycled, if too much of the positive electrode lithium replenishing additive is added to the positive electrode active material layer, the excess lithium will cause lithium ions to precipitate on the negative electrode surface during charging, forming lithium dendrites. If too little is added, the initial efficiency of the battery will be reduced, affecting its performance.

[0087] In some embodiments, the mass percentage of the conductive agent in the lithium core-containing positive electrode active material layer is 0.2-20 wt %; the mass percentage of the binder in the lithium core-containing positive electrode active material layer is 0.5-20 wt %.

[0088] In some embodiments, the preparation method of the positive electrode sheet includes: fully mixing a positive electrode active material, a positive electrode lithium supplement additive, a conductive agent, an adhesive and a solvent, coating the mixture on a positive electrode current collector, and drying the mixture to obtain a positive electrode sheet.

[0089] A fourth aspect of an embodiment of the present application provides a secondary battery, characterized in that the lithium-core secondary battery includes a positive electrode plate.

[0090] The fourth aspect of the present application provides a secondary battery, which includes a positive electrode plate, and the positive electrode plate includes a positive electrode lithium supplement additive, so that the obtained secondary battery has the characteristics of high capacity and long cycle, improves the overall electrochemical performance of the battery, and is conducive to wide use.

[0091] In some embodiments, the initial charging capacity of the secondary battery is ≥380 mAh / g. The obtained secondary battery has an improved initial charging capacity and an improved performance of the secondary battery due to the inclusion of a positive electrode lithium supplement additive in the positive electrode plate.

[0092] In some embodiments, during the charging process, the secondary battery generates gas, which dislodges at least a portion of the positive electrode lithium supplement sealing agent from the pores and / or cracks of the encapsulation layer, allowing the lithium ions of the positive electrode lithium supplement additive to migrate. This stimulates the release of lithium ions from the lithium-containing core material during use of the secondary battery containing the positive electrode lithium supplement additive, achieving truly efficient lithium supplementation and improving the overall conductivity of the material. This results in a battery material with high capacity and long cycle life.

[0093] The following describes the details in conjunction with specific embodiments.

[0094] Example A1

[0095] Positive electrode lithium supplement additive and preparation method thereof

[0096] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O, and the material of the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises tar; and the lithium-containing core D 50 The thickness of the encapsulation layer is 5 μm and 10 nm.

[0097] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0098] Fe(NO3)3·9H2O and LiNO3 were added to a 15wt% PVP aqueous solution at a molar ratio of 1:4.98 and mixed thoroughly. The mixture was then spray-dried at 280°C and crushed. In a nitrogen atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and held for 15 hours. After cooling, the product was mechanically crushed and graded to obtain in-situ carbon-coated LiFeO2·1.99Li2O powder. Furthermore, the in-situ carbon-coated LiFeO2·1.99Li2O powder was placed in a rotary furnace with N2 protection, heated to 500°C at a rate of 200°C / h and held for 1 hour, and then cooled to obtain a tar & carbon-coated LiFeO2·1.99Li2O powder as a positive electrode lithium supplement additive.

[0099] Example A2

[0100] Positive electrode lithium supplement additive and preparation method thereof

[0101] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O·0.005Al2O3, the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises tar; and the D 50The thickness of the encapsulation layer is 3μm and 14nm.

[0102] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0103] Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added to a 15wt% aqueous citric acid solution at a molar ratio of 1:4.98:0.01 and thoroughly mixed. The mixture was then spray-dried at 280°C and crushed. In a nitrogen atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and held for 15 hours. After cooling, the product was mechanically crushed and graded to obtain a tar-and-carbon composite-coated LiFeO2·1.99Li2O·0.005Al2O3 powder, a positive electrode lithium supplement.

[0104] Example A3

[0105] Positive electrode lithium supplement additive and preparation method thereof

[0106] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O·0.01CuO, the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises tar; and the D 50 The thickness of the encapsulation layer is 6 μm and 20 nm.

[0107] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0108] Fe2O3, LiOH, and CuO were thoroughly mixed in a molar ratio of 1:10.1:0.01. In a nitrogen atmosphere, the mixture was heated to 900°C at a rate of 300°C / h and held for 20 hours. After cooling, the product was mechanically crushed and graded to obtain LiFeO2·2.025Li2O·0.01CuO powder. The crushed powder was placed in a rotary furnace under nitrogen protection and heated to 700°C at a rate of 200°C / h. Acetylene was then introduced at 1 L / min and held for 0.5 hours. The powder was then cooled to obtain a tar and carbon-coated LiFeO2·1.99Li2O·0.01CuO powder, a lithium-rich cathode additive.

[0109] Example A4

[0110] Positive electrode lithium supplement additive and preparation method thereof

[0111] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O·0.005Al2O3, the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises tar; and the D 50 The thickness of the encapsulation layer is 8 μm and 30 nm.

[0112] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0113] Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added to a 15wt% citric acid solution at a molar ratio of 1:4.98:0.01, mixed thoroughly, spray-dried at 280°C, and crushed. In an air atmosphere, the mixture was heated at a rate of 300°C / h to 850°C and held for 15 hours. After cooling, the product was mechanically crushed and graded to obtain in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder. The crushed powder was placed in a rotary furnace under nitrogen protection and heated at a rate of 200°C / h to 700°C. The mixture was then heated for 1 hour with 1L / min of acetylene and 10L / min of N2. The powder was then cooled to obtain the tar- and carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder, a lithium-rich cathode additive.

[0114] Example A5

[0115] Positive electrode lithium supplement additive and preparation method thereof

[0116] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O·0.01CuO, the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises tar; and the D 50 The thickness of the encapsulation layer is 9 μm and 40 nm.

[0117] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0118] Fe2O3, LiOH, and CuO were thoroughly mixed in a molar ratio of 1:10.1:0.01. In a nitrogen atmosphere, the mixture was heated to 900°C at a rate of 300°C / h and held for 20 hours. After cooling, the product was mechanically crushed and graded to obtain LiFeO2·2.025Li2O·0.01CuO powder. The crushed powder was placed in a rotary furnace under nitrogen protection and heated to 900°C at a rate of 200°C / h. The mixture was then heated to 1.99Li2O·0.01CuO for 2 hours under a flow of 1 L / min acetone and 20 L / min N2. The powder was then cooled to obtain a tar and carbon-coated LiFeO2·1.99Li2O·0.01CuO powder, a lithium-rich cathode additive.

[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 and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O·0.01MnO2, the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises tar; and the D 50 The thickness of the encapsulation layer is 50 nm.

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

[0123] Fe2O3, LiOH, and MnO2 were thoroughly mixed in a molar ratio of 1:10.1:0.01. In a nitrogen atmosphere, the mixture was heated to 900°C at a rate of 300°C / h and held for 20 hours. After cooling, the product was mechanically crushed and graded to obtain LiFeO2·2.025Li2O·0.01MnO powder. The crushed powder was placed in a rotary furnace under nitrogen protection and heated to 700°C at a rate of 200°C / h. The mixture was then heated to 1.99Li2O·0.01MnO2 powder, a tar and carbon-coated lithium-ion supplement for the positive electrode.

[0124] Example A7

[0125] Positive electrode lithium supplement additive and preparation method thereof

[0126] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O, and the material of the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises polyethylene; and the lithium-containing core D 50The thickness of the encapsulation layer is 5 μm and 10 nm.

[0127] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0128] Fe(NO3)3·9H2O and LiNO3 were added to a 15wt% PVP aqueous solution at a molar ratio of 1:4.98 and mixed thoroughly. The mixture was then spray-dried at 280°C and crushed. In a nitrogen atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and held for 15 hours. After cooling, the product was mechanically crushed and graded to obtain in-situ carbon-coated LiFeO2·1.99Li2O powder. Furthermore, the in-situ carbon-coated LiFeO2·1.99Li2O powder was mixed with 5wt% low-density polyethylene (PE) and placed in a rotary furnace under N2 protection. The temperature was raised to 500°C at a rate of 200°C / h and held for 1 hour. The mixture was then cooled to obtain a polyethylene and carbon-coated LiFeO2·1.99Li2O powder, a positive electrode lithium supplement additive.

[0129] Example A8

[0130] Positive electrode lithium supplement additive and preparation method thereof

[0131] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O·0.005Al2O3, the encapsulation layer comprises an encapsulation material and a sealing agent embedded in the pores of the encapsulation material, wherein the encapsulation material comprises a conductive carbon material, and the material of the sealing agent comprises polypropylene; and the D 50 The thickness of the encapsulation layer is 3μm and 14nm.

[0132] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0133] Fe(NO3)3·9H2O, LiNO3, and Al(NO3)3 were added to a 15wt% citric acid aqueous solution at a molar ratio of 1:4.98:0.01 and thoroughly mixed. The mixture was then spray-dried at 280°C and crushed. In a nitrogen atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and held for 15 hours. After cooling, the product was mechanically crushed and graded. Furthermore, the in-situ carbon-coated LiFeO2·1.99Li2O·0.005Al2O3 powder was mixed with 10wt% PP, placed in a rotary furnace with N2 protection, and heated to 400°C at a rate of 200°C / h and held for 1 hour to obtain a positive electrode lithium supplement additive of polypropylene and carbon composite-coated LiFeO2·1.99Li2O·0.005Al2O3 powder.

[0134] Comparative Example A1

[0135] Positive electrode lithium supplement additive and preparation method thereof

[0136] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O, and the material of the encapsulation layer comprises a conductive carbon material; and the D 50 The thickness of the encapsulation layer is 50 nm.

[0137] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0138] Fe(NO3)3·9H2O and LiNO3 were added to a 15wt% PVP aqueous solution at a molar ratio of 1:4.98 and thoroughly mixed. The mixture was then spray-dried at 280°C and crushed. In an air atmosphere, the temperature was raised to 850°C at a rate of 300°C / h and held for 15 hours. After cooling, the product was mechanically crushed and graded to obtain tar & C-coated LiFeO2·1.99Li2O powder. The powder was then heated to 700°C under vacuum and held for 0.5 hours to remove the tar, ultimately yielding an additive containing a lithium core coated with a conductive carbon material.

[0139] Comparative Example A2

[0140] Positive electrode lithium supplement additive and preparation method thereof

[0141] The positive electrode lithium supplement additive comprises a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, wherein the lithium-containing core is LiFeO2·1.99Li2O·0.01CuO, and the material of the encapsulation layer comprises a conductive carbon material; and the D 50 The thickness of the encapsulation layer is 50 nm.

[0142] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0143] Fe2O3, LiOH, and CuO were thoroughly mixed at a molar ratio of 1:10.1:0.01. In a nitrogen atmosphere, the mixture was heated at a rate of 300°C / h to 900°C and held for 20 hours. After cooling, the product was mechanically crushed and classified to obtain LiFeO2·2.025Li2O·0.01CuO powder. The crushed powder was placed in a rotary furnace under nitrogen protection and heated at a rate of 200°C / h to 700°C. A flow of 1L / min of acetylene was maintained for 0.5 hours, and the mixture was cooled to obtain tar- and carbon-coated LiFeO2·1.99Li2O·0.01CuO powder. The mixture was heated to 650°C under vacuum and held for 0.5 hours. The tar was removed, resulting in an additive containing a lithium core coated with a conductive carbon material.

[0144] Example B1

[0145] Preparation of positive electrode sheets and lithium secondary batteries

[0146] The positive electrode lithium supplement additive obtained in Example A1 was mixed with polyvinylidene fluoride and SP-Li in a mass ratio of 93:3:4, and the mixture was ball-milled and stirred to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil, roll-pressed, and vacuum-dried at 110° C. overnight to obtain a positive electrode sheet.

[0147] Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte solution. The concentration of LiPF6 was 1 mol / L. The positive electrode sheet, polypropylene microporous separator, lithium sheet, and electrolyte solution were assembled to obtain a lithium secondary battery.

[0148] The preparation methods of the positive electrode sheets and lithium secondary batteries of Examples B2 to B8 are exactly the same as those of Example B1, except that the "positive electrode lithium replenishing additive obtained in Example A1" is replaced with the "positive electrode lithium replenishing additive obtained in corresponding Examples A2 to A8".

[0149] The preparation methods of the positive electrode sheets and lithium secondary batteries of Comparative Examples A1 to A2 are exactly the same as those of Example B1, except that the "positive electrode lithium replenishing additive obtained in Example A1" is replaced with the "positive electrode lithium replenishing additive obtained in Comparative Examples A1 to A2".

[0150] Performance Testing

[0151] 1. The morphology of the positive electrode lithium supplement additives of Example A1, Example A5 and Comparative Example A1 was characterized by scanning electron microscopy.

[0152] 2. X-ray diffraction was used to characterize the morphology of the positive electrode lithium supplement additives of Example A1 and Example A5.

[0153] 3. The doping element M and tar amount of the positive electrode lithium supplement additives of Examples A1 to A8 and Comparative Examples A1 to A2, and the first charge gram capacity of the secondary batteries of Examples B1 to B8 and Comparative Examples B1 to B2 were tested.

[0154] The content of the doping element M in the positive electrode lithium supplement additives of Examples A1 to A8 and Comparative Examples A1 to A2 was analyzed by inductively coupled plasma (ICP) emission spectrometry.

[0155] Tar content can be measured using TPD-MS (Temperature Programmed Desorption-Mass Spectrometry). Specifically, 100 mg of sample is placed in a silica sample cell and heated from room temperature to 1000°C at a rate of 10°C / min in 50 ml / min of He. The generated gases are then analyzed by mass spectrometry.

[0156] The electrochemical performance is tested by first charging the battery at a capacity of 100 gram. The test conditions are as follows: the assembled battery is placed at room temperature for 24 hours and then the charge and discharge test is performed. The charge and discharge voltage is 2.7V-4.3V.

[0157] Result Analysis

[0158] 1. The morphology of the positive electrode lithium supplement additives of Example A1, Example A5 and Comparative Example A1 was characterized by scanning electron microscopy. The results are analyzed as follows:

[0159] Please see the results Figure 2 、 Figure 3 、 Figure 4 ,in, Figure 2 This is a scanning electron microscope image of the positive electrode lithium supplement additive provided in Example A1 of the present application. Figure 3 This is a scanning electron microscope image of the positive electrode lithium supplement additive provided in Example A2 of the present application. Figure 4 This is a scanning electron microscope image of the lithium-rich cathode additive provided in Comparative Example A1 of this application. Figure 2 It can be seen that the positive electrode lithium supplement additive of Example A1 has many irregular particles and a relatively rough interface. Figure 3 It can be seen that the surface of the positive electrode lithium supplement additive of Example A5 is relatively smooth. Figure 4 It was found that the interface of the lithium-rich iron-based composite material in Comparative Example A1 without the additive coating was also relatively rough.

[0160] 2. X-ray diffraction was used to characterize the morphology of the positive electrode lithium supplement additives of Example A1 and Example A5. The results are analyzed as follows:

[0161] The positive electrode lithium supplement additives of Example A1 and Example A5 were characterized by X-ray diffraction. The results are as follows: Figure 5 and Figure 6 ,in, Figure 5 This is the X-ray diffraction pattern of the positive electrode lithium supplement additive provided in Example A1 of the present application, Figure 6 This is the X-ray diffraction pattern of the positive electrode lithium supplement additive provided in Example A5 of the present application. Figure 5 It can be seen that the lithium-rich iron composite material has a main peak of Li5FeO4 and a partial diffraction peak of LiFeO2. Figure 6 It can be seen that the lithium-rich iron composite material is mainly Li5FeO4, with less LiFeO2.

[0162] 3. The doping element M and tar content of the positive electrode lithium supplement additives of Examples A1 to A6 and Comparative Examples A1 to A2, as well as the first charge gram capacity of the secondary batteries of Examples B1 to B8 and Comparative Examples B1 to B2, were tested. The results are analyzed as follows:

[0163] Please refer to Table 1 for the test results. The y value of the doping element M in Table 1 is the content of the doping element M in the lithium supplement additive. It can be seen from Table 1 that after the lithium-rich iron-based composite materials of Examples 1-8 of the present application are coated with carbon, the prepared positive electrode slurry does not show jelly phenomenon and is easy to coat. When it is added to a lithium secondary battery, the positive electrode can have a higher initial gram capacity and a lower initial efficiency, thereby compensating for the reduction in energy density caused by the irreversible lithium loss of the first negative electrode. It can be seen from the comparative example experiments that the lithium-rich iron-based composite materials of Comparative Examples 1 and 2 are not coated, and absorb water during the preparation of the positive electrode slurry, resulting in the formation of jelly, which is not conducive to the coating of the positive electrode slurry.

[0164] Table 1

[0165]

[0166]

[0167] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A positive electrode lithium supplement additive, characterized in that: The positive electrode lithium supplement additive includes a lithium-containing core and an encapsulation layer coated on the surface of the lithium-containing core, the encapsulation layer has pores and / or cracks, and a sealing agent is distributed at least in the pores and / or cracks to seal the pores and / or cracks; wherein the material of the sealing agent includes an organic hydrophobic material, and the organic hydrophobic material includes at least one of tar, polyethylene, and polypropylene; during use of the positive electrode lithium supplement additive, the sealing agent at least partially escapes from the pores and / or cracks of the encapsulation layer.

2. The positive electrode lithium supplement additive according to claim 1, characterized in that The material of the encapsulation layer includes a conductive hydrophobic material.

3. The positive electrode lithium supplement additive according to claim 2, characterized in that The tar includes at least one of xylene, phenanthrene, anthracene, pyrene, benzopyrene, and benzopyrene-free; and / or, The conductive hydrophobic material includes a conductive carbon material.

4. The positive electrode lithium supplement additive according to claim 1, characterized in that The mass ratio of the lithium-containing core to the encapsulation layer is 95-99:1-5; and / or, In the encapsulation layer, the mass content of the sealing agent is 100-6000 ppm.

5. The positive electrode lithium supplement additive according to claim 1, characterized in that The lithium core material includes Li x M y O z , wherein 0<x≤6, 0<y≤3, 0<z≤4, and M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, and Zr.

6. The positive electrode lithium supplement additive according to claim 5, characterized in that The material containing the lithium core includes a lithium-rich iron composite material, and the lithium-rich iron composite material includes aLiFeO2·bLi2O·cN x O y , wherein a+b≥0.98, c≤0.02, 1.8≤b / a≤2.1, a, b, c are molar numbers; 1≤y / x≤2.5; and N includes at least one of Ni, Co, Mn, Ti, Al, Cu, V, and Zr.

7. The positive electrode lithium supplement additive according to any one of claims 1 to 5, characterized in that The lithium-containing core satisfies: 1 μm ≤ D 50 ≤10μm, D 10 / D 50 ≥0.3, D 90 / D 50 ≤2; and / or, The specific surface area of ​​the lithium-containing core is 0.5-20 m 2 / g; and / or, The thickness of the encapsulation layer is 5-100 nm.

8. A method for preparing a positive electrode lithium supplement additive, characterized in that: The steps include: The positive electrode lithium supplement additive according to claim 1 provides lithium-containing core material particles, encapsulation layer material precursor and sealing agent material precursor respectively; In an inert atmosphere, forming a coating layer using the encapsulation layer material precursor and the sealing agent material precursor, and coating the lithium-containing core material particles to prepare a precursor; In an inert atmosphere, the precursor is post-processed so that the coating layer forms an encapsulation layer, and the sealing agent is distributed at least in the pores and / or cracks of the encapsulation layer to seal the pores and / or cracks, thereby obtaining a positive electrode lithium supplement additive.

9. The method for preparing the positive electrode lithium supplement additive according to claim 8, characterized in that: The step of preparing the precursor comprises: In an inert atmosphere, the lithium-containing core material particles, the encapsulation layer material precursor and the sealing agent material precursor are mixed and then subjected to in-situ composite coating, and a coating layer is formed by using the encapsulation layer material precursor and the sealing agent material precursor to coat the lithium-containing core material particles; or, The encapsulation layer material precursor and the sealing agent material precursor are provided, the lithium-containing core material particles are placed in an inert atmosphere, and the encapsulation layer material precursor and the sealing agent material precursor are used to coat the lithium-containing core material by vapor deposition to form a coating layer, which is coated on the lithium-containing core material particles.

10. The method for preparing the positive electrode lithium supplement additive according to claim 8 or 9, characterized in that: In the step of preparing the precursor, the preparation conditions are: heating to 600-1000°C at a heating rate of 10-500°C / h and reacting for 4-48 hours; and / or, In the step of post-treating the precursor, the post-treating conditions are: heating to 600-1000° C. at a heating rate of 0-500° C. / h, and heat treating for 0.5-20 h.

11. The method for preparing the positive electrode lithium supplement additive according to claim 8 or 9, characterized in that: The preparation method of the lithium-containing core material particles comprises: providing a lithium source and an M metal source, uniformly mixing the lithium source and the M metal source according to a molar ratio according to the lithium-containing core material particles, and drying and crushing the mixture to obtain lithium-containing core material particles; Wherein, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium oxide; The M metal source includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, and Zr.

12. A positive electrode plate, characterized in that: 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, a binder, a conductive agent and a positive electrode lithium replenishing additive, wherein the positive electrode lithium replenishing additive is selected from the positive electrode lithium replenishing additive according to any one of claims 1 to 7 or is prepared by the preparation method of the positive electrode lithium replenishing additive according to any one of claims 8 to 11.

13. A secondary battery, characterized in that: The secondary battery comprises the positive electrode sheet according to claim 12 .

14. The secondary battery according to claim 13, wherein: The secondary battery generates gas during the charging process, and the gas removes at least part of the sealing agent of the positive electrode lithium supplement additive from the pores and / or cracks of the packaging layer.

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