Lithium supplementing additive, preparation method and application thereof

Abstract

This application discloses a lithium replenishment additive, its preparation method, and its application. The lithium replenishment additive includes a core and a functional encapsulation layer covering the core. The core includes a lithium replenishment material, which is a unidirectional capacity lithium-containing material that performs lithium-ion de-intercalation during the first charge and does not allow lithium-ion re-intercalation during discharge. The lithium replenishment additive, through its unidirectional capacity lithium replenishment material, effectively de-lithiates during the first charge and prevents lithium-ion re-intercalation into the material during discharge, thereby ensuring the lithium replenishment effect and improving the initial efficiency and overall electrochemical performance of the battery containing the lithium replenishment additive. The preparation method of the lithium replenishment additive ensures stable structure and electrochemical performance, is highly efficient, and saves production costs.

Description

Technical Field

[0001] This application belongs to the field of secondary batteries, specifically relating to a lithium supplementation additive, its preparation method, and its application. Background Technology

[0002] With increasing awareness of environmental protection and the energy crisis, lithium-ion batteries, as a green and environmentally friendly energy storage technology, are becoming increasingly popular. Lithium-ion batteries are widely used due to their high capacity density, long cycle life, and high stability. With the widespread application of electronic products and the booming development of electric vehicles, the market for lithium-ion batteries is expanding, but at the same time, there are increasing demands on their specific capacity and cycle performance.

[0003] During the first charge and discharge cycle of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the negative electrode surface. This film converts a significant amount of active lithium into lithium carbonate, lithium fluoride, and alkyl lithium, resulting in lithium loss from the positive electrode material and reducing the battery's initial coulombic efficiency and capacity. In lithium-ion battery systems using graphite negative electrodes, approximately 10% of the lithium source is consumed during the first charge. When using high-specific-capacity negative electrode materials, such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide), and amorphous carbon negative electrodes, the consumption of positive electrode lithium source is further aggravated.

[0004] To further improve the energy density of lithium-ion batteries, pre-lithiation of the positive or negative electrode is an effective method. However, current positive or negative electrode pre-lithiation materials have the following drawbacks: excessive activity, leading to reactions with moisture, carbon dioxide, and other environmental elements during storage, transportation, and processing. This results in the inability to maintain stable storage for extended periods, reduced lithium replenishment efficiency, and decreased processing performance, ultimately leading to a decline in the electrochemical performance of the prepared electrode sheets and other battery components. Therefore, a safer and easier-to-operate positive electrode pre-lithiation process has attracted increasing attention.

[0005] Although existing lithium replenishment materials are coated with a coating layer to protect them, the publicly available lithium replenishment materials are generally reversible capacity materials. Although they can release lithium ions during the first charge, they can still insert lithium ions during the discharge process. This results in the lithium replenishment performance of existing lithium replenishment materials being less than ideal, such as limited specific capacity, high initial efficiency (high reversible specific capacity), and high cost. Summary of the Invention

[0006] The purpose of this application is to overcome the above-mentioned deficiencies of the prior art and provide a lithium supplement additive and its preparation method to solve the technical problem that existing lithium supplement additives are unstable or have reversible capacity characteristics, which prevents them from fully realizing their theoretical specific capacity.

[0007] Another objective of this application is to provide an electrode sheet and a secondary battery containing the electrode sheet, so as to solve the technical problems of unsatisfactory initial coulombic efficiency and battery capacity of existing secondary batteries.

[0008] To achieve the aforementioned objectives, a first aspect of this application provides a lithium replenishment additive. This lithium replenishment additive includes a core and a functional encapsulation layer covering the core. The core includes a lithium replenishment material, which is a unidirectional lithium-containing material that allows lithium-ion extraction during the first charge and prevents lithium-ion insertion during discharge.

[0009] Furthermore, the unit cell of the lithium-supplementing material is an antifluorite structure with a crystal space group of P42 / nmc

[137] ; and / or

[0010] Furthermore, the lithium replenishment material includes the chemical formula xLi6MO4·(1-x)Li2O, wherein 0<x≤1 in the chemical formula, and M includes at least one of Cr, Mn, Fe, Co, Ni, Cu, and Zn.

[0011] Furthermore, the particle size of the nuclei is 100 nm-50 μm.

[0012] Furthermore, the functional encapsulation layer includes at least one of an ion conductor encapsulation layer and an electronic conductor encapsulation layer.

[0013] Furthermore, the material of the electronic conductor encapsulation layer includes at least one of conductive carbon material, conductive polymer, or conductive oxide.

[0014] Furthermore, the material of the ion conductor encapsulation layer includes at least one of perovskite, NASICON, garnet, or polymer solid electrolytes.

[0015] Furthermore, the thickness of the electronic conductor encapsulation layer is 1-100 nm.

[0016] Furthermore, the thickness of the ion conductor encapsulation layer is 1-200 nm.

[0017] Furthermore, the electronic conductor encapsulation layer is made of conductive carbon materials and lithium carbonate, and the electronic conductor encapsulation layer is in contact with the core.

[0018] Furthermore, the content of lithium carbonate in the electronic conductor encapsulation layer is 0.5-1.5 wt%.

[0019] A second aspect of this application provides a method for preparing a lithium-supplementing additive. The method for preparing the lithium-supplementing additive of this application includes the following steps:

[0020] Provided a core material for lithium replenishment, the core material including a lithium replenishment material, the lithium replenishment material being a lithium-containing material with unidirectional capacity that allows lithium-ion desorption during the first charge and prevents lithium-ion insertion during discharge;

[0021] In a first protective atmosphere, a functional encapsulation layer is formed on the surface of the core material, and the functional encapsulation layer completely covers the core material to obtain a lithium supplementation additive.

[0022] Furthermore, the formed functional encapsulation layer includes an electronic conductor encapsulation layer, and the method for forming the functional encapsulation layer on the surface of the core material includes the following steps:

[0023] An electronic conductor encapsulation layer is formed on the surface of the core material, fully covering the core material; and the material of the electronic conductor encapsulation layer includes at least one of conductive carbon material, conductive polymer or conductive oxide.

[0024] Alternatively, the formed functional encapsulation layer may include an ion conductor encapsulation layer, and the method for forming the functional encapsulation layer on the surface of the core material includes the following steps:

[0025] An ion conductor encapsulation layer is formed on the surface of the core material, fully covering the core material; and the material of the ion conductor encapsulation layer includes at least one of perovskite, NASICON, garnet, or polymer solid electrolytes.

[0026] Alternatively, the formed functional encapsulation layer may comprise a composite layer of an electronic conductor encapsulation layer and an ion conductor encapsulation layer. The method for forming the functional encapsulation layer on the surface of the core material includes the following steps:

[0027] First, an electronic conductor encapsulation layer is formed on the surface of the core material, fully covering the core material; then, an ion conductor encapsulation layer is formed on the outer surface of the electronic conductor encapsulation layer; and the material of the electronic conductor encapsulation layer includes at least one of conductive carbon material, conductive polymer or conductive oxide, and the material of the ion conductor encapsulation layer includes at least one of perovskite type, NASICON type, garnet type or polymer type solid electrolyte.

[0028] Furthermore, the material of the formed electronic conductor encapsulation layer includes a mixture of conductive carbon material and lithium carbonate; the method for forming the electronic conductor encapsulation layer includes the following steps:

[0029] A conductive carbon coating layer is formed on the surface of the core material to fully cover the core material, and then heat treatment is performed in a protective atmosphere.

[0030] Furthermore, the lithium replenishing material includes a lithium replenishing material with the chemical formula xLi6MO4·(1-x)Li2O, which is prepared according to the following preparation method:

[0031] According to the elemental stoichiometry of xLi6MO4·(1-x)Li2O, the metal oxide of M is mixed with the lithium source to obtain the precursor of xLi6MO4·(1-x)Li2O; wherein, 0<x≤1 in the chemical formula, and M includes at least one of Cr, Mn, Fe, Co, Ni, Cu, and Zn.

[0032] In the second protective atmosphere, the precursor is sintered and the unit cell of xLi6MO4·(1-x)Li2O is an antifluorite structure with a crystal space group of P42 / nmc

[137] .

[0033] Furthermore, the sintering temperature is 400-1000℃ and the time is 1-24h.

[0034] Furthermore, the sintering process involves heating the temperature to 400-1000℃ at a rate of 0.5-10℃ / min.

[0035] Furthermore, the second protective atmosphere is an atmosphere formed by any one of the protective gases, including nitrogen, argon, a nitrogen-argon mixture, a nitrogen-hydrogen mixture, and an argon-hydrogen mixture.

[0036] Furthermore, the M metal oxide includes at least one of CrO, Cr2O3, CrO2, CrO3, MnO, Mn2O3, MnO2, Mn3O4, FeO, Fe2O3, Fe3O4, CoO, Co2O3, CoO2, Co3O4, NiO, Ni2O3, CuO, and ZnO.

[0037] Furthermore, the lithium source includes at least one of LiOH, LiOH·H2O, Li2O, Li2CO3, LiNO3, and LiAc.

[0038] A third aspect of this application provides an electrode sheet comprising a current collector and an electrode active layer bonded to the surface of the current collector, wherein the electrode active layer is doped with the lithium supplementation additive of this application or a lithium supplementation additive prepared by the lithium supplementation additive preparation method of this application.

[0039] A fourth aspect of this application provides a secondary battery. This application includes a positive electrode and a negative electrode, wherein the positive or negative electrode is an electrode sheet.

[0040] Compared with the prior art, this application has the following technical effects:

[0041] The lithium replenishment additive of this application contains a core with lithium-replenishing material, thus providing abundant lithium. During the first charge cycle, this lithium-replenishing additive acts as a "sacrificial agent," releasing as many lithium ions as possible in one go to replenish the irreversible lithium ions consumed during the formation of the SEI film at the negative electrode. This maintains a sufficient lithium-ion supply within the battery system, improving the battery's initial efficiency and overall electrochemical performance. Furthermore, the lithium-replenishing material in the core is a unidirectional capacity lithium-containing material that performs lithium-ion extraction during the first charge and does not re-intercalate during discharge. This gives the lithium replenishment additive unidirectional capacity characteristics, effectively removing lithium during the first charge and preventing lithium ions from re-intercalating into the material during discharge, thereby ensuring the lithium replenishment effect of the additive. In addition, the functional encapsulation layer in the lithium replenishment additive effectively protects the core, isolating the lithium-replenishing material from external moisture and carbon dioxide, ensuring the stability of the core and thus guaranteeing the lithium replenishment effect and stability of the additive. It also exhibits good processing performance.

[0042] The method for preparing the lithium-replenishing additive in this application can effectively prepare lithium-replenishing additives with a core-shell structure, and can effectively encapsulate the core containing unidirectional capacity-replenishing lithium material in the functional encapsulation layer, thereby ensuring excellent lithium-replenishing effect, stable lithium-replenishing performance, and good processing performance of the prepared lithium-replenishing additive. In addition, the preparation method of the lithium-replenishing additive can ensure the stability of the structure and electrochemical performance of the prepared lithium-replenishing additive, and is highly efficient, saving production costs.

[0043] Because the electrode sheet of this application contains the lithium replenishing additive of this application, during the charging and discharging process, the lithium replenishing additive can act as a lithium source and a "sacrificial agent" during the first charging cycle to replenish the irreversible lithium ions consumed by the formation of the SEI film on the negative electrode, thereby maintaining an abundance of lithium ions in the battery system and improving the battery's first efficiency and overall electrochemical performance.

[0044] Because the secondary battery of this application contains the electrode sheet of this application, the lithium-ion battery of this application has excellent initial coulombic efficiency, battery capacity and cycle performance, long life and stable electrochemical performance. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0046] Figure 1This is a schematic diagram of the structure of the lithium supplementary additive in the embodiments of this application; wherein, Figure a is a primary particle core; Figure b is a secondary particle core;

[0047] Figure 2 for Figure 1 The diagram shows a structural schematic of one type of lithium supplementation additive.

[0048] Figure 3 for Figure 1 The diagram shows another structural schematic of the lithium supplement additive.

[0049] Figure 4 for Figure 1 The diagram shows a third structural representation of the lithium supplement additive.

[0050] Figure 5 This is a schematic flowchart of the lithium supplementation additive preparation method according to an embodiment of this application;

[0051] Figure 6 XRD patterns of the lithium supplementation additives provided in Examples 1 and 2;

[0052] Figure 7 Lithium replenishment capacity curves of lithium-ion batteries containing lithium replenishment additives provided in Examples 1 and 2 and Comparative Example 1. Detailed Implementation

[0053] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0054] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0055] 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 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 both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0056] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may 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 this application.

[0057] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0058] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0059] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0060] Firstly, embodiments of this application provide a lithium replenishment additive. The lithium replenishment additive of this application includes a core and a functional encapsulation layer covering the core; that is, the lithium replenishment additive of this application has a core-shell structure. As shown in the embodiments, the structure of the lithium replenishment additive of this application is as follows: Figures 1 to 4 As shown, it includes a core body 10 and a functional encapsulation layer 20 covering the core body 10.

[0061] The core 10 includes a lithium replenishing material, which is a unidirectional lithium-containing material that allows lithium ions to be extracted during the first charge and does not intercalate during discharge. In other words, in the lithium replenishing additive of this embodiment, the core 10 serves as the lithium source for replenishment. Thus, the core 10 is rich in lithium, ensuring that the lithium replenishing additive of this embodiment can provide abundant lithium. When added to the electrode as an additive, it acts as a "sacrificial agent" during the first charge cycle, releasing as many lithium ions as possible at once to replenish the irreversible lithium ions consumed in the formation of the SEI film on the negative electrode.

[0062] Meanwhile, the lithium replenishing material contained in the core 10 also possesses unidirectional capacity characteristics. This unidirectional capacity characteristic means that the lithium replenishing material can extract lithium ions during the first charge and does not exhibit lithium ion insertion characteristics during discharge. Because the lithium replenishing material possesses unidirectional capacity characteristics, the lithium replenishing additive of this application embodiment has unidirectional capacity characteristics, thereby ensuring the excellent lithium replenishing effect of the lithium replenishing additive of this application embodiment.

[0063] In the embodiment, the cell of the lithium replenishing material contained in the core 10 is an antifluorite structure with a crystal space group of P42 / nmc

[137] . The lithium ions in the cell of this crystal structure lithium replenishing material are more stable, which can improve the unidirectional capacity characteristics of the lithium replenishing material mentioned above, and is more conducive to the extraction of lithium ions during the first charging process. Moreover, it can better avoid lithium ion insertion during discharge, thereby improving the lithium replenishing effect of the lithium replenishing additive in this embodiment, so that the lithium replenishing additive in this embodiment can exert its full theoretical specific capacity. In addition, the conductivity of this crystal structure lithium replenishing material is excellent, and combined with its unidirectional capacity characteristics, it can effectively reduce the polarization phenomenon during charging.

[0064] Based on the unidirectional capacity characteristics of the lithium replenishing material contained in the core 10 described above, in this embodiment, the lithium replenishing material may include the chemical formula xLi6MO4·(1-x)Li2O. Wherein, 0<x≤1 in the chemical formula, and M includes at least one of Cr, Mn, Fe, Co, Ni, Cu, and Zn. These lithium replenishing materials have a stable antifluorite structure cell and a crystal structure with space group P42 / nmc

[137] , which has better unidirectional capacity characteristics, higher conductivity, better lithium replenishment effect, and lower polarization phenomenon during charging. For example, when the lithium replenishing material is xLi6MO4·(1-x)Li2O, Li6MO4 is an antifluorite structure cell with a crystal structure space group of P42 / nmc

[137] , which gives xLi6MO4·(1-x)Li2O excellent unidirectional capacity characteristics, higher conductivity, better lithium replenishment effect, and lower polarization phenomenon during charging. Furthermore, the Li6MO4 contained in xLi6MO4·(1-x)Li2O acts as a catalyst for Li2O, enabling Li2O to decompose and provide lithium ions during the first charging process. It also has a synergistic effect with Li6MO4, enhancing the lithium replenishment function and effectiveness of xLi6MO4·(1-x)Li2O. Additionally, the lithium replenishment material of this core 10 can be a positive electrode lithium replenishment material.

[0065] In this embodiment, the core 10 can be at least one of primary particles and secondary particles, specifically at least one of primary particles and secondary particles formed from the lithium-supplementing material contained in the core 10. Among them, primary particles include... Figure 1 As shown in Figure a, secondary particles are as follows: Figure 1As shown in Figure b. In other embodiments, the particle size of the core 10 can be 100 nm to 50 μm. For example, when the core 10 is as follows... Figure 1 When the primary particles are as shown in Figure a, the particle size of the primary particles, which is also the particle size distribution of the core 10, is 100 nm-10 μm; when the core 10 is as shown in Figure a... Figure 1 The secondary particles shown in Figure b have a particle size distribution of 200 nm to 50 μm, which is also the particle size distribution of the core 10. These secondary particles refer to aggregated particles formed by the aggregation of one or more primary particles. By controlling the morphology and size of the core 10, the processability of the lithium-replenishing additive in lithium battery slurry preparation is improved, while ensuring abundant lithium ions. Furthermore, smaller primary particle sizes allow for the extraction of more lithium.

[0066] Furthermore, although the lithium-supplementing material contained in the core 10 in the above embodiments, such as xLi6MO4·(1-x)Li2O, is rich in lithium, it is unstable in the presence of water and carbon dioxide. It easily reacts with water and carbon dioxide, thereby reducing the lithium-supplementing effect of the lithium-supplementing additive in this application embodiment and also reducing its processing performance. For example, it can cause a sharp increase in the viscosity of slurries containing the aforementioned lithium-supplementing material, leading to rapid gelation and loss of fluidity, making subsequent processing impossible. Therefore, based on the core 10 in the above embodiments, the functional encapsulation layer 20 contained in the lithium-supplementing additive in the above embodiments is coated onto the core 10 to form a complete encapsulation layer. Thus, the functional encapsulation layer 20 can effectively protect the core 10, isolating the core 10, specifically the lithium-supplementing material, from external moisture and carbon dioxide, ensuring the lithium-supplementing effect and stability of the lithium-supplementing material contained in the core 10, and ensuring the stability and uniformity of the lithium-supplementing additive in the electrode active slurry and active layer, thereby improving the processing performance of the lithium-supplementing additive. Therefore, in the embodiments of this application, the functional encapsulation layer 20 should at least have the property of isolating moisture and carbon dioxide, such as being a dense encapsulation layer.

[0067] Based on the aforementioned functions of the functional encapsulation layer 20, the material of the functional encapsulation layer 20 can be a material capable of forming at least the function of isolating moisture and carbon dioxide, such as including at least one of ceramics, polymers or carbon materials.

[0068] Furthermore, since the functional encapsulation layer 20 covers the surface of the core 10, the lithium ions in the lithium-replenishing material contained in the core 10 need to pass through the functional encapsulation layer 20 during the initial lithium removal and charging process. Therefore, the electrochemical performance and thickness of the functional encapsulation layer 20 will also affect the lithium ion removal and migration efficiency. Thus, in addition to isolating it from adverse factors such as moisture and carbon dioxide, the functional encapsulation layer 20 ideally also possesses good ionic conductivity characteristics. In this embodiment, the functional encapsulation layer 20 may include an ion conductor encapsulation layer.

[0069] Furthermore, also based on the functional encapsulation layer 20 covering the surface of the core 10, the conductivity of the lithium-replenishing additive during or after its lithium-replenishing process will affect the battery's rate capability and first-efficiency electrochemical performance. Therefore, in addition to isolating moisture and carbon dioxide, the functional encapsulation layer 20 should ideally also possess good electronic conductivity. In this embodiment, the functional encapsulation layer 20 may include an electronic conductor encapsulation layer.

[0070] Therefore, as an embodiment of this application, the functional encapsulation layer 20 contained in the lithium supplement additive may include at least one of an ion conductor encapsulation layer and an electronic conductor encapsulation layer. Therefore, the functional encapsulation layer 20 has at least the following structure:

[0071] In one embodiment, such as Figure 2 As shown, the functional encapsulation layer 20 includes an electronic conductor encapsulation layer 21.

[0072] In another embodiment, such as Figure 3 As shown, the functional encapsulation layer 20 includes an ion conductor encapsulation layer 22.

[0073] In another embodiment, such as Figure 4 As shown, the functional encapsulation layer 20 includes a composite layer of an electronic conductor encapsulation layer 21 and an ion conductor encapsulation layer 22, with the electronic conductor encapsulation layer 21 covering the core 10 and the ion conductor encapsulation layer 22 covering the outer surface of the electronic conductor encapsulation layer 21. Of course, based on... Figure 4 The functional encapsulation layer 20 of the composite structure shown can also cover the core 10, while the electronic conductor encapsulation layer 21 covers the outer surface of the ion conductor encapsulation layer 22.

[0074] The electronic conductor encapsulation layer 21 added to the aforementioned functional encapsulation layer 20 enhances the electronic conductivity of the functional encapsulation layer 20, thereby enhancing the electronic conductivity of the lithium supplement additive and helping to reduce the internal impedance of the electrode. Simultaneously, during and after the release of the core 10 as a "sacrifice," the electronic conductor encapsulation layer 21 can be reused, acting as an auxiliary conductive agent within the electrode. Based on the function of the electronic conductor encapsulation layer 21, when the functional encapsulation 20 contains only the electronic conductor encapsulation layer 21, the electronic conductor encapsulation layer 21 should have a dense structure and be fully encapsulated. When the functional encapsulation 20 includes at least the electronic conductor encapsulation layer 21 and the ion conductor encapsulation layer 22, the electronic conductor encapsulation layer 21 can be a non-fully encapsulated layer structure or a non-dense structure, but the composite encapsulation layer formed by the electronic conductor encapsulation layer 21 and the ion conductor encapsulation layer 22 should be able to isolate harmful components such as moisture and carbon dioxide.

[0075] In some embodiments, the thickness of the electronic conductor encapsulation layer 21 is 1-100 nm, more specifically 1-50 nm, and even more specifically 2-20 nm. In other embodiments, the mass content of the electronic conductor encapsulation layer 21 in the lithium supplementation additive is 0.1-30%, more specifically 0.1-10%, and more preferably 0.5-5%.

[0076] In this embodiment, the material of the electronic conductor encapsulation layer 21 includes at least one of carbon materials, conductive polymers, or conductive oxides. Specifically, the carbon material includes at least one of amorphous carbon, carbon nanotubes, graphite, carbon black, and graphene. Specifically, the conductive polymer includes [C6H7O6Na]. n Organic polymers with the structure [C6H7O2(OH)2OCH2COONa] n Organic polymers with the structure [C3H4O2] n Organic polymers with the structure [C3H3O2M] a ] n Organic polymers with the structure [C3H3N] n It is an organic polymer with a structure containing -[CH2-CF2]. n One or more of the following: organic polymers with a -[NHCO]- structure, organic polymers containing an imide ring -[CO-N-CO]- structure on the main chain, and polyvinylpyrrolidone, wherein M aIt is an alkali metal element. In some embodiments of this application, the polymer includes one or more of polyvinylidene fluoride, sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, polyacrylate, polyacrylonitrile, polyamide, polyimide, polyvinylpyrrolidone, polyethylene oxide (PEO), polypyrrole (PPy), polytetrafluoroethylene (PTFE), and polyurethane (PU). In some embodiments of this application, the polymer includes one or more of sodium carboxymethyl cellulose and polyacrylic acid. Sodium carboxymethyl cellulose and polyacrylic acid are two-dimensional planar polymers with good adhesive properties, which can effectively coat the lithium-rich material core, thereby avoiding contact between the lithium-rich material core and air and improving the stability of the lithium supplementation additive. In the embodiments of this application, the molecular weight of the polymer is greater than or equal to 100,000. The molecular weight of the polymer can be, but is not limited to, 100,000, 150,000, 200,000, 300,000, 500,000, or 1,000,000. The higher the molecular weight of the polymer, the higher the density and structural strength of the polymer layer, which is more conducive to achieving protection of the core 10. In specific embodiments, the conductive oxide can include at least one of In2O3, ZnO, and SnO2. By adjusting the thickness and material of the electronic conductor encapsulation layer 21, its electronic conductivity can be further improved.

[0077] In a further embodiment, the electronic conductor encapsulation layer 21 is made of conductive carbon material and lithium carbonate, and the electronic conductor encapsulation layer 21 is in contact with the core 10, that is, it is coated on the surface of the core 10. The lithium carbonate content in the electronic conductor encapsulation layer 21 is 0.5-1.5 wt%. Using a mixture of conductive carbon material and lithium carbonate as the material of the electronic conductor encapsulation layer 21 can, on the one hand, improve the density of the electronic conductor encapsulation layer 21, improve its ability to isolate moisture and carbon dioxide, and improve the stability of the lithium replenishment additive in storage, processing, and lithium replenishment; on the other hand, the mixture of conductive carbon material and lithium carbonate improves the conductivity of the electronic conductor encapsulation layer 21, stimulating the specific capacity of the lithium replenishment additive; and thirdly, it can also reduce processing difficulties caused by residual alkali in the core.

[0078] In this embodiment, the aforementioned ion conductor encapsulation layer 22 enhances the ionic conductivity of the functional package 20, thereby enhancing the ionic conductivity of the lithium-supplementing additive, which is beneficial for the outward transport of lithium ions from the core. Simultaneously, after the core 10 releases all lithium ions as a "sacrifice," the ion conductor encapsulation layer 22 can be reused, playing an auxiliary role in enhancing ion transport within the electrode. Based on the function of the ion conductor encapsulation layer 22, when the functional package 20 contains only the ion conductor encapsulation layer 22, the ion conductor encapsulation layer 22 should have a dense structure and be fully encapsulated. When the functional package 20 includes at least the ion conductor encapsulation layer 22 and the electronic conductor encapsulation layer 21, the ion conductor encapsulation layer 22 is a non-fully encapsulated layer structure, or it can be a non-dense structure. However, the composite encapsulation layer formed by the ion conductor encapsulation layer 22 and the electronic conductor encapsulation layer 21 should be able to isolate harmful components such as moisture and carbon dioxide. In one embodiment, the thickness of the ion conductor encapsulation layer 22 is 1-200 nm, further 1-50 nm, even further 2-20 nm, and even further 5-20 nm. In another embodiment, the material of the ion conductor encapsulation layer 22 includes at least one of perovskite, NASICON, garnet, or polymer solid electrolytes. In a specific embodiment, the perovskite type includes Li... 3x La 2 / 3-x TiO3(LLTO), specifically Li 0.5 La 0.5 TiO3, Li 0.33 La 0.57 TiO3, Li 0.29 La 0.57 TiO3, Li 0.33 Ba 0.25 La 0.39 TiO3, (Li 0.33 La 0.56 ) 1.005 Ti 0.99 Al 0.01O3 Li 0.5 La 0.5 Ti 0.95 Zr 0.05 At least one of O3, etc., NASICON type such as but not limited to Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP), garnet type including Li7La3Zr2O 12 (LLZO), Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 6.5 La3Zr 1.5 Ta 0.5 O12 At least one of the following, polymer-type solid electrolytes include at least one of PEO / PPO / PVDF, etc., containing dissolved lithium salts. By adjusting the thickness and material of the ion conductor encapsulation layer 22, its ionic conductivity can be further improved.

[0079] Secondly, embodiments of this application also provide a method for preparing the lithium-supplementing additive described above. The process flow of this lithium-supplementing additive preparation method is as follows: Figure 5 As shown, combined with Figures 1 to 4 Its preparation method includes the following steps:

[0080] Step S01: Provide a core material for lithium replenishment;

[0081] Step S02: In a first protective atmosphere, a functional encapsulation layer is formed on the surface of the core material, and the functional encapsulation layer completely covers the core material to obtain a lithium supplementation additive.

[0082] In step S01, the core material is the same material contained in the core 10 of the lithium replenishing additive in the above-described embodiment. Therefore, the core material includes a lithium replenishing material, which is a lithium-containing material with unidirectional capacity that allows lithium-ion extraction during the first charge and prevents lithium-ion insertion during discharge. The functional encapsulation layer in step S02 is the functional encapsulation layer 20 contained in the lithium replenishing additive in the above-described embodiment. Therefore, to save space, the core material in step S01 and the functional encapsulation layer in step S02 will not be described in detail here.

[0083] In the embodiments, when the lithium replenishment material includes the chemical formula xLi6MO4·(1-x)Li2O, each lithium replenishment material can be mixed with the source compounds of each element according to the stoichiometric ratio of the elements contained in each lithium replenishment material and then sintered. The sintering conditions are controlled so that the generated lithium replenishment material has the unidirectional capacity characteristics mentioned above, specifically having an antifluorite structure cell with a crystal space group of P42 / nmc

[137] .

[0084] For example, when the lithium replenishing material is xLi6MO4·(1-x)Li2O, the lithium replenishing material of xLi6MO4·(1-x)Li2O is prepared according to the following preparation method:

[0085] Step S011: According to the elemental stoichiometry of xLi6MO4·(1-x)Li2O, the M metal oxide and the lithium source are mixed to obtain the precursor of xLi6MO4·(1-x)Li2O.

[0086] Step S012: In the second protective atmosphere, the precursor is sintered to make the cell of xLi6MO4·(1-x)Li2O an antifluorite structure with a crystal space group of P42 / nmc

[137] .

[0087] In step S011, the stoichiometric ratio of the elements can be a molar ratio or a mass ratio converted from the chemical formula. In the embodiments, the M metal oxide may include at least one of CrO, Cr2O3, CrO2, CrO3, MnO, Mn2O3, MnO2, Mn3O4, FeO, Fe2O3, Fe3O4, CoO, Co2O3, CoO2, Co3O4, NiO, Ni2O3, CuO, and ZnO. The lithium source may include at least one of LiOH, LiOH·H2O, Li2O, Li2CO3, LiNO3, and LiAc.

[0088] In other embodiments, the mixing of the M metal oxide with the lithium source can be a solid-phase mixing process or a liquid-phase mixing process, or a combination of solid and liquid phases.

[0089] Solid-phase mixing involves mixing the M metal oxide with the lithium source in a specific ratio, followed by mechanical stirring or high-energy ball milling to form a homogeneous solid precursor. Liquid-phase mixing involves first dissolving the lithium source in a solvent, then adding the metal oxide, stirring until a homogeneous mixture is formed, and finally evaporating the solvent to form a homogeneous precursor.

[0090] In step S012, the sintering process is used to sinter the precursor to form a supplementary material, which has the unidirectional capacity characteristics described above, namely, lithium ion extraction during the first charge and non-intercalation of lithium ions during discharge. Specifically, the unit cell with an antifluorite structure and its crystal space group is P42 / nmc

[137] . In the embodiments, the sintering temperature can be 400-1000℃, further 400-900℃, and even further 450-850℃; the time can be 1-24h, further 3-15h, and even further 5-12h. The sintering process can be carried out by heating to 400-1000℃ at a heating rate of 0.5-10℃ / min, further 1-6℃ / min, and even further 2-5℃ / min. By controlling the sintering process, the resulting lithium-supplementing material, such as xLi6MO4·(1-x)Li2O, has an antifluorite structure cell and a crystal structure space group of P42 / nmc

[137] . In the embodiments, the second protective atmosphere can be an atmosphere formed by any of the protective gases including nitrogen, argon, nitrogen-argon mixture, nitrogen-hydrogen mixture, and argon-hydrogen mixture, which can effectively ensure the stability of the crystal structure and electrochemical performance of the sintered product.

[0091] The method for forming the functional encapsulation layer in step S02 can be carried out according to the structure of the functional encapsulation layer 20 contained in the lithium supplement additive of the above-described application embodiments. The first protective atmosphere can be a conventional oxygen-free atmosphere, such as a protective atmosphere formed by at least one gas selected from nitrogen, argon, and a nitrogen-argon mixture.

[0092] In the embodiments, when the formed functional encapsulation layer structure is as follows: Figure 2 When the electronic conductor encapsulation layer 21 is included, the method for forming a functional encapsulation layer on the surface of the core material includes the following steps:

[0093] Step S021: In the first protective atmosphere, an electronic conductor encapsulation layer 21 that fully covers the core material is formed on the surface of the core material.

[0094] When the material of the electronic conductor encapsulation layer 21 is at least one of carbon material, conductive polymer, or conductive oxide, the precursor material for forming the electronic conductor encapsulation layer 21 includes precursors of carbon material, conductive polymer, or conductive oxide. The carbon material, conductive polymer, and conductive oxide are all as described above regarding the materials used in the lithium supplementation additive for the electronic conductor encapsulation layer 21. The precursors of the carbon material, conductive polymer, or conductive oxide are also the precursors for forming the aforementioned carbon material, conductive polymer, or conductive oxide. The method and conditions for forming the electronic conductor encapsulation layer 21 of carbon material, conductive polymer, and conductive oxide are specifically based on the method for forming carbon material, conductive polymer, or conductive oxide.

[0095] In a specific embodiment, when the material of the electronic conductor encapsulation layer 21 is a conductive polymer layer, the method for forming the electronic conductor encapsulation layer 21 may include, but is not limited to, the following steps:

[0096] The core material is dispersed in a solution containing a conductive polymer, and then vacuum dried to form an electronic conductor encapsulation layer 21 of the conductive polymer on the surface of the core material. The solvent in the solution is a solvent capable of uniformly dispersing or dissolving the polymer, such as one or more of N-methylpyrrolidone, methanol, ethanol, isopropanol, acetone, tetrahydrofuran, and diethyl ether.

[0097] In another specific embodiment, when the material of the electronic conductor encapsulation layer 21 is a carbon material layer, the method for forming the electronic conductor encapsulation layer 21 may include, but is not limited to, the following steps:

[0098] The nucleus material is dispersed in a carbon source-containing solution, dried, and then carbonized to form an electronic conductor encapsulation layer 21 of carbon material on the surface of the nucleus material. The carbon source can be at least one of a solid-phase carbon source, a liquid-phase carbon source, or a gaseous carbon source. The solid-phase carbon source can be at least one of starch, glucose, fructose, sucrose, cellulose, lignin, amino acids, PEO, epoxy resin, phenolic resin, etc.; the liquid-phase carbon source can be at least one of a five- to sixteen-carbon liquid-phase alkane, a liquid-phase olefin, or a liquid-phase alkyne. The carbonization temperature can be 400-1000℃, further 400-900℃, and even further 450-850℃; the carbonization time is 1-12h, further 1-8h, and even further 1-5h. In another embodiment, the carbonization process can be carried out at a heating rate of 0.5-10℃ / min, further 1-6℃ / min, and even further 2-5℃ / min to 400-1000℃. When the carbon source is PEO, the core material can be mixed evenly with PEO. PEO reaches its melting point at 300°C and is evenly coated on the surface of the core material. The coated material is then sintered in an inert atmosphere at 600°C for 16 hours. Once sintering is complete, a carbon layer is formed.

[0099] In addition, when the carbon source is a gaseous carbon source, a carbon material layer can be deposited in situ on the surface of the core material by introducing a gaseous carbon source into the aforementioned carbonization treatment environment. Specifically, the gaseous carbon source can be at least one of methane, ethane, propane, butane, ethylene, propylene, butene, pentene, acetylene, propyne, and butyne.

[0100] In this embodiment, when the material of the formed electronic conductor encapsulation layer 21 includes a mixture of conductive carbon material and lithium carbonate, the method for forming the electronic conductor encapsulation layer 21 includes the following steps:

[0101] After forming a conductive carbon coating layer that fully covers the core material on the surface of the core material, heat treatment is performed in a protective atmosphere to form a conductive carbon coating layer.

[0102] The protective atmosphere can be, but is not limited to, an 80% Vol N2 / CO2 protective atmosphere. The heat treatment can be, but is not limited to, heating to 500℃ at a rate of 200℃ / h and holding for 1 hour. By controlling the heat treatment conditions, a certain amount of lithium carbonate is generated in the conductive carbon coating layer.

[0103] In another embodiment, when the formed functional encapsulation layer is as follows: Figure 3 The method for forming a functional encapsulation layer on the surface of the core material, including the ion conductor encapsulation layer 22, comprises the following steps:

[0104] Step S022: In the first protective atmosphere, an ion conductor encapsulation layer 22 that fully covers the core material is formed on the surface of the core material.

[0105] When the material of the ion conductor encapsulation layer 22 is at least one of perovskite, NASICON, garnet, or polymer solid electrolyte, the precursor material for forming the ion conductor encapsulation layer 22 includes a precursor of the perovskite, NASICON, garnet, or polymer solid electrolyte, and the method and conditions for forming the ion conductor encapsulation layer 22 are specifically formed according to the method for forming the perovskite, NASICON, garnet, or polymer solid electrolyte.

[0106] In another embodiment, when the formed functional encapsulation layer is as follows: Figure 4 When the composite layer shown includes an electronic conductor encapsulation layer 21 and an ion conductor encapsulation layer 22, the method for forming a functional encapsulation layer 20 on the surface of the core material includes the following steps:

[0107] Step S023: In the first protective atmosphere, an electronic conductor encapsulation layer 21 that fully covers the core material is first formed on the surface of the core material, and then an ion conductor encapsulation layer 22 is formed on the outer surface of the electronic conductor encapsulation layer 21.

[0108] Therefore, the above-described method for preparing lithium-replenishing additives can effectively prepare the core-shell structure lithium-replenishing additives described in the embodiments of the above application. Furthermore, it allows the functional encapsulation layer to effectively coat the core containing unidirectional capacity lithium-replenishing material, thereby ensuring that the prepared lithium-replenishing additive possesses the excellent lithium-replenishing effect, stable lithium-replenishing performance, and good processing performance described in the embodiments of the above application. Moreover, the relevant performance of the prepared lithium-replenishing additive can be optimized by controlling the materials and process conditions of the core and functional encapsulation layer. In addition, the method for preparing lithium-replenishing additives ensures the stability of the structure and electrochemical performance of the prepared additives, and is highly efficient, saving production costs.

[0109] Thirdly, this application also provides an electrode sheet. The electrode sheet of this application includes a current collector and an electrode active layer bonded to the surface of the current collector. The electrode active layer is doped with the lithium replenishing additive described in the above application. Because the electrode sheet of this application contains the aforementioned lithium replenishing additive, during charging and discharging, the lithium replenishing additive contained in the electrode sheet plays the role described above. It can act as a lithium source and be consumed first as a "sacrificial agent" during the first charging cycle to replenish the irreversible lithium ions consumed in the formation of the SEI film at the negative electrode, thereby maintaining an abundance of lithium ions in the battery system and improving the battery's initial efficiency and overall electrochemical performance.

[0110] The electrode sheet can be a conventional electrode sheet for secondary batteries, such as one that includes a current collector and an electrode active layer bonded to the surface of the current collector.

[0111] In one embodiment, the mass content of the lithium-supplementing additive described in the above-mentioned embodiments in the electrode active layer can be 0.1-30%; preferably, 0.1-10%. The electrode active layer includes, in addition to the lithium-supplementing additive, electrode active material, binder, and conductive agent. The binder can be a commonly used electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives. In this embodiment, the conductive agent can be a commonly used conductive agent, such as one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. The electrode active material can be selected according to the type of electrode, such as positive or negative electrode. The positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. Therefore, the type of lithium replenishing additive mentioned above should be compatible with the type of electrode active material. For example, when the electrode active material is a positive electrode active material, the lithium replenishing additive mentioned above should be suitable for use as a positive electrode lithium replenishing additive; when the electrode active material is a negative electrode active material, the lithium replenishing additive mentioned above should be suitable for use as a negative electrode lithium replenishing additive.

[0112] In the embodiments, the electrode sheet preparation process can be as follows: mixing electrode active material, lithium supplementation additive, conductive agent and binder to obtain electrode slurry, coating the electrode slurry on current collector, and preparing positive electrode sheet through drying, rolling and die cutting and other steps.

[0113] Fourthly, this application also provides a secondary battery. The secondary battery of this application includes necessary components such as a positive electrode, a negative electrode, a separator, and an electrolyte, and of course, other necessary or auxiliary components. The positive electrode and / or negative electrode are the same as those described in the embodiments of this application, meaning that the positive electrode active layer contains the lithium-supplementing additive described in the embodiments of this application. The negative electrode may also contain the lithium-supplementing additive described in the embodiments of this application in its negative electrode active layer.

[0114] Because the secondary battery of this application embodiment contains the lithium replenishing additive mentioned in the above application embodiment, based on the excellent lithium replenishing performance of the lithium replenishing additive mentioned in the above application embodiment or further having ion conductivity and / or electronic conductivity, the secondary battery of this application embodiment is endowed with excellent first coulombic efficiency, battery capacity and cycle performance, long life and stable electrochemical performance.

[0115] The following examples illustrate the lithium supplement additives, their preparation methods, and applications in this application.

[0116] 1. Examples of lithium supplementation additives and their preparation methods:

[0117] Example 1

[0118] This embodiment provides a lithium supplement additive and its preparation method. The lithium supplement additive comprises a Li6MnO4 lithium supplement material core with an anti-fluorite structure and a dense carbon layer coating the core. The core has a particle size of approximately 5-10 μm, and the dense carbon layer has a thickness of approximately 30 nm.

[0119] The preparation method of the lithium supplement additive in this embodiment includes the following steps:

[0120] S1. Preparation of Li6MnO4 lithium supplementary material with anti-fluorite structure:

[0121] MnO and LiOH were mixed in a solid phase according to stoichiometric ratio and ball-milled for 2 hours at a speed of 30 Hz. The homogeneous mixture was then sintered at 800 °C under a nitrogen atmosphere for 10 hours to obtain Li6MnO4 material with an antifluorite structure.

[0122] S2. Preparation of dense carbon functional encapsulation layer:

[0123] Li6MnO4 material and glucose powder were mixed at a mass ratio of 2:1 and ball-milled for 4 hours at a speed of 40 Hz under a nitrogen atmosphere. The homogeneous mixture was then sintered at 800°C for 2 hours under a nitrogen atmosphere to obtain Li6MnO4@C material with a dense carbon coating.

[0124] Example 2

[0125] This embodiment provides a lithium supplement additive and its preparation method. The lithium supplement additive comprises a core of anti-fluorite structure 0.9Li6CoO4·0.1Li2O lithium supplement material and a dense carbon layer coating the core. The core has a particle size of approximately 1-5 μm, and the dense carbon layer has a thickness of approximately 20 nm.

[0126] The preparation method of the lithium supplement additive in this embodiment includes the following steps:

[0127] Preparation of S1.0.9Li6CoO4·0.1Li2O lithium supplement material:

[0128] CoO and LiOH were mixed in a solid phase at a molar ratio of 0.9:5.6 and ball-milled for 2 hours at a speed of 25 Hz. The homogeneous reactants were then sintered at 750 °C under a nitrogen atmosphere for 8 hours to obtain a 0.9Li6CoO4·0.1Li2O material with an antifluorite structure.

[0129] S2. Preparation of dense carbon functional encapsulation layer:

[0130] 0.9Li6CoO4·0.1Li2O material was mixed with glucose powder at a mass ratio of 3:1 and ball-milled for 3 hours at 35 Hz under nitrogen atmosphere. The uniformly mixed reactants were then sintered at 750°C under nitrogen atmosphere for 2 hours to obtain 0.9Li6CoO4·0.1Li2O@C material with a dense carbon coating.

[0131] Example 3

[0132] This embodiment provides a lithium supplement additive and its preparation method. The lithium supplement additive comprises an anti-fluorite structure Li6FeO4 lithium supplement material core and a dense carbon layer coating the core. The core has a particle size of approximately 5-20 μm, and the dense carbon layer has a thickness of approximately 5 nm.

[0133] The preparation method of the lithium supplement additive in this embodiment includes the following steps:

[0134] S1. Preparation of Lithium-Supplementing Materials with Anti-Fluorite Structure:

[0135] FeO and LiOH were mixed in solid phase according to stoichiometric ratio and ball-milled for 2 hours at 30 Hz. The homogeneous reactants were then sintered at 700 °C under a nitrogen-hydrogen mixed atmosphere for 8 hours to obtain Li6FeO4 material with an antifluorite structure.

[0136] S2. Preparation of dense carbon functional encapsulation layer:

[0137] Li6FeO4 material and glucose powder were mixed at a mass ratio of 5:1 and ball-milled for 2 hours at 30 Hz under a nitrogen atmosphere. The homogeneous mixture was then sintered at 700°C under a nitrogen-hydrogen mixed atmosphere for 2 hours to obtain Li6FeO4@C material with a dense carbon coating.

[0138] Example 4

[0139] This embodiment provides a lithium supplement additive and its preparation method. The lithium supplement additive comprises a core of 0.8Li6ZnO4·0.2Li2O lithium supplement material with an anti-fluorite structure and a dense carbon layer covering the core. The average particle size of the core is 1-5 μm, and the thickness of the dense carbon layer is ~10 nm.

[0140] The preparation method of the lithium supplement additive in this embodiment includes the following steps:

[0141] S1. Preparation of lithium-supplementing material with anti-fluorite structure: 0.8Li6ZnO4·0.2Li2O

[0142] ZnO and LiOH were mixed in a solid phase at a molar ratio of 0.8:5.2 and ball-milled for 3 hours at a speed of 45 Hz. The homogeneous reactants were then sintered at 750 °C under an argon atmosphere for 6 hours to obtain a 0.8Li6ZnO4·0.2Li2O material with an antifluorite structure.

[0143] S2. Preparation of dense carbon functional encapsulation layer:

[0144] 0.8Li6ZnO4·0.2Li2O material was mixed with glucose powder at a mass ratio of 3:1 and ball-milled for 4 hours at 40 Hz under nitrogen atmosphere. The homogeneous mixture was then sintered at 750℃ under argon atmosphere for 2 hours to obtain 0.8Li6ZnO4·0.2Li2O@C material with a dense carbon coating.

[0145] Comparative Example 1

[0146] This comparative example provides a lithium supplement additive and its preparation method. The lithium supplement additive includes a Li2NiO2 lithium supplement material core and a dense carbon layer covering the core.

[0147] The preparation method of this comparative lithium supplement additive includes the following steps:

[0148] Li2NiO2 cathode lithium supplementation additive and glucose powder were mixed at a mass ratio of 2:1 and ball-milled for 2 hours at 30 Hz under nitrogen atmosphere protection. The uniformly mixed reactants were then sintered at 700°C under nitrogen atmosphere protection for 2 hours to obtain Li2NiO2@C material with a dense carbon coating.

[0149] 2. Example of a lithium-ion battery:

[0150] The lithium replenishing additives provided in Examples 1 to 4 and the lithium replenishing additives provided in the comparative examples were assembled into positive electrode electrodes and lithium-ion batteries respectively according to the following methods:

[0151] Positive electrode: The lithium supplementation additives provided in Examples 1 to 4 above were mixed with SP and PVDF respectively according to the mass ratio of lithium supplementation additive: SP:PVDF = 95:2:3. An appropriate amount of NMP solvent was added and the mixture was ball-milled and stirred for 60 min at a speed of 30 Hz. After homogenization, coating, drying and cutting, positive electrode sheets were prepared. The positive electrode sheets were baked in a vacuum oven at 100 ℃ to remove trace amounts of water.

[0152] Negative electrode: Lithium metal sheet with a diameter of 16mm;

[0153] Electrolyte: 1 mol / L LiPF6 solution, the solvent of which is composed of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1;

[0154] Diaphragm: Polypropylene microporous diaphragm;

[0155] Lithium-ion battery assembly: Lithium-ion batteries are assembled in an inert atmosphere glove box according to the assembly sequence of lithium metal sheet-separator-electrolyte-positive electrode.

[0156] Related feature tests

[0157] 1. Characteristic testing of lithium supplementation additives

[0158] The lithium-replenishing additives provided in Examples 1 to 4 were subjected to XRD analysis. The XRD patterns of the lithium-replenishing additives provided in Examples 1 and 2 are shown below. Figure 6 As shown in the XRD patterns, the peak positions of the lithium-supplementing additives in Examples 1 and 2 match the standard peak positions of Li6MO4 materials with an antifluorite cell and a crystal space group of P42 / nmc

[137] in the crystal structure database. Other examples provide XRD patterns of the lithium-supplementing additives and... Figure 6 Similarly, the peak positions in the XRD patterns all match the antifluorite structure in the crystal structure database.

[0159] 2. Electrochemical performance of lithium-ion batteries:

[0160] The lithium-ion batteries containing the lithium-replenishing additives of Examples 1 to 4 and the lithium-ion battery containing Comparative Example 1 were tested for their lithium-replenishing capacity performance according to the following methods:

[0161] The voltage was charged to 4.3V at a constant current and constant voltage rate of 0.05C, with a cutoff current of 0.02C; after resting for 5 minutes, it was discharged to 2.8V at a constant current rate of 0.05C. The measured results are as follows: Figure 7 As shown.

[0162] The results showed that the lithium-ion battery containing the lithium replenishment additive provided in Example 1 had a charging replenishment capacity of 473 mAh / g, a discharging capacity of 18 mAh / g, and an initial efficiency of 3.8%; the lithium-ion battery containing the lithium replenishment additive provided in Example 2 had a charging replenishment capacity of 588 mAh / g, a discharging capacity of 49 mAh / g, and an initial efficiency of 8.3%; and the lithium-ion battery containing the lithium replenishment additive provided in Comparative Example 1 had a charging replenishment capacity of 405 mAh / g, a discharging capacity of 130 mAh / g, and an initial efficiency of 32%. The lithium replenishment capacity test results of lithium-ion batteries containing lithium replenishment additives provided in other examples were similar to those of Examples 1 and 2, but all were significantly better than Comparative Example 1. The lithium replenishment capacity test shows that xLi6MO4·(1-x)Li2O material with antifluorite structure and crystal structure space group P42 / nmc

[137] can obtain a higher lithium replenishment capacity than the existing technology solution (Comparative Example 1) as a positive electrode lithium replenishment additive. At the same time, it obtains a lower first efficiency, that is, a lower reversible specific capacity, which makes the lithium replenishment efficiency higher. Meanwhile, xLi6MO4·(1-x)Li2O material has abundant reserves of some transition metals and is also more cost-effective than the existing market technology solution, and has a better market prospect.

[0163] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A lithium supplement additive, the lithium supplement additive comprising a core and a functional encapsulation layer covering the core, characterized in that: The core includes a lithium replenishing material, and the lithium replenishing material is a lithium-containing material with unidirectional capacity that allows lithium ions to be extracted during the first charge and does not allow lithium ions to be inserted during discharge; the unit cell of the lithium replenishing material is an antifluorite structure, and its crystal structure space group is P42 / nmc [137]; the lithium replenishing material includes the chemical formula xLi6MO4·(1-x)Li2O, wherein 0 < x < 1 in the chemical formula, and M includes at least one of Cr, Mn, Fe, Co, Ni, Cu, and Zn.

2. The lithium supplement additive according to claim 1, characterized in that: The functional encapsulation layer includes at least one of an ion conductor encapsulation layer and an electronic conductor encapsulation layer.

3. The lithium supplement additive according to claim 1 or 2, characterized in that: The particle size of the nucleus is 100nm-50μm.

4. The lithium supplement additive according to claim 2, characterized in that: The material of the electronic conductor encapsulation layer includes at least one of conductive carbon material, conductive polymer, or conductive oxide; and / or The material of the ion conductor encapsulation layer includes at least one of perovskite, NASICON, garnet, or polymer solid electrolytes; and / or The thickness of the electronic conductor encapsulation layer is 1-100 nm; and / or The thickness of the ion conductor encapsulation layer is 1-200 nm.

5. The lithium supplement additive according to claim 4, characterized in that: The electronic conductor encapsulation layer is made of conductive carbon material and lithium carbonate, and the electronic conductor encapsulation layer is in contact with the core.

6. The lithium supplement additive according to claim 5, characterized in that: The lithium carbonate content in the electronic conductor encapsulation layer is 0.5-1.5 wt%.

7. A method for preparing a lithium supplement additive, comprising the following steps: Provided a core material for lithium replenishment, the core material comprising a lithium replenishment material, the lithium replenishment material being a lithium-containing material with unidirectional capacity that undergoes lithium-ion desorption during the first charge and does not undergo lithium-ion insertion during discharge; the unit cell of the lithium replenishment material is an antifluorite structure with a crystal space group of P42 / nmc [137]; the lithium replenishment material comprises a material with the chemical formula xLi6MO4·(1-x)Li2O, wherein, In the chemical formula, 0 < x < 1, and M includes at least one of Cr, Mn, Fe, Co, Ni, Cu, and Zn; In a first protective atmosphere, a functional encapsulation layer is formed on the surface of the core material, such that the functional encapsulation layer completely covers the core material, thereby obtaining a lithium supplementation additive.

8. The preparation method according to claim 7, characterized in that, The formed functional encapsulation layer includes an electronic conductor encapsulation layer, and the method for forming the functional encapsulation layer on the surface of the core material includes the following steps: An electronic conductor encapsulation layer that fully covers the core material is formed on the surface of the core material; or The formed functional encapsulation layer includes an ion conductor encapsulation layer, and the method for forming the functional encapsulation layer on the surface of the core material includes the following steps: An ion conductor encapsulation layer that fully covers the core material is formed on the surface of the core material; or The formed functional encapsulation layer comprises a composite layer of an electronic conductor encapsulation layer and an ion conductor encapsulation layer. The method for forming the functional encapsulation layer on the surface of the core material includes the following steps: First, an electronic conductor encapsulation layer that fully covers the core material is formed on the surface of the core material; then, an ion conductor encapsulation layer is formed on the outer surface of the electronic conductor encapsulation layer. The material of the electronic conductor encapsulation layer includes at least one of conductive carbon material, conductive polymer or conductive oxide, and the material of the ion conductor encapsulation layer includes at least one of perovskite type, NASICON type, garnet type or polymer type solid electrolyte.

9. The preparation method according to claim 8, characterized in that, The material used to form the electronic conductor encapsulation layer includes a mixture of conductive carbon material and lithium carbonate; the method for forming the electronic conductor encapsulation layer includes the following steps: A conductive carbon coating layer is formed on the surface of the core material to fully cover the core material, and then heat treatment is performed in a protective atmosphere.

10. The preparation method according to any one of claims 7-8, characterized in that, The lithium supplement material of xLi6MO4·(1-x)Li2O is prepared by the following method: According to the elemental stoichiometry of xLi6MO4·(1-x)Li2O, the metal oxide of M is mixed with the lithium source to obtain the precursor of xLi6MO4·(1-x)Li2O; wherein, 0<x≤1 in the chemical formula, and M includes at least one of Cr, Mn, Fe, Co, Ni, Cu, and Zn. In a second protective atmosphere, the precursor is sintered to make the cell of xLi6MO4·(1-x)Li2O an antifluorite structure with a crystal space group of P42 / nmc [137].

11. The preparation method according to claim 10, characterized in that, The sintering treatment is performed at a temperature of 400-1000℃ for a time of 1-24 hours; and / or The sintering process is performed by heating to 400-1000℃ at a heating rate of 0.5-10℃ / min; and / or The second protective atmosphere is an atmosphere formed by any one of the protective gases selected from nitrogen, argon, a nitrogen-argon mixture, a nitrogen-hydrogen mixture, and an argon-hydrogen mixture; and / or The M metal oxide includes at least one selected from CrO, Cr2O3, CrO2, CrO3, MnO, Mn2O3, MnO2, Mn3O4, FeO, Fe2O3, Fe3O4, CoO, Co2O3, CoO2, Co3O4, NiO, Ni2O3, CuO, and ZnO; and / or The lithium source includes at least one of LiOH, LiOH·H2O, Li2O, Li2CO3, LiNO3, and LiAc.

12. An electrode sheet, comprising a current collector and an electrode active layer bonded to the surface of the current collector, characterized in that: The electrode active layer is doped with the lithium supplementation additive as described in any one of claims 1-6 or the lithium supplementation additive prepared by the preparation method described in any one of claims 7-11.

13. A secondary battery, comprising a positive electrode and a negative electrode, characterized in that: The positive or negative electrode is the electrode sheet as described in claim 12.

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