An air-stable positive electrode prelithiation material, a preparation method and application thereof

Abstract

The application belongs to the field of positive electrode pre-lithiation materials, and specifically discloses an air-stable positive electrode pre-lithiation material, a preparation method and application thereof, which comprises positive electrode pre-lithiation material particles, the surface of any single positive electrode pre-lithiation material particle is provided with a dense protective layer, the protective layer and the surface of the positive electrode pre-lithiation material particle are seamlessly attached, the protective layer is made of a high polymer formed by in-situ polymerization, the thickness of the protective layer is 5 nm-5 microns, the protective layer accounts for 0.01%-10% of the total mass of the air-stable positive electrode pre-lithiation material, and the protective layer is dense to isolate water and oxygen. The application also provides a preparation method and application thereof, and is used for adding in electrode materials to prepare lithium ion battery electrodes, and in operation, can release lithium ions to supplement the active lithium lost in the charging and discharging process of the battery. The material and method can provide efficient surface protection for air-sensitive positive electrode pre-lithiation materials and help the lithium ion transmission of the materials.

Description

Technical Field

[0001] This application belongs to the field of cathode pre-lithiation, and more specifically, relates to an air-stable cathode pre-lithiation material and its preparation method. Background Technology

[0002] With the rapid development of portable electronic devices and electric vehicles, developing lithium-ion batteries (LIBs) with higher energy density has become one of the core research goals. However, irreversible lithium loss during the first charge-discharge process, caused by the formation of a solid electrolyte interphase (SEI) film on the surface of the electrode active materials and interfacial side reactions, significantly reduces the actual reversible capacity and energy density of the battery. This SEI formation severely affects the electrochemical performance of the battery, leading to a decrease in energy density and cycle life.

[0003] Pre-storing additional lithium sources in the battery system can effectively compensate for the loss of active lithium (ALL) during cycling. Therefore, pre-lithiation is widely regarded as one of the most important and practical methods for next-generation LIBs, providing longer cycle life and higher energy density.

[0004] Sacrificial cathode prelithiation is considered a key strategy for improving battery energy density due to its ease of operation and compatibility with existing processes. Among these, high-lithium prelithiation materials (such as lithium-rich antifluorite compounds) are considered crucial for enhancing battery energy density due to their extremely high theoretical specific capacity, suitable operating potential, and low cost. However, these materials generally face serious environmental sensitivity challenges: the highly active lithium in their crystal structure readily undergoes irreversible reactions with water vapor (H2O) and carbon dioxide (CO2) in the air, leading to the rapid formation of an insulating lithium compound passivation layer (such as Li2CO3 and LiOH) on the surface. This not only blocks ion channels and consumes effective lithium sources but also causes a sharp decline in the release of active lithium.

[0005] Taking the lithium-rich material Li5FeO4 (LFO) as an example, the lithium-rich material Li5FeO4 (LFO) stands out due to its unique advantages: up to 867 mAh g⁻¹. - ¹ Its extremely high theoretical specific capacity far exceeds that of mainstream pre-lithiation reagents, and its electrochemical window is 3.55~4.3 V, which is a perfect match for LiFePO4 and ternary cathodes. The high abundance of iron in the Earth's crust makes its cost low, and its decomposition products have environmentally friendly properties. The lithium migration barrier of the anti-fluorite structure three-dimensional ion channel is only 0.35 eV. These multiple advantages make it one of the most promising candidate materials for application.

[0006] However, the practical application of LFO is severely limited by its environmental sensitivity: its crystal structure contains highly active [Li4O] tetrahedral units, and exposed Li + It readily undergoes an irreversible reaction with H2O / CO2 in the air: Li5FeO4+H2O→LiFeO2+2LiOH+1 / 2H2↑ LiOH + CO2 → Li2CO3 + H2O The aforementioned reaction leads to the formation of an insulating Li₂CO₃ / LiOH passivation layer on the surface, blocking lithium-ion diffusion channels and consuming active lithium. Studies have shown that even after short-term exposure to environmental conditions, the specific capacity of LFO decreases sharply (retention rate ≤50%). This extreme environmental sensitivity necessitates strict humidity control during the entire process of LFO material production, from post-synthesis storage and electrode slurry preparation (which typically involves wet stirring and coating) to battery assembly. This significantly increases production costs and fundamentally limits the feasibility of its large-scale production and commercial application.

[0007] This type of chemical instability caused by high lithium content is not unique to LFO, but rather a serious challenge faced by many high-capacity pre-lithiated materials (such as lithium-rich systems like Li6CoO4, Li6MnO4, Li6NiO4, and Li2O) during storage, electrode fabrication, and battery assembly. Existing processes often rely on strictly inert atmospheres or ultra-low humidity environments to avoid material degradation, which significantly increases production complexity and cost, fundamentally limiting their large-scale application.

[0008] Furthermore, coating methods are frequently used to modify these materials, but common surface coating methods (such as carbon coating and inorganic physical coating) have not completely solved this problem. Conventional physical coatings consist of small, discontinuous, and non-dense particles, making them difficult to effectively block H2O / CO2. While conventional carbon coating can form a dense layer, the reducing properties of the carbon source during the high-temperature coating process can lead to the reduction of transition metals in Li6CoO4, Li6NiO4, Li6MnO4, and Li5FeO4, such as Co in Li6CoO4. 2+ Ni in Li6NiO4 2 + Mn in Li6MnO4 2+ Fe in Li5FeO4 3+ This can damage the material structure and cause it to fail. Therefore, to overcome the application bottlenecks of materials such as Li6CoO4, Li6NiO4, Li6MnO4, and Li5FeO4, the key lies in developing a modification method that can simultaneously achieve surface passivation and ensure rapid lithium-ion transport. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this application is to provide an air-stable cathode pre-lithiation material, its preparation method, and its application. The aim is to provide a modification method that offers efficient surface protection and ensures rapid lithium-ion transport for lithium-rich materials such as Li5FeO4, Li6CoO4, Li6NiO4, and Li6MnO4.

[0010] To achieve the above objectives, in a first aspect, this application provides an air-stable cathode pre-lithiation material, comprising cathode pre-lithiation material particles. Each individual cathode pre-lithiation material particle has a dense protective layer conformally shaped to its surface. The protective layer is seamlessly bonded to the surface of the cathode pre-lithiation material particle. The protective layer is made of a polymer formed by in-situ polymerization, with a thickness of 5 nm to 5 μm. The protective layer accounts for 0.01% to 10% of the total mass of the cathode pre-lithiation material. The protective layer is dense enough to isolate gases and water. The gases include air, oxygen, carbon dioxide, and other gases that may affect the stability of the cathode pre-lithiation material particles.

[0011] In the above-described inventive concept, each individual cathode pre-lithiation material particle has a dense protective layer conformally shaped to its surface, effectively isolating each particle from water and oxygen, thus achieving maximum possible surface passivation. The protective layer thickness ranges from 5 nm to 5 μm, offering a wide range of thicknesses that can be flexibly and controllably prepared to meet specific engineering needs. The protective layer accounts for only 0.01% to 10% of the total mass of the air-stable cathode pre-lithiation material. Given its relatively small proportion, the introduction of the protective layer does not significantly affect the overall properties and performance of the cathode pre-lithiation material.

[0012] It is important to clarify here that the protective layer material is a polymer formed through in-situ polymerization. It must be in-situ polymerized; only in-situ polymerization can form a continuous protective layer, and only in-situ polymerization can create a dense, shape-adaptive protective layer that fully covers the particle surface. Fully coating means that external oxygen and moisture can easily penetrate and corrode the cathode pre-lithiation material particles. Furthermore, in-situ polymerized polymers are usually amorphous, making them more conductive for lithium, and their thickness is controllable and uniform; even a very thin layer can form a complete protection. The in-situ polymerization process is easy to control; for example, the composition and thickness of the protective layer can be adjusted by controlling the temperature, the amount of initiator, and the stirring speed.

[0013] In more detail, in-situ polymerization offers several advantages: During in-situ polymerization, monomers polymerize directly on the material surface, resulting in a polymer layer that bonds tightly to the substrate without interfacial gaps. This allows for dense and seamless conformal coating, effectively blocking the penetration of corrosive gases or electrolytes. Because the polymerization reaction occurs on the material surface, the resulting polymer layer perfectly conforms to the microstructure of particles or interfaces, achieving conformal coverage. Even on complex surfaces, it forms a defect-free, dense protective layer, thus completely preventing external media from eroding the internal material. In-situ polymerization typically produces amorphous polymers with a relatively loose molecular arrangement, which is beneficial for lithium-ion conduction. Furthermore, by adjusting the reaction conditions, precise control of the protective layer thickness can be achieved, forming a uniform and complete protective layer even at extremely thin (e.g., nanoscale) thicknesses, balancing lithium conductivity and barrier properties. During in-situ polymerization, the composition, crosslinking degree, thickness and morphology of the polymer layer can be actively controlled by adjusting key parameters such as reaction temperature, initiator dosage and stirring speed, thereby optimizing the protection effect for different material systems and exhibiting good process adaptability and repeatability.

[0014] In practical engineering, some polymer protective layers are inherently lithium-conducting and can be used directly without limiting the impact on the cathode pre-lithiation material. Other polymer protective layers are not lithium-conducting and act like a protective garment on the surface of the cathode pre-lithiation material particles, isolating them from water and oxygen while hindering lithium-ion conduction. For non-lithium-conducting protective layers, an electrolyte capable of dissolving the protective layer material should be selected and assembled into the lithium-ion battery before use. During the battery's first operation, the electrolyte naturally dissolves the non-lithium-conducting protective layer, exposing the cathode pre-lithiation material itself, thus achieving air stability and lithium replenishment capability.

[0015] Furthermore, the protective layer material is selected from one or more of polycarbonates, polyethers, polyacrylates, polysiloxanes, and polysulfides. Specifically, it includes polyamides, polycarbonates, polyoxymethylene, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polypropylene oxide, polyethylene oxide, polytetrahydrofuran, polypropylene carbonate, polyethylene carbonate, polypropylene carbonate, polyvinyl carbonate, polyethylene carbonate, polyethylene oxide, polyethylene oxide, polyethylene glycol diacrylate, polyacrylic acid, polymethyl methacrylate, polyvinylidene fluoride, and polydimethylsiloxane.

[0016] Among them, polycarbonates are polymerized from one or more of monomers such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, etc. Polyethers are polymerized from one or more of monomers such as 1,3-dioxolane, tetrahydrofuran, ethylene oxide, propylene oxide, trioxane, etc. Polyacrylates are polymerized from one or more of monomers such as methyl acrylate, ethyl acrylate, trifluoroethyl methacrylate, acrylonitrile, etc. Polysiloxanes are polymerized from one or more of monomers such as organochlorosilane, methylchlorosilane, dimethyldichlorosilane, methylphenyldichlorosilane, methyltrimethoxysilane, methyltriethoxysilane, octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, hexamethyldisiloxane, etc. Polysulfates are polymerized from monomers such as ethylene sulfate, propylene sulfate, fluoroethylene sulfate, vinylene sulfate, 1,3,2-dioxathiolane-2,2-dioxide and its derivatives, etc.

[0017] The protective layer material has good film-forming properties and can be in-situ polymerized by an initiator. Whether it can conduct lithium or not can be adopted. For materials that cannot conduct lithium, they can be modified by adding lithium salts to make them have the ability to conduct lithium.

[0018] Furthermore, the positive electrode prelithiation material is selected from any one or more of Li5FeO4, Li8FeO6, Li6FeO4, Li3FeO4, LiFeO2, Li2FeO2, Li6CoO4, Li2CoO3, Li8CoO6, Li2CoO2, Li2MnO3, Li2MnO2, Li6MnO4, Li5Mn2O7, Li2NiO2, Li2NiO3, Li3N, Li2O2 and Li2O, or the positive electrode prelithiation material is a lithium salt of multiple metals Li （1+a） M x N （1-x） O b where 0 < x < 1, 0 < a ≤ 10, 2 ≤ b ≤ 6, O is oxygen element, M and N are different metal elements, and M and N are respectively selected from one of Zr, V, Fe, Mn, Ni and Co. For example, the lithium salt of multiple metals is Li6Ni 0.5 Mn 0.5 O4, Li6Co 0.3 Mn 0.7 O4 and Li 5.5 Fe 0.5 Mn 0.5 O4, etc.

[0019] According to the second aspect of the present invention, a method for preparing the positive electrode prelithiation material as described above is further provided, which includes the following steps: S1: Dissolve the precursor of the polymer protective layer in the first solvent to obtain a precursor solution. Dissolve the initiator in the second solvent, then add the positive electrode pre-lithiation material particles and disperse them evenly to attach the initiator to the surface of the positive electrode pre-lithiation material particles to obtain a suspension. The first and second solvents are miscible. S2: Stir and heat the suspension to the set temperature, maintain the temperature and stir continuously, and gradually add the precursor solution. Under the action of the initiator, the precursor of the polymer protective layer self-polymerizes in situ on the surface of the positive electrode pre-lithiation material particles to form a dense protective layer that can isolate water and oxygen. The heat preservation temperature is 10℃~100℃, and the continuous heat preservation and stirring time is 6 h~24 h. S3: Separate the reaction product, wash and dry it to obtain positive electrode pre-lithiation material particles with a dense protective layer on the surface.

[0020] In the above-mentioned methods, the initiator includes anionic initiators, alkali metal alkoxides, organic bases, phosphide anionic initiators, cationic initiators, and complexing initiators. The polymer precursor is selected based on the material of the polymer protective layer, choosing its corresponding monomer and an initiator that can promote its polymerization into a film. The initiator is selected based on the chosen polymer precursor solution; the specific initiator is not limited.

[0021] Furthermore, the precursor of the polymer protective layer is dissolved in the first solvent to obtain a precursor solution. A lithium salt is added to the precursor solution. The amount of lithium salt added is 1%-10% of the total weight of the air-stable positive electrode pre-lithiation material to provide the lithium conduction performance of the protective layer. The lithium salt is selected from one or more of LiPF6, LiBF4, LiBOB, LiDFOB, LiTFSI, LiFSI, and LiPO2F2.

[0022] Furthermore, in step S1, the first solvent and the second solvent are the same solvent.

[0023] Furthermore, the first solvent and the second solvent are respectively selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), 1,2-dimethoxypropane (DMP), dimethoxymethane (DMM), ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-Me-THF), methyl formate (MF), methyl acetate (MA), methyl butyrate (MB), and ethyl propionate (EP). The first solvent is used to dissolve the precursor of the polymer protective layer, and monomers forming polycarbonate, polyether, polyacrylate, and polysiloxane may become precursors of the polymer protective layer.

[0024] Furthermore, in step S2, during the continuous heat preservation and stirring, the stirring is mechanical stirring or ultrasonic vibration stirring at 200 rpm to 2000 rpm. Stirring or vibration stirring at 200 rpm to 2000 rpm is beneficial for the contact and reaction between the initiator and the precursor, and for the in-situ polymerization of organic polymer to form a protective layer on the surface of the positive electrode pre-lithiation material.

[0025] According to a third aspect of the invention, the application of the cathode pre-lithiation material as described above is also provided, which is used to add to the cathode material to prepare a lithium-ion battery cathode. In operation, the air-stable cathode pre-lithiation material releases its own lithium ions to compensate for the loss of active lithium during battery charging and discharging.

[0026] Furthermore, when the protective layer itself can conduct lithium ions, it can be directly added to the positive electrode material to prepare a lithium-ion battery positive electrode. Alternatively, when the protective layer itself cannot conduct lithium ions, an electrolyte that can dissolve the protective layer can be selected to assemble a lithium-ion battery. When the battery is working, the electrolyte naturally dissolves the protective layer to expose the positive electrode pre-lithiation material particles, thereby assisting the positive electrode pre-lithiation material in releasing its own lithium ions to compensate for the loss of active lithium during battery charging and discharging.

[0027] This invention utilizes a polymer film to coat pre-lithiated cathode material particles, breaking through traditional understanding. Traditional methods often employ physical coating, which is ineffective at blocking the attack of water and carbon dioxide from the air. While carbon coatings can isolate air, the high-temperature preparation process (>600℃) damages the pre-lithiated material structure, reducing lithium replenishment efficiency. Furthermore, the porous nature of carbon materials can absorb moisture in humid environments, accelerating the degradation of the pre-lithiated material. Although carbon coatings improve electronic conductivity, the resulting continuous conductive network hinders the selective release of lithium ions, causing the pre-lithiated material to lose its lithium replenishment function. Traditional methods abandon organic coating because it is conventionally believed that pre-lithiated materials must be exposed to release lithium ions, and continuous organic coatings would impede lithium release. This invention eliminates this concern by adding lithium salts to a non-lithium-conducting protective layer, enabling the release of lithium ions.

[0028] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: (1) The method in this invention application is to coat microscopic individual particles to form a shell structure, which is a protective layer at the nanometer to micrometer scale with a thickness of tens of nanometers to several micrometers. A polymer film is used for coating, and the polymer protective layer has excellent chemical stability, strong interfacial bonding with the electrode material, appropriate mechanical strength, and controllable polymerization process.

[0029] Polymer film coating differs from conventional carbon coating and inorganic coating. Polymer protective layer coating offers numerous advantages, such as superior interfacial properties and structural stability. Polymer films typically possess better flexibility and adhesion, enabling them to form tight interfacial contact with active material particles, effectively buffering volume changes during charge and discharge. Their molecular structure is highly designable; specific functional groups can be introduced to achieve chemical bonding with the particle surface, enhancing the stability and integrity of the coating layer. The functional designability and comprehensive performance of polymer protective layers are outstanding. Through molecular structure design, multifunctional integration can be achieved. It can adjust electronic conductivity, maintain electronic insulation to avoid side reactions, and introduce lithium-ion transport channels by adding lithium salts. Simultaneously, it exhibits good electrolyte wettability and chemical stability, effectively inhibiting transition metal dissolution and electrode material corrosion, providing comprehensive protection for electrode materials. The process adaptability and application potential of polymer protective layers are significant. The lower formation temperature of polymer protective layers avoids the damage to the material structure caused by high-temperature processing. The thickness of the protective layer can be precisely controlled by the polymerization conditions to achieve uniform nanoscale coating. The protective layer is compatible with existing battery manufacturing processes, and some polymer materials can be used as binders to simplify the electrode preparation process.

[0030] (2) The preparation method of the present invention is simple. The precursor of the polymer protective layer is dissolved in the first solvent to obtain the precursor solution. The initiator is dissolved in the second solvent, and then the positive electrode pre-lithiation material particles are added and dispersed evenly to attach the initiator to the surface of the positive electrode pre-lithiation material particles to obtain a suspension. Under the action of the initiator, the precursor of the polymer protective layer is self-polymerized in situ on the surface of the positive electrode pre-lithiation material particles to form a dense protective layer that can isolate water and oxygen. The in situ self-polymerization of the surface can realize the conformal coating and tight adhesion of the protective layer. Attached Figure Description

[0031] Figure 1a This is a SEM image of pre-lithiated cathode material particles with a dense protective layer; Figure 1b This is a SEM image of the original pre-lithiated cathode material particles without a protective layer; Figure 2 This is a SEM image of the edge of the positive electrode pre-lithiation material particles in Example 1; Figure 3 This is a comparison chart of thermogravimetric analysis of pre-lithiated cathode material particles and uncoated pure Li5FeO4 in Example 1; Figure 4 The performance comparison curves of the batteries in Comparative Example 1 and Example 6 are shown. Figure 5a It is a curve showing the charging capacity of a Li5FeO4 material without an in-situ polymer protective layer after being exposed to an environment with an air humidity of 20% for a certain period of time and then charged to 4.5 V for a lithium half-cell. Figure 5b It is a curve showing the charging capacity of a Li5FeO4 material with an in-situ polymer protective layer after being exposed to an environment with an air humidity of 20% for a certain period of time and then charged to 4.5 V for a lithium half-cell. Figure 6a The XRD pattern is the image of Li5FeO4 before it is coated and then exposed to an environment with an air humidity of 20% for a certain period of time. Figure 6b The XRD pattern is obtained after Li5FeO4 coating is exposed to an environment with an air humidity of 20% for a certain period of time. Figure 7 These are photographs showing the color changes of different pre-lithiated materials before and after they were in situ coated with a polyvinyl carbonate protective layer. Figure 8 Infrared spectra of Li2O, NCM, and Li2NiO2 materials with polyvinyl carbonate protective layers. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0033] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0034] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0035] The embodiments of this application are described below with reference to the accompanying drawings. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0036] Example 1 This embodiment prepares an air-stable pre-lithiated cathode material and performs testing and characterization on it. In this embodiment, the polymer protective layer itself has lithium-conducting properties.

[0037] This embodiment includes the following steps: S1: The precursor vinylene carbonate, used for the polymer protective layer, is dissolved in the first solvent, tetrahydrofuran (THF), to obtain a precursor solution with a concentration of 0.5 g / ml. -1 The initiator azobisisobutyronitrile (AIBN) was dissolved in the second solvent 2-methyltetrahydrofuran (2-Me-THF), and then positive electrode pre-lithiation material particles, specifically Li5FeO4, with an average particle size of 5 μm (the particle size of a single particle is approximately 1 μm to 11 μm), were added. The ratio of the initiator, the positive electrode pre-lithiation material particles, and the second solvent was 1 g: 2 g: 10 ml. The mixture was stirred to ensure uniform dispersion of the positive electrode pre-lithiation material particles and to attach the initiator to the surface of the particles, thus obtaining a suspension.

[0038] S2: Stir and heat the suspension to the set temperature of 100 °C. Maintain this temperature and stir continuously while gradually adding the precursor solution, with a precursor solution to suspension mass ratio of 5:1. The precursor of the polymer protective layer polymerizes in situ on the surface of the pre-lithiated cathode material particles under the action of the initiator, forming a dense protective layer that isolates water and oxygen. Maintain this temperature and stir continuously for 24 hours, using mechanical stirring at 200 rpm or ultrasonic vibration stirring.

[0039] S3: Separate the product obtained from the reaction, wash it with dimethyl ethylene glycol (DME), and then dry it in a vacuum oven at a temperature of 80°C.

[0040] In this embodiment, positive electrode pre-lithiation material particles with a dense protective layer of polyvinyl carbonate on a conformal surface are obtained. Figure 1a This is a SEM image of pre-lithiated cathode material particles with a dense protective layer; Figure 1b This is a SEM image of the original pre-lithiated cathode material particles without a protective coating. Figure 2 The image shows an SEM image of the edge of the positive electrode pre-lithiation material particles in Example 1. Combining the two images, it can be seen that the surface of any single positive electrode pre-lithiation material particle has a dense protective layer that conforms to the shape, and the protective layer and the surface of the positive electrode pre-lithiation material particle are seamlessly attached.

[0041] Using TEM, the thickness of the protective polyvinyl carbonate layer was found to be 20 nm. Figure 3 This is a comparison chart of thermogravimetric analysis of the cathode pre-lithiation material particles and uncoated pure Li5FeO4 in Example 1. The comparison shows that, after thermogravimetric analysis, the mass of the protective layer accounts for 1% of the total mass of the air-stable cathode pre-lithiation material.

[0042] Using in-situ XRD, it was found that the dense protective layer can indeed isolate water and oxygen. The specific test results are as follows: after exposure for 50 h in an environment with air humidity ≤20%, the peak intensity of XRD remains almost unchanged and no new impurity peaks appear.

[0043] Example 2 This embodiment prepares an air-stable pre-lithiated cathode material and performs testing and characterization on it. In this embodiment, the polymer protective layer itself does not have lithium-conducting properties; instead, it is doped with a lithium salt to give it lithium-conducting capabilities.

[0044] S1: Dissolve ethylene carbonate, the precursor of the polymer protective layer, in the first solvent, dimethyl glycol ether (DME), to obtain a precursor solution with a concentration of 0.5 g / ml. -1 A lithium salt, specifically 0.2 g of LiTFSI, is added to the precursor solution. The amount of lithium salt added is 10% of the total weight of the air-stable cathode pre-lithiation material.

[0045] The initiator Li2S8 was dissolved in the second solvent, dimethyl carbonate (DMC), and then pre-lithiated cathode material particles, specifically Li2NiO2, with a particle size of 11 μm, were added. The ratio of the initiator, the pre-lithiated cathode material particles, and the second solvent was 1 g: 2 g: 10 ml.

[0046] Stirring is used to disperse the positive electrode pre-lithiation material particles evenly and to attach the initiator to the surface of the positive electrode pre-lithiation material particles to obtain a suspension.

[0047] S2: Stir and heat the suspension to the set temperature of 10 °C. Maintain this temperature and stir continuously while gradually adding the precursor solution at a mass ratio of 5:1 (precursor solution to suspension). Under the action of the initiator, the precursor of the polymer protective layer undergoes in-situ self-polymerization on the surface of the pre-lithiated cathode material particles, forming a dense protective layer that isolates water and oxygen. Maintain this temperature and stir continuously for 24 hours. Stirring is performed using mechanical stirring at 2000 rpm or ultrasonic vibration.

[0048] S3: Separate the product obtained from the reaction, wash it with dimethyl ethylene glycol (DME), and then dry it in a vacuum oven at a temperature of 80°C.

[0049] In this embodiment, cathode pre-lithiation material particles with a dense protective layer conforming to the surface were obtained. SEM images show that each individual cathode pre-lithiation material particle has a dense protective layer conforming to the surface, and the protective layer is seamlessly attached to the surface of the cathode pre-lithiation material particle.

[0050] Using TEM, the thickness of the protective polyethylene carbonate layer was found to be 50 nm. Thermogravimetric analysis showed that the mass of the protective layer accounted for 0.1% of the total mass of the air-stable cathode pre-lithiation material.

[0051] Using in-situ XRD, it was found that the dense protective layer can indeed isolate water and oxygen. Specifically, the peak intensity of XRD remained almost unchanged and no new impurity peaks appeared after 50 hours of exposure in an environment with air humidity ≤20%.

[0052] Example 3 The difference between this embodiment and Embodiment 1 is that in step S1, the precursor ethylene oxide of the polymer protective layer is dissolved in the first solvent to obtain a precursor solution. Both the second solvent and the first solvent are dimethoxymethane, and the positive electrode pre-lithiation material is Li6CoO4 with a particle size of 7μm.

[0053] In this embodiment, cathode pre-lithiation material particles with a dense protective layer conforming to the surface were obtained. SEM images show that each individual cathode pre-lithiation material particle has a dense protective layer conforming to the surface, and the protective layer is seamlessly attached to the surface of the cathode pre-lithiation material particle.

[0054] Using TEM, the thickness of the protective layer was found to be 1 μm. After thermogravimetric analysis, the mass of the protective layer accounted for 5% of the total mass of the air-stable cathode pre-lithiation material.

[0055] Using in-situ XRD, it was found that the dense protective layer can indeed isolate water and oxygen. Specifically, after exposure to an environment with air humidity ≤20% for 50 h, the peak intensity of XRD remained almost unchanged and no new impurity peaks appeared.

[0056] Example 4 This embodiment prepares an air-stable pre-lithiated cathode material and performs testing and characterization on it. In this embodiment, the polymer protective layer itself does not have lithium-conducting properties, nor is it modified by lithium salt doping, and it does not provide lithium-ion transport channels.

[0057] This embodiment includes the following steps: S1: The precursor methyl methacrylate, used for the polymer protective layer, is dissolved in the first solvent, diethyl carbonate (DEC), to obtain a precursor solution with a concentration of 0.5 g / mL. -1 Sodium hydroxide, the initiator, is dissolved in ethyl methyl carbonate (EMC) as the second solvent. Then, pre-lithiated cathode material particles, specifically Li₂O with a particle size of 500 nm, are added. The ratio of initiator, pre-lithiated cathode material particles, and the second solvent is 1 g: 2 g: 10 mL. The mixture is stirred to ensure uniform dispersion of the pre-lithiated cathode material particles and to attach the initiator to the surface of the particles, resulting in a suspension.

[0058] S2: Stir and heat the suspension to the set temperature of 50 °C. Maintain this temperature and stir continuously while gradually adding the precursor solution at a mass ratio of 5:1 (precursor solution to suspension). Under the action of the initiator, the precursor of the polymer protective layer undergoes in-situ self-polymerization on the surface of the pre-lithiated cathode material particles, forming a dense protective layer that isolates water and oxygen. Maintain this temperature and stir continuously for 6 hours. Stirring is performed using mechanical stirring at 300 rpm or ultrasonic vibration.

[0059] S3: Separate the product obtained from the reaction, wash it with ethyl methyl carbonate (EMC), and then dry it in a vacuum oven at a temperature of 80°C.

[0060] In this embodiment, cathode pre-lithiation material particles with a conformal surface and a dense protective layer were obtained. SEM images show that each individual cathode pre-lithiation material particle has a conformal surface with a dense protective layer, and the protective layer is seamlessly bonded to the surface of the cathode pre-lithiation material particle.

[0061] Using TEM, the thickness of the protective polymethyl methacrylate layer was found to be 5 nm. Thermogravimetric analysis showed that the mass of the protective layer accounted for 0.01% of the total mass of the air-stable cathode pre-lithiation material.

[0062] Using in-situ XRD, it was found that the dense protective layer of polymethyl methacrylate can indeed isolate water and oxygen. Specifically, the peak intensity of XRD remained almost unchanged and no new impurity peaks appeared after 50 h of exposure in an environment with air humidity ≤20%.

[0063] Example 5 This embodiment prepares an air-stable pre-lithiated cathode material and performs testing and characterization on it. In this embodiment, the polymer protective layer itself has lithium-conducting properties.

[0064] This embodiment includes the following steps: S1: The precursor ethylene oxide, used for the polymer protective layer, is dissolved in the first solvent, ethylene carbonate (EC), to obtain a precursor solution with a concentration of 0.5 g / mL. -1 Sodium hydroxide, the initiator, is dissolved in propylene carbonate (PC) as the second solvent, and then pre-lithiated cathode material particles, specifically Li6MnO4, with a particle size of 10 μm, are added. The ratio of the initiator, the pre-lithiated cathode material particles, and the second solvent is 1 g : 1 g : 5 ml.

[0065] Stirring is used to disperse the positive electrode pre-lithiation material particles evenly and to attach the initiator to the surface of the positive electrode pre-lithiation material particles to obtain a suspension.

[0066] S2: Stir and heat the suspension to the set temperature of 70°C. Maintain this temperature and stir continuously while gradually adding the precursor solution at a mass ratio of 5:1 (precursor solution to suspension). Under the action of the initiator, the precursor of the polymer protective layer undergoes in-situ self-polymerization on the surface of the pre-lithiated cathode material particles, forming a dense protective layer that isolates water and oxygen. Maintain this temperature and stir continuously for 12 hours. Stirring is performed using mechanical stirring at 1500 rpm or ultrasonic vibration.

[0067] S3: The product obtained from the reaction is separated, washed with ethylene carbonate (EC), and then dried in a vacuum oven at a temperature of 80 °C.

[0068] In this embodiment, cathode pre-lithiation material particles with a conformal surface and a dense protective layer were obtained. SEM images show that each individual cathode pre-lithiation material particle has a conformal surface with a dense protective layer, and the protective layer is seamlessly bonded to the surface of the cathode pre-lithiation material particle.

[0069] TEM analysis revealed that the protective polyethylene oxide layer was 50 nm thick. Thermogravimetric analysis showed that the protective layer accounted for 3% of the total mass of the air-stable pre-lithiation cathode material.

[0070] Using in-situ XRD, it was found that the dense protective layer can indeed isolate water and oxygen. Specifically, the peak intensity of XRD remained almost unchanged and no new impurity peaks appeared after 50 hours of exposure in an environment with air humidity ≤20%.

[0071] In fact, the first and second solvents can also be one or more of 1,2-dimethoxypropane, methyl formate, methyl acetate, methyl butyrate, and ethyl propionate. All of these solvents can dissolve the precursor or initiator of the polymer protective layer and are similar and compatible with each other.

[0072] In Example 2, a lithium salt, specifically LiTFSI, was added to the first solvent. However, the lithium salt could also be one or more of LiPF6, LiBF4, LiBOB, LiDFOB, LiTFSI, LiFSI, and LiPO2F2. All of these lithium salts possess lithium-ion conductivity and can be incorporated into the first solvent, ultimately forming a protective layer that imparts lithium conductivity to the protective layer.

[0073] In Examples 1 to 5, the cathode pre-lithiation material particles are Li5FeO4, Li2NiO2, Li6CoO4, Li2O, and Li6MnO4, respectively. In practice, the cathode pre-lithiation material can also be selected from any one or more of Li8FeO6, Li6FeO4, Li3FeO4, LiFeO2, Li2FeO2, Li2CoO3, Li8CoO6, Li2CoO2, Li2MnO3, Li2MnO2, Li5Mn2O7, Li2NiO3, Li3N, and Li2O2. The above-mentioned optional cathode pre-lithiation material particles and Li5FeO4, Li6NiO2, Li2MnO4, and Li6MnO4 are all suitable for this purpose. i2NiO2, Li6CoO4, Li2O, and Li6MnO4 all share similar properties, such as a high lithium molar ratio, a significantly higher molar fraction of lithium in their chemical composition compared to conventional cathode active materials, thermodynamic instability (easily reacting with the environment), strong oxy- and hydrophilic properties, and readily reacting with moisture (H2O) and carbon dioxide (CO2) when exposed to air. They do not contain corrosive elements such as fluorine and chlorine, nor do they contain volatile or toxic components. They also do not have chemical conflicts with commonly used cathode matrix materials (LiCoO2, NCM, LFP), binders (PVDF, PAA), and conductive agents (carbon black, CNT).

[0074] In Examples 1 to 5, the protective layer materials are respectively: polyvinyl carbonate, polyethylene carbonate, polyethylene oxide, polymethyl methacrylate, and polyethylene oxide. In practice, the protective layer material can also be selected from the following: polyamide, polycarbonate, polyoxymethylene, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polypropylene oxide, polytetrahydrofuran, polypropylene carbonate, polypropylene carbonate, polyethylene carbonate, polypropylene oxide, polyethylene glycol diacrylate, polyacrylic acid, polyvinylidene fluoride, and polydimethylsiloxane. Polymers that meet the following conditions are generally suitable protective layer materials: (1) Excellent water and oxygen barrier properties, which can effectively isolate H2O and CO2 in the air and prevent hydrolysis and carbonation of pre-lithiation materials; (2) Good chemical stability, which does not react chemically with pre-lithiation materials (lithium-rich compounds such as Li5FeO4 and Li2NiO2) and does not introduce acidic / basic groups (to avoid catalyzing the decomposition of pre-lithiation materials); (3) Easy film formation, which can form a uniform film on the surface of pre-lithiation material particles through conventional processes such as solution coating (such as dip coating and spray coating), in-situ polymerization (such as interface polymerization and photocuring), and melt coating; (4) Dispersion compatibility: It has good compatibility with the positive electrode slurry system (solvents such as NMP and water), and does not gel, separate, or precipitate after dissolution or dispersion. It can be uniformly mixed with pre-lithiation material particles, positive electrode active materials, etc.

[0075]

[0076] In the table, the mass percentage refers to the proportion of the protective layer mass to the total mass of the positive electrode pre-lithiation material.

[0077] Example 20 In this embodiment, the positive electrode pre-lithiation material prepared in Example 1 is added to the positive electrode material to prepare a lithium-ion battery positive electrode. The specific preparation method is as follows: the positive electrode pre-lithiation material prepared in Example 1 is added to the positive electrode slurry to obtain a mixed slurry. The mass ratio of the mixed slurry is: lithium iron phosphate (LFP): polyvinylidene fluoride (PVDF): conductive carbon = 8:1:1. The obtained slurry is uniformly coated on aluminum foil, and then cut into circular positive electrode sheets with a diameter of 10 mm. The positive electrode shell, spring sheet, gasket, positive electrode sheet, separator, lithium sheet, and negative electrode shell are then assembled into a coin cell, and its charge / discharge capacity is tested in an electrochemical workstation. During operation, the air-stable positive electrode pre-lithiation material releases its own lithium ions to compensate for the lithium loss in the positive electrode. The battery performance is: the first-cycle charging capacity in a lithium iron phosphate-lithium half-cell is 235 mAh g. -1 .

[0078] Example 21 In this embodiment, the positive electrode pre-lithiation material prepared in Example 4 is added to the positive electrode material to prepare a lithium-ion battery positive electrode. The specific preparation method is as follows: the positive electrode pre-lithiation material prepared in Example 1 is added to the positive electrode slurry to obtain a mixed slurry. The formula of the mixed slurry is lithium iron phosphate (LFP): polyvinylidene fluoride (PVDF): conductive carbon = 8:1:1. The obtained slurry is uniformly coated on aluminum foil, and then cut into circular positive electrode sheets with a diameter of 10 mm. Then, the positive electrode shell, spring sheet, gasket, positive electrode sheet, separator, lithium sheet, and negative electrode shell are assembled into a coin cell, and its charge and discharge capacity is tested in an electrochemical workstation. The electrolyte is an electrolyte with ethyl methyl carbonate (EMC) as the solvent, which can dissolve the protective layer polymethyl methacrylate.

[0079] During operation, the air-stable pre-lithiated cathode material releases its own lithium ions to compensate for lithium loss from the cathode. The battery performance is a first-cycle charge capacity of 220 mAh g in a lithium iron phosphate-lithium half-cell configuration. -1 .

[0080] Example 22 In this embodiment, the prepared positive electrode pre-lithiation material is added to the positive electrode material to prepare a lithium-ion battery positive electrode. The specific preparation method is as follows: the polycarbonate-coated Li6FeO4 positive electrode pre-lithiation material prepared in Example 7 is added to the positive electrode slurry to obtain a mixed slurry. The formulation of the mixed slurry is: lithium iron phosphate (LFP): polyvinylidene fluoride (PVDF): conductive carbon = 7:1:2. The obtained slurry is uniformly coated on aluminum foil, and then cut into circular positive electrode sheets with a diameter of 10 mm. The positive electrode shell, spring sheet, gasket, positive electrode sheet, separator, lithium sheet, and negative electrode shell are then assembled into a coin cell, and its charge / discharge capacity is tested in an electrochemical workstation. The electrolyte used is a tetrahydrofuran (THF) solvent and LTFSI solute, which can dissolve the protective polycarbonate layer.

[0081] During operation, the air-stable pre-lithiated cathode material releases its own lithium ions to compensate for lithium loss from the cathode. The battery performance is as follows: 223 mAh g⁻¹ in the first charge cycle of a lithium iron phosphate-lithium half-cell. -1 .

[0082] Example 23 In this embodiment, the prepared positive electrode pre-lithiation material is added to the positive electrode material to prepare a lithium-ion battery positive electrode. The specific preparation method is as follows: the polyphenylene ether-coated Li8CoO6 positive electrode pre-lithiation material prepared in Example 11 is added to the positive electrode slurry to obtain a mixed slurry. The formula of the mixed slurry is lithium iron phosphate (LFP): polyvinylidene fluoride (PVDF): conductive carbon = 6:1:3. The obtained slurry is uniformly coated on aluminum foil, then cut into circular positive electrode sheets with a diameter of 10 mm. The positive electrode shell, spring sheet, gasket, positive electrode sheet, separator, lithium sheet, and negative electrode shell are then assembled into a coin cell, and its charge / discharge capacity is tested in an electrochemical workstation. The electrolyte used is a solvent containing chloroform and a solute of LiPF6, which can dissolve the protective polyphenylene ether layer.

[0083] During operation, the air-stable pre-lithiated cathode material releases its own lithium ions to compensate for lithium loss from the cathode. The battery performance is a first-cycle charge capacity of 213 mAh g in a lithium iron phosphate-lithium half-cell configuration. -1 .

[0084] Example 24 In this embodiment, the prepared positive electrode pre-lithiation material is added to the positive electrode material to prepare a lithium-ion battery positive electrode. The specific preparation method is as follows: the polyvinyl sulfate-coated Li2NiO3 positive electrode pre-lithiation material prepared in Example 16 is added to the positive electrode slurry to obtain a mixed slurry. The formula of the mixed slurry is lithium iron phosphate (LFP): polyvinylidene fluoride (PVDF): conductive carbon = 5:2:3. The obtained slurry is uniformly coated on aluminum foil, and then cut into circular positive electrode sheets with a diameter of 10 mm. The positive electrode shell, spring sheet, gasket, positive electrode sheet, separator, lithium sheet, and negative electrode shell are then assembled into a coin cell, and its charge / discharge capacity is tested in an electrochemical workstation. The electrolyte used is an electrolyte with ethyl methyl carbonate (EMC) as the solvent and LFSI as the solute, which can dissolve the protective polyvinyl sulfate ester layer.

[0085] During operation, the air-stable pre-lithiated cathode material releases its own lithium ions to compensate for lithium loss from the cathode. The battery performance is a first-cycle charge capacity of 218 mAh g in a lithium iron phosphate-lithium half-cell configuration. -1 .

[0086] Comparative Example 1 This comparative example is the same as Example 6 except that the pre-lithiation material prepared in Example 1 was removed from the cathode material. The battery performance is 168 mAh g⁻¹ in the first charge cycle of a lithium iron phosphate-lithium half-cell. -1 .visible Figure 4 During the first charge cycle, lithium iron phosphate batteries can only release 168 mAh g when charged to 4.5V. -1 The charging capacity was [not specified], and after discharging to 2.5V, only 150 mAh g remained. -1 The discharge capacity of the lithium iron phosphate half-cell with the addition of the positive electrode pre-lithiation material prepared in Example 1 can release 235 mAh g under the same first charge-discharge conditions. -1 The charging capacity and 165 mAh g -1 With its higher discharge capacity, the battery performance is significantly better.

[0087] Example 25 In this embodiment, the positive electrode pre-lithiation material is a multi-metal site lithium salt Li6Ni. 0.5 Mn 0.5 O4, the rest is the same as in Example 5.

[0088] Example 26 In this embodiment, the positive electrode pre-lithiation material is a multi-metal-site lithium salt Li6Co. 0.3 Mn 0.7 O4, the rest is the same as in Example 1.

[0089] Example 27 In this embodiment, the positive electrode pre-lithiation material is a multi-metal-site lithium salt Li6Fe. 0.5 Mn 0.5 O4, the rest is the same as in Example 4.

[0090] Comparative Example 2 Compared to Example 1, this comparative example has no polyvinyl carbonate (VC) protective layer on the surface of the positive electrode pre-lithiation material; otherwise, it is the same as Example 1. The battery performance is 657 mAh g⁻¹ in the first charge cycle of a Li₅FeO₄-lithium half-cell. -1 See also Figure 5a After being exposed to an environment with 20% humidity for 6 hours, Li5FeO4 could only release 171 mAh g⁻¹ when charged to 4.5 V in a lithium half-cell. -1 The charging capacity, Figure 5b The positive electrode pre-lithiation material Li5FeO4, coated with polyvinyl carbonate as described in Example 1, after being exposed to air for 100 h, still released 580 mAh g of lithium in its half-cell after charging to 4.5 V. -1 Its charging capacity, material air stability, and battery performance are significantly superior. (See also...) Figure 6a After exposure to an environment with 20% humidity for 6 hours, the intensity of the characteristic peaks in the XRD pattern of Li5FeO4 decreased significantly. Figure 6b The positive electrode pre-lithiation material Li5FeO4 coated with polyvinyl carbonate in Example 1 showed almost no change in its characteristic peaks in XRD after being exposed to air for 100 h, and no other impurity peaks were generated, indicating that the material has significantly better air stability.

[0091] Figure 7 These are photos showing the color changes of polyvinyl carbonate (PVC) before and after coating with different materials. The first row shows Li₂O and NCM811 (chemical formula: LiNi) respectively. 0.8 Co 0.1 Mn 0.1 The first row shows optical images of Li2O, NCM, and Li2NiO2 materials before coating, and the second row shows optical images of Li2O, NCM, and Li2NiO2 materials after coating with polyvinyl carbonate. It can be seen that the color changed significantly after coating, indicating that the surface coating method of the present invention has universality.

[0092] Figure 8 The infrared spectra of Li2O, NCM, and Li2NiO2 materials after being coated with polyvinyl carbonate are shown in the figures. As can be seen from the figures, the peaks of each functional group in the infrared spectra indicate that the surface of the material is indeed coated with polyvinyl carbonate.

[0093] The above illustration uses polyvinyl carbonate as an example of a polymer protective layer formed by in-situ polymerization. In fact, the method of this invention is universal and is not limited to polyvinyl carbonate.

[0094] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An air-stable positive electrode pre-lithiation material, characterized in that, It includes positive electrode pre-lithiation material particles, each of which has a dense protective layer on its surface, and the protective layer is seamlessly attached to the surface of the positive electrode pre-lithiation material particle. The protective layer is made of a polymer formed by in-situ polymerization on the surface of the positive electrode pre-lithiation material particles. The thickness of the protective layer is 5nm to 5μm, and the mass of the protective layer accounts for 0.01% to 10% of the total mass of the positive electrode pre-lithiation material. The protective layer is dense enough to isolate gas and water.

2. The positive electrode pre-lithiation material as described in claim 1, characterized in that, The protective layer material is selected from one or more of polycarbonate, polyether, polyacrylate, polysiloxane and polysulfate.

3. The positive electrode pre-lithiation material as described in claim 1 or 2, characterized in that, The positive electrode pre-lithiation material is selected from any one or more of Li5FeO4, Li8FeO6, Li6FeO4, Li3FeO4, LiFeO2, Li2FeO2, Li6CoO4, Li2CoO3, Li8CoO6, Li2MnO3, Li6MnO4, Li5Mn2O7, Li2NiO2, Li2NiO3, Li3N, Li2O2, and Li2O, or The cathode prelithiation material is a lithium salt of multi-metal Li （1+a） M x N （1-x） O b , where 0 < x < 1, 0 < a ≤ 10, 2 ≤ b ≤ 6, O is oxygen element, M and N are different metal elements, and M and N are respectively selected from one of Zr, V, Fe, Mn, Ni and Co.

4. A method for preparing the positive electrode pre-lithiation material as described in any one of claims 1-3, characterized in that, It includes the following steps: S1: Dissolve the precursor of the polymer protective layer in the first solvent to obtain a precursor solution. The initiator is dissolved in the second solvent, and then the positive electrode pre-lithiation material particles are added and dispersed evenly to attach the initiator to the surface of the positive electrode pre-lithiation material particles, thus obtaining a suspension. The first and second solvents are miscible. S2: Stir and heat the suspension to the set temperature, continue stirring and maintain the temperature, and gradually add the precursor solution. Under the action of the initiator, the precursor of the polymer protective layer undergoes in-situ polymerization on the surface of the positive electrode pre-lithiation material particles to form a dense protective layer that can isolate gases and water. The heat preservation temperature is 10℃~100℃, and the continuous heat preservation and stirring time is 6 h~24 h. S3: Separate the reaction product, wash and dry it to obtain positive electrode pre-lithiation material particles with a dense protective layer on the surface.

5. The method as described in claim 4, characterized in that, In step S1, Lithium salts are added to the precursor solution to impart lithium conductivity to the protective layer. The lithium salt is selected from one or more of LiPF6, LiBF4, LiBOB, LiDFOB, LiTFSI, LiFSI, and LiPO2F2.

6. The method as described in claim 5, characterized in that, In step S1, the first solvent and the second solvent are the same solvent.

7. The method as described in claims 3-6, characterized in that, The first solvent and the second solvent are respectively selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, 1,2-dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, methyl formate, methyl acetate, methyl butyrate and ethyl propionate.

8. The method as described in claim 5, characterized in that, In step S2, the stirring is mechanical stirring or ultrasonic vibration stirring at 200 rpm to 2000 rpm.

9. The application of the positive electrode pre-lithiation material as described in any one of claims 1-3, characterized in that, It is used to add to the cathode material to prepare a composite cathode for lithium-ion batteries. During operation, the air-stable pre-lithiated cathode material releases its own lithium ions to compensate for the loss of active lithium during the battery charging and discharging process.

10. The application as described in claim 9, characterized in that, When the protective layer itself can conduct lithium ions, it can be directly added to the cathode material to prepare a lithium-ion battery cathode. When the protective layer itself cannot conduct lithium ions, an electrolyte that can dissolve the protective layer is selected to assemble a lithium-ion battery. When the battery is working, the electrolyte naturally dissolves the protective layer to expose the positive electrode pre-lithiation material particles themselves. The exposed positive electrode pre-lithiation material releases its own lithium ions to compensate for the loss of active lithium during the battery charging and discharging process.

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