Positive electrode lithium supplementing material and preparation method thereof, positive electrode plate and lithium ion battery

Abstract

The invention discloses a positive electrode lithium supplementing material and a preparation method thereof, a positive electrode plate and a lithium ion battery. The positive electrode lithium supplementing material comprises a lithium-rich inner core, and a first coating layer and a second coating layer which sequentially coat the lithium-rich inner core, the first coating layer is a conductive carbon layer, and the second coating layer is an inorganic matter-polymer electrolyte composite layer. The lithium-rich core is coated by adopting a solid-phase and liquid-phase double-layer compact coating technology, so that the air stability of the positive electrode lithium supplementing material is remarkably improved. Through optimal design of the second coating layer structure, an electron and ion dual-channel transmission network is constructed, so that the problem that the electrochemical performance is reduced due to excessive coating is effectively avoided while the stability of the material is ensured.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a positive electrode lithium replenishment material and its preparation method, a positive electrode sheet, and a lithium-ion battery. Background Technology

[0002] During the initial charge and discharge of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the negative electrode side, accompanied by an irreversible phase transition reaction. Both processes lead to the consumption of active lithium. This lithium originates from lithium ions released by the positive electrode material during the initial charging phase, thus reducing the number of lithium carriers available for subsequent reversible insertion / extraction reactions. This results in an imbalance in the total amount of lithium ions within the battery, leading to a decline in the overall electrochemical performance, particularly manifested as a decrease in initial coulombic efficiency and a reduction in specific capacity.

[0003] To compensate for lithium loss, a technical solution involving the introduction of a small amount of lithium-rich lithium replenishing agent (approximately 0.53 wt%) into cathode materials has been proposed in recent years. This method is considered a promising lithium compensation strategy due to its simplicity and high compatibility with existing electrode fabrication processes. However, existing lithium replenishing agents still face a series of key technical challenges: On the one hand, lithium replenishing agents typically have high lithium content, which easily leads to significant crystal structure phase transitions during delithiation, resulting in slow lithium-ion release kinetics and difficulty in achieving rapid and complete lithium release, exhibiting poor rate performance. On the other hand, high lithium content also leads to high surface chemical activity, easily causing an increase in residual alkali content and side reactions with moisture and carbon dioxide in the environment during storage and processing, resulting in material performance degradation. Furthermore, lithium replenishing agents are prone to causing gelation of the system during electrode slurry preparation, affecting slurry stability and coating processability, severely restricting their practical application in industrial production.

[0004] Although existing studies have attempted to improve the air stability and cycle performance of lithium replenishing agents through dense coating and element doping, such modification methods often come at the cost of sacrificing some intrinsic lithium replenishing capacity and have limited improvement in environmental stability. They are difficult to balance high lithium replenishing efficiency with good process adaptability, and therefore have not yet been applied on a large scale in commercial cells.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a positive electrode lithium replenishment material and its preparation method, a positive electrode sheet and a lithium-ion battery, so as to improve the problems of high residual lithium, poor rate performance and air stability of lithium replenishment agents, which cannot ideally realize the theoretical lithium replenishment capacity of lithium replenishment agents.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a positive electrode lithium replenishment material, which includes a lithium-rich core and a first coating layer and a second coating layer sequentially coating the lithium-rich core; the first coating layer is a conductive carbon layer, and the second coating layer is an inorganic-polymer electrolyte composite layer.

[0008] In an optional embodiment, the lithium-rich core is a lithium metal oxide (Li). x MO y Wherein, 1≤x≤6, 2≤y≤4, and M is one or more metallic or non-metallic elements that can form tetrahedral or octahedral structures with lithium; preferably, M is selected from one or more of C, P, S, N, Mn, Ni, Cu, Co, Fe, Al, Ti, Mg and Zr. In an optional embodiment, the lithium-rich core is a binary or multi-component lithium compound Li. a N b , where 1≤a≤3, 1≤b≤6, and N is selected from one or more of O, C, P, S, N and F.

[0009] In an optional embodiment, the thickness of the first coating layer is 1 nm to 200 nm, and the mass of the first coating layer accounts for 0.5% to 5% of the total mass of the positive electrode lithium replenishment material.

[0010] In an optional embodiment, the thickness of the second coating layer is 1 nm to 100 nm, the mass of the second coating layer accounts for 0.1% to 2% of the total mass of the positive electrode lithium replenishment material, and in the inorganic-polymer electrolyte composite layer, the mass ratio of inorganic solid electrolyte to polymer electrolyte is (0.05 to 0.3):1.

[0011] In an optional embodiment, the inorganic solid electrolyte is a perovskite-type mixed electron-ion conductor Li. 0.34 La 0.55 DO 3-δ Metal D is selected from at least one of Co and Mn, and δ is a natural number between 0 and 0.5; or the inorganic solid electrolyte is a garnet-type mixed electron-ion conductor Li. 7.3 La3Zr 2-c E c O 12 Where 0.3≤c≤0.5, and metal E is selected from one or more of Fe, Co and Ni.

[0012] In an optional embodiment, the polymer corresponding to the polymer electrolyte is selected from one or more of PEO, PVC, PEC, PPC, PTMC, PAN, PDMS, PVDF, PMMA and derivatives of the above polymers, and the molecular weight of the polymer is ≥20000g / mol.

[0013] In a second aspect, the present invention provides a method for preparing a positive electrode lithium replenishment material as described in any of the foregoing embodiments, comprising: The lithium-rich core is uniformly mixed with a carbon source and coated to obtain a lithium-replenishing material with the first coating layer. The mixed solution containing inorganic solid electrolyte and polymer is thoroughly mixed with the lithium replenishing material having the first coating layer. After solid-liquid separation, the mixture is dried to obtain the positive electrode lithium replenishing material.

[0014] In an optional embodiment, the carbon source is C. d H e O f Where d, e, and f are any combination of natural numbers, and the carbon source contains ≥40% C.

[0015] In an optional embodiment, after the lithium-rich core is uniformly mixed with the carbon source, it is kept at 500℃ to 900℃ for 3 to 15 hours under the protection of an inert gas with a flow rate of 3 mL / min to 20 mL / min; preferably, the inert gas is selected from any one of nitrogen, argon and helium.

[0016] In an optional embodiment, the method for preparing the positive electrode lithium replenishment material has at least one of the following characteristics: (1) The amount of polymer added is based on the ratio of polymer monomer to Li + The molar ratio is controlled at (0.5-8):1, where Li + The residual lithium on the surface of the lithium replenishment material having the first coating layer; (2) The solvent used in the mixed solution is selected from one or more of alcohols, ethers, acetals, lipids, nitrogen-containing compound solvents and multifunctional solvents, preferably one or more of N-methylpyrrolidone, ethanol, ethylene glycol and tetrahydrofuran; (3) The mixed solution and the lithium replenishing material with the first coating layer are thoroughly mixed by stirring for 0.5h to 2h; (4) The drying is carried out at a temperature of 60℃~120℃ for 6h~24h.

[0017] Thirdly, the present invention also provides a positive electrode sheet comprising the positive electrode lithium replenishment material as described in any of the foregoing embodiments.

[0018] Fourthly, the present invention also provides a lithium-ion battery comprising a positive electrode as described in the foregoing embodiments.

[0019] The present invention has the following beneficial effects: This invention provides a cathode lithium replenishment agent with a dual-layer coating structure, aiming to significantly improve the electrochemical performance and environmental stability of lithium-rich core materials. The first coating layer is a conductive carbon film layer easily synthesized via a solid-state method. This layer not only effectively enhances the electronic conductivity of the lithium-rich core but also improves its air stability to a certain extent. The second coating layer is an inorganic-polymer electrolyte composite layer prepared via a liquid-phase method. Compared to solid-phase coating, liquid-phase coating achieves a more uniform and dense coverage, effectively compensating for potential structural discontinuities in the solid-phase coating process. The polymer used undergoes a microgelation reaction under alkaline conditions, thus tightly adhering to the surface of the carbon-coated lithium replenishment material and the microscopic defect regions within the carbon layer, forming a highly efficient barrier layer at the molecular scale. This prevents moisture and carbon dioxide in the air from contacting the internal lithium-rich core, significantly improving the material's air stability.

[0020] Furthermore, this polymer can capture residual lithium species on the surface of lithium-replenishing materials and convert them in situ into polymer electrolyte components with ionic conductivity. Based on this, a nanoscale hybrid ion-electron conductor with both electronic and ion conductivity is introduced as an inorganic filler, dispersed in the polymer matrix at a predetermined ratio. This design, on the one hand, disrupts the ordered arrangement of polymer segments, promoting the formation of amorphous regions and facilitating rapid lithium-ion migration; on the other hand, it constructs an electronic conduction pathway throughout the coating layer, forming a "dual-channel" network structure that synergistically conducts lithium ions and electrons.

[0021] The aforementioned multi-level synergistic mechanism not only significantly enhances the ion and electron transport capabilities within the lithium replenisher but also substantially reduces interfacial polarization between the lithium replenisher material and the electrolyte, thereby optimizing the overall electrochemical kinetics. In summary, this invention, by constructing a functionally graded bilayer coating structure, achieves comprehensive regulation of the conductivity, interfacial stability, and environmental tolerance of lithium-rich lithium replenishers, providing reliable technical support for their practical application in high-energy-density lithium-ion batteries. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of the positive electrode lithium replenishment material according to an embodiment of the present invention; Figure 2 This is a process flow diagram for preparing the positive electrode lithium replenishment material according to an embodiment of the present invention; Figure 3This is a scanning electron microscope image of the positive electrode lithium replenishment material of Embodiment 1 of the present invention; Figure 4 A comparison diagram of charge-discharge curves of positive electrode lithium replenishment materials in embodiments and comparative examples of the present invention; Figure 5 This is a comparison chart of the weight change curves of the positive electrode lithium replenishment materials under constant temperature and humidity in the embodiments and comparative examples of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0026] In the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships may exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural 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 a single or multiple.

[0027] Some embodiments of the present invention provide a positive electrode lithium replenishment material, see [link to relevant documentation]. Figure 1 It includes a lithium-rich core and a first coating layer and a second coating layer sequentially covering the lithium-rich core; the first coating layer is a conductive carbon layer, and the second coating layer is an inorganic-polymer electrolyte composite layer (i.e., an electrolyte coating layer).

[0028] This lithium replenishment agent employs a solid-phase and liquid-phase dual-layer dense coating technology to coat the lithium-rich core, significantly improving the air stability of the cathode lithium replenishment material. Through optimized design of the second coating layer structure, a dual-channel electron and ion transport network is constructed, effectively avoiding the problem of electrochemical performance degradation due to over-coating while ensuring material stability.

[0029] In some implementations, the lithium-rich core is a lithium-containing metal oxide (Li). x MO y Wherein, 1≤x≤6, 2≤y≤4, and M is one or more metallic or non-metallic elements capable of forming tetrahedral or octahedral structures with lithium; preferably, M is selected from one or more of C, P, S, N, Mn, Ni, Cu, Co, Fe, Al, Ti, Mg, and Zr. Alternatively, the lithium-rich core is a binary or multi-component lithium compound LiaNb, where 1≤a≤3, 1≤b≤6, and N is selected from one or more of O, C, P, S, N, and F.

[0030] Furthermore, in some embodiments, to avoid excessive residual lithium on the surface of the lithium-rich core, which could lead to excessive polymer gelation, the lithium-rich core is Li... x MO y (1≤x≤6、2≤y≤4), M is Fe, Co, Ni, Mn, and more preferably Fe.

[0031] In some embodiments, the thickness of the first coating layer is 1nm to 200nm. For example, the thickness can be selected as 1nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, or 200nm, or between any two thicknesses. The mass of the first coating layer accounts for 0.5% to 5% of the total mass of the positive electrode lithium replenishment material. For example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0032] If the first coating layer is too thin, a complete physical barrier cannot be formed, allowing the electrolyte to penetrate into the lithium replenisher, causing premature decomposition and loss of lithium replenishment capability. Furthermore, the thin carbon layer's electronic conduction path is discontinuous, significantly reducing lithium replenishment efficiency. Conversely, if the first coating layer is too thick, it significantly increases the resistance to lithium-ion and electron transport. Even if the lithium replenisher releases lithium ions, they cannot migrate quickly to the positive or negative electrode, resulting in slower battery charging and discharging speeds (decreased rate performance), and some lithium ions may even be consumed during transport. If the first coating layer content is too low, the carbon layer cannot completely cover the lithium replenisher surface, and the exposed lithium replenisher will react directly with the electrolyte, causing problems such as gas buildup and electrolyte consumption. Simultaneously, insufficient electronic conductivity hinders the lithium replenishment reaction. Conversely, if the first coating layer content is too high, excess carbon will occupy internal battery space as an "inert component," reducing the battery's energy density. Excess carbon may also adsorb lithium ions from the electrolyte, causing lithium loss and negating the lithium replenisher's effect.

[0033] In some embodiments, the thickness of the second coating layer is 1nm to 100nm. For example, the thickness can be selected as 1nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc. The mass of the second coating layer accounts for 0.1% to 2% of the total mass of the positive electrode lithium replenishment material. For example, it can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%, etc.

[0034] Similarly, the thickness of the second coating layer can resolve the core contradiction between "protection" and "electron and ion transport." An inappropriate thickness will directly disrupt the balance between efficiency and safety in the lithium replenishment process. If the content of the second coating layer is too low, it will not be able to completely cover the surface of the lithium replenishing agent, leaving exposed areas that cannot effectively isolate moisture and carbon dioxide from the air. If the content of the second coating layer is too high, it will occupy the internal space of the battery as an "ineffective component," reducing the proportion of active material per unit volume / weight and directly leading to a decrease in battery energy density. At the same time, excessive polymer may form dense accumulation inside the electrodes, increasing ion transport resistance and slowing down the battery's charging and discharging speed.

[0035] In some embodiments, the mass ratio of inorganic solid electrolyte to polymer electrolyte in the inorganic-polymer electrolyte composite layer is (0.05~0.3):1. For example, the mass ratio may be 0.05:1, 0.1:1, 1.5:1, 2:1, 2.5:1 or 3:1, etc.

[0036] In some embodiments, the inorganic solid electrolyte is a perovskite-type mixed electron-ion conductor, Li. 0.34 La 0.55 DO 3-δMetal D is selected from at least one of Co and Mn, and δ is a natural number between 0 and 0.5, representing the non-stoichiometric deviation of oxygen in the oxide; or the inorganic solid electrolyte is a garnet-type mixed electron-ion conductor Li. 7.3 La3Zr 2-c E c O 12 Where 0.3≤c≤0.5, and metal E is selected from one or more of Fe, Co and Ni.

[0037] Nanoscale hybrid ion-electron conductors, possessing both electron and ion conduction functions, are added as inorganic fillers in a specific ratio to reduce the orderliness of polymer electrolyte chain segments, resulting in inorganic-polymer composite electrolytes, which further enhance the Li... + It enhances diffusion capabilities in polymers, increases electron transport channels, constructs an ion-electron dual-channel network, and reduces interfacial polarization between the lithium core and the electrolyte.

[0038] In some embodiments, the polymer electrolyte corresponds to one or more polymers selected from PEO, PVC, PEC, PPC, PTMC, PAN, PDMS, PVDF, PMMA and derivatives of the above polymers, and the molecular weight of the polymer is ≥20000 g / mol.

[0039] Furthermore, some embodiments of the present invention also provide a method for preparing a positive electrode lithium replenishment material as described in any of the foregoing embodiments, comprising: uniformly mixing a lithium-rich core with a carbon source to coat it to obtain a lithium replenishment material having a first coating layer; thoroughly mixing a mixed solution having an inorganic solid electrolyte and a polymer with the lithium replenishment material having the first coating layer, separating the solid and liquid, and drying to obtain a positive electrode lithium replenishment material.

[0040] Specifically, in some implementations, see [link to implementation details]. Figure 2 The preparation method of this positive electrode lithium replenishment material includes the following steps: S1. The lithium-rich core and carbon source are uniformly mixed and kept at a certain temperature for a period of time under an inert atmosphere at a certain flow rate to obtain a lithium replenishment material with a first coating layer.

[0041] In some implementations, the carbon source is C. d H e O f Where d, e, and f are any combination of natural numbers, and the carbon source has a C content of ≥40%. For example, the carbon source can be glucose (d=6, e=12, f=6), asphalt (d=14, e=10, f=0) or sucrose (d=12, e=22, f=11).

[0042] In some embodiments, the inert gas flow rate is 3 mL / min to 20 mL / min, the holding temperature is 500℃ to 900℃, and the holding time is 3 to 15 h.

[0043] For reference, the inert gas is selected from any one of nitrogen, argon, and helium. The gas flow rate is any natural number from 3 to 20, such as 5, 7, or 9 mL / min; the holding temperature is any natural number from 500 to 900, such as 550, 600, 650, 700, 750, 800, 850, or 900 °C; and the holding time is any natural number from 3 to 15, such as 5, 7, 9, 11, 13, or 15 h.

[0044] S2. The high-purity polymer is completely dissolved in an organic solvent to obtain a transparent solution. Then, mixed electron-ion conductor nanoparticles are added to the transparent solution and stirred until homogeneous to obtain a uniform slurry. The lithium-replenishing material with the first coating layer from step S1 is added to the slurry, and stirring is continued to allow the polymer to fully capture the residual lithium free in the lithium-rich core in the slurry and attach it to the surface of the lithium-rich core. After stirring for a period of time, a double-coated cathode lithium-replenishing material slurry is obtained.

[0045] Specifically, in some embodiments, the amount of polymer added is based on the ratio of polymer monomer to Li. + The molar ratio is controlled at (0.5-8):1, where Li + Residual lithium on the surface of the lithium replenishment material having the first coating layer.

[0046] In some embodiments, the organic solvent used is selected from one or more of alcohols, ethers, acetals, lipids, nitrogen-containing compound solvents, and multifunctional solvents, preferably one or more of N-methylpyrrolidone, ethanol, ethylene glycol, and tetrahydrofuran.

[0047] Continue stirring to allow the polymer to fully capture the residual lithium free in the lithium-rich core in the slurry. The stirring time is 0.5h to 2h, for example, 0.5h.

[0048] S3. Filter, vacuum filter or pressure filter the positive electrode lithium replenishment material slurry obtained in step S2, and then vacuum dry it to obtain the target double-coated positive electrode lithium replenishment material.

[0049] In some implementations, the drying temperature is 60℃~120℃ and the drying time is 6h~24h.

[0050] Furthermore, some embodiments of the present invention also provide a positive electrode sheet, which includes the positive electrode lithium replenishment material as described in any of the foregoing embodiments.

[0051] Furthermore, some embodiments of the present invention also provide a lithium-ion battery comprising a positive electrode as described in the foregoing embodiments.

[0052] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0053] This embodiment provides a method for preparing a positive electrode lithium supplementation material, the specific steps of which are as follows: (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of glucose:Li5FeO4=4:96 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace. The excess air was quickly removed by vacuuming. Then, N2 was introduced. The air flow rate was set to 15 mL / min, the heating rate was set to 5℃ / min, and the process curve was set to 600℃ for 12 h. The material was cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0054] (2) Preparation of double-coated cathode lithium replenishment material: According to the polymer polyethylene oxide (PEO) monomer (-CH2-CH2-O-) and the residual lithium (Li) on the surface of the pre-recoated carbon-coated cathode lithium replenishment material. + The molar ratio of PEO and Li5FeO4 was 2:1. Taking 500g of carbon-coated Li5FeO4 with a residual lithium content of 0.5914% as an example, 37.4897g of PEO was used. The PEO was thoroughly dissolved in 800mL of N-methylpyrrolidone solution in a water bath at 60℃. Then, the solid electrolyte Li5FeO4 was dissolved... 0.34 La 0.55 CoO 3-δ Add 4.1655g of Li at a PEO mass ratio of 1:9. 0.34 La 0.55 CoO 3-δ Stir for 30 minutes to uniformly disperse it in the polymer electrolyte solution. Finally, add 500g of carbon-coated Li5FeO4, heat and stir in a water bath for 0.5h, filter, and dry the filter residue in a vacuum oven at 100℃ for 12h to obtain a double-coated positive electrode lithium replenishment material.

[0055] Example 2 This embodiment provides a method for preparing a positive electrode lithium supplementation material, the specific steps of which are as follows: (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of asphalt:Li5FeO4=5:95 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace. The excess air was quickly removed by vacuuming. Then Ar was introduced. The air flow rate was set to 20 mL / min, the heating rate was set to 3℃ / min, and the process curve was set to 700℃ for 8 h. The material was cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0056] (2) Preparation of double-coated cathode lithium replenishment material: According to the polymer polyacrylonitrile (PAN) monomer (C3H3N) and the residual lithium (Li) on the surface of the pre-coated carbon-coated cathode lithium replenishment material. + The molar ratio of PAN and Li5FeO4 was 1:1. Taking 500g of carbon-coated Li5FeO4 with a residual lithium content of 0.6011% as an example, 22.9494g of PAN was used. PEO was fully dissolved in 800mL of ethylene glycol solution in a water bath at a temperature of 60℃. Then, the solid electrolyte Li5FeO4 was dissolved in the solution. 7.3 La3Zr 1.7 Ni 0.3 O 12 Add 4.5898g of Li at a mass ratio of 1:5 with PAN. 7.3 La3Zr 1.7 Ni 0.3 O 12 Stir for 45 minutes to uniformly disperse it in the polymer electrolyte solution. Finally, add 500g of carbon-coated Li5FeO4, heat and stir in a water bath for 0.8h, filter, and dry the filter residue in a vacuum oven at 120℃ for 8h to obtain a double-coated positive electrode lithium replenishment material.

[0057] Example 3 This embodiment provides a method for preparing a positive electrode lithium supplementation material, the specific steps of which are as follows: (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of sucrose:Li5FeO4=5:95 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace, and the excess air was quickly removed by vacuuming. Then, N2 was introduced, and the air flow rate was set to 18 mL / min. The heating rate was set to 10℃ / min. The process curve was set to 750℃ and held for 8 h. The material was cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0058] (2) Preparation of double-coated cathode lithium replenishment material: According to the polyvinyl carbonate (PEC) monomer (C3H4O3) and the residual lithium (Li) on the surface of the pre-coated carbon-coated cathode lithium replenishment material. + The molar ratio of PEC to Li₅FeO₄ is 0.5:1. Taking 500g of carbon-coated Li₅FeO₄ with a residual lithium content of 0.5854% as an example, 18.5547g of PEC is used. PEC is thoroughly dissolved in a mixed solution of 400mL ethanol and 400mL N-methylpyrrolidone in a water bath at 60℃. Then, following the solid electrolyte Li₅FeO₄... 7.3 La3Zr 1.7 Co 0.3 O 12 Add 4.6387g Li to PEC at a mass ratio of 1:4. 7.3 La3Zr 1.7 Co 0.3 O 12 Stir for 45 minutes to ensure uniform dispersion in the polymer electrolyte solution. Finally, add 500g of carbon-coated Li5FeO4, heat and stir in a water bath for 1 hour, filter, and dry the filter residue in a vacuum oven at 80℃ for 15 hours to obtain a double-coated positive electrode lithium replenishment material.

[0059] Example 4 This embodiment provides a method for preparing a positive electrode lithium supplementation material, the specific steps of which are as follows: (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of L-ascorbic acid:Li5FeO4=6:94 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace, and the excess air was quickly removed by vacuuming. Then, N2 was introduced, the air flow rate was set to 10 mL / min, the heating rate was set to 5℃ / min, the process curve was set to 800℃ and held for 7 h, and then cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0060] (2) Preparation of double-coated cathode lithium replenishment material: according to the polytrimethylene carbonate (PTMC) monomer (C4H6O3) and the residual lithium (Li) on the surface of the pre-coated carbon-coated cathode lithium replenishment material. +The molar ratio of PTMC to Li₅FeO₄ is 0.5:1. Taking 500g of carbon-coated Li₅FeO₄ with a residual lithium content of 0.5901% as an example, 21.6792g of PTMC is used. The PTMC is thoroughly dissolved in 800mL of ethanol solution in a water bath at 60℃. Then, following the solid electrolyte Li₅FeO₄... 7.3 La3Zr 1.7 Ni 0.3 O 12 Add 3.6132g Li to PTMC at a mass ratio of 1:6. 7.3 La3Zr 1.7 Ni 0.3 O 12 Stir for 60 minutes to ensure uniform dispersion in the polymer electrolyte solution. Finally, add 500g of carbon-coated Li5FeO4, heat and stir in a water bath for 45 minutes, filter, and dry the filter residue in a vacuum oven at 100℃ for 12 hours to obtain a double-coated positive electrode lithium replenishment material.

[0061] Example 5 This embodiment provides a method for preparing a positive electrode lithium supplementation material, the specific steps of which are as follows: (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of asphalt:Li5FeO4=5:95 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace. The excess air was quickly removed by vacuuming. Then Ar was introduced. The air flow rate was set to 20 mL / min, the heating rate was set to 3℃ / min, and the process curve was set to 700℃ for 8 h. The material was cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0062] (2) Preparation of double-coated cathode lithium replenishment material: According to the polymer polyacrylonitrile (PAN) monomer (C3H3N) and the residual lithium (Li) on the surface of the pre-coated carbon-coated cathode lithium replenishment material. + The molar ratio of PAN and Li5FeO4 is 1:1. Taking 500g of carbon-coated Li5FeO4 with a residual lithium content of 0.5986% as an example, 22.8540g of PAN is used. PEO is fully dissolved in 800mL of ethylene glycol solution in a water bath at a temperature of 60℃. Then, according to the solid electrolyte Li 0.34 La 0.55 MnO 3-δ Add 7.618g of Li at a mass ratio of 1:3 with PAN. 0.34 La 0.55 MnO3-δ Stir for 45 minutes to uniformly disperse it in the polymer electrolyte solution. Finally, add 500g of carbon-coated Li5FeO4, heat and stir in a water bath for 0.8h, filter, and dry the filter residue in a vacuum oven at 120℃ for 8h to obtain a double-coated positive electrode lithium replenishment material.

[0063] Comparative Example 1 This comparative example serves as a comparison with the embodiments, using an uncoated Li5FeO4 matrix as the comparative example.

[0064] Comparative Example 2 This comparative example serves as a comparison with the embodiments, and it is a carbon-coated cathode material with only a first coating layer but without a second coating layer.

[0065] The preparation of this carbon-coated cathode lithium replenishment material is exactly the same as step S1 in Example 1: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of glucose:Li5FeO4=4:96 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace, and excess air was quickly removed by vacuuming. Then, N2 was introduced, and the air flow rate was set to 15 mL / min, the heating rate was set to 5℃ / min, and the process curve was set to 600℃ for 12 h. After natural cooling, the material was discharged from the furnace and coarsely crushed by a jaw crusher and roller crushed, and then finely crushed by a mechanical mill to obtain carbon-coated positive lithium supplement material.

[0066] Comparative Example 3 This comparative example serves as a comparison with the embodiments. In preparation step S2, no inorganic solid electrolyte was added, while the remaining steps were exactly the same as in Example 1. (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of glucose:Li5FeO4=4:96 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace. The excess air was quickly removed by vacuuming. Then, N2 was introduced. The air flow rate was set to 15 mL / min, the heating rate was set to 5℃ / min, and the process curve was set to 600℃ for 12 h. The material was cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0067] (2) Preparation of double-coated cathode lithium replenishment material: According to the polymer polyethylene oxide (PEO) monomer (-CH2-CH2-O-) and the residual lithium (Li) on the surface of the pre-recoated carbon-coated cathode lithium replenishment material. +The molar ratio of PEO and Li5FeO4 was 2:1. Taking 500g of carbon-coated Li5FeO4 with a residual lithium content of 0.5891% as an example, 37.3439g of PEO was used. The PEO was fully dissolved in 800mL of N-methylpyrrolidone solution in a water bath at a temperature of 60℃. Then, 500g of carbon-coated Li5FeO4 was added. After heating and stirring in a water bath for 0.5h, the mixture was filtered. The filter residue was dried in a vacuum oven at 100℃ for 12h to obtain a double-coated positive electrode lithium replenishment material.

[0068] Comparative Example 4 This comparative example serves as a comparison with the embodiments. In preparation step S2, non-conductive inorganic nanoparticles TiO2 were added, while the remaining steps were exactly the same as in Example 1. (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of glucose:Li5FeO4=4:96 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace. The excess air was quickly removed by vacuuming. Then, N2 was introduced. The air flow rate was set to 15 mL / min, the heating rate was set to 5℃ / min, and the process curve was set to 600℃ for 12 h. The material was cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0069] (2) Preparation of double-coated cathode lithium replenishment material: According to the polymer polyethylene oxide (PEO) monomer (-CH2-CH2-O-) and the residual lithium (Li) on the surface of the pre-recoated carbon-coated cathode lithium replenishment material. + The molar ratio of PEO and Li5FeO4 was 2:1. Taking 500g of carbon-coated Li5FeO4 with a residual lithium content of 0.5891% as an example, 37.3439g of PEO was used. The PEO was fully dissolved in 800mL of N-methylpyrrolidone solution in a water bath at a temperature of 60℃. Then, according to the mass ratio of non-conductive inorganic nanoparticles TiO2 to PEO of 1:9, 4.1655g of TiO2 was added and stirred for 30min to make it uniformly dispersed in the polymer electrolyte solution. Finally, 500g of carbon-coated Li5FeO4 was added, and the mixture was heated and stirred in a water bath for 0.5h. After filtration, the filter residue was dried in a vacuum oven at 100℃ for 12h to obtain a double-coated positive electrode lithium replenishment material.

[0070] Comparative Example 5 This comparative example serves as a comparison with the embodiments, in which an ion-conducting inorganic solid electrolyte Li was added in preparation step S2. 0.33 La 0.56TiO3, the remaining steps are exactly the same as in Example 1: (1) Preparation of carbon-coated positive electrode lithium supplement material: Under a dry and dehumidified environment (dew point ≤ -20℃), the raw materials were accurately weighed according to the mass ratio of glucose:Li5FeO4=4:96 and premixed in a high-speed mixer for 10 min. Then, the premixed material was mixed in a coating mixer for 30 min. After the mixture was uniform, the material to be sintered was transferred to a vacuum box furnace. The excess air was quickly removed by vacuuming. Then, N2 was introduced. The air flow rate was set to 15 mL / min, the heating rate was set to 5℃ / min, and the process curve was set to 600℃ for 12 h. The material was cooled naturally. After the reaction was completed, the material was crushed by a jaw crusher and roller crushed and then finely crushed by a mechanical mill to obtain the carbon-coated positive electrode lithium supplement material.

[0071] (2) Preparation of double-coated cathode lithium replenishment material: According to the polymer polyethylene oxide (PEO) monomer (-CH2-CH2-O-) and the residual lithium (Li) on the surface of the pre-recoated carbon-coated cathode lithium replenishment material. + The molar ratio of PEO and Li5FeO4 was 2:1. Taking 500g of carbon-coated Li5FeO4 with a residual lithium content of 0.5891% as an example, 37.3439g of PEO was used. The PEO was fully dissolved in 800mL of N-methylpyrrolidone solution in a water bath at a temperature of 60℃. Then, according to the method of ion-conducting inorganic solid electrolyte nanoparticles Li5FeO4... 0.33 La 0.56 TiO3 to PEO in a mass ratio of 1:9, add 4.1655g Li 0.33 La 0.56 TiO3 was stirred for 30 minutes to ensure uniform dispersion in the polymer electrolyte solution. Finally, 500g of carbon-coated Li5FeO4 was added, and the mixture was heated and stirred in a water bath for 0.5 hours. After filtration, the filter residue was dried in a vacuum oven at 100°C for 12 hours to obtain a double-coated positive electrode lithium replenishment material.

[0072] Performance testing 1. Scanning electron microscopy (SEM) analysis was performed on the examples. Figure 3 The image is an SEM image of Example 1. It can be seen from the image that the substrate surface is very smooth after solid-liquid phase coating and is covered by a dense coating layer. This coating layer can effectively isolate moisture and CO2 in the air, preventing the lithium-rich core from deteriorating. At the same time, the carbon layer and the mixed ion-electron conductor can provide electron and ion channels, improving the rate performance and lithium replenishment capacity of the substrate.

[0073] 2. The coin cell capacity, rate performance, residual lithium, and resistivity of the examples and comparative examples were tested. Residual lithium was tested according to the method in GB / T 41704—2022. Lithium sheets were used as the negative electrode, and coin cell half-cells were assembled to test the lithium replenishment capacity. The batteries were placed in a constant temperature battery box at 45°C, with a rate of 0.067C and a charge / discharge voltage range of 2.5-4.2V. The testing system was a LAND MonV7 testing system from Wuhan Landian Electronics Co., Ltd. Table 1 shows the test data for each performance characteristic. Figure 4 The charging and discharging curves of the corresponding samples are shown. The data shows that after double-layer coating, Examples 1-5 exhibit the highest lithium replenishment capacity, exceeding 770 mAh / g. Comparative Example 1, lacking a conductive layer, struggles to achieve its capacity, with a charging capacity of only 545.5 mAh / g. Comparative Example 2 lacks a second electro-ionic conductor coating layer compared to the examples. Comparative Examples 3, 4, and 5, compared to the examples, respectively lack inorganic filler, contain non-conductive inorganic filler, and contain ion-conducting inorganic filler. The test results show that their charging capacities are also slightly lower than the examples. This may be because the polymer electrolyte coating layer in Comparative Example 3 has higher orderliness and weaker ionic conductivity, while Comparative Examples 4 and 5 lack electron pathways. Furthermore, Examples 1, 2, 3, 4, and 5 also demonstrate good rate performance, achieving charging capacities exceeding 640 mAh / g at a 1C charging rate. This is likely due to the synergistic effect of the conductive carbon film layer and the inorganic-polymer electrolyte composite layer in Examples 1-5, providing a uniform and abundant electron network and ion channels, facilitating the release of Li. + The polarization and diffusion resistance encountered are relatively small. At the same time, after coating, the resistance of the matrix and the residual lithium are reduced. Both carbon coating and polymer coating have the effect of reducing residual lithium. Carbon coating can encapsulate residual lithium in the matrix to prevent residual lithium precipitation, while polymer can also capture free residual lithium. After mixing with solid electrolyte, the resistance is further reduced and the rate performance is improved.

[0074] Table 1 Electrochemical Properties

[0075] To evaluate the air stability of the samples, Examples 1-5 and Comparative Examples 1-5 were subjected to isothermal and humidity-controlled storage experiments. The weight change of the samples and the coin capacity after storage were tested at different storage times. The storage experiment methods and results are as follows: Weigh 10g of each sample from the examples and comparative examples, spread them evenly in a petri dish, and then place the petri dish in a constant temperature and humidity chamber with humidity set at 20% and temperature at 25°C. Weighing times were 1, 2, 4, 8, 12, and 24 hours. Data are shown in [the table below]. Figure 5As shown in the figure, the horizontal axis represents the resting time in hours (h), and the vertical axis represents the moisture absorption rate in μg / g / s. The results show that after dense coating, the air stability of Examples 1-5 and Comparative Examples 3-5 is significantly improved; after resting for 2 hours, the weight remains essentially unchanged. The coin cell capacity after 24 hours of resting is shown in Table 1. The table shows that the capacity of the examples decreased by 20-30 mAh / g, but Comparative Example 1 showed gelation, making it impossible to test the coin cell capacity. Comparative Example 2 also showed a significant decrease in lithium replenishment capacity of over 100 mAh / g. This directly proves that the double-coated positive electrode lithium replenishment material provided in this application has extremely high air stability.

[0076] In summary, the embodiments of this invention are based on a double-layer coating design. The first coating layer is a conductive carbon layer formed by solid-phase coating, located between the lithium-rich core and the second coating layer. Its main function is to improve the overall electronic conductivity of the material and, to a certain extent, enhance the material's stability to the air environment. The second coating layer is an inorganic-polymer electrolyte composite layer applied by liquid-phase coating. The liquid-phase coating process can effectively compensate for defects such as non-dense film and uneven coverage that may occur during solid-phase coating, thereby achieving efficient barrier properties against moisture and carbon dioxide at the molecular scale, preventing them from reacting with the lithium-rich core, and significantly improving the material's environmental tolerance. This inorganic-polymer electrolyte composite layer forms a polymer electrolyte in situ by capturing residual lithium on the surface of the lithium-replenishing material in the polymer matrix, and further introduces nanoscale mixed ion-electron conductive inorganic fillers, which are uniformly dispersed in the polymer matrix in a predetermined ratio. This design, on the one hand, disrupts the regular arrangement of polymer chains, inhibits crystallization, and improves ion mobility; on the other hand, it constructs a continuous ion-electron synergistic conduction channel, forming a highly efficient ion-electron dual transport network. Furthermore, this coating layer can effectively reduce the interfacial impedance between the lithium-rich material and the electrolyte, decrease interfacial polarization, and improve electrochemical kinetic performance. Therefore, the above double-layer coating structure design synergistically enhances the ion conductivity and electronic conductivity of the lithium-rich core, while significantly improving the chemical stability of the material in the air environment. This effectively avoids the degradation of electrochemical performance due to environmental sensitivity during storage and practical applications, and has good prospects for industrial application.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cathode lithium replenishment material, characterized in that, It includes a lithium-rich core and a first coating layer and a second coating layer sequentially covering the lithium-rich core; the first coating layer is a conductive carbon layer and the second coating layer is an inorganic-polymer electrolyte composite layer.

2. The positive electrode lithium replenishment material according to claim 1, characterized in that, The lithium-rich core is a lithium metal oxide (Li). x MO y Wherein, 1≤x≤6, 2≤y≤4, and M is one or more metallic or non-metallic elements that can form tetrahedral or octahedral structures with lithium; preferably, M is selected from one or more of C, P, S, N, Mn, Ni, Cu, Co, Fe, Al, Ti, Mg and Zr. And / or, the lithium-rich core is a binary or multi-component lithium compound Li. a N b , where 1≤a≤3, 1≤b≤6, and N is selected from one or more of O, C, P, S, N and F.

3. The positive electrode lithium replenishment material according to claim 1, characterized in that, The thickness of the first coating layer is 1nm~200nm, and the mass of the first coating layer accounts for 0.5%~5% of the total mass of the positive electrode lithium replenishment material.

4. The positive electrode lithium replenishment material according to any one of claims 1 to 3, characterized in that, The thickness of the second coating layer is 1nm~100nm, and the mass of the second coating layer accounts for 0.1%~2% of the total mass of the positive electrode lithium replenishment material. In the inorganic-polymer electrolyte composite layer, the mass ratio of inorganic solid electrolyte to polymer electrolyte is (0.05~0.3):

1.

5. The positive electrode lithium replenishment material according to claim 4, characterized in that, The inorganic solid electrolyte is a perovskite-type mixed electron-ion conductor, Li. 0.34 La 0.55 DO 3-δ Metal D is selected from at least one of Co and Mn, and δ is a natural number between 0 and 0.5; or the inorganic solid electrolyte is a garnet-type mixed electron-ion conductor Li. 7.3 La3Zr 2-c E c O 12 Where 0.3≤c≤0.5, and metal E is selected from one or more of Fe, Co and Ni; And / or, the polymer corresponding to the polymer electrolyte is selected from one or more of PEO, PVC, PEC, PPC, PTMC, PAN, PDMS, PVDF, PMMA and derivatives of the above polymers, and the molecular weight of the polymer is ≥20000g / mol.

6. A method for preparing a positive electrode lithium replenishment material as described in any one of claims 1 to 5, characterized in that, It includes: The lithium-rich core is uniformly mixed with a carbon source and coated to obtain a lithium-replenishing material with the first coating layer. The mixed solution containing inorganic solid electrolyte and polymer is thoroughly mixed with the lithium replenishing material having the first coating layer. After solid-liquid separation, the mixture is dried to obtain the positive electrode lithium replenishing material.

7. The method for preparing the positive electrode lithium replenishment material according to claim 6, characterized in that, The carbon source is C. d H e O f Where d, e, and f are any combination of natural numbers, and the carbon source contains ≥40% C. And / or, after the lithium-rich core is uniformly mixed with the carbon source, it is kept at 500℃ to 900℃ for 3 to 15 hours under the protection of an inert gas with a flow rate of 3 mL / min to 20 mL / min; preferably, the inert gas is selected from any one of nitrogen, argon and helium.

8. The method for preparing the positive electrode lithium replenishment material according to claim 6, characterized in that, It has at least one of the following characteristics: (1) The amount of polymer added is based on the ratio of polymer monomer to Li + The molar ratio is controlled at (0.5-8):1, where Li + The residual lithium on the surface of the lithium replenishment material having the first coating layer; (2) The solvent used in the mixed solution is selected from one or more of alcohols, ethers, acetals, lipids, nitrogen-containing compound solvents and multifunctional solvents, preferably one or more of N-methylpyrrolidone, ethanol, ethylene glycol and tetrahydrofuran; (3) The mixed solution and the lithium replenishing material with the first coating layer are thoroughly mixed by stirring for 0.5h to 2h; (4) The drying is carried out at a temperature of 60℃~120℃ for 6h~24h.

9. A positive electrode sheet, characterized in that, It includes the positive electrode lithium replenishment material as described in any one of claims 1 to 5.

10. A lithium-ion battery, characterized in that, It includes the positive electrode sheet as described in claim 9.

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