A positive electrode lithium supplementing agent, a preparation method thereof, a positive electrode sheet, and a battery

Abstract

The application provides a positive electrode lithium supplement agent, a preparation method of the positive electrode lithium supplement agent, a positive electrode sheet and a battery. 1‑x M x O4, wherein M is a metal doping element, and the value range of x is 0.01<=x<=0.1; the second positive electrode base material comprises one or more of LiPO3, Al2O3 and ZrO2; the positive electrode lithium supplement agent provided by the application effectively solves the key technical bottlenecks of structural instability, serious interface side reaction and poor rate performance of lithium ferrite positive electrode lithium supplement agents in practical application by accurately controlling the doping ratio and combining with a functional inorganic coating layer, and is suitable for a lithium ion battery system with high energy density, long service life and high safety.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a positive electrode lithium replenishing agent and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage systems, and other fields, the market has placed higher demands on the energy density, cycle life, and safety performance of lithium-ion batteries. As a key material for improving the energy density of lithium-ion batteries, cathode lithium replenishment agents can effectively compensate for lithium loss during the first charge and discharge process, thereby improving the battery's initial efficiency.

[0003] Lithium ferrite (Li5FeO4) has become an important research direction for cathode lithium supplementation agents due to its advantages such as high theoretical lithium supplementation capacity (up to 865 mAh / g), low cost, and good safety. However, existing lithium ferrite supplementation agents have the following problems in practical applications: Poor environmental stability: Lithium iron oxide is prone to react with moisture (H2O) and carbon dioxide (CO2) in the air to generate impurities such as LiOH and Li2CO3, which not only reduces lithium replenishment efficiency, but also leads to problems such as slurry agglomeration and electrode cracking in the battery manufacturing process, affecting production stability. Limited improvement in battery performance: When the amount of lithium iron phosphate additive is 0.5%-10%, the improvement effect on the first efficiency and cycle life of the whole battery is not as expected. Moreover, it is easy to have side reactions with the electrolyte during high-temperature storage, generating gases (such as H2, CO2, etc.), which leads to battery swelling and capacity decay. Existing modification solutions are insufficient: In existing technologies, the modification of lithium ferrite is mostly concentrated on single surface coating or element doping, which is difficult to solve the problems of environmental stability, battery performance and high-temperature storage gas generation at the same time. Moreover, some solutions have defects such as complex preparation process, high cost and difficulty in industrialization. Therefore, how to overcome the above-mentioned technical problems and defects has become a key issue that needs to be solved. Summary of the Invention

[0004] In view of the fact that existing modifications of lithium ferrite are mostly focused on single surface coating or element doping, it is difficult to solve the problems of environmental stability, battery performance and high-temperature storage gas generation at the same time. This invention provides a positive electrode lithium replenishment agent and its preparation method, positive electrode sheet and battery.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A first aspect of the present invention provides a positive electrode lithium replenishment agent, the positive electrode lithium replenishment agent comprising a core and a coating layer covering the surface of the core; the core comprising a first positive electrode substrate material, the first positive electrode substrate material comprising lithium ferrite, the chemical formula of the lithium ferrite being Li5Fe 1-x M xO4, where M is a metal dopant element and x takes values ​​in the range of 0.01 ≤ x ≤ 0.1; The coating layer includes a second positive electrode substrate material, which includes one or more of LiPO3, Al2O3, and ZrO2.

[0006] Optionally, M is selected from one or more of the elements Mg, Al, Zn, Ni, and Co.

[0007] Optionally, M is selected from Mg and Al elements, and the molar ratio of Mg to Al is 1:1 to 3:1.

[0008] Optionally, the second positive electrode substrate material includes LiPO3 and Al2O3, wherein the mass ratio of LiPO3 to Al2O3 is 2:1 to 4:1.

[0009] Optionally, the mass ratio of the core to the covering layer is 100:(1-5).

[0010] Optionally, the thickness of the coating layer is 5-20 nm.

[0011] A second aspect of the present invention provides a method for preparing a positive electrode lithium supplement, comprising the following steps: S1. Mix lithium source, iron source and metal doping source into a uniform slurry, dry and sinter the slurry to obtain the first positive electrode substrate material lithium ferrite; S2. The coating source is mixed with lithium ferrite to form a suspension. The mixture is centrifuged, dried and sintered to obtain the positive electrode lithium replenishing agent.

[0012] Optionally, in step S1, the lithium source includes one or more of Li2CO3 and LiOH·H2O; the iron source includes one or more of Fe2O3 and Fe(NO3)3·9H2O; and the metal doping source includes one or more of Mg(NO3)2·6H2O and Al(NO3)3·9H2O.

[0013] Optionally, in step S1, drying and sintering the slurry includes the following steps: S11. Spray dry the slurry; the inlet temperature of the spray dryer is 200-250℃, and the outlet temperature of the spray dryer is 80-100℃, to obtain precursor powder; S12. Place the precursor powder in an atmosphere furnace and heat it to 600-700℃ at a heating rate of 2-5℃ / min in an air atmosphere. Hold the temperature for 4-6 hours and then cool it to room temperature.

[0014] Optionally, in step S2, the coating source includes one or more of LiPO3 solution and Al(NO3)3·9H2O ethanol solution.

[0015] Optionally, in step S2, centrifuging, drying, and sintering the mixture to obtain the positive electrode lithium supplement includes the following steps: S21. Centrifuge the mixture and collect the precipitate; S22. The precipitate is dried under vacuum at a temperature of 80-100℃ for 8-12 hours. Then, it is sintered at a temperature of 300-400℃ for 2-3 hours.

[0016] A third aspect of the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on both sides of the positive current collector, wherein the positive active material layer comprises a positive active material, a positive lithium supplement agent, a conductive agent and a binder, wherein the positive lithium supplement agent is the positive lithium supplement agent described above, or the positive lithium supplement agent is the positive lithium supplement agent prepared by the preparation method described above.

[0017] Optionally, based on the total mass of the positive electrode active material layer as 100%, the percentage of the positive electrode lithium supplement agent in the total mass of the positive electrode active material layer is 0.5%-10%, the percentage of the positive electrode active material in the total mass of the positive electrode active material layer is 80%-95%, the percentage of the conductive agent in the total mass of the positive electrode active material layer is 2%-5%, and the percentage of the binder in the total mass of the positive electrode active material layer is 2%-5%.

[0018] A fourth aspect of the present invention provides a battery comprising the above-described positive electrode, negative electrode, separator, and electrolyte; the electrolyte includes an additive selected from one or more of fluoroethylene carbonate, lithium difluorophosphate, and adiponitrile.

[0019] Optionally, the additive is selected from fluoroethylene carbonate and lithium difluorophosphate, wherein the mass ratio of fluoroethylene carbonate to lithium difluorophosphate is 1:1 to 2:1.

[0020] Optionally, the additive accounts for 1%-5% of the total mass of the electrolyte.

[0021] According to the positive electrode lithium replenisher provided by the present invention, by constructing a dense and chemically stable coating layer on the core surface, the present invention effectively suppresses the side reactions between lithium ferrite and electrolyte, reduces the dissolution of transition metal ions, and thus significantly extends the cycle life of the battery. Furthermore, by introducing an appropriate amount of metal dopant elements into the core, the electronic structure and lithium-ion diffusion channels are regulated without destroying the Li5FeO4 main lattice, improving the intrinsic electronic conductivity and lithium-ion migration rate of the material; simultaneously, the LiPO3 coating layer has a certain lithium-ion conductivity, further reducing the interfacial impedance, enabling the material to maintain a high capacity even at high rates. The present invention employs a dual modification strategy of "bulk doping + surface coating." Bulk doping (M element) enhances lattice stability from the inside, alleviating volume strain during charge and discharge; the surface coating layer constructs a physical / chemical barrier from the outside, preventing HF corrosion and oxygen loss; the synergistic effect of these two methods significantly improves the structural degradation problem under high voltage or high temperature conditions. Furthermore, the coating layer is an inert oxide, possessing excellent thermal stability and chemical inertness. This effectively reduces the oxidative decomposition of the cathode-electrolyte interface at high potentials, lowers the generation of gases such as CO2 and O2, and improves battery safety. Compared to traditional low-voltage cathode lithium replenishers such as lithium iron phosphate (LiFePO4), Li5FeO4-based materials exhibit higher theoretical specific capacity (>200mAh / g) and a higher operating voltage platform. Through the doping-coating composite design of this invention, while retaining the high capacity advantage, it overcomes the inherent defects such as rapid cycle decay and interface instability, achieving a good balance between energy density and durability. Detailed Implementation

[0022] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0024] In one embodiment, a first aspect of the present invention provides a positive electrode lithium replenishment agent, the positive electrode lithium replenishment agent comprising a core and a coating layer covering the surface of the core; the core comprising a first positive electrode substrate material, the first positive electrode substrate material comprising lithium ferrite, the chemical formula of the lithium ferrite being Li5Fe 1-x M x O4, where M is a metal dopant element and x takes values ​​in the range of 0.01 ≤ x ≤ 0.1; The coating layer includes a second positive electrode substrate material, which includes one or more of LiPO3, Al2O3, and ZrO2.

[0025] Specifically, the value of x is any one point value or any two point values ​​from 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1; in a preferred embodiment, the value of x is 0.01≤x≤0.08.

[0026] When the value of x is in the range of 0.01≤x≤0.1, it can stabilize the crystal structure, suppress lattice distortion caused by lithium-ion insertion / extraction during charging and discharging, improve electronic conductivity and / or lithium-ion diffusion rate, improve the cycle stability and rate performance of the material, and at the same time avoid significant damage to the main phase structure, maintaining a high specific capacity. When the value of x is less than 0.01, the doping amount of the metal dopant is too low, the doping effect is not obvious, and it is difficult to effectively control the lattice parameters or electronic structure; the improvement on the electrochemical performance of the material (such as cycle life and rate capability) is limited; it cannot fully suppress the dissolution of Fe or interfacial side reactions, and the overall performance improvement is weak. When the value of x is greater than 0.1, the excessive doping amount of the metal dopant will lead to excessive lattice distortion or even phase transition, destroying the original spinel or layered structure of Li5FeO4; the lithium-ion migration channel is blocked, and the ionic conductivity decreases; the reversible lithium content in the active material decreases, resulting in a significant decrease in specific capacity; and impurity phases (such as metal oxide second phases) are generated, affecting the material uniformity and electrochemical reversibility.

[0027] This invention effectively suppresses side reactions between lithium ferrite and the electrolyte by constructing a dense and chemically stable coating layer on the core surface, reducing the dissolution of transition metal ions and thus significantly extending the cycle life of the battery. Furthermore, the introduction of appropriate metal doping elements into the core, without disrupting the Li5FeO4 main lattice, modulates the electronic structure and lithium-ion diffusion channels, improving the intrinsic electronic conductivity and lithium-ion migration rate of the material. Simultaneously, the LiPO3 coating layer possesses a certain lithium-ion conductivity, further reducing interfacial impedance and enabling the material to maintain high capacity even at high rates. This invention employs a dual modification strategy of "bulk doping + surface coating." Bulk doping (M element) enhances lattice stability from within, mitigating volume strain during charge and discharge; the surface coating layer constructs a physical / chemical barrier from the outside, preventing HF corrosion and oxygen loss. The synergistic effect of these two methods significantly improves the structural degradation problem under high voltage or high temperature conditions. Furthermore, the coating layer is an inert oxide, possessing excellent thermal stability and chemical inertness. This effectively reduces the oxidative decomposition of the cathode-electrolyte interface at high potentials, lowers the generation of gases such as CO2 and O2, and improves battery safety. Compared to traditional low-voltage cathode lithium replenishers such as lithium iron phosphate (LiFePO4), Li5FeO4-based materials exhibit higher theoretical specific capacity (>200mAh / g) and a higher operating voltage platform. Through the doping-coating composite design of this invention, while retaining the high capacity advantage, it overcomes the inherent defects such as rapid cycle decay and interface instability, achieving a good balance between energy density and durability.

[0028] In summary, the positive electrode lithium replenishment agent provided by this invention effectively solves the key technical bottlenecks faced by lithium iron ferrite positive electrode lithium replenishment agents in practical applications, such as structural instability, severe interfacial side reactions, and poor rate performance, by precisely controlling the doping ratio and combining it with a functional inorganic coating layer. It is suitable for lithium-ion battery systems with high energy density, long life and high safety.

[0029] In one embodiment, M is selected from one or more of the elements Mg, Al, Zn, Ni, and Co.

[0030] Specifically, selecting the aforementioned metal elements as metal dopant elements can optimize the crystal structure of lithium ferrite and reduce active sites; the surface coating layer can form a dense barrier, and the two work together to inhibit the reaction of lithium ferrite with H2O and CO2. According to the test, after the modified lithium ferrite was placed in air with 60% humidity and 25°C for 72 hours, the content of LiOH and Li2CO3 impurities was less than 0.5%, which is much lower than the more than 5% of unmodified lithium ferrite, and the process stability was greatly improved.

[0031] In one embodiment, M is selected from Mg and Al elements, and the molar ratio of Mg to Al is 1:1 to 3:1.

[0032] Specifically, the molar ratio of Mg to Al is any one value or a range of any two values ​​from 1:1, 2:1, or 3:1; in a preferred embodiment, the molar ratio of Mg to Al is 1:1-2:1.

[0033] When the molar ratio of Mg to Al is 1:1 to 3:1, the crystal structure stability of lithium ferrite can be improved by suppressing the Frenkel defect, and the reactivity with H2O and CO2 can be reduced. When the molar ratio of Mg to Al is less than 1:1, it will lead to Al... 3+ With its small radius and high charge, Mg can over-substitute Fe sites in the crystal lattice, potentially blocking lithium-ion diffusion channels. This significantly reduces the intrinsic electronic conductivity of the material, leading to deterioration in rate performance. When the molar ratio of Mg to Al is greater than 3:1, it results in an excess of Mg, which disrupts the local charge balance of Li5FeO4, causing disordered lithium sites or cation mixing. This exacerbates lattice expansion, reduces structural stability, and makes the material prone to phase separation or collapse during deep cycling. Some Mg may segregate at grain boundaries or surfaces, forming insulating byproducts (such as MgO), increasing interfacial impedance and thus weakening cycling and rate performance.

[0034] In one embodiment, the second positive electrode substrate material includes LiPO3 and Al2O3, wherein the mass ratio of LiPO3 to Al2O3 is 2:1 to 4:1.

[0035] Specifically, the mass ratio of LiPO3 to Al2O3 is any one value or a range of any two values ​​from 2:1, 3:1 or 4:1; in a preferred embodiment, the mass ratio of LiPO3 to Al2O3 is 2:1-3:1.

[0036] When the mass ratio of LiPO3 to Al2O3 is 2:1-4:1, a dense physical barrier can be formed, further isolating H2O and CO2, while improving the compatibility of lithium ferrite with the positive electrode lithium replenisher and electrolyte. When the mass ratio of LiPO3 to Al2O3 is less than 2:1, the proportion of insulating Al2O3 in the coating layer is too high, significantly increasing the interfacial lithium-ion transport resistance and intensifying battery polarization. Although the physical barrier effect is enhanced, the ionic conductivity decreases, leading to a deterioration in rate performance, especially with significant capacity decay at high current densities. The coating layer may also be too rigid, causing issues during charging and discharging. Volume changes can easily generate microcracks, which weakens the protective effect. When the mass ratio of LiPO3 to Al2O3 is greater than 4:1, the Al2O3 content in the coating layer is insufficient, the physical barrier effect is weakened, and it is difficult to effectively isolate corrosive substances such as H2O, CO2 and HF. Although LiPO3 has ionic conductivity, its chemical stability is poor. It is easy to hydrolyze or react with electrolyte in high voltage or humid environments to generate phosphate byproducts, which destroys the interfacial stability. The density of the coating layer decreases, and pores or discontinuous areas may appear, which cannot effectively inhibit Fe dissolution and interfacial oxidative decomposition, and the cycle performance deteriorates instead.

[0037] In one embodiment, the mass ratio of the core to the covering layer is 100:(1-5).

[0038] Specifically, the mass ratio of the kernel to the coating layer is any one value or a range of any two values ​​from 100:5, 100:4, 100:3, 100:2 or 100:1; in a preferred embodiment, the mass ratio of the kernel to the coating layer is 100:(2-4).

[0039] When the mass ratio of the core to the coating layer is 100:(1-5), the coating layer has a moderate thickness and uniform distribution, effectively covering the core surface and forming a continuous and dense protective interface, significantly inhibiting the electrolyte's erosion of the lithium ferrite core; without significantly sacrificing specific capacity, it improves the material's cycle stability, rate performance, and high-temperature storage performance. When the mass ratio of the core to the coating layer is less than 100:5, the coating layer is too thick or locally piled up, hindering the rapid migration of lithium ions at the electrode / electrolyte interface and increasing charge transfer impedance; when the mass ratio of the core to the coating layer is greater than 100:1, the coating layer is discontinuous and has insufficient coverage, failing to form a complete and effective physical / chemical barrier; some areas of the core surface are directly exposed to the electrolyte, exacerbating side reactions, transition metal dissolution, and interfacial impedance growth.

[0040] In one embodiment, the thickness of the coating layer is 5-20 nm.

[0041] Specifically, the thickness of the coating layer is any one value or a range of any two values ​​selected from 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, or 20nm; in a preferred embodiment, the thickness of the coating layer is 8-17nm.

[0042] When the coating layer thickness is 5-20 nm, the coating layer is of moderate thickness and uniform distribution, effectively covering the core surface and forming a continuous and dense protective interface, significantly inhibiting the electrolyte's erosion of the lithium ferrite core; without significantly sacrificing specific capacity, it improves the material's cycle stability, rate performance, and high-temperature storage performance. When the coating layer thickness is less than 5 nm, the coating layer is discontinuous and has insufficient coverage, failing to form a complete and effective physical / chemical barrier; some areas of the core surface are directly exposed to the electrolyte, exacerbating side reactions, transition metal dissolution, and interfacial impedance growth; when the coating layer thickness is greater than 20 nm, the coating layer is too thick or locally accumulated, hindering the rapid migration of lithium ions at the electrode / electrolyte interface and increasing charge transfer impedance.

[0043] A second aspect of the present invention provides a method for preparing a positive electrode lithium supplement, comprising the following steps: S1. Mix lithium source, iron source and metal doping source into a uniform slurry, dry and sinter the slurry to obtain the first positive electrode substrate material lithium ferrite; S2. The coating source is mixed with lithium ferrite to form a suspension. The mixture is centrifuged, dried and sintered to obtain the positive electrode lithium replenishing agent.

[0044] This invention, through the aforementioned preparation method, constructs a dense and chemically stable coating layer on the core surface, effectively suppressing side reactions between lithium ferrite and the electrolyte, reducing the dissolution of transition metal ions, and thus significantly extending the battery's cycle life. Furthermore, the introduction of appropriate metal doping elements into the core, without disrupting the Li5FeO4 main lattice, modulates the electronic structure and lithium-ion diffusion channels, improving the material's intrinsic electronic conductivity and lithium-ion migration rate. This invention employs a dual modification strategy of "bulk doping + surface coating." Bulk doping (M element) enhances lattice stability from within, mitigating volume strain during charge and discharge; the surface coating layer constructs a physical / chemical barrier from the outside, preventing HF corrosion and oxygen loss. The synergistic effect of these two methods significantly improves the structural degradation problem under high voltage or high temperature conditions.

[0045] In one embodiment, in step S1, the lithium source includes one or more of Li2CO3 and LiOH·H2O; the iron source includes one or more of Fe2O3 and Fe(NO3)3·9H2O; and the metal doping source includes one or more of Mg(NO3)2·6H2O and Al(NO3)3·9H2O.

[0046] Nitrate precursors (such as Fe(NO3)3·9H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O) are highly soluble in water or polar solvents, facilitating atomic-level homogeneous mixing; during subsequent calcination, nitrate ions (NO3)... - It can decompose to produce gas (NO). x O2 helps promote particle dispersion, inhibit agglomeration, and form porous or loose structures, which is beneficial for lithium-ion diffusion; Using high-purity, easily weighable hydrated nitrate as the Mg / Al doping source facilitates precise control of the dopant element M content (x value), ensuring the optimal concentration of Li5Fe. 1-x M x In O4, x is stably within the optimized range of 0.01–0.1, thus avoiding local phase separation or performance fluctuations caused by uneven doping. In one embodiment, the drying and sintering of the slurry in step S1 includes the following steps: S11. Spray dry the slurry; the inlet temperature of the spray dryer is 200-250℃, and the outlet temperature of the spray dryer is 80-100℃, to obtain precursor powder; S12. Place the precursor powder in an atmosphere furnace and heat it to 600-700℃ at a heating rate of 2-5℃ / min in an air atmosphere. Hold the temperature for 4-6 hours and then cool it to room temperature.

[0047] Specifically, the inlet temperature of the spray dryer is any one value or a range of any two values ​​among 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃ or 250℃; in a preferred embodiment, the inlet temperature of the spray dryer is 210-240℃.

[0048] Specifically, the outlet temperature of the spray dryer is any one value or a range of any two values ​​among 80°C, 85°C, 90°C, 95°C, or 100°C; in a preferred embodiment, the outlet temperature of the spray dryer is 85°C-95°C.

[0049] Specifically, the drying temperature is any one value or a range of any two values ​​selected from 600℃, 605℃, 610℃, 615℃, 620℃, 625℃, 630℃, 635℃, 640℃, 645℃, 650℃, 655℃, 660℃, 665℃, 670℃, 675℃, 680℃, 685℃, 690℃, 695℃, or 700℃; in a preferred embodiment, the drying temperature is 620℃-680℃.

[0050] Specifically, the drying time is any one value or a range of any two values ​​from 4h, 4.2h, 4.4h, 4.6h, 4.8h, 5h, 5.2h, 5.4h, 5.6h, 5.8h, or 6h; in a preferred embodiment, the drying time is 4.6-5.4h.

[0051] The preparation method employs mature processes such as spray drying and low-temperature calcination, which are cost-controllable and suitable for industrial production.

[0052] In one embodiment, in step S2, the coating source includes one or more of LiPO3 solution and Al(NO3)3·9H2O ethanol solution.

[0053] Specifically, after high-temperature treatment, LiPO3 can be converted into stable Li3PO4, which has good ionic conductivity and chemical stability; it can suppress side reactions between electrode materials and electrolytes, and improve cycle stability and rate performance.

[0054] Al(NO3)3·9H2O, when dissolved in ethanol, can serve as an aluminum source. Ethanol, as a solvent, helps to uniformly disperse the precursor and improves the uniformity of the coating. During subsequent heat treatment, it decomposes to form an Al2O3 coating layer, which improves the structural stability of the material and reduces the dissolution of transition metals. Al2O3 is an inert oxide that can effectively isolate the active material from the corrosion of the electrolyte.

[0055] In one embodiment, step S2, centrifuging, drying, and sintering the mixture to obtain the positive electrode lithium supplement agent, includes the following steps: S21. Centrifuge the mixture and collect the precipitate; S22. The precipitate is dried under vacuum at a temperature of 80-100℃ for 8-12 hours. Then, it is sintered at a temperature of 300-400℃ for 2-3 hours.

[0056] Specifically, the drying temperature is any one value or a range of any two values ​​among 80°C, 85°C, 90°C, 95°C, or 100°C; in a preferred embodiment, the drying temperature is 85°C-95°C.

[0057] Specifically, the drying time is any one value or a range of any two values ​​from 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h; in a preferred embodiment, the drying time is 9-11h.

[0058] Specifically, the sintering temperature is any one value or a range of any two values ​​selected from 300℃, 305℃, 310℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, 355℃, 360℃, 365℃, 370℃, 375℃, 380℃, 385℃, 390℃, 395℃, or 400℃; in a preferred embodiment, the sintering temperature is 320℃-380℃.

[0059] Specifically, the sintering time is any one value or a range of any two values ​​from 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h; in a preferred embodiment, the sintering time is 2.2-2.8h.

[0060] Drying is carried out at 80–100℃, which can gently and efficiently remove free water, adsorbed water and low-boiling-point solvents from the precipitate, avoiding particle agglomeration or structural collapse caused by rapid heating; sintering (300–400℃) can completely decompose and remove crystal water, residual organic matter or coordination solvent molecules, ensuring high purity and chemical stability of the product; the gradient heating drying strategy avoids thermal stress concentration, particle sintering or pore collapse caused by one-step high-temperature drying, which is conducive to maintaining the original morphology, specific surface area and porous structure of the precipitate, which is crucial for subsequent applications.

[0061] A third aspect of the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on both sides of the positive current collector. The positive active material layer comprises a positive active material, a positive lithium supplement agent, a conductive agent, and a binder. The positive lithium supplement agent is the positive lithium supplement agent described above, or the positive lithium supplement agent is the positive lithium supplement agent prepared by the preparation method described above.

[0062] Specifically, the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer can be disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0063] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on the polymer material substrate. Exemplarily, the polymer material can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. In some embodiments, the positive electrode active material also includes one or more of ternary materials (NCM / NCA), lithium iron phosphate, lithium cobalt oxide, and lithium manganese oxide.

[0064] In some embodiments, the adhesive may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0065] In some embodiments, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0066] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode lithium supplement, positive electrode active material, positive electrode lithium supplement, conductive agent, binder and any other components in a solvent (e.g. N-methylpyrrolidone), to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0067] In one embodiment, with the total mass of the positive electrode active material layer as 100%, the percentage of the positive electrode lithium supplement agent in the total mass of the positive electrode active material layer is 0.5%-10%; the percentage of the positive electrode active material in the total mass of the positive electrode active material layer is 80%-95%; the percentage of the conductive agent in the total mass of the positive electrode active material layer is 2%-5%; and the percentage of the binder in the total mass of the positive electrode active material layer is 2%-5%.

[0068] Specifically, the percentage of the positive electrode lithium supplement agent in the total mass of the positive electrode active material layer is any one value or a range of any two values ​​selected from 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%; in a preferred embodiment, the percentage of the positive electrode lithium supplement agent in the total mass of the positive electrode active material layer is 1%-5%.

[0069] When the positive electrode lithium replenishing agent accounts for 0.5%-10% of the total mass of the positive electrode active material layer, it can effectively exert its lithium replenishment efficiency, effectively suppress the side reactions between lithium ferrite and electrolyte, reduce the dissolution of transition metal ions, and thus significantly extend the cycle life of the battery. When the positive electrode lithium replenishing agent accounts for less than 0.5% of the total mass of the positive electrode active material layer, it is sparsely distributed in the positive electrode, making it difficult to form an effective protective layer or conductive network, and failing to significantly improve interface stability or suppress the dissolution of transition metals, resulting in insignificant improvement in cycle performance. When the positive electrode lithium replenishing agent accounts for more than 10% of the total mass of the positive electrode active material layer, excessive introduction will reduce the overall energy density of the positive electrode; at the same time, it may increase the interface impedance due to particle accumulation or extended ion diffusion paths, leading to a decrease in the conductivity of the positive electrode.

[0070] Specifically, the percentage content of the positive electrode active material in the total mass of the positive electrode active material layer is any one value or a range of any two values ​​selected from 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or 95%; in a preferred embodiment, the percentage content of the positive electrode active material in the total mass of the positive electrode active material layer is 83%-92%.

[0071] When the positive electrode active material accounts for 80%-95% of the total mass of the positive electrode active material layer, it can serve as the main electrochemical active component, fully leveraging its advantages such as high specific capacity, excellent rate performance, or good cycle stability. At the same time, it reserves an appropriate amount of space for the positive electrode lithium supplement, achieving synergistic optimization of both in terms of electrochemical performance and structural stability, thereby obtaining battery performance that balances high conductivity and long lifespan. When the positive electrode active material accounts for less than 80% of the total mass of the positive electrode active material layer, its proportion in the positive electrode is insufficient, resulting in a significant decrease in overall reversible capacity, making it difficult to meet the design requirements for high energy density. At the same time, the relative excess of the positive electrode lithium supplement may introduce too many inactive or low-activity phases, increasing interfacial impedance and deteriorating rate performance and voltage plateau stability. When the percentage of the positive electrode active material in the total mass of the positive electrode active material layer exceeds 95%, the content of the positive electrode lithium replenisher is too low, and it cannot effectively perform its functions such as interface protection, suppression of side reactions, compensation for lithium loss, or improvement of thermal stability. This causes the battery to be prone to problems such as accelerated capacity decay, increased gas production, or decreased safety performance under high voltage, high temperature, or long cycle conditions.

[0072] Specifically, the percentage of the conductive agent in the total mass of the positive electrode active material layer is any one value or a range of any two values ​​from 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%; in a preferred embodiment, the percentage of the conductive agent in the total mass of the positive electrode active material layer is 2.5%-4.5%.

[0073] When the conductive agent accounts for 2%-5% of the total mass of the positive electrode active material layer, it can construct an efficient and continuous electronic conduction network between active particles and between the active material and the current collector, effectively improving the rate performance, cycle stability and charge / discharge efficiency of the battery. When the conductive agent accounts for less than 2% of the total mass of the positive electrode active material layer, the conductive network is discontinuous or insufficiently covered, resulting in a significant decrease in rate performance and low capacity utilization. When the conductive agent accounts for more than 5% of the total mass of the positive electrode active material layer, although the electronic conductivity is further enhanced, it will dilute the proportion of active material in the positive electrode and reduce the overall volumetric / weight specific capacity of the electrode.

[0074] Specifically, the percentage of the binder in the total mass of the positive electrode active material layer is any one value or a range of any two values ​​from 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%; in a preferred embodiment, the percentage of the binder in the total mass of the positive electrode active material layer is 2.5%-4.5%.

[0075] When the binder accounts for 2%-5% of the total mass of the positive electrode active material layer, it can form a sufficient and uniform bonding network between the active material particles and between the active material and the current collector (such as aluminum foil), taking into account good cycle stability, electrolyte wettability, and lithium-ion transport kinetics. When the binder accounts for less than 2% of the total mass of the positive electrode active material layer, the bonding force is insufficient, resulting in poor adhesion of the electrode coating. During rolling, slitting, or battery cycling, problems such as powder shedding, peeling, or particle contact failure are likely to occur. When the binder accounts for more than 5% of the total mass of the positive electrode active material layer, the excessive polymer binder will coat the surface of the active material, hindering the lithium-ion insertion / extraction path. At the same time, it will crowd out the conductive agent and pore space, reduce the electron / ion conduction efficiency of the electrode, and reduce the active material loading per unit area, resulting in a decrease in specific capacity and a deterioration in rate performance.

[0076] A fourth aspect of the present invention provides a battery comprising the above-described positive electrode, negative electrode, separator, and electrolyte; the electrolyte includes an additive selected from one or more of fluoroethylene carbonate, lithium difluorophosphate, and adiponitrile.

[0077] The electrolyte, by introducing fluoroethylene carbonate, lithium difluorophosphate, and / or adiponitrile as additives, can construct a highly stable, low-impedance interfacial protective film in situ on the surface of the positive and / or negative electrodes, effectively inhibiting electrolyte decomposition, transition metal dissolution, and gas generation. It not only significantly improves the battery's cycle life, high-temperature storage performance, and high-voltage stability, but also improves low-temperature discharge capability and safety performance, making it particularly suitable for high-energy-density lithium-ion battery systems such as high-nickel ternary, silicon-carbon anode, or high-voltage lithium cobalt oxide.

[0078] Furthermore, the electrolyte includes lithium salts and non-aqueous organic solvents; Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate. The non-aqueous organic solvent is selected from one or more combinations of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluorocarbonate (such as TFPC), sulfones (such as EMS), and nitriles (such as adiponitrile ADN).

[0079] Furthermore, the electrolyte may also contain one or more of the following: overcharge protectant, flame retardant, HF scavenger (such as lithium difluorophosphate LiDFP), and high voltage stabilizer (such as adiponitrile ADN and triphenylphosphine oxide TPPO).

[0080] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer is coated on both sides of the negative electrode current collector.

[0081] Specifically, the negative electrode current collector is selected from a metallic material that can conduct electrons. Preferably, the negative electrode current collector includes metals such as stainless steel, Al, Ni, tin, copper, nickel, titanium, and iron, or their alloys. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0082] Specifically, the negative electrode active material layer includes: a negative electrode active material, a conductive agent, and a binder.

[0083] In one embodiment, the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, silicon materials, and lithium metal materials; the conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and the binder includes one or more of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, waterborne acrylic resin, polyacrylic acid, carboxymethyl cellulose, and carboxymethyl cellulose modified materials.

[0084] Specifically, the separator can be any separator material suitable for lithium-ion batteries in the art, such as, but not limited to, one or more combinations of single-layer polypropylene, single-layer polyethylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0085] The electrode assembly can consist of a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode and serves as a barrier. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to these.

[0086] In some embodiments, the battery is prepared as follows: the positive electrode, separator, and negative electrode are wound or stacked in sequence to form an electrode assembly, which is then placed in, for example, an aluminum-plastic film, injected with electrolyte, formed, and packaged to produce a lithium-ion battery.

[0087] While the exemplary embodiments described above use lithium-ion batteries as examples, those skilled in the art will understand after reading this application that, without departing from the spirit of this application, specific examples of the battery can include all types of primary or secondary batteries. In particular, the battery is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0088] In one embodiment, the additive is selected from fluoroethylene carbonate and lithium difluorophosphate, wherein the mass ratio of the fluoroethylene carbonate and the lithium difluorophosphate is 1:1 to 2:1.

[0089] FEC can form a stable SEI film on the surface of modified lithium ferrite, suppressing side reactions; LiPO2F2 can suppress the decomposition of electrolyte and reduce the generation of gases such as H2 and CO2; the synergistic effect of the two significantly improves the high-temperature storage stability of the battery.

[0090] Specifically, the mass ratio of the fluoroethylene carbonate to the lithium difluorophosphate is any one value or a range of any two values ​​from 1:1, 6:5, 7:5, 8:5, 9:5 or 2:1; in a preferred embodiment, the mass ratio of the fluoroethylene carbonate to the lithium difluorophosphate is 6:5-9:5.

[0091] When the mass ratio of fluoroethylene carbonate to lithium difluorophosphate is 1:1 to 2:1, FEC can form a stable SEI film on the modified lithium ferrite surface, suppressing side reactions; LiPO2F2 can suppress electrolyte decomposition and reduce the generation of gases such as H2 and CO2; the synergistic effect of the two significantly improves the high-temperature storage stability of the battery. When the mass ratio of fluoroethylene carbonate to lithium difluorophosphate is less than 1:1, the FEC content is relatively insufficient, making it difficult to construct a complete and continuous SEI film on the negative electrode, resulting in a high initial irreversible capacity and continuous electrolyte consumption during cycling; when the mass ratio of fluoroethylene carbonate to lithium difluorophosphate is greater than 2:1, excess FEC may be over-reduced or polymerized during cycling or high-temperature storage, generating a thick and high-impedance SEI layer, increasing the interface resistance; FEC is prone to oxidative decomposition under high voltage or high temperature, producing byproducts such as HF, CO2, and C2H4, which exacerbates the gas generation problem.

[0092] In one embodiment, the additive accounts for 1%-5% of the total mass of the electrolyte.

[0093] Specifically, the additive accounts for any one or a range of any two values ​​from 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5% of the total mass of the electrolyte; in a preferred embodiment, the additive accounts for 2%-4% of the total mass of the electrolyte.

[0094] When the additive accounts for 1%-5% of the total mass of the electrolyte, it can effectively participate in the film-forming reaction at the electrode / electrolyte interface without significantly changing the bulk ionic conductivity and viscosity of the electrolyte. This results in the formation of a dense and stable SEI film at the negative electrode and a protective CEI layer at the positive electrode, significantly improving the battery's cycle life, high-temperature storage stability, and safety performance. When the additive content is less than 1%, its concentration in the electrolyte is too low, making it difficult to form a continuous and effective functional interface film on the electrode surface or to sufficiently suppress side reactions. This leads to high interfacial impedance, accelerated capacity decay during cycling, and significant gas expansion or capacity drop during high-temperature storage, failing to achieve the expected modification effect. When the additive content exceeds 5%, excessive additive increases electrolyte viscosity, reduces lithium-ion migration rate, deteriorates rate performance, and reduces the proportion of the main solvent, thus lowering the overall ionic conductivity of the electrolyte.

[0095] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0096] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0097] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0098] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.

[0099] Table 1. Design of positive electrode lithium replenishing agents for Examples 1-21 and Comparative Examples 1-5; Table 2. Electrolyte design for Examples 1 and 22-31; Example 1 This embodiment illustrates the positive electrode lithium replenishment agent, positive electrode sheet, and battery disclosed in this invention; it includes the following operational steps: Preparation of positive electrode lithium supplement: (1) Core preparation: Weigh Li2CO3 (0.5 mol), Fe2O3 (0.24 mol), Mg(NO3)2·6H2O (0.01 mol), and Al(NO3)3·9H2O (0.01 mol), add deionized water, and stir to form a slurry; spray dry (inlet temperature 220℃, outlet temperature 90℃) to obtain the precursor; keep at 650℃ for 5 h in air atmosphere to obtain Li5Fe 0.96 Mg 0.02 Al 0.02 O4 kernel; (2) Weigh 100g of kernels, add anhydrous ethanol and ultrasonically disperse for 40min; weigh 3g of LiPO3 solution (mass fraction 50%) and 1.5g of Al(NO3)3・9H2O, add them to the suspension, stir at 55℃ for 3h; centrifuge, vacuum dry (90℃, 10h), calcine at 350℃ for 2.5h to obtain surface-coated modified lithium ferrite.

[0100] Preparation of positive electrode: Lithium ferrite, LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black and binder PVDF are mixed in a ratio of 3:88:4:5 to prepare a positive electrode slurry. The positive electrode slurry is coated onto the surface of the positive electrode current collector on a coating machine. After drying, rolling and die cutting, the required positive electrode sheet is obtained.

[0101] Preparation of negative electrode: A negative electrode slurry was prepared by mixing the negative electrode active material graphite and the binder SBR in a ratio of 98:2. The negative electrode slurry is coated onto the negative electrode current collector copper foil on a coating machine, and the negative electrode sheet is obtained after drying, rolling, die cutting and other processes.

[0102] Electrolyte preparation: Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:1:1, with a lithium hexafluorophosphate concentration of 1 mol / L. Then, 2% FEC and 1.5% LiPO2F were added and stirred until homogeneous to form an electrolyte.

[0103] Preparation of the diaphragm: PE porous polymer film is used as the membrane substrate; Battery manufacturing: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then stacked in this manner to form a battery cell. The battery cell is placed into a pre-formed battery casing, and the assembled battery cell is baked and dried. Then, the prepared electrolyte is injected, and the battery undergoes vacuum sealing, settling, and formation processes to obtain the battery.

[0104] Example 2-31 Examples 2-21 illustrate the positive electrode lithium replenishment agent, positive electrode sheet, and battery disclosed in this invention, and include most of the operating steps in Example 1, except that: The parameters of the positive electrode lithium replenisher shown in Table 1 are used.

[0105] Examples 22-31 illustrate the positive electrode lithium replenishment agent, positive electrode sheet, and battery disclosed in this invention, and include most of the operating steps in Example 1, except that: The parameters of the electrolyte shown in Table 2 were used.

[0106] Comparative Examples 1-5 Comparative Examples 1-5 are used to illustrate the positive electrode lithium replenishment agent, positive electrode sheet, and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being: The parameters of the positive electrode lithium replenisher shown in Table 1 are used.

[0107] Performance testing The following performance tests were performed on the batteries prepared in Examples 1-31 and Comparative Examples 1-5: Impurity content test after 72 hours of exposure to air: 5g each of the modified lithium ferrite supplement powder prepared in Examples 1-31 and Comparative Examples 1-5 were placed in clean petri dishes, with a thickness controlled at 1-2mm. The petri dishes were placed in a constant temperature and humidity chamber, with environmental parameters set to 25℃ and 60% relative humidity, and exposed for 72 hours, avoiding vibration or contamination of the samples during this period. Impurity content was determined (using XRD quantitative analysis + acid-base titration method for synergistic verification).

[0108] (1) Quantitative analysis by X-ray diffraction (XRD) ① Take 2g of the exposed sample and grind it under argon protection until the particle size is <10μm to prevent the introduction of CO2 and H2O from the air during the grinding process. ② Spread the ground sample evenly in the XRD sample trough, compact it and make the surface smooth. Use an X-ray diffractometer (Cu target Kα rays, λ=1.5406Å), set the tube voltage to 40kV, tube current to 40mA, scanning range 2θ=10°~60°, scanning speed 5° / min, step size 0.02°. ③ Plot standard curves for Li₂CO₃ (characteristic peaks 2θ = 21.5°, 29.4°) and LiOH (characteristic peak 2θ = 38.5°): Prepare a series of standard mixed samples with Li₂CO₃ and LiOH mass fractions of 0.1%~2%, scan them according to the above parameters, and establish a linear relationship with the ratio of the characteristic peak intensity of impurities to the characteristic peak intensity of lithium ferrite (2θ = 35.6°) as the ordinate and the impurity mass fraction as the abscissa. ④ Test the XRD patterns of the samples, substitute them into the standard curves, calculate the mass fractions of Li₂CO₃ and LiOH, and the sum of the two is the total impurity content.

[0109] (2) Verification of acid-base titration method ① Take 5g of the exposed sample (accurate to 0.0001g), add 50mL of boiled and cooled deionized water (to eliminate CO2 interference in the water) under an argon atmosphere, sonicate for 30min, and filter to separate the filtrate from the insoluble lithium ferrite. ② Add 2 drops of phenolphthalein indicator to the filtrate, and titrate with 0.01mol / L standard HCl solution until the solution changes from red to colorless. Record the volume consumed, V1, corresponding to the LiOH content. ③ Continue to add 2 drops of methyl orange indicator to the solution, and titrate with the above standard HCl solution until the solution changes from yellow to orange. Record the volume consumed, V2, corresponding to the Li2CO3 content. ④ Calculate the total impurity content: m(LiOH) = c × V1 × 24 m(Li2CO3) = c × V² × 74 Impurity content (%) = (m(LiOH) + m(Li2CO3)) / m(sample) × 100% In the formula, c is the concentration of HCl solution (mol / L), 24 is the molar mass of LiOH (g / mol), and 74 is the molar mass of Li2CO3 (g / mol).

[0110] (3) Result confirmation The average value of the XRD quantitative analysis and acid-base titration results is taken as the final impurity content, ensuring that the data deviation is <0.05%.

[0111] Battery initial efficiency test: The pouch batteries assembled in the examples and comparative examples were placed in a 25°C constant temperature chamber and left to stand for 2 hours to allow the battery temperature to match the ambient temperature. Constant current constant voltage (CC-CV) charging mode was used: the batteries were charged at a constant current rate of 0.5C until the cutoff voltage of 4.4V, followed by constant voltage charging until the current dropped to 0.05C. The total charging capacity C was recorded. 充 After standing for 1 hour, a constant current (CC) discharge mode was used: discharge at a rate of 0.5C to the cutoff voltage of 3.0V, and the discharge capacity C was recorded. 放 First-efficacy (%) = C 放 / C 充 ×100%.

[0112] Battery cycle stability method: The battery is charged and discharged at a constant temperature of 25°C with a voltage range of 3.0V~4.4V, and after 100 cycles at a 1C rate, its capacity retention rate is tested.

[0113] Capacity decay test after 30 days of storage at 60℃: ① Charge the battery to 4.4V at a rate of 0.5C, let it stand for 2 hours, and record the discharge capacity C before storage. 前 (The test method is the same as the discharge procedure in the first-efficiency test). ② Place the fully charged battery in a 60℃ constant temperature chamber and store it for 30 days. During this period, observe the appearance of the battery weekly to confirm that there is no leakage, bulging, or damage. ③ After storage, remove the battery and place it in a 25℃ constant temperature chamber for 4 hours to allow it to return to room temperature.

[0114] ④ Discharge to 3.0V at a rate of 0.5C, and record the discharge capacity C after storage. 后 ⑤ Calculate the capacity decay rate: Capacity decay (%) = (C 前- C 后 ) / C 前 ×100%.

[0115] Gas generation rate test after 30 days of storage at 60℃: The gas generated during battery storage was collected using the water displacement method and converted to the volume under standard conditions (0℃, 101.325kPa). The gas generation rate was calculated based on the battery's rated capacity. ① Preparation before storage: After weighing the fully charged battery (same as step ① of the capacity decay test), the tab interface was sealed with high-temperature resistant tape to ensure no gas leakage. The battery length L, width W, and thickness h0 were measured using vernier calipers to calculate the initial volume. ② High-temperature storage: The battery was placed in a 60℃ constant temperature chamber and stored for 30 days. ③ Gas collection: The battery was removed and cooled to 25℃. The edge of the battery's aluminum-plastic film (the area without tabs) was pierced with a syringe needle and connected to a gas measuring tube filled with deionized water (inverted in a beaker of water) through a conduit. The battery was slowly squeezed to completely expel the internal gas into the gas measuring tube, and the gas volume V1 (volume at 25℃ and atmospheric pressure) was read. ④ Standard volume conversion: V 标 =V1×(TO In the formula / T1)×(P1 / P0), T O =273.15K (standard temperature), T1=298.15K (room temperature), P1 is the atmospheric pressure at the time of measurement (kPa), P0=101.325kPa (standard atmospheric pressure). ⑤ Calculate the gas production rate: Gas production rate (mL / Ah) = V 标 In the formula / C0, C0 is the rated capacity of the battery (Ah).

[0116] The test results are shown in Table 3.

[0117] Table 3 Battery electrochemical performance Comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that when the value of x is in the range of 0.01 ≤ x ≤ 0.1, the crystal structure is stable, it is not easily reacted with H2O and CO2 in the air, the impurity content is low, and the electronic conductivity and lithium-ion diffusion rate are high, resulting in higher initial battery efficiency, higher cycle stability, higher high-temperature storage capacity, and lower gas generation rate, which significantly improves battery performance. When the value of x is less than 0.01, the doping amount of the metal dopant is too low, the doping effect is not obvious, and it is difficult to effectively control the lattice parameters or electronic structure; it is easy to react with H2O and CO2 in the air, and the impurity content is significantly increased (the impurity content of Comparative Example 1 is 1.8%, which is much higher than the 0.28%-0.35% of Examples 1-3); at the same time, the electronic conductivity and lithium-ion diffusion rate are low. The battery's initial efficiency (82.5%) and cycle stability (75.2%) deteriorated significantly, and the high-temperature storage capacity decay (18.5%) and gas generation rate (3.5 mL / Ah) increased significantly, failing to leverage the lithium replenishment agent's performance-enhancing effect. When the value of x is greater than 0.1, excessive doping of metal dopants can lead to excessive lattice distortion or even phase transition, making it prone to reacting with H2O and CO2 in the air, resulting in a slight increase in impurity content of 0.85%, which is much higher than in Examples 1-3. At the same time, lithium-ion migration channels are blocked, ionic conductivity decreases, and the battery's initial efficiency (88.5%) and cycle stability (84%) deteriorate significantly, while the high-temperature storage capacity decay (9.5%) and gas generation rate (2 mL / Ah) both increase, failing to effectively leverage the lithium replenishment agent's performance-enhancing effect.

[0118] Comparing Examples 1-3 and Comparative Example 3, it can be seen that when lithium ferrite is not doped with Mg and Al, the Frenkel defects in the crystal structure cannot be effectively suppressed, the lattice stability is insufficient, and it is easy to react with H2O and CO2 in the air, resulting in a significant increase in impurity content of 1.5%, which is much higher than that in Examples 1-3. At the same time, the electronic conductivity and lithium-ion diffusion rate are low, the battery's initial efficiency (83.0%) and cycle stability (76.5%) are significantly deteriorated, the high-temperature storage capacity decay (16.8%) and gas generation rate (3.2 mL / Ah) are significantly increased, and the lithium replenishment agent cannot play a role in improving battery performance.

[0119] Comparing Examples 1-3 and Comparative Example 4, it can be seen that when there is no coating layer on the outside of lithium ferrite, the surface lacks a dense physical barrier, and the core is directly exposed to air and electrolyte. It is easy to react with H2O, CO2 and corrosive substances in the electrolyte, with an impurity content of 1.2%, and the interface side reactions are aggravated. The electrode / electrolyte interface impedance increases, resulting in the battery's first efficiency (85.5%) and capacity retention rate after 100 cycles (80.2%) being lower than those in Examples 1-3. Fe dissolution and electrolyte decomposition are aggravated during high-temperature storage, and the capacity decay (12.5%) and gas production rate (2.8 mL / Ah) increase significantly, resulting in a significant decrease in process stability and long-term battery performance.

[0120] Comparing Examples 1-3 and Comparative Example 5, it can be seen that when lithium ferrite is not modified, there is neither metal doping to optimize the crystal structure nor a coating layer to provide surface protection. The crystal has many active sites and an unstable structure. After contact with air, the impurity content is as high as 6.8%, which is far higher than that of Examples 1-3. During the lithium replenishment process, the side reactions are severe, the battery's initial efficiency is only 84.8%, the cycle capacity retention rate is 79.5%, the capacity decay is 16.3% after 30 days of storage at 60°C, and the gas production rate is 2.2 mL / Ah. All performances are at the worst level and cannot meet the requirements of lithium-ion batteries for the environmental stability and electrochemical performance of the lithium replenishment agent.

[0121] Comparing Examples 1 and 4-7, it can be seen that when the molar ratio of Mg to Al is 1:1-3:1, it can suppress the Frenkel defect of lithium ferrite, improve the crystal structure stability, reduce the reactivity with H2O and CO2, and result in lower impurity content. Simultaneously, it leads to higher electronic conductivity and lithium-ion diffusion rate, higher initial battery efficiency, higher cycle stability, higher high-temperature storage capacity, and lower gas production rate, significantly improving battery performance. When the molar ratio of Mg to Al is less than 1:1, it can cause Al... 3+With a small radius and high charge, it excessively substitutes Fe sites in the crystal lattice, resulting in an unstable crystal structure. After contact with air, the impurity content is 0.42%, slightly higher than in Examples 1 and 4-5. It may block the lithium-ion diffusion channels. The battery's initial efficiency is 91.5%, the cycle capacity retention rate is 89.2%, the capacity decay is 5.8% after 30 days of storage at 60°C, and the gas production rate is 1.2 mL / Ah. All performance characteristics are reduced, and it cannot effectively meet the requirements of lithium-ion batteries for the environmental stability and electrochemical performance of lithium replenishment agents. When the molar ratio of Mg to Al is greater than 3:1, it leads to an excess of Mg, which disrupts the local charge balance of Li5FeO4, causing disordered lithium sites or mixed cations; lattice expansion intensifies, structural stability decreases, and the impurity content after contact with air is 0.45%, slightly higher than in Examples 1 and 4-5; some Mg may segregate at grain boundaries or surfaces, forming insulating byproducts (such as MgO), increasing interfacial impedance, resulting in a battery initial efficiency of 9%, a cycle capacity retention of 88.5%, a capacity decay of 6.2% after 30 days of storage at 60℃, and a gas production rate of 1.3 mL / Ah. All performance characteristics are reduced, failing to effectively meet the requirements of lithium-ion batteries for environmental stability and electrochemical performance of lithium replenishment agents.

[0122] Comparing Examples 1 and 8, and Examples 18-19, it can be seen that when lithium ferrite has only one metal doping element (Example 18 is Mg single doping, Example 19 is Al single doping), the ability of a single doping element to regulate the lattice structure is limited, and it is impossible to simultaneously optimize electronic conductivity and lithium-ion diffusion rate. The impurity content (0.38%-0.40%) is higher than that in Example 1, and the battery's first efficiency (90.8%-91.2%) and cycle capacity retention (88.6%-89.0%) are slightly lower. The high-temperature storage capacity decay (5.5%-5.6%) and gas generation rate (1.1-1.15 mL / Ah) increase. When lithium ferrite has two or more metal doping elements (Example 1 is Mg-Al composite doping, Example 8 is Zn-Ni-Co composite doping), different metal ions synergistically regulate the lattice parameters, which can both suppress defect generation and improve interface compatibility. The impurity content is lower and the electrochemical performance is better. In particular, the synergistic effect of Mg-Al composite doping is the best, and the overall performance is the best.

[0123] Comparing Examples 1 and 9-12, it can be seen that when the mass ratio of the core to the coating layer is 100:(1-5), or the thickness of the coating layer is 5-20 nm, the coating layer has a moderate thickness and uniform distribution, effectively covering the core surface and forming a continuous and dense protective interface. It is less likely to react with H2O and CO2 in the air, has a low impurity content, and simultaneously exhibits high electronic conductivity and lithium-ion diffusion rate, resulting in higher initial battery efficiency, higher cycle stability, higher high-temperature storage capacity, and lower gas generation rate, significantly improving battery performance. However, when the mass ratio of the core to the coating layer is less than 100:5, or when the thickness of the coating layer is greater than 20 nm, the coating layer is too thick or locally accumulates, hindering the rapid diffusion of lithium ions at the electrode / electrolyte interface. Rapid migration increases charge transfer impedance; impurity content (0.55%) is higher than in Example 1, resulting in slightly lower initial battery efficiency (89.5%) and cycle capacity retention (86.2%), while high-temperature storage capacity decay (7.5%) and gas generation rate (1.8 mL / Ah) increase; when the mass ratio of the core to the coating layer is greater than 100:1, or when the thickness of the coating layer is less than 5 nm, the coating layer is discontinuous and has insufficient coverage, failing to form a complete and effective physical / chemical barrier; a portion of the core surface is directly exposed to the electrolyte, resulting in an impurity content (0.62%) higher than in Example 1, leading to slightly lower initial battery efficiency (88.8%) and cycle capacity retention rate (85%), while high-temperature storage capacity decay (8.2%) and gas generation rate (2 mL / Ah) increase; Comparing Examples 1 and 13-16, it can be seen that when the mass ratio of LiPO3 to Al2O3 is 2:1-4:1, a dense physical barrier can be formed, further isolating H2O and CO2, resulting in lower impurity content. Simultaneously, it improves the compatibility of lithium ferrite with the positive electrode lithium replenisher and electrolyte; the battery exhibits higher initial efficiency, higher cycle stability, higher high-temperature storage capacity, and lower gas generation rate, significantly enhancing battery performance. When the mass ratio of LiPO3 to Al2O3 is less than 2:1, the proportion of insulating Al2O3 in the coating layer becomes too high, significantly increasing the interfacial lithium-ion transport resistance, decreasing ionic conductivity, and resulting in slightly lower initial efficiency (90.5%), cycle capacity retention (88%), and lower high-temperature storage capacity decay (6%) and gas generation rate (1.25 mL / Ah). The coating layer may be too rigid, making it prone to microcracks under charge-discharge volume changes and easily reacting with air. The impurity content (0.4%) is higher than in Example 1. When the mass ratio of LiPO3 to Al2O3 is greater than 4:1, the Al2O3 content in the coating layer is insufficient, weakening the physical barrier effect and making it difficult to effectively isolate corrosive substances such as H2O, CO2, and HF. The impurity content (0.48%) is higher than in Example 1. Although LiPO3 has ionic conductivity, its chemical stability is poor. It is easily hydrolyzed or reacts with the electrolyte in high voltage or humid environments to generate phosphate byproducts, which damages the interfacial stability. The battery's initial efficiency (89.8%) and cycle capacity retention (87.2%) are slightly lower, while the high-temperature storage capacity decay (6.5%) and gas generation rate (1.4 mL / Ah) increase.

[0124] Comparing Examples 1, 17, and 20-21, it can be seen that when the coating layer contains only one type of metal oxide, the single coating layer has performance shortcomings: LiPO3 single coating has poor chemical stability, is easily hydrolyzed to produce byproducts, has an impurity content of up to 0.50%, and deteriorates high-temperature storage performance; Al2O3 single coating has strong insulation, high interfacial impedance, and the battery's initial efficiency is only 88.5%, with a cycle retention rate of 85.8%; when the coating layer contains two or more metal oxides, complementary performance can be achieved, LiPO3 improves ionic conductivity, Al2O3 and ZrO2 enhance physical barriers and chemical stability, have lower impurity content (0.24%-0.30%), and have better initial efficiency, cycle and high-temperature storage performance. Example 17, with its three-component composite coating, has the best performance.

[0125] Comparing Examples 1 and 22-25, it can be seen that when the mass ratio of the fluoroethylene carbonate to the lithium difluorophosphate is 1:1-2:1, FEC can form a stable SEI film on the modified lithium ferrite surface, suppressing side reactions; LiPO2F2 can suppress the decomposition of the electrolyte, reduce the generation of gases such as H2 and CO2, and has a low impurity content. Simultaneously, the battery exhibits higher initial efficiency, higher cycle stability, higher high-temperature storage capacity, and lower gas production rate, significantly improving battery performance. When the mass ratio of the fluoroethylene carbonate to the lithium difluorophosphate is less than 1:1, the FEC content is relatively insufficient, making it difficult to construct a complete and continuous SEI film on the negative electrode. The impurity content (0.31%) is higher than in Examples 1 and 22-23; the battery's initial efficiency (92.9%) and cycle capacity retention (91.6%) are slightly lower, while the high-temperature storage capacity decay (4.3%) and gas production rate (0.82 mL / Ah) increase. When the mass ratio of the fluoroethylene carbonate to the lithium difluorophosphate is greater than 2:1... Excessive FEC may be over-reduced or polymerized during cycling or high-temperature storage, generating a thick and high-impedance SEI layer, increasing the interface resistance; FEC is prone to oxidative decomposition under high voltage or high temperature, producing byproducts such as HF, CO2, and C2H4, with impurity content (0.43%) higher than in Examples 1 and 22-23; the battery's initial efficiency (90.2%) and cycle capacity retention (87.8%) are slightly lower, while the high-temperature storage capacity decay (6.3%) and gas production rate (1.35 mL / Ah) increase.

[0126] Comparing Examples 1 and 26-29, it can be seen that when the additive accounts for 1%-5% of the total mass of the electrolyte, it can effectively participate in the film-forming reaction at the electrode / electrolyte interface without significantly changing the bulk ionic conductivity and viscosity of the electrolyte. This results in the formation of a dense and stable SEI film at the negative electrode and a protective CEI layer at the positive electrode, significantly improving the battery's cycle life, high-temperature storage stability, and safety performance. The amount of impurities generated is low, and the battery exhibits higher initial efficiency, higher cycle stability, higher high-temperature storage capacity, and lower gas production rate, significantly enhancing battery performance. However, when the additive content is less than 1%, its concentration in the electrolyte is too low to form a continuous film on the electrode surface. The battery has a continuous and effective functional interface film or sufficient suppression of side reactions. The impurity content (0.6%) is higher than that of Examples 1 and 26-27. The battery's initial efficiency (86.8%) and cycle capacity retention (83%) are slightly lower, while the high-temperature storage capacity decay (9%) and gas generation rate (2.2 mL / Ah) increase. When the content of the additive exceeds 5%, the excessive additive will increase the electrolyte viscosity, reduce the lithium-ion migration rate, and deteriorate the rate performance. The impurity content (0.58%) is higher than that of Examples 1 and 26-27. The battery's initial efficiency (87.5%) and cycle capacity retention rate (84.2%) are slightly lower, while the high-temperature storage capacity decay (8.5%) and gas generation rate (2.1 mL / Ah) increase.

[0127] Comparing Examples 1 and 30-31, it can be seen that when the electrolyte contains only fluoroethylene carbonate, although an SEI film can be formed on the electrode surface, it cannot effectively inhibit electrolyte decomposition. During high-temperature storage, the electrolyte will still undergo side reactions with modified lithium ferrite, resulting in a capacity decay of 5.5% and a gas production rate of 1.12 mL / Ah, which is better than the comparative example but worse than Example 1. When the electrolyte contains only lithium difluorophosphate, electrolyte decomposition can be inhibited, but it is difficult to form a stable and dense SEI film. Interfacial side reactions continue to occur, and the battery's initial efficiency (90.0%) and cycle retention rate (87.5%) are lower than those of Example 1. The capacity decay (5.8%) and gas production rate (1.18 mL / Ah) during high-temperature storage are slightly higher. A single additive cannot achieve a synergistic modification effect and it is difficult to take into account various electrochemical performances.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A positive electrode lithium replenishing agent, characterized in that: The positive electrode lithium replenishment agent includes a core and a coating layer covering the surface of the core; the core includes a first positive electrode substrate material, which includes lithium ferrite with the chemical formula Li5Fe. 1-x M x O4, where M is a metal dopant element and x takes values ​​in the range of 0.01 ≤ x ≤ 0.1; The coating layer includes a second positive electrode substrate material, which includes one or more of LiPO3, Al2O3, and ZrO2.

2. The positive electrode lithium replenishing agent according to claim 1, characterized in that: M is selected from one or more of the elements Mg, Al, Zn, Ni, and Co.

3. The positive electrode lithium replenishing agent according to claim 2, characterized in that: M is selected from Mg and Al elements, and the molar ratio of Mg to Al is 1:1 to 3:

1.

4. The positive electrode lithium replenishing agent according to claim 1, characterized in that: The second cathode substrate material includes LiPO3 and Al2O3, wherein the mass ratio of LiPO3 to Al2O3 is 2:1 to 4:

1.

5. The positive electrode lithium replenishing agent according to claim 1, characterized in that: The mass ratio of the core to the coating layer is 100:(1-5).

6. The positive electrode lithium replenishing agent according to claim 1, characterized in that: The thickness of the coating layer is 5-20 nm.

7. The method for preparing the positive electrode lithium replenishing agent according to any one of claims 1-6, characterized in that: Includes the following steps: S1. Mix lithium source, iron source and metal doping source into a uniform slurry, dry and sinter the slurry to obtain the first positive electrode substrate material lithium ferrite; S2. The coating source is mixed with lithium ferrite to form a suspension. The mixture is centrifuged, dried and sintered to obtain the positive electrode lithium replenishing agent.

8. The method for preparing the positive electrode lithium replenishing agent according to claim 7, characterized in that: In step S1, the lithium source includes one or more of Li2CO3 and LiOH·H2O; the iron source includes one or more of Fe2O3 and Fe(NO3)3·9H2O; and the metal doping source includes one or more of Mg(NO3)2·6H2O and Al(NO3)3·9H2O.

9. The method for preparing the positive electrode lithium replenishing agent according to claim 7, characterized in that: In step S1, drying and sintering the slurry includes the following steps: S11. Spray dry the slurry; the inlet temperature of the spray dryer is 200-250℃, and the outlet temperature of the spray dryer is 80-100℃, to obtain precursor powder; S12. Place the precursor powder in an atmosphere furnace and heat it to 600-700℃ at a heating rate of 2-5℃ / min in an air atmosphere. Hold the temperature for 4-6 hours and then cool it to room temperature.

10. The method for preparing the positive electrode lithium replenishing agent according to claim 7, characterized in that: In step S2, the coating source includes one or more of LiPO3 solution and Al(NO3)3·9H2O ethanol solution.

11. The method for preparing the positive electrode lithium replenishing agent according to claim 7, characterized in that: In step S2, the mixture is centrifuged, dried, and sintered to obtain the positive electrode lithium supplement, which includes the following steps: S21. Centrifuge the mixture to separate the precipitate; S22. The precipitate is dried under vacuum conditions at a temperature of 80-100℃ for 8-12 hours. Then sintering is carried out at a temperature of 300-400℃ for 2-3 hours.

12. A positive electrode plate, characterized in that: The device includes a positive current collector and a positive active material layer disposed on both sides of the positive current collector. The positive active material layer includes a positive active material, a positive lithium supplement agent, a conductive agent, and a binder. The positive lithium supplement agent is the positive lithium supplement agent according to any one of claims 1-6, or the positive lithium supplement agent is the positive lithium supplement agent prepared by the preparation method according to any one of claims 7-11.

13. The positive electrode sheet according to claim 12, characterized in that: With the total mass of the positive electrode active material layer as 100%, the percentage of the positive electrode lithium supplement agent in the total mass of the positive electrode active material layer is 0.5%-10%, the percentage of the positive electrode active material in the total mass of the positive electrode active material layer is 80%-95%, the percentage of the conductive agent in the total mass of the positive electrode active material layer is 2%-5%, and the percentage of the binder in the total mass of the positive electrode active material layer is 2%-5%.

14. A battery, characterized in that: It includes the positive electrode, negative electrode, separator, and electrolyte as described in any one of claims 12-13; the electrolyte includes an additive selected from one or more of fluoroethylene carbonate, lithium difluorophosphate, and adiponitrile.

15. The battery according to claim 14, characterized in that: The additive is selected from fluoroethylene carbonate and lithium difluorophosphate, and the mass ratio of fluoroethylene carbonate to lithium difluorophosphate is 1:1 to 2:

1.

16. The battery according to claim 14, characterized in that: The additive accounts for 1%-5% of the total mass of the electrolyte.

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