Lithium iron oxide-based lithium supplementing material, preparation method and application

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a lithium-iron-ferrite-based lithium supplementing material, a preparation method and application. The lithium-iron-ferrite-based lithium supplementing material comprises a lithium-iron-ferrite base and a composite coating layer on the outer surface of the lithium-iron-ferrite base; and the composite coating layer is a mixed layer containing carbon, lithium fluoride and aluminum oxide. The composite coating layer containing carbon, lithium fluoride and aluminum oxide is constructed in situ on the surface of lithium-iron-ferrite particles, so that the coating layer has the functions of electronic conduction, ion transmission, mechanical support and chemical isolation, and the air stability, the electrochemical lithium supplementing capacity and the battery cycle performance of the lithium-iron-ferrite-based lithium supplementing material are improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium ferrite-based lithium replenishment material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and good environmental adaptability, have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage. With the continuous development of high-energy-density battery systems, anode materials such as graphite, silicon-carbon, and hard carbon experience significant irreversible lithium loss during the first charge-discharge cycle due to the formation of the solid electrolyte interphase (SEI) film. This leads to a decrease in the battery's initial coulombic efficiency, thus limiting further improvements in actual energy density. Therefore, introducing an additional active lithium source into the battery system to compensate for the irreversible lithium loss during the initial cycle has become one of the important technical routes for improving the energy density and cycle stability of lithium-ion batteries.

[0003] Among existing lithium replenishment technologies, cathode lithium replenishment has attracted much attention due to its good compatibility with existing cathode slurry preparation, coating, and battery assembly processes. Lithium ferrite (especially Li5FeO4) is considered a promising cathode lithium replenishment additive due to its high theoretical lithium replenishment capacity, low raw material cost, and environmental friendliness. However, as a lithium-rich oxide, Li5FeO4 has poor structural and surface chemical stability, and it easily undergoes side reactions with moisture and carbon dioxide in the air, generating residual alkali or inert byproducts such as LiOH and Li2CO3. These byproducts not only significantly reduce the effective lithium replenishment capacity of lithium ferrite but also increase electrode interface impedance, leading to a series of problems such as decreased slurry processing stability, increased electrolyte side reactions, and battery cycle performance degradation.

[0004] To improve the air stability of lithium ferrite supplements, existing technologies typically employ methods such as carbon coating, oxide coating, phosphate coating, or other inorganic protective layers. While carbon coating can improve the electronic conductivity of the material to some extent, its long-term barrier properties against moisture and carbon dioxide are limited. Metal oxide coatings such as alumina provide good chemical stability and physical isolation, but their poor electronic conductivity may affect the electrochemical decomposition kinetics of lithium ferrite. Furthermore, a single inorganic lithium salt or oxide coating layer cannot simultaneously meet the multiple performance requirements of mechanical stability, ion transport, electron transport, and air protection.

[0005] In summary, there is an urgent need to develop a composite coating structure that can simultaneously improve the air stability and electrochemical reaction kinetics of lithium ferrite, enabling it to maintain high lithium replenishment activity during storage, electrode processing, and battery service, while reducing its adverse effects on cathode interface stability and battery cycle life. Therefore, this invention provides an improved lithium ferrite composite coating scheme to address at least some of the problems existing in the prior art. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a lithium ferrite-based lithium replenishment material, its preparation method, and its application. By constructing a composite coating layer containing carbon, lithium fluoride, and aluminum oxide in situ on the surface of lithium ferrite particles, the coating layer simultaneously possesses electronic conduction, ion transport, mechanical support, and chemical isolation functions, thereby improving the air stability, electrochemical lithium replenishment capacity, and battery cycle performance of the lithium ferrite replenishment agent.

[0007] The objective of this invention is achieved through the following technical solution: The present invention provides a lithium ferrite-based lithium supplementation material, comprising a lithium ferrite matrix and a composite coating layer located on the outer surface of the lithium ferrite matrix; the composite coating layer is a mixed layer containing carbon, lithium fluoride and aluminum oxide.

[0008] In some embodiments, the lithium ferrite matrix is ​​Li5FeO4.

[0009] In some embodiments, the thickness of the composite coating layer is 2-50 nm, preferably 5-30 nm.

[0010] In some embodiments, based on the total mass of the lithium replenishing material, the composite coating layer contains 0.1 wt.%-10 wt.% carbon, 0.1 wt.%-15 wt.% lithium fluoride, and 0.05 wt.%-10 wt.% alumina.

[0011] This invention also provides a method for preparing a lithium ferrite-based lithium supplementation material, comprising the following steps: S1. Iron source and lithium source are mixed and calcined to obtain lithium ferrite matrix material; S2. The lithium ferrite matrix material, fluoropolymer, aluminum source and solvent are mixed and then dried and calcined to obtain lithium ferrite-based lithium supplementation material.

[0012] In some embodiments, the molar ratio of Li to Fe in the lithium source and iron source is 4.5:1 to 6.5:1.

[0013] In some embodiments, in step S2, the fluoropolymer is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and vinylidene fluoride-hexafluoropropylene copolymer, preferably polyvinylidene fluoride; the aluminum source is at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride, aluminum acetylacetone, and aluminum sol, preferably aluminum isopropoxide; the mass ratio of the lithium ferrite matrix material, the fluoropolymer, and the aluminum source is 100:(0.5-20):(0.1-20).

[0014] In some embodiments, in step S2, the calcination atmosphere is at least one of argon, nitrogen, and helium; the calcination temperature is 400-900 °C, preferably 500-800 °C; and the calcination time is 1-24 h.

[0015] The present invention also provides a positive electrode sheet, comprising the lithium ferrite-based lithium supplementation material as described above or the lithium ferrite-based lithium supplementation material prepared by the preparation method described above.

[0016] The present invention also provides a secondary battery, comprising the positive electrode sheet as described above; Preferably, the secondary battery is a lithium-ion battery.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention constructs a composite coating layer containing carbon, lithium fluoride, and aluminum oxide in situ on the surface of lithium ferrite particles, enabling the coating layer to simultaneously possess electronic conduction, ion transport, mechanical support, and chemical isolation functions, thereby improving the air stability, electrochemical lithium replenishment capacity, and battery cycle performance of lithium ferrite replenishing agents.

[0018] Other features and beneficial effects of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other beneficial effects of the invention can be realized and obtained by means of the structures particularly pointed out in the description, claims and drawings. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 These are optical photographs of the materials obtained in Example 1 and Comparative Example 1, where a is Bare-LFO and b is CLA@LFO; Figure 2The images show SEM images of the materials obtained in Example 1 and Comparative Example 1, where ac represents CLA@LFO and df represents Bare-LFO. Figure 3 These are TEM images of the materials obtained in Example 1 and Comparative Example 1, where a is CLA@LFO and b is Bare-LFO; Figure 4 The images shown are the refined XRD patterns of the materials obtained in Example 1 and Comparative Example 1, where a represents CLA@LFO and b represents Bare-LFO. Figure 5 The images are XPS plots of the materials obtained in Example 1 and Comparative Example 1, where a is a narrow spectrum of C 1s and b is a narrow spectrum of F 1s. Figure 6 The TOF-SIMS test pattern of the material obtained in Example 1; Figure 7 EDS test results for the material obtained in Example 1; Figure 8 The figures are electrochemical performance curves of the materials obtained in Example 1 and Comparative Example 1, where a represents CLA@LFO and b represents Bare-LFO. Figure 9 SEM images of the materials obtained in Example 1 and Comparative Example 1 after exposure to air for different times (1, 4, 8, 12, 24 h), where a is CLA@LFO; b is Bare-LFO; Figure 10 The graphs show the electrochemical performance of the materials obtained in Example 1 and Comparative Example 1 after exposure to air for different times (1, 4, 24 h), where a represents CLA@LFO and b represents Bare-LFO. Figure 11 The following are electrochemical performance curves of the half-cells in Examples 1 and 5: (a) First charge-discharge curve; (b) Comparison of rate performance at 0.2 C, 0.5 C, 1 C, and 2 C; (c) Cyclic test curve under a voltage range of 2.5-4.2 V and a rate of 0.5 C. Figure 12 The following are electrochemical performance curves of the full cells in Examples 1 and 5: (a) First charge-discharge curve; (b) Cyclic test curve under voltage range of 2.5-4.2 V and 0.5 C rate. Figure 13 The graphs show the electrochemical performance of the materials obtained in Example 1 and Comparative Example 4. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a lithium ferrite-based lithium supplementation material, comprising a lithium ferrite matrix and a composite coating layer located on the outer surface of the lithium ferrite matrix; the composite coating layer is a mixed layer containing carbon, lithium fluoride and aluminum oxide.

[0023] The lithium ferrite matrix is ​​Li5FeO4; the thickness of the composite coating layer is 2-50 nm (not limited to 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm, 45 nm, 46 nm, 47 nm, 48 nm, 49 nm, 50 nm), preferably 5-30 nm; the carbon content in the composite coating layer is 0.1% based on the total mass of the lithium replenishing material. The lithium fluoride content is 0.1 wt.%-10 wt.% (not limited to 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1.5 wt.%, 2.0 wt.%, 2.5 wt.%, 3.0 wt.%, 3.5 wt.%, 4.0 wt.%, 4.5 wt.%, 5.0 wt.%, 5.5 wt.%, 6.0 wt.%, 6.5 wt.%, 7.0 wt.%, 7.5 wt.%, 8.0 wt.%, 8.5 wt.%, 9.0 wt.%, 9.5 wt.%, 10 wt.%), preferably 0.5 wt.%-5 wt.%; the lithium fluoride content is 0.1 wt.%-15 wt.% (not limited to 0.1 wt.%). wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9wt.%, 1.0 wt.%, 1.5 wt.%, 2.0 wt.%, 2.5 wt.%, 3.0 wt.%, 3.5 wt.%, 4.0 wt.%, 4.5 wt.%, 5.0 wt.%, 5.5 wt.%, 6.0 wt.%, 6.5 wt.%, 7.0 wt.%, 7.5 wt.%, 8.0 wt.%, 8.5 wt.%, 9.0wt.%, 9.5 wt.%, 10 wt.%, 10.5 wt.%, 11.0 wt.%, 11.5 wt.%, 12.0 wt.%, 12.5 wt.%, 13.0wt.%, 13.5 wt.%, 14.0 wt.%, 14.5 wt.%, 15 wt.%, preferably 0.5 wt.%-8 wt.%; the mass content of alumina is 0.05 wt.%-10 wt.% (not limited to 0.05 wt.%, 0.06 wt.%, 0.07 wt.%, 0.08 wt.%, 0.09 wt.%, 0.1 wt.%, 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, 2.0 wt.%, 2.5 wt.%, 3.0 wt.%, 3.5 wt.%, 4.0 wt.%, 4.5 wt.%, 5.0 wt.%, 5.5 wt.%, 6.0 wt.%, 6.5 wt.%, 7.0 wt.%, 7.5 wt.%, 8.0 wt.%, 8.5 wt.%, 9.0 wt.%, 9.5 wt.%, 10 wt.%). (wt.%), preferably 0.1 wt.%-5 wt.%.

[0024] It should be noted that the carbon component in the composite coating layer is mainly used to improve the electronic conductivity of the lithium ferrite surface and form an electronic conduction network, and together with LiF and Al2O3, constitutes the composite protective layer. When the carbon content is too low (<0.1 wt.%), it is difficult to form a continuous conductive network and cannot effectively reduce the charge transfer impedance; when the carbon content is too high (>10 wt.%), it will reduce the effective content of Li5FeO4 per unit mass of material and may form an excessively thick carbon layer that hinders Li. +The LiF component primarily enhances the chemical stability and mechanical integrity of the coating layer and improves lithium-ion transport. It also helps form a stable fluorine-containing interface, suppressing side reactions during air exposure and electrochemical cycling. When the LiF content is too low (<0.1 wt.%), the coating layer stability is insufficient; when the LiF content is too high (>15 wt.%), it may consume excessive surface-active lithium and form an excessively thick insulating phase, leading to increased interfacial impedance. The Al2O3 component mainly acts as a chemically inert barrier, preventing direct contact between H2O and CO2 in the air and the Li5FeO4 matrix, and reducing the generation of residual alkali byproducts and interfacial side reactions. When the Al2O3 content is too low (<0.05 wt.%), an effective protective layer cannot be formed; when the content is too high (>10 wt.%), it easily forms agglomerated particles or an excessively thick insulating layer, increasing interfacial impedance and reducing lithium replenishment kinetics. In this invention, C, LiF, and Al2O3 are not simply superimposed, but form a synergistic composite coating layer on the Li5FeO4 surface. The carbon phase provides an electron conduction network, reducing charge transfer resistance during delithiation; LiF provides a stable fluorine-containing inorganic interface, enhancing the integrity of the coating layer and suppressing side reactions; Al2O3 acts as an outer chemical barrier, effectively blocking H2O and CO2 from the air. When the contents of these three components are within an appropriate range, both improved air stability and enhanced lithium replenishment kinetics can be achieved simultaneously; if any component is too low, the protection or transport functions will be insufficient; if any component is too high, it will cause dilution of the active material, excessive coating thickness, or increased interfacial impedance.

[0025] It should be noted that the mass fraction ranges of carbon, lithium fluoride, and aluminum oxide are not single test values, but are determined based on a comprehensive analysis of the feeding ratios of PVDF and aluminum isopropoxide during the preparation process, the possible conversion reactions of each precursor during heat treatment, the thickness of the composite coating layer, and the air stability and lithium replenishment performance of the resulting material. Specifically, PVDF undergoes dehydrogenation fluorination and carbonization reactions during inert atmosphere heat treatment, providing both carbon and fluorine sources; the carbonization residue forms a carbon phase, and fluorine-containing active species react with lithium species on the Li5FeO4 surface to generate LiF. Aluminum isopropoxide decomposes thermally to form Al2O3. Therefore, by adjusting the amount of PVDF and aluminum isopropoxide added, the relative contents of carbon, LiF, and Al2O3 in the composite coating layer can be adjusted. The above-mentioned mass fraction ranges are determined by combining the surface coating integrity, capacity retention after air exposure, and changes in electrochemical impedance under different feeding ratios.

[0026] This invention also provides a method for preparing a lithium ferrite-based lithium supplementation material, comprising the following steps: S1. Iron source and lithium source are mixed and calcined to obtain lithium ferrite matrix material; S2. The lithium ferrite matrix material, fluoropolymer, aluminum source and solvent are mixed and then dried and calcined to obtain lithium ferrite-based lithium supplementation material.

[0027] For step S1, the iron source includes one or more of Fe2O3, FeOOH, Fe3O4, Fe(NO3)3, and FeCl3; the lithium source includes one or more of Li2O, LiOH, Li2CO3, LiNO3, and CH3COOLi; the molar ratio of Li to Fe in the lithium source and iron source is 4.5:1-6.5:1 (not limited to 4.5:1, 4.6:1, 4.7:1, 4.8:1). The ratios are 4.9:1, 5:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1, 5.6:1, 5.7:1, 5.8:1, 5.9:1, 6:1, 6.1:1, 6.2:1, 6.3:1, 6.4:1, 6.5:1, preferably 5.0:1-5.8:1; the calcination atmosphere is at least one of air, oxygen, or an oxygen-containing atmosphere; the calcination temperature is 400-800℃ (not limited to 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃), preferably 500-700℃; the calcination time is 2-24 h, preferably 6-12 h.

[0028] In step S2, the fluoropolymer is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and vinylidene fluoride-hexafluoropropylene copolymer, preferably polyvinylidene fluoride; the aluminum source is at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride, aluminum acetylacetonate, and aluminum sol, preferably aluminum isopropoxide; the solvent includes one or more of N-methylpyrrolidone, ethanol, isopropanol, acetone, and dimethylformamide, preferably N-methylpyrrolidone. The mass ratio of the lithium ferrite matrix material, the fluoropolymer, and the aluminum source is 100:(0.5-20):(0.1-20). The mixing method includes one or more of ball milling, sand milling, magnetic stirring, ultrasonic dispersion, planetary stirring, or homogenization. The drying temperature is 60-160 ℃, and the drying time is 2-24 h. The calcination atmosphere is an inert atmosphere, including one or more of argon, nitrogen, and helium; the calcination temperature is 400-900℃ (not limited to 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, and 900℃), preferably 500-800℃, and more preferably 550-700℃; the calcination time is 1-24 h.

[0029] It should be noted that in existing technologies, the surface modification of air-sensitive lithium-rich oxides such as lithium ferrite typically employs a stepwise coating route: carbon coating followed by oxide coating, or oxide coating followed by conductivity modification. This is because when aluminum and carbon / fluorinated carbon sources coexist in the same heat treatment system, competitive reactions such as aluminum hydrolysis and condensation, pyrolysis and agglomeration, defluorination corrosion of fluorinated polymers, and excessive consumption of lithium species on the lithium ferrite surface easily occur, making it difficult to control the composition and spatial distribution of the coating layer. Those skilled in the art generally anticipate that one-step mixed calcination may form discontinuous carbon layers, agglomerated Al2O3 particles, or excessive LiF / Li2CO3 byproducts, thereby increasing interfacial impedance and reducing the effective lithium replenishment capacity of lithium ferrite. Therefore, directly mixing and calcining aluminum, carbon / fluorine sources with lithium ferrite is not considered a conventional preferred method for obtaining high-performance composite-coated lithium ferrite replenishing agents. This invention selects at least one of the following solvent systems that are soluble / dispersible in one or more of N-methylpyrrolidone, ethanol, isopropanol, acetone, and dimethylformamide: aluminum isopropoxide, aluminum nitrate, aluminum chloride, aluminum acetylacetonate, and aluminum sol, as the aluminum source. It also uses at least one of polyvinylidene fluoride, polytetrafluoroethylene, and vinylidene fluoride-hexafluoropropylene copolymer as both the carbon and fluorine source, enabling uniform contact between the aluminum source, the fluoropolymer, and lithium ferrite particles during liquid-phase homogenization. In subsequent inert atmosphere heat treatment, the fluoropolymer undergoes gradual dehydrofluorination and carbonization to form a continuous carbon skeleton. Simultaneously, the released fluorine-containing active species react in situ with lithium species on the lithium ferrite surface to generate LiF. The aluminum source simultaneously pyrolyzes to form highly dispersed Al2O3. By controlling the ratio of fluoropolymer to aluminum source, solvent dispersion state, heating rate and calcination temperature, this invention avoids Al2O3 agglomeration and excessive corrosion of lithium ferrite by fluorinated species, and obtains a continuous and dense C-LiF-Al2O3 composite coating layer, achieving simultaneous improvement in air stability, lithium replenishment capacity and interfacial kinetics.

[0030] The calcination temperature in step S2 has a significant impact on the formation of the composite coating layer and the performance of the lithium replenishment material. When the temperature is below 400℃, the fluoropolymer is difficult to fully dehydrofluorinate and carbonize, and the aluminum source is also difficult to completely decompose thermally. This results in the incomplete in-situ formation of the carbon phase, lithium fluoride, and alumina, and the resulting coating layer is usually discontinuous and not dense, failing to effectively block the contact between H2O and CO2 in the air and the Li5FeO4 matrix. Therefore, the material is still prone to generating byproducts such as LiOH and Li2CO3 after exposure to air, leading to increased interfacial impedance and low lithium replenishment capacity retention. When the calcination temperature is in the range of 500-800℃, the fluoropolymer can undergo more complete dehydrofluorination and carbonization reactions, forming a carbon-based conductive network. At the same time, the released fluorinated active species can react with lithium species on the Li5FeO4 surface to generate LiF in situ; the aluminum source can also thermally decompose to form Al2O3. Together, these three components form a continuous and dense C-LiF-Al2O3 composite coating layer, giving the material good air stability, electronic conductivity, and interfacial chemical stability. Materials obtained within this temperature range can effectively suppress the formation of byproducts such as LiOH and Li2CO3 during air exposure, while maintaining high lithium replenishment capacity and low interfacial impedance. When the calcination temperature exceeds 900℃, the coating layer may undergo excessive carbonization, sintering shrinkage, local agglomeration, or thickening of the inorganic phase. While this may increase the density of the coating layer, it also lengthens the lithium-ion and electron transport paths and increases interfacial polarization. Furthermore, excessively high temperatures may cause grain growth in the Li5FeO4 matrix, loss of surface-active lithium, or decreased structural stability, thereby reducing the effective lithium replenishment capacity and affecting electrochemical kinetics. Therefore, higher heat treatment temperatures are not always better; a balance must be struck between sufficient precursor conversion, coating layer densification, and preservation of the Li5FeO4 matrix structure. Excessively high heat treatment temperatures are not conducive to obtaining composite-coated lithium ferrite materials that possess both high air stability and high lithium replenishment activity.

[0031] The present invention also provides a positive electrode sheet, comprising the lithium ferrite-based lithium supplementation material as described above or the lithium ferrite-based lithium supplementation material prepared by the preparation method described above.

[0032] The present invention also provides a secondary battery, comprising the positive electrode sheet as described above; Preferably, the secondary battery is a lithium-ion battery.

[0033] The present invention will be further described in detail below with reference to specific embodiments. These embodiments will enable those skilled in the art to gain a more comprehensive understanding of the invention, but do not limit the invention in any way. Where techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0034] In the description of this invention, it should be noted that all terms used in this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and should not be construed as limiting the invention; it should be further understood that the terms used in this invention should be understood to have the same meaning as those in the context of this specification and in the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this invention.

[0035] Example 1: This embodiment provides a lithium ferrite-based lithium supplementation material and its preparation method.

[0036] The lithium ferrite-based lithium supplementation material includes a Li5FeO4 matrix and a composite coating layer on the outer surface of the Li5FeO4 matrix; the thickness of the composite coating layer is 15.82 nm.

[0037] The specific preparation method is as follows: (1) Preparation of Li5FeO4 matrix Using Fe₂O₃ with a purity of 99.5% and Li₂O with a purity of 99.9% as initial raw materials, the two raw materials were precisely weighed according to a Li:Fe molar ratio of 5:5:1. They were then mixed and ground in a grinding apparatus until homogeneous to obtain an LFO precursor mixture. This precursor mixture was transferred to a ceramic boat and placed in a high-temperature furnace. Under an Ar atmosphere, it was sintered at a constant temperature of 600 °C for 12 hours. After naturally cooling to room temperature, it was ground and pulverized to obtain Li₅FeO₄ matrix material (LFO) powder, which was sealed and stored for later use, labeled Bare-LFO.

[0038] (2) Preparation of CLA@LFO samples Weigh 1 g of the pure phase LFO powder prepared above and 0.01 g of aluminum isopropoxide accurately and mix them evenly. Slowly disperse the mixture in 10 ml of 5% polyvinylidene fluoride (PVDF) solution (dissolved in N-methylpyrrolidone (NMP)). Place the mixture in a homogenizer and homogenize for 2 hours to ensure that the LFO particles are evenly dispersed in the solution system without agglomeration, and obtain a homogenized coating precursor mixture.

[0039] The homogenized coating precursor mixture was transferred to a ceramic boat, spread evenly, and then placed in a tube furnace. An inert Ar gas was introduced as a protective atmosphere, and after purging the furnace, the programmed temperature rise was initiated: 5 °C / min. -1The heating rate was increased from room temperature (20 °C) to 600 °C. After reaching the target temperature, the sample was sintered at a constant temperature for 12 hours. After sintering, the sample was naturally cooled to room temperature in the furnace. The sample was then removed and ground evenly to obtain C-LiF-Al2O3 composite coated Li5FeO4 cathode lithium supplement, denoted as CLA@LFO, which was sealed and stored for later use.

[0040] This embodiment also provides a lithium ferrite-based lithium supplementary electrode and its preparation method. The specific steps are as follows: (1) Slurry preparation: Weigh Super P, binder, and lithium supplement material (CLA@LFO) in a mass ratio of 6:2:2. Pre-grind and mix Super P and lithium supplement material manually in an agate mortar. Then add an appropriate amount of N-methylpyrrolidone (NMP) to adjust the viscosity of the slurry. Stir for 5 min using a gradient speed stirring process to obtain the final slurry. The binder is commercial PVDF binder.

[0041] (2) Coating and drying: The obtained lithium replenishing agent slurry is evenly coated onto the current collector aluminum foil using a scraper. The coating thickness is controlled so that the areal density of the lithium replenishing agent material is 2 mg / cm³. -2 Subsequently, the obtained electrode was placed in a vacuum environment at 80°C and dried for 2 hours until the surface was completely dry. The dried electrode was then placed in a glove box for later use.

[0042] This embodiment also provides a positive electrode sheet and its preparation method. The specific steps are as follows: (1) Slurry preparation: Super P, binder, and cathode material were weighed in a mass ratio of 8:1:1. Super P and cathode material were pre-mixed by manual grinding in an agate mortar. Then, an appropriate amount of N-methylpyrrolidone (NMP) was added to adjust the viscosity of the slurry. The mixture was stirred for 5 minutes using a gradient speed stirring process to ensure uniform mixing and obtain the final slurry. The binder was the commercial binder PVDF, and the cathode material was LiFePO4 (LFP).

[0043] (2) Coating and drying: The obtained positive electrode slurry is evenly coated onto the current collector aluminum foil using a scraper, and the coating thickness is controlled so that the areal density of the positive electrode material is 5 mg / cm³. -2 Subsequently, the obtained electrode was placed in a vacuum environment at 80 °C and dried for 2 h until the surface was completely dry. The dried electrode was then placed in a glove box for later use.

[0044] This embodiment also provides a lithium battery, the specific assembly method of which is as follows: Assembly was completed in an argon atmosphere glove box with a water and oxygen content of less than 0.01 ppm. The battery model used was CR2025 coin cell. The half-cell system used lithium metal sheet as the counter electrode, and the full cell used graphite (Gr) as the counter electrode. The electrolyte used was LB-291 electrolyte produced by Suzhou Duoduo Chemical Technology Co., Ltd. (composed of 1 mol L-1 lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of diethyl carbonate (DEC): dimethyl carbonate (DMC): ethylene carbonate (EC) in a volume ratio of 1:1:1, with 10% by mass of fluoroethylene carbonate (FEC) and 2% by mass of vinylene carbonate (VC) added as additives).

[0045] The battery assembly process is as follows: Inside the glove box, the positive electrode shell, positive electrode sheet, electrolyte, separator, lithium sheet (replaced with negative electrode sheet, gasket, and spring in a full cell) are stacked layer by layer with the negative electrode shell in sequence, ensuring that all components are centered and aligned, and an appropriate amount of electrolyte is added. Then, a coin cell sealing machine is used for pressure sealing, and after sealing, the cells are left to stand for 24 hours. Half-cells (Li||LFP, Li||LFO) and full cells (Gr||LFP) are assembled, and then electrochemical performance tests and characterization are performed.

[0046] The electrochemical testing method is as follows: The Li||LFO half-cell test condition is 0.05 C. The Li||LFP half-cell test condition is 0.5 C rate. For the Gr||LFP full-cell test, the battery is first activated with a small current of 0.1 C for two cycles to allow the electrode materials to fully adapt to the charge-discharge process, and then cyclic testing is performed at a 0.5 C rate. To test the air stability of CLA@LFO, CLA@LFO is placed in air for 1-24 hours to fully contact the air, simulating air exposure conditions that may be encountered in actual use. Then, the positive electrode is reassembled and the battery is assembled according to normal procedures, and its performance changes are tested.

[0047] Example 2: This embodiment provides a lithium ferrite-based lithium supplement material and its preparation method. Compared with Example 1, in step (2), the heat treatment temperature is 500 °C. Other conditions are the same.

[0048] Example 3: This embodiment provides a lithium ferrite-based lithium supplement material and its preparation method. Compared with Example 1, in step (2), the heat treatment temperature is 700 °C. Other conditions are the same.

[0049] Example 4: This embodiment provides a lithium ferrite-based lithium supplement material and its preparation method. Compared with Example 1, in step (2), the heat treatment temperature is 800 °C. Other conditions are the same.

[0050] Example 5: This embodiment also provides a positive electrode sheet and its preparation method. The difference between this method and the positive electrode sheet preparation method in Example 1 is that the positive electrode material is LFP + 2 wt% CLA@LFO, while other conditions remain the same.

[0051] The assembly of the half-cell (Li||LFP+2 wt% CLA@LFO) and the full-cell (Gr||LFP+CLA@LFO) was the same as in Example 1.

[0052] Comparative Example 1 (without coating): This comparative example provides a lithium ferrite-based lithium replenishing material and its preparation method. Compared with Example 1, the lithium replenishing material is a Li5FeO4 matrix without a coating layer, labeled as LFO or Bare-LFO, and other conditions are the same.

[0053] Comparative Example 2 (coating without aluminum oxide): This comparative example provides a lithium ferrite-based lithium supplement material and its preparation method. Compared with Example 1, no aluminum source is added during the preparation, while other conditions remain the same.

[0054] Comparative Example 3 (coating without carbon and lithium fluoride): This comparative example provides a lithium ferrite-based lithium supplement material and its preparation method. Compared with Example 1, no polyvinylidene fluoride (PVDF) solution was added during the preparation, while other conditions remained the same.

[0055] Comparative Example 4 (Stepwise preparation of the coating layer): This comparative example provides a lithium ferrite-based lithium supplementation material and its preparation method. The specific steps are as follows: (1) The preparation method of the Li5FeO4 matrix is ​​the same as that in Example 1. (2) Preparation of coated precursors 1 g of the Li5FeO4 matrix material obtained in step (1) was dispersed in 10 ml of a 5% (w / w) polyvinylidene fluoride (PVDF) solution (dissolved in N-methylpyrrolidone (NMP)). The mixture was stirred by planetary stirring, ultrasonication, or homogenization to obtain a uniform coated precursor slurry. The obtained coated precursor slurry was dried to obtain coated precursor powder. The powder was placed in a tube furnace and heated at 5 °C for 1 minute under an argon atmosphere. -1 The temperature was increased to 600℃ at a heating rate, held for 12 h, and then naturally cooled to room temperature. After grinding, C-LiF-coated Li5FeO4 cathode lithium supplement was obtained.

[0056] (3) Subsequently, 0.01 g of Al2O3 (purchased from ACMEC reagent, purity 99.99%) was uniformly mixed with 1 g of C-LiF-coated Li5FeO4 to obtain a mixed powder. The powder was placed in a tube furnace and heated at 5 °C for 1 min under an argon atmosphere. -1 The temperature was increased to 600 °C at a heating rate, held for 12 h, and then naturally cooled to room temperature. After grinding, a multilayer coated Li5FeO4 cathode lithium supplement was obtained, denoted as LFO@C+1 wt%Al2O3.

[0057] Physical photographs of the lithium replenishment materials (CLA@LFO and LFO) obtained in Example 1 and Comparative Example 1 ( Figure 1 A comparison revealed that the CLA@LFO sample exhibited a distinct black color, a color change that demonstrates the successful coating of the composite coating layer onto the LFO surface. Figure 2 Images of CLA@LFO and pure lithium ferrite (Bare-LFO) obtained using scanning electron microscopy (SEM, Zeiss GeminiSEM 500) are shown. The images reveal that CLA@LFO particles exhibit a regular spherical morphology with a smooth and dense surface, indicating that the C-LiF-Al2O3 composite coating has uniformly and continuously covered the LFO particle surface, forming a complete protective layer structure. In contrast, Bare-LFO particles have a rough surface and contain numerous fine amorphous particles, suggesting the lack of coating modification and protection, and thus reacting with substances such as H2O and CO2 in the air to generate impurities such as Li2CO3. The dense coating morphology of CLA@LFO effectively prevents contact between air, moisture, and LFO particles, reducing the risk of air degradation of the material.

[0058] Transmission electron microscopy (TEM, JEM-2100) results revealed the microstructural differences between the lithium-supplementing materials CLA@LFO and Bare-LFO obtained in Example 1 and Comparative Example 1. Figure 3 As shown, the CLA@LFO particles exhibit a dense, continuous coating layer on their surface, with a measured thickness of approximately 15.82 nm. This indicates that the coating process can construct a uniform and controllable protective layer on the LFO particle surface. In contrast, the Bare-LFO particles show no clearly defined coating layer; only amorphous material is observed adhering to the surface. This amorphous phase is presumably a Li2CO3 byproduct generated from the reaction of LFO with CO2 and H2O in air. This suggests that uncoated LFO is prone to reaction with air, leading to failure. The presence of the dense coating layer on the CLA@LFO surface effectively blocks contact between air, moisture, and the LFO substrate, inhibiting the formation of byproducts such as Li2CO3.

[0059] X-ray diffraction (XRD, Rigaku Ultima IV type) and Rietveld refinement characterization were performed on CLA@LFO and Bare-LFO samples to analyze the influence of the coating process on the bulk crystal structure of LFO. The refined spectra ( Figure 4 As can be seen, the diffraction peaks of CLA@LFO and Bare-LFO are completely matched with the standard Li5FeO4 phase, indicating that the carbon-based composite coating layer content is low, does not damage the bulk crystal structure of LFO, and does not introduce impurity phases during the coating process.

[0060] The refined fitting results show that the weighted profile factor (Rp) of CLA@LFO is 1.803%, slightly lower than that of Bare-LFO (2.176%), indicating that CLA@LFO has a better refined fitting degree. It is speculated that its surface coating layer can effectively reduce crystal defects on the particle surface and improve structural integrity. This suggests that the coating strategy only modifies the surface of LFO particles and does not change their bulk structure.

[0061] To investigate the surface chemical composition of CLA@LFO and Bare-LFO and their changes after air exposure, the samples were characterized by X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific K-ALPHA type). The results are as follows: Figure 5 As shown, in the high-resolution spectrum of CLA@LFO, the C 1s spectrum exhibits a characteristic peak of CF bonds (binding energy 290 eV), and the corresponding F 1s spectrum also shows a characteristic peak of LiF (binding energy 685 eV), confirming the presence of a C-LiF composite layer in the coating. In contrast, the C 1s spectrum of Bare-LFO shows an extremely weak CF signal, and the F 1s spectrum lacks a significant LiF characteristic peak.

[0062] To further reveal the microscopic elemental distribution of the CLA@LFO lithium supplement surface coating, three-dimensional elemental imaging analysis was performed using time-of-flight secondary ion mass spectrometry (TOF-SIMS, Beijing IONTOF M6 technology). Figure 6 As shown, Li3 exhibits the lithium content of CLA@LFO lithium supplementation. + F - Al 3+ Fe 3+ and C - Three-dimensional distribution image of ions, elemental distribution state. Fe 3+ and Li + As a characteristic element of the lithium ferrite matrix, its three-dimensional distribution exhibits a high-concentration, densely aggregated state, indicating that the CLA@LFO lithium supplement maintains a complete lithium ferrite crystal framework and that the matrix has good crystallinity. 3+ Ions in three-dimensional space with Fe 3+The regions exhibit a high degree of spatial overlap, confirming that Al elements are uniformly and densely distributed on the surface or in the interstitial spaces of the lithium ferrite matrix. - The three-dimensional distribution of ions exhibits a relatively uniform state, and is similar to that of Li. + The distribution areas highly overlap. This phenomenon indicates that LiF was formed during the preparation of CLA@LFO. LiF, as a highly ionicly conductive inorganic fluoride, is uniformly distributed between the Al2O3 coating layer and the substrate, constructing excellent ion-conducting channels. This is beneficial for improving the lithium supplementation agent's performance at high potentials. + Release kinetics are crucial. The aforementioned elemental distribution characteristics confirm that the C-LiF-Al2O3 composite coating has successfully achieved uniform coating of the lithium ferrite matrix.

[0063] In addition, SEM-EDS results ( Figure 7 The data showed that the CLA@LFO particles exhibited a uniformly distributed trace Al element signal and a significantly enhanced C element signal, which, together with the XPS and TOF-SIMS data above, confirmed the successful introduction of Al2O3 and carbon into the composite coating layer and the uniform coating of LiF.

[0064] At a rate of 0.05 C (1 C = 700 mAh g) -1 The electrochemical decomposition performance of CLA@LFO and Bare-LFO was tested, and the results are as follows: Figure 8 As shown, the decomposition capacity of CLA@LFO can reach 736 mAh g. -1 In comparison, Bare-LFO had a final decomposition capacity of 647.6 mAh g. -1 The decomposition capacity of CLA@LFO was approximately 13.7% higher than that of the control. This performance difference indicates that the C-LiF-Al2O3 composite coating layer on the surface of CLA@LFO not only enhances electronic conductivity and reduces charge transfer resistance through the carbon phase, but also suppresses side reactions on the electrolyte and lithium replenishment surface through the combined action of LiF and Al2O3, reducing irreversible capacity loss. In contrast, Bare-LFO, lacking a protective coating layer, suffers from additional capacity decay due to the formation of byproducts such as Li2CO3 on its surface. The carbon-based composite coating layer significantly improves the electrochemical decomposition capacity and reaction stability of LFO while maintaining its lithium replenishment activity.

[0065] The morphological evolution of CLA@LFO and Bare-LFO after exposure to air for 1 h, 4 h, 8 h, 12 h, and 24 h was characterized by SEM. The results are as follows: Figure 9As shown, for the CLA@LFO sample, the particle surface remained relatively smooth and dense throughout the entire 24-hour air exposure period, without significant byproduct accumulation or morphological deterioration. Even after 24 hours of exposure, no significant amorphous material was generated on the particle surface, indicating that the C-LiF-Al2O3 composite coating effectively blocked the contact between air, moisture, and the LFO substrate. In contrast, the morphology of the Bare-LFO sample deteriorated significantly with prolonged air exposure. After 1 hour of exposure, a small number of fine amorphous particles appeared on the particle surface; after 4 hours, obvious roughening and particle agglomeration began to appear on the surface; from 8 to 24 hours, the amorphous byproducts on the surface continued to thicken and increase, eventually forming a thick layer of coating. This byproduct was Li2CO3 generated by the reaction of LFO with CO2 and H2O in the air. This morphological evolution result demonstrates the protective effect of the C-LiF-Al2O3 composite coating; its dense structure can effectively slow down the air degradation rate of LFO and significantly improve the air stability of the lithium supplement.

[0066] At a rate of 0.05 C (1 C = 700 mAh g) -1 The electrochemical decomposition performance of CLA@LFO and Bare-LFO after air exposure for 0 h, 1 h, and 24 h was tested to evaluate the effect of the coating layer on the electrochemical stability of the lithium supplement. Results are shown below. Figure 10 For the CLA@LFO sample, its decomposition curve showed only a slight change after air exposure: the initial decomposition capacity was 736 mAh g. -1 After 1 hour of exposure, the capacity was 721 mAh g. -1 It remained at 643 mAh g after 24 hours of exposure. -1 The capacity decay rate was only 4.3%, and the shape of the potential-capacity curve did not deteriorate significantly. In contrast, the decomposition performance of the Bare-LFO sample deteriorated significantly with prolonged air exposure: the initial decomposition capacity was 647.6 mAh g⁻¹. -1 After 1 hour of exposure, the capacity decreased to 592 mAh g. -1 After 24 hours of exposure, it further decreased to 523 mAh g. -1 The capacity decay rate is as high as 19.2%, and there is a significant capacity drop in the low potential region (2.0-3.8 V). This phenomenon is caused by irreversible capacity loss due to byproducts such as Li2CO3 generated on the surface.

[0067] The above results indicate that the C-LiF-Al2O3 composite coating can effectively block the contact between air and the LFO substrate and inhibit the formation of byproducts, thereby maintaining the high decomposition capacity and electrochemical stability of the lithium replenisher after air exposure.

[0068] The electrochemical performance of the LFP half-cell with 2 wt% CLA@LFO added (Example 5) and the pure LFP cathode (Example 1) was tested. The results are as follows: Figure 11 As shown, at a C rate of 0.05 (1 C = 170 mAh g), -1 The first charge capacity of the Li||LFP+2 wt% CLA@LFO battery is 176.28 mAh g. -1 The second charge capacity is 163.1 mAh g. -1 The charging curves for the first and second cycles overlap, with the only exception being a segment in the high-potential region (4.0-4.5 V) of the first cycle, where the capacity is 13.18 mAh. -1 This provides an additional platform, corresponding to the electrochemical decomposition and lithium pre-intercalation process of the CLA@LFO lithium supplement. The rate performance of Li||LFP (Example 1) and Li||LFP+2 wt% CLA@LFO (Example 5) batteries at 0.2 C, 0.5 C, 1 C, and 2 C rates was further tested. The test results show that the discharge specific capacity of the Li||LFP+2 wt% CLA@LFO battery at the above rates is 164.85, 160.55, 154.56, and 145.32 mAh g, respectively. -1 The specific discharge capacities of the Li||LFP battery at the aforementioned rates are 163.17, 158.34, 151.2, and 138.6 mAh g, respectively. -1 At all tested rates, its rate performance was superior to that of the LFP cathode. In long-cycle testing at 0.5 C rate, the Li||LFP+2 wt% CLA@LFO battery exhibited better cycle stability: after 400 cycles, its capacity remained at 144.8 mAh g⁻¹. -1 The capacity retention rate was 88.78%; in comparison, the capacity of the Li||LFP battery increased from 159.0 mAh g in the first cycle. -1 Reduced to 141.1 mAh g on the 400th lap. -1 The capacity retention rate was 88.75%. After using CLA@LFO lithium replenisher, the capacity retention rate of the LFP cathode remained unchanged. This result shows that CLA@LFO lithium replenisher can not only compensate for the capacity loss in the first cycle, but also has no destructive effect on LFP after decomposition.

[0069] The first charge-discharge cycle of a Gr||LFP full cell with 2 wt% CLA@LFO (Gr||LFP+CLA@LFO, Example 5) and a Gr||LFP full cell without CLA@LFO (Example 1) was tested in the voltage range of 2.5–4.2 V and at a rate of 0.05 C (1 C = 170 mAh g⁻¹). The results are as follows. Figure 12 As shown, the first charge capacity of the Gr||LFP battery is 158.2 mAh g. -1 The first discharge specific capacity is 142.7 mAh g. -1 The coulombic efficiency is 90.2%. The first-week charge specific capacity of the Gr||LFP+CLA@LFO battery is 177 mAh g. -1 The first-cycle discharge specific capacity can reach 156.0 mAh g. -1 The battery achieved a first-discharge specific capacity of 13.3 mAh g after lithium replenishment. -1 The improvement, considering only the quality of the LFP cathode, resulted in a coulombic efficiency increase from 90.2% to 98.6% after lithium replenishment. After 200 constant-current charge-discharge cycles at 0.5 C, the Gr||LFP+CLA@LFO battery still maintained a capacity of 131.5 mAh g. -1 The discharge specific capacity of the battery was 88.4%, corresponding to a capacity retention rate of 88.4%. In contrast, the discharge specific capacity of the blank control group battery decreased to 113.3 mAh g. -1 The capacity retention rate was 79.4%, with the lithium-added group showing a slight improvement in capacity retention compared to the control group. This performance difference is attributed to the fact that CLA@LFO compensates for the loss of active lithium caused by the formation of the SEI film on the graphite anode, reducing irreversible lithium loss and thus significantly improving the cycle stability and coulombic efficiency of the entire battery. This provides an effective technical path for optimizing the battery's performance.

[0070] Furthermore, the material with a coating layer mainly composed of carbon and a small amount of lithium fluoride (Comparative Example 2) showed improved electronic conductivity and partial air stability compared to the completely uncoated Li5FeO4 (Comparative Example 1); however, due to the lack of an alumina chemical barrier, its long-term barrier ability against moisture and carbon dioxide was lower than that of the C-LiF-Al2O3 composite coating material in Example 1. The lithium-supplementing material with only an alumina coating (Comparative Example 3) showed improved air stability compared to the completely uncoated Li5FeO4 (Comparative Example 1); however, due to the lack of a carbon conductive network and lithium fluoride ion transport / mechanical support components, its electrochemical decomposition kinetics were lower than that of the C-LiF-Al2O3 composite coating material in Example 1. The material LFO@C+1 wt%Al2O3 obtained by stepwise coating of alumina with carbon and lithium fluoride (Comparative Example 4) showed improved electronic conductivity and partial air stability compared to CLA@LFO obtained by one-step coating. Figure 13 The results showed that the battery assembled with the coating lithium replenishment material prepared by the two-step method had a significantly higher charging voltage plateau, a more severe polarization, and a significantly reduced lithium replenishment capacity release.

[0071] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A lithium ferrite-based lithium supplementation material, characterized in that, It includes a lithium ferrite matrix and a composite coating layer located on the outer surface of the lithium ferrite matrix; the composite coating layer is a mixed layer containing carbon, lithium fluoride and aluminum oxide.

2. The lithium ferrite-based lithium supplementation material according to claim 1, characterized in that, The lithium ferrite matrix is ​​Li5FeO4.

3. The lithium ferrite-based lithium supplementation material according to claim 1, characterized in that, The thickness of the composite coating layer is 2-50 nm, preferably 5-30 nm.

4. The lithium ferrite-based lithium supplementation material according to claim 1, characterized in that, Based on the total mass of the lithium replenishment material, the composite coating layer contains 0.1 wt.%-10 wt.% carbon, 0.1 wt.%-15 wt.% lithium fluoride, and 0.05 wt.%-10 wt.% alumina.

5. A method for preparing a lithium ferrite-based lithium supplementation material, characterized in that, Includes the following steps: S1. Iron source and lithium source are mixed and calcined to obtain lithium ferrite matrix material; S2. The lithium ferrite matrix material, fluoropolymer, aluminum source and solvent are mixed and then dried and calcined to obtain lithium ferrite-based lithium supplementation material.

6. The preparation method according to claim 5, characterized in that, The molar ratio of Li to Fe in the lithium source and iron source is 4.5:1 to 6.5:

1.

7. The preparation method according to claim 5, characterized in that, In step S2, the fluoropolymer is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and vinylidene fluoride-hexafluoropropylene copolymer, preferably polyvinylidene fluoride; the aluminum source is at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride, aluminum acetylacetone, and aluminum sol, preferably aluminum isopropoxide; the mass ratio of the lithium ferrite matrix material, the fluoropolymer, and the aluminum source is 100:(0.5-20):(0.1-20).

8. The preparation method according to claim 5, characterized in that, In step S2, the calcination atmosphere is at least one of argon, nitrogen, and helium; the calcination temperature is 400-900 ℃, preferably 500-800 ℃; and the calcination time is 1-24 h.

9. A positive electrode sheet, characterized in that, Includes lithium ferrite-based lithium supplementation materials as described in any one of claims 1-4, or lithium ferrite-based lithium supplementation materials prepared by the preparation method described in any one of claims 5-8.

10. A secondary battery, characterized in that, Including the positive electrode sheet as described in claim 9; Preferably, the secondary battery is a lithium-ion battery.

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