Lithium ferrite composite material as well as preparation method and application thereof

Abstract

The invention discloses a lithium ferrite composite material as well as a preparation method and application thereof, and the preparation method of the lithium ferrite composite material comprises the following steps: heating a mixed system containing lithium ferrite, fluosilicate and a solvent, coating the surface of the lithium ferrite with the fluosilicate, and carrying out post-treatment on the heated mixed system to obtain the lithium ferrite composite material. The lithium ferrite composite material is obtained. The lithium ferrite composite material provided by the invention can weaken the gelation phenomenon during slurry stirring in the preparation step of the positive pole piece of the lithium ion battery, and has relatively high specific capacity and good rate capability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium iron oxide composite material, and particularly relates to a lithium iron oxide composite material, a preparation method thereof and application thereof. BACKGROUND

[0002] Global warming and fossil energy depletion have brought great challenges to energy conversion and storage, and the development of new materials plays a crucial role in addressing these two issues. Lithium ion batteries have become the ideal power source for portable electronic devices and future large-scale energy storage and vehicle power batteries due to their high energy density, high power density, long cycle life, good safety and no pollution. The key to improving the performance of lithium ion batteries is to develop new lithium storage materials with high capacity, high rate and long life. However, during the first cycle formation process, SEI film is formed, resulting in irreversible loss of lithium ions. Lithium iron oxide is an important pre-lithiation material due to its high specific capacity and is widely used in lithium ion battery positive slurry. However, during the stirring process, lithium iron oxide often gels, which reduces its stability and performance.

[0003] In the prior art, a composite lithium iron oxide composite material is disclosed in Chinese Patent No. CN114447307A. The composite lithium iron oxide composite material comprises lithium iron oxide and a polymer layer coated on the surface of the lithium iron oxide. The polymer layer is an olefin-acrylate copolymer. Although the above-mentioned composite lithium iron oxide composite material has improved the gelation problem during the preparation of the slurry, the presence of the coating layer (olefin-acrylate copolymer) reduces the surface area of the lithium iron oxide particles, resulting in a decrease in their electrochemical activity and a decrease in the pre-lithiation effect.

[0004] The information disclosed in this BACKGROUND section is only intended to increase an understanding of the general context in which the present application can be practiced and is not admitted to be prior art. SUMMARY

[0005] The present application aims to provide a lithium iron oxide composite material, a preparation method thereof and application thereof. The lithium iron oxide composite material can reduce the gelation phenomenon during the positive slurry stirring of lithium ion batteries, and the prepared lithium iron oxide composite material has high specific capacity and good rate performance.

[0006] To achieve the above-mentioned purpose, a preparation method of a lithium iron oxide composite material is provided in an embodiment of the present application, comprising the following steps:

[0007] heating a mixed system comprising lithium iron oxide, fluorosilicate and a solvent, so that the fluorosilicate is coated on the surface of the lithium iron oxide;

[0008] post-treating the heated mixed system to obtain a lithium iron oxide composite material.

[0009] In one or more embodiments of the present invention, the molar ratio of lithium ferrite to fluorosilicate in the mixed system is 1:(0.05 to 0.2).

[0010] In one or more embodiments of the present invention, the fluorosilicate includes at least one of zinc fluorosilicate, sodium fluorosilicate, and ferrous fluorosilicate; and / or,

[0011] The solvent includes at least one of acetone and ethanol.

[0012] In one or more embodiments of the present invention, the heating temperature of the mixing system is 70-80°C; the heating time is 8-12 hours.

[0013] In one or more embodiments of the present invention, post-processing of the heated mixture includes:

[0014] After cooling the mixture, it is filtered or centrifuged, and the resulting solid is dried to obtain a lithium ferrite composite material.

[0015] A specific embodiment of the present invention also provides a lithium ferrite composite material, the lithium ferrite composite material comprising lithium ferrite and a coating layer covering the surface of the lithium ferrite, the coating layer being a fluorosilicate.

[0016] In one or more embodiments of the present invention, the lithium ferrite composite material is in the form of irregular granules, and the particle size of the lithium ferrite composite material is 3 to 10 μm.

[0017] A specific embodiment of the present invention also provides an application of the lithium ferrite composite material as described above or the lithium ferrite composite material prepared by the preparation method of the lithium ferrite composite material as described above in the field of lithium-ion batteries.

[0018] A specific embodiment of the present invention also provides a positive electrode sheet, the raw materials of which include the lithium ferrite composite material as described above or the lithium ferrite composite material prepared by the method described above for preparing lithium ferrite composite material.

[0019] In one or more embodiments of the present invention, the raw material of the positive electrode sheet further includes a positive electrode material, and the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the positive electrode material.

[0020] In one or more embodiments of the present invention, the cathode material is at least one of lithium cobalt oxide, lithium manganese oxide, and ternary materials.

[0021] A specific embodiment of the present invention also provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, an electrolyte and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0022] Compared with the prior art, the lithium ferrite composite material, the preparation method thereof and the application thereof have the following beneficial effects:

[0023] (1) The coating of the fluorosilicate can form a conductive network structure on the surface of the lithium ferrite particles, promote the transmission of lithium ions in the electrode (positive electrode sheet), and improve the charge and discharge rate performance of the electrode. The coating of the fluorosilicate can increase the interface heating area of the lithium ferrite particles and the electrolyte in the battery (electrolyte), promote ion transmission, and improve the charge and discharge performance of the battery. That is, the rate performance of the lithium ferrite composite material, the positive electrode sheet and the lithium ion battery is improved;

[0024] (2) The coating of the fluorosilicate can enhance the compatibility of the lithium ferrite particles with other materials and weaken the gelation phenomenon of the slurry;

[0025] (3) The fluorosilicate can inhibit the phase transition and structural instability of the lithium ferrite composite material and the positive electrode material at high temperatures, improve the thermal stability of the lithium ferrite composite material and the positive electrode material, and thus improve the safety performance of the battery;

[0026] (4) The preparation method of the lithium ferrite composite material has the advantages of simple process and convenient operation. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0028] Figure 1 The flow chart of the preparation method of the lithium ferrite composite material in an example of the present application;

[0029] Figure 2 The SEM image of the lithium ferrite composite material in Example 1 of the present application;

[0030] Figures 3a to 3c The EDS image of the lithium ferrite composite material in Example 1 of the present application;

[0031] Figure 4 The charge and discharge curve graph of the electrode prepared from the lithium ferrite material in Example 1 of the present application at different rates;

[0032] Figure 5 The charge and discharge curve graph of the electrode prepared from the lithium ferrite material in Comparative Example 1 of the present application at different rates;

[0033] Figure 6The electrochemical impedance spectrograms of the batteries prepared by the lithium iron oxide composite material in Example 1 of the present application, the batteries prepared by the lithium iron oxide material in Comparative Example 1, and the batteries prepared by the blank group;

[0034] Figure 7 The cycle curves of the batteries prepared by the lithium iron oxide composite material in Example 1 of the present application and the lithium iron oxide material in Comparative Example 1;

[0035] Figure 8 The cycle curves of the batteries prepared by the lithium iron oxide composite material in Example 1 of the present application and the batteries prepared by the blank group. DETAILED DESCRIPTION

[0036] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0037] As shown in the preparation method of a lithium iron oxide composite material in an example of the present application, the method comprises the following steps: Figure 1

[0038] S1, heating a mixed system comprising lithium iron oxide (Li5FeO4), fluorosilicate and a solvent, so that the fluorosilicate is coated on the surface of the lithium iron oxide;

[0039] S2, post-treating the heated mixed system to obtain a lithium iron oxide composite material.

[0040] It can be understood that the prepared lithium iron oxide composite material can be considered as being coated with a layer of fluorosilicate on the surface of the lithium iron oxide particles, that is, through the compounding of lithium iron oxide and fluorosilicate, the problem of gelation caused by the easy hydrolysis of lithium iron oxide in the stirring process of preparing the positive electrode sheet is solved; at the same time, the lithium iron oxide composite material also has excellent electrochemical activity and good prelithiation effect. The lithium iron oxide composite material of the present application can be considered as a prelithiation reagent, a lithium supplementing agent, etc.

[0041] Preferably, the molar ratio of lithium iron oxide to fluorosilicate in the mixed system is 1:(0.05-0.2). High-purity lithium iron oxide, fluorosilicate and organic solvent can be prepared to ensure the purity and quality of the chemicals, thereby ensuring the performance of the prepared lithium iron oxide composite material.

[0042] If the molar ratio of lithium iron oxide to fluorosilicate is lower than 1:0.05, due to the too low amount of fluorosilicate, the coating property of fluorosilicate is poor, thereby the problems caused by the use of only lithium iron oxide in the background art occur.​

[0043] If the molar ratio of lithium ferrite and fluorosilicate is higher than 1:0.02, the coating layer (fluorosilicate) will be too heavy, the lithium supplement effect of lithium ferrite will be reduced, the specific capacity of lithium ferrite composite material will be reduced, the weight ratio of the coating layer will be too large, and the slurry will be prone to have a too large viscosity, the stability of lithium ferrite composite material will be reduced, and some of the lithium ferrite composite material will fall off, the coating layer will be too thick and prone to have a serious polarization, and a voltage hysteresis will occur, the corresponding lithium supplement potential will shift to a high potential, a high-voltage standing process needs to be set, and electrolyte decomposition will occur.

[0044] The fluorosilicate can include at least one of zinc fluorosilicate, sodium fluorosilicate, and ferrous fluorosilicate; and the solvent is an organic solvent, for example, the solvent includes at least one of acetone and ethanol.

[0045] It can be understood that in the mixed system, the lithium ferrite is not dissolved in the solvent, but dispersed in the solvent. The amount of solvent added can be determined according to the total number of moles of lithium ferrite and fluorosilicate to ensure that the fluorosilicate is fully dissolved and the lithium ferrite is fully dispersed. For example, the amount of solvent added can be 20-50 times the total number of moles of lithium ferrite and fluorosilicate.

[0046] In the present application, the heating temperature of the mixed system is 70-80℃; and the heating time is 8-12h. Such temperature and time are to ensure that the fluorosilicate can completely coat the lithium ferrite particles.

[0047] The post-treatment of the heated mixed system includes:

[0048] After the mixed system is cooled, it is filtered or centrifuged, and the obtained solid is dried to obtain the lithium ferrite composite material.

[0049] Specifically, cooling can be considered as cooling to room temperature (about 25℃); and the above drying process can specifically include solvent drying, crushing or screening, etc., so that the obtained lithium ferrite composite material is in a granular shape and meets the required particle shape and size requirements.

[0050] A specific example of the present application also provides a lithium ferrite composite material, which includes lithium ferrite and a coating layer coated on the surface of the lithium ferrite, and the coating layer is a fluorosilicate. The lithium ferrite composite material of the present application can be prepared by the above-mentioned method for preparing lithium ferrite composite material, or can be prepared by other methods.

[0051] Specifically, the lithium ferrite composite material of the present application is in an irregular granular shape, and the particle size of the lithium ferrite composite material is 3-10μm. Such shape and particle size make the lithium ferrite composite material have a larger specific surface area, thereby having excellent electrical properties.

[0052] The application further provides an application of the lithium ferrite composite material or the lithium ferrite composite material prepared by the preparation method of the lithium ferrite composite material in the field of lithium ion batteries.

[0053] The application further provides an anode sheet, raw materials of the anode sheet comprising the lithium ferrite composite material or the lithium ferrite composite material prepared by the preparation method of the lithium ferrite composite material.

[0054] Specifically, the raw materials of the anode sheet further comprise an anode material, and the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the anode material. The raw materials of the anode sheet can further comprise a conductive agent and a binder, etc. The conductive agent and the binder are common raw materials for anode sheets on the market. For example, the conductive agent can be carbon black, carbon nanotubes, etc.; and the binder can be a polyvinylidene fluoride (PVDF) binder, etc. The mass of the lithium ferrite composite material being less than or equal to 5% of the mass of the anode material means that in the raw materials of the anode sheet, the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the anode material.

[0055] The anode material is at least one of lithium cobaltate, lithium manganate and a ternary material. The ternary material (NCM) refers to a material composed of nickel, cobalt and manganese (aluminum) for preparing an anode of a lithium ion battery, such as NCM523, NCM811 and the like.

[0056] The application further provides a lithium ion battery comprising the anode sheet, an electrolyte and a cathode sheet. It can be understood that the lithium ion battery can further comprise a diaphragm structure. The electrolyte can also be regarded as an electrolyte solution.

[0057] The lithium ferrite composite material, the preparation method thereof and the application thereof will be described in detail below with reference to specific examples and comparative examples.

[0058] Example 1

[0059] Lithium ferrite with a purity of 99.5% and zinc fluosilicate were selected, and acetone was selected as an organic solvent. The lithium ferrite and the zinc fluosilicate were mixed uniformly in acetone (5 ml of acetone for every 1 g of solid (lithium ferrite and zinc fluosilicate)) according to a molar ratio of 1:0.05, and the uniformity of the mixed system was ensured. The mixed system was placed in a reaction kettle and kept at 70°C for 8 h. After the heating was completed, the mixed system was cooled to room temperature, and after filtration, the collected precipitate was dried to obtain a lithium ferrite composite material.

[0060] Figure 3a An EDS diagram of the lithium ferrite composite material prepared in this example; Figure 3bEDS pattern of lithium fluoride in the lithium ferrite composite prepared in this example; Figure 3c EDS pattern of iron in the lithium ferrite composite prepared in this example.

[0061] By Figure 2 , Figure 3a , Figure 3b and Figure 3c It can be seen that the lithium ferrite composite prepared in this example is irregularly shaped and has a particle size of 3-5 μm, and the surface is smooth.

[0062] Example 2

[0063] Lithium ferrite of 99.8% purity and sodium fluorosilicate were selected, and ethanol was used as an organic solvent. Lithium ferrite and sodium fluorosilicate were mixed uniformly in ethanol (5 ml of ethanol per 1 g of solid (lithium ferrite and sodium fluorosilicate)) at a molar ratio of 1:0.1, and the uniformity of the mixed system was ensured. The mixed system was placed in a reaction kettle and kept at 80°C for 10 h. After the heating was completed, the mixed system was cooled to room temperature, and after filtration, the collected precipitate was dried to obtain a lithium ferrite composite. The lithium ferrite composite was irregularly shaped and had an average particle size of about 5 μm.

[0064] Example 3

[0065] Lithium ferrite of 99.7% purity and ferrous fluorosilicate were selected, and acetone and ethanol were used as organic solvents (volume ratio of acetone to ethanol was 3:1). Lithium ferrite and ferrous fluorosilicate were mixed uniformly in the organic solvent (5 ml of organic solvent per 1 g of solid (lithium ferrite and ferrous fluorosilicate)) at a molar ratio of 1:0.15, and the uniformity of the mixed system was ensured. The mixed system was placed in a reaction kettle and kept at 75°C for 12 h. After the heating was completed, the mixed system was cooled to room temperature, and after filtration, the collected precipitate was dried to obtain a lithium ferrite composite. The lithium ferrite composite was irregularly shaped and had an average particle size of about 6 μm.

[0066] Example 4

[0067] Lithium ferrite of 99.8% purity, zinc fluorosilicate, and sodium fluorosilicate were selected, and ethanol was used as an organic solvent. Lithium ferrite and fluorosilicate (zinc fluorosilicate and sodium fluorosilicate) were mixed uniformly in acetone (5 ml of acetone per 1 g of solid (lithium ferrite, zinc fluorosilicate, and sodium fluorosilicate)) at a molar ratio of 1:0.2, and the uniformity of the mixed system was ensured. The mixed system was placed in a reaction kettle and kept at 78°C for 9 h. After the heating was completed, the mixed system was cooled to room temperature, and after filtration, the collected precipitate was dried to obtain a lithium ferrite composite. The lithium ferrite composite was irregularly shaped and had an average particle size of about 4 μm.

[0068] Comparative Example 1

[0069] Lithium ferrite (commercially available) was selected as the lithium ferrite material.

[0070] Comparative Example 2

[0071] Lithium carbonate and iron oxide with a mass ratio of 7:1 were mixed, and lithium ferrite powder was obtained after calcination at 800°C for 10h in an argon atmosphere. An ethylene-methyl methacrylate copolymer with a weight average molecular weight of 50000 was dispersed in dimethyl sulfoxide solvent to form an ethylene-methyl methacrylate copolymer solution with a mass concentration of 5%. Then, the lithium ferrite powder and the ethylene-methyl methacrylate copolymer solution were stirred for 60min. The solvent was removed at a pressure of -250kpa (relative to atmospheric pressure) and a temperature of 140°C, and then the mixture was cooled to obtain the lithium ferrite material.

[0072] The lithium ferrite composite materials prepared in Examples 1-4 and the lithium ferrite materials of Comparative Examples 1 and 2 were subjected to the following performance tests:

[0073] The lithium ferrite composite material (or lithium ferrite material) was uniformly mixed with conductive agent carbon black and binder polyvinylidene fluoride at a ratio of 8:1:1 to obtain a composite electrode, which was used as a working electrode. A lithium sheet was used as a counter electrode, and a solution of LiPF6 (ED:DMC:EMC = 1:1:1 (by volume)) with a concentration of 1mol / L was used as an electrolyte to assemble a lithium ion battery. Then, the battery was subjected to charge-discharge test between 2.5-4.5V to obtain the test results shown in Table 1 and the charge-discharge curve graphs shown in Figure 4 and Figure 5

[0074] The lithium ferrite composite materials prepared in Examples 1-4 and the lithium ferrite material of Comparative Example 1 were subjected to the following performance tests:

[0075] The slurry (in which lithium iron phosphate, lithium ferrite composite material (or lithium ferrite material), and conductive agent carbon black and binder were uniformly mixed at a ratio of 75:5:10:10) prepared from the lithium ferrite composite materials prepared in Examples 1-4 and the lithium ferrite material of Comparative Example 1 was subjected to deterioration time test under different air humidity conditions to obtain the test results shown in Table 2.

[0076] The lithium ferrite composite material prepared in Example 1 and the lithium ferrite materials of Comparative Examples 1 and 2 were subjected to the following performance tests:

[0077] ​A composite electrode was prepared by uniformly mixing lithium iron phosphate and lithium ferrite composite materials (or lithium ferrite material) with conductive agent carbon black and binder polyvinylidene fluoride at a ratio of 75:X:10:10. Graphite was used as the counter electrode, with N / P = 1.1. A 1 mol / L LiPF6 solution (ED:DMC:EMC = 1:1:1 (volume ratio)) was used as the electrolyte to assemble a lithium-ion battery. The first cycle charge-discharge test was conducted between 2.7 and 4.5 V, and the subsequent cycle test was conducted between 2.8 and 3.65 V. The test results are shown in Table 3. Figure 7 and Figure 8 The cyclic curve graph.

[0078] The lithium ferrite composite material prepared in Example 1 and the lithium ferrite material in Comparative Example 1 were subjected to the following performance tests:

[0079] A composite electrode, obtained by uniformly mixing lithium iron phosphate, lithium ferrite composite material (or lithium ferrite material) with conductive agent carbon black and binder polyvinylidene fluoride in a ratio of 75:5:10:10, was used as the working electrode. Graphite was used as the counter electrode, with N / P = 1.1. A lithium-ion battery was assembled using a 1 mol / L LiPF6 solution (ED:DMC:EMC = 1:1:1 (volume ratio)) as the electrolyte. Electrochemical impedance spectroscopy (EIS) tests were performed (a blank group was added, i.e., the working electrode of the lithium-ion battery in the blank group did not contain the lithium ferrite composite material). The results were as follows: Figure 6 The electrochemical impedance spectroscopy shown ( Figure 6 (The data with triangles on the curve represents data from Example 1). (Through...) Figure 6 It can be seen that the electrochemical impedance of the battery prepared by the lithium ferrite composite material in Example 1 is close to that of the battery in the blank group, while the electrochemical impedance of the battery prepared by the lithium ferrite material in Comparative Example 1 is significantly greater than that of the battery in the blank group.

[0080] Table 1

[0081]

[0082] Through Table 1 and Figure 4 and Figure 5 As can be seen from the data of Example 1 and Comparative Example 1, the lithium ferrite composite material of the present invention has a higher irreversible capacity and a better lithium replenishment effect, regardless of whether it is at a low rate or a high rate.

[0083] Table 2

[0084] Air humidity 20% Air humidity 40% Air humidity 60% Air humidity 80% Comparative Example 1 1h 0.6h 0.5h 0.2h Example 1 ＞8h ＞8h ＞6h ＞4h Example 2 ＞8h ＞8h ＞6h ＞4h Example 3 ＞8h ＞8h ＞6h ＞4h Example 4 ＞8h ＞8h ＞6h ＞4h

[0085] As can be seen from the data in Table 2, regardless of whether the humidity is low or high, the deterioration time of the slurry prepared in the embodiment of the present invention is significantly longer than that of the slurry prepared in Comparative Example 1. This is because the lithium ferrite composite material of the present invention can effectively reduce the gelation phenomenon of lithium ferrite in the slurry preparation process, which is beneficial to the storage and transportation of the slurry and is more suitable for actual industrial production.

[0086] Table 3

[0087]

[0088] Through Table 3 and Figure 7 and Figure 8 The data shows that adding lithium ferrite composite material (also known as lithium replenisher or pre-lithiation agent) can effectively improve the battery capacity retention rate. Furthermore, with the same number of lithium ferrite composite materials, the battery with the lithium ferrite composite material of this invention exhibits a significantly better capacity retention rate than the battery with the lithium ferrite material of Comparative Example 1.

[0089] As can be seen from the data in Tables 1 and 3 and common knowledge, the thick coating of lithium ferrite material in Comparative Example 2 leads to a decrease in its electrochemical activity and pre-lithiation effect. The resistivity of lithium ferrite material itself is relatively high, and its addition causes an increase in the resistance of the battery system. It can only reduce the alkalinity, resulting in a decrease in the lithium replenishment effect and high resistance.

[0090] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0091] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a lithium ferrite composite material, characterized in that, Includes the following steps: Heating a mixture containing lithium ferrite, fluorosilicate, and a solvent causes the fluorosilicate to coat the surface of the lithium ferrite. The heated mixture was post-treated to obtain a lithium ferrite composite material.

2. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, The molar ratio of lithium ferrite to fluorosilicate in the mixed system is 1:(0.05~0.2).

3. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, The fluorosilicate includes at least one of zinc fluorosilicate, sodium fluorosilicate, and ferrous fluorosilicate; and / or, The solvent includes at least one of acetone and ethanol.

4. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, The heating temperature of the mixture is 70–80°C; the heating time is 8–12 hours.

5. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, Post-treatment of the heated mixture includes: After cooling the mixture, it is filtered or centrifuged, and the resulting solid is dried to obtain a lithium ferrite composite material.

6. A lithium ferrite composite material, characterized in that, The lithium ferrite composite material includes lithium ferrite and a coating layer covering the surface of the lithium ferrite, wherein the coating layer is a fluorosilicate.

7. The lithium ferrite composite material according to claim 6, characterized in that, The lithium ferrite composite material is in the form of irregular particles, and the particle size of the lithium ferrite composite material is 3 to 10 μm.

8. The application of a lithium ferrite composite material as described in claim 6 or a lithium ferrite composite material prepared by any one of the preparation methods of lithium ferrite composite materials as described in claims 1 to 5 in the field of lithium-ion batteries.

9. A positive electrode sheet, characterized in that, Its raw materials include lithium ferrite composite materials as described in claim 6 or 7, or lithium ferrite composite materials prepared by the method described in any one of claims 1 to 5.

10. The positive electrode sheet according to claim 9, characterized in that, The raw materials for the positive electrode sheet also include positive electrode material, and the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the positive electrode material.

11. The positive electrode sheet according to claim 10, characterized in that, The cathode material is at least one of lithium cobalt oxide, lithium manganese oxide, and ternary materials.

12. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the positive electrode as described in any one of claims 9 to 11.

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