Lithium ferrite positive electrode composite material and preparation method thereof, positive electrode plate and secondary battery

Abstract

The invention provides a lithium ferrite positive electrode composite material and a preparation method thereof, a positive electrode plate and a secondary battery, and belongs to the technical field of battery materials, the lithium ferrite positive electrode composite material sequentially comprises a lithium ferrite core, a catalyst layer and a carbon layer from inside to outside; the catalyst layer comprises transition metal elements, the mass ratio of the catalyst layer to the carbon layer is (5-10): (90-95), and the mass ratio of the total mass of the catalyst layer and the carbon layer to the lithium ferrite core is (1.5-5): (95-98.5). According to the lithium ferrite composite material, the surface of the lithium ferrite core is provided with the catalyst layer containing the transition metal element, so that the coating combination effect of the carbon coating layer can be improved, the lithium ferrite composite material with low internal resistance and high air stability is obtained, and the electrochemical performance of a secondary battery prepared from the lithium ferrite composite material is further improved.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to a lithium ferrite positive electrode composite material and a preparation method thereof, a positive electrode sheet and a secondary battery. Background Art

[0002] With the rapid development of new energy, lithium-ion batteries have attracted widespread attention for their potential use in new energy vehicles. Lithium ferrite (Li5FeO4), a key cathode material for lithium batteries, has attracted considerable attention due to its high theoretical capacity and low cost. However, lithium ferrite has significant environmental stability issues, particularly its tendency to react with moisture and carbon dioxide in the air, leading to performance degradation.

[0003] Carbon coating is a commonly used modification method. Although introducing a carbon layer on the surface of lithium ferrite can improve its conductivity and structural stability to a certain extent, there are problems such as poor bonding between the carbon coating and the lithium ferrite core, which leads to increased internal resistance and affects the battery's charge and discharge efficiency. In addition, the environmental stability of lithium ferrite is insufficient, which restricts the application of Li5FeO4 as a positive electrode material in lithium-ion batteries.

[0004] Therefore, it is necessary to provide an improved lithium ferrite positive electrode composite material and a preparation method thereof to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a lithium ferrite positive electrode composite material and its preparation method, a positive electrode sheet and a secondary battery, aiming to solve the technical problems of large internal resistance and insufficient air stability of the lithium ferrite positive electrode composite material.

[0006] In a first aspect, an embodiment of the present application provides a lithium ferrite positive electrode composite material, which includes, from the inside to the outside, a lithium ferrite core, a catalytic layer, and a carbon layer; wherein the catalytic layer contains a transition metal element, and the mass ratio of the catalytic layer to the carbon layer is (5~10): (90~95), and the mass ratio of the total mass of the catalytic layer and the carbon layer to the lithium ferrite core is (1.5~5): (95~98.5).

[0007] In the technical solution of the embodiment of the present application, the provided lithium ferrite positive electrode composite material includes, from the inside to the outside, a lithium ferrite core, a catalytic layer and a carbon layer, wherein a catalytic layer containing a transition metal element is formed on the surface of the lithium ferrite core. On the one hand, the transition metal can form a metallic bond with the lithium ferrite core and form a van der Waals force with the carbon layer, thereby anchoring the carbon layer and improving the bonding effect between the carbon layer and the core; on the other hand, the transition metal can increase the degree of graphitization of the carbon element and improve the coating effect of the carbon coating layer compared with amorphous carbon, thereby not only reducing the internal resistance of the lithium ferrite composite material and improving the charge and discharge efficiency of the secondary battery prepared therefrom, but also the graphitized coating layer formed can isolate the lithium ferrite in the core from reacting with moisture and carbon dioxide in the air, thereby improving the air stability of the lithium ferrite positive electrode composite material.

[0008] In some embodiments, the D50 particle size of the lithium ferrite core is 1-3 μm.

[0009] In this embodiment, controlling the particle size of the lithium ferrite core facilitates a simplified preparation process and yields a highly conductive lithium ferrite positive electrode composite material. If the particle size of the lithium ferrite core is too small, the adhesion between the particles increases, making uniform dispersion during preparation difficult. If the particle size of the lithium ferrite core is too large, the electron transport path in the composite material becomes longer, reducing the conductivity of the lithium ferrite positive electrode composite material.

[0010] In some embodiments, the combined thickness of the catalytic layer and the carbon layer is 200-300 nm.

[0011] In this embodiment, by controlling the thickness of the coating layer within an appropriate range, effective protection of the lithium ferrite core is achieved while also facilitating an increase in the specific capacity of the lithium ferrite positive electrode composite material. If the coating layer is too thin, it is easily damaged and cannot fully protect the lithium ferrite core. If the coating layer is too thick, the energy density of the lithium ferrite positive electrode composite material is affected, thereby reducing the specific capacity.

[0012] In some embodiments, the transition metal element is at least one of iron, cobalt, and nickel.

[0013] In this embodiment, transition metal elements such as iron, cobalt, and nickel can form catalytic active centers on the surface of the lithium ferrite core, promote the uniform growth of the carbon source on the surface of the lithium ferrite core to form a dense carbon coating layer, thereby improving the degree of bonding between the carbon layer and the lithium ferrite core.

[0014] In a second aspect, an embodiment of the present application provides a method for preparing the lithium ferrite positive electrode composite material as described in the first aspect, comprising the following steps: Providing lithium ferrite, a transition metal-containing compound, and a carbon source solution; uniformly mixing the transition metal-containing compound and the carbon source solution to obtain a first slurry; dispersing lithium ferrite in the first slurry to obtain a second slurry; removing the solvent from the second slurry to obtain an intermediate product; The intermediate product is sintered to obtain a lithium ferrite positive electrode composite material.

[0015] In the technical solution of the embodiment of the present application, first, lithium ferrite is dispersed in a first slurry containing a transition metal compound and a carbon source, so that the transition metal compound can be evenly dispersed on the surface of the lithium ferrite, and then a catalytic layer containing the transition metal element is formed on the surface of the lithium ferrite; thereafter, through sintering treatment, the carbon source can be continuously precipitated on the catalytic active center of the transition metal element and grow into a uniform and dense carbon coating layer, thereby improving the degree of graphitization of the carbon layer, thereby improving the coating effect of the carbon layer on the lithium ferrite core, and thus obtaining a lithium ferrite positive electrode composite material with low internal resistance and good air stability.

[0016] In some embodiments, the mass ratio of the transition metal-containing compound and the carbon source in the first slurry is (5~10):(90~95); the mass ratio of the sum of the mass of the carbon source and the transition metal-containing compound in the second slurry to lithium ferrite is (1.5~5):(95~98.5); the carbon source in the carbon source solution includes at least one of asphalt, paraffin, tar, phenolic resin, and PAN; the solvent in the carbon source solution is an organic solvent; the transition metal-containing compound includes at least one of iron oxide, iron chloride, cobalt oxide, cobalt chloride, nickel oxide, and nickel chloride.

[0017] In this embodiment, by controlling the mass ratio of the transition metal-containing compound and the carbon source within a suitable range, it is easy to obtain a good catalytic effect and balance the internal resistance of the lithium ferrite positive electrode composite material. If the amount of the transition metal-containing compound is too large, the internal resistance of the lithium ferrite composite material will increase, affecting the charge and discharge efficiency of the prepared secondary battery; and if the amount of the transition metal-containing compound is too small, the catalytic effect will not be achieved, and the coating and bonding effect of the carbon coating layer and the lithium ferrite core will be reduced. By controlling the mass ratio of the sum of the mass of the carbon source and the transition metal-containing compound to the mass of lithium ferrite, it is easy to control the thickness of the coating layer. If the amount of the coating layer material is too large, the thickness of the coating layer is too large, which will reduce the gram capacity of the lithium ferrite positive electrode composite material; and if the amount of the coating layer material is too small, the thickness of the coating layer is too small, and it will not be able to effectively protect the lithium ferrite core.

[0018] In some embodiments, the preparation method of lithium ferrite provided includes: calcining a mixture of an iron source and a lithium source at 600~750℃ for 24~48 hours under an inert atmosphere; wherein the iron source is Fe2O3; the lithium source is a mixture of lithium oxide and lithium hydroxide; the lithium source is a mixture of lithium hydroxide and lithium oxide in a molar ratio of 1:(1.5~2.5); the molar ratio of Fe and Li in the mixture is 1:(5.0~5.5); and heating the mixture to 600~750℃ at a heating rate of 2~10℃ / min.

[0019] In this embodiment, the mixture of the iron source and the lithium source is calcined at 600-750°C for 24-48 hours under an inert atmosphere, which facilitates the complete reaction of the iron source and the lithium source and produces a lithium ferrite material with a good crystalline structure. If the calcination temperature is too low or the calcination time is too short, the crystallinity of the lithium ferrite material will be poor, while if the sintering temperature is too high or the sintering time is too long, the structure of the lithium ferrite material will be damaged.

[0020] In some embodiments, in the step of sintering the intermediate product, the sintering temperature is 600-700° C., and the sintering time is 10-24 h.

[0021] In this embodiment, by controlling the sintering temperature and time, a uniform carbon coating can be formed while maintaining the structure of the lithium ferrite core. If the sintering temperature is too low, the carbon source cannot be fully carbonized; while if the sintering temperature is too high, the structure of the lithium ferrite in the core will be affected.

[0022] In a third aspect, an embodiment of the present application provides a positive electrode plate, which includes the lithium ferrite positive electrode composite material described in the first aspect, or includes the lithium ferrite positive electrode composite material prepared by the preparation method of the lithium ferrite positive electrode composite material described in the second aspect.

[0023] In the technical solution of the embodiment of the present application, the positive electrode plate includes the lithium ferrite positive electrode composite material described in the first aspect, and thus has lower resistance and good air stability.

[0024] In a fourth aspect, an embodiment of the present application provides a secondary battery, which includes the positive electrode sheet described in the third aspect.

[0025] In the technical solution of the embodiment of the present application, the secondary battery includes the positive electrode plate described in the third aspect, and thus has higher capacity performance and charge and discharge efficiency.

[0026] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0028] Figure 1 This is a schematic diagram of the structure of the lithium ferrite positive electrode composite material in the embodiment of this application; In the figure, 1. Lithium ferrite core; 2. Catalytic layer; 3. Carbon layer. DETAILED DESCRIPTION

[0029] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0031] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0032] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0034] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0035] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0036] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0037] Li5FeO4, as an important lithium battery cathode material, has attracted much attention due to its high theoretical capacity and low cost. However, lithium ferrite has significant issues with environmental stability, especially when it comes into contact with moisture and carbon dioxide in the air, which can cause it to react easily, leading to a decrease in performance. Existing technologies typically introduce a carbon coating on the surface of lithium ferrite, but this suffers from problems such as poor bonding between the carbon coating and the lithium ferrite core, which increases internal resistance and affects the battery's charge and discharge efficiency, as well as insufficient environmental stability of lithium ferrite.

[0038] In order to solve the technical problems of large internal resistance and poor air stability of lithium ferrite positive electrode composite materials prepared by the prior art, the present application provides a lithium ferrite positive electrode composite material and its preparation method, a positive electrode plate and a secondary battery, wherein, by providing a catalytic layer containing transition metal elements on the surface of the lithium ferrite core, the coating and bonding effect of the carbon coating layer can be improved, thereby obtaining a lithium ferrite composite material with low internal resistance and high air stability, thereby improving the electrical performance of the positive electrode plate and the secondary battery.

[0039] Please refer to Figure 1In the first aspect, an embodiment of the present application provides a lithium ferrite positive electrode composite material, which includes, from the inside to the outside, a lithium ferrite core 1, a catalytic layer 2 and a carbon layer 3; wherein the catalytic layer 2 contains a transition metal element, and the mass ratio of the catalytic layer 2 to the carbon layer 3 is (5~10): (90~95), and the mass ratio of the total mass of the catalytic layer 2 and the carbon layer 3 to the lithium ferrite core 1 is (1.5~5): (95~98.5).

[0040] In the present application, the provided lithium ferrite positive electrode composite material includes, from the inside to the outside, a lithium ferrite core, a catalyst layer, and a carbon layer, wherein the catalyst layer contains a transition metal element. By forming a catalyst layer containing a transition metal element on the surface of the lithium ferrite core, on the one hand, the transition metal can form a metallic bond with the lithium ferrite core and simultaneously form a van der Waals force with the carbon layer, anchoring the carbon layer, thereby improving the bonding effect between the carbon layer and the core; on the other hand, the transition metal can increase the degree of graphitization of the carbon element, thereby improving the coating effect of the carbon coating layer compared to amorphous carbon, thereby not only reducing the internal resistance of the lithium ferrite positive electrode composite material and improving the charge and discharge efficiency of the secondary battery prepared therefrom, but also the formed graphitized coating layer can isolate the lithium ferrite in the core from reacting with moisture and carbon dioxide in the air, thereby improving the air stability of the lithium ferrite positive electrode composite material.

[0041] Among them, the mass ratio of the catalytic layer to the carbon layer is (5~10):(90~95), and the mass ratio of the total mass of the catalytic layer and the carbon layer to the lithium ferrite core is (1.5~5):(95~98.5). For the catalytic layer, if the proportion of the catalytic layer is too large, the internal resistance of the lithium ferrite composite material will increase, and if the proportion of the catalytic layer is too small, the catalytic effect will not be achieved, resulting in poor coating and bonding effect of the carbon layer; for the total coating layer formed by the catalytic layer and the carbon layer, if the proportion of the total coating layer is too large, the energy density will decrease, thereby reducing the gram capacity of the secondary battery prepared therefrom, and if the proportion of the total coating layer is too small, complete and continuous coating cannot be achieved, and the Li5FeO4 core and the air cannot be effectively isolated.

[0042] Specifically, the mass ratio of the catalytic layer to the carbon layer can be 5:90, 5:95, 8:90, 8:95, 10:90, 10:95 or any value between (5~10):(90~95); the mass ratio of the total mass of the catalytic layer and the carbon layer to the lithium ferrite core can be 1.5:95, 1.5:98.5, 2:98, 4:96, 5:96 or any value between (1.5~5):(95~98.5).

[0043] Furthermore, in some embodiments, the D50 particle size of the lithium ferrite core is 1-3 μm, specifically 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or any value between 1-3 μm.

[0044] In this application, by controlling the particle size of the lithium ferrite core, it is advantageous to simplify the preparation process and obtain a lithium ferrite positive electrode composite material with higher conductivity. If the particle size of the lithium ferrite core is too small, the adhesion between the particles will increase, making it difficult to evenly disperse them during preparation; if the particle size of the lithium ferrite core is too large, the electron transmission path in the composite material will become longer, reducing the conductivity of the lithium ferrite positive electrode composite material.

[0045] Furthermore, in some embodiments, the sum of the thicknesses of the catalytic layer and the carbon layer is 200-300 nm, specifically 200 nm, 220 nm, 250 nm, 280 nm, 300 nm or any value between 200-300 nm.

[0046] In the present application, by controlling the thickness of the coating layer within an appropriate range, effective protection of the lithium ferrite core is achieved while also facilitating an increase in the gram capacity of the lithium ferrite positive electrode composite material. If the coating layer is too thin, it is easily damaged and cannot fully exert its protective effect on the lithium ferrite core; and if the coating layer is too thick, on the one hand, if the thickness of the catalytic layer is too large, the internal resistance of the lithium ferrite positive electrode composite material will increase, and if the thickness of the carbon layer is too large, the diffusion rate of lithium ions will be reduced, thereby reducing the energy density of the lithium ferrite positive electrode composite material and, in turn, reducing the gram capacity of the secondary battery prepared therefrom.

[0047] Furthermore, in some embodiments, the transition metal element is at least one of iron, cobalt, and nickel.

[0048] In the present application, transition metal elements such as iron, cobalt, and nickel can form catalytic active centers on the surface of the lithium ferrite core, promote the uniform growth of the carbon source on the surface of the lithium ferrite core to form a dense carbon coating layer, thereby improving the degree of bonding between the carbon layer and the lithium ferrite core.

[0049] In a second aspect, an embodiment of the present application provides a method for preparing the lithium ferrite positive electrode composite material as described in the first aspect, comprising the following steps: Providing lithium ferrite, a transition metal-containing compound, and a carbon source solution; uniformly mixing the transition metal-containing compound and the carbon source solution to obtain a first slurry; dispersing lithium ferrite in the first slurry to obtain a second slurry; removing the solvent from the second slurry to obtain an intermediate product; The intermediate product is sintered to obtain a lithium ferrite positive electrode composite material.

[0050] In the present application, first, lithium ferrite is dispersed in a first slurry containing a transition metal compound and a carbon source, so that the transition metal compound can be evenly dispersed on the surface of the lithium ferrite, thereby forming a catalytic layer containing the transition metal element on the surface of the lithium ferrite; thereafter, through a sintering treatment, the carbon source can be continuously precipitated on the catalytic active center of the transition metal element and grow into a uniform and dense carbon coating layer, thereby improving the degree of graphitization of the carbon layer, thereby improving the coating effect of the carbon layer on the lithium ferrite core, and thus obtaining a lithium ferrite positive electrode composite material with low internal resistance and good air stability.

[0051] Furthermore, in some embodiments, the mass ratio of the transition metal-containing compound and the carbon source in the first slurry is (5~10):(90~95); the mass ratio of the sum of the mass of the carbon source and the transition metal-containing compound in the second slurry to lithium ferrite is (1.5~5):(95~98.5); the carbon source in the carbon source solution includes at least one of asphalt, paraffin, tar, phenolic resin, and PAN; the solvent in the carbon source solution is an organic solvent; the transition metal-containing compound includes at least one of iron oxide, iron chloride, cobalt oxide, cobalt chloride, nickel oxide, and nickel chloride.

[0052] Specifically, in the first slurry, the mass ratio of the transition metal-containing compound to the carbon source can be 5:90, 5:92, 5:95, 8:90, 8:94, 10:90, 10:95 or any value between (5~10):(90~95); in the second slurry, the mass ratio of the sum of the mass of the carbon source and the transition metal-containing compound to the lithium ferrite can be 1.5:95, 1.5:96, 1.5:98.5, 3:95, 3:97, 5:95, 5:98.5 or any value between (1.5~5):(95~98.5).

[0053] In the present application, by controlling the mass ratio of the transition metal-containing compound and the carbon source within a suitable range, it is easy to obtain a good catalytic effect and balance the internal resistance of the lithium ferrite positive electrode composite material. If the amount of the transition metal-containing compound is too large, the internal resistance of the lithium ferrite positive electrode composite material will increase, affecting the charge and discharge efficiency of the prepared secondary battery; and if the amount of the transition metal-containing compound is too small, the catalytic effect will not be achieved, and the coating and bonding effect of the carbon coating layer and the lithium ferrite core will be reduced. By controlling the mass ratio of the sum of the mass of the carbon source and the transition metal-containing compound to the mass of lithium ferrite, it is easy to control the thickness of the coating layer. If the amount of the coating layer material is too large, the thickness of the coating layer is too large, which will reduce the gram capacity of the lithium ferrite positive electrode composite material; and if the amount of the coating layer material is too small, the thickness of the coating layer is too small, and it will not be able to effectively protect the lithium ferrite core.

[0054] Furthermore, in some embodiments, the organic solvent may be selected from at least one of dichloromethane, DMF, n-hexane, DMC, and thionyl chloride.

[0055] Furthermore, in some embodiments, the preparation method of lithium ferrite provided includes: calcining a mixture of an iron source and a lithium source at 600~750℃ for 24~48 hours under an inert atmosphere; wherein the iron source is Fe2O3; the lithium source is a mixture of lithium oxide and lithium hydroxide; the lithium source is a mixture of lithium hydroxide and lithium oxide in a molar ratio of 1:(1.5~2.5); the molar ratio of Fe and Li in the mixture is 1:(5.0~5.5); and heating the mixture to 600~750℃ at a heating rate of 2~10℃ / min.

[0056] Specifically, the calcination temperature can be 600°C, 650°C, 700°C, 750°C, or any value between 600°C and 750°C, and the calcination time can be 24 hours, 28 hours, 32 hours, 36 hours, 40 hours, 44 hours, 48 ​​hours, or any value between 24 hours and 48 hours. The molar ratio of lithium hydroxide to lithium oxide in the lithium source can be 1:1.5, 1:1.8, 1:2, 1:2.5, or any value between (1.5 and 2.5); and the molar ratio of Fe to Li in the mixture of the iron source and the lithium source can be 1:5.0, 1:5.2, 1:5.3, 1:5.4, 1:5.5, or any value between 1:(5.0 and 5.5).

[0057] In this application, the mixture of the iron source and the lithium source is calcined at 600-750°C for 24-48 hours under an inert atmosphere to facilitate the complete reaction between the iron source and the lithium source and obtain a lithium ferrite material with a good crystalline structure. If the calcination temperature is too low or the calcination time is too short, the crystallinity of the lithium ferrite material will be poor, while if the sintering temperature is too high or the sintering time is too long, the structure of the lithium ferrite material will be damaged.

[0058] Furthermore, in some embodiments, in the step of sintering the intermediate product, the sintering temperature is 600-700°C, and the sintering time is 10-24 hours. Specifically, the sintering temperature can be 600°C, 620°C, 640°C, 660°C, 700°C, or any value between 600-700°C, and the sintering time can be 10 hours, 15 hours, 18 hours, 20 hours, 24 hours, or any value between 10-24 hours.

[0059] In this application, by controlling the sintering temperature and time, a uniform carbon coating can be formed while maintaining the structure of the lithium ferrite core. If the sintering temperature is too low, the carbon source cannot be fully carbonized; if the sintering temperature is too high, the structure of the lithium ferrite in the core will be affected.

[0060] In a third aspect, an embodiment of the present application provides a positive electrode plate, which includes the lithium ferrite positive electrode composite material described in the first aspect, or includes the lithium ferrite positive electrode composite material prepared by the preparation method of the lithium ferrite positive electrode composite material described in the second aspect.

[0061] In the present application, the positive electrode plate includes the lithium ferrite positive electrode composite material described in the first aspect, or includes the lithium ferrite positive electrode composite material prepared by the preparation method of the lithium ferrite positive electrode composite material described in the second aspect, and thus has lower resistance and good air stability.

[0062] In a fourth aspect, an embodiment of the present application provides a secondary battery, which includes the positive electrode sheet described in the third aspect.

[0063] In the present application, the secondary battery includes the positive electrode sheet described in the third aspect, and thus has higher capacity performance and charge and discharge efficiency.

[0064] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0065] 1. Preparation method Example 1 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0066] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0067] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0068] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 5:95.

[0069] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 1.5:98.5.

[0070] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0071] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0072] Example 2 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0073] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0074] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0075] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 8:92.

[0076] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 1.5:98.5.

[0077] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0078] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0079] Example 3 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0080] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0081] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0082] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 10:90.

[0083] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 1.5:98.5.

[0084] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0085] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0086] Example 4 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 hours until they are evenly mixed to obtain a mixed raw material.

[0087] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0088] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0089] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 5:95.

[0090] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass of Li5FeO4 powder was 3:97.

[0091] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0092] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0093] Example 5 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0094] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0095] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0096] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 5:95.

[0097] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 5:95.

[0098] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0099] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0100] Example 6 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3 and Li2O, where the molar ratio of Fe element to Li element is 1:5.1, place them in a mixer, and stir for 4 hours until they are evenly mixed to obtain a mixed raw material.

[0101] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0102] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0103] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 5:95.

[0104] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 1.5:98.5.

[0105] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0106] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0107] Example 7 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0108] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0109] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0110] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Fe2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Fe2O3 nanoparticles to asphalt was 5:95.

[0111] (5) Li5FeO4 powder was dispersed in the first slurry, and Fe2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Fe2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 1.5:98.5.

[0112] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0113] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0114] Example 8 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0115] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0116] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1-3 μm.

[0117] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; NiO nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of NiO nanoparticles to asphalt was 5:95.

[0118] (5) Li5FeO4 powder was dispersed in the first slurry, and NiO nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of NiO nanoparticles and asphalt to the mass of Li5FeO4 powder was 1.5:98.5.

[0119] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0120] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0121] Comparative Example 1 A method for preparing a lithium ferrite positive electrode material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0122] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0123] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm, that is, lithium ferrite positive electrode material.

[0124] Comparative Example 2 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0125] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0126] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0127] (4) Weigh asphalt and completely dissolve it in dichloromethane to obtain a carbon source solution.

[0128] (5) Li5FeO4 powder is dispersed in a carbon source solution, and the Li5FeO4 is evenly dispersed by ball milling to obtain a slurry; wherein the mass ratio of the asphalt to the Li5FeO4 powder is 1.5:98.5.

[0129] (6) The slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0130] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0131] Comparative Example 3 A method for preparing a lithium ferrite positive electrode composite material comprises the following steps: (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 h until they are evenly mixed to obtain a mixed raw material.

[0132] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0133] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0134] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 15:85.

[0135] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 1.5:98.5.

[0136] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0137] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0138] Comparative Example 4 (1) Weigh nano-Fe2O3, Li2O and LiOH, where the molar ratio of Fe element to Li element is 1:5.1 and the molar ratio of LiOH to Li2O in the lithium source is 1:2, place them in a mixer and stir for 4 hours until they are evenly mixed to obtain a mixed raw material.

[0139] (2) The mixed raw materials were sent to a sintering furnace for calcination under an inert atmosphere. The sintering furnace was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 48 hours to obtain Li5FeO4 positive electrode active material.

[0140] (3) The Li5FeO4 positive electrode active material is crushed to obtain Li5FeO4 powder with a D50 of 1~3μm.

[0141] (4) Asphalt was weighed and completely dissolved in dichloromethane to obtain a carbon source solution; Co2O3 nanoparticles and the carbon source solution were evenly mixed to obtain a first slurry; wherein the mass ratio of Co2O3 nanoparticles to asphalt was 5:95.

[0142] (5) Li5FeO4 powder was dispersed in the first slurry, and Co2O3 nanoparticles were uniformly dispersed on the surface of Li5FeO4 by ball milling to obtain a second slurry; wherein the mass ratio of the total mass of Co2O3 nanoparticles and asphalt to the mass ratio of Li5FeO4 powder was 10:90.

[0143] (6) The second slurry is heated and stirred until the dichloromethane is completely evaporated to obtain an intermediate product.

[0144] (7) The intermediate product was placed in a tube furnace, heated to 650°C, and kept warm for 10 hours to obtain a lithium ferrite positive electrode composite material.

[0145] 2. Test Method (1) Compacted density: Take a 1.5 g sample, use a cylinder with a diameter of 12.95 mm and a height of 32.2 mm, pressurize from 0 to 3.5 T, maintain the pressure at 3.5 T for 10 s, then release the pressure, measure its volume V, and calculate its 3.5 T compacted density = 1.5 g / V.

[0146] (2) Powder internal resistance: Use a powder resistance tester to test the powder internal resistance of the positive electrode material at 100 MPa.

[0147] (3) Charge and discharge specific capacity: The lithium ferrite positive electrode materials prepared in the above examples and comparative examples were assembled into button-type half-cells. Specifically, the above positive electrode materials, conductive agent (Super P), and binder (PVDF) were mixed into a slurry at a mass ratio of 8:1:1, and the slurry was evenly coated on aluminum foil to form a positive electrode sheet. The negative electrode sheet used metal lithium sheet, and the electrolyte used 1M LiPF6 (EC:DMC=1:1 volume ratio). In a vacuum glove box, the battery case, positive and negative electrode sheets, diaphragm (single-layer polypropylene (PP) diaphragm), spring sheet, and gasket were assembled into a button cell.

[0148] The prepared button battery was charged at a constant current of 0.05C (C is the battery's rated capacity) to a cutoff voltage of 4.0V. The charging time and current were recorded, and the charge specific capacity was calculated according to the formula: Charge specific capacity (mAh / g) = Charge current (mA) × Charge time (h) / Battery active material mass (g) After charging, the battery was allowed to rest for a period of time to allow the electrolyte to diffuse evenly and the voltage to stabilize. The battery was then discharged at the same constant current to the cutoff voltage. The discharge time and current were recorded, and the discharge specific capacity was calculated. Based on the recorded charge and discharge data, the charge specific capacity and discharge specific capacity were calculated, respectively. The discharge specific capacity is typically used as the nominal specific capacity of a battery and compared with the charge specific capacity to evaluate the battery's charge and discharge performance.

[0149] (4) Charge and discharge efficiency: First, charge the battery to full capacity at a constant current of 0.05C (C is the rated capacity of the battery), and record the charging time and charging capacity. Then, discharge the battery to the cutoff voltage at the same constant current, and record the discharge time and discharge capacity. Calculate the charge and discharge efficiency using the formula "Charge and discharge efficiency = (discharge capacity / charge capacity) × 100%."

[0150] (5) Air stability: The lithium ferrite positive electrode materials prepared in the above examples and comparative examples were exposed to air at room temperature for 7 days. Then, button batteries were prepared according to the same method as above, and the charge specific capacity of the button batteries was tested.

[0151] 3. Analysis of test results of various embodiments and comparative examples Table 1

[0152] The data from Examples 1 to 3 show that as the transition metal element content in the catalytic layer increases, the compacted density of the prepared lithium ferrite positive electrode composite material gradually decreases, the powder internal resistance increases, and the capacity performance and air stability of the button-type battery prepared therefrom gradually decrease, but the charge and discharge efficiency increases. The data from Examples 1 and 4-5 show that the powder internal resistance of the lithium ferrite positive electrode composite material first increases and then decreases with increasing coating layer dosage, while its compacted density first decreases and then increases with increasing coating layer dosage. The capacity performance and air stability of the secondary battery prepared therefrom first decrease and then increase, while the charge and discharge efficiency first increases and then decreases.

[0153] It can be seen from the data of Example 1 and Example 6 that when a single lithium source is used to prepare the lithium ferrite core, the compaction density of the prepared lithium ferrite positive electrode composite material decreases slightly, but the internal resistance of the powder increases significantly. The capacity performance and air stability of the secondary battery prepared therefrom are reduced, and the charge and discharge efficiency remains basically unchanged.

[0154] From the data of Examples 1 and 7-8, it can be seen that the type of transition metal element in the catalytic layer has a great influence on the performance of the lithium ferrite positive electrode composite material. Among them, when the transition metal element is cobalt, the prepared lithium ferrite positive electrode composite material has the lowest powder internal resistance and the best air stability.

[0155] Furthermore, compared with Example 1, the lithium ferrite positive electrode material of Comparative Example 1 does not contain a coating layer, resulting in a higher powder internal resistance and significantly reduced air stability, thereby reducing the capacity performance of the secondary battery prepared therefrom.

[0156] Furthermore, compared with Example 1, the lithium ferrite positive electrode composite material of Comparative Example 2 does not contain a catalytic layer. Therefore, the bonding effect of the carbon coating layer on the surface of the lithium ferrite core is poor, resulting in an increase in the internal resistance of the lithium ferrite positive electrode composite material, and the capacity performance and air stability of the secondary battery prepared therefrom are both reduced.

[0157] Furthermore, compared with Example 1, the content of the catalytic layer in the lithium ferrite positive electrode composite material of Comparative Example 3 is too large, resulting in an increase in the internal resistance of the lithium ferrite positive electrode composite material, affecting the capacity performance and air stability of the secondary battery prepared therefrom.

[0158] Furthermore, compared with Example 1, the coating layer content in the lithium ferrite positive electrode material of Comparative Example 4 is too large, resulting in a significant increase in the powder internal resistance of the lithium ferrite positive electrode composite material. Therefore, the capacity performance and air stability of the secondary battery prepared therefrom are poor.

[0159] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium ferrite positive electrode composite material, characterized in that: The lithium ferrite positive electrode composite material comprises a lithium ferrite core, a catalyst layer and a carbon layer in sequence from the inside to the outside; The catalytic layer contains a transition metal element, the mass ratio of the catalytic layer to the carbon layer is (5-10): (90-95), and the mass ratio of the total mass of the catalytic layer and the carbon layer to the lithium ferrite core is (1.5-5): (95-98.5).

2. The lithium ferrite positive electrode composite material according to claim 1, characterized in that The D50 particle size of the lithium ferrite core is 1-3 μm.

3. The lithium ferrite positive electrode composite material according to claim 1, characterized in that The sum of the thickness of the catalytic layer and the carbon layer is 200-300 nm.

4. The lithium ferrite positive electrode composite material according to claim 1, characterized in that The transition metal element is at least one of iron, cobalt and nickel.

5. A method for preparing the lithium ferrite positive electrode composite material according to any one of claims 1 to 4, characterized in that: The following steps are involved: Providing lithium ferrite, a transition metal-containing compound, and a carbon source solution; uniformly mixing the transition metal-containing compound and the carbon source solution to obtain a first slurry; dispersing the lithium ferrite in the first slurry to obtain a second slurry; removing the solvent from the second slurry to obtain an intermediate product; The intermediate product is sintered to obtain a lithium ferrite positive electrode composite material.

6. The method for preparing the lithium ferrite positive electrode composite material according to claim 5, characterized in that: In the first slurry, the mass ratio of the transition metal-containing compound to the carbon source is (5-10): (90-95); and / or, In the second slurry, the mass ratio of the sum of the mass of the carbon source and the transition metal-containing compound to the lithium ferrite is (1.5-5): (95-98.5); and / or, The carbon source in the carbon source solution includes at least one of asphalt, paraffin, tar, phenolic resin, and PAN; and / or, The solvent in the carbon source solution is an organic solvent; and / or, The transition metal-containing compound includes at least one of iron oxide, iron chloride, cobalt oxide, cobalt chloride, nickel oxide, and nickel chloride.

7. The method for preparing the lithium ferrite positive electrode composite material according to claim 5, characterized in that: The preparation method of the lithium ferrite provided comprises: calcining a mixture of an iron source and a lithium source at 600-750° C. for 24-48 hours under an inert atmosphere; Wherein, the iron source is Fe2O3; and / or, The lithium source is a mixture of lithium oxide and lithium hydroxide; and / or, The lithium source is a mixture of lithium hydroxide and lithium oxide in a molar ratio of 1: (1.5-2.5); and / or, The molar ratio of Fe to Li in the mixture is 1:(5.0-5.5); and / or, The mixture is heated to 600-750° C. at a heating rate of 2-10° C. / min.

8. The method for preparing the lithium ferrite positive electrode composite material according to claim 5, wherein: In the step of sintering the intermediate product, the sintering temperature is 600-700° C. and the sintering time is 10-24 h.

9. A positive electrode plate, characterized in that: The invention comprises the lithium ferrite positive electrode composite material according to any one of claims 1 to 4, or comprises the lithium ferrite positive electrode composite material prepared by the preparation method of the lithium ferrite positive electrode composite material according to any one of claims 5 to 8.

10. A secondary battery, characterized in that: Including the positive electrode sheet according to claim 9.

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