Phosphate-based cathode materials and preparation methods, cathode sheets, and secondary batteries

Abstract

This application belongs to the field of battery materials technology, and particularly relates to a phosphate-based cathode material and its preparation method, as well as a cathode sheet and a secondary battery. The phosphate-based cathode material includes a phosphate-based active material core and a shell layer covering the outer surface of the core. The shell layer includes a modified Al2O3 inner layer and a conductive polymer outer layer sequentially covering the outer surface of the core. The modified Al2O3 inner layer includes an Al2O3 substrate and F and Ta elements chemically bonded to the substrate. The conductive polymer outer layer includes a polyaniline-lithium phytate composite material. In the phosphate-based cathode material, the double-shell coating structure effectively inhibits the dissolution of metal ions such as manganese, improves interfacial stability, thereby significantly reducing interfacial side reactions, simultaneously enhancing electronic and ionic conductivity, improving rate performance, and greatly increasing cycle life.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and particularly relates to a phosphate-based cathode material and its preparation method, as well as a cathode sheet and a secondary battery. Background Technology

[0002] The rapid development of new energy vehicles and energy storage technologies has highlighted the crucial role of advanced power battery systems. High performance, safety, and cost-effectiveness have become primary development goals. Lithium-ion batteries (LIBs) have become a leading energy storage solution due to their high energy density and environmental benefits.

[0003] Phosphate-based cathode materials have attracted widespread attention as promising cathode materials for lithium-ion batteries due to their advantages such as low cost, high safety, long cycle life, high voltage, good low-temperature performance, and high energy density. However, inherent scientific challenges such as poor electronic conductivity, manganese dissolution during cycling, and large particle size that hinders lithium-ion diffusion have reduced the rate performance and cycle stability of lithium manganese iron phosphate batteries. Summary of the Invention

[0004] The purpose of this application is to provide a phosphate-based cathode material and its preparation method, as well as a cathode sheet and a secondary battery, aiming to solve, to some extent, the problem that the rate performance and cycle stability of existing phosphate-based cathode materials need to be improved.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, this application provides a phosphate-based cathode material, comprising a phosphate-based active material core and a shell layer covering the outer surface of the core. The shell layer comprises a modified Al2O3 inner layer and a conductive polymer outer layer sequentially covering the outer surface of the core. The modified Al2O3 inner layer comprises an Al2O3 substrate and F and Ta elements chemically bonded to the substrate. The conductive polymer outer layer comprises a polyaniline-lithium phytate composite material.

[0007] In some possible implementations, the F element in the modified Al2O3 inner layer forms Al-OF bonds and Al-F bonds with the Al2O3 substrate.

[0008] In some possible implementations, the Ta element forms a Ta-O-Al bond with the Al2O3 substrate.

[0009] In some possible implementations, the Al2O3 substrate forms an Al2O3 substrate layer on the outer surface of the core, and the F and Ta elements are chemically bonded to the outer surface of the substrate layer.

[0010] In some possible implementations, the modified Al2O3 inner layer in the phosphate-based cathode material has a mass fraction of 0.01wt% to 1wt%.

[0011] In some possible implementations, the modified Al2O3 inner layer contains 8% to 15% F by mass, based on the mass of the Al2O3 substrate; and / or, the Ta by mass is 25% to 35%.

[0012] In some possible implementations, the molar ratio of F to Ta in the modified Al2O3 inner layer is (3~5):1.

[0013] In some possible implementations, in the polyaniline-lithium phytate composite material, lithium phytate is grafted onto the polyaniline chain to form a composite polymer chain, and the composite polymer chain is wound around the outer surface of the modified Al2O3 inner layer to form a three-dimensional conductive network structure.

[0014] In some possible implementations, the polyaniline-lithium phytate composite material in the phosphate-based cathode material has a mass percentage content of 3wt% to 8wt%.

[0015] In some possible implementations, the phosphate-based active material in the core has the chemical formula LiMn. x A y Fe 1-x-y PO4, wherein A is selected from at least one of Ti, V, Mg, and In, x is 0~1, and y is 0~1.

[0016] Secondly, this application provides a method for preparing a phosphate-based cathode material, comprising the following steps:

[0017] Precursor materials for preparing phosphate-based active materials;

[0018] An alumina coating layer is prepared on the outer surface of the precursor material to obtain an alumina-coated active material;

[0019] The alumina-coated active material is dispersed in a mixed solution of tantalum salt and fluoride, and then subjected to thermal mixing treatment to obtain a fluorine and tantalum-modified alumina-coated active material.

[0020] The active material coated with fluorine and tantalum modified alumina is dispersed in a mixed solution of aniline and lithium phytate. An oxidant is added to initiate a polymerization reaction. After heat treatment of the reaction product, a conductive polymer outer layer of polyaniline-lithium phytate composite material is formed on the surface of the fluorine and tantalum modified alumina coating layer, thus obtaining a double-coated phosphate-based cathode material.

[0021] In some possible implementations, the preparation of the precursor material includes the following steps: ball milling and mixing raw material components including iron source, manganese source and phosphorus source, drying at a temperature of 80℃~120℃ for 2h~4h, and then pre-sintering at a temperature of 650℃~750℃ for 4h~8h under an inert atmosphere at a heating rate of 3℃ / min~8℃ / min to obtain the precursor material.

[0022] In some possible implementations, the step of preparing an alumina coating on the outer surface of the precursor material includes: mixing the precursor material with a solution of an aluminum salt, then introducing carbon dioxide to react and obtain an aluminum hydroxide-coated precursor material; and calcining the aluminum hydroxide-coated precursor material to obtain the alumina-coated active material.

[0023] In some possible implementations, the aluminum salt includes at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate.

[0024] In some possible implementations, the mass ratio of the precursor material to the aluminum salt is (25~35):(1~3).

[0025] In some possible implementations, the mass fraction of the aluminum salt solution is 20% to 40%.

[0026] In some possible implementations, the calcination treatment conditions include: calcining at 750°C to 850°C for 5 to 10 hours in an inert atmosphere at a heating rate of 3°C / min to 8°C / min.

[0027] In some possible implementations, the total mass fraction of the tantalum salt and fluoride in the mixed solution is 20% to 40%.

[0028] In some possible implementations, the molar ratio of the tantalum salt to the fluoride in the mixed solution of the tantalum salt and the fluoride is 1:(3~5).

[0029] In some possible implementations, the tantalum salt includes at least one of lithium tantalate, tantalum pentachloride, potassium tantalate, and sodium tantalate.

[0030] In some possible implementations, the fluoride includes at least one of ammonium fluoride, sodium fluoride, potassium fluoride, and lithium fluoride.

[0031] In some possible implementations, the molar ratio of the alumina-coated active material to the tantalum element in the tantalum salt and the fluorine element in the fluoride is (4~6):1:(3~5).

[0032] In some possible implementations, the thermal mixing treatment includes the steps of: stirring at a temperature of 50℃~70℃ for 2h~3h, allowing to stand and age for 10h~15h, filtering and drying, and then treating at a temperature of 400℃~500℃ for 2h~3h.

[0033] In some possible implementations, the preparation of the lithium phytate includes the steps of: mixing phytic acid and lithium salt solution, adjusting the pH value to 9-13, and obtaining the lithium phytate; wherein the molar ratio of the lithium salt to the phytic acid is (0.4-0.6):1.

[0034] In some possible implementations, the molar ratio of aniline to lithium phytate in the mixed solution of aniline and lithium phytate is (10~40):(1~3).

[0035] In some possible implementations, the oxidant includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0036] In some possible implementations, the amount of oxidant added is 0.5 wt% to 1 wt% of the mass of the aniline.

[0037] In some possible implementations, the operation of dispersing the fluorine and tantalum-modified alumina-coated active material into a mixed solution of aniline and lithium phytate includes: ultrasonic treatment for 20 to 60 minutes, followed by stirring for 20 to 60 minutes.

[0038] In some possible implementations, the polymerization reaction lasts for 12 to 24 hours and at a temperature of 20°C to 40°C.

[0039] In some possible implementations, the heat treatment temperature is 100℃~150℃ and the duration is 1h~3h.

[0040] Thirdly, this application provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active layer formed on at least one surface of the current collector, the positive electrode active layer comprising the above-described phosphate-based positive electrode material and / or the phosphate-based positive electrode material prepared by the above-described method.

[0041] Fourthly, this application provides a secondary battery, which includes the aforementioned positive electrode plate.

[0042] The phosphate-based cathode material provided in the first aspect of this application comprises a modified Al2O3 inner layer and a conductive polymer outer layer sequentially coated on the outer surface of the phosphate-based active material core, forming a double-shell coating structure. In the modified Al2O3 inner layer, Al2O3 acts as a dense coating layer, inhibiting metal ion dissolution while reducing direct contact between the cathode active material and the electrolyte, thus improving interfacial performance. The fluorine (F) element chemically bonded to the Al2O3 substrate significantly enhances the conductivity of Al2O3. The F-modified Al2O3, acting as a physical protective layer, better reduces metal ion dissolution and electrolyte erosion, suppresses side reactions, and enhances the overall structural stability of the cathode material. Simultaneously, the ta (Ta) element chemically bonded to the Al2O3 substrate results in a denser and more uniform Al2O3 coating layer, enhancing resistance to electrolyte erosion and mechanical stability. Therefore, the modified Al2O3 inner layer, primarily modified with F and secondarily modified with Ta, decouples the two functions of "high-strength physical barrier of Al2O3" and "interfacial chemical optimization of F and tantalum modification," achieving a synergistic effect of 1+1>2. Furthermore, the conductive polymer outer layer includes a polyaniline-lithium phytate composite material (PANi-Li). As a highly conductive polymer, polyaniline, being intrinsically conductive, provides an efficient electron transport path through its conjugated π-electron system in its main chain. The carboxyl groups in phytate form hydrogen bonds with the modified Al2O3, replacing the hydrogen ions of the carboxyl groups with lithium ions, directly eliminating the interference of protons on lithium ion transport. Moreover, the binding energy between lithium ions and sulfonic acid groups is higher than that between hydrogen ions, thus lithium phytate can form a more stable ion transport channel. The abundant phosphate groups in lithium phytate can undergo protonation doping with the imine nitrogen atoms on the polyaniline chain, significantly enhancing the charge delocalization within the polyaniline chain and thereby improving its intrinsic conductivity. When this composite material coats the surface of the phosphate-based active material core, the fibrous structure of polyaniline interweaves to form a three-dimensional electronic conduction network covering the surface of the phosphate-based active material core particles. This effectively bridges the conductive gaps between individual phosphate-based cathode material particles, providing a continuous electron transport channel for the electrode reaction and thus compensating for the inherent electronic conductivity deficiency of the phosphate-based active material. Furthermore, the conductive polymer outer layer containing the polyaniline-lithium phytate composite material effectively blocks direct contact between the electrolyte and the surface of the phosphate-based active material core particles, reducing the occurrence of side reactions at the electrode-electrolyte interface. This reduces the catalytic dissolution tendency of metal ions such as manganese in the electrolyte. The lithium phosphate groups in lithium phytate have a certain ability to capture hydrogen ions, which can locally neutralize acidic species, reduce interfacial acidity, mitigate the erosion of the crystal structure by HF, and inhibit the dissolution reaction of metal ions from the source.Therefore, the double-shell coating structure of this application effectively suppresses the dissolution of metal ions such as manganese and improves the interface stability through the synergistic design of "modified Al2O3 inner layer (barrier + ion conduction) + polyaniline-lithium phytate composite material outer layer (electronic conduction + secondary protection)". This significantly reduces the interfacial side reactions of phosphate-based cathode materials, enhances electronic and ionic conductivity simultaneously, improves rate performance, and greatly improves cycle life.

[0043] The method for preparing phosphate-based cathode materials provided in the second aspect of this application employs a step-by-step, sequential coating and modification process. First, an alumina base layer is constructed on the surface of the active material. Then, synergistic modification of fluorine and tantalum elements is achieved through thermal mixing of tantalum salt and fluoride, forming a dense and interface-stable modified alumina inner layer. Next, under oxidative polymerization conditions, a three-dimensional conductive network outer layer of polyaniline-lithium phytate composite material is generated in situ outside the modified alumina inner layer. This process design ensures the sequential formation of functional layers and tight interfacial bonding, achieving not only the integration of multiple functions—physical barrier, ion conduction, and electron transport—but also strong process controllability and good coating uniformity. This is beneficial for the large-scale preparation of double-coated phosphate-based cathode materials with high cycle stability, high rate performance, and structural integrity.

[0044] The positive electrode sheet provided in the third aspect of this application comprises a phosphate-based positive electrode material with a double-coated structure in its positive electrode active layer. This material, through the synergistic effect of the modified Al2O3 inner layer and the polyaniline-lithium phytate composite outer layer, can be further transformed into excellent electrochemical performance at the electrode scale. This results in higher structural stability and a lower tendency for interfacial side reactions in the positive electrode material particles, helping to maintain the integrity of the electrode during long-term cycling. Simultaneously, the uniform and continuous conductive polymer network significantly improves the electron transport efficiency within the positive electrode sheet, reduces electrode polarization, and achieves higher discharge capacity, better rate performance, and longer cycle life.

[0045] The secondary battery provided in the fourth aspect of this application benefits from the dual synergistic protection and conduction enhancement effects of the "modified alumina inner layer" and the "polyaniline-lithium phytate composite material outer layer" in the positive electrode, achieving a significant comprehensive performance improvement at the battery level. Due to the effective suppression of interfacial side reactions, the reduction of manganese dissolution, and the synergistic optimization of electron / ion transport inside the electrode, the rate performance of the secondary battery can be improved, and the structural integrity and safety of the battery during cycling can be enhanced. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic flowchart of the preparation method of the phosphate-based cathode material provided in the embodiments of this application;

[0048] Figure 2 These are X-ray diffraction (XRD) test patterns of the lithium manganese iron phosphate cathode materials prepared in Example 1 and Comparative Example 1 of this application;

[0049] Figure 3 This is a 1C first-cycle charge-discharge curve of a lithium-ion battery using lithium manganese iron phosphate cathode material in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0050] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0051] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0052] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0053] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0054] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0055] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as µg, mg, g, or kg.

[0056] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0057] The first aspect of this application provides a phosphate-based cathode material, comprising a phosphate-based active material core and a shell layer covering the outer surface of the core. The shell layer comprises a modified Al2O3 inner layer and a conductive polymer outer layer sequentially covering the outer surface of the core. The modified Al2O3 inner layer comprises an Al2O3 substrate and F and Ta elements chemically bonded to the substrate. The conductive polymer outer layer comprises a polyaniline-lithium phytate composite material.

[0058] The phosphate-based cathode material provided in the first aspect of this application comprises a modified Al2O3 inner layer and a conductive polymer outer layer sequentially coated on the outer surface of the phosphate-based active material core, forming a double-shell coating structure. In the modified Al2O3 inner layer, Al2O3 acts as a dense coating layer, inhibiting metal ion dissolution while reducing direct contact between the cathode active material and the electrolyte, thus improving interfacial performance. The sulfur (F) element chemically bonded to the Al2O3 substrate significantly enhances the conductivity of Al2O3. The F-modified Al2O3, acting as a physical protective layer, better reduces metal ion dissolution and electrolyte erosion, suppresses side reactions, and enhances the overall structural stability of the cathode material. Simultaneously, the ta (Ta) element chemically bonded to the Al2O3 substrate forms a denser and more uniform Al2O3 coating layer, enhancing resistance to electrolyte erosion and mechanical stability. Therefore, the modified Al2O3 inner layer, primarily modified with F and secondarily modified with Ta, decouples the two functions of "high-strength physical barrier of Al2O3" and "interfacial chemical optimization of F and tantalum modification," achieving a synergistic effect of 1+1>2. Furthermore, the conductive polymer outer layer includes a polyaniline-lithium phytate composite material (PANi-Li). As a highly conductive polymer, polyaniline, being intrinsically conductive, provides an efficient electron transport path through its conjugated π-electron system in its main chain. The carboxyl groups in phytate form hydrogen bonds with the modified Al2O3, replacing the hydrogen ions of the carboxyl groups with lithium ions, directly eliminating the interference of protons on lithium ion transport. Moreover, the binding energy between lithium ions and sulfonic acid groups is higher than that between hydrogen ions, thus lithium phytate can form a more stable ion transport channel. The abundant phosphate groups in lithium phytate can undergo protonation doping with the imine nitrogen atoms on the polyaniline chain, significantly enhancing the charge delocalization within the polyaniline chain and thereby improving its intrinsic conductivity. When this composite material coats the surface of the phosphate-based active material core, the fibrous structure of polyaniline interweaves to form a three-dimensional electronic conduction network covering the surface of the phosphate-based active material core particles. This effectively bridges the conductive gaps between individual phosphate-based cathode material particles, providing a continuous electron transport channel for the electrode reaction and thus compensating for the inherent electronic conductivity deficiency of the phosphate-based active material. Furthermore, the conductive polymer outer layer containing the polyaniline-lithium phytate composite material effectively blocks direct contact between the electrolyte and the surface of the phosphate-based active material core particles, reducing the occurrence of side reactions at the electrode-electrolyte interface. This reduces the catalytic dissolution tendency of metal ions such as manganese in the electrolyte. The lithium phosphate groups in lithium phytate have a certain ability to capture hydrogen ions, which can locally neutralize acidic species, reduce interfacial acidity, mitigate the erosion of the crystal structure by HF, and inhibit the dissolution reaction of metal ions from the source.Therefore, the dual-shell coating structure of this application, through the synergistic design of "modified Al2O3 inner layer (barrier + ion conduction) + polyaniline-lithium phytate composite material outer layer (electronic conduction + secondary protection)," effectively suppresses the dissolution of metal ions such as manganese, improves interface stability, thereby significantly reducing the interface side reactions of phosphate-based cathode materials, simultaneously enhancing electronic and ionic conductivity, improving rate performance, and greatly increasing cycle life.

[0059] In some possible implementations, the phosphate-based active material in the core has the chemical formula LiMn. x A y Fe 1-x- y PO4, wherein A is selected from at least one of Ti, V, Mg, and In, x is 0~1, and y is 0~1. Exemplarily, the phosphate-based active material in this application embodiment can be lithium iron phosphate, doped lithium iron phosphate, lithium manganese iron phosphate, or doped lithium manganese iron phosphate, etc. In some specific embodiments, the phosphate-based active material is selected from lithium manganese iron phosphate.

[0060] In some possible implementations, the fluorine element (F) in the modified Al₂O₃ inner layer forms Al-OF and Al-F bonds with the Al₂O₃ substrate. In this case, the core process after fluorination modification of alumina is the fluoride ion exchange (F₂O₃). - The fluorine atoms partially replace the hydroxyl (-OH) or oxygen atoms on the surface of alumina, thereby forming surface fluorine-containing species, which are mainly composed of Al-OF and Al-F bonds.

[0061] In some possible implementations, Ta (Ta) forms Ta-O-Al bonds with the Al2O3 substrate. In this case, tantalum doping modification can form a denser and more uniform coating layer, improving structural stability. Tantalum has extremely strong acid and alkali resistance, and the Ta-O-Al bonds formed by alumina modification can effectively resist electrolyte corrosion, extending battery cycle life. Fluorine-tantalum composite modification can form an AlF3-Ta-O-Al composite structure, enhancing interfacial bonding. The effect of fluorine-tantalum composite modification far exceeds that of simple superposition, producing a synergistic effect of 1+1>2.

[0062] In some possible implementations, an Al2O3 substrate layer is formed on the outer surface of the core, with F and Ta elements chemically bonded to the outer surface of the substrate layer. In this case, the surface-fluorinated alumina is mainly composed of Al-OF and Al-F bonds. The modified material is not a complete conversion of alumina into aluminum fluoride compounds, but rather forms a structure of "alumina substrate layer + fluoride / fluorine complex surface layer". The presence of the surface layer significantly alters the properties of alumina, such as reducing the surface hydroxyl content and enhancing chemical stability, thus significantly enhancing lithium-ion conductivity and improving rate performance. Simultaneously, tantalum doping on the Al2O3 substrate layer forms a denser and more uniform coating layer, improving structural stability. Tantalum has extremely strong acid and alkali resistance, and the formed Ta-O-Al bonds effectively resist electrolyte corrosion, extending battery cycle life.

[0063] In some possible implementations, the modified Al₂O₃ inner layer in phosphate-based cathode materials has a mass fraction of 0.01 wt% to 1 wt%. In this case, it acts as an ultrathin functional interface layer, enabling continuous coating, effectively suppressing manganese leaching and electrolyte erosion, while minimizing resistance to lithium-ion diffusion. This design, synergistically with the outer polyaniline-lithium phytate composite conductive network, optimizes electron and ion conduction while maintaining the high energy density of the cathode material, contributing to improved cycle stability and rate performance.

[0064] For example, in phosphate-based cathode materials, the mass fraction of the modified Al2O3 inner layer can be any typical but non-limiting point value or a range between any two points, such as 0.01wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, etc., preferably 0.5wt%.

[0065] In some possible implementations, the modified Al2O3 inner layer contains 8%–15% F by mass, based on the mass of the Al2O3 substrate; and / or 25%–35% Ta by mass. In this case, F doping can effectively improve the interfacial lithium-ion conductivity without excessively affecting structural stability, while Ta doping enhances the density and electrolyte corrosion resistance of the coating layer. The two work synergistically in the inner layer, providing a foundation for achieving high cycle stability and good rate performance.

[0066] For example, in the modified Al2O3 inner layer, based on the mass of the Al2O3 substrate, the mass percentage of F element can be any typical but non-limiting point value or a range between any two point values, such as 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., and the mass percentage of Ta element can be any typical but non-limiting point value or a range between any two point values, such as 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, etc.

[0067] In some possible implementations, the molar ratio of F to Ta in the modified Al2O3 inner layer is (3~5):1. In this case, a bilayer synergistic modification is formed in the modified Al2O3 inner layer, with F modification as the main component and Ta modification as the auxiliary component. F doping effectively improves the interfacial lithium-ion conductivity, while Ta doping enhances the density and electrolyte corrosion resistance of the coating layer. The two work synergistically in the inner layer, providing a foundation for achieving high cycle stability and good rate performance.

[0068] In some possible implementations, in polyaniline-lithium phytate composite materials, lithium phytate is grafted onto the polyaniline chains to form composite polymer chains. These composite polymer chains are then wound around the outer surface of the modified Al2O3 inner layer to form a three-dimensional conductive network structure. In this case, the structure can provide continuous and uniformly covered electron transport channels for the phosphate-based active material particles, effectively bridging adjacent active particles and compensating for the insufficient conductivity of the inner Al2O3 layer. Simultaneously, its winding and coating form helps to enhance interfacial bonding and structural integrity, improving overall electronic conductivity while synergistically suppressing electrolyte erosion and side reactions in the inner layer, thereby improving the overall electrochemical performance of the cathode material.

[0069] In some possible implementations, the mass percentage of polyaniline-lithium phytate composite material in phosphate-based cathode materials is 3wt% to 8wt%. In this case, this content range helps to balance the conductivity of the electrode with the proportion of active material, avoiding unnecessary increase in impedance or reduction in energy density due to excessive coating. This, in conjunction with the inner modified alumina, comprehensively improves rate performance and cycle stability while maintaining the high capacity characteristics of the cathode material.

[0070] For example, in phosphate-based cathode materials, the mass percentage of polyaniline-lithium phytate composite material can be any typical but non-limiting point value or a range between any two points, such as 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%.

[0071] The phosphate-based cathode material described in the above embodiments of this application can be prepared by the methods described in the following embodiments.

[0072] Secondly, embodiments of this application provide a method for preparing a phosphate-based cathode material, as shown in the attached figure. Figure 1 As shown, it includes the following steps:

[0073] S10. Precursor materials for preparing phosphate-based active materials;

[0074] S20. An alumina coating layer is prepared on the outer surface of the precursor material to obtain an alumina-coated active material;

[0075] S30. The alumina-coated active material is dispersed in a mixed solution of tantalum salt and fluoride, and subjected to thermal mixing treatment to obtain a fluorine and tantalum-modified alumina-coated active material;

[0076] S40. The active material coated with fluorine and tantalum modified alumina is dispersed in a mixed solution of aniline and lithium phytate. An oxidant is added to initiate a polymerization reaction. After heat treatment of the reaction product, a conductive polymer outer layer of polyaniline-lithium phytate composite material is formed on the surface of the fluorine and tantalum modified alumina coating layer, thus obtaining a double-coated phosphate-based cathode material.

[0077] The method for preparing phosphate-based cathode materials in this application involves a step-by-step, sequential coating and modification process. First, an alumina base layer is constructed on the surface of the active material. Then, synergistic modification of fluorine and tantalum elements is achieved through thermal mixing of tantalum salt and fluoride, forming a dense and interface-stable modified alumina inner layer. Next, under oxidative polymerization conditions, a three-dimensional conductive network outer layer of polyaniline-lithium phytate composite material is generated in situ outside the modified alumina inner layer. This process design ensures the sequential formation of functional layers and tight interfacial bonding, achieving not only the integration of multiple functions—physical barrier, ion conduction, and electron transport—but also strong process controllability and good coating uniformity. This is beneficial for the large-scale preparation of double-coated phosphate-based cathode materials with high cycle stability, high rate performance, and structural integrity.

[0078] In step S10 above:

[0079] In some possible implementations, the preparation of the precursor material includes the following steps: ball milling and mixing raw material components, including iron, manganese, and phosphorus sources, followed by drying at 80℃~120℃ for 2h~4h, and then pre-sintering at 650℃~750℃ for 4h~8h under an inert atmosphere with a heating rate of 3℃ / min~8℃ / min to obtain the precursor material. In this case, ball milling ensures uniform dispersion of the raw materials, low-temperature drying effectively removes solvents and avoids component segregation, and the moderate pre-sintering (650℃~750℃) in an inert atmosphere promotes the initial crystallization of the precursor and the formation of a porous and loose structure. This is beneficial for the uniform wetting and adhesion of aluminum salts, modifiers, and polymer solutions during the subsequent coating process, thus laying an important foundation for constructing a complete, dense, and firmly bonded functional coating layer.

[0080] For example, the drying temperature can be any typical but non-limiting value or a range between any two values, such as 80℃, 90℃, 100℃, 110℃, and 120℃; the drying time can be any typical but non-limiting value or a range between any two values, such as 2h, 3h, and 4h. The heating rate can be any typical but non-limiting value or a range between any two values, such as 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, and 8℃ / min. The pre-sintering temperature can be any typical but non-limiting value or a range between any two values, such as 650℃, 660℃, 670℃, 680℃, 690℃, and 700℃, preferably 680℃. The pre-sintering time can be any typical but non-limiting value or a range between any two values, such as 4h, 5h, 6h, 7h, and 8h, preferably 6h.

[0081] In some possible implementations, the ball milling mixing time is 1 hour to 2 hours, preferably 1 hour. This ensures that all raw material components are thoroughly and uniformly mixed.

[0082] In some possible implementations, a small amount of carbon source may be added to the raw material components. For example, the carbon source may be one or more of glucose, sucrose, PEG, and citric acid, preferably glucose. These carbon sources are all common organic compounds with good water solubility and controllable pyrolysis behavior. They can promote the uniform dispersion of the components during ball milling and provide a reducing atmosphere and inhibit the oxidation of metal elements during pre-sintering.

[0083] In some possible implementations, the iron source is one or more of FeSO4, FeCO3, ferrous oxalate, FeCl2, and ferrous acetate, preferably FeSO4. These compounds have good solubility or dispersibility in water or solvents, which is beneficial for achieving atomic-level homogeneous mixing through ball milling, thereby promoting homogeneous reactions in subsequent pre-sintering and generating a well-crystallized and accurately composed lithium manganese iron phosphate active material precursor.

[0084] In some possible implementations, the phosphorus source is one or both of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, preferably ammonium dihydrogen phosphate. These compounds have good solubility or dispersibility in water or solvents, which is beneficial for achieving atomic-level homogeneous mixing through ball milling, thereby promoting homogeneous reactions in subsequent pre-sintering and generating a well-crystallized and accurately composed lithium manganese iron phosphate active material precursor.

[0085] In some possible implementations, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium oxalate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium citrate, and lithium tartrate, preferably lithium carbonate. These compounds have good solubility or dispersibility in water or solvents, which is beneficial for achieving atomic-level homogeneous mixing through ball milling, thereby promoting homogeneous reactions in subsequent pre-sintering and generating a well-crystallized and accurately composed lithium manganese iron phosphate active material precursor.

[0086] In some possible implementations, the molar ratio of the selected iron source to the manganese source can be 1:1, 2:3, 3:2, 1:4, etc., with 1:1 being the preferred ratio. These ratios can produce relatively mature lithium manganese iron phosphate. Typical ratios such as 1:1, 2:3, 3:2, and 1:4 correspond to lithium manganese iron phosphate (LMFP) with different manganese-iron ratios, such as common systems like LMFP-55, 46, 64, and 28.

[0087] In step S20 above:

[0088] In some possible implementations, the step of preparing an alumina coating on the outer surface of the precursor material includes: mixing the precursor material with a solution of an aluminum salt, then reacting it with carbon dioxide to obtain an aluminum hydroxide-coated precursor material; and calcining the aluminum hydroxide-coated precursor material to obtain an alumina-coated active material. In this case, an aluminum hydroxide coating is generated in situ on the surface of the active material precursor using a carbon dioxide-assisted precipitation method, which is then calcined to transform it into an alumina layer. This mild wet chemical process can form a uniform and continuous aluminum hydroxide coating on the particle surface, and subsequent heat treatment densifies it into a stable alumina structure, providing an ideal substrate for subsequent fluorine and tantalum modification.

[0089] In some possible implementations, the aluminum salt includes at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate; these aluminum salts all have good solubility and are common water-soluble salts that can fully dissociate in solution to provide aluminum ions, ensuring efficient reaction with the introduced carbon dioxide, and uniformly and controllably precipitating an aluminum hydroxide layer on the surface of the precursor material.

[0090] In some possible implementations, the mass ratio of precursor material to aluminum salt is (25~35):(1~3); under this ratio, it is ensured that the aluminum salt can be uniformly and densely attached to the surface of the precursor material, and a uniform and dense aluminum hydroxide coating layer is generated in situ on the surface of the precursor material by carbon dioxide-assisted precipitation.

[0091] For example, the mass ratio of the precursor material to the aluminum salt can be any typical but non-limiting point value or an interval between any two point values, such as 25:1, 25:2, 25:3, 26:1, 26:2, 26:3, 28:1, 28:2, 28:3, 30:1, 30:2, 30:3, 32:1, 32:2, 32:3, 35:1, 35:2, 35:3.

[0092] In some possible implementations, the mass fraction of the aluminum salt solution is 20% to 40%; in this case, the concentration of the aluminum salt solution is conducive to uniform dispersion, adhesion, and reaction with the precursor material.

[0093] For example, the mass fraction of the aluminum salt solution can be any typical but non-limiting point value or an interval between any two point values, such as 20%, 23%, 25%, 27%, 30%, 33%, 35%, 38%, 40%.

[0094] In some possible implementations, the calcination conditions include: calcining at 750℃~850℃ for 5h~10h in an inert atmosphere with a heating rate of 3℃ / min~8℃ / min. Under these conditions, the aluminum hydroxide layer on the precursor surface can be fully dehydrated and transformed into a dense alumina coating with suitable crystallinity without damaging the bulk structure of the active material. This controlled heat treatment process effectively avoids cracking or peeling of the coating caused by drastic temperature changes or thermal stress, ensuring the integrity and uniformity of the alumina layer and providing a stable and robust substrate for subsequent fluorine and tantalum modification.

[0095] For example, the inert atmosphere for calcination can be nitrogen, argon, helium, etc. The heating rate can be any typical but non-limiting value or a range between any two values, such as 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, etc. The calcination temperature can be any typical but non-limiting value or a range between any two values, such as 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, etc. The calcination time can be any typical but non-limiting value or a range between any two values, such as 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0096] In step S30 above:

[0097] In some possible implementations, the total mass fraction of tantalum salt and fluoride in the mixed solution is 20%–40%. This provides a moderate and sufficient modifier concentration environment for the alumina coating. This range ensures that fluoride and tantalum ions effectively diffuse to the alumina surface and shallow layers during heat treatment, achieving sufficient fluorine substitution and tantalum doping to form stable Al-OF, Al-F, and Ta-O-Al bonded structures. It also avoids problems such as uneven material dispersion or excessively thick surface deposition caused by overly concentrated solutions, optimizing the inner layer's ionic conductivity, density, and corrosion resistance.

[0098] In some possible implementations, the molar ratio of tantalum salt to fluoride in a mixed solution is 1:(3~5). This ensures sufficient fluoride ions to undergo adequate substitution reactions with the alumina surface during subsequent heat treatment, effectively forming Al-F and Al-OF bonds to improve ionic conductivity. Simultaneously, it promotes tantalum doping via Ta-O-Al bonds, enhancing the density and chemical stability of the coating layer. Excessive tantalum concentration should be avoided as it can block lithium-ion channels, while excessive fluoride concentration may exacerbate material corrosion.

[0099] For example, in a mixed solution of tantalum salt and fluoride, the molar ratio of tantalum salt to fluoride can be any point value or a range between any two point values, such as 1:3, 1:4, 1:5, etc.

[0100] In some possible implementations, the tantalum salt includes at least one of lithium tantalate, tantalum pentachloride, potassium tantalate, and sodium tantalate. Among them, lithium tantalate can serve as both a tantalum source and a supplementary lithium source, which helps maintain the lithium balance of the material system; tantalum pentachloride, potassium tantalate, and sodium tantalate are all common tantalum compounds that are readily soluble in water or can be dispersed by adjusting the pH, and can effectively release tantalum ions in solution, and form stable Ta-O-Al bonds with the alumina layer through subsequent heat treatment.

[0101] In some possible implementations, the fluoride includes at least one of ammonium fluoride, sodium fluoride, potassium fluoride, and lithium fluoride. Among them, ammonium fluoride can decompose to produce ammonia and HF during heat treatment, which helps to promote the reactivity of fluorine with the alumina surface; while alkali metal fluorides such as lithium fluoride, sodium fluoride, and potassium fluoride can provide fluoride ions, and some alkali metal ions may participate in interfacial stabilization or form conduction channels.

[0102] In some possible implementations, the molar ratio of the alumina-coated active material to the tantalum in the tantalum salt and the fluorine in the fluoride is (4~6):1:(3~5). The alumina-coated active material ratio ensures the capacity of the phosphate-based cathode material. The fluorine in the fluoride is in 3~5 times excess relative to the tantalum in the tantalum salt, ensuring sufficient fluorination substitution on the alumina surface to optimize ion conduction. The fixed proportion of tantalum salt provides an appropriate amount of structural dopant, enhancing the density and chemical stability of the coating while avoiding ion channel blockage that might result from excessive tantalum.

[0103] For example, the molar ratio of the alumina-coated active material to the tantalum element in the tantalum salt and the fluorine element in the fluoride can be any typical but non-limiting point value or a range between any two point values, such as 6:1:3, 6:1:4, 6:1:5, 5:1:3, 5:1:4, 5:1:5, 4:1:3, 4:1:4, 4:1:5.

[0104] In some possible implementations, the thermal mixing process includes the following steps: stirring at 50℃~70℃ for 2h~3h, followed by static aging for 10h~15h, filtration and drying, and then treatment at 400℃~500℃ for 2h~3h. In this case, low-temperature stirring promotes uniform adsorption and initial reaction of the modifier, static aging ensures sufficient diffusion and penetration of fluorine and tantalum ions to the surface and shallow layers of the alumina layer, and subsequent medium-temperature heat treatment (400℃~500℃) promotes the formation of stable Al-F and Al-OF bonds between fluorine ions and alumina, while tantalum ions achieve structural doping through Ta-O-Al bonds. This segmented temperature and time control, while avoiding phase transformation of the active material, achieves sufficient chemical modification and structural densification of the inner layer coating, providing a key process guarantee for obtaining a modified alumina inner layer with high ionic conductivity, strong corrosion resistance, and interface stability.

[0105] For example, in the heat mixing process, the stirring temperature can be any typical but non-limiting point value or a range between any two points, such as 50℃, 55℃, 60℃, 65℃, 70℃, etc.; the settling and aging time can be any typical but non-limiting point value or a range between any two points, such as 10h, 11h, 12h, 13h, 14h, 15h, etc.; and the heat treatment temperature can be any typical but non-limiting point value or a range between any two points, such as 400℃, 410℃, 420℃, 430℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, etc.

[0106] In step S40 above:

[0107] In some possible implementations, the preparation of lithium phytate includes the following steps: mixing phytic acid and a lithium salt solution, adjusting the pH to 9-13 to obtain lithium phytate; wherein the molar ratio of lithium salt to phytic acid is (0.4-0.6):1. In this case, by precisely controlling the pH of the reaction system within the strongly alkaline range of 9-13, sufficient deprotonation of the phosphate groups in the phytic acid molecule is ensured, which facilitates the efficient and uniform substitution of hydrogen ions by lithium ions to form a structurally well-defined lithium phytate product, and effectively suppresses the hydrolysis or structural instability of lithium phytate under acidic conditions. Simultaneously, limiting the molar ratio of lithium salt to phytic acid to (0.4-0.6):1 achieves lithiation of the phytic acid molecule, introducing sufficient lithium ions to provide subsequent ion transport channels and eliminating the competitive interference of protons on lithium ion migration.

[0108] For example, the molar ratio of lithium salt to phytic acid can be any typical but non-limiting point value or a range between any two point values, such as 0.4:1, 0.5:1, or 0.6:1, preferably 0.5:1.

[0109] In some possible implementations, the lithium salt includes one or more combinations of lithium carbonate, lithium chloride, lithium nitrate, and lithium sulfate. In this case, these lithium salts are readily available, highly water-soluble, and stably provide lithium ions. They can all react effectively with phytic acid under alkaline conditions to lithilate phytic acid molecules, forming lithium phytate.

[0110] In some possible implementations, the molar ratio of aniline to lithium phytate in a mixed solution is (10~40):(1~3). In this case, this ratio ensures a sufficient excess of aniline as a monomer, thereby generating a polyaniline backbone of sufficient length to form a continuous three-dimensional network during oxidative polymerization. Simultaneously, a limited amount of lithium phytate can be effectively grafted onto the polyaniline chain, providing lithium-ion transport channels while achieving protonation doping through its phosphate groups, significantly improving the intrinsic conductivity of the composite polymer.

[0111] For example, the molar ratio of aniline to lithium phytate can be any typical but non-limiting point value or a range between any two point values, such as 10:3, 20:3, 10:1, 40:1, etc., preferably 20:3.

[0112] In some possible implementations, the oxidant includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate. In this case, these oxidants are all strong oxidizing agents with good water solubility, capable of effectively initiating the oxidative polymerization reaction of aniline in neutral to weakly acidic aqueous solutions, promoting the in-situ formation of a polyaniline-lithium phytate composite conductive network in the presence of aniline monomers.

[0113] In some possible implementations, the amount of oxidant added is 0.5 wt% to 1 wt% of the mass of aniline. In this case, the amount of oxidant can ensure that the oxidative polymerization reaction of aniline proceeds at a moderate and controllable rate, avoiding both incomplete polymerization or discontinuous coating layer caused by insufficient initiator, and excessive reaction, excessively wide polymer molecular weight distribution, or localized excessive stacking caused by excessive initiator.

[0114] For example, the amount of oxidant added is any typical but non-limiting point value or a range between any two point values, such as 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt% of the mass of aniline.

[0115] In some possible implementations, dispersing the fluorine- and tantalum-modified alumina-coated active material into a mixed solution of aniline and lithium phytate involves ultrasonic treatment for 20 to 60 minutes, followed by stirring for another 20 to 60 minutes. In this case, this combined operation ensures that the surface of the fluorine / tantalum-modified alumina coating is fully and uniformly wetted and contacted by the aniline and lithium phytate mixture, laying a crucial physical foundation for the subsequent in-situ oxidative polymerization reaction to generate a continuous and complete three-dimensional conductive network coating layer of the polyaniline-lithium phytate composite material on the surface of each particle.

[0116] For example, the duration of ultrasonic treatment can be any typical but non-limiting point value or an interval between any two point values, such as 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes, and the stirring duration can be any typical but non-limiting point value or an interval between any two point values, such as 20 minutes, 30 minutes, 40 minutes, 50 minutes, or 60 minutes.

[0117] In some possible implementations, the polymerization reaction lasts for 12 to 24 hours at a temperature of 20°C to 40°C. This ensures that the monomers are fully polymerized and a complete polyaniline-lithium phytate composite coating layer with an ideal chain structure is gradually formed on the modified alumina surface, while avoiding uneven coating, excessive polymer crosslinking, or damage to the inner layer structure that may be caused by high temperature or excessively fast reaction.

[0118] For example, the duration of the polymerization reaction can be any typical but non-limiting point value or a range between any two points, such as 12h, 15h, 18h, 20h, or 24h. The temperature can be any typical but non-limiting point value or a range between any two points, such as 20℃, 30℃, or 40℃.

[0119] In some possible implementations, the heat treatment temperature is 100℃~150℃, and the duration is 1h~3h. In this case, the low-temperature heat treatment step effectively removes residual moisture or solvents from the polyaniline-lithium phytate composite coating layer under mild conditions, and promotes further cross-linking and stabilization between polymer chains. This enhances the density of the outer coating, the adhesion to the modified alumina inner layer, and the overall structural integrity without damaging the already formed conductive network structure.

[0120] For example, the temperature of the heat treatment can be any typical but non-limiting point value or an interval between any two points, such as 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc., and the duration can be any typical but non-limiting point value or an interval between any two points, such as 1h, 2h, 3h, etc.

[0121] Thirdly, embodiments of this application provide a positive electrode sheet, which includes a current collector and a positive electrode active layer formed on at least one surface of the current collector. The positive electrode active layer includes the phosphate-based positive electrode material described above and / or the phosphate-based positive electrode material prepared by the above method.

[0122] The positive electrode sheet provided in this application embodiment comprises a phosphate-based positive electrode material with a double-coated structure in its positive electrode active layer. This material, through the synergistic effect of the modified Al2O3 inner layer and the polyaniline-lithium phytate composite outer layer, can be further transformed into excellent electrochemical performance at the electrode scale. This results in higher structural stability and a lower tendency for interfacial side reactions in the positive electrode material particles, helping to maintain the integrity of the electrode during long-term cycling. Simultaneously, the uniform and continuous conductive polymer network significantly improves the electron transport efficiency within the positive electrode sheet, reduces electrode polarization, and achieves higher discharge capacity, better rate performance, and longer cycle life.

[0123] In some possible implementations, the preparation of the positive electrode active layer includes the following steps: mixing the above-mentioned phosphate-based positive electrode material, conductive agent and binder to form an electrode slurry, coating the electrode slurry onto the current collector, and then preparing the positive electrode sheet through steps such as drying, rolling and die cutting.

[0124] In some possible implementations, the mass percentage of phosphate-based cathode material in the cathode active layer of the cathode sheet is 90% to 95%. Specifically, the mass percentage of phosphate-based cathode material in the cathode active material layer can be 90%, 91%, 92%, 93%, 94%, 95%, etc.

[0125] In some possible implementations, the current collector of the positive electrode includes, but is not limited to, any one of copper foil or aluminum foil.

[0126] In some possible implementations, the binder content in the positive electrode active material layer is 2wt% to 5wt%. In specific embodiments, the binder content can be typical but not limited to 2wt%, 3wt%, 4wt%, 5wt%, etc.

[0127] In some possible implementations, the binder includes one or more of the following: polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0128] In some possible implementations, the conductive agent content in the positive electrode active material layer is 0.7wt% to 5wt%. In specific embodiments, the conductive agent content can be typical but not limited to 0.7wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, etc.

[0129] In some possible implementations, the conductive agent includes graphite, carbon black, acetylene black, graphene, carbon fiber, and C. 60 And one or more of carbon nanotubes.

[0130] Fourthly, embodiments of this application provide a secondary battery, which includes the aforementioned positive electrode sheet.

[0131] The secondary battery provided in this application benefits from the dual synergistic protection and conduction enhancement effects of the "modified alumina inner layer" and the "polyaniline-lithium phytate composite material outer layer" in the positive electrode, achieving a significant comprehensive performance improvement at the battery level. Due to the effective suppression of interfacial side reactions, the reduction of manganese dissolution, and the synergistic optimization of electron / ion transport inside the electrode, the rate performance of the secondary battery can be improved, and the structural integrity and safety of the battery during cycling can be enhanced.

[0132] In some possible implementations, the negative electrode active material of the secondary battery includes, but is not limited to, carbon materials such as graphite, soft carbon (e.g., coke), and hard carbon, or nitrides, tin-based oxides, tin alloys, and nano-anode materials. The current collector includes, but is not limited to, any one of copper foil and aluminum foil.

[0133] In some possible implementations, the steps for making the negative electrode sheet include: mixing the negative electrode active material with conductive agents such as conductive carbon black, binders such as carboxymethyl cellulose and styrene-butadiene rubber, and solvents such as water in a mass ratio of (80~99):(1~5):(2~10):100 to make a positive electrode mixed slurry, then degassing under vacuum, discharging the material, coating it on a coating machine, and obtaining the negative electrode sheet after rolling, slitting, and die-cutting.

[0134] In some possible implementations, the membrane is capable of blocking electrons while allowing ions to pass through. Exemplary membranes include, but are not limited to, at least one material selected from polypropylene fibers, polyacrylonitrile fibers, polyvinyl formal fibers, poly(ethylene glycol terephthalate), polyethylene terephthalate, polyamide fibers, and poly(p-phenylene terephthalamide).

[0135] In some possible implementations, the electrolyte comprises at least one soluble metal salt. In some specific embodiments, the metal salt includes LiClO4, LiBF4, LiPF6, LiAsF6, LiCF3SO3, LiTDI, Li[(CF3SO2)2N], Li[(FSO2)2N], Li[(C m F 2m+1 SO2)(C n F 2n+1 At least one of SO2(N)[m, n], where m and n are natural numbers. These electrolytic salts can ensure high ionic conductivity of the electrolyte and do not undergo harmful side reactions with electrode materials, electrolyte, diaphragm, etc., and have good chemical stability.

[0136] In some possible implementations, the secondary battery includes at least one of a battery cell, a battery module, and a battery pack.

[0137] In some possible implementations, the battery cell types include lithium-ion batteries, as well as novel batteries such as lithium metal batteries.

[0138] In some possible implementations, the battery cells of this application can be assembled into a battery module. The battery module can contain multiple battery cells, the specific number of which can be adjusted according to the application and capacity of the battery module. The battery module may also include a housing with a receiving space in which multiple battery cells are received.

[0139] In one possible implementation, battery cells and / or battery modules can also be assembled into a battery pack, and the number of battery cells or battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0140] To enable those skilled in the art to clearly understand the above-described implementation details and operations of this application, and to demonstrate the significant improvement in the performance of the phosphate-based cathode material, its preparation method, cathode sheet, and secondary battery in the embodiments of this application, the following examples illustrate the above technical solutions.

[0141] Example 1

[0142] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0143] Its preparation includes the following steps:

[0144] 1. Glucose (3% by weight of total raw materials), along with FeSO4, manganese oxalate, ammonium dihydrogen phosphate, and lithium carbonate, were placed in a zirconia ball mill jar according to the molar ratio of Li:Fe:Mn:P = 2:1:1:2. Anhydrous ethanol was added, and the mixture was ball-milled for 60 min. After removal, it was dried in a constant temperature oven at 100℃ for 1 h to obtain a mixture. The mixture was then placed in a tube furnace and calcined at 680℃ for 6 h under a nitrogen atmosphere at a rate of 5℃ / min to obtain a mixed precursor material.

[0145] 2. Add the mixed precursor material to an aluminum chloride solution and pass CO2 through to obtain an aluminum hydroxide-coated precursor material.

[0146] 3. Filter the slurry of the aluminum hydroxide-coated precursor material, wash it with ethanol, and dry it in a constant temperature oven at 100℃ for 1 hour to obtain aluminum hydroxide-coated precursor material powder; calcine the aluminum hydroxide-coated precursor material powder at 780℃ for 8 hours under a nitrogen atmosphere at a rate of 5℃ / min to obtain alumina-coated lithium manganese iron phosphate cathode material, wherein the mass of alumina is controlled to account for 0.5wt% of the cathode material.

[0147] 4. Prepare a 30% (w / w) mixed solution of lithium tantalate and ammonium fluoride, wherein the molar ratio of tantalum to fluorine is 1:4. In a mixture of lithium tantalate and ammonium fluoride, stir the alumina-coated lithium manganese iron phosphate cathode material at 60°C for 2-3 hours, allow it to stand for aging for 12 hours, then filter and dry it. Finally, heat-treat it at 350°C–400°C for 2-3 hours to form a fluorine- and tantalum-modified alumina coating layer on the surface of the lithium manganese iron phosphate cathode material, thus obtaining a fluorine- and tantalum-modified alumina-coated lithium manganese iron phosphate cathode material.

[0148] 5. Phytic acid and lithium carbonate solution were mixed, with a molar ratio of phytic acid to lithium carbonate of 0.5:1. The pH was adjusted to 9-13 to obtain lithium phytate. Fluorine- and tantalum-modified alumina-coated lithium manganese iron phosphate cathode material was added to an aqueous solution of aniline and lithium phytate (containing 100 mmol aniline and 15 mmol lithium phytate), and subjected to ultrasonication for 30 minutes followed by stirring for 30 minutes. Subsequently, 60 mmol ammonium persulfate was added to the solution, and the mixture was stirred overnight. After washing and drying, it was heat-treated at 120℃ for 2 hours to form a polyaniline-lithium phytate composite coating layer in situ on the surface of the fluorine- and tantalum-modified alumina coating, ultimately yielding the lithium manganese iron phosphate cathode material.

[0149] Example 2

[0150] A lithium manganese iron phosphate cathode material comprises a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:3), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0151] The only difference between its preparation method and Example 1 is that in step 4, the molar ratio of tantalum to fluorine in the 30% lithium tantalate and ammonium fluoride mixed solution is 1:3.

[0152] Example 3

[0153] A lithium manganese iron phosphate cathode material comprises a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:5), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0154] The only difference between its preparation method and Example 1 is that in step 4, the molar ratio of tantalum to fluorine in the 30% lithium tantalate and ammonium fluoride mixed solution is 1:5.

[0155] Example 4

[0156] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0157] The only difference between its preparation method and that of Example 1 is that in step 5, the amount of aniline used is 50 mmol.

[0158] Example 5

[0159] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0160] The only difference between its preparation method and that of Example 1 is that in step 5, the amount of aniline used is 150 mmol.

[0161] Example 6

[0162] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0163] The only difference between its preparation method and that of Example 1 is that in step 5, the amount of aniline used is 200 mmol.

[0164] Example 7

[0165] A lithium manganese iron phosphate cathode material comprises a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.25wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5wt%.

[0166] The only difference between its preparation method and Example 1 is that in step 3, the obtained alumina is coated with lithium manganese iron phosphate cathode material, wherein the mass of alumina accounts for 0.25 wt% of the cathode material.

[0167] Example 8

[0168] A lithium manganese iron phosphate cathode material comprises a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 1 wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0169] The difference between its preparation method and Example 1 is only that: in step 3, the obtained alumina is coated with lithium manganese iron phosphate cathode material, wherein the mass of alumina accounts for 1 wt% of the cathode material.

[0170] Example 9

[0171] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=5:2:3:5) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0172] The only difference between its preparation method and Example 1 is that in step 1, the Li:Fe:Mn:P ratio in the prepared lithium manganese iron phosphate is 5:2:3:5.

[0173] Example 10

[0174] A lithium manganese iron phosphate cathode material comprises a lithium manganese iron phosphate active material (Li:Fe:Mn:P=5:1:4:5) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage content of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage content of the polyaniline-lithium phytate composite outer layer is 5wt%.

[0175] The only difference between its preparation method and Example 1 is that in step 1, the Li:Fe:Mn:P ratio in the prepared lithium manganese iron phosphate is 5:1:4:5.

[0176] Example 11

[0177] A lithium iron phosphate cathode material includes a lithium iron phosphate active material core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5 wt% (the molar ratio of tantalum to fluorine is 1:4), and the mass percentage of the polyaniline-lithium phytate composite outer layer is 5 wt%.

[0178] The only difference between its preparation method and that of Example 1 is that the active material is lithium iron phosphate cathode material.

[0179] Comparative Example 1

[0180] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and an Al2O3 inner layer and a polyaniline-lithium phytate composite material outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage content of the Al2O3 inner layer is 0.5wt% (the alumina layer is not modified by F and Ta), and the mass percentage content of the polyaniline-lithium phytate composite material outer layer is 5wt%.

[0181] The only difference between its preparation method and that of Example 1 is that step 4 is not performed and the alumina layer is not modified by F and Ta.

[0182] Comparative Example 2

[0183] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine- and tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite material outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine- and tantalum-modified Al2O3 inner layer is 0.5wt% (the molar ratio of tantalum to fluorine is 1:4).

[0184] The only difference between its preparation method and that of Example 1 is that step 5 is not performed, and no coating layer containing polyaniline-lithium phytate composite material is formed.

[0185] Comparative Example 3

[0186] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a fluorine-modified Al2O3 inner layer and a polyaniline-lithium phytate composite material outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the fluorine-modified Al2O3 inner layer is 0.5wt%, and the mass percentage of the polyaniline-lithium phytate composite material outer layer is 5wt%.

[0187] The preparation method differs from Example 1 only in that step 4 involves only F modification, including the following steps: preparing a 30% ammonium fluoride solution. The alumina-coated lithium manganese iron phosphate cathode material is stirred in ammonium fluoride at 60°C for 2-3 hours, allowed to stand for aging for 12 hours, then filtered and dried. Finally, it is heat-treated at 350-400°C for 2-3 hours to form a fluorine-modified alumina coating layer on the surface of the lithium manganese iron phosphate cathode material, thus forming a fluorine-modified alumina-coated lithium manganese iron phosphate cathode material.

[0188] Comparative Example 4

[0189] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a tantalum-modified Al2O3 inner layer and a polyaniline-lithium phytate composite material outer layer sequentially coated on the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the tantalum-modified Al2O3 inner layer is 0.5wt%, and the mass percentage of the polyaniline-lithium phytate composite material outer layer is 5wt%.

[0190] The preparation method differs from Example 1 only in that step 4 involves tantalum modification, including the following steps: preparing a 30% lithium tantalate solution. The alumina-coated lithium manganese iron phosphate cathode material is stirred in the lithium tantalate solution at 60°C for 2-3 hours, allowed to stand for aging for 12 hours, then filtered and dried. Finally, it is heat-treated at 350-400°C for 2-3 hours to form a tantalum-modified alumina coating layer on the surface of the lithium manganese iron phosphate cathode material, thus forming a tantalum-modified alumina-coated lithium manganese iron phosphate cathode material.

[0191] Comparative Example 5

[0192] A lithium manganese iron phosphate cathode material includes a lithium manganese iron phosphate active material (Li:Fe:Mn:P=2:1:1:2) core and a polyaniline-lithium phytate composite material outer layer covering the outer surface of the core; wherein, based on the mass of the lithium manganese iron phosphate cathode material, the mass percentage of the polyaniline-lithium phytate composite material outer layer is 5wt%.

[0193] The preparation method differs from Example 1 only in that steps 2-4 are omitted, and only a polyaniline-lithium phytate composite material coating layer is included. The steps are as follows:

[0194] 1. Glucose (3% by weight of total raw materials), along with FeSO4, manganese oxalate, ammonium dihydrogen phosphate, and lithium carbonate, were placed in a zirconia ball mill jar according to the molar ratio of Li:Fe:Mn:P = 2:1:1:2. Anhydrous ethanol was added, and the mixture was ball-milled for 60 min. After removal, it was dried in a constant temperature oven at 100℃ for 1 h to obtain a mixture. The mixture was then placed in a tube furnace and calcined at 680℃ for 6 h under a nitrogen atmosphere at a rate of 5℃ / min to obtain a mixed precursor material.

[0195] 2. The mixed precursor materials were calcined at 780℃ for 8 hours under a nitrogen atmosphere at a rate of 5℃ / min to obtain lithium manganese iron phosphate cathode material.

[0196] 3. Phytic acid and lithium carbonate solution were mixed, with a molar ratio of phytic acid to lithium carbonate of 0.5:1. The pH was adjusted to 9-13 to obtain lithium phytate. Lithium manganese iron phosphate cathode material was added to an aqueous solution of aniline and lithium phytate (containing 100 mmol aniline and 15 mmol lithium phytate), and subjected to ultrasonication for 30 minutes followed by stirring for 30 minutes. Subsequently, 60 mmol ammonium persulfate was added to the solution, and the mixture was stirred overnight. After washing and drying, it was heat-treated at 120℃ for 2 hours to form a polyaniline-lithium phytate composite coating layer in situ on the surface of lithium manganese iron phosphate, ultimately obtaining the lithium manganese iron phosphate cathode material.

[0197] Furthermore, to verify the progressiveness of the embodiments of this application, the following performance tests were performed on the above embodiments and comparative examples:

[0198] A. X-ray diffraction (XRD) tests were performed on the lithium manganese iron phosphate cathode materials prepared in Example 1 and Comparative Example 1, respectively. The XRD patterns are shown in the attached figures. Figure 2 As shown. (From the appendix) Figure 2 It can be seen that the cathode materials prepared in Example 1 and Comparative Example 1 are both lithium manganese iron phosphate cathode materials.

[0199] B. The lithium manganese iron phosphate cathode materials prepared in the above examples and comparative examples are applied to lithium-ion batteries for electrochemical performance testing. The preparation of the lithium-ion battery includes the following steps:

[0200] 1. Preparation of positive electrode sheet: The positive electrode material of lithium manganese iron phosphate (LMFP): conductive agent (SP): polyvinylidene fluoride (PVDF): N-methylpyrrolidone (NMP) is mixed in a mass ratio of 93.5:2.5:4:100. The mixture is stirred in a ball mill for 2 hours to obtain a uniform positive electrode slurry. The prepared positive electrode slurry is added to aluminum foil and evenly smoothed with a scraper. After the positive electrode sheet is dried at 130℃, it is rolled under a pressure of 10 MPa to obtain a rolled electrode sheet. A Φ15mm round sheet is cut from the middle area and weighed.

[0201] 2. The battery assembly process is as follows: The prepared positive electrode sheet is attached to the positive electrode metal shell with conductive adhesive, a lithium metal sheet is used as the electrode, a Celgard 2400 microporous membrane is used as the separator, and a 1.0 mol / L LiPF6 solution is used as the electrolyte. The solvent of the electrolyte is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The battery is assembled into a button cell in a glove box.

[0202] The electrochemical performance of the above coin cells was tested using a LAND electrochemical analyzer. The charging cutoff voltage was 4.3 V, and the discharging cutoff voltage was 2.5 V. The resulting lithium-ion batteries underwent the following performance tests:

[0203] Rate performance test: The battery was tested at room temperature (25℃) at 0.1 C and 1 C rates.

[0204] Cyclic performance test: 300 cycles were performed at 25℃, 2.5-4.3V, and 2C rate to obtain the cycle capacity retention rate.

[0205] The test results are shown in Table 1 below. The 1C first-cycle charge-discharge curves of the lithium-ion batteries using lithium manganese iron phosphate cathode materials in Example 1 and Comparative Example 1 are attached. Figure 3 As shown:

[0206]

[0207] As shown in Table 1 above, the lithium manganese iron phosphate or lithium iron phosphate cathode materials prepared in Examples 1-11 of this application, through the synergistic design of a double-shell coating structure of "modified Al2O3 inner layer (barrier + ion conduction) + polyaniline-lithium phytate composite outer layer (electron conduction + secondary protection)," effectively suppress manganese ion dissolution, improve interface stability, and exhibit significantly better rate performance than the comparative examples. In Example 1, the manganese dissolution was as low as 70.09 ppm. Examples 1 and 2-3 demonstrate that the method of this application is applicable to different molar ratios of tantalum and fluorine in the fluorine- or tantalum-modified Al2O3 inner layer. Examples 1 and 4-6 show that the method of this application is applicable to different coating effects of the polyaniline-lithium phytate composite outer layer when the amount of aniline varies. Comparison of Examples 1, 7, and 8 shows that the method of this application is applicable to cases with different alumina content. Through Examples 9 and 10, the method of this application is applicable to lithium manganese iron phosphate active materials with different Li:Fe:Mn:P elemental ratios. Furthermore, the relatively high manganese leaching amount in Examples 9 and 10 is due to the larger manganese-iron ratio and higher manganese content in Examples 9 and 10.

[0208] By comparing Example 1 and Comparative Example 1, it can be seen that the various properties of Example 1 are improved compared with those of Comparative Example 1, where the alumina layer is not modified by F and Ta. This is because the conductivity and density of the alumina coating layer are increased after modification with fluorine and tantalum, which is beneficial to the transport of lithium ions and reduces the erosion of the cathode material by the electrolyte, thereby improving the cycle performance of the lithium manganese iron phosphate cathode material and reducing the manganese dissolution rate.

[0209] By comparing Example 1 and Comparative Example 2, it can be seen that the performance of Example 1 is improved compared with Comparative Example 2, which does not have a polyaniline-lithium phytate composite coating layer. This is because the polyaniline-lithium phytate composite material, as a highly conductive polymer, can effectively compensate for the deficiency of the intrinsic electronic conductivity of lithium manganese iron phosphate, thereby improving the cycle performance of the lithium manganese iron phosphate cathode material.

[0210] By comparing Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that the performance of Comparative Example 3 (Al2O3 inner layer without Ta modification) and Comparative Example 4 (Al2O3 inner layer without F modification) is significantly lower than that of Example 1. The reason is that the alumina layer in Comparative Example 3 and Comparative Example 4 is only modified in one aspect, which has a poor effect on improving conductivity and a limited effect on improving the structural stability of the material, resulting in a decrease in the performance of the lithium-ion battery.

[0211] By comparing Example 1 and Comparative Example 5, it can be seen that the performance of Comparative Example 5, which does not have a fluorine or tantalum-modified Al2O3 inner layer, is significantly lower than that of Example 1. The reason is that the lithium manganese iron phosphate cathode material obtained in Example 1 also has a fluorine and tantalum dual-modified alumina coating layer, which can optimize the performance of the coating layer, provide a lithium ion transport path, thereby improving the cycle performance of the lithium manganese iron phosphate cathode material and reducing the manganese dissolution rate.

[0212] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A phosphate-based positive electrode material, characterized by, The phosphate-based active material includes an inner core of phosphate-based active material and a shell layer coated on the outer surface of the inner core, the shell layer including a modified Al2O3 inner layer and a conductive polymer outer layer coated on the outer surface of the inner core in sequence; wherein the modified Al2O3 inner layer includes an Al2O3 base material and F element and Ta element chemically combined in the base material; and the conductive polymer outer layer includes a polyaniline-lithium phytate composite material. In the core, the chemical formula of the phosphate-based active material is LiMn x A y Fe 1-x-y PO4, wherein A is selected from at least one of Ti, V, Mg, In, x is 0-1, and y is 0-1. In the modified Al2O3 inner layer, the F element forms Al-O-F bond and Al-F bond with the Al2O3 base material; and the Ta element forms Ta-O-Al bond with the Al2O3 base material. In the polyaniline-lithium phytate composite material, lithium phytate is grafted on the chain of polyaniline to form a composite polymer chain, and the composite polymer chain is wound on the outer surface of the modified Al2O3 inner layer to form a three-dimensional conductive network structure.

2. The phosphate-based cathode material of claim 1, wherein, The Al2O3 base material forms an Al2O3 base material layer on the outer surface of the inner core, and the F element and the Ta element are chemically combined on the outer surface of the base material layer.

3. The phosphate-based positive electrode material according to any one of claims 1 to 2, wherein the phosphate-based positive electrode material is a lithium iron phosphate-based positive electrode material. In the phosphate-based positive electrode material, the mass fraction of the modified Al2O3 inner layer is 0.01wt%-1wt%. And / or, in the modified Al2O3 inner layer, the mass percentage of the F element based on the mass of the Al2O3 base material is 8%-15%; and / or, the mass percentage of the Ta element is 25%-35%; And / or, in the modified Al2O3 inner layer, the molar ratio of the F element to the Ta element is (3-5):

1.

4. The phosphate-based cathode material of claim 3, wherein, In the phosphate-based positive electrode material, the mass percentage of the polyaniline-lithium phytate composite material is 3wt%-8wt%.

5. A method for producing the phosphate-based positive electrode material according to any one of claims 1 to 4, characterized by, The method includes the following steps: Preparation of a precursor material of a phosphate-based active material; Preparation of an alumina coating layer on the outer surface of the precursor material to obtain an alumina-coated active material; Dispersing the alumina-coated active material into a mixed solution of tantalum salt and fluoride, and performing heat mixing treatment to obtain a fluorine and tantalum modified alumina-coated active material; Dispersing the fluorine and tantalum modified alumina-coated active material into a mixed solution of aniline and lithium phytate, adding an oxidizing agent to initiate polymerization, and performing heat treatment on the reaction product to form a conductive polymer outer layer of polyaniline-lithium phytate composite material on the surface of the fluorine and tantalum modified alumina coating layer, thereby obtaining a phosphate-based positive electrode material with double coating layers.

6. The method for producing a phosphate-based cathode material according to claim 5, wherein The preparation of the precursor material includes the following steps: ball-milling raw material components including iron source, manganese source and phosphorus source, drying at a temperature of 80-120℃ for 2-4h, and then pre-sintering at a temperature of 650-750℃ at a temperature rising rate of 3-8℃ / min in an inert atmosphere for 4-8h to obtain the precursor material; And / or, the step of preparing an alumina coating layer on the outer surface of the precursor material includes mixing the precursor material with a solution of aluminum salt, and then introducing carbon dioxide to react and obtain an aluminum hydroxide-coated precursor material; Performing calcination treatment on the aluminum hydroxide-coated precursor material to obtain the alumina-coated active material.

7. The method for producing a phosphate-based cathode material according to claim 6, wherein The aluminum salt comprises at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate; The mass ratio of the precursor material to the aluminum salt is (25-35):(1-3); The mass fraction of the solution of the aluminum salt is 20%-40%; The calcination treatment comprises: in an inert atmosphere, heating at a heating rate of 3 ℃ / min-8 ℃ / min to 750 ℃-850 ℃ for 5 h-10 h.

8. The method for producing a phosphate-based positive electrode material according to any one of claims 5 to 7, characterized by, In the mixed solution of the tantalum salt and the fluoride, the total mass fraction of the tantalum salt and the fluoride is 20%-40%; The molar ratio of the tantalum salt to the fluoride in the mixed solution of the tantalum salt and the fluoride is 1:(3-5); The tantalum salt comprises at least one of lithium tantalate, pentachlorotantalum, potassium tantalate, and sodium tantalate; The fluoride comprises at least one of ammonium fluoride, sodium fluoride, potassium fluoride, and lithium fluoride; The molar ratio of the aluminum oxide-coated active material to the tantalum element in the tantalum salt and the fluorine element in the fluoride is (4-6):1:(3-5); The heat mixing treatment comprises the steps of: stirring for 2 h-3 h at a temperature of 50 ℃-70 ℃, then standing for 10 h-15 h, filtering and drying, and then treating at a temperature of 400 ℃-500 ℃ for 2 h-3 h.

9. The method for producing a phosphate-based cathode material according to claim 8, wherein The preparation of the lithium phytate comprises the steps of: mixing a phytic acid solution and a lithium salt solution, and adjusting the pH value to 9-13 to obtain the lithium phytate; wherein the molar ratio of the lithium salt to the phytic acid is (0.4-0.6):1; The molar ratio of the aniline to the lithium phytate in the mixed solution of the aniline and the lithium phytate is (10-40):(1-3); The oxidizing agent comprises at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; The addition amount of the oxidizing agent is 0.5wt%-1wt% of the mass of the aniline; The operation of dispersing the fluorine and tantalum modified aluminum oxide-coated active material into the mixed solution of the aniline and the lithium phytate comprises: ultrasonic treatment for 20 min-60 min, and then stirring for 20 min-60 min; The polymerization reaction is performed for 12 h-24 h at a temperature of 20 ℃-40 ℃; The heat treatment is performed at a temperature of 100 ℃-150 ℃ for 1 h-3 h.

10. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises a current collector and a positive electrode active layer formed on at least one surface of the current collector, and the positive electrode active layer comprises the phosphate-based positive electrode material according to any one of claims 1-4 and / or the phosphate-based positive electrode material prepared by the method according to any one of claims 5-9.

11. A secondary battery characterized by comprising: The secondary battery comprises the positive electrode sheet according to claim 10.

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