A composite cathode material precursor, a preparation method and application thereof

Abstract

The present disclosure provides a composite positive electrode material precursor, a preparation method and application thereof. The composite positive electrode material precursor comprises a porous iron phosphate inner core, a carbon-coated inner layer of doped metal phosphide coated on the surface of the inner core, and an iron phosphate-coated outer layer coated on the surface of the carbon-coated inner layer; and at least a part of the carbon-coated inner layer is arranged in the pores of the porous iron phosphate inner core. The present disclosure arranges the carbon-coated inner layer of doped metal phosphide on the surface and in the pores of the porous iron phosphate inner core, which can significantly improve the conductivity of the material, reduce the use of conductive carbon, improve the rate performance and low-temperature performance of the material, and avoid a significant reduction in tap density. Furthermore, the present disclosure forms the iron phosphate-coated outer layer on the surface of the carbon-coated inner layer, which effectively avoids the direct contact of the metal phosphide with the electrolyte, reduces the occurrence of side reactions, and thus improves the cycle performance of the lithium ion battery.

Description

Technical Field

[0001] This disclosure belongs to the field of battery technology, specifically relating to a composite cathode material precursor, its preparation method, and its application. Background Technology

[0002] Currently, lithium battery cathode materials mainly include lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, and ternary materials. Compared with other lithium battery cathode materials, lithium iron phosphate cathode materials have advantages such as high safety, long cycle life, and low manufacturing cost, making them one of the most promising lithium-ion battery cathode materials. However, the inherent defects of the material, such as low electronic conductivity and low lithium-ion diffusion coefficient, need to be overcome in order to maximize the performance of the material and meet market needs.

[0003] As a precursor to lithium iron phosphate (LFP), iron phosphate's structure, morphology, conductivity, and dispersibility directly affect LFP's performance. Currently, conductivity is typically improved by coating the material with a conductive substance, primarily by coating the surface with carbon to prepare LFP / carbon composites. However, this method only increases the surface conductivity of the LFP; the internal conductivity remains unchanged, and the compaction density of the carbon-coated material decreases.

[0004] Metal phosphides are often used in supercapacitors, lithium-ion battery anode materials, or hydrogen evolution processes. They possess some metallic properties and have electronic conductivity far exceeding that of oxides. Therefore, coating lithium iron phosphate with metal phosphides can effectively improve its electrochemical performance. However, the coating on the surface of lithium iron phosphate is prone to contact with the electrolyte, leading to corrosion.

[0005] Therefore, how to avoid direct contact between metal phosphides and electrolytes, reduce the occurrence of side reactions, and thus improve the cycle performance of lithium-ion batteries is an urgent problem to be solved. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] To address the shortcomings of existing technologies, the present disclosure aims to provide a composite cathode material precursor, its preparation method, and its applications. This disclosure involves setting a carbon-coated inner layer doped with metal phosphide on the surface and within the pores of a porous iron phosphate core. This significantly improves the material's conductivity, reduces the amount of conductive carbon used, and enhances both rate performance and low-temperature performance while preventing a substantial decrease in tap density. Furthermore, this disclosure forms an iron phosphate-coated outer layer on the surface of the carbon-coated inner layer, effectively preventing direct contact between the metal phosphide and the electrolyte, reducing side reactions, and thus improving the cycle performance of lithium-ion batteries.

[0008] To achieve this objective, the present disclosure adopts the following technical solution:

[0009] In a first aspect, this disclosure provides a composite cathode material precursor, the composite cathode material precursor comprising a porous iron phosphate core, a carbon-coated inner layer doped with metal phosphide coated on the surface of the core, and an iron phosphate-coated outer layer coated on the surface of the carbon-coated inner layer.

[0010] At least a portion of the carbon-coated inner layer is disposed within the pores of the porous iron phosphate core.

[0011] This disclosure involves incorporating a carbon-coated inner layer doped with metal phosphides on the surface and within the pores of a porous iron phosphate core. This significantly improves the material's conductivity, reduces the amount of conductive carbon used, and enhances both rate performance and low-temperature performance while preventing a substantial decrease in tap density. Furthermore, this disclosure forms an iron phosphate-coated outer layer on the surface of the carbon-coated inner layer, effectively preventing direct contact between the metal phosphides and the electrolyte, reducing side reactions, and thus improving the cycle performance of the lithium-ion battery.

[0012] As an optional technical solution of this disclosure, the particle size D50 of the porous iron phosphate core is 0.5-1.0 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1.0 μm, etc.

[0013] In one embodiment, the average pore size of the porous iron phosphate core is 10-20 nm, for example, it can be 10 nm, 15 nm or 20 nm, and the porosity is 5-20%, for example, it can be 5%, 10%, 15% or 20%.

[0014] In this disclosure, the porous iron phosphate core has an average pore size of 10-20 nm and a porosity of 5-20%, which helps to control the doping content of metal phosphides and carbon in the pores of iron phosphate, thereby improving the conductivity of iron phosphate while maintaining the stability of the iron phosphate structure.

[0015] As an optional technical solution of this disclosure, the metal phosphide is M2P or M3P, where M is a transition metal.

[0016] In one embodiment, the transition metal includes any one or a combination of at least two of Ni, Co, or Ti.

[0017] In one embodiment, the doping amount of the metal phosphide is 0.5-2 wt.%, based on the mass of the carbon-coated inner layer, for example, it can be 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1.2 wt.%, 1.5 wt.%, or 2 wt.%, etc.

[0018] In this disclosure, if the amount of metal phosphide doping is too small, the electronic conductivity of iron phosphate will be too small; if the amount of metal phosphide doping is too large, the ionic conductivity will be too small, affecting lithium ion diffusion.

[0019] In one embodiment, the thickness of the carbon-coated inner layer is 5-20 nm, for example, it can be 5 nm, 10 nm, 15 nm or 20 nm.

[0020] In one embodiment, the thickness of the iron phosphate coating is 100-600 nm, for example, it can be 100 nm, 200 nm, 300 nm, 400 nm, 500 nm or 600 nm.

[0021] In one embodiment, the thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is 1:(20-120), for example, it can be 1:20, 1:40, 1:60, 1:80, 1:100 or 1:120, etc.

[0022] In this disclosure, if the thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is too small, i.e., the thickness of the iron phosphate-coated outer layer is too large, the overall conductivity of the iron phosphate particles will be poor. If the thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is too large, i.e., the thickness of the iron phosphate-coated outer layer is too small, it will easily lead to uneven coating, and the metal phosphides doped in the carbon-coated inner layer will easily be exposed to contact with the electrolyte, affecting the electrochemical performance of lithium iron phosphate.

[0023] In a second aspect, this disclosure provides a method for preparing a composite cathode material precursor as described in the first aspect, the method comprising the following steps:

[0024] (1) Mix porous iron phosphate material, phosphorus source, polymer monomer, initiator, metal salt and solvent, and react to obtain porous iron phosphate coated with polymer coating layer doped with phosphorus and metal.

[0025] (2) The porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal is used as a seed crystal, and mixed with an iron source, a phosphorus source and a catalyst to carry out a hydrothermal reaction to obtain a hydrothermal product.

[0026] (3) The hydrothermal products are sintered to obtain the composite cathode material precursor.

[0027] In this disclosure, the phosphorus source and the metal ions in the metal salt will coordinate. The addition of an initiator can cause the polymer monomers after coordination of the metal ions in the reaction system to undergo a polymerization reaction, thereby depositing on the pores and surface of the porous iron phosphate material to form a polymer coating layer doped with phosphorus and metal. Subsequently, it is used as a seed crystal to synthesize iron phosphate. After hydrothermal reaction treatment, the polymer coating layer doped with phosphorus and metal undergoes carbonization, and metal phosphides are generated. Since the electronic conductivity of metal phosphides is high, the conductivity of the material can be significantly improved, thereby reducing the use of conductive carbon. While improving the rate performance and low temperature performance of the material, the tap density is avoided from being significantly reduced.

[0028] Furthermore, since metal phosphides are highly susceptible to corrosion due to direct contact with the electrolyte, which reduces the lifespan of the electrode material, the formation of an iron phosphate layer on the seed crystal surface avoids direct contact between the metal phosphides and the electrolyte, reduces side reactions, and thus improves the cycle performance of the lithium-ion battery.

[0029] As an optional technical solution of this disclosure, the preparation method of the porous iron phosphate material in step (1) includes:

[0030] Iron-based metal-organic framework materials and phosphate buffers were mixed and synthesized to obtain porous iron phosphate materials.

[0031] In one embodiment, the concentration of the phosphate buffer solution is 0.1-1 mol / L, for example, it can be 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.7 mol / L or 0.9 mol / L, etc.

[0032] In one embodiment, the pH of the solution after mixing the iron-based metal-organic framework material and the phosphate buffer is 4-8, for example, it can be 4, 5, 6, 7 or 8.

[0033] In one embodiment, the temperature of the synthesis reaction is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C, and the time is 12-24h, for example, 12h, 15h, 20h or 24h.

[0034] In one embodiment, the phosphate buffer comprises any one or a combination of at least two of disodium hydrogen phosphate-citrate buffer, disodium hydrogen phosphate-sodium dihydrogen phosphate buffer, disodium hydrogen phosphate-potassium dihydrogen phosphate buffer, or PBS buffer.

[0035] In one embodiment, the method for preparing the iron-based metal-organic framework material includes:

[0036] The iron source, organic acid and solvent are mixed and subjected to a hydrothermal reaction to obtain the iron-based metal-organic framework material.

[0037] In one embodiment, the iron source comprises ferric chloride hexahydrate.

[0038] In one embodiment, the organic acid includes pyromellitic acid.

[0039] In one embodiment, the solvent includes water.

[0040] In one embodiment, the temperature of the hydrothermal reaction is 120-150°C, for example, 120°C, 130°C, 140°C or 150°C, and the time is 36-48h, for example, 36h, 38h, 40h, 42h, 44h, 46h or 48h.

[0041] In one embodiment, after the hydrothermal reaction, washing and drying steps are also performed.

[0042] In one embodiment, the solid-liquid ratio of the iron source, organic acid, and solvent is 1g:(3-6)g:(1-3)mL, wherein the range of organic acid selection “(3-6)g” can be, for example, 3g, 4g, 5g, or 6g, and the range of solvent selection “(1-3)mL” can be, for example, 1mL, 2mL, or 3mL.

[0043] In one embodiment, the phosphorus source in step (1) includes an organic phosphorus source, which includes hexachlorocyclotriphosphazene and / or triisopropyl phosphite.

[0044] The polymer monomer in step (1) includes any one or a combination of at least two of 4,4-dihydroxybiphenyl, 4,4-dihydroxydiphenyl sulfone, or 4,4-diaminobiphenyl.

[0045] The initiator in step (1) includes any one or a combination of at least two of benzylamine, 4-nitro-N-methylamine or 4-dinitrosoaniline.

[0046] The metal salt in step (1) is a transition metal salt, which includes any one or a combination of at least two of nickel nitrate, nickel sulfate, nickel chloride, cobalt nitrate, cobalt sulfate, cobalt chloride, titanium nitrate, titanium sulfate, or titanium chloride.

[0047] In this disclosure, hexachlorocyclotriphosphazene is used as the phosphorus source to coordinate with metal ions in transition metal salts. An initiator is added to cause the polymer monomers coordinated with the metal ions in the reaction system to undergo a polymerization reaction, thereby depositing a polymer coating layer doped with phosphorus and metal on the pores and surface of porous iron phosphate, which can effectively improve the electrochemical performance of lithium iron phosphate.

[0048] In one embodiment, the solid-liquid ratio of the porous iron phosphate material and the solvent in step (1) is (3-5) mg:1 mL, for example, it can be 3 mg:1 mL, 3.5 mg:1 mL, 4 mg:1 mL, 4.5 mg:1 mL or 5 mg:1 mL, etc.

[0049] In this disclosure, the solid-liquid ratio of the porous iron phosphate material and the solvent is (3-5) mg:1 mL, which can effectively control the concentration of the reactants during the coating process and make the coating layer more uniform.

[0050] In one embodiment, the mass ratio of the porous iron phosphate material, phosphorus source, polymer monomer, and metal salt in step (1) is 1:(2-3):(3-6):(8-10), wherein the phosphorus source is selected in the range of "2-3", for example, 2.2, 2.4, 2.6, or 2.8, the polymer monomer is selected in the range of "3-6", for example, 3, 4, 5, or 6, and the metal salt is selected in the range of "8-10", for example, 8, 8.5, 9, 9.5, or 10.

[0051] In this disclosure, if the mass ratio of phosphorus source to metal salt is too small, it will result in excessive subsequent formation of metal phosphides, affecting the conductivity of ferric phosphate ions; if the mass ratio of phosphorus source to metal salt is too large, it will result in insufficient subsequent formation of metal phosphides, affecting the electronic conductivity of ferric phosphate.

[0052] In one embodiment, the mixing method in step (1) includes: adding porous iron phosphate material, phosphorus source, polymer monomer and metal salt to a solvent and mixing to obtain a mixed solution, and then adding an initiator to the mixed solution to continue mixing.

[0053] In this disclosure, the above-mentioned mixing method helps to increase the polymerization reaction rate and make the coating layer more uniform.

[0054] In one embodiment, the volume ratio of the initiator to the mixed solution is (1-2):40, for example, it can be 1:40, 1.2:40, 1.4:40, 1.6:40, 1.8:40 or 2:40, etc.

[0055] In this disclosure, if the volume ratio of the initiator to the mixed solution is too small, the polymerization reaction will be incomplete, the resulting coating layer will be too thin, and the equipment utilization rate will be reduced; if the volume ratio of the initiator to the mixed solution is too large, the polymerization reaction will be too fast, the polymerization time will be too short, and the resulting coating layer will be uneven.

[0056] In one embodiment, the temperature of the reaction in step (1) is 150-250°C, for example, 150°C, 175°C, 200°C, 225°C or 250°C, and the time is 12-24h, for example, 12h, 15h, 20h or 24h.

[0057] In this disclosure, the reaction described in step (1) is carried out at a temperature of 150-250°C for 12-24 hours, which can control the polymerization reaction to form a more uniform coating layer and reduce the generation of side reactions.

[0058] As an optional technical solution of this disclosure, the iron source in step (2) is a trivalent iron salt.

[0059] In one embodiment, the phosphorus source in step (2) includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

[0060] In one embodiment, the catalyst comprises any one or a combination of at least two of ethylenediamine, 2-hydroxyethylamine, or malondiamide.

[0061] In this disclosure, the purpose of adding a catalyst is to regulate the growth direction of iron phosphate, so that the product has a more uniform morphology, a more complete structure, and a higher degree of crystallinity.

[0062] In one embodiment, the molar ratio of iron atoms in the iron source, phosphorus atoms in the phosphorus source, and ethylenediamine in step (2) is 1:(1-4):(15-20), wherein the range of phosphorus atoms in the phosphorus source “1-4” can be, for example, 1, 2, 3, or 4, and the range of ethylenediamine “15-20” can be, for example, 15, 16, 17, 18, 19, or 20.

[0063] In this disclosure, the purpose of adding a catalyst during the growth of iron phosphate on the surface of the seed crystal is to regulate the growth direction of the iron phosphate crystal, so as to make the product morphology more uniform and the crystallinity higher.

[0064] In this disclosure, if the molar ratio of iron atoms in the iron source to the catalyst is too small, the formation rate of iron phosphate will be reduced, side reactions will easily occur, and the purity of the iron phosphate coating layer will be reduced; if the molar ratio of iron atoms in the iron source to the catalyst is too large, the formation of the iron phosphate coating layer will be uneven.

[0065] In one embodiment, the mass of the seed crystal in step (2) accounts for 10-20% of the mass of the composite cathode material precursor, for example, it can be 10%, 12%, 14%, 16%, 18% or 20%, etc.

[0066] In this disclosure, if the ratio of the mass of the seed crystal to the mass of the composite cathode material precursor is too small, the crystal growth will be slow, reducing the formation rate of the iron phosphate coating layer; if the ratio of the mass of the seed crystal to the mass of the composite cathode material precursor is too large, the uniformity of the iron phosphate coating layer will be reduced.

[0067] In one embodiment, the temperature of the hydrothermal reaction in step (2) is 150-190°C, for example, 150°C, 160°C, 170°C, 180°C or 190°C, and the time is 1-5h, for example, 1h, 2h, 3h, 4h or 5h.

[0068] In this disclosure, if the temperature of the hydrothermal reaction is too low, the reaction rate will be too low and the content of iron phosphate in the outer coating will be too low; if the temperature of the hydrothermal reaction is too high, side reactions are likely to occur, reducing the purity of iron phosphate.

[0069] As an optional technical solution of this disclosure, the sintering process in step (3) is carried out in a vacuum atmosphere;

[0070] In one embodiment, the sintering temperature in step (3) is 550-750℃, for example, 550℃, 600℃, 650℃, 700℃ or 750℃, and the time is 3-6h, for example, 3h, 4h, 5h or 6h.

[0071] In this disclosure, if the sintering temperature is too low, the iron phosphate coating layer will not be completely carbonized, resulting in reduced conductivity and stability; if the sintering temperature is too high, it will easily lead to too many defects in the iron phosphate crystals, resulting in impurity phases and reduced structural stability.

[0072] As an optional technical solution of this disclosure, the preparation method includes the following steps:

[0073] (I) Dissolve the iron source and organic acid in water and mix them evenly. Then carry out a hydrothermal reaction at 120-150℃ for 36-48h. After the reaction is completed, wash and centrifuge the precipitate and then dry it at 130-140℃ for 12-24h to obtain the iron-based metal-organic framework material.

[0074] The solid-liquid ratio of the iron source, organic acid, and solvent is 1g:(3-6)g:(1-3)mL;

[0075] (II) After the iron-based metal-organic framework material is crushed, it is soaked in a phosphate buffer solution with a concentration of 0.1-1 mol / L and the pH of the solution is controlled at 4-8 while stirring. Then, a synthesis reaction is carried out at 70-90℃ for 12-24 h. After the reaction is completed, the product is washed and dried to obtain porous iron phosphate material.

[0076] (III) Add porous iron phosphate material, organic phosphorus source, polymer monomer and transition metal salt to solvent and stir to mix evenly to obtain a mixed solution. Then add initiator to it and continue stirring and mixing. Then react at 150-250℃ for 12-24h. After the reaction is completed, filter and wash to obtain porous iron phosphate coated with polymer coating layer doped with phosphorus and metal.

[0077] The solid-liquid ratio of porous iron phosphate material to solvent is (3-5) mg: 1 mL, the mass ratio of porous iron phosphate material, phosphorus source, polymer monomer and metal salt is 1:(2-3):(3-6):(8-10), and the volume ratio of initiator and mixed solution is (1-2):40.

[0078] (IV) The porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal is used as a seed crystal, and mixed with trivalent iron salt, phosphoric acid and catalyst, and subjected to a hydrothermal reaction at 150-190℃ for 1-5 hours to obtain a hydrothermal product.

[0079] The molar ratio of iron atoms in the iron source, phosphorus atoms in the phosphoric acid and catalyst is 1:(1-4):(15-20), and the mass of the seed crystal accounts for 10-20% of the mass of the composite cathode material precursor.

[0080] (V) The hydrothermal products are sintered in a vacuum atmosphere to obtain the composite cathode material precursor.

[0081] The sintering process involves a temperature of 550-750℃ and a duration of 3-6 hours.

[0082] Thirdly, this disclosure provides a cathode material, which is obtained by sintering the composite cathode material precursor described in the first aspect with a lithium source.

[0083] Fourthly, this disclosure provides a method for preparing the cathode material as described in the third aspect, the method comprising the following steps:

[0084] The composite cathode material precursor and lithium source are mixed, and the molar ratio of lithium, iron and phosphorus in the reaction system is adjusted to (1-1.2):1:1. Then, an organic carbon source is added and ball-milled and mixed. After calcination in a nitrogen atmosphere at 750-850℃ for 12-24h, the cathode material is obtained.

[0085] In one embodiment, the positive electrode material is lithium iron phosphate.

[0086] In one embodiment, the organic carbon source includes starch.

[0087] Fifthly, this disclosure provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises the positive electrode material as described in the third aspect.

[0088] The numerical range described in this disclosure includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this disclosure will not exhaustively list the specific point values ​​included in the range.

[0089] Compared with the prior art, this disclosure has the following beneficial effects:

[0090] This disclosure involves incorporating a carbon-coated inner layer doped with metal phosphides on the surface and within the pores of a porous iron phosphate core. This significantly improves the material's conductivity, reduces the amount of conductive carbon used, and enhances both rate performance and low-temperature performance while preventing a substantial decrease in tap density. Furthermore, this disclosure forms an iron phosphate-coated outer layer on the surface of the carbon-coated inner layer, effectively preventing direct contact between the metal phosphides and the electrolyte, reducing side reactions, and thus improving the cycle performance of the lithium-ion battery.

[0091] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0092] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0093] Figure 1 This is a SEM image of the composite cathode material precursor prepared in Example 1 of this disclosure. Detailed Implementation

[0094] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0095] Example 1

[0096] This embodiment provides a composite cathode material precursor, which includes a porous iron phosphate core, a carbon-coated inner layer doped with metal phosphide covering the surface of the core, and an iron phosphate-coated outer layer covering the surface of the carbon-coated inner layer.

[0097] At least a portion of the carbon-coated inner layer is disposed in the pores of the porous iron phosphate core;

[0098] The porous iron phosphate core has a particle size D50 of 0.7 μm, an average pore size of 15 nm, and a porosity of 15%.

[0099] The metal phosphide is nickel phosphide, and the doping amount of the metal phosphide is 1.2 wt.% based on the mass of the carbon-coated inner layer;

[0100] The thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is 1:70.

[0101] This embodiment also provides a method for preparing the above-mentioned composite cathode material precursor, the preparation method comprising the following steps:

[0102] (1) The iron source and organic acid were dissolved in water and mixed evenly. Then, the mixture was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 135°C for 42 hours. After the reaction was completed, the precipitate was washed with deionized water and centrifuged. Then, it was dried at 135°C for 18 hours to obtain an iron-based metal-organic framework material.

[0103] The iron source is ferric chloride hexahydrate, the organic acid is tricarboxylic acid, and the solid-liquid ratio of the iron source, organic acid and solvent is 1g:4g:2mL.

[0104] (2) After the iron-based metal-organic framework material is crushed, it is soaked in a phosphate buffer solution with a concentration of 0.5 mol / L and the pH of the solution is controlled at 6 while stirring. Then, the synthesis reaction is carried out at 80°C for 18 h. After the reaction is completed, the product is washed with deionized water and vacuum dried to obtain porous iron phosphate material.

[0105] The phosphate buffer solution is a disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution.

[0106] (3) The porous iron phosphate material, organic phosphorus source, polymer monomer and transition metal salt are added to methanol and stirred and mixed evenly to obtain a mixed solution. Then an initiator is added to it and stirring is continued. Then it is placed in a reaction vessel and reacted at 200°C for 18 hours. After the reaction is completed, it is filtered and washed to obtain porous iron phosphate coated with a polymer coating layer doped with phosphorus and metal.

[0107] The organic phosphorus source is hexachlorocyclotriphosphazene, the polymer monomer is 4,4-dihydroxybiphenyl, the transition metal salt is nickel nitrate, the initiator is benzylamine, the solid-liquid ratio of porous iron phosphate material and methanol is 4 mg: 1 mL, the mass ratio of porous iron phosphate material, organic phosphorus source, polymer monomer and metal salt is 1:2.5:4.5:9, and the volume ratio of initiator and mixed solution is 1.5:40.

[0108] (4) The porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal is used as a seed crystal, and mixed evenly with trivalent iron salt, phosphoric acid and ethylenediamine. Then, a hydrothermal reaction is carried out at 170°C for 3 hours to obtain a hydrothermal product.

[0109] The iron source is ferric sulfate, and the molar ratio of iron atoms in the iron source, phosphorus atoms in phosphoric acid, and ethylenediamine is 1:2:17. The mass of the seed crystal accounts for 15% of the mass of the composite cathode material precursor.

[0110] (5) The hydrothermal product is placed in a vacuum tube furnace under a vacuum atmosphere and sintered at 650°C for 4 hours to remove the crystal water and carbonized polymer coating layer, thereby obtaining the composite cathode material precursor.

[0111] This embodiment also provides a method for preparing a cathode material, the method comprising the following steps:

[0112] The above-mentioned composite cathode material precursor and lithium carbonate were mixed, and the molar ratio of lithium, iron and phosphorus in the reaction system was adjusted to 1.1:1:1. Then, starch of 10% by mass of lithium iron phosphate product was added and ball-milled with ethanol as medium. After drying, the mixture was placed in a muffle furnace and calcined in a nitrogen atmosphere at 800°C for 18 hours to obtain the cathode material, namely lithium iron phosphate.

[0113] Figure 1 This embodiment shows that the iron phosphate particles prepared in this example have a small particle size and a relatively uniform particle distribution.

[0114] Example 2

[0115] This embodiment provides a composite cathode material precursor, which includes a porous iron phosphate core, a carbon-coated inner layer doped with metal phosphide covering the surface of the core, and an iron phosphate-coated outer layer covering the surface of the carbon-coated inner layer.

[0116] At least a portion of the carbon-coated inner layer is disposed in the pores of the porous iron phosphate core;

[0117] The porous iron phosphate core has a particle size D50 of 0.5 μm, an average pore size of 10 nm, and a porosity of 5%.

[0118] The metal phosphide is cobalt phosphide, and the doping amount of the metal phosphide is 0.5 wt.% based on the mass of the carbon-coated inner layer.

[0119] The thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is 1:20.

[0120] This embodiment also provides a method for preparing the above-mentioned composite cathode material precursor, the preparation method comprising the following steps:

[0121] (1) The iron source and organic acid were dissolved in water and mixed evenly. Then, the mixture was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 150°C for 36 hours. After the reaction was completed, the precipitate was washed with deionized water and centrifuged. Then, it was dried at 130°C for 24 hours to obtain an iron-based metal-organic framework material.

[0122] The iron source is ferric chloride hexahydrate, the organic acid is tricarboxylic acid, and the solid-liquid ratio of the iron source, organic acid and solvent is 1g:3g:1mL.

[0123] (2) After the iron-based metal-organic framework material is crushed, it is soaked in a phosphate buffer solution with a concentration of 0.1 mol / L and the pH of the solution is controlled at 8 while stirring. Then, the synthesis reaction is carried out at 70°C for 24 h. After the reaction is completed, the product is washed with deionized water and vacuum dried to obtain porous iron phosphate material.

[0124] The phosphate buffer solution is a disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution.

[0125] (3) The porous iron phosphate material, organic phosphorus source, polymer monomer and transition metal salt are added to methanol and stirred and mixed evenly to obtain a mixed solution. Then an initiator is added to it and stirring is continued. Then it is placed in a reaction vessel and reacted at 250°C for 12 hours. After the reaction is completed, it is filtered and washed to obtain porous iron phosphate coated with a polymer coating layer doped with phosphorus and metal.

[0126] The organophosphorus source is hexachlorocyclotriphosphazene, the polymer monomer is 4,4-dihydroxybiphenyl, the transition metal salt is cobalt nitrate, the initiator is benzylamine, the solid-liquid ratio of porous iron phosphate material and methanol is 5 mg: 1 mL, the mass ratio of porous iron phosphate material, organophosphorus source, polymer monomer and metal salt is 1:3:6:10, and the volume ratio of initiator and mixed solution is 2:40.

[0127] (4) The porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal is used as a seed crystal, and mixed evenly with trivalent iron salt, phosphoric acid and ethylenediamine. Then, a hydrothermal reaction is carried out at 190°C for 1 hour to obtain a hydrothermal product.

[0128] The iron source is ferric sulfate, and the molar ratio of iron atoms in the iron source, phosphorus atoms in phosphoric acid, and ethylenediamine is 1:4:15. The mass of the seed crystal accounts for 20% of the mass of the composite cathode material precursor.

[0129] (5) The hydrothermal product is placed in a vacuum tube furnace under a vacuum atmosphere and sintered at 550°C for 6 hours to remove the water of crystallization and the carbonized polymer coating layer, thereby obtaining the composite cathode material precursor.

[0130] This embodiment also provides a method for preparing a cathode material, the method comprising the following steps:

[0131] The above-mentioned composite cathode material precursor and lithium carbonate were mixed, and the molar ratio of lithium, iron and phosphorus in the reaction system was adjusted to 1:1:1. Then, starch of 10% of the mass of lithium iron phosphate product was added and ball-milled with ethanol as the medium. After drying, the mixture was placed in a muffle furnace and calcined in a nitrogen atmosphere at 750°C for 24 hours to obtain the cathode material, namely lithium iron phosphate.

[0132] Example 3

[0133] This embodiment provides a composite cathode material precursor, which includes a porous iron phosphate core, a carbon-coated inner layer doped with metal phosphide covering the surface of the core, and an iron phosphate-coated outer layer covering the surface of the carbon-coated inner layer.

[0134] At least a portion of the carbon-coated inner layer is disposed in the pores of the porous iron phosphate core;

[0135] The porous iron phosphate core has a particle size D50 of 1.0 μm, an average pore size of 20 nm, and a porosity of 20%.

[0136] The metal phosphide is iron phosphide, and the doping amount of the metal phosphide is 2 wt.% based on the mass of the carbon-coated inner layer.

[0137] The thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is 1:120.

[0138] This embodiment also provides a method for preparing the above-mentioned composite cathode material precursor, the preparation method comprising the following steps:

[0139] (1) The iron source and organic acid were dissolved in water and mixed evenly. Then, the mixture was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 48 hours. After the reaction was completed, the precipitate was washed with deionized water and centrifuged. Then, it was dried at 140°C for 12 hours to obtain an iron-based metal-organic framework material.

[0140] The iron source is ferric chloride hexahydrate, the organic acid is tricarboxylic acid, and the solid-liquid ratio of the iron source, organic acid and solvent is 1g:3g:1mL.

[0141] (2) After the iron-based metal-organic framework material is crushed, it is soaked in a phosphate buffer solution with a concentration of 1 mol / L and the pH of the solution is controlled at 4 while stirring. Then, the synthesis reaction is carried out at 90°C for 12 h. After the reaction is completed, the product is washed with deionized water and vacuum dried to obtain porous iron phosphate material.

[0142] The phosphate buffer solution is a disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution.

[0143] (3) The porous iron phosphate material, organic phosphorus source, polymer monomer and transition metal salt are added to methanol and stirred and mixed evenly to obtain a mixed solution. Then an initiator is added to it and stirring is continued. Then it is placed in a reaction vessel and reacted at 150°C for 24 hours. After the reaction is completed, it is filtered and washed to obtain porous iron phosphate coated with a polymer coating layer doped with phosphorus and metal.

[0144] Among them, the organophosphorus source is hexachlorocyclotriphosphazene, the polymer monomer is 4,4-dihydroxybiphenyl, the transition metal salt is ferric chloride, the initiator is benzylamine, the solid-liquid ratio of porous ferric phosphate material and methanol is 3 mg: 1 mL, the mass ratio of porous ferric phosphate material, organophosphorus source, polymer monomer and metal salt is 1:2:3:8, and the volume ratio of initiator and mixed solution is 1:40.

[0145] (4) The porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal is used as a seed crystal, and mixed evenly with trivalent iron salt, phosphoric acid and ethylenediamine. Then, a hydrothermal reaction is carried out at 150°C for 5 hours to obtain the hydrothermal product.

[0146] The iron source is ferric sulfate, and the molar ratio of iron atoms in the iron source, phosphorus atoms in phosphoric acid, and ethylenediamine is 1:1:20. The mass of the seed crystal accounts for 20% of the mass of the composite cathode material precursor.

[0147] (5) The hydrothermal product is placed in a vacuum tube furnace under a vacuum atmosphere and sintered at 750°C for 3 hours to remove the water of crystallization and the carbonized polymer coating layer, thereby obtaining the composite cathode material precursor.

[0148] This embodiment also provides a method for preparing a cathode material, the method comprising the following steps:

[0149] The above-mentioned composite cathode material precursor and lithium carbonate were mixed, and the molar ratio of lithium, iron and phosphorus in the reaction system was adjusted to 1.2:1:1. Then, starch of 10% by mass of lithium iron phosphate product was added and ball-milled with ethanol as medium. After drying, the mixture was placed in a muffle furnace and calcined in a nitrogen atmosphere at 850°C for 12 hours to obtain the cathode material, namely lithium iron phosphate.

[0150] Example 4

[0151] The difference between this embodiment and Embodiment 1 is that the amount of organic phosphorus source and metal salt in step (3) is adjusted so that the doping amount of metal phosphide in the carbon-coated inner layer is 0.1%. The remaining preparation methods and parameters are consistent with those in Embodiment 1.

[0152] Example 5

[0153] The difference between this embodiment and Embodiment 1 is that the amount of organic phosphorus source and metal salt in step (3) is adjusted so that the doping amount of metal phosphide in the carbon-coated inner layer is 3%. The remaining preparation methods and parameters are consistent with those in Embodiment 1.

[0154] Example 6

[0155] The difference between this embodiment and Embodiment 1 is that the amount of each parameter in step (4) is adjusted so that the thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is 1:1. The remaining preparation methods and parameters are consistent with those in Embodiment 1.

[0156] Example 7

[0157] The difference between this embodiment and Embodiment 1 is that the amount of each parameter in step (4) is adjusted so that the thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is 1:220. The remaining preparation methods and parameters are consistent with those in Embodiment 1.

[0158] Example 8

[0159] The difference between this embodiment and embodiment 1 is that the amount of initiator in step (3) is adjusted so that the volume ratio of initiator to the mixed solution is 0.5:40.

[0160] The remaining preparation methods and parameters are consistent with those in Example 1.

[0161] Example 9

[0162] The difference between this embodiment and embodiment 1 is that the amount of initiator in step (3) is adjusted so that the volume ratio of initiator to the mixed solution is 5:40.

[0163] The remaining preparation methods and parameters are consistent with those in Example 1.

[0164] Example 10

[0165] The difference between this embodiment and embodiment 1 is that the amount of ethylenediamine in step (4) is adjusted so that the ratio of the amount of iron atoms in the iron source to the amount of ethylenediamine is 1:25.

[0166] The remaining preparation methods and parameters are consistent with those in Example 1.

[0167] Example 11

[0168] The difference between this embodiment and embodiment 1 is that the amount of ethylenediamine in step (4) is adjusted so that the ratio of the amount of iron atoms in the iron source to the amount of ethylenediamine is 1:10.

[0169] The remaining preparation methods and parameters are consistent with those in Example 1.

[0170] Example 12

[0171] The difference between this embodiment and embodiment 1 is that the mass of the seed crystal in step (4) accounts for 5% of the mass of the composite cathode material precursor.

[0172] The remaining preparation methods and parameters are consistent with those in Example 1.

[0173] Example 13

[0174] The difference between this embodiment and embodiment 1 is that the mass of the seed crystal in step (4) accounts for 25% of the mass of the composite cathode material precursor.

[0175] The remaining preparation methods and parameters are consistent with those in Example 1.

[0176] Example 14

[0177] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (5) is 500°C.

[0178] The remaining preparation methods and parameters are consistent with those in Example 1.

[0179] Example 15

[0180] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (5) is 800°C.

[0181] The remaining preparation methods and parameters are consistent with those in Example 1.

[0182] Comparative Example 1

[0183] The difference between this comparative example and Example 1 is that step (3) is omitted, so that the surface of the porous iron phosphate core does not contain a carbon-coated inner layer doped with metal phosphides.

[0184] The remaining preparation methods and parameters are consistent with those in Example 1.

[0185] Comparative Example 2

[0186] The difference between this comparative example and Example 1 is that step (4) is omitted, so that the composite cathode material precursor does not contain an outer layer coated with iron phosphate.

[0187] The remaining preparation methods and parameters are consistent with those in Example 1.

[0188] Comparative Example 3

[0189] The difference between this comparative example and Example 1 is that no metal phosphide doping is performed on the carbon-coated inner layer, that is, step (3) is replaced by the following steps:

[0190] Porous iron phosphate material and glucose were added to methanol and stirred for 2 hours to mix evenly. Then the mixture was dried and calcined at 400°C under a nitrogen atmosphere for 5 hours to form carbon-coated porous iron phosphate material. The solid-liquid ratio of porous iron phosphate material to methanol was 4 mg: 1 mL, and the volume ratio of glucose to methanol was 1.5: 40.

[0191] The remaining preparation methods and parameters are consistent with those in Example 1.

[0192] Performance testing

[0193] The positive electrode materials prepared in the above embodiments and comparative examples are used to make positive electrode slurry, which is then used to prepare positive electrode sheets. These slurries are then assembled with negative electrode sheets, electrolyte, and separators to obtain a 2025 coin cell. Specific steps include:

[0194] Lithium iron phosphate cathode material, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5 and added to N-methylpyrrolidone. The mixture was stirred until homogeneous to obtain a cathode slurry. The cathode slurry was uniformly coated onto an aluminum foil current collector and dried to obtain a cathode electrode sheet. Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a mass ratio of 1:1:1 to prepare an electrolyte with a LiPF6 concentration of 1.0 mol / L. A 2025 coin cell was assembled using a polyethylene membrane as the separator and a lithium metal sheet as the negative electrode sheet.

[0195] Electrochemical performance tests were conducted on the above-mentioned coin cells: charge-discharge tests were performed at room temperature of 2-3.75V.

[0196] The test results are shown in Table 1.

[0197] Table 1

[0198]

[0199]

[0200] analyze:

[0201] As shown in the table above, this disclosure effectively improves the poor conductivity of lithium iron phosphate materials by doping a highly conductive metal phosphide during the preparation of lithium iron phosphate. While ensuring high specific capacity, the rate capability and cycle performance of the material are greatly improved, and the tap density is significantly reduced. At the same time, the setting of the outer layer of iron phosphate avoids direct contact between the metal phosphide and the electrolyte, reducing the occurrence of side reactions, thereby improving the cycle performance of lithium-ion batteries.

[0202] A comparison of the data results from Examples 1 and 4-5 shows that if the amount of metal phosphide doping in the carbon-coated inner layer is too small, the electronic conductivity and compaction density of the material will decrease, thereby reducing the discharge capacity of lithium iron phosphate. If the amount of metal phosphide doping in the carbon-coated inner layer is too large, the ionic conductivity of the material will decrease, thereby reducing the rate performance of the material.

[0203] A comparison of the data results from Examples 1 and 6-7 shows that if the thickness ratio of the inner carbon coating layer to the outer iron phosphate coating layer is too small, the external conductivity of lithium iron phosphate decreases, reducing the battery's rate performance; if the thickness ratio of the inner carbon coating layer to the outer iron phosphate coating layer is too large, the compaction density of lithium iron phosphate decreases, and the metal phosphides doped in the inner carbon coating layer are easily exposed to contact with the electrolyte, thereby reducing the battery's cycle performance.

[0204] A comparison of the data results from Examples 1 and 8-9 shows that if the volume ratio of the initiator to the mixed solution is too small, the polymerization reaction will be insufficient, resulting in a thin carbon coating layer, which in turn reduces the rate performance and cycle performance of the battery. If the volume ratio of the initiator to the mixed solution is too large, the carbon coating layer will be uneven, which in turn reduces the compaction density and cycle stability of the material.

[0205] A comparison of the data results from Examples 1 and 10-11 shows that if the ratio of the amount of iron atoms to ethylenediamine in the iron source is too small, side reactions are likely to occur during the formation of iron phosphate, thereby reducing the rate performance and cycle performance of the battery; if the ratio of the amount of iron atoms to ethylenediamine in the iron source is too large, the iron phosphate coating layer will be unevenly formed, thereby reducing the rate performance and cycle performance of the battery.

[0206] A comparison of the data results from Examples 1 and 12-13 shows that if the mass ratio of the seed crystal to the mass of the composite cathode material precursor is too small, the formation rate of the iron phosphate coating layer will be reduced, thereby reducing the compaction density and cycle performance of lithium iron phosphate. If the mass ratio of the seed crystal to the mass of the composite cathode material precursor is too large, it will easily lead to uneven coating of the iron phosphate outer layer, thereby reducing the rate performance and cycle performance of the battery material.

[0207] A comparison of the data results from Examples 1 and 14-15 shows that if the sintering temperature is too low, the iron phosphate coating layer will not be completely carbonized, which will reduce the conductivity and stability of lithium iron phosphate; if the sintering temperature is too high, it will easily lead to too many defects in the iron phosphate crystals, which will reduce the cycle stability of lithium iron phosphate.

[0208] A comparison of the data results from Example 1 and Comparative Example 1 shows that if the surface of the porous iron phosphate core does not contain a carbon coating inner layer doped with metal phosphides, the conductivity inside the lithium iron phosphate will decrease, thereby reducing the rate performance and cycle performance of the battery.

[0209] A comparison of the data results from Example 1 and Comparative Example 2 shows that if the composite cathode material precursor does not contain an outer layer coated with iron phosphate, the metal phosphide is easily exposed in the electrolyte, thereby reducing the cycle performance of the battery.

[0210] A comparison of the data results from Example 1 and Comparative Example 3 shows that if no metal phosphide is doped on the carbon-coated inner layer, the metal phosphide doped in this disclosure can improve the conductivity of lithium iron phosphate and increase the compaction density compared with a simple carbon layer.

Claims

1. A composite positive electrode material precursor, comprising a porous iron phosphate inner core, a carbon-coated inner layer of doped metal phosphide coated on a surface of the inner core, and an iron phosphate-coated outer layer coated on a surface of the carbon-coated inner layer. The average pore size of the porous iron phosphate inner core is 10-20 nm, and the porosity is 5-20%. The doping amount of the metal phosphide is 0.5-2 wt.% based on the mass of the carbon-coated inner layer. The thickness ratio of the carbon-coated inner layer to the iron phosphate-coated outer layer is 1:(20-120). At least a part of the carbon-coated inner layer is arranged in the pores of the porous iron phosphate inner core. 2.A method for preparing the composite positive electrode material precursor according to claim 1, comprising the following steps: (1) mixing a porous iron phosphate material, a phosphorus source, a polymer monomer, an initiator, a metal salt and a solvent to perform a reaction to obtain a porous iron phosphate coated with a polymer coating layer doped with phosphorus and metal; (2) mixing the porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal as a seed crystal with an iron source, a phosphorus source and a catalyst to perform a hydrothermal reaction to obtain a hydrothermal product; (3) performing a sintering treatment on the hydrothermal product to obtain the composite positive electrode material precursor.

3. The production method according to claim 2, wherein The phosphorus source in step (1) comprises an organic phosphorus source, and the organic phosphorus source comprises hexachlorocyclotriphosphazene and / or triisopropyl phosphite. The polymer monomer in step (1) comprises any one or a combination of at least two of 4,4-dihydroxydiphenyl, 4,4-dihydroxydiphenyl sulfone or 4,4-diaminodiphenyl. The initiator in step (1) comprises any one or a combination of at least two of benzylamine, 4-nitro-N-methylamine or 4-dinitrosophenylamine. The metal salt in step (1) is a transition metal salt, and the transition metal salt comprises any one or a combination of at least two of nickel nitrate, nickel sulfate, nickel chloride, cobalt nitrate, cobalt sulfate, cobalt chloride, titanium nitrate, titanium sulfate or titanium chloride.

4. The production method according to claim 2, wherein The solid-liquid ratio of the porous iron phosphate material and the solvent in step (1) is (3-5) mg:1 mL.

5. The production method according to claim 2, wherein The mass ratio of the porous iron phosphate material, the phosphorus source, the polymer monomer and the metal salt in step (1) is 1:(2-3):(3-6):(8-10).

6. The production method according to claim 2, wherein The mixing manner in step (1) comprises: mixing the porous iron phosphate material, the phosphorus source, the polymer monomer and the metal salt in the solvent to obtain a mixed solution, and then adding the initiator into the mixed solution to continue mixing.

7. The production method according to claim 6, wherein The volume ratio of the initiator to the mixed solution is (1-2):

40.

8. The production method according to claim 2, wherein The reaction temperature in step (1) is 150-250 ℃, and the reaction time is 12-24 h.

9. The production method according to claim 2, wherein, The catalyst in step (2) comprises any one or a combination of at least two of ethylenediamine, 2-hydroxyethylamine or malonamide.

10. The production method according to claim 2, wherein, The ratio of the amount of substance of iron atoms in the iron source, phosphorus atoms in the phosphorus source and the catalyst in step (2) is 1:(1-4):(15-20).

11. The production method according to claim 2, wherein, The mass of the seed crystal in step (2) accounts for 10-20% of the mass of the composite positive electrode material precursor.

12. The method of making according to claim 2, wherein, The temperature of the hydrothermal reaction in step (2) is 150-190 ℃, and the time is 1-5 h.

13. The method of making according to claim 2, wherein, The sintering treatment in step (3) is performed at a temperature of 550-750°C for 3-6h.

14. The production method according to claim 2, wherein, The preparation method comprises the following steps: (I) dissolving the iron source and the organic acid in water and mixing uniformly, then performing a hydrothermal reaction at 120-150°C for 36-48h, after the reaction, washing and centrifuging the obtained precipitate, and then drying at 130-140°C for 12-24h to obtain the iron-based metal organic framework material; wherein the solid-liquid ratio of the iron source, the organic acid and the solvent is 1g:(3-6)g:(1-3)mL; (II) crushing the iron-based metal organic framework material, then immersing it in a phosphate buffer solution with a concentration of 0.1-1mol / L, and stirring while controlling the pH of the solution to be 4-8, then performing a synthesis reaction at 70-90°C for 12-24h, after the reaction, washing and drying the product to obtain the porous iron phosphate material; (III) adding the porous iron phosphate material, the organic phosphorus source, the polymer monomer and the transition metal salt into the solvent and stirring to mix uniformly to obtain a mixed solution, then adding the initiator to continue stirring and mixing, and then performing a reaction at 150-250°C for 12-24h, after the reaction, performing suction filtration and washing to obtain the porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal; wherein the solid-liquid ratio of the porous iron phosphate material and the solvent is (3-5)mg:1mL, the mass ratio of the porous iron phosphate material, the phosphorus source, the polymer monomer and the metal salt is 1:(2-3):(3-6):(8-10), and the volume ratio of the initiator and the mixed solution is (1-2):40; (IV) using the porous iron phosphate coated with the polymer coating layer doped with phosphorus and metal as a seed crystal, mixing it with the ferric salt, the phosphoric acid and the catalyst, and performing a hydrothermal reaction at 150-190°C for 1-5h to obtain a hydrothermal product; wherein the molar ratio of the iron atoms in the iron source, the phosphorus atoms in the phosphoric acid and the catalyst is 1:(1-4):(15-20), and the mass of the seed crystal accounts for 10-20% of the mass of the composite cathode material precursor; (V) performing sintering treatment on the hydrothermal product in a vacuum atmosphere to obtain the composite cathode material precursor; wherein the sintering treatment is performed at a temperature of 550-750°C for 3-6h.

15. A cathode material obtained by mixing and sintering the composite cathode material precursor of claim 1 and a lithium source.

16. A lithium ion battery comprising the cathode material of claim 15.

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