Lithium iron phosphate battery materials, their precursors, preparation methods, and applications

Abstract

This application relates to the field of battery materials technology, providing a lithium iron phosphate battery material, its precursor, its preparation method, and its applications. The disclosed lithium iron phosphate precursor is spherical, comprising an iron phosphate shell and a carbon-iron oxide network structure within the iron phosphate shell. The disclosed preparation method of the precursor includes using nano-hydrogel particles as templates to adsorb ferric ions onto the surface of the nano-hydrogel particles, then reacting the ferric ions with phosphate ions, followed by calcination to carbonize the nano-hydrogel particles. The disclosed lithium iron phosphate battery material comprises a lithium iron phosphate shell and a carbon-lithium iron phosphate structure within the lithium iron phosphate shell. The disclosed preparation method includes mixing and sintering the precursor with a lithium source. The lithium iron phosphate battery material provided in this application has a unique microstructure that is beneficial for increasing the wetting area of ​​the electrolyte and shortening the lithium ion transport path, thereby improving the rate performance of the battery.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and provides a lithium iron phosphate battery material, its precursor, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, as important energy storage devices with advantages such as high energy density and long cycle life, have been widely used in portable electronic products. With the rapid development of electric vehicles and smart grids, the demand for lithium-ion batteries with even better performance is becoming increasingly urgent.

[0003] Lithium iron phosphate (LiFePO4) cathode materials have rapidly gained market share due to their superior safety, environmental friendliness, high capacity, and cost-effectiveness. However, LiFePO4 is also subject to market controversy due to its low ion transport rate and poor conductivity. The morphology and preparation method of the precursor have a significant impact on the performance of LiFePO4; therefore, finding suitable process conditions to prepare high-quality LiFePO4 precursors is extremely important.

[0004] Therefore, this application is hereby submitted. Summary of the Invention

[0005] The purpose of this application includes providing lithium iron phosphate battery materials, their precursors and preparation methods, cathodes and batteries.

[0006] In a first aspect, this application provides a lithium iron phosphate precursor, which is spherical and includes an iron phosphate shell and a first network structure located within the iron phosphate shell. The first network structure is a carbon network interwoven with iron oxide.

[0007] In an optional embodiment, the precursor particle size is 300–600 nm.

[0008] Secondly, this application provides a method for preparing a lithium iron phosphate precursor, comprising:

[0009] Using nano-hydrogel particles as templates, ferric ions are adsorbed onto the surface and interior of the nano-hydrogel particles in a solution system to obtain a solution containing a first intermediate, wherein the surface and interior of the nano-hydrogel particles have at least one of -COOH and amino groups.

[0010] Phosphate ions are mixed with the solution containing the first intermediate, so that at least a portion of the phosphate ions react with the ferric ions on the surface of the first intermediate. Then, solid-liquid separation and drying are performed sequentially to obtain the second intermediate.

[0011] The second intermediate is placed in an oxygen-containing environment and calcined to carbonize the nano-hydrogel particles in the second intermediate and oxidize the ferric ions that have entered the nano-hydrogel particles to iron oxide.

[0012] In an optional embodiment, the nano-hydrogel particles are obtained by reacting anhydride-acylated chitosan with acid in a solution system to form self-assembly particles.

[0013] In an optional embodiment, the reaction of anhydride-acylated chitosan with acid includes:

[0014] An anhydride-acylated chitosan solution was added dropwise to an acidic solution. The pH of the reaction system was controlled at 1.8–2.2 throughout the process, and the concentration of the anhydride-acylated chitosan solution was 0.2–0.4 g / L. The reaction yielded a solution of nano-hydrogel particles.

[0015] In an optional embodiment, the volume ratio of the acidic solution to the anhydride-acylated chitosan solution is 1:1.8 to 2.2.

[0016] In an optional embodiment, the acidic solution is a solution of at least one of formic acid, hydrochloric acid, acetic acid, and lactic acid.

[0017] In an optional embodiment, anhydride-acylated chitosan is obtained by reacting chitosan with anhydride compounds.

[0018] In an optional embodiment, the anhydride compound is selected from at least one of maleic anhydride and succinic anhydride;

[0019] In an optional implementation, the drying method is freeze drying.

[0020] In an optional embodiment, the method of adsorbing ferric ions onto the surface of nano-hydrogel particles to obtain the first intermediate includes:

[0021] The solution containing nano-hydrogel particles is mixed with a ferric salt solution and reacted for 10–14 h. During this process, the pH of the solution system is maintained at 1.8–2.2, so that some of the ferric ions are adsorbed onto the surface of the nano-hydrogel particles and some enter the interior of the nano-hydrogel particles.

[0022] Optionally, the solution containing the nano-hydrogel particles is mixed with the ferric salt so that the concentration of ferric ions in the mixed solution is 0.5 to 1 mol / L.

[0023] In an optional embodiment, an intermediate mixture is obtained by mixing a solution containing nano-hydrogel particles with a ferric salt solution and reacting for 10–14 hours.

[0024] After obtaining the intermediate mixture, the process also includes adding ferric salts to the intermediate mixture to ensure that ferric salt ions are fully adsorbed on the surface of the nano-hydrogel particles.

[0025] Optionally, the ferric salt is added according to the measurable concentration of ferric ions in the solution after replenishment being 0.5 to 1 mol / L, wherein the measurable ferric ions are the total ferric ions in the solution minus the ferric ions that enter the interior of the nano-hydrogel particles;

[0026] In an optional embodiment, the ferric salt solution is a solution of at least one of ferric nitrate and ferric chloride.

[0027] Optionally, mixing phosphate ions with the solution containing the first intermediate, such that at least a portion of the phosphate ions react with ferric ions on the surface of the first intermediate, includes the following methods:

[0028] The phosphate ions are mixed with the solution containing the first intermediate, the reaction temperature is controlled at 55-65℃, the reaction time is 5-9 h, and the pH of the solution system during the reaction process is controlled at 1.8-2.2.

[0029] In an optional embodiment, the reaction of phosphate ions with ferric ions on the surface of the first intermediate is carried out under stirring at a speed of 600–900 rpm.

[0030] In an optional embodiment, the phosphate group is provided by at least one of hydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

[0031] In an optional embodiment, the second intermediate is calcined in an oxygen-containing environment at a temperature of 500–700°C for 4–8 hours.

[0032] In an optional embodiment, the second intermediate is calcined in an oxygen-containing environment, wherein the oxygen volume content in the calcination atmosphere is 5-10%.

[0033] Thirdly, this application provides a lithium iron phosphate battery material, which is spherical and includes a lithium iron phosphate shell and a second network structure located within the lithium iron phosphate shell. The second network structure is a carbon network interwoven with lithium iron phosphate.

[0034] In an optional embodiment, the particle size of the lithium iron phosphate battery material is 300–600 nm.

[0035] In an optional embodiment, the lithium iron phosphate casing surface also has a carbon coating layer.

[0036] Fourthly, this application provides a method for preparing lithium iron phosphate battery materials, comprising:

[0037] The mixture of the lithium iron phosphate precursor provided in this application or the lithium iron phosphate precursor prepared by the preparation method provided in this application and the source material is sintered. The source material includes a lithium source and a phosphorus source. During the sintering process, a portion of the lithium source reacts with the iron phosphate on the surface of the precursor to generate lithium iron phosphate, and the phosphorus source and a portion of the lithium source react with the iron oxide inside the precursor to generate lithium iron phosphate. In an optional embodiment, the sintering atmosphere is an inert atmosphere, the sintering temperature is 600-850°C, and the sintering time is 6-15 hours.

[0038] In an optional embodiment, the mixture is obtained by mixing the precursor and source material with a dispersant, grinding and stirring for 1 to 2 hours, and then drying.

[0039] In an optional implementation, the dispersant is ethanol.

[0040] In an optional embodiment, the source material also includes a carbon source, which accounts for 1 to 3% of the mass of the mixture.

[0041] In an optional embodiment, the carbon source is selected from at least one of glucose, sucrose, soluble starch, carbon black, and graphene.

[0042] In an optional embodiment, the molar ratio of Li:Fe:P in the mixture is 1-1.05:1:1-1.05.

[0043] In an optional embodiment, the phosphorus source is selected from at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0044] In an optional embodiment, the lithium source is selected from at least one of lithium carbonate and lithium hydroxide.

[0045] Fourthly, this application provides a positive electrode, which is made from the lithium iron phosphate battery material provided in this application or the lithium iron phosphate battery material prepared by the preparation method provided in this application.

[0046] Fifthly, this application provides a battery, including the positive electrode provided in this application.

[0047] Beneficial effects:

[0048] The lithium iron phosphate precursor provided in this application has special structural characteristics, which enable it to be mixed with lithium and phosphorus sources and sintered to form lithium iron phosphate battery materials. The outer shell is lithium iron phosphate, and the interior is a loose carbon network interwoven lithium iron phosphate structure. This is beneficial to increasing the wetting area of ​​the electrolyte, shortening the lithium ion transport path, and improving the rate performance of the battery.

[0049] The method for preparing the lithium iron phosphate precursor provided in this application uses nano-hydrogel particles as templates. Ferrous ions are adsorbed through the physical adsorption of the nano-hydrogel particles and through the chemical adsorption of ferric ions via metal-coordination crosslinking by the -COOH or amino groups on their surface. These ferric ions then react with phosphate groups. After the reaction, sintering is performed to carbonize the hydrogel, simultaneously generating iron oxide, thus preparing a spherical lithium iron phosphate precursor with an internal carbon network interwoven with iron oxide structure. This preparation method is simple to operate and can produce the lithium iron phosphate precursor provided in this application.

[0050] The lithium iron phosphate battery material provided in this application has a lithium iron phosphate shell and a loose carbon network interwoven with lithium iron sulfate structure inside, which is beneficial to increasing the wetting area of ​​the electrolyte, and has a shorter lithium ion transport path and higher rate performance.

[0051] The method for preparing lithium iron phosphate battery materials provided in this application can produce the lithium iron phosphate battery materials provided in this application. Attached Figure Description

[0052] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a microstructure diagram showing the external morphology of the lithium iron phosphate cathode material prepared in Example 1;

[0054] Figure 2 This is a microstructure diagram of the internal morphology of the lithium iron phosphate cathode material prepared in Example 1. Detailed Implementation

[0055] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0056] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0057] This application provides a lithium iron phosphate precursor, which is spherical and includes an iron phosphate shell and a first network structure located within the iron phosphate shell. The first network structure is a carbon network interwoven with iron oxide.

[0058] The lithium iron phosphate precursor provided in this application has special structural characteristics, which allow it to be mixed with a lithium source and sintered to form a lithium iron phosphate battery material. The outer shell is lithium iron phosphate, and the interior is a loose network structure of lithium iron phosphate and carbon. This is beneficial for increasing the wetting area of ​​the electrolyte, shortening the lithium ion transport path, and improving the rate performance of the battery. When the precursor is made into a lithium iron phosphate battery material, a phosphorus source can be added and sintered together, so that the iron oxide interwoven on the carbon network structure reacts with phosphorus and lithium to generate lithium iron phosphate. In this way, lithium iron phosphate can be distributed inside the sphere, further improving the capacity of the material.

[0059] Optionally, the precursor has a particle size of 300–600 nm (e.g., 300 nm, 400 nm, 500 nm or 600 nm).

[0060] This application provides a method for preparing a lithium iron phosphate precursor, including:

[0061] Using nano-hydrogel particles as templates, ferric ions are adsorbed onto the surface and interior of the nano-hydrogel particles in a solution system to obtain a solution containing a first intermediate, wherein the surface and interior of the nano-hydrogel particles have at least one of -COOH and amino groups.

[0062] Phosphate ions are mixed with the solution containing the first intermediate, so that at least a portion of the phosphate ions react with the ferric ions on the surface of the first intermediate. Then, solid-liquid separation and drying are performed sequentially to obtain the second intermediate.

[0063] The second intermediate is placed in an oxygen-containing environment and calcined to carbonize the nano-hydrogel particles in the second intermediate and oxidize the ferric ions that have entered the nano-hydrogel particles to iron oxide.

[0064] The method for preparing lithium iron phosphate precursor provided in this application uses nano-sized spherical hydrogel ions as templates to adsorb ferric ions on their surface and react with phosphate ions to form a layer of ferric phosphate dihydrate on the spherical surface. Then, calcination is performed to dehydrate the ferric phosphate dihydrate to generate ferric phosphate, and the hydrogel ions are carbonized to oxidize the ferric ions, forming a carbon network interwoven with iron oxide structure inside the ferric phosphate shell.

[0065] In some embodiments, the preparation method of lithium iron phosphate precursor specifically includes:

[0066] S1. Preparation of anhydride-acylated chitosan solution

[0067] An anhydride compound is reacted with chitosan using sodium carbonate as a catalyst to obtain anhydride-acylated chitosan. The molar ratio of chitosan to anhydride is 1:2, and the molar ratio of anhydride to sodium carbonate is 5:4.

[0068] Optionally, the anhydride compound is selected from at least one of maleic anhydride and succinic anhydride.

[0069] The anhydride-acylated chitosan was ground into powder and then mixed with deionized water to fully dissolve the anhydride-acylated chitosan, thus obtaining an anhydride-acylated chitosan solution.

[0070] Optionally, anhydride-acylated chitosan is mixed with deionized water at a ratio of 1–2 g:5 L (e.g., 1 g:5 L, 1.5 g:5 L, or 2 g:5 L) to obtain a solution with a concentration of 0.2–0.4 g / L (e.g., 0.2 g / L, 0.3 g / L, or 0.4 g / L). The anhydride-acylated chitosan solution within this concentration range produces nano-hydrogel particles of suitable size, ensuring the final production of lithium iron phosphate battery materials with good electrochemical performance. Optimal concentrations are achieved, particularly around 0.28 g / L, for example, 0.25–0.3 g / L (e.g., 0.25 g / L, 0.28 g / L, or 0.3 g / L).

[0071] S2. Preparation of nano-hydrogel particles

[0072] When an anhydride-acylated chitosan solution is added dropwise to an acidic solution, the anhydride-acylated chitosan molecules self-assemble into hydrogel nanoparticles with a particle size of 300–600 nm (e.g., 300 nm, 400 nm, 500 nm, or 600 nm) due to the presence of vinyl carbon-carbon double bonds and hydrogen bonding on the side chains of the chitosan molecules. These hydrogel nanoparticles have a large number of -COOH and amino groups distributed on their surface and inside. The pH of the solution system is controlled at 1.8–2.2 (e.g., 1.8, 2.0, or 2.2) throughout the reaction process.

[0073] The pH of the solution increases during the self-assembly process to generate nano-hydrogel particles. To ensure that the pH is within the range of 1.8 to 2.2, an acidic solution is also used to adjust the pH during the reaction process.

[0074] Optionally, the volume ratio of the acidic solution to the anhydride-acylated chitosan solution is 1:1.8 to 2.2 (e.g., 1:1.8, 1:2, or 1:2.2). Optionally, the dropping rate of the anhydride-acylated chitosan solution is 1 to 2 ml / drop (e.g., 1 ml / drop, 1.5 ml / drop, or 2 ml / drop).

[0075] Optionally, the acidic solution is a solution of at least one of formic acid, hydrochloric acid, acetic acid, and lactic acid.

[0076] S3. Preparation of the first intermediate product

[0077] Add ferric salt to a solution containing nano-hydrogel particles and react for 10–14 h (e.g., 10 h, 12 h, or 14 h), maintaining the solution pH at 1.8–2.2 (e.g., 1.8, 2.0, or 2.2) throughout the reaction to obtain an intermediate mixture.

[0078] Optionally, ferric salts may be added at a concentration of 0.5–1 mol / L (e.g., 0.5 mol / L, 0.8 mol / L, or 1 mol / L) of ferric ions in the mixed solution.

[0079] In an optional embodiment, since some ferric ions will enter into the nano-hydrogel particles, after the reaction is completed, ferric salt is added to the solution to ensure that ferric ions are fully adsorbed on the surface of the nano-hydrogel particles, thus obtaining a solution containing the first intermediate.

[0080] Optionally, the ferric salt is added according to a measurable ferric ion concentration of 0.5 to 1 mol / L in the solution after replenishment. The measurable ferric ion concentration is the total ferric ions in the solution minus the ferric ions that have entered the interior of the nano-hydrogel particles (or the sum of the free ferric ions in the solution and all ferric ions located on the surface of the nano-hydrogel particles).

[0081] Optionally, the ferric salt solution is a solution of at least one of ferric nitrate and ferric chloride.

[0082] When an anhydride-acylated chitosan solution is selected to prepare nano-hydrogel particles, since the prepared nano-hydrogel particles not only have -COOH and amino groups on the surface, but also have -COOH and amino groups inside, when a ferric salt solution is added to the solution containing nano-hydrogel particles in this step, the ferric ions will not only be adsorbed on the surface of the nano-hydrogel particles, but some of the ferric ions will also enter the nano-hydrogel particles.

[0083] S4. Preparation of the second intermediate product

[0084] A solution containing phosphate ions is added to a solution containing the first intermediate, causing the phosphate ions to react with the ferric ions on the surface of the first intermediate to form ferric phosphate. Solid-liquid separation, washing, and drying are then performed. During drying, the water adsorbed within the hydrogel evaporates, forming a network structure to obtain a second intermediate with ferric phosphate dihydrate on the surface and a network structure inside.

[0085] Alternatively, solid-liquid separation can be achieved through filtration.

[0086] Optionally, the detergent used for washing is deionized water.

[0087] Alternatively, the drying method can be freeze drying.

[0088] Optionally, the reaction temperature is controlled at 55–65°C (e.g., 55°C, 60°C, or 65°C), the reaction time is 5–9 h (e.g., 5 h, 6 h, 7 h, 8 h, or 9 h), and the pH of the solution system during the reaction process is controlled at 1.8–2.2 (e.g., 1.8, 2.0, or 2.2).

[0089] In this step, the molar ratio of the added phosphate ions to the measurable ferric ions in the solution is 1:1.

[0090] Optionally, to make the reaction more complete and efficient, the reaction is carried out under stirring at a speed of 600 to 900 rpm (e.g., 600 rpm, 700 rpm, 800 rpm or 900 rpm).

[0091] Optionally, the solution containing phosphate is a solution of at least one of hydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

[0092] S5, calcination

[0093] The second intermediate product is calcined in an oxygen-containing environment to dehydrate ferric phosphate dihydrate and carbonize the nano-hydrogel particles, causing the ferric iron inside the nano-hydrogel particles to oxidize to iron oxide, forming a carbon network interwoven with iron oxide structure.

[0094] Optionally, the calcination temperature is 500–700°C (e.g., 500°C, 600°C, or 700°C), and the time is 4–8 hours (e.g., 4 hours, 6 hours, or 8 hours).

[0095] Optionally, the second intermediate is calcined in an atmosphere where oxygen is present, with an oxygen volume content of 5 to 10% (e.g., 5%, 8%, or 10%).

[0096] Controlling the oxygen content within the above range can effectively prevent the further oxidation of the carbonized network carbon structure during operation.

[0097] This application provides a lithium iron phosphate battery material, which is spherical and includes a lithium iron phosphate shell and a second network structure located inside the lithium iron phosphate shell. The second network structure is composed of carbon and lithium iron phosphate.

[0098] This lithium iron phosphate battery material has a lithium iron phosphate outer shell and a loose carbon network interwoven with lithium iron phosphate structure inside. This structure helps to increase the wetting area of ​​the electrolyte, shorten the lithium ion transport path, and improve the rate performance of the battery.

[0099] Optionally, the particle size of the lithium iron phosphate battery material is 300–600 nm (e.g., 300 nm, 400 nm, 500 nm or 600 nm).

[0100] Optionally, to improve the conductivity of lithium iron phosphate battery materials, the surface of the lithium iron phosphate casing also has a carbon coating layer.

[0101] This application provides a method for preparing a lithium iron phosphate battery material, comprising:

[0102] The lithium iron phosphate precursor provided in the embodiments of this application or the lithium iron phosphate precursor prepared by the preparation method provided in the embodiments of this application is sintered with the source material, which includes a lithium source and a phosphorus source. During the sintering process, a portion of the lithium source reacts with the iron phosphate on the surface of the precursor to generate lithium iron phosphate, and the phosphorus source and a portion of the lithium source react with the iron oxide inside the precursor to generate lithium iron phosphate.

[0103] The method for preparing lithium iron phosphate battery materials provided in this application can produce lithium iron phosphate battery materials with a spherical shape, including a lithium iron phosphate shell and a carbon network interwoven lithium iron phosphate structure located within the lithium iron phosphate shell.

[0104] In some embodiments, the preparation method of lithium iron phosphate battery materials can specifically be as follows:

[0105] S6, Mixed

[0106] The precursor, source material, and dispersant are placed in a grinding mill and ground and stirred for 1-2 hours (e.g., 1 hour, 1.5 hours, or 2 hours); then placed in a drying oven and dried at 60-70°C (e.g., 60°C, 65°C, or 70°C) to obtain a mixture. The source material includes lithium and phosphorus sources.

[0107] Optionally, the lithium source is selected from at least one of lithium carbonate and lithium hydroxide.

[0108] Optionally, the raw materials also include a carbon source, which participates in sintering and can form a carbon coating layer on the surface of the lithium iron phosphate battery material. In this way, the resulting lithium iron phosphate has an internal carbon network and an external carbon coating structure, which is beneficial to improving conductivity.

[0109] Optionally, the carbon source accounts for 1 to 3% (e.g., 1%, 2% or 3%) of the mass of the mixture.

[0110] Optionally, the carbon source is selected from at least one of glucose, sucrose, soluble starch, carbon black, and graphene.

[0111] Optionally, the phosphorus source is selected from at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0112] Optionally, to improve the performance of the obtained material, the molar ratio of Li:Fe:P in the mixture is 1 to 1.05:1:1 to 1.05 (e.g., 1:1:1, 1.02:1:1, 1.05:1:1, 1:1:1.02 or 1:1:1.05).

[0113] Optionally, the dispersant is ethanol.

[0114] S7, Sintering

[0115] The mixture is placed in a tube furnace and held at 600–850°C (e.g., 600°C, 700°C, 800°C or 850°C) for 6–15 hours (e.g., 6 hours, 8 hours, 10 hours, 12 hours or 15 hours) under an inert atmosphere to obtain lithium iron phosphate battery materials.

[0116] Optionally, the inert atmosphere is nitrogen or argon.

[0117] The preparation method described in the above steps of this application uses an anhydride-acylated hydrogel as a template. Utilizing the abundant -COOH and amino groups in the hydrogel, iron ions are physically adsorbed and cross-linked with metals on and inside the hydrogel, resulting in the adsorption of a large number of ferric ions both inside and outside the hydrogel. Then, phosphate ions are introduced into the hydrogel and the ferric salt solution. The phosphate ions react with the ferric ions adsorbed on the hydrogel surface to form ferric phosphate on the hydrogel surface. After filtration and drying, the hydrogel inside the ferric phosphate shell forms a network structure. Finally, calcination in a low-oxygen atmosphere dehydrates the ferric phosphate dihydrate to form ferric phosphate, and carbonizes the internal network structure. Simultaneously, the coordinated iron forms iron oxide in situ, resulting in a structure with an outer shell of ferric phosphate and an inner carbon network of interwoven iron oxide. Finally, the above products are mixed with phosphorus source, carbon source and lithium source and calcined. Iron phosphate reacts with lithium source to form lithium iron phosphate shell, iron oxide inside reacts with lithium source and phosphorus source to form lithium iron phosphate, and carbon source forms carbon coating layer during calcination. Finally, a structure is formed in which the outer shell of lithium iron phosphate has carbon coating layer and the inner structure is lithium iron phosphate with carbon network interwoven.

[0118] The final lithium iron phosphate product contains both carbon and lithium iron phosphate on both the inside and outside, exhibiting high conductivity. The resulting lithium iron phosphate and carbon-coated shell has a structure of interwoven carbon network lithium iron phosphate with a tight outer layer and a loose inner layer, which is beneficial for increasing the wetting area of ​​the electrolyte. At the same time, the shell layer is a lithium iron phosphate layer with a loose network structure inside, which helps to shorten the lithium ion transport path and improve the rate performance of the battery.

[0119] The positive electrode provided in this application embodiment is made from the lithium iron phosphate battery material provided in this application embodiment or the lithium iron phosphate battery material prepared by the preparation method provided in this application embodiment.

[0120] The battery provided in this application embodiment includes the positive electrode provided in this application embodiment. The battery can be a single battery cell or a battery module.

[0121] This application also provides an electrical device that includes the battery provided in this application embodiment. This electrical device can be, for example, a household appliance or an electric vehicle.

[0122] Example 1

[0123] Take succinic anhydride-acylated chitosan and grind it into powder.

[0124] Succinic anhydride-acylated chitosan powder was dissolved in deionized water at a mass-to-volume ratio of 1.4 g: 5 L. The mixture was stirred at room temperature to obtain anhydride-acylated chitosan solution.

[0125] A chitosan solution with an anhydride acylation was slowly added dropwise to an aqueous formic acid solution with a pH of 2 at a rate of 1 ml / drop using a syringe pump. The volume ratio of the chitosan solution with anhydride acylation to the aqueous formic acid solution was 2:1. The pH of the solution was maintained in the range of 1.8-2.2 throughout the dropwise addition process to obtain a self-assembled nanohydrogel particle solution, wherein the particle size range of the nanohydrogel particles was 300-700 nm.

[0126] Ferric chloride was added to the nano-hydrogel particle solution to bring the concentration of ferric chloride in the solution to 0.8 mol / L. After uniform mixing, the solution was stirred continuously for 12 h to obtain an intermediate mixture. Ferric chloride was then added to the intermediate mixture to bring the measurable concentration of ferric ions in the solution to 0.8 mol / L, resulting in a solution containing the first intermediate product.

[0127] An ammonium phosphate solution was added to the solution containing the first intermediate to achieve a measurable molar ratio of ferric ions to phosphate ions of 1:1. The reaction was carried out at a pH of 1.8-2.2 for 6 hours at a rotation speed of 700 rpm and a reaction temperature of 60°C. The precipitate was then filtered, washed, and freeze-dried to obtain the second intermediate.

[0128] The second intermediate was placed in an atmosphere with an oxygen content of 8% and calcined at 600°C for 6 hours to obtain the lithium iron phosphate precursor.

[0129] The lithium iron phosphate precursor was ground and stirred together with lithium carbonate, ammonium phosphate, glucose and ethanol in a grinder for 2 hours. Then it was placed in a drying oven and dried at 65°C to allow all the ethanol to evaporate, resulting in a mixture. In the mixture, the Li:Fe:P ratio was 1.02:1:1.02, and the glucose mass was 2% of the mixture mass.

[0130] The mixture is placed in a tube furnace and kept at 800°C for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate battery materials.

[0131] Example 2

[0132] Take succinic anhydride-acylated chitosan and grind it into powder.

[0133] Succinic anhydride-acylated chitosan powder was dissolved in deionized water at a mass-volume ratio of 2g:5L. The mixture was stirred at room temperature to obtain an anhydride-acylated chitosan solution.

[0134] A chitosan solution with an anhydride acylation was slowly added dropwise to an aqueous formic acid solution with a pH of 2 at a rate of 2 ml / drop using a syringe pump. The volume ratio of the chitosan solution with anhydride acylation to the aqueous formic acid solution was 2:1. The pH of the solution was maintained in the range of 1.8-2.2 throughout the dropwise addition process to obtain a self-assembled nanohydrogel particle solution, wherein the particle size range of the nanohydrogel particles was 300-700 nm.

[0135] Ferric chloride was added to the nano-hydrogel particle solution to bring the concentration of ferric chloride in the solution to 0.8 mol / L. After uniform mixing, the solution was stirred continuously for 12 h to obtain an intermediate mixture. Ferric chloride was then added to the intermediate mixture to bring the measurable concentration of ferric ions in the solution to 0.8 mol / L, resulting in a solution containing the first intermediate product.

[0136] An ammonium phosphate solution was added to the solution containing the first intermediate to achieve a measurable molar ratio of ferric ions to phosphate ions of 1:1. The reaction was carried out at a pH of 1.8-2.2 for 6 hours at a rotation speed of 700 rpm and a reaction temperature of 60°C. The precipitate was then filtered, washed, and freeze-dried to obtain the second intermediate.

[0137] The second intermediate was placed in an atmosphere with an oxygen content of 8% and calcined at 600°C for 6 hours to obtain the lithium iron phosphate precursor.

[0138] The lithium iron phosphate precursor was ground and stirred together with lithium carbonate, ammonium phosphate, glucose and ethanol in a grinder for 2 hours. Then it was placed in a drying oven and dried at 65°C to allow all the ethanol to evaporate, resulting in a mixture. In the mixture, the Li:Fe:P ratio was 1.02:1:1.02, and the glucose mass was 2% of the mixture mass.

[0139] The mixture is placed in a tube furnace and kept at 800°C for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate battery materials.

[0140] Example 3

[0141] Take succinic anhydride-acylated chitosan and grind it into powder.

[0142] Succinic anhydride-acylated chitosan powder was dissolved in deionized water at a mass-to-volume ratio of 1 g: 5 L. The mixture was stirred at room temperature to obtain an anhydride-acylated chitosan solution.

[0143] A chitosan solution with an anhydride acylation was slowly added dropwise to an aqueous formic acid solution with a pH of 2 at a rate of 1 ml / drop using a syringe pump. The volume ratio of the chitosan solution with anhydride acylation to the aqueous formic acid solution was 2:1. The pH of the solution was maintained in the range of 1.8-2.2 throughout the dropwise addition process to obtain a self-assembled nanohydrogel particle solution, wherein the particle size range of the nanohydrogel particles was 300-700 nm.

[0144] Ferric chloride was added to the nano-hydrogel particle solution to bring the concentration of ferric chloride in the solution to 0.8 mol / L. After uniform mixing, the solution was stirred continuously for 12 h to obtain an intermediate mixture. Ferric chloride was then added to the intermediate mixture to bring the measurable concentration of ferric ions in the solution to 0.8 mol / L, resulting in a solution containing the first intermediate product.

[0145] An ammonium phosphate solution was added to the solution containing the first intermediate to achieve a measurable molar ratio of ferric ions to phosphate ions of 1:1. The reaction was carried out at a pH of 1.8-2.2 for 6 hours at a rotation speed of 700 rpm and a reaction temperature of 60°C. The precipitate was then filtered, washed, and freeze-dried to obtain the second intermediate.

[0146] The second intermediate was placed in an atmosphere with an oxygen content of 8% and calcined at 600°C for 6 hours to obtain the lithium iron phosphate precursor.

[0147] The lithium iron phosphate precursor was ground and stirred together with lithium carbonate, ammonium phosphate, glucose and ethanol in a grinder for 2 hours. Then it was placed in a drying oven and dried at 65°C to allow all the ethanol to evaporate, resulting in a mixture. In the mixture, the Li:Fe:P ratio was 1.02:1:1.02, and the glucose mass was 2% of the mixture mass.

[0148] The mixture is placed in a tube furnace and kept at 800°C for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate battery materials.

[0149] Example 4

[0150] Take succinic anhydride-acylated chitosan and grind it into powder.

[0151] Succinic anhydride-acylated chitosan powder was dissolved in deionized water at a mass-to-volume ratio of 1.4 g: 5 L. The mixture was stirred at room temperature to obtain anhydride-acylated chitosan solution.

[0152] Acid-acidified chitosan solution was slowly added dropwise to a lactic acid aqueous solution with a pH of 2 at a rate of 1 ml / drop using a syringe pump. The volume ratio of the acid-acidified chitosan solution to the formic acid aqueous solution was 2:1. The pH of the solution was maintained in the range of 1.8-2.2 throughout the dropwise addition process to obtain a self-assembled nanohydrogel particle solution, wherein the particle size range of the nanohydrogel particles was 600-1000 nm.

[0153] Ferric chloride was added to the nano-hydrogel particle solution to bring the concentration of ferric chloride in the solution to 0.8 mol / L. After uniform mixing, the solution was stirred continuously for 12 h to obtain an intermediate mixture. Ferric chloride was then added to the intermediate mixture to bring the measurable concentration of ferric ions in the solution to 0.8 mol / L, resulting in a solution containing the first intermediate product.

[0154] An ammonium phosphate solution was added to the solution containing the first intermediate to achieve a measurable molar ratio of ferric ions to phosphate ions of 1:1. The reaction was carried out at a pH of 1.8-2.2 for 6 hours at a rotation speed of 700 rpm and a reaction temperature of 60°C. The precipitate was then filtered, washed, and freeze-dried to obtain the second intermediate.

[0155] The second intermediate was placed in an atmosphere with an oxygen content of 8% and calcined at 600°C for 6 hours to obtain the lithium iron phosphate precursor.

[0156] The lithium iron phosphate precursor was ground and stirred together with lithium carbonate, ammonium phosphate, glucose and ethanol in a grinder for 2 hours. Then it was placed in a drying oven and dried at 65°C to allow all the ethanol to evaporate, resulting in a mixture. In the mixture, the Li:Fe:P ratio was 1.02:1:1.02, and the glucose mass was 2% of the mixture mass.

[0157] The mixture is placed in a tube furnace and kept at 800°C for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate battery materials.

[0158] Example 5

[0159] This embodiment is basically the same as Embodiment 1, except that the anhydride-acylated chitosan used to prepare the nano-hydrogel particles is maleic anhydride-acylated chitosan.

[0160] Example 6

[0161] Take succinic anhydride-acylated chitosan and grind it into powder.

[0162] Succinic anhydride-acylated chitosan powder was dissolved in deionized water at a mass-to-volume ratio of 1.4 g: 5 L. The mixture was stirred at room temperature to obtain anhydride-acylated chitosan solution.

[0163] A chitosan solution with anhydride acylation was slowly added dropwise at a rate of 1 ml / drop to an aqueous formic acid solution with a pH of 2 using a syringe pump. The volume ratio of the chitosan solution with anhydride acylation to the aqueous formic acid solution was 2:1. The pH of the solution was maintained in the range of 1.8-2.2 throughout the addition process to obtain a self-assembled nanohydrogel particle solution. The particle size range of the nanohydrogel particles was 300-700 nm.

[0164] Ferric chloride was added to the nano-hydrogel particle solution to bring the concentration of ferric chloride in the solution to 0.5 mol / L. After uniform mixing, the solution was stirred continuously for 0 h to obtain an intermediate mixture. Ferric chloride was then added to the intermediate mixture to bring the measurable concentration of ferric ions in the solution to 0.5 mol / L, resulting in a solution containing the first intermediate product.

[0165] An ammonium phosphate solution was added to the solution containing the first intermediate to achieve a measurable molar ratio of ferric ions to phosphate ions of 1:1. The reaction was carried out at a pH of 1.8-2.2 for 6 hours at a rotation speed of 600 rpm and a reaction temperature of 60°C. The precipitate was then filtered, washed, and freeze-dried to obtain the second intermediate.

[0166] The second intermediate was placed in an atmosphere with an oxygen content of 8% and calcined at 600°C for 6 hours to obtain the lithium iron phosphate precursor.

[0167] The lithium iron phosphate precursor was ground and stirred together with lithium hydroxide, ammonium dihydrogen phosphate, sucrose and ethanol in a grinder for 2 hours. Then it was placed in a drying oven and dried at 70°C to allow all the ethanol to evaporate, resulting in a mixture. In the mixture, the ratio of Li:Fe:P was 1.05:1:1.05, and the mass of glucose was 1% of the mass of the mixture.

[0168] The mixture is placed in a tube furnace and kept at 600°C for 15 hours under a nitrogen atmosphere to obtain lithium iron phosphate battery materials.

[0169] Example 7

[0170] Take succinic anhydride-acylated chitosan. Grind the succinic anhydride-acylated chitosan into powder.

[0171] Succinic anhydride-acylated chitosan powder was dissolved in deionized water at a mass-to-volume ratio of 1.4 g: 5 L. The mixture was stirred at room temperature to obtain anhydride-acylated chitosan solution.

[0172] A chitosan solution with an anhydride acylation was slowly added dropwise to an aqueous formic acid solution with a pH of 2 at a rate of 2 ml / drop using a syringe pump. The volume ratio of the chitosan solution with anhydride acylation to the aqueous formic acid solution was 2:1. The pH of the solution was maintained in the range of 1.8-2.2 throughout the dropwise addition process to obtain a self-assembled nanohydrogel particle solution, wherein the particle size range of the nanohydrogel particles was 300-700 nm.

[0173] Ferric chloride was added to the nano-hydrogel particle solution to bring the concentration of ferric chloride in the solution to 1 mol / L. After uniform mixing, the solution was stirred continuously for 12 h to obtain an intermediate mixture. Ferric chloride was then added to the intermediate mixture to bring the measurable concentration of ferric ions in the solution to 1 mol / L, resulting in a solution containing the first intermediate product.

[0174] An ammonium phosphate solution was added to the solution containing the first intermediate to achieve a measurable molar ratio of ferric ions to phosphate ions of 1:1. The reaction was carried out at a pH of 1.8-2.2 for 9 hours at a rotation speed of 900 rpm and a reaction temperature of 65°C. The precipitate was then filtered, washed, and freeze-dried to obtain the second intermediate.

[0175] The second intermediate was placed in an atmosphere with an oxygen content of 8% and calcined at 600°C for 6 hours to obtain the lithium iron phosphate precursor.

[0176] The lithium iron phosphate precursor was ground and stirred together with lithium hydroxide, ammonium dihydrogen phosphate, sucrose and ethanol in a grinder for 2 hours. Then it was placed in a drying oven and dried at 60°C to allow all the ethanol to evaporate, resulting in a mixture. In the mixture, the ratio of Li:Fe:P was 1.05:1:1.05, and the mass of glucose was 3% of the mass of the mixture.

[0177] The mixture is placed in a tube furnace and kept at 850°C for 6 hours under a nitrogen atmosphere to obtain lithium iron phosphate battery materials.

[0178] Comparative Example

[0179] This comparative example provides the most common existing methods for preparing lithium iron phosphate battery materials, specifically:

[0180] A 1 mol / L ferric chloride solution was stirred thoroughly, followed by a 1 mol / L ammonium phosphate solution to ensure a 1:1 molar ratio of ferric salt to phosphate. The reaction was carried out at 700 rpm and 60°C for 6 hours, with the pH adjusted to 1.8-2.2 to ensure complete reaction of the ferric phosphate. After filtration and washing, the product was freeze-dried. The dried product was then calcined in an 8% oxygen atmosphere to obtain the ferric phosphate precursor.

[0181] The precursor was then ground and stirred in a grinder with lithium carbonate, ammonium phosphate, glucose and ethanol for 2 hours. Then it was placed in a drying oven and dried at 60°C to allow all the ethanol to evaporate, resulting in a mixture. In the mixture, the ratio of Li:Fe:P was 1.02:1:1.02, and the mass of glucose was 2% of the mass of the mixture.

[0182] The mixture is placed in a tube furnace and kept at 800°C for 10 hours under a nitrogen atmosphere to obtain lithium iron phosphate battery materials.

[0183] Experimental Example 1

[0184] A microstructure image of the external surface of the lithium iron phosphate battery material prepared in Example 1 was captured, as shown below. Figure 1 As shown, from Figure 1 It can be seen that the lithium iron phosphate battery material is spherical;

[0185] A microstructure image of the internal structure of the lithium iron phosphate battery material particles obtained in Example 1 was captured, as shown below. Figure 2 As shown, from Figure 2 It can be seen that the particles have a loose network structure inside.

[0186] Experiment Example 2

[0187] Electrochemical performance testing:

[0188] The binder, conductive agent, and lithium iron phosphate battery material powder prepared in the various embodiments or comparative examples were mixed in a mass ratio of 1:1:8. N-methylpyrrolidone was added to form a slurry, which was then uniformly coated onto aluminum foil. After vacuum drying, the slurry was removed, rolled, and punched into circular electrode sheets. Coin cells were then assembled in a glove box. Constant current charge-discharge cycle tests were performed on the coin cells, with charge-discharge voltages ranging from 2.5 to 4.2 V.

[0189] The rate performance and specific surface area of ​​the coin cells made from the cathode materials in the above embodiments and comparative examples were tested, mainly focusing on the rate specific capacity at 0.2C, 3C, and 10C; the specific surface area of ​​the corresponding products was measured using a specific surface area meter. The test results are shown in Table 1.

[0190] Table 1 Test results for each embodiment and comparative example

[0191]

[0192] As can be seen from the table above, the lithium iron phosphate battery materials prepared in each embodiment of the present invention have higher rate performance and larger specific surface area compared with the comparative example.

[0193] Comparing Example 1 and Example 2, the concentration of the anhydride-acylated chitosan solution in Example 2 was higher than that in Example 1. The results showed that the electrochemical performance of the prepared lithium iron phosphate battery material was slightly worse. The reason for this may be that the higher concentration of the anhydride-acylated chitosan solution in Example 2 resulted in a larger particle size of the prepared nano-hydrogel particles, which in turn resulted in a larger particle size of the prepared lithium iron phosphate battery material, thus causing a slight decrease in rate performance.

[0194] Comparing Example 1 and Example 3, the concentration of the anhydride-acylated chitosan solution in Example 3 was lower than that in Example 1. The results showed that the electrochemical performance of the prepared lithium iron phosphate battery material was slightly worse. The reason for this may be that the concentration of the anhydride-acylated chitosan solution in Example 3 was lower, resulting in a smaller particle size of the prepared nano-hydrogel particles. Consequently, the particle size of the prepared lithium iron phosphate battery material was smaller, which may have led to agglomeration, resulting in a slight decrease in rate performance.

[0195] Comparing Example 1 and Example 4, Example 4 uses lactic acid solution as an acidic solution to prepare nano-hydrogel particles. The results show that the electrochemical performance of the prepared lithium iron phosphate battery material is slightly worse. The reason may be that the lactic acid solution has a tendency to aggregate particle size, which increases the particle size of the prepared lithium iron phosphate battery material, thus slightly reducing the rate performance.

[0196] In summary, the lithium iron phosphate precursor provided in this application has unique structural characteristics, which enable it to be mixed with a lithium source and sintered to form lithium iron phosphate battery materials. The outer shell is lithium iron phosphate, while the interior is a loose carbon network interwoven with iron oxide structure. This is beneficial for increasing the wetting area of ​​the electrolyte, shortening the lithium ion transport path, and improving the rate performance of the battery.

[0197] The method for preparing lithium iron phosphate precursor provided in this application can produce the lithium iron phosphate precursor provided in this application.

[0198] The lithium iron phosphate battery material provided in this application has a lithium iron phosphate outer shell and a loose carbon network interwoven lithium iron phosphate structure inside, which is beneficial to increasing the wetting area of ​​the electrolyte, shortening the lithium ion transport path, and improving the rate performance of the battery.

[0199] The method for preparing lithium iron phosphate battery material provided in this application can produce the lithium iron phosphate battery material provided in this application.

Claims

1. A lithium iron phosphate precursor, characterized in that, The precursor is spherical and includes an iron phosphate shell and a first network structure located within the iron phosphate shell. The first network structure is a carbon network interwoven with iron oxide.

2. The lithium iron phosphate precursor according to claim 1, characterized in that, The precursor has a particle size of 300~600nm.

3. A method for preparing a lithium iron phosphate precursor, characterized in that, include: Using nano-hydrogel particles as templates, ferric ions are adsorbed onto the surface and interior of the nano-hydrogel particles in a solution system to obtain a solution containing a first intermediate, wherein the surface and interior of the nano-hydrogel particles have at least one of -COOH and amino groups. Phosphate ions are mixed with the solution containing the first intermediate, so that at least a portion of the phosphate ions react with the ferric ions on the surface of the first intermediate. Then, solid-liquid separation and freeze-drying are performed sequentially to obtain the second intermediate. The second intermediate is placed in an oxygen-containing environment and calcined to carbonize the nano-hydrogel particles in the second intermediate and to oxidize the ferric ions that have entered the nano-hydrogel particles to iron oxide. The nano-hydrogel particles are obtained by reacting anhydride-acylated chitosan with acid in a solution system for self-assembly. The ways in which anhydride-acylated chitosan reacts with acid include: An anhydride-acylated chitosan solution was added dropwise to an acidic solution, and the pH of the reaction system was controlled at 1.8~2.2 throughout the process to obtain a solution of nano-hydrogel particles. The methods for adsorbing ferric ions onto the surface and interior of the nano-hydrogel particles to obtain a product containing the first intermediate include: The solution containing the nano-hydrogel particles is mixed with ferric salt and reacted. During this process, the pH of the solution system is maintained at 1.8~2.2, so that some of the ferric ions are adsorbed onto the surface of the nano-hydrogel particles and some enter the interior of the nano-hydrogel particles. The method of mixing phosphate ions with the solution containing the first intermediate, so that at least a portion of the phosphate ions react with ferric ions on the surface of the first intermediate, includes: The phosphate ions are mixed with the solution containing the first intermediate, and the reaction temperature is controlled at 55~65℃, while the pH of the solution system during the reaction process is controlled at 1.8~2.

2. The second intermediate product is calcined in an oxygen-containing environment at a temperature of 500-700°C for 4-8 hours.

4. The preparation method according to claim 3, characterized in that, The concentration of the anhydride-acylated chitosan solution is 0.2~0.4 g / L.

5. The preparation method according to claim 3, characterized in that, The volume ratio of the acidic solution to the anhydride-acylated chitosan solution is 1:1.8~2.

2.

6. The preparation method according to claim 3, characterized in that, The acidic solution is a solution of at least one of formic acid, hydrochloric acid, acetic acid, and lactic acid.

7. The preparation method according to claim 3, characterized in that, The anhydride-acylated chitosan is obtained by reacting chitosan with anhydride compounds.

8. The preparation method according to claim 7, characterized in that, The anhydride compound is selected from at least one of maleic anhydride and succinic anhydride.

9. The preparation method according to any one of claims 3 to 8, characterized in that, The reaction time for mixing the solution containing the nano-hydrogel particles with the ferric salt is 10-14 h.

10. The preparation method according to any one of claims 3 to 8, characterized in that, The solution containing the nano-hydrogel particles was mixed with the ferric salt so that the concentration of ferric ions in the mixed solution was 0.5~1 mol / L.

11. The preparation method according to any one of claims 3 to 8, characterized in that, After obtaining the intermediate mixture, the process further includes adding the ferric salt to the intermediate mixture so that the surface of the nano-hydrogel particles can fully adsorb ferric salt ions.

12. The preparation method according to claim 11, characterized in that, The ferric salt is added according to the measurable ferric ion concentration in the solution after replenishment being 0.5~1 mol / L. The measurable ferric ion concentration is the total ferric ions in the solution minus the ferric ions that enter the interior of the nano-hydrogel particles.

13. The preparation method according to any one of claims 3 to 8, characterized in that, The ferric salt solution is a solution of at least one of ferric nitrate and ferric chloride.

14. The preparation method according to any one of claims 3 to 8, characterized in that, The phosphate ions are mixed with the solution containing the first intermediate, and the reaction time is 5-9 hours.

15. The preparation method according to any one of claims 3 to 8, characterized in that, The solution containing the first intermediate also contains free ferric ions. When at least a portion of the phosphate ions react with the ferric ions on the surface of the first intermediate, a portion of the phosphate ions also react with the free ferric ions in the solution to generate ferric phosphate, which is then deposited on the surface of the nano-hydrogel particles.

16. The preparation method according to any one of claims 3 to 8, characterized in that, The reaction between phosphate ions and ferric ions on the surface of the first intermediate is carried out under stirring at a speed of 600-900 rpm.

17. The preparation method according to any one of claims 3 to 8, characterized in that, The phosphate group is provided by at least one of hydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

18. The preparation method according to any one of claims 3 to 8, characterized in that, The second intermediate product is calcined in an oxygen-containing environment, with an oxygen volume content of 5-10% in the calcination atmosphere.

19. A lithium iron phosphate battery material, characterized in that, The lithium iron phosphate battery material is spherical and includes a lithium iron phosphate shell and a second network structure located within the lithium iron phosphate shell. The second network structure is a carbon network interwoven with lithium iron phosphate.

20. The lithium iron phosphate battery material according to claim 19, characterized in that, The particle size of the lithium iron phosphate battery material is 300~600nm.

21. The lithium iron phosphate battery material according to claim 19, characterized in that, The lithium iron phosphate casing also has a carbon coating layer on its surface.

22. A method for preparing a lithium iron phosphate battery material, characterized in that, include: The mixture of the lithium iron phosphate precursor as described in claim 1 or 2, or the lithium iron phosphate precursor prepared by the preparation method as described in any one of claims 3 to 18, and the source material is sintered, wherein the source material includes a lithium source and a phosphorus source. During the sintering process, a portion of the lithium source reacts with the iron phosphate on the surface of the precursor to generate lithium iron phosphate, and the phosphorus source and a portion of the lithium source react with the iron oxide inside the precursor to generate lithium iron phosphate.

23. The preparation method according to claim 22, characterized in that, The sintering atmosphere is inert, the sintering temperature is 600~850℃, and the sintering time is 6~15h.

24. The preparation method according to claim 22, characterized in that, The mixture is obtained by mixing the precursor and the source material with a dispersant, grinding and stirring for 1-2 hours, and then drying.

25. The preparation method according to claim 24, characterized in that, The dispersant is ethanol.

26. The preparation method according to claim 22, characterized in that, The source material also includes a carbon source, which accounts for 1 to 3% of the mass of the mixture.

27. The preparation method according to claim 26, characterized in that, The carbon source is selected from at least one of glucose, sucrose, soluble starch, carbon black, and graphene.

28. The preparation method according to claim 22, characterized in that, In the mixture, the molar ratio of Li:Fe:P is 1~1.05:1:1~1.

05.

29. The preparation method according to claim 22, characterized in that, The phosphorus source is selected from at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

30. The preparation method according to claim 22, characterized in that, The lithium source is selected from at least one of lithium carbonate and lithium hydroxide.

31. A positive electrode, characterized in that, The lithium iron phosphate battery material is prepared by any one of the lithium iron phosphate battery materials as described in any one of claims 19 to 21 or by any one of the preparation methods as described in claims 22 to 29.

32. A battery, characterized in that, Includes the positive electrode as described in claim 31.

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