Composite phosphate-based positive electrode material, preparation method therefor, and use thereof

Abstract

Disclosed in the present application is the technical field of battery materials. Particularly, the present application relates to a composite phosphate-based positive electrode material, a preparation method therefor, and use thereof. The composite phosphate-based positive electrode material comprises a plurality of composite phosphate-based positive electrode particles and a plurality of doped composite phosphate-based positive electrode particles with a particle size gradation. The composite phosphate-based positive electrode particles comprise a phosphate-based active core and a heteroatom-doped carbon coating layer I. The doped composite phosphate-based positive electrode particles comprise a titanium-doped phosphate-based active core and a heteroatom-doped carbon coating layer II. The particle size of the composite phosphate-based positive electrode particles is greater than that of the doped composite phosphate-based positive electrode particles. An inorganic carbon source is distributed between the composite phosphate-based positive electrode particles and the doped composite phosphate-based positive electrode particles. By means of doping of titanium in active particles, doping of heteroatoms in the carbon coating layers, and filling active particles with different particle sizes, different morphologies, and different densities with each other to form a gradation, the compaction density and the gram capacity of the material are improved.

Description

Composite phosphate-based cathode materials, their preparation methods and applications

[0001] This application claims priority to Chinese Patent Application No. 202410683317.3, filed on May 29, 2024, entitled "Composite Phosphate-Based Cathode Material and its Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery materials technology, and in particular to a composite phosphate-based cathode material, its preparation method, and its application. Background Technology

[0003] The statements herein are provided only as background information relevant to this application and do not necessarily constitute prior art. Lithium iron phosphate (LFP) of the olivine phase has become a very popular cathode material in lithium-ion batteries due to its high energy density, low cost, safety, and excellent cycle stability at ambient temperatures. However, the relatively low energy density of battery systems composed of LFP limits its application in power batteries.

[0004] Currently, the specific capacity of phosphate-based cathode materials such as lithium iron phosphate (LFP) is already close to its theoretical value, leaving little room for improvement. Increasing the compaction density of these materials to improve their energy density is one of the mainstream methods. However, existing methods for preparing phosphate-based cathode materials are not very effective in improving their compaction density, and they often sacrifice some of the specific capacity while increasing the volumetric compaction density. Therefore, how to improve both the compaction density and specific capacity of phosphate-based cathode materials remains a pressing issue that needs to be addressed.

[0005] Application content

[0006] One of the objectives of this application is to provide a composite phosphate-based cathode material, its preparation method, and its application, with the aim of improving the compaction density and specific capacity of the phosphate-based cathode material.

[0007] The technical solution adopted in the embodiments of this application is:

[0008] In a first aspect, a composite phosphate-based cathode material is provided, comprising a plurality of composite phosphate-based cathode particles with a particle size distribution and doped composite phosphate-based cathode particles, wherein the composite phosphate-based cathode particles comprise a phosphate-based active core and a heteroatom-doped carbon coating layer I; the doped composite phosphate-based cathode particles comprise a titanium-doped phosphate-based active core and a heteroatom-doped carbon coating layer II; the particle size of the composite phosphate-based cathode particles is larger than the particle size of the doped composite phosphate-based cathode particles; and an inorganic carbon source is distributed between the composite phosphate-based cathode particles and the doped composite phosphate-based cathode particles.

[0009] Secondly, a method for preparing a composite phosphate-based cathode material is provided, comprising the following steps:

[0010] Phosphate-based active particles were prepared by a single sintering process.

[0011] Titanium-doped phosphate-based active particles are prepared by a single sintering process, wherein the particle size of the phosphate-based active particles is larger than that of the titanium-doped phosphate-based active particles.

[0012] The phosphate-based active particles and the titanium-doped phosphate-based active particles are mixed with a composite carbon source and a heteroatom source, and then sintered to obtain a composite phosphate-based cathode material; wherein the composite carbon source includes an organic carbon source and an inorganic carbon source.

[0013] Thirdly, an application of a composite phosphate-based cathode material is provided, in which the above-mentioned composite phosphate-based cathode material is applied to cathode sheets and / or secondary batteries.

[0014] The beneficial effects of the composite phosphate-based cathode material provided in this application embodiment are as follows: it includes composite phosphate-based cathode particles with a graded particle size distribution and doped composite phosphate-based cathode particles. Both types of cathode particles have a heteroatom-doped carbon coating layer on their outer surface. Heteroatom doping improves the conductivity, cycle stability, and thermal stability of the carbon coating layer. The core of the doped composite phosphate-based cathode particles is doped with titanium atoms, which helps to reduce the crystal size of the phosphate-based active core and improve its conductivity and ion diffusion rate. This results in the composite phosphate-based cathode particles having a larger particle size than the doped composite phosphate-based cathode particles. Through the mutual filling between composite phosphate-based cathode materials and doped composite phosphate-based cathode particles of different sizes, morphologies, and densities, a graded distribution is formed, improving the compaction density and specific capacity, and other electrochemical properties, of the composite phosphate-based cathode material.

[0015] The beneficial effects of the preparation method of the composite phosphate-based cathode material provided in this application are as follows: phosphate-based active particles and titanium-doped phosphate-based active particles are prepared by a single sintering process, and the active particles are initially crystallized after the single sintering. Titanium doping can reduce the crystal size of the phosphate-based cathode particles, thereby improving their conductivity and ion diffusion rate. Therefore, titanium doping can improve the electrochemical performance of the phosphate-based active particles and also make the particle size of the titanium-doped phosphate-based active particles smaller than that of the undoped phosphate-based active particles. The two types of phosphate-based active particles with different particle sizes and doping conditions are mixed with a composite carbon source and a heteroatom source, and then sintered to optimize the crystallization of the active particles. Simultaneously, the organic carbon source and impurity atom source form a uniform heteroatom-doped carbon coating layer on the surface of the active particles, and the inorganic carbon source forms conductive bridges between the composite particles coated with different heteroatom-doped carbon coating layers, resulting in the composite phosphate-based cathode material. In the prepared composite phosphate-based cathode material, composite phosphate-based active particles of different sizes, morphologies, and densities, along with doped composite phosphate-based cathode particles, inter-fill each other to form a gradation, which can better improve the compaction density of the composite phosphate-based cathode material, thereby increasing its specific capacity. Furthermore, the doping of titanium in the active particles and the doping of heteroatoms in the carbon coating layer can improve the electrochemical properties of the composite phosphate-based cathode material, such as specific capacity, conductivity, and ion diffusion rate.

[0016] The beneficial effects of the composite phosphate-based cathode material provided in this application are as follows: the composite phosphate-based cathode material has the characteristics of high compaction density and high specific capacity, and can be directly applied to cathode sheets or secondary batteries to improve the energy density, cycle life and other electrochemical performance of cathode sheets and secondary batteries. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or exemplary technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 is a schematic flowchart of the preparation method of the composite phosphate-based cathode material provided in the embodiments of this application;

[0019] Figure 2 is a SEM image of the composite phosphate-based cathode material provided in Example 1 of this application;

[0020] Figure 3 is a SEM image of the composite phosphate-based cathode material provided in Comparative Example 1 of this application. Embodiments of the present invention

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of this application.

[0022] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly or indirectly attached to that other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to that other component. The terms "upper," "lower," "left," "right," etc., indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, and are for ease of description only, not to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. "A plurality" means two or more, unless otherwise explicitly defined.

[0023] Currently, the specific capacity of phosphate-based cathode materials such as lithium iron phosphate in the market is already close to its theoretical value, leaving little room for improvement. Increasing the compaction density of phosphate-based cathode materials such as lithium iron phosphate to improve their energy density is one of the mainstream methods currently used.

[0024] In some embodiments, two lithium iron phosphate materials are obtained by sintering large-particle and small-particle lithium iron phosphate materials at different temperatures to obtain two materials. These two materials are then mixed in a certain proportion and sintered a second time to obtain a high-compaction, high-performance lithium iron phosphate cathode material. In other embodiments, two doped precursors with different doping ratios and particle sizes are prepared, and then doped lithium iron phosphate with high compaction density and high energy density is obtained through particle size and elemental gradation. However, these methods have limited effect on improving the compaction density of phosphate-based cathode materials such as lithium iron phosphate, and therefore have poor effect on improving the specific capacity of phosphate-based cathode materials.

[0025] Therefore, in order to improve the compaction density of phosphate-based cathode materials such as lithium iron phosphate, and thus enhance the specific capacity and energy density of the battery, this application provides a high-compact, high-performance composite phosphate-based cathode material, its preparation method, and its applications. The following examples will further illustrate the proposed solution.

[0026] To illustrate the technical solutions described in this application, the following detailed description is provided in conjunction with specific drawings and embodiments.

[0027] In a first aspect, embodiments of this application provide a composite phosphate-based cathode material, comprising a plurality of composite phosphate-based cathode particles with a particle size distribution and doped composite phosphate-based cathode particles, wherein the composite phosphate-based cathode particles include a phosphate-based active core and a heteroatom-doped carbon coating layer I; the doped composite phosphate-based cathode particles include a titanium-doped phosphate-based active core and a heteroatom-doped carbon coating layer II, the particle size of the composite phosphate-based cathode particles is larger than the particle size of the doped composite phosphate-based cathode particles; an inorganic carbon source is distributed between the composite phosphate-based cathode particles and the doped composite phosphate-based cathode particles.

[0028] This application describes a composite phosphate-based cathode material comprising a plurality of composite phosphate-based cathode particles with varying particle sizes and doped composite phosphate-based cathode particles. Both types of cathode particles have a heteroatom-doped carbon coating layer on their outer surface. Heteroatom doping improves the conductivity, cycle stability, and thermal stability of the carbon coating layer. The core of the doped composite phosphate-based cathode particles is doped with titanium atoms, which helps reduce the crystal size of the phosphate-based active core and improves its conductivity and ion diffusion rate. This results in the composite phosphate-based cathode particles having a larger particle size than the doped composite phosphate-based cathode particles. Through the mutual filling of composite phosphate-based cathode materials and doped composite phosphate-based cathode particles of different sizes, morphologies, and densities, a gradation is formed, improving the compaction density and specific capacity, among other electrochemical properties, of the composite phosphate-based cathode material.

[0029] In some possible implementations, the D50 particle size of the composite phosphate-based cathode particles is 500 nm to 700 nm. In some possible implementations, the D50 particle size of the doped composite phosphate-based cathode particles is 100 nm to 200 nm. In some possible implementations, the size of the inorganic carbon source is 200 nm to 400 nm. In these cases, both the composite phosphate-based cathode particles and the doped composite phosphate-based cathode particles have small particle sizes and large active surface areas, which is beneficial for electron and ion migration and transport. Furthermore, the particle size of the phosphate-based active particles is larger than that of the titanium-doped phosphate-based active particles, allowing the smaller active particles to fill the gaps between the larger active particles, creating a mutually filling gradation effect.

[0030] In some possible implementations, the inorganic carbon source has a one-dimensional or two-dimensional continuous structure, creating a conductive bridge between the composite phosphate-based cathode particles and the doped composite phosphate-based cathode particles. In this case, the inorganic carbon source forms a conductive bridge between the composite phosphate-based cathode particles and the doped composite phosphate-based cathode particles, increasing the compaction density of the composite phosphate-based cathode material, thereby increasing the specific capacity of the composite phosphate-based cathode material.

[0031] In some possible implementations, the mass ratio of composite phosphate-based cathode particles to doped composite phosphate-based cathode particles is 1:(1~4). In this case, the ratio of phosphate-based active particles to titanium-doped phosphate-based active particles sufficiently ensures that active particles of different sizes, morphologies, and densities fill each other in the composite phosphate-based cathode material, forming a sufficient gradation and improving the compaction density and specific capacity of the composite phosphate-based cathode material. For example, the mass ratio of composite phosphate-based cathode particles to doped composite phosphate-based cathode particles can be any typical but non-limiting point value such as 1:1, 1:2, 1:3, 1:4, or a range between any two points.

[0032] In some possible implementations, the heteroatoms include at least one of boron, nitrogen, phosphorus, and fluorine atoms. In this case, doping with impurity atoms such as boron may improve the performance of the carbon coating layer, such as enhancing the conductivity, cycle stability, and thermal stability of the carbon layer, thereby improving the electrochemical performance of the composite phosphate-based cathode material.

[0033] In some possible implementations, the heteroatom doping percentages in the heteroatom-doped carbon coating layer I and heteroatom-doped carbon coating layer II of the composite phosphate-based cathode particles and doped composite phosphate-based cathode particles are independently 2% to 5%. In this case, the heteroatom doping content is beneficial for enhancing the conductivity, cycle stability, and thermal stability of the carbon coating layer, while also ensuring the crystal structure and graphitization degree of the carbon coating layer, thus ensuring the electronic and ionic conductivity of the composite phosphate-based cathode material.

[0034] In some possible implementations, the titanium doping mass percentage in the titanium-doped phosphate-based active core is 0.1% to 0.8%. In this case, the titanium doping content can effectively reduce the crystal size of the phosphate-based active particles, thereby improving the conductivity and ion diffusion rate of the phosphate-based active particles.

[0035] In some possible implementations, the heteroatom-doped carbon coating layer I in the composite phosphate-based cathode particles has a mass percentage of 0.5% to 1%. In some possible implementations, the heteroatom-doped carbon coating layer II in the doped composite phosphate-based cathode particles has a mass percentage of 1% to 2%. In this case, the mass percentage of the heteroatom-doped carbon coating layer sufficiently ensures a uniform and complete coating effect on the active core, improving the stability and conductivity of the composite phosphate-based cathode material.

[0036] In some possible implementations, the compaction density of the composite phosphate-based cathode material is not less than 2.7 g / cm³. 3The composite phosphate-based cathode material in this application improves the compaction density of the composite phosphate-based cathode material by creating a gradation effect through the mutual filling between several composite phosphate-based cathode particles of different sizes, morphologies, and densities, and doped composite phosphate-based cathode particles. This results in a compaction density of not less than 2.7 g / cm³. 3 This significantly improves the specific capacity of composite phosphate-based cathode materials.

[0037] In some embodiments, the composite phosphate-based cathode material is used to make a button battery, and the 1C charge / discharge capacity reaches 145 mAh / g or higher.

[0038] The composite phosphate-based cathode material of this application can be prepared by the method described in the following examples.

[0039] Secondly, embodiments of this application provide a method for preparing a composite phosphate-based cathode material, as shown in Figure 1, including the following steps:

[0040] S10. Phosphate-based active particles are prepared by a single sintering process;

[0041] S20. Titanium-doped phosphate-based active particles are prepared by a single sintering process, wherein the particle size of the phosphate-based active particles is larger than that of the titanium-doped phosphate-based active particles.

[0042] S30. Phosphate-based active particles, titanium-doped phosphate-based active particles, composite carbon source and heteroatom source are mixed and then sintered to obtain composite phosphate-based cathode material; wherein, the composite carbon source includes organic carbon source and inorganic carbon source.

[0043] The method for preparing composite phosphate-based cathode materials provided in this application involves preparing phosphate-based active particles and titanium-doped phosphate-based active particles through a single sintering process. The sintering process initially crystallizes the obtained active particles. Titanium doping reduces the crystal size of the phosphate-based cathode particles, thereby improving their conductivity and ion diffusion rate. Therefore, titanium doping not only improves the electrochemical performance of the phosphate-based active particles but also results in a smaller particle size for the titanium-doped phosphate-based active particles compared to undoped particles. The two types of phosphate-based active particles with different particle sizes and doping conditions are mixed with a composite carbon source and a heteroatom source, followed by sintering to optimize the crystallization of the active particles. Simultaneously, the organic carbon source and impurity atom source form a uniform heteroatom-doped carbon coating layer on the surface of the active particles. The inorganic carbon source forms conductive bridges between the composite particles coated with different heteroatom-doped carbon coating layers, resulting in the composite phosphate-based cathode material. In the composite phosphate-based cathode material prepared in this application, composite phosphate-based active particles of different sizes, morphologies, and densities, along with doped composite phosphate-based cathode particles, fill each other to form a gradation, which can better improve the compaction density of the composite phosphate-based cathode material, thereby increasing its specific capacity. Furthermore, the doping of titanium in the active particles and the doping of heteroatoms in the carbon coating layer can improve the electrochemical properties of the composite phosphate-based cathode material, such as specific capacity, conductivity, and ion diffusion rate.

[0044] In step S10 above:

[0045] In some possible implementations, the phosphate-based active particles can be lithium manganese iron phosphate, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate-based materials doped with other metal elements, lithium iron phosphate-based materials doped with other metal elements, lithium manganese phosphate-based materials doped with other metal elements, etc. Doping with metal elements can improve the electrochemical performance of phosphate-based cathode materials. The phosphate-based cathode materials in the embodiments of this application have broad selectivity and strong practicality, and can meet different application requirements.

[0046] In some possible implementations, the preparation of phosphate-based active particles includes the steps of: mixing a first carbon source, a first iron source, a first phosphorus source, a first lithium source, and a first doped metal source, followed by a single sintering process (I) to obtain phosphate-based active particles. In the raw material components used to prepare the phosphate-based active particles in this application embodiment, the carbon source can reduce the risk of oxidation of the metal raw material components during sintering. The doped metal source can improve the electrochemical performance of the phosphate-based active material. A single sintering process causes the raw material components to react and generate phosphate-based active particle crystals.

[0047] In some possible implementations, the phosphate-based active particles can be lithium iron phosphate active particles. In the raw material composition for preparing lithium iron phosphate active particles, the molar ratio of iron, phosphorus and lithium is (0.85~1.15):(0.85~1.15):(0.85~1.15), specifically 1:(0.85~1.15):(0.85~1.15).

[0048] In some possible implementations, the conditions for a single sintering process I include sintering for 4 to 10 hours at a temperature of 700℃ to 800℃ in an inert atmosphere. The inert atmosphere can be nitrogen, argon, helium, etc. Under these sintering conditions, the first carbon source, the first iron source, the first phosphorus source, the first lithium source, and the first doped metal source react to generate phosphate-based active particle crystals. The temperature and sintering time are advantageous in ensuring both the quality of the phosphate-based active particle crystals and achieving a suitable particle size. For example, the sintering temperature can be any typical but non-limiting point value or a range between any two points, such as 700℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, or 800℃; the sintering time can be any typical but non-limiting point value or a range between any two points, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0049] In some possible implementations, the mass percentage of the first carbon source in the raw material composition for preparing phosphate-based active particles is 0.5% to 1%; under these conditions, the carbon source content can inhibit the oxidation of the metal raw material composition. For example, the mass percentage of the first carbon source in the raw material composition for preparing phosphate-based active particles can be any typical but non-limiting value such as 0.5%, 0.6%, 0.8%, or 1.0%, or a range between any two values.

[0050] In some possible implementations, the first carbon source is selected from at least one of glucose, sucrose, PEG (polyethylene glycol), and citric acid. Under high-temperature sintering conditions, these carbon sources can all decompose, volatilize, and deposit on the surface of the active particles to form a carbon coating layer.

[0051] In some possible implementations, the first doped metal source is selected from at least one of the following: manganese source, nickel source, cobalt source, magnesium source, and vanadium source.

[0052] In some possible implementations, the first iron source is selected from at least one of FeSO4, FeCO3, ferrous oxalate, FeCl2, and ferrous acetate.

[0053] In some possible implementations, the first phosphorus source is selected from at least one of: ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0054] In some possible implementations, the first lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium oxalate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium oxide, lithium citrate, and lithium tartrate.

[0055] The raw material components used in the above embodiments of this application all have a purity of ≥99%, and all of the above raw material components have good solubility and dispersibility, which is beneficial for the preparation of phosphate-based active particles.

[0056] In step S20 above:

[0057] In some possible implementations, the preparation of titanium-doped phosphate-based active particles includes the following steps: mixing a titanium source, a second carbon source, a second iron source, a second phosphorus source, a second lithium source, and a second doped metal source, followed by a first sintering treatment II, and then grinding to obtain titanium-doped phosphate-based active particles. In the raw material composition for preparing titanium-doped phosphate-based active particles in this application embodiment, titanium doping can reduce the crystal size of the phosphate-based active particles, thereby improving the conductivity and ion diffusion rate of the phosphate-based active particles. Therefore, titanium doping can both improve the electrochemical performance of phosphate-based active particles and make the particle size of titanium-doped phosphate-based active particles smaller than that of undoped phosphate-based active particles. The carbon source can reduce the risk of oxidation of the metal raw material components during sintering. The doped metal source can improve the electrochemical performance of the phosphate-based active material.

[0058] In some possible implementations, the conditions for the first sintering treatment II include sintering for 4 to 10 hours at an inert atmosphere at a temperature of 600℃ to 700℃. The inert atmosphere can be nitrogen, argon, helium, etc. Under these sintering conditions, the titanium source, the second carbon source, the second iron source, the second phosphorus source, the second lithium source, and the second doped metal source react to generate titanium-doped phosphate-based active particle crystals. The temperature of the first sintering treatment II is lower than that of the first sintering treatment I. Sintering at a relatively lower temperature ensures that the particle size of the titanium-doped phosphate-based active particles is smaller than that of the undoped phosphate-based active particles. This results in different particle sizes between the titanium-doped phosphate-based active particles and the undoped phosphate-based active particles, creating a particle size distribution and improving the electrochemical performance, such as the specific capacity, of the composite phosphate-based cathode material.

[0059] For example, the sintering temperature can be any typical but non-limiting point value or a range between any two points, such as 600℃, 620℃, 650℃, 670℃, 680℃, 700℃; the sintering time can be any typical but non-limiting point value or a range between any two points, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h.

[0060] In some possible implementations, the D50 particle size of the phosphate-based active particles is 500 nm to 700 nm. In other possible implementations, the D50 particle size of the titanium-doped phosphate-based active particles is 100 nm to 200 nm. In these cases, both the phosphate-based and titanium-doped phosphate-based active particles have small particle sizes and large active surface areas, which is beneficial for electron and ion migration and transport. Furthermore, the larger particle size of the phosphate-based active particles allows them to fill the gaps between the larger particles, creating a mutually filling gradation effect, increasing the compaction density of the composite phosphate-based cathode material, and thus improving its specific capacity.

[0061] For example, the D50 particle size of phosphate-based active particles can be any typical but non-limiting point value such as 500nm, 550nm, 600nm, 650nm, 700nm, or a range between any two points; the D50 particle size of titanium-doped phosphate-based active particles can be any typical but non-limiting point value such as 100nm, 120nm, 150nm, 180nm, 200nm, or a range between any two points.

[0062] In some possible implementations, the mass percentage of the second carbon source in the raw material composition for preparing titanium-doped phosphate-based active particles is 1%–2%, and the mass percentage of the titanium source is 0.5%–2%. Under these conditions, the carbon source content can suppress the oxidation of the metal raw material composition. The titanium source content can effectively reduce the crystal size of the phosphate-based active particles, thereby improving the conductivity and ion diffusion rate of the phosphate-based active particles. For example, in the raw material composition for preparing titanium-doped phosphate-based active particles, the mass percentage of the second carbon source can be any typical but non-limiting value such as 1%, 1.2%, 1.5%, or 2%, or a range between any two values; the mass percentage of the titanium source can be any typical but non-limiting value such as 0.5%, 1%, 1.5%, or 2%, or a range between any two values.

[0063] In some possible implementations, the titanium source is selected from at least one of: titanium dioxide, dibutyl phthalate, titanium tetrachloride, titanium trichloride, and ammonium fluorotitanate; during the sintering process, these titanium sources can be uniformly doped into the phosphate-based active particles, reducing the crystal size and improving the electrochemical performance of the material.

[0064] In some possible implementations, the second carbon source is selected from at least one of glucose, sucrose, PEG (polyethylene glycol), and citric acid. Under high-temperature sintering conditions, these carbon sources can all decompose, volatilize, and deposit on the surface of the active particles to form a carbon coating layer.

[0065] In some possible implementations, the second doped metal source is selected from at least one of manganese, nickel, cobalt, magnesium, and vanadium sources, specifically manganese source, in which case the active material is lithium manganese iron phosphate.

[0066] In some possible implementations, the second iron source is selected from at least one of FeSO4, FeCO3, ferrous oxalate, FeCl2, and ferrous acetate.

[0067] In some possible implementations, the second phosphorus source is selected from at least one of ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0068] In some possible implementations, the second lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium oxalate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium oxide, lithium citrate, and lithium tartrate.

[0069] The raw material components used in the above embodiments of this application all have a purity of ≥99%, and all of the above raw material components have good solubility and dispersibility, which is beneficial for preparing titanium-doped phosphate-based active particles.

[0070] In step S30 above:

[0071] In some possible implementations, the composite carbon source includes both organic and inorganic carbon sources. This application employs a composite carbon source, wherein the organic carbon source decomposes into highly graphitized carbon and is uniformly distributed on the surface of the active particles. The inorganic carbon source, as a flocculent continuous carbon source, can be distributed between different active particles, thereby constructing a conductive bridge between them. This results in better interparticle electron conduction between large and small active particles, improving the electronic and ionic conductivity of the composite phosphate-based cathode material.

[0072] In some possible implementations, the organic carbon source includes at least one of glucose, sucrose, PEG, and citric acid. These organic carbon sources decompose into highly graphitized carbon during sintering and uniformly coat the surface of the active particles.

[0073] In some possible implementations, the inorganic carbon source includes at least one of carbon black, carbon nanotubes, and graphene; these inorganic carbon sources have one-dimensional or two-dimensional continuous structures such as flocculent or sheet-like structures, and can be distributed between different active particles, thereby constructing a conductive bridge between different active particles.

[0074] In some possible implementations, the size of the inorganic carbon source is 200 nm to 400 nm. Under this size condition, the inorganic carbon source can form better conductive bridges between different active particles. For example, the size of the inorganic carbon source can be any typical but non-limiting point value such as 200 nm, 300 nm, or 400 nm, or a range between any two point values.

[0075] In some possible implementations, the mass ratio of organic carbon source to inorganic carbon source is (4~6):1. At this ratio, the organic and inorganic carbon sources exhibit better compatibility, forming a uniform and complete coating layer on the surface of the active particles and establishing stable conductive bridges between the particles. For example, the mass ratio of organic carbon source to inorganic carbon source can be any typical but non-limiting value such as 4:1, 5:1, or 6:1, or a range between any two values.

[0076] In some possible implementations, the heteroatom source includes at least one of boron, nitrogen, phosphorus, and fluorine sources. In this case, doping with impurity atoms such as boron may improve the performance of the carbon coating layer, such as enhancing the conductivity, cycle stability, and thermal stability of the carbon layer, thereby improving the electrochemical performance of the composite phosphate-based cathode material.

[0077] In some possible implementations, the boron source includes at least one of boron trioxide and boric acid; these boron sources can be uniformly doped into the carbon coating layer during solid-state sintering, thereby improving the electrical conductivity and other properties of the carbon coating layer.

[0078] In some possible implementations, the sintering conditions include: heating to 300℃~600℃ at a rate of 1℃ / min~10℃ / min and holding for 1~3 hours under an inert atmosphere, followed by sintering at 700℃~800℃ for 4~10 hours. The inert atmosphere can be nitrogen, argon, helium, etc. Under these solid-state sintering conditions, impurities such as water vapor, oxygen, and solvents in the solid mixture are first removed by sintering at a relatively low temperature, followed by sintering at a higher temperature. This optimizes the crystallization of both phosphate-based and titanium-doped phosphate-based active particles and allows the composite carbon source and impurity atom sources to form a uniform heteroatom-doped carbon coating layer on the surface of the active particles, resulting in a composite phosphate-based cathode material.

[0079] For example, the heating rate can be any typical but non-limiting point value or a range between any two points, such as 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min. The first-stage holding temperature can be any typical but non-limiting point value or a range between any two points, such as 300℃, 400℃, 500℃, and 600℃, and the holding time can be 1 hour, 2 hours, 3 hours, etc. The second-stage sintering temperature can be any typical but non-limiting point value or a range between any two points, such as 700℃, 720℃, 740℃, 760℃, 780℃, or 800℃. The sintering time can be any typical but non-limiting point value or a range between any two points, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, and 10 h.

[0080] In some possible implementations, the mass ratio of phosphate-based active particles, titanium-doped phosphate-based active particles, composite carbon source, and heteroatom source is 1:(1~4):(0.02~0.05):(0.005~0.1). Under this ratio, the composite carbon source can form a uniform and complete carbon coating layer on the surface of the active particles, while heteroatoms are uniformly doped into the carbon coating layer, improving the electrochemical performance of the composite phosphate-based cathode material. Furthermore, the ratio of phosphate-based active particles to titanium-doped phosphate-based active particles ensures that active particles of different sizes, morphologies, and densities fill each other within the composite phosphate-based cathode material, forming a sufficient gradation and improving the compaction density and specific capacity of the composite phosphate-based cathode material. For example, the mass ratio of phosphate-based active particles, titanium-doped phosphate-based active particles, composite carbon source and heteroatom source can be any typical but non-limiting ratio such as 1:1:0.02:0.005, 1:2:0.05:0.01, 1:4:0.05:0.1, etc.

[0081] Thirdly, embodiments of this application provide an application of a composite phosphate-based cathode material, which is applied to cathode sheets and / or secondary batteries.

[0082] The composite phosphate-based cathode material provided in this application has the characteristics of high compaction density and high specific capacity. It can be directly applied to cathode sheets or secondary batteries to improve the energy density, cycle life and other electrochemical performance of cathode sheets and secondary batteries.

[0083] In some possible implementations, a positive electrode is provided, comprising a current collector and a positive electrode active layer formed on the surface of the current collector, wherein the positive electrode active layer contains the aforementioned composite phosphate-based positive electrode material. The positive electrode of this application, due to the use of the aforementioned composite phosphate-based positive electrode material in the positive electrode active layer, improves the energy density, cycle life, and other electrochemical performance of the positive electrode.

[0084] In some possible implementations, the preparation of the positive electrode active layer includes the following steps: mixing the above-mentioned composite phosphate-based positive electrode material, conductive agent and binder to form an electrode slurry, coating the electrode slurry onto the current collector, and then preparing the positive electrode sheet through steps such as drying, rolling and die cutting.

[0085] In some possible implementations, the mass percentage of the composite phosphate-based cathode material in the cathode active layer of the cathode sheet is 90% to 95%. Specifically, the mass percentage of the composite phosphate-based cathode material in the cathode active material layer can be 90%, 91%, 92%, 93%, 94%, 95%, etc.

[0086] In some possible implementations, the current collector of the positive electrode includes, but is not limited to, any one of copper foil or aluminum foil.

[0087] In some possible implementations, the binder content in the positive electrode active material layer is 2wt% to 5wt%. In specific embodiments, the binder content can be typical but not limited to 2wt%, 3wt%, 4wt%, 5wt%, etc.

[0088] In some possible implementations, the binder includes one or more of the following: polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0089] In some possible implementations, the conductive agent content in the positive electrode active material layer is 1wt% to 5wt%. In specific embodiments, the conductive agent content can be a typical but not limited content such as 3wt%, 4wt%, or 5wt%.

[0090] In some possible implementations, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes.

[0091] In some possible implementations, a secondary battery is provided, which includes the aforementioned positive electrode. The secondary battery provided in this application, due to including the aforementioned positive electrode with excellent electrochemical performance such as high energy density and long cycle life, improves the energy density, cycle stability, and other electrochemical performance of the secondary battery.

[0092] This application does not specifically limit the negative electrode, electrolyte, separator, etc. in the secondary battery of the embodiments, and can be applied to any battery system.

[0093] In some possible implementations, the negative electrode active material of the secondary battery includes, but is not limited to, carbon materials such as graphite, soft carbon (e.g., coke), and hard carbon, or nitrides, tin-based oxides, tin alloys, and nano-anode materials. The current collector includes, but is not limited to, any one of copper foil and aluminum foil.

[0094] In some possible implementations, the steps for making the negative electrode sheet include: mixing the negative electrode active material with conductive agents such as conductive carbon black, binders such as carboxymethyl cellulose and styrene-butadiene rubber, and solvents such as water in a mass ratio of (80~99):(1~5):(2~10):100 to form a negative electrode mixed slurry, then degassing under vacuum, discharging the material, coating it on a coating machine, and obtaining the negative electrode sheet after rolling, slitting, and die-cutting.

[0095] In some possible implementations, the membrane is capable of blocking electrons while allowing ions to pass through. Exemplary membranes include, but are not limited to, at least one material selected from polypropylene fibers, polyacrylonitrile fibers, polyvinyl formal fibers, poly(ethylene glycol terephthalate), polyethylene terephthalate, polyamide fibers, and poly(p-phenylene terephthalamide).

[0096] In some possible implementations, the electrolyte comprises at least one soluble metal salt. In some specific embodiments, the metal salt includes LiClO4, LiBF4, LiPF6, LiAsF6, LiCF3SO3, LiTDI, Li[(CF3SO2)2N], Li[(FSO2)2N], Li[(C m F 2m+1 SO2)(C n F 2n+1 At least one of SO2(N)[m, n], where m and n are natural numbers. These electrolytic salts can ensure high ionic conductivity of the electrolyte and do not undergo harmful side reactions with electrode materials, electrolyte, diaphragm, etc., and have good chemical stability.

[0097] In some possible implementations, the secondary battery includes at least one of a battery cell, a battery module, and a battery pack.

[0098] In some possible implementations, the battery cell types include lithium-ion batteries, as well as novel batteries such as lithium-air batteries and lithium metal batteries.

[0099] In some possible implementations, the battery cells of this application can be assembled into a battery module. The battery module can contain multiple battery cells, the specific number of which can be adjusted according to the application and capacity of the battery module. Furthermore, the battery module may also include a housing with a receiving space in which multiple battery cells are received.

[0100] In one possible implementation, battery cells and / or battery modules can also be assembled into a battery pack, and the number of battery cells or battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0101] To enable those skilled in the art to clearly understand the above-described implementation details and operations, and to demonstrate the significant advancements in the performance of the composite phosphate-based cathode material, its preparation method, and its application in the embodiments of this application, the following examples illustrate the above technical solutions.

[0102] Example 1

[0103] A high-pressure, high-performance LiFePO4 composite cathode material is prepared by the following steps:

[0104] 1. Prepare raw materials by mixing 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate. Then add 0.8 g glucose as a carbon source and ball mill to obtain a precursor. Then heat treat it in a tube furnace and sinter at 750℃ for 8 h in N2 atmosphere to obtain coarse LFP with a particle size of 500nm~700nm.

[0105] 2. 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate were mixed to obtain raw materials. Then, 1.6 g glucose was added as a carbon source and 0.8 g titanium dioxide was added and ball-milled to obtain a precursor. The precursor was then heat-treated in a tube furnace and sintered at 650 °C for 8 h under a N2 atmosphere to obtain fine LFP. After sand milling, small-particle-size LFP with a particle size of 100 nm to 200 nm was obtained, in which titanium dioxide accounted for 1% of the total mass.

[0106] 3. 10 g of crude LFP and 10 g of small-particle-size LFP were graded, and 0.5 g of citric acid, 0.1 g of graphene and 0.03864 g of boron trioxide were added for wet ball milling, and then dried in a drying oven at 80℃ for 8 h.

[0107] 4. Under a nitrogen atmosphere, the solid mixture obtained in step (3) is heat-treated at 180°C for 30 min, then heated from 180°C to 350°C at a rate of 5°C / min and held for 2 h, then heated from 350°C to 780°C at a rate of 5°C / min and held for 8 h. After cooling, it is crushed to obtain high-compacted lithium iron phosphate cathode material.

[0108] Example 2

[0109] A high-pressure, high-performance LiFePO4 composite cathode material is prepared by the following steps:

[0110] 1. Prepare raw materials by mixing 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate. Then add 0.8 g glucose as a carbon source and ball mill to obtain a precursor. Then heat treat it in a tube furnace and sinter at 750℃ for 8 h in N2 atmosphere to obtain coarse LFP with a particle size of 500nm~700nm.

[0111] 2. 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate were mixed to obtain raw materials. Then, 1.6 g glucose was added as a carbon source and 0.8 g titanium dioxide was added and ball-milled to obtain a precursor. The precursor was then heat-treated in a tube furnace and sintered at 650 °C for 8 h under a N2 atmosphere to obtain fine LFP. After sand milling, small-particle-size LFP with a particle size of 100 nm to 200 nm was obtained, in which titanium dioxide accounted for 1% of the total mass.

[0112] 3. 6 g of crude LFP and 12 g of small-particle-size LFP were graded, and 0.5 g of citric acid, 0.1 g of graphene and 0.03864 g of boron trioxide were added for wet ball milling, and then dried in a drying oven at 80°C for 8 h.

[0113] 4. Under a nitrogen atmosphere, the solid mixture obtained in step (3) is heat-treated at 180°C for 30 min, then heated from 180°C to 350°C at a rate of 5°C / min and held for 2 h, then heated from 350°C to 780°C at a rate of 5°C / min and held for 8 h. After cooling, it is crushed to obtain high-compacted lithium iron phosphate cathode material.

[0114] Example 3

[0115] A high-pressure, high-performance LiFePO4 composite cathode material is prepared by the following steps:

[0116] 1. Prepare raw materials by mixing 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate. Then add 0.8 g glucose as a carbon source and ball mill to obtain a precursor. Then heat treat it in a tube furnace and sinter at 750℃ for 8 h in N2 atmosphere to obtain coarse LFP with a particle size of 500nm~700nm.

[0117] 2. 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate were mixed to obtain raw materials. Then, 1.6 g glucose was added as a carbon source and 0.8 g titanium dioxide was added and ball-milled to obtain a precursor. The precursor was then heat-treated in a tube furnace and sintered at 650 °C for 8 h under a N2 atmosphere to obtain fine LFP. After sand milling, small-particle-size LFP with a particle size of 100 nm to 200 nm was obtained, in which titanium dioxide accounted for 1% of the total mass.

[0118] 3. 5 g of crude LFP and 15 g of small-particle-size LFP were graded, and 0.5 g of citric acid, 0.1 g of graphene and 0.03864 g of boron trioxide were added for wet ball milling, and then dried in a drying oven at 80°C for 8 h.

[0119] 4. Under a nitrogen atmosphere, the solid mixture obtained in step (3) is heat-treated at 180°C for 30 min, then heated from 180°C to 350°C at a rate of 5°C / min and held for 2 h, then heated from 350°C to 780°C at a rate of 5°C / min and held for 8 h. After cooling, it is crushed to obtain high-compacted lithium iron phosphate cathode material.

[0120] Example 4

[0121] A high-pressure, high-performance LiFePO4 composite cathode material is prepared by the following steps:

[0122] 1. Prepare raw materials by mixing 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate. Then add 0.8 g glucose as a carbon source and ball mill to obtain a precursor. Then heat treat it in a tube furnace and sinter at 750℃ for 8 h in N2 atmosphere to obtain coarse LFP with a particle size of 500nm~700nm.

[0123] 2. 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate were mixed to obtain raw materials. Then, 1.6 g glucose was added as a carbon source and 0.8 g titanium dioxide was added and ball-milled to obtain a precursor. The precursor was then heat-treated in a tube furnace and sintered at 650 °C for 8 h under a N2 atmosphere to obtain fine LFP. After sand milling, small-particle-size LFP with a particle size of 100 nm to 200 nm was obtained, in which titanium dioxide accounted for 1% of the total mass.

[0124] 3. 4 g of crude LFP and 16 g of small-particle-size LFP were graded, and 0.5 g of citric acid, 0.1 g of graphene and 0.03864 g of boron trioxide were added for wet ball milling, and then dried in a drying oven at 80°C for 8 h.

[0125] 4. Under a nitrogen atmosphere, the solid mixture obtained in step (3) is heat-treated at 180°C for 30 min, then heated from 180°C to 350°C at a rate of 5°C / min and held for 2 h, then heated from 350°C to 780°C at a rate of 5°C / min and held for 8 h. After cooling, it is crushed to obtain high-compacted lithium iron phosphate cathode material.

[0126] Example 5

[0127] A high-pressure, high-performance LiFePO4 composite cathode material differs from Example 1 in that: in step 2, the amount of titanium dioxide added is 0.5%, and the particle size of the resulting fine LFP is 500 nm to 600 nm.

[0128] Example 6

[0129] A high-pressure, high-performance LiFePO4 composite cathode material differs from Example 1 in that: in step 2, the amount of titanium dioxide added is 1.5%, and the particle size of the resulting fine LFP is 200nm~300nm.

[0130] Example 7

[0131] A high-pressure, high-performance LiFePO4 composite cathode material differs from Example 1 in that: in step 2, the amount of titanium dioxide added is 2%, and the particle size of the resulting fine LFP is less than 100 nm.

[0132] Example 8

[0133] A high-pressure, high-performance LiFePO4 composite cathode material differs from Example 1 in that, in step 3, boron trioxide is replaced with melamine.

[0134] Comparative Example 1

[0135] A LiFePO4 composite cathode material is prepared by the following steps:

[0136] 1. Prepare raw materials by mixing 10.5 g of lithium carbonate, 40 g of FeSO4 and 30 g of ammonium dihydrogen phosphate. Then add 0.8 g of glucose as a carbon source and ball mill to obtain a precursor. Then heat treat it in a tube furnace and sinter at 750℃ for 8 h in N2 atmosphere to obtain lithium iron phosphate.

[0137] 2. Transfer 2.4 g of glucose and 60 g of lithium iron phosphate to a 500 mL ball mill jar, add 50 g of ethanol as solvent, and wet ball mill at 450 r / min for 4 h. Transfer to a drying oven and dry at 80℃ for 8 h to obtain a solid lithium iron phosphate mixture.

[0138] 3. Under a nitrogen atmosphere, the solid mixture obtained in step (3) is heat-treated at 180°C for 30 min, then heated from 180°C to 350°C at a rate of 5°C / min and held for 2 h, then heated from 350°C to 780°C at a rate of 5°C / min and held for 8 h. After cooling, it is crushed to obtain high-compacted lithium iron phosphate cathode material.

[0139] Comparative Example 2

[0140] A LiFePO4 composite cathode material was prepared in the same way as in Example 1, except that titanium dioxide was not added in step 2. After grinding and refining, the particle size of the fine LFP obtained was 300nm~500nm.

[0141] Comparative Example 3

[0142] A LiFePO4 composite cathode material is prepared in the same way as in Example 2, except that graphene and boron trioxide are not added in step 3.

[0143] Comparative Example 4

[0144] A LiFePO4 composite cathode material, the preparation of which includes the following steps:

[0145] 1. Prepare raw materials by mixing 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate. Then add 0.8 g glucose as a carbon source and ball mill to obtain a precursor. Then heat treat it in a tube furnace and sinter at 750℃ for 8 h in N2 atmosphere to obtain coarse LFP with a particle size of 500nm~700nm.

[0146] 2. 10.5 g lithium carbonate, 40 g FeSO4 and 30 g ammonium dihydrogen phosphate were mixed to obtain raw materials. Then, 1.6 g glucose was added as a carbon source and 0.8 g titanium dioxide was ball-milled to obtain a precursor. The precursor was then heat-treated in a tube furnace and sintered at 650℃ for 8 h in a N2 atmosphere to obtain fine LFP. After sand milling, small-particle-size LFP with a particle size of 100 nm to 200 nm was obtained, in which titanium dioxide accounted for 1% of the total mass.

[0147] 3. Crude LFP was wet-milled with 0.5 g of citric acid, 0.1 g of graphene, and 0.03864 g of boron trioxide, and then dried in a drying oven at 80℃ for 8 h. Under a nitrogen atmosphere, it was heat-treated at 180℃ for 30 min, then heated from 180℃ to 350℃ at a rate of 5℃ / min and held at that temperature for 2 h. Then, it was heated from 350℃ to 780℃ at a rate of 5℃ / min and held at that temperature for 8 h. After cooling, the crude LFP was composited.

[0148] 4. Fine LFP was wet-milled with 0.5 g of citric acid, 0.1 g of graphene, and 0.03864 g of boron trioxide, and then dried in a drying oven at 80°C for 8 h. Under a nitrogen atmosphere, it was heat-treated at 180°C for 30 min, then heated from 180°C to 350°C at a rate of 5°C / min and held at that temperature for 2 h. The temperature was then increased from 350°C to 780°C at a rate of 5°C / min and held at that temperature for 8 h. After cooling, the fine LFP was composited.

[0149] 5. Mix the composite coarse LFP and composite fine LFP at a mass ratio of 1:1 to obtain the composite lithium iron phosphate cathode material.

[0150] To verify the progressiveness of the embodiments of this application, the following performance tests were performed on the above embodiments and comparative examples:

[0151] 1. The morphology of the composite phosphate-based cathode materials prepared in Example 1 and Comparative Example 1 was observed using scanning electron microscopy (SEM). The SEM image of the composite phosphate-based cathode material in Example 1 is shown in Figure 2, and the SEM image of the composite phosphate-based cathode material in Comparative Example 1 is shown in Figure 3. It can be seen that the composite phosphate-based cathode materials prepared in this application include particles of different sizes, morphologies, and varying degrees of looseness and density, which can better improve the compaction density of the composite phosphate-based cathode material, thereby increasing its specific capacity.

[0152] 2. The compaction density of the composite phosphate-based cathode materials prepared in the above embodiments and comparative examples was tested. The test conditions were as follows: the compaction density was measured under a pressure of 3T, according to GB / T 24533-2009.

[0153] 3. The composite phosphate-based cathode materials prepared in the above embodiments and comparative examples are applied to lithium-ion batteries, and their electrochemical performance is tested. The preparation method of the lithium-ion battery includes the following steps:

[0154] ① The preparation of the positive electrode is as follows: The composite phosphate-based positive electrode material prepared according to the above embodiment or comparative example by mass ratio: SP:PVDF:NMP=93.5:2.5:4:100 was mixed evenly in a ball mill for 2 h to obtain a positive electrode slurry. The prepared positive electrode slurry was added to an aluminum foil and evenly scraped with a scraper. After the positive electrode was dried at 130℃, it was rolled under a pressure of 10Mpa to obtain a rolled electrode. A Φ15mm round piece was cut from the middle area and weighed.

[0155] ② The battery assembly process is as follows: The prepared positive electrode is attached to the positive electrode metal shell with conductive adhesive, a lithium metal sheet is used as the electrode, a Celgard 2400 microporous membrane is used as the separator, and a 1.0 mol / L LiPF6 solution is used as the electrolyte. The solvent of the electrolyte is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The battery is assembled into a button cell in a glove box.

[0156] The electrochemical performance of the above coin cells was tested using a LAND electrochemical tester. The charging termination voltage was 3.75 V and the discharge termination voltage was 2.0 V.

[0157] The lithium-ion batteries using the composite phosphate-based cathode materials prepared in the above embodiments and comparative examples were subjected to charge-discharge tests at 0.1 C and 1 C rates at room temperature (25°C).

[0158] The test results are shown in Table 1 below:

[0159] Table 1

[0160] Number | Compacted Density (g / cm³) | 0.1C Discharge Capacity (25℃) (mAh / g) | 1C Discharge Capacity (25℃) (mAh / g) | Example 1 | 2.70 | 5158.6 | 146.7 | Example 2 | 2.74 | 5159.3 | 146.9 | Example 3 | 2.72 | 9158.5 | 145.8 | Example 4 | 2.71 | 1157.5 | 145.1 | Example 5 | 2.65 | 3154. Example 6141.2 Example 62.628 156.3 142.6 Example 7 2.601 157.4 144.5 Example 8 2.669 158.4 144.8 Comparative Example 1 2.532 148.6 132.2 Comparative Example 2 2.594 151.2 135.8 Comparative Example 3 2.678 152.3 140.4 Comparative Example 4 2.683 154.4 141.9

[0161] The test results above show that the composite phosphate-based cathode material prepared in this application, due to its gradation of particles with different morphologies, sizes, and densities, can better improve the compaction density and specific capacity. Furthermore, the doping of titanium in the core and the doping of heteroatoms such as boron in the carbon coating layer can improve the electrochemical performance of the composite phosphate-based cathode material, including capacity and cycle stability. Therefore, the compaction density of the composite phosphate-based cathode material in this application is not less than 2.6 g / cm³. 3 The applied batteries exhibit better 0.1 C and 1 C rate charge / discharge performance.

[0162] Comparing Examples 1 to 4, it can be seen that large-diameter phosphate-based active particles and small-diameter titanium-doped phosphate-based active particles have good gradation effects in the mass ratio range of 1:(1~4), which improves the compaction density and electrochemical performance of the composite phosphate-based cathode material.

[0163] Comparing Examples 1 and 5-8, it is evident that when the titanium source content is 1%-1.5% in Examples 1 and 6, the composite phosphate-based cathode material exhibits better 0.1 C and 1 C rate charge-discharge performance after being applied to the battery. Doping with heteroatoms such as boron and nitrogen can improve the compaction density and electrochemical performance of the composite phosphate-based cathode material.

[0164] In contrast, Comparative Example 1, which is a composite lithium iron phosphate cathode material coated only with carbon material, Comparative Example 2, which is a composite lithium iron phosphate cathode material without titanium source doping, Comparative Example 3, which has no boron atoms in the carbon coating layer and no inorganic carbon source added to form conductive bridges between particles, and Comparative Example 4, which directly prepares particles of different sizes and then mixes them, all reduced the compaction density and specific capacity of the composite lithium iron phosphate cathode material.

[0165] The above are merely optional embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A composite phosphate-based cathode material, characterized in that, The cathode material comprises a plurality of composite phosphate-based cathode particles with a particle size distribution and doped composite phosphate-based cathode particles. The composite phosphate-based cathode particles include a phosphate-based active core and a heteroatom-doped carbon coating layer I. The doped composite phosphate-based cathode particles include a titanium-doped phosphate-based active core and a heteroatom-doped carbon coating layer II. The particle size of the composite phosphate-based cathode particles is larger than that of the doped composite phosphate-based cathode particles. An inorganic carbon source is distributed between the composite phosphate-based cathode particles and the doped composite phosphate-based cathode particles.

2. The composite phosphate-based cathode material as described in claim 1, characterized in that, The D50 particle size of the composite phosphate-based cathode particles is 500nm~700nm; And / or, the D50 particle size of the doped composite phosphate-based cathode particles is 100nm~200nm; And / or, the size of the inorganic carbon source is 200 nm to 400 nm; And / or, the inorganic carbon source has a one-dimensional or two-dimensional continuous structure, forming a conductive bridge between the composite phosphate-based cathode particles and the doped composite phosphate-based cathode particles.

3. The composite phosphate-based cathode material as described in claim 1, characterized in that, The mass ratio of the composite phosphate-based cathode particles to the doped composite phosphate-based cathode particles is 1:(1~4).

4. The composite phosphate-based cathode material as described in claim 1, characterized in that, In the titanium-doped phosphate-based active core, the mass percentage of titanium doping is 0.1% to 0.8%. And / or, the heteroatom includes at least one of boron, nitrogen, phosphorus, and fluorine atoms; And / or, in the heteroatom-doped carbon coating layer I and the heteroatom-doped carbon coating layer II, the heteroatom doping mass percentage content is independently 2%~5%.

5. The composite phosphate-based cathode material as described in claim 1, characterized in that, In the composite phosphate-based cathode particles, the mass percentage of the heteroatom-doped carbon coating layer I is 0.5% to 1%. And / or, in the doped composite phosphate-based cathode particles, the mass percentage of the heteroatom-doped carbon coating layer II is 1% to 2%.

6. The composite phosphate-based cathode material according to any one of claims 3 to 5, characterized in that, The compaction density of the composite phosphate-based cathode material is not less than 2.7 g / cm³. 3 .

7. A method for preparing a composite phosphate-based cathode material, characterized in that, Includes the following steps: Phosphate-based active particles were prepared by a single sintering process. Titanium-doped phosphate-based active particles are prepared by a single sintering process, wherein the particle size of the phosphate-based active particles is larger than that of the titanium-doped phosphate-based active particles. The phosphate-based active particles and the titanium-doped phosphate-based active particles are mixed with a composite carbon source and a heteroatom source, and then sintered to obtain a composite phosphate-based cathode material; wherein the composite carbon source includes an organic carbon source and an inorganic carbon source.

8. The method for preparing the composite phosphate-based cathode material as described in claim 7, characterized in that, The preparation of the phosphate-based active particles includes the following steps: mixing and treating a first carbon source, a first iron source, a first phosphorus source, a first lithium source and a first doped metal source, and then performing a sintering treatment I to obtain the phosphate-based active particles. And / or, the preparation of the titanium-doped phosphate-based active particles includes the following steps: mixing a titanium source, a second carbon source, a second iron source, a second phosphorus source, a second lithium source, and a second doped metal source, followed by a first sintering treatment II, and then grinding to obtain the titanium-doped phosphate-based active particles.

9. The method for preparing the composite phosphate-based cathode material as described in claim 8, characterized in that, The conditions for the first sintering treatment I include: sintering for 4 to 10 hours in an inert atmosphere at a temperature of 700℃ to 800℃. And / or, the conditions for the first sintering treatment II include: sintering for 4 to 10 hours in an inert atmosphere at a temperature of 600°C to 700°C.

10. The method for preparing the composite phosphate-based cathode material as described in claim 8, characterized in that, The D50 particle size of the phosphate-based active particles is 500 nm to 700 nm. And / or, the D50 particle size of the titanium-doped phosphate-based active particles is 100 nm to 200 nm.

11. The method for preparing the composite phosphate-based cathode material as described in claim 8, characterized in that, In the raw material components for preparing the phosphate-based active particles, the mass percentage of the first carbon source is 0.5% to 1%. And / or, in the raw material composition for preparing the titanium-doped phosphate-based active particles, the mass percentage of the second carbon source is 1% to 2%, and the mass percentage of the titanium source is 0.5% to 2%.

12. The method for preparing the composite phosphate-based cathode material according to any one of claims 7 to 11, characterized in that, The heteroatom source includes at least one of the following: boron source, nitrogen source, phosphorus source, and fluorine source.

13. The method for preparing the composite phosphate-based cathode material according to any one of claims 7 to 11, characterized in that, The sintering conditions include: heating to 300℃~600℃ at a rate of 1℃ / min~10℃ / min under an inert atmosphere, holding for 1~3 hours, and then heating to 700℃~800℃ for 4~10 hours.

14. The method for preparing the composite phosphate-based cathode material according to any one of claims 7 to 11, characterized in that, The mass ratio of the phosphate-based active particles, the titanium-doped phosphate-based active particles, the composite carbon source, and the heteroatom source is 1:(1~4):(0.02~0.05):(0.005~0.1).

15. The method for preparing the composite phosphate-based cathode material as described in claim 12, characterized in that, The organic carbon source includes at least one of glucose, sucrose, PEG, and citric acid. And / or, the inorganic carbon source includes at least one of carbon black, carbon nanotubes, and graphene.

16. The method for preparing the composite phosphate-based cathode material as described in claim 12, characterized in that, The inorganic carbon source has a size of 200 nm to 400 nm. And / or, the mass ratio of the organic carbon source to the inorganic carbon source is (4~6):

1.

17. An application of a composite phosphate-based cathode material, characterized in that, The composite phosphate-based cathode material as described in any one of claims 1 to 6 or the composite phosphate-based cathode material prepared by the method described in any one of claims 7 to 16 is applied to cathode sheets and / or secondary batteries.

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