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

Abstract

Disclosed in the present application are a doped phosphate-based positive electrode material, and a preparation method therefor and the use thereof. The doped phosphate-based positive electrode material comprises a phosphate-based active material and a doping metal element, which is doped in the crystal structure of the phosphate-based active material. Under a pressure of 100-500 MPa, the doped phosphate-based positive electrode material has a maximum particle deformation quantity of less than 50% and a reversible particle deformation quantity of less than 10%. By doping the metal element in the crystal structure of the phosphate-based active material, the structure of the doped phosphate-based positive electrode material is optimized, the structural stability of the doped phosphate-based positive electrode material is improved, the compression modulus of the positive electrode material is improved, and the chemical components and electronic structure of the surface of the positive electrode material can also be changed, such that the doped phosphate-based positive electrode material has the characteristics of a relatively high ionic conductivity, electronic conductivity, gram volume, cycling stability, etc.

Description

Phosphate-doped cathode materials, their preparation methods and applications

[0001] This application claims priority to Chinese Patent Application No. 202411500865.4, filed on October 25, 2024, entitled "Phosphate-doped 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 technology, and in particular to a doped phosphate-based cathode material, its preparation method, and its application. Background Technology

[0003] The statements herein provide background information relevant to this application only and do not necessarily constitute prior art. With the gradual promotion of clean energy, lithium-ion batteries are widely used in new energy vehicles, energy storage power stations, and other fields due to their advantages such as high energy density, long cycle life, and environmental friendliness. Among these, the cathode material is a key component of lithium-ion batteries, and its performance directly determines the overall performance of the battery. Lithium iron phosphate is a commonly used cathode material for lithium-ion batteries, but its low electronic conductivity, small lithium-ion diffusion coefficient, and low compaction density limit its application in the field of power batteries.

[0004] To address these issues, metal doping is employed to improve the electronic conductivity and lithium-ion diffusion coefficient of lithium iron phosphate (LFP). For example, high-valence elements such as cobalt, nickel, and manganese are incorporated into the LFP crystal lattice. However, while these elements improve some performance characteristics of LFP, they also sacrifice others. For instance, manganese doping can increase the operating voltage and energy density of LFP, but it significantly reduces electronic conductivity.

[0005] Therefore, preparing phosphate-based cathode materials with both high electronic conductivity and lithium-ion diffusion coefficient, as well as stable structure, and improving their overall performance, is of great significance for promoting the development of lithium-ion batteries.

[0006] Application content

[0007] One of the objectives of this application is to provide a doped phosphate-based cathode material, its preparation method, and its application, aiming to solve to some extent the problems of low electronic conductivity and small ion diffusion coefficient of existing phosphate-based cathode materials.

[0008] The technical solution adopted in the embodiments of this application is:

[0009] In a first aspect, this application provides a doped phosphate-based cathode material, comprising a phosphate-based active material and a doped metal element in the crystal structure of the phosphate-based active material; the doped phosphate-based cathode material, under a pressure of 100 MPa to 500 MPa, has a maximum particle deformation of less than 50% and a reversible deformation of less than 10%.

[0010] Secondly, this application provides a method for preparing a phosphate-doped cathode material, comprising the following steps:

[0011] Obtain raw material components and doped metal source for preparing phosphate-based active materials, and prepare a precursor mixture by liquid phase method using the raw material components and the doped metal source;

[0012] In an inert atmosphere, the precursor mixture is sintered once, then pulverized and sintered a second time to obtain a phosphate-doped cathode material. The phosphate-doped cathode material has a maximum particle deformation of less than 50% and a reversible deformation of less than 10% under a pressure of 100MPa to 500MPa.

[0013] Thirdly, this application provides an application of a doped phosphate-based cathode material, which is used in cathode sheets and / or secondary batteries.

[0014] The first aspect of this application provides a doped phosphate-based cathode material that optimizes structural stability by doping the crystal structure of the phosphate-based active material with metal elements. This results in the doped phosphate-based cathode material exhibiting a maximum particle deformation of less than 50% and a reversible deformation of less than 10% under pressures of 100 MPa to 500 MPa. This improves the compressive modulus of the cathode material. A larger reversible deformation is more beneficial in mitigating the mechanical stress caused by volume expansion during lithium delithiation and lithium insertion, increasing reversibility, and thus improving the cycle performance and durability of the battery, enhancing its safety in battery applications. It also helps to improve the stability of ion and electron transport in the cathode material, giving it a longer cycle life. Furthermore, by doping with metal elements, while improving the compressive modulus of the cathode material, it is also possible to change the chemical composition and electronic structure of the cathode material surface, improving the ionic and electronic conductivity of the material, thereby increasing the energy density and power density of the battery.

[0015] The method for preparing doped phosphate-based cathode materials provided in the second aspect of this application involves preparing a precursor mixture of raw material components and doping metal sources, including titanium and molybdenum sources, using a liquid-phase method. Then, in an inert atmosphere, the mixture undergoes a first sintering, pulverization, and a second sintering process sequentially to incorporate the doping metal elements into the crystal lattice of the phosphate-based active material, thereby obtaining the doped phosphate-based cathode material. In the liquid-phase system used, the raw materials are thoroughly mixed, and the stoichiometry is controllable, which is beneficial for the incorporation of the doping metal elements into the crystal lattice of the phosphate-based active material. The two sintering and pulverization processes improve sintering efficiency and control material particle size, thereby enhancing uniformity. The preparation process of this application is simple and suitable for large-scale industrial production and application. The prepared doped phosphate-based cathode material optimizes the structure of the doped phosphate-based cathode material by doping the crystal structure of the phosphate-based active material with metal elements, thereby improving the structural stability and compressive modulus of the doped phosphate-based cathode material. At the same time, it can change the chemical composition and electronic structure of the cathode material surface, so that the doped phosphate-based cathode material has high ionic conductivity, electronic conductivity, specific capacity, cycle stability and other properties.

[0016] The phosphate-doped cathode material provided in the third aspect of this application has high electronic conductivity, ion diffusion coefficient, crystal structure stability, charge-discharge cycle stability, capacity and other characteristics. It can be directly applied to cathode sheets or to secondary batteries to improve the charge-discharge specific energy, discharge plateau, cycle capacity retention rate and rate performance of cathode sheets and secondary batteries, and comprehensively improve the dynamic performance and cycle stability of 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 doped phosphate-based cathode material provided in the embodiments of this application;

[0019] Figure 2 is a SEM image of the doped phosphate-based cathode material provided in Embodiments 1, 2, Comparative Example 1 and Comparative Example 2 of this application;

[0020] Figure 3 is the XRD pattern of the doped phosphate-based cathode material provided in Examples 1, 2, 1, and 2 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] The term "compression modulus," also known as the compressive modulus or unconfined deformation modulus, describes the ratio of vertical compressive stress to total vertical strain in a phosphate-doped cathode material when it is completely indeformable laterally. It is denoted by the symbol Es. It is an important indicator of the compressibility of phosphate-doped cathode materials.

[0024] To illustrate the technical solutions described in this application, the following detailed description is provided in conjunction with specific drawings and embodiments.

[0025] The first aspect of this application provides a doped phosphate-based cathode material, comprising a phosphate-based active material and a doped metal element in the crystal structure of the phosphate-based active material; the doped phosphate-based cathode material, under a pressure of 100 MPa to 500 MPa, has a maximum particle deformation of less than 50% and a reversible deformation of less than 10%.

[0026] The first aspect of this application provides a doped phosphate-based cathode material. By doping the crystal structure of the phosphate-based active material with metal elements, the structure of the doped phosphate-based cathode material is optimized, and the stability of the crystal structure is improved. This results in the maximum deformation of the particles being less than 50% and the reversible deformation being less than 10% under pressures of 100 MPa to 500 MPa. This significantly improves the structural stability and compressive modulus of the doped phosphate-based cathode material. A higher compressive modulus results in smaller irreversible and maximum deformations; the difference between irreversible and maximum deformations represents the reversible deformation. Within a certain range, a larger reversible deformation is better. A larger reversible deformation helps alleviate the mechanical stress caused by volume expansion during lithium delithiation and lithium insertion, increasing reversibility and thus improving the cycle performance and durability of the battery, enhancing its safety in battery applications, and also contributing to improved stability of ion and electron transport in the cathode material, resulting in higher compaction density, stronger anti-polarization ability, and longer cycle life. Furthermore, by doping with metal elements, the compressive modulus of the cathode material can be improved, while the chemical composition and electronic structure of the cathode material surface can also be changed, thereby improving the ionic and electronic conductivity of the material, thus increasing the energy density and power density of the battery, and extending the cycle life and anti-interference ability of the battery.

[0027] For example, the pressure condition can be a typical but non-limiting arbitrary point value or an interval between any two points, such as 100MPa, 200MPa, 300MPa, 400MPa, 500MPa, etc. The maximum deformation of a single particle of the phosphate-doped cathode material can be a typical but non-limiting arbitrary point value or an interval between any two points, such as 49%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc. The reversible deformation can be a typical but non-limiting arbitrary point value or an interval between any two points, such as 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1.5%, 1%, 0.5%, 0.3%, etc.

[0028] In some possible implementations, under pressures of 100 MPa to 400 MPa, the maximum deformation of the particles in the doped phosphate-based cathode material is 20% to 30%, and the reversible deformation is 1.5% to 5%. In this case, the doped phosphate-based cathode material exhibits better lattice stability and compressive modulus. A higher compressive modulus results in smaller irreversible and maximum deformations; the difference between irreversible and maximum deformations represents the amount of reversible deformation. Within a certain range, a larger reversible deformation is better, as it helps alleviate the mechanical stress caused by volume expansion during lithium delithiation and lithium insertion, increasing reversibility. This is more conducive to improving the cycle performance and durability of the battery, enhancing its safety in battery applications, and also helps improve the stability of ion and electron transport in the cathode material, resulting in higher compaction density, stronger anti-polarization ability, and longer cycle life.

[0029] In some possible implementations, the doping metal element includes at least one of V (vanadium), Ti (titanium), Mo (molybdenum), and Mg (magnesium). Doping these metal elements into the crystal structure of phosphate-based active materials can improve the structural stability of the doped phosphate-based cathode material, improve the compressive modulus of the cathode material, and change the chemical composition and electronic structure of the cathode material surface, thereby improving the ionic and electronic conductivity of the material.

[0030] In some possible implementations, the phosphate-based active material contains iron, with the doping metal element incorporated into the iron sites of the phosphate-based active material. In this case, the electrochemical performance and structural stability of the phosphate-based active material can be better optimized.

[0031] In some possible implementations, the doping metal elements include titanium and molybdenum. In some possible implementations, the doping metal elements, including titanium and molybdenum, are doped into the iron sites of the phosphate-based active material. In this case, the iron sites are simultaneously doped with titanium and molybdenum. Titanium doping at the iron sites can reduce the cell volume of the phosphate-based active material, shorten the lithium-ion transport path, thereby improving the electronic conductivity and ion diffusion rate of the doped phosphate-based cathode material, improving battery polarization, and increasing energy efficiency. Molybdenum doping at the iron sites can improve the isotropy of the phosphate-based cathode material, improve the compressive modulus and lattice stability, resulting in more spherical particles, stronger reversibility, and better mitigation of mechanical stress caused by volume expansion during lithium delithiation and lithium insertion, thereby improving the battery's energy density and cycle stability. Through the synergistic effect of the doped titanium and molybdenum, the band structure and electronic density of states of the cathode material can be significantly affected, improving ion and electron transport rates, improving lattice stability, material isotropy and reversibility, and comprehensively enhancing the electrochemical performance of the phosphate-based cathode material.

[0032] In some possible implementations, the molar ratio of iron, titanium, and molybdenum at the iron sites in the crystal structure of the doped phosphate-based cathode material is (0.94~0.98):(0.01~0.04):(0.01~0.02). In this case, the content of titanium and molybdenum doped into the iron sites of the phosphate-based active material sufficiently ensures the improvement of the conductivity and ion diffusion rate of the doped phosphate-based cathode material, as well as the improvement of its isotropy, compressive modulus, and lattice stability. For example, in the iron sites of the crystal structure of the phosphate-doped cathode material, the molar ratio of iron, titanium, and molybdenum can be any typical but non-limiting point value ratio or a range between any two point value ratios, such as 0.98:0.01:0.01, 0.97:0.02:0.01, 0.97:0.01:0.02, 0.96:0.01:0.03, 0.96:0.02:0.02, 0.95:0.01:0.04, 0.95:0.02:0.03, 0.94:0.02:0.04.

[0033] In some possible implementations, in phosphate-doped cathode materials, the particle size D10 is 0.20 μm to 0.80 μm, the particle size D50 is 0.8 μm to 3.2 μm, the particle size D90 is 2 μm to 11 μm, and the particle size D99 is 3 μm to 20 μm. For example, the particle size D10 can be typical values ​​such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.61 μm, 0.618 μm, 0.62 μm, 0.63 μm, 0.64 μm, 0.65 μm, 0.66 μm, 0.669 μm, 0.67 μm, 0.68 μm, 0.69 μm, 0.70 μm, and 0.80 μm. The particle size D50 can be any non-restricted point value or an interval between any two point values; typical but non-restricted point values ​​or intervals between any two point values, such as 0.8μm, 1μm, 1.5μm, 1.6μm, 1.67μm, 1.7μm, 1.8μm, 1.87μm, 1.9μm, 2.0μm, 2.5μm, 3μm, 3.2μm, etc.; the particle size D90 can be... Typical but non-restrictive arbitrary point values ​​or intervals between any two point values, such as 2μm, 5μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6.0μm, 8μm, 10μm, and 11μm; particle size D99 can be 3μm, 5μm, 8μm, 10μm, 11μm, etc. Typical but non-restrictive arbitrary point values ​​or intervals between any two point values, such as 11.2μm, 11.3μm, 11.5μm, 11.7μm, 11.9μm, 12.0μm, 12.1μm, 12.3μm, 12.5μm, 12.6μm, 12.7μm, 12.8μm, 12.9μm, 13.0μm, 15μm, 18μm, and 20μm.

[0034] In some possible implementations, the particle size range of the doped phosphate-based cathode material is 1 to 6. The particle size range is calculated using the formula (D90-D10) / D50. A smaller particle size range indicates more uniform particle size and higher dimensional consistency. For example, in the doped phosphate-based cathode material, the particle size range can be any typical but not limiting point value such as 1, 2, 3, 4, 5, or 6, or a range between any two points.

[0035] The phosphate-doped cathode materials described in the above embodiments of this application utilize smaller particles to shorten the diffusion path of lithium ions within the cathode material, facilitating lithium ion insertion and extraction, thereby improving the battery's rate performance, i.e., its performance at high charge and discharge rates. Furthermore, smaller particles increase the specific surface area of ​​the active material, increasing the number of active sites for electrochemical reactions, thus enhancing the battery's electrochemical reaction performance. Appropriate particle size distribution helps optimize the battery's energy density, enabling the battery to maintain both high energy output and good cycle stability. Therefore, in the phosphate-doped cathode materials, the particle size D10 is 0.20 μm to 0.80 μm, the particle size D50 is 0.8 μm to 3.2 μm, the particle size D90 is 2 μm to 11 μm, and the particle size D99 is 3 μm to 20 μm. For example, when the particle size range (D90-D10) / D50 is 1 to 6, the cathode material can meet the requirements of battery performance, manufacturing process and safety, and maximize cost-effectiveness.

[0036] In some possible implementations, the outer surface of the phosphate-doped cathode material particles also has a carbon coating layer. In this case, the carbon coating layer can not only improve the structural stability of the phosphate-doped cathode material, but also improve its conductivity, cycle stability, and the stability of the cathode material-electrolyte interface, and mitigate stress caused by volume changes.

[0037] In some possible implementations, the carbon coating thickness in the doped phosphate-based cathode material is 2 nm to 10 nm. Specifically, the thickness of the carbon coating can be any typical but not limiting value, such as 2 nm, 4 nm, 5 nm, 8 nm, or 10 nm, or a range between any two values. In this case, the carbon coating is relatively thin and uniform, which is beneficial for improving the structural and cycle stability, electronic conductivity, ion diffusion coefficient, specific capacity, and other electrochemical properties of the doped phosphate-based cathode material.

[0038] In some possible implementations, the carbon coating content in the doped phosphate-based cathode material is 0.8% to 2% by mass. Specifically, it can be any typical but non-limiting value, such as 0.8%, 1%, 1.2%, 1.5%, 1.8%, or 2%, or a range between any two values. In this case, the carbon coating content ensures that the carbon material can form a uniform and stable carbon coating structure on the surface of the doped phosphate-based cathode material, which is beneficial to improving the structural and cycle stability, electronic conductivity, ion diffusion coefficient, specific capacity, and other electrochemical properties of the doped phosphate-based cathode material.

[0039] In some possible implementations, phosphate-doped cathode materials include lithium iron phosphate (LFP). In this case, titanium and molybdenum are simultaneously doped into the iron sites of the LFP, which can significantly improve the ionic and electronic conductivity of the LFP, increase the ion diffusion coefficient, and simultaneously improve the lattice stability, cycle stability, energy density, and other properties of the material.

[0040] In some possible implementations, the molar ratio of lithium, iron, titanium, molybdenum, and phosphorus in the doped lithium iron phosphate is (0.98~1.05):(0.94~0.98):(0.01~0.04):(0.01~0.02):(0.98~1.05). In this case, the doped phosphate-based cathode material simultaneously exhibits excellent ionic conductivity, electronic conductivity, ion diffusion coefficient, cycle stability, and energy density.

[0041] The phosphate-doped cathode material described in the above embodiments of this application can be prepared by the methods described in the following embodiments.

[0042] Secondly, embodiments of this application provide a method for preparing a phosphate-doped cathode material, as shown in Figure 1, including the following steps:

[0043] S10. Obtain the raw material components and doping metal source for preparing phosphate-based active materials, and prepare a precursor mixture of the raw material components and doping metal source by liquid phase method; wherein, the doping metal source includes titanium source and molybdenum source;

[0044] S20. In an inert atmosphere, the precursor mixture is sintered once, then crushed and sintered a second time to obtain a phosphate-doped cathode material; the phosphate-doped cathode material has a maximum particle deformation of less than 50% and a reversible deformation of less than 10% under a pressure of 100MPa~500MPa.

[0045] The method for preparing doped phosphate-based cathode materials in this application involves mixing raw material components with dopant metal sources, including titanium and molybdenum sources, using a liquid-phase method to form a precursor mixture. Then, in an inert atmosphere, the mixture undergoes a first sintering, pulverization, and a second sintering process to incorporate the dopant metal elements into the crystal lattice of the phosphate-based active material, resulting in the doped phosphate-based cathode material. The liquid-phase system used ensures thorough mixing of the raw materials and controllable stoichiometry, which is beneficial for the incorporation of the dopant metal elements into the crystal lattice of the phosphate-based active material. The two sintering and pulverization processes improve sintering efficiency and control material particle size, enhancing uniformity. The preparation process described in this application is simple and suitable for large-scale industrial production and application. The prepared doped phosphate-based cathode material optimizes the structure of the doped phosphate-based cathode material by doping metal elements into the crystal structure of the phosphate-based active material, thereby improving the structural stability and compressive modulus of the cathode material. At the same time, it can change the chemical composition and electronic structure of the cathode material surface, so that the doped phosphate-based cathode material has high ionic conductivity, electronic conductivity, specific capacity, cycle stability and other properties.

[0046] In step S10 above:

[0047] In some possible implementations, the raw material components for preparing phosphate-based active materials include lithium, iron, and phosphorus sources.

[0048] In some possible implementations, the doped metal source includes at least one of vanadium, titanium, molybdenum, and magnesium.

[0049] In some embodiments, a precursor mixture is prepared by dissolving the lithium source, iron source, phosphorus source, and doped metal source respectively, and then performing two sintering and pulverizing processes to obtain the doped lithium iron phosphate material.

[0050] In some possible implementations, the doping metal sources include vanadium and titanium sources. In the doped phosphate-based cathode material, the molar ratio of lithium, iron, titanium, molybdenum, and phosphorus is (0.98~1.05):(0.94~0.98):(0.01~0.04):(0.01~0.02):(0.98~1.05). In this case, the doped phosphate-based cathode material simultaneously exhibits excellent electronic conductivity, ion diffusion coefficient, cycle stability, and energy density.

[0051] In some possible implementations, the liquid-phase process involves dissolving the raw material components and the doped metal source in an acidic solution with a concentration of 30%–45%, followed by autothermal evaporation to obtain a precursor mixture. In this case, the raw materials are thoroughly mixed in the liquid-phase system, and the stoichiometry is controllable, which is beneficial for the incorporation of titanium and molybdenum into the crystal structure of phosphate-based active materials. Furthermore, autothermal evaporation utilizes the solvation energy and reaction heat of the raw materials to evaporate the solvent, reducing the need for an external heat source and contributing to cost reduction and energy conservation.

[0052] In some possible implementations, the concentration of the acidic solution is 30% to 45%, and the acidic solution includes nitric acid. In this case, the acidic solution has good solubility for both the raw material component and the doped metal source, which is beneficial for the self-thermal evaporation reaction of the raw material component and the doped metal source in the liquid phase system to obtain a precursor mixture. In some embodiments, the concentration of the acidic solution such as nitric acid can be a typical but non-limiting arbitrary point value or a range between any two points, such as 30%, 32%, 35%, 36%, 38%, 40%, 42%, 44%, or 45%.

[0053] In some possible implementations, the titanium source includes at least one of titanic acid, titanate, and titanate ester.

[0054] In some possible implementations, the molybdenum source includes at least one of molybdenum oxide, molybdenum sulfide, molybdate, molybdenum chloride, and molybdenum fluoride.

[0055] In some possible implementations, the vanadium source includes at least one of vanadium oxide, vanadate, and vanadium nitrate.

[0056] In some possible implementations, the magnesium source includes at least one of magnesium oxide, magnesium halide, magnesium nitrate, and magnesium acetate.

[0057] In some possible implementations, the lithium source includes at least one of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0058] In some possible implementations, the iron source includes at least one of ferric nitrate, ferrous oxalate, and elemental iron.

[0059] In some possible implementations, the phosphorus source includes at least one of hydrogen phosphate and orthophosphate.

[0060] The doped metal source and raw material components used in the above embodiments of this application have high purity, and all of the above components have good solubility, which is beneficial for preparing doped phosphate-based cathode materials.

[0061] In step S20 above:

[0062] In some possible implementations, the flow rate of the inert atmosphere during a single sintering process is 50 mL / min to 150 mL / min; specifically, the flow rate of the inert atmosphere can be 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 140 mL / min, or 150 mL / min. In some possible implementations, the inert atmosphere includes at least one of nitrogen, argon, and helium. In this case, the inert atmosphere can sufficiently ensure the synthesis of the doped phosphate-based cathode material, prevent the material from being oxidized at high temperatures, and improve the crystal structure of the doped phosphate-based cathode material.

[0063] In some possible implementations, the heating rate for a single sintering step is 1℃ / min to 5℃ / min, the temperature is 500℃ to 650℃, and the duration is 10h to 16h. In this case, the initial formation of the phosphate-based cathode material is achieved during the single sintering process, and a good balance can be achieved between particle size and the release of volatile components.

[0064] For example, the heating rate of a single sintering 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; the holding temperature can be any typical but non-limiting point value or a range between any two points, such as 500℃, 550℃, 600℃, 650℃; and the holding time can be any typical but non-limiting point value or a range between any two points, such as 10h, 12h, 14h, 16h.

[0065] In some possible implementations, a carbon source is added during a single sintering process. In this case, adding a carbon source during a single sintering process can both reduce the material and coat the initially formed doped phosphate-based cathode material, which is beneficial for adjusting the particle size, morphology, and other characteristics of the doped phosphate-based cathode material. This improves the coating effect of the carbon material on the active material and enhances the particle size, specific surface area, morphology, and other properties of the doped phosphate-based cathode material.

[0066] In some possible implementations, the carbon source includes at least one of glucose, fructose, sucrose, methanol, ethanol, and ethylene glycol. These carbon sources can all play a reducing role under sintering conditions and can initially coat the doped phosphate-based cathode material, adjusting its particle size, morphology, and other characteristics.

[0067] In some possible implementations, the amount of carbon source added during a single sintering process is 100 mL / kg to 200 mL / kg. In this case, the carbon content added during a single sintering process is beneficial for controlling the compaction density, specific surface area, electrical conductivity, and other properties of the finished product. For example, the amount of carbon source added during a single sintering process can be any typical but non-limiting point value or a range between any two points, such as 100 mL / kg, 110 mL / kg, 120 mL / kg, 130 mL / kg, 140 mL / kg, 150 mL / kg, 160 mL / kg, 170 mL / kg, 180 mL / kg, 190 mL / kg, or 200 mL / kg.

[0068] In some possible implementations, the flow rate of the inert atmosphere during the secondary sintering process is 50 mL / min to 150 mL / min. Specifically, the flow rate of the inert atmosphere can be 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 140 mL / min, or 150 mL / min. In some possible implementations, the inert atmosphere includes at least one of nitrogen, argon, and helium. In this case, the inert atmosphere can sufficiently ensure the synthesis of the doped phosphate-based cathode material, prevent the material from being oxidized at high temperatures, and improve the crystal structure of the doped phosphate-based cathode material.

[0069] In some possible implementations, the heating rate for secondary sintering is 1℃ / min to 5℃ / min, the temperature is 650℃ to 850℃, and the duration is 14h to 20h. In this case, secondary sintering can make the crystals of the doped phosphate-based cathode material more complete and have higher crystallinity, and it is also beneficial to improve the graphitization degree of the carbon coating layer.

[0070] For example, the heating rate of the secondary sintering 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; the holding temperature can be any typical but non-limiting point value or a range between any two points, such as 650℃, 700℃, 750℃, 800℃, 850℃; and the holding time can be any typical but non-limiting point value or a range between any two points, such as 14h, 16h, 18h, 20h.

[0071] In some possible implementations, a carbon source is added during the secondary sintering process. In this case, the amount of carbon source added during the secondary sintering process is beneficial for forming a complete carbon coating layer and improving the morphology of the doped phosphate-based cathode material.

[0072] In some possible implementations, the carbon source includes at least one of glucose, fructose, sucrose, methanol, ethanol, and ethylene glycol; these carbon sources can be uniformly coated on the surface of the phosphate-doped cathode material during high-temperature sintering.

[0073] In some possible implementations, the amount of carbon source added during the secondary sintering process is 10 mL / kg to 20 mL / kg. In this case, the carbon content in the doped phosphate cathode material can form a complete and uniform coating layer, improving the particle size, specific surface area, morphology, and other properties of the doped phosphate cathode material. This, in turn, improves the compaction density, active specific surface area, cycle stability, and other properties of the doped phosphate cathode material, and also helps to ensure the capacity of the doped phosphate cathode material.

[0074] For example, the amount of carbon source added during the secondary sintering process can be any typical but non-limiting point value or an interval between any two point values, such as 10 mL / kg, 12 mL / kg, 14 mL / kg, 15 mL / kg, 16 mL / kg, 18 mL / kg, 20 mL / kg.

[0075] In some possible implementations, the particle size D10 of the doped phosphate-based cathode material is 0.20 μm to 0.80 μm, the particle size D50 is 0.8 μm to 3.2 μm, the particle size D90 is 2 μm to 11 μm, and the particle size D99 is 3 μm to 20 μm.

[0076] In some possible implementations, the particle size range (D90-D10) / D50 in the doped phosphate-based cathode material is 1~6.

[0077] In some possible implementations, the thickness of the carbon coating layer in the doped phosphate-based cathode material is 2 nm to 10 nm.

[0078] In some possible implementations, the carbon coating in the phosphate-doped cathode material has a mass percentage of 0.8% to 2%.

[0079] In some possible implementations, the maximum deformation of the phosphate-doped cathode material is 20% to 30% and the reversible deformation is 1.5% to 5% under pressure conditions of 100 MPa to 400 MPa.

[0080] The beneficial effects of the above embodiments of this application have been discussed above and will not be repeated here.

[0081] Thirdly, embodiments of this application provide an application of a doped phosphate-based cathode material, in which the doped phosphate-based cathode material or the doped phosphate-based cathode material prepared by the above method is applied to cathode sheets and / or secondary batteries.

[0082] The phosphate-doped cathode material provided in this application has high electronic conductivity, ion diffusion coefficient, crystal structure stability, charge-discharge cycle stability, capacity, and other characteristics. It can be directly applied to cathode sheets or secondary batteries to improve the charge-discharge specific energy, discharge plateau, cycle capacity retention rate, rate performance, and other properties of cathode sheets and secondary batteries, thereby comprehensively improving the dynamic performance and cycle stability of the battery.

[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 doped phosphate-based positive electrode material. The positive electrode of this application, due to the use of the aforementioned doped phosphate-based positive electrode material in the positive electrode active layer, improves the electrochemical performance of the positive electrode, such as charge / discharge specific energy, discharge plateau, and cycle capacity retention.

[0084] In some possible implementations, the preparation of the positive electrode active layer includes the following steps: mixing the above-mentioned doped 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 phosphate-based cathode material doped in the positive electrode active layer of the cathode sheet is 93% to 97%. Specifically, the mass percentage of phosphate-based cathode material doped in the positive electrode active material layer can be 93%, 94%, 95%, 96%, 97%, 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 2.5wt% to 3wt%. In specific embodiments, the binder content can be typical but not limited to 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3.0wt%, etc.

[0088] In some possible implementations, the binder includes one or more of the following: polyvinylidene chloride, polymethyl methacrylate, 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 0.5wt% to 2.5wt%. In specific embodiments, the conductive agent content can be typical but not limited to 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, etc.

[0090] Among some possible implementations, conductive agents include carbon nanotubes, graphite, carbon black, acetylene black, graphene, carbon fibers, and C. 60 And one or more of carbon nanotubes.

[0091] In some embodiments, the solvent in the positive electrode slurry includes one of N-methylpyrrolidone, dimethyl sulfoxide, and dimethylformamide, with a content of 35% to 60%.

[0092] 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 good stability, high energy density, good rate performance, and good cycle stability, improves the electrochemical performance of the secondary battery, including charge / discharge specific energy, discharge plateau, and cycle capacity retention.

[0093] In some possible implementations, the fabrication of a secondary battery includes the following steps:

[0094] ① The above-mentioned doped phosphate-based cathode material, conductive agent, and cathode binder are added to the solvent in sequence and stirred in a vacuum environment for 2 hours to obtain cathode slurry;

[0095] ② The positive electrode slurry is evenly coated onto the aluminum foil, with an areal density of 8 mg / cm³. 2 ~10mg / cm 2 Then bake at 100℃~130℃ for 2h~3h;

[0096] ③ The aluminum foil loaded with the positive electrode material is placed in a roller press and rolled; the compaction density of the electrode sheet is 2.0 g / cm³. 3 ~2.5g / cm 3 The rolled positive electrode sheet is cut into round sheets with a diameter of 14mm~16mm and a thickness of 0.05mm~0.10mm; and baked in a vacuum drying oven for 2h~3h.

[0097] ④ Assemble the positive electrode, separator, negative electrode and electrolyte into a secondary battery in a glove box filled with argon gas.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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).

[0102] 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.

[0103] In some possible implementations, the secondary battery includes at least one of a battery cell, a battery module, and a battery pack.

[0104] In some possible implementations, the battery cell types include lithium-ion batteries, as well as novel batteries such as lithium metal batteries.

[0105] In some possible implementations, the battery cells of this application can be assembled into a battery module. The number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. For example, the battery module may also include a housing with a receiving space in which multiple battery cells are received.

[0106] 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.

[0107] To enable those skilled in the art to clearly understand the above-described implementation details and operations of this application, and to demonstrate the significant advancements in the performance of the phosphate-doped cathode materials, their preparation methods, and applications in the embodiments of this application, the following examples illustrate the above technical solutions.

[0108] Example 1

[0109] A method for preparing titanium-molybdenum co-doped lithium iron phosphate includes the following steps:

[0110] 1. Distribute 36.95g Li₂CO₃, 404g Fe(NO₃)₃·9H₂O, 0.798g TiO₂, 2.06g Na₂MoO₄, 97.99g H₃PO₄, and 3.6g C₆H₂O into the following containers respectively: 12 After dissolving O6 in 40% nitric acid solution, the solution is heated until it begins to spontaneously heat up in the reactor. The external heat source is then turned off, and the precursor is obtained after the solution in the system evaporates spontaneously.

[0111] 2. The precursor obtained in step 1 is pulverized, and the resulting powder is subjected to a first sintering in a tube furnace. The nitrogen flow rate is set to 60 mL / min; when the temperature is raised to 500℃ (heating rate: 5℃ / min), ethylene glycol is introduced at a flow rate of 0.2 mL / min; the temperature is further raised to 550℃ (heating rate: 3℃ / min) and held for 6.5 h; then the ethylene glycol is turned off, and the mixture is allowed to cool naturally to room temperature to obtain the first sintered material.

[0112] 3. The sintered material obtained in step 2 is pulverized, and the resulting powder is sintered a second time in a tube furnace. The nitrogen flow rate is set to 60 mL / min, and the temperature is raised to 500℃ (heating rate: 5℃ / min). Ethylene glycol is then introduced at a flow rate of 0.02 mL / min; the temperature is further raised to 760℃ (heating rate: 3℃ / min) and held for 7.5 h; then the ethylene glycol is turned off, and the material is allowed to cool naturally to room temperature to obtain the sintered material. This material is pulverized to obtain a titanium-molybdenum co-doped lithium iron phosphate material, wherein the molar ratio of titanium doping is 0.01, and the molar ratio of molybdenum doping is 0.01.

[0113] Example 2

[0114] A titanium-molybdenum co-doped lithium iron phosphate material differs from Example 1 in that the amount of TiO2 added in step 1 is 3.19g and the amount of Na2MoO4 added is 4.12g, so that the molar ratio of titanium in the product is 0.04 and the molar ratio of molybdenum is 0.02.

[0115] Example 3

[0116] A titanium-molybdenum co-doped lithium iron phosphate material differs from Example 1 in that 3.19g of TiO2 is added in step 1, while Na2MoO4 is not added, resulting in a titanium molar ratio of 0.04 in the product.

[0117] Example 4

[0118] A titanium-molybdenum co-doped lithium iron phosphate material differs from Example 1 in that 4.12g of Na2MoO4 is added in step 1, but TiO2 is not added, so that the molar ratio of molybdenum in the product is 0.02.

[0119] Example 5

[0120] A titanium-molybdenum co-doped lithium iron phosphate material differs from Example 1 in that the amount of TiO2 added in step 1 is 3.99g and the amount of Na2MoO4 added is 6.18g, so that the molar ratio of titanium in the product is 0.05 and the molar ratio of molybdenum is 0.03.

[0121] Example 6

[0122] A titanium-zirconium co-doped lithium iron phosphate material differs from Example 1 in that Na2MoO4 is not added in step 1, but 3.19g TiO2 and 6.54g (CH3COO)2Zr are added, so that the molar ratio of titanium in the product is 0.04 and the molar ratio of zirconium is 0.02.

[0123] Comparative Example 1

[0124] A lithium iron phosphate material, which differs from Example 1 in that Na2MoO4 and TiO2 are not added in step 1.

[0125] To verify the progressiveness of the embodiments of this application, the following characterization and testing were performed on each embodiment and comparative example:

[0126] 1. The materials prepared in Examples 1, 2, 3, and 4 were subjected to electron microscopy tests. The test results are shown in Figure 2, which contains scanning electron microscope images of Examples 1, 2, 3, and 4.

[0127] As can be seen from Example 3 in the attached figure, titanium doping reduces the particle size, which is beneficial to improving kinetic performance.

[0128] As can be seen from Example 4 in the attached figure, molybdenum doping reduces the difference in binding energy between different crystal planes of lithium iron phosphate, enabling isotropic particle growth and increasing roundness.

[0129] As shown in Examples 1 and 2 of the accompanying drawings, after titanium-molybdenum co-doping, the lithium iron phosphate particle size decreases and the roundness increases, which is beneficial to improving the compaction density. Within the scope of the patent, the higher the doping amount, the greater the increase in compaction density.

[0130] 2. The crystal structures of the materials prepared in Examples 1-4 were tested, and the test results are shown in Figure 3 as X-ray diffraction patterns of Examples 1, 2, 3, and 4. It can be seen that, compared with pure lithium iron phosphate, the characteristic peak of the 211 crystal plane of the doped material shifts to a higher angle, and no detectable impurity phase is generated, proving that titanium and molybdenum elements are incorporated into the lithium iron phosphate crystal structure.

[0131] 3. Particle size: The materials prepared in the above embodiments and comparative examples were tested using a laser particle size analyzer to determine the particle size distribution of D10, D50, D90, D99 and (D90-D10) / D50.

[0132] 4. The compressive modulus of the cathode materials prepared in the above embodiments and comparative examples was tested under the conditions of 0 MPa to 350 MPa. The test results are shown in Table 1 below.

[0133] 5. Compacted density test: The test pressure is 3T;

[0134] The test results are shown in Table 1 below:

[0135] Table 1

[0136]

[0137] As can be seen from the test results in Table 1, the materials prepared in the embodiments of this application, after being doped with titanium and molybdenum, exhibit increased compaction density, increased reversible deformation, and improved compressive modulus. Under pressure conditions of 100 MPa to 400 MPa, the doped phosphate-based cathode materials prepared in the embodiments of this application exhibit a maximum particle deformation of 20% to 30% and a reversible deformation of 1.5% to 5%.

[0138] 6. Electrochemical Performance Testing: The doped lithium iron phosphate cathode materials prepared in each example and comparative example were applied to lithium-ion batteries. The specific preparation methods are as follows:

[0139] ① Take 9.4g of the finished material prepared in the example or comparative example, 0.3g of polyvinylidene fluoride, and 0.3g of carbon black, add them to 10g of N-methylpyrrolidone solution, and stir in a vacuum mixer for 2.5h to obtain the positive electrode slurry;

[0140] ② The positive electrode slurry is evenly coated onto the aluminum foil, with an areal density of 8.8 mg / cm³. 2 Then bake at 120℃ for 2.5 hours;

[0141] ③ The aluminum foil loaded with the positive electrode material is placed in a roller press and rolled; the compaction density of the electrode sheet is 2.2 g / cm³. 3 The rolled positive electrode sheet was cut into round sheets with a diameter of 14 mm and a thickness of 0.06 mm; and baked in a vacuum drying oven for 2.5 hours.

[0142] ④ Assemble the positive electrode, separator (polypropylene membrane, 18 mm in diameter), negative electrode (lithium sheet, 16.5 mm in diameter) and 160 μL of electrolyte (1 mol / L LiPF6 / EC and DMC mixed at a volume ratio of 1:1) into a coin cell lithium-ion battery in a glove box.

[0143] A. Kinetic Test: The prepared lithium-ion batteries were subjected to constant current charge-discharge tests at a current density of 1C under ambient temperature (25℃). The test results are shown in Table 2.

[0144] Table 2

[0145] Sample No. Charge Specific Capacity (mAh / g) Discharge Specific Capacity (mAh / g) Efficiency (%) Median Voltage Difference (V) Constant Current Charge Ratio (%) Example 1 155.5 142.3 91.55 0.12 149 4.4 Example 2 157.3 144.4 91.84 0.11 139 5.2 Example 3 149.7 138.2 92.20 0.11 319 4.2 Example 4 154.6 139.18 9.97 0.14 749 3.4 Example 5 157.8 141.6 89.69 0.12 799 4.0 Example 6 151.2 136.5 90.28 0.13 489 2.5 Comparative Example 1 146.5 128.4 87.64 0.16 369 1.6

[0146] The test results above show that titanium doping in Example 3 can improve ion and electron transport rates, thereby improving electrochemical polarization and median voltage difference, and thus improving energy efficiency. Molybdenum doping in Example 4 can increase the charge-discharge specific capacity of lithium iron phosphate and improve its room-temperature kinetic performance. The test results of Examples 1 and 2 show that titanium-molybdenum co-doping significantly improves the charge-discharge specific capacity and coulombic efficiency of lithium iron phosphate, reduces the median voltage difference and discharge end slope, and increases the constant current charge-in ratio, thus demonstrating reduced electrochemical polarization and significantly improved kinetic performance. The charge-discharge specific capacity of Example 5 decreases slightly, but is still greater than that of Comparative 1 without any doping. Compared with Example 6, Examples 1 and 2 have higher energy densities.

[0147] B. Cyclic Performance Testing: Under high temperature (45°C), after two cycles of 0.1C charge-discharge, a 1C constant current cycle was performed. The capacity retention during high-temperature cycling is summarized in Table 3:

[0148] Table 3

[0149] Sample Number | Number of Cycles with 95% Capacity Retention | Number of Cycles with 80% Capacity Retention Example 1: 206 | 239 Example 2: 221 | 257 Example 3: 178 | 202 Example 4: 166 | 197 Example 5: 185 | 236 Example 6: 161 | 184 Comparative Example 1: 121 | 132

[0150] The test results above show that titanium doping in Example 3 can reduce electrochemical polarization and improve energy efficiency, thereby improving capacity retention during cycling. Molybdenum doping in Example 4 can enhance the isotropic and reversible deformation of lithium iron phosphate, thus better mitigating particle volume changes caused by lithium ion insertion and extraction, and maintaining the structural stability of the material during cycling. The test results of Example 1 show that co-doping with molybdenum and titanium increases energy density, improves capacity retention, and slows down cycle decay. Example 2 shows better high-temperature cycling performance and represents the best ratio. Example 5 exhibits a slightly faster decay rate in the early stages of cycling, but the decay rate slows down later, and the overall capacity retention is still better than Example 6 and Comparative Example 1. Comparative Example 1, without any doping, shows the fastest cycle decay and the worst high-temperature cycling performance.

[0151] As can be seen from the above electrochemical performance tests, the phosphate-based cathode material prepared by doping in the embodiments of this application has a maximum particle deformation of 20% to 30% and a reversible deformation of 1.5% to 5% under a pressure of 100 MPa to 400 MPa. Within this parameter range, the electrochemical performance of the phosphate-based cathode material can be better improved.

[0152] 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 phosphate-doped cathode material, characterized in that, It includes phosphate-based active materials and doped metal elements in the crystal structure of the phosphate-based active materials; the doped phosphate-based cathode material has a maximum particle deformation of less than 50% and a reversible deformation of less than 10% under a pressure of 100MPa to 500MPa.

2. The doped phosphate-based cathode material as described in claim 1, characterized in that, The doped phosphate-based cathode material exhibits a maximum particle deformation of 20% to 30% and a reversible deformation of 1.5% to 5% under pressure conditions of 100 MPa to 400 MPa.

3. The doped phosphate-based cathode material as described in claim 1 or 2, characterized in that, The doped metal element includes at least one of V, Ti, Mo, and Mg.

4. The phosphate-doped cathode material as described in claim 3, characterized in that, The doped metal elements include titanium and molybdenum.

5. The doped phosphate-based cathode material as described in claim 4, characterized in that, The phosphate-based active material contains iron, and the doped metal element is doped into the iron sites of the phosphate-based active material.

6. The doped phosphate-based cathode material as described in claim 5, characterized in that, In the iron sites of the phosphate-doped cathode material, the molar ratio of iron, titanium, and molybdenum is (0.94~0.98):(0.01~0.04):(0.01~0.02).

7. The phosphate-doped cathode material as described in claim 5, characterized in that, In the doped phosphate-based cathode material, the particle size D10 is 0.20 μm to 0.80 μm, the particle size D50 is 0.8 μm to 3.2 μm, the particle size D90 is 2 μm to 11 μm, and the particle size D99 is 3 μm to 20 μm.

8. The phosphate-doped cathode material as described in claim 5, characterized in that, In the doped phosphate-based cathode material, the particle size range is 1 to 6.

9. The doped phosphate-based cathode material according to any one of claims 1, 2, or 4-8, characterized in that, The outer surface of the particles of the doped phosphate-based cathode material also has a carbon coating layer; And / or, the doped phosphate-based cathode material includes doped lithium iron phosphate.

10. The doped phosphate-based cathode material as described in claim 9, characterized in that, In the doped phosphate-based cathode material, the thickness of the carbon coating layer is 2 nm to 10 nm; And / or, in the doped phosphate-based cathode material, the carbon coating layer has a mass percentage content of 0.8% to 2%.

11. The doped phosphate-based cathode material as described in claim 9, characterized in that, In the doped lithium iron phosphate, the molar ratio of lithium, iron, titanium, molybdenum and phosphorus is (0.98~1.05):(0.94~0.98):(0.01~0.04):(0.01~0.02):(0.98~1.05).

12. A method for preparing a phosphate-doped cathode material, characterized in that, Includes the following steps: Obtain raw material components and doped metal source for preparing phosphate-based active materials, and prepare a precursor mixture by liquid phase method using the raw material components and the doped metal source; In an inert atmosphere, the precursor mixture is sintered once, then pulverized and sintered a second time to obtain a phosphate-doped cathode material. The phosphate-doped cathode material has a maximum particle deformation of less than 50% and a reversible deformation of less than 10% under a pressure of 100MPa to 500MPa.

13. The method for preparing the doped phosphate-based cathode material as described in claim 12, characterized in that, The raw material components for preparing the phosphate-based active material include lithium source, iron source and phosphorus source; And / or, the doped metal source includes at least one of vanadium source, titanium source, molybdenum source, and magnesium source.

14. The method for preparing the doped phosphate-based cathode material as described in claim 12, characterized in that, The heating rate for the first sintering is 1℃ / min~5℃ / min, the temperature is 500℃~650℃, and the duration is 10h~16h. And / or, the heating rate of the secondary sintering is 1℃ / min~5℃ / min, the temperature is 650℃~850℃, and the duration is 14h~20h; And / or, the flow rate of the inert atmosphere during the primary sintering and the secondary sintering processes is independently 50 mL / min to 150 mL / min; And / or, a carbon source is added during the primary sintering and the secondary sintering processes.

15. The method for preparing the doped phosphate-based cathode material as described in claim 12, characterized in that, The doped phosphate-based cathode material exhibits a maximum particle deformation of 20% to 30% and a reversible deformation of 1.5% to 5% under pressure conditions of 100 MPa to 400 MPa.

16. The method for preparing the doped phosphate-based cathode material as described in claim 13, characterized in that, The doped metal source includes a vanadium source and a titanium source; in the doped phosphate-based cathode material, the molar ratio of lithium, iron, titanium, molybdenum and phosphorus is (0.98~1.05):(0.94~0.98):(0.01~0.04):(0.01~0.02):(0.98~1.05).

17. The method for preparing the doped phosphate-based cathode material as described in claim 14, characterized in that, The carbon source includes at least one of glucose, fructose, sucrose, methanol, ethanol, and ethylene glycol; And / or, the amount of carbon source added during the primary sintering process is 100 mL / kg to 200 mL / kg; And / or, the amount of carbon source added during the secondary sintering process is 10 mL / kg to 20 mL / kg.

18. An application of a phosphate-doped cathode material, characterized in that, The doped phosphate-based cathode material according to any one of claims 1 to 11 or the doped phosphate-based cathode material prepared by the method according to any one of claims 12 to 17 is applied to cathode sheets and / or secondary batteries.

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