Composite cathode material, preparation method and application thereof

Abstract

The embodiment of the present application provides a kind of composite positive electrode material and its preparation method and application.The composite positive electrode material includes carbon-containing composite particles, the carbon-containing composite particles include phosphate lithium ion positive electrode material particles and carbon material, carbon material is at least partially coated on the surface of phosphate lithium ion positive electrode material particles, the morphology of carbon-containing composite particles includes sheet and spherical shape.Carbon material makes the electronic conductivity of composite positive electrode material significantly improve, the gap between sheet carbon-containing composite particles can be filled by spherical carbon-containing composite particles, to improve the tap density of composite positive electrode material.Sheet carbon-containing composite particles can also promote the exposure of (010) crystal face in the crystal structure of phosphate lithium ion positive electrode material, shorten the deintercalation path of Li + , improve the lithium ion conductivity of composite positive electrode material, improve low-temperature discharge capacity, to improve the electrochemical performance of positive electrode composite material in low-temperature environment.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and in particular relates to a composite cathode material, its preparation method and application. Background Technology

[0002] Cathode materials are crucial active materials in lithium-ion batteries. During the charging and discharging process, electrochemical oxidation / reduction reactions occur in the cathode material, with lithium ions repeatedly inserting and de-entering. The role of cathode materials has driven their research and development, propelling the advent of the electric vehicle era. Lithium-ion batteries require rapid charging / discharging capabilities, higher energy density, better mechanical stability, longer cycle life, and lower cost to meet the higher parameter requirements and market demands of electric vehicles. The widespread adoption and application of lithium-ion batteries in electric vehicles, in turn, further spurred research and development in cathode materials.

[0003] In recent years, research on cathode materials for lithium-ion batteries has mainly focused on materials such as LiCoO2, LiNiO2, LiMn2O4, LiFePO4, and LiMnFePO4 (lithium manganese iron phosphate). Among them, lithium iron phosphate is a cathode material with excellent stability, good cycle performance, and safety. However, lithium iron phosphate also suffers from problems such as a low voltage plateau, low energy density, and poor low-temperature performance. By adding manganese to lithium iron phosphate to create lithium manganese iron phosphate, not only can the voltage plateau of the cathode material be effectively improved, but the energy density of the cathode material can also be increased. This allows lithium manganese iron phosphate to inherit the thermal stability and safety of lithium iron phosphate while also having higher output power and energy density than lithium iron phosphate.

[0004] There are also some defects in existing lithium manganese iron phosphate batteries. For example, lithium manganese iron phosphate has poor electronic conductivity, is close to an insulator, and has a worse ion diffusion coefficient than lithium iron phosphate. Furthermore, the higher the manganese content in lithium manganese iron phosphate, the worse the kinetic performance and fast charging performance of the batteries made from lithium manganese iron phosphate. Summary of the Invention

[0005] The purpose of this application is to provide a composite cathode material and its preparation method, thereby solving the technical problem of poor electronic and ionic conductivity in lithium manganese iron phosphate in the prior art. The embodiments of this application also provide an electrode, a secondary battery, and an electrical device.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, embodiments of this application provide a composite cathode material. The composite cathode material of this application includes carbon-containing composite particles, which comprise phosphate-based lithium-ion cathode material particles and carbon material. The carbon material at least partially coats the surface of the phosphate-based lithium-ion cathode material particles, and the morphology of the carbon-containing composite particles includes sheet-like and near-spherical shapes.

[0008] In this embodiment, the composite cathode material uses carbon material to coat the surface of phosphate-based lithium-ion cathode material particles, forming sheet-like and near-spherical carbon-containing composite particles. The carbon material significantly improves the electronic conductivity of the composite cathode material, and the gaps between the sheet-like carbon-containing composite particles can be filled by the near-spherical carbon-containing composite particles, thereby increasing the tap density of the composite cathode material. Furthermore, the sheet-like carbon-containing composite particles can also promote the exposure of the (010) crystal plane in the crystal structure of the phosphate-based lithium-ion cathode material, thereby shortening the Li... + The insertion / extraction pathway is improved to enhance the lithium-ion conductivity of the composite cathode material and increase its low-temperature discharge capacity, thereby improving the electrochemical performance of the cathode composite material in low-temperature environments.

[0009] Secondly, embodiments of this application provide a method for preparing a composite cathode material. The method for preparing the composite cathode material according to embodiments of this application includes the following steps:

[0010] Phosphate-based lithium-ion cathode material precursor particles are mixed with a carbon source and a solvent. The carbon source is used to pre-coat the phosphate-based lithium-ion cathode material precursor particles to obtain composite cathode material precursor particles. The temperature of the pre-coating treatment is ≤95℃.

[0011] The composite cathode material precursor particles are sintered to obtain the composite cathode material.

[0012] The sintering process includes a first sintering process, a second sintering process, and a third sintering process performed sequentially, with the temperatures of the first sintering process, the second sintering process, and the third sintering process increasing sequentially.

[0013] The preparation method in this application employs a liquid-phase method for low-temperature pre-coating of phosphate-based lithium-ion cathode material precursor particles. This improves the dispersibility of the phosphate-based lithium-ion cathode material precursor particles and the uniformity of carbon source coating. It allows for a reduction in the thickness of the carbon source coating layer while maintaining the same coating ratio, resulting in a thinner and more uniform carbon layer within the carbon-containing composite particles. This facilitates the construction of an interconnected three-dimensional conductive network, thereby improving the electronic conductivity of the composite cathode material. The excellent particle dispersibility and uniform carbon source coating in the liquid-phase coating method effectively reduce the agglomeration rate between particles during subsequent sintering. This results in sintered, near-spherical carbon-containing composite particles with smoother surfaces, clearer particle differentiation, and more regular particle morphology. By combining a three-stage sintering method with progressively increasing temperatures, not only is the purity of the crystal effectively improved, but also the morphology of some carbon-containing composite particles forms a plate-like structure while others retain a near-spherical structure. This allows the composite cathode material prepared by the method of this application to achieve the coexistence of near-spherical and plate-like carbon-containing composite particles.

[0014] Furthermore, in the sintering process of the preparation method in this application embodiment, the carbon source is subjected to in-situ carbothermic reduction, so that the carbon source on the surface of the composite cathode material precursor particles can not only form carbon material coating the particles, but also serve as a reducing outer layer on the particle surface, reducing Mn in the particles. 3+ and Fe 3+ The generation of carbon and further reduces the thickness of the carbon layer in the carbon-containing composite particles, improving the processing performance of the composite cathode material. The preparation method in this application also eliminates the need for an external reducing atmosphere such as hydrogen, and employs a one-step calcination process, effectively improving production safety and reducing production costs.

[0015] Thirdly, this application provides an electrode, including a current collector and an electrode active layer bonded to the surface of the current collector, wherein the electrode active layer contains the composite positive electrode material described above.

[0016] The electrode in this embodiment contains the composite cathode material described above. This composite cathode material has a high tap density, good electronic and ionic conductivity, and a large low-temperature discharge capacity. It can effectively reduce electrode polarization, improve the capacity and energy density per unit volume of the electrode in this embodiment, and improve the performance of the electrode in low-temperature environments.

[0017] A fourth aspect of this application provides a secondary battery, including a positive electrode and a negative electrode, wherein the positive electrode is the electrode of this application embodiment.

[0018] The secondary battery of this application embodiment contains the electrode of this application embodiment. The electrode has high capacity, high energy density per unit volume, and good electrochemical performance at low temperature, thereby improving the capacity and charge / discharge efficiency of the secondary battery and improving the low-temperature performance of the secondary battery.

[0019] Fifthly, embodiments of this application provide an electrical device. The electrical device in this application includes a secondary battery as described in this application.

[0020] Since the power device in this application embodiment contains the secondary battery described in the above application embodiment, the power device in this application embodiment has a long standby or battery life and good low temperature resistance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a SEM image of the composite cathode material in Example A1. Detailed Implementation

[0023] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0024] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0025] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0026] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0027] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0028] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0029] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0030] To address the technical problems of low electronic and ionic conductivity in lithium manganese iron phosphate in the prior art, this application proposes the following technical solution.

[0031] In a first aspect, embodiments of this application provide a composite cathode material. The composite cathode material of this application includes carbon-containing composite particles, which comprise phosphate-based lithium-ion cathode material particles and carbon material. The carbon material at least partially coats the surface of the phosphate-based lithium-ion cathode material particles, and the morphology of the carbon-containing composite particles includes sheet-like and near-spherical shapes.

[0032] The quasi-spherical shape in this application can be spherical or approximately spherical, such as an ellipsoid, hexahedron, octahedron, dodecahedron, or other polyhedrons, and is not specifically limited. When the carbon-containing composite particles have a quasi-spherical appearance, they can be regular or irregular quasi-spherical, and are not specifically limited.

[0033] In this application embodiment, the composite cathode material is achieved by coating the surface of phosphate-based lithium-ion cathode material particles with carbon material, thereby significantly improving the electronic conductivity of the composite cathode material. Furthermore, based on the olivine structure of the phosphate-based lithium-ion cathode material, Li… +The insertion / extraction behavior of lithium ions is based on one-dimensional channels, i.e., based on the 010 crystal plane. Under low-temperature conditions, the insertion / extraction ability of lithium ions is weaker. The plate-like carbon-containing composite particles can expose more of the (010) crystal plane in the crystal structure of phosphate-based lithium-ion cathode materials, making Li... + The insertion / extraction path is shorter, which can effectively improve the lithium-ion insertion / extraction rate at low temperatures, thereby increasing the lithium-ion conductivity and low-temperature discharge capacity of the composite cathode material in this application embodiment. This results in the composite cathode material exhibiting better electrochemical performance at low temperatures. Furthermore, by controlling the morphology of the carbon-containing composite particles, including sheet-like and spherical shapes, the gaps between the sheet-like carbon-containing composite particles are filled by spherical carbon-containing composite particles, thereby increasing the compaction density of the composite cathode material and improving the volumetric energy density of the single-cell battery containing this composite cathode material.

[0034] In some embodiments, the particle size of the near-spherical carbon-containing composite particles can be 150–500 nm, optionally 200–300 nm. In exemplary embodiments, the particle size of the near-spherical carbon-containing composite particles can be a typical but non-limiting particle size such as 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or any particle size between any two particle size ranges.

[0035] By ensuring that the content and particle size of the near-spherical carbon-containing composite particles are within the above-mentioned range, the bonding between the near-spherical carbon-containing composite particles and the sheet-like carbon-containing composite particles is further promoted, the gap between the carbon-containing composite particles in the composite cathode material is further reduced, and the tap density of the composite cathode material is further improved.

[0036] In some embodiments, the diameter of the plane of the sheet-like carbon-containing composite particles can be 200-600 nm, optionally 400-600 nm. In exemplary embodiments, the diameter of the sheet-like carbon-containing composite particles can be a typical but non-limiting diameter such as 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, or a diameter between any two diameter ranges.

[0037] In some embodiments, the thickness of the sheet-like carbon-containing composite particles can be 3 to 4 nm. In exemplary embodiments, the thickness of the sheet-like carbon-containing composite particles can be a typical but non-limiting thickness such as 3 nm, 3.1 nm, 3.2 nm, 3.3 nm, 3.4 nm, 3.5 nm, 3.6 nm, 3.7 nm, 3.8 nm, 3.9 nm, 4 nm, or any two thickness ranges.

[0038] The ratio of near-spherical carbon-containing composite particles to flake-shaped carbon-containing composite particles can be 1:(0.01 to 0.1). Optionally, in the example, the ratio of near-spherical carbon-containing composite particles to flake-shaped carbon-containing composite particles can be 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, etc., which are typical but non-limiting ratios or any ratio range between any two ratios.

[0039] By controlling the planar diameter and thickness of the sheet-like carbon composite particles within the aforementioned range, and by controlling the ratio of the number of spherical carbon composite particles to sheet-like carbon composite particles within the same range, the lithium-ion conductivity of the composite cathode material is further improved, and the mutual bonding between the sheet-like and spherical structures in the composite cathode material is further promoted, thereby further improving the tap density of the composite cathode material.

[0040] In this application, the planar surface of the sheet-like structure can be a regular shape, such as a circle, ellipse, square, hexagon, etc., and is not specifically limited; the planar surface of the sheet-like structure can also be an irregular shape. In some embodiments, the carbon-containing composite particles can be sheet-like structures of uniform thickness, with different regions of the plane of the same sheet-like carbon-containing composite particle having the same or similar thickness. In other embodiments, the carbon-containing composite particles can be sheet-like structures of uneven thickness, with different regions of the same sheet-like carbon-containing composite particle having different thicknesses. For example, the plane of the sheet-like structure can have protrusions, depressions, or inclinations, resulting in different thicknesses in different regions of the plane. Also, the thickness of the region near the center of the plane of the same sheet-like carbon-containing composite particle can be less than the thickness of the region near the edge of the plane.

[0041] In some embodiments, the phosphate-based lithium-ion cathode material particles contained in the composite cathode materials of the above embodiments may contain at least one phosphate-based lithium-ion cathode material selected from lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate. In some embodiments, lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate may not be doped with other elements; in another embodiment, lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate may also be doped with other elements, such as transition metal elements like Zn and Al, or non-metallic elements like C, S, and N, etc., without specific limitations.

[0042] In some embodiments, the mass content of carbon material in the composite cathode material of the above embodiments can be 0.01% to 5.00%. In exemplary examples, the mass content of carbon material in the composite cathode material can be typical but not limiting contents such as 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a content value between any two content ranges.

[0043] The coating layer formed by carbon materials on the surface of phosphate-based lithium-ion cathode material particles is called a carbon coating layer. In some embodiments, the thickness of the carbon coating layer can be 2 to 3 nm. In exemplary examples, the thickness of the carbon coating layer can be typical but not limiting thicknesses such as 2 nm, 2.1 nm, 2.2 nm, 2.3 nm, 2.4 nm, 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm, and 3 nm, or any thickness between two thickness ranges.

[0044] The carbon materials within the above-mentioned content range and the carbon coating layer within the above-mentioned thickness range effectively improve the electronic conductivity of the composite cathode material while increasing the mass ratio of phosphate-based lithium-ion cathode material particles in the carbon-containing composite particles, thereby further increasing the lithium-ion content of the composite cathode material and improving the specific capacity of the composite cathode material.

[0045] In some embodiments, the compaction density of the composite cathode material in the above embodiments can be 2.1–2.4 g / cm³. 3 In the example, the compaction density of the composite cathode material can be 2.1 g / cm³. 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 Typical but non-restrictive compaction density or any compaction density between any two values.

[0046] In some embodiments, the specific surface area of ​​the composite cathode material in the above embodiments can be 17–21 m². 2 / g, in the example, the specific surface area of ​​the composite cathode material can be 17m². 2 / g, 17.5m 2 / g、18m 2 / g, 18.5m 2 / g、19m 2 / g, 19.5m 2 / g、20m 2 / g, 20.5m 2 / g、21m 2 / g is a typical but not limiting specific surface area, or any specific surface area between any two numerical ranges.

[0047] By controlling parameters such as the sheet-like particles, near-spherical particles, carbon content, pressing density, and specific surface area of ​​the composite cathode material, the resistivity of the composite cathode material can be further reduced, the lithium-ion diffusion coefficient of the composite cathode material can be increased, and the charge-discharge capacity of the composite cathode material can be improved.

[0048] In some embodiments, the resistivity of the composite cathode material in the above embodiments can be 14 to 41 Ω·m. In the exemplary examples, the resistivity of the composite cathode material can be typical but not limiting resistivity such as 14 Ω·m, 15 Ω·m, 20 Ω·m, 25 Ω·m, 30 Ω·m, 35 Ω·m, 40 Ω·m, 41 Ω·m, or any resistivity between any two numerical ranges.

[0049] In some embodiments, the lithium-ion diffusion coefficient of the composite cathode material described above can be 5 × 10⁻⁶. - 13 cm 2 / S~9.5×10 -12 cm 2 In the example, the lithium-ion diffusion coefficient of the composite cathode material can be 5 × 10⁻⁶. -13 cm 2 / S、5.8×10 -13 cm 2 / S、6×10 -13 cm 2 / S、7×10 -13 cm 2 / S、8×10 -13 cm 2 / S、9×10 -13 cm 2 / S、1×10 - 12 cm 2 / S、2×10 -12 cm 2 / S、3×10 -12 cm 2 / S、4×10 -12 cm 2 / S、5×10 -12 cm 2 / S、6×10 -12 cm 2 / S、7×10 - 12 cm 2 / S、8×10 -12 cm 2 / S、9×10 -12 cm 2 / S, 9.5×10 -12 cm 2 / S is a typical but not limiting lithium-ion diffusion coefficient, or the magnitude of the lithium-ion diffusion coefficient between any two numerical ranges.

[0050] In some embodiments, the 0.1C discharge capacity of the composite cathode material in the above embodiments can be 140-150 mA·h / g. In the exemplary examples, the 0.1C discharge capacity of the composite cathode material can be a typical but not limiting discharge capacity such as 140 mA·h / g, 141 mA·h / g, 142 mA·h / g, 143 mA·h / g, 144 mA·h / g, 145 mA·h / g, 146 mA·h / g, 147 mA·h / g, 148 mA·h / g, 149 mA·h / g, 150 mA·h / g, or the discharge capacity between any two numerical ranges.

[0051] Secondly, embodiments of this application provide a method for preparing the aforementioned composite cathode material. The method for preparing the composite cathode material according to embodiments of this application includes the following steps:

[0052] S10. The phosphate-based lithium-ion cathode material precursor particles are mixed with a carbon source and a solvent, and the carbon source is used to pre-coat the phosphate-based lithium-ion cathode material precursor particles to obtain composite cathode material precursor particles, wherein the temperature of the pre-coating treatment is ≤95℃.

[0053] S20. The precursor particles of the composite cathode material are sintered to obtain the composite cathode material.

[0054] The sintering process in step S20 includes a first sintering process, a second sintering process, and a third sintering process performed sequentially, with the temperatures of the first sintering process, the second sintering process, and the third sintering process increasing sequentially. After the sintering process, the phosphate-based lithium-ion cathode material precursor particles will generate phosphate-based lithium-ion cathode materials. The carbon source is carbonized to generate carbon materials. Therefore, the composite cathode material precursor particles will generate the carbon-containing composite particles mentioned above.

[0055] The preparation method of this application uses a liquid-phase method at low temperature to pre-coat the carbon source. The carbon source is dispersed in a solvent, and during the drying process, the carbon source is uniformly coated on the surface of the phosphate-based lithium-ion cathode material precursor particles to form a carbon source layer, thus obtaining a composite cathode material precursor. The liquid-phase coating method makes the resulting composite cathode material precursor particles more dispersed, and the carbon source coating on the surface of the phosphate-based lithium-ion cathode material precursor particles is more uniform and complete. Under the premise of the same coating rate, the thickness of the carbon source coating layer can be reduced, which is conducive to building an interconnected three-dimensional conductive network and improving the electronic conductivity of the composite cathode material. The liquid-phase coating method combined with the subsequent three-stage sintering process with successively increasing temperatures results in some carbon-containing composite particles forming a nanosheet-like morphology, while others have a regular spherical structure. This allows for the coexistence of sheet-like and spherical carbon-containing composite particles in the composite cathode material, effectively improving the tap density of the composite cathode material and enhancing its electronic conductivity and lithium-ion conductivity. Furthermore, the carbon source layer can undergo in-situ carbothermic reduction during sintering, enabling it not only to carbonize and form a carbon coating layer but also to serve as a reducing outer layer on the particle surface, reducing Mn content in the particles. 3+ and Fe 3+ The generation of this process improves the purity of phosphate-based lithium-ion cathode materials. The preparation method in this application also eliminates the need for an external reducing atmosphere such as hydrogen, and employs a one-step calcination process, effectively improving production safety and reducing production costs.

[0056] Step S10:

[0057] In step S10, phosphate-based lithium-ion cathode material precursor particles are mixed with a carbon source and a solvent. The carbon source is used to pre-coat the phosphate-based lithium-ion cathode material precursor particles, and the temperature of the pre-coating treatment is controlled to be ≤95℃ to obtain composite cathode material precursor particles. This achieves low-temperature pre-coating of phosphate-based lithium-ion cathode material precursor particles with a carbon source using a liquid phase method.

[0058] In some embodiments, phosphate-based lithium-ion cathode material precursor particles can be mixed with a carbon source and a solvent to obtain a mixed slurry, and then the mixed slurry can be dried to coat the carbon source on the surface of the phosphate-based lithium-ion cathode material precursor particles to form a carbon source layer, thereby obtaining composite cathode material precursor particles.

[0059] In some embodiments, the phosphate-based lithium-ion cathode material precursor particles contain lithium. By including lithium in the phosphate-based lithium-ion cathode material precursor particles, the mixing process between the phosphate-based lithium-ion cathode material precursor particles and the lithium source is further reduced. At the same time, the lithium can be encapsulated within the carbon source, reducing the impact of lithium on the carbon source and the morphology and structure of the composite cathode material particles during sintering. This facilitates the formation of a composite cathode material in which sheet-like carbon-containing composite particles and near-spherical carbon-containing composite particles coexist.

[0060] In some embodiments, the particle size of the phosphate-based lithium-ion cathode material particles can be set according to the particle size of the phosphate-based lithium-ion cathode material particles in the carbon-containing composite particles mentioned above.

[0061] In some embodiments, the preparation method of phosphate-based lithium-ion cathode material precursor particles may include the following steps: preparing an aqueous solution of a lithium source, a phosphorus source, an iron source and / or a manganese source, performing a hydrothermal reaction, drying, and pulverizing to obtain phosphate-based lithium-ion cathode material precursor particles.

[0062] In the preparation of phosphate-based lithium-ion cathode materials such as lithium manganese iron phosphate, iron and manganese need to be mixed at the atomic level. Inhomogeneous mixing of iron and manganese may lead to impurities, such as the formation of impurity phases like Fe2P, Fe2O3, and Mn2O3. By preparing phosphate-based lithium-ion cathode material precursor particles using a solution method, the presence of iron and manganese in the precursor particles allows for atomic-level mixing of lithium, iron, manganese, and phosphorus, significantly improving the uniformity of iron and manganese mixing. Combined with subsequent sintering, this further enhances the uniformity of the phosphate-based lithium-ion cathode material solid solution.

[0063] In some embodiments, the lithium source may include at least one of Li2CO3, LiH2PO4, LiOH·H2O, CH3COOLi, and LiNO3. In exemplary embodiments, the lithium source may include a combination of Li2CO3 and LiH2PO4, a combination of LiOH·H2O and LiH2PO4, a combination of Li2CO3 and LiOH·H2O, a combination of Li2CO3 and CH3COOLi, or a combination of LiNO3 and CH3COOLi.

[0064] In some embodiments, the iron source may include any one of Fe(NO3)3, Fe2O3 or FeSO4·7H2O. In an exemplary embodiment, the iron source may include a combination of Fe(NO3)3 and Fe2O3, a combination of FeSO4·7H2O and Fe2O3, or a combination of Fe(NO3)3 and FeSO4·7H2O.

[0065] In some embodiments, the manganese source may include at least one of Mn(NO3)3, Mn2O3, or MnSO4·7H2O. In an exemplary embodiment, the manganese source may include a combination of Mn(NO3)3 and Mn2O3, a combination of MnSO4·7H2O and Mn2O3, or a combination of Mn(NO3)3 and MnSO4·7H2O.

[0066] In some embodiments, the phosphorus source may include at least one of (NH4)3PO4, NH4H2PO4, LiH2PO4 or H3PO4. In exemplary embodiments, the phosphorus source may include a combination of (NH4)3PO4 and NH4H2PO4, a combination of LiH2PO4 and NH4H2PO4, or a combination of (NH4)3PO4 and H3PO4.

[0067] In some embodiments, the molar ratio of the lithium source, iron source, manganese source, and phosphorus source can be set as needed. For example, the general formula for phosphate-based lithium-ion cathode materials can be LiMn. (1-x) Fe x For PO4, 0 ≤ x ≤ 1, when x is 0.4, the molar ratio of lithium, iron, manganese and phosphorus can be Li:Fe:Mn:P = 1:0.4:0.6:1.

[0068] In some embodiments, the hydrothermal reaction can be carried out in a container with a polytetrafluoroethylene coating to reduce the influence of metal ions in the container.

[0069] In some examples, the hydrothermal reaction temperature can be 150–200°C, and the time can be 6–24 hours. In exemplary cases, the hydrothermal reaction temperature can be typical but not limiting temperatures such as 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C, or any temperature range between two such ranges. The hydrothermal reaction time can be typical but not limiting times such as 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, and 24 hours. Controlling the hydrothermal reaction time and temperature within this range further promotes the hydrothermal reaction and reduces the occurrence of side reactions.

[0070] In some embodiments, after the hydrothermal reaction, solid-liquid separation can be performed by centrifugation, filtration, or vacuum filtration to collect the solid, which is then dried and pulverized to obtain lithium iron phosphate cathode material precursor particles. In further embodiments, the drying method can be hot air drying or natural drying, whichever is not limited; the pulverization method can be grinding with a mortar and pestle or grinding with a ball mill, whichever is not limited.

[0071] In some embodiments, the mixing of phosphate-based lithium-ion cathode material precursor particles, carbon source, and solvent can be performed under a protective atmosphere. Mixing under a protective atmosphere further reduces metal ion oxidation and improves the purity of the phosphate-based lithium-ion cathode material.

[0072] In some embodiments, the carbon source may include at least one of glucose, cetyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG-400, PEG-1000, PEG-2000, PEG-3000, PEG-4000), sucrose, and graphite. These carbon sources are readily dispersed in solvents such as water. For example, carbon sources such as glucose, CTAB, PEG, and sucrose can dissolve or swell in water, thereby ensuring sufficient dispersion in the solvent. This further improves the mixing uniformity of the components in the slurry and enhances the uniformity of the carbon source coating on the surface of the phosphate-based lithium-ion cathode material precursor particles.

[0073] In some embodiments, the solvent may include at least one of the solvents such as water, ethanol, and acetone. Carbon sources such as glucose, CTAB, PEG, and sucrose have good solubility in these solvents, allowing the carbon sources to fully dissolve, swell, and disperse in the solvent, thereby improving the uniformity of the mixed slurry.

[0074] In some embodiments, the mixing mass ratio of phosphate-based lithium-ion cathode material precursor particles and carbon source can be 1:0.01 to 0.1. In exemplary examples, the mixing ratio of phosphate-based lithium-ion cathode material precursor particles and carbon source can be typical but non-limiting ratios such as 1:0.01, 1:0.02, 1:0.05, 1:0.07, and 1:0.1, or any ratio within a range of two such ratios. This ratio of phosphate-based lithium-ion cathode material particles and carbon source effectively controls the carbon source content in the composite cathode material precursor particles, thereby further controlling the carbon source content in the composite cathode material. This effectively improves the electronic conductivity of the composite cathode material while increasing the content of phosphate-based lithium-ion cathode material in the composite cathode material, further improving the specific capacity of the composite cathode material.

[0075] In some embodiments, the mass ratio of phosphate-based lithium-ion cathode material precursor particles to solvent in the mixed slurry can be 1:(1.5 to 2.5), and further, the mass ratio of phosphate-based lithium-ion cathode material precursor particles, solvent, and carbon source in the mixed slurry can be 1:(1.5 to 2.5):(0.01 to 0.1), optionally 1:2:(0.01 to 0.1). In exemplary examples, the mass ratio of phosphate-based lithium-ion cathode material precursor particles, solvent, and carbon source can be typical but not limiting mass ratios such as 1:2:0.01, 1:2:0.05, and 1:2:0.1, or any ratio between any two mass ratio ranges. Mixed slurries within this mass ratio range allow the carbon source to dissolve and disperse, further improving the dispersibility of the phosphate-based lithium-ion cathode material precursor particles, thereby improving the uniformity of the carbon source's coating on the phosphate-based lithium-ion cathode material precursor particles.

[0076] In some embodiments, the mixed slurry can be further heat-treated to partially evaporate the water in the mixed slurry, causing the mixed slurry to gel and further promoting the uniform coating of the carbon source onto the surface of the phosphate-based lithium-ion cathode material precursor particles. In further embodiments, the heat treatment temperature can be 60–95°C, and the heat treatment time can be 6–12 hours. In exemplary examples, the heat treatment temperature can be typical but not limiting temperatures such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, and 95°C, and the heat treatment time can be typical but not limiting times such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours. During the heat treatment process, stirring and other operations can also be performed to improve the uniformity of the mixed slurry. Through heat treatment, the high molecular weight carbon sources of CTAB and PEG are fully dissolved or swollen, promoting the gelation of the mixed slurry and ensuring that the carbon source is uniformly coated onto the surface of the phosphate-based lithium-ion cathode material particles.

[0077] In some embodiments, the heat treatment can be carried out under a protective atmosphere such as nitrogen or argon to reduce the oxidation of metal ions during the heat treatment process.

[0078] In some embodiments, the drying treatment of the mixed slurry can be hot air drying. In a specific example, the mixed slurry can be placed in a forced-air drying oven and dried for 6 to 24 hours, and then ground to obtain composite cathode material precursor particles.

[0079] In some embodiments, under a protective atmosphere of 0.25 MPa nitrogen, phosphate-based lithium-ion cathode material precursor, water, and carbon source are added to a three-necked flask in a mass ratio of 1:2:0.01 to 0.1 and mixed to obtain a mixed slurry. The three-necked flask containing the mixed slurry is placed in a water bath at 60 to 90°C and heated and stirred for 6 to 12 hours. After the reaction is completed, the gel-like mixed slurry is taken out and placed in a forced-air drying oven for drying. The solid obtained after drying is then ground using an agate mortar and pestle to obtain composite cathode material precursor particles.

[0080] In the preparation method of this application embodiment, the phosphate-based lithium-ion cathode material precursor particles are coated by liquid phase method, which makes the mixing between materials more uniform and the dispersion between the phosphate-based lithium-ion cathode material precursor particles better. This improves the uniformity of carbon source coating on the surface of the phosphate-based lithium-ion cathode material precursor particles, forming a composite structure of phosphate-based lithium-ion cathode material precursor particles-carbon source layer, and obtaining composite cathode material precursor particles.

[0081] Step S20:

[0082] In step S20, the precursor particles of the composite cathode material are sintered to form a crystalline structure, resulting in phosphate-based lithium-ion cathode material particles. This process carbonizes the carbon source, forming carbon material that at least partially coats the surface of the phosphate-based lithium-ion cathode material particles. Consequently, the phosphate-based lithium-ion cathode material particles and the carbon material form carbon-containing composite particles, yielding the composite cathode material. By controlling the sintering process to be a three-stage process, the morphology of the carbon-containing composite particles includes both plate-like and spherical shapes.

[0083] In some embodiments, the sintering process can be carried out under a protective atmosphere of nitrogen or argon to further reduce the oxidation of metal ions and carbon sources.

[0084] In some embodiments, the temperature of the first sintering treatment can be between 150 and 350°C. In exemplary examples, the temperature of the first sintering treatment can be typical but not limiting temperatures such as 150°C, 180°C, 200°C, 230°C, 250°C, 280°C, 300°C, 320°C, and 350°C, or any temperature range between two such ranges. The first sintering treatment within this temperature range effectively removes volatile components, further reducing the impact of volatile components on particle formation in subsequent sintering processes, while simultaneously reaching the critical conditions for carbonization of the carbon source.

[0085] In some embodiments, the first sintering treatment time can be 2 to 6 hours. In exemplary examples, the first sintering treatment time can be a typical but not limiting time such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours. Controlling the first sintering treatment time within this range further promotes the volatilization of volatile substances in the composite cathode material precursor particles, thereby facilitating the formation of subsequent crystal particles.

[0086] In some embodiments, the temperature of the second sintering treatment can be 450–650°C. In exemplary embodiments, the temperature of the second sintering treatment can be typical but not limiting temperatures such as 450°C, 480°C, 500°C, 530°C, 550°C, 580°C, 600°C, 630°C, and 650°C, or any temperature range between two such ranges. The second sintering treatment within this temperature range effectively promotes the nucleation and crystal formation of phosphate-based lithium-ion cathode materials, while simultaneously causing the carbon source to carbonize and form carbon materials.

[0087] In some embodiments, the second sintering treatment time can be 4 to 8 hours. In exemplary examples, the second sintering treatment time can be typical but not limiting times such as 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours. Controlling the second sintering treatment time within this range further promotes the carbonization of the carbon source and the formation of phosphate-based lithium-ion cathode material crystals, thereby initially forming a carbon-containing composite particle structure of carbon material coated with phosphate-based lithium-ion cathode material.

[0088] In some embodiments, the temperature of the third sintering treatment can be 600–800°C. In exemplary examples, the temperature of the third sintering treatment can be a typical but non-limiting temperature such as 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, or 800°C, or a temperature between any two temperature ranges. By controlling the temperature of the third sintering treatment within this range, the crystals of the phosphate-based lithium-ion cathode material are further purified, and the formation of nanosheet-like structures of some carbon-containing composite particles is promoted, thereby obtaining a composite cathode material having sheet-like carbon-containing composite particles and spherical carbon-containing composite particles.

[0089] In some embodiments, the third sintering treatment time can be 4 to 8 hours. In exemplary examples, the third sintering treatment time can be typical but not limiting times such as 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours. Controlling the third sintering treatment time within this range promotes the formation of sheet-like structures from some carbon-containing composite particles with regular spherical structures.

[0090] In some embodiments, the heating rates of the first, second, and third sintering processes are independently 2–15 °C / min. In exemplary examples, the heating rates of the first, second, and third sintering processes are typically, but not limitingly, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, and 15 °C / min, or any range of heating rates. Controlling the heating rates of the first, second, and third sintering processes within this range effectively promotes the formation of carbon-containing composite particles while further shortening the sintering time and improving production efficiency.

[0091] In existing technologies, the solid-phase method for preparing phosphate-based lithium-ion cathode materials places high demands on the grinding conditions and machinery used in ball milling, and is prone to problems such as uneven material mixing, leading to irregular particles and the formation of impurity phases. The preparation method of this application utilizes the aforementioned liquid-phase method to prepare the precursor for phosphate-based lithium-ion cathode materials. This achieves atomic-level mixing of iron and manganese elements in the phosphate-based lithium-ion cathode material, promoting the uniform formation of lithium iron phosphate solid solution, effectively reducing the formation of impurity phases in the phosphate-based lithium-ion cathode material, and improving the crystal purity of the phosphate-based lithium-ion cathode material.

[0092] Furthermore, the preparation method in this application also utilizes a low-temperature pre-coating of carbon source using a liquid-phase method to form a phosphate-based lithium-ion cathode material precursor particle-carbon source layer structure, thereby obtaining composite cathode material precursor particles. Because the carbon source is coated using a liquid-phase method, the dispersion of materials is more uniform, further promoting the separation of phosphate-based lithium-ion cathode material precursor particles and ensuring uniform coating of the carbon source on the surface of the phosphate-based lithium-ion cathode material particles, resulting in a more regular morphology for the composite cathode material precursor particles. By preparing composite cathode material precursor particles using a liquid-phase method, combined with a three-stage sintering process with progressively increasing temperatures, the composite cathode material precursor particles form carbon-containing composite particles with a near-spherical structure, and some of the carbon-containing composite particles form a plate-like structure, thus obtaining a composite cathode material in which plate-like carbon-containing composite particles and near-spherical carbon-containing composite particles coexist.

[0093] Thirdly, this application provides an electrode, including a current collector and an electrode active layer bonded to the surface of the current collector, wherein the electrode active layer contains the composite positive electrode material described above.

[0094] The electrode in this embodiment contains the composite cathode material described above. This composite cathode material has a high tap density, good electronic and ionic conductivity, and a large low-temperature discharge capacity. It can effectively reduce the polarization of the electrode in this embodiment, improve the electrode capacity and energy density per unit volume, and improve the electrode performance in low-temperature environments.

[0095] The electrode in this application can be a conventional electrode for a secondary battery, such as an electrode active layer including a current collector and an electrode current collector surface bonded to the current collector.

[0096] In some embodiments, the electrode active layer includes, in addition to the composite positive electrode material, a binder and a conductive agent. The binder can be a commonly used electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives. In the embodiments of this application, the conductive agent can be a commonly used conductive agent, such as one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes.

[0097] In some embodiments, the electrode preparation process may be as follows: mixing composite positive electrode material, conductive agent and binder to obtain electrode slurry, coating the electrode slurry on current collector, and preparing electrode sheet by drying, rolling, die cutting and other steps.

[0098] A fourth aspect of this application provides a secondary battery, including a positive electrode and a negative electrode, wherein the positive electrode is the electrode of this application embodiment.

[0099] The secondary battery of this application embodiment includes necessary components such as a positive electrode, a negative electrode, a separator, and an electrolyte, and of course, other necessary or auxiliary components. The positive electrode is the electrode described in the above-described embodiment of this application, meaning that the positive electrode active layer contains the composite positive electrode material described in the above-described embodiment of this application.

[0100] The secondary battery of this application embodiment contains the electrode of this application embodiment. The electrode has high capacity and high energy density per unit volume, which improves the capacity and charge / discharge efficiency of the secondary battery and improves the low-temperature performance of the secondary battery.

[0101] Fifthly, embodiments of this application provide an electrical device. The electrical device in this application includes a secondary battery as described in this application.

[0102] Since the power device in this application embodiment contains the secondary battery described in the above application embodiment, the power device in this application embodiment has a long standby or battery life and good low temperature resistance.

[0103] In some embodiments, the electrical device used in this application may be, but is not limited to, a mobile phone, tablet, laptop, electric toy, power tool, electric vehicle, electric car, ship, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0104] 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 composite cathode material, its preparation method, and its application in the embodiments of this application, the following examples illustrate the above technical solutions.

[0105] 1. Examples of composite cathode materials and their preparation methods:

[0106] Example A1

[0107] This embodiment provides a composite cathode material. The composite cathode material of this embodiment includes carbon-containing composite particles, the morphology of which includes nanosheets and near-spherical shapes. The carbon-containing composite particles comprise phosphate-based lithium-ion cathode material particles and carbon material coating the phosphate-based lithium-ion cathode material particles.

[0108] The method for preparing the composite cathode material in this embodiment is as follows:

[0109] Step S1: Take 746 mg of lithium carbonate, 968 mg of ferric nitrate, 1252 mg of manganese nitrate, 1151 mg of ammonium dihydrogen phosphate, and 40 mL of water, mix them thoroughly, and place them in a 50 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene. After sealing the hydrothermal reactor, transfer it to a 180°C forced-air drying oven and react for 12 hours. Then, remove the stainless steel reactor from the forced-air drying oven and allow it to cool naturally to room temperature. Take the cooled reaction solution, filter it using a Buchner funnel, wash the filter cake three times with 25 mL of water, and place the filter cake in a fume hood to dry naturally, obtaining a blocky solid. Grind the blocky solid into powder using an agate mortar and pestle to obtain phosphate-based lithium-ion cathode material precursor particles.

[0110] Step S2: Take the phosphate-based lithium-ion cathode material precursor particles, water, and carbon source PEG-400 from step S1 (mass ratio 1:2:0.05), add them to a three-necked flask, and purge the flask with 0.25 MPa nitrogen gas as a protective gas. Place the flask in a 90°C water bath and stir for 12 hours to allow some water to evaporate. Cool to obtain a gel-like mixed slurry. Remove the gel-like mixed slurry and place it in a quartz boat. Place the quartz boat containing the mixed slurry in a forced-air drying oven and dry for 12 hours. Then, grind the dried solid into powder in an agate mortar to obtain composite cathode material precursor particles.

[0111] Step S3: Take the composite cathode material precursor particles from step S2 and sinter them under a nitrogen atmosphere. The sintering process consists of three stages: a first sintering process, a second sintering process, and a third sintering process. The first sintering process involves heating from room temperature to 200°C at a rate of 5°C / min and sintering at 200°C for 4 hours. The second sintering process involves heating from 200°C to 550°C at a rate of 5°C / min and sintering at 550°C for 6 hours. The third sintering process involves heating from 550°C to 750°C at a rate of 5°C / min and sintering at 750°C for 6 hours. After the three sintering stages, the temperature is reduced from 750°C to room temperature at a rate of 2°C / min to obtain the composite cathode material of this embodiment.

[0112] Example A2

[0113] This embodiment provides a composite cathode material. The composite cathode material of this embodiment includes carbon-containing composite particles, the morphology of which includes nanosheets and near-spherical shapes. The carbon-containing composite particles comprise phosphate-based lithium-ion cathode material particles and carbon material coating the phosphate-based lithium-ion cathode material particles.

[0114] The method for preparing the composite cathode material in this embodiment is as follows:

[0115] Step S1 is basically the same as step S1 in Example A1, except that the hydrothermal reaction conditions are 150°C for 6 hours.

[0116] Step S2: Take 20g of phosphate-based lithium-ion cathode material precursor particles, 40g of water, and 0.2g of glucose from Step S1 (the mass ratio of phosphate-based lithium-ion cathode material precursor particles, water, and carbon source is 1:2:0.01), add them to a three-necked flask, and purge the flask with 0.25Mpa nitrogen gas as a protective gas. Place the flask in a 60℃ water bath and stir for 6 hours. After cooling, a gel-like mixed slurry is obtained. The gel-like mixed slurry is taken out and placed in a quartz boat. The quartz boat containing the mixed slurry is placed in a forced-air drying oven and dried for 6 hours. Then, the dried solid is placed in an agate mortar and ground into powder to obtain composite cathode material precursor particles.

[0117] Step S3: Take the composite cathode material precursor particles from step S2 and sinter them under a nitrogen atmosphere. The sintering process consists of three stages: a first sintering process, a second sintering process, and a third sintering process. The first sintering process involves heating from room temperature to 150°C at a rate of 2°C / min and sintering at 150°C for 2 hours. The second sintering process involves heating from 150°C to 450°C at a rate of 2°C / min and sintering at 450°C for 4 hours. The third sintering process involves heating from 450°C to 600°C at a rate of 2°C / min and sintering at 600°C for 6 hours. After the three stages of sintering, the temperature is reduced from 600°C to room temperature at a rate of 2°C / min to obtain the composite cathode material of this embodiment.

[0118] Example A3

[0119] This embodiment provides a composite cathode material. The composite cathode material of this embodiment includes carbon-containing composite particles, the morphology of which includes nanosheets and near-spherical shapes. The carbon-containing composite particles comprise phosphate-based lithium-ion cathode material particles and carbon material coating the phosphate-based lithium-ion cathode material particles.

[0120] The method for preparing the composite cathode material in this embodiment is as follows:

[0121] Step S1 is basically the same as step S1 in Example A1, except that the hydrothermal reaction conditions are 200°C for 24 hours.

[0122] Step S2: Take 20g of phosphate-based lithium-ion cathode material precursor particles, 40g of water, and 2g of hexadecyltrimethylammonium bromide (CTAB) from Step S1 (the mass ratio of phosphate-based lithium-ion cathode material precursor particles, water, and carbon source is 1:2:0.1), add them to a three-necked flask, and purge the flask with 0.25 MPa nitrogen gas as a protective gas. Place the flask in a water bath at 95°C and stir for 12 hours. After cooling, a gel-like mixed slurry is obtained. The gel-like mixed slurry is taken out and placed in a quartz boat. The quartz boat containing the mixed slurry is placed in a forced-air drying oven and dried for 24 hours. Then, the dried solid is placed in an agate mortar and ground into powder to obtain composite cathode material precursor particles.

[0123] Step S3: Take the composite cathode material precursor particles from step S2 and sinter them under a nitrogen atmosphere. The sintering process consists of three stages: a first sintering process, a second sintering process, and a third sintering process. The first sintering process involves heating from room temperature to 350°C at a rate of 15°C / min and sintering at 350°C for 6 hours. The second sintering process involves heating from 650°C to 650°C at a rate of 15°C / min and sintering at 650°C for 8 hours. The third sintering process involves heating from 650°C to 800°C at a rate of 15°C / min and sintering at 800°C for 8 hours. After the three sintering stages, the temperature is reduced from 800°C to room temperature at a rate of 2°C / min to obtain the composite cathode material of this embodiment.

[0124] Comparative Example A1

[0125] This comparative example provides a composite cathode material, which includes lithium iron phosphate and carbon materials. The preparation method of this comparative example composite cathode material is as follows:

[0126] Step S1: Take 746 mg of lithium carbonate, 968 mg of ferric nitrate, 1252 mg of manganese nitrate, 1151 mg of ammonium dihydrogen phosphate, and 40 mL of water, add them to a 500 mL agate ball mill jar, add carbon source PEG-400 according to the carbon source ratio of Example A1, add 50 mL of anhydrous ethanol, and then ball mill at a speed of 400 r / min for 5 h. Place it in a vacuum drying oven and dry it at 80 °C for 10 h to obtain the precursor of the comparative example composite cathode material.

[0127] Step S2: The composite cathode material precursor from step S1 is placed in a tube furnace and calcined at high temperature under nitrogen protection. The calcination temperature is 700℃ and the calcination time is 13h to obtain the comparative example of lithium iron phosphate.

[0128] Comparative Example A2

[0129] This comparative example provides a composite cathode material. The composite cathode material of this comparative example comprises carbon-containing composite particles, which include a phosphate-based lithium-ion cathode material and a carbon material coated on the phosphate-based lithium-ion cathode material. The preparation method of this comparative example composite cathode material is as follows:

[0130] Step S1 is the same as step S1 in embodiment A1.

[0131] Step S2 is the same as step S2 in Example A1.

[0132] Step S3: The composite cathode material precursor particles from step S2 are sintered to obtain the composite cathode material. The sintering process consists of two stages: a first sintering process and a second sintering process. The first sintering process involves heating from room temperature to 200°C at a rate of 5°C / min and sintering at 200°C for 4 hours. The second sintering process involves heating from 200°C to 750°C at a rate of 5°C / min and sintering at 750°C for 6 hours. After both stages of sintering, the temperature is reduced from 750°C to room temperature at a rate of 2°C / min to obtain the composite cathode material of this embodiment.

[0133] The hydrothermal reaction conditions, the mass ratio of phosphate-based lithium-ion cathode precursor particles, water, and carbon source, the heating rate of the sintering treatment, and the sintering temperatures and times for the first, second, and third sintering treatments in the preparation methods of the composite cathode materials of Examples A1 to A3 and Comparative Examples A1 to A2 are shown in Table 1. The structural morphology of the composite cathode materials of Examples A1 to A3 and Comparative Examples A1 to A2 are also shown in Table 1.

[0134] 2. Lithium-ion batteries and their preparation methods

[0135] Example B1

[0136] Example B1 provides a lithium-ion battery. This example uses the composite positive electrode material from Example A1 as the positive electrode active material, a commercially available lithium metal negative electrode, a polypropylene microporous membrane as the separator, and an electrolyte containing ethylene carbonate, ethyl methyl carbonate, and LiPF6. The assembly process of this example lithium-ion battery is as follows:

[0137] Using the composite positive electrode material of Example A1 as the positive electrode active material, the composite positive electrode material of Example A1 was ball-milled and stirred with polyvinylidene fluoride and SP-Li at a mass ratio of 80:10:10 to prepare a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil, rolled, and vacuum dried at 110°C overnight to obtain a positive electrode sheet.

[0138] G2: Electrolyte preparation: Ethyl carbonate and methyl ethyl carbonate are mixed in a volume ratio of 3:7 to obtain a carbonate mixture. LiPF6 is added to the carbonate mixture to make the concentration of LiPF6 1 mol / L, thus obtaining the electrolyte.

[0139] G3: Lithium-ion battery assembly: In an inert atmosphere glove box, coin cells are assembled in the order of lithium metal sheet-separator-electrolyte-positive electrode to obtain the lithium-ion battery of this embodiment.

[0140] Examples B2 to B3, Comparative Examples B1 to B2

[0141] Examples B2 to B3 and Comparative Examples B1 to B2 each provide a lithium-ion battery. The lithium-ion batteries of Examples B2 to B3 and Comparative Examples B1 to B2 are basically the same as the lithium-ion battery of Example B1 and their preparation methods, except that: the positive electrode active material of the lithium-ion battery of Example B2 is the composite positive electrode material of Example A2; the positive electrode active material of the lithium-ion battery of Example B3 is the composite positive electrode material of Example A3; and so on, the positive electrode active material of the lithium-ion battery of Comparative Example B2 is the composite positive electrode material of Comparative Example A2.

[0142] 3. Relevant performance tests

[0143] 3.1 Relevant Properties of Composite Cathode Materials

[0144] The composite cathode materials of Examples A1 to A2 and Comparative Examples A1 to A2 were subjected to electron microscopy to observe their morphology. The particle morphology of the composite cathode material of Example A1 is as follows: Figure 1 As shown in Table 1, the morphological observation results of each embodiment and comparative example are shown in Table 1.

[0145] The composite cathode materials from Examples A1 to A2 and Comparative Examples A1 to A2 were subjected to particle size analysis, and their compaction density, carbon content, specific surface area, resistivity, and lithium-ion diffusion coefficient D were also measured. Li The tests are shown in Table 1.

[0146] Table 1

[0147]

[0148] In Table 1, the particle size D50 of the composite cathode material was measured using a laser particle size analyzer. The composite cathode material exhibits agglomeration of both flaky and near-spherical particles. The laser particle size analyzer measures the particle size of the agglomerated particles. Table 1 shows the particle size of the composite cathode material particles compared to... Figure 1 There is a difference in diameter between spherical particles and plate-shaped particles.

[0149] like Figure 1As shown, the composite cathode material in Example A1 contains particles with two morphological types: regularly shaped quasi-spherical particles (as shown in box 1) and nanosheet-like particles (as shown in box 2). The diameter of the quasi-spherical particles is approximately 200–300 nm, and the planar diameter of the nanosheet-like particles is approximately 400–600 nm. In the composite cathode material of Example A1, the microstructure of the particles exhibits a stacked structure of nanosheet-like and quasi-spherical particles (as shown in box 3). The gaps between the nanosheet-like particles are filled by the quasi-spherical particles, effectively improving the compaction density of the composite cathode material. As shown in Table 1, the particles in the composite cathode materials of Examples A2 and A3 both exhibit nanosheet-like and quasi-spherical shapes.

[0150] As shown in Table 1, the composite cathode materials of Examples A1 to A3 have high specific surface areas, indicating the presence of plate-like particles in these materials. Table 1 also shows that the composite cathode materials of Examples A1 to A3 all have high compaction densities, with the compaction density of the composite cathode material of Example A1 being significantly higher than that of the composite cathode material of Comparative Example A2. The difference in preparation methods between the composite cathode materials of Examples A1 and Comparative Example A2 lies in the fact that the composite cathode material of Example A1 was prepared through a three-stage sintering process, while the composite cathode material of Comparative Example A2 was prepared through a two-stage sintering process. This indicates that the composite cathode materials and their preparation methods in this application significantly improve the compaction density of the composite cathode materials.

[0151] The composite cathode materials of Examples A1 to A3 all exhibit low resistivity and good lithium-ion diffusion coefficient. The resistivity of Example A1 is significantly lower than that of the composite cathode material of Comparative Example A2, indicating that the composite cathode materials prepared by the methods of this application have good electrical conductivity and electrochemical performance. The lithium-ion diffusion coefficient of the composite cathode material of Example A1 is significantly higher than that of the composite cathode material of Comparative Example A2, indicating that the composite cathode materials of this application have good lithium-ion conductivity.

[0152] 3.2 Lithium-ion battery related performance

[0153] Electrochemical performance tests were conducted on the lithium-ion batteries of the above embodiments and comparative examples. The test conditions were determined according to industry standard test methods. The discharge capacity at 0.1C, 1C, 5C and 10C and the charge-discharge capacity retention rate after 50 cycles at 1C were tested at room temperature. The results are shown in Table 2.

[0154] Table 2

[0155]

[0156] As shown in Table 2, the initial charge and initial discharge capacities of the lithium-ion batteries in Examples B1 to B3 at 0.1C are significantly higher than those of the lithium-ion batteries in Comparative Examples B1 and B2. The discharge capacities at 5C and 10C of the lithium-ion batteries in Examples B1 to B3 are also significantly higher than those in Comparative Examples B1 and B2. Furthermore, the lithium-ion batteries in Examples B1 to B3 exhibit better cycle stability. The capacity retention rate of the lithium-ion batteries in Examples B1 to B3 after 50 cycles at 1C is significantly higher than that of the lithium-ion batteries in Comparative Examples B1 and B2 after 50 cycles at 1C. In Comparative Example B1, the composite cathode material was prepared using a solid-state method, while in Comparative Example B2, the composite cathode material was prepared by two sintering processes. The crystallinity of the sintered particles obtained by this method is inferior to that of the composite cathode materials in the examples. This indicates that the composite cathode material and its preparation method in this application significantly improve the electrochemical performance of the composite cathode material, improve its electronic conductivity and lithium-ion diffusion coefficient, and enhance its energy density and cycle stability.

[0157] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite cathode material, characterized in that, The carbon-containing composite particles include phosphate-based lithium ion positive electrode material particles and a carbon material, the carbon material at least partially coating the surface of the phosphate-based lithium ion positive electrode material particles, and the morphology of the carbon-containing composite particles includes flaky and spherical-like shapes. The composite positive electrode material is obtained by pre-coating phosphate-based lithium ion positive electrode material precursor particles with a carbon source at a temperature of ≤95℃, and then sintering. The sintering process includes first, second and third sintering processes performed in sequence, and the temperatures of the first, second and third sintering processes increase in sequence.

2. The composite cathode material of claim 1, wherein, The carbon-containing composite particles satisfy at least one of the following (1) to (4): (1) The number ratio of the spherical-like carbon-containing composite particles to the flaky carbon-containing composite particles is 1:(0.01-0.1); (2) The particle size of the spherical-like carbon-containing composite particles is 150-500 nm; (3) The planar diameter of the flaky carbon-containing composite particles is 200-600 nm; (4) The thickness of the flaky carbon-containing composite particles is 3-4 nm.

3. The composite cathode material of claim 1 or 2, wherein, The mass content of the carbon material in the composite positive electrode material is 0.01%-5.00%; The coating layer formed by the carbon material on the surface of the phosphate-based lithium ion positive electrode material particles has a thickness of 2-3 nm.

4. The composite cathode material of claim 1 or 2, wherein, The phosphate-based lithium ion positive electrode material particles contain at least one of doped or undoped lithium iron phosphate, doped or undoped lithium manganese phosphate, and doped or undoped lithium manganese iron phosphate.

5. The method for preparing the composite cathode material according to any one of claims 1-4, wherein the lithium transition metal oxide is LiMn2O4. The method includes the following steps: Mixing phosphate-based lithium ion positive electrode material precursor particles with a carbon source and a solvent, pre-coating the phosphate-based lithium ion positive electrode material precursor particles with the carbon source to obtain composite positive electrode material precursor particles, wherein the pre-coating temperature is ≤95℃; Sintering the composite positive electrode material precursor particles to obtain a composite positive electrode material; The sintering process includes first, second and third sintering processes performed in sequence, and the temperatures of the first, second and third sintering processes increase in sequence.

6. The production method according to claim 5, wherein The sintering process satisfies at least one of the following (1) to (7): (1) The temperature of the first sintering process is 150-350℃; (2) The time of the first sintering process is 2-6 h; (3) The temperature of the second sintering process is 450-650℃; (4) The time of the second sintering process is 4-8 h; (5) The temperature of the third sintering process is 650-800℃; (6) The time of the third sintering process is 4-8 h; (7) The heating rates of the first, second and third sintering processes are independently 2-15℃ / min.

7. The preparation method of claim 5 or 6, characterized in that, The preparation method of the phosphate-based lithium ion positive electrode material precursor particle comprises the following steps: preparing a lithium source, a phosphorus source, an iron source and / or a manganese source into an aqueous solution, performing a hydrothermal reaction, drying, and crushing to obtain the phosphate-based lithium ion positive electrode material precursor particle; and / or The mixing mass ratio of the phosphate-based lithium ion positive electrode material precursor particle and the carbon source is 1:0.01-0.1; and / or The carbon source comprises at least one of glucose, cetyltrimethylammonium bromide, polyethylene glycol, sucrose or graphite.

8. An electrode characterized by, The composite positive electrode material comprises the composite positive electrode material as claimed in any one of claims 1-4 or the composite positive electrode material prepared by the preparation method as claimed in any one of claims 5-7.

9. A secondary battery characterized by comprising: The electrode comprises the electrode as claimed in claim 8.

10. An electrical device, characterized by The secondary battery comprises the secondary battery as claimed in claim 9.

Images