Composite positive electrode material and preparation method therefor and use thereof

Abstract

Embodiments of the present application provide a composite positive electrode material and a preparation method therefor and a use thereof. The composite positive electrode material comprises carbon-containing composite particles, the carbon-containing composite particles comprise phosphate-based lithium ion positive electrode material particles and a carbon material, the carbon material is at least partially coated on the surfaces of the phosphate-based lithium ion positive electrode material particles, and the morphology of the carbon-containing composite particles comprises flaky and quasi-spherical shapes. The carbon material enables the electronic conductivity of the composite positive electrode material to be remarkably improved, and gaps between the flaky carbon-containing composite particles can be filled with the quasi-spherical carbon-containing composite particles, thereby increasing the tap density of the composite positive electrode material. The flaky carbon-containing composite particles can also promote exposure of the (010) crystal plane in the crystal structure of the phosphate-based lithium ion positive electrode material, shorten the deintercalation pathway of Li+, improve the lithium ion conductivity of the composite positive electrode material, and increase the low-temperature discharge capacity, thereby improving the electrochemical performance of the positive electrode composite material in a low-temperature environment.

Description

Composite cathode material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on March 5, 2024, with application number 202410251268.6 and application name “Composite positive electrode materials, preparation methods and applications thereof”. Technical Field

[0002] The present application belongs to the technical field of battery materials, and in particular relates to a composite positive electrode material and a preparation method and application thereof. Background Art

[0003] Cathode materials are key active materials in lithium-ion batteries. During the charge and discharge process, they undergo electrochemical oxidation / reduction reactions, repeatedly inserting and extracting lithium ions from the cathode material. Precisely because of this role, their research and development has propelled the advent of the electric vehicle era. Driven by current market demand and the "Dual Carbon Strategy" policy, lithium-ion batteries are required to possess rapid charge / discharge capabilities, higher energy density, improved mechanical stability, longer cycle life, and lower costs to meet the higher performance and market demands of electric vehicles. The promotion and application of lithium-ion batteries in electric vehicles has, in turn, further promoted the research and development of cathode materials.

[0004] In recent years, research on lithium-ion battery cathode materials has primarily focused on materials such as LiCoO2, LiNiO2, LiMn2O4, LiFePO4, and LiMnFePO4 (lithium iron manganese phosphate). Among these, lithium iron phosphate is a cathode material with excellent stability, good cycling performance, and safety. However, lithium iron phosphate also suffers from issues such as a low voltage platform, low energy density, and poor low-temperature performance. By adding manganese to lithium iron phosphate to create lithium iron manganese phosphate, not only can the voltage platform of the cathode material be effectively increased, but also its energy density can be improved. This allows lithium iron manganese phosphate to inherit the thermal stability and safety of lithium iron phosphate while also having the advantages of higher output power and energy density than lithium iron phosphate.

[0005] There are still some defects in the existing lithium manganese iron phosphate. For example, the electronic conductivity of lithium manganese iron phosphate is poor, which is close to that of an insulator. The ion diffusion coefficient of lithium manganese iron phosphate is also worse than that of lithium iron phosphate. In addition, the higher the manganese content in lithium manganese iron phosphate, the worse the dynamic performance and fast charging performance of the battery prepared with lithium manganese iron phosphate. Technical issues

[0006] The purpose of this application is to provide a composite positive electrode material and its preparation method to solve the technical problem of poor electronic and ionic conductivity of lithium manganese iron phosphate in the prior art. At the same time, the embodiments of this application also provide an electrode, a secondary battery, and an electrical device. Technical Solutions

[0007] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0008] In a first aspect, embodiments of the present application provide a composite positive electrode material. The composite positive electrode material of the embodiments of the present application includes carbon-containing composite particles, the carbon-containing composite particles including 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 carbon-containing composite particles having morphologies including flakes and spherical shapes.

[0009] The composite positive electrode material of the embodiment of the present application is formed by coating the surface of the phosphate-based lithium ion positive electrode material particles with carbon material to form flaky and spherical carbon-containing composite particles. The carbon material significantly improves the electronic conductivity of the composite positive electrode material, and the gaps between the flaky carbon-containing composite particles can be filled with spherical carbon-containing composite particles, thereby increasing the tap density of the composite positive electrode material. In addition, the flaky carbon-containing composite particles can also promote the exposure of the (010) crystal plane in the crystal structure of the phosphate-based lithium ion positive electrode material, thereby shortening the Li + The deintercalation and intercalation paths of the composite cathode material are improved, the lithium ion conductivity of the composite cathode material is improved, and the low-temperature discharge capacity is increased, so as to improve the electrochemical performance of the cathode composite material in a low-temperature environment.

[0010] In some embodiments, the carbon-containing composite particles satisfy at least one of the following (1) to (4):

[0011] (1) The ratio of the number of the spherical carbon-containing composite particles to the number of the flaky carbon-containing composite particles is 1:(0.01-0.1);

[0012] (2) The particle size of the spherical carbon-containing composite particles is 150 to 500 nm;

[0013] (3) The planar diameter of the flaky carbon-containing composite particles is 200 to 600 nm;

[0014] (4) The thickness of the flaky carbon-containing composite particles is 3 to 4 nm.

[0015] In the embodiment, the particle size of the spherical carbon-containing composite particles is 200-300 nm.

[0016] In the embodiment, the planar diameter of the flaky carbon-containing composite particles is 400-600 nm.

[0017] In some embodiments, the mass content of the carbon material in the composite positive electrode material is 0.01% to 5.00%.

[0018] In some embodiments, 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 to 3 nm.

[0019] In some embodiments, the plane of the sheet-like structure includes at least one of a regular and an irregular shape; wherein the regular shape includes at least one of a circle, an ellipse, a square, and a hexagon.

[0020] In some embodiments, 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.

[0021] In an embodiment, the doping element contained in at least one of the doped lithium iron phosphate, the doped lithium manganese phosphate, and the doped lithium manganese iron phosphate includes at least one of a transition metal element and a non-metal element.

[0022] In an embodiment, the transition metal element includes at least one of Zn and Al.

[0023] In an embodiment, the non-metallic element includes at least one of C, S, and N.

[0024] In some embodiments, the composite cathode material includes at least one of the following (1) to (4):

[0025] (1) The specific surface area of ​​the composite positive electrode material is 17 to 21 m 2 / g;

[0026] (2) The resistivity of the composite positive electrode material is 14 to 41 Ω·m;

[0027] (3) The lithium ion diffusion coefficient of the composite positive electrode material can be 5×10 -13 cm 2 / S~9.5×10 -12 cm 2 / S;

[0028] (4) The 0.1C discharge capacity of the composite positive electrode material can be 140 to 150 mA·h / g.

[0029] In a second aspect, the present invention provides a method for preparing a composite positive electrode material. The method for preparing a composite positive electrode material according to the present invention comprises the following steps:

[0030] Mixing phosphate-based lithium-ion cathode material precursor particles with a carbon source and a solvent, and pre-coating the phosphate-based lithium-ion cathode material precursor particles with the carbon source to obtain composite cathode material precursor particles, wherein the pre-coating treatment temperature is ≤95° C.;

[0031] The composite cathode material precursor particles are sintered to obtain the composite cathode material.

[0032] The sintering process includes a first sintering process, a second sintering process and a third sintering process which are performed in sequence, and the temperatures of the first sintering process, the second sintering process and the third sintering process are increased in sequence.

[0033] The preparation method of the embodiment of the present application adopts a liquid phase method to pre-coat the phosphate-based lithium-ion positive electrode material precursor particles at low temperature, thereby improving the dispersibility of the phosphate-based lithium-ion positive electrode material precursor particles and the uniformity of the carbon source coating. It can reduce the thickness of the carbon source coating layer on the basis of having the same coating rate, so as to form a carbon layer thickness with better uniformity and relatively thin thickness in the carbon-containing composite particles, which is conducive to building an interconnected three-dimensional conductive network and improving the electronic conductivity of the composite positive electrode material. The good particle dispersion and good carbon source coating uniformity in the liquid phase coating method effectively reduce the agglomeration rate between particles during the subsequent sintering process, so that the composite positive electrode material precursor particles are sintered to form spherical carbon-containing composite particles with a smoother surface, clearer distinction between particles, and more regular particle morphology. Combined with the three-stage sintering method with sequentially increasing temperatures, not only the purity of the crystals is effectively improved, but also the morphology of some carbon-containing composite particles forms a flaky structure, while some carbon-containing composite particles retain a spherical structure, so that the composite positive electrode material prepared by the preparation method of the embodiment of the present application can achieve the coexistence of spherical carbon-containing composite particles and flaky carbon-containing composite particles.

[0034] In addition, the carbon source is subjected to in-situ carbon thermal reduction during the sintering process of the preparation method of the embodiment of the present application, so that the carbon source on the surface of the composite positive electrode material precursor particles can not only form a carbon material coating the particles, but also serve as a reduced outer layer on the surface of the particles, reducing the Mn in the particles. 3+ and Fe 3+ The production of carbon composite particles can be further reduced, and the thickness of the carbon layer in the carbon-containing composite particles can be further reduced, thereby improving the processing performance of the composite positive electrode material. The preparation method of the embodiment of the present application also does not require the addition of a reducing atmosphere such as hydrogen, and adopts a one-step roasting process, which effectively improves production safety and reduces production costs.

[0035] In some embodiments, the sintering process conditions satisfy at least one of the following (1) to (7):

[0036] (1) The temperature of the first sintering treatment is 150-350° C.;

[0037] (2) The first sintering treatment time is 2 to 6 hours;

[0038] (3) The temperature of the second sintering treatment is 450-650° C.;

[0039] (4) The second sintering treatment time is 4 to 8 hours;

[0040] (5) The temperature of the third sintering treatment is 600-800° C.;

[0041] (6) The third sintering treatment takes 4 to 8 hours;

[0042] (7) The heating rates of the first sintering treatment, the second sintering treatment, and the third sintering treatment are independently 2 to 15° C. / min.

[0043] In some embodiments, the method for preparing the phosphate-based lithium-ion positive electrode material precursor particles includes 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 phosphate-based lithium-ion positive electrode material precursor particles.

[0044] In some embodiments, the mixing mass ratio of the phosphate-based lithium-ion cathode material precursor particles to the carbon source is 1:0.01 to 0.1.

[0045] In some embodiments, the mass ratio of the phosphate-based lithium-ion cathode material precursor particles to the solvent is 1:(1.5-2.5).

[0046] In some embodiments, the carbon source comprises at least one of glucose, cetyltrimethylammonium bromide, polyethylene glycol, sucrose, or graphite.

[0047] In some embodiments, the sintering process is performed under a protective atmosphere.

[0048] In a third aspect, the present application provides an electrode, comprising a current collector and an electrode active layer bonded to the surface of the current collector, wherein the electrode active layer contains the above-mentioned composite positive electrode material.

[0049] The electrode of the embodiment of the present application contains the composite positive electrode material described above in the present application. The composite positive electrode material has a high tap density, good electronic conductivity and ionic conductivity, and a large low-temperature discharge capacity. It can effectively reduce the polarization of the electrode, increase the capacity and energy density per unit volume of the electrode of the embodiment of the present application, and improve the performance of the electrode in a low-temperature environment.

[0050] A fourth aspect of an embodiment of the present application provides a secondary battery, comprising a positive electrode and a negative electrode, wherein the positive electrode is an electrode of an embodiment of the present application.

[0051] The secondary battery of the embodiment of the present application contains the electrode of the embodiment of the present application, which has high capacity, high energy density per unit volume, good electrochemical performance at low temperatures, increases the capacity and charge and discharge efficiency of the secondary battery, and improves the low-temperature resistance of the secondary battery.

[0052] In a fifth aspect, an embodiment of the present application provides an electric device, which includes a secondary battery according to an embodiment of the present application.

[0053] Since the electric device of the embodiment of the present application contains the secondary battery of the embodiment of the present application, the electric device of the embodiment of the present application has a long standby or battery life time and good low temperature tolerance. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained like these drawings without any creative work.

[0055] FIG1 is a SEM image of the composite cathode material of Example A1. Modes for Carrying Out the Invention

[0056] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0057] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0058] 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 refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0059] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can 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 the present application.

[0060] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0061] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass in the examples of this application may be μg, mg, g, kg, etc., which are mass units known in the chemical industry.

[0062] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features being referred to. For example, without departing from the scope of the embodiments of this application, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0063] In order to solve the technical problems of low electronic conductivity and low ionic conductivity of lithium manganese iron phosphate in the prior art, the present application proposes the following technical solutions.

[0064] In a first aspect, embodiments of the present application provide a composite positive electrode material. The composite positive electrode material of the embodiments of the present application includes carbon-containing composite particles, the carbon-containing composite particles including 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 carbon-containing composite particles having morphologies including flakes and spherical shapes.

[0065] The spherical shape in this application can be a sphere or an approximately spherical shape, such as an ellipsoid, a hexahedron, an octahedron, a dodecahedron, or other polyhedron, without specific limitations. When the carbon-containing composite particles have a spherical shape, they can be regular or irregular spherical shapes, without specific limitations.

[0066] The composite cathode material of the present application is coated with carbon material on the surface of the phosphate-based lithium-ion cathode material particles, which significantly improves the electronic conductivity of the composite cathode material. + The deintercalation behavior of lithium ions is based on a one-dimensional channel, that is, based on the 010 crystal plane. Under low temperature conditions, the deintercalation ability of lithium ions is weaker. The flaky carbon-containing composite particles can expose more (010) crystal planes in the crystal structure of the phosphate-based lithium ion cathode material, making Li+ The deintercalation path is shorter and the deintercalation rate of lithium ions under low temperature conditions can be effectively improved, thereby improving the lithium ion conductivity and low-temperature discharge capacity of the composite positive electrode material of the embodiment of the present application, so that the composite positive electrode material of the embodiment of the present application exhibits better electrochemical performance under low temperature conditions. In addition, by controlling the morphology of the carbon-containing composite particles to include flakes and spherical shapes, the gaps between the flake-shaped carbon-containing composite particles are filled with spherical carbon-containing composite particles, thereby increasing the compaction density of the composite positive electrode material and improving the volume energy density of the single battery cell containing the composite positive electrode material.

[0067] In some embodiments, the particle size of the spherical carbon-containing composite particles can be 150 to 500 nm, and optionally 200 to 300 nm. In exemplary embodiments, the particle size of the spherical carbon-containing composite particles can be 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or any other typical but non-limiting particle size, or any particle size between any two particle size ranges.

[0068] By making the content and particle size of the spherical carbon-containing composite particles within the above range, the fit between the spherical carbon-containing composite particles and the flaky carbon-containing composite particles is further promoted, the gaps between the carbon-containing composite particles in the composite positive electrode material are further reduced, and the tap density of the composite positive electrode material is further improved.

[0069] In some embodiments, the diameter of the plane of the flaky carbon-containing composite particles can be 200 to 600 nm, optionally 400 to 600 nm. In exemplary embodiments, the diameter of the flaky carbon-containing composite particles can be 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, or other typical but non-limiting diameters, or a diameter size between any two diameter ranges.

[0070] In some embodiments, the thickness of the flaky carbon-containing composite particles can be 3 to 4 nm. In exemplary embodiments, the thickness of the flaky carbon-containing composite particles can be 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 other typical but non-limiting thicknesses, or a thickness between any two thickness ranges.

[0071] The quantitative ratio of the spherical carbon-containing composite particles to the flaky carbon-containing composite particles can be 1:(0.01-0.1), or optionally, in an exemplary embodiment, the quantitative ratio of the spherical carbon-containing composite particles to the flaky 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, and other typical but non-limiting quantitative ratios or any quantitative ratio between any two ratio ranges.

[0072] By controlling the planar diameter and thickness of the flaky carbon-containing composite particles to be within the above range, and controlling the number ratio of the spherical carbon-containing composite particles to the flaky carbon-containing composite particles to be within this range, the lithium ion conductivity of the composite positive electrode material is further improved, and the mutual fit between the flaky structure and the spherical structure in the composite positive electrode material is further promoted, thereby further improving the tap density of the composite positive electrode material.

[0073] In the present application, the plane of the sheet structure can be a regular shape, such as a circle, an ellipse, a square, a hexagon, etc., without specific limitation; the plane of the sheet structure can also be an irregular shape. In some embodiments, the carbon-containing composite particles can be a sheet structure with uniform thickness, and the thicknesses corresponding to different regions of the plane of the same sheet-like carbon-containing composite particle are the same or similar. In other embodiments, the carbon-containing composite particles can be a sheet structure with uneven thickness, and the thicknesses corresponding to different regions of the same sheet-like carbon-containing composite particle are different. For example, there can be protrusions, depressions or inclinations in the plane of the sheet structure, so that the thicknesses corresponding to different regions of the plane are different. For example, the thickness of the same sheet-like carbon-containing composite particle near the center of the plane can be less than the thickness of the area near the edge of the plane.

[0074] In some embodiments, the phosphate-based lithium-ion positive electrode material particles contained in the composite positive electrode materials of the above embodiments may contain at least one of lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate. In some embodiments, the lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate may not be doped with other elements; in another embodiment, the lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate may be doped with other elements, such as transition metal elements such as Zn and Al, or non-metallic elements such as C, S, and N, without limitation.

[0075] In some embodiments, the mass content of the carbon material contained in the composite positive electrode materials of the above embodiments can be 0.01% to 5.00%. In the exemplary embodiments, the mass content of the carbon material in the composite positive electrode material can be 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% and other typical but non-limiting contents or a content value between any two content ranges.

[0076] The coating layer formed by the carbon material on the surface of the phosphate-based lithium-ion positive electrode material particles is a carbon coating layer. In some embodiments, the thickness of the carbon coating layer can be 2 to 3 nm. In a demonstration example, the thickness of the carbon coating layer can be 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, 3 nm, and other typical but non-limiting thicknesses, or a thickness between any two thickness ranges.

[0077] The carbon material within the above-mentioned content range and the carbon coating layer within the thickness range effectively improve the electronic conductivity of the composite positive electrode material while increasing the mass proportion of phosphate-based lithium ion positive electrode material particles in the carbon-containing composite particles, thereby further increasing the lithium ion content of the composite positive electrode material and improving the specific capacity of the composite positive electrode material.

[0078] In some embodiments, the compaction density of the composite cathode material of each embodiment can be 2.1-2.4 g / cm 3 In the exemplary embodiment, the compaction density of the composite cathode material can be 2.1 g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 Typical but non-limiting compacted densities or any compacted density between any two values.

[0079] In some embodiments, the specific surface area of ​​the composite cathode material of each embodiment can be 17 to 21 m 2 / g, in the exemplary embodiment, the specific surface area of ​​the composite positive electrode material can be 17m 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 Typical but non-limiting specific surface areas such as 1 / 2g or any specific surface area between any two numerical ranges.

[0080] By controlling parameters such as flaky particles, spherical particles, carbon material content, pressing density and specific surface area of ​​the composite positive electrode material, the resistivity of the composite positive electrode material can be further reduced, the lithium ion diffusion coefficient of the composite positive electrode material can be increased, and the charge and discharge capacity of the composite positive electrode material can be improved.

[0081] In some embodiments, the resistivity of the composite positive electrode material of the above-mentioned embodiments can be 14 to 41 Ω·m. In the exemplary embodiments, the resistivity of the composite positive electrode material can be typical but non-limiting resistivities 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.

[0082] In some embodiments, the lithium ion diffusion coefficient of the composite positive electrode material of each embodiment can be 5×10 -13 cm 2 / S~9.5×10 -12 cm 2 / S, in the exemplary embodiment, the lithium ion diffusion coefficient of the composite cathode material can be 5×10 -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 and other typical but non-limiting lithium ion diffusion coefficients, or the lithium ion diffusion coefficients between any two numerical ranges.

[0083] In some embodiments, the 0.1C discharge capacity of the composite positive electrode material of each of the above embodiments can be 140-150 mA·h / g. In a demonstration example, the 0.1C discharge capacity of the composite positive electrode material can be 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 and other typical but non-limiting discharge capacities, or a discharge capacity between any two numerical ranges.

[0084] In a second aspect, the present invention provides a method for preparing the composite positive electrode material. The method for preparing the composite positive electrode material in the present invention comprises the following steps:

[0085] S10, mixing phosphate-based lithium-ion cathode material precursor particles with a carbon source and a solvent, and pre-coating the phosphate-based lithium-ion cathode material precursor particles with the carbon source to obtain composite cathode material precursor particles, wherein the pre-coating treatment temperature is ≤95° C.;

[0086] S20, sintering the composite cathode material precursor particles to obtain a composite cathode material.

[0087] 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 in sequence. After the sintering process, the phosphate-based lithium-ion positive electrode material precursor particles will generate a phosphate-based lithium-ion positive electrode material, and the carbon source will be carbonized to generate a carbon material. Therefore, the composite positive electrode material precursor particles will generate the carbon-containing composite particles mentioned above.

[0088] The preparation method of the embodiment of the present application uses a liquid phase method to pre-coat a carbon source under low temperature conditions, disperse the carbon source in a solvent, and during the drying process, the carbon source is uniformly coated on the surface of the phosphate-based lithium-ion positive electrode material precursor particles to form a carbon source layer to prepare a composite positive electrode material precursor. The liquid phase coating method makes the prepared composite positive electrode material precursor particles more dispersed, and the carbon source is more uniformly and completely coated on the surface of the phosphate-based lithium-ion positive electrode material precursor particles. Under the premise of having the same coverage 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 positive electrode material. The liquid phase coating method is combined with a subsequent three-stage sintering treatment with increasing temperatures. Some carbon-containing composite particles form a nano-sheet morphology structure, and some carbon-containing composite particles have a regular spherical structure, so that the flaky carbon-containing composite particles and the spherical carbon-containing composite particles coexist in the composite positive electrode material, effectively improving the tap density of the composite positive electrode material and improving the electronic conductivity and lithium ion conductivity of the composite positive electrode material. In addition, the carbon source layer can also be carbonized in situ during the sintering process, so that the carbon source layer can not only carbonize to form a carbon coating layer, but also serve as a reduced outer layer on the particle surface, reducing the Mn content in the particles. 3+ and Fe 3+ The production of phosphate-based lithium-ion positive electrode materials improves the purity of the phosphate-based lithium-ion positive electrode materials. The preparation method of the embodiment of the present application also does not require the addition of a reducing atmosphere such as hydrogen, and adopts a one-step roasting process, which effectively improves production safety and reduces production costs.

[0089] Step S10:

[0090] Through step S10, the phosphate-based lithium-ion positive electrode material precursor particles are mixed with a carbon source and a solvent, and the phosphate-based lithium-ion positive electrode material precursor particles are pre-coated with the carbon source, and the temperature of the pre-coating treatment is controlled to be ≤95°C to obtain composite positive electrode material precursor particles, thereby realizing low-temperature pre-coating of the phosphate-based lithium-ion positive electrode material precursor particles with the carbon source using a liquid phase method.

[0091] In some embodiments, phosphate-based lithium-ion positive electrode material precursor particles can be mixed with a carbon source and a solvent to obtain a mixed slurry, and then the mixed slurry is dried to allow the carbon source to coat the surface of the phosphate-based lithium-ion positive electrode material precursor particles to form a carbon source layer, thereby preparing composite positive electrode material precursor particles.

[0092] In some embodiments, the phosphate-based lithium-ion cathode material precursor particles contain lithium. The inclusion of lithium in the phosphate-based lithium-ion cathode material precursor particles further reduces the mixing process between the phosphate-based lithium-ion cathode material precursor particles and the lithium source, while allowing the lithium element to be encapsulated within the carbon source. This reduces the impact of the lithium element on the carbon source during sintering and on the morphology and structure of the composite cathode material particles, thereby facilitating the formation of a composite cathode material comprising both flaky carbon-containing composite particles and spherical carbon-containing composite particles.

[0093] In some embodiments, the particle size of the phosphate-based lithium ion positive electrode material particles can be set according to the particle size of the phosphate-based lithium ion positive electrode material particles in the carbon-containing composite particles described above.

[0094] In some embodiments, the preparation method of phosphate-based lithium-ion positive electrode material precursor particles may include 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 phosphate-based lithium-ion positive electrode material precursor particles.

[0095] During the preparation of phosphate-based lithium-ion cathode materials such as lithium iron manganese phosphate, iron and manganese need to be mixed at the atomic level. Uneven mixing of iron and manganese may lead to impure phases, such as the formation of impure phases such as Fe2P, Fe2O3, and Mn2O3. When phosphate-based lithium-ion cathode material precursor particles are prepared by a solution method, when the phosphate-based lithium-ion cathode material precursor particles contain iron and manganese, the lithium, iron, manganese, and phosphorus in the phosphate-based lithium-ion cathode material precursor particles are mixed at the atomic level, greatly improving the mixing uniformity of iron and manganese. Combined with the subsequent sintering treatment, the uniformity of the phosphate-based lithium-ion cathode material solid solution is further improved.

[0096] In some embodiments, the lithium source may include at least one of Li2CO3, LiH2PO4, LiOH·H2O, CH3COOLi, and LiNO3. In an exemplary embodiment, 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, and a combination of LiNO3 and CH3COOLi.

[0097] In some embodiments, the iron source may include any one of Fe(NO3)3, Fe2O3 or FeSO4·7H2O. In a demonstrative example, the iron source may include a combination of Fe(NO3)3 and Fe2O3, a combination of FeSO4·7H2O and Fe2O3, and a combination of Fe(NO3)3 and FeSO4·7H2O.

[0098] In some embodiments, the manganese source may include at least one of Mn(NO3)3, Mn2O3 or MnSO4·7H2O. In exemplary embodiments, the manganese source may include a combination of Mn(NO3)3 and Mn2O3, a combination of MnSO4·7H2O and Mn2O3, and a combination of Mn(NO3)3 and MnSO4·7H2O.

[0099] 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, and a combination of (NH4)3PO4 and H3PO4.

[0100] In some embodiments, the molar ratio of the lithium source, iron source, manganese source and phosphorus source can be set as required. For example, the general formula of the phosphate-based lithium ion positive electrode material can be LiMn (1-x) Fe x 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.

[0101] In some embodiments, the hydrothermal reaction can be performed in a container with a polytetrafluoroethylene coating to reduce the effect of metal ions in the container.

[0102] In some examples, the temperature of the hydrothermal reaction can be 150-200° C., and the time can be 6-24 hours. In exemplary embodiments, the temperature of the hydrothermal reaction can be 150° C., 160° C., 170° C., 180° C., 190° C., 200° C., or a temperature between any two temperature ranges. The time of the hydrothermal reaction can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, or a typical but non-limiting time. Controlling the time and temperature of the hydrothermal reaction within this range further promotes the progress of the hydrothermal reaction and reduces the occurrence of side reactions.

[0103] In some embodiments, after the hydrothermal reaction, solid-liquid separation can be performed by centrifugation, filtration, suction filtration, or the like, and the solid can be collected, 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, and the specific pulverization method can be grinding in a mortar or a ball mill, and the specific pulverization method is not limited.

[0104] In some embodiments, the mixing of the phosphate-based lithium-ion cathode material precursor particles, the carbon source, and the solvent can be performed under a protective atmosphere. Mixing under a protective atmosphere can further reduce oxidation of metal ions and improve the purity of the phosphate-based lithium-ion cathode material.

[0105] 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 can be fully dispersed in a solvent such as water. For example, carbon sources such as glucose, CTAB, PEG, and sucrose can dissolve or swell in water, thereby being fully dispersed in the solvent to further improve the mixing uniformity of the components in the mixed slurry and improve the uniformity of the carbon source coating on the surface of the phosphate-based lithium-ion cathode material precursor particles.

[0106] In some embodiments, the solvent may include at least one of water, ethanol, acetone, and the like. Carbon sources such as glucose, CTAB, PEG, and sucrose have good solubility in these solvents, allowing the carbon source to fully dissolve, swell, and disperse in the solvent, thereby improving the uniformity of the mixed slurry.

[0107] In some embodiments, the mixing mass ratio of the phosphate-based lithium-ion positive electrode material precursor particles and the carbon source can be 1:0.01 to 0.1. In exemplary embodiments, the mixing ratio of the phosphate-based lithium-ion positive electrode material precursor particles and the carbon source can be a typical but non-limiting ratio such as 1:0.01, 1:0.02, 1:0.05, 1:0.07, 1:0.1, or a ratio between any two ratio ranges. This ratio of phosphate-based lithium-ion positive electrode material particles and carbon source effectively controls the carbon source content in the composite positive electrode material precursor particles, thereby further controlling the carbon source content in the composite positive electrode material. This effectively improves the electronic conductivity of the composite positive electrode material, thereby increasing the content of the phosphate-based lithium-ion positive electrode material in the composite positive electrode material, and further improving the specific capacity of the composite positive electrode material.

[0108] In some embodiments, the mass ratio of the phosphate-based lithium-ion cathode material precursor particles to the solvent in the mixed slurry can be 1:(1.5-2.5). Furthermore, the mass ratio of the phosphate-based lithium-ion cathode material precursor particles, the solvent, and the carbon source in the mixed slurry can be 1:(1.5-2.5):(0.01-0.1), and can optionally be 1:2:(0.01-0.1). In an exemplary embodiment, the mass ratio of the phosphate-based lithium-ion cathode material precursor particles, the solvent, and the carbon source can be a typical but non-limiting mass ratio such as 1:2:0.01, 1:2:0.05, 1:2:0.1, or a ratio between any two mass ratio ranges. A mixed slurry within this mass ratio range allows the carbon source to dissolve and disperse, and further improves the dispersibility of the phosphate-based lithium-ion cathode material precursor particles, thereby improving the uniformity of the carbon source coating on the phosphate-based lithium-ion cathode material precursor particles.

[0109] In some embodiments, the mixed slurry can also be heated to partially volatilize the water in the mixed slurry, gel the mixed slurry, and further promote the carbon source to be evenly coated on the surface of the phosphate-based lithium-ion positive electrode material precursor particles. In a further embodiment, the temperature of the heat treatment can be 60 to 95°C, and the heating treatment time can be 6 to 12 hours. In an exemplary embodiment, the temperature of the heat treatment can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, etc., which are typical but non-limiting temperatures, and the heating treatment time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc., which are typical but non-limiting times. During the heat treatment process, stirring and other operations can also be performed to improve the uniformity of the mixed slurry. By heating, the high molecular weight carbon sources of CTAB and PEG are fully dissolved or swollen, promoting the gelation of the mixed slurry, so that the carbon source is evenly coated on the surface of the phosphate-based lithium-ion positive electrode material particles.

[0110] In some embodiments, the heat treatment may be performed under a protective atmosphere such as nitrogen or argon to reduce oxidation of metal ions during the heat treatment.

[0111] In some embodiments, the mixed slurry may be dried by hot air drying. In a specific example, the mixed slurry may be dried in a forced air drying oven for 6 to 24 hours and then ground to obtain composite positive electrode material precursor particles.

[0112] In some embodiments, a phosphate-based lithium-ion positive electrode material precursor, water, and a carbon source can be added to a three-necked flask in a mass ratio of 1:2:0.01-0.1 under a protective atmosphere of 0.25 MPa nitrogen, and mixed to obtain a mixed slurry; the three-necked flask containing the mixed slurry is placed in a 60-90°C water bath and heated with stirring for 6-12 hours. After the reaction is completed, the gel-like mixed slurry is taken out and placed in a blast drying oven to dry. The solid obtained after drying is then ground with an agate mortar to obtain composite positive electrode material precursor particles.

[0113] In the preparation method of the embodiment of the present application, the phosphate-based lithium-ion positive electrode material precursor particles are coated by a liquid phase method, so that the mixing between the materials is more uniform, and the phosphate-based lithium-ion positive electrode material precursor particles have better dispersion, thereby improving the uniformity of the carbon source coating on the surface of the phosphate-based lithium-ion positive electrode material precursor particles, forming a composite structure of phosphate-based lithium-ion positive electrode material precursor particles-carbon source layer, and obtaining composite positive electrode material precursor particles.

[0114] Step S20:

[0115] In step S20, the composite cathode material precursor particles are sintered to form a crystal structure of the phosphate-based lithium-ion cathode material precursor particles to obtain phosphate-based lithium-ion cathode material particles. The carbon source is carbonized to form a carbon material, and the carbon material is at least partially coated on the surface of the phosphate-based lithium-ion cathode material particles, thereby forming carbon-containing composite particles of the phosphate-based lithium-ion cathode material particles and the carbon material to obtain a composite cathode material. By controlling the sintering process to a three-stage sintering process, the carbon-containing composite particles have morphologies including flakes and spherical shapes.

[0116] In some embodiments, the sintering process may be performed under a protective atmosphere of nitrogen or argon to further reduce oxidation of metal ions and carbon sources.

[0117] In some embodiments, the temperature of the first sintering process may be 150° C. to 350° C. In exemplary embodiments, the temperature of the first sintering process may be 150° C., 180° C., 200° C., 230° C., 250° C., 280° C., 300° C., 320° C., 350° C., or any temperature range between any two of these temperatures. The first sintering process within this temperature range effectively removes volatile components, further reducing the impact of volatile components on particle formation during the subsequent sintering process, while achieving critical conditions for carbonization of the carbon source.

[0118] In some embodiments, the first sintering treatment may last for 2 to 6 hours. In exemplary embodiments, the first sintering treatment may last for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or other typical but non-limiting periods. 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 subsequent formation of crystal particles.

[0119] In some embodiments, the temperature of the second sintering process may be 450° C. to 650° C. In exemplary embodiments, the temperature of the second sintering process may be 450° C., 480° C., 500° C., 530° C., 550° C., 580° C., 600° C., 630° C., 650° C., or any temperature between any two temperature ranges. The second sintering process within this temperature range effectively promotes nucleation and crystal formation of the phosphate-based lithium-ion cathode material, while simultaneously carbonizing the carbon source to form a carbon material.

[0120] In some embodiments, the second sintering treatment may be performed for 4 to 8 hours. In exemplary embodiments, the second sintering treatment may be performed for a typical but non-limiting time of 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours. Controlling the second sintering treatment time within this range further promotes carbonization of the carbon source and formation of phosphate-based lithium-ion cathode material crystals, thereby initially forming a carbon-containing composite particle structure of the phosphate-based lithium-ion cathode material coated with carbon material.

[0121] In some embodiments, the temperature of the third sintering treatment may be 600°C to 800°C, optionally 650°C to 800°C. In exemplary embodiments, the temperature of the third sintering treatment may be 600°C, 620°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C, or any temperature range between any two of the above. Controlling the temperature of the third sintering treatment within this range further purifies the crystals of the phosphate-based lithium-ion cathode material and promotes the formation of nano-sheet structures in some carbon-containing composite particles, thereby obtaining a composite cathode material having flaky carbon-containing composite particles and spherical carbon-containing composite particles.

[0122] In some embodiments, the third sintering treatment may last for 4 to 8 hours. In exemplary embodiments, the third sintering treatment may last for a typical but non-limiting time, such as 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours. Controlling the third sintering treatment time within this range promotes the formation of a flake structure from some of the carbon-containing composite particles having a regular spherical structure.

[0123] In some embodiments, the heating rates of the first, second, and third sintering processes are independently 2-15°C / min. In exemplary embodiments, the heating rates of the first, second, and third sintering processes are independently 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, 15°C / min, or other typical but non-limiting heating rates, or any heating rate range between any two heating rate ranges. By controlling the heating rates of the first, second, and third sintering processes within the range, the formation of carbon-containing composite particles is effectively promoted while further shortening the sintering process time and improving production efficiency.

[0124] In the prior art, the solid-phase method for preparing phosphate-based lithium-ion cathode materials has high requirements for the grinding conditions and machinery of ball milling mixing, and is prone to uneven material mixing, which easily leads to technical problems such as irregular particles and the generation of impurities. The preparation method of the embodiment of the present application uses the above-mentioned liquid-phase method to prepare a phosphate-based lithium-ion cathode material precursor, so that the iron and manganese elements in the phosphate-based lithium-ion cathode material are mixed at the atomic level to promote the uniform formation of lithium iron phosphate solid solution, effectively reduce the generation of impurities in the phosphate-based lithium-ion cathode material, and improve the crystal purity of the phosphate-based lithium-ion cathode material.

[0125] In addition, the preparation method of the embodiment of the present application also pre-coates the carbon source at low temperature by the liquid phase method to form a structure of phosphate lithium ion positive electrode material precursor particles-carbon source layer to prepare composite positive electrode material precursor particles. Since the carbon source is coated by the liquid phase method, the dispersion between the materials is more uniform, which further promotes the separation of the phosphate lithium ion positive electrode material precursor particles, and promotes the carbon source to be evenly coated on the surface of the phosphate lithium ion positive electrode material particles, so that the composite positive electrode material precursor particles have a more regular morphology. The composite positive electrode material precursor particles are prepared by the liquid phase method, combined with a three-stage sintering method in which the temperature is successively increased, so that the composite positive electrode material precursor particles form carbon-containing composite particles with a spherical structure, and some of the carbon-containing composite particles form a flaky structure to obtain a composite positive electrode material in which flaky carbon-containing composite particles and spherical carbon-containing composite particles coexist.

[0126] In a third aspect, the present application provides an electrode, comprising a current collector and an electrode active layer bonded to the surface of the current collector, wherein the electrode active layer contains the above-mentioned composite positive electrode material.

[0127] The electrode of the embodiment of the present application contains the composite positive electrode material described above in the present application. The composite positive electrode material has a high tap density, good electronic conductivity and ionic conductivity, and a large low-temperature discharge capacity. It can effectively reduce the polarization of the electrode of the embodiment of the present application, increase the capacity and energy density per unit volume of the electrode, and improve the performance of the electrode in a low-temperature environment.

[0128] The electrode of the present application may be a conventional electrode of a secondary battery, such as a current collector and an electrode active layer bonded to the surface of the current collector.

[0129] In some embodiments, the electrode active layer includes, in addition to the composite positive electrode material, a binder and a conductive agent, wherein 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 an embodiment of the present 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.

[0130] In some embodiments, the electrode preparation process can be: mixing the composite positive electrode material, the conductive agent and the binder to obtain an electrode slurry, coating the electrode slurry on the current collector, and preparing the electrode plate through steps such as drying, rolling, and die cutting.

[0131] A fourth aspect of an embodiment of the present application provides a secondary battery, comprising a positive electrode and a negative electrode, wherein the positive electrode is an electrode of an embodiment of the present application.

[0132] The secondary battery of the embodiment of the present application includes necessary components such as a positive electrode, a negative electrode, a separator, and an electrolyte, and of course also includes other necessary or auxiliary components. Among them, the positive electrode is the electrode of the embodiment of the present application, that is, the positive electrode active layer contained in the positive electrode contains the composite positive electrode material of the embodiment of the present application.

[0133] The secondary battery of the embodiment of the present application contains the electrode of the embodiment of the present application, which has high capacity and high energy density per unit volume, thereby increasing the capacity and charge and discharge efficiency of the secondary battery and improving the low-temperature resistance of the secondary battery.

[0134] In a fifth aspect, an embodiment of the present application provides an electric device, which includes a secondary battery according to an embodiment of the present application.

[0135] Since the electric device of the embodiment of the present application contains the secondary battery of the embodiment of the present application, the electric device of the embodiment of the present application has a long standby or battery life time and good low temperature tolerance.

[0136] In some embodiments, the electric device of the present application can be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, etc. Among them, the electric toy can include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc. The spacecraft can include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0137] In order to make the above implementation details and operations of this application clearly understood by those skilled in the art, as well as to significantly demonstrate the advanced performance of the composite positive electrode material and its preparation method and application in the embodiments of this application, the above technical solution is illustrated by multiple embodiments below.

[0138] 1. Composite cathode material and preparation method thereof:

[0139] Example A1

[0140] This embodiment provides a composite positive electrode material. The composite positive electrode material of this embodiment includes carbon-containing composite particles, the carbon-containing composite particles having morphologies including nanosheets and spherical shapes, and the carbon-containing composite particles include phosphate-based lithium ion positive electrode material particles and a carbon material coating the phosphate-based lithium ion positive electrode material particles.

[0141] The preparation method of the composite positive electrode material in this embodiment is as follows:

[0142] Step S1, taking 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, mixing them evenly, and placing them in a 50 mL stainless steel hydrothermal kettle lined with polytetrafluoroethylene; sealing the hydrothermal kettle and transferring it to a 180° C. forced drying oven to react for 12 hours, then removing the stainless steel reactor from the forced drying oven and naturally cooling it to room temperature; taking the cooled reaction solution, filtering it with a Buchner funnel, washing the filter cake with 25 mL of water three times, and then placing the filter cake in a fume hood and naturally drying it to obtain a block solid, which was ground into powder using an agate mortar to prepare phosphate-based lithium ion positive electrode material precursor particles;

[0143] Step S2, taking the phosphate-based lithium-ion positive electrode material precursor particles in step S1, and adding them, water and carbon source PEG-400 in a mass ratio of 1:2:0.05 to a three-necked flask, filling the three-necked flask with 0.25 MPa nitrogen as a protective gas, placing the three-necked flask in a 90°C water bath and stirring for 12 hours, allowing part of the water to evaporate, and cooling to obtain a gel-like mixed slurry; taking out the gel-like mixed slurry, placing it in a quartz boat, placing the quartz boat containing the mixed slurry in a blast drying oven and drying it for 12 hours, then placing the dried solid in an agate mortar and grinding it into powder to obtain composite positive electrode material precursor particles;

[0144] Step S3, take the composite positive electrode material precursor particles in step S2 and perform sintering treatment under a nitrogen atmosphere; wherein the sintering treatment is divided into three stages: a first sintering treatment, a second sintering treatment and a third sintering treatment. The first sintering treatment is to increase the temperature from room temperature to 200°C at a heating rate of 5°C / min, and sinter at 200°C for 4h; the second sintering treatment is to increase the temperature from 200°C to 550°C at a heating rate of 5°C / min, and sinter at 550°C for 6h; the third sintering treatment is to increase the temperature from 550°C to 750°C at a heating rate of 5°C / min, and sinter at 750°C for 6h; after three stages of sintering treatment, cool from 750°C to room temperature at a cooling rate of 2°C / min to obtain the composite positive electrode material of this embodiment.

[0145] Example A2

[0146] This embodiment provides a composite positive electrode material. The composite positive electrode material of this embodiment includes carbon-containing composite particles, the carbon-containing composite particles having morphologies including nanosheets and spherical shapes, and the carbon-containing composite particles include phosphate-based lithium ion positive electrode material particles and a carbon material coating the phosphate-based lithium ion positive electrode material particles.

[0147] The preparation method of the composite positive electrode material in this embodiment is as follows:

[0148] Step S1 is basically the same as step S1 of Example A1, except that the hydrothermal reaction conditions are 150° C. and 6 h;

[0149] Step S2, taking 20g of the phosphate-based lithium ion positive electrode material precursor particles, 40g of water, and 0.2g of glucose in step S1 (the mass ratio of the phosphate-based lithium ion positive electrode material precursor particles, water, and carbon source is 1:2:0.01), and adding them to a three-necked flask, filling the three-necked flask with 0.25Mpa nitrogen as a protective gas, placing the three-necked flask in a 60°C water bath and stirring for 6 hours, and then cooling to obtain a gel-like mixed slurry; taking out the gel-like mixed slurry, placing it in a quartz boat, placing the quartz boat containing the mixed slurry in a blast drying oven and drying it for 6 hours, and then placing the dried solid in an agate mortar and grinding it into powder to obtain composite positive electrode material precursor particles;

[0150] Step S3, take the composite positive electrode material precursor particles in step S2 and perform sintering treatment under a nitrogen atmosphere; wherein the sintering treatment is divided into three stages: a first sintering treatment, a second sintering treatment and a third sintering treatment. The first sintering treatment is to increase the temperature from room temperature to 150°C at a heating rate of 2°C / min, and sinter at 150°C for 2h; the second sintering treatment is to increase the temperature from 150°C to 450°C at a heating rate of 2°C / min, and sinter at 450°C for 4h; the third sintering treatment is to increase the temperature from 450°C to 600°C at a heating rate of 2°C / min, and sinter at 600°C for 6h; after three stages of sintering treatment, cool from 600°C to room temperature at a cooling rate of 2°C / min to obtain the composite positive electrode material of this embodiment.

[0151] Example A3

[0152] This embodiment provides a composite positive electrode material. The composite positive electrode material of this embodiment includes carbon-containing composite particles, the carbon-containing composite particles having morphologies including nanosheets and spherical shapes, and the carbon-containing composite particles include phosphate-based lithium ion positive electrode material particles and a carbon material coating the phosphate-based lithium ion positive electrode material particles.

[0153] The preparation method of the composite positive electrode material in this embodiment is as follows:

[0154] Step S1 is basically the same as step S1 of Example A1, except that the hydrothermal reaction conditions are 200° C. and 24 h;

[0155] Step S2, taking 20g of the phosphate-based lithium ion positive electrode material precursor particles, 40g of water, and 2g of cetyltrimethylammonium bromide (CTAB) in step S1 (the mass ratio of the phosphate-based lithium ion positive electrode material precursor particles, water, and carbon source is 1:2:0.1), and adding them to a three-necked flask, filling the three-necked flask with 0.25Mpa nitrogen as a protective gas, placing the three-necked flask in a 95°C water bath and stirring for 12 hours, and then cooling to obtain a gel-like mixed slurry; taking out the gel-like mixed slurry, placing it in a quartz boat, placing the quartz boat containing the mixed slurry in a blast drying oven and drying it for 24 hours, then placing the dried solid in an agate mortar and grinding it into powder to obtain composite positive electrode material precursor particles;

[0156] Step S3, take the composite positive electrode material precursor particles in step S2 and perform sintering treatment under a nitrogen atmosphere; wherein, the sintering treatment is divided into three stages: a first sintering treatment, a second sintering treatment and a third sintering treatment. The first sintering treatment is to increase the temperature from room temperature to 350°C at a heating rate of 15°C / min, and sinter at 350°C for 6 hours; the second sintering treatment is to increase the temperature from 650°C to 650°C at a heating rate of 15°C / min, and sinter at 650°C for 8 hours; the third sintering treatment is to increase the temperature from 650°C to 800°C at a heating rate of 15°C / min, and sinter at 800°C for 8 hours; after three stages of sintering treatment, cool from 800°C to room temperature at a cooling rate of 2°C / min to obtain the composite positive electrode material of this embodiment.

[0157] Comparative Example A1

[0158] This comparative example provides a composite positive electrode material, which includes lithium iron phosphate and carbon material. The preparation method of the composite positive electrode material in this comparative example is as follows:

[0159] Step S1, taking 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, adding them to a 500 mL agate ball mill, and adding carbon source PEG-400 according to the carbon source ratio of Example A1, and then adding 50 mL of anhydrous ethanol and ball milling at a ball mill speed of 400 r / min for 5 h. The ball mill was placed in a vacuum drying oven at 80°C and dried for 10 h to obtain a composite positive electrode material precursor of this comparative example;

[0160] Step S2: placing the composite cathode material precursor in step S1 in a tubular furnace and calcining it at a high temperature under nitrogen protection at a temperature of 700° C. for 13 h to obtain the lithium iron phosphate of this comparative example.

[0161] Comparative Example A2

[0162] This comparative example provides a composite positive electrode material. The composite positive electrode material of this comparative example includes carbon-containing composite particles, which include a phosphate-based lithium ion positive electrode material and a carbon material coated on the phosphate-based lithium ion positive electrode material. The composite positive electrode material of this comparative example is prepared as follows:

[0163] Step S1, same as step S1 of embodiment A1;

[0164] Step S2, same as step S2 in embodiment A1;

[0165] Step S3, take the composite positive electrode material precursor particles in step S2 and perform sintering treatment to obtain a composite positive electrode material; wherein, the sintering treatment is divided into two stages: a first sintering treatment and a second sintering treatment; the first sintering treatment is to increase the temperature from room temperature to 200°C at a heating rate of 5°C / min, and sinter at 200°C for 4 hours; the second sintering treatment is to increase the temperature from 200°C to 750°C at a heating rate of 5C / min, and sinter at 750°C for 6 hours; after two stages of sintering treatment, the temperature is lowered from 750°C to room temperature at a cooling rate of 2°C / min to obtain the composite positive plate material of this embodiment.

[0166] The hydrothermal reaction conditions, the mass ratio of the phosphate-based lithium-ion cathode material precursor particles, water, and carbon source, the sintering temperature rise rate, 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 and A2 are shown in Table 1. The structural morphologies of the composite cathode materials of Examples A1 to A3 and Comparative Examples A1 and A2 are shown in Table 1.

[0167] 2. Lithium-ion battery and its preparation method

[0168] Example B1

[0169] Example B1 provides a lithium-ion battery. This example lithium-ion battery utilizes the composite positive electrode material of Example A1 as the positive electrode active material, a commercial lithium metal negative electrode, a polypropylene microporous separator, and an electrolyte comprising ethylene carbonate, ethyl methyl carbonate, and LiPF6. The assembly process of this example lithium-ion battery is as follows:

[0170] G1: Positive electrode sheet. The composite positive electrode material of Example A1 was used as the positive electrode active material. The composite positive electrode material of Example A1 was ball-milled with polyvinylidene fluoride and SP-Li in a mass ratio of 80:10:10 to prepare a positive electrode slurry. The positive electrode slurry was coated on the surface of an aluminum foil, rolled, and vacuum-dried at 110°C overnight to obtain a positive electrode sheet.

[0171] G2: Preparation of electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7 to prepare a carbonate mixture, and LiPF6 was added to the carbonate mixture to make the concentration of LiPF6 1 mol / L to prepare an electrolyte.

[0172] G3: Lithium-ion battery assembly: In an inert atmosphere glove box, button cells were assembled in the order of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet to obtain the lithium-ion battery of this embodiment.

[0173] Example B2 to Example B3, Comparative Example B1 to Comparative Example B2

[0174] Examples B2 and B3 and Comparative Examples B1 and B2 each provide a lithium ion battery. The lithium ion batteries of Examples B2 and B3 and Comparative Examples B1 and B2 are substantially the same as the lithium ion battery of Example B1 and its preparation method, 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.

[0175] 3. Related performance tests

[0176] 3.1 Related properties of composite cathode materials

[0177] The composite cathode materials of Examples A1 and A2 and Comparative Examples A1 and A2 were scanned with an electron microscope to observe their morphology. The particle morphology of the composite cathode material of Example A1 is shown in Figure 1 , and the morphology observation results of the various Examples and Comparative Examples are shown in Table 1 .

[0178] Take the composite positive electrode materials of Examples A1 to A2 and Comparative Examples A1 to A2 above, and perform particle size analysis, and perform compaction density, carbon content, specific surface area, resistivity and lithium ion diffusion coefficient D Li The test is shown in Table 1.

[0179] Table 1

[0180] Among them, the particle size D50 of the composite positive electrode material in Table 1 is measured by a laser particle size analyzer. The flaky particles and spherical particles in the composite positive electrode material are agglomerated. The laser particle size analyzer measures the particle size of the agglomerated particles. The particle size of the composite positive electrode material particles in Table 1 is different from the diameter of the spherical particles and the particle size of the flaky particles in Figure 1.

[0181] As shown in Figure 1, the particles in the composite positive electrode material of Example A1 include two types of particles with regular morphology: spherical particles (as shown in box 1) and nano-flake particles (as shown in box 2). The diameter of the spherical particles is about 200 to 300 nm, and the planar diameter of the nano-flake particles is about 400 to 600 nm. In the composite positive electrode material of Example A1, the microscopic morphology of the particles shows a structure in which nano-flake particles and spherical particles are stacked on each other (as shown in box 3). The gaps between the nano-flake particles are filled with spherical particles, which effectively improves the compaction density of the composite positive electrode material. As shown in Table 1, the particles in the composite positive electrode materials of Example A2 and Example A3 are both nano-flake and spherical.

[0182] At the same time, as shown in Table 1, the composite positive electrode materials of Examples A1 to A3 have a high specific surface area, indicating that flaky particles are present in the composite positive electrode materials of Examples A1 to A3. As shown in Table 1, the composite positive electrode materials of Examples A1 to A3 all have a high compaction density, and the compaction density of the composite positive electrode material of Example A1 is significantly higher than the compaction density of the composite positive electrode material of Comparative Example A2. The difference in the preparation methods of the composite positive electrode material of Example A1 and the composite positive electrode material of Comparative Example A2 is that the composite positive electrode material of Example A1 is prepared by three-stage sintering, and the composite positive electrode material of Comparative Example A2 is prepared by two-stage sintering, which shows that the composite positive electrode materials of the embodiments of the present application and their preparation methods significantly improve the compaction density of the composite positive electrode materials.

[0183] The composite positive electrode materials of Examples A1 to A3 all have low resistivity and good lithium ion diffusion coefficients. The resistivity of Example A1 is significantly lower than that of the composite positive electrode material of Comparative Example A2, indicating that the composite positive electrode materials prepared by the preparation methods of the present application examples have good electrical conductivity and electrochemical properties. The lithium ion diffusion coefficient of the composite positive electrode material of Example A1 is significantly higher than that of the composite positive electrode material of Comparative Example A2, indicating that the composite positive electrode materials of the present application examples have good lithium ion conductivity.

[0184] 3.2 Lithium-ion battery related performance

[0185] The electrochemical performance of the lithium-ion batteries of the above embodiments and comparative examples was tested according to industry standard test methods. The discharge capacities at 0.1C, 1C, 5C, and 10C, as well as the charge-discharge capacity retention rate after 50 cycles at 1C, were tested at room temperature. The results are shown in Table 2.

[0186] Table 2

[0187] As shown in Table 2, the first charge capacity and first discharge capacity of the lithium ion batteries of Examples B1 to B3 at 0.1C are significantly higher than those of the lithium ion batteries of Comparative Examples B1 and B2, and the discharge capacities of the lithium ion batteries of Examples B1 to B3 at 5C and 10C are also significantly higher than those of the lithium ion batteries of Comparative Examples B1 and B2. In addition, the lithium ion batteries of Examples B1 to B3 have better cycle stability, and the capacity retention rate of the lithium ion batteries of Examples B1 to B3 1C after 50 cycles is significantly higher than the capacity retention rate of the lithium ion batteries of Comparative Examples B1 and B2 1C after 50 cycles. Among them, the composite positive electrode material used in Comparative Example B1 is prepared by a solid phase method, and the composite positive electrode material used in Comparative Example B2 is sintered twice. The crystallinity of the particles sintered by this scheme is worse than that of the composite positive electrode material in the embodiment. This shows that the composite positive electrode material of the embodiment of the present application and its preparation method significantly improve the electrochemical properties of the composite positive electrode material, improve the electronic conductivity and lithium ion diffusion coefficient of the composite positive electrode material, and improve the energy density and cycle stability of the composite positive electrode material.

[0188] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A composite positive electrode material, characterized in that The carbon-containing composite particles include phosphate-based lithium-ion positive electrode material particles and carbon materials. The carbon materials are at least partially coated on the surface of the phosphate-based lithium-ion positive electrode material particles. The carbon-containing composite particles have morphologies including flakes and spherical shapes.

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

3. The composite cathode material according to claim 2, wherein The particle size of the spherical carbon-containing composite particles is 200 to 300 nm; The plane diameter of the flaky carbon-containing composite particles is 400 to 600 nm.

4. The composite cathode material according to any one of claims 1 to 3, wherein The mass content of the carbon material in the composite positive electrode material is 0.01% to 5.00%; and / or 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 to 3 nm.

5. The composite cathode material according to any one of claims 1 to 4, characterized in that The plane of the sheet structure includes at least one of regular and irregular shapes; wherein the regular shape includes at least one of circular, elliptical, square, and hexagonal.

6. The composite cathode material according to any one of claims 1 to 5, characterized in that 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.

7. The composite cathode material according to claim 6, wherein The doping element contained in at least one of the doped lithium iron phosphate, the doped lithium manganese phosphate and the doped lithium manganese iron phosphate includes at least one of a transition metal element and a non-metal element.

8. The composite cathode material according to claim 7, wherein The transition metal element includes at least one of Zn and Al; and / or The non-metallic element includes at least one of C, S, and N.

9. The composite cathode material according to any one of claims 1 to 8, wherein: The composite cathode material includes at least one of the following (1) to (4): (1) The specific surface area of ​​the composite positive electrode material is 17 to 21 m 2 / g; (2) The resistivity of the composite positive electrode material is 14 to 41 Ω·m; (3) The lithium ion diffusion coefficient of the composite positive electrode material can be 5×10 -13 cm 2 / S~9.5×10 -12 cm 2 / S; (4) The 0.1C discharge capacity of the composite positive electrode material can be 140 to 150 mA·h / g.

10. The method for preparing a composite positive electrode material according to any one of claims 1 to 9, wherein: The steps include: Mixing phosphate-based lithium-ion cathode material precursor particles with a carbon source and a solvent, and pre-coating the phosphate-based lithium-ion cathode material precursor particles with the carbon source to obtain composite cathode material precursor particles, wherein the pre-coating treatment temperature is ≤95° C.; Sintering the composite cathode material precursor particles to obtain a composite cathode material; The sintering process includes a first sintering process, a second sintering process and a third sintering process which are performed in sequence, and the temperatures of the first sintering process, the second sintering process and the third sintering process are increased in sequence.

11. The preparation method according to claim 10, characterized in that The sintering treatment conditions satisfy at least one of the following (1) to (7): (1) The temperature of the first sintering treatment is 150-350° C.; (2) The first sintering treatment time is 2 to 6 hours; (3) The temperature of the second sintering treatment is 450-650° C.; (4) The second sintering treatment time is 4 to 8 hours; (5) The temperature of the third sintering treatment is 600-800° C.; (6) The third sintering treatment takes 4 to 8 hours; (7) The heating rates of the first sintering treatment, the second sintering treatment, and the third sintering treatment are independently 2 to 15° C. / min.

12. The preparation method according to claim 10 or 11, characterized in that: The method for preparing the phosphate-based lithium ion cathode material precursor particles 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 pulverizing to obtain the phosphate-based lithium ion cathode material precursor particles; and / or The mixing mass ratio of the phosphate-based lithium-ion cathode material precursor particles to the carbon source is 1:0.01-0.1; and / or The mass ratio of the phosphate-based lithium-ion cathode material precursor particles to the solvent is 1:(1.5-2.5); and / or The carbon source includes at least one of glucose, cetyltrimethylammonium bromide, polyethylene glycol, sucrose or graphite.

13. The preparation method according to any one of claims 10 to 12, characterized in that: The sintering process is carried out under a protective atmosphere.

14. An electrode, characterized in that The invention comprises the composite positive electrode material according to any one of claims 1 to 9 or the composite positive electrode material prepared by the composite positive electrode material preparation method according to any one of claims 10 to 13.

15. A secondary battery, characterized in that: Comprising the electrode as claimed in claim 14.

16. An electrical device, characterized in that: The secondary battery according to claim 15 is included.

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