Fluorine-nitrogen co-doped carbon-coated positive electrode material and preparation method thereof

Abstract

The invention relates to a fluorine-nitrogen co-doped carbon-coated positive electrode material and a preparation method thereof, and the cycle performance of the positive electrode material is effectively improved by arranging a fluorine-nitrogen co-doped carbon-coated layer on the surface of a positive electrode active material. When the positive electrode material is applied to a battery system, the cycle life of the battery can be prolonged.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a fluorine-nitrogen co-doped carbon-coated positive electrode material and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0002] With technological advancements, clean energy sources such as batteries are gradually replacing traditional fossil fuels, providing power for a wide range of scenarios. Cathode materials are a key component in determining battery performance. Existing cathode materials, such as lithium manganese iron phosphate, lithium manganese oxide, and lithium-rich manganese-based cathode materials, suffer from poor cycling performance, restricting their application in the battery field. Therefore, there is an urgent need to improve the cycling performance of cathode materials. Summary of the Invention

[0003] In view of the problems existing in the background technology, the present application provides a fluorine-nitrogen co-doped carbon-coated positive electrode material, which has good cycle performance.

[0004] The fluorine-nitrogen co-doped carbon-coated positive electrode material provided in the first aspect of the present application comprises a core particle and a carbon coating layer. The core particle comprises a positive electrode active material. The carbon coating layer is coated on the surface of the core particle. The surface of the carbon coating layer facing away from the core particle is doped with fluorine atoms. The interior of the carbon coating layer is doped with nitrogen atoms. The positive electrode active material comprises one or more of a lithium transition metal oxide and a phosphate containing lithium and a transition metal.

[0005] The carbon coating layer of the present invention is doped with nitrogen atoms internally and fluorine atoms on the surface away from the core particle. By providing a fluorine-nitrogen co-doped carbon coating layer on the surface of the positive electrode active material, the cycling performance of the positive electrode material is effectively improved. Applying the positive electrode material of the present invention to a battery system can increase the battery's cycle life.

[0006] In some embodiments, according to the first aspect, a first example of the first aspect is provided, wherein the atomic doping percentage of nitrogen atoms in the carbon coating layer is 5.0%-8.5%.

[0007] By optimizing the doping amount of nitrogen atoms, the cycle performance of the positive electrode material can be further improved.

[0008] In some embodiments, according to the first aspect, a second example of the first aspect is provided, wherein the atomic percentage of fluorine atoms doped on the surface of the carbon coating layer is 2.0%-6.0%.

[0009] By optimizing the atomic percentage of fluorine atoms doped on the surface of the carbon coating layer, the cycle performance of the positive electrode material can be further improved.

[0010] In some embodiments, according to the first aspect, a third example of the first aspect is provided, wherein the thickness of the carbon coating layer is 5-50 nm.

[0011] By optimizing the thickness of the carbon coating layer, the cycle performance of the positive electrode material can be further improved.

[0012] In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, wherein the transition metal includes one or more of manganese, nickel, and cobalt. Optionally, the positive electrode active material includes one or more of lithium manganese iron phosphate (LMFP), lithium manganate (LMO), and a lithium-rich manganese-based positive electrode material.

[0013] The transition metal elements contained in these positive electrode active materials will have dissolution problems, resulting in poor cycle performance. However, using the fluorine-nitrogen co-doped carbon coating layer of the present application to coat these positive electrode active materials can significantly reduce the dissolution of transition metal ions from the positive electrode, thereby improving the cycle performance of the positive electrode material.

[0014] A second aspect of the present application provides a method for preparing a fluorine-nitrogen co-doped carbon-coated positive electrode material. The preparation method comprises the following steps:

[0015] After mixing the positive electrode active material with the organic carbon source, the organic carbon source is polymerized, thereby coating the surface of the positive electrode active material with polymerized carbon to obtain a polymerized carbon-coated positive electrode material;

[0016] After mixing the polymeric carbon-coated positive electrode material with a nitrogen source, performing a primary calcination under an inert atmosphere to obtain a nitrogen-doped carbon-coated positive electrode material; and

[0017] The nitrogen-doped carbon-coated cathode material is mixed with a fluorine source and then subjected to secondary calcination under an inert atmosphere to obtain a fluorine-nitrogen co-doped carbon-coated cathode material.

[0018] After the initial calcination, the polymerized carbon will be carbonized into a rigid carbon skeleton, and nitrogen atoms will be doped inside and on the surface of the carbon coating. After the secondary calcination, the fluorine atoms will replace the residual defect sites, oxygen sites and nitrogen sites on the surface of the carbon coating, thereby doping the surface of the carbon coating with fluorine atoms. However, since the carbon skeleton of the coating layer is rigid during the secondary calcination, the fluorine atoms almost only undergo substitution reactions on the surface, and the nitrogen atoms doped inside the shell are not affected. Therefore, the method of the present application can be used to coat the surface of the positive electrode active material with a fluorine-nitrogen co-doped carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0019] In some embodiments, according to the second aspect, a first example of the second aspect is provided, wherein the organic carbon source comprises a combination of a small molecule organic carbon source and a macromolecular organic carbon source. The small molecule organic carbon source comprises one or more of glucose, sucrose, and trehalose. The macromolecular organic carbon source comprises one or more of starch, hemicellulose, cellulose, and lignin.

[0020] This application uses a combination of a small molecule organic carbon source and a macromolecular organic carbon source as a "dual carbon source". During the hydrothermal treatment process, the small molecule organic carbon source will first polymerize on the surface of the positive electrode active material, providing rich nucleation sites for the subsequent polymerization of oligomeric carbon; then, the CO bonds in the macromolecular organic carbon source break to produce oligomers, which are then uniformly polymerized on the surface of the nucleation sites, thereby achieving a uniform coating of a carbon layer on the surface of the positive electrode active material. Compared to using only a small molecule organic carbon source or a macromolecular organic carbon source, the dual carbon source of this application can uniformly coat the carbon coating layer on the surface of the positive electrode active material, improve the uniformity of the carbon coating layer, and help improve the cycle performance of the positive electrode material.

[0021] In some embodiments, according to the second aspect, a second example of the second aspect is provided, wherein the mass ratio of the small molecule organic carbon source to the macromolecular organic carbon source is 5:100-25:100.

[0022] By optimizing the mass ratio of small molecule organic carbon sources to macromolecular organic carbon sources, it is beneficial to further improve the uniformity of the carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0023] In some embodiments, according to the second aspect, a third example of the second aspect is proposed, and the preparation of a polymeric carbon-coated positive electrode material includes: dispersing the positive electrode active material in a dispersion of an organic carbon source, causing the organic carbon source to undergo hydrothermal polymerization, thereby coating the surface of the positive electrode active material with polymeric carbon to obtain a polymeric carbon-coated positive electrode material.

[0024] The polymerized carbon formed in this step has a non-rigid carbon skeleton and contains a relatively high concentration of oxygen-containing components. In subsequent steps, these oxygen-containing components can react with nitrogen-containing substances, such as ammonia, to achieve nitrogen doping within the carbon coating. Therefore, the formation of non-rigid polymerized carbon is a prerequisite for nitrogen doping within the carbon coating. Using a hydrothermal method to polymerize the organic carbon source onto the surface of the positive electrode active material to form polymerized carbon is low-cost, easy to operate, and suitable for industrial application.

[0025] In some embodiments, according to the second aspect, a fourth example of the second aspect is provided, wherein the temperature of the hydrothermal polymerization is 160-220° C. and the time of the hydrothermal polymerization is 12-30 hours.

[0026] By optimizing the temperature and time of hydrothermal polymerization, the organic carbon source can be fully reacted and evenly coated on the surface of the positive electrode active material, which is beneficial to improving the cycle performance of the positive electrode material.

[0027] In some embodiments, according to the second aspect, a fifth example of the second aspect is proposed, and the preparation of a fluorine-nitrogen co-doped carbon-coated positive electrode material includes: dispersing the nitrogen-doped carbon-coated positive electrode material in a dispersion of a fluorine source, ultrasonically dispersing, drying, grinding, and then performing secondary calcination.

[0028] Compared with directly mixing the nitrogen-doped carbon-coated positive electrode material with the solid fluorine source, the present application disperses the nitrogen-doped carbon-coated positive electrode material in a dispersion of the fluorine source and then ultrasonically disperses it, which can improve the dispersion uniformity and is beneficial to uniformly doping fluorine atoms on the surface of the nitrogen-doped carbon coating layer, thereby helping to improve the cycle performance of the positive electrode material.

[0029] In some embodiments, according to the second aspect, a sixth example of the second aspect is provided, wherein the mass ratio of the nitrogen-doped carbon-coated positive electrode material to the fluorine source is 50:1-10:1.

[0030] Optimizing the mass ratio of the nitrogen-doped carbon-coated cathode material to the fluorine source is beneficial to controlling the doping amount of fluorine atoms on the surface of the carbon coating layer, thereby improving the cycle performance of the cathode material.

[0031] In some embodiments, according to the second aspect, a seventh example of the second aspect is provided, wherein the mass ratio of the polymeric carbon-coated positive electrode material to the nitrogen source is 10:1-1:1.

[0032] By optimizing the mass ratio of the polymeric carbon-coated positive electrode material to the nitrogen source, it is beneficial to control the amount of nitrogen atoms doped inside the carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0033] In some embodiments, according to the second aspect, an eighth example of the second aspect is provided, wherein physical grinding is performed after mixing the polymeric carbon-coated positive electrode material with the nitrogen source and before performing the primary calcination.

[0034] Physical grinding is beneficial to uniformly disperse and mix the polymeric carbon-coated positive electrode material and the nitrogen source, which is beneficial to the subsequent uniform doping of nitrogen atoms inside the carbon coating layer, further improving the cycle performance of the positive electrode material.

[0035] In some embodiments, according to the second aspect, a ninth example of the second aspect is provided, wherein the temperature of the initial calcination is 400-1000° C., and the calcination time is 0.5-10 h.

[0036] During the high-temperature calcination process, the polymerized carbon undergoes thermal polymerization. As the oxygen-containing components in the polymerized carbon layer decrease, the polymerized carbon layer gradually transforms from a non-rigid carbon skeleton to a rigid carbon skeleton. Furthermore, during the high-temperature calcination process, the nitrogen source undergoes pyrolysis to produce ammonia, which can react with the oxygen-containing components in the polymerized carbon and defect sites in the carbon skeleton, thereby achieving nitrogen doping in the carbon skeleton. By optimizing the conditions of the initial calcination, it is beneficial to fully carbonize the polymerized carbon into a rigid carbon skeleton, reduce the residual non-rigid carbon skeleton, and improve conductivity. It is also beneficial to promote the full reaction of ammonia with the oxygen-containing components in the polymerized carbon and defect sites in the carbon skeleton, improve doping uniformity, and thus enhance the cycle performance of the positive electrode material.

[0037] In some embodiments, according to the second aspect, a tenth example of the second aspect is provided, wherein the temperature of the initial calcination is 500-800° C., and the calcination time is 2-5 hours.

[0038] Further optimizing the initial calcination conditions will help improve the cycle performance of the positive electrode material.

[0039] In some embodiments, according to the second aspect, an eleventh example of the second aspect is provided, wherein the conditions for the secondary calcination include: a calcination temperature of 600-800° C., and a calcination time of 0.5-2.0 h.

[0040] During the secondary high-temperature calcination process, the fluorine source undergoes thermal decomposition, releasing fluorine atoms. Since fluorine atoms have a more negative electronegativity than oxygen atoms, they can replace defect sites, oxygen sites, and nitrogen sites on the surface of the carbon coating, thereby achieving fluorine atom doping on the surface of the carbon coating. By optimizing the conditions of the secondary calcination, the uniform doping of fluorine atoms on the surface of the carbon coating is facilitated, the number of oxygen- and nitrogen-containing sites on the surface of the carbon coating is reduced, and the side reactions on the surface of the carbon coating during high-voltage charge and discharge are reduced. This, in turn, reduces the occurrence of gas production during battery charge and discharge, thereby improving the cycle performance of the positive electrode material.

[0041] In some embodiments, according to the second aspect, a twelfth example of the second aspect is provided, wherein the nitrogen source includes one or more of dicyandiamide, melamine, melem, urea, and hexamethylenetetramine.

[0042] When these substances are used as nitrogen sources, they can decompose and produce ammonia during the initial calcination process, which reacts with the oxygen-containing components in the polymerized carbon and the defect sites in the carbon skeleton, thereby achieving nitrogen doping in the carbon skeleton.

[0043] In some embodiments, according to the second aspect, a thirteenth example of the second aspect is provided, wherein the fluorine source includes one or more of an organic fluorine source and an inorganic fluorine source. The organic fluorine source includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoroethylene-vinylidene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene-trifluoroethylene copolymer, and a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene. The inorganic fluorine source includes one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

[0044] Using these substances as fluorine sources can decompose and release fluorine atoms during the secondary calcination process, replacing the residual defect sites, oxygen sites and nitrogen sites on the surface of the carbon coating layer, thereby achieving fluorine atom doping on the surface of the carbon coating layer.

[0045] The third aspect of the present application provides a secondary battery, which includes the fluorine-nitrogen co-doped carbon-coated positive electrode material of the first aspect of the present application or the fluorine-nitrogen co-doped carbon-coated positive electrode material obtained according to the preparation method of the second aspect of the present application.

[0046] A fourth aspect of the present application provides an electrical device, which includes the secondary battery according to the third aspect of the present application.

[0047] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying any creative work.

[0049] Figure 1 Schematic diagram of the structure of the fluorine-nitrogen co-doped carbon-coated positive electrode material prepared in one embodiment of the present application.

[0050] Figure 2 This is a flow chart of preparing a fluorine-nitrogen co-doped carbon-coated positive electrode material according to one embodiment of the present application.

[0051] Description of reference numerals:

[0052] 100, core particle; 200, polymerized carbon layer; 300, carbon coating layer; 301, N atom; 302, F atom. DETAILED DESCRIPTION

[0053] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0055] In the description of the embodiments of the present application, “multiple” means more than two, including two, unless otherwise clearly and specifically defined.

[0056] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0057] With technological advancements, clean energy sources such as batteries are gradually replacing traditional fossil fuels, providing power for a wide range of scenarios. Cathode materials are a key factor in determining battery performance. Existing cathode materials, such as lithium iron manganese phosphate, lithium manganese oxide, and lithium-rich manganese-based cathode materials, suffer from poor cycling performance, restricting their application in the battery field. Therefore, there is an urgent need to improve the cycling performance of cathode materials.

[0058] The use of carbon-coated positive electrode materials can improve the cycle performance of positive electrode materials to a certain extent. However, as the requirements for battery cycle life continue to increase, the cycle performance of positive electrode materials still needs to be further improved. Studies have found that doping nitrogen atoms in the carbon coating layer is beneficial to improving the conductivity of the positive electrode material, thereby improving the cycle performance and rate performance of the positive electrode material. However, the doping of nitrogen atoms will lead to the presence of more side reaction sites on the surface of the carbon coating layer. Coupled with the oxygen sites on the surface of the carbon coating layer, this makes the surface of the carbon coating layer prone to side reactions at high voltages, limiting the improvement of the cycle performance of the positive electrode material.

[0059] In order to solve the above problems, the first aspect of the present application provides a fluorine-nitrogen co-doped carbon-coated positive electrode material. Figure 1 , which includes a core particle 100 and a carbon coating layer 300. The core particle 100 includes a positive electrode active material. The carbon coating layer 300 is coated on the surface of the core particle 100. The surface of the carbon coating layer 300 away from the core particle 100 is doped with fluorine atoms 302. The interior of the carbon coating layer 300 is doped with nitrogen atoms 301. The positive electrode active material includes one or more of a lithium transition metal oxide and a phosphate containing lithium and a transition metal.

[0060] The carbon coating layer of the present invention is doped with nitrogen atoms internally and fluorine atoms on the surface away from the core particle. By providing a fluorine-nitrogen co-doped carbon coating layer on the surface of the positive electrode active material, the cycling performance of the positive electrode material is effectively improved. The principle of improving the cycling performance of the positive electrode material by coating with a fluorine-nitrogen co-doped carbon coating is speculated as follows.

[0061] First, doping fluorine atoms on the surface of the carbon coating can reduce the number of defect sites, nitrogen sites and oxygen sites on the surface of the carbon coating, thereby reducing the occurrence of surface side reactions of the carbon coating during high-voltage charging and discharging, and then reducing the occurrence of gas production during multiple charging and discharging of the battery.

[0062] Secondly, when the positive electrode material contains transition metal elements, the positive electrode material will dissolve transition metal ions during multiple charge and discharge processes, and the nitrogen atoms doped in the carbon coating layer can coordinate with the transition metal ions to anchor the transition metal ions, which can effectively reduce the dissolution of transition metal ions from the positive electrode.

[0063] In summary, the present application can achieve the above two improvement effects by coating the surface of the positive electrode material with a fluorine-nitrogen co-doped carbon coating layer, and the above two improvement effects synergistically enhance the cycle performance of the fluorine-nitrogen co-doped carbon-coated positive electrode material.

[0064] Since the positive electrode material of the present application has good cycle performance, applying it to a battery system can improve the cycle life of the battery.

[0065] The technical solutions described in the embodiments of the present application are applicable to positive electrode materials, and are also applicable to the preparation process of positive electrode materials, secondary batteries using positive electrode materials, and electrical devices using secondary batteries.

[0066] In some embodiments, the atomic doping percentage of nitrogen atoms in the carbon coating layer may be 5.0%-8.5%.

[0067] In the present application, the “atomic doping percentage of nitrogen atoms inside the carbon coating layer” refers to the surface nitrogen content percentage obtained by X-ray photoelectron spectroscopy (XPS) measurement and analysis at 2 nm of the carbon coating shell layer after argon ion etching.

[0068] By optimizing the doping amount of nitrogen atoms, the dissolution of transition metal ions can be reduced, thereby improving the cycle performance of the positive electrode material.

[0069] In some specific embodiments, the atomic doping percentage of nitrogen atoms in the carbon coating layer may be 5.7%, 7.3%, or 8.5%.

[0070] In some embodiments, the atomic percentage of fluorine atoms doped on the surface of the carbon coating layer may be 2.0%-6.0%.

[0071] In the present application, the “atomic percentage of fluorine atoms doped on the surface of the carbon coating layer” refers to the percentage of surface fluorine element content obtained by X-ray photoelectron spectroscopy (XPS) measurement and analysis.

[0072] By optimizing the atomic percentage of fluorine atoms doped on the surface of the carbon coating, it is beneficial to reduce the side reaction sites on the surface of the carbon coating, reduce the occurrence of side reactions on the surface of the positive electrode material during battery charging and discharging, and reduce gas production, which is beneficial to further improve the cycle performance of the positive electrode material.

[0073] In some specific embodiments, the atomic percentage of fluorine atoms doped on the surface of the carbon coating layer may be 2.0%, 3.2%, 4.6% or 5.9%.

[0074] In some embodiments, the carbon coating layer may have a thickness of 5-50 nm.

[0075] By optimizing the thickness of the carbon coating layer, the cycle performance of the positive electrode material can be further improved.

[0076] In some embodiments, the carbon coating layer may have a thickness of 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm.

[0077] In some embodiments, the transition metal includes one or more of manganese, nickel, and cobalt. Alternatively, the positive electrode active material includes one or more of lithium manganese iron phosphate, lithium manganate, and lithium-rich manganese-based positive electrode materials.

[0078] The transition metal elements contained in these positive electrode active materials will have dissolution problems, resulting in poor cycle performance. However, using the fluorine-nitrogen co-doped carbon coating layer of the present application to coat these positive electrode active materials can significantly improve the dissolution of transition metal ions from the positive electrode, thereby improving the cycle performance of the positive electrode material.

[0079] A second aspect of the present application provides a method for preparing a fluorine-nitrogen co-doped carbon-coated positive electrode material. The preparation method comprises the following steps:

[0080] After mixing the positive electrode active material with the organic carbon source, the organic carbon source is polymerized, thereby coating the surface of the positive electrode active material with polymerized carbon to obtain a polymerized carbon-coated positive electrode material;

[0081] After mixing the polymeric carbon-coated positive electrode material with a nitrogen source, performing a primary calcination under an inert atmosphere to obtain a nitrogen-doped carbon-coated positive electrode material; and

[0082] The nitrogen-doped carbon-coated cathode material is mixed with a fluorine source and then subjected to secondary calcination under an inert atmosphere to obtain a fluorine-nitrogen co-doped carbon-coated cathode material.

[0083] After the initial calcination, the polymerized carbon will be carbonized into a rigid carbon skeleton, and nitrogen atoms will be doped inside and on the surface of the carbon coating. After the secondary calcination, fluorine atoms will replace the defect sites, oxygen sites, and nitrogen sites on the surface of the carbon coating, thereby doping fluorine atoms on the surface of the carbon coating. However, since the carbon skeleton of the coating layer is rigid during the secondary calcination, the fluorine atoms almost only undergo substitution reactions on the surface, and the doped nitrogen atoms inside are not affected. Therefore, the method of the present application can be used to coat the surface of the positive electrode active material with a fluorine-nitrogen co-doped carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0084] In addition, the preparation method of the present application has good universality and is applicable to various positive electrode materials.

[0085] In some embodiments, the organic carbon source comprises a combination of a small molecule organic carbon source and a macromolecular organic carbon source. The small molecule organic carbon source comprises one or more of glucose, sucrose, and trehalose. The macromolecular organic carbon source comprises one or more of starch, hemicellulose, cellulose, and lignin.

[0086] The present application adopts a combination of a small molecule organic carbon source and a macromolecular organic carbon source as a "dual carbon source". During the hydrothermal treatment process, the small molecule organic carbon source will first polymerize on the surface of the positive electrode active particles, providing rich nucleation sites for the subsequent polymerization of oligomeric carbon; then, the CO bonds in the macromolecular organic carbon source gradually break to produce oligomers, and the oligomers are uniformly polymerized on the surface of the nucleation sites, thereby achieving a uniform coating of a carbon layer on the surface of the positive electrode active material. Compared to using only a small molecule organic carbon source or a macromolecular organic carbon source, the dual carbon source of the present application can uniformly coat the carbon coating layer on the surface of the positive electrode active material, improve the uniformity of the carbon coating layer, and help improve the cycle performance of the positive electrode material.

[0087] In some specific embodiments, the mass ratio of the positive electrode active material to the organic carbon source may be 1:0.5-1:3.

[0088] By optimizing the mass ratio of the positive electrode active material to the organic carbon source, it is beneficial to accurately control the thickness of the carbon coating layer coated on the surface of the positive electrode active material, and to improve the coating uniformity, thereby improving the cycle performance of the positive electrode material.

[0089] In some specific embodiments, the mass ratio of the positive electrode active material to the organic carbon source can be 1:0.5, 1:1, 1:2, or 1:3.

[0090] In some embodiments, the mass ratio of the small molecule organic carbon source to the macromolecular organic carbon source may be 5:100-25:100.

[0091] By optimizing the mass ratio of small molecule organic carbon sources to macromolecular organic carbon sources, it is beneficial to further improve the uniformity of the carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0092] In some specific embodiments, the mass ratio of the small molecule organic carbon source to the macromolecular organic carbon source can be 5:100, 10:100, 15:100, 20:100 or 25:100.

[0093] In some embodiments, preparing a polymeric carbon-coated positive electrode material includes: dispersing a positive electrode active substance in a dispersion of an organic carbon source, hydrothermally polymerizing the organic carbon source, thereby coating the surface of the positive electrode active substance with polymeric carbon to obtain a polymeric carbon-coated positive electrode material.

[0094] The polymerized carbon formed in this step has a non-rigid carbon skeleton and contains a relatively high concentration of oxygen-containing components. In subsequent steps, these oxygen-containing components can react with nitrogen-containing substances, such as ammonia, to achieve nitrogen doping within the carbon coating. Therefore, the formation of non-rigid polymerized carbon is a prerequisite for nitrogen doping within the carbon coating. Using a hydrothermal method to polymerize the organic carbon source onto the surface of the positive electrode active material to form polymerized carbon is low-cost, easy to operate, and suitable for industrial application.

[0095] In some embodiments, the dispersion of the organic carbon source includes the organic carbon source and a dispersant, which may include water.

[0096] In some embodiments, the temperature of the hydrothermal polymerization may be 160-220° C. The time of the hydrothermal polymerization may be 12-30 hours.

[0097] By optimizing the temperature and time of hydrothermal polymerization, the organic carbon source can be fully reacted and evenly coated on the surface of the positive electrode active material, which is beneficial to improving the cycle performance of the positive electrode material.

[0098] In some embodiments, the temperature of the hydrothermal polymerization can be 160°C, 180°C, 200°C, or 220°C.

[0099] In some embodiments, the hydrothermal polymerization time can be 12 h, 18 h, 24 h, or 30 h.

[0100] In some embodiments, preparing a fluorine-nitrogen co-doped carbon-coated cathode material comprises: dispersing the nitrogen-doped carbon-coated cathode material in a dispersion of a fluorine source, ultrasonically dispersing, drying, grinding, and then performing secondary calcination.

[0101] Compared with directly mixing the nitrogen-doped carbon-coated positive electrode material with a solid fluorine source, the present application disperses the nitrogen-doped carbon-coated positive electrode material in a dispersion of the fluorine source and then ultrasonically disperses it, which can improve the dispersion uniformity and is beneficial to uniformly doping fluorine atoms on the surface of the nitrogen-doped carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0102] In some specific embodiments, the fluorine source dispersion includes a fluorine source and a dispersant, which may include one or both of water and ethanol.

[0103] In some embodiments, the mass ratio of the nitrogen-doped carbon-coated cathode material to the fluorine source may be 50:1-10:1.

[0104] Optimizing the mass ratio of the nitrogen-doped carbon-coated cathode material to the fluorine source is beneficial to controlling the doping amount of fluorine atoms on the surface of the carbon coating layer, thereby improving the cycle performance of the cathode material.

[0105] In some specific embodiments, the mass ratio of the nitrogen-doped carbon-coated cathode material to the fluorine source can be 50:1, 40:1, 30:1, 20:1, or 10:1.

[0106] In some embodiments, the mass ratio of the polymeric carbon-coated cathode material to the nitrogen source may be 10:1-1:1.

[0107] By optimizing the mass ratio of the polymeric carbon-coated positive electrode material to the nitrogen source, it is beneficial to control the amount of nitrogen atoms doped inside the carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0108] In some specific embodiments, the mass ratio of the polymeric carbon-coated cathode material to the nitrogen source can be 10:1, 8:1, 6:1, 4:1, 2:1 or 1:1.

[0109] In some embodiments, physical milling is performed after mixing the polymeric carbon-coated cathode material with the nitrogen source and before performing the initial calcination.

[0110] Physical grinding is beneficial to uniformly disperse and mix the polymeric carbon-coated positive electrode material and the nitrogen source, which is beneficial to improving the uniformity of nitrogen atom doping inside the carbon coating layer and further improving the cycle performance of the positive electrode material.

[0111] In some specific embodiments, the physical grinding time can be 5-60 min, for example, 5 min, 10 min, 20 min, 30 min, 40 min or 60 min.

[0112] In some embodiments, the primary calcination temperature may be 400-1000° C. and the calcination time may be 0.5-10 h.

[0113] During the high-temperature calcination process, the polymerized carbon undergoes thermal polymerization. As the oxygen-containing components in the polymerized carbon layer decrease, the polymerized carbon layer gradually transforms from a non-rigid carbon skeleton to a rigid carbon skeleton. Furthermore, during the high-temperature calcination process, the nitrogen source undergoes pyrolysis to produce ammonia, which can react with the oxygen-containing components in the polymerized carbon and defect sites in the carbon skeleton, thereby achieving nitrogen doping in the carbon skeleton. By optimizing the conditions of the initial calcination, it is beneficial to fully carbonize the polymerized carbon into a rigid carbon skeleton, reduce the residual non-rigid carbon skeleton, and improve conductivity. It is also beneficial to promote the full reaction of ammonia with the oxygen-containing components in the polymerized carbon and defect sites in the carbon skeleton, improve doping uniformity, and thus enhance the cycle performance of the positive electrode material.

[0114] In some specific embodiments, the calcination temperature of the primary calcination may be 400°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or 1000°C.

[0115] Alternatively, the calcination temperature of the primary calcination may be 500-800°C.

[0116] In some specific embodiments, the calcination time of the primary calcination may be 0.5-10 h, for example, 0.5 h, 1 h, 2 h, 4 h, 8 h, or 10 h.

[0117] Optionally, the calcination time of the primary calcination may be 2-5 hours.

[0118] In some specific embodiments, the heating rate of the primary calcination may be 1.0-10.0° C. / min, for example, 1.0° C. / min, 2.0° C. / min, 5.0° C., or 10.0° C. / min.

[0119] In some embodiments, the conditions for the secondary calcination include: a calcination temperature of 600-800° C., and a calcination time of 0.5-2.0 h.

[0120] During the secondary high-temperature calcination process, the fluorine source undergoes thermal decomposition and releases fluorine atoms. Since fluorine atoms have a more negative electronegativity than oxygen atoms, they can replace defect sites, oxygen sites, and nitrogen sites on the surface of the carbon coating, thereby achieving fluorine atom doping on the surface of the carbon coating. By optimizing the conditions of the secondary calcination, it is beneficial for fluorine atoms to fully replace the residual defect sites, oxygen sites, and nitrogen sites on the surface of the carbon coating, reducing the number of defect sites, oxygen sites, and nitrogen sites on the surface of the carbon coating, reducing the side reactions on the surface of the carbon coating during high-voltage charge and discharge, and then reducing the occurrence of gas production during battery charge and discharge, thereby improving the cycle performance of the positive electrode material.

[0121] In some specific embodiments, the calcination temperature of the secondary calcination may be 600°C, 650°C, 700°C, 750°C, or 800°C.

[0122] In some specific embodiments, the calcination time of the secondary calcination may be 0.5 h, 1.0 h, or 2.0 h.

[0123] In some specific embodiments, the heating rate of the secondary calcination may be 2.0-5.0° C. / min, for example, 2.0° C. / min, 3° C. / min, or 5.0° C. / min.

[0124] In some embodiments, the nitrogen source may include one or more of dicyandiamide, melamine, melem, urea, and hexamethylenetetramine.

[0125] Using these substances as nitrogen sources, they can all decompose and produce ammonia during the initial calcination process, thereby reacting with the oxygen-containing components in the polymerized carbon and the defect sites in the carbon skeleton, thereby achieving nitrogen doping in the carbon skeleton. Of course, the types of nitrogen sources are not limited to the above substances. The examples below verify that melamine and dicyandiamide can achieve nitrogen doping in the carbon skeleton, and after experimental verification, the other substances or similar substances listed above can achieve the same doping effect as melamine and dicyandiamide, which are not listed one by one in the examples.

[0126] In some embodiments, the fluorine source may include one or more of an organic fluorine source and an inorganic fluorine source. The organic fluorine source may include one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoroethylene-vinylidene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene-trifluoroethylene copolymer, a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene. The inorganic fluorine source may include one or more of ammonium fluoride, sodium fluoride, and potassium fluoride. Of course, the types of fluorine sources are not limited to the above substances. The examples below demonstrate that polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and ammonium fluoride can achieve fluorine doping in the carbon skeleton, and experimentally verified that the other substances or similar substances listed above can achieve the same doping effect as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and sodium fluoride, which are not listed one by one in the examples.

[0127] When these substances are used as fluorine sources, they can decompose and release fluorine atoms during the secondary calcination process, replacing the defect sites, oxygen sites and nitrogen sites on the surface of the carbon coating layer, thereby achieving fluorine atom doping on the surface of the carbon coating layer.

[0128] In some embodiments, the inert atmosphere includes one or more of nitrogen, argon, and helium.

[0129] The third aspect of the present application provides a secondary battery, which includes the fluorine-nitrogen co-doped carbon-coated positive electrode material of the first aspect of the present application or the fluorine-nitrogen co-doped carbon-coated positive electrode material obtained according to the preparation method of the second aspect of the present application.

[0130] A fourth aspect of the present application provides an electrical device, which includes the secondary battery according to the third aspect of the present application.

[0131] Example

[0132] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0133] Characterization method of fluorine-nitrogen co-doped carbon-coated positive electrode material of the present application

[0134] 1. Test method for the atomic doping percentage of nitrogen atoms inside the carbon coating layer

[0135] XPS elemental analysis was performed after etching the sample under inert atmosphere to analyze the dopant atoms within the carbon coating. The etching depth was 2nm. The specific steps included: attaching the sample to the sample stage with insulating adhesive in a glove box, placing it in an inert gas conveyor, and then placing it in the sample chamber. The sample stage was then evacuated and photographed. The X-ray source was then activated and the sample was tested.

[0136] 2. Test method for the atomic percentage of fluorine atoms doped on the surface of the carbon coating layer

[0137] XPS surface elemental analysis under an inert atmosphere was used to analyze the dopant atoms on the carbon coating surface. The specific steps included: attaching the sample to the sample stage with insulating tape in a glove box, placing it in an inert gas conveyor, and then placing it in the injection chamber. The sample stage was then evacuated and photographed. Finally, the X-ray source was activated and the sample was tested.

[0138] 3. Test method for thickness of carbon coating

[0139] Transmission electron microscopy (TEM) was used for testing. The specific steps included dispersing 5 mg of powder in 0.5 mL of anhydrous ethanol, ultrasonically dispersing, then dropping the dispersion on a carbon support film, placing it in the sample rod of the TEM, placing it in the TEM, vacuuming it for 10 minutes, and then testing it.

[0140] Example 1

[0141] (1) Preparation of fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate

[0142] according to Figure 2 The process for preparing fluorine and nitrogen co-doped carbon-coated lithium manganese iron phosphate material specifically includes the following steps:

[0143] (1-1) Preparation of polymeric carbon-coated lithium manganese iron phosphate material:

[0144] Disperse 50g of lithium manganese iron phosphate, 5g of glucose, and 100g of cellulose in 300mL of water, stir for 10min, and transfer to a 500mL hydrothermal reactor. Place the reactor in an oven and maintain it at 220℃ for 12h to complete the hydrothermal polymerization. After cooling to room temperature, remove the upper transparent dispersion and collect the bottom precipitate by centrifugation; then, wash it with deionized water and anhydrous ethanol three times each, and dry it at 70℃ to obtain a polymerized carbon-coated lithium manganese iron phosphate material, such as Figure 2 As shown, it includes a core particle 100 and a polymeric carbon layer 200.

[0145] (1-2) Preparation of nitrogen-doped carbon-coated lithium manganese iron phosphate material:

[0146] 100g of the polymeric carbon-coated lithium manganese iron phosphate material prepared in step (1-1) was physically ground with 50g of melamine for 30min, then placed in a high-temperature furnace, continuously introduced with nitrogen, and started the initial high-temperature calcination, controlling the heating rate to be 2.0℃ / min, the calcination temperature to be 800℃, and the calcination time to be 2.0h. After the calcination is completed, the nitrogen-doped carbon-coated lithium manganese iron phosphate material can be obtained after natural cooling. Figure 2 As shown, it includes a core particle 100, a carbon coating layer 300, and nitrogen atoms 301 doped inside the carbon coating layer.

[0147] (1-3) Preparation of fluorine and nitrogen co-doped carbon-coated lithium manganese iron phosphate material:

[0148] 200g of the nitrogen-doped carbon-coated lithium manganese iron phosphate material prepared in step (1-2) was mixed with 500g of polytetrafluoroethylene ethanol dispersion (polytetrafluoroethylene mass concentration is 2wt%), ultrasonically dispersed for 10min, and dried and ground. The ground sample was placed in a high-temperature furnace, nitrogen was continuously introduced, and a secondary high-temperature calcination was started. The heating rate was controlled to be 2.0℃ / min, the calcination temperature was 750℃, and the calcination time was 2.0h. After the calcination was completed, the fluorine and nitrogen co-doped carbon-coated lithium manganese iron phosphate material was obtained after natural cooling, such as Figure 1 shown.

[0149] After characterization, in the fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material, the atomic doping percentage of nitrogen atoms inside the carbon coating layer is 7.3%, the atomic percentage of fluorine atoms doped on the surface of the carbon coating layer is 4.6%, and the thickness of the carbon coating layer is 38.3nm.

[0150] (2) Preparation of positive electrode sheet:

[0151] 1 kg of the fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material prepared in step (1), 20 g of a conductive agent (carbon nanotubes), and 20 g of a binder (PVDF) were added to 1 kg of NMP (N-methylpyrrolidone) and stirred for 3 hours to obtain a positive electrode slurry. The slurry was coated on the surface of aluminum foil and then dried in an oven at 90°C. After subsequent roller pressing, a positive electrode sheet was obtained.

[0152] (3) Preparation of lithium-ion batteries:

[0153] The positive electrode sheet, graphite negative electrode sheet and separator prepared in step (2) are wound to obtain a battery cell, which is then packaged and injected with electrolyte to obtain the corresponding battery.

[0154] (4) Battery test:

[0155] The battery is charged and discharged using the LAND test system.

[0156] The first stage: let it stand for 5 minutes, then charge it to 4.2V at a constant current of 10mA; then, charge it at a constant voltage of 4.2V, and let it stand for 10 minutes when the charging current ends at 2mA; then, discharge it at a constant current of 8mA, and let it stand for 50 hours when the discharge voltage ends at 2.0V.

[0157] The second cycle test process is as follows: 45°C, constant current charging to 4.2V at a current of 120mA, then constant voltage charging at 4.2V, charging when the current value is 2mA, and standing for 10 minutes; then, constant current discharge at a current of 120mA, stop when the discharge voltage reaches 2.0V, stand for 10 minutes, and the discharge capacity is recorded as the first cycle discharge capacity; the above process is recorded as the first cycle; then the charge and discharge cycle is continued, the number of cycles is set to 500, and the discharge capacity of the 500th cycle is recorded.

[0158] Specific capacity retention rate after 500 cycles: the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle.

[0159] Examples 2-6

[0160] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the parameters listed in Table 1 below were different from those in Example 1. The characterization results of the fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and the test results of the lithium-ion battery are shown in Table 1 below.

[0161] Table 1

[0162]

[0163] As can be seen from Table 1, by controlling the mass ratio of the polymeric carbon-coated positive electrode material to the nitrogen source, the doping percentage of nitrogen atoms inside the carbon coating layer can be controlled. When the atomic doping percentage of nitrogen atoms is in the range of 5.0%-8.5%, it is beneficial to improve the cycle performance of the positive electrode material.

[0164] Examples 7-11

[0165] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the parameters listed in Table 2 below were different from those in Example 1. The characterization results of the fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and the test results of the lithium-ion battery are shown in Table 2 below.

[0166] Table 2

[0167]

[0168] As can be seen from Table 2, by controlling the mass concentration of the preparation parameter polytetrafluoroethylene ethanol dispersion, the mass ratio of the nitrogen-doped carbon-coated positive electrode material to the fluorine source can be controlled, thereby controlling the atomic percentage of fluorine atoms doped on the surface of the carbon coating layer. When the percentage of fluorine atoms is in the range of 2.0%-6.0%, it is beneficial to improve the cycle performance of the positive electrode material.

[0169] Examples 12-15

[0170] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the mass of the macromolecular organic carbon source and the thickness of the carbon coating layer were different from those in Example 1, as shown in Table 3 below. The characterization results of the fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and the test results of the lithium-ion battery are shown in Table 3 below.

[0171] Table 3

[0172]

[0173] It can be seen from Table 3 that by controlling the mass of the macromolecular organic carbon source, the thickness of the carbon coating layer can be controlled, and when the thickness of the carbon coating layer is in the range of 5-50 nm, it is beneficial to improve the cycle performance of the positive electrode material.

[0174] Example 16

[0175] A fluorine-nitrogen co-doped carbon-coated cathode material and a lithium-ion battery were prepared according to the method described in Example 1, except that 50 g of lithium manganese oxide was used instead of 50 g of lithium iron manganese phosphate. The characterization results of the fluorine-nitrogen co-doped carbon-coated cathode material and the test results of the lithium-ion battery are shown in Table 4 below.

[0176] Table 4

[0177]

[0178] Examples 17-19

[0179] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the parameters listed in Table 5 below were different from those in Example 1. The characterization results of the fluorine-nitrogen co-doped carbon-coated positive electrode material and the test results of the lithium-ion battery are shown in Table 5 below.

[0180] Table 5

[0181]

[0182]

[0183] It can be seen from Table 5 that when the mass ratio of glucose to cellulose is controlled within the range of 5:100-25:100, the uniformity of the carbon coating layer can be improved, which is beneficial to improving the cycle performance of the positive electrode material.

[0184] Examples 20-21

[0185] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the hydrothermal polymerization conditions were different from those in Example 1, as shown in Table 6 below. The characterization results of the fluorine-nitrogen co-doped carbon-coated positive electrode material and the test results of the lithium-ion battery are shown in Table 6 below.

[0186] Table 6

[0187]

[0188] It can be seen from Table 6 that optimizing the conditions of hydrothermal polymerization is beneficial to improving the uniformity of the carbon coating layer, thereby improving the cycle performance of the positive electrode material.

[0189] Examples 22-26

[0190] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the initial calcination conditions were different from those in Example 1, as shown in Table 7 below. The characterization results of the fluorine-nitrogen co-doped carbon-coated positive electrode material and the test results of the lithium-ion battery are shown in Table 7 below.

[0191] Table 7

[0192]

[0193] It can be seen from Table 7 that the conditions of the initial calcination, including the calcination temperature and calcination time, affect the capacity retention rate of the battery. By optimizing the conditions of the initial calcination, the cycle performance of the positive electrode material can be improved.

[0194] Examples 27-30

[0195] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the secondary calcination conditions were different from those in Example 1, as shown in Table 8 below. The characterization results of the fluorine-nitrogen co-doped carbon-coated positive electrode material and the test results of the lithium-ion battery are shown in Table 8 below.

[0196] Table 8

[0197]

[0198]

[0199] It can be seen from Table 8 that the conditions of the secondary calcination, including the heating rate, calcination temperature and calcination time, affect the capacity retention rate of the battery. By optimizing the conditions of the primary calcination, the cycle performance of the positive electrode material can be improved.

[0200] Example 31

[0201] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the type of nitrogen source was different from that in Example 1, as shown in Table 9 below. The characterization results of the fluorine-nitrogen co-doped carbon-coated positive electrode material and the test results of the lithium-ion battery are shown in Table 9 below.

[0202] Table 9

[0203]

[0204] Examples 32-33

[0205] A fluorine-nitrogen co-doped carbon-coated lithium manganese iron phosphate material and a lithium-ion battery were prepared according to the method described in Example 1, except that the type of fluorine source was different from that in Example 1, as shown in Table 10 below. The characterization results of the fluorine-nitrogen co-doped carbon-coated positive electrode material and the test results of the lithium-ion battery are shown in Table 10 below.

[0206] Table 10

[0207]

[0208] Comparative Example 1

[0209] The lithium iron manganese phosphate material was directly used as the positive electrode material to prepare the positive electrode sheet, and the lithium ion battery process and test process were the same as those in Example 1. The test results of the lithium ion battery are shown in Table 11 below.

[0210] Table 11

[0211]

[0212] Comparative Example 2

[0213] The polymeric carbon-coated lithium manganese iron phosphate material prepared in step (1-1) of Example 1 was placed in a high-temperature furnace, nitrogen was continuously introduced, and the initial high-temperature calcination was started. The heating rate was controlled to be 2.0°C / min, the calcination temperature was 800°C, and the calcination time was 2.0h. After the calcination was completed, the carbon-coated lithium manganese iron phosphate material was obtained after natural cooling. The carbon-coated lithium manganese iron phosphate material was directly used as the positive electrode material for the preparation of the positive electrode sheet. The battery process and test process were the same as in Example 1. The test results of the lithium-ion battery are shown in Table 12 below.

[0214] Table 12

[0215]

[0216] Comparative Example 3

[0217] The nitrogen-doped carbon-coated lithium manganese iron phosphate material prepared in step (1-2) of Example 1 was directly used as the positive electrode material to prepare the positive electrode sheet. The battery process and testing procedures were the same as those in Example 1. The test results of the lithium-ion battery are shown in Table 13 below.

[0218] Table 13

[0219]

[0220] Comparative Example 4

[0221] The carbon-coated lithium manganese iron phosphate material (200g) prepared in Comparative Example 2 was mixed with 500g of polytetrafluoroethylene ethanol dispersion (2wt%), stirred for 10min, and dried and ground. The ground sample was placed in a high-temperature furnace, nitrogen was continuously introduced, and a secondary high-temperature calcination was started. The heating rate was controlled to be 2.0℃ / min, the calcination temperature was 750℃, and the calcination time was 2.0h. After the calcination was completed, the fluorine-doped carbon-coated lithium manganese iron phosphate material (fluorine was doped on the surface of the carbon coating layer) was obtained after natural cooling. The fluorine-doped carbon-coated lithium manganese iron phosphate material was directly used as the positive electrode material for the preparation of the positive electrode sheet. The battery process and test process were the same as those in Example 1. The test results of the lithium-ion battery are shown in Table 14 below.

[0222] Table 14

[0223]

[0224] It can be seen from the above examples and comparative examples that the present application effectively improves the cycle performance of the positive electrode material by providing a fluorine-nitrogen co-doped carbon coating layer on the surface of the positive electrode active material.

[0225] The foregoing description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed herein are intended to be encompassed within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A fluorine-nitrogen co-doped carbon-coated positive electrode material, characterized in that: The positive electrode material includes: a core particle comprising a positive electrode active material; and a carbon coating layer, wherein the carbon coating layer is coated on the surface of the core particle, the surface of the carbon coating layer away from the core particle is doped with fluorine atoms, and the interior of the carbon coating layer is doped with nitrogen atoms; The positive electrode active material includes one or more of lithium transition metal oxide and phosphate containing lithium and transition metal.

2. The fluorine-nitrogen co-doped carbon-coated positive electrode material according to claim 1, characterized in that: The atomic doping percentage of nitrogen atoms in the carbon coating layer is 5.0%-8.5%.

3. The fluorine-nitrogen co-doped carbon-coated positive electrode material according to claim 1 or 2, characterized in that: The atomic percentage of fluorine atoms doped on the surface of the carbon coating layer is 2.0%-6.0%.

4. The fluorine-nitrogen co-doped carbon-coated positive electrode material according to any one of claims 1 to 3, characterized in that: The thickness of the carbon coating layer is 5-50 nm.

5. The fluorine-nitrogen co-doped carbon-coated positive electrode material according to any one of claims 1 to 4, characterized in that: The transition metal includes one or more of manganese, nickel, and cobalt; optionally, the positive electrode active material includes one or more of lithium manganese iron phosphate, lithium manganate, and lithium-rich manganese-based positive electrode materials.

6. A method for preparing a fluorine-nitrogen co-doped carbon-coated positive electrode material, characterized in that: The following steps are involved: After mixing a positive electrode active material with an organic carbon source, polymerizing the organic carbon source, thereby coating the surface of the positive electrode active material with polymerized carbon to obtain a polymerized carbon-coated positive electrode material; After mixing the polymeric carbon-coated positive electrode material with a nitrogen source, performing a primary calcination under an inert atmosphere to obtain a nitrogen-doped carbon-coated positive electrode material; and The nitrogen-doped carbon-coated cathode material is mixed with a fluorine source and then subjected to secondary calcination under an inert atmosphere to obtain the fluorine-nitrogen co-doped carbon-coated cathode material.

7. The preparation method according to claim 6, characterized in that The organic carbon source includes a combination of a small molecule organic carbon source and a macromolecule organic carbon source; The small molecule organic carbon source includes one or more of glucose, sucrose, and trehalose; The macromolecular organic carbon source includes one or more of starch, hemicellulose, cellulose, and lignin.

8. The preparation method according to claim 7, characterized in that The mass ratio of the small molecule organic carbon source to the macromolecular organic carbon source is 5:100-25:

100.

9. The preparation method according to any one of claims 6 to 8, characterized in that The preparation of the polymeric carbon-coated positive electrode material includes: dispersing the positive electrode active material in the dispersion of the organic carbon source, hydrothermally polymerizing the organic carbon source, thereby coating the surface of the positive electrode active material with polymeric carbon to obtain the polymeric carbon-coated positive electrode material.

10. The preparation method according to claim 9, characterized in that The temperature of the hydrothermal polymerization is 160-220° C., and the time of the hydrothermal polymerization is 12-30 hours.

11. The preparation method according to any one of claims 6 to 10, characterized in that: The preparation of the fluorine-nitrogen co-doped carbon-coated positive electrode material comprises: dispersing the nitrogen-doped carbon-coated positive electrode material in the dispersion of the fluorine source, ultrasonically dispersing, drying, grinding, and then performing the secondary calcination.

12. The preparation method according to claim 11, characterized in that The mass ratio of the nitrogen-doped carbon-coated positive electrode material to the fluorine source is 50:1-10:

1.

13. The preparation method according to any one of claims 6 to 12, characterized in that: The mass ratio of the polymeric carbon-coated positive electrode material to the nitrogen source is 10:1-1:

1.

14. The preparation method according to any one of claims 6 to 13, characterized in that: After the polymeric carbon-coated cathode material is mixed with the nitrogen source and before the primary calcination, physical grinding is performed.

15. The preparation method according to any one of claims 6 to 14, characterized in that: The temperature of the initial calcination is 400-1000° C., and the calcination time is 0.5-10 hours.

16. The preparation method according to claim 15, characterized in that The temperature of the initial calcination is 500-800° C., and the calcination time is 2-5 hours.

17. The preparation method according to any one of claims 6 to 16, characterized in that: The conditions for the secondary calcination include: a calcination temperature of 600-800° C. and a calcination time of 0.5-2.0 h.

18. The preparation method according to any one of claims 6 to 17, characterized in that: The nitrogen source includes one or more of dicyandiamide, melamine, melem, urea, and hexamethylenetetramine.

19. The preparation method according to any one of claims 6 to 18, characterized in that: The fluorine source includes one or more of an organic fluorine source and an inorganic fluorine source; The organic fluorine source includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoroethylene-vinylidene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene-trifluoroethylene copolymer, and copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene; The inorganic fluorine source includes one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

20. A secondary battery, characterized in that: It comprises the fluorine-nitrogen co-doped carbon-coated positive electrode material according to any one of claims 1 to 5 or the fluorine-nitrogen co-doped carbon-coated positive electrode material obtained according to the preparation method according to any one of claims 6 to 19.

21. An electrical device, characterized in that: A secondary battery according to claim 20 is included.

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