Positive electrode material, preparation method thereof and battery

Abstract

The invention relates to the field of batteries, in particular to a positive electrode material, a preparation method thereof and a battery. The positive electrode material comprises a polyanion material and a coating layer coating at least part of the surface of the polyanion material, the coating layer comprises a doped carbon material, the doped carbon material comprises a carbon material matrix and doping elements doped in the carbon material matrix, and the doping elements comprise N, S and B. The preparation method of the positive electrode material comprises the following steps: mixing a polyanion material and a carbon source, and carrying out first calcination to obtain a polyanion material positive electrode material with a carbon material coating layer; and mixing and grinding the polyanion positive electrode material with the carbon coating layer, a nitrogen source, a sulfur source and a boron source, and performing secondary calcination to obtain the positive electrode material. The positive electrode material provided by the invention has excellent conductivity, good structural stability and rate capability.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a positive electrode material, a preparation method thereof, and a battery. Background Art

[0002] In recent years, the rapid development of lithium-ion batteries has led to a significant depletion of lithium resources, resulting in a gradual increase in the cost of lithium batteries and limiting their large-scale application. Potassium, an alkali metal element in the same main group as lithium, is not only abundant in the Earth's crust but also shares a similar energy storage mechanism with lithium-ion batteries. However, due to its large ionic radius, potassium ions diffuse slowly in the bulk phase, resulting in low electronic conductivity and poor rate performance. Therefore, finding suitable potassium storage materials is key to the development of potassium-ion batteries.

[0003] At present, although some transition metal oxides, Prussian blue compounds and polyanion cathode materials have shown suitable potassium storage performance, their advantages and disadvantages are also quite prominent. For example, although layered oxide cathode materials have high theoretical specific capacity and K + The two-dimensional diffusion in the layer is fast, but the working potential of the layered oxide is low and the interaction between the oxygen layers is strong. + Phase transition is very likely to occur during the deintercalation process, which seriously affects the structural stability and leads to poor electrochemical cycle performance of the material. In contrast to the lower working potential of layered transition metal oxides, Prussian blue compounds exhibit higher working voltages, but due to their unique structural defects, they attract a large number of water molecules for coordination, making them extremely unstable in the air. Polyanionic materials have a stable framework structure and K + The volume change during the intercalation and deintercalation process is minimal, demonstrating excellent structural stability, high operating potential, and cycling stability. Therefore, polyanion materials are a highly promising class of cathode materials for potassium-ion batteries. Conventional polyanion materials, while structurally stable, suffer from relatively poor electrical conductivity, limiting their application in battery cathode materials. Summary of the Invention

[0004] In view of this, the present invention is dedicated to providing a positive electrode material and a preparation method thereof and a battery, so as to solve the problem of poor conductivity of polyanion materials in the prior art.

[0005] In order to solve the above technical problems, this application is implemented as follows:

[0006] The present invention provides a positive electrode material, which comprises a polyanion material and a coating layer coated on at least a portion of the surface of the polyanion material;

[0007] The coating layer includes a doped carbon material, wherein the doped carbon material includes a carbon material matrix and doping elements doped in the carbon material matrix, and the doping elements include N, S, and B.

[0008] In any embodiment, the coating layer has a thickness of 10 nm to 30 nm.

[0009] In any embodiment, the mass of the carbon material matrix is ​​8% to 15% of the mass of the polyanion material.

[0010] In any embodiment, the mass of the N element is 0.5% to 1% of the mass of the polyanion material.

[0011] In any embodiment, the mass of the S element is 0.5% to 1% of the mass of the polyanion material.

[0012] In any embodiment, the mass of the B element is 0.5% to 1% of the mass of the polyanion material.

[0013] In any embodiment, the polyanionic material comprises a potassium ion type polyanionic material.

[0014] In any embodiment, the potassium ion type polyanionic material comprises a phosphate type potassium ion type anionic material.

[0015] In any embodiment, the phosphate-based potassium ion anion material comprises β-KVOPO4.

[0016] A second aspect of the present invention provides a method for preparing a positive electrode material, comprising the following steps:

[0017] The polyanion material and the carbon source are mixed and then subjected to a first calcination to obtain a polyanion material positive electrode material having a carbon material coating layer;

[0018] A polyanion material positive electrode material having a carbon coating layer, a nitrogen source, a sulfur source and a boron source are mixed and ground, and then subjected to a second calcination to obtain a positive electrode material;

[0019] Wherein, the positive electrode material comprises a polyanion material and a coating layer coated on at least a portion of the surface of the polyanion material;

[0020] The coating layer includes a doped carbon material, wherein the doped carbon material includes a carbon material matrix and doping elements doped in the carbon material matrix, and the doping elements include N, S, and B.

[0021] In any embodiment, the polyanionic material comprises a potassium ion type polyanionic material; preferably, the potassium ion type polyanionic material comprises β-KVOPO4.

[0022] In any embodiment, the method for preparing β-KVOPO4 comprises the following steps:

[0023] Mixing a vanadium source, a phosphorus source and a first solvent and performing a first sintering to obtain a β-VOPO4 precursor;

[0024] The β-VOPO4 precursor and the potassium source are mixed and subjected to a second sintering to obtain β-KVOPO4.

[0025] In any embodiment, the molar ratio of the vanadium source to the phosphorus source is 1:(1-2).

[0026] In any embodiment, the vanadium source includes at least one of vanadium dioxide, vanadium trioxide, vanadium pentoxide, and ammonium metavanadate.

[0027] In any embodiment, the phosphorus source includes at least one of ammonium phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

[0028] In any embodiment, the method further comprises a first drying step after the vanadium source, the phosphorus source and the first solvent are mixed.

[0029] In any embodiment, the temperature of the first drying is 80-100° C., and the time of the first drying is 8-16 hours.

[0030] In any embodiment, the temperature of the first sintering is 500-800° C., and the time of the first sintering is 6-18 hours.

[0031] In any embodiment, the molar ratio of the β-VOPO4 precursor to the potassium source is 2:(1-2).

[0032] In any embodiment, the potassium source includes at least one of potassium dihydrogen phosphate, potassium carbonate, and potassium oxalate.

[0033] In any embodiment, the mixing of the β-VOPO4 precursor and the potassium source further comprises: ball milling and a second drying.

[0034] In any embodiment, the ball milling is wet ball milling, the liquid medium of the wet ball milling includes water, and the mass ratio of balls, materials and water in the wet ball milling is (4-6):1:1.

[0035] In any embodiment, the temperature of the second drying is 80-100° C., and the time of the second drying is 8-16 hours.

[0036] In any embodiment, the temperature of the second sintering is 600-900° C., the time of the second sintering is 8-16 hours, and the atmosphere of the second sintering is an inert atmosphere.

[0037] In any embodiment, the inert atmosphere includes at least one of argon, helium, neon, and nitrogen.

[0038] In any embodiment, the carbon source comprises at least one of sucrose, glucose, and citric acid.

[0039] In any embodiment, the temperature of the first calcination is 400° C. to 700° C., the time of the first calcination is 2 h to 5 h, and the atmosphere of the first calcination is an inert atmosphere; preferably, the inert atmosphere includes argon.

[0040] In any embodiment, the nitrogen source comprises at least one of melamine, dopamine, and thiourea.

[0041] In any embodiment, the sulfur source includes at least one of thiourea, sodium lauryl sulfate, and cysteine.

[0042] In any embodiment, the boron source comprises boric acid and / or potassium ammonium borate.

[0043] In any embodiment, the temperature of the second calcination is 400° C. to 600° C., the time of the second calcination is 2 hours to 5 hours, and the atmosphere of the second calcination is an inert atmosphere.

[0044] In any embodiment, the inert atmosphere includes at least one of argon, helium, neon, and nitrogen.

[0045] A third aspect of the present invention further provides a battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises the above-mentioned positive electrode material, or comprises a positive electrode material prepared by the above-mentioned method for preparing the positive electrode material;

[0046] In any embodiment, the battery is a potassium ion battery.

[0047] Through the above technical solution, the beneficial technical effects of the present invention are:

[0048] The positive electrode material of the present application mainly includes a polyanion material and a doped carbon material coated on the surface of the polyanion material, wherein the doped carbon material includes a carbon material matrix and doping elements nitrogen (N), sulfur (S) and boron (B). For example, the carbon material can be first coated on the surface of the polyanion material, and then the doping elements N, S and B are introduced into the coated carbon material. The carbon material coated on the surface of the polyanion material forms a continuous conductive network on the surface of the polyanion material, reduces the contact resistance between the interfaces and accelerates electron transfer, thereby improving the conductivity and rate performance of the material; and the doping elements N, S and B introduced into the coated carbon material can significantly improve the conductivity of the carbon layer, and at the same time can introduce defects on the surface of the material, provide more reaction sites, and cooperate with the coated carbon material to construct an excellent conductive network, which greatly improves the low conductivity problem of the potassium ion positive electrode material, further improves the electronic conduction and ion diffusion capacity of the material, and effectively improves the rate performance of the material. In addition, direct contact between the positive electrode material and the electrolyte is further prevented, reducing the occurrence of side reactions; the positive electrode material provided also has a relatively stable structure.

[0049] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0050] The present invention discloses a positive electrode material, a method for preparing the same, and a battery. Those skilled in the art can refer to the contents of this document and appropriately improve the process parameters to achieve the desired results. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments. It is obvious that relevant personnel can modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0051] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0052] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0056] As analyzed in the background art, in lithium-ion batteries, although several cathode materials such as transition metal oxides, Prussian blue compounds and polyanion materials have shown suitable potassium storage performance, the disadvantages of these materials are also quite prominent. In comparison, polyanion materials have a stable framework structure, K + The volume change during the intercalation and deintercalation process is small, showing excellent structural stability, and also has high working potential and cycle stability. Therefore, polyanion materials are a class of highly promising cathode materials for potassium ion batteries.

[0057] Although conventional polyanion materials have relatively stable structures, their electrical conductivity is relatively poor, and it is difficult to significantly improve their conductivity through simple carbon coating and single-atom doping techniques. Therefore, there is an urgent need to develop a polyanion cathode material with high electrical conductivity.

[0058] In view of this, the present application proposes a positive electrode material and a preparation method thereof and a battery, wherein the positive electrode material has high electrical conductivity. The present application and optional embodiments are described in more detail below.

[0059] [Cathode material]

[0060] In some embodiments, a positive electrode material is provided, the positive electrode material comprising a polyanion material and a coating layer coated on at least a portion of the surface of the polyanion material;

[0061] The coating layer includes a doped carbon material, the doped carbon material includes a carbon material matrix and doping elements doped in the carbon material matrix, and the doping elements include N, S and B.

[0062] It should be noted that, in this application, the term "coating" is not limited to direct coating but also includes indirect coating. For example, when a coating layer coats a polyanionic material, there may be no other structure between the coating layer and the outer surface of the polyanionic material, or there may be one or more layers of other structures between the coating layer and the outer surface of the polyanionic material. Preferably, there is no other structure between the coating layer and the outer surface of the polyanionic material.

[0063] The coating layer is formed or coated on at least a portion of the surface of the polyanionic material, which can protect or improve the polyanionic material, increase the structural stability of the polyanionic material, and optimize the conductivity of the positive electrode material. The coating layer is formed on at least a portion of the surface of the polyanionic material, meaning that the coating layer can completely encapsulate the polyanionic material within the coating layer, or can also coat only a portion of the outer surface of the polyanionic material; that is, the coating layer can completely coat the polyanionic material or can coat a portion of the surface of the polyanionic material, preferably completely coating the polyanionic material.

[0064] The cathode material of the present application has a core-shell structure, wherein the core is a polyanionic material, preferably a polyanionic material containing potassium ions, and the outer shell or shell layer includes a coating layer containing a doped carbon material. That is, the cathode material mainly includes a polyanionic material and a doped carbon material coated on the surface of the polyanionic material, wherein the doped carbon material includes a carbon material matrix and doping elements N, S, and B. For example, during preparation, the carbon material can be first coated on the surface of the polyanionic material, and then the doping elements N, S, and B can be introduced into the coated carbon material. Thus, the carbon material coated on the surface of the polyanion material forms a continuous conductive network on the surface of the polyanion material, reducing the contact resistance between the interfaces and accelerating electron transfer, thereby improving the conductivity and rate performance of the material. The doping elements N, S, and B introduced into the coated carbon material can significantly improve the conductivity of the carbon layer. At the same time, they can introduce defects on the surface of the material, providing more reaction sites, forming a synergistic effect with the carbon coating layer, that is, they work together with the coated carbon material to build an excellent conductive network, greatly improving the low conductivity of the potassium ion positive electrode material, further improving the material's electronic conduction and ion diffusion capabilities, and effectively improving the material's rate performance. At the same time, it further prevents direct contact between the positive electrode material and the electrolyte, reducing the occurrence of side reactions; the positive electrode material also has a relatively stable structure.

[0065] Therefore, the cathode material provided by this application can be a potassium storage cathode material with a stable structure and good conductivity. This cathode material first coats the surface of the polyanion material with a carbon material, and then introduces doping elements N, S, and B into the coated carbon material. This not only forms a uniform carbon layer on the surface of the cathode material, but also can generate multiple defects in the carbon layer, introduce more reactive sites, and greatly improve the conductivity of the material.

[0066] The positive electrode material of the present application is preferably a potassium ion positive electrode material, which is suitable for use in potassium ion batteries to solve the problem of poor conductivity when the existing potassium ion batteries use polyanion materials as positive electrodes.

[0067] In this application, the term "polyanionic material" generally refers to a compound having a series of tetrahedral (XO4) n- Anion unit and its derivative unit (X m O 3m+1 ) n- (X=S, P, Si, As, Mo or W) and polyhedral unit MO x (M represents a transition metal) A class of compounds having a structure. The polyanion material of the present application can be a potassium ion type polyanion material, such as β-KVOPO4.

[0068] Generally speaking, the anion unit in the polyanion material can not only allow the ions to conduct rapidly in the open structure, but also stabilize the redox couple of the transition metal; at the same time, the framework structure is stable, K + The volume change during the deintercalation process is small, showing excellent structural stability, as well as high working potential and cycle stability. This application introduces multiple heteroatoms such as N, S, and B on the basis of carbon coating, not only forming a uniform carbon layer on the surface of the positive electrode material, but also generating multiple defects on the carbon layer, introducing more reactive sites, and greatly improving the conductivity of the material.

[0069] In this application, the term "carbon material" refers to a material primarily composed of carbon and without a consistent structure or properties. The "carbon material" herein can be a carbonized product of biomass, such as sucrose, glucose, or citric acid. Using biomass, such as sucrose, glucose, or citric acid, as a precursor, the carbon material produced by pyrolysis is uniformly deposited on the surface of the polyanionic material to form a coating. Furthermore, biomass-derived carbon materials can not only improve electrical conductivity but also maintain integrity and prevent side reactions.

[0070] This application introduces doping elements N, S, and B simultaneously into the coating carbon material on the basis of polyanionic material coating the carbon material. Compared with other doping elements, the selection of these three doping elements can achieve seven synergistic effects. For example, the electron-deficient characteristics of B combined with the electron-rich characteristics of N can adjust the electron density of the carbon material. S atom doping can produce a synergistic effect by co-doping with N atoms, changing the charge density of adjacent carbon atoms, resulting in a redistribution of the spin density in the matrix material, thereby forming abundant active sites. That is, due to the synergistic effect between the three atoms of N, S, and B, the simultaneous introduction of N, S, and B can provide more surface defects and reactive sites compared to single atom doping, further improving the electronic conduction and ion diffusion of the material, thereby improving the conductive properties of the material.

[0071] The potassium ion battery prepared from the positive electrode material of the present invention exhibits the characteristics of high conductivity, long cycle life, excellent cycle stability, etc., which is conducive to the effective promotion and application of polyanion materials in future commercial applications.

[0072] In some embodiments, the coating layer has a thickness of 10 nm to 30 nm. For example, the coating layer may have a thickness of 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 28 nm, or 30 nm, or a range of any two thereof.

[0073] In the present application, the thickness of the coating layer is controlled within an appropriate range, which can avoid the situation where the coating layer is too thin and the conductive properties of the polyanion material cannot be improved. When the coating layer is too thick, excessive carbon material will passivate the polyanion material matrix and reduce the cycle performance and rate performance of the material.

[0074] In some embodiments, the mass of the carbon material matrix is ​​8% to 15% of the mass of the polyanionic material. As an example, the mass of the carbon material matrix can be any one of 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15% of the mass of the polyanionic material, or a range of values ​​therebetween.

[0075] In this application, when the mass of the carbon material matrix is ​​too small, the effect of improving the conductive properties of the polyanion material will not be achieved. When the mass of the carbon material matrix is ​​too large, the excess carbon material matrix will block the polyanion material matrix, reducing the material's cycle performance and rate performance. It is understood that within the range defined in this application, the conductive properties, cycle performance, and rate performance of the polyanion material can be improved. If this range is exceeded, its corresponding performance will inevitably be affected. However, for some relatively low or less demanding applications, the conductive properties, overshoot performance, cycle performance, and rate performance of the polyanion material can also be improved to a certain extent.

[0076] In some embodiments, the mass of the N element is 0.5% to 1% of the mass of the polyanionic material. As an example, the mass of the N element can be any one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1% of the mass of the polyanionic material, or a range therebetween.

[0077] In some embodiments, the mass of the S element is 0.5% to 1% of the mass of the polyanionic material. As an example, the mass of the S element can be any one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1% of the mass of the polyanionic material, or a range of any two thereof.

[0078] In some embodiments, the mass of the B element is 0.5% to 1% of the mass of the polyanionic material. As an example, the mass of the B element can be any one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1% of the mass of the polyanionic material, or a range therebetween.

[0079] In this application, controlling the doping amounts of the doping elements N, S, and B within the above-mentioned mass ranges helps the doping atoms replace carbon atoms or form interstitial atoms, creating more defects, introducing more reactive sites, and improving conductivity. Too little doping will not improve the conductivity of the carbon material coating. Too much doping will result in an excessively high defect density in the carbon material coating, leading to a decrease in the stability of the material structure and hindering the improvement of conductivity.

[0080] In some embodiments, the polyanionic material comprises a potassium ion-type polyanionic material.

[0081] Preferably, in some embodiments, the potassium ion type polyanion material includes a phosphate type potassium ion type anion material.

[0082] More preferably, in some embodiments, the phosphate potassium ion type anion material includes β-KVOPO4. The three-dimensional framework structure of the β phase in β-KVOPO4 is + The volume change during the embedding and de-embedding process is small, and it has excellent structural stability, resulting in excellent cycle stability.

[0083] Thus, the provided cathode materials, such as the N, S, and B co-doped carbon-coated potassium ion battery cathode materials, introduce multiple heteroatoms of N, S, and B on the basis of carbon coating, not only forming a uniform carbon layer on the surface of the cathode material, but also generating multiple defects in the carbon layer, introducing more reactive sites, and greatly improving the conductivity of the material. At the same time, the N, S, and B co-doped carbon-coated potassium ion battery cathode material has a relatively stable structure.

[0084] [Method for preparing positive electrode material]

[0085] In some embodiments, a method for preparing a positive electrode material is provided, the method comprising the following steps:

[0086] The polyanion material and the carbon source are mixed and then subjected to a first calcination to obtain a polyanion material positive electrode material having a carbon material coating layer;

[0087] A polyanion material positive electrode material having a carbon coating layer, a nitrogen source, a sulfur source and a boron source are mixed and ground, and then subjected to a second calcination to obtain a positive electrode material;

[0088] Wherein, the positive electrode material comprises a polyanion material and a coating layer coated on at least a portion of the surface of the polyanion material;

[0089] The coating layer includes a doped carbon material, the doped carbon material includes a carbon material matrix and doping elements doped in the carbon material matrix, and the doping elements include N, S and B.

[0090] The present application provides a method for preparing a positive electrode material, which comprises mixing a polyanion material and a carbon source, calcining the mixture, and then mixing the mixture with a nitrogen source, a sulfur source, and a boron source, and then calcining the mixture to obtain a positive electrode material. The preparation method has simple process, convenient operation, strong feasibility, low production cost, and is easy to achieve large-scale production. The positive electrode material prepared by this method has good structural stability, good electrical conductivity, and good electrochemical properties.

[0091] In the synthesis process of the positive electrode material of the embodiment of the present application, not only a uniform carbon layer is formed on the surface of the positive electrode material, but also three heteroatoms are introduced to collaboratively construct a better conductive network, which greatly improves the low conductivity of the positive electrode material, especially the potassium ion positive electrode material, effectively improves the rate performance of the material, further prevents direct contact between the positive electrode material and the electrolyte, and reduces the occurrence of side reactions.

[0092] It should be understood that all the features and advantages described above for the “positive electrode material” are also applicable to the “method for preparing the positive electrode material” and will not be described in detail here.

[0093] In some embodiments, the polyanionic material comprises a potassium ion-type polyanionic material.

[0094] Preferably, in some embodiments, the potassium ion type polyanion material includes β-KVOPO4.

[0095] In some embodiments, β-KVOPO4 can be purchased or prepared by the following preparation method. Exemplarily, the preparation method of β-KVOPO4 includes the following steps:

[0096] Mixing a vanadium source, a phosphorus source and a first solvent and performing a first sintering to obtain a β-VOPO4 precursor;

[0097] The β-VOPO4 precursor and the potassium source are mixed and subjected to a second sintering to obtain β-KVOPO4.

[0098] In some specific embodiments, the method for preparing the positive electrode material includes the following steps (a) to (c):

[0099] Step (a): Prepare polyanion positive electrode material, taking β-KVOPO4 as an example.

[0100] In some embodiments, in step (a), a vanadium source and a phosphorus source are added to a first solvent for dissolution, a first drying, and a first sintering to obtain a β-VOPO4 precursor; the β-VOPO4 precursor and a potassium source are ball-milled, a second drying, and a second sintering to obtain β-KVOPO4. Exemplarily, a certain molar ratio of vanadium source, phosphorus source and other raw materials are first weighed separately, and the β-VOPO4 precursor is synthesized by dissolving in water, drying, and high-temperature sintering; then the synthesized β-VOPO4 precursor and potassium source are weighed according to a certain molar ratio and subjected to processes such as ball milling with water, drying, and high-temperature sintering in an inert gas atmosphere to synthesize the β-VOPO4 precursor positive electrode material.

[0101] Optionally, in step (a), the vanadium source includes but is not limited to at least one of vanadium dioxide, vanadium trioxide, vanadium pentoxide and ammonium metavanadate.

[0102] Optionally, in step (a), the phosphorus source includes but is not limited to at least one of ammonium phosphate, diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0103] Optionally, in step (a), the potassium source includes but is not limited to at least one of potassium dihydrogen phosphate, potassium carbonate and potassium oxalate.

[0104] In this application, by selecting the above-mentioned vanadium source, phosphorus source and potassium source, the high-valent vanadium source is combined with the high-solubility phosphorus source to ensure the uniformity of the precursor and reduce the generation of impurities; the high reactivity of the potassium source promotes K + Effective incorporation forms a stable β-phase structure. The selected vanadium, phosphorus, and potassium sources, through valence matching, dissolution / decomposition characteristics, and reactivity, synergistically enable the efficient synthesis of β-KVOPO4, which has high purity, ideal crystal structure, and optimized physical and chemical properties, making it suitable for electrochemical applications.

[0105] Optionally, in step (a), the molar ratio of the vanadium source to the phosphorus source is 1:(1-2). As an example, the molar ratio of the vanadium source to the phosphorus source can be any one of 1:1, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2, or a range between any two of them.

[0106] Optionally, in step (a), the molar ratio of the β-VOPO4 precursor to the potassium source is 2:(1-2). As an example, the molar ratio of the β-VOPO4 precursor to the potassium source can be any one of 2:1, 2:1.2, 2:1.5, 2:1.8, 2:2, or a range between any two of them.

[0107] In this application, by controlling the usage ratio of vanadium source, phosphorus source and potassium source within the above range, the PO4 3- Skeleton stability, improve cycle life, ensure K + Occupying lattice sites improves structural stability. That is, when the molar ratio of the vanadium source, phosphorus source, and potassium source is within the above range, β-KVOPO4 with excellent purity and structure can be produced, providing conditions for the subsequent preparation of positive electrode materials with high conductivity.

[0108] In step (a), the first drying can be performed by conventional operations of those skilled in the art, such as drying by forced air drying. As an example, the temperature of the first drying is 80 to 100° C., and the time of the first drying is 8 to 16 hours. As an example, the temperature of the first drying can be any one of 80° C., 82° C., 84° C., 85° C., 86° C., 88° C., 90° C., 92° C., 95° C., 98° C., and 100° C., or a range between any two thereof, and the time of the first drying can be any one of 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, and 16h, or a range between any two thereof.

[0109] Optionally, in step (a), the first sintering temperature is 500-800° C., and the first sintering time is 6-18 hours. As an example, the first sintering temperature can be any one of 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., and 800° C., or a range between any two thereof, and the first sintering time can be any one of 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, and 16 hours, or a range between any two thereof.

[0110] In the present application, by controlling the temperature and time of the first sintering within the above ranges, while ensuring high phase purity and moderate crystallinity, excessive particle growth is avoided, making it suitable for battery positive electrode materials.

[0111] In step (a), ball milling can be performed using conventional operations performed by those skilled in the art, such as wet ball milling. For example, the liquid medium for wet ball milling includes water; the mass ratio of balls, feedstock, and water in wet ball milling is (4-6):1:1. For example, the mass ratio of balls, feedstock, and water in wet ball milling can be any one of 4:1:1, 4.2:1:1, 4.5:1:1, 4.8:1:1, 5:1:1, 5.5:1:1, 5.8:1:1, and 6:1:1, or a range between any two of these values.

[0112] In step (a), the second drying can be carried out by conventional operations of those skilled in the art, such as drying by forced air drying. As an example, the temperature of the second drying is 80 to 100° C., and the time of the second drying is 8 to 16 hours. As an example, the temperature of the second drying can be any one of 80° C., 82° C., 84° C., 85° C., 86° C., 88° C., 90° C., 92° C., 95° C., 98° C., and 100° C., or a range between any two thereof, and the time of the second drying can be any one of 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, and 16 hours, or a range between any two thereof.

[0113] Optionally, in step (a), the second sintering temperature is 600-900°C, the second sintering time is 8-16 hours, and the second sintering atmosphere is an inert atmosphere. As an example, the second sintering temperature can be any one of 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, and 900°C, or a range between any two of them, and the second sintering time is any one of 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, and 16 hours, or a range between any two of them, and the inert atmosphere includes at least one of argon, helium, neon, and nitrogen.

[0114] In the present application, by controlling the temperature and time of the second sintering within the above range, K + The diffusion rate is significantly improved, which can quickly fill the vacancies in the vanadium-phosphorus skeleton to form a uniform β-KVOPO4 phase; the grain size is moderate, the crystallinity is high and the grain boundaries are clear, balancing the ion conductivity and structural stability.

[0115] Therefore, the β-KVOPO4 prepared in this application not only has a more uniform material particle size, but is also suitable for potassium ion battery positive electrode materials.

[0116] As an example, step (a) includes: adding 1 mol of ammonium metavanadate and 1 mol to 2 mol of ammonium dihydrogen phosphate to 100 mL of water, stirring for 3 hours to dissolve in a constant temperature water bath at 80°C, then placing it in a blower box at 80 to 100°C for drying for 8 to 16 hours, and then sintering at 500 to 800°C for 6 to 18 hours to obtain a β-VOPO4 precursor; mixing 1 mol of β-VOPO4 precursor and 2 mol to 2.5 mol of potassium carbonate, and wet ball milling, wherein the mass ratio of balls, materials and water in the wet ball milling is (4 to 6): 1:1, and after the wet ball milling is completed, placing it in a blower box at 80 to 100°C for drying for 8 to 16 hours, and then sintering at 600 to 900°C in an inert atmosphere for 8 to 16 hours, and naturally cooling to room temperature and then grinding to obtain β-KVOPO4.

[0117] Step (b): Carbon coating

[0118] In some embodiments, in step (b), the polyanion material and the carbon source are ground and mixed, and then a first calcination is performed, and then naturally cooled to room temperature and ground to obtain a polyanion material positive electrode material having a carbon material coating layer.

[0119] In some embodiments, in step (b), the carbon source comprises at least one of sucrose, glucose, and citric acid.

[0120] In some embodiments, in step (b), the amount of carbon source added satisfies that the mass of the carbon material matrix is ​​8% to 15% of the mass of the polyanion material.

[0121] In this application, when the mass of the carbon material matrix is ​​too small, it will not be able to improve the conductive properties of the polyanion material. When the mass of the carbon material matrix is ​​too large, the excessive carbon material matrix will degrade the polyanion material matrix and reduce the cycle performance and rate performance of the material.

[0122] In some embodiments, in step (b), the first calcination temperature is 400° C. to 700° C., the first calcination time is 2 h to 5 h, and the first calcination atmosphere is an inert atmosphere; preferably, the inert atmosphere includes argon. As an example, the first calcination temperature can be any one of 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., and 700° C., or a range between any two thereof, and the first calcination time can be any one of 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, and 5 h, or a range between any two thereof.

[0123] During the first calcination, the carbon source undergoes pyrolysis at high temperature to form an amorphous carbon precursor. As the temperature rises, the amorphous carbon gradually graphitizes, that is, the carbon source is adsorbed and pyrolyzed on the surface of the polyanion material to form a continuous carbon coating to form a conductive carbon layer. At the same time, the high temperature promotes the crystal growth of the polyanion material, reduces lattice defects, and improves the electrical conductivity of the material. In addition, controlling the temperature and time of the first calcination within an appropriate range can ensure that the carbon source forms a carbon coating layer of appropriate thickness and uniformity on the surface of the polyanion material.

[0124] In the present invention, unless otherwise specified, room temperature refers to 10 to 30°C.

[0125] As an example, step (b) includes: grinding and mixing the polyanion material β-KVOPO4 and the carbon source glucose, and then performing a first calcination at 400°C to 700°C in an inert atmosphere for 2h to 5h, and then naturally cooling to room temperature, and grinding to obtain a polyanion material positive electrode material with a carbon material coating layer.

[0126] Step (c): performing element doping.

[0127] In some embodiments, in step (c), the polyanion material positive electrode material having a carbon material coating layer is mixed with a nitrogen source, a sulfur source, and a boron source and ground, followed by a second calcination, and then naturally cooled to room temperature to obtain a positive electrode material.

[0128] In some embodiments, in step (c), the nitrogen source comprises at least one of melamine, dopamine, and thiourea.

[0129] In some embodiments, in step (c), the sulfur source comprises at least one of thiourea, sodium lauryl sulfate, and cysteine.

[0130] In some embodiments, in step (c), the boron source comprises boric acid and / or potassium ammonium borate.

[0131] In some embodiments, in step (c), the amount of nitrogen source, sulfur source and boron source added satisfies that the nitrogen element, sulfur element and boron element are 0.5% to 1% of the mass of the polyanionic material respectively.

[0132] In some embodiments, in step (c), the second calcination temperature is 400° C. to 600° C., the second calcination time is 2 h to 5 h, and the second calcination atmosphere is an inert atmosphere. As an example, the second calcination temperature can be any one of 400° C., 420° C., 450° C., 480° C., 500° C., 520° C., 550° C., 580° C., and 600° C., or a range between any two thereof, and the second calcination time can be any one of 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, and 5 h, or a range between any two thereof, and the inert atmosphere includes at least one of argon, helium, neon, and nitrogen.

[0133] In the second calcination, the nitrogen element in the nitrogen source, the sulfur element in the sulfur source, and the boron element in the boron source replace the carbon atoms in the carbon layer, realizing the synergistic doping and structural modification process of nitrogen, sulfur, and boron in the carbon layer, and optimizing the material performance through chemical reactions and physical changes at high temperatures. Through the synergistic doping of nitrogen, sulfur, and boron and modification of the carbon layer, the comprehensive improvement of the material conductivity, ion diffusion rate, and structural stability is achieved. The key is to balance the doping efficiency and material integrity by precisely controlling the calcination conditions (temperature, atmosphere, time) and element ratios, and ultimately optimize the electrochemical properties of the polyanion material (such as high specific capacity and long cycle life).

[0134] As an example, step (c) includes:

[0135] The polyanion material positive electrode material with a carbon material coating layer is mixed with a nitrogen source, a sulfur source, and a boron source and ground, and then subjected to a second calcination at 400° C. to 600° C. in an inert atmosphere for 2 h to 5 h, and then naturally cooled to room temperature to obtain a positive electrode material.

[0136] [Battery]

[0137] The third aspect of the present invention further provides a battery, which includes a positive electrode sheet, and the positive electrode sheet includes the above-mentioned positive electrode material, or includes the positive electrode material prepared by the above-mentioned method for preparing the positive electrode material.

[0138] In some embodiments, the battery is a potassium ion battery.

[0139] The battery may be a secondary battery or a primary battery, preferably a secondary battery. For example, the battery may be a potassium ion secondary battery, a potassium primary battery, etc., but is not limited thereto. The battery structure of the present application includes but is not limited to a soft-pack potassium ion battery, a square hard-shell battery, or a cylindrical hard-shell battery.

[0140] The battery includes the above-mentioned positive electrode material provided in the embodiments of the present application. Therefore, the battery, such as a potassium ion secondary battery, also has the characteristics of excellent electrochemical performance.

[0141] It should be noted that, in the specific implementation manner, the present application is explained using a potassium ion battery as an example of a secondary battery, but the battery of the present application is not limited to a potassium ion battery.

[0142] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0143] In this embodiment, the specific materials and structures of the negative electrode current collector and the negative electrode active material layer in the negative electrode sheet are not limited, and any negative electrode sheet structure and composition known in the art that can be used in secondary batteries can be selected.

[0144] In some embodiments, the battery further includes an electrolyte and a separator.

[0145] The electrolyte can be an electrolyte solution. The electrolyte solution used in the embodiments of the present application can be an electrolyte solution known in the prior art. The specific type and structure of the electrolyte solution can be any electrolyte solution known in the art for use in secondary batteries, such as an ester electrolyte solution or an ether electrolyte solution. This is not limited to this and will not be further described here.

[0146] The present application does not particularly limit the type of separator. Any known porous separator with good chemical and mechanical stability can be used. As an example, the separator can be made of at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0147] 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.

[0148] Example 1

[0149] The preparation of the positive electrode material comprises the following steps:

[0150] (1) Ammonium metavanadate and ammonium dihydrogen phosphate were added to 100 mL of deionized water at a molar ratio of 1:1, stirred and dissolved in a constant temperature water bath at 80°C for 3 h, then placed in a blower oven at 85°C for drying for 12 h, and then the dried product was placed in a muffle furnace and sintered at 650°C for 14 h to obtain a β-VOPO4 precursor;

[0151] (2) The β-VOPO4 precursor and potassium carbonate were mixed in a molar ratio of 2:1 and wet ball milled. The mass ratio of balls, materials and water in the wet ball milling was 4:1:1. After the wet ball milling, the mixture was placed in an 85°C blower for drying for 12 hours. The dried product was then placed in a high-temperature tube furnace under an argon atmosphere at 600°C for 10 hours. After naturally cooling to room temperature, it was ground to obtain β-KVOPO4.

[0152] (3) β-KVOPO4 and glucose are ground and mixed, and the ground product is placed in a high-temperature tube furnace in an argon atmosphere at 500°C for a first calcination for 4 hours, and then naturally cooled to room temperature and ground to obtain a polyanion material positive electrode material β-KVOPO4@C with a carbon material coating layer; wherein the mass of the carbon material matrix in β-KVOPO4@C is 10% of the mass of the polyanion material;

[0153] (4) After β-KVOPO4@C was mixed with thiourea and boric acid and ground, the ground sample was placed in a high-temperature tube furnace in an argon atmosphere at 500°C for a second calcination for 4 hours, and then naturally cooled to room temperature for rigorous calcination to obtain a positive electrode material; wherein, in the positive electrode material, the mass of the N element was 0.6% of the mass of the polyanion material, the mass of the S element was 0.6% of the mass of the polyanion material, and the mass of the B element was 0.6% of the mass of the polyanion material.

[0154] Example 2

[0155] The preparation of the positive electrode material comprises the following steps:

[0156] (1) Ammonium metavanadate and ammonium dihydrogen phosphate were added to 100 mL of deionized water at a molar ratio of 1:1, stirred and dissolved in a constant temperature water bath at 80°C for 3 h, then placed in a blower oven at 85°C for drying for 12 h, and then the dried product was placed in a muffle furnace and sintered at 650°C for 14 h to obtain a β-VOPO4 precursor;

[0157] (2) The β-VOPO4 precursor and potassium carbonate were mixed in a molar ratio of 2:1 and wet ball milled. The mass ratio of balls, materials and water in the wet ball milling was 4:1:1. After the wet ball milling, the mixture was placed in an 85°C blower for drying for 12 hours. The dried product was then placed in a high-temperature tube furnace under an argon atmosphere at 600°C for 10 hours. After naturally cooling to room temperature, it was ground to obtain β-KVOPO4.

[0158] (3) β-KVOPO4 and glucose are ground and mixed, and the ground product is placed in a high-temperature tube furnace in an argon atmosphere at 500°C for a first calcination for 4 hours, and then naturally cooled to room temperature and ground to obtain a polyanion material positive electrode material β-KVOPO4@C with a carbon material coating layer; wherein the mass of the carbon material matrix in β-KVOPO4@C is 10% of the mass of the polyanion material;

[0159] (4) After β-KVOPO4@C was mixed with thiourea and boric acid and ground, the ground sample was placed in a high-temperature tube furnace in an argon atmosphere at 600°C for a second calcination for 4 hours, and then naturally cooled to room temperature for rigorous calcination to obtain a positive electrode material; wherein, in the positive electrode material, the mass of the N element was 0.5% of the mass of the polyanion material, the mass of the S element was 0.5% of the mass of the polyanion material, and the mass of the B element was 0.5% of the mass of the polyanion material.

[0160] Example 3

[0161] The difference between this embodiment and embodiment 1 is that:

[0162] In the positive electrode material, the mass of the N element is 0.7% of the mass of the polyanion material, the mass of the S element is 0.7% of the mass of the polyanion material, and the mass of the B element is 0.7% of the mass of the polyanion material.

[0163] The rest are the same as in Example 1.

[0164] Example 4

[0165] The difference between this embodiment and embodiment 1 is that:

[0166] In the positive electrode material, the mass of the N element is 0.5% of the mass of the polyanion material, the mass of the S element is 0.5% of the mass of the polyanion material, and the mass of the B element is 0.5% of the mass of the polyanion material.

[0167] The rest are the same as in Example 1.

[0168] Example 5

[0169] The difference between this embodiment and embodiment 1 is that:

[0170] The mass of the carbon material matrix in β-KVOPO4@C is 8% of the mass of the polyanion material.

[0171] The rest are the same as in Example 1.

[0172] Example 6

[0173] The difference between this embodiment and embodiment 1 is that:

[0174] The mass of the carbon material matrix in β-KVOPO4@C is 15% of the mass of the polyanion material.

[0175] The rest are the same as in Example 1.

[0176] Example 7

[0177] The difference between this embodiment and embodiment 1 is that:

[0178] The temperature of the second calcination is 400° C., and the time of the second calcination is 2 h.

[0179] The rest are the same as in Example 1.

[0180] Comparative Example 1

[0181] The difference between this embodiment and embodiment 1 is that:

[0182] In step (4), after β-KVOPO4@C and melamine are mixed and ground, the ground sample is placed in a high-temperature tube furnace in an argon atmosphere at 500°C for a second calcination for 4 hours, and then naturally cooled to room temperature for rigorous calcination to obtain a positive electrode material; wherein, in the positive electrode material, the mass of the N element is 0.6% of the mass of the polyanion material.

[0183] The rest are the same as in Example 1.

[0184] Comparative Example 2

[0185] The difference between this embodiment and embodiment 1 is that:

[0186] In step (4), after β-KVOPO4@C and cysteine ​​are mixed and ground, the ground sample is placed in a high-temperature tube furnace in an argon atmosphere at 600°C for a second calcination for 4 hours, and then naturally cooled to room temperature for rigorous calcination to obtain a positive electrode material; wherein, in the positive electrode material, the mass of the S element is 0.6% of the mass of the polyanion material.

[0187] The rest are the same as in Example 1.

[0188] Comparative Example 3

[0189] The difference between this embodiment and embodiment 1 is that:

[0190] In step (4), after β-KVOPO4@C and boric acid are mixed and ground, the ground sample is placed in a high-temperature tube furnace in an argon atmosphere at 600°C for a second calcination for 4 hours, and then naturally cooled to room temperature for rigorous calcination to obtain a positive electrode material; wherein, in the positive electrode material, the mass of the B element is 0.6% of the mass of the polyanion material.

[0191] The rest are the same as in Example 1.

[0192] Comparative Example 4

[0193] The difference between this embodiment and embodiment 1 is that:

[0194] In step (4), after β-KVOPO4@C and thiourea are mixed and ground, the ground sample is placed in a high-temperature tube furnace in an argon atmosphere at 600°C for a second calcination for 4 hours, and then naturally cooled to room temperature for calcination to obtain a positive electrode material; wherein, in the positive electrode material, the mass of the N element is 0.6% of the mass of the polyanion material, and the mass of the S element is 0.6% of the mass of the polyanion material.

[0195] The rest are the same as in Example 1.

[0196] Performance Testing

[0197] 1. Preparation of button batteries

[0198] The positive electrode materials prepared in the embodiment and the comparative example were respectively ground uniformly with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10, and added to N-methylpyrrolidone (NMP) solvent to obtain a slurry; the obtained slurry was evenly applied on an aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours to obtain a positive electrode sheet; 0.8 mol / L KPF6 ethylene carbonate and propylene carbonate (mass ratio of 3:7) + 1 wt% fluoroethylene carbonate solution was used as a potassium ion battery electrolyte, and glass fiber and a metal potassium sheet were respectively used as a potassium ion battery separator and a negative electrode to assemble into a CR2032 type button half-cell; the battery assembly was carried out in an argon-filled glove box, and the water and oxygen concentrations were both less than 0.1 ppm.

[0199] 2. Electrical performance test: The CR2032 button half-cell prepared above was tested with a Blue Power CT2001A battery test system at 2.0-4.0V (vs. K + / K), and carry out cycle tests at room temperature (25°C) at current densities of 20mA / g, 50mA / g, 100mA / g, 150mA / g, and 200mA / g, respectively; specifically including:

[0200] (1) First coulombic efficiency: Under constant temperature conditions of 25°C, charge to 4V at a current density of 20mA / g, and record the charge capacity at this time as the first charge capacity; under constant temperature conditions of 25°C, continue to discharge to 2V at a current density of 20mA / g, and record the discharge capacity at this time as the first discharge capacity; First coulombic efficiency = first charge capacity / first discharge capacity*100%; The first coulombic efficiency at current densities of 50mA / g, 100mA / g, 150mA / g, and 200mA / g are similar to the above, except that the current density is changed to 50mA / g, 100mA / g, 150mA / g, and 200mA / g respectively. The test results are shown in Table 1.

[0201] (2) 200-cycle capacity retention rate: Under constant temperature conditions of 25°C, charge to 4V at a current density of 20mA / g, and then discharge to 2V at a constant current density of 20mA / g. This is a complete charge and discharge cycle. Record 1 cycle. Repeat this process until the number of cycles is equal to 200. End the test and record the charge capacity of the 200th cycle. Then, the capacity retention rate of the 200th cycle = the charge capacity of the 200th cycle / the charge capacity of the 1st cycle * 100%; the 200-cycle capacity retention rates at current densities of 50mA / g, 100mA / g, 150mA / g, and 200mA / g are similar to the above, except that the current density is changed to 50mA / g, 100mA / g, 150mA / g, and 200mA / g respectively. The test results are shown in Table 2.

[0202] Table 1

[0203]

[0204]

[0205] Table 2

[0206]

[0207] It can be seen from Table 1 and Table 2 that the positive electrode materials prepared in Examples 1 to 7 of the present application have better first efficiency, rate performance and capacity retention than those in Comparative Examples 1 to 4. Among them, the rate performance and capacity retention of the positive electrode materials in Comparative Examples 1 to 4 are worse than those in Example 1. This is because the carbon material coating layer of the positive electrode materials prepared in Comparative Examples 1 to 4 is doped with only a single atom of N, S or B, or the carbon material coating layer is doped with only N and S, indicating that the co-doping of N, S and B synergistically constructs a better conductive network, greatly improving the low conductivity problem of the positive electrode material, and effectively improving the rate performance and capacity retention of the material.

[0208] In addition, the amount of N, S, and P doping in the positive electrode material prepared in Example 1 is higher than that in Example 2, thereby forming more surface defects and reaction active sites on the surface of the carbon material, further improving the electronic conduction and ion diffusion of the material, and thus Example 1 has better rate performance and higher capacity retention than Example 2. This shows that the positive electrode material of the present invention with β-KVOPO4 as the core and N, S, and B co-doped carbon material as the coating layer not only has a uniform carbon coating layer, but also has more defects, can construct a better conductive network, greatly improve the conductivity of the potassium ion positive electrode material, and effectively improve the rate performance of the material.

[0209] Therefore, the positive electrode material of the present invention with β-KVOPO4 as the core and the N, S, and B co-doped carbon material as the coating layer has far-reaching significance in the application of positive electrode materials for potassium storage secondary batteries.

[0210] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material includes a polyanion material and a coating layer coated on at least a portion of the surface of the polyanion material; The coating layer includes a doped carbon material, wherein the doped carbon material includes a carbon material matrix and doping elements doped in the carbon material matrix, and the doping elements include N, S, and B.

2. The positive electrode material according to claim 1, characterized in that The thickness of the coating layer is 10nm to 30nm; And / or, the mass of the carbon material matrix is ​​8% to 15% of the mass of the polyanion material; And / or, the mass of the N element is 0.5% to 1% of the mass of the polyanion material; And / or, the mass of the S element is 0.5% to 1% of the mass of the polyanion material; And / or, the mass of the B element is 0.5% to 1% of the mass of the polyanion material.

3. The positive electrode material according to claim 1 or 2, characterized in that The polyanion material includes a potassium ion type polyanion material; Preferably, the potassium ion type polyanion material comprises a phosphate potassium ion type anion material; Preferably, the phosphate potassium ion type anion material includes β-KVOPO4.

4. A method for preparing a positive electrode material, characterized in that: The following steps are involved: The polyanion material and the carbon source are mixed and then subjected to a first calcination to obtain a polyanion material positive electrode material having a carbon material coating layer; A polyanion material positive electrode material having a carbon coating layer, a nitrogen source, a sulfur source and a boron source are mixed and ground, and then subjected to a second calcination to obtain a positive electrode material; Wherein, the positive electrode material comprises a polyanion material and a coating layer coated on at least a portion of the surface of the polyanion material; The coating layer includes a doped carbon material, wherein the doped carbon material includes a carbon material matrix and doping elements doped in the carbon material matrix, and the doping elements include N, S, and B.

5. The method for preparing the positive electrode material according to claim 4, wherein: The polyanion material includes a potassium ion type polyanion material; preferably, the potassium ion type polyanion material includes β-KVOPO4; Preferably, the preparation method of β-KVOPO4 comprises the following steps: Mixing a vanadium source, a phosphorus source and a first solvent and performing a first sintering to obtain a β-VOPO4 precursor; The β-VOPO4 precursor and the potassium source are mixed and subjected to a second sintering to obtain β-KVOPO4.

6. The method for preparing the positive electrode material according to claim 5, wherein: The preparation method of β-KVOPO4 satisfies at least one of the following conditions (1) to (6): (1) The molar ratio of the vanadium source to the phosphorus source is 1:(1-2); Preferably, the vanadium source includes at least one of vanadium dioxide, vanadium trioxide, vanadium pentoxide and ammonium metavanadate; Preferably, the phosphorus source includes at least one of ammonium phosphate, diammonium hydrogen phosphate and ammonium dihydrogen phosphate; (2) the step of mixing the vanadium source, the phosphorus source and the first solvent further includes a first drying step; Preferably, the temperature of the first drying is 80-100° C., and the time of the first drying is 8-16 hours; (3) The temperature of the first sintering is 500-800° C., and the time of the first sintering is 6-18 hours; (4) The molar ratio of the β-VOPO4 precursor to the potassium source is 2:(1-2); Preferably, the potassium source includes at least one of potassium dihydrogen phosphate, potassium carbonate and potassium oxalate; (5) After the β-VOPO4 precursor and the potassium source are mixed, the following steps are further included: ball milling and a second drying; Preferably, the ball milling is wet ball milling, the liquid medium of the wet ball milling includes water, and the mass ratio of balls, materials and water in the wet ball milling is (4-6):1:1; Preferably, the temperature of the second drying is 80-100°C, and the time of the second drying is 8-16 hours; (6) The temperature of the second sintering is 600-900° C., the time of the second sintering is 8-16 hours, and the atmosphere of the second sintering is an inert atmosphere; Preferably, the inert atmosphere includes at least one of argon, helium, neon and nitrogen.

7. The method for preparing the positive electrode material according to claim 4, wherein: The carbon source includes at least one of sucrose, glucose and citric acid; And / or, the temperature of the first calcination is 400° C. to 700° C., the time of the first calcination is 2 h to 5 h, and the atmosphere of the first calcination is an inert atmosphere; preferably, the inert atmosphere includes argon.

8. The method for preparing the positive electrode material according to claim 4, wherein: The nitrogen source comprises at least one of melamine, dopamine and thiourea; and / or, the sulfur source comprises at least one of thiourea, sodium lauryl sulfate and cysteine; And / or, the boron source includes boric acid and / or potassium borate.

9. The method for preparing a positive electrode material according to any one of claims 4 to 8, characterized in that: The temperature of the second calcination is 400° C. to 600° C., the time of the second calcination is 2 h to 5 h, and the atmosphere of the second calcination is an inert atmosphere; Preferably, the inert atmosphere includes at least one of argon, helium, neon and nitrogen.

10. A battery comprising a positive electrode, characterized in that: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 3, or the positive electrode material prepared by the preparation method of the positive electrode material according to any one of claims 4 to 9; Preferably, the battery is a potassium ion battery.

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