Positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a positive electrode material and a preparation method and application thereof. The positive electrode material comprises a matrix and a coating layer coating the surface of the matrix, wherein the matrix comprises a ferric sodium pyrophosphate material; the structural general formula of the ferric sodium pyrophosphate is Na (4-y) M1yFe (3-a-b) M2aM3b (PO4) 2P2O7, 0 < y < = 0.3, 0 < a and b < = 0.4, M1 comprises at least one of Li, K and Ca alkali metals, and M2 and M3 respectively comprise at least one of Mn, V, Nb, Cr, Zn, Cu, Co, Ni, Ti and Zr, through dual strategy modification of M1 doped to a sodium layer for supporting and high-potential redox metal elements M2 and M3, the energy density of the positive electrode material is remarkably improved, and the positive electrode material has a good application prospect. Meanwhile, good cycling stability and rate capability are kept, so that the low-temperature performance of the battery is further improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, as an alternative technology to lithium-ion batteries, have attracted widespread attention due to the abundance and low cost of sodium resources. Among the many cathode materials for sodium-ion batteries, sodium iron pyrophosphate has become a research hotspot due to its high theoretical capacity (129 mAh / g), structural stability, abundant iron resources, and environmental friendliness.

[0003] Sodium iron pyrophosphate materials have the following inherent drawbacks: a low voltage plateau, based on Fe... 2+ / Fe 3+ The working voltage of the redox electron pair is about 3.0-3.1V, which limits the further improvement of energy density. At the same time, the intrinsic electronic conductivity of sodium iron pyrophosphate is poor, resulting in poor rate performance. The phase transition of sodium iron pyrophosphate during charge and discharge further affects its cycle stability. How to improve the working voltage and energy density of sodium iron pyrophosphate has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a cathode material, its preparation method, and its application. By introducing a high-potential redox metal element to partially replace iron ions in the cathode material, the working voltage and energy density of the cathode material are significantly improved, while maintaining good cycle stability and rate performance.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a positive electrode material is provided, comprising: The matrix and the carbon coating layer covering the surface of the matrix; The matrix comprises sodium iron pyrophosphate material; the general structural formula of the sodium iron pyrophosphate material is Na. (4-y) M 1 y Fe (3-a-b) M 2 a M 3 b (PO4)2P2O7, where 0 < y ≤ 0.3, 0 < a, b ≤ 0.4; M 1 It is an alkali metal element; M 2 M is the first transition metal element. 3 It is the second transition metal element; The first transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB; the second transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB.

[0006] In some of these embodiments, the cathode material satisfies the relationship Kv>3, where , V m 2 V m 3 M is a transition metal element 2 M 3 The intrinsic redox potential, X i r represents the mole fraction of each transition metal. i Let r be the radius of each metal ion. Fe The radius of the iron ion is denoted as φ.

[0007] In some of these embodiments, the Dv50 particle size of the matrix is ​​2 μm to 20 μm.

[0008] In some of these embodiments, the M 1 It includes at least one of Li, K, and Ca.

[0009] In some of these embodiments, the M 2 It includes at least one of Mn, V, Cu, Co, and Ni.

[0010] In some of these embodiments, the M 3 It includes at least one of Mn, V, Cu, Co, and Ni.

[0011] According to another aspect of the present invention, the present invention provides a method for preparing the cathode material described in the above technical solution, comprising the following steps: a) Sodium source, iron source, phosphorus source, M 1 Source, M 2 Source, M 3 The mixture is obtained by mixing the source and the carbon source; b) The mixture is mixed with a solvent and ball-milled to obtain a mixed slurry, and the mixed slurry is spray-dried to obtain a precursor powder; c) The precursor powder is sintered under an inert atmosphere; Among them, M 1 It is an alkali metal element; M 2 M is the first transition metal element. 3 It is the second transition metal element.

[0012] In some embodiments, the sodium source includes at least one of sodium carbonate, sodium acetate, sodium oxalate, and sodium nitrate.

[0013] In some embodiments, the iron source includes at least one of ferric oxide, ferric phosphate, ferrous oxalate, and ferric nitrate.

[0014] In some of these embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid.

[0015] In some embodiments, the carbon source includes at least one of glucose, sucrose, citric acid, oxalic acid, polyethylene glycol, and conductive carbon black.

[0016] In some embodiments, the alkali metal element is selected from at least one of Li, K, and Ca; optionally, the M 1 The source includes at least one of lithium carbonate, lithium acetate, lithium dihydrogen phosphate, potassium carbonate, potassium hydroxide, calcium oxide, calcium carbonate, and calcium acetate.

[0017] In some embodiments, the first transition metal element includes at least one selected from Mn, V, Cu, Co, and Ni; optionally, M... 2 The source includes at least one of manganese dioxide, manganese acetate, manganese tetroxide, cobalt oxide, cobalt acetate, cobalt carbonate, vanadium pentoxide, copper oxide, nickel oxide, nickel carbonate, and nickel acetate.

[0018] In some embodiments, the second transition metal element includes at least one selected from Mn, V, Cu, Co, and Ni; optionally, the M 3 The source includes at least one of manganese dioxide, manganese acetate, manganese tetroxide, cobalt oxide, cobalt acetate, cobalt carbonate, vanadium pentoxide, copper oxide, nickel oxide, nickel carbonate, and nickel acetate.

[0019] In some of these embodiments, in step b), the solid content of the mixture in the material after mixing the mixture with the solvent is 30% to 70%.

[0020] In some of these embodiments, in step b), the conditions for the ball milling process include: a rotation speed of 300 rpm to 600 rpm and a time of 6 to 12 hours.

[0021] In some of these embodiments, in step b), the solvent includes at least one of anhydrous ethanol, methanol, isopropanol, and pure water.

[0022] In some of these embodiments, in step b), the spray drying includes an inlet temperature of 120°C to 220°C and an outlet temperature of 90°C to 120°C.

[0023] In some of these embodiments, in step b), the spray drying includes a feed rate of 1 rpm / s to 5 rpm / s.

[0024] In some of these embodiments, in step b), the spray drying includes a spray pressure of 0.3 MPa to 0.7 MPa.

[0025] In some of these embodiments, in step b), the inert atmosphere includes at least one of helium, neon, argon, krypton, xenon, and nitrogen.

[0026] In some embodiments, in step b), the sintering temperature of the first sintering includes 300°C to 400°C, and the sintering time of the first sintering is 2h to 4h.

[0027] In some of these embodiments, in step b), the second sintering temperature includes 600°C to 750°C, and the sintering time of the second sintering is 10h to 15h.

[0028] According to another aspect of the present invention, a battery is provided, including a positive electrode sheet; the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector in the thickness direction, the positive active material layer including the positive electrode material described in the above technical solution or the positive electrode material prepared by the preparation method described in the above technical solution.

[0029] According to another aspect of the present invention, an electrical device is provided, comprising the battery mentioned in the above-described technical solution.

[0030] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. This invention introduces metal elements (Li, K, Ca, etc.) that can be doped into the sodium layer to provide support, thereby increasing the interlayer spacing, which is beneficial for sodium ion transport. At the same time, it suppresses the collapse and expansion of the entire sodium layer structure during the sodium insertion / extraction process, which is beneficial for structural stability and significantly improves the cycling stability of the material.

[0031] 2. In a preferred embodiment of the present invention, a high-potential redox metal is introduced to replace some of the iron ions to achieve the purpose of providing voltage. The doping amount of the high-potential redox metal element is controlled to meet the requirement of Kv>3, so as to ensure the stability of the crystal structure while ensuring the high voltage of the cathode material and improve the cycle stability of the cathode material.

[0032] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0034] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0036] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0040] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0041] Sodium iron pyrophosphate has become an ideal choice for cathode materials in lithium-ion batteries due to its high theoretical capacity, stable structure, abundant iron resources, and environmental friendliness. However, sodium iron pyrophosphate materials have the following inherent defects: a low voltage plateau limits further improvement in energy density; poor intrinsic electronic conductivity leads to poor rate performance; and phase transitions are prone to occur during charge and discharge, thus affecting the cycle stability of the battery.

[0042] Currently, existing technologies mainly focus on improving conductivity and cycling performance through carbon coating, lithium doping, and particle morphology control, but there is relatively little research on improving voltage plateau.

[0043] In summary, through in-depth research, the inventors of this invention have discovered a solution to address the problems of low voltage plateau and limited energy density in existing sodium iron pyrophosphate cathode materials. This invention provides a modified material and its preparation method that partially replaces iron sites by introducing high-potential redox metal elements. The aim is to significantly improve the material's operating voltage and energy density while maintaining good cycle stability and rate performance. Specifically, this invention employs the following technical solution: According to one aspect of the present invention, a positive electrode material is provided, comprising: The matrix and the carbon coating layer covering the surface of the matrix; The matrix comprises sodium iron pyrophosphate material; the general structural formula of the sodium iron pyrophosphate material is Na. (4-y) M 1 y Fe (3-a-b) M 2 a M 3 b (PO4)2P2O7, where 0 < y ≤ 0.3, 0 < a, b ≤ 0.4; M 1 It is an alkali metal element; M 2 M is the first transition metal element. 3 It is the second transition metal element; The first transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB; the second transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB.

[0044] In a specific embodiment of the present invention, the matrix comprises sodium iron pyrophosphate; sodium iron pyrophosphate has the following advantages: (1) high theoretical capacity, with a specific capacity of 129 mAh / g, far exceeding that of traditional iron-based polyanionic materials; (2) stable structure, with large three-dimensional open sodium ion diffusion channels inside. This structure allows for small volume changes during sodium removal and insertion, effectively reducing structural losses during charging and discharging; (3) abundant iron resources, promoting low-cost industrialization; (4) environmentally friendly and pollution-free. The present invention improves upon lithium iron phosphate in the prior art, improves the inherent defects of sodium iron pyrophosphate, increases the voltage of its overall platform, and further improves the energy density.

[0045] In a specific embodiment of the present invention, the lithium iron phosphate material includes the alkali metal element M. 1 This widens the interlayer spacing of the sodium layer; the alkali metal element M 1 The doping includes at least one of the alkali metals Li, K, and Ca. Doping with the aforementioned alkali metal elements facilitates sodium ion transport and suppresses potential collapse and expansion of the entire sodium layer during sodium insertion / extraction, thus improving the material's structural stability and cycle stability. Furthermore, addressing the issue of low voltage plateau and limited energy density in sodium iron pyrophosphate cathode materials, this application also dops sodium iron pyrophosphate with a first transition metal element M. 2 Second transition metal element M 3 The first transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB; the second transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB. In this application, there are no special restrictions on the type and source of the first and second transition metal elements, as long as the requirement of relation Kv > 3 is met.

[0046] It needs to be further explained that, among them , V m 2 V m 3 M is a transition metal element 2 M 3 The intrinsic redox potential, X i r represents the mole fraction of each transition metal. i Let r be the radius of each metal ion. FeThe ionic radius of the iron ion is used in this application. However, more high-potential redox metal doping is not necessarily better. Since the size of the doped ions usually differs from that of the Fe ions, it can cause local expansion or contraction of the crystal lattice, altering the bond length and bond energy of the metal-oxygen bond, thus affecting the average voltage of the cathode material. Indiscriminate addition of high-potential metal elements may lead to an imbalance in the transition metal layer support system, causing structural damage to the crystal, resulting in poorer cycle stability and a decrease in average voltage. Therefore, in the preferred embodiment of this invention, it is necessary to control the amount of transition metal element M. 2 M 3 The selection satisfies the requirement of Kv>3 mentioned in this invention.

[0047] In a specific embodiment of the present invention, the particle size of the positive electrode material is 2μm to 20μm, specifically any one of 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, and 20μm, or any range between two of them. It should be further noted that controlling the particle size within the above range can avoid the increase in specific surface area caused by excessively small particle size, thereby reducing side reactions and improving the cycle stability and life of the battery. Excessively large particle size will lead to a longer diffusion path of lithium ions in the active material, increased resistance, and decreased rate performance.

[0048] In a specific embodiment of the present invention, the M 1 Including at least one of Li, K, and Ca, it should be further noted that M 1 As alkali metal elements, doping with these alkali metal elements can effectively broaden ion diffusion paths, enhance conductivity, strengthen the crystal lattice framework, and improve the thermal stability of materials.

[0049] In a specific embodiment of the present invention, the M 2 Includes at least one of Mn, V, Cu, Co, and Ni, wherein M 3 Including at least one of Mn, V, Cu, Co, and Ni, it should be further noted that these transition metal elements, such as Mn, V, Cu, and Ni, have variable oxidation states. During the charging and discharging process, the redox reactions of these ions can promote electron transport, reduce the resistance of the material, and improve the electronic conductivity. At the same time, the introduction of these elements can enhance the stability of the sodium iron pyrophosphate crystal structure and improve the cycle performance.

[0050] In summary, this invention introduces metal elements (Li, K, Ca, etc.) that can be doped into the sodium layer to provide support, thereby increasing the interlayer spacing and facilitating sodium ion transport. Simultaneously, it suppresses the collapse and expansion of the entire sodium layer structure during the sodium insertion / extraction process, improving structural stability and significantly enhancing the material's cycle stability. Furthermore, the introduction of high-potential redox metals to replace some iron ions provides voltage. By controlling the doping amount of these high-potential redox metals to meet the requirement of Kv > 3, the invention ensures both high voltage and crystal structure stability of the cathode material, improving its cycle stability and significantly increasing its operating voltage and energy density while maintaining good cycle stability and rate performance.

[0051] According to another aspect of the present invention, the present invention provides a method for preparing the cathode material described in the above technical solution, comprising the following steps: a) Sodium source, iron source, phosphorus source, M 1 Source, M 2 Source, M 3 The mixture is obtained by mixing the source and the carbon source; b) The mixture is mixed with a solvent and ball-milled to obtain a mixed slurry, and the mixed slurry is spray-dried to obtain a precursor powder; c) The precursor powder is sintered under an inert atmosphere; Among them, M 1 It is an alkali metal element; M 2 M is the first transition metal element. 3 It is the second transition metal element.

[0052] This invention first uses sodium source, iron source, phosphorus source, and M... 1 Source, M 2 Source, M 3 The raw materials and carbon source are weighed according to the general formula stoichiometric ratio and mixed to obtain a raw material mixture.

[0053] In a specific embodiment of the present invention, the sodium source includes at least one of sodium carbonate, sodium acetate, sodium oxalate, and sodium nitrate. In a preferred embodiment of the present invention, sodium carbonate is used as the sodium source. The iron source includes at least one of ferric oxide, ferric phosphate, ferrous oxalate, and ferric nitrate. In a preferred embodiment of the present invention, ferric oxide is used as the iron source. 1 The source includes at least one of lithium source, potassium source, and calcium source; in a preferred embodiment of the present invention, lithium source is used as M. 1The lithium source includes at least one of lithium carbonate, lithium acetate, lithium nitrate, lithium dihydrogen phosphate, and lithium sulfate. In a preferred embodiment of the present invention, the lithium source is lithium carbonate. The potassium source includes at least one of potassium carbonate, potassium acetate, and potassium hydroxide. The calcium source includes at least one of calcium oxide, calcium carbonate, calcium hydroxide, and calcium acetate. 2 The source includes at least one of manganese, vanadium, niobium, chromium, zinc, copper, cobalt, nickel, titanium, and zirconium sources. In a preferred embodiment of the present invention, the M... 2 The source is selected as a manganese source, which includes at least one of manganese dioxide, manganese carbonate, manganese acetate, manganese malonate, and manganese tetroxide. In a preferred embodiment of the present invention, the manganese source is selected as manganese malonate; in a preferred embodiment of the present invention, the M... 3 The source is selected as a nickel source, which includes at least one of nickel oxide, nickel carbonate, and nickel acetate. In a preferred embodiment of the present invention, nickel oxide is selected as the nickel source. In a preferred embodiment of the present invention, the vanadium source includes at least one of vanadium dioxide, vanadium pentoxide, and vanadium dioxide. In a preferred embodiment of the present invention, the niobium source includes at least one of niobium monoxide and niobium pentoxide. In a preferred embodiment of the present invention, the chromium source includes at least one of chromium oxide, chromium trioxide, and chromium trioxide. In a preferred embodiment of the present invention, the zinc source includes at least one of zinc oxide, zinc sulfate, zinc nitrate, and zinc acetate. In a preferred embodiment of the present invention, the copper source includes at least one of copper oxide and cuprous oxide. In a preferred embodiment of the present invention, the cobalt source includes at least one of cobalt oxide, cobalt acetate, and cobalt carbonate. In a preferred embodiment of the present invention, the peptide source includes at least one of titanium oxide, peptide dioxide, and dipeptide trioxide. In a preferred embodiment of the present invention, the zirconium source includes at least one of zirconium monoxide and zirconium dioxide. In a preferred embodiment of the present invention, the carbon source includes at least one of glucose, sucrose, citric acid, oxalic acid, polyethylene glycol, and conductive carbon black.

[0054] The bulk dopant element in the dopant source is the same as that described in the above technical solution, and will not be repeated here. Specifically, one or more of the above-mentioned bulk dopant elements well known to those skilled in the art, such as nitrates, hydroxides, oxides, peroxides, sulfates, and carbonates, can be used as the bulk dopant source. This invention does not impose any special restrictions on the source of the above-mentioned lithium, potassium, calcium, manganese, vanadium, niobium, chromium, zinc, copper, cobalt, nickel, titanium, zirconium, and carbon sources; commercially available products well known to those skilled in the art can be used.

[0055] In a specific embodiment of the present invention, the ratio of the lithium source, potassium source, calcium source, manganese source, vanadium source, niobium source, chromium source, zinc source, copper source, cobalt source, nickel source, titanium source, zirconium source, and carbon source can be formulated according to the limiting conditions of each component in the cathode material described in the above technical solution, and the present invention will not elaborate further on this.

[0056] In a specific embodiment of the present invention, in step a), the solid content of the mixture in the material after mixing the mixture with the solvent is 30% to 70%, for example, 30%, 40%, 50%, 60%, 70%, or any two of these ranges. By controlling the solid content of the mixture in the solvent within the above range, problems such as low ball milling efficiency and precursor agglomeration that may be caused by too low solid content can be avoided, as well as problems such as uneven ball milling and precursor cracking that may be caused by too high solid content.

[0057] In a specific embodiment of the present invention, the mixing process is preferably carried out in a ball mill to ensure uniform mixing of the raw materials. In addition, the process includes the addition of a solvent and milling media. The solvent preferably includes anhydrous ethanol, and the milling media preferably includes zirconia balls. The mixing speed is preferably 300 rpm to 600 rpm, specifically 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, or any range between two of these values. The mixing time is preferably 6 hours to 12 hours, specifically 6 hours, 8 hours, 10 hours, 12 hours, or any range between two of these values. By controlling the ball milling parameters within the above ranges, uniform mixing of the raw materials can be ensured, which is beneficial for the smooth progress of subsequent steps.

[0058] In a specific embodiment of the present invention, the inlet temperature of the spray dryer is preferably 120℃~220℃, specifically 120℃, 140℃, 160℃, 180℃, 220℃, or any two of these ranges, and the outlet temperature is 90℃~120℃, for example 90℃, 100℃, 110℃, 120℃, or any two of these ranges. By controlling the inlet and outlet temperatures of the spray dryer within the above ranges, the drying efficiency of the droplets can be improved, while avoiding damage to the raw material properties caused by excessively high temperatures.

[0059] In a specific embodiment of the present invention, the spray drying includes a feed rate of 1 rpm / s to 5 rpm / s, for example, 1 rpm / s, 3 rpm / s, 5 rpm / s, or any two of these ranges. By controlling the feed rate of the spray drying within the above range, the stability of the atomization effect can be ensured, and the uneven distribution of droplets that may be caused by too low a rotation speed can be avoided. At the same time, the problem of incomplete product drying caused by too high a rotation speed can be avoided.

[0060] In a specific embodiment of the present invention, the spray drying includes a spray pressure of 0.3 MPa to 0.7 MPa, for example, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, or any two of these ranges. By controlling the spray pressure within the above range, it is possible to ensure the stable generation of uniform droplets and avoid insufficient pressure, which would result in insufficient kinetic energy of the sprayed material, making it unable to be fully broken down and causing large-diameter droplets or droplet agglomeration, thereby reducing drying efficiency. At the same time, when the spray pressure is too high, extremely fine droplets may be generated, and the generated droplets may be discharged with the exhaust gas, thereby reducing the product droplet yield.

[0061] In a specific embodiment of the present invention, the inert atmosphere includes at least one of helium, neon, argon, krypton, xenon, and nitrogen. In this application, there are no restrictions on the selection and source of the inert atmosphere, as long as it can prevent the oxidation of the raw materials.

[0062] In a specific embodiment of the present invention, the sintering temperature of the first sintering is 300℃~400℃ and the sintering time is 2h~4h. It should be further noted that controlling the temperature of the first sintering within the above range can ensure sufficient evaporation of moisture and removal of low-boiling-point impurities, while avoiding decomposition of raw materials or other side reactions caused by excessively high temperatures.

[0063] In a specific embodiment of the present invention, the sintering temperature of the second sintering is 600℃~750℃, and the sintering time is 10h~15h. By controlling the second sintering temperature within the above range, the raw materials such as sodium source, iron source, and phosphorus source can fully undergo chemical reactions to form a complete positive electrode material crystal phase. At the same time, excessively high temperatures are avoided, which may lead to the decomposition of raw material components or the generation of impurity phases, affecting the cycle performance of the positive electrode material crystal. Furthermore, the selection of the above sintering temperature and time can ensure that the carbon source is cracked and uniformly coated with a layer of carbon on the surface of the positive electrode material particles, which can improve the conductivity of the material, improve the rate performance, reduce the side reactions between the positive electrode material and the electrolyte, and improve the cycle stability of the battery. If the temperature is not suitable, the carbon source may not be fully cracked or the coating may be uneven, ultimately affecting the performance of the positive electrode material.

[0064] According to another aspect of the present invention, a battery is provided, comprising a positive electrode sheet; the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector in the thickness direction, the positive active material layer comprising the positive electrode material described in the above-described technical solution or the positive electrode material prepared by the preparation method described in the above-described technical solution. Thus, the battery possesses all the features and advantages of the positive electrode material described in the above-described technical solution, which will not be repeated here.

[0065] In a specific embodiment of the present invention, the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer is disposed on one or both of the two opposite surfaces of the positive electrode current collector. The positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as a metal foil; the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer; the composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0066] The present invention does not impose any special restrictions on the preparation method of the positive electrode sheet. The positive electrode sheet can be obtained by coating the positive electrode slurry onto the positive electrode current collector and then drying it, which is well known to those skilled in the art.

[0067] In a specific embodiment of the present invention, the positive electrode active material layer preferably includes a binder and a conductive agent in addition to the positive electrode material. The mass ratio of the positive electrode material, binder, and conductive agent is (70~99):(0.5~15):(0.5~15). The binder may include one or more of polyvinylidene fluoride (PVDF), sodium alginate, polyvinyl alcohol, polymethyl methacrylate, hydrogenated nitrile rubber, polytetrafluoroethylene, and polyacrylic acid, thereby improving the bonding strength between the positive electrode active material layer and the positive electrode current collector. The conductive agent may include one or more of superconducting (SP), acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In a specific embodiment of this application, the mass ratio of the positive electrode material, binder, and conductive agent is 90:5:5.

[0068] In a specific embodiment of the present invention, the positive electrode material, binder and conductive agent are dissolved in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is then coated on the positive electrode current collector, and after drying and other processes, a positive electrode sheet can be obtained.

[0069] In a specific embodiment of the present invention, the battery preferably includes a negative electrode, an electrolyte, and a separator, in addition to the positive electrode. All of these can be made from raw materials well-known to those skilled in the art for preparing lithium-ion batteries, and the present invention does not impose any special limitations on them. The battery may also include an outer packaging, which can be used for encapsulation. This outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell, or it can be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0070] According to another aspect of the present invention, an electrical device is provided, comprising the battery described in the above-described technical solution. Thus, the electrical device possesses all the features and advantages of the battery described in the above-described technical solution, which will not be repeated here. Specifically, the battery can serve as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, and energy storage systems.

[0071] The present invention does not impose any particular limitation on the shape of the battery, which can be cylindrical, square or other arbitrary shapes, and those skilled in the art can choose according to specific practical needs.

[0072] The present application will be specifically described below with reference to the embodiments, but the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0073] Example 1 Synthesis of cathode materials (Na) 3.7 Li 0.3 Fe 2.7 Mn 0.2 Ni 0.1 (PO4)2P2O7@C) The raw materials were weighed according to the general stoichiometric ratio. The raw materials included: Na2CO3, Li2CO3, Fe2O3 (mass), C4H6MnO4, NiO, NH4H4PO4, and glucose. The weighed raw materials were added to anhydrous ethanol (purity ≥99.5%) and zirconia balls with a diameter of 3 mm. The mixture was ball-milled, with a solid content of 60% in the solution and a total mass ratio of zirconia balls to powder of 10:1. The mixture was ball-milled under vacuum at a rotation speed of 500 rpm, alternating between forward and reverse rotation, changing direction every 30 minutes, for a total of 8 hours. After ball milling, a slurry was obtained. The slurry was then spray-dried using a spray drying instrument. The spray inlet temperature was controlled at 130℃, the outlet temperature at 90℃, the feed rate at 2 rpm / s, and the spray pressure at 0.5 MPa to obtain the precursor powder. The precursor powder was then transferred to a tube furnace for calcination. The first sintering was carried out in a nitrogen atmosphere at a temperature of 350°C for 3 hours. After the reaction was completed, the second sintering was started at a temperature of 650°C for 10 hours. After the reaction was completed, the material was naturally cooled and passed through a 400-mesh sieve to obtain the cathode material with a particle size of 10 μm.

[0074] Example 2 The preparation method provided in Example 1 was used, with the only difference being that the sodium source in the raw materials was changed from sodium carbonate to sodium acetate to prepare the positive electrode material.

[0075] Example 3 The preparation method provided in Example 1 is used, with the only difference being that the iron source in the raw materials is changed from iron oxide to iron phosphate to prepare the positive electrode material.

[0076] Example 4 Synthesis of cathode materials (Na) 3.7 Li 0.3 Fe 2.7 Co 0.2 Ni 0.1 (PO4)2P2O7@C) The preparation method provided in Example 1 is different in that the manganese source is changed to a cobalt source, and the raw material of the cobalt source is cobalt acetate. The raw materials weighed above are added to anhydrous ethanol (purity ≥99.5%) and zirconia balls with a diameter of 3 mm, and mixed by ball milling. The solid content of the solution is 65%, and the mass ratio of zirconia balls to powder is 8:1. Under vacuum, the ball milling is carried out at a rotation speed of 500 rpm, alternating between forward and reverse rotation, switching directions every 30 minutes, for a total of 10 hours. After ball milling, a slurry is obtained. The slurry is then spray-dried using a spray drying instrument. The spray inlet temperature is controlled at 200°C, the outlet temperature at 110°C, the feed rate at 4 rpm / s, and the spray pressure at 0.7 MPa to obtain precursor powder. The precursor powder was then transferred to a tube furnace for calcination. The first sintering was carried out in a nitrogen atmosphere, with the sintering temperature controlled at 360℃ and the sintering time at 3 hours. After the reaction was completed, the second sintering was started, with the sintering temperature adjusted to 680℃ and the sintering time adjusted to 10 hours. After the reaction was completed, the material was naturally cooled and passed through a 300-mesh sieve to obtain the final cathode material with a particle size of 12μm.

[0077] Example 5 Synthesis of cathode materials (Na) 3.7 Li 0.3 Fe 2.7 Mn 0.2 V 0.1 (PO4)2P2O7@C) The preparation method provided in Example 1 is different in that the nickel source is changed to a vanadium source, and the raw material for the cobalt source is vanadium pentoxide (V2O5), with a mass of 9.1 g (0.05 mol). The raw material obtained above is added to anhydrous ethanol (purity ≥99.5%) and zirconia balls with a diameter of 3 mm, and mixed by ball milling. The solid content of the solution is 50%, and the mass ratio of zirconia balls to powder is 12:1. Under vacuum, the ball milling is carried out at a rotation speed of 500 rpm, alternating between forward and reverse rotation, switching directions every 30 min, for a total of 10 h. After ball milling, a slurry is obtained, which is then spray-dried using a spray drying instrument. The spray inlet temperature is controlled at 120℃, the outlet temperature at 100℃, the feed rate at 3 rpm / s, and the spray pressure at 0.4 MPa to obtain precursor powder. The precursor powder was then transferred to a tube furnace for calcination. The first sintering was carried out in a nitrogen atmosphere at a temperature of 320°C for 3 hours. After the reaction was completed, the second sintering was started at a temperature of 650°C for 13 hours. After the reaction was completed, the material was naturally cooled and passed through a 500-mesh sieve to obtain the cathode material with a particle size of 6 μm.

[0078] Comparative Example 1 Synthesis of cathode materials (Na) 3.7 Li 0.3 Fe2Mn 0.5Ni 0.5 (PO4)2P2O7@C) The preparation method provided in Example 1 was followed, except that the general structural formula of the cathode material was adjusted. The corresponding raw material mass was weighed according to the above general structural formula. The raw material mass obtained above was added to anhydrous ethanol and zirconia balls with a diameter of 3 mm. The mixture was ball-milled, wherein the solution contained 60% solids and the mass ratio of zirconia balls to powder was 10:1. The mixture was ball-milled for 8 hours under vacuum at a rotation speed of 500 rpm, alternating between forward and reverse rotation, switching directions every 30 minutes. After ball milling, a slurry was obtained. The slurry was then spray-dried using a spray drying instrument. The spray inlet temperature was controlled at 220°C, the outlet temperature at 110°C, the feed rate at 2 rpm / s, and the spray pressure at 0.5 MPa to obtain precursor powder. The precursor powder was then transferred to a tube furnace for calcination. The first sintering was carried out in a nitrogen atmosphere at a temperature of 350°C for 3 hours. After the reaction was completed, the second sintering was started at a temperature of 650°C for 10 hours. After the reaction was completed, the material was naturally cooled and passed through a 400-mesh sieve to obtain the cathode material with a particle size of 10 μm.

[0079] Comparative Example 2 Synthesis of cathode material (Na4Fe2Mn) 0.5 Ni 0.5 (PO4)2P2O7@C) The preparation method provided in Example 1 differs in that the general structural formula of the cathode material is adjusted, and the corresponding raw material mass is weighed according to the above general structural formula to prepare the cathode material.

[0080] Performance testing: 1. Electrode fabrication and electrochemical performance testing: Using the final products prepared in Examples 1-5 and Comparative Example 1 as positive electrode materials, to test the electrochemical performance of the lithium-ion positive electrode materials obtained in the examples and comparative examples, the positive electrode materials obtained in the examples or comparative examples, conductive carbon black, and binder polyvinylidene fluoride were mixed in a mass ratio of 90:5:5. Using N-methylpyrrolidone (NMP) as a solvent, the mixture was prepared into a slurry, uniformly coated onto aluminum foil, dried at a suitable temperature, rolled, and then vacuum dried at 120°C for 12 hours to obtain a positive electrode sheet. The electrode sheet was cut, weighed, and placed in a glove box. In the glove box, using a sodium metal sheet as the negative electrode and a polypropylene porous membrane as the separator, sodium hexafluorophosphate (NaPF6) was dissolved in a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. The electrolyte concentration was 1 mol / L. CR2032 button batteries were assembled in an argon-filled glove box.

[0081] 2. Electrochemical performance testing: Equipment: Xinwei Battery Testing System (CT-4008T); Test program: (1) Initial specific capacity test: Charge the capacitor to 4.05V at a constant current of 0.1C at 25℃, then discharge it to 2V at a constant current of 0.1C, and record the initial specific capacity.

[0082] (2) Cyclic performance test: Charge to 3.65V with 1C constant current, discharge to 2.5V with 1C constant current, and record the discharge specific capacity as the first discharge specific capacity. Repeat the above steps and record the discharge specific capacity on the 500th time. Data processing: 500-cycle capacity retention (%) = (500th discharge specific capacity / 1st discharge specific capacity) × 100%.

[0083] The test results are shown in Table 1 below.

[0084] Table 1 Analyze the results in Table 1: By comparing the results of Examples 1 to 3, it can be seen that when the general formula of the target product is the same, the use of different sodium and iron sources as raw materials has little effect on the battery's initial charge capacity, 500-cycle retention rate, and average voltage. It can be inferred that when using different types of raw materials with different transition metal sources protected by this invention, the inventive purpose of this invention can be well achieved.

[0085] By comparing the results of Example 1, Examples 4-5, it can be seen that when M is adjusted... 2 Source and M 3 When considering the transition metal type of the source, experimental results show that the initial charge capacity, 500-cycle retention rate, and average voltage of the battery are not significantly different. Therefore, it can be inferred that when using the M protected by this invention... 2 Source and M 3 All transition metals from the source can effectively achieve the inventive objective of this invention.

[0086] Comparative analysis: Based on the data from Comparative Example 1 and Example 1, it can be seen that in the general formula of Comparative Example 1, the value of b is 0.5, which does not meet the range of b≤0.4 protected by this invention. The experimental results show that the battery prepared by Comparative Example 1 has a significant decrease in both specific capacity and cycle retention rate compared with Examples 1 to 5.

[0087] Based on the data from Comparative Example 2 and Example 1, it can be seen that when M is not present in the general structural formula... 1Even if Kv meets the conditions of this invention, the specific capacity of the source under the supporting metal element is reduced in both the initial charge and the 500-cycle stability.

[0088] In summary, ensuring that the structural formula meets the requirements of the general formula parameters protected by this invention can effectively achieve the inventive objective of this invention.

[0089] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0090] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the scope of the present invention to the specific details described above.

[0091] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that, Includes a matrix and a carbon coating layer covering the surface of the matrix; The matrix comprises sodium iron pyrophosphate material; the general structural formula of the sodium iron pyrophosphate material is Na. (4-y) M 1 y Fe (3-a-b) M 2 a M 3 b (PO4)2P2O7, where 0 < y ≤ 0.3, 0 < a, b ≤ 0.4; M 1 It is an alkali metal element; M 2 M is the first transition metal element. 3 It is the second transition metal element; The first transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB; the second transition metal element includes at least one element from Group VB, Group VII, Group VIII, and Group IB.

2. The cathode material according to claim 1, characterized in that, The cathode material satisfies the relationship Kv>3; in, , V m2 For M 2 The intrinsic redox potential, V m 3 For M 3 The intrinsic redox potential, X i r represents the mole fraction of each transition metal. i Let r be the ionic radius of each metal ion. Fe denoted as , where is the ionic radius of the iron ion.

3. The cathode material according to claim 1, characterized in that, The Dv50 particle size of the cathode material is 2μm~20μm.

4. The cathode material according to claim 1, characterized in that, The M 1 Including at least one of Li, K, and Ca; And / or, the M 2 Including at least one of Mn, V, Cu, Co, and Ni; And / or, the M 3 It includes at least one of Mn, V, Cu, Co, and Ni.

5. A method for preparing a positive electrode material, characterized in that, Includes the following steps: a) Sodium source, iron source, phosphorus source, M 1 Source, M 2 Source, M 3 The mixture is obtained by mixing the source and the carbon source; b) The mixture is mixed with a solvent and ball-milled to obtain a mixed slurry, and the mixed slurry is spray-dried to obtain a precursor powder; c) The precursor powder is sintered under an inert atmosphere; Among them, M 1 It is an alkali metal element; M 2 M is the first transition metal element. 3 It is the second transition metal element.

6. The preparation method according to claim 5, characterized in that, The sodium source includes at least one of sodium carbonate, sodium acetate, sodium oxalate, and sodium nitrate. And / or, the iron source includes at least one of ferric oxide, ferric phosphate, ferrous oxalate, and ferric nitrate; And / or, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; And / or, the carbon source includes at least one of glucose, sucrose, citric acid, oxalic acid, polyethylene glycol, and conductive carbon black; And / or, the alkali metal element is selected from at least one of Li, K, and Ca; optionally, the M 1 The source includes at least one of lithium carbonate, lithium acetate, lithium dihydrogen phosphate, potassium carbonate, potassium hydroxide, calcium oxide, calcium carbonate, and calcium acetate; And / or, the first transition metal element includes at least one selected from Mn, V, Cu, Co, and Ni; optionally, the M 2 The source includes at least one of manganese dioxide, manganese acetate, manganese tetroxide, cobalt oxide, cobalt acetate, cobalt carbonate, vanadium pentoxide, copper oxide, nickel oxide, nickel carbonate, and nickel acetate; And / or, the second transition metal element includes at least one of Mn, V, Cu, Co, and Ni; optionally, the M 3 The source includes at least one of manganese dioxide, manganese acetate, manganese tetroxide, cobalt oxide, cobalt acetate, cobalt carbonate, vanadium pentoxide, copper oxide, nickel oxide, nickel carbonate, and nickel acetate.

7. The preparation method according to claim 5, characterized in that, In step b), the solid content of the mixture in the material after mixing the mixture with the solvent is 30% to 70%.

8. The preparation method according to claim 5, characterized in that, In step b), The conditions for ball milling include: a rotation speed of 200 rpm to 600 rpm and a time of 6 to 12 hours; And / or, the solvent includes at least one of anhydrous ethanol, methanol, isopropanol, and pure water; And / or, the spray drying includes an inlet temperature of 120°C to 220°C and an outlet temperature of 90°C to 120°C; And / or, the spray drying includes a feed rate of 1 rpm / s to 5 rpm / s; And / or, the spray drying includes a spray pressure of 0.3 MPa to 0.7 MPa; And / or, the inert atmosphere includes at least one of helium, neon, argon, krypton, xenon, and nitrogen; And / or, the sintering temperature of the first sintering includes 300℃~400℃, and the sintering time of the first sintering is 2h~4h; And / or, the second sintering temperature includes 600℃~750℃, and the second sintering time is 10h~15h.

9. A battery, characterized in that, It includes a positive electrode sheet; the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes the positive electrode material according to any one of claims 1 to 4 or the positive electrode material prepared by the preparation method according to any one of claims 5 to 8.

10. An electrical device, characterized in that, Includes the battery as described in claim 9.

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