Sodium-ion battery positive electrode material, preparation method thereof, positive electrode sheet, sodium-ion battery and electric device

Abstract

The embodiment of the application discloses a sodium ion battery positive electrode material and a preparation method thereof, a positive electrode sheet, a sodium ion battery and an electric equipment. The sodium ion battery positive electrode material comprises a core and a coating layer arranged on the core. The core comprises a layered oxide, and the coating layer comprises a metal sodium-containing oxygen acid salt and a conductive polymer. The metal sodium-containing oxygen acid salt is a good sodium ion conductor, the electronic conductivity of the conductive polymer is high, the coating layer containing the metal sodium-containing oxygen acid salt and the conductive polymer can improve the stability of the positive electrode material and electrolyte, and can simultaneously improve the electronic conductivity and ionic conductivity of the surface of the positive electrode material, reduce the sodium ion diffusion impedance, and effectively improve the rate performance and cycle performance of the positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a sodium ion battery positive electrode material, a preparation method thereof, a positive electrode sheet, a sodium ion battery and an electric device. BACKGROUND

[0002] Layered oxide positive electrode materials have high reversible specific sodium storage capacity and are promising sodium ion battery positive electrode materials for large-scale applications. However, the surface of the layered oxide positive electrode material is eroded by HF, a byproduct of electrolyte decomposition, during the cycling process, leading to the dissolution of transition metal ions and the irreversible transformation of the structure. In addition, the layered oxide positive electrode material releases active oxygen at a high state of charge, further exacerbating the decomposition of the electrolyte and the capacity decay of the positive electrode material. To solve the above problems, a coating layer is usually provided on the surface of the layered oxide positive electrode material to protect the positive electrode material. The existing coating layer is usually an oxide, such as aluminum oxide and titanium oxide. However, the oxide coating layer has poor electronic conductivity, which hinders electron transport and reduces the kinetic properties of the material. On the other hand, the oxide coating layer is a poor conductor of sodium ions, which hinders the migration of sodium ions and increases the impedance of the electrochemical process. Therefore, there is a need for a sodium ion battery positive electrode material with good cycle stability and excellent electrochemical performance. SUMMARY

[0003] Therefore, the present application provides a sodium ion battery positive electrode material, a preparation method thereof, a positive electrode sheet, a sodium ion battery and an electric device. The sodium ion battery positive electrode material has a coating layer composed of a metal sodium-containing oxygen acid salt and a conductive polymer. The metal sodium-containing oxygen acid salt is a good sodium ion conductor, and the conductive polymer has high electronic conductivity. The coating layer can improve the stability of the positive electrode material and the electrolyte, and can also improve the electronic conductivity and ionic conductivity of the surface of the positive electrode material, reduce the diffusion impedance of sodium ions, and effectively improve the rate performance and cycle performance of the positive electrode material.

[0004] In a first aspect, the present application provides a sodium ion battery positive electrode material, which includes a core and a coating layer provided on the core. The core includes a layered oxide, and the coating layer includes a metal sodium-containing oxygen acid salt and a conductive polymer.

[0005] In the present application, the metal sodium-containing oxygen acid salt includes at least one of sodium molybdate and sodium tungstate, and / or the conductive polymer includes at least one of polypyrrole, polypyridine and polyaniline.

[0006] In the present application, the mass percentage of the metal sodium-containing oxygen acid salt in the coating layer is 0.1% to 99.9%, and the mass percentage of the conductive polymer is 0.1% to 99.9%.

[0007] In the embodiment of the present application, the mass percentage of the sodium salt of metal oxoacid in the coating layer is 5%-95%, and the mass percentage of the conductive polymer is 5%-95%.

[0008] In the embodiment of the present application, the mass of the coating layer is 0.05%-10% of the mass of the sodium ion battery cathode material, and the mass of the inner core is 90%-99.5% of the mass of the sodium ion battery cathode material.

[0009] In the embodiment of the present application, the thickness of the coating layer is 1 nm-15 nm.

[0010] In the embodiment of the present application, the coating rate of the coating layer on the surface of the inner core is 40%-100%.

[0011] In the embodiment of the present application, the layered oxide includes an O3 phase sodium ion layered oxide, and the chemical general formula of the O3 phase sodium ion layered oxide is Na x1 Ni x2 Fe x3 Mn x4 M x5 O2, wherein M includes at least one of Ti, W, Mo, V, Zr, Cr and Al, 0.6≤x1≤1.1, 0

[0012] In the embodiment of the present application, the particle size D50 of the sodium ion battery cathode material is 0.5 μm-20 μm.

[0013] The sodium ion battery cathode material provided by the embodiment of the present application has a coating layer composed of a sodium salt of metal oxoacid and a conductive polymer. The sodium salt of metal oxoacid is a good sodium ion conductor, and the electronic conductivity of the conductive polymer is high. The coating layer can improve the stability of the cathode material and the electrolyte, and can also improve the electronic conductivity and ionic conductivity of the surface of the cathode material, reduce the sodium ion diffusion impedance, and effectively improve the rate performance and cycle performance of the cathode material.

[0014] In a second aspect, the embodiment of the present application provides a preparation method of the sodium ion battery cathode material of the first aspect, comprising:

[0015] Mixing the layered oxide and the sodium salt of metal oxoacid, and performing first calcination under an oxygen-containing atmosphere to obtain a semi-finished product;

[0016] Mixing the semi-finished product and the conductive polymer, and performing second calcination under an inert atmosphere to obtain the sodium ion battery cathode material.

[0017] In the embodiment of the present application, the temperature of the first calcination is 5-100 DEG C higher than the melting point of the sodium salt of metal oxyacid, and the time of the first calcination is 0.5-10 hours; the oxygen-containing atmosphere includes air or oxygen.

[0018] In the embodiment of the present application, the temperature of the second calcination is 5-100 DEG C higher than the melting point of the conductive polymer, and the time of the second calcination is 0.5-10 hours; the inert atmosphere includes argon or nitrogen.

[0019] The preparation method provided by the embodiment of the present application can obtain a relatively uniform coating layer on the surface of the sodium-ion positive electrode material through simple solid-phase mixing and heat treatment, and the coating process is simple and easy to mass-produce and apply. Meanwhile, the coating process of the present technology does not need water or other solvents, which can effectively avoid the damage of water to the structure of the sodium-ion battery positive electrode material. Meanwhile, subsequent wastewater treatment is not needed, which is environmentally friendly and saves trouble. Compared with the existing process, the coating layer obtained by the present solution is more uniform.

[0020] In a third aspect, the embodiment of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and an active material layer arranged on the positive electrode current collector, and the active material layer comprises the sodium-ion battery positive electrode material of the first aspect or the sodium-ion battery positive electrode material prepared by the preparation method of the second aspect.

[0021] The positive electrode sheet provided by the embodiment of the present application comprises the sodium-ion battery positive electrode material with the coating layer of the sodium salt of metal oxyacid and the conductive polymer, which can effectively improve the conductivity and stability of the positive electrode sheet.

[0022] In a fourth aspect, the embodiment of the present application provides a sodium-ion battery, which comprises the positive electrode sheet of the third aspect.

[0023] The sodium-ion battery provided by the embodiment of the present application comprises the positive electrode sheet with good conductivity and stability, which improves the cycle performance and rate performance of the sodium-ion battery.

[0024] In a fifth aspect, the embodiment of the present application provides an electric device, which comprises the sodium-ion battery of the fourth aspect.

[0025] The electric device provided by the present application comprises the sodium-ion battery, which has good cycle performance and rate performance, and is beneficial to improving the endurance of the electric device and the market competitiveness of the electric device. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used by the embodiments of the present application will be described below.

[0027] Figure 1is a structural schematic diagram of a sodium ion battery positive electrode material provided by an embodiment of the present application. DETAILED DESCRIPTION

[0028] The following is a preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements are also considered to be within the scope of the present application.

[0029] In recent years, with the large-scale commercial application of lithium ion batteries, the problem of lithium resource shortage and price rise has attracted people's attention. Sodium ion batteries have a broad prospect in the application of future large-scale energy storage devices due to their abundant sodium reserves, considerable energy density and low cost. Layered oxide positive electrode materials exhibit great application potential in sodium ion batteries, with high reversible sodium storage specific capacity. However, this material is easily eroded by HF, a by-product of electrolyte decomposition, during the cycling process, leading to the dissolution of transition metal ions and irreversible structural changes. In addition, at high state of charge, the layered oxide positive electrode material will release active oxygen, further accelerating the decomposition of the electrolyte and the capacity decay of the positive electrode material. To improve the stability of the positive electrode material and the electrolyte, a method of setting a coating layer on the surface of the layered oxide positive electrode material is usually used for protection. The existing coating layer materials are mostly oxides, such as aluminum oxide and titanium oxide. However, the electronic conductivity and sodium ion conductivity of these oxide coating layers are poor, which may hinder the transmission of electrons and the migration of sodium ions, increase the impedance of the electrochemical process, and reduce the kinetic characteristics of the material. Based on this, an embodiment of the present application provides a sodium ion battery positive electrode material.

[0030] Reference Figure 1 , Figure 1 is a structural schematic diagram of a sodium ion battery positive electrode material provided by an embodiment of the present application. The sodium ion battery positive electrode material 100 includes a core 110 and a coating layer 111 arranged on the core 110, the core 110 includes a layered oxide, and the coating layer 111 includes a metal sodium oxoacid salt and a conductive polymer, the metal sodium oxoacid salt and the conductive polymer are uniformly distributed in the coating layer 111.

[0031] The sodium ion battery positive electrode material 100 provided by the embodiment of the present application contains a coating layer 111 composed of a metal sodium oxoacid salt and a conductive polymer, the metal sodium oxoacid salt is a good sodium ion conductor, and the electronic conductivity of the conductive polymer is high. The coating layer 111 can not only improve the stability of the positive electrode material and the electrolyte, but also improve the electronic conductivity and ionic conductivity of the surface of the positive electrode material at the same time, reduce the sodium ion diffusion impedance, and thus effectively improve the rate performance and cycle performance of the positive electrode material. In addition, during the battery cycling process, the coating layer 111 can induce the formation of a high-quality electrochemical interface (CEI) layer on the surface of the positive electrode material, reduce the migration impedance of sodium ions in the CEI layer, and improve the reaction kinetics.

[0032] In the embodiments of the present application, the sodium salt of metal oxyacid includes at least one of sodium molybdate and sodium tungstate, the sodium salt of metal oxyacid has high chemical stability, can increase the oxidation resistance and corrosion resistance of the positive electrode material, has good sodium ion conductivity, and can improve the rate performance and cycle performance of the positive electrode material.

[0033] In the embodiments of the present application, the conductive polymer includes at least one of polypyrrole, polypyridine and polyaniline, the conductive polymer can reduce the electrochemical interface reaction between the positive electrode material and the electrolyte, has good ion conductivity, and is beneficial to improving the rate performance and cycle performance of the positive electrode material.

[0034] In the embodiments of the present application, in the coating layer, the mass percentage of the sodium salt of metal oxyacid is 0.1% to 99.9%, and the mass percentage of the conductive polymer is 0.1% to 99.9%. In some embodiments of the present application, the mass percentage of the sodium salt of metal oxyacid is 5% to 95%, and the mass percentage of the conductive polymer is 5% to 95%, so that the sodium ion conductivity and the electronic conductivity of the coating layer can be better balanced. In some embodiments, the mass percentage of the sodium salt of metal oxyacid in the coating layer is, for example, 0.1%, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 99.9%, and the mass percentage of the conductive polymer in the coating layer is, for example, 99.9%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 1%, or 0.1%.

[0035] In the embodiments of the present application, the mass of the coating layer can be 0.05% to 10% of the mass of the positive electrode material of the sodium ion battery. Controlling the mass of the coating layer can increase the stability and conductivity of the positive electrode material without affecting the capacity of the positive electrode material. In some embodiments, the mass of the coating layer can be, for example, 0.05%, 0.1%, 0.25%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the mass of the positive electrode material of the sodium ion battery. In the embodiments of the present application, in the coating layer, the mass of the inner core is 90% to 99.5% of the mass of the positive electrode material of the sodium ion battery, and controlling the mass of the inner core can ensure the capacity of the positive electrode material and balance the stability and conductivity of the positive electrode material. In some embodiments, the mass of the inner core can be, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 96.5%, 97%, 98%, 99%, or 99.5% of the mass of the positive electrode material of the sodium ion battery.

[0036] In an embodiment of the present invention, the thickness of the coating layer 111 can be 1nm-15nm. Controlling the appropriate coating layer thickness can increase the stability and conductivity of the positive electrode material without affecting the capacity of the positive electrode material. In an embodiment of the present application, the thickness of the coating layer 111 can be obtained by FIB-TEM (Focused Ion Beam-Transmission Electron Microscope) testing. In some embodiments, the thickness of the coating layer 111 can be, for example, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm or 15nm. In an embodiment of the present invention, the coating layer can coat part or all of the surface of the kernel, and the morphology of the coating layer can be a film, a granular, or a mixed morphology of a film and a granular.

[0037] In an embodiment of the present invention, the coverage of the coating layer 111 on the surface of the core 110 is between 40% and 100%. This means that the coating layer 111 covers greater than 40% of the surface area of ​​the core 110. This high coverage of the coating layer on the core surface reduces contact between the core and the electrolyte, effectively preventing corrosion of the layered oxide by the electrolyte. In some embodiments, the coverage of the coating layer on the core can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%.

[0038] In the embodiment of the present invention, the layered oxide includes an O3 phase sodium ion layered oxide, and the chemical formula of the O3 phase sodium ion layered oxide is Na x1 Ni x2 Fe x3 Mn x4 M x5O2, wherein M is a doping element, M includes at least one of Ti, W, Mo, V, Zr, Cr and Al, 0.6≤x1≤1.1, 0

[0039] In some embodiments, the particle size D50 of the sodium-ion battery cathode material 100 can be 0.5 μm-20 μm. In some embodiments, the particle size D50 of the sodium-ion battery cathode material 100 can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm. The shape of the sodium-ion battery cathode material 100 can be various, such as spherical or spherical agglomerates, or blocks. The smaller the particle size of the cathode material, the higher the capacity of the cathode material, the faster the diffusion of sodium ions in the material, the better the kinetic performance of the material, and the better the rate performance of the battery. The larger the particle size of the cathode material, the fewer side reactions on the surface of the cathode material during the battery cycle process, the better the cycle performance of the cathode material, and the better the cycle storage performance. In some embodiments, the particle size of the cathode material is set to the above range, which can ensure the cycle performance of the cathode material and the rate performance of the prepared battery.

[0040] In some embodiments, the application also provides a preparation method of the sodium-ion battery cathode material. The preparation method comprises:

[0041] mixing the layered oxide and the sodium salt of the metal oxyacid, and performing first calcination under an oxygen-containing atmosphere to obtain a semi-finished product;

[0042] Mixing the semi-finished product with the conductive polymer, and performing a second calcination under an inert atmosphere to obtain a sodium-ion battery positive electrode material.

[0043] The preparation method provided by the embodiment of the present application can obtain a relatively uniform coating layer on the surface of the sodium-ion positive electrode material through simple solid-phase mixing and heat treatment, and the coating process is simple and easy to mass-produce and apply. Meanwhile, the coating process of the present technology does not need water or other solvents, which can effectively avoid the damage of water to the structure of the sodium-ion battery positive electrode material. Meanwhile, subsequent wastewater treatment is not required, which is environmentally friendly and saves trouble. Compared with the existing process, the coating layer obtained by the present solution is more uniform.

[0044] In the embodiment of the present application, the temperature of the first calcination is 5-100℃ higher than the melting point of the sodium salt of metal oxyacid, and the time of the first calcination is 0.5-10h, wherein the melting point of the sodium salt of metal oxyacid refers to the melting temperature of the sodium salt of metal oxyacid. The temperature of the first calcination is higher than the melting temperature of the sodium salt of metal oxyacid, which can make the sodium salt of metal oxyacid melt and flow during the heat treatment at a temperature higher than the melting point, and then uniformly cover the surface of the layered oxide particles, so that the positive electrode material covered with a uniform coating layer can be obtained after cooling. Controlling the temperature and time of the first calcination within the above range is beneficial to the uniform coating of the coating layer and can avoid the generation of by-products. In some embodiments, the temperature of the first calcination is 5℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃ higher than the melting point of the sodium salt of metal oxyacid, and the time of the first calcination can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0045] In the embodiment of the present application, the melting point of the sodium salt of metal oxyacid can be determined by thermogravimetric analysis and differential scanning calorimetry (TG-DSC).

[0046] In the embodiment of the present application, the oxygen-containing atmosphere includes air or oxygen. Since the temperature of the first calcination is relatively high, calcination under an oxygen-containing atmosphere can avoid the loss of oxygen from the layered oxide.

[0047] In some embodiments, the second calcination is performed at a temperature that is 5-100 °C higher than the melting point of the conductive polymer. The melting point of the conductive polymer refers to the melting temperature of the conductive polymer. The second calcination is performed at a temperature that is higher than the melting temperature of the conductive polymer, which allows the conductive polymer to melt and flow during the heat treatment at a temperature higher than the melting point, and then uniformly cover the surface of the semi-finished product. After cooling, the positive electrode material covered with a uniform coating layer can be obtained. Controlling the temperature and time of the second calcination within the above range is beneficial to the uniform coating of the coating layer, and can avoid chemical reactions (such as carbonization) of the conductive polymer, so as to ensure that the conductive polymer is still in the form of the conductive polymer (itself) after the second calcination and is coated on the surface of the positive electrode material. In some embodiments, the temperature of the second calcination is 5 °C, 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, or 100 °C higher than the melting point of the conductive polymer. The time of the second calcination can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0048] In some embodiments, the second calcination is performed in an inert atmosphere, so as to avoid oxidation of the conductive polymer to generate by-products. Specifically, the inert atmosphere includes argon or nitrogen.

[0049] In some embodiments, the purity of the sodium salt of a metal oxyacid and the conductive polymer is greater than 99%, so as to avoid impurities affecting the conductivity and stability of the positive electrode material.

[0050] In some embodiments, the active material layer further includes a conductive agent and a binder, and the application does not make specific limitations on these materials, and suitable materials can be selected according to actual application requirements. Specifically, the conductive agent includes but is not limited to one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, and carbon nanotube. The binder includes but is not limited to one or more of polyvinylidene fluoride, soluble polytetrafluoroethylene, butadiene rubber, hydroxypropyl methyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0051] In some embodiments, the active material layer further includes a conductive agent and a binder, and the application does not make specific limitations on these materials, and suitable materials can be selected according to actual application requirements. Specifically, the conductive agent includes but is not limited to one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, and carbon nanotube. The binder includes but is not limited to one or more of polyvinylidene fluoride, soluble polytetrafluoroethylene, butadiene rubber, hydroxypropyl methyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0052] The positive electrode sheet provided in some embodiments includes the sodium ion battery positive electrode material having the coating layer of the sodium salt of a metal oxyacid and the conductive polymer, which can effectively improve the conductivity and stability of the positive electrode sheet.

[0053] The embodiment of the present application provides a sodium ion battery, which comprises the positive plate in any of the above-mentioned embodiments.

[0054] The sodium ion battery provided by the embodiment of the present application comprises the positive plate with good conductivity and stability, and the cycle performance and the rate performance of the sodium ion battery are improved.

[0055] The embodiment of the present application provides a power-consuming device, and the power-consuming device comprises the sodium ion battery in any of the above-mentioned embodiments. Specifically, the power-consuming device includes but is not limited to an electric vehicle, an electric motorcycle, an electric bicycle, a mobile power source, a drone, a mobile phone, a computer, a camera, an electric tool, a smart home or a wearable device.

[0056] The power-consuming device provided by the present application contains the sodium ion battery, and the sodium ion battery has good cycle performance and rate performance, which is beneficial to improve the endurance of the power-consuming device and improve the market competitiveness of the power-consuming device.

[0057] The technical solutions of the present application are further described below through specific embodiments and comparative examples.

[0058] Embodiment 1

[0059] 100g of O3 phase sodium ion layered oxide NaNi 0.39 Mn 0.3 Fe 0.3 V 0.01 O2 (D50=10 μm) is mixed with 0.5g of sodium molybdate (melting temperature is 687℃), and then the mixture is placed in an oxygen atmosphere at 700℃ for the first calcination, and the time is 3h, and the semi-finished product is obtained after cooling. Then the semi-finished product is mixed with 0.5g of polypyrrole (melting temperature is 200℃), and then the mixture is placed in an N2 atmosphere at 220℃ for the second calcination, and the time is 1h, and the sodium ion battery positive electrode material is obtained after cooling. The coating layer of the sodium ion battery positive electrode material comprises sodium molybdate and polypyrrole, the thickness of the coating layer is 5nm, the mass of the coating layer is 1% of the mass of the sodium ion battery positive electrode material, the mass percentage of sodium molybdate in the coating layer is 50%, and the mass percentage of polypyrrole in the coating layer is 50%.

[0060] Embodiment 2

[0061] The difference from embodiment 1 is that the O3 phase sodium ion layered oxide is NaNi 0.39 Mn 0.3 Fe 0.3 Al 0.01 O2 (D50=10 μm).

[0062] Embodiment 3

[0063] The difference from Example 1 is that the amount of sodium molybdate is 3 g, the thickness of the coating layer of the sodium-ion battery positive electrode material is 7 nm, the mass of the coating layer is 3.4% of the mass of the sodium-ion battery positive electrode material, the mass percentage of sodium molybdate in the coating layer is 86%, and the mass percentage of polypyrrole in the coating layer is 14%.

[0064] Example 4

[0065] The difference from Example 1 is that the amount of sodium molybdate is 10 g, the thickness of the coating layer of the sodium-ion battery positive electrode material is 10 nm, the mass of the coating layer is 9.5% of the mass of the sodium-ion battery positive electrode material, the mass percentage of sodium molybdate in the coating layer is 95%, and the mass percentage of polypyrrole in the coating layer is 5%.

[0066] Example 5

[0067] The difference from Example 1 is that the amount of polypyrrole is 3 g, the thickness of the coating layer of the sodium-ion battery positive electrode material is 5 nm, the mass of the coating layer is 3.4% of the mass of the sodium-ion battery positive electrode material, the mass percentage of sodium molybdate in the coating layer is 14%, and the mass percentage of polypyrrole in the coating layer is 86%.

[0068] Example 6

[0069] The difference from Example 1 is that the amount of polypyrrole is 10 g, the thickness of the coating layer of the sodium-ion battery positive electrode material is 8 nm, the mass of the coating layer is 9.5% of the mass of the sodium-ion battery positive electrode material, the mass percentage of sodium molybdate in the coating layer is 5%, and the mass percentage of polypyrrole in the coating layer is 95%.

[0070] Example 7

[0071] The difference from Example 1 is that the temperature of the first calcination is 780°C.

[0072] Example 8

[0073] The difference from Example 1 is that the temperature of the first calcination is 740°C.

[0074] Example 9

[0075] The difference from Example 1 is that the temperature of the second calcination is 300°C.

[0076] Example 10

[0077] The difference from Example 1 is that the temperature of the second calcination is 280°C.

[0078] Comparative Example 1

[0079] The difference from Example 1 is that the sodium-ion battery positive electrode material only contains the core NaNi0.39 Mn 0.3 Fe 0.3 V 0.01 O2(D50 = 10 pm), without coating layer.

[0080] Comparative Example 2

[0081] The difference from Example 1 is that the coating layer of the sodium-ion battery cathode material is polypyrrole, the amount of polypyrrole is 0.5 g, it does not contain sodium molybdate, the thickness of the coating layer is 3 nm, the mass of the coating layer is 0.5% of the mass of the sodium-ion battery cathode material, and the mass percentage of polypyrrole in the coating layer is 100%.

[0082] Comparative Example 3

[0083] The difference from Example 1 is that the coating layer of the sodium-ion battery cathode material is sodium molybdate, the amount of sodium molybdate is 0.5 g, it does not contain polypyrrole, the thickness of the coating layer is 3 nm, the mass of the coating layer is 0.5% of the mass of the sodium-ion battery cathode material, and the mass percentage of sodium molybdate in the coating layer is 100%.

[0084] Comparative Example 4

[0085] The difference from Example 1 is that the atmosphere for the second calcination is oxygen.

[0086] The sodium-ion battery cathode materials prepared in Examples 1-10 and Comparative Examples 1-4 were assembled into sodium-ion button half-cells according to the following method:

[0087] The sodium-ion battery cathode material, polyvinylidene fluoride, and conductive carbon black were mixed in a mass ratio of 94:3:3, and then the mixed powder was added to an N-methylpyrrolidone (NMP) solution and stirred uniformly. Then, the slurry was uniformly coated on an aluminum foil using a coater, and then placed in a vacuum drying oven at a temperature of 120°C for 12h, and then rolled into a positive electrode sheet. A CR-2025 type button sodium-ion battery was assembled in an argon-filled glove box, with a sodium sheet as the negative electrode, a polypropylene separator as the separator, and an electrolyte solute of 1 mol / L NaPF6 and a solvent of a mixed solution of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) with a volume ratio of 1:1, to obtain the sodium-ion button half-cells of Examples 1-10 and Comparative Examples 1-4.

[0088] The first cycle coulombic efficiency, rate performance, and cycle performance of the sodium-ion button half-cells of Examples 1-10 and Comparative Examples 1-4 were tested, and the results are shown in Table 1.

[0089] First cycle coulombic efficiency test method: 0.1C constant current charging to 4.0V, then constant voltage charging, cutoff current is 0.02C, then 0.1C constant current discharging to 2.0V.

[0090] Rate performance test method: charge to 4.0 V at 0.1 C, then constant voltage charge, the cutoff current is 0.02 C, then discharge to 2.0 V at 0.1 C, repeat the above steps three times, then charge to 4.0 V at 0.5 C, then constant voltage charge, the cutoff current is 0.02 C, then discharge to 2.0 V at 10 C.

[0091] Cycle performance test method: charge to 4.0 V at 0.1 C, then constant voltage charge, the cutoff current is 0.02 C, then discharge to 2.0 V at 0.1 C, repeat the above steps three times, then charge and discharge at 1 C current density, the charge and discharge interval is 2.0-4.0 V, record the first discharge capacity as C1, record the discharge capacity after 100 cycles as C100, 100 cycle capacity retention rate % = (C100 / C1) x 100%.

[0092] Table 1 Electrochemical performance test results

[0093]

[0094] From Table 1, it can be known that the battery of Example 1-2 has higher first cycle coulombic efficiency, discharge specific capacity at 0.1 C, discharge specific capacity at 10 C and capacity retention rate compared with Comparative Examples 1-3, indicating that coating a coating layer with a metal oxyacid sodium salt and a conductive polymer on the surface of a layered oxide is conducive to improving the electrochemical performance of the battery prepared therefrom. From Example 1, Example 3, Example 4, Example 5 and Example 6, it can be known that when the mass of the coating layer is 1%-3.4% of the mass of the sodium ion battery positive electrode material, the electrochemical performance of the prepared positive electrode material can be better improved. From Example 1, Example 7 and Example 8, it can be known that when the temperature of the first calcination is set to be higher than the melting point of the metal oxyacid sodium salt by 13-53 ℃, it is conducive to better improving the electrochemical performance of the prepared positive electrode material. From Example 1, Example 9 and Example 10, it can be known that when the temperature of the second calcination is set to be higher than the melting point of the conductive polymer by 20-80 ℃, it is conducive to better improving the electrochemical performance of the prepared positive electrode material. From Example 1 and Comparative Example 4, it can be known that performing the second calcination in an oxygen atmosphere can significantly reduce the electrochemical performance of the prepared positive electrode material, indicating that the gas atmosphere of the second calcination must be an inert atmosphere.

[0095] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A sodium ion battery cathode material, characterized in that The invention comprises a core and a coating layer arranged on the core, wherein the core comprises a layered oxide, and the coating layer comprises a sodium salt of a metal oxyacid and a conductive polymer.

2. The sodium ion battery positive electrode material according to claim 1, wherein The sodium salt of metal oxyacid includes at least one of sodium molybdate and sodium tungstate; and / or the conductive polymer includes at least one of polypyrrole, polypyridine and polyaniline.

3. The sodium ion battery positive electrode material according to claim 1, wherein In the coating layer, the mass percentage of the metal oxyacid sodium salt is 0.1%-99.9%, and the mass percentage of the conductive polymer is 0.1%-99.9%.

4. The sodium ion battery positive electrode material according to claim 3, wherein In the coating layer, the mass percentage of the sodium salt of the metal oxyacid is 5%-95%, and the mass percentage of the conductive polymer is 5%-95%.

5. The sodium ion battery positive electrode material according to claim 1, wherein The mass of the coating layer is 0.05%-10% of the mass of the sodium ion battery positive electrode material, and the mass of the core is 90%-99.5% of the mass of the sodium ion battery positive electrode material.

6. The sodium ion battery cathode material according to claim 1, wherein The coating layer has a thickness of 1 nm to 15 nm.

7. The sodium ion battery cathode material according to claim 1, wherein The coverage rate of the coating layer on the surface of the core is 40%-100%.

8. The sodium ion battery cathode material according to claim 1, wherein The layered oxide includes an O3 phase sodium ion layered oxide, and the chemical formula of the O3 phase sodium ion layered oxide is Na x1 Ni x2 Fe x3 Mn x4 M x5 O2, wherein M includes at least one of Ti, W, Mo, V, Zr, Cr and Al, 0.6≤x1≤1.1, 0<x2<1, 0<x3<1, 0<x4<1, 0<x5≤0.2, and x2+x3+x4+x5=1.

9. The sodium ion battery cathode material according to claim 1, wherein The particle size D50 of the sodium ion battery positive electrode material is 0.5 μm-20 μm.

10. The method for preparing a positive electrode material for a sodium ion battery according to any one of claims 1 to 9, wherein: include: The layered oxide is mixed with a sodium salt of a metal oxyacid and calcined for the first time in an oxygen-containing atmosphere to obtain a semi-finished product; The semi-finished product is mixed with a conductive polymer and calcined for a second time under an inert atmosphere to obtain the sodium ion battery positive electrode material.

11. The preparation method according to claim 10, characterized in that The temperature of the first calcination is 5° C. to 100° C. higher than the melting point of the sodium salt of the metal oxyacid, and the time of the first calcination is 0.5 h to 10 h; the oxygen-containing atmosphere includes air or oxygen.

12. The preparation method according to claim 10, wherein The temperature of the second calcination is 5° C. to 100° C. higher than the melting point of the conductive polymer, and the time of the second calcination is 0.5 h to 10 h; the inert atmosphere includes argon or nitrogen.

13. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and an active material layer arranged on the positive electrode current collector, wherein the active material layer comprises the sodium ion battery positive electrode material according to any one of claims 1 to 9 or the sodium ion battery positive electrode material prepared by the preparation method according to any one of claims 10 to 12.

14. A sodium ion battery, characterized in that: The sodium ion battery comprises the positive electrode sheet according to claim 13.

15. An electrical device, characterized in that: The electrical equipment includes the sodium ion battery according to claim 14.

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