Cathode active material, positive electrode, sodium-ion battery, battery assembly, and electric system

Abstract

A cathode active material, a positive electrode, a sodium-ion battery, a battery assembly, and an electric system. The cathode active material satisfies: the compaction rebound rate ε of the cathode active material ranging from 3% to 10%, wherein the compaction rebound rate ε=1-(compaction density after rebound / maximum compaction density). The stability and integrity of the structure of the material can be maintained during an electrochemical process, thereby significantly improving the cycling performance.

Description

Positive electrode active material, positive electrode, sodium ion battery, battery component and power consumption system

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 29, 2024, with application number 202410383621.6 and application name “Positive electrode active material, positive electrode, sodium ion battery, battery assembly and power system”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of sodium ion batteries, and in particular to a positive electrode active material, a positive electrode, a sodium ion battery, a battery assembly, and an electricity consumption system. Background Art

[0003] The global abundance of sodium is much higher than that of lithium, and sodium-ion batteries have a significant cost advantage over lithium-ion batteries. However, the poor cycling stability of existing sodium-ion batteries limits their application. The cycling stability of the battery is limited by the inherent toughness of the battery's positive electrode active material. The inherent toughness of the material helps the material maintain structural stability and integrity during the electrochemical process. The post-compression rebound rate is a parameter standard that can fully reflect the toughness of the positive electrode active material. Therefore, how to control the post-compression rebound rate of the positive electrode active material in sodium-ion batteries has become a key issue.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a positive electrode active material, a positive electrode, a sodium ion battery, a battery assembly and a power system to solve the problem of poor cycle performance of sodium ion batteries.

[0006] To achieve the purpose of this application, this application provides the following technical solutions:

[0007] In a first aspect, the present application provides a positive electrode active material, which satisfies: the post-compression rebound rate ε of the positive electrode active material is 3% to 10%, wherein the post-compression rebound rate ε is (compaction density after rebound / maximum compaction density).

[0008] Since the rebound characteristics of a material are related to its toughness, representing the change in rebound before and after a certain pressure (pressurization and decompression), materials with a higher post-compression rebound rate exhibit better plasticity. Therefore, by setting the post-compression rebound rate of the positive electrode active material within the above range, it can be ensured that the positive electrode active material is more likely to maintain its original shape and structure during the ion insertion and extraction process. The positive electrode active material itself has a certain toughness, which helps the material maintain structural stability and integrity during the electrochemical process, thereby significantly improving cycle performance.

[0009] In one embodiment, the post-compression rebound rate ε of the positive electrode active material is 5% to 10%.

[0010] In one embodiment, the maximum compaction density of the positive electrode active material is 3.0 g / cm 3 ~3.6g / cm 3 .

[0011] In one embodiment, the maximum compaction density of the positive electrode active material is 3.2 g / cm 3 ~3.6g / cm 3 .

[0012] In one embodiment, the positive electrode active material includes a sodium ion layered transition metal oxide.

[0013] In one embodiment, the positive electrode active material has the general structural formula: Na x AO2 wherein A is one or more of Ni, Cu, Fe, Mn, Co, Cr, Li, Mo, Sn, Zn, Zr, Nb, Ru, Y, W, Al, Mg, Ti, Ca, Sr, Ir, Ba, V, 0.7≤x≤1.2.

[0014] In one embodiment, x satisfies: 0.9≤x≤1.02.

[0015] In one embodiment, the positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

[0016] In a second aspect, the present application provides a method for preparing the positive electrode active material according to the first aspect, comprising the following steps:

[0017] a) placing a metal source in water to precipitate a first precursor, wherein the precipitation temperature is 30-80° C. and the precipitation time is 4-24 hours;

[0018] b) mixing the first precursor with a sodium source and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor;

[0019] c) solid-phase sintering the second precursor at 300-800° C. for 10-24 hours to obtain the positive electrode active material.

[0020] In a third aspect, the present application provides a positive electrode, comprising a current collector and the positive electrode active material described in the first aspect disposed on the current collector.

[0021] In one embodiment, the positive electrode active material layer includes the positive electrode active material, a conductive agent, and a binder.

[0022] In one embodiment, the conductive agent is one or more of carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, and graphene.

[0023] In one embodiment, the binder is one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

[0024] In one embodiment, the surface density of the positive electrode is not less than 340 g / m 2 The compaction density of the positive electrode is not less than 2.9g / cm 3 .

[0025] In a fourth aspect, the present application provides a sodium ion battery comprising the positive electrode described in the third aspect.

[0026] In one embodiment, the battery further comprises a negative electrode, wherein the surface density of the negative electrode is 150 to 210 g / m 2 The compaction density of the negative electrode is not less than 0.9 g / cm 3 .

[0027] In one embodiment, the sodium ion battery further comprises an electrolyte;

[0028] The electrolyte includes one or more of an organic solvent, a sodium salt solute, and an electrolyte additive.

[0029] In one embodiment, the organic solvent is one or more of ethylene carbonate, propylene carbonate, butyl carbonate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl formate, methyl acetate, dioxolane, and 4-methyl-1,3-dioxolane.

[0030] In one embodiment, the sodium salt solute is one or more of NaBF4, NaClO4, NaPF6, NaAsF6, NaCF3SO3, Na(CF3SO2)2N, and NaC4F9SO3.

[0031] In a fifth aspect, the present application provides a battery assembly comprising the sodium ion battery described in the fourth aspect.

[0032] In a sixth aspect, the present application provides an electricity consumption system, comprising the sodium ion battery described in the fourth aspect or the battery assembly described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the implementation methods or the description of the prior art. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] FIG1 is a schematic diagram of the cross-sectional structure of a positive electrode sheet according to an embodiment;

[0035] FIG2 is a schematic diagram showing the calculation of the rebound rate ε of a positive electrode active material according to an embodiment;

[0036] FIG. 3 is a SEM image of a positive electrode active material according to an embodiment. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used in this application includes any and all combinations of one or more of the relevant listed items.

[0039] The following describes some embodiments of the present application in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features therein may be combined with each other.

[0040] The present application provides a positive electrode 100 , as shown in FIG1 and FIG3 , including a current collector 10 and a positive electrode active material disposed on the current collector 10 , wherein the positive electrode active material includes sodium ions.

[0041] Specifically, the positive electrode 100 can be a sodium ion positive electrode, and thus is used in a sodium ion battery. After the positive electrode 100 is formed, a positive electrode active material layer 20 is formed on the current collector 10. The positive electrode active material layer 20 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material is the active ingredient in a sodium ion battery, used to provide sodium ions.

[0042] In the process of manufacturing the positive electrode 100, the positive electrode slurry is placed on the current collector 10, and then rolled and heated to form the positive electrode active material layer 20. The positive electrode slurry includes all the materials of the positive electrode active material layer 20.

[0043] Optionally, the current collector 10 may be a foam metal mesh, a metal film material, etc., specifically including any one of copper foil and aluminum foil.

[0044] Optionally, the conductive agent can be one or more of carbon nanotubes (CNTs), single-walled carbon nanotubes (SWCNTs), conductive carbon black (SP), and graphene; the binder can be one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA).

[0045] Optionally, the mass content of the positive electrode active material in the slurry should be no less than 95%, the mass content of the conductive agent should be no more than 2%, and the mass content of the binder should be no more than 3%.

[0046] Optionally, the surface density of the positive electrode 100 is not less than 340 g / m 2 The compaction density of the positive electrode 100 is not less than 2.9g / cm 3 .

[0047] The positive electrode active material provided in the present application meets the following conditions: the post-compression rebound rate ε of the positive electrode active material is 3% to 10%, wherein the post-compression rebound rate ε=1-(compaction density after rebound / maximum compaction density).

[0048] The post-compression rebound rate ε of the positive electrode active material is 3% to 10%, and can be, but is not limited to, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0049] As you can understand, the positive electrode active material layer will rebound after rolling, meaning that part of the positive electrode active material returns to its pre-rolling state. The rebound rate of the positive electrode active material is the degree to which the density decreases when the pressure is released after the positive electrode active material is rolled to its maximum density. The greater the rebound rate, the easier it is for the positive electrode active material, deformed by compression, to return to its original state.

[0050] Layered sodium cathode active materials can experience cracking and pulverization during cycling due to the continuous release and insertion of sodium ions. Industrialization often involves toughening and modifying the material skeleton through doping with various elements or optimizing the sintering process, thereby improving the stability of the material structure and thus achieving improved cycling performance. However, due to the typically low levels of doping elements, macroscopic characterization of the material matrix's stability is difficult.

[0051] Since the rebound characteristics of a material are related to its toughness, representing the change in rebound before and after a certain pressure (pressurization and decompression), materials with a higher post-compression rebound rate exhibit better plasticity. Therefore, by setting the post-compression rebound rate of the positive electrode active material within the above range, it can be ensured that the positive electrode active material is more likely to maintain its original shape and structure during the ion insertion and extraction process. The positive electrode active material itself has a certain toughness, which helps the material maintain structural stability and integrity during the electrochemical process, thereby significantly improving cycle performance.

[0052] Among them, for the positive electrode active material in the battery, the post-compression rebound rate ε test method can adopt the following method:

[0053] 1) Discharge the battery to 1.5V using a low current (such as 0.05C / 0.1C / 0.2C), disassemble it in an inert environment, and remove the positive electrode.

[0054] 2) Clean the positive electrode sheet with an organic solvent, which can be one or more of an alcohol, ester, or ether. Scrape the powder to remove the positive electrode material powder. Ultrasonic cleaning is performed on the scraped positive electrode material powder for 10 minutes to remove the upper floating material. Solvent is added again and ultrasonic cleaning is repeated for 10 minutes. This cleaning is repeated three times. The bottom layer is removed and vacuum-dried to a moisture content of less than 500 ppm to obtain the positive electrode active material to be tested. The post-compression rebound rate of the positive electrode active material to be tested is then tested.

[0055] For example, as shown in FIG2 , a predetermined mass (e.g., 1.0 g) of positive electrode active material is filled in a mold and vibrated at a frequency of 300 times / min until the density of the positive electrode active material reaches a tap density (e.g., 3 g / cm 3 ), and then compressed at a constant speed (e.g., 10 mm / min) so that the density of the positive electrode active material reaches the maximum compaction density (e.g., 3.6 g / cm 3 , T1 in Figure 2). Then, release the pressure, and when the pressing surface stops moving due to elasticity, measure the density after pressure release (i.e., the compacted density after rebound) (T2 in Figure 2). The post-compression rebound rate is calculated from the obtained value using the post-compression rebound rate ε = 1 - (compacted density after rebound / maximum compacted density).

[0056] The measurement of tap density means putting a certain amount of powder into a container, vibrating it under certain conditions until the volume of the powder in the container no longer decreases, reading the volume of the powder, and then dividing the weight of the powder by the volume to get the tap density. The tap density test is carried out in accordance with GB / T 31057.2-2018 "Tests for physical properties of granular materials Part 2: Measurement of tap density". Test equipment: BT-1001 intelligent powder comprehensive tester. Weigh a certain mass m of positive electrode active material and put it into the test container. Try to keep the powder surface in a horizontal state. Vibrate at a frequency of 300 times / min until the volume of the positive electrode active material no longer decreases. Read the powder volume v. Tap density = m / vg / cm 3 .

[0057] In one embodiment, the positive electrode active material has a post-compression springback rate ε of 5% to 10%. Optionally, the post-compression springback rate ε of the positive electrode active material may be, but is not limited to, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%. Meeting the above post-compression springback rates can further ensure the stability and integrity of the positive electrode active material, thereby achieving higher cycle performance.

[0058] In one embodiment, the maximum compaction density of the positive electrode active material is 3.0 g / cm 3 ~3.6g / cm 3 , can be but not limited to 3.0g / cm 3 、3.05g / cm 3 , 3.1g / cm 3 、3.15g / cm 3 、3.2g / cm 3 , 3.25g / cm 3 , 3.3g / cm 3 、3.35g / cm 3 、3.4g / cm 3 、3.45g / cm 3 、3.5g / cm 3 、3.6g / cm 3 .

[0059] During the production of power batteries, the compaction density has a significant impact on battery performance. Experiments have shown that compaction density is closely related to sheet capacity, efficiency, internal resistance, and battery cycle performance. Finding the optimal compaction density is very important for battery design. Generally speaking, the greater the compaction density, the higher the battery capacity can be, so compaction density is also considered one of the reference indicators for material energy density. The compaction density is not only related to the size and density of the particles, but also to the particle gradation. Particles with a high compaction density generally have a good normal distribution. It can be considered that under certain process conditions, the greater the compaction density, the higher the battery capacity.

[0060] In one embodiment, the maximum compaction density of the positive electrode active material is 3.2 g / cm 3 ~3.6g / cm 3 Optionally, the maximum compaction density of the positive electrode active material may be, but is not limited to, 3.2 g / cm 3 , 3.25g / cm 3 , 3.3g / cm 3 、3.35g / cm 3 、3.4g / cm 3 、3.45g / cm 3 、3.5g / cm 3 、3.55g / cm 3 、3.6g / cm 3 Meeting the above-mentioned maximum compaction density can further ensure that the positive electrode active material has a higher capacity.

[0061] In one embodiment, the positive electrode active material includes a sodium ion layered transition metal oxide.

[0062] In one embodiment, the positive electrode active material has the general structural formula: Na x AO2 wherein A is one or more of Ni, Cu, Fe, Mn, Co, Cr, Li, Mo, Sn, Zn, Zr, Nb, Ru, Y, W, Al, Mg, Ti, Ca, Sr, Ir, Ba, V, 0.7≤x≤1.2.

[0063] In one embodiment, x satisfies: 0.9≤x≤1.02. Optionally, the specific value of x can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, or 1.02.

[0064] In one embodiment, the positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

[0065] In one embodiment, the preparation method of the above positive electrode active material includes:

[0066] a) precipitating an M source to form a first M source precursor at a temperature of 30-80° C. for 4-24 hours;

[0067] b) mixing the M source precursor with the sodium source, and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor;

[0068] c) solid-phase sintering the second precursor at 300-800° C. for 10-24 hours to obtain the positive electrode active material.

[0069] Wherein, in step a), the M source may include one or more metal sources;

[0070] In step b), in addition to being mixed with the sodium source, the M source may also be mixed with other doping elements, that is, step b) may further include mixing the M source precursor with the sodium source and other doping elements, and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor;

[0071] Step c) may further include mixing the second precursor and the coating element and then performing solid phase sintering at 300-800° C. for 10-24 hours.

[0072] The maximum compaction density, post-compression rebound rate ε, etc. can be adjusted by adjusting the reaction raw materials, the temperature and duration of each step of the reaction, and other factors.

[0073] In one embodiment, the present application further provides a sodium ion battery, comprising the positive electrode, negative electrode and separator in the above embodiment, wherein the positive electrode and negative electrode are respectively arranged on opposite sides of the separator.

[0074] Sodium-ion battery models include but are not limited to soft-pack batteries, square batteries, and cylindrical batteries.

[0075] Optionally, the negative electrode includes a current collector and a negative electrode material disposed on the current collector. After the negative electrode is formed, a negative electrode material layer is formed on the current collector, and the negative electrode material layer includes a negative electrode material, a conductive agent, and a binder. The negative electrode material can be hard carbon.

[0076] Optionally, the ratio of negative electrode material in the slurry should be no less than 93%, the conductive agent content should be no more than 3%, and the binder content should be no more than 4%. The surface density of the obtained negative electrode is 150-210 g / m 2 , the negative electrode compaction density is not less than 0.9g / cm 3 .

[0077] Optionally, the diaphragm can be a conventional polyethylene (propylene) diaphragm, a rubber-coated diaphragm, a ceramic diaphragm, etc.

[0078] Optionally, the sodium ion battery further includes an electrolyte, which includes an organic solvent, a sodium salt solute, and an electrolyte additive.

[0079] Optionally, the organic solvent in the electrolyte can be: ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), γ-butyrolactone (GBL), ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl formate (MF), methyl acetate (MA), dioxolane (DOL), 4-methyl-1,3-dioxolane (4MeDOL), etc., or a combination thereof; the sodium salt solute can be: NaBF4, NaClO4, NaPF6, NaAsF6, NaCF3SO3, Na(CF3SO2)2N, NaC4F9SO3, etc., or a combination thereof; the electrolyte additive can be: FEC, VC, PS, DTD, TEP, TMP, etc., or a combination thereof.

[0080] Optionally, the sodium ion battery can be a wound cell, a laminated cell or a single cell.

[0081] In one embodiment, the present application further provides a battery assembly comprising the sodium ion battery described above. The battery assembly may be a battery pack or a battery group.

[0082] In one embodiment, the present application further provides an electric power system, comprising the battery assembly and an electrical appliance as described above, wherein the battery assembly supplies power to the electrical appliance. Optionally, the electric power system may be a vehicle or an energy storage power station.

[0083] In one embodiment, the present application further provides a method for manufacturing a sodium ion battery, comprising at least the following steps:

[0084] Step S1: The positive electrode active material, the conductive agent and the binder uniformly dispersed in the solvent N-methylpyrrolidone (NMP) are uniformly coated on the surface of the aluminum foil (current collector), and the positive electrode is obtained after baking.

[0085] Specifically, the positive electrode active material and other auxiliary materials were evenly dispersed in the ratio of positive electrode active material: PVDF: CNT: SP: NMP = 97:1:1.5:0.5:30, coated on aluminum foil, baked at 120 ° C to obtain the positive electrode, and rolled to 3.0 g / cm 3 .

[0086] Step S2: The negative electrode material, the conductive agent, and the binder uniformly dispersed in the solvent deionized water are uniformly coated on the surface of the aluminum foil (current collector), and the negative electrode is obtained after baking.

[0087] Specifically, hard carbon, conductive agent SP, and binder SBR were uniformly mixed in deionized water at a ratio of 93:3:4, and evenly coated on the surface of aluminum foil. After baking at 110°C, the negative electrode was obtained and rolled to 0.95g / cm 3 .

[0088] Step S3: Wind or stack the positive electrode, separator, and negative electrode in order to obtain a core.

[0089] Step S4: After the core is encased, electrolyte is injected, and a complete secondary sodium ion battery is obtained through aging, formation, aging and capacity separation.

[0090] Specifically, after the core is shelled, the electrolyte (solute is 1 mol / L NaPF6, solvent is EC:EMC=1:1 (v:v)+3% FEC) is injected, and after aging, formation, aging and capacity separation, a complete secondary sodium ion battery is obtained.

[0091] The present application is further described below with reference to Examples and Comparative Examples. This application provides Examples 1 through 12, as well as Comparative Examples 1 through 5. The types of positive electrode active materials used in these Examples and Comparative Examples are shown in Table 1. Batteries in each of these Examples were prepared according to the sodium-ion battery manufacturing method described above.

[0092] The positive electrode active materials in the examples and comparative examples were subjected to compression rebound tests, and the batteries were subjected to cycle tests and energy density tests. The specific test methods are as follows:

[0093] Powder compaction and post-compression rebound rate: 1 gram of powder is placed in a standard container and vibrated at a frequency of 300 vibrations / min until the density of the positive electrode active material reaches the tap density. Then, compression is continued at a constant speed (10 mm / min) until a pressure of 5 tons is reached. This is recorded as the pre-rebound compaction density, also known as the maximum compaction density. When the pressure is removed and the pressing surface stops moving, the post-rebound compaction density is measured and the post-compression rebound rate is calculated. The testing equipment used is the Sansi Zongheng UTM7305.

[0094] Cycle test: The battery was charged to 4.0 V at 1C, discharged to 1.5 V at 1C, and cycled until the SOH was 80%. The number of cycles was recorded (SOH = discharge capacity after cycle / discharge capacity of the first cycle).

[0095] Please refer to Table 1 for specific test results.

[0096] Table 1

[0097] From the data in Table 1 above, it can be concluded that the greater the change in the rebound of the powder before and after pressing, the better the toughness of the material. Conversely, the smaller the rebound rate of the material after pressing, the stronger the rigidity. Due to the large radius of sodium ions, the change in the unit cell volume during the process of sodium intercalation and deintercalation aggravates the cracking of the material. The material with a larger rebound rate after pressing can show better plasticity, so that the material is more inclined to maintain the original structure during the process of sodium intercalation and deintercalation, and thus has better cycle performance.

[0098] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", and "outside" are based on the orientation or positional relationship described in the accompanying drawings. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present application.

[0099] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made in accordance with the claims of the present application are still within the scope covered by the present application.

Claims

1. A positive electrode active material, wherein The positive electrode active material satisfies: The post-compression rebound rate ε of the positive electrode active material is 3% to 10%, wherein the post-compression rebound rate ε=1-(compression density after rebound / maximum compression density).

2. The positive electrode active material according to claim 1, wherein The post-compression rebound rate ε of the positive electrode active material is 5% to 10%.

3. The positive electrode active material according to claim 1 or 2, wherein The positive electrode active material satisfies the following conditions: the maximum compaction density of the positive electrode active material is 3.0 g / cm 3 ~3.6g / cm 3 .

4. The positive electrode active material according to claim 3, wherein The positive electrode active material satisfies the following conditions: the maximum compaction density of the positive electrode active material is 3.2 g / cm 3 ~3.6g / cm 3 .

5. The positive electrode active material according to any one of claims 1 to 4, wherein The positive electrode active material includes a sodium ion layered transition metal oxide.

6. The positive electrode active material according to any one of claims 1 to 5, wherein The general structural formula of the positive electrode active material is: Na x AO2 wherein A is one or more of Ni, Cu, Fe, Mn, Co, Cr, Li, Mo, Sn, Zn, Zr, Nb, Ru, Y, W, Al, Mg, Ti, Ca, Sr, Ir, Ba, and V, and 0.7≤x≤1.

2.

7. The positive electrode active material according to claim 6, wherein x satisfies: 0.9≤x≤1.

02.

8. The positive electrode active material according to claim 1, wherein The positive electrode active material is one or more of single crystal, quasi-single crystal, and polycrystalline.

9. A method for preparing the positive electrode active material according to any one of claims 1 to 8, wherein: The following steps are involved: a) placing a metal source in water to precipitate a first precursor, wherein the precipitation temperature is 30-80° C. and the precipitation time is 4-24 hours; b) mixing the first precursor with a sodium source and performing solid phase sintering at 600-1100° C. for 10-24 hours to obtain a second precursor; c) solid-phase sintering the second precursor at 300-800° C. for 10-24 hours to obtain the positive electrode active material.

10. A positive electrode, wherein The invention comprises a current collector and the positive electrode active material according to any one of claims 1 to 8 arranged on the current collector.

11. The positive electrode according to claim 10, wherein The positive electrode active material layer includes the positive electrode active material, a conductive agent, and a binder.

12. The positive electrode according to claim 11, wherein The conductive agent is one or more of carbon nanotubes, single-walled carbon nanotubes, conductive carbon black, and graphene.

13. The positive electrode according to claim 11 or 12, wherein The binder is one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

14. The positive electrode according to any one of claims 10 to 13, wherein The surface density of the positive electrode is not less than 340g / m 2 The compaction density of the positive electrode is not less than 2.9g / cm 3 .

15. A sodium ion battery, wherein: The method comprises the positive electrode according to any one of claims 10 to 14.

16. The sodium ion battery according to claim 15, wherein The battery also includes a negative electrode, the surface density of which is 150 to 210 g / m 2 The compaction density of the negative electrode is not less than 0.9 g / cm 3 .

17. The sodium ion battery according to claim 15 or 16, wherein: The sodium ion battery also includes an electrolyte; The electrolyte includes one or more of an organic solvent, a sodium salt solute, and an electrolyte additive.

18. The sodium ion battery according to claim 17, wherein: The organic solvent is one or more of ethylene carbonate, propylene carbonate, butyl carbonate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl formate, methyl acetate, dioxolane, and 4-methyl-1,3-dioxolane.

19. The sodium ion battery according to claim 17, wherein: The sodium salt solute is one or more of NaBF4, NaClO4, NaPF6, NaAsF6, NaCF3SO3, Na(CF3SO2)2N, and NaC4F9SO3.

20. A battery assembly, wherein: Comprising the sodium ion battery according to any one of claims 15 to 19.

21. An electricity system, wherein: Comprising the sodium ion battery according to any one of claims 15 to 19 or the battery assembly according to claim 20.

Images