Positive electrode active material of sodium ion battery, preparation method of positive electrode active material, positive electrode plate and secondary battery

Abstract

The invention relates to the technical field of secondary batteries, in particular to a sodium ion battery positive electrode active material and a preparation method thereof, a positive electrode plate and a secondary battery, the sodium ion battery positive electrode active material comprises a polyanion material, the chemical formula of the polyanion material is Na < 3-x > A < x > V < 2-y > B < y > (PO4) 2F3, 0lt, x is less than or equal to 0.3, 0lt; y is less than or equal to 0.2, the doping element A is one or more of Li and K, and the doping element B is one or more of Y, Cr, Fe and Mg. The sodium-ion battery positive electrode active material obtained by co-doping the vanadium sodium fluorophosphate with the doping elements A and B has obviously improved capacity performance, cycling stability and rate capability.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and specifically relates to a sodium-ion battery positive electrode active material, a preparation method thereof, a positive electrode sheet, and a secondary battery. Background Art

[0002] Lithium-ion batteries have high energy density and are widely used in new energy electric vehicles and energy storage fields. However, due to the limited and expensive lithium resources, it is difficult for lithium-ion batteries to meet the growing demands of new energy electric vehicles and energy storage. Since sodium resources are abundant and the cost of sodium resources is much lower than that of lithium resources, and sodium and lithium elements have similar electrochemical properties, developing safe and high-performance sodium-ion batteries is the future development direction.

[0003] Sodium vanadium fluorophosphate, the positive electrode active material of sodium-ion batteries, is a very promising material. However, due to its own structure, there are some factors that limit the capacity performance: on the one hand, since the [V2O8F3] double octahedrons in the crystal structure are connected by [PO4], and [PO4] is an extremely stable tetrahedral structure with electronic insulation, which leads to very low electronic conductivity of sodium vanadium fluorophosphate, resulting in poor rate performance of sodium batteries using sodium vanadium fluorophosphate. On the other hand, since Na + has a relatively large radius, and the width of the deintercalation / insertion channels during charge and discharge is limited, so the migration rate of Na + is relatively low, resulting in poor rate performance and cycling performance of sodium batteries. Summary of the Invention

[0004] The present application provides a sodium-ion battery positive electrode active material, a preparation method thereof, a positive electrode sheet, and a secondary battery to solve the problems of poor cycling performance and rate performance of the existing sodium vanadium fluorophosphate material.

[0005] In the first aspect, the present application provides a sodium-ion battery positive electrode active material, the sodium-ion battery positive electrode active material includes a polyanion material, and the chemical formula of the polyanion material is Na 3-x A x V 2-y B y (PO4)2F3, 0 < x ≤ 0.3, 0 < y ≤ 0.2, the doping element A is one or more of Li and K, and the doping element B is one or more of Y, Cr, Fe, and Mg.

[0006] In an optional embodiment, in the sodium-ion battery positive electrode active material, the doping site of the doping element A is the Na1 site, and the doping site of the doping element B is the V site. In the sodium vanadium fluorophosphate material, Na +Located at two different sites, namely the Na1 site and the Na2 site. "The doping site of dopant element A is the Na1 site" means that dopant element A can replace the Na at the Na1 site, which does not participate in the charging and discharging process. + It is located at the Na1 site. In sodium vanadium fluorophosphate materials, V... 3+ Located at the V site, "the doping site of dopant element B is the V site" means that dopant element B can replace the V site. 3+ It is located at site V.

[0007] In one optional embodiment, the surface of the polyanionic material is further provided with a carbon coating layer, wherein the mass percentage of the polyanionic material is 92-94% and the mass percentage of the carbon coating layer is 6-8% based on the total mass of the sodium-ion battery positive electrode active material; and / or, the thickness of the carbon coating layer is 4-7 nm.

[0008] In one alternative implementation, dopant A is K and dopant B is Cr.

[0009] In one optional embodiment, in the chemical formula of the polyanionic material, 0.1 ≤ x ≤ 0.2, 0.08 <y≤0.12。

[0010] Secondly, this application also provides a method for preparing the sodium-ion battery positive electrode active material, comprising the following steps: weighing Na source, A source, V source, B source and P source according to stoichiometric ratio, mixing with carbon source and water, gelling, drying, grinding and calcining to obtain sodium-ion battery positive electrode active material, wherein at least one of Na source and V source is a fluoride, and at least one of A source and B source is a fluoride.

[0011] In one optional embodiment, the gelation temperature is 50-80°C, optionally 55-70°C; the mixing time is 8-12 hours.

[0012] In one alternative embodiment, the process further includes a drying step to form a dry gel after mixing to form a wet gel.

[0013] In one optional embodiment, the calcination includes a first calcination and a second calcination. The temperature of the first calcination is 200-500℃, optionally 300-400℃, and the time is 2-4 hours. The temperature of the second calcination is 500-800℃, optionally 550-650℃, and the time is 5-8 hours.

[0014] In one alternative embodiment, the heating rate from room temperature to the temperature of the first calcination or the heating rate from the temperature of the first calcination to the temperature of the second calcination is 3-6 °C / min.

[0015] In one alternative embodiment, the calcination is carried out in an inert gas atmosphere.

[0016] In one optional embodiment, the ratio of the total number of moles of Na source, A source, V source, B source, P source and carbon source to the volume of water is 0.4725 mol: 55-90 ml; alternatively, it is 0.4725 mol: 70-80 ml.

[0017] In one optional embodiment, the Na source includes sodium fluoride; and / or, the V source includes one or more of vanadium tetrafluoride, vanadium pentoxide, ammonium metavanadate, and sodium vanadate; and / or, the carbon source includes one or more of citric acid and glucose; and / or, the P source includes one or more of ammonium dihydrogen phosphate and ammonium phosphate; and / or, the A source includes one or more of the fluoride of A, the chloride of A, and the nitrate of A; and / or, the B source includes one or more of the fluoride of B, the chloride of B, and the nitrate of B; and / or, the molar ratio of the added carbon source to the V source is 1-1.5:1.

[0018] Thirdly, this application provides a positive electrode sheet, comprising:

[0019] Positive current collector, and

[0020] A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the sodium-ion battery positive electrode active material described above or the sodium-ion battery positive electrode active material prepared by any of the above preparation methods;

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

[0022] Fourthly, this application provides a secondary battery, including the positive electrode sheet described above.

[0023] Fifthly, this application provides an electrical device including the aforementioned secondary battery.

[0024] The technical solution of this application has the following advantages:

[0025] 1. The sodium-ion battery positive electrode active material provided in this application includes a polyanionic material, wherein the polyanionic material has the chemical formula Na. 3-x A x V 2-y B y(PO4)2F3, where 0 < x ≤ 0.3, 0 < y ≤ 0.2, the doping element A is one or more of Li and K, and the doping element B is one or more of Y, Cr, Fe, and Mg. The sodium-ion battery cathode active material obtained by co-doping the doping elements A and B has significantly improved capacity performance, cycle stability, and rate performance.

[0026] Among them, the doping site of the doping element A is at the Na1 position that does not participate in the charge-discharge process, and the doping site of the doping element B is at the V position. The combined use of the doping elements A and B can play a role in supporting the structure and broadening the Na + migration channel, which can comprehensively improve the capacity performance, cycle stability, and rate performance of the sodium-ion battery cathode active material sodium fluorophosphate vanadate.

[0027] 2. For the sodium-ion battery cathode active material provided by this application, by specifying that the doping element A is K and the doping element B is Cr, the cycle stability and rate performance of the sodium-ion battery cathode active material can be further improved.

[0028] By controlling 0.1 ≤ x ≤ 0.2 and 0.08 < y ≤ 0.12, the cycle stability and rate performance of the sodium-ion battery cathode active material can be further improved.

[0029] 3. The preparation method of the sodium-ion battery cathode active material provided by this application is simple in operation, convenient for processing, and easy for industrial production. In particular, controlling the gelation temperature to be 50 - 80°C, optionally 55 - 70°C, or controlling the calcination temperature to be 500 - 800°C, optionally 550 - 650°C; controlling the total molar amount of the Na source, A source, V source, B source, P source, and carbon source to the volume ratio of water to be 0.4725 mol : 55 - 90 ml; optionally 0.4725 mol : 70 - 80 ml; can further improve the cycle stability and rate performance of the sodium-ion battery cathode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1This is a SEM mapping image (elemental mapping image) of the positive electrode active material of the coin cell prepared in Example 2 of this application after it is fully charged; Electron Image 1 is an electronic image, Na Ka1-2 is a Na elemental distribution mapping image, and Li Ka1-2 is a Li elemental distribution mapping image.

[0032] Figure 2 This is a SEM mapping image of the positive electrode active material of the coin cell prepared in Example 1 of this application after it is fully charged; Electron Image 1 is an electronic image, Na Ka1-2 is a Na element distribution mapping image, and K Ka1-2 is a K element distribution mapping image.

[0033] Figure 3 This is a SEM mapping image of the sodium-ion battery positive electrode active material prepared in Example 1 of this application;

[0034] Figure 4 These are XRD patterns of the positive electrode active materials of sodium-ion batteries in Example 2 and Comparative Example 1 of this application;

[0035] Figure 5 These are the cycle performance test results of the coin cells prepared in Examples 1, 2 and Comparative Example 1 of this application;

[0036] Figure 6 These are the rate performance test results of the coin cells prepared in Example 2 and Comparative Example 1 of this application;

[0037] Figure 7 These are SEM images of the sodium-ion battery positive electrode active materials prepared in Example 1 and Comparative Example 1 of this application;

[0038] Figure 8 These are Raman images of the sodium-ion battery positive electrode active materials prepared in Example 1 and Comparative Example 1 of this application;

[0039] Figure 9 This is a TEM (transmission electron microscope) image of the sodium-ion battery positive electrode active material prepared in Example 1 of this application;

[0040] Figure 10 The image shows the thermogravimetric analysis (TGA) plot of the sodium-ion battery positive electrode active material prepared in Example 1 of this application, where loss represents mass loss. Detailed Implementation

[0041] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0043] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0044] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0045] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0047] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0048] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0049] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0050] Sodium vanadium fluorophosphate has very low electronic conductivity and low migration rate, resulting in poor rate performance and cycling performance of sodium batteries.

[0051] To solve the problems existing in the above-mentioned related technologies, according to the first aspect of the present application, the present application provides a positive electrode active material for a sodium ion battery, and the chemical formula of the positive electrode active material for the sodium ion battery is Na 3-x A x V 2-y B y (PO4)2F3, 0 < x ≤ 0.3, 0 < y ≤ 0.2, the doping element A is one or more of Li and K, and the doping element B is one or more of Y, Cr, Fe, and Mg.

[0052] The positive electrode active material for a sodium ion battery obtained by co-doping with doping elements A and B in the present application has significantly improved capacity performance, cycling stability, and rate performance. Among them, the doping site of doping element A is at the Na1 position that does not participate in the charge-discharge process, and the doping site of doping element B is at the V position. The combined use of doping elements A and B can play a role in supporting the structure and broadening the Na + migration channels, and comprehensively improve the capacity performance, cycling stability, and rate performance of the positive electrode active material sodium vanadium fluorophosphate for a sodium ion battery. For example, x is 0.01, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3, and y is 0.01, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3.

[0053] In an optional embodiment, a carbon coating layer is further provided on the surface of the positive electrode active material for a sodium ion battery; based on the total mass of the positive electrode active material for a sodium ion battery, the mass ratio of the polyanion material is 92-94%, and the mass ratio of the carbon coating layer is 6-8%. For example, the mass ratio of the polyanion material is 92%, 93%, 94%, and the mass ratio of the carbon coating layer is 6%, 7%, 8%. The mass ratio of the carbon coating layer is measured by thermogravimetric analysis. Instrument model: METTLER of Switzerland, test atmosphere: oxygen. Temperature range: 25-800 °C, heating rate 10 °C / min.

[0054] In one optional embodiment, the carbon coating layer has a thickness of 4-7 nm; the carbon coating layer is beneficial for further improving the capacity performance of sodium vanadium fluorophosphate, the positive electrode active material of sodium-ion batteries. For example, the thickness of the carbon coating layer is 4 nm, 5 nm, 6 nm, or 7 nm. The coating layer thickness was measured using a transmission electron microscope (TEM). The TEM model used was a JEOL JEM2100plus; the results are shown below. Figure 10 .

[0055] In one optional embodiment, the particle size of the sodium-ion battery positive electrode active material is 300-500 nm. For example, the particle sizes of the sodium-ion battery positive electrode active material are 300 nm, 350 nm, 400 nm, 450 nm, and 500 nm.

[0056] In one alternative implementation, dopant A is K and dopant B is Cr.

[0057] In one optional embodiment, in the chemical formula of the polyanionic material, 0.1 ≤ x ≤ 0.2, 0.08 <y≤0.12。

[0058] Secondly, this application also provides a method for preparing the sodium-ion battery positive electrode active material, comprising the following steps: weighing Na source, A source, V source, B source and P source according to stoichiometric ratio, mixing with carbon source and water, gelling, drying, grinding and calcining to obtain sodium-ion battery positive electrode active material, wherein at least one of Na source and V source is a fluoride, and at least one of A source and B source is a fluoride.

[0059] In one alternative embodiment, the gelation temperature is 50-80°C; the mixing time is 8-12 hours. For example, the gelation temperature is 50°C, 60°C, 70°C, or 80°C, and the mixing time is 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0060] In one optional embodiment, the calcination includes a first calcination and a second calcination. The first calcination is carried out at a temperature of 200-500°C for 2-4 hours; the second calcination is carried out at a temperature of 500-800°C for 5-8 hours. For example, the first calcination temperature is 200°C, 300°C, 400°C, or 500°C, and the time is 2 hours, 3 hours, or 4 hours; the second calcination temperature is 500°C, 600°C, 700°C, or 800°C, and the time is 5 hours, 6 hours, or 8 hours. By employing the above two-stage calcination, an excellent crystal structure can be obtained. By controlling the calcination temperature and time of the two-stage calcination, the structural stability and cycle life can be further improved.

[0061] In one optional embodiment, the ratio of the total moles of Na source, A source, V source, B source, P source, and carbon source to the volume of water is 0.4725 mol: 55-90 ml; for example, the ratio of the total moles of Na source, A source, V source, B source, P source, and carbon source to the volume of water is 0.4725 mol: 55 ml, 0.4725 mol: 60 ml, 0.4725 mol: 70 ml, 0.4725 mol: 80 ml, or 0.4725 mol: 90 ml.

[0062] In one optional embodiment, the Na source includes sodium fluoride; and / or, the V source includes one or more of vanadium tetrafluoride, vanadium pentoxide, ammonium metavanadate, and sodium vanadate; and / or, the carbon source includes one or more of citric acid and glucose; and / or, the P source includes one or more of ammonium dihydrogen phosphate and ammonium phosphate; and / or, the A source includes one or more of the fluoride of A, the chloride of A, and the nitrate of A; and / or, the B source includes one or more of the fluoride of B, the chloride of B, and the nitrate of B; and / or, the molar ratio of the added carbon source to the V source is 1-1.5:1.

[0063] Thirdly, this application provides a positive electrode sheet, comprising:

[0064] Positive current collector, and

[0065] A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the sodium-ion battery positive electrode active material described above or the sodium-ion battery positive electrode active material prepared by any of the above preparation methods.

[0066] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0067] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0068] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0069] In some embodiments, the binder may optionally comprise 0.1-3.5% of the total weight of the positive electrode active material layer, optionally 0.5-2.5%.

[0070] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0071] In some embodiments, the conductive agent may optionally account for 0.05-5% of the total weight of the positive electrode active material layer, and optionally 0.5-3%.

[0072] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0073] Fourthly, this application provides a secondary battery, including the positive electrode sheet described above.

[0074] In some embodiments, the secondary battery further includes a negative electrode, an electrolyte, and a separator.

[0075] In a sodium-ion battery, the negative electrode typically includes a negative current collector and a layer of negative active material disposed on the negative current collector, wherein the negative active material layer includes a negative active material.

[0076] The negative electrode sheet may also consist only of a negative current collector, i.e., without a negative electrode active material. The negative electrode sheet may also include a pre-deposited metallic phase on the negative current collector. The negative current collector can be made of conventional metal foil, carbon-coated metal foil, or porous metal plate, etc. As an example, the negative current collector can be made of copper foil or aluminum foil.

[0077] The specific type of the negative electrode active material is not limited; any active material known in the art that can be used as a negative electrode in sodium-ion batteries can be used. Those skilled in the art can select according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of sodium metal, carbon materials, alloy materials, transition metal oxides and / or sulfides, phosphorus-based materials, and titanate materials. Specifically, the carbon material may include one or more of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials; the alloy material may include alloys formed from one or more of Si, Ge, Sn, Pb, and Sb; the general formula of the transition metal oxides and sulfides is M. x N y M includes one or more of Fe, Co, Ni, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based material may include one or more of red phosphorus, white phosphorus, and black phosphorus; the titanate material may include Na2Ti3O7 and Na2Ti6O7. 13 Na4Ti5O 12 Li4Ti5O 12 One or more of NaTi2(PO4)3. These materials are all commercially available.

[0078] The negative electrode active material layer may also optionally include a binder and a conductive agent. The conductive agent is used to improve the conductivity of the negative electrode active material layer, and the binder is used to firmly bond the negative electrode active material and the conductive agent to the negative electrode current collector. This application does not specifically limit the types of conductive agents and binders, which can be selected according to actual needs.

[0079] As an example, conductive agents may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0080] As an example, the adhesive may include one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0081] The negative electrode active material layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). However, this application is not limited to this, and other materials that can be used as thickeners for the negative electrode sheet of sodium-ion batteries may also be used.

[0082] As for the aforementioned separator, this application does not have any particular limitations. Any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0083] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte may include an electrolyte salt and a solvent.

[0084] As an example, the electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0085] As an example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), and methyl butyrate. One or more of the following: (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), diethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxopentane, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0086] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0087] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0088] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0089] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0090] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0091] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0092] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0093] Fifthly, this application provides an electrical device including the aforementioned secondary battery.

[0094] In some embodiments, the aforementioned electrical device may also include a battery module or battery pack assembled from the aforementioned secondary batteries. The secondary batteries, battery modules, or battery packs can be used 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, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0095] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements. An example electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0096] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0097] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0098] Example 1

[0099] This embodiment provides a positive electrode active material for a sodium-ion battery, comprising a polyanionic material and a carbon coating layer encapsulating the polyanionic material. The chemical formula of the polyanionic material is: Na. 2.85 K 0.15 V 1.9 Cr 0.1(PO4)2F3, based on the total mass of the positive electrode active material of sodium-ion batteries, the mass proportion of polyanionic material is 93%, and the mass proportion of carbon coating layer is 7%; the thickness of carbon coating layer is 5 nm as measured by TEM (see...). Figure 9 ).

[0100] The preparation method of the above-mentioned sodium-ion battery positive electrode active material is as follows:

[0101] (1) Sol-gel: Add 0.01425mol NaF, 0.00075mol KF, 0.0095mol NH4VO3, 0.0005mol Cr(NO3)3, 0.01mol NH4H2PO4 and 0.012mol citric acid to a beaker containing 90ml of deionized water and stir at 55℃ for 10 hours until the water evaporates to obtain a wet gel.

[0102] (2) Drying: The obtained wet gel was dried in an oven at 85°C for 12 hours to obtain a dry gel.

[0103] (3) Grinding and calcination: The obtained dry gel was ground in a mortar for 30 min, and then the ground precursor was calcined in a tube furnace under an argon atmosphere at high temperature: 350℃ for 3 h (first calcination), 600℃ for 6 h (second calcination), with a heating rate of 5℃ / min. After calcination, 5% K-doped and 5% Cr-doped Na were obtained. 2.85 K 0.15 V 1.9 Cr 0.1 (PO4)2F3@C. 5% K doping means that the molar number of K accounts for 5% of the total molar number of Na and K, and 5% Cr doping means that the molar number of Cr accounts for 5% of the total molar number of Cr and V.

[0104] This embodiment also provides a secondary battery, the preparation method of which is as follows:

[0105] (1) Preparation of positive electrode sheet

[0106] Weigh out the sodium-ion battery positive electrode active material, conductive agent (conductive carbon black Super P), and binder (polyvinylidene fluoride PVDF) according to a mass ratio of 8:1:1, and set aside. First, disperse the binder in N-methylpyrrolidone (NMP) to form a 5% (w / w) PVDF solution. Mix the sodium-ion battery positive electrode active material and conductive agent, grind thoroughly for 1 hour, add the PVDF solution, and continue grinding for another hour to obtain the positive electrode slurry. Evenly coat the positive electrode slurry onto the positive electrode current collector aluminum foil, and obtain the positive electrode sheet after baking, cold pressing, and cutting.

[0107] (2) Preparation of negative electrode sheet

[0108] A sodium metal sheet is used as the negative electrode, and the electrode thickness is 500 nm.

[0109] (3) Preparation of electrolyte

[0110] Ethyl carbonate (EC) and propylene carbonate (PC) were mixed at a volume ratio of 1:1. 5 wt% fluoroethylene carbonate was added to the mixture. After mixing, NaClO4 was dissolved in the mixture, and the concentration of NaClO4 in the solution was 1 mol / L to obtain the electrolyte.

[0111] (4) Preparation of button cells

[0112] First, place the positive electrode shell, then place a pad, place the positive electrode plate on the pad, add 3 drops of electrolyte, place a polyethylene separator on the positive electrode plate, add 4 drops of electrolyte, place the negative electrode plate, place the negative electrode shell, and seal the opening to obtain a button cell.

[0113] Example 2

[0114] This embodiment provides a sodium-ion battery positive electrode active material and its preparation method, which is basically the same as that in Example 1, except that 0.00075 mol KF is replaced with 0.00075 mol LiF. The chemical formula of the resulting polyanionic material is: Na 2.85 Li 0.15 V 1.9 Cr 0.1 (PO4)2F3.

[0115] This embodiment also provides a secondary battery, which is basically the same as that in Embodiment 1, except that the sodium-ion battery positive electrode active material provided in this embodiment is used instead of the sodium-ion battery positive electrode active material in Embodiment 1.

[0116] Example 3

[0117] This embodiment provides a sodium-ion battery positive electrode active material and its preparation method, which is basically the same as that in Example 1, except that 0.0005 mol Cr(NO3)3 is replaced with 0.0005 mol Y(NO3)3. The chemical formula of the resulting polyanionic material is: Na 2.85 K 0.15 V 1.9 Y 0.1 (PO4)2F3.

[0118] This embodiment also provides a secondary battery, which is basically the same as that in Embodiment 1, except that the sodium-ion battery positive electrode active material provided in this embodiment is used instead of the sodium-ion battery positive electrode active material in Embodiment 1.

[0119] Example 4

[0120] This embodiment provides a sodium-ion battery positive electrode active material and its preparation method, which is basically the same as that in Example 1, except that 0.00075 mol KF is replaced with 0.00075 mol LiF and 0.0005 mol Cr(NO3)3 is replaced with 0.0005 mol Y(NO3)3. The chemical formula of the resulting polyanionic material is: Na 2.85 Li 0.15 V 1.9 Y 0.1 (PO4)2F3.

[0121] This embodiment also provides a secondary battery, which is basically the same as that in Embodiment 1, except that the sodium-ion battery positive electrode active material provided in this embodiment is used instead of the sodium-ion battery positive electrode active material in Embodiment 1.

[0122] Example 5

[0123] This embodiment provides a sodium-ion battery positive electrode active material and its preparation method, which is basically the same as that in Example 1, except that 0.0005 mol Cr(NO3)3 is replaced with 0.0005 mol Fe(NO3)3. The chemical formula of the resulting polyanionic material is: Na 2.85 K 0.15 V 1.9 Fe 0.1 (PO4)2F3.

[0124] This embodiment also provides a secondary battery, which is basically the same as that in Embodiment 1, except that the sodium-ion battery positive electrode active material provided in this embodiment is used instead of the sodium-ion battery positive electrode active material in Embodiment 1.

[0125] Example 6

[0126] This embodiment provides a sodium-ion battery positive electrode active material and its preparation method, which is basically the same as that in Example 1, except that 0.0005 mol Cr(NO3)3 is replaced with 0.0005 mol Fe(NO3)3 and 0.00075 mol KF is replaced with 0.00075 mol LiF. The chemical formula of the resulting polyanionic material is: Na 2.85 Li 0.15 V 1.9 Fe 0.1 (PO4)2F3.

[0127] This embodiment also provides a secondary battery, which is basically the same as that in Embodiment 1, except that the sodium-ion battery positive electrode active material provided in this embodiment is used instead of the sodium-ion battery positive electrode active material in Embodiment 1.

[0128] Example 7

[0129] The preparation method is the same as in Example 1, except that the amounts of NaF, KF, NH4VO3, and Cr(NO3)3 are different. In this example, the amount of NaF is adjusted to 0.0145 mol, the amount of KF is adjusted to 0.0005 mol, the amount of NH4VO3 is adjusted to 0.0094 mol, and the amount of Cr(NO3)3 is adjusted to 0.0006 mol.

[0130] Example 8

[0131] The preparation method is the same as in Example 1, except that the amounts of NaF, KF, NH4VO3, and Cr(NO3)3 are different. In this example, the amount of NaF is adjusted to 0.014 mol, the amount of KF is adjusted to 0.001 mol, the amount of NH4VO3 is adjusted to 0.0096 mol, and the amount of Cr(NO3)3 is adjusted to 0.0004 mol.

[0132] Example 9

[0133] The preparation method is the same as in Example 1, except that the amounts of NaF, KF, NH4VO3, and Cr(NO3)3 are different. In this example, the amount of NaF is adjusted to 0.01475 mol, the amount of KF is adjusted to 0.00025 mol, the amount of NH4VO3 is adjusted to 0.009 mol, and the amount of Cr(NO3)3 is adjusted to 0.001 mol.

[0134] Example 10

[0135] The preparation method is the same as in Example 1, except that the amounts of NaF, KF, NH4VO3, and Cr(NO3)3 are different. In this example, the amount of NaF is adjusted to 0.0135 mol, the amount of KF is adjusted to 0.0015 mol, the amount of NH4VO3 is adjusted to 0.00975 mol, and the amount of Cr(NO3)3 is adjusted to 0.00025 mol.

[0136] Example 11

[0137] The preparation method is the same as in Example 1, except that the temperature is adjusted to 50°C in step (1).

[0138] Example 12

[0139] The preparation method is the same as in Example 1, except that the temperature is adjusted to 80°C in step (1).

[0140] Example 13

[0141] The preparation method is the same as in Example 1, except that the temperature is adjusted to 70°C in step (1).

[0142] Example 14

[0143] The preparation method is the same as in Example 1, except that the calcination temperature in the second calcination in step (3) is adjusted to 500°C.

[0144] Example 15

[0145] The preparation method is the same as in Example 1, except that the calcination temperature in the second calcination in step (3) is adjusted to 800°C.

[0146] Example 16

[0147] The preparation method is the same as in Example 1, except that the calcination temperature of the second calcination in step (3) is adjusted to 550°C.

[0148] Example 17

[0149] The preparation method is the same as in Example 1, except that the calcination temperature in the second calcination in step (3) is adjusted to 650°C.

[0150] Example 18

[0151] The preparation method is the same as in Example 1, except that the amount of water used in step (1) is adjusted to 55 ml.

[0152] Example 19

[0153] The preparation method is the same as in Example 1, except that the amount of water used in step (1) is adjusted to 70 ml.

[0154] Example 20

[0155] The preparation method is the same as in Example 1, except that the amount of water used in step (1) is adjusted to 80 ml.

[0156] Example 21

[0157] This embodiment provides a positive electrode active material for a sodium-ion battery, comprising a polyanionic material and a carbon coating layer encapsulating the polyanionic material. The chemical formula of the polyanionic material is: Na. 2.85 K 0.15 V 1.9 Cr 0.1 Based on the total mass of the positive electrode active material of sodium-ion batteries (PO4)2F3, the mass ratio of polyanionic material is 96%, and the mass ratio of carbon coating layer is 4%. The thickness of carbon coating layer is 8 nm as measured by TEM.

[0158] The preparation method is as follows:

[0159] (1) Sol-gel: Add 0.01425mol NaF, 0.00075mol KF, 0.0095mol NaVO3, 0.0005mol CrCl3, 0.01mol NH4H2PO4 and 0.01mol glucose to a beaker containing 90ml of deionized water and stir at 55℃ for 10 hours until the water evaporates to obtain a wet gel.

[0160] (2) Drying: The obtained wet gel was dried in an oven at 85°C for 12 hours to obtain a dry gel.

[0161] (3) Grinding and calcination: The obtained dry gel was ground in a mortar for 30 min, and then the ground precursor was calcined in a tube furnace under an argon atmosphere at high temperature: 350℃ for 3 h (first calcination), 600℃ for 6 h (second calcination), with a heating rate of 5℃ / min. After calcination, 5% K-doped and 5% Cr-doped Na were obtained. 2.85 K 0.15 V 1.9 Cr 0.1 (PO4)2F3@C.

[0162] Comparative Example 1

[0163] This comparative example provides a method for preparing a positive electrode active material for sodium-ion batteries, comprising the following steps: 0.015 mol NaF, 0.01 mol NH4VO3, 0.01 mol NH4H2PO4, and 0.012 mol citric acid are added to a beaker containing 90 ml of deionized water and stirred at 55°C for 10 hours until the water evaporates to obtain a wet gel. The obtained wet gel is dried in an oven at 85°C for 12 hours to obtain a dry gel. The obtained dry gel is ground in a mortar for 30 minutes, and then the ground precursor is calcined at high temperature in a tube furnace under an argon atmosphere: 350°C for 3 hours; 600°C for 6 hours, with a heating rate of 5°C / min. After calcination, Na3V2(PO4)2F3@C is obtained.

[0164] Experimental Example 1

[0165] 1. XRD tests were performed on the sodium-ion battery positive electrode active materials prepared in Example 2 and Comparative Example 1. The XRD scanning range was 10-80° with a step size of 0.5°s. -1 The testing instrument was a D8 ADVANCE model manufactured by Bruker GmbH, Germany. Results are shown below. Figure 4As shown, because B and V are both in the transition period and have similar properties, if the B doping were not at the V site, the crystal structure would definitely change. However, the XRD test results show that the crystal structure has not changed and still matches the XRD standard card of sodium vanadium fluorophosphate Na3V2(PO4)2F3(NVPF). In conclusion, the B doping site is at the V site.

[0166] 2. Scanning electron microscopy (SEM) was used to examine the morphology and perform Raman analysis of the sodium-ion battery positive electrode active materials prepared in Example 2 and Comparative Example 1. The SEM instrument used was a JEOL JSM-6390A model with an accelerating voltage of 3.5 kV. The Raman instrument was a DXR2 manufactured by Thcrmo Scientific, USA. The results are shown below. Figure 7 and 8 As shown, from Figure 7 It can be seen that the comparative example shows obvious agglomeration and uneven particle size distribution. In contrast, the example does not exhibit agglomeration and has a uniform particle size distribution. Figure 8 As can be seen, the degree of graphitization of carbon in the sodium-ion battery positive electrode active materials obtained in Example 1 and Comparative Example 1 is the same, indicating that the introduction of dopant elements has no effect on the degree of graphitization, and that the improvement in electrochemical performance is only due to the introduction of dopant elements.

[0167] 3. Take the coin cells from Examples 1 and 2, charge them at 0.2C to the cutoff voltage (4.3V), disassemble the cells, clean the active materials with NMP, and test the mapping of the positive electrode active materials using a scanning electron microscope (SEM). The results are shown in [Figure 1]. Figure 1 and 2 ,from Figure 1 It can be seen that Li can still be detected after the battery is fully charged, indicating that Li... + It did not come out of the embedding, indicating that Li + It did not participate in the electrochemical reaction, meaning it was doped at the Na1 site, which does not participate in the electrochemical reaction. From Figure 2 It can be seen that K can still be detected after the battery is fully charged, indicating that K... + It did not come out of the embedding, indicating that K + The dopant did not participate in the electrochemical reaction, meaning it was doped at the Na1 site, which is not involved in the electrochemical reaction. The Na1 site is very stable, and during synthesis, it tends to remain in a stable state. The mapping diagram of the sodium-ion battery positive electrode active material prepared in Example 1 was tested and is shown in [see attached image]. Figure 3 As shown, Na, K, and Cr elements can be detected, proving that K and Cr elements have been successfully doped.

[0168] 4. Cyclic performance test method: The temperature atmosphere is 25℃, the potential range is 2.5-4.3V, and the current density is 0.5C. Charge to 4.3V with a constant current of 0.5C, discharge to 2.5V with a constant current of 0.5C, cycle 100 times, and calculate the capacity retention rate after 100 cycles. Capacity retention rate = discharge capacity on the 100th cycle / discharge capacity on the 1st cycle.

[0169] 5. Rate Performance Test Method: At 25℃, first charge at 0.5C to 4.3V, then discharge at 0.5C to 2.5V, repeating 5 cycles; then charge at 1C to 4.3V, then discharge at 1C to 2.5V, repeating 5 cycles; then charge at 2C to 4.3V, then discharge at 2C to 2.5V, repeating 5 cycles; then charge at 5C to 4.3V, then discharge at 5C to 2.5V, repeating 5 cycles; then charge at 10C to 4.3V, then discharge at 10C to 2.5V, repeating 5 cycles; finally, charge at 0.5C to 4.3V, then discharge at 0.5C to 2.5V, repeating 5 cycles. Current densities are 0.5C, 1C, 2C, 5C, 10C, and 0.5C. Each current density is cycled 5 times. Record the first discharge capacity at 0.5C and the first discharge specific capacity at 10C.

[0170] Table 1. Results of Capacity Performance, Rate Performance, and Cycle Performance

[0171]

[0172]

[0173] From the table above and Figure 5 and 6 As can be seen, compared with Comparative Example 1, the batteries made from the sodium-ion battery positive electrode active material used in the various embodiments of the present invention have significantly improved cycle performance, rate performance, and capacity performance.

[0174] Comparing Examples 1-6, it can be seen that the batteries made from the sodium-ion battery positive electrode active materials used in Example 1 (doped with K and Cr) and Example 3 (doped with K and Y) can better balance excellent cycle performance, rate performance, and capacity performance, especially Example 1.

[0175] Comparing Examples 1 and 7-10, it can be seen that Examples 1, 7 and 8, by controlling the amount of NaF, KF, NH4VO3 and Cr(NO3)3, allow the x and y in the chemical formula of the polyanionic material to be controlled within the selectable range, so that the battery made of sodium-ion battery positive electrode active material can better balance excellent cycle performance, rate performance and capacity performance.

[0176] Comparing Examples 1 and 11-13, it can be seen that Examples 1 and 13, by controlling the gelation temperature within a selectable range, enable the batteries made from sodium-ion battery cathode active materials to better balance excellent cycle performance, rate performance, and capacity performance.

[0177] Comparing Examples 1 and 14-17, it can be seen that Examples 1 and 16-17, by controlling the calcination temperature within a selectable range, enable the batteries made from sodium-ion battery cathode active materials to better balance excellent cycle performance, rate performance, and capacity performance.

[0178] Compared with Examples 1 and 18-20, Examples 19-20 further improve the cycle performance, rate performance, and capacity performance of batteries made from sodium-ion battery cathode active materials by limiting the ratio of the total number of moles of Na source, A source, V source, B source, P source, and carbon source to the volume of water within a selectable range.

[0179] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A positive electrode active material for sodium-ion batteries, characterized in that, The positive electrode active material of the sodium ion battery includes a polyanion material, and the chemical formula of the polyanion material is Na 3-x A x V 2-y B y (PO4)2F3, where 0 < x ≤ 0.3 and 0 < y ≤ 0.2, and the doping element A is one or more of Li and K, and the doping element B is one or more of Y, Cr, Fe, and Mg.

2. The sodium-ion battery positive electrode active material according to claim 1, characterized in that, In the sodium-ion battery positive electrode active material, the doping site of doping element A is the Na1 site, and the doping site of doping element B is the V site.

3. The sodium-ion battery positive electrode active material according to claim 1 or 2, characterized in that, The surface of the polyanionic material is further provided with a carbon coating layer. Based on the total mass of the sodium-ion battery positive electrode active material, the mass ratio of the polyanionic material is 92-94%, the mass ratio of the carbon coating layer is 6-8%, and / or the thickness of the carbon coating layer is 4-7 nm.

4. The sodium-ion battery positive electrode active material according to any one of claims 1-3, characterized in that, In the chemical formula of the polyanionic material, 0.1 ≤ x ≤ 0.2, 0.08 <y≤0.12。 5. A method for preparing the positive electrode active material of a sodium-ion battery according to any one of claims 1-4, characterized in that, The process includes the following steps: weighing Na source, A source, V source, B source and P source according to stoichiometric ratio, mixing with carbon source and water, gelling, drying, grinding and calcining to obtain sodium-ion battery positive electrode active material, wherein at least one of Na source and V source is a fluoride, and at least one of A source and B source is a fluoride.

6. The method for preparing the positive electrode active material of a sodium-ion battery according to claim 5, characterized in that, The gelation temperature is 50-80℃, or 55-70℃; the mixing time is 8-12h.

7. The method for preparing the positive electrode active material of a sodium-ion battery according to claim 5 or 6, characterized in that, The calcination includes a first calcination and a second calcination. The temperature of the first calcination is 200-500℃, optionally 300-400℃, and the time is 2-4 hours. The temperature of the second calcination is 500-800℃, optionally 550-650℃, and the time is 5-8 hours.

8. The method for preparing the positive electrode active material of a sodium-ion battery according to any one of claims 5-7, characterized in that, The ratio of the total moles of Na, A, V, B, P, and carbon sources to the volume of water is 0.4725 mol: 55-90 ml; alternatively, it can be 0.4725 mol: 70-80 ml.

9. The method for preparing the positive electrode active material of a sodium-ion battery according to any one of claims 5-8, characterized in that, The Na source includes sodium fluoride; and / or, the V source includes one or more of vanadium tetrafluoride, vanadium pentoxide, ammonium metavanadate, and sodium vanadate; and / or, the carbon source includes one or more of citric acid and glucose; and / or, the P source includes one or more of ammonium dihydrogen phosphate and ammonium phosphate; and / or, the A source includes one or more of the fluoride of A, the chloride of A, and the nitrate of A; and / or, the B source includes one or more of the fluoride of B, the chloride of B, and the nitrate of B; and / or, the molar ratio of the added carbon source to the V source is 1-1.5:

1.

10. A positive electrode plate, characterized in that, include: Positive current collector, and A positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising the sodium-ion battery positive electrode active material according to any one of claims 1-4 or the sodium-ion battery positive electrode active material prepared by any one of claims 5-9; Optionally, the positive electrode active material layer further includes at least one of a binder and a conductive agent.

11. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 10.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 11.

Images