Battery monomer and preparation method thereof, secondary battery and power utilization device

Abstract

The invention relates to the technical field of new energy, specifically relates to the technical field of batteries, and particularly relates to a battery monomer, a preparation method thereof, a secondary battery and an electric device. The battery monomer comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises a core part and a coating layer coating at least part of the surface of the core part, the core part comprises sodium-containing positive electrode active material particles, the coating layer comprises lithium-containing positive electrode active material particles, and the crystal structure of the sodium-containing positive electrode active material particles is the same as that of the lithium-containing positive electrode active material particles. The battery monomer has good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, specifically to the field of battery technology, and particularly to a battery cell and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Sodium-ion batteries have become a hot research topic for companies due to their advantages such as low manufacturing cost and good safety performance. However, current sodium-ion batteries still suffer from low cycle performance, which further limits their application. Summary of the Invention

[0003] This invention provides a battery cell and its preparation method, a secondary battery, and an electrical device, wherein the battery cell has good cycle performance.

[0004] In a first aspect, embodiments of the present invention provide a battery cell, the battery cell including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer, the positive electrode film layer being located on at least one side of the positive current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including a core and a coating layer covering at least a portion of the surface of the core, wherein the core includes sodium-containing positive electrode active material particles, the coating layer includes lithium-containing positive electrode active material particles, and the crystal structure of the sodium-containing positive electrode active material particles is the same as the crystal structure of the lithium-containing positive electrode active material particles.

[0005] In the battery cell provided by the embodiments of the present invention, the positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core comprises sodium-containing positive electrode active material particles, and the coating layer comprises lithium-containing positive electrode active material particles, thereby enabling the positive electrode active material to possess good electronic conductivity. Furthermore, the crystal structure of the sodium-containing positive electrode active material particles is the same as that of the lithium-containing positive electrode active material particles, which allows for good lattice matching between the core and the coating layer, enhancing the bonding force between them and improving the cycle performance of the battery cell. Therefore, the battery cell provided by the embodiments of the present invention has excellent cycle performance.

[0006] In some embodiments of the present invention, the crystal structure of the sodium-containing positive electrode active material particles includes a layered crystal structure and / or a spinel crystal structure.

[0007] In some embodiments of the present invention, the chemical formula of the sodium-containing positive electrode active material particles includes NaM. m K b O f, where 0 < m ≤ 2, 0 ≤ b ≤ 0.2, 2 ≤ f ≤ 4, the M element includes transition metal elements, and the K element includes at least one of C, Si, W, Zr, and Ti. The chemical formula of the lithium-containing cathode active material particles includes LiN n G g O t , where 0 < n ≤ 2, 0 ≤ g ≤ 0.2, 2 ≤ t ≤ 4, the M element includes transition metal elements, and the G element includes at least one of C, Si, W, Zr, and Ti.

[0008] In some embodiments of the present invention, the average particle size r of the core and the thickness d of the coating layer satisfy: 5 ≤ r / d ≤ 30.

[0009] In some embodiments of the present invention, 10 nm ≤ d ≤ 40 nm.

[0010] In some embodiments of the present invention, 0.5 μm ≤ r ≤ 1.5 μm.

[0011] In some embodiments of the present invention, the battery cell further includes a housing, the positive electrode sheet is located inside the housing, and reinforcing ribs are provided inside the housing.

[0012] In a second aspect, an embodiment of the present invention provides a method for preparing a battery cell as described in the first aspect of the present invention. The preparation method includes:

[0013] Providing sodium-containing cathode active material particles;

[0014] Adding a lithium source to a solvent to form a lithium-containing precursor solution;

[0015] Mixing the sodium-containing cathode active material particles and the lithium-containing precursor solution and subjecting them to spray drying to form a lithium-containing coating slurry layer on at least part of the surface of the sodium-containing cathode active material particles;

[0016] Performing heat treatment on the sodium-containing cathode active material particles having a lithium-containing coating slurry layer to obtain a cathode active material, where the cathode active material includes a core and a coating layer coated on at least part of the surface of the core, the core includes the sodium-containing cathode active material particles, the coating layer includes lithium-containing cathode active material particles, and the crystal structures of the sodium-containing cathode active material particles and the lithium-containing cathode active material particles are the same;

[0017] Adding the cathode active material, a conductive agent, and a binder to an organic solvent to make a cathode slurry; then coating the cathode slurry on the surface of a cathode current collector to form a cathode slurry layer, and after drying, obtaining a cathode electrode sheet;

[0018] The positive electrode sheet, negative electrode sheet, separator, and electrolyte are assembled to obtain a battery cell.

[0019] In some embodiments of the present invention, during the spray drying process, the inlet air temperature is 180°C to 220°C, the atomization pressure is 0.2 MPa to 0.5 MPa, and the feeding rate is 5 mL / min to 10 mL / min.

[0020] In some embodiments of the present invention, the chemical formula of the sodium-containing positive electrode active material particles includes NaM m K b O f , where 0 < m ≤ 2, 0 ≤ b ≤ 0.2, 2 ≤ f ≤ 4, the M element includes transition metal elements, and the K element includes at least one of C, Si, W, Zr, and Ti.

[0021] In some embodiments of the present invention, the volume molar concentration of lithium element in the lithium-containing precursor solution is 0.2 mol / L to 0.5 mol / L.

[0022] In some embodiments of the present invention, the temperature of the heat treatment is 300°C to 600°C, and the time of the heat treatment is 2 h to 5 h.

[0023] In a third aspect, embodiments of the present invention provide a secondary battery, including the battery cell of the first aspect of the present invention or the battery cell prepared by the preparation method of the second aspect of the present invention.

[0024] In a fourth aspect, embodiments of the present invention provide an electrical device, including the secondary battery of the third aspect of the present invention. Detailed Embodiments

[0025] Hereinafter, embodiments of the battery cell of the present invention, its preparation method, secondary battery, and electrical device are specifically and publicly described in detail. However, there may be cases where unnecessary details are omitted. For example, there are cases where the detailed description of well-known matters and the repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present invention and is not intended to limit the subject matter recited in the claims.

[0026] The "range" disclosed in this invention 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 the 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 understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​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 invention, 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.

[0027] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0028] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0029] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0030] This invention provides a battery cell including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer, the positive electrode film layer being located on at least one side of the positive current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including a core and a coating layer covering at least a portion of the surface of the core, wherein the core includes sodium-containing positive electrode active material particles, the coating layer includes lithium-containing positive electrode active material particles, and the crystal structure of the sodium-containing positive electrode active material particles is the same as the crystal structure of the lithium-containing positive electrode active material particles.

[0031] In this article, sodium-containing positive electrode active material particles refer to positive electrode active material particles that can store energy through sodium ion deintercalation / intercalation, or positive electrode active material particles that can reversibly deintercalate and intercalate sodium ions.

[0032] In this article, lithium-containing cathode active material particles refer to cathode active material particles that can store energy through lithium ion deintercalation / intercalation, or cathode active material particles that can reversibly deintercalate and intercalate lithium ions.

[0033] In this paper, the coating layer refers to the layered structure covering the core, which may completely or partially cover the core. Furthermore, each coating layer may be a complete or partial coating. The coating layer can be detected using equipment and methods commonly used in the art, such as ion polishing cross-sectional morphology analysis (CP) of the positive electrode active material to observe the core and coating layer of the positive electrode active material.

[0034] In this paper, the crystal structure of the core and the coating layer can be tested using methods and equipment well known in the art. For example, when performing ion polishing cross-sectional morphology (CP) analysis on the positive electrode active material, the samples that have undergone ion polishing cross-sectional morphology (CP) analysis were measured using an X-ray powder diffractometer. Specifically, a Brucker D8A-A25 X-ray diffractometer from Brucker AxS GmbH, Germany, was used with CuKα rays as the radiation source. The ray wavelength scanning 2θ angle range was 10° to 90°, and the scanning rate was 4° / min.

[0035] In the battery cell provided in this embodiment of the invention, the positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core comprises sodium-containing positive electrode active material particles, and the coating layer comprises lithium-containing positive electrode active material particles. This allows the positive electrode active material to possess good electronic conductivity. Furthermore, the crystal structure of the sodium-containing positive electrode active material particles is the same as that of the lithium-containing positive electrode active material particles, enabling better lattice matching between the core and the coating layer, enhancing the bonding force between them, and thus improving the cycle performance of the battery cell.

[0036] Therefore, the battery cell provided by the embodiments of the present invention has good cycle performance.

[0037] In some embodiments, the crystal structure of the sodium-containing positive electrode active material particles includes a layered crystal structure and / or a spinel crystal structure.

[0038] In the above embodiments, the crystal structure of the sodium-containing positive electrode active material particles includes the structure described above, which can help improve the energy density of the battery cell.

[0039] In some embodiments, the chemical formula of the sodium-containing cathode active material particles includes NaM m K b O2, where 0 < m ≤ 1, 0 ≤ b ≤ 0.2, the M element includes transition metal elements, and the K element includes at least one of C, Si, W, Zr, and Ti; the chemical formula of the lithium-containing cathode active material particles includes LiN n G g O2, where 0 < n ≤ 1, 0 ≤ g ≤ 0.2, the M element includes transition metal elements, and the G element includes at least one of C, Si, W, Zr, and Ti.

[0040] In this article, the chemical compositions of the sodium-containing cathode active material particles and the lithium-containing cathode active material can be measured by inductively coupled plasma emission spectrometry (ICP). For example, the cathode electrode sheet is obtained by disassembling the battery cell. The cathode electrode sheet is immersed in DMC solution for 20 h, and the excess electrolyte and sodium salts are washed away. Subsequently, the powder is scraped off and immersed in N-methylpyrrolidone (NMP) for 2 d to 3 d to dissolve PVDF. Then, it is filtered and washed to remove the residual NMP and impurities, and finally dried to obtain the cathode active material; the cathode active material is subjected to FIB sectioning (focused ion beam, FEI Helios G4), and then elemental analysis is performed on the cut section by inductively coupled plasma emission spectrometry. The above tests can obtain the proportions of each element, and the chemical formula is determined through the proportions of each element.

[0041] In some embodiments, the average particle size r of the core and the thickness d of the coating layer satisfy: 5 ≤ r / d ≤ 30.

[0042] In this article, the thickness of the coating layer refers to the wall thickness value from the inner surface to the outer surface of the coating layer. The thickness of the coating layer of the cathode active material can be measured by transmission electron microscopy (TEM). First, the cathode active material is dispersed in an absolute ethanol solution to obtain a dispersion liquid. Then, the dispersion liquid is dropped onto a copper mesh, dried, and sampled. In a high-vacuum environment, the electron beam generated by the electron gun penetrates the sample and is focused to form an image. By observing the image on the display screen, the thickness of the coating layer is measured using the built-in calibration tool, and the average value is calculated after measuring in multiple regions to obtain the thickness of the coating layer.

[0043] In the above embodiments, when the average particle size r of the core and the thickness d of the coating layer are within the above ranges, it can help the battery cell to balance the energy density and cycle performance.

[0044] Exemplarily, r / d can be, but is not limited to, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or the value range composed of any two of the above numerical values.

[0045] In some implementations, 10nm ≤ d ≤ 40nm.

[0046] For example, d can be, but is not limited to, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, or a range of values ​​consisting of any two of the above.

[0047] In some implementations, 0.5μm≤r≤1.5μm.

[0048] For example, r can be, but is not limited to, a range of values ​​of 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, or any two of the above values.

[0049] In some embodiments, the battery cell also includes a housing, with the positive electrode plate located inside the housing, and reinforcing ribs provided inside the housing.

[0050] In the above embodiments, the addition of reinforcing ribs can help improve the compressive strength of the battery cells.

[0051] A battery cell, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to activate its active materials and continue to be used. Typically, a battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrodes and mainly serves to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0052] The following is a detailed introduction to each part of a single battery cell.

[0053] [Positive electrode plate]

[0054] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0055] 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 material substrate and a metal layer formed on at least one side of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0056] In some embodiments, the positive electrode film 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.

[0057] In some embodiments, the positive electrode film 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.

[0058] 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.

[0059] [Negative electrode plate]

[0060] In some embodiments, the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector.

[0061] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0062] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one side of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0063] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxysulfides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxysulfides, and tin alloys. However, the present invention is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0064] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0065] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0066] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0067] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0068] Electrolyte

[0069] In some implementations, the battery cell also includes an electrolyte.

[0070] During the charging and discharging process of a single battery cell, active ions repeatedly insert and extract between the positive and negative electrode plates, while the electrolyte acts as a conductor for these active ions. This invention does not impose any particular restrictions on the type of electrolyte; it can be selected according to actual needs.

[0071] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This invention does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0072] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0073] In some embodiments, the electrolyte salt may be selected from one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0074] In some embodiments, the solvent may be selected from at least one of ether solvents, carbonate solvents, fluoroether diluents, and sulfone solvents.

[0075] As an example, the solvent may be selected from one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0076] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0077] [Isolation membrane]

[0078] In some embodiments, the battery cell further includes a separator. The present invention does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0079] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0080] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0081] In some embodiments, the battery cell may include a housing. The housing may be used to encapsulate the electrode assembly and electrolyte described above.

[0082] In some embodiments, the casing of the battery cell can be a rigid casing, such as a hard plastic casing, an aluminum casing, or a steel casing. The casing of the battery cell can also be a pouch, such as a pouch-type pouch. The material of the pouch can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0083] The present invention does not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape.

[0084] In some embodiments, the housing may include a shell and a cover plate. The shell may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The shell has an opening communicating with the receiving cavity, and the cover plate can be placed over the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator can be formed into electrode assemblies using a winding process or a stacking process. The electrode assemblies are encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assemblies. The number of electrode assemblies contained in a single battery cell can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0085] Preparation method of battery cell

[0086] Secondly, embodiments of the present invention provide a method for preparing a battery cell as described in the first aspect of the present invention, the method comprising:

[0087] Provides sodium-containing positive electrode active material particles;

[0088] A lithium source is added to a solvent to form a lithium-containing precursor solution;

[0089] Sodium-containing positive electrode active material particles and lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles.

[0090] The sodium-containing positive electrode active material particles with a lithium-containing coating slurry layer are heat-treated to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a part of the surface of the core. The core includes the sodium-containing positive electrode active material particles, the coating layer includes lithium-containing positive electrode active material particles, and the crystal structures of the sodium-containing positive electrode active material particles and the lithium-containing positive electrode active material particles are the same;

[0091] The positive electrode active material, a conductive agent, and a binder are added to an organic solvent to form a positive electrode slurry; then the positive electrode slurry is coated on the surface of a positive electrode current collector to form a positive electrode slurry layer, and after drying, a positive electrode plate is obtained;

[0092] The positive electrode plate, a negative electrode plate, a separator, and an electrolyte are assembled to obtain a battery cell.

[0093] In some embodiments, during the spray drying process, the inlet air temperature is 180°C to 220°C, the atomization pressure is 0.2 MPa to 0.5 MPa, and the feeding rate is 5 mL / min to 10 mL / min.

[0094] In some embodiments, the chemical formula of the sodium-containing positive electrode active material particles includes NaMmKbO2, where 0 < m ≤ 1, 0 ≤ b ≤ 0.2, the M element includes transition metal elements, and the K element includes at least one of C, Si, W, Zr, and Ti.

[0095] In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, and lithium acetate.

[0096] In some embodiments, the volume molar concentration of lithium element in the lithium-containing precursor solution is 0.2 mol / L to 0.5 mol / L.

[0097] In some embodiments, the heat treatment temperature is 300°C to 600°C, and the heat treatment time is 2 h to 5 h. <>

[0098] Secondary batteries

[0099] In a third aspect, an embodiment of the present invention provides a secondary battery, which includes the battery cell in the above embodiment or the battery cell prepared by the above preparation method.

[0100] In this article, a "secondary battery" refers to a secondary battery cell, a battery module, or a battery pack.

[0101] In some embodiments, the battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0102] In a battery module, multiple battery cells can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these battery cells can be secured using fasteners.

[0103] In some embodiments, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0104] 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.

[0105] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0106] Electrical appliances

[0107] Fourthly, the present invention also provides an electrical device, which includes a secondary battery provided by the present invention. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of 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.

[0108] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0109] The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0110] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0111] I. Implementation Examples

[0112] The following describes embodiments of the present invention. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0113] Example 1

[0114] This embodiment provides a method for preparing a single battery cell, including:

[0115] 1) Preparation of positive electrode active materials

[0116] 500g of NaNiO2 layered oxide is provided, wherein the average particle size of the layered oxide is 0.5μm;

[0117] 4.4 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0118] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0119] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 600°C for 3 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least part of the surface of the core. The core includes NaNiO2 layered oxide, and the coating layer includes LiNiO2 layered oxide. The thickness of the coating layer is approximately 20 nm.

[0120] 2) Preparation of positive electrode sheet

[0121] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0122] 3) Preparation of negative electrode sheet

[0123] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0124] 4) Separating membrane

[0125] Polypropylene film is used as the separator.

[0126] 5) Preparation of electrolyte

[0127] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0128] 6) Battery manufacturing

[0129] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0130] Example 2

[0131] This invention provides a method for preparing a single battery cell, comprising:

[0132] 1) Preparation of positive electrode active materials

[0133] 500g of NaNiO2 layered oxide is provided, wherein the average particle size of the layered oxide is 0.5μm;

[0134] 6.6 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.3 mol / L.

[0135] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 200°C, the atomization pressure is 0.3 MPa, and the feed rate is 6 mL / min.

[0136] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer were kept at 600°C for 3.5 h to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least part of the surface of the core. The core includes NaNiO2 layered oxide, the coating layer includes LiNiO2 layered oxide, and the thickness of the coating layer is approximately 40 nm.

[0137] 2) Preparation of positive electrode sheet

[0138] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0139] 3) Preparation of negative electrode sheet

[0140] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0141] 4) Separating membrane

[0142] Polypropylene film is used as the separator.

[0143] 5) Preparation of electrolyte

[0144] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0145] 6) Battery manufacturing

[0146] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0147] Example 3

[0148] This invention provides a method for preparing a single battery cell, comprising:

[0149] 1) Preparation of positive electrode active materials

[0150] 500g of NaNiO2 layered oxide is provided, wherein the average particle size of the layered oxide is 0.5μm;

[0151] 8.8 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.4 mol / L.

[0152] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 250°C, the atomization pressure is 0.4 MPa, and the feed rate is 7 mL / min.

[0153] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 600°C for 4 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes NaNiO2 layered oxide, and the coating layer includes LiNiO2 layered oxide. The thickness of the coating layer is approximately 50 nm.

[0154] 2) Preparation of positive electrode sheet

[0155] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0156] 3) Preparation of negative electrode sheet

[0157] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0158] 4) Separating membrane

[0159] Polypropylene film is used as the separator.

[0160] 5) Preparation of electrolyte

[0161] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0162] 6) Battery manufacturing

[0163] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0164] Example 4

[0165] This invention provides a method for preparing a single battery cell, comprising:

[0166] 1) Preparation of positive electrode active materials

[0167] 500g of NaNiO2 layered oxide is provided, wherein the average particle size of the layered oxide is 0.5μm;

[0168] 11.1 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.5 mol / L.

[0169] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 280°C, the atomization pressure is 0.5 MPa, and the feed rate is 8 mL / min.

[0170] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer were heat-treated at 600°C for 4.5 h to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes NaNiO2 layered oxide, and the coating layer includes LiNiO2 layered oxide. The thickness of the coating layer is approximately 55 nm.

[0171] 2) Preparation of positive electrode sheet

[0172] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0173] 3) Preparation of negative electrode sheet

[0174] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0175] 4) Separating membrane

[0176] Polypropylene film is used as the separator.

[0177] 5) Preparation of electrolyte

[0178] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0179] 6) Battery manufacturing

[0180] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0181] Example 5

[0182] This invention provides a method for preparing a single battery cell, comprising:

[0183] 1) Preparation of positive electrode active materials

[0184] 500g of NaNiO2 layered oxide is provided, wherein the average particle size of the layered oxide is 0.8μm;

[0185] 4.4 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0186] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0187] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 600°C for 3 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least part of the surface of the core. The core includes NaNiO2 layered oxide, and the coating layer includes LiNiO2 layered oxide. The thickness of the coating layer is approximately 20 nm.

[0188] 2) Preparation of positive electrode sheet

[0189] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0190] 3) Preparation of negative electrode sheet

[0191] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0192] 4) Separating membrane

[0193] Polypropylene film is used as the separator.

[0194] 5) Preparation of electrolyte

[0195] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0196] 6) Battery manufacturing

[0197] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0198] Example 6

[0199] This invention provides a method for preparing a single battery cell, comprising:

[0200] 1) Preparation of positive electrode active materials

[0201] 500g of layered NaNiO2 oxide is provided, wherein the average particle size of the layered oxide is 1μm;

[0202] 4.4 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0203] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0204] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 600°C for 3 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least part of the surface of the core. The core includes NaNiO2 layered oxide, and the coating layer includes LiNiO2 layered oxide. The thickness of the coating layer is approximately 20 nm.

[0205] 2) Preparation of positive electrode sheet

[0206] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0207] 3) Preparation of negative electrode sheet

[0208] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0209] 4) Separating membrane

[0210] Polypropylene film is used as the separator.

[0211] 5) Preparation of electrolyte

[0212] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0213] 6) Battery manufacturing

[0214] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0215] Example 7

[0216] This invention provides a method for preparing a single battery cell, comprising:

[0217] 1) Preparation of positive electrode active materials

[0218] 500g of layered NaNiO2 oxide is provided, wherein the average particle size of the layered oxide is 2μm;

[0219] 4.4 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0220] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0221] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 600°C for 3 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least part of the surface of the core. The core includes NaNiO2 layered oxide, and the coating layer includes LiNiO2 layered oxide. The thickness of the coating layer is approximately 20 nm.

[0222] 2) Preparation of positive electrode sheet

[0223] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0224] 3) Preparation of negative electrode sheet

[0225] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0226] 4) Separating membrane

[0227] Polypropylene film is used as the separator.

[0228] 5) Preparation of electrolyte

[0229] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0230] 6) Battery manufacturing

[0231] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0232] Example 8

[0233] This invention provides a method for preparing a single battery cell, comprising:

[0234] 1) Preparation of positive electrode active materials

[0235] 500g of NaNiO2 layered oxide is provided, wherein the average particle size of the layered oxide is 2.5μm;

[0236] 4.4 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0237] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0238] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 600°C for 3 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least part of the surface of the core. The core includes NaNiO2 layered oxide, and the coating layer includes LiNiO2 layered oxide. The thickness of the coating layer is approximately 20 nm.

[0239] 2) Preparation of positive electrode sheet

[0240] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0241] 3) Preparation of negative electrode sheet

[0242] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0243] 4) Separating membrane

[0244] Polypropylene film is used as the separator.

[0245] 5) Preparation of electrolyte

[0246] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0247] 6) Battery manufacturing

[0248] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0249] Example 9

[0250] This embodiment provides a method for preparing a single battery cell, including:

[0251] 1) Preparation of positive electrode active materials

[0252] Provides 500g of NaNi with spinel crystal structure 0.5 Mn 1.5 O4, wherein the NaNi 0.5 Mn 1.5 The average particle size of O4 is 0.5 μm;

[0253] 4.4 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0254] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0255] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 350°C for 3 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes NaNi. 0.5 Mn 1.5 O4, the coating layer includes LiNi 0.5 Mn1.5 O4, and the coating thickness is approximately 20 nm.

[0256] 2) Preparation of positive electrode sheet

[0257] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0258] 3) Preparation of negative electrode sheet

[0259] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0260] 4) Separating membrane

[0261] Polypropylene film is used as the separator.

[0262] 5) Preparation of electrolyte

[0263] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0264] 6) Battery manufacturing

[0265] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0266] The differences between Examples 2-9 and Example 1 are shown in Table 1.

[0267] Comparative Example 1

[0268] This comparative example provides a method for preparing a single battery cell, including:

[0269] 1) Preparation of positive electrode sheet

[0270] 500g of spinel crystal structure NaNi 0.5 Mn 1.5 O4 (NaNi) 0.5 Mn 1.5 O4 (with an average particle size of 0.5 μm), polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0271] 2) Preparation of negative electrode sheet

[0272] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0273] 3) Separating membrane

[0274] Polypropylene film is used as the separator.

[0275] 4) Preparation of electrolyte

[0276] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0277] 5) Battery manufacturing

[0278] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0279] Comparative Example 2

[0280] This comparative example provides a method for preparing a single battery cell, including:

[0281] 1) Preparation of positive electrode sheet

[0282] 500g of layered NaNiO2 (average particle size 0.5μm), polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0283] 2) Preparation of negative electrode sheet

[0284] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0285] 3) Separating membrane

[0286] Polypropylene film is used as the separator.

[0287] 4) Preparation of electrolyte

[0288] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0289] 5) Battery manufacturing

[0290] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0291] Comparative Example 3

[0292] This comparative example provides a method for preparing a single battery cell, including:

[0293] 1) Preparation of positive electrode sheet

[0294] 500g of layered NaCoO2 (average particle size 0.5μm), polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0295] 2) Preparation of negative electrode sheet

[0296] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0297] 3) Separating membrane

[0298] Polypropylene film is used as the separator.

[0299] 4) Preparation of electrolyte

[0300] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0301] 5) Battery manufacturing

[0302] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0303] Comparative Example 4

[0304] This comparative example provides a method for preparing a single battery cell, including:

[0305] 1) Preparation of positive electrode active materials

[0306] Provides 500g of NaNi with spinel crystal structure 0.5 Mn 1.5 O4, wherein the NaNi0.5 Mn 1.5 The average particle size of O4 is 0.5 μm;

[0307] 4.4 g of lithium carbonate was added to 600 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0308] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0309] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heated at 200°C for 1 hour to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes NaNi. 0.5 Mn 1.5 O4, the coating layer includes LiNiO2 with a spinel crystal structure, and the thickness of the coating layer is approximately 20 nm.

[0310] 2) Preparation of positive electrode sheet

[0311] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0312] 3) Preparation of negative electrode sheet

[0313] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0314] 4) Separating membrane

[0315] Polypropylene film is used as the separator.

[0316] 5) Preparation of electrolyte

[0317] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0318] 6) Battery manufacturing

[0319] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0320] Comparative Example 5

[0321] This comparative example provides a method for preparing a single battery cell, including:

[0322] 1) Preparation of positive electrode active materials

[0323] 500g of NaNiO2 layered oxide is provided, wherein the average particle size of the layered oxide is 0.5μm;

[0324] 4.4 g of lithium carbonate and 6 g of manganese sulfate were added to 800 mL of water to form a lithium precursor solution, wherein the volume molar concentration of lithium in the lithium precursor solution was approximately 0.2 mol / L.

[0325] The sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. During the spray drying process, the inlet air temperature is 190°C, the atomization pressure is 0.25 MPa, and the feed rate is 5 mL / min.

[0326] Sodium-containing positive electrode active material particles with a lithium-coated slurry layer were heated at 600°C for 5 hours to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core comprises a layered NaNiO2 oxide, and the coating layer comprises LiNiO2. 0.5 Mn 1.5 O4, and the coating thickness is approximately 20 nm.

[0327] 2) Preparation of positive electrode sheet

[0328] The above-mentioned positive electrode active material, polyvinylidene fluoride binder, and carbon black conductive agent were mixed at a mass ratio of 8:1:1, and 1000 mL of N-methylpyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of aluminum foil to form a positive electrode slurry layer with a thickness of 100 μm (single-sided). After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0329] 3) Preparation of negative electrode sheet

[0330] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and carbon black (Super P) (conductive agent) were mixed in 1000 mL of deionized water solvent at a weight ratio of 96:1:3 to prepare a cathode slurry. The cathode slurry was uniformly coated onto the surface of copper foil to form a 100 μm thick (single-sided) cathode slurry layer. After drying, pressing, trimming, cutting, and slitting, the cathode sheets were prepared.

[0331] 4) Separating membrane

[0332] Polypropylene film is used as the separator.

[0333] 5) Preparation of electrolyte

[0334] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium bis(fluorosulfonyl)imide (NaFSI), 1,2-dimethoxyethane (DME), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed in a molar ratio of 1:1.2:1 and stirred until homogeneous to obtain the electrolyte.

[0335] 6) Battery manufacturing

[0336] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly, with the separator positioned between the positive and negative electrodes. Tabs are welded to the electrode assembly, and the assembly with the tabs is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed to obtain a non-charged battery cell. This non-charged battery cell then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a complete battery cell.

[0337] The differences between Comparative Examples 1-5 are shown in Table 1.

[0338] II. Battery Performance Testing

[0339] 1. Cycle count test

[0340] The prepared sodium secondary battery was left to stand for 30 minutes at 25°C, then charged to 3.65V with a constant current of 0.33C, and then charged to 0.05C with a constant voltage of 3.65V. After standing for 1 hour, it was discharged to 1.5V with a constant current of 0.33C to obtain the initial capacity (C0). After standing for 1 hour, it was charged to 3.65V with a constant current of 0.33C again, and then charged to 0.05C with a constant voltage of 3.65V until the current dropped to 0.05C. After standing for 1 hour, it was discharged to 1.5V with a constant current of 0.33C to obtain the intermediate capacity (C1). The above steps were repeated for the same battery, and the number of cycles N when the cycle capacity decayed to 80% was recorded. The test results are shown in Table 1.

[0341] The test results are shown in Table 1.

[0342] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0343] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below. Table 1 Test results of Examples 1-9 and Comparative Examples 1-5

[0344]

[0345]

[0346] As can be seen from the comparison of Examples 1-9 and Comparative Examples 1-5, the crystal structure of the sodium-containing positive electrode active material particles in the core is the same as the crystal structure of the lithium-containing positive electrode active material particles in the coating layer, which enables the battery cell to have good cycle performance.

[0347] The test results of Examples 1-8 show that the average particle size r of the core and the thickness d of the coating layer satisfy: 5≤r / d≤30, which can further improve the cycle performance of the battery cell.

[0348] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A battery cell, characterized in that, The battery cell includes a positive electrode sheet, which comprises: Positive current collector, and A positive electrode film layer is located on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes sodium-containing positive electrode active material particles, and the coating layer includes lithium-containing positive electrode active material particles. The crystal structure of the sodium-containing positive electrode active material particles is the same as that of the lithium-containing positive electrode active material particles.

2. The battery cell according to claim 1, characterized in that, The crystal structure of the sodium-containing positive electrode active material particles includes a layered crystal structure and / or a spinel crystal structure.

3. The battery cell according to claim 2, characterized in that, The chemical formula of the sodium-containing positive electrode active material particles includes NaM m K b O f , where 0 < m ≤ 2, 0 ≤ b ≤ 0.2, 2 ≤ f ≤ 4, the M element includes transition metal elements, and the K element includes at least one of C, Si, W, Zr, and Ti; Alternatively, the chemical formula of the lithium-containing positive electrode active material particles includes LiN n G g O t , where 0 < n ≤ 2, 0 ≤ g ≤ 0.2, 2 ≤ t ≤ 4, the M element includes transition metal elements, and the G element includes at least one of C, Si, W, Zr, and Ti.

4. The battery cell according to claim 1, characterized in that, The average particle size r of the core and the thickness d of the coating layer satisfy: 5 ≤ r / d ≤ 30.

5. The battery cell according to claim 4, characterized in that, 10nm≤d≤40nm; And / or, 0.5μm≤r≤1.5μm.

6. The battery cell according to claim 1, characterized in that, The battery cell also includes a housing, the positive electrode is located inside the housing, and the housing is provided with reinforcing ribs.

7. A method for preparing a battery cell according to any one of claims 1 to 6, characterized in that, The preparation method includes: Provides sodium-containing positive electrode active material particles; A lithium source is added to a solvent to form a lithium-containing precursor solution; Sodium-containing positive electrode active material particles and the lithium-containing precursor solution are mixed and spray-dried to form a lithium-containing coating slurry layer on at least a portion of the surface of the sodium-containing positive electrode active material particles. The sodium-containing positive electrode active material particles with a lithium-coated slurry layer are heat-treated to obtain a positive electrode active material. The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes the sodium-containing positive electrode active material particles, and the coating layer includes lithium-containing positive electrode active material particles. The crystal structure of the sodium-containing positive electrode active material particles is the same as that of the lithium-containing positive electrode active material particles. The positive electrode active material, conductive agent, and binder are added to an organic solvent to prepare a positive electrode slurry; then the positive electrode slurry is coated onto the surface of the positive electrode current collector to form a positive electrode slurry layer, and after drying, a positive electrode sheet is obtained; The positive electrode, negative electrode, separator, and electrolyte are assembled to obtain a single battery cell.

8. The preparation method according to claim 7, characterized in that, During the spray drying process, the inlet air temperature is 180℃~220℃, the atomization pressure is 0.2MPa~0.5MPa, and the feed rate is 5mL / min~10mL / min; And / or, the chemical formula of the sodium-containing positive electrode active material particles includes NaM m K b O f , where 0 < m ≤ 2, 0 ≤ b ≤ 0.2, 2 ≤ f ≤ 4, the M element includes transition metal elements, and the K element includes at least one of C, Si, W, Zr, and Ti; And / or, the volume molar concentration of lithium in the lithium-containing precursor solution is 0.2 mol / L to 0.5 mol / L; And / or, the heat treatment temperature is 300℃~600℃, and the heat treatment time is 2h~5h.

9. A secondary battery, characterized in that, The battery cell includes any one of claims 1 to 6 or the battery cell prepared by the preparation method described in claims 6 to 7.

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

Images