Positive electrode active material, method of making the same, and positive electrode sheet, battery, and electric device comprising the same

Abstract

The application discloses a positive electrode active material, a preparation method thereof, and a positive electrode sheet, a battery and an electric device comprising the same. The positive electrode active material comprises a substrate and a coating layer formed on at least a part of the surface of the substrate; the substrate comprises a sodium-containing layered transition metal oxide; the coating layer comprises a sodium supplementing material; the coating layer comprises Na elements, M elements and O elements, M represents a transition metal; and the coating layer satisfies: the concentration of the Na elements presents a decreasing trend from the surface of the coating layer away from the substrate to the surface of the coating layer close to the substrate. The application can make the battery have high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

Description

Technical Field

[0001] This application relates to a positive electrode active material, a method for preparing the same, and a positive electrode sheet, battery, and electrical device containing the same. Background Technology

[0002] In recent years, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Currently, lithium batteries still occupy the core position in the battery industry, but they also face significant challenges, such as the increasing scarcity of lithium resources. Sodium resources are far more abundant and widely distributed than lithium resources, and their cost is much lower than that of lithium. Therefore, sodium batteries have become a promising next-generation electrochemical system to replace lithium batteries. Similar to lithium batteries, sodium batteries form a solid electrolyte interphase (SEI) film on the surface of the negative electrode during the first charge. This process irreversibly consumes the active sodium of the positive electrode, thereby reducing the battery's initial discharge capacity and initial coulombic efficiency.

[0003] Adding sodium to the positive electrode is one of the effective methods to solve the above problems. Currently, methods for adding sodium to the positive electrode mainly include sodium powder spraying and the introduction of sodium additives. The sodium powder spraying method has extremely stringent environmental requirements, making large-scale production and application difficult. The sodium additive method involves adding sodium additives to the positive electrode slurry to form the positive electrode sheet. Within the operating range of a sodium battery, the sodium additive decomposes and provides active sodium, thereby compensating for the loss of active sodium and improving the battery's initial discharge specific capacity and initial coulombic efficiency. However, currently used sodium additives have the following problems: the products after sodium removal from the additive are inactive, thus reducing the battery's energy density; and the additive easily decomposes and produces gas, thus affecting the battery's cycle performance.

[0004] The above statements are for the purpose of providing background information in relation to this application only and do not necessarily constitute prior art. Summary of the Invention

[0005] This application provides a positive electrode active material, a method for preparing the same, and a positive electrode sheet, a battery, and an electrical device containing the same, which enables the battery to have high initial discharge capacity, high initial coulombic efficiency, and good cycle performance.

[0006] The first aspect of this application provides a positive electrode active material, the positive electrode active material comprising a substrate and a coating layer formed on at least a portion of the surface of the substrate; the substrate comprises a sodium-containing layered transition metal oxide; the coating layer comprises a sodium-supplementing material, the coating layer comprising Na, M, and O elements, where M represents a transition metal; and the coating layer satisfies the following: the concentration of Na element decreases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate.

[0007] The positive electrode active material includes a substrate and a coating layer formed on at least a portion of the substrate surface. The coating layer includes a sodium-replenishing material. During the first charge of the battery, the active sodium in the sodium-replenishing material can compensate for the active sodium loss caused by the formation of the SEI film on the negative electrode, thereby improving the battery's initial discharge specific capacity and initial coulombic efficiency. The concentration of Na in the coating layer decreases from the surface of the coating layer away from the substrate to the surface of the coating layer closer to the substrate, which facilitates the removal of active sodium, thus contributing to a higher initial discharge specific capacity and a higher initial coulombic efficiency.

[0008] The coating layer includes Na, M, and O elements, thus reducing the risk of sodium-containing materials decomposing and generating gas in the coating layer. This ensures good adhesion between the positive electrode film and the positive electrode current collector, resulting in excellent battery cycle performance. Furthermore, the positive electrode active material provided in this embodiment is stable in air and has low environmental requirements.

[0009] Therefore, the positive electrode active material provided in this application embodiment can enable the battery to have high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0010] In any embodiment, the sodium-containing layered transition metal oxide includes an element M′, where M′ represents a transition metal, and the average valence of the M′ element in the sodium-containing layered transition metal oxide is greater than the average valence of the M element in the coating layer. The lower average valence of the transition metal element in the coating layer results in higher stability and a lower risk of decomposition and gas generation, thereby further improving the adhesion between the positive electrode film and the positive electrode current collector, reducing the positive electrode contact resistance, and ultimately further improving the cycle performance of the battery.

[0011] In any embodiment, the coating layer satisfies the following condition: the average valence of element M increases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate. This can improve the stability of the coating layer, reduce the risk of coating layer decomposition and gas generation, thereby further improving the adhesion between the positive electrode film layer and the positive electrode current collector, reducing the positive electrode contact resistance, and thus further improving the cycle performance of the battery.

[0012] In any embodiment, in the coating layer, M includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti, and may be selected as including two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

[0013] In any embodiment, in the sodium-containing layered transition metal oxide, M′ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti, and may be selected as including two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

[0014] In any embodiment, the coating layer is formed in situ on at least a portion of the substrate surface. Because the coating layer is formed in situ on at least a portion of the substrate surface, the bonding strength between the coating layer and the substrate is high. After the active sodium in the sodium-replenishing material is removed, the remaining material (i.e., the residual product after sodium removal from the sodium-replenishing material) can also allow the coating layer to isolate the electrolyte from direct contact with the substrate, thereby reducing battery side reactions and further improving the battery's cycle performance. Furthermore, after the active sodium in the sodium-replenishing material is removed, the remaining material (i.e., the residual product after sodium removal from the sodium-replenishing material) can stably exist in the coating layer, thereby reducing the probability of transition metal ions in the remaining material (i.e., the residual product after sodium removal from the sodium-replenishing material) dissolving into the electrolyte, further improving the battery's cycle performance.

[0015] In any embodiment, the thickness H of the coating layer and the average diameter D of the positive electrode active material satisfy: 0 < H / D ≤ 0.15, optionally, 0.02 ≤ H / D ≤ 0.11. This effectively reduces side reactions between the electrolyte and the substrate, thereby improving the battery's cycle performance and contributing to high initial discharge specific capacity and high initial coulombic efficiency.

[0016] In any embodiment, the weight content of the coating layer in the positive electrode active material is 2%-40%, optionally 5%-20%, based on the total weight of the positive electrode active material. This allows the battery to possess high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0017] In any embodiment, the volume distribution particle size Dv50 of the positive electrode active material is 1μm-10μm, optionally 3μm-8μm. A volume distribution particle size Dv50 within the above range can further improve the ion transport and electron transport performance of the positive electrode active material, and can also reduce side reactions between the electrolyte and the matrix material, thereby contributing to improved battery cycle performance and / or rate performance.

[0018] In any embodiment, the molar ratio of Na, M, and O in the coating layer is (1-6):(1-2):(2-4), and optionally, the molar ratio of Na, M, and O is (1-6):1:(2-4). This can improve the initial discharge specific capacity and initial coulombic efficiency of the battery.

[0019] In any embodiment, the coating layer includes one or more of NaMO2, Na2MO2, Na2MO3, Na3MO2, Na3MO3, Na4MO3, Na5MO3, Na5MO4, and Na6MO4, and may optionally include two or more of NaMO2, Na2MO2, Na2MO3, Na3MO2, Na3MO3, Na4MO3, Na5MO3, Na5MO4, and Na6MO4. Optionally, M independently includes any one of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

[0020] In any embodiment, the sodium-containing layered transition metal oxide includes Na. c N d M″ e P f O g Q h , 0.67≤c≤1.2, 0≤d≤1 / 3, 0<e≤1, 0≤f≤1 / 3, 1.9≤g≤2, 0≤h≤0.1, and the values ​​of c, d, e, f, g, and h satisfy the charge balance of the chemical formula; M″ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti, and may be selected as two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; N includes one or more metallic elements from Group IA, Group IIA, and Zn, and may be selected as one or more of Li, Mg, Ca, and Zn; P includes one or more of a first metallic element and a first nonmetallic element, wherein the first metallic element The first nonmetallic element includes one or more nonmetallic elements from Groups IA, IIA, IIIA, IVA, VA, IIB, IVB, VB, and VIB, and may be selected from Li, Zr, Sb, Nb, Mg, Ca, Mo, Zn, W, Bi, Sn, Ge, Al, Ba, and Sr. The second nonmetallic element includes one or more nonmetallic elements from Groups IIIA, IVA, VA, and VIA, and may be selected from Si, P, B, S, and Se. Q includes one or more nonmetallic elements from Groups VA and VIIA, and may be selected from F, Cl, and N.

[0021] In any embodiment, the sodium-containing layered transition metal oxide includes one or more of the O3 phase, P2 phase, and P3 phase.

[0022] In any embodiment, the sodium-supplementing material in the coating layer has a weight content of 97% or more, optionally 97%-99%, based on the total weight of the coating layer.

[0023] In any embodiment, the coating layer further includes one or more of sodium oxide, sodium hydroxide, and sodium carbonate.

[0024] In any embodiment, the sodium-containing layered transition metal oxide includes an M′ element and a non-variable valence metal element, where M′ represents a transition metal, and the coating layer also includes one or more of oxides of non-variable valence metal elements and salts of non-variable valence metal elements.

[0025] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps: providing a sodium-containing layered transition metal oxide and an aryl sodium solution; mixing the sodium-containing layered transition metal oxide and the aryl sodium solution to react, and after the reaction is completed, washing and drying to obtain a powder; sintering the obtained powder under an inert gas atmosphere to obtain a positive electrode active material, wherein the positive electrode active material comprises a matrix and a coating layer formed on at least a portion of the surface of the matrix; the matrix comprises a sodium-containing layered transition metal oxide; the coating layer comprises a sodium-supplementing material, the coating layer comprising Na, M, and O elements, where M represents a transition metal; and the coating layer satisfies the following condition: the concentration of Na element decreases from the surface of the coating layer away from the matrix to the surface of the coating layer near the matrix.

[0026] The preparation method of the positive electrode active material provided in this application embodiment is simple and suitable for large-scale production.

[0027] The positive electrode active material prepared by the preparation method provided in the embodiments of this application can enable the battery to have high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0028] In any embodiment, in the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution, the molar ratio of the sodium-containing layered transition metal oxide to the Na element in the aryl sodium is 1:(0.01-0.2), optionally 1:(0.05-0.1). When the molar ratio of the sodium-containing layered transition metal oxide to the Na element in the aryl sodium is within the above range, it is beneficial to form a coating layer in situ on the substrate surface, and also beneficial to obtain a positive electrode active material with high structural stability, thereby contributing to a battery that possesses both high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0029] In any embodiment, in the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution, the reaction temperature is 15℃-60℃, optionally 25℃-45℃. A reaction temperature within this range is beneficial for increasing the reaction rate, shortening the reaction time, improving the bonding strength between the coating layer and the substrate, and reducing the probability of coating layer detachment during sintering. Furthermore, a reaction temperature within this range is also beneficial for reducing sodium loss and for the battery to possess high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0030] In any embodiment, the reaction time for mixing the sodium-containing layered transition metal oxide with the aryl sodium solution is 5 h-20 h, optionally 8 h-16 h. A reaction time within this range is beneficial for increasing the reaction rate, shortening the reaction time, improving the bonding strength between the coating layer and the substrate, and reducing the probability of coating layer detachment during sintering. Furthermore, a reaction time within this range also helps reduce sodium loss and contributes to a battery exhibiting high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0031] In any embodiment, in the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution, the reaction is carried out under stirring conditions. Optionally, the stirring speed is 100 r / min-1000 r / min, more preferably 200 r / min-700 r / min.

[0032] In any embodiment, in the step of sintering the obtained powder under an inert gas atmosphere, the sintering temperature is 500℃-950℃, optionally 600℃-900℃. When the sintering temperature is within the above range, it is beneficial for the reduced transition metal element and / or low-valence transition metal oxide to react with Na₂O to generate sodium-supplementing material. It also helps to improve the bonding strength between the coating layer and the substrate, thereby contributing to a battery that possesses high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0033] In any embodiment, in the step of sintering the obtained powder under an inert gas atmosphere, the holding time for sintering is 3h-9h, optionally 5h-8h. When the holding time for sintering is within the above range, it is beneficial for the reduced transition metal element and / or low-valence transition metal oxide to react with Na2O to generate sodium-supplementing material. It also helps to improve the bonding strength between the coating layer and the substrate, thereby contributing to a battery that possesses high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0034] In any embodiment, the step of sintering the obtained powder under an inert gas atmosphere includes one or more of argon, helium, nitrogen, and a hydrogen-argon mixture.

[0035] In any embodiment, the concentration of the aryl sodium solution is 0.5 mol / L to 3.5 mol / L, and can be selected as 1 mol / L to 2 mol / L. When the concentration of the aryl sodium solution is within the above range, it is beneficial for the battery to possess high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0036] In any embodiment, the aryl sodium includes one or more of sodium naphthylene, sodium biphenyl, sodium phenylene, sodium phenanthrene, sodium anthracene, sodium pyrene, sodium bipyridine, and sodium tetraphenylene. These aryl sodiums have high electronegativity, which is beneficial for reducing transition metals in the surface layer of sodium-containing layered transition metal oxides.

[0037] In any embodiment, the solvent of the aryl sodium solution includes an aprotic solvent. Therefore, when the sodium-containing layered transition metal oxide reacts with the aryl sodium solution, the extraction of sodium from the interlayers of the sodium-containing layered transition metal oxide can be reduced, thereby contributing to good cycle performance of the battery.

[0038] Optionally, the aprotic solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, N,N-dimethylformamide, diethyl ether, diisopropyl ether, diethylene glycol dimethyl ether, methyl tert-butyl ether, diethyl ether, acetonitrile, and dimethyl sulfoxide. When the aprotic solvent is within the above range, it can reduce the extraction of sodium from the interlayer of sodium-containing layered transition metal oxides, thereby contributing to good cycle performance of the battery.

[0039] In any embodiment, the sodium-containing layered transition metal oxide includes Na. c N d M″ e P f O g Q h, 0.67≤c≤1.2, 0≤d≤1 / 3, 0<e≤1, 0≤f≤1 / 3, 1.9≤g≤2, 0≤h≤0.1, and the values ​​of c, d, e, f, g, and h satisfy the charge balance of the chemical formula; M″ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti, and may be selected as two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; N includes one or more metallic elements from Group IA, Group IIA, and Zn, and may be selected as one or more of Li, Mg, Ca, and Zn; P includes one or more of a first metallic element and a first nonmetallic element, wherein the first metallic element The first nonmetallic element includes one or more nonmetallic elements from Groups IA, IIA, IIIA, IVA, VA, IIB, IVB, VB, and VIB, and may be selected from Li, Zr, Sb, Nb, Mg, Ca, Mo, Zn, W, Bi, Sn, Ge, Al, Ba, and Sr. The second nonmetallic element includes one or more nonmetallic elements from Groups IIIA, IVA, VA, and VIA, and may be selected from Si, P, B, S, and Se. Q includes one or more nonmetallic elements from Groups VA and VIIA, and may be selected from F, Cl, and N.

[0040] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the preparation method of the second aspect of this application.

[0041] In any embodiment, the weight content of the positive electrode active material in the positive electrode film layer is 50%-99%, optionally 80%-99%, based on the total weight of the positive electrode film layer.

[0042] A fourth aspect of this application provides a battery that includes the positive electrode sheet of the third aspect of this application.

[0043] The fifth aspect of this application provides an electrical device that includes the battery of the fourth aspect of this application, said battery being used to provide electrical energy.

[0044] The electrical device of this application includes the battery provided in this application, and therefore has at least the same advantages as the battery. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0047] Figure 2 yes Figure 1 An exploded view of the implementation method of the battery cell.

[0048] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0049] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0050] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0051] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses the battery of this application as a power source.

[0052] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0053] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode active material, its preparation method, and embodiments of the positive electrode sheet, battery, and power device comprising it. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0054] 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.

[0055] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0056] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0057] Unless otherwise specified, all steps in this application 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 method may also include step (c), indicating 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.

[0058] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0059] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0060] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0061] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0062] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0063] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0064] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0065] A single battery cell generally includes an electrode assembly and an electrolyte. The electrode assembly typically includes a positive electrode and a negative electrode. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited in this regard.

[0066] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0067] In some embodiments, such as Figure 2As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0068] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0069] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0070] 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 adjusted according to the application and capacity of the battery pack.

[0071] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0072] The battery provided in the embodiments of this application is a sodium battery, which may include, for example, a sodium-ion battery, a sodium metal battery, a sodium metal battery without a negative electrode, etc. The embodiments of this application are not limited to this.

[0073] A sodium-metal-free battery typically refers to a battery in which no negative electrode active material layer is actively placed on the negative electrode side during the battery manufacturing process. For example, a sodium metal layer or a carbonaceous active material layer is not formed at the negative electrode during manufacturing. During the first charge, sodium ions gain electrons on the negative electrode side and deposit on the surface of the negative electrode current collector to form metallic sodium. During discharge, the metallic sodium can be converted back into sodium ions and return to the positive electrode, achieving cyclic charging and discharging. Compared to other batteries, sodium-metal-free batteries can achieve higher energy density due to the absence of a negative electrode active material layer. In some embodiments, to improve battery performance, conventional materials that can be used as negative electrode active materials, such as carbon materials, can also be placed on the negative electrode side of a sodium-metal-free battery. Although these materials have a certain capacity, their content is small and they are not used as the main negative electrode active material in the battery; therefore, such a battery can still be considered a sodium-metal-free battery. The Cell Balance (CB) value of a sodium metal battery without a negative electrode is typically very small; for example, in some embodiments, the CB value can be less than or equal to 0.1. The CB value is the capacity per unit area of ​​the negative electrode divided by the capacity per unit area of ​​the positive electrode. Because a sodium metal battery without a negative electrode contains little or no negative electrode active material, the capacity per unit area of ​​the negative electrode is small, resulting in a very small CB value, typically less than or equal to 0.1.

[0074] Currently, sodium-supplementing additives used in battery cathodes have the following problems: After the active sodium in some sodium-supplementing additives is released, a high proportion of by-products are left in the cathode film. These by-products are not reactive, which reduces the energy density of the battery. At the same time, the transition metal ions in the by-products can easily dissolve into the electrolyte. Subsequently, these transition metal ions will be reduced and deposited on the anode, which will damage the structure of the SEI film, reduce the battery capacity, and affect the extraction and insertion of sodium ions. Some organic additives (such as sodium oxalate) and inorganic additives (such as sodium carbonate, sodium nitride, sodium peroxide, etc.) are also prone to decomposition and gas production, which will leave more pores in the cathode film. This will reduce the adhesion between the cathode film and the cathode current collector, increase the contact resistance of the cathode, and thus affect the electrochemical performance of the battery.

[0075] In view of this, embodiments of this application propose a novel positive electrode active material that can be used in sodium batteries, enabling sodium batteries to possess high initial discharge capacity, high initial coulombic efficiency, and good cycle performance.

[0076] The positive electrode active material provided in this application includes a substrate and a coating layer formed on at least a portion of the substrate surface. The substrate includes a sodium-containing layered transition metal oxide, and the coating layer includes a sodium-replenishing material. The coating layer includes Na, M, and O elements, where M represents a transition metal. Furthermore, the coating layer satisfies the following condition: the concentration of Na decreases from the surface of the coating layer away from the substrate to the surface of the coating layer closer to the substrate.

[0077] The positive electrode active material includes a substrate and a coating layer formed on at least a portion of the substrate surface. The coating layer includes a sodium-replenishing material. During the first charge of the battery, the active sodium in the sodium-replenishing material can compensate for the active sodium loss caused by the formation of the SEI film on the negative electrode, thereby improving the battery's initial discharge specific capacity and initial coulombic efficiency. The concentration of Na in the coating layer decreases from the surface of the coating layer away from the substrate to the surface of the coating layer closer to the substrate, which facilitates the removal of active sodium, thus contributing to a higher initial discharge specific capacity and a higher initial coulombic efficiency.

[0078] The coating layer includes Na, M, and O elements, thus reducing the risk of sodium-containing materials decomposing and generating gas in the coating layer. This ensures good adhesion between the positive electrode film and the positive electrode current collector, resulting in excellent battery cycle performance. Furthermore, the positive electrode active material provided in this embodiment is stable in air and has low environmental requirements.

[0079] Therefore, the positive electrode active material provided in this application embodiment can enable the battery to have high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0080] The concentration of Na at different locations in the coating layer can be measured using methods such as electron probe microanalysis (EPMA), inductively coupled plasma atomic emission spectrometry (ICP-AES), time-of-flight secondary ion mass spectrometry (ToF-SIMS), EDAX-SEM analysis, X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS).

[0081] In some embodiments, the coating layer is formed in situ on at least a portion of the substrate surface. Because the coating layer is formed in situ on at least a portion of the substrate surface, the bonding strength between the coating layer and the substrate is high. After the active sodium in the sodium-replenishing material is removed, the remaining material (i.e., the residual product after sodium removal from the sodium-replenishing material) can also allow the coating layer to isolate the electrolyte from direct contact with the substrate, thereby reducing battery side reactions and further improving the battery's cycle performance. Furthermore, after the active sodium in the sodium-replenishing material is removed, the remaining material (i.e., the residual product after sodium removal from the sodium-replenishing material) can stably exist in the coating layer, thereby reducing the probability of transition metal ions in the remaining material (i.e., the residual product after sodium removal from the sodium-replenishing material) dissolving into the electrolyte, further improving the battery's cycle performance.

[0082] In some embodiments, the sodium-containing layered transition metal oxide includes an element M′, where M′ represents a transition metal, and the average valence of the element M′ in the sodium-containing layered transition metal oxide can be greater than the average valence of the element M in the coating layer. The lower average valence of the transition metal element in the coating layer results in higher stability and a lower risk of decomposition and gas generation, thereby further improving the adhesion between the positive electrode film and the positive electrode current collector, reducing the positive electrode contact resistance, and ultimately further improving the cycle performance of the battery.

[0083] In some embodiments, the coating layer satisfies the following condition: the average valence of element M increases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate. This can improve the stability of the coating layer, reduce the risk of gas generation from coating layer decomposition, thereby further improving the adhesion between the positive electrode film and the positive electrode current collector, reducing the positive electrode contact resistance, and thus further improving the cycle performance of the battery.

[0084] The average valence of transition metal element M′ in sodium-containing layered transition metal oxides and the average valence of transition metal element M in the coating layer can be measured using X-ray photoelectron spectroscopy (XPS). During the test, high-purity argon gas is used as the etching gas to etch the positive electrode active material sample. By controlling conditions such as light energy and etching time, the average valence of transition metal element M at different locations in the positive electrode active material, such as the coating layer and the average valence of transition metal element M′ in the sodium-containing layered transition metal oxide matrix, can be determined. The testing instrument can be an escalab 250Xi X-ray photoelectron spectrometer from Thermo Fisher Scientific.

[0085] In some embodiments, the thickness H of the coating layer and the average diameter D of the positive electrode active material satisfy the following condition: 0 < H / D ≤ 0.15, optionally, 0.02 ≤ H / D ≤ 0.11. This effectively reduces side reactions between the electrolyte and the substrate, thereby improving the battery's cycle performance and contributing to high initial discharge specific capacity and high initial coulombic efficiency.

[0086] The thickness H of the coating layer can be determined using methods known in the art. As an example, a cross-section of the positive electrode active material particles can be prepared using a cross-section polisher (e.g., the JEOL IB-09010CP argon ion cross-section polisher from Japan), the cross-section passing through the core of the positive electrode active material particles. Then, elemental analysis using energy dispersive spectroscopy (EDS) combined with transmission electron microscopy (TEM) or scanning electron microscopy (SEM) surface scanning is used to obtain the elemental distribution map in the cross-section. The thickness of the coating layer is obtained based on the elemental distribution of the cross-section. During testing, the thickness values ​​of the coating layer at multiple (e.g., more than 10) different locations on the cross-section can be statistically analyzed, and the average value is recorded as the thickness of the coating layer.

[0087] The average diameter D of the positive electrode active material is the average of the diameters of multiple positive electrode active material particles. For example, based on the elemental distribution diagram of the cross-section of the positive electrode active material particles obtained above, the diameters of multiple (e.g., more than 10) different positions on the cross-section can be obtained, and the average value can be recorded as the average diameter D of the positive electrode active material.

[0088] In some embodiments, the volumetric particle size Dv50 of the positive electrode active material can be 1 μm-10 μm, and optionally 3 μm-8 μm. A volumetric particle size Dv50 within the above range can further improve the ion transport and electron transport performance of the positive electrode active material, and can also reduce side reactions between the electrolyte and the matrix material, thereby contributing to improved battery cycle performance and / or rate performance.

[0089] The volume distribution particle size Dv50 of the positive electrode active material has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer according to GB / T 19077-2016. The testing instrument can be the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0090] In some embodiments, the weight content of the coating layer in the positive electrode active material can be 2%-40%, optionally 5%-20%, based on the total weight of the positive electrode active material. This allows the battery to possess high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0091] In some embodiments, in the sodium-containing layered transition metal oxide, M′ may include one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti, and may optionally include two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

[0092] In some embodiments, the sodium-containing layered transition metal oxide includes Na. c N d M″ e P f O g Q h , 0.67≤c≤1.2, 0≤d≤1 / 3, 0<e≤1, 0≤f≤1 / 3, 1.9≤g≤2, 0≤h≤0.1, and the values ​​of c, d, e, f, g, and h satisfy the charge balance of the chemical formula; M″ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; N includes one or more metallic elements from Group IA, Group IIA, and Zn; P includes one or more of a first metallic element and a first nonmetallic element, wherein the first metallic element includes one or more metallic elements from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, and Group VIB, and the first nonmetallic element includes one or more nonmetallic elements from Group IIIA, Group IVA, Group VA, and Group VIA; Q includes one or more nonmetallic elements from Group VA and Group VIIA.

[0093] Optionally, M″ may include two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

[0094] Optionally, N may include one or more elements selected from Li, Mg, Ca, and Zn.

[0095] Optionally, the first metallic element may include one or more elements selected from Li, Zr, Sb, Nb, Mg, Ca, Mo, Zn, W, Bi, Sn, Ge, Al, Ba, and Sr.

[0096] Optionally, the first nonmetallic element may include one or more elements selected from Si, P, B, S, and Se.

[0097] Optionally, Q may include one or more elements selected from F, Cl, and N.

[0098] The elemental content in the matrix and coating layer of the positive electrode active material can be determined using inductively coupled plasma atomic emission spectrometry (ICP) in accordance with EPA 6010D-2014. For example, the cross-section of the positive electrode active material particles can be prepared using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL Corporation of Japan); then, referring to JY / T010-1996, the cross-section of the positive electrode active material particles can be scanned using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and the content can be determined using inductively coupled plasma atomic emission spectrometry (ICP).

[0099] In some embodiments, the sodium-containing layered transition metal oxide may include, but is not limited to, one or more of the O3 phase, P2 phase, and P3 phase.

[0100] In some embodiments, M in the coating layer may include one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti, and may be selected as two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

[0101] In some embodiments, the molar ratio of Na, M, and O in the coating layer can be (1-6):(1-2):(2-4), and optionally, the molar ratio of Na, M, and O can be (1-6):1:(2-4). This can improve the initial discharge specific capacity and initial coulombic efficiency of the battery.

[0102] In some embodiments, the coating layer may include one or more of NaMO2, Na2MO2, Na2MO3, Na3MO2, Na3MO3, Na4MO3, Na5MO3, Na5MO4, and Na6MO4. Optionally, M may independently include any one of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti. Optionally, the coating layer may include two or more of NaMO2, Na2MO2, Na2MO3, Na3MO2, Na3MO3, Na4MO3, Na5MO3, Na5MO4, and Na6MO4.

[0103] In some embodiments, the sodium-supplementing material in the coating layer may contain more than 97% by weight, optionally 97%-99%, based on the total weight of the coating layer.

[0104] In some embodiments, the coating layer may further include one or more of sodium oxide, sodium hydroxide, and sodium carbonate.

[0105] In some embodiments, the sodium-containing layered transition metal oxide may include an M′ element and a non-variable valence metal element, where M′ represents a transition metal, and the coating layer may also include one or more of an oxide of a non-variable valence metal element and a salt of a non-variable valence metal element.

[0106] In some embodiments, the morphology of the positive electrode active material may include, but is not limited to, one or more of spherical single crystals, plate-like single crystals, and spherical polycrystalline materials.

[0107] The term "single crystal" also includes quasi-single crystals, which refer to particles composed of a few or a dozen primary particles aggregated together. The term "spherical" also includes quasi-spherical, which refers to particles whose shape is basically spherical or whose aspect ratio is close to 1, for example, an aspect ratio not greater than 1.3, or optionally not greater than 1.2.

[0108] The morphology of the positive electrode active material can be tested using a scanning electron microscope (SEM), for example, according to JY / T010-1996. The testing instrument can be a ZEISS Sigma 300 scanning electron microscope from Germany.

[0109] [Preparation Method]

[0110] This application also provides a method for preparing a positive electrode active material.

[0111] The method includes the following steps: providing a sodium-containing layered transition metal oxide and an aryl sodium solution; mixing the sodium-containing layered transition metal oxide and the aryl sodium solution to react, and after the reaction, washing and drying to obtain a powder; sintering the obtained powder under an inert gas atmosphere to obtain a positive electrode active material. The positive electrode active material includes a substrate and a coating layer formed on at least a portion of the surface of the substrate; the substrate includes a sodium-containing layered transition metal oxide; the coating layer includes a sodium-supplementing material, and the coating layer includes Na, M, and O elements, where M represents a transition metal; and the coating layer satisfies the following condition: the concentration of Na decreases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate.

[0112] The coating layer of the positive electrode active material is obtained by mixing and reacting a sodium-containing layered transition metal oxide with an aryl sodium solution, followed by sintering. Aryl sodium has reducing properties; therefore, after the reaction of the sodium-containing layered transition metal oxide with the aryl sodium solution, the aryl sodium can reduce the transition metal in the surface layer of the sodium-containing layered transition metal oxide. After washing and drying, Na₂O, elemental transition metals, and / or low-valence transition metal oxides can be formed on the surface of the sodium-containing layered transition metal oxide. During subsequent sintering, Na₂O reacts with elemental transition metals and / or low-valence transition metal oxides to generate sodium-replenishing material. Therefore, in-situ sodium replenishment can be achieved through the mixing and reaction of sodium-containing layered transition metal oxides with an aryl sodium solution and sintering.

[0113] The preparation method of the positive electrode active material provided in this application embodiment is simple and suitable for large-scale production.

[0114] The positive electrode active material prepared by the preparation method provided in the embodiments of this application can exist stably in air and has low environmental requirements.

[0115] When the positive electrode active material prepared by the preparation method provided in the embodiments of this application is charged for the first time, the active sodium in the sodium-supplementing material can compensate for the loss of active sodium caused by the formation of SEI film on the negative electrode, thereby improving the first discharge specific capacity and first coulombic efficiency of the battery.

[0116] The positive electrode active material prepared by the preparation method provided in the embodiments of this application can make the concentration of Na element in the coating layer decrease from the surface of the coating layer away from the substrate to the surface of the coating layer close to the substrate. This is beneficial to promote the removal of active sodium, and thus also helps the battery to have a higher initial discharge specific capacity and a higher initial coulombic efficiency.

[0117] The positive electrode active material prepared by the preparation method provided in this application has a low risk of decomposition and gas generation during battery charging and discharging. This allows for good adhesion between the positive electrode film and the positive electrode current collector, reduces the positive electrode contact resistance, and thus enables the battery to have good cycle performance.

[0118] Therefore, the positive electrode active material prepared by the preparation method provided in the embodiments of this application can enable the battery to have high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0119] The coating layer of the positive electrode active material prepared by the preparation method provided in this application is generated in situ on at least a portion of the substrate surface, thus resulting in a high bonding strength between the coating layer and the substrate. After the active sodium in the sodium-to-be-added material is removed, the remaining material (i.e., the residual product after sodium removal from the sodium-to-be-added material) can also allow the coating layer to isolate the electrolyte from direct contact with the substrate, thereby reducing battery side reactions and further improving the battery's cycle performance. In addition, after the active sodium in the sodium-to-be-added material is removed, the remaining material (i.e., the residual product after sodium removal from the sodium-to-be-added material) can stably exist in the coating layer, thereby reducing the probability of transition metal ions in the remaining material (i.e., the residual product after sodium removal from the sodium-to-be-added material) dissolving into the electrolyte, which further improves the battery's cycle performance.

[0120] The sodium-containing layered transition metal oxide includes the element M′, where M′ represents a transition metal. The positive electrode active material prepared by the method provided in this application allows the average valence of the M′ element in the sodium-containing layered transition metal oxide to be higher than the average valence of the M element in the coating layer. The lower average valence of the transition metal element in the coating layer results in higher stability and a lower risk of decomposition and gas generation. This further enhances the adhesion between the positive electrode film and the positive electrode current collector, reduces the positive electrode contact resistance, and consequently improves the battery's cycle performance.

[0121] The coating layer of the positive electrode active material prepared by the preparation method provided in this application satisfies the following condition: the average valence of element M increases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate. This can improve the stability of the coating layer, reduce the risk of gas generation from coating layer decomposition, and thus further improve the adhesion between the positive electrode film layer and the positive electrode current collector, reduce the positive electrode contact resistance, and further improve the cycle performance of the battery.

[0122] In some embodiments, the solute aryl sodium in the aryl sodium solution may include one or more of sodium naphthyl, sodium biphenyl, sodium phenylene, sodium phenanthrene, sodium anthracene, sodium pyrene, sodium bipyridine, and sodium tetraphenylene. These aryl sodiums have high electronegativity, which is beneficial for reducing transition metals on the surface of sodium-containing layered transition metal oxides.

[0123] In some embodiments, the solvent of the aryl sodium solution includes an aprotic solvent. Therefore, when sodium-containing layered transition metal oxides react with the aryl sodium solution, the extraction of sodium from the interlayers of the sodium-containing layered transition metal oxides can be reduced, thereby contributing to good cycle performance of the battery.

[0124] In some embodiments, the aprotic solvent may include, but is not limited to, one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, N,N-dimethylformamide, diethyl ether, diisopropyl ether, diethylene glycol dimethyl ether, methyl tert-butyl ether, diethyl ether, acetonitrile, and dimethyl sulfoxide. When the aprotic solvent is within the above range, it can reduce the extraction of sodium from the interlayer of sodium-containing layered transition metal oxides, thereby contributing to good cycle performance of the battery.

[0125] In some embodiments, the concentration of the aryl sodium solution can be 0.5 mol / L to 3.5 mol / L, for example, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.5 mol / L, or any range of the above values.

[0126] When the concentration of the aryl sodium solution is within the above-mentioned range, it is beneficial for the in-situ formation of a coating layer on the substrate surface and also helps to reduce the residual alkali content on the surface of the prepared positive electrode active material. Residual alkali mainly includes sodium hydroxide and sodium carbonate. Residual alkali easily leads to gelation or solidification of the positive electrode slurry, affecting its coating; sodium carbonate in residual alkali has poor thermal stability and easily decomposes and generates gas under high pressure; residual alkali lacks electrochemical activity, and its increased content hinders sodium ion transport. Therefore, when the concentration of the aryl sodium solution is within the above-mentioned range, it is beneficial for the battery to possess high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0127] Optionally, the concentration of the sodium arylate solution can be 1 mol / L to 2 mol / L.

[0128] Aryl sodium solutions can be prepared according to methods known in the art, and the embodiments of this application are not limited thereto. For example, metallic sodium and aromatic compounds can be reacted in an aprotic solvent to generate highly reactive aryl sodium, thus obtaining an aryl sodium solution.

[0129] In some embodiments, in the step of reacting a sodium-containing layered transition metal oxide with an aryl sodium solution, the molar ratio of the sodium-containing layered transition metal oxide to the Na element in the aryl sodium can be 1:(0.01-0.2), or optionally 1:(0.05-0.1).

[0130] When the molar ratio of sodium-containing layered transition metal oxides to Na in aryl sodium is within the above range, it is beneficial to generate a coating layer in situ on the substrate surface. It is also beneficial to obtain a positive electrode active material with high structural stability, which in turn helps the battery to have high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0131] In some embodiments, the reaction step of mixing a sodium-containing layered transition metal oxide with an aryl sodium solution can be carried out under stirring conditions. This is beneficial for increasing the reaction rate and shortening the reaction time. Optionally, the stirring speed can be 100 r / min-1000 r / min, more preferably 200 r / min-700 r / min.

[0132] In some embodiments, in the step of reacting a sodium-containing layered transition metal oxide with an aryl sodium solution, the reaction temperature can be 15°C-60°C, for example, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, or any range of the above values.

[0133] When the reaction temperature is within the above range, it is beneficial to increase the reaction rate, shorten the reaction time, and also to improve the bonding strength between the coating layer and the substrate, reducing the probability of coating layer detachment during sintering. Furthermore, when the reaction temperature is within the above range, it is also beneficial to reduce sodium loss and to ensure that the battery possesses high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0134] Optionally, the reaction temperature can be 25℃-45℃.

[0135] In some embodiments, in the step of reacting a sodium-containing layered transition metal oxide with an aryl sodium solution, the reaction time can be 5h-20h, for example, 5h, 6h, 7h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, or any range of the above values.

[0136] When the reaction time is within the above-mentioned range, it is beneficial to increase the reaction rate, shorten the reaction time, and also to improve the bonding strength between the coating layer and the substrate, reducing the probability of coating layer detachment during sintering. Furthermore, when the reaction time is within the above-mentioned range, it is also beneficial to reduce sodium loss and to ensure that the battery possesses high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0137] Optionally, the reaction time can be 8h-16h.

[0138] In some embodiments, in the step of sintering the obtained powder under an inert gas atmosphere, the sintering temperature can be 500°C-950°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or any range of the above values.

[0139] When the sintering temperature is within the above range, it is beneficial for the reduced transition metal elements and / or low-valence transition metal oxides to react with Na2O to generate sodium-supplementing materials. It is also beneficial for improving the bonding strength between the coating layer and the substrate, thereby enabling the battery to have both high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0140] Optionally, the sintering temperature can be 600℃-900℃.

[0141] In some embodiments, in the step of sintering the obtained powder under an inert gas atmosphere, the holding time for sintering can be 3h-9h, for example, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or any range of the above values.

[0142] When the holding time of sintering is within the above range, it is beneficial for the reduced transition metal elements and / or low-valence transition metal oxides to react with Na2O to generate sodium-supplementing materials. It is also beneficial for improving the bonding strength between the coating layer and the substrate, thereby enabling the battery to have both high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0143] Optionally, the holding time for sintering can be 5-8 hours.

[0144] By adjusting one or more of the following parameters: the type of aryl sodium, the concentration of the aryl sodium solution, the molar ratio of sodium-containing layered transition metal oxide to Na in the aryl sodium, the reaction parameters of the sodium-containing layered transition metal oxide and the aryl sodium solution (such as reaction temperature, reaction time, stirring rate), sintering temperature, and sintering holding time, the thickness and weight content of the coating layer can be adjusted.

[0145] In some embodiments, the inert gas may include one or more of argon, helium, nitrogen, and a mixture of hydrogen and argon.

[0146] In some embodiments, the sodium-containing layered transition metal oxide includes Na. c N d M″ e P f O g Q h, 0.67≤c≤1.2, 0≤d≤1 / 3, 0<e≤1, 0≤f≤1 / 3, 1.9≤g≤2, 0≤h≤0.1, and the values ​​of c, d, e, f, g, and h satisfy the charge balance of the chemical formula; M″ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; N includes one or more metallic elements from Group IA, Group IIA, and Zn; P includes one or more of a first metallic element and a first nonmetallic element, wherein the first metallic element includes one or more metallic elements from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, and Group VIB, and the first nonmetallic element includes one or more nonmetallic elements from Group IIIA, Group IVA, Group VA, and Group VIA; Q includes one or more nonmetallic elements from Group VA and Group VIIA.

[0147] Optionally, M″ may include two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

[0148] Optionally, N may include one or more elements selected from Li, Mg, Ca, and Zn.

[0149] Optionally, the first metallic element may include one or more elements selected from Li, Zr, Sb, Nb, Mg, Ca, Mo, Zn, W, Bi, Sn, Ge, Al, Ba, and Sr.

[0150] Optionally, the first nonmetallic element may include one or more elements selected from Si, P, B, S, and Se.

[0151] Optionally, Q may include one or more elements selected from F, Cl, and N.

[0152] In some embodiments, the sodium-containing layered transition metal oxide may include, but is not limited to, one or more of the O3 phase, P2 phase, and P3 phase.

[0153] The method for preparing the positive electrode active material according to the embodiments of this application can prepare the positive electrode active material as described in this application. Unless otherwise specified, all raw materials used in the above preparation method can be obtained commercially.

[0154] [Positive electrode plate]

[0155] This application also provides a positive electrode sheet.

[0156] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the positive electrode active material described above or the positive electrode active material prepared by the preparation method described above. This allows the battery to possess high initial discharge specific capacity, high initial coulombic efficiency, and good cycle performance.

[0157] In some embodiments, the content of the positive electrode active material in the positive electrode film layer can be 50% to 99%, optionally 85% to 99%, based on the total weight of the positive electrode film layer.

[0158] The positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0159] The positive electrode film may also include other positive electrode active materials known in the art, such as, but not limited to, one or more of fluorides, sulfides, phosphates, pyrophosphates, metal-organic frameworks / metal hexacyanides, and organic compounds. These other positive electrode active materials may be used alone or in combination of two or more.

[0160] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0161] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resins, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0162] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0163] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0164] [Negative electrode plate]

[0165] Each battery cell includes a negative electrode. The structure and composition of the negative electrode can be selected according to the type of battery cell, and the embodiments of this application are not limited in this regard.

[0166] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0167] The negative electrode active material can be any material known in the art, such as, but not limited to, one or more of soft carbon, hard carbon, and mesophase micro carbon spheres.

[0168] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0169] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0170] In some embodiments, the negative electrode film layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0171] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0172] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0173] In some embodiments, the negative electrode sheet may include a negative current collector and a metal layer disposed on at least one surface of the negative current collector, wherein the metal material in the metal layer may include, but is not limited to, one or more of elemental sodium and sodium alloys.

[0174] Sodium alloys can be alloys formed by metallic sodium with other metallic or non-metallic elements. For example, other metallic elements in sodium alloys may include, but are not limited to, one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, while non-metallic elements in sodium alloys may include one or more of boron, carbon, and silicon.

[0175] In some embodiments, the negative electrode sheet may be a sodium sheet (foil) or a sodium alloy sheet (foil).

[0176] In some embodiments, the negative electrode may include a negative current collector to assemble a sodium metal battery cell without a negative electrode.

[0177] In some embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil. Examples of three-dimensional porous current collectors include copper mesh, nickel mesh, copper foam, nickel foam, and aluminum foam. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, aluminum, aluminum alloys, silver, and silver alloys. Examples of polymer material substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0178] [Electrolytes]

[0179] A single battery cell includes an electrolyte. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte may include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0180] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0181] In some embodiments, as an example, the electrolyte salt may include, but is not limited to, one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0182] In some embodiments, the solvent may include, but is not limited to, one or more of ester solvents, sulfone solvents, and ether solvents. For example, the solvent may include, but is not limited to, one or more of 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 ester 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), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetrahydrofuran.

[0183] In some embodiments, the electrolyte may optionally include additives. For example, the 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, additives that improve battery low-temperature power performance, etc.

[0184] [Isolation membrane]

[0185] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is placed between the positive and negative electrodes, primarily to prevent internal short circuits.

[0186] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0187] In some embodiments, the material of the separator may include, but is not limited to, one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0188] The methods for preparing a single battery cell are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a single battery cell. As an example, the positive electrode, separator, and negative electrode can be wound and / or stacked to form an electrode assembly. The electrode assembly is then placed in an outer package, dried, and injected with the electrolyte. After encapsulation, settling, and formation processes, a single battery cell is obtained. Multiple single battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple single battery cells can also be directly assembled into a battery pack.

[0189] Electrical appliances

[0190] This application also provides an electrical device, which includes a battery provided in this application embodiment. The battery is used to provide electrical energy. The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as 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.

[0191] Electrical devices can choose the specific type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0192] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0193] Another example of an electrical 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.

[0194] Example

[0195] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0196] Example 1

[0197] (1) Preparation of positive electrode active material

[0198] The nickel-manganese precursor was prepared by hydroxide co-precipitation, and then sintered with sodium nitrate at high temperature to obtain the target product Na. 1.05 Ni 0.55 Mn 0.45 O2. Na 1.05 Ni 0.55 Mn 0.45 O2 was added to a 1.5 mol / L sodium naphthalene tetrahydrofuran solution, and the reaction was carried out at a reaction temperature of 25℃ and a stirring speed of 500 r / min for 8 h. Afterwards, the mixture was washed 2-3 times with ethanol, and the resulting powder was placed in a box furnace, purged with nitrogen, and sintered at 750℃ for 5 h to obtain the positive electrode active material. 1.05 Ni 0.55 Mn 0.45 The molar ratio of O2 to Na in sodium naphthalene is 1:0.1.

[0199] (2) Preparation of positive electrode sheet

[0200] The above-mentioned positive electrode active material is mixed with acetylene black and PVDF in a weight ratio of 95:3:2. Then, an appropriate amount of NMP is added and stirred thoroughly to form a uniform positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil, and then dried and cold-pressed to obtain the positive electrode sheet.

[0201] (3) Preparation of negative electrode sheet

[0202] Hard carbon, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a weight ratio of 95:2:2:1. Then, an appropriate amount of deionized water was added and the mixture was stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry was coated onto the negative electrode current collector copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0203] (4) Preparation of electrolyte

[0204] In an argon-filled glove box with a water content of <1ppm, diethylene glycol dimethyl ether and tetrahydrofuran were mixed at a weight ratio of 1:3, and NaPF6 with a concentration of 1.0mol / L was added. After stirring evenly, an electrolyte was obtained.

[0205] (5) Battery manufacturing

[0206] The positive electrode, separator (a 12μm thick polypropylene film), and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried battery. The battery is then obtained through vacuum sealing, settling, formation, and shaping processes.

[0207] Examples 2 to 6

[0208] Except for the different types of aryl sodium in the aryl sodium solution or the different types of aprotic solvents used in the preparation of the positive electrode active material in step (1), the battery preparation process is the same as in Example 1. Specific parameters are detailed in Table 1.

[0209] Examples 7 to 11

[0210] Except for the sintering temperature in the preparation of the positive electrode active material in step (1), the battery preparation process is the same as in Example 1. Specific parameters are detailed in Table 1.

[0211] Examples 12 to 15

[0212] Except for the different concentration of the sodium arylate solution in the preparation of the positive electrode active material in step (1), the battery preparation process is the same as in Example 1. Specific parameters are detailed in Table 1.

[0213] Examples 16 to 19

[0214] Except for the difference in the molar ratio of sodium-containing layered transition metal oxide to sodium aryl sodium in step (1) of the preparation of the positive electrode active material, the battery preparation process is the same as in Example 1. Specific parameters are detailed in Table 1.

[0215] Examples 20 to 23

[0216] Except for the different reaction temperatures of the sodium-containing layered transition metal oxide and the aryl sodium solution in the preparation of the positive electrode active material in step (1), the battery fabrication process is the same as in Example 1. Specific parameters are detailed in Table 1.

[0217] Examples 24 to 27

[0218] Except for the different types of sodium-containing layered transition metal oxides used in the preparation of the positive electrode active material in step (1), the battery fabrication process is the same as in Example 1. Specific parameters are detailed in Table 1.

[0219] Comparative Example 1

[0220] In addition to using Na 1.05 Ni 0.55 Mn 0.45 Apart from using O2 as the positive electrode active material, the battery preparation process is the same as in Example 1.

[0221] Comparative Example 2

[0222] Except for the different preparation process of the positive electrode active material in step (1), the preparation process of the battery is the same as that in Example 1.

[0223] The nickel-manganese precursor was prepared by hydroxide co-precipitation, and then sintered with sodium nitrate at high temperature to obtain the target product Na. 1.05 Ni 0.55 Mn 0.45 O2. Na 1.05 Ni 0.55 Mn 0.45 O2 was added to a 1.5 mol / L sodium naphthalene tetrahydrofuran solution, and the reaction was carried out at a reaction temperature of 25℃ and a stirring speed of 500 r / min for 8 h. The mixture was then washed 2-3 times with ethanol to obtain the positive electrode active material. Na 1.05 Ni 0.55 Mn 0.45 The molar ratio of O2 to Na in sodium naphthalene is 1:0.1.

[0224] Comparative Example 3

[0225] Except for the different preparation process of the positive electrode sheet in step (2), the preparation process of the battery is the same as that in Example 1.

[0226] The nickel-manganese precursor was prepared by hydroxide co-precipitation, and then sintered with sodium nitrate at high temperature to obtain the target product Na. 1.05 Ni 0.55 Mn 0.45 O2. The target product Na... 1.05 Ni 0.55 Mn 0.45 O2, Na2NiO2, acetylene black, and PVDF are mixed in a weight ratio of 85:10:3:2. Then, an appropriate amount of NMP is added and the mixture is stirred thoroughly to form a uniform positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil, and then dried and cold-pressed to obtain the positive electrode sheet.

[0227] Comparative Example 4

[0228] Except for the different preparation process of the positive electrode sheet in step (2), the preparation process of the battery is the same as that in Example 1.

[0229] The nickel-manganese precursor was prepared by hydroxide co-precipitation, and then sintered with sodium nitrate at high temperature to obtain the target product Na. 1.05 Ni 0.55 Mn 0.45 O2. The target product Na... 1.05 Ni 0.55 Mn 0.45 O2, Na2CO3, acetylene black, and PVDF are mixed in a weight ratio of 85:10:3:2. Then, an appropriate amount of NMP is added and the mixture is stirred thoroughly to form a uniform positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil, and then dried and cold-pressed to obtain the positive electrode sheet.

[0230] Test section

[0231] (1) Battery capacity test

[0232] At 25°C, the battery prepared above is first charged to 4.2V with a constant current of 1C, then further charged with a constant voltage to a current of 0.05C, and then discharged to 2.5V with a constant current of 1C. This is one charge-discharge cycle, and the discharge capacity of this cycle is taken as the battery capacity.

[0233] (2) Battery cycle performance test

[0234] At 25°C, the prepared battery was first charged to 4.2V with a constant current of 1C, then further charged to 0.05C with a constant voltage, and finally discharged to 2.5V with a constant current of 1C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The battery was subjected to cyclic charge-discharge tests in the above manner. When the battery's discharge capacity decreased to 80% of the discharge capacity of the first cycle, the test was stopped, and the number of cycles was recorded.

[0235] (3) Initial discharge specific capacity and initial coulombic efficiency test of button cells

[0236] The positive electrode sheet prepared above (the positive electrode film layer on one surface of the aluminum foil needs to be wiped off) is cut into appropriately sized round pieces along with the separator and sodium metal sheet and stacked in sequence, so that the separator is placed between the positive electrode sheet and the sodium metal sheet to play a role in isolation. The separator is impregnated with the electrolyte prepared above, and then compacted to obtain a coin cell.

[0237] At 25°C, the coin cell was charged at a constant current of 0.1C to 4.2V to obtain the initial charge capacity; then it was discharged at a constant current of 0.1C to 2.6V to obtain the initial discharge capacity. The initial discharge specific capacity (mAh / g) of the positive electrode active material = the initial discharge capacity of the coin cell / the mass of the positive electrode active material. The initial coulombic efficiency of the positive electrode active material = the initial discharge capacity of the coin cell / the initial charge capacity of the coin cell.

[0238] The test results are shown in Table 2.

[0239] Table 1

[0240]

[0241] Table 2

[0242]

[0243] As can be seen from the test results of Examples 1 to 27 and Comparative Examples 1 to 4, the positive electrode active material provided in the embodiments of this application can enable sodium batteries to have high initial discharge specific capacity, high initial coulombic efficiency and good cycle performance.

[0244] The coating layer of the positive electrode active material includes a sodium-replenishing material. During the first charge of the battery, the active sodium in the sodium-replenishing material can compensate for the active sodium loss caused by the formation of the SEI film on the negative electrode, thereby improving the battery's initial discharge specific capacity and initial coulombic efficiency. The coating layer also satisfies the requirement that the Na concentration decreases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate, which is beneficial for promoting the release of active sodium, thus contributing to a higher initial discharge specific capacity and higher initial coulombic efficiency. The positive electrode active material has a low risk of decomposition and gas generation during battery charging and discharging, which allows for good adhesion between the positive electrode film and the positive electrode current collector, reduces the positive electrode contact resistance, and consequently, enables the battery to have good cycle performance.

[0245] The coating layer is generated in situ on at least a portion of the substrate surface, resulting in a high bonding strength between the coating layer and the substrate. After the active sodium in the sodium replenishment material is removed, the remaining material (i.e., the residual product after sodium replenishment material is removed) can also enable the coating layer to isolate the electrolyte from direct contact with the substrate, thereby reducing battery side reactions and decreasing the probability of transition metal ions in the remaining material (i.e., the residual product after sodium replenishment material is removed) dissolving into the electrolyte, thus enabling the battery to have better cycle performance.

[0246] The coating layer of the positive electrode active material provided in this application is obtained by mixing and reacting a sodium-containing layered transition metal oxide with an aryl sodium solution, followed by sintering. In the above embodiments, the sodium-containing layered transition metal oxide matrix is ​​a multi-component material, which also makes the sodium-supplementing material in the coating layer generated in situ on the matrix surface usually multiphase. Table 2 only shows some of the main sodium-supplementing material components of the coating layer; of course, the coating layer may also contain other components. Furthermore, the average valence of the transition metal element M′ in the matrix of the positive electrode active material provided in this application is greater than the average valence of the transition metal element M in the coating layer. The lower average valence of the transition metal element in the coating layer results in higher stability and lower risk of decomposition and gas generation, thereby further improving the adhesion between the positive electrode film layer and the positive electrode current collector, reducing the positive electrode contact resistance, and further improving the cycle performance of the battery.

[0247] Comparative Example 1 uses positive electrode active material without sodium supplementation to prepare a battery. As can be seen from the test results in Table 2, the battery has low initial coulombic efficiency, low discharge capacity and poor cycle performance.

[0248] The positive electrode active material prepared in Comparative Example 2 was not sintered. Therefore, after reduction with sodium naphthalene, Na₂O was generated on the surface of the positive electrode active material. This Na₂O absorbed moisture from the environment, generating residual alkalis such as Na₂CO₃, which in turn affected the battery's performance. The test results in Table 2 show that the battery exhibited low initial coulombic efficiency, low discharge capacity, and poor cycle performance.

[0249] Comparative Example 3 involved directly adding the sodium-supplementing additive Na2NiO2 to the positive electrode slurry, which improved the initial coulombic efficiency and initial discharge specific capacity of the battery. However, the battery's cycle performance remained poor. This is because after the active sodium in the sodium-supplementing additive Na2NiO2 is extracted, it leaves a high proportion of byproducts in the positive electrode film. The transition metal ions in these byproducts easily dissolve into the electrolyte, and subsequently, these transition metal ions are reduced and deposited on the negative electrode. This damages the structure of the SEI film, reduces the battery's discharge capacity, and affects the extraction and insertion of sodium ions, thus leading to poor battery cycle performance.

[0250] In Comparative Example 4, sodium-added additive Na2CO3 was directly added to the positive electrode slurry. Na2CO3 easily decomposes and produces gas, leaving more pores in the positive electrode film. This reduces the adhesion between the positive electrode film and the positive electrode current collector, and also increases the positive electrode contact resistance. The test results in Table 2 show that the battery has low initial coulombic efficiency, low discharge capacity, and poor cycle performance.

[0251] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. 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 this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes a matrix and a coating layer formed on at least a portion of the surface of the matrix; The matrix comprises a sodium-containing layered transition metal oxide; The coating layer includes a sodium-supplementing material, and the coating layer includes Na, M and O elements, where M represents a transition metal; Furthermore, the coating layer satisfies the following condition: the concentration of Na element decreases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate.

2. The positive electrode active material according to claim 1, characterized in that, The sodium-containing layered transition metal oxide includes an element M′, where M′ represents a transition metal, and the average valence of the element M′ in the sodium-containing layered transition metal oxide is greater than the average valence of the element M in the coating layer.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The coating layer satisfies the following condition: the average valence of element M increases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate.

4. The positive electrode active material according to claim 2, characterized in that, In the coating layer, M includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; and / or, In the sodium-containing layered transition metal oxide, M′ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

5. The positive electrode active material according to claim 4, characterized in that, In the coating layer, M includes two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; and / or, In the sodium-containing layered transition metal oxide, M′ includes two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

6. The positive electrode active material according to any one of claims 1-5, characterized in that, The coating layer is generated in situ on at least a portion of the surface of the substrate.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The thickness H of the coating layer and the average diameter D of the positive electrode active material satisfy the following condition: 0 < H / D ≤ 0.

15.

8. The positive electrode active material according to claim 7, characterized in that, 0.02≤H / D≤0.

11.

9. The positive electrode active material according to any one of claims 1-8, characterized in that, The weight content of the coating layer in the positive electrode active material is 2%-40%, based on the total weight of the positive electrode active material.

10. The positive electrode active material according to claim 9, characterized in that, The weight content of the coating layer in the positive electrode active material is 5%-20%, based on the total weight of the positive electrode active material.

11. The positive electrode active material according to any one of claims 1-10, characterized in that, The volume distribution particle size Dv50 of the positive electrode active material is 1μm-10μm.

12. The positive electrode active material according to claim 11, characterized in that, The volume distribution particle size Dv50 of the positive electrode active material is 3μm-8μm.

13. The positive electrode active material according to any one of claims 1-12, characterized in that, In the coating layer, the chemical molar ratio of Na, M and O is (1-6):(1-2):(2-4).

14. The positive electrode active material according to claim 13, characterized in that, The chemical molar ratio of Na, M, and O is (1-6):1:(2-4).

15. The positive electrode active material according to any one of claims 1-14, characterized in that, The coating layer includes one or more of NaMO2, Na2MO2, Na2MO3, Na3MO2, Na3MO3, Na4MO3, Na5MO3, Na5MO4, and Na6MO4.

16. The positive electrode active material according to claim 15, characterized in that, The coating layer includes two or more of the following: NaMO2, Na2MO2, Na2MO3, Na3MO2, Na3MO3, Na4MO3, Na5MO3, Na5MO4, and Na6MO4.

17. The positive electrode active material according to claim 15, characterized in that, M can independently include any one of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

18. The positive electrode active material according to any one of claims 1-17, characterized in that, The sodium-containing layered transition metal oxide includes Na c N d M′′ e P f O g Q h , 0.67≤c≤1.2, 0≤d≤1 / 3, 0<e≤1, 0≤f≤1 / 3, 1.9≤g≤2, 0≤h≤0.1, and the values ​​of c, d, e, f, g, and h satisfy the charge balance of the chemical formula; M′′ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; N includes one or more metallic elements from Group IA, Group IIA, and Zn; P includes one or more of a first metallic element and a first nonmetallic element, wherein the first metallic element includes one or more metallic elements from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, and Group VIB, and the first nonmetallic element includes one or more nonmetallic elements from Group IIIA, Group IVA, Group VA, and Group VIA; Q includes one or more nonmetallic elements from Group VA and Group VIIA.

19. The positive electrode active material according to claim 18, characterized in that, The sodium-containing layered transition metal oxide includes one or more of the following: O3 phase, P2 phase, and P3 phase.

20. The positive electrode active material according to claim 18, characterized in that, M′′ includes two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

21. The positive electrode active material according to claim 18, characterized in that, N includes one or more elements selected from Li, Mg, Ca, and Zn.

22. The positive electrode active material according to claim 18, characterized in that, The first metallic element includes one or more elements selected from Li, Zr, Sb, Nb, Mg, Ca, Mo, Zn, W, Bi, Sn, Ge, Al, Ba, and Sr. The first nonmetallic element includes one or more elements selected from Si, P, B, S, and Se.

23. The positive electrode active material according to claim 18, characterized in that, Q includes one or more elements from F, Cl, and N.

24. The positive electrode active material according to any one of claims 1-23, characterized in that, The sodium-supplementing material in the coating layer has a weight content of 97% or more, based on the total weight of the coating layer.

25. The positive electrode active material according to claim 24, characterized in that, The sodium-supplementing material in the coating layer has a weight content of 97%-99%, based on the total weight of the coating layer.

26. The positive electrode active material according to claim 24 or 25, characterized in that, The coating layer also includes one or more of sodium oxide, sodium hydroxide, and sodium carbonate.

27. The positive electrode active material according to any one of claims 24-26, characterized in that, The sodium-containing layered transition metal oxide includes an M′ element and a non-variable valence metal element, where M′ represents a transition metal, and the coating layer also includes one or more of the oxides of the non-variable valence metal element and the salts of the non-variable valence metal element.

28. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: Provides a solution of layered transition metal oxides and sodium arylates containing sodium; The sodium-containing layered transition metal oxide is mixed with the sodium aryl solution and reacted. After the reaction is completed, the mixture is washed and dried to obtain a powder. The obtained powder was sintered under an inert gas atmosphere to obtain the positive electrode active material. The positive electrode active material includes a substrate and a coating layer formed on at least a portion of the surface of the substrate; the substrate includes a sodium-containing layered transition metal oxide; the coating layer includes a sodium-supplementing material, and the coating layer includes Na, M, and O elements, where M represents a transition metal; and the coating layer satisfies the following condition: the concentration of Na element decreases from the surface of the coating layer away from the substrate to the surface of the coating layer near the substrate.

29. The preparation method according to claim 28, characterized in that, In the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution, the molar ratio of the sodium-containing layered transition metal oxide to the Na element in the aryl sodium is 1:(0.01-0.2).

30. The preparation method according to claim 29, characterized in that, In the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution, the molar ratio of the sodium-containing layered transition metal oxide to the Na element in the aryl sodium is 1:(0.05-0.1).

31. The preparation method according to any one of claims 28-30, characterized in that, In the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution. The reaction temperature is 15℃-60℃; and / or, The reaction time is 5h-20h.

32. The preparation method according to claim 31, characterized in that, In the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution. The reaction temperature is 25℃-45℃; and / or, The reaction time is 8-16 hours.

33. The preparation method according to any one of claims 28-32, characterized in that, In the step of reacting the sodium-containing layered transition metal oxide with the aryl sodium solution, the reaction is carried out under stirring conditions.

34. The preparation method according to claim 33, characterized in that, The stirring speed is 100r / min-1000r / min.

35. The preparation method according to claim 34, characterized in that, The stirring speed is 200r / min-700r / min.

36. The preparation method according to any one of claims 28-35, characterized in that, In the step of sintering the obtained powder under an inert gas atmosphere, The sintering temperature is 500℃-950℃; and / or, The holding time for sintering is 3-9 hours; and / or, The inert gas includes one or more of argon, helium, nitrogen, and a mixture of hydrogen and argon.

37. The preparation method according to claim 36, characterized in that, The sintering temperature is 600℃-900℃; and / or, The holding time for sintering is 5-8 hours.

38. The preparation method according to any one of claims 28-37, characterized in that, The concentration of the aryl sodium solution is 0.5 mol / L to 3.5 mol / L; and / or, The aryl sodium includes one or more of sodium naphthyl, sodium biphenyl, sodium phenylene, sodium phenanthrene, sodium anthracene, sodium pyrene, sodium bipyridine, and sodium tetraphenylene; and / or, The solvent for the aryl sodium solution includes an aprotic solvent.

39. The preparation method according to claim 38, characterized in that, The concentration of the aryl sodium solution is 1 mol / L-2 mol / L; and / or, The aprotic solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, N,N-dimethylformamide, diethyl ether, diisopropyl ether, diethylene glycol dimethyl ether, methyl tert-butyl ether, diethyl ether, acetonitrile, and dimethyl sulfoxide.

40. The preparation method according to any one of claims 28-39, characterized in that, The sodium-containing layered transition metal oxide includes Na c N d M′′ e P f O g Q h , 0.67≤c≤1.2, 0≤d≤1 / 3, 0<e≤1, 0≤f≤1 / 3, 1.9≤g≤2, 0≤h≤0.1, and the values ​​of c, d, e, f, g, and h satisfy the charge balance of the chemical formula; M′′ includes one or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti; N includes one or more metallic elements from Group IA, Group IIA, and Zn; P includes one or more of a first metallic element and a first nonmetallic element, wherein the first metallic element includes one or more metallic elements from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, and Group VIB, and the first nonmetallic element includes one or more nonmetallic elements from Group IIIA, Group IVA, Group VA, and Group VIA; Q includes one or more nonmetallic elements from Group VA and Group VIIA.

41. The preparation method according to claim 40, characterized in that, The sodium-containing layered transition metal oxide includes one or more of the following: O3 phase, P2 phase, and P3 phase.

42. The preparation method according to claim 40, characterized in that, M′′ includes two or more of Ni, Mn, Fe, Co, Cr, Cu, V, and Ti.

43. The preparation method according to claim 40, characterized in that, N includes one or more elements selected from Li, Mg, Ca, and Zn.

44. The preparation method according to claim 40, characterized in that, The first metallic element includes one or more elements selected from Li, Zr, Sb, Nb, Mg, Ca, Mo, Zn, W, Bi, Sn, Ge, Al, Ba, and Sr. The first nonmetallic element includes one or more elements selected from Si, P, B, S, and Se.

45. The preparation method according to claim 40, characterized in that, Q includes one or more elements from F, Cl, and N.

46. ​​A positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, characterized in that, The positive electrode film layer comprises the positive electrode active material according to any one of claims 1-27 or the positive electrode active material prepared by the preparation method according to any one of claims 28-45.

47. The positive electrode sheet according to claim 46, characterized in that, The positive electrode active material in the positive electrode film layer has a weight content of 50%-99%, based on the total weight of the positive electrode film layer.

48. The positive electrode sheet according to claim 47, characterized in that, The positive electrode active material in the positive electrode film layer has a weight content of 80%-99%, based on the total weight of the positive electrode film layer.

49. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 46-48.

50. An electrical device, characterized in that, Includes the battery of claim 49, the battery being used to provide electrical energy.

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