Positive electrode material and preparation method thereof, sodium secondary battery and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a positive electrode material, a preparation method thereof, a sodium secondary battery and an electric device. The positive electrode material comprises single-crystal particles and / or single-crystal-like particles of layered transition metal oxide. The design mode provided by the invention is beneficial to improving the cycle service life of the sodium secondary battery.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a positive electrode material and its preparation method, as well as a sodium secondary battery and an electrical device. Background Technology

[0002] Secondary batteries are widely used in various consumer electronics products and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect.

[0003] As the application of rechargeable batteries becomes more and more widespread, the requirements for battery performance are also becoming higher and higher. Summary of the Invention

[0004] In view of the above problems, this application provides a cathode material and its preparation method, a sodium secondary battery and an electrical device, which improves the cycle life of the sodium secondary battery by increasing the content of single crystal particles and / or single crystal-like particles in the cathode material.

[0005] In a first aspect, this application provides a sodium secondary battery, which includes a positive electrode, a separator, and a negative electrode stacked together; the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector; the positive electrode film layer includes a positive electrode active material; the positive electrode active material includes single crystal particles and / or quasi-single crystal particles of layered transition metal oxides; the shape of the single crystal particles and / or quasi-single crystal particles includes any one or more of spherical, quasi-spherical, polygonal sheet, and polygonal columnar shapes;

[0006] Furthermore, the positive electrode active material satisfies the following conditions:

[0007] (1) The volumetric particle size distribution Dv50 is 3μm~7μm;

[0008] (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

[0009] In some embodiments of this application, the mass percentage content of single crystal particles in the above-mentioned positive electrode active material is 20% to 40%.

[0010] In some embodiments of this application, the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is 60% to 80%.

[0011] In some embodiments of this application, the volumetric particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0012] In some embodiments of this application, the volumetric particle size distribution Dv50 of the quasi-single crystal particles is 3μm to 5μm and does not include 5μm.

[0013] In some embodiments of this application, the chemical formula of the layered transition metal oxide is Na. x M y O z M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2.

[0014] In some embodiments of this application, the layered transition metal oxide is a nickel-iron-manganese layered transition metal oxide, and the chemical formula of the aforementioned nickel-iron-manganese layered transition metal oxide is NaNi. a Fe b Mn c M1 d O2, where a+b+c+d=1, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg, or Zn.

[0015] In some embodiments of this application, the compaction density of the positive electrode film is 3.0 g / cm³. 3 ~3.4g / cm 3 .

[0016] In some embodiments of this application, the sodium secondary battery further includes an electrolyte comprising one or more of carboxylic acid ester compounds, carbonate compounds, and ether compounds.

[0017] The second aspect of this application discloses a positive electrode active material for sodium secondary batteries, the positive electrode active material comprising single crystal particles and / or quasi-single crystal particles of layered transition metal oxides;

[0018] The shapes of the aforementioned single crystal particles and / or single crystal-like particles include any one or more of the following: spherical, quasi-spherical, polygonal plate-like, and polygonal columnar.

[0019] The above-mentioned positive electrode active material meets the following conditions:

[0020] (1) The volumetric particle size distribution Dv50 is 3μm~7μm;

[0021] (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

[0022] In some embodiments of this application, the mass percentage content of single crystal particles in the above-mentioned positive electrode active material is 20% to 40%.

[0023] In some embodiments of this application, the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is 60% to 80%.

[0024] In some embodiments of this application, the volumetric particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0025] In some embodiments of this application, the volumetric particle size distribution Dv50 of the quasi-single crystal particles is 3μm to 5μm, excluding 5μm.

[0026] In some embodiments of this application, the tap density of the positive electrode active material is 1.55 g / cm³. 3 ~1.80g / cm 3 .

[0027] A third aspect of this application is to provide a method for preparing a positive electrode active material for sodium secondary batteries, the method comprising:

[0028] Provides precursors for cathode materials;

[0029] Preparation of intermediate products for cathode materials: The cathode material precursor is mixed with sodium carbonate and calcined for the first time to obtain intermediate products for cathode materials. The intermediate products for cathode materials contain polycrystalline particles of layered transition metal oxides.

[0030] Preparation of positive electrode active material: Disperse the dispersant into the solvent to form a mixed solvent, disperse the above-mentioned positive electrode material intermediate product into the above-mentioned mixed solvent, and obtain the positive electrode active material by a second calcination. The above-mentioned positive electrode active material includes single crystal particles and / or single crystal-like particles of layered transition metal oxides, and the mass percentage content of the above-mentioned single crystal particles and single crystal-like particles in the above-mentioned positive electrode active material is >98%.

[0031] The above dispersant meets the following conditions:

[0032] (1) The dispersant is soluble in one or more of alcohol solvents, acetone, and water;

[0033] (2) The decomposition temperature of the dispersant is less than or equal to 600℃. The decomposition temperature of the dispersant is the temperature corresponding to the decomposition peak of the thermogravimetric curve of the dispersant.

[0034] In some embodiments of this application, the dispersant includes polyvinylpyrrolidone and its modified compounds.

[0035] In some embodiments of this application, the mass of the dispersant added is 0.5% to 5% of the mass of the solvent;

[0036] In some embodiments of this application, the mass ratio of the above-mentioned cathode material intermediate product to the volume ratio of the above-mentioned mixed solvent is (10g~20g) / (20mL~100mL).

[0037] In some embodiments of this application, the solvents mentioned above include one or more of alcohols, acetone, and water.

[0038] In some embodiments of this application, the alcohol solvents mentioned above include one or more of ethanol, ethylene glycol, and glycerol.

[0039] In some embodiments of this application, the first calcination temperature is 850℃~970℃, and the holding time is 7h~15h.

[0040] In some embodiments of this application, the second calcination temperature is 600℃~1000℃, and the holding time is 3h~24h.

[0041] In some embodiments of this application, the first calcination and the second calcination are carried out in an oxygen-containing atmosphere.

[0042] In some embodiments of this application, after the aforementioned cathode material intermediate product is dispersed in the aforementioned mixed solvent and before the second calcination, the process further includes:

[0043] The above mixed solvent is heated and stirred until the solvent evaporates to dryness.

[0044] In some embodiments of this application, after the first calcination, the process further includes coarse crushing, fine crushing and sieving to obtain a cathode material intermediate product, wherein the volume particle size distribution Dv50 of the cathode material intermediate product is 8μm to 12μm.

[0045] In some embodiments of this application, the molar amount of metal atoms in the above-mentioned cathode material precursor is N1, and the molar amount of sodium atoms in the above-mentioned sodium carbonate is N2, satisfying N1 / N2 = 1:(0.5~1.1).

[0046] The fourth aspect of this application is to provide an electrical device comprising the sodium secondary battery described in the first aspect, the positive electrode active material described in the second aspect, or the positive electrode active material prepared by the preparation method described in the third aspect.

[0047] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0048] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0049] Figure 1 This is a schematic diagram of the battery structure of some embodiments of this application;

[0050] Figure 2 This is an exploded structural diagram of a battery according to some embodiments of this application;

[0051] Figure 3 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0052] Figure 4 This is a schematic diagram of the battery pack structure according to some embodiments of this application;

[0053] Figure 5 This is a schematic diagram of the structure of a sodium secondary battery according to some embodiments of this application;

[0054] Figure 6A , 6B This is a schematic diagram of the structure of the positive electrode sheet in some embodiments of this application;

[0055] Figure 7A , Figure 7B , Figure 8A , Figure 8B , Figure 9 , Figure 10 , Figure 11A , Figure 11B , Figure 12 Scanning electron microscope images of cathode materials prepared in some preparation examples and comparative examples of this application.

[0056] The reference numerals in the detailed embodiments are as follows:

[0057] 10000, vehicles;

[0058] 1000, Battery; 2000, Controller; 3000, Motor;

[0059] 100. Battery cell;

[0060] 200. Box body; 210. First part; 220. Second part;

[0061] 10. Secondary batteries;

[0062] 101. Housing; 102. Electrode assembly; 103. Cover plate;

[0063] 1. Negative electrode plate;

[0064] 2. Positive electrode plate; 21. Positive current collector; 22. Positive electrode film;

[0065] 3. Separating membrane;

[0066] First direction: the x-axis of the coordinate axis, or it can be the stacking direction or the thickness direction of the separator film;

[0067] The y-axis of the coordinate axis represents the length or width of the isolation membrane. Detailed Implementation

[0068] The following detailed description, with appropriate reference to the accompanying drawings, discloses the cathode material, its preparation method, and embodiments of the sodium secondary battery and power application device of this application. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0069] 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 also 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 "a–b" 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.

[0070] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0071] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0072] 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 mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0073] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0074] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0075] Unless otherwise specified, in this application, the terms "first," "second," etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features.

[0076] Unless otherwise specified, in this application, the term "multiple" means two or more (including two), similarly, "multiple sets" means two or more (including two sets), and "multiple pieces" means two or more (including two pieces).

[0077] Unless otherwise specified, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0078] Due to their advantages such as high energy density, long cycle life, and safety and reliability, rechargeable batteries have been widely used in various products. In recent years, with the significant increase in demand for rechargeable batteries as an energy source, higher requirements have been placed on their performance, such as cycle life.

[0079] Sodium-ion batteries, due to their cost and resource advantages and similar working principle to lithium-ion batteries, hold promise as a low-cost new energy storage technology. The core technology of sodium-ion batteries lies in the electrode materials. Based on the microstructure of the electrode materials, the cathode materials of sodium-ion batteries can be divided into monocrystalline and polycrystalline types. Monocrystalline materials have higher load voltages, thus increasing energy density. Furthermore, monocrystalline materials lack grain boundaries, resulting in higher crystallinity, layered stability, and anisotropy, leading to superior safety and cycle performance. In addition, monocrystalline materials have smaller surface areas, which can reduce interfacial side reactions to some extent.

[0080] However, existing methods for preparing single-crystal materials have technical drawbacks due to their cumbersome processes. When the cathode materials prepared by these methods are used in sodium secondary batteries, the cycle life of the batteries is not ideal.

[0081] To address the aforementioned technical problems, this application discloses a sodium secondary battery, comprising a positive electrode, a separator, and a negative electrode stacked together; the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including single crystal particles and / or quasi-single crystal particles of layered transition metal oxides; the single crystal particles and / or quasi-single crystal particles include any one or more of spherical, quasi-spherical, polygonal sheet, and polygonal columnar shapes;

[0082] Furthermore, the above-mentioned positive electrode active materials meet the following conditions:

[0083] (1) The volumetric particle size distribution Dv50 is 3μm~7μm;

[0084] (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

[0085] The positive electrode active material provided in this application comprises single crystal particles and / or quasi-single crystal particles, which are beneficial for improving the cycle life of sodium secondary batteries.

[0086] Therefore, the sodium secondary battery provided in this application is beneficial for improving the battery's cycle life and energy density, thereby enhancing the user experience. The sodium secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte composed of the aforementioned sodium secondary battery. The outer packaging of the sodium secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the sodium secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, including but not limited to polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0087] This application does not impose any particular limitation on the shape of the sodium secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured sodium secondary battery (secondary battery 10).

[0088] According to some embodiments of this application, reference is made to Figure 2 The outer packaging may include a housing 101 and a cover plate 103. The housing 101 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 102 by a winding process or a stacking process. The electrode assembly 102 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 102. The secondary battery 10 may contain one or more electrode assemblies 102, which can be selected by those skilled in the art according to specific practical needs.

[0089] The electrode assembly 102 provided in this application is beneficial to improving the performance of a secondary battery when applied in a secondary battery. The secondary battery can be a power source for an electrical device or an energy storage unit for an electrical device. The electrical device is applied in the power field, such as mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited to the above fields.

[0090] For ease of explanation, some embodiments of this application are illustrated using a vehicle as an example of an electrical device.

[0091] Please refer to Figure 3 , Figure 3This is a schematic diagram of the structure of a vehicle 10000 provided in some embodiments of this application. The vehicle 10000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 1000 is disposed inside the vehicle 10000, and the battery 10000 can be located at the bottom, front, or rear of the vehicle 10000. The battery 10000 can be used to power the vehicle 10000; for example, the battery 10000 can serve as the operating power source for the vehicle 10000. The vehicle 10000 may also include a controller 2000 and a motor 3000. The controller 2000 is used to control the battery 10000 to supply power to the motor 3000, for example, to meet the power needs of the vehicle 10000 during startup, navigation, and driving.

[0092] In some embodiments of this application, the battery 1000 can not only serve as the operating power source for the vehicle 10000, but also as the driving power source for the vehicle 10000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 10000.

[0093] Please refer to Figure 4 , Figure 4 This is an exploded view of a battery 1000 provided in some embodiments of this application. The battery 1000 includes a housing 200 and a battery cell 100. A conventional battery cell includes a primary battery or a secondary battery. This application specifically protects a secondary battery 10. The battery cell 100 is housed within the housing 200. The housing 200 provides space for the battery cell 100, and the housing 200 can adopt various structures.

[0094] In some embodiments, the housing 200 may include a first portion 210 and a second portion 220, which overlap each other, and together define a receiving space for accommodating the secondary battery 100. The second portion 220 may be a hollow structure with one open end, and the first portion 210 may be a plate-like structure, with the first portion 210 covering the open side of the second portion 220 so that the first portion 210 and the second portion 220 together define the receiving space; alternatively, the first portion 210 and the second portion 220 may both be hollow structures with one open side, with the open side of the first portion 210 covering the open side of the second portion 220. Of course, the housing 200 formed by the first portion 210 and the second portion 220 may be of various shapes, such as a cylinder, a cuboid, etc.

[0095] In battery 1000, there can be multiple battery cells 100, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 100 are connected in both series and parallel configurations. Multiple battery cells 100 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 100 is housed within housing 200. Alternatively, battery 1000 can also be composed of multiple battery cells 100 first connected in series, parallel, or in a mixed manner to form battery modules, and then these modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within housing 200. Battery 1000 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 100.

[0096] Sodium secondary battery

[0097] This application discloses a sodium secondary battery in some embodiments, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode, separator, and negative electrode are sequentially stacked together to form the sodium secondary battery using a winding or stacking process. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a positive active material, which comprises single-crystal particles and / or quasi-single-crystal particles of layered transition metal oxides; the single-crystal particles and / or quasi-single-crystal particles include any one or more of the following: spherical, quasi-spherical, polygonal sheet-like, and polygonal columnar.

[0098] Furthermore, the above-mentioned positive electrode active materials meet the following conditions:

[0099] (1) The volumetric particle size distribution Dv50 is 3μm~7μm;

[0100] (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

[0101] The positive electrode, separator, and negative electrode in this application can be formed into a secondary battery using winding or stacking processes. Specifically, this application... Figure 5 The diagram illustrates a secondary battery 10 formed using a stacking method, combined with... Figure 5 It is known that a negative electrode 1 or a positive electrode 2 is placed between two adjacent separators 3, and the negative electrode 1 and the positive electrode 2 are alternately arranged along the stacking direction (coordinate axis x direction). The number and size of the negative electrode 1 and / or the positive electrode 2 can be selected according to the actual situation, and will not be elaborated in this application. Furthermore, this application... Figure 5 The image only illustrates one type of lamination method; other lamination or winding methods are within the scope of protection of this application.

[0102] like Figure 6A and 6B The diagram illustrates that the positive electrode 2 includes a positive current collector 21 and a positive electrode film 22 located on at least one side surface of the positive current collector 21. Figure 6B This diagram illustrates the placement of a positive electrode film layer 22 on either side of the surface of the positive electrode current collector 21. Figure 6A The diagram illustrates the simultaneous formation of a positive electrode film layer 22 on both sides of the positive electrode current collector 21. The positive electrode film layer 22 can be formed on the surface of the positive electrode current collector 21 in any manner conventional in the art, such as coating or deposition.

[0103] In this application, a single crystal particle refers to a single particle or primary particle with a complete crystal shape (complete crystal edges and crystal faces), and the crystal lattice inside the particle is periodically arranged.

[0104] In this application, quasi-single-crystal particles refer to irregularly shaped particles formed by the aggregation of a small number of large-diameter single-crystal particles.

[0105] The shapes of the single-crystal particles and / or quasi-single-crystal particles in this application are obtained by observing the shape with the naked eye from electron micrographs taken of the positive electrode active material. Among them, polygon refers to at least quadrilaterals and above.

[0106] The single-crystal particles and / or quasi-single-crystal particles provided in this application have suitable particle size and specific surface area, which is beneficial to improving the cycle life of sodium secondary batteries.

[0107] The measurement method for the volumetric particle size distribution Dv50 of the positive electrode active material in this application includes: referring to GB / T 19077-

[0108] In 2016, the volumetric particle size distribution curve of the positive electrode active material was obtained, and the particle size corresponding to the cumulative volumetric distribution percentage reaching 50% was taken as the average particle size Dv50. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. Deionized water was used as the solvent, and the positive electrode active material was ultrasonically treated for 5 minutes before testing.

[0109] In some embodiments of this application, the volumetric particle size distribution Dv50 of the positive electrode active material includes 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, and 4. The value is any one of the following: 9μm, 5.0μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6.0μm, 6.1μm, 6.2μm, 6.3μm, 6.4μm, 6.5μm, 6.6μm, 6.7μm, 6.8μm, 6.9μm, 7.0μm, or any one of the values ​​within the above range.

[0110] The surface area (BET) of the positive electrode active material in this application is measured using the nitrogen adsorption specific surface area analysis method, referring to GB / T 19587-2004, and the specific surface area of ​​the positive electrode active material is calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a TRISTAR II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0111] In some embodiments of this application, the specific surface area BET of the positive electrode active material comprises 0.30 m². 2 / g, 0.31m 2 / g, 0.32m 2 / g, 0.33m 2 / g, 0.34m 2 / g, 0.35m 2 / g, 0.36m 2 / g, 0.37m 2 / g, 0.38m 2 / g, 0.39m 2 / g, 0.40m 2 / g, 0.41m 2 / g, 0.42m 2 / g, 0.43m 2 / g, 0.44m 2 / g, 0.45m 2 / g, 0.46m 2 / g, 0.47m 2 / g, 0.48m 2 / g, 0.49m 2 / g, 0.50m 2 Any one of / g or any one of the above range values.

[0112] The single-crystal particles and / or quasi-single-crystal particles provided in this application have suitable particle size and specific surface area, which can reduce the probability of interfacial side reactions to a certain extent, thus improving the cycle life of sodium secondary batteries.

[0113] At the same time, the single crystal particles and / or quasi-single crystal particles provided in this application can also be loaded with higher voltages, which is also beneficial to improving the energy density of the battery.

[0114] In some embodiments of this application, the mass percentage content of single crystal particles in the above-mentioned positive electrode active material is 20% to 40%.

[0115] The method for determining the mass percentage content of single crystal particles in the positive electrode active material in this application includes obtaining a portion of the positive electrode active material in the positive electrode film layer, weighing it as m0, separating the single crystal particles in the positive electrode active material under a high-power electron microscope, weighing it as m1, and calculating (m1÷m0)×100% as the mass percentage content of single crystal particles in the positive electrode active material.

[0116] In these embodiments, this application discloses that the mass percentage content of single crystal particles in the above-mentioned positive electrode active material includes any one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, and 40%, or any one of the above-mentioned range values.

[0117] In some embodiments of this application, the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is 60% to 80%.

[0118] The method for determining the mass percentage content of single-crystal-like particles in the positive electrode active material in this application includes obtaining a portion of the positive electrode active material in the positive electrode film layer, weighing it as m0, separating the single-crystal-like particles in the positive electrode active material under a high-power electron microscope, weighing it as m2, and calculating (m2÷m0)×100% as the mass percentage content of single-crystal particles in the positive electrode active material.

[0119] In these embodiments, this application discloses that the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is any one of 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any one of the above range values.

[0120] In some embodiments of this application, the positive electrode active material is disclosed to include single crystal particles and single crystal-like particles, and the sum of the mass percentage content of single crystal particles and the mass percentage content of single crystal-like particles is less than or equal to 100%.

[0121] In some embodiments of this application, the volumetric particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0122] As described above, single crystal particles are separated, and then the volumetric particle size distribution curve of the single crystal particles is obtained with reference to GB / T 19077-2016. The particle size corresponding to the cumulative volume distribution percentage reaching 50% is taken as the average particle size Dv50.

[0123] In these embodiments, this application discloses that the volumetric particle size distribution Dv50 of the single crystal particles includes any one of 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, and 7.0 μm or satisfies any one of the above range values.

[0124] In some embodiments of this application, the volumetric particle size distribution Dv50 of the quasi-single crystal particles is 3μm to 5μm, excluding 5μm.

[0125] As described above, the quasi-single crystal particles were separated, and then the volumetric particle size distribution curve of the quasi-single crystal particles was obtained with reference to GB / T 19077-2016. The particle size corresponding to the cumulative volume distribution percentage reaching 50% was taken as the average particle size Dv50.

[0126] In these embodiments, this application discloses that the volumetric particle size distribution Dv50 of the quasi-single crystal particles includes any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, and 4.9 μm or satisfies any one of the above range values.

[0127] In some embodiments of this application, the chemical formula of the above-mentioned layered transition metal oxide is Na. x M y O z M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2.

[0128] This application discloses in some embodiments that the aforementioned layered transition metal oxide is a nickel-iron-manganese layered transition metal oxide with the chemical formula NaNi. a Fe b Mn c M1 d O2, where a+b+c+d=1, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg, or Zn.

[0129] In these embodiments, this application discloses that a, b, c, and d are each independently selected from any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, and 1.0, or satisfy any of the above range values.

[0130] In some embodiments, this application discloses that M1 is selected from one or more of Co, Al, and Fe.

[0131] In some embodiments of this application, the compaction density of the positive electrode film is 3.0 g / cm³. 3 ~3.4g / cm 3 .

[0132] The compaction density of the positive electrode film in this application can be used to characterize the energy density of the material. The compaction density of the positive electrode film is calculated as: compaction density = areal density / thickness. The thickness includes the distance between the two end faces of the positive electrode film along the thickness direction. The areal density is calculated as: weight of a single side of the positive electrode film / area of ​​a single side of the positive electrode film. The weight of a single side of the positive electrode film can be obtained by weighing, and the area of ​​a single side of the positive electrode film can be obtained using an area calculation formula based on the film shape. This application primarily discusses the compaction density of the positive electrode film after formation and before recycling. As those skilled in the art know, the compaction density of the positive electrode film decreases with battery use, and may even drop as low as 3.0 g / cm³. 3 .

[0133] The compaction density of the positive electrode film in this application is 3.0 g / cm³. 3 ~3.4g / cm 3 This is to illustrate that the sodium secondary battery of this application has a relatively high energy density.

[0134] This application discloses in these embodiments that the compaction density of the positive electrode film layer includes 3.0 g / cm³.3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 Any one of the above values ​​or any one of the above range values.

[0135] In some embodiments of this application, the sodium secondary battery further includes an electrolyte, which can be liquid, solid, or gel-like. Specifically, solid electrolyte refers to a solid electrolyte, liquid electrolyte to a liquid electrolyte, and gel-like electrolyte to a gel electrolyte. The sodium secondary battery of this application uses a liquid electrolyte. This electrolyte contains an organic solvent. The organic solvent contains one or more of carboxylic acid esters, carbonates, and ethers. The carboxylic acid esters include one or more of ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), propyl acetate (PA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL); the carbonates include one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), and fluoroethylene carbonate (FEC). The ethers include at least one of tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran, dimethyl tetrahydropyran, 1,2-dimethoxyethane, dipropylene glycol dimethyl ether, or dimethyl phthalate. The organic solvents of this application further include one or two of nitrile solvents and sulfone solvents. The nitrile solvents include one or more of acetonitrile (AN), glutaronitrile (GLN), and adiponitrile (ADN). The sulfone solvents include at least one or a combination of two of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0136] According to some embodiments of this application, the electrolyte further comprises a film-forming stabilizer, which includes a positive electrode film-forming stabilizer and a negative electrode film-forming stabilizer. The positive electrode film-forming stabilizer includes carbonate additives and / or sulfate additives. The carbonate additives include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The sulfate additives include cyclic sulfonate additives and / or alkyl sulfate additives; further, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro1,3-propanesulfonate lactone (FPS); the alkyl sulfate additives include one or more of vinyl sulfate (DTD), diethyl sulfate (DES), and dimethyl sulfate (DMS). The negative electrode film-forming stabilizer includes one or more of sodium boron salts, phosphorus-containing sodium salts, and sulfur-containing sodium salts; the sodium boron salts include sodium tetrafluoroborate (NaBF4) and sodium bis(oxalato)borate.

[0137] Sodium difluorooxalate borate (NaBOB) and sodium difluorooxalate borate (NaDFOB) are among the following: phosphorus-containing lithium salts include sodium difluorophosphate (NaPO2F2), sodium fluorophosphate (Na2PO3F), and sodium phosphate (Na3PO4). Sulfur-containing sodium salts include sodium fluorosulfonate (NaFSO3), sodium sulfate (Na2SO4), and sodium aminosulfonate (NaSO3NH2) are among the following:

[0138] [Positive electrode plate]

[0139] According to some embodiments of this application, as described above, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector. The positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes single-crystal particles and / or quasi-single-crystal particles of layered transition metal oxides; the single-crystal particles and / or quasi-single-crystal particles include any one or more of the following: spherical, quasi-spherical, polygonal sheet-like, and polygonal columnar.

[0140] Furthermore, the above-mentioned positive electrode active materials meet the following conditions:

[0141] (1) The volumetric particle size distribution Dv50 is 3μm~7μm;

[0142] (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

[0143] In this application, a single crystal particle refers to a single particle or primary particle with a complete crystal shape (complete crystal edges and crystal faces), and the crystal lattice inside the particle is periodically arranged.

[0144] In this application, quasi-single-crystal particles refer to irregularly shaped particles formed by the aggregation of a small number of large-diameter single-crystal particles.

[0145] The shapes of the single-crystal particles and / or quasi-single-crystal particles in this application are obtained by observing the shape with the naked eye from electron micrographs taken of the positive electrode active material. Among them, polygon refers to at least quadrilaterals and above.

[0146] The single-crystal particles and / or quasi-single-crystal particles provided in this application have higher structural stability, which is beneficial to improving the cycle life of sodium secondary batteries.

[0147] The measurement method for the volumetric particle size distribution Dv50 of the positive electrode active material in this application includes: referring to GB / T 19077-

[0148] In 2016, the volumetric particle size distribution curves of single-crystal particles and / or single-crystal-like particles were obtained. The particle size corresponding to a cumulative volumetric distribution percentage of 50% was taken as the average particle size Dv50. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. Deionized water was used as the solvent, and the single-crystal particles and / or single-crystal-like particles were ultrasonically treated for 5 minutes before testing.

[0149] In some embodiments of this application, the volumetric particle size distribution Dv50 of the positive electrode active material includes 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, and 4. The value is any one of the following: 9μm, 5.0μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6.0μm, 6.1μm, 6.2μm, 6.3μm, 6.4μm, 6.5μm, 6.6μm, 6.7μm, 6.8μm, 6.9μm, 7.0μm, or any one of the values ​​within the above range.

[0150] The surface area (BET) of the positive electrode active material in this application is measured using the nitrogen adsorption specific surface area analysis method, referring to GB / T 19587-2004, and the specific surface area of ​​the positive electrode active material is calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a TRISTAR II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0151] In some embodiments of this application, the specific surface area BET of the positive electrode active material comprises 0.30 m². 2 / g, 0.31m 2 / g, 0.32m 2 / g, 0.33m 2 / g, 0.34m 2 / g, 0.35m 2 / g, 0.36m 2 / g, 0.37m 2 / g, 0.38m 2 / g, 0.39m 2 / g, 0.40m 2 / g, 0.41m 2 / g, 0.42m 2 / g, 0.43m 2 / g, 0.44m 2 / g, 0.45m 2 / g, 0.46m 2 / g, 0.47m 2 / g, 0.48m 2 / g, 0.49m 2 / g, 0.50m 2 Any one of / g or any one of the above range values.

[0152] The single-crystal particles and / or quasi-single-crystal particles provided in this application have suitable specific surface area and particle size, which can reduce the probability of interfacial side reactions to a certain extent, thus improving the cycle life of sodium secondary batteries.

[0153] At the same time, the single crystal particles and / or quasi-single crystal particles provided in this application can also be loaded with higher voltages, which is also beneficial to improving the energy density of the battery.

[0154] In some embodiments of this application, the mass percentage content of single crystal particles in the above-mentioned positive electrode active material is 20% to 40%.

[0155] The method for determining the mass percentage content of single crystal particles in the positive electrode active material in this application includes obtaining a portion of the positive electrode active material in the positive electrode film layer, weighing it as m0, separating the single crystal particles in the positive electrode active material under a high-power electron microscope, weighing it as m1, and calculating (m1÷m0)×100% as the mass percentage content of single crystal particles in the positive electrode active material.

[0156] In these embodiments, this application discloses that the mass percentage content of single crystal particles in the above-mentioned positive electrode active material includes any one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, and 40%, or any one of the above-mentioned range values.

[0157] In some embodiments of this application, the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is 60% to 80%.

[0158] The method for determining the mass percentage content of single-crystal-like particles in the positive electrode active material in this application includes obtaining a portion of the positive electrode active material in the positive electrode film layer, weighing it as m0, separating the single-crystal-like particles in the positive electrode active material under a high-power electron microscope, weighing it as m2, and calculating (m2÷m0)×100% as the mass percentage content of single-crystal particles in the positive electrode active material.

[0159] In these embodiments, this application discloses that the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is any one of 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any one of the above range values.

[0160] In some embodiments of this application, the positive electrode active material is disclosed to include single crystal particles and single crystal-like particles, and the sum of the mass percentage content of single crystal particles and the mass percentage content of single crystal-like particles is less than or equal to 100%.

[0161] In some embodiments of this application, the volumetric particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0162] As described above, single crystal particles are separated, and then the volumetric particle size distribution curve of the single crystal particles is obtained with reference to GB / T 19077-2016. The particle size corresponding to the cumulative volume distribution percentage reaching 50% is taken as the average particle size Dv50.

[0163] In these embodiments, this application discloses that the volumetric particle size distribution Dv50 of the single crystal particles includes any one of 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, and 7.0 μm or satisfies any one of the above range values.

[0164] In some embodiments of this application, the volumetric particle size distribution Dv50 of the quasi-single crystal particles is 3μm to 5μm and does not include 5μm.

[0165] As described above, the quasi-single crystal particles were separated, and then the volumetric particle size distribution curve of the quasi-single crystal particles was obtained with reference to GB / T 19077-2016. The particle size corresponding to the cumulative volume distribution percentage reaching 50% was taken as the average particle size Dv50.

[0166] In these embodiments, this application discloses that the volumetric particle size distribution Dv50 of the quasi-single crystal particles includes any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, and 4.9 μm or satisfies any one of the above range values.

[0167] In some embodiments of this application, the chemical formula of the above-mentioned layered transition metal oxide is Na. x M y O z M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2.

[0168] This application discloses in some embodiments that the aforementioned layered transition metal oxide is a nickel-iron-manganese layered transition metal oxide, and the chemical formula of the nickel-iron-manganese layered transition metal oxide is NaNi. a Fe b Mn c M1 d O2, where a+b+c+d=1, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg, or Zn.

[0169] In these embodiments, this application discloses that a, b, c, and d are each independently selected from any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, and 1.0, or satisfy any of the above range values.

[0170] In some embodiments of this application, the compaction density of the positive electrode film is 3.0 g / cm³. 3 ~3.4g / cm 3 .

[0171] The compaction density of the positive electrode film layer in this application can be used to characterize the energy density of the material. The compaction density of the positive electrode film layer = the areal density of the positive electrode film layer / the thickness of the positive electrode film layer. The thickness of the positive electrode film layer includes the distance between the two end faces of the positive electrode film layer along the thickness direction. The areal density of the positive electrode film layer = the weight of a single positive electrode film layer / the area of ​​a single positive electrode film layer. The weight of a single positive electrode film layer can be obtained by weighing, and the area of ​​a single positive electrode film layer can be obtained by using the area calculation formula according to the shape of the film layer.

[0172] The compaction density of the positive electrode film in this application is 3.0 g / cm³. 3 ~3.4g / cm 3 This is to illustrate that the sodium secondary battery of this application has a relatively high energy density.

[0173] This application discloses in these embodiments that the compaction density of the positive electrode film layer includes 3.0 g / cm³. 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 Any one of the above values ​​or any one of the above range values.

[0174] In some embodiments of this application, the positive electrode active material, in addition to the aforementioned layered transition metal oxide, also includes at least one of a polyanionic compound and a Prussian blue compound. The polyanionic compound includes one or more of sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, and NaFePO4. The Prussian blue compound is Na... x M1M2(CN)6, wherein M1 and M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0 < x ≤ 2.

[0175] In some embodiments of this application, the positive electrode film layer, in addition to the aforementioned positive electrode active material, also includes conductive agents, binders, etc. The conductive agents include, but are not limited to, one or more combinations of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binders include, but are not limited to, one or more combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0176] In some embodiments of this application, the positive current collector can be a metal foil or a composite current collector. The metal foil can be an aluminum foil, and the composite current collector can include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material, such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy, on a polymer substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0177] The method for forming the positive electrode film in this application includes mixing the above-mentioned raw materials with a solvent (such as N-methylpyrrolidone) in a certain mass ratio to form a positive electrode slurry, and uniformly coating the positive electrode slurry onto both sides of the positive electrode current collector; controlling the coating weight on one side to be 0.25g~0.50g / 1540.25mm. 2 After drying, it is then compacted to a certain compaction density (3.0 g / cm³) using a cold press. 3 ~3.4g / cm 3 This yields a positive electrode sheet containing a positive electrode film.

[0178] [Negative electrode plate]

[0179] According to some embodiments of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side surface of the negative electrode current collector. The negative electrode film layer contains a negative electrode active material.

[0180] The negative electrode active material in this application comprises carbonaceous materials, including one or more combinations of artificial graphite, natural graphite, soft carbon, and hard carbon. Among these, artificial graphite, natural graphite, soft carbon, and hard carbon encompass any form of material conventional in the art, and include any manufacturer and model conventional in the art. Simultaneously, the negative electrode active material may also comprise silicon-based materials, including one or two of silicon-oxygen materials or silicon-carbon materials. In addition, the negative electrode active material may also comprise silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 Li-Al alloys are used. However, this application is not limited to these materials; other conventional materials that can be used as negative electrode active materials in sodium secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0181] The method for preparing artificial graphite in this application includes: providing raw materials, crushing and shaping → granulation → graphitization treatment → surface roughening treatment to obtain artificial graphite material. The raw materials in these embodiments of this application can be one or more of raw coke and calcined coke; preferably, the raw materials include one or more of needle-shaped raw petroleum coke, non-needle-shaped raw petroleum coke, needle-shaped coal-based raw coke, non-needle-shaped coal-based raw coke, calcined needle-shaped coke, and calcined petroleum coke. The crushing in this application can be performed using devices and methods known in the art, such as air jet mills, mechanical mills, or roller mills. During the crushing process, a large number of excessively small particles are usually generated, and sometimes excessively large particles are also generated. Therefore, after crushing, grading can be performed as needed to remove excessively small and excessively large particles from the crushed powder. Grading can obtain granular products with a better particle size distribution, which is beneficial for subsequent molding and / or granulation processes. Grading can be performed using devices and methods known in the art, such as grading sieves, gravity classifiers, or centrifugal classifiers. The shaping in this application can be performed using equipment (e.g., molding machines or other molding equipment) and methods known in the art. For example, polishing the edges of the resulting granular product facilitates subsequent operations and improves the stability of the product. The granulation process in this application includes using equipment known in the art, such as a granulator. A granulator typically includes a stirred reactor and a reactor temperature control module. Furthermore, the median particle size of the resulting product can be controlled by adjusting process conditions during granulation, such as stirring speed, heating rate, granulation temperature, and cooling rate. The graphitization process in this application includes high-temperature graphitization and low-temperature graphitization. In some embodiments, one or both of high-temperature and low-temperature graphitization can be appropriately selected for treatment according to specific needs. Alternatively, high-temperature and / or low-temperature graphitization can be repeated. High-temperature graphitization can yield graphite with an appropriate degree of graphitization and interlayer spacing. Graphite prepared at an appropriate graphitization temperature can achieve an appropriate degree of graphitization and interlayer spacing, thereby enabling the composite artificial graphite to obtain high structural stability and specific capacity. The surface roughening process in this application includes using conventional methods in the art, such as physical methods.

[0182] In addition to the negative electrode active material, the negative electrode film layer of this application also includes binders, conductive agents, dispersants, etc. The binders include, but are not limited to, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, styrene-butadiene rubber (SBR), etc. The conductive agents include any type conventional in the art, such as graphite, superconducting carbon, carbon black (e.g., acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers, or a combination of two or more of these. The dispersants also include any type conventional in the art, such as cellulose and its salts, specifically including, but not limited to, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0183] The method for forming the negative electrode film in this application includes mixing the above-mentioned raw materials with a solvent (such as deionized water) in a certain mass ratio to form a negative electrode slurry, defoaming the negative electrode slurry, and then uniformly coating the negative electrode slurry onto both sides of the negative electrode current collector; controlling the single-sided coating weight to be 0.13g~0.25g / 1540.25mm. 2 Drying, followed by compaction using a cold press to a specific compaction density (1.65 g / cm³). 3 < Compacted density ≤ 2.0 g / cm³ 3 This yields a negative electrode sheet containing a negative electrode film.

[0184] Electrolyte

[0185] In some embodiments of this application, the sodium secondary battery further includes an electrolyte, which can be liquid, solid, or gel-like. Solid state refers to a solid electrolyte, liquid state to a liquid electrolyte, and gel-like state to a gel electrolyte. The sodium secondary battery of this application uses a liquid electrolyte, i.e., an electrolyte solution. This electrolyte solution contains an electrolyte salt and an organic solvent. The electrolyte salt can be any type conventional in the art, including, but not limited to, inorganic metal salts such as NaClO4, NaAsF6, NaPF6, NaBF4, NaSbF6, NaSO3F, NaN(FSO2)2, etc.; fluorine-containing organometallic salts such as NaCF3SO3, NaN(FSO2)(CF3SO2), NaN(CF3SO2)2, NaN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonylimide sodium, cyclic 1,2-tetrafluoroethane disulfonylimide sodium, NaN(CF3SO2)(C4F5SO2)2, etc. 9SO2), NaC(CF3SO2)3, NaPF4(CF3)2, NaPF4(C2F5)2, NaPF4(CF3SO2)2, NaPF4(C2F5SO2)2, NaBF2(CF3)2, NaBF2(C2F5)2, NaBF2(CF3SO2)2, NaBF2(C2F5SO2)2, etc.; and metal salts containing dicarboxylic acid complexes, such as sodium bis(oxalate oxy)borate, sodium difluorooxalate oxyborate, sodium tri(oxalate oxy)phosphate, sodium difluorobis(oxalate oxy)phosphate, sodium tetrafluoro(oxalate oxy)phosphate, etc.

[0186] According to some embodiments of this application, the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L. In these embodiments, this application discloses that the concentration of the electrolyte salt is any one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, and 4 mol / L, or any value within the above range. The concentration of the electrolyte salt in the electrolyte described herein refers to the concentration at the time of preparation. In actual use, the electrolyte salt will be consumed during battery cycling, resulting in a decrease in concentration.

[0187] As described above, the organic solvent comprises one or more of carboxylic acid esters, carbonates, and ethers. Specifically, the carboxylic acid esters comprise one or more of ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), propyl acetate (PA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL); the carbonates comprise one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), and fluoroethylene carbonate (FEC). The ethers comprise at least one of tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran, dimethyl tetrahydropyran, 1,2-dimethoxyethane, dipropylene glycol dimethyl ether, or dimethyl phthalate. The organic solvents of this application further include one or two of nitrile solvents and sulfone solvents. The nitrile solvents include one or more of acetonitrile (AN), glutaronitrile (GLN), and adiponitrile (ADN). The sulfone solvents include at least one or a combination of two of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0188] According to some embodiments of this application, the electrolyte further comprises a film-forming stabilizer, which includes a positive electrode film-forming stabilizer and a negative electrode film-forming stabilizer. The positive electrode film-forming stabilizer includes carbonate additives and / or sulfate additives. The carbonate additives include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The sulfate additives include cyclic sulfonate additives and / or alkyl sulfate additives; further, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro1,3-propanesulfonate lactone (FPS); the alkyl sulfate additives include one or more of vinyl sulfate (DTD), diethyl sulfate (DES), and dimethyl sulfate (DMS). The negative electrode film-forming stabilizer includes one or more of sodium boron salts, phosphorus-containing sodium salts, and sulfur-containing sodium salts; the sodium boron salts include sodium tetrafluoroborate (NaBF4) and sodium bis(oxalato)borate.

[0189] Sodium difluorooxalate borate (NaBOB) and sodium difluorooxalate borate (NaDFOB) are among the following: phosphorus-containing lithium salts include sodium difluorophosphate (NaPO2F2), sodium fluorophosphate (Na2PO3F), and sodium phosphate (Na3PO4). Sulfur-containing sodium salts include sodium fluorosulfonate (NaFSO3), sodium sulfate (Na2SO4), and sodium aminosulfonate (NaSO3NH2) are among the following:

[0190] [Isolation membrane]

[0191] Some embodiments of this application disclose a separator membrane. This application does not have any particular limitation on the type of separator membrane, and any well-known porous structure separator membrane with good chemical and mechanical stability can be selected.

[0192] In some embodiments, the separator includes a substrate material layer, the substrate material of which includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

[0193] In some embodiments, the separator includes a substrate material layer and a coating disposed on the surface of the substrate material layer; the substrate material of the substrate material layer includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide; the coating includes a ceramic coating and / or a polymer coating. The substrate material layer has good lithium ion permeability, which is beneficial to lithium ion migration; the coating disposed on the surface of the substrate material layer can further improve the mechanical properties of the separator. Optionally, the ceramic particles in the ceramic coating include one or more of SiO2, Al2O3, AlOOH, CaO, TiO2, MgO, ZnO, ZrO2, Mg(OH)2, and BaSO4. Optionally, the polymer material of the polymer coating includes one or more of polyethylene (PE), polypropylene (PP), poly(p-phenylene terephthalamide) (PPTA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), and polyamide (PA). The polymer coating can be made of the same or different material as the substrate material layer, and the thicknesses of the polymer coating and the substrate material layer can be different. Optionally, the thickness of the polymer coating is less than the thickness of the substrate material layer.

[0194] In other embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0195] Positive electrode active material for sodium secondary batteries

[0196] Some embodiments of this application disclose a positive electrode active material for sodium secondary batteries. This positive electrode active material comprises single-crystal particles and / or quasi-single-crystal particles of layered transition metal oxides. The single-crystal particles and / or quasi-single-crystal particles include any one or more of spherical, quasi-spherical, polygonal sheet-like, and polygonal columnar shapes. The positive electrode active material satisfies the following conditions:

[0197] (1) The volumetric particle size distribution Dv50 is 3μm~7μm;

[0198] (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

[0199] In this application, a single crystal particle refers to a single particle or primary particle with a complete crystal shape (complete crystal edges and crystal faces), and the crystal lattice inside the particle is periodically arranged.

[0200] In this application, quasi-single-crystal particles refer to irregularly shaped particles formed by the aggregation of a small number of large-diameter single-crystal particles.

[0201] The shapes of the single-crystal particles and / or quasi-single-crystal particles in this application are obtained by observing the shape with the naked eye from electron micrographs taken of the positive electrode active material. Among them, polygon refers to at least quadrilaterals and above.

[0202] The single-crystal particles and / or quasi-single-crystal particles provided in this application have suitable particle size and specific surface area, which is beneficial to improving the cycle life of sodium secondary batteries.

[0203] The measurement method for the volumetric particle size distribution Dv50 of the positive electrode active material in this application includes: referring to GB / T 19077-

[0204] In 2016, the volumetric particle size distribution curves of single-crystal particles and / or single-crystal-like particles were obtained. The particle size corresponding to a cumulative volumetric distribution percentage of 50% was taken as the average particle size Dv50. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. Deionized water was used as the solvent, and the single-crystal particles and / or single-crystal-like particles were ultrasonically treated for 5 minutes before testing.

[0205] In some embodiments of this application, the volumetric particle size distribution Dv50 of the positive electrode active material includes 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, and 4. The value is any one of the following: 9μm, 5.0μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6.0μm, 6.1μm, 6.2μm, 6.3μm, 6.4μm, 6.5μm, 6.6μm, 6.7μm, 6.8μm, 6.9μm, 7.0μm, or any one of the values ​​within the above range.

[0206] The surface area (BET) of the positive electrode active material in this application is measured using the nitrogen adsorption specific surface area analysis method, referring to GB / T 19587-2004, and the specific surface area of ​​single crystal particles and / or quasi-single crystal particles is calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a TRISTAR II3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0207] In some embodiments of this application, the specific surface area BET of the positive electrode active material comprises 0.30 m². 2 / g, 0.31m 2 / g, 0.32m 2 / g, 0.33m 2 / g, 0.34m 2 / g, 0.35m 2 / g, 0.36m 2 / g, 0.37m 2 / g, 0.38m 2 / g, 0.39m 2 / g, 0.40m 2 / g, 0.41m 2 / g, 0.42m 2 / g, 0.43m 2 / g, 0.44m 2 / g, 0.45m 2 / g, 0.46m 2 / g, 0.47m 2 / g, 0.48m 2 / g, 0.49m 2 / g, 0.50m 2 Any one of / g or any one of the above range values.

[0208] The single-crystal particles and / or quasi-single-crystal particles provided in this application have suitable specific surface area and particle size, which can reduce the probability of interfacial side reactions to a certain extent, thus improving the cycle life of sodium secondary batteries.

[0209] At the same time, the single crystal particles and / or quasi-single crystal particles provided in this application can also be loaded with higher voltages, which is also beneficial to improving the energy density of the battery.

[0210] In some embodiments of this application, the mass percentage content of single crystal particles in the above-mentioned positive electrode active material is 20% to 40%.

[0211] The method for determining the mass percentage content of single crystal particles in the positive electrode active material in this application includes obtaining a portion of the positive electrode active material in the positive electrode film layer, weighing it as m0, separating the single crystal particles in the positive electrode active material under a high-power electron microscope, weighing it as m1, and calculating (m1÷m0)×100% as the mass percentage content of single crystal particles in the positive electrode active material.

[0212] In these embodiments, this application discloses that the mass percentage content of single crystal particles in the above-mentioned positive electrode active material includes any one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, and 40%, or any one of the above-mentioned range values.

[0213] In some embodiments of this application, the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is 60% to 80%.

[0214] The method for determining the mass percentage content of single-crystal-like particles in the positive electrode active material in this application includes obtaining a portion of the positive electrode active material in the positive electrode film layer, weighing it as m0, separating the single-crystal-like particles in the positive electrode active material under a high-power electron microscope, weighing it as m2, and calculating (m2÷m0)×100% as the mass percentage content of single-crystal particles in the positive electrode active material.

[0215] In these embodiments, this application discloses that the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is any one of 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any one of the above range values.

[0216] In some embodiments of this application, the positive electrode active material is disclosed to include single crystal particles and single crystal-like particles, and the sum of the mass percentage content of single crystal particles and the mass percentage content of single crystal-like particles is less than or equal to 100%.

[0217] In some embodiments of this application, the volumetric particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0218] As described above, single crystal particles are separated, and then the volumetric particle size distribution curve of the single crystal particles is obtained with reference to GB / T 19077-2016. The particle size corresponding to the cumulative volume distribution percentage reaching 50% is taken as the average particle size Dv50.

[0219] In these embodiments, this application discloses that the volumetric particle size distribution Dv50 of the single crystal particles includes any one of 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, and 7.0 μm or satisfies any one of the above range values.

[0220] This application discloses in these embodiments that the specific surface area (BET) of the single crystal particles comprises 0.30 m². 2 / g, 0.31m 2 / g, 0.32m 2 / g, 0.33m 2 / g, 0.34m 2 / g, 0.35m 2 / g, 0.36m 2 / g, 0.37m 2 / g, 0.38m 2 / g, 0.39m 2 / g, 0.40m 2 Any one of / g or any one of the above range values.

[0221] In some embodiments of this application, the volumetric particle size distribution Dv50 of the quasi-single crystal particles is 3μm to 5μm and does not include 5μm.

[0222] As described above, the quasi-single crystal particles were separated, and then the volumetric particle size distribution curve of the quasi-single crystal particles was obtained with reference to GB / T 19077-2016. The particle size corresponding to the cumulative volume distribution percentage reaching 50% was taken as the average particle size Dv50.

[0223] In these embodiments, this application discloses that the volumetric particle size distribution Dv50 of the quasi-single crystal particles includes any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, and 4.9 μm or satisfies any one of the above range values.

[0224] In some embodiments of this application, the chemical formula of the above-mentioned layered transition metal oxide is Na. x M y O z M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2.

[0225] This application discloses in some embodiments that the aforementioned layered transition metal oxide is a nickel-iron-manganese layered transition metal oxide, and the chemical formula of the nickel-iron-manganese layered transition metal oxide is NaNi. a Fe b Mn c M1 d O2, where a+b+c+d=1, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg, or Zn.

[0226] In these embodiments, this application discloses that a, b, c, and d are each independently selected from any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, and 1.0, or satisfy any of the above range values.

[0227] In some embodiments of this application, the positive electrode active material, in addition to the aforementioned layered transition metal oxide, also includes at least one of a polyanionic compound and a Prussian blue compound. The polyanionic compound includes one or more of sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, and NaFePO4. The Prussian blue compound is Na... xM1M2(CN)6, wherein M1 and M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0 < x ≤ 2.

[0228] In some embodiments of this application, the tap density of the above-mentioned single crystal particles and / or quasi-single crystal particles is 1.55 g / cm³. 3 ~1.80g / cm 3 .

[0229] The tap density in this application includes any concept conventional in the art, which can be obtained by testing with instruments or methods known in the art, such as by testing with reference to standard GB / T5162-2006.

[0230] This application discloses in these embodiments that the tap density of single-crystal particles and / or quasi-single-crystal particles is 1.55 g / cm³. 3 1.56g / cm 3 1.57g / cm 3 1.58g / cm 3 1.59g / cm 3 1.60g / cm 3 1.61 g / cm 3 1.62g / cm 3 1.63g / cm 3 1.64 g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.67 g / cm 3 1.68g / cm 3 1.69 g / cm 3 1.70g / cm 3 1.71 g / cm 3 1.72g / cm 3 1.73g / cm 3 1.74 g / cm 3 1.75g / cm 3 1.76 g / cm 3 1.77g / cm 3 1.78g / cm 3 1.79g / cm 3 1.80g / cm 3 Any one of the above values ​​or any one of the above range values.

[0231] Preparation method of positive electrode active material for sodium secondary batteries

[0232] Some embodiments of this application disclose a method for preparing a positive electrode active material for sodium secondary batteries, including the following steps:

[0233] S1. Provide a cathode material precursor, including the following preparation process:

[0234] S11, according to the chemical formula Ni x Fe y Mn z Prepare a mixed solution of metal salts with a molar concentration of (2.0 ± 0.4) mol / L in (OH)₂, where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z = 1. Simultaneously prepare a sodium hydroxide solution with a mass fraction of 25%–35%, an ammonia solution with a mass fraction of 15%–25%, and a chelating agent solution (ethylenediaminetetraacetic acid or N-hydroxyethylidene diamine) with a mass fraction of 0.001%–0.25%. Add deionized water to the reaction vessel, followed by the ammonia solution, chelating agent solution, and sodium hydroxide solution in sequence, controlling the pH at 10.3–12.5 and the reaction temperature at 40℃–70℃ ± 1℃.

[0235] S12. Add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor. The flow rate ratio of the four solutions is (15-125):(3-55):(1-7):(0.1-2). After nucleation for 3-5 hours, adjust the flow rate of sodium hydroxide to lower the pH to below 11.6 to complete the nucleation process. Continue to add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor for co-precipitation reaction. The flow rate ratio of the four solutions is (15-125):(3-55):(1-7):(0.1-2). Control the reaction pH at 10.3-11.6. After the reaction is maintained for 40-90 hours, the growth process of precursor particles is completed.

[0236] S13. Transfer the solution in the above reaction vessel to a centrifuge for solid-liquid separation to obtain a positive electrode material precursor containing water. Then dry the wet precursor material at 110℃~120℃ for 10h~20h to obtain the finished positive electrode material precursor.

[0237] S2. Preparation of intermediate products for cathode materials: Take cathode material precursor and sodium carbonate and mix them. The molar amount of metal atoms in the cathode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, satisfying N1 / N2 = 1:(0.5~1.1).

[0238] The cathode material intermediate is prepared by first calcination in an oxygen-containing atmosphere (such as air or pure oxygen) at a temperature of 850℃ to 970℃ for 7 to 15 hours, followed by cooling to room temperature. The intermediate is then subjected to coarse crushing, fine crushing, and sieving to obtain the intermediate product. The volumetric particle size distribution (Dv50) of this intermediate product is 8 μm to 12 μm. This intermediate product contains polycrystalline particles of layered transition metal oxides, with a polycrystalline particle content of approximately 100% by mass. The mass percentage of polycrystalline particles is measured by observing the particle morphology under a high-power electron microscope, which shows that almost all particles are polycrystalline. In this application, polycrystalline particles refer to a single particle containing multiple crystals. The crystal lattice of each crystal is periodically arranged, but the orientation of these crystals is arbitrary. Such crystals generate diffraction points due to their internal periodic structure. These diffraction points appear on a circle with a radius equal to the interplanar spacing 1 / d. Different crystal planes result in different circle radii, thus creating multiple rings.

[0239] S3. Preparation of positive electrode active material: Disperse the dispersant into the solvent to form a mixed solvent, disperse the above-mentioned positive electrode material intermediate product into the above-mentioned mixed solvent, control the mass ratio of the above-mentioned positive electrode material intermediate product to the volume ratio of the above-mentioned mixed solvent to be (10g~20g) / (20mL~100mL), and then heat and stir the obtained mixture until the solvent evaporates to dryness;

[0240] The positive electrode active material is then obtained by a second calcination in an oxygen-containing atmosphere (such as air or pure oxygen), with the second calcination temperature being 600℃~1000℃ and the holding time being 3h~24h. The positive electrode active material obtained in this application includes single crystal particles and / or single crystal-like particles of layered transition metal oxides, and the mass percentage content of the single crystal particles and single crystal-like particles in the above-mentioned positive electrode active material is >98%. The method for measuring the mass percentage content of the single crystal particles and single crystal-like particles includes obtaining a portion of the positive electrode active material and weighing it as m. 0， The particle morphology was observed under a high-power electron microscope. Under the high-power electron microscope, the single crystal particles and quasi-single crystal particles in the positive electrode active material were separated and weighed as m3. The mass percentage of single crystal particles in the positive electrode active material was calculated as (m3÷m0)×100%.

[0241] In some embodiments of this application, the dispersant described above satisfies the following conditions:

[0242] (1) The dispersant is soluble in one or more of alcoholic solvents, acetone, and water;

[0243] (2) The decomposition temperature of the dispersant is less than or equal to 600℃. The decomposition temperature of the dispersant is the temperature corresponding to the decomposition peak of the thermogravimetric curve of the above dispersant.

[0244] The method for obtaining the decomposition temperature of the dispersant in this application includes: taking 10 mg to 20 mg of dispersant sample powder, drying it to remove moisture, placing it in a thermal analysis crucible, setting the test temperature range to 0℃~600℃, setting the heating rate to 10℃ / min, and placing it in a thermogravimetric analyzer to obtain a thermogravimetric analysis curve (TG curve). Then, taking the first derivative of each point on the TG curve with respect to the time axis, the differential thermogravimetric curve (DTG curve) is obtained. The DTG curve shows the change in the rate of thermogravimetric change over time, and the temperature corresponding to a rate of thermogravimetric change greater than zero is the decomposition temperature.

[0245] The dispersant selected in this application is easy to dissolve in the solvent and also easy to remove during the second calcination.

[0246] In some embodiments of this application, the dispersant includes polyvinylpyrrolidone and its modified compounds. Polyvinylpyrrolidone in this application refers to a polymer obtained by polymerizing vinylpyrrolidone monomer. Modified compounds of polyvinylpyrrolidone in this application include polymers obtained by polymerizing vinylpyrrolidone monomer with other monomers, such as olefins, alkynes, and epoxides.

[0247] The polyvinylpyrrolidone and its modified compounds of this application contain atoms such as nitrogen and oxygen. These atoms readily interact with one or more polar solvents, such as alcohols, acetone, and water. At the same time, these atoms also readily interact with metal ions of layered transition metal oxides, thereby dispersing the layered transition metal oxide particles in the solvent.

[0248] In some embodiments of this application, the mass of the dispersant added is 0.5% to 5% of the mass of the solvent.

[0249] In these embodiments, this application discloses that the amount of the dispersant added is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or 2.6% of the solvent mass. 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0% or any of the values ​​within the above range.

[0250] In some embodiments of this application, the solvents mentioned above include one or more of alcohols, acetone, and water;

[0251] The aforementioned alcohol solvents include one or more of ethanol, ethylene glycol, and glycerol. The solvents used in this application are primarily used for the uniform dispersion of polyvinylpyrrolidone and its modified compounds.

[0252] In some embodiments of this application, the solvent includes ethanol and water in a volume ratio of 1:1.

[0253] In some embodiments of this application, after the above-mentioned cathode material intermediate product is dispersed in the above-mentioned mixed solvent and before the second calcination, the following steps are further included:

[0254] The above mixed solvent is heated to 70℃~100℃ and stirred until the solvent evaporates to dryness.

[0255] In some embodiments of this application, the mass percentage content of single crystal particles and quasi-single crystal particles in the positive electrode active material is 100%.

[0256] In some embodiments of this application, the mass percentage content of single-crystal particles in the positive electrode active material is 20% to 40%; the mass percentage content of quasi-single-crystal particles in the positive electrode active material is 60% to 80%.

[0257] In some embodiments of this application, after the first calcination, the process further includes coarse crushing, fine crushing and sieving to obtain a cathode material intermediate product, wherein the volume particle size distribution Dv50 of the cathode material intermediate product is 8μm to 12μm.

[0258] The method for determining the volumetric particle size distribution Dv50 of the cathode material intermediate product in this application is as described above, and will not be repeated here. In these embodiments, this application discloses that the volumetric particle size distribution Dv50 of the cathode material intermediate product is any one of 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, and 12μm or any one of the above range values.

[0259] In some embodiments of this application, the molar amount of metal atoms in the cathode material precursor is N1, and the molar amount of sodium atoms in sodium carbonate is N2, satisfying N1 / N2 = 1:(0.5~1.1).

[0260] The cathode material precursor product in this application undergoes a solid-state reaction with sodium carbonate during the first calcination. The material generated by this reaction mainly consists of polycrystalline particles formed by agglomeration. There are gaps between the individual crystals of these polycrystalline particles. After being soaked in a solvent containing polyvinylpyrrolidone and its modified compounds, the interaction force between the individual crystals is weakened, and during the second calcination, they decompose into single crystal particles or quasi-single crystal particles.

[0261] Preparation method of sodium secondary battery

[0262] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Three copper wires are added for the electrodes, and the tabs are welded together to form a stacked battery cell. The stacked battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a sodium secondary battery is obtained.

[0263] The secondary battery of this application will be described in detail below with reference to specific embodiments.

[0264] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0265] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0266] This application may employ conventional inorganic chemistry techniques within the art. In the following examples, efforts have been made to ensure the accuracy of the figures used (including quantities, temperatures, reaction times, etc.), but some experimental errors and biases should be considered. Temperatures (in degrees Celsius) used in the following examples are expressed in °C, and pressures are at or near atmospheric pressure. All reagents were purchased from AR-grade suppliers, and all reactions were carried out under argon protection. Unless otherwise stated, all reagents were obtained commercially.

[0267] Experimental materials:

[0268] 1. Polyvinylpyrrolidone: Aladdin (the decomposition temperature of polyvinylpyrrolidone is 450℃);

[0269] 2. Ethanol: Aladdin;

[0270] 3. Acetone: Aladdin.

[0271] Experimental setup:

[0272] 1. Box furnace: Kejing OTF-1200X-S.

[0273] 2. Scanning electron microscope: Zeiss LEEQ0344.

[0274] Preparation Example 1-1

[0275] A layered oxide polycrystalline particle (chemical formula: NaNi) is provided. 0.4 Fe 0.2 Mn 0.4 Preparation method of O2—NFM424:

[0276] S1. Provide a precursor, including the following preparation process:

[0277] S11, according to the chemical formula Ni x Fey Mn z Prepare a mixed solution of metal salts with a molar concentration of (2.0±0.4) mol / L in (OH)2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1. Simultaneously prepare a 30% sodium hydroxide solution, a 20% ammonia solution, and a 0.1% chelating agent solution (ethylenediaminetetraacetic acid). Add deionized water to the reaction vessel, followed by the ammonia solution, chelating agent solution, and sodium hydroxide solution, controlling the pH at 10.8 and the reaction temperature at 40℃~70℃±1℃.

[0278] S12. Add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor. The flow rate ratio of the four solutions is 15:30:5:1. After nucleation for 5 hours, adjust the flow rate of sodium hydroxide to reduce the pH to below 11.6 to complete the nucleation process. Continue to add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor for co-precipitation reaction. The flow rate ratio of the four solutions is 15:30:5:1. Control the reaction pH at 10.5. After maintaining the reaction for 48 hours, the growth process of precursor particles is completed.

[0279] S13. Transfer the solution in the above reaction vessel to a centrifuge for solid-liquid separation to obtain a positive electrode material precursor containing water. Then dry the wet precursor material at 120°C for 20 hours to obtain the finished precursor product.

[0280] S2. Preparation of layered oxide polycrystalline particles: Take the cathode material precursor and mix it with sodium carbonate, wherein the molar amount of metal atoms in the cathode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, satisfying N1 / N2 = 1:1.02.

[0281] The product is first calcined in an oxygen-containing atmosphere (such as air or pure oxygen) at a temperature of 850°C for 13 hours. The temperature is then lowered to room temperature, followed by coarse crushing, fine crushing, and sieving to obtain layered oxide polycrystalline particles.

[0282] Characteristic 1:

[0283] To obtain scanning electron microscope (SEM) images of the precursor and polycrystalline particles in Preparation Example 1-1 above: each sample was placed on the sample stage, placed in the electron microscope chamber, vacuumed, the electron beam was turned on, and appropriate parameters were set for characterization: the parameters for observing the morphology were 3kV, the aperture was 30μm, and the working distance was 5mm.

[0284] like Figure 7A and 7B Indication, among which, Figure 7A SEM images of the precursor. Figure 7B SEM images of polycrystalline particles; combined with Figure 7A It can be seen that the precursors are uniform in size, and the particles are plate-like, combined with Figure 7B It can be seen that after sodium supplementation and sintering, the overall size of the particles does not change much, and the morphology is spherical.

[0285] Test 1:

[0286] Referring to GB / T 19077-2016, the volumetric particle size distribution curve of the polycrystalline particles was obtained. The particle size corresponding to the cumulative volume distribution percentage reaching 50% was taken as the average particle size Dv50. The Dv50 of the polycrystalline particles in this preparation example 1-1 is 10.5 μm.

[0287] Preparation Example 1-1a

[0288] The layered oxide polycrystalline particles obtained in Preparation Example 1-1 were further processed, and the specific steps are as follows:

[0289] S3. Provide a mixed solvent: Mix ethanol and water in a volume ratio of 1:1 to form 500 mL of solvent. Add polyvinylpyrrolidone to the solvent and mix well to form a mixed solvent. The mass of polyvinylpyrrolidone added is 2% of the mass of the solvent.

[0290] Dispersion: Take 10g of the layered oxide polycrystalline particles obtained in Preparation Example 1-1 and disperse them in 30mL of the above mixed solvent, stir and mix well to obtain a mixture;

[0291] Heating: Transfer the mixture to a crucible, heat the mixed solvent to 80°C, and stir under the heat until the solvent is completely evaporated, controlling the stirring speed to 500 rpm. After the solvent is evaporated, the remaining solid is left.

[0292] Second calcination: The solid is transferred to a box furnace and calcined in air, with the furnace temperature controlled at around 900℃ and held for 12 hours;

[0293] Temperature drop to room temperature: obtain layered oxide positive electrode active material.

[0294] Characteristic 2:

[0295] Scanning electron microscope (SEM) images of the solid obtained by heating in the above preparation example 1-1a and the layered oxide positive electrode active material obtained by cooling to room temperature were obtained: Each sample was placed on the sample stage, put into the electron microscope chamber, vacuumed, the electron beam was turned on, and appropriate parameters were set for characterization: the parameters for observing the morphology were 3kV, the aperture was 30μm, and the working distance was 5mm.

[0296] like Figure 8A and 8B Indication, among which, Figure 8A The image shows the SEM image of the solid material obtained by heating. Figure 8BSEM images of layered oxide cathode active materials obtained by cooling to room temperature; combined with Figure 8A It is known that adding a dispersant is beneficial for dispersing polycrystalline materials, and combining Figure 8B It can be seen that after the second calcination, the particles undergo solid solution treatment, resulting in larger particle size and better morphology, mainly in the form of flakes.

[0297] Test 2:

[0298] (1) Referring to GB / T 19077-2016, the volume particle size distribution curve of the layered oxide positive electrode active material was obtained. The particle size corresponding to the cumulative volume distribution percentage reaching 50% was taken as the average particle size Dv50. The Dv50 of the layered oxide positive electrode active material of this preparation example 1-1a is 5.1 μm.

[0299] (2) Referring to GB / T 19587-2004, the specific surface area was tested using the nitrogen adsorption specific surface area analysis method, and the specific surface area BET of the layered oxide positive electrode active material was calculated using the BET (Brunauer Emmett Teller) method. The specific surface area BET of the layered oxide positive electrode active material in this preparation example 1-1a was 0.45 m². 2 / g.

[0300] (3) Referring to GB / T5162-2006, the tap density of the layered oxide cathode active material was found to be 1.68 g / cm³. 3 .

[0301] (4) Combining the SEM images in characterization 2 above, the layered oxide positive electrode active material with mass m0 is separated to obtain layered oxide single crystal particles with mass m1 and layered oxide-like single crystal particles with mass m2.

[0302] According to the formula (m1÷m0)×100%, the mass percentage content of single crystal particles in the above-mentioned layered oxide cathode active material is about 60%.

[0303] According to the formula: (m2÷m0)×100%, the mass percentage content of the single-crystal particles in the above-mentioned layered oxide cathode active material is about 40%.

[0304] Then, following the GB / T 19077-2016 standard, the particle size Dv50 of the single crystal particles and the single crystal-like particles was measured, and the specific surface area BET of the single crystal particles and the single crystal-like particles was measured according to the GB / T 19587-2004 standard. See Table 1 below for details.

[0305] Preparation Example 1-1b

[0306] The layered oxide polycrystalline particles obtained in Preparation Example 1-1 were further processed. The difference between this processing method and that in Preparation Example 1-1a is that the mass of polyvinylpyrrolidone added was 5% of the solvent mass, and the temperature of the box furnace was controlled at about 995°C during the second calcination, and the temperature was held for 10 hours. Everything else was the same as in Preparation Example 1-1a.

[0307] The data in Table 1 below were obtained according to the test method of Preparation Example 1-1a described above.

[0308] Preparation Example 1-1c

[0309] The layered oxide polycrystalline particles obtained in Preparation Example 1-1 were further processed. The difference between this processing method and that in Preparation Example 1-1a is that the mass of polyvinylpyrrolidone added was 0.5% of the solvent mass, and the temperature of the box furnace was controlled at about 600°C during the second calcination, and the temperature was held for 24 hours. Everything else was the same as in Preparation Example 1-1a.

[0310] The data in Table 1 below were obtained according to the test method of Preparation Example 1-1a described above.

[0311] Preparation Example 1-1d

[0312] The layered oxide polycrystalline particles obtained in Preparation Example 1-1 were further processed. The difference between this processing method and that in Preparation Example 1-1a is that acetone and water were mixed at a volume ratio of 1:2 to form 500 mL of solvent, and the temperature of the box furnace was controlled at about 610°C during the second calcination, and the temperature was held for 10 h. Everything else was the same as in Preparation Example 1-1a.

[0313] The data in Table 1 below were obtained according to the test method of Preparation Example 1-1a described above.

[0314] Preparation Example 1-1e

[0315] A method for preparing layered oxide positive electrode activity is provided, the method comprising:

[0316] S1. Provide a precursor, including the following preparation process:

[0317] S11, according to the chemical formula Ni x Fe y Mn zPrepare a mixed solution of metal salts with a molar concentration of (2.0±0.4) mol / L in (OH)2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1. Simultaneously prepare a 30% sodium hydroxide solution, a 20% ammonia solution, and a 0.1% chelating agent solution (ethylenediaminetetraacetic acid). Add deionized water to the reaction vessel, followed by the ammonia solution, chelating agent solution, and sodium hydroxide solution, controlling the pH at 10.8 and the reaction temperature at 40℃~70℃±1℃.

[0318] S12. Add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor. The flow rate ratio of the four solutions is 15:30:5:1. After nucleation for 5 hours, adjust the flow rate of sodium hydroxide to reduce the pH to below 11.6 to complete the nucleation process. Continue to add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor for co-precipitation reaction. The flow rate ratio of the four solutions is 15:30:5:1. Control the reaction pH at around 10.5. After the reaction is maintained for 48 hours, the growth process of precursor particles is completed.

[0319] S13. Transfer the solution in the above reaction vessel to a centrifuge for solid-liquid separation to obtain a positive electrode material precursor containing water. Then dry the wet precursor material at 120°C for 20 hours to obtain the finished precursor product.

[0320] S2, Dispersion precursor finished product:

[0321] S21: Provide a mixed solvent: Take ethanol and water at a volume ratio of 1:1 and mix them to form 500 mL of solvent. Add polyvinylpyrrolidone to the solvent and mix well to form a mixed solvent. The mass of polyvinylpyrrolidone added is 2% of the mass of the solvent.

[0322] S22: Dispersion: Take 10g of the above-mentioned precursor product and disperse it in 30mL of the above-mentioned mixed solvent, stir and mix well to obtain a mixture;

[0323] S23: Heating: Transfer the mixture to a crucible, heat the mixed solvent to 80°C, and stir under the heat until the solvent is completely evaporated, controlling the stirring speed to 500 rpm, leaving solids;

[0324] S3, calcination:

[0325] The remaining solid was mixed with sodium carbonate to obtain a mixture, wherein the molar amount of metal atoms in the remaining solid was N1 and the molar amount of sodium atoms in the sodium carbonate was N2, satisfying N1 / N2 = 1:1.02; the mixture was placed in a box furnace and calcined in air at a temperature of 850°C for 13 hours, and then cooled to room temperature to obtain a layered oxide positive electrode active material.

[0326] Characteristic 3:

[0327] Scanning electron microscope (SEM) images of the layered oxide positive electrode active materials prepared in the above preparation examples 1-1e were obtained: Each sample was placed on the sample stage, placed in the electron microscope chamber, vacuumed, the electron beam was turned on, and appropriate parameters were set for characterization: the parameters for observing the morphology were 3kV, the aperture was 30μm, and the working distance was 5mm.

[0328] like Figure 9 Indication, combined Figure 9 It can be seen that the particles after the precursor is dispersed are agglomerated. The Dv50 of the primary particles is about 1.5 μm, and the Dv50 of the agglomerated particles is about 8.5 μm. This indicates that the dispersant has a poor dispersion effect on the precursor.

[0329] Preparation Example 2-1

[0330] A layered oxide polycrystalline particle (chemical formula: NaNi) is provided. 1 / 3 Fe 1 / 3 Mn 1 / 3 Preparation method of O2—NFM333)2:

[0331] S1. Provide a precursor, including the following preparation process:

[0332] S11, according to the chemical formula Ni x Fe y Mn z Prepare a mixed solution of metal salts with a molar concentration of (2.0±0.4) mol / L in (OH)2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1. Simultaneously prepare a 30% sodium hydroxide solution, a 20% ammonia solution, and a 0.1% chelating agent solution (ethylenediaminetetraacetic acid). Add deionized water to the reaction vessel, followed by the ammonia solution, chelating agent solution, and sodium hydroxide solution, controlling the pH at 10.8 and the reaction temperature at 40℃~70℃±1℃.

[0333] S12. Add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor. The flow rate ratio of the four solutions is 40:30:5:1. After nucleation for 5 hours, adjust the flow rate of sodium hydroxide to reduce the pH to below 11.6 to complete the nucleation process. Continue to add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor for co-precipitation reaction. The flow rate ratio of the four solutions is 40:30:5:1. Control the reaction pH at 10.8. After maintaining the reaction for 48 hours, the growth process of precursor particles is completed.

[0334] S13. Transfer the solution in the above reaction vessel to a centrifuge for solid-liquid separation to obtain a positive electrode material precursor containing water. Then dry the wet precursor material at 120°C for 20 hours to obtain the finished precursor product.

[0335] S2. Preparation of layered oxide polycrystalline particles: Take the cathode material precursor and mix it with sodium carbonate, wherein the molar amount of metal atoms in the cathode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, satisfying N1 / N2 = 1:1.05.

[0336] The layered oxide polycrystalline particles are obtained by first calcination in an oxygen-containing atmosphere (such as air or pure oxygen) at a temperature of 900℃ for 10 hours, followed by cooling to room temperature and then coarse crushing, fine crushing and sieving.

[0337] Characteristic 4:

[0338] To obtain scanning electron microscope (SEM) images of the polycrystalline particles prepared in Example 2-1 above: each sample was placed on the sample stage, placed in the electron microscope chamber, vacuumed, the electron beam was turned on, and appropriate parameters were set for characterization: the parameters for observing the morphology were 3kV, the aperture was 30μm, and the working distance was 5mm.

[0339] like Figure 10 Indication, combined Figure 10 It can be seen that polycrystalline particles formed by agglomeration can be clearly observed, and the volumetric particle size distribution Dv50 of the particles is 10.8 μm.

[0340] Preparation Example 2-1a

[0341] The layered oxide polycrystalline particles obtained in Preparation Example 2-1 were further processed, and the specific steps are as follows:

[0342] S3. Provide a mixed solvent: Mix ethanol and water in a volume ratio of 1:1 to form 500 mL of solvent. Add polyvinylpyrrolidone to the solvent and mix well to form a mixed solvent. The mass of polyvinylpyrrolidone added is 2% of the mass of the solvent.

[0343] Dispersion: Take 20g of the layered oxide polycrystalline particles obtained in Preparation Example 2-1 and disperse them in 40mL of the above mixed solvent, stir and mix well to obtain a mixture;

[0344] Heating: Transfer the mixture to a crucible, heat the mixed solvent to 80°C, and stir while maintaining the temperature until the solvent is completely evaporated, leaving only solids;

[0345] Second calcination: The solid is transferred to a box furnace and calcined in air, with the furnace temperature controlled at around 700℃ and held for 5 hours;

[0346] Temperature drop to room temperature: obtain layered oxide positive electrode active material.

[0347] Characteristic 5:

[0348] Scanning electron microscope (SEM) images of the solid obtained by heating in Preparation Example 2-1a and the layered oxide positive electrode active material obtained by cooling to room temperature were obtained: Each sample was placed on the sample stage, placed in the electron microscope chamber, vacuumed, the electron beam was turned on, and appropriate parameters were set for characterization: morphology parameters were 3kV, aperture 30μm, and working distance 5mm.

[0349] like Figure 11A and 11B Indication, among which, Figure 11A The image shows the SEM image of the solid material obtained by heating. Figure 11B SEM images of layered oxide cathode active materials obtained by cooling to room temperature; combined with Figure 11A It is known that adding a dispersant and wet stirring will affect the microstructure of polycrystalline particles, causing the particles to break and their surface morphology to change. Figure 11B It is known that after high-temperature calcination, the broken particles will solidify and become larger.

[0350] The data in Table 1 below were obtained according to the test method of Preparation Example 1-1a described above.

[0351] Preparation Example 2-1b

[0352] The layered oxide polycrystalline particles obtained in Preparation Example 2-1 were further processed. The difference between this processing method and that in Preparation Example 2-1a is that the mass of polyvinylpyrrolidone added was 5% of the solvent mass, and the temperature of the box furnace was controlled at about 985°C during the second calcination, and the temperature was held for 10 hours. Everything else was the same as in Preparation Example 2-1a.

[0353] The data in Table 1 below were obtained according to the test method of Preparation Example 2-1a described above.

[0354] Preparation Example 2-1c

[0355] The layered oxide polycrystalline particles obtained in Preparation Example 2-1 were further processed. The difference between this processing method and that in Preparation Example 2-1a is that the mass of polyvinylpyrrolidone added was 0.5% of the solvent mass, and the temperature of the box furnace was controlled at about 600°C during the second calcination, and the temperature was held for 24 hours. Everything else was the same as in Preparation Example 2-1a.

[0356] The data in Table 1 below were obtained according to the test method of Preparation Example 2-1a described above.

[0357] Preparation Example 2-1d

[0358] The layered oxide polycrystalline particles obtained in Preparation Example 2-1 were further processed. The difference between this processing method and that in Preparation Example 2-1a is that acetone and water were mixed at a volume ratio of 1:2 to form 500 mL of solvent, and the temperature of the box furnace was controlled at about 610°C during the second calcination, and the temperature was held for 10 h. Everything else was the same as in Preparation Example 2-1a.

[0359] The data in Table 1 below were obtained according to the test method of Preparation Example 2-1a described above.

[0360] Preparation Example 2-1e

[0361] A method for preparing layered oxide positive electrode activity is provided. The method differs from preparation example 2-1a in that polyvinylpyrrolidone is not added in step S3, while the rest remains the same as preparation example 2-1a.

[0362] Characteristic 6:

[0363] To obtain scanning electron microscope (SEM) images of the layered oxide positive electrode active material prepared in Example 2-1e above: each sample was placed on the sample stage, placed in the electron microscope chamber, vacuumed, the electron beam was turned on, and appropriate parameters were set for characterization: the parameters for observing the morphology were 3kV, the aperture was 30μm, and the working distance was 5mm.

[0364] like Figure 12 Indication, combined Figure 12 It can be seen that without the addition of a dispersant, the polycrystalline particle material still maintains its original morphology. Furthermore, the particle size, specific surface area and tap density were measured, and the results are shown in Table 1 below.

[0365] Preparation Example 3-1

[0366] A layered oxide polycrystalline particle (chemical formula: NaNi) is provided. 0.4 Fe 0.2 Mn 0.3 Al 0.1 Preparation method of O2:

[0367] S1. Provide a precursor, including the following preparation process:

[0368] S11, according to the chemical formula Ni x Fe y Mn z Al gPrepare a mixed solution of metal salts with a molar concentration of (2.0±0.4) mol / L in (OH)2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤g≤1, and x+y+z+g=1. Simultaneously prepare a 30% sodium hydroxide solution, a 20% ammonia solution, and a 0.1% chelating agent solution (ethylenediaminetetraacetic acid). Add deionized water to the reaction vessel, followed by the addition of ammonia, chelating agent solution, and sodium hydroxide solution, controlling the pH at 10.5 and the reaction temperature at 40℃~70℃±1℃.

[0369] S12. Add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor. The flow rate ratio of the four solutions is 50:30:5:1. After nucleation for 5 hours, adjust the flow rate of sodium hydroxide to reduce the pH to below 11.6 to complete the nucleation process. Continue to add metal salt solution, sodium hydroxide solution, ammonia water and chelating agent solution to the reactor for co-precipitation reaction. The flow rate ratio of the four solutions is 50:30:5:1. Control the reaction pH at 10.5. After the reaction is maintained for 48 hours, the growth process of precursor particles is completed.

[0370] S13. Transfer the solution in the above reaction vessel to a centrifuge for solid-liquid separation to obtain a positive electrode material precursor containing water. Then dry the wet precursor material at 120°C for 20 hours to obtain the finished precursor product.

[0371] S2. Preparation of layered oxide polycrystalline particles: Take the cathode material precursor and mix it with sodium carbonate, wherein the molar amount of metal atoms in the cathode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, satisfying N1 / N2 = 1:1.02.

[0372] The layered oxide polycrystalline particles are obtained by first calcination in an oxygen-containing atmosphere (such as air or pure oxygen) at a temperature of 950°C for 10 hours, followed by cooling to room temperature and then coarse crushing, fine crushing and sieving.

[0373] Preparation Example 3-1a

[0374] The layered oxide polycrystalline particles obtained in Preparation Example 3-1 were further processed, and the specific steps are as follows:

[0375] S3. Provide a mixed solvent: Mix ethanol and water in a volume ratio of 1:1 to form 500 mL of solvent. Add polyvinylpyrrolidone to the solvent and mix well to form a mixed solvent. The mass of polyvinylpyrrolidone added is 2% of the mass of the solvent.

[0376] Dispersion: Take 20g of the layered oxide polycrystalline particles obtained in Preparation Example 3-1 and disperse them in 50mL of the above mixed solvent, stir and mix well to obtain a mixture;

[0377] Heating: Transfer the mixture to a crucible, heat the mixed solvent to 80°C, and stir while maintaining the temperature until the solvent is completely evaporated, leaving only solids;

[0378] Second calcination: The solid is transferred to a box furnace and calcined in air, with the furnace temperature controlled at around 700℃ and held for 5 hours;

[0379] Temperature drop to room temperature: obtain layered oxide positive electrode active material.

[0380] The data in Table 1 below were obtained according to the test method of Preparation Example 1-1a described above.

[0381] Table 1

[0382]

[0383]

[0384] Example 1-1a

[0385] A sodium secondary battery is provided, comprising a positive electrode, a separator and a negative electrode arranged sequentially according to a stacking process, and an electrolyte.

[0386] Preparation of the separating membrane:

[0387] A PE substrate with a thickness of 12μm is provided.

[0388] Preparation of negative electrode sheet:

[0389] Hard carbon, acetylene black, and PAA binder were added to a mixer in a weight ratio of 90:5:5. Deionized water was then added, and the mixture was stirred under vacuum until homogeneous, yielding a negative electrode slurry with a solid content of 60 wt%. The negative electrode slurry was then uniformly coated onto both sides of the copper foil used as the negative electrode current collector, with a coating width of 75 mm and a coating surface density of 11 mg / cm³. 2 The film was dried using a nine-section drying oven with sequential temperature settings of 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃, followed by compaction using a cold press to achieve a single-sided coating weight of 0.15g / 1540.25mm for the negative electrode film. 2 .

[0390] Preparation of electrolyte:

[0391] In an environment with a water content of less than 10 ppm, the non-aqueous organic solvent EC / EMC is mixed evenly at a volume ratio of 3:7, and then NaPF6 sodium salt (sodium salt concentration of 1 mol / L) is added and mixed evenly to obtain the electrolyte.

[0392] Preparation of positive electrode sheet:

[0393] The layered oxide cathode material prepared in Example 1, acetylene black, and PVDF were added to a mixer in a ratio of 95:2.5:2.5. Then, N-methylpyrrolidone was added and stirred until homogeneous to form a cathode slurry with a solid content of 60%. The cathode slurry was coated onto both surfaces of the cathode current collector aluminum foil, with a coating width of 70 mm and a coating surface density of 19 mg / cm³. 2 The material is heated and dried using a multi-section oven with temperatures set sequentially at 120℃, 100℃, and 90℃. Then, it is compacted using a cold press to obtain a positive electrode sheet with a compacted density of 2.7 g / cm³. 3 The positive electrode sheet has a single-sided coating weight of 0.34g / 1540.25mm. 2 .

[0394] Preparation of sodium secondary batteries:

[0395] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Three copper wires are added for the electrodes, and the tabs are welded together to form a stacked battery cell. The stacked battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a sodium secondary battery is obtained.

[0396] Example 1-1b

[0397] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is a layered oxide positive electrode active material prepared in Example 1-1b, and the rest is the same as in Example 1-1a.

[0398] Example 1-1c

[0399] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 1-1c, and the rest is the same as in Example 1-1a.

[0400] Example 1-1d

[0401] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Examples 1-1d, and the rest is the same as in Examples 1-1a.

[0402] Comparative Example 1

[0403] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 1-1e, and the rest is the same as in Example 1-1a.

[0404] Example 2-1a

[0405] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 2-1a, and the rest is the same as in Example 1-1a.

[0406] Example 2-1b

[0407] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 2-1b, and the rest is the same as in Example 2-1a.

[0408] Example 2-1c

[0409] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 2-1c, and the rest is the same as in Example 2-1a.

[0410] Example 2-1d

[0411] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 2-1d, and the rest is the same as in Example 2-1a.

[0412] Comparative Example 2

[0413] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 2-1e, and the rest is the same as in Example 2-1a.

[0414] Example 3-1a

[0415] A sodium secondary battery is provided, wherein the positive electrode active material of the sodium secondary battery is the layered oxide positive electrode active material prepared in Example 3-1a, and the rest is the same as in Example 1-1a.

[0416] [Performance Testing]

[0417] The battery's capacity retention was tested after 200 cycles at 25°C.

[0418] 1C long cycle: Charge to 4.1V at 1C, maintain constant voltage at 0.05C → let stand for 5 minutes → discharge to 1.5V at 1C; this constitutes one cycle. Record the discharge capacity at this point as Q1. After 200 cycles under the above conditions, record the discharge capacity as Q. 200 The capacity retention rate is (Q1-Q 200 ) / Q1×100%.

[0419] Table 2

[0420] Serial Number Positive electrode active material 25℃, capacity retention Example 1-1a Preparation Example 1-1a 86.3％ Example 1-1b Preparation Example 1-1b 84.0％ Example 1-1c Preparation Example 1-1c 83.5％ Example 1-1d Preparation Example 1-1d 80.9％ Comparative Example 1 Preparation Example 1-1e 76.1％ Example 2-1a Preparation Example 2-1a 89.2％ Example 2-1b Preparation Example 2-1b 87.5％ Example 2-1c Preparation Example 2-1c 85.5％ Example 2-1d Preparation Example 2-1d 85.6％ Comparative Example 2 Preparation Example 2-1e 78.6％ Example 3-1a Preparation Example 3-1a 83.8％

[0421] As can be seen from the above embodiments, the design method provided in this application can improve the cycle life of sodium secondary batteries by increasing the content of single crystal particles and / or single crystal-like particles in the positive electrode material for sodium secondary batteries.

[0422] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium secondary battery, characterized in that: It includes a positive electrode, a separator, and a negative electrode stacked together; The positive electrode includes a positive current collector and a positive film layer located on at least one side surface of the positive current collector; The positive electrode film layer includes a positive electrode active material; The positive electrode active material includes single crystal particles and / or single crystal-like particles of layered transition metal oxides; The shape of the single crystal particles and / or quasi-single crystal particles includes any one or more of the following: spherical, quasi-spherical, polygonal plate-like, and polygonal columnar. Furthermore, the positive electrode active material satisfies the following conditions: (1) The volumetric particle size distribution Dv50 is 3μm~7μm; (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

2. The sodium secondary battery according to claim 1, characterized in that: The single crystal particles in the positive electrode active material have a mass percentage content of 20% to 40%. and / or; The mass percentage content of the quasi-single crystal particles in the positive electrode active material is 60% to 80%.

3. The sodium secondary battery according to any one of claims 1 to 2, characterized in that: The volumetric particle size distribution Dv50 of the single crystal particles is 5μm to 7μm; and / or; The volumetric particle size distribution Dv50 of the quasi-single crystal particles is 3μm to 5μm and does not include 5μm.

4. The sodium secondary battery according to any one of claims 1 to 3, characterized in that: The chemical formula of the layered transition metal oxide is Na. x M y O z M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2.

5. The sodium secondary battery according to any one of claims 1 to 4, characterized in that: The layered transition metal oxide is a nickel-iron-manganese layered transition metal oxide, and the chemical formula of the nickel-iron-manganese layered transition metal oxide is NaNi. a Fe b Mn c M1 d O2, where a+b+c+d=1, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg, or Zn.

6. The sodium secondary battery according to any one of claims 1 to 5, characterized in that: The compaction density of the positive electrode film is 3.0 g / cm³. 3 ~3.4g / cm 3 .

7. The sodium secondary battery according to any one of claims 1 to 6, characterized in that: The sodium secondary battery also includes an electrolyte, which comprises one or more of carboxylic acid esters, carbonates, and ethers.

8. A positive electrode active material for sodium secondary batteries, characterized in that: Including single-crystal particles and / or single-crystal-like particles of layered transition metal oxides; The shape of the single crystal particles and / or quasi-single crystal particles includes any one or more of the following: spherical, quasi-spherical, polygonal plate-like, and polygonal columnar. The positive electrode active material satisfies the following conditions: (1) The volumetric particle size distribution Dv50 is 3μm~7μm; (2) The specific surface area BET is 0.3m². 2 / g~0.5m 2 / g.

9. The positive electrode active material according to claim 8, characterized in that: The single crystal particles in the positive electrode active material have a mass percentage content of 20% to 40%. and / or; The mass percentage content of the quasi-single crystal particles in the positive electrode active material is 60% to 80%.

10. The positive electrode active material according to any one of claims 8 to 9, characterized in that: The volumetric particle size distribution Dv50 of the single crystal particles is 5μm to 7μm; and / or; The volumetric particle size distribution Dv50 of the quasi-single crystal particles is 3μm to 5μm and does not include 5μm.

11. The positive electrode active material according to any one of claims 8 to 10, characterized in that: The tap density of the positive electrode active material is 1.55 g / cm³. 3 ~1.80g / cm 3 .

12. A method for preparing a positive electrode active material for sodium secondary batteries, characterized in that: include: Provides precursors for cathode materials; Preparation of intermediate products for cathode materials: The cathode material precursor is mixed with sodium carbonate and calcined for the first time to obtain intermediate products for cathode materials. The intermediate products for cathode materials contain polycrystalline particles of layered transition metal oxides. Preparation of positive electrode active material: Disperse the dispersant into a solvent to form a mixed solvent, disperse the intermediate product of the positive electrode material into the mixed solvent, and obtain the positive electrode active material by a second calcination. The positive electrode active material includes single crystal particles and / or single crystal-like particles of layered transition metal oxides, and the mass percentage content of the single crystal particles and single crystal-like particles in the positive electrode active material is >98%. The dispersant satisfies the following conditions: (1) The dispersant is soluble in one or more of alcohol solvents, acetone, and water; (2) The decomposition temperature of the dispersant is less than or equal to 600°C, and the decomposition temperature of the dispersant is the temperature corresponding to the decomposition peak of the thermogravimetric curve of the dispersant.

13. The preparation method according to claim 12, characterized in that: The dispersant includes polyvinylpyrrolidone and its modified compounds; and / or; The mass of the dispersant added is 0.5% to 5% of the mass of the solvent; and / or; The mass ratio of the intermediate product of the cathode material to the volume ratio of the mixed solvent is (10g~20g) / (20mL~100mL).

14. The preparation method according to any one of claims 12 to 13, characterized in that: The solvent includes one or more of alcohol solvents, acetone, and water; The alcohol solvents include one or more of ethanol, ethylene glycol, and glycerol.

15. The preparation method according to any one of claims 12 to 14, characterized in that: The first calcination temperature is 850℃~970℃, and the holding time is 7h~15h; and / or; The second calcination temperature is 600℃~1000℃, and the holding time is 3h~24h; and / or; The first calcination and the second calcination are carried out in an oxygen-containing atmosphere.

16. The preparation method according to any one of claims 12 to 15, characterized in that: After the intermediate product of the cathode material is dispersed into the mixed solvent and before the second calcination, the process further includes: The mixed solvent is heated and stirred until the solvent evaporates to dryness.

17. The preparation method according to any one of claims 12 to 16, characterized in that: After the first calcination, the process also includes coarse crushing, fine crushing and sieving to obtain an intermediate product of the cathode material, wherein the volume particle size distribution Dv50 of the intermediate product of the cathode material is 8μm to 12μm.

18. The preparation method according to any one of claims 12 to 17, characterized in that: The molar amount of metal atoms in the cathode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, satisfying N1 / N2 = 1:(0.5~1.1).

19. An electrical appliance, characterized in that: The sodium secondary battery includes any one of claims 1 to 7, or any one of claims 8 to 11, or any one of claims 12 to 18, and the sodium secondary battery positive electrode active material prepared by the preparation method described in any one of claims 12 to 18.

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