Positive active material for sodium-ion battery, preparation method thereof, positive electrode sheet, battery monomer, battery and electric device

Abstract

The application provides a positive electrode active material for a sodium ion battery, a preparation method of the positive electrode active material, a positive electrode sheet, a battery cell, a battery and a power utilization device. The positive electrode active material comprises: a sodium-containing metal oxide; and a coating layer covering at least part of the surface of the sodium-containing metal oxide, wherein the coating layer comprises a sodium fluorophosphate salt, and the sodium fluorophosphate salt comprises one or more of Fe and Ni elements. The positive electrode active material improves the volume change of the positive electrode active material in the charge-discharge cycle, improves the cycle stability and cycle life of the positive electrode sheet containing the positive electrode active material in the battery cell, and thus the battery cell, the battery and the power utilization device comprising the positive electrode sheet also have corresponding advantages.

Description

Technical Field

[0001] This application relates to the field of battery device technology, specifically to a positive electrode active material for sodium-ion batteries and its preparation method, positive electrode sheet, battery cell, battery, and power-consuming device. Background Technology

[0002] Sodium-ion batteries, as a representative of battery cells, rely on the repeated insertion and extraction of active ions between the positive and negative electrodes for charging and discharging. They have outstanding characteristics such as high energy density, long cycle life, no pollution, and no memory effect.

[0003] Therefore, rechargeable battery cells, as a clean energy source, have gradually expanded from electronic products to large-scale devices such as electric vehicles, in order to align with sustainable development strategies for the environment and energy. This, in turn, places higher demands on the cycle stability of battery cells. Summary of the Invention

[0004] This application provides a positive electrode active material for sodium-ion batteries, a method for preparing the same, a positive electrode sheet, a battery cell, a battery, and an electrical device. While maintaining high specific capacity, it improves the volume change of the positive electrode active material during charge-discharge cycles, and enhances the cycle stability and cycle life of the positive electrode sheet containing the positive electrode active material in the battery cell. Therefore, the battery cell, battery, and electrical device including the positive electrode sheet also have corresponding advantages.

[0005] In a first aspect, embodiments of this application provide a positive electrode active material, comprising:

[0006] Sodium-containing metal oxide particles; and

[0007] The coating layer at least partially coats the sodium-containing metal oxide particles, and the coating layer includes sodium fluorophosphate, which includes one or more of the elements Fe and Ni.

[0008] According to the technical solution of this application embodiment, on the one hand, the coating layer can reduce the direct contact between sodium-containing metal oxides and electrolytes, reduce the occurrence of side reactions related to sodium-containing metal oxides, reduce the dissolution and loss of sodium-containing metal oxides, and improve the structural stability of the positive electrode active material, thereby improving the cycle stability of the battery cell containing the positive electrode active material. On the other hand, sodium-containing metal oxides have a large volume deformation during charge-discharge cycles, but the sodium fluorophosphate structure in its surface coating layer is stable, and the volume deformation generated during the active ion extraction / intercalation process is very small. Such a coating structure limits the volume change of sodium-containing metal oxides during charge-discharge cycles, improving the structural stability of the positive electrode material and the cycle stability of the battery.

[0009] When the positive electrode active material contains sodium metal oxide and sodium fluorophosphate, the positive electrode containing this positive electrode active material has a higher initial coulombic efficiency in the battery cell, thereby improving the cycle performance of the battery cell.

[0010] Therefore, the positive electrode active material of this application embodiment is applied to a battery cell. The positive electrode active material has high structural stability and smaller deformation during charging and discharging, which enhances the structural stability of the battery cell. At the same time, the positive electrode active material has a higher initial coulombic efficiency when applied to the battery, thereby improving the cycle performance of the battery cell and extending the cycle life of the battery cell.

[0011] In some optional embodiments, based on the total mass of the positive electrode active material, the positive electrode active material includes sodium fluorophosphate with a mass percentage W1 of 0.8%-5%, optionally 2%-4%.

[0012] According to the embodiments of this application, when the mass ratio of sodium fluorophosphate in the positive electrode active material is within the above-mentioned suitable range, the positive electrode active material can have both low impedance and high specific capacity, thereby improving the specific capacity of sodium-containing metal oxides in the positive electrode active material, thereby improving the cycle stability of the battery and extending the cycle life of the battery.

[0013] In some alternative implementations, the average particle size Dv of the positive electrode active material 1 The ratio of 50 to the average thickness d of the coating layer in the cross section of the positive electrode active material is 1:(0.02-0.2), or optionally 1:(0.024-0.18).

[0014] According to an embodiment of this application, the average particle size Dv of the positive electrode active material is... 1 The ratio of 50 to the average thickness d of the coating layer in the cross section of the positive electrode active material is within the above range, which can further control the thickness and content of the coating layer, so that the positive electrode active material has good charge and discharge capacity, and improves the cycle stability and cycle life of the battery cell containing the positive electrode material.

[0015] In some alternative implementations, the average particle size Dv of the positive electrode active material 1 50 is 5μm-20μm, and can be selected as 5μm-15μm.

[0016] This is not intended to be limited by any theory or explanation, but rather to consider the volume distribution particle size Dv of the positive electrode active material. 1 When 50 meets the given range, the positive electrode active material can have a smaller specific surface area, thereby reducing its hygroscopicity, especially when in contact with air, thus effectively reducing its water content. This is beneficial for improving battery cycle performance and extending battery cycle life.

[0017] In some alternative embodiments, the average thickness d of the coating layer is 0.1-2 μm, optionally 0.2-1.5 μm, and more preferably 0.5-1 μm.

[0018] According to embodiments of this application, when the average thickness d of the coating layer is within the aforementioned suitable range, the positive electrode active material can achieve better stability. Therefore, applying the positive electrode active material to a single battery cell can further improve the battery's cycle stability, reduce internal resistance and capacity decay, thereby further extending the battery's cycle life.

[0019] In some alternative embodiments, sodium fluorophosphate has the general formula Na. x A y (PO4) z F, where A includes any combination of one or more of the elements Fe and Ni; 0 < x ≤ 2, 0 < y ≤ 2, 0 < z ≤ 2; optionally, x + y - 3Z = 1 or x + 2y - 3Z = 1.

[0020] According to embodiments of this application, sodium fluorophosphate is a polyanionic compound that exhibits very small deformation during battery charge-discharge processes, thus demonstrating good cycle stability. Due to its small proportion in the positive electrode active material, even with a relatively compact structure, it does not significantly inhibit the migration rate of sodium ions during charge-discharge processes. The aforementioned type of sodium fluorophosphate can serve as a zero-strain material to further improve the stability of the positive electrode active material during charge-discharge electrochemical cycling.

[0021] In some alternative embodiments, the sodium-containing metal oxide particles include those with the structural formula Na. a Ni b Co c Mn f M d O e Metal oxides, wherein 0.5≤a≤1.2, 0≤b≤2, 0≤c≤2, 0≤f≤1, 0≤d≤1.5, 1≤e≤4, A includes one or more of Li and Na; M includes any one or a combination of at least two of Fe, Al, Zr, Y, La, Zn, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Ti, Mg, Ta, Nb, V, Sc, Sr, B and Cu.

[0022] In some alternative implementations, b+c+d+f = 1 or b+c+d+f = 2.

[0023] Secondly, embodiments of this application provide a method for preparing the positive electrode active material of the first aspect, comprising:

[0024] An aqueous solution containing a sodium fluorophosphate precursor is mixed with an organic suspension containing a sodium metal oxide to obtain a mixture.

[0025] The solvent in the mixture is removed, and solid-state sintering is carried out in a protective atmosphere to transform the sodium fluorophosphate precursor into sodium fluorophosphate and form one or more coating layers that at least partially coat the sodium metal oxide particles, thereby obtaining the positive electrode active material.

[0026] According to the embodiments of this application, mixing an aqueous solution containing a sodium fluorophosphate precursor with an organic suspension can further improve the uniformity of the coating, so that each sodium-containing metal oxide is coated by the coating layer, which is beneficial to improve the homogeneity of the positive electrode active material, thereby improving the cycle stability of the positive electrode sheet containing the positive electrode active material and reducing the imbalance of active ion insertion / extraction in the positive electrode film layer of the positive electrode sheet.

[0027] In some alternative embodiments, the sodium fluorophosphate precursor includes a soluble fluoride salt, a soluble metal salt, or a soluble phosphate, wherein the soluble metal salt includes a salt of any one or at least two of the metal elements selected from Fe and Ni, and a soluble sodium salt.

[0028] In some alternative implementations, the soluble sodium salt and the soluble phosphate are the same substance.

[0029] In some alternative implementations, the soluble sodium salt and the fluorinated salt are the same substance.

[0030] In some alternative embodiments, the organic suspension includes an organic solvent, said organic solvent including at least one of ethanol and acetone.

[0031] In some alternative implementations, the solid-state sintering temperature is 500-950 degrees Celsius, optionally 600-800 degrees Celsius.

[0032] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, wherein the positive electrode film layer includes a positive electrode active material of the first aspect, or a positive electrode active material prepared by the method of the second aspect.

[0033] According to the embodiments of this application, the positive electrode sheet containing the positive electrode active material can improve its cycle stability in a single battery cell and reduce the probability of a sharp change in its cycle capacity.

[0034] Fourthly, embodiments of this application provide a battery cell that includes a positive electrode sheet as described in the third aspect. Battery cells including a positive electrode sheet also possess the corresponding advantages of positive electrode active materials.

[0035] Fifthly, embodiments of this application provide a battery, which includes the battery cell of the fourth aspect.

[0036] Sixthly, embodiments of this application provide an electrical device including the battery of the fifth aspect of this application, said battery being used to provide electrical energy. The electrical device including the battery also has the corresponding advantages of the positive electrode active material.

[0037] 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

[0038] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0039] Figure 1 The present application provides schematic diagrams of the structure of a single battery cell according to some embodiments.

[0040] Figure 2 An exploded view of a battery cell provided in some embodiments of this application is shown;

[0041] Figure 3 The present application shows a schematic diagram of the structure of a battery module provided in some embodiments;

[0042] Figure 4 The present application shows a schematic diagram of the structure of a battery pack provided in some embodiments;

[0043] Figure 5 It shows Figure 4 An exploded view of the battery pack shown.

[0044] Figure 6 A schematic diagram of an electrical device provided in some embodiments of this application is shown.

[0045] The reference numerals in the attached diagram are explained as follows: 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate.

[0046] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0047] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the phosphate composite positive electrode active material, its preparation method, positive electrode sheet, battery cell, battery, and power 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 a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0048] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0051] 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.

[0052] 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.

[0053] 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).

[0054] In this document, the term "cladding layer" refers to a layer of material covering the core, which may completely or partially cover the core. The use of "cladding layer" is for ease of description only and is not intended to limit the invention. Furthermore, each cladding layer may be a complete or partial covering.

[0055] Unless otherwise specified, in this application, the terms "first," "second," "third," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0056] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0057] In this application, the battery undergoes Na insertion / extraction and consumption during charging and discharging, resulting in different Na molar contents at different discharge states. In the examples of cathode materials in this application, the Na molar contents refer to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the Na molar contents change after charge-discharge cycles.

[0058] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0059] In this application, the battery cell may include sodium-ion batteries, etc., and the embodiments of this application are not limited thereto. The battery cell may be an aqueous battery or an oil-based battery, and the embodiments of this application are not limited thereto. The battery cell may be flat, cuboid, or other shapes, and the embodiments of this application are not limited thereto.

[0060] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0061] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0062] Sodium fluorophosphate (Sodium fluorophosphate) is used as a cathode material in battery cells. Benefiting from the inductive effect of fluorine, it exhibits a high operating voltage (2.0V-4.0V) while also possessing a relatively low theoretical specific capacity (100mAh g⁻¹) and small volume change (<4%), making it a near-zero strain material and a promising cathode material for sodium-ion batteries. However, the widespread application of Sodium fluorophosphate faces two main challenges: firstly, its poor conductivity leads to suboptimal rate performance; secondly, the low sodium utilization rate of the active material limits its actual capacity (especially for bulk materials). The low electronic conductivity and poor cycle performance of Sodium fluorophosphate significantly affect its electrochemical performance. Furthermore, variations in raw material mixing, synthesis processes, and methods during synthesis can easily lead to the formation of impurity phases, affecting its discharge specific capacity and cycle stability. Therefore, these factors limit the widespread application of this material.

[0063] Layered oxides have advantages such as high theoretical specific capacity and high compaction density, with a specific capacity of 100-200 mAh·g. -1 For example, NaCoO2. Layered oxides are among the most promising commercially viable cathode materials for sodium-ion batteries. However, they also suffer from drawbacks such as slightly poor cycle performance and poor stability in air. Modifying layered oxides is a primary means of improving the cycle performance of electrode materials.

[0064] In view of this, the inventors have improved the phosphate composite positive electrode active material. Therefore, this application provides a positive electrode active material that can improve the cycle stability and cycle life of battery cells containing this positive electrode active material while maintaining its high specific capacity.

[0065] Positive electrode active material

[0066] In a first aspect, embodiments of this application provide a positive electrode active material, comprising:

[0067] Sodium-containing metal oxide particles; and

[0068] The coating layer at least partially coats the sodium-containing metal oxide particles, and the coating layer includes sodium fluorophosphate, which includes one or more of the elements Fe and Ni.

[0069] According to the technical solution of this application embodiment, on the one hand, the coating layer can reduce the direct contact between sodium-containing metal oxides and electrolytes, reduce the occurrence of side reactions related to sodium-containing metal oxides, reduce the dissolution and loss of sodium-containing metal oxides, and improve the structural stability of the positive electrode active material, thereby improving the cycle stability of the battery cell containing the positive electrode active material. On the other hand, sodium-containing metal oxides have a large volume deformation during charge-discharge cycles, but the sodium fluorophosphate structure in its surface coating layer is stable, and the volume deformation generated during the active ion extraction / intercalation process is very small. Such a coating structure limits the volume change of sodium-containing metal oxides during charge-discharge cycles, improving the structural stability of the positive electrode material and the cycle stability of the battery.

[0070] When the positive electrode active material contains sodium metal oxide and sodium fluorophosphate, the positive electrode containing this positive electrode active material has a higher initial coulombic efficiency in the battery cell, thereby improving the cycle stability of the battery cell.

[0071] The reason for the improved initial coulombic efficiency of the positive electrode active material in this application compared to simple layered metal oxides may be that sodium fluorophosphate containing Fe and Ni elements has higher conductivity than sodium-containing metal oxide particles. Even though the degree of deintercalation and intercalation of active sodium ions in sodium fluorophosphate is slightly weaker than that in layered metal oxides, it contains Fe and Ni elements, and their combined action with fluorine enhances the ability of sodium fluorophosphate to deintercalate and intercalate sodium ions. Therefore, its conductivity and efficiency in deintercalating and intercalating active sodium ions are enhanced, thereby improving its initial coulombic efficiency.

[0072] Sodium fluorophosphate contains Fe and Ni elements, which are present in the coating layer of sodium fluorophosphate. On the one hand, Fe and Ni are relatively common metals, so sodium fluorophosphate is relatively low cost as a cathode material. Sodium, iron and nickel atoms in sodium fluorophosphate can provide a higher theoretical capacity in the electrochemical cycle of the battery cell, which is beneficial to increasing the energy density of the battery. Moreover, sodium fluorophosphate containing Fe and Ni elements has a better cycle life, which can provide a longer battery life.

[0073] Fe is present in sodium fluorophosphate, which can improve its magnetic properties. When sodium fluorophosphate is included in the positive electrode active material or within the battery cell, it can counteract some of the electric field forces within the cell, thus facilitating the insertion and extraction of active sodium ions and improving the initial coulombic efficiency. Furthermore, the presence of Fe in sodium fluorophosphate can enhance its stability and corrosion resistance.

[0074] Ni is present in sodium fluorophosphate, which can improve the sodium ion insertion / extraction capacity of sodium fluorophosphate. During the charge and discharge process of a single battery cell, each nickel element can insert or release multiple active sodium ions, thereby storing more charge and improving the initial coulombic efficiency. Ni exhibits good electrochemical stability in sodium-ion batteries, reducing the risk of severe structural damage or accumulation of electrochemical reaction byproducts in the positive electrode active material during multiple charge-discharge cycles, thus contributing to long-term stability.

[0075] Therefore, the positive electrode active material of this application embodiment is applied to a battery cell. The positive electrode active material has high structural stability and smaller deformation during charging and discharging, which enhances the structural stability of the battery cell. At the same time, the positive electrode active material has a higher initial coulombic efficiency when applied to the battery, thereby improving the cycle performance of the battery cell and extending the cycle life of the battery cell.

[0076] In some embodiments, the positive electrode active material has a core-shell structure, wherein the core material includes a sodium-containing metal oxide; and the shell includes sodium fluorophosphate.

[0077] Not intended to be limited to any theory or explanation, in the positive electrode active material of this application embodiment, the sodium-containing metal oxide has relatively poor stability in air. The coating layer is disposed on the surface of the sodium-containing metal oxide, which can reduce the contact between the sodium-containing metal oxide and air. In the battery cell, it can also reduce the contact between the sodium-containing metal oxide and the electrolyte, thereby improving the stability of the positive electrode active material.

[0078] In some optional embodiments, based on the total mass of the positive electrode active material, the positive electrode active material includes sodium fluorophosphate with a mass percentage W1 of 0.8%-5%, optionally 2%-4%.

[0079] Optionally, the positive electrode active material includes sodium fluorophosphate with a mass percentage W1 of any value or a range of any two of the above values, which can be 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%, 2.6%, 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%.

[0080] According to the embodiments of this application, when the mass proportion of sodium fluorophosphate in the positive electrode active material is within the aforementioned suitable range, the positive electrode active material can have a thinner coating layer. The relatively small mass proportion of sodium fluorophosphate in the positive electrode active material does not significantly inhibit the migration rate of sodium ions during charge and discharge. This can improve the initial coulombic efficiency of the positive electrode active material.

[0081] The mass percentage of sodium fluorophosphate in the positive electrode active material has a meaning known in the art and can be determined using equipment and methods known in the art. As an example, a certain mass of the positive electrode material is dissolved in aqua regia, diluted a certain factor, and then tested by inductively coupled plasma atomic emission spectrometry (ICP-AES) to obtain the content of a certain metal element in the coating. The mass of sodium fluorophosphate is then calculated based on the content of the metal element. In some embodiments, the ratio of the mass of sodium fluorophosphate to the mass of the positive electrode active material can be considered as the mass percentage of the coating layer.

[0082] According to the embodiments of this application, the mass ratio of sodium fluorophosphate in the positive electrode active material is within the above-mentioned suitable range, which can improve the specific capacity of the positive electrode active material, thereby improving the cycle stability of the battery and extending the cycle life of the battery.

[0083] In some alternative implementations, the average particle size Dv of the positive electrode active material 1 The ratio of 50 to the average thickness d of the coating layer in the cross section of the positive electrode active material is 1:(0.02-0.2), or optionally 1:(0.024-0.18).

[0084] Optionally, the average particle size Dv of the positive electrode active material 1The ratio of 50 to the average thickness d of the coating layer in the cross-section of the positive electrode active material can be 1:0.021, 1:0.026, 1:0.031, 1:0.036, 1:0.041, 1:0.046, 1:0.051, 1:0.056, 1:0.061, 1:0.066, 1:0.071, 1:0.076, 1:0.081, 1:0.086, 1:0.091, 1:0.096, 1:0.101, or 1:0. The range of any value from 106, 1:0.111, 1:0.116, 1:0.121, 1:0.126, 1:0.131, 1:0.136, 1:0.141, 1:0.146, 1:0.151, 1:0.156, 1:0.161, 1:0.166, 1:0.171, 1:0.176, 1:0.181, 1:0.186, 1:0.191, 1:0.196, 1:0.2 or any range of any two of the above values.

[0085] According to an embodiment of this application, the average particle size Dv of the positive electrode active material is... 1 The ratio of 50 to the average thickness d of the coating layer in the cross section of the positive electrode active material is within the above range, which can further control the thickness and content of the coating layer, so that the positive electrode active material has both good specific surface area and large specific capacity, thereby improving the cycle stability and cycle life of the battery cell containing the positive electrode sheet.

[0086] In some alternative implementations, the average particle size Dv of the positive electrode active material 1 50 is 5μm-20μm, and can be selected as 5μm-15μm.

[0087] Optionally, the average particle size Dv of the positive electrode active material 1 50 can be any value from 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or a range of any two of the above values.

[0088] This is not intended to be limited by any theory or explanation, but rather to consider the volume distribution particle size Dv of the positive electrode active material. 1 When 50 meets the given range, the positive electrode active material can have a suitable specific surface area, which is beneficial to improving the cycle performance of the battery and extending the cycle life of the battery.

[0089] In addition, the average particle size Dv of the positive electrode active material 1When 50% of the value meets the given range, the hygroscopicity of the positive electrode active material can be reduced, especially when it comes into contact with air, thereby effectively reducing the water content of the positive electrode active material. This improves the performance of the positive electrode sheet containing the positive electrode active material in the battery cell.

[0090] Volume distribution particle size Dv of positive electrode active material 1 The value 50 has a well-known meaning in the art, representing the particle size corresponding to a cumulative particle size distribution percentage of 50% in a volumetric particle size distribution of the positive electrode active material. The volumetric particle size distribution (Dv50) can be determined using equipment and methods known in the art. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0091] In some alternative embodiments, the average thickness d of the coating layer is 0.1-2 μm, optionally 0.2-1.5 μm, and more preferably 0.5-1 μm.

[0092] Optionally, the average thickness d of the coating layer can be any value from 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, or a range consisting of any two of the above values.

[0093] According to embodiments of this application, when the average thickness d of the coating layer is within the aforementioned suitable range, the positive electrode active material can possess a larger specific surface area and better stability. Therefore, applying the positive electrode active material to a single battery cell can further improve the battery's cycle stability, reduce its internal resistance and capacity decay, thereby further extending the battery's cycle life.

[0094] The average thickness of the aforementioned coating layers can all have meanings known in the art and can be measured using equipment and methods known in the art. As an example, it can be obtained by the following method: The positive electrode active material is uniformly mixed with a binder and coated onto the surface of the positive electrode current collector. The mixture is then dried and cold-pressed to prepare a positive electrode sheet (when sampling from a battery, the battery can be directly disassembled, the positive electrode sheet removed, and dried); a randomly selected area is subjected to argon-ion cross-section polishing, and an electron microscope (SEM) image is taken at a magnification of 3000x or higher (e.g., 3000x or 5000x); the SEM image is processed, and the contrast is adjusted appropriately until the outline of the positive electrode active material is clearly visible; the particle size of each positive electrode active material in the cross-section and the thickness of the single-layer coating layer are statistically analyzed using software to obtain the volume distribution particle size Dv of the sodium-containing metal oxide. 1 50. Coating thickness. As another example, the positive electrode active material powder can also be directly subjected to argon ion cross-section polishing and SEM images can be taken to determine the average thickness of the coating layer.

[0095] In some alternative embodiments, sodium fluorophosphate has the general formula Na. x A y (PO4) z F, where A includes any one or more of the elements Fe and Ni; 0 < x ≤ 2, 0 < y ≤ 2, 0 < z ≤ 2. In some optional embodiments, x + y - 3Z = 1 or x + 2y - 3Z = 1.

[0096] In some alternative implementations, A includes any one or a combination of Fe and Ni elements.

[0097] According to embodiments of this application, sodium fluorophosphate is a polyanionic compound that exhibits very small deformation during battery charge and discharge, thus demonstrating good cycle stability. The aforementioned type of sodium fluorophosphate is a zero-strain material, further enhancing the stability of the positive electrode active material during charge-discharge electrochemical cycles.

[0098] According to embodiments of this application, during the charge-discharge cycle of a battery, the sodium fluorophosphate containing the aforementioned sodium fluorophosphate exhibits minimal volume change during the extraction and insertion of active sodium ions, thereby reducing the volume change of the positive electrode active material during charge-discharge cycles. This improves the stability of the positive electrode active material, thereby enhancing the cycle stability of the battery and extending its cycle life.

[0099] In some alternative embodiments, the sodium-containing metal oxide particles include those with the structural formula Na. a Ni b Co c Mn fM d O e The metal oxide of, where 0.5 ≤ a ≤ 1.2, 0 ≤ b ≤ 2, 0 ≤ c ≤ 2, 0 ≤ f ≤ 1, 0 ≤ d ≤ 1.5, 1 ≤ e ≤ 4, A includes one or more of Li and Na; M includes any one or a combination of at least two of the elements Fe, Al, Zr, Y, La, Zn, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Ti, Mg, Ta, Nb, V, Sc, Sr, B, and Cu; optionally, b + c + d + f = 1 or b + c + d + f = 2.

[0100] In some optional embodiments, the sodium-containing metal oxide has the general formula Na a MO2, where 0.2 < a ≤ 2; M is any one or a combination of several of the elements Mn, Fe, Ni, Co, Al, Zr, Y, La, Zn, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Ti, Mg, Ta, Nb, V, Sc, Sr, B, and Cu.

[0101] According to an embodiment of the present application, Fe can be divalent positive in the sodium-containing metal oxide.

[0102] According to an embodiment of the present application, during the charge and discharge cycle of the battery with the positive electrode active material containing the above general formula, a certain amount of active sodium released from the sodium-containing metal oxide has a reduced volume change under the coating of the coating layer, which can improve the stability of the sodium-containing metal oxide, thereby improving the cycle stability of the battery and extending the cycle life of the battery.

[0103] As an example of the above sodium-containing metal oxide, for example, the following can be listed:

[0104] Na 1-x Cu h Fe k Mn l M 1 m O 2-y where M 1 is one or several of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, 0 < x ≤ 0.5, 0 < h ≤ 0.24, 0 ≤ k ≤ 0.32, 0 < l ≤ 0.68, 0 ≤ m < 0.1, h + k + l + m = 1, 0 ≤ y < 0.2; <00​​​​​​​​​​It is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0106] Na a Li b Ni c Mn d Fe e O2, where 0.5≤a≤1, 0 <b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0107] As an example, the positive electrode active material may include NaCoO2, NaNiO2, NaMnO2, NaMn2O4, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3O2, NaNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, NaNi 0.8 Co 0.1 Mn 0.1 O2, NaNi 0.85 Co 0.15 Al 0.05 O2, NaMn 0.33 Ni 0.27 Fe 0.33 Zn 0.06 O2, NaMn 0.33 Ni 0.27 Fe 0.33 Zn 0.06 O2, Na 0.8 Ni 0.365 Fe 0.07 Mn 0.545 La 0.02 One or more of O2, NaFePO4, and NaMnPO4.

[0108] Methods for preparing positive electrode active materials

[0109] Secondly, embodiments of this application provide a method for preparing the positive electrode active material of the first aspect, comprising:

[0110] Step a, providing an organic suspension containing sodium-containing metal oxides;

[0111] Step b: Mix the aqueous solution containing the sodium fluorophosphate precursor with the organic suspension to obtain a mixture;

[0112] Step c: Remove the solvent from the mixture and perform solid-state sintering in a protective atmosphere to form a coating layer on the surface of the sodium-containing metal oxide, thereby obtaining a positive electrode active material, wherein the coating layer comprises sodium fluorophosphate.

[0113] In step a, the sodium-containing metal oxide can be as described in any embodiment of the first aspect, and the embodiments of the sodium-containing metal oxide have been described and illustrated in detail above, and will not be repeated here. The sodium-containing metal oxide is commercially available or can be prepared by methods known in the art.

[0114] In step b, the coating layer may be as described in any embodiment of the first aspect. The embodiments of the components of the coating layer have been described in detail above and will not be repeated here.

[0115] In some alternative embodiments, the sodium fluorophosphate precursor includes a soluble fluoride salt, a soluble metal salt, a soluble phosphate, and a soluble sodium salt, wherein the soluble metal salt includes a combination of a salt of any one or at least two of the metal elements selected from Fe and Ni and a soluble sodium salt.

[0116] In some embodiments, soluble phosphates include monohydrogen phosphates and dihydrogen phosphates. Examples include ammonium hydrogen phosphate (NH4H2PO4), sodium hydrogen phosphate (NaH2PO4), and potassium hydrogen phosphate (KH2PO4).

[0117] Monohydrogen phosphate, also known as monohydrogen phosphate, can be sodium dihydrogen phosphate (Na2HPO4), potassium dihydrogen phosphate (K2HPO4), etc.

[0118] Dihydrogen phosphates, also known as dihydrogen phosphates, can be sodium dihydrogen phosphate (NaH2PO4), potassium dihydrogen phosphate (KH2PO4), etc. Fluoride-containing salts can be sodium fluoride, ammonium fluoride, potassium fluoride, etc.

[0119] In some embodiments, the soluble sodium salt can be a sodium-containing compound known in the art for preparing phosphate-based positive electrode active materials. For example, the soluble sodium salt may include one or more of sodium hydroxide, sodium carbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium nitrate, and sodium acetate. In the method for preparing the positive electrode active material provided in this application, the amount of each raw material added can conform to the stoichiometric ratio of the target phosphate composite positive electrode active material.

[0120] In some embodiments, the amount of sodium source added may be slightly excessive, for example, 100%-110% of the theoretical mass of the sodium source, where the theoretical mass of the sodium source refers to the mass calculated based on the stoichiometry of the positive electrode active material.

[0121] In some alternative embodiments, the soluble metal salt and the soluble phosphate are the same substance. The soluble metal salt includes one or more of nickel chloride, nickel nitrate, nickel sulfate, nickel nitrate, nickel acetate, ferrous chloride, ferric chloride, ferrous nitrate, ferric nitrate, ferrous sulfate, ferric sulfate, and ferric acetate.

[0122] In some alternative embodiments, the soluble sodium salt and the soluble phosphate are the same substance. It can be sodium hydrogen phosphate (NaH₂PO₄) or sodium dihydrogen phosphate (Na₂HPO₄).

[0123] In some alternative embodiments, the soluble sodium salt and the fluorinated salt are the same substance. It can be sodium fluoride.

[0124] In some alternative embodiments, the organic suspension includes an organic solvent, said organic solvent including at least one of ethanol and acetone.

[0125] In some alternative embodiments, the average particle size Dv of the sodium-containing metal oxide 2 50 ranges from 4.8μm to 16μm, with options from 6μm to 12μm.

[0126] Optionally, the average particle size Dv of the sodium-containing metal oxide 2 50 can be any value among 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, and 16μm, or a range consisting of any two of the above values.

[0127] Not intended to be limited to any theory or explanation, when the average particle size Dv of sodium-containing metal oxides 2 When 50 meets the given range, the hygroscopicity of sodium-containing metal oxides can be reduced, allowing them to be better coated by the coating layer. This, in turn, helps improve the cycle stability of the battery.

[0128] In some optional embodiments, the solid-state sintering temperature is 500-950 degrees Celsius, optionally 600-800 degrees Celsius. In step c, the solid-state sintering temperature and time can be those known in the art, and can be adjusted as needed by those skilled in the art.

[0129] Positive electrode sheet

[0130] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, wherein the positive electrode film layer includes a positive electrode active material of the first aspect, or a positive electrode active material prepared by the method of the second aspect.

[0131] The positive electrode sheet of this application embodiment includes the positive electrode active material of the first aspect, or the positive electrode active material prepared according to the method of the second aspect. When applied to a battery cell, it can improve the cycle stability of the battery cell and extend the cycle life of the battery cell.

[0132] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0133] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] In some embodiments, the positive electrode film may further include a second positive electrode active material, which may be a positive electrode active material known in the art for sodium-ion batteries. As an example, the second positive electrode material may also include one or more of sodium-containing transition metal oxides, polyanionic compounds, and Prussian blue compounds. The sodium-ion battery of this application embodiment can use a negative electrode sheet with hard carbon as the negative electrode active material, combined with a positive electrode sheet including one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds as the positive electrode active material, thereby enabling the sodium-ion battery to have high capacity performance and energy density.

[0135] Examples of the aforementioned polyanionic compounds include:

[0136] A 1 f M 3 g (PO4) i O j X 1 3-j Where A is one or more of H, Li, Na, K, and NH4, and M 3 It is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, X 1 It is one or more of F, Cl and Br, 0 <f≤4,0<g≤2,1≤i≤3,0≤j≤2;

[0137] Na n M4 PO4X 2 , where M 4 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, and X 2 is one or more of F, Cl, and Br; 0 < n ≤ 2;

[0138] Na p M 5 q (SO4)3, where M 5 is one or more of Mn, Fe, Co, Ni, Cu, and Zn; 0 < p ≤ 2, 0 < q ≤ 2;

[0139] Na s Mn t Fe 3-t (PO4)2(P2O7), where 0 < s ≤ 4, 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2, or 3.

[0140] As an example of the above Prussian blue compounds, for example, the following can be listed:

[0141] A u M 6 v [M 7 (CN)6] w ·xH2O, where A is H + , NH4 + , one or more of alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more of transition metal cations; 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ and Ra 2+ one or more of them, M 6 and M 7 are each independently cations of one or more of the transition metal elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, and W. Optionally, A is Li + , Na<​+ One or more of them, M 6 It is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni, and Cu, M 7 It is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni and Cu.

[0142] In some implementations, the conductive agent has a weight percentage of 0.5 wt% or greater in the positive electrode material layer. This is beneficial for constructing a better electronic conductivity network.

[0143] In some implementations, the binder has a weight percentage of 0.5 wt% or greater in the cathode material layer, which is beneficial for obtaining good adhesion performance.

[0144] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0145] In some embodiments, the positive electrode film may optionally include a conductive agent and an optional dispersant. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0147] battery cell

[0148] Fourthly, embodiments of this application provide a battery cell including the positive electrode sheet of the third aspect.

[0149] A single battery cell includes the aforementioned positive electrode and negative electrode. The structure and composition of the negative electrode can be selected according to the type of battery cell, and this application embodiment does not limit this.

[0150] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0151] The negative electrode active material may be any material known in the art. As an example, the negative electrode active material may include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and sodium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0152] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0153] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0154] In some embodiments, the negative electrode film layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0155] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0156] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional negative electrode conductive agent, optional negative electrode binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0157] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0158] In some embodiments, the negative electrode sheet may include a negative current collector and a metal layer disposed on at least one surface of the negative current collector, the metal layer may include one or more of elemental sodium and sodium alloy.

[0159] Sodium alloys can be alloys formed from metallic sodium with other metallic or non-metallic elements. For example, other metallic elements in sodium alloys may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, while non-metallic elements may include one or more of boron, carbon, and silicon.

[0160] In some embodiments, the negative electrode may also include a negative current collector but not a metal layer, thereby enabling the assembly of a metal-free battery cell.

[0161] In some embodiments, the negative electrode sheet can also be made directly from sodium elemental or sodium alloy sheets (or foils).

[0162] [Electrolytes]

[0163] The electrolyte acts as a conductor of active ions between the positive and negative electrode plates. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte may include one or more of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0164] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0165] In some embodiments, the electrolyte may include an organic solvent and a sodium salt, and any organic solvent and sodium salt suitable for sodium-ion batteries may be selected according to actual needs. As an example, the organic solvent may be one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC); the sodium salt may be one or more of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0166] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0167] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery performance, such as additives improving battery overcharge performance, additives improving battery high-temperature or low-temperature performance, etc. In some embodiments, the electrolyte may also optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery performance, such as additives improving battery overcharge performance, additives improving battery high-temperature performance, additives improving battery low-temperature power performance, etc.

[0168] [Isolation membrane]

[0169] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0170] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0171] The methods for preparing battery cells are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with the electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0172] Battery

[0173] Fifthly, embodiments of this application provide a battery, including the battery cell of the fourth aspect.

[0174] The battery mentioned in the embodiments of this application may be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application may include battery cells, battery modules, or battery packs.

[0175] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0176] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, comprising a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0177] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0178] The battery cells mentioned in the embodiments of this application include sodium-ion primary battery cells, sodium-ion battery cells, sodium metal battery cells, and sodium metal battery cells without negative electrodes, etc., but the embodiments of this application are not limited to these.

[0179] The battery cell includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to this.

[0180] The battery cell also includes an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0181] In some embodiments, such as Figure 2As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0182] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0183] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0184] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0185] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0186] Electrical appliances

[0187] Sixthly, embodiments of this application provide an electrical device including the battery of the fifth aspect, the battery being used to provide electrical energy. The battery can be a power source for the electrical device or an energy storage unit for the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, tablets, 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.

[0188] Electrical devices can choose the specific type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0189] Figure 6 This is a schematic diagram illustrating an example of an electrical device. This device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used as the power source.

[0190] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0191] Example

[0192] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0193] Example 1-1

[0194] Based on the chemical formula of layered oxide cathode material NaNi 0.5 Mn 0.5 The molar ratio of different elements in O2 was determined by weighing sodium carbonate, nickel nitrate, and manganese nitrate and adding them to 200 mL of deionized water. The mixture was stirred until the solutes were fully dissolved to obtain a mixed solution. 2 g of citric acid was added to the mixed solution, and the mixture was heated and stirred at 100 °C until it evaporated to dryness, yielding a gel. The resulting gel was dried in a vacuum drying oven at 100 °C, crushed, and pre-calcined at 500 °C for 5 h in a tube furnace under a high-purity inert gas atmosphere (99.9% argon). Then, it was sintered at 1000 °C for 15 h and cooled to room temperature to obtain a pure-phase layered oxide cathode material, NaNi. 0.5 Mn 0.5 O2.

[0195] The pure-phase layered oxide cathode material prepared above was added to 70 mL of ethanol solvent and stirred on a magnetic stirrer for 2 hours to obtain a cathode material suspension. Ferrous nitrate was weighed and added to the suspension according to the mass ratio of sodium ferrophosphate to cathode material (0.001:1). A mixed solution of sodium fluoride, sodium carbonate, and ammonium dihydrogen phosphate was prepared using deionized water as a solvent and added dropwise to the suspension while stirring until homogeneous. The solvent was evaporated in a 100°C oven, and the dried mixture was then placed in a tube furnace under a high-purity inert gas atmosphere (99.9% argon) and sintered at 600°C for 8 hours. After cooling to room temperature, sodium ferrophosphate-coated NaNi was obtained. 0.5 Mn 0.5 O2 positive electrode active material.

[0196] NaNi coated with sodium ferrous fluorophosphate in Example 1-1 0.5 Mn 0.5 O2 positive electrode active material, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are mixed evenly in a weight ratio of 84.37:30:28.86:2.9:1.1 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated onto the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0197] Examples 1-2 to Examples 1-7

[0198] The difference between this embodiment and Embodiment 1-1 is that the mass fraction of sodium fluorophosphate in the positive electrode active material is different.

[0199] Examples 1-8 to Examples 1-9

[0200] The difference between this embodiment and Embodiment 1-1 is that the average particle size Dv150 of the positive electrode active material and the average thickness d of the coating layer in the cross section of the positive electrode active material are different.

[0201] Example 2-1

[0202] The difference between this embodiment and Embodiment 1-1 is that the type of coating layer is different. In Embodiment 2-1, the pure phase layered oxide cathode material prepared above was added to 70 mL of ethanol solvent and stirred on a magnetic stirrer for 2 hours to obtain a cathode material suspension; nickel nitrate was weighed according to the mass ratio of sodium nickel fluorophosphate to cathode material (0.15:1) and added to the suspension; a mixed solution of sodium fluoride, sodium carbonate, and ammonium dihydrogen phosphate was prepared using deionized water as a solvent and added dropwise to the suspension and stirred until uniform; the solvent was evaporated in a 95°C oven, and then the dried mixture was placed in a tube furnace with a high-purity inert gas atmosphere (99.9% argon) and sintered at 500°C for 10 hours, and then cooled to room temperature to obtain the cathode active material coated with sodium nickel fluorophosphate.

[0203] Example 3-1

[0204] Based on the chemical formula Na of the layered oxide cathode material 0.8 Ni 0.365 Fe 0.07 Mn 0.545 La 0.02 The molar ratio of different elements in O2 was determined by weighing sodium carbonate, nickel nitrate, ferric nitrate, manganese nitrate, and lanthanum nitrate and adding them to 200 mL of deionized water. The mixture was stirred until the solutes were fully dissolved to obtain a mixed solution. 2 g of ascorbic acid was added to the mixed solution, and the mixture was heated and stirred at 85°C until it reached dryness, yielding a gel. The resulting gel was dried in a vacuum drying oven at 85°C, crushed, and pre-calcined in a tube furnace under a high-purity inert gas atmosphere (99.9% argon) at 400°C for 6 hours, followed by sintering at 900°C for 14 hours. After cooling to room temperature, a pure-phase layered oxide cathode material, Na, was obtained. 0.8 Ni 0.365 Fe 0.07 Mn 0.545 La 0.02 O2.

[0205] The pure-phase layered oxide cathode material prepared above was added to 70 mL of ethanol solvent and stirred on a magnetic stirrer for 3 hours to obtain a cathode material suspension. Ferrous nitrate was weighed and added to the suspension according to the mass ratio of sodium ferrous fluorophosphate to cathode material (0.05:1). A mixed solution of sodium fluoride, sodium carbonate, and ammonium dihydrogen phosphate was prepared using deionized water as a solvent and added dropwise to the suspension while stirring until homogeneous. The solvent was evaporated in an oven at 85°C, and the dried mixture was then placed in a tube furnace under a high-purity inert gas atmosphere (99.9% argon) and sintered at 800°C for 6 hours. After cooling to room temperature, sodium ferrous fluorophosphate-coated Na₂CO₃ was obtained. 0.8 Ni 0.365 Fe 0.07 Mn 0.545 La 0.02 O2 positive electrode active material.

[0206] Example 3-2

[0207] The difference between this embodiment and Embodiment 3-1 is that: based on the chemical formula of the layered oxide cathode material NaMn... 0.33 Ni 0.27 Fe 0.33 Zn 0.06The molar ratio of different elements in O2 was determined by weighing sodium carbonate, manganese nitrate, nickel nitrate, ferrous nitrate, and zinc nitrate, adding them to 200 mL of deionized water, and stirring to fully dissolve the solutes to obtain a mixed solution. 1 g of citric acid was added to the mixed solution, and the mixture was heated and stirred at 95°C until it reached dryness, yielding a gel. The resulting gel was dried in a vacuum drying oven at 95°C, crushed, and pre-calcined at 500°C for 6 hours in a tube furnace under a high-purity inert gas atmosphere (99.9% argon). It was then sintered at 950°C for 17 hours and cooled to room temperature to obtain a pure-phase layered oxide cathode material, NaMn. 0.33 Ni 0.27 Fe 0.33 Zn 0.06 O2 is then used for coating to obtain the positive electrode active material.

[0208] Example 3-3

[0209] Based on the chemical formula of layered oxide cathode material NaMn 0.33 Ni 0.27 Fe 0.33 Zn 0.06 The molar ratio of different elements in O2 was determined by weighing sodium carbonate, manganese nitrate, nickel nitrate, ferrous nitrate, and zinc nitrate, adding them to 200 mL of deionized water, and stirring to fully dissolve the solutes to obtain a mixed solution. 1 g of citric acid was added to the mixed solution, and the mixture was heated and stirred at 95°C until it reached dryness, yielding a gel. The resulting gel was dried in a vacuum drying oven at 95°C, crushed, and pre-calcined at 500°C for 6 hours in a tube furnace under a high-purity inert gas atmosphere (99.9% argon). It was then sintered at 950°C for 17 hours and cooled to room temperature to obtain a pure-phase layered oxide cathode material, NaMn. 0.33 Ni 0.27 Fe 0.33 Zn 0.06 O2.

[0210] The pure-phase layered oxide cathode material prepared above was added to 70 mL of ethanol solvent and stirred on a magnetic stirrer for 2 hours to obtain a cathode material suspension. Nickel nitrate was weighed according to the mass ratio of sodium nickel fluorophosphate to cathode material (0.15:1) and added to the suspension. A mixed solution of sodium fluoride, sodium carbonate, and ammonium dihydrogen phosphate was prepared using deionized water as a solvent and added dropwise to the suspension while stirring until homogeneous. The solvent was evaporated in a 95°C oven, and the dried mixture was then placed in a tube furnace under a high-purity inert gas atmosphere (99.9% argon) and sintered at 500°C for 10 hours. After cooling to room temperature, sodium nickel fluorophosphate-coated NaMn was obtained. 0.33 Ni 0.27 Fe 0.33 Zn 0.06 O2 positive electrode active material.

[0211] Examples 3-4

[0212] The difference between this embodiment and Embodiments 3-3 is that the layered oxide in the positive electrode active material is Na. 0.8 Ni 0.36 5Fe 0.07 Mn 0.545 La 0.02 O2 is then used for coating to obtain the positive electrode active material.

[0213] Comparative Example 1

[0214] Based on the chemical formula of layered oxide cathode material NaNi 0.5 Mn 0.5 The molar ratio of different elements in O2 was determined by weighing sodium carbonate, nickel nitrate, and manganese nitrate and adding them to 200 mL of deionized water. The mixture was stirred until the solutes were fully dissolved to obtain a mixed solution. 2 g of citric acid was added to the mixed solution, and the mixture was heated and stirred at 100 °C until it evaporated to dryness, yielding a gel. The resulting gel was dried in a vacuum drying oven at 100 °C, crushed, and pre-calcined at 500 °C for 5 h in a tube furnace under a high-purity inert gas atmosphere (99.9% argon). Then, it was sintered at 1000 °C for 15 h and cooled to room temperature to obtain a pure-phase layered oxide positive electrode active material, NaNi. 0.5 Mn 0.5 O2. Its volume is the same as that of the positive electrode active material in Example 1-1.

[0215] Comparative Example 2

[0216] Based on the chemical formula Na of the layered oxide cathode material 0.8 Ni 0.365 Fe 0.07 Mn 0.545 La 0.02 The molar ratio of different elements in O2 was determined by weighing sodium carbonate, nickel nitrate, ferric nitrate, manganese nitrate, and lanthanum nitrate and adding them to 200 mL of deionized water. The mixture was stirred until the solutes were fully dissolved to obtain a mixed solution. 2 g of ascorbic acid was added to the mixed solution, and the mixture was heated and stirred at 85°C until it reached dryness, yielding a gel. The resulting gel was dried in a vacuum drying oven at 85°C, crushed, and pre-calcined in a tube furnace under a high-purity inert gas atmosphere (99.9% argon) at 400°C for 6 hours, followed by sintering at 900°C for 14 hours. After cooling to room temperature, a pure-phase layered oxide positive electrode active material, Na, was obtained. 0.8 Ni 0.365 Fe 0.07 Mn 0.545 La 0.02 O2. Its volume is the same as that of the positive electrode active material in Example 1-1.

[0217] Comparative Example 3

[0218] Based on the chemical formula of layered oxide cathode material NaMn 0.33 Ni0.27 Fe 0.33 Zn 0.06 The molar ratio of different elements in O2 was determined by weighing sodium carbonate, manganese nitrate, nickel nitrate, ferrous nitrate, and zinc nitrate, adding them to 200 mL of deionized water, and stirring to fully dissolve the solutes to obtain a mixed solution. 1 g of citric acid was added to the mixed solution, and the mixture was heated and stirred at 95°C until dry to obtain a gel. The resulting gel was dried in a vacuum drying oven at 95°C, crushed, pre-calcined at 500°C for 6 h in a tube furnace under a high-purity inert gas atmosphere (99.9% argon), and then sintered at 950°C for 17 h. After cooling to room temperature, a pure-phase layered oxide positive electrode active material, NaMn, was obtained. 0.33 Ni 0.27 Fe 0.33 Zn 0.06 O2. Its volume is the same as that of the positive electrode active material in Example 1-1.

[0219] Test section

[0220] 1) Initial Coulombic Efficiency Test: Combine the above positive electrode with the sodium plate to form a coin cell. Charge the coin cell at 1C to 4.35V at 2.5-4.35V, then charge it at a constant voltage of 4.35V to a current of 0.05C. Let it stand for 5 minutes, and then discharge it at 1C to 2.5V. The ratio of the discharge capacity to the charge capacity at this time is the initial coulombic efficiency at the 1C rate.

[0221] 2) Capacity retention rate test: Combine the above positive electrode sheet with the sodium sheet to form a coin cell. At 25℃ and 2.5-4.35V, charge the coin cell at 1C to 4.35V, then charge it at 4.35V at a constant voltage until the current reaches 0.05C. Let it stand for 5 minutes, then discharge it at 1C to 2.5V, and measure the discharge capacity at this step. Repeat this process 200 times and calculate the capacity retention rate.

[0222] According to the results in Table 1, compared with Comparative Example 1, Example 3-1, and Comparative Example 2, Example 3-2 and Comparative Example 3, when the same mass of positive electrode active material is used in the positive electrode sheet, the positive electrode material of the examples improves the structural stability of the positive electrode active material while maintaining a high coulombic efficiency, thereby improving the cycle stability of the battery cell containing the positive electrode active material.

[0223] 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.

[0224]

Claims

1. A positive electrode active material for sodium-ion batteries, wherein, include: Sodium-containing metal oxide particles, wherein the sodium-containing metal oxide particles include those with the structural formula Na a Ni b Co c Mn f M d O e Metal oxides, wherein 0.5≤a≤1.2, 0≤b≤2, 0≤c≤2, 0≤f≤1, 0≤d≤1.5, 1≤e≤4, and M includes any one or at least two combinations of the elements Fe, Al, Zr, Y, La, Zn, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Ti, Mg, Ta, Nb, V, Sc, Sr, B, and Cu; and A coating layer, at least partially coating the sodium-containing metal oxide particles, wherein the coating layer comprises sodium fluorophosphate, the sodium fluorophosphate having the structural formula Na. x A y (PO4) z F, where A includes any one or a combination of two of the elements Fe and Ni; 0 < x ≤ 2, 0 < y ≤ 2, 0 < z ≤ 2.

2. The positive electrode active material according to claim 1, wherein, Based on the total mass of the positive electrode active material, the positive electrode active material includes sodium fluorophosphate with a mass percentage W1 of 0.8%-5%.

3. The positive electrode active material according to claim 1 or 2, wherein, Based on the total mass of the positive electrode active material, the positive electrode active material includes sodium fluorophosphate with a mass percentage W1 of 2%-4%.

4. The positive electrode active material according to claim 1 or 2, wherein, The average particle size Dv of the positive electrode active material 1 The ratio of 50 to the average thickness d of the coating layer in the cross section of the positive electrode active material is 1:(0.02-0.2).

5. The positive electrode active material according to claim 1 or 2, wherein, The average particle size Dv of the positive electrode active material 1 The ratio of 50 to the average thickness d of the coating layer in the cross section of the positive electrode active material is 1:(0.024-0.18).

6. The positive electrode active material according to claim 1 or 2, wherein, The average particle size Dv of the positive electrode active material 1 50 represents 5μm-20μm.

7. The positive electrode active material according to claim 1 or 2, wherein, The average particle size Dv of the positive electrode active material 1 505μm-15μm.

8. The positive electrode active material according to claim 1 or 2, wherein, The average thickness d of the coating layer is 0.1-2 μm.

9. The positive electrode active material according to claim 1 or 2, wherein, The average thickness d of the coating layer is 0.2-1.5 μm.

10. The positive electrode active material according to claim 1 or 2, wherein, The average thickness d of the coating layer is 0.5-1 μm.

11. The positive electrode active material according to claim 1 or 2, wherein, In the structural formula of the sodium fluorophosphate, x+y-3Z=1 or x+2y-3Z=1.

12. The positive electrode active material according to claim 1 or 2, wherein in the structural formula of the sodium fluorophosphate, b+c+d+f=1 or b+c+d+f=2.

13. A method for preparing a positive electrode active material according to any one of claims 1-12, comprising: An aqueous solution containing a sodium fluorophosphate precursor is mixed with an organic suspension containing sodium metal oxide particles to obtain a mixture. The solvent in the mixture is removed, and solid-state sintering is performed in a protective atmosphere to transform the sodium fluorophosphate precursor into sodium fluorophosphate and form a coating layer that at least partially covers the sodium-containing metal oxide particles, thereby obtaining a positive electrode active material.

14. The method according to claim 13, wherein, The sodium fluorophosphate precursor includes a soluble fluoride salt, a soluble metal salt, and a soluble phosphate, wherein the soluble metal salt includes a salt of any one or at least two of the metal elements selected from Fe and Ni, and a soluble sodium salt.

15. The method according to claim 14, wherein, The soluble sodium salt and the soluble phosphate are the same substance.

16. The method of claim 14, wherein, The soluble sodium salt and the fluorine-containing salt are the same substance.

17. The method according to claim 13, wherein, The method satisfies at least one of the following conditions: (1) The organic suspension includes an organic solvent, which includes at least one of ethanol and acetone; (2) The solid-phase sintering temperature is 500-950 degrees Celsius.

18. The method according to claim 13, wherein, The solid-state sintering temperature is 600-800 degrees Celsius.

19. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer comprising a positive electrode active material according to any one of claims 1-12, or a positive electrode active material prepared by the method according to any one of claims 13-18.

20. A battery cell, wherein, Including the positive electrode sheet according to claim 19.

21. A battery, wherein, It includes multiple battery cells as described in claim 20.

22. An electrical appliance, wherein, Includes the battery according to claim 21, the battery being used to provide electrical energy.

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