Battery cell, battery apparatus and electrical apparatus

Abstract

A battery cell, a battery apparatus and an electrical apparatus, relating to the technical field of batteries. The battery cell comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector; the positive electrode film layer comprises a positive electrode active material and carbon nanotubes; the positive electrode active material has a layered crystal structure; the ratio of the average tube length of the carbon nanotubes to the Dv50 particle size of the positive electrode active material is (2-10):1. The carbon nanotubes improve the conductivity of the positive electrode active material having the layered crystal structure, and inhibit volume expansion of the positive electrode active material during cycling, such that the sheet resistance and sheet rebound of the positive electrode sheet are small, allowing the formed battery cell to exhibit excellent cycle performance.

Description

Battery cells, battery packs and electrical devices

[0001] This application claims priority to patent application 202411874011.2, filed on December 18, 2024, entitled “Battery Cell, Battery Device and Power Consumption Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a battery cell, a battery device, and an electrical device. Background Technology

[0003] Sodium-ion batteries have excellent performance and broad application prospects. One of the common positive electrode active materials is a layered crystal structure. However, the electronic conductivity of layered crystal structure positive electrode active materials is poor, which easily leads to a large film resistance of the formed positive electrode film. This, in turn, causes a large temperature rise in the cell during charging and discharging, triggering over-temperature protection and affecting the cycle performance of the battery cell. Summary of the Invention

[0004] In view of the above problems, this application provides a battery cell, a battery device, and an electrical device. In the battery cell, carbon nanotubes improve the conductivity of the positive electrode active material with a layered crystal structure, suppress the volume expansion of the positive electrode active material during cycling, and make the film resistance and electrode rebound of the positive electrode sheet smaller, resulting in excellent cycle performance of the battery cell.

[0005] In a first aspect, this application provides a battery cell, the battery cell including a positive electrode sheet;

[0006] The positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector;

[0007] The positive electrode film layer includes a positive electrode active material and carbon nanotubes;

[0008] The positive electrode active material has a layered crystal structure;

[0009] The ratio between the average tube length of the carbon nanotubes and the Dv50 particle size of the positive electrode active material is (2-10):1.

[0010] In the technical solution of this application, a positive electrode active material with a layered crystal structure and carbon nanotubes are used in combination in the positive electrode film layer. The carbon nanotubes can improve the electronic conductivity of the positive electrode active material, reduce the film resistance of the positive electrode film, reduce the temperature rise of the cell during charging and discharging, reduce over-temperature protection, and improve the cycle performance of the battery. In addition, during the charging and discharging process of the battery, the positive electrode active material may undergo volume expansion. This expansion force may cause the electrode to rebound. By controlling the ratio between the average tube length of the carbon nanotube and the Dv50 particle size of the positive electrode active material within the specified range, the carbon nanotubes can form a good constraint on the positive electrode active material, reduce electrode rebound, and improve the cycle performance of the battery. In summary, the positive electrode film resistance and electrode rebound of the present application are small, resulting in excellent cycle performance of the formed battery cell.

[0011] In some embodiments, the average length of the carbon nanotubes is 9-120 μm, optionally 16-50 μm; and / or;

[0012] The diameter of the carbon nanotubes is 5-10 nm.

[0013] In the technical solution of this application, the average tube length and tube diameter of the carbon nanotubes are within the specified range. In addition to reducing the film resistance and electrode rebound of the positive electrode, the carbon nanotubes themselves are not prone to agglomeration or breakage during the electrode or battery processing, resulting in better battery cycle performance.

[0014] In some embodiments, the carbon nanotubes account for 0.1%-0.6% of the total mass of the positive electrode film layer, which is 100%.

[0015] In the technical solution of this application, the mass ratio of carbon nanotubes in the positive electrode film is within the specified range. While improving the conductivity of the positive electrode active material and forming good binding of the positive electrode active material, it also has less aggregation and has less impact on the content of main materials such as the positive electrode active material. Therefore, it can effectively reduce electrode rebound and film resistance, while basically not affecting the core role of the positive electrode active material, and can form a battery with excellent cycle performance.

[0016] In some embodiments, the positive electrode film layer further includes a zero-dimensional conductive agent.

[0017] In the technical solution of this application, the positive electrode film layer also includes a zero-dimensional conductive agent. Compared with carbon nanotubes, the zero-dimensional conductive agent has a lower cost and is easier to disperse in the positive electrode slurry, making it easier to process. Therefore, while meeting the performance requirements of the battery cell, the zero-dimensional conductive agent and carbon nanotubes can be used together to reduce production costs and processing difficulty.

[0018] In some embodiments, the mass percentage of the zero-dimensional conductive agent is 0.5%-3%, optionally 1%-3%, based on the total mass of the positive electrode film layer being 100%.

[0019] In the technical solution of this application, the mass ratio of the zero-dimensional conductive agent in the positive electrode film is within the specified range. When the mass ratio is appropriate, the positive electrode slurry formed during the preparation of the electrode sheet has high preservation stability and basically does not affect the normal coating of the slurry. Moreover, the zero-dimensional conductive agent itself has less agglomeration between particles, which has less impact on the polarization of the battery cell. It can cooperate well with carbon nanotubes, reduce the film resistance of the electrode sheet, and improve the conductivity of the positive electrode sheet.

[0020] In some embodiments, the positive electrode film layer further includes a binder;

[0021] With the total mass of the positive electrode film layer being 100%, the mass percentage of the binder is 1%-4%.

[0022] In the technical solution of this application, the mass ratio of the binder in the positive electrode film layer is within the specified range, which can effectively bond the positive electrode active material, carbon nanotubes, and zero-dimensional conductive agents, resulting in good cycle performance of the battery during use.

[0023] In some embodiments, the positive electrode active material includes sodium-zinc based positive electrode active material and / or sodium-copper based positive electrode active material.

[0024] In some embodiments, the chemical formula of the sodium-zinc based positive electrode active material is Na. q M x Zn y O2, wherein M includes any one or at least two of Ti, V, Cr, Mn, Fe, Co, and Ni, and 0.81≤q≤1.1, 0.8<x+y≤1, 0.02≤y≤0.10; and / or;

[0025] The sodium-zinc-based positive electrode active material includes a lath-like shape; and / or;

[0026] The Dv50 particle size of the sodium-zinc based positive electrode active material is 3-8 μm.

[0027] In the technical solution of this application, the chemical formula of the sodium-zinc-based positive electrode active material is as described above. The lamellar sodium-zinc-based positive electrode active material has obvious grain boundaries, few defects, few side reactions with the electrolyte, and produces less gas in actual operation, resulting in good battery cycle stability.

[0028] In the technical solution of this application, the Dv50 particle size of the sodium-zinc-based positive electrode active material is within the specified range. The slurry coating performance formed by the sodium-zinc-based positive electrode active material is excellent and does not significantly increase the processing difficulty. Moreover, the particles are not easily agglomerated, resulting in stable long-term battery performance. At the same time, when the sodium-zinc-based positive electrode active material is used in batteries, the diffusion path of active ions is relatively short, the solid-phase diffusion resistance is small, and the electrochemical reaction rate at the interface is fast, which is beneficial to improving the rate performance of the battery.

[0029] In some embodiments, the positive electrode active material is a sodium-zinc based positive electrode active material, and the carbon nanotubes account for 0.2%-0.6% of the total mass of the positive electrode film layer (100%); and / or;

[0030] The adhesive comprises 1%-3.5% by mass.

[0031] In the technical solution of this application, the positive electrode active material is a sodium-zinc based positive electrode active material. Choosing a strip-shaped sodium-zinc based positive electrode active material is more conducive to improving battery performance. The sodium-zinc based positive electrode active material requires relatively high pressure during cold pressing. Therefore, choosing a relatively high mass ratio of carbon nanotubes in the positive electrode film layer is more conducive to improving battery performance. In actual use, the sodium-zinc based positive electrode active material produces less gas and the electrode rebound is lower. Therefore, a relatively low mass ratio of binder is sufficient to meet the requirements, thereby further improving energy density.

[0032] In some embodiments, the chemical formula of the sodium-copper based positive electrode active material is Na. p Z a Cu b O2, wherein Z includes any one or at least two combinations of Ti, V, Cr, Mn, Fe, Co, Ni or Zn, and 0.81≤p≤1.1, 0.8<a+b≤1, 0.03≤b≤0.2; and / or;

[0033] The sodium-copper-based positive electrode active material includes at least one of the following shapes: spherical and near-spherical; and / or;

[0034] The Dv50 particle size of the sodium-copper-based positive electrode active material is 5-12 μm.

[0035] In the technical solution of this application, the chemical formula of the sodium-copper-based positive electrode active material is as described above. The spherical or near-spherical sodium-copper-based positive electrode active material has relatively rounded edges and corners, and can have a high compaction density during the cold pressing of the electrode sheet. At the same time, the sodium-copper-based positive electrode active material is not easily damaged, which would affect the performance of the battery cell. The Dv50 particle size of the sodium-copper-based positive electrode active material is controlled within the above-mentioned range. The slurry coating performance formed by the sodium-copper-based positive electrode active material is excellent, and it does not increase the processing difficulty. Moreover, the particles are not easy to agglomerate, and the battery performance is stable. At the same time, when the sodium-zinc-based positive electrode active material is used in the battery, the diffusion path of active ions is relatively short, the solid phase diffusion resistance is small, and the electrochemical reaction rate at the interface is fast, which is beneficial to improving the rate performance of the battery.

[0036] In some embodiments, the positive electrode active material is a sodium-copper based positive electrode active material, and the carbon nanotubes account for 0.1%-0.6% of the total mass of the positive electrode film layer (100%); and / or;

[0037] The adhesive comprises 1.1%-4% by mass.

[0038] In the technical solution of this application, selecting a spherical or near-spherical shape with a relatively regular shape for the sodium-copper-based positive electrode active material is more conducive to improving battery performance, such as rate performance. Moreover, the pressure of the sodium-copper-based positive electrode active material during the cold pressing process is relatively small. Therefore, the basic requirements can be met even if the mass ratio of carbon nanotubes in the positive electrode film is relatively low. However, the sodium-copper-based positive electrode active material generates a large amount of gas in actual use, resulting in a high electrode rebound. Therefore, appropriately controlling the content of binder within a certain range can reduce electrode rebound to a certain extent, slow down cell expansion, and improve cycle performance.

[0039] In some embodiments, when the positive electrode sheet is cold-pressed, the diaphragm resistance first decreases and then increases as the pressure increases. The pressure at which the diaphragm resistance reaches an inflection point during cold pressing is greater than or equal to 30T, and optionally 30-60T.

[0040] In the technical solution of this application, due to the nano-characteristics of carbon nanotubes, their pressure resistance fracture is relatively difficult to test and observe. This application combines the film resistance of the electrode sheet for correlation evaluation. The pressure at which the film resistance reaches the inflection point during cold pressing is within the above range. The carbon nanotubes in the positive electrode film have high strength and less fracture in actual operation, which is more conducive to improving the stability of the battery.

[0041] In a second aspect, this application provides a battery device comprising a plurality of battery cells according to the first aspect.

[0042] Thirdly, this application provides an electrical device, which includes the battery cell described in the first aspect, or the battery device described in the second aspect.

[0043] 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, specific embodiments of this application are given below. Attached Figure Description

[0044] 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:

[0045] Figure 1 is a scanning electron microscope image of carbon nanotubes and positive electrode active materials in the positive electrode film layer of some embodiments of this application;

[0046] Among them, 1-carbon nanotubes; 2-positive electrode active material.

[0047] Figure 2 is a scanning electron microscope image of sodium-zinc based positive electrode active material of some embodiments of this application.

[0048] Figure 3 is a scanning electron microscope image of sodium-copper-based positive electrode active material of some embodiments of this application.

[0049] Figure 4 shows the installation of some embodiments and comparative examples of this application during the performance testing process. Detailed Implementation

[0050] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0052] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0053] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0054] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is 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 "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 "2-10" indicates that all real numbers between "2-10" have been listed in this article; "2-10" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0056] Positive electrode active materials with layered crystal structures have poor electronic conductivity, which easily leads to a large film resistance in the formed positive electrode film. This, in turn, causes a large temperature rise in the cell during charging and discharging, triggering over-temperature protection and affecting the performance of the battery cell.

[0057] This application combines a positive electrode active material with a layered crystal structure with carbon nanotubes, and controls the ratio between the average tube length of the carbon nanotubes and the Dv50 particle size of the positive electrode active material within a specific range, thereby reducing the film resistance and electrode rebound of the positive electrode sheet and improving the cycle performance of the battery cell.

[0058] [Battery cell]

[0059] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0060] The battery cell can be a sodium-ion battery, a sodium-lithium-ion battery, a sodium metal battery, etc., but this application does not limit this.

[0061] [Electrode Assembly]

[0062] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the negative and positive electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions or sodium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0063] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0064] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0065] In some implementations, the electrode assembly is a stacked structure.

[0066] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0067] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0068] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0069] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0070] In some embodiments, the electrode assembly has tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0071] Positive electrode sheet

[0072] In some embodiments, the positive electrode can be a positive electrode sheet; this application provides a battery cell, the battery cell including a positive electrode sheet;

[0073] The positive electrode includes a positive current collector and a positive film layer disposed on at least one (e.g., one or two) surfaces of the positive current collector;

[0074] The positive electrode film layer includes a positive electrode active material and carbon nanotubes;

[0075] The positive electrode active material has a layered crystal structure;

[0076] The ratio between the average tube length of the carbon nanotube and the Dv50 particle size of the positive electrode active material is (2-10):1, where 2-10 can be 4, 5, 6, 7, 8, 9, etc.

[0077] In this application, the average length of carbon nanotubes can be obtained in the following way: when observing with a scanning electron microscope or a transmission electron microscope or equivalent electron microscope, the length of carbon nanotubes in one or more fields of view is distributed within a certain range, and the average value is taken as the average length of carbon nanotubes.

[0078] In this application, the Dv50 particle size of the positive electrode active material refers to the particle size corresponding to a cumulative volume distribution that reaches 50% in the particle size distribution. This application obtains the Dv50 particle size using laser diffraction or electron microscopy; specifically, laser diffraction analyzes the particle size distribution by measuring the scattered light signal generated by the laser light emitted by the particles; electron microscopy observes the particle size in different fields of view using scanning electron microscopy or transmission electron microscopy and performs statistical analysis.

[0079] In this application, the specific components in the positive electrode film layer can be determined by the following method:

[0080] (1) Disassemble the battery cell, take out the positive electrode sheet, soak the positive electrode sheet in a solvent (such as DMC (dimethyl carbonate)) for 2 hours, then rinse it with DMC solution for 2 minutes, twice, and finally dry it at 80°C for 2 hours to obtain the positive electrode film sample.

[0081] (2) Fix the positive electrode film sample to the sample stage of the scanning electron microscope (e.g., Sigma 300) using conductive adhesive to ensure that the sample remains stable and does not drift during vacuuming; place the sample into the sample chamber of the scanning electron microscope and vacuum it, turn on the power of the scanning electron microscope and start the system software, adjust the contrast and brightness of the scanning electron microscope to a suitable range, and observe and take pictures by adjusting the magnification (e.g., 5000 times) and focal length. Statistically analyze the ratio between the average tube length of carbon nanotubes and the Dv50 particle size of the positive electrode active material. Taking Figure 1 as an example, the elongated structure in the figure is carbon nanotube 1, and the plate-like structure is positive electrode active material 2. The average tube length of some carbon nanotubes is marked out for example, which can intuitively analyze the ratio between the average tube length of carbon nanotubes and the Dv50 particle size of the positive electrode active material.

[0082] In the technical solution of this application embodiment, a positive electrode active material with a layered crystal structure and carbon nanotubes are used in combination in the positive electrode film layer. The carbon nanotubes can improve the electronic conductivity of the positive electrode active material with a layered crystal structure, reduce the film resistance of the positive electrode film, reduce the temperature rise of the cell during charging and discharging, reduce over-temperature protection, and improve the cycle performance of the battery. In addition, during the charging and discharging process of the battery, the positive electrode active material may undergo volume expansion. This expansion force may cause the electrode to rebound. By controlling the ratio between the average tube length of the carbon nanotube and the Dv50 particle size of the positive electrode active material within the specified range, the carbon nanotubes can form a good constraint on the positive electrode active material, reduce electrode rebound, and improve the cycle performance of the battery. In summary, the positive electrode film resistance and electrode rebound of the present application are small, resulting in excellent cycle performance of the formed battery cell.

[0083] In some embodiments, the carbon nanotubes include any one or a combination of at least two of single-walled carbon nanotubes, oligo-walled carbon nanotubes, or multi-walled carbon nanotubes.

[0084] In some embodiments, the average length of the carbon nanotubes is 9-120 μm, such as 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, etc., and optionally 16-50 μm; and / or;

[0085] The diameter of the carbon nanotubes is 5-10 nm, such as 6 nm, 7 nm, 8 nm, 9 nm, etc.

[0086] In the technical solution of this application embodiment, the average tube length and tube diameter of the carbon nanotubes are within the specified range. On the basis of reducing the film resistance and electrode rebound of the positive electrode, the carbon nanotubes themselves are not prone to agglomeration or breakage during the electrode or battery processing, resulting in better battery cycle performance.

[0087] In some embodiments, the carbon nanotubes account for 0.1%-0.6% of the total mass of the positive electrode film, for example, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0088] In the technical solution of this application embodiment, the mass ratio of carbon nanotubes in the positive electrode film layer is within the specified range. The mass ratio of carbon nanotubes in the positive electrode film layer is within the specified range. On the basis of improving the conductivity of the positive electrode active material and forming good binding of the positive electrode active material, the carbon nanotubes themselves agglomerate less and have less impact on the content of the main materials such as the positive electrode active material. Therefore, it can effectively reduce the electrode rebound and film resistance, while basically not affecting the core role of the positive electrode active material, and can form a battery with excellent cycle performance.

[0089] In some embodiments, the positive electrode film layer further includes a zero-dimensional conductive agent.

[0090] In the technical solution of this application embodiment, the positive electrode film layer also includes a zero-dimensional conductive agent. Compared with carbon nanotubes, the zero-dimensional conductive agent has a lower cost and is easier to disperse in the positive electrode slurry, making it easier to process. Therefore, while meeting the performance requirements of the battery cell, the zero-dimensional conductive agent and carbon nanotubes can be used together to reduce production costs and processing difficulty.

[0091] In some embodiments, the mass percentage of the zero-dimensional conductive agent is 0.5%-3% based on the total mass of the positive electrode film layer as 100%, optionally 1%-3%, such as 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, etc.

[0092] In the technical solution of this application embodiment, the mass ratio of the zero-dimensional conductive agent in the positive electrode film layer is within the specified range. When the mass ratio is appropriate, the positive electrode slurry formed during the preparation of the electrode sheet has high preservation stability and basically does not affect the normal coating of the slurry. Moreover, the zero-dimensional conductive agent itself has less agglomeration between particles, which has less impact on the polarization of the cell. It can cooperate well with carbon nanotubes, reduce the film resistance of the electrode sheet, and improve the conductivity of the positive electrode sheet.

[0093] As an example, the zero-dimensional conductive agent includes carbon black, optionally acetylene black and / or Ketjen black.

[0094] In some embodiments, the positive electrode film layer further includes any one or a combination of at least two of carbon dots, graphene, or carbon nanofibers.

[0095] In some embodiments, the positive electrode film layer further includes a binder;

[0096] Based on the total mass of the positive electrode film layer being 100%, the mass percentage of the binder is 1%-4%, for example, 1.5%, 2%, 2.5%, 3%, 3.5%, etc.

[0097] In the technical solution of this application embodiment, the mass ratio of the binder in the positive electrode film layer is within the range, which can effectively bond the positive electrode active material, carbon nanotubes, and zero-dimensional conductive agents, resulting in good cycle performance of the battery during use.

[0098] As an example, the adhesive includes any one or a combination of at least two of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0099] In some embodiments, the positive electrode active material includes sodium-zinc based positive electrode active material and / or sodium-copper based positive electrode active material.

[0100] In some embodiments, the chemical formula of the sodium-zinc based positive electrode active material is Na q M x Zn y O2, wherein M includes any one or at least two combinations of Ti, V, Cr, Mn, Fe, Co, and Ni, and 0.81 ≤ q ≤ 1.1 (e.g., 0.82, 0.85, 0.9, 0.95, etc.), 0.8 < x + y ≤ 1 (e.g., 0.82, 0.85, 0.9, 0.95, etc.), 0.02 ≤ y ≤ 0.10 (e.g., 0.04, 0.06, 0.08, etc.); and / or;

[0101] The sodium-zinc-based positive electrode active material includes a lath shape, as shown in Figure 2 (scanning electron microscope image); and / or;

[0102] The Dv50 particle size of the sodium-zinc based positive electrode active material is 3-8 μm, such as 4 μm, 5 μm, 6 μm, 7 μm, etc.

[0103] In this application, the sodium-zinc-based positive electrode active material can be a commercially available product or it can be prepared in-house; the shape of the sodium-zinc-based positive electrode active material is controlled by the preparation process. For example, the preparation method of the strip-shaped sodium-zinc-based positive electrode active material includes the following steps:

[0104] Raw material preparation: Select appropriate transition metal sources and sodium sources, such as metal oxides, carbonates, hydroxides or nitrates.

[0105] Mixing: The raw materials are mixed according to a predetermined stoichiometric ratio to ensure the homogeneity of the materials.

[0106] Pretreatment: The mixed raw materials may need to be pretreated, such as ball milling, to increase the contact area of ​​the raw materials and promote subsequent reactions.

[0107] Heat treatment: The pretreated raw materials are sintered at high temperature to form the positive electrode active material. This step may involve one or two sintering processes to optimize the structure and properties of the material.

[0108] Post-processing: Sintered materials may require crushing, grading, and surface treatments such as coating or doping to improve their electrochemical properties.

[0109] Quality control: Strict quality control is carried out on the final product, including testing of particle size distribution, specific surface area, chemical composition and structure.

[0110] In the technical solution of this application embodiment, the chemical formula of the sodium-zinc-based positive electrode active material is as described above. The lamellar sodium-zinc-based positive electrode active material has obvious grain boundaries, few defects, few side reactions with electrolyte, low gas production in actual operation, and good cycle stability of the resulting battery.

[0111] In the technical solution of this application embodiment, the Dv50 particle size of the sodium-zinc-based positive electrode active material is within the specified range. The slurry coating performance formed by the sodium-zinc-based positive electrode active material is excellent and does not significantly increase the processing difficulty. Moreover, the particles are not easily agglomerated, resulting in stable long-term battery performance. At the same time, when the sodium-zinc-based positive electrode active material is used in batteries, the diffusion path of active ions is relatively short, the solid-phase diffusion resistance is small, and the electrochemical reaction rate at the interface is fast, which is beneficial to improving the rate performance of the battery.

[0112] In some embodiments, the positive electrode active material is a sodium-zinc based positive electrode active material, and the carbon nanotubes account for 0.2%-0.6% of the total mass of the positive electrode film, for example, 0.3%, 0.4%, 0.5%, etc.; and / or;

[0113] The adhesive comprises 1%-3.5% by mass, for example, 1.5%, 2%, 2.5%, 3%, etc.

[0114] In the technical solution of this application embodiment, the positive electrode active material is a sodium-zinc based positive electrode active material. Choosing a strip-shaped sodium-zinc based positive electrode active material is more conducive to improving battery performance. The sodium-zinc based positive electrode active material requires relatively high pressure during cold pressing. Therefore, choosing a relatively high mass ratio of carbon nanotubes in the positive electrode film layer is more conducive to improving battery performance. In actual use, the sodium-zinc based positive electrode active material produces less gas and the electrode rebound is lower. Therefore, a relatively low mass ratio of binder is sufficient to meet the requirements, thereby further improving energy density.

[0115] In some embodiments, the chemical formula of the sodium-copper based positive electrode active material is Na. p Z a Cu b O2, wherein Z includes any one or at least two combinations of Ti, V, Cr, Mn, Fe, Co, Ni or Zn, and 0.81≤p≤1.1 (e.g. 0.82, 0.85, 0.9, 0.95, etc.), 0.8<a+b≤1 (e.g. 0.82, 0.85, 0.9, 0.95, etc.), 0.03≤b≤0.2 (e.g. 0.05, 0.1, 0.15, etc.); and / or;

[0116] The sodium-copper-based positive electrode active material includes at least one shape selected from spherical and near-spherical, as shown in Figure 3; and / or;

[0117] The Dv50 particle size of the sodium-copper-based positive electrode active material is 5-12 μm, such as 6 μm, 8 μm, 10 μm, etc.

[0118] In this application, the sodium-copper-based positive electrode active material can be a commercially available product or can be made in-house; the shape of the sodium-copper-based positive electrode active material is controlled by the preparation process, and the preparation method of the spherical sodium-copper-based positive electrode active material is similar to the processing process of the sodium-zinc-based positive electrode active material described above.

[0119] In the technical solution of this application embodiment, the chemical formula of the sodium-copper-based positive electrode active material is as described above. The spherical or near-spherical sodium-copper-based positive electrode active material has relatively rounded edges and corners, and can have a high compaction density during the cold pressing of the electrode sheet. At the same time, the sodium-copper-based positive electrode active material is not easily damaged, which affects the performance of the battery cell. The Dv50 particle size of the sodium-copper-based positive electrode active material is controlled within the above-mentioned range. The slurry coating performance formed by the sodium-copper-based positive electrode active material is excellent, and it does not increase the processing difficulty. Moreover, the particles are not easy to agglomerate, and the battery performance is stable. At the same time, when the sodium-zinc-based positive electrode active material is used in the battery, the diffusion path of active ions is relatively short, the solid phase diffusion resistance is small, and the electrochemical reaction rate at the interface is fast, which is beneficial to improving the rate performance of the battery.

[0120] In some embodiments, the positive electrode active material is a sodium-copper based positive electrode active material, and the carbon nanotubes account for 0.1%-0.6% of the total mass of the positive electrode film, for example, 0.2%, 0.3%, 0.4%, 0.5%, etc.; and / or;

[0121] The adhesive comprises 1.1%-4% by mass, for example, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, etc.

[0122] In the technical solution of this application embodiment, selecting a spherical or near-spherical shape with a relatively regular shape for the sodium-copper-based positive electrode active material is more conducive to improving battery performance, such as rate performance. Moreover, the pressure of the sodium-copper-based positive electrode active material during the cold pressing process is relatively small. Therefore, the basic requirements can be met even if the mass ratio of carbon nanotubes in the positive electrode film is relatively low. However, the sodium-copper-based positive electrode active material generates a large amount of gas in actual use, resulting in a high electrode rebound. Therefore, appropriately controlling the content of binder within a certain range can reduce electrode rebound to a certain extent, slow down cell expansion, and improve cycle performance.

[0123] In some embodiments, when the positive electrode sheet is cold-pressed, the diaphragm resistance first decreases and then increases as the pressure increases. The pressure at which the diaphragm resistance reaches an inflection point during cold pressing is greater than or equal to 30T, such as 40T, 50T, 60T, etc., and optionally 30-60T.

[0124] In this application, the determination of the inflection point includes the following steps:

[0125] (1) The positive electrode sheet was cut into small circular pieces with a radius of about 22 mm as samples. The samples were cold-pressed under different pressures and the film resistance was tested by the two-probe method. The instrument used was BER2500 (IEST Yuanneng Technology). The electrode diameter was adjusted to 14 mm and the pressure was 10 MPa.

[0126] (2) Plot a graph with pressure on the horizontal axis and diaphragm resistance on the vertical axis, and observe the lowest value of the diaphragm resistance, or directly observe and determine the lowest value of the diaphragm resistance, which is the inflection point.

[0127] In the technical solution of this application embodiment, due to the nanoscale characteristics of carbon nanotubes, their pressure resistance fracture is relatively difficult to test and observe. Since carbon nanotubes are one-dimensional conductive materials with a slender structure, one of the reasons for improving conductivity in the positive electrode film is that carbon nanotubes easily form a conductive network in a "line-to-line" manner. If carbon nanotubes are broken under pressure, the conductive network they form is destroyed, the long-range conductivity decreases, the overall conductivity deteriorates, and the film resistance increases. Therefore, this application combines the film resistance of the electrode sheet for correlation evaluation. The pressure at which the film resistance reaches the inflection point during cold pressing is within the above-mentioned range. The carbon nanotubes in the positive electrode film have high strength and less fracture in actual operation, which is more conducive to improving the cycle performance of the battery.

[0128] 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.

[0129] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0130] Preparation of positive electrode sheet

[0131] In some embodiments, the method for preparing the positive electrode sheet includes: dissolving a positive electrode material, such as a positive electrode active material having a layered crystal structure, carbon nanotubes, a binder, and other arbitrary components (such as zero-dimensional conductive agents) in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector (such as a metal foil) to form a positive electrode film; and drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0132] As an example, in the preparation process, the binder is first dispersed in the solvent for the first time. The first dispersion speed is 500-2000 rpm, such as 1000 rpm, 1500 rpm, etc., and the first dispersion time is 30-60 min, such as 35 min, 40 min, 45 min, 50 min, 55 min, etc.

[0133] Then, any other components (such as zero-dimensional conductive agents) are dispersed a second time in the above mixture. The second dispersion speed is 500-2000 rpm, such as 1000 rpm, 1500 rpm, etc., and the second dispersion time is 20-40 min, such as 25 min, 30 min, 35 min, etc.

[0134] Finally, the positive electrode active material and carbon nanotubes are dispersed for the third time in the above mixture. The speed of the third dispersion is 500-2000 rpm, such as 1000 rpm or 1500 rpm, and the dispersion time is 15-30 min, such as 25 min.

[0135] As an example, after coating, the total thickness of the positive current collector and the positive electrode film layer is 150-250 μm, such as 200 μm.

[0136] As an example, the drying temperature is 50-150℃, such as 105℃, and the drying time is 15-50min, such as 20min, 25min, 30min, 35min, 40min, 45min, etc.

[0137] In some embodiments, the method for preparing the positive electrode sheet includes:

[0138] (1) First, disperse the adhesive in the solvent for the first time. The first dispersion speed is 500-2000 rpm and the first dispersion time is 30-60 min.

[0139] (2) Then, any other components (such as zero-dimensional conductive agents) are dispersed in the above mixture for the second time. The second dispersion speed is 500-2000 rpm and the second dispersion time is 20-40 min.

[0140] (3) The positive electrode active material and carbon nanotubes are then dispersed in the above mixture for the third time to obtain the positive electrode slurry. The speed of the third dispersion is 500-2000 rpm and the time of the third dispersion is 15-30 min.

[0141] (4) Finally, the positive electrode slurry is coated on the positive electrode current collector (e.g., metal foil) to form a positive electrode film. The total thickness of the positive electrode current collector and the positive electrode film is 150-250 μm. After drying at 50-150℃ for 15-50 min, cold pressing, and slitting, the positive electrode sheet is obtained.

[0142] Negative electrode sheet

[0143] In some embodiments, the battery cell further includes a negative electrode sheet, which may include a negative current collector.

[0144] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0145] As an example, 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.

[0146] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0147] As an example, the negative electrode active material in the negative electrode film layer can be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and sodium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0148] In some embodiments, the negative electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not have a negative electrode active material.

[0149] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0150] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0151] In some embodiments, the method for preparing the negative electrode sheet includes: dissolving a negative electrode material, such as a negative electrode active material, a conductive agent, a binder, and other arbitrary components in a solvent (e.g., water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector to form a negative electrode film layer; and obtaining the negative electrode sheet by drying, cold pressing, and slitting.

[0152] electrolytes

[0153] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0154] Liquid electrolytes include electrolyte salts and solvents.

[0155] In some embodiments, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0156] 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. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0157] 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 that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0158] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid—sodium salt.

[0159] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0160] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0161] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ionic conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline sodium superconducting ionic conductor (sodium germanium phosphate sulfur, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0162] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0163] Isolation component

[0164] In some embodiments, the battery cell further includes a separator disposed between the positive and negative electrodes.

[0165] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0166] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. 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. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0167] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0168] [Battery Device]

[0169] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0170] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0171] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0172] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0173] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0174] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0175] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0176] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0177] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0178] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0179] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0180] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0181] [Electrical appliances]

[0182] This application provides an electrical device, which includes the aforementioned battery cell.

[0183] In some embodiments, the electrical device includes at least one of the battery modules or battery packs provided in any embodiment of this application.

[0184] The battery cells, battery modules, or battery packs described in this application can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include 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., including but not limited to these.

[0185] [Example]

[0186] Example 1

[0187] Positive electrode sheet: Sodium-zinc based positive electrode active material, carbon nanotubes, zero-dimensional conductive agent (SP), and binder (PVDF) are dissolved in a solvent (N-methylpyrrolidone) at a mass ratio of 95:0.5:2:2.5 to form a positive electrode slurry. The positive electrode slurry is coated on a positive electrode current collector (aluminum foil) to form a positive electrode film. The total thickness of the positive electrode current collector and the positive electrode film is 200 μm. After drying (105℃, 30 min), cold pressing (50T), and slitting, the positive electrode sheet is obtained.

[0188] Negative electrode sheet: The negative electrode active material (hard carbon), binder (linear acrylic acid), and conductive agent (zero-dimensional conductive agent) are dissolved in a solvent (water) at a mass ratio of 0.95:0.05:0.05 to form a negative electrode slurry. The negative electrode slurry is coated on a negative electrode current collector (copper foil) to form a negative electrode film. After drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0189] Separating membrane: A polyethylene membrane with a thickness of 13μm is used.

[0190] Electrolyte: Composed of sodium hexafluorophosphate and a mixed solvent, wherein the mixed solvent consists of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, and the molar concentration of sodium hexafluorophosphate is 1 mol / L.

[0191] Battery cell: The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain the cell; the cell is placed in the outer packaging, electrolyte is added, and after vacuum sealing, standing, formation, shaping, capacity measurement and other processes, the battery cell is obtained.

[0192] Examples 2-7 and Comparative Examples 1-3 (containing sodium-zinc based positive electrode active materials)

[0193] Except for the parameters in Table 1, the battery cells were prepared according to the method described in Example 1.

[0194] Table 1

[0195] In the table, the particle size of the positive electrode active material is Dv50. The diameter of the carbon nanotubes in each example and comparative example is between 5-10 nm. The tube length of Example 1 is between 16-50 μm, with an average tube length of 33 μm. The tube diameters of the other examples or comparative examples are similar.

[0196] The content of each component refers to the mass content based on the positive electrode film mass meter;

[0197] "—" indicates data that is not involved.

[0198] Table 2 shows the film resistance of the positive electrode in Examples 2-7 and Comparative Examples 1-3 under different cold pressing conditions:

[0199] Table 2

[0200] The positive electrode sheet was cut into small circular pieces with a radius of about 22 mm as samples, and cold-pressed under different pressures. The film resistance was tested by a dual-probe method. As shown in the table above, the inflection point value of the film resistance of the positive electrode sheet of the sodium-zinc based positive electrode active material described in this application is in the range of 40-60T.

[0201] Examples 8-11 and Comparative Examples 4-6 (containing sodium-copper based positive electrode active materials)

[0202] Except for the parameters in Table 3, the battery cells were prepared according to the method described in Example 1.

[0203] Table 3

[0204] Table 4 shows the film resistance of the positive electrode in Examples 8-11 and Comparative Examples 4-6 under different cold pressing conditions:

[0205] Table 4

[0206] The positive electrode sheet was cut into small circular pieces with a radius of about 22 mm as samples, and cold-pressed under different pressures. The film resistance was tested by a dual-probe method. As shown in the table above, the inflection point value of the film resistance of the positive electrode sheet of the sodium copper-based positive electrode active material described in this application is in the range of 30-50T.

[0207] [Performance Testing]

[0208] Install the battery cells as shown in Figure 4. The initial pressure sensor reading is 2000N. Then connect the positive and negative terminals to the testing machine (Xinwei Charge / Discharge Machine - 5V100A) to begin performance testing. The test environment temperature is 25℃ and the relative humidity RH < 20%. Cycle the battery cells according to the process shown in Table 5.

[0209] Table 5

[0210] In the table, C represents the rated capacity value. For example, if the rated capacity is 10Ah, then 1C represents 10, 1 / 3C represents 3.33, and 4C represents 40.

[0211] (1) The capacity retention rate after 500 cycles is calculated according to the following formula: Capacity retention rate (%) = Cn / C1 × 100%.

[0212] (2) The growth rate of expansion force after 500 cycles is calculated according to the following formula: Growth rate of expansion force (%) = Fn / F1 × 100% - 1.

[0213] (3) DCR growth rate after 500 cycles: DCR refers to the internal resistance of the battery in a DC circuit, expressed in ohms (Ω). DCR1 is the DCR before the cycle, and DCR2 is the DCR after the cycle.

[0214] The testing process for DCR1 is shown in Table 6:

[0215] Table 6

[0216] DCR1=(U1-U2) / 4C.

[0217] The testing process for DCR2 is shown in Table 7:

[0218] Table 7

[0219] DCR2=(U4-U3) / 4C.

[0220] The DCR growth rate over 500 cycles is calculated using the following formula: DCR growth rate = DCR2 / DCR1 × 100% - 1.

[0221] The results of the above tests are summarized in Table 8-9.

[0222] Table 8

[0223] Analysis of the data from Comparative Examples 1-2 and Example 1 shows that the battery cells of Comparative Examples 1-2 have lower capacity retention, higher DCR growth rate, and higher expansion force growth rate after 500 cycles. This proves that the battery cells formed by controlling the average tube length of carbon nanotubes and the Dv50 particle size of sodium zinc-based positive electrode active material within the range of (2-10):1 in this application have better performance.

[0224] Analysis of the data from Comparative Example 3 and Example 1 shows that the battery cell of Comparative Example 3 has a lower capacity retention rate, a higher DCR growth rate, and a higher expansion force growth rate after 500 cycles, proving that the battery cell formed by adding carbon nanotubes has better performance.

[0225] Analysis of Examples 5 and 1 shows that the battery cell of Example 5 has a lower capacity retention rate, a higher DCR growth rate, and a higher expansion force growth rate after 500 cycles, proving that the battery cell formed by combining carbon nanotubes with a mass content of 1%-3% zero-dimensional conductive agent has better performance.

[0226] Table 9

[0227] Analysis of the data from Comparative Examples 4-5 and Example 8 shows that the battery cells of Comparative Examples 4-5 have lower capacity retention, higher DCR growth rate, and higher expansion force growth rate after 500 cycles. This proves that the battery cells formed by controlling the average tube length of carbon nanotubes and the Dv50 particle size of sodium copper-based positive electrode active material within the range of (2-10):1 in this application have better performance.

[0228] Analysis of the data from Comparative Example 6 and Example 8 shows that the battery cell of Comparative Example 6 has a lower capacity retention rate, a higher DCR growth rate, and a higher expansion force growth rate after 500 cycles, proving that the battery cell formed by adding carbon nanotubes has better performance.

[0229] Analysis of Examples 9 and 8 shows that the battery cell of Example 9 has a lower capacity retention rate, a higher DCR growth rate, and a higher expansion force growth rate after 500 cycles, proving that the battery cell formed by combining carbon nanotubes with a mass content of 1%-3% zero-dimensional conductive agent has better performance.

[0230] 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 battery cell, wherein, The battery cell includes a positive electrode sheet; The positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector; The positive electrode film layer includes a positive electrode active material and carbon nanotubes; The positive electrode active material has a layered crystal structure; The ratio between the average tube length of the carbon nanotubes and the Dv50 particle size of the positive electrode active material is (2-10):

1.

2. The battery cell according to claim 1, wherein, The carbon nanotubes have an average tube length of 9-120 μm, optionally 16-50 μm; and / or; The diameter of the carbon nanotubes is 5-10 nm.

3. The battery cell according to claim 1 or 2, wherein, With the total mass of the positive electrode film layer being 100%, the mass percentage of the carbon nanotubes is 0.1%-0.6%.

4. The battery cell according to any one of claims 1-3, wherein, The positive electrode film also includes a zero-dimensional conductive agent.

5. The battery cell according to claim 4, wherein, With the total mass of the positive electrode film layer being 100%, the mass percentage of the zero-dimensional conductive agent is 0.5%-3%, optionally 1%-3%.

6. The battery cell according to any one of claims 1-5, wherein, The positive electrode film layer also includes a binder; With the total mass of the positive electrode film layer being 100%, the mass percentage of the binder is 1%-4%.

7. The battery cell according to any one of claims 1-6, wherein, The positive electrode active material includes sodium-zinc based positive electrode active material and / or sodium-copper based positive electrode active material.

8. The battery cell according to claim 7, wherein, The chemical formula of the sodium-zinc based positive electrode active material is Na. q M x Zn y O2, wherein M includes any one or at least two of Ti, V, Cr, Mn, Fe, Co, and Ni, and 0.81≤q≤1.1, 0.8<x+y≤1, 0.02≤y≤0.10; and / or; The sodium-zinc-based positive electrode active material includes a lath-like shape; and / or; The Dv50 particle size of the sodium-zinc based positive electrode active material is 3-8 μm.

9. The battery cell according to claim 7 or 8, wherein, The positive electrode active material is a sodium-zinc based positive electrode active material, and the carbon nanotubes account for 0.2%-0.6% of the total mass of the positive electrode film layer (100%); and / or; The adhesive comprises 1%-3.5% by mass.

10. The battery cell according to claim 7, wherein, The chemical formula of the sodium-containing copper-based positive electrode active material is Na. p Z a Cu b O2, wherein Z includes any one or at least two combinations of Ti, V, Cr, Mn, Fe, Co, Ni or Zn, and 0.81≤p≤1.1, 0.8<a+b≤1, 0.03≤b≤0.2; and / or; The sodium-copper-based positive electrode active material includes at least one of the following shapes: spherical and near-spherical; and / or; The Dv50 particle size of the sodium-copper-based positive electrode active material is 5-12 μm.

11. The battery cell according to claim 7 or 10, wherein, The positive electrode active material is a sodium-copper based positive electrode active material, and the carbon nanotubes account for 0.1%-0.6% of the total mass of the positive electrode film layer (100%); and / or; The adhesive comprises 1.1%-4% by mass.

12. The battery cell according to any one of claims 1-11, wherein, During the cold pressing of the positive electrode sheet, the diaphragm resistance first decreases and then increases as the pressure increases. The pressure at which the diaphragm resistance reaches an inflection point during cold pressing is greater than or equal to 30T, and optionally 30-60T.

13. A battery device, wherein, The battery device comprises a plurality of battery cells according to any one of claims 1-12.

14. An electrical appliance, wherein, The electrical device includes a battery cell as described in any one of claims 1-12, or a battery device as described in claim 13.

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