Battery cell, battery device, and electric device

Abstract

The present disclosure provides a battery cell, a battery device and a power consumption device, the battery cell comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer provided on at least one side surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising lithium-containing transition metal phosphate particles, a D V90 - D V10 ) / D V50 of 4-8; and a mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 60%-80% based on a total mass of the positive electrode film layer.

Description

Technical Field

[0001] This application relates to the field of battery cell technology, and more particularly to a battery cell, a battery device, and an electrical device. Background Technology

[0002] In recent years, battery cells have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] Cathode active materials are a crucial component of battery cells. Lithium-containing transition metal phosphate materials possess characteristics such as structural stability, good safety, and long cycle life, demonstrating broad development prospects. However, with increasing market demands for energy density and kinetics in lithium-containing transition metal phosphate battery cells, current technologies struggle to simultaneously improve these properties, making this a pressing technical challenge in the field. Summary of the Invention

[0004] In view of the above problems, this application provides a battery cell, a battery device, and an electrical device, which are described below.

[0005] A first aspect of this application provides a battery cell including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one surface of the positive current collector. The positive electrode film includes a positive electrode active material, which comprises lithium transition metal phosphate particles. The particles in the positive electrode film have a (D) % ... V90 -D V10 ) / D V50 The mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 4-8% based on the total mass of the positive electrode film layer.

[0006] In this application, by controlling the (D) of the particles V90 -D V10 ) / D V50A particle size distribution of 4-8 helps to construct a reasonable particle size distribution. Small particles can fill the gaps between large particles, forming a denser packing structure, reducing porosity, and thus increasing the compaction density of the electrode sheet, thereby improving the energy density of the battery. However, the proportion of large particles is still relatively large, increasing the tortuosity inside the positive electrode film, increasing the lithium-ion transport path length, leading to local polarization, increasing battery impedance, and adversely affecting battery kinetics. This application further improves the roundness of particles in the positive electrode film. When the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film is within the above range, it is beneficial to form regular and continuous pore channels, reducing the degree of tortuosity and bifurcation of pore channels, improving lithium-ion transport efficiency, and achieving a balance between the kinetics and cycle life of the battery cell.

[0007] In any embodiment, based on the total mass of the positive electrode film layer, the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 65%-75%. Highly rounded particles, due to their regular shape, can be packed more tightly after rolling, but an excessively high proportion may lead to increased slippage between particles, affecting the stability of the positive electrode film layer and causing a decrease in compaction density. Therefore, maintaining the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer within the aforementioned range helps to achieve a balance between high compaction density and low tortuosity in the positive electrode film layer.

[0008] In any embodiment, based on the total mass of the positive electrode film layer, the mass percentage of particles with a roundness of 0.4 or less in the positive electrode film layer is 5%-20%, optionally 10%-15%. When high-roundness particles are stacked, large porosity may exist between the particles, limiting further improvement in compaction density. Therefore, a mixing strategy of low-roundness and high-roundness particles is adopted. By filling particles of different shapes and sizes together, porosity is reduced, forming a denser packing structure, thereby improving compaction density.

[0009] In any embodiment, the particles in the positive electrode film layer (D V90 -D V10 ) / D V50 The value is 5-7. The particle size (D) in the positive electrode film layer... V90 -D V10 ) / D V50 Within the aforementioned range, high energy density can be achieved while maintaining low tortuosity of the positive electrode film, further optimizing polarization and lifespan during battery cycling.

[0010] In any embodiment, the one-sided density of the positive electrode film is 200 mg / 1540.25 mm². 2 -450mg / 1540.25mm 2The areal density of the cathode film has a significant impact on the lithium-ion transport rate. Too low an areal density may sacrifice energy density, while too high an areal density may lengthen the ion transport path, leading to a decrease in the ion transport rate. An areal density within the aforementioned range helps improve the battery's energy density and kinetic performance.

[0011] In any embodiment, the D of the particles in the positive electrode film layer V50 The particle size is 0.5μm-0.9μm, with a selectable range of 0.6μm-0.8μm. The particle size D in the positive electrode film... V50 The size of the σ affects both the compaction density and tortuosity of the positive electrode film. V50 If the particle size is too large, the porosity between particles also increases, making it difficult to improve the compaction density of the positive electrode film; D V50 If the particle size is too small, the ion transport pathways between particles become fragmented and discontinuous, reducing ion transport efficiency. Simultaneously, the electrolyte's inability to permeate further obstructs these ion transport pathways. The D-value of particles in the positive electrode film... V50 Within the aforementioned range, further improve the energy density and cycle life of individual battery cells.

[0012] In any embodiment, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the first peak of the bimodal distribution located between 0.45 μm and 0.75 μm.

[0013] In any embodiment, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the first peak of the bimodal distribution located at 0.6 μm-0.7 μm.

[0014] In any embodiment, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the second peak of the bimodal distribution located between 0.6 μm and 0.97 μm.

[0015] In any embodiment, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the second peak of the bimodal distribution located between 0.7 μm and 0.91 μm.

[0016] The bimodal distribution of the volume distribution curve of particles in the positive electrode film indicates that the positive electrode film contains large and small particles of different sizes. The first peak and / or the second peak are within the above range, which is beneficial for filling the gaps between large particles with small particles, which is beneficial for increasing the compaction density of the electrode sheet, thereby further improving the energy density of the battery.

[0017] In any embodiment, the positive electrode film layer includes a conductive agent, and the mass percentage of the conductive agent is 0.5%-1% based on the total mass of the positive electrode film layer. The fact that the mass percentage of the conductive agent is within the above range, based on the total mass of the positive electrode film layer, ensures that the positive electrode film layer has good electronic conductivity and a high loading of active materials, achieving a balance between kinetic performance and energy density.

[0018] In any embodiment, the conductive agent includes a one-dimensional conductive agent, which may be selected from one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers. The one-dimensional conductive agent has a fibrous structure with lengths reaching the micrometer scale, enabling the formation of a continuous linear conductive network in the electrode. This achieves an effective conductive network at a lower addition amount, reducing the amount of conductive agent used and thus further improving the energy density of the battery.

[0019] In any embodiment, the conductive agent includes a zero-dimensional conductive agent, which may be one or more of conductive carbon black, Ketjen black, and hard carbon. Zero-dimensional conductive agents establish a conductive network of point contacts between active materials, generally possessing a high specific surface area. They effectively fill the gaps between active materials, further enhancing the conductivity of the electrode and improving the overall kinetic performance of the battery.

[0020] In any embodiment, the porosity of the positive electrode film is 15%-25%, optionally 18.2%-22.9%. Controlling the porosity of the positive electrode film within the above range allows the positive electrode active material to have a high compaction density and energy density after rolling. A certain porosity facilitates the wetting of the positive electrode active material by the electrolyte, further optimizing ion transport efficiency, reducing polarization, and improving the cycle life of the battery.

[0021] In any embodiment, the lithium-containing transition metal phosphate comprises a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z ,

[0022] Wherein, 0.1≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; Y includes one or more of O and F.

[0023] The aforementioned lithium-containing transition metal phosphate materials exhibit good thermal stability and cycle stability, which helps to improve the safety and cycle performance of batteries.

[0024] In any embodiment, the tortuosity of the positive electrode film is 2.3-2.7. A tortuosity within this range indicates a straighter transport path for lithium ions within the positive electrode film, a shorter diffusion path for lithium ions in the electrolyte, reduced diffusion resistance, decreased accumulation and concentration gradient of lithium ions within the electrode, reduced polarization effect, and superior kinetic performance, thereby improving battery cycle life.

[0025] In any embodiment, the compaction density of the positive electrode film sheet in its fully loaded state is 2.40 g / cm³. 3 -2.65g / cm 3 A positive electrode film compaction density within the above-mentioned range is beneficial for improving the energy density of the battery cell.

[0026] A second aspect of this application provides a battery device including the battery cell of the first aspect of this application.

[0027] A third aspect of this application provides an electrical device, including at least one of the battery cell of the first aspect of this application and the battery device of the third aspect of this application.

[0028] The above description is merely 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

[0029] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0030] Figure 1 This is a cross-sectional polished electron microscope image of the positive electrode film layer in one embodiment of this application;

[0031] Figure 2 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0032] Figure 3 yes Figure 2 An exploded view of a battery cell according to one embodiment of this application is shown.

[0033] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0034] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0035] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0036] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming 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 those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0044] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0045] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0046] 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.

[0047] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0048] 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, and the embodiments of this application are not limited in this respect. Figure 2 The example shown is a rectangular battery cell 5.

[0049] A single battery cell includes electrode components and an electrolyte.

[0050] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0051] In some implementations, such as Figure 3 As shown, the outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 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.

[0052] Electrode assemblies typically include positive and negative electrodes. The negative electrode is the electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging. The positive electrode is the electrode that absorbs or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0053] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0054] In some implementations, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0055] In some implementations, 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, with the specific number adjustable according to the application and capacity of the battery module. Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 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.

[0056] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0057] 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.

[0058] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 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.

[0059] In recent years, the market demand for high-energy-density batteries has become increasingly strong. To obtain high-pump-density electrodes and high-energy-density batteries, the industry commonly uses a method of constructing larger particle sizes to form a dense packing. However, increasing the particle size means increasing the proportion of large particles. Studies have shown that an increased proportion of large particles will increase the internal tortuosity of the electrode, resulting in greater ion transport resistance, ohmic polarization, and may also lead to an increase in local concentration gradients, causing concentration polarization. All of these factors combined lead to a decrease in the kinetic performance of the battery cell and severe polarization in the later stages of cycling.

[0060] A first aspect of this application provides a battery cell comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one surface of the positive current collector. The positive electrode film includes a positive electrode active material comprising lithium transition metal phosphate particles. The particles in the positive electrode film have a (D) % ... V90 -D V10 ) / D V50 The mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 4-8% based on the total mass of the positive electrode film layer.

[0061] The particles in the positive electrode film (D) V90 -D V10 ) / D V50 A value less than 4 indicates a small difference in particle size distribution, insignificant gradation effect, and a lack of smaller particles filling the gaps between larger particles. The particle size distribution (D) of the particles in the polar film layer... V90 -D V10 ) / D V50 If the particle size is greater than 8, the difference in particle size is too large, making it difficult to achieve optimal close packing. This has a limited effect on improving electrode compaction, making it difficult to further improve electrode compaction by increasing particle size distribution, and will seriously degrade the dynamic performance of the battery.

[0062] In this application, by controlling the (D) of the particles V90 -D V10 ) / D V50 A particle size distribution of 4-8 helps to construct a reasonable particle size distribution. Small particles can fill the gaps between large particles, forming a denser packing structure, reducing porosity, and thus increasing the compaction density of the electrode, thereby improving the energy density of the battery. However, the proportion of large particles is still relatively large, increasing the tortuosity inside the positive electrode film, increasing the lithium-ion transport path length, leading to local polarization, increasing battery impedance, and adversely affecting battery kinetics. This application further improves the roundness of particles in the positive electrode film. When the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film is within the above range, it is beneficial to form regular and continuous pore channels, such as... Figure 1As shown, this reduces the degree of tortuosity and bifurcation of pore channels, improves lithium-ion transport efficiency, and achieves a balance between the dynamics and cycle life of the battery cell.

[0063] Lithium-containing transition metal phosphates refer to phosphate materials containing lithium and transition metal elements, and can be detected by any method known in the art. For example, they can be detected by combining X-ray diffraction (XRD) with energy dispersive spectroscopy (EDS).

[0064] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0065] In this application, the term "D" V10 D V50 D V90 "This has a well-known meaning in the art and can be tested using methods known in the art. As an example, the method is as follows: Take 2g of the film layer powder sample, add 200ml of NMP solution and 5g of sodium dodecyl sulfate (SDS), and ultrasonically disperse at 60℃ for 30min, 60min, 90min… Take solutions with different dispersion times and use a laser particle size analyzer (e.g., a Malvern 2000 (MasterSizer 2000) laser particle size analyzer) to measure the sample according to GB / T 19077-2016 / ISO 13320:2009 standard. If the particle size distribution fluctuation is >5%, continue to increase the ultrasonic dispersion time; if the particle size distribution fluctuation of the solution measured at the last two dispersion times is ≤5%, it indicates complete dispersion and accurate test results, and the results can be output to obtain a particle size distribution map based on volume distribution." V10 “D” V50 "and "D V90 "These correspond to the particle sizes when the percentage of particle size distribution reaches 10%, 50%, and 90%, respectively."

[0066] Lithium-containing transition metal phosphates, due to their low hardness, small initial particle size, regular morphology, and good mechanical stability, result in a particle size distribution after the positive electrode film layer is rolled and pressed, which is essentially similar to the particle size distribution of the original positive electrode active material. Therefore, the particle size distribution of the positive electrode active material can be equivalent to the particle size distribution of the particles in the positive electrode film layer. Thus, the particle size distribution of the particles in the positive electrode film layer of this application can be obtained by testing the particle size distribution of the positive electrode active material or by testing the particle size distribution of particles obtained from scraping powder from the positive electrode film layer.

[0067] In some embodiments, the particles in the positive electrode film layer (D V90 -D V10 ) / D V50The values ​​can be 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8, or any range of values ​​between the two above.

[0068] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film can be selected as 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or any value range between the above two.

[0069] In this application, "roundness" is measured as follows: A prepared positive electrode sheet, or a positive electrode sheet disassembled from a battery, is subjected to CP-SEM testing. A number of points are randomly selected in the positive electrode film layer for imaging, with a maximum of 10 points (e.g., 10, 20, 50, 100). AVIZO software is used to identify particles in the images, and the longest inner diameter, shortest inner diameter, and area of ​​each particle are measured. The ratio of the shortest inner diameter to the longest inner diameter is used as the roundness of the particle. Data for all identified particles is obtained, and the roundness and area of ​​each particle are calculated. The ratio of the sum of the areas of all particles with a roundness greater than or equal to 0.75 in the positive electrode film layer to the sum of the areas of all identified particles is equivalent to the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer.

[0070] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film is 65%-75%.

[0071] Highly rounded particles, due to their regular shape, can be packed more tightly after rolling. However, an excessively high proportion may lead to increased slippage between particles, affecting the stability of the cathode film and causing a decrease in compaction density. Therefore, maintaining the mass percentage of particles with a roundness greater than or equal to 0.75 in the cathode film within the aforementioned range helps to achieve a balance between high compaction density and low tortuosity in the cathode film.

[0072] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a roundness of less than or equal to 0.4 in the positive electrode film is 5%-20%, and optionally 10%-15%.

[0073] In some embodiments, the mass percentage of particles with a roundness of less than or equal to 0.4 in the positive electrode film layer can be selected as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any value range between the above two.

[0074] In this application, "roundness" is measured with reference to the method described above. The ratio of the sum of the areas of all particles with a roundness of less than or equal to 0.4 in the positive electrode film to the sum of the areas of all identified particles is equivalent to the mass percentage of particles with a roundness of less than or equal to 0.4 in the positive electrode film.

[0075] When highly rounded particles are packed together, large pores may exist between the particles, limiting further increases in compaction density. Therefore, a mixing strategy of low-rounded and high-rounded particles is adopted. By filling the gaps between particles of different shapes and sizes, porosity is reduced, forming a denser packing structure, thereby improving compaction density.

[0076] In some embodiments, the particles in the positive electrode film layer (D V90 -D V10 ) / D V50 It is 5-7.

[0077] The particles in the positive electrode film (D) V90 -D V10 ) / D V50 Within the aforementioned range, high energy density can be achieved while maintaining low tortuosity of the positive electrode film, further optimizing polarization and lifespan during battery cycling.

[0078] In some embodiments, the one-sided density of the positive electrode film is 200 mg / 1540.25 mm². 2 -450mg / 1540.25mm 2 .

[0079] In some embodiments, the unilateral density of the positive electrode film layer can be selected as 200 mg / 1540.25 mm². 2 210mg / 1540.25mm 2 220mg / 1540.25mm 2 230mg / 1540.25mm 2 240mg / 1540.25mm 2 250mg / 1540.25mm 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 310mg / 1540.25mm 2 320mg / 1540.25mm 2 330mg / 1540.25mm 2 340mg / 1540.25mm 2 350mg / 1540.25mm 2 360mg / 1540.25mm 2 370mg / 1540.25mm 2 380mg / 1540.25mm 2 390mg / 1540.25mm 2 400mg / 1540.25mm 2 410mg / 1540.25mm 2 420mg / 1540.25mm 2 430mg / 1540.25mm 2 440mg / 1540.25mm 2 450mg / 1540.25mm 2 Or the range of values ​​between any two of the above.

[0080] In this application, the one-sided density of the positive electrode film layer has a well-known meaning in the art and can be tested using methods known in the art. For example, take a positive electrode sheet that has been coated on one side and cold-pressed (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1. Then wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the current collector, and record it as M0. The one-sided density of the positive electrode film layer = (M1-M0) / S1. To ensure the accuracy of the test results, multiple sets (e.g., 10 sets) of samples can be tested, and the average value can be calculated as the test result.

[0081] The areal density of the cathode film has a significant impact on the lithium-ion transport rate. Too low an areal density may sacrifice energy density, while too high an areal density may lengthen the ion transport path, leading to reduced ion transport efficiency. An areal density within the aforementioned range helps improve the battery's energy density and kinetic performance.

[0082] In some embodiments, the D of the particles in the positive electrode film layer V50 The range is 0.5μm-0.9μm, with an optional range of 0.6μm-0.8μm.

[0083] In some embodiments, the D of the particles in the positive electrode film layer V50 The options are 0.5μm, 0.51μm, 0.52μm, 0.53μm, 0.54μm, 0.55μm, 0.56μm, 0.57μm, 0.58μm, 0.59μm, 0. 6μm, 0.61μm, 0.62μm, 0.63μm, 0.64μm, 0.65μm, 0.66μm, 0.67μm, 0.68μm, 0.69μm, 0.7μm, 0. 71μm, 0.72μm, 0.73μm, 0.74μm, 0.75μm, 0.76μm, 0.77μm, 0.78μm, 0.79μm, 0.8μm, 0.81μm, 0.82μm, 0.83μm, 0.84μm, 0.85μm, 0.86μm, 0.87μm, 0.88μm, 0.89μm, 0.9μm, or any value range between the two above.

[0084] Particle D in the positive electrode film V50 The size of the σ affects both the compaction density and tortuosity of the positive electrode film. V50 If the particle size is too large, the porosity between particles also increases, making it difficult to improve the compaction density of the positive electrode film; D V50 If the particle size is too small, the ion transport pathways between particles will be fragmented and discontinuous, reducing the efficiency of ion transport. Simultaneously, electrolyte penetration will be difficult, further obstructing ion transport pathways. The D-value of particles in the positive electrode film... V50 Within the aforementioned range, further improve the energy density and cycle life of individual battery cells.

[0085] In some embodiments, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the first peak of the bimodal distribution located between 0.45 μm and 0.75 μm.

[0086] In any embodiment, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the first peak of the bimodal distribution located at 0.6 μm-0.7 μm.

[0087] In any embodiment, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the second peak of the bimodal distribution located between 0.6 μm and 0.97 μm.

[0088] In any embodiment, the particle size distribution curve of the particles in the positive electrode film layer exhibits a bimodal distribution, with the second peak of the bimodal distribution located between 0.7 μm and 0.91 μm.

[0089] In some embodiments, the first peak of the bimodal distribution is located in the range of 0.45 μm, 0.46 μm, 0.47 μm, 0.48 μm, 0.49 μm, 0.5 μm, 0.51 μm, 0.52 μm, 0.53 μm, 0.54 μm, 0.55 μm, 0.56 μm, 0.57 μm, 0.58 μm, 0.59 μm, 0.6 μm, 0.61 μm, 0.62 μm, 0.63 μm, 0.64 μm, 0.65 μm, 0.66 μm, 0.67 μm, 0.68 μm, 0.69 μm, 0.7 μm, 0.71 μm, 0.72 μm, 0.73 μm, 0.74 μm, 0.75 μm, or any two of the above values.

[0090] In some embodiments, the second peak of the bimodal distribution is located at 0.6 μm, 0.61 μm, 0.62 μm, 0.63 μm, 0.64 μm, 0.65 μm, 0.66 μm, 0.67 μm, 0.68 μm, 0.69 μm, 0.7 μm, 0.71 μm, 0.72 μm, 0.73 μm, 0.74 μm, 0.75 μm, 0.76 μm, 0.77 μm, 0. 78μm, 0.79μm, 0.8μm, 0.81μm, 0.82μm, 0.83μm, 0.84μm, 0.85μm, 0.86μm, 0.87μm, 0.88μm, 0.89μm, 0.9μm, 0.91μm, 0.92μm, 0.93μm, 0.94μm, 0.95μm, 0.96μm, 0.97μm, or any value range between the two above.

[0091] The volume distribution curve of particles in the positive electrode film can be determined using the test method described above, referring to GB / T19077-2016. A bimodal distribution in the volume distribution curve indicates that the positive electrode film contains both large and small particles of varying sizes. The first peak and / or the second peak being within the aforementioned range facilitates the filling of voids between large particles by smaller particles, thereby increasing the compaction density of the electrode and further improving the battery's energy density.

[0092] In some embodiments, the positive electrode film layer includes a conductive agent, and the mass percentage of the conductive agent is 0.5%-1% based on the total mass of the positive electrode film layer.

[0093] In some embodiments, the positive electrode film layer includes a conductive agent, and the mass percentage of the conductive agent, based on the total mass of the positive electrode film layer, can be selected as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any value range between the above two.

[0094] Based on the total mass of the positive electrode film, the mass ratio of the conductive agent is within the above range, which makes the positive electrode film have good electronic conductivity and a high loading of active materials, thus achieving a balance between kinetic performance and energy density.

[0095] In some embodiments, the conductive agent includes a one-dimensional conductive agent, which may be one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0096] In this application, the term "one-dimensional conductive agent" refers to a conductive material that has a significant single dimension in space, while exhibiting nanoscale conductivity in the other two dimensions. One-dimensional conductive agents include, but are not limited to, single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0097] One-dimensional conductive agents possess a fibrous structure with lengths reaching the micrometer scale, enabling the formation of continuous linear conductive networks within the electrode. This allows for the achievement of an effective conductive network at lower addition levels, reducing the amount of conductive agent used and thus further improving the battery's energy density.

[0098] In some embodiments, the conductive agent includes a zero-dimensional conductive agent, which may be one or more of conductive carbon black, Ketjen black, and hard carbon.

[0099] In this application, the term "zero-dimensional conductive agent" refers to a conductive material with a zero-dimensional structure, characterized by its similar size in all directions and its point-like structure. These conductive agents improve the conductivity of the material through point contacts between particles.

[0100] Zero-dimensional conductive agents establish a conductive network of point contacts between active materials. They generally have a high specific surface area, which can effectively fill the gaps between active materials, further improving the conductivity of the electrode and enhancing the overall dynamic performance of the battery.

[0101] In some embodiments, the porosity of the positive electrode film is 15%-25%, optionally 18.2%-22.9%.

[0102] In some embodiments, the porosity of the positive electrode film layer can be selected as 15%, 15.1%, 15.2%, 15.3%, 15.4%, 15.5%, 15.6%, 15.7%, 15.8%, 15.9%, 16.0%, 16.1%, 16.2%, 16.3%, 16.4%, 16.5%, 16.7%, 16.8%, 16.9%, 17.0%, 17.1%, 17.2%, 17.3%. %, 17.4%, 17.5%, 17.6%, 17.7%, 17.8%, 17.9%, 18.0%, 18.1%, 18.2%, 18.3%, 18.4%, 18.5%, 18.6%, 18.7%, 18.8%, 18.9%, 19%, 19.1%, 19.2%, 19.3%, 19.4%, 19.5%, 19.6%, 19.7%, 19.8%, 19.9%, 20%, 20.1%, 20.2%, 20.3%, 20.4%, 20.5%, 20.6%, 20.7%, 20.8%, 20.9%, 21%, 21.1%, 21.2%, 21.3%, 21.4%, 21.5%, 21.6%, 21.7%, 21.8%, 21.9%, 22%, 22.1%, 22.2%, 22.3%, 22.4%, 22.5%, 22.6%. 22.7%, 22.8%, 22.9%, 23.0%, 23.1%, 23.2%, 23.3%, 23.4%, 23.5%, 23.6%, 23.7%, 23.8%, 23.9%, 24.0%, 24.1%, 24.2%, 24.3%, 24.4%, 24.5%, 24.6%, 24.7%, 24.8%, 24.9%, 25.0%, or any value range between the two mentioned above.

[0103] In this application, the term "porosity" has a commonly known meaning in the art and can be tested using methods known in the art. As an example, the method is as follows: Using an AccuPyc II 1340 fully automated true density analyzer from Micromeritics, USA, and referring to the porosity testing method in GB / T 24586-2009, 30 small circular pieces with a diameter of 14 mm were cut from the positive electrode sheet, and the thickness of the positive electrode film was measured. Based on the principle of gas adsorption, an inert gas such as helium or nitrogen was used as the medium to test the true volume of the 30 small circular pieces with a diameter of 14 mm. Then, based on the relationship between the apparent volume and true volume of the positive electrode film obtained from the area of ​​the small circular pieces, the thickness and number of the positive electrode film, the porosity was calculated.

[0104] By controlling the porosity of the positive electrode film within the above range, the positive electrode active material has a high compaction density and energy density after rolling. A certain porosity is beneficial for the electrolyte to wet the positive electrode active material, further optimizing the ion transport efficiency, reducing polarization, and improving the cycle life of the battery.

[0105] In some embodiments, the lithium-containing transition metal phosphate comprises a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z ,

[0106] Wherein, 0.1≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; Y includes one or more of O and F.

[0107] In some implementations, x can be selected as 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.15, 1.3 or any value range between the above two.

[0108] In some implementations, y can be selected as 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.15, 1.3 or any value range between the above two.

[0109] In some implementations, x+y can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3 or any value range between the above two.

[0110] In some implementations, 'a' can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or any value range between the two above.

[0111] In some implementations, b can be selected as 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or any value range between the above two.

[0112] In some implementations, a+b can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or any value range between the above two.

[0113] In some implementations, c can be selected as 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or any value range between the above two.

[0114] In some implementations, z can be selected as 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, or a range of any two of the above.

[0115] The aforementioned lithium-containing transition metal phosphate materials exhibit good thermal stability and cycle stability, which helps to improve the safety and cycle performance of batteries.

[0116] In some embodiments, the tortuosity of the positive electrode film is 2.3-2.7.

[0117] In some embodiments, the tortuosity of the positive electrode film can be selected as 2.3, 2.31, 2.32, 2.33, 2.34, 2.35, 2.36, 2.37, 2.38, 2.39, 2.4, 2.41, 2.42, 2.43, 2.44, 2.45, 2.46, 2.47, 2.48, 2.49, 2.5, 2.51, 2.52, 2.53, 2.54, 2.55, 2.56, 2.57, 2.58, 2.59, 2.6, 2.61, 2.62, 2.63, 2.64, 2.65, 2.66, 2.67, 2.68, 2.69, 2.7 or any value range between the two.

[0118] When the tortuosity of the positive electrode film is within the above range, it means that the transport path of lithium ions inside the positive electrode film is straighter, the diffusion path of lithium ions in the electrolyte is shorter, the diffusion resistance is reduced, the accumulation and concentration gradient of lithium ions inside the electrode are reduced, the polarization effect is reduced, the kinetic performance is better, and thus the cycle life of the battery is improved.

[0119] In some embodiments, the cold-pressed compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.75g / cm 3 .

[0120] In some embodiments, the cold-pressed compaction density of the positive electrode film can be selected as 2.55 g / cm³. 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 2.6g / cm 3 2.61 g / cm 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 2.66 g / cm 3 2.67 g / cm 3 2.68g / cm 3 2.69 g / cm 3 2.7g / cm 3 2.71 g / cm 3 2.72 g / cm 3 2.73 g / cm 3 2.74 g / cm 3 2.75g / cm 3 Or the range of values ​​between any two of the above.

[0121] In this application, the compaction density after cold pressing can be tested using methods known in the art. As an example, the positive electrode obtained after cold pressing is cut into small circular pieces with an area of ​​S, and its mass is obtained as W1. The thickness T1 of the positive electrode is measured using a micrometer. Then, the positive electrode film layer of the weighed electrode is wiped off, the mass of the current collector is weighed and recorded as W2, and the thickness T2 of the current collector is measured using a micrometer. Then, the compaction density PD of the positive electrode film layer is PD = (W1-W2) / [(T1-T2)×S].

[0122] In the process of preparing a battery cell, after the positive electrode slurry is coated onto the positive electrode current collector, it is vacuum dried, cold-pressed, slit, and prepared into a positive electrode sheet. The compaction density obtained in the cold pressing step will be different from the compaction density when the positive electrode film is fully expanded. This is because after the electrode sheet is made, due to charging and discharging, the positive electrode sheet will exhibit a slight rebound phenomenon. At this time, the compaction density of the positive electrode film in the fully expanded state will be slightly lower than the compaction density of the initial cold pressing.

[0123] In some embodiments, the compaction density of the positive electrode film layer in the fully loaded state is 2.40 g / cm³. 3 -2.65g / cm 3 .

[0124] In some embodiments, the compaction density of the positive electrode film layer in the fully loaded state is 2.40 g / cm³. 3 2.41 g / cm 3 2.42 g / cm 3 2.43 g / cm 3 2.44 g / cm 3 2.45g / cm 3 2.46 g / cm 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.50g / cm 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 3 2.54 g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 2.60g / cm 3 2.61 g / cm 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 Or the range of values ​​between any two of the above.

[0125] In this application, the fully discharged state refers to the state in which the battery is placed at 25°C, left to stand for 2 hours, and then discharged at a constant current of 1 / 3C to 2.0V after the battery temperature is maintained at 25°C, left to stand for 15 minutes, and then discharged at a constant current of 0.04C to 2.0V.

[0126] In this application, the compaction density of the positive electrode film layer under full-displacement state can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven environment and left to stand for 2 hours. After the battery temperature is maintained at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.0V and left to stand for 15 minutes. Then, it is discharged at a constant current of 0.04C to 2.0V. The battery is disassembled to obtain the positive electrode sheet. The residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and it is cut into small circular pieces with an area of ​​S. The mass of the circular pieces is obtained as W1, and the thickness of the positive electrode sheet is measured using a micrometer. Then, the positive electrode film layer of the above-weighed electrode sheet is wiped off, the mass of the current collector is weighed and recorded as W2, and the thickness of the current collector is measured using a micrometer. Then, the compaction density of the positive electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0127] A compaction density of the positive electrode film within the above-mentioned range is beneficial to improving the energy density of the battery cell.

[0128] 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.).

[0129] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the base coating, such as lithium transition metal phosphate, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a base coating slurry; dispersing the components such as lithium transition metal oxide, conductive agent, binder and so on in a solvent to form a positive electrode film slurry; firstly coating the base coating slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, coating the positive electrode film slurry onto the surface of the base coating, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0130] [Negative electrode plate]

[0131] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0132] 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.

[0133] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer 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 (copper, copper 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 negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material 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 batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0135] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0136] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0138] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0139] [Electrolytes]

[0140] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0141] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0142] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0143] 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.

[0144] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0145] [Isolation membrane]

[0146] In some embodiments, the battery cell also includes a separator. 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.

[0147] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0148] [Battery cell]

[0149] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0150] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0151] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0152] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 The example shown is a square-structured battery cell 5.

[0153] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0154] [Battery Device]

[0155] This application also provides a battery device, which includes the battery cell provided in this application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0156] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0157] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 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.

[0158] Optionally, the battery module 5 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0159] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0160] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0161] [Electrical appliances]

[0162] In addition, this application embodiment also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application embodiment. The battery cell, battery module, or battery pack 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., but is not limited thereto.

[0163] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0164] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0165] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0166] Example

[0167] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0168] Example 1

[0169] 1) Preparation of positive electrode sheet

[0170] Preparation of positive electrode film slurry: D V50 It is 0.7 μm, (D V90 -D V10 ) / D V50 Lithium iron phosphate particles (LiFePO4) with a diameter of 6.0 mm, conductive carbon black, carbon nanotube conductive agent, and PVDF binder were mixed at a mass ratio of 98:0.4:0.6:1. NMP solvent was added, and the mixture was stirred under vacuum until the system was homogeneous to obtain a positive electrode film slurry. Based on the total mass of lithium iron phosphate, particles with a roundness ≥0.75 mm accounted for 70% of the lithium iron phosphate, and particles with a roundness ≤0.4 mm accounted for 15%.

[0171] The positive electrode film slurry was uniformly coated on the surface of the undercoat layer away from the positive electrode current collector, with a single-sided coating mass of 300 mg / 1540.25 mm. 2 After being air-dried at room temperature, the material was transferred to an oven for further drying, and then cold-pressed to obtain the positive electrode sheet. The cold-pressed compaction density of the positive electrode film was 2.7 g / cm³. 3 The single-sided coating quality here does not include the solvent quality, but only the solid content quality of the coating.

[0172] Electrode slitting (one out of two): The positive electrode is slitting on a slitting machine at a speed of 0.5 m / s. The slitting blade is made of steel and the negative pressure of the slitting machine is -10 kPa.

[0173] Electrode cutting: The slit electrode sheets are wound and cut, with a winding speed of 0.6m / s, a core length of 3m, and a steel cutting blade. The winding machine is under a negative pressure of -10KPa.

[0174] 2) Preparation of negative electrode sheet

[0175] Graphite anode active material, polyvinyl alcohol binder, and SP-Li conductive agent were thoroughly mixed and ball-milled in a deionized water solvent system at a mass ratio of 90:5:5 to obtain anode slurry. The anode slurry was then mixed at a concentration of 140 mg / 1540.25 mm. 2 The single-sided coating quality is double-sided coated on the surface of copper foil, and vacuum dried overnight at 110°C to obtain the negative electrode sheet.

[0176] 3) Preparation of the diaphragm

[0177] A polyethylene film with a thickness of 13 μm was used as the diaphragm.

[0178] 4) Preparation of electrolyte

[0179] Lithium hexafluorophosphate (LiPF6) was dissolved in ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 to form a homogeneous solution, resulting in an electrolyte with a LiPF6 concentration of 1 mol / L.

[0180] 5) Battery assembly

[0181] The electrodes are arranged in the order of "separator-negative electrode-separator-positive electrode". One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft to wind the positive electrode, negative electrode, and two separators, resulting in a wound bare cell. The bare cell is placed in an outer packaging, injected with the electrolyte, and sealed to obtain a battery cell.

[0182] The preparation method of Example 2 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, and the D of the lithium iron phosphate particles are different. V50 It is 0.5μm, (D V90 -D V10 ) / D V50 The density is 8.0; the cold-pressed compaction density of the positive electrode film is 2.74 g / cm³. 3 .

[0183] The preparation method of Example 3 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the D of the lithium iron phosphate particles... V50 It is 0.6 μm, (D V90 -D V10 ) / D V50 The density is 7.0; the cold-pressed compaction density of the positive electrode film is 2.72 g / cm³. 3 .

[0184] The preparation method of Example 4 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the D of the lithium iron phosphate particles... V50 It is 0.8μm, (D V90 -D V10 ) / D V50 The density is 5.0; the cold-pressed compaction density of the positive electrode film is 2.68 g / cm³. 3 .

[0185] The preparation method of Example 5 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the D of the lithium iron phosphate particles... V50 It is 0.9 μm, (D V90 -D V10 ) / D V50The density is 4.0; the cold-pressed compaction density of the positive electrode film is 2.66 g / cm³. 3 .

[0186] The preparation method of Example 6 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The particle size is 0.66 μm. In lithium iron phosphate, particles with a roundness ≥ 0.75 μm account for 80%, and particles with a roundness ≤ 0.4 μm account for 10%. The cold-pressed compaction density of the positive electrode film is 2.67 g / cm³. 3 .

[0187] The preparation method of Example 7 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the D of the lithium iron phosphate particles... V50 The particle size is 0.68 μm, and the proportion of particles with a roundness ≥0.75 in lithium iron phosphate is 75%; the cold-pressed compaction density of the positive electrode film is 2.69 g / cm³. 3 .

[0188] The preparation method of Example 8 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The particle size is 0.72 μm, and the proportion of particles with a roundness ≥ 0.75 in lithium iron phosphate is 65%; the cold-pressed compaction density of the positive electrode film is 2.68 g / cm³. 3 .

[0189] The preparation method of Example 9 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The particle size is 0.74 μm, and the proportion of particles with a roundness ≥ 0.75 μm in lithium iron phosphate is 60%; the cold-pressed compaction density of the positive electrode film is 2.66 g / cm³. 3 .

[0190] The preparation method of Example 10 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The particle size is 0.65 μm, and the proportion of lithium iron phosphate particles with a wettability ≤0.4% is 0%; the cold-pressed compaction density of the positive electrode film is 2.65 g / cm³. 3 .

[0191] The preparation method of Example 11 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The particle size is 0.67 μm, and the proportion of lithium iron phosphate particles with a wettability ≤0.4 is 5%; the cold-pressed compaction density of the positive electrode film is 2.66 g / cm³. 3 .

[0192] The preparation method of Example 12 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The particle size is 0.69 μm, and the proportion of lithium iron phosphate particles with a wettability ≤0.4% is 10%; the cold-pressed compaction density of the positive electrode film is 2.68 g / cm³. 3 .

[0193] The preparation method of Example 13 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The particle size is 0.73 μm, and the proportion of lithium iron phosphate particles with a wettability ≤0.4 is 20%; the cold-pressed compaction density of the positive electrode film is 2.67 g / cm³. 3 .

[0194] The preparation method of Example 14 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the single-sided coating mass of the positive electrode film slurry is 450 mg / 1540.25 mm. 2 The cold-pressed compaction density of the positive electrode film is 2.60 g / cm³. 3 .

[0195] The preparation method of Example 15 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the single-sided coating mass of the positive electrode film slurry is 380 mg / 1540.25 mm. 2 The cold-pressed compaction density of the positive electrode film is 2.66 g / cm³. 3 .

[0196] The preparation method of Example 16 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the single-sided coating mass of the positive electrode film slurry is 250 mg / 1540.25 mm. 2 The cold-pressed compaction density of the positive electrode film is 2.72 g / cm³. 3 .

[0197] The preparation method of Example 17 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the single-sided coating mass of the positive electrode film slurry is 200 mg / 1540.25 mm. 2 The cold-pressed compaction density of the positive electrode film is 2.75 g / cm³. 3 .

[0198] The preparation method of Example 18 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50The thickness is 0.9 μm; the cold-pressed compaction density of the positive electrode film is 2.63 g / cm³. 3 .

[0199] The preparation method of Example 19 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, and the D of the lithium iron phosphate particles are different. V50 The thickness is 0.85 μm; the cold-pressed compaction density of the positive electrode film is 2.67 g / cm³. 3 .

[0200] The preparation method of Example 20 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 The thickness is 0.5 μm; the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0201] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the proportion of lithium iron phosphate particles with a roundness ≥0.75 is 50%; and the cold-pressed compaction density of the positive electrode film is 2.67 g / cm³. 3 .

[0202] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the proportion of lithium iron phosphate particles with a roundness ≥0.75 is 90%, and the proportion of particles with a roundness ≤0.4 is 0%; the cold-pressed compaction density of the positive electrode film is 2.58 g / cm³. 3 .

[0203] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 It is 0.5μm, (D V90 -D V10 ) / D V50 The density is 9.0; the cold-pressed compaction density of the positive electrode film is 2.71 g / cm³. 3 .

[0204] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry are different, and the D of the lithium iron phosphate particles is different. V50 It is 0.9 μm, (D V90 -D V10 ) / D V50 The density is 3.0; the cold-pressed compaction density of the positive electrode film is 2.50 g / cm³. 3 .

[0205] Performance testing

[0206] 1. Roundness Test Method

[0207] At 25°C, slit positive electrode sheets prepared in each embodiment and comparative example were subjected to CP-SEM testing. A random number of points were photographed (≥10 points, e.g., 10, 20, 50, 100, etc.). AVIZO software was used to identify particles in the images, and the shortest diameter, longest diameter, and area of ​​each particle were measured. Roundness was calculated as shortest diameter / longest diameter. The ratio of the sum of the areas of all particles with a roundness greater than or equal to 0.75 to the sum of the areas of all identified particles was used as the mass percentage of particles with a roundness greater than or equal to 0.4 in the positive electrode film. Similarly, the mass percentage of particles with a roundness less than or equal to 0.3 in the positive electrode film was obtained.

[0208] 2. Porosity Testing Methods

[0209] At 25°C, the slit positive electrode sheets prepared in each embodiment and comparative example were taken and cut into small circular pieces with a diameter of 14 mm. The samples were then measured using a vacuum density tester (e.g., a Micromeritics AccuPycII1340 fully automatic true density tester) according to GB / T 24586-2009 standard. The number of samples tested was greater than or equal to 30 pieces, and the average value was taken as the final result.

[0210] 3. Tortuousness Test Method

[0211] At 25°C, the slit positive electrode sheets prepared in each example and comparative example were punched into small round pieces of 14 mm. The positive electrode sheets were assembled into symmetrical cells in a glove box (humidity ≤1 ppm). After injecting electrolyte, the cells were allowed to stand for at least 12 hours to allow the electrolyte to fully wet the electrode sheets. The impedance change was detected by EIS testing. The test procedure was as follows: upper limit frequency 1 kHz, lower limit frequency 500 mHz, perturbation voltage 5 mV, symmetrical cell voltage range -1 V to 1 V. The ion diffusion impedance Rion was obtained by fitting the test data. The electrolyte formulation was as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight ratio of 4:3:3 to obtain an organic solution. LiPF6 was then dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L.

[0212] The tortuosity of the electrode is determined as follows: The area A of the small circular plate (1.5386 cm²) is... 2 The tortuosity of the electrode is calculated by substituting the following values: the thickness d (cm) of the small disc, the conductivity k (S / m) of the electrolyte, the porosity ε of the electrode, and the ion diffusion resistance Rion (Ω).

[0213]

[0214] 4. Battery Energy Density Test Method

[0215] The battery cells prepared in each embodiment and comparative example were left to stand at 25°C for 2 hours to ensure the temperature of the battery cells remained at 25°C. The battery cells were then charged at 1 / 3C at 25°C to the charging cutoff voltage of 3.65V, and then continued to be charged at this charging cutoff voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of the battery cell). After the battery cells were left to stand at 25°C for 1 hour, they were discharged at 0.33C at 25°C to the discharge cutoff voltage of 2.5V, and the total discharge energy of the battery cells was recorded as E0.

[0216] The mass of the battery cell is measured as M0.

[0217] The mass energy density of a single battery cell = discharge energy of the single battery cell E0 / mass of the single battery cell M0.

[0218] 5. Cyclic performance testing methods

[0219] At 25°C, the battery cells prepared in each embodiment and comparative example were charged at a constant current of 1C to 50% SOC, then charged at 0.87C to 80% SOC, and then charged at 0.33C to a cutoff voltage of 3.65V. Constant voltage charging was then continued at this cutoff voltage until the current reached 0.05C. Finally, constant current charging at 1C was performed to a discharge cutoff voltage of 2.5V. This constitutes one charge-discharge cycle. The discharge capacity of the battery cell at this point is recorded as the discharge capacity E1 of the battery's first cycle. This charging and discharging process was repeated 1000 times, and the discharge capacity of the battery cell at this point is recorded as E2. Capacity retention rate @1000Cls = E2 / E1 × 100%.

[0220] The battery cells for each embodiment and comparative example were prepared according to the above method. The specific parameters and performance are shown in Tables 1 and 2 below.

[0221] Table 1

[0222]

[0223] Table 2

[0224]

[0225] By comparing the examples and comparative examples, it can be seen that by controlling the particles in the positive electrode film layer (D... V90 -D V10 ) / D V50The mass ratio is 4-8. Based on the total mass of the positive electrode film layer, the mass ratio of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 60%-80%. While the battery has a high energy density, it can improve the tortuosity deterioration problem caused by large gradation and improve the cycle life of the battery.

[0226] By comparing Examples 1-5, it can be seen that the particles in the positive electrode film layer (D V90 -D V10 ) / D V50 The value is 5-7; the particle's D V50 When the thickness is 0.6μm-0.8μm, the tortuosity and compaction density in the positive electrode are balanced, which is beneficial to improving the mass energy density and cycle life of the battery.

[0227] By comparing Examples 1, 6-9, it can be seen that when the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 65%-75%, a balance between the battery's mass energy density and cycle life is further achieved.

[0228] By comparing Examples 1, 10 to 13, it can be seen that when the mass percentage of particles with a roundness of less than or equal to 0.4 in the positive electrode film layer is 5%-20%, and further 10%-15%, it is beneficial to improve the energy density of the battery.

[0229] By comparing Examples 1 and 14-17, it can be seen that the single-sided density of the positive electrode film layer is 200 mg / 1540.25 mm. 2 -450mg / 1540.25mm 2 At this time, higher battery energy density can be achieved and cycle life can be optimized.

[0230] By comparing Examples 1, 18-20, it can be seen that the D of the particles in the positive electrode film layer... V50 A thickness of 0.6μm-0.8μm is beneficial for reducing the tortuosity of the positive electrode film and improving the cycle life of the battery.

[0231] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, said battery cell comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes lithium transition metal phosphate particles. The particles in the positive electrode film layer have a (D) V90 -D V10 ) / D V50 It is 6-8; The particle size distribution curve of the positive electrode film layer exhibits a bimodal distribution, with the first peak located at 0.45 μm-0.75 μm and the second peak located at 0.6 μm-0.97 μm. Based on the total mass of the positive electrode film, the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film is 60%-80%, and the mass percentage of particles with a roundness less than or equal to 0.4 in the positive electrode film is 5%-20%. The roundness refers to the ratio of the shortest inner diameter to the longest inner diameter of the particle.

2. The battery cell according to claim 1, characterized in that, Based on the total mass of the positive electrode film, the mass percentage of particles with a roundness greater than or equal to 0.75 in the positive electrode film is 65%-75%.

3. The battery cell according to claim 1, characterized in that, Based on the total mass of the positive electrode film, the mass percentage of particles with a roundness of less than or equal to 0.4 in the positive electrode film is 10%-15%.

4. The battery cell according to claim 1, characterized in that, The particles in the positive electrode film (D) V90 -D V10 ) / D V50 It is 6-7.

5. The battery cell according to claim 1, characterized in that, The single-sided density of the positive electrode film is 200 mg / 1540.25 mm². 2 -450mg / 1540.25mm 2 .

6. The battery cell according to claim 1, characterized in that, D of the particles in the positive electrode film V50 The range is 0.5μm-0.9μm.

7. The battery cell according to claim 1, characterized in that, D of the particles in the positive electrode film V50 The thickness is 0.6μm-0.8μm.

8. The battery cell according to claim 1, characterized in that, The particle size distribution curve of the positive electrode film layer exhibits a bimodal distribution, with the first peak located at 0.6 μm-0.7 μm.

9. The battery cell according to claim 1, characterized in that, The particle size distribution curve of the positive electrode film layer exhibits a bimodal distribution, with the second peak located between 0.7 μm and 0.91 μm.

10. The battery cell according to claim 1, characterized in that, The positive electrode film layer includes a conductive agent, and the mass percentage of the conductive agent is 0.5%-1% based on the total mass of the positive electrode film layer.

11. The battery cell according to claim 10, characterized in that, The conductive agent includes a one-dimensional conductive agent, which may be selected from one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

12. The battery cell according to claim 10 or 11, characterized in that, The conductive agent includes a zero-dimensional conductive agent, which may be selected from one or more of conductive carbon black, Ketjen black, and hard carbon.

13. The battery cell according to claim 1, characterized in that, The porosity of the positive electrode film is 15%-25%.

14. The battery cell according to claim 1, characterized in that, The porosity of the positive electrode film is 18.2%-22.9%.

15. The battery cell according to claim 1, characterized in that, The lithium-containing transition metal phosphate comprises components represented by the following general formula: Li x A y Me a M b P 1-c X c Y z , Wherein, 0.1≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; Y includes one or more of O and F.

16. The battery cell according to claim 1, characterized in that, The tortuosity of the positive electrode film is 2.3-2.

7.

17. The battery cell according to claim 1, characterized in that, The compaction density of the positive electrode film layer in its fully discharged state is 2.40 g / cm³. 3 -2.65g / cm 3 .

18. A battery device, characterized in that, The battery device includes a battery cell as described in any one of claims 1 to 17, and the battery device includes at least one of a battery module, a battery pack, and an energy storage device.

19. An electrical appliance, characterized in that, Includes the battery cell according to any one of claims 1 to 17 or the battery device according to claim 18.

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