Battery cell, battery device and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device, the battery monomer comprises a positive pole piece, a negative pole piece and an electrolyte, the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one side surface of the positive current collector, the positive film layer comprises a positive active material, and the negative film layer comprises a negative active material. The positive electrode active material comprises lithium-containing transition metal phosphate particles, and (DV90-DV10) / DV50 of the particles in the positive electrode film layer is 4-8; based on the total mass of the positive electrode film layer, the mass ratio of particles with roundness greater than or equal to 0.75 in the positive electrode film layer is 60%-80%.

Description

Technical Field

[0001] The present application relates to the technical field of battery cells, and in particular to a battery cell, a battery device and an electrical device. Background Art

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

[0003] The positive electrode active material is an important component of the battery cell. Lithium-containing transition metal phosphate materials have the characteristics of stable structure, good safety and long cycle life, and have broad development prospects. As the market's requirements for the energy density and kinetics of lithium-containing transition metal phosphate system battery cells increase, it is difficult to achieve the above-mentioned performance improvements at the same time in the existing technology, which has become a technical problem that needs to be solved urgently in this field. Summary of the invention

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

[0005] The first aspect of the present application provides a battery cell, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium-containing transition metal phosphate particles, wherein the particles in the positive electrode film layer have a (D V90 -D V10 ) / D V50 is 4-8; based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 60%-80%.

[0006] In this application, by controlling the particle (D V90 -D V10 ) / D V504-8, which helps to build a reasonable particle grading. Small particles can be filled in the gaps between large particles to form a more compact stacking structure, reduce porosity, thereby increasing the compaction density of the pole piece, and then improving the energy density of the battery. However, the proportion of large particles is still large, which increases the tortuosity inside the positive electrode film layer, increases the length of the lithium ion transmission path, leads to local polarization, increases battery impedance, and has an adverse effect on the dynamics of the battery. The present application further improves the roundness of the particles in the positive electrode film layer. When the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is within the above range, it is conducive to the formation of regular and continuous pore channels, reduces the bending and bifurcation of the pore channels, improves the lithium ion transmission efficiency, and achieves a balance between the dynamics and cycle life of the battery cell.

[0007] In any embodiment, based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 65%-75%. Due to their regular shape, highly rounded particles can be stacked in a more compact manner after rolling, but too high a proportion may increase the sliding between particles, affect the stability of the positive electrode film layer, and reduce the compaction density. Therefore, keeping the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer within the above range helps to achieve a balance between high compaction density and low tortuosity of the positive electrode film layer.

[0008] In any embodiment, based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness of less than or equal to 0.4 in the positive electrode film layer is 5%-20%, and can be optionally 10%-15%. When high-roundness particles are stacked, there may be large pores between the particles, which limits the further improvement of the compaction density. To this end, a mixing strategy of low-roundness particles and high-roundness particles is adopted, and particles of different shapes and sizes are filled with each other to reduce porosity and form a tighter stacking structure, thereby improving the compaction density.

[0009] In any embodiment, the particles in the positive electrode film layer (D V90 -D V10 ) / D V50 5-7. The particles in the positive electrode film layer (D V90 -D V10 ) / D V50 Within the above range, high energy density can be achieved while taking into account the low tortuosity of the positive electrode film layer, further optimizing the polarization and service life during the battery cycle.

[0010] In any embodiment, the single-side density of the positive electrode film layer is 200 mg / 1540.25 mm 2 -450mg / 1540.25mm 2The coating surface density of the positive electrode film layer has a significant impact on the transmission rate of lithium ions. Too low a surface density may sacrifice energy density, while too high a surface density may increase the ion transmission path, resulting in a decrease in ion transmission rate. The surface density of the positive electrode film layer within the above range helps to improve the energy density and kinetic performance of the battery.

[0011] In any embodiment, the D of the particles in the positive electrode film layer V50 The particle size of the positive electrode film layer is 0.5μm-0.9μm, and can be 0.6μm-0.8μm. V50 The size of D will affect the compaction density and tortuosity of the positive electrode film. V50 If the value is too large, the pores between particles will increase, and the compaction density of the positive electrode film will be difficult to increase; V50 If the particle size is too small, the ion conduction path between particles will be segmented and discontinuous, which will reduce the efficiency of ion transmission. At the same time, the electrolyte is difficult to penetrate, which will block the ion transmission path. V50 Within the above range, the energy density and cycle life of the single battery are further improved.

[0012] In any embodiment, the particle size volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, and the first peak of the bimodal distribution is located at 0.45 μm-0.75 μm.

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

[0014] In any embodiment, the particle size volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, and the second peak of the bimodal distribution is located at 0.6 μm-0.97 μm.

[0015] In any embodiment, the particle size volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, and the second peak of the bimodal distribution is located at 0.7 μm-0.91 μm.

[0016] The volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, indicating that the positive electrode film layer includes large particles and small particles of different sizes. The first peak position and / or the second peak position is within the above range, which is beneficial to filling the gaps between large particles with small particles, which is beneficial to improving 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 proportion of the conductive agent is 0.5%-1% based on the total mass of the positive electrode film layer. Based on the total mass of the positive electrode film layer, the mass proportion of the conductive agent is within the above range, so that the positive electrode film layer has good electronic conductivity, and the positive electrode film layer has a high active material loading, achieving a balance between kinetic performance and energy density.

[0018] In any embodiment, the conductive agent includes a one-dimensional conductive agent, which can 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 a length of up to micrometers, and can form a continuous linear conductive network in the electrode. An effective conductive network is achieved at a lower addition amount, reducing the amount of conductive agent used, thereby further improving the energy density of the battery.

[0019] In any embodiment, the conductive agent includes a zero-dimensional conductive agent, which can be one or more of conductive carbon black, Ketjen black, and hard carbon. The zero-dimensional conductive agent is a conductive network that establishes point contacts between active materials, generally has a high specific surface area, can effectively fill the gaps between active materials, further improve the conductivity of the electrode, and improve the overall dynamic performance of the battery.

[0020] In any embodiment, the porosity of the positive electrode film layer is 15%-25%, and can be 18.2%-22.9%. The porosity of the positive electrode film layer is controlled within the above range, so that the positive electrode active material has a higher compaction density and energy density after rolling. A certain porosity is conducive to the infiltration of the electrolyte into the positive electrode active material, further optimizing the ion transmission efficiency, reducing polarization, and improving the cycle life of the battery.

[0021] In any embodiment, the lithium-containing transition metal phosphate includes a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z , Among them, 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; and Y includes one or more of O and F.

[0022] The above-mentioned lithium-containing transition metal phosphate material has good thermal stability, cycle stability, etc., which helps to improve the safety performance and cycle performance of the battery.

[0023] In any embodiment, the tortuosity of the positive electrode film layer is 2.3-2.7. The tortuosity of the positive electrode film layer is within the above range, which means that the transmission path of lithium ions in the positive electrode film layer 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 in the electrode are reduced, the polarization effect is reduced, and the kinetic performance is better, thereby achieving an increase in the battery cycle life.

[0024] In any embodiment, the compaction density of the positive electrode film sheet in the full state is 2.40 g / cm 3 -2.65g / cm 3 The compaction density of the positive electrode film layer is within the above range, which is beneficial to improving the energy density of the battery cell.

[0025] A second aspect of the present application provides a battery device, comprising the battery cell of the first aspect of the present application.

[0026] A third aspect of the present application provides an electrical device, comprising at least one of the battery cell of the first aspect of the present application and the battery device of the third aspect of the present application.

[0027] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the multiple drawings represent the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments disclosed in the present application and should not be regarded as limiting the scope of the present application.

[0029] Figure 1 This is an electron microscope morphology image of a polished cross section of a positive electrode film layer in one embodiment of the present application; Figure 2 is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 3 yes Figure 2 An exploded view of a battery cell according to an embodiment of the present application is shown; Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application; Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 6 yes Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown; Figure 7 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0030] Description of reference numerals: 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0031] Hereinafter, the battery cells, battery devices and power devices of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0032] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0034] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0035] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0036] In the present application, the terms "plurality" and "multiple" refer to two or more.

[0037] Unless otherwise specified, the terms used in this application have the commonly understood meanings that are commonly understood by those skilled in the art.

[0038] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0039] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module or a battery pack.

[0040] A battery cell is the smallest unit of a battery, which can independently realize the functions of charging and discharging. The battery cell can be cylindrical, rectangular or in other shapes, etc., which is not limited in the embodiments of the present application. Figure 2 The battery cell 5 is a rectangular parallelepiped structure as an example.

[0041] A battery cell includes an electrode assembly and an electrolyte.

[0042] The battery cell may also include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte. The outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0043] In some embodiments, Figure 3 As shown, the outer package may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.

[0044] The electrode assembly usually includes a positive electrode plate and a negative electrode plate. The negative electrode plate is an electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging. The positive electrode plate is an electrode that releases or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0045] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a box and battery cells, and the battery cells or battery modules are accommodated in the box. In some embodiments, the box may serve as part of the chassis structure of the vehicle. For example, part of the box may become at least a part of the floor of the vehicle, or part of the box may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0046] In some embodiments, the battery may be an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0047] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module. Figure 4 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 4 As shown, in the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0048] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0049] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0050] Figure 5 and Figure 6 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 5 and Figure 6 As shown, the battery pack 1 may include a box body and a plurality of battery modules 4 disposed in the box body. The box body includes an upper box body 2 and a lower box body 3, and the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the box body in any manner.

[0051] In recent years, the market demand for high energy density batteries has become increasingly strong. In order to obtain high compaction density pole pieces and high energy density batteries, the industry's common method is to construct a larger particle gradation to form a dense stack. However, increasing the gradation means an increase in the proportion of large particles. Studies have shown that an increase in the proportion of large particles will increase the internal tortuosity of the pole piece, making the ion transmission resistance greater, resulting in ohmic polarization, and may lead to an increase in local concentration gradients, resulting in concentration polarization, which in turn leads to a decrease in the kinetic performance of the battery cell and severe polarization in the late cycle.

[0052] The first aspect of the present application provides a battery cell, wherein the battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium-containing transition metal phosphate particles, wherein the particles in the positive electrode film layer have a (D V90 -D V10 ) / D V50 is 4-8; based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 60%-80%.

[0053] The particles in the positive electrode film (D V90 -D V10 ) / D V50 Less than 4 means that the particle size distribution is small, the grading effect is not significant, and there is a lack of smaller particles to fill the gaps between larger particles. V90 -D V10 ) / D V50 If it is greater than 8, the particle size difference is too large, and it is difficult to achieve optimal dense packing. The effect on improving the compaction of the electrode is limited. It is difficult to further improve the compaction of the electrode by increasing the particle size distribution, and it will seriously deteriorate the kinetic performance of the battery.

[0054] In this application, by controlling the particle (D V90 -D V10 ) / D V50 4-8, which helps to build a reasonable particle grading. Small particles can fill the gaps between large particles to form a more compact stacking structure, reduce porosity, and thus increase the compaction density of the pole piece, thereby improving the energy density of the battery. However, the proportion of large particles is still relatively large, which increases the tortuosity inside the positive electrode film layer, increases the length of the lithium ion transmission path, leads to local polarization, increases battery impedance, and has an adverse effect on the battery dynamics. The present application further improves the roundness of the particles in the positive electrode film layer. When the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is within the above range, it is conducive to the formation of regular and continuous pore channels, such as Figure 1As shown, the bending and bifurcation of the pore channels are reduced, the lithium ion transmission efficiency is improved, and the dynamics and cycle life of the battery cell are taken into consideration.

[0055] Lithium-containing transition metal phosphate refers to a phosphate material containing lithium and transition metal elements, and can be detected by any known method in the art, for example, by combining an X-ray diffractometer (XRD) with an energy spectrum analyzer.

[0056] In the present application, the term "particle" refers to particles with identifiable complete boundaries in the field of view of the positive electrode film layer under a certain magnification, such as 10,000 times. Defects and scratches may exist inside the particles, but complete boundaries sufficient to separate the particles cannot be identified inside the particles.

[0057] In this application, the term "D V10 , D V50 , D V90 " has a well-known meaning in the art and can be tested by methods known in the art. As an example, the method is as follows: take 2g of film scraping powder sample, add 200ml NMP solution and 5g sodium dodecyl sulfate SDS, and disperse it under ultrasonic stirring at 60°C for 30min, 60min, 90min..., take the solutions with different dispersion time respectively, use a laser particle size analyzer (for example, Malvern 2000 (MasterSizer 2000) laser particle size analyzer), and measure the sample with reference to GB / T 19077-2016 / ISO 13320:2009 standard. When the particle size distribution fluctuation is greater than 5%, continue to increase the ultrasonic dispersion time; when the particle size distribution fluctuation of the solution measured at the last two dispersion time is ≤5%, it means that the dispersion is complete and the test result is accurate. The result can be output to obtain a particle size distribution diagram based on volume distribution. "D V10 ”, “D V50 ” and “D V90 " respectively correspond to the particle sizes when the percentage of particle size distribution reaches 10%, 50%, and 90%.

[0058] Due to its low hardness, small initial particle size, regular morphology and good mechanical stability, the particle size distribution of the lithium-containing transition metal phosphate after rolling the positive electrode film layer is basically similar to the particle size distribution of the original positive electrode active material, and 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. Therefore, the particle size distribution test of the positive electrode active material or the particle size distribution test of the particles obtained by scraping the positive electrode film layer can obtain the particle size distribution of the particles in the positive electrode film layer of the present application.

[0059] In some embodiments, the particles in the positive electrode film layer (D V90 -D V10 ) / D V50The amount can be selected from 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 a numerical range between any two of the above.

[0060] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of particles in the positive electrode film layer having a roundness greater than or equal to 0.75 may be selected to be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or a numerical range between any two of the above.

[0061] In this application, "roundness" is measured in the following way: take a prepared positive electrode sheet, or a positive electrode sheet disassembled from a battery, and perform a CP-SEM test. Randomly select a number of points in the positive electrode film layer for shooting, and the number of points is ≥10, which can be 10, 20, 50, 100, etc. The particles in the photographed picture are identified by AVIZO software, and the longest inner diameter, shortest inner diameter and area of ​​the particles are measured. The ratio of the shortest inner diameter to the longest inner diameter is used as the roundness of the particle. Obtain the data of all identified particles, and calculate the roundness and area of ​​each particle. 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 proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer.

[0062] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of particles having a roundness greater than or equal to 0.75 in the positive electrode film layer is 65%-75%.

[0063] Due to their regular shapes, highly rounded particles can be packed more densely after rolling, but a too high ratio may increase the slippage between particles, affecting the stability of the positive electrode film layer and reducing the compaction density. Therefore, keeping the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer within the above range helps to achieve a balance between high compaction density and low tortuosity of the positive electrode film layer.

[0064] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness less than or equal to 0.4 in the positive electrode film layer is 5%-20%, and can be optionally 10%-15%.

[0065] In some embodiments, the mass proportion of particles with a roundness less than or equal to 0.4 in the positive electrode film layer can be selected to be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a numerical range between any two of the above.

[0066] In the present application, "roundness" is measured with reference to the method described above in the present application, and the ratio of the sum of the areas of all particles in the positive electrode film layer with a roundness less than or equal to 0.4 to the sum of the areas of all identified particles is equivalent to the mass proportion of particles in the positive electrode film layer with a roundness less than or equal to 0.4.

[0067] When high-roundness particles are stacked, there may be large pores between the particles, which limits the further increase of compaction density. To this end, a mixing strategy of low-roundness particles and high-roundness particles is adopted. Through the mutual filling of particles of different shapes and sizes, the porosity is reduced, and a tighter stacking structure is formed, thereby improving the compaction density.

[0068] In some embodiments, the particles in the positive electrode film layer (D V90 -D V10 ) / D V50 Is 5-7.

[0069] The particles in the positive electrode film (D V90 -D V10 ) / D V50 Within the above range, high energy density can be achieved while taking into account the low tortuosity of the positive electrode film layer, further optimizing the polarization and service life during the battery cycle.

[0070] In some embodiments, the single-side density of the positive electrode film layer is 200 mg / 1540.25 mm 2 -450mg / 1540.25mm 2 .

[0071] In some embodiments, the single-side density of the positive electrode film layer can be 200 mg / 1540.25 mm 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 a numerical range between any two of the above.

[0072] In the present application, the single-side density of the positive electrode film layer has a well-known meaning in the art and can be tested by methods known in the art. For example, take a single-sided coated and cold-pressed positive electrode sheet (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), punch it into small discs with an area of ​​S1, weigh it, and record it as M1. Then wipe off the positive electrode film layer of the above-weighed positive electrode sheet, weigh the weight of the current collector, and record it as M0. Single-side density of the positive electrode film layer = (M1-M0) / S1. In order to ensure the accuracy of the test results, multiple groups (for example, 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result.

[0073] The coating surface density of the positive electrode film layer has a significant impact on the transmission rate of lithium ions. Too low a surface density may sacrifice energy density, while too high a surface density may increase the ion transmission path, resulting in reduced ion transmission efficiency. The surface density of the positive electrode film layer within the above range helps to improve the energy density and kinetic performance of the battery.

[0074] In some embodiments, the D of the particles in the positive electrode film layer is V50 It is 0.5μm-0.9μm, and can be optionally 0.6μm-0.8μm.

[0075] In some embodiments, the D of the particles in the positive electrode film layer is 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 a numerical range between any two of the above.

[0076] Particle D in the positive electrode film V50 The size of D will affect the compaction density and tortuosity of the positive electrode film. V50 If the value is too large, the pores between particles will increase, and the compaction density of the positive electrode film will be difficult to increase; V50 If the particle size is too small, the ion conduction path between particles will be segmented and discontinuous, which will reduce the efficiency of ion transmission. At the same time, the electrolyte will be difficult to penetrate and the ion transmission path will be blocked. V50 Within the above range, the energy density and cycle life of the single battery are further improved.

[0077] In some embodiments, the particle size volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, and the first peak of the bimodal distribution is located at 0.45 μm-0.75 μm.

[0078] In any embodiment, the particle size volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, and the first peak of the bimodal distribution is located at 0.6 μm-0.7 μm.

[0079] In any embodiment, the particle size volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, and the second peak of the bimodal distribution is located at 0.6 μm-0.97 μm.

[0080] In any embodiment, the particle size volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, and the second peak of the bimodal distribution is located at 0.7 μm-0.91 μm.

[0081] In some embodiments, the first peak of the bimodal distribution is at 0.45μm, 0.46μm, 0.47μm, 0.48μm, 0.49μm, 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 or a range of values ​​between any two of the above.

[0082] 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 a numerical range between any two of the above.

[0083] The volume distribution curve of the particles in the positive electrode film layer can refer to GB / T19077-2016 and be tested using the test method described above. The volume distribution curve of the particles in the positive electrode film layer presents a bimodal distribution, indicating that the positive electrode film layer includes large particles and small particles of different sizes. The first peak position and / or the second peak position is within the above range, which is conducive to filling the gaps between large particles with small particles, and is conducive to improving the compaction density of the pole piece, thereby further improving the energy density of the battery.

[0084] In some embodiments, the positive electrode film layer includes a conductive agent, and based on the total mass of the positive electrode film layer, the mass proportion of the conductive agent is 0.5%-1%.

[0085] In some embodiments, the positive electrode film layer includes a conductive agent. Based on the total mass of the positive electrode film layer, the mass proportion of the conductive agent can be selected to be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a numerical range between any two of the above.

[0086] Based on the total mass of the positive electrode film layer, the mass proportion of the conductive agent is within the above range, so that the positive electrode film layer has good electronic conductivity and a high active material loading in the positive electrode film layer, achieving a balance between kinetic performance and energy density.

[0087] In some embodiments, the conductive agent includes a one-dimensional conductive agent, which can be selected from one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0088] In this application, the term "one-dimensional conductive agent" refers to a conductive material that has a single significant dimension in space and behaves as a nanoscale 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, carbon nanofibers, etc.

[0089] One-dimensional conductive agents have a fibrous structure with a length of up to micrometers, which can form a continuous linear conductive network in the electrode. An effective conductive network can be achieved at a lower addition amount, reducing the amount of conductive agent used, thereby further improving the energy density of the battery.

[0090] In some embodiments, the conductive agent includes a zero-dimensional conductive agent, which can be one or more of conductive carbon black, Ketjen black, and hard carbon.

[0091] In this application, the term "zero-dimensional conductive agent" refers to a conductive material with a zero-dimensional structure, the main feature of which is that the size is similar in all directions and presents a point-like structure. This type of conductive agent improves the conductivity of the material through point contact between particles.

[0092] Zero-dimensional conductive agents are conductive networks that establish point contacts between active materials. They generally have a high specific surface area and can effectively fill the gaps between active materials, further enhancing the conductivity of the electrode and improving the overall kinetic performance of the battery.

[0093] In some embodiments, the porosity of the positive electrode film layer is 15%-25%, and can be optionally 18.2%-22.9%.

[0094] In some embodiments, the porosity of the positive electrode film layer may be 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 a range between any two of the above.

[0095] In this application, the term "porosity" has a well-known meaning in the art and can be tested by methods known in the art. As an example, the method is as follows: using the AccuPyc II 1340 fully automatic true density tester of Micromeritics, USA, and referring to the porosity test method in GB / T 24586-2009, 30 small discs with a diameter of 14 mm are cut from the positive electrode sheet, and the thickness of the positive electrode film layer is measured. Based on the principle of gas adsorption, an inert gas such as helium or nitrogen is used as a medium to test the true volume of 30 small discs with a diameter of 14 mm, and then the relationship between the apparent volume and the true volume of the positive electrode film layer calculated based on the area of ​​the small discs, the thickness and number of the positive electrode film layer is calculated to calculate the porosity.

[0096] The porosity of the positive electrode film layer is controlled within the above range, so that the positive electrode active material has a higher compaction density and energy density after rolling. A certain porosity is conducive to the infiltration of the electrolyte into the positive electrode active material, further optimizing the ion transmission efficiency, reducing polarization, and improving the cycle life of the battery.

[0097] In some embodiments, the lithium-containing transition metal phosphate includes a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z , Among them, 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; and Y includes one or more of O and F.

[0098] In some embodiments, x can be 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 a range of values ​​therebetween.

[0099] In some embodiments, 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 a range of values ​​between any two of the above.

[0100] In some embodiments, x+y can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3 or a numerical range therebetween.

[0101] In some embodiments, 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 a range of values ​​therebetween.

[0102] In some embodiments, 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 a range of values ​​therebetween.

[0103] In some embodiments, 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 a range of values ​​therebetween.

[0104] In some embodiments, 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 a numerical range therebetween.

[0105] In some embodiments, 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 numerical range therebetween.

[0106] The above-mentioned lithium-containing transition metal phosphate material has good thermal stability, cycle stability, etc., which helps to improve the safety performance and cycle performance of the battery.

[0107] In some embodiments, the tortuosity of the positive electrode film layer is 2.3-2.7.

[0108] In some embodiments, the tortuosity of the positive electrode film layer may be 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 a range of values ​​between any two of the above.

[0109] The tortuosity of the positive electrode film layer is within the above range, which means that the transmission path of lithium ions inside the positive electrode film layer is straighter, the diffusion path of lithium ions in the electrolyte is shorter, the diffusion resistance is reduced, and the accumulation and concentration gradient of lithium ions inside the electrode are reduced. The polarization effect is reduced and the kinetic performance is better, thereby achieving an increase in the battery cycle life.

[0110] In some embodiments, the cold pressed density of the positive electrode film layer is 2.5 g / cm 3 -2.75g / cm 3 .

[0111] In some embodiments, the cold pressed density of the positive electrode film layer can be 2.55 g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.59g / cm 3 , 2.6g / cm 3 , 2.61g / cm 3 , 2.62g / cm 3 , 2.63g / cm 3 , 2.64g / cm 3 , 2.65g / cm 3 , 2.66g / cm 3 , 2.67g / cm 3 , 2.68g / cm 3 , 2.69g / cm 3 , 2.7g / cm 3 , 2.71g / cm 3 , 2.72g / cm 3 , 2.73g / cm 3 , 2.74g / cm 3 , 2.75g / cm 3 Or a numerical range between any two of the above.

[0112] In this application, the compaction density after cold pressing can be tested by methods known in the art. As an example, the positive electrode sheet obtained after cold pressing is cut into small discs with an area of ​​S, and its mass is W1, and the thickness T1 of the positive electrode sheet is measured using a micrometer, and then the positive electrode film layer of the weighed electrode sheet is wiped off, and the mass of the current collector is weighed, recorded as W2, and the thickness T2 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].

[0113] In the process of preparing battery cells, after the positive electrode slurry is applied to the positive electrode current collector, vacuum drying, cold pressing, slitting, and preparing the positive electrode sheet will be performed. The compaction density obtained in the cold pressing step will be different from the compaction density of the full discharge after obtaining the positive electrode film layer. The reason is that after the electrode sheet is made, the positive electrode sheet will rebound slightly due to charging and discharging. At this time, the compaction density of the positive electrode film layer in the full discharge state will be slightly less than the compaction density of the initial cold pressing.

[0114] In some embodiments, the compaction density of the positive electrode film layer in a fully charged state is 2.40 g / cm 3 -2.65g / cm 3 .

[0115] In some embodiments, the compaction density of the positive electrode film layer in a fully charged state is 2.40 g / cm 3 , 2.41g / cm 3 , 2.42g / cm 3 , 2.43g / cm 3 , 2.44g / cm 3 , 2.45g / cm 3 , 2.46g / cm 3 , 2.47g / cm 3 , 2.48g / cm 3 , 2.49g / cm 3 , 2.50g / cm 3 , 2.51g / cm 3 , 2.52g / cm 3 , 2.53g / cm 3 , 2.54g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.59g / cm 3 , 2.60g / cm 3 , 2.61g / cm 3 , 2.62g / cm 3 , 2.63g / cm 3 , 2.64g / cm 3 , 2.65g / cm 3 Or a numerical range between any two of the above.

[0116] In this application, the full discharge state means placing the battery at 25°C, leaving it to stand for 2 hours, and when the battery temperature remains at 25°C, discharging the battery at a constant current of 1 / 3C to 2.0V, leaving it to stand for 15 minutes, and discharging it at a constant current of 0.04C to 2.0V.

[0117] In the present application, the compaction density of the positive electrode film layer in the full state can be tested by 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. When the battery temperature is maintained at 25°C, the battery is discharged to 2.0V at a constant current of 1 / 3C and then left to stand for 15 minutes. It is discharged to 2.0V at a constant current of 0.04C, the battery is disassembled, the positive electrode plate is obtained, the residual electrolyte is treated with dimethyl carbonate solvent, the plate is dried, and it is cut into small discs with an area of ​​S, and its mass is obtained as W1, and the thickness T1 of the positive electrode plate is measured using a micrometer, and then the positive electrode film layer of the above-mentioned weighed plate is wiped off, and the mass of the current collector is weighed, 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 = (W1-W2) / [(T1-T2)×S].

[0118] The compaction density of the positive electrode film layer is within the above range, which is beneficial to improving the energy density of the battery cell.

[0119] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] In some embodiments, the positive electrode plate can be prepared in the following manner: the components for preparing the primer layer, such as lithium-containing transition metal phosphate, conductive agent, binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a primer layer slurry; the components such as lithium-containing transition metal oxide, conductive agent, binder are dispersed in a solvent to form a positive electrode film layer slurry; the primer layer slurry is first coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode film layer slurry is then coated on the surface of the primer layer, and after drying, cold pressing and other processes, the positive electrode plate can be obtained.

[0121] [Negative electrode] The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector.

[0122] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0123] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0124] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. 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, 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, the present application is not limited to these materials, and other traditional 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.

[0125] In some embodiments, the negative electrode film layer may further include a binder, which 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).

[0126] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0127] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0128] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0129] [Electrolytes] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0130] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0131] In some embodiments, the electrolyte salt can 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0132] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0133] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0134] [Isolation film] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0135] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0136] [Battery Cell] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0137] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0138] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0139] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 3 The battery cell 5 is a square structure as an example.

[0140] In some embodiments, reference Figure 3 , the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0141] [Battery device] The present application also provides a battery device, which includes the battery cell provided in the present application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0142] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0143] Figure 4 4 is an example of a battery module. Figure 4 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0144] Optionally, the battery module 5 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0145] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0146] Figure 5 and Figure 6 1 is a battery pack 1 as an example. Figure 5 and Figure 6 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0147] [Electrical devices] In addition, an embodiment of the present application further provides an electric device, which includes at least one of the battery cells, battery modules, or battery packs provided in the embodiments of the present application. The battery cells, battery modules, or battery packs can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0148] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0149] Figure 7 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of battery cells, a battery pack or a battery module can be used.

[0150] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0151] Example Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0152] Example 1 1) Preparation of positive electrode Preparation of positive electrode film slurry: D V50 0.7μm, (D V90 -D V10 ) / D V50 Lithium iron phosphate particles (LiFePO4) with a mass ratio of 6.0, conductive carbon black, carbon nanotube conductive agent, and binder PVDF are mixed in a mass ratio of 98:0.4:0.6:1, a solvent NMP is added, and the mixture is stirred under the action of a vacuum stirrer until the system is uniform to obtain a positive electrode film slurry, wherein, based on the total mass of the lithium iron phosphate, particles with a roundness of ≥0.75 in the lithium iron phosphate account for 70%, and particles with a roundness of ≤0.4 account for 15%; The positive electrode film slurry is evenly coated on the surface of the base coating away from the positive electrode current collector, and the single-sided coating mass is 300mg / 1540.25mm 2 After drying at room temperature, the film was transferred to an oven for further drying, and then cold pressed to obtain the positive electrode sheet. The cold pressed density of the positive electrode film layer was 2.7 g / cm 3 The single-sided coating mass here does not include the solvent mass, but only the solid content mass in the coating.

[0153] Electrode sheet slitting (one out of two): The positive electrode sheet is slitting on the slitting machine, the slitting speed is 0.5m / s, the slitting knife is made of steel, and the negative pressure of the slitting machine is -10KPa.

[0154] Pole piece cutting: The slit pole pieces are wound and cut, with a winding speed of 0.6m / s, each winding core length of 3m, the cutting knife is made of steel, and the negative pressure in the winding machine is -10KPa.

[0155] 2) Preparation of negative electrode The graphite negative electrode active material, polyvinyl alcohol binder, and SP-Li conductive agent were fully mixed and ball-milled in a deionized water solvent system at a mass ratio of 90:5:5 to obtain a negative electrode slurry. The negative electrode slurry was mixed at a mass ratio of 140 mg / 1540.25 mm 2 The single-sided coating quality was double-sided coated on the surface of the copper foil and vacuum dried overnight at a temperature of 110°C to obtain the negative electrode sheet.

[0156] 3) Preparation of diaphragm A polyethylene film with a thickness of 13 μm was used as the separator.

[0157] 4) Preparation of electrolyte 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 uniform solution, thereby obtaining an electrolyte with a LiPF6 concentration of 1 mol / L.

[0158] 5) Battery assembly Place them in the order of "diaphragm-negative electrode sheet-diaphragm-positive electrode sheet", fix one end of the positive electrode sheet, negative electrode sheet and two separators to the discharge roller, and fix the other end to the winding shaft after stacking together. Use a motor to rotate the winding shaft, wind up the positive electrode sheet, negative electrode sheet and two separators, and obtain a wound bare cell. Place the bare cell in an outer package, inject the above-mentioned electrolyte and package it to obtain a battery cell.

[0159] The preparation method of Example 2 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 D of the lithium iron phosphate particles is V50 0.5μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 2.74 g / cm 3 .

[0160] 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 of the positive electrode film slurry, the D of the lithium iron phosphate particles is V50 0.6μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 2.72 g / cm 3 .

[0161] 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 of the positive electrode film slurry, the D of the lithium iron phosphate particles is V50 0.8μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 2.68 g / cm 3 .

[0162] 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 of the positive electrode film slurry, the D of the lithium iron phosphate particles is V50 0.9μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 2.66 g / cm 3 .

[0163] The preparation method of Example 6 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 D of the lithium iron phosphate particles is V50The particle size of lithium iron phosphate is 0.66 μm, the particle size with roundness ≥0.75 accounts for 80%, and the particle size with roundness ≤0.4 accounts for 10%; the cold pressed density of the positive electrode film is 2.67 g / cm 3 .

[0164] 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 of the positive electrode film slurry, the D of the lithium iron phosphate particles is V50 The particle size of lithium iron phosphate is 0.68 μm, and the proportion of particles with a roundness of ≥0.75 is 75%; the cold pressed density of the positive electrode film is 2.69 g / cm 3 .

[0165] The preparation method of Example 8 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 D of the lithium iron phosphate particles is V50 The particle size of lithium iron phosphate is 0.72 μm, and the proportion of particles with a roundness of ≥0.75 is 65%; the cold pressed density of the positive electrode film is 2.68 g / cm 3 .

[0166] The preparation method of Example 9 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 D of the lithium iron phosphate particles is V50 The particle size of lithium iron phosphate is 0.74 μm, and the proportion of particles with a roundness of ≥0.75 is 60%; the cold pressed density of the positive electrode film is 2.66 g / cm 3 .

[0167] The preparation method of Example 10 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 D of the lithium iron phosphate particles is V50 The particle size of lithium iron phosphate is 0.65 μm, and the proportion of particles with a wetness of ≤0.4 is 0%. The cold pressed density of the positive electrode film is 2.65 g / cm 3 .

[0168] The preparation method of Example 11 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 D of the lithium iron phosphate particles is V50 The particle size of lithium iron phosphate is 0.67 μm, and the proportion of particles with a wetness of ≤0.4 is 5%. The cold pressed density of the positive electrode film is 2.66 g / cm 3 .

[0169] The preparation method of Example 12 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 D of the lithium iron phosphate particles is V50 The particle size of lithium iron phosphate is 0.69 μm, and the proportion of particles with a wetness of ≤0.4 is 10%; the cold pressed density of the positive electrode film is 2.68 g / cm3 .

[0170] The preparation method of Example 13 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 D of the lithium iron phosphate particles is V50 The particle size of lithium iron phosphate is 0.73 μm, and the proportion of particles with a wetness of ≤0.4 is 20%. The cold pressed density of the positive electrode film is 2.67 g / cm 3 .

[0171] 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, in the preparation step 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 density of the positive electrode film is 2.60g / cm 3 .

[0172] 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, in the preparation step 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 density of the positive electrode film is 2.66g / cm 3 .

[0173] 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 step 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 density of the positive electrode film is 2.72g / cm 3 .

[0174] 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, in the preparation step 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 density of the positive electrode film is 2.75g / cm 3 .

[0175] The preparation method of Example 18 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 D of the lithium iron phosphate particles is V50 The cold pressed density of the positive electrode film is 2.63 g / cm 3 .

[0176] The preparation method of Example 19 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the D of the lithium iron phosphate particles is V50The cold pressed density of the positive electrode film is 2.67 g / cm 3 .

[0177] The preparation method of Example 20 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 D of the lithium iron phosphate particles is V50 The cold pressed density of the positive electrode film is 2.73 g / cm 3 .

[0178] 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 step of the positive electrode film slurry, the proportion of particles with a roundness ≥ 0.75 in lithium iron phosphate is 50%; the cold pressed density of the positive electrode film is 2.67 g / cm 3 .

[0179] 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 step of the positive electrode film slurry, the proportion of particles with a roundness ≥ 0.75 in lithium iron phosphate is 90%, and the proportion of particles with a roundness ≤ 0.4 is 0%; the cold pressed density of the positive electrode film is 2.58 g / cm 3 .

[0180] The preparation method of Comparative Example 3 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 D of the lithium iron phosphate particles is V50 0.5μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 2.71 g / cm 3 .

[0181] The preparation method of Comparative Example 4 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 D of the lithium iron phosphate particles is V50 0.9μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 2.50 g / cm 3 .

[0182] Performance Testing 1. Roundness test method At 25°C, take the cut positive electrode sheets prepared in each embodiment and comparative example, and carry out CP-SEM test. Randomly take a number of points for shooting, and take the number of points ≥10, which can be 10, 20, 50, 100, etc. Use AVIZO software to identify the particles in the pictures taken, and measure the shortest diameter, longest diameter and area of ​​each particle. Roundness = 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 is equivalent to the mass proportion of particles with a roundness greater than or equal to 0.4 in the positive electrode film layer. Similarly, the mass proportion of particles with a roundness less than or equal to 0.3 in the positive electrode film layer is obtained.

[0183] 2. Porosity test method At 25°C, take the cut positive electrode sheets prepared in each embodiment and comparative example, cut the sheets into small discs with a diameter of 14 mm, and use a vacuum density tester (for example, AccuPycII1340 fully automatic true density tester from Micromeritics, USA) to measure the samples with reference to GB / T 24586-2009 standard. The number of test samples is greater than or equal to 30, and the average value is taken as the final result.

[0184] 3. Tortuosity test method At 25°C, the positive electrode sheets prepared in each embodiment and comparative example were punched into 14 mm small discs, and the positive electrode sheets were assembled into symmetrical batteries in a glove box (humidity ≤ 1ppm). After the electrolyte was injected, it was left to stand for more than 12 hours to allow the electrolyte to fully infiltrate the sheets. The impedance change was detected by EIS test. The test process was: upper limit frequency 1kHz, lower limit frequency 500mHz, disturbance voltage 5mV, symmetrical battery voltage range -1V~1V; the ion diffusion impedance Rion was obtained by fitting the test data. The formula of the electrolyte is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 4:3:3 to obtain an organic solution, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L.

[0185] The tortuosity of the pole piece is as follows: the area A (1.5386cm 2 ), the thickness of the small disc d (cm), the electrolyte conductivity k (S / m), the porosity ε of the electrode, and the ion diffusion impedance Rion (Ω) are substituted into the following formula to calculate the electrode tortuosity.

[0186]

[0187] 4. Battery energy density test method The battery cells prepared in each embodiment and comparative example were left at 25°C for 2 hours to ensure that the temperature of the battery cells was 25°C. After charging the battery cells at 1 / 3C to a charge cut-off voltage of 3.65V at 25°C, constant voltage charging was continued at the charge cut-off voltage until the current reached 0.05C and the charge was cut off (where C represents the rated capacity of the battery cells). After the battery cell pool was left at 25°C for 1 hour, the battery cells were discharged at 0.33C at 25°C to a discharge cut-off voltage of 2.5V, and the total discharge energy of the battery cells was recorded as E0.

[0188] The mass of the battery cell is measured as M0.

[0189] The mass energy density of a battery cell = the discharge energy of the battery cell E0 / the mass of the battery cell M0.

[0190] 5. Cyclic performance test method At 25°C, the battery cells prepared in each embodiment and comparative example were charged to 50% SOC at 1C constant current, then charged to 80% SOC at 0.87C, and then charged to 3.65V at 0.33C. The battery cells were then charged at a constant voltage at the charge cut-off voltage until the current reached 0.05C. The battery cells were then discharged at a constant current of 1C to a discharge cut-off voltage of 2.5V. This was a charge and discharge process. The discharge capacity of the battery cell was recorded as the discharge capacity of the first cycle of the battery, E1. The battery was charged and discharged repeatedly for 1,000 times. The discharge capacity of the battery cell was recorded as E2. The capacity retention rate @1000Cls=E2 / E1×100%.

[0191] The battery cells of each embodiment and comparative example were prepared according to the above method. The specific parameters and performances are shown in Tables 1 and 2 below. Table 1

[0192] Table 2

[0193] By comparing the embodiment and the comparative example, it can be seen that by controlling the particle size of the positive electrode film layer, the particle size of the positive electrode film layer (D V90 -D V10 ) / D V50 is 4-8, based on the total mass of the positive electrode film layer, the mass of the particles with a roundness greater than or equal to 0.75 in the positive electrode film layer accounts for 60%-80%; while the battery has a higher energy density, it can improve the tortuosity deterioration problem caused by large grading and improve the cycle life of the battery.

[0194] By comparing Examples 1 to 5, it can be seen that the particles in the positive electrode film layer (D V90 -DV10 ) / D V50 5-7; D of the particles V50 When it is 0.6μm-0.8μm, the tortuosity and compaction density in the positive electrode sheet are balanced, which is beneficial to improving the mass energy density and cycle life of the battery.

[0195] By comparing Examples 1 and 6 to 9, it can be seen that when the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 65%-75%, the battery's mass energy density and cycle life are further balanced.

[0196] By comparing Examples 1 and 10 to 13, it can be seen that when the mass proportion of particles with a roundness of less than or equal to 0.4 in the positive electrode film layer is 5%-20%, and further accounts for 10%-15%, it is beneficial to improve the energy density of the battery.

[0197] By comparing Examples 1, 14 to 17, it can be seen that the single-side density of the positive electrode film layer is 200 mg / 1540.25 mm 2 -450mg / 1540.25mm 2 When the battery is heated and cooled, a higher battery energy density can be achieved and the cycle life can be optimized.

[0198] By comparing Examples 1, 18 to 20, it can be seen that the D V50 When it is 0.6μm-0.8μm, it is beneficial to reduce the tortuosity of the positive electrode film layer and improve the cycle life of the battery.

[0199] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side surface of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises lithium-containing transition metal phosphate particles, and the particles in the positive electrode film layer have a (D V90 -D V10 ) / D V50 4-8; Based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness greater than or equal to 0.75 in the positive electrode film layer is 60%-80%.

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

3. The battery cell according to claim 1, characterized in that: Based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness less than or equal to 0.4 in the positive electrode film layer is 5%-20%.

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

5. The battery cell according to claim 1, characterized in that: The particles in the positive electrode film layer (D V90 -D V10 ) / D V50 Is 5-7.

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

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

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

9. The battery cell according to claim 1, characterized in that: The particle size volume distribution curve of the particles of the positive electrode film layer presents a bimodal distribution, and the first peak of the bimodal distribution is located at 0.45 μm-0.75 μm.

10. The battery cell according to claim 1, characterized in that: The particle size volume distribution curve of the particles of the positive electrode film layer presents a bimodal distribution, and the first peak of the bimodal distribution is located at 0.6 μm-0.7 μm.

11. The battery cell according to claim 1, characterized in that: The particle size volume distribution curve of the particles of the positive electrode film layer presents a bimodal distribution, and the second peak of the bimodal distribution is located at 0.6 μm-0.97 μm.

12. The battery cell according to claim 1, characterized in that: The particle size volume distribution curve of the particles of the positive electrode film layer presents a bimodal distribution, and the second peak of the bimodal distribution is located at 0.7 μm-0.91 μm.

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

14. The battery cell according to claim 13, characterized in that: The conductive agent includes a one-dimensional conductive agent, and the one-dimensional conductive agent can be selected from one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

15. The battery cell according to claim 13 or 14, characterized in that: The conductive agent includes a zero-dimensional conductive agent, which can be selected from one or more of conductive carbon black, Ketjen black, and hard carbon.

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

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

18. The battery cell according to claim 1, characterized in that: The lithium-containing transition metal phosphate comprises components shown in the following general formula: Li x A y Me a M b P 1-c X c Y z , Among them, 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; and Y includes one or more of O and F.

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

7.

20. The battery cell according to claim 1, characterized in that: The compaction density of the positive electrode film layer in the full state is 2.40g / cm 3 -2.65g / cm 3 .

21. A battery device, characterized in that: The battery device comprises the battery cell according to any one of claims 1 to 20, and the battery device comprises at least one of a battery module, a battery pack, and an energy storage device.

22. An electrical device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 20 or the battery device according to claim 21.

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