Battery monomer, battery device, power utilization device and energy storage device

Abstract

The invention provides a battery monomer, a battery device, a power utilization device and an energy storage 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 of the surface of the positive current collector, the positive film layer comprises a positive active material, and the negative electrode film layer comprises a negative active material. Based on the total mass of the positive electrode film layer, the mass ratio of the positive electrode active material is 97.5%-99.2%; based on the total mass of the positive electrode film layer, the mass ratio of particles with roundness greater than or equal to 0.6 in the positive electrode film layer is 60%-90%.

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, an electrical device and an energy storage 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] With the popularization of single-cell battery applications, higher requirements are placed on their energy density. Summary of the invention

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

[0005] A first aspect of the present application provides a battery cell, comprising a positive electrode plate, a negative electrode plate and an electrolyte, wherein the positive electrode plate comprises a positive electrode collector and a positive electrode film layer arranged on at least one side of the surface of the positive electrode collector, the positive electrode film layer comprises a positive electrode active material, and based on the total mass of the positive electrode film layer, the mass proportion of the positive electrode active material is 97.5%-99.2%; based on the total mass of the positive electrode film layer, the mass proportion of particles in the positive electrode film layer with a roundness greater than or equal to 0.6 is 60%-90%.

[0006] Studies have shown that increasing the loading of positive active materials in the positive electrode film layer is beneficial to improving the compaction density of the positive electrode film layer and the energy density of the battery. However, in order to maintain the dynamic performance of the positive electrode sheet and even the battery cell, the content of the conductive agent in the positive electrode film layer is positively correlated with the loading of the positive electrode active material. A high loading of positive active materials requires a higher content of conductive agent, which leads to a sharp reduction in the content of the binder and a decrease in the internal bonding force of the positive electrode film layer.

[0007] In this application, the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer have a mass proportion within the above range. The increase in the roundness of the particles makes the arrangement of the particles in the positive electrode film layer more uniform, and the surface flatness of the film layer is improved, thereby increasing the number of contact points between the particles and the current collector near the current collector side, and increasing the bonding force between the positive electrode film layer and the current collector. On the other hand, the particles with high roundness can be tightly packed during rolling, and the particles are in good contact, so that the particles inside the positive electrode film layer have good electronic conductivity, and help to reduce the degree of curvature of the pore channels between the particles. The conductive agent is evenly distributed in the electrode to build an efficient conductive network, further improving the electronic conductivity. Therefore, in the highly loaded positive electrode film layer, the particles have a high sphericity, which can reduce the amount of conductive agent without affecting the conductive performance, and instead increase the binder content, thereby improving the internal bonding force of the positive electrode film layer. At the same time, the particles with high roundness are prone to slip under the action of external forces, and the compaction density of the pole piece can be improved under low rolling pressure. Thereby, the internal bonding force of the positive electrode film layer is taken into account while maintaining the high energy density of the battery.

[0008] In any embodiment, based on the total mass of the positive electrode film layer, the mass proportion of the positive electrode active material is 98.2%-98.6%. The mass proportion of the positive electrode active material is within the above range, which further improves the battery energy density and takes into account the internal bonding force of the positive electrode film layer.

[0009] 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 0.6 in the positive electrode film layer is 70%-80%. The roundness of the particles in the positive electrode film layer has a direct impact on the compaction density and energy density. Even if all the particles are perfect spheres, they cannot be completely densely packed due to the limitations of the geometric arrangement. The anisotropic shape characteristics of particles with less roundness will affect their random stacking behavior, which means that a moderate deviation from the spherical shape may help the particles to stack more closely. Studies have shown that the mass proportion of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is in the range of 70%-80%, which can further improve the compaction density of the positive electrode film layer and the energy density of the battery cell.

[0010] In any embodiment, the ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer is 9-21, and can be optionally 12-18. The compactness of the particle stacking in the positive electrode film layer can be further optimized. Particles with a roundness less than or equal to 0.3 can fill the gaps between particles with high roundness due to their diverse shapes (such as elliptical, wedge-shaped, etc.). The combination of high-roundness and low-roundness particles significantly improves the space utilization of the stack, thereby improving the compaction density of the pole piece and the energy density of the battery.

[0011] In any embodiment, based on the total mass of the positive electrode film layer, the mass proportion of particles in the positive electrode film layer whose particle size R1 satisfies 3μm≤R1≤6μm is 55%-80%. Particles whose particle size R1 satisfies 3μm≤R1≤6μm have a larger specific surface area, so that particles per unit mass or volume can provide more interfaces to interact with binders and conductive agents. When the amount of binder and conductive agent is constant, it not only optimizes dispersion but also enhances internal bonding. The mass proportion of particles whose particle size R1 satisfies 3μm≤R1≤6μm is within the above range, and helps to form a tighter particle stacking with particles of other particle sizes. Thereby enhancing the internal bonding of the positive electrode film layer while taking into account the overall stability and compaction density.

[0012] In any embodiment, based on the total mass of the positive electrode film layer, the mass proportion of particles in the positive electrode film layer whose particle size R2 satisfies 9μm≤R2≤15μm is 5.5%-9.5%. This is conducive to the formation of the film layer skeleton, so that the film layer can withstand higher rolling pressure, and further improves the battery energy density by increasing the compaction density of the pole piece.

[0013] In any embodiment, the positive electrode film layer includes a binder, and the mass content of the binder is 0.4%-1.5% based on the total mass of the positive electrode film layer, and can be optionally 0.6%-1.2%. The amount of binder used is positively correlated with the internal bonding force of the positive electrode film layer. If the amount of binder is too small, the internal bonding force of the positive electrode film layer is low; if the amount of binder is too high, the resistance of the electrode film sheet will be deteriorated and the load of active materials in the positive electrode film layer will be reduced. The mass content of the binder within the above range can maximize the internal bonding force, strengthen the bonding between particles inside the positive electrode film layer, and further reduce the probability of particles falling off in the positive electrode film layer.

[0014] In any embodiment, the D of the positive electrode active material particles V50 0.4μm-1.5μm, optionally 0.5μm-0.9μm, where D V50 Refers to the particle size corresponding to the cumulative volume distribution reaching 50% in the volume cumulative distribution curve. Appropriate D V50 It helps to optimize the accumulation of particles and ensure the stability and conductivity of the structure in the film layer. Particles that are too large may extend the lithium ion diffusion path, reduce the ion transfer rate, and cause polarization. Particles that are too small may increase the specific surface area, increase side reactions, and affect the cycle life of the battery. Therefore, it is necessary to reasonably control the particle size distribution and the D of the positive electrode active material particles. V50 Within the above range, both the energy density and the cycle life of the battery are taken into consideration.

[0015] In any embodiment, the positive electrode film layer includes a one-dimensional conductive agent, and the one-dimensional conductive agent includes one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers. The one-dimensional conductive agent constructs a long-range conductive network through a linear structure. In addition to enhancing conductivity, it also improves the internal bonding force of the film layer.

[0016] In any embodiment, the length of the one-dimensional conductive agent is about the same as the D of the positive electrode active material particles. V50 The ratio of is 5-25, and can be 10-25. The length of the one-dimensional conductive agent reflects its own "overlapping ability" and also plays a role in enhancing the bonding. The length of the one-dimensional conductive agent is related to the D of the positive electrode active material particles. V50 The larger the ratio of D to , the more material particles a single one-dimensional conductive agent can overlap within its length range, the more stable the internal network structure is, and the stronger the conductivity and adhesion of the positive electrode film layer are. If the length of the one-dimensional conductive agent is too long, it is easy to agglomerate during the preparation of the positive electrode film layer slurry. Therefore, the length of the one-dimensional conductive agent is related to the D of the particles in the positive electrode film layer. V50 The ratio of is within the above range to balance the processability, conductivity and adhesion of the positive electrode film layer.

[0017] In any embodiment, based on the total mass of the positive electrode film layer, the mass proportion of the one-dimensional conductive agent is 0.2%-0.6%, and can be 0.3%-0.5%, so that the positive electrode film layer has good electronic conductivity, and the amount of the conductive agent is reduced as much as possible to increase the binder content and enhance the internal bonding force of the positive electrode film layer while keeping the total amount of the positive electrode film layer unchanged.

[0018] In any embodiment, the positive electrode active material includes a lithium-containing transition metal phosphate, and 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 Formula I, 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.

[0019] 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.

[0020] In any embodiment, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate and modified materials thereof.

[0021] In any embodiment, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and modified materials thereof.

[0022] Compared with traditional lithium-containing transition metal phosphate materials, lithium iron phosphate materials and their modified materials have good thermal stability and structural stability, and their gram capacity is relatively high, which is beneficial to improve the energy density while improving the safety and cycle performance of the battery.

[0023] In any embodiment, the positive electrode film layer includes a zero-dimensional conductive agent, and the zero-dimensional conductive agent includes one or more of conductive carbon black, Ketjen black, and acetylene black. Optionally, the zero-dimensional conductive agent includes conductive carbon black. The zero-dimensional conductive agent forms a conductive path through point contact between particles, providing a short-range conductive path and adhesion. The one-dimensional conductive agent constructs a long-range conductive network through a linear structure. The zero-dimensional and one-dimensional conductive agents are used in combination to give full play to their respective advantages, build an efficient conductive network, improve the overall performance of the battery, and further reduce the internal resistance of the battery and the possibility of particle shedding in the pole piece.

[0024] In any embodiment, the bonding strength between the positive electrode film layer and the positive electrode current collector is 15N / m-50N / m. This indicates that the positive electrode film layer has good adhesion to the current collector, and can effectively improve the separation between the positive electrode film layer and the current collector. This also reflects the high bonding inside the positive electrode film layer, which can reduce particle peeling in the positive electrode film layer.

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

[0026] A third aspect of the present application provides an electrical device, which includes the battery device of the second aspect of the present application.

[0027] The fourth aspect of the present application provides an energy storage device, which includes the power consumption device of the third aspect of the present application.

[0028] 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

[0029] 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.

[0030] 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.

[0031] Description of reference numerals: 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0032] 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.

[0033] "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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In the present application, the terms "plurality" and "multiple" refer to two or more.

[0038] Unless otherwise specified, the terms used in this application have the commonly understood meanings that are commonly understood by those skilled in the art.

[0039] 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.

[0040] 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 cell, a battery module or a battery pack.

[0041] 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.

[0042] A battery cell includes an electrode assembly and an electrolyte.

[0043] 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).

[0044] In some embodiments, Figure 3As 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.

[0045] 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.

[0046] 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.

[0047] In some embodiments, the battery may be an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] Figure 5 and Figure 6 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 5and 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.

[0052] In recent years, the market demand for high energy density batteries has become increasingly strong. In order to obtain high energy density batteries, the industry's common method is to continuously increase the loading amount of active materials in the positive electrode film layer, but the increase in the loading amount of active materials will reduce the content of binders and conductive agents in the positive electrode film layer, resulting in a decrease in adhesion, particle peeling inside the positive electrode film layer, and interface separation between the positive electrode film layer and the current collector, which affects the cycle life of the battery cell. Therefore, how to prepare a battery cell that takes into account both high energy density and high internal adhesion is a technical problem that needs to be solved urgently in this field.

[0053] A first aspect of the present application provides a battery cell, which includes a positive electrode plate, a negative electrode plate and an electrolyte, wherein the positive electrode plate includes a positive electrode collector and a positive electrode film layer arranged on at least one side of the surface of the positive electrode collector, the positive electrode film layer includes a positive electrode active material, and based on the total mass of the positive electrode film layer, the mass proportion of the positive electrode active material is 97.5%-99.2%; based on the total mass of the positive electrode film layer, the mass proportion of particles in the positive electrode film layer with a roundness greater than or equal to 0.6 is 60%-90%.

[0054] Studies have shown that by increasing the loading of positive active materials in the positive electrode film layer, when the mass proportion of positive active materials is 97.5%-99.2%, it is beneficial to improve the compaction density of the positive electrode film layer and the energy density of the battery. However, in order to maintain the dynamic performance of the positive electrode sheet and even the battery cell, the content of the conductive agent in the positive electrode film layer is positively correlated with the loading of the positive electrode active material. A high loading of positive active materials requires a higher content of conductive agent, which leads to a sharp reduction in the content of the binder and a decrease in the internal bonding force of the positive electrode film layer.

[0055] In the present application, the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer have a mass proportion within the above range. The increase in the roundness of the particles makes the arrangement of the particles in the positive electrode film layer more uniform, and the surface flatness of the film layer is improved, thereby increasing the number of contact points between the particles and the current collector close to the current collector side, and increasing the bonding force between the positive electrode film layer and the current collector. On the other hand, the particles with high roundness can be densely packed during rolling, and the particles are in good contact with each other, so that the particles inside the positive electrode film layer have good electronic conductivity, and help reduce the degree of curvature of the pore channels between the particles. The conductive agent is evenly distributed in the electrode to build an efficient conductive network, further improving the electronic conductivity performance, such as Figure 1As shown, therefore, in the highly loaded positive electrode film layer, particles with high sphericity can reduce the amount of conductive agent without affecting the conductivity, and increase the binder content, thereby improving the internal bonding force of the positive electrode film layer. At the same time, particles with high roundness are easy to slip under the action of external forces, and the compaction density of the pole piece can be improved under low rolling pressure. Thus, the internal bonding force of the positive electrode film layer is taken into account while maintaining the high energy density of the battery.

[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 some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the positive electrode active material may be selected to be 97.5%, 97.6%, 97.7%, 97.8%, 97.9%, 98.0%, 98.1%, 98.2%, 98.3%, 98.4%, 98.5%, 98.6%, 98.7%, 98.8%, 98.9%, 99.0%, 99.1%, 99.2% or a numerical range between any two of the above.

[0058] Because the space per unit volume of the positive electrode membrane is limited, and additives such as binders and conductive agents other than the positive electrode active materials cannot provide specific capacity, in order to increase the energy density of the battery, it is necessary to increase the loading amount of the positive electrode active material as much as possible.

[0059] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer can be selected to be 60%, 65%, 70%, 75%, 80%, 85%, 90% or a numerical range between any two of the above.

[0060] 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, perform a CP-SEM test, randomly select a number of points for shooting, and take the number of points ≥10, which can be 10, 20, 50, 100, etc., identify the particles in the photographed picture through AVIZO software, and measure the area of ​​each particle, and measure the longest inner diameter, shortest inner diameter and area of ​​the particle, and take the ratio of the shortest inner diameter to the longest inner diameter 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 0.6 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 0.6 in the positive electrode film layer.

[0061] Those skilled in the art can adjust the roundness of the particles by any known process. For example, the roundness of the particles can be adjusted by grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, adding surfactants, and adjusting the parameters of each process.

[0062] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the positive electrode active material is 98.2%-98.6%.

[0063] The mass proportion of the positive electrode active material is within the above range, which further improves the battery energy density while taking into account the internal bonding force 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 having a roundness greater than or equal to 0.6 in the positive electrode film layer is 70%-80%.

[0065] The roundness of the particles in the positive electrode film layer has a direct impact on the compaction density and energy density. Even if all the particles are perfectly spherical, they cannot be completely densely packed due to the limitations of the geometric arrangement. The anisotropic shape characteristics of particles with less roundness will affect their random stacking behavior, which means that a moderate deviation from the spherical shape may help the particles to stack more densely. Studies have shown that the mass proportion of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is in the range of 70%-80%, which can further improve the compaction density of the positive electrode film layer and the energy density of the battery cell.

[0066] In some embodiments, the ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer is 9-21, and can be optionally 12-18.

[0067] In some embodiments, the ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer can be selected to be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or a numerical range between any two of the above.

[0068] In the present application, "the ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer" 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 with a roundness greater than or equal to 0.6 identified in the positive electrode film layer to the sum of the areas of all particles with a roundness less than or equal to 0.3 in the positive electrode film layer is equivalent to the ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer.

[0069] The ratio of the mass of particles with a roundness of 0.6 or more to the mass of particles with a roundness of 0.3 or less in the positive electrode film layer is within the above range, which can further optimize the compactness of the particle stacking in the positive electrode film layer. Particles with a roundness of 0.3 or less can fill the gaps between particles with high roundness due to their diverse shapes (such as elliptical, wedge-shaped, etc.). The combination of high-roundness and low-roundness particles significantly improves the space utilization of the stack, thereby improving the compaction density of the pole piece and the energy density of the battery.

[0070] 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 whose particle size R1 satisfies 3 μm≤R1≤6 μm is 55%-80%.

[0071] 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 whose particle size R1 satisfies 3μm≤R1≤6μm can be selected as 55%, 56%, 57%, 58%, 59%, 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.

[0072] In the present application, based on the total mass of the positive electrode film layer, the mass proportion of particles in the positive electrode film layer whose particle size R1 satisfies 3μm≤R1≤6μm can be determined by the following method: refer to the method described above in this application to identify the particles in the photographed picture, identify the particles in the photographed picture by AVIZO software, and measure the particle size and area of ​​each particle, and the ratio of the sum of the areas of all particles whose particle size R1 satisfies 3μm≤R1≤6μm to the sum of the areas of all identified particles is equivalent to the mass proportion of particles whose particle size R1 satisfies 3μm≤R1≤6μm in the positive electrode film layer.

[0073] Particles with a particle size R1 that satisfies 3μm≤R1≤6μm have a larger specific surface area, so that particles per unit mass or volume can provide more interfaces for interaction with binders and conductive agents. Under the condition of a certain amount of binder and conductive agent, it not only optimizes dispersion but also enhances internal bonding. The mass proportion of particles with a particle size R1 that satisfies 3μm≤R1≤6μm is within the above range and helps to form a tighter particle stack with particles of other particle sizes. This enhances the internal bonding of the positive electrode film layer while taking into account the overall stability and compaction density.

[0074] In some embodiments, based on the total mass of the positive electrode film layer, the mass of particles in the positive electrode film layer whose particle size R2 satisfies 9 μm≤R2≤15 μm accounts for 5.5%-9.5%.

[0075] 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 whose particle size R2 satisfies 9μm≤R2≤15μm can be selected as 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9.0%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5% or a numerical range between any two of the above.

[0076] In the present application, based on the total mass of the positive electrode film layer, the mass proportion of particles in the positive electrode film layer whose particle size R2 satisfies 9μm≤R2≤15μm can be determined by the following method: refer to the method described above in this application to identify the particles in the photographed picture, identify the particles in the photographed picture by AVIZO software, and measure the particle size and area of ​​each particle, and the ratio of the sum of the areas of all particles whose particle size R2 satisfies 9μm≤R2≤15μm to the sum of the areas of all identified particles is equivalent to the mass proportion of particles whose particle size R2 satisfies 9μm≤R2≤15μm in the positive electrode film layer.

[0077] The mass proportion of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film layer is within the above range, which is conducive to the formation of the film layer skeleton, allowing the film layer to withstand higher rolling pressure, and further improves the battery energy density by increasing the compaction density of the electrode sheet.

[0078] In some embodiments, the positive electrode film layer includes a binder, and based on the total mass of the positive electrode film layer, the mass content of the binder is 0.4%-1.5%, and can be optionally 0.6%-1.2%.

[0079] In some embodiments, the positive electrode film layer includes a binder. Based on the total mass of the positive electrode film layer, the mass content of the binder can be selected to be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a numerical range between any two of the above.

[0080] The amount of binder used is positively correlated with the internal bonding force of the positive electrode film. If the amount of binder used is too small, the internal bonding force of the positive electrode film is low; if the amount of binder used is too high, the resistance of the electrode film will deteriorate and the loading amount of active materials in the positive electrode film will be reduced. The mass content of the binder within the above range can maximize the internal bonding force, strengthen the bonding between the particles inside the positive electrode film, and further reduce the probability of particles falling off in the positive electrode film.

[0081] In some embodiments, the D of the positive electrode active material particles is V50 0.4μm-1.5μm, optionally 0.5μm-0.9μm, where D V50 Refers to the particle size corresponding to when the cumulative volume distribution reaches 50% in the volume cumulative distribution curve.

[0082] In some embodiments, the D of the positive electrode active material particles is V50 The optional value may be 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm or a numerical range between any two of the above.

[0083] Appropriate D V50 It helps to optimize the accumulation of particles and ensure the stability and conductivity of the structure in the film layer. Particles that are too large may extend the lithium ion diffusion path, reduce the ion transfer rate, and cause polarization. Particles that are too small may increase the specific surface area, increase side reactions, and affect the cycle life of the battery. Therefore, it is necessary to reasonably control the particle size distribution and the D of the positive electrode active material particles. V50 Within the above range, both the energy density and the cycle life of the battery are taken into consideration.

[0084] In some embodiments, the positive electrode film layer includes a one-dimensional conductive agent, and the one-dimensional conductive agent includes one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0085] 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.

[0086] One-dimensional conductive agents build long-range conductive networks through linear structures. In addition to enhancing conductivity, they also improve the internal adhesion of the film layer.

[0087] In some embodiments, the length of the one-dimensional conductive agent is about the same as the D of the positive electrode active material particles. V50 The ratio is 5-25, and can be optionally 10-25.

[0088] In some embodiments, the length of the one-dimensional conductive agent is about the same as the D of the positive electrode active material particles. V50 The ratio can be selected as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or a numerical range between any two of the above.

[0089] The length of the one-dimensional conductive agent reflects its own "lapping ability" and also plays a role in enhancing the bonding. The length of the one-dimensional conductive agent is related to the D V50 The larger the ratio of D to , the more material particles a single one-dimensional conductive agent can overlap within its length range, the more stable the internal network structure is, and the stronger the conductivity and adhesion of the positive electrode film layer are. If the length of the one-dimensional conductive agent is too long, it is easy to agglomerate during the preparation of the positive electrode film layer slurry. Therefore, the length of the one-dimensional conductive agent is related to the D of the particles in the positive electrode film layer. V50 The ratio of is within the above range to balance the processability, conductivity and adhesion of the positive electrode film layer.

[0090] Based on the total mass of the positive electrode film layer, the mass proportion of the one-dimensional conductive agent is 0.2%-0.6%, and can be optionally 0.3%-0.5%.

[0091] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the one-dimensional conductive agent can be selected to be 0.2%, 0.3%, 0.4%, 0.5%, 0.6% or a numerical range between any two of the above.

[0092] Based on the total mass of the positive electrode film layer, the mass content of the one-dimensional conductive agent is within the above range, so that the positive electrode film layer has good electronic conductivity, and the amount of conductive agent is reduced as much as possible while the total amount of the positive electrode film layer remains unchanged to increase the binder content and enhance the internal bonding force of the positive electrode film layer.

[0093] In some embodiments, the positive electrode active material includes a lithium-containing transition metal phosphate, and 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 Formula I, 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.

[0094] Lithium-containing transition metal phosphate refers to a phosphate material containing lithium and transition metal elements, which has the characteristics of stable structure, good safety and long cycle life. It has been widely used in lithium-ion batteries and can be detected by any known method in the art. For example, it can be detected by combining an X-ray diffractometer (XRD) with an energy spectrum analyzer and an inductively coupled plasma mass spectrometer.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] In some embodiments, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate and modified materials thereof.

[0104] 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.

[0105] In some embodiments, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and modified materials thereof.

[0106] Compared with traditional lithium-containing transition metal phosphate materials, lithium iron phosphate materials and their modified materials have good thermal stability and structural stability, and their gram capacity is relatively high, which is beneficial to improve the energy density while improving the safety and cycle performance of the battery.

[0107] In some embodiments, the lithium-containing transition metal phosphate includes a first lithium-containing transition metal phosphate and a second lithium-containing transition metal phosphate.

[0108] In some embodiments, the particle size D of the first lithium-containing transition metal phosphate particles is V50 0.4μm-0.75μm.

[0109] In some embodiments, the particle size D of the first lithium-containing transition metal phosphate particles is V50 The numerical range can be selected from any two of 0.40μm, 0.45μm, 0.50μm, 0.55μm, 0.60μm, 0.65μm, 0.70μm, and 0.75μm.

[0110] In some embodiments, the particle size D of the second lithium-containing transition metal phosphate particles is V50 1μm-1.5μm.

[0111] In some embodiments, the particle size D of the second lithium-containing transition metal phosphate particles is V50 The optional value may be 1 μm, 1.05 μm, 1.10 μm, 1.15 μm, 1.20 μm, 1.25 μm, 1.30 μm, 1.35 μm, 1.40 μm, 1.45 μm, 1.5 μm or a numerical range between any two of the above.

[0112] The combination of the first lithium-containing transition metal phosphate particles and the second lithium-containing transition metal phosphate particles that meet the above-mentioned particle size range is beneficial to improving the particle grading, achieving close stacking of particles in the positive electrode film layer, and further increasing the compaction density of the electrode sheet, thereby increasing the energy density of the battery.

[0113] In some embodiments, based on the total mass of the positive electrode film layer, the mass of the first lithium-containing transition metal phosphate particles accounts for 55%-80%.

[0114] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the first lithium-containing transition metal phosphate particles can be selected to be 55%, 60%, 65%, 70%, 75%, 80% or a numerical range therebetween.

[0115] In some embodiments, based on the total mass of the positive electrode film layer, the mass of the second lithium-containing transition metal phosphate particles accounts for 20%-45%.

[0116] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the second lithium-containing transition metal phosphate particles can be selected to be 20%, 25%, 30%, 35%, 40%, 45% or a numerical range therebetween.

[0117] Controlling the mass contents of the first lithium-containing transition metal phosphate particles and the second lithium-containing transition metal phosphate particles to meet the above ranges is beneficial to improving the compaction density of the electrode sheet, so that the battery has excellent energy density.

[0118] In some embodiments, based on the mass of the first lithium-containing transition metal phosphate particles, the mass of particles having a roundness greater than or equal to 0.6 in the first lithium-containing transition metal phosphate accounts for 60%-90%.

[0119] In some embodiments, based on the mass of the first lithium-containing transition metal phosphate particles, the mass percentage of particles in the first lithium-containing transition metal phosphate having a roundness greater than or equal to 0.6 can be selected to be 60%, 65%, 70%, 75%, 80%, 85%, 90% or a numerical range between any two of the above.

[0120] In some embodiments, based on the mass of the second lithium-containing transition metal phosphate particles, the mass proportion of particles having a roundness greater than or equal to 0.6 in the second lithium-containing transition metal phosphate can be selected to be 60%-90%.

[0121] In some embodiments, based on the mass of the second lithium-containing transition metal phosphate particles, the mass percentage of particles in the second lithium-containing transition metal phosphate having a roundness greater than or equal to 0.6 can be selected to be 60%, 65%, 70%, 75%, 80%, 85%, 90% or a numerical range between any two of the above.

[0122] The mass proportions of the first lithium-containing transition metal phosphate particles and the second lithium-containing transition metal phosphate particles in the positive electrode film layer with a roundness greater than or equal to 0.6 are respectively within the above ranges, which is beneficial to reducing the porosity in the film layer by improving the slippage of the particles during the preparation of the positive electrode film layer to achieve a high compaction density; at the same time, it is beneficial to reduce the degree of curvature of the pore channels between the particles, which helps to uniformly distribute the conductive agent in the electrode and effectively construct the conductive network, improve the electronic conduction performance, and increase the amount of binder and reduce the amount of conductive agent while keeping the total amount of the positive electrode film layer unchanged, thereby achieving an increase in the bonding strength of the positive electrode film layer and the energy density of the battery.

[0123] In some embodiments, the positive electrode film layer includes a zero-dimensional conductive agent, and the zero-dimensional conductive agent includes one or more of conductive carbon black, Ketjen black, and acetylene black. Optionally, the zero-dimensional conductive agent includes conductive carbon black.

[0124] 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.

[0125] Zero-dimensional conductive agents form conductive paths through point contact between particles, providing short-range conductive paths and adhesion. Zero-dimensional and one-dimensional conductive agents are used in combination to give full play to their respective advantages, build an efficient conductive network, improve the overall performance of the battery, and further reduce the internal resistance of the battery and the possibility of particle shedding in the pole piece.

[0126] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector is 15 N / m-50 N / m.

[0127] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector may be 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m or a numerical range between any two of the above.

[0128] The bonding strength in the embodiment of the present application is within the above range, which means that the adhesion performance of the positive electrode film layer and the current collector is good, and the separation between the positive electrode film layer and the current collector can be effectively improved. It also reflects from the side that the high bonding property inside the positive electrode film layer can reduce the particle peeling in the positive electrode film layer.

[0129] In some embodiments, the cold pressed density of the positive electrode plate is 2.55 g / cm 3 -2.75g / cm 3 .

[0130] In some embodiments, the cold pressed density of the positive electrode sheet can be 2.55 g / 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 , 2.66g / cm 3 , 2.67g / cm 3 , 2.68g / cm 3 , 2.69g / cm 3 , 2.70g / 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.

[0131] 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].

[0132] 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 is different from the compaction density of the positive electrode sheet after it is fully discharged. 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 fully discharged state will be slightly less than the compaction density of the initial cold pressing.

[0133] In some embodiments, the compaction density of the positive electrode sheet in the full state is 2.40 g / cm 3 -2.65g / cm 3 .

[0134] In some embodiments, the compaction density of the positive electrode sheet in the full 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.

[0135] In this application, the full discharge state refers to placing the battery at 25°C, leaving it to stand for 2h, and when the battery temperature remains at 25°C, discharging the battery at a constant current of 1 / 3C to 2.5V, leaving it to stand for 30min, and discharging it at a constant current of 0.04C to 2.5V.

[0136] 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 2h. When the battery temperature is maintained at 25°C, the battery is discharged to 2.5V at a constant current of 1 / 3C and then left to stand for 30min. It is discharged to 2.5V 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, 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 is PD = (W1-W2) / [(T1-T2)×S].

[0137] The compaction density of the positive electrode sheet within the above range is beneficial to maintaining the high energy density of the battery cell while improving the yield rate in the electrode sheet cutting process, thereby meeting the performance and efficiency requirements.

[0138] 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.).

[0139] [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.

[0140] 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.

[0141] 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.).

[0142] 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.

[0143] 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).

[0144] 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.

[0145] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0146] 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.

[0147] [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.

[0148] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] [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.

[0153] 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.

[0154] [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.

[0155] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0156] In some embodiments, the volume energy density of the battery cell is 650Wh / L-720Wh / L.

[0157] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape.

[0158] [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.

[0159] [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.

[0160] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0161] 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.

[0162] An embodiment of the present application also provides an energy storage device, which includes the battery device provided in the embodiment of the present application.

[0163] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a battery cell may be used as a power source.

[0164] 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.

[0165] In each embodiment of the present application, the roundness ratio of the positive electrode active material is regulated by the following method: YHC-92 lithium iron phosphate (D V50 =0.55μm, average roundness 0.92), YHC-53 lithium iron phosphate (D V50 =0.55μm, average roundness 0.53), YHC-21 lithium iron phosphate (D V50 =0.55μm, average roundness 0.21); ZLC-95 lithium iron phosphate (D V50 =1.25μm, average roundness 0.95), ZLC-56 lithium iron phosphate (D V50 =1.25μm, average roundness 0.56), ZLC-16 lithium iron phosphate (D V50 =1.25μm, average roundness 0.16); artificial mixing is performed according to the proportion of particles of each roundness of the positive electrode active material used in the embodiment. As an example, when the demand for positive electrode active material is D V50 =0.55μm lithium iron phosphate particles, the mass of particles with a roundness greater than or equal to 0.6 accounts for 80%, and the ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 is 15; based on the total mass of the positive electrode active material, YHC-92 lithium iron phosphate with a mass proportion of 80%, YHC-21 lithium iron phosphate with a mass proportion of 5.3%, and YHC-53 lithium iron phosphate is used to fill the remaining mass proportion, and mixing is performed to obtain a mixture and test it. When the roundness of the mixture meets the requirements, it is stored as an active material raw material for subsequent preparation of pole pieces.

[0166] Example 1 1) Preparation of positive electrode Preparation of positive electrode film slurry: D V50 The first lithium iron phosphate particles (LiFePO 4 ), D V50 The second lithium iron phosphate particles (LiFePO 4) are mixed in a mass ratio of 7:3 to obtain a positive electrode active material, the positive electrode active material, the one-dimensional conductive agent, the zero-dimensional conductive agent, and the binder PVDF are mixed in a mass ratio of 98.4:0.3:0.3:1, and the solvent NMP is added, and the system is stirred under the action of a vacuum mixer until the system is uniform to obtain a positive electrode film slurry. Among them, the zero-dimensional conductive agent is a Super-P conductive agent, the one-dimensional conductive agent is a carbon nanotube conductive agent, the mass of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles accounts for 80%, and the ratio of the mass of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles to the mass of particles with a roundness less than or equal to 0.3 is 15; the mass of particles with a roundness greater than or equal to 0.3 in the second lithium iron phosphate particles accounts for 80%, and the ratio of the mass of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles to the mass of particles with a roundness less than or equal to 0.3 is 15; the D of the positive electrode active material V50 The length of the one-dimensional conductive agent is 0.7 μm, and the D V50 The ratio is 15.

[0167] 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-side coating weight is 300 mg / 1540.25 mm 2 After drying at room temperature, the film was transferred to an oven for further drying, and then cold pressed to obtain a positive electrode sheet. The thickness of the single-side positive electrode film layer after cold pressing was 70.8 μm, and the cold pressed compaction density of the positive electrode film layer was 2.75 g / cm 3 The single-sided coating mass here does not include the solvent mass, but only the solid content mass in the coating.

[0168] Pole 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 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.

[0169] 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 weight was double-sided coated on the surface of the copper foil and vacuum dried overnight at a temperature of 110°C to obtain a negative electrode sheet.

[0170] 3) Preparation of diaphragm A polyethylene film with a thickness of 13 μm was used as the separator.

[0171] 4) Preparation of electrolyte Lithium hexafluorophosphate (LiPF 6 ) 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 to obtain LiPF 6 The concentration of the electrolyte is 1 mol / L.

[0172] 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.

[0173] 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 step of the positive electrode film slurry, the mass ratio of the positive electrode active material, the one-dimensional conductive agent, the zero-dimensional conductive agent, and the binder PVDF is 97.5:0.6:0.3:1.6; the cold pressed density of the positive electrode film is 2.73 g / cm 3 .

[0174] 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 step of the positive electrode film slurry, the mass ratio of the positive electrode active material, the conductive carbon black, the carbon nanotube conductive agent, and the binder PVDF is 98.8:0.2:0.3:0.7; the cold pressed density of the positive electrode film is 2.75 g / cm 3 .

[0175] 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, in the preparation step of the positive electrode film slurry, the mass proportion of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 60%; the mass proportion of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 60%; the cold pressed density of the positive electrode film layer is 2.68 g / cm 3 .

[0176] 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, in the preparation step of the positive electrode film slurry, the mass proportion of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 70%; the mass proportion of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 70%; the cold pressed density of the positive electrode film layer is 2.72 g / cm 3 .

[0177] 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, in the preparation step of the positive electrode film slurry, the mass proportion of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 90%; the mass proportion of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 90%; the cold pressed density of the positive electrode film layer is 2.70 g / cm 3 .

[0178] 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 step of the positive electrode film slurry, the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 9; the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 9; the cold pressed density of the positive electrode film layer is 2.68 g / cm 3 .

[0179] 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 step of the positive electrode film slurry, the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 12; the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 12; the cold pressed density of the positive electrode film layer is 2.72 g / cm 3 .

[0180] 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 step of the positive electrode film slurry, the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 18; the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 18; the cold pressed density of the positive electrode film layer is 2.73 g / cm 3 .

[0181] 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 step of the positive electrode film slurry, the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 21; the ratio of the mass of the particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles to the mass of the particles with a roundness less than or equal to 0.3 is 21; the cold pressed density of the positive electrode film layer is 2.70 g / cm 3 .

[0182] 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 step of the positive electrode film slurry, the mass ratio of the first lithium iron phosphate particles to the second lithium iron phosphate particles is 6.7:3.3; the cold pressed density of the positive electrode film is 2.68 g / cm 3 .

[0183] 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 mass ratio of the first lithium iron phosphate particles to the second lithium iron phosphate particles is 8:2; the D of the positive electrode active material is V50 The cold pressed density of the positive electrode film is 2.65g / cm 3 .

[0184] 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 step of the positive electrode film slurry, the D of the second lithium iron phosphate particles is V50 The cold pressed density of the positive electrode film is 2.68 g / cm 3 .

[0185] The preparation method of Example 14 is substantially 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 second lithium iron phosphate particles is V50 The cold pressed density of the positive electrode film is 2.70 g / cm 3 .

[0186] The preparation method of Example 15 is substantially 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 second lithium iron phosphate particles is V50 The cold pressed density of the positive electrode film is 2.73 g / cm 3 .

[0187] 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 D of the second lithium iron phosphate particles is V50 The cold pressed density of the positive electrode film is 2.70 g / cm 3 .

[0188] The preparation method of Example 17 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the length of the one-dimensional conductive agent is equal to the D of the particles of the positive electrode active material. V50 The ratio is 5; the cold pressed density of the positive electrode film is 2.73g / cm 3 .

[0189] 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 length of the one-dimensional conductive agent is equal to the D of the particles of the positive electrode active material. V50 The ratio is 10; the cold pressed density of the positive electrode film is 2.75g / cm 3 .

[0190] The preparation method of Example 19 is substantially 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 length of the one-dimensional conductive agent is equal to the D of the particles of the positive electrode active material. V50 The ratio is 20; the cold pressed density of the positive electrode film is 2.71g / cm 3 .

[0191] 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 length of the one-dimensional conductive agent is equal to the D of the particles of the positive electrode active material. V50 The ratio is 25; the cold pressed density of the positive electrode film is 2.72g / cm 3 .

[0192] The preparation method of Example 21 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 mass ratio of the positive electrode active material, the one-dimensional conductive agent, the zero-dimensional conductive agent, and the binder PVDF is 98.4:0.2:0.5:1; the cold pressed density of the positive electrode film is 2.73 g / cm 3 .

[0193] The preparation method of Example 22 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 mass ratio of the positive electrode active material, the one-dimensional conductive agent, the zero-dimensional conductive agent, and the binder PVDF is 98.4:0.4:0.3:1; the cold pressed density of the positive electrode film is 2.73 g / cm 3 .

[0194] The preparation method of Example 23 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 mass ratio of the positive electrode active material, the one-dimensional conductive agent, the zero-dimensional conductive agent, and the binder PVDF is 98.4:0.5:0.1:1; the cold pressed density of the positive electrode film is 2.72 g / cm 3 .

[0195] The preparation method of Example 24 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 mass ratio of the positive electrode active material, the one-dimensional conductive agent, the zero-dimensional conductive agent, and the binder PVDF is 98.4:0.6:0:1; the cold pressed density of the positive electrode film is 2.70 g / cm 3 .

[0196] 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 mass ratio of the positive electrode active material, the one-dimensional conductive agent, the zero-dimensional conductive agent, and the binder PVDF is 97:0.6:0.3:2.1; the cold pressed density of the positive electrode film is 2.72 g / cm 3 .

[0197] 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, in the preparation step of the positive electrode film slurry, the mass proportion of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 50%; the mass proportion of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 50%; the cold pressed density of the positive electrode film layer is 2.73 g / cm 3 .

[0198] The preparation method of comparative example 3 is basically the same as that of embodiment 1, except that, in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film slurry, the mass proportion of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 95%; the mass proportion of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 95%; the cold pressed density of the positive electrode film layer is 2.63 g / cm 3 .

[0199] Performance Testing 1. CP-SEM characterization method of positive electrode cross section The sample to be characterized was prepared as follows: first, the positive electrode sheet was cut into a sample to be tested with a size of 2 cm × 2 cm, and the sample to be tested was fixed on the sample stage by paraffin. Then, the sample stage was placed in the sample holder and locked, the power supply and vacuum of the argon ion cross-section polisher IB-19500CP were turned on, the argon gas flow rate was set to 0.15 MPa, the control voltage was set to 8 kV, and the polishing time was set to 2 hours, and the sample stage was adjusted to the swing mode to start polishing. After the polishing was completed, the sample to be characterized was obtained.

[0200] Microscopic morphology characterization: The samples were characterized using a scanning electron microscope ZEISS Sigma300. The sample test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, multiple different areas can be randomly selected from the sample to be tested for scanning tests, and the cross-sectional morphology images can be taken at a fixed magnification of 5k times.

[0201] 2. Roundness test method At 25°C, take the cut positive electrode sheets prepared in each embodiment and comparative example, and perform 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 photographed pictures, 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 0.6 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 0.6 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.

[0202] 3. Pole piece bonding strength test At 25°C, take the cold-pressed positive electrode sheets prepared in each embodiment and comparative example, cut them into test specimens with a length of L: 100 mm and a width of W: 20 mm, and set them aside; stick one side of the double-sided tape to the surface of the steel plate, and adhere the electrode to be tested on the other side, and compact it with a roller to make it completely fit with the electrode; bend one end of the collector in the opposite direction, and the bending angle is 180°; use a high-speed rail tensile testing machine for testing, fix one end of the steel plate to the clamp below the tensile testing machine, and fix the bent end of the collector to the upper clamp, adjust the angle of the collector to ensure that the upper and lower ends are in a vertical position, and then stretch the sample at a speed of 50 mm / min until the collector is completely peeled off from the surface of the electrode, record the displacement and force in the process, and record the strength when the force is balanced as the bonding force of the electrode as N1, and the bonding strength of the electrode can be calculated using the formula N1 / W.

[0203] 4. Pole powder shedding test At 25°C, the cold-pressed positive electrode sheets prepared in each embodiment and comparative example were taken and sheared by a die-cutting and wrap-around integrated machine. The slitting speed was set to 0.5 m / s, the pressure of the slitting machine was -10 kPa, and the number of shearing knives was 2000. The powder after shearing was collected, its weight was weighed and recorded as W, and the proportion of leaked metal was recorded as W g / 2000 knives.

[0204] 5. Battery internal resistance DCR test method At 25°C, the battery cells prepared in each embodiment and comparative example were charged at a constant current of 1 / 3C to a charge cut-off voltage of 4.3V, and then continued to be charged at a constant voltage at the charge cut-off voltage until the current reached 0.05C, and then discharged at 1 / 3C to 50% SOC. After standing for 5 minutes, they were pulse-discharged at 3C for 30 seconds.

[0205] The voltage was recorded before and after each pulse discharge, and the DCR under different conditions was calculated. The calculation formula was DCR = (voltage before pulse discharge after standing still - voltage before standing still after pulse discharge) / pulse current.

[0206] 6. 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.

[0207] Measure the length, width and height of the battery cell, and calculate the volume value V0 of the battery cell = length × width × height.

[0208] The volume energy density of a battery cell = battery cell discharge energy E0 / battery cell volume V0.

[0209] The battery cells of each embodiment and comparative example were prepared according to the above method. The specific parameters and performances are shown in Table 1, Table 2 and Table 3 below. Table 1

[0210] By comparing the embodiments and the comparative examples, it can be seen that, based on the total mass of the positive electrode film layer, the mass proportion of the positive electrode active material is controlled to be 97.5%-99.2%, and the mass proportion of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 60%-90%; while the battery has a higher energy density, the powder shedding problem caused by the decrease in internal bonding force due to the high active material loading can be improved.

[0211] By comparing Example 1 and Examples 4-6, it can be seen that, based on the total mass of the positive electrode film layer, when the mass proportion of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 70%-80%, while the amount of powder loss is low, it is beneficial to further improve the battery energy density.

[0212] By comparing Example 1 and Examples 6-10, it can be seen that the ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer is 9-21. When the ratio is further 12-18, it is conducive to forming a tighter stacking, thereby improving the energy density of the battery.

[0213] Table 2

[0214] By comparing Example 1 with Examples 11-12, it can be seen that, based on the total mass of the positive electrode film layer, when the mass proportion of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film layer is 55%-80%, it is beneficial to achieve a balance between bonding strength and battery energy density.

[0215] By comparing Example 1 and Examples 13-16, it can be seen that, based on the total mass of the positive electrode film layer, when the mass proportion of particles in the positive electrode film layer whose particle size R2 satisfies 3μm≤R1≤6μm is 5.5%-9.5%, it is beneficial to improve the volume energy density of the battery.

[0216] By comparing Example 1 and Examples 17-20, it can be seen that the length of the one-dimensional conductive agent is related to the D of the particles in the positive electrode film layer. V50 The ratio is 5-25, and further when the ratio is 10-25, it is beneficial to improve the bonding strength and reduce the amount of powder falling off.

[0217] Table 3

[0218] By comparing Example 1 and Examples 21-24, it can be seen that when the mass proportion of the one-dimensional conductive agent is 0.2%-0.6% based on the total mass of the positive electrode film layer, the technical effect of enhancing the bonding strength and reducing the DC internal resistance can be achieved. When the mass proportion of the one-dimensional conductive agent is 0.3%-0.5%, low cost, low powder loss and low DC internal resistance can be taken into account.

[0219] 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 arranged on at least one side of the surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, and based on the total mass of the positive electrode film layer, the mass proportion of the positive electrode active material is 97.5%-99.2%; Based on the total mass of the positive electrode film layer, the mass proportion of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 60%-90%.

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 the positive electrode active material is 98.2%-98.6%.

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 greater than or equal to 0.6 in the positive electrode film layer is 70%-80%.

4. The battery cell according to claim 1, characterized in that: The ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer is 9-21.

5. The battery cell according to claim 1, characterized in that: The ratio of the mass of particles with a roundness greater than or equal to 0.6 to the mass of particles with a roundness less than or equal to 0.3 in the positive electrode film layer is 12-18.

6. 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 in the positive electrode film layer whose particle size R1 satisfies 3μm≤R1≤6μm is 55%-80%.

7. 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 in the positive electrode film layer whose particle size R2 satisfies 9μm≤R2≤15μm is 5.5%-9.5%.

8. The battery cell according to claim 1, characterized in that: The positive electrode film layer includes a binder, and based on the total mass of the positive electrode film layer, the mass proportion of the binder is 0.4%-1.5%.

9. The battery cell according to claim 1, characterized in that: The positive electrode film layer includes a binder, and based on the total mass of the positive electrode film layer, the mass proportion of the binder is 0.6%-1.2%.

10. The battery cell according to claim 1, characterized in that: The positive electrode active material particles have a D V50 0.4μm-1.5μm, among which, D V50 Refers to the particle size corresponding to when the cumulative volume distribution reaches 50% in the volume cumulative distribution curve.

11. The battery cell according to claim 1, characterized in that: The positive electrode active material particles have a D V50 0.5μm-0.9μm, among which, D V50 Refers to the particle size corresponding to when the cumulative volume distribution reaches 50% in the volume cumulative distribution curve.

12. The battery cell according to claim 10 or 11, characterized in that: The positive electrode film layer includes a one-dimensional conductive agent, and the one-dimensional conductive agent includes one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

13. The battery cell according to claim 12, characterized in that: The length of the one-dimensional conductive agent is related to the D V50 The ratio is 5-25.

14. The battery cell according to claim 12, characterized in that: The length of the one-dimensional conductive agent is related to the D V50 The ratio is 10-25.

15. The battery cell according to claim 12, characterized in that: Based on the total mass of the positive electrode film layer, the mass proportion of the one-dimensional conductive agent is 0.2%-0.6%.

16. The battery cell according to claim 12, characterized in that: Based on the total mass of the positive electrode film layer, the mass proportion of the one-dimensional conductive agent is 0.3%-0.5%.

17. The battery cell according to claim 1, characterized in that: The positive electrode active material includes a lithium-containing transition metal phosphate, and the lithium-containing transition metal phosphate includes a component shown in the following general formula: Li x A y Me a M b P 1-c X c Y z Formula I 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.

18. The battery cell according to claim 17, characterized in that: The lithium-containing transition metal phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate and modified materials thereof.

19. The battery cell according to claim 17 or 18, characterized in that: The lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and modified materials thereof.

20. The battery cell according to claim 1, characterized in that The positive electrode film layer includes a zero-dimensional conductive agent, which includes one or more of conductive carbon black, Ketjen black, and acetylene black. Optionally, the zero-dimensional conductive agent includes conductive carbon black.

21. The battery cell according to claim 1, characterized in that: The bonding strength between the positive electrode film layer and the positive electrode current collector is 15N / m-50N / m.

22. A battery device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 21.

23. An electrical device, characterized in that: The electrical device comprises the battery device as claimed in claim 22, and the battery device is used to provide electrical energy.

24. An energy storage device, characterized in that: The energy storage device comprises the electrical device as claimed in claim 23, wherein the electrical device is used to store electrical energy.

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