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, and in a cross-sectional view of the positive film layer, the positive pole piece comprises a positive pole piece and a negative pole piece, based on the total area of the particles in the positive electrode film layer, the area ratio of the particles with roundness greater than or equal to 0.6 in the positive electrode film layer is 60%-90%.

Description

[0001] This application is a divisional application based on the invention with application number 202510452481.8, application date April 11, 2025, applicant CATL, and invention title "Battery cell, battery device, power consumption device and energy storage device". Technical Field

[0002] This application relates to the field of battery cell technology, and in particular to a battery cell, battery device, power consumption device, and energy storage device. Background Technology

[0003] In recent years, battery cells have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0004] With the widespread application of single-cell batteries, higher requirements are being placed on their energy density. Summary of the Invention

[0005] In view of the above-mentioned issues, this application provides a battery cell, a battery device, an electrical device, and an energy storage device, which are described below.

[0006] The first aspect of this application provides a battery cell, including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the surface of the positive current collector. The positive electrode film layer includes a positive electrode active material. Based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode active material is 97.5%-99.2%. Based on the total mass of the positive electrode film layer, the mass percentage of particles with a sphericity greater than or equal to 0.6 in the positive electrode film layer is 60%-90%.

[0007] Studies have shown that increasing the loading of positive electrode active material 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 kinetic performance of the positive electrode sheet and even the battery cell, the content of conductive agent in the positive electrode film layer is positively correlated with the loading of positive electrode active material. A high loading of positive electrode active material requires a higher content of conductive agent, which leads to a sharp reduction in the binder content and a decrease in the internal adhesion of the positive electrode film layer.

[0008] This application utilizes the principle that particles with a roundness of ≥0.6 constitute a significant portion of the positive electrode film. Increased particle roundness leads to more uniform particle arrangement and improved surface smoothness, thereby increasing the number of contact points between the particles and the current collector near the current collector and enhancing the adhesion between them. Furthermore, highly rounded particles can be tightly packed during rolling, resulting in good inter-particle contact and excellent electronic conductivity within the positive electrode film. This also helps reduce the tortuosity of the pore channels between particles, allowing for uniform distribution of the conductive agent and constructing a highly efficient conductive network, further improving electronic conductivity. Therefore, in a high-load positive electrode film, high particle sphericity allows for a reduction in the amount of conductive agent without affecting conductivity, instead increasing the binder content and thus improving the internal adhesion of the positive electrode film. Simultaneously, highly rounded particles are prone to slippage under external force, enabling increased electrode compaction density even at low rolling pressures. This ensures that the internal adhesion of the positive electrode film is maintained while keeping the battery's energy density high.

[0009] In any embodiment, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 60%-90%.

[0010] In any embodiment, based on the total mass of the positive electrode film, the mass percentage of the positive electrode active material is 98.2%-98.6%. A mass percentage of the positive electrode active material within this range further improves the battery energy density while also ensuring the internal adhesion of the positive electrode film.

[0011] In any embodiment, based on the total mass of the positive electrode film layer, the mass percentage of particles with a roundness of ≥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 particles are perfectly spherical, complete close packing cannot be achieved due to limitations in geometric arrangement. The anisotropic shape characteristics of particles with lower roundness affect their random packing behavior, meaning that a moderate deviation from spherical shape may contribute to more compact particle packing. Studies have shown that having a mass percentage of particles with a roundness of ≥0.6 in the positive electrode film layer within the range of 70%-80% can further improve the compaction density of the positive electrode film layer and the energy density of the battery cell.

[0012] In any embodiment, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 70%-80%.

[0013] In any embodiment, the ratio of the mass of particles with a roundness of ≥0.6 to the mass of particles with a roundness of ≤0.3 in the positive electrode film layer is 9-21, optionally 12-18. This can further optimize the compactness of particle packing in the positive electrode film layer. Particles with a roundness of ≤0.3, due to their diverse shapes (e.g., elliptical, wedge-shaped), can fill the gaps between high-roundness particles. The combination of high-roundness and low-roundness particles significantly improves the space utilization of the packing, thereby increasing the compaction density of the electrode and the energy density of the battery.

[0014] In any embodiment, in the cross-sectional view of the positive electrode film, the ratio of the area of ​​particles with a roundness greater than or equal to 0.6 to the area of ​​particles with a roundness less than or equal to 0.3 in the positive electrode film is 9-21.

[0015] In any embodiment, in the cross-sectional view of the positive electrode film, the ratio of the area of ​​particles with a roundness greater than or equal to 0.6 to the area of ​​particles with a roundness less than or equal to 0.3 in the positive electrode film is 12-18.

[0016] In any embodiment, based on the total mass of the positive electrode film layer, the mass percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film layer is 55%-80%. Particles with a particle size R1 satisfying 3μm≤R1≤6μm have a larger specific surface area, allowing a unit mass or volume of particles to provide more interfaces for interaction with the binder and conductive agent. With a fixed amount of binder and conductive agent, this optimizes dispersion and enhances internal adhesion. The mass percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm within the above range also helps to form a denser particle packing with particles of other sizes. This enhances the internal adhesion of the positive electrode film layer while maintaining overall stability and compaction density.

[0017] In any embodiment, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film is 55%-80%.

[0018] In any embodiment, based on the total mass of the positive electrode film, the mass percentage of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film is 5.5%-9.5%. This is beneficial for the formation of the film skeleton, enabling the film to withstand higher rolling pressure, and further improving the battery energy density by increasing the compaction density of the electrode.

[0019] In any embodiment, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film is 5.5%-9.5%.

[0020] In any embodiment, the positive electrode film layer includes a binder, and the mass content of the binder, based on the total mass of the positive electrode film layer, is 0.4%-1.5%, optionally 0.6%-1.2%. The amount of binder is positively correlated with the internal adhesion of the positive electrode film layer. If the amount of binder is too small, the internal adhesion of the positive electrode film layer is low; if the amount of binder is too large, it will worsen the electrode film resistance and reduce the loading of active material in the positive electrode film layer. The mass content of binder within the above range can maximize the internal adhesion, strengthen the adhesion between particles inside the positive electrode film layer, and further reduce the probability of particle detachment from the positive electrode film layer.

[0021] In any embodiment, the D of the positive electrode active material particles V50 The range is 0.4μm-1.5μm, with a selectable range of 0.5μm-0.9μm, where D V50 This refers to the particle size at which the cumulative volume distribution reaches 50% in the cumulative volume distribution curve. Appropriate D V50 This helps optimize particle packing, ensuring the stability and conductivity of the film structure. Overly large particles may prolong the lithium-ion diffusion path, reducing ion transport rates and leading to polarization. Conversely, overly small particles may increase specific surface area, resulting in more side reactions and affecting battery cycle life. Therefore, rationally controlling the particle size distribution is crucial for the optimal D-value of the positive electrode active material particles. V50 Within the aforementioned range, the energy density and cycle life of the battery are balanced.

[0022] In any embodiment, the positive electrode film layer includes a one-dimensional conductive agent, which 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 adhesion within the film layer.

[0023] In any embodiment, the length of the one-dimensional conductive agent is related to the D-axis of the positive electrode active material particles. V50 The ratio is 5-25, optionally 10-25. The length of the one-dimensional conductive agent reflects its "overlapping ability" and also plays a certain role in enhancing adhesion. The length of the one-dimensional conductive agent is related to the D-axis of the positive electrode active material particles. V50A higher ratio indicates that a single one-dimensional conductive agent has more material particles attached to it within its length range, resulting in a more stable internal network structure and stronger conductivity and adhesion of the positive electrode film. If the length of the one-dimensional conductive agent is too long, it is prone to agglomeration during the preparation of the positive electrode film slurry. Therefore, the length of the one-dimensional conductive agent and the ratio of the length of the particles in the positive electrode film are important factors to consider. V50 The ratio within the above range balances the processability, conductivity, and adhesion of the positive electrode film.

[0024] In any embodiment, based on the total mass of the positive electrode film, the mass percentage of the one-dimensional conductive agent is 0.2%-0.6%, optionally 0.3%-0.5%. This ensures that the positive electrode film has good electronic conductivity, and minimizes the amount of conductive agent used while keeping the total amount of the positive electrode film constant, thereby increasing the binder content and enhancing the internal adhesion of the positive electrode film.

[0025] In any embodiment, the positive electrode active material comprises a lithium-containing transition metal phosphate, wherein the lithium-containing transition metal phosphate comprises components represented by the following general formula: Li x A y Me a M b P 1-c X c Y z Formula I, Wherein, 0.1≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; Y includes one or more of O and F.

[0026] The aforementioned lithium-containing transition metal phosphate materials exhibit good thermal stability and cycle stability, which helps to improve the safety and cycle performance of batteries.

[0027] In any embodiment, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorinated vanadium phosphate, lithium manganese iron phosphate, and their modified materials.

[0028] In any embodiment, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and its modified materials.

[0029] Compared to traditional lithium-containing transition metal phosphate materials, lithium iron phosphate materials and their modified materials have good thermal and structural stability, as well as relatively high specific capacity, which is beneficial for improving energy density while enhancing battery safety and cycle performance.

[0030] In any embodiment, 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. The zero-dimensional conductive agent forms conductive paths through point contacts between particles, providing short-range conductive paths and adhesion. The one-dimensional conductive agent, on the other hand, constructs a long-range conductive network through a linear structure. Combining zero-dimensional and one-dimensional conductive agents leverages their respective advantages to construct a highly efficient conductive network, improves the overall battery performance, and further reduces the battery's internal resistance and the possibility of particle detachment from the electrode.

[0031] In any embodiment, the adhesion strength between the positive electrode film layer and the positive electrode current collector is 15 N / m-50 N / m. This indicates good adhesion performance within the positive electrode film layer and to the current collector, effectively reducing separation between the positive electrode film layer and the current collector. It also reflects the high adhesion within the positive electrode film layer, which can reduce particle delamination within the positive electrode film layer.

[0032] A second aspect of this application provides a battery device comprising the battery cell of the first aspect of this application.

[0033] A third aspect of this application provides an electrical device that includes the battery device of the second aspect of this application.

[0034] A fourth aspect of this application provides an energy storage device that includes the electrical device of the third aspect of this application.

[0035] The above description is merely an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0036] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0037] Figure 1 This is a cross-sectional polished electron microscope image of the positive electrode film layer in one embodiment of this application; Figure 2This is a schematic diagram of a battery cell according to one embodiment of this application; Figure 3 yes Figure 2 An exploded view of a battery cell according to one embodiment of this application is shown. Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application; Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application; Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown; Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0038] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0040] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

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

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

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

[0046] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

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

[0048] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 2 The example shown is a rectangular battery cell 5.

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

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

[0051] In some implementations, such as Figure 3 As shown, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

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

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

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

[0055] In some implementations, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, with the specific number adjustable according to the application and capacity of the battery module. Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

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

[0057] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0058] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0059] In recent years, the market demand for high-energy-density batteries has become increasingly strong. To obtain high-energy-density batteries, the industry commonly increases the loading of active materials in the positive electrode film. However, increasing the loading of active materials reduces the content of binders and conductive agents in the positive electrode film, leading to decreased adhesion, particle peeling within the positive electrode film, and interfacial separation at the contact surface between the positive electrode film and the current collector, thus affecting the cycle life of the battery cell. Therefore, how to fabricate battery cells that balance high energy density and high internal adhesion is a pressing technical problem that needs to be solved in this field.

[0060] The first aspect of this application provides a battery cell, the battery cell comprising a positive electrode, a negative electrode, and an electrolyte, the positive electrode comprising a positive current collector and a positive electrode film disposed on at least one side of the surface of the positive current collector, the positive electrode film comprising a positive electrode active material, the positive electrode active material comprising 97.5%-99.2% of the total mass of the positive electrode film, and the particles with a roundness greater than or equal to 0.6 comprising 60%-90% of the total mass of the positive electrode film.

[0061] Studies have shown that increasing the loading of positive electrode active material in the positive electrode film, with a mass ratio of 97.5%-99.2%, is beneficial for improving the compaction density of the positive electrode film and the energy density of the battery. However, to maintain the kinetic performance of the positive electrode sheet and even the battery cell, the content of conductive agent in the positive electrode film is positively correlated with the loading of positive electrode active material. A high loading of positive electrode active material requires a higher content of conductive agent, which leads to a sharp reduction in the binder content and a decrease in the internal adhesion of the positive electrode film.

[0062] This application achieves this by ensuring that particles with a roundness of ≥0.6 constitute a significant portion of the positive electrode film. Increased particle roundness leads to more uniform particle arrangement and improved surface smoothness, thereby increasing the number of contact points between the particles and the current collector near the current collector and enhancing the adhesion between them. Furthermore, highly rounded particles can be tightly packed during rolling, resulting in good inter-particle contact and excellent electronic conductivity within the positive electrode film. This also helps reduce the tortuosity of the pore channels between particles, allowing for uniform distribution of the conductive agent within the electrode and constructing a highly efficient conductive network, further improving electronic conductivity. Figure 1 As shown, in a high-load positive electrode film, particles with high sphericity can reduce the amount of conductive agent without affecting conductivity, thereby increasing the binder content and improving the internal adhesion of the positive electrode film. Simultaneously, highly rounded particles are prone to slippage under external force, achieving increased electrode compaction density even with low rolling pressure. This balances high energy density of the battery with good internal adhesion of the positive electrode film.

[0063] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0064] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of the positive electrode active material can be selected as 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 any value range between the above two.

[0065] Because the space of the positive electrode film per unit volume is limited, and additives such as binders and conductive agents other than the positive electrode active material cannot provide specific capacity, in order to improve the energy density of the battery, it is necessary to increase the loading of the positive electrode active material as much as possible.

[0066] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a roundness greater than or equal to 0.6 in the positive electrode film can be selected as 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value range between the above two.

[0067] In this application, "roundness" is measured as follows: A prepared positive electrode sheet, or a positive electrode sheet disassembled from a battery, is subjected to CP-SEM testing. A random number of points are photographed (≥10 points, such as 10, 20, 50, 100, etc.). AVIZO software is used to identify particles in the photographed images, and the area of ​​each particle is measured. The longest inner diameter, shortest inner diameter, and area of ​​each particle are also measured. The ratio of the shortest inner diameter to the longest inner diameter is used as the roundness of the particle. All identified particle data are obtained, and the roundness and area of ​​each particle are calculated. The ratio of the sum of the areas of all particles with a roundness greater than or equal to 0.6 in the positive electrode film to the sum of the areas of all identified particles is equivalent to the mass percentage of particles with a roundness greater than or equal to 0.6 in the positive electrode film.

[0068] In some embodiments, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 60%-90%.

[0069] In some embodiments, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film can be selected as 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value range between the above two.

[0070] Those skilled in the art can control the roundness of particles using any known process. For example, particle roundness can be adjusted through processes such as grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, and adding surfactants, as well as by adjusting the parameters of each process.

[0071] In some embodiments, the mass percentage of the positive electrode active material is 98.2%-98.6% based on the total mass of the positive electrode film.

[0072] By maintaining the above-mentioned mass ratio of positive electrode active material, the energy density of the battery is further improved, while also taking into account the internal adhesion of the positive electrode film.

[0073] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 70%-80%.

[0074] In some embodiments, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 70%-80%.

[0075] The roundness of particles in the cathode film directly affects the compaction density and energy density. Even if all particles are perfectly spherical, complete close packing cannot be achieved due to geometric constraints. The anisotropic shape characteristics of particles with lower roundness affect their random packing behavior, meaning that a moderate deviation from spherical shape may contribute to more compact particle packing. Studies have shown that when the mass proportion of particles with a roundness greater than or equal to 0.6 in the cathode film is in the range of 70%-80%, the compaction density of the cathode film and the energy density of the battery cell can be further improved.

[0076] 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 selected as 12-18.

[0077] 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 as 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or any value range between the two above.

[0078] In this 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 this application. 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 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.

[0079] In some embodiments, in the cross-sectional view of the positive electrode film, the ratio of the area of ​​particles with a roundness greater than or equal to 0.6 to the area of ​​particles with a roundness less than or equal to 0.3 in the positive electrode film is 9-21.

[0080] In some embodiments, in the cross-sectional view of the positive electrode film, the ratio of the area of ​​particles with a roundness greater than or equal to 0.6 to the area of ​​particles with a roundness less than or equal to 0.3 in the positive electrode film is 12-18.

[0081] In some embodiments, in the cross-sectional view of the positive electrode film, the ratio of the area of ​​particles with a roundness greater than or equal to 0.6 to the area of ​​particles with a roundness less than or equal to 0.3 in the positive electrode film can be selected as 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or any value range between the two above.

[0082] When the ratio of the mass of particles with a roundness of ≥0.6 to the mass of particles with a roundness of ≤0.3 in the positive electrode film layer is within the aforementioned range, the compactness of particle packing in the positive electrode film layer can be further optimized. Particles with a roundness of ≤0.3, due to their diverse shapes (e.g., elliptical, wedge-shaped), can fill the gaps between high-roundness particles. The combination of high-roundness and low-roundness particles significantly improves the space utilization of the packing, thereby increasing the compaction density of the electrode and the energy density of the battery.

[0083] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film is 55%-80%.

[0084] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film 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 any value range between the above two.

[0085] In some embodiments, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film is 55%-80%.

[0086] In some embodiments, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film 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 any value range between the above two.

[0087] In this application, based on the total mass of the positive electrode film layer, the mass percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film layer can be determined by the following method: Identify the particles in the captured image using the method described above in this application, identify the particles in the captured image using AVIZO software, and measure the particle size and area of ​​each particle. The ratio of the sum of the areas of all particles with a particle size R1 satisfying 3μm≤R1≤6μm to the sum of the areas of all identified particles is equivalent to the mass percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film layer.

[0088] Particles with a particle size R1 satisfying 3μm≤R1≤6μm have a larger specific surface area, allowing for more interfacial interactions with binders and conductive agents per unit mass or volume. With a fixed amount of binder and conductive agent, this optimizes dispersion and enhances internal adhesion. The proportion of particles with a particle size R1 satisfying 3μm≤R1≤6μm within this range also facilitates the formation of a denser particle packing with particles of other sizes. This enhances the internal adhesion of the positive electrode film while maintaining overall stability and compaction density.

[0089] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film is 5.5%-9.5%.

[0090] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film 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 any value range between the above two.

[0091] In some embodiments, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film is 5.5%-9.5%.

[0092] In some embodiments, in the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area percentage of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film 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 any value range between the above two.

[0093] In this application, based on the total mass of the positive electrode film layer, the mass percentage of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film layer can be determined by the following method: Identify the particles in the captured image using the method described above in this application, identify the particles in the captured image using AVIZO software, and measure the particle size and area of ​​each particle. The ratio of the sum of the areas of all particles with a particle size R2 satisfying 9μm≤R2≤15μm to the sum of the areas of all identified particles is equivalent to the mass percentage of particles with a particle size R2 satisfying 9μm≤R2≤15μm in the positive electrode film layer.

[0094] In the positive electrode film, the mass proportion of particles with a particle size R2 satisfying 9μm≤R2≤15μm is within the above range, which is conducive to the formation of the film skeleton, enabling the film to withstand higher rolling pressure, and further improving the battery energy density by increasing the compaction density of the electrode sheet.

[0095] In some embodiments, the positive electrode film layer includes a binder, and the mass content of the binder is 0.4%-1.5%, optionally 0.6%-1.2%, based on the total mass of the positive electrode film layer.

[0096] In some embodiments, the positive electrode film layer includes a binder, and the mass content of the binder, based on the total mass of the positive electrode film layer, can be selected as 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 any value range between the above two.

[0097] The amount of binder is positively correlated with the internal adhesion of the positive electrode film. Too little binder results in low internal adhesion, while too much binder worsens the electrode film resistance and reduces the loading of active material in the positive electrode film. Maintaining the binder content within the specified range maximizes internal adhesion, strengthens the bond between particles within the positive electrode film, and further reduces the probability of particle detachment.

[0098] In some embodiments, the D of the positive electrode active material particles V50 The range is 0.4μm-1.5μm, with a selectable range of 0.5μm-0.9μm, where D V50 This refers to the particle size at which the cumulative volume distribution reaches 50% in the cumulative volume distribution curve.

[0099] In some embodiments, the D of the positive electrode active material particles V50 The value can be selected as 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm or any value range between the two above.

[0100] Appropriate D V50 This helps optimize particle packing, ensuring the stability and conductivity of the film structure. Overly large particles may prolong the lithium-ion diffusion path, reducing ion transport rates and leading to polarization. Conversely, overly small particles may increase specific surface area, resulting in more side reactions and affecting battery cycle life. Therefore, rationally controlling the particle size distribution is crucial for the optimal D-value of the positive electrode active material particles. V50 Within the aforementioned range, the energy density and cycle life of the battery are balanced.

[0101] In some embodiments, the positive electrode film layer includes a one-dimensional conductive agent, which includes one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0102] In this application, the term "one-dimensional conductive agent" refers to a conductive material that has a significant single dimension in space, while exhibiting nanoscale conductivity in the other two dimensions. One-dimensional conductive agents include, but are not limited to, single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0103] One-dimensional conductive agents construct long-range conductive networks through linear structures. In addition to enhancing conductivity, they also improve the adhesion within the film layer.

[0104] In some embodiments, the length of the one-dimensional conductive agent is related to the D-axis of the positive electrode active material particles. V50 The ratio is 5-25, and can be selected as 10-25.

[0105] In some embodiments, the length of the one-dimensional conductive agent is related to the D-axis 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 any value range between the two mentioned above.

[0106] The length of the one-dimensional conductive agent reflects its "overlapping ability" and also plays a role in enhancing adhesion. The length of the one-dimensional conductive agent is related to the D-axis of the positive electrode active material particles. V50 A higher ratio indicates that a single one-dimensional conductive agent has more material particles attached to it within its length range, resulting in a more stable internal network structure and stronger conductivity and adhesion of the positive electrode film. If the length of the one-dimensional conductive agent is too long, it is prone to agglomeration during the preparation of the positive electrode film slurry. Therefore, the length of the one-dimensional conductive agent and the ratio of the length of the particles in the positive electrode film are important factors to consider. V50 The ratio within the above range balances the processability, conductivity, and adhesion of the positive electrode film.

[0107] Based on the total mass of the positive electrode film, the mass percentage of the one-dimensional conductive agent is 0.2%-0.6%, and can be selected as 0.3%-0.5%.

[0108] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of the one-dimensional conductive agent can be selected as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or any value range between the two above.

[0109] Based on the total mass of the positive electrode film, the mass content of the one-dimensional conductive agent is within the above range, which makes the positive electrode film have good electronic conductivity, and reduces the amount of conductive agent as much as possible to increase the binder content and enhance the internal adhesion of the positive electrode film while keeping the total amount of the positive electrode film unchanged.

[0110] In some embodiments, the positive electrode active material comprises a lithium-containing transition metal phosphate, wherein the lithium-containing transition metal phosphate comprises components represented by the following general formula: Li x A y Me a M b P 1-c X c Y z Formula I, Wherein, 0.1≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; Y includes one or more of O and F.

[0111] Lithium-containing transition metal phosphates refer to phosphate materials containing lithium and transition metal elements. They are characterized by structural stability, good safety, and long cycle life, and have been widely used in lithium-ion batteries. They can be detected by any method known in the art. For example, they can be detected by combining X-ray diffraction (XRD) with energy dispersive spectroscopy (EDS) or inductively coupled plasma mass spectrometry (ICP-MS).

[0112] In some implementations, x can be selected as 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.15, 1.3 or any value range between the above two.

[0113] In some implementations, y can be selected as 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.15, 1.3 or any value range between the above two.

[0114] In some implementations, x+y can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3 or any value range between the above two.

[0115] In some implementations, 'a' can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or any value range between the two above.

[0116] In some implementations, b can be selected as 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or any value range between the above two.

[0117] In some implementations, a+b can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or any value range between the above two.

[0118] In some implementations, c can be selected as 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or any value range between the above two.

[0119] In some implementations, z can be selected as 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, or a range of any two of the above.

[0120] In some embodiments, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorinated vanadium phosphate, lithium manganese iron phosphate, and their modified materials.

[0121] The aforementioned lithium-containing transition metal phosphate materials exhibit good thermal stability and cycle stability, which helps to improve the safety and cycle performance of batteries.

[0122] In some embodiments, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and its modified materials.

[0123] Compared to traditional lithium-containing transition metal phosphate materials, lithium iron phosphate materials and their modified materials have good thermal and structural stability, as well as relatively high specific capacity, which is beneficial for improving energy density while enhancing battery safety and cycle performance.

[0124] 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.

[0125] In some embodiments, the particle size D of the first lithium transition metal phosphate particle V50 The range is 0.4μm-0.75μm.

[0126] In some embodiments, the particle size D of the first lithium transition metal phosphate particle is... V50 The value can be selected as any value between two of the following: 0.40μm, 0.45μm, 0.50μm, 0.55μm, 0.60μm, 0.65μm, 0.70μm, and 0.75μm.

[0127] In some embodiments, the particle size D of the second lithium transition metal phosphate particle V50 The size is 1μm-1.5μm.

[0128] In some embodiments, the particle size D of the second lithium transition metal phosphate particle V50 The value can be selected as 1μm, 1.05μm, 1.10μm, 1.15μm, 1.20μm, 1.25μm, 1.30μm, 1.35μm, 1.40μm, 1.45μm, 1.5μm or any value range between the two above.

[0129] Using a combination of first lithium-containing transition metal phosphate particles and second lithium-containing transition metal phosphate particles that meet the above particle size range is beneficial to improving particle gradation, achieving close packing of particles in the positive electrode film layer, further improving the compaction density of the electrode sheet, and thus improving the energy density of the battery.

[0130] In some embodiments, the first lithium transition metal phosphate particles account for 55%-80% of the total mass of the positive electrode film.

[0131] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of the first lithium transition metal phosphate particles can be selected as 55%, 60%, 65%, 70%, 75%, 80%, or any value range between the above two.

[0132] In some embodiments, the mass percentage of the second lithium-containing transition metal phosphate particles is 20%-45% based on the total mass of the positive electrode film.

[0133] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of the second lithium transition metal phosphate particles can be selected as 20%, 25%, 30%, 35%, 40%, 45%, or any value range between the two mentioned above.

[0134] Controlling the mass content of the first lithium-containing transition metal phosphate particles and the second lithium-containing transition metal phosphate particles to meet the above-mentioned ranges is beneficial to improving the compaction density of the electrode sheet, thus enabling the battery to have excellent energy density.

[0135] In some embodiments, based on the mass of the first lithium transition metal phosphate particles, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium transition metal phosphate is 60%-90%.

[0136] In some embodiments, based on the mass of the first lithium transition metal phosphate particles, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium transition metal phosphate can be selected as 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value range between the above two.

[0137] In some embodiments, based on the mass of the second lithium transition metal phosphate particles, the mass percentage of particles with a roundness greater than or equal to 0.6 in the second lithium transition metal phosphate can be selected as 60%-90%.

[0138] In some embodiments, based on the mass of the second lithium transition metal phosphate particles, the mass percentage of particles with a roundness greater than or equal to 0.6 in the second lithium transition metal phosphate can be selected as 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value range between the above two.

[0139] The proportions of particles with a roundness greater than or equal to 0.6 in the first and second lithium-containing transition metal phosphate particles of the positive electrode film are within the aforementioned range. This is beneficial for reducing the porosity of the film by improving the slipability of the particles during the preparation of the positive electrode film, thereby achieving high compaction density. At the same time, it helps to reduce the tortuosity of the pore channels between particles, which is conducive to the uniform distribution of conductive agent in the electrode and the effective construction of conductive network, thereby improving electronic conductivity. With the total amount of positive electrode film remaining unchanged, the amount of binder can be increased and the amount of conductive agent can be reduced, thereby improving the adhesion of the positive electrode film and the energy density of the battery.

[0140] In some embodiments, 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, and optionally the zero-dimensional conductive agent includes conductive carbon black.

[0141] In this application, the term "zero-dimensional conductive agent" refers to a conductive material with a zero-dimensional structure, characterized by its similar size in all directions and a point-like structure. These conductive agents improve the conductivity of the material through point contacts between particles.

[0142] Zero-dimensional conductive agents form conductive paths through point contacts between particles, providing short-range conductive paths and adhesion. Combining zero-dimensional and one-dimensional conductive agents leverages their respective advantages to construct a highly efficient conductive network, improving overall battery performance and further reducing internal resistance and the likelihood of particle detachment from the electrodes.

[0143] In some embodiments, the bonding strength between the positive electrode film and the positive electrode current collector is 15 N / m to 50 N / m.

[0144] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector can be selected as 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 any value range between the above two.

[0145] The adhesion strength in the embodiments of this application is within the above-mentioned range, indicating good adhesion performance inside the positive electrode film and to the current collector, which can effectively improve the separation phenomenon between the positive electrode film and the current collector. It also reflects the high adhesion inside the positive electrode film, which can reduce particle peeling in the positive electrode film.

[0146] In some embodiments, the cold-pressed compaction density of the positive electrode sheet is 2.55 g / cm³. 3 -2.75g / cm 3 .

[0147] In some embodiments, the cold-pressed compaction density of the positive electrode sheet can be selected as 2.55 g / cm³. 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 2.60g / cm 3 2.61 g / cm 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 2.66 g / cm 3 2.67 g / cm 3 2.68g / cm 3 2.69 g / cm3 2.70 g / cm 3 2.71 g / cm 3 2.72 g / cm 3 2.73 g / cm 3 2.74 g / cm 3 2.75g / cm 3 Or the range of values ​​between any two of the above.

[0148] In this application, the compaction density after cold pressing can be tested using methods known in the art. As an example, the positive electrode obtained after cold pressing is cut into small circular pieces with an area of ​​S, and its mass is obtained as W1. The thickness T1 of the positive electrode is measured using a micrometer. Then, the positive electrode film layer of the weighed electrode is wiped off, the mass of the current collector is weighed and recorded as W2, and the thickness T2 of the current collector is measured using a micrometer. Then, the compaction density PD of the positive electrode film layer is PD = (W1-W2) / [(T1-T2)×S].

[0149] In the process of preparing a battery cell, after the positive electrode slurry is coated onto the positive electrode current collector, it is vacuum dried, cold-pressed, slit, and prepared into a positive electrode sheet. The compaction density obtained in the cold pressing step will be different from the compaction density when the positive electrode sheet is fully displaced. This is because after the electrode sheet is made, due to charging and discharging, the positive electrode sheet will exhibit a slight rebound phenomenon. At this time, the compaction density of the positive electrode film layer in the fully displaced state will be slightly lower than the compaction density of the initial cold pressing.

[0150] In some embodiments, the compacted density of the positive electrode sheet in its fully packed state is 2.40 g / cm³. 3 -2.65g / cm 3 .

[0151] In some embodiments, the compacted density of the positive electrode sheet in its fully packed state is 2.40 g / cm³. 3 2.41 g / cm 3 2.42 g / cm 3 2.43 g / cm 3 2.44 g / cm 3 2.45g / cm 3 2.46 g / cm 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.50g / cm 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 3 2.54 g / cm3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 2.60g / cm 3 2.61 g / cm 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 Or the range of values ​​between any two of the above.

[0152] In this application, the fully discharged state refers to the state in which the battery is placed at 25°C, left to stand for 2 hours, and then discharged at a constant current of 1 / 3C to 2.5V after the battery temperature is maintained at 25°C. After standing for 30 minutes, the battery is discharged at a constant current of 0.04C to 2.5V.

[0153] In this application, the compaction density of the positive electrode film layer under full-displacement state can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven environment and left to stand for 2 hours. After the battery temperature is maintained at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.5V and left to stand for 30 minutes. Then, it is discharged at a constant current of 0.04C to 2.5V. The battery is disassembled to obtain the positive electrode sheet. The residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and it is cut into small circular pieces with an area of ​​S. The mass of the circular pieces is obtained as W1, and the thickness of the positive electrode sheet is measured using a micrometer. Then, the positive electrode film layer of the above-weighed electrode sheet is wiped off, the mass of the current collector is weighed and recorded as W2, and the thickness of the current collector is measured using a micrometer. Then, the compaction density of the positive electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0154] The compaction density of the positive electrode sheet within the above range is beneficial to improving the yield rate during the electrode sheet cutting process while maintaining the high energy density of the battery cell, thus meeting performance and efficiency requirements.

[0155] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0156] [Negative electrode plate] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0157] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0158] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0159] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0160] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0161] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0162] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0163] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0164] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0165] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0166] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0167] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0168] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0169] [Isolation membrane] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0170] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0171] [Battery cell] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0172] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0173] In some embodiments, the volumetric energy density of the battery cell is 650Wh / L-720Wh / L.

[0174] This application does not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape.

[0175] [Battery Device] This application also provides a battery device, which includes the battery cell provided in this application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0176] [Electrical appliances] In addition, this application embodiment also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application embodiment. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0177] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0178] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0179] This application also provides an energy storage device, which includes the battery device provided in this application.

[0180] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0181] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0182] In the embodiments of this application, the roundness ratio of the positive electrode active material is controlled in the following way: YHC-92 type lithium iron phosphate (D) produced by Hunan Yuneng New Energy Battery Materials Co., Ltd. is selected. V50 =0.55μm, average roundness 0.92), YHC-53 type lithium iron phosphate (D V50 =0.55μm, average roundness 0.53), YHC-21 type lithium iron phosphate (D V50 =0.55μm, average roundness 0.21); ZLC-95 type lithium iron phosphate (D V50 =1.25μm, average roundness 0.95), ZLC-56 type lithium iron phosphate (D V50 =1.25μm, average roundness 0.56), ZLC-16 type lithium iron phosphate (D V50 =1.25μm, average roundness 0.16); the particles were manually mixed according to the proportion of roundness particles of the positive electrode active material used in the examples. As an example, when the required positive electrode active material is D... V50 In lithium iron phosphate particles with a diameter of 0.55 μm, particles with a roundness of ≥0.6 account for 80% of the mass, and the ratio of the mass of particles with a roundness of ≥0.6 to the mass of particles with a roundness of ≤0.3 is 15. Based on the total mass of the positive electrode active material, YHC-92 lithium iron phosphate with a mass ratio of 80% and YHC-21 lithium iron phosphate with a mass ratio of 5.3% are selected, and YHC-53 lithium iron phosphate is used to fill the remaining mass ratio. The mixture is then mixed and tested. When the roundness of the mixture meets the requirements, it is stored as a raw material for the subsequent preparation of the electrode sheet.

[0183] Example 1 1) Preparation of positive electrode sheet Preparation of positive electrode film slurry: D V50 The first lithium iron phosphate particle (LiFePO4) is 0.55 μm, and D V50Lithium iron phosphate particles (LiFePO4) with a diameter of 1.25 μm were mixed at a mass ratio of 7:3 to obtain a positive electrode active material. The positive electrode active material, a one-dimensional conductive agent, a zero-dimensional conductive agent, and a binder PVDF were mixed at a mass ratio of 98.4:0.3:0.3:1. NMP solvent was added, and the mixture was stirred under vacuum until the system was homogeneous to obtain a positive electrode film slurry. Wherein, the zero-dimensional conductive agent is a Super-P conductive agent, the one-dimensional conductive agent is a carbon nanotube conductive agent, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 80%, and the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 15; the mass percentage of particles with a roundness greater than or equal to 0.3 in the second lithium iron phosphate particles is 80%, and the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles 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-value of the positive electrode active material particles is... V50 The ratio is 15.

[0184] The positive electrode film slurry was uniformly coated on the surface of the undercoat layer away from the positive electrode current collector, with a single-sided coating weight of 300 mg / 1540.25 mm. 2 After being air-dried at room temperature, the material was transferred to an oven for further drying, and then cold-pressed to obtain the positive electrode sheet. The thickness of the positive electrode film on one side after cold pressing was 70.8 μm, and the cold-pressed compaction density of the positive electrode film was 2.75 g / cm³. 3 The single-sided coating quality here does not include the solvent quality, but only the solid content quality of the coating.

[0185] Electrode slitting (one-out-two): The positive electrode is slitting on a slitting machine at a speed of 0.5 m / s. The slitting blade is made of steel, and the slitting machine is under a negative pressure of -10 kPa. Electrode cutting: The slit electrode sheets are wound and cut, with a winding speed of 0.6m / s, a core length of 3m, and a steel blade. The winding machine is under a negative pressure of -10kPa.

[0186] 2) Preparation of negative electrode sheet Graphite anode active material, polyvinyl alcohol binder, and SP-Li conductive agent were thoroughly mixed and ball-milled in a deionized water solvent system at a mass ratio of 90:5:5 to obtain anode slurry. The anode slurry was then mixed at a concentration of 140 mg / 1540.25 mm. 2 The single-sided coating weight is applied to the copper foil surface and vacuum dried overnight at 110°C to obtain the negative electrode sheet.

[0187] 3) Preparation of the diaphragm A polyethylene film with a thickness of 13 μm was used as the diaphragm.

[0188] 4) Preparation of electrolyte Lithium hexafluorophosphate (LiPF6) was dissolved in ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 to form a homogeneous solution, resulting in an electrolyte with a LiPF6 concentration of 1 mol / L.

[0189] 5) Battery assembly The electrodes are arranged in the order of "separator-negative electrode-separator-positive electrode". One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft to wind the positive electrode, negative electrode, and two separators, resulting in a wound bare cell. The bare cell is placed in an outer packaging, injected with the electrolyte, and sealed to obtain a battery cell.

[0190] The preparation method of Example 2 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass ratio of the positive active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 97.5:0.6:0.3:1.6; and the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0191] The preparation method of Example 3 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass ratio of the positive electrode active material, conductive carbon black, carbon nanotube conductive agent, and PVDF binder is 98.8:0.2:0.3:0.7; and the cold-pressed compaction density of the positive electrode film is 2.75 g / cm³. 3 .

[0192] The preparation method of Example 4 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 60%; the mass percentage of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 60%; and the cold-pressed compaction density of the positive electrode film is 2.68 g / cm³. 3 .

[0193] The preparation method of Example 5 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 70%; the mass percentage of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 70%; and the cold-pressed compaction density of the positive electrode film is 2.72 g / cm³. 3 .

[0194] The preparation method of Example 6 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 90%; the mass percentage of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 90%; and the cold-pressed compaction density of the positive electrode film is 2.70 g / cm³. 3 .

[0195] The preparation method of Example 7 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 9; the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 9; and the cold-pressed compaction density of the positive electrode film is 2.68 g / cm³. 3 .

[0196] The preparation method of Example 8 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 12; the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 12; and the cold-pressed compaction density of the positive electrode film is 2.72 g / cm³. 3 .

[0197] The preparation method of Example 9 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 18; the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 18; and the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0198] The preparation method of Example 10 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 2:1; the mass ratio of particles with a roundness greater than or equal to 0.6 to particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is also 2:1; and the cold-pressed compaction density of the positive electrode film is 2.70 g / cm³. 3 .

[0199] The preparation method of Example 11 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass ratio of the first lithium iron phosphate particles to the second lithium iron phosphate particles is 6.7:3.3; and the cold-pressed compaction density of the positive electrode film is 2.68 g / cm³. 3 .

[0200] 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... V50 The thickness is 0.63 μm; the cold-pressed compaction density of the positive electrode film is 2.65 g / cm³. 3 .

[0201] 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 steps of the positive electrode film slurry, the D of the second lithium iron phosphate particles... V50 The thickness is 0.95 μm; the cold-pressed compaction density of the positive electrode film is 2.68 g / cm³. 3 .

[0202] The preparation method of Example 14 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the D of the second lithium iron phosphate particles... V50 The thickness is 1.15 μm; the cold-pressed compaction density of the positive electrode film is 2.70 g / cm³. 3 .

[0203] The preparation method of Example 15 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation steps of the positive electrode film slurry, the D of the second lithium iron phosphate particles... V50 The thickness is 1.35 μm; the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0204] The preparation method of Example 16 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the D of the second lithium iron phosphate particles... V50 The thickness is 1.50 μm; the cold-pressed compaction density of the positive electrode film is 2.70 g / cm³. 3 .

[0205] 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 related to the D-axis of the positive electrode active material particles. V50 The ratio is 5; the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0206] 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 related to the D-axis of the positive electrode active material particles. V50 The ratio is 10; the cold-pressed compaction density of the positive electrode film is 2.75 g / cm³. 3 .

[0207] The preparation method of Example 19 is basically the same as that of Example 1, except that in the preparation steps of the positive electrode sheet and the positive electrode film slurry, the length of the one-dimensional conductive agent is related to the D-axis of the positive electrode active material particles. V50 The ratio is 20; the cold-pressed compaction density of the positive electrode film is 2.71 g / cm³. 3 .

[0208] 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 related to the D-axis of the positive electrode active material particles. V50 The ratio is 25; the cold-pressed compaction density of the positive electrode film is 2.72 g / cm³. 3 .

[0209] 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 of the positive electrode film slurry, the mass ratio of the positive active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 98.4:0.2:0.5:1; and the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0210] 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 of the positive electrode film slurry, the mass ratio of the positive active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 98.4:0.4:0.3:1; and the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0211] 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 of the positive electrode film slurry, the mass ratio of the positive active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 98.4:0.5:0.1:1; and the cold-pressed compaction density of the positive electrode film is 2.72 g / cm³. 3 .

[0212] 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 of the positive electrode film slurry, the mass ratio of the positive active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 98.4:0.6:0:1; and the cold-pressed compaction density of the positive electrode film is 2.70 g / cm³. 3 .

[0213] 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 of the positive electrode film slurry, the mass ratio of the positive active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 97:0.6:0.3:2.1; and the cold-pressed compaction density of the positive electrode film is 2.72 g / cm³. 3 .

[0214] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 50%; the mass percentage of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 50%; and the cold-pressed compaction density of the positive electrode film is 2.73 g / cm³. 3 .

[0215] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, the mass percentage of particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 95%; the mass percentage of particles with a roundness greater than or equal to 0.6 in the second lithium iron phosphate particles is 95%; and the cold-pressed compaction density of the positive electrode film is 2.63 g / cm³. 3 .

[0216] Performance testing 1. CP-SEM characterization method for cross-section of positive electrode sheet The sample to be characterized was prepared as follows: First, the positive electrode sheet was cut into a 2cm × 2cm sample and fixed on the sample stage with paraffin wax. Then, the sample stage was installed in the sample holder and locked in place. The power supply of the IB-19500CP argon ion cross-section polisher was turned on and a vacuum was drawn. The argon flow rate was set to 0.15MPa, the control voltage to 8kV, and the polishing time to 2 hours. The sample stage was adjusted to the swing mode to start polishing. After polishing, the sample to be characterized was obtained.

[0217] Microscopic morphology characterization: The samples were characterized using a ZEISS Sigma300 scanning electron microscope. Sample testing can be performed according to JY / T010-1996. To ensure the accuracy of the test results, multiple different regions were randomly selected from the sample for scanning tests, and cross-sectional morphology images were taken at a fixed magnification of 5kx.

[0218] 2. Roundness Test Method At 25°C, slit positive electrode sheets prepared in each embodiment and comparative example were subjected to CP-SEM testing. A random number of points were photographed (≥10 points, e.g., 10, 20, 50, 100, etc.). AVIZO software was used to identify particles in the captured images, and the shortest diameter, longest diameter, and area of ​​each particle were measured. Roundness was calculated as shortest diameter / longest diameter. The ratio of the sum of the areas of all particles with a roundness greater than or equal to 0.6 to the sum of the areas of all identified particles was used as the mass percentage of particles with a roundness greater than or equal to 0.6 in the positive electrode film. Similarly, the mass percentage of particles with a roundness less than or equal to 0.3 in the positive electrode film was obtained.

[0219] 3. Electrode bonding strength test At 25°C, take the cold-pressed positive electrode sheets prepared in each embodiment and comparative example, and cut them into test specimens with a length L: 100mm and a width W: 20mm, for later use; stick one side of the double-sided adhesive to the surface of the steel plate, and stick the electrode sheet to be tested to the other side, and press it with a pressure roller to make it completely adhered to the electrode sheet; bend one end of the current collector in the opposite direction with a bending angle of 180°; use a high-speed rail tensile testing machine to test, fix one end of the steel plate to the lower clamp of the tensile testing machine, fix the bent end of the current collector to the upper clamp, adjust the angle of the current collector to ensure that the upper and lower ends are in a vertical position, and then stretch the specimen at a speed of 50mm / min until the current collector is completely peeled off from the surface of the electrode sheet, record the displacement and force during the process, and take the strength when the force is balanced as the bonding force of the electrode sheet as N1. The bonding strength of the electrode sheet can be calculated using the formula N1 / W.

[0220] 4. Electrode powder shedding test At 25°C, the cold-pressed positive electrode sheets prepared in each embodiment and comparative example were taken and sheared using a die-cutting and wrapping integrated machine. The shearing speed was set to 0.5 m / s, the pressure of the shearing machine was -10 kPa, and the number of shearing blades was 2000. The powder dropped after shearing was collected and weighed and recorded as W. The percentage of leaked metal was recorded as W g / 2000 blades.

[0221] 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 the charging cutoff voltage of 4.3V, and then charged at a constant voltage of the same voltage until the current was 0.05C. They were then discharged at 1 / 3C to 50% SOC, left to stand for 5 minutes, and then pulsed discharged at 3C for 30 seconds.

[0222] Record the voltage before and after each pulse discharge, and calculate the DCR under different conditions. The calculation formula is DCR = (voltage before pulse discharge after resting - voltage before resting after pulse discharge) / pulse current.

[0223] 6. Battery Energy Density Test Method The battery cells prepared in each embodiment and comparative example were left to stand at 25°C for 2 hours to ensure the temperature of the battery cells remained at 25°C. At 25°C, the battery cells were charged at 1 / 3C to the charging cutoff voltage of 3.65V, and then continued to be charged at this charging cutoff voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of the battery cell). After the battery cells were left to stand at 25°C for 1 hour, they were discharged at 25°C at 0.33C to the discharge cutoff voltage of 2.5V, and the total discharge energy of the battery cells was recorded as E0.

[0224] Measure the length, width, and height of the battery cell, and calculate the volume of the battery cell, V0 = length × width × height.

[0225] The volumetric energy density of a single battery cell = discharge energy of the single battery cell E0 / volume of the single battery cell V0.

[0226] The battery cells for each embodiment and comparative example were prepared according to the above method. The specific parameters and performance are shown in Tables 1, 2 and 3 below. Table 1

[0227] By comparing the examples and comparative examples, it can be seen that, based on the total mass of the positive electrode film, the mass ratio of the positive electrode active material is controlled to be 97.5%-99.2%, and the mass ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 60%-90%. While the battery has a high energy density, the problem of powder shedding caused by the decrease in internal adhesion due to the high active material loading can be improved.

[0228] By comparing Examples 1 and 4-6, it can be seen that, based on the total mass of the positive electrode film, when the mass ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 70%-80%, it is beneficial to further improve the energy density of the battery while maintaining a low amount of powder removal.

[0229] By comparing Examples 1 and 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, and a further ratio of 12-18 is beneficial to forming a more compact packing, thereby improving the energy density of the battery.

[0230] Table 2

[0231] By comparing Examples 1 and 11-12, it can be seen that, based on the total mass of the positive electrode film, when the mass percentage of particles with a particle size R1 satisfying 3μm≤R1≤6μm in the positive electrode film is 55%-80%, it is beneficial to achieve a balance between bonding strength and battery energy density.

[0232] By comparing Examples 1 and 13-16, it can be seen that, based on the total mass of the positive electrode film, when the mass percentage of particles with a particle size R2 satisfying 3μm≤R1≤6μm in the positive electrode film is 5.5%-9.5%, it is beneficial to improve the volumetric energy density of the battery.

[0233] By comparing Examples 1 and 17-20, it can be seen that the length of the one-dimensional conductive agent is related to the D-axis of the particles in the positive electrode film. V50 When the ratio is 5-25, and even further when the ratio is 10-25, it is beneficial to improve the bonding strength and reduce the amount of powder falling off.

[0234] Table 3

[0235] By comparing Examples 1 and Examples 21-24, it can be seen that, based on the total mass of the positive electrode film, when the mass percentage of the one-dimensional conductive agent is 0.2%-0.6%, the technical effects of enhanced bonding strength and reduced DC internal resistance can be achieved. When the mass percentage of the one-dimensional conductive agent is 0.3%-0.5%, low cost, low powder removal, and low DC internal resistance can be achieved simultaneously.

[0236] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, said battery cell comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the surface of the positive current collector. In the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 60%-90%.

2. The battery cell according to claim 1, characterized in that, The positive electrode film layer includes a positive electrode active material. Based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode active material is 97.5%-99.2%, and optionally 98.2%-98.6%.

3. The battery cell according to claim 1 or 2, characterized in that, In the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a roundness greater than or equal to 0.6 in the positive electrode film is 70%-80%.

4. The battery cell according to any one of claims 1 to 3, characterized in that, In the cross-sectional view of the positive electrode film, the ratio of the area of ​​particles with a roundness greater than or equal to 0.6 to the area of ​​particles with a roundness less than or equal to 0.3 is 9-21.

5. The battery cell according to any one of claims 1 to 4, characterized in that, In the cross-sectional view of the positive electrode film, the ratio of the area of ​​particles with a roundness greater than or equal to 0.6 to the area of ​​particles with a roundness less than or equal to 0.3 is 12-18.

6. The battery cell according to any one of claims 1 to 5, characterized in that, In the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a particle size R1 satisfying 3μm≤R1≤6μm is 55%-80%.

7. The battery cell according to any one of claims 1 to 6, characterized in that, In the cross-sectional view of the positive electrode film, based on the total area of ​​the particles in the positive electrode film, the area ratio of particles with a particle size R2 satisfying 9μm≤R2≤15μm is 5.5%-9.5%.

8. The battery cell according to any one of claims 1 to 7, characterized in that, The positive electrode film layer includes a binder, and the mass percentage of the binder is 0.4%-1.5% based on the total mass of the positive electrode film layer.

9. The battery cell according to any one of claims 1 to 8, characterized in that, The positive electrode film layer includes a binder, and the mass percentage of the binder is 0.6%-1.2% based on the total mass of the positive electrode film layer.

10. The battery cell according to any one of claims 1 to 9, characterized in that, The positive electrode active material particles D V50 The range is 0.4μm-1.5μm, where D V50 This refers to the particle size at which the cumulative volume distribution reaches 50% in the cumulative volume distribution curve.

11. The battery cell according to any one of claims 1 to 10, characterized in that, The positive electrode active material particles D V50 The range is 0.5μm-0.9μm, where D V50 This refers to the particle size at which the cumulative volume distribution reaches 50% in the cumulative volume 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, which 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 of the positive electrode active material particles. V50 The ratio is 5-25.

14. The battery cell according to claim 12 or 13, characterized in that, The length of the one-dimensional conductive agent is related to the D of the positive electrode active material particles. V50 The ratio is 10-25.

15. The battery cell according to any one of claims 12 to 14, characterized in that, Based on the total mass of the positive electrode film, the mass percentage of the one-dimensional conductive agent is 0.2%-0.6%.

16. The battery cell according to any one of claims 12 to 15, characterized in that, Based on the total mass of the positive electrode film, the mass percentage of the one-dimensional conductive agent is 0.3%-0.5%.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The positive electrode active material includes lithium-containing transition metal phosphates.

18. The battery cell according to claim 17, characterized in that, The lithium-containing transition metal phosphate comprises components represented by the following general formula: Li x A y Me a M b P 1-c X c Y z Formula I Wherein, 0.1≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; Y includes one or more of O and F.

19. The battery cell according to claim 17 or 18, characterized in that, The lithium-containing transition metal phosphates include one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorinated vanadium phosphate, lithium manganese iron phosphate, and their modified materials.

20. The battery cell according to any one of claims 17 to 19, characterized in that, The lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and its modified materials.

21. The battery cell according to any one of claims 1 to 20, 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, and optionally includes conductive carbon black.

22. The battery cell according to any one of claims 1 to 21, characterized in that, The cold-pressed compaction density of the positive electrode sheet is 2.55 g / cm³. 3 -2.75g / cm 3 .

23. The battery cell according to any one of claims 1 to 22, characterized in that, The compacted density of the positive electrode sheet in its fully loaded state is 2.40 g / cm³. 3 -2.65g / cm 3 .

24. The battery cell according to any one of claims 1 to 23, characterized in that, The bonding strength between the positive electrode film and the positive electrode current collector is 15 N / m-50 N / m.

25. The battery cell according to any one of claims 1 to 24, characterized in that, The battery cell also includes a separator, and the battery cell includes a wound bare cell, which is formed by the positive electrode, the negative electrode and the separator.

26. The battery cell according to any one of claims 1 to 25, characterized in that, The wound bare battery cell is formed by winding the positive electrode, the negative electrode, and the separator.

27. The battery cell according to any one of claims 1 to 26, characterized in that, The wound bare cell is formed by winding the positive electrode, the negative electrode, and the two separators.

28. The battery cell according to any one of claims 1 to 27, characterized in that, The volumetric energy density of the battery cell is 180Wh / L-200Wh / L.

29. A battery device, characterized in that, Includes the battery cell as described in any one of claims 1 to 28.

30. An electrical device, characterized in that, The electrical device includes the battery device as described in claim 28, the battery device being used to provide electrical energy.

31. An energy storage device, characterized in that, The energy storage device includes the electrical device as described in claim 28, the electrical device being used to store electrical energy.

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