Battery cell, battery device, power consuming device, and energy storage device

Abstract

The disclosure provides a battery monomer, a battery device, a power consumption device and an energy storage device, the battery monomer comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the mass percentage of the positive electrode active material being 97.5%-99.2% based on the total mass of the positive electrode film layer; the mass percentage of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer being 60%-90% based on the total mass of the positive electrode film layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery monomer, in particular to a battery monomer, a battery device, a power utilization device and an energy storage device. BACKGROUND

[0002] In recent years, battery monomers are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] With the popularization of monomer batteries, higher requirements are put forward for their energy density. SUMMARY

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

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

[0006] Studies have shown that by increasing the loading amount of the positive electrode active material in the positive electrode film layer, it is beneficial to increase 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 thus the battery monomer, the content of the conductive agent in the positive electrode film layer is positively correlated with the loading amount of the positive electrode active material. High loading amount of the positive electrode active material requires higher content of the conductive agent, thereby leading to a sharp decrease in the content of the binder and a decrease in the internal adhesion of the positive electrode film layer.

[0007] The particles with a roundness greater than or equal to 0.6 in the positive electrode film layer have a mass ratio in the above range, the increase in the roundness of the particles on one hand makes the arrangement of the particles in the positive electrode film layer more uniform, the flatness of the film layer surface is improved, thereby increasing the number of contact points of the particles close to the current collector with the current collector, increasing the adhesion between the positive electrode film layer and the current collector. On the other hand, the particles with high roundness can be tightly packed in the rolling, the particles are in good contact with each other, so that the particles in the positive electrode film layer have good electron conductivity, and the bending degree of the pore channel between the particles is reduced, the conductive agent is uniformly distributed in the electrode, a high-efficiency conductive network is constructed, and the electron conductivity is further improved. Therefore, in the positive electrode film layer with high loading, the particles with high sphericity can reduce the amount of conductive agent without affecting the conductivity, thereby increasing the content of the binder, thereby improving the internal adhesion of the positive electrode film layer. At the same time, the particles with high roundness are easy to slip under external force, and the compaction density of the electrode sheet can be improved under low rolling pressure. Thus, the internal adhesion of the positive electrode film layer is considered under the condition of maintaining the high energy density of the battery.

[0008] In any embodiment, the mass ratio of the positive electrode active material is 98.2%-98.6% based on the total mass of the positive electrode film layer. The mass ratio of the positive electrode active material in the above range further improves the energy density of the battery, and the internal adhesion of the positive electrode film layer is considered.

[0009] In any embodiment, the mass ratio of the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 70%-80% based on the total mass of the positive electrode film layer. The roundness of the particles in the positive electrode film layer has a direct impact on the compaction density and energy density. Even if all the particles are perfect spheres, the geometric arrangement is limited and cannot achieve complete close packing. The anisotropic shape characteristics of the particles with small roundness will affect the random packing behavior, which means that moderate deviation from the spherical shape may help the particles to pack more tightly. Studies have shown that the mass ratio of the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer in the range of 70%-80% can further improve the compaction density of the positive electrode film layer and the energy density of the battery.

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

[0011] In any embodiment, the mass percentage of particles with a particle size R1 satisfying 3 pm≤R1≤6 pm in the positive electrode film layer is 55%-80% based on the total mass of the positive electrode film layer. The particles with a particle size R1 satisfying 3 pm≤R1≤6 pm have a larger specific surface area, so that a unit mass or volume of the particles can provide more interfaces for interaction with the binder and the conductive agent. In the case of a certain amount of the binder and the conductive agent, the dispersion is optimized, and the internal adhesion is enhanced. The mass percentage of the particles with a particle size R1 satisfying 3 pm≤R1≤6 pm is in the above range, and helps to form a tighter particle packing together with particles of other sizes. Thus, the internal adhesion of the positive electrode film layer is enhanced, and the overall stability and the compaction density are taken into account.

[0012] In any embodiment, the mass percentage of particles with a particle size R2 satisfying 9 pm≤R2≤15 pm in the positive electrode film layer is 5.5%-9.5% based on the total mass of the positive electrode film layer. This is conducive to the formation of the film layer skeleton, so that the film layer can withstand higher roll pressure, and the compaction density of the electrode sheet is further improved, thereby improving the energy density of the battery.

[0013] In any embodiment, the positive electrode film layer comprises a binder, and the mass content of the binder is 0.4%-1.5%, or 0.6%-1.2% based on the total mass of the positive electrode film layer. The amount of the binder is positively correlated with the internal adhesion of the positive electrode film layer. If the amount of the binder is too small, the internal adhesion of the positive electrode film layer is low. If the amount of the binder is too high, the electrode sheet resistance is deteriorated, and the loading of the active material in the positive electrode film layer is reduced. The mass content of the binder in the above range can maximize the internal adhesion, strengthen the adhesion between the particles in the positive electrode film layer, and further reduce the probability of particle shedding in the positive electrode film layer.

[0014] In any embodiment, the positive active material particles have a D V50 of 0.4 pm-1.5 pm, or 0.5 pm-0.9 pm, wherein D V50 refers to the particle size corresponding to the cumulative volume distribution of 50% in the volume cumulative distribution curve. The appropriate D V50 helps to optimize the particle packing, and ensure the stability and conductivity of the film layer structure. Too large particles can cause the lithium ion diffusion path to be lengthened, reduce the ion transmission rate, and cause polarization. Too small particles can increase the specific surface area, cause the side reaction to increase, and affect the cycle life of the battery. Therefore, the particle size distribution of the positive active material particles is reasonably controlled, and the D V50 is in the above range, so that the energy density and the cycle life of the battery are taken into account.

[0015] In any embodiment, the positive electrode film layer comprises one-dimensional conductive agents, which comprise one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers. The one-dimensional conductive agents construct a long-range conductive network through linear structures. In addition to enhancing conductivity, the one-dimensional conductive agents also improve internal adhesion of the film layer.

[0016] In any embodiment, the length of the one-dimensional conductive agents is 5-25 times, optionally 10-25 times, the D V50 of the positive electrode active material particles. The length of the one-dimensional conductive agents reflects the “lapping capability” of the one-dimensional conductive agents themselves, and also plays a role in enhancing adhesion. The greater the ratio of the length of the one-dimensional conductive agents to the D V50 of the positive electrode active material particles, the more material particles that are lapped by a single one-dimensional conductive agent within the length of the one-dimensional conductive agent, the more stable the internal network structure that is constructed, and the stronger the conductivity and adhesion of the positive electrode film layer. If the length of the one-dimensional conductive agents is too long, then the one-dimensional conductive agents are prone to agglomeration during preparation of the positive electrode film layer slurry. Therefore, the ratio of the length of the one-dimensional conductive agents to the D V50 of the particles in the positive electrode film layer is within the above range, which balances the processability, conductivity, and adhesion of the positive electrode film layer.

[0017] In any embodiment, the mass fraction of the one-dimensional conductive agents is 0.2%-0.6%, optionally 0.3%-0.5%, based on the total mass of the positive electrode film layer. This allows the positive electrode film layer to have good electronic conductivity, and also allows the content of the one-dimensional conductive agents to be reduced as much as possible to increase the content of the binder and enhance internal adhesion of the positive electrode film layer, while the total amount of the positive electrode film layer remains unchanged.

[0018] In any embodiment, the positive electrode active material comprises a lithium-containing transition metal phosphate, which comprises a component represented by the following general formula:

[0019] Li x A y Me a M b P 1-c X c Y z Formula I,

[0020] 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 comprises one or more of Na, K, Mg; Me comprises one or more of Mn, Fe, Co, Ni; M comprises 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, Ce; X comprises one or more of S, Si, Cl, B, C, N; Y comprises one or more of O, F.

[0021] The above lithium-containing transition metal phosphate material has good thermal stability, cycle stability, etc., which helps to improve the safety performance and cycle performance of the battery.

[0022] In any embodiment, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, fluorinated lithium vanadium phosphate, lithium manganese iron phosphate, and modified materials thereof.

[0023] In any embodiment, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and modified materials thereof.

[0024] Compared with conventional lithium-containing transition metal phosphate materials, the lithium iron phosphate material and modified materials thereof have relatively high gravimetric capacity while having good thermal stability and structural stability, which is conducive to improving the energy density while improving the safety performance and cycle performance of the battery.

[0025] In any embodiment, the positive electrode film layer includes zero-dimensional conductive agents, which include one or more of conductive carbon black, ketjen black, and acetylene black, and optionally the zero-dimensional conductive agents include conductive carbon black. The zero-dimensional conductive agents form conductive paths through point contact between particles, providing short-range conductive paths and adhesion. The one-dimensional conductive agents, on the other hand, construct long-range conductive networks through linear structures. The use of zero-dimensional and one-dimensional conductive agents in combination takes full advantage of their respective advantages, constructs an efficient conductive network, and improves the overall performance of the battery, further reducing the possibility of particle peeling in the battery.

[0026] 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 represents good adhesion of the positive electrode film layer to the current collector, which can effectively improve the separation phenomenon between the positive electrode film layer and the current collector. It also reflects the high adhesion of the positive electrode film layer, which can reduce particle peeling in the positive electrode film layer.

[0027] The second aspect of the present application provides a battery device including the battery cell of the first aspect of the present application.

[0028] The third aspect of the present application provides a power consuming device including the battery device of the second aspect of the present application.

[0029] The fourth aspect of the present application provides an energy storage device including the power consuming device of the third aspect of the present application.

[0030] The above description is only a summary of the technical solutions of the present application. In order to enable one skilled in the art to better understand the technical means of the present application and to implement the same according to the content of the description, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more apparent and easy to understand, the specific embodiments of the present application are described below. BRIEF DESCRIPTION OF DRAWINGS

[0031] In the drawings, like reference numerals refer to like elements throughout the various drawings. The drawings are not necessarily to scale, the emphasis instead being placed upon illustrating principles of the application. It should be understood that the drawings only depict some embodiments in accordance with the disclosure and should not be considered limiting of the scope of the application.

[0032] Figure 1 is a cross-section polished electron microscope morphology diagram of the positive electrode film layer in an embodiment of the present application;

[0033] Figure 2 is a schematic diagram of a battery cell in an embodiment of the present application;

[0034] Figure 3 is a schematic diagram of a battery module in an embodiment of the present application; Figure 2 is an exploded view of the battery cell in an embodiment of the present application shown in FIG. 5;

[0035] Figure 4 is a schematic diagram of a battery module in an embodiment of the present application;

[0036] Figure 5 is a schematic diagram of a battery pack in an embodiment of the present application;

[0037] Figure 6 is an exploded view of the battery pack in an embodiment of the present application shown in FIG. 9; Figure 5

[0038] Figure 7 is a schematic diagram of a power consuming device using a secondary battery as a power source in an embodiment of the present application.

[0039] BRIEF DESCRIPTION OF DRAWINGS

[0040] 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION​

[0041] Hereinafter, specific embodiments of the battery cell, the battery device, and the electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed description is omitted. For example, there are cases where detailed description of matters known well, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0042] The ranges disclosed herein are defined by their lower and upper limits, given that a range is defined by selecting a lower limit and an upper limit, the selected lower and upper limits define the boundaries of a particular range. Ranges defined by the endpoints can include the endpoints, or can not include the endpoints, and are understood to be open-ended, unless expressly stated otherwise. For example, if a range of "60-120" and "80-110" is stated, it is understood that a range of "60-110" and "80-120" is also explicitly stated. Also, a range of "1-2" is understood to include the endpoints, "1" and "2", unless expressly stated otherwise. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand manner of describing a range associated with any and all sub-ranges between the upper value "a" and the lower value "b" and are understood to have been stated explicitly, wherein "a" and "b" are real numbers. For example, a numerical range of "0-5" is understood to have been explicitly stated as "0-5" and all real numbers in between, such as "1-4.3", "4.7-5", etc., have been explicitly stated. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0044] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0045] If not otherwise specified, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method mentioned above can further comprise step (c), which means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0046] In the present application, the term "a plurality of" or "a plurality of" refers to two or more than two.

[0047] Unless otherwise specified, the terms used in the present application have the commonly known meanings as understood by a person skilled in the art.

[0048] Unless otherwise specified, the values of the parameters mentioned in the present application can be measured by various test methods commonly used in the art, for example, the test methods given in the examples of the present application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0049] The battery mentioned in the examples of the present 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 the present application can comprise a battery cell, a battery cell, a battery module or a battery pack, etc.

[0050] The battery cell is the smallest unit that makes up the battery, which can realize the function of charging and discharging by itself. The battery cell can be in the shape of a cylinder, a cuboid or other shapes, which are not limited in the examples of the present application. For example, Figure 2 is a battery cell 5 in the shape of a cuboid as an example.

[0051] The battery cell comprises an electrode assembly and an electrolyte.

[0052] The battery cell can also comprise an outer package, which can be used to package the electrode assembly and the electrolyte. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0053] In some embodiments, as Figure 3As shown, the outer package can include a housing 51 and a top cover assembly 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening in communication with the receiving cavity, and the top cover assembly 53 is used to cover the opening to seal the receiving cavity. The electrode assembly 52 is packaged in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to requirements.

[0054] The electrode assembly generally includes a positive electrode sheet and a negative electrode sheet. The negative electrode sheet is an electrode that undergoes a reaction of absorbing or lithiating lithium ions during charging and releasing or delithiating lithium during discharging. The positive electrode sheet is an electrode that undergoes a reaction of releasing or delithiating lithium ions during charging and absorbing or lithiating lithium during discharging.

[0055] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in a mixed connection through a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a box body and battery cells, and the battery cells or battery modules are contained in the box body. In some embodiments, the box body can be part of the chassis structure of the vehicle. For example, part of the box body can be at least part of the floor of the vehicle, or part of the box body can be at least part of the cross beam and the longitudinal beam of the vehicle.

[0056] In some embodiments, the battery can be an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0057] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 4 is a schematic diagram of a battery module 4 as an example. As shown, Figure 4 In the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the multiple battery cells 5 can be fixed by fasteners.

[0058] Optionally, the battery module 4 can further include a housing having a receiving space, and the multiple battery cells 5 are contained in the receiving space.

[0059] In some embodiments, the above-mentioned battery module 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.

[0060] Figure 5 and Figure 6 is a schematic diagram of a battery pack 1 as an example. As shown, Figure 5and Figure 6 As shown in the figure, the battery pack 1 can include a box body and a plurality of battery modules 4 arranged in the box body. The box body includes an upper box body 2 and a lower box body 3, the upper box body 2 is used to cover the lower box body 3, and forms a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the box body in any manner.

[0061] In recent years, the market demand for high energy density batteries is increasingly strong. In order to obtain a battery with high energy density, the industry commonly used method is to continuously increase the loading amount of active material in the positive electrode film layer, but the increase of the loading amount of active material will reduce the content of the binder and the conductive agent in the positive electrode film layer, which will reduce the adhesion, cause the peeling of the particles in the positive electrode film layer, and cause the separation of the interface of the contact surface between the positive electrode film layer and the current collector, which will affect the cycle life of the battery cell. Therefore, how to prepare a battery cell with high energy density and high internal adhesion is a technical problem that needs to be solved in the field.

[0062] The first aspect of the present application provides a battery cell, the battery cell comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the mass fraction of the positive electrode active material being 97.5%-99.2% based on the total mass of the positive electrode film layer; the mass fraction of the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer being 60%-90% based on the total mass of the positive electrode film layer.

[0063] Studies have shown that by increasing the loading amount of positive electrode active material in the positive electrode film layer, when the mass fraction of the positive electrode active material is 97.5%-99.2%, it is beneficial to improve the compaction density of the positive electrode film layer and the energy density of the battery. However, in order to maintain the kinetic performance of the positive electrode sheet and the battery cell, the content of the conductive agent in the positive electrode film layer is positively correlated with the loading amount of the positive electrode active material, and a high loading amount of the positive electrode active material requires a higher content of the conductive agent, thereby causing a sharp decrease in the content of the binder, and a decrease in the adhesion in the positive electrode film layer.

[0064] The present application has the mass fraction of the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer in the above range, the increase in the roundness of the particles on the one hand makes the arrangement of the particles in the positive electrode film layer more uniform, and the flatness of the film layer surface is improved, thereby increasing the number of contact points between the particles close to the current collector and the current collector, and increasing the adhesion between the positive electrode film layer and the current collector. On the other hand, the particles with high roundness can be tightly packed in the rolling process, and the particles are in good contact with each other, so that the particles in the positive electrode film layer have good electronic conductivity, and the bending degree of the pore channel between the particles is reduced, the conductive agent is uniformly distributed in the electrode, a high-efficiency conductive network is constructed, and the electronic conductivity is further improved, such as Figure 1As shown, therefore, in the high-load positive electrode film layer, the particles with high sphericity can reduce the amount of conductive agent without affecting the conductive performance, and in turn increase the binder content, thereby improving the internal adhesion of the positive electrode film layer. At the same time, the particles with high sphericity are prone to slip under external force, and the increase in the compaction density of the electrode sheet can be achieved at a low roll pressure. Thus, the internal adhesion of the positive electrode film layer is taken into account while maintaining the high energy density of the battery.

[0065] In the present application, the term "particle" refers to a particle in the field of view of the positive electrode film layer under a certain magnification, for example, 10,000 times, having a recognizable complete boundary. Defects and scratches can exist inside the particle, but the complete boundary inside the particle cannot be recognized enough to divide the particle.

[0066] In some embodiments, the mass percentage of the positive electrode active material based on the total mass of the positive electrode film layer 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 a numerical range between any two of the above.

[0067] Because the space in the unit volume of the positive electrode film layer is limited, and the binder, conductive agent and other additives 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 amount of the positive electrode active material as much as possible.

[0068] In some embodiments, the mass percentage of the particles with a sphericity greater than or equal to 0.6 in the positive electrode film layer based on the total mass of the positive electrode film layer can be selected as 60%, 65%, 70%, 75%, 80%, 85%, 90%, or a numerical range between any two of the above.

[0069] In the present application, the "sphericity" is measured as follows: taking a prepared positive electrode sheet, or a positive electrode sheet disassembled from a battery, performing CP-SEM testing, randomly taking a number of points for shooting, the number of points ≥10, which can be 10, 20, 50, 100, etc., identifying the particles in the pictures obtained by shooting through AVIZO software, and measuring the area of each particle, and measuring the longest inner diameter, the shortest inner diameter and the area of the particle, and taking the ratio of the shortest inner diameter and the longest inner diameter as the sphericity of the particle. Obtain all the particle data identified, calculate the sphericity and area of each particle. The ratio of the sum of the areas of all the particles with a sphericity greater than or equal to 0.6 in the positive electrode film layer to the sum of the areas of all the particles identified is equivalent to the mass percentage of the particles with a sphericity greater than or equal to 0.6 in the positive electrode film layer.

[0070] The skilled person can control the roundness of the particles by any known process. As an example, the roundness of the particles can be controlled by processes such as grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, adding surfactants, and adjusting 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 layer.

[0072] The mass percentage of the positive electrode active material in the above range further improves the energy density of the battery while taking into account the internal adhesion of the positive electrode film layer.

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

[0074] The roundness of the particles in the positive electrode film layer has a direct impact on the compaction density and the energy density. Even if all the particles are perfect spheres, complete close packing cannot be achieved due to the geometric arrangement. The anisotropic shape characteristics of particles with a small roundness affect their random packing behavior, which means that a moderate deviation from the spherical shape can help the particles to pack more closely. Studies have shown that the mass percentage of the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer in 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.

[0075] In some embodiments, the ratio of the mass of the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the positive electrode film layer is 9-21, optionally 12-18.

[0076] In some embodiments, the ratio of the mass of the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the positive electrode film layer is optionally 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or a numerical range between any two of the above values.

[0077] In this application, the ratio of the mass of the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the positive electrode film layer is measured by the method described above, and the ratio of the sum of the areas of all the particles with a roundness greater than or equal to 0.6 to the sum of the areas of all the 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 the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the positive electrode film layer.

[0078] The ratio of the mass of the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the positive electrode film layer is within the above range, which can further optimize the tightness of the particle accumulation in the positive electrode film layer. The particles with a roundness less than or equal to 0.3 can fill the gaps between the high roundness particles due to the diversity of their shapes (such as ellipses, wedges, etc.). The space utilization of the accumulation body is significantly improved by the cooperation of high roundness and low roundness particles, thereby improving the compaction density of the electrode sheet and the energy density of the battery.

[0079] In some embodiments, the mass proportion of the particles with a particle size R1 satisfying 3 μm≤R1≤6 μm in the positive electrode film layer is 55%-80%, based on the total mass of the positive electrode film layer.

[0080] In some embodiments, the mass proportion of the particles with a particle size R1 satisfying 3 μm≤R1≤6 μm in the positive electrode film layer can be selected from 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 numerical range between any two of the above values, based on the total mass of the positive electrode film layer.

[0081] In the present application, the mass proportion of the particles with a particle size R1 satisfying 3 μm≤R1≤6 μm in the positive electrode film layer can be determined by the following method: referring to the method described above in the present application to identify the particles in the photographed picture, identifying the particles in the photographed picture by AVIZO software, measuring the particle size and area of each particle, and equating the ratio of the sum of the areas of all the particles with a particle size R1 satisfying 3 μm≤R1≤6 μm to the sum of the areas of all the identified particles to the mass proportion of the particles with a particle size R1 satisfying 3 μm≤R1≤6 μm in the positive electrode film layer.

[0082] The particles with a particle size R1 satisfying 3 μm≤R1≤6 μm have a larger specific surface area, so that a unit mass or volume of the particles can provide more interfaces for interaction with the binder and the conductive agent. In the case of a certain amount of binder and conductive agent, the dispersion is optimized and the internal adhesion is enhanced. The mass proportion of the particles with a particle size R1 satisfying 3 μm≤R1≤6 μm is within the above range, which helps to form a tighter particle accumulation with particles of other particle sizes. Thus, the internal adhesion of the positive electrode film layer is enhanced, and the overall stability and compaction density are considered.

[0083] In some embodiments, the mass proportion of the particles with a particle size R2 satisfying 9 μm≤R2≤15 μm in the positive electrode film layer is 5.5%-9.5%, based on the total mass of the positive electrode film layer.

[0084] In some embodiments, the mass percentage of the particles with particle size R2 satisfying 9 pm≤R2≤15 pm in the positive electrode film layer, based on the total mass of the positive electrode film layer, can be 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9.0%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, or a numerical range between any two of the above.

[0085] In the present application, the mass percentage of the particles with particle size R2 satisfying 9 pm≤R2≤15 pm in the positive electrode film layer, based on the total mass of the positive electrode film layer, can be determined by the following method: referring to the method described above in the present application to identify the particles in the photographed picture, identifying the particles in the photographed picture by AVIZO software, and measuring the particle size and area of each particle, and equating the ratio of the sum of the areas of all the particles with particle size R2 satisfying 9 pm≤R2≤15 pm to the sum of the areas of all the identified particles to the mass percentage of the particles with particle size R2 satisfying 9 pm≤R2≤15 pm in the positive electrode film layer.

[0086] The mass percentage of the particles with particle size R2 satisfying 9 pm≤R2≤15 pm in the positive electrode film layer in the above range is beneficial to the formation of the film layer skeleton, so that the film layer can withstand higher roll pressure, further improving the compaction density of the pole piece and the energy density of the battery.

[0087] In some embodiments, the positive electrode film layer comprises 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%, which can be 0.6%-1.2%.

[0088] In some embodiments, the positive electrode film layer comprises a binder, and the mass content of the binder, based on the total mass of the positive electrode film layer, can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or a numerical range between any two of the above.

[0089] The amount of the binder and the internal adhesion of the positive electrode film layer are positively correlated. If the amount of the binder is too small, the internal adhesion of the positive electrode film layer is low. If the amount of the binder is too high, the film resistance of the electrode sheet is deteriorated, and the loading of the active material in the positive electrode film layer is reduced. The mass content of the binder in the above range can maximize the internal adhesion, strengthen the adhesion between the particles in the positive electrode film layer, and further reduce the probability of particle shedding in the positive electrode film layer.

[0090] In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm. V50 In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm. V50 In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm.

[0091] In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm. V50 In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm.

[0092] In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm. V50 In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm. V50 In some embodiments, the D50 of the positive electrode active material particles is 0.4 pm to 1.5 pm, optionally 0.5 pm to 0.9 pm.

[0093] In some embodiments, the positive electrode film layer comprises one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0094] In some embodiments, the positive electrode film layer comprises one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0095] In some embodiments, the positive electrode film layer comprises one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers.

[0096] In some embodiments, the length of the one-dimensional conductive agent and the D50 of the positive electrode active material particles are in a ratio of 5 to 25, optionally 10 to 25. V50 In some embodiments, the length of the one-dimensional conductive agent and the D50 of the positive electrode active material particles are in a ratio of 5 to 25, optionally 10 to 25.

[0097] In some embodiments, the ratio of the length of the one-dimensional conductive agent to the D V50 may be selected from 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, or a numerical range between any two of the above values.

[0098] The length of the one-dimensional conductive agent reflects its own "lapping capability" and also plays a role in enhancing adhesion. The greater the ratio of the length of the one-dimensional conductive agent to the D V50 of the particles in the positive electrode film layer, the more material particles a single one-dimensional conductive agent lapped in its length range, the more stable the internal network structure constructed, and the stronger the conductivity and adhesion of the positive electrode film layer. If the length of the one-dimensional conductive agent is too long, it is easy to agglomerate during the preparation of the positive electrode film layer slurry. Therefore, the ratio of the length of the one-dimensional conductive agent to the D V50 of the particles in the positive electrode film layer is within the above range, the processability, conductivity, and adhesion of the positive electrode film layer are balanced.

[0099] The mass fraction of the one-dimensional conductive agent based on the total mass of the positive electrode film layer is 0.2%-0.6%, which can be selected from 0.3%-0.5%.

[0100] In some embodiments, the mass fraction of the one-dimensional conductive agent based on the total mass of the positive electrode film layer can be selected from 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or a numerical range between any two of the above values.

[0101] The mass content of the one-dimensional conductive agent based on the total mass of the positive electrode film layer is within the above range, so that the positive electrode film layer has good electronic conductivity, and the amount of conductive agent is reduced as much as possible to increase the binder content and enhance the internal adhesion of the positive electrode film layer under the condition that the total amount of the positive electrode film layer is unchanged.

[0102] In some embodiments, the positive electrode active material includes a lithium-containing transition metal phosphate, which includes a component represented by the following general formula:

[0103] Li x A y Me a M b P 1-c X c Y z Formula I,

[0104] 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 comprises one or more of Na, K, Mg; Me comprises one or more of Mn, Fe, Co, Ni; M comprises 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, Ce; X comprises one or more of S, Si, Cl, B, C, N; Y comprises one or more of O, F.

[0105] The lithium-containing transition metal phosphate refers to a phosphate material containing lithium and transition metal elements, having the characteristics of structural stability, good safety, and long cycle life, and has been widely used in lithium ion batteries, which can be detected by any known manner in the art. For example, it can be detected by X-ray diffractometer (XRD) and energy spectrum analyzer, inductively coupled plasma mass spectrometer.

[0106] In some embodiments, 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 a numerical range between any two of the above.

[0107] In some embodiments, y can be selected as 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.15, 1.3, or a numerical range between any two of the above.

[0108] In some embodiments, x+y can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, or a numerical range between any two of the above.

[0109] In some embodiments, a can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or a numerical range between any two of the above.

[0110] In some embodiments, b can be selected from 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a numerical range between any two of the above.

[0111] In some embodiments, a+b can be selected from 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, or a numerical range between any two of the above.

[0112] In some embodiments, c can be selected from 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a numerical range between any two of the above.

[0113] In some embodiments, z can be selected from 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, or a numerical range between any two of the above.

[0114] In some embodiments, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium fluorophosphate, lithium manganese iron phosphate, and modified materials thereof.

[0115] The lithium-containing transition metal phosphate material described above has good thermal stability, cycle stability, etc., which helps to improve the safety performance and cycle performance of the battery.

[0116] In some embodiments, the lithium-containing transition metal phosphate includes one or more of lithium iron phosphate and modified materials thereof.

[0117] Compared with conventional lithium-containing transition metal phosphate materials, the lithium iron phosphate material and modified materials thereof have relatively high gravimetric capacity while having good thermal stability and structural stability, which is conducive to improving the safety performance and cycle performance of the battery while improving the energy density.

[0118] 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.

[0119] In some embodiments, the particle size D V50 of the first lithium-containing transition metal phosphate particles can be 0.4 μm-0.75 μm.

[0120] In some embodiments, the particle size D V50 of the first lithium-containing transition metal phosphate particles can be 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm, or a numerical range between any two of the above.

[0121] In some embodiments, the particle size D50 of the second lithium-containing transition metal phosphate particles is 1.5-2.5 pm. V50 The particle size D50 can be 1 pm, 1.05 pm, 1.10 pm, 1.15 pm, 1.20 pm, 1.25 pm, 1.30 pm, 1.35 pm, 1.40 pm, 1.45 pm, 1.5 pm, 1.55 pm, 1.60 pm, 1.65 pm, 1.70 pm, 1.75 pm, 1.80 pm, 1.85 pm, 1.90 pm, 1.95 pm, 2.0 pm, 2.05 pm, 2.10 pm, 2.15 pm, 2.20 pm, 2.25 pm, 2.30 pm, 2.35 pm, 2.40 pm, 2.45 pm, or a numerical range between any two of the above.

[0122] In some embodiments, the particle size D50 of the second lithium-containing transition metal phosphate particles is 1.5-2.5 pm. V50 The particle size D50 can be 1 pm, 1.05 pm, 1.10 pm, 1.15 pm, 1.20 pm, 1.25 pm, 1.30 pm, 1.35 pm, 1.40 pm, 1.45 pm, 1.5 pm, 1.55 pm, 1.60 pm, 1.65 pm, 1.70 pm, 1.75 pm, 1.80 pm, 1.85 pm, 1.90 pm, 1.95 pm, 2.0 pm, 2.05 pm, 2.10 pm, 2.15 pm, 2.20 pm, 2.25 pm, 2.30 pm, 2.35 pm, 2.40 pm, 2.45 pm, or a numerical range between any two of the above.

[0123] The first lithium-containing transition metal phosphate particles and the second lithium-containing transition metal phosphate particles that meet the above particle size ranges are matched with each other, which is beneficial to improve the particle gradation, realize the close packing of the particles in the positive electrode film layer, further improve the compaction density of the electrode sheet, and thus improve the energy density of the battery.

[0124] In some embodiments, the mass percentage of the first lithium-containing transition metal phosphate particles in the total mass of the positive electrode film layer is 55%-80%.

[0125] In some embodiments, the mass percentage of the first lithium-containing transition metal phosphate particles in the total mass of the positive electrode film layer can be 55%, 60%, 65%, 70%, 75%, 80%, or a numerical range between any two of the above.

[0126] In some embodiments, the mass percentage of the second lithium-containing transition metal phosphate particles in the total mass of the positive electrode film layer is 20%-45%.

[0127] In some embodiments, the mass percentage of the second lithium-containing transition metal phosphate particles in the total mass of the positive electrode film layer can be 20%, 25%, 30%, 35%, 40%, 45%, or a numerical range between any two of the above.

[0128] The mass content of the first lithium-containing transition metal phosphate particles and the second lithium-containing transition metal phosphate particles is controlled to meet the above ranges, respectively, which is beneficial to improve the compaction density of the electrode sheet, so that the battery has excellent energy density.

[0129] In some embodiments, the mass percentage of the first lithium-containing transition metal phosphate particles in the total mass of the positive electrode film layer is 55%-80%.

[0130] In some embodiments, the mass fraction of the particles with a roundness greater than or equal to 0.6 in the first lithium-containing transition metal phosphate is 60%, 65%, 70%, 75%, 80%, 85%, 90%, or a numerical range between any two of the above values, based on the mass of the first lithium-containing transition metal phosphate particles.

[0131] In some embodiments, the mass fraction of the particles with a roundness greater than or equal to 0.6 in the second lithium-containing transition metal phosphate is 60%-90%, based on the mass of the second lithium-containing transition metal phosphate particles.

[0132] In some embodiments, the mass fraction of the particles with a roundness greater than or equal to 0.6 in the second lithium-containing transition metal phosphate is 60%, 65%, 70%, 75%, 80%, 85%, 90%, or a numerical range between any two of the above values, based on the mass of the second lithium-containing transition metal phosphate particles.

[0133] The mass fraction of the particles with a roundness greater than or equal to 0.6 in the first lithium-containing transition metal phosphate particles and the second lithium-containing transition metal phosphate particles in the positive electrode film layer is within the above range, respectively, which is beneficial to reducing the porosity in the film layer by improving the slippability of the particles during the preparation of the positive electrode film layer, achieving high compaction density; at the same time, it is beneficial to reducing the bending degree of the pore channel between the particles, which helps to uniformly distribute the conductive agent in the electrode and effectively construct the conductive network, improves the electronic conductivity, increases the amount of binder, and reduces the amount of conductive agent under the condition that the total amount of the positive electrode film layer remains unchanged, thereby improving the adhesion of the positive electrode film layer and the energy density of the battery.

[0134] In some embodiments, the positive electrode film layer comprises a zero-dimensional conductive agent, and the zero-dimensional conductive agent comprises one or more of conductive carbon black, Ketjen black, and acetylene black, and optionally, the zero-dimensional conductive agent comprises conductive carbon black.

[0135] In this application, the term "zero-dimensional conductive agent" refers to a conductive material with a zero-dimensional structure, which is mainly characterized by a size similar in all directions, presenting a point-like structure. Such a conductive agent improves the conductivity of the material through point contact between particles.

[0136] The zero-dimensional conductive agent forms a conductive path through point contact between particles, providing a short-range conductive path and adhesion. The zero-dimensional and one-dimensional conductive agents are used in combination to fully utilize their respective advantages, construct an efficient conductive network, and improve the overall performance of the battery, further reducing the internal resistance of the battery and the possibility of particle shedding in the electrode sheet.

[0137] In some embodiments, the adhesion strength between the positive electrode film layer and the positive electrode current collector is 15 N / m-50 N / m.

[0138] In some embodiments, the adhesion strength between the positive electrode film layer and the positive electrode current collector can be selected to be 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m, or a numerical range between any two of the above.

[0139] The adhesion strength in the embodiments of the present application is within the above range, which represents good adhesion performance of the positive electrode film layer internally and to the current collector, and can effectively improve the separation phenomenon between the positive electrode film layer / current collector. It also reflects the high adhesion of the positive electrode film layer internally, which can reduce particle peeling in the positive electrode film layer.

[0140] In some embodiments, the cold-pressed compacted density of the positive electrode tab can be selected to be 2.55 g / cm 3 - 2.75 g / cm 3 .

[0141] In some embodiments, the cold-pressed compacted density of the positive electrode tab can be selected to be 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , 2.58 g / cm 3 , 2.59 g / cm 3 , 2.60 g / cm 3 , 2.61 g / cm 3 , 2.62 g / cm 3 , 2.63 g / cm 3 , 2.64 g / cm 3 , 2.65 g / cm 3 , 2.66 g / cm 3 , 2.67 g / cm 3 , 2.68 g / cm 3 , 2.69 g / cm 3 , 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 , 2.75 g / cm 3 or a numerical range between any two of the above.

[0142] In the present application, the compacted density after cold pressing can be tested by methods known in the art. As an example, the positive electrode sheet obtained after cold pressing is cut into small round pieces with an area of S, the mass W1 thereof is obtained, and the thickness T1 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 T2 of the current collector is measured using a micrometer, then the compacted density PD of the positive electrode film layer is (W1-W2) / [(T1-T2)XS].

[0143] In the process of preparing the battery cell, after the positive electrode slurry is coated to the positive electrode current collector, vacuum drying, cold pressing, slitting, and preparation of the positive electrode sheet will be performed. The compacted density obtained in the cold pressing step and the compacted density obtained after full discharge of the positive electrode sheet will be different, because after being made into a sheet, the positive electrode sheet will have a small rebound phenomenon due to charging and discharging, at which time the compacted density of the positive electrode film layer under full discharge will be slightly less than the compacted density of the initial cold pressing.

[0144] In some embodiments, the compacted density of the positive electrode sheet under full discharge is 2.40g / cm 3 -2.65g / cm 3 .

[0145] In some embodiments, the compacted density of the positive electrode sheet under full discharge is 2.40g / cm 3 , 2.41g / cm 3 , 2.42g / cm 3 , 2.43g / cm 3 , 2.44g / cm 3 , 2.45g / cm 3 , 2.46g / cm 3 , 2.47g / cm 3 , 2.48g / cm 3 , 2.49g / cm 3 , 2.50g / cm 3 , 2.51g / cm 3 , 2.52g / cm 3 , 2.53g / cm 3 , 2.54g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.59g / cm 3 , 2.60g / cm 3 , 2.61g / cm 3 , 2.62g / cm 32.63 g / cm3 3 2.64 g / cm3 3 2.65 g / cm3 3 or a numerical range between any two of the above.

[0146] In the present application, the full discharge state refers to the following: placing the battery in a 25°C oven environment, standing for 2h, waiting for the battery temperature to remain at 25°C, discharging the battery at 1 / 3C constant current to 2.5V, standing for 30min, discharging at 0.04C constant current to 2.5V.

[0147] In the present application, the compaction density of the positive electrode film layer in the full discharge state can be tested by methods known in the art. As an example, place the battery in a 25°C oven environment, stand for 2h, wait for the battery temperature to remain at 25°C, discharge the battery at 1 / 3C constant current to 2.5V, stand for 30min, discharge at 0.04C constant current to 2.5V, disassemble the battery, obtain the positive electrode sheet, treat the residual electrolyte with dimethyl carbonate solvent, dry the sheet, cut into small round pieces with an area of S, obtain the mass W1, and use a micrometer to measure the thickness T1 of the positive electrode sheet, then wipe off the positive electrode film layer of the above weighed sheet, weigh the mass of the current collector, denoted as W2, and use a micrometer to measure the thickness T2 of the current collector, then the compaction density PD of the positive electrode film layer is (W1-W2) / [(T1-T2) x S].

[0148] The compaction density of the positive electrode sheet within the above range is beneficial to improving the yield rate during the cutting process of the sheet while maintaining the high energy density of the battery monomer, meeting the performance and efficiency requirements.

[0149] In some embodiments, the positive electrode current collector can use a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. The composite current collector can include a high polymer material base layer and a metal layer formed on at least one surface of the high polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a high polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0150] [Negative electrode sheet]

[0151] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0152] As an example, the negative electrode current collector has two opposite surfaces in the thickness direction of itself, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0153] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0154] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0155] In some embodiments, the negative film layer can further optionally include a binder. The binder can 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).

[0156] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0157] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) etc.

[0158] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-described components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector, and subjecting to drying, cold pressing, etc. to obtain the negative electrode sheet.

[0159] [Electrolyte]

[0160] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present application and can be selected as desired. For example, the electrolyte can be liquid, gel, or all-solid.

[0161] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0162] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0163] In some embodiments, the solvent can 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, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0164] In some embodiments, the electrolyte solution can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0165] [Separator]

[0166] In some embodiments, the battery cell further includes a separator. The type of separator is not particularly limited in the present application and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0167] In some embodiments, the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0168] [Battery Cell]

[0169] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0170] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0171] In some embodiments, the battery cell has a volumetric energy density of 650 Wh / L-720 Wh / L.

[0172] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape.

[0173] [Battery device]

[0174] The battery device according to an embodiment of the present application includes the battery cell according to an embodiment of the present application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0175] [Power consumption device]

[0176] In addition, the power consumption device according to an embodiment of the present application includes at least one of the battery cell, the battery module, or the battery pack according to an embodiment of the present application. The battery cell, the battery module, or the battery pack can be used as a power source of the power consumption device, or can be used as an energy storage unit of the power consumption device. The power consumption device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0177] The battery cell, the battery module, or the battery pack can be selected according to the use requirement of the power consumption device.

[0178] Figure 7 The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the battery cell for the power consumption device, the battery pack or the battery module can be used.

[0179] The energy storage device according to an embodiment of the present application includes the battery device according to an embodiment of the present application.

[0180] The device according to another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery cell can be used as a power source.

[0181] Embodiments

[0182] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application and cannot be understood as a limitation of the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0183] In the embodiments of the present application, the proportion of the roundness of the positive active material is controlled by the following method: YHC-92 type lithium iron phosphate (LiFePO4) produced by Hunan Yunneng New Energy Battery Material Co., Ltd. is selected, D V50 = 0.55 μm, average roundness 0.92), YHC-53 type lithium iron phosphate (LiFePO4), D V50 = 0.55 μm, average roundness 0.53), YHC-21 type lithium iron phosphate (LiFePO4), D V50 = 0.55 μm, average roundness 0.21); ZLC-95 type lithium iron phosphate (LiFePO4), D V50 = 1.25 μm, average roundness 0.95), ZLC-56 type lithium iron phosphate (LiFePO4), D V50 = 1.25 μm, average roundness 0.56), ZLC-16 type lithium iron phosphate (LiFePO4), D V50 = 1.25 μm, average roundness 0.16); according to the proportion of each roundness particle of the positive active material used in the embodiments, artificial mixing is performed. As an example, when the demand for the positive active material is that the mass proportion of the particles with roundness greater than or equal to 0.6 in the lithium iron phosphate particles with D V50 = 0.55 μm is 80%, and the ratio of the mass of the particles with roundness greater than or equal to 0.6 to the mass of the particles with roundness less than or equal to 0.3 is 15; based on the total mass of the positive active material, YHC-92 type lithium iron phosphate with a mass proportion of 80% and YHC-21 lithium iron phosphate with a mass proportion of 5.3% are selected, and YHC-53 type lithium iron phosphate is used to fill the remaining mass proportion, mixing is performed to obtain a mixture, and detection is performed, when the roundness in the mixture meets the demand, it is stored as an active material raw material for subsequent preparation of the electrode sheet.

[0184] Embodiment 1

[0185] 1) Preparation of the positive electrode sheet

[0186] Preparation of the positive electrode film layer slurry: the first lithium iron phosphate particles (LiFePO4) with D V50 = 0.55 μm, the second lithium iron phosphate particles (LiFePO4) with D V50The second lithium iron phosphate particles (LiFePO4) with a size of 1.25 μm are mixed in a mass ratio of 7:3 to obtain a positive electrode active material, the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF are mixed in a mass ratio of 98.4:0.3:0.3:1, a solvent NMP is added, and the system is stirred under the action of a vacuum stirrer until it is uniform to obtain a positive electrode film layer slurry. The zero-dimensional conductive agent is Super-P conductive agent, the one-dimensional conductive agent is carbon nanotube conductive agent, the mass ratio of the particles with a roundness greater than or equal to 0.6 in the first lithium iron phosphate particles is 80%, and the ratio of the mass of the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 15; the mass ratio of the particles with a roundness greater than or equal to 0.3 in the second lithium iron phosphate particles is 80%, and the ratio of the mass of the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 15; the D V50 of the positive electrode active material is 0.7 μm, and the ratio of the length of the one-dimensional conductive agent to the D V50 of the positive electrode active material is 15.

[0187] The positive electrode film layer slurry is uniformly coated on the surface of the base coating layer away from the positive electrode current collector, and the single-sided coating weight is 300 mg / 1540.25 mm 2 After air drying at room temperature, the positive electrode film layer slurry is transferred to an oven for further drying, and then cold-pressed to obtain a positive electrode sheet. The thickness of the single-sided positive electrode film layer after cold-pressing is 70.8 μm, and the cold-pressing density of the positive electrode film layer is 2.75 g / cm 3 ; here, the single-sided coating weight does not include the mass of the solvent, but only the mass of the solid content in the coating.

[0188] Sheet slitting (one out of two): the positive electrode sheet is cut on a slitting machine at a slitting speed of 0.5 m / s, the slitting knife is made of steel, and the negative pressure of the slitting machine is-10 kPa.

[0189] Sheet cutting: the cut positive electrode sheet is wound and cut, wherein the winding speed is 0.6 m / s, the length of each winding core is 3 m, the cutting knife is made of steel, and the negative pressure in the winding machine is-10 kPa.

[0190] 2) Preparation of a negative electrode sheet

[0191] The graphite negative electrode active material, polyvinyl alcohol binder, and SP-Li conductive agent are mixed and ball milled in a deionized water solvent system in a mass ratio of 90:5:5 to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the copper foil surface in a single-sided coating weight of 140 mg / 1540.25 mm 2 , and vacuum dried at a temperature of 110°C overnight to obtain a negative electrode sheet.

[0192] 3) Preparation of the separator

[0193] A polyethylene film with a thickness of 13 μm was used as the separator.

[0194] 4) Preparation of the electrolyte

[0195] Lithium hexafluorophosphate (LiPF6) was dissolved in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 to form a uniform solution, obtaining an electrolyte with a LiPF6 concentration of 1 mol / L.

[0196] 5) Assembly of the battery

[0197] The positive electrode sheet, the negative electrode sheet and one end of the two separators were fixed to the discharge roller in the order of "separator-negative electrode sheet-separator-positive electrode sheet", and the other end was fixed to the winding shaft after being stacked together. The winding shaft was rotated by a motor to wind the positive electrode sheet, the negative electrode sheet and the two separators, obtaining a wound bare cell. The bare cell was placed in an outer package, injected with the above electrolyte and packaged, obtaining a battery monomer.

[0198] The preparation method of Example 2 was basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent and binder PVDF was 97.5:0.6:0.3:1.6; and the cold-pressing compaction density of the positive electrode film layer was 2.73 g / cm 3 .

[0199] The preparation method of Example 3 was basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the positive electrode active material, conductive carbon black, carbon nanotube conductive agent and binder PVDF was 98.8:0.2:0.3:0.7; and the cold-pressing compaction density of the positive electrode film layer was 2.75 g / cm 3 .

[0200] The preparation method of Example 4 was basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the first lithium iron phosphate particles with a roundness greater than or equal to 0.6 was 60%; the mass ratio of the second lithium iron phosphate particles with a roundness greater than or equal to 0.6 was 60%; and the cold-pressing compaction density of the positive electrode film layer was 2.68 g / cm 3 .

[0201] The preparation method of Example 5 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 9; the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 9; and the cold-pressing density of the positive electrode film layer is 2.68 g / cm 3 .

[0202] The preparation method of Example 6 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 90%; the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 90%; and the cold-pressing density of the positive electrode film layer is 2.70 g / cm 3 .

[0203] 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, in the preparation step of the positive electrode film layer slurry, the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 9; the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 9; and the cold-pressing density of the positive electrode film layer is 2.68 g / cm 3 .

[0204] 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, in the preparation step of the positive electrode film layer slurry, the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 12; the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 12; and the cold-pressing density of the positive electrode film layer is 2.72 g / cm 3 .

[0205] 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, in the preparation step of the positive electrode film layer slurry, the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 18; the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 18; and the cold-pressing density of the positive electrode film layer is 2.73 g / cm 3 .

[0206] 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, in the preparation step of the positive electrode film layer slurry, the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the first lithium iron phosphate particles is 21; the mass ratio of the particles with a roundness greater than or equal to 0.6 to the particles with a roundness less than or equal to 0.3 in the second lithium iron phosphate particles is 21; and the cold-pressing density of the positive electrode film layer is 2.70 g / cm 3 .

[0207] 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, in the preparation step of the positive electrode film layer 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-pressing density of the positive electrode film layer is 2.68 g / cm 3 .

[0208] 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, in the preparation step of the positive electrode film layer slurry, the mass ratio of the first lithium iron phosphate particles to the second lithium iron phosphate particles is 8:2; the D V50 of the positive electrode active material is 0.63 μm; and the cold-pressing density of the positive electrode film layer is 2.65 g / cm 3 .

[0209] 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, in the preparation step of the positive electrode film layer slurry, the D V50 of the second lithium iron phosphate particles is 0.95 μm; and the cold-pressing density of the positive electrode film layer is 2.68 g / cm 3 .

[0210] The preparation method of Example 14 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the D V50 of the second lithium iron phosphate particles is 1.15 μm; and the cold-pressing density of the positive electrode film layer is 2.70 g / cm 3 .

[0211] The preparation method of Example 15 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the D V50 of the second lithium iron phosphate particles is 1.35 μm; and the cold-pressing density of the positive electrode film layer is 2.73 g / cm 3 .

[0212] 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, in the preparation step of the positive electrode film layer slurry, the D V50was 1.50 μm; the cold-pressing compactness of the positive electrode film layer was 2.70 g / cm 3 .

[0213] The preparation method of Example 17 was substantially the same as that of Example 1, except that in the preparation of the positive electrode sheet, the ratio of the length of the one-dimensional conductive agent to the D V50 of the particles of the positive electrode active material was 5; the cold-pressing compactness of the positive electrode film layer was 2.73 g / cm 3 .

[0214] The preparation method of Example 18 was substantially the same as that of Example 1, except that in the preparation of the positive electrode sheet, the ratio of the length of the one-dimensional conductive agent to the D V50 of the particles of the positive electrode active material was 10; the cold-pressing compactness of the positive electrode film layer was 2.75 g / cm 3 .

[0215] The preparation method of Example 19 was substantially the same as that of Example 1, except that in the preparation of the positive electrode sheet, the ratio of the length of the one-dimensional conductive agent to the D V50 of the particles of the positive electrode active material was 20; the cold-pressing compactness of the positive electrode film layer was 2.71 g / cm 3 .

[0216] The preparation method of Example 20 was substantially the same as that of Example 1, except that in the preparation of the positive electrode sheet, the ratio of the length of the one-dimensional conductive agent to the D V50 of the particles of the positive electrode active material was 25; the cold-pressing compactness of the positive electrode film layer was 2.72 g / cm 3 .

[0217] The preparation method of Example 21 was substantially the same as that of Example 1, except that in the preparation of the positive electrode sheet, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF was 98.4:0.2:0.5:1; the cold-pressing compactness of the positive electrode film layer was 2.73 g / cm 3 .

[0218] The preparation method of Example 22 was substantially the same as that of Example 1, except that in the preparation of the positive electrode sheet, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF was 98.4:0.4:0.3:1; the cold-pressing compactness of the positive electrode film layer was 2.73 g / cm 3 .

[0219] The preparation method of example 23 is basically the same as that of example 1, except that the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 98.4:0.5:0.1:1; and the cold-pressing density of the positive electrode film layer is 2.72 g / cm 3 .

[0220] The preparation method of example 24 is basically the same as that of example 1, except that the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 98.4:0.6:0:1; and the cold-pressing density of the positive electrode film layer is 2.70 g / cm 3 .

[0221] The preparation method of comparative example 1 is basically the same as that of example 1, except that the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 97:0.6:0.3:2.1; and the cold-pressing density of the positive electrode film layer is 2.72 g / cm 3 .

[0222] The preparation method of comparative example 2 is basically the same as that of example 1, except that the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 97:0.6:0.3:2.1; and the cold-pressing density of the positive electrode film layer is 2.72 g / cm 3 .

[0223] The preparation method of comparative example 3 is basically the same as that of example 1, except that the preparation of the positive electrode sheet, in the preparation step of the positive electrode film layer slurry, the mass ratio of the positive electrode active material, one-dimensional conductive agent, zero-dimensional conductive agent, and binder PVDF is 97:0.6:0.3:2.1; and the cold-pressing density of the positive electrode film layer is 2.72 g / cm 3 .

[0224] Performance test

[0225] 1. Positive electrode sheet cross-section CP-SEM characterization method

[0226] The sample to be characterized is prepared as follows: first, the positive electrode sheet is cut into a sample to be measured with a size of 2 cm x 2 cm, and the sample to be measured is fixed on a sample stage by paraffin. Then, the sample stage is locked and fixed on the sample holder, the power supply of the argon ion cross-section polisher IB-19500CP is turned on and vacuumized, the argon gas flow is set to 0.15 MPa, the control voltage is set to 8 kV, and the polishing time is set to 2 hours, the sample stage is adjusted to the swing mode to start polishing, and the sample to be characterized is obtained after polishing.

[0227] Micro-morphology characterization: the sample is characterized by scanning electron microscope ZEISS Sigma300, and the sample test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, a plurality of different areas in the sample to be tested can be randomly selected for scanning test, and a cross-sectional morphology graph is taken under a fixed magnification of 5k times.

[0228] 2. Roundness test method

[0229] At 25°C, the slit positive electrode sheet prepared in each example and comparative example is subjected to CP-SEM test, a plurality of points are randomly taken for shooting, the number of points is ≥10, which can be 10, 20, 50, 100, etc., the particles in the pictures obtained by shooting are identified by AVIZO software, and the shortest diameter, the longest diameter and the area of each particle are measured, and the roundness = shortest diameter / longest diameter. The ratio of the sum of the areas of all particles with roundness greater than or equal to 0.6 to the sum of the areas of all particles identified is equivalent to the mass fraction of particles with roundness greater than or equal to 0.6 in the positive electrode film layer. Similarly, the mass fraction of particles with roundness less than or equal to 0.3 in the positive electrode film layer is obtained.

[0230] 3. Test of adhesion strength of electrode sheet

[0231] At 25°C, the cold-pressed positive electrode sheet prepared in each example and comparative example is cut into a test sample with a size of L: 100 mm x W: 20 mm, and is ready for use; one side of the double-sided adhesive tape is pasted on the surface of the steel plate, the other side is bonded with the electrode sheet to be tested, and the pressure roller is used to compact it to make it completely adhere to the electrode sheet; the current collector is reversely bent at one end with an angle of 180°; a high-iron tension machine is used for testing, one end of the steel plate is fixed to the lower clamp of the tension machine, and the bent end of the current collector is fixed to the upper clamp; adjust the angle of the current collector to ensure that the upper and lower ends are in a vertical position, then stretch the sample at a speed of 50 mm / min until the current collector is completely peeled off from the surface of the electrode sheet, record the displacement and force in the process, and the strength at the force balance is taken as the adhesion of the electrode sheet, recorded as N1, and the adhesion strength of the electrode sheet can be calculated by the formula N1 / W.

[0232] 4. Test of powder shedding amount of electrode sheet

[0233] At 25 °C, the positive electrode tab prepared by cold pressing of each example and the comparative example was sheared by a die-cutting wrap-around integrated machine, the slitting speed was set to 0.5 m / s, the pressure of the slitting machine was -10 kPa, the number of shearing knives was 2000, the powder falling after shearing was collected, and its weight was recorded as W, and the proportion of metal leakage was recorded as W g / 2000 knives.

[0234] 5. Test method of battery internal resistance DCR

[0235] At 25 °C, the battery monomer prepared by each example and the comparative example was charged at 1 / 3C constant current to the charge cut-off voltage 4.3V, then constant voltage charging was continued at the charge cut-off voltage until the current was 0.05C, then discharged to 50% SOC at 1 / 3C, and after 5 min of standing, discharged at 3C pulse for 30 s.

[0236] The voltage at each pulse discharge was recorded before and after each pulse discharge, and the DCR under different conditions was calculated, and the calculation formula was DCR= (voltage after pulse discharge before standing - voltage before pulse discharge after standing) / pulse current.

[0237] 6. Test method of battery energy density

[0238] The battery monomer prepared by each example and the comparative example was placed at 25 °C for 2 h to ensure that the temperature of the battery monomer was 25 °C. The battery monomer was charged at 1 / 3C to the charge cut-off voltage 3.65V at 25 °C, then constant voltage charging was continued at the charge cut-off voltage until the current was 0.05C, and the charge cut-off (wherein C represents the rated capacity of the battery monomer). After the battery monomer was placed at 25 °C for 1 h, the battery monomer was discharged at 0.33C to the discharge cut-off voltage 2.5V at 25 °C, and the total discharge energy of the battery monomer was recorded as E0.

[0239] The length, width and height of the battery monomer were measured, and the volume value V0 of the battery monomer was calculated as length x width x height.

[0240] The volumetric energy density of the battery monomer = discharge energy E0 of the battery monomer / volume V0 of the battery monomer.

[0241] The battery monomers of each example and the comparative example were prepared according to the above method, and the specific parameters and performances are shown in Table 1, Table 2 and Table 3.

[0242] Table 1

[0243]

[0244] By comparing the examples and the comparative examples, it can be seen that, based on the total mass of the positive electrode film layer, the mass ratio of the positive electrode active material is controlled to be 97.5%-99.2%, and the mass ratio of the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 60%-90%; while the battery has a high energy density, the problem of powder falling caused by the decrease in internal adhesion due to high active material load can be improved.

[0245] By comparing example 1, examples 4-6, it can be seen that, based on the total mass of the positive electrode film layer, the mass ratio of the particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 70%-80%, which is conducive to further improving the battery energy density while reducing the amount of powder falling.

[0246] By comparing example 1, examples 6-10, it can be seen that the ratio of the mass of the particles with a roundness greater than or equal to 0.6 to the mass of the particles with a roundness less than or equal to 0.3 in the positive electrode film layer is 9-21, and further, the ratio is 12-18, which is conducive to forming a more compact packing, thereby improving the energy density of the battery.

[0247] Table 2

[0248]

[0249] By comparing example 1, examples 11-12, it can be seen that, based on the total mass of the positive electrode film layer, the mass ratio of the particles with a particle size R1 satisfying 3 μm≤R1≤6 μm in the positive electrode film layer is 55%-80%, which is conducive to achieving a balance between adhesion strength and battery energy density.

[0250] By comparing example 1, examples 13-16, it can be seen that, based on the total mass of the positive electrode film layer, the mass ratio of the particles with a particle size R2 satisfying 3 μm≤R1≤6 μm in the positive electrode film layer is 5.5%-9.5%, which is conducive to improving the volumetric energy density of the battery.

[0251] By comparing example 1, examples 17-20, it can be seen that, based on the length of the one-dimensional conductive agent and the D V50 of the particles in the positive electrode film layer, the ratio is 5-25, and further, the ratio is 10-25, which is conducive to improving adhesion strength and reducing the amount of powder falling.

[0252] Table 3

[0253]

[0254] It can be seen from the comparison of Example 1 and Examples 21-24 that when the mass ratio of the one-dimensional conductive agent to the total mass of the positive electrode film layer is 0.2%-0.6%, the technical effects of enhancing the bonding strength and reducing the direct current resistance can be achieved. When the mass ratio of the one-dimensional conductive agent is 0.3%-0.5%, low cost, low powder loss and low direct current resistance can be achieved.

[0255] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having substantially the same configuration and achieving the same effects as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the elements of the embodiments are also included in the scope of the present application.

Claims

1. A battery cell comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, characterized by, The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, The positive electrode film layer comprises a positive electrode active material, a binder and a one-dimensional conductive agent, the positive electrode active material comprises a lithium-containing transition metal phosphate, 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 the binder is 0.4%-1.5%, and the mass percentage of the one-dimensional conductive agent is 0.2%-0.6%. The mass percentage of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 60%-80% based on the total mass of the positive electrode film layer, wherein the roundness is measured by the following method: the positive electrode tab is subjected to ion beam polishing-scanning electron microscope testing, a plurality of points are randomly taken, the particles in the taken pictures are identified by AVIZO software, the longest inner diameter and the shortest inner diameter of the particles are measured, and the ratio of the shortest inner diameter to the longest inner diameter of the particles is taken as the roundness of the particles.

2. The battery cell of claim 1, wherein, The mass percentage of the positive electrode active material is 98.2%-98.6% based on the total mass of the positive electrode film layer.

3. The battery cell of claim 1, wherein, The mass percentage of particles with a roundness greater than or equal to 0.6 in the positive electrode film layer is 70%-80% based on the total mass of the positive electrode film layer.

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

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

6. The battery cell of claim 1, wherein, The mass percentage of particles with a particle size R1 satisfying 3 μm≤R1≤6 μm in the positive electrode film layer is 55%-80% based on the total mass of the positive electrode film layer.

7. The battery cell of claim 1, wherein, The mass percentage of particles with a particle size R2 satisfying 9 μm≤R2≤15 μm in the positive electrode film layer is 5.5%-9.5% based on the total mass of the positive electrode film layer.

8. The battery cell of claim 1, wherein, The positive electrode film layer comprises 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.

9. The battery cell of claim 1, wherein, D50 of the positive electrode active material particles V50 is 0.4 μm to 1.5 μm, wherein D V50 D50 refers to the particle diameter at which the cumulative volume distribution reaches 50% in the volume cumulative distribution curve.

10. The battery cell of claim 1, wherein, D50 of the positive electrode active material particles V50 is 0.5 μm to 0.9 μm, wherein D V50 D50 refers to the particle diameter at which the cumulative volume distribution reaches 50% in the volume cumulative distribution curve.

11. The battery cell according to claim 9 or 10, characterized in that The one-dimensional conductive agent comprises one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanofibers.

12. The battery cell of claim 11, wherein, the length of the one-dimensional conductive agent to the D V50 of the positive electrode active material particles is 5-25.

13. The battery cell of claim 11, wherein, The length of the one-dimensional conductive agent is 10-25 times the D V50 of the positive electrode active material particles.

14. The battery cell of claim 1, wherein, The mass percentage of the one-dimensional conductive agent is 0.3%-0.5% based on the total mass of the positive electrode film layer.

15. The battery cell of claim 1, wherein, The lithium-containing transition metal phosphate comprises a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z 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 comprises one or more of Na, K, Mg; Me comprises one or more of Mn, Fe, Co, Ni; M comprises 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, Ce; X comprises one or more of S, Si, Cl, B, C, N; Y comprises one or more of O, F.

16. The battery cell of claim 15, wherein, The lithium-containing transition metal phosphate comprises one or more of lithium iron phosphate, lithium manganese phosphate, fluorinated lithium vanadium phosphate, lithium manganese iron phosphate, and modified materials thereof.

17. The battery cell of claim 15 or 16, wherein, The lithium-containing transition metal phosphate comprises one or more of lithium iron phosphate and modified materials thereof.

18. The battery cell of claim 1, wherein, The positive electrode film layer comprises a zero-dimensional conductive agent, and the zero-dimensional conductive agent comprises one or more of conductive carbon black, ketjen black, and acetylene black.

19. The battery cell of claim 18, wherein, The zero-dimensional conductive agent comprises conductive carbon black.

20. The battery cell of claim 1, wherein, The adhesion strength between the positive electrode film layer and the positive electrode current collector is 15 N / m-50 N / m.

21. A battery device, characterized by The battery device comprises the battery cell as claimed in any one of claims 1 to 20.

22. An electrical device, comprising: The power utilization device comprises the battery device as claimed in claim 21, and the battery device is used to provide electric energy.

23. An energy storage device, comprising: The energy storage device comprises the power utilization device as claimed in claim 22, and the power utilization device is used to store electric energy.

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