Battery cell, battery device, electric device, and energy storage device

Abstract

The invention provides a battery monomer, a battery device, a power utilization device and an energy storage device. The single battery comprises a laminated battery cell, the laminated battery cell comprises a positive pole piece and a negative pole piece, and the compaction density of the positive pole piece is 2.3 g / cm < 3 >-2.6 g / cm < 3 >; the density of the single side surface of the positive electrode film layer is 0.25 g / 1540.25 mm < 2 > to 0.45 g / 1540.25 mm < 2 >; in the tangent plane of the positive electrode film layer along the thickness direction of the positive electrode plate, LR1A50 is 0.6-0.8 in a sphericity-like area cumulative distribution curve of particles of which the particle size R1 is greater than or equal to 1000nm; the median C50 of the graphitization degree is 0.95-1.20 in a cumulative distribution curve of the graphitization degree C value obtained by the positive electrode film layer in a surface scanning mode of a laser microscopic confocal Raman spectrometer. The battery monomer provided by the invention has high capacity and good cycle performance.

Description

Technical Field

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

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

[0003] With the market's pursuit of the battery's endurance mileage and service life, higher requirements are put forward for the battery capacity and cycle performance. However, it is difficult for the existing technology to simultaneously improve the above performances, and how to balance the two has become a technical problem urgently to be solved in this field. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a battery cell with both high capacity and good cycle performance.

[0005] In the first aspect of the present application, a battery cell is provided. The battery cell includes a laminated battery core. The laminated battery core includes a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes lithium-containing transition metal phosphate particles with carbon materials provided on at least part of the surface; when the battery cell is in a fully discharged state, the tap density of the positive electrode plate is 2.3 g / cm 3 -2.6 g / cm 3 ; the areal density of a single side of the positive electrode film layer is 0.25 g / 1540.25 mm 2 -0.45 g / 1540.25 mm 2 ; in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.6-0.8; in the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of a laser confocal Raman spectrometer for the positive electrode film layer, the median C 50 of the graphitization degree is 0.95-1.20; wherein, the graphitization degree C value is I G / I D ,I G represents the intensity of the G peak of the Raman spectrum at 1580±100 cm -1 ,and I D represents the intensity of the D peak of the Raman spectrum at 1350±100 cm -1 .

[0006] Research shows that stress concentration areas in the film layer are prone to crack under the action of cyclic expansion, becoming the starting point of film layer shedding, which is more significant in thick-coated battery cells. Compared with ternary materials, the structure of lithium-containing transition metal phosphates is more stable and not easily broken under high pressure. Lithium-containing transition metal phosphates need to withstand higher pressure during the compaction process of the electrode sheet to pursue an increase in compaction density. However, when the battery cell is in a fully discharged state, the compaction density of the positive electrode sheet is greater than 2.6 g / cm 3 , which will cause overpressure of the electrode sheet and exacerbate stress concentration, increasing the risk of film layer shedding during the cycle; while the compaction density of the positive electrode sheet is less than 2.3 g / cm 3 will result in insufficient contact between the particles in the positive electrode film layer, leading to an increase in the internal resistance of the battery and affecting the energy density of the battery cell; the single-sided areal density of the positive electrode film layer is lower than 0.25 g / 1540.25 mm 2 , which cannot meet the requirements of high energy density. When the single-sided areal density of the positive electrode film layer is higher than 0.45 g / 1540.25 mm 2 , the positive electrode film layer is too thick, and the volume expansion during the cycle is significant and the stress concentration is exacerbated, increasing the risk of film layer shedding.

[0007] Stacked battery cells are beneficial to improving the space utilization rate of the battery, and further improving the volume energy density and capacity of the battery cell. The applicant found that in thick-coated stacked battery cells, stress concentration usually comes from local stress generated during the compaction process. On the one hand, during the compaction process, particles with low sphericity have sharp stress-bearing surfaces and the sliding friction increases during compaction, making it easier to trigger stress concentration; while lithium-containing transition metal phosphate particles often need to be sintered at high temperature. Along with grain boundary melting and particle growth, the sphericity of the particles will decrease, and the median sphericity of the particles usually does not exceed 0.8. When in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode sheet, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is less than 0.6, large local stress will be formed during the compaction of the particles, and the risk of film layer shedding during the cycle will increase significantly; on the other hand, the median graphitization degree C 50 reflects the degree of order of the carbon material layer. When the graphitization degree is higher than 1.2, its concentration is lower. Therefore, considering the material uniformity, the graphitization degree of the carbon material layer is usually not higher than 1.2. When C 50 is less than 0.95, the slipperiness of the carbon layer structure decreases, resulting in large friction between particles during compaction and difficulty in sliding, further increasing the stress during the compaction process, thereby increasing the probability of film layer shedding during the cycle.

[0008] The battery cell provided by this application adopts the processes of thick coating and stacked battery cells, and controls the compaction density of the positive electrode sheet to be 2.3 g / cm when the battery cell is in a fully discharged state 3-2.6 g / cm 3 ; The single-sided surface density of the positive electrode film layer is 0.25 g / 1540.25 mm 2 -0.45 g / 1540.25 mm 2 , while increasing the battery capacity, relieve stress concentration, reduce the probability of film layer peeling, and improve the cycle life of the battery; further, by controlling in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, in the cumulative area distribution curve of the sphericity of particles with particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.6 - 0.8, and in the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median C of the graphitization degree 50 is 0.95 - 1.20, improve the sphericity of large particles in the positive electrode film layer and the graphitization degree of the positive electrode film layer, improve the local stress generated during the compaction process, thereby further reducing the probability of film layer peeling and improving the cycle life of the battery.

[0009] In summary, the battery cell of the present application improves its capacity diving problem while having good capacity, and takes into account the cycle life of the battery.

[0010] In any implementation manner, the single-sided coating surface density of the positive electrode film layer is 0.3 g / 1540.25 mm 2 - 0.45 g / 1540.25 mm 2 .

[0011] In any implementation manner, the single-sided coating surface density of the positive electrode film layer is 0.35 g / 1540.25 mm 2 - 0.4 g / 1540.25 mm 2 .

[0012] The single-sided coating surface density of the positive electrode film layer further within the above range helps to further increase the capacity of the battery and take into account the cycle performance.

[0013] In any implementation manner, in the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median C of the graphitization degree 50 is 1.01 - 1.13.

[0014] The graphitization degree of the positive electrode film layer further within the above range helps to further increase the ease of slip of the particles in the positive electrode film layer, reduce the stress concentration in the positive electrode film layer, and thus further improve the long-cycle stability of the battery cell.

[0015] In any implementation manner, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode sheet, in the cumulative area distribution curve of the sphericity of particles with particle size R1 satisfying R1≥1000 nm, LR1A50 is 0.65 - 0.75.

[0016] In any embodiment, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000nm, L R1A50 is 0.67 - 0.72.

[0017] In the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000nm, L R1A50 Within the range of 0.65 - 0.75, and further within the range of 0.67 - 0.72, it is beneficial to further reduce the stress concentration at large particles in the positive electrode film layer of the thick-coated laminated cell, thereby reducing the probability of film layer peeling and improving the cycle life of the battery.

[0018] In any embodiment, the single-sided thickness H of the positive electrode film layer is 70μm - 120μm.

[0019] In any embodiment, the single-sided thickness H of the positive electrode film layer is 90μm - 120μm.

[0020] When the single-sided thickness of the positive electrode film layer is within the above range, it helps to increase the loading amount of the positive electrode active material in the battery, thereby increasing the capacity of the battery.

[0021] In any embodiment, the single-sided thickness H of the positive electrode film layer is 100μm - 120μm.

[0022] Increasing the thickness of the positive electrode film layer helps to increase the loading amount of the positive electrode active material and the capacity of the battery. However, the applicant has found that when the single-sided thickness of the positive electrode film layer is greater than or equal to 100μm, during the battery cycling process, the volume expansion of the positive electrode film layer is more significant, resulting in greater stress, and the stress concentration phenomenon in the positive electrode film layer is more significant, increasing the risk of film layer peeling, which in turn affects the cycling performance of the battery. In the embodiments of the present application, the capacity of the battery is increased by increasing the thickness of the positive electrode film layer, and at the same time, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, the sphericity of particles with a particle size R1 satisfying R1≥1000nm, and in the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median C of the graphitization degree 50 Improve the slip degree between particles in the positive electrode film layer and reduce the stress concentration generated during the electrode pressing process, so as to balance the cycling performance of the battery while increasing the battery capacity. In any embodiment, based on the total area of particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the area ratio of particles with a particle size R1 satisfying R1≥1000nm is 12% - 50%.

[0023] In any embodiment, based on the total area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm is 12%-40%.

[0024] Large particles with a particle size R1 satisfying R1≥1000 nm contribute to improving the compaction density of the positive electrode sheet, thereby increasing the volume energy density of the battery cell. However, researchers have found that stress concentration is likely to occur at these large particles, increasing the risk of peeling off of the positive electrode film layer. Therefore, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is in the range of 12%-50%, further in the range of 12%-40%, which can not only improve the compaction density of the electrode sheet but also prevent the film layer from peeling off too frequently, thereby improving the energy density of the thick-coated lithium-containing transition metal phosphate battery while alleviating the capacity plunge problem and taking into account the cycle life of the battery.

[0025] In any embodiment, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is less than or equal to 5%.

[0026] In any embodiment, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is 0.2%-2.5%.

[0027] In any embodiment, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is 0.2%-2%.

[0028] When the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is within the above range, the stress concentration degree in the local area of the film layer can be effectively reduced, so that the stress during the compaction process of the film layer can be evenly dispersed throughout the entire area of the film layer, thereby reducing the probability of film layer peeling off while increasing the battery energy density, alleviating the capacity plunge problem of the thick-coated lithium-containing transition metal phosphate battery, and improving the battery cycle life.

[0029] In any embodiment, in the cumulative distribution curve of the coating value B obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median B of the coating value 50 is 0.30-0.60, where the coating value B is I P / I D where I P represents the intensity of the P peak of the Raman spectrum at 948±100 cm -1 and I D represents the intensity of the D peak of the Raman spectrum at 1350±100 cm -1 .

[0030] Median B of the coating value of the positive electrode film layer 50 Within the above range, it indicates that the carbon material layer of the positive electrode active material is relatively dense and uniform, which is beneficial to improving the slip uniformity of the positive electrode film layer during the rolling process and reducing the stress concentration phenomenon in the thick-coated positive electrode film layer; in addition, with the help of the dense and uniform carbon material layer, the large particles in the positive electrode film layer are more likely to achieve slip during the compaction process, thereby reducing the stress concentration phenomenon at the large particles in the thick-coated positive electrode film layer, reducing the probability of the positive electrode film layer peeling off, improving the problem of battery capacity drop, and increasing the cycle life of the battery.

[0031] In any embodiment, the lithium-containing transition metal phosphate particles in the positive electrode film layer include the components represented by the following general formula: Li m Fe x P y O j Q q Formula I, wherein Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.8 ≤ m ≤ 1.15, 0.9 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 ≤ q ≤ 0.1.

[0032] In any embodiment, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate fluoride, lithium manganese iron phosphate and their modified materials.

[0033] In any embodiment, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate and its doped modified materials, coated modified materials.

[0034] In any embodiment, the iron dissolution rate of the positive electrode material in the positive electrode film layer is 658 ppm - 1921 ppm.

[0035] In any embodiment, the iron dissolution rate of the positive electrode material in the positive electrode film layer is 658 ppm - 1485 ppm.

[0036] In any embodiment, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of titanium element is 500 ppm - 8000 ppm.

[0037] In any embodiment, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of titanium element is 1000 ppm - 3000 ppm.

[0038] Introducing titanium element into lithium-containing transition metal phosphate particles requires adding a titanium source during the preparation of the cathode active material. The titanium source is often an inert material, and attaching to the surface of the lithium-containing transition metal phosphate raw material can play a role in reducing the reaction activity and reducing the growth of particle size. Improving the graphitization degree of the cathode active material often requires a higher sintering temperature or a longer sintering time. However, this will also increase the particle size in the cathode film layer, increase the stress concentration in the cathode film layer, and cause the film layer peeling phenomenon in the cathode film layer. In the embodiments of the present application, by adding a high content of titanium element to the lithium-containing transition metal phosphate particles, the reaction activity of the synthesis raw material of the cathode active material is reduced, so that the cathode active material can control the proportion of large particles while having a high graphitization degree, reduce the stress concentration in the cathode film layer, and reduce the probability of film layer peeling in the cathode film layer, taking into account the cycle life of the battery while improving the energy density of the battery.

[0039] At the same time, the doping of titanium element in the cathode active material is beneficial to causing lattice distortion, reducing the Li-O bond energy, increasing the lithium ion transmission rate, and improving the kinetic performance of the battery. In the thick coating film layer, the lithium ion diffusion is uneven, and there is often a significant lithium ion concentration gradient. In the embodiments of the present application, by adding a high content of titanium element to the lithium-containing transition metal phosphate particles, the solid-phase transmission rate of the cathode active material is improved, and the kinetic problems of the thick electrode plate battery are improved.

[0040] In any embodiment, based on the total mass of the lithium-containing transition metal phosphate particles in the cathode film layer, the mass content of vanadium element is 500 ppm - 5000 ppm.

[0041] In any embodiment, based on the total mass of the lithium-containing transition metal phosphate particles in the cathode film layer, the mass content of vanadium element is 500 ppm - 3000 ppm.

[0042] The vanadium element in the cathode film layer can be in multiple valence states. Among them, vanadium with a +5 valence (V 5+ ) can be doped at the phosphorus element site. Because of its larger radius, it can cause lattice distortion and expand the lithium ion diffusion channel, thereby increasing the ionic conductivity of the cathode active material and improving the kinetic performance of the battery; vanadium with a +3 valence (V 3+ ) can be doped at the transition metal site, and lithium vacancies are generated through charge compensation, thereby increasing the electronic conductivity of the cathode active material. In addition, improving the distribution uniformity of vanadium element in the lithium-containing transition metal phosphate particles helps to further improve the kinetic performance of the cathode film layer and the reaction uniformity of the cathode film layer, thereby further improving the kinetic performance and cycle performance of the battery monomer.

[0043] The mass content of vanadium element within the above range helps to improve the kinetic performance of the positive electrode sheet and that of the thick-coated lithium-containing transition metal phosphate battery. Meanwhile, the synergistic effect of titanium element, vanadium element and carbon nanotubes in the positive electrode film layer helps to form a good three-dimensional network, further improving the electronic conductivity and ionic conductivity of the positive electrode film layer, thereby further improving the kinetic performance of the thick-coated lithium-containing transition metal phosphate battery.

[0044] In any implementation manner, the porosity of the positive electrode film layer is 14% - 28%.

[0045] When the porosity of the positive electrode film layer is within the above range, the positive electrode film layer has good electrolyte infiltration rate and tortuosity, which helps the diffusion of lithium ions in the liquid and solid phases, helps to reduce the concentration polarization of the thick electrode sheet, and improves the kinetic performance of the battery. At the same time, it helps to alleviate the volume expansion of the thick-coated electrode sheet during the cycling process, reduce the mechanical stress of the film layer and the stress concentration phenomenon, thereby reducing the risk of film layer shedding of the thick-coated electrode sheet.

[0046] Especially in the thick-coated soft-pack battery, the gap between the housing and the electrode sheet is small, the volume occupancy rate of the film layer is large, the accommodation volume of the electrolyte is reduced, and when the porosity of the positive electrode film layer is within the above range, it helps to improve the liquid retention rate of the battery cell and the kinetic performance of the battery.

[0047] In any implementation manner, the positive electrode film layer further includes a conductive agent. Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the agglomeration region of the conductive agent is 0.5% - 2.5%.

[0048] Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, when the area ratio of the agglomeration region of the conductive agent is within the above range, it indicates that the conductive agent in the positive electrode film layer is evenly dispersed and is easy to form a uniform conductive network, which is particularly beneficial to reducing the problem of kinetic decline caused by the increase in the ion transport path in the thick-coated film layer, reducing the local polarization and even lithium plating problems generated during the cycling of the battery, and improving the cycle life of the battery.

[0049] At the same time, research shows that the large-sized first particles in the lithium-containing transition metal phosphate particles are prone to rebound. When the agglomeration area of the conductive agent is within the above range, it can inhibit the rebound of the lithium-containing transition metal phosphate particles by virtue of the uniform distribution of the conductive agent, form a mechanical restraint on the particles and even the film layer, improve the cohesive force of the film layer, reduce the film layer powdering and shedding phenomena, and improve the cycle life of the battery.

[0050] In any implementation manner, the positive electrode film layer further includes a conductive agent. Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the agglomeration region of the conductive agent is 0.5% - 1.7%.

[0051] In the embodiments of the present application, the area ratio of the agglomeration region of the conductive agent is further within the above range, indicating that the conductive agent is more uniformly distributed in the positive electrode film layer, and the content of the conductive agent is relatively low. While improving the kinetic performance of the positive electrode film layer, it helps to reduce the occupation of the space of the positive electrode active material by excessive conductive agent, thereby further improving the volumetric energy density of the battery while improving the battery kinetic performance.

[0052] In any embodiment, the conductive agent includes carbon nanotubes, and the carbon nanotubes include one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0053] Due to the one-dimensional structure of carbon nanotubes, a network structure can be formed in the positive electrode film layer. On the one hand, the high elastic modulus of carbon nanotubes enables its network structure to not only serve as a bridge for stress propagation but also have a binding effect on the thick-coated positive electrode film layer, inhibiting the rebound of lithium-containing transition metal phosphate particles, effectively alleviating stress concentration, reducing the risk of film layer peeling, and thus improving the problem of battery capacity sudden drop. On the other hand, the excellent conductivity of carbon nanotubes makes its network structure an efficient electron transport channel. Even if there is local film layer peeling, the thick electrode can still maintain high electron transport efficiency in the in-plane direction and thickness direction, thereby delaying the occurrence of the capacity sudden drop problem and further improving the kinetic performance and cycle life of the battery.

[0054] In any embodiment, the conductive agent further includes conductive carbon black.

[0055] Conductive carbon black has a relatively high specific surface area and thus has good liquid retention ability. The thick electrode has a large swelling force during the cycling process, making the electrolyte easy to be extruded. The distribution of conductive carbon black in the positive electrode film layer is beneficial to improving the liquid retention ability of the thick electrode, further alleviating the phenomenon of capacity sudden drop during battery cycling, and improving the cycle life of the battery.

[0056] In any embodiment, the agglomeration region of the conductive agent includes carbon nanotubes and conductive carbon black.

[0057] Researchers found that due to their high surface energy, carbon nanotubes are prone to agglomeration, resulting in uneven dispersion in the positive electrode film layer and unable to form an effective carbon nanotube network structure. The surface energy of conductive carbon black is relatively close to that of carbon nanotubes, and it can adsorb on the surface of carbon nanotubes to form a physical barrier, increasing the resistance to carbon nanotube agglomeration, reducing the direct contact between carbon nanotubes, thereby inhibiting agglomeration and improving the distribution uniformity of carbon nanotubes in the positive electrode film layer. On the one hand, this helps to improve the conductivity of the thick-coated positive electrode film layer and enhance the kinetic performance of the battery; on the other hand, it helps to exert the binding effect of carbon nanotubes on the positive electrode film layer, reduce the risk of shedding of the thick-coated positive electrode film layer, and further improve the kinetic performance and cycle life of the battery. In addition, the agglomeration of carbon nanotubes in the agglomeration region of the conductive agent will also cause local blockage of the ion transport path in the agglomeration region of the conductive agent. The combination of conductive carbon black can improve the lithium ion transport ability in this region, reduce local polarization, and further improve the cycle stability of the battery.

[0058] In any implementation, based on the mass of the positive electrode film layer, the mass content C1 of carbon nanotubes satisfies: 0 < C1 ≤ 2.5%, and the mass content C2 of conductive carbon black satisfies: 0 < C2 ≤ 2.5%.

[0059] When the mass contents of carbon nanotubes and conductive carbon black are within the above ranges, the agglomeration phenomenon of carbon nanotubes can be effectively alleviated and a good conductive network structure can be formed, thereby effectively reducing the stress concentration in the positive electrode film layer, improving the liquid retention rate of the positive electrode plate during long-term cycling, further reducing the risk of film layer shedding and the degree of polarization of the electrode plate, improving the kinetic performance of the battery and taking into account the problem of capacity drop, and improving the cycle life of the battery.

[0060] In any implementation, the positive electrode film layer further includes a dispersant, and the dispersant includes hydrogenated nitrile butadiene rubber (HNBR).

[0061] HNBR is obtained by hydrogenating the double bonds of nitrile butadiene rubber. Its highly saturated main chain structure gives it excellent oil resistance, heat resistance, and aging resistance, etc. This enables it to remain stable in different environments and systems when used as a dispersant, and is not prone to degradation or deterioration, thus effectively exerting the dispersing effect. The HNBR molecular chain contains both polar nitrile groups and non-polar hydrocarbon segments at the same time. The polar nitrile groups can interact with the surfaces of some polar substances or particles, such as adsorbing on the surface of the dispersed particles through hydrogen bonds, electrostatic interactions, etc.; the non-polar hydrocarbon segments have good lipophilicity and can be well extended and dispersed in non-polar or weakly polar media, enabling the particles to be evenly dispersed in the medium.

[0062] After HNBR adsorbs on the surface of the particles in the slurry, its long-chain molecules will form a physical barrier around the particles, preventing the particles from approaching and aggregating with each other, and keeping the particles in a relatively independent dispersed state in the system. At the same time, HNBR can reduce the surface tension between the dispersion medium and the dispersed particles, making the particles easier to be wetted by the medium, thereby promoting the dispersion of the particles in the medium. At the same time, it can also reduce the interfacial energy between the particles, reducing the aggregation phenomenon of the particles driven by the interfacial energy. Further, when the slurry is dried into a film, the elastic network structure of HNBR can buffer the shrinkage stress generated by the volatilization of the solvent, reduce the re-aggregation of the conductive agent due to capillary force during this process, reduce the area ratio of the agglomeration region of the conductive agent, and improve the kinetic performance and cycle life of the battery.

[0063] In any embodiment, based on the mass of the positive electrode film layer, the mass content of the dispersant is 0.5% - 2%.

[0064] When the mass content of the dispersant is within the above range, it can achieve uniform dispersion of the particles in the positive electrode film layer while maintaining a high loading amount of the positive electrode film layer, reduce the stress concentration of the thick-coated lithium-containing transition metal phosphate positive electrode film layer, and effectively alleviate the problem of battery capacity drop.

[0065] In any embodiment, the battery cell further includes a separator disposed between the positive electrode plate and the negative electrode plate. The separator includes a base film, a ceramic layer disposed on at least one side of the base film, and an adhesive layer disposed on the side of at least one ceramic layer away from the base film. The adhesive layer is a continuous layer with a porous structure, and the adhesive layer includes a polyvinylidene fluoride-based polymer.

[0066] In any embodiment, the battery cell further includes a separator disposed between the positive electrode plate and the negative electrode plate. The separator includes a base film, ceramic layers disposed on both sides of the base film, and an adhesive layer disposed on the sides of the ceramic layers away from the base film.

[0067] In any embodiment, the polyvinylidene fluoride-based polymer includes one or more of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0068] In any embodiment, the polyvinylidene fluoride-based polymer includes polyvinylidene fluoride (PVDF).

[0069] In the prior art, the adhesive layer of the separator usually uses aqueous PVDF, which presents an island structure in the separator. On the one hand, this is beneficial for providing gaps for the expansion of the battery cell, and on the other hand, it is convenient for manufacturing; however, the contact area between such a separator adhesive layer and the electrode plate is small, and the adhesive force is weak.

[0070] The separator provided by the embodiment of the present application uses a continuous layer with a porous structure as the adhesive layer. The porous structure provides space for the expansion of the thick-coated battery cell and improves its stability. At the same time, compared with the adhesive layer in the prior art, it has a larger bonding area with the electrode sheet, so that the bonding between the separator and the electrode sheet is more firm and uniform. Further, when the positive electrode film layer rebounds, it is beneficial to maintain the interfacial contact between the separator and the positive electrode film layer and reduce the occurrence probability of film layer peeling off.

[0071] Compared with wound battery cells, the extrusion between the separator and the electrode sheet in laminated battery cells is smaller, and the separator and the electrode sheet are prone to relative displacement, which will disturb the film layer and the film layer is prone to powder falling or peeling off. In addition, it may also cause the positive and negative electrodes to overlap each other, increasing the risk of internal short circuit in the battery cell. Therefore, the separator provided by the embodiment of the present application is particularly suitable for laminated battery cells. The increased bonding force between the porous adhesive layer and the electrode sheet helps to improve the bonding force between the separator and the electrode sheet and reduce the relative displacement between the separator and the electrode sheet. This not only helps to reduce the disturbance to the positive electrode film layer and the probability of film layer peeling off, but also helps to reduce the risk of short circuit caused by the overlap of the positive and negative electrodes.

[0072] In summary, when the polyvinylidene fluoride-based polymer in the adhesive layer of the embodiment of the present application is selected from the above materials, it helps to form a continuous and uniform porous adhesive layer. First, the bonding force between the adhesive layer and the electrode sheet is increased and evenly distributed, which helps to reduce the stress concentration phenomenon in the thick-coated lithium-containing transition metal phosphate positive electrode film layer and reduce the risk of film layer peeling off, thereby helping to further improve the cycle life of the battery. Second, the stable bonding between the adhesive layer and the positive electrode sheet or the negative electrode sheet helps to reduce the direct contact between the positive electrode sheet and the negative electrode sheet caused by the relative displacement between the electrode sheet and the separator, reduce the risk of internal short circuit, and help to improve the battery safety performance. Second, the porous adhesive layer helps to maintain the porosity of the separator, reserve space for the expansion of the battery cell, and further improve the cycle life of the battery.

[0073] In any embodiment, the thickness of the base film in the separator is 7 μm - 9 μm.

[0074] In any embodiment, the single-sided thickness of the ceramic layer in the separator is 2 μm - 4 μm.

[0075] In any embodiment, the single-sided thickness of the adhesive layer in the separator is 1 μm - 5 μm.

[0076] If the thickness of the bonding layer is too low, the void space in the separator is small and the bonding force between the separator and the electrode is low. On the one hand, after the film layer expands, the stress increases and the probability of the film layer peeling off increases, affecting the cycle life of the battery. On the other hand, the probability of positive-negative lap short circuit increases, thus affecting the safety performance of the battery. If the thickness of the bonding layer is too large, the space occupancy rate of the battery is large, thus affecting the volumetric energy density of the battery. In the embodiments of the present application, the thickness of the bonding layer is within the above range, which helps to balance the cycle life, safety performance and volumetric energy density of the battery.

[0077] In any embodiment, a bottom coating is provided in the bottom region of the positive electrode film layer close to the positive current collector. The bottom coating includes a conductive agent and a binder. The conductive agent includes carbon nanotubes and conductive carbon black, and the binder includes polyvinylidene fluoride (PVDF).

[0078] In any embodiment, the thickness of the bottom coating is 0.5 μm - 5 μm.

[0079] The bottom coating provided by the embodiments of the present application helps to improve the bonding force between the positive electrode film layer and the positive current collector and relieve the stress concentration phenomenon at large particles, thereby reducing the probability of the positive electrode film layer peeling off and improving the cycle stability of the battery. At the same time, compared with the direct contact between the positive current collector and the positive electrode film layer, the contact area between the bottom coating and the positive electrode film layer increases, which helps to increase the area of electron transfer between the current collector and the positive electrode film layer, thereby reducing the internal resistance of the electrode and improving the kinetic performance of the battery.

[0080] In any embodiment, the battery cell includes a housing, and the stacked electrode assembly is accommodated in the housing. The dimension of the housing in the length direction is L1, the dimension of the housing in the width direction is W1, and the dimension of the housing in the thickness direction is H1, where 450 mm ≤ L1 ≤ 1300 mm, 100 mm ≤ W1 ≤ 150 mm; 14 mm ≤ H1 ≤ 22 mm.

[0081] In any embodiment, the dimension of the housing in the length direction is L1, and 450 mm ≤ L1 ≤ 650 mm.

[0082] When the dimension L1 of the housing in the length direction satisfies 450 mm ≤ L1 ≤ 650 mm, the length of the battery cell is short, which helps to shorten the diffusion path of the current, reduce the internal resistance of the electrode, thereby reducing the heat generation of the battery and improving its kinetic performance; in addition, the shorter housing length helps to shorten the diffusion path of the electrolyte during the infiltration process, improve the infiltration rate and uniformity of the electrolyte, further promote the uniformity of lithium ion deintercalation during the cycle process, relieve the stress concentration phenomenon, reduce the risk of film layer peeling off, and improve the cycle stability of the battery cell.

[0083] In any embodiment, the dimension of the housing in the length direction is L1, and 900 mm ≤ L1 ≤ 1300 mm.

[0084] When the dimension L1 of the housing in the length direction satisfies 900 mm ≤ L1 ≤ 1300 mm, the dimension of the battery cell is relatively long, which helps to reduce the volume ratio of the housing in the battery cell and increase the loading ratio of the active material. At the same time, the relatively long battery cell can reduce the number of battery cells required in the battery module, simplify the structural design of the battery module, reduce the number and complexity of the structural components in the module, thereby improving the space utilization rate of the battery pack, and further helping to improve the volume energy density of the battery cell.

[0085] In any embodiment, the material of the housing is a soft-pack material, and the soft-pack material includes an aluminum-plastic composite film.

[0086] In any embodiment, the material of the housing includes a composite film formed by one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), polyethylene (PE) and aluminum.

[0087] The soft-pack material has a relatively high elongation rate, so its housing is thinner, lighter and softer, which helps to improve the space utilization rate of the battery cell, thereby increasing the energy density of the battery cell. In addition, the high barrier property of aluminum can effectively reduce the penetration of water and oxygen into the battery interior, reduce the decomposition of the electrolyte and the oxidation degree of the electrode material, thereby increasing the battery life.

[0088] In any embodiment, at 25 °C, the capacity of the battery cell is 95 Ah - 300 Ah.

[0089] In any embodiment, at 25 °C, the capacity of the battery cell is 150 Ah - 190 Ah.

[0090] The second aspect of the present application provides a battery device, including the battery cell provided by the first aspect of the present application.

[0091] The third aspect of the present application provides an electrical device, the electrical device includes the battery device provided by the second aspect, and the battery device is used to provide electrical energy.

[0092] The fourth aspect of the present application provides an energy storage device, the energy storage device includes the battery device provided by the second aspect, and the battery device is used to store electrical energy. Description of the Drawings

[0093] Figure 1 is a schematic diagram of a separator of an embodiment of the present application; Figure 2 is a schematic diagram of a separator of the prior art; Figure 3 is a schematic diagram of the surface topography of an adhesive layer of an embodiment of the present application; Figure 4It is a schematic diagram of a soft-pack laminated battery of the present application; Figure 5 It is a schematic diagram of an electrical device according to an embodiment of the present application.

[0094] Explanation of reference numerals: 5 Battery cell; 50 Housing; 20 Separator; 201 Base film; 202 Ceramic layer; 203 Adhesive layer; X Length direction; Y Width direction; Z Thickness direction. Detailed implementation manners

[0095] Hereinafter, embodiments of the lithium-ion secondary battery, battery device, electrical device, and energy storage device of the present application that are specifically disclosed will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where the detailed description of well-known matters and the repeated description of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0096] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0097] If there is no special instruction, 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.

[0098] Unless otherwise specified, all technical features and optional technical features of this 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 this application.

[0099] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0100] In this application, the terms "a plurality of" and "a variety of" refer to two or more than two.

[0101] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0102] Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various commonly used testing methods in the art. For example, they can be measured according to the testing methods given in the embodiments of this application. Unless otherwise specified, the testing temperature of each parameter is 25 °C.

[0103] In the embodiments of this application, the battery device may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly may include a plurality of pouch battery cells, and the plurality of pouch battery cells are connected in series, parallel or in a hybrid connection through a busbar component. For example, the battery cell assembly is usually formed by arranging a plurality of pouch battery cells; the battery cell assembly can be a battery module, and the battery module is formed by arranging and fixing a plurality of pouch battery cells to form an independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with cable ties.

[0104] The battery device can be a battery pack, and the battery pack includes a box body and one or more battery cell assemblies, and the battery cell assemblies are accommodated in the box body. The battery cell assembly can be a battery module, and the battery cell assembly can be accommodated in the box body by fixing the battery module in the box body; the battery cell assembly can also be accommodated in the box body by directly fixing a plurality of pouch battery cells to the box body.

[0105] In an embodiment of the present application, the battery box may include a first battery box and a second battery box. The first battery box and the second battery box are snapped together so that a closed space is formed inside the battery box to accommodate the battery cell assembly. Here, "closed" means covered or closed, which can be sealed or non-sealed. The first battery box can be a top cover or a bottom plate. For example, the battery box may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame so that a closed space is formed inside the battery box to accommodate the battery cell assembly.

[0106] In an embodiment of the present application, the battery box can be part of the chassis structure of a vehicle. For example, part of the battery box can become at least part of the vehicle floor, or part of the battery box can become at least part of the crossbeam and longitudinal beam of the vehicle.

[0107] In an embodiment of the present application, the battery cell can be a secondary battery, which refers to a battery cell that can be activated by charging after discharging so as to be used continuously; the battery cell can be a lithium-ion battery. The battery cell can be in a flat shape.

[0108] The battery mentioned in the embodiment of the present application can be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application can include battery cells, battery modules, battery packs, etc.

[0109] The battery cell is the smallest unit that makes up the battery and can independently perform the functions of charging and discharging.

[0110] When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or in a hybrid connection through a busbar component. 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, and the battery pack includes a battery box and battery cells, and the battery cells or battery modules are accommodated in the battery box. In some embodiments, the battery box can be part of the chassis structure of a vehicle. For example, part of the battery box can become at least part of the vehicle floor, or part of the battery box can become at least part of the crossbeam and longitudinal beam of the vehicle.

[0111] 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.

[0112] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0113] In some embodiments, the above-mentioned battery module can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0114] The battery cell includes an electrode assembly and an electrolyte.

[0115] The electrode assembly generally includes a positive electrode tab and a negative electrode tab. The negative electrode tab is the electrode where the reaction of absorbing or lithiating lithium ions during charging and releasing or delithiating lithium during discharging occurs. The positive electrode tab is the electrode where the reaction of releasing or delithiating lithium ions during charging and absorbing or lithiating lithium during discharging occurs.

[0116] Although lithium-containing transition metal phosphate as the positive electrode active material has significant advantages in terms of cycle stability, its intrinsic specific capacity is significantly lower than that of ternary materials. The applicant found that adopting a thick coating process in the electrode preparation process has become an effective technical means to make up for the disadvantage of low capacity of lithium-containing phosphate. However, this process improvement also brings new technical challenges: the thick electrode tab will generate a larger volume expansion during long-term cycling, resulting in an increase in internal stress, so that the film layer is prone to partial or even complete detachment from the electrode tab under the action of stress. On the one hand, the detachment of the film layer brings about the loss of the positive electrode active material participating in the charge and discharge reaction. On the other hand, it forms an "island" effect, that is, isolated regions are formed between some active material particles or between the particles and the conductive agent, and good electrical contact cannot be formed, and thus they cannot participate in the charge and discharge reaction of the battery, resulting in a drop in battery capacity; at the same time, this part of the material affects ion transport, increases the internal resistance of the battery, causes local overheating of the battery and increases the risk of thermal runaway, seriously affecting the service life of the battery. Therefore, how to keep the battery capacity stable during cycling while increasing the energy density is still a technical problem that needs to be urgently solved at present.

[0117] The first aspect of the present application provides a battery cell. The battery cell includes a laminated battery core. The laminated battery core includes a positive electrode tab and a negative electrode tab. The positive electrode tab includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes lithium-containing transition metal phosphate particles with carbon materials provided on at least part of the surface; when the battery cell is in a fully discharged state, the compaction density of the positive electrode tab is 2.3 g / cm 3 -2.6 g / cm 3 ; the areal density of a single side of the positive electrode film layer is 0.25 g / 1540.25 mm 2 -0.45 g / 1540.25 mm 2 ; in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode tab, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.6 - 0.8; in the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of a laser confocal Raman spectrometer for the positive electrode film layer, the median C 50 of the graphitization degree is 0.95 - 1.20; wherein, the graphitization degree C value is I G / ID , I G represents the intensity of the G peak of the Raman spectrum at 1580 ± 100 cm -1 , and I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 100 cm -1 .

[0118] Research shows that stress concentration areas in the film layer are prone to crack under the action of cyclic expansion, becoming the starting point of film layer shedding, which is more significant in thick-coated battery cells. Compared with ternary materials, the structure of lithium-containing transition metal phosphates is more stable and not easily broken under high pressure. Lithium-containing transition metal phosphates need to withstand higher pressure during the compaction process of the electrode sheet to pursue an increase in compaction density. However, when the battery cell is in a fully discharged state, the compaction density of the positive electrode sheet is greater than 2.6 g / cm 3 , which will cause overpressure of the electrode sheet, aggravate stress concentration, and increase the risk of film layer shedding during the cycle; while the compaction density of the positive electrode sheet is less than 2.3 g / cm 3 will result in insufficient contact between the particles of the positive electrode film layer, leading to an increase in the internal resistance of the battery and affecting the energy density of the battery cell; the single-sided areal density of the positive electrode film layer is lower than 0.25 g / 1540.25 mm 2 , which cannot meet the requirements of high energy density. The single-sided areal density of the positive electrode film layer is higher than 0.45 g / 1540.25 mm 2 , the positive electrode film layer is too thick, the volume expansion during the cycle is significant, the stress concentration is aggravated, and the risk of film layer shedding is increased.

[0119] Stacked electrode battery cells are beneficial to improving the space utilization rate of the battery, and further improving the volume energy density and capacity of the battery cell. The applicant found that in thick-coated stacked electrode battery cells, stress concentration usually comes from local stress generated during the compaction process. On the one hand, during the compaction process, particles with low sphericity have sharp stress-bearing surfaces and are not prone to particle slip during compaction. The mutual hindrance between particles under stress is likely to cause stress concentration. When in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode sheet, in the cumulative distribution curve of the sphericity area of particles with a particle size R1 satisfying R1 ≥ 1000 nm, L R1A50 is less than 0.6, large local stress will be formed during the compaction of the particles, and the risk of film layer shedding during the cycle will increase significantly; on the other hand, the median C of the graphitization degree 50 reflects the degree of order of the carbon material layer. When C 50When it is less than 0.95, the slipperiness of the carbon layer structure decreases, resulting in large friction between particles during compaction and difficulty in slippage, further increasing the stress during the compaction process, thereby increasing the probability of film layer peeling off during the cycling process. Lithium-containing transition metal phosphate particles often need to be sintered at high temperatures. As the sintering temperature or time increases, the grain boundaries of the particles melt, the particles grow, and the graphitization degree increases, but the sphericity of the particles will decrease. In order to balance the sphericity and graphitization degree of the particles in the film layer and reduce the short-board effect of stress concentration caused by either of them during the compaction process, the median sphericity of particles with a particle size R1 satisfying R1≥1000nm often does not exceed 0.8; and the median C of the graphitization degree of the positive electrode film layer 50 is usually not higher than 1.2.

[0120] The battery cell provided by this application adopts the processes of thick coating and laminated cell, and controls the compaction density of the positive electrode sheet to be 2.3g / cm 3 -2.6g / cm 3 ; the single-sided areal density of the positive electrode film layer is 0.25g / 1540.25mm 2 -0.45g / 1540.25mm 2 , while increasing the battery capacity, relieving stress concentration, reducing the probability of film layer peeling off, and improving the cycle life of the battery; further, by controlling in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000nm, L R1A50 is 0.6 - 0.8, and in the cumulative distribution curve of the C value of the graphitization degree obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median C of the graphitization degree 50 is 0.95 - 1.20, improving the sphericity of large particles in the positive electrode film layer and the graphitization degree of the positive electrode film layer, improving the local stress generated during the compaction process, thereby further reducing the probability of film layer peeling off and improving the cycle life of the battery.

[0121] In summary, the battery cell of this application improves its capacity diving problem while having a high capacity, and balances the cycle life of the battery.

[0122] In this application, a laminated cell refers to a cell formed by stacking a positive electrode sheet, a separator, and a negative electrode sheet together.

[0123] In this application, the positive electrode film layer contains lithium-containing transition metal phosphate, but the positive electrode film layer does not simply refer to the positive electrode active material layer. Other film layers that are connected to the positive electrode active material layer and are difficult to distinguish, such as the bottom coating layer, the liquid retention layer, etc., are collectively referred to as the positive electrode film layer.

[0124] In the present application, the lithium-containing transition metal phosphate refers to a phosphate material containing lithium element and transition metal element, which can be detected by any well-known method in the art. For example, it can be detected by combining an X-ray diffractometer (XRD) with an energy spectrometer and an inductively coupled plasma mass spectrometer.

[0125] In the present application, the carbon material disposed on at least a part of the surface of the lithium-containing transition metal phosphate particles can be detected by any well-known method in the art. As an example, by combining a transmission electron microscope and an energy spectrometer to characterize the lithium-containing transition metal phosphate particles, the carbon material disposed on at least a part of the surface of the lithium-containing transition metal phosphate particles can be observed.

[0126] In the present application, the fully discharged state means that the battery is placed in an oven environment at 25°C, left to stand for 2 h, and after the battery temperature remains at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.5V and then at a constant current of 0.1C to 2.0V.

[0127] In the present application, the tap density of the positive electrode plate can be tested by a method known in the art. As an example, the battery is placed in an oven environment at 25°C, left to stand for 2 h, and after the battery temperature remains at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.5V and then at a constant current of 0.1C to 2.0V. The battery is disassembled to obtain the positive electrode plate, and the residual electrolyte is treated with a dimethyl carbonate solvent. The electrode plate is dried, cut into small round pieces with an area of S, and its mass is obtained as W1. The thickness T1 of the positive electrode plate is measured using a micrometer. Then, the positive electrode film layer of the above-weighted electrode plate is wiped off, and the mass of the current collector is weighed and recorded as W2. The thickness T2 of the current collector is measured using a micrometer. Then, the tap density PD of the positive electrode plate = (W1 - W2) / [(T1 - T2)×S].

[0128] In some embodiments, when the battery cell is in the fully discharged state, the tap density of the positive electrode plate can be selected as 2.3 g / cm 3 、2.31 g / cm 3 、2.32 g / cm 3 、2.33 g / cm 3 、2.34 g / cm 3 、2.35 g / cm 3 、2.36 g / cm 3 、2.37 g / cm 3 、2.38 g / cm 3 、2.39 g / cm 3 、2.40 g / cm 3 、2.41 g / cm 3 、2.42 g / cm 3 、2.43 g / cm 3 、2.44 g / cm3 , 2.45 g / cm 3 , 2.46 g / cm 3 , 2.47 g / cm 3 , 2.48 g / cm 3 , 2.49 g / cm 3 , 2.50 g / cm 3 , 2.52 g / cm 3 , 2.55 g / cm 3 , 2.60 g / cm 3 or the numerical range between any two of them.

[0129] In this application, the single-sided coating areal density of the positive electrode film layer has the meaning well-known in the art and can be tested by methods known in the art. For example, take a single-sided coated and cold-pressed positive electrode plate (if it is a double-sided coated positive electrode plate, the positive electrode film layer on one side can be wiped off first), punch it into small round pieces with an area of S1, weigh it, and record it as M1. Then wipe off the positive electrode film layer of the above-mentioned weighed positive electrode plate and weigh the weight of the current collector, and record it as M0. The single-sided areal density of the positive electrode film layer = (M1 - M0) / S1. To ensure the accuracy of the test results, multiple groups (for example, 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result. The higher the single-sided coating areal density of the positive electrode film layer, the greater the load per unit area, which helps to improve the volumetric energy density of the battery cell.

[0130] In some embodiments, the single-sided coating areal density of the positive electrode film layer can be selected as 0.25 g / 1540 mm 2 , 0.26 g / 1540 mm 2 , 0.27 g / 1540 mm 2 , 0.28 g / 1540 mm 2 , 0.29 g / 1540 mm 2 , 0.30 g / 1540 mm 2 , 0.31 g / 1540 mm 2 , 0.32 g / 1540 mm 2 , 0.33 g / 1540 mm 2 , 0.34 g / 1540 mm 2 , 0.35 g / 1540 mm 2 , 0.36 g / 1540 mm 2 , 0.37 g / 1540 mm 2 , 0.38 g / 1540 mm 2 , 0.39 g / 1540 mm 2 , 0.40 g / 1540 mm 2 , 0.41 g / 1540 mm2 、0.42 g / 1540 mm 2 、0.43 g / 1540 mm 2 、0.44 g / 1540 mm 2 、0.45 g / 1540 mm 2 or a numerical range between any two of them.

[0131] In some embodiments, the single-sided coating areal density of the positive electrode film layer is 0.3 g / 1540.25 mm 2 - 0.45 g / 1540.25 mm 2 .

[0132] In some embodiments, the single-sided coating areal density of the positive electrode film layer is 0.35 g / 1540.25 mm 2 - 0.4 g / 1540.25 mm 2 .

[0133] The single-sided coating areal density of the positive electrode film layer being further within the above range helps to further improve the capacity of the battery and balance the cycle performance.

[0134] In this application, the term "particle" refers to a particle with an identifiable complete boundary in the field of view of the positive electrode film layer at a certain magnification, such as 10,000 times. There may be defects and scratches inside the particle, but no complete boundary sufficient to divide the particle can be identified inside the particle. The positive electrode film layer in this application can be either a freshly prepared positive electrode film layer or a positive electrode film layer disassembled from a battery.

[0135] In this application, the method for identifying particles is as follows: The positive electrode film layer is cut along the thickness direction of the electrode plate by an argon ion beam (as an example, the following can be selected: equipment model: Leica EMTIC3XCP, working voltage: 6 kV, working duration: 6 h). After the cut surface is exposed, a scanning electron microscope (as an example, the following can be selected: equipment model: Hitachi SU8230, working voltage: 3 kV, beam current: high, probe model: U(LA100), working distance < 5 mm) is used to observe the cut surface of the positive electrode film layer along the thickness direction of the electrode plate. An image is collected in the secondary electron mode at a non-edge position on the cut surface of the positive electrode film layer by a field emission scanning electron microscope (after observing the edge of the electrode plate under the scanning electron microscope, adjust the field of view to the central part of the sample). An electron micrograph is taken at a magnification of 10,000 times, and the particles in the electron micrograph are analyzed using ImageJ software (version 1.46r, win64). The specific method of using ImageJ software is as follows: Load the scanning electron micrograph to be analyzed; Use the Cellpose plug-in software in it to identify particles, and on this basis, perform manual correction; Use ImageJ to read and count data. The specific method of using the Cellpose plug-in software to identify particles is as follows: Set the segmentation diameter parameter (diameter in the Segmantation module) to 15 pixels, click "runcyto3" to identify particles; Manually mark the particles in the image that are not recognized by the software, not completely recognized by the software, or have recognition errors. The particles in the image that are not recognized by the software, not completely recognized by the software, or have recognition errors mainly include the following types: 1. Due to the particle being too large or having scratches on the particle surface, the particle cannot be recognized or cannot be completely recognized; 2. During the argon ion beam cutting process, scratches will be generated on the particle surface, and the software may misjudge the scratches as the particle boundary during the recognition process, resulting in recognition errors; 3. Due to the particle being too small, it fails to be recognized; 4. The particle is located at the edge of the electron microscope field of view, and the inside of the particle is penetrated by the edge, and the morphology cannot be completely shown, and the local part is recognized instead of the whole, resulting in recognition errors.For the particles that are not recognized or have recognition errors as described above, manual calibration is performed. The specific process is as follows: Delete the particles located at the edges of the scanning electron microscope that cannot completely display large particles; Determine whether there are crack scratches inside other particles that are not recognized or have recognition errors. If there are no crack scratches inside the particle, then determine it as a single particle, and manually mark it according to the particle boundary observed manually; In response to the presence of crack scratches inside the particle, determine whether the crack scratches penetrate the particle. If they do not penetrate the particle, then determine it as a single particle and perform manual marking; In response to the crack scratches penetrating the particle, determine whether the crack scratches are linear or irregular; In response to the crack scratches being irregular, determine it as the boundary between particles and divide the particles along this boundary; In response to the crack scratches being linear, perform contrast; In response to the contrast being not obvious and there being no sense of crack, determine it as a scratch and mark it as a single particle; In response to the contrast being strong and there being a sense of crack, determine it as the boundary between particles and mark it as two particles. After manual marking, delete the information irrelevant to the particles during the automatic image processing process, that is, the determination and marking of the particles in the picture are completed.

[0136] In this application, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, the sphericity test method for particles with a particle size R1 satisfying R1≥1000 nm is as follows: Refer to the method described above in this application to identify the particles in the cross-section of the positive electrode film layer, and use the "Shape Descriptor" analysis function in ImageJ to analyze the morphology of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode plate. According to the software manual (ImageJ User Guide IJ 1.46r), the "Round" parameter obtained by analysis represents the ratio of the pixel area of the particle to the area of a circle with the fitted major axis as the diameter, and can be used to characterize the sphericity of the particle. When the particle is closer to a sphere, the ratio of the pixel area to the area of a circle with the fitted major axis as the diameter is closer to 1. Therefore, the sphericity of the particle is characterized by the "Round" parameter of the obtained particle. Arrange the sphericities of at least 1000 particles with a particle size R1 satisfying R1≥1000 nm in ascending order. With the sphericity as the horizontal axis and the cumulative area ratio as the vertical axis, obtain the sphericity cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm in the positive electrode film layer. L R1A1 50 is the sphericity L value corresponding to the cumulative area ratio of 50% on the vertical axis in the sphericity L value cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm.

[0137] In some embodiments, in the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, L R1A50It can be 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.705, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80 or a numerical range between any two of them.

[0138] Those skilled in the art can adjust the sphericity of the particles through any known process. As an example, the sphericity of the particles can be adjusted by processes such as grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, adding surfactants, etc., as well as by adjusting the parameters of each process.

[0139] In this application, the cumulative distribution curve of the graphitization degree C value refers to a curve obtained by arranging at least 100 obtained C values in ascending order, with the graphitization degree on the horizontal axis and the cumulative quantity ratio on the vertical axis. C 50 It is the C value corresponding to the cumulative quantity ratio of 50% on the vertical axis in the cumulative distribution curve of the graphitization degree C value. The median graphitization degree C 50 Compared with the point value, it can reflect the overall graphitization degree of the particles in the positive electrode film layer, that is, the ease of slippage; compared with the average value, it can reduce the influence of extreme values during the test and improve the confidence level of the test results.

[0140] The graphitization degree C value of the positive electrode film layer can be obtained through the surface scanning mode of a laser confocal Raman spectrometer. As an example, specifically, a laser confocal Raman spectrometer (high-precision Renishaw laser confocal Raman spectrometer) is used, with an excitation wavelength of 532 nm. An appropriate amount of the positive electrode film layer is taken to perform surface scanning on its surface or a cross-section along the thickness direction of the electrode sheet. The scanning area is 45 μm × 45 μm, divided into 10 × 10 grids. The grid vertices are used as test points, with a step size of 5 μm, and the total number of scanning points is 100 points. Thus, the C values at different positions and the cumulative distribution curve of the C value in the surface scanning area are obtained. The positive electrode film layer in this application can be either a freshly prepared positive electrode film layer or a positive electrode film layer disassembled from a battery. It is inevitable that there are residual electrolyte salt particles on the surface of the positive electrode film layer disassembled from the battery. To improve the test accuracy, it is preferred to perform surface scanning on the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet to characterize the graphitization degree of the positive electrode film layer.

[0141] The graphitization degree C value of the positive electrode film layer is obtained through the peak intensity ratio of the G peak (G-band) and D peak (D-band) of the Raman spectrum. The position of the G peak is 1580 ± 100 cm -1 , which characterizes the carbon sp 2 hybrid structure; the position of the D peak is 1350 ± 100 cm -1, which characterizes the disordered structure, where disorder means that there is no regular arrangement among the carbon atoms in the structure. In a graphite crystal, the carbon atoms in the same layer form covalent bonds through sp 2 hybridization, and the van der Waals force exists between layers, making the carbon in the graphite structure prone to slip. Therefore, the C value can characterize the graphitization degree of the positive electrode film layer. It can be understood that the graphitization degree in the positive electrode film layer mainly comes from the carbon material treated by graphitization in the positive electrode film layer, that is, the carbon material layer of the positive electrode active material. Although the carbon nanotube conductive agent rich in sp 2 hybridized structure also has a relatively high I G / I D , due to its small addition content and small tube diameter, its addition in the positive electrode film layer shows an extreme value in the Raman surface scanning test of the positive electrode film layer and will not affect the graphitization degree C 50 in the positive electrode film layer. Therefore, the graphitization degree of the positive electrode film layer can also be used to characterize the graphitization degree of the positive electrode active material.

[0142] Those skilled in the art can adjust the graphitization degree of the active material particles through any known process. As an example, adjusting the carbon source, sintering temperature, sintering time, sintering pressure, and sintering atmosphere can all achieve the adjustment of the graphitization degree of the active material particles.

[0143] The higher the graphitization degree of the carbon on the surface of the positive electrode active material, the higher the proportion of graphitic carbon in the positive electrode film layer, and the easier it is for the particles to slip through the carbon structure with a high graphitization degree in the coating layer, reducing the stress concentration phenomenon in the electrode sheet.

[0144] In some embodiments, in the cumulative distribution curve of the graphitization degree C value obtained by the positive electrode film layer in the surface scanning mode of the laser confocal Raman spectrometer, the median C of the graphitization degree 50 can be selected as 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20 or the numerical range between any two of them.

[0145] In some embodiments, in the cumulative distribution curve of the graphitization degree C value obtained by the positive electrode film layer in the surface scanning mode of the laser confocal Raman spectrometer, the median C of the graphitization degree 50 is 1.01 - 1.13.

[0146] When the graphitization degree of the positive electrode film layer is further within the above range, it helps to further improve the slip degree of the particles in the positive electrode film layer, reduce the stress concentration in the positive electrode film layer, and thus further improve the long-cycle stability of the battery cell.

[0147] In some embodiments, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode tab, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.65 - 0.75.

[0148] In some embodiments, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode tab, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.67 - 0.72.

[0149] In the cross-section of the positive electrode film layer along the thickness direction of the positive electrode tab, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is in the range of 0.65 - 0.75, and further in the range of 0.67 - 0.72, which is beneficial to further reducing the stress concentration at large particles in the positive electrode film layer of the thick-coated stacked cell, thereby reducing the probability of film layer detachment and improving the cycle life of the battery.

[0150] In some embodiments, the single-sided thickness H of the positive electrode film layer is 70 μm - 120 μm.

[0151] In some embodiments, the single-sided thickness H of the positive electrode film layer is 90 μm - 120 μm.

[0152] The thickness of the positive electrode film layer can be detected by any well-known method in the art. As an example, the thickness of the positive electrode film layer in the cross-section of the positive electrode tab along the thickness direction is measured by a scanning electron microscope.

[0153] In some embodiments, the single-sided thickness H of the positive electrode film layer can be selected as 70 μm, 71 μm, 72 μm, 73 μm, 74 μm, 75 μm, 76 μm, 77 μm, 78 μm, 79 μm, 80 μm, 81 μm, 82 μm, 83 μm, 84 μm, 85 μm, 86 μm, 87 μm, 88 μm, 89 μm, 90 μm, 91 μm, 92 μm, 93 μm, 94 μm, 95 μm, 96 μm, 97 μm, 98 μm, 99 μm, 100 μm, 101 μm, 102 μm, 103 μm, 104 μm, 105 μm, 106 μm, 107 μm, 108 μm, 109 μm, 110 μm, 111 μm, 112 μm, 113 μm, 114 μm, 115 μm, 116 μm, 117 μm, 118 μm, 119 μm, 120 μm or any value range between any two of them.

[0154] When the single-sided thickness of the positive electrode film layer is within the above range, it helps to increase the loading amount of the positive electrode active material in the battery, thereby increasing the capacity of the battery.

[0155] In some embodiments, the single-sided thickness H of the positive electrode film layer is 100 μm - 120 μm.

[0156] Increasing the thickness of the positive electrode film layer helps to increase the loading amount of the positive electrode active material and the capacity of the battery. However, the applicant has found that when the single-sided thickness of the positive electrode film layer is greater than or equal to 100 μm, during the battery cycling process, the volume expansion of the positive electrode film layer is more significant, resulting in greater stress, more significant stress concentration in the positive electrode film layer, an increased risk of film layer detachment, and thus affecting the cycling performance of the battery. In the embodiments of the present application, the capacity of the battery is increased by increasing the thickness of the positive electrode film layer, and at the same time, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, the median C of the graphitization degree C in the cumulative distribution curve of the graphitization degree obtained in the surface scanning mode of the laser confocal Raman spectrometer for spherical particles with a particle size R1 satisfying R1 ≥ 1000 nm 50 , improving the degree of slip between particles in the positive electrode film layer and reducing the stress concentration generated during the compaction of the electrode plate, so as to take into account the cycling performance of the battery while increasing the battery capacity.

[0157] In some embodiments, based on the total area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the area ratio of the particles with a particle size R1 satisfying R1 ≥ 1000 nm is 12% - 50%.

[0158] It can be understood that the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, especially particles above 50 nm, mainly come from the positive electrode active material. Therefore, in the embodiments of the present application, by observing and statistically analyzing the particle area in the cross-section of the positive electrode plate along the thickness direction of the electrode plate, the distribution of lithium-containing transition metal phosphate particles in the positive electrode film layer can be accurately and objectively reflected.

[0159] In the prior art, a laser particle size analyzer is usually used to statistically analyze the particle size of the positive electrode active material by the Malvern laser diffraction method. However, the applicant's research shows that due to the easy agglomeration of lithium-containing transition metal phosphate particles, the test results obtained by the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of their particle aggregates, and cannot truly reflect the particle size of the particles in the positive electrode active material, let alone the dispersion state of the positive electrode active material in the film layer, because the dispersion degree of the positive electrode active material in the film layer will increase during the processes of pulping and film forming and rolling. The test results obtained by the Malvern laser diffraction method are affected by the particle size, specific surface area, and agglomeration degree of the positive electrode active material. Compared with the actual dispersion situation in the electrode plate, the number of large particles obtained by this test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size obtained by the Malvern laser diffraction method cannot be equated or analogized to the particle size statistically obtained in the embodiments of the present application.

[0160] In the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the method for testing the area ratio of particles with a particle size R1 satisfying R1≥1000 nm is as follows: Refer to the method described above in this application to identify the particles in the positive electrode film layer. Import the image after the particles are determined and marked into the ImageJ software for analysis. Complete the scale setting according to the scanning electron microscope image, and perform statistical analysis on the particle size, area, sphericity, and roughness of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet through the "Feret diameter", "Area", "Round", and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter obtained by analysis represents the maximum distance between all parallel lines in the two-dimensional projection of the particle, which characterizes the particle size of the particle; the "Area" parameter obtained represents the pixel area of the particle. Since particles with a particle size less than 50 nm have large errors in the statistical process and are difficult to accurately identify, and the particle size of the conductive agent is generally less than 50 nm, which will cause large errors in the statistical results. Therefore, in the particle size statistics process of this application, particles with a particle size less than 50 nm are not counted, and the particle statistical data corresponding to "AR", "Round", or "Solidity" displayed as "NaN" are deleted. Calculate the sum of the "Area" parameters of the particles with a particle size R1 satisfying R1≥1000 nm and the sum of the "Area" parameters of all particles, which are respectively used as the area of the particles with a particle size R1 satisfying R1≥1000 nm and the total area of the counted particles. Divide the sum of the areas of the particles with a particle size R1 satisfying R1≥1000 nm by the total area of the counted particles to obtain the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet.

[0161] In some embodiments, based on the total area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm can be 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any numerical range between any two of them.

[0162] In some embodiments, based on the total area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm is 12%-40%.

[0163] Large particles with a particle size R1 satisfying R1≥1000nm contribute to improving the compaction density of the positive electrode sheet, thereby increasing the volumetric energy density of the single battery; however, researchers have found that stress concentration is likely to occur at these large particles, increasing the risk of shedding of the positive electrode film layer. Therefore, when the proportion of the area of particles with a particle size R1 satisfying R1≥1000nm in the cross-section of the positive electrode film layer along the thickness direction of the sheet is in the range of 12%-50%, and further in the range of 12%-40%, it can not only improve the compaction density of the sheet but also prevent the probability of film layer shedding from being too high, thereby improving the energy density of the thick-coated lithium-containing transition metal phosphate battery while alleviating the capacity plunge problem and taking into account the cycle life of the battery.

[0164] In some embodiments, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000nm in the cross-section of the positive electrode film layer along the thickness direction of the sheet is less than or equal to 5%.

[0165] The distribution uniformity of the particles with a particle size R1 satisfying R1≥1000nm in the cross-section of the positive electrode film layer along the thickness direction of the sheet can be tested by methods known in the art. As an example, the cross-section of the positive electrode film layer along the thickness direction of the sheet is divided into three layers of equal thickness along the thickness direction of the sheet (when a bottom coating is coated on the surface of the positive electrode current collector and then the positive electrode active material layer is coated, in the cross-section of the positive electrode film layer along the thickness direction of the sheet, the area from 5μm close to the positive electrode current collector to the surface of the positive electrode film layer far from the positive electrode current collector is divided into three layers of equal thickness along the thickness direction of the sheet), namely the lower layer close to the positive electrode current collector, the upper layer far from the positive electrode current collector, and the middle layer placed between the upper layer and the lower layer; 10 non-overlapping fields of view are randomly selected in each of the upper layer, the middle layer, and the lower layer, and scanning electron microscope images are taken at a magnification of 10k; the 10 scanning electron microscope images taken for each layer are respectively imported into ImageJ software for analysis, and according to the above-mentioned "test method for the proportion of the area of particles with a particle size R1 satisfying R1≥1000nm in the cross-section of the positive electrode film layer along the thickness direction of the sheet", the proportion of the area of particles with a particle size R1 satisfying R1≥1000nm in the 10 images corresponding to the upper layer, the middle layer, and the lower layer is obtained, a total of 3 values. The range of the 3 values of the upper layer, the middle layer, and the lower layer is the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000nm in the cross-section of the positive electrode film layer along the thickness direction of the sheet, where the range is the difference between the maximum value and the minimum value of the 3 values of the upper layer, the middle layer, and the lower layer. The smaller the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000nm in the cross-section of the positive electrode film layer along the thickness direction of the sheet, the more uniform the distribution of the large particles with a particle size R1 satisfying R1≥1000nm in the positive electrode film layer, which helps to reduce the stress concentration phenomenon at the large particles in the positive electrode film layer, reduce the probability of delamination and shedding, and improve the cycle performance of the battery.

[0166] In some embodiments, in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 1%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5% or the numerical range between any two of them.

[0167] In some embodiments, in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm is 0.2%-2.5%.

[0168] In some embodiments, in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm is 0.2%-2%.

[0169] When the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet is within the above range, the stress concentration degree in the local area of the film layer can be effectively reduced, so that the stress during the film layer compaction process can be evenly dispersed in the entire area of the film layer, thereby reducing the probability of film layer shedding while increasing the battery energy density, alleviating the problem of capacity drop of the thick-coated lithium-containing transition metal phosphate battery, and improving the battery cycle life.

[0170] In some embodiments, in the cumulative distribution curve of the coating value B obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median B of the coating value 50 is 0.30-0.60, where the coating value B is I P / I D where I P represents the intensity of the P peak of the Raman spectrum at 948±100 cm -1 and I D represents the intensity of the D peak of the Raman spectrum at 1350±100 cm -1 .

[0171] The cumulative distribution curve of the coating value B refers to a curve obtained by arranging at least 100 obtained B values in ascending order, with the coating value on the horizontal axis and the cumulative quantity ratio on the vertical axis. To reduce the influence of the extreme values of the coating value in the non-particle region of the positive electrode film layer on the test results, the median B of the coating value is used. 50 Evaluate the compactness of the carbon material layer on the positive electrode active material. B 50 It is the B value corresponding to the cumulative quantity ratio of 50% on the vertical axis in the cumulative distribution curve of the coating value B.

[0172] In this application, the coating value B of the positive electrode film layer can be obtained by scanning with a laser confocal Raman spectrometer. As an example, specifically, a laser confocal Raman spectrometer (Renishaw high-precision laser confocal Raman spectrometer) is used, with an excitation wavelength of 532 nm. An appropriate amount of the positive electrode film layer is taken, and surface scanning or cross-section scanning along the thickness direction of the electrode sheet is performed. The scanning area is 45 μm × 45 μm, divided into 10 × 10 grids. The grid vertices are used as test points, with a step size of 5 μm and a total number of scanning points of 100. Thus, the B values at different sites and the cumulative distribution curve of the B value of the surface scanning area are obtained. The positive electrode film layer in this application can be either a freshly prepared positive electrode film layer or a positive electrode film layer disassembled from a battery. The surface of the positive electrode film layer disassembled from a battery inevitably has residual electrolyte salt particles. To improve the test accuracy, it is preferred to perform surface scanning on the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet to characterize the coating value of the positive electrode film layer.

[0173] The coating value B of the positive electrode film layer is obtained from the peak intensity ratio of the P peak (P-band) and D peak (D-band) of the Raman spectrum. The position of the P peak is 948 ± 100 cm -1 , which characterizes the phosphate group PO4 3- , and the position of the D peak is 1350 ± 100 cm -1 , which characterizes the disordered structure, where disorder means that there is no regular arrangement between carbon atoms in the structure. During the test, an excitation wavelength of 532 nm is selected, and the test depth is relatively shallow. Therefore, in the test results obtained by the positive electrode film layer in the surface scanning mode of the laser confocal Raman spectrometer, the carbon structure peak shows a higher intensity compared to the phosphate group structure peak.

[0174] Those skilled in the art can adjust the coating value of the active material particles through any known process. As an example, adjusting the type of carbon source, the addition amount of carbon source, sintering temperature, sintering time, sintering pressure, and sintering atmosphere can all achieve the adjustment of the coating value of the active material particles. The coating value B can reflect the compactness of the carbon material layer on the surface of the lithium-containing transition metal phosphate particles. The denser the carbon material layer, the relatively lower the intensity of the phosphate group structure detected in the Raman spectrum, and the smaller the coating value B of the positive electrode film layer.

[0175] In some embodiments, the positive electrode film layer further includes a coating layer provided on at least a part of the surface of the lithium-containing transition metal phosphate particles. In the cumulative distribution curve of the coating value B obtained in the surface scanning mode of a laser confocal Raman spectrometer for the positive electrode film layer, the median B of the coating values 50 is optionally 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6 or a numerical range between any two of them.

[0176] The median B of the coating values of the positive electrode film layer 50 within the above range indicates that the carbon material layer of the positive electrode active material is relatively dense and uniform, which is beneficial to improving the slip uniformity of the positive electrode film layer during the rolling process and reducing the stress concentration phenomenon in the thick-coated positive electrode film layer; in addition, with the help of the dense and uniform carbon material layer, the large particles in the positive electrode film layer are more likely to achieve slip during the compaction process, thereby reducing the stress concentration phenomenon at the large particles in the thick-coated positive electrode film layer, reducing the probability of the positive electrode film layer falling off, improving the problem of battery capacity diving, and increasing the cycle life of the battery.

[0177] In some embodiments, the lithium-containing transition metal phosphate particles in the positive electrode film layer include the components represented by the following general formula: Li m Fe x P y O j Q q Formula I, wherein Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.8 ≤ m ≤ 1.15, 0.9 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 ≤ q ≤ 0.1.

[0178] In some embodiments, m can be optionally 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15 or a numerical range between any two of them; x can be optionally 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0 or a numerical range between any two of them; y can be optionally 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or a numerical range between any two of them; j can be optionally 3.5, 3.6, 3.7, 3.8, 3.9, 4 or a numerical range between any two of them; q can be optionally 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or a numerical range between any two of them.

[0179] In some embodiments, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate fluoride, lithium manganese iron phosphate and their modified materials.

[0180] In some embodiments, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate and its doped modified materials, coated modified materials.

[0181] In some embodiments, the iron dissolution rate of the positive electrode material in the positive electrode film layer is 658 ppm - 1921 ppm.

[0182] The iron dissolution rate of the positive electrode material in the positive electrode film layer can be tested by methods well-known in the art. As an example, weigh 7.5 g of the positive electrode material powder obtained by scraping powder from the positive electrode film layer sample, add it to 100.3 g of ascorbic acid solution with a mass concentration of 0.3% (the solvent is ultrapure water), stir it at a speed of 500 revolutions per minute for 305 minutes, then quickly suck the solution with a 5 mL syringe, filter the solution through a 0.45 μm pore size filter head into a test tube, pipette 1 mL of the supernatant with a pipette gun, add it to a glass volumetric flask and dilute it 50 times, and test it with an inductively coupled plasma mass spectrometer (ICP-OES) to obtain the iron element concentration in the solution. Through the formula: (ICP test iron element concentration × solution volume / mass of the solution participating in volume fixing) × 100.3 g / mass of the positive electrode material powder, the solution volume is 50 mL, and the mass of the solution participating in volume fixing is 1 g, calculate the iron dissolution rate of the positive electrode material in the positive electrode film layer.

[0183] In some embodiments, the iron dissolution rate of the cathode material in the cathode film layer can be 658 ppm, 700 ppm, 800 ppm, 890 ppm, 900 ppm, 1000 ppm, 1058 ppm, 1076 ppm, 1100 ppm, 1143 ppm, 1200 ppm, 1236 ppm, 1300 ppm, 1311 ppm, 1384 ppm, 1349 ppm, 1400 ppm, 1485 ppm, 1500 ppm, 1531 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1921 ppm, or a numerical range between any two of them.

[0184] In some embodiments, the iron dissolution rate of the cathode material in the cathode film layer is 658 ppm - 1485 ppm.

[0185] The iron element dissolved in the cathode material mainly comes from the lithium-containing transition metal phosphate in the cathode active material. The level of the iron dissolution rate depends on the one hand on the number of lattice defects in the lithium-containing transition metal phosphate, and on the other hand on the integrity and density of the carbon material layer on the surface of the cathode active material. A lower iron dissolution rate means fewer lattice defects in the lithium-containing transition metal phosphate, which is beneficial to reducing the corrosion of the lattice in a weak acid environment; and the more complete and dense the carbon material layer on the surface of the cathode active material, the more it inhibits the dissolution of iron ions in a weak acid environment. The cathode material with an iron dissolution rate within the above range has relatively few lattice defects and a complete and dense carbon material layer, which is beneficial to improving the compressive resistance and easy slippage degree of the particles in the cathode film layer under a large rolling pressure, increasing the tap density of the cathode film layer and reducing the stress concentration in the cathode film layer, improving the energy density of the battery and taking into account the problem of battery capacity drop.

[0186] In some embodiments, based on the total mass of the lithium-containing transition metal phosphate particles in the cathode film layer, the mass content of titanium element is 500 ppm - 8000 ppm.

[0187] The types and contents of elements in the lithium-containing transition metal phosphate particles in the cathode film layer can be tested by any well-known method in the art. As an example, the inductively coupled plasma emission spectrometry is used to test the titanium element and its content with reference to Appendix C of GB / T 33822-2017.

[0188] In some embodiments, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of titanium element can be 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm, 8000 ppm or the numerical range between any two of them.

[0189] In some embodiments, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of titanium element is 1000 ppm - 3000 ppm.

[0190] Introducing titanium element into the lithium-containing transition metal phosphate particles requires adding a titanium source during the preparation of the positive electrode active material. The titanium source is often an inert material, and attaching to the surface of the lithium-containing transition metal phosphate raw material can play a role in reducing the reaction activity and reducing the growth of particle size. Improving the graphitization degree of the positive electrode active material often requires a higher sintering temperature or a longer sintering time, but this will also increase the size of the particles in the positive electrode film layer, increase the stress concentration in the positive electrode film layer, and cause the film layer peeling phenomenon of the positive electrode film layer. In the embodiments of the present application, by adding a high content of titanium element to the lithium-containing transition metal phosphate particles, the reaction activity of the synthesis raw material of the positive electrode active material is reduced, so that the positive electrode active material can control the proportion of large particles while having a high graphitization degree, reduce the stress concentration in the positive electrode film layer, and reduce the probability of film layer peeling of the positive electrode film layer, taking into account the cycle life of the battery while improving the energy density of the battery.

[0191] At the same time, the doping of titanium element in the positive electrode active material is beneficial to causing lattice distortion, reducing the Li-O bond energy, increasing the lithium ion transmission rate, and improving the kinetic performance of the battery. The lithium ion diffusion in the thick coating film layer is uneven, and there is often a significant lithium ion concentration gradient. In the embodiments of the present application, by adding a high content of titanium element to the lithium-containing transition metal phosphate particles, the solid-phase transmission rate of the positive electrode active material is improved, and the kinetic problems of the thick electrode sheet battery are improved.

[0192] In some embodiments, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of vanadium element is 500 ppm - 5000 ppm.

[0193] The types and contents of elements in the lithium-containing transition metal phosphate particles in the positive electrode film layer can be tested by any well-known method in the art. As an example, the vanadium element and its content are tested by inductively coupled plasma emission spectrometry with reference to Appendix C of GB / T 33822-2017.

[0194] In some embodiments, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of the vanadium element can be optionally 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm.

[0195] In some embodiments, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of the vanadium element is 500 ppm - 3000 ppm.

[0196] The vanadium element in the positive electrode film layer can exist in multiple valence states. Among them, vanadium with a +5 valence (V 5+ ) can be doped at the phosphorus element site. Due to its relatively large radius, it can cause lattice distortion and expand the diffusion channels of lithium ions, thereby improving the ionic conductivity of the positive electrode active material and the kinetic performance of the battery; vanadium with a +3 valence (V 3+ ) can be doped at the transition metal site, generating lithium vacancies through charge compensation, thereby improving the electronic conductivity of the positive electrode active material. In addition, the improvement of the uniformity of the distribution of the vanadium element in the lithium-containing transition metal phosphate particles helps to further improve the kinetic performance of the positive electrode film layer and the reaction uniformity of the positive electrode film layer, thereby further improving the kinetic performance and cycle performance of the battery cell.

[0197] The mass content of the vanadium element within the above range helps to improve the kinetic performance of the positive electrode plate and the kinetic performance of the thick-coated lithium-containing transition metal phosphate battery. At the same time, the synergistic effect of titanium element, vanadium element and carbon nanotubes in the positive electrode film layer helps to form a good three-dimensional network, further improving the electronic conductivity and ionic conductivity of the positive electrode film layer, thereby further improving the kinetic performance of the thick-coated lithium-containing transition metal phosphate battery.

[0198] In some embodiments, the porosity of the positive electrode film layer is 14% - 28%.

[0199] In this application, the porosity of the positive electrode film layer can be tested in the following manner. Import the scanning electron microscope image of the cross-section of the positive electrode film layer obtained in the manner described above along the thickness direction of the electrode sheet into the ImageJ software. Select the straight line tool, use the straight line to mark the scale length in the picture, click "Analyze Set Scale", and set the scale parameters in the software according to the scale length in the picture. Select the rectangular tool, select the part of the picture outside the scale area, use "Image Duplicate" to copy the selected area, and use "Image Type 8 bit" to adjust the picture format; select "Analyze Set Measurements", and select the following 5 options: "Area", "Mean gray value", "Area Fraction", "Limit to threshold", "Feret’s diameter", where "Decimal places" is selected as 3. Then, select "Image"-"Adjust"-"Threshold" in sequence, and set 0 and 100 in turn at the position of the "Threshold" box selection. Then, the pore data in the cross-section electron microscope image can be exported using the Analyze-Measure function. Use "Image"-"Overlay"-"Flatten" to export and obtain the pore picture; click "Apply" in "Threshold", and then click "Analyze"-"Analyze Particles", and check the left four columns to obtain the pore statistical data.

[0200] It can be understood that in the embodiments of this application, the "pores" in the cross-section of the positive electrode film layer are identified through picture color difference and threshold. This "pore" is not the pore data obtained from the exhaust test, and is mainly used to characterize the gap between particles in the cross-section of the positive electrode film layer. This method is superior to the exhaust method because the porosity obtained by the exhaust method is related to the pores between particles and the holes in the carbon material layer on the particle surface, and cannot objectively reflect the pores between particles.

[0201] In some embodiments, the porosity of the positive electrode film layer can be selected as 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28% or the numerical range between any two of them.

[0202] When the porosity of the positive electrode film layer is within the above range, the positive electrode film layer has good electrolyte wettability and tortuosity, which helps the diffusion of lithium ions in the liquid and solid phases, helps reduce the concentration polarization of the thick electrode, and improves the kinetic performance of the battery. At the same time, it helps to alleviate the volume expansion of the thick-coated electrode during cycling, reduce the mechanical stress of the film layer and the stress concentration phenomenon, thereby reducing the risk of film layer peeling of the thick-coated electrode.

[0203] Especially in thick-coated soft-pack batteries, the gap between the housing and the electrode is small, the volume occupancy rate of the film layer is large, the volume of the electrolyte accommodation is reduced, and when the porosity of the positive electrode film layer is within the above range, it helps to improve the liquid retention rate of the battery cell and improve the battery kinetic performance.

[0204] In some embodiments, the positive electrode film layer further includes a conductive agent. Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode, the area ratio of the agglomeration region of the conductive agent is 0.5% - 2.5%.

[0205] In this application, based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode, the area ratio of the agglomeration region of the conductive agent can be tested by the following method. Observe the cross-section of the positive electrode film layer along the thickness direction of the electrode through a scanning electron microscope by a similar method as described above, and measure the area of the agglomeration region of the conductive agent in the scanning electron microscope image at a magnification of 3k times. Since the conductive agent is generally a carbon-based material, such as conductive carbon black, carbon nanotubes, etc., at a high magnification of the scanning electron microscope, the aggregated conductive agent can be seen, and the agglomeration region of the conductive agent often appears as a black agglomeration compared to other regions in the positive electrode film layer. With the help of image analysis software, the agglomeration region of the conductive agent refers to the region in the scanning electron microscope image where the conductive agent is significantly aggregated and appears black. Specifically, import the scanning electron microscope image at a magnification of 3k times into ImageJ, screen out the black agglomeration regions of the conductive agent with Feret greater than or equal to 2μm, and count the sum of the areas of the screened regions as the area of the agglomeration region of the conductive agent. The area ratio of the agglomeration region of the conductive agent is the ratio of the area of the agglomeration region of the conductive agent to the total area of the imported scanning electron microscope image. Randomly select 3 non-overlapping scanning electron microscope images, and calculate the average value of the area ratio of the agglomeration region of the conductive agent as the "area ratio of the agglomeration region of the conductive agent based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode".

[0206] In some embodiments, the positive electrode film layer further includes a conductive agent. Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the agglomerated region of the conductive agent can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5% or the numerical range between any two of them.

[0207] Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, when the area ratio of the agglomerated region of the conductive agent is within the above range, it indicates that the conductive agent in the positive electrode film layer is evenly dispersed, which is conducive to forming a uniform conductive network, especially beneficial to reducing the problem of kinetic decline caused by the increase of the ion transport path in the thick coating film layer, reducing local polarization and even lithium plating problems generated during the battery cycle, and improving the cycle life of the battery.

[0208] At the same time, research shows that large-sized first particles in lithium-containing transition metal phosphate particles are prone to rebound. When the agglomerated area of the conductive agent is within the above range, it can suppress the rebound of lithium-containing transition metal phosphate particles by virtue of the uniform distribution of the conductive agent, form a mechanical restraint on the particles and even the film layer, improve the cohesion of the film layer, reduce the phenomenon of film layer powder falling and peeling, and improve the cycle life of the battery.

[0209] In some embodiments, the positive electrode film layer further includes a conductive agent. Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the agglomerated region of the conductive agent is 0.5% - 1.7%.

[0210] In the embodiments of the present application, when the area ratio of the agglomerated region of the conductive agent is further within the above range, it indicates that the conductive agent is more evenly distributed in the positive electrode film layer, and the content of the conductive agent is relatively low. While improving the kinetic performance of the positive electrode film layer, it helps to reduce the occupation of the space of the positive electrode active material by excessive conductive agent, thereby further improving the volumetric energy density of the battery while improving the kinetic performance of the battery.

[0211] In some embodiments, the conductive agent includes carbon nanotubes, and the carbon nanotubes include one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0212] In the present application, the term "carbon nanotubes" refers to carbon atoms with sp 2A nanomaterial formed by the curling of graphene sheets formed by hybrid bonding, with several to dozens of coaxial hollow tubes. The diameter is usually in the range of several to dozens of nanometers, and the length can vary from microns to centimeters, showing a high aspect ratio. It can be classified according to the number of graphene layers into: single-walled carbon nanotubes (SWCNTs), few-walled carbon nanotubes (FWCNTs), and multi-walled carbon nanotubes (MWCNTs). Carbon nanotubes have excellent electrical conductivity and a high elastic modulus.

[0213] Due to the one-dimensional structure of carbon nanotubes, a network structure can be formed in the positive electrode film layer. On the one hand, the high elastic modulus of carbon nanotubes enables their network structure to not only serve as a bridge for stress propagation but also have a binding effect on the thick-coated positive electrode film layer, suppressing the rebound of lithium-containing transition metal phosphate particles, effectively alleviating stress concentration, reducing the risk of film layer shedding, and thus improving the problem of battery capacity plunge; on the other hand, the excellent electrical conductivity of carbon nanotubes makes their network structure an efficient electron transport channel. Even if there is local film layer shedding, the thick electrode can still maintain high electron transport efficiency in the in-plane direction and thickness direction, thereby delaying the occurrence of the capacity plunge problem and further improving the kinetic performance and cycle life of the battery.

[0214] In some embodiments, the conductive agent further includes conductive carbon black.

[0215] Conductive carbon black has a high specific surface area and thus has good liquid retention ability. The thick electrode has a large swelling force during the cycling process, making the electrolyte easy to be extruded. The distribution of conductive carbon black in the positive electrode film layer is beneficial to improving the liquid retention ability of the thick electrode, further alleviating the phenomenon of capacity plunge during battery cycling, and improving the cycle life of the battery.

[0216] In some embodiments, the agglomeration region of the conductive agent includes carbon nanotubes and conductive carbon black.

[0217] Researchers found that due to their high surface energy, carbon nanotubes are prone to agglomeration, resulting in uneven dispersion in the positive electrode film layer and unable to form an effective carbon nanotube network structure. The surface energy of conductive carbon black is relatively close to that of carbon nanotubes, and it can adsorb on the surface of carbon nanotubes to form a physical barrier, increasing the resistance to carbon nanotube agglomeration, reducing the direct contact between carbon nanotubes, thereby inhibiting the agglomeration phenomenon and improving the distribution uniformity of carbon nanotubes in the positive electrode film layer. On the one hand, this helps to improve the conductivity of the thick-coated positive electrode film layer and enhance the kinetic performance of the battery; on the other hand, it helps to exert the binding effect of carbon nanotubes on the positive electrode film layer, reduce the risk of shedding of the thick-coated positive electrode film layer, and further improve the kinetic performance and cycle life of the battery. In addition, the agglomeration of carbon nanotubes in the region of conductive agent agglomeration will also cause blockage of the local ion transport path in the conductive agent agglomeration region. The combination of conductive carbon black can improve the lithium ion transport ability in this region, reduce local polarization, and further improve the cycle stability of the battery.

[0218] In some embodiments, based on the mass of the positive electrode film layer, the mass content C1 of carbon nanotubes satisfies: 0 < C1 ≤ 2.5%, and the mass content C2 of conductive carbon black satisfies: 0 < C2 ≤ 2.5%.

[0219] In some embodiments, based on the mass of the positive electrode film layer, the mass content C1 of carbon nanotubes can be selected from 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5% or the numerical range between any two of them.

[0220] In some embodiments, based on the mass of the positive electrode film layer, the mass content C2 of conductive carbon black can be selected from 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5% or the numerical range between any two of them.

[0221] When the mass contents of carbon nanotubes and conductive carbon black are within the above ranges, the agglomeration phenomenon of carbon nanotubes can be effectively alleviated and a good conductive network structure can be formed, thereby effectively reducing the stress concentration in the positive electrode film layer, increasing the liquid retention rate of the positive electrode plate during long-term cycling, further reducing the risk of shedding of the electrode film layer and the degree of polarization, improving the kinetic performance of the battery and taking into account the problem of capacity drop, and improving the cycle life of the battery.

[0222] In some embodiments, the positive electrode film layer further includes a dispersant, and the dispersant includes hydrogenated nitrile rubber (HNBR).

[0223] HNBR is obtained by hydrogenating the double bonds of nitrile rubber. Its highly saturated main chain structure endows it with excellent oil resistance, heat resistance, aging resistance, etc. This enables it to remain stable in different environments and systems when used as a dispersant, and is not prone to degradation or deterioration, thus effectively exerting the dispersing effect. The HNBR molecular chain contains both polar nitrile groups and non-polar hydrocarbon segments. The polar nitrile groups can interact with some polar substances or the surfaces of particles, such as adsorbing on the surfaces of the particles to be dispersed through hydrogen bonding, electrostatic interaction, etc.; the non-polar hydrocarbon segments have good lipophilicity and can be well extended and dispersed in non-polar or weakly polar media, enabling the particles to be evenly dispersed in the media.

[0224] When HNBR adsorbs on the surfaces of the particles in the slurry, its long-chain molecules will form a physical barrier around the particles, preventing the particles from approaching and aggregating with each other, and keeping the particles in a relatively independent dispersed state in the system. At the same time, HNBR can reduce the surface tension between the dispersion medium and the particles to be dispersed, making the particles more easily wetted by the medium, thereby promoting the dispersion of the particles in the medium. At the same time, it can also reduce the interfacial energy between the particles and reduce the aggregation phenomenon of the particles driven by the interfacial energy. Further, when the slurry is dried into a film, the elastic network structure of HNBR can buffer the shrinkage stress generated by the volatilization of the solvent, reduce the re-aggregation of the conductive agent due to capillary force during this process, reduce the area ratio of the agglomeration region of the conductive agent, and improve the kinetic performance and cycle life of the battery.

[0225] In some embodiments, based on the mass of the positive electrode film layer, the mass content of the dispersant is 0.5% - 2%.

[0226] In some embodiments, based on the mass of the positive electrode film layer, the mass content of the dispersant can be selected as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2% or any value range between any two of them.

[0227] When the mass content of the dispersant is within the above range, it can achieve uniform dispersion of the particles in the positive electrode film layer while maintaining a high loading amount of the positive electrode film layer, reduce the stress concentration in the thick-coated lithium-containing transition metal phosphate positive electrode film layer, and effectively alleviate the problem of battery capacity drop.

[0228] In some embodiments, the battery cell further includes a separator 20 disposed between the positive electrode plate and the negative electrode plate. The separator 20 includes a base film 201, a ceramic layer 202 disposed on at least one side of the base film 201, and an adhesive layer 203 disposed on the side of at least one ceramic layer 202 away from the base film 201. The adhesive layer 203 is a continuous layer with a porous structure, and the adhesive layer 203 includes a vinylidene fluoride-based polymer.

[0229] In some embodiments, the battery cell further includes a separator disposed between the positive electrode plate and the negative electrode plate. The separator includes a base film, ceramic layers disposed on both sides of the base film, and adhesive layers disposed on both sides of the ceramic layers away from the base film.

[0230] In some embodiments, the vinylidene fluoride-based polymer includes one or more of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0231] In some embodiments, the vinylidene fluoride-based polymer includes polyvinylidene fluoride (PVDF).

[0232] In the prior art, the adhesive layer of the separator usually uses aqueous PVDF, which presents an island structure in the separator, as Figure 2 shown. On the one hand, this is beneficial to provide a gap for the expansion of the battery cell, and on the other hand, it is convenient for manufacturing; however, the contact area between such a separator adhesive layer and the electrode plate is small, and the adhesive force is weak.

[0233] The separator provided by the embodiment of the present application uses a continuous layer with a porous structure as the adhesive layer, as Figure 1 and Figure 3 shown. Its porous structure provides space for the expansion of the thick-coated battery cell and improves its stability; at the same time, compared with the adhesive layer in the prior art, its bonding area with the electrode plate is larger, so that the bonding between the separator and the electrode plate is more firm and uniform; further, when the positive electrode film layer rebounds, it is beneficial to maintain the interface contact between the separator and the positive electrode film layer and reduce the occurrence probability of film layer peeling.

[0234] It can be understood that the continuous adhesive layer may break and deform into a block structure due to contact or extrusion stress with the positive electrode plate or the negative electrode plate during the manufacturing or cycling process of the electrode plate. The continuous structure referred to in the present application means that at the microscopic level, such as observed under a scanning electron microscope or an optical microscope, the adhesive layer of the separator is continuous. In order to reflect the true morphology of the separator, during the sampling process, it is preferably sampled in the area where the adhesive layer of the separator in the battery does not bond with the positive electrode plate or the negative electrode plate. As an example, sampling is performed at the position of the separator beyond the positive electrode plate and the negative electrode plate; or sampling is performed on the separator near the surface of the electrode assembly. The bonding between this separator sampling area and the positive electrode plate or the negative electrode plate is less, and it can better reflect the true state of the separator.

[0235] Compared with wound electrodes, in a laminated electrode, the extrusion between the separator and the electrode is smaller, and relative displacement between the separator and the electrode is likely to occur, thereby disturbing the film layer and making the film layer prone to powder shedding or peeling off. In addition, it may also cause the positive and negative electrodes to be mutually overlapped, increasing the risk of internal short circuit in the electrode. Therefore, the separator provided in the embodiments of the present application is particularly suitable for laminated electrodes. The increased adhesion between the porous adhesive layer and the electrode helps to improve the adhesion between the separator and the electrode and reduce the relative displacement between the separator and the electrode. This helps to reduce the disturbance to the positive electrode film layer and the probability of film layer peeling off, and also helps to reduce the risk of short circuit caused by the overlap of the positive and negative electrodes.

[0236] In summary, when the vinylidene fluoride-based polymer in the adhesive layer of the embodiments of the present application is selected from the above materials, it helps to form a continuous and uniform porous adhesive layer. First, the adhesion between this adhesive layer and the electrode is improved and evenly distributed, which helps to reduce the stress concentration phenomenon in the thick-coated lithium-containing transition metal phosphate positive electrode film layer and reduce the risk of film layer peeling off, thereby helping to further improve the cycle life of the battery. Second, the adhesive layer stably adheres to the positive electrode or the negative electrode, which helps to reduce the direct contact between the positive electrode and the negative electrode caused by the relative displacement between the electrode and the separator, reduce the risk of internal short circuit, and help to improve the battery safety performance. Second, the porous adhesive layer helps to maintain the porosity of the separator, reserve space for the expansion of the electrode, and further improve the cycle life of the battery.

[0237] In some embodiments, the material of the base film may include, but is not limited to, one or more of glass fiber, non-woven fabric, polyethylene (PE), and polypropylene (PP).

[0238] In some embodiments, the ceramic layer includes one or more of aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), silicon dioxide (SiO2), and boron nitride (BN).

[0239] The ceramic particles have flame retardancy and a relatively high hardness value, and are not easily deformed when heated, so their dimensional stability is excellent. The low thermal conductivity of the ceramic material can further prevent the expansion of certain thermal runaway points in the battery to form an overall thermal runaway, thereby improving the safety performance of the battery cell.

[0240] In some embodiments, the thickness of the base film in the separator is 7 μm - 9 μm.

[0241] In some embodiments, the thickness of the base film in the separator can be selected as 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or the numerical range between any two of them.

[0242] In some embodiments, the single-sided thickness of the ceramic layer in the separator is 2 μm - 4 μm.

[0243] In some embodiments, the thickness of the ceramic layer on one side of the separator can be selected as 2μm, 2.5μm, 3μm, 3.5μm, 4μm or the numerical range between any two of them.

[0244] In some embodiments, the thickness of the adhesive layer on one side of the separator is 1μm - 5μm.

[0245] In some embodiments, the thickness of the adhesive layer on one side of the separator can be selected as 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or the numerical range between any two of them.

[0246] In the present application, "thickness" has the meaning well-known in the art and can be measured using methods and instruments known in the art. As an example, it can be tested using a high-precision micrometer (such as Mitutoyo 293 - 100 type with an accuracy of 0.1μm).

[0247] If the thickness of the adhesive layer is too low, the void space in the separator is small and the adhesion between the separator and the electrode is low. On the one hand, after the film layer expands, the stress increases and the probability of the film layer peeling off increases, affecting the cycle life of the battery; on the other hand, the probability of positive-negative lap short circuit increases, thus affecting the safety performance of the battery. If the thickness of the adhesive layer is too large, it occupies a large space in the battery, thus affecting the volumetric energy density of the battery. In the embodiments of the present application, the thickness of the adhesive layer within the above range helps to balance the cycle life, safety performance and volumetric energy density of the battery.

[0248] In some embodiments, a bottom coating is provided in the bottom region of the positive electrode film layer close to the positive electrode current collector. The bottom coating includes a conductive agent and a binder. The conductive agent includes carbon nanotubes and conductive carbon black, and the binder includes polyvinylidene fluoride (PVDF).

[0249] In some embodiments, the thickness of the bottom coating is 0.5μm - 5μm.

[0250] In some embodiments, the thickness of the bottom coating can be selected as 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or the numerical range between any two of them.

[0251] The bottom coating provided in the embodiments of the present application helps to improve the adhesion between the positive electrode film layer and the positive electrode current collector and relieve the stress concentration phenomenon at large particles, thereby reducing the probability of the positive electrode film layer peeling off and improving the cycle stability of the battery. At the same time, compared with the direct contact between the positive electrode current collector and the positive electrode film layer, the contact area between the bottom coating and the positive electrode film layer increases, which helps to increase the area of electron transfer between the current collector and the positive electrode film layer, thereby reducing the internal resistance of the electrode and improving the kinetic performance of the battery.

[0252] In some embodiments, such as Figure 4 shown, the battery cell 5 includes a housing 50, and the laminated battery core is accommodated in the housing 50. The size of the housing 50 in the length direction X is L1, the size of the housing 50 in the width direction Y is W1, and the size of the housing 50 in the thickness direction Z is H1. Among them, 450mm ≤ L1 ≤ 1300mm, 100mm ≤ W1 ≤ 150mm; 14mm ≤ H1 ≤ 22mm.

[0253] In some embodiments, L1 can be selected from 450mm, 480mm, 490mm, 500mm, 510mm, 520mm, 530mm, 540mm, 550mm, 560mm, 570mm, 580mm, 590mm, 600mm, 610mm, 620mm, 630mm, 640mm, 650mm, 660mm, 670mm, 680mm, 690mm, 700mm, 710mm, 720mm, 750mm, 800mm, 850mm, 900mm, 950mm, 1000mm, 1050mm, 1100mm, 1150mm, 1200mm, 1250mm, 1300mm or the numerical range between any two of them.

[0254] In some embodiments, W1 can be selected from 100mm, 110mm, 120mm, 130mm, 140mm, 150mm or the numerical range between any two of them.

[0255] In some embodiments, H1 can be selected from 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm or the numerical range between any two of them.

[0256] In some embodiments, the size of the housing in the length direction is L1, and 450mm ≤ L1 ≤ 650mm.

[0257] When the size L1 of the housing in the length direction satisfies 450mm ≤ L1 ≤ 650mm, the length of the battery cell is shorter, which helps to shorten the diffusion path of the current, reduce the internal resistance of the electrode sheet, thereby reducing the heat generation of the battery and improving its kinetic performance; in addition, the shorter housing length helps to shorten the diffusion path of the electrolyte during the infiltration process, improve the infiltration rate and uniformity of the electrolyte, further promote the uniformity of lithium ion deintercalation during the cycle process, relieve the stress concentration phenomenon, reduce the risk of film layer shedding, and improve the cycle stability of the battery cell.

[0258] In some embodiments, the size of the housing in the length direction is L1, and 900mm ≤ L1 ≤ 1300mm.

[0259] When the dimension L1 of the housing in the length direction satisfies 900 mm ≤ L1 ≤ 1300 mm, the dimension of the battery cell is relatively long, which helps to reduce the volume ratio of the housing in the battery cell and increase the load ratio of the active material. At the same time, the longer battery cell can reduce the number of battery cells required in the battery module, simplify the structural design of the battery module, reduce the number and complexity of the structural components in the module, thereby improving the space utilization rate of the battery pack, and further helping to increase the volume energy density of the battery cell.

[0260] In some embodiments, such as Figure 4 shown, the material of the housing 50 is a soft-pack material, and the soft-pack material includes an aluminum-plastic composite film.

[0261] In some embodiments, the material of the housing includes a composite film formed by one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), polyethylene (PE) and aluminum.

[0262] The soft-pack material has a high elongation rate, so its housing is thinner, lighter and softer, which helps to improve the space utilization rate of the battery cell, thereby increasing the energy density of the battery cell. In addition, the high barrier property of aluminum can effectively reduce the penetration of water and oxygen into the battery interior, reduce the decomposition of the electrolyte and the oxidation degree of the electrode material, thereby increasing the battery life.

[0263] In some embodiments, at 25 °C, the capacity of the battery cell is 95 Ah - 300 Ah.

[0264] In some embodiments, at 25 °C, the capacity of the battery cell is 150 Ah - 190 Ah.

[0265] In this application, the capacity of the battery cell has the meaning well-known in the art and can be tested by methods known in the art. As an example, at 25 °C, it is charged at a 0.5C charging rate to 3.65 V, then charged at a constant voltage of 3.65 V to 0.05C, left standing for 10 min, and then discharged at a 1C discharge rate to 2.5 V, and the discharge capacity of the battery cell is taken as the capacity of the battery cell.

[0266] In some embodiments, at 25 °C, the capacity of the battery cell may be optionally 95Ah, 100Ah, 105Ah, 110Ah, 115Ah, 120Ah, 125Ah, 130Ah, 135Ah, 140Ah, 145Ah, 150Ah, 155Ah, 158 Ah, 159Ah, 160Ah, 161Ah, 165Ah, 170Ah, 175Ah, 178 Ah, 180Ah, 185Ah, 190Ah, 200Ah, 210Ah, 220Ah, 230Ah, 240Ah, 250Ah, 270Ah, 280Ah, 290Ah, 300Ah or the numerical range between any two of them.

[0267] The second aspect of the present application provides a battery device, including the battery cell provided by the first aspect of the present application.

[0268] The battery device disclosed in the embodiments of the present application can be used in electrical equipment that uses the battery device as a power source or various energy storage systems that use the battery device as an energy storage element. In addition to being used in vehicles, the battery device can also be used in, but not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery cars, electric vehicles, ships, spacecraft, and so on. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric aircraft toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spaceships, etc.

[0269] The third aspect of the present application provides an electrical device that uses the battery device as a power source. The electrical device includes at least one of the battery cell, battery module, or battery pack provided by the present application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. As the electrical device, the battery cell, battery module, or battery pack can be selected according to its usage requirements.

[0270] Figure 5 is an electrical device as an example. The electrical device disclosed in the embodiments of the present application can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. A battery device is provided inside the vehicle, and the battery device can be provided at the bottom, head, or tail of the vehicle. The battery device can be used for the power supply of the vehicle. For example, the battery device can be used as the operating power source of the vehicle. The vehicle may further include a controller and a motor. The controller is used to control the battery device to supply power to the motor. For example, it is used for the working power requirements during the start, navigation, and driving of the vehicle. In some embodiments of the present application, the battery device can not only be used as the operating power source of the vehicle, but also as the driving power source of the vehicle, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle.

[0271] The fourth aspect of the present application provides an energy storage device using a battery device as a power source. The energy storage device may be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system, etc.

[0272] Embodiment Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those specific technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0273] Embodiment 1 (1) Preparation of the positive electrode active material Lithium dihydrogen phosphate, ferrous oxalate, a carbon source, titanium dioxide, and vanadium pentoxide are mixed evenly and ground in methanol to obtain a mixed raw material. Among them, the ratio of lithium dihydrogen phosphate to ferrous oxalate is such that the molar ratio of lithium to iron is 1.025:1.0; the carbon source includes polyethylene glycol with a weight average molecular weight of 500, polyethylene glycol with a weight average molecular weight of 2000, and polyethylene glycol with a weight average molecular weight of 4000 in a mass ratio of 2:6:2; the particle size D 10 of ferrous oxalate is 6.5 μm, the particle size D 50 is 62 μm, the particle size D 90 is 108 μm, the mass content of Fe element in ferrous oxalate is 30.5%, and the mass content of trivalent iron element is 0.03%.

[0274] The mixed raw material is ball-milled multiple times in a ball mill and demagnetized to obtain a mixed slurry. By controlling the number of grinding times and time, the particle size Dv 50 of the ground mixed slurry is 3.15 μm.

[0275] The mixed slurry is spray-dried to obtain a dry precursor powder. The appearance of the dry precursor powder material is light yellow and the color is uniform.

[0276] The precursor powder is placed in a sintering furnace. Under a nitrogen atmosphere, it is heated from 25°C to 360°C at a rate of 2°C / min and held at this temperature for 3.5 h, and then heated to a second temperature of 785°C at a rate of 5°C / min and held at this temperature for 10 h. After that, it is cooled down. Among them, based on the total mass of the positive electrode active material, the mass content of Ti element is 1050 ppm, and the mass content of V element is 950 ppm.

[0277] The obtained material was crushed by air jet milling method at a classification frequency of 21 Hz and a crushing air pressure of 0.54 MPa with a certain air volume to obtain the lithium iron phosphate cathode active material with carbon material on its surface.

[0278] The above D10, D50, D90, and Dv50 refer to the data obtained by Malvern laser scattering method.

[0279] (2)Preparation of the positive electrode sheet The above-mentioned cathode active material, conductive agent, and binder polyvinylidene fluoride were mixed in a solvent N-methylpyrrolidone according to a mass ratio of 94.1:1.9:3, and then a dispersant HNBR with a mass ratio of 1% was added and fully mixed in a stirring tank, stirred, and dispersed to form a cathode slurry; among them, the stirring includes pre-stirring and main stirring, the stirring speed of pre-stirring is lower than that of main stirring, the revolution speed of pre-stirring is 25 rpm, the rotation speed is 500 rpm, and the pre-stirring time is 15 min. After completing the stirring process, the cathode slurry is transported to the coating process; the conductive agent includes conductive carbon black and multi-walled carbon nanotubes with a mass ratio of 0.9:1, the specific surface area of conductive carbon black is 80 m 2 / g, the oil absorption value is 180 mL / 100 g, the average length of carbon nanotubes is 20 μm, and the specific surface area is 280 m 2 / g; The cathode slurry was transferred and coated on aluminum foil and dried, and then hot-pressed to obtain a positive electrode sheet with a single-sided density of 0.38 g / 1540.25 mm 2 and a compaction density of 2.36 g / cm 3 Here, the compaction density refers to the compaction density under the full discharge state of the battery monomer.

[0280] The hot-pressing process includes three hot roll pressing processes, and the hot roll pressing pressure increases in turn. The hot roll pressures are 35 tons, 55 tons, and 75 tons in turn; the hot roll temperature is 65 °C. Before the first entry into the hot roll compaction, the electrode sheet is heated, and the heating temperature is 50 °C.

[0281] The positive electrode sheet was slit and punched into a specified shape, and the punched positive electrode sheets were sorted by weight through a weighing and sorting machine for stacking by a stacker.

[0282] Among them, in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, in the cumulative area distribution curve of the sphericity of the particles with a particle size R1 satisfying R1≥1000 nm, the median L R1A50 of sphericity is 0.721; the median C 50is 1.11; based on the total area of particles in the cross section of the positive electrode film along the thickness direction of the electrode, the area of particles with a particle size R1 satisfying R1 ≥ 1000nm accounts for 35.28%; in the cross section of the positive electrode film along the thickness direction of the electrode, the distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000nm is 1.97%; the median B of the positive electrode film coating value B is 50 is 0.441; the iron dissolution rate of the positive electrode material is 976ppm; based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area of the agglomerated region of the conductive agent accounts for 1.91%; the porosity of the positive electrode film layer is 15.06%.

[0283] (3) Preparation of negative electrode sheet A mixture of artificial graphite and natural graphite (weight ratio of 1:1), conductive carbon black, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) are evenly mixed in a weight percentage of 96:0.5:2.0:1.5, and deionized water is added. After stirring and dispersion, a negative electrode slurry is obtained. The negative electrode slurry is coated on a base copper foil, and after drying, compacting, slitting and sheeting, a negative electrode sheet is obtained.

[0284] The negative electrode sheets are stripped and punched into specified shapes, and the punched negative electrode sheets are sorted by weight using a weighing sorting machine for stacking by a stacking machine.

[0285] (4) Diaphragm Dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP), stir evenly, add polyethylene glycol (PEG) as a pore-forming agent, and stir and mix thoroughly to obtain a bonding layer solution. Apply the bonding layer solution on the base film with ceramic layers on both sides, pre-volatilize at 80°C and dry at 110°C, then immerse in deionized water to dissolve PEG, and obtain a diaphragm with a porous bonding layer.

[0286] The thickness of the base film is 8 μm, the thickness of the single-sided ceramic layer is 3 μm, and the thickness of the single-sided adhesive layer is 1 μm.

[0287] (5) Electrolyte In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed evenly.

[0288] Then, lithium hexafluorophosphate was added and dissolved in an organic solvent so that the concentration of lithium hexafluorophosphate in the electrolyte was 1.05 mol / L, and vinylene carbonate (VC) was added and stirred evenly to obtain the electrolyte of Example 1.

[0289] Among them, based on the total mass of the electrolyte, the mass content of dimethyl carbonate is 26%, the mass content of ethyl methyl carbonate is 43.3%, the mass content of ethylene carbonate is 17.3%, and the mass content of vinylene carbonate is 0.9%.

[0290] (6)Preparation of the battery Use a laminator to stack the positive electrode sheet, separator, and negative electrode sheet in sequence. The separator should be able to isolate the positive and negative electrodes to obtain a laminated battery cell. Apply adhesive to the laminated battery cell to tightly wrap the cell. Place the laminated battery cell with adhesive in the outer package, and the outer package is a soft-packaging material, an aluminum-plastic film, which is composed of an inner layer of polypropylene, a middle layer of aluminum foil, and an outer layer of nylon. Among them, the aluminum-plastic film outer package is formed and trimmed by a punching and forming machine to obtain the target shape and size. Then, heat-seal the aluminum-plastic film to meet the requirement that the sealing tensile strength of the aluminum-plastic film ≥ 25 N / 8 mm. The battery is subjected to vacuum baking and standing, and the electrolyte is injected using a flat-head needle, and then encapsulated. Then, hot pressing and cold pressing operations are performed on the soft-pack battery. The temperature of hot pressing is 45 °C, the time is 2 minutes, and the pressure is 90 kg / cm 2 , and the temperature of cold pressing is 25 °C, the time is 2 minutes, and the pressure is 90 kg / cm 2 . Finally, after processes such as formation, vacuum exhaust, and edge trimming, the battery monomer is obtained. The size of the battery monomer in the length direction is 600 mm, the size in the width direction is 125 mm, and the size in the thickness direction is 20 mm.

[0291] The preparation methods of Examples 2 - 10 are basically the same as that of Example 1, except that the preparation method of the positive electrode active material is adjusted as follows: Example 2 The preparation method of Example 2 is basically the same as that of Example 1, except that in the preparation of the positive electrode active material, the second temperature is adjusted to 765 °C.

[0292] Example 3 The preparation method of Example 3 is basically the same as that of Example 1, except that in the preparation of the positive electrode active material, the second temperature is adjusted to 735 °C.

[0293] Example 4 The preparation method of Example 4 is basically the same as that of Example 1, except that in the preparation of the positive electrode active material, the carbon source is replaced with polyethylene glycol with a molecular weight of 500 and polyethylene glycol with a molecular weight of 2000 at a mass ratio of 2:8.

[0294] Example 5 The preparation method of Example 5 is basically the same as that of Example 1, except that in the preparation of the positive electrode active material, the carbon source is replaced with polyethylene glycol with a molecular weight of 500.

[0295] Example 6 The preparation method of Example 6 is basically the same as that of Example 1, except that in the preparation of the positive electrode active material, the carbon source is replaced by polyethylene glycol with a molecular weight of 2000.

[0296] Example 7 The preparation method of Example 7 is basically the same as that of Example 3, except that in the preparation of the positive electrode active material, the carbon source is replaced by polyethylene glycol with a molecular weight of 500 and glucose with a mass ratio of 2:8.

[0297] Example 8 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, the coating weight is adjusted, and parameters such as the hot roll pressing pressure, hot roll temperature, transfer coating speed, and heating temperature before the first entry into hot roll compaction are adaptively adjusted, so that the single-sided density of the positive electrode film layer obtained by cold pressing is 0.43 g / 1540.25mm 2 ; and the thickness of the battery is appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0298] Example 9 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, the coating weight is adjusted, and parameters such as the hot roll pressing pressure, hot roll temperature, transfer coating speed, and heating temperature before the first entry into hot roll compaction are adaptively adjusted so that the single-sided density of the positive electrode film layer obtained by cold pressing is 0.26 g / 1540.25mm 2 ; and the thickness of the battery is appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0299] Example 10 The preparation method of Example 10 is basically the same as that of Example 1, except that parameters such as the hot roll pressing pressure, hot roll temperature, transfer coating speed, and heating temperature before the first entry into hot roll compaction are adjusted to obtain a positive electrode sheet with a single-sided density of 0.41 g / 1540.25mm 2 and a compaction density of 2.52 g / cm 3 . Here, the compaction density refers to the compaction density under the full discharge state of the battery monomer. And the thickness of the battery is appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0300] Comparative Example 1 The preparation method of Comparative Example 1 is basically the same as that of Example 3, except that in the preparation of the positive electrode active material, the carbon source is replaced by glucose.

[0301] Comparative Example 2 The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that when preparing the positive electrode sheet, the coating weight is adjusted, and parameters such as the hot roll pressing pressure, hot roll temperature, transfer coating speed, and heating temperature before the first entry into the hot roll compaction are adaptively adjusted, so that the single-sided density of the positive electrode film layer obtained by cold pressing is 0.24 g / 1540.25mm 2 ; and the thickness of the battery is appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0302] Test method 1. Capacity of the battery cell At 25°C, charge the battery cell at a charging rate of 0.5C of the nominal capacity of the battery cell to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, let it stand for 10 min, then discharge at a discharge rate of 1C to 2.5V, let it stand for 10 min, and calculate the capacity C during the discharge process through the formula C = I×t, with the unit of Ah.

[0303] 2. Number of cycles corresponding to the capacity decay to 80% At 25°C, charge the battery cell at a charging rate of 0.5C of the nominal capacity of the battery cell to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, let it stand for 10 min, then discharge at a discharge rate of 1C to 2.5V, let it stand for 10 min. The above one charge and discharge is one cycle, and the test is stopped until the battery capacity decays to 80% of the nominal capacity, denoted as the number of cycles @80% SOH.

[0304] Test results The test results of the above examples and comparative examples are shown in Table 1.

[0305] Table 1

[0306] It can be seen from the comparison between the examples and the comparative examples that the battery cell includes a stacked cell, the stacked cell includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector, and the positive electrode film layer includes lithium-containing transition metal phosphate particles with carbon materials provided on at least part of the surface; when the battery cell is in a fully discharged state, the compaction density of the positive electrode sheet is 2.3 g / cm 3 -2.6 g / cm 3 ; the single-sided density of the positive electrode film layer is 0.25 g / 1540.25mm 2 -0.45 g / 1540.25mm 2 , in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode sheet, among the cumulative distribution curves of the sphericity area of the particles with a particle size R1 satisfying R1≥1000nm, L R1A50is 0.6 - 0.8; in the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median C50 of the graphitization degree is 0.95 - 1.20, which helps to improve the cycle stability during the long cycle of the battery cell while maintaining good capacity.

[0307] As can be seen from the comparison of Examples 1 - 3, in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, in the cumulative spherical area distribution curve of the particles with a particle size R1 satisfying R1≥1000nm, L R1A50 is 0.65 - 0.75 within the range of 0.67 - 0.72, and the battery cell has good long cycle stability.

[0308] As can be seen from the comparison of Example 1, Examples 3 - 6 and Example 7, in the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median C 50 is further optionally 1.01 - 1.13, which helps to further improve the long cycle stability of the battery cell.

[0309] As can be seen from the comparison of Example 1 and Examples 8 - 10, the single-sided coating areal density of the positive electrode film layer is further in the range of 0.35g / 1540.25mm 2 - 0.4g / 1540.25mm 2 range, which helps to further balance the capacity and long cycle stability of the battery.

[0310] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the main idea of this application, various deformations that can be thought of by those skilled in the art applied to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The battery cell includes a stacked electrode assembly, the stacked electrode assembly includes a positive electrode plate and a negative electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, and the positive electrode film layer includes lithium-containing transition metal phosphate particles with carbon materials provided on at least part of the surface; When the battery cell is in a fully discharged state, the compaction density of the positive electrode plate is 2.3 g / cm 3 -2.6 g / cm 3 ; The single-sided density of the positive electrode film layer is 0.25 g / 1540.25 mm 2 -0.45 g / 1540.25 mm 2 ; In the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000nm, L R1A50 is 0.6 - 0.8; In the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of the laser confocal Raman spectrometer for the positive electrode film layer, the median C of the graphitization degree 50 is 0.95 - 1.20; where the graphitization degree C value is I G / I D , I G represents the intensity of the G peak of the Raman spectrum at 1580 ± 100 cm -1 , and I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 100 cm -1 .

2. The battery cell according to claim 1, characterized in that, The single-sided density of the positive electrode film layer is 0.3 g / 1540.25 mm 2 - 0.45 g / 1540.25 mm 2 .

3. The battery cell according to claim 1 or 2, characterized in that In the cumulative distribution curve of the graphitization degree C value obtained in the surface scanning mode of the laser microconfocal Raman spectrometer for the positive electrode film layer, the median C of the graphitization degree 50 is 1.01 - 1.

13.

4. The battery cell according to claim 3, wherein, The single-sided density of the positive electrode film layer is 0.35 g / 1540.25 mm 2 - 0.4 g / 1540.25 mm 2 .

5. The battery cell according to claim 4, wherein In the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000nm, L R1A50 is 0.65 - 0.

75.

6. The battery cell according to claim 4, wherein In the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, in the cumulative area distribution curve of the sphericity of particles with a particle size R1 satisfying R1≥1000nm, L R1A50 is 0.67 - 0.

72.

7. The battery cell according to claim 1 or 2, characterized in that, The single-sided thickness H of the positive electrode film layer is 70 μm - 120 μm.

8. The battery cell according to claim 1 or 2, characterized in that, The single-sided thickness H of the positive electrode film layer is 90 μm - 120 μm.

9. The battery cell according to claim 1 or 2, characterized in that, The single-sided thickness H of the positive electrode film layer is 100 μm - 120 μm.

10. The battery cell according to claim 1 or 2, characterized in that, Based on the total area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the area ratio of the particles with a particle size R1 satisfying R1 ≥ 1000 nm is 12% - 50%; and / or, In the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the distribution uniformity of the particles with a particle size R1 satisfying R1 ≥ 1000 nm is less than or equal to 5%.

11. The battery cell according to claim 1 or 2, characterized in that, Based on the total area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the area ratio of the particles with a particle size R1 satisfying R1 ≥ 1000 nm is 12% - 40%; and / or, In the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the distribution uniformity of the particles with a particle size R1 satisfying R1 ≥ 1000 nm is 0.2% - 2.5%.

12. The battery cell according to claim 1 or 2, characterized in that, In the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the distribution uniformity of the particles with a particle size R1 satisfying R1 ≥ 1000 nm is 0.2% - 2%.

13. The battery cell according to claim 1 or 2, characterized in that, In the cumulative distribution curve of the coating value B obtained in the surface scanning mode of the laser microscopic confocal Raman spectrometer for the positive electrode film layer, the median B of the coating value 50 is 0.30 - 0.60, where the coating value B is I P / I D , where I P represents the intensity of the P peak of the Raman spectrum at 948 ± 100 cm -1 , and I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 100 cm -1 .

14. The battery cell according to claim 1, characterized in that, The lithium-containing transition metal phosphate particles in the positive electrode film layer include the components represented by the following general formula: Li m Fe x P y O j Q q Formula I Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.8 ≤ m ≤ 1.15, 0.9 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 ≤ q ≤ 0.

1.

15. The battery cell according to claim 1, wherein The iron dissolution rate of the positive electrode material in the positive electrode film layer is 658 ppm - 1921 ppm.

16. The battery cell according to claim 1, wherein The iron dissolution rate of the positive electrode material in the positive electrode film layer is 658 ppm - 1485 ppm.

17. The battery cell according to claim 1, characterized in that, The lithium-containing transition metal phosphate particles include titanium element. Based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of the titanium element is 500 ppm - 8000 ppm.

18. The battery cell according to claim 1, characterized in that, The lithium-containing transition metal phosphate particles include titanium element. Based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of the titanium element is 1000 ppm - 3000 ppm.

19. The battery cell according to claim 1, wherein The lithium-containing transition metal phosphate particles include vanadium element. Based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of the vanadium element is 500 ppm - 5000 ppm.

20. The battery cell according to claim 1, characterized in that, The lithium-containing transition metal phosphate particles include vanadium element. Based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of the vanadium element is 500 ppm - 3000 ppm.

21. The battery cell according to claim 1, characterized in that, The porosity of the positive electrode film layer is 14% - 28%.

22. The battery cell according to claim 1, wherein, The positive electrode film layer further includes a conductive agent. Based on the total area of the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the agglomeration region of the conductive agent is 0.5% - 2.5%.

23. The battery cell according to claim 22, characterized in that, The area ratio of the agglomeration region of the conductive agent is 0.5% - 1.7%.

24. The battery cell according to claim 22, characterized in that, The conductive agent includes carbon nanotubes, and the carbon nanotubes include one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

25. The battery cell according to claim 22, wherein, The conductive agent further includes conductive carbon black.

26. The battery cell according to claim 22, wherein, The agglomeration region of the conductive agent further includes carbon nanotubes and conductive carbon black.

27. The battery cell according to claim 26, characterized in that, Based on the mass of the positive electrode film layer, the mass content C1 of the carbon nanotubes satisfies: 0 < C1 ≤ 2.5%, and the mass content C2 of the conductive carbon black satisfies: 0 < C2 ≤ 2.5%.

28. The battery cell according to claim 1, characterized in that, The positive electrode film layer further includes a dispersant, and the dispersant includes hydrogenated nitrile butadiene rubber (HNBR).

29. The battery cell according to claim 28, wherein, Based on the mass of the positive electrode film layer, the mass content of the dispersant is 0.5% - 2%.

30. The battery cell according to claim 1, characterized in that, The battery cell further includes a separator disposed between the positive electrode sheet and the negative electrode sheet. The separator includes a base film, ceramic layers disposed on both sides of the base film, and a bonding layer disposed on the side of at least one of the ceramic layers away from the base film. The bonding layer is a continuous layer with a porous structure, and the bonding layer includes a polyvinylidene fluoride-based polymer.

31. The battery cell according to claim 30, wherein The separator satisfies at least one of the following conditions: (1) The thickness of the base film is 7μm - 9μm; (2) The thickness of the single-sided ceramic layer is 2μm - 4μm; (3) The thickness of the single-sided bonding layer is 1μm - 5μm.

32. The battery cell according to claim 1, characterized in that, The positive electrode film layer is provided with a bottom coating in the bottom region close to the positive electrode current collector. The bottom coating satisfies at least one of the following conditions: (1) The bottom coating includes a conductive agent and a binder. The conductive agent includes carbon nanotubes and conductive carbon black, and the binder includes polyvinylidene fluoride (PVDF); (2) The thickness of the bottom coating is 0.5μm - 5μm.

33. The battery cell according to claim 1, wherein, The battery cell includes a housing. The stacked electrode core is accommodated in the housing. The size of the housing in the length direction is L1, the size of the housing in the width direction is W1, and the size of the housing in the thickness direction is H1. Among them, 450mm ≤ L1 ≤ 1300mm, 100mm ≤ W1 ≤ 150mm; 14mm ≤ H1 ≤ 22mm.

34. The battery cell according to claim 33, wherein, The size of the housing in the length direction is L1, 450mm ≤ L1 ≤ 650mm.

35. The battery cell according to claim 33, characterized in that, The size of the housing in the length direction is L1, 900mm ≤ L1 ≤ 1300mm.

36. The battery cell according to claim 33, wherein, The material of the housing is a soft package material, and the soft package material includes an aluminum-plastic composite film. The aluminum-plastic composite film includes a composite film formed by one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), and polyethylene (PE) and aluminum.

37. The battery cell according to claim 1, characterized in that, At 25°C, the capacity of the battery cell is 95Ah - 300Ah.

38. The battery cell according to claim 1, characterized in that, At 25°C, the capacity of the battery cell is 150Ah - 190Ah.

39. A battery device, characterized in that, Including the battery cell according to any one of claims 1 - 38.

40. An electric device, characterized in that, The electrical device includes the battery device as described in claim 39, and the battery device is used to provide electrical energy.

41. A energy storage device, characterized in that, The energy storage device includes the battery device as described in claim 39, and the battery device is used to store electrical energy.

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