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

Abstract

The present application provides a battery cell, a battery device, an electrical device, and an energy storage device. The battery cell includes a laminated cell and a shell, and the shell is a soft-pack material; the shell includes a first sealing area provided at at least one end of the laminated cell extending in the width direction, the first sealing area includes a double-folded edge structure extending in the length direction, and a packaging glue is provided on the double-folded edge structure, and the packaging glue is continuously provided along the length direction and fixes the double-folded edge structure; the positive electrode film layer includes lithium-containing transition metal phosphate particles; based on the total area of ​​the particles in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, the area of ​​the particles with a particle size R1 satisfying R1 ≥ 1000 nm accounts for 12%-50%; the thickness H of the single side of the positive electrode film layer is 70μm-120μm; when the battery cell is in a fully discharged state, the compaction density of the positive electrode plate is 2.3g / cm 3 ‑2.6g / cm 3 ; The mass proportion of dimethyl carbonate in the electrolyte is 18%-32%.

Description

Technical Field

[0001] The present application relates to the field of battery technology, 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 hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] As national, industry, and market standards increase the capacity and reliability of power devices, higher requirements are being placed on battery cells. However, achieving these performance improvements simultaneously is difficult with existing technologies, creating a pressing technical challenge in this field. Summary of the Invention

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

[0005] The first aspect of the present application provides a battery cell, comprising a laminated cell and a shell, wherein the laminated cell is accommodated in the shell, and the shell is a soft-pack material; the shell comprises a first sealing area, and the first sealing area is arranged at at least one end of the laminated cell extending in the width direction; the first sealing area comprises a double-folded edge structure extending in the length direction, and a packaging glue is arranged on the double-folded edge structure, and the packaging glue is continuously arranged in the length direction and fixes the double-folded edge structure; the laminated cell comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the positive electrode sheet comprises a positive current collector. The invention relates to a battery cell and a positive electrode film layer provided on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises lithium-containing transition metal phosphate particles, and at least a portion of the surface of the lithium-containing transition metal phosphate particles is provided with a carbon material; based on the total area of ​​the particles in the cross section of the positive electrode film layer along the thickness direction of the positive electrode sheet, the area of ​​the particles whose particle size R1 satisfies R1 ≥ 1000 nm accounts for 12%-50%; the thickness of a single side of the positive electrode film layer is recorded as H, and H is 70μm-120μm; when the battery cell is in a fully discharged state, the compaction density of the positive electrode sheet is 2.3g / cm 3 -2.6g / cm 3 The electrolyte includes a solvent, and the solvent includes dimethyl carbonate (DMC); based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate is 18%-32%.

[0006] The gram capacity of lithium-containing transition metal phosphates is relatively low. Studies have shown that when the thickness H of the positive electrode film layer on one side is less than 70μm, the battery capacity is difficult to meet market demand. In the embodiment of the present application, by controlling the thickness H of the positive electrode film layer on one side within the range of 70μm-120μm, it is beneficial to increase the space utilization of the active material, and further adopt a soft-package material shell, thereby reducing the weight of the battery cell and improving the mass energy density of the battery. However, the thicker positive electrode film layer undergoes significant volume changes due to lithium insertion and removal during the charge and discharge cycle, resulting in mechanical stress accumulation, which in turn causes the expansion and contraction of the electrode material, the pole piece rebounds, the thickness increases, and the mechanical stress on the packaging structure increases. At the same time, the thicker film layer means that the internal heat is more difficult to conduct, which is prone to local overheating, exacerbating the side reactions and gas production of the electrolyte, and further increasing the internal pressure of the battery cell. Compared with the winding type, the laminated cell structure reduces the corner gap and improves the volume energy density, but the laminated cell lacks the restraining effect brought by the winding structure, and has little restriction on the rebound of the thick coated film layer, which deteriorates the reliability of the battery cell. Compared to hard-shell materials, soft-pack materials have lower mechanical strength and are less able to withstand internal pressure. They also have lower thermal conductivity, making heat buildup more likely inside the battery cells, further exacerbating gassing issues. Over extended use, excessive internal pressure could cause the seal to break.

[0007] In the embodiment of the present application, the first sealing area includes a double folding structure extending along the long side direction to further improve the sealing strength of the first sealing area. The double folding forms a multiple sealing barrier by folding the soft package material of the shell twice. Even if the first layer of folding structure is due to the rebound stress from the high thickness of the positive electrode film layer in the battery cell and the electrolyte gas production defects, the second layer of folding structure can still maintain the seal. At the same time, due to battery processing, the soft package material is hot-melt bonded, and the double folding can make the heat-sealed area more uniform, improving the poor sealing situation in local areas. The sealing is the weak link in the mechanical strength of the soft package battery cell, in order to further enhance the reliability of the package. The inventor sets a packaging glue on the double folding structure. The packaging glue is continuously set along the long side direction and fixes the double folding structure, which can cover the micro cracks or defects in the heat-sealed area in the sealing area of ​​the soft package material; and the double folding structure will have a certain elastic memory after heat sealing, and may rebound after long-term use. The packaging glue can fix the double folding structure and maintain the stability of the structure. In the embodiment of the present application, the compaction density of the positive electrode sheet is further controlled to be 2.3g / cm3 by controlling the battery cell in the fully discharged state. 3 -2.6g / cm 3On the one hand, it makes the battery cell have a higher capacity, and on the other hand, it makes a certain buffer space between the particle stacking structure, reducing the stress exerted on the packaging structure by the rebound of the pole piece. In order to further reduce the stress inside the battery cell, the inventors regulated the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000nm in the positive electrode film layer and the mass ratio of dimethyl carbonate in the electrolyte. The inventors found that under the same expansion rate, the expansion of small particles is more easily absorbed through the tiny pore structure between the particles than that of large particles. The absolute value of the expansion change of large particles is large and more difficult to be eliminated. When the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000nm is greater than 50%, it is easy to cause stress concentration, obvious rebound, and increase the internal pressure of the battery cell; when the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000nm is less than 12%, it will limit the grading and compaction density of the positive electrode film layer, and cannot effectively increase the battery capacity. Therefore, controlling the particle size R1 to meet the requirement that R1 ≥ 1000 nm accounts for 12%-50% of the particle area will help further improve the reliability of the battery cell while taking into account the energy density. Dimethyl carbonate has many advantages such as low viscosity, excellent low-temperature performance, and low cost. The mass proportion of dimethyl carbonate in the electrolyte is less than 18%, which makes it difficult to form a low-viscosity system. The overall ionic conductivity of the electrolyte is difficult to improve, which increases the ohmic impedance inside the battery, leading to greater Joule heat. The antioxidant capacity of chain carbonates is weak, and the symmetrical structure of dimethyl carbonate is more easily decomposed under high voltage or high temperature conditions. The mass proportion of dimethyl carbonate is higher than 32%, and long-cycle gas production is serious, which increases the probability of packaging failure. By controlling the mass proportion of dimethyl carbonate in the electrolyte to 18%-32%, the low viscosity of the electrolyte and the risk of gas production can be balanced. The above technical means work together to achieve a balance between battery energy density and reliability.

[0008] In any embodiment, the thickness of a single side of the positive electrode film layer is denoted as H, and H is 90 μm-120 μm, and can be optionally 100 μm-120 μm.

[0009] The single-sided thickness of the positive electrode film layer within the above range is conducive to further improving the energy density. The applicant has found that when the single-sided thickness of the positive electrode film layer is greater than 100μm, the rebound phenomenon of the positive electrode sheet is more serious. The embodiments of the present application strengthen the structural strength of the shell through the double-folded structure of the first sealing area, reducing the probability of the seal being broken due to the internal stress of the film layer rebound. The battery has enhanced reliability while maintaining a high energy density.

[0010] In any embodiment, the shell includes at least one second sealing area, which is arranged at at least one end of the laminated battery core along the length direction of the shell, and the second sealing area is arranged on the tab side of the laminated battery core.

[0011] The second sealing area is set on the side of the pole ear. The pole ear needs to be connected to the lead-out piece. The connection strength between the lead-out piece and the shell material is relatively weak, which makes it easy for the gas to rush out from the second sealing area, which is conducive to achieving directional pressure relief of the battery, reducing the impact on adjacent battery cells when the seal fails, and improving the overall safety and reliability of the battery device.

[0012] In any embodiment, a plurality of rubber rings surrounding along the width direction are provided on the outer periphery of the laminated battery core, and the rubber rings surrounding along the width direction are arranged at intervals along the length direction.

[0013] The rubber rings that surround the battery cell in the width direction are arranged at intervals in the length direction, which is beneficial to increasing the binding force on the battery cell. It is especially suitable for battery cells with thick coating films. It can effectively reduce the rebound rate of the positive electrode film layer and the rebound pressure on the sealing area, thereby further reducing the probability of failure of the sealing area and improving the reliability of the battery cell.

[0014] In any embodiment, based on the total area of ​​particles in a cross section of the positive electrode film along the thickness direction of the positive electrode sheet, the area of ​​particles having a particle size R1 satisfying R1 ≥ 1000 nm accounts for 12%-37%.

[0015] When the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000 nm is within the above range, the expansion force exerted by the rebound of large particles on the soft package material and the sealing area is further reduced, thereby improving the reliability of the battery cell.

[0016] In any embodiment, in the cross section of the positive electrode film along the thickness direction of the electrode, the median of the sphericity L in the cumulative distribution curve of the sphericity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is R1A50 It is 0.6-0.8, optionally 0.65-0.75, and further optionally 0.67-0.75.

[0017] In the cumulative distribution curve of sphericity of particles with a particle size R1 of R1 ≥ 1000 nm, L R1A50 Within the above range, the particles are more approximately spherical and easy to roll. They can offset the volume changes caused by the rebound of the thick positive electrode film layer or the expansion of charge and discharge by rearranging the stacking relationship within a certain spatial range, reduce the burden on the first sealing area, and thus improve the reliability of the battery cell.

[0018] In any embodiment, in a cross section of the positive electrode film along the thickness direction of the electrode sheet, the distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is less than or equal to 5%, and may be 0.2%-2%, and further may be 0.2%-0.9%.

[0019] The distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm in the cross-section of the positive electrode film along the thickness direction of the electrode is within the above range, which can effectively reduce the stress concentration in local areas of the film layer, so that the rebound stress of the thick coating layer during the cycle process can be evenly dispersed in the entire area of ​​the film layer, reducing the rebound rate of the positive electrode film layer, thereby increasing the battery energy density while reducing the probability of failure of the packaging structure and improving battery reliability.

[0020] In any embodiment, the solvent in the electrolyte further includes one or both of ethyl methyl carbonate (EMC) and ethylene carbonate (EC).

[0021] In any embodiment, based on the total mass of the electrolyte, ethyl methyl carbonate (EMC) accounts for 39%-49% by mass.

[0022] The viscosity of ethyl methyl carbonate (EMC) is 0.65 mPa·s at 25°C, which is higher than DMC but lower than EC. At the same time, it still maintains good fluidity at low temperatures. Together with DMC, it plays a role in reducing the overall viscosity of the electrolyte, increasing the migration rate of lithium ions in the electrolyte, and reducing Joule heat. In addition, compared with DMC, EMC has higher oxidation stability and thermal stability, which further reduces the decomposition and gas production of the electrolyte and improves the reliability of the battery cell.

[0023] In any embodiment, based on the total mass of the electrolyte, the mass proportion of ethylene carbonate (EC) is 13%-22%.

[0024] Ethylene carbonate (EC) has an extremely high dielectric constant, which can effectively dissolve lithium salts, improve the ionic conductivity of the electrolyte, and ensure the smooth migration of lithium ions. EC within the above mass percentage range can decompose on the surface of the negative electrode active material and form a stable SEI film, reducing side reactions and improving cycle life.

[0025] In any embodiment, based on the total mass of the electrolyte, the total mass of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) accounts for 52%-71%.

[0026] The total mass content of EC and EMC is within the above range, and they can complement each other, overcoming the problems of high EC viscosity and poor thermal stability and mechanical strength of the SEI film formed by EMC, realizing the optimization of electrolyte performance, and further reducing the pressure of Joule heat and SEI film decomposition gas production on the sealing area from the perspective of optimizing ionic conductivity and SEI film.

[0027] In any embodiment, the electrolyte includes an electrolyte salt, the electrolyte salt includes lithium hexafluorophosphate (LiPF6), and the concentration of lithium hexafluorophosphate in the electrolyte is 0.9 mol / L to 1.2 mol / L.

[0028] Lithium hexafluorophosphate (LiPF6) is highly soluble in carbonate solvents, forming a high-concentration electrolyte that ensures high lithium ion conductivity within the electrolyte. It also induces the formation of a stable SEI film at low-potential anodes, reducing lithium deposition and improving cycle life. Excessive LiPF6 concentration significantly increases electrolyte viscosity, restricting lithium ion diffusion and reducing ionic conductivity. Furthermore, LiPF6's decomposition products, including PF5, react with trace amounts of water in the electrolyte to form HF, which corrodes the electrodes and SEI film and exacerbates solvent decomposition and gassing. A LiPF6 concentration within this range achieves an optimal balance between ionic conductivity and electrolyte stability.

[0029] In any embodiment, based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate is 18%-26%.

[0030] The mass proportion of dimethyl carbonate is within the above range. The introduction of EC and EMC with a larger proportion further reduces its gas production capacity and probability, thereby improving the long-term reliability of the battery cell.

[0031] In any embodiment, in the cumulative distribution curve of the graphitization degree C value of the positive electrode film layer obtained in the surface scanning mode of the laser microconfocal Raman spectrometer, the median value of the graphitization degree C 50 The graphitization degree C is 0.95-1.20, and the graphitization degree C value is 1 G / I D , where I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at .

[0032] Studies have shown that the stress of the film layer under the action of cyclic expansion can easily lead to an increase in internal mechanical pressure, causing the packaging structure to fail. By controlling the graphitization degree C value cumulative distribution curve of the positive electrode film layer obtained in the laser microconfocal Raman spectrometer surface scanning mode, the median graphitization degree C 50 The graphitization degree of the positive electrode film layer is 0.95-1.20, which improves the slippage of particles in the positive electrode film layer, reduces the stress concentration phenomenon during the compaction process of the thick coating film layer, and reduces the rebound degree of the positive electrode film layer due to local stress concentration during the cycle process, thereby increasing the reliability of the battery cell while improving the volume energy density of the battery cell.

[0033] In any embodiment, in the cumulative distribution curve of the coating value B obtained by the laser microconfocal Raman spectrometer surface scanning mode, the median coating value B 50is 0.30-0.60, where the coating value B is I P / I D , where I P Indicates that the Raman spectrum is at 948±100cm -1 The P peak intensity at I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at .

[0034] Median B of the coating value of the positive electrode film 50 Being within the above range indicates that the carbon material on the surface of the positive electrode active material is relatively dense and uniform, which is beneficial to improving the slip uniformity of the positive electrode film during rolling, reducing stress concentration in the positive electrode film, reducing the rebound degree of the positive electrode sheet, and improving the reliability of the battery cell.

[0035] In any embodiment, the lithium-containing transition metal phosphate particles include iron element, and the iron dissolution rate of the positive electrode film layer is 658 ppm-1921 ppm, and can be optionally 658 ppm-1485 ppm.

[0036] The iron dissolved in the positive electrode film mainly comes from the lithium-containing transition metal phosphate in the positive electrode active material. The iron dissolution rate depends on the number of lattice defects in the lithium-containing transition metal phosphate and the integrity and density of the carbon material on the surface of the positive electrode active material. The lower the iron dissolution rate, the fewer lattice defects in the lithium-containing transition metal phosphate, which helps reduce lattice corrosion in a weak acid environment. The more complete and dense the carbon material on the surface of the positive electrode active material, the more it inhibits the dissolution of iron ions in a weak acid environment. The positive electrode film with an iron dissolution rate within the above range has relatively few lattice defects, and the surface of the positive electrode active material has a complete and dense carbon material, which helps to improve the compressive resistance and slippage of the particles in the positive electrode film under large rolling pressure, increase the compaction density of the positive electrode film and reduce stress concentration in the positive electrode film, improve the energy density of the battery and improve the reliability of the battery.

[0037] In any embodiment, 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 total area of ​​the agglomerated region of the conductive agent accounts for 0.5%-2.5%, and can be optionally 0.5%-1.7%.

[0038] Based on the total area of ​​the cross-section of the positive electrode film along the thickness direction of the electrode, the total area of ​​the agglomerated region of the conductive agent accounts for 0.5%-2.5%, indicating that the conductive agent is evenly dispersed in the positive electrode film layer and is easy to form a uniform conductive network. This is particularly beneficial for reducing the problem of kinetic degradation caused by the increase in the ion transmission path of the thick coating film layer, and reducing the local polarization and even lithium precipitation problems caused by the battery during the cycle. At the same time, studies have shown that large-sized particles in lithium-containing transition metal phosphate particles are prone to rebound. The agglomerated area of ​​the conductive agent within the above range can suppress the rebound of the lithium-containing transition metal phosphate with the help of the uniform distribution of the conductive agent, form mechanical constraints on the particles and even the film layer, improve the cohesion of the film layer, reduce the probability of failure in the sealing area, and improve the reliability of the battery.

[0039] In any embodiment, the conductive agent comprises carbon nanotubes, and the carbon nanotubes comprise one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0040] The high aspect ratio of carbon nanotubes facilitates the overlapping of multiple positive electrode particles in the thickness direction, forming long-range conductive pathways while increasing the binding force between the particles. This not only improves the dynamic performance of thick-coated positive electrode films, reduces local polarization and even lithium plating during battery cycling, and increases the cycle life of the battery. Furthermore, by forming a network structure within the positive electrode film, it acts as a bridge for stress propagation, effectively alleviating stress concentration, reducing electrode rebound, and improving the reliability of the battery cells. Furthermore, carbon nanotubes have a high specific surface area and hollow structure, resulting in excellent electrolyte retention. Thick electrodes experience significant expansion forces during cycling, making electrolytes easily squeezed out. The presence of carbon nanotubes within the positive electrode film helps improve the electrolyte retention of thick electrodes, mitigates the phenomenon of capacity drops during cycling, and improves the cycle life of battery cells.

[0041] In any embodiment, the conductive agent further comprises conductive carbon black.

[0042] Conductive carbon black has a high specific surface area, which in turn provides excellent electrolyte retention. Thick electrodes experience significant expansion during cycling, making it easier for the electrolyte to be squeezed out. The distribution of conductive carbon black within the positive electrode film helps improve the electrolyte retention of thick electrodes, mitigate the phenomenon of capacity drop during cycling, and improve the battery's cycle life.

[0043] In any embodiment, the agglomerated regions of the conductive agent include carbon nanotubes and conductive carbon black.

[0044] 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 and carbon nanotubes is relatively close, 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 agglomeration region of the conductive agent will also cause local blockage of the 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.

[0045] In any embodiment, 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%.

[0046] When the mass contents of carbon nanotubes and conductive carbon black in the positive electrode film layer 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 and improving the reliability of the battery cell; and improving the liquid retention rate of the positive electrode plate during long-term cycling, reducing the degree of polarization, and improving the problem of capacity diving of the battery cell.

[0047] In any embodiment, the positive electrode film layer further includes a dispersant, and the dispersant includes hydrogenated nitrile rubber HNBR.

[0048] HNBR is derived from nitrile rubber by hydrogenating its double bonds to saturate them. Its highly saturated backbone structure imparts excellent oil resistance, heat resistance, and aging resistance. This makes it stable in diverse environments and systems when used as a dispersant, resisting degradation or deterioration, thus effectively exerting its dispersing properties. The HNBR molecular chain contains both polar nitrile groups and non-polar hydrocarbon segments. The polar nitrile groups interact with hydroxyl (-OH) groups or metal oxide sites on the surface of lithium-containing transition metal phosphate particles (e.g., hydrogen bonding and dipole interactions), enhancing particle compatibility with solvents and reducing interfacial tension, especially for large particles. This facilitates more uniform particle dispersion, reduces aggregation caused by hydrophobicity, improves the dispersion of large particles in the cathode film, and reduces stress concentration caused by rebound. The non-polar hydrocarbon segments, with their excellent lipophilicity, allow for excellent stretching and dispersion in non-polar or weakly polar media, ensuring uniform particle dispersion. When HNBR is adsorbed onto the surface of particles in the slurry, its long-chain molecules form a physical barrier around the particles, preventing them from approaching and aggregating, allowing them to remain relatively independently dispersed within the system. At the same time, HNBR can reduce the surface tension between the dispersion medium and the dispersed particles, making the particles more easily wetted by the medium, thereby promoting their dispersion within the medium. It can also reduce the interfacial energy between particles, particularly reducing the aggregation of conductive agents driven by interfacial energy, thereby improving the cycle life of battery cells.

[0049] In any embodiment, based on the mass of the positive electrode film layer, the mass content of the dispersant is 0.5%-2%.

[0050] The mass content of the dispersant is within the above range, which can achieve uniform dispersion of particles in the positive electrode film layer while maintaining a high load of the positive electrode film layer, slow down the rebound caused by stress concentration of the thickly coated lithium transition metal phosphate positive electrode film layer, reduce the rebound rate of the positive electrode film layer, and improve the reliability of the battery cell.

[0051] In any embodiment, the porosity of the positive electrode film layer is 14%-28%.

[0052] A positive electrode film porosity within this range not only improves electrolyte retention, enhances ion diffusion in thick-coated electrodes and the positive electrode film, and improves battery dynamics, but also mitigates rebound or volume increase during charge and discharge, reduces the impact of expansion stress on the seal area, and maintains high battery reliability.

[0053] In any embodiment, the battery cell also includes a diaphragm arranged between the positive electrode plate and the negative electrode plate, the diaphragm includes a base film and a ceramic layer arranged on both sides of the base film and an adhesive layer arranged on at least one side of the ceramic layer away from the base film, the adhesive layer is a continuous layer of a porous structure, and the adhesive layer includes a vinylidene fluoride polymer.

[0054] The diaphragm provided in the embodiment of the present application uses a continuous layer of a porous structure as a bonding layer, which has a larger bonding area than the bonding layer in the prior art, so that the bonding between the diaphragm and the positive electrode film layer is more firm and uniform; particles with a particle size R1 satisfying R1 ≥ 1000 nm are prone to stress concentration during the cycle, resulting in rebound problems. The diaphragm provided in the embodiment of the present application uses a continuous layer of a porous structure as a bonding layer, which is particularly suitable for thick-coated laminated cells, improving the rebound phenomenon of thick-coated laminated cells during long cycles, reducing the expansion stress inside the battery, and improving the reliability of the sealing area and the battery cell as a whole. In addition, the thick-coated battery cell is prone to relative displacement between the electrode sheet and the diaphragm in the process of dragging the outer electrode sheet and welding the electrode ear, which makes the film layer prone to powder loss, and even the positive and negative electrodes overlap with each other, resulting in the risk of internal short circuit. The continuous layer of the porous structure in the embodiment of the present application is used as a bonding layer to also reduce the above risks.

[0055] In any embodiment, the positive electrode film layer is provided with a primer layer in the bottom region near the positive electrode current collector, and the primer layer satisfies at least one of the following conditions: (1) the primer layer comprises a conductive agent and a binder, the conductive agent comprises carbon nanotubes and conductive carbon black, and the binder comprises a vinylidene fluoride polymer; (2) the thickness of the primer layer is 0.5 μm-5 μm.

[0056] The undercoat provided in the embodiments of the present application helps improve the adhesion between the positive electrode film and the positive electrode current collector and alleviates stress concentration at large particles, thereby reducing the rebound of the positive electrode film and improving the reliability of the battery cell. Furthermore, compared to direct contact between the positive electrode current collector and the positive electrode film, the undercoat increases the contact area between the positive electrode film and the positive electrode film, helping to increase the area for electron transfer between the current collector and the positive electrode film, thereby reducing the internal resistance of the electrode sheet and improving the dynamic performance of the battery.

[0057] In any embodiment, the lithium transition metal phosphate particles in the positive electrode film layer include components represented by the following general formula: Li m Fe x P y O j Q qFormula 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, and Br, 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0058] Selecting an appropriate modifying element Q can improve the lattice change rate of the positive electrode active material during the lithium insertion and extraction process, reduce the oxygen activity on the particle surface, and improve the structural stability of the material, thereby increasing the material's gram capacity during the cycle and improving the cycle stability of the battery cell.

[0059] In any embodiment, 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 titanium element is 500ppm-8000ppm, and can be optionally 1000ppm-3000ppm.

[0060] The introduction of titanium into lithium-containing transition metal phosphate particles requires the addition of a titanium source during the preparation of the positive electrode active material. Titanium sources are often inert materials, and adhering to the surface of lithium-containing transition metal phosphate raw materials can reduce the reaction activity and reduce the growth of particle size. Increasing 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 of the positive electrode film layer, and cause the film layer of the positive electrode film layer to fall off. In the embodiment of the present application, by adding a high content of titanium into the lithium-containing transition metal phosphate particles, the reaction activity of the raw materials for synthesizing the positive electrode active material is reduced, so that the positive electrode active material can achieve control of the proportion of large particles while having a high degree of graphitization, reduce the rebound rate of the positive electrode film layer, and improve the energy density of the battery while taking into account the reliability of the battery. At the same time, the doping of titanium in the positive electrode active material is conducive to causing lattice distortion, reducing 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, often accompanied by a significant lithium ion concentration gradient. The embodiment of the present application improves the solid-phase transmission rate of the positive electrode active material by adding a high content of titanium to the lithium-containing transition metal phosphate particles, thereby improving the kinetic problems of thick electrode batteries.

[0061] In any embodiment, the lithium-containing transition metal phosphate particles include vanadium. Based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of vanadium is 500ppm-5000ppm, and can be optionally 500ppm-3000ppm.

[0062] The vanadium element in the positive electrode film can be in a variety of valence states, among which the +5 valence vanadium (V 5+) can be doped in the phosphorus element site, because its large radius can cause lattice distortion, expand the diffusion channel of lithium ions, thereby improving the ionic conductivity of the positive electrode active material and improving the kinetic performance of the battery; + trivalent vanadium (V 3+ ) can be doped at the transition metal sites to generate lithium vacancies through charge compensation, thereby improving the electronic conductivity of the positive electrode active material. In addition, the distribution uniformity of vanadium elements in the lithium-containing transition metal phosphate particles is improved, which helps to further improve the kinetic performance of the positive electrode film layer and the uniformity of the positive electrode film layer reaction, thereby improving the kinetic performance and cycle performance of the battery cell. The mass content of vanadium elements within the above range helps to improve the kinetic performance of the positive electrode sheet and improve the kinetic performance of thick-coated lithium-containing transition metal phosphate batteries. At the same time, the synergistic effect of titanium elements, vanadium elements 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 thick-coated lithium-containing transition metal phosphate batteries.

[0063] In any embodiment, the soft package material includes an aluminum-plastic composite film, optionally, 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.

[0064] In any embodiment, at least one of the laminated battery cells is accommodated in the shell, the size of the shell in the length direction is L0, the size of the shell in the width direction is W0, and the size of the shell in the thickness direction is H0, wherein 450mm≤L0≤1300mm, 100mm≤W0≤150mm; 14mm≤H0≤22mm.

[0065] In any embodiment, a length L0 of the housing satisfies: 450 mm ≤ L0 ≤ 650 mm.

[0066] When the length dimension L0 of the shell satisfies the following conditions: 450mm≤L0≤650mm, the length of the battery cell is shorter, which helps to shorten the diffusion path of the current and reduce the internal resistance of the electrode, thereby reducing the heat generation of the battery and improving its dynamic performance; in addition, the shorter shell 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 insertion and extraction during the cycle, alleviate stress concentration, reduce the rebound amplitude of the membrane layer, and improve the reliability of the battery cell.

[0067] In any embodiment, a length L0 of the housing satisfies: 900 mm ≤ L0 ≤ 1300 mm.

[0068] When the length dimension L0 of the housing satisfies the following conditions: 900mm≤L0≤1300mm, the battery cell is longer, which helps reduce the volume share of the housing within the battery cell and increase the active material load share. Furthermore, longer battery cells can reduce the number of batteries required within the battery module, simplify the structural design of the battery module, and reduce the number and complexity of structural components within the module, thereby improving the space utilization of the battery pack and, in turn, helping to increase the volumetric energy density of the battery cell.

[0069] In any embodiment, at 25° C., the capacity of the battery cell is 105Ah-300Ah, optionally 150Ah-190Ah.

[0070] A second aspect of the present application provides a battery device comprising the battery cell of the first aspect of the present application.

[0071] A third aspect of the present application provides an electrical device, comprising the battery device of the second aspect of the present application, wherein the battery device is used to provide electrical energy.

[0072] A fourth aspect of the present application provides an energy storage device, comprising the battery device of the second aspect of the present application, wherein the battery device is used to store electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 is a front view of a battery cell according to an embodiment of the present application;

[0074] Figure 2 is a schematic diagram of a diaphragm according to one embodiment of the present application;

[0075] Figure 3 is a schematic diagram of a diaphragm of the prior art;

[0076] Figure 4 It is a schematic diagram of an electrical device according to one embodiment of the present application.

[0077] 5 Battery cell; 50 Housing; 51 First sealing area; 52 Second sealing area; 53 Lead-out member; 20 Diaphragm; 201 Base film; 202 Ceramic layer; 203 Adhesive layer; X length direction; Y width direction; Z thickness direction. DETAILED DESCRIPTION

[0078] Below, the embodiments of the battery cells, battery devices, electrical devices, and energy storage devices of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following 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.

[0079] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0080] Unless otherwise specified, 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.

[0081] 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 deemed to be included in the disclosure of this application.

[0082] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0083] In this application, the terms "plurality" and "multiple" refer to two or more.

[0084] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0085] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0086] In embodiments of the present application, a battery device may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple soft-pack battery cells connected in series, parallel, or parallel via a busbar assembly. For example, a battery cell assembly is typically formed by arranging multiple soft-pack battery cells; a battery cell assembly may be a battery module, which is formed by arranging and securing multiple soft-pack battery cells to form a single module. For example, a battery module may be formed by bundling multiple battery cells using cable ties.

[0087] The battery device may be a battery pack, which includes a housing and one or more battery cell assemblies housed within the housing. The battery cell assemblies may be battery modules, which may be housed within the housing by securing the battery modules within the housing. Alternatively, the battery cell assemblies may be housed within the housing by directly securing multiple soft-pack battery cells to the housing.

[0088] In an embodiment of the present application, the housing may include a first housing and a second housing. The first housing and the second housing are fastened together to form an enclosed space within the housing to accommodate the battery cell assembly. Enclosed here means covered or closed, and may be sealed or unsealed. The first housing may be a top cover or a bottom plate. For example, the housing may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame to form an enclosed space within the housing to accommodate the battery cell assembly.

[0089] In the embodiment of the present application, the box body can be used as part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0090] In the embodiment of the present application, the battery cell may be a secondary battery, which refers to a battery cell that can be recharged to activate the active material after discharge and continue to be used; the battery cell may be a lithium-ion battery. The battery cell may be flat.

[0091] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0092] A battery cell is the smallest unit that makes up a battery and is capable of independently performing charge and discharge functions. When there are multiple battery cells, they are connected in series, in parallel, or in mixed circuits via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeams or longitudinal beams.

[0093] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0094] In some embodiments, battery cells can be assembled into battery modules, which can contain multiple battery cells, the specific number of which can be adjusted based on the application and capacity of the battery module. In some embodiments, the battery modules can also be assembled into battery packs, the number of battery modules in which can be adjusted based on the application and capacity of the battery pack.

[0095] A battery cell includes an electrode assembly and an electrolyte.

[0096] The electrode assembly usually includes a positive electrode sheet and a negative electrode sheet. The negative electrode sheet is the electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging. The positive electrode sheet is the electrode that releases or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0097] Although lithium-containing transition metal phosphates have significant advantages in cycle stability as positive electrode active materials, their intrinsic gram capacity is significantly lower than that of ternary materials. The applicant found that the use of 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 phosphates, and the use of a soft-pack shell is lighter, further improving the theoretical mass energy density of the battery cell. However, this process improvement also brings new technical challenges: on the one hand, thick pole pieces have higher expansion stress during long-term cycling; on the other hand, the heat generated by thick pole pieces during operation is difficult to dissipate effectively, and local high temperatures cause the electrolyte to decompose, generate gas, and increase the internal pressure of the battery. Due to the limited mechanical strength of the soft-pack packaging, internal expansion and pressure increase may cause the battery cell to swell, and even cause the package to rupture and fail.

[0098] The first aspect of the present application provides a battery cell, such as Figure 1 As shown, it includes a laminated battery cell and a shell 50, the laminated battery cell is accommodated in the shell 50, and the shell 50 is a soft package material; the shell 50 includes a first sealing area 51, and the first sealing area 51 is provided at least one end of the laminated battery cell extending in the width direction (Y direction); the first sealing area includes a double folding structure extending in the length direction (X direction), and the double folding structure is provided with a packaging glue, and the packaging glue is continuously provided along the length direction (X direction) and fixes the double folding structure; the laminated battery cell includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the positive electrode sheet The invention comprises a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises lithium-containing transition metal phosphate particles, and at least a portion of the surface of the lithium-containing transition metal phosphate particles is provided with a carbon material; based on the total area of ​​the particles in the cross section of the positive electrode film layer along the thickness direction of the positive electrode sheet, the area of ​​the particles whose particle size R1 satisfies R1 ≥ 1000 nm accounts for 12%-50%; the thickness of a single side of the positive electrode film layer is recorded as H, and H is 70μm-120μm; when the battery cell is in a fully discharged state, the compaction density of the positive electrode sheet is 2.3g / cm 3 -2.6g / cm 3 The electrolyte includes a solvent, and the solvent includes dimethyl carbonate (DMC); based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate is 18%-32%.

[0099] The gram capacity of lithium-containing transition metal phosphates is relatively low. Studies have shown that when the thickness H of the positive electrode film layer on one side is less than 70μm, the battery capacity is difficult to meet market demand. In the embodiment of the present application, by controlling the thickness H of the positive electrode film layer on one side within the range of 70μm-120μm, it is beneficial to increase the space utilization of the active material, and further adopt a soft-package material shell, thereby reducing the weight of the battery cell and improving the mass energy density of the battery. However, the thicker positive electrode film layer undergoes significant volume changes due to lithium insertion and removal during the charge and discharge cycle, resulting in mechanical stress accumulation, which in turn causes the expansion and contraction of the electrode material, the pole piece rebounds, the thickness increases, and the mechanical stress on the packaging structure increases. At the same time, the thicker film layer means that the internal heat is more difficult to conduct, which is prone to local overheating, exacerbating the side reactions and gas production of the electrolyte, and further increasing the internal pressure of the battery cell. Compared with the winding type, the laminated cell structure reduces the corner gap and improves the volume energy density, but the laminated cell lacks the restraining effect brought by the winding structure, and has little restriction on the rebound of the thick coated film layer, which deteriorates the reliability of the battery cell. Compared to hard-shell materials, soft-pack materials have lower mechanical strength and are less able to withstand internal pressure. They also have lower thermal conductivity, making heat buildup more likely inside the battery cells, further exacerbating gassing issues. Over extended use, excessive internal pressure could cause the seal to break.

[0100] In the embodiment of the present application, the first sealing area includes a double folding structure extending along the long side direction to further improve the sealing strength of the first sealing area. The double folding forms a multiple sealing barrier by folding the soft package material of the shell twice. Even if the first layer of folding structure is due to the rebound stress from the high thickness of the positive electrode film layer in the battery cell and the electrolyte gas production defects, the second layer of folding structure can still maintain the seal. At the same time, due to battery processing, the soft package material is hot-melt bonded, and the double folding can make the heat-sealed area more uniform, improving the poor sealing situation in local areas. The sealing is the weak link in the mechanical strength of the soft package battery cell, in order to further enhance the reliability of the package. The inventor sets a packaging glue on the double folding structure. The packaging glue is continuously set along the long side direction and fixes the double folding structure, which can cover the micro cracks or defects in the heat-sealed area in the sealing area of ​​the soft package material; and the double folding structure will have a certain elastic memory after heat sealing, and may rebound after long-term use. The packaging glue can fix the double folding structure and maintain the stability of the structure. In the embodiment of the present application, the compaction density of the positive electrode sheet is further controlled to be 2.3g / cm3 by controlling the battery cell in the fully discharged state. 3 -2.6g / cm 3On the one hand, it makes the battery cell have a higher capacity, and on the other hand, it makes a certain buffer space between the particle stacking structure, reducing the stress exerted on the packaging structure by the rebound of the pole piece. In order to further reduce the stress inside the battery cell, the inventors regulated the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000nm in the positive electrode film layer and the mass ratio of dimethyl carbonate in the electrolyte. The inventors found that under the same expansion rate, the expansion of small particles is more easily absorbed through the tiny pore structure between the particles than that of large particles. The absolute value of the expansion change of large particles is large and more difficult to be eliminated. When the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000nm is greater than 50%, it is easy to cause stress concentration, obvious rebound, and increase the internal pressure of the battery cell; when the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000nm is less than 12%, it will limit the grading and compaction density of the positive electrode film layer, and cannot effectively increase the battery capacity. Therefore, controlling the particle size R1 to meet the requirement that R1 ≥ 1000 nm accounts for 12%-50% of the particle area will help further improve the reliability of the battery cell while taking into account the energy density. Dimethyl carbonate has many advantages such as low viscosity, excellent low-temperature performance, and low cost. The mass proportion of dimethyl carbonate in the electrolyte is less than 18%, which makes it difficult to form a low-viscosity system. The overall ionic conductivity of the electrolyte is difficult to improve, which increases the ohmic impedance inside the battery, leading to greater Joule heat. The antioxidant capacity of chain carbonates is weak, and the symmetrical structure of dimethyl carbonate is more easily decomposed under high voltage or high temperature conditions. The mass proportion of dimethyl carbonate is higher than 32%, and long-cycle gas production is serious, which increases the probability of packaging failure. By controlling the mass proportion of dimethyl carbonate in the electrolyte to 18%-32%, the low viscosity of the electrolyte and the risk of gas production can be balanced. The above technical means work together to achieve a balance between battery energy density and reliability.

[0101] In this application, the term "double fold" refers to a reinforcing structure formed by folding the seal area in half. By initially folding the seal area and then bending it again in the direction or opposite direction of the initial fold, the seal area becomes stronger than a single fold, capable of withstanding greater internal pressure without breaking or failing. Further folding the seal area exponentially increases the process difficulty and cost without significantly improving the seal area's strength.

[0102] Lithium-containing transition metal phosphate refers to a phosphate material containing lithium and a transition metal element, and can be detected by any method known in the art, for example, by combining an X-ray diffractometer (XRD) with an energy dispersive spectrometer.

[0103] In this application, the term "particle" refers to particles with identifiable complete boundaries in the field of view of the positive electrode film layer under a certain magnification, such as 10,000 times. Defects and scratches may exist inside the particles, but complete boundaries sufficient to separate the particles cannot be identified inside the particles.

[0104] The specific method for identifying particles is as follows: the positive electrode film layer is cut along the thickness direction of the electrode by an argon ion beam (as an example, the following equipment model can be selected: Leica EMTIC3XCP, working voltage: 6kV, working time: 6h), and after the cross section is exposed, a scanning electron microscope is used (as an example, the following equipment model can be selected: Hitachi SU8230, working voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) to observe the cross section of the positive electrode film layer along the thickness direction of the electrode. The field emission scanning electron microscope is used to collect images in the secondary electron mode at the non-edge position of the cross section of the positive electrode film layer (after observing the edge of the electrode under the scanning electron microscope, adjust the field of view to the center of the sample), and the electron microscope image is taken at a magnification of 10k times. The particles in the electron microscope image are analyzed using ImageJ software (1.46r, win64 version). The specific instructions for using ImageJ software are as follows: load the SEM image to be analyzed; use the Cellpose plug-in to identify particles and perform manual correction based on this; and use ImageJ to read and analyze the data. The specific method for identifying particles using the Cellpose plug-in is as follows: set the segmentation diameter parameter (diameter in the Segmentation module) to 15 pixels, click "runcyto3" to perform particle identification, and manually mark any particles in the image that were not identified, were not fully identified, or were incorrectly identified. Particles that were not identified, were not fully identified, or were incorrectly identified by the software primarily include the following: 1. Particles that are too large or have scratches on the particle surface, resulting in incomplete or incomplete identification; 2. Scratches on the particle surface caused by the argon ion beam cutting process may cause the software to misinterpret these scratches as particle boundaries, leading to identification errors; 3. Particles that were not successfully identified due to being too small; 4. Particles located at the edge of the electron microscope field of view, with the particle interior penetrated by the edge, preventing the complete morphology from being displayed, and partial recognition instead of the entire particle, resulting in identification errors.Manual calibration is performed on the unidentified or misidentified particles. The specific process is as follows: particles located around the edges of the scanning electron microscope and not fully displayed are deleted; other unidentified or misidentified particles are determined to have internal cracks and scratches. If no cracks and scratches are present, the particle is determined to be a single particle and manually labeled based on the manually observed particle boundary; if a crack and scratch are present, it is determined whether the crack and scratch penetrate the particle. If not, the particle is determined to be a single particle and manually labeled; if a crack and scratch penetrate the particle, it is determined whether the crack and scratch are linear or irregular; if the crack and scratch are irregular, it is determined to be the boundary between particles and the particles are divided along this boundary; if the crack and scratch are linear, contrast comparison is performed; if the contrast and scratch are not obvious and there is no crack, it is determined to be a scratch and labeled as a single particle; if the contrast and scratch are strong and there is a crack, it is determined to be the boundary between particles and labeled as two particles. After manual labeling, information irrelevant to the particles during the automatic image processing is deleted, thus completing the determination and labeling of the particles in the image.

[0105] It is understood that the particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, especially those larger than 50 nm, are primarily derived from the positive electrode active material. Therefore, the present embodiment can accurately and objectively reflect the distribution of lithium-containing transition metal phosphate particles in the positive electrode film layer by observing and counting the particle area in the cross-section of the positive electrode sheet along the thickness direction of the electrode sheet.

[0106] In the prior art, a laser particle size analyzer is usually used to count the particle size of the positive electrode active material through the Malvern laser diffraction method. However, the applicant's research shows that since lithium-containing transition metal phosphate particles are easy to agglomerate, the test results obtained by the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of its particle agglomerates, which 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 positive electrode active material in the film layer will be more dispersed during the process of slurrying and film rolling. The test results obtained by the Malvern laser diffraction method are affected by the particle size, specific surface area, and degree of agglomeration of the positive electrode active material. Compared with the actual dispersion in the electrode, the number of large particles obtained by the 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 test cannot be equivalent to or analogous to the particle size obtained by statistics in the embodiments of the present application.

[0107] The specific method for testing the area percentage of particles with a particle size R1 of ≥ 1000 nm in a cross-section of the positive electrode film along the thickness of the electrode is as follows: Identify the particles in the positive electrode film using the method described above in this application. Import the images of the identified and labeled particles into ImageJ software for analysis. Scale settings are performed based on the SEM images. Statistical analysis is performed using the "Feret Diameter," "Area," "Roundness," and "Solidity" analysis functions to determine the particle size, area, sphericity, and roughness of the particles in the cross-section of the positive electrode film along the thickness of the electrode. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, which characterizes the particle size; the "Area" parameter represents the pixel area of ​​the particle. To achieve statistically significant sample size, at least 10 SEM images are collected for each film layer, and the particle sizes of at least 1000 particles are statistically analyzed. Since particles with a particle size of less than 50 nm have large errors in the statistical process and are difficult to identify accurately, and the particle size of the conductive agent is generally less than 50 nm, which will cause large errors in the statistical results, particles with a particle size of less than 50 nm are not counted in the particle size statistical process of this application, and the particle statistical data corresponding to AR, Round or Solidity displayed as "NaN" are deleted. Calculate the sum of the "Area" parameters of 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 ​​particles with a particle size R1 satisfying R1 ≥ 1000 nm and the total area of ​​the particles counted. The sum of the areas of particles with a particle size R1 satisfying R1 ≥ 1000 nm is divided by the total area of ​​the particles counted as the area ratio of 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.

[0108] 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 positive electrode sheet, the area proportion of particles whose particle size R1 satisfies R1 ≥ 1000 nm can be selected as 12%, 12.11%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 34.89%, 34.97%, 35%, 36%, 36.71%, 36.75%, 36.83%, 36.92%, 36.95%, 37%, 38%, 38.09%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 49.99%, 50% or a numerical range between any two of the above.

[0109] In some embodiments, the single-sided thickness of the positive electrode film layer is recorded as H, and H can be selected from 70μm, 70.45μm, 75μm, 80μm, 85μm, 90μm, 91.88μm, 95μm, 96.75μm, 100μm, 105μm, 106.02μm, 106.09μm, 106.10μm, 106.34μm, 106.66μm, 106.79μm, 110μm, 115μm, 119.49μm, 120μm or a numerical range between any two of the above.

[0110] In some embodiments, when the battery cell is in a fully charged state, the compaction density of the positive electrode sheet can be 2.3 g / cm 3 , 2.31g / cm 3 , 2.32g / cm 3 , 2.33g / cm 3 , 2.34g / cm 3 , 2.35g / cm 3 , 2.36g / cm 3 , 2.37g / cm 3 , 2.38g / cm 3 , 2.39g / cm 3 , 2.4g / cm 3 , 2.41g / cm 3 , 2.42g / cm 3 , 2.43g / cm 3 , 2.44g / cm 3 , 2.45g / cm 3 , 2.46g / cm 3 , 2.47g / cm 3 , 2.48g / cm 3 , 2.49g / cm 3 , 2.5g / cm 3 , 2.51g / cm 3 , 2.52g / cm 3 , 2.53g / cm 3 , 2.54g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.59g / cm 3 , 2.6g / cm 3 Or a numerical range between any two of the above.

[0111] In this application, the fully discharged state refers to the state after the battery is placed in a 25°C oven environment, left to stand for 2 hours, and the battery temperature is maintained at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.5V, and then discharged at a constant current of 0.1C to 2.0V.

[0112] In this application, the compaction density of the positive electrode sheet can be tested using methods known in the art. As an example, place the battery in a 25°C oven environment and let it stand for 2 hours. When the battery temperature is maintained at 25°C, discharge the battery at a constant current of 1 / 3C to 2.5V and then at a constant current of 0.1C to 2.0V. Disassemble the battery to obtain the positive electrode sheet, treat the residual electrolyte with dimethyl carbonate solvent, dry the sheet, cut it into small discs with an area of ​​S, and obtain its mass as W1. Use a micrometer to measure the thickness T1 of the positive electrode sheet, then wipe off the positive electrode film layer of the weighed sheet, weigh the mass of the current collector, record it as W2, and use a micrometer to measure the thickness T2 of the current collector. The compaction density of the positive electrode sheet PD = (W1-W2) / [(T1-T2)×S].

[0113] In some embodiments, based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate can be selected as 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32% or a numerical range between any two of the above.

[0114] In some embodiments, the encapsulating adhesive includes a long strip of blue adhesive. The long strip of blue adhesive has high viscosity, which makes the shell sealing area more firmly bonded, further enhances the strength of the first sealing area, and improves the reliability of the battery cell.

[0115] Dimethyl carbonate has good solubility in lithium hexafluorophosphate. As an electrolyte component, it can provide sufficient lithium ion concentration to meet the necessary ion conduction conditions. Furthermore, dimethyl carbonate has a low viscosity, which helps increase the electrolyte's ionic conductivity and improve the rate capability and low-temperature performance of the battery cells.

[0116] In any embodiment, the thickness of a single side of the positive electrode film layer is denoted as H, and H is 90 μm-120 μm, and can be optionally 100 μm-120 μm.

[0117] The single-sided thickness of the positive electrode film layer within the above range is conducive to further improving the energy density. The applicant has found that when the single-sided thickness of the positive electrode film layer is greater than 100μm, the rebound phenomenon of the positive electrode sheet is more serious. The embodiments of the present application strengthen the structural strength of the shell through the double-folded structure of the first sealing area, reducing the probability of the seal being broken due to the internal stress of the film layer rebound. The battery has enhanced reliability while maintaining a high energy density.

[0118] In some embodiments, as Figure 1 As shown, the shell 50 includes at least one second sealing area 52, which is arranged at at least one end of the laminated core along the length direction of the shell, and the second sealing area 52 is arranged on the tab side of the laminated core.

[0119] It is understandable that the positive electrode tab and the negative electrode tab can be arranged on the same side of the laminated battery core, or on different sides of the laminated battery core.

[0120] In some embodiments, the battery cell 5 further includes a lead-out member 53, which is connected to the tab of the battery cell. For example, the lead-out member 53 can be welded to the tab. The lead-out member 53 is a conductive member, at least a portion of which is located outside the housing 50. The lead-out member 53 serves as an electrode lead-out terminal of the battery cell 5 and is used to facilitate electrical connection between the battery cell 5 and other battery cells 5 or other components. For example, the lead-out member 53 can be in the form of a sheet.

[0121] Correspondingly, the lead-out member 53 also includes a positive electrode lead-out member and a negative electrode lead-out member. The positive electrode lead-out member is connected to the positive electrode tab, and the negative electrode lead-out member is connected to the negative electrode tab.

[0122] In some embodiments, the second sealing area is arranged on the side of the pole ear, and the pole ear needs to be connected to the lead-out piece. The connection strength between the lead-out piece and the shell material is relatively weak, which makes it easy for the gas to rush out from the second sealing area, which is conducive to achieving directional pressure relief of the battery, reducing the impact on adjacent battery cells when the seal fails, and improving the overall safety and reliability of the battery device.

[0123] In some embodiments, a plurality of rubber rings surrounding the laminated battery core along the width direction are provided on the outer periphery of the laminated battery core, and the rubber rings surrounding the width direction are arranged at intervals along the length direction.

[0124] The rubber rings that surround the battery cell in the width direction are arranged at intervals in the length direction, which is beneficial to increasing the binding force on the battery cell. It is especially suitable for battery cells with thick coating films. It can effectively reduce the rebound rate of the positive electrode film layer and the rebound pressure on the sealing area, thereby further reducing the probability of failure of the sealing area and improving the reliability of the battery cell.

[0125] In some embodiments, based on the total area of ​​particles in a cross section of the positive electrode film along the thickness direction of the positive electrode sheet, the area of ​​particles with a particle size R1 satisfying R1 ≥ 1000 nm accounts for 12%-37%.

[0126] When the area ratio of particles with a particle size R1 satisfying R1 ≥ 1000 nm is within the above range, the expansion force exerted by the rebound of large particles on the soft package material and the sealing area is further reduced, thereby improving the reliability of the battery cell.

[0127] In some embodiments, in the cross section of the positive electrode film along the thickness direction of the electrode, in the cumulative distribution curve of the sphericity of particles with a particle size R1 satisfying R1 ≥ 1000 nm, the median of the sphericity L R1A50 It is 0.6-0.8, optionally 0.65-0.75, and further optionally 0.67-0.75.

[0128] The specific method for testing the sphericity of particles with a particle size R1 of ≥ 1000 nm in a cross-section of the positive electrode film along the thickness of the electrode sheet is as follows: Identify the particles in the positive electrode film according to the method described above in this application. Import the image of the identified and identified particles into ImageJ software for analysis. Set the scale based on the scanning electron micrograph. Statistically analyze the particle size and sphericity of the particles in the cross-section of the positive electrode film along the thickness of the electrode sheet using the "Feret Diameter" and "Round" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter obtained from the analysis represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, which characterizes the particle size. According to the software manual (ImageJ User Guide IJ 1.46r), the "Round" parameter obtained from the analysis represents the ratio of the pixel area of ​​the particle to the area of ​​a circle with the fitted major diameter as the diameter, which can be used to characterize the particle's sphericity. The closer the particle is to a spherical shape, the closer the ratio of the pixel area to the area of ​​a circle with the fitted major diameter as the diameter is to 1. Therefore, the "Round" parameter of the particles obtained by analysis is used to characterize the sphericity of the particles. In order to meet the statistically significant sample number, no less than 10 scanning electron microscope images are collected for each film layer, and the particle sizes of no less than 1000 particles are counted. The sphericity of the particles with a particle size R1 satisfying R1 ≥ 1000nm is arranged in order from small to large, and the sphericity cumulative distribution curve of the positive electrode film particles is obtained with sphericity as the horizontal axis and cumulative area percentage as the vertical axis. R1A50 In the cumulative distribution curve of the sphericity L value of particles with a particle size R1 satisfying R1 ≥ 1000 nm, the sphericity L value corresponding to the cumulative area of ​​the vertical axis accounts for 50%.

[0129] In some embodiments, in the cross section of the positive electrode film along the thickness direction of the electrode, in the cumulative distribution curve of the sphericity of particles with a particle size R1 satisfying R1 ≥ 1000 nm, the median of the sphericity L R1A50 The optional value is 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.673, 0.68, 0.687, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.745, 0.75, 0.76, 0.77, 0.78, 0.79, 0.8 or a numerical range between any two of the above.

[0130] Those skilled in the art can adjust the sphericity of the particles by any known process. For example, the sphericity of the particles can be adjusted by grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, adding surfactants, and adjusting the parameters of each process.

[0131] In the cumulative distribution curve of sphericity of particles with a particle size R1 of R1 ≥ 1000 nm, L R1A50 Within the above range, the particles are more approximately spherical and easy to roll. They can offset the volume changes caused by the rebound of the thick positive electrode film layer or the expansion of charge and discharge by rearranging the stacking relationship within a certain spatial range, reduce the burden on the first sealing area, and thus improve the reliability of the battery cell.

[0132] In some embodiments, in a cross section of the positive electrode film layer along the thickness direction of the electrode sheet, the distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is less than or equal to 5%, and may be 0.2%-2%, and further may be 0.2%-0.9%.

[0133] The distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm in a cross section of the positive electrode film along the thickness direction of the electrode sheet can be tested using methods known in the art. As an example, the cross-section of the positive electrode film layer along the thickness direction of the electrode piece is divided into three layers of equal thickness along the thickness direction of the electrode piece, namely, a lower layer close to the positive electrode current collector, an upper layer away from the positive electrode current collector, and a middle layer located between the upper and lower layers; 10 non-overlapping fields of view are selected in the upper layer, the middle layer and the lower layer, respectively, and scanning electron microscope images are taken at a magnification of 10k; the 30 scanning electron microscope images taken are respectively imported into ImageJ software for analysis, and according to the above-mentioned "test method for the area ratio of 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 piece", the area ratio of particles with a diameter R1 satisfying R1 ≥ 1000 nm in 30 images is tested, with a total of 30 values; the range of the 30 values ​​obtained is the distribution uniformity of 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 piece, where the range is the difference between the maximum and minimum values ​​​​among the 30 values. The smaller the distribution uniformity of 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, the more uniform the distribution of large particles with a particle size R1 satisfying R1 ≥ 1000 nm 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 rebound rate of the positive electrode film layer and the impact on the shell and sealing area, and improve the reliability of the battery cell.

[0134] In some embodiments, the distribution uniformity of the particles having a particle size R1 satisfying R1 ≥ 1000 nm in the cross section of the positive electrode film along the thickness direction of the electrode piece can be selected to be 0.01%, 0.1%, 0.2%, 0.24%, 0.3%, 0.4%, 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.99%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.47%, 1.5%, 1.6%, 1.7%, 1.8%, 1.81%, 1.82%, 1.85%, 1.9%, 1.94%, 1.95%, 1.98%, 1 .99%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.45%, 2.5%, 2.6%, 2.7%, 2.8%, 2.81%, 2.82%, 2.83%, 2.85%, 2.9%, 2.94%, 2.98%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 4.91%, 5% or any range therebetween.

[0135] In some embodiments, the distribution uniformity of the particles with a particle size R1 satisfying R1 ≥ 1000 nm in a cross section of the positive electrode film layer along the thickness direction of the electrode piece is 0.2%-2%.

[0136] In some embodiments, the distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm in a cross section of the positive electrode film along the thickness direction of the electrode piece is 0.2%-0.9%.

[0137] The distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm in the cross-section of the positive electrode film along the thickness direction of the electrode is within the above range, which can effectively reduce the stress concentration in local areas of the film layer, so that the rebound stress of the thick coating layer during the cycle process can be evenly dispersed in the entire area of ​​the film layer, reducing the rebound rate of the positive electrode film layer, thereby increasing the battery energy density while reducing the probability of failure of the packaging structure and improving battery reliability.

[0138] In some embodiments, the solvent in the electrolyte further includes one or both of ethyl methyl carbonate (EMC) and ethylene carbonate (EC).

[0139] The types and qualities of the solvent and electrolyte salt in the electrolyte can be obtained by testing the electrolyte using methods known to those skilled in the art. For example, the composition of the electrolyte can be measured by liquid chromatography, ultraviolet spectrophotometry, ultraviolet-visible spectrophotometry, etc. For example, the battery cell is disassembled, and free electrolyte is obtained from the battery cell. The free electrolyte in the battery cell is diluted to 3 to 10 times with acetonitrile to obtain the electrolyte dilution to be tested. A GC-MS 3100 organic component gas chromatograph is used to place the above electrolyte dilution in the instrument for full scan qualitative analysis. The injection port temperature is 250°C, and the scanning range is: 35μm~270μm. After the test is completed, a total ion current chromatogram of each organic compound is obtained. The type of organic compound corresponding to the peak position of the chromatogram is compared, and the corresponding content percentage of each organic compound is calculated based on the peak area. For example, an ion chromatograph (IC) can be used to test the inorganic content in an electrolyte. A quantitative amount of electrolyte is weighed (the dilution concentration is in the middle of the standard curve), and the volume is made up to 100 mL with ultrapure water. The ion chromatograph is automatically sampled and tested, and the inorganic ion chromatogram is tested. The corresponding inorganic species are compared according to the peak position of the chromatogram.

[0140] In some embodiments, based on the total mass of the electrolyte, the mass proportion of ethyl methyl carbonate (EMC) is 39%-49% based on the total mass of the electrolyte.

[0141] In some embodiments, based on the total mass of the electrolyte, the mass proportion of ethyl methyl carbonate (EMC) can be selected to be 39%, 40%, 40.3%, 41%, 42%, 43%, 43.3%, 44%, 45%, 46%, 47%, 47.3%, 48%, 49% or a numerical range therebetween.

[0142] The viscosity of ethyl methyl carbonate (EMC) is 0.65 mPa·s at 25°C, which is higher than DMC but lower than EC. At the same time, it still maintains good fluidity at low temperatures. Together with DMC, it plays a role in reducing the overall viscosity of the electrolyte, increasing the migration rate of lithium ions in the electrolyte, and reducing Joule heat. In addition, compared with DMC, EMC has higher oxidation stability and thermal stability, which further reduces the decomposition and gas production of the electrolyte and improves the reliability of the battery cell.

[0143] In some embodiments, based on the total mass of the electrolyte, the mass proportion of ethylene carbonate (EC) is 13%-22%.

[0144] In some embodiments, based on the total mass of the electrolyte, the mass proportion of ethylene carbonate (EC) based on the total mass of the electrolyte can be selected as 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22% or a numerical range between any two of the above.

[0145] Ethylene carbonate (EC) has an extremely high dielectric constant, which can effectively dissolve lithium salts, improve the ionic conductivity of the electrolyte, and ensure the smooth migration of lithium ions. EC within the above mass percentage range can decompose on the surface of the negative electrode active material and form a stable SEI film, reducing side reactions and improving cycle life.

[0146] In some embodiments, based on the total mass of the electrolyte, the total mass of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) accounts for 52%-71%.

[0147] In some embodiments, based on the total mass of the electrolyte, the total mass proportion of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) can be selected to be 52%, 53%, 54%, 54.66%, 55%, 56%, 57%, 58%, 59%, 60%, 60.66%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 68.66%, 69%, 70%, 71% or a numerical range therebetween.

[0148] The total mass content of EC and EMC is within the above range, and they can complement each other, overcoming the problems of high EC viscosity and poor thermal stability and mechanical strength of the SEI film formed by EMC, realizing the optimization of electrolyte performance, and further reducing the pressure of Joule heat and SEI film decomposition gas production on the sealing area from the perspective of optimizing ionic conductivity and SEI film.

[0149] In some embodiments, the electrolyte includes an electrolyte salt, the electrolyte salt includes lithium hexafluorophosphate (LiPF6), and the concentration of lithium hexafluorophosphate in the electrolyte is 0.9 mol / L to 1.2 mol / L.

[0150] In some embodiments, the concentration of lithium hexafluorophosphate in the electrolyte is 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, or any range therebetween.

[0151] Lithium hexafluorophosphate (LiPF6) is highly soluble in carbonate solvents, forming a high-concentration electrolyte that ensures high lithium ion conductivity. It also induces the formation of a stable SEI film at low-potential anodes, reducing lithium deposition and improving cycle life. Excessive LiPF6 concentration significantly increases electrolyte viscosity, restricting lithium ion diffusion and causing a decrease in ionic conductivity. Furthermore, LiPF6's decomposition products, including PF5, react with trace amounts of water in the electrolyte to form HF, which corrodes the electrodes and SEI film and exacerbates solvent decomposition and gassing. A LiPF6 concentration within this range achieves an optimal balance between ionic conductivity and electrolyte stability.

[0152] In some embodiments, based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate is 18%-26%.

[0153] The mass proportion of dimethyl carbonate is within the above range. The introduction of EC and EMC with a larger proportion further reduces its gas production capacity and probability, thereby improving the long-term reliability of the battery cell.

[0154] In some embodiments, the electrolyte further comprises vinylene carbonate (VC), and based on the total mass of the electrolyte, the mass proportion of vinylene carbonate is 0.5%-1.5%.

[0155] Vinylene carbonate undergoes a reduction reaction on the anode surface before other solvent components, forming a dense SEI film rich in organolithium compounds. This SEI film has high lithium ion conductivity, which helps improve the kinetic performance of the battery cell. The SEI film also possesses high mechanical strength and chemical stability, inhibiting the continued decomposition of the electrolyte, thereby reducing the consumption of active lithium and the production of side reactions and gas.

[0156] In some embodiments, in the cumulative distribution curve of the graphitization degree C value of the positive electrode film obtained in the surface scanning mode of the laser microconfocal Raman spectrometer, the median value of the graphitization degree C is 50 The graphitization degree C is 0.95-1.20, and the graphitization degree C value is 1 G / I D , where I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at .

[0157] In this application, the graphitization degree C value of the positive electrode film layer can be obtained by the surface scanning mode of a laser microconfocal Raman spectrometer. As an example, specifically, a laser microconfocal Raman spectrometer (high-precision Renishaw laser microconfocal Raman spectrometer) is used, an excitation wavelength of 532nm is selected, and an appropriate amount of positive electrode film is taken to perform a surface scan on its surface or a cross-section along the thickness direction of the electrode. The scanning area is 45μm×45μm, divided into 10×10 grids, with the grid vertex as the test point, the step size is 5μm, and the total number of scanning points is 100 points. In this way, the C values ​​of different sites and the cumulative distribution curve of the C value of the surface scan area are obtained.

[0158] The positive electrode film layer in this application can be either freshly prepared or obtained from a disassembled battery. The surface of a disassembled battery positive electrode film layer inevitably contains residual electrolyte salt particles. To improve test accuracy, it is preferred to perform a surface scan of the positive electrode film layer along the thickness direction of the electrode sheet to characterize the degree of graphitization of the positive electrode film layer.

[0159] The graphitization degree C value of the positive electrode film is obtained by the peak intensity ratio of the G peak (G-band) and the D peak (D-band) of the Raman spectrum. The G peak position is 1580±100cm -1 , which characterizes carbon sp 2 Hybrid structure; D peak position is 1350±100cm -1 , which characterizes a disordered structure, where disorder means that there is no regular arrangement between the carbon atoms in the structure. In graphite crystals, the carbon atoms in the same layer are arranged in sp 2 Hybridization forms covalent bonds, and the interlayer is van der Waals force, which makes the carbon in the graphite structure easy to slide. Therefore, the C value can characterize the graphitization degree of the positive electrode film. It can be understood that the graphitization degree in the positive electrode film mainly comes from the carbon material that has been graphitized in the positive electrode film, that is, the carbon material on the surface of the positive electrode active material. Although it is rich in sp 2 The hybrid structure of carbon nanotube conductive agent also has a relatively high I G / I D However, due to its low content and small diameter, its addition to the positive electrode film layer shows an extreme value in the Raman surface scan test of the positive electrode film layer, and will not affect the graphitization degree C in the positive electrode film layer. 50 Therefore, the graphitization degree of the positive electrode film can also be used to characterize the graphitization degree of the positive electrode active material.

[0160] The cumulative distribution curve of graphitization degree C value refers to a curve obtained by arranging at least 100 C values ​​obtained in ascending order, with graphitization degree as the horizontal axis and cumulative number percentage as the vertical axis. 50 The C value corresponding to the cumulative number of the vertical axis in the cumulative distribution curve of graphitization degree C is 50%. The median C value of graphitization degree50 Compared with the point value, it can reflect the overall graphitization degree of the particles in the positive electrode film layer, that is, the degree of slippage; compared with the mean value, it can reduce the influence of extreme values ​​during the test process and improve the confidence of the test results.

[0161] Those skilled in the art can adjust the degree of graphitization of the active material particles by any known process. As an example, adjusting the carbon source, sintering temperature, sintering time, sintering pressure, and sintering atmosphere can all adjust the degree of graphitization of the active material particles. The higher the degree of graphitization of the carbon on the surface of the positive electrode active material, the higher the proportion of graphite-structured carbon in the positive electrode film layer, and the easier it is for the particles to slip due to the highly graphitized carbon structure on the surface of the active material particles, thereby reducing stress concentration in the electrode.

[0162] In some embodiments, in the cumulative distribution curve of the graphitization degree C value of the positive electrode film obtained in the surface scanning mode of the laser microconfocal Raman spectrometer, the median value of the graphitization degree C is 50 The optional value is 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 a numerical range between any two of the above.

[0163] Studies have shown that the stress of the film layer under the action of cyclic expansion can easily lead to an increase in internal mechanical pressure, causing the packaging structure to fail. By controlling the graphitization degree C value cumulative distribution curve of the positive electrode film layer obtained in the laser microconfocal Raman spectrometer surface scanning mode, the median graphitization degree C 50 The graphitization degree of the positive electrode film layer is 0.95-1.20, which improves the slippage of particles in the positive electrode film layer, reduces the stress concentration phenomenon during the compaction process of the thick coating film layer, and reduces the rebound degree of the positive electrode film layer due to local stress concentration during the cycle process, thereby increasing the reliability of the battery cell while improving the volume energy density of the battery cell.

[0164] In some embodiments, in the cumulative distribution curve of the coverage value B obtained by the laser microconfocal Raman spectrometer surface scanning mode, the median coverage value B 50 is 0.30-0.60, where the coating value B is I P / I D , where I P Indicates that the Raman spectrum is at 948±100cm -1 The P peak intensity at I D Indicates that the Raman spectrum is at 1350±100cm -1The D peak intensity at .

[0165] In this application, the coating value B value of the positive electrode film layer can be obtained by scanning with a laser micro-confocal Raman spectrometer. As an example, specifically, a laser micro-confocal Raman spectrometer (high-precision Renishaw laser micro-confocal Raman spectrometer) is used, an excitation wavelength of 532nm is selected, and an appropriate amount of positive electrode film is taken to perform a surface scan on its surface or a cross-section along the thickness direction of the electrode. The scanning area is 45μm×45μm, divided into 10×10 grids, with the grid vertex as the test point, the step size is 5μm, and the total number of scanning points is 100 points, thereby obtaining the B value of different sites and the cumulative distribution curve of the B value of the surface scan area.

[0166] The coating value B value of the positive electrode film layer is obtained by the peak intensity ratio of the P peak (P-band) and the D peak (D-band) of the Raman spectrum. The P peak position is 948±100cm -1 , which characterizes phosphate PO4 3- structure; D peak position is 1350±100cm -1 , which characterizes a disordered structure, where disorder refers to the irregular arrangement of carbon atoms within the structure. Raman spectroscopy is a surface analysis instrument, so the carbon structure peak of the cathode film, as measured by a confocal laser microscope in surface scanning mode, exhibits a higher intensity than the phosphate structure peak, which is more abundant in the bulk phase.

[0167] Those skilled in the art can adjust the coating value of active material particles by any known process. As an example, adjusting the carbon source type, carbon source addition amount, sintering temperature, sintering time, sintering pressure, and sintering atmosphere can all adjust the coating value of active material particles. The coating value B value can reflect the density of the carbon material on the surface of the lithium-containing transition metal phosphate particles. The denser the carbon material, the relatively lower the phosphate structure strength detected in the Raman spectrum, and the smaller the coating value B value of the positive electrode film layer.

[0168] The cumulative distribution curve of the coverage value B value refers to the curve obtained by arranging at least 100 B values ​​obtained in order from small to large, with the coverage value as the horizontal axis and the cumulative number percentage as the vertical axis. 50 It is the B value corresponding to when the cumulative number of the vertical axis in the cumulative distribution curve of the coverage value B value accounts for 50%.

[0169] In some embodiments, in the cumulative distribution curve of the coverage value B obtained by the laser microconfocal Raman spectrometer surface scanning mode, the median coverage value B 50The amount can be selected from 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.355, 0.36, 0.368, 0.369, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.446, 0.45, 0.456, 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 range of values ​​between any two of the above.

[0170] In order to reduce the influence of the extreme value of the coating value caused by the non-particle area in the positive electrode film layer on the test results, the median of the coating value B is used. 50 Evaluate the density of carbon material on the surface of positive electrode active material.

[0171] Median B of the coating value of the positive electrode film 50 Being within the above range indicates that the carbon material on the surface of the positive electrode active material is relatively dense and uniform, which is beneficial to improving the slip uniformity of the positive electrode film during rolling, reducing stress concentration in the positive electrode film, reducing the rebound degree of the positive electrode sheet, and improving the reliability of the battery cell.

[0172] In some embodiments, the lithium-containing transition metal phosphate particles include iron, and the iron dissolution rate of the positive electrode film layer is 658 ppm-1921 ppm, and can be optionally 658 ppm-1485 ppm.

[0173] The iron dissolution rate of the positive electrode film layer can be tested in the following way. Specifically, the electrode was disassembled and cleaned from the battery, and then filled into small discs with a diameter of 14 mm. Several small disc samples were taken so that the total mass of the sample was about 5 g. The samples were added to 100.3 g of ascorbic acid solution with a mass concentration of 0.3% (the solvent was ultrapure water). After stirring at 500 revolutions per minute for 5 minutes, the solution was quickly aspirated using a 5 mL syringe, and the solution was filtered into a test tube using a 0.45 μm pore filter. 1 mL of the supernatant was aspirated with a pipette, added to a glass volumetric flask and diluted 50 times. The solution was tested using an inductively coupled plasma mass spectrometer (ICP-OES) to obtain the iron concentration in the solution. The formula: [(ICP test iron concentration × solution volume / mass of the fixed volume solution) × 100.3 g / (mass of the electrode of the small disc - mass of the current collector of the small disc)], the solution volume was 50 mL, and the mass of the fixed volume solution was 1 g, and the iron dissolution rate of the positive electrode film was calculated. Preferably, the current collector mass of the small disc is calculated by multiplying the disc thickness by the area and the density. The disc thickness can be equivalently measured by measuring the current collector thickness of the uncoated area with a thickness gauge. It is understood that although the current collector in the coated area will expand during the compaction process, resulting in a slight decrease in thickness compared to the uncoated area, this decrease is negligible and will not significantly affect the test results.

[0174] In some embodiments, the lithium-containing transition metal phosphate particles include iron element, and the iron dissolution rate of the positive electrode film layer can be 658ppm, 700ppm, 800ppm, 890pm, 900ppm, 1000ppm, 1058pm, 1076pm, 1100ppm, 1143pm, 1200ppm, 1236pm, 1300ppm, 1311pm, 1384pm, 1349pm, 1400ppm, 1485pm, 1500ppm, 1531pm, 1600ppm, 1700ppm, 1800ppm, 1921ppm or a numerical range between any two of the above.

[0175] The iron dissolved in the positive electrode film mainly comes from the lithium-containing transition metal phosphate in the positive electrode active material. The iron dissolution rate depends on the number of lattice defects in the lithium-containing transition metal phosphate and the integrity and density of the carbon material on the surface of the positive electrode active material. The lower the iron dissolution rate, the fewer lattice defects in the lithium-containing transition metal phosphate, which helps reduce lattice corrosion in a weak acid environment. The more complete and dense the carbon material on the surface of the positive electrode active material, the more it inhibits the dissolution of iron ions in a weak acid environment. The positive electrode film with an iron dissolution rate within the above range has relatively few lattice defects, and the surface of the positive electrode active material has a complete and dense carbon material, which helps to improve the compressive resistance and slippage of the particles in the positive electrode film under large rolling pressure, increase the compaction density of the positive electrode film and reduce stress concentration in the positive electrode film, improve the energy density of the battery and improve the reliability of the battery.

[0176] In some embodiments, the positive electrode film layer further includes a conductive agent, and based on the total area of ​​the cross section of the positive electrode film layer along the thickness direction of the electrode sheet, the total area of ​​the agglomerated region of the conductive agent accounts for 0.5%-2.5%.

[0177] In the present 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 agglomerated region of the conductive agent can be tested by the following method. A similar method as described above is used to observe the cross-section of the positive electrode film layer along the thickness direction of the electrode through a scanning electron microscope, and the area of ​​the conductive agent agglomerated region in the scanning electron microscope image is measured at a magnification of 3k times. Since the conductive agent is generally a carbon-based material, such as conductive carbon black, carbon nanotubes, etc., the aggregated conductive agent can be seen under the high magnification of the scanning electron microscope, and the conductive agent agglomeration region often appears black agglomerate compared to other areas in the positive electrode film layer. With the help of image analysis software, the conductive agent agglomeration area refers to the area in the scanning electron microscope image where the conductive agent is obviously aggregated and appears black. Specifically, a scanning electron microscope image at a magnification of 3k was imported into ImageJ, and black conductive agent agglomeration regions with a Feret greater than or equal to 2μm were screened out. The sum of the areas of the screened regions was recorded as the area of ​​the conductive agent agglomeration region. The area ratio of the conductive agent agglomeration region was the ratio of the area of ​​the conductive agent agglomeration region to the total area of ​​the imported scanning electron microscope image. Three non-overlapping scanning electron microscope images were randomly selected, and the average of the area ratios of the conductive agent agglomeration regions was calculated as the "area ratio of the conductive agent agglomeration region based on the total area of ​​the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet."

[0178] In some embodiments, based on the total area of ​​the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the total area proportion of the agglomerated region of the conductive agent can be selected as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.68%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.41%, 2.5% or a numerical range between any two of the above.

[0179] Based on the total area of ​​the cross-section of the positive electrode film layer along the thickness direction of the electrode, the total area of ​​the agglomerated region of the conductive agent accounts for 0.5%-2.5%, indicating that the conductive agent is evenly dispersed in the positive electrode film layer and is easy to form a uniform conductive network, which is particularly beneficial to reducing the problem of kinetic degradation caused by the growth of the ion transmission path in the thick coating film layer, and reducing the local polarization and even lithium plating problems generated by the battery during the cycle.

[0180] At the same time, studies have shown that large-sized particles in lithium-containing transition metal phosphate particles are prone to rebound. The agglomeration area of ​​the conductive agent within the above range can suppress the rebound of the lithium-containing transition metal phosphate with the help of the uniform distribution of the conductive agent, form mechanical constraints on the particles and even the film layer, improve the cohesion of the film layer, reduce the probability of failure of the sealing area, and improve the reliability of the battery.

[0181] In some embodiments, the positive electrode film layer further includes a conductive agent, and 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 0.5%-1.7%.

[0182] In the embodiments of the present application, the area ratio of the agglomerated region of the conductive agent is further within the above range, indicating 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 space occupied by the positive electrode active material due to excessive conductive agent, thereby further improving the volume energy density of the battery while improving the battery kinetic performance.

[0183] 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.

[0184] In this application, the term "carbon nanotube" refers to a carbon nanotube composed of carbon atoms in the form of sp 2A nanomaterial consisting of several to dozens of coaxial hollow tubes formed by the curling of hybrid-bonded graphene sheets. Diameters typically range from a few to tens of nanometers, and lengths can range from microns to centimeters, exhibiting a high aspect ratio. Based on the number of graphene layers, carbon nanotubes can be classified as single-walled carbon nanotubes (SWCNTs), few-walled carbon nanotubes (FWCNTs), and multi-walled carbon nanotubes (MWCNTs). Carbon nanotubes possess excellent electrical conductivity and a high elastic modulus.

[0185] The high aspect ratio structural characteristics of carbon nanotubes are conducive to overlapping multiple positive electrode particles in the thickness direction, forming a long-range conductive path while increasing the binding force between the particles. This is beneficial to improving the dynamic performance of thick-coated positive electrode film layers, reducing local polarization and even lithium plating problems generated by the battery during the cycle process, and increasing the cycle life of the battery; it can also form a network structure in the positive electrode film layer as a bridge for stress propagation, effectively alleviating stress concentration, reducing the degree of pole piece rebound, and improving the reliability of battery cells.

[0186] Furthermore, carbon nanotubes have a high specific surface area and hollow structure, resulting in excellent electrolyte retention. Thick electrodes experience significant expansion during cycling, making electrolytes more susceptible to extrusion. Carbon nanotubes in the positive electrode film improve the electrolyte retention of thick electrodes, alleviating the capacity drop during cycling and improving the cycle life of battery cells.

[0187] In some embodiments, the conductive agent further comprises conductive carbon black.

[0188] Conductive carbon black has a high specific surface area, which in turn provides excellent electrolyte retention. Thick electrodes experience significant expansion during cycling, making it easier for the electrolyte to be squeezed out. The distribution of conductive carbon black within the positive electrode film helps improve the electrolyte retention of thick electrodes, mitigate the phenomenon of capacity drop during cycling, and improve the battery's cycle life.

[0189] In some embodiments, the agglomerated regions of the conductive agent include carbon nanotubes and conductive carbon black.

[0190] 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 the inability to form an effective carbon nanotube network structure. The surface energy of conductive carbon black is relatively close to that of carbon nanotubes, which 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 agglomeration area of the conductive agent will also cause blockage of the local ion transport path in the agglomeration area of the conductive agent. The combination of conductive carbon black can improve the lithium ion transport ability in this area, reduce local polarization, and further improve the cycle stability of the battery.

[0191] In some embodiments, 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%.

[0192] In some embodiments, based on the mass of the positive electrode film layer, the mass content C1 of the carbon nanotubes can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.67%, 0.7%, 0.8%, 0.9%, 1.0%, 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.

[0193] In some embodiments, based on the mass of the positive electrode film layer, the mass content C2 of the conductive carbon black can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 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.

[0194] When the mass contents of carbon nanotubes and conductive carbon black in the positive electrode film layer 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 rebound of the thick-coated positive electrode film layer and improving the reliability of the battery cell; and improving the liquid retention rate of the positive electrode plate during long-term cycling, reducing the degree of polarization, and improving the problem of capacity drop of the battery cell.

[0195] In some embodiments, the positive electrode film layer further includes a dispersant, and the dispersant includes hydrogenated nitrile rubber HNBR.

[0196] HNBR is derived from nitrile rubber by hydrogenating its double bonds to saturate them. Its highly saturated backbone structure imparts excellent oil resistance, heat resistance, and aging resistance. This makes it stable in diverse environments and systems when used as a dispersant, resisting degradation or deterioration, thus effectively exerting its dispersing properties. The HNBR molecular chain contains both polar nitrile groups and non-polar hydrocarbon segments. The polar nitrile groups interact with hydroxyl (-OH) groups or metal oxide sites on the surface of lithium-containing transition metal phosphate particles (e.g., hydrogen bonding and dipole interactions), enhancing particle compatibility with solvents and reducing interfacial tension, especially for large particles. This facilitates more uniform particle dispersion, reduces aggregation caused by hydrophobicity, improves the dispersion of large particles in the cathode film, and reduces stress concentration caused by rebound. The non-polar hydrocarbon segments, with their excellent lipophilicity, allow for excellent stretching and dispersion in non-polar or weakly polar media, ensuring uniform particle dispersion.

[0197] When HNBR is adsorbed onto the surface of particles in the slurry, its long-chain molecules form a physical barrier around the particles, preventing them from approaching and aggregating, allowing them to remain relatively independently dispersed within the system. At the same time, HNBR can reduce the surface tension between the dispersion medium and the dispersed particles, making the particles more easily wetted by the medium, thereby promoting their dispersion within the medium. It can also reduce the interfacial energy between particles, particularly reducing the aggregation of conductive agents driven by interfacial energy, thereby improving the cycle life of battery cells.

[0198] In some embodiments, the mass content of the dispersant is 0.5%-2% based on the mass of the positive electrode film layer.

[0199] 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 numerical range therebetween.

[0200] The mass content of the dispersant is within the above range, which can achieve uniform dispersion of particles in the positive electrode film layer while maintaining a high load of the positive electrode film layer, slow down the rebound caused by stress concentration of the thickly coated lithium transition metal phosphate positive electrode film layer, reduce the rebound rate of the positive electrode film layer, and improve the reliability of the battery cell.

[0201] In some embodiments, the porosity of the positive electrode film layer is 14%-28%.

[0202] In this application, the porosity of the positive electrode film layer can be tested in the following way. Import the cross-sectional scanning electron microscope image of the positive electrode film layer along the thickness direction of the electrode obtained in the manner described above into the ImageJ software, select the straight line tool, use the straight line to mark the ruler length in the image, click "Analyze Set Scale", and set the ruler parameters in the software according to the ruler length in the image. Select the rectangle tool, select the part of the image outside the ruler area, use "Image Duplicate" to copy the selected area, and use "Image Type 8 bit" to adjust the image format; select "Analyze Set Measurements", select the following 5 options: "Area", "Mean gray value", "Area Fraction", "Limit to threshold", "Feret's diameter", select 3 for "Decimal places", select "Image"-"Adjust"-"Threshold" in turn, set 0 and 100 in the "Threshold" box position in turn, and then use the Analyze-Measure function to export the pore data in the cross-sectional scanning electron microscope image. Use "Image" - "Overlay" - "Flatten" to export and obtain the pore image; click "Apply" in "Threshold", then click "Analyze" - "Analyze Particles", check the four columns on the left, and you can get the pore statistics.

[0203] It is understood that in the embodiments of this application, "pores" in the positive electrode film cross section are identified by using image color difference and threshold values. This "pore" is not the pore data obtained in the exhaust test, but is mainly used to characterize the cross-sectional area between particles in the positive electrode film cross section. 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 pores in the carbon material on the surface of the lithium iron phosphate particles, and thus cannot objectively reflect the pores between particles.

[0204] A positive electrode film porosity within this range not only improves electrolyte retention, enhances ion diffusion in thick-coated electrodes and the positive electrode film, and improves battery dynamics, but also mitigates rebound or volume increase during charge and discharge, reduces the impact of expansion stress on the seal area, and maintains high battery reliability.

[0205] In some embodiments, the porosity of the positive electrode film layer may be 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28% or any range therebetween.

[0206] In some embodiments, as Figure 2 As shown, the battery cell also includes a separator 20 arranged between the positive electrode plate and the negative electrode plate, the separator 20 includes a base film 201 and a ceramic layer 202 arranged on both sides of the base film 201 and a bonding layer 203 with at least one side arranged on the ceramic layer 202 away from the base film 201, the bonding layer 203 is a continuous layer of a porous structure, and the bonding layer 203 includes a vinylidene fluoride polymer.

[0207] In some embodiments, the vinylidene fluoride polymer includes one or more of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0208] In some embodiments, the vinylidene fluoride-based polymer includes polyvinylidene fluoride (PVDF).

[0209] like Figure 3 As shown, in the prior art, aqueous PVDF is often used as the bonding layer of the diaphragm, which presents an island-like structure in the diaphragm. This is beneficial for providing gaps for the expansion of the battery cell and is easy to manufacture. However, the contact area between the bonding layer of such a diaphragm and the electrode is small, and the bonding force is weak.

[0210] The diaphragm provided in the embodiment of the present application uses a continuous layer of porous structure as a bonding layer, such as Figure 2 As shown, compared with the adhesive layer in the prior art, the bonding area with the electrode is larger, so that the bonding between the diaphragm and the electrode is more firm and uniform; further, when the positive electrode film rebounds, it is beneficial to maintain the interface contact between the diaphragm and the positive electrode film, reducing the probability of film shedding.

[0211] It is understandable that the continuous adhesive layer may break and deform into a block structure due to contact or extrusion with the positive electrode sheet or the negative electrode sheet during the manufacturing or circulation process of the electrode sheet. The continuous structure referred to in this application means that at the microscopic level, such as when observed under a scanning electron microscope or an optical microscope, the adhesive layer of the diaphragm is continuous. In order to reflect the true morphology of the diaphragm, during the sampling process, it is preferred to sample the area where the adhesive layer of the diaphragm in the battery is not bonded to the positive electrode sheet or the negative electrode sheet. As an example, sampling is performed at the position of the diaphragm beyond the positive electrode sheet and the negative electrode sheet; or sampling is performed on the diaphragm near the surface of the electrode assembly. The diaphragm sampling area has less adhesion to the positive electrode sheet or the negative electrode sheet, and can better reflect the true state of the diaphragm.

[0212] The diaphragm provided in the embodiment of the present application uses a continuous layer of a porous structure as a bonding layer, which has a larger bonding area than the bonding layer in the prior art, so that the bonding between the diaphragm and the positive electrode film layer is more firm and uniform; particles with a particle size R1 satisfying R1 ≥ 1000 nm are prone to stress concentration during the cycle, resulting in rebound problems. The diaphragm provided in the embodiment of the present application uses a continuous layer of a porous structure as a bonding layer, which is particularly suitable for thick-coated laminated cells, improving the rebound phenomenon of thick-coated laminated cells during long cycles, reducing the expansion stress inside the battery, and improving the reliability of the sealing area and the battery cell as a whole. In addition, the thick-coated battery cell is prone to relative displacement between the electrode sheet and the diaphragm in the process of dragging the outer electrode sheet and welding the electrode ear, which makes the film layer prone to powder loss, and even the positive and negative electrodes overlap with each other, resulting in the risk of internal short circuit. The continuous layer of the porous structure in the embodiment of the present application is used as a bonding layer to also reduce the above risks.

[0213] 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).

[0214] In some embodiments, the ceramic layer includes one or more of aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), titanium oxide (TiO 2 ), silicon oxide (SiO 2 ), and boron nitride (BN).

[0215] Ceramic particles are flame-retardant and have a high hardness, making them resistant to deformation under heat and resulting in excellent dimensional stability. The low thermal conductivity of ceramic materials further prevents certain thermal runaway points in the battery from expanding into overall thermal runaway, thereby improving the safety of the battery cells.

[0216] In some embodiments, the positive electrode film layer is provided with a primer layer in the bottom region near the positive electrode current collector, the primer layer comprises a conductive agent and a binder, the conductive agent comprises carbon nanotubes and conductive carbon black, and the binder comprises a vinylidene fluoride polymer.

[0217] In some embodiments, the positive electrode film layer is provided with a primer layer in a bottom region close to the positive electrode current collector, and the primer layer has a thickness of 0.5 μm-5 μm.

[0218] In some embodiments, the thickness of the primer layer may be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any range therebetween.

[0219] The undercoat provided in the embodiments of the present application helps improve the adhesion between the positive electrode film and the positive electrode current collector and alleviates stress concentration at large particles, thereby reducing the rebound of the positive electrode film and improving the reliability of the battery cell. Furthermore, compared to direct contact between the positive electrode current collector and the positive electrode film, the undercoat increases the contact area between the positive electrode film and the positive electrode film, helping to increase the area for electron transfer between the current collector and the positive electrode film, thereby reducing the internal resistance of the electrode sheet and improving the dynamic performance of the battery.

[0220] In some embodiments, the lithium-containing transition metal phosphate particles in the positive electrode film layer include components represented by the following general formula:

[0221] Li m Fe x P y O j Q q Formula I,

[0222] 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, and Br, 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0223] In some embodiments, m can be selected from 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 any range therebetween; x can be selected from 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any range therebetween. ; y can be selected as 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or any numerical range therebetween; j can be selected as 3.5, 3.6, 3.7, 3.8, 3.9, 4 or any numerical range therebetween; q can be selected as 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any numerical range therebetween.

[0224] Selecting an appropriate modifying element Q can improve the lattice change rate of the positive electrode active material during the lithium insertion and extraction process, reduce the oxygen activity on the particle surface, and improve the structural stability of the material, thereby increasing the material's gram capacity during the cycle and improving the cycle stability of the battery cell.

[0225] In some embodiments, the lithium-containing transition metal phosphate particles include titanium. Based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of titanium is 500ppm-8000ppm, and can be optionally 1000ppm-3000ppm.

[0226] The type and content of elements in the lithium-containing transition metal phosphate particles in the positive electrode film can be tested by any method known in the art. As an example, titanium element and content are tested using inductively coupled plasma optical emission spectrometry in accordance with Appendix C of GB / T 33822-2017.

[0227] In some embodiments, based on the total mass of the lithium transition metal phosphate particles in the positive electrode film layer, the mass content of the titanium element can be selected as 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, 5500ppm, 6000ppm, 6500ppm, 7000ppm, 7500ppm, 8000ppm or any numerical range therebetween.

[0228] The introduction of titanium elements into lithium-containing transition metal phosphate particles requires the addition of a titanium source during the preparation of the positive electrode active material. Titanium sources are often inert materials, and adhering to the surface of the lithium-containing transition metal phosphate raw material can reduce the reaction activity and reduce the growth of particle size. Increasing 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 of the positive electrode film layer, and cause the film layer of the positive electrode film layer to fall off. In the embodiment of the present application, by adding a high content of titanium elements to the lithium-containing transition metal phosphate particles, the reaction activity of the raw materials for synthesizing the positive electrode active material is reduced, so that the positive electrode active material can achieve control of the proportion of large particles while having a high degree of graphitization, reduce the rebound rate of the positive electrode film layer, and improve the energy density of the battery while taking into account the reliability of the battery.

[0229] At the same time, doping titanium into the positive electrode active material can help induce lattice distortion, reduce Li-O bond energy, increase lithium ion transfer rate, and improve the battery's kinetic performance. Uneven lithium ion diffusion in thick coatings is often accompanied by a significant lithium ion concentration gradient. The present invention improves the solid-phase transfer rate of the positive electrode active material by adding a high content of titanium to lithium-containing transition metal phosphate particles, thereby improving the kinetics of thick-electrode batteries.

[0230] In some embodiments, the lithium-containing transition metal phosphate particles include vanadium. Based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer, the mass content of vanadium is 500ppm-5000ppm, and can be optionally 500ppm-3000ppm.

[0231] In some embodiments, based on the total mass of the lithium transition metal phosphate particles in the positive electrode film layer, the mass content of the vanadium element can be selected to be 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, or 5000ppm.

[0232] The vanadium element in the positive electrode film can be in a variety of valence states, among which the +5 valence vanadium (V 5+ ) can be doped in the phosphorus element site, because its large radius can cause lattice distortion, expand the diffusion channel of lithium ions, thereby improving the ionic conductivity of the positive electrode active material and improving the kinetic performance of the battery; + trivalent vanadium (V 3+ ) can be doped into transition metal sites, generating lithium vacancies through charge compensation, thereby improving the electronic conductivity of the cathode active material. Furthermore, the improved uniformity of vanadium distribution within the lithium-containing transition metal phosphate particles helps further enhance the kinetic performance and reaction uniformity of the cathode film, thereby improving the kinetic performance and cycling performance of the battery cells.

[0233] A vanadium content within the above range helps improve the kinetic performance of the positive electrode sheet and the kinetic performance of thick-coated lithium transition metal phosphate batteries. Furthermore, the synergistic effect of titanium, vanadium, and carbon nanotubes in the positive electrode film helps form a good three-dimensional network, further enhancing the electronic and ionic conductivity of the positive electrode film, thereby further improving the kinetic performance of thick-coated lithium transition metal phosphate batteries.

[0234] In some embodiments, the lithium-containing transition metal phosphate in the positive electrode film layer includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate, and modified materials thereof.

[0235] In some embodiments, the lithium-containing transition metal phosphate in the positive electrode film layer includes one or more of lithium iron phosphate and its doped modified materials and coated modified materials.

[0236] The above-mentioned lithium-containing transition metal phosphate material has good thermal stability, cycle stability, etc., which helps to improve the safety performance and cycle performance of the battery.

[0237] In some embodiments, the soft package material includes an aluminum-plastic composite film, optionally 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.

[0238] Compared with hard shell materials such as aluminum shells and steel shells, soft package materials are lighter in weight, which is conducive to further improving the energy density of lithium-containing transition metal phosphate batteries.

[0239] In some embodiments, at least one of the laminated battery cells is accommodated in the shell, the size of the shell in the length direction is L0, the size of the shell in the width direction is W0, and the size of the shell in the thickness direction is H0, wherein 450mm≤L0≤1300mm, 100mm≤W0≤150mm; 14mm≤H0≤22mm.

[0240] In some embodiments, L0 can be selected as 450mm, 460mm, 470mm, 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 a numerical range between any two of the above.

[0241] In some embodiments, W0 can be selected as 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm or a numerical range between any two of the above.

[0242] In some embodiments, H0 can be selected as 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, or a numerical range therebetween.

[0243] In some embodiments, a length L0 of the housing satisfies: 450 mm ≤ L0 ≤ 650 mm.

[0244] When the length dimension L0 of the shell satisfies the following conditions: 450mm≤L0≤650mm, the length of the battery cell is shorter, which helps to shorten the diffusion path of the current and reduce the internal resistance of the electrode, thereby reducing the heat generation of the battery and improving its dynamic performance; in addition, the shorter shell 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 insertion and extraction during the cycle, alleviate stress concentration, reduce the rebound amplitude of the membrane layer, and improve the reliability of the battery cell.

[0245] In some embodiments, a length L0 of the housing satisfies: 900 mm ≤ L0 ≤ 1300 mm.

[0246] When the length dimension L0 of the housing satisfies the following conditions: 900mm≤L0≤1300mm, the battery cell is longer, which helps reduce the volume share of the housing within the battery cell and increase the active material load share. Furthermore, longer battery cells can reduce the number of batteries required within the battery module, simplify the structural design of the battery module, and reduce the number and complexity of structural components within the module, thereby improving the space utilization of the battery pack and, in turn, helping to increase the volumetric energy density of the battery cell.

[0247] In some embodiments, at 25° C., the capacity of the battery cell is 105Ah-300Ah, optionally 150Ah-190Ah.

[0248] In this application, the capacity of a battery cell has a meaning well known in the art and can be tested using methods known in the art. As an example, the battery is charged to 3.65V at a 0.5C charge rate, which corresponds to its nominal capacity. Then, it is charged to 0.05C at a constant voltage of 3.65V and allowed to rest for 10 minutes. Then, it is discharged to 2.5V at a 1C discharge rate and allowed to rest for 10 minutes. The capacity during the discharge process is calculated using the formula C = I × t, in units of Ah.

[0249] In some embodiments, at 25°C, the capacity of the battery cell may be 125Ah, 130Ah, 135Ah, 140Ah, 145Ah, 150Ah, 155Ah, 160Ah, 165Ah, 170Ah, 175Ah, 180Ah, 185Ah, 190Ah, 200Ah, 210Ah, 220Ah, 230Ah, 240Ah, 250Ah, 260Ah, 270Ah, 280Ah, 290Ah, 300Ah or any range therebetween.

[0250] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0251] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0252] In some embodiments, the negative electrode film layer includes a negative electrode active material. For example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, and hard carbon. However, this application is not limited to these materials; other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used singly or in combination.

[0253] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0254] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0255] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0256] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, compaction and other processes, the negative electrode sheet can be obtained.

[0257] A second aspect of the present application provides a battery device, comprising the battery cell provided in the first aspect of the present application.

[0258] The battery device disclosed in the embodiments of the present application can be used in various energy storage systems that use the battery device as a power source or use the battery device as an energy storage element. In addition to being used in vehicles, the battery device can also be used for, but not limited to, mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the like, and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, and the like.

[0259] In addition, the present application also provides an electrical device using a battery device as a power source, the electrical device including at least one of the battery cells, battery modules, or battery packs provided herein. The battery cells, battery modules, or battery packs can be used as a power source for the electrical device or as an energy storage unit for the electrical device.

[0260] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0261] Figure 4 It is an electric device as an example. The electric device disclosed in the embodiment 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 to power the vehicle. For example, the battery device can be used as an operating power source for the vehicle. The vehicle may also include a controller and a motor, and the controller is used to control the battery device to power the motor, for example, for the working power requirements of the vehicle during starting, navigation and driving. In some embodiments of the present application, the battery device can be used not only 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.

[0262] An embodiment of the present application also provides an energy storage device that uses 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.

[0263] Example

[0264] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0265] Example 1

[0266] (1) Preparation of positive electrode active material

[0267] Lithium carbonate, iron phosphate, titanium dioxide, vanadium pentoxide, sucrose, glucose, and polyethylene glycol are added to deionized water and mixed in a premixing tank, wherein the ratio of lithium carbonate and iron phosphate is such that the molar ratio of lithium to iron is 1.025:1.0, and based on the total mass of the mixed raw materials, the mass content of sucrose is 2%, the mass content of glucose is 4%, and the mass content of polyethylene glycol is 5%. After uniform mixing, a mixed raw material with a solid content of 38% is obtained;

[0268] Among them, the particle size Dv50 of lithium carbonate is 6μm; the morphology of iron phosphate particles is spherical; titanium dioxide and vanadium pentoxide are both nanoparticles; the purity of sucrose is ≥98%; the water content of glucose is <0.5%; and the weight average molecular weight of polyethylene glycol is 1500.

[0269] The mixed raw materials were ground twice in a sand mill, coarsely ground for 1 hour and then finely ground. The slurry temperature was controlled to be less than 40°C during the grinding process to obtain a mixed slurry. The particle size Dv50 of the solid particles in the mixed slurry was 0.45 μm, and spray drying was performed to obtain a dry precursor powder. After drying, its particle size D50 was 55.55 μm.

[0270] The precursor powder was sintered in a nitrogen atmosphere in two stages to obtain the positive electrode active material: the temperature was raised from 25°C to 450°C at a heating rate of 2°C / min (the first heating stage) and kept at this temperature for 3 hours; the temperature was raised from 450°C to 780°C at a heating rate of 5°C / min (the second heating stage) and kept at this temperature for 12 hours; the ventilation volume in the heating stage was greater than that in the constant temperature stage, with a ratio of 1.5:1, and the total ventilation volume was 1350cm 3 / h, and cooling after the end; a lithium iron phosphate positive electrode active material with a surface carbon material having a particle size Dv50 of 1.65 μm is obtained by air flow crushing, wherein, based on the total mass of the positive electrode active material, the mass content of the Ti element is 1050 ppm, and the mass content of the V element is 950 ppm.

[0271] The above D50 and Dv50 refer to the data obtained by Malvern laser scattering method.

[0272] (2) Preparation of positive electrode

[0273] The positive electrode active material, conductive agent, and binder polyvinylidene fluoride are mixed in a solvent N-methylpyrrolidone at a mass ratio of 95:2:3, and are fully mixed, stirred, and dispersed in a stirring tank to form a positive electrode slurry; after the stirring process is completed, the positive electrode slurry is transported to the coating process; the conductive agent includes conductive carbon black and multi-walled carbon nanotubes at a mass ratio of 1:1, and the specific surface area of ​​the conductive carbon black is 80m 2 / g, the oil absorption value is 180mL / 100g, the average length of the carbon nanotubes is 20μm, and the specific surface area is 280m 2 / g.

[0274] The positive electrode slurry was transferred onto aluminum foil for drying and hot pressing to obtain a positive electrode sheet with a single-side thickness of 106.μ9m and a compaction density of 2.35g / cm 3The positive electrode sheet. The compaction density here refers to the compaction density of the battery cell in the fully discharged state. The transfer coating speed is 20 m / min. The hot pressing process includes three hot roller pressing steps, with the hot roller pressing pressure increasing to 40 tons, 60 tons, and 80 tons respectively. The hot roller temperature is 60°C. Before the first hot roller compaction, the electrode sheet is heated to 40°C.

[0275] The positive electrode sheets are striped and punched into specified shapes, and the punched positive electrode sheets are sorted by weight using a weighing sorting machine for stacking by a stacking machine.

[0276] Among them, in the cross section of the positive electrode film along the thickness direction of the electrode, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1 ≥ 1000 nm, the median of the sphericity L R1A50 The median graphitization degree of the positive electrode film is 0.689; 50 is 1.009; the median value B of the positive electrode film coating value B 50 is 0.46; the iron dissolution rate of the positive electrode material is 974ppm; 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 1.68%; the porosity of the positive electrode film layer is 16.03%.

[0277] (3) Preparation of negative electrode sheet

[0278] A mixture of artificial graphite and natural graphite (mass ratio of 1:1), conductive carbon black, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) are mixed evenly 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.

[0279] 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.

[0280] (4) Diaphragm

[0281] Polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone (NMP) and stirred thoroughly. Polyethylene glycol (PEG) was then added as a pore-forming agent and thoroughly stirred to produce a bonding layer solution. This bonding layer solution was then applied to the base film with ceramic layers on both sides. After pre-evaporation at 80°C and drying at 110°C, the solution was immersed in deionized water to dissolve the PEG, resulting in a separator with a porous bonding layer.

[0282] 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.

[0283] (5) Electrolytes

[0284] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the organic solvents dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed uniformly. Lithium hexafluorophosphate was then added and dissolved in the organic solvent to a concentration of 1.05 mol / L. Vinylene carbonate (VC) was then added and stirred uniformly to obtain the electrolyte of Example 1. Calculated based on the total mass of the electrolyte, the mass content of dimethyl carbonate was 26%, the mass content of ethyl methyl carbonate was 43.3%, the mass content of ethylene carbonate was 17.3%, and the mass content of vinylene carbonate was 0.9%.

[0285] (6) Preparation of batteries:

[0286] Use a stacking machine to stack the positive electrode sheets, separators, and negative electrode sheets in order. The separator must be able to isolate the positive and negative electrodes to obtain a stacked battery cell. The stacked battery cell is glued to tightly wrap the battery cell. The glued stacked battery cell is placed in an outer package. The outer package is a soft-pack aluminum-plastic film. The aluminum-plastic film 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 punched and trimmed by a pit forming machine to obtain the target shape and size. The aluminum-plastic film is then heat-sealed to meet the packaging tension of the aluminum-plastic film ≥25N / 8mm. The battery is vacuum-baked and left to stand. The electrolyte is injected and packaged using a flat-head needle. Then, the soft-pack battery is hot-pressed and cold-pressed. The hot pressing temperature is 45°C, the time is 2 minutes, and the pressure is 90kg / cm 2 The cold pressing temperature is 25℃, the time is 2 minutes, and the pressure is 90kg / cm 2 Finally, after the formation, vacuum exhaust, trimming, and folding processes, the battery cell is obtained. The folding process is double folding. The battery cell has a length of 600mm, a width of 125mm, and a thickness of 20mm.

[0287] The preparation methods of Examples 2-5 are basically the same as those of Example 1, except that the preparation method of the positive electrode sheet is adjusted, as follows:

[0288] Example 2

[0289] The positive electrode slurry of Example 1 was coated on aluminum foil and dried. By adjusting the pressure, calendering speed, roller gap, holding time, calendering times, and coating surface density in the hot pressing process, a positive electrode sheet with a single-side thickness of 70.45 μm was obtained by hot pressing; the compaction density was 2.35 g / cm 3The compacted density here refers to the compacted density of the battery cell when it is fully discharged. The test method is described below. Keep the number of laminate layers unchanged and adjust the thickness of the battery cell according to the thickness of the positive electrode film layer.

[0290] Example 3

[0291] The positive electrode slurry of Example 1 was coated on aluminum foil and dried. By adjusting the pressure, calendering speed, roller gap, holding time, calendering times, and coating surface density in the hot pressing process, a positive electrode sheet with a single-side thickness of 91.88 μm was obtained by hot pressing; the compaction density was 2.36 g / cm 3 The compacted density here refers to the compacted density of the battery cell when it is fully discharged. The test method is described below. Keep the number of laminate layers unchanged and adjust the thickness of the battery cell according to the thickness of the positive electrode film layer.

[0292] Example 4

[0293] The positive electrode slurry of Example 1 was coated on aluminum foil and dried. By adjusting the pressure, calendering speed, roller gap, holding time, calendering times, and coating surface density in the hot pressing process, a positive electrode sheet with a single-side thickness of 119.49 μm was obtained by hot pressing; the compaction density was 2.35 g / cm 3 The compacted density here refers to the compacted density of the battery cell when it is fully discharged. The test method is described below. Keep the number of laminate layers unchanged and adjust the thickness of the battery cell according to the thickness of the positive electrode film layer.

[0294] Example 5

[0295] The positive electrode slurry of Example 1 was coated on aluminum foil and dried. By adjusting the pressure, calendering speed, roller gap, holding time, calendering times, and coating surface density in the hot pressing process, a positive electrode sheet with a single-side thickness of 96.75 μm was obtained by hot pressing; the compaction density was 2.55 g / cm 3 The compacted density here refers to the compacted density of the battery cell when it is fully discharged. The test method is described below. Keep the number of laminate layers unchanged and adjust the thickness of the battery cell according to the thickness of the positive electrode film layer.

[0296] The preparation methods of Examples 6 and 7 are basically the same as those of Example 1, except that the preparation method of the electrolyte is adjusted, as follows:

[0297] Example 6

[0298] The proportions of the solvents in the electrolyte were adjusted so that, based on the total mass of the electrolyte, the mass content of dimethyl carbonate was 18%, the mass content of ethyl methyl carbonate was 47.3%, the mass content of ethylene carbonate was 21.3%, and the mass content of vinylene carbonate was 0.9%.

[0299] Example 7

[0300] The proportions of the solvents in the electrolyte were adjusted so that, based on the total mass of the electrolyte, the mass content of dimethyl carbonate was 32%, the mass content of ethyl methyl carbonate was 40.3%, the mass content of ethylene carbonate was 14.3%, and the mass content of vinylene carbonate was 0.9%.

[0301] The preparation methods of Examples 8-12 are basically the same as those of Example 1, except that the preparation methods of the positive electrode active material and the positive electrode sheet are adjusted, as follows:

[0302] Example 8

[0303] (1) Lithium dihydrogen phosphate, ferrous oxalate, polyethylene glycol with a weight average molecular weight of 1000, polyethylene glycol with a weight average molecular weight of 1600, titanium dioxide, and vanadium pentoxide were mixed uniformly in methanol and ground to obtain a mixed raw material. The ratio of lithium dihydrogen phosphate and ferrous oxalate was such that the molar ratio of lithium to iron was 1.025:1.0. The particle size D10 of the ferrous oxalate was 6.5 μm, the particle size D50 was 62 μm, and the particle size D90 was 108 μm. The mass content of Fe element in the ferrous oxalate was 30.5%, and the mass content of trivalent iron element was 0.03%.

[0304] The mixed raw materials are ball milled several times in a ball mill and demagnetized to obtain a mixed slurry. The grinding times and time are controlled, and the particle size of the mixed slurry after grinding is D V 50 is 3.15μm.

[0305] The mixed slurry is spray-dried to obtain a dry precursor powder material, and the dry precursor powder material has a light yellow appearance and a uniform color.

[0306] The precursor powder was placed in a sintering furnace and heated at a rate of 2°C / min from 25°C to 360°C under a nitrogen atmosphere. The temperature was then maintained at this temperature for 3.5 hours. The temperature was then increased at a rate of 5°C / min to a second temperature of 780°C, maintained at this temperature for 10 hours, and then cooled. The mass content of Ti was 1050 ppm and the mass content of vanadium was 950 ppm, based on the total mass of the positive electrode active material.

[0307] The obtained material was crushed by air flow pulverization with a classification frequency of 21 Hz and a pulverization pressure of 0.54 MPa to obtain a lithium iron phosphate positive electrode active material with a carbon material provided on the surface.

[0308] The above D10, D50, D90, and Dv50 refer to the data obtained by Malvern laser scattering method.

[0309] (2) Preparation of positive electrode

[0310] The above-mentioned positive electrode active material, conductive agent, and binder polyvinylidene fluoride are mixed in a solvent N-methylpyrrolidone according to a mass ratio of 95:2:3, and are fully mixed, stirred, and dispersed in a stirring tank to form a positive electrode slurry; after completing the stirring process, the positive electrode slurry is transported to the coating process; wherein, 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 25rpm, the rotation speed is 500rpm, and the pre-stirring time is 15min. The conductive agent includes conductive carbon black and multi-walled carbon nanotubes in a mass ratio of 1:1, and the specific surface area of ​​the conductive carbon black is 80m 2 / g, the oil absorption value is 180mL / 100g, the average length of the carbon nanotubes is 20μm, and the specific surface area is 280m 2 / g.

[0311] The positive electrode slurry was transferred onto aluminum foil for drying and hot pressing to obtain a positive electrode film with a single-side thickness of 106.34 μm and a compaction density of 2.35 g / cm 3 The compaction density here refers to the compaction density of the battery cell when it is fully discharged.

[0312] The hot pressing process includes three hot roller pressing processes, and the hot roller pressing pressure increases successively, and the hot roller pressure is 35 tons, 55 tons, and 75 tons respectively; the hot roller temperature is 65°C, and before entering the hot roller compaction for the first time, the electrode is heated to 50°C.

[0313] The positive electrode sheets are striped and punched into specified shapes, and the punched positive electrode sheets are sorted by weight using a weighing sorting machine for stacking by a stacking machine.

[0314] Example 9

[0315] (1) Preparation of positive electrode active materials

[0316] Lithium carbonate, iron phosphate, sucrose, glucose, titanium dioxide, and vanadium pentoxide were added to water and mixed in a premixing tank at a speed of 1800 rpm, wherein the ratio of lithium carbonate and iron phosphate was such that the molar ratio of iron to phosphorus was 0.97, the mass content of glucose relative to iron phosphate was 3.8%, and the mass content of sucrose relative to iron phosphate was 1.9%;

[0317] The mixed raw materials were ground twice in a sand mill. The first grinding was performed using zirconia balls with a diameter of 0.6 mm and a rotation speed of 500 rpm. The grinding time was 1 h and the grinding chamber pressure was less than 0.3 MPa. The second grinding was performed to obtain a mixed slurry. The particle size D of the mixed slurry was V 50 is 0.435μm;

[0318] The mixed slurry is spray-dried to obtain a precursor powder,

[0319] The precursor powder is sintered to obtain a lithium iron phosphate positive electrode material, and the sintering process includes:

[0320] First sintering: sintering the precursor powder in a nitrogen atmosphere at a heating rate of 5°C / min from 25°C to 765°C, and keeping the temperature for 10 hours, and then cooling to obtain a first sintered product;

[0321] Grinding and mixing: add 0.5% sucrose, 1% glucose and 3.0% polyethylene glycol to the first sintered product; grind the product into two groups (third grinding), wherein the D V50 When the particle size reached 1.02 μm, the grinding was stopped (grinding conditions: 550 rpm, grinding time 1 h), and the first group of grinding products was obtained; the D of the particles in the second group was V50 When the particle size reaches 0.42 μm, grinding is stopped (grinding conditions: 500 rpm, grinding time 4 h) to obtain a second group of ground products; the first group of ground products and the second group of ground products are mixed in a mass ratio of 70:30 to obtain a mixed intermediate product; the mixed intermediate product is spray-dried;

[0322] Second sintering: the dried mixed intermediate product was sintered in a nitrogen atmosphere, heated from 25° C. to 800° C. at a heating rate of 5° C. / min, and kept at this temperature for 10 h. After cooling, a second sintered product was obtained.

[0323] After sintering, the product was cooled to below 100°C and crushed using a jet milling method to obtain a lithium iron phosphate cathode active material with a carbon material provided on its surface. The jet milling was performed at a grading frequency of 23 Hz and a crushing pressure of 0.55 MPa. The mass content of the Ti element, based on the total mass of the cathode active material, was 1050 ppm, and the mass content of the V element was 950 ppm.

[0324] (2) Preparation of positive electrode

[0325] The above-mentioned positive electrode active material, conductive agent, and binder polyvinylidene fluoride are mixed in a solvent N-methylpyrrolidone according to a mass ratio of 95:2:3, and are fully mixed, stirred, and dispersed in a stirring tank to form a positive electrode slurry; after completing the stirring process, the positive electrode slurry is transported to the coating process; wherein, 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 25rpm, the rotation speed is 500rpm, and the pre-stirring time is 15min. The conductive agent includes conductive carbon black and multi-walled carbon nanotubes in a mass ratio of 1:1, and the specific surface area of ​​the conductive carbon black is 80m 2 / g, the oil absorption value is 180mL / 100g, the average length of the carbon nanotubes is 20μm, and the specific surface area is 280m 2 / g.

[0326] The positive electrode slurry was transferred onto aluminum foil for drying and hot pressing to obtain a positive electrode film with a single-side thickness of 106.66 μm and a compaction density of 2.36 g / cm 3 The positive electrode sheet. The compaction density here refers to the compaction density of the battery cell when it is fully discharged. The drying temperature is 95°C and the speed is 2.0m / min.

[0327] The hot pressing process includes three hot roller pressing processes, and the hot roller pressing pressure increases successively, and the hot roller pressure is 35 tons, 55 tons, and 75 tons respectively; the hot roller temperature is 65°C, and before entering the hot roller compaction for the first time, the electrode is heated to 50°C.

[0328] The positive electrode sheets are striped and punched into specified shapes, and the punched positive electrode sheets are sorted by weight using a weighing sorting machine for stacking by a stacking machine.

[0329] Example 10

[0330] The preparation method of Example 10 is basically the same as that of Example 1, except that the preparation process of the positive electrode active material and the hot pressing process of the positive electrode sheet are slightly different. The specific differences include:

[0331] (1) The carbon sources in the mixed raw material are sucrose and glucose. The mass of sucrose is 2 wt% of the mass of ferric phosphate, and the mass of glucose is 5.7 wt% of the mass of ferric phosphate.

[0332] (2) The temperature rise and sintering process is different. The precursor powder is sintered at least twice in a nitrogen atmosphere. The first sintering temperature is 750℃ and the holding time is 8 hours to obtain the primary sintered product.

[0333] 1.5 wt% (based on the mass of the calcined product) of glucose, 3.0 wt% (based on the mass of the calcined product) of polyethylene glycol, titanium dioxide and vanadium pentoxide were added to the primary calcined product, and after being ground evenly, the product was divided into two groups for secondary grinding. The grinding parameters of the two groups were different, and the D of the particles after the first group was controlled. V50 The D of the second group of milled particles is 2.0 μm. V50 The first and second groups of ground particles were mixed at a mass ratio of 30:70, spray-dried, and sintered for the second time. The second sintering temperature was 800°C and the temperature was maintained for 10 hours.

[0334] Based on the total mass of the positive electrode active material, the mass content of the titanium element is 1050 ppm, and the mass content of the vanadium element is 950 ppm.

[0335] (3) The positive electrode slurry was transferred onto aluminum foil for drying and hot pressing to obtain a positive electrode film with a single-side thickness of 106.79 μm and a compaction density of 2.36 g / cm 3 The positive electrode sheet. The compaction density here refers to the compaction density of the battery cell when it is fully discharged. The drying temperature is 95°C and the speed is 2.0m / min.

[0336] The hot pressing process includes three hot roller pressing processes, and the hot roller pressing pressure increases successively, and the hot roller pressure is 35 tons, 55 tons, and 70 tons respectively; the hot roller temperature is 65°C, and before entering the hot roller compaction for the first time, the electrode is heated to 50°C.

[0337] Example 11

[0338] The preparation method of Example 11 is basically the same as that of Example 1, except that the sintering process of the positive electrode active material and the hot pressing process of the positive electrode sheet are different. Specifically:

[0339] (1) The precursor powder was sintered in a nitrogen atmosphere in two stages to obtain the positive electrode active material: the temperature was raised from 25°C to 440°C at a heating rate of 2°C / min (the first heating stage) and kept at this temperature for 2.5 hours; the temperature was raised from 440°C to 760°C at a heating rate of 5°C / min (the second heating stage) and kept at this temperature for 11 hours; the particle size Dv was obtained by air flow pulverization. 50 The surface of the lithium iron phosphate positive electrode active material is provided with carbon material, and the classification frequency of the air flow milling is 25 Hz and the milling pressure is 0.55 MPa.

[0340] (2) The positive electrode slurry was transferred onto aluminum foil for drying and hot pressing to obtain a positive electrode film with a single-side thickness of 106.10 μm and a compaction density of 2.35 g / cm 3The positive electrode sheet. The compaction density here refers to the compaction density of the battery cell when it is fully discharged. The transfer coating speed is 20 m / min.

[0341] The hot pressing process includes three hot roller pressing processes. The hot roller pressing pressure increases successively, and the hot roller pressure is 45 tons, 60 tons, and 80 tons respectively; the hot roller temperature is 60°C. Before entering the hot roller compaction for the first time, the electrode is heated at a heating temperature of 40°C.

[0342] Example 11

[0343] The preparation method of Example 11 is similar to the preparation method of Example 8, except that, when preparing the positive electrode sheet, the above-mentioned positive electrode active material, conductive agent, and binder polyvinylidene fluoride are uniformly mixed in a solvent N-methylpyrrolidone at a mass ratio of 94.52:1.99:2.99, and then, based on the total mass of the positive electrode active material, conductive agent, binder polyvinylidene fluoride and dispersant, 0.5% by mass of dispersant HNBR is added, and the mixture is fully mixed in a stirring tank, stirred, and dispersed to form a positive electrode slurry.

[0344] Example 12

[0345] The preparation method of Example 12 is similar to the preparation method of Example 11, except that, when preparing the positive electrode sheet, the above-mentioned positive electrode active material, conductive agent, and binder polyvinylidene fluoride are uniformly mixed in a solvent N-methylpyrrolidone at a mass ratio of 93.57:1.97:2.96, and then, based on the total mass of the positive electrode active material, conductive agent, binder polyvinylidene fluoride and dispersant, a dispersant HNBR is added with a mass ratio of 1.5%.

[0346] The preparation method of Example 13 is basically the same as that of Example 1, except that the preparation method of the positive electrode sheet is adjusted, as follows:

[0347] Example 13

[0348] The conductive agent used in Example 12 includes 2% by weight of conductive carbon black, excluding carbon nanotubes, and the specific surface area of ​​the conductive carbon black is 85m 2 / g, oil absorption value is 200ml / 100g.

[0349] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that the preparation process of the battery is different. Specifically:

[0350] In Comparative Example 1, the folding process is a single folding process.

[0351] The preparation methods of Comparative Examples 2 and 3 are basically the same as those of Example 1, except that the preparation method of the positive electrode sheet is adjusted, as follows:

[0352] Comparative Example 2

[0353] The positive electrode slurry of Example 1 was coated on aluminum foil and dried. By adjusting the pressure, calendering speed, roll gap, holding time, calendering times, and coating surface density in the hot pressing process, the single-side thickness of the positive electrode film obtained by hot pressing was 65.08 μm and the compacted density was 2.35 g / cm 3 The compacted density here refers to the compacted density of the battery cell when it is fully discharged. The test method is described below. Keep the number of laminate layers unchanged and adjust the thickness of the battery cell according to the thickness of the positive electrode film layer.

[0354] Comparative Example 3

[0355] The positive electrode slurry of Example 1 was coated on aluminum foil and dried. By adjusting the pressure, calendering speed, roller gap, holding time, calendering times, and coating surface density in the hot pressing process, the single-side thickness of the positive electrode film obtained by hot pressing was 125.64 μm and the compaction density was 2.52 g / cm 3 The compacted density here refers to the compacted density of the battery cell when it is fully discharged. The test method is described below. Keep the number of laminate layers unchanged and adjust the thickness of the battery cell according to the thickness of the positive electrode film layer.

[0356] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that the preparation method of the electrolyte is adjusted, as follows:

[0357] Comparative Example 4

[0358] The proportions of the solvents in the electrolyte were adjusted so that, based on the total mass of the electrolyte, the mass content of dimethyl carbonate was 36%, the mass content of ethyl methyl carbonate was 38.3%, the mass content of ethylene carbonate was 12.3%, and the mass content of vinylene carbonate was 0.9%.

[0359] The preparation method of Comparative Example 5 is basically the same as that of Example 1, except that the preparation method of the positive electrode active material is adjusted, as follows:

[0360] Comparative Example 5

[0361] The precursor powder was sintered in a nitrogen atmosphere in two stages to produce the cathode active material: the temperature was increased from 25°C to 500°C (first stage) at a heating rate of 2°C / min and held for 3.5 hours; the temperature was increased from 500°C to 800°C (second stage) at a heating rate of 5°C / min and held for 13 hours. The resulting lithium iron phosphate cathode active material, with a surface-coated carbon material and a particle size Dv50 of 1.6 μm, was obtained by airflow pulverization at a grading frequency of 25 Hz and a pulverization pressure of 0.55 MPa.

[0362] Test Method

[0363] 1. Electrode compaction density test (full discharge)

[0364] Place the battery cell in a 25°C oven environment and let it stand for 2 hours. When the battery temperature remains at 25°C, discharge the battery at a constant current of 1 / 3C to 2.0V, disassemble the battery, obtain the positive electrode plate, use dimethyl carbonate solvent to treat the residual electrolyte, dry the plate, cut it into small discs with an area of ​​S, and obtain its mass as W1. Use a caliper to measure the thickness T1 of the positive electrode plate, then wipe off the positive electrode film layer of the weighed plate, weigh the mass of the current collector, record it as W2, and use a caliper to measure the thickness T2 of the current collector, then the compaction density of the positive electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0365] 2. Bounce rate test

[0366] The compacted positive electrode sheet was measured using a laser thickness gauge to measure the initial thickness of the positive electrode film on one side, denoted as T0 (μm). The sheet was then assembled with other components and processed into a battery cell. At 25°C, the cell was charged to 3.65V at a 0.5C charge rate, equivalent to the nominal capacity of the cell. The cell was then charged to 0.05C at 3.65V, allowed to rest for 10 minutes, and then discharged to 2.5V at a 1C discharge rate, allowed to rest for 10 minutes. This cycle was considered one cycle. After repeating this cycle 100 times, the cell was disassembled to obtain the positive electrode sheet. The cell was allowed to rest for 1 hour, and the thickness of the positive electrode film on one side after the cycle was measured using a laser thickness gauge, denoted as T1 (μm). The cell's rebound rate was calculated as: rebound rate = (T1 - T0) / T0 × 100%.

[0367] 3. Gas production test

[0368] At 25°C, charge the battery to 3.65V at a 0.5C charge rate based on the nominal capacity of the battery cell. Then, charge it to 0.05C at a constant voltage of 3.65V and let it rest for 10 minutes. Then, discharge it to 2.5V at a 1C discharge rate and let it rest for 10 minutes. Measure the initial thickness (T2) of the battery cell in μm using a laser thickness gauge at 25°C. This charge and discharge cycle is considered one cycle. Repeat this cycle 100 times, let it rest for 1 hour, and measure the thickness (T3) of the battery cell after the cycle in μm using a laser thickness gauge. Calculate the gas production of the battery cell: Gas production = (T3 - T2) / T2 × 100%.

[0369] The battery cells of each embodiment and comparative example were prepared according to the above method. The specific parameters and performances are shown in the table below.

[0370] Table 1

[0371]

[0372] In Comparative Example 1, only a first sealing area with a single folded edge is provided, resulting in packaging failure and poor reliability during long-term cycling. In Comparative Example 2, the thickness of the positive electrode film layer is small, the space occupied by the positive electrode active material is low, and the capacity of the battery cell is low; in Comparative Example 3, the thickness of the positive electrode film layer is too large, the rebound phenomenon is serious, the pressure in the sealing area increases, and the long-term reliability of the battery cell is affected. In Comparative Example 4, the DMC content in the electrolyte is too large, which is easy to produce gas, increase the internal pressure of the battery cell, cause packaging failure, and reduce the reliability of the battery cell. In Comparative Example 5, the area of ​​particles with a particle size R1 that satisfies R1 ≥ 1000nm accounts for too large a proportion, the positive electrode film layer rebounds seriously, and the sealing area of ​​the battery cell is extremely prone to failure.

[0373] See Figure 1 The specific description of the battery cells in the embodiments of the present application is as follows:

[0374] The battery cell comprises a laminated core and a shell, wherein the laminated core is accommodated in the shell, and the shell is a soft-pack material; the shell comprises a first sealing area, and the first sealing area is arranged at least at one end of the laminated core extending in the width direction; the first sealing area comprises a double-folded edge structure extending in the length direction, and a packaging glue is arranged on the double-folded edge structure, and the packaging glue is continuously arranged in the length direction and fixes the double-folded edge structure; the laminated core comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the positive electrode sheet comprises a positive electrode current collector and a current collector arranged in the A positive electrode film layer on at least one side of a positive electrode current collector, the positive electrode film layer comprising lithium-containing transition metal phosphate particles, at least part of the surface of the lithium-containing transition metal phosphate particles being provided with a carbon material; based on the total area of ​​particles in a cross-section of the positive electrode film layer along the thickness direction of the positive electrode sheet, the area of ​​particles having a particle size R1 satisfying R1 ≥ 1000 nm accounts for 12%-50%; the thickness of a single side of the positive electrode film layer is denoted as H, and H is 70 μm-120 μm; when the battery cell is in a fully discharged state, the compaction density of the positive electrode sheet is 2.3 g / cm 3 -2.6g / cm 3 The electrolyte includes a solvent, and the solvent includes dimethyl carbonate (DMC); based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate is 18%-32%.

[0375] In this way, the capacity and energy density of the battery cell are improved through the laminated cell structure, the larger thickness of the positive electrode film layer, the high pressure density and the large area proportion of the R1 particle size particles. The cooperation of the double folded edge structure and the packaging glue in the first sealing area can greatly improve the mechanical strength of the sealing area and reduce the possibility of seal failure due to internal pressure during long cycles of the battery cell.

[0376] As can be seen from Examples 1, 8, 9, 11 and Example 10, based on the total area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the positive electrode plate, when the proportion of the area of the particles with a particle size R1 satisfying R1≥1000nm is 12%-40%, the bounce rate is further reduced, which is beneficial to improving the long-term reliability of the battery cell.

[0377] Table 2

[0378]

[0379] As can be seen from Examples 1, 8-11, based on the total area of the particles 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 the particles with a particle size R1 satisfying R1≥1000nm, the median L R1A50 is 0.6-0.8; when the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000nm is less than or equal to 5%, the battery cell has a smaller bounce rate and gas generation rate. In the cumulative area distribution curve of the sphericity of the particles with a particle size R1 satisfying R1≥1000nm, the median L R1A50 is 0.67-0.75; when the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000nm is in the range of 0.2%-2%, it helps to further improve the long-cycle stability of the battery.

[0380] Table 3

[0381]

[0382] As can be seen from Examples 8, 11, 12, when the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000nm is in the range of 0.2%-0.9%, it helps to further reduce the stress concentration, reduce the bounce of the positive electrode film layer, and thus improve the long-cycle reliability of the battery.

[0383] Table 4

[0384]

[0385] As can be seen from the comparison between Example 1 and Example 13, the conductive agent includes carbon nanotubes, and the mass content C1 of the carbon nanotubes satisfies: 0<C1≤2.5%, which is beneficial to reducing the bounce of the positive electrode film layer during cycling, and thus improving the long-term reliability of the battery.

[0386] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical idea and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that: The battery comprises a laminated core and a shell, wherein the laminated core is accommodated in the shell, and the shell is made of a soft packaging material; the shell comprises a first sealing area, which is arranged at at least one end of the laminated core extending in the width direction; the first sealing area comprises a double-folded edge structure extending in the length direction, and the double-folded edge structure is provided with a packaging glue, and the packaging glue is continuously provided along the length direction to fix the double-folded edge structure; The laminated battery core includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet 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, and at least a portion of the surface of the lithium-containing transition metal phosphate particles is provided with a carbon material. Based on the total area of ​​particles in the cross section of the positive electrode film along the thickness direction of the positive electrode sheet, the area of ​​particles with a particle size R1 satisfying R1 ≥ 1000 nm accounts for 12%-50%; The thickness of the positive electrode film layer on one side is denoted as H, and H is 70 μm-120 μm; The battery cell is in a fully charged state, and the compaction density of the positive electrode sheet is 2.3 g / cm 3 -2.6g / cm 3 ; The electrolyte includes a solvent, and the solvent includes dimethyl carbonate (DMC); based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate is 18%-32%; In the cross section of the positive electrode film along the thickness direction of the electrode sheet, the distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is 0.2%-2%; In the cross section of the positive electrode film along the thickness direction of the electrode sheet, the median of the sphericity L in the cumulative distribution curve of the sphericity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is R1A50 0.6-0.8; In the cumulative distribution curve of the graphitization degree C of the positive electrode film obtained in the surface scanning mode of the laser microconfocal Raman spectrometer, the median value of the graphitization degree C 50 The graphitization degree C is 0.95-1.20, and the graphitization degree C value is 1 G / I D , where I G Indicates that the Raman spectrum is at 1580±100cm -1 The G peak intensity at I D Indicates that the Raman spectrum is at 1350±100cm -1 D peak intensity at ; In the cumulative distribution curve of the coating value B obtained by the laser microconfocal Raman spectrometer in the surface scanning mode of the positive electrode film layer, the median of the coating value B 50 is 0.30-0.60, where the coating value B is I P / I D , where I P Indicates that the Raman spectrum is at 948±100cm -1 The P peak intensity at I D Indicates that the Raman spectrum is at 1350±100cm -1 The D peak intensity at .

2. The battery cell according to claim 1, wherein: H is 90μm-120μm.

3. The battery cell according to claim 1, wherein: H is 100μm-120μm.

4. The battery cell according to claim 1, wherein: The shell includes at least one second sealing area, which is arranged at at least one end of the laminated battery core along the length direction of the shell, and the second sealing area is arranged on the tab side of the laminated battery core.

5. The battery cell according to claim 1, characterized in that A plurality of rubber rings surrounding along the width direction are provided on the outer periphery of the laminated battery core, and the rubber rings surrounding along the width direction are arranged at intervals along the length direction.

6. The battery cell according to claim 1, characterized in that Based on the total area of ​​particles in the cross section of the positive electrode film layer along the thickness direction of the positive electrode sheet, the area of ​​particles with a particle size R1 satisfying R1 ≥ 1000 nm accounts for 12%-37%.

7. The battery cell according to claim 1, characterized in that In the cross section of the positive electrode film along the thickness direction of the electrode sheet, the median of the sphericity L in the cumulative distribution curve of the sphericity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is R1A50 It is 0.65-0.

75.

8. The battery cell according to claim 1, wherein: In the cross section of the positive electrode film along the thickness direction of the electrode sheet, the median of the sphericity L in the cumulative distribution curve of the sphericity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is R1A50 It is 0.67-0.

75.

9. The battery cell according to claim 1, characterized in that In a cross section of the positive electrode film layer along the thickness direction of the electrode sheet, the distribution uniformity of particles with a particle size R1 satisfying R1 ≥ 1000 nm is 0.2%-0.9%.

10. The battery cell according to claim 1, characterized in that The electrolyte further satisfies at least one of the following conditions: (1) The solvent in the electrolyte further comprises one or both of ethyl methyl carbonate (EMC) and ethylene carbonate (EC); (2) Based on the total mass of the electrolyte, the mass proportion of ethyl methyl carbonate (EMC) is 39%-49%; (3) Based on the total mass of the electrolyte, the mass proportion of ethylene carbonate (EC) is 13%-22%; (4) Based on the total mass of the electrolyte, the total mass of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) accounts for 52% to 71%; (5) The electrolyte includes an electrolyte salt, the electrolyte salt includes lithium hexafluorophosphate (LiPF6), and the concentration of lithium hexafluorophosphate in the electrolyte is 0.9 mol / L to 1.2 mol / L; (6) Based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate is 18%-26%.

11. The battery cell according to claim 1, wherein The lithium-containing transition metal phosphate particles include iron element, and the iron dissolution rate of the positive electrode film layer is 658ppm-1921ppm.

12. The battery cell according to claim 11, characterized in that The iron dissolution rate of the positive electrode film layer is 658ppm-1485ppm.

13. The battery cell according to claim 1, characterized in that 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 total area of ​​the agglomerated region of the conductive agent accounts for 0.5%-2.5%.

14. The battery cell according to claim 13, characterized in that Based on the total area of ​​the cross section of the positive electrode film layer along the thickness direction of the electrode sheet, the total area of ​​the agglomerated region of the conductive agent accounts for 0.5%-1.7%.

15. The battery cell according to claim 14, 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.

16. The battery cell according to claim 15, characterized in that The conductive agent further includes conductive carbon black.

17. The battery cell according to claim 16, characterized in that The agglomerated regions of the conductive agent include carbon nanotubes and conductive carbon black.

18. The battery cell according to claim 17, 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%.

19. 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 rubber HNBR.

20. The battery cell according to claim 19, characterized in that Based on the mass of the positive electrode film layer, the mass content of the dispersant is 0.5%-2%.

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, characterized in that The battery cell also includes a separator arranged between the positive electrode plate and the negative electrode plate, the separator includes a base film and a ceramic layer arranged on both sides of the base film and an adhesive layer arranged on at least one side of the ceramic layer away from the base film, the adhesive layer is a continuous layer with a porous structure, and the adhesive layer includes a vinylidene fluoride polymer.

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

24. The battery cell according to claim 1, characterized in that The lithium-containing transition metal phosphate particles in the positive electrode film layer include 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, and Br, 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.

1.

25. 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 500ppm-8000ppm.

26. The battery cell according to claim 25, characterized in that 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 1000ppm-3000ppm.

27. 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 500ppm-5000ppm.

28. The battery cell according to claim 27, characterized in that 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 500ppm-3000ppm.

29. The battery cell according to claim 1, characterized in that The soft package material comprises an aluminum-plastic composite film.

30. The battery cell according to claim 1, wherein The soft package material 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.

31. The battery cell according to claim 1, characterized in that At least one of the laminated battery cells is accommodated in the shell, the size of the shell in the length direction is L0, the size of the shell in the width direction is W0, and the size of the shell in the thickness direction is H0, wherein 450mm≤L0≤1300mm, 100mm≤W0≤150mm; 14mm≤H0≤22mm.

32. The battery cell according to claim 31, characterized in that The length dimension L0 of the shell satisfies: 450 mm ≤ L0 ≤ 650 mm.

33. The battery cell according to claim 31, characterized in that The length dimension L0 of the shell satisfies: 900 mm ≤ L0 ≤ 1300 mm.

34. The battery cell according to claim 1, characterized in that At 25° C., the capacity of the battery cell is 105Ah-300Ah.

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

36. A battery device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 35.

37. An electrical device, characterized in that: The electrical device comprises the battery device as claimed in claim 36, and the battery device is used to provide electrical energy.

38. An energy storage device, characterized in that: The energy storage device comprises the battery device as claimed in claim 36, wherein the battery device is used to store electrical energy.

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