Battery cell, battery apparatus and energy storage apparatus

Abstract

A battery cell, a battery apparatus and an energy storage apparatus. The battery cell comprises an electrode assembly and an electrolyte. The electrode assembly comprises a positive electrode sheet, a separator, and a negative electrode sheet. The negative electrode sheet comprises a negative current collector and a negative film layer arranged on at least one side of the negative current collector. The positive electrode sheet comprises a positive current collector and a positive film layer arranged on at least one side of the positive current collector. The total coating area of the positive film layer included in the battery cell is greater than or equal to 11 m2, and the compacted density of the positive film layer is greater than or equal to 2.5 g / cm3. The electrolyte comprises vinylene carbonate; on the basis of the total mass of the electrolyte, the mass fraction of vinylene carbonate is 0.1%-8%.

Description

Battery cells, battery devices and energy storage devices

[0001] Cross-references

[0002] This application incorporates, by reference, patent application No. PCT / CN2025 / 085927, filed on March 28, 2025, entitled “Lithium-ion secondary battery, battery device, power device, preparation of positive electrode active material”, and patent application No. PCT / CN2025 / 140531, filed on December 5, 2025, entitled “Battery cell, battery device and energy storage device”. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a battery cell, battery device and energy storage device. Background Technology

[0004] Energy conservation and emission reduction are key to sustainable social development. Rechargeable batteries, with their ability to store or release energy as needed, are widely used in various energy storage systems and are an important component in promoting energy transition and sustainable development. For the new energy industry, battery technology is a crucial factor in its development.

[0005] With increasing market demands for higher energy storage capacity and longer lifespan in energy storage batteries, higher requirements are being placed on battery capacity and cycle performance. However, existing technologies struggle to simultaneously improve these performance characteristics, making the challenge of achieving a balance between these performance goals a pressing technical problem in this field. Summary of the Invention

[0006] This application aims to at least solve one of the technical problems existing in the background art. To this end, one object of this application is to provide a battery cell with high capacity and good cycle performance.

[0007] This application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The total coating area of ​​the positive electrode film layer included in the battery cell is greater than or equal to 11 m². 2 The compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3 The electrolyte includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.1%-8% based on the total mass of the electrolyte.

[0008] In this embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is greater than or equal to 11m².2 Furthermore, the compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3 This can effectively improve the capacity of a single battery cell. However, the applicant found that when the coating area of ​​the positive electrode film is within the aforementioned range, the size of the positive electrode sheet is relatively large, which easily leads to uneven current distribution in the positive electrode sheet. In high current density areas, the local reaction of the positive electrode film is more intense, and the local thickness rebound is greater, generating greater local stress. This, in turn, squeezes the negative electrode, causing the negative electrode SEI film to rupture, affecting the cycle performance of the battery cell. In addition, when the compaction density of the positive electrode film is within the aforementioned range, the stress in high current density areas further increases after the overall thickness rebound of the positive electrode film increases, increasing the probability of SEI film rupture and further deteriorating the cycle performance of the battery cell. In this application, the embodiment further adds vinylene carbonate to the electrolyte, which helps to form a dense and stable SEI film on the negative electrode side, improves the damage to the negative electrode SEI film caused by excessive local stress, and improves the cycle performance of the battery cell. However, the applicant further found that as the content of vinylene carbonate increases, the thickness of the negative electrode SEI film increases, the interfacial impedance increases, thereby affecting the energy conversion efficiency of the battery cell. In this embodiment, the total mass of the electrolyte is controlled, and the mass ratio of vinylene carbonate is 0.1%-8%, which helps to balance the cycle performance and energy conversion efficiency of large-coated, high-density battery cells.

[0009] In any embodiment, the mass percentage of vinylene carbonate is 0.5%-8% based on the total mass of the electrolyte.

[0010] In any embodiment, the mass percentage of vinylene carbonate is 0.5%-5% based on the total mass of the electrolyte.

[0011] In any embodiment, the mass percentage of vinylene carbonate is further within the above range, which helps to form an SEI film of suitable thickness and further improve the energy conversion efficiency of the battery cell.

[0012] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0013] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -120m 2 .

[0014] In a single battery cell, if the total coating area of ​​the positive electrode film is further within the aforementioned range, it helps to improve the uniformity of current distribution in the positive electrode film, improve the consistency of the reaction degree of the positive electrode film, alleviate the problem of excessive local stress, reduce the probability of SEI film rupture, and further improve the cycle performance of the battery cell.

[0015] In any embodiment, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -3g / cm 3 .

[0016] In any embodiment, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm 3 .

[0017] The compaction density of the positive electrode film is within the above range, which helps to reduce the rebound of the positive electrode film, reduce the stress in the high current region, and further improve the cycle performance of the battery cell.

[0018] In any embodiment, the density of any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.45g / 1540.25mm 2 .

[0019] Increasing the surface density of the positive electrode film helps to improve the loading of active materials in the battery cell, thereby increasing the battery cell capacity. However, the applicant has found that in large-area, high-density positive electrode sheets, the local reaction rate and lithium-ion efficiency rate in the current density region increase, which easily leads to local concentration polarization. Furthermore, with the increase in the surface density of the positive electrode film, the lithium-ion migration path increases, and the lithium-ion concentration near the current collector side is lower, further exacerbating local concentration polarization and thus affecting the cycle performance of the battery cell. In the embodiments of this application, the density of any side of the positive electrode film is within the above-mentioned range, and the total coating area of ​​the positive electrode film contained in the battery cell is greater than or equal to 11m². 2 The compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3 The electrolyte includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.1%-8% based on the total mass of the electrolyte, which combines high capacity, good cycle performance and energy conversion efficiency.

[0020] In any embodiment, the density of any side of the positive electrode film is 0.35 g / 1540.25 mm. 2 -0.4g / 1540.25mm 2 .

[0021] In any embodiment, the thickness of the positive current collector is 8μm-15μm.

[0022] The thickness of the positive electrode current collector within the above range helps to reduce the resistance of the positive electrode current collector, improve the uniformity of current distribution within the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0023] In any embodiment, the first direction, the second direction, and the thickness direction of the positive electrode sheet are perpendicular to each other; the positive electrode sheet includes a positive electrode tab, which is disposed at one end of the positive current collector extending along the first direction; in the second direction, the size of the positive current collector in the positive electrode sheet is L1, and the total size of the positive electrode tab near the end of the positive current collector is L2, where 5% ≤ L2 / L1 × 100% ≤ 25%.

[0024] In any implementation, the first direction is the length direction of the positive electrode sheet, and the second direction is the width direction of the positive electrode sheet.

[0025] In any implementation, the first direction is the width direction of the positive electrode sheet, and the second direction is the length direction of the positive electrode sheet.

[0026] The second direction, which is the length direction of the positive electrode sheet, helps to shorten the diffusion path of current within the positive electrode sheet, improve the uniformity of current distribution within the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0027] If L2 / L1×100% is within the above range, it means that the positive electrode tab has a larger size ratio along the second direction, which helps to improve the uniformity of current distribution in the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0028] In any embodiment, in the second direction, the dimension of the end of the single positive electrode tab near the current collector is 40mm-80mm.

[0029] The size of a single positive electrode tab within the above range helps to improve the uniformity of current distribution within the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0030] In any embodiment, the number of layers of the positive electrode sheet is N1, and the number of layers of the positive electrode sheet with the positive electrode tab is N2, where 0.5 ≤ N2 / N1.

[0031] In any embodiment, the number of layers of the positive electrode sheet is N1, and the number of layers of the positive electrode sheet with the positive electrode tab is N2, where 0.5≤N2 / N1≤1.

[0032] When N2 / N1 is within the above range, it indicates that there are more positive electrode tabs in the battery cell, which helps to improve the uniformity of current distribution in the positive electrode, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0033] In any embodiment, the number of layers of the positive electrode sheet is N1, and the number of layers of the positive electrode sheet with the positive electrode tab is N2, where 0.75≤N2 / N1≤1.

[0034] In any embodiment, the electrolyte comprises a linear carbonate solvent, which further comprises one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0035] The applicant discovered that the high current density of the positive electrode film results in a high delithiation rate, while the corresponding negative electrode film exhibits a high lithium insertion rate. This leads to localized lithium plating in the negative electrode film, affecting the cycle performance of the battery cell. Linear carbonates have low viscosity, and the electrolyte includes dimethyl carbonate and other types of linear carbonates, which helps to further reduce viscosity, increase the lithium-ion diffusion rate, improve localized lithium plating, and alleviate concentration polarization, thereby further improving the cycle performance of the battery cell.

[0036] In any embodiment, the mass percentage of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

[0037] In any embodiment, the mass percentage of dimethyl carbonate is 35%-50% based on the total mass of the electrolyte.

[0038] Compared to other linear carbonates, dimethyl carbonate has a lower viscosity, and its mass percentage is further within the above range, which helps to further reduce electrolyte viscosity, increase lithium-ion migration rate, help alleviate local lithium plating and concentration polarization, and thus further improve the cycle performance of battery cells.

[0039] In any embodiment, the linear carbonate solvent includes ethyl methyl carbonate, and the mass percentage of ethyl methyl carbonate is 10%-50% based on the total mass of the electrolyte.

[0040] In any embodiment, the linear carbonate solvent includes ethyl methyl carbonate, and the ethyl methyl carbonate accounts for 25%-30% of the total mass of the electrolyte.

[0041] In any embodiment, the electrolyte comprises a cyclic carbonate solvent, which includes one or more of ethylene carbonate and propylene carbonate.

[0042] Cyclic carbonates have a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the conductivity of the electrolyte and helping to alleviate concentration polarization, thus further improving the cycle performance of the battery cells.

[0043] In any embodiment, the cyclic carbonate solvent includes ethylene carbonate, and the mass percentage of ethylene carbonate is 10%-40% based on the total mass of the electrolyte.

[0044] In any embodiment, the cyclic carbonate solvent includes propylene carbonate, and the mass percentage of propylene carbonate is 0.5%-10% based on the total mass of the electrolyte.

[0045] Propylene carbonate has a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the electrolyte conductivity. In the embodiments of this application, the mass percentage of propylene carbonate is within the above-mentioned range, which helps to improve the cycle performance of the battery cell.

[0046] In any embodiment, the electrolyte includes additives, including the ethylene carbonate and fluoroethylene carbonate.

[0047] In this embodiment, the addition of the above-mentioned ethylene carbonate and fluoroethylene carbonate to the electrolyte helps to further improve the stability of the SEI film, alleviate the rupture phenomenon of the SEI film under local stress, and further improve the cycle performance of the battery cell.

[0048] In any embodiment, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 0.05%-5% of the total mass of the electrolyte.

[0049] In any embodiment, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 2%-3% of the total mass of the electrolyte.

[0050] When the mass percentage of fluoroethylene carbonate is within the above range, it helps to form an SEI film of suitable thickness, taking into account both the stability of the SEI film and the interfacial impedance, thereby balancing the cycle performance and energy conversion efficiency of the battery cell.

[0051] In any embodiment, the linear carbonate solvent includes ethyl methyl carbonate, and the additive includes fluoroethylene carbonate.

[0052] The applicant discovered that the combined use of ethyl methyl carbonate and fluoroethylene carbonate helps improve the cycle performance of battery cells.

[0053] In any embodiment, the cyclic carbonate solvent includes propylene carbonate, and the additive includes vinylene carbonate.

[0054] Propylene carbonate readily undergoes a co-intercalation reaction at the negative electrode, thus affecting the cycle performance of the battery cell. The applicant discovered that using propylene carbonate in combination with ethylene carbonate can effectively mitigate the co-intercalation reaction of propylene carbonate, further improving the cycle performance of the battery cell.

[0055] In any embodiment, the electrolyte comprises an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0056] In any embodiment, the electrolyte solution comprises lithium bisfluorosulfonylimide, and the mass percentage of lithium bisfluorosulfonylimide is 1%-7% based on the total mass of the electrolyte solution.

[0057] Lithium difluorosulfonylimide helps form a dense and stable SEI film on the negative electrode side, thereby helping to improve the SEI film rupture caused by excessive local stress and further improving the cycle performance of the battery cell.

[0058] In any embodiment, the electrolyte solution comprises lithium bisfluorosulfonylimide, and the mass percentage of lithium bisfluorosulfonylimide is 2%-7% based on the total mass of the electrolyte solution.

[0059] In any embodiment, the electrolyte comprises lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate is 2%-10% based on the total mass of the electrolyte.

[0060] In any embodiment, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 0.5-5.5.

[0061] As the content of lithium difluorosulfonylimide increases, the SEI film becomes thicker. When the mass ratio of lithium hexafluorophosphate and lithium difluorosulfonylimide is within the above range, the electrolyte has a suitable active lithium concentration and the SEI film has a suitable thickness, thus balancing the conductivity of the electrolyte and the interfacial impedance on the negative electrode side, further improving the cycle performance and energy conversion efficiency of the battery cell.

[0062] In any embodiment, the positive electrode film layer includes a positive electrode active material, which includes lithium transition metal phosphate particles with carbon material disposed on at least a portion of their surface.

[0063] Lithium-containing transition metal phosphates, as positive electrode active materials, have the advantage of good structural stability, which helps to further improve the cycle performance of battery cells.

[0064] In any embodiment, based on the total area of ​​particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is 8.0%-20.0%.

[0065] If the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is within the above range, it indicates that there are more large-sized particles in the positive electrode film layer, which helps to improve the compaction density of the positive electrode film layer and increase the capacity of the battery cell.

[0066] In any embodiment, based on the total area of ​​particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is 10.0%-20.0%.

[0067] In any embodiment, based on the total area of ​​particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a particle size R2 satisfying 200nm≤R2<1000nm is 15.0%-25.0%.

[0068] Particles with a particle size R2 satisfying 1000nm≤R2<200nm represent smaller positive electrode active materials in the positive electrode film layer. Their area proportion is within the above range, which helps to further improve the compaction density of the positive electrode film layer through particle gradation, and further improve the capacity of the battery cell.

[0069] In any embodiment, based on the total area of ​​particles in the cross section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a particle size R2 satisfying 200nm≤R2<1000nm is 16%-20%.

[0070] The median C of the graphitization degree of the positive electrode film 50 Within the aforementioned range, it helps to improve the electronic conductivity of the positive electrode film, enhance the uniformity of current distribution in the positive electrode sheet, thereby mitigating the problem of excessive local stress and alleviating concentration polarization and local lithium plating, further improving the cycle performance of the battery cell. Furthermore, it also helps to reduce the internal resistance of the positive electrode sheet, improving the energy conversion efficiency of the battery cell.

[0071] In any embodiment, the median C of the graphitization degree C value in the cumulative distribution curve of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The value ranges from 0.97 to 1.13.

[0072] In any embodiment, the positive electrode active material includes titanium, and the mass percentage of titanium is 2000ppm-6000ppm based on the total mass of the positive electrode active material.

[0073] The inclusion of titanium in the positive electrode active material, and its mass percentage within the aforementioned range, helps to improve the structural stability of the positive electrode active material and further enhance the cycle performance of the battery cell.

[0074] In any embodiment, the positive electrode active material includes one or more of lithium iron phosphate, lithium iron phosphate doped and modified materials, and lithium iron phosphate coated and modified materials.

[0075] In any embodiment, the positive electrode active material comprises the components shown in Formula I:

[0076] Li m Fe x P y O j Q q Formula I,

[0077] 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, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0078] In any embodiment, the negative electrode film layer includes a negative electrode active material, the negative electrode active material including graphite, the negative electrode graphite including graphite bulk particles and carbon material disposed on at least a portion of the surface of the graphite bulk particles.

[0079] In any embodiment, the graphite bulk particles include secondary particles.

[0080] The graphite bulk includes secondary particles, which helps increase the number of lithium-ion insertion sites, improve the kinetic performance of the negative electrode, alleviate local lithium plating, and further improve the cycle performance of the battery cell.

[0081] In any embodiment, the carbon material comprises amorphous carbon.

[0082] Amorphous carbon is approximately amorphous, with a disordered internal arrangement exhibiting long-range randomness and rich in microporous structure. This helps increase the number of lithium-ion insertion faces and electrolyte wetting ability, thereby accelerating the lithium-ion insertion rate. This, in turn, helps improve the lithium insertion rate of the negative electrode, alleviates the local lithium plating phenomenon of the negative electrode, and further improves the cycle performance of the battery cell.

[0083] In any embodiment, the Dv50 of the negative electrode active material is 9μm-18μm.

[0084] Within the aforementioned range, the Dv50 of the negative electrode active material helps to increase the number of lithium-ion insertion sites, improve the kinetic performance of the negative electrode, alleviate local lithium plating, and further improve the cycle performance of the battery cell.

[0085] In any embodiment, the Dv90 of the negative electrode active material is 21μm-35μm.

[0086] In any embodiment, the Dv99 of the negative electrode active material is 27μm-65μm.

[0087] In any embodiment, the Dv99 of the negative electrode active material is 33μm-41μm.

[0088] In any embodiment, the separator includes a base film and a coating disposed on at least one side of the base film. The coating includes ceramic particles and a binder. The ceramic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0089] Ceramic-coated separators exhibit higher mechanical stability and compression resistance during cycling. On the one hand, they help reduce the pressure of local high rebound of the positive electrode on the negative electrode film and improve its damage to the SEI film. On the other hand, they can maintain good thickness stability under local high stress, thereby further improving the cycle performance of the battery cell.

[0090] In any embodiment, the adhesive includes one or more of polyvinylidene fluoride and polymethyl methacrylate.

[0091] In any embodiment, the thickness of the base film is 3μm-9μm.

[0092] In any embodiment, the thickness of the base film is 4μm-7μm.

[0093] In any embodiment, the thickness of the coating on one side is 3μm-8μm.

[0094] In any embodiment, the porosity of the isolation membrane is 20%-70%.

[0095] The porosity of the separator within the above range helps to reduce its resistance to lithium-ion diffusion, increase the lithium-ion migration rate, further alleviate concentration polarization, and further improve the cycle performance of the battery cell.

[0096] In any embodiment, the porosity of the isolation membrane is 20%-50%.

[0097] In any embodiment, the battery cell further includes a housing and an end cap assembly. The housing has a housing opening, the electrode assembly is housed within the housing, and the end cap assembly covers the housing opening. The end cap assembly includes a cover plate and electrode terminals. The cover plate has mounting holes, and the electrode terminals include a first connecting portion and a second connecting portion connected together. The first connecting portion is located on the side of the cover plate facing the electrode assembly and is electrically connected to the electrode assembly. The second connecting portion passes through the mounting holes and protrudes from the surface of the cover plate on the side away from the electrode assembly. The cross-sectional area of ​​the first connecting portion perpendicular to the thickness direction of the cover plate is larger than the area of ​​the mounting hole.

[0098] This helps to improve the connection strength and structural stability between the electrode terminals and the cover plate, making it less prone to cracking or loosening under the high expansion force in the later stages of battery cell cycling, thereby extending the cycle life of the battery cell.

[0099] In any embodiment, the capacity of the battery cell is 400Ah-3000Ah.

[0100] A second aspect of this application provides a battery device, which includes the battery cell provided in the first aspect.

[0101] A third aspect of this application provides an energy storage device, which includes the battery device provided in the second aspect, the battery device being used to store electrical energy.

[0102] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0103] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0104] Figure 1 is a schematic diagram of a battery cell provided in some embodiments of this application;

[0105] Figure 2 is an exploded view of a single battery cell provided in some embodiments of this application;

[0106] Figure 3 is a schematic diagram of a battery module provided in some embodiments of this application;

[0107] Figure 4 is a schematic diagram of a battery pack provided in some embodiments of this application;

[0108] Figure 5 is an exploded view of a battery pack provided in some embodiments of this application.

[0109] Explanation of reference numerals in the attached figures:

[0110] The reference numerals in the attached diagram are explained as follows: 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate. Detailed Implementation

[0111] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and energy storage device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0112] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0113] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0114] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0115] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0116] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0117] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0118] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0119] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0120] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0121] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0122] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, and the embodiments of this application are not limited to this. Figure 1 shows a cuboid battery cell 5 as an example.

[0123] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0124] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0125] In some embodiments, individual battery cells can be assembled into a battery module. The number of battery cells in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As shown in Figure 2, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0126] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0127] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0128] Figures 3 and 4 are schematic diagrams of a battery pack 1 as an example. As shown in Figures 3 and 4, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 and forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0129] The battery provided in this application embodiment may include a lithium-ion battery.

[0130] A single battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited in this regard.

[0131] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0132] In some embodiments, as shown in FIG5, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0133] Electrode assemblies typically include positive and negative electrodes. The negative electrode is the electrode that absorbs or lithiates lithium ions during battery charging and releases or delithiates lithium during discharge. The positive electrode is the electrode that releases or delithiates lithium ions during battery charging and absorbs or lithiates lithium during discharge.

[0134] With the increasing market demand, the requirements for energy storage battery capacity are constantly rising. Increasing the coating area and compaction density of the positive electrode film in a single battery cell helps to improve the loading of positive electrode active materials, thereby increasing the capacity of the battery cell. However, the applicant has found that the cycle performance of battery cells with large coating areas and high compaction densities deteriorates significantly. Therefore, how to balance the capacity and cycle performance of battery cells has become an urgent technical problem to be solved.

[0135] Therefore, in a first aspect, this application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The total coating area of ​​the positive electrode film layer included in the battery cell is greater than or equal to 11 m². 2 The compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3 The electrolyte includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.1%-8% based on the total mass of the electrolyte.

[0136] In this embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is greater than or equal to 11m². 2 Furthermore, the compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3This can effectively improve the capacity of a single battery cell. However, the applicant found that when the coating area of ​​the positive electrode film is within the aforementioned range, the size of the positive electrode sheet is relatively large, which easily leads to uneven current distribution in the positive electrode sheet. In high current density areas, the local reaction of the positive electrode film is more intense, and the local thickness rebound is greater, generating greater local stress. This, in turn, squeezes the negative electrode, causing the negative electrode SEI film to rupture, affecting the cycle performance of the battery cell. In addition, when the compaction density of the positive electrode film is within the aforementioned range, the stress in high current density areas further increases after the overall thickness rebound of the positive electrode film increases, increasing the probability of SEI film rupture and further deteriorating the cycle performance of the battery cell. In this application, the embodiment further adds vinylene carbonate to the electrolyte, which helps to form a dense and stable SEI film on the negative electrode side, improves the damage to the negative electrode SEI film caused by excessive local stress, and improves the cycle performance of the battery cell. However, the applicant further found that as the content of vinylene carbonate increases, the thickness of the negative electrode SEI film increases, the interfacial impedance increases, thereby affecting the energy conversion efficiency of the battery cell. In this embodiment, the total mass of the electrolyte is controlled, and the mass ratio of vinylene carbonate is 0.1%-8%, which helps to balance the cycle performance and energy conversion efficiency of large-coated, high-density battery cells.

[0137] In this application, the total coating area of ​​the positive electrode film layer contained in the battery cell refers to the sum of the areas of all positive current collectors in the battery cell covered by the positive electrode film layer; wherein, for a double-sided coated positive electrode sheet, its coating area is the sum of the areas of both sides of the positive current collector covered by the positive electrode film layer; for a battery cell including multiple electrode components, the total coating area of ​​the positive film layer is the sum of the areas of all positive current collectors in the multiple electrode components covered by the positive electrode film layer.

[0138] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell can be 11m². 2 12m 2 13m 2 14m 2 15m 2 16m 2 17m 2 18m 2 19m 2 19.4m 2 20m 2 21m 2 22m 2 23m 2 24m 2 25m 2 26m 2 27m 2 28m 2 29m 2 30m 232m 2 34m 2 36m 2 38m 2 40m 2 42m 2 44m 2 46m 2 48m 2 50m 2 55m 2 60m 2 65m 2 70m 2 75m 2 80m 2 85m 2 90m 2 95m 2 100m 2 105m 2 110m 2 115m 2 120m 2 125m 2 130m 2 135m 2 140m 2 145m 2 150m 2 Or a range of values ​​between any two.

[0139] In this application, the compaction density of the positive electrode sheet can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven and left to stand for 2 hours. Once the battery temperature is maintained at 25°C, the individual battery cells are discharged at a constant power of 0.5P until the voltage of the individual cells reaches 2.5V, and then left to stand for 30 minutes. The battery is then disassembled to obtain the positive electrode sheet. The residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and it is cut into small circular pieces with an area of ​​S, yielding a mass of W1. The thickness T1 of the positive electrode sheet is measured using a micrometer. The positive electrode film layer of the weighed electrode sheet is then wiped off, and the mass of the current collector is weighed and recorded as W2. The thickness T2 of the current collector is measured using a micrometer. The compaction density of the positive electrode sheet is then calculated as PD = (W1 - W2) / [(T1 - T2) × S], in g / cm³. 3 .

[0140] In some embodiments, the compaction density of the positive electrode film can be 2.5 g / cm³. 3 2.52g / cm 3 2.54 g / cm 3 2.56 g / cm 3 2.58g / cm3 2.6g / cm 3 2.62 g / cm 3 2.64 g / cm 3 2.66 g / cm 3 2.68g / cm 3 2.7g / cm 3 2.72 g / cm 3 2.74 g / cm 3 2.76 g / cm 3 2.78g / cm 3 2.8g / cm 3 2.82 g / cm 3 2.84 g / cm 3 2.86 g / cm 3 2.88g / cm 3 2.9g / cm 3 2.92g / cm 3 2.94 g / cm 3 2.96 g / cm 3 2.98g / cm 3 3g / cm 3 Or the range of values ​​between any two.

[0141] In this application, the types and mass percentages of each component in the electrolyte can be obtained by detecting the electrolyte using any method known to those skilled in the art. For example, the composition and content of the electrolyte can be characterized using one or more of the following methods: gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectrometry (GC-MS). For example, referring to GB / T-9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" and / or GB / T6041-2002 "General Rules for Mass Spectrometry Analysis Methods", gas chromatography and mass spectrometry are coupled. After gas chromatography separates the components in the sample, the components are broken into ion fragments in mass spectrometry and separated according to mass-to-charge ratio (m / z) to form specific mass spectra, obtaining qualitative analysis of each organic component in the electrolyte. Then, the organic components in the electrolyte are separated in the chromatographic column, and detection signal spectra of each component are generated. Component qualitative analysis is performed using retention time, and quantitative analysis is performed by standardizing and correcting peak area, obtaining quantitative analysis of the organic components in the electrolyte. Referring to JY / T-020, the types of anions of electrolyte salts in the electrolyte are detected by ion chromatography and quantitatively analyzed. Referring to JY / T0578-2020, nuclear magnetic resonance spectroscopy (NMR) is used to obtain qualitative and quantitative analysis of the components in the electrolyte.

[0142] The electrolyte referred to in this article can be either fresh electrolyte or electrolyte obtained from the disassembly of a battery cell. The electrolyte obtained from the disassembly of a battery cell can be either the free electrolyte in the battery casing or the electrolyte obtained by centrifugation from the electrodes.

[0143] In some embodiments, based on the total mass of the electrolyte, the mass percentage of vinylene carbonate can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.1%, 4.3%, 4.5%, 4.7%, 4.9%, 5.1%, 5.3%, 5.5%, 5.7%, 5.9%, 6.1%, 6.3%, 6.5%, 6.7%, 6.9%, 7%, 7.1%, 7.3%, 7.5%, 7.7%, 7.9%, 8%, or any range between the two.

[0144] In some embodiments, the mass percentage of vinylene carbonate is 0.5%-8% based on the total mass of the electrolyte.

[0145] In some embodiments, the mass percentage of vinylene carbonate is 0.5%-5% based on the total mass of the electrolyte.

[0146] In some embodiments, the mass percentage of vinylene carbonate is further within the above range, which helps to form an SEI film of suitable thickness and further improve the energy conversion efficiency of the battery cell.

[0147] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0148] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -120m 2 .

[0149] In a single battery cell, if the total coating area of ​​the positive electrode film is further within the aforementioned range, it helps to improve the uniformity of current distribution in the positive electrode film, improve the consistency of the reaction degree of the positive electrode film, alleviate the problem of excessive local stress, reduce the probability of SEI film rupture, and further improve the cycle performance of the battery cell.

[0150] In some embodiments, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -3g / cm 3 .

[0151] In some embodiments, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm 3 .

[0152] The compaction density of the positive electrode film is within the above range, which helps to reduce the rebound of the positive electrode film, reduce the stress in the high current region, and further improve the cycle performance of the battery cell.

[0153] In some embodiments, the density of any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.45g / 1540.25mm 2 .

[0154] In this application, the density of any side of the positive electrode film layer refers to the areal density of a single-sided positive electrode film layer disposed on any side of the positive electrode current collector, which can be tested using methods and instruments known in the art. As an example, take a single-sided coated and cold-pressed positive electrode sheet (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1. Then wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the current collector, and record it as M0. The density of any side of the positive electrode film layer = (M1-M0) / S1, in g / 1540mm². 2 To ensure the accuracy of the test results, multiple groups (e.g., 10 groups) of samples can be tested, and the average value can be calculated as the test result.

[0155] In some embodiments, the density of any side of the positive electrode film can be 0.30 g / 1540 mm. 2 0.31g / 1540mm 2 0.32g / 1540mm 2 0.33g / 1540mm 2 0.34g / 1540mm 2 0.35g / 1540mm 2 0.36g / 1540mm 2 0.37g / 1540mm 2 0.38g / 1540mm 2 0.39g / 1540mm 2 0.40g / 1540mm 2 0.41g / 1540mm 2 0.42g / 1540mm 2 0.43g / 1540mm 2 0.44g / 1540mm 20.45g / 1540mm 2 Or the range of values ​​between any two.

[0156] Increasing the surface density of the positive electrode film helps to improve the loading of active materials in the battery cell, thereby increasing the battery cell capacity. However, the applicant has found that in large-area, high-density positive electrode sheets, the local reaction rate and lithium-ion efficiency rate in the current density region increase, which easily leads to local concentration polarization. Furthermore, with the increase in the surface density of the positive electrode film, the lithium-ion migration path increases, and the lithium-ion concentration near the current collector side is lower, further exacerbating local concentration polarization and thus affecting the cycle performance of the battery cell. In the embodiments of this application, the density of any side of the positive electrode film is within the above-mentioned range, and the total coating area of ​​the positive electrode film contained in the battery cell is greater than or equal to 11m². 2 The compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3 The electrolyte includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.1%-8% based on the total mass of the electrolyte, which combines high capacity, good cycle performance and energy conversion efficiency.

[0157] In some embodiments, the density of any side of the positive electrode film is 0.35 g / 1540.25 mm. 2 -0.4g / 1540.25mm 2 .

[0158] In some embodiments, the thickness of the positive current collector is 8 μm-15 μm.

[0159] In this application, the thickness of the positive current collector can be tested using methods and instruments known in the art. For example, a high-precision micrometer or a scanning electron microscope can be used to photograph the cross-section of the positive electrode film along the thickness direction, and the photographed image can be imported into ImageJ software for testing.

[0160] In some embodiments, the thickness of the positive current collector can be 8 μm, 8.1 μm, 8.2 μm, 8.3 μm, 8.4 μm, 8.5 μm, 8.6 μm, 8.7 μm, 8.8 μm, 8.9 μm, 9 μm, 9.1 μm, 9.2 μm, 9.3 μm, 9.4 μm, 9.5 μm, 9.6 μm, 9.7 μm, 9.8 μm, 9.9 μm, 10 μm, 10.1 μm, 10.2 μm, 10.3 μm, 10.4 μm, 10.5 μm, 10.6 μm, 10.7 μm, 10.8 μm, 10.9 μm, 11 μm, 11.1 μm, 11.2 μm, 11.3 μm, 11.4 μm, 11.5 μm, 1 1.6μm, 11.7μm, 11.8μm, 11.9μm, 12μm, 12.1μm, 12.2μm, 12.3μm, 12.4μm, 12.5μm, 12.6μm, 12.7μm, 12.8μm, 12.9μm, 13μm, 13.1μm, 13.2μm, 13.3μm, 13.4μm, 13.5μm, 13.6μm, 13.7μm, 13.8μm, 13.9μm, 14μm, 14.1μm, 14.2μm, 14.3μm, 14.4μm, 14.5μm, 14.6μm, 14.7μm, 14.8μm, 14.9μm, 15μm, or any range between the two.

[0161] The thickness of the positive electrode current collector within the above range helps to reduce the resistance of the positive electrode current collector, improve the uniformity of current distribution within the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0162] In some embodiments, the first direction, the second direction, and the thickness direction of the positive electrode sheet are perpendicular to each other; the positive electrode sheet includes a positive electrode tab disposed at one end of the positive current collector extending along the first direction; in the second direction, the size of the positive current collector in the positive electrode sheet is L1, and the total size of the positive electrode tab near the end of the positive current collector is L2, where 5% ≤ L2 / L1 × 100% ≤ 25%.

[0163] In some implementations, the first direction is the length direction of the positive electrode sheet, and the second direction is the width direction of the positive electrode sheet.

[0164] In some implementations, the first direction is the width direction of the positive electrode sheet, and the second direction is the length direction of the positive electrode sheet.

[0165] The second direction, which is the length direction of the positive electrode sheet, helps to shorten the diffusion path of current within the positive electrode sheet, improve the uniformity of current distribution within the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0166] In some implementations, L2 / L1×100% can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%, 25%, or any value range between the two.

[0167] If L2 / L1×100% is within the above range, it means that the positive electrode tab has a larger size ratio along the second direction, which helps to improve the uniformity of current distribution in the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0168] In some embodiments, in the second direction, the dimension of the end of the single positive electrode tab near the current collector is 40mm-80mm.

[0169] In some embodiments, in the second direction, the dimension of the end of a single positive electrode tab near the current collector can be 40mm, 41mm, 42mm, 43mm, 44mm, 45mm, 46mm, 47mm, 48mm, 49mm, 50mm, 51mm, 52mm, 53mm, 54mm, 55mm, 56mm, 57mm, 58mm, 59mm, 60mm, 61mm, 62mm, 63mm, 64mm, 65mm, 66mm, 67mm, 68mm, 69mm, 70mm, 71mm, 72mm, 73mm, 74mm, 75mm, 76mm, 77mm, 78mm, 79mm, 80mm, or any value between the two.

[0170] The size of a single positive electrode tab within the above range helps to improve the uniformity of current distribution within the positive electrode sheet, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0171] In some embodiments, the number of layers of the positive electrode sheet is N1, and the number of layers of the positive electrode sheet with the positive electrode tab is N2, where 0.5 ≤ N2 / N1.

[0172] In this application, the number of layers of the positive electrode sheet has the following meanings: In a stacked battery cell, one positive electrode sheet is equivalent to one layer of positive electrode sheet, meaning the number of layers of the positive electrode sheet is equal to the number of positive electrode sheets. In a wound battery cell, the number of layers of the positive electrode sheet is equal to the sum of the number of layers of the positive electrode sheets in all wound electrode assemblies. In a wound electrode assembly, starting from the inner edge of the positive electrode sheet along the winding direction, one complete turn back to that starting point is counted as one turn of the positive electrode sheet. Using that starting point as the boundary, this turn of the positive electrode sheet can be divided into two layers of positive electrode sheets with equal dimensions along the winding direction. When the last turn of the positive electrode sheet is insufficient to form a complete turn; when the size of the last turn is less than 1 / 2 of the size of the last turn, it is not counted in the number of layers of the positive electrode sheet; when the size of the last turn is greater than or equal to 1 / 2 of the size of the last turn, it is counted as one layer of the positive electrode sheet. The size of the last turn refers to the circumference of the turn containing the last turn.

[0173] In some embodiments, the number of layers of the positive electrode sheet is N1, and the number of layers of the positive electrode sheet with the positive electrode tab is N2, where 0.5 ≤ N2 / N1 ≤ 1.

[0174] When N2 / N1 is within the above range, it indicates that there are more positive electrode tabs in the battery cell, which helps to improve the uniformity of current distribution in the positive electrode, thereby improving the problem of excessive local stress and alleviating concentration polarization, and further improving the cycle performance of the battery cell.

[0175] In some embodiments, the number of layers of the positive electrode sheet is N1, and the number of layers of the positive electrode sheet with the positive electrode tab is N2, where 0.75≤N2 / N1≤1.

[0176] In some embodiments, the electrolyte comprises a linear carbonate solvent, which further comprises one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0177] The applicant discovered that the high current density of the positive electrode film results in a high delithiation rate, while the corresponding negative electrode film exhibits a high lithium insertion rate. This leads to localized lithium plating in the negative electrode film, affecting the cycle performance of the battery cell. Linear carbonates have low viscosity, and the electrolyte includes dimethyl carbonate and other types of linear carbonates, which helps to further reduce viscosity, increase the lithium-ion diffusion rate, improve localized lithium plating, and alleviate concentration polarization, thereby further improving the cycle performance of the battery cell.

[0178] In some embodiments, the dimethyl carbonate accounts for 15%-50% of the total mass of the electrolyte.

[0179] In some embodiments, based on the total mass of the electrolyte, the mass percentage of dimethyl carbonate can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any range between the two.

[0180] In some embodiments, the dimethyl carbonate accounts for 35%-50% of the total mass of the electrolyte.

[0181] Compared to other linear carbonates, dimethyl carbonate has a lower viscosity, and its mass percentage is further within the above range, which helps to further reduce electrolyte viscosity, increase lithium-ion migration rate, help alleviate local lithium plating and concentration polarization, and thus further improve the cycle performance of battery cells.

[0182] In some embodiments, the linear carbonate solvent includes ethyl methyl carbonate, and the ethyl methyl carbonate accounts for 10%-50% of the total mass of the electrolyte.

[0183] In some embodiments, the linear carbonate solvent includes ethyl methyl carbonate, and the mass percentage of ethyl methyl carbonate based on the total mass of the electrolyte can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any value between the two.

[0184] In some embodiments, the linear carbonate solvent includes ethyl methyl carbonate, and the ethyl methyl carbonate accounts for 25%-30% of the total mass of the electrolyte.

[0185] In some embodiments, the electrolyte comprises a cyclic carbonate solvent, which includes one or more of ethylene carbonate and propylene carbonate.

[0186] Cyclic carbonates have a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the conductivity of the electrolyte and helping to alleviate concentration polarization, thus further improving the cycle performance of the battery cells.

[0187] In some embodiments, the cyclic carbonate solvent includes ethylene carbonate, and the ethylene carbonate accounts for 10%-40% of the total mass of the electrolyte.

[0188] In some embodiments, the cyclic carbonate solvent includes ethylene carbonate, and the mass percentage of ethylene carbonate based on the total mass of the electrolyte can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any range between the two.

[0189] In some embodiments, the cyclic carbonate solvent includes propylene carbonate, and the propylene carbonate accounts for 0.5%-10% of the total mass of the electrolyte.

[0190] In some embodiments, the cyclic carbonate solvent includes propylene carbonate, and the mass percentage of propylene carbonate based on the total mass of the electrolyte can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any value between the two.

[0191] Propylene carbonate has a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the electrolyte conductivity. In the embodiments of this application, the mass percentage of propylene carbonate is within the above-mentioned range, which helps to improve the cycle performance of the battery cell.

[0192] In some embodiments, the electrolyte includes additives, including the ethylene carbonate and fluoroethylene carbonate.

[0193] In this embodiment, the addition of the above-mentioned ethylene carbonate and fluoroethylene carbonate to the electrolyte helps to further improve the stability of the SEI film, alleviate the rupture phenomenon of the SEI film under local stress, and further improve the cycle performance of the battery cell.

[0194] In some embodiments, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 0.05%-5% of the total mass of the electrolyte.

[0195] In some embodiments, the additive includes fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate based on the total mass of the electrolyte can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 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%, or 1.8%. %, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or any range of two.

[0196] In some embodiments, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 2%-3% of the total mass of the electrolyte.

[0197] When the mass percentage of fluoroethylene carbonate is within the above range, it helps to form an SEI film of suitable thickness, taking into account both the stability of the SEI film and the interfacial impedance, thereby balancing the cycle performance and energy conversion efficiency of the battery cell.

[0198] In some embodiments, the linear carbonate solvent includes ethyl methyl carbonate, and the additive includes fluoroethylene carbonate.

[0199] The applicant discovered that the combined use of ethyl methyl carbonate and fluoroethylene carbonate helps improve the cycle performance of battery cells.

[0200] In some embodiments, the cyclic carbonate solvent includes propylene carbonate, and the additive includes vinylene carbonate.

[0201] Propylene carbonate readily undergoes a co-intercalation reaction at the negative electrode, thus affecting the cycle performance of the battery cell. The applicant discovered that using propylene carbonate in combination with ethylene carbonate can effectively mitigate the co-intercalation reaction of propylene carbonate, further improving the cycle performance of the battery cell.

[0202] In some embodiments, the electrolyte comprises an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0203] In some embodiments, the electrolyte solution comprises lithium bisfluorosulfonylimide, wherein the lithium bisfluorosulfonylimide accounts for 1%-7% of the total mass of the electrolyte solution.

[0204] In some embodiments, the electrolyte comprises lithium difluorosulfonylimide, and the mass percentage of lithium difluorosulfonylimide based on the total mass of the electrolyte can be 1%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.1%, 4.3%, 4.5%, 4.7%, 4.9%, 5.1%, 5.3%, 5.5%, 5.7%, 5.9%, 6.1%, 6.3%, 6.5%, 6.7%, 6.9%, 7%, or any range between the two.

[0205] Lithium difluorosulfonylimide helps form a dense and stable SEI film on the negative electrode side, thereby helping to improve the SEI film rupture caused by excessive local stress and further improving the cycle performance of the battery cell.

[0206] In some embodiments, the electrolyte solution comprises lithium bisfluorosulfonylimide, wherein the lithium bisfluorosulfonylimide accounts for 2%-7% of the total mass of the electrolyte solution.

[0207] In some embodiments, the electrolyte comprises lithium hexafluorophosphate, wherein the mass percentage of lithium hexafluorophosphate is 2%-10% based on the total mass of the electrolyte.

[0208] In some embodiments, the electrolyte comprises lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate based on the total mass of the electrolyte can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any value between the two.

[0209] In some embodiments, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonyl imide in the electrolyte is 0.5-5.5.

[0210] In some embodiments, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte can be 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, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, or any range between the two.

[0211] As the content of lithium difluorosulfonylimide increases, the SEI film becomes thicker. When the mass ratio of lithium hexafluorophosphate and lithium difluorosulfonylimide is within the above range, the electrolyte has a suitable active lithium concentration and the SEI film has a suitable thickness, thus balancing the conductivity of the electrolyte and the interfacial impedance on the negative electrode side, further improving the cycle performance and energy conversion efficiency of the battery cell.

[0212] In some embodiments, the positive electrode film layer includes a positive electrode active material, which includes lithium transition metal phosphate particles with at least a portion of their surface disposed of carbon material.

[0213] In this application, lithium-containing transition metal phosphates refer to phosphate materials containing lithium and transition metal elements, which can be detected by any method known in the art. For example, they can be detected by combining X-ray diffraction (XRD) with energy dispersive spectroscopy (EDS) or inductively coupled plasma mass spectrometry (ICP-MS).

[0214] In this application, the carbon-coated material disposed on at least a portion of the surface of a lithium-containing transition metal phosphate can be detected by any method known in the art. As an example, the carbon-coated material disposed on at least a portion of the surface of the lithium-containing transition metal phosphate can be observed by characterizing the phosphate using a transmission electron microscope coupled with energy dispersive spectroscopy. It should be noted that the elements in the carbon-coated material are not limited to carbon, but may also include other non-carbon elements. The carbon coating layer containing the carbon-coated material is not limited to a film, but also includes island-shaped, irregular, or discontinuous coating layers.

[0215] Lithium-containing transition metal phosphates, as positive electrode active materials, have the advantage of good structural stability, which helps to further improve the cycle performance of battery cells.

[0216] In some embodiments, based on the total area of ​​particles in the cross section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is 8.0%-20.0%.

[0217] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0218] In this application, the particle identification method is as follows: The positive electrode film layer is cut along the thickness direction of the electrode sheet using an argon ion beam (for example, a Leica EMTIC3XCP device can be used, operating voltage: 6kV, operating time: 6h). After exposing the cut surface, a scanning electron microscope (for example, a Hitachi SU8230 device can be used, operating voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) is used to observe the cut surface of the positive electrode film layer along the thickness direction of the electrode sheet. Images are acquired using a field emission scanning electron microscope at a non-edge location in the cut surface of the positive electrode film layer (after observing the electrode edge under the scanning electron microscope, the field of view is adjusted to the center of the sample) in secondary electron mode. Electron micrographs are taken at 10kx magnification, and the particles in the electron micrographs are analyzed using ImageJ software (1.46r, win64 version). The specific steps for using ImageJ software are as follows: Load the scanning electron microscope (SEM) image to be analyzed; use the Cellpose plugin to identify particles, and then perform manual corrections; use ImageJ to read and analyze data. The specific method for using the Cellpose plugin to identify particles is as follows: Set the segmentation diameter parameter (diameter in the Segmentation module) to 15 pixels, click "runcyto3" to identify particles; manually mark particles in the image that were not identified by the software, were not fully identified, or were identified incorrectly. Particles that were not identified by the software, were not fully identified, or were identified incorrectly mainly include the following: 1. Particles that are too large or have scratches on their surface, making them unidentifiable or incompletely identifiable; 2. During argon ion beam cutting, scratches may be generated on the particle surface, and the software may misinterpret these scratches as particle boundaries, leading to identification errors; 3. Particles that are too small and were not successfully identified; 4. Particles located at the edge of the SEM field of view, with the interior penetrated by the edge, preventing a complete view of the morphology, resulting in identification errors due to partial identification replacing the whole.For the unidentified or misidentified particles mentioned above, manual calibration is performed. The specific process is as follows: 1. Delete large particles located around the edges of the scanning electron microscope that are not fully displayed. 2. Determine if any unidentified or misidentified particles have internal cracks or scratches. If no cracks or scratches are found, classify it as a single particle and manually mark it based on the observed particle boundary. 3. If cracks or scratches are found inside the particle, determine if they penetrate the particle. If not, classify it as a single particle and manually mark it. 4. If cracks or scratches penetrate the particle, determine if they are linear or irregular. 5. If the cracks or scratches are irregular, classify them as the boundary between particles and divide the particles along this boundary. 6. If the cracks or scratches are linear, perform contrast comparison. 7. If the contrast is not obvious and there is no crack-like appearance, classify it as a scratch and mark it as a single particle. 8. If the contrast is strong and there is a crack-like appearance, classify it as the boundary between particles and mark it as two particles. After manual marking, delete information irrelevant to the particles from the automatic image processing, thus completing the particle identification and marking in the image.

[0219] In existing technologies, laser particle size analyzers are typically used to statistically analyze the particle size of positive electrode active materials using Malvern laser diffraction. However, the applicant's research indicates that because lithium-containing transition metal phosphate particles are prone to agglomeration, the test results obtained by Malvern laser diffraction based on the principle of laser scattering often only reflect the particle size of the agglomerates, and cannot accurately reflect the particle size of the positive electrode active material, let alone its dispersion state in the film layer. This is because the dispersion of the positive electrode active material in the film layer increases during slurry preparation and film forming rolling. The test results obtained by Malvern laser diffraction are affected by the particle size, specific surface area, and degree of agglomeration of the positive electrode active material. Compared to the actual dispersion in the electrode sheet, the number of large particles obtained by this test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size obtained by Malvern laser diffraction cannot be equated with or analogized to the particle size statistically obtained in the embodiments of this application.

[0220] In this application, the method for testing the area ratio of particles with a diameter R1 satisfying 1500nm≤R1≤5000nm, based on the total area of ​​particles in the cross-section along the thickness direction of the positive electrode film, is as follows: The image after particle identification and labeling is imported into ImageJ software for analysis. A scale is set according to the scanning electron microscope image. The particle diameter, area, sphericity, and roughness in the cross-section along the thickness direction of the positive electrode film are statistically analyzed using the "Feret," "Area," "Round," and "Solidity" analysis functions. According to the software manual (ImageJUserGuide IJ1.46r), the obtained "Feret" parameter represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, thus characterizing the particle diameter; the obtained "Area" parameter represents the pixel area of ​​the particle. Because particles smaller than 50nm have a large error margin in the statistical process and are difficult to identify accurately, and because the particle size of conductive agents is generally smaller than 50nm, which will also introduce a large error into the statistical results, particles smaller than 50nm are not counted in the particle size statistics of this application, and the statistical data of particles whose AR, Round, or Solidity is displayed as "NaN" are deleted. The sum of the "Area" parameters of particles with particle size R1 satisfying 1500nm≤R1≤5000nm and the sum of the "Area" parameters of all particles are calculated, and these are respectively used as the area of ​​particles with particle size R1 satisfying 1500nm≤R1≤5000nm and the total area of ​​the counted particles. The area ratio of particles with particle size R1 satisfying 1500nm≤R1≤5000nm is calculated by dividing the sum of the areas of particles with particle size R1 satisfying 1500nm≤R1≤5000nm by the total area of ​​the counted particles.

[0221] In some embodiments, based on the total area of ​​particles in the cross-section of the positive electrode film along the electrode thickness direction, the area percentage of particles with a particle size R1 satisfying 1500nm ≤ R1 ≤ 5000nm can be 8.0%, 8.2%, 8.4%, 8.6%, 8.8%, 9.0%, 9.2%, 9.4%, 9.6%, 9.8%, 10.0%, 10.2%, 10.4%, 10.6%, 10.8%, 11.0%, 11.2%, 11.4%, 11.6%, 11.8%, 12.0%, 12.2%, 12.4%, 12.6%, 12.8%, 13.0%, and 13. 2%, 13.4%, 13.6%, 13.8%, 14.0%, 14.2%, 14.4%, 14.6%, 14.8%, 15.0%, 15.2%, 15.4%, 15.6%, 15.8%, 16.0%, 16.2%, 16.4%, 16.6%, 16.8%, 17.0%, 17.2%, 17.4%, 17.6%, 17.8%, 18.0%, 18.2%, 18.4%, 18.6%, 18.8%, 19.0%, 19.2%, 19.4%, 19.6%, 19.8%, 20.0%, or any range between two of these values.

[0222] If the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is within the above range, it indicates that there are more large-sized particles in the positive electrode film layer, which helps to improve the compaction density of the positive electrode film layer and increase the capacity of the battery cell.

[0223] In some embodiments, based on the total area of ​​particles in the cross section of the positive electrode film along the electrode thickness direction, the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is 10.0%-20.0%.

[0224] In some embodiments, based on the total area of ​​particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area ratio of particles with a particle size R2 satisfying 200nm≤R2<1000nm is 15.0%-25.0%.

[0225] In this application, the area ratio of particles with a particle size R2 satisfying 200nm≤R2<1000nm is determined by referring to the test method described above, which determines the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm based on the total area of ​​particles in the cross section of the positive electrode film along the electrode thickness direction.

[0226] In some embodiments, based on the total area of ​​particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, the area percentage of particles with a particle size R2 satisfying 200nm≤R2<1000nm can be 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, 17.5%, 18.0%, 18.5%, 19.0%, 19.5%, 20.0%, 20.5%, 21.0%, 21.5%, 22.0%, 22.5%, 23.0%, 23.5%, 24.0%, 24.5%, 25.0%, or any value range between the two.

[0227] Particles with a particle size R2 satisfying 1000nm≤R2<200nm represent smaller positive electrode active materials in the positive electrode film layer. Their area proportion is within the above range, which helps to further improve the compaction density of the positive electrode film layer through particle gradation, and further improve the capacity of the battery cell.

[0228] In some embodiments, based on the total area of ​​particles in the cross section of the positive electrode film along the electrode thickness direction, the area ratio of particles with a particle size R2 satisfying 200nm≤R2<1000nm is 16%-20%.

[0229] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The value ranges from 0.95 to 1.2, where the degree of graphitization C is I. G / I D I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ - 1 The intensity of peak D at that location.

[0230] In this application, the graphitization degree C value of the positive electrode film can be obtained by surface scanning mode of a laser confocal Raman spectrometer. As an example, specifically, a laser confocal Raman spectrometer (high-precision Renishaw laser confocal Raman spectrometer) is used, with an excitation wavelength of 532 nm. An appropriate amount of the positive electrode film is taken and surface scanned on its surface or along the thickness direction of the electrode. The scanning area is 45 μm × 45 μm, divided into 10 × 10 grids, with grid vertices as test points, a step size of 5 μm, and a total of 100 scan points. Thus, the C values ​​at different sites and the cumulative distribution curve of the C values ​​in the surface scan area are obtained.

[0231] The positive electrode film in this application can be either a freshly prepared positive electrode film or a positive electrode film obtained from disassembly of a battery. The surface of a positive electrode film obtained from disassembly of a battery inevitably contains residual electrolyte salts. To improve testing accuracy, it is preferable to perform a surface scan on a cross-section of the positive electrode film along the electrode thickness direction to characterize the degree of graphitization of the positive electrode film.

[0232] Those skilled in the art can control the degree of graphitization of active material particles using any known process. As an example, adjusting the carbon source, optimizing the nucleation process, sintering temperature, sintering time, sintering pressure, and sintering atmosphere can all achieve the adjustment of the degree of graphitization of active material particles.

[0233] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 It can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, or any value range between the two.

[0234] The median C of the graphitization degree of the positive electrode film 50 Within the aforementioned range, it helps to improve the electronic conductivity of the positive electrode film, enhance the uniformity of current distribution in the positive electrode sheet, thereby mitigating the problem of excessive local stress and alleviating concentration polarization and local lithium plating, further improving the cycle performance of the battery cell. Furthermore, it also helps to reduce the internal resistance of the positive electrode sheet, improving the energy conversion efficiency of the battery cell.

[0235] In some embodiments, the median C of the graphitization degree C in the cumulative distribution curve of the positive electrode film obtained in laser microscopy confocal Raman spectroscopy instrument scanning mode is... 50 The value ranges from 0.97 to 1.13.

[0236] In some embodiments, the positive electrode active material includes titanium, and the mass percentage of titanium is 2000ppm-6000ppm based on the total mass of the positive electrode active material.

[0237] The types and contents of elements in positive electrode active materials can be tested using any method known in the art. As an example, inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to test the titanium content, referring to Appendix C of GB / T 33822-2017.

[0238] In some embodiments, the positive electrode active material includes titanium, and the mass percentage of titanium, based on the total mass of the positive electrode active material, can be 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, 3100ppm, 3200ppm, 3300ppm, 3400ppm, 3500ppm, 3600ppm, or 3700ppm. 3800ppm, 3900ppm, 4000ppm, 4100ppm, 4200ppm, 4300ppm, 4400ppm, 4500ppm, 4600ppm, 4700ppm, 4800ppm, 4900ppm, 5000ppm, 5100ppm, 5200ppm, 5300ppm, 5400ppm, 5500ppm, 5600ppm, 5700ppm, 5800ppm, 5900ppm, 6000ppm, or any range of values ​​between two of these.

[0239] The inclusion of titanium in the positive electrode active material, and its mass percentage within the aforementioned range, helps to improve the structural stability of the positive electrode active material and further enhance the cycle performance of the battery cell.

[0240] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate, lithium iron phosphate doped and modified materials, and lithium iron phosphate coated and modified materials.

[0241] In some embodiments, the positive electrode active material comprises the components shown in Formula I:

[0242] Li m Fe x P y O j Q q Formula I,

[0243] 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, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0244] In some implementations, m can be selected as 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 value range between two of these; x can be selected as 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any value range between two of these. y can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or any value between two of these; j can be 3.5, 3.6, 3.7, 3.8, 3.9, 4 or any value between two of these; q can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any value between two of these.

[0245] In some embodiments, the negative electrode film layer includes a negative electrode active material, the negative electrode active material including graphite, the negative electrode graphite including graphite bulk particles and carbon material disposed on at least a portion of the surface of the graphite bulk particles.

[0246] In some embodiments, the graphite bulk particles include secondary particles.

[0247] Primary particles refer to particles in the positive electrode film layer that have identifiable complete boundaries in the field of view at a certain magnification, such as 10,000x. These particles may contain defects or scratches, but no identifiable complete boundary sufficient to divide them. Secondary particles are formed by the aggregation of primary particles. They typically have a more regular shape, such as spherical or near-spherical, and usually consist of more than 50 primary particles. This aggregation is a hard aggregation caused by chemical bonding of primary particles, giving secondary particles a clear boundary that makes them difficult to disperse under external forces such as ultrasound. However, after cutting a cross-section of a secondary particle, it can be seen that it is formed by the aggregation of numerous primary particles. The boundary of a secondary particle is formed by the partial boundaries of the multiple outermost primary particles constituting the secondary particle, and the boundary of the secondary particle can be spherical or near-spherical.

[0248] The graphite bulk includes secondary particles, which helps increase the number of lithium-ion insertion sites, improve the kinetic performance of the negative electrode, alleviate local lithium plating, and further improve the cycle performance of the battery cell.

[0249] In some embodiments, the carbon material includes amorphous carbon.

[0250] Amorphous carbon refers to carbon materials with a very low degree of graphitization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). The carbon atoms in amorphous carbon structures are not arranged in a regular pattern; therefore, amorphous carbon can be characterized by transmission electron microscopy (TEM). By using focused ion beam (FIB) to cut a thin slice approximately 100 nm thick from the middle of the negative electrode active material particles, and then performing TEM on the slice, it can be observed that the surface region includes a coating layer. The lattice fringes in the coating layer exhibit long-range disorder and short-range order, and the electron diffraction pattern shows a halo-like appearance, indicating that the coating layer contains amorphous carbon.

[0251] Amorphous carbon is approximately amorphous, with a disordered internal arrangement exhibiting long-range randomness and rich in microporous structure. This helps increase the number of lithium-ion insertion faces and electrolyte wetting ability, thereby accelerating the lithium-ion insertion rate. This, in turn, helps improve the lithium insertion rate of the negative electrode, alleviates the local lithium plating phenomenon of the negative electrode, and further improves the cycle performance of the battery cell.

[0252] In some embodiments, the Dv50 of the negative electrode active material is 9 μm-18 μm.

[0253] In this application, Dv50, Dv90, and Dv99 have meanings known in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, 90%, and 99%, respectively, which can be determined using instruments and methods known in the art. For example, particle size distribution can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0254] It is worth noting that the negative electrode sheet, negative electrode film layer and negative electrode active material used for testing in this application can be freshly prepared or obtained by disassembling, washing and drying (and scraping off powder) from the battery.

[0255] In some embodiments, the Dv50 of the negative electrode active material can be 9 μm, 9.2 μm, 9.4 μm, 9.6 μm, 9.8 μm, 10 μm, 10.2 μm, 10.4 μm, 10.6 μm, 10.8 μm, 11 μm, 11.2 μm, 11.4 μm, 11.6 μm, 11.8 μm, 12 μm, 12.2 μm, 12.4 μm, 12.6 μm, 12.8 μm, 13 μm, 13.2 μm, 13 ... 0.4μm, 13.6μm, 13.8μm, 14μm, 14.2μm, 14.4μm, 14.6μm, 14.8μm, 15μm, 15.2μm, 15.4μm, 15.6μm, 15.8μm, 16μm, 16.2μm, 16.4μm, 16.6μm, 16.8μm, 17μm, 17.2μm, 17.4μm, 17.6μm, 17.8μm, 18μm, or any range of values ​​between the two.

[0256] Within the aforementioned range, the Dv50 of the negative electrode active material helps to increase the number of lithium-ion insertion sites, improve the kinetic performance of the negative electrode, alleviate local lithium plating, and further improve the cycle performance of the battery cell.

[0257] In some embodiments, the Dv90 of the negative electrode active material is 21 μm-35 μm.

[0258] In some embodiments, the Dv90 of the negative electrode active material can be 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm or any value range between the two.

[0259] In some embodiments, the Dv99 of the negative electrode active material is 27μm-65μm.

[0260] In some embodiments, the Dv99 of the negative electrode active material can be 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm, 42μm, 43μm, 44μm, 45μm, 46μm, 47μm, 48μm, 49μm, 50μm, 51μm, 52μm, 53μm, 54μm, 55μm, 56μm, 57μm, 58μm, 59μm, 60μm, 61μm, 62μm, 63μm, 64μm, 65μm, or any value range between the two.

[0261] In some embodiments, the Dv99 of the negative electrode active material is 33μm-41μm.

[0262] In some embodiments, the separator includes a base film and a coating disposed on at least one side of the base film. The coating includes ceramic particles and a binder. The ceramic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

[0263] Ceramic-coated separators exhibit higher mechanical stability and compression resistance during cycling. On the one hand, they help reduce the pressure of local high rebound of the positive electrode on the negative electrode film and improve its damage to the SEI film. On the other hand, they can maintain good thickness stability under local high stress, thereby further improving the cycle performance of the battery cell.

[0264] In some embodiments, the adhesive includes one or more of polyvinylidene fluoride and polymethyl methacrylate.

[0265] In some embodiments, the thickness of the base film is 3 μm-9 μm.

[0266] In some embodiments, the thickness of the base film can be 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, 8.2 μm, 8.4 μm, 8.6 μm, 8.8 μm, 9 μm, or any value range between the two.

[0267] In some embodiments, the thickness of the base film is 4 μm-7 μm.

[0268] In some embodiments, the thickness of the base film can be 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, or any value range between the two.

[0269] In some embodiments, the coating has a single-sided thickness of 3 μm-8 μm.

[0270] In some embodiments, the porosity of the separator is 20%-70%.

[0271] In this application, porosity refers to the percentage of the volume of the pores in the separator to the total volume of the separator, expressed as porosity ε = (V1 - V2) / V1 × 100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample. Porosity can be determined using methods known in the art. As an example, it can be tested according to the standard GB / T 36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the influence on porosity testing, in order to obtain more accurate test values.

[0272] In some embodiments, the porosity of the isolation membrane can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, or any value between the two.

[0273] The porosity of the separator within the above range helps to reduce its resistance to lithium-ion diffusion, increase the lithium-ion migration rate, further alleviate concentration polarization, and further improve the cycle performance of the battery cell.

[0274] In some embodiments, the porosity of the separator is 20%-50%.

[0275] In some embodiments, the battery cell further includes a housing and an end cap assembly. The housing has a housing opening, the electrode assembly is housed within the housing, and the end cap assembly closes the housing opening. The end cap assembly includes a cover plate and electrode terminals. The cover plate has mounting holes, and the electrode terminals include a first connecting portion and a second connecting portion connected together. The first connecting portion is located on the side of the cover plate facing the electrode assembly and is electrically connected to the electrode assembly. The second connecting portion passes through the mounting holes and protrudes from the surface of the cover plate on the side away from the electrode assembly. The cross-sectional area of ​​the first connecting portion perpendicular to the thickness direction of the cover plate is larger than the area of ​​the mounting hole.

[0276] This helps to improve the connection strength and structural stability between the electrode terminals and the cover plate, making it less prone to cracking or loosening under the high expansion force in the later stages of battery cell cycling, thereby extending the cycle life of the battery cell.

[0277] In some embodiments, the capacity of the battery cell is 400Ah-3000Ah.

[0278] In this application, the capacity of a single battery cell can be tested using methods and instruments known in the art. As an example, at 25°C, the battery cell is discharged at a constant power of 0.5P until its voltage reaches 2.5V, and then allowed to stand for 30 minutes. Then, the battery cell is subjected to a charge-discharge cycle test at a constant power of 0.5P: First charge-discharge cycle: The battery cell is charged at a constant power of 0.5P to 3.65V, allowed to stand for 30 minutes, and then discharged at a constant power of 0.5P to 2.5V. The discharge capacity Q1 is recorded, and Q1 is the capacity of the battery cell, in Ah.

[0279] In some implementations, the capacity of a single battery cell can be 400Ah, 450Ah, 500Ah, 550Ah, 600Ah, 650Ah, 700Ah, 750Ah, 800Ah, 850Ah, 900Ah, 950Ah, 1000Ah, 1050Ah, 1100Ah, 1150Ah, 1200Ah, 1250Ah, 1300Ah, 1350Ah, 1400Ah, 1450Ah, 1500Ah, 1550Ah, 1600Ah, 1650Ah, or 1700Ah. h, 1750Ah, 1800Ah, 1850Ah, 1900Ah, 1950Ah, 2000Ah, 2050Ah, 2100Ah, 2150Ah, 2200Ah, 2250Ah, 2300Ah, 2350Ah, 2400Ah, 2450Ah, 2500Ah, 2550Ah, 2600Ah, 2650Ah, 2700Ah, 2750Ah, 2800Ah, 2850Ah, 2900Ah, 2950Ah, 3000Ah, or any range of two.

[0280] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0281] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0282] In some embodiments, the positive electrode active material layer can be prepared by dispersing the components used to prepare the positive electrode active material layer, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, a positive electrode active material layer can be obtained.

[0283] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0284] In some embodiments, the negative electrode film layer may optionally 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).

[0285] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0286] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0287] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0288] A second aspect of this application provides a battery device, including the battery cell provided in the first aspect of this application.

[0289] The third aspect of this application provides an energy storage device that uses the battery device provided in the second aspect 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.

[0290] Example

[0291] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0292] I. Preparation Method

[0293] 1. Preparation of Example 1

[0294] (1) Positive electrode plate

[0295] ① Preparation of positive electrode active materials

[0296] Lithium dihydrogen phosphate, ferrous oxalate, polyethylene glycol, and titanium dioxide were mixed evenly in methanol and ground to obtain a mixed raw material. The ratio of lithium dihydrogen phosphate to ferrous oxalate resulted in a lithium to iron molar ratio of 1.03:1.0. The ferrous oxalate had particle sizes Dv10 of 6.1 μm, Dv50 of 60.5 μm, and Dv90 of 105.5 μm. The ferrous oxalate contained 30.9% Fe by mass and 0.03% ferric iron by mass.

[0297] The mixed raw materials were ball-milled multiple times and demagnetized in a ball mill to obtain a mixed slurry. The number of grinding cycles and time were controlled, and the particle size Dv50 of the ground mixed slurry was 3.0 μm.

[0298] The spray-dried slurry yields a dried precursor powder, which is light yellow in appearance and uniform in color.

[0299] The precursor powder was placed in a sintering furnace and heated from 25°C to 350°C at a rate of 2°C / min under a nitrogen atmosphere and held at that temperature for 3 hours. Then, the temperature was increased to a second temperature of 770°C at a rate of 5°C / min and held at that temperature for 10 hours. After the process, the temperature was lowered and cooled.

[0300] The obtained material was crushed using an airflow pulverization method with a staged frequency of 22Hz and a pulverizing airflow of 0.55MPa to obtain carbon-coated lithium iron phosphate cathode active material.

[0301] The positive electrode active material contains 1.2% carbon by mass and 5000 ppm titanium by mass.

[0302] The Dv10, Dv50, and Dv90 mentioned above refer to data obtained through the Malvern laser scattering method.

[0303] ② Preparation of the positive electrode film

[0304] The prepared positive electrode active material, conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 97:0.8:2.2 with N-methylpyrrolidone (N-methylpyrrolidone) in a stirring tank to form a positive electrode slurry. After the stirring process, the positive electrode slurry was transferred and coated onto a current collector aluminum foil, dried, compacted, slit, and sheeted to obtain the positive electrode sheet. The density of any side of the positive electrode film was 310 mg / 1540 cm³. 2 .

[0305] Among them, based on the total area of ​​particles in the cross-section along the thickness direction of the positive electrode film, the area proportion of particles with a diameter R1 satisfying 1500nm≤R1≤5000nm is 14.47%; based on the total area of ​​lithium transition metal phosphate particles in the cross-section along the thickness direction of the positive electrode film, the area proportion of particles with a diameter R2 satisfying 1000nm≤R2<1500nm is 19.72%; in the cumulative distribution curve of graphitization degree C obtained by laser microscopy confocal Raman spectroscopy instrument scanning mode, the median C of graphitization degree is... 50 It is 1.02.

[0306] (2) Negative electrode plate

[0307] A negative electrode active material, conductive carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in deionized water at a mass ratio of 97:0.8:1.2:1 to prepare a negative electrode slurry. The negative electrode slurry was then coated onto a copper current collector foil, dried, compacted, slit, and sheeted to obtain the negative electrode sheet. The density of any side of the negative electrode film was 155 mg / 1540.25 cm³. 2 .

[0308] The negative electrode active material is graphite, which includes graphite bulk particles and an amorphous carbon coating layer. The graphite bulk particles include secondary particles. Based on the total mass of the negative electrode active material in the negative electrode film, the mass percentage of amorphous carbon is 2.4%. The Dv50 of the negative electrode active material is 12 μm, the Dv90 is 26 μm, and the Dv99 is 36 μm.

[0309] (3) Separating membrane

[0310] The separator membrane includes a base membrane and coatings disposed on both sides of the base membrane. The base membrane is a polyethylene membrane with a thickness of 7 μm; the coatings include alumina and polyvinylidene fluoride (PVDF), and the coating thickness on one side is 6 μm.

[0311] (4) Electrolyte

[0312] Based on the total mass of the electrolyte, the electrolyte comprises 35% dimethyl carbonate (DMC), 21% ethyl methyl carbonate (EMC), 20% ethylene carbonate (EC), 10% propylene carbonate (PC), 3% lithium bis(fluorosulfonyl)imide (LiFSI), 6% lithium hexafluorophosphate (LiPF6), 2% fluoroethylene carbonate (FEC), and 3% vinylene carbonate (VC).

[0313] (5) Battery cell

[0314] The positive electrode, separator, and negative electrode are stacked in sequence. The separator must be able to isolate the anode and cathode. The bare cell is obtained by winding. The bare cell is placed in the housing, the top cover assembly is closed, electrolyte is injected, and the battery cell undergoes processes such as encapsulation, formation, and venting to obtain a single battery cell. The end cover assembly includes a cover plate and electrode terminals. The cover plate has mounting holes. The electrode terminals include a first connecting part and a second connecting part connected together. The first connecting part is located on the side of the cover plate facing the electrode assembly and is electrically connected to the electrode assembly. The second connecting part passes through the mounting holes and protrudes from the surface of the cover plate away from the electrode assembly. The cross-sectional area of ​​the first connecting part perpendicular to the thickness direction of the cover plate is larger than the area of ​​the mounting holes.

[0315] When a single battery cell is discharged to 0% SOC, the compaction density of the positive electrode film is 2.56 g / cm³. 3 The compaction density of the negative electrode film is 1.5 g / cm³. 3 The process of discharging a single battery cell to 0% SOC involves placing the battery in a 25°C oven for 2 hours, maintaining the battery temperature at 25°C, and then discharging the single battery cell at a constant power of 0.5P until the voltage of the single battery cell reaches 2.5V.

[0316] A positive electrode tab is disposed at one end extending along the width direction of the positive electrode sheet. One positive electrode tab is disposed for each turn of the positive electrode sheet. Along the length direction of the positive electrode sheet, the dimension of a single positive electrode tab near the current collector is 48 mm. In the positive electrode sheet, the dimension of the positive current collector is L1, and the total dimension of the positive electrode tab near the positive current collector is L2. L2 / L1×100%=17.8%.

[0317] The length of a single positive electrode film is 13687 mm and the width is 178 mm. The battery cell contains four electrode components, and all positive electrode sheets are coated on both sides. The total coating area of ​​the positive electrode film in the battery cell is 21.68 m². 2 .

[0318] 2. Preparation of other embodiments

[0319] Examples 2-3 and Comparative Example 1 are prepared in basically the same way as Example 1, except that the length of the positive current collector and the length of the positive electrode film are adjusted so that the total coating area of ​​the positive electrode film contained in the battery cell is different, as detailed in Table 2.

[0320] The preparation methods of Examples 4-6 are basically the same as those of Example 1. The difference is that the sintering temperature of the precursor powder in the preparation of the positive electrode active material is adjusted (specifically as follows), and the thickness of the positive electrode film layer, the compaction density of the positive electrode film layer, and the density of any side are kept constant.

[0321] Example 4: The precursor powder was placed in a sintering furnace and heated from 25°C to 350°C at a rate of 2°C / min under a nitrogen atmosphere, and held at this temperature for 3 hours. Then, the temperature was increased to a second temperature of 755°C at a rate of 5°C / min and held at this temperature for 10 hours. Afterward, the material was cooled. The density of any side of the positive electrode film was 304 mg / 1540 cm³. 2 The compaction density of the positive electrode film is detailed in Table 2.

[0322] Example 5: The mixed raw materials were ball-milled multiple times and demagnetized in a ball mill to obtain a mixed slurry. The number of grinding cycles and time were controlled, and the particle size Dv50 of the ground mixed slurry was 4.0 μm. The density of any side of the positive electrode film was 306 mg / 1540 cm³. 2 The compaction density of the positive electrode film is detailed in Table 2.

[0323] Example 6: The precursor powder was placed in a sintering furnace and heated from 25°C to 350°C at a rate of 2°C / min under a nitrogen atmosphere, and held at this temperature for 3 hours. Then, the temperature was increased to a second temperature of 790°C at a rate of 5°C / min and held at this temperature for 10 hours. Afterward, the temperature was lowered and cooled. The density of any side of the positive electrode film was 0.315 mg / 1540 cm³. 2 The compaction density of the positive electrode film is detailed in Table 5.

[0324] Comparative Example 2 was prepared using the same method as Example 1, except that the thickness of the positive electrode film was kept constant, and the compaction density and density of any side of the positive electrode film were adjusted. The density of any side of the positive electrode film was 291 mg / 1540 cm³. 2 The compaction density of the positive electrode film is detailed in Table 2.

[0325] Examples 7-16 and Comparative Examples 3-4 are prepared in basically the same way as Example 1, except that the electrolyte is adjusted, as detailed in Table 1.

[0326] Table 1

[0327] The preparation method of Example 17 is basically the same as that of Example 1, except that the positive electrode tab and the positive electrode terminal in the top cover assembly are connected by an adapter piece.

[0328] II. Testing Methods

[0329] 1. Cyclic performance test

[0330] At 25℃, the battery cells were discharged at a constant power of 0.5P until the voltage of the battery cell reached 2.5V, and then allowed to rest for 30 minutes. Next, the battery cells were subjected to a charge-discharge cycle test at a constant power of 0.5P: First charge-discharge cycle: The battery cell was charged at a constant power of 0.5P to 3.65V, allowed to rest for 30 minutes, and then discharged at a constant power of 0.5P to 2.5V, recording the discharge capacity Q1; subsequently, after allowing the battery to rest for 30 minutes, the first charge-discharge cycle was repeated; this cycle was repeated 10,000 times, and the discharge capacity Qn was recorded. The capacity retention rate of the battery cell is calculated as Qn / Q1 × 100%.

[0331] 2. Real-Time Efficiency (RTE) Test

[0332] At 25℃, the battery cells were discharged at a constant power of 0.5P until the voltage of the battery cells reached 2.5V, and then allowed to stand for 30 minutes. Then, the battery cells were subjected to a charge-discharge test at a constant power of 0.5P: the battery cells were charged at a constant power of 0.5P to 3.65V, and the charging voltage-charging capacity curve was recorded; after standing for 30 minutes, the cells were discharged at a constant power of 0.5P to 2.5V, and the discharging voltage-discharging capacity curve was recorded.

[0333] In the charging voltage-charging capacity curve, the charging energy W1 is obtained by integrating the charging voltage relative to the charging capacity in the range of 2.5V to 3.6V; in the discharging voltage-discharging capacity curve, the discharging energy W2 is obtained by integrating the discharging voltage relative to the discharging capacity in the range of 2.5V to 3.6V; RTE = W2 / W1 × 100%.

[0334] III. Test Results

[0335] The test results of the above embodiments and comparative examples are detailed in Tables 2-6.

[0336] As shown in Tables 2-6, a single battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The total coating area of ​​the positive electrode film layer included in the single battery cell is greater than or equal to 11 m². 2 The compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3The electrolyte includes vinylene carbonate, which accounts for 0.1%-8% of the total mass of the electrolyte. The battery cells have high capacity, good cycle performance and high energy conversion efficiency.

[0337] Table 2

[0338] As shown in Table 2, the total coating area of ​​the positive electrode film in the battery cell is greater than or equal to 11m². 2 The compaction density of the positive electrode film is greater than or equal to 2.5 g / cm³. 3 This helps to increase the capacity of individual battery cells, while also providing good cycle performance and energy conversion efficiency.

[0339] Table 3

[0340] In Example 10, the capacity is 587 Ah.

[0341] As shown in Table 3, based on the total mass of the electrolyte, the mass percentage of vinylene carbonate is 0.1%-8%, resulting in battery cells exhibiting both good cycle performance and energy conversion efficiency. Furthermore, based on the total mass of the electrolyte, the mass percentage of vinylene carbonate is 0.5%-5%, which helps to further improve the cycle performance and energy conversion efficiency of the battery cells.

[0342] Table 4

[0343] As shown in Table 4, when the mass percentage of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte, the battery cells exhibit good cycle performance. Furthermore, when the mass percentage of dimethyl carbonate is in the range of 35%-50% based on the total mass of the electrolyte, it helps to further improve the cycle performance of the battery cells.

[0344] Table 5

[0345] As shown in Table 5, the electrolyte includes both methyl ethyl carbonate and fluoroethylene carbonate, which helps to improve the cycle performance of the battery cells.

[0346] Table 6

[0347] As shown in Table 6, the ratio N2 / N1 of the number of layers of the positive electrode sheet with positive electrode tabs to the number of layers of the positive electrode sheet is in the range of 0.75-1, which helps to further improve the energy conversion efficiency of the battery cell.

[0348] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The device includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The total coating area of ​​the positive electrode film layer contained in the battery cell is greater than or equal to 11m². 2 ; The compaction density of the positive electrode film layer is greater than or equal to 2.5 g / cm³. 3 ; The electrolyte includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.1%-8% based on the total mass of the electrolyte.

2. The battery cell according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of vinylene carbonate is 0.5%-8%, optionally 0.5%-5%.

3. The battery cell according to claim 1 or 2, characterized in that, The total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 11m is optional 2 -120m 2 .

4. The battery cell according to any one of claims 1-3, characterized in that, The compaction density of the positive electrode film is 2.5 g / cm³. 3 -3g / cm 3 2.5g / cm³ is an option. 3 -2.8g / cm 3 .

5. The battery cell according to any one of claims 1-4, characterized in that, The density of any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.45g / 1540.25mm 2 Available in 0.35g / 1540.25mm. 2 -0.4g / 1540.25mm 2 .

6. The battery cell according to any one of claims 1-5, characterized in that, The thickness of the positive electrode current collector is 8μm-15μm.

7. The battery cell according to any one of claims 1-6, characterized in that, The first direction, the second direction, and the thickness direction of the positive electrode sheet are perpendicular to each other; The positive electrode plate includes a positive electrode tab, which is disposed at one end of the positive current collector extending along the first direction; in the second direction, the dimension of the positive current collector in the positive electrode plate is L1, and the total dimension of the end of the positive electrode tab near the positive current collector is L2. 5% ≤ L2 / L1 ≤ 25%, Optionally, in the second direction, the dimension of the end of the single positive electrode tab closest to the current collector is 40mm-80mm.

8. The battery cell according to claim 7, characterized in that, The number of layers of the positive electrode sheet is N1, and the number of layers of the positive electrode sheet with the positive electrode tab is N2, 0.5≤N2 / N1, which can be selected as 0.5≤N2 / N1≤1, and further selected as 0.75≤N2 / N1≤1.

9. The battery cell according to any one of claims 1-8, characterized in that, The electrolyte includes linear carbonate solvents, which further include one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

10. The battery cell according to claim 9, characterized in that, The linear carbonate solvent satisfies at least one of the following conditions: (1) The linear carbonate solvent includes dimethyl carbonate, and the mass percentage of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte, and can be optionally 35%-50%; (2) The linear carbonate solvent includes ethyl methyl carbonate, and the mass percentage of ethyl methyl carbonate is 10%-50% based on the total mass of the electrolyte, and can be selected as 25%-30%.

11. The battery cell according to any one of claims 1-10, characterized in that, The electrolyte includes cyclic carbonate solvents, which include one or more of ethylene carbonate and propylene carbonate.

12. The battery cell according to claim 11, characterized in that, The cyclic carbonate solvent satisfies at least one of the following conditions: (1) The cyclic carbonate solvent includes ethylene carbonate, and the mass percentage of ethylene carbonate is 10%-40% based on the total mass of the electrolyte; (2) The cyclic carbonate solvent includes propylene carbonate, and the mass percentage of propylene carbonate is 0.5%-10% based on the total mass of the electrolyte.

13. The battery cell according to any one of claims 1-12, characterized in that, The electrolyte includes additives, including the ethylene carbonate and fluoroethylene carbonate.

14. The battery cell according to claim 13, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 0.05%-5%, optionally 2%-3%.

15. The battery cell according to any one of claims 1-14, characterized in that, The electrolyte comprises ethyl methyl carbonate and fluoroethylene carbonate.

16. The battery cell according to any one of claims 1-15, characterized in that, The electrolyte includes propylene carbonate and vinylene carbonate.

17. The battery cell according to any one of claims 1-16, characterized in that, The electrolyte includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium difluorosulfonylimide.

18. The battery cell according to claim 17, characterized in that, The electrolyte salt comprises lithium bis(fluorosulfonyl)imide, and the lithium bis(fluorosulfonyl)imide accounts for 1%-7% of the total mass of the electrolyte, optionally 2%-7%; and / or, The electrolyte salt includes lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate is 2%-10% based on the total mass of the electrolyte.

19. The battery cell according to claim 17 or 18, characterized in that, The electrolyte salt includes lithium hexafluorophosphate and lithium difluorosulfonylimide, and the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 0.5-5.

5.

20. The battery cell according to any one of claims 1-19, characterized in that, The positive electrode film layer includes a positive electrode active material, which includes lithium transition metal phosphate particles with carbon material disposed on at least a portion of their surface.

21. The battery cell according to claim 20, characterized in that, Based on the total area of ​​particles in the cross-section along the thickness direction of the positive electrode film, the area ratio of particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is 8.0%-20.0%, and can be selected as 10.0%-20.0%.

22. The battery cell according to claim 20 or 21, characterized in that, Based on the total area of ​​particles in the cross-section along the thickness direction of the positive electrode film, the area ratio of particles with a particle size R2 satisfying 200nm≤R2<1000nm is 15.0%-25.0%, and can be selected as 16%-20%.

23. The battery cell according to any one of claims 20-22, characterized in that, In the cumulative distribution curve of the graphitization degree C value of the positive electrode film obtained in the laser microscopy confocal Raman spectroscopy instrument scanning mode, the median C of the graphitization degree is... 50 The value is 0.95-1.2, and can be selected as 0.97-1.

13.

24. The battery cell according to any one of claims 1-23, characterized in that, The positive electrode active material includes titanium, and the mass percentage of titanium is 2000ppm-6000ppm based on the total mass of the positive electrode active material.

25. The battery cell according to any one of claims 1-24, characterized in that, The positive electrode active material includes one or more of lithium iron phosphate, lithium iron phosphate doped and modified materials, and lithium iron phosphate coated and modified materials.

26. The battery cell according to any one of claims 1-25, characterized in that, The positive electrode active material comprises the component shown in general formula I: 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, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.

1.

27. The battery cell according to any one of claims 1-26, characterized in that, The negative electrode film layer includes a negative electrode active material, the negative electrode active material includes graphite, and the negative electrode graphite includes graphite bulk particles and carbon material disposed on at least a portion of the surface of the graphite bulk particles.

28. The battery cell according to claim 27, characterized in that, The graphite bulk particles include secondary particles; and / or, the carbon material includes amorphous carbon.

29. The battery cell according to claim 27 or 28, characterized in that, The negative electrode active material satisfies at least one of the following conditions: (1) The Dv50 of the negative electrode active material is 9μm-18μm; (2) The Dv90 of the negative electrode active material is 21μm-35μm; (3) The Dv99 of the negative electrode active material is 27μm--65μm, and can be selected as 33μm-41μm.

30. The battery cell according to any one of claims 1-29, characterized in that, The electrode assembly further includes a separator film disposed on at least one side of the positive electrode sheet. The separator film includes a base film and a coating disposed on at least one side of the base film. The coating includes ceramic particles and a binder. The ceramic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Optionally, the adhesive includes one or more of polyvinylidene fluoride and polymethyl methacrylate.

31. The battery cell according to claim 30, characterized in that, The thickness of the base film is 3μm-9μm, optionally 4μm-7μm; and / or, the thickness of the coating on one side is 3μm-8μm.

32. The battery cell according to claim 30 or 31, characterized in that, The porosity of the isolation membrane is 20%-70%, optionally 20%-50%.

33. The battery cell according to any one of claims 1-32, characterized in that, The battery cell also includes a housing and an end cap assembly. The housing has a housing opening, the electrode assembly is housed within the housing, and the end cap assembly covers the housing opening. The end cap assembly includes a cover plate and an electrode terminal. The cover plate has a mounting hole. The electrode terminal includes a first connecting part and a second connecting part connected together. The first connecting part is located on the side of the cover plate facing the electrode assembly and is electrically connected to the electrode assembly. The second connecting part passes through the mounting hole and protrudes from the surface of the cover plate away from the electrode assembly. The cross-sectional area of ​​the first connecting portion perpendicular to the thickness direction of the cover plate is greater than the area of ​​the mounting hole.

34. The battery cell according to any one of claims 1-33, characterized in that, The capacity of the battery cell is 400Ah-3000Ah.

35. A battery device, characterized in that, Includes the battery cell according to any one of claims 1-34.

36. An energy storage device, characterized in that, Includes the battery device of claim 35, the battery device being used for storing electrical energy.

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