Battery cell, secondary battery, electric apparatus, preparation method, computer device and computer-readable storage medium

Abstract

The present application provides a battery cell. The battery cell comprises a multi-layer structure formed of positive electrode sheets, negative electrode sheets and separators, wherein each separator is arranged between a positive electrode sheet and a negative electrode sheet. The battery cell can provide a charging rate greater than or equal to 2C. The multi-layer structure at least comprises a non-planar region, wherein in the non-planar region, the distance L1 between inner opposite surfaces of any adjacent positive and negative electrode sheets at any position has an appropriate value, such that the battery cell has an acceptable cycle life at the charging rate.

Description

Battery cell, secondary battery, electric device, manufacturing method, computer equipment and computer-readable storage medium Technical Field

[0001] The present application relates to the technical field of secondary batteries, and further to a battery cell, a secondary battery, an electrical device, a preparation method, a computer device, and a computer-readable storage medium. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, secondary batteries, primarily lithium-ion batteries, have been increasingly used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the accelerating pace of life, the demand for fast-charging secondary batteries is becoming increasingly significant. Achieving good cycle performance and a long battery life in fast-charging mode has become a key issue in the development and promotion of fast-charging batteries.

[0004] Summary of the Invention

[0005] According to various embodiments and examples of the present application, the present application provides a battery cell, a secondary battery, an electrical device, a manufacturing method, a computer device, and a computer-readable storage medium. The battery cell can provide a high charge rate while also achieving good cycle performance and a long service life.

[0006] In the first aspect, the present application provides a battery cell, which includes a multilayer structure formed by a positive electrode sheet, a negative electrode sheet and a separator; the separator is arranged between the positive electrode sheet and the negative electrode sheet; the battery cell can provide a charging rate greater than or equal to 2C; the multilayer structure includes at least a non-flat area; in the non-flat area, the distance between the inner relative surfaces of any adjacent positive electrode sheet and negative electrode sheet at any position is recorded as L1, and L1 has a suitable value so that the battery cell has an acceptable cycle life at the aforementioned charging rate.

[0007] In this application, unless otherwise specified, "acceptable cycle life" refers to the cycle life required of a battery cell. For example, this can be expressed as: the battery cell can cycle at least a predetermined number of times at a specified charge rate. The cycle life requirement can be determined according to international standards, national standards, industry standards, or agreed standards, as long as the battery cell has practical application value.

[0008] In some embodiments, a battery cell is provided, comprising an electrode assembly and an electrolyte, wherein the electrode assembly is immersed in the electrolyte; the electrode assembly comprises a multilayer structure formed by a positive electrode sheet, a negative electrode sheet, and a separator; the separator is disposed between the positive electrode sheet and the negative electrode sheet;

[0009] The battery cell can provide a charge rate greater than or equal to 2C, or the maximum charge rate of the battery cell is greater than or equal to 2C;

[0010] The multilayer structure includes at least a non-straight region, wherein, in the non-straight region, in a cross section perpendicular to the thickness direction of the multilayer structure, the connecting line of the thickness centers of each structural layer in the multilayer structure is a non-straight line; in the non-straight region, the distance between the inner relative surfaces of any adjacent positive electrode sheet and the negative electrode sheet at any position is recorded as L1,

[0011] In the electrode assembly, L1≤MAX; wherein MAX is the acceptable maximum value of L1 when the battery cell is at the corresponding maximum charge rate.

[0012] In some embodiments, MAX is in the range of: 100 μm <MAX<175μm。

[0013] In other embodiments, a battery cell is provided, comprising an electrode assembly and an electrolyte, wherein the electrode assembly is immersed in the electrolyte; the electrode assembly comprises a multilayer structure formed by a positive electrode sheet, a negative electrode sheet, and a separator; the separator is disposed between the positive electrode sheet and the negative electrode sheet;

[0014] The battery cell can provide a charge rate greater than or equal to 2C, or the maximum charge rate of the battery cell is greater than or equal to 2C;

[0015] The multilayer structure includes at least a non-straight region, wherein, in the non-straight region, in a cross section perpendicular to the thickness direction of the multilayer structure, the connecting line of the thickness centers of each structural layer in the multilayer structure is a non-straight line; in the non-straight region, the distance between the inner relative surfaces of any adjacent positive electrode sheet and the negative electrode sheet at any position is recorded as L1,

[0016] In the electrode assembly, L1<175 μm.

[0017] In the battery cell provided in the present application, the electrode assembly includes a multilayer structure formed by a positive electrode sheet, a negative electrode sheet and an isolation membrane. The multilayer structure includes at least a non-flat area. In the non-flat area, the distance between the inner relative surfaces of any adjacent positive electrode sheet and negative electrode sheet is recorded as L1. By controlling L1 within an appropriate range, the non-flat area of ​​the electrode assembly does not have an abnormal L1 value that is too high, which can provide a suitable transmission distance for fast ion conduction under the fast charging system, reduce or control the internal resistance between the positive and negative electrode sheets, reduce the potential difference between the positive and negative electrode sheets, and facilitate the rapid deintercalation of active ions, which is conducive to reducing the risk of lithium plating, and can reduce or delay lithium plating, thereby improving the cycle performance and service life of the fast charging battery.

[0018] L1 can be controlled within an appropriate range by controlling L1≤MAX or L1<175μm. MAX is the maximum acceptable value of L1 for the battery cell at the corresponding maximum charge rate. This allows the battery cell to control the degree of lithium plating below a certain level when L1≤MAX is satisfied, thereby achieving an acceptable cycle life. This also means that when L1 in a battery cell is greater than MAX, the battery cell may not be able to achieve an acceptable cycle life.

[0019] In some embodiments, MAX is determined according to an acceptable self-discharge rate range of the battery cell, so that a battery cell having a characteristic of L1=MAX has an acceptable self-discharge rate.

[0020] In some embodiments, MAX satisfies the following condition: the self-discharge parameter K value of the battery cell, after cycling a preset number of cycles at its maximum charge rate, where at least a portion of the cell satisfies L=MAX, is within an acceptable range;

[0021] The battery cell includes at least a portion of the positive electrode sheet, at least a portion of the separator, and at least a portion of the negative electrode sheet, which are arranged in sequence, and also includes at least a portion of the electrolyte; L is the distance between the positive electrode sheet and the negative electrode sheet in the battery cell, that is, the distance between the inner relative surfaces of the positive electrode sheet and the negative electrode sheet in the battery cell;

[0022] During the process of cycling the preset number of times at the maximum charge rate, each cycle is charged to 70% SOC and then discharged to 3% SOC. After the last cycle, the self-discharge parameter K value is tested by charging to 70% SOC.

[0023] When L1 has an appropriate value, the risk of lithium plating in the battery cell is reduced, thereby suppressing self-discharge. Therefore, the appropriate MAX value can be determined based on the acceptable range of self-discharge rates. For example, the appropriate MAX value can be determined based on the acceptable range of self-discharge parameter K.

[0024] In some embodiments, MAX is selected from any of the following:

[0025] The battery cell can provide a charge rate greater than or equal to 3C, MAX = 173 μm;

[0026] The battery cell can provide a charge rate greater than or equal to 4C, MAX = 157 μm; and

[0027] The battery cell can provide a charge rate greater than or equal to 6C, MAX=133 μm.

[0028] When the battery cell has a relatively high charge rate, by controlling L1 to have a relatively low value, it is beneficial to provide a spacing that is more suitable for rapid conduction of active ions in a fast charging system with a relatively high charge rate, and is more conducive to reducing the risk of lithium plating in the fast charging system, thereby being more conducive to improving the cycle performance and service life of the battery cell.

[0029] In some embodiments, the battery cell can provide at least one charging rate of 3C to 6C.

[0030] In some embodiments, the battery cell is capable of providing at least one of a 3C, 4C, and 6C charge rate.

[0031] In some embodiments, the battery cell can provide at least one charge rate of 4C to 6C.

[0032] In some embodiments, the battery cell is capable of providing the charge rate under at least one temperature condition between 20°C and 40°C;

[0033] Optionally, the battery cell can provide the charging rate under at least one temperature condition between 20°C and 30°C.

[0034] The aforementioned battery cells can provide a fast charging system with various charging rates.

[0035] In some embodiments, in the electrode assembly, the battery cells can provide a charge rate greater than or equal to 3C, and L1 is less than or equal to 173 μm, that is, there is no L1 greater than 173 μm;

[0036] Optionally, the battery cell can provide a charge rate greater than or equal to 4C, and in the electrode assembly, L1 is less than or equal to 157 μm, that is, there is no L1 greater than 157 μm;

[0037] Optionally, the battery cell can provide a charge rate greater than or equal to 6C, and in the electrode assembly, L1 is less than or equal to 133 μm, that is, there is no L1 greater than 133 μm.

[0038] By controlling the L1 value in the non-flat area of ​​the electrode assembly within the aforementioned range, it is helpful to better reduce the risk of lithium plating, thereby better improving the cycle performance and service life of the fast-charging battery.

[0039] In some embodiments, in the non-straight area, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and the negative electrode sheets, and the gap spacing at any position is recorded as g1, then the corresponding parameters at any position satisfy L1>g1.

[0040] The positive electrode, separator, and negative electrode located in the non-straight area are not planar but bent at a certain angle. The different degrees of bending on the inside and outside result in inconsistent forces on the inside and outside. By setting a gap between the positive and negative electrode sheets so that L1>g1, space is reserved for the expansion of the sheet during the charge and discharge cycle, which helps release the expansion force of the sheet and reduces the risk of cracking when the internal and external forces are inconsistent. This helps improve the structural stability of the sheet, reduces the degree of deformation and cracking risk of the sheet, and improves the cycle performance and service life of the fast-charging battery.

[0041] In some embodiments, in the electrode assembly, g1 is less than or equal to 160 μm, that is, there is no g1 greater than 160 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0042] In some embodiments, in the electrode assembly, g1 is less than or equal to 144 μm, that is, there is no g1 greater than 144 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0043] In some embodiments, in the electrode assembly, g1 is less than or equal to 120 μm, that is, there is no g1 greater than 120 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0044] By controlling g1 in the non-flat area of ​​the electrode assembly within the aforementioned range, it is beneficial to better control L1 within an appropriate range to avoid excessively high L1 abnormal values, which is beneficial to better reduce or delay lithium plating and better improve the cycle performance and service life of the fast-charging battery.

[0045] In some embodiments, in the electrode assembly, g1 is greater than or equal to 24 μm.

[0046] By controlling g1 in the non-flat area of ​​the electrode assembly within the aforementioned range, it is beneficial to reserve more sufficient expansion force release space for the expansion of the electrode, which is beneficial to better improve the structural stability of the electrode and reduce the degree of deformation and cracking risk of the electrode, thereby better improving the cycle performance and service life of the fast-charging battery.

[0047] In some embodiments, in the electrode assembly, 24 μm ≤ g1 ≤ 160 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0048] In some embodiments, in the electrode assembly, 24 μm≤g1≤144 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0049] In some embodiments, in the electrode assembly, 24 μm ≤ g1 ≤ 120 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0050] By controlling g1 within the aforementioned range, it is beneficial to reserve more sufficient space for the expansion of the electrode to better improve the structural stability of the electrode and reduce the degree of deformation and cracking risk of the electrode. It is also beneficial to better control L1 to reduce or delay lithium plating, thereby better improving the cycle performance and service life of the fast-charging battery.

[0051] In addition, controlling g1 within the aforementioned range is also beneficial for fully utilizing the electrolyte and fully soaking the electrode plates.

[0052] In some embodiments, the battery cell satisfies at least one of the following characteristics:

[0053] In the multi-layer structure, the number of layers of the negative electrode sheet along the thickness direction of the multi-layer structure is multiple;

[0054] The multilayer structure includes a multilayer winding structure formed by winding the positive electrode sheet, the negative electrode sheet, and the separator, and the non-straight area is located at a corner area of ​​the multilayer winding structure;

[0055] The multi-layer structure further includes a flat region.

[0056] In some embodiments, at least a portion of the non-straight areas are smoothly connected non-straight areas; in the smoothly connected non-straight areas, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the center connection line of the layer thickness of each structural layer in the multilayer structure is a smooth curve.

[0057] By setting at least a part of the non-straight area as a smoothly connected non-straight area, it is beneficial to reduce the internal stress of the pole piece in the non-straight connection area, improve the structural stability of the pole piece, reduce the degree of deformation and cracking risk of the pole piece, and increase the service life of the pole piece.

[0058] In some embodiments, at least a portion of the non-straight area is an arc-shaped area; in the arc-shaped area, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the shape of the layer thickness center connection line of each structural layer in the multilayer structure is an arc.

[0059] By setting at least a portion of the non-straight area as a smooth arc connection, it is more conducive to reducing the internal stress of the pole piece in the non-straight connection area, and is more conducive to improving the structural stability of the pole piece, reducing the degree of deformation and cracking risk of the pole piece, and increasing the service life of the pole piece.

[0060] In some embodiments, at least a portion of the non-straight region is an arc region or an arc-like region;

[0061] In the arc region, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the shape of the connecting line of the layer thickness centers of each structural layer in the multilayer structure is an arc shape;

[0062] In the arc-like region, in a cross section perpendicular to the thickness direction of the multilayer structure, the standard deviation of the curvature radius of the thickness center connecting line of each structural layer in the multilayer structure at each position is ±10%.

[0063] By setting at least a portion of the non-straight area to a smooth arc or quasi-arc connection, it is more conducive to reducing the internal stress of the pole piece in the non-straight connection area, and is more conducive to improving the structural stability of the pole piece, reducing the degree of deformation and cracking risk of the pole piece, and increasing the service life of the pole piece.

[0064] In some embodiments, in the non-flat region, the difference between the maximum thickness and the minimum thickness of the negative electrode sheet of any layer at any position is recorded as δ N , satisfying δ N ≤6μm;

[0065] Optionally, in the non-straight region, δ N ≤4μm.

[0066] In some embodiments, in the non-flat region, the average thickness of the negative electrode sheet is denoted as d mN ;

[0067] In the non-flat area, the thickness and d of the negative electrode sheet of any layer at any position mN The difference is in the range of -3μm to 3μm;

[0068] Optionally, in the non-flat region, the thickness and d of the negative electrode sheet of any layer at any position are mN The difference is in the range of -2μm to 2μm.

[0069] By adjusting δ N And adjust the thickness of the negative electrode sheet and d mN The thickness consistency of the electrode sheet can be adjusted by one or more parameter values ​​such as the difference between the positive and negative electrode sheets. The higher the thickness consistency of the electrode sheet, the more conducive it is to improving the uniformity of the distance L1 between the positive and negative electrode sheets and the gap g1 between the positive and negative electrode sheets, and the more conducive it is to uniform distribution of stress within the electrode sheet.

[0070] In some embodiments, in the non-flat region, the thickness of the negative electrode sheet of any layer at any position is recorded as D N , then D N ≤143μm; optionally, the battery cell can provide a charging rate greater than or equal to 3C.

[0071] In some embodiments, in the non-straight region, D N ≤135μm; optionally, the battery cell can provide a charging rate greater than or equal to 4C.

[0072] In some embodiments, in the non-straight region, D N ≤119μm; optionally, the battery cell can provide a charging rate greater than or equal to 6C.

[0073] In some embodiments, in the non-straight region, D N ≥55μm.

[0074] Adjusting the thickness of the negative electrode sheet within the aforementioned range is more conducive to improving the uniformity of the distance L1 between the positive and negative electrode sheets and the gap g1 between the positive and negative electrode sheets. In addition, the lower the thickness of the negative electrode sheet, the smaller the stress difference between the thickness center and the surface of the sheet, which is more conducive to improving the structural stability of the sheet and reducing the degree of deformation and cracking risk of the sheet.

[0075] In some embodiments, the negative electrode sheet includes a negative electrode active material layer;

[0076] In any selected area of ​​the negative electrode active material layer in any layer of the non-flat area, the single-side density of the negative electrode active material layer is recorded as σ N ; Among them, σ N The ratio of the weight of the negative electrode active material layer located on one side of the negative electrode plate in the corresponding selected area to the area of ​​the negative electrode active material layer in the corresponding selected area; the area of ​​any selected area of ​​any layer of the negative electrode active material layer is greater than or equal to 1540.25 mm 2 ; σ N≤170mg / 1540.25mm 2 ;

[0077] Optionally, the battery cell can provide a charging rate greater than or equal to 3C.

[0078] In some embodiments, in the non-flat region, σ N ≤160mg / 1540.25mm 2 ; Optionally, the battery cell can provide a charging rate greater than or equal to 4C.

[0079] In some embodiments, in the non-flat region, σ N ≤150mg1540.25 / mm 2 ; Optionally, the battery cell can provide a charging rate greater than or equal to 6C.

[0080] By adjusting the density of the negative electrode sheet on a single side within the aforementioned range, the thickness of the active material layer can be indirectly adjusted, thereby indirectly regulating the thickness of the negative electrode sheet. For example, the thickness of the active material layer can be indirectly adjusted within a suitable compaction density range.

[0081] In some embodiments, in the non-flat region, σ N ≥120mg / 1540.25mm 2 .

[0082] By adjusting the single-side density of the negative electrode sheet within the aforementioned range, it is helpful to provide a more appropriate compaction density.

[0083] In some embodiments, the negative electrode sheet includes a negative electrode active material layer;

[0084] The thickness of a single side of the negative electrode active material layer is 31.5 μm to 49.5 μm, and can be optionally 34 μm to 38.5 μm.

[0085] By adjusting the thickness of the negative active material layer on one side of the negative electrode sheet, the thickness of the active material layer can be indirectly adjusted, and thus the thickness of the negative electrode sheet can be indirectly controlled. For example, the thickness of the active material layer can be indirectly adjusted within a suitable compaction density range.

[0086] In some embodiments, in any selected area of ​​the negative electrode active material layer in any layer of the non-flat region, the single-side compaction density of the negative electrode active material layer is recorded as p N ; Among them, ρ N The ratio of the weight of the negative electrode active material layer located on one side of the negative electrode plate in the corresponding selected area to the volume of the negative electrode active material layer in the corresponding selected area; the area of ​​any selected area of ​​any layer of the negative electrode active material layer is greater than or equal to 1540.25 mm2 ; 1.52g / cm 3 ≤ρ N ≤1.70g / cm 3 ;

[0087] Optionally, in the non-straight area, 1.55 g / cm 3 ≤ρ N ≤1.60g / cm 3 .

[0088] By adjusting the compaction density of the negative electrode active material layer in the negative electrode sheet, the thickness of the active material layer can be indirectly adjusted, and then the thickness of the negative electrode sheet can be indirectly controlled.

[0089] In some embodiments, the negative electrode active material layer includes a negative electrode active material;

[0090] The negative electrode active material D v 50 is in the range of 6.5μm to 12μm, wherein the D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%;

[0091] Optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0092] In some embodiments, the D of the negative electrode active material v 50 is in the range of 7μm to 12μm; optionally, the battery cell can provide a charging rate greater than or equal to 4C.

[0093] In some embodiments, the D of the negative electrode active material v 50 is in the range of 8μm to 12μm; optionally, the battery cell can provide a charging rate greater than or equal to 3C.

[0094] By adjusting the particle size distribution characteristics of the negative electrode active material in the negative electrode active material layer (such as D v 50), can regulate the ion transport channel in the negative electrode active material layer, thereby affecting the fast charging capability of the battery. v The smaller 50 is, the more conducive it is to shortening the ion transmission path and providing a higher charging rate.

[0095] In some embodiments, the negative electrode active material includes a carbon-based material;

[0096] Optionally, the carbon-based material includes one or more of graphite material, soft carbon and hard carbon.

[0097] In some embodiments, the negative electrode active material includes a silicon-based material;

[0098] Optionally, the silicon-based material includes one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys.

[0099] By adjusting the type of negative electrode active material in the negative electrode active material, the expansion characteristics of the negative electrode sheet can be adjusted.

[0100] In some embodiments, the negative electrode sheet is an expandable negative electrode sheet;

[0101] In the same charge and discharge cycle, the negative electrode is charged to a SOC greater than or equal to 70% and discharged to a SOC less than or equal to 10%. The thickness of the negative electrode during charging is greater than the thickness during discharging. The ratio of the thickness during charging to the thickness during discharging is recorded as R. N , then R N >1;

[0102] Optionally, in the non-straight region, R N ≥1.17.

[0103] In some embodiments, in the non-straight region, R N ≤1.50, optionally, R N ≤1.36.

[0104] In some embodiments, regarding R N The determination is that during the same charge and discharge cycle, the SOC is charged to 97% and discharged to 3%;

[0105] Optionally, during the same charge and discharge cycle, the battery is charged to full charge and discharged to full discharge.

[0106] In some embodiments, in the non-flat region, during at least one charge-discharge cycle, the negative electrode is charged to a SOC greater than or equal to 70% and discharged to a SOC less than or equal to 10%. The difference in thickness between the negative electrode sheet during charge and discharge is denoted as δ dN , satisfying δ dN / 2 <g1;

[0107] Wherein, in the non-straight area, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets, and the gap spacing at any position is recorded as g1.

[0108] In some embodiments, regarding δ dN Determination, during the at least one charge and discharge cycle, charging to 97% SOC and discharging to 3% SOC;

[0109] Optionally, during the at least one charge-discharge cycle, the battery is charged to full charge and discharged to full discharge.

[0110] In some embodiments, the separator includes a base film and a negative electrode side separator coating located on a side of the base film close to the negative electrode plate, and the negative electrode side separator coating includes compressible particles;

[0111] Optionally, the isolation membrane is provided with a positive electrode side diaphragm coating on the side close to the positive electrode plate, and the positive electrode side diaphragm coating includes the compressible particles. The compressible particles in the positive electrode side diaphragm coating and the compressible particles in the negative electrode side diaphragm coating may be the same or different.

[0112] As battery cells age, the irreversible expansion of the electrode gradually consumes the initial gap g1 between the positive and negative electrode sheets. By applying a separator coating containing compressible particles on the negative electrode side of the separator, further space can be reserved for electrode sheet expansion when the initial g1 is depleted, further improving electrode sheet stability and reducing the risk of electrode sheet cracking.

[0113] When a diaphragm coating containing sticky compressible particles is provided on both sides of the isolation membrane, the coating melts after hot pressing, and the diaphragm in the flat area can be better bonded to the electrodes on both sides, so that the distance between the positive and negative electrodes in the flat area is smaller, which is conducive to better achieving a high charging rate.

[0114] In some embodiments, the compressible particles include polymer particles; wherein the glass transition temperature of the polymer particles is less than or equal to 120° C.;

[0115] Optionally, the glass transition temperature of the polymer particles is greater than or equal to 10°C; further optionally, the glass transition temperature of the polymer particles is greater than or equal to 15°C; further optionally, the glass transition temperature of the polymer particles is greater than or equal to 50°C.

[0116] In some embodiments, the polymer particles include a cross-linked structure;

[0117] Optionally, the polymer particles have a partially cross-linked structure;

[0118] Further optionally, the cross-linking degree of the polymer particles is less than or equal to 90%.

[0119] Compressible particles may include compressible polymer particles, and the compressibility of the polymer particles can be adjusted by adjusting one or both of the glass transition temperature (Tg) and the degree of crosslinking of the particles. Generally, the lower the Tg, the lower the elastic modulus, the easier the particles are to deform, and thus the greater the compressibility. Generally, the lower the degree of crosslinking of the particles, the lower the rigidity, the easier it is to deform under external force, and thus the greater the compressibility.

[0120] In some embodiments, the compressible particles include sticky polymer particles, and the sticky polymer particles include one or more of polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0121] Compressible particles can have a certain degree of stickiness, such as sticky polymer particles such as polyacrylate and polyvinylidene fluoride. Taking a wound structure as an example, a separator coating containing sticky compressible particles can achieve a certain degree of adhesion between the separator and the negative electrode sheet, thereby helping to avoid the formation of excessively high L1 and g1.

[0122] In some embodiments, the compressible particles have a D v 50 is in the range of 5 μm to 10 μm, wherein the D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%;

[0123] Optionally, the compressible particles have a D v 50 is in the range of 5μm to 8.5μm.

[0124] By controlling the particle size of the compressible particles within the aforementioned range, the thickness consistency of the diaphragm coating can be improved.

[0125] In some embodiments, the weight proportion of the compressible particles in the negative electrode side separator coating is 10 wt% to 30 wt%;

[0126] Optionally, the negative electrode side separator coating further includes ceramic particles.

[0127] In some embodiments, the weight percentage of the compressible particles in the negative electrode separator coating is 15 wt % to 20 wt %.

[0128] By controlling the weight percentage of compressible particles in the separator coating, the compressible thickness of the negative-side separator coating can be adjusted, thereby adjusting the compressible space reserved for electrode expansion. By controlling the weight percentage of compressible particles in the separator coating within the aforementioned range, the stability of the electrode can be improved and the risk of electrode cracking can be reduced.

[0129] In some embodiments, in any selected area of ​​the negative electrode side separator coating layer in any layer in the non-flat region, the surface density of the negative electrode side separator coating layer is denoted as σ g ; Among them, σ gThe ratio of the weight of the negative electrode side separator coating of the corresponding selected area to the area of ​​the negative electrode side separator coating of the corresponding selected area is equal to or greater than 1540.25 mm 2 ;

[0130] The average surface density σ of the negative electrode side separator coating mG is equal to the average value of the ratio of the weight of each layer of the negative electrode side separator coating to the area of ​​the corresponding layer of the negative electrode side separator coating;

[0131] The negative electrode side separator coating meets one or more of the following characteristics:

[0132] In the non-flat area, the difference between the maximum surface density and the minimum surface density of any layer of the negative electrode side separator coating in any selected area is 0 g / m 2 ~0.4g / m 2 ;

[0133] In the non-flat region, the surface density of any layer of the negative electrode side separator coating in any selected area is σ mG The difference is -0.2g / m 2 ~0.2g / m 2 .

[0134] In some embodiments, in the non-flat region, the average thickness of the negative electrode side separator coating is d mG ;

[0135] The negative electrode side separator coating meets one or more of the following characteristics:

[0136] In the non-flat area, the thickness of any layer of the negative electrode side separator coating at any position is 2 μm to 6 μm;

[0137] In the non-flat region, the difference between the maximum thickness and the minimum thickness of any layer of the negative electrode side separator coating at any position is recorded as δ G , then 0μm≤δ G ≤2μm;

[0138] In the non-flat region, the thickness of any layer of the negative electrode side separator coating at any position is mG The difference is -2μm to 2μm, and can be optionally -1.5μm to 1.5μm.

[0139] By controlling the average surface density σ of the negative electrode side separator coating mG , the difference between the maximum surface density and the minimum surface density of any layer of the negative electrode side separator coating in any selected area in the non-flat area, the average thickness of the negative electrode side separator coating in the non-flat area, and the difference between the maximum thickness and the minimum thickness of any layer of the negative electrode side separator coating at any position in the non-flat area are recorded as δG , the thickness of any negative electrode side separator coating at any position in the non-flat area and d mG One or more of the parameters such as the difference can adjust the setting amount of the negative electrode side diaphragm coating, and thus adjust the size of the reserved space.

[0140] In some embodiments, the ionic conductivity of the electrolyte is 8 mS / cm to 18 mS / cm at at least one temperature between 20° C. and 35° C.

[0141] By adjusting the ionic conductivity of the electrolyte, the battery's fast charging capability can be adjusted. The higher the ionic conductivity, the more conducive it is to achieving a higher charge rate.

[0142] In some embodiments, the electrolyte comprises an electrolyte salt and an electrolyte solvent, and the electrolyte solvent comprises a low-viscosity solvent;

[0143] The low-viscosity solvent includes one or more of diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, ethyl acetate, methyl acetate, propyl acetate, and a solvent having a viscosity less than or equal to that of at least one of the aforementioned reagents at 25°C.

[0144] In some embodiments, the electrolyte solvent further comprises a dissociative solvent, wherein the dissociative solvent has the ability to dissolve and dissociate the electrolyte salt;

[0145] Optionally, the dissociation solvent includes one or more of ethylene carbonate and propylene carbonate.

[0146] In some embodiments, the weight proportion of the low-viscosity solvent in the electrolyte solvent is 10 wt % to 90 wt %, optionally 10 wt % to 60 wt %, and further optionally 10 wt % to 40 wt %.

[0147] By adding a low-viscosity solvent to the electrolyte, the transmission resistance of active ions can be reduced and the transmission rate of active ions can be increased, thereby improving the ionic conductivity of the electrolyte and further improving the fast charging performance of the battery.

[0148] By providing a dissociative solvent in the electrolyte, the electrolyte salt can be dissolved and dissociated, thereby playing the role of conducting active ions.

[0149] By controlling the weight proportion of the low-viscosity solvent in the electrolyte solvent within the aforementioned range, it is beneficial to have a faster active ion transfer rate while dissolving and dissociating the electrolyte salt, and is more conducive to improving the ionic conductivity of the electrolyte and enhancing the fast charging performance of the battery.

[0150] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active substance;

[0151] The positive electrode active material includes a lithium-containing active material;

[0152] Optionally, the positive electrode active material includes one or more of lithium-containing phosphates, lithium transition metal oxides, and modified products of any of the foregoing substances;

[0153] Optionally, the lithium-containing phosphate includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon;

[0154] Optionally, the lithium transition metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified products of any of the foregoing substances;

[0155] Any of the aforementioned modified substances is a positive electrode active material containing a modifying element, wherein the modifying element exists in the form of a doping element, a coating element, or a combination of a doping element and a coating element.

[0156] By adjusting the type of positive electrode active material in the positive electrode sheet, the active ion supply side kinetics can be adjusted, thereby adjusting the fast charging capability of the battery.

[0157] In some embodiments, in the non-flat region, the thickness of the isolation film at any position is recorded as d1, and the corresponding parameters at any position satisfy L1=g1+d1;

[0158] In the electrode assembly, 4 μm≤d1≤13 μm; optionally, in the electrode assembly, 7 μm≤d1≤13 μm.

[0159] By adjusting the thickness of the separator, the distance between the positive and negative electrodes can be adjusted, thereby adjusting the internal resistance between the positive and negative electrodes, which in turn affects the battery's fast charging capability. The shorter the distance between the positive and negative electrodes, the more conducive it is to achieving a higher charge rate.

[0160] In some embodiments, in the electrode assembly, 28 μm≤L1≤173 μm; optionally, in the electrode assembly, 31 μm≤L1≤173 μm.

[0161] By controlling L1 in the non-flat area of ​​the electrode assembly within the aforementioned range, it is beneficial to reserve more sufficient space for the expansion of the electrode to better improve the structural stability of the electrode, reduce the degree of deformation and cracking risk of the electrode, and better reduce or delay lithium plating, thereby better improving the cycle performance of the battery and increasing the service life of the battery.

[0162] In some embodiments, the battery cell satisfies any of the following conditions:

[0163] Case B1: The battery cell can provide a charge rate of 3C, 28μm≤L1≤173μm;

[0164] Case B2: The battery cell can provide a charge rate of 4C, 28μm≤L1≤157μm;

[0165] Case B3: the battery cell can provide a charge rate of 6C, and 28 μm≤L1≤133 μm.

[0166] In some embodiments, in the non-flat region, there is a gap between the inner facing surfaces of any adjacent positive electrode sheets and the negative electrode sheets, and the gap spacing at any position is denoted as g1;

[0167] The negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active substance; the particle size corresponding to the cumulative volume distribution percentage of the multi-particle mixture reaching 50% is recorded as D v 50;

[0168] The battery cell meets one or more of the following characteristics:

[0169] In the case B1, 24 μm ≤ g1 ≤ 160 μm;

[0170] In the case B1, the D v 50 is 8μm~12μm;

[0171] In the case B2, 24 μm ≤ g1 ≤ 144 μm;

[0172] In the case B2, the D v 50 is 7μm~12μm;

[0173] In the case B3, 24 μm ≤ g1 ≤ 120 μm;

[0174] In the case B3, the D v 50 is 6.5μm~12μm.

[0175] In a second aspect of the present application, a secondary battery is provided, comprising the battery cell described in the first aspect of the present application.

[0176] In a third aspect of the present application, an electrical device is provided, which includes at least one of the battery cell described in the first aspect of the present application and the secondary battery described in the second aspect of the present application.

[0177] In a fourth aspect of the present application, a method for preparing a battery cell is provided, comprising the following steps:

[0178] Disposing a separator between a positive electrode sheet and a negative electrode sheet, controlling the positions of the positive electrode sheet and the negative electrode sheet according to a preset gap distance between the positive electrode sheet and the negative electrode sheet, forming a multilayer structure with the positive electrode sheet, the negative electrode sheet, and the separator, and subjecting at least a portion of the multilayer structure to a non-flat region through a process including cold pressing, thereby preparing an electrode assembly that has not been subjected to chemical formation treatment; wherein, in the non-flat region, in a cross section perpendicular to the thickness direction of the multilayer structure, a connecting line of the center thicknesses of the structural layers in the multilayer structure is a non-straight line; and

[0179] Immersing the electrode assembly that has not been subjected to formation treatment in an electrolyte and subjecting it to a process including formation to prepare a battery cell having a charge rate that meets a preset value; wherein the preset charge rate value is greater than or equal to 2C;

[0180] in,

[0181] The prepared battery cell is the battery cell described in the first aspect of the present application. In the non-flat region of the battery cell, the distance between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets at any position is recorded as L1.

[0182] In some embodiments, the method for preparing a battery cell includes the following steps: determining a preset range of L1 according to an acceptable self-discharge rate range, so that the prepared battery cell has an acceptable self-discharge rate.

[0183] In some embodiments, the multilayer structure includes a multilayer winding structure formed by winding the positive electrode sheet, the negative electrode sheet, and the separator, and the non-straight region is located at a corner region of the multilayer winding structure;

[0184] In the step of forming the positive electrode sheet, the negative electrode sheet and the separator into a multilayer structure, L1 is controlled within a preset range by controlling the winding tension.

[0185] In some embodiments, in the non-flat region of the electrode assembly that has not been subjected to chemical formation treatment, the distance between the inner opposing surfaces of any adjacent positive electrode sheet and the negative electrode sheet at any position is recorded as L0, and L0 ≥ L1;

[0186] In the electrode assembly that has not been subjected to chemical formation treatment, L0 is less than or equal to 213 μm, that is, there is no L0 greater than 213 μm;

[0187] Optionally, the battery cell can provide a charge rate greater than or equal to 3C;

[0188] Optionally, in the electrode assembly that has not been subjected to formation treatment, L0 is less than or equal to 193 μm, that is, there is no L0 greater than 193 μm. Further, optionally, the battery cell can provide a charge rate greater than or equal to 4C;

[0189] Optionally, in the electrode assembly that has not been subjected to formation treatment, L0 is less than or equal to 163 μm, that is, there is no L0 greater than 163 μm. Further optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0190] By controlling the L0 value in the non-flat area of ​​the electrode assembly that has not been subjected to chemical formation treatment within the aforementioned range, it is beneficial to better reduce the risk of lithium plating for the battery cells obtained after chemical formation treatment, thereby better improving the cycle performance and service life of the battery cells.

[0191] In some embodiments, in the non-flat area of ​​the electrode assembly that has not been subjected to chemical formation treatment, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and the negative electrode sheets, and the gap spacing at any position is recorded as g0, then the corresponding parameters at any position satisfy L0>g0.

[0192] In some embodiments, in the electrode assembly that has not been subjected to chemical formation treatment, g0 is less than or equal to 200 μm, that is, there is no g0 greater than 200 μm;

[0193] Optionally, the battery cell can provide a charging rate greater than or equal to 3C.

[0194] In some embodiments, in the electrode assembly that has not been subjected to chemical formation treatment, g0 is less than or equal to 180 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0195] In some embodiments, in the electrode assembly that has not been subjected to chemical formation treatment, g0 is less than or equal to 150 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0196] By controlling g0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, for the battery cells obtained after the formation treatment, it is beneficial to better control the L1 of the battery cells within an appropriate range to avoid excessively high L1 abnormal values, which is beneficial to better reduce or delay lithium plating and better improve the cycle performance and service life of the battery cells.

[0197] In some embodiments, in the electrode assembly that has not been subjected to chemical formation treatment, g0 is greater than or equal to 30 μm.

[0198] By controlling g0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, for the battery cell obtained after the formation treatment, it is beneficial to reserve more sufficient expansion force release space for the expansion of the electrode, which is beneficial to better improve the structural stability of the electrode and reduce the degree of deformation and cracking risk of the electrode, better improve the cycle performance of the battery cell and increase the service life of the battery.

[0199] In some embodiments, in the electrode assembly that has not been subjected to formation treatment, 30 μm≤g0≤200 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0200] In some embodiments, in the electrode assembly that has not been subjected to formation treatment, 30 μm≤g0≤180 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0201] In some embodiments, in the electrode assembly that has not been subjected to formation treatment, 30 μm≤g0≤150 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0202] By controlling g0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, for the battery cells obtained after the formation treatment, it is beneficial to reserve more sufficient space for the expansion of the pole pieces to better improve the structural stability of the pole pieces, reduce the degree of deformation and cracking risk of the pole pieces, and also to better control the L1 of the battery cells to reduce or delay lithium plating, thereby better improving the cycle performance of the battery cells and increasing the service life of the batteries.

[0203] In some embodiments, in the electrode assembly that has not been subjected to chemical formation treatment, 34 μm≤L0≤213 μm; optionally, in the electrode assembly that has not been subjected to chemical formation treatment, 37 μm≤L0≤213 μm.

[0204] By controlling L0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, for the battery cells obtained after the formation treatment, it is beneficial to reserve more sufficient space for the expansion of the pole pieces to better improve the structural stability of the pole pieces, reduce the degree of deformation and cracking risk of the pole pieces, and better reduce or delay lithium plating, thereby better improving the cycle performance of the battery cells and increasing the service life of the batteries.

[0205] In some embodiments, the method for preparing the battery cell satisfies any of the following conditions:

[0206] Case A1: The battery cell can provide a charge rate of 3C, 34μm≤L0≤213μm;

[0207] Case A2: The battery cell can provide a charge rate of 4C, 34μm≤L0≤193μm;

[0208] Case A3: the battery cell can provide a charge rate of 6C, and 34 μm≤L0≤163 μm.

[0209] In some embodiments, in the non-flat region of the electrode assembly that has not been subjected to chemical formation treatment, there is a gap between the inner opposing surfaces of any adjacent positive electrode sheet and the negative electrode sheet, and the gap spacing at any position is denoted as g0;

[0210] The method for preparing the battery cell meets one or more of the following characteristics:

[0211] In the case A1, 30 μm ≤ g0 ≤ 200 μm;

[0212] In the case A2, 30 μm ≤ g0 ≤ 180 μm;

[0213] In the case A3, 30 μm ≤ g0 ≤ 150 μm.

[0214] In a fifth aspect of the present application, a computer device is provided, comprising a memory and a processor, wherein the memory stores a computer program, wherein when the processor executes the computer program, the steps of the method for preparing the battery cell described in the fourth aspect of the present application are implemented.

[0215] In a sixth aspect of the present application, a computer-readable storage medium is provided, on which a computer program is stored, wherein when the computer program is executed by a processor, the steps of the method for preparing the battery cell described in the fourth aspect of the present application are implemented.

[0216] The details of one or more embodiments or examples of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0217] In order to better describe and illustrate the embodiments, examples or examples provided in this application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the currently described embodiments, examples or examples, and any of the currently understood best modes of these applications. Moreover, the same figure numbers are used to represent the same components in all the drawings. It should also be noted that the drawings are drawn in a simplified form and are only used to assist in the explanation of this application for convenience and clarity. The various dimensions of each component shown in the drawings are arbitrarily shown and may be accurate or not drawn to scale. For example, in order to make the illustration clearer, the dimensions of the components are appropriately exaggerated in some places in the drawings. Unless otherwise specified, the components in the drawings are not drawn to scale. This application does not limit every dimension of every component.

[0218] In the attached figure:

[0219] FIG1 is a schematic structural diagram of an electrode assembly in a battery cell according to an embodiment of the present application.

[0220] FIG2 is a partial enlarged view of a non-flat region of an electrode assembly in a battery cell according to an embodiment of the present application.

[0221] FIG3 is a side view of an electrode assembly having a wound structure in a battery cell in some embodiments of the present application.

[0222] FIG4 is a side view of an electrode assembly having a wound structure in a battery cell according to an embodiment of the present application.

[0223] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0224] FIG. 6 is an exploded view of the battery cell shown in FIG. 5 according to an embodiment of the present application.

[0225] FIG7 is a schematic diagram of a battery module according to an embodiment of the present application.

[0226] FIG8 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0227] FIG9 is an exploded view of the battery pack shown in FIG8 according to an embodiment of the present application.

[0228] FIG10 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0229] FIG11 is a diagram showing the internal structure of a computer device according to an embodiment of the present application.

[0230] Description of reference numerals:

[0231] 52, electrode assembly; 22, non-flat area; 120, positive electrode sheet; 1200, layer thickness center line of the positive electrode sheet; 140, isolation membrane; 160, negative electrode sheet; 1600, layer thickness center line of the negative electrode sheet; 101, first electrode sheet surface; 102, second electrode sheet surface; 103, third electrode sheet surface; 104, fourth electrode sheet surface; X0, layer thickness direction of the multi-layer structure; X1, different layer thickness positions of the positive electrode sheet in an X0 direction; X2, different layer thickness positions of the negative electrode sheet in an X0 direction; 1, battery pack; 2, upper case; 3, lower case; 4, battery module; 5, battery cell; 51, shell; 53, cover plate; 6, electrical device. DETAILED DESCRIPTION

[0232] Below, some embodiments and examples of the battery cell, secondary battery, electrical device, preparation method, computer equipment and computer-readable storage medium of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0233] " scope " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3,4 and 5 are also listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0234] In this application, references to "plurality," "multiple," "multiple," "several," and the like, unless otherwise specified, refer to a quantity greater than or equal to two. For example, "one or more" refers to one or greater than or equal to (≥, greater than or equal to) two. It is understood that references to "any number" of items refer to any suitable combination of multiple items, i.e., any combination of "any number" of items that is not conflicting and that enables the implementation of this application.

[0235] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0236] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor do they constitute independent or alternative embodiments that are mutually exclusive of other embodiments. Those skilled in the art will understand, both explicitly and implicitly, that the embodiments described herein may be combined with other embodiments. References to "implementations" herein should be understood in a similar manner.

[0237] Those skilled in the art will appreciate that, in the methods of each embodiment or embodiment, the order in which each step is written does not mean a strict order of execution and constitutes any limitation to the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present application can be performed in sequence, or can be performed randomly, or can preferably be performed in sequence. For example, method M includes steps (a) and (b), indicating that method M may include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For another example, method M may also include step (c), indicating that step (c) can be added to method M in any order, for example, method M may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0238] In this application, in open technical features or technical solutions described with words such as "contain," "include," and "include," unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or not. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" or "A is selected from a1, a2, and a3", and the feature or solution of "A includes not only a1, a2, and a3, but also other members."

[0239] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0240] In this application, "optionally," "optional," and "optional" mean optional, that is, they refer to either option selected from the two parallel options of "yes" or "no." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" is independent. Unless otherwise specified, the descriptions "optionally include," "optionally include," etc. in this application, using "optionally include" as an example, mean "may include or not include."

[0241] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more relevant listed items, and also include any and all combinations of the relevant listed items, wherein the arbitrary and all combinations include any two relevant listed items, any more relevant listed items, or a combination of all relevant listed items. For example, "A and / or B" means a group consisting of A, B, and "a combination of A and B." Among them, "including A and / or B" can mean "including A, including B, and including A and B", and can also mean "including A, including B, or including A and B", which can be appropriately understood according to the sentence in which it is located.

[0242] As used herein, "combination thereof", "any combination thereof", "any combination thereof" and the like include all suitable combinations of any two or more of the listed items.

[0243] Herein, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc. shall be based on the technical solution that can implement the present application.

[0244] Herein, the terms "preferred," "better," "more preferable," "suitable," "comparatively better," and "preferable" are used solely to describe preferred implementations or examples and should not be construed as limiting the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, each "preferred" term is considered independent unless otherwise specified and there are no contradictions or mutual constraints.

[0245] In this application, "further", "further", "particularly", "for example", "such as", "example", "for example", etc. are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0246] In this application, the terms "first," "second," "third," "fourth," etc. in "the first aspect," "the second aspect," "the third aspect," "the fourth aspect," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor should they be understood as implicitly indicating the importance or quantity of the indicated technical features. Furthermore, "first," "second," "third," "fourth," etc. serve only as non-exhaustive enumeration and description, and should be understood not to constitute a closed-ended limitation on quantity.

[0247] In this application, the term "room temperature" generally refers to 4°C to 35°C, and may refer to 20°C ± 5°C. In some embodiments of this application, room temperature refers to 20°C to 30°C.

[0248] In this application, when referring to a data range, if the unit is followed only by the right endpoint, it means that the units of the left and right endpoints are the same. For example, "3~5h" or "3-5h" both mean that the units of the left endpoint "3" and the right endpoint "5" are both hours, and both have the same meaning as "3h~5h". Similarly, descriptions of other parameters such as temperature and size are to be understood in the same manner.

[0249] The weight or mass of the relevant components mentioned in the embodiments or examples of the present application can not only refer to the content of each component, but also represent the proportional relationship of weight or mass between each component. Therefore, as long as the content of the relevant components in accordance with the embodiments or examples of the present application is proportionally enlarged or reduced, it is within the scope described in the present application. Further, the mass involved in the embodiments or examples of the present application can be mass units known to the chemical industry such as micrograms (μg), milligrams (mg), grams (g), kilograms (kg). Unless otherwise specified, the mass ratio is equal to the corresponding weight ratio, such as the mass of substance A is m1 and the weight is W1, the mass of substance B is m2 and the weight is W2, then the mass ratio m1 / m2 of the two is numerically equal to the corresponding weight ratio W1 / W2.

[0250] In this application, unless otherwise specified, wt% represents weight percentage by weight, which is numerically equal to the corresponding mass percentage by mass.

[0251] In this application, "greater than or equal to", "greater than or equal to", and "≥" have the same meaning and can be used interchangeably; "less than or equal to", "less than or equal to", and "≤" have the same meaning and can be used interchangeably; "greater than" can be equivalently expressed as ">", and "less than" can be equivalently expressed as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be regarded as providing two solutions of "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be regarded as providing two solutions of "less than" and "equal to".

[0252] In this application, exemplary descriptions such as "in some embodiments (or examples)" and "in one embodiment (or example)" may include but are not limited to the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0253] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy. Generally, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0254] In the present application, unless otherwise specified, the electrode plate can be a positive electrode plate or a negative electrode plate, and the "active material" in the electrode plate refers to a substance that can reversibly embed and release active ions. Unless otherwise specified, "negative electrode active material" refers to a substance used for the negative electrode plate that can reversibly embed and release active ions; "positive electrode active material" refers to a substance used for the positive electrode plate that can reversibly release and embed active ions. When the battery cell or secondary battery is charged, the active ions are released from the positive electrode and embedded in the negative electrode through the electrolyte; when the battery cell or secondary battery is discharged, the active ions are released from the negative electrode and embedded in the positive electrode. The active ions are not particularly limited. In some embodiments, the active ions may include lithium ions. Without limitation, the active ions may be lithium ions, which corresponds to a lithium-ion battery cell or a lithium-ion secondary battery.

[0255] In this application, "electrode sheet" and "electrode electrode sheet" have the same meaning and can be used interchangeably; "electrode active material", "electrode active substance", "active material" and "active substance" have the same meaning and can be used interchangeably; "positive electrode active substance" and "positive electrode active material" have the same meaning and can be used interchangeably; "negative electrode active substance" and "negative electrode active material" have the same meaning and can be used interchangeably. "Positive electrode active substance" and "positive electrode active material" have the same meaning and can be used interchangeably; "negative electrode active substance" and "negative electrode active material" have the same meaning and can be used interchangeably.

[0256] In this application, unless otherwise specified, an "electrode active material layer" includes at least one of the positive electrode active material layer of a positive electrode sheet and the negative electrode active material layer of a negative electrode sheet. Depending on the specific circumstances, the electrode active material layer may refer to either the positive electrode active material layer or the negative electrode active material layer. It is understood that the positive electrode active material layer contains a positive electrode active substance, and the negative electrode active material layer contains a negative electrode active substance. In this application, an "electrode active material layer" may also be simply referred to as an "active material layer."

[0257] In this application, “separator” and “diaphragm” have the same meaning and can be used interchangeably.

[0258] For fast-charging battery cells or fast-charging secondary battery systems, lithium deposition is a serious problem in the corners of the wound structure. This may be because the distance between the positive and negative electrodes in these corners is too large, resulting in a long active ion transmission path. This makes it difficult for active ions to embed into the negative electrode in time, leading to lithium deposition.

[0259] For traditional non-fast-charging battery systems (such as 1C charging rate), the required rate of active ions moving back and forth between the positive and negative electrodes is relatively low. Therefore, there is no need to strictly control the distance between the positive and negative electrodes in the corner area of ​​the electrode assembly. A larger distance between the positive and negative electrodes can be allowed without significantly affecting the cycle performance and service life of the non-fast-charging battery system. In the non-fast-charging batteries currently available on the market, a larger distance between the positive and negative electrodes is always inevitable.

[0260] In fast-charging systems, however, there are high requirements for the transfer and deintercalation rates of active ions between the positive and negative electrodes. The loose control of the distance between the positive and negative electrodes in traditional non-fast-charging systems is not suitable for fast-charging battery systems. A larger distance between the positive and negative electrodes will significantly increase the risk of lithium plating in fast-charging systems.

[0261] In the first aspect, the present application provides a battery cell, which includes a multilayer structure formed by a positive electrode sheet, a negative electrode sheet and a separator; the separator is arranged between the positive electrode sheet and the negative electrode sheet; the battery cell can provide a charging rate greater than or equal to 2C; the multilayer structure includes at least a non-flat area; in the non-flat area, the distance between the inner relative surfaces of any adjacent positive electrode sheet and negative electrode sheet at any position is recorded as L1, and L1 has a suitable value so that the battery cell has an acceptable cycle life at the aforementioned charging rate.

[0262] In this application, unless otherwise specified, "having an acceptable cycle life" refers to the cycle life that the battery cell needs to meet, which can be expressed as: it can cycle at least a preset number of times at a specified charging rate. The cycle life requirements can be determined according to international standards, national standards, industry standards or agreed standards, as long as the battery cell can have practical application value. For example, the preset number of cycles can be 1200 cycles. According to different application requirements or battery specification requirements, the preset number of cycles can be adjusted according to the required cycle life. In this application, unless otherwise specified, the "multi-layer structure" in the battery cell refers to the multi-layer structure formed by the positive electrode sheet, the negative electrode sheet and the isolation membrane, corresponding to the region in the electrode assembly that includes the positive electrode sheet, the negative electrode sheet and the isolation membrane along the layer thickness direction of the multi-layer structure. Among them, the positive electrode sheet, the negative electrode sheet and the isolation membrane respectively correspond to a structural layer in the multi-layer structure.

[0263] In this application, the "thickness direction of a multilayer structure" refers to the direction in which the layers of the multilayer structure are stacked, which can be referred to as the X0 direction in Figure 2. The negative curvature at any location or region of a non-flat region corresponds to the "concave side," and the positive curvature corresponds to the "convex side." In the non-flat region shown in Figure 2, the left side of the non-flat region corresponds to the convex side of the non-flat region, and the right side corresponds to the concave side of the non-flat region.

[0264] In the present application, “the inner relative surfaces between any adjacent positive electrode sheet and negative electrode sheet” can be understood in combination with the following description: for any adjacent positive electrode sheet and negative electrode sheet, the positive electrode sheet and the negative electrode sheet respectively have two surfaces at different positions in the stacking direction, and along the stacking direction, in the direction gradually away from the concave side of the non-straight area (refer to the X0 direction in Figure 2), the four surfaces can be respectively recorded as the first electrode sheet surface 101, the second electrode sheet surface 102, the third electrode sheet surface 103 and the fourth electrode sheet surface 104, wherein the first electrode sheet surface 101 and the second electrode sheet surface 102 are surfaces of the same electrode sheet, and the third electrode sheet surface 103 is the same electrode sheet. Surface 103 and fourth electrode surface 104 are surfaces of the same electrode electrode; since second electrode surface 102 and third electrode surface 103 are located between the two electrodes, second electrode surface 102 and third electrode surface 103 correspond to "inner relative surfaces between any adjacent positive electrode and negative electrode"; wherein, the area between second electrode surface 102 and third electrode surface 103 corresponds to the "inner side" of adjacent electrodes; the area of ​​first electrode surface 101 away from the second electrode surface 102 and the area of ​​fourth electrode surface 104 away from the third electrode surface 103 correspond to the "outer side" of adjacent electrodes.

[0265] The first electrode surface 101 and the second electrode surface 102 can correspond to either the positive electrode or the negative electrode, and the third electrode surface 103 and the fourth electrode surface 104 can correspond to either the negative electrode or the positive electrode. However, when one of the first electrode surface 101 and the third electrode surface 103 is located at the positive electrode, the other is located at the negative electrode. FIG2 only illustrates the example of the case where the first electrode surface 101 is located at the negative electrode 160 and the third electrode surface 103 is located at the positive electrode 120.

[0266] The shortest distance between any set of second pole piece surfaces 102 and third pole piece surfaces 103 at any position corresponds to L1. See Figure 2. Based on different positions on the second pole piece surface 102 near the concave side of the non-straight region, the shortest distance from that position to each position of the corresponding third pole piece surface 103 is recorded as the shortest distance between the two pole piece surfaces at that position. Corresponding to L1 at that position (see the partial schematic portion in Figure 1), each L1 between the second pole piece surface 102 and the third pole piece surface 103 can be the same or different.

[0267] In the present application, the multilayer structure in the battery cell provided in the first aspect includes at least a "non-straight area" and may also include a "straight area". The "non-straight area" means that the structural layers in the multilayer structure are not flat, but have bends. The "straight area" means that the structural layers in the multilayer structure are all flat. In the cross section perpendicular to the thickness direction of the multilayer structure (which can be recorded as a cross section), the contour lines on both sides of each structural layer in the non-straight area are non-straight lines (that is, there are concave and convex shapes, the "concave" side corresponds to the inner side, the "convex side" corresponds to the outer side, and usually, the center of curvature is located on the concave side), while the contour lines on both sides of each structural layer in the straight area are straight or basically straight. In the straight area, each structural layer in the multilayer structure is planar, and the stress conditions of each structural layer at different layer thickness positions are basically the same; in the non-straight area, each structural layer in the multilayer structure is curved, and the stress conditions of each structural layer at different layer thickness positions are inconsistent, and the internal stress conditions of each structural layer at different layer thickness positions are also inconsistent. Taking the negative electrode as an example, when the negative electrode expands, the force distribution of each structural layer in the straight area is relatively uniform, while the force of each structural layer on the two side surfaces in the non-straight area is inconsistent. For example, in the non-straight area, the first electrode surface 101 and the second electrode surface 102 have inconsistent internal stress conditions due to their different curvatures, and the third electrode surface 103 and the fourth electrode surface 104 have inconsistent internal stress conditions due to their different curvatures (see Figure 2).

[0268] Since the structural layers located in the non-straight region form a curved surface with a certain bend, the layer thickness directions of the multilayer structure at different bends may be non-parallel. For example, the two X0 directions marked in FIG. 2 are not parallel.

[0269] The aforementioned "different layer thickness locations" refer to different locations along the thickness direction of the corresponding structure. Taking the non-flat region in Figure 2 as an example, the different layer thickness locations of each structural layer in the multilayer structure refer to different locations of the corresponding structural layer along the X0 direction. For example, the positive electrode sheet or the negative electrode sheet may have different curvatures at different locations along the X0 direction, resulting in different levels of internal stress at different layer thickness locations. Figure 2 shows different layer thickness locations X1 of the positive electrode sheet along the X0 direction, and different layer thickness locations X2 of the negative electrode sheet along the X0 direction. In some embodiments, the separator 140 in the multilayer structure includes a first separator and a second separator. In some embodiments, the multilayer structure includes a first separator, a negative electrode sheet 160, a second separator, and a positive electrode sheet 120, arranged in sequence. Furthermore, a wound structure can be formed with the first separator as the innermost structural layer. In this case, in the wound multilayer structure, the positive electrode sheet 120 and the negative electrode sheet 160 are always separated by the separator 140 (see Figure 1). The first isolation film and the second isolation film are defined the same as the "isolator film" above and below. The first isolation film and the second isolation film may be the same or different.

[0270] In one embodiment, a battery cell includes an electrode assembly 52 as shown in FIG1 , which comprises a multilayer structure formed by a positive electrode sheet 120, a negative electrode sheet 160, and a separator 140. Separator 140 is disposed between positive electrode sheet 120 and negative electrode sheet 140. The multilayer structure includes a non-flat region 22 and a flat region. In FIG1 , the multilayer structure includes a first separator, a negative electrode sheet, a second separator, and a positive electrode sheet, disposed in that order.

[0271] In one embodiment, as shown in FIG2 , in a cross section perpendicular to the thickness direction of the multilayer structure (which may be referred to as a cross section), the connecting line of the thickness centers of the structural layers located in the non-straight region 22 is a curved line, while the connecting line of the thickness centers of the structural layers located in the straight region is a straight line. The connecting line 1600 of the thickness centers of the negative electrode sheet includes a straight portion located in the straight region and a curved portion located in the non-straight region. The connecting line 1200 of the thickness centers of the positive electrode sheet also includes a straight portion located in the straight region and a curved portion located in the non-straight region.

[0272] In this application, the shortest distance between the inner facing surfaces of any adjacent positive and negative electrode sheets at any location in the non-flat region can be denoted as L1, or as the "positive-negative electrode sheet spacing" in the non-flat region. The representation of L1 can also be found in the partial schematic portion of the non-flat region shown in Figure 2. Figure 2 also schematically illustrates the thickness d1 of the separator in the non-flat region.

[0273] In this application, unless otherwise specified, the spacing L1 between the positive and negative electrodes in the non-straight region refers to the shortest distance between any position on the surface of the inner electrode and the outer electrode in the inner relative surfaces between the adjacent positive electrode and the negative electrode. Among them, the electrode electrode close to the concave side of the non-straight region in the adjacent positive electrode and the negative electrode is recorded as the "inner electrode", and the electrode electrode away from the concave side of the non-straight region (that is, close to the convex side of the non-straight region) is recorded as the "outer electrode". Taking the non-straight region shown in Figure 2 as an example, of any two adjacent electrode electrodes, the electrode electrode on the left corresponds to the outer electrode, and the electrode electrode on the right corresponds to the inner electrode.

[0274] In this application, the electrode assembly can be disassembled from the battery cell to test L1. The value of L1 can be tested using a micrometer, and statistical analysis can also be performed using distance measurement software based on the cross-sectional view of the electrode assembly (see Figures 3 and 4). The cross-sectional view of the electrode assembly can be obtained by a CT measuring machine (such as the ZEISS industrial CT machine METROTOM 1500), and the corresponding cross-sectional view can also be recorded as a CT scan cross-sectional view. The cross-section of the electrode assembly can show the relative positions between the structural layers in the multi-layer structure. Taking the winding structure as an example, the cross-section of the electrode assembly is parallel to the winding direction.

[0275] Based on the CT scan cross-sectional image, the uniformity of the spacing between the positive and negative electrode sheets in the non-straight area can be preliminarily judged with the naked eye. When the unevenness of the spacing between the positive and negative electrode sheets is observable to the naked eye, the cross-section of the electrode assembly shows wrinkles of the electrode sheets or fluctuations in the spacing between the positive and negative electrode sheets that can be discerned by the naked eye, with larger L1 and smaller L1 appearing. By testing the L1 in the area where the spacing between the positive and negative electrode sheets is obviously uneven, the maximum L1 and minimum L1 measured are selected, which can be recorded as the "maximum spacing between the positive and negative electrode sheets" and "minimum spacing between the positive and negative electrode sheets" in the non-straight area, respectively. When the unevenness of the spacing between the positive and negative electrode sheets cannot be observed with the naked eye, different positions in the non-straight area are randomly selected for testing, and the maximum L1 and minimum L1 obtained from the test are recorded, where the number of randomly selected test positions is usually ≥6, and for example, ≥10, ≥15, ≥20, etc.

[0276] The test values ​​of parameters such as g1, d1, d2, L2 involved in the context of this application can also be obtained by using a micrometer test or by statistical analysis based on CT scan cross-sectional images.

[0277] In the present application, when the multilayer structure includes a flat area, the "distance between the positive and negative electrode sheets" in the flat area can also be recorded as L2, and the thickness of the isolation film in the flat area can be recorded as d2.

[0278] Taking the winding structure as a non-limiting example, the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, wound and hot pressed, and the middle main body area of ​​the multilayer structure can be flattened to form a straight area, and non-straight areas (also called corner areas) are formed on both sides of the straight area. Figures 3 and 4 show side views of the electrode assembly with a winding structure included in the battery cell in some embodiments. The side view of the electrode assembly can show the interlayer spacing of each structural layer of the multilayer structure, and the side view is perpendicular to the winding direction of each structural layer. After hot pressing, the thickness difference between the electrode sheet in the non-straight area and the straight area is not much; for the separator, when the separator is provided with a separator coating including compressible particles, since the compressible particles in the straight area can undergo deformation or morphological changes (such as melting and then solidifying), the thickness of the separator may be different between the non-straight area and the straight area.

[0279] It will be appreciated that a battery cell can be charged at a charge rate that is less than or equal to its maximum charge rate.

[0280] In this application, unless otherwise specified, the battery cell provided in the first aspect is capable of providing a charge rate greater than or equal to 2C. In this case, the maximum charge rate of the battery cell is greater than or equal to 2C. As a non-limiting example, the battery cell is capable of providing at least one charge rate of 3C to 6C. In some embodiments, the battery cell is capable of providing at least one charge rate of 3C, 4C, and 6C. In some embodiments, the battery cell is capable of providing at least one charge rate of 4C to 6C.

[0281] As a non-limiting example, the maximum charge rate of the battery cell can be selected from 2C to 6C, or from 3C to 6C, or any of the following charge rates or an interval consisting of any two of the following charge rates: 2C, 2.5C, 3C, 3.5C, 4C, 4.5C, 5C, 5.5C and 6C.

[0282] In this application, unless otherwise specified, "charge rate" refers to the ratio of charging current to capacity when charging to 97% SOC at a constant current within one hour, with charging current measured in A and capacity measured in A·h. Unless otherwise specified, the test temperature during "constant current charging" may be 20°C to 40°C, further such as 20°C to 30°C, and further such as 20°C, 25°C, 30°C, etc.

[0283] In this application, unless otherwise specified, “SOC (State of Charge)” has a commonly known meaning in the art, indicating the state of charge of a battery and reflecting the remaining power of the battery.

[0284] In some embodiments, the remaining capacity of the battery can be tested by the following method: the battery to be tested is discharged to 2.5V at a rate of 1 / 3C (this parameter can be appropriately adjusted according to the cut-off voltage of the battery), and after standing for 30 minutes, it is discharged at a constant voltage of 2.5V until the current is less than 0.05C, thereby calculating the remaining capacity.

[0285] In this application, unless otherwise specified, the "three-electrode stacking cell method" is used to test the "maximum charge rate" of the battery cell. The same positive electrode sheet, negative electrode sheet, separator and electrolyte as those in the battery cell can be prepared, or the positive electrode sheet, negative electrode sheet, separator and electrolyte disassembled or extracted from the battery cell itself can be used to assemble a three-electrode stacking cell. The following method is used to test at different charge rates to obtain a lithium precipitation window curve: charge at a certain charge rate, detect the anode potential in real time until the lithium potential is 0V, and calculate the SOC state at the charge rate; change different charge rates to test the SOC at the corresponding charge rate, so that the test results can cover the entire SOC range. The interval between different charge rates can be 0.1C, 0.2C, 0.25C, 0.4C or 0.5C. The smaller the interval, the higher the accuracy; use SOC as the horizontal axis and charge rate as the vertical axis to obtain the lithium precipitation window curve. The maximum charge rate in the lithium plating window curve is taken as the maximum charge rate of the battery cell to be tested.

[0286] In this application, unless otherwise specified, a battery cell "capable of providing a charge rate Cx" means that the battery cell can be charged under the condition of a charge rate Cx; for example, it can be charged to 97% SOC, but is not limited to this SOC state.

[0287] The statement that "multiple parallel samples are prepared by the same method" means that they are prepared by assembling the same positive electrode plate, negative electrode plate, separator, and electrolyte in the same manner. The positive electrode plate, negative electrode plate, separator, and electrolyte used can also be directly disassembled or extracted from the battery cells to be analyzed. Unless otherwise specified, the preparation process includes a formation step. After the formation step, the following steps may also be included: liquid addition and aging. The test samples can be multiple identical battery cells that have not been charged for the first time after being manufactured, or multiple identical battery cells that have undergone the same number of cycles as parallel samples, or multiple battery cells in the same state characterized by other means in the art, such as having the same SOC state.

[0288] In some embodiments, a battery cell is provided. The battery cell includes an electrode assembly and an electrolyte, and the electrode assembly is immersed in the electrolyte; the electrode assembly includes a multilayer structure formed by a positive electrode plate, a negative electrode plate, and a separator; the separator is disposed between the positive electrode plate and the negative electrode plate;

[0289] The battery cell is capable of providing a charging rate greater than or equal to 2C, or the maximum charging rate of the battery cell is greater than or equal to 2C;

[0290] The multilayer structure at least includes a non-planar region. In the non-planar region, in a cross-section perpendicular to the layer thickness direction of the multilayer structure, the center connection line of the layer thickness of each structural layer in the multilayer structure is non-linear; in the non-planar region, the distance between the inner opposite surfaces of any adjacent positive electrode plate and negative electrode plate at any position is denoted as L1.

[0291] In the electrode assembly, L1 ≤ MAX; where MAX is the acceptable maximum value of L1 when the battery cell is at the corresponding maximum charging rate.

[0292] In some embodiments, MAX is within the following range: 100μm < MAX < 175μm. MAX can also be any one of the following values or selected from any interval formed by any two of the following values: 133μm, 134μm, 135μm, 136μm, 138μm, 140μm, 145μm, 150μm, 155μm, 156μm, 157μm, 158μm, 160μm, 165μm, 170μm, 172μm, 173μm, etc.

[0293] In this application, unless otherwise specified, "MAX" is the acceptable maximum value of L1 when the battery cell is at the corresponding maximum charging rate, which enables the battery cell to control the degree of lithium plating below a certain level when L1 ≤ MAX so as to achieve an acceptable cycle life, and also means that when there is a situation where L1 in the battery cell is greater than MAX, the battery cell may not be able to achieve an acceptable cycle life.

[0294] In this application, unless otherwise specified, "MAX" corresponds to the permissible upper limit of the distance L1 between the positive and negative electrode sheets in the non-flat region. L1 values ​​exceeding MAX are considered abnormal values. In the battery cells provided in this application, the multilayer structure located in the non-flat region does not have L1 exceeding MAX. Battery cells with different maximum charge rates may correspond to different MAX values. In this application, generally speaking, the higher the maximum charge rate of a battery cell, the lower the MAX value may be.

[0295] In this application, unless otherwise specified, the following method can be used to confirm the MAX value of a battery cell: multiple positive electrodes, multiple negative electrodes and multiple isolation membranes can be disassembled from multiple identical battery cells, and the electrolyte is extracted. The isolation membrane is then set between the positive electrode sheet and the negative electrode sheet to assemble into an electrode assembly, which is then placed in a shell and injected with electrolyte to assemble multiple identical battery cells. Different L values ​​are set for the multiple battery cells (L is the distance between the positive electrode sheet and the negative electrode sheet in the battery cell, that is, the distance between the inner relative surfaces of the positive electrode sheet and the negative electrode sheet in the battery cell). Take the battery cell with an L value of 100μm for the first test: charge the battery cell to 97% SOC at the maximum charge rate (measured by the above method) and then discharge it to 3% SOC at a rate of 1C. Repeat the steps of "charging the battery cell to 97% SOC at the maximum charge rate and then discharging it to 3% SOC at a rate of 1C" for a preset number of times (which may correspond numerically to the preset number of cycles defined as "having an acceptable cycle life") and observe the lithium deposition on the surface of the negative electrode. If no lithium is deposited on the surface of the negative electrode, continue to test the remaining battery cell samples with the L value increasing by 1μm until lithium is deposited on the negative electrode surface. Stop the test and the L value at this time is the MAX value of the battery to be tested. The number of parallel samples should be sufficient to test and obtain the MAX.

[0296] In some embodiments, MAX may be determined based on an acceptable self-discharge rate range of the battery cell, such that a battery cell having a characteristic of L1 = MAX has an acceptable self-discharge rate.

[0297] In the present application, the “acceptable self-discharge rate range of a battery cell” may be a self-discharge rate range determined according to international standards, national standards, industry standards, or agreed standards.

[0298] In some embodiments, MAX satisfies the following condition: after cycling a battery cell having at least a portion of its area satisfying L=MAX for a preset number of cycles (which may correspond to the preset number of cycles defined as “having an acceptable cycle life”) at its maximum charge rate, the self-discharge parameter K value is within an acceptable range;

[0299] The battery cell includes at least a portion of a positive electrode sheet, at least a portion of a separator, and at least a portion of a negative electrode sheet, which are arranged in sequence, and also includes at least a portion of an electrolyte; L is the distance between the positive electrode sheet and the negative electrode sheet in the battery cell, that is, the distance between the inner relative surfaces of the positive electrode sheet and the negative electrode sheet in the battery cell;

[0300] During the preset number of cycles at the maximum charge rate, the battery is charged to 70% SOC and then discharged to 3% SOC in each cycle. After the last cycle, it is charged to 70% SOC to test the self-discharge parameter K value.

[0301] In the present application, the “acceptable range of the self-discharge parameter K value” may be a K value range determined according to international standards, national standards, industry standards, or agreed standards.

[0302] When L1 has an appropriate value, the risk of lithium plating in the battery cell is reduced, thereby suppressing self-discharge. Therefore, the appropriate MAX value can be determined based on the acceptable range of self-discharge rates. For example, the appropriate MAX value can be determined based on the acceptable range of self-discharge parameter K.

[0303] In this application, unless otherwise specified, "self-discharge parameter K value" has a well-known meaning in the art, which refers to the voltage drop of the battery per unit time, and is used to measure the self-discharge rate of the lithium battery. The larger the K value, the more serious the self-discharge. In this application, the K value can be obtained using conventional methods in the art. Unless otherwise specified, the test temperature can be 20°C to 30°C, such as 25°C. The following test method can be used: the battery to be tested is placed under test temperature conditions and stored for a period of time t. The open circuit voltage (OCV) at the initial moment and at the end of the test can be recorded as OCV1 and OCV2 respectively, then K = (OCV1-OCV2) / t, the test time t can be in hours (h) or days (d), and accordingly, the K value unit can be mV / h or mV / d. In this application, unless otherwise specified, the test time t can be 24h to 96h, for example, any one of 24h, 36h, 48h and 96h, or any time within the interval consisting of any two of the foregoing time periods.

[0304] In some embodiments, MAX is selected from any of the following:

[0305] The battery cell can provide a charge rate greater than or equal to 3C, MAX = 173μm;

[0306] The battery cell can provide a charge rate greater than or equal to 4C, MAX = 157μm; and

[0307] The battery cell can provide a charge rate greater than or equal to 6C, MAX=133μm.

[0308] When the battery cell has a relatively high charge rate, by controlling L1 to have a relatively low value, it is beneficial to provide a spacing that is more suitable for rapid conduction of active ions in a fast charging system with a relatively high charge rate, and is more conducive to reducing the risk of lithium plating in the fast charging system, thereby being more conducive to improving the cycle performance and service life of the battery cell.

[0309] In other embodiments, a battery cell is provided, comprising an electrode assembly and an electrolyte, wherein the electrode assembly is immersed in the electrolyte; the electrode assembly comprises a multilayer structure formed by a positive electrode sheet, a negative electrode sheet, and a separator; the separator is disposed between the positive electrode sheet and the negative electrode sheet;

[0310] The battery cell can provide a charge rate greater than or equal to 2C, or the maximum charge rate of the battery cell is greater than or equal to 2C;

[0311] The multilayer structure includes at least a non-flat region, wherein in the non-flat region, in a cross section perpendicular to the thickness direction of the multilayer structure, the connecting line of the thickness centers of each structural layer in the multilayer structure is a non-straight line; in the non-flat region, the distance between the inner relative surfaces of any adjacent positive electrode sheet and negative electrode sheet at any position is recorded as L1,

[0312] In the electrode assembly, L1 < 175 μm.

[0313] In the battery cell provided in the present application, the electrode assembly includes a multilayer structure formed by a positive electrode sheet, a negative electrode sheet and an isolation membrane. The multilayer structure includes at least a non-flat area. In the non-flat area, the distance between the inner relative surfaces of any adjacent positive electrode sheet and negative electrode sheet is recorded as L1. By controlling L1 within an appropriate range, the non-flat area of ​​the electrode assembly does not have an abnormal L1 value that is too high, which can provide a suitable transmission distance for fast ion conduction under the fast charging system, reduce or control the internal resistance between the positive and negative electrode sheets, reduce the potential difference between the positive and negative electrode sheets, and facilitate the rapid deintercalation of active ions, which is conducive to reducing the risk of lithium plating, and can reduce or delay lithium plating, thereby improving the cycle performance and service life of the fast charging battery.

[0314] L1 can be controlled within an appropriate range by controlling L1≤MAX or L1<175μm.

[0315] As a non-limiting example, the maximum charge rate of the battery cell may be greater than or equal to 3C.

[0316] As a non-limiting example, the maximum charging rate of the battery cell can be one of the charging rates from 2C to 6C, can also be one of the charging rates from 3C to 6C, and can also be any one of the following charging rates or any one of the charging rates within the range formed by any two of the following charging rates: 2C, 2.5C, 3C, 3.5C, 4C, 4.5C, 5C, 5.5C, and 6C.

[0317] In some embodiments, the battery cell can provide at least one charging rate from 2C to 6C. Optionally, the battery cell can provide at least one charging rate from 3C to 6C. Further optionally, the battery cell can provide at least one charging rate from 4C to 6C. Without limitation, the charging rates that the battery cell can provide include at least one charging rate within the range formed by any two of the following charging rates: 2C, 2.5C, 3C, 3.5C, 4C, 4.5C, 5C, 5.5C, and 6C. In some of these embodiments, the battery cell can provide at least one charging rate of 3C, 4C, and 6C.

[0318] In some embodiments, the battery cell can provide a charging rate under at least one temperature condition from 20°C to 40°C;

[0319] Optionally, the battery cell can provide a charging rate under at least one temperature condition from 20°C to 30°C. Non-limiting examples of "at least one temperature condition from 20°C to 40°C" are 20°C, 25°C, 30°C, etc. <U+

[0320] The aforementioned battery cell can provide a fast charging system with multiple specifications of charging rates.

[0321] In some embodiments, the value range of MAX is 100μm < MAX < 175μm, and it can be optionally 133μm to 173μm. MAX can also be any one of the following values or any one of the values within the range formed by any two of the following values: 133μm, 140μm, 150μm, 157μm, 160μm, 170μm, 173μm, etc. ]>

[0322] In some embodiments, the battery cell can provide a charging rate greater than or equal to 3C. In the electrode assembly, L1 is all less than or equal to 173μm, that is, there is no L1 greater than 173μm.

[0323] In some embodiments, the battery cell can provide a charging rate greater than or equal to 4C. In the electrode assembly, L1 is all less than or equal to 157μm, that is, there is no L1 greater than 157μm.

[0324] In some embodiments, the battery cells can provide a charge rate greater than or equal to 6C, and in the electrode assembly, L1 is less than or equal to 133 μm, that is, there is no L1 greater than 133 μm.

[0325] By controlling the L1 value in the non-flat area of ​​the electrode assembly within the aforementioned range, it is helpful to better reduce the risk of lithium plating, thereby better improving the cycle performance and service life of the fast-charging battery.

[0326] In some embodiments, in a non-flat region, a gap exists between the inner facing surfaces of any adjacent positive and negative electrode sheets. The gap spacing at any location is denoted as g1, and the corresponding parameters at any location satisfy L1>g1. g1 can also be denoted as the "positive and negative electrode sheet gap" or "positive and negative electrode sheet gap spacing" in the non-flat region.

[0327] In this application, unless otherwise specified, in the non-straight area, there is a gap between the inner relative surfaces of any adjacent positive electrode sheet and negative electrode sheet, the gap spacing at any position is recorded as g1, and the thickness of the isolation membrane between the inner relative surfaces at any position is recorded as d1. d1 can also be recorded as the "isolation membrane thickness" of the non-straight area. d1 can be determined as follows: the distance between the line segment corresponding to L1 and the two intersection points of the isolation membrane. The gap spacing g1 between the positive and negative electrode sheets in the non-straight area refers to the gap spacing L1 between the adjacent positive and negative electrode sheets minus the thickness d1 of the isolation membrane between the two sheets, that is, g1 = L1-d1.

[0328] The positive electrode, separator, and negative electrode located in the non-straight region are not planar, but rather bent at a certain angle. Due to the different degrees of bending on the inside and outside, the forces on the inside and outside are inconsistent. The "inside" refers to the concave side near the non-straight region, and the "outside" refers to the convex side near the non-straight region. By setting a gap between the positive and negative electrode sheets so that L1>g1, space can be reserved for the expansion of the sheets during the charge and discharge cycle, which is beneficial for releasing the expansion force of the sheets and reducing the risk of sheet cracking when the forces on the inside and outside are inconsistent. This helps to improve the structural stability of the sheets, reduce the degree of deformation and cracking risk of the sheets, and improve the cycle performance and service life of fast-charging batteries.

[0329] The test value of d1 can also be obtained by using a micrometer test or by statistical analysis based on the aforementioned CT scan cross-sectional diagram. The electrode assembly can be disassembled from the battery cell to test d1.

[0330] g1 can be calculated as g1 = L1 - d1, or as the sum of the distance between the separator and the surface of the positive electrode tab and the distance between the separator and the surface of the negative electrode tab. Separator thickness d1, the distance between the separator and the surface of the positive electrode tab, and the distance between the separator and the surface of the negative electrode tab can be calculated using a method similar to that for L1.

[0331] Based on the CT scan cross-sectional image, the uniformity of the gap between the positive and negative electrodes in the non-straight area can be preliminarily judged with the naked eye. When the unevenness of the gap between the positive and negative electrodes can be observed with the naked eye, the fluctuation of the gap between the positive and negative electrodes will appear on the cross-section of the electrode assembly, with larger g1 and smaller g1 appearing. By testing the g1 in the area where the gap between the positive and negative electrodes is obviously uneven, the maximum g1 and minimum g1 measured are selected, which can be recorded as the "maximum positive and negative electrode gap" and "minimum positive and negative electrode gap" in the non-straight area, respectively. When the unevenness of the gap between the positive and negative electrodes cannot be observed with the naked eye, different positions in the non-straight area are randomly selected for testing, and the maximum g1 and minimum g1 obtained from the test are recorded, where the number of randomly selected test positions is usually ≥6, and for example, ≥10, ≥15, ≥20, etc.

[0332] The distance L1 between the positive and negative electrodes in the non-flat region can be controlled by controlling the gap g1 between the positive and negative electrodes and the thickness d1 of the separator in the non-flat region. Fluctuations in both g1 and d1 affect the uniformity of L1, with fluctuations in the gap g1 having a greater impact on the range of L1 fluctuations. By keeping g1 below an appropriate value, L1 can be kept within an appropriate range. Controlling g1 can prevent abnormally high L1 values.

[0333] Taking the winding process as an example, the negative electrode sheet, separator, and positive electrode sheet are stacked and placed in the required position order. Taking the number of separators as an example, they are respectively recorded as the first separator and the second separator. They can be placed in the order of the first separator, the negative electrode sheet, the second separator, and the positive electrode sheet. Please refer to Figure 1. It is used to form a multilayer structure consisting of four structural layers, namely the first separator, the negative electrode sheet, the second separator, and the positive electrode sheet. When winding, a certain winding tension is applied to each structural layer so that a certain reserved gap is maintained between each structural layer for winding. By controlling the winding tension, each structural layer is kept flat and tight during the winding process, and after the winding tension is removed, the shrinkage effect on each structural layer can be minimized, thereby achieving control over the non-flat areas g1 and L1. After winding, hot pressing is performed to form a flat region and a non-flat region at the end of the flat region (the non-flat region can also be referred to as a corner region). The structural layers in the flat region are pressed into a flat surface, with adjacent layers bonded to each other. The structural layers in the non-flat region are curved, typically forming an arc-shaped surface. In the multi-layer structure formed by winding and hot pressing, a certain amount of space can be formed between the structural layers in the non-flat region, including the space g1 between the positive and negative electrode sheets.

[0334] Among them, the maximum value of g1 can be limited by one or more of the following methods, thereby helping to avoid the occurrence of abnormal L1 exceeding MAX: (1) Controlling the winding tension within an appropriate range, which can not only keep the electrode and the separator flat and tight during the winding process so that each structural layer maintains a certain gap during the winding process, but also prevent the electrode or the separator from shrinking and wrinkling after winding, so that the g1 of the non-flat area is within an appropriate range, which helps to avoid the abnormal L1 exceeding MAX. (2) By improving the thickness consistency of the electrode, including improving the thickness consistency of the negative electrode, the stress uniformity of each position of the electrode can be improved, which is conducive to reducing the probability of electrode deformation after the winding tension is applied, and is conducive to avoiding the occurrence of excessive g1, and thus helping to avoid the abnormal L1 exceeding MAX.

[0335] The uniformity of g1 can be improved by one or more of the following methods: (1) when a membrane coating is provided on the surface of the isolation membrane, the uniformity of g1 can be improved by improving the thickness consistency of the membrane coating; (2) when a membrane coating is provided on the surface of the isolation membrane, the uniformity of g1 can be improved by improving the surface density uniformity of the membrane coating; (3) when a membrane coating containing compressible particles is provided on the surface of the isolation membrane, when the particle size of the compressible particles has a certain distribution width, the thickness of the isolation membrane in the non-flat area may have a certain inconsistency. By controlling the particle size parameters of the compressible particles within a suitable range (for example, the D of the compressible particles can be controlled to be within a suitable range), the uniformity of g1 can be improved. v 50 is within the following range: 5μm~10μm), which is beneficial to improving the thickness consistency of the diaphragm coating.

[0336] In some embodiments, the upper limit of the allowable value of g1 in the non-flat region is denoted as g max , that is, in the electrode assembly, g1 is less than or equal to g max , at this time, there is no electrode assembly greater than g max g1. Without limitation, g max The value range of g can be 96μm~160μm. max It can also be any of the following values ​​or any value selected from the interval formed by any two of the following values: 96μm, 100μm, 110μm, 120μm, 130μm, 140μm, 144μm, 150μm, 160μm, etc.

[0337] In some embodiments, in the electrode assembly, g1 is less than or equal to 160 μm, that is, there is no g1 greater than 160 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0338] In some embodiments, in the electrode assembly, g1 is less than or equal to 144 μm, that is, there is no g1 greater than 144 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0339] In some embodiments, in the electrode assembly, g1 is less than or equal to 120 μm, that is, there is no g1 greater than 120 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0340] By controlling g1 in the non-flat area of ​​the electrode assembly within the aforementioned range, it is beneficial to better control L1 within an appropriate range to avoid excessively high L1 abnormal values, which is beneficial to better reduce or delay lithium plating and better improve the cycle performance and service life of the fast-charging battery.

[0341] In some embodiments, the allowable lower limit of g1 in the non-flat region is denoted as g min , that is, in the electrode assembly, g1 is greater than or equal to g min , at this time, there is no electrode assembly less than g min In some embodiments, g min 24μm.

[0342] In some embodiments, in the electrode assembly, g1 is greater than or equal to 24 μm.

[0343] By controlling g1 in the non-flat area of ​​the electrode assembly within the aforementioned range, it is beneficial to reserve more sufficient expansion force release space for the expansion of the electrode, which is beneficial to better improve the structural stability of the electrode and reduce the degree of deformation and cracking risk of the electrode, thereby better improving the cycle performance and service life of the fast-charging battery.

[0344] In some embodiments, in the electrode assembly, 24 μm ≤ g1 ≤ 160 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0345] In some embodiments, in the electrode assembly, 24 μm ≤ g1 ≤ 144 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0346] In some embodiments, in the electrode assembly, 24 μm ≤ g1 ≤ 120 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0347] By controlling g1 within the aforementioned range, it is beneficial to reserve more sufficient space for the expansion of the electrode to better improve the structural stability of the electrode and reduce the degree of deformation and cracking risk of the electrode. It is also beneficial to better control L1 to reduce or delay lithium plating, thereby better improving the cycle performance and service life of the fast-charging battery.

[0348] In addition, controlling g1 within the aforementioned range is also beneficial for fully utilizing the electrolyte and fully soaking the electrode plates.

[0349] In some embodiments, in a multi-layer structure, the number of negative electrode sheets along the thickness direction of the multi-layer structure is multiple, i.e., equal to or greater than 2. Taking a wound structure as an example, when wound n times (n is an integer greater than or equal to 2), the number of negative electrode sheets along the thickness direction of the multi-layer structure is n.

[0350] In some embodiments, the multilayer structure includes a multilayer winding structure formed by winding a positive electrode sheet, a negative electrode sheet, and a separator, and the non-straight region is located at a corner region of the multilayer winding structure.

[0351] In some embodiments, the multilayer structure further includes a flat region. In this case, the multilayer structure includes a non-flat region and a flat region.

[0352] In some embodiments, at least a portion of the non-straight region is a smoothly connected non-straight region; in the smoothly connected non-straight region, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the center connection line of the layer thickness of each structural layer in the multilayer structure is a smooth curve.

[0353] By setting at least a part of the non-straight area as a smoothly connected non-straight area, it is beneficial to reduce the internal stress of the pole piece in the non-straight connection area, improve the structural stability of the pole piece, reduce the degree of deformation and cracking risk of the pole piece, and increase the service life of the pole piece.

[0354] In some embodiments, at least a portion of the non-straight area is an arc-shaped area; in the arc-shaped area, in a cross section perpendicular to the thickness direction of the multilayer structure, the shape of the layer thickness center connection line of each structural layer in the multilayer structure is an arc.

[0355] By setting at least a portion of the non-straight area as a smooth arc connection, it is more conducive to reducing the internal stress of the pole piece in the non-straight connection area, and is more conducive to improving the structural stability of the pole piece, reducing the degree of deformation and cracking risk of the pole piece, and increasing the service life of the pole piece.

[0356] In some embodiments, at least a portion of the non-straight region is an arc region or an arc-like region;

[0357] In the arc region, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the shape of the connecting line of the layer thickness centers of each structural layer in the multilayer structure is an arc shape;

[0358] In the arc-like region, in a cross section perpendicular to the thickness direction of the multilayer structure, the standard deviation of the curvature radius of the thickness center connecting line of each structural layer in the multilayer structure at each position is ±10%.

[0359] By setting at least a portion of the non-straight area to a smooth arc or quasi-arc connection, it is more conducive to reducing the internal stress of the pole piece in the non-straight connection area, and is more conducive to improving the structural stability of the pole piece, reducing the degree of deformation and cracking risk of the pole piece, and increasing the service life of the pole piece.

[0360] In this application, in the non-flat area, the difference between the maximum thickness and the minimum thickness of the electrode sheet of any layer at any position is recorded as δ B It is understandable that B Greater than or equal to 0μm. B The smaller it is, the more uniform the thickness of the electrode sheet is.

[0361] In some embodiments, in the non-flat region, δ B ≤6μm; optionally, in non-flat areas, δ B ≤4μm.

[0362] In this application, the average thickness of the electrode sheet in the non-flat area is denoted as d m .d m The smaller the range, the more uniform the thickness of the electrode sheet.

[0363] In some embodiments, in the non-flat region, the thickness and d of the electrode sheet of any layer at any position are m The difference is in the range of -3μm to 3μm;

[0364] Optionally, in the non-flat area, the thickness and d of the electrode sheet of any layer at any position m The difference is in the range of -2μm to 2μm.

[0365] By adjusting δ B And adjust the electrode thickness and d m The thickness consistency of the electrode sheet can be adjusted by one or more parameter values ​​such as the difference between the positive and negative electrode sheets. The higher the thickness consistency of the electrode sheet, the more conducive it is to improving the uniformity of the distance L1 between the positive and negative electrode sheets and the gap g1 between the positive and negative electrode sheets, and the more conducive it is to uniform distribution of stress within the electrode sheet.

[0366] In this application, in the non-flat region, the difference between the maximum thickness and the minimum thickness of the negative electrode sheet of any layer at any position is recorded as δ N It is understandable that N Greater than or equal to 0μm. N The smaller it is, the more uniform the thickness of the negative electrode sheet is.

[0367] In some embodiments, in the non-flat region, δ N ≤6μm; optionally, in non-flat areas, δ N ≤4μm.

[0368] In this application, the average thickness of the negative electrode sheet in the non-flat area is recorded as d mN .d mN The smaller the range, the more uniform the thickness of the negative electrode sheet.

[0369] In some embodiments, in the non-flat region, the thickness and d of the negative electrode sheet of any layer at any position are mN The difference is in the range of -3μm to 3μm;

[0370] Optionally, in the non-flat region, the thickness and d of the negative electrode sheet of any layer at any position are mN The difference is in the range of -2μm to 2μm.

[0371] By adjusting δ N And adjust the thickness of the negative electrode sheet and d mN The thickness consistency of the electrode sheet can be adjusted by one or more parameter values ​​such as the difference between the positive and negative electrode sheets. The higher the thickness consistency of the electrode sheet, the more conducive it is to improving the uniformity of the distance L1 between the positive and negative electrode sheets and the gap g1 between the positive and negative electrode sheets, and the more conducive it is to uniform distribution of stress within the electrode sheet.

[0372] In this application, in the non-flat area, the thickness of the negative electrode sheet of any layer at any position is recorded as D N .

[0373] In some embodiments, in the non-flat region, D N ≤143μm; optionally, the battery cell can provide a charging rate greater than or equal to 3C.

[0374] In some embodiments, in the non-flat region, D N ≤135μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0375] In some embodiments, in the non-flat region, D N ≤119μm; optionally, the battery cell can provide a charging rate greater than or equal to 6C.

[0376] In some embodiments, in the non-flat region, D N ≥55μm.

[0377] Without limitation, in the non-flat region, D N The thickness may be any of the following or a range consisting of two of the following thicknesses: 55 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 105 μm, 110 μm, 115 μm, 119 μm, 120 μm, 130 μm, 135 μm, 140 μm, 143 μm, etc. N Non-limiting examples include 55 μm to 119 μm, 60 μm to 110 μm, 55 μm to 135 μm, 55 μm to 143 μm, etc.

[0378] Adjusting the thickness of the negative electrode sheet within the aforementioned range is more conducive to improving the uniformity of the distance L1 between the positive and negative electrode sheets and the gap g1 between the positive and negative electrode sheets. In addition, the lower the thickness of the negative electrode sheet, the smaller the stress difference between the thickness center and the surface of the sheet, which is more conducive to improving the structural stability of the sheet and reducing the degree of deformation and cracking risk of the sheet.

[0379] In this application, the negative electrode sheet includes a negative electrode active material layer; in any selected area of ​​any negative electrode active material layer in the non-flat area, the single-side density of the negative electrode active material layer is recorded as σ N ; Among them, σ N The ratio of the weight of the negative electrode active material layer located on one side of the negative electrode sheet in the corresponding selected area to the area of ​​the negative electrode active material layer in the corresponding selected area is equal to or greater than 1540.25 mm. 2 .

[0380] In some embodiments, in the non-flat region, σN ≤170mg / 1540.25mm 2 ; Optionally, the battery cell can provide a charging rate greater than or equal to 3C.

[0381] In some embodiments, in the non-flat region, σ N ≤160mg / 1540.25mm 2 ; Optionally, the battery cell is capable of providing a charge rate greater than or equal to 4C.

[0382] In some embodiments, in the non-flat region, σ N ≤150mg / 1540.25mm 2 ; Optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0383] By adjusting the density of the negative electrode sheet on a single side within the aforementioned range, the thickness of the active material layer can be indirectly adjusted, thereby indirectly regulating the thickness of the negative electrode sheet. For example, the thickness of the active material layer can be indirectly adjusted within a suitable compaction density range.

[0384] In some embodiments, in the non-flat region, σ N ≥120mg / 1540.25mm 2 .

[0385] Without limitation, in the non-flat region, σ N It can be any of the following surface densities or a range consisting of the following two surface densities: 170mg / 1540.25mm 2 、160mg / 1540.25mm 2 、150mg / 1540.25mm 2 、130mg / 1540.25mm 2 、120mg / 1540.25mm 2 wait.

[0386] By adjusting the single-side density of the negative electrode sheet within the aforementioned range, it is helpful to provide a more appropriate compaction density.

[0387] In some embodiments, the negative electrode sheet includes a negative electrode active material layer; the thickness of the negative electrode active material layer on a single side is 31.5 μm to 49.5 μm, and optionally 34 μm to 38.5 μm. The thickness of the negative electrode active material layer on a single side can also be any of the following thicknesses, or a range consisting of any two of the following thicknesses: 31.5 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48.5 μm, etc.

[0388] In this application, unless otherwise specified, the "single-sided thickness of the negative electrode active material layer" refers to the thickness of the negative electrode active material layer on one side of the negative electrode plate. When negative electrode active material layers are provided on both sides of the negative electrode plate, the thicknesses on both sides of the negative electrode plate can be the same or different.

[0389] By adjusting the thickness of the negative active material layer on one side of the negative electrode sheet, the thickness of the active material layer can be indirectly adjusted, and thus the thickness of the negative electrode sheet can be indirectly controlled. For example, the thickness of the active material layer can be indirectly adjusted within a suitable compaction density range.

[0390] In this application, in any selected area of ​​any negative electrode active material layer in the non-flat area, the single-side compaction density of the negative electrode active material layer is recorded as ρ N ; Among them, ρ N The ratio of the weight of the negative electrode active material layer located on one side of the negative electrode sheet in the corresponding selected area to the volume of the negative electrode active material layer in the corresponding selected area. Without limitation, the area of ​​any selected area of ​​any negative electrode active material layer may be greater than or equal to 1540.25 mm 2 .

[0391] In some embodiments, in the non-straight region, 1.52 g / cm 3 ≤ρ N ≤1.70g / cm 3 .

[0392] In some embodiments, in the non-straight region, 1.55 g / cm 3 ≤ρ N ≤1.60g / cm 3 .

[0393] Without limitation, in the non-flat region, ρ N It can also be any of the following compacted densities or a range consisting of any two of the following compacted densities: 1.52 g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 wait.

[0394] By adjusting the compaction density of the negative electrode active material layer in the negative electrode sheet, the thickness of the active material layer can be indirectly adjusted, and then the thickness of the negative electrode sheet can be indirectly controlled.

[0395] In some embodiments, the negative electrode active material layer includes a negative electrode active material;

[0396] D of negative electrode active material v50 is in the range of 6.5μm to 12μm, where D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%.

[0397] In some embodiments, the D of the negative electrode active material v 50 In the range of 6.5μm to 12μm, the battery cell can provide a charging rate greater than or equal to 6C.

[0398] In some embodiments, the D of the negative electrode active material v 50 is in the range of 7μm to 12μm; optionally, the battery cell can provide a charging rate greater than or equal to 4C.

[0399] In some embodiments, the D of the negative electrode active material v 50 is in the range of 8μm to 12μm; optionally, the battery cell can provide a charging rate greater than or equal to 3C.

[0400] In a non-limiting manner, the D of the negative electrode active material v 50 can also be any of the following values ​​or an interval consisting of any two of the following values: 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0401] In the context of this application, the volume cumulative distribution particle size D can be used v N (where N represents any value selected from 0 to 100) is used to characterize the particle size of the material, which refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches N%. The particle size is less than or equal to D v The volume percentage of N is N%. v N can be obtained from the volume cumulative distribution curve of the material particle size. If there is no other explanation, the volume cumulative distribution curve starts from zero from the small particle size side. v 50 is used as an example. In this application, if there is no other description, D v 50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%. This parameter indicates that the particle size of 50% of the material volume is less than or equal to D v 50, and 50% of the volume of the material has a particle size larger than D v 50. Those skilled in the art will understand that v The particle size distribution of the particle size distribution is defined as 50, and can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer or the LS-909 laser particle size analyzer (Omega), manufactured by Malvern Instruments Ltd., UK.

[0402] By adjusting the particle size distribution characteristics of the negative electrode active material in the negative electrode active material layer (such as D v 50), can regulate the ion transport channel in the negative electrode active material layer, thereby affecting the fast charging capability of the battery. v The smaller 50 is, the more conducive it is to shortening the ion transmission path and providing a higher charging rate.

[0403] In some embodiments, the negative electrode active material includes a carbon-based material. Without limitation, the carbon-based material may include one or more of graphite, soft carbon, and hard carbon.

[0404] In some embodiments, the negative electrode active material includes a silicon-based material. Without limitation, the silicon-based material may include one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0405] By adjusting the type of negative electrode active material in the negative electrode active material, the expansion characteristics of the negative electrode sheet can be adjusted.

[0406] In some embodiments, the negative electrode sheet is an expandable negative electrode sheet.

[0407] In this application, unless otherwise specified, "expandable negative electrode sheet" refers to the volume expansion of the negative electrode sheet under charging conditions relative to the volume of the negative electrode sheet under discharge conditions. N Characterizes the expansion of the negative electrode sheet. Generally, when charging and discharging a battery cell or a secondary battery, the negative electrode sheet will expand due to factors such as the embedding behavior of active ions and the change in grain spacing. N The value can be regulated by adjusting the composition of the negative electrode active material layer. For example, the R N value.

[0408] In this application, unless otherwise specified, according to the cut-off voltage of the battery cell, in the same charge and discharge cycle, when charged to greater than or equal to 70% SOC and discharged to less than or equal to 10% SOC, the thickness of the negative electrode sheet during charging is greater than the thickness during discharging, and the ratio of the thickness during charging to the thickness during discharging is recorded as R N For the expandable negative electrode, R N >1. R N The larger the value, the greater the volume expansion of the negative electrode under charging conditions. "In the same charge and discharge cycle" can refer to the first charge and discharge of the battery cell.

[0409] In some embodiments, in the non-flat region, R N ≥1.17.

[0410] In some embodiments, in the non-flat region, R N ≥1.28.

[0411] In some embodiments, in the non-flat region, R N ≤1.50, optionally, R N ≤1.36.

[0412] In some embodiments, in the non-flat region, 1.17≤R N ≤1.50.

[0413] In some embodiments, in the non-flat region, 1.17≤R N ≤1.36.

[0414] In some embodiments, in the non-flat region, 1.28≤R N ≤1.50.

[0415] In some embodiments, regarding R N In the same charge and discharge cycle, the battery is charged to 97% SOC and discharged to 10% SOC.

[0416] In some embodiments, regarding R N For the determination of charge and discharge, in the same charge and discharge cycle, charge to full charge and discharge to full discharge.

[0417] Without limitation, R N It can also be any of the following values ​​or an interval consisting of any two of the following values: 1.17, 1.20, 1.22, 1.24, 1.25, 1.26, 1.28, 1.30, 1.32, 1.33, 1.34, 1.35, 1.36, 1.40, 1.42, 1.44, 1.45, 1.46, 1.48, 1.50, etc.

[0418] In some embodiments, in the non-flat region, during at least one charge-discharge cycle, the negative electrode sheet is charged to a SOC greater than or equal to 70% and discharged to a SOC less than or equal to 10%. The difference in thickness between the negative electrode sheet during charge and discharge is δ dN , satisfying δ dN / 2 <g1;

[0419] Among them, the definition of g1 is consistent with the above; in the non-flat area, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets, and the gap spacing at any position is recorded as g1.

[0420] In some embodiments, regarding δ dN The battery is measured by charging to 97% SOC and discharging to 10% SOC during at least one charge and discharge cycle.

[0421] In some embodiments, regarding the measurement of δ dN During at least one charge-discharge cycle, charge to full charge and discharge to full discharge.

[0422] When the negative electrode sheet satisfies δ dN When g1 < δ / 2, when the negative electrode sheet expands in the charged state, there is still a gap between the positive and negative electrode sheets in the non-flat area, which can fully release the expansion force of the negative electrode sheet and is beneficial to improving the stability of the negative electrode sheet and reducing the risk of electrode sheet cracking.

[0423] In some embodiments, the separator includes a base film and a negative electrode side separator coating located on the side of the base film close to the negative electrode sheet, and the negative electrode side separator coating includes compressible particles.

[0424] As the usage time of the battery cell increases, the irreversible expansion part of the electrode sheet gradually consumes the initial gap distance g1 between the positive and negative electrode sheets. By providing a separator coating containing compressible particles on the negative electrode side of the separator, further reserved space for electrode sheet expansion can be provided when the initially set g1 is exhausted, which can further improve the stability of the electrode sheet and reduce the risk of electrode sheet cracking.

[0425] In some embodiments, the separator is provided with a positive electrode side separator coating on the side close to the positive electrode sheet, and the positive electrode side separator coating includes compressible particles.

[0426] When both the compressible particles in the positive electrode side separator coating and the compressible particles in the negative electrode side separator coating are present, they can be the same or different.

[0427] When separator coatings containing sticky compressible particles are provided on both sides of the separator, after hot pressing, the coatings melt, which can bond the separator in the flat area to the electrode sheets on both sides well, making the distance between the positive and negative electrode sheets in the flat area smaller, and is beneficial to better achieving a high charge rate.

[0428] Non-limitingly, the separator coating on either side of the separator can be obtained by coating a separator coating liquid on the base film and drying. The separator coating liquid can be obtained by dispersing the components of the separator coating in a solvent. A non-limiting example of the solvent in the separator coating liquid can be water.

[0429] In some embodiments, the compressible particles include polymer particles; wherein, the glass transition temperature of the polymer particles is less than or equal to 120 °C; optionally, the glass transition temperature of the polymer particles is greater than or equal to 10 °C; further optionally, the glass transition temperature of the polymer particles is greater than or equal to 15 °C; still further optionally, the glass transition temperature of the polymer particles is greater than or equal to 50 °C.

[0430] Without limitation, the glass transition temperature of the polymer particles can be any of the following temperatures or an interval consisting of any two of the following temperatures: 10°C, 15°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, etc. For example, it can be selected from any of the following ranges: 50°C to 60°C, etc.

[0431] In some embodiments, the polymer particles include a crosslinked structure; alternatively, the polymer particles have a partially crosslinked structure; further alternatively, the polymer particles have a degree of crosslinking less than or equal to 90%; and even further alternatively, the polymer particles have a degree of crosslinking less than or equal to 90% and greater than or equal to 30%. For example, the degree of crosslinking of the polymer particles can be any of the following percentages, or a range consisting of any two of the following percentages: 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.

[0432] Compressible particles may include compressible polymer particles, and the compressibility of the polymer particles can be adjusted by adjusting one or both of the glass transition temperature (Tg) and the degree of crosslinking of the particles. Generally, the lower the Tg, the lower the elastic modulus, the easier the particles are to deform, and thus the greater the compressibility. Generally, the lower the degree of crosslinking of the particles, the lower the rigidity, the easier it is to deform under external force, and thus the greater the compressibility.

[0433] In the present application, the glass transition temperature (Tg) of the polymer material can be characterized by a differential scanning calorimeter (DSC). The DSC test temperature range is 30°C to 200°C, the heating / cooling rate is 5°C / min to 10°C / min, and an inert atmosphere, such as an argon atmosphere, is used. The Tg can be tested by a method comprising the following steps: placing the polymer sample in a test container, and after the temperature reaches the initial temperature of 30°C, heating it for the first time, maintaining it at the highest temperature of 200°C for 3 minutes; cooling it for the first time, maintaining it at the lowest temperature of 30°C for 3 minutes; and heating it for the second time to 200°C. The second heating curve is used to draw a graph, and the intersection of the reverse extension line of the glassy region and the transition region curve is taken as the glass transition temperature. Before testing, the sample to be tested can be dried.

[0434] In the present application, "cross-linked structure" has a well-known meaning in the art, and refers to a three-dimensional network structure.

[0435] In this application, unless otherwise specified, the degree of crosslinking of a polymer material may be tested using a swelling method. A solvent may be used to dissolve and remove uncrosslinked components, and the percentage of the remaining crosslinked mass to the initial mass of the polymer material may be recorded as the degree of crosslinking of the polymer material. Furthermore, the degree of crosslinking may be tested using a method comprising the following steps:

[0436] (1) The sample is vacuum dried at 105°C for 1 hour;

[0437] (2) Weigh a sample with a mass of m0 and fully immerse it in a solvent under heating conditions; the heating temperature can be 60°C and the immersion time can be 12 hours;

[0438] (3) The soaked sample is washed with filter paper and rinsed with a large amount of solvent; the solvent can be dimethyl carbonate (DMC), or other suitable solvents can be selected as long as the solvent can dissolve and remove the uncrosslinked components in the sample;

[0439] (4) heating the filter paper and the filtered material in a vacuum to remove the solvent; the heating temperature may be 60° C. and the heating time may be 1 h;

[0440] (5) After drying, weigh the filtered material and record the mass of the filtered material as m1. The cross-linking degree = (1-(m0-m1) / m0)×100%.

[0441] In some embodiments, the compressible particles include sticky polymer particles, and the sticky polymer particles include one or more of polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0442] Compressible particles can have a certain degree of stickiness, such as sticky polymer particles such as polyacrylate and polyvinylidene fluoride. Taking a wound structure as an example, a separator coating containing sticky compressible particles can achieve a certain degree of adhesion between the separator and the negative electrode sheet, thereby helping to avoid the formation of excessively high L1 and g1.

[0443] In some embodiments, the D of the compressible particles v 50 is in the range of 5μm to 10μm, where D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%. Alternatively, the D of the compressible particles v 50 is in the range of 5μm to 8.5μm.

[0444] Without limitation, the D of the compressible particles v 50 can also be any of the following values ​​or an interval consisting of any two of the following values: 5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0445] By controlling the particle size of the compressible particles within the aforementioned range, the thickness consistency of the diaphragm coating can be improved. In addition, the L1 value or g1 value can also be adjusted by controlling the particle size of the compressible particles.

[0446] Without limitation, the weight proportion of the compressible particles in the negative electrode side separator coating can be 0wt% to 30wt%, or can be any of the following percentages or an interval consisting of any two of the following percentages: 0wt%, 1wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 16wt%, 20wt%, 25wt%, 30wt%, etc.

[0447] In some embodiments, the weight proportion of the compressible particles in the negative electrode side separator coating is 10 wt % to 30 wt %, and can be optionally 15 wt % to 20 wt %.

[0448] By controlling the weight percentage of compressible particles in the separator coating, the compressible thickness of the negative-side separator coating can be adjusted, thereby adjusting the compressible space reserved for electrode expansion. By controlling the weight percentage of compressible particles in the separator coating within the aforementioned range, the stability of the electrode can be improved and the risk of electrode cracking can be reduced.

[0449] In some embodiments, the negative electrode side separator coating includes ceramic particles. The ceramic particles can be any of those known in the art that can be used for separator surface coatings.

[0450] In some embodiments, the negative electrode separator coating comprises ceramic particles and compressible particles. In some embodiments, the negative electrode separator coating comprises ceramic particles and compressible particles. The weight percentage of the compressible particles in the negative electrode separator coating can be referred to as defined above.

[0451] In this application, in any selected area of ​​any layer of negative electrode side separator coating in the non-flat area, the surface density of the negative electrode side separator coating is recorded as σ g ; Among them, σ g The ratio of the weight of the negative electrode side separator coating of the corresponding selected area to the area of ​​the negative electrode side separator coating of the corresponding selected area is equal to the weight of the negative electrode side separator coating of the corresponding selected area. Without limitation, the area of ​​any selected area of ​​any layer of the negative electrode side separator coating can be greater than or equal to 1540.25 mm 2 .

[0452] In this application, in the non-flat region, the average surface density σ of the negative electrode side separator coating is mG It is equal to the average value of the ratio of the weight of each layer of the negative electrode side separator coating to the area of ​​the corresponding layer of the negative electrode side separator coating.

[0453] In some embodiments, in the non-flat region, the negative electrode side separator coating satisfies one or more of the following characteristics:

[0454] In the non-flat area, the difference between the maximum and minimum surface densities of any negative electrode side separator coating in any selected area is 0 g / m2 ~0.4g / m 2 ;

[0455] In the non-flat region, the surface density of any negative electrode side separator coating in any selected area is related to σ mG The difference is -0.2g / m 2 ~0.2g / m 2 .

[0456] In this application, the average thickness of the negative electrode side separator coating in the non-flat area is recorded as d mG .

[0457] In this application, in the non-flat region, the difference between the maximum thickness and the minimum thickness of any layer of the negative electrode side separator coating at any position is recorded as δ G .

[0458] In some embodiments, in the non-flat region, the negative electrode side separator coating satisfies one or more of the following characteristics:

[0459] In the non-flat area, the thickness of any negative electrode side separator coating at any position is 2 μm to 6 μm;

[0460] 0μm≤δ G ≤2μm;

[0461] In the non-flat region, the thickness of any negative electrode side separator coating at any position is proportional to d mG The difference is -2μm to 2μm, and can be optionally -1.5μm to 1.5μm.

[0462] By controlling the average surface density σ of the negative electrode side separator coating mG , the difference between the maximum surface density and the minimum surface density of any layer of the negative electrode side separator coating in any selected area in the non-flat area, the average thickness of the negative electrode side separator coating in the non-flat area, and the difference between the maximum thickness and the minimum thickness of any layer of the negative electrode side separator coating at any position in the non-flat area are recorded as δ G , the thickness of any negative electrode side separator coating at any position in the non-flat area and d mG One or more of the parameters such as the difference can adjust the setting amount of the negative electrode side diaphragm coating, and thus adjust the size of the reserved space.

[0463] In some embodiments, the ionic conductivity of the electrolyte is 8 mS / cm to 18 mS / cm at at least one temperature between 20° C. and 35° C.;

[0464] Optionally, under at least one temperature condition between 20° C. and 30° C., the ionic conductivity of the electrolyte is 8 mS / cm to 18 mS / cm.

[0465] Without limitation, the ionic conductivity test conditions of the electrolyte may be 20° C., 25° C., 30° C., 35° C., etc.

[0466] Without limitation, under at least one temperature condition of 20°C to 35°C (optionally 20°C to 30°C), the ionic conductivity of the electrolyte can be any of the following ionic conductivities, or can be a range consisting of any two of the following ionic conductivities: 8mS / cm, 9mS / cm, 10mS / cm, 11mS / cm, 12mS / cm, 14mS / cm, 15mS / cm, 16mS / cm, 18mS / cm, etc.

[0467] By adjusting the ionic conductivity of the electrolyte, the battery's fast charging capability can be adjusted. The higher the ionic conductivity, the more conducive it is to achieving a higher charge rate.

[0468] In this application, unless otherwise specified, ionic conductivity can be measured using a conductivity meter, such as a DDSJ-318 conductivity meter. The test can be performed using a method comprising the following steps:

[0469] Pre-treatment: Take the standard liquid and keep it at a constant temperature of 25℃ (deviation ±0.1℃), and take the test liquid and keep it at a constant temperature of the test temperature (deviation ±0.1℃)

[0470] Test: Test the instrument with two standard solutions at 25°C. After calibration, clean the electrode and place the sample electrode vertically into the liquid to be tested. Click to start the test and wait for the data to stabilize for more than 10 seconds before recording the test results.

[0471] In some embodiments, the electrolyte includes an electrolyte salt and an electrolyte solvent, and the electrolyte solvent includes a low-viscosity solvent. Without limitation, the low-viscosity solvent may include one or more of diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, ethyl acetate, methyl acetate, propyl acetate, and a solvent having a viscosity less than or equal to that of at least one of the foregoing agents at 25° C.

[0472] In some embodiments, the electrolyte solvent further comprises a dissociative solvent. Unless otherwise specified, the dissociative solvent has the ability to dissolve and dissociate the electrolyte salt.

[0473] Without limitation, the dissociation solvent may include one or more of ethylene carbonate and propylene carbonate.

[0474] In some embodiments, the weight proportion of the low-viscosity solvent in the electrolyte solvent is 10 wt% to 90 wt%, optionally 10 wt% to 80 wt%, further optionally 10 wt% to 60 wt%, and further optionally 10 wt% to 40 wt%.

[0475] By adding a low-viscosity solvent to the electrolyte, the transmission resistance of active ions can be reduced and the transmission rate of active ions can be increased, thereby improving the ionic conductivity of the electrolyte and further improving the fast charging performance of the battery.

[0476] By providing a dissociative solvent in the electrolyte, the electrolyte salt can be dissolved and dissociated, thereby playing the role of conducting active ions.

[0477] By controlling the weight proportion of the low-viscosity solvent in the electrolyte solvent within the aforementioned range, it is beneficial to have a faster active ion transfer rate while dissolving and dissociating the electrolyte salt, and is more conducive to improving the ionic conductivity of the electrolyte and enhancing the fast charging performance of the battery.

[0478] In this application, unless otherwise specified, the viscosity of the solvent or electrolyte can be tested by conventional methods in the art, and can be measured using instruments and methods known in the art. For example, reference can be made to the national standard GB / T10247-2008 "Viscosity Measurement Method", and the test can be performed based on the rotational viscometer in Appendix D of the national standard GB / T10247-2008.

[0479] Unless otherwise specified, the viscosity of a solvent or electrolyte can be tested using the following method: A certain mass of electrolyte sample is placed in a sample container and tested using a Brookfield DV2TLV rotational viscometer. At a certain temperature, the shear force exerted on the rotor as it rotates continuously at a constant speed within the sample causes the spring to generate torque, which is proportional to the viscosity, resulting in the viscosity value. The test equipment meets the following environmental conditions: 1. External environment: Temperature: 15°C to 28°C, Humidity: RH <80%; 2. Internal environment: The sample container is two-thirds submerged in a water bath, with water as the medium, which is used to maintain the sample at a constant temperature.

[0480] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing active material.

[0481] Without limitation, the positive electrode active material includes one or more of lithium-containing phosphates, lithium transition metal oxides, and modified products of any of the foregoing substances. Without limitation, the lithium-containing phosphate includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Without limitation, the lithium transition metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified products of any of the foregoing substances. Any of the foregoing modified substances is a positive electrode active material containing a modifying element, and the modifying element exists in the form of a doping element, a coating element, or a combination of a doping element and a coating element.

[0482] By adjusting the type of positive electrode active material in the positive electrode sheet, the active ion supply side kinetics can be adjusted, thereby adjusting the fast charging capability of the battery.

[0483] In some embodiments, in the electrode assembly, 4 μm ≤ d1 ≤ 13 μm; alternatively, in the electrode assembly, 7 μm ≤ d1 ≤ 13 μm. The definition of d1 is consistent with the above: in the non-flat region, the thickness of the separator at any location is denoted as d1. Furthermore, the corresponding parameters at any location satisfy L1 = g1 + d1.

[0484] Without limitation, in the electrode assembly, the thickness d1 of the non-flat area isolation membrane can also be any of the following thicknesses or a range consisting of any two of the following thicknesses: 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 13μm, etc.

[0485] By adjusting the thickness of the separator, the distance between the positive and negative electrodes can be adjusted, thereby adjusting the internal resistance between the positive and negative electrodes, which in turn affects the battery's fast charging capability. The shorter the distance between the positive and negative electrodes, the more conducive it is to achieving a higher charge rate.

[0486] In some embodiments, in the electrode assembly, 28 μm ≤ L1 ≤ 173 μm; optionally, in the electrode assembly, 31 μm ≤ L1 ≤ 173 μm.

[0487] Without limitation, in the electrode assembly, L1 can be any of the following values ​​or an interval consisting of any two of the following values: 28μm, 30μm, 31μm, 32μm, 35μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 173μm, etc.

[0488] By controlling L1 in the non-flat area of ​​the electrode assembly within the aforementioned range, it is beneficial to reserve more sufficient space for the expansion of the electrode to better improve the structural stability of the electrode, reduce the degree of deformation and cracking risk of the electrode, and better reduce or delay lithium plating, thereby better improving the cycle performance of the battery and increasing the service life of the battery.

[0489] In some embodiments, the battery cell satisfies any of the following conditions:

[0490] Case B1: The battery cell can provide a 3C charge rate, 28μm≤L1≤173μm;

[0491] Case B2: The battery cell can provide a 4C charge rate, 28μm≤L1≤157μm;

[0492] Case B3: The battery cell can provide a charge rate of 6C, 28μm≤L1≤133μm.

[0493] In some embodiments, in the non-flat region, there is a gap between the inner facing surfaces of any adjacent positive electrode sheets and negative electrode sheets, and the gap spacing at any position is denoted as g1;

[0494] In the non-flat area, the thickness of the negative electrode sheet of any layer at any position is recorded as D N The negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material; the particle size corresponding to the cumulative volume distribution percentage of the multi-particle mixture reaches 50% is recorded as D v 50;

[0495] The battery cell meets one or more of the following characteristics:

[0496] In case B1, 24 μm ≤ g1 ≤ 160 μm;

[0497] In case B1, the D of the negative electrode active material v 50 is 8μm~12μm;

[0498] In case B2, 24 μm ≤ g1 ≤ 144 μm;

[0499] In case B2, the D of the negative electrode active material v 50 is 7μm~12μm;

[0500] In case B3, 24 μm ≤ g1 ≤ 120 μm;

[0501] In case B3, the D of the negative electrode active material v 50 is 6.5μm~12μm;

[0502] In case B4, 24 μm ≤ g1 ≤ 96 μm.

[0503] For a conventional winding structure, after winding and hot pressing, the surface under pressure forms a flat area, and two corner areas (i.e., two non-flat areas) connecting the two flat areas are naturally formed at both ends of the flat area, thereby obtaining a multi-layer winding structure.

[0504] Based on the conventional overhang design, for the battery cell provided in the first aspect of the present application, the total length of the positive electrode sheet in the non-straight area (L P1 ) relative to the total length of the positive electrode sheet in the multilayer structure (L P ) to reflect the proportion of non-flat areas in the P ). For the winding structure, the multi-layer structure in the battery cell is a multi-layer winding structure, F P The total length of the positive electrode sheet in the corner area is proportional to the total length of the positive electrode sheet in the multi-layer winding structure. P1 ) can be measured by the total length of the positive electrode (L P ) minus the total length of the positive electrode in the straight area (L P2 ) and obtained. Without limitation, F P The total length of the positive electrode in the straight area (L P2 ) and the total length of the used or disassembled positive electrode sheet (L P ) Calculated: F P =(L P -L P2 ) / L P ×100%. It can be understood that in the battery cell provided in the first aspect of the present application, F P Greater than 0. Without limitation, F P It can be less than 20%, further less than 15%, and further less than 10%. P It can be any of the following percentages or an interval consisting of any two of the following percentages: 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, etc. For example, F P It can be selected from any of the following ranges: 5% to 15%, 8% to 12%, etc.

[0505] The following is some description about the positive electrode.

[0506] In a non-limiting manner, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0507] The positive electrode active material may refer to but is not limited to the above description.

[0508] Without limitation, the positive electrode active material may be a battery positive electrode active material known in the art. As non-limiting examples, the positive electrode active material may include one or more of the following materials: olivine-structured lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials; other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.80 Co 0.15 Al 0.05 O2. An example of lithium iron phosphate is LiFePO4 (also referred to as LFP). An example of lithium manganese phosphate is LiMnPO4.

[0509] Taking a battery cell and a secondary battery whose active ions include lithium ions as an example, it is understandable that lithium (Li) is deintercalated and consumed during the charge and discharge process of the battery, and the Li content in the positive electrode plate is different when the battery is discharged to different states. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the Li content can be the initial state of the material or the non-initial state after the charge and discharge cycle. The positive electrode active material is applied to the positive electrode plate in the battery system. After the charge and discharge cycle, the Li content in the positive electrode active material contained in the positive electrode plate usually changes. Among them, the Li content can be measured using atomic molar content, but is not limited to this. Regarding "Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials or new substances obtained by appropriate modification on the basis of the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive electrode active material, and a non-limiting example is coating modification.

[0510] In the exemplary descriptions of the positive electrode active material in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the atomic molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by atomic molar content, but is not limited to this.

[0511] For battery cells and secondary batteries whose active ions include lithium ions, the atomic ratio in the chemical formula may include the atomic molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2V and 5V).

[0512] Without limitation, the weight percentage of the positive electrode active material in the positive electrode active material layer may be ≥85 wt %, further ≥90 wt %, and further ≥95 wt %.

[0513] As a non-limiting example, the positive electrode current collector has two surfaces facing away from each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0514] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, the metal material may include but is not limited to at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, the polymer material substrate may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0515] In some embodiments, the positive electrode active material layer optionally includes a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. Typically, the weight percentage of the binder in the positive electrode active material layer may be 0 to 10 wt%, further 0 to 8 wt%, and further 1 wt% to 5 wt%, based on the total weight of the positive electrode active material layer.

[0516] In some embodiments, the positive electrode active material layer optionally includes a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typically, the weight percentage of the conductive agent in the positive electrode active material layer may be 0 to 8 wt%, and further may be 0 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0517] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. Cold pressing can be performed using a cold rolling mill. The type of solvent can include but is not limited to any of the aforementioned embodiments, for example, it can include N-methylpyrrolidone (NMP), and can further be NMP. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 3000mPa·s to 25000mPa·s, and can optionally be 3000mPa·s to 10000mPa·s. The compacted density of the positive electrode sheet can be 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 The obtained positive electrode sheet can be used for winding process.

[0518] The "compacted density" used in this application has a meaning well known in the art and is one of the reference indicators of material energy density. In this application, unless otherwise specified, the compacted density of an electrode plate refers to the ratio of the mass of the active material layer to its volume. The compacted density of a positive electrode plate refers to the ratio of the mass of the positive electrode active material layer to its volume, and the compacted density of a negative electrode plate refers to the ratio of the mass of the negative electrode active material layer to its volume. It can be obtained by testing using conventional methods in this field. The area of ​​the plate does not change much before and after cold pressing.

[0519] The following is some description about the negative electrode.

[0520] In a non-limiting manner, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material. The definition of the negative electrode active material can be found in the above text.

[0521] Without limitation, the weight percentage of the negative electrode active material in the negative electrode active material layer may be ≥85 wt %, further ≥90 wt %, and further ≥95 wt %.

[0522] As a non-limiting example, the negative electrode current collector has two surfaces facing away from each other in its thickness direction, and the negative electrode active material layer may be disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0523] 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 material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate. In the negative electrode current collector, the metal material may include but is not limited to one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, the polymer material substrate may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0524] Without limitation, the negative electrode active material can adopt the negative electrode active material for batteries known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following substances or materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials or substances, and other traditional materials or substances that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0525] In some embodiments, the negative electrode active material includes one or more of a carbon-based material, a silicon-based material, a tin-based material, and lithium titanate, as well as modified forms of any of the foregoing materials, wherein the modified form includes one or more of a doping modification and a coating modification. Both the doping modification method and the coating modification method can adopt or refer to existing modification methods in the art, including but not limited to the selection of element types and doping amounts. Carbon-based materials may include but are not limited to one or more of graphite materials, soft carbon, hard carbon, etc. Graphite materials may include one or more of artificial graphite and natural graphite.

[0526] In some embodiments, the negative electrode active material includes a carbon-based material and a silicon-based material. Without limitation, the combined mass of the carbon-based material and the silicon-based material may account for ≥85% of the total mass of the negative electrode active material, optionally ≥90%, further optionally ≥95%, further optionally ≥96%, and further optionally 100%. The combined mass of the graphite material and the silicon-based material may also account for any of the following percentages, or a percentage greater than or equal to any of the following percentages and less than or equal to 100%, or a range consisting of any two of the following percentages: 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, and the like. The definitions of carbon-based materials and silicon-based materials can be found above. For example, the carbon-based material can be a graphite material. The content of the carbon-based material and the silicon-based material can also be found in any suitable embodiment described above.

[0527] In some embodiments, the negative electrode active material includes a carbon-based material. Without limitation, the mass percentage of the carbon-based material in the negative electrode active material can be ≥85%, optionally ≥90%, further optionally ≥95%, further optionally ≥96%, etc., further optionally 100%, etc. The mass percentage of the carbon-based material in the negative electrode active material can also be any of the following percentages, or greater than or equal to any of the following percentages and less than or equal to 100%, or selected from the interval consisting of any two of the following percentages: 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, etc. The definition of carbon-based materials can be found above. For example, the carbon-based material can be a graphite material.

[0528] In some embodiments, the negative electrode active material layer optionally includes a binder. Without limitation, the binder may include, but is not limited to, one or more 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). Without limitation, the weight percentage of the binder in the negative electrode active material layer may be 0-10 wt %, further 0-5 wt %, further 1 wt %-5 wt %, and further optionally 1 wt %-3 wt %.

[0529] In some embodiments, the negative electrode active material layer optionally includes a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight percentage of the conductive agent in the negative electrode active material layer may be 0 to 15 wt %, further preferably 0 to 10 wt %, and even more preferably 0 to 5 wt %.

[0530] In some embodiments, the negative electrode active material layer may optionally include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)). The weight percentage of the other additives in the negative electrode active material layer may be 0-15 wt %, further optionally 0-10 wt %, further optionally 0-5 wt %, further optionally 0-3 wt %, further optionally 0-2 wt %.

[0531] In some embodiments, a negative electrode sheet can be prepared by dispersing the aforementioned components for preparing a negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry. Furthermore, the negative electrode slurry is coated on at least one surface of a negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained. The negative electrode current collector surface coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30 wt% to 70 wt%, optionally 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, optionally 3000 mPa·s to 10000 mPa·s. The compaction density of the negative electrode sheet can be described above. The resulting negative electrode sheet can be used in a winding process.

[0532] The electrolyte will be described below.

[0533] The electrolyte conducts ions between the positive and negative electrodes. In this application, the electrolyte includes a liquid electrolyte. A liquid electrolyte can also be referred to as an electrolyte solution. The electrolyte includes an electrolyte salt.

[0534] In some embodiments, the electrolyte is an electrolyte solution.

[0535] In some embodiments, the electrolyte is a non-aqueous electrolyte. Further, the non-aqueous electrolyte includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt also includes an electrolyte lithium salt. The concentration of the electrolyte salt can generally be 0.5 mol / L to 5 mol / L.

[0536] In some embodiments, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0537] The solvent in the non-aqueous electrolyte may include a base solvent and an ester solvent. The type and amount of the ester solvent can refer to the above description.

[0538] In some embodiments, the base solvent in the non-aqueous electrolyte may include fluoroethylene carbonate (FEC), ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC, ), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE) One or more.

[0539] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0540] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0541] The separator will be described below.

[0542] In some embodiments, the battery cell includes a separator, which can be any known porous separator with good chemical and mechanical stability.

[0543] Some embodiments of the isolation membrane can be found in the above text.

[0544] In some embodiments, the separator includes at least a base film and optionally includes a negative electrode side separator coating located on a side of the base film close to the negative electrode plate. The negative electrode side separator coating may include compressible particles.

[0545] In some embodiments, the separator is provided with a positive electrode side separator coating on a side close to the positive electrode sheet. The positive electrode side separator coating may include compressible particles.

[0546] The compressible particles in the separator coating on the positive electrode side may be the same as or different from the compressible particles in the separator coating on the negative electrode side.

[0547] In some embodiments, the material of the base film may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0548] The isolation film can be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different.

[0549] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be wound together to form an electrode assembly with a multi-layer wound structure. After the winding process is completed, further steps such as hot pressing, assembly into a shell, liquid injection, high-temperature stabilization (e.g., stabilization at 40°C to 50°C), formation, liquid replenishment, and aging can be performed to obtain a formed battery cell. Liquid injection can also be used to obtain an unformed battery cell.

[0550] In some embodiments, after the positive electrode sheets and negative electrode sheets prepared by cold pressing and slitting are die-cut to form the tabs, they are stacked in the order of "isolation membrane-negative electrode sheet-isolation membrane-positive electrode sheet", wound in the same direction, and then undergo processes such as hot pressing, assembly into a shell, liquid injection, high-temperature standing (such as standing at 40°C to 50°C), formation, liquid replenishment, and aging to obtain a wound battery that is a formed battery cell.

[0551] In a second aspect of the present application, a secondary battery is provided, comprising the battery cell described in the first aspect of the present application.

[0552] The definition of battery cells can be found in the context, for example, in the first aspect of the present application.

[0553] As you can understand, a secondary battery typically consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are embedded in and extracted from the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0554] In some embodiments, the secondary battery is a lithium-ion secondary battery.

[0555] In some embodiments, the secondary battery is a lithium ion secondary battery, and the electrolyte salt may include an electrolyte lithium salt.

[0556] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0557] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0558] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0559] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG5 shows a battery cell 5 with a square structure as an example.

[0560] In some embodiments, referring to Figure 6, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0561] The secondary battery may be a battery module 4 or a battery pack 1 .

[0562] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0563] FIG7 shows an example battery module 4. Referring to FIG7 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0564] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0565] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0566] Figures 8 and 9 illustrate an example battery pack 1. Referring to Figures 8 and 9 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0567] In a third aspect of the present application, an electrical device is provided, which includes at least one of the battery cell described in the first aspect of the present application and the secondary battery described in the second aspect of the present application.

[0568] In some embodiments, the present application further provides an electrical device, which includes a secondary battery of any embodiment provided in the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, electric tools, etc., but are not limited thereto. The electrical device can also be used in military equipment, aerospace and other fields, and can also be used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations.

[0569] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0570] Figure 10 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0571] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0572] In a fourth aspect of the present application, a method for preparing a battery cell is provided, which can be used to prepare the battery cell described in the first aspect of the present application.

[0573] A method for preparing a battery cell is provided, comprising the following steps:

[0574] Disposing a separator between a positive electrode sheet and a negative electrode sheet, controlling the positions of the positive electrode sheet and the negative electrode sheet according to a preset gap distance between the positive electrode sheet and the negative electrode sheet, forming a multilayer structure with the positive electrode sheet, the negative electrode sheet, and the separator, and subjecting at least a portion of the multilayer structure to a non-flat region through a process including cold pressing, thereby preparing an electrode assembly that has not been subjected to a chemical formation treatment; wherein, in the non-flat region, in a cross section perpendicular to a thickness direction of the multilayer structure, a line connecting the center thicknesses of the structural layers in the multilayer structure is a non-straight line; and

[0575] Immersing the electrode assembly, which has not been subjected to a formation treatment, in an electrolyte and subjecting it to a treatment process including a formation process to prepare a battery cell having a charge rate that meets a preset value; wherein the preset charge rate value is greater than or equal to 2C;

[0576] in,

[0577] The prepared battery cell is the battery cell described in the first aspect of the present application. In the non-flat region of the battery cell, the distance between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets at any position is recorded as L1.

[0578] The definition and value of L1 can be found in the previous article.

[0579] In some embodiments, the method for preparing a battery cell includes the following steps: determining a preset range of L1 according to an acceptable self-discharge rate range, so that the prepared battery cell has an acceptable self-discharge rate.

[0580] In some embodiments, the multilayer structure includes a multilayer winding structure formed by winding a positive electrode sheet, a negative electrode sheet, and a separator, and the non-straight region is located at a corner region of the multilayer winding structure;

[0581] In the step of forming the positive electrode sheet, the negative electrode sheet, and the separator into a multilayer structure including a non-flat region, L1 is controlled within a preset range by controlling the winding tension.

[0582] In some embodiments, the winding tension may be 700 gf to 1000 gf, or may be any one of the following winding tensions or a range consisting of any two of the following winding tensions: 700 gf, 800 gf, 900 gf, and 1000 gf.

[0583] In this application, unless otherwise specified, in a non-flat area of ​​an electrode assembly that has not been subjected to formation treatment, the distance between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets at any position is recorded as L0, and L0 ≥ L1.

[0584] In this application, in the non-flat region of the electrode assembly that has not been subjected to formation treatment, the acceptable maximum value of L0 is recorded as MAX0.

[0585] In some embodiments, the value of MAX0 ranges from 113 μm to 213 μm. MAX0 can also be any of the following values ​​or any value selected from an interval consisting of any two of the following values: 113 μm, 140 μm, 150 μm, 160 μm, 163 μm, 170 μm, 180 μm, 190 μm, 193 μm, 200 μm, 213 μm, etc.

[0586] In some embodiments, in electrode assemblies that have not been subjected to formation treatment, L0 is less than or equal to 213 μm, that is, there is no L0 greater than 213 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0587] In some embodiments, in electrode assemblies that have not been subjected to formation treatment, L0 is less than or equal to 193 μm, that is, there is no L0 greater than 193 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0588] In some embodiments, in electrode assemblies that have not been subjected to formation treatment, L0 is less than or equal to 163 μm, that is, there is no L0 greater than 163 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0589] By controlling the L0 value in the non-flat area of ​​the electrode assembly that has not been subjected to chemical formation treatment within the aforementioned range, it is beneficial to better reduce the risk of lithium plating for the battery cells obtained after chemical formation treatment, thereby better improving the cycle performance and service life of the battery cells.

[0590] In some embodiments, in a non-flat area of ​​an electrode assembly that has not been subjected to formation treatment, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets, and the gap spacing at any position is recorded as g0, then the corresponding parameters at any position satisfy L0>g0.

[0591] In this application, in the non-flat area of ​​the electrode assembly that has not been subjected to chemical formation treatment, the allowable upper limit of g0 is recorded as g 0max , that is, in the electrode components that have not been chemically treated, g0 is less than or equal to g 0max At this time, there is no electrode component that is not subjected to chemical treatment and has a mass greater than g 0max of g0.

[0592] In some embodiments, in an electrode assembly that has not been subjected to a formation treatment, g 0max The value range of g can be 30μm~200μm. 0maxIt can also be any of the following values ​​or any value selected from the interval formed by any two of the following values: 30μm, 50μm, 60μm, 80μm, 100μm, 150μm, 160μm, 180μm, 200μm, etc.

[0593] In some embodiments, in electrode assemblies that have not undergone formation treatment, g0 is less than or equal to 200 μm, that is, there is no g0 greater than 200 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0594] In some embodiments, in the electrode assembly, g0 is less than or equal to 180 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0595] In some embodiments, in the electrode assembly, g0 is less than or equal to 150 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0596] By controlling g0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, it is beneficial to better control L1 within an appropriate range for the battery cells obtained after formation treatment to avoid excessively high L1 abnormal values, which is beneficial to better reduce or delay lithium plating and better improve the cycle performance and service life of the battery cells.

[0597] In the application, the allowable lower limit of g0 in the non-flat area of ​​the electrode assembly that has not been chemically treated is recorded as g 0min , that is, in the electrode components that have not been chemically treated, g0 is greater than or equal to g 0min At this time, there is no electrode component that is less than g 0min of g0.

[0598] In some embodiments, in an electrode assembly that has not been subjected to a formation treatment, g 0min 30μm.

[0599] In some embodiments, in electrode assemblies that have not been subjected to chemical formation treatment, g0 is greater than or equal to 30 μm.

[0600] By controlling g0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, for the battery cell obtained after the formation treatment, it is beneficial to reserve more sufficient expansion force release space for the expansion of the electrode, which is beneficial to better improve the structural stability of the electrode and reduce the degree of deformation and cracking risk of the electrode, better improve the cycle performance of the battery cell and increase the service life of the battery.

[0601] In some embodiments, in an electrode assembly that has not been subjected to a formation treatment, 30 μm ≤ g0 ≤ 200 μm; optionally, the battery cell can provide a charge rate greater than or equal to 3C.

[0602] In some embodiments, in an electrode assembly that has not been subjected to formation treatment, 30 μm ≤ g0 ≤ 180 μm; optionally, the battery cell can provide a charge rate greater than or equal to 4C.

[0603] In some embodiments, in an electrode assembly that has not been subjected to formation treatment, 30 μm ≤ g0 ≤ 150 μm; optionally, the battery cell can provide a charge rate greater than or equal to 6C.

[0604] By controlling g0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, for the battery cells obtained after the formation treatment, it is beneficial to reserve more sufficient space for the expansion of the pole pieces to better improve the structural stability of the pole pieces, reduce the degree of deformation and cracking risk of the pole pieces, and also to better control the battery cell L1 to reduce or delay lithium plating, thereby better improving the cycle performance of the battery cell and increasing the service life of the battery.

[0605] In some embodiments, in an electrode assembly that has not been subjected to a formation treatment, 34 μm ≤ L1 ≤ 213 μm; optionally, in an electrode assembly that has not been subjected to a formation treatment, 37 μm ≤ L1 ≤ 213 μm.

[0606] By controlling L0 in the non-flat area of ​​the electrode assembly that has not been subjected to formation treatment within the aforementioned range, for the battery cells obtained after the formation treatment, it is beneficial to reserve more sufficient space for the expansion of the pole pieces to better improve the structural stability of the pole pieces, reduce the degree of deformation and cracking risk of the pole pieces, and better reduce or delay lithium plating, thereby better improving the cycle performance of the battery cells and increasing the service life of the batteries.

[0607] In some embodiments,

[0608] The preparation method of the battery cell satisfies any of the following conditions:

[0609] Case A1: The battery cell can provide a 3C charge rate, 34μm≤L0≤213μm;

[0610] Case A2: The battery cell can provide a 4C charge rate, 34μm≤L0≤193μm;

[0611] Case A3: The battery cell can provide a charge rate of 6C, 34μm≤L0≤163μm.

[0612] In some embodiments, the method for preparing a battery cell satisfies one or more of the following characteristics:

[0613] In case A1, 30 μm ≤ g0 ≤ 200 μm;

[0614] In case A2, 30 μm ≤ g0 ≤ 180 μm;

[0615] In case A3, 30 μm ≤ g0 ≤ 150 μm.

[0616] In some embodiments, the prepared battery cell is at least one of the aforementioned battery cells.

[0617] In a fifth aspect of the present application, a computer device is provided, comprising a memory and a processor, wherein the memory stores a computer program, wherein when the processor executes the computer program, the steps of the method for preparing a battery cell described in the fourth aspect of the present application are implemented.

[0618] In a sixth aspect of the present application, a computer-readable storage medium is provided, on which a computer program is stored, wherein when the computer program is executed by a processor, the steps of the method for preparing a battery cell described in the fourth aspect of the present application are implemented.

[0619] In yet another aspect of the present application, a computer program product is provided, comprising a computer program, wherein when the computer program is executed by a processor, the steps of the preparation method described in the fourth aspect of the present application are implemented.

[0620] The computer device may be a terminal, and its internal structure diagram may be as shown in FIG11 . The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner may be implemented through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, a method for determining the battery performance of an energy storage system is implemented. The display screen of the computer device may be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device may be a touch layer covering the display screen, or a key, trackball, or touchpad provided on the computer device housing, or an external keyboard, touchpad, or mouse.

[0621] Those skilled in the art will understand that the structure shown in FIG11 is merely a block diagram of a portion of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different arrangement of components.

[0622] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned method implementation can be implemented by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned method implementations. Among them, any reference to memory, database or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processor involved in the various embodiments provided herein may be, but are not limited to, a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, and the like.

[0623] The following describes some embodiments of the present application. The embodiments described are only a portion of the embodiments of the present application, rather than all of the embodiments. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limiting the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0624] If the techniques or conditions are not specified in the examples, the methods were carried out according to the description above, or according to the techniques or conditions described in the literature in the field, or according to the product instructions. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially or can be synthesized according to conventional methods from commercially available products.

[0625] In the following specific examples, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations caused by instrument testing accuracy or operational accuracy are allowed.

[0626] In the following examples, room temperature refers to 20°C to 30°C.

[0627] In the following examples, sufficient parallel samples of the positive electrode sheet, the negative electrode sheet, and the separator were prepared for testing and assembling parallel samples of battery cells.

[0628] In the following examples, the compressible PVDF particles used are v 50 is in the range of 5μm to 8.5μm, the glass transition temperature Tg is in the range of 10℃ to 120℃ (further in the range of 50℃ to 60℃), and the crosslinking degree is less than or equal to 90% (further in the range of 30% to 90%).

[0629] In the following examples, the percentage of the total length of the positive electrode sheet in the non-straight region relative to the total length of the positive electrode sheet is less than or equal to ? ?%.

[0630] In the following examples, the following methods are used to test the relevant parameters of the raw materials.

[0631] 1. D v 50

[0632] In the following examples, unless otherwise specified, the D v 50 and the D of the compressible particles in the negative electrode side separator coating v 50 The test was performed using a Malvern 2000 laser particle size analyzer with reference to the standard procedure GB / T19077-2016 / ISO13320:2009.

[0633] 2. R N

[0634] In this application, unless otherwise specified, the parameter R that characterizes the expansion of the negative electrode sheet is N The test was carried out by the following method: at least two battery cell samples were prepared from negative electrode sheets with a known thickness of D0.

[0635] One of the battery samples to be tested was placed in a constant temperature environment at 25°C for 2 hours, then charged at a constant current of 0.33C to 70% SOC (4.0V), and placed in a static state for 10 minutes. The battery cell was disassembled and the negative electrode sheet in the non-flat area was removed. The thickness D of the negative electrode sheet during charging was measured. N1 ;

[0636] Another battery sample to be tested was placed at a constant temperature of 25°C for 2 hours, then charged to 70% SOC at a constant current of 0.33C, placed at rest for 10 minutes, and then discharged to 10% SOC (3.5V) at a constant current of 0.33C. The battery cell was disassembled, and the negative electrode sheet in the non-flat area was removed. The thickness D of the negative electrode sheet during discharge was measured. N2 ;

[0637] After the charge and discharge are completed, the negative electrode pieces are taken out and the thickness of the pieces is measured with a micrometer to calculate the R N =D N1 / D N2 .

[0638] 3. Glass transition temperature (Tg)

[0639] The glass transition temperature (Tg) of the polymer materials was characterized by differential scanning calorimetry (DSC).

[0640] The DSC test temperature range is 30°C to 200°C, the heating / cooling rate is 5°C / min to 10°C / min, and an inert atmosphere, such as argon atmosphere, is used.

[0641] Tg was determined using a method comprising the following steps:

[0642] Before testing, the samples to be tested were dried in a vacuum oven at 60°C for 24 h;

[0643] Place the sample in a test container. After the temperature reaches an initial temperature of 30°C, perform the first heating, maintaining the maximum temperature at 200°C for 3 minutes. Then perform the first cooling, maintaining the minimum temperature at 30°C for 3 minutes. Then perform the second heating to 200°C. Use the second heating curve to plot the glass transition temperature, taking the intersection of the glassy region and the reverse extension of the transition region curve as the glass transition temperature.

[0644] 4. Degree of cross-linking of compressible particles used in diaphragm coatings

[0645] The degree of cross-linking of the compressible particles used in the separator coating was tested using a method comprising the following steps:

[0646] (1) The sample was vacuum dried at 105°C for 1 h;

[0647] (2) Weigh a sample of mass m0 and fully immerse it in a solvent under heating conditions; the heating temperature is 60°C and the immersion time is 12 hours;

[0648] (3) The soaked sample was placed on filter paper and rinsed with a large amount of solvent; the solvent was dimethyl carbonate (DMC);

[0649] (4) The filter paper and the filtered material were heated under vacuum to remove the solvent; the heating temperature was 60°C and the heating time was 1 hour;

[0650] (5) After drying, weigh the filtered material and record the mass of the filtered material as m1. The cross-linking degree = (1-(m0-m1) / m0)×100%.

[0651] In the following examples, the MAX value in Example 1 is 157 μm, and the MAX value in Example 2 is 133 μm.

[0652] Example 1. Target maximum charging rate ≥ 4C

[0653] (1) Preparation of positive electrode sheet

[0654] The nickel-cobalt-manganese ternary material (LiNi 0.65 Co 0.1 M n0.25 O2), lithium iron phosphate material (LFP), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 94:3:2:1 to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on both sides of the positive electrode current collector, and then dried and cold pressed (the compaction density is (3.35g / cm 3 ), cut to obtain a positive electrode sheet. The thickness of the positive electrode sheet is about 79.5 μm, and the thickness fluctuation range is within ±2 μm.

[0655] (2) Preparation of negative electrode sheet

[0656] Artificial graphite (D v 50 is 12 μm), conductive agent carbon black, binder styrene polybutadiene rubber (SBR) and thickener sodium hydroxymethyl cellulose (CMC-Na) are dissolved in solvent deionized water in a weight ratio of 97:0.4:1.5:1.1, and the negative electrode slurry is prepared after being evenly mixed.

[0657] The negative electrode slurry is coated on both sides of the current collector copper foil and dried. The coating density on one side is 160mg / 1540.25mm 2 , drying, cold pressing (compacted density 1.6g / cm 3 ), cut to obtain a negative electrode sheet. The thickness of the negative electrode sheet is about 110 μm, and the thickness fluctuation range meets: within ± 2 μm; the thickness of the negative electrode active material layer on one side is 48.5 μm.

[0658] In this example, R N In the range of 1.17 to 1.36.

[0659] (3) Preparation of isolation membrane

[0660] A PP diaphragm with a thickness of 7 μm was selected as the base membrane. Ceramic particles and polyvinylidene fluoride (PVDF, compressible particles) were mixed with solvent water in a weight ratio of 8:2 to make a coating solution. The coating solution was applied to both sides of the base membrane and dried. A diaphragm coating with a thickness of 2 μm was formed on both sides of the base membrane. The thickness fluctuation range was within ±1.5 μm. The surface density fluctuation range of the diaphragm coating on one side was within ±0.2 g / m 2 within the range.

[0661] (4) Preparation of electrolyte

[0662] The electrolyte consists of electrolyte lithium salt and a solvent, and the solvent is a combination of a base solvent and an ester solvent.

[0663] The organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 as the base solvent. The carbonate solvent DMC was added, and 1 mol / L of the electrolyte lithium salt lithium hexafluorophosphate (LiPF6) was evenly dispersed and stirred to obtain an electrolyte solution. The solvent content was adjusted to achieve an ionic conductivity of 10 mS / cm at 25°C.

[0664] (5) Battery assembly

[0665] After the prepared positive and negative electrode sheets are die-cut to remove the tabs, they are stacked in the order of "separator-negative electrode sheet-separator-positive electrode sheet" and wound in the same direction into an electrode assembly with a winding tension within the range of 700gf to 1000gf. They are then hot-pressed to form non-straight areas (corner areas) and straight areas, assembled into shells, injected with liquid, left to stand at high temperature (45±5°C), formed, replenished with liquid, and aged to obtain a wound battery, which is a "formed battery cell".

[0666] In this example, after winding, only the electrode assembly with L1 ≤ 180 μm is used for the next step of hot pressing and other processes.

[0667] Example 2. Target maximum charge rate ≥ 6C

[0668] The positive electrode sheet, negative electrode sheet, separator and electrolyte were prepared and the battery was assembled using the same method as in Example 1, except that:

[0669] The D of the negative electrode active material in step (2) v 50 is 8μm, and the single-side coating density of the negative electrode active material layer is 130mg / 1540.25mm 2 , the thickness of the negative electrode sheet is different, and the thickness of the negative electrode sheet is about 95μm;

[0670] In step (5), during the winding process, the winding tension is appropriately increased, and only the electrode assembly prepared by winding with L1 ≤ 150 μm is used for the next step of hot pressing and other processes.

[0671] Comparative Example 1.

[0672] The positive electrode sheet, negative electrode sheet, separator and electrolyte and the assembled battery are prepared by the method basically the same as Example 1, except that: in step (5), the winding tension is lowered so that the maximum L1 in the non-flat area of ​​the electrode assembly exceeds 180μm.

[0673] Comparative Example 2.

[0674] The positive electrode sheet, negative electrode sheet, separator and electrolyte and the assembled battery are prepared by the method basically the same as Example 2, except that: in step (5), the winding tension is lowered so that the maximum L1 in the non-flat area of ​​the electrode assembly exceeds 180μm.

[0675] Test method:

[0676] 1. Test of electrolyte ion conductivity

[0677] Instrument: DDSJ-318 conductivity meter.

[0678] Pre-treatment: Take the standard liquid and keep it at a constant temperature of 25℃ (deviation ±0.1℃), and take the test liquid and keep it at a constant temperature of the test temperature (deviation ±0.1℃)

[0679] Test: Test the instrument with two standard solutions at 25°C. After calibration, clean the electrode and place the sample electrode vertically into the liquid to be tested. Click to start the test and wait for the data to stabilize for more than 10 seconds before recording the test results.

[0680] 2. Determination of L1, d1 and g1

[0681] Instrument: ZEISS METROTOM 1500 industrial CT machine.

[0682] Methods: The cross section of the coiled structure was scanned in a direction parallel to the coiling direction to obtain a CT scan cross-sectional image.

[0683] (1) L1, d1 and g1 of battery cells

[0684] The test targets the battery cells obtained after formation. "After formation" refers to the "battery cells obtained after formation" after the formation, rehydration, aging and other processes.

[0685] The spacing L1 between the positive and negative electrodes in the non-straight region refers to the shortest distance between any position P on the inner surface of the adjacent positive electrode and negative electrode, pointing to the outer electrode. Of the two adjacent positive and negative electrode electrodes, the electrode electrode closer to the concave side of the non-straight region is denoted as the "inner electrode," and the electrode electrode farther from the concave side of the non-straight region (i.e., closer to the convex side of the non-straight region) is denoted as the "outer electrode."

[0686] At position P, d1 can be determined as follows: the distance between the two intersection points of the line segment corresponding to L1 and the isolation film.

[0687] At position P, the gap g1 between the positive and negative electrode sheets can be determined as follows: g1 = L1 - d1.

[0688] (2) Maximum L1 and minimum L1 of battery cells

[0689] The battery cells obtained after formation are used as test objects.

[0690] When the unevenness of the distance between the positive and negative electrodes can be observed with the naked eye, the L1 of the area where the distance between the positive and negative electrodes is obviously uneven is tested, and the maximum L1 and minimum L1 measured are selected, which can be recorded as the "maximum distance between the positive and negative electrodes" and "minimum distance between the positive and negative electrodes" in the non-flat area respectively.

[0691] When the unevenness of the distance between the positive and negative electrodes cannot be observed with the naked eye, randomly select different positions in the non-flat area for testing, and record the maximum L1 and minimum L1 obtained in the test. The number of randomly selected test positions is ≥10.

[0692] Table 1

[0693] (3) L0, d0 and g0 of electrode components without chemical formation treatment, maximum L0 and minimum L0.

[0694] The test targets unformed electrode assemblies. "Before formation" refers to the electrode assembly after winding, hot pressing, and before assembly into a casing.

[0695] L0, d0, g0, maximum L0 and minimum L0 are obtained by testing in the same way as L1, d1, g1, maximum L1 and minimum L1.

[0696] In an electrode assembly that has not been subjected to formation treatment, the distance L0 between the positive and negative electrode sheets in the non-flat area refers to the shortest distance from any position P on the inner relative surface of the adjacent positive electrode sheet to the outer electrode sheet.

[0697] At position P, d0 can be determined as follows: the distance between the two intersection points of the line segment corresponding to L0 and the isolation film.

[0698] At position P, the gap g0 between the positive and negative electrode sheets can be determined as follows: g0 = L0 - d0.

[0699] 3. Test method for maximum charge rate of battery cells

[0700] Three-electrode stacked cell method: Use the same positive electrode, negative electrode, separator and electrolyte as the battery cell to be tested to assemble a three-electrode stacked cell. Use the following method to test at different charge rates to obtain the lithium deposition window curve: Use a charge rate of 1C for charging (with 4.0V as the upper limit), detect the anode potential in real time until the lithium potential is 0V, and calculate the SOC state at this charge rate; increase the charge rate by 0.1C as a gradient to test the SOC at the corresponding charge rate, so that the test results can cover the entire SOC range, with the interval between different charge rates being 0.1C; use SOC as the horizontal axis and charge rate as the vertical axis to obtain the lithium deposition window curve. The maximum charge rate in the lithium deposition window curve is used as the maximum charge rate of the battery cell to be tested.

[0701] 4. Testing of battery cell cycle performance and observation and analysis of lithium plating and pole piece cracking

[0702] At 25°C, the prepared battery was charged at the maximum charge rate to 97% SOC, then discharged at a constant current rate of 1C to 3% SOC. Taking polarization into account, the battery was then discharged at a constant current rate of 1 / 3C to 3% SOC. The number of cycles required for capacity decay to 80% SOH was calculated. This can be recorded as "Cycling performance (number of cycles to 80% SOH)."

[0703] After the cycle is completed, the battery is fully charged and disassembled to observe the lithium deposition in the corner area of ​​the disassembly interface, and visually observe whether there are signs of cracking (fracture) in the non-flat area.

[0704] Test results and analysis

[0705] According to the test results of the maximum charge rate, the maximum charge rate of the battery cell prepared in Example 1 is 5.0C, and the maximum charge rate of the battery cell prepared in Example 2 is 6.1C.

[0706] In Example 1 and Example 2, based on the number of cycles when the capacity decays to 80% SOH, both are considered to have acceptable cycle life.

[0707] In Example 1 and Example 2, the battery monomers obtained after formation control the spacing L1 between the positive and negative electrode sheets in the non-flat area within the range of ≤173μm, and there is no L1 greater than 173μm in the non-flat area. Among them, the L1 of the battery monomers obtained after formation in Example 1 all satisfy L1≤157μm, and the L1 of the battery monomers obtained after formation in Example 2 all satisfy L1≤133μm. The battery monomers prepared in Example 1 and Example 2 can provide a charging rate of ≥2C, and can also achieve good cycle performance and a long service life. Among them, the maximum charging rate of Example 1 satisfies ≥4C, and the maximum charging rate of Example 2 satisfies ≥6C.

[0708] There is no corner cracking in both Example 1 and Example 2.

[0709] The battery cell obtained after formation in Comparative Example 1 has L1 larger than 173 μm. Compared with Example 1, the lithium plating of the negative electrode in Comparative Example 1 is significantly aggravated, the charge rate is reduced, and the number of cycles for capacity decay to 80% SOH is significantly reduced.

[0710] The battery cell obtained after formation in Comparative Example 2 has L1 larger than 173 μm. Compared with Example 2, the lithium plating of the negative electrode in Comparative Example 2 is significantly aggravated, the charge rate is reduced, and the number of cycles for capacity decay to 80% SOH is significantly reduced.

[0711] Table 1.

[0712] Table 2.

[0713] The above description of various implementation modes and embodiments tends to emphasize the differences between the various implementation modes and embodiments. The same or similar aspects thereof can be referenced with each other and will not be described in detail herein for the sake of brevity.

[0714] It should be noted that the present application is not limited to the above-mentioned embodiments and examples. The above-mentioned embodiments and examples are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical idea and exerting the same effects are all included in the technical scope of the present application. In addition, without departing from the scope of the subject matter of the present application, other methods of constructing the embodiments or examples by applying various modifications that can be thought of by those skilled in the art, or by combining some of the constituent elements in the embodiments or examples are also included in the scope of the present application.

Claims

1. A battery cell comprising an electrode assembly and an electrolyte, wherein the electrode assembly is immersed in the electrolyte; the electrode assembly comprises a multilayer structure formed by a positive electrode sheet, a negative electrode sheet, and a separator; the separator is disposed between the positive electrode sheet and the negative electrode sheet; The battery cell can provide a charge rate greater than or equal to 2C, or the maximum charge rate of the battery cell is greater than or equal to 2C; The multilayer structure comprises at least a non-flat region, wherein In the non-straight region, in a cross section perpendicular to the thickness direction of the multilayer structure, the connecting line of the thickness centers of each structural layer in the multilayer structure is a non-straight line; in the non-straight region, the distance between the inner relative surfaces of any adjacent positive electrode sheet and the negative electrode sheet at any position is recorded as L1, In the electrode assembly, L1≤MAX; wherein MAX is the acceptable maximum value of L1 when the battery cell is at the corresponding maximum charge rate.

2. The battery cell according to claim 1, wherein: MAX is within the following range: 100μm <MAX<175μm。 3. The battery cell according to claim 1 or 2, wherein: MAX is determined according to an acceptable self-discharge rate range of the battery cell, so that a battery cell having the characteristic of L1=MAX has an acceptable self-discharge rate.

4. The battery cell according to any one of claims 1 to 3, wherein MAX satisfies the following condition: the self-discharge parameter K value of the battery cell, after cycling a preset number of cycles at its maximum charge rate, where at least a portion of the cell satisfies L=MAX, is within an acceptable range; The battery cell includes at least a portion of the positive electrode sheet, at least a portion of the separator, and at least a portion of the negative electrode sheet, which are arranged in sequence, and also includes at least a portion of the electrolyte; L is the distance between the positive electrode sheet and the negative electrode sheet in the battery cell, that is, the distance between the inner relative surfaces of the positive electrode sheet and the negative electrode sheet in the battery cell; During the process of cycling the preset number of times at the maximum charge rate, each cycle is charged to 70% SOC and then discharged to 3% SOC. After the last cycle, the self-discharge parameter K value is tested by charging to 70% SOC.

5. The battery cell according to claim 1, wherein MAX is selected from any of the following values: The battery cell can provide a charge rate greater than or equal to 3C, MAX = 173 μm; The battery cell can provide a charge rate greater than or equal to 4C, MAX = 157 μm; and The battery cell can provide a charge rate greater than or equal to 6C, MAX=133 μm.

6. A battery cell comprising an electrode assembly and an electrolyte, wherein the electrode assembly is immersed in the electrolyte; the electrode assembly comprises a multilayer structure formed by a positive electrode sheet, a negative electrode sheet, and a separator; the separator is disposed between the positive electrode sheet and the negative electrode sheet; The battery cell can provide a charge rate greater than or equal to 2C, or the maximum charge rate of the battery cell is greater than or equal to 2C; The multilayer structure comprises at least a non-flat region, wherein In the non-straight region, in a cross section perpendicular to the thickness direction of the multilayer structure, the connecting line of the thickness centers of each structural layer in the multilayer structure is a non-straight line; in the non-straight region, the distance between the inner relative surfaces of any adjacent positive electrode sheet and the negative electrode sheet at any position is recorded as L1, In the electrode assembly, L1<175 μm.

7. The battery cell according to any one of claims 1 to 6, wherein: The battery cell can provide at least one charging rate of 3C to 6C; Optionally, the battery cell can provide at least one of a charging rate of 3C, 4C and 6C; Optionally, the battery cell can provide at least one charging rate of 4C to 6C.

8. The battery cell according to any one of claims 1 to 7, wherein The battery cell is capable of providing the charge rate under at least one temperature condition between 20°C and 40°C; Optionally, the battery cell can provide the charging rate under at least one temperature condition between 20°C and 30°C.

9. The battery cell according to any one of claims 1 to 8, wherein The battery cells can provide a charge rate greater than or equal to 3C, and in the electrode assembly, L1 is less than or equal to 173 μm, that is, there is no L1 greater than 173 μm; Optionally, the battery cell can provide a charge rate greater than or equal to 4C, and in the electrode assembly, L1 is less than or equal to 157 μm, that is, there is no L1 greater than 157 μm; Optionally, the battery cell can provide a charge rate greater than or equal to 6C, and in the electrode assembly, L1 is less than or equal to 133 μm, that is, there is no L1 greater than 133 μm.

10. The battery cell according to any one of claims 1 to 9, wherein In the non-flat area, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets, and the gap spacing at any position is recorded as g1, then the corresponding parameters at any position satisfy L1>g1.

11. The battery cell according to claim 10, wherein: In the electrode assembly, g1 is less than or equal to 160 μm, that is, there is no g1 greater than 160 μm; Optionally, the battery cell can provide a charge rate greater than or equal to 3C; Optionally, in the electrode assembly, g1 is less than or equal to 144 μm, that is, there is no g1 greater than 144 μm. Further, optionally, the battery cell can provide a charge rate greater than or equal to 4C; Optionally, in the electrode assembly, g1 is less than or equal to 120 μm, that is, there is no g1 greater than 120 μm. Further optionally, the battery cell can provide a charging rate greater than or equal to 6C.

12. The battery cell according to claim 10, wherein: In the electrode assembly, g1 is greater than or equal to 24 μm.

13. The battery cell according to claim 10, wherein: In the electrode assembly, 24 μm ≤ g1 ≤ 160 μm; Optionally, the battery cell can provide a charge rate greater than or equal to 3C; Optionally, in the electrode assembly, 24 μm ≤ g1 ≤ 144 μm, and further optionally, the battery cell can provide a charge rate greater than or equal to 4C; Optionally, in the electrode assembly, 24 μm ≤ g1 ≤ 120 μm. Further optionally, the battery cell can provide a charge rate greater than or equal to 6C.

14. The battery cell according to any one of claims 1 to 13, which satisfies at least one of the following characteristics: In the multi-layer structure, the number of layers of the negative electrode sheet along the thickness direction of the multi-layer structure is multiple; The multilayer structure includes a multilayer winding structure formed by winding the positive electrode sheet, the negative electrode sheet, and the separator, and the non-straight area is located at a corner area of ​​the multilayer winding structure; The multi-layer structure further includes a flat region.

15. The battery cell according to any one of claims 1 to 14, wherein At least a portion of the non-straight areas are smoothly connected non-straight areas; in the smoothly connected non-straight areas, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the center connection line of the layer thickness of each structural layer in the multilayer structure is a smooth curve.

16. The battery cell according to claim 15, wherein: At least a portion of the non-straight area is an arc-shaped area; in the arc-shaped area, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the shape of the layer thickness center connection line of each structural layer in the multilayer structure is an arc.

17. The battery cell according to claim 16, wherein: At least a portion of the non-straight area is an arc area or an arc-like area; In the arc region, in a cross section perpendicular to the layer thickness direction of the multilayer structure, the shape of the connecting line of the layer thickness centers of each structural layer in the multilayer structure is an arc shape; In the arc-like region, in a cross section perpendicular to the thickness direction of the multilayer structure, the standard deviation of the curvature radius of the thickness center connecting line of each structural layer in the multilayer structure at each position is ±10%.

18. The battery cell according to any one of claims 1 to 17, wherein In the non-flat region, the difference between the maximum thickness and the minimum thickness of the negative electrode sheet at any position of any layer is recorded as δ N , satisfying δ N ≤6μm; Optionally, in the non-straight region, δ N ≤4μm.

19. The battery cell according to claim 18, wherein: In the non-flat area, the average thickness of the negative electrode sheet is recorded as d mN ; In the non-flat area, the thickness and d of the negative electrode sheet of any layer at any position mN The difference is in the range of -3μm to 3μm; Optionally, in the non-flat region, the thickness and d of the negative electrode sheet of any layer at any position are mN The difference is in the range of -2μm to 2μm.

20. The battery cell according to any one of claims 1 to 19, wherein In the non-flat area, the thickness of the negative electrode sheet of any layer at any position is recorded as D N , where D N ≤143μm; Optionally, the battery cell can provide a charge rate greater than or equal to 3C; Optionally, in the non-straight region, D N ≤135μm, further optionally, the battery cell can provide a charge rate greater than or equal to 4C; Optionally, in the non-straight region, D N ≤119μm, further optionally, the battery cell can provide a charging rate greater than or equal to 6C.

21. The battery cell according to claim 20, wherein: In the non-flat region, D N ≥55μm.

22. The battery cell according to any one of claims 1 to 21, wherein: The negative electrode plate includes a negative electrode active material layer; In any selected area of ​​the negative electrode active material layer in any layer of the non-flat area, the single-side density of the negative electrode active material layer is recorded as σ N ; Among them, σ N The ratio of the weight of the negative electrode active material layer located on one side of the negative electrode plate in the corresponding selected area to the area of ​​the negative electrode active material layer in the corresponding selected area; the area of ​​any selected area of ​​any layer of the negative electrode active material layer is greater than or equal to 1540.25 mm 2 ; s N ≤170mg / 1540.25mm 2 ; Optionally, the battery cell can provide a charge rate greater than or equal to 3C; Optionally, in the non-flat region, σ N ≤160mg / 1540.25mm 2 , further optionally, the battery cell can provide a charging rate greater than or equal to 4C; Optionally, in the non-flat region, σ N ≤150mg / 1540.25mm 2 , further optionally, the battery cell can provide a charging rate greater than or equal to 6C.

23. The battery cell according to claim 22, wherein: In the non-flat region, σ N ≥120mg / 1540.25mm 2 .

24. The battery cell according to any one of claims 1 to 23, wherein The negative electrode plate includes a negative electrode active material layer; The thickness of a single side of the negative electrode active material layer is 31.5 μm to 49.5 μm, and can be optionally 34 μm to 38.5 μm.

25. The battery cell according to any one of claims 22 to 24, wherein In any selected area of ​​the negative electrode active material layer in any layer of the non-flat area, the single-side compaction density of the negative electrode active material layer is recorded as p N ; Among them, ρ N The ratio of the weight of the negative electrode active material layer located on one side of the negative electrode plate in the corresponding selected area to the volume of the negative electrode active material layer in the corresponding selected area; the area of ​​any selected area of ​​any layer of the negative electrode active material layer is greater than or equal to 1540.25 mm 2 ; 1.52g / cm 3 ≤ρ N ≤1.70g / cm 3 ; Optionally, in the non-straight area, 1.55 g / cm 3 ≤ρ N ≤1.60g / cm 3 .

26. The battery cell according to any one of claims 22 to 25, wherein: The negative electrode active material layer includes a negative electrode active material; The negative electrode active material D v 50 is in the range of 6.5μm to 12μm, wherein the D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%; Optionally, the battery cell can provide a charge rate greater than or equal to 6C; Optionally, the D of the negative electrode active material v 50 is within the range of 7 μm to 12 μm. Further optionally, the battery cell can provide a charge rate greater than or equal to 4C; Optionally, the D of the negative electrode active material v 50 is in the range of 8μm to 12μm. Further optionally, the battery cell can provide a charging rate greater than or equal to 3C.

27. The battery cell according to claim 26, wherein: The negative electrode active material includes a carbon-based material; Optionally, the carbon-based material includes one or more of graphite material, soft carbon and hard carbon.

28. The battery cell according to any one of claims 26 to 27, wherein: The negative electrode active material includes a silicon-based material; Optionally, the silicon-based material includes one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys.

29. The battery cell according to any one of claims 1 to 28, wherein The negative electrode sheet is an expandable negative electrode sheet; In the same charge and discharge cycle, the negative electrode is charged to a SOC greater than or equal to 70% and discharged to a SOC less than or equal to 10%. The thickness of the negative electrode during charging is greater than the thickness during discharging. The ratio of the thickness during charging to the thickness during discharging is recorded as R. N , then R N >1; Optionally, in the non-straight region, R N ≥1.

17.

30. The battery cell according to claim 29, wherein In the non-flat region, R N ≤1.50, optionally, R N ≤1.

36.

31. The battery cell according to claim 29 or 30, wherein: During the same charge-discharge cycle, the battery is charged to 97% SOC and discharged to 3% SOC. Optionally, during the same charge and discharge cycle, the battery is charged to full charge and discharged to full discharge.

32. The battery cell according to claim 29, wherein In the non-flat region, during at least one charge-discharge cycle, the negative electrode is charged to a SOC greater than or equal to 70% and discharged to a SOC less than or equal to 10%. The difference in thickness between the negative electrode sheet during charge and discharge is denoted as δ dN , satisfying δ dN / 2 <g1; Wherein, in the non-straight area, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and negative electrode sheets, and the gap spacing at any position is recorded as g1.

33. The battery cell according to claim 32, wherein: During the at least one charge-discharge cycle, the battery is charged to 97% SOC and discharged to 3% SOC; Optionally, during the at least one charge-discharge cycle, the battery is charged to full charge and discharged to full discharge.

34. The battery cell according to any one of claims 1 to 33, wherein The separator includes a base film and a negative electrode side separator coating located on a side of the base film close to the negative electrode plate, wherein the negative electrode side separator coating includes compressible particles; Optionally, the isolation membrane is provided with a positive electrode side diaphragm coating on the side close to the positive electrode plate, and the positive electrode side diaphragm coating includes the compressible particles. The compressible particles in the positive electrode side diaphragm coating and the compressible particles in the negative electrode side diaphragm coating may be the same or different.

35. The battery cell according to claim 34, wherein: The compressible particles include polymer particles; wherein the glass transition temperature of the polymer particles is less than or equal to 120° C.; Optionally, the glass transition temperature of the polymer particles is greater than or equal to 10°C; further optionally, the polymer particles The glass transition temperature of the polymer particles is greater than or equal to 15°C; further optionally, the glass transition temperature of the polymer particles is greater than or equal to 50°C.

36. The battery cell according to claim 35, wherein: The polymer particles include a cross-linked structure; Optionally, the polymer particles have a partially cross-linked structure; Further optionally, the cross-linking degree of the polymer particles is less than or equal to 90%.

37. The battery cell according to any one of claims 34 to 36, wherein: The compressible particles include sticky polymer particles, which include one or more of polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

38. The battery cell according to any one of claims 34 to 37, wherein: The D of the compressible particles v 50 is in the range of 5 μm to 10 μm, wherein the D v 50 represents the particle size corresponding to when the cumulative volume distribution percentage of the multi-particle mixture reaches 50%; Optionally, the compressible particles have a D v 50 is in the range of 5μm to 8.5μm.

39. The battery cell according to any one of claims 34 to 38, wherein The weight proportion of the compressible particles in the negative electrode side separator coating is 10wt% to 30wt%; Optionally, the negative electrode side separator coating further includes ceramic particles.

40. The battery cell according to claim 39, wherein The weight proportion of the compressible particles in the negative electrode side separator coating is 15 wt % to 20 wt %.

41. The battery cell according to any one of claims 34 to 40, wherein: In any selected area of ​​the negative electrode side separator coating layer in any layer in the non-flat area, the surface density of the negative electrode side separator coating layer is recorded as σ g ; Among them, σ g The ratio of the weight of the negative electrode side separator coating of the corresponding selected area to the area of ​​the negative electrode side separator coating of the corresponding selected area is equal to or greater than 1540.25 mm 2 ; The average surface density σ of the negative electrode side separator coating mG is equal to the average value of the ratio of the weight of each layer of the negative electrode side separator coating to the area of ​​the corresponding layer of the negative electrode side separator coating; The negative electrode side separator coating meets one or more of the following characteristics: In the non-flat area, the difference between the maximum surface density and the minimum surface density of any layer of the negative electrode side separator coating in any selected area is 0 g / m 2 ~0.4g / m 2 ; In the non-flat region, the surface density of any layer of the negative electrode side separator coating in any selected area is σ mG The difference is -0.2g / m 2 ~0.2g / m 2 .

42. The battery cell according to any one of claims 34 to 41, wherein In the non-flat area, the average thickness of the negative electrode side separator coating is recorded as d mG ; The negative electrode side separator coating meets one or more of the following characteristics: In the non-flat area, the thickness of any layer of the negative electrode side separator coating at any position is 2 μm to 6 μm; In the non-flat region, the difference between the maximum thickness and the minimum thickness of any layer of the negative electrode side separator coating at any position is recorded as δ G , then 0μm≤δ G ≤2μm; In the non-flat region, the thickness of any layer of the negative electrode side separator coating at any position is mG The difference is -2μm to 2μm, and can be optionally -1.5μm to 1.5μm.

43. The battery cell according to any one of claims 1 to 42, wherein: Under at least one temperature condition between 20° C. and 35° C., the ion conductivity of the electrolyte is 8 mS / cm to 18 mS / cm.

44. The battery cell according to any one of claims 1 to 43, wherein The electrolyte comprises an electrolyte salt and an electrolyte solvent, wherein the electrolyte solvent comprises a low-viscosity solvent; The low-viscosity solvent includes one or more of diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, ethyl acetate, methyl acetate, propyl acetate, and a solvent having a viscosity less than or equal to that of at least one of the aforementioned reagents at 25°C.

45. The battery cell according to claim 44, wherein The electrolyte solvent further includes a dissociation solvent, which has the ability to dissolve and dissociate the electrolyte salt; Optionally, the dissociation solvent includes one or more of ethylene carbonate and propylene carbonate.

46. ​​The battery cell according to claim 44 or 45, wherein: The weight proportion of the low-viscosity solvent in the electrolyte solvent is 10 wt % to 90 wt %, optionally 10 wt % to 60 wt %, and further optionally 10 wt % to 40 wt %.

47. The battery cell according to any one of claims 1 to 46, wherein: The positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active substance; The positive electrode active material includes a lithium-containing active material; Optionally, the positive electrode active material includes one or more of lithium-containing phosphates, lithium transition metal oxides, and modified products of any of the foregoing substances; Optionally, the lithium-containing phosphate includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon; Optionally, the lithium transition metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified products of any of the foregoing substances; Any of the aforementioned modified substances is a positive electrode active material containing a modifying element, wherein the modifying element exists in the form of a doping element, a coating element, or a combination of a doping element and a coating element.

48. The battery cell according to any one of claims 1 to 47, wherein In the non-flat area, the thickness of the isolation film at any position is recorded as d1, and the corresponding parameters at any position satisfy L1=g1+d1; In the electrode assembly, 4 μm ≤ d1 ≤ 13 μm; Optionally, in the electrode assembly, 7 μm≤d1≤13 μm.

49. The battery cell according to any one of claims 1 to 47, wherein In the electrode assembly, 28 μm ≤ L1 ≤ 173 μm; Optionally, in the electrode assembly, 31 μm≤L1≤173 μm.

50. The battery cell according to any one of claims 1 to 49, wherein The battery cell meets any of the following conditions: Case B1: The battery cell can provide a charge rate of 3C, 28μm≤L1≤173μm; Case B2: The battery cell can provide a charge rate of 4C, 28μm≤L1≤157μm; Case B3: the battery cell can provide a charge rate of 6C, and 28 μm≤L1≤133 μm.

51. The battery cell according to claim 50, wherein: In the non-flat area, there is a gap between the inner facing surfaces of any adjacent positive electrode sheets and negative electrode sheets, and the gap spacing at any position is denoted as g1; The negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active substance; the particle size corresponding to the cumulative volume distribution percentage of the multi-particle mixture reaching 50% is recorded as D v 50; The battery cell meets one or more of the following characteristics: In the case B1, 24 μm ≤ g1 ≤ 160 μm; In the case B1, the D v 50 is 8μm~12μm; In the case B2, 24 μm ≤ g1 ≤ 144 μm; In the case B2, the D v 50 is 7μm~12μm; In the case B3, 24 μm ≤ g1 ≤ 120 μm; In the case B3, the D v 50 is 6.5μm~12μm.

52. A secondary battery comprising the battery cell according to any one of claims 1 to 50.

53. The secondary battery according to claim 52, wherein The secondary battery is a lithium-ion secondary battery.

54. An electrical device comprising at least one of the battery cell according to any one of claims 1 to 50 and the secondary battery according to claim 52 or 53.

55. A method for preparing a battery cell, wherein: The method for preparing the battery cell comprises the following steps: Disposing a separator between a positive electrode sheet and a negative electrode sheet, controlling the positions of the positive electrode sheet and the negative electrode sheet according to a preset gap distance between the positive electrode sheet and the negative electrode sheet, forming a multilayer structure with the positive electrode sheet, the negative electrode sheet, and the separator, and subjecting at least a portion of the multilayer structure to a non-flat region through a process including cold pressing, thereby preparing an electrode assembly that has not been subjected to chemical formation treatment; wherein, in the non-flat region, in a cross section perpendicular to the thickness direction of the multilayer structure, a connecting line of the center thicknesses of the structural layers in the multilayer structure is a non-straight line; and Immersing the electrode assembly that has not been subjected to formation treatment in an electrolyte and subjecting it to a process including formation to prepare a battery cell having a charge rate that meets a preset value; wherein the preset charge rate value is greater than or equal to 2C; in, The prepared battery cell is the battery cell according to any one of claims 1 to 50, and in the non-flat area of ​​the battery cell, the distance between the inner relative surfaces of any adjacent positive electrode sheets and the negative electrode sheets at any position is recorded as L1. 56 . The method for preparing a battery cell according to claim 55 , comprising the step of determining a preset range of L1 according to an acceptable self-discharge rate range, so that the prepared battery cell has an acceptable self-discharge rate.

57. The method for preparing a battery monomer according to claim 55 or 56, wherein: The multilayer structure includes a multilayer winding structure formed by winding the positive electrode sheet, the negative electrode sheet, and the separator, and the non-straight area is located at a corner area of ​​the multilayer winding structure; In the step of forming the positive electrode sheet, the negative electrode sheet and the separator into a multilayer structure, the winding tension is controlled to form L1 Control within the preset range.

58. The method for preparing a battery monomer according to any one of claims 55 to 57, wherein: In the non-flat area of ​​the electrode assembly that has not been subjected to chemical formation treatment, the distance between the inner relative surfaces of any adjacent positive electrode sheet and the negative electrode sheet at any position is recorded as L0, and L0 ≥ L1; In the electrode assembly that has not been subjected to chemical formation treatment, L0 is less than or equal to 213 μm, that is, there is no L0 greater than 213 μm; Optionally, the battery cell can provide a charge rate greater than or equal to 3C; Optionally, in the electrode assembly that has not been subjected to formation treatment, L0 is less than or equal to 193 μm, that is, there is no L0 greater than 193 μm. Further, optionally, the battery cell can provide a charge rate greater than or equal to 4C; Optionally, in the electrode assembly that has not been subjected to formation treatment, L0 is less than or equal to 163 μm, that is, there is no L0 greater than 163 μm. Further optionally, the battery cell can provide a charging rate greater than or equal to 6C.

59. The method for preparing a battery cell according to claim 58, wherein: In the non-flat area of ​​the electrode assembly that has not been subjected to chemical formation treatment, there is a gap between the inner relative surfaces of any adjacent positive electrode sheets and the negative electrode sheets. The gap spacing at any position is recorded as g0, and the corresponding parameters at any position satisfy L0>g0.

60. The method for preparing a battery cell according to claim 59, wherein: In the electrode assembly that has not been subjected to chemical formation treatment, g0 is less than or equal to 200 μm, that is, there is no g0 greater than 200 μm; Optionally, the battery cell can provide a charge rate greater than or equal to 3C; Optionally, in the electrode assembly that has not been subjected to chemical formation treatment, g0 is less than or equal to 180 μm. Further optionally, the battery cell can provide a charge rate greater than or equal to 4C; Optionally, in the electrode assembly that has not been subjected to formation treatment, g0 is less than or equal to 150 μm. Further optionally, the battery cell can provide a charge rate greater than or equal to 6C.

61. The method for preparing a battery cell according to claim 59, wherein: In the electrode assembly that has not been subjected to chemical formation treatment, g0 is greater than or equal to 30 μm.

62. The method for preparing a battery cell according to claim 59, wherein: In the electrode assembly that has not been subjected to chemical formation treatment, 30 μm ≤ g0 ≤ 200 μm; Optionally, the battery cell can provide a charge rate greater than or equal to 3C; Optionally, in the electrode assembly that has not been subjected to formation treatment, 30 μm ≤ g0 ≤ 180 μm, and further optionally, the battery cell can provide a charge rate greater than or equal to 4C; Optionally, in the electrode assembly that has not been subjected to formation treatment, 30 μm≤g0≤150 μm. Further optionally, the battery cell can provide a charge rate greater than or equal to 6C.

63. The method for preparing a battery monomer according to any one of claims 58 to 62, wherein: In the electrode assembly that has not been subjected to chemical formation treatment, 34 μm ≤ L0 ≤ 213 μm; Optionally, in the electrode assembly that has not been subjected to chemical formation treatment, 37 μm≤L0≤213 μm.

64. The method for preparing a battery monomer according to any one of claims 58 to 62, wherein: The method for preparing the battery cell satisfies any of the following conditions: Case A1: The battery cell can provide a charge rate of 3C, 34μm≤L0≤213μm; Case A2: The battery cell can provide a charge rate of 4C, 34μm≤L0≤193μm; Case A3: the battery cell can provide a charge rate of 6C, and 34 μm≤L0≤163 μm.

65. The method for preparing a battery cell according to claim 64, wherein: In the non-flat area of ​​the electrode assembly that has not been subjected to chemical formation treatment, there is a gap between the inner opposing surfaces of any adjacent positive electrode sheet and the negative electrode sheet, and the gap spacing at any position is recorded as g0; The method for preparing the battery cell meets one or more of the following characteristics: In the case A1, 30 μm ≤ g0 ≤ 200 μm; In the case A2, 30 μm ≤ g0 ≤ 180 μm; In the case A3, 30 μm ≤ g0 ≤ 150 μm.

66. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 55 to 65 are implemented.

67. A computer-readable storage medium having a computer program stored thereon, wherein: When the computer program is executed by a processor, the steps of the method according to any one of claims 55 to 65 are implemented.

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