Battery cell and electric device

Abstract

The invention provides a battery monomer and an electric device. Comprising a battery cell, the battery cell comprises a positive pole piece, a negative pole piece and a diaphragm arranged between the positive pole piece and the negative pole piece, the positive pole piece, the negative pole piece and the diaphragm extend along a first direction, and the lengths of the positive pole piece, the negative pole piece and the diaphragm along the first direction are greater than those along a second direction; the second direction is perpendicular to the first direction and is the same as the height direction of the battery monomers, the positive pole piece, the negative pole piece and the diaphragm are laminated along a third direction, the third direction is perpendicular to the first direction and the second direction, the negative pole piece comprises a negative current collector and a negative pole film layer positioned on at least one side of the negative current collector, and the compaction density of the negative pole film layer is 1.5 g / cm < 3 >-1.78 g / cm < 3 >; the diaphragm comprises a base membrane and a coating located on at least one side of the base membrane, the coating comprises organic particles, and the cumulative number distribution particle size D50 of the organic particles is 10-18 microns.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a battery cell and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on its energy density, cycle performance, and safety performance. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell and an electrical device. The battery cell can achieve a balance of high energy density, good cycle performance, and safety performance.

[0004] To this end, the first aspect of this application provides a battery cell, the battery cell comprising a cell and a casing, the cell comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the negative electrode comprising a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, wherein the compaction density of the negative electrode film layer is 1.5 g / cm³. 3 -1.78g / cm 3 The separator includes a base membrane and a coating located on at least one side of the base membrane. The coating includes organic particles, and the cumulative particle size D50 of the organic particles is 10μm-18μm. This is beneficial for improving the energy density of the battery cell, while also improving the structural stability of the electrode and the electrolyte wetting effect, thus balancing the safety and cycle performance of the battery cell.

[0005] In some embodiments, the compaction density of the negative electrode sheet is 1.60 g / cm³. 3 -1.70g / cm 3 This further contributes to the high energy density of individual battery cells.

[0006] In some embodiments, the thickness of the negative electrode current collector is 3μm-6μm; and / or the tensile strength of the negative electrode current collector is 300MPa-550MPa. This allows the battery cell to achieve both high energy density and good cycle performance and safety.

[0007] In some embodiments, the thickness of the negative electrode current collector is 4μm-5μm; and / or, the tensile strength of the negative electrode current collector is 400MPa-450MPa. This further facilitates the battery cell to achieve both high energy density and good cycle performance and safety performance.

[0008] In some embodiments, based on the thickness of the negative electrode sheet, the thickness ratio of the negative electrode current collector is 2.69%-4.87%. This helps to reduce the volume occupied by the current collector and improve the energy density of the battery cell.

[0009] In some embodiments, the elongation at break of the negative electrode current collector is 2%-4%. This is beneficial for improving the structural stability of the negative electrode sheet and enhancing the safety and cycle performance of the battery cell. In some optional embodiments, the elongation at break of the negative electrode current collector is 2.8%-3.2%.

[0010] In some embodiments, the coating weight of the negative electrode sheet is 0.1 g / 1540 mm. 2 -0.2g / 1540mm 2 This is beneficial for increasing the energy density of individual battery cells.

[0011] In some embodiments, the organic particles in the coating have a D50 of 10 μm-14 μm. This helps to reduce the risk of electrode breakage and improve the safety performance and cycle stability of the battery cell.

[0012] In some embodiments, the polymer particles are made of one or more of the following polymers: polyacrylic acid polymers, polyvinylidene fluoride polymers, polyacrylonitrile polymers, and polyimide polymers. This is beneficial for improving the cycle performance of the battery cell.

[0013] In some embodiments, the thickness of the base film is 5 μm-12 μm. In some alternative embodiments, the thickness of the base film is 5 μm-9 μm.

[0014] In some embodiments, the separator further includes ceramic layers located on both sides of the base membrane, with the ceramic layers situated between the base membrane and the coating. This helps reduce the risk of separator puncture and cell thermal runaway, and also improves the electrolyte wetting effect, thereby enhancing the safety and cycle performance of the battery cell.

[0015] In some embodiments, the thickness of the ceramic layer is 0.8 μm to 1.2 μm. This is beneficial for improving the safety performance of the battery while maintaining the energy density of the individual battery cells.

[0016] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector, wherein the compaction density of the positive electrode film layer is 2.50 g / cm³. 3 -2.8g / cm 3The thickness of the positive electrode current collector is 9μm-15μm, and / or the tensile strength of the positive electrode current collector is 200MPa-400MPa. This allows the battery cell to have high energy density while maintaining good safety and cycle performance.

[0017] In some embodiments, the compaction density of the positive electrode sheet is 2.65 g / cm³. 3 -2.8g / cm 3 The thickness of the positive electrode current collector is 9μm-13μm, and / or the tensile strength of the positive electrode current collector is 230MPa-270MPa. This further contributes to improving the energy density, cycle performance, and safety performance of the battery cell.

[0018] In some embodiments, based on the thickness of the positive electrode sheet, the thickness ratio of the positive current collector is 4.65%-7.74%. This is beneficial to improving the energy density of the battery cell.

[0019] In some embodiments, the elongation at break of the positive electrode current collector is 0.6%-3%. This is beneficial for improving the structural stability of the positive electrode sheet and enhancing the safety and cycle performance of the battery cell. In some optional embodiments, the elongation at break of the positive electrode current collector is 1.5%-2.45%.

[0020] In some embodiments, the coating weight of the positive electrode sheet is 0.3g / 1540mm. 2 -0.4g / 1540mm 2 This is beneficial for increasing the energy density of individual battery cells.

[0021] In some embodiments, the battery cell is a wound cell, wherein the positive electrode, the negative electrode, and the separator are stacked and wound in a predetermined order. In a cross-section perpendicular to the axial direction Y of the wound cell, the wound cell includes a large surface area and bending areas located on both sides of the large surface area along the first direction X. In the large surface area, the positive electrode, the negative electrode, and the separator are stacked along the second direction Z. The first direction X and the second direction Z are perpendicular to each other and perpendicular to the axial direction Y. Taking the bending position of the innermost separator in the wound cell as the starting point, in a direction at 45° to the second direction, in the bending area, the average gap between the positive electrode or the negative electrode and the adjacent separator is 30μm-40μm. This helps to reduce the problem of cracking in the electrode bending area and also helps to improve the wetting effect of the electrolyte, thereby improving the cycle performance of the battery cell.

[0022] In some embodiments, the surface of the positive electrode sheet is provided with recesses, and the density of the recesses is 4-8 per cm³.2 The deepest part of the depression has a height of 5μm-10μm.

[0023] In some embodiments, the length of the cell along the second direction is greater than or equal to 150 mm. This is beneficial for increasing the energy density of the battery cell.

[0024] In some embodiments, the length of the battery cell along the second direction is 150mm-180mm.

[0025] In some embodiments, the electrolyte injection coefficient of the battery cell is 2.3-2.8 g / Ah. This helps maintain the wetting effect of the electrolyte and improves the cycle life of the battery cell.

[0026] A second aspect of this application also provides an electrical device comprising the battery cell described in the first aspect of this application. Therefore, the electrical device of this application possesses at least all the advantages of the aforementioned battery cell. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application; Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown. Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application; Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application; Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown; Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application; Figure 7 This is a structural schematic diagram of a section perpendicular to the axial direction of a wound battery cell according to an embodiment of this application; Figure 8 This is a schematic diagram of the structure of the positive electrode sheet according to one embodiment of this application; Figure 9 This is a CT image of the battery cell prepared in Example 1 of this application.

[0028] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 10 Positive electrode sheet; 101 Positive current collector; 102 Positive film layer. Detailed Implementation

[0029] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell and the power supply device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] With increasingly stringent requirements for battery cell energy density, high-energy-density battery cells have become the main development direction. In high-energy-density battery cells, to improve energy density, thinner current collectors are typically used to reduce their volume within the cell, and the coating weight and compaction density of the positive and negative electrode sheets increase significantly. This leads to an increased risk of electrode breakage during cell manufacturing. For battery cells with wound structures, the risk of electrode cracking at corners also increases during the winding process. Higher compaction density electrodes generate greater expansion forces during charge and discharge, which can easily lead to electrode breakage and cell failure, affecting the safety and cycle stability of the battery cell. Furthermore, the greater expansion during charge and discharge of higher compaction density electrodes reduces the gap between the electrode and the separator, hindering the electrolyte from fully wetting the electrode and thus affecting the cycle performance of the battery cell.

[0035] Based on this, this application proposes a battery cell and an electrical device. The battery cell of this application can achieve both high energy density and good safety and cycle performance.

[0036] The present application and its optional embodiments will be described in more detail below with appropriate reference to the accompanying drawings.

[0037] The battery cell of this application includes a cell and a casing. The cell includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The negative electrode includes a negative current collector and a negative active material layer located on at least one side of the negative current collector. The compaction density of the negative electrode film layer is 1.5 g / cm³. 3 -1.78g / cm 3 The diaphragm includes a base membrane and a coating located on at least one side of the base membrane. The coating includes organic particles, and the cumulative distribution of the organic particles has a particle size D50 of 10 μm-18 μm.

[0038] In this application, the compaction density of the negative electrode sheet is made to be 1.5 g / cm³. 3 -1.78g / cm3 This is beneficial for improving the energy density of individual battery cells. A negative electrode with a high compaction density will experience significant volume expansion during cycling, which will compress the gap between the positive and negative electrode sheets and the separator. This leads to a decrease in the wetting effect of the electrolyte on the positive and negative electrode sheets, affecting the cycle performance of the battery cell. More seriously, the large expansion force may cause the negative electrode sheet to crack, resulting in safety risks. Therefore, by including a coating in the separator, the coating comprising organic particles, wherein the cumulative distribution of the organic particles has a particle size D50 of 10μm-18μm, a suitable gap is created between the positive and negative electrode sheets and the separator, which can accommodate more volume expansion. This reduces the pressure of the expansion force on the negative electrode sheet during cycling, lowers the risk of negative electrode sheet breakage, and improves the safety of the battery cell. Furthermore, it also helps maintain good electrolyte wetting of the positive and negative electrode sheets, improving the cycle performance of the battery cell. In summary, this application improves the structural stability of the negative electrode sheet and the wetting effect of the electrolyte by giving the negative electrode sheet a high energy density and using a separator with a specific structure, thereby enabling the battery cell to have a high energy density while taking into account safety and cycle performance.

[0039] The battery cell of this application includes at least one cell, for example, it may include 1, 2, 3, or 4 cells. Each cell includes a positive electrode, a negative electrode, and a separator. The positive electrode, negative electrode, and separator are stacked along a third direction, which is perpendicular to the height direction of the battery cell. During charging and discharging, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrode plates. The separator is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while also allowing ions to pass through. In some embodiments, the positive electrode, negative electrode, and separator are stacked sequentially in the order of "separator-negative electrode-separator-positive electrode".

[0040] The components of the battery cell in this application are described in detail below.

[0041] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0042] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0043] In this application, the compaction density of the negative electrode film is 1.5 g / cm³. 3 -1.78g / cm 3By maintaining the compaction density of the negative electrode film within the aforementioned range, it is beneficial to improve the energy density of the battery cell. For example, the compaction density of the negative electrode film can be 1.5 g / cm³. 3 1.53g / cm 3 1.55g / cm 3 1.58g / cm 3 1.60g / cm 3 1.63g / cm 3 1.65g / cm 3 1.68g / cm 3 1.70g / cm 3 1.72g / cm 3 1.74 g / cm 3 1.76 g / cm 3 1.78g / cm 3 Or a value between any two of these values. In some alternative embodiments, the compaction density of the negative electrode film is 1.60 g / cm³. 3 -1.70g / cm 3 This will help to further improve the energy density of individual battery cells.

[0044] In this application, the compaction density of the electrode film layer (e.g., positive electrode film layer or negative electrode film layer) has a meaning known in the art and can be tested using methods known in the art. Exemplarily, the test method is as follows: After disassembling a freshly prepared secondary battery, the negative electrode sheet is removed and dried at a certain temperature and time (e.g., drying at 60°C for more than 4 hours), and then its parameters are tested. The negative electrode sheet is punched into small circular pieces with an area of ​​S1, and its weight is recorded as M1. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, and the weight of the negative current collector is weighed and recorded as M0. The surface density of the negative electrode film layer = (M1-M0) / S1. Then, the compaction density of the negative electrode film layer is calculated according to the following formula: The compaction density of the negative electrode sheet = the surface density of the negative electrode film layer / the thickness of the negative electrode film layer. The thickness of the negative electrode film is a well-known concept in the art and can be tested using methods known in the art, such as a micrometer (e.g., Mitutoyo 293-100 with an accuracy of 0.1 μm).

[0045] In some embodiments, the thickness of the negative electrode current collector is 3μm-6μm; and / or the tensile strength of the negative electrode current collector is 300MPa-550MPa. By keeping the thickness of the negative electrode current collector within the above range, it is beneficial to reduce the volumetric proportion of the negative electrode current collector in the battery cell, thereby increasing the volumetric energy density of the battery cell. By keeping the tensile strength of the negative electrode current collector within the above range, it is beneficial to reduce the risk of breakage of the negative electrode current collector due to the high compaction density of the negative electrode sheet, improving the structural stability of the negative electrode sheet, thereby improving the safety and cycle stability of the battery cell. By keeping the thickness and tensile strength of the negative electrode current collector within the above range, it is beneficial for the battery cell to achieve a balance between high volumetric energy density, cycle performance, and safety performance. For example, the thickness of the negative electrode current collector can be 3.0 μm, 3.5 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, 5.5 μm, 6.0 μm, or a value within a range of any two of these values. In some alternative embodiments, the thickness of the negative electrode current collector is 4 μm-5 μm.

[0046] In this application, the thickness of the current collector (e.g., positive current collector or negative current collector) can be tested using methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100 model, with an accuracy of 0.1 μm).

[0047] For example, the tensile strength of the negative electrode current collector can be 350 MPa, 400 MPa, 410 MPa, 415 MPa, 420 MPa, 430 MPa, 435 MPa, 440 MPa, 445 MPa, 450 MPa, 480 MPa, 500 MPa, 530 MPa, 550 MPa, or a value within a range of any two of these values. In some alternative embodiments, the tensile strength of the negative electrode current collector is 400 MPa to 450 MPa.

[0048] In this application, the tensile strength of the current collector (positive current collector or negative current collector) is a well-known concept in the art and can be tested using known methods. An exemplary test method is as follows: After disassembling the battery cell, a positive electrode or a negative electrode is obtained. The film layer on the positive electrode or the negative electrode is removed and cleaned to obtain a positive current collector or a negative current collector (hereinafter collectively referred to as the current collector). A universal testing machine is used to test the tensile strength. The specific steps are as follows: the current collector is clamped at both ends of the universal testing machine clamp, and a tensile force is applied to both ends by the universal testing machine until the current collector breaks. The maximum tensile force (Fm, in N) at the time of breakage is measured by the force sensor on the universal testing machine. Then, the tensile strength is calculated according to the following formula: tensile strength Rm = Fm / A0, where A0 is the original cross-sectional area of ​​the current collector, i.e., the thickness × width of the current collector.

[0049] In some embodiments, based on the thickness of the negative electrode sheet, the thickness percentage of the negative electrode current collector is 2.69%-4.87%. By keeping the thickness of the negative electrode current collector within this range, it is beneficial to reduce the volume occupied by the current collector and increase the volume percentage of the active material on the negative electrode sheet, thereby increasing the energy density of the battery cell. Exemplarily, based on the thickness of the negative electrode sheet, the thickness percentage of the negative electrode current collector is 2.69%, 2.77%, 2.81%, 3.00%, 3.20%, 3.48%, 3.54%, 3.62%, 3.80%, 4.0%, 4.30%, 4.50%, 4.87%, or a value between any two of these ranges. In some optional embodiments, based on the thickness of the negative electrode sheet, the thickness percentage of the negative electrode current collector is 2.73%-3.62%.

[0050] In this application, the thickness percentage of the current collector (e.g., negative electrode current collector or positive electrode current collector) can be tested using methods known in the art. Exemplarily, the specific testing method includes: disassembling the secondary battery to obtain a negative electrode or positive electrode, measuring the thickness of the negative electrode or positive electrode using a micrometer, and recording it as d1. After wiping away the film layer on the negative electrode or positive electrode, the negative electrode current collector or positive electrode current collector is obtained, and its thickness is measured using a micrometer, and recorded as d2. The thickness percentage of the negative electrode current collector, based on the total thickness of the negative electrode, is calculated as d2 / d1 × 100%. The thickness percentage of the positive electrode current collector in the positive electrode is calculated using the same method.

[0051] In some embodiments, the elongation at break of the negative electrode current collector is 2%-4%. An elongation at break within this range indicates good ductility of the negative electrode current collector, enabling it to withstand significant deformation without easily breaking, which is beneficial for improving the structural stability of the negative electrode sheet and enhancing the safety and cycle performance of the battery cell. Exemplarily, the elongation at break of the negative electrode current collector is a value within the range of 2%, 2.2%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, or any two of these values. In some optional embodiments, the elongation at break of the negative electrode current collector is 2.8%-3.2%.

[0052] In this application, the elongation at break of the current collector (positive current collector or negative current collector) has a meaning known in the art and can be tested using known methods. An exemplary test method is as follows: After disassembling the battery cell to obtain the positive or negative electrode sheet, the film layer on the positive or negative electrode sheet is removed and cleaned to obtain the positive or negative current collector (hereinafter collectively referred to as the current collector). A universal testing machine is used to perform a tensile strength test. Specifically, the current collector is clamped at both ends of the universal testing machine's clamps, and a tensile force is applied to both ends by the universal testing machine until the current collector breaks. The displacement of the clamps is recorded by the universal testing machine from the start of the applied tensile force to the point when the current collector breaks. The maximum elongation of the current collector is calculated using the following formula: Elongation at break , where L0 is the initial length of the current collector.

[0053] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0054] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0055] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0056] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0057] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0058] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0059] In some embodiments, the coating weight of the negative electrode sheet is 0.1 g / 1540 mm. 2 -0.2g / 1540mm 2 By keeping the coating weight of the negative electrode sheet within the aforementioned range, it is beneficial to improve the energy density of the battery cell. For example, the coating type of the negative electrode sheet can be 0.1g / 1540mm. 2 0.14g / 1540mm 2 0.146g / 1540mm 2 0.150g / 1540mm 2 1.153g / 1540mm 2 0.160g / 1540mm 20.165g / 1540mm 2 0.170g / 1540mm 2 0.180g / 1540mm 2 0.185g / 1540mm 2 0.190g / 1540mm 2 0.195g / 1540mm 2 0.200g / 1540mm 2 Or the value between any two of them within a range.

[0060] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0061] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0062] In some embodiments, the compaction density of the positive electrode film is 2.50 g / cm³. 3 -2.80g / cm 3 By maintaining the compaction density of the positive electrode film within the aforementioned range, it is beneficial to further improve the energy density of the battery cell. For example, the compaction density of the positive electrode film can be 2.50 g / cm³. 3 2.55g / cm 3 2.60g / cm 3 2.65g / cm 3 2.70 g / cm 3 2.75g / cm 3 2.80g / cm 3 Or values ​​between any two of these values. In some alternative embodiments, the compaction density of the positive electrode film is 2.65 g / cm³. 3 -2.80g / cm 3 .

[0063] In some embodiments, the thickness of the positive electrode current collector is 9 μm-15 μm. By keeping the thickness of the positive electrode current collector within this range, it is beneficial to reduce the volume occupied by the current collector in the battery cell, thereby allowing the battery cell to accommodate more active material and increasing the energy density of the battery cell. Exemplarily, the thickness of the positive electrode current collector can be 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a value between any two of these values. In some alternative embodiments, the thickness of the positive electrode current collector is 9 μm-13 μm.

[0064] In some embodiments, the tensile strength of the positive electrode current collector is 200 MPa-400 MPa. When the positive electrode sheet has a high compaction density and the positive electrode current collector is relatively thin, the current collector is prone to breakage during electrode manufacturing, and greater volume expansion occurs during the charging and discharging of the battery cell, increasing the risk of electrode breakage. By ensuring the tensile strength of the positive electrode current collector is within the aforementioned range, it demonstrates that the positive electrode current collector has better compressive strength, reducing the risk of electrode breakage, improving the structural stability of the electrode, and thus improving the safety and cycle performance of the battery cell. Exemplarily, the tensile strength of the positive electrode current collector can be 200 MPa, 220 MPa, 230 MPa, 235 MPa, 240 MPa, 245 MPa, 250 MPa, 255 MPa, 260 MPa, 265 MPa, 270 MPa, 300 MPa, 350 MPa, 400 MPa, or a value within a range of any two of these values. In some alternative embodiments, the tensile strength of the positive current collector is 230 MPa-270 MPa.

[0065] In some embodiments, based on the thickness gauge of the positive electrode sheet, the thickness percentage of the positive current collector is 4.56%-7.74%. By keeping the thickness of the positive current collector within this range, it is beneficial to reduce the volume occupied by the current collector and increase the volume percentage of the active material on the positive electrode sheet, thereby increasing the energy density of the battery cell. For example, based on the thickness gauge of the positive electrode sheet, the thickness percentage of the positive current collector is 4.56%, 5.98%, 6.10%, 7.4%, 7.52%, 7.74%, or a value between any two of these ranges.

[0066] In some embodiments, the elongation at break of the positive electrode current collector is 0.6%-3%. By ensuring the elongation at break of the positive electrode current collector is within this range, it indicates that the current collector has good ductility, can withstand large deformations without easily breaking, which is beneficial for improving the structural stability of the positive electrode sheet and enhancing the safety and cycle performance of the battery cell. Exemplarily, the elongation at break of the positive electrode current collector is a value within the range of 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, or any two of these values. In some optional embodiments, the elongation at break of the positive electrode current collector is 1.5%-2.45%.

[0067] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0068] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites.

[0069] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0070] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0071] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0072] In some embodiments, the coating weight of the positive electrode is 0.3 g / 1540 mm. 2 -0.4g / 1540mm2 By keeping the coating weight of the positive electrode within the aforementioned range, it is beneficial to improve the energy density of the battery cell. For example, the coating weight of the positive electrode can be 0.30 g / 1540 mm. 2 0.32g / 1540mm 2 0.33g / 1540mm 2 0.34g / 1540mm 2 0.35g / 1540mm 2 0.36g / 1540mm 2 0.38g / 1540mm 2 0.40g / 1540mm 2 Or the value between any two of them within a range.

[0073] [Septum] In this application, the diaphragm includes a base membrane and a coating located on at least one side of the base membrane.

[0074] In this application, the polymer coating includes organic particles with a cumulative particle size distribution (D50) of 10 μm to 18 μm. By ensuring the D50 of the organic particles is within this range, the gap between the positive and negative electrode sheets and the separator can be increased. This allows for greater volume expansion during charge and discharge, reducing expansion force and thus decreasing the risk of electrode breakage due to expansion during cycling, thereby improving battery safety and cycle stability. Exemplarily, the cumulative particle size distribution (D50) of the organic particles can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 16 μm, 18 μm, or a value within a range of any two of these values. In some alternative embodiments, the cumulative particle size distribution (D50) of the organic particles is 10 μm to 14 μm.

[0075] In this application, the cumulative distribution particle size D50 of organic particles has a known meaning in the art and can be tested using known methods. An exemplary testing method is as follows: After disassembling the battery cell, a separator is obtained, and the separator is cut into 5mm*5mm pieces for testing. The polymer coating surface of the separator is examined using a scanning electron microscope (SEM). To obtain a clearer image of the particle morphology, a backscattered grain mode can be used for imaging. The SEM image of the coating surface is analyzed using image processing software such as Digital Micrograph. The longest diameter (i.e., particle size) of the organic particles is measured, and the longest diameters of all organic particles are counted. All the longest diameters of the organic particles are arranged in ascending order, and the longest diameter of the organic particles corresponding to a cumulative distribution of 50% is recorded as D50.

[0076] In some embodiments, the organic particles are made of one or more of the following polymers: polyacrylic acid polymers, polyvinylidene fluoride polymers, polyacrylonitrile polymers, and polyimide polymers. These materials have strong electronegativity, and the resulting organic particles have a porous structure, enabling them to interact strongly with the solvent in the electrolyte. This enhances the adsorption and retention of the electrolyte, thereby improving the cycle performance of the battery cell.

[0077] In this application, polyacrylic acid polymers refer to a class of polymeric compounds obtained through addition polymerization reactions using acrylic acid and its derivatives, such as acrylates, acrylates, and acrylamides, as monomers. Examples of polyacrylic acid polymers include, but are not limited to, polyacrylic acid, polyacrylates, and polyacrylamide. Polyvinylidene fluoride polymers refer to a class of fluorine-containing polymeric compounds obtained through polymerization reactions using vinylidene fluoride monomers as the main component. Examples of polyvinylidene fluoride polymers include, but are not limited to, polyvinylidene fluoride and polyvinylidene fluoride-chlorotrifluoroethylene copolymers. Polyacrylonitrile polymers refer to a class of polymers with cyano groups as characteristic functional groups obtained through polymerization reactions using acrylonitrile monomers as the main component. Examples of polyacrylonitrile polymers include, but are not limited to, polyacrylonitrile homopolymers and acrylonitrile copolymers, such as acrylonitrile-methyl acrylate copolymers. Polyimide polymers refer to a class of heterocyclic polymers containing imide ring structures in their polymer backbone. In some optional embodiments, the materials of the organic particles include polyacrylates, polyvinylidene fluoride, polyacrylonitrile homopolymers, and polyimides.

[0078] This application does not impose any particular restrictions on the type of base membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0079] In some embodiments, the base membrane can be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0080] In some embodiments, the thickness of the base film is 5 μm-12 μm. By keeping the thickness of the base film within this range, on the one hand, the volume occupied by the separator in the battery cell can be reduced, which is beneficial to increasing the volume ratio of active materials in the battery cell and improving the energy density of the battery cell. On the other hand, it can reduce the risk of separator cracking. For example, the thickness of the base film can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value within a range of any two of these values. In some optional embodiments, the thickness of the base film is 5 μm-9 μm.

[0081] In some embodiments, the separator further includes ceramic layers located on both sides of the base membrane, with the ceramic layers situated between the base membrane and the coating. The ceramic layers in the separator can suppress the shrinkage of the base membrane at high temperatures, reducing the risk of thermal runaway. Furthermore, they can improve the mechanical strength of the separator and reduce the risk of lithium dendrite puncture. The microporous structure of the ceramic layers can also improve the wetting effect of the electrolyte, thereby improving the cycle performance of the battery cells.

[0082] This application does not impose any particular limitation on the type of ceramic layer; any known ceramic material with good chemical and mechanical stability can be selected. In some embodiments, the ceramic layer material may be selected from one or more of alumina, boehmite, and silicon dioxide.

[0083] In some embodiments, the thickness of the ceramic layer is 0.8 μm to 1.2 μm. Maintaining the ceramic layer thickness within this range improves the mechanical strength of the separator, reduces the risk of separator puncture and cell thermal runaway, and also helps reduce the volume occupied by the separator, thereby increasing the energy density of the battery cell. Exemplarily, the thickness of the ceramic layer can be 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1.0 μm, 1.1 μm, 1.2 μm, or a value within a range of any two of these values.

[0084] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid.

[0085] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0086] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0087] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0088] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0089] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0090] In some implementations, reference Figure 7 The battery cell is a wound battery cell. The positive electrode, the negative electrode, and the separator are stacked and wound in a preset order. In a cross-section perpendicular to the axial direction Y of the wound battery cell, the wound battery cell includes a large surface area and bending areas located on both sides of the large surface area along the first direction X. In the large surface area, the positive electrode, the negative electrode, and the separator are stacked along the second direction Z. The first direction X and the second direction Z are perpendicular to each other and perpendicular to the axial direction Y. Taking the bending position of the innermost separator of the wound battery cell as the starting point, in a direction at 45° to the second direction, in the bending area, the average gap between the positive electrode or the negative electrode and the adjacent separator is 30μm-40μm. By keeping the average gap within the above range, more volume expansion generated during charging and discharging can be accommodated, reducing the problem of electrode cracking caused by expansion, especially in the bending area. Furthermore, a suitable gap can improve the electrolyte's climbing height, enhance electrode wetting, and improve the battery's cycle performance. For example, the average gap value can be 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, or a range consisting of any two of these values.

[0091] In this application, starting from the bending position of the innermost separator in the wound cell, the average gap between the positive or negative electrode and the adjacent separator in the bending area at a 45° angle to the second direction can be tested using computed tomography (CT) technology. CT testing generates a three-dimensional image of the internal structure of the cell through X-ray penetration and computer reconstruction technology, clearly displaying the internal structures of the battery, such as the electrodes, separator, and electrolyte, thereby allowing the measurement of the gap between the positive or negative electrode and the separator. The specific testing steps are as follows: The cell prepared during the battery cell manufacturing process or the cell disassembled from a battery cell is placed in a CT device (e.g., Zeiss Xradia CrystalCT). The CT scan is performed on a computed tomography (CT) platform to obtain CT images of a cross-section of the battery cell perpendicular to the axial direction of the wound cell. Image analysis tools, such as PowerPoint software, are used to assist in measuring the average gap between the electrode and adjacent separator in the stacking direction of the battery cell in the CT image. An exemplary measurement method includes the following specific steps: In the CT image of the battery cell, within the bending area, a ray is marked with the bending position of the innermost separator in the winding structure as the starting point, at a 45° angle to the second direction. Along the marked ray direction, the total thickness of the battery cell from the starting position of the innermost winding layer to the fourth winding position is measured, and the average gap between the four measured layers is calculated. Average gap = (actual total thickness - single layer thickness of positive electrode × number of layers of positive electrode - single layer thickness of negative electrode × number of layers of negative electrode - single layer thickness of separator × number of layers of separator) / (total number of layers of positive electrode, negative electrode and separator - 1). Using the same method as above, continue counting 5 layers from the inside out, and calculate the average gap value between each 5-layer cell. The last part with less than 5 layers is treated as a group and its average gap is calculated. The average value of each calculated average gap value is taken as the average gap between the electrode and the adjacent separator.

[0092] In some implementations, reference Figure 8 The surface of the positive electrode sheet is provided with depressions, and the density of the depressions is 4-8 per cm³. 2 The deepest point of the depression is 5μm-10μm. (Reference) Figure 8 The positive electrode 10 includes a positive current collector 101 and a positive electrode film 102. The positive electrode film includes a first surface 102a away from the positive current collector 101 and a second surface 102b opposite to it. A recess 1021 is provided on the first surface of the positive electrode film in the thickness direction of the positive electrode. The density of the recesses on the surface of the positive electrode refers to the number of recesses per unit area on the surface of the positive electrode. The depth of the recess refers to the vertical distance from the deepest point of the recess to the first surface of the positive electrode film. By providing recesses on the surface of the positive electrode, it is beneficial to further increase the gap between the positive electrode and the adjacent separator, reduce the problem of electrode breakage due to large volume expansion during the charge and discharge cycle of the battery cell, and facilitate the full wetting of the electrolyte, thereby improving the cycle performance of the battery cell.

[0093] In this application, the indentation density and the deepest point of the indentation on the surface of the positive electrode sheet can be measured using methods known in the art. For example, the indentation density on the surface of the positive electrode sheet can be measured as follows: after disassembling the secondary battery to obtain the positive electrode sheet, the obtained positive electrode sheet is unfolded, the indentations on the electrode sheet surface are counted, and the area of ​​the electrode sheet is calculated. The indentation density is then calculated as: total number of indentations on the surface of the positive electrode sheet / area of ​​the positive electrode sheet. The depth of the deepest recess can be measured using the following method: After disassembling the secondary battery, the positive electrode is obtained. The positive electrode is then cut using an ion beam. The specific steps of ion beam cutting include: cutting the positive electrode into 6mm*6mm pieces using ceramic scissors, attaching it to a sample stage coated with paraffin wax, ensuring the positive electrode protrudes slightly (<1mm) from the edge of the sample stage; polishing the positive electrode at 7.5KV for 50 minutes; and cutting according to the following parameters: mode: Optiplan, voltage: 1KV, probe: T1, current: 50pA, working distance: 4mm. Then, the cross-section of the positive electrode is examined using a scanning electron microscope (SEM) to obtain an SEM image. The recess on the positive electrode is located in the SEM image, and the distance from the deepest point of the recess to the surface of the positive electrode is measured using the scale tool in the SEM. This distance is recorded as the depth of the deepest recess.

[0094] In this application, the depressions on the positive electrode sheet can be obtained by methods known in the art, such as by using an electrode pressure roller with a raised structure, during the preparation of a wound cell by a winding device, the positive electrode sheet is passed through the electrode pressure roller, thereby forming a depression pattern on the positive electrode sheet.

[0095] In some embodiments, the height of the battery cell is greater than or equal to 150 mm. By keeping the cell height within this range, it is advantageous to increase the amount of active material accommodated in the battery cell, thereby increasing the energy density of the battery cell. In some alternative embodiments, the cell height is 150 mm to 180 mm. In embodiments where the cell is a wound cell, the cell height refers to the length of the cell along the axial direction of the wound cell.

[0096] In some embodiments, the electrolyte injection coefficient of the battery cell is 2.3 g / Ah to 2.8 g / Ah. By keeping the electrolyte injection coefficient within this range, it is beneficial for the electrolyte to fully wet the positive and negative electrodes, and to maintain a good electrolyte wetting effect throughout the entire lifespan of the battery cell, thereby improving the cycle life of the battery cell. Exemplarily, the electrolyte injection coefficient of the battery cell can be 2.3 g / Ah, 2.4 g / Ah, 2.5 g / Ah, 2.6 g / Ah, 2.7 g / Ah, 2.8 g / Ah, or a value within a range of any two of these values.

[0097] In this application, the electrolyte injection coefficient of a battery cell refers to the mass of electrolyte injected per unit capacity of the battery. It can be measured using methods known in the art. An exemplary method is as follows: During battery manufacturing, the electrolyte injection volume is set using an injection machine, and then the electrolyte injection coefficient is calculated according to the following formula: Electrolyte injection volume = Electrolyte injection volume / Battery cell capacity; Alternatively, the battery cell can be disassembled, the free electrolyte collected, and the electrode assembly centrifuged to obtain the electrolyte adsorbed on the electrode assembly. The combined free electrolyte and the centrifuged electrolyte adsorbed on the electrode assembly constitute the electrolyte injection volume of the battery cell, and the electrolyte injection coefficient of the battery cell is then calculated according to the above formula.

[0098] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0099] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, aluminum-plastic film, etc. Examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0100] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0101] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0102] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0103] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0104] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0105] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0106] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0107] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack 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, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0108] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0109] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0110] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0111] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0112] Example 1 Preparation of battery cells Preparation of the positive electrode: Lithium iron phosphate (LFP) active material, carbon black conductive agent, and PVDF binder were mixed in a weight ratio of 98.2:0.3:1.5. N-methylpyrrolidone (NMP) solvent was added, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto both surfaces of an aluminum foil current collector. The aluminum foil had a thickness of 12 μm and a tensile strength of 270 MPa. The coating weight of the positive electrode slurry was 0.3383 g / 1540.25 mm. 2 (Based on weight excluding solvent), after drying and cold pressing, a positive electrode sheet is obtained, with a compacted density of 2.75 g / cm³. 3 .

[0113] Preparation of negative electrode sheet: Artificial graphite (discharge capacity 357.5 mAh / g), carbon black (conductive agent), carboxymethyl cellulose (binder), and water were mixed in a weight ratio of 97.9:0.4:1.7:100. The mixture was thoroughly stirred to obtain a uniform negative electrode slurry. This slurry was then coated onto both sides of a copper foil current collector. The copper foil had a thickness of 4 μm and a tensile strength of 500 MPa. The coating weight of the negative electrode slurry was 0.1526 g / 1540.25 mm. 2 (Based on weight excluding solvent), after drying and cold pressing, a negative electrode sheet is obtained, with a compacted density of 1.70 g / cm³. 3 .

[0114] Electrolyte preparation: In an argon-atmospheric glove box with a water content of <10 ppm, ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in the mixture to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0115] Preparation of the diaphragm: A 5μm thick porous PE membrane was used as the base membrane. A ceramic coating slurry was uniformly coated on both sides of the base membrane. After drying and cold pressing, a ceramic-coated membrane was obtained, with a ceramic coating thickness of 1μm on each side of the base membrane. Then, a polymer coating slurry was uniformly coated on the side of the ceramic-coated membrane closest to the negative electrode to obtain a separator, with a polymer coating thickness of 24μm. The preparation methods of the ceramic coating slurry and the polymer coating slurry are shown below: Preparation of ceramic coating slurry: Boehmite, styrene-butadiene rubber and polyacrylate were weighed in a mass ratio of 93:6.5:0.5, mixed and dispersed in deionized water to obtain ceramic coating slurry; the ceramic coating slurry was transferred to the base film (PE) using a coating roller and dried to obtain a ceramic coating with a thickness of 1μm.

[0116] Preparation of polymer coating: Polyvinylidene fluoride particles with a D50 of 14 μm and N-methylpyrrolidone (NMP) solvent are mixed to form a polymer slurry. The polymer slurry is coated onto a base film coated with a ceramic coating. The polymer coating is located on the ceramic coating and on the side close to the negative electrode.

[0117] Assembly of individual battery cells: The negative electrode, positive electrode, and separator are stacked sequentially in the order of "separator-negative electrode-separator-positive electrode," with the separator positioned between the positive and negative electrodes to provide separation. The layers are then wound to form a coil structure. This coil structure is then cold-pressed in a cold press at a pressure of 7 MPa to obtain a coiled bare cell with a length of 150 mm along the second direction. The coiled bare cell is placed in an outer packaging, injected with the electrolyte, and then sealed for formation to obtain a battery cell.

[0118] Parameter testing methods: (1) Thickness of the current collector After disassembling the battery cell, negative or positive electrode sheets are obtained. After drying, the film layer on the surface of the negative or positive electrode sheets is removed to obtain the current collector. Then, the thickness of the current collector is measured using a micrometer (Mitutoyo 293-100 type, with an accuracy of 0.1μm).

[0119] (2) Tensile strength of the current collector After disassembling the battery cell, negative or positive electrode sheets are obtained. After drying, the film layer on the surface of the negative or positive electrode sheets is removed to obtain the current collector. The current collector is clamped at both ends of the clamp of a universal testing machine, and a tensile force is applied to both ends by the universal testing machine until the current collector breaks. The maximum tensile force (Fm, in N) at the breaking point is measured by the force sensor on the universal testing machine. Then, the tensile strength is calculated according to the following formula: Tensile strength Rm = Fm / A0, where A0 is the original cross-sectional area of ​​the current collector.

[0120] (3) Elongation at break of the current collector After disassembling a single battery cell, negative or positive electrode sheets are obtained. After drying, the film layer on the surface of the negative or positive electrode sheets is removed to obtain a current collector. The current collector is clamped at both ends of a universal testing machine, and a tensile force is applied to both ends until the current collector breaks. The displacement of the clamps is recorded using the universal testing machine from the start of the applied tensile force until the current collector breaks. The maximum elongation of the current collector is calculated using the following formula: Elongation at break , where L0 is the initial length of the current collector.

[0121] (4) Thickness ratio of current collector After disassembling the battery cell, negative or positive electrode sheets are obtained. After drying, the thickness d1 of the negative or positive electrode sheet is measured with a micrometer. Then, the film layer on the surface of the negative or positive electrode sheet is wiped off to obtain the current collector. The thickness d2 of the negative or positive current collector is measured with a micrometer. Then, the thickness ratio of the current collector is calculated: current collector thickness ratio = d2 / d1 × 100%.

[0122] (5) Compacted density of the electrode sheet After disassembling the battery cell, remove the electrode sheets (negative or positive) and dry them at 60°C for 4 hours. Measure the thickness of the electrode sheets using a micrometer (e.g., Mitutoyo 293-100, 0.1μm accuracy). Then, cut the electrode sheets into small circular pieces with an area of ​​S1, weigh them, and record the weight as M1. Next, wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the negative current collector, and record the weight as M0. Calculate the areal density of the electrode sheet = (M1 - M0) / S1. Then, calculate the compacted density of the electrode sheet according to the following formula: Compacted density of the electrode sheet = Areal density of the film layer / Thickness of the film layer.

[0123] (6) Cumulative distribution of organic particles by particle size D50 After disassembling the battery cells, the separator was obtained and cut into 5mm*5mm pieces for testing. Scanning electron microscopy (SEM) was used to examine the coating surface of the separator. To obtain clearer images of the particle morphology, backscattered grain mode was used for imaging. The SEM images of the coating surface were analyzed using image processing software such as Digital Micrograph. The longest diameter (i.e., particle size) of the organic particles was measured, and the longest diameters of all organic particles were counted. All the longest diameters of the organic particles were arranged in ascending order, and the longest diameter of the organic particles corresponding to a cumulative distribution of 50% was recorded as D50.

[0124] (7) Average gap The battery cells obtained from disassembling individual battery cells are placed in a CT scanner (Zeiss Xradia CrystalCT). The CT scan is performed on a computed tomography (CT) platform to obtain CT images of a cross-section of the battery cell perpendicular to its height. Figure 9 A CT image of the battery cell prepared in the embodiment is shown. The average gap between the electrode and adjacent separator in the stacking direction of the CT image of the battery cell was measured using image analysis software (PowerPoint). The specific steps are as follows: In the CT image of the battery cell, within the bending area, a ray is marked with the bending position of the innermost separator in the winding structure as the starting point, at a 45° angle to the second direction. Along the marked ray direction, the total thickness of the battery cell is measured from the starting position of the innermost winding layer to the fourth winding position. The average gap between the four measured layers is calculated as follows: Average gap = (Actual total thickness - Single layer thickness of positive electrode × Number of layers of positive electrode - Single layer thickness of negative electrode × Number of layers of negative electrode - Single layer thickness of separator × Number of layers of separator) / (Total number of layers of positive electrode, negative electrode, and separator - 1). Using the same method as described above, continue counting 5 layers from the inside out, calculating the average gap value between each 5-layer cell. The last few layers (less than 5 layers) are grouped together, and their average gap is calculated. The average of these calculated average gap values ​​is taken as the average gap between the electrode and the adjacent separator. In the cell prepared in Example 1, in the bending region, starting from the bending position of the innermost separator layer wound around the cell, the average gap between the electrode and the adjacent separator in a direction at 45° to the second direction is 34 μm.

[0125] Example 2-14 Battery cells were prepared using a method similar to that in Example 1, except that the parameters of the positive electrode, negative electrode, separator, or cell were adjusted according to the parameters shown in Tables 1-3.

[0126] Examples 15-16 The battery cell was prepared using a method similar to that in Example 1, except that the parameters of the positive electrode, negative electrode, separator, or cell were adjusted according to the parameters shown in Tables 1-3. The assembly steps of the battery cell included: stacking the negative electrode, positive electrode, and separator in the order of "separator-negative electrode-separator-positive electrode" so that the separator is placed between the positive and negative electrode to act as an separator; forming the electrode assembly into a winding structure using a winding machine, wherein the positive electrode passes through a pattern roller and forms a depression on it, and then forms a winding structure by a winding needle.

[0127] Comparative Example 1 Battery cells were prepared using a method similar to that in Example 1, except that the parameters of the positive electrode, negative electrode, and separator were adjusted according to the parameters shown in Tables 1-3. The separator did not have a polymer coating.

[0128] Comparative Examples 2-5 Battery cells were prepared using a method similar to that in Example 1, except that the parameters of the positive electrode, negative electrode, separator, and cell were adjusted according to the parameters shown in Tables 1-3.

[0129] Table 1: Parameters of the negative electrode sheets in Examples 1-16 and Comparative Examples 1-5

[0130] Table 2: Parameters of the positive electrode in Examples 1-16 and Comparative Examples 1-5

[0131] Table 3: Parameters of the separator and battery cell in Examples 1-16 and Comparative Examples 1-5

[0132] In addition, the battery cells obtained in Examples 1-16 and Comparative Examples 1-5 were subjected to performance tests according to the following method. The test results are shown in Table 4 below.

[0133] Battery cell performance testing (1) Electrode integrity (i.e., whether the electrode is broken or cracked at the corner) The battery cell is disassembled to obtain the electrode assembly. The electrode assembly is then subjected to X-ray computed tomography (CT) scan to obtain CT images of the electrode assembly. These CT images can reveal whether the internal electrode plates of the aluminum shell have broken.

[0134] (2) Energy density At 25℃, a single battery cell is charged at a constant current of 0.33C to a cutoff voltage of 3.8V, and then charged at a constant voltage of 3.8V to a current of 0.05C. At this point, the battery cell is fully charged. After the fully charged battery cell is left to stand for 5 minutes, it is discharged at a constant current of 0.33C to a cutoff voltage of 2.0V. The discharge capacity at this point is the actual capacity of the battery cell at 0.33C, denoted as C0. Then, the secondary battery is charged at a constant current of 0.33C0 to a cutoff voltage of 3.8V, and then charged at a constant voltage to a current of 0.05C. At this point, the battery cell is fully charged. After the fully charged secondary battery is left to stand for 5 minutes, it is discharged at a constant current of 0.33C0 to a cutoff voltage of 2.0V. This charging and discharging process is repeated 3 times. The discharge energies Q1, Q2, and Q3 of the battery cell during the three charging and discharging processes are obtained respectively, and the average discharge energy Q = (Q1 + Q2 + Q3) / 3 is calculated. The energy density (Wh / L) of a secondary battery = the discharge energy Q of the secondary battery / the volume V of the secondary battery.

[0135] (3) Cycle life The prepared battery cell was left to stand for 5 minutes; then it was charged at a constant current of 1C to 3.8V, and then charged at a constant voltage of 3.8V to a current of 0.05C; left to stand for 5 minutes; then discharged at a constant current of 1C to 2.0V, and the discharge capacity D1 of the first cycle was recorded; the above steps were repeated until the recorded discharge capacity Dn = 70%D1, and the number of cycles n was recorded.

[0136] Table 4: Performance test results of Examples 1-16 and Comparative Examples 1-5

[0137] Based on the above results, the battery cells prepared in Examples 1-16 can achieve both high energy density and good cycle performance, and no electrode breakage occurred during cycling, demonstrating excellent cycle life. In contrast, the separator in Comparative Example 1 did not include a polymer coating, resulting in an excessively small gap between the electrode and the separator in the cell. During cycling, the expansion and compression of the electrode led to the breakage of the negative electrode, causing cell failure. In the battery cell of Comparative Example 2, the separator included a polymer coating, resulting in improved cycle life compared to Comparative Example 1. However, due to the excessively small D50 of the polymer particles, negative electrode breakage still occurred during long-term cycling, leading to cell failure. In the battery cell of Comparative Example 3, the D50 of the polymer particles was too large, resulting in an excessively large gap between the electrode and the separator in the cell. This led to poor electrolyte wetting and a tendency for lithium plating. During the battery cell manufacturing process, purple spots appeared at the corners of the cell after formation, rendering the cell unsuitable for production standards and thus rejected. In Comparative Example 4, the negative electrode sheet in the battery cell has a low compaction density. Although the battery cell has a long cycle life, the low compaction density results in a low energy density, making it difficult to meet market demands. In Comparative Example 5, the negative electrode film layer of the battery cell has an excessively high compaction density, which can easily lead to the breakage of the negative electrode sheet and cell failure during cycling.

[0138] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The battery includes a cell and a housing. The cell includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein, The compaction density of the negative electrode film is 1.5 g / cm³. 3 -1.78g / cm 3 ; The diaphragm includes a base membrane and a coating located on at least one side of the base membrane. The coating includes organic particles, and the cumulative distribution of the organic particles has a particle size D50 of 10 μm-18 μm.

2. The battery cell according to claim 1, characterized in that, The compaction density of the negative electrode sheet is 1.60 g / cm³. 3 -1.70g / cm 3 .

3. The battery cell according to claim 1 or 2, characterized in that, The thickness of the negative electrode current collector is 3μm-6μm; and / or the tensile strength of the negative electrode current collector is 300MPa-550MPa.

4. The battery cell according to claim 3, characterized in that, The thickness of the negative electrode current collector is 4μm-5μm; and / or, the tensile strength of the negative electrode current collector is 400MPa-450MPa.

5. The battery cell according to any one of claims 1-4, characterized in that, Based on the thickness of the negative electrode sheet, the thickness ratio of the negative current collector is 2.69%-4.87%.

6. The battery cell according to any one of claims 1-5, characterized in that, The elongation at break of the negative electrode current collector is 2%-4%.

7. The battery cell according to any one of claims 1-6, characterized in that, The coating weight of the negative electrode sheet is 0.1g / 1540mm. 2 -0.2g / 1540mm 2 .

8. The battery cell according to any one of claims 1-7, characterized in that, In the coating, the organic particles have a D50 of 10μm-14μm.

9. The battery cell according to any one of claims 1-8, characterized in that, The organic particles are made of one or more of the following polymers: polyacrylic acid polymers, polyvinylidene fluoride polymers, polyacrylonitrile polymers, and polyimide polymers.

10. The battery cell according to any one of claims 1-8, characterized in that, The thickness of the base film is 5μm-12μm.

11. The battery cell according to any one of claims 1-10, characterized in that, The diaphragm also includes ceramic layers located on both sides of the base membrane, and the ceramic coating is located between the base membrane and the coating.

12. The battery cell according to claim 11, characterized in that, The thickness of the ceramic layer is 0.8μm-1.2μm.

13. The battery cell according to any one of claims 1-12, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector, wherein, The compaction density of the positive electrode film is 2.50 g / cm³. 3 -2.80g / cm 3 ; and / or the thickness of the positive current collector is 9μm-15μm, and / or the tensile strength of the positive current collector is 200MPa-400MPa.

14. The battery cell according to claim 13, characterized in that, The compaction density of the positive electrode sheet is 2.65 g / cm³. 3 -2.8g / cm 3 ; and / or the thickness of the positive current collector is 9μm-13μm, and / or the tensile strength of the positive current collector is 230MPa-270MPa.

15. The battery cell according to claim 13 or 14, characterized in that, Based on the thickness gauge of the positive electrode sheet, the thickness ratio of the positive current collector is 4.56%-7.74%.

16. The battery cell according to any one of claims 13-15, characterized in that, The elongation at break of the positive current collector is 0.6%-3%.

17. The battery cell according to any one of claims 13-16, characterized in that, The coating weight of the positive electrode sheet is 0.3g / 1540mm. 2 -0.4g / 1540mm 2 .

18. The battery cell according to any one of claims 1-17, characterized in that, The battery cell is a wound battery cell. The positive electrode, the negative electrode, and the separator are stacked and wound in a preset order. In a cross-section perpendicular to the axial direction Y of the wound battery cell, the wound battery cell includes a large surface area and bending areas located on both sides of the large surface area along the first direction X. In the large surface area, the positive electrode, the negative electrode, and the separator are stacked along the second direction Z. The first direction X and the second direction Z are perpendicular to each other and perpendicular to the axial direction Y. Starting from the bending position of the innermost separator in the wound cell, in a direction at 45° to the second direction, the average gap between the positive electrode or the negative electrode and the adjacent separator in the bending area is 30μm-40μm.

19. The battery cell according to any one of claims 1-18, characterized in that, The surface of the positive electrode sheet has depressions, and the density of the depressions is 4-8 per cm³. 2 The deepest part of the depression is 5μm-10μm.

20. The battery cell according to any one of claims 1-19, characterized in that, The height of the battery cell is greater than or equal to 150mm.

21. The battery cell according to claim 20, characterized in that, The height of the battery cell is 150mm-180mm.

22. The battery cell according to any one of claims 1-21, characterized in that, The electrolyte injection coefficient of the battery cell is 2.3-2.8 g / Ah.

23. An electrical device comprising a battery cell according to any one of claims 1-22.

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