Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery which comprises a battery cell and a membrane shell for packaging the battery cell, the battery cell comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive plate, a diaphragm and a negative plate, and the positive plate, the diaphragm and the negative plate are sequentially stacked; the pole piece on the outermost side in the electrode assembly is a positive single-sided piece; the membrane shell comprises a protective layer, a metal layer and a sealing layer which are sequentially stacked, and the sealing layer is close to the battery cell; the protruding direction of a first protruding part contained in the positive electrode single-sided sheet faces the sealing layer; when the capacity retention ratio of the battery is greater than or equal to 98%, the battery meets the following conditions: 20 < = A / B < = 500, and A is the thickness of the sealing layer corresponding to the edge of the outermost pole piece in the electrode assembly; and B is the cyclic expansion rate of the battery at 45 DEG C. According to the positive single-sided sheet, the abrasion to the sealing layer can be relieved, and the thickness (A) of the residual sealing layer of the membrane shell can meet the requirements of the cycle performance and the safety performance of the battery in the later period.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery. Background Technology

[0002] Lithium-ion batteries (LIBS) are the primary energy source for smart devices and electric vehicles, but their long-term durability and safety are major obstacles limiting their widespread use in heavy machinery. To improve energy density, stacked batteries have an outermost single-sided electrode sheet, where one side of the current collector is coated with paste (active material layer) and the other side is an empty foil. The outermost layer (top and bottom layers) of the stacked cell along the electrode stacking direction is also a single-sided electrode sheet, with the empty foil area facing the sealing layer (PP layer) of the membrane housing. During battery formation or cycling, the edge of the electrode sheet on the empty foil side can cause indentations or even wear on the sealing layer of the membrane housing. In severe cases, this can lead to exposure of the middle metal layer of the membrane housing, folding of the current collector in the single-sided electrode sheet, resulting in battery leakage, bulging, and short circuits, seriously affecting the safety performance of lithium-ion batteries. Furthermore, as the energy density requirements for lithium-ion batteries increase, whether the remaining thickness of the membrane housing sealing layer after wear can meet the requirements for subsequent battery cycle performance and safety is becoming increasingly important for battery manufacturers. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a battery that, by providing protrusions on the positive electrode single-sided sheet, can reduce the wear of the membrane sealing layer by the edge of the positive electrode single-sided sheet. Furthermore, by controlling the range of the ratio between the thickness (A) of the sealing layer corresponding to the edge of the outermost positive electrode single-sided sheet in the electrode assembly when the battery's capacity retention rate is greater than or equal to 98% and the battery's cycle expansion rate (B) at 45°C, it can be ensured that the thickness of the remaining sealing layer after the empty foil area of ​​the positive electrode single-sided sheet wears on the membrane during high-temperature cycling can meet the requirements of subsequent battery cycle performance and safety performance.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] This invention provides a battery, including a battery cell and a membrane housing encapsulating the battery cell; the battery cell includes an electrode assembly and an electrolyte, the electrode assembly includes a positive electrode, a separator, and a negative electrode, the positive electrode, the separator, and the negative electrode being stacked sequentially; along the thickness direction of the battery cell, the outermost electrode of the electrode assembly is a single-sided positive electrode, the single-sided positive electrode including a first positive current collector and a first positive active layer disposed on the inner surface of the first positive current collector, the inner surface being away from the membrane housing; the membrane housing includes a protective layer, a metal layer, and a sealing layer stacked sequentially, the sealing layer being close to the battery cell. The battery has a core; a receiving groove for accommodating the battery core is formed on the membrane shell, the receiving groove includes a bottom wall and a side wall surrounding the bottom wall, and the sealing layer of the bottom wall faces the battery core; the positive electrode single-sided sheet includes a first protrusion, and along the thickness direction of the battery core, the protrusion direction of the first protrusion faces the sealing layer; when the capacity retention rate of the battery is greater than or equal to 98%, the battery satisfies the following formula: 20≤A / B≤500, where A is the thickness of the sealing layer corresponding to the edge of the outermost electrode sheet of the electrode assembly, in μm; B is the cycle expansion rate of the battery at 45°C.

[0006] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0007] To improve energy density, the outermost electrode of a laminated battery cell electrode assembly is typically designed as a single-sided positive electrode sheet, meaning one side of the positive current collector surface is coated with paste (positive active layer) while the other side is an empty foil. However, because the active layer is only located on the surface of the current collector side, uneven stress often occurs on both sides of the current collector, easily leading to curling of the single-sided positive electrode sheet. This exacerbates wear on the membrane sealing layer corresponding to the edge of the single-sided positive electrode sheet, and the curled edges of the single-sided positive electrode sheet are more prone to lifting during cycling, severely affecting the battery's safety and cycle performance. The battery of this invention, by providing a first protrusion on the outermost single-sided positive electrode sheet of the electrode assembly and controlling the protrusion direction of the first protrusion towards the sealing layer, can improve the electrode sheet curling caused by single-sided paste coating, thereby reducing wear on the membrane sealing layer by the edge of the single-sided positive electrode sheet and preventing lifting of the edge of the single-sided positive electrode sheet during cycling. This invention addresses the issue of edge wear caused by the curling of the positive electrode single-sided sheet, which exacerbates edge wear. Furthermore, the edge of the electrode on the empty foil side of the single-sided sheet can still cause indentations or even wear on the sealing layer of the membrane during battery formation or cycling. Moreover, the wear on the sealing layer intensifies in the later stages of cycling. This invention further controls the ratio (A) of the sealing layer thickness corresponding to the edge of the outermost electrode (i.e., the positive electrode single-sided sheet) in the electrode assembly to the battery's cyclic expansion rate (B) at 45°C when the battery's capacity retention rate is greater than or equal to 98%, i.e., A / B, satisfying the relationship: 20≤A / B≤500. This ensures that the remaining sealing layer thickness after wear on the membrane during high-temperature cycling can meet the requirements of later battery cycling, ensuring sufficient safety margin for the sealing layer thickness within the battery's effective lifespan, and further achieving a synergistic improvement in battery cycle performance and battery safety.

[0008] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0009] Figure 1 The diagram shown is a schematic diagram of the bottom wall of the membrane housing groove provided in an embodiment of the present invention.

[0010] Figure 2 The figure shown is a schematic cross-sectional view of the bottom wall of the membrane housing groove provided in an embodiment of the present invention.

[0011] Figure 3The diagram shown is a schematic diagram of a double-pit membrane shell provided in an embodiment of the present invention.

[0012] Figure 4 The diagram shown is a schematic diagram of a single-pit membrane shell provided in an embodiment of the present invention.

[0013] Figure 5 The diagram shown is a schematic diagram of the concave-convex structure of the positive electrode sheet provided in an embodiment of the present invention.

[0014] Figure 6 The diagram shown is a schematic diagram of the negative electrode groove structure provided in an embodiment of the present invention.

[0015] Figure 7 The image shown is a CP section test diagram of the original sealing layer under a 3D microscope according to an embodiment of the present invention.

[0016] Figure 8 The image shown is a CP section test diagram of the sealing layer after 50 cycles using a 3D microscope, provided by an embodiment of the present invention.

[0017] Explanation of reference numerals in the attached drawings: 1. First region; 2. Edge; 3. Chamfer; 4. Sealing layer; 5. Metal layer; 6. Protective layer; 7. Receiving groove; 8. First protrusion; 9. Groove. Detailed Implementation

[0018] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0019] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0020] Terminology Explanation

[0021] In this invention, the terms "battery", "lithium battery", "lithium-ion battery" and "lithium-ion secondary battery" all have the same meaning and refer to lithium-ion secondary batteries.

[0022] In this invention, the term "protective layer" refers to the outermost structure of the membrane shell, which is used to resist external mechanical impacts and block oxygen and moisture. Its function is to protect the inner metal layer and sealing layer from damage by the external environment.

[0023] In this invention, the term "metal layer" refers to the intermediate layer structure of the membrane shell, which is made of a high-barrier metal material. Its function is to isolate the electrolyte from the external environment and provide structural support.

[0024] In this invention, the term "sealing layer" refers to the innermost structure of the membrane shell, which is in direct contact with the battery cell and has the functions of sealing the battery cell, resisting electrolyte corrosion and mechanical stress, such as the PP layer.

[0025] In this invention, the edge of the outermost positive or negative electrode in the electrode assembly has a specific meaning depending on the cell structure: for stacked cells, "the edge of the outermost electrode in the electrode assembly" refers to the four edges of the outermost positive electrode (positive single-sided sheet) in the electrode assembly (i.e., the two edges of the outermost positive electrode in the length direction of the cell + the two edges in the width direction of the cell).

[0026] This invention provides a battery, including a battery cell and a membrane housing encapsulating the battery cell; the battery cell includes an electrode assembly and an electrolyte, the electrode assembly includes a positive electrode, a separator, and a negative electrode, the positive electrode, the separator, and the negative electrode being stacked sequentially; along the thickness direction of the battery cell, the outermost electrode of the electrode assembly is a single-sided positive electrode, the single-sided positive electrode including a first positive current collector and a first positive active layer disposed on the inner surface of the first positive current collector, the inner surface being away from the membrane housing; the membrane housing includes a protective layer, a metal layer, and a sealing layer stacked sequentially, the sealing layer being close to the battery cell; a receiving groove for accommodating the battery cell is formed on the membrane housing, the receiving groove encapsulating the battery cell... The battery includes a bottom wall and side walls surrounding the bottom wall, with the sealing layer of the bottom wall facing the battery cell; the positive electrode single-sided sheet includes a first protrusion, and along the thickness direction of the battery cell, the protrusion direction of the first protrusion faces the sealing layer; when the capacity retention rate of the battery is greater than or equal to 98%, the battery satisfies the following formula: 20≤A / B≤500 (for example, 20, 40, 60, 80, 100, 200, 300, 400, 500 or within any two of the above values), where A is the thickness of the sealing layer corresponding to the edge of the outermost electrode sheet of the electrode assembly, in μm; B is the cycle expansion rate of the battery at 45°C.

[0027] The electrode assembly in this invention is composed of a positive electrode, a separator, and a negative electrode stacked sequentially; therefore, the battery cell of this invention is a stacked battery cell. To improve the energy density of the stacked battery cell, the outermost electrode of the electrode assembly in this invention is configured as a single-sided electrode with paste coated only on one side of the current collector, i.e., a positive single-sided electrode. The positive single-sided electrode includes a first positive current collector and a first positive active layer disposed on the inner surface of the first positive current collector, with the inner surface facing away from the membrane shell. It can be understood that the "inner surface of the first positive current collector" refers to the surface of the first positive current collector closer to the inner separator and negative electrode of the electrode assembly, distinguished from the surface of the first positive current collector closer to the outer sealing layer of the electrode assembly.

[0028] However, since the positive active layer of the positive electrode single-sided sheet is only set on the surface of the positive current collector, it often leads to uneven stress on both sides of the current collector, which easily causes the positive electrode single-sided sheet to curl. Furthermore, since the first positive active layer is set on the surface of the first positive current collector facing the inside of the electrode assembly, the positive electrode single-sided sheet will curl inward toward the inside of the electrode assembly (the edge area of ​​the positive electrode single-sided sheet will also lift up toward the sealing layer side while the positive electrode single-sided sheet curls up, and the positive electrode single-sided sheet will be concave toward the inside of the electrode assembly). This will cause the wear of the membrane sealing layer corresponding to the edge of the positive electrode single-sided sheet to be aggravated, and the edge of the curled positive electrode single-sided sheet is more likely to further lift up during the cycle, which seriously affects the safety performance and cycle performance of the battery.

[0029] Therefore, based on the above-mentioned structural design and existing problems of the positive electrode single-sided sheet, the present invention provides a first protrusion on the outermost positive electrode single-sided sheet of the electrode assembly, and controls the first protrusion to face the sealing layer along the thickness direction of the cell. This allows the positive electrode single-sided sheet to be provided with a rolling pressure opposite to the electrode curling direction during the process of setting the first protrusion, thereby improving the electrode curling problem caused by unilateral paste application, making the positive electrode single-sided sheet tend to be straight, and effectively solving the electrode curling problem. This can significantly reduce the wear of the positive electrode single-sided sheet edge on the membrane sealing layer, and also avoid the problem of the positive electrode single-sided sheet edge easily lifting during cycling, thereby effectively improving the safety performance and cycle performance of the battery.

[0030] Furthermore, in this invention, the A value reflects the remaining thickness of the easily worn area of ​​the sealing layer corresponding to the edge of the outermost electrode in the electrode assembly. This area is usually the part of the battery most prone to wear due to factors such as battery expansion stress and high-temperature corrosion penetration of electrolyte during long-term use. Its remaining thickness is directly related to whether the sealing layer can continuously block external erosion of the cell and prevent electrolyte leakage. The B value reflects the cycle expansion rate of the battery under high-temperature conditions. The cycle expansion of the battery under high-temperature conditions is generally greater than that under normal temperature conditions, and the corrosion penetration of electrolyte into the sealing layer is also higher than that under normal temperature conditions. By providing a first protrusion on the outermost positive electrode single-sided sheet of the electrode assembly, the problem of accelerated edge wear caused by the curling of the positive electrode single-sided sheet can be eliminated. However, the edge of the electrode on the empty foil side of the single-sided sheet can still cause indentation or even wear on the sealing layer of the membrane during battery formation or cycling. Moreover, the wear of the sealing layer will be more severe in the later stages of cycling. Based on this, by further controlling the A / B ratio within the above range (20≤A / B≤500), this invention can ensure that the thickness of the remaining sealing layer after the edge of the empty foil area of ​​the outermost electrode (positive electrode single-sided sheet) of the electrode assembly wears on the membrane during high-temperature cycling can meet the requirements of later battery cycling. This ensures that the sealing layer thickness has sufficient safety margin during the effective lifespan of the battery, and achieves a synergistic improvement in battery cycle performance and battery safety in the later stages.

[0031] Specifically, if the A / B ratio is too small (i.e., A is too small or B is too large), it means that the remaining thickness of the sealing layer after wear of the outermost electrode edge during high-temperature cycling is insufficient. In this case, even if the battery has good initial sealing performance, micro-cracks or damage may occur in the later stages of cycling due to the excessive thinness of the sealing layer, leading to electrolyte leakage, cell oxidation failure, or even thermal runaway and other safety hazards. If the A / B ratio is too large (i.e., A is too large or B is too small), it may reflect that the initial design of the sealing layer is too thick, which may reduce the battery's volumetric energy density, increase process costs, or excessively suppress the volume expansion during high-temperature cycling, possibly due to insufficient active materials, resulting in accelerated capacity decay, which does not meet the battery's requirements for high capacity and energy density. When the A / B ratio is controlled within the range of 20 to 500, it ensures that the sealing layer still has sufficient thickness to maintain sealing performance after long-term cycling, providing a safety margin for later battery cycles, while avoiding the impact on the battery's energy density and cycle capacity retention rate due to excessive restriction of the expansion rate, ultimately achieving a synergistic improvement in the battery's high-temperature cycling performance and safety performance.

[0032] In summary, by providing protrusions on the positive electrode single-sided sheet, this invention can reduce the wear of the membrane sealing layer by the edge of the positive electrode single-sided sheet, effectively improving the safety and cycle performance of the battery. Furthermore, by controlling the range of the ratio between the thickness (A) of the sealing layer corresponding to the edge of the outermost positive electrode single-sided sheet in the electrode assembly when the battery's capacity retention rate is greater than or equal to 98% and the cycle expansion rate (B) of the battery at 45°C, the thickness of the remaining sealing layer after the empty foil area of ​​the positive electrode single-sided sheet wears on the membrane during high-temperature cycling can be guaranteed, thereby meeting the requirements of subsequent battery cycle performance and safety performance.

[0033] The present invention provides a method for testing the battery's capacity retention rate and cycle expansion rate at 45°C, comprising the following steps: Cyclic testing of the battery in a test cabinet under test conditions of 45°C ± 2°C, specifically: resting for 5 minutes, discharging at 0.2C to the lower limit voltage; resting for 5 minutes, charging at 0.7C to the upper limit voltage, stopping at 0.025C, resting for 5 minutes, discharging at 0.2C to the lower limit voltage; initial capacity testing: resting for 5 minutes, charging at 3.2C to 4.37V, charging at 2.0C to 4.37V, charging at 1.2C to 4.53V, charging at 0.7C to 4.58V, stopping at 0.05C, measuring and recording the data under fully charged conditions. For example, voltage and thickness; after standing for 5 minutes, discharge at 0.7C to 3V, stand for 5 minutes, charge at 3.2C to 4.37V, charge at 2.0C to 4.37V, charge at 1.2C to 4.53V, charge at 0.7C to 4.58V, cut off at 0.05C, stand for 5 minutes, discharge at 0.7C to 3V, repeat this N times (N within 50T), and measure the capacity retention rate of the battery. Capacity retention rate (%) = (capacity of battery in N cycles - initial battery capacity) / initial battery capacity * 100%; calculate the cycle expansion rate B (%) of the battery at 45℃ = (full charge thickness of battery in N cycles - sample thickness of battery) / sample thickness of battery * 100%.

[0034] This invention discloses a method for testing the thickness A of the sealing layer corresponding to the edge of the outermost electrode in an electrode assembly. First, the battery is disassembled. Then, the membrane casing is cut open with scissors, and the cell is removed. A cross-sectional CP test is performed on the obtained membrane casing receiving groove along the width direction of the cell using a 3D microscope or SEM microscope. The thickness of the sealing layer in the receiving groove corresponding to the edge is measured using image analysis software. Any 3-5 points on the sealing layer corresponding to the edge of the outermost electrode can be taken, and the average value is taken as the sealing layer thickness A. Specifically, for stacked cells, when taking points, it is necessary to take points on the sealing layer corresponding to the four edges of the outermost electrode to measure the thickness. To reflect the overall integrity, one point can be taken at each of the four edges, and the average value is taken. It is important to note that after each point is taken, a cross-sectional CP test needs to be performed again using a 3D microscope or SEM microscope at the measured location.

[0035] In one example, the bottom wall includes a first region 1, such as Figure 1 As shown, the thickness of the sealing layer in the first region 1 is greater than the thickness of the sealing layers in other regions of the membrane housing besides the first region. When the battery's capacity retention rate is greater than or equal to 98%, the battery satisfies the following formula: 0.4 ≤ A / X ≤ 0.99, where the value of A / X can be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.99, or within any two of the above values. Wherein, A is the thickness of the sealing layer corresponding to the edge of the outermost electrode in the electrode assembly, in μm; X is the thickness of the sealing layer in the first region 1, in μm. First region 1, as... Figure 1 The thickness of the sealing layer in the middle region of the bottom wall is equal to the thickness of the normal sealing layer inside the membrane shell that has not been worn. By controlling the ratio A / X of the sealing layer thickness A corresponding to the edge of the outermost electrode in the electrode assembly to the sealing layer thickness X in the first region, which satisfies 0.4≤A / X≤0.99, the remaining thickness of the sealing layer can be further controlled. This ensures that when the battery capacity retention rate is greater than or equal to 98%, the thickness margin of the sealing layer after wear of the electrode single-sided sheet edge is within a certain range, thereby meeting the safety performance requirements of later cycles and achieving a synergistic improvement in the battery's high-temperature cycle performance and safety performance.

[0036] In one instance, A is 10μm-50μm, for example, it can be 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or within any two of the above values.

[0037] In one instance, X is 25μm-60μm, for example, it can be 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or within any two of the above values.

[0038] In one example, the receiving groove further includes an edge and a chamfer. The edge connects the bottom wall and the side wall, and the chamfer is formed by a chamfer transition between adjacent edges. The thickness of the sealing layer in the chamfer is less than the thickness of the sealing layer in the edge, and the thickness of the sealing layer in the edge is less than the thickness of the sealing layer in the first region. Generally, after the membrane shell is dented, the sealing layer of the membrane shell will suffer local damage. Among them, the edge and chamfer of the membrane shell are most prone to local damage, resulting in a thinner sealing layer in these areas. Moreover, the chamfer causes the most severe local damage to the membrane shell. Therefore, after denting the membrane shell, the thickness of the sealing layer in the chamfer is less than the thickness of the sealing layer in the edge. The denting in the first region causes the least local damage and expansion wear. Therefore, the thickness of the sealing layer in the edge is even less than the thickness of the sealing layer in the first region.

[0039] In one example, the difference between the thickness of the sealing layer in the first region and the thickness of the sealing layer in the chamfered portion is H1, where 10μm≤H1≤16μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, or within any two of the above values.

[0040] In one example, the difference between the thickness of the sealing layer in the first region and the thickness of the sealing layer in the ridge is H2, where 4μm≤H2≤12μm, for example, 4μm, 6μm, 8μm, 10μm, 12μm or within any two of the above values.

[0041] In this invention, the chamfered portion can be defined as a circular area with a radius of 3mm centered at the corner center, forming the chamfered portion of the receiving groove. The edge portion can be defined as the area within 3mm of the four sides of the bottom wall of the receiving groove on a plane located on the bottom wall of the receiving groove. For example... Figure 1 As shown, Figure 1 This is a schematic diagram of the bottom wall of the membrane housing accommodating groove. Figure 2 This is a schematic cross-sectional view of the membrane housing groove. (Combined with...) Figure 1 and Figure 2 It can be seen that a single receiving groove includes four edges 2 and four chamfered portions 3, as well as a first region 1 located at the center of the receiving groove. The chamfered portions 3 are located in the first region 1 located at the center of the receiving groove. Figure 1 The area enclosed by the red circle with radius R (R = 3 mm). Figure 2 The membrane shell includes an inner sealing layer 4 near the battery cell, a middle metal layer 5, and an outer protective layer 6. The thickness difference between the sealing layer 4 in the first region 1 and the sealing layer 4 in the chamfered region 3 ranges from 10 μm to 16 μm. The thickness difference between the sealing layer 4 in the first region 1 and the sealing layer 4 in the edge region 2 ranges from 4 μm to 12 μm.

[0042] In this invention, the testing methods for the thickness of the sealing layer in the first region of the receiving groove, the thickness of the sealing layer at the edge, and the thickness of the sealing layer at the chamfer are similar to the testing method for the sealing layer thickness A. Specifically, the battery is disassembled, and the membrane casing is cut open with scissors to remove the battery cell. A 3D microscope or SEM microscope is used to perform a cross-sectional CP test on the obtained membrane casing receiving groove along the width direction of the battery cell. Image analysis software is used to measure the thickness of the sealing layer in the first region and the thickness of the sealing layer at the edge according to the set partitions. The thickness of the sealing layer in the first region can be measured at any 3-5 points, and the average value is taken. The thickness of the sealing layer at the edge requires multiple cross-sectional slices. After measuring 3-5 thicknesses in different cross-sectional CP images, the average value is taken, which is the thickness of the sealing layer at the edge. When the obtained membrane casing receiving groove is sliced ​​along the width direction of the battery cell using a 3D microscope past the center of the corner, the thickness of the sealing layer at the chamfer can be obtained. Cross-sectional slices are performed on four different chamfer sections, and the sealing layer thickness at four points is measured. The average value is taken, which is the thickness of the sealing layer at the chamfer. Figure 3 and Figure 4 As shown, there are two types of membrane shells, among which, Figure 3 The membrane housing shown includes two receiving slots 7; Figure 4 The membrane housing shown contains only one receiving slot 7.

[0043] In one example, the electrode plate located inside the positive single-sided sheet in the electrode assembly is a positive double-sided sheet, which also includes the first protrusion, and the first protrusion faces the sealing layer along the protrusion direction in the thickness direction of the cell. In this invention, by simultaneously providing a protrusion structure facing the sealing layer on the positive electrode plate inside the positive single-sided sheet of the electrode assembly, the volume expansion stress generated by the battery during cycling (e.g., the high expansion stress generated during the charging and discharging of the silicon negative electrode) can be released, reducing the overall expansion rate of the cell. Simultaneously, the three-dimensional structure formed by the protrusion and the recess can improve the wettability of the electrolyte in the electrode assembly, increase the electrolyte storage space, and optimize the ion conduction path.

[0044] In one instance, such as Figure 5 As shown, the protrusion height of the first protrusion 8 along the thickness direction of the battery cell is h1, where 3μm ≤ h1 ≤ 30μm, for example, 3μm, 5μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm, or within any two of the above values. The higher the protrusion height of the first protrusion, the greater the deformation space of the positive electrode sheet, which can better release the expansion stress generated during cycling, reduce cell expansion, and thus reduce membrane wear. However, the protrusion height of the first protrusion cannot be too high, as excessive height can easily damage the positive electrode sheet during processing, leading to positive electrode sheet breakage or process breakage.

[0045] In one instance, such as Figure 5 As shown, the distance between the centers of the protrusions of two adjacent first protrusions 8 is L1, where 3mm ≤ L1 ≤ 10mm. L1 can be, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, or any two of the above values. Each first protrusion can be understood as an arc segment, and the center of the arc segment is the center of the protrusion, the center of the complete circle that generates the arc segment. The distance from this center of the protrusion to all points on the arc segment is equal. "The distance between the centers of the protrusions of two adjacent first protrusions" refers to the shortest straight-line distance between the centers of the protrusions of two adjacent first protrusions.

[0046] In one instance, such as Figure 5 As shown, the distance between the protruding edges of two adjacent first protrusions 8 is L2, 0.5mm≤L2≤8mm, for example, 0.5mm, 1mm, 2mm, 4mm, 6mm, 8mm, or within any two of the above values. The distance between the two closest endpoints of the arc segments of two adjacent first protrusions intersecting the positive electrode sheet is the distance along the width direction of the positive electrode sheet.

[0047] For the first protrusion of the positive electrode double-sided sheet, this invention, by controlling the values ​​of L1 and L2 within the aforementioned range, ensures a suitable spacing between adjacent first protrusions, releasing expansion stress while improving electrolyte wettability. Avoiding excessively small L1 and / or L2 results in overly dense spacing of the first protrusions on the positive electrode sheet, preventing the electrode sheet from extending sufficiently to meet the required density. This also leads to the first protrusions' height not meeting the defined range, limiting further deformation space and increasing the risk of breakage. Conversely, when the spacing between protrusions exceeds 8mm, the spacing becomes too sparse, resulting in insufficient support area for the first protrusions, thus failing to improve electrolyte wettability and buffer expansion stress.

[0048] In one example, along the thickness direction of the battery cell, the positive electrode sheet includes a convex region and a planar region. The region of the positive electrode sheet where the first protrusion is located is the convex region, and the region of the positive electrode sheet other than the convex region is the planar region. The positive electrode sheet satisfies the following formula: 0.4 ≤ S1 / S ≤ 0.7, for example, 0.4, 0.5, 0.6, 0.7, or any two of the above values, where S1 is the projected area of ​​the convex region along the thickness direction of the battery cell, and S is the total projected area of ​​the positive electrode sheet. By limiting the ratio of the projected area of ​​the convex region (S1) to the total projected area of ​​the positive electrode sheet (S) to the above range, this invention allows the protrusions to be distributed on the positive electrode sheet at a reasonable density. This not only releases the expansion stress generated by battery cycling and improves electrolyte wettability through a sufficient number of first protrusions, but also avoids the positive electrode sheet strength decreasing due to excessively dense first protrusions or the stress release being insufficient due to excessively sparse first protrusions, thus achieving a balance between wear resistance and electrode performance. In this invention, the thickness direction of the battery cell is the superposition direction of the positive electrode, negative electrode and separator in the electrode assembly, and the thickness direction of the battery cell is perpendicular to the plane where the positive electrode (flat positive double-sided sheet), negative electrode and separator are located.

[0049] In one example, the negative electrode includes a second protrusion, and the second protrusion is positioned away from the sealing layer along a protrusion direction in the thickness direction of the negative electrode. In this invention, the thickness direction of the negative electrode is the same as the thickness direction of the battery cell.

[0050] In one example, the protrusion height of the second protrusion along the thickness direction of the negative electrode sheet is h2, 3μm≤h2≤30μm, for example, 3μm, 5μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm or within any two of the above values.

[0051] In one example, the distance between the centers of the protrusions of two adjacent second protrusions is L3, 3mm≤L3≤10mm, for example, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or within any two of the above values.

[0052] In one example, the distance between the protruding edges of two adjacent second protrusions is L4, 0.5mm≤L4≤8mm, for example, 0.5mm, 1mm, 2mm, 4mm, 6mm, 8mm or within any two of the above values.

[0053] The definitions of the protrusion height, protrusion center, and protrusion edge in the second protrusion are the same as those in the first protrusion, and will not be repeated here.

[0054] In one example, along the thickness direction of the negative electrode sheet, the negative electrode sheet includes a convex region and a planar region. The region of the negative electrode sheet where the second protrusion is located is the convex region, and the region of the negative electrode sheet other than the convex region is the planar region. The negative electrode sheet satisfies the following formula: 0.4≤M1 / M≤0.7, for example, 0.4, 0.5, 0.6, 0.7, or within any two of the above values, where M1 is the projected area of ​​the convex region along the thickness direction of the negative electrode sheet; and M is the total projected area of ​​the negative electrode sheet.

[0055] Furthermore, in this invention, a second protrusion can be provided on the negative electrode sheet. By providing a second protrusion on the negative electrode sheet with the protrusion direction opposite to the sealing layer, and limiting the height, spacing and projected area ratio of the second protrusion, the cyclic expansion stress of the negative electrode can be released, and the electrolyte wetting can be optimized in conjunction with the positive electrode structure. At the same time, the second protrusion is prevented from directly squeezing the sealing layer, reducing the risk of wear.

[0056] In one example, a first protrusion / second protrusion can be provided on the entire surface of the positive electrode / negative electrode. The first protrusion / second protrusion can be evenly distributed at intervals or unevenly distributed at intervals, preferably evenly distributed at intervals.

[0057] In one example, the first protrusion / second protrusion can be provided only in a local area of ​​the positive / negative electrode, such as the edge area or the arc area.

[0058] In one example, the negative electrode sheet includes a negative electrode current collector and negative electrode active layers disposed on both sides of the negative electrode current collector. The surface of the negative electrode active layer has grooves, wherein the diameter of the grooves is 80μm-150μm, for example, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, or within any two of the above values. In this invention, several more grooves can be further formed on the surface of the negative electrode active layer to provide deformation buffer space during battery charging and discharging expansion (e.g., expansion of silicon-containing negative electrodes), effectively suppressing the elongation of the electrode sheet in the height / width direction (XY direction), and further reducing the elongation of the positive electrode in the XY direction, thereby reducing the wear of the sealing layer caused by the edge compression of the outermost electrode sheet.

[0059] like Figure 6 As shown, multiple groove structures 9 can be formed on the surface of the negative electrode active layer.

[0060] In one example, the spacing between adjacent grooves is 500μm-2000μm, for example, 500μm, 600μm, 800μm, 1000μm, 1200μm, 1400μm, 1600μm, 1800μm, 2000μm or within any two of the above values.

[0061] In one example, the depth of the groove is 5μm-30μm, for example, 5μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm or within any two of the above values.

[0062] In one example, the angle between the groove and the height direction of the negative electrode sheet is 0°-90°, for example, it can be 0°, 5°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90° or within any two of the above values.

[0063] In one example, the groove includes a first edge, which is the edge closest to the edge of the negative electrode sheet. The vertical distance between the first edge and any point on the edge of the negative electrode sheet is 0.2mm-1mm, for example, it can be 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1mm, or within any two of the above values. It is understood that the groove has several edges along its extension direction, with the edge closest to the edge of the negative electrode sheet being the first edge. This limitation of the vertical distance between the first edge and any point on the edge of the negative electrode sheet prevents the negative electrode sheet from being cut directly into the groove location during die-cutting, thus avoiding powder shedding from the negative electrode edge.

[0064] In one example, the electrode assembly has a double-sided positive electrode located inside the single-sided positive electrode sheet. The positive electrode sheet includes a second positive current collector and a second positive active layer disposed on both sides of the second positive current collector. The surface of the second positive active layer has recessed holes located in the edge region (the area near the edge of the positive electrode sheet). Further, providing a recessed hole structure in the edge region of the positive electrode sheet can reduce the local current density (CB value) in the sub-region, thereby reducing the expansion of the negative electrode sheet corresponding to the edge region or arc region of the positive electrode sheet, and reducing wear on the sealing layer.

[0065] In one example, the diameter of the recess is 70μm-200μm, for example, 70μm, 90μm, 100μm, 120μm, 140μm, 160μm, 180μm, 200μm or within any two of the above values.

[0066] In one example, the hole spacing between adjacent recesses is 200μm-1000μm, for example, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm or within any two of the above values.

[0067] In one example, the depth of the concave hole is 5μm-20μm, for example, 5μm, 10μm, 15μm, 20μm or within any two of the above values.

[0068] In one example, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes a carbon-based material, and the carbon-based material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, graphene, soft carbon, hard carbon, soft carbon-coated graphite material, or hard carbon-coated graphite material.

[0069] In one example, the negative electrode active material further includes a silicon-carbon composite material, which comprises a porous carbon matrix and silicon material located in the internal channels of the porous carbon matrix.

[0070] In one example, the negative electrode active material comprises the carbon-based material and the silicon-carbon composite material, and the silicon content is C based on the total weight of the negative electrode active layer. Si 1%≤C Si ≤50%, for example, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or within any two of the above values.

[0071] In one example, the specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g-10m 2 / g, for example, 0.5m 2 / g, 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g or within the range of any two of the above values.

[0072] In one example, the particle size Dv50 of the silicon-carbon composite material is 6 μm-15 μm, for example, 6 μm, 8 μm, 10 μm, 11 μm, 13 μm, 15 μm, or within any two of the above values. The particle size Dv50 of the silicon-carbon composite material in this invention can be tested using a laser particle size analyzer; in this invention, it is measured using a Malvern Mastersizer 3000 laser particle size analyzer.

[0073] In one example, the resistivity of the silicon-carbon composite material powder ranges from 0.1 Ω·cm to 1000 Ω·cm, for example, it can be 0.1 Ω·cm, 1 Ω·cm, 10 Ω·cm, 50 Ω·cm, 100 Ω·cm, 500 Ω·cm, 1000 Ω·cm, or within any two of the above values.

[0074] In one example, the silicon content in the silicon-carbon composite material is 30%-75%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or within any two of the above values.

[0075] This invention limits the parameters of the silicon-carbon composite material to meet the above range, which can improve the energy density of the battery while setting the expansion stress generated by the battery during the cycle within a controllable range, reduce the wear of the sealing layer during the battery cycle, and reduce the risk of battery leakage, gas swelling and short circuit fire that may be caused by the sealing layer cracking in the later stage of the cycle.

[0076] In one example, the sphericity of the silicon-carbon composite material is C, 0.4≤C≤1, for example, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1. The sphericity C of the silicon-carbon composite material and the thickness A of the sealing layer corresponding to the edge of the outermost electrode in the electrode assembly satisfy the following relationship: 30≤A / C≤100, where the value of A / C is, for example, 30, 40, 50, 60, 70, 80, 90 or 100. Wherein, when 0.4≤C≤0.7, A is 20μm-50μm, for example, it can be 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or any two of the above values; when 0.7<C≤1, A is 10μm-35μm, for example, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, or any two of the above values. For example, the average sphericity of the silicon-carbon composite material can be determined using scanning electron microscopy, specifically including the following steps: 1. Capturing a two-dimensional image of the particles, ensuring the image is clear; 2. Extracting the particle outline using software (such as Photoshop, dedicated particle size analysis software) and calculating the sphericity.

[0077] The sphericity of silicon-carbon composites affects the isotropy of expansion stress. When the sphericity of silicon particles in the composite material meets the aforementioned range, the expansion stress is distributed more uniformly. Conversely, blocky or irregularly shaped silicon particles may generate greater stress concentration locally, exacerbating wear on the sealing layer. Therefore, silicon-carbon composites with high sphericity may cause less wear on the sealing layer, allowing for a smaller remaining sealing layer A. Conversely, a thicker sealing layer is required to resist wear during cycling.

[0078] In one example, the negative electrode active material includes the carbon-based material and the silicon-carbon composite material, and the electrolyte contains 13%-25% fluorocarbonate, for example, 13%, 15%, 20%, 25% or within any two of the above values.

[0079] In one example, the negative electrode active material comprises only the carbon-based material, and the content of fluorocarbonate in the electrolyte is 3%-10%, for example, it can be 3%, 5%, 8%, 10% or within any two of the above values.

[0080] An appropriate amount of fluorocarbonate in the electrolyte can promote the formation of a uniform, dense, and elastic SEI film, effectively buffering volume expansion during battery cycling. If the fluorocarbonate content is too low, the SEI film is unstable, leading to continuous electrolyte decomposition, accelerated capacity decay, and decreased cycle performance. If the fluorocarbonate content is too high, the SEI film is too thick, increasing interfacial impedance, hindering lithium-ion migration, and potentially generating byproducts due to excessive fluorocarbonate decomposition, which in turn reduces cycle stability. This invention adjusts the fluorocarbonate content in the electrolyte according to the different negative electrode active material systems. When the negative electrode active material includes silicon-carbon composite material, the fluorocarbonate content in the electrolyte is increased to buffer the higher expansion stress generated by the silicon-carbon composite material and reduce SEI cracking. When the negative electrode active material only includes the aforementioned carbon-based material, the fluorocarbonate content in the electrolyte can be reduced accordingly to reduce side reactions and thus optimize the battery's cycle performance and safety performance.

[0081] In one example, the fluorocarbonate may be at least one of fluoroethylene carbonate and difluoroethylene carbonate.

[0082] In one example, the fluorocarbonate is selected from fluoroethylene carbonate.

[0083] In one example, the sealing layer includes a substrate and a toughening agent. The substrate comprises polypropylene or modified polypropylene, and the toughening agent comprises at least one of a polyolefin elastomer, EPDM rubber, and a styrene-ethylene-butene-styrene copolymer. Adding a toughening agent to the sealing layer can improve its impact resistance and flexibility, reduce wear during cycling, and enhance battery safety performance.

[0084] In one example, the tensile strength of the sealing layer is greater than or equal to 20 MPa, for example, it can be 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa or any value greater than 20 MPa.

[0085] In one example, the elongation at break of the sealing layer is 300%-800%, for example, it can be 300%, 400%, 500%, 600%, 700%, 800% or any value within the range of the two values ​​mentioned above.

[0086] In one example, the puncture strength of the sealing layer is greater than or equal to 10 N / mm, for example, it can be 10 N / mm, 20 N / mm, 30 N / mm, 40 N / mm or any value greater than or equal to 10 N / mm.

[0087] In one example, the softening temperature of the sealing layer is 100°C-160°C, for example, it can be 100°C, 120°C, 140°C, 160°C or within any two of the above values.

[0088] In one example, the crystallinity of the sealing layer is 30%-70%, for example, it can be 30%, 40%, 50%, 60%, 70%, or within any two of the above values.

[0089] In one example, the swelling rate of the sealing layer is less than or equal to 6%. In this invention, the swelling rate is tested by immersing the sealing layer in an electrolyte at 60°C (such as 1M LiPF6 in EC / DMC) for 7 days and measuring the change in the thickness of the sealing layer.

[0090] Tensile strength is the maximum tensile force that a material can withstand per unit area before fracture; elongation at break is the elongation at fracture, reflecting toughness; puncture strength reflects the hardness of the sealing layer; softening point is the temperature at which the sealing layer begins to deform under heat or pressure, mainly to prevent damage to the sealing layer caused by high temperature and high pressure during formation (edge ​​effect); crystallinity is the proportion of crystalline regions in the sealing layer, directly affecting hardness, heat resistance, and barrier properties; molecular weight affects the mechanical strength of the sealing layer; swelling rate reflects the electrolyte resistance of the sealing layer. This invention, by limiting the above performance parameters of the sealing layer, can improve the toughness, puncture resistance, and corrosion resistance of the sealing layer, thereby improving the wear resistance of the sealing layer and enhancing the safety performance in the later stages of battery cycling.

[0091] In one example, the sealing layer has a protective coating on the side facing the battery cell, and this protective coating corresponds to the edge of the outermost electrode in the electrode assembly. The protective coating further reduces wear on the sealing layer and improves battery cycle safety.

[0092] In one example, the thickness of the protective coating is 2μm-10μm, for example, 2μm, 4μm, 6μm, 8μm, 10μm, or within any two of these values. Limiting the thickness of the protective coating can prevent excessive thickness from degrading the battery energy density, and prevent excessive thickness from having little effect on battery safety.

[0093] In one example, the protective coating includes at least one of an organic coating, an inorganic coating, and a composite coating. The organic coating includes at least one of a polyurethane coating, a fluorocarbon coating, an acrylic resin coating, and an epoxy resin coating. The inorganic coating includes at least one of a nano-alumina coating, a diamond-like carbon coating, and a silica sol coating. The composite coating includes an organosilicon-modified coating or a graphene-reinforced coating.

[0094] In one instance, the protective layer comprises a nylon material.

[0095] In one instance, the metal layer comprises aluminum.

[0096] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0097] Example 1

[0098] (1) Preparation of battery cells

[0099] Preparation of the positive electrode double-sided sheet: Lithium cobalt oxide, conductive agent (a mixture of conductive carbon black and carbon nanotubes), and polyvinylidene fluoride (PVDF) are placed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of 97.60:1.35:1.05 and stirred evenly to obtain a positive electrode slurry; the above positive electrode slurry is evenly coated on both sides of aluminum foil, and after drying, rolling and cutting, a positive electrode double-sided sheet is obtained.

[0100] Preparation of positive electrode single-sided sheet: Lithium cobalt oxide, conductive agent (a mixture of conductive carbon black and carbon nanotubes), and polyvinylidene fluoride (PVDF) are placed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of 97.60:1.35:1.05 and stirred evenly to obtain a positive electrode slurry; the above positive electrode slurry is uniformly coated on one side of an aluminum foil, and after drying, rolling, and slitting, a positive electrode single-sided sheet is obtained.

[0101] Preparation of the negative electrode: Artificial graphite and silicon-carbon composite material (including a porous carbon matrix and silicon material located in the pores within the carbon matrix, wherein the specific surface area of ​​the silicon-carbon composite material is 4.8 m²) are used. 2The silicon-carbon composite material contains 45% silicon, 11.2 μm of polyacrylic acid (PAA), sodium carboxymethyl cellulose, and acetylene black. These components are added to a vacuum mixer in a mass ratio of 57.6:38.4:2.7:0.65:0.65, along with an appropriate amount of deionized water. The mixture is thoroughly mixed under vacuum until a uniform, free-flowing negative electrode slurry is formed. This negative electrode slurry is then uniformly coated onto both sides of a copper foil. After drying, rolling, and slitting, the negative electrode sheet is obtained. The silicon content in the active layer of the negative electrode is 15% by weight.

[0102] Membrane preparation: An 8μm thick substrate is used. A ceramic layer is coated on one side of the substrate, and an adhesive layer is coated on the other side of both the ceramic layer and the substrate. The substrate is composed of PE, and the ceramic layer includes alumina. The adhesive layer is PVDF.

[0103] Protrusions are provided on the positive double-sided sheet, the positive single-sided sheet, and the negative sheet. The positive double-sided sheet and the positive single-sided sheet are provided with a first protrusion, and the negative sheet is provided with a second protrusion. Specifically, the prepared positive or negative sheet is rolled by a roller to form a specific first protrusion / second protrusion on the surface of the electrode sheet (the distance between the centers of adjacent first protrusions / second protrusions is 4.1 mm, the shortest distance between the edges of adjacent first protrusions / second protrusions is 2.2 mm, the height of the first protrusion / second protrusion is 18.4 μm, and the proportion of the orthogonal projection area of ​​the first protrusion / second protrusion on the first surface is 43%). The protrusion direction of the first protrusion of the positive double-sided sheet and the positive single-sided sheet faces the sealing layer, and the protrusion direction of the second protrusion of the negative sheet faces away from the sealing layer.

[0104] Preparation of electrolyte: In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) are mixed evenly in a mass ratio of 2:1.5:2. LiPF6 (14wt% based on the total mass of the non-aqueous electrolyte) and fluoroethylene carbonate (FEC) (20wt% based on the total mass of the non-aqueous electrolyte) are slowly added to the mixed solution and stirred evenly to obtain the non-aqueous electrolyte.

[0105] The prepared positive double-sided sheet, positive single-sided sheet, negative sheet and separator are stacked in the following order to form an electrode assembly: the outermost electrode is the positive single-sided sheet, and the middle ones are arranged in the following cycle: separator, negative sheet, positive double-sided sheet. Obtain a bare battery cell; solder tabs onto the bare battery cell; obtain a laminated battery cell; attach an adhesive to the outside of the laminated battery cell. The first adhesive is attached to both sides of the laminated battery cell along the width direction, and the edge of the first adhesive extends from both sides of the laminated battery cell along the width direction to the surface of the laminated battery cell along the thickness direction. The first adhesive includes a first side adhesive, a second side adhesive, a third side adhesive, and a fourth side adhesive, which respectively cover the four corners of the positive electrode single-sided sheet (or extend beyond the four corners to the outside of the electrode). By setting adhesive tape in the edge area of ​​the laminated battery cell that is prone to wear of the sealing layer, the adhesive tape can cover the corner area of ​​the battery cell, so that it forms a protective layer between the membrane shell and the positive electrode single-sided sheet, thereby reducing the wear of the membrane shell at the corner of the positive electrode single-sided sheet and improving the safety performance of the corner of the laminated battery cell.

[0106] (2) Packaging

[0107] The battery cell obtained in step (1) is placed in a battery casing. A receiving groove is formed on the casing membrane. The receiving groove includes a bottom wall and side walls surrounding the bottom wall. The sealing layer of the bottom wall faces the battery cell. The sealing layer includes a substrate and a toughening agent. The original thickness of the sealing layer is 32.10 μm. Figure 7 As shown, the substrate comprises polypropylene, and the toughening agent comprises a polyolefin elastomer; the sealing layer has a tensile strength of 23 MPa, an elongation at break of 520%, a puncture strength of 18 N / mm, a softening temperature of 123°C, a crystallinity of 54%, and a swelling rate of 4.2%. A protective coating (polyurethane coating, 6 μm thick) is then applied to the side of the sealing layer facing the battery cell, corresponding to the edge of the outermost electrode in the electrode assembly.

[0108] The prepared electrolyte is injected into the battery cell, and after processes such as settling, aging, formation, degassing, aging, and sorting, a lithium-ion battery is obtained. See Table 1 for details.

[0109] Sample Group 2

[0110] This group follows the same procedure as Example 1, with the only difference being that the original thickness of the sealing layer is changed, so that the thickness A of the sealing layer after 50 cycles is altered. See Table 1 for details.

[0111] Sample Group 3

[0112] This group followed the example 1, with the only difference being that the specific surface area, particle size Dv50, and sphericity C of the silicon-carbon composite material were changed, which altered the battery's 50-cycle expansion rate B at 45 degrees Celsius. See Table 1 for details.

[0113] Sample Group 4

[0114] This group follows the same procedure as Example 1, with the only difference being that the original thickness of the sealing layer was changed, which altered the thickness A of the sealing layer after 50 cycles. The specific surface area, particle size Dv50, and sphericity C of the silicon-carbon composite material were also changed, which altered the 50-cycle expansion rate B of the battery at 45 degrees Celsius. See Table 1 for details.

[0115] Sample 5

[0116] This group follows the same procedure as Example 1, the only difference being that no protrusions are provided on all positive electrode single-sided plates. See Table 1 for other details.

[0117] Test Example 1

[0118] The lithium-ion batteries obtained from the samples (multiple parallel batteries were prepared for each sample for subsequent disassembly) were subjected to the following tests:

[0119] Measure and record the initial thickness of the battery.

[0120] The first stage of cycling (until capacity retention is greater than or equal to 98%) is performed. The specific process includes: cycling the battery in a test cabinet under test conditions of 45℃±2℃. The specific method is as follows: rest for 5 minutes, discharge at 0.2C to the lower limit voltage; rest for 5 minutes, charge at 0.7C to the upper limit voltage, cut off at 0.025C, rest for 5 minutes, discharge at 0.2C to the lower limit voltage; initial capacity test: rest for 5 minutes, charge at 3.2C to 4.37V, 2.0C... Charge to 4.37V, then charge at 1.2C to 4.53V, then charge at 0.7C to 4.58V, and cut off at 0.05C. Measure and record the data under full charge, such as voltage and thickness. Let stand for 5 minutes, then discharge at 0.7C to 3V. Let stand for 5 minutes, then charge at 3.2C to 4.37V, then charge at 2.0C to 4.37V, then charge at 1.2C to 4.53V, then charge at 0.7C to 4.58V, and cut off at 0.05C. Let stand for 5 minutes, then discharge at 0.7C to 3V. Repeat this process 50 times.

[0121] Test and calculate the capacity retention rate after 50 cycles. Capacity retention rate (%) = (Battery capacity after 50 cycles - Initial battery capacity) / Initial battery capacity * 100%. Record the results in Table 1 (all are not lower than 98%).

[0122] Measure and calculate the battery thickness after 50 cycles. The battery cycle expansion rate B (%) = (full charge thickness after 50 cycles - battery sample thickness) / battery sample thickness * 100%. Record the results in Table 1.

[0123] For each sample, disassemble a parallel battery and measure the thickness of the sealing layer corresponding to the outermost edge of the electrode tab; specifically, for Sample Groups 1 - 4, take two points on the sealing layer corresponding to the top and bottom edges of the outermost electrode tab along the direction of the ear extension respectively for measurement, and take the average of the 4 points, denoted as Thickness A; for Sample 5, take one point on the sealing layer at each of the four edges of the outermost electrode tab for measurement, and take the average of the 4 points, denoted as Thickness A. The thickness A of the sealing layer after 50 cycles of Example 1 is 20.0 μm, as Figure 8 shown; for Samples 1 - 4, take 3 - 5 points in the sealing layer corresponding to the first region in the middle of the electrode tab for measurement and take the average, denoted as Thickness X, and record the results in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] Test Example 2

[0128] (1) Micro-drop test after 600 cycles:

[0129] Then conduct a micro-drop test on the remaining parallel batteries of each sample after 600 cycles: For the parallel batteries of each sample after 600 cycles, at 25°C, load each sample battery in the fully charged state into the drop fixture for assembly and start the drop test. Set the height to 10 cm, and the drop surface is facing the battery MI. The sequence is as follows: the ear surface, the bottom surface, the front surface, the back surface, the left surface, and the right surface, a total of 6 surfaces in one round, and each surface is dropped 1000 times, for a total of 6000W times. After each surface drop, visually judge whether there is no breakage or leakage of the aluminum-plastic film. If there is no such situation, it is judged as qualified; otherwise, it is unqualified. Test 10 batteries for each sample of the parallel batteries of each sample. If all pass, it is 10PASS / 10; if two do not pass, it is 8PASS / 10, and record the results in Table 2.

[0130] (2) Cycle capacity retention rate after 600 cycles:

[0131] Test and calculate the capacity retention rate of each sample battery after 600 cycles. The 600-cycle capacity retention rate (%) = (capacity of the battery after 600 cycles - initial capacity of the battery) / initial capacity of the battery * 100%, and record the results in Table 2.

[0132] (3) Cycle expansion rate after 600 cycles:

[0133] Measure and calculate the battery thickness of each sample battery after 600 cycles. The expansion rate (%) after 600 cycles = (full charge thickness after 600 cycles - battery sample thickness) / battery sample thickness * 100%. Record the results in Table 2.

[0134] Table 2

[0135]

[0136]

[0137] As shown in Table 2, by setting protrusions on the positive electrode single-sided sheet, the wear of the membrane sealing layer by the edge of the positive electrode single-sided sheet can be reduced. Controlling A / B within a suitable range ensures that the remaining thickness (A) of the sealing layer in the membrane can meet the requirements of subsequent battery cycle performance and safety. Further controlling A / X within a suitable range can further improve the battery's cycle performance and safety.

[0138] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, Includes the battery cell and the membrane housing that encapsulates the battery cell; The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode, which are stacked sequentially. Along the thickness direction of the battery cell, the outermost electrode in the electrode assembly is a single-sided positive electrode, which includes a first positive current collector and a first positive active layer disposed on the inner surface of the first positive current collector. The inner surface faces away from the membrane shell. The membrane shell includes a protective layer, a metal layer, and a sealing layer stacked sequentially, with the sealing layer close to the battery cell. The membrane shell has a receiving groove for accommodating the battery cell. The receiving groove includes a bottom wall and a side wall surrounding the bottom wall. The sealing layer of the bottom wall is disposed facing the battery cell. The positive electrode single-sided sheet includes a first protrusion, and along the thickness direction of the battery cell, the protrusion direction of the first protrusion faces the sealing layer; When the capacity retention rate of the battery is greater than or equal to 98%, the battery satisfies the following formula: 20≤A / B≤500, where A is the thickness of the sealing layer corresponding to the edge of the outermost electrode in the electrode assembly, in μm; and B is the cyclic expansion rate of the battery at 45°C.

2. The battery according to claim 1, wherein the bottom wall includes a first region, the thickness of the sealing layer in the first region is greater than the thickness of the sealing layer in other regions of the membrane housing excluding the first region, wherein, When the capacity retention rate of the battery is greater than or equal to 98%, the battery satisfies the following formula: 0.4≤A / X≤0.99, where A is the thickness of the sealing layer corresponding to the edge of the outermost electrode in the electrode assembly, in μm; and X is the thickness of the sealing layer in the first region, in μm. And / or, A is 10μm-50μm, X is 15μm-60μm.

3. The battery according to claim 2, wherein the receiving groove further comprises a ridge portion and a chamfered portion, the ridge portion being connected between the bottom wall and the side wall, and the chamfered portion being formed by a chamfered transition between adjacent ridge portions; the thickness of the sealing layer of the chamfered portion is less than the thickness of the sealing layer of the ridge portion, and the thickness of the sealing layer of the ridge portion is less than the thickness of the sealing layer in the first region.

4. The battery according to claim 1, wherein, The sealing layer includes a substrate and a toughening agent. The substrate includes polypropylene or modified polypropylene, and the toughening agent includes at least one of polyolefin elastomer, ethylene propylene diene monomer (EPDM) rubber, and styrene-ethylene-butene-styrene copolymer. And / or, the tensile strength of the sealing layer is greater than or equal to 20 MPa; And / or, the elongation at break of the sealing layer is 300%-800%; And / or, the puncture strength of the sealing layer is greater than or equal to 10 N / mm; And / or, the softening temperature of the sealing layer is 100℃-160℃; And / or, the crystallinity of the sealing layer is 30%-70%; And / or, the swelling ratio of the sealing layer is less than or equal to 6%.

5. The battery according to claim 1, wherein, The electrode assembly containing the electrode inside the positive single-sided sheet is a positive double-sided sheet. The positive double-sided sheet includes the first protrusion, and the first protrusion faces the sealing layer along the protrusion direction of the cell thickness. The distance between the centers of the protrusions of two adjacent first protrusions is L1, 3mm≤L1≤10mm, and / or the distance between the edges of the protrusions of two adjacent first protrusions is L2, 0.5mm≤L2≤8mm, and / or the protrusion height of the first protrusion along the cell thickness direction is h1, 3μm≤h1≤30μm. And / or, the negative electrode sheet includes a second protrusion, and the second protrusion is away from the sealing layer along the protrusion direction in the thickness direction of the negative electrode sheet, wherein the distance between the centers of the protrusions of two adjacent second protrusions is L3, 3mm≤L3≤10mm, and / or, the distance between the edges of the protrusions of two adjacent second protrusions is L4, 0.5mm≤L4≤8mm, and / or, the protrusion height of the second protrusion along the thickness direction of the negative electrode sheet is h2, 3μm≤h2≤30μm.

6. The battery according to claim 1, wherein, The negative electrode sheet includes a negative electrode current collector and negative electrode active layers disposed on both sides of the negative electrode current collector. The surface of the negative electrode active layer is provided with grooves, wherein the diameter of the grooves is 80μm-150μm. And / or, the spacing between adjacent grooves is 500μm-2000μm; And / or, the depth of the groove is 5μm-30μm; And / or, the angle between the groove and the height direction of the negative electrode sheet is 0°-90°; And / or, the groove includes a first edge, which is the edge closest to the edge of the negative electrode sheet, and the vertical distance between the first edge and any point on the edge of the negative electrode sheet is 0.2mm-1mm; And / or, the electrode in the electrode assembly located inside the positive single-sided sheet is a positive double-sided sheet, the positive double-sided sheet includes a second positive current collector and a second positive active layer disposed on both sides of the second positive current collector, the surface of the second positive active layer is provided with recessed holes, the recessed holes are located in the edge region; the diameter of the recessed holes is 70μm-200μm, the hole spacing between adjacent recessed holes is 200μm-1000μm, and the hole depth of the recessed holes is 5μm-20μm.

7. The battery according to claim 1, wherein, The negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes a carbon-based material, and the carbon-based material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, graphene, soft carbon, hard carbon, soft carbon-coated graphite material, or hard carbon-coated graphite material. And / or, the negative electrode active material further includes a silicon-carbon composite material, the silicon-carbon composite material comprising a porous carbon matrix and silicon material located in the internal channels of the porous carbon matrix.

8. The battery according to claim 7, wherein, The negative electrode active material comprises the carbon-based material and the silicon-carbon composite material, and based on the total weight of the negative electrode active layer, the silicon content is C. Si 1%≤C Si ≤50%; And / or, the specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g-10m 2 / g; And / or, the particle size Dv50 of the silicon-carbon composite material is 6μm-15μm; And / or, the powder resistivity of the silicon-carbon composite material is in the range of 0.1 Ω·cm to 1000 Ω·cm; preferably, the silicon content in the silicon-carbon composite material is 30% to 75%; And / or, the sphericity of the silicon-carbon composite material is C, 0.4≤C≤1, and the sphericity C of the silicon-carbon composite material and the thickness A of the sealing layer corresponding to the edge of the outermost electrode in the electrode assembly satisfy the following relationship: 30≤A / C≤100, where, when 0.4≤C≤0.7, A is 20μm-50μm; when 0.7<C≤1, A is 10μm-35μm.

9. The battery according to claim 7, wherein, The negative electrode active material includes the carbon-based material and the silicon-carbon composite material, and the electrolyte contains 13%-25% fluorinated carbonate. And / or, the negative electrode active material comprises only the carbon-based material, and the electrolyte contains 3%-10% fluorocarbonate.

10. The battery according to claim 1, wherein, The sealing layer has a protective coating on the side facing the battery cell, and the protective coating corresponds to the edge of the outermost electrode in the electrode assembly; Preferably, the thickness of the protective coating is 2μm-10μm; Preferably, the protective coating includes at least one of an organic coating, an inorganic coating, and a composite coating; the organic coating includes at least one of a polyurethane coating, a fluorocarbon coating, an acrylic resin coating, and an epoxy resin coating; the inorganic coating includes at least one of a nano-alumina coating, a diamond-like carbon coating, and a silica sol coating; and the composite coating includes an organosilicon-modified coating or a graphene-reinforced coating.

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