A wound lithium ion battery

Abstract

The present invention relates to the technical field of lithium batteries, and provides a wound lithium-ion battery. In the wound lithium-ion battery, in a single-sided area of ​​a negative electrode sheet at the center of a winding core, a plurality of recessed portions are provided on a side of a negative electrode current collector where a negative electrode active layer is not provided, and the projections of the first end of a first negative electrode active layer and the first end of a second negative electrode active layer in different bending areas overlap in the thickness direction of the winding core. The overlapping of the recessed portions and the projections of the negative electrode active layers can significantly increase the liquid retention in the center of the winding core, improve the wettability of the electrolyte, and thus improve the cycle performance of the battery and reduce lithium plating.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a wound lithium-ion battery. Background Art

[0002] In the production process of wound lithium batteries, in order to improve the energy density of the battery, the gap between the cells is usually minimized to make the cells more closely arranged. This tight winding method can reduce the overall volume of the battery, so that more cells can be loaded into a limited space, increasing the energy density of the battery. However, this tight winding method will also cause the center gap between the cells to become smaller, and the storage space for the electrolyte will also be reduced accordingly. The electrolyte may not be able to fully infiltrate all areas of the cell, resulting in poor infiltration, affecting the performance and cycle life of the battery. Summary of the invention

[0003] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a wound lithium-ion battery, in which, in the single-sided area of ​​the negative electrode sheet at the center of the winding core, a plurality of recessed portions are arranged on the side of the negative electrode current collector where the negative electrode active layer is not arranged, and the projections of the head end of the first negative electrode active layer and the head end of the second negative electrode active layer in different bending areas in the thickness direction of the winding core overlap. The overlapping of the recessed portions and the projections of the negative electrode active layers can work together to significantly increase the liquid retention amount in the center of the winding core, improve the wettability of the electrolyte, thereby improving the cycle performance of the battery and reducing lithium plating.

[0004] In order to achieve the above-mentioned object, the first aspect of the present invention provides a wound lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound multiple times in a winding direction to form a winding core;

[0005] The negative electrode sheet comprises:

[0006] A negative electrode current collector layer, comprising a first surface and a second surface arranged opposite to each other along a second direction, wherein the first direction is perpendicular to the second direction;

[0007] A first negative electrode active layer located on the first surface and a second negative electrode active layer located on the second surface; along the first direction, the first end of the first negative electrode active layer exceeds the first end of the second negative electrode active layer; the portion where the first end of the first negative electrode active layer exceeds the first end of the second negative electrode active layer is a single-sided area of ​​the negative electrode sheet;

[0008] At least a portion of the second surface located in the single-surface area is recessed toward the first surface to form a plurality of first recessed portions; the depth h1 of the first recessed portions is 2 μm-30 μm;

[0009] The negative electrode sheet comprises a straight region and a bending region, the first end of the first negative electrode active layer and the first end of the second negative electrode active layer are respectively located in different bending regions, and along the thickness direction of the winding core, the projections of the first end of the first negative electrode active layer and the first end of the second negative electrode active layer overlap;

[0010] The electrolyte includes fluoroethylene carbonate, and the mass proportion of fluoroethylene carbonate is 0.5% to 4% based on the total mass of the electrolyte.

[0011] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0012] (1) The wound lithium-ion battery provided by the present invention has a concave portion and a projection of the negative electrode active layer that overlap and work together to significantly increase the amount of liquid retained in the center of the winding core, improve the wettability of the electrolyte, and thus improve the cycle performance of the battery and reduce lithium plating;

[0013] (2) The wound lithium-ion battery provided by the present invention adjusts the FEC content in the electrolyte to a lower range, which can reduce the corrosion of FEC on the negative electrode collector; the provision of a recessed portion on one side of the negative electrode sheet and the reduction of the FEC content in the electrolyte work together to further improve the cycle performance of the battery.

[0014] The endpoints and any values ​​of the range disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, in the absence of special instructions, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The figure shows a schematic diagram of the structure of the winding core in an example.

[0016] Figure 2 Shown is a schematic structural diagram of a negative electrode sheet in an example.

[0017] Figure 3 The figure shows a schematic diagram of a structure in which a recessed portion is provided on a single side of a negative electrode sheet in an example.

[0018] Figure 4 The figure shows a schematic diagram of a structure in which a concave portion and a convex portion are arranged on a single side of a negative electrode sheet in an example.

[0019] Figure 5 The figure shows a schematic diagram of a structure in which a negative electrode sheet is provided with a plurality of recessed grooves in an example.

[0020] Figure 6The figure shows a schematic diagram of the cross-sectional structure of a positive electrode sheet having a recessed portion and a raised portion in an example.

[0021] Figure 7 The figure shows a schematic diagram of the structure in which a positive electrode sheet is provided with a recessed portion and a raised portion in an example. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0023] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0024] In the present invention, the term "C4-C8 carboxylate" refers to a carboxylate in which the number of carbon atoms in the hydrocarbon group (i.e., the carbon chain connected to the carboxyl group) in the carboxylate molecule is between 4 and 8.

[0025] A first aspect of the present invention provides a wound lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound multiple times in a winding direction to form a winding core;

[0026] The negative electrode sheet comprises:

[0027] A negative electrode current collector layer, comprising a first surface and a second surface arranged opposite to each other along a second direction, wherein the first direction is perpendicular to the second direction;

[0028] A first negative electrode active layer located on the first surface and a second negative electrode active layer located on the second surface; along the first direction, the first end of the first negative electrode active layer exceeds the first end of the second negative electrode active layer; the portion where the first end of the first negative electrode active layer exceeds the first end of the second negative electrode active layer is a single-sided area of ​​the negative electrode sheet;

[0029] At least a portion of the second surface located in the single-surface area is recessed toward the first surface to form a plurality of first recessed portions; the depth h1 of the recessed portions is 2 μm-30 μm;

[0030] The negative electrode sheet comprises a straight region and a bending region, the first end of the first negative electrode active layer and the first end of the second negative electrode active layer are respectively located in different bending regions, and along the thickness direction of the winding core, the projections of the first end of the first negative electrode active layer and the first end of the second negative electrode active layer overlap;

[0031] The electrolyte includes fluoroethylene carbonate, and the mass proportion of fluoroethylene carbonate is 0.5% to 4% based on the total mass of the electrolyte.

[0032] Illustratively, based on the total mass of the electrolyte, the mass proportion of fluoroethylene carbonate may be, for example, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4.0%, preferably 0.5%-2%.

[0033] In the present invention, in the single-sided area of ​​the negative electrode sheet located at the center of the winding core, a plurality of recessed portions are provided on the side of the negative electrode current collector where the negative electrode active layer is not provided, and the recessed portions can store more electrolyte; at the same time, along the thickness direction of the winding core, the projections of the head end of the first negative electrode active layer and the head end of the second negative electrode active layer in different bending areas overlap, which can increase the gap in the center of the winding core and provide a larger liquid storage space to store more electrolyte. The overlapping of the recessed portions and the projection of the negative electrode active layer can work together to significantly increase the liquid retention amount in the center of the winding core, improve the wettability of the electrolyte, and thereby improve the cycle performance of the battery and reduce lithium plating.

[0034] In addition, fluoroethylene carbonate (FEC) in the electrolyte can generate a more stable and denser SEI film, effectively protecting the negative electrode and preventing further decomposition of the electrolyte; however, FEC will interact with the strong Lewis acid PF5 generated by the decomposition of LiPF6 under high temperature conditions, and then undergo a de-F reaction to generate HF, which will produce a corrosion reaction on the surface of the negative electrode current collector. Moreover, the arrangement of a recessed portion on the single-sided area of ​​the negative electrode sheet will increase the surface area of ​​the negative electrode current collector, further exacerbating the corrosion of the negative electrode current collector. The corrosion of the negative electrode current collector will increase the internal resistance of the battery, reduce the bonding force between the negative electrode active material and the negative electrode current collector, reduce the battery cycle capacity, and affect the safety of the battery. The present invention adjusts the FEC content in the electrolyte to between 0.5% and 4%, which can not only ensure that FEC participates in the formation of the negative electrode SEI film, but also reduce the corrosion of FEC on the negative electrode current collector; the arrangement of a recessed portion on the single-sided area of ​​the negative electrode sheet and the reduction of the FEC content in the electrolyte, the two work together to further improve the cycle performance of the battery.

[0035] The present invention increases the liquid storage space in the middle of the battery cell by adjusting the design of the winding core structure, thereby improving the liquid storage capacity of the battery.

[0036] In some embodiments, Figure 1 As shown, the positive electrode sheet 1, the separator 2 and the negative electrode sheet 3 are stacked and wound multiple times along the winding direction to form a winding core, and the winding direction is the length direction (first direction) of the negative electrode sheet 3. The negative electrode sheet 3 at the center of the winding core includes a section of negative electrode current collector empty foil area 31 (such as Figure 1 ), and a single-sided region 32 with a negative electrode active layer on one side (as shown in red line Figure 1 shown by the green line).

[0037] In some embodiments, the structure of the negative electrode sheet when it is not wound is as follows Figure 2As shown, the negative electrode sheet 3 includes a negative electrode current collector layer 33, a first negative electrode active layer 34 and a second negative electrode sheet active layer 35; along the second direction, the negative electrode current collector layer 33 includes a first surface 331 and a second surface 332, the first negative electrode active layer 34 is located on the first surface 331, and the second negative electrode active layer 35 is located on the second surface 332. Figure 1 and Figure 2 As shown, when the negative electrode sheet 3, the positive electrode sheet 1 and the separator 2 are wound together to form a core, the leading end of the first negative electrode active layer 34 will exceed the leading end of the second negative electrode active layer 35 to form a single-sided area 32, that is, in the single-sided area 32, only the first surface 331 of the negative electrode collector layer 33 is provided with the first negative electrode active layer 34, and the second surface 332 is the exposed negative electrode collector layer 33 (also called empty foil).

[0038] In some embodiments, a part or all of the second surface of the single-sided region is recessed toward the first surface to form a plurality of first recessed portions.

[0039] In some embodiments, the depth h1 of the first recessed portion is 2 μm-30 μm, for example, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm or any point value in the range of any two of the above points, preferably 5 μm-20 μm. The "depth of the first recessed portion" can be interpreted as the maximum vertical distance (along the second direction) from the top of the first recessed portion close to the negative electrode current collector to the second surface of the negative electrode sheet, such as Figure 3 As shown in h1 in . When the depth of the first concave portion is further adjusted to meet the above range, it is possible to avoid the situation where the depth of the first concave portion is too deep, resulting in a fragile structure of the concave portion, which is easily broken by mechanical extrusion and wear, and the negative electrode active particles are reduced in lithium insertion and extraction rate and the negative electrode active material is pulverized, and the SEI film is continuously broken and regenerated, affecting the thickness uniformity of the SEI film and the cycle performance of the battery; it is also possible to avoid the depth of the first concave portion being too shallow, unable to provide more liquid storage space, resulting in insufficient electrolyte retention, and more FEC needs to be added to reduce the decomposition of the electrolyte, but the increase in FEC content will lead to more serious corrosion of the negative electrode collector, which is not conducive to the formation of the SEI film and cannot effectively improve the cycle performance of the battery.

[0040] In some embodiments, the average spacing L1 of adjacent first recessed portions is 0.5 mm-10 mm, for example, it can be 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or any point value in the range of any two of the above point values, preferably 0.5 mm-4 mm. "The average spacing of adjacent first recessed portions" can be interpreted as the shortest straight distance between the edges of the two adjacent and closest first recessed portions on the surface of the negative electrode sheet in the length direction of the negative electrode sheet, recorded as the average spacing of adjacent first recessed portions, such as Figure 3 When the average spacing between adjacent first recessed portions is within the above range, the area of ​​the first recessed portions can be controlled, the arrangement density is within a suitable range, and the number of the first recessed portions is controlled, which can effectively improve the storage of the electrolyte and the wettability of the electrolyte, and avoid the problem of instability of the single-sided structure of the negative electrode sheet caused by too small an average spacing.

[0041] In some embodiments, the diameter D1 of the first recessed portion is 0.2 mm-6 mm, for example, 0.2 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm or any point value in the range of any two of the above points, preferably 0.3 mm-2 mm. The "diameter of the first recessed portion" can be interpreted as the maximum straight-line distance between the two edges of a first recessed portion in a direction parallel to the negative electrode sheet, such as Figure 3 As shown in D1. When the diameter of the first recessed portion is further adjusted within the above range, it is possible to avoid the first recessed portion having a too large diameter, which may cause physical structural damage to the negative electrode single-sided area and cause the recessed portion structure to break, and cause the negative electrode active particles to insert and extract lithium at a reduced rate and the negative electrode active material to pulverize, and cause the SEI film to continuously break and regenerate, affecting the thickness uniformity of the SEI film and the battery cycle performance; it is also possible to avoid the diameter being too small, which may not provide more liquid storage space, resulting in insufficient electrolyte retention, and the need to add more FEC to reduce the decomposition of the electrolyte, but the increase in FEC content may lead to more serious corrosion of the negative electrode collector, which is not conducive to the formation of the SEI film and cannot effectively improve the battery cycle performance.

[0042] In some embodiments, Figure 3As shown, in the single-sided area 32 of the negative electrode sheet 3, at least part of the second surface 332 is recessed toward the first surface 331 to form a plurality of first recessed portions 4, and a plurality of first raised portions 5 are correspondingly arranged on the first surface 331. The first recessed portions 4 and the first raised portions 5 can be arranged by an embossing process, and the gap directly formed by the plurality of raised portions 5 on the first surface 331 and the positive electrode sheet 1 can also provide more liquid storage space, further improving the liquid retention of the wound battery.

[0043] In some embodiments, the outer surface of the first protrusion has a first circumscribed sphere, the inner surface of the first protrusion has a second circumscribed sphere, and the first circumscribed sphere and the second circumscribed sphere are arranged with the same sphere center; the radius of the first circumscribed sphere is recorded as R1 mm, and the radius of the second circumscribed sphere is recorded as R2 mm; the relationship between R1 and R2 satisfies: R1 / R2=1.01~1.1. The ratio of R1 / R2 can be, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, or any point value in the range of the above two point values.

[0044] In some embodiments, Figure 4 As shown, the outer surface of the first protrusion 5 has a first circumscribed ball 51, and the inner surface of the first protrusion 5 has a second circumscribed ball 52, and the first circumscribed ball 51 and the second circumscribed ball 52 are arranged with the same sphere center. The radius of the first circumscribed ball 51 is R1, and when R1 / R2 meets the above range, it can avoid that the R1 / R2 ratio is too large, that is, the flatness of the first protrusion is too large, so that the gap formed by the several protrusions on the first surface and the positive electrode sheet is small, resulting in insufficient electrolyte retention, and more FEC needs to be added to reduce the decomposition of the electrolyte, but the increase in FEC content will lead to more serious corrosion of the negative electrode collector, which is not conducive to the formation of the SEI film and cannot effectively improve the cycle performance of the battery.

[0045] In some embodiments, the radius R1 of the first circumscribed sphere is 0.15 mm to 3 mm, for example, R1 can be 0.15 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, or any point value in the range of any two of the above values. The radius R2 of the second circumscribed sphere is 0.01 mm to 3 mm, for example, R2 can be 0.01 mm, 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, or any point value in the range of any two of the above values. By limiting the diameters of the inner and outer surfaces of the first protrusion, the projection area of ​​the first protrusion in the direction perpendicular to the thickness of the negative electrode sheet can be adjusted. When R1 is less than 0.1 mm or R2 is less than 0.1 mm, the projection area of ​​the protrusion is too small, and the protrusions are too sharp, which may easily cause damage to the negative electrode sheet; when R1 is greater than 3 mm or R2 is greater than 3 mm, the projection area of ​​the protrusion is too large, which may cause the protrusion to be excessively deformed under the action of extrusion force, extension force and cyclic expansion force during formation during the manufacturing process, thereby causing the structure of the protrusion to collapse.

[0046] In some embodiments, Figure 4 As shown, the distance between the top of the first protrusion 5 and the common sphere center is R3mm, and the height h2 of the first protrusion 5 is the maximum outer surface radius R3 of the first protrusion 5 minus the thickness H1 of the single-sided area of ​​the negative electrode sheet. The height h2 of the first protrusion 5 is 2 μm-30 μm. When the height of the first protrusion meets the above range, it can avoid the situation that the height of the first protrusion is too high, causing the structure of the protrusion to be fragile, and the structure is easily broken by mechanical extrusion and wear, and the negative electrode active particles The rate of lithium insertion and extraction is reduced and the negative electrode active material is pulverized, and the SEI film is continuously ruptured and regenerated, affecting the thickness uniformity of the SEI film and affecting the cycle performance of the battery.

[0047] In some embodiments, the height h2 of the first protrusion is 2 μm-30 μm, for example, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm or any point value in the range of any two of the above points, preferably 5 μm-20 μm. The "height of the first protrusion" can be interpreted as the maximum vertical distance (along the second direction) from the top of the height of the first protrusion to the surface of the negative electrode active layer, such as Figure 3 As shown in h2.

[0048] In some embodiments, the average spacing L2 of adjacent first protrusions is 0.5 mm-10 mm, for example, 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or any point value in the range of any two of the above point values, preferably 0.5 mm-4 mm. "The average spacing of adjacent first protrusions" can be interpreted as the shortest straight distance between the edges of the two adjacent and closest first protrusions on the surface of the negative electrode sheet in the length direction of the negative electrode sheet, recorded as the average spacing of adjacent first protrusions, such as Figure 3 As shown in L2.

[0049] In some embodiments, the diameter D2 of the first protrusion is 0.2 mm-6 mm, for example, 0.2 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm or any point value in the range of any two of the above points, preferably 0.3 mm-2 mm. The "diameter of the first protrusion" can be interpreted as the maximum straight-line distance between the two edges of a first protrusion in a direction parallel to the negative electrode sheet, such as Figure 3 As shown in D2.

[0050] In some embodiments, in the single-sided area of ​​the negative electrode sheet, the first recessed portion and the first raised portion may be arranged in a uniformly spaced arrangement, or the arrangement may be adjusted according to actual needs, such as partially arranged in multiple rows and columns with uniform spacing, or partially arranged in multiple rows and columns with non-uniform spacing.

[0051] In some embodiments, the first concave portion or the first convex portion (embossing pattern) is a regular or irregular shape, such as a circle, a square, a hexagon, other regular shapes or irregular shapes, preferably a regular shape, such as preferably a circle.

[0052] In some embodiments, in the thickness direction of the negative electrode sheet, the first negative electrode active layer and / or the second negative electrode active layer are provided with a plurality of recessed grooves. Specifically, the plurality of recessed grooves may be provided only on the first negative electrode active layer, or the plurality of recessed grooves may be provided only on the second negative electrode active layer, or the plurality of recessed grooves may be provided on both the first negative electrode active layer and the second negative electrode active layer.

[0053] In some embodiments, Figure 5As shown, the first negative electrode active layer 34 or the second negative electrode active layer 35 is provided with a plurality of linear recessed grooves 36. The linear recessed grooves can be formed by laser drilling or wire punching. For example, laser drilling utilizes a high power density laser beam to irradiate the surface of the negative electrode sheet, so that the negative electrode active layer is quickly heated to the vaporization temperature, evaporated to form holes, and the electrolyte can quickly diffuse from the pores on the surface of the negative electrode active layer to the inside of the negative electrode, thereby improving the electrolyte infiltration ability.

[0054] In some embodiments, the recessed groove may be disposed in part or all of the first negative electrode active layer, and / or the recessed groove may be disposed in part or all of the second negative electrode active layer recessed groove. For example: the recessed groove may be disposed on the surface of the first negative electrode active layer located in the single-sided area, or on the entire surface of the first negative electrode active layer, or only on the surface of the first negative electrode active layer in the bending area. Another example: the recessed groove may be disposed on the entire surface of the second negative electrode active layer, or only on the surface of the second negative electrode active layer in the bending area. The location of the recessed groove in the first negative electrode active layer and the second negative electrode active layer may be selected as needed. The recessed groove may be disposed on the surface of the negative electrode active layer by laser, embossing, or the like.

[0055] In some embodiments, the width of the depressed groove is 30 μm to 170 μm (for example, it can be 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 110 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm or any point value in the range composed of any two of the above point values); and / or, the depth of the depressed groove is 3 μm to 60 μm (for example, it can be 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm or any point value in the range composed of any two of the above point values); and / or, the spacing of the depressed groove is 0.5 mm to 8 mm (for example, it can be 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm or any point value in the range composed of any two of the above point values). When the width, depth and spacing of the depression groove meet the above ranges, the depression groove, the first depression portion and the projection of the negative electrode active layer overlap and work together to store more electrolyte, further improve the wettability of the electrolyte, and further improve the cycle performance of the battery.

[0056] In some embodiments, Figure 6 and Figure 7As shown, in the thickness direction of the positive electrode sheet 1, the positive electrode sheet 1 includes a positive electrode current collector 11, and a positive electrode active layer 12 arranged on the two side surfaces of the positive electrode current collector 11. The positive electrode sheet 1 includes a third surface 13 and a fourth surface 14 arranged opposite to each other, and the third surface 13 is provided with a plurality of second protrusions 131 at intervals, and the fourth surface 14 is provided with a plurality of second recesses 141 correspondingly. In other embodiments, the fourth surface is provided with a plurality of second protrusions at intervals, and the third surface is provided with a plurality of second recesses correspondingly; wherein the thickness of the positive electrode sheet is recorded as H2 μm, the height of the second protrusion is recorded as h3 μm, L=h3 / H2, L=5%~30%.

[0057] For example, L can be 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 29%, 30%, or any point value in the range formed by any two of the above point values. By adjusting the ratio L of the height of the second protrusion to the thickness of the positive electrode sheet, a plurality of protrusion structures of appropriate sizes can be formed on the positive electrode sheet, thereby increasing the storage space of the electrolyte, promoting the uniform distribution and penetration of the electrolyte, and effectively improving the wettability of the positive electrode sheet.

[0058] The positive electrode sheet includes a third surface and a fourth surface. If embossing is performed from the third surface toward the fourth surface, a second protrusion will be formed on the fourth surface and a second depression will be formed on the third surface; conversely, a second depression will be formed on the fourth surface and a second protrusion will be formed on the third surface. The positive electrode sheet contains a second protrusion and correspondingly also contains a second depression. The space formed by the second depression and the second protrusion can improve the wettability of the electrolyte, improve the distribution of the electrolyte, increase the liquid storage capacity of the battery, and further improve the cycle performance of the battery.

[0059] In some embodiments, the height h3 of the second protrusion and / or the depth of the second depression is 2 μm-30 μm, for example, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm or any point value in the range of any two of the above point values, preferably 5 μm-20 μm. The "height of the second protrusion" can be interpreted as the maximum vertical distance (along the thickness direction) from the top of the height of the second protrusion to the third surface of the positive electrode sheet, such as Figure 7 The “depth of the second recessed portion” can be interpreted as the maximum vertical distance (along the thickness direction) from the top of the second recessed portion to the fourth surface of the positive electrode sheet, as shown in h3 in FIG. Figure 7 As shown in h4.

[0060] In some embodiments, the average spacing M1 of adjacent second protrusions or the average spacing M2 of adjacent second recesses is 0.5 mm-10 mm, for example, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm or any point value in the range composed of any two of the above point values; "the average spacing of adjacent second protrusions" can be interpreted as the shortest straight distance between the edges of two adjacent and nearest second protrusions on the surface of the positive electrode sheet in the length direction of the positive electrode sheet, such as Figure 7 As shown in M1; "the average spacing between adjacent second recessed portions" can be interpreted as the shortest straight distance between the edges of two adjacent and closest second recessed portions on the surface of the positive electrode sheet in the length direction of the positive electrode sheet, such as Figure 7 As shown in M2.

[0061] In some embodiments, the diameter N1 of the second protrusion and / or the diameter N2 of the second depression is 0.2 mm-6 mm, for example, 0.2 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, or any point value in the range of any two of the above point values. The "diameter of the second protrusion" or "diameter of the second depression" can be interpreted as the maximum straight-line distance between the two edges of two adjacent second protrusions or two adjacent second depressions in the direction parallel to the positive electrode sheet, such as Figure 1 As shown in the figure, N1 and N2 are shown.

[0062] In the positive electrode sheet, when the second protrusion and the second recess meet the above conditions, the recess is set in the single-sided area of ​​the negative electrode sheet, and the projection of the negative electrode active layer overlaps to further increase the battery's liquid retention capacity, improve the electrolyte wettability and long cycle performance.

[0063] In some embodiments, the positive electrode sheet includes a positive electrode collector and a positive electrode active layer disposed on the surface of at least a portion of the positive electrode collector, and the positive electrode active layer includes lithium iron phosphate. The lithium iron phosphate battery has good cycle performance and safety performance and relatively low cost.

[0064] In some embodiments, the Dv50 of the lithium iron phosphate is 0.5 μm to 2 μm (for example, Dv50 is 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.8 μm, 2.0 μm, or any point value in the range consisting of any two of the above points). When the Dv50 of the lithium iron phosphate particles is within the above range, the lithium ion diffusion path is shorter, which can enhance the battery rate performance.

[0065] In some embodiments, the specific surface area of ​​the lithium iron phosphate is 5 m 2 / g~20 m 2 / g (e.g., a specific surface area of ​​5 m 2 / g, 8 m 2 / g, 10 m 2 / g, 12 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 18 m 2 / g, 20 m 2 / g or any point value in the range formed by any two of the above point values). When the specific surface area of ​​the lithium iron phosphate particles is within the above range, the side reaction between the lithium iron phosphate active material and the electrolyte is less, which is beneficial to improving the cycle performance of the battery.

[0066] In some embodiments, the compaction density of the positive electrode sheet is 2.5 g / cm 3 ~3 g / cm 3 , and / or, the single-sided surface density of the positive electrode sheet is 20 mg / cm 2 ~40 mg / cm 2 .

[0067] In some embodiments, the compaction density of the negative electrode sheet is 1.6 g / cm 3 ~1.9 g / cm 3 And / or, the single surface density of the negative electrode sheet is 8 mg / cm 2 ~18 mg / cm 2 .

[0068] When the active material of the positive electrode includes lithium iron phosphate, since the specific capacity of lithium iron phosphate itself is relatively low, in order to improve the overall energy density of the battery cell, the present invention adjusts the compaction density and surface density of the positive and negative electrodes within the above range. With the increase of the compaction density and surface density of the positive and negative electrodes, the dynamics of the battery will decrease, and the electrolyte infiltration will be difficult; the present invention can increase the liquid retention of the positive electrode pores, the negative electrode pores, and the diaphragm pores by setting a first recessed portion and a recessed groove on the negative electrode sheet, and setting a second recessed portion on the positive electrode sheet, reduce the impedance of each interface, accelerate the conduction of lithium ions, and improve the cycle performance of the battery.

[0069] Although increasing the compaction density of the positive and negative electrodes can increase the energy density of the battery, it will cause the wettability of the electrolyte and the active material to deteriorate. Uneven electrolyte infiltration will lead to uneven current density distribution, and the formed electrolyte interface film (SEI) will be unstable, affecting the battery cycle performance. At the same time, incomplete electrolyte infiltration directly affects the performance of the battery, leading to the occurrence of lithium precipitation and causing a series of safety issues. To solve these problems, the present invention further proposes the following solutions:

[0070] In some embodiments, the battery includes an electrolyte, the electrolyte includes a first solvent and a second solvent; the first solvent includes ethylene carbonate; the second solvent includes at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0071] In some embodiments, the total mass of the first solvent and the second solvent accounts for ≥60% of the total mass of the electrolyte, and the mass ratio of the first solvent to the second solvent is 0.2 to 0.6, for example, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6 or any point value in the range of the above two point values. The viscosity of ethylene carbonate in the first solvent is lower than the viscosity of the several carbonates listed in the second solvent. When the mass ratio of the first solvent and the second solvent is adjusted within the above range, the viscosity of the electrolyte can be reduced, the fluidity of the electrolyte can be improved, the wettability of the electrolyte can be improved, the problem of poor wettability caused by the increase in the compaction density of the positive and negative electrodes can be alleviated, lithium precipitation can be reduced, and the safety performance of the battery can be improved.

[0072] In some embodiments, the electrolyte includes a third solvent, and the third solvent includes a C4-C8 carboxylate; the total mass of the third solvent accounts for 0-20% of the total mass of the electrolyte. The C4-C8 carboxylate has a relatively low viscosity. Adding the C4-C8 carboxylate to the electrolyte can maintain a relatively low viscosity of the electrolyte, further improve the fluidity of the electrolyte, and help improve the wettability of the electrolyte, so that the electrolyte can more easily penetrate into the middle of the core, overlap with the first recessed portion in the center of the core and the projection of the negative electrode active layer, increase the liquid retention of the battery, increase the transmission rate of lithium ions, and ensure the uniformity of the transmission rate of lithium ions in the thickness direction of the battery, thereby improving the high-rate cycle performance of the battery.

[0073] In some embodiments, the C4-C8 carboxylic acid ester includes at least one of propyl propionate, ethyl propionate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, and propyl butyrate.

[0074] In some embodiments, the negative electrode active material includes a silicon material, and the silicon material includes at least one of silicon oxygen, silicon carbon, nano silicon, and a silicon alloy.

[0075] In some embodiments, the negative electrode active material further includes a carbon material, and the carbon material includes at least one of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0076] In some embodiments, the negative electrode active material includes a carbon material and a silicon material, and the mass proportion of silicon element is 1-30%.

[0077] The test method for the content ratio of silicon element can be tested by thermogravimetric analysis, for example, using Shimadzu DTG-60 thermogravimetric analyzer for testing. The test conditions include: sample weight 5 mg, air as atmosphere, heating rate 10℃ / min from room temperature to 900℃ and constant temperature for 40 min. The relationship between the mass ratio of silicon-carbon material (denoted as x) and the final weight residual percentage of the entire test (denoted as y) is: x=7y / 15.

[0078] In some embodiments, the negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder. The types of the negative electrode conductive agent and the negative electrode binder are not specifically limited, and conventional conductive agents and binders in the art can be selected. The types of the negative electrode conductive agent include but are not limited to at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder. The negative electrode binder includes butadiene styrene rubber emulsion, polytetrafluoroethylene emulsion, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxylated chitosan.

[0079] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent is not specifically limited, for example, conventional conductive agents in the art can be selected, including but not limited to acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, graphene, one or more. The positive electrode binder is not specifically limited, for example, conventional binders in the art can be selected, including but not limited to one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyethylene oxide.

[0080] In the present invention, the type of the diaphragm is not specifically limited. For example, conventional lithium-ion battery diaphragms in the art can be selected, including but not limited to woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, diaphragm paper, rolled membranes, polyethylene microporous membranes, polypropylene microporous membranes, etc.

[0081] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0083] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0084] Example 1-1:

[0085] 1. Preparation of positive electrode

[0086] Lithium iron phosphate, conductive agent and PVDF were placed in NMP at a mass ratio of 97.60:1.35:1.05 and stirred evenly to prepare a positive electrode slurry; the positive electrode slurry was evenly coated on the front and back sides of the aluminum foil, and the coating surface density was 0.02 g / cm 2 ; After drying and roller pressing (roller pressing compaction is 2.65 g / cm 3 ) and cut to obtain a positive electrode sheet; the thickness H2 of the positive electrode sheet is 100 microns.

[0087] 2. Preparation of negative electrode sheet

[0088] Artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose were placed in deionized water at a mass ratio of 97.2:0.5:1.3:1; the above slurry was stirred evenly to obtain a negative electrode slurry; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil, and the coating surface density was 8.1 g / cm2， After drying and roller pressing (roller pressing compaction is 1.73 g / cm 3 ) and slitting to obtain a negative electrode sheet; a special roller containing convex portions is used to perform convex portion processing on a single-side area of ​​the slit negative electrode sheet, and embossing is performed from the side of the exposed copper foil to the side of the negative electrode slurry, the depth h1 of the first concave portion is 10 μm, the average spacing L1 between adjacent first concave portions is 3.0 mm, and the diameter D1 of the first concave portion is 1.0 mm. The depth h2 of the first convex portion is 20 μm, the average spacing L2 between adjacent first convex portions is 3.0 mm, and the diameter D2 of the first convex portion is 1.0 mm.

[0089] 3. Preparation of diaphragm

[0090] The diaphragm of the present application adopts a 5 μm thick substrate + 2 μm boehmite + 2 μm PVDF.

[0091] 4. Preparation of electrolyte

[0092] The electrolyte includes lithium salt LiPF6, solvent, additives vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS) and diethylene sulfate (DTD), the solvent includes vinyl carbonate (EC) and ethyl methyl carbonate (EMC), and the mass ratio of the two is EC:EMC=3:7; the contents of VC, FEC, PS and DTD in the electrolyte are 1.5%, 1%, 1% and 0.5% respectively.

[0093] 5. Preparation of lithium-ion batteries

[0094] The above-cut positive electrode sheets, separators and negative electrode sheets are stacked in sequence and wound into a wound-type battery cell. The projections of the first end of the first negative electrode active layer and the first end of the second negative electrode active layer overlap along the thickness direction of the winding core. The battery cell is packaged, injected, formed, and sealed again to obtain a lithium-ion battery.

[0095] 6. Battery performance test:

[0096] (1) Calculation of liquid retention coefficient: Liquid retention coefficient = liquid retention volume / battery capacity. A certain amount of electrolyte is injected according to the production process, and then the battery undergoes formation and sorting, and part of the electrolyte will be consumed. During the secondary sealing process, the excess electrolyte will be extracted and packaged. Liquid retention volume = battery cell mass + electrolyte injection volume - battery cell mass after secondary sealing.

[0097] (2) 25℃ cycle test

[0098] Test the thickness D0 of the fully charged cell. Place the battery in a (25±3)℃ environment. Charge the battery to 3.65V at 2C and 2.5C constant currents. Charge it to a cutoff current of 0.05C at 3.65V constant voltage. Discharge it at 0.5C. Record the initial capacity Q0. Follow the steps in the above instructions to cycle 2000 times. Use the discharge capacity as the battery capacity Q3. Calculate the capacity retention rate (%). Then fully charge the battery, take out the cell, test the fully charged thickness D3, calculate the thickness change rate (%), and record the result. The calculation formula used is as follows:

[0099] Thickness change rate (%) = (D3-D0) / D0×100%; Capacity retention rate (%) = Q3 / Q0×100%.

[0100] (3) 45℃ cycle test:

[0101] Test the thickness D0 of the fully charged cell. Place the battery in a (45±3)℃ environment. Charge the battery to 3.65V at 2C constant current. Charge it to a cutoff current of 0.05C at 3.65V constant voltage. Discharge it at 0.5C. Record the initial capacity Q0. Cycle it 1500 times according to the steps in the above description. Take the discharge capacity as the capacity Q3 of the battery. Calculate the capacity retention rate (%). Then fully charge the battery. After taking out the cell, test the fully charged thickness D3. Calculate the thickness change rate (%). Record the results as shown in Table 2. The calculation formula used is as follows:

[0102] Thickness change rate (%) = (D3-D0) / D0×100%; Capacity retention rate (%) = Q3 / Q0×100%.

[0103] The groups of Examples 1-4 and Comparative Examples 1-6 are carried out with reference to Example 1-1, and the main differences are shown in Table 1. Among them, the depth h1 of the first recessed portion is changed in the group of Example 1 and Comparative Examples 1 and 2. The average spacing L1 between adjacent first recessed portions is changed in the group of Example 2. The diameter D1 of the first recessed portion is changed in the group of Example 3. The mass proportion of fluoroethylene carbonate (FEC) in the electrolyte is changed in the group of Example 4 and Comparative Examples 2 and 3. For Comparative Example 1, the L value is too small and is not within the protection range. In Comparative Example 5, the first recessed portion is not set on the negative electrode sheet, and in Comparative Example 6, the projections of the head end of the first negative electrode active layer and the head end of the second negative electrode active layer do not overlap.

[0104] Table 1

[0105]

[0106] Note: “ / ” indicates the corresponding parameter of the measurement.

[0107] It can be seen from Table 1 that in the wound lithium-ion battery provided by the present invention, the overlapping of the recessed portion and the projection of the negative electrode active layer can increase the liquid retention in the center of the core, improve the wettability of the electrolyte, improve the cycle performance of the battery, and reduce battery expansion.

[0108] The fifth embodiment was carried out with reference to the first embodiment 1-1, and the main differences are shown in Table 2. The fifth embodiment changed the radius R1 and the radius R2 of the first protrusion.

[0109] Table 2

[0110]

[0111] It can be seen from Table 2 that when R1 and R2, as well as R1 / R2, are limited to meet the protection scope of the present invention, the cycle performance of the battery can be improved and the battery expansion can be reduced.

[0112] The sixth embodiment was carried out with reference to the first embodiment, and the main differences are shown in Table 3. In the sixth embodiment, the cut negative electrode sheet was laser grooved, and grooves were set on the entire surface of the negative electrode sheet, where the grooves were matrix grooves; the laser-treated negative electrode sheet was cleaned and sheeted to obtain a negative electrode sheet. In the sixth embodiment, the width, depth and spacing of the concave grooves were changed.

[0113] Table 3

[0114]

[0115] It can be seen from Table 3 that the overlapping effect of the depression groove, the first depression portion and the projection of the negative electrode active layer can further improve the liquid retention of the battery and further improve the cycle performance of the battery.

[0116] The Example 7 group was carried out with reference to the Example 1-1, and the main differences are shown in Table 4. Among them, the cut positive electrode sheet was processed with a special roller containing a convex portion, and the depth of the second concave portion in Example 7-1 was 20 μm, the average spacing of the second concave portion was 230 μm, and the diameter of the second concave portion was 100 μm. In Examples 7-2 to 7-5, the depth of the second concave portion was changed.

[0117] Table 4

[0118]

[0119] It can be seen from Table 4 that when the second protrusion and the second depression are embossed in the positive electrode sheet and meet the conditions of the present invention, the negative electrode sheet is provided with a depression on one side, and the projection of the negative electrode active layer overlaps, which can further increase the liquid retention of the battery and enhance the long cycle performance of the battery.

[0120] The Example 8 group was carried out with reference to the Example 1-1, and the main differences are shown in Table 5. Among them, the Example 8 group changed the Dv50 and specific surface area of ​​the lithium iron phosphate.

[0121] Table 5

[0122]

[0123] It can be seen from Table 5 that when the Dv50 and specific surface area of ​​the lithium iron phosphate particles are within the range of the present invention, the rate performance and cycle performance of the battery can be better.

[0124] Example 9 and Example 10 were carried out with reference to Example 1-1, and the main differences are shown in Table 6. In Example 9, the ratio of the first solvent and the second solvent was changed, and the type of the second solvent was changed. In Example 9-3, the second solvent was a combination of ethyl methyl carbonate (accounting for 60%) and dimethyl carbonate (accounting for 10%); in Example 9-4, the second solvent was a combination of ethyl methyl carbonate (accounting for 60%), dimethyl carbonate (accounting for 5%) and diethyl carbonate (accounting for 5%). In Example 10, carboxylic acid esters were also added to the electrolyte, wherein ethyl acetate was added in Example 10-1; the amount of carboxylic acid esters added was changed in Example 10-2; ethyl propionate was added in Example 10-3; and a combination of ethyl propionate (accounting for 5%) and propyl propionate (accounting for 5%) was added in Example 10-4.

[0125] Table 6

[0126]

[0127] It can be seen from Table 6 that the combination of the first solvent and the second solvent in the electrolyte can increase the battery's liquid retention capacity and improve the battery's cycle performance. Adding a carboxylate solvent to the electrolyte can improve the battery's high-rate cycle performance.

[0128] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0129] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A wound lithium-ion battery, characterized in that: It includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound multiple times in a winding direction to form a winding core; The negative electrode sheet comprises: A negative electrode current collector layer, comprising a first surface and a second surface arranged opposite to each other along a second direction, wherein the first direction is perpendicular to the second direction; A first negative electrode active layer located on the first surface and a second negative electrode active layer located on the second surface; along the first direction, the first end of the first negative electrode active layer exceeds the first end of the second negative electrode active layer; the portion where the first end of the first negative electrode active layer exceeds the first end of the second negative electrode active layer is a single-sided area of ​​the negative electrode sheet; At least a portion of the second surface located in the single-surface area is recessed toward the first surface to form a plurality of first recessed portions; the depth h1 of the first recessed portions is 2 μm-30 μm; The negative electrode sheet comprises a straight region and a bending region, the first end of the first negative electrode active layer and the first end of the second negative electrode active layer are respectively located in different bending regions, and along the thickness direction of the winding core, the projections of the first end of the first negative electrode active layer and the first end of the second negative electrode active layer overlap; The electrolyte includes fluoroethylene carbonate, and the mass proportion of fluoroethylene carbonate is 0.5% to 4% based on the total mass of the electrolyte.

2. The battery according to claim 1, characterized in that The average spacing L1 between adjacent first recessed portions is 0.5 mm to 10 mm; And / or, the diameter D1 of the first recessed portion is 0.2 mm-6 mm.

3. The battery according to claim 1, characterized in that The depth h1 of the first recessed portion is 5 μm-20 μm; and / or, an average spacing L1 between adjacent first recessed portions is 0.5 mm to 4 mm; And / or, the diameter D1 of the first recessed portion is 0.3 mm-2 mm.

4. The battery according to claim 1, characterized in that In the single-surface area, at least a portion of the second surface is recessed toward the first surface to form a plurality of first recessed portions, and a plurality of first raised portions are correspondingly arranged on the first surface; The outer surface of the first protrusion has a first circumscribed ball, the inner surface of the first protrusion has a second circumscribed ball, and the first circumscribed ball and the second circumscribed ball are arranged with the same sphere center; The radius of the first circumscribed sphere is recorded as R1 mm, and the radius of the second circumscribed sphere is recorded as R2 mm; the relationship between R1 and R2 satisfies: R1 / R2=1.01~1.1; R1 is 0.15 mm~3 mm and / or R2 is 0.01 mm~3 mm.

5. The battery according to claim 1, characterized in that In the thickness direction of the negative electrode sheet, the first negative electrode active layer and / or the second negative electrode active layer is provided with a plurality of concave grooves; The width of the concave groove is 30 μm to 170 μm; and / or, the depth of the concave groove is 3 μm to 60 μm; and / or, the spacing between the concave grooves is 0.5 mm to 8 mm.

6. The battery according to claim 5, characterized in that The width of the concave groove is 40 μm to 100 μm; and / or, the depth of the concave groove is 3 μm to 30 μm; and / or, the spacing between the concave grooves is 1 mm to 5 mm.

7. The battery according to claim 1, characterized in that In the thickness direction of the positive electrode sheet, the positive electrode sheet includes a third surface and a fourth surface arranged opposite to each other, the third surface is provided with a plurality of second protrusions at intervals, and the fourth surface is provided with a plurality of second recesses correspondingly; and / or the fourth surface is provided with a plurality of second protrusions at intervals, and the third surface is provided with a plurality of second recesses correspondingly; The thickness of the positive electrode sheet is recorded as H2 μm, the height of the second protrusion is recorded as h3 μm, L=h3 / H2, L=5%~30%.

8. The battery according to any one of claims 1 to 7, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on the surface of at least a portion of the positive electrode current collector, wherein the positive electrode active layer includes lithium iron phosphate; The Dv50 of the lithium iron phosphate is 0.5 μm to 2 μm; The specific surface area of ​​the lithium iron phosphate is 5 m 2 / g~20 m 2 / g.

9. The battery according to any one of claims 1 to 7, characterized in that: The compaction density of the positive electrode sheet is 2.5 g / cm 3 ~3 g / cm 3 ; And / or, the single-sided surface density of the positive electrode sheet is 20 mg / cm 2 ~40 mg / cm 2 ; And / or, the compaction density of the negative electrode sheet is 1.6 g / cm 3 ~1.9 g / cm 3 ; And / or, the single surface density of the negative electrode sheet is 8 mg / cm 2 ~18 mg / cm 2 .

10. The battery according to any one of claims 1 to 7, characterized in that: The battery includes an electrolyte, the electrolyte including a first solvent and a second solvent; The first solvent comprises ethylene carbonate; The second solvent comprises at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate; The ratio of the total mass of the first solvent and the second solvent to the total mass of the electrolyte is ≥ 60%; The mass ratio of the first solvent to the second solvent is 0.2-0.

6.

11. The battery according to claim 10, characterized in that The electrolyte includes a third solvent, and the third solvent includes a C4-C8 carboxylic acid ester; The ratio of the total mass of the third solvent to the total mass of the electrolyte is 0-20%; The C4-C8 carboxylic acid ester includes at least one of propyl propionate, ethyl propionate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, and propyl butyrate.

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