A battery

Abstract

The application provides a battery, an electrode assembly of which is formed by stacking a positive electrode sheet, a separator and a negative electrode sheet, the positive electrode sheet comprises two single-sided positive electrode sheets located at the outermost sides and at least one double-sided positive electrode sheet located at the inner side; the single-sided positive electrode sheet is provided with a first positive electrode active layer on one side close to the center of the electrode assembly, and the double-sided positive electrode sheet is provided with a second positive electrode active layer on both sides; the negative electrode sheet comprises a negative electrode current collector and negative electrode active layers on both sides of the negative electrode current collector, wherein the surface of the first negative electrode active layer opposite to the single-sided positive electrode sheet comprises a first groove, and at least one surface of the second negative electrode active layer opposite to the double-sided positive electrode sheet comprises a second groove, and the battery satisfies the relationship formula: 0 2 −h 1 , h 1 is the depth of the first groove, and h 2 is the depth of the second groove. The battery of the application can optimize the distribution of the electrolyte of the negative electrode active layer, and is beneficial to improving the cycle stability and safety of the battery.

Description

Technical Field

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

[0002] As the mainstream electrochemical energy storage device, the cycle life and reliability of lithium-ion batteries are the core performance indicators.

[0003] However, during battery cycling, the negative electrode active material in the negative electrode sheet is prone to volume expansion, leading to the separation of the negative electrode active layer from the negative electrode current collector, which damages the integrity of the electrode structure. Furthermore, as the electrode sheet compaction density and active layer thickness increase, the penetration path of the electrolyte into the electrode becomes longer, the wetting resistance increases, and the lithium-ion transport performance of the battery decreases, reducing the battery's cycle stability and safety. Therefore, laser wire drilling is often performed on the surface area of ​​the negative electrode active layer to form grooves (or trenches, recesses) with a certain depth and width. This alleviates the internal stress caused by the volume change of the negative electrode active material during charging and discharging, while improving the electrolyte wetting and ion transport of the negative electrode sheet, thereby improving the battery's cycle life and reliability. Summary of the Invention

[0004] In the practical application of wire bonding of the negative electrode active layer, it was found that after long-term cycling of stacked batteries, the negative electrode platform area (excluding the area of ​​the groove and the area between adjacent grooves) opposite to the single positive electrode sheet of the stacked battery is prone to severe purple spots caused by electrolyte shortage or even drying. In contrast, the negative electrode area opposite to the double positive electrode sheets shows normal or mild purple spots. These purple spots seriously affect the battery capacity retention, safety and cycle performance consistency.

[0005] To address the issues of purple spots or lithium plating appearing in the negative electrode plateau region corresponding to a single-sided positive electrode in existing stacked batteries, this invention provides a battery. The battery of this invention can alleviate the internal stress caused by volume changes in the negative electrode active material, while effectively mitigating the electrolyte shortage problem in the negative electrode plateau region corresponding to a single-sided positive electrode in stacked batteries, reducing the generation of purple spots, and improving the battery's cycle stability and safety.

[0006] To achieve the above objectives, the present invention provides a battery comprising a stacked electrode assembly, the electrode assembly comprising a positive electrode, a separator, and a negative electrode stacked together. In the thickness direction of the electrode assembly, the positive electrode comprises two single-sided positive electrode sheets located on the outermost sides of the electrode assembly and at least one double-sided positive electrode sheet located inside the electrode assembly. The single-sided positive electrode sheet comprises a first positive current collector and a first positive active layer located on the side surface of the first positive current collector near the center of the electrode assembly. The double-sided positive electrode sheet comprises a second positive current collector and second positive active layers located on both sides of the second positive current collector. The negative electrode sheet includes a negative electrode current collector and negative electrode active layers respectively located on both surface sides of the negative electrode current collector. The negative electrode active layer corresponding to the single-sided positive electrode sheet is the first negative electrode active layer, and the negative electrode active layer corresponding to the double-sided positive electrode sheet is the second negative electrode active layer. The surface of the first negative electrode active layer away from the negative electrode current collector is the first surface, and the first surface includes a first groove. The surface of the second negative electrode active layer away from the negative electrode current collector is the second surface, and at least one of the second surfaces includes a second groove. The battery satisfies the relational expression: 0 < a ≤ 25 μm, where a = h - h 1 , h 1 is the depth of the first groove, and h 2 is the depth of the second groove.

[0007] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: By controlling the battery to satisfy the relational expression: 0 < a ≤ 25 μm, the present invention enables the first negative electrode active layer corresponding to the single-sided positive electrode sheet to have a first groove with a relatively shallow depth, and the second negative electrode active layer corresponding to the double-sided positive electrode sheet to have a relatively deep second groove, realizing differential regulation of the distribution and storage capacity of the electrolyte in the first negative electrode active layer and the second negative electrode active layer, reducing the depth of the first groove on the surface of the first negative electrode active layer and the accommodation capacity of the electrolyte. When the single-sided positive electrode sheet is subjected to pressure extrusion, the electrolyte can be more retained in the platform area on the surface of the first negative electrode active layer and will not be extruded into the first groove, effectively alleviating the problems of lack of electrolyte in the platform area of the first negative electrode active layer corresponding to the single-sided positive electrode sheet and the generation of purple spots. At the same time, it can also ensure that the internal stress caused by the volume change of the negative electrode active material is effectively alleviated and maintain good electrolyte wettability of the battery, so that the battery has both cycle stability and safety.

[0008] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section.

[0009] In the ranges disclosed herein, the endpoints and any values are not limited to the exact 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 each range, between the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The figure shows a three-dimensional view of the battery assembly of the present invention.

[0011] Figure 2The image shown is one of the cross-sectional schematic diagrams of the negative electrode sheet of the present invention.

[0012] Figure 3 The image shown is a second cross-sectional schematic diagram of the negative electrode sheet of the present invention.

[0013] Figure 4 The image shown is one of the surface schematic diagrams of the negative electrode sheet of the present invention.

[0014] Figure 5 The image shown is a second schematic diagram of the surface of the negative electrode sheet of the present invention.

[0015] Figure 6 The third schematic diagram of the surface of the negative electrode sheet of the present invention is shown.

[0016] Figure 7 The fourth schematic diagram shows the surface of the negative electrode sheet of the present invention.

[0017] Figure 8 The diagram shown is a cross-sectional schematic of the single-sided positive electrode sheet of the present invention undergoing warping deformation. 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 invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0020] This invention provides a battery comprising a stacked electrode assembly, the electrode assembly including a positive electrode, a separator, and a negative electrode stacked together. In the thickness direction of the electrode assembly, the positive electrode includes two single-sided positive electrode sheets located on the outermost sides of the electrode assembly and at least one double-sided positive electrode sheet located inside the electrode assembly. The single-sided positive electrode sheet includes a first positive current collector and a first positive active layer located on the side surface of the first positive current collector near the center of the electrode assembly. The double-sided positive electrode sheet includes a second positive current collector and second positive active layers located on both sides of the second positive current collector. The negative electrode sheet includes a negative electrode current collector and negative electrode active layers respectively located on both side surfaces of the negative electrode current collector. The negative electrode active layer corresponding to the single-sided positive electrode sheet is the first negative electrode active layer, and the negative electrode active layer corresponding to the double-sided positive electrode sheet is the second negative electrode active layer. The surface of the first negative electrode active layer away from the negative electrode current collector is the first surface, and the first surface includes a first groove. The surface of the second negative electrode active layer away from the negative electrode current collector is the second surface, and at least one of the second surfaces includes a second groove. The battery satisfies the relationship: 0 < a ≤ 25 μm (for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm or 25 μm), where a = h 2 -h 1 , h 1 is the depth of the first groove, and h 2 is the depth of the second groove.

[0021] According to a specific embodiment, as Figure 1 shown, the battery includes an electrode assembly 4 with a laminated structure. The electrode assembly 4 includes a positive electrode sheet 1, a separator 2, and a negative electrode sheet 3 stacked on top of each other. In the thickness direction W of the electrode assembly 4, the positive electrode sheet 1 includes 2 single-sided positive electrode sheets 11 located on the outermost sides of the electrode assembly and 1 double-sided positive electrode sheet 12 located inside the electrode assembly. The single-sided positive electrode sheet 11 includes a first positive electrode current collector 111 and a first positive electrode active layer 112 located on the side surface of the first positive electrode current collector close to the center of the electrode assembly; the double-sided positive electrode sheet 12 includes a second positive electrode current collector 121 and second positive electrode active layers 122 located on both side surfaces of the second positive electrode current collector; the negative electrode sheet 3 includes a negative electrode current collector 31 and negative electrode active layers 32 respectively located on both side surfaces of the negative electrode current collector. The negative electrode active layer corresponding to the single-sided positive electrode sheet 11 is the first negative electrode active layer 321, and the negative electrode active layer corresponding to the double-sided positive electrode sheet 12 is the second negative electrode active layer 322.

[0022] According to a specific embodiment, as Figure 2 shown, the surface of the first negative electrode active layer 321 away from the negative electrode current collector 31 is the first surface 3211, and the first surface 3211 includes a first groove 3212. As Figure 3 shown, the surface of the second negative electrode active layer 322 away from the negative electrode current collector 31 is the second surface 3221, and the second surface 3221 includes a second groove 3222. The battery satisfies the relationship: 0 < a ≤ 25 μm, where a = h 2 -h 1 , h1 h is the depth of the first groove. 2 The depth of the second groove.

[0023] In this invention, such as Figure 1 As shown, the surface of the first positive current collector 111 of the single-sided positive electrode 11 facing the outside of the battery assembly is an empty foil 113.

[0024] In this invention, the depth of the first groove refers to the maximum vertical distance from any point on the bottom of the first groove to the first surface in the thickness direction of the negative electrode sheet (e.g., ...). Figure 2 Chinese h 1 (As shown). When the number of the first grooves is greater than 1, the depth of the first groove is the average depth. For example, when the number of the first grooves is less than or equal to 20, the depth of the first groove is the average depth of all the first grooves; when the number of the first grooves is greater than 20, the depth of the first groove is the average depth of any 20 first grooves.

[0025] In this invention, the depth of the second groove refers to the maximum vertical distance from any point on the bottom of the second groove to the second surface in the thickness direction of the negative electrode sheet (e.g., ...). Figure 3 Chinese h 2 (As shown). When the number of the second grooves is greater than 1, the depth of the second groove is the average depth. For example, when the number of the second grooves is less than or equal to 20, the depth of the second groove is the average depth of all the second grooves; when the number of the second grooves is greater than 20, the depth of the second groove is the average depth of any 20 second grooves.

[0026] In this invention, the depth of the first groove and the depth of the second groove can both be measured by a 3D profilometer.

[0027] Research findings show that setting grooves on the surface of the negative electrode active layer is beneficial for alleviating the volume change stress of the negative electrode active material and improving the wettability of the battery. However, in a stacked battery, the single-sided positive electrode sheet only has a positive electrode active layer on one side of its positive electrode current collector, while the other side is an empty foil, resulting in an asymmetric structure of the electrode sheet. This asymmetric structure causes the single-sided positive electrode sheet to warp and deform towards the empty foil side, generating warping stress inside the single-sided positive electrode sheet, which will exert a certain extrusion on the corresponding negative electrode active layer. At the same time, the single-sided positive electrode sheet is located on the outermost side of the stacked battery and will directly be subjected to the pressure of the pressing plate during the rolling process. Under the action of these pressures, there is a certain height difference between the surface plateau area and the grooves of the negative electrode active layer corresponding to the single-sided positive electrode sheet. The electrolyte in the plateau area (the area excluding the grooves and the area between adjacent grooves) is more easily squeezed and migrates into the grooves. If the groove depth is too deep, it will further exacerbate the loss and drying of the electrolyte in the plateau area, thus forming a "broken bridge" for lithium-ion transmission, hindering ion transmission. After long-term cycling of the stacked battery, the side reactions on the surface of the negative electrode sheet corresponding to the single-sided positive electrode sheet intensify or the lithium-ion distribution is uneven, eventually resulting in purple spots or lithium deposition, reducing the long-term cycling stability of the battery and bringing safety hazards such as diaphragm piercing, battery short circuit, and fire. The double-sided positive electrode sheet has active layers on both sides of the positive electrode current collector and is located inside the stacked battery, and the pressure on the surface of the corresponding negative electrode sheet is relatively small. Therefore, less electrolyte in the plateau area (the area excluding the grooves and the area between adjacent grooves) is lost.

[0028] Based on this, the present invention differentiates the depths of the first grooves on the surface of the first negative electrode active layer corresponding to the single-sided positive electrode sheet and the second grooves on the surface of the second negative electrode active layer corresponding to the double-sided positive electrode sheet in the stacked battery, such that the battery satisfies the relationship: 0 < a ≤ 25 μm. On the one hand, the first negative electrode active layer corresponding to the single-sided positive electrode sheet has shallower first grooves on its surface, reducing the electrolyte accommodation capacity of the first grooves. When subjected to the warping stress of the single-sided positive electrode sheet and external direct pressure, more electrolyte can be retained in the plateau area on the surface of the first negative electrode active layer and will not be squeezed into the first grooves, effectively alleviating the risk of electrolyte loss and drying in the plateau area and suppressing the generation of purple spots. On the other hand, the second negative electrode active layer corresponding to the double-sided positive electrode sheet has deeper second grooves on its surface, which can ensure a larger accommodation space for the expansion of the negative electrode active material, enabling the expansion stress of the negative electrode active material during cycling to be effectively released at the second grooves, reducing internal stress accumulation, improving the integrity of the negative electrode sheet structure, and at the same time increasing the storage amount of the electrolyte on the surface of the negative electrode sheet, ensuring good wettability of the electrolyte to the negative electrode sheet and good lithium-ion transmission performance, thereby effectively improving the long-term cycling stability and safety of the battery.

[0029] In the present invention, the plateau region of the first negative electrode active layer refers to the region on the surface of the first negative electrode active layer other than the first grooves. For example, Figure 5 the region 32112 without the first grooves in Figure 2 and the region 3216 between two adjacent first grooves in

[0030] In the present invention, by controlling the battery to satisfy the relation: 0 < a ≤ 25 μm, compared with the prior art, the long cycle stability and safety of the battery can already be improved. To further improve the effect, one or more technical features can be further optimized.

[0031] In some embodiments, 0 < h 1 ≤ 20 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm.

[0032] In some embodiments, 3 μm ≤ h 2 ≤ 27 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or 27 μm.

[0033] In some embodiments, 5 μm ≤ a ≤ 15 μm, for example, 5 μm, 5.5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0034] According to a specific embodiment, 0 < h 1 ≤ 20 μm, 3 μm ≤ h 2 ≤ 25 μm, and the battery satisfies the relation: 0 < a ≤ 25 μm.

[0035] According to a specific embodiment, 0 < h 1 ≤ 20 μm, 3 μm ≤ h 2 ≤ 25 μm, and the battery satisfies the relation: 5 μm ≤ a ≤ 15 μm.

[0036] In some embodiments, such as Figure 7As shown, the first surface 3211 of the first negative electrode active layer is composed of an edge region 32114 and a central region 32115. The edge region 32114 is the area enclosed by the four peripheral edge lines 32116 of the first negative electrode active layer and a first line 32117. The first line 32117 is a parallel line parallel to the four peripheral edge lines 32116 of the first negative electrode active layer. The central region 32115 is the area of ​​the first surface excluding the edge region 32114. The perpendicular distance between the first line 32117 and the four peripheral edge lines 32116 of the first negative electrode active layer is H. 1 The vertical distance between the center of the first negative electrode active layer and the edge line of the first negative electrode active layer is H. 2 15%≤H 1 / H 2 ≤65% (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or 65%).

[0037] In some embodiments, the battery satisfies the following relationship: 0 < h 3 -h 4 h 4 h 3 h is the depth of the first groove located in the edge region. 4 The depth of the first groove located in the central region.

[0038] In this invention, the center of the first negative electrode active layer refers to, for example, Figure 7 As shown, the intersection of the centerline 321151 on the surface of the first negative electrode active layer in the negative electrode tab extension direction Z and the centerline 321152 in the first direction K.

[0039] In some embodiments, such as Figure 4 and Figure 5 As shown, the negative electrode 3 includes a negative electrode tab 33, which is connected to the negative electrode current collector. In this invention, as... Figure 4 As shown, the direction along the extension direction of the negative electrode tab is direction Z, and the direction perpendicular to the extension direction Z of the negative electrode tab is the first direction K.

[0040] Because the warping deformation of the single-sided positive electrode is the warping of the two edges of the single-sided positive electrode 11 towards the empty foil 113 (as shown in the image). Figure 8 As shown in the figure, the compressive pressure applied by the single-sided positive electrode sheet is concentrated in the center of the first negative electrode active layer, making it easier for the electrolyte in the center of the first negative electrode active layer to be squeezed into the first groove, while the pressure on the surrounding edge areas of the first negative electrode active layer is smaller. Therefore, the present invention controls the battery to satisfy the following relationship: 0 < h 3 -h 4 With a depth of ≤20μm, the first groove in the central region of the first negative electrode active layer is relatively shallow, which reduces the height difference between the central plateau region and the first groove. This further ensures that the electrolyte in the central plateau region of the first negative electrode active layer is not squeezed into the first groove. At the same time, the first groove in the edge region of the first negative electrode active layer, which is subject to less squeezing force, is relatively deep. This also maximizes the effect of the first groove in the edge region in alleviating the expansion of the negative electrode active material and improving the wettability of the electrolyte. This enhances the uniformity of electrolyte distribution in the first negative electrode active layer, further reducing or even preventing the appearance of purple spots in the plateau region of the first negative electrode active layer, and improving the long-cycle performance and safety of the battery.

[0041] In some embodiments, 0 < h 3 ≤20μm, for example, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0042] In some embodiments, 0≤h 4 ≤20μm, for example, 0, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0043] According to one specific implementation, 0 < h 3 ≤20μm, 0≤h 4 ≤20μm, the battery satisfies the relationship: 0<h 3 -h 4 ≤20μm, h 4 ≥0.

[0044] In some embodiments, such as Figure 4As shown, along the extension direction Z of the negative electrode tab, the first groove 3212 penetrates both sides of the first surface 3211, and the direction perpendicular to the extension direction Z of the negative electrode tab is the first direction K. The first groove 3212 is evenly distributed on the first surface 3211 along the first direction K.

[0045] In this invention, the first groove penetrating the first surface refers to, as... Figure 4 As shown, in the extending direction Z of the negative electrode tab, the first groove 3212 extends from one side edge 34 of the negative electrode sheet to the other side edge 35.

[0046] In some embodiments, such as Figure 5 As shown, the first surface 3211 includes a first region 32111, a second region 32112, and a third region 32113 that are sequentially adjacent along the first direction K. The first region 32111, the second region 32112, and the third region 32113 have the same size in the first direction K. The first region 32111 and the third region 32113 both include a first groove 3212, while the second region 32112 does not have a groove.

[0047] In this invention, the first region, the second region, and the third region are equal in size in a first direction, meaning that the length or width of the first region, the second region, and the third region are the same in a specific direction, for example, as shown in the figure. Figure 4 As shown, in the first direction K, the width L of the first region 1 The width L of the second zone 2 and the width L of the third zone 3 The same.

[0048] In this invention, by adopting the above-mentioned technical solution, the first and third regions on both sides of the first negative electrode active layer each include a first groove, while the second region in the middle has no groove. Since the second region has no groove, the contact area between the electrolyte and the first negative electrode active layer can be reduced, thereby reducing the heat generated by side reactions and improving the furnace temperature performance of the battery. At the same time, since the second region has no groove, there is no weak area such as a groove in the middle of the first negative electrode active layer. When the needle is pierced from the center of the battery, the middle position of the first negative electrode active layer will not undergo brittle fracture to generate debris that pierces the separator. Therefore, during needle piercing, the short circuit of the first negative electrode active layer in the middle second region can be reduced or even avoided, thereby improving the safety of the battery. Furthermore, during the charging and discharging process, the current density in the first and third regions located at the edges of the first negative electrode active layer is usually higher than that in the second region in the middle. This results in a greater demand for lithium-ion intercalation in the first and third regions on the sides. However, the electrolyte is prone to insufficient distribution in the first and third regions on the sides, leading to poorer lithium-ion intercalation kinetics and easier lithium plating. By adopting a method in which the first and third regions on both sides include a first groove and the second region in the middle has no groove, the electrolyte retention capacity in the first and third regions on both sides of the first negative electrode active layer can be enhanced, which helps to balance the current distribution and reduce the risk of lithium plating caused by the reduction of electrolyte in the first and third regions.

[0049] In some embodiments, along the extending direction of the negative electrode tab, the second groove penetrates both sides of the second surface, and the direction perpendicular to the extending direction of the negative electrode tab is the first direction. The second groove is evenly distributed on the second surface along the first direction.

[0050] In some embodiments, such as Figure 6 As shown, the second surface 3221 includes a fourth region 32211, a fifth region 32212 and a sixth region 32213 that are sequentially adjacent along the first direction K. The fourth region, the fifth region and the sixth region have the same size in the first direction K. The fourth region 32211 and the sixth region 32213 both include the second groove 3222, while the fifth region 32212 does not have a groove.

[0051] By adopting the above scheme, the fourth and sixth regions on both sides of the second negative electrode active layer include the second groove, while the fifth region in the middle has no groove. Since the fifth region has no groove, the contact area between the electrolyte and the second negative electrode active layer can be reduced, thereby reducing the heat generated by side reactions and improving the furnace temperature performance of the battery. At the same time, since the fifth region has no groove, there is no weak area such as a groove in the middle of the second negative electrode active layer. When the needle is pierced from the center of the battery, the middle position of the second negative electrode active layer will not undergo brittle fracture to generate debris that pierces the separator. Therefore, during needle piercing, the short circuit of the second negative electrode active layer in the middle fifth region can be further reduced or even avoided, thereby improving the safety of the battery. Furthermore, during the charging and discharging process, the current density in the fourth and sixth regions on both sides of the second negative electrode active layer is usually higher than that in the fifth region in the middle. This results in a greater lithium-ion intercalation kinetic pressure in the fourth and sixth regions, making lithium plating more likely. By adopting a design where the fourth and sixth regions on both sides include a second groove and the fifth region in the middle has no groove, the electrolyte retention capacity in the fourth and sixth regions on both sides of the second negative electrode active layer can be enhanced, which helps to balance the current distribution and reduce the risk of lithium plating caused by the reduction of electrolyte in the fourth and sixth regions.

[0052] In some embodiments, the width of the first groove is 0.05mm-0.2mm, for example, 0.05mm, 0.06mm, 0.08mm, 0.1mm, 0.12mm, 0.15mm, 0.18mm or 0.2mm.

[0053] In some embodiments, the spacing between two adjacent first grooves is 1mm-20mm, for example, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 15mm, 18mm or 20mm.

[0054] In some embodiments, the spacing between two adjacent first grooves is 3mm-6mm.

[0055] In some embodiments, the width of the first groove is 0.05mm-0.2mm, and the spacing between two adjacent first grooves is 1mm-20mm. The first negative electrode active layer corresponding to the single-sided positive electrode sheet adopts a relatively narrow first groove and a wide spacing first groove, which can expand the size of the plateau area on the surface of the first negative electrode active layer and limit the amount of electrolyte that the first groove can hold, thereby further reducing or even preventing electrolyte loss from the plateau area.

[0056] In some embodiments, the width of the second groove is 0.07mm-0.22mm, for example, 0.07mm, 0.08mm, 0.1mm, 0.12mm, 0.15mm, 0.18mm, 0.2mm or 0.22mm.

[0057] In some embodiments, the spacing between two adjacent second grooves is 1mm-18mm, for example, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 12mm, 14mm, 16mm or 18mm.

[0058] In some embodiments, the spacing between two adjacent second grooves is 2mm-5mm.

[0059] In some embodiments, the width of the second groove is 0.07mm-0.22mm, and the spacing between two adjacent second grooves is 1mm-18mm. Corresponding to the double-sided positive electrode sheet, the second negative electrode active layer employs relatively wide second grooves and narrowly spaced second grooves. The pressure environment of the second negative electrode active layer is relatively mild. The main requirements for the second negative electrode active layer are efficient buffering and a more reliable electrolyte reservoir. Therefore, the width of the second groove can be increased, and the spacing between the second grooves can be reduced, resulting in a denser distribution of stress relief points and electrolyte storage points.

[0060] In this invention, when the morphology of the groove includes one or more of lines and slots, the width of the groove refers to the average distance between the two long sides in the orthogonal projection of the line and slot onto the surface of the negative electrode sheet. For example, 10 points are randomly selected on any one of the long sides, the width corresponding to each point is measured, and the average value is taken as the average distance between the two long sides. For the first groove, when the number is less than or equal to 20, its width is the average of the widths of all the first grooves; when the number is greater than 20, its width is the arithmetic mean of the widths of any 20 first grooves. The method for calculating the width of the second groove is the same as that for the first groove.

[0061] In this invention, the distance between two adjacent grooves refers to the minimum distance between two adjacent edge lines in the orthographic projection of the two adjacent grooves onto the surface of the negative electrode sheet. During measurement, 10 points are randomly selected on any one of the two adjacent edge lines. A normal line is drawn through each point, and the length of the segment intercepted by the two edge lines is measured. The arithmetic mean of the 10 points is taken as the distance between the adjacent grooves. For the first groove, when the number of first grooves is greater than 2, the distance between adjacent first grooves is the average distance. For example, two adjacent first grooves are considered as one group for measuring their distance, and the arithmetic mean of the distances of any 20 groups of adjacent first grooves is the distance between two adjacent first grooves. When there are fewer than 20 groups of adjacent first grooves, the distance between the first grooves is the arithmetic mean of the distances of all adjacent first grooves. The calculation method for the distance between two adjacent second grooves is the same as that for the first groove.

[0062] In this invention, the width of the first groove, the width of the second groove, the distance between two adjacent first grooves, and the distance between two adjacent second grooves can all be obtained by observing and measuring the surface of the negative electrode active layer using SEM.

[0063] In some embodiments, the first negative electrode active layer includes first silicon-based particles, the second negative electrode active layer includes second silicon-based particles, and the weight percentage of the first silicon-based particles in the first negative electrode active layer is C. 1 The weight percentage of the second silicon-based particles in the second negative electrode active layer is C. 2 The relation is satisfied: C 1 <C 2 .

[0064] In this invention, the weight percentage C of the first silicon-based particles in the first negative electrode active layer is set. 1 The weight percentage C of the second silicon-based particles in the second negative electrode active layer is less than that of the second silicon-based particles. 2 This ensures that the volume expansion of silicon-based particles in the first negative electrode active layer under high pressure is small, allowing the first negative electrode active layer to better cooperate with the shallow depth of the first groove, thereby further improving the structural stability and electrolyte wettability of the battery, reducing purple spots and lithium plating, and improving the overall performance of the battery.

[0065] In some embodiments, 0 < C 2 -C 1 ≤5%, for example, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0066] The present invention further controls the battery to satisfy 0 < C 2 -C 1 ≤5%, when C 1 With C 2 If the difference is too large, it will lead to a large difference in the expansion rate and reaction kinetics of the first negative electrode active layer and the second negative electrode active layer. During the cycle, the inconsistent contraction and expansion of the negative electrode in different regions will cause internal stress in the battery module, which may cause the interface separation of the negative electrode and the positive electrode, thereby deteriorating the long-term cycle stability of the battery.

[0067] In some embodiments, the first silicon-based particle includes at least one of bulk silicon, spherical silicon, and quasi-spherical silicon.

[0068] In some embodiments, the sphericity of the spherical silicon is greater than 0.8, for example, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.

[0069] In some embodiments, the sphericity of the spheroidal silicon is 0.6-0.8, for example, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78 or 0.8.

[0070] In some embodiments, the first silicon-based particle is a silicon-carbon composite particle, and the surface of the silicon-carbon composite particle includes a coating layer covering at least a portion of the surface of the silicon-carbon composite particle, which helps the first silicon-based particle to form a more stable SEI film under harsh operating conditions, reduces side reactions, and thereby further improves the long-cycle stability of the battery.

[0071] In some embodiments, the weight percentage of the first silicon-based particles in the first negative electrode active layer is 4%-100%, for example, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%.

[0072] In some embodiments, the second silicon-based particle includes at least one of bulk silicon, spherical silicon, and quasi-spherical silicon.

[0073] In some embodiments, the second silicon-based particle is a silicon-carbon composite particle, the surface of which includes a coating layer covering at least a portion of the surface of the silicon-carbon composite particle, which helps the second silicon-based particle form a more stable SEI film under harsh operating conditions, reduces side reactions, and thus further improves the long-cycle stability of the battery.

[0074] In some embodiments, the weight percentage of the second silicon-based particles in the second negative electrode active layer is 4%-100%, for example, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%.

[0075] According to one specific embodiment, the weight percentage of the first silicon-based particles in the first negative electrode active layer is 4%-100%, and the weight percentage of the second silicon-based particles in the second negative electrode active layer is 4%-100%. The battery satisfies the relationship: 0 < C. 2 -C 1≤5%.

[0076] In some embodiments, the first negative electrode active layer includes a first negative electrode binder, and the second negative electrode active layer further includes a second negative electrode binder, wherein the weight percentage of the first negative electrode binder in the first negative electrode active layer is D. 1 The weight percentage of the second negative electrode binder in the second negative electrode active layer is D. 2 The relationship is satisfied: D 1 >D 2 .

[0077] In this invention, by controlling D 1 >D 2 This allows the first negative electrode active layer, located under high pressure, to have a higher binder content, thereby enhancing the adhesion between the internal components of the first negative electrode active layer and between the first negative electrode active layer and the first negative electrode current collector. This ensures that under expansion stress or extrusion pressure, the first negative electrode binder can still firmly bond the negative electrode active material, the negative electrode conductive agent, and the first negative electrode current collector, effectively preventing damage and peeling of the microstructure of the negative electrode active layer caused by the expansion of the negative electrode active material or mechanical extrusion.

[0078] In some embodiments, 1%≤D 1 -D 2 ≤10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, further provides sufficient bonding strength for the first negative electrode active layer in the high-pressure region.

[0079] In some embodiments, the weight percentage D of the first negative electrode binder in the first negative electrode active layer is... 1 It ranges from 4% to 15%, for example, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0080] In some embodiments, the weight percentage D of the second negative electrode binder in the second negative electrode active layer is... 2 It ranges from 2% to 10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0081] In some embodiments, the first negative electrode binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride (PVDF), acrylic acid-vinylidene fluoride copolymer, acrylonitrile-vinylidene fluoride copolymer, polyurethane, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, and styrene-acrylic rubber.

[0082] In some embodiments, the second negative electrode binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride (PVDF), acrylic acid-vinylidene fluoride copolymer, acrylonitrile-vinylidene fluoride copolymer, polyurethane, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, and styrene-acrylic rubber.

[0083] In some embodiments, the first negative electrode active layer includes a first negative electrode conductive agent, and the second negative electrode active layer includes a second negative electrode conductive agent. The first negative electrode conductive agent and the second negative electrode conductive agent are each independently selected from at least one of carbon nanotubes and conductive carbon fibers. The weight percentage of the first negative electrode conductive agent in the first negative electrode active layer is E. 1 The weight percentage of the second negative electrode conductive agent in the second negative electrode active layer is E. 2 The relationship is satisfied: E 1 >E 2 .

[0084] Because high aspect ratio conductive agents such as carbon nanotubes and conductive carbon fibers can construct a three-dimensional conductive network with higher elasticity and toughness in the negative electrode active layer, this invention controls E 1 >E 2 In the first negative electrode active layer, a higher weight ratio of high aspect ratio first negative electrode conductive agent is used to construct a three-dimensional conductive network with higher elasticity and toughness. When the volume of the first negative electrode active layer changes repeatedly, the three-dimensional conductive network is not easy to break, thereby ensuring the stability of the electronic pathway, avoiding side reactions caused by poor local conductivity, improving the dynamic performance of the first negative electrode active layer, further reducing the generation of purple spots, and improving the long-cycle stability and safety of the battery.

[0085] In some embodiments, 0.5% ≤ E 1 -E 2 ≤4.5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%.

[0086] In some embodiments, the weight percentage E of the first negative electrode conductive agent in the first negative electrode active layer is... 1 The range is 0.5% to 5%, for example, 0.5%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0087] In some embodiments, the weight percentage E of the second negative electrode conductive agent in the second negative electrode active layer is... 2 The range is 0.2%-4%, for example, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%.

[0088] In one embodiment, the first negative electrode active layer may further include a third negative electrode conductive agent, which may include one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, and metal powder.

[0089] In one embodiment, the second negative electrode active layer may further include a fourth negative electrode conductive agent, which may include one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, and metal powder.

[0090] In some embodiments, the surface of the first positive electrode active layer away from the first positive electrode current collector includes a plurality of recesses, wherein the depth of the recesses is 10μm-35μm, for example, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm, 32μm or 35μm.

[0091] In this invention, the surface of the positive electrode active layer away from the first positive electrode current collector includes a plurality of recesses, wherein "a plurality of" means that the number of recesses is greater than or equal to 1, for example, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40 or 50.

[0092] In this invention, the shape of the recess is at least one of a circle, a square, and a rectangle.

[0093] In this invention, the depth of the recess refers to the maximum vertical distance from any point at the bottom of the recess to the surface of the positive electrode sheet in the thickness direction of the positive electrode sheet. When the number of recesses is greater than 1, the depth of the recess is the average depth. For example, when the number of recesses is less than or equal to 20, the depth of the recess is the average depth of all recesses; when the number of recesses is greater than 20, the depth of the recess is the average depth of any 20 recesses. In this invention, the depth of the recess can be obtained by 3D profilometry or SEM testing.

[0094] In this invention, a number of recesses are generated on the surface of the first positive electrode active layer away from the first positive electrode current collector by embossing the single-sided positive electrode sheet.

[0095] In this invention, by controlling the surface of the first positive electrode active layer of the single-sided positive electrode sheet away from the first positive electrode current collector to include several recesses, and controlling the depth of the recesses to be 10μm-35μm, the microstructure of the single-sided positive electrode sheet can be reconstructed, the warping stress of the single-sided positive electrode sheet can be balanced, and the warping problem of the single-sided positive electrode sheet itself can be improved. This reduces the extrusion force of the single-sided positive electrode sheet on the first negative electrode active layer, reduces the extrusion of the plateau region in the first negative electrode active layer by the single-sided positive electrode sheet, further reduces the loss of electrolyte in the plateau region, and improves the first negative electrode active layer. This not only addresses the purple spot problem in the plateau region of the first negative electrode, but also prevents the adhesion between the single-sided positive electrode and the separator from failing or increasing in spacing due to warping stress, thus avoiding the increase in lithium-ion transport impedance caused by this. This further suppresses the purple spot problem exacerbated by the increased impedance. On the other hand, the embossed recesses form a certain gap, providing a buffer space for the single-sided positive electrode, which can buffer the extrusion force acting on the surface of the first negative electrode active layer to a certain extent, further reducing the loss of electrolyte from the plateau region of the first negative electrode active surface into the first groove, thereby improving the long-cycle stability and safety of the battery.

[0096] In some embodiments, the battery satisfies the following relationship: 0 < a / b ≤ 2.5 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, or 2.5), where b is the depth of the recess.

[0097] The research found that the greater the depth of the concave part, the stronger the ability of the single-sided positive electrode sheet to actively reduce the warpage stress and maintain the interface stability, and the smaller the increase in the lithium-ion transfer impedance caused thereby. At this time, the warpage stress from the single-sided positive electrode sheet is reduced, and the depth of the first groove in the first negative electrode active layer can be appropriately increased, so as to reduce the difference between the depth of the second groove and the depth of the first groove, that is, a, to alleviate the electrolyte loss in the plateau region. Based on this, the present invention controls the battery to satisfy the following relationship: when 0 < a / b ≤ 2.5, the warpage stress of the single-sided positive electrode sheet can be reduced, the extrusion force of the single-sided positive electrode sheet on the first negative electrode active layer can be reduced, the electrolyte loss in the plateau region can be further reduced, and it is ensured that the warpage stress will not increase the lithium-ion transfer distance between the negative electrode sheet and the positive electrode sheet, and the second groove and the first groove have appropriate depths, which can increase the overall electrolyte storage capacity on the surface of the first negative electrode active layer, thereby minimizing the probability of purple spots on the negative electrode sheet. When a / b > 2.5, it means that the depth of the concave part is too small, the warpage stress of the single-sided positive electrode sheet is not reduced, and the depth difference between the second groove and the first groove needs to be too large to improve the electrolyte loss in the plateau region, which may instead lead to poor electrolyte infiltration in the plateau region of the negative electrode active layer and insufficient lithium-ion transfer kinetics, causing new performance degradation; when a / b ≤ 0, the depth of the concave part is too large, the warpage stress of the single-sided positive electrode sheet is low, and the depths of the second groove and the first groove tend to be the same, and the problem of electrolyte loss in the plateau region cannot be improved, and purple spots appear on the first negative electrode active layer.

[0098] In some embodiments, the battery satisfies the following relationship: 0.2 ≤ a / b ≤ 1.5.

[0099] According to a specific embodiment, 0 < a ≤ 25 μm, b is 10 μm - 35 μm, and the battery satisfies the following relationship: 0 < a / b ≤ 2.5.

[0100] According to a specific embodiment, 5 μm ≤ a ≤ 15 μm, b is 10 μm - 35 μm, and the battery satisfies the following relationship: 0 < a / b ≤ 2.5.

[0101] According to a specific embodiment, 0 < a ≤ 25 μm, b is 10 μm - 35 μm, and the battery satisfies the following relationship: 0.2 ≤ a / b ≤ 1.5.

[0102] According to a specific embodiment, 5 μm ≤ a ≤ 15 μm, b is 10 μm - 35 μm, and the battery satisfies the following relationship: 0.2 ≤ a / b ≤ 1.5.

[0103] In some embodiments, the first positive electrode active layer further includes a first positive electrode active material, a first positive electrode conductive agent, and a first positive electrode binder.

[0104] In some embodiments, the second positive electrode active layer further includes a second positive electrode active material, a second positive electrode conductive agent, and a second positive electrode binder.

[0105] In some embodiments, the first positive electrode active material and the second positive electrode active material may each independently include one or more of lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide.

[0106] In some embodiments, the first positive electrode conductive agent and the second positive electrode conductive agent may each independently include one or more of conductive carbon black, carbon nanotubes, conductive graphite, and graphene.

[0107] In some embodiments, the first positive electrode binder and the second positive electrode binder may each independently include one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0108] In some embodiments, in the first positive electrode active layer, the weight percentage of the first positive electrode active material is 80%-99.8% (e.g., 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, or 99.8%), the weight percentage of the first positive electrode conductive agent is 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%), and the weight percentage of the first positive electrode binder is 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%).

[0109] In some embodiments, in the second positive electrode active layer, the weight percentage of the second positive electrode active material is 80%-99.8% (e.g., 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, or 99.8%), the weight percentage of the second positive electrode conductive agent is 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%), and the weight percentage of the second positive electrode binder is 0.1%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%).

[0110] In some embodiments, the separator includes a first separator located between the negative electrode and the single-sided positive electrode. The first separator includes a carrier layer and a coating layer located on at least one surface of the carrier layer. The battery satisfies the relationship: 1.8 ≤ B.1 / A 1 ≤12 (e.g., 1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, or 12), where A 1 B represents the coverage of the first groove on the surface of the first negative electrode active layer. 1 The coverage of the adhesive layer on the surface of the carrier layer.

[0111] In this invention, the coverage rate of the first groove on the surface of the first negative electrode active layer refers to the proportion of the total projected area of ​​all the first grooves on the surface of the first negative electrode active layer away from the negative electrode current collector in the total area of ​​the surface of the first negative electrode active layer. The coverage rate of the first groove on the surface of the negative electrode active layer can be measured by the following method: take an SEM image of the surface of the negative electrode sheet, and use image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.) within a 100mm×100mm area of ​​the surface of the negative electrode active layer to identify the first grooves, calculate the sum of the projected areas of all the first grooves in the image, and then divide it by the total area of ​​the surface region of the negative electrode active layer in the image to obtain the coverage rate of the first groove on the surface of the negative electrode active layer in the image. Take images of any three areas of the surface of the negative electrode sheet, and calculate the arithmetic mean of the coverage results of all measured areas as the coverage rate of the first groove on the surface of the first negative electrode active layer.

[0112] In this invention, the coverage rate of the adhesive layer on the surface of the carrier layer refers to the proportion of the projected area of ​​the adhesive layer on the carrier layer surface to the total surface area of ​​the carrier layer. In this invention, when the adhesive layer is located on one side of the carrier layer, B 1 This refers to the coverage of the adhesive layer on the surface of the carrier layer; when the adhesive layer is located on both sides of the carrier layer, B 1 This refers to the coverage of the adhesive layer on the surface of the carrier layer on either side. The coverage of the adhesive layers on both sides can be the same or different, and the calculation based on the coverage of the adhesive layer on either side always satisfies the relationship: 1.8 ≤ B. 1 / A 1 ≤12.

[0113] In this invention, the coverage of the adhesive layer on the surface of the carrier layer can be measured by scanning electron microscopy (SEM): An SEM image of the diaphragm surface is captured, and image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.) is used to arbitrarily select a 100μm × 100μm area as the analysis region, dividing this area into Y...1 In a uniform 100×100 grid, if the area covered by the orthographic projection of the adhesive layer on the carrier layer surface of a single square exceeds half the area of ​​the square, then the square is considered to be occupied by the adhesive layer; otherwise, the square is considered not occupied by the adhesive layer. The number of squares occupied by the adhesive layer is counted, X. 1 , through (X 1 / Y 1 The percentage of the orthographic projection area of ​​the adhesive layer on the carrier layer surface to the total surface area of ​​the carrier layer is calculated by multiplying the area by 100%. Five regions on the surface of the adhesive layer are randomly selected and SEM images are taken for measurement. The arithmetic mean of the five measurements is taken as the coverage rate of the adhesive layer on the surface of the carrier layer.

[0114] When wire bonding is performed on the surface of the negative electrode active layer to form grooves, the active layer in that area is permanently removed. While this brings benefits in terms of electrochemistry and stress regulation, it also weakens the bonding anchor between the negative electrode sheet and the separator. The greater the coverage of the first groove on the surface of the first negative electrode active layer, the lower the adhesion between the negative electrode sheet and the separator, and the stronger the requirement for separator adhesion. The coverage of the adhesive layer on the surface of the carrier layer needs to be increased accordingly. Therefore, this invention further controls the battery to satisfy the relationship: 1.8 ≤ B 1 / A 1 ≤12 can achieve a balance between the stress buffering effect of the negative electrode, the wettability of the electrolyte, and the adhesion between the negative electrode and the separator. When B 1 / A 1 When the value is less than 1.8, the coverage of the adhesive layer is insufficient, and the coverage of the first groove is too high, which easily leads to poor adhesion. When B... 1 / A 1 When the coating coverage is greater than 12, the low thermal conductivity of the coating may worsen the furnace temperature performance of the battery. If the coverage of the first groove is too low, it will be difficult to fully utilize the stress buffering and electrolyte wetting improvement functions.

[0115] In some embodiments, 18%≤B 1 ≤98%, for example, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98%.

[0116] In some embodiments, 0.25% ≤ A 1 ≤15%, for example, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0117] In some embodiments, 2%≤A 1 ≤9.5%.

[0118] According to one specific implementation, 18%≤B 1 ≤98%, 0.25%≤A 1 ≤15%, the battery satisfies the relationship: 1.8≤B 1 / A 1 ≤12.

[0119] According to one specific implementation, 18%≤B 1 ≤98%, 2%≤A 1 ≤9.5%, the battery satisfies the relationship: 1.8≤B 1 / A 1 ≤12.

[0120] In some embodiments, the adhesive layer comprises a porous structure formed by the first polymer as a continuous phase, or the adhesive layer comprises a second polymer in a particulate form.

[0121] In some embodiments, the first polymer includes at least one of fluoropolymers, acrylate polymers, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, ethylene-vinyl acetate copolymer, lithium polystyrene sulfonate, polyethylene oxide, cyanoethyl polyvinyl alcohol, butadiene-acrylonitrile copolymer and its derivatives, aramid, phenolic resin, polyimide, and polyetherimide.

[0122] In some embodiments, the second polymer includes at least one of fluoropolymers, acrylate polymers, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resins, epoxy resins, ethylene-vinyl acetate copolymers, lithium polystyrene sulfonate, polyethylene oxide, cyanoethyl polyvinyl alcohol, butadiene-acrylonitrile copolymers and their derivatives, aramid fibers, phenolic resins, polyimides, and polyetherimides.

[0123] In this invention, the fluoropolymer includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0124] In this invention, the acrylate polymers include one or more of the following: polymethyl methacrylate, polybutyl acrylate, acrylate monomer-acrylonitrile copolymer, acrylate monomer-ethylene copolymer, acrylate monomer-acrylonitrile-ethylene copolymer, styrene-acrylate monomer copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0125] In this invention, the acrylate monomers include one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, ethyl methacrylate, n-propyl acrylate, octyl acrylate, isooctyl acrylate, octadecyl acrylate, isobutyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0126] In some embodiments, the carrier layer includes a ceramic coating and a substrate layer, wherein the ceramic coating is located on at least one side surface of the substrate layer.

[0127] In some embodiments, the ceramic coating comprises ceramic particles, the ceramic particles being composed of at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin oxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium dioxide, zirconium titanate, barium titanate, and magnesium fluoride.

[0128] In some embodiments, the ceramic coating includes an adhesive comprising at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene.

[0129] In some embodiments, the substrate layer comprises at least one of polyolefin, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), or polymer derivatives thereof.

[0130] In some embodiments, the battery further includes an electrolyte, which is a conventional electrolyte in the art.

[0131] In some instances, the battery is a lithium-ion rechargeable battery.

[0132] 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.

[0133] Example 1 (1) Preparation of single-sided and double-sided positive electrode plates The positive electrode active material (lithium cobalt oxide), positive electrode binder (polyvinylidene fluoride PVDF500), and positive electrode conductive agent (conductive carbon black: carbon nanotubes (weight ratio) = 1:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2 and continuously stirred under the action of a stirrer to form a uniform and flowing positive electrode slurry. Subsequently, the positive electrode slurry was coated on one side of the positive electrode current collector (aluminum foil) and dried in a vacuum oven at 120°C for 6 hours. Then, it was rolled, embossed to form concave areas, and cut to obtain the desired single-sided positive electrode sheet. The positive electrode slurry was coated on both sides of the positive electrode current collector (aluminum foil) and dried in a vacuum oven at 120°C for 6 hours. Then, it was rolled and cut to obtain the desired double-sided positive electrode sheet. The surface of the first positive electrode active layer of the single-sided positive electrode sheet away from the first positive electrode current collector includes several concave areas with a depth of 15.8 μm (b is 15.8 μm).

[0134] (2) Preparation of negative electrode sheet The first carbon-based material (artificial graphite), the first silicon-based particles (silicon-carbon composite particles), the first negative electrode conductive agent (carbon nanotubes), the third negative electrode conductive agent (conductive carbon black), and the first negative electrode binder (styrene-butadiene rubber: sodium carboxymethyl cellulose: polyacrylic acid (weight ratio) = 4.5:0.5:3) were mixed in an aqueous solvent at a weight ratio of 65:25:1:1:8. The mixture was continuously stirred under the action of a stirrer to form a homogeneous, flowing first negative electrode slurry. The first negative electrode slurry was coated onto one side of the negative electrode current collector (copper foil) and dried in a 120℃ vacuum oven for 6 hours. Then, after rolling and wire bonding, the first negative electrode active layer corresponding to the single-sided positive electrode sheet was obtained. Subsequently, the mixture was mixed at a weight ratio of 65:25:1:1:8. A second carbon-based material (artificial graphite), a second silicon-based particle (silicon-carbon composite particle), a second negative electrode conductive agent (carbon nanotubes), a fourth negative electrode conductive agent (conductive carbon black), and a second negative electrode binder (styrene-butadiene rubber: sodium carboxymethyl cellulose: polyacrylic acid (mass ratio) = 4.5:0.5:3) were mixed in an aqueous solvent at a weight ratio of 5:1:1:8. The mixture was continuously stirred under the action of a stirrer to form a uniform and flowing second negative electrode slurry. The second negative electrode slurry was coated on the other side of the negative electrode current collector (copper foil) and dried in a vacuum oven at 120°C for 6 hours. After rolling and wire bonding, the second negative electrode active layer corresponding to the double-sided positive electrode sheet was obtained. Finally, the desired negative electrode sheet was obtained by slitting.

[0135] In this design, the wire bonding depth on the first surface of the first negative electrode active layer is relatively shallow, and the depth of the first groove formed is 10.1 μm (h). 1 The diameter of the groove is 10.1 μm. The first groove penetrates both edges of the first surface and is uniformly distributed on the first surface along the first direction (perpendicular to the extension direction of the negative electrode tab). The width of the first groove is 0.16 mm, the spacing between two adjacent first grooves is 4.5 mm, and the coverage of the first groove on the surface of the first negative electrode active layer is 7.11% (A). 1 (7.11%), the wire bonding depth is the same in the central and edge regions of the first negative electrode active layer, and the depth of the first groove in the edge region is 10.1 μm (h 3 The depth of the first groove in the central region is 10.1 μm (h). 4 It is 10.1 μm, h 4 ≥0), the second surface of the second negative electrode active layer has a deeper wire bonding depth, and the depth of the second groove formed is 16.5μm (h 2 The second groove is 16.5 μm wide and extends through both edges of the second surface. It is evenly distributed on the second surface along the first direction (the direction perpendicular to the extension direction of the negative electrode tab). The width of the second groove is 0.18 mm and the distance between two adjacent second grooves is 3.4 mm.

[0136] (3) Electrolyte preparation In an argon-filled glove box (moisture content <1 ppm, oxygen content <1 ppm), the following non-fluorinated solvents, propyl propionate, ethyl propionate, propylene carbonate, and ethylene carbonate, were mixed in a volume ratio of 3:4:2:1 to form a homogeneous solvent. Then, 21.2% of fluoroethylene carbonate, 16% of LiPF6, and 2.4% of 1,3,6-hexanetricarbonate based on the total weight of the electrolyte were slowly added and stirred until homogeneous to obtain the desired lithium-ion battery electrolyte.

[0137] (4) Preparation of diaphragm Ceramic particles (boehmite) and binder (polyacrylic acid) are added to deionized water at a weight ratio of 95:5. After thorough stirring, a first slurry with a solid content of 25% is obtained. The first slurry is coated onto one side of the substrate layer (polyethylene) using a gravure roller. After drying in a multi-section oven at 60°C, a carrier layer with ceramic coating located on one side of the substrate layer is formed. Polyvinylidene fluoride (a granular second polymer) was added to deionized water to obtain a second slurry with a solid content of 8%. This second slurry was coated onto both sides of a carrier layer using a gravure roller, and then dried in a multi-section oven at 60°C to form a coating layer. This process yielded a diaphragm, where the coating layer covered 57.8% of the carrier layer surface (B...). 1 (57.8%).

[0138] (5) Lithium-ion battery preparation The positive electrode, separator, and negative electrode prepared above are stacked to form an electrode assembly, which is then subjected to electrolyte injection, vacuum sealing, room temperature settling, and high-temperature formation processes to obtain the desired lithium-ion battery, where a = h. 2 -h 1 =16.5μm-10.1μm=6.4μm, a / b=6.4μm / 15.8μm=0.41, B 1 / A 1 =57.8% / 7.11%=8.13.

[0139] Examples 2-5 Examples 2-5 are performed with reference to Example 1, except that the features in Table 1 are changed, as detailed in Table 1.

[0140] Table 1 Table 1 Example 6 This embodiment is based on Embodiment 1, except that the first surface of the first negative electrode active layer includes a first region, a second region, and a third region that are sequentially adjacent along the first direction. The dimensions of the first region, the second region, and the third region are equal in the first direction. The first region and the third region both include a first groove, while the second region does not have a groove. The second surface of the second negative electrode active layer includes a fourth region, a fifth region, and a sixth region that are sequentially adjacent along the first direction. The dimensions of the fourth region, the fifth region, and the sixth region are equal in the first direction. The fourth region and the sixth region both include a second groove, while the fifth region does not have a groove.

[0141] Example 7 This set of examples is used to illustrate when h 3 -h 4 The impact of changes.

[0142] This embodiment is based on Embodiment 2, except that h 3 -h 4 Changes have occurred; see Table 2 for details.

[0143] Table 2 Example 8 group Example 8-1 This embodiment is based on Embodiment 1, except that there is no recess on the surface of the first positive electrode active layer away from the first positive electrode current collector.

[0144] Example 8-2 This embodiment is based on Embodiment 1, except that the depth of the recess is 1.8 μm (b is 1.8 μm), and a / b = 6.4 μm / 1.8 μm = 3.56.

[0145] Example 9 group This set of examples is used to illustrate when B 1 / A 1 The impact of changes.

[0146] Example 9-1 This embodiment is based on Embodiment 1, except that the coverage of the adhesive layer on the surface of the carrier layer is 8.5% (B). 1 (8.5%), B 1 / A 1 =8.5% / 7.11%=1.2.

[0147] Example 9-2 This embodiment is based on Embodiment 1, except that the coverage of the adhesive layer on the surface of the carrier layer is 95.2% (B). 1 (95.2%), B 1 / A 1=95.2% / 7.11%=13.39.

[0148] Example 10 group This set of examples is used to illustrate the weight percentage C of the first silicon-based particles in the first negative electrode active layer. 1 And / or the weight percentage C of the second silicon-based particles in the second negative electrode active layer 2 The impact of changes.

[0149] This embodiment is based on Embodiment 1, except that the weight percentage C of the first silicon-based particles in the first negative electrode active layer is [not specified]. 1 And / or the weight percentage C of the second silicon-based particles in the second negative electrode active layer 2 The changes have been made; please refer to Table 3 for details.

[0150] Table 3 The " / " indicates that the data does not exist. Example 11 group This set of examples illustrates the weight percentage D of a negative electrode binder in the first negative electrode active layer. 1 and / or the weight percentage D of the second negative electrode binder in the second negative electrode active layer 2 The impact of changes.

[0151] This embodiment is based on Embodiment 1, except that the weight percentage D of the first negative electrode binder in the first negative electrode active layer is [not specified]. 1 and / or the weight percentage D of the second negative electrode binder in the second negative electrode active layer 2 The changes have been made; please refer to Table 4 for details.

[0152] Table 4 The " / " indicates that the data does not exist. Example 12 group This set of examples is used to illustrate when the weight ratio E of the first negative electrode conductive agent in the first negative electrode active layer is... 1 and / or the weight percentage E of the second negative electrode conductive agent in the second negative electrode active layer 2 The impact of changes.

[0153] This embodiment is based on Embodiment 1, except that the weight percentage E of the first negative electrode conductive agent in the first negative electrode active layer is [not specified]. 1 and / or the weight percentage E of the second negative electrode conductive agent in the second negative electrode active layer 2 The changes have been made; please refer to Table 5 for details.

[0154] Table 5 The " / " indicates that the data does not exist. Comparative Example 1 This comparative example is based on Example 1, except that the first negative electrode active layer is not wired and the first surface of the first negative electrode active layer does not have grooves.

[0155] Comparative Example 2 This comparative example is based on Example 1, except that the depths of the first and second grooves are the same, with the depth of the first groove being 10.1 μm (h). 1 The depth of the second groove is 10.1 μm (h). 2 (10.1 μm), a = 0.

[0156] Comparative Example 3 This comparative example is based on Example 1, except that the depth of the first groove is 10.1 μm (h). 1 The depth of the second groove is 7.5 μm (h = 10.1 μm). 2 (7.5μm), a<0.

[0157] Comparative Example 4 This comparative example is based on Example 1, except that the depth of the first groove is 0.2 μm (h). 1 The depth of the second groove is 26.8 μm (h = 0.2 μm). 2 (26.8 μm), a=h 2 -h 1 =26.8μm-0.2μm=26.6μm, a / b=26.6μm / 15.8μm=1.68.

[0158] Test case The batteries prepared in the examples and comparative examples were subjected to the following performance tests, and the test results are shown in Table 6: (1) Cyclic capacity retention rate and battery thickness expansion rate at 25℃: At 25℃±2℃, the battery was charged at a constant current and constant voltage of 0.7C to the upper limit voltage of 4.53V, then cut off at 0.05C, and then discharged at a constant current of 0.2C to the lower limit voltage of 3V. The initial discharge capacity is denoted as C. 1 The initial battery thickness is h. 1After 10 minutes of rest, the cycle is as follows: 3C constant current / constant voltage charging to 4.25V, cut off at 2C, then 2C constant current / constant voltage charging to 4.48V, cut off at 1.5C, then 1.5C constant current / constant voltage charging to the upper limit voltage of 4.53V, cut off at 0.18C, rest for 5 minutes, and then discharge at 0.7C to the lower limit voltage of 3V. After 800 cycles, 0.7C constant current / constant voltage charging is performed to the upper limit voltage of 4.53V, cut off at 0.05C, and then 0.2C constant current discharging is performed to the lower limit voltage of 3V. The final discharge capacity is recorded as C. 2 The final battery thickness is denoted as h. 2 Capacity retention rate = (C 2 / C 1 )×100%, thickness expansion rate = (h 2 -h 1 ) / h 1 ×100%.

[0159] (2) Purple spots condition: After cycling at 25℃ for 800T, the battery was charged to 4.53V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C. After standing for 10 minutes, the battery was disassembled and the negative electrode was removed. The evaluation criteria for the purple spots on the negative electrode were as follows: no purple spots were grade 0; the area of ​​purple spots on the surface of the negative electrode was less than or equal to 2%; the area of ​​purple spots on the surface of the negative electrode was greater than 2% and less than or equal to 5%; the area of ​​purple spots on the surface of the negative electrode was greater than 5% and less than or equal to 10%; the area of ​​purple spots on the surface of the negative electrode was greater than 10% and less than or equal to 20%; and the area of ​​purple spots on the surface of the negative electrode was greater than 20%; and the negative electrode was grade 5.

[0160] (3) Pass rate of needle puncture performance test: At 25℃, the battery is discharged at a current of 0.5C to a voltage of 3V, then charged at a constant current of 0.5C to a voltage of 4.53V, and then charged at a constant voltage of 4.53V to a current of 0.05C. After standing for 5 minutes, a steel needle with a length of 100mm, a diameter of 3mm, and a taper of 15° is inserted into the middle of the battery at a speed of 25mm / s. The needle is left in the battery for 5 minutes, and the battery is observed to see if it catches fire or smokes. If the battery does not catch fire or smoke, it is considered to have passed the needle penetration test. If the battery catches fire or smokes, it is considered to have failed the needle penetration test. 20 samples are tested. The number of batteries that pass the needle penetration test is recorded as X, and the result is recorded as "X / 20".

[0161] (4) Pass rate of 130℃ furnace temperature test: At 25°C, hang the fully charged battery in a circulating air oven (heat transfer to non-integral battery components is not allowed). Note that the voltage and temperature leads need to be properly insulated (to avoid short circuits). Start heating from room temperature (25°C) to 130°C ± 2°C at a rate of (5 ± 2) °C / min, and place it at 130°C ± 2°C for 60 min. Observe whether the battery catches fire or explodes. If the battery does not catch fire or explode, it is judged that the oven temperature test passes; if the battery catches fire or explodes, it is judged that the oven temperature test fails. Test 20 samples, and record the number of batteries passing the oven temperature test as X, and the result is recorded as "X / 20".

[0162] Table 6 " / " indicates that this test was not performed on the batteries of the examples, so the data does not exist here.

[0163] As can be seen from Table 6, by comparing the comparative examples and the examples, the normal temperature cycle capacity retention rate of the examples is improved, the purple spot area is reduced, and the thickness expansion rate is decreased. This shows that by controlling the battery to satisfy the relationship: 0 < a ≤ 25 μm, the problem of electrolyte shortage in the platform area of the negative electrode corresponding to the single-sided positive electrode in the laminated battery is alleviated, thereby improving the cycle performance of the battery, reducing the thickness expansion rate, and reducing the generation of purple spots.

[0164] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a stacked electrode assembly, which includes a positive electrode, a separator, and a negative electrode stacked together. In the thickness direction of the electrode assembly, the positive electrode includes two single-sided positive electrode sheets located on the outermost side of the electrode assembly and at least one double-sided positive electrode sheet located inside the electrode assembly. The single-sided positive electrode sheet includes a first positive current collector and a first positive active layer located on the side surface of the first positive current collector near the center of the electrode assembly. The double-sided positive electrode sheet includes a second positive current collector and a second positive active layer located on both sides of the second positive current collector. The negative electrode sheet includes a negative electrode current collector and negative electrode active layers respectively located on both surface sides of the negative electrode current collector. The negative electrode active layer corresponding to the single-sided positive electrode sheet is the first negative electrode active layer, and the negative electrode active layer corresponding to the double-sided positive electrode sheet is the second negative electrode active layer. The surface of the first negative electrode active layer away from the negative electrode current collector is the first surface, and the first surface includes a first groove. The surface of the second negative electrode active layer away from the negative electrode current collector is the second surface, and at least one of the second surfaces includes a second groove. The battery satisfies the relationship: 0 < a ≤ 25 μm, where a = h 2 - h 1 , h 1 is the depth of the first groove, and h 2 is the depth of the second groove.

2. The battery according to claim 1, wherein, 0<h 1 ≤20μm; And / or, 3μm≤h 2 ≤27μm; And / or, 5μm≤a≤15μm.

3. The battery according to claim 1, wherein, The first surface of the first negative electrode active layer consists of an edge region and a central region. The edge region is the area enclosed by the four edges of the first negative electrode active layer and a first line. The first line is a parallel line parallel to the four edges of the first negative electrode active layer. The central region is the area of ​​the first surface excluding the edge region. The perpendicular distance between the first line and the four edges of the first negative electrode active layer is H. 1 The vertical distance between the center of the first negative electrode active layer and the edge line of the first negative electrode active layer is H. 2 15%≤H 1 / H 2 If ≤65%, then the battery satisfies the following relationship: 0<h 3 -h 4 ≤20μm, h 4 ≥0, h 3 h is the depth of the first groove located in the edge region. 4 The depth of the first groove located in the central region.

4. The battery according to claim 1, wherein, The surface of the first positive electrode active layer away from the first positive electrode current collector includes a plurality of recesses, wherein the depth of the recesses is 10μm-35μm; preferably, the battery satisfies the following relationship: 0<a / b≤2.5, more preferably 0.2≤a / b≤1.5, where b is the depth of the recess.

5. The battery according to claim 1, wherein, The negative electrode plate includes a negative electrode tab, which is connected to the negative electrode current collector. Along the extension direction of the negative electrode tab, the first groove penetrates both sides of the first surface. The direction perpendicular to the extension direction of the negative electrode tab is the first direction. The first groove is evenly distributed on the first surface along the first direction. Alternatively, the first surface includes a first region, a second region, and a third region that are sequentially adjacent along the first direction. The dimensions of the first region, the second region, and the third region are equal in the first direction. The first region and the third region both include the first groove, while the second region does not have a groove. And / or, along the extending direction of the negative electrode tab, the second groove penetrates both sides of the second surface, and the direction perpendicular to the extending direction of the negative electrode tab is the first direction. The second groove is evenly distributed on the second surface along the first direction. Or, the second surface includes a fourth region, a fifth region, and a sixth region that are sequentially adjacent along the first direction. The fourth region, the fifth region, and the sixth region have the same size in the first direction. The fourth region and the sixth region both include the second groove, and the fifth region does not have a groove.

6. The battery according to claim 1, wherein, The separator includes a first separator located between the negative electrode and the single-sided positive electrode. The first separator includes a carrier layer and a coating layer located on at least one surface of the carrier layer. The battery satisfies the relationship: 1.8 ≤ B. 1 / A 1 ≤12, where A 1 B represents the coverage of the first groove on the surface of the first negative electrode active layer. 1 The coverage of the adhesive layer on the surface of the carrier layer.

7. The battery according to claim 6, wherein, 18%≤B 1 ≤98%； And / or, 0.25%≤A 1 ≤15%, preferably 2%≤A 1 ≤9.5%; And / or, the coating layer comprises a porous structure formed by the first polymer as a continuous phase, or, the coating layer comprises a second polymer in a particulate form.

8. The battery according to claim 1, wherein, The width of the first groove is 0.05mm-0.2mm; And / or, the distance between two adjacent first grooves is 1mm-20mm, preferably 3mm-6mm; And / or, the width of the second groove is 0.07mm-0.22mm; And / or, the spacing between two adjacent second grooves is 1mm-18mm, preferably 2mm-5mm.

9. The battery according to any one of claims 1-8, wherein, The first negative electrode active layer includes first silicon-based particles, and the second negative electrode active layer includes second silicon-based particles. The weight percentage of the first silicon-based particles in the first negative electrode active layer is C. 1 The weight percentage of the second silicon-based particles in the second negative electrode active layer is C. 2 The relation is satisfied: C 1 <C 2 Preferably, 0 < C 2 -C 1 ≤5%; And / or, the first negative electrode active layer includes a first negative electrode binder, and the second negative electrode active layer further includes a second negative electrode binder, wherein the weight percentage of the first negative electrode binder in the first negative electrode active layer is D. 1 The weight percentage of the second negative electrode binder in the second negative electrode active layer is D. 2 The relationship is satisfied: D 1 >D 2 Preferably, 1% ≤ D 1 -D 2 ≤10%; And / or, the first negative electrode active layer includes a first negative electrode conductive agent, and the second negative electrode active layer includes a second negative electrode conductive agent. The first negative electrode conductive agent and the second negative electrode conductive agent are each independently selected from at least one of carbon nanotubes and conductive carbon fibers. The weight percentage of the first negative electrode conductive agent in the first negative electrode active layer is E. 1 The weight percentage of the second negative electrode conductive agent in the second negative electrode active layer is E. 2 The relationship is satisfied: E 1 >E 2 Preferably, 0.5% ≤ E 1 -E 2 ≤4.5%.

10. The battery according to claim 9, wherein, The weight percentage of the first silicon-based particles in the first negative electrode active layer is 4%-100%; And / or, the weight percentage of the second silicon-based particles in the second negative electrode active layer is 4%-100%; And / or, the first negative electrode binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, acrylic acid-vinylidene fluoride copolymer, acrylonitrile-vinylidene fluoride copolymer, polyurethane, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, and styrene-acrylic rubber. And / or, the second negative electrode binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, acrylic acid-vinylidene fluoride copolymer, acrylonitrile-vinylidene fluoride copolymer, polyurethane, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, and styrene-acrylic rubber.

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