Roll core and battery

Abstract

The invention provides a roll core and a battery. The roll core is formed by winding a positive plate, a diaphragm and a negative plate, the positive plate comprises a positive current collector and a positive active layer, and the positive plate comprises a first plane area located on the innermost ring of the roll core and a first arc section connected with the first plane area; a groove is formed in the positive electrode active layer of the first arc section, and is positioned on the surface of one side, facing the diaphragm, of the positive electrode active layer; the diaphragm comprises a base body and a polymer layer located on at least one surface of the base body, first coating areas corresponding to the straight areas and second coating areas corresponding to the arc areas are distributed on the polymer layer at intervals in the winding direction, each first coating area comprises a plurality of first protrusions, and each second coating area comprises a plurality of second protrusions; the height H1 from the first protrusions to the base body is smaller than the height H2 from the second protrusions to the base body. The roll core can prevent active particles in the inner layer bending area of the positive plate from extruding the diaphragm, so that the diaphragm is prevented from being damaged and micro-short-circuited.

Description

Technical Field

[0001] This application relates to the technical field of new energy materials, and particularly relates to a core and a battery. Background Art

[0002] Lithium-ion batteries, also commonly known as lithium batteries, are rechargeable batteries and are widely used in consumer products, digital products, power products, medical and security fields, etc.

[0003] How to charge lithium batteries is one of the key technologies in the application of lithium batteries. In the prior art, when charging lithium batteries, a two-stage charging method of constant current (CC) charging and constant voltage (CV) charging is generally adopted. That is, first, a constant current is used to charge the lithium battery with constant current until the voltage of the battery cell of the lithium battery reaches the cell charging limit voltage. Then, the cell charging limit voltage is used to charge the lithium battery with constant voltage. At this time, the charging current gradually decreases. When the charging current decreases to the charging cut-off current, the charging ends, and the battery cell of the lithium battery reaches the fully charged state.

[0004] However, in order to pursue a higher energy density, the core in the prior art often adds silicon to the negative active layer of the negative electrode sheet to improve the energy density. However, the core with a silicon-doped negative electrode sheet often has difficulty reducing to the preset charging cut-off current during the charging process and is difficult to reach the fully charged state. Summary of the Invention

[0005] This application provides a core and a battery, which optimize the core structure and prevent the problem that the core with a silicon-doped negative electrode sheet is difficult to reduce to the preset charging cut-off current during the charging process and is difficult to reach the fully charged state.

[0006] To achieve the above object, this application provides the following technical solutions:

[0007] In the first aspect of this application, a core is provided. The core is wound by a positive electrode sheet, a separator, and a negative electrode sheet which are stacked in sequence; the core includes a connected straight region and an arc region;

[0008] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on the positive electrode current collector. The positive electrode sheet includes a first planar region located in the innermost circle of the core and a first arc segment connected to the first planar region; a groove is provided on the positive electrode active layer of the first arc segment, and the groove is located on the surface of the positive electrode active layer facing the separator;

[0009] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on the negative electrode current collector. The negative electrode active layer includes a silicon-carbon composite material and / or a silicon-oxygen composite material, and the silicon content range in the negative electrode active layer is less than or equal to 50 wt%.

[0010] The separator includes a substrate and a polymer layer on at least one surface of the substrate. The polymer layer is spaced along the winding direction with a first coating area corresponding to the straight area and a second coating area corresponding to the arc area. The first coating area includes a plurality of first protrusions, and the second coating area includes a plurality of second protrusions; along the width direction of the core, the projection of the second coating area and the projection of the groove at least partially overlap.

[0011] Along the thickness direction of the separator, the height H1 of the first protrusion from the substrate is less than the height H2 of the second protrusion from the substrate.

[0012] In a possible implementation, the depth of the groove is greater than the height H2 of the second protrusion from the substrate, and / or the separator further includes a ceramic layer between the substrate and the polymer layer. The ceramic layer is disposed opposite to the second protrusion and the groove, and / or the thickness of the ceramic layer is 3-20 microns.

[0013] In a possible implementation, the ratio of the depth of the groove to the thickness of the positive electrode active layer is 0.05-0.45, and / or the thickness of the positive electrode sheet is 40μm-80μm; and / or along the width direction of the positive electrode sheet, the distance between the groove and the edge of the positive electrode sheet is 0.1mm-3mm, and / or the depth of the groove is 5 microns-20 microns.

[0014] In a possible implementation, the positive electrode sheet further includes a second planar region connected to the first arc segment. The boundary of the groove is located on the first planar region and / or the second planar region. Along the length direction of the positive electrode sheet, the distance between the groove and the boundary between the straight area and the arc area is 0.1mm-5mm.

[0015] In a possible implementation, the H1 and the H2 satisfy the relationship: H2:H1 = 0.3~0.8, and / or the H1 and / or H2 is 0.15-5 microns. Preferably, the H1 and / or H2 is 0.5-3 microns.

[0016] In a possible implementation, along the winding direction of the positive electrode sheet, the positive electrode sheet includes a plurality of spaced arc segments. The positive electrode sheet includes a plurality of grooves, and the plurality of grooves are respectively disposed on at most three arc segments of the positive electrode sheet along the winding direction.

[0017] In a possible implementation, the separator satisfies at least one of the following characteristics:

[0018] a. The multiple first protrusions and / or the multiple second protrusions are independently arranged at intervals;

[0019] b. The multiple first protrusions and / or the multiple second protrusions are independently arranged in a matrix;

[0020] c. The maximum circumscribed circle diameter of the first protrusion and / or the second protrusion is 200 μm to 430 μm;

[0021] d. There are multiple first voids between the multiple first protrusions, and / or there are multiple second voids between the multiple second protrusions. Along the winding direction of the core, the maximum circumscribed circle diameter of each first void and / or each second void is 5 μm - 80 μm; preferably, the maximum circumscribed circle diameter of each first void and / or each second void is 10 μm - 60 μm.

[0022] In a possible implementation, the negative electrode active layer includes a silicon-carbon composite material, and the silicon-carbon composite material satisfies at least one of the following characteristics:

[0023] The silicon-carbon composite material includes spherical silicon-carbon composite material and block-shaped silicon-carbon composite material, and / or,

[0024] The average sphericity of the silicon-carbon composite material is 0.6 - 0.9, and / or,

[0025] The porosity of the negative electrode sheet is 5 - 50%, and / or,

[0026] The silicon-carbon composite material includes a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon coating layer located on the surface of the porous carbon matrix. The carbon coating layer covers the silicon grains, and / or,

[0027] The silicon-carbon composite material includes open pores and / or closed pores. Closed pores refer to the pores in the porous carbon substrate covered by the carbon coating layer, and open pores refer to the pores on the porous carbon substrate not covered by the carbon coating layer. The area of the open pores is smaller than the area of the closed pores.

[0028] In a possible implementation, the first protrusion includes a first polymer, and the first protrusion is formed by fusing the first polymer. The first polymer satisfies at least one of the following conditions:

[0029] a. The first polymer includes non-granular polymer, granular polymer, and partially molten granular polymer;

[0030] b. The first polymer includes first polymer particles, and all and / or part of the first polymer particles are fused together;

[0031] c. The second protrusion includes second polymer particles; the second polymer particles are in a granular shape and / or part of them are fused together.

[0032] In a possible implementation manner, the first polymer particles and the second polymer particles independently include one or more of PMMA, PMMA-HFP, PVDF, and PVDF-HFP, and / or

[0033] The first protrusion and / or the second protrusion are in one or more of an island shape, a column shape, a cup shape, a dot shape, a regular polygon, or an irregular polygon.

[0034] The winding core provided in the first aspect of the present application has at least the following beneficial effects:

[0035] By providing a groove on the part of the positive electrode active layer of the positive electrode sheet located in the arc region, the thickness of the active layer in this region is reduced, thereby reducing the extrusion degree of the positive electrode active particles on the inner side of the electrode sheet during winding, and reducing the stacking thickness of the inner active material layer, thereby preventing the relatively hard positive electrode active material on the inner side of the positive electrode sheet from extruding the separator during winding, causing the separator to deform or become thinner, and avoiding the risk of the positive electrode active particles piercing the separator. At the same time, the reduction of the stacking thickness between the electrode sheet and the separator can also reduce the extrusion degree on the side of the positive electrode sheet close to the separator, improve the stress state in this region, and prevent the positive electrode active particles from falling off;

[0036] Furthermore, by setting that along the thickness direction of the separator, the height H1 of the first protrusion from the substrate is less than the height H2 of the second protrusion from the substrate, that is, the protrusion height of the second protrusion in the arc region is greater. Thus, on the one hand, it can resist the extrusion of the relatively hard silicon particles on the separator after expansion, and on the other hand, it can also resist the extrusion of the relatively hard positive electrode active particles on the separator, preventing the separator in the arc region from becoming thinner.

[0037] At the same time, the second protrusion in the arc region has a greater thickness, and in cooperation with the groove, it can effectively expand the bending space of the first arc segment of the positive electrode sheet to provide sufficient space for the electrolyte to enter or flow back. Moreover, through the cooperation of the second protrusion and the groove, the arc radius of the first arc segment of the positive electrode sheet is expanded, preventing the positive electrode active particles on both sides of the first arc segment of the positive electrode sheet from squeezing each other, and further reducing the stacking thickness of the positive electrode active material;

[0038] In addition, the second protrusion has a greater thickness. This is mainly because the winding stress at the first arc segment is greater. By making the thickness of the first protrusion greater, the extrusion stress can be effectively dispersed, preventing the diaphragm from thinning and also preventing the positive active particles from piercing the diaphragm, thereby reducing the K value. During the charging process, it can be smoothly reduced to the preset charging cut-off current at a predetermined time, reaching the fully charged state.

[0039] The second aspect of the present application provides a battery, including a housing and a wound core as described in any technical solution of the first aspect disposed in the housing.

[0040] The battery provided by the second aspect of the present application has all the beneficial effects of the wound core provided by the first aspect of the present application, which will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 Schematic diagram of the overall structure of the wound core provided by the embodiment of the present application;

[0043] Figure 2 For Figure 1 Schematic diagram of the enlarged structure of the inner layer A area in the provided wound core;

[0044] Figure 3 Schematic cross-sectional structure diagram of the wound core provided by the embodiment of the present application;

[0045] Figure 4 Schematic cross-sectional structure diagram of the positive electrode sheet of the wound core provided by the embodiment of the present application;

[0046] Figure 5 Schematic unfolded structure diagram of the positive electrode sheet of the wound core provided by the embodiment of the present application;

[0047] Figure 6 SEM image of the surface of the separator provided by the embodiment of the present application;

[0048] Figure 7 SEM image of the polymer layer on the surface of the separator provided by the embodiment of the present application;

[0049] Figure 8 SEM comparison diagram of the positive electrode sheet of the wound core provided by the embodiment of the present application before and after the groove is provided.

[0050] Description of the reference numerals:

[0051] 100, positive electrode sheet; 110, positive current collector; 120, positive active layer; 121, groove; 130, first arc segment; 140, first planar region; 150, second planar region; 200, separator; 210, substrate; 220, polymer layer; 221, first protrusion; 222, first void; 223, second protrusion; 224, second void; 230, ceramic layer; 300, negative electrode sheet; 310, negative current collector; 320, negative active layer; 400, straight region; 500, arc region.

[0052] Through the above drawings, specific embodiments of the present application have been shown, and there will be more detailed descriptions hereinafter. These drawings and textual descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. Detailed Description of the Embodiments

[0053] As described in the background art, lithium-ion batteries, also often referred to as lithium batteries, are rechargeable batteries and are widely used in consumer products, digital products, power products, medical and security fields, etc.

[0054] How to charge a lithium battery is one of the key technologies in the application of lithium batteries. In the prior art, when charging a lithium battery, a two-stage charging method of constant current (CC) charging and constant voltage (CV) charging is generally adopted. That is, first, the lithium battery is charged with a constant current until the voltage of the battery cell of the lithium battery reaches the charging limit voltage of the cell. Then, the lithium battery is charged with the charging limit voltage of the cell, and at this time, the charging current gradually decreases. When the charging current decreases to the charging cut-off current, the charging ends, and the battery cell of the lithium battery reaches the fully charged state.

[0055] However, in order to pursue a higher energy density, the prior art often adds silicon to the negative active layer of the negative electrode sheet in the wound core to improve the energy density. However, the wound core of the silicon-doped negative electrode sheet often has difficulty in reducing to the preset charging cut-off current during the charging process and is difficult to reach the fully charged state.

[0056] In view of the above technical problems, through research, it is found that the main reason is that the winding stress on the inner circle of the core is the greatest, and the bending radius of the A side (the side facing the core, the inner circle) of the first bending area of the positive electrode sheet is too small, close to 180 degrees. The two straight sections on the inner side of the positive electrode sheet are almost folded together, resulting in the extrusion and dropping of positive electrode particles. At the same time, due to the relatively large hardness of the silicon-based material of the silicon-doped negative electrode sheet and the large expansion of the silicon-based material during charge and discharge, the diaphragm is simultaneously squeezed by the silicon-based material with relatively large hardness and positive electrode particles on both sides. As a result, the diaphragm is overstretched, causing the thickness of the diaphragm at this part to become thinner, or the ceramic layer on the diaphragm to be squeezed off, or the holes on the diaphragm to be deformed or even enlarged. Even the holes on the diaphragm are enlarged, and the positive electrode particles that are severely squeezed and dropped on the inner side or the positive electrode active material particles on the inner side pierce the diaphragm and come into contact with the negative electrode sheet, resulting in a large number of local micro-shorts and an increase in the K value. Consequently, it is difficult for the battery to reduce to the preset charging cut-off current during the charging process and it is difficult to reach the fully charged state;

[0057] The embodiment of the present application provides a core and a battery. By providing a groove on the part of the positive electrode active layer of the positive electrode sheet located in the arc area, the thickness of the active layer in this area is reduced, thereby reducing the degree of extrusion of the positive electrode active particles on the inner side of the electrode sheet during winding and reducing the stacking thickness of the inner active material layer. Thus, it is possible to prevent the relatively hard positive electrode active material on the inner side of the positive electrode sheet from squeezing the diaphragm during winding, causing the diaphragm to deform or become thinner, and avoiding the risk of positive electrode active particles piercing the diaphragm. At the same time, the reduction of the stacking thickness between the electrode sheet and the diaphragm can also reduce the degree of extrusion on the side of the positive electrode sheet close to the diaphragm, improve the stress state in this area, and prevent the positive electrode active particles from falling off;

[0058] Furthermore, by setting the height H1 of the first protrusion from the substrate to be less than the height H2 of the second protrusion from the substrate, that is, the protrusion height of the second protrusion in the arc area is greater. Thus, on the one hand, it can resist the extrusion of the diaphragm by the expanded silicon particles with relatively large hardness, and on the other hand, it can also resist the extrusion of the diaphragm by the relatively hard positive electrode active particles, preventing the diaphragm in the arc area from becoming thinner. At the same time, the second protrusion in the arc area has a greater thickness and, in cooperation with the groove, can effectively expand the bending space of the first arc section of the positive electrode sheet to provide sufficient space for the electrolyte to enter or flow back. Moreover, through the cooperation of the second protrusion and the groove, the arc radius of the first arc section of the positive electrode sheet is expanded, preventing the positive electrode active particles on both sides of the first arc section of the positive electrode sheet from squeezing each other, and further reducing the stacking thickness of the positive electrode active material. In addition, the greater thickness of the second protrusion is mainly considered because the winding stress at the first arc section is greater. By having a greater thickness of the first protrusion, the extrusion stress can be effectively dispersed, preventing the diaphragm from becoming thinner and also preventing the positive electrode active particles from piercing the diaphragm, thereby achieving a reduction in the K value and smoothly reducing to the preset charging cut-off current according to the predetermined time during the charging process and reaching the fully charged state.

[0059] In order to make the above objects, features, and advantages of the embodiments of the present application more apparent and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0060] Referring to Figures 1 to 8 , the core provided by the embodiment of the present application is wound by a positive electrode sheet 100, a separator 200, and a negative electrode sheet 300 which are sequentially stacked; the core includes a connected flat area 400 and an arc area 500;

[0061] The positive electrode sheet includes a first planar region located in the innermost circle of the core and a first arc segment connected to the first planar region; a groove is provided on the positive electrode active layer of the first arc segment of the positive electrode sheet (100), and the groove is located on the surface of the positive electrode active layer facing the separator; the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on the negative electrode current collector, the negative electrode active layer includes a silicon-carbon composite material and / or a silicon-oxygen composite material, and the silicon content range in the negative electrode active layer is less than or equal to 50 wt%; wherein, the first planar region and the flat area (400) are oppositely arranged, and the first arc segment and the arc area (500) are oppositely arranged.

[0062] In this embodiment, the separator includes a matrix and a polymer layer on at least one surface of the matrix. The polymer layer is spaced apart in the winding direction and has a first coating area corresponding to the flat area and a second coating area corresponding to the arc area. The first coating area includes a plurality of first protrusions, and the second coating area includes a plurality of second protrusions; along the width direction of the core, the projection of the second coating area and the projection of the groove at least partially overlap; along the thickness direction of the separator, the height H1 of the first protrusion from the matrix is less than the height H2 of the second protrusion from the matrix.

[0063] In some embodiments, the positive electrode sheet (100) includes a positive electrode current collector and a positive electrode active layer located thereon. The positive electrode active layer includes positive electrode active particles, including one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium manganese iron phosphate, etc.; the positive electrode current collector serves as a conductive substrate and can be an integral flat aluminum foil. The aluminum foil has a high electrical conductivity and a small resistance, which can improve the maximum charge-discharge rate of the battery. Moreover, the aluminum foil has a certain strength and ductility, and is not prone to breakage or deformation during production processes such as winding or stacking, so as to ensure the structural integrity of the positive electrode sheet. In another embodiment, the negative electrode current collector of the negative electrode sheet can be an integral flat copper foil. The copper foil has a high electrical conductivity and a small resistance, which can improve the maximum charge-discharge rate of the battery. Moreover, the copper foil has a certain strength and ductility, and is not prone to breakage or deformation during production processes such as winding or stacking, so as to ensure the structural integrity of the negative electrode sheet.

[0064] In another embodiment, a groove is provided on the positive electrode active layer of the first arc section of the positive electrode sheet, which can be formed, for example, by laser back-and-forth cleaning, or by mechanical grinding, or by scraping with a scraper.

[0065] In this way, by providing a groove 121 on the portion of the positive electrode active layer 120 of the positive electrode sheet 100 located in the arc region, the thickness of the active layer in this region is reduced, thereby reducing the degree of extrusion of the positive electrode active particles on the inner side of the electrode sheet during winding, and reducing the stacking thickness of the inner active material layer, so as to prevent the relatively hard positive electrode active material on the inner side of the positive electrode sheet 100 from extruding the separator 200 during winding, causing the separator 200 to deform or become thinner, and avoiding the risk of the positive electrode active particles piercing the separator 200. At the same time, the reduction of the stacking thickness between the electrode sheet and the separator 200 can also reduce the degree of extrusion on the side of the positive electrode sheet 100 close to the separator 200, improve the stress state in this region, and prevent the positive electrode active particles from falling off. Furthermore, by setting that along the thickness direction of the separator, the height H1 of the first protrusion from the substrate is less than the height H2 of the second protrusion from the substrate, that is, the protrusion height of the second protrusion in the arc region is greater. Thus, on the one hand, it can resist the extrusion of the relatively hard silicon particles on the separator after expansion, and on the other hand, it can also resist the extrusion of the relatively hard positive electrode active particles on the separator, preventing the separator in the arc region from becoming thinner. At the same time, the second protrusion in the arc region has a greater thickness and, in cooperation with the groove, can effectively expand the bending space of the first arc section of the positive electrode sheet to provide sufficient space for the electrolyte to enter or flow back. Moreover, through the cooperation of the second protrusion and the groove, the arc radius of the first arc section of the positive electrode sheet is expanded, preventing the positive electrode active particles on both sides of the first arc section of the positive electrode sheet from squeezing each other, and further reducing the stacking thickness of the positive electrode active material. In addition, the second protrusion has a greater thickness mainly considering that the winding stress received at the first arc section is greater. By having a greater thickness of the first protrusion, the extrusion stress can be effectively dispersed, preventing the separator from becoming thinner and also preventing the positive electrode active particles from piercing the separator.

[0066] Exemplarily, along the thickness direction of the separator 200, polymer layers 220 are provided on both surfaces of the substrate 210. That is to say, the second protrusions are formed on both side surfaces of the substrate 210, and the second protrusions are respectively disposed opposite to the arc regions of the positive electrode sheet and the negative electrode sheet. In this way, by controlling the height of the polymer layer 220 in the arc region to be greater than that in the flat region 400, the extrusion stress between the positive electrode sheet 100 and the separator 200 can be effectively dispersed in the arc region, preventing the separator 200 from becoming thinner and reserving space for the expansion of the electrode sheet.

[0067] In a specific embodiment, the substrate 210 includes a first surface close to the positive electrode sheet and a second surface close to the negative electrode sheet. A ceramic layer and a polymer layer located on the ceramic layer are formed on the first surface of the substrate 210. The ceramic layer includes ceramic particles, which can be, for example, boehmite, alumina, melamine, silver oxide, etc. A polymer layer is formed on the second surface of the substrate 210. The ceramic layer and the polymer layer on the first surface of the substrate 210 are disposed opposite to the groove on the first arc segment of the positive electrode sheet. By arranging the ceramic layer and the groove opposite to each other, the ceramic layer can effectively block the positive active particles that may fall, preventing the positive active particles from falling onto the negative electrode sheet and causing micro-short circuit. In a specific embodiment, the thickness of the ceramic layer is 3-20 microns, which can be, for example, 3, 5, 7, 10, 15, 18, 20 microns, ensuring both the structural strength and bending strength of the ceramic layer while ensuring that the ceramic layer can fully block the positive active particles.

[0068] In a possible implementation, the height H2 of the second protrusion of the separator from the substrate is less than the depth of the groove, that is, the projection of the second coating area and the projection of the groove at least partially overlap, and the second protrusion is received in the groove. Due to the formation of the groove, the space of the arc segment of the positive electrode sheet is larger, further protecting the second protrusion on the separator and preventing the polymer particles on the second protrusion from being squeezed by the positive electrode sheet or the negative electrode sheet and falling off.

[0069] In a specific embodiment, the silicon-carbon composite material includes a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon coating layer located on the surface of the porous carbon matrix, and the carbon coating layer covers the silicon grains. In the present invention, the silicon grains can be disposed in the pores of the porous carbon matrix by a deposition method. By disposing the silicon grains in the pores and forming a carbon layer on the surface of the porous carbon matrix, the carbon layer can be a shaped carbon or an amorphous carbon. When the silicon grains expand, sufficient expansion space can be provided inside the porous carbon matrix, thereby preventing the overall structure of the silicon-carbon composite material from deforming. And the carbon layer can restrain the outward expansion force of the porous carbon matrix during the silicon expansion process, ensuring the structural strength of the silicon-carbon material, thus avoiding problems such as cracking, pulverization, and shedding of the negative active layer, improving the volumetric energy density and cycling performance of the battery. At the same time, the carbon coating layer covers the silicon grains, which can reduce the side reaction between the silicon grains and the electrolyte and reduce the generation of gases such as hydrogen fluoride.

[0070] In a specific embodiment, the silicon-carbon composite material includes open pores and / or closed pores. The closed pores refer to the pores in the porous carbon substrate covered by the carbon coating layer, and the open pores refer to the pores on the porous carbon substrate not covered by the carbon coating layer. The area of the open pores is smaller than the area of the closed pores. When the carbon layer is provided with open pores, it can improve the wettability of the electrolyte to the negative electrode sheet and reduce the expansion performance of the silicon grains, thereby reducing the impedance of the battery and improving the volumetric energy density and cycling performance of the battery.

[0071] In a specific embodiment, the silicon-carbon composite material includes a spherical silicon-carbon composite material and a block-type silicon-carbon composite material. By combining the two shapes of silicon-carbon composite materials, it is possible to take into account that the expansion energy of silicon grains in all directions approaches to be equal, and at the same time, it can also ensure that the silicon-carbon composite material has a higher bonding area to prevent the silicon-carbon composite material from falling off during the expansion process.

[0072] In an optional embodiment, the average sphericity of the silicon-carbon composite material is 0.6-0.9; illustratively, it can be 0.6, 0.6, 0.8, 0.9. The silicon-carbon composite material with sphericity controlled within this range can help reduce the mechanical stress and stress concentration of the silicon-carbon composite material during the charging and discharging process, help maintain the structural stability of the silicon-carbon composite material, reduce particle breakage or structural damage, and thus extend the service life of the battery.

[0073] In a specific embodiment, the silicon content in the negative electrode active layer is less than or equal to 50wt%, such as 10, 15, 25, 30, 35, 45%, etc. When the silicon content in the silicon-carbon composite material is within the above range, it can avoid the silicon content in the silicon-carbon composite material being too high, resulting in excessive expansion of the silicon-carbon composite material, causing the overall structure of the silicon-carbon composite material to deform, thereby avoiding cracking and pulverization of the negative electrode active layer. At the same time, it can also prevent the harder positive electrode active material on the inner side of the first fold of the positive electrode sheet and the expanded silicon-based particles from jointly squeezing the diaphragm during the winding process, thereby causing the diaphragm to deform or become thinner, avoiding the risk of positive electrode active particles piercing the diaphragm, ensuring the energy of the silicon-carbon composite material, and improving the cycle performance and volume energy density of the battery. In a specific example, the porosity of the negative electrode sheet is 5-50%.

[0074] In some embodiments, the ratio of the depth of the groove 121 to the thickness of the positive electrode active layer 120 is 0.05-0.45, wherein the positive electrode active layer refers to the active layer located on a single side of the positive electrode, for example, the ratio of the depth of the groove 121 to the thickness of the positive electrode active layer 120 is 0.05, 0.25 or 0.45, and / or, the thickness of the positive electrode sheet 100 is 45μm to 75μm, for example, the overall thickness of the positive electrode sheet 100 is 45μm, 60μm or 75μm.

[0075] In this way, by controlling the ratio of the thickness of the electrode tab to the depth of the groove 121, it is possible to prevent the groove 121 from being too deep and exposing the current collector (risk of foil leakage). The exposed foil may come into contact with the active material layer of the negative electrode tab, posing a risk of short circuit. Moreover, the exposed foil will also react with the electrolyte side reaction, reducing the amount of electrolyte retained. At the same time, ensure that the depth of the groove 121 is deep enough to effectively reduce the stacking thickness of the active layer in the first arc segment, control the balance of surface density and compaction density, optimize the energy density and structural strength of the core, and avoid uneven internal resistance caused by the electrode tab being too thick or too thin.

[0076] In some possible embodiments, the depth of the groove 121 is 5 - 20 micrometers. For example, the depth of the groove 121 is 5 micrometers, 12 micrometers, or 20 micrometers.

[0077] In some embodiments, along the width direction of the positive electrode tab 100, the distance between the groove 121 and the edge of the positive electrode tab 100 is 0.1 mm - 3 mm. For example, the distance between the groove 121 and the edge of the positive electrode tab 100 is 0.1 mm, 1.5 mm, or 3 mm. This is mainly because the edge of the electrode tab in the width direction has to go through metal knife cutting, and the active particles at the edge of the electrode tab are relatively loose. If a groove is formed, it is easy to have the situation of positive active particles falling off at the edge of the positive electrode. By forming the edge, it can effectively prevent the positive active particles at the edge of the positive electrode tab from falling off.

[0078] In some embodiments, the positive electrode tab further includes a second planar region connected to the first arc segment. The boundary of the groove is located on the first planar region and / or the second planar region. Along the length direction of the positive electrode tab 100, the distance between the groove 121 and the boundary between the straight region 400 and the arc region 500 is 0.1 mm - 5 mm. Exemplarily, the distance between the groove 121 and the boundary between the straight region 400 and the arc region 500 is 0.1 mm, 2.5 mm, or 5 mm. That is to say, while the projection of the groove always covers the entire first arc segment, it also includes a part located on the first planar region and / or the second planar region. The width of the groove is greater than the width of the first arc segment. With such a setting, the positive active material participating in the charge and discharge reaction in the arc region can be further reduced, the CB value of this region can be increased, and the probability of lithium precipitation on the negative electrode tab can be reduced. At the same time, the stress on both sides of the intersection point between the first planar region and the first arc segment is different, and it is easy to have powder falling off. By having the boundary located on the first planar region, the powder falling off caused by uneven stress on both sides at the intersection point can be avoided. By controlling it within 0.1 mm - 5 mm, if it is less than 0.1 mm, the residual amount of positive active material particles is relatively large, and there is a risk of powder falling off and lithium precipitation; if it is greater than 5 mm, it means that the width of the groove is too large, resulting in excessive loss of the active material layer of the positive electrode, affecting the battery capacity and energy density.

[0079] In some embodiments, in the arc region 500, along the winding direction of the positive electrode sheet, the positive electrode sheet includes a plurality of arc segments arranged at intervals, and the positive electrode sheet includes a plurality of grooves, and the plurality of grooves are respectively arranged on at most three arc segments of the positive electrode sheet along the winding direction.

[0080] That is to say, grooves are provided in the arc segments of at most the first three folds of the positive electrode sheet. The main consideration is that the bending radius of the arc segments of at most the first three folds of the positive electrode sheet is the smallest, and at the same time, the extrusion stress received is the largest. By providing grooves in the arc segments of at most the first three folds of the positive electrode sheet, the stacking thickness of the positive active particles in the first three layers and the problem of stress concentration are mainly reduced, and the problem that the hard particles in the 100th layer of the positive electrode sheet pierce through the separator 200 due to extrusion is improved.

[0081] In some embodiments, H1 and H2 satisfy the relationship: H2:H1 = 0.3 to 0.8. For example, H2:H1 = 0.3, or H2:H1 = 0.5, or H2:H1 = 0.8. If H2:H1 is less than 0.3, the height of the first protrusion 221 is too small, which easily causes the force of the separator 200 in the flat region 400 being squeezed to be too large and causes a short circuit. If it is greater than 0.8, the heights of the second protrusion 223 and the first protrusion 221 are close. When the silicon-doped electrode sheet expands during the charge and discharge process, it is difficult for the separator 200 to effectively disperse stress, which easily causes stress concentration in the arc region 500 of the separator 200, resulting in stretching or tearing, and further causing the problem of too large K value.

[0082] Based on the above embodiments, what can be improved is that H1 is 0.15 micrometers to 5 micrometers. For example, H1 is 0.15 micrometers, or H1 is 2.5 micrometers, or H1 is 5 micrometers; or H2 is 0.15 micrometers to 5 micrometers. For example, H2 is 0.15 micrometers, or H2 is 2.6 micrometers, or H2 is 5 micrometers. That is to say, H1 and H2 are each independently any value within 0.15 micrometers to 5 micrometers, as long as H1:H2 = 0.3 to 0.8 is satisfied.

[0083] In some embodiments, H1 is 0.5 micrometers to 3 micrometers. For example, H1 is 0.5 micrometers, or H1 is 3 micrometers; or H2 is 0.5 micrometers to 3 micrometers. For example, H2 is 0.5 micrometers, or H2 is 3 micrometers.

[0084] By controlling the first protrusion 221 and the second protrusion 223 within the above range, the gap between the electrode sheet and the substrate of the separator 200 can be increased for storing the electrolyte, providing electrolyte for the later cycle (during the cycle, the electrode sheet expands and squeezes the polymer layer 220 of the separator 200. The polymer layer 220 has elasticity, increasing the storage amount of the electrolyte and also reserving space for the expansion of the electrode sheet).

[0085] In some possible implementation manners, the multiple first protrusions and / or the multiple second protrusions in the separator are independently arranged at intervals; in some specific embodiments, the multiple first protrusions and / or the multiple second protrusions are independently arranged in a matrix pattern.

[0086] In some embodiments, there are multiple first voids 222 between the multiple first protrusions 221, and / or there are multiple second voids 224 between the multiple second protrusions 223. With such a design, the first voids 222 and the second voids 224 can not only provide a accommodation space for the expansion of the silicon-doped negative electrode sheet 300, but also accommodate relatively hard positive active particles, preventing the separator 200 from being excessively thinned or the ceramic layer 230 from shedding powder, and further preventing the positive active particles squeezed and fallen onto the negative electrode sheet 300, causing the problem of micro short circuit.

[0087] In some embodiments, along the winding direction of the core, the maximum circumscribed circle diameter of the void area formed by the multiple first voids 222 and / or the multiple second voids 224 is 5 μm - 80 μm. For example, the maximum circumscribed circle diameter of the void area formed by the multiple first voids 222 is 5 μm, or the maximum circumscribed circle diameter of the void area formed by the multiple first voids 222 is 80 μm. When the voids are too small, the raised polymer particles are more concentrated. During formation hot pressing, the particles swell and block the pores of the separator; when the voids are too large, the adhesion between the polymer layer and the separator matrix layer and the electrode sheet is weak, and delamination is likely to occur.

[0088] Furthermore, preferably, the maximum circumscribed circle diameter of each first void and / or each second void is 10 μm - 60 μm. For example, the maximum circumscribed circle diameter of the void area formed by the multiple first voids 222 is 10 μm, or the maximum circumscribed circle diameter of the void area formed by the multiple first voids 222 is 60 μm. It can be understood that if the voids are too small, it is difficult to provide space for the expansion of the silicon-doped negative electrode sheet; if they are too large, the protrusions are too dispersed, and it is difficult to disperse stress, reduce the extrusion degree of the positive active particles on the inner side of the first fold during winding, and reduce the stacking thickness of the inner active material layer.

[0089] In some embodiments, the maximum circumscribed circle diameter of the first protrusion and / or the second protrusion is 200 μm - 430 μm; when the maximum circumscribed circle diameter of the first protrusion and / or the second protrusion is within the above range, the polymer layer has better adhesion with the electrode sheet and the separator carrier layer, and can improve the safety and service life of the battery.

[0090] In some possible implementation manners, the first protrusion includes a first polymer, and the first protrusion is formed by the fusion of the first polymer. In some embodiments, the first polymer includes a non-granular polymer, a granular polymer, and a partially molten granular polymer (that is, having both a non-granular polymer and a granular polymer).

[0091] The state of the first polymer is closely related to the function of the first protrusion in the polymer layer. When the first polymer is non-granular, it can enable better adhesion between the separator and the electrode plate. When the first polymer is granular, it can provide more space for the expansion of the silicon-doped negative electrode plate, reduce the stacking thickness of the positive electrode plate, increase the electrolyte storage capacity, and provide sufficient electrolyte for the later cycles of the battery. When the first polymer has both granular and non-granular polymers, it can not only increase the adhesion between the separator and the electrode plate, but also have appropriate expansion space and electrolyte storage capacity, thus improving the comprehensive performance of the battery.

[0092] In some other embodiments, the first polymer includes first polymer particles, and all and / or part of the first polymer particles are fused. In another implementation, the second protrusion includes second polymer particles; the second polymer particles are granular and / or partially fused.

[0093] In some embodiments, the first polymer particles and / or the second polymer particles include one or more of Poly(methyl methacrylate) (abbreviated as PMMA), Poly(methyl methacrylate-co-hexafluoropropylene) (abbreviated as PMMA-HFP), Polyvinylidene fluoride (abbreviated as PVDF), and Polyvinylidene fluoride-co-hexafluoropropylene (abbreviated as PVDF-HFP). In some embodiments, the first protrusion and / or the second protrusion are one or more of island-shaped, column-shaped, cup-shaped, dot-shaped, regular polygon-shaped, or irregular polygon-shaped.

[0094] Example 1

[0095] Preparation of positive and negative electrode plates

[0096] (1) Negative electrode slurry:

[0097] Mix artificial graphite, silicon-carbon composite material, conductive carbon black, polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber according to a mass ratio of 76.88:19.22:0.5:1.3:0.4:0.9, add deionized water solvent, stir well according to the known batching process, and pass through a 150-mesh sieve to prepare a negative electrode slurry with a solid content of 40% - 45%.

[0098] (2) Negative electrode coating

[0099] The negative electrode slurry is coated onto the copper foil by a coater in a known coating method, dried at a temperature of 100 °C, and then the negative electrode sheet is roll-pressed and slit to obtain a negative electrode sheet of the required size. The coating length is 1240 mm ± 1 mm, and the coating thickness of the single-sided negative electrode active layer is 45 microns ± 2 microns.

[0100] (3) Positive electrode slurry

[0101] Lithium cobaltate as the positive electrode active material, a conductive agent, and a binder are added to a stirring tank in a mass ratio of 97.2:1.5:1.3, and an N-methylpyrrolidone (N-Methyl-2-Pyrrolidone, abbreviated as NMP) solvent is added. Thorough stirring is carried out according to a known batching process, and it is passed through a 200-mesh sieve to prepare a positive electrode slurry. The solid content of the positive electrode slurry is 70% - 75%.

[0102] (4) Positive electrode coating

[0103] The positive electrode slurry is coated onto the aluminum foil by a coater in a known coating method, dried at a temperature of 120 °C, and then the positive electrode sheet is roll-pressed and slit to obtain a positive electrode sheet of the required size. The coating length is 1243 ± 1 mm;

[0104] (5) Forming a groove on the positive electrode

[0105] Laser etching is carried out at the position of the arc area by a laser, and the material on the positive electrode active material layer etched off is sucked away to form a groove with a certain depth and width.

[0106] (6) Separator

[0107] S1. Preparation of polymer coating slurry: Weigh PMMA powder (first polymer particle / second polymer particle), styrene-butadiene rubber, n-butanol (dispersant), sodium carboxymethyl cellulose (thickener), ethylene oxide polymer (surfactant) = 30:3:1:2:0.2 (mass ratio), add deionized water and stir for 10 minutes, heat to 50 °C to make a mixture, and filter it through a 400-mesh stainless steel sieve to obtain a polymer slurry. The viscosity of the slurry is 3 Pa·s; the solid content is 31%.

[0108] S2. Preparation of ceramic layer slurry: Boehmite: styrene-butadiene latex (adhesive): sodium carboxymethyl cellulose (thickener) = 85:6:9 (mass ratio), add deionized water and stir for 10 minutes, heat to 50 °C to make a mixture, and filter it through a 400-mesh stainless steel sieve to obtain a ceramic layer slurry. The viscosity of the slurry is 5 Pa·s; the solid content is 37%.

[0109] S3. The ceramic layer slurry is coated on one side of a polyethylene base film with a thickness of 5 μm and a porosity of 38% by intaglio coating method at a coating rate of 20 m / min. A three-stage oven is used for drying, and the temperatures of each stage oven are 55 °C, 70 °C, and 60 °C respectively. After drying, a separator with a ceramic layer is obtained, and the thickness of the ceramic layer is 2 μm.

[0110] S4. By using the island-shaped intaglio coating method, the polymer coating slurry is respectively coated on the first coating area and the second coating area on both sides of the separator with a ceramic layer. The coating thickness of the first coating area is H1, and the coating thickness of the second coating area is H2. The coating rate is 20 m / min. A three-stage oven is used for drying, and the temperatures of each oven are 55 °C, 70 °C, and 60 °C respectively. After drying, a separator is obtained. Its areal density is 3.5 g / m 2 。

[0111] (7) Assembling the battery cell

[0112] The positive electrode sheet and the negative electrode sheet prepared in the above steps (1) and (5) and the separator are wound together to form a core, packaged with an aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. After being formed by the hot pressing forming process, the battery cell can be obtained.

[0113] The preparation process of the positive electrode electrolyte is as follows: In a solvent formed by mixing propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a weight ratio of approximately 1:1:0.5:1, LiPF6 is added and mixed evenly. The concentration of LiPF6 is approximately 1 mol / L, and the electrolyte is obtained after mixing evenly.

[0114] Performance parameters of each example and comparative example

[0115]

[0116]

[0117]

[0118] Table 2 Electrochemical parameters of each example and comparative example

[0119]

[0120] It can be seen from Examples 1, 2, 3 and Comparative Examples 2, 3 that when H2:H1 is too small, the smaller the H1 of the flat area glue layer, the thinner the glue layer of the separator in the flat area during the hot pressing forming process, which is more likely to cause the total thickness of the separator in the flat area to become thinner, and then lead to more micro-shorts in the battery and a larger K value;

[0121] As can be seen from Examples 1, 2, and 3, when the maximum circumscribed circle diameters of the first void and the second void are controlled within a certain range, the polymer protrusions are relatively evenly dispersed. After hot pressing the flat area, the protrusions swell, increasing the contact area with the electrode tab. Therefore, the bonding strength between the separator and the electrode tab is higher than that of the arc section;

[0122] Similarly, as can be seen from Comparative Examples 4 and 5, when the maximum circumscribed circle diameters of the first void and the second void are relatively small, the protrusions are more concentrated. When the maximum circumscribed circle diameter is relatively large, delamination occurs between the separator and the electrode tab, and the peel strength is significantly reduced;

[0123] As can be seen from Comparative Examples 1-5, surface sweeping was not performed in the arc area, the positive active material particles fell off, the K value deteriorated significantly, and it was difficult to reduce the charging current to the preset cut-off current, that is, it was difficult to reach the fully charged state.

[0124] As can be seen from Table 2, after laser surface sweeping in the arc area, the thickness of the active layer in this area is reduced, thereby reducing the extrusion degree of the positive active particles on the inner side of the electrode tab during winding, reducing the stacking thickness of the inner active material layer, thereby preventing the relatively hard positive active material on the inner side of the positive electrode tab 100 from extruding the separator 200 during winding, causing the separator 200 to deform or become thinner, and avoiding the risk of the positive active particles piercing the separator 200. Moreover, after surface sweeping, the internal stress in the wound core is released, the battery deformation is reduced, and the thickness expansion rate is significantly reduced. Further, by controlling H2:H1 within the range of 0.3-0.8, on the one hand, it can resist the extrusion of the relatively hard silicon particles on the separator after swelling, and on the other hand, it can also resist the extrusion of the relatively hard positive active particles on the separator, prevent the separator in the arc area from becoming thinner, further reduce the self-discharge situation, effectively reduce the K value, and enable the charging current to be reduced to the preset charging cut-off current according to the predetermined time during charging, reaching the fully charged state.

[0125] Test method:

[0126] 1. The test method for the bonding strength of the first bonding area (flat area) and the second bonding area (arc area) includes: anatomize the battery, select a separator and a positive electrode tab sample with a length of 8 mm * 8 mm width, stick the positive electrode tab on the steel plate with 3M tape, and place the separator and the positive electrode tab at a 180-degree angle on a universal tensile machine at a speed of 100 mm / min and a test displacement of 50 mm. The test result is recorded as the bonding strength between the separators (unit: N / m).

[0127] 2. The method for measuring the K value: After fully charging the lithium-ion battery, measure the voltage and record it as U1. After standing for a period of time, measure the voltage and record it as U2, and record the time as t1; then the K value = (U1 - U2) / t1

[0128] 3. Cycle capacity retention test: At an ambient temperature of 25°C, after 200 charge-discharge cycles, the calculation of the capacity retention rate = the discharge capacity of the Nth time / the discharge capacity of the first time * 100%.

[0129] 4. Cycle expansion rate test: At an ambient temperature of 25°C, after 200 charge-discharge cycles, the calculation of the expansion rate = (the full charge thickness of the Nth time / the full charge thickness of the first time - 1) * 100%.

[0130] 5. Current after a predetermined charging time: At an ambient temperature of 25°C, the charging regime is constant current and constant voltage charging at 1.8C until 4.48V, and then constant current charging for 4 hours, and observe the final cut-off current.

[0131] In a second aspect, an embodiment of the present application provides a battery, which includes a housing and a winding core as described in any embodiment of the first aspect disposed inside the housing.

[0132] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0133] In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0134] In the present application, unless otherwise clearly specified and limited, the terms "mounted", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0135] In this application, unless otherwise clearly defined or limited, the first feature being "on" or "under" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "below" and "beneath" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the horizontal height of the first feature is less than that of the second feature.

[0136] In this specification, the various embodiments or implementation manners are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0137] It should be noted that the embodiments referred to as "an embodiment", "embodiment", "exemplary embodiment", "some embodiments", etc. in the specification may include specific features, structures or characteristics, but not every embodiment necessarily includes such specific features, structures or characteristics. Moreover, such phrases do not necessarily refer to the same embodiment. In addition, when combining a specific feature, structure or characteristic with an embodiment, it is within the knowledge scope of those skilled in the art to implement such a feature, structure or characteristic in combination with other embodiments, whether explicitly or implicitly described.

[0138] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of this application, rather than to limit it; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the various embodiments of this application.

Claims

1. A core, characterized in that, The core is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet which are sequentially stacked; the core includes a flat region and an arc region connected to each other; The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on the positive electrode current collector. The positive electrode sheet includes a first planar region located in the innermost circle of the core and a first arc segment connected to the first planar region; a groove is provided on the positive electrode active layer of the first arc segment, and the groove is located on the surface of the positive electrode active layer facing the separator; The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on the negative electrode current collector. The negative electrode active layer includes a silicon-carbon composite material and / or a silicon-oxygen composite material, and the silicon content range in the negative electrode active layer is less than or equal to 50 wt%; The separator includes a substrate and a polymer layer on at least one surface of the substrate. The polymer layer is spaced along the winding direction and has a first coating region corresponding to the flat region and a second coating region corresponding to the arc region. The first coating region includes a plurality of first protrusions, and the second coating region includes a plurality of second protrusions; along the width direction of the core, the projection of the second coating region and the projection of the groove at least partially overlap; Along the thickness direction of the separator, the height H1 of the first protrusion from the substrate is less than the height H2 of the second protrusion from the substrate.

2. The core according to claim 1, characterized in that, The depth of the groove is greater than the height H2 of the second protrusion from the substrate, and / or the separator further includes a ceramic layer between the substrate and the polymer layer. The ceramic layer is disposed opposite to the second protrusion and the groove, and / or the thickness of the ceramic layer is 3-20 microns.

3. The core according to claim 1, characterized in that, The ratio of the depth of the groove to the thickness of the positive electrode active layer is 0.05-0.45, and / or the thickness of the positive electrode sheet is 40 μm-80 μm; and / or, along the width direction of the positive electrode sheet, the distance between the groove and the edge of the positive electrode sheet is 0.1 mm-3 mm, and / or the depth of the groove is 5 microns-20 microns.

4. The core according to claim 1, characterized in that, The positive electrode sheet further includes a second planar region connected to the first arc segment. The boundary of the groove is located on the first planar region and / or the second planar region. Along the length direction of the positive electrode sheet, the distance between the groove and the boundary between the flat region and the arc region is 0.1 mm-5 mm.

5. The core according to claim 1, characterized in that, H1 and H2 satisfy the relationship: H2:H1 = 0.3 to 0.8, and / or H1 and / or H2 is 0.15-5 microns. Preferably, H1 and / or H2 is 0.5-3 microns.

6. The core roll according to claim 1, characterized in that, Along the winding direction of the positive electrode sheet, the positive electrode sheet includes a plurality of arc segments arranged at intervals. The positive electrode sheet includes a plurality of grooves, and the plurality of grooves are respectively provided on at most three arc segments of the positive electrode sheet along the winding direction.

7. The core according to claim 1, characterized in that, The separator satisfies at least one of the following characteristics: a. The plurality of first protrusions and / or the plurality of second protrusions are independently arranged at intervals; b. The plurality of first protrusions and / or the plurality of second protrusions are independently arranged in a matrix; c. The maximum circumscribed circle diameter of the first protrusion and / or the second protrusion is 200 μm to 430 μm; d. There are a plurality of first voids between the plurality of first protrusions, and / or there are a plurality of second voids between the plurality of second protrusions. Along the winding direction of the core, the maximum circumscribed circle diameter of each of the first voids and / or each of the second voids is 5 μm - 80 μm; preferably, the maximum circumscribed circle diameter of each of the first voids and / or each of the second voids is 10 μm - 60 μm.

8. The core according to claim 1, characterized in that, The negative electrode active layer includes a silicon-carbon composite material, and the silicon-carbon composite material satisfies at least one of the following characteristics: The silicon-carbon composite material includes spherical silicon-carbon composite material and block-shaped silicon-carbon composite material, and / or, The average sphericity of the silicon-carbon composite material is 0.6 - 0.9, and / or, The porosity of the negative electrode sheet is 5 - 50%, and / or, The silicon-carbon composite material includes a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon coating layer located on the surface of the porous carbon matrix. The carbon coating layer covers the silicon grains, and / or, The silicon-carbon composite material includes open pores and / or closed pores. Closed pores refer to the pores in the porous carbon substrate covered by the carbon coating layer, and open pores refer to the pores on the porous carbon substrate not covered by the carbon coating layer. The area of the open pores is smaller than the area of the closed pores.

9. The core according to claim 1, characterized in that, The first protrusion includes a first polymer, and the first protrusion is formed by fusing the first polymer. The first polymer satisfies at least one of the following conditions: a. The first polymer includes non-granular polymer, granular polymer, and partially molten granular polymer; b. The first polymer includes first polymer particles, and all and / or part of the first polymer particles are fused; c. The second protrusion includes second polymer particles; the second polymer particles are granular and / or partially fused.

10. The core according to claim 9, characterized in that, The first polymer particles and the second polymer particles independently include one or more of PMMA, PMMA-HFP, PVDF, and PVDF-HFP, and / or, The first protrusion and / or the second protrusion is / are in one or more of the shapes of island, column, cup, dot, regular polygon, or irregular polygon.

11. A battery, characterized in that, It includes a housing and a core as described in any one of claims 1 - 10 provided in the housing.

Images