Battery cell and battery

Abstract

The invention relates to the technical field of batteries, and particularly provides a battery cell and a battery. Wherein the battery cell comprises a negative plate, a first diaphragm, a second diaphragm and a positive plate; the negative plate comprises a negative current collector and negative active material layers, the surfaces of the two sides of the negative current collector are coated with the negative active material layers, and concave parts are formed in the surfaces of the negative active material layers; the edge of the first diaphragm and the edge of the second diaphragm both exceed the negative plate and form a first exceeding part and a second exceeding part, and the negative plate comprises a first negative section and a second negative section; the first exceeding part and the second exceeding part corresponding to the first negative electrode section are mutually connected to form a first composite region, and the peel strength F1 of the first composite region is greater than the peel strength F2 between the first exceeding part and the second exceeding part corresponding to the second negative electrode section. The battery energy density can be improved, the charging and discharging rate can be improved, and the safety risk of the battery can be avoided.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and specifically proposes a battery cell and a battery. Background Art

[0002] At present, the battery cells of some batteries are formed by winding the positive electrode sheet, the separator and the negative electrode sheet (this type of battery cell can be called a wound core); Figure 1 In some traditional winding cores, the innermost part of the negative electrode sheet has a plain foil area (no active material layer is coated on both sides of the negative electrode current collector) and a single-sided coating area (only one side of the negative electrode current collector is coated with an active material layer). The space utilization rate inside the battery is relatively low, which affects the battery volume energy density. Summary of the Invention

[0003] The purpose of this application is to solve at least some of the technical problems mentioned above, and this purpose is achieved through the following technical solutions:

[0004] In the first aspect, the present application proposes a battery cell, which includes a negative electrode sheet, a separator and a positive electrode sheet stacked and wound in sequence; the battery cell includes a straight section and a bent section, the negative electrode sheet includes a negative electrode collector and a negative electrode active material layer, the negative electrode active material layer is coated on both sides of the negative electrode collector, the negative electrode active material layer includes a silicon-carbon composite material, the surface of the negative electrode active material layer is provided with a recess, the innermost circle of the negative electrode sheet includes a negative electrode winding starting section; the innermost circle of the positive electrode sheet includes a first positive electrode straight section and a first positive electrode bent section connected to the first positive electrode straight section, the first positive electrode bent section is the area where the positive electrode sheet is bent for the first time along its winding direction, and the negative electrode winding starting section has a negative electrode winding starting end facing the first positive electrode bent section; the separator includes a first separator and a second separator Membrane, along the first direction, a first diaphragm and a second diaphragm are respectively provided on both sides of the negative electrode sheet; along the second direction, the edge of the first diaphragm and the edge of the second diaphragm both extend beyond the edge of the negative electrode sheet and form a first protruding portion and a second protruding portion respectively, the negative electrode sheet includes a first negative electrode segment located in the straight section of the innermost circle of the battery cell, and the remaining portion of the negative electrode sheet except the first negative electrode segment is the second negative electrode segment; along the same side of the second direction, the first protruding portion and the second protruding portion corresponding to the first negative electrode segment are at least partially interconnected to form a first composite area, and the peeling strength F1 between the first protruding portion and the second protruding portion in the first composite area is greater than the peeling strength F2 between the first protruding portion and the second protruding portion corresponding to the second negative electrode segment; wherein the first direction and the second direction are perpendicular to each other.

[0005] In some embodiments, the first protrusion corresponding to the second negative electrode segment is not connected to the second protrusion and forms a gap, or the first protrusion corresponding to the second negative electrode segment is partially connected to the second protrusion; and / or, along the third direction, the first separator and the second separator respectively include a third protrusion and a fourth protrusion that extend beyond the starting segment of the negative electrode winding, and at least portions of the third protrusion and the fourth protrusion are interconnected to form a second composite area; wherein the first direction, the second direction and the third direction are perpendicular to each other.

[0006] In some embodiments, a plurality of recesses are provided on the surface of the negative electrode active material layer, and the plurality of recesses are spaced apart along the third direction; the edge of the negative electrode sheet at the starting section of the negative electrode winding is a first edge; wherein the first direction, the second direction and the third direction are perpendicular to each other; the recess is arranged parallel to the first edge, and the distance between the recess closest to the first edge and the first edge is d1, and satisfies 1mm≤d1≤15mm; or, the recess is arranged at an angle to the first edge, and the angle between the recess and the first edge is θ, and satisfies 2°≤θ≤80°; and / or, the width of the recess is 50μm to 150μm; and / or, the spacing between two adjacent recesses is 0.5mm to 3.5mm; and / or, the depth of the recess is 5μm to 30μm.

[0007] In some embodiments, the battery cell also includes a first insulating member, and along the first direction, at least part of the first insulating member is arranged on opposite sides of the starting section of the negative electrode winding, and the projection of the first insulating member along the first direction at least partially overlaps with the starting section of the negative electrode winding. The first insulating member includes a first substrate layer and a first adhesive layer arranged on the surface of at least one side of the first substrate layer; along the first direction, the first insulating member is fixed on opposite sides of the starting section of the negative electrode winding; and / or, along the first direction, the first insulating member is fixed on the first diaphragm and the second diaphragm arranged opposite to the starting section of the negative electrode winding.

[0008] In some embodiments, when the first substrate layer is provided with a first adhesive layer on the surface of the side facing the negative electrode winding starting section, along the first direction, the first insulating member is provided between the negative electrode winding starting section and the first separator and the second separator provided corresponding to the negative electrode winding starting section, and the first adhesive layer is bonded to the negative electrode winding starting section; or, when the first substrate layer is provided with a first adhesive layer on the surface of the side facing the negative electrode winding starting section, the first adhesive layer is bonded to the first separator and the second separator on the side away from the negative electrode winding starting section; or, when the first substrate layer is provided with a first adhesive layer on the surface of the side away from the negative electrode winding starting section When there is one adhesive layer, the first insulating member is arranged between the negative electrode winding starting section and the first separator and the second separator arranged corresponding to the negative electrode winding starting section, and the first adhesive layer is bonded to the surface of the first separator and the second separator facing the negative electrode winding starting section; or, when the first substrate layer is provided with the first adhesive layer on both side surfaces along the first direction, the first insulating member is arranged between the negative electrode winding starting section and the first separator and the second separator arranged corresponding to the negative electrode winding starting section, and the first adhesive layer is respectively bonded to the negative electrode winding starting section and the first separator and the second separator arranged opposite to the negative electrode winding starting section.

[0009] In some embodiments, along the third direction, the dimension of the first insulating member extending beyond the starting end of the negative electrode winding is d2, and satisfies 2mm≤d2≤10mm; and / or, along the third direction, the overlapping dimension of the first insulating member and the first separator and the second separator is d3; and / or, along the third direction, the overlapping dimension of the first insulating member and the starting section of the negative electrode winding is d3, and satisfies 1mm≤d3≤10mm; wherein the first direction, the second direction and the third direction are perpendicular to each other.

[0010] In some embodiments, along the third direction, the dimension of the first separator and the second separator extending beyond the negative electrode winding starting end is greater than or equal to the dimension of the first insulating member extending beyond the negative electrode winding starting end; wherein the first direction, the second direction and the third direction are perpendicular to each other.

[0011] In some embodiments, the first positive bending section of the positive electrode sheet is provided with a second insulating member; along the third direction, the two ends of the second insulating member respectively exceed the two ends of the first insulating member, and the size of the exceeding portion is d4, and satisfies 0.2mm≤d4≤10mm; wherein the first direction, the second direction and the third direction are perpendicular to each other; and / or, the second insulating member includes a second substrate layer and a second adhesive layer provided on at least one side of the second substrate layer, the second adhesive layer is intermittently provided to form a first blank area on the second substrate layer, at least part of the first blank area is provided opposite to the first positive bending section, and the positive electrode sheet is provided with a second blank area. The two straight sections connected to the first positive electrode bending section are respectively the first positive electrode straight section and the second positive electrode straight section, and the second adhesive layer is arranged facing the first positive electrode straight section and the second positive electrode straight section respectively; and / or, the second adhesive layer is arranged facing the negative electrode winding starting section; and / or, the second adhesive layer is arranged facing the first diaphragm and the second diaphragm; and / or, the second adhesive layer and the part of the second substrate layer arranged corresponding to it are provided with pores for metal cations to pass through; and / or, the area of ​​the second adhesive layer is S1, the area of ​​the entire second insulating member is S, and 0.2≤S1 / S≤0.8 is satisfied.

[0012] In some embodiments, the negative active material layer is provided with grooves exposing the negative current collector, and the grooves include a first groove and a second groove; along the second direction, the difference between the size of the first groove and the size of the second groove is d5, and satisfies 1mm≤d5≤15mm.

[0013] In a second aspect, the present application proposes a battery comprising the battery cell of the first aspect.

[0014] The technical solution proposed in this application has at least the following technical effects:

[0015] In the present application, a negative electrode active material layer is coated on both sides of the negative electrode current collector, and one end of the negative electrode winding starting section faces the first positive electrode bending section, which increases the space utilization rate inside the battery and improves the battery volume energy density. In addition, a recess is provided on the surface of the negative electrode active material layer, which can increase the contact area between the negative electrode active material layer and the electrolyte, allowing the electrolyte to fully penetrate the negative electrode active material layer and improve the reaction rate. In addition, the first protrusion and the second protrusion corresponding to the first negative electrode section are bonded to each other to form a first composite area. When the battery temperature rises, the first and second separators shrink and cover the negative electrode sheet, preventing the exposed negative electrode sheet from directly contacting the positive electrode sheet and causing an internal short circuit. In addition, the peel strength F2 between the first and second protrusions corresponding to the second negative electrode section is less than the peel strength F1 of the first composite area, thereby preventing the first and second separators from exerting excessive stress on the negative electrode sheet, thereby causing deformation of the negative electrode sheet. At the same time, it also prevents excessive stress from causing the recess to collapse and the active material to fall off, thereby causing battery safety issues. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to better integrate the contents shown in the drawings with the contents described in the specific embodiments, a brief introduction to the drawings is given below. It is understood that the drawings mentioned below are only schematic illustrations of the relevant technical solutions and some embodiments of the technical solutions of this application. Without making any creative efforts, those skilled in the art can also create drawings showing other embodiments.

[0017] Specifically, the annotations to the drawings of the specification are as follows:

[0018] Figure 1 This is a schematic diagram of the structure of the battery cell before improvement;

[0019] Figure 2 This is a schematic diagram of the structure of the battery cell described in some embodiments of the present application;

[0020] Figure 3 is a schematic diagram of the cross-sectional structure of the first negative electrode segment described in some embodiments of the present application;

[0021] Figure 4 Schematic diagram of the cross-sectional structure of the recess described in some embodiments of the present application;

[0022] Figure 5 A top view of the recess described in some embodiments of the present application;

[0023] Figure 6 A connection diagram of the first insulating member described in some embodiments of the present application;

[0024] Figure 7 This is another connection diagram of the first insulating member described in some embodiments of the present application;

[0025] Figure 8 A schematic structural diagram of a second insulating member described in some embodiments of the present application;

[0026] Figure 9 This is another structural schematic diagram of the second insulating member described in some embodiments of the present application;

[0027] Figure 10 This is a top view of the groove described in some embodiments of the present application.

[0028] Specifically, the annotations of the accompanying drawings are as follows:

[0029] Before improvement:

[0030] 10', negative electrode sheet; 110, plain foil area; 120, single-side coating area; 20', separator; 30', positive electrode sheet;

[0031] After improvement:

[0032] 10. Negative electrode sheet; 100. Negative electrode winding starting section; 101. Negative electrode winding starting end; 102. First negative electrode section; 104. Recess; 105. First groove; 106. Second groove; 107. First edge; 108. Negative electrode current collector; 109. Negative electrode active material layer; 20. Separator; 201. First separator; 2011. First protruding portion; 202. Second separator; 2021. Second protruding portion; 30. Positive electrode sheet; 301. First positive electrode bent section; 302. First positive electrode straight section; 303. Second positive electrode straight section; 40. Tab; 50. First insulating member; 60. Second insulating member; 601. Second substrate layer; 602. Second adhesive layer; Z, first direction; X, second direction; Y, third direction. DETAILED DESCRIPTION

[0033] To make the contents of the embodiments of this application clearer, the following description will be made in conjunction with the accompanying drawings. It is understood that the contents mentioned below are only some of the embodiments of this application, and all embodiments are listed in detail. Therefore, without inventive work, other embodiments obtained based on the following embodiments fall within the scope of protection of this application.

[0034] It should be understood that the terms used herein are for the purpose of describing specific embodiments only and are not intended to strictly limit the technical solutions unless the context clearly indicates otherwise. For example, the use of "a," "an," and "the" to modify a feature does not exclude the possibility that the feature may be plural in other embodiments.

[0035] It should be understood that the terms "include," "comprising," and "having" are open-ended, indicating the presence of the stated features but not excluding the possibility of additional features in the embodiment. Similarly, when terms such as first, second, etc. are used herein to describe multiple features, they are merely used to distinguish one feature from another and do not imply a sequence or order unless the context clearly indicates otherwise.

[0036] It should be understood that, unless the context clearly indicates otherwise, the terms "disposed," "connected," and "installed" should be interpreted broadly. For example, they may refer to fixed, detachable, or integral connections; they may be directly connected or indirectly connected through a medium. Those skilled in the art will understand the specific meanings of these terms in the context of the text based on the specific circumstances.

[0037] In addition, for the convenience of description, the text will use terms of spatial relative relationships to illustrate the position of one feature relative to another feature, such as "inside", "outside", "end", "side", "upper", "middle", "lower", "high", "lower", "axial", "circumferential", "radial", "horizontal", "vertical", "first direction", "second direction", etc. It can be understood that the spatial relative relationship between two features should include other specific situations in addition to those shown in the drawings of the specification.

[0038] The background technology is further analyzed below in conjunction with the accompanying drawings.

[0039] At present, the battery cell assembly of some batteries is formed by winding the positive electrode sheet 30', the separator 20' and the negative electrode sheet 10' (this battery cell assembly can be called a winding core); Figure 1 In some winding cores, the innermost end of the negative electrode sheet 10' has a plain foil area 110 (no active material layer is coated on both sides of the negative electrode current collector) and a single-sided coating area 120 (only one side of the negative electrode current collector is coated with an active material layer). The space utilization rate inside the battery is low, affecting the battery volume energy density.

[0040] In some improved cores, refer to Figure 2 The cell structure is that the negative electrode winding starting section 100 has a negative electrode winding starting end 101 facing the first positive electrode bending section 301, that is, a plug-in cell structure, and its negative electrode sheet 10 is a double-sided coating area (both sides of the negative electrode current collector 108 are coated with a negative electrode active material layer 109), thereby improving the battery volume energy density; it should be noted that, Figure 2 The plug-in battery cell structure has a high internal density and slow heat dissipation. The positive electrode sheet 30 and the negative electrode sheet 10 are directly opposite to each other, and the negative active material layer 109 of the negative electrode sheet 10 includes a silicon-carbon composite material that is prone to large expansion. The heat generated during the charge and discharge process is large. The negative electrode sheet 10 is covered with a diaphragm 20 on both sides along its thickness direction. When the internal temperature of the battery rises during the charge and discharge process, the temperature of the battery cell is high and difficult to dissipate. In particular, the temperature of the area of ​​the first negative electrode segment 102 located in the innermost layer of the battery cell is higher, and the heat is more difficult to dissipate, which makes the diaphragm 20 on both sides of the innermost part of the negative electrode sheet 10 easily shrink due to heat, thereby exposing the negative electrode sheet 10, which may cause direct contact between the negative electrode sheet 10 and the positive electrode sheet 30, causing an internal short circuit, affecting battery safety.

[0041] In addition, a recess 104 is provided on the negative electrode active material layer 109 in the negative electrode sheet 10, and along the width direction of the negative electrode sheet 10, the separators 20 on both sides of the negative electrode sheet 10 respectively extend beyond the negative electrode sheet 10 and are connected to each other to form a composite area; since the separators 20 on both sides of the negative electrode sheet 10 are the same length during composite, the outer separator 20 will be stretched after winding, and the degree of stretching of the outer separator 20 becomes greater and greater from the inside to the outside along the winding direction of the core. If the size of the composite area of ​​the separators 20 on both sides of the outer layer of the negative electrode sheet 10 is longer, that is, the peeling strength of the composite area of ​​the separator 20 is greater, the outer separator 20 and the inner separator 20 will be bound to generate a greater tension, thereby squeezing the negative electrode sheet 10 and causing the negative electrode sheet 10 to deform; at the same time, the setting of the recess 104 itself will cause the peeling strength of the negative electrode active material layer 109 to decrease. When the outer separator 20 is stretched, the outer separator 20 will be stretched. When the extension is large, the negative electrode active material layer 109 on the negative electrode sheet 10 is squeezed, which can easily cause the structure of the recess 104 to collapse, causing the negative electrode active material layer 109 in the recess 104 area to fall off; further, when the negative electrode active material layer 109 falls off, it will mainly cause the following safety risks: 1. The active material capacity per unit area of ​​the negative electrode sheet 10 is reduced, resulting in a smaller CB value between the positive and negative electrodes, and a risk of lithium precipitation; 2. The adhesion between the negative electrode sheet 10 and the diaphragm 20 is reduced, and the diaphragm 20 is prone to loosening and wrinkling, causing battery deformation, and the battery casing is prone to unevenness; 3. When the negative electrode active material layer 109 falls off more seriously, the battery capacity will decay rapidly, which will manifest as a poor K value; 4. After falling off, the negative electrode active material layer 109 may directly contact the positive electrode sheet 30, causing an internal short circuit in the battery.

[0042] The embodiments of the present application are described below in conjunction with the drawings. It can be understood that the technical features involved in the different embodiments described below can be combined with each other as long as there is no conflict between them.

[0043] First, refer to Figures 2 to 4, the embodiment of the present application proposes a battery cell, which includes a negative electrode sheet 10, a separator 20 and a positive electrode sheet 30 stacked and wound in sequence; the battery cell includes a straight section and a bent section, the negative electrode sheet 10 includes a negative electrode current collector 108 and a negative electrode active material layer 109, both sides of the negative electrode current collector 108 are coated with a negative electrode active material layer 109, the negative electrode active material layer 109 includes a silicon-carbon composite material, and a concave portion 104 is provided on the surface of the negative electrode active material layer 109, The innermost circle of the sheet 10 includes a negative electrode winding starting section 100; the innermost circle of the positive electrode sheet 30 includes a first positive electrode straight section 302 and a first positive electrode bent section 301 connected to the first positive electrode straight section 302. The first positive electrode bent section 301 is the area where the positive electrode sheet 30 is first bent along its winding direction. The negative electrode winding starting section 100 has a negative electrode winding starting end 101 facing the first positive electrode bent section 301; the separator 20 includes a first separator 201 and a second separator 202. 02, along the first direction Z, a first separator 201 and a second separator 202 are respectively provided on both sides of the negative electrode sheet 10; along the second direction X, the edges of the first separator 201 and the edges of the second separator 202 both extend beyond the edge of the negative electrode sheet 10 and form a first protruding portion 2011 and a second protruding portion 2021, respectively. The negative electrode sheet 10 includes a first negative electrode segment 102 located in the straight section of the innermost circle of the battery cell, and the remaining portion of the negative electrode sheet 10 except the first negative electrode segment 102 is the second negative electrode segment; along the same side of the second direction X, the first protruding portion 2011 and the second protruding portion 2021 corresponding to the first negative electrode segment 102 are at least partially connected to each other to form a first composite area, and the peel strength F1 between the first protruding portion 2011 and the second protruding portion 2021 in the first composite area is greater than the peel strength F2 between the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment; wherein the first direction Z and the second direction X are perpendicular to each other.

[0044] It can be understood that the negative electrode winding start segment 100 is a portion of the first negative electrode segment 102 .

[0045] In this embodiment, the negative electrode active material layer 109 is coated on both sides of the negative electrode current collector 108, and one end of the negative electrode winding starting section 100 is facing the first positive electrode bending section 301, so the space utilization rate inside the battery is large, and the battery volume energy density is improved; and the surface of the negative electrode active material layer 109 is provided with a recess 104, which can increase the contact area between the negative electrode active material layer 109 and the electrolyte, so that the electrolyte can fully infiltrate the negative electrode active material layer 109 and improve the reaction rate.

[0046] In addition, the first protruding portion 2011 and the second protruding portion 2021 corresponding to the first negative electrode segment 102 are bonded to each other to form a first composite area. When the battery temperature rises, the first diaphragm 201 and the second diaphragm 202 shrink and cover the negative electrode sheet 10, thereby preventing the negative electrode sheet 10 from being exposed and causing contact between the positive electrode sheet 30 and the negative electrode sheet 10, thereby preventing a short circuit.

[0047] Furthermore, according to the above analysis, when the separator 20 is compounded, since the lengths of the separators 20 on both sides of the negative electrode sheet 10 are the same, the outer separator 20 will be stretched after winding, and the degree of stretching of the outer separator 20 becomes larger and larger from the inside to the outside along the winding direction of the core. If the size of the compound area of ​​the separator 20 on both sides of the second negative electrode segment is longer, that is, the peeling strength F2 of the compound area of ​​the separator 20 is larger, the outer separator 20 and the inner separator 20 will be bound to each other and generate a larger tension, thereby squeezing the negative electrode sheet 10 and may cause the negative electrode sheet 10 to deform; at the same time, the setting of the recess 104 itself will cause the peeling strength of the negative electrode active material layer 109 to decrease. When the outer separator 20 is stretched more, it squeezes the negative electrode sheet 10. The negative electrode active material layer 109 may also easily cause the structure of the recess 104 to collapse, causing the negative electrode active material layer 109 in the recess 104 area to fall off, and cause the following problems: 1. The active material capacity per unit area of ​​the negative electrode sheet 10 is reduced, resulting in a smaller CB value between the positive and negative electrodes, and a risk of lithium plating; 2. The adhesion between the negative electrode sheet 10 and the separator 20 is reduced, and the separator 20 is prone to loosening and wrinkling, causing battery deformation and unevenness of the battery casing; 3. When the negative electrode active material layer 109 falls off more seriously, the battery capacity will decay rapidly, resulting in a poor K value; 4. After falling off, the negative electrode active material layer 109 may directly contact the positive electrode sheet 30, causing an internal short circuit in the battery.

[0048] In this embodiment, the peel strength F2 between the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment is smaller than the peel strength F1 of the first composite area, which can achieve at least the following effects: first, the peel strength F1 of the first composite area is relatively large, thereby ensuring the connection strength of the first composite area. When the inner layer of the winding core is not easy to dissipate heat and the temperature is high, the first separator 201 and the second separator 202 corresponding to the first negative electrode segment 102 will not cause the negative electrode sheet 10 to be exposed even after shrinkage due to heat, thereby avoiding direct contact between the negative electrode sheet 10 and the positive electrode sheet 30 and causing a short circuit; second, the peel strength F2 between the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment is relatively small, that is, the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment are relatively small. The restraining force between the first diaphragm 201 and the second diaphragm 202 is relatively small. For example, when the first diaphragm 201 is located on the outside of the second diaphragm 202, the tension on the first diaphragm 201 can be released, thereby alleviating the problem of large internal tension. Therefore, the first diaphragm 201 and the second diaphragm 202 will not generate a large extrusion force on the negative electrode sheet 10, thereby avoiding deformation of the negative electrode sheet 10 and simultaneously avoiding excessive extrusion of the negative active material layer 109 on the negative electrode sheet 10, so that the recessed portion 104 structure on the negative active material layer 109 will not collapse and the negative active material layer 109 will not fall off in large quantities, thereby preventing the battery safety problems such as lithium plating risk, battery deformation, poor battery K value and internal short circuit caused by the falling off of the negative active material layer 109 mentioned in the above analysis.

[0049] It should be noted that, in the present application, a spatial rectangular coordinate system is established with the thickness direction of the battery cell as the first direction Z, the height direction of the battery cell as the second direction X, and the width direction of the battery cell as the third direction Y; that is, the thickness direction of the negative electrode sheet 10 is the first direction Z, the width direction of the negative electrode sheet 10 is the second direction X, and the length direction of the negative electrode sheet 10 is the third direction Y; it can be understood that the thickness, width and length directions of the positive electrode sheet 30 are the same as the thickness, width and length directions of the negative electrode sheet 10, respectively.

[0050] It should also be noted that the negative electrode active material layer 109 includes a binder, which includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polymethacrylate, styrene acrylic emulsion, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

[0051] In addition, the diaphragm 20 includes a base film and a functional layer coated on one side of the base film, the functional layer includes a polymer, and the polymer is selected from polyvinylidene fluoride, polytetrafluoroethylene, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene modified and its copolymer, polyvinylidene fluoride-hexafluoropropylene homopolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride-trichloroethylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride-trichloroethylene homopolymer, polyvinylidene fluoride-chloro At least one of trifluoroethylene homopolymer, polyacrylonitrile, polyimide, polymethyl methacrylate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, styrene-butadiene rubber, polyvinyl alcohol and copolymer-modified polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, water-based polyurethane, ethylene-vinyl acetate copolymer, polyacrylic acid copolymer, lithium polystyrene sulfonate, pure benzene latex, polyvinyl pyrrolidone, polyethylene oxide, cellulose acetate, butyl cellulose acetate, propyl cellulose acetate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose.

[0052] It should be understood that the means of controlling F1 to be greater than F2 may be to choose a different polymer for the diaphragm 20, to control the content of the polymer in the functional layer, or to control the thickness of the functional layer of the diaphragm 20. In some embodiments, the thickness of the diaphragm 20 is 4 μm-20 μm, and the thickness of the functional layer is 0.5 μm-20 μm; or if the first diaphragm 201 and the second diaphragm 202 are thermally composited, different peel strengths can also be achieved by controlling the temperature of the thermal composite or the composite pressure, or by selecting different composite area positions.

[0053] Optionally, 0.001 N / mm≤F1≤0.02 N / mm.

[0054] In some embodiments, the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment are not connected and form a gap portion, or the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment are partially connected to each other; and / or, along the third direction Y, the first separator 201 and the second separator 202 respectively include a third protruding portion and a fourth protruding portion that extend beyond the negative electrode winding starting segment 100, and at least portions of the third protruding portion and the fourth protruding portion are interconnected to form a second composite region; wherein the first direction Z, the second direction X, and the third direction Y are perpendicular to each other.

[0055] Specifically, two configurations for the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment are proposed above. In some embodiments, the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment are not connected, that is, F2 = 0 N / mm. Obviously, in this case, F2 is less than F1. Alternatively, in other embodiments, the first protruding portion 2011 and the second protruding portion 2021 corresponding to the second negative electrode segment are partially connected, while ensuring that F2 < F1. This is also a desirable implementation. The effect of F2 < F1 has been analyzed above and will not be repeated here.

[0056] Optionally, along the third direction Y, the length of the first composite region is 5 mm to 30 mm.

[0057] In addition, the first separator 201 and the second separator 202 extend beyond the negative electrode winding starting section 100 along the third direction Y and are connected to each other, further wrapping the negative electrode sheet 10. When the battery temperature rises, the first separator 201 and the second separator 202 shrink and cover the negative electrode sheet 10, thereby preventing the negative electrode sheet 10 from being exposed and directly contacting the positive electrode sheet 30, causing an internal short circuit.

[0058] In some embodiments, a plurality of recesses 104 are provided on the surface of the negative electrode active material layer 109, and the plurality of recesses 104 are spaced apart along the third direction Y; the edge of the negative electrode sheet 10 at the negative electrode winding starting section 100 is a first edge 107; wherein the first direction Z, the second direction X and the third direction Y are perpendicular to each other; Figure 4 and Figure 10 , the concave portion 104 is arranged parallel to the first edge 107, the distance between the concave portion 104 closest to the first edge 107 and the first edge 107 is d1, and satisfies 1mm≤d1≤15mm; or, referring to Figure 5 , the recess 104 is arranged at an angle to the first edge 107, the angle between the recess 104 and the first edge 107 is θ, and satisfies 2°≤θ≤80°; and / or, the width of the recess 104 is 50μm to 150μm; and / or, the spacing between two adjacent recesses 104 is 0.5mm to 3.5mm; and / or, the depth of the recess 104 is 5μm to 30μm.

[0059] In this embodiment, two distribution modes of the recesses 104 are proposed. One is that the recesses 104 are arranged parallel to the first edge 107 , and the other is that the recesses 104 are arranged at an angle to the first edge 107 . Both of the above are desirable implementation modes.

[0060] Specifically, when the recess 104 is arranged parallel to the first edge 107 and the distance d1 between the recess 104 closest to the first edge 107 and the first edge 107 is small, due to the small width of the recess 104 and the small spacing between adjacent recesses 104, when the negative electrode sheet 10 is cut to form the first edge 107, it is easier to cut into the inside of the recess 104, thereby causing the negative electrode active material layer 109 at the recess 104 structure to fall off, or directly cut into the negative electrode active material layer 109 between adjacent recesses 104, causing the negative electrode active material layer 109 to fall off, which may further cause battery safety problems such as lithium plating risk, battery deformation, poor battery K value and internal short circuit.

[0061] The analysis of various battery safety issues that may be caused by the falling of the negative electrode active material layer 109 has been explained in the above content and will not be repeated here or in the following.

[0062] In addition, if the distance d1 between the recess 104 closest to the first edge 107 and the first edge 107 is large, the area of ​​the recess 104 region will be reduced, that is, the contact area between the negative electrode active material layer 109 and the electrolyte will be reduced, affecting the degree of electrolyte infiltration of the negative electrode active material layer 109. In other words, it affects the kinetic properties of lithium ions in the electrolyte, slowing the binding rate between the negative electrode sheet 10 and lithium ions, which may cause lithium plating. Therefore, the value of d1 should be moderate to avoid the above-mentioned battery safety issues. For example, d1 can be any value among 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm and 15mm, or a range between any two of these values.

[0063] Furthermore, when the recess 104 is arranged at an angle to the first edge 107, the negative electrode sheet 10 is prevented from being cut into the recess 104 and causing the negative electrode active material layer 109 to fall off, or from being cut directly into the negative electrode active material layer 109 between adjacent recesses 104 and causing the negative electrode active material layer 109 to fall off. Therefore, the recess 104 under this structure is relatively strong, and the negative electrode active material layer 109 at the recess 104 structure is less likely to fall off. Specifically, θ can be any value among 2°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, and 80°, or a range between any two of these values, to ensure that the recess 104 is arranged at an angle to the first edge 107.

[0064] Furthermore, when θ is less than 2°, the recess 104 is almost parallel to the first edge 107, and it is obvious that the distance between the recess 104 and the first edge 107 is relatively close. Therefore, the negative electrode active material layer 109 analyzed above is likely to fall off, which may lead to battery safety problems such as lithium plating risk, battery deformation, poor battery K value, and internal short circuit; when θ is greater than 80°, the recess 104 is approximately perpendicular to the first edge 107, that is, the recess 104 is approximately parallel to the first separator 201 and the second separator 202. When the first separator 201 and the second separator 202 shake along the width direction of the negative electrode sheet 10, the recess 104 is easily adhered to the first separator 201 and the second separator 202 and falls off, which may also lead to battery safety problems such as lithium plating risk, battery deformation, poor battery K value, and internal short circuit.

[0065] In some embodiments, reference Figure 6 and Figure 7 The battery cell also includes a first insulating member 50. Along the first direction Z, at least part of the first insulating member 50 is arranged on opposite sides of the negative electrode winding starting section 100, and the projection of the first insulating member 50 along the first direction Z at least partially overlaps with the negative electrode winding starting section 100. The first insulating member 50 includes a first substrate layer and a first adhesive layer provided on at least one side surface of the first substrate layer; along the first direction Z, the first insulating member 50 is fixed on opposite sides of the negative electrode winding starting section 100; and / or, along the first direction Z, the first insulating member 50 is fixed on the first separator 201 and the second separator 202 arranged opposite to the negative electrode winding starting section 100.

[0066] In this embodiment, the first insulating member 50 is wrapped around the negative electrode winding starting end 101 and separates the negative electrode winding starting end 101 from the first positive electrode bending section 301 to avoid short circuit and prevent the negative electrode active material layer 109 from falling into the battery and causing safety risks.

[0067] In some embodiments, reference Figure 6 and Figure 7, when the first substrate layer is provided with a first adhesive layer on the surface facing the negative electrode winding starting section 100, along the first direction Z, the first insulating member 50 is provided between the negative electrode winding starting section 100 and the first separator 201 and the second separator 202 corresponding to the negative electrode winding starting section 100, and the first adhesive layer is bonded to the negative electrode winding starting section 100; or, when the first substrate layer is provided with a first adhesive layer on the surface facing the negative electrode winding starting section 100, the first adhesive layer is bonded to the surface of the first separator 201 and the second separator 202 away from the negative electrode winding starting section 100; or, when the first substrate layer is provided with a first adhesive layer on the surface away from the negative electrode winding starting section 100, the first insulating member 50 is arranged between the negative electrode winding starting section 100 and the first separator 201 and the second separator 202 corresponding to the negative electrode winding starting section 100, and the first adhesive layer is bonded to the surface of the first separator 201 and the second separator 202 facing the negative electrode winding starting section 100; or, when the first substrate layer is provided with a first adhesive layer on both side surfaces along the first direction Z, the first insulating member 50 is arranged between the negative electrode winding starting section 100 and the first separator 201 and the second separator 202 corresponding to the negative electrode winding starting section 100, and the first adhesive layer is respectively bonded to the negative electrode winding starting section 100 and the first separator 201 and the second separator 202 opposite to the negative electrode winding starting section 100.

[0068] In this embodiment, a specific connection method of the first insulating member 50 is proposed, that is, the first insulating member 50 includes a first substrate layer and a first adhesive layer, and the first adhesive layer is provided on one or both sides of the first substrate layer. The first insulating member 50 utilizes the first adhesive layer to bond with the first diaphragm 201, the second diaphragm 202 and / or the negative electrode winding starting section 100.

[0069] In some embodiments, reference Figure 8 , along the third direction Y, the dimension of the first insulating member 50 extending beyond the negative electrode winding starting end 101 is d2, and satisfies 2mm≤d2≤10mm; and / or, along the third direction Y, the overlapping dimension of the first insulating member 50 with the first separator 201 and the second separator 202 is d3; and / or, along the third direction Y, the overlapping dimension of the first insulating member 50 with the negative electrode winding starting section 100 is d3, and satisfies 1mm≤d3≤10mm.

[0070] It should be understood that when d2 is small, that is, the redundancy reserved for the first insulating member 50 is small, when the negative electrode sheet 10 is deformed, the tension of the first insulating member 50 is large, so it is easy to separate from the negative electrode sheet 10, and the negative electrode active material layer 109 adheres to it and falls off, which may cause battery safety problems such as lithium plating risk, battery deformation, poor battery K value and internal short circuit; in addition, when d2 is large, the first insulating member 50 reserves a large amount of redundancy, taking up too much space, and the redundant part of the first insulating member 50 may also fold back to the surface of the negative electrode sheet 10, affecting the local thickness of the battery, and thus affecting the battery volume energy density.

[0071] Therefore, in this embodiment, the dimension d2 of the first insulating member 50 extending beyond the negative electrode winding starting end 101 should be moderate, so that the first insulating member 50 can not only provide a good covering effect on the negative electrode winding starting end 101, but also will not be too redundant and occupy too much space. It can be understood that d2 can take any value among 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm and 10 mm, or be in a range between any two of these values.

[0072] In addition, when d3 is small, that is, the connection strength is small, the first insulating member 50 is easily disconnected from the separator 20 and / or the negative electrode sheet 10, and is easily adhered to the negative electrode active material layer 109 and falls off, which may lead to battery safety issues such as lithium plating risk, battery deformation, poor battery K value, and internal short circuit. In addition, when d3 is large, the overlap size of the first insulating member 50 and the separator 20 and / or the negative electrode sheet 10 is large, that is, the thickness accumulation area is too large, affecting the local thickness of the battery and thus affecting the battery volume energy density. Therefore, the overlap size of the first insulating member 50 and the first separator 201 and the second separator 202, or the overlap size of the first insulating member 50 and the negative electrode winding starting section 100 should also be moderate, that is, d3 should be moderate, so that it can achieve a more stable connection effect and avoid causing local thickness accumulation areas of the battery or increasing the area in the battery that does not participate in lithium insertion and extraction, thereby reducing the battery energy density. It can be understood that d3 can take any value among 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm and 10mm, or a range between any two values ​​therein.

[0073] In some embodiments, reference Figure 7 Along the third direction Y, the dimension of the first separator 201 and the second separator 202 extending beyond the negative electrode winding starting end 101 is greater than or equal to the dimension of the first insulating member 50 extending beyond the negative electrode winding starting end 101 .

[0074] In this embodiment, the first separator 201 and the second separator 202 are larger than the negative electrode winding starting end 101, and the insulation effect is good, which prevents the positive electrode sheet 30 from directly contacting the negative electrode sheet 10 and shorting. Figure 7 The first separator 201, the second separator 202 and the first insulating member 50 can be cut synchronously, that is, the size of the first separator 201 and the second separator 202 exceeding the starting end 101 of the negative electrode winding is equal to the size of the first insulating member 50 exceeding the starting end 101 of the negative electrode winding. The first insulating member 50 includes an upper and a lower section and is bonded together, which is easy to operate.

[0075] In some embodiments, reference Figure 8 , the first positive bending section 301 of the positive electrode sheet 30 is provided with a second insulating member 60; along the third direction Y, both ends of the second insulating member 60 respectively exceed both ends of the first insulating member 50, and the size of the exceeding portion is d4, and satisfies 0.2mm≤d4≤10mm; and / or, referring to Figure 9 The second insulating member 60 includes a second substrate layer 601 and a second adhesive layer 602 provided on at least one side of the second substrate layer 601. The second adhesive layer 602 is intermittently provided to form a first blank area on the second substrate layer 601. At least a portion of the first blank area is arranged opposite to the first positive electrode bending section 301. The two straight sections connected to the first positive electrode bending section 301 on the positive electrode sheet 30 are respectively the first positive electrode straight section 302 and the second positive electrode straight section 303. The second adhesive layer 602 faces the first positive electrode straight section 302 and the second positive electrode straight section 303 respectively. 02 and the second positive electrode straight section 303 are arranged; and / or, the second adhesive layer 602 is arranged facing the negative electrode winding starting section 100; and / or, the second adhesive layer 602 is arranged facing the first separator 201 and the second separator 202; and / or, the second adhesive layer 602 and the portion of the second substrate layer 601 arranged corresponding thereto are provided with pores for allowing metal cations to pass through; and / or, the area of ​​the second adhesive layer 602 is S1, the area of ​​the entire second insulating member 60 is S, and 0.2≤S1 / S≤0.8 is satisfied.

[0076] In this embodiment, a second insulating member 60 is provided at the first positive electrode bending section 301, thereby further avoiding direct contact and short circuit between the first positive electrode bending section 301 and the negative electrode winding starting end 101. The second insulating member 60 extends beyond the first insulating member 50, ensuring that the negative electrode winding starting end 101 is fully covered by the first insulating member 50 while ensuring that the first positive electrode bending section 301 is fully covered, preventing the lithium ions in the positive electrode active layer in the first positive electrode bending section 301 from being released and causing lithium deposition, while ensuring that d4 is within an appropriate range, reducing the overlap of the first insulating member 50 and the second insulating member 60, resulting in a local thickness accumulation area of ​​the battery or an increase in the area in the battery that does not participate in lithium insertion and extraction, thereby reducing the battery energy density.

[0077] In addition, the second insulating member 60 uses an intermittently arranged second adhesive layer 602 to respectively connect the first positive electrode straight section 302 and the second positive electrode straight section 303 to ensure the stability of the second insulating member 60; and the second insulating member 60 forms a first blank area on the second substrate layer 601, and the first blank area is arranged opposite to the first positive electrode bending section 301, thereby reducing the adhesion of the second adhesive layer 602 to the positive electrode sheet 30, reducing the binding force on the positive electrode sheet 30, and preventing the positive electrode sheet 30 from breaking when bending.

[0078] Specifically, the portion where the second insulating member 60 is connected to the straight section of the positive electrode sheet 30 can also allow metal cations to pass through, further reducing the area between the positive electrode sheet 30 and the negative electrode sheet 10 that does not participate in the lithium insertion and extraction reaction, thereby avoiding reducing the energy density of the battery.

[0079] It can be understood that d4 can take any value among 0.2mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm and 10mm, or a range between any two of them; S1 / S can take any value among 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8, or a range between any two of them.

[0080] In some embodiments, reference Figure 10 The negative electrode active material layer 109 is provided with grooves exposing the negative electrode current collector 108, and the grooves include a first groove 105 and a second groove 106; along the second direction X, the difference between the size of the first groove 105 and the size of the second groove 106 is d5, and satisfies 1mm≤d5≤15mm.

[0081] In this embodiment, the first groove 105 and the second groove 106 can be tab grooves, and the sizes of the first groove 105 and the second groove 106 are different, that is, a larger groove is set on the negative electrode active material layer 109 to connect the corresponding tab 40, thereby increasing the flow capacity, while retaining the smaller groove to avoid excessive loss of active material and affect the energy density. Of course, the first groove 105 and the second groove 106 can also refer to a groove body used to set other structures, such as a groove body in a battery cell corresponding to the tab groove, which is generally provided with an isolation tape for isolating the burrs at the welding point of the tab 40; specifically, setting first grooves 105 and second grooves 106 of different sizes can adapt to the isolation tapes of different sizes set in the battery, further improving the battery energy density; it should be noted that in the present application, the two surfaces of the negative electrode collector 108 are double-sided coated sheets completely coated with the negative electrode active layer 109, that is, there is no single-sided coating area on the negative electrode sheet 10, and the negative electrode sheet 10 does not need to be changed during the coating process to improve the coating efficiency, but the negative electrode sheet 10 without a single-sided coating area is difficult to locate the cutting position when cutting. At this time, setting first grooves 105 and second grooves 106 of different sizes on the negative electrode sheet 10 is also conducive to positioning the length position of the negative electrode sheet 10, ensuring the cutting size of the negative electrode sheet 10, reducing the difficulty of cutting, and thus improving the preparation efficiency of the battery.

[0082] It can be understood that d5 can take any value among 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm and 15mm, or a range between any two values.

[0083] Specifically, some detailed examples and comparative examples are listed below to illustrate the present application:

[0084] 1. Preparation of negative electrode sheet 10

[0085] Silicon-carbon composite material, graphite, conductive carbon black, polyacrylic acid, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 43.1:53.8:0.5:1.3:0.4:0.9, added to deionized water and stirred evenly to form a negative electrode slurry, which is then evenly coated on both sides of the negative electrode current collector 108 copper foil along its thickness direction to form a negative electrode active material layer 109. After drying and rolling, the negative electrode sheet 10 is formed, and a recess 104 is opened on the negative electrode active material layer 109.

[0086] 2. Preparation of positive electrode sheet 30

[0087] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and conductive carbon (SuperP) are dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 98:1:1 and stirred evenly to form a positive electrode slurry, which is then evenly coated on both sides of the positive electrode current collector aluminum foil along its thickness direction. After drying and rolling, a positive electrode sheet 30 is formed.

[0088] 3. Battery Assembly

[0089] The negative electrode sheet 10, the separator 20, and the positive electrode sheet 30 are stacked in order, wherein the separator 20 includes a first separator 201 and a second separator 202, and the two sides of the negative electrode sheet 10 along its thickness direction are covered with the first separator 201 and the second separator 202 respectively, and the first separator 201 and the second separator 202 exceed the negative electrode sheet 10 along the width direction of the negative electrode sheet 10 and are compounded, and a first insulating member 50 is provided at one end of the negative electrode sheet 10, and the negative electrode sheet 10, the separator 20, and the positive electrode sheet 30 are wound to obtain a battery cell, wherein the end of the negative electrode sheet 10 provided with the first insulating member 50 is the negative electrode winding starting end 101, and the negative electrode winding starting end 101 is opposite to the first positive electrode bending section 301, and the second insulating member 60 is provided at the position of the first positive electrode bending section 301; then the battery cell is placed in a shell for packaging, and then the processes of liquid injection, secondary sealing, formation, and sorting are carried out to obtain the battery.

[0090] It should be noted that each of the following embodiments and comparative examples was tested on 100 battery samples. For example, a short-circuit rate of 1% means that one battery out of the 100 tested batteries had a short circuit, a K value defect rate of 4% means that the K values ​​of four batteries out of the 100 tested batteries did not meet the standard, and a lithium plating ratio of 6% means that lithium plating occurred in six batteries out of the 100 tested batteries.

[0091] Example 1-1: The recess 104 is parallel to the first edge 107; the width of the recess 104 is 100 μm, the distance between two adjacent recesses 104 is 1.2 mm, and the depth of the recess 104 is 17 μm; d4 = 2 mm, d5 = 3 mm, and S1 / S = 0.5;

[0092] Example 1-2: The width of the concave portion 104 is 90 μm, the distance between two adjacent concave portions 104 is 2 mm, and the depth of the concave portion 104 is 20 μm. Except for the parameters in the table, the remaining data are the same as those in Example 1-1.

[0093] Examples 2 to 7, Comparative Examples 1 and 2, and Examples 11 to 16: Except for the parameters in the table, the remaining data are the same as those of Examples 1-2;

[0094] Examples 8 to 10 and Examples 17 and 18: The recess 104 is arranged at an angle to the first edge 107. Except for the parameters in the table, the remaining data are the same as those of Examples 1-2.

[0095] Test method:

[0096] 1. Energy density: The batteries prepared in the comparative example and the example were charged and discharged at 0.5C / 0.5C for capacity calibration and weighed, and the thickness, width and height of the battery cells were measured. The battery cell volume V = height * thickness * width was calculated, and the weight volume energy density was calculated. Volume energy density (ED) = (V nominal *C) / V;

[0097] Among them, V nominal : Nominal voltage of the battery (unit: V),

[0098] C: nominal capacity of the battery (unit: Ah),

[0099] V: Battery volume (unit: cm 3 );

[0100] 2. Short circuit rate: Use an insulation resistance tester to connect the positive and negative tabs of the wound battery cell. Apply a small current (such as 1.8mA), a high voltage (such as 100V), a pressure of 0.1MPa to 0.2MPa, and a time of 2s to 3s to the core. The insulation resistance tester outputs the internal resistance value. If the internal resistance is less than 20MPa, it is a short circuit.

[0101] 3. K value defective rate:

[0102] Test method for a defective K value: Charge the battery at 1C constant current and constant voltage at 25°C to 4.5V, then cut off at 0.02C. Let it rest for 5 minutes and measure the battery's open-circuit voltage (0CV1) (unit: V). Then, place the battery in an open circuit at (25±2)°C for 24 hours. Measure the battery's voltage (0CV2) after the open circuit. Calculate the battery's self-discharge coefficient (K): K = (0CV1 - 0CV2) / 24. The normal range for the self-discharge coefficient (K) is -0.02 to 0.08. Any value outside this range is considered defective. A total of 100 battery samples were tested.

[0103] 4. Battery lithium deposition test:

[0104] Battery lithium deposition test method: Charge the obtained battery to a fully charged state (SOC=100%), then disassemble it in a humidity-free environment, and observe whether the surface of the negative electrode is golden yellow and whether there is silver-white / silver-gray / dark gray substance. If there is an area of ​​silver-white / silver-gray or dark gray substance, it is considered that the battery has undergone lithium deposition.

[0105] 5. Peel strength test method:

[0106] Sample preparation: disassemble the two layers of separator 20 on both sides of the negative electrode sheet 10 in the battery, take the separator 20 corresponding to the first negative electrode segment 102, put it into DMC (electrolytic solvent) for cleaning, and then bake it at 60°C for 2 hours to dry the separator 20. Then, hot press the two layers of separator 20 for 2 seconds to 3 seconds at 95°C and 0.3 MPa to bond the two layers of separator 20 together; cut a sample of the hot-pressed and laminated separator 20 of a certain size (for example, the cut size can be 100mm*20mm, but the size is not limited to this, as long as it meets the test conditions), and stick the sample flat on a stainless steel plate with a double-sided tape layer, and then tear off about 10mm of the surface separator 20; fix the stainless steel plate with the sample on a tensile testing machine, and then tighten the torn section of the separator 20 to the tensile clamp of the testing machine;

[0107] Test: Set the peel speed to 50mm / min, set the sample width to 20mm, clear the tensile testing machine data, and then click Start Test. The test can be ended when the peel force is stable and no longer changes. Then read the average peel force and divide it by the actual sample width (for example, 20mm) to get the peel strength.

[0108] In addition, the peel strength test between the separators 20 corresponding to the second negative electrode segment can refer to the above method, but adopt the combined conditions of temperature and pressure less than 95°C and 0.3 MPa (for example, 85°C and 0.1 MPa). However, if, after disassembling the battery, it is observed that the two layers of separators 20 corresponding to the second negative electrode segment are not connected to each other, that is, a gap is formed, then the second peel strength F2 can be considered to be 0 N / mm.

[0109] Table 1

[0110]

[0111]

[0112] Table 2

[0113] project Energy density (Wh / L) Short circuit rate K value defective rate Whether lithium is deposited Example 1-1 880 1％ 4％ no Example 1-2 879.5 1％ 4％ no Example 2 880 1％ 5％ no Example 3 879 1％ 4％ no Example 4 880 1％ 4％ no Example 5 879 1％ 5％ no Example 6 880 1％ 4％ no Example 7 878 1％ 4％ no Example 8 880 1％ 4％ no Example 9 880 1％ 4％ no Example 10 879.5 1％ 4％ no Comparative Example 1 880 6％ 10％ Lithium deposition ratio 6% Comparative Example 2 879 7％ 10％ Lithium deposition ratio 6% Example 11 878.8 6％ 7％ Lithium deposition ratio 6% Example 12 878 1％ 4％ Lithium deposition ratio 3% Example 13 880 4％ 10％ Lithium deposition ratio 3% Example 14 873 1％ 4％ no Example 15 880 3％ 9％ Lithium deposition ratio 3% Example 16 874 1％ 4％ no Example 17 880 5％ 15％ Lithium deposition ratio 3% Example 18 879 2％ 5％ Lithium deposition ratio 1%

[0114] In combination with Table 1 and Table 2, referring to Example 1-1 and Example 1-2, Comparative Example 1 and Comparative Example 2, it can be seen that when F1-F2>0, that is, F1>F2, the short-circuit rate and K-value defective rate of the battery are at a low level, and lithium plating does not occur, indicating that when F1>F2, the diaphragm 20 will not excessively squeeze the recess 104, causing the negative electrode active material layer 109 to fall off; when F1-F2≤0, that is, F1≤F2, the short-circuit rate and K-value defective rate of the battery are both high, which means that the battery is prone to internal short circuit, and the battery capacity is prone to significant attenuation, and the probability of lithium plating in the battery is also high, indicating that when F1≤F2, the internal tension of the diaphragm 20 is large, and it is easy to squeeze the recess 104, causing the negative electrode active material layer 109 to fall off.

[0115] In combination with Table 1 and Table 2, referring to Examples 1-2, 2, 3, 11 and 12, it can be seen that when the concave portion 104 is parallel to the first edge 107, and when 1 mm ≤ d1 ≤ 15 mm, the short circuit rate and K value defective rate of the battery are both at a low level, and the battery has no risk of lithium plating, indicating that when 1 mm ≤ d1 ≤ 15 mm, the distance between the concave portion 104 closest to the first edge 107 and the first edge 107 is moderate, which can not only ensure the area of ​​the concave portion 104 region, so that the electrolyte has a sufficient infiltration effect on the negative electrode active material layer 109, but also prevent the concave portion 104 from being affected by the cutting of the first edge 107 and the negative electrode active material layer 109 falling off; when d1 < 1 mm, the short circuit rate and K value defective rate of the battery are both high, and the battery has a high risk of lithium plating, indicating that when d1 < 1 mm, the concave portion 104 closest to the first edge 107 and the first edge 1 07 is close. When the negative electrode sheet 10 is cut to form the first edge 107, it is easy to cut into the inside of the recess 104, thereby causing the negative electrode active material layer 109 at the recess 104 structure to fall off, or directly cut into the negative electrode active material layer 109 between adjacent recesses 104, causing the negative electrode active material layer 109 to fall off; when d1>15mm, although the short circuit rate and K value defect rate of the battery can also be maintained at a low level, the battery has a certain risk of lithium plating, which means that when d1>15mm, the distance between the recess 104 closest to the first edge 107 and the first edge 107 is large, which will reduce the area of ​​the recess 104 region, that is, reduce the contact area between the negative electrode active material layer 109 and the electrolyte, affect the degree of electrolyte infiltration of the negative electrode active material layer 109, that is, affect the kinetic properties of lithium ions in the electrolyte, slow down the binding rate of the negative electrode sheet 10 and lithium ions, and thus cause lithium plating.

[0116] In combination with Table 1 and Table 2, referring to Examples 1-2, 4, 5, 13 and 14, it can be seen that when 2mm≤d2≤10mm, the short circuit rate and K value defective rate of the battery are both at a low level, and the energy density of the battery is high, and there is no lithium plating phenomenon, which shows that when 2mm≤d2≤10mm, the size of the first insulating member 50 exceeding the negative electrode winding starting end 101 is relatively moderate, and the first insulating member 50 can have a good coating effect on the negative electrode winding starting end 101, and is not prone to disconnection and adhesion of the negative electrode active material layer 109 to fall off, and is not too redundant and takes up too much space; when d2<2 .... It is higher and lithium plating will occur, which means that when d2 is less than 2 mm, the first insulating member 50 has a smaller amount of redundancy reserved. When the negative electrode sheet 10 is deformed, the tension of the first insulating member 50 is larger, making it easy to separate from the negative electrode sheet 10 and causing the negative electrode active material layer 109 to fall off. When d2 is greater than 10 mm, although the short circuit rate and K value defective rate of the battery can be maintained at a low level and there is no lithium plating, the energy density of the battery is lower, which means that when d2 is greater than 10 mm, the first insulating member 50 has a larger amount of redundancy reserved, which occupies too much space. The redundant part of the first insulating member 50 may also be folded back to the surface of the negative electrode sheet 10, affecting the local thickness of the battery and further affecting the volume energy density of the battery.

[0117] In combination with Table 1 and Table 2, referring to Examples 1-2, 6, 7, 15 and 16, it can be seen that when 1mm≤d3≤10mm, the short circuit rate and K value defective rate of the battery are both at a low level, and the energy density of the battery is high, and no lithium plating occurs, indicating that when 1mm≤d3≤10mm, the overlapping size of the first insulating member 50 and the diaphragm 20 and / or the negative electrode sheet 10 is relatively moderate, which can not only achieve a relatively stable connection effect, but also avoid causing local thickness accumulation of the battery or causing an increase in the area of ​​the battery that does not participate in lithium insertion and extraction, thereby reducing the battery energy density; when d3<1 mm, the short-circuit rate and K-value defective rate of the battery are high, and lithium plating occurs, indicating that when d3 is less than 1 mm, the connection strength is small, the first insulating member 50 is easily disconnected from the diaphragm 20 and / or the negative electrode sheet 10, and the negative electrode active material layer 109 is easily adhered and falls off; when d3 is greater than 10 mm, although the short-circuit rate and K-value defective rate of the battery can also be maintained at a low level, the energy density of the battery is low, indicating that when d3 is greater than 10 mm, the overlapping size of the first insulating member 50 and the diaphragm 20 and / or the negative electrode sheet 10 is large, that is, the thickness accumulation area is too large, which affects the local thickness of the battery, and thus affects the battery volume energy density.

[0118] In combination with Table 1 and Table 2, referring to Examples 8 to 10, and Examples 17 and 10, it can be seen that when the recess 104 is set at an angle to the first edge 107, and when 2°≤θ≤80°, the short-circuit rate and K value defect rate of the battery are both at a low level, and lithium plating does not occur. This shows that when 2°≤θ≤80°, the angle between the recess 104 and the first edge 107 can be ensured, and the value of θ is moderate, which avoids cutting into the recess 104 when the negative electrode sheet 10 is cut to form the first edge 107, thereby preventing the negative electrode active material layer 109 at the recess 104 from falling off, or directly cutting into the negative electrode active material layer 109 between adjacent recesses 104, thereby preventing the negative electrode active material layer 109 from falling off. Therefore, the recess 104 under this structure is relatively firm, and the negative electrode active material layer 109 at the recess 104 structure is not prone to falling off. When θ is less than 2°, the short-circuit rate and K-value defective rate of the battery are significantly increased, and lithium plating occurs, indicating that when θ is less than 2°, the recess 104 is almost parallel to the first edge 107, and it is obvious that the distance between the recess 104 and the first edge 107 is relatively close, so the negative electrode active material layer 109 obtained from the above analysis is prone to falling off; when θ is greater than 80°, the short-circuit rate and K-value defective rate of the battery are also slightly increased, and lithium plating occurs, indicating that when θ is greater than 80°, the recess 104 is approximately perpendicular to the first edge 107, that is, the recess 104 is approximately parallel to the first separator 201 and the second separator 202. When the first separator 201 and the second separator 202 shake along the width direction of the negative electrode sheet 10, the recess 104 is easily adhered to the first separator 201 and the second separator 202 and falls off.

[0119] In the second aspect, an embodiment of the present application proposes a battery comprising the battery cell of the first aspect. Therefore, the battery of the second aspect has all the technical effects of the battery cell of the first aspect, and its specific technical effects are not repeated here. It should be understood that the battery of this embodiment also includes other components, such as a housing, a seal, etc., and other components are not described. Optionally, the battery proposed in this embodiment may be, but is not limited to, a soft-pack battery, a cylindrical battery, a square battery, etc.

[0120] In particular, the term "and / or" in this application should be understood as follows:

[0121] In the first case, the term “and / or” located between a first subject and a second subject includes any one of the following meanings: (1) only the first subject; (2) only the second subject; and (3) the first subject and the second subject.

[0122] In the second case, the term "and / or" between the last two entities in three or more entities means including at least any one of the entities. For example, "the first entity, the second entity and / or the third entity" has the same meaning as "the first entity and / or the second entity and / or the third entity", specifically including the following combinations: (1) only the first entity; (2) only the second entity; (3) only the third entity; (4) the first entity and the second entity without the third entity; (5) the first entity and the third entity without the second entity; (6) the second entity and the third entity without the first entity; and (7) the first entity, the second entity and the third entity;

[0123] In addition, the character “ / ” in this application indicates that the objects before and after it are in an “or” relationship.

[0124] Finally, although the above content describes the embodiments of the present application in conjunction with the accompanying drawings, those skilled in the art can also make various modifications and variations without departing from the concept of the present application, and such modifications and variations shall fall within the scope of protection of the present application.

Claims

1. A battery cell, characterized in that: The invention relates to a battery cell comprising a negative electrode sheet (10), a separator (20) and a positive electrode sheet (30) which are sequentially stacked and wound; the battery cell comprises a straight section and a bent section; the negative electrode sheet (10) comprises a negative electrode current collector (108) and a negative electrode active material layer (109); both sides of the negative electrode current collector (108) are coated with the negative electrode active material layer (109); the negative electrode active material layer (109) comprises a silicon-carbon composite material; a concave portion (104) is provided on the surface of the negative electrode active material layer (109); and the innermost circle of the negative electrode sheet (10) comprises a negative electrode winding starting section (100); The innermost circle of the positive electrode sheet (30) includes a first positive electrode straight section (302) and a first positive electrode bent section (301) connected to the first positive electrode straight section (302); the first positive electrode bent section (301) is a region where the positive electrode sheet (30) is bent for the first time along its winding direction; and the negative electrode winding starting section (100) has a negative electrode winding starting end (101) facing the first positive electrode bent section (301); The diaphragm (20) includes a first diaphragm (201) and a second diaphragm (202). Along a first direction (Z), the first diaphragm (201) and the second diaphragm (202) are respectively provided on both sides of the negative electrode sheet (10); along a second direction (X), the edge of the first diaphragm (201) and the edge of the second diaphragm (202) both extend beyond the edge of the negative electrode sheet (10) and form a first extending portion (2011) and a second extending portion (2021), respectively. The negative electrode sheet (10) includes a first negative electrode segment (102) located in the innermost straight section of the battery cell. Except for the first negative electrode segment, the negative electrode sheet (10) includes a first negative electrode segment (201) and a second negative electrode segment (202) located in the innermost straight section of the battery cell. The remaining portion of (102) is a second negative electrode segment; along the same side of the second direction (X), the first protruding portion (2011) and the second protruding portion (2021) corresponding to the first negative electrode segment (102) are at least partially interconnected to form a first composite area, and the peeling strength F1 between the first protruding portion (2011) and the second protruding portion (2021) in the first composite area is greater than the peeling strength F2 between the first protruding portion (2011) and the second protruding portion (2021) corresponding to the second negative electrode segment; wherein the first direction (Z) and the second direction (X) are perpendicular to each other.

2. The battery cell according to claim 1, characterized in that The first protruding portion (2011) and the second protruding portion (2021) corresponding to the second negative electrode segment are not connected and form a gap, or the first protruding portion (2011) and the second protruding portion (2021) corresponding to the second negative electrode segment are partially connected to each other; And / or, along the third direction (Y), the first separator (201) and the second separator (202) respectively include a third protruding portion and a fourth protruding portion that extend beyond the negative electrode winding starting section (100), and at least parts of the third protruding portion and the fourth protruding portion are interconnected to form a second composite area; wherein the first direction (Z), the second direction (X) and the third direction (Y) are perpendicular to each other.

3. The battery cell according to claim 1, characterized in that The surface of the negative electrode active material layer (109) is provided with a plurality of recesses (104), and the plurality of recesses (104) are arranged at intervals along the third direction (Y); the edge of the negative electrode sheet (10) at the negative electrode winding starting section (100) is a first edge (107); wherein the first direction (Z), the second direction (X), and the third direction (Y) are perpendicular to each other; The recess (104) is arranged parallel to the first edge (107), and the distance between the recess (104) closest to the first edge (107) and the first edge (107) is d1, and satisfies 1mm≤d1≤15mm; Alternatively, the recess (104) and the first edge (107) are arranged at an angle, the angle between the recess (104) and the first edge (107) is θ, and satisfies 2°≤θ≤80°; And / or, the width of the recess (104) is 50 μm to 150 μm; and / or, the distance between two adjacent recesses (104) is 0.5 mm to 3.5 mm; and / or, the depth of the recess (104) is 5 μm to 30 μm.

4. The battery cell according to claim 1, characterized in that The battery cell further comprises a first insulating member (50), wherein at least a portion of the first insulating member (50) is disposed on opposite sides of the negative electrode winding starting section (100) along the first direction (Z), and a projection of the first insulating member (50) along the first direction (Z) at least partially overlaps with the negative electrode winding starting section (100), and the first insulating member (50) comprises a first substrate layer and a first adhesive layer disposed on at least one side surface of the first substrate layer; Along the first direction (Z), the first insulating member (50) is fixed to opposite sides of the negative electrode winding starting section (100); And / or, along the first direction (Z), the first insulating member (50) is fixed on the first separator (201) and the second separator (202) arranged opposite to the negative electrode winding starting section (100).

5. The battery cell according to claim 4, characterized in that: When the first adhesive layer is provided on a surface of the first substrate layer facing the negative electrode winding starting section (100), along the first direction (Z), the first insulating member (50) is provided between the negative electrode winding starting section (100) and the first separator (201) and the second separator (202) provided corresponding to the negative electrode winding starting section (100), and the first adhesive layer is bonded to the negative electrode winding starting section (100); Alternatively, when the first adhesive layer is provided on a surface of the first substrate layer facing the negative electrode winding starting section (100), the first adhesive layer is bonded to the surfaces of the first separator (201) and the second separator (202) on a side away from the negative electrode winding starting section (100); Alternatively, when the first adhesive layer is provided on a surface of the first substrate layer on a side away from the negative electrode winding starting section (100), the first insulating member (50) is provided between the negative electrode winding starting section (100) and the first separator (201) and the second separator (202) provided corresponding to the negative electrode winding starting section (100), and the first adhesive layer is bonded to the surfaces of the first separator (201) and the second separator (202) on a side facing the negative electrode winding starting section (100); Alternatively, when the first adhesive layer is provided on both side surfaces of the first substrate layer along the first direction (Z), the first insulating member (50) is provided between the negative electrode winding starting section (100) and the first separator (201) and the second separator (202) arranged corresponding to the negative electrode winding starting section (100), and the first adhesive layer is respectively bonded to the negative electrode winding starting section (100) and the first separator (201) and the second separator (202) arranged opposite to the negative electrode winding starting section (100).

6. The battery cell according to claim 4, characterized in that Along the third direction (Y), the first insulating member (50) extends beyond the negative electrode winding starting end (101) by a dimension d2, and satisfies 2mm≤d2≤10mm; and / or, along the third direction (Y), the overlapping dimension between the first insulating member (50), the first diaphragm (201) and the second diaphragm (202) is d3; And / or, along the third direction (Y), the overlapping dimension of the first insulating member (50) and the negative electrode winding starting section (100) is d3, and satisfies 1mm≤d3≤10mm; wherein the first direction (Z), the second direction (X) and the third direction (Y) are perpendicular to each other.

7. The battery cell according to claim 5, characterized in that Along the third direction (Y), the size of the first separator (201) and the second separator (202) extending beyond the negative electrode winding starting end (101) is greater than or equal to the size of the first insulating member (50) extending beyond the negative electrode winding starting end (101); wherein the first direction (Z), the second direction (X) and the third direction (Y) are perpendicular to each other.

8. The battery cell according to claim 4, characterized in that The first positive bent section (301) of the positive electrode sheet (30) is provided with a second insulating member (60); Along the third direction (Y), two ends of the second insulating member (60) respectively extend beyond two ends of the first insulating member (50), and a dimension of the extended portion is d4, and satisfies 0.2 mm ≤ d4 ≤ 10 mm; wherein the first direction (Z), the second direction (X), and the third direction (Y) are perpendicular to each other; And / or, the second insulating member (60) comprises a second substrate layer (601) and a second adhesive layer (602) provided on at least one side of the second substrate layer (601), the second adhesive layer (602) being intermittently provided to form a first blank area on the second substrate layer (601), at least a portion of the first blank area being provided opposite to the first positive electrode bending section (301), the two straight sections on the positive electrode sheet (30) connected to the first positive electrode bending section (301) being the first positive electrode straight section (302) and the second positive electrode straight section (303), respectively, and the second adhesive layer (602) being provided facing the first positive electrode straight section (302) and the second positive electrode straight section (303), respectively; and / or, the second adhesive layer (602) is arranged facing the negative electrode winding starting section (100); and / or, the second adhesive layer (602) is arranged facing the first diaphragm (201) and the second diaphragm (202); And / or, the second adhesive layer (602) and a portion of the second substrate layer (601) corresponding thereto are provided with pores for allowing metal cations to pass through; And / or, the area of ​​the second adhesive layer (602) is S1, the area of ​​the entire second insulating member (60) is S, and 0.2≤S1 / S≤0.8 is satisfied.

9. The battery cell according to any one of claims 1 to 8, characterized in that: The negative electrode active material layer (109) is provided with a groove exposing the negative electrode current collector (108), and the groove includes a first groove (105) and a second groove (106); Along the second direction (X), the difference between the size of the first groove (105) and the size of the second groove (106) is d5, and satisfies 1mm≤d5≤15mm.

10. A battery, characterized in that: A battery cell comprising the battery cell according to any one of claims 1 to 9.

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