Roll core and battery

Abstract

The invention relates to the technical field of energy storage devices, and particularly discloses a roll core and a battery. The roll core comprises an electrode assembly, wherein the electrode assembly comprises a first pole piece, a diaphragm and a second pole piece which are stacked in sequence and are wound from the head to the tail; the first gummed paper layer is at least adhered to the part of the single-sided area facing the second pole piece, and one end of the first gummed paper layer is positioned on one side of the second pole piece facing the winding center; one end of the second gummed paper layer is adhered to the tail part of the single-side area of the outermost ring and is far away from one side of the winding center, the other end of the second gummed paper layer at least extends to the first gummed paper layer along the winding direction and is adhered, the tensile strength of the second gummed paper layer is F1, the tensile strength of the first current collector is F2, and F1 and F2 meet the following relation: 0.6 < = F1 / F2 < = 1.2. The second gummed paper layer of the roll core does not cover the first active layer, so that the capacity and the energy density of the battery are improved. In addition, by limiting the ratio of the tensile strength of the second gummed paper layer to the tensile strength of the first current collector, the fracture risk of the first current collector in the circulation process is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage devices, and more specifically, to a winding core and a battery. Background Art

[0002] A battery generally refers to a device that can generate electrical energy. As an energy source, a battery has stable voltage and current, can provide stable power for a long time, is less affected by external factors, and is easy to charge and discharge. Therefore, it is usually used to power external devices (such as mobile phones, tablets, laptops and other portable or mobile electronic devices).

[0003] The battery cell is an important structure of the battery. The wound battery cell (roll core) is a commonly used battery cell structure, which is made by stacking the positive electrode sheet, separator and negative electrode sheet in sequence and winding them. The tail end of the roll core is closed with adhesive tape, that is, the positive electrode sheet or negative electrode sheet on the outermost layer is fixed to the outer surface of the roll core with adhesive tape to ensure the stability and reliability of the roll core.

[0004] However, when using adhesive tape for finishing, the electrode sheets of the battery cell are prone to breakage during recycling, thus affecting the reliability of the battery cell. Summary of the Invention

[0005] In view of this, the purpose of the present application is to provide a winding core and a battery, the structural design of which can effectively solve the problem of electrode sheet breakage that is prone to occur during the cycle of the battery cell.

[0006] In order to achieve the above objectives, this application provides the following technical solutions: A winding core, comprising: An electrode assembly comprising a first electrode sheet, a separator, and a second electrode sheet stacked in sequence and wound from head to tail, the first electrode sheet comprising a first current collector and a first active layer, the first electrode sheet having a single-sided region with the first active layer provided only on a surface of the first current collector facing the winding center of the electrode assembly, at least a portion of the single-sided region being located at the outermost circle of the electrode assembly, the tail end of the first active layer in the single-sided region being flush with the tail end of the first current collector, the second electrode sheet comprising a second current collector and a second active layer, the first active layer or the second active layer comprising a silicon-based material, the silicon-based material comprising at least one of elemental silicon, a silicon-oxygen compound, a silicon-carbon compound, or a silicon alloy; a first adhesive paper layer, bonded to at least a portion of the single-sided area facing the second pole piece, and extending along the winding direction, with one end of the first adhesive paper layer being located on a side of the second pole piece facing the winding center; The second adhesive paper layer has one end bonded to the tail of the single-sided area of the outermost circle and away from the side of the winding center, and the other end extends at least to the first adhesive paper layer along the winding direction and is bonded, wherein the tensile strength of the second adhesive paper layer is F1, the tensile strength of the first current collector is F2, and F1 and F2 satisfy the following relationship: 0.6≤F1 / F2≤1.2.

[0007] Optionally, in the winding core, the tail end of the diaphragm located between the first pole piece on the outermost circle and the adjacent second pole piece extends beyond the tail end of the first pole piece along the winding direction, and the extending portion is bonded to the second adhesive tape layer.

[0008] Optionally, in the above-mentioned winding core, the length of the bonding portion between the second adhesive tape layer and the diaphragm is L1, and L1 is ≥ 2 mm; And / or, the thickness of the single-sided area is H, and L1 and H satisfy the following relationship: 40≤L1 / H≤200.

[0009] Optionally, in the winding core, along the winding direction, the tail end of the second pole piece extends beyond the first pole piece and is located between the first adhesive paper layer and the second adhesive paper layer.

[0010] Optionally, in the above-mentioned winding core, the peeling strength between the second adhesive tape layer and the side of the single-sided area away from the winding center is R, and 0.02N / mm≤R≤0.2N / mm.

[0011] Optionally, in the winding core, the first electrode sheet is a positive electrode sheet, and the second electrode sheet is a negative electrode sheet; the electrode assembly includes a straight area, a first bending area, and a second bending area, and along the first direction, the first bending area and the second bending area are connected to two ends of the straight area; The positive electrode sheet includes a first bent section located in the first bent area, and a positive electrode winding starting section and a first straight section located in the straight area. Along the second direction, the positive electrode winding starting section is arranged opposite to the first straight section. The first straight section and the positive electrode winding starting section are respectively connected to two ends of the first bent section. The end of the positive electrode winding starting section away from the first bent section is the positive electrode winding starting end of the positive electrode sheet. The negative electrode sheet includes a negative electrode winding start section, a second bent section located in the second bent region, and a second straight section located in the straight region. The negative electrode winding start section is located in the straight region and, along the second direction, is located between the positive electrode winding start section and the first straight section. Along the first direction, the end of the negative electrode winding start section facing the first bent section is the negative electrode winding start end of the negative electrode sheet. Along the second direction, the second straight section and the negative electrode winding start section are arranged opposite to each other, and the second straight section and the negative electrode winding start section are respectively connected to two ends of the second bent section. The negative electrode active layer on one side of the negative electrode winding starting section is arranged opposite to the positive electrode active layer on the positive electrode winding starting section, and the negative electrode active layer on the other side of the negative electrode winding starting section is arranged opposite to the positive electrode active layer on the first straight section. The separator has a separator winding starting end, and the separator winding starting end is flush with the positive electrode winding starting end, or the separator winding starting end is flush with the negative electrode winding starting end. The positive electrode active layers on both sides of the positive electrode winding starting section are respectively arranged opposite to the negative electrode active layer on the negative electrode winding starting section and the negative electrode active layer on the second straight section. The first direction and the second direction are perpendicular to the extension direction of the winding axis of the electrode assembly; And / or, the mass percentage of the silicon-based material is 5%-50%, including endpoint values.

[0012] Optionally, in the winding core, a third adhesive paper layer is provided on a side of the first bent section facing the negative electrode winding starting end; The third adhesive paper layer includes a substrate and an adhesive layer, wherein the adhesive layers are spaced apart on a side of the substrate facing the positive electrode sheet; The area of the substrate on which the adhesive layer is provided is S1, the area of the substrate is S, and S1 and S satisfy the following relationship: 0.2≤S1 / S≤0.8.

[0013] Optionally, in the winding core, a groove is provided on the surface of the negative electrode sheet, and a distance between the groove and the tail end of the negative electrode sheet is greater than or equal to 2 mm; Alternatively, the extension direction of the groove is at a preset angle θ with the extension direction of the winding axis of the electrode assembly, wherein 2°≤θ≤80°; the gap between adjacent grooves is d, the width of the negative electrode sheet is W1, and d and W1 satisfy the following relationship: 5≤W1 / d≤250.

[0014] Optionally, in the above-mentioned winding core, the length of the second adhesive tape layer bonded to the single-sided area away from the winding center is greater than or equal to 3 mm; And / or, the electrode assembly includes a tab, and projections of two ends of the first adhesive tape layer in the thickness direction of the electrode assembly are respectively spaced from projections of the tab in the thickness direction of the electrode assembly; And / or, it also includes a fourth adhesive paper layer, which is arranged on the side of the first current collector in the outermost circle away from the winding center, and the fourth adhesive paper layer is spaced apart from the first adhesive paper layer.

[0015] The winding core provided by the present application is used, and at the end position, a first adhesive paper layer and a second adhesive paper layer are matched. The first adhesive paper layer is bonded to at least the portion of the single-sided area facing the second electrode. One end of the second adhesive paper layer is bonded to the tail of the single-sided area and one side away from the winding center, and the other end extends at least to the first adhesive paper layer along the winding direction and is bonded. The tensile strength of the second adhesive paper layer is F1, and the tensile strength of the first current collector is F2. F1 and F2 satisfy the following: 0.6≤F1 / F2≤1.2. During the winding core cycle, since one of the first current collector and the second current collector contains silicon-based material, silicon-based material has a high specific capacity and can improve energy density. However, silicon-based material tends to expand rapidly in volume during the charge and discharge process, causing one of the first and second electrode sheets containing silicon-based material to expand, and driving the other to expand and extend to a certain extent, which can easily cause the first current collector or the second current collector to break. In addition, since the first active layer is only provided on one side of the single-sided area, there is a risk of tearing when the elongation difference between the first current collector and the second adhesive paper layer in the single-sided area is large. In the present application, by setting the ratio of the tensile strength of the second adhesive tape layer to the tensile strength of the first current collector within the above range, the extension difference between the two can be reduced, thereby reducing the risk of breakage of the first current collector and the second current collector during the cycle.

[0016] In addition, since the second adhesive paper layer is arranged on the side of the single-sided area away from the winding center, that is, the second adhesive paper layer is bonded to the first current collector rather than the first active layer on the first current collector, the second adhesive paper layer is avoided from covering the first active layer, so it does not affect the area of the first active layer, thereby improving the capacity and energy density of the battery.

[0017] To achieve the above objectives, the present application further provides a battery comprising any of the above-mentioned winding cores. Since the above-mentioned winding cores have the above-mentioned technical effects, the battery comprising the winding cores should also have corresponding technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 This is a schematic structural diagram of a winding core according to a specific embodiment of the present application; Figure 2 It is a partial enlarged schematic diagram of the winding core; Figure 3 Schematic diagram of the structure of the first pole piece; Figure 4 Schematic diagram of the structure of the third adhesive tape layer; Figure 5 Schematic diagram of the structure of a second pole piece; Figure 6 Schematic diagram of the structure of another second pole piece.

[0020] Reference numerals: 1-electrode assembly; 2-first adhesive tape layer; 3-second adhesive tape layer; 4-third adhesive tape layer; 5-fourth adhesive tape layer; 11-first pole piece; 12-second pole piece; 13-diaphragm; 14-pole tab; 111 - first current collector; 112 - first active layer; 1121 - first surface active layer; 1122 - second surface active layer; 01 - single-sided area; 02 - double-sided area; 1a-straight area; 1b-first bending area; 1c-second bending area; 11a-first bending section; 11b-positive electrode winding starting section; 11c-positive electrode winding starting end; 11d-first straight section; 12a-negative electrode winding starting section; 12b-negative electrode winding starting end; 12c-second bent section; 12d-second straight section; 121-groove; 31-substrate; 32-adhesive layer. DETAILED DESCRIPTION

[0021] The embodiments of the present application disclose a winding core and a battery to reduce the risk of electrode sheet breakage during the cycle of the battery cell.

[0022] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] The battery cell provided in this application is applicable to but not limited to lithium-ion batteries, sodium-ion batteries and other wound battery cells, i.e., coiled cores. Figure 1-Figure 3The electrode assembly 1 is the core structure of the winding core, including a first electrode sheet 11, a second electrode sheet 12 and a diaphragm 13. One of the first electrode sheet 11 and the second electrode sheet 12 is a positive electrode sheet, and the other is a negative electrode sheet, that is, the polarities of the two are opposite. Among them, the diaphragm 13 is provided between the positive electrode sheet and the negative electrode sheet to form a physical isolation to avoid the risk of short circuit caused by direct contact between the positive electrode sheet and the negative electrode sheet. The first electrode sheet 11 includes a first current collector 111 and a first active layer 112 provided on the first current collector 111. The second electrode sheet 12 includes a second current collector and a second active layer provided on the second current collector. The winding core also includes a tab 14, which is used to lead the circuit in the winding core to achieve connection with the peripheral circuit. The number of tabs 14 is usually two, corresponding to the first electrode sheet 11 and the second electrode sheet 12 respectively, and the two tabs 14 are spaced apart along the projection of the thickness direction of the electrode assembly 1. Illustratively, the first electrode tab 14 is provided on the first current collector 111 of the first electrode sheet 11 , and the second electrode tab 14 is provided on the second current collector of the second electrode sheet 12 .

[0024] The first electrode sheet 11, the separator 13, and the second electrode sheet 12 are stacked and wound to form a winding core. Specifically, the winding starts from the head end of the electrode assembly 1, is wound in the same direction, and ends at the tail end of the electrode assembly 1 to form a winding core. In this application, the first electrode sheet 11 is regarded as the outermost circle. The first electrode sheet 11 includes a single-sided area 01 and a double-sided area 02. The double-sided area 02 is an area where the first active layer 112 is provided on one side of the first current collector 111 facing the winding center of the electrode assembly 1 and on the side away from the winding center. The single-sided area 01 is an area where the first active layer 112 is provided only on the side of the first current collector 111 facing the winding center of the electrode assembly 1. Specifically, at the end position, in order to improve the energy density of the battery, especially the outermost circle of the electrode assembly 1, the single-sided area 01 of the first pole piece 11 is used to correspond to the second pole piece 12, that is, the side of the first current collector 111 facing the winding center of the electrode assembly 1 is coated with the first active layer 112 to correspond to the second pole piece 12, and the side of the first current collector 111 away from the winding center is no longer coated with the first active layer 112.

[0025] It should be noted that during the winding process of the core, in order to ensure the tightness of the internal film layers, it is necessary to tighten the first electrode piece 11, the diaphragm 13 and the second electrode piece 12 during the winding process. Therefore, a tape layer needs to be provided at the tail end of the first electrode piece 11 to fix the first electrode piece 11 to the outermost circle of the electrode assembly 1, thereby preventing the electrodes from loosening or deformation.

[0026] However, during the development of this application, the inventors discovered that using adhesive tape for finishing, on the one hand, causes a loss in battery energy density when the tape is attached to the first active layer 112 of the single-sided area 01, covering the area of the first active layer 112. On the other hand, if the tensile strength of the adhesive tape significantly differs from the tensile strength of the first current collector 111 of the first electrode sheet 11, the winding core may break at the penultimate or second bend of the first electrode sheet 11 during recycling. Therefore, it is necessary to carefully manage the relationship between the tensile strength of the adhesive tape and the tensile strength of the current collector.

[0027] This application optimizes the winding core's tail end structure, combining the tensile strength of the adhesive tape with the tensile strength of the current collector to improve battery energy density while effectively reducing the risk of first pole piece 11 fracture and enhancing winding core reliability. The following embodiments primarily describe the winding core's tail end structure and the adhesive tape layer's structure.

[0028] It should be noted that in this application, the width direction of the electrode assembly 1 is also the width direction of the first electrode sheet 11 before winding, and is also the extension direction of the winding axis of the electrode assembly 1; the length direction of the electrode assembly 1 is also the length direction of the first electrode sheet 11 before winding, and is recorded as the first direction; the thickness direction of the electrode assembly 1 is also the thickness direction of the first electrode sheet 11 before winding, and is recorded as the second direction. The descriptions of the length, width, and thickness of each component are consistent with the length, width, and thickness of the electrode assembly 1, respectively.

[0029] In some embodiments, see Figure 1-Figure 3The winding core provided in the present application includes an electrode assembly 1, a first adhesive paper layer 2 and a second adhesive paper layer 3. The electrode assembly 1 includes a first electrode sheet 11, a diaphragm 13 and a second electrode sheet 12 stacked in sequence and wound from the head to the tail. The first electrode sheet 11 includes a first current collector 111 and a first active layer 112, and the second electrode sheet includes a second current collector and a second active layer. The first active layer 112 or the second active layer includes a silicon-based material, and the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbon compound or silicon alloy. The first electrode sheet 11 has a double-sided region 02 on both sides of the first current collector 111, and a single-sided region 01 on the side of the first current collector 111 facing the winding center, wherein the first active layer 112 is provided. At least part of the single-sided region 01 is located at the outermost circle of the electrode assembly 1, and the tail end of the first active layer 112 of the single-sided region 01 is flush with the tail end of the first current collector 111. It should be understood that the term "flush" mentioned herein and below in this application does not imply absolute flushness. Taking into account fluctuations in equipment tolerances, the flushing of A and B in this application refers to a margin of error of 0 to 5 mm between A and B. The flushing of the tail end of the first active layer 112 in the single-sided region 01 with the tail end of the first current collector 111 herein refers to a margin of error of 0 to 5 mm between the tail end of the first active layer 112 in the single-sided region 01 and the tail end of the first current collector 111. This means that the distance between the tail end of the first active layer 112 in the single-sided region 01 and the tail end of the first current collector 111 is within the range of 0 mm to 0.5 mm, inclusive. In this embodiment, the empty foil area where the first active layer 112 is not coated on both sides of the first current collector 111 is eliminated, and a continuous coating method is directly adopted, thereby improving the space utilization within the electrode assembly 1 and thereby increasing the energy density of the battery.

[0030] For ease of explanation, the first active layer 112 disposed on the surface of the first current collector 111 facing the winding center is referred to as the first surface active layer 1121, and the first active layer 112 disposed on the surface of the first current collector 111 away from the winding center is referred to as the second surface active layer 1122. That is, the first electrode sheet 11 is located at the outermost circle of the electrode assembly 1. The first electrode sheet 11 includes the first current collector 111, the first surface active layer 1121 disposed on the side of the first current collector 111 facing the winding center of the electrode assembly 1, and the first surface active layer 1121 disposed on the side of the first current collector 111 away from the winding center. The tail end of the first surface active layer 1121 extends beyond the tail end of the first surface active layer 1121 along the winding direction and is flush with the tail end of the first current collector 111.

[0031] The first adhesive tape layer 2 is bonded to at least the portion of the single-sided region 01 facing the second electrode sheet 12. The first adhesive tape layer 2 extends along the winding direction, with one end located on the side of the second electrode sheet 12 facing the winding center. That is, one end of the first adhesive tape layer 2 is bonded to the side of the first electrode sheet 11 away from the winding center and located in the direction of the second electrode sheet 12 facing the winding center. In one example, one end of the first adhesive tape layer 2 is bonded to the end of the double-sided region 02 facing the second electrode sheet 12; in another example, one end of the first adhesive tape layer 2 is bonded to the end where the single-sided region 01 and the double-sided region 02 connect, facing the second electrode sheet 12. The other end of the first adhesive tape layer 2 extends along the winding direction at least to the portion of the single-sided region 01 facing the second electrode sheet 12. That is, the other end is bonded to at least the first current collector 111 facing the single-sided region 01 and the second electrode sheet 12. The provision of the first adhesive tape layer 2 can separate the second electrode sheet 12 from the first current collector 111, preventing contact between the two and potentially affecting battery performance. Exemplarily, one end of the first adhesive tape layer 2 is bonded to the tail of the double-sided region 02, away from the winding center. Specifically, one end of the first adhesive tape layer 2 is bonded to the tail of the first surface active layer 1121, specifically covering a predetermined length of the first surface active layer 1121, typically several millimeters. The other end of the first adhesive tape layer 2 extends along the winding direction to the first current collector 111 of the single-sided region 01 and extends a certain length beyond the second electrode 12 along the winding direction, where it is bonded. Because burrs typically form at the tail end of the first active layer 112 coated on the first current collector 111, bonding one end of the first adhesive tape layer 2 to the tail of the double-sided region 02 helps prevent burrs at the tail end of the first active layer 112 from piercing the separator 13 and causing a short circuit within the winding core, thereby improving the reliability of the winding core.

[0032] One end of the second adhesive paper layer 3 is bonded to the tail of the outermost single-sided area 01 and away from the side of the winding center, that is, one end of the second adhesive paper layer 3 is bonded to the tail of the first current collector 111, and the other end extends at least to the first adhesive paper layer 2 along the winding direction and is bonded. The tail of the single-sided area 01 is the portion within a certain length range of the tail end of the single-sided area 01. It can be understood that the other end of the second adhesive paper layer 3 can extend to be flush with the tail end of the first adhesive paper layer 2 or a certain distance away from the tail end of the first adhesive paper layer 2 along the winding direction. In some embodiments, it can also slightly exceed the tail end of the first adhesive paper layer 2. The second adhesive paper layer 3 can fix the tail of the outermost first electrode 11 to prevent the electrode assembly 1 from loosening and spreading. The second adhesive paper layer 3 is bonded to the tail of the single-sided area 01, and specifically can cover a preset length of the tail of the single-sided area 01.

[0033] The tensile strength of the second adhesive tape layer 3 is F1, and the tensile strength of the first current collector 111 is F2. F1 and F2 satisfy the following relationship: 0.6 ≤ F1 / F2 ≤ 1.2. For example, the ratio F1 / F2 can be one of 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, and 1.2. Alternatively, the F1 / F2 value can be any value within the range of 0.6 to 1.2.

[0034] The winding core provided by the present application is used, and at the end position, a first adhesive paper layer 2 and a second adhesive paper layer 3 are matched. The first adhesive paper layer 2 is bonded to at least the portion of the single-sided area 01 facing the second electrode 12. One end of the second adhesive paper layer 3 is bonded to the end of the single-sided area 01 and away from the side of the winding center, and the other end extends at least to the first adhesive paper layer 2 along the winding direction and is bonded. The tensile strength of the second adhesive paper layer 3 is F1, and the tensile strength of the first current collector 111 is F2. F1 and F2 satisfy the following: 0.6≤F1 / F2≤1.2. During the winding core cycle, since one of the first current collector 111 and the second current collector contains silicon-based material, silicon-based material has a high specific capacity and can improve energy density. However, silicon-based material tends to expand rapidly in volume during charge and discharge, causing one of the first electrode 11 and the second electrode 12 containing silicon-based material to expand, and driving the other to expand and extend to a certain extent, which can easily cause the first current collector 111 or the second current collector to break. Furthermore, because the first active layer 112 is provided on only one side of the single-sided region 01, there is a risk of tearing when there is a significant difference in the ductility between the first current collector 111 and the second adhesive tape layer 3 in the single-sided region 01. In this application, by setting the ratio of the tensile strength of the second adhesive tape layer 3 to the tensile strength of the first current collector 111 within the aforementioned range, the difference in ductility between the two can be reduced, thereby reducing the risk of breakage of the first and second current collectors 111 during cycling.

[0035] In addition, since the second adhesive paper layer 3 is arranged on the side of the single-sided area 01 away from the winding center, that is, the second adhesive paper layer 3 is bonded to the first current collector 111 of the first electrode 11, rather than the first active layer 112 inside the first current collector 111, the second adhesive paper layer 3 is avoided from covering the first active layer 112, so it does not affect the area of the first active layer 112, thereby improving the capacity and energy density of the battery.

[0036] In some embodiments, the first adhesive tape layer 2 includes a substrate and an adhesive layer disposed on the substrate. The substrate may be made of, but is not limited to, PET (Polyethylene Terephthalate), PI (Polyimide), or PP (Polypropylene). The adhesive layer may include, but is not limited to, acrylic adhesive or silicone. As needed, the adhesive layer may be disposed on both sides of the substrate, forming a double-sided adhesive layer, or only on one side, forming a single-sided adhesive layer. The second adhesive tape layer 3 may be configured similarly to or differently from the first adhesive tape layer 2.

[0037] In some embodiments, see Figure 1-Figure 3 , along the winding direction, the tail end of the diaphragm 13 located between the first pole piece 11 and the adjacent second pole piece 12 on the outermost circle extends beyond the tail end of the first pole piece 11 along the winding direction, and the extending portion is bonded to the second adhesive tape layer 3. That is, the tail end of the diaphragm 13 between the single-sided area 01 of the first pole piece 11 and the opposite second pole piece 12 extends beyond the tail end of the first pole piece 11 along the winding direction, which can more effectively separate the first pole piece 11 from the second pole piece 12 to prevent the two from contacting and short-circuiting. In addition, the portion of the diaphragm 13 that extends beyond the first pole piece 11 is bonded to the second adhesive tape layer 3, which can position the diaphragm 13, preventing the heat generated during the use of the winding core from causing the diaphragm 13 to shrink, which may cause the first pole piece 11 and the second pole piece 12 to contact with each other, thereby improving the safety performance of the battery.

[0038] In some embodiments, see Figure 1-Figure 3 , the length of the bonding portion between the second adhesive paper layer 3 and the diaphragm 13 is L1, and L1 ≥ 2 mm. Exemplarily, L1 can be one of 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm and 6 mm, and can also be any value greater than or equal to 2 mm. It can be understood that the length of the bonding portion between the second adhesive paper layer 3 and the diaphragm 13 refers to the length of the portion where the second adhesive paper layer 3 and the diaphragm 13 overlap and bond in the length direction of the electrode assembly 1. If the length of the bonding portion between the second adhesive paper layer 3 and the diaphragm 13 is too small, the bonding area between the two is correspondingly small, the bonding is not strong, and when the diaphragm 13 is heated, it is difficult for the second adhesive paper layer 3 to suppress the shrinkage of the diaphragm 13. Therefore, the length of the second adhesive paper layer 3 adhering to the diaphragm 13 is set to be no less than 2.0 mm, which can ensure the area of the second adhesive paper layer 3 adhering to the diaphragm 13, thereby ensuring the reliable adhesion of the second adhesive paper layer 3 to the diaphragm 13, so that the diaphragm 13 can still effectively separate the first electrode 11 and the second electrode 12 from each other when heat is generated during the use of the battery cell, thereby reducing the short circuit risk of the battery and improving the safety performance of the battery.

[0039] In some embodiments, see Figure 1-Figure 3 The length of the bonding portion between the second adhesive tape layer 3 and the separator 13 is L1, and the thickness of the single-sided area 01 is H. L1 and H satisfy the following relationship: 40≤L1 / H≤200. For example, the ratio of L1 / H can be one of 40, 50, 60, 70, 80, 100, 120, 140, 160, 180, and 200. Alternatively, the value of L1 / H can be any value within the range of 40 to 200. It is understood that the thickness of the single-sided area 01 is the thickness of the first current collector 111 and the first active layer 112 provided on one side of the first current collector 111, that is, the total thickness of the first current collector 111 and the first active layer 1121. The longer the bonding length between the second adhesive tape layer 3 and the separator 13, the stronger the bonding. However, if the length of the bonding portion between the second adhesive tape layer 3 and the separator 13 is too long, it will affect the energy density of the battery. This is because the second adhesive tape layer 3 is bonded to the portion of the separator 13 that extends beyond the first electrode 11. The longer the bond length, the shorter the first electrode 11, thus reducing the battery's energy density. Therefore, by limiting the length of the bonded portion between the second adhesive tape layer 3 and the separator 13 and the thickness of the single-sided area 01, and by ensuring that 40 ≤ L1 / H ≤ 200, the weak adhesion of the second adhesive tape layer 3 caused by an excessively small L1 / H ratio can be avoided. This ensures that the second adhesive tape layer 3 adheres securely to the separator 13, effectively separating the first and second electrode sheets 11 and 12 from each other even when the separator 13 generates heat during battery cell use. This reduces the risk of battery short circuits and improves battery safety. It also avoids the reduction in battery energy density caused by an excessively large L1 / H ratio, ensuring that the second adhesive tape layer 3 maintains good adhesion to the separator 13 during the expansion of the first electrode sheet 11 during charge and discharge, preventing the separator 13 from shrinking. Exemplarily, the thickness of the first current collector 111 ranges from 8 to 15 μm.

[0040] In some embodiments, see Figure 1-Figure 3 , along the winding direction, the tail end of the second electrode piece 12 extends beyond the first electrode piece 11. The tail end of the diaphragm 13 can be flush with the tail end of the second electrode piece 12 or slightly extend beyond the tail end of the second electrode piece 12. The tail end of the second electrode piece 12 extends beyond the tail end of the first electrode piece 11, and the diaphragm 13 is provided between the two. This arrangement can better prevent the first electrode piece 11 and the second electrode piece 12 from contacting each other during the cycle, and facilitates the adhesion of the diaphragm 13 to the second adhesive tape layer 3.

[0041] In some embodiments, see Figure 1-Figure 3, along the winding direction, the tail end of the second electrode sheet 12 is located between the first adhesive paper layer 2 and the second adhesive paper layer 3. The second adhesive paper layer 3 is bonded to the first current collector 111 and the first adhesive paper layer 2 respectively to form a closed space in the length direction between the three. The tail end of the second electrode sheet 12 is arranged in this space. Under the wrapping effect of the first adhesive paper layer 2 and the second adhesive paper layer 3, it can prevent dust from falling off the end of the second electrode sheet 12 from falling into the battery, causing the risk of large battery self-discharge or even short circuit, thereby further improving the reliability of the battery. In some examples, the ends of the first adhesive paper layer 2 and the second adhesive paper layer 3 in the width direction of the electrode assembly 1 exceed the width of the second electrode sheet 12, and the edges of the width ends of the first adhesive paper layer 2 and the second adhesive paper layer 3 can be bonded. Exemplarily, the portion of the second electrode sheet 12 that exceeds the first electrode sheet 11 in the winding direction is located between the first adhesive paper layer 2 and the second adhesive paper layer 3, and the second adhesive paper layer 3 is bonded to the separator 13 between the first electrode sheet 11 and the second electrode sheet 12. That is, along the winding direction, the second adhesive paper layer 3 is adhered to the first current collector 111 and the diaphragm 13 at the tail of the first pole piece 11 in sequence, and then adhered to the first adhesive paper layer 2, and a closed space is formed on the side facing the second pole piece 12. The tail end of the second pole piece 12 is wrapped in the closed space, so that the second pole piece 12 can be effectively protected to prevent powder loss and folding of the diaphragm 13, thereby improving the safety performance of the battery.

[0042] In some embodiments, the peel strength between the second adhesive tape layer 3 and the side of the single-sided area 01 away from the winding center is R, and 0.02 N / mm ≤ R ≤ 0.2 N / mm. For example, the value of R can be one of 0.02 N / mm, 0.04 N / mm, 0.06 N / mm, 0.08 N / mm, 0.1 N / mm, 0.12 N / mm, 0.14 N / mm, 0.16 N / mm, 0.18 N / mm, 0.19 N / mm, and 0.2 N / mm. Alternatively, the value of R can be any value within the range of 0.02 N / mm to 0.2 N / mm. It is understood that peel strength refers to the maximum force required to peel a unit width of materials adhered together from the contact surface. The peeling angle can be 90 degrees or 180 degrees, and the unit is Newton / meter (N / mm). Peel strength is used to reflect the bonding strength of the materials. If the peel strength R is less than 0.02N / mm, the second adhesive paper layer 3 will not be tightly bonded to the single-sided area 01, making it difficult to reliably restrain the first electrode 11 during the expansion process. If the peel strength R is greater than 0.2N / mm, the restraint will be too tight during the cyclic expansion process, causing the stress on the first electrode 11 to increase, and there is a risk of breaking. By setting R≥0.02N / mm, it can be ensured that the second adhesive paper layer 3 can reliably restrain the first current collector 111, and will not fall off due to the expansion of the first electrode 11 during the cycle, causing the risk of lithium deposition in the tail cycle. At the same time, by setting R≤0.2N / mm, it can be ensured that the second adhesive paper layer 3 will not restrain the first current collector 111 too tightly, preventing the first electrode 11 from expanding and breaking during the cycle.

[0043] In some embodiments, the first electrode 11 is a positive electrode, and the second electrode 12 is a negative electrode, that is, the positive electrode is used as the final step. Accordingly, the first current collector 111 is a positive electrode current collector, and the first active layer 112 is a positive electrode active layer. Common active materials of the positive electrode active layer include: lithium cobalt oxide ( ), lithium manganate ( ) 、Lithium iron phosphate ( ), lithium nickel cobalt manganese oxide ( ) and so on. The positive electrode current collector of the positive electrode sheet is usually made of aluminum foil. Common active materials of the negative electrode active layer include graphite, silicon-based materials, disordered carbon, etc., and the negative electrode current collector is usually made of copper foil. Compared with the negative electrode sheet, the material of the positive electrode sheet is more likely to break after cycling. Therefore, the structural design of the tail end and the corresponding matching design of the first adhesive paper layer 2 and the second adhesive paper layer 3 in the present application are particularly suitable for the case where the first electrode sheet 11 is a positive electrode sheet, that is, the case where the positive electrode sheet is the tail end, and can effectively prevent the positive electrode sheet from breaking.

[0044] In some embodiments, see Figure 1-Figure 2The electrode assembly 1 includes a straight area 1a and a first bending area 1b. Along the first direction, the first bending area 1b is connected to one end of the straight area 1a; the positive electrode sheet includes a first bending section 11a located in the first bending area 1b and a positive electrode winding starting section 11b and a first straight section 11d located in the straight area 1a. Along the second direction, the positive electrode winding starting section 11b is arranged opposite to the first straight section 11d. The first straight section 11d and the positive electrode winding starting section 11b are respectively connected to the two ends of the first bending section 11a. The end of the positive electrode winding starting section 11b away from the first bending section 11a is the positive electrode winding starting end 11c of the positive electrode sheet; the negative electrode sheet includes a negative electrode winding starting section 12a. The negative electrode winding starting section 12a is located in the straight area 1a, and along the second direction, the negative electrode winding The starting section 12a is located between the positive electrode winding starting section 11b and the first straight section 11d. Along the first direction, the end of the negative electrode winding starting section 12a facing the first bent section 11a is the negative electrode winding starting end 12b of the negative electrode sheet; wherein, the negative electrode active layer on one side of the negative electrode winding starting section 12a is arranged opposite to the positive electrode active layer of the positive electrode winding starting section 11b, and the negative electrode active layer on the other side of the negative electrode winding starting section 12a is arranged opposite to the positive electrode active layer of the first straight section 11d. The diaphragm 13 has a diaphragm 13 winding starting end, and the diaphragm 13 winding starting end is flush with the positive electrode winding starting end 11c, or the diaphragm 13 winding starting end is flush with the negative electrode winding starting end 12b; the first direction and the second direction are perpendicular to the extension direction of the winding axis of the electrode assembly 1.

[0045] The first bend section 11a is the first bend formed during the winding process of the positive electrode sheet. The first bend section 11a is the innermost electrode sheet of the first bend region 1b. The two ends of the first bend section 11a are connected to the positive electrode winding start section 11b and the first straight section 11d, respectively. Both the positive electrode winding start section 11b and the first straight section 11d are located in the straight region 1a. The positive electrode winding start section 11b is the starting section of the positive electrode sheet winding. The positive electrode winding start end 11c is the end of the positive electrode sheet located inside the electrode assembly 1 along its winding direction. The end of the positive electrode winding start section 11b facing away from the first bend section 11a along the first direction is the positive electrode winding start end 11c.

[0046] The negative electrode winding starting section 12a is the starting section of the negative electrode sheet winding, and the negative electrode winding starting end 12b is the end of the negative electrode sheet located inside the electrode assembly 1 along its winding direction. Along the first direction, the negative electrode winding starting end 12b is arranged facing the first bending section 11a. When viewed along the second direction, the connection position between the straight area 1a and the first bending area 1b can overlap with the negative electrode winding starting end 12b. Of course, when viewed along the second direction, the connection position between the straight area 1a and the first bending area 1b can also not overlap with the negative electrode winding starting end 12b, and the negative electrode winding starting end 12b can be located in the first bending area 1b or the negative electrode winding starting end 12b can be located in the straight area 1a. Along the second direction, the negative electrode winding starting section 12a is arranged between the positive electrode winding starting section 11b and the first straight section 11d. Viewed along the second direction, the positive electrode winding start section 11 b and the negative electrode winding start section 12 a are overlapped, and the first straight section 11 d and the negative electrode winding start section 12 a are overlapped.

[0047] The negative electrode active layers on both sides of the negative electrode winding starting section 12a are respectively arranged opposite to the positive electrode active layer of the positive electrode winding starting section 11b and the positive electrode active layer of the first straight section 11d, that is, there are negative electrode active layers on both sides of the negative electrode winding starting section 12a. During the manufacturing process of the negative electrode sheet, the number of changes in the coating method of the negative electrode active layer is reduced or the double-sided continuous coating of the negative electrode active layer is always adopted, which is beneficial to improving production efficiency and also beneficial to improving the energy density of the battery cell.

[0048] The separator 13's winding starting end is flush with the positive electrode winding starting end 11c, and the separator 13 and the positive electrode sheet can be wound synchronously, or the separator 13's winding starting end is flush with the negative electrode winding starting end 12b, and the separator 13 and the negative electrode sheet can be wound synchronously, thereby further improving production efficiency.

[0049] In some embodiments, the electrode assembly 1 further includes a second bending zone 1c, and along the first direction, the second bending zone 1c is located on the side of the straight zone 1a away from the first bending zone 1b; the negative electrode sheet further includes a second bending section 12c located in the second bending zone 1c and a second straight section 12d located in the straight zone 1a, and along the second direction, the second straight section 12d and the negative electrode winding starting section 12a are arranged opposite to each other, and the second straight section 12d and the negative electrode winding starting section 12a are respectively connected to the two ends of the second bending section 12c; wherein, the positive electrode active layers on both sides of the positive electrode winding starting section 11b are respectively arranged opposite to the negative electrode active layer of the negative electrode winding starting section 12a and the negative electrode active layer of the second straight section 12d.

[0050] The second bend section 12c is the first bend section formed during the winding process of the negative electrode sheet. The second bend section 12c is the innermost negative electrode sheet in the second bend region 1c. The negative electrode winding starting section 12a and the second straight section 12d are both located in the straight region 1a. The negative electrode winding starting section 12a and the second straight section 12d are respectively connected to the two ends of the second bend section 12c along the winding direction of the negative electrode sheet. The negative electrode winding starting section 12a is the starting section of the negative electrode sheet winding, and the negative electrode winding starting end 12b is the end of the negative electrode sheet located inside the electrode assembly 1 along its winding direction. The end of the negative electrode winding starting section 12a facing away from the second bend section 12c along the first direction is the negative electrode winding starting end 12b. The direction in which the negative electrode winding starting section 12a faces away from the second bend section 12c is opposite to the direction in which the positive electrode winding starting section 11b faces away from the first bend section 11a. Along the first direction, the positive electrode winding start end 11c is disposed facing the second bending section 12c, and the negative electrode winding start end 12b is disposed facing the first bending section 11a, so the positive and negative electrode sheets have opposite winding directions.

[0051] The winding directions of the positive electrode sheet and the negative electrode sheet are opposite. It can be understood that the positive electrode winding starting end 11c of the positive electrode sheet and the negative electrode winding starting end 12b of the negative electrode sheet are in opposite directions. In this embodiment, the positive electrode winding starting end 11c of the positive electrode sheet is set toward the second bending section 12c located in the second bending area 1c, and the negative electrode winding starting end 12b of the negative electrode sheet is set toward the first bending section 11a located in the first bending area 1b.

[0052] When viewed along the second direction, the connection between the straight region 1a and the second bent region 1c can overlap with the positive electrode winding starting end 11c. Of course, when viewed along the second direction, the connection between the straight region 1a and the second bent region 1c can also not overlap with the positive electrode winding starting end 11c, with the positive electrode winding starting end 11c located in the second bent region 1c or the positive electrode winding starting end 11c located in the straight region 1a.

[0053] Along the second direction, the positive electrode winding starting section 11b is arranged between the negative electrode winding starting section 12a and the second straight section 12d. Observed along the second direction, the negative electrode winding starting section 12a and the positive electrode winding starting section 11b overlap, and the second straight section 12d and the positive electrode winding starting section 11b overlap.

[0054] The positive electrode active layers on both sides of the positive electrode winding starting section 11b are arranged opposite to the negative electrode active layer of the negative electrode winding starting section 12a and the negative electrode active layer of the second straight section 12d, respectively. That is, positive electrode active layers are provided on both sides of the positive electrode winding starting section 11b, which is not only beneficial to improving the energy density of the battery cell, but also can reduce the number of changes in the coating method during the manufacturing process of the positive electrode sheet or always adopt double-sided continuous coating, which is beneficial to improving production efficiency.

[0055] For example, along the winding direction, based on the distance from the tail end of the single-sided region 01, the first bend region 1b is closer to the tail end of the single-sided region 01 relative to the second bend region 1c. Correspondingly, the second bend region 1c is farther away from the tail end of the single-sided region 01 relative to the first bend region 1b. Furthermore, as the winding radius increases, the stress in the bend segments closer to the outside becomes more concentrated, and thus the first electrode sheet 11 is more likely to break. It is understood that the direction from the first bend region 1b at one end of the electrode assembly 1 to the second bend region 1c at the other end is the length direction of the electrode assembly 1; on a plane parallel to the straight segments, the direction perpendicular to the length direction is the width direction of the electrode assembly 1; and the direction from one straight segment of the electrode assembly 1 to another straight segment is the thickness direction of the electrode assembly 1.

[0056] In some embodiments, the mass percentage of the silicon-based material is 5% to 50%, including endpoint values. Exemplarily, the mass percentage of the silicon-based material can be one of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50%. Alternatively, the mass percentage of the silicon-based material can be any point value within the range of 5% to 50%. If the mass percentage of the silicon-based material is less than 5%, the effect of improving the energy density is not good. If the mass percentage of the silicon-based material is greater than 50%, it will expand significantly during the charge and discharge process, which may easily cause the first current collector 111 or the second current collector to break. By setting the mass percentage of the silicon-based material to 5% to 50%, the risk of the first current collector 111 or the second current collector breaking is reduced while improving the energy density of the battery.

[0057] The mass percentage of the silicon-based material is calculated as follows: Assuming the mass percentage of the silicon-based material is X, X×1750+(1-X)×358=gram capacity of the negative electrode active material, the mass percentage of the silicon-based material X can be calculated.

[0058] Among them, the test method of the negative electrode capacity is as follows: First, the negative electrode sheet was removed from the fully charged secondary battery and the electrolyte in the negative electrode sheet was dried in an electric oven at 60°C. The negative electrode active material layer powder was scraped from the negative electrode sheet with a knife, weighed on a balance to obtain a weight of m1 = 100 mg, and immersed in a hydrochloric acid solution (mass fraction 10%) for 3 hours. The remaining solid matter was then filtered out and baked in an electric oven at 60°C for 24 hours, after which the solid weight m2 was measured. The mass ratio X of the negative electrode active material in the original electrode sheet formulation was calculated as (m1 - m2) / m1. The negative electrode active material layer powder was scraped from the negative electrode sheet again with a knife, weighed on a balance to obtain a weight of m3 = 100 mg, and mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 65 wt%, which was then stirred evenly. The slurry was evenly coated on the copper foil on the negative electrode current collector. After the electrode was dried, it was assembled with the metal lithium sheet, separator 13, and electrolyte to form a battery. Finally, the battery was charged at a constant current rate of 0.1C to 4.5V, then charged at a constant voltage rate of 4.5V to 0.02C, and then discharged at a constant current rate of 0.1C to 2.8V. The effective capacity of the battery was obtained by dividing the effective capacity by the weight of the effective active material powder m4 (m4 = m3 × x) to obtain the gram capacity of the negative electrode active material.

[0059] In some embodiments, see Figure 1 、 Figure 2 and Figure 4 A third adhesive tape layer 4 is provided on the side of the first bent section 11a facing the negative electrode winding starting end 12b. Since the first bent section 11a faces the negative electrode winding starting end 12b, to improve the battery's energy density, the negative electrode winding starting end 12b should be as close to the first bent section 11a as possible. At the same time, to prevent the negative electrode winding starting end 12b from contacting the positive electrode sheet, the third adhesive tape layer 4 is provided on the side of the first bent section 11a facing the negative electrode winding starting end 12b. This can separate the negative electrode winding starting end 12b from the positive electrode sheet, preventing problems such as short circuits caused by direct contact between the positive and negative electrodes.

[0060] At the same time, the third adhesive paper layer 4 separates the negative electrode winding starting end 12 b, which helps to prevent the burrs of the negative electrode winding starting end 12 b from piercing the separator 13 .

[0061] In addition, since the stress of the positive electrode sheet in the first bending area 1b is relatively large, by setting a third adhesive paper layer 4 in the first bending area of the positive electrode sheet along the winding direction, even if the first current collector 111 of the first bending section 11a is broken, the third adhesive paper layer 4 can effectively connect the two sides of the first current collector 111 at the break, and the third adhesive paper layer 4 can cover the first active layer 112, thereby reducing the probability of active material particles in this area scratching the diaphragm 13 and reducing the risk of lithium plating.

[0062] In some embodiments, see Figure 4 The third adhesive tape layer 4 includes a substrate 31 and an adhesive layer 32. The adhesive layer 32 is spaced apart on the side of the substrate 31 facing the positive electrode sheet. The adhesive layer 32 is the adhesive portion and is spaced apart on the substrate 31, meaning that some areas of the substrate 31 are devoid of adhesive layer 32. This arrangement reduces the adhesion between the third adhesive tape layer 4 and the positive electrode sheet, lowering the restraining force on the positive electrode sheet, thereby preventing the positive electrode sheet from breaking when bent. The specific materials of the substrate 31 and the adhesive layer 32 can be the same as or different from those of the first adhesive tape layer 2.

[0063] In some embodiments, the area of the adhesive layer 32 provided on the substrate 31 is S1, the area of the substrate 31 is S, and S1 and S satisfy the following relationship: 0.2 ≤ S1 / S ≤ 0.8. For example, the ratio of S1 / S can be one of 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, and 0.8. Alternatively, the ratio of S1 / S can be any value within the range of 0.2 to 0.8. If the ratio of S1 / S is too large, the total area of the adhesive layer 32 is large, resulting in strong adhesion to the positive electrode sheet, forming an excessively large binding force, which can cause the positive electrode sheet to break when bent. If the ratio of S1 / S is too small, the total area of the adhesive layer 32 is small, the binding force on the positive electrode sheet is too small, and the adhesive layer 32 is easily detached from the positive electrode sheet, failing to separate the positive electrode sheet from the head end of the negative electrode sheet. By setting the ratio of S1 / S within the range of 0.2≤S1 / S≤0.8, while ensuring good adhesion to the positive electrode sheet, the adhesion to the positive electrode sheet can be reduced, the restraining force on the electrode sheet can be reduced, and the positive electrode sheet can be prevented from breaking when bent.

[0064] In some embodiments, see Figure 5, a groove 121 is provided on the surface of the negative electrode sheet. The groove 121 at least provides a buffer space for the expansion of the bent section, solves the excessive extension of the negative electrode sheet along the length direction, and prevents the winding core from loosening. Furthermore, the spacing between the groove 121 and the tail end of the negative electrode sheet is L2, L2 ≥ 2mm. Exemplarily, L2 can be one of 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm and 6mm, and can also be any value greater than or equal to 2mm. Since the groove 121 usually destroys the adhesion of the surface layer of the negative electrode sheet, when it is too close to the cutting end of the negative electrode sheet, it is very easy to cause cutting and powdering. On the one hand, powdering may cause battery short circuit, and on the other hand, when the powdering area is large, it is easy to generate lithium plating risk. Therefore, by setting the spacing L2 between the groove 121 and the tail end of the negative electrode sheet to L2 ≥ 2mm, it is possible to reduce the risk of powdering at the tail end of the negative electrode sheet, thereby reducing the risk of battery short circuit or even lithium plating caused by this, and further improving the safety performance of the battery.

[0065] In some embodiments, see Figure 6 The surface of the negative electrode sheet is provided with a groove 121, and the extension direction of the groove 121 forms a preset angle θ with the extension direction of the winding axis of the electrode assembly 1, wherein 2°≤θ≤80°. For example, θ can be one of 2°, 5°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, and 80°, and can also be any value between 2° and 80°. Unlike the above embodiment, in this embodiment, the extension direction of the groove 121 is adjusted to be inclined with respect to the width direction of the electrode assembly 1. Even if the groove 121 extends to the tail end of the negative electrode sheet, due to its smaller width at the tail end, it is less likely to cause powder loss during cutting, and even if powder is lost, the amount of powder is relatively small, thereby effectively preventing the problem of powder loss during cutting of the negative electrode sheet and improving the safety performance of the battery. At the same time, in this embodiment, the groove 121 can extend to the tail end of the negative electrode sheet, thereby providing space for its extension at the tail end.

[0066] In some embodiments, the gap between adjacent grooves 121 is d, the width of the negative electrode sheet is W1, and d and W1 satisfy the following relationship: 5≤W1 / d≤250. Exemplarily, the ratio of W1 / d can be one of 5, 10, 50, 80, 100, 120, 150, 180, 200, 220, and 250, or any value within the range of 5 to 250. If the ratio of W1 / d is too small, the grooves 121 can significantly affect the adhesion of the surface layer of the negative electrode sheet, easily causing powder loss. If the ratio of W1 / d is too large, the grooves 121 provide little buffer space for expansion, failing to address the problem of excessive longitudinal expansion of the negative electrode sheet. By setting the ratio of W1 / d to 5≤W1 / d≤250, sufficient buffer space can be provided for the expansion of the negative electrode sheet during cycling while preventing powder loss.

[0067] In some embodiments, see Figure 1 and Figure 2 , the length of the second adhesive paper layer 3 bonded to the single-sided area 01 away from the winding center is greater than or equal to 3mm. That is, the length of the second adhesive paper layer 3 bonded to the single-sided area 01 away from the winding center is L3, L3 ≥ 3mm. Exemplarily, L3 can be one of 3mm, 3.5mm, 4mm, 4.5mm, 5mm and 6mm, and can also be any point value greater than or equal to 3mm. It can be understood that the length of the second adhesive paper layer 3 bonded to the single-sided area 01 away from the winding center is the length of the second adhesive paper layer 3 bonded to the first current collector 111 of the single-sided area 01. If the length of the second adhesive paper layer 3 bonded to the single-sided area 01 away from the winding center is too small, the bonding force between the second adhesive paper layer 3 and the single-sided area 01 is small, and the winding core is easily spread out due to loose adhesion, which increases the risk of electrochemical corrosion caused by contact between the second pole piece 12 and the membrane shell. By setting the length of the second adhesive tape layer 3 bonded to the single-sided area 01 away from the winding center to be no less than 3 mm, the adhesion area is ensured and the bonding force is increased, thereby ensuring that the second adhesive tape layer 3 is firmly bonded to the single-sided area 01.

[0068] In some embodiments, see Figure 1 and Figure 2 The electrode assembly 1 includes a tab 14, and the projections of the two ends of the first adhesive paper layer 2 in the thickness direction of the electrode assembly 1 are respectively spaced apart from the projections of the tab 14 of the electrode assembly 1 in the thickness direction of the electrode assembly 1. That is, in the thickness direction of the electrode assembly 1, i.e., the second direction, the projections of the two ends of the first adhesive paper layer 2 are spaced apart from the projections of the tab 14, and the projections of the first adhesive paper layer 2 and the tab 14 in the thickness direction of the electrode assembly 1 do not overlap. This prevents thickness accumulation caused by the partial overlap of the projections of the first adhesive paper layer 2 and the tab 14 in the thickness direction, and its impact on the overall thickness of the battery, thereby avoiding its impact on the battery energy density.

[0069] In some embodiments, see Figure 1 and Figure 2, the distance between the projection of the tail end of the first adhesive paper layer 2 in the thickness direction of the electrode assembly 1 and the projection of the electrode tab 14 of the electrode assembly 1 in the thickness direction of the electrode assembly 1 is L4, and L4 ≥ 2mm. It can be understood that when the electrode assembly 1 includes multiple tabs 14, L4 is the distance between the projection of the tail end of the first adhesive paper layer 2 and the projection of the tab 14 closest to it in the thickness direction of the electrode assembly 1. Exemplarily, L4 can be one of 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm and 6mm, and can also be any value greater than or equal to 2mm. The distance L4 is not less than 2mm, which can reliably prevent the first adhesive paper layer 2 and the tab 14 from overlapping in the opposite direction of the thickness of the electrode assembly 1.

[0070] In some embodiments, see Figure 1 and Figure 2 , the distance between the projection of the head end of the first adhesive paper layer 2 in the thickness direction of the electrode assembly 1 and the projection of the electrode tab 14 of the electrode assembly 1 in the thickness direction of the electrode assembly 1 is L5, and L5 ≥ 2mm. It can be understood that when the electrode assembly 1 includes multiple tabs 14, L5 is the distance between the projection of the head end of the first adhesive paper layer 2 and the projection of the tab 14 closest to it in the thickness direction of the electrode assembly 1. Exemplarily, L5 can be one of 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm and 6mm, and can also be any value greater than or equal to 2mm. The distance L5 is not less than 2mm, which can reliably prevent the first adhesive paper layer 2 and the tab 14 from overlapping in the opposite direction of the thickness of the electrode assembly 1.

[0071] In some embodiments, see Figure 1 and Figure 2 The middle portion of the first adhesive tape layer 2 is located outside the outermost layer of the first bend region 1b, and both ends extend into the straight section. This means that the first adhesive tape layer 2 can extend along the winding direction and bypass the first bend region 1b, thereby improving bonding reliability. Furthermore, during battery cycling, the outermost layer of the first bend region 1b is subject to more concentrated stress and is more susceptible to breakage. This arrangement of the first adhesive tape layer 2 effectively prevents electrolyte corrosion of the outermost first current collector 111, thereby preventing breakage of the first current collector 111. Furthermore, if the outermost layer of the first bend region 1b breaks and causes the winding core to loosen, the first adhesive tape layer 2 can, through its own elastic deformation, effectively offset the gap created by the loosening, thereby reducing the loosening displacement of the first bend segment 11a.

[0072] In some embodiments, see Figure 1 and Figure 2The middle portion of the second adhesive tape layer 3 extends beyond the outermost layer of the first bend region 1b, with both ends extending beyond the straight section. This means that the second adhesive tape layer 3 can extend along the winding direction and bypass the first bend region 1b, improving bonding reliability. It should be understood that the outermost layer of the first bend region 1b refers to the outermost layer of the first bend region 1b, away from the winding center of the electrode assembly 1.

[0073] In some embodiments, the projection of the tail end of the negative electrode sheet in the thickness direction of the electrode assembly 1 is located at the junction of the first bending region 1 b and the straight region 1 a .

[0074] In some embodiments, the core further comprises a fourth adhesive paper layer 5, which is disposed on the side of the first current collector 111 of the outermost circle away from the center of the core. The provision of the fourth adhesive paper layer 5 facilitates bonding and fixing the core to a shell such as an aluminum-plastic film disposed outside the core. Furthermore, the fourth adhesive paper layer 5 is spaced apart from the first adhesive paper layer 2 and the second adhesive paper layer 3, thereby preventing the fourth adhesive paper layer 5 from overlapping with the first adhesive paper layer 2 and the second adhesive paper layer 3 and causing thickness accumulation, thereby affecting the overall thickness of the battery and, in turn, the energy density of the battery. Exemplarily, along the winding direction, the first adhesive paper layer 2 extends beyond the second adhesive paper layer 3, and the gap between the fourth adhesive paper layer 5 and the first adhesive paper layer 2 is L6, where L6 is ≥ 1 mm. Exemplarily, L6 can be one of 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, and 6 mm, or any value greater than or equal to 1 mm. The spacing L6 is not less than 1 mm, which can reliably prevent the fourth adhesive paper layer 5 and the first adhesive paper layer 2 from overlapping in the thickness direction of the electrode assembly 1 .

[0075] Based on the winding core provided in the above embodiments, the present application further provides a battery, which includes any of the winding cores in the above embodiments. Since the battery adopts the winding core in the above embodiments, the beneficial effects of the battery can be referred to the above embodiments.

[0076] The present invention is further described below by way of specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, materials, and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis methods. Example 1

[0077] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) are added to a stirring tank in a mass ratio of 97.2:1.5:1.3, and then NMP solution is added and stirred thoroughly to prepare a uniform positive electrode active slurry. The prepared positive electrode active slurry is coated on the functional surface of the positive electrode current collector (aluminum foil), and then dried to remove the solvent. The positive electrode sheet is then obtained through roller pressing, slitting, and sheeting processes.

[0078] Graphite mixed with silicon-based materials, , sodium carboxymethyl cellulose are added into a stirring tank in a mass ratio of 97:1.5:1.5, and then deionized water is added. After sufficient stirring, a uniform negative electrode active slurry is obtained. The negative electrode active slurry is coated on the functional surface of the negative electrode collector (copper foil), and then dried to remove moisture. The desired negative electrode sheet is obtained by rolling, slitting and sheeting.

[0079] A polyethylene (PE) porous polymer film is used as the separator.

[0080] The positive electrode sheet, separator, and negative electrode sheet are stacked in this order and then wound to obtain a roll core. The roll core obtained above is placed in an outer packaging aluminum-plastic film, the aluminum-plastic film is sealed on the top and sides, and then baked to remove moisture. The electrolyte (containing 1 mol / L LiTFSI solute and a uniform mixture of DEC:EC:DMC with a solvent volume ratio of 1:1:1) is injected into the outer packaging. The lithium-ion battery is obtained after vacuum packaging, standing, chemical formation, and shaping.

[0081] Among them, the positive electrode sheet includes a single-sided area and a double-sided area. The winding tail is the single-sided area of the positive electrode collector, and the positive electrode collector in the single-sided area is flush with the tail end of the positive electrode active layer.

[0082] One end of the first adhesive paper layer is bonded to the tail end of the double-sided area and away from the winding center, and the other end is bonded around the first bending area along the winding direction. The first adhesive paper layer includes a PET base material and an acrylic adhesive layer.

[0083] One end of the second adhesive tape layer is bonded to the tail end of the single-sided area and away from the winding center, and the other end passes around the first bending area along the winding direction and is bonded to the first adhesive tape layer. The second adhesive tape layer is made of the same material as the first adhesive tape layer.

[0084] Among them, the tensile strength F1 of the second adhesive paper layer and the tensile strength F2 of the positive electrode current collector, the peel strength R between the second adhesive paper layer and the side of the single-sided area away from the winding center, and the length L1 of the bonding part between the second adhesive paper layer and the separator are shown in Table 1.

[0085] The prepared battery was tested. The following are some specific testing methods and steps for relevant parameters.

[0086] 1. The tensile strength of the second adhesive tape layer is the ratio of F1 to the tensile strength of the positive electrode current collector F2. The tensile strength test of the second adhesive tape layer was conducted by clamping the two ends of the second adhesive tape layer in the fixture of the tensile testing machine, selecting "Tensile Test" with a tensile rate of 30 mm / min and a switch condition of breakpoint ≥ 50% to obtain the tensile strength F1 of the second adhesive tape layer; The tensile strength of the positive electrode current collector is measured at the junction of the single-sided and double-sided areas of the positive electrode sheet. Specifically, along the length of the positive electrode sheet, the single-sided and double-sided areas are 50 mm each. The width of the positive electrode current collector is 15 mm. The positive electrode active coating on the surface of the positive electrode current collector is cleaned and removed. The same test method as for the first adhesive tape layer is then used to measure the tensile strength F2 of the positive electrode current collector.

[0087] 2. Peel strength R between the second adhesive tape layer and the single-sided area away from the winding center Cut off the part where the second adhesive paper layer and the positive electrode current collector are bonded, measure its width (mm), peel off the second adhesive paper layer and the positive electrode current collector from one end, and clamp the peeled second adhesive paper layer in a fixture. Clamp the positive electrode current collector in the fixture of the tensile testing machine and perform a peel test at a rate of 200 mm / min to obtain the peel force, which is then divided by the width of the test sample to obtain the peel strength R.

[0088] 3. The length L1 of the bonding part between the second adhesive tape layer and the diaphragm and the thickness of the single-sided area Use a measuring ruler to measure the length L1 of the bonding portion between the second adhesive tape layer and the diaphragm, and use a micrometer to measure the thickness of the single-sided area.

[0089] 4. Battery energy density The battery energy density is calculated by the following formula: Energy density = (battery capacity * platform voltage) / (battery length * width * thickness) The length, width and thickness of the battery are measured with a measuring ruler to detect the battery capacity, and the voltage of the detection platform is read to obtain the energy density by calculating the above formula.

[0090] 5. Appearance test during the cycle In a 45°C constant temperature room, use a constant current and voltage cycle of 0.5C to the upper voltage limit, then 0.05C to the end, let stand for 5 minutes, and discharge at 0.5C to 3.0V for 500 cycles. Observe for fractures in the first and second bends, and inspect for lithium deposition at the tail of the negative electrode. Twenty lithium-ion batteries were tested, and the number of lithium-ion batteries with fractures in the first or second bend was counted. The percentage of lithium-ion batteries with fractures in the first or second bend relative to the total number of lithium-ion batteries tested (20) was calculated as the first and second bend fracture ratio. The number of lithium-ion batteries with lithium deposition at the tail of the negative electrode was also counted, and the percentage of lithium-ion batteries with lithium deposition at the tail of the negative electrode was calculated as the tail lithium deposition ratio.

[0091] 6. Short circuit test pass rate Charge at a constant current of 1.0C to 4.2V, then charge at a constant voltage until the current drops to 0.05C, and then stop charging; let it stand for 1 hour, then measure the OCV; short-circuit the positive and negative electrodes of the lithium-ion battery with a copper wire with a resistance of no more than 0.1 ohm at room temperature; the lithium-ion battery is discharged until it catches fire or explodes, or until the lithium-ion battery is completely discharged, and the test can be stopped when the surface temperature of the lithium-ion battery returns to a temperature close to the ambient temperature. 20 lithium-ion batteries are tested, and the number of lithium-ion batteries that meet the judgment standard is counted. The percentage of lithium-ion batteries that meet the judgment standard to the total number of lithium-ion batteries tested (20) is calculated as the short-circuit test pass rate of the lithium-ion battery, and the percentage of lithium-ion batteries that do not meet the standard to the total number of lithium-ion batteries tested (20) is calculated as the short-circuit ratio; Judgment standard: the battery does not leak, smoke, catch fire, or explode, and the battery surface temperature does not exceed 150°C.

[0092] The battery was tested according to the method described above, and the results are shown in Table 2. Example 2

[0093] The preparation process is basically the same as that of Example 1, except that the tensile strength F1 of the second adhesive paper layer is adjusted by setting the thickness of the second adhesive paper layer so that the ratio of the tensile strength F1 of the second adhesive paper layer to the tensile strength F2 of the positive electrode collector, F1 / F2, is 1; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 3

[0094] The preparation process is basically the same as that of Example 1, except that the ratio of the tensile strength F1 of the second adhesive tape layer to the tensile strength F2 of the positive electrode current collector, F1 / F2, is 1.2; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 4

[0095] The preparation process is basically the same as that of Example 2, except that the peel strength R between the second adhesive tape layer and the side of the single-sided area away from the winding center is 0.06N / mm; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 5

[0096] The preparation process is basically the same as that of Example 2, except that the peel strength R between the second adhesive tape layer and the side of the single-sided area away from the winding center is 0.2N / mm; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 6

[0097] The preparation process is basically the same as that of Example 2, except that the peel strength R between the second adhesive tape layer and the side of the single-sided area away from the winding center is 0.01N / mm; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 7

[0098] The preparation process is basically the same as that of Example 2, except that the peel strength R between the second adhesive tape layer and the side of the single-sided area away from the winding center is 0.3N / mm; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 8

[0099] The preparation process is basically the same as that of Example 2, except that the length L1 of the bonding portion between the second adhesive paper layer and the diaphragm is 2.0 mm, and the ratio L1 / H of the length L1 of the bonding portion between the second adhesive paper layer and the diaphragm to the thickness H of the single-sided area is 40; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 9

[0100] The preparation process is basically the same as that of Example 8, except that the length L1 of the bonding portion between the second adhesive paper layer and the diaphragm is 10.0 mm, and the ratio L1 / H of the length L1 of the bonding portion between the second adhesive paper layer and the diaphragm to the thickness H of the single-sided area is 200; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 10

[0101] The preparation process is basically the same as that of Example 8, except that the length L1 of the bonding portion between the second adhesive paper layer and the diaphragm is 1.0 mm, and the ratio L1 / H of the length L1 of the bonding portion between the second adhesive paper layer and the diaphragm to the thickness H of the single-sided area is 20; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 11

[0102] The preparation process is basically the same as that of Example 2, except that the thickness H of the single-sided area is 0.2 mm, and the ratio L1 / H of the length L1 of the bonding portion between the second adhesive tape layer and the diaphragm to the thickness H of the single-sided area is 20; other conditions remain unchanged, and the battery of this embodiment is obtained. Example 12

[0103] The preparation process is basically the same as that of Example 2, except that the thickness H of the single-sided area is 0.016 mm, and the ratio L1 / H of the length L1 of the bonding portion between the second adhesive tape layer and the diaphragm to the thickness H of the single-sided area is 250; other conditions remain unchanged, and the battery of this embodiment is obtained.

[0104] Comparative Example 1 The preparation process is basically the same as that of Example 2, except that the ratio of the tensile strength F1 of the second adhesive tape layer to the tensile strength F2 of the positive electrode current collector, F1 / F2, is 0.5; other conditions remain unchanged, and the battery of this embodiment is obtained.

[0105] Comparative Example 2 The preparation process is basically the same as that of Example 2, except that the ratio of the tensile strength F1 of the second adhesive tape layer to the tensile strength F2 of the positive electrode current collector, F1 / F2, is 1.5; other conditions remain unchanged, and the battery of this embodiment is obtained.

[0106] Table 1

[0107] Table 2

[0108] As shown in Examples 1-3 and Comparative Examples 1-2, when the ratio (F1 / F2) of the tensile strength F1 of the second adhesive tape layer to the tensile strength F2 of the positive electrode current collector is between 0.6 and 1.2, the breakage rate in the first and second bend regions is low, which reduces the risk of positive electrode sheet fracture, improves the reliability of the winding core and battery, and reduces the proportion of lithium deposition at the tail. When F1 / F2 is less than 0.6 (Comparative Example 1) or greater than 1.2 (Comparative Example), the breakage rate in the first and second bend regions is high, indicating a greater risk of positive electrode sheet fracture and poor winding core and battery reliability.

[0109] As shown in Examples 2 and 4-7, when the peel strength R between the second adhesive tape layer and the side of the single-sided region away from the winding center is 0.06-0.2, the tail portion of the battery exhibits a low rate of lithium deposition and a low rate of tape breakage in the first and second bend regions, improving the reliability of the winding core and battery. When R is less than 0.06 (Example 6), the second adhesive tape layer easily separates from the single-sided region due to expansion, resulting in a high rate of lithium deposition in the tail portion. When R is greater than 0.2 (Example 7), the first and second bend regions exhibit a high rate of tape breakage, indicating a higher risk of positive electrode tape breakage.

[0110] As shown in Examples 2 and 8-12, when the ratio (L1 / H)—the length L1 of the second adhesive tape layer bonded to the separator—to the thickness H of the single-sided area is between 40 and 200, the battery has a high energy density, a low short-circuit rate, and high safety. When L1 / H is less than 40 (Examples 10 and 11), the second adhesive tape layer and separator are not firmly bonded, resulting in a high short-circuit rate. When L1 / H is greater than 200 (Example 12), the battery has a low capacity density.

[0111] Furthermore, in Examples 2, 8, and 11, when the length L1 of the bond between the second adhesive tape layer and the separator is greater than or equal to 2 mm, the second adhesive tape layer and the separator are reliably bonded, and the battery short-circuit rate is low. When L1 is less than 2 mm (Example 10), the second adhesive tape layer and the separator are not firmly bonded, resulting in a more susceptible battery short-circuit and poor safety.

[0112] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0113] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A winding core, characterized in that: include: An electrode assembly (1) comprises a first pole piece (11), a diaphragm (13) and a second pole piece (12) stacked in sequence and wound from the head to the tail, the first pole piece (11) comprising a first current collector (111) and a first active layer (112), and the first pole piece (11) comprises a single-sided region (01) having the first active layer (112) only on a surface of the first current collector (111) facing the winding center of the electrode assembly (1), at least part of the single-sided region (01) being located at the outermost circle of the electrode assembly (1), the tail end of the first active layer (112) of the single-sided region (01) being flush with the tail end of the first current collector (111), the second pole piece (12) comprising a second current collector and a second active layer, the first active layer (112) or the second active layer comprising a silicon-based material, the silicon-based material comprising at least one of elemental silicon, a silicon oxide compound, a silicon carbon compound or a silicon alloy; A first adhesive paper layer (2) is bonded to at least a portion of the single-sided area (01) facing the second pole piece (12), and the first adhesive paper layer (2) extends along the winding direction, with one end thereof being located on a side of the second pole piece (12) facing the winding center; The second adhesive paper layer (3) has one end bonded to the tail of the single-sided area (01) of the outermost circle and away from the side of the winding center, and the other end extends at least to the first adhesive paper layer (2) along the winding direction and is bonded, wherein the tensile strength of the second adhesive paper layer (3) is F1, the tensile strength of the first current collector (111) is F2, and F1 and F2 satisfy the following relationship: 0.6≤F1 / F2≤1.

2.

2. The winding core according to claim 1, characterized in that The tail end of the diaphragm (13) located between the first pole piece (11) and the adjacent second pole piece (12) on the outermost circle extends beyond the tail end of the first pole piece (11) along the winding direction, and the extending portion is bonded to the second adhesive tape layer (3).

3. The winding core according to claim 2, characterized in that The length of the bonding portion between the second adhesive paper layer (3) and the diaphragm (13) is L1, and L1 is ≥ 2 mm; And / or, the thickness of the single-sided area (01) is H, and L1 and H satisfy the following relationship: 40≤L1 / H≤200.

4. The winding core according to claim 1, wherein: Along the winding direction, the tail end of the second pole piece (12) extends beyond the first pole piece (11) and is located between the first adhesive paper layer (2) and the second adhesive paper layer (3).

5. The winding core according to claim 1, characterized in that The peeling strength between the second adhesive tape layer (3) and the side of the single-sided area (01) away from the winding center is R, and 0.02N / mm≤R≤0.2N / mm.

6. The winding core according to any one of claims 1 to 5, characterized in that: The first electrode (11) is a positive electrode, and the second electrode (12) is a negative electrode; the electrode assembly (1) comprises a straight region (1a), a first bending region (1b), and a second bending region (1c); along a first direction, the first bending region (1b) and the second bending region (1c) are connected to two ends of the straight region (1a); The positive electrode sheet comprises a first bending section (11a) located in the first bending area (1b) and a positive electrode winding starting section (11b) and a first straight section (11d) located in the straight area (1a); along the second direction, the positive electrode winding starting section (11b) and the first straight section (11d) are arranged opposite to each other; the first straight section (11d) and the positive electrode winding starting section (11b) are respectively connected to two ends of the first bending section (11a); and the end of the positive electrode winding starting section (11b) facing away from the first bending section (11a) is the positive electrode winding starting end (11c) of the positive electrode sheet; The negative electrode sheet comprises a negative electrode winding starting section (12a), a second bending section (12c) located in the second bending area (1c), and a second straight section (12d) located in the straight area (1a); the negative electrode winding starting section (12a) is located in the straight area (1a), and along the second direction, the negative electrode winding starting section (12a) is located between the positive electrode winding starting section (11b) and the first straight section (11d); along the first direction, the end of the negative electrode winding starting section (12a) facing the first bending section (11a) is the negative electrode winding starting end (12b) of the negative electrode sheet; along the second direction, the second straight section (12d) and the negative electrode winding starting section (12a) are arranged relative to each other, and the second straight section (12d) and the negative electrode winding starting section (12a) are respectively connected to the two ends of the second bending section (12c); The negative electrode active layer on one side of the negative electrode winding starting section (12a) is arranged opposite to the positive electrode active layer of the positive electrode winding starting section (11b), and the negative electrode active layer on the other side of the negative electrode winding starting section (12a) is arranged opposite to the positive electrode active layer of the first straight section (11d). The diaphragm (13) has a diaphragm winding starting end, and the diaphragm winding starting end is flush with the positive electrode winding starting end (11c), or the diaphragm winding starting end is flush with the negative electrode winding starting end (12b); the positive electrode active layers on both sides of the positive electrode winding starting section (11b) are arranged opposite to the negative electrode active layer of the negative electrode winding starting section (12a) and the negative electrode active layer of the second straight section (12d). The first direction and the second direction are perpendicular to the extension direction of the winding axis of the electrode assembly (1); And / or, the mass percentage of the silicon-based material is 5%-50%, including endpoint values.

7. The winding core according to claim 6, characterized in that A third adhesive paper layer (4) is provided on the side of the first bent section (11a) facing the negative electrode winding starting end (12b); The third adhesive paper layer (4) comprises a substrate (31) and an adhesive layer (32), wherein the adhesive layer (32) is spaced apart on a side of the substrate (31) facing the positive electrode sheet; The area of the adhesive layer (32) provided on the substrate (31) is S1, the area of the substrate (31) is S, and S1 and S satisfy the following relationship: 0.2≤S1 / S≤0.

8.

8. The winding core according to claim 6, characterized in that A groove (121) is provided on the surface of the negative electrode sheet, and a distance between the groove (121) and the tail end of the negative electrode sheet is greater than or equal to 2 mm; Alternatively, the extension direction of the groove (121) and the extension direction of the winding axis of the electrode assembly (1) form a preset angle θ, wherein 2°≤θ≤80°; the gap between adjacent grooves (121) is d, the width of the negative electrode sheet is W1, and d and W1 satisfy the following relationship: 5≤W1 / d≤250.

9. The winding core according to claim 1, characterized in that The length of the second adhesive tape layer (3) bonded to the single-sided area (01) away from the winding center is greater than or equal to 3 mm; And / or, the electrode assembly (1) includes a tab (14), and projections of both ends of the first adhesive paper layer (2) in the thickness direction of the electrode assembly (1) are spaced from projections of the tab (14) in the thickness direction of the electrode assembly (1); And / or, it further includes a fourth adhesive paper layer (5), wherein the fourth adhesive paper layer (5) is arranged on the side of the first current collector (111) in the outermost circle away from the winding center, and the fourth adhesive paper layer (5) is spaced apart from the first adhesive paper layer (2).

10. A battery, characterized in that: The invention comprises a winding core according to any one of claims 1 to 9.

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