Core and battery

Abstract

This application provides a core. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector. The negative active material layer contains silicon. A first exposed foil groove is provided on the surface of the negative electrode sheet, and a portion of the negative current collector is exposed on the bottom wall of the first exposed foil groove. The first exposed foil groove is disposed near a second arc segment, and the negative active material layer is disposed on the periphery of the first exposed foil groove. The negative electrode sheet also includes a negative electrode tab and a first protective adhesive, with a portion of the negative electrode tab located in the first exposed foil groove and electrically connected to the negative current collector. The first protective adhesive covers a portion of the negative electrode tab in the first exposed foil groove. Along a second direction, the two sides of the first protective adhesive have gaps with the two opposite sidewalls of the first exposed foil groove. On the side near the second arc segment, the side of the first protective adhesive has a first gap m with the sidewall of the first exposed foil groove, and the sidewall of the first exposed foil groove has a second distance n with the second arc segment. The ratio of m to n satisfies: 1 ≤ n / m ≤ 20.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular, to a winding core and a battery. Background Technology

[0002] Lithium-ion batteries have advantages such as high energy density, low self-discharge rate and long life, and are widely used in various electronic devices, such as smartphones, laptops and electric vehicles.

[0003] With the rapid development of battery technology, the requirements for the energy density of lithium-ion batteries are becoming increasingly stringent. To improve the energy density of lithium-ion batteries, silicon is typically doped into the negative electrode active material layer.

[0004] However, after silicon doping, there is a problem that the electrodes are prone to breakage. Summary of the Invention

[0005] In view of this, embodiments of this application provide a core and a battery having therein to improve the energy density of the battery and reduce the risk of electrode breakage.

[0006] In a first aspect, embodiments of this application provide a core. The core includes a negative electrode sheet, a separator, and a positive electrode sheet sequentially stacked and wound. The core has a straight section and a first arcuate section and a second arcuate section located on both sides of the straight section. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer contains silicon. A first exposed foil groove is provided on the surface of the negative electrode sheet, and a portion of the negative electrode current collector is exposed on the bottom wall of the first exposed foil groove. The first exposed foil groove is disposed near a second arcuate section, and the negative electrode active material layer is disposed around the periphery of the first exposed foil groove. The negative electrode sheet also includes a negative electrode tab and a first protective adhesive, a portion of the negative electrode tab being located in the first exposed foil groove and electrically connected to the negative electrode current collector, and the negative electrode tab extending along a first direction and beyond a first edge of the negative electrode sheet. The first protective adhesive covers a portion of the negative electrode tab in the first exposed foil groove. Along a second direction, the two sides of the first protective adhesive have gaps with the two opposite sidewalls of the first exposed foil groove, and the second direction is perpendicular to the first direction. On the side near the second arc segment, the side edge of the first protective adhesive has a first gap m with the side wall of the first exposed foil groove, and the side wall of the first exposed foil groove has a second distance n with the second arc segment. The ratio of m to n satisfies: 1≤n / m≤20.

[0007] Alternatively, the ratio of m to n satisfies: 2.5 ≤ n / m ≤ 7.5.

[0008] Alternatively or supplementally, the core also includes a third protective adhesive. The third protective adhesive covers the outer surface of the second arc segment and extends into the straight segment. Along the fourth direction, the orthographic projection of the third protective adhesive at least partially overlaps with the orthographic projection of the first gap m.

[0009] Alternatively, the dimensions of the third protective adhesive on the straight sections on both sides of the arc segment on the non-end side of the core are L3 and L4, respectively; the values ​​of L3 and L4 satisfy: 0 mm < L3 ≤ 8 mm, 0 mm < L4 ≤ 8 mm, and / or, the thickness of the core is H, and the ratios of L3 and L4 to H satisfy: 0.1 ≤ L3 / H ≤ 3.5, 0.1 ≤ L4 / H ≤ 3.5, respectively.

[0010] Alternatively or supplementarily, the negative electrode active material layer includes a negative electrode active material, which includes graphite and silicon carbide materials. The silicon content in the silicon carbide material is f, wherein 35 wt% ≤ f ≤ 70 wt%; and / or, the silicon content in the negative electrode active material layer is e, where e satisfies: 0.35 wt% ≤ e ≤ 35 wt%.

[0011] Alternatively or supplementarily, the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer stacked sequentially. The first negative electrode active material layer is located on the side of the second negative electrode active material layer away from the negative electrode current collector. The silicon content in the first negative electrode active material layer is greater than the silicon content in the second negative electrode active material layer, and the silicon content in the second negative electrode active material layer is greater than or equal to 0.

[0012] Alternatively or supplementarily, the thickness ratio of the first negative electrode active material layer to the negative electrode active material layer is y, and e and y satisfy: 0.05%≤e*y≤20%.

[0013] Alternatively, the negative electrode active material layer is provided with a recessed groove, which includes a plurality of spaced recessed grooves; along the width direction of the negative electrode sheet, the gap between the bottom wall of the first exposed foil groove and the recessed groove is G1, and the value of G1 satisfies: 0 mm < G1 ≤ 5 mm, and / or, along the length direction of the negative electrode sheet, the gaps between the side walls of the first exposed foil groove and the recessed groove are G2, and the value of G2 satisfies: 0 mm < G2 ≤ ​​5 mm, and / or, along the width direction of the negative electrode sheet, the gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0 mm < G3 ≤ 5 mm.

[0014] Alternatively or supplementarily, the ratio of the intensity S of the negative electrode current collector to the depth h of the recessed groove satisfies: 3≤S / h≤120; and the value of h ranges from 3 μm to 35 μm, and / or the value of S ranges from 100 MPa to 650 MPa.

[0015] Alternatively or supplementarily, the positive electrode sheet includes a positive electrode active material layer and a positive electrode current collector. A stepped groove is provided in the projected area of ​​the negative electrode tab on the positive electrode sheet, and a second protective adhesive is disposed within the stepped groove. Along a third direction, the stepped groove includes a first groove and a second groove arranged sequentially. The first groove has a width L1 and a depth h1. The second groove has a width L2 and a depth h2. L1 is greater than or equal to the width of the second protective adhesive. The width of the negative electrode tab is W3, and L2 ≥ W3. The width of the first exposed foil groove is W1, and the width of the second protective adhesive is greater than or equal to W1. The thickness of the second protective adhesive ≤ h1 ≤ h2. h1 + h2 ≤ the thickness of the positive electrode active material layer. The third direction is perpendicular to the first and second directions.

[0016] Secondly, embodiments of this application also provide a battery comprising the aforementioned winding core.

[0017] According to the core provided in the embodiments of this application, by controlling n / m within the above range, firstly, it is possible to maintain an appropriate distance between the empty foil area on the right side of the first exposed foil groove and the second arc segment, that is, to maintain an appropriate distance from the place where stress concentration is severe, which can alleviate the stress concentration phenomenon.

[0018] Secondly, this design ensures that the tensile / compressive stresses of the copper foil on the weaker left side of the exposed foil groove and the stronger expansion stress on the right side are more similar, meaning that the exposed copper foil on both sides of the exposed foil groove experiences similar stress. This effectively reduces the phenomenon of copper foil being squeezed or stretched in different directions due to the imbalance of stress on the copper foil on both sides of the exposed foil groove, thus lowering the probability of fatigue fracture of the copper foil on both sides of the exposed foil groove.

[0019] Thirdly, the distance between the first exposed foil groove 24 and the second arc segment 101b can be reasonably adjusted according to the size of m, which can better alleviate the breakage problem of silicon-doped batteries near the negative electrode tab 23. When n / m is too small, the distance is too close to the stress concentration point, and it cannot effectively alleviate the breakage problem of silicon-doped batteries near the negative electrode tab. At the same time, due to process errors, the first exposed foil groove may be partially or entirely located in the bending section with high stress. When n / m is too large, the negative electrode tab is closer to the center of the cell, and the electrolyte corrosion rate of the copper foil on the left side of the exposed foil is faster, making it more prone to breakage. Attached Figure Description

[0020] Figure 1 This is a three-dimensional structural diagram of a core according to an embodiment of this application.

[0021] Figure 2 for Figure 1 A cross-sectional view of the middle core along BB.

[0022] Figure 3 for Figure 2 A magnified view of a portion of region C.

[0023] Figure 4 for Figure 3 Enlarged schematic diagram of the negative electrode tab and its surrounding structures.

[0024] Figure 5 for Figure 4 Top view of the negative electrode tab and its surrounding structures.

[0025] Figure 6 This is a schematic diagram of the negative electrode tab and its surrounding structure according to another embodiment of this application.

[0026] Figure 7 for Figure 6 Top view of the negative electrode tab and its surrounding structures.

[0027] Figure 8 for Figure 1 The right view.

[0028] Figure 9 for Figure 1 The left view.

[0029] Figure 10 This is a schematic diagram of a negative electrode structure according to an embodiment of this application.

[0030] Figure 11 for Figure 10 A schematic diagram of the local structure of region D in the middle.

[0031] Figure 12 for Figure 10 A schematic diagram of the partial structure at both ends of the middle section.

[0032] Figure 13 This is a cross-sectional view of the negative electrode sheet according to an embodiment of this application.

[0033] Figure 14 This is a schematic diagram of a battery structure according to an embodiment of this application.

[0034] Figure 15 This is a schematic diagram of a battery structure according to another embodiment of this application.

[0035] Figure label:

[0036] 1000, battery;

[0037] 100. Core; 101. Arc segment; 101a. First arc segment; 101b. Second arc segment; 102. Straight segment;

[0038] 10. Positive electrode sheet; 11. Positive electrode active material layer; 12 / 12', stepped groove; 121 / 121', first groove; 122 / 122', second groove; 13. Positive electrode current collector; 14. Positive electrode tab; 15. Second exposed foil groove;

[0039] 20. Negative electrode sheet; 21. Negative electrode active material layer; 211. First negative electrode active material layer; 212. Second negative electrode active material layer; 22. Negative electrode current collector; 23. Negative electrode tab; 24 / 24'. First exposed foil groove; 25 / 25'. Third groove; 26. Straight portion; 27. Arc portion; 28. Recessed groove portion; 281. Recessed groove;

[0040] 30 / 30', First protective adhesive; 40 / 40', Second protective adhesive; 50, Third protective adhesive; 60, Fourth protective adhesive; 70, Fifth protective adhesive;

[0041] 80. Finishing protective adhesive; 90. Diaphragm;

[0042] 200. Shell. Detailed Implementation

[0043] Improving energy density is a continuous direction for the improvement of lithium-ion batteries. Currently, doping silicon into the negative electrode active material layer is a technology that can be mass-produced and effectively improve the energy density of lithium-ion batteries. However, there is a risk of electrode breakage due to silicon expansion.

[0044] During charging and discharging, silicon can expand by up to 300%, which is hundreds of times greater than that of graphite. Furthermore, because silicon has a cubic structure, the stress is released in all directions during expansion, potentially leading to problems never encountered in lithium-ion batteries with pure graphite as the negative electrode active material, such as electrode breakage.

[0045] Taking a lithium-ion battery with a wound core as an example, the inventors discovered that the area near the tab on the negative electrode sheet is more prone to breakage.

[0046] In response to this situation, the inventor conducted research and analysis, as detailed below.

[0047] The core includes a positive electrode sheet, a negative electrode sheet, and a separator arranged in layers. The positive electrode sheet and the negative electrode sheet are wound together with the separator to form a core having a straight section and arc sections located on both sides of the straight section.

[0048] As is known, the metal conductors that lead the positive and negative electrodes out of the battery cell, i.e., the tabs, are usually fixed to the current collector by welding. Taking the negative electrode sheet as an example, before welding the negative electrode tabs, the negative electrode active material layer on the tab welding area of ​​the negative electrode sheet is usually removed by means of laser or scraper, exposing the negative electrode current collector and forming a foil groove for welding the tabs.

[0049] On the tab welding area side, to prevent short circuits caused by the tabs contacting each other and by welding burrs puncturing the diaphragm, protective adhesive is usually applied to the negative tab. To simplify the processing of the exposed foil groove and facilitate the application of the protective adhesive, the exposed foil groove is usually formed into a through groove in a single process, with gaps left between the applied protective adhesive and the sides of the exposed foil groove. However, direct contact between the exposed metal foil (e.g., copper foil) and the electrolyte can easily lead to oxidation / corrosion, resulting in a decrease in the strength of this area.

[0050] During the winding process of the battery cell, the curved sections on both sides need to be tightened and turned, resulting in a greater tension force on the curved sections than on the straight sections in the middle. Therefore, the tightness and fit of the curved sections are greater than that of the straight sections, and the tension force on the straight sections is greater closer to the curved sections. The stress is greatest at the junction of the straight and curved sections, resulting in stress concentration. Furthermore, there is a mutual pulling force between the straight and curved sections, which is greater closer to the curved sections on the straight sections. The junction between the two is subjected to opposing pulling forces from both sides, creating a stress concentration area. These factors cause the cross-section of the battery cell to be essentially elliptical under the action of force, i.e., bulging in the middle of the straight sections and gradually decreasing towards the curved sections on both sides. Therefore, the gaps between the electrodes in the middle region of the straight sections of the wound core are larger, and the gaps between the electrodes gradually decrease towards the curved sections on both sides (the cross-section of the gaps resembles a normal distribution curve), resulting in a smaller electrolyte storage capacity towards the curved sections on both sides.

[0051] In addition, to improve the energy density of the battery, silicon is usually doped into the negative electrode active material layer of the negative electrode sheet. Silicon tends to expand during charging. As mentioned above, during charging, due to the smaller electrolyte storage capacity, the reaction kinetics are correspondingly poor. The lithium insertion / extraction rate of the negative electrode active material layer in the straight section on the right side of the exposed foil groove (the side closer to the arc section) is slower than that in the straight section closer to the middle region of the negative electrode sheet (i.e., the region on the left side of the negative electrode tab). Therefore, the expansion rate of the straight section on the right side of the exposed foil groove is slower, and the recovery rate from the expanded state is also slower. The stress generated by the inconsistent volume changes on both sides further exacerbates the stress concentration on the side of the exposed foil groove closer to the arc section, especially at the junction of the arc section and the straight section. During multiple charge-discharge cycles, stress fatigue fracture is prone to occur at this point.

[0052] Then, during the charging process, as mentioned above, the gap between the electrodes in the straight section on the right side of the exposed foil groove on the negative electrode (the side near the arc section) is small, which results in less space to alleviate the expansion when silicon expands during charging, and also aggravates the stress concentration in this area.

[0053] In addition, welding the negative electrode tab in the exposed foil groove will cause unevenness of the surface in that area and the presence of certain welding stress.

[0054] In addition, the arc segment of the core and the area where it intersects with the straight segment are themselves areas of structural stress concentration.

[0055] Additionally, along the width direction of the battery cell, the different gap sizes on both sides of the exposed foil groove cause the electrolyte to concentrate on the side of the exposed foil groove closest to the arc segment (i.e., Figure 3 The accumulation on the right side of the middle cell is greater than that on the side closest to the center of the cell (i.e., Figure 3 The electrolyte accumulation on the right side of the exposed foil tank (left side) is less than that on the left side. Furthermore, the electrolyte flow rate on the right side of the exposed foil tank is stronger than that on the left side, resulting in a weaker corrosion rate of the copper foil on the right side compared to the left side. In other words, the copper foil on the right side of the exposed foil tank is stronger than that on the left side. As the number of charge-discharge cycles of the battery cell increases, the electrolyte inside the cell is gradually consumed, and the amount of electrolyte accumulated on the side of the exposed foil tank near the arc segment gradually decreases to near zero. This means that the same electrolyte reaction and corrosion rate on the copper foil on the right side of the exposed foil tank is weaker than that on the left side, and the copper foil on the right side of the exposed foil tank is stronger than that on the left side.

[0056] Based on the above research and analysis, it can be concluded that the copper foil on the right side of the exposed foil groove has a higher strength than that on the left side, and the stress on the copper foil on the right side of the exposed foil groove is more concentrated. The mismatch between the strength and / or stress state of the two after corrosion leads to a large difference in the tensile and / or compressive conditions of the empty foil areas on both sides of the negative electrode tab during the charge and discharge cycle of the battery cell, making it more prone to breakage.

[0057] To address the aforementioned problems, embodiments of this application provide a winding core 100 and a battery 1000. Below, in conjunction with… Figures 1 to 15 The winding core 100 and the battery 1000 are described.

[0058] It should be understood that there are many ways to implement this application, and it should not be construed as being limited to the embodiments described herein. The embodiments described herein are only for a more thorough and clear understanding of this disclosure.

[0059] It should be noted that, in this embodiment, the winding center of the core 100 can refer to its winding axis. It is understood that, during the winding process, the positive electrode 10, negative electrode 20, and separator 90 are wound around this winding axis into the aforementioned flat structure. Here, "flat structure" refers to a core 100 whose thickness is less than its length. It is understood that the positive electrode 10 and negative electrode 20 have a starting end and a ending end. During the winding process, the positive electrode 10 and negative electrode 20 are wound from the starting end to the ending end.

[0060] For ease of explanation, the embodiments of this application refer to the "width direction," "thickness direction," and "length direction" of the core 100. The width direction of the core 100 refers to the direction from one arc segment 101 to another arc segment 101, that is, the length direction of the positive and negative electrode sheets, which is indicated by arrow U in the figure; the length direction of the core 100 refers to the direction parallel to the winding axis A, which is indicated by arrow R in the figure; the thickness direction (fourth direction) of the core 100 refers to the direction perpendicular to both the width direction and the length direction, which is indicated by arrow V in the figure.

[0061] In addition, this article will also mention the length direction (second direction), width direction (first direction), and thickness direction (third direction) of each electrode. The length direction of the electrode refers to the direction from the starting end of the winding to the ending end, indicated by arrow X in the figure; the width direction of the electrode is perpendicular to the length direction, that is, from one edge of the electrode to the other edge, indicated by arrow Y in the figure; the thickness direction of the electrode is perpendicular to both the length and width directions, indicated by arrow Z in the figure. After the electrode is wound, its length direction is the winding direction.

[0062] Exemplary winding core

[0063] See 1 to Figure 13 The core 100 may include a negative electrode sheet 20, a separator 90, and a positive electrode sheet 10 arranged in sequence. The core formed by winding the positive electrode sheet 10 and the negative electrode sheet 20 with the separator 90 in between has a straight section 102 and arcuate sections 101 located on both sides of the straight section 102. The arcuate sections 101 may include a first arcuate section 101a and a second arcuate section 101b distributed along the width direction on opposite sides of the straight section 102.

[0064] The positive electrode sheet 10 may include a positive current collector 13 and a positive active material layer 11 disposed thereon. The two positive active material layers 11 may be located on opposite sides in the thickness direction of the positive current collector 13.

[0065] The negative electrode 20 may include a negative electrode current collector 22 and a negative electrode active material layer 21 disposed on at least one side of the negative electrode current collector 22. Exemplarily, at least a portion of the negative electrode current collector 22 may have two negative electrode active material layers 21, which may be located on opposite sides in the thickness direction of the negative electrode current collector 22. The negative electrode active material layer 21 contains silicon.

[0066] Understandably, along its length, the negative electrode 20 includes multiple straight portions 26 and multiple arcuate portions 27, which are arranged alternately. After winding, the arcuate portions 27 of the negative electrode 20 are located in the arcuate segment 101 of the core 100, and the straight portions 26 of the negative electrode 20 are located in the straight segment 102 of the core 100.

[0067] By way of example only, the positive electrode current collector 13 can be a strip of metal foil, and the positive electrode active material layer 11 can contain a positive electrode active material capable of reversibly absorbing and releasing charge carriers. Furthermore, they can further include conductive materials, binders, and various additives. By way of example only, the metal foil mentioned here can be aluminum foil, the positive electrode active material can be a lithium transition metal composite oxide such as lithium nickel cobalt manganese composite oxide, the conductive material can be a carbon-based material such as acetylene black, and the binder can be polyvinylidene fluoride, etc. Positive electrode active material layers 11 are respectively disposed on the upper and lower sides of the positive electrode current collector 13.

[0068] By way of example only, the negative electrode current collector 22 can be a strip of metal foil, and its active material layer can contain a negative electrode active material capable of reversibly absorbing and releasing charge carriers, a binder, a dispersant, and various additives. By way of example only, the metal foil mentioned here can be copper foil, the negative electrode active material can be a carbon-based material such as graphite doped with silicon, the binder can be a rubber such as styrene-butadiene rubber, and the dispersant can be a cellulose such as carboxymethyl cellulose. Negative electrode active material layers 21 are respectively provided on the upper and lower sides of the negative electrode current collector 22.

[0069] The separator 90 is a component that insulates the positive electrode 10 and the negative electrode 20. As some examples, the separator 90 can be a porous strip made of resin composed of polyolefin resins such as polyethylene and polypropylene. Of course, other materials can also be used to construct the separator 90.

[0070] refer to Figures 1 to 13 A first exposed foil groove 24 may be provided on the surface of the negative electrode sheet 20, and the bottom wall of the first exposed foil groove 24 exposes a portion of the negative electrode current collector 22. For example, the first exposed foil groove 24 is located near the second arc segment 101b, and a negative electrode active material layer 21 is provided on the periphery of the first exposed foil groove 24.

[0071] The negative electrode sheet 20 may further include a negative electrode tab 23 and a first protective adhesive 30. A portion of the negative electrode tab 23 is located in the first exposed foil groove 24 and is electrically connected to the negative electrode current collector 22. For example, the portion of the negative electrode tab 23 may be soldered within the first exposed foil groove 24. The first protective adhesive 30 may cover the portion of the negative electrode tab 23 within the first exposed foil groove 24. The negative electrode tab 23 may extend along a first direction and beyond the first edge of the negative electrode sheet 20.

[0072] Along the second direction (the length direction of the negative electrode 20), the two sides of the first protective adhesive 30 can have gaps with the two opposite sidewalls of the first exposed foil groove 24, respectively. The second direction is perpendicular to the first direction.

[0073] In some examples, along the first direction (the width direction of the negative electrode 20), the bottom edge of the first protective adhesive 30 may have a gap with the lower wall of the first exposed foil groove 24 away from the first edge.

[0074] On the side near the second arc segment 101b, the side of the first protective adhesive 30 has a first gap m with the side wall of the first exposed foil groove 24, and the side wall of the first exposed foil groove 24 has a second distance n with the second arc segment 101b. The ratio of m to n satisfies: 1≤n / m≤20.

[0075] For example, m satisfies 0 mm < m ≤ 6 mm, such as 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, etc.

[0076] For example, n satisfies 0 mm < n ≤ 30 mm, such as 1 mm, 2 mm, 3 mm, 5 mm, 7 mm, 9 mm, 12 mm, 15 mm, 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, etc.

[0077] It should be noted that the negative electrode tab 23 can also be disposed in the first exposed foil groove 24 in other ways, such as being integrally formed with the negative electrode current collector 22; the negative electrode sheet 20 has a first edge and a second edge in the extension width direction, and the first edge and the second edge are the two longer sides of the negative electrode sheet 20, which is not limited in this application.

[0078] By controlling n / m within the aforementioned range, firstly, it ensures that the empty foil area on the right side of the first exposed foil groove 24 maintains an appropriate distance from the second arc segment 101b, i.e., an appropriate distance from areas of severe stress concentration, thus alleviating stress concentration. Secondly, it makes the tensile / compressive conditions of the copper foil on the weaker left side of the exposed foil groove and the copper foil on the stronger right side of the exposed foil groove more consistent, i.e., the stress states of the exposed copper foil on both sides of the exposed foil groove are similar. This effectively reduces the phenomenon of copper foil being squeezed or stretched in different directions due to the imbalance of stress on the copper foil on both sides of the exposed foil groove, lowering the probability of fatigue fracture of the copper foil on both sides of the exposed foil groove.

[0079] Thirdly, the distance between the first exposed foil groove 24 and the second arc segment 101b can be reasonably adjusted according to the size of m, which can better alleviate the breakage problem of silicon-doped batteries near the negative electrode tab 23. When n / m is too small, the distance is too close to the stress concentration point, and it cannot effectively alleviate the breakage problem of silicon-doped batteries near the negative electrode tab. At the same time, due to process errors, the first exposed foil groove may be partially or entirely located in the bending section with high stress. When n / m is too large, the negative electrode tab is closer to the center of the cell, and the electrolyte corrosion rate of the copper foil on the left side of the exposed foil is faster, making it more prone to breakage.

[0080] Meanwhile, the first protective adhesive 30 is housed in the first exposed foil groove 24, which can avoid increasing the ineffective thickness. The molding process of the first exposed foil groove 24 is simple, and the application process of the first protective adhesive 30 is simple.

[0081] Preferably, 2.5 ≤ n / m ≤ 7.5.

[0082] By controlling the ratio of n to m within this range, the exposed copper foil on both sides of the exposed foil groove is placed closer to the arc segment. This ensures that the ratio of the distance between the exposed copper foil on both sides of the exposed foil groove and the arc segment is within 0.35 of the width of the entire straight segment, which corresponds to the smooth latter half of the curve on the right side of the normal distribution curve. In this part, the corrosion difference of the exposed copper foil on both sides of the exposed foil groove will not be too large, meaning the strength difference between the exposed copper foil on both sides of the exposed foil groove is low (close), which can better mitigate the breakage problem of silicon-doped batteries near the negative electrode tab 23.

[0083] Optionally, n / m can also be any value among 3, 3.5, 4, 4.5, 5, 5.5, 6 or 7, without further restrictions.

[0084] For example, a first exposed foil groove 24' is also provided on the negative electrode active material layer 21 on the other side of the negative electrode sheet at the position corresponding to the first exposed foil groove 24. Correspondingly, a first protective adhesive 30' is also attached in the first exposed foil groove 24' so that the stress state of the upper and lower sides of the negative electrode sheet in this area is approximately the same.

[0085] Similarly, the first protective adhesive 30' in the first exposed foil groove 24' can be completely contained within the first exposed foil groove 24', which can prevent the entire first protective adhesive 30' on this side from protruding above the negative electrode active material layer 21, resulting in ineffective thickness and reducing the energy density of the battery. Generally, the thickness of the first protective adhesive 30' is relatively thin, and the remaining space of the first exposed foil groove 24' on this side can be used to absorb silicon expansion and reduce stress concentration. In addition, the first protective adhesive 30 and 30' are respectively provided in the two first exposed foil grooves 24 and 24', which can make the stress state on both sides of the welding area of ​​the negative electrode tab 12 similar, and can avoid the breakage of the negative electrode sheet 20 caused by stress abrupt change and silicon expansion.

[0086] Next, refer to Figures 3 to 5 A stepped groove 12 can be provided in the projection area of ​​the negative electrode tab 23 on the positive electrode 10, and a second protective adhesive 40 can be provided in the stepped groove 12. For example, the stepped groove is located on the positive electrode active material layer 11 on the positive electrode 10 near the negative electrode 20.

[0087] Along a third direction (the thickness direction of the positive electrode 10), the stepped groove 12 may include a first groove 121 and a second groove 122 arranged sequentially. The first groove 121 may have a width L1 and a depth h1, and the second groove 122 may have a width L2 and a depth h2. Here, L1 is greater than or equal to the width of the second protective adhesive 40. The width of the first exposed foil groove is W1. The width of the negative electrode tab is W3, and L2 ≥ W3. The width of the second protective adhesive 40 is greater than or equal to W1, and the thickness of the second protective adhesive 40 is ≤ h1 ≤ h2, where h1 + h2 ≤ the thickness of the positive electrode active material layer. The third direction is perpendicular to the first and second directions.

[0088] For example, a stepped groove 12' may be provided in the projection area of ​​the negative electrode tab 23 on the positive electrode 10, and a second protective adhesive 40' may be provided in the stepped groove 12. For example, the stepped groove 12' is located on the positive electrode active material layer 11 on the side of the positive electrode 10 away from the negative electrode 20.

[0089] A second protective adhesive 40, 40' is disposed within the first groove 121, 121' in the projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10. The width of the second protective adhesive 40, 40' is less than or equal to the width of the first groove 121, 121', and its thickness is less than or equal to the depth of the first groove 121, 121'. This prevents the second protective adhesive 40, 40' from protruding from the positive electrode active material layer and increasing the volume of the battery 1000, thereby improving the energy density of the battery 1000. In addition, it can alleviate the decrease in the N / P ratio in this area caused by the first exposed foil grooves 24, 24'. The width of the second groove 122, which is arranged sequentially with the first groove 121, is greater than or equal to the width of the negative electrode tab 23. This allows the high point of the welding area of ​​the negative electrode tab 23 to be accommodated in the second groove 122, avoiding an increase in the ineffective volume of the battery 1000. This can further improve the energy density of the battery 1000 and also prevent the high point of the welding area of ​​the negative electrode tab 23 from piercing the separator 90 and causing a short circuit between the positive and negative electrodes. Moreover, when the second grooves 122 and 122' penetrate the bottom of the positive electrode active material layer, the second protective adhesives 40 and 40' can directly contact the negative electrode current collector 22, so that the second protective adhesives 40 and 40' are firmly bonded to the positive electrode sheet 10, thus preventing the second protective adhesives 40 and 40' from falling off.

[0090] Return to reference Figure 2 And at the same time refer to Figure 8 and Figure 9 The core 100 may also include a third protective adhesive 50, which covers the outer surface of the second arc segment 101b.

[0091] The arc segment 101 of the core 100 is a stress concentration area. The greater its thickness and the larger the size of the arc segment 101, the larger the area of ​​stress concentration. In particular, the outermost electrode sheet of the arc segment 101 experiences greater tensile stress when the core 100 expands, making it prone to breakage at this location. Applying a third protective adhesive 50 to the outer side of the arc segment 101 on the non-end side of the core 100 can improve the overall strength of this area, better resist the tensile stress during core expansion, and thus reduce the risk of breakage of the outermost electrode sheet of the arc segment 101.

[0092] In one example, a third protective adhesive 50 can be applied to the outer side of the arc segment 101 of the core 100, meaning the third protective adhesive 50 can extend a certain distance to the adjacent straight segment 102. This can better improve the overall strength of this area, better resist the tensile stress when the core 100 expands, and thus better reduce the risk of breakage of the outermost electrode sheet of the arc segment 101.

[0093] In one example, along the fourth direction (the thickness direction of the core 100), the orthographic projection of the third protective adhesive 50 may at least partially overlap with the orthographic projection of the first gap m. For example, the orthographic projection of the third protective adhesive 50 in the fourth direction may partially cover the first gap m, or the orthographic projection of the third protective adhesive 50 in the fourth direction may completely cover the first gap m.

[0094] In this way, while improving the overall strength of the area covered by the third protective adhesive 50, the structural strength at the gap m can be appropriately increased to prevent breakage at this point.

[0095] Continue to refer to Figure 2 , Figure 8 and Figure 9 The dimensions of the third protective adhesive 50 on the straight sections 102 on both sides of the arc section 101 on the non-end side of the core 100 are L3 and L4, respectively. The values ​​of L3 and L4 satisfy: 0 mm < L3 ≤ 8 mm (e.g., 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, etc.) and 0 mm < L4 ≤ 8 mm (e.g., 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, etc.).

[0096] The thickness of core 100 is H, and the ratios of L3 and L4 to H satisfy the following conditions: 0.1≤L3 / H≤3.5 (e.g., 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.) and 0.1≤L4 / H≤3.5 (e.g., 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.).

[0097] In one example, the following conditions can be met simultaneously: the third protective adhesive 50 is applied to the arc segment 101 (e.g., the second arc segment 101b) and part of the straight segment 102 on the non-ending side of the core 100, and the dimensions of the third protective adhesive 50 on the straight segments 102 on both sides of the arc segment 101 on the non-ending side of the core 100 are L3 and L4, respectively. The values ​​of L3 and L4 satisfy: 0mm < L3 ≤ 8mm, 0mm < L4 ≤ 8mm, respectively. The thickness of the core 100 is H, and the ratios of L3 and L4 to H satisfy: 0.1 ≤ L3 / H ≤ 3.5, 0.1 ≤ L4 / H ≤ 3.5, respectively.

[0098] By controlling the extension of the third protective adhesive 50 to the straight section 102 within the aforementioned range based on the thickness of the core 100, the overall strength of the area where the third protective adhesive 50 is applied can be significantly improved. Simultaneously, it avoids energy reduction caused by increasing the ineffective volume of the battery cell due to the application of the third protective adhesive 50.

[0099] Return to reference Figure 1 At the end of the core 100, a protective adhesive 80 can be provided to prevent the core 100 from unraveling. A fourth protective adhesive 60 and a fifth protective adhesive 70 can be respectively attached to both sides of the empty foil area at the end of the positive electrode sheet 10. The fourth protective adhesive 60 and the fifth protective adhesive 70 can partially extend to the positive electrode active material layer 11 to prevent the foil from short-circuiting with the negative electrode active material layer 21 and generating heat, which would affect the performance of the battery 1000.

[0100] In this embodiment, the negative electrode active material of the negative electrode active material layer 21 may include graphite and silicon carbide materials. The Si content in the negative electrode active material layer 21 is e, 0.35 wt% ≤ e ≤ 35 wt%. For example, 0.5 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc.

[0101] In this application, the mass percentage of Si in the negative electrode active material layer 21 can be obtained by methods conventional in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed. Then, the negative electrode sheet is immersed in DMC solvent for 12 hours, followed by rinsing with DMC solvent to remove the lithium salt adhering to the negative electrode sheet, and then dried. The negative electrode sheet is then subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere), and the negative electrode active material layer can be peeled off from the negative electrode current collector. The negative electrode active material layer is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the sample amount is 5 mg to 15 mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 min, allowing the non-silicon components in the negative electrode active material layer to volatilize, while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash content of the negative electrode active material layer. The mass content of element Si in the negative electrode active coating can be calculated based on the mass of ash. The calculation formula is as follows: Mass content of element Si in negative electrode active coating = (molecular weight of silicon / molecular weight of silicon dioxide) * (1 - mass of ash / mass of test sample) = (7 / 15) * (1 - mass of ash / mass of test sample).

[0102] The silicon content in the silicon-carbon material is f, where f satisfies 35 wt% to 70 wt%. For example, the silicon-carbon material is particulate silicon formed from graphite and silicon. The silicon content in the particulate silicon is f, where f satisfies 35 wt% to 70 wt% (e.g., 38 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, etc.), and the particulate silicon can be formed by silicon deposition on graphite particles.

[0103] By controlling the content of particulate silicon in the negative active material within the above range, the energy density of the battery can be increased by silicon doping while keeping the silicon content at a low level, thus minimizing the impact of silicon expansion.

[0104] In addition, granular silicon has the characteristics of high silicon content at the edge of the particles and low silicon content in the middle of the particles. This can improve the energy density of the battery and increase the charging rate of the battery. At the same time, it can help reduce the expansion of granular silicon and thus alleviate the overall expansion and contraction rate within the first gap.

[0105] refer to Figure 13The negative electrode active material layer 21 may include a first negative electrode active material layer 211 and a second negative electrode active material layer 212 stacked sequentially, with the first negative electrode active material layer 211 located on the side of the second negative electrode active material layer 212 away from the negative electrode current collector 22. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, and the silicon content in the second negative electrode active material layer 212 is greater than or equal to 0.

[0106] The expansion of silicon particles is significant, and during this expansion, they cause the surrounding graphite particles to extend, thus causing the current collector to stretch as a whole. The silicon content in the first negative electrode active material layer 211 is greater than that in the second negative electrode active material layer 212, which reduces the impact of silicon particle expansion on the negative electrode current collector 22, reducing the stretching of the negative electrode sheet 20 and the resulting stress concentration that could lead to breakage of the negative electrode current collector 22. Furthermore, the stress generated by the expansion of silicon particles compresses the graphite in all directions, and the silicon particles and surrounding graphite particles form pores, further causing the entire electrode sheet to expand and generate stress. The greater silicon content in the first negative electrode active material layer 211 reduces the amount of lower graphite in contact with the silicon particles, thus reducing the impact on the lower graphite layer and consequently mitigating the effect of silicon expansion on the graphite. This appropriately alleviates the expansion of the electrode sheet and reduces the resulting stress.

[0107] In one example, particulate silicon is doped in the first negative electrode active material layer 21.

[0108] As mentioned above, placing granular silicon on top of the negative electrode 20 can better reduce the impact of granular silicon expansion on the negative electrode current collector 22, reduce the elongation of the negative electrode 20 and the resulting stress concentration that could lead to breakage of the negative electrode current collector 22. Simultaneously, it better alleviates electrode expansion and further reduces the resulting stress.

[0109] The thickness ratio of the first negative electrode active material layer 21 to the thickness of the negative electrode active material layer 21 is y, and the ratio of e to y satisfies: 0.05% ≤ e*y ≤ 20%.

[0110] In this way, the content of silicon-carbon material in the negative electrode active material layer 21 can be more reasonably controlled according to the thickness of the negative electrode active material layer 21, avoiding the situation where the content of silicon-carbon material is too low and cannot effectively provide the energy density of the battery, or the content is too high and causes severe expansion during charging.

[0111] refer to Figures 10 to 12 The negative electrode current collector active material layer 21 may be provided with a recessed groove 28, which includes a plurality of recessed grooves 281 spaced apart.

[0112] For example, the extension direction of the recessed groove 28 may be perpendicular to the length direction of the negative electrode current collector 22.

[0113] Along the width direction of the negative electrode 20, the gap between the bottom wall of the first exposed foil groove 24 and the recessed groove 281 is G1. The value of G1 satisfies: 0 mm < G1 ≤ 5 mm, for example 0.5 mm, 0.8 mm, 1.2 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, etc.

[0114] Along the length of the negative electrode 20, the gaps between the sidewalls of the first exposed foil groove 24 and the recessed groove 281 are G2, and the value of G2 satisfies: 0 mm < G2 ≤ ​​5 mm, for example 0.5 mm, 0.8 mm, 1.2 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, etc.

[0115] Along the width direction of the negative electrode, the gap between the recessed groove and the edge of the negative electrode is G3. The value of G3 satisfies: 0 mm < G3 ≤ 5 mm, for example, 0.5 mm, 0.8 mm, 1.2 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, etc.

[0116] In one example, the following conditions can be met simultaneously: along the width direction of the negative electrode 20, the gap between the bottom wall of the first exposed foil groove 24 and the recessed groove 281 is G1, and the value of G1 satisfies: 0 mm < G1 ≤ 5 mm. Along the length direction of the negative electrode 20, the gaps between the side walls of the first exposed foil groove 24 and the recessed groove 281 are G2, and the value of G2 satisfies: 0 mm < G2 ≤ ​​5 mm. Along the width direction of the negative electrode, the gap between the recessed groove and the edge of the negative electrode is G3, and the value of G3 satisfies: 0 mm < G3 ≤ 5 mm.

[0117] By creating recessed grooves 28 on the negative electrode active material layer 21 of the negative electrode sheet 20, the electrolyte storage capacity can be increased, thereby better receiving lithium ions from the positive electrode. This improves the negative electrode reaction kinetics, allowing the negative electrode to have better reaction kinetics to receive lithium ions, thus mitigating lithium plating problems and increasing the energy density of the battery 1000. However, when laser-forming the recessed grooves 28, the heat-affected zone is large, and the strength of the negative electrode current collector 22 will decrease under the influence of heat. Furthermore, the passivation layer of the negative electrode current collector 22 may be damaged, for example, the passivation layer of the copper foil may be damaged.

[0118] By leaving a certain gap in the area near the first exposed foil groove 24 and at both ends of the negative electrode sheet 20 (i.e., the edge of the negative electrode active material layer 21 along its length) without setting a recessed groove 28, the electrolyte can be prevented from entering the first exposed foil groove 24. This can prevent the copper foil, after being damaged by the electrolyte immersion, from being corroded by the electrolyte immersion and then fractured due to the superimposed silicon expansion stress.

[0119] Furthermore, the recessed groove 28 maintains a certain distance from the edges of the negative electrode sheet 20 on both sides, i.e., from the edge of the negative electrode active material layer 21 in the width direction. This can improve the negative electrode reaction kinetics while preventing powder shedding and burrs from occurring during the subsequent cutting of the negative electrode sheet 20, which would affect the K-value of the cell. Here, the K-value refers to the voltage drop of the battery per unit time.

[0120] The ratio of the intensity S of the negative electrode current collector 22 to the depth h of the multiple recessed grooves 281 satisfies: 3≤s / h≤120, for example 4, 8, 10, 15, 20, 30, 40, 60, 80, 90, 100, 110, etc.

[0121] The value of h ranges from 3 μm to 35 μm (e.g., 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, etc.).

[0122] The value of s ranges from 100 MPa to 650 MPa (e.g., 120 MPa, 150 MPa, 180 MPa, 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa, etc.).

[0123] In one example, the following conditions can be met simultaneously: the ratio of the intensity S of the negative electrode current collector 22 to the depth h of the multiple recessed grooves 281 satisfies: 3 ≤ s / h ≤ 120. The value of h ranges from 3 μm to 35 μm. The value of s ranges from 100 MPa to 650 MPa.

[0124] This allows the depth of the recessed groove 28 to match the strength S of the negative electrode current collector 22, preventing the recessed groove 28 from being too shallow to effectively store electrolyte, and also preventing the recessed groove 28 from being too deep to affect the strength of the negative electrode current collector 22.

[0125] It is understood that the extension direction of the recessed groove 28 can also be set to other directions as needed. For example, the extension direction of the recessed groove 28 can be parallel to the length direction of the negative electrode current collector 22. In addition, the recessed groove 28 can be continuously provided on the negative electrode active material layer 21 or spaced apart, that is, multiple recessed groove segments are spaced apart on the negative electrode active material layer 21.

[0126] As mentioned above, the heat generated during laser forming of the recessed groove 281 can affect the strength of the negative electrode current collector 22. By controlling the depth of the recessed groove 281 within a certain range based on the strength of the negative electrode current collector 22, it is possible to improve the negative electrode reaction kinetics while matching a suitable groove depth. This avoids a mismatch between groove depth and strength, which could excessively affect the strength of the negative electrode current collector 22, thereby causing the negative electrode sheet 20 to break due to the superimposed silicon expansion stress.

[0127] Continue to refer to Figure 6 Embodiments of this application also provide a core 100. The core 100 may include a negative electrode 20 sheets, a separator 90 and a positive electrode 30 that are sequentially stacked and wound.

[0128] The core 100 has a straight section 102 and a first arc segment 101a and a second arc segment 101b located on both sides of the straight section 102. The negative electrode 20 includes a negative electrode current collector 22 and a negative electrode active material layer 21 disposed on at least one side surface of the negative electrode current collector 22. The negative electrode active material layer 21 contains silicon.

[0129] The surface of the negative electrode 20 may be provided with a first exposed foil groove 24. The bottom wall of the first exposed foil groove 24 exposes the negative electrode current collector 22. The first exposed foil groove 24 is located close to the second arc segment 101b, and the periphery of the first exposed foil groove 24 is provided with a negative electrode active material layer 21.

[0130] The negative electrode sheet 20 also includes a negative electrode tab 23 and a first protective adhesive 30. A portion of the negative electrode tab 23 is located in the first exposed foil groove 24 and electrically connected to the negative electrode current collector 22. The negative electrode tab 23 extends along a first direction and beyond the first edge of the negative electrode sheet 20. The first protective adhesive 30 covers a portion of the negative electrode tab 23 in the first exposed foil groove 24. A third groove 25 is provided on the negative electrode active material layer 21 around the first exposed foil groove 24. The portion of the first protective adhesive 30 that exceeds the width of the first exposed foil groove 24 is accommodated within the third groove 25. The width of the first protective adhesive 30 is W3, and the width of the third groove is W4, where W3 and W4 satisfy: W4 ≥ W2.

[0131] In this way, the edge of the first protective adhesive 30 can be contained in the negative electrode active material layer 21, avoiding protrusion from the negative electrode active material layer 21 and causing an increase in the volume of the battery 1000, thereby improving the energy density of the battery 1000.

[0132] For example, on the other side of the negative electrode active material layer 21, a first exposed foil groove 24' is also provided at the position corresponding to the first exposed foil groove 24. A third groove 25' is provided on the negative electrode active material layer 21 around the first exposed foil groove 24'. Correspondingly, a first protective adhesive 30' is also attached inside the first exposed foil groove 24'. The first protective adhesive 30' covers the first exposed foil groove 24'. The third groove 25' is provided on the negative electrode active material layer 21 around the first exposed foil groove 24', and the portion of the first protective adhesive 30' that exceeds the width of the first exposed foil groove 24' is accommodated in the third groove 25'. The width of the first protective adhesive 30' is W3, and the width of the third groove 25' is W4. W3 and W4 satisfy: W4≥W2, so that the stress state on the upper and lower sides of the negative electrode in this area is approximately consistent.

[0133] Similarly, the edge of the first protective adhesive 30' can be contained within the negative electrode active material layer 21, preventing it from protruding beyond the negative electrode active material layer 21 and causing an increase in the volume of the battery 1000, thereby improving the energy density of the battery 1000. Generally, the first protective adhesive 30' is relatively thin, and the remaining space of the first exposed foil groove 24' on this side can be used to absorb silicon expansion and reduce stress concentration.

[0134] In addition, the first protective adhesive 30 and 30' are respectively provided in the two first exposed foil grooves 24 and 24', which can make the stress state on both sides of the welding area of ​​the negative electrode tab 12 similar, and can avoid the breakage of the negative electrode sheet 20 caused by stress abrupt change and silicon expansion.

[0135] Next, refer to Figures 3 to 5 A stepped groove 12 can be provided in the projection area of ​​the negative electrode tab 23 on the positive electrode 10, and a second protective adhesive 40 can be provided in the stepped groove 12. For example, the stepped groove is located on the positive electrode active material layer 11 on the positive electrode 10 near the negative electrode 20.

[0136] Along the third direction, the stepped groove 12 may include a first groove 121 and a second groove 122 arranged sequentially. The first groove 121 may have a width L1 and a depth h1, and the second groove 122 may have a width L2 and a depth h2. Here, L1 is greater than or equal to the width of the second protective adhesive 40. The width of the first exposed foil groove is W1. The width of the negative electrode tab is W3, and L2 ≥ W3. The width of the second protective adhesive 40 is greater than or equal to W1, the thickness of the second protective adhesive 40 is ≤ h1 ≤ h2, and h1 + h2 ≤ the thickness of the positive electrode active material layer. The third direction is perpendicular to the first and second directions.

[0137] For example, a stepped groove 12' may be provided in the projection area of ​​the negative electrode tab 23 on the positive electrode 10, and a second protective adhesive 40' may be provided in the stepped groove 12. For example, the stepped groove 12' is located on the positive electrode active material layer 11 on the side of the positive electrode 10 away from the negative electrode 20.

[0138] A second protective adhesive 40, 40' is provided in the first groove 121, 121' in the projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10. The width of the second protective adhesive 40, 40' is less than or equal to the width of the first groove 121, 121', and its thickness is less than or equal to the depth of the first groove 121, 121'. This can prevent the second protective adhesive 40, 40' from protruding from the positive electrode active material layer and increasing the volume of the battery 1000, thereby improving the energy density of the battery 1000.

[0139] Furthermore, this can alleviate the decrease in the N / P ratio in this area caused by the first exposed foil grooves 24 and 24'. The width of the second groove 122, which is arranged sequentially with the first groove 121, is greater than or equal to the width of the negative electrode tab 23. This allows the high point of the welding area of ​​the negative electrode tab 23 to be accommodated in the second groove 122, avoiding an increase in the ineffective volume of the battery 1000. This can further improve the energy density of the battery 1000 and also prevent the high point of the welding area of ​​the negative electrode tab 23 from piercing the separator 90, causing a short circuit between the positive and negative electrodes. Moreover, when the second grooves 122 and 122' penetrate the bottom of the positive electrode active material layer, the second protective adhesive 40 and 40' can directly contact the negative electrode current collector 22, making the second protective adhesive 40 and 40' more firmly bonded to the positive electrode sheet 10 and preventing the second protective adhesive 40 and 40' from falling off.

[0140] Return to reference Figure 2 And at the same time refer to Figure 8 and Figure 9 The core 100 may also include a third protective adhesive 50, which covers at least the outer side of the second arc segment 101b.

[0141] The arc segment 101 of the core 100 is a stress concentration area. The greater its thickness and the larger the size of the arc segment 101, the larger the area of ​​stress concentration. In particular, the outermost electrode sheet of the arc segment 101 experiences greater tensile stress when the core 100 expands, making it prone to breakage at this location. Applying a third protective adhesive 50 to the outer side of the arc segment 101 on the non-end side of the core 100 can improve the overall strength at this location, better resist the tensile stress during cell expansion, and thus reduce the risk of breakage of the outermost electrode sheet of the arc segment 101.

[0142] In one example, a third protective adhesive 50 can be applied to the outer side of the arc segment 101 of the core 100, meaning the third protective adhesive 50 can extend a certain distance to the adjacent straight segment 102. This can better improve the overall strength at this point, better resist the tensile stress when the core 100 expands, and thus better reduce the risk of breakage of the outermost electrode sheet of the arc segment 101.

[0143] Continue to refer to Figure 2 , Figure 8 and Figure 9 The third protective adhesive 50 is applied to the arc segment 101 (e.g., the second arc segment 101b) and part of the straight segment 102 on the non-end side of the core 100. The dimensions of the third protective adhesive 50 on the straight segment 102 on both sides of the arc segment 101 on the non-end side of the core 100 are L3 and L4, respectively. The values ​​of L3 and L4 satisfy: 0mm < L3 ≤ 8mm (e.g., 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, etc.) and 0mm < L4 ≤ 8mm (e.g., 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, etc.).

[0144] The thickness of core 100 is H, and the ratios of L3 and L4 to H satisfy the following conditions: 0.1≤L3 / H≤3.5 (e.g., 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.) and 0.1≤L4 / H≤3.5 (e.g., 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.).

[0145] In one example, the following conditions can be met simultaneously: the third protective adhesive 50 is applied to the arc segment 101 (e.g., the second arc segment 101b) and part of the straight segment 102 on the non-ending side of the core 100, and the dimensions of the third protective adhesive 50 on the straight segments 102 on both sides of the arc segment 101 on the non-ending side of the core 100 are L3 and L4, respectively. The values ​​of L3 and L4 satisfy: 0mm < L3 ≤ 8mm, 0mm < L4 ≤ 8mm, the thickness of the core 100 is H, and the ratios of L3 and L4 to H satisfy: 0.1 ≤ L3 / H ≤ 3.5, 0.1 ≤ L4 / H ≤ 3.5, respectively.

[0146] By controlling the extension of the third protective adhesive 50 to the straight section 102 within the aforementioned range based on the thickness of the core 100, the overall strength of the area where the third protective adhesive 50 is applied can be significantly improved. Simultaneously, it avoids energy reduction caused by increasing the ineffective volume of the battery cell due to the application of the third protective adhesive 50.

[0147] refer to Figure 6 and Figure 7 In some alternative embodiments, the width of the first exposed foil groove 24 is W1, the width of the first protective adhesive 30 is W2, and the width of the negative electrode tab 23 is W3, where W2 > W1 > W3. In other words, the first protective adhesive 30 completely covers the first exposed foil groove 24, and its edge extends from the first exposed foil groove 24 into the negative electrode active material layer 21 to prevent the negative current collector 22 from being exposed and directly oxidized by the electrolyte, causing the negative electrode sheet 20 to break.

[0148] Return to reference Figure 1At the end of the core 100, a protective adhesive 80 can be provided to prevent the core 100 from unraveling. A fourth protective adhesive 60 and a fifth protective adhesive 70 can be respectively attached to both sides of the empty foil area at the end of the positive electrode sheet 10. The fourth protective adhesive 60 and the fifth protective adhesive 70 can partially extend to the positive electrode active material layer 11 to prevent the foil from short-circuiting with the negative electrode active material layer 21 and generating heat, which would affect the performance of the battery 1000.

[0149] In this embodiment, the negative electrode active material layer 21 may include graphite and silicon carbide materials. The Si content in the negative electrode active material layer is e, 0.35 wt% ≤ e ≤ 35 wt%. For example, the silicon content in the negative electrode active material is e, 0.35 wt% ≤ e ≤ 35 wt% (e.g., 0.5 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc.).

[0150] The silicon content in the silicon-carbon material is f, where f satisfies 35 wt% to 70 wt%. For example, the silicon-carbon material is particulate silicon formed from graphite and silicon. The silicon content in the particulate silicon is f, where f satisfies 35 wt% to 0 wt% (e.g., 38 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, etc.), and the particulate silicon can be formed by silicon deposition on graphite particles.

[0151] By controlling the content of particulate silicon in the negative active material within the above range, the energy density of the battery can be increased by silicon doping while keeping the silicon content at a low level, thus minimizing the impact of silicon expansion.

[0152] In addition, granular silicon has the characteristics of high silicon content at the edge of the particles and low silicon content in the middle of the particles, which can improve the energy density of the battery and increase the charging rate of the battery, while also helping to reduce the expansion of granular silicon.

[0153] refer to Figure 13 The negative electrode active material layer 21 may include a first negative electrode active material layer 211 and a second negative electrode active material layer 212 stacked sequentially, with the first negative electrode active material layer 211 located on the side of the second negative electrode active material layer 212 away from the negative electrode current collector 22. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, and the silicon content in the second negative electrode active material layer 212 is greater than or equal to 0.

[0154] The expansion of silicon particles is significant, and during this expansion, they cause the surrounding graphite particles to extend, thus causing the current collector to stretch as a whole. The silicon content in the first negative electrode active material layer 211 is greater than that in the second negative electrode active material layer 212, which reduces the impact of silicon particle expansion on the negative electrode current collector 22, reducing the stretching of the negative electrode sheet 20 and the resulting stress concentration that could lead to breakage of the negative electrode current collector 22. Furthermore, the stress generated by the expansion of silicon particles compresses the graphite in all directions, and the silicon particles and surrounding graphite particles form pores, further causing the entire electrode sheet to expand and generate stress. The greater silicon content in the first negative electrode active material layer 211 reduces the amount of lower graphite in contact with the silicon particles, thus reducing the impact on the lower graphite layer and consequently mitigating the effect of silicon expansion on the graphite. This appropriately alleviates the expansion of the electrode sheet and reduces the resulting stress.

[0155] In one example, particulate silicon is doped in the first negative electrode active material layer 21.

[0156] As mentioned above, placing granular silicon on top of the negative electrode 20 can better reduce the impact of granular silicon expansion on the negative electrode current collector 22, reduce the elongation of the negative electrode 20 and the resulting stress concentration that could lead to breakage of the negative electrode current collector 22. Simultaneously, it better alleviates electrode expansion and further reduces the resulting stress.

[0157] The thickness ratio of the first negative electrode active material layer 21 to the thickness of the negative electrode active material layer 21 is y, and the ratio of e to y satisfies: 0.05% ≤ e*y ≤ 20%.

[0158] In this way, the content of silicon-carbon material in the negative electrode active material layer 21 can be more reasonably controlled according to the thickness of the negative electrode active material layer 21, avoiding the situation where the content of silicon-carbon material is too low and cannot effectively provide the energy density of the battery, or the content is too high and causes severe expansion during charging.

[0159] refer to Figures 10 to 12 The negative electrode current collector active material layer 21 may be provided with a recessed groove 28, which includes a plurality of recessed grooves 281 spaced apart.

[0160] For example, the extension direction of the recessed groove 28 may be perpendicular to the length direction of the negative electrode current collector 22.

[0161] Along the width direction of the negative electrode 20, the gap between the bottom wall of the first exposed foil groove 24 and the recessed groove 281 is G1. The value of G1 satisfies: 0 mm < G1 ≤ 5 mm, for example 0.5 mm, 0.8 mm, 1.2 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, etc.

[0162] Along the length of the negative electrode 20, the gaps between the sidewalls of the first exposed foil groove 24 and the recessed groove 281 are G2, and the value of G2 satisfies: 0 mm < G2 ≤ ​​5 mm, for example 0.5 mm, 0.8 mm, 1.2 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, etc.

[0163] Along the width direction of the negative electrode, the gap between the recessed groove and the edge of the negative electrode is G3. The value of G3 satisfies: 0 mm < G3 ≤ 5 mm, for example, 0.5 mm, 0.8 mm, 1.2 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, etc.

[0164] In one example, the following conditions can be met simultaneously: along the width direction of the negative electrode 20, the gap between the bottom wall of the first exposed foil groove 24 and the recessed groove 281 is G1, and the value of G1 satisfies: 0 mm < G1 ≤ 5 mm. Along the length direction of the negative electrode 20, the gaps between the side walls of the first exposed foil groove 24 and the recessed groove 281 are G2, and the value of G2 satisfies: 0 mm < G2 ≤ ​​5 mm. Along the width direction of the negative electrode, the gap between the recessed groove and the edge of the negative electrode is G3, and the value of G3 satisfies: 0 mm < G3 ≤ 5 mm.

[0165] By creating recessed grooves 28 on the negative electrode active material layer 21 of the negative electrode sheet 20, the electrolyte storage capacity can be increased, thereby better receiving lithium ions from the positive electrode. This improves the negative electrode reaction kinetics, allowing the negative electrode to have better reaction kinetics to receive lithium ions, thus mitigating lithium plating problems and increasing the energy density of the battery 1000. However, when laser-forming the recessed grooves 28, the heat-affected zone is large, and the strength of the negative electrode current collector 22 will decrease under the influence of heat. Furthermore, the passivation layer of the negative electrode current collector 22 may be damaged, for example, the passivation layer of the copper foil may be damaged.

[0166] By leaving a certain gap in the area near the first exposed foil groove 24 and at both ends of the negative electrode sheet 20 (i.e., the edge of the negative electrode active material layer 21 along its length) without setting the recessed groove 28, it is possible to avoid the copper foil, after being damaged by the electrolyte immersion, being corroded by the electrolyte immersion and then fractured due to the superimposed silicon expansion stress.

[0167] Furthermore, the recessed groove 28 maintains a certain distance from the edges of the negative electrode sheet 20 on both sides, i.e., from the edge of the negative electrode active material layer 21 in the width direction. This can improve the negative electrode reaction kinetics while preventing powder shedding and burrs from occurring during the subsequent cutting of the negative electrode sheet 20, which would affect the K-value of the cell. Here, the K-value refers to the voltage drop of the battery per unit time.

[0168] The ratio of the intensity S of the negative electrode current collector 22 to the depth h of the multiple recessed grooves 281 satisfies: 3≤s / h≤120, for example 4, 8, 10, 15, 20, 30, 40, 60, 80, 90, 100, 110, etc.

[0169] The value of h ranges from 3 μm to 35 μm (e.g., 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, etc.).

[0170] The value of s ranges from 100 MPa to 650 MPa (e.g., 120 MPa, 150 MPa, 180 MPa, 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa, etc.).

[0171] In one example, the following conditions can be met simultaneously: the ratio of the intensity S of the negative electrode current collector 22 to the depth h of the multiple recessed grooves 281 satisfies: 3 ≤ s / h ≤ 120. The value of h ranges from 3 μm to 35 μm. The value of s ranges from 100 MPa to 650 MPa.

[0172] This allows the depth of the recessed groove 28 to match the strength S of the negative electrode current collector 22, preventing the recessed groove 28 from being too shallow to effectively store electrolyte, and also preventing the recessed groove 28 from being too deep to affect the strength of the negative electrode current collector 22.

[0173] It is understood that the extension direction of the recessed groove 28 can also be set to other directions as needed. For example, the extension direction of the recessed groove 28 can be parallel to the length direction of the negative electrode current collector 22. In addition, the recessed groove 28 can be continuously provided on the negative electrode active material layer 21 or spaced apart, that is, multiple recessed groove segments are spaced apart on the negative electrode active material layer 21.

[0174] As mentioned above, the heat generated during laser forming of the recessed groove 281 can affect the strength of the negative electrode current collector 22. By controlling the depth of the recessed groove 281 within a certain range based on the strength of the negative electrode current collector 22, it is possible to improve the negative electrode reaction kinetics while matching a suitable groove depth. This avoids a mismatch between groove depth and strength, which could excessively affect the strength of the negative electrode current collector 22, thereby causing the negative electrode sheet 20 to break due to the superimposed silicon expansion stress.

[0175] Exemplary battery

[0176] On the other hand, such as Figure 14 and 15As shown in the illustration, this application also provides a battery 1000. The battery 1000 includes the aforementioned winding core 100.

[0177] refer to Figure 14 and 15 The battery 1000 may include a winding core 100 and a housing 200. The housing 200 may have a receiving cavity, which may house one or more winding cores 100.

[0178] like Figure 14 As shown, in some embodiments, the housing 200 may be square. That is, the battery 1000 may be a square battery 1000. The material of the housing 200 may be the same as conventionally used materials and is not particularly limited. For example, the housing 200 may be made of metal, specifically aluminum (alloy) or iron (alloy).

[0179] like Figure 15 As shown, in some embodiments, the housing 200 is flat and made of a relatively soft material, such as an aluminum-plastic film. That is, in this embodiment, the battery 1000 can be a pouch battery 1000.

[0180] It is foreseeable that in other examples of embodiments of this application, the battery 1000 may also be implemented as a type other than a square battery 1000 and a pouch battery 1000.

[0181] It should be noted that the structure of other aspects of the battery 1000 can be the same as that of the conventional battery 1000. For the sake of brevity, this application embodiment will not describe it in detail.

[0182] The battery 1000 provided according to the embodiments of this application has the same effect as the winding core 100 described above, as detailed above, and will not be repeated here.

[0183] Below, to provide a more in-depth understanding and illustration of the winding core 100 and the battery 1000 of this application, some embodiments and comparative examples of the fabrication of the winding core 100 are provided. Accordingly, structural parameters and characterization parameters of the corresponding embodiments are provided.

[0184] Example 1

[0185] The battery cell is prepared using the following steps.

[0186] Preparation of the positive electrode 10: Lithium cobalt oxide, conductive carbon black (Super P, SP), and polyvinylidene fluoride (PVDF) are mixed in a mass percentage of 97.6:1.4:1, and N-methylpyrrolidone (NMP) is added and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil, and then baked and rolled sequentially to obtain a positive electrode 10 with a thickness of 80 μm. A second exposed foil groove 15 is provided on the positive electrode 10. The positive electrode tab is welded into the second exposed foil groove 15 by laser or ultrasonic welding to obtain a positive electrode 10 with a positive electrode tab 13. Stepped grooves 12 are cleaned on the positive electrode 10 using a fixed scraper. The first groove 121 of the stepped groove 12 has a depth h1 of 15 μm and a width L1 = 22 mm, and the second groove 122 has a depth h2 of 21 μm and a width L2 = 4 mm. mm. The sum of the depths of the first groove 121 and the second groove 122 is 36 μm, which is equal to the thickness of the positive electrode active material layer. The positive electrode termination adhesive (fourth protective adhesive 60 and fifth protective adhesive 70) has a thickness of 12 μm and a width of 20 mm. Protective adhesive is attached to the portion of the positive electrode tab 13 located in the second exposed foil groove 15.

[0187] Preparation of the negative electrode 20: A negative electrode active material doped with particulate silicon was mixed with SP, carboxymethyl cellulose lithium (CMC-Li), and polyacrylic acid (PAA) in a mass percentage ratio of 97:0.4:0.1:2.5. The silicon content in the particulate silicon was 50 wt%, and the silicon content e in the negative electrode active material layer was 5 wt%. Deionized water was then added to prepare the first negative electrode slurry. Graphite was mixed with SP, CMC-Li, and styrene butadiene rubber (SBR) in a mass percentage ratio of 97:0.4:0.1:2.5 to prepare the second negative electrode slurry. The second negative electrode slurry was coated onto the surface of the negative electrode current collector 22, and the silicon-doped first negative electrode slurry was coated onto the surface of the second negative electrode slurry. After baking and rolling, a negative electrode 20 with a thickness of 95 μm was obtained. A first exposed foil groove 24, 24' with a width W1 = 12 mm is provided at a certain position on the negative electrode sheet 20. A copper-plated nickel tab with a width of 6 mm is laser- or ultrasonically welded into the first exposed foil groove 24. A first protective adhesive 30, 30' is attached to the surface of the tab and the first exposed foil groove 24, 24'. The width of the first protective adhesive is 9 mm, and the distance between the edge of the first protective adhesive 30, 30' and the first exposed foil groove 24 is m = 2 mm. The distance between the edge of the first exposed foil groove 24 and the arc segment 27 is n = 10 mm. A recessed groove 28 is formed on the surface of the negative electrode sheet 20 using a laser. The depth of the laser line, i.e., the depth of the recessed groove 281, is h = 20 μm. The distance G3 between the recessed groove 28 and the edge of the first exposed foil groove 24 and the negative electrode active material layer 21 along the width direction of the negative electrode sheet 20 is 0.5 mm. Along the length of the negative electrode sheet 20, the distance between the recessed groove 28 and the two ends of the negative electrode active material layer is 0.5 mm. The gaps G2 between the side walls of the first exposed foil groove 24 and the recessed groove 281 are 0.5 mm each, and the gap G1 between the bottom wall of the first exposed foil groove 24 and the recessed groove 281 is 0.5 mm. y is 0.1, and e*y is 0.5%.

[0188] After the positive and negative electrode sheets 20 are slit and formed, they are wound together with the separator 90 to obtain the core 100. The non-tail side of the core 100 is covered with a third protective adhesive 50. The width of the third protective adhesive 50 is 15 mm (referring to the length of the third protective adhesive 50 along the winding direction). The dimensions L3 and L4 of the third protective adhesive 50 extending to the straight section 102 are 3 mm.

[0189] Then, after packaging, baking, electrolyte injection, formation, secondary sealing, sorting and open circuit voltage (OCV) testing, the lithium-ion battery 1000 is obtained.

[0190] It should be noted that the electrolyte is a commercially available conventional electrolyte, and the lithium salt in the electrolyte is LiFP6. The baking and rolling of the positive electrode 10 and negative electrode 20, as well as the encapsulation, post-encapsulation baking, and formation processes, are standard procedures and will not be described in detail here. Additionally, the application of the fourth protective adhesive 60, the fifth protective adhesive 70, and the finishing protective adhesive 80 at the corresponding processes and locations will not be detailed here.

[0191] Example 2

[0192] The difference between Example 2 and Example 1 is that in Example 2, the projection area of ​​the negative electrode tab 23 on the positive electrode plate 10 is not provided with a stepped groove 12.

[0193] Example 3

[0194] The difference between Example 3 and Example 1 is that the width of the first protective adhesive 30 is greater than the setting method of the first exposed foil groove 24. A first exposed foil groove 24 with a width W1=9 mm is provided at a certain position of the negative electrode sheet 20. The width of the first protective adhesive 30 attached to the surface of the negative electrode tab 23 is 12 mm. A third groove 25 is provided around the first exposed foil groove 24 on the negative electrode active material layer 21. The width of the third groove is 14 mm.

[0195] Example 4

[0196] The difference between Example 4 and Example 1 is that the value of m is adjusted to 1.5 mm.

[0197] Example 5

[0198] The difference between Example 5 and Example 1 is that the value of m is adjusted to 5mm.

[0199] Example 6

[0200] The difference between Example 6 and Example 1 is that the value of n is adjusted to 20mm.

[0201] Example 7

[0202] The difference between Example 7 and Example 1 is that the value of m is adjusted to 1 mm.

[0203] Example 8

[0204] The difference between Example 8 and Example 1 is that the value of m is adjusted to 1 mm.

[0205] Example 9

[0206] The difference between Example 9 and Example 1 is that the value of m is adjusted to 3mm.

[0207] Example 10

[0208] The difference between Example 10 and Example 1 is that the value of n is adjusted to 7mm.

[0209] Example 11

[0210] The difference between Example 11 and Example 1 is that the outer side of the arc segment 101 on the non-end side of the core 100 is not provided with a third protective adhesive 50.

[0211] Example 12

[0212] The difference between Example 12 and Example 1 is that the width of the third protective adhesive 50 provided on the outer side of the arc segment 101 on the non-end side of the core 100 is 42 mm, and the dimensions L3 and L4 of the third protective adhesive 50 extending to the straight segment 102 are 18 mm.

[0213] Example 13

[0214] The difference between Example 13 and Example 1 is that there is no pre-reserved gap between the recessed groove 28 formed by laser wire forming and the edge of the first exposed foil groove 24, the edge of the negative electrode active material layer 21 in the width direction, and the edge of the negative electrode active material layer 21 in the length direction.

[0215] Example 14

[0216] The difference between Example 14 and Example 1 is that the depth h of the recessed groove 281 formed by laser wire bonding 28 is 30 μm, and the tensile strength of the copper foil is 80 MPa.

[0217] Example 15

[0218] The difference between Example 15 and Example 1 is that the depth h of the recessed groove 281 formed by laser wire cutting in Example 8 is 4 μm, and the tensile strength of the copper foil is 600 MPa.

[0219] Example 16

[0220] The difference between Example 16 and Example 1 is that the silicon content in the silicon particles is 30%, and the silicon content in the negative electrode active material layer is e = 0.3%, y = 0.17, and e*y = 0.05%.

[0221] Example 17

[0222] The difference between Example 17 and Example 1 is that the silicon content in the particulate silicon is 70 wt%, and the silicon content in the negative electrode active material layer is 35 wt%. y is 0.5, and e*y is 17.5%.

[0223] Example 18

[0224] The difference between Example 18 and Example 1 is that the silicon content in the particulate silicon is 35%, the silicon content in the negative electrode active material layer is 0.35 wt%, and e*y is 0.035%.

[0225] Example 19

[0226] The difference between Example 19 and Example 1 is that the silicon content in the granular silicon is 70 wt%, the silicon content in the negative electrode active material layer is 42%, the proportion of the paste on the upper layer of the negative electrode is 0.5, and e*y is 21%.

[0227] Example 20

[0228] The difference between Example 20 and Example 1 is that a first exposed foil groove 24 with a width W1=9 mm is provided at a certain position of the negative electrode sheet 20, the width of the first protective adhesive 30 attached to the surface of the negative electrode tab 23 is W2=12 mm, and a third groove 25 is not provided on the negative electrode active material layer 21.

[0229] Comparative Example 1

[0230] The difference between the comparative example and Example 1 is that the distance between the side edge of the first protective adhesive 30 on the negative electrode 20 and the side wall of the first exposed foil groove 24 is m=3 mm, and the distance between the side wall of the first exposed foil groove 24 and the arc segment 27 is n=2 mm.

[0231] The batteries prepared in each embodiment and comparative example were tested.

[0232] The test conditions for the K value are as follows: After storing the battery at a temperature of 45℃±3℃ (e.g., in a high-temperature room) for 48 h to 60 h, take out the battery and let it stand at 25℃±3℃ (e.g., in a constant temperature room) for 24 h, and test the battery voltage V1. Then, let it stand in a constant temperature room at 25℃±3℃ for 72 h to 96 h (e.g., 72 h), and test the voltage V2. The voltage drop (K value) = (V1-V2) / the interval between the two tests.

[0233] The fracture test conditions were as follows: 10 batteries (10 pcs) prepared for each example and comparative example were grouped together and charged to the upper limit voltage at a constant current and constant voltage of 1C under temperature conditions of 45℃±3℃ (e.g., in a constant temperature room). The batteries were then cut off with a cutoff current of 0.05C, left to stand for 10 minutes, and then discharged to 3.0V at 0.5C. After 600 cycles of re-discharge under the above test conditions, the 10 pcs of batteries were disassembled. If any pc of battery was fractured, it was considered fractured; if none of them were fractured, it was considered unfractured.

[0234] Volumetric energy density (ED): The volumetric energy density of a lithium-ion battery is ED = E / V, where E is the discharge energy of the lithium-ion battery, measured in joules (J) or kilowatt-hours (kWh), and V is the volume of the lithium-ion battery, measured in cubic meters (m³) or liters (L). The testing method involves charging the lithium-ion battery at a current of 0.2C to its upper voltage limit, then charging it at a constant voltage until the current drops to 0.02C, and then discharging it at a current of 0.2C until it reaches 3.0V. The energy discharged is E. The volume of the lithium-ion battery is obtained by measuring its thickness, width, and length and calculating their product. The volumetric energy density is then calculated by dividing E by V.

[0235] The capacity of a lithium-ion battery refers to the maximum energy that the battery can store and discharge as current under specific conditions, usually expressed in ampere-hours (Ah) or milliampere-hours (mAh). The formula for calculating battery capacity is: Capacity (Ah) = Current (A) × Time (h).

[0236] Specifically, the test method for the capacity of lithium-ion batteries is as follows: charge the lithium-ion battery to the upper limit voltage at a current of 0.2C, then charge it at a constant voltage until the current drops to 0.02C, and then discharge it at a current of 0.2C until it reaches 3.0V. The resulting discharge capacity is the battery capacity.

[0237] Tables 1 and 2 show the relevant parameters, fracture conditions, and K values ​​for each embodiment and comparative example.

[0238] Table 1

[0239]

[0240] Table 2

[0241]

[0242] As can be seen from Table 1, by controlling the ratio of n to m, the breakage of the empty foil on both sides of the negative electrode tab can be effectively reduced.

[0243] It should be noted that, in this application, "battery" refers to an energy storage device capable of repeated charging and discharging, which can be interpreted as the concept of a "secondary battery." In the embodiments of this application, the concept of "secondary battery" may include lithium-ion secondary batteries, etc.

[0244] It should be understood that the term "comprising" and its variations used in the embodiments of this application are open-ended, meaning "including but not limited to". The term "according to" means "at least partially according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "a plurality of" means "more than one", which implies covering two, three or more cases.

[0245] It should be understood that although terms such as "first" or "second" may be used in embodiments of this application to describe various elements, such as first protective adhesive and second protective adhesive, these elements are not defined by these terms, which are only used to distinguish one element from another.

[0246] The scope of protection of the embodiments of this application is not limited to the above embodiments. Any variations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be included within the scope of protection of the embodiments of this application. Therefore, the scope of protection of the embodiments of this application should be determined by the scope of the claims.

Claims

1. A type of winding core, characterized in that, It includes a negative electrode sheet, a separator and a positive electrode sheet that are sequentially stacked and wound, and the wound core has a straight section and a first arc section and a second arc section located on both sides of the straight section respectively; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer contains silicon element, and the silicon content in the negative electrode active material layer is e, where e satisfies: 0.35 wt% ≤ e ≤ 35 wt%. The surface of the negative electrode sheet is provided with a first foil-exposing groove, the bottom wall of the first foil-exposing groove exposes part of the negative electrode current collector, the first foil-exposing groove is disposed close to the second arc segment, and the negative electrode active material layer is disposed on the periphery of the first foil-exposing groove. The negative electrode sheet also includes a negative electrode tab and a first protective adhesive. Part of the negative electrode tab is located in the first exposed foil groove and is electrically connected to the negative current collector. The negative electrode tab extends along a first direction and extends beyond the first edge of the negative electrode sheet. The first protective adhesive covers a portion of the negative electrode tab in the first exposed foil groove; along the second direction, the two sides of the first protective adhesive have gaps with the two opposite sidewalls of the first exposed foil groove, and the second direction is perpendicular to the first direction; as well as On the side near the second arc segment, the side edge of the first protective adhesive has a first gap m with the side wall of the first exposed foil groove, and the side wall of the first exposed foil groove has a second distance n with the second arc segment. Wherein, the ratio of m to n satisfies: 1≤n / m≤20; the strength S of the negative electrode current collector ranges from 100 MPa to 650 MPa.

2. The winding core according to claim 1, characterized in that, The ratio of m to n satisfies: 2.5 ≤ n / m ≤ 7.

5.

3. The winding core according to claim 1, characterized in that, Also includes: A third protective adhesive covers the outer surface of the second arc segment and extends to the straight segment. Along the fourth direction, the orthographic projection of the third protective adhesive at least partially overlaps with the orthographic projection of the first gap m.

4. The winding core according to claim 3, characterized in that, The dimensions of the third protective adhesive on the straight sections on both sides of the arc segment on the non-end side of the core are L3 and L4, respectively. The values ​​of L3 and L4 satisfy: 0 mm < L3 ≤ 8 mm, 0 mm < L4 ≤ 8 mm; and / or The thickness of the core is H, and the ratios of L3 and L4 to H satisfy: 0.1≤L3 / H≤3.5, 0.1≤L4 / H≤3.5 respectively.

5. The winding core according to claim 1, characterized in that, The negative electrode active material layer includes a negative electrode active material, which includes graphite and silicon carbon materials. The silicon content in the silicon carbon material is f, wherein 35 wt% ≤ f ≤ 70 wt%.

6. The winding core according to claim 5, characterized in that, The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer stacked sequentially. The first negative electrode active material layer is located on the side of the second negative electrode active material layer away from the negative electrode current collector. The silicon content in the first negative electrode active material layer is greater than the silicon content in the second negative electrode active material layer, and the silicon content in the second negative electrode active material layer is greater than or equal to 0.

7. The winding core according to claim 6, characterized in that, The thickness ratio of the first negative electrode active material layer to the negative electrode active material layer is y, and e and y satisfy: 0.05% < e*y < 20%.

8. The winding core according to any one of claims 1 to 7, characterized in that, The negative electrode active material layer is provided with a recessed groove portion, and the recessed groove portion includes a plurality of spaced recessed grooves; Along the width direction of the negative electrode sheet, the gap between the bottom wall of the first exposed foil groove and the recessed groove is G1, and the value of G1 satisfies: 0 mm < G1 ≤ 5 mm, and / or, Along the length of the negative electrode sheet, the gaps between the sidewalls on both sides of the first exposed foil groove and the recessed groove are G2, respectively, and the value of G2 satisfies: 0 mm < G2 ≤ ​​5 mm, and / or, Along the width direction of the negative electrode sheet, the gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0 mm < G3 ≤ 5 mm.

9. The winding core according to claim 8, characterized in that, The ratio of the intensity S of the negative electrode current collector to the depth h of the recessed groove satisfies: 3 ≤ S / h ≤ 120; and The value of h ranges from 3 μm to 35 μm.

10. The winding core according to claim 1, characterized in that, The positive electrode sheet includes a positive electrode active material layer and a positive electrode current collector. A stepped groove is provided in the projection area of ​​the negative electrode tab on the positive electrode sheet. A second protective adhesive is provided in the stepped groove. Along the third direction, the stepped groove includes a first groove and a second groove arranged in sequence. The first groove has a width L1 and a depth h1, and the second groove has a width L2 and a depth h2. The third direction is perpendicular to the first direction and the second direction. Wherein, L1 is greater than or equal to the width of the second protective adhesive; and / or, The width of the negative electrode tab is W3, L2 ≥ W3; and / or, The width of the first exposed foil groove is W1, and the width of the second protective adhesive is greater than or equal to W1; and / or, The thickness of the second protective adhesive is ≤h1≤h2; and / or, h1+h2≤thickness of the positive electrode active material layer.

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

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