Electrode assembly and battery having the same

Abstract

The embodiment of the invention provides an electrode assembly and a battery with the same. The electrode assembly comprises a positive plate, a diaphragm and a negative plate which are stacked and wound, the positive plate comprises a positive current collector and a positive active layer, the positive active layer comprises a first positive active layer and a second positive active layer which are arranged on the two opposite sides in the thickness direction of the positive current collector, and the first positive active layer is provided with a tab groove and at least one first concave part; the at least one first concave part is distributed in the first area of the first positive electrode active layer, a positive electrode lug is arranged in the lug groove and electrically connected with the positive electrode current collector, the positive plate is provided with a first plate edge and a second plate edge in the width direction, and the lug groove, the first area and the first plate edge are arranged on the same side in the width direction of the positive plate; the first region extends along the length direction of the positive plate, and a distance D1 is formed between the first region and the tab groove, and D1 is greater than or equal to 0.2 mm. According to the technical scheme, the risk of lithium precipitation at the side edge of the tab can be reduced.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of batteries, and in particular, to an electrode assembly and a battery having the same. Background Art

[0002] The electrode assembly usually includes a positive electrode sheet and a negative electrode sheet stacked and distributed with a separator between them. The positive electrode sheet usually includes a current collector and an active layer arranged on opposite sides of the positive electrode sheet in the thickness direction. Some positive electrode sheets adopt a tab-centered structure, that is, the active material layer is provided with a tab groove, and the tab is connected to the current collector portion exposed by the tab groove. Batteries with such positive electrode sheets may have the problem of lithium deposition at the tab side edge and the tab groove edge, affecting the safety performance of the battery. Summary of the invention

[0003] In view of this, an embodiment of the present invention provides an electrode assembly and a battery having the same, so as to reduce the risk of lithium deposition at the side edge of the tab and improve the safety performance of the battery.

[0004] On the one hand, an embodiment of the present invention provides an electrode assembly. The electrode assembly includes a positive electrode sheet, a separator and a negative electrode sheet which are stacked and wound. The positive electrode sheet includes a positive electrode collector and a positive electrode active layer. The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer which are arranged on opposite sides in the thickness direction of the positive electrode collector. The first positive electrode active layer is provided with a pole ear groove and at least one first recess. At least one first recess is distributed in the first region of the first positive electrode active layer. A positive pole ear is arranged in the pole ear groove, and the positive pole ear is electrically connected to the positive electrode collector. The positive electrode sheet has a first pole sheet edge and a second pole sheet edge in its width direction, and the pole ear groove, the first region and the first pole sheet edge are arranged on the same side in the width direction of the positive electrode sheet, and the first region extends along the length direction of the positive electrode sheet and has a spacing D1 with the pole ear groove, and D1≥0.2mm.

[0005] In some embodiments, the second positive electrode active layer is provided with an exposed groove and at least one second recessed portion, at least one second recessed portion is distributed in the second region of the second positive electrode active layer, the exposed groove, the second region and the edge of the first electrode sheet are arranged on the same side in the width direction of the positive electrode sheet, the pole tab groove has two first groove edges in the length direction of the positive electrode sheet, the exposed groove has two second groove edges in the length direction of the positive electrode sheet, the orthographic projections of the two second groove edges on the first positive electrode active layer are respectively located on the outsides of the two first groove edges, and each second groove edge has a transition zone between the orthographic projection on the first positive electrode active layer and the first groove edge located on the same side of the pole tab groove.

[0006] In some embodiments, the transition region has a dimension D2 in the length direction of the positive electrode sheet, wherein D1 ≥ D2, preferably, 1.1 ≤ D1 / D2 ≤10.

[0007] In some embodiments, there is a distance D3 between the second region and the exposed groove, 0.5 mm≤D1≤15 mm, 0.5 mm≤D2≤5 mm, 0.2 mm≤D3≤10 mm.

[0008] In some embodiments, the first groove edge located on the first side of the pole tab groove in the length direction of the positive electrode sheet has a distance D11 from the first region, and the first groove edge located on the second side of the pole tab groove in the length direction of the positive electrode sheet has a distance D12 from the first region, |D11-D12|≤10.

[0009] In some embodiments, the second groove edge located on the first side of the exposed groove in the length direction of the positive electrode sheet has a distance D31 from the second region, and the second groove edge located on the second side of the exposed groove in the length direction of the positive electrode sheet has a distance D32 from the second region, |D31-D32|≤10.

[0010] In some embodiments, 1 / 35≤W2 / W1≤1 / 2; and / or, 2mm≤W2≤20mm; and / or, 0.1mm≤D4≤10mm. Here, W1 is the size of the positive electrode sheet in its width direction, W2 is the size of the first region in the width direction of the positive electrode sheet, and D4 is the distance from the first region to the edge of the active layer of the first positive electrode active layer, and the edge of the active layer is closer to the edge of the first electrode sheet than the edge of the second electrode sheet.

[0011] In some embodiments, the positive electrode ear is welded to the positive electrode collector and has multiple welding points, at least one first recess includes multiple first recesses, and the multiple welding points and the multiple first recesses satisfy: 5μm≤H1≤30μm; and / or, 30μm≤H2≤500μm; and / or, 1≤H2 / H1≤100; and / or, 100μm≤D5≤300μm; and / or, τ1≥τ2; and / or, 9 pieces / mm 2 ≤τ1≤120pcs / mm 2 ; and / or, 4 / mm2≤τ2≤64 / mm2. Here, H1 is the depth of the plurality of first recesses, H2 is the depth of the plurality of solder joints, D5 is the spacing between the plurality of first recesses, τ1 is the distribution density of the plurality of first recesses, and τ2 is the distribution density of the plurality of solder joints.

[0012] In some embodiments, the electrode assembly further includes a first tape, the first tape covers the positive electrode ear and a portion of the first region, and the area of ​​the first region covered by the first tape is S1, 0.1 mm 2 ≤S1≤500mm 2 .

[0013] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer, the negative electrode active layer contains a receiving recess, the positive electrode ear on the negative electrode sheet at least partially overlaps with the receiving recess, and the positive projection of the first region on the negative electrode sheet is located outside the receiving recess.

[0014] In some embodiments, the negative electrode sheet further includes a second tape, wherein the second tape is located in the receiving recess; or, the second tape is partially located outside the receiving recess, and the orthographic projection of the portion of the second tape located outside the receiving recess on the positive electrode sheet partially overlaps with the first area and has an overlapping area S2, 0.1 mm 2 ≤S2≤500mm 2 .

[0015] In some embodiments, the positive electrode sheet also includes a third tape, the orthographic projection of the negative electrode ear of the negative electrode sheet on the positive electrode sheet falls on the first area, the third tape is arranged at a position of the positive electrode sheet corresponding to the negative electrode ear, the orthographic projection of the third tape on the positive electrode sheet overlaps with the orthographic projection of the negative electrode ear on the positive electrode sheet, and the overlapping part covers a part of the first area.

[0016] In some embodiments, the third tape has a first tape edge and a second tape edge along the width direction of the positive electrode sheet, the first tape edge extends outward beyond the positive electrode sheet in the width direction of the positive electrode sheet, the second tape edge extends inward beyond the corresponding area in the width direction of the positive electrode sheet, and the second tape edge has a spacing D6 with the corresponding area, D6≤20mm.

[0017] In some embodiments, the first positive electrode active layer is further provided with a third region, at least one third recess is provided in the third region, the third region extends along the length direction of the positive electrode sheet, and the third region is closer to the edge of the second electrode sheet relative to the edge of the first electrode sheet; and / or, the second positive electrode active layer is further provided with a fourth region, at least one third recess is provided in the fourth region, the fourth region extends along the length direction of the positive electrode sheet, and the fourth region is closer to the edge of the second electrode sheet relative to the edge of the first electrode sheet.

[0018] In some embodiments, the electrode assembly has a flat portion and a curved portion, the positive electrode sheet includes an arc segment located in the curved portion, the positive electrode active layer has a fifth region, at least one fifth recess is provided in the fifth region, and the fifth region is at least partially provided in the arc segment.

[0019] In some embodiments, the positive electrode sheet also includes a straight section located in the flat portion, and the two straight sections along the length direction of the positive electrode sheet are respectively connected to the two ends of the arc section, and the two edges of the fifth region in the length direction of the positive electrode sheet are respectively located in the two straight sections.

[0020] In some embodiments, at least one first recess is arranged non-linearly.

[0021] In some embodiments, the first region is divided into at least two sections arranged along the length direction of the positive electrode sheet by at least one first splicing region; and / or, the fifth region is divided into at least two sections arranged along the width direction by at least one second splicing region; and / or, the first region and the fifth region are separated by a third splicing region.

[0022] In some embodiments, the first stitching area has a dimension W3 along the length direction of the positive electrode sheet, 0.1mm≤W3≤20mm; and / or, the second stitching area has a dimension W4 along the width direction of the positive electrode sheet, 0mm≤W4≤20mm; and / or, the third stitching area has a dimension W5 along the width direction of the positive electrode sheet, 0mm≤W5≤20mm.

[0023] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer that are stacked, and the negative electrode active layer is provided with a plurality of grooves that are spaced apart.

[0024] In some embodiments, 5 μm ≤ H3 ≤ 30 μm; and / or, 0.5 mm ≤ D7 ≤ 5 mm,

[0025] Among them, H3 is the groove depth of the plurality of grooves, and D7 is the groove spacing of the plurality of grooves.

[0026] In a possible implementation, the negative electrode sheet includes a stacked negative electrode current collector and a negative electrode active layer; the material of the negative electrode active layer includes one or more of graphite and silicon-based materials, and the material of the negative electrode active layer is a silicon-based material with a silicon content of 3 to 30 wt%.

[0027] In another aspect, an embodiment of the present invention further provides a lithium ion secondary battery, which includes the electrode assembly in the above aspect.

[0028] According to the implementation method provided by the embodiment of the present invention, the multiple recesses provided in the first area on the positive electrode active layer can reduce the active material of the positive electrode active layer, reduce the amount of lithium ions received by the negative electrode sheet, thereby reducing the risk of lithium precipitation at the edge of the side of the pole ear, and improving the safety performance of the battery. In addition, the recesses can increase the storage capacity of the electrolyte, which is beneficial to the transmission of lithium ions. At the same time, since there is a sufficiently large gap between each first area and the edge of the first groove on the same side of the pole ear groove, when the recesses are formed, it is possible to avoid the powder falling from the positive electrode active layer, causing the powder to pierce the diaphragm and cause a short circuit, and to avoid the powder falling into the positive pole ear welding area and affecting the welding effect, thereby further improving the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 FIG. 4 is a schematic structural diagram of a battery according to an embodiment of the present invention.

[0030] Figure 2 FIG. 4 is a schematic structural diagram of a battery according to another embodiment of the present invention.

[0031] Figure 3 Schematic diagram of the structure of an electrode assembly according to an embodiment of the disclosure.

[0032] Figure 4 For along Figure 3 Schematic diagram of the cross-section taken along line BB.

[0033] Figure 5 It shows Figure 4 Schematic diagram of the structure on opposite sides of the positive electrode sheet in the thickness direction.

[0034] Fig. 6A and 6B for Figure 5 Schematic diagram of the structure of a part of the positive electrode.

[0035] Figure 7 for Fig. 6A A partial enlarged view of the positive electrode in the .

[0036] Figure 8 It shows Figure 5 Schematic diagram of the structure of the positive electrode ear of the positive electrode sheet.

[0037] Figures 9A to 9C for Figure 4 Schematic diagram of the structure of a portion of an electrode assembly.

[0038] Fig.10 for Figure 5 Schematic diagram of the structure of a part of the positive electrode.

[0039] Fig.11 for Figure 5 Schematic diagram of the structure of another part of the positive electrode.

[0040] Fig.12 for Figure 4 Schematic diagram of the structure of a part of the electrode assembly.

[0041] Fig.13 for Figure 5 Schematic diagram of the structure of a part of an area of ​​the positive electrode sheet.

[0042] Fig.14 for Figure 5 Schematic diagram of the structure of the positive electrode.

[0043] Fig.15 for Figure 4 Schematic diagram of the structure of the negative electrode sheet.

[0044] Fig.16 for Fig.15 Schematic diagram of the cross section of the groove in. DETAILED DESCRIPTION

[0045] Many specific details are listed herein to provide a deep understanding of the overall structure, function, and use of the embodiments described in the specification and shown in the drawings. Well-known operations, parts, and elements are not described in detail to avoid making the description in the specification too redundant. The reader will understand that the embodiments described and shown herein are non-limiting examples, so that it can be recognized that the specific structural and functional details mentioned herein can be representative and exemplary. These embodiments can be modified and changed without departing from the scope of the claims.

[0046] <Exemplary Battery>

[0047] In the embodiment of the present invention, "battery" refers to a storage device that can be repeatedly charged and discharged, which can be interpreted as the concept of "secondary battery". In the embodiment of the present invention, the concept of "secondary battery" can include, but is not limited to, lithium ion secondary batteries, sodium ion secondary batteries, etc.

[0048] The battery 100 according to the first embodiment of the present invention is Figure 1 Reference Figure 1 The battery 100 may include an electrode assembly 10 and a packaging body 20. The packaging body 20 may be provided with a cavity, and one or more electrode assemblies 10 may be accommodated in the cavity.

[0049] like Figure 1 As shown, the package 20 may be in a square shape. That is, the battery 100 may be a square battery. The material of the package 20 may be the same as that used in the past, and there is no particular limitation. For example, the package 20 may be made of metal, in particular, may be made of aluminum (alloy) or iron (alloy).

[0050] According to another embodiment of the present invention, a battery 100 is Figure 2 As shown in Figure 2 As shown, in this embodiment, the packaging body 20 is flat and made of a relatively soft material, such as an aluminum-plastic film. That is, in this embodiment, the battery 100 can be a soft-pack battery.

[0051] It is foreseeable that in other examples of the embodiments of the present invention, the battery 100 may also be implemented as other types besides the square battery and the soft-pack battery, for example, a cylindrical battery.

[0052] It should be noted that other aspects of the structure of the battery 100 may be the same as the structure of a conventional battery, and for the purpose of brevity, this embodiment of the present invention will not be described in detail.

[0053] <Exemplary Electrode Assembly>

[0054] refer to Figure 3 and Figure 4, the electrode assembly 10 may include a positive electrode sheet 11, a negative electrode sheet 12 and a separator 13 arranged in a stacked manner. The separator 13 is a member that insulates the positive electrode sheet 11 and the negative electrode sheet 12. The positive electrode sheet 11 and the negative electrode sheet 12 can be wound with the winding axis A as the winding center through the separator 13. For example, the electrode assembly 10 can be wound into a flat structure. In this article, flat means that the width is greater than the thickness. For example, the ratio B / C of the width B and the thickness C of the electrode assembly 10 can satisfy 1.1≤A / B≤200. The electrode assembly 10 may include two curved portions 181 and a flat portion 182, and the flat portion 182 is located between the two curved portions 181. For example, in some examples, the electrode assembly 10 can also be wound into a cylindrical shape.

[0055] In the case where the electrode assembly 10 is flat, for the convenience of description, the present embodiment will use the "width direction" and "thickness direction" of the electrode assembly 10. Here, the "width direction" refers to the direction from one curved portion to another curved portion, which is indicated by arrow U in the figure; the "thickness direction" refers to the thickness direction of the electrode sheet before winding, which is perpendicular to the "width direction", which is indicated by arrow V in the figure.

[0056] refer to Figure 4 The positive electrode sheet 11 may include a positive current collector 14, a first positive active layer 151 and a second positive active layer 152, which may be collectively referred to as a positive active layer 15. The first positive active layer 151 and the second positive active layer 152 may be located at opposite sides of the thickness direction of the current collector 14. The negative electrode sheet 12 may include a stacked negative current collector 121 and two negative active layers 122, which may be located at opposite sides of the thickness direction of the negative current collector 121.

[0057] By way of example only, the positive electrode current collector 14 may be a strip of metal foil, and the positive electrode active layer 15 may include a positive electrode active material that can reversibly absorb and release charge carriers. In addition, they may further include a conductive material, a binder, and various additives. By way of example only, the metal foil mentioned here may be an aluminum foil, the positive electrode active material mentioned may be a lithium transition metal composite oxide such as a lithium nickel cobalt manganese composite oxide, the conductive material mentioned may be a carbon material such as acetylene black, and the binder mentioned may be polyvinylidene fluoride, etc.

[0058] By way of example only, the negative electrode current collector 121 may be a strip of metal foil or a composite current collector, and the negative electrode active layer 122 may include a negative electrode active material capable of reversibly absorbing and releasing charge carriers, a binder, a dispersant, and various additives, etc. By way of example only, the metal foil mentioned here may be copper foil, the negative electrode active material mentioned may be a carbon material such as graphite, the binder mentioned may be a rubber such as styrene-butadiene rubber, and the dispersant mentioned may be a cellulose such as carboxymethyl cellulose.

[0059] It can be understood that when the electrode assembly is unfolded, the winding direction of a certain element is consistent with its length direction, or in other words, the direction from its starting end to its ending end is its length direction. Therefore, in the unfolded view, arrow X also indicates the length direction of the positive electrode sheet. In the figure of the unfolded electrode assembly, the width direction of elements such as the positive electrode sheet, the negative electrode sheet, the separator, the current collector and the active layer is indicated by arrow Y in the figure, and the direction indicated by arrow Y is perpendicular to the direction indicated by arrow X.

[0060] refer to Figure 5 , the positive electrode active layer 15 may be provided with at least one first recess 16. As an example, the at least one first recess 16 may be implemented as a plurality of holes 16, and the plurality of holes 16 may be distributed in at least one region of the positive electrode active layer 15. For example, the plurality of holes 16 may be formed on the positive electrode active layer 15 by laser drilling. Due to the presence of the plurality of holes 16, the positive active material in at least one region will be reduced, and the amount of lithium ions received by the negative active material at the corresponding position will be reduced, so that the lithium precipitation phenomenon will be alleviated. At the same time, the presence of the plurality of holes 16 will increase the storage capacity of the electrolyte, which is beneficial to the transmission of lithium ions.

[0061] It can be understood that in other embodiments, the concave portion on the positive electrode active layer 15 can also be implemented as a groove, and the present disclosure does not impose any particular limitation on this.

[0062] refer to Figure 5 and Fig. 6A, the positive electrode sheet 11 has two opposite edges in its width direction, namely, a first electrode sheet edge 111 and a second electrode sheet edge 112. The first electrode sheet edge 111 can be called a pole ear side edge, because the positive electrode ear 19a of the positive electrode sheet 11 is arranged at the first electrode sheet edge 111. At least one region may include a first region 161, which is arranged on the first positive electrode active layer 151, extends along the length direction of the positive electrode sheet 11, and is close to the first electrode sheet edge 111. In other words, the first region 161 is closer to the first electrode sheet edge 111 than the second electrode sheet edge 112. At least one recess 16 may include a plurality of first recesses 16, and the plurality of first recesses 16 are arranged in the first region 161. This can reduce the active material of the positive electrode active layer near the first electrode sheet edge 111, reduce the amount of lithium ions received by the negative electrode sheet, and thus reduce the risk of lithium deposition near the first electrode sheet edge 111.

[0063] Continue to refer Figure 5 and Fig. 6A , the first positive electrode active layer 151 may be provided with a tab groove 1511. The tab groove 1511, the first region 161 and the first electrode edge 111 are arranged on the same side in the width direction of the positive electrode 11, that is, the tab groove 1511 is closer to the first electrode edge 111 than the second electrode edge 112. The positive tab 19a may be connected to the portion of the positive electrode current collector 14 exposed by the tab groove 1511, for example, by welding. Figure 5 and Fig. 6A As shown, the first region 161 crosses the tab groove 1511 and is divided into two parts by the tab groove 1511, that is, divided into two first region parts 161a and 161b. The tab groove 1511 has two first groove edges 1512a and 1512b in the length direction of the positive electrode sheet 11. In the length direction of the positive electrode sheet 11, the first region part 161a and the first groove edge 1512a are located on the same side of the tab groove 1511, and the first region part 161b and the first groove edge 1512b are located on the same side of the tab groove 1511.

[0064] After the first positive electrode active layer 151 is disposed on the positive electrode current collector 14, a portion of the active material of the first positive electrode active layer 151 may be removed to form the tab groove 1511. For example, a portion of the active material of the first positive electrode active layer 151 may be scraped off with a scraper. Before removing this portion of the active material, an adhesion weakening agent, such as an N-methylpyrrolidone (NMP) solvent, may be applied thereto, so that the adhesion of the active material in the applied area is lower than that in the unapplied area. Subsequently, the applied area may be scraped off and other operations may be performed to form the tab groove 1511.

[0065] After the tab groove 1511 is formed, the active material near the tab groove 1511 has weaker adhesion than other areas due to the effect of the adhesion weakening agent. If the two first area parts 161a and 161b are too close to the two first groove edges 1512a and 1512b of the tab groove 1511, some holes 16 will fall in the area with poor adhesion, which will cause the positive active layer 15 to lose powder. On the one hand, the fallen powder may pierce the diaphragm 13 and cause a short circuit. On the other hand, the fallen powder may fall on the welding area of ​​the positive tab 19a, deteriorating the welding effect. Both aspects will reduce the safety performance of the battery 100.

[0066] In view of this, according to an embodiment of the present invention, continue to refer to Figure 5 and Fig. 6A , each first region portion has a spacing D1 with the edge of the first groove on the same side of the tab groove 1511, and the spacing D1 is greater than or equal to 0.2 mm. In this way, since each first region portion has a sufficiently large spacing with the edge of the first groove on the same side of the tab groove 1511, it is possible to prevent the positive electrode active layer 15 from falling powder during drilling, causing the powder to pierce the diaphragm and cause a short circuit, and to prevent the powder from falling into the positive tab welding area and affecting the welding effect, thereby improving the safety performance of the battery 100.

[0067] It should be noted that the distance D1 may be the shortest distance between the first region portion and the edge of the first groove located on the same side of the tab groove 1511 .

[0068] refer to Figure 5 and Figure 6B , the second positive electrode active layer 152 may be provided with an exposure groove 1521, and at least one region may include a second region 162 provided in the second positive electrode active layer 152. The plurality of recesses 16 may include at least one second recess provided in the second region. The exposure groove 1521 and the second region 162 are close to the first edge 111. That is, the exposure groove 1521 and the second region 162 are closer to the first electrode edge 111 relative to the second electrode edge 112. The second region 162 may extend along the length direction of the positive electrode sheet 11 and be divided into two second region portions 162a, 162b by the exposure groove 1521. The exposure groove 1521 may have two second groove edges 1522a, 1522b in the length direction of the positive electrode sheet 11. The second region portion 162 a and the second groove edge 1522 a are located on the same side of the exposed groove 1521 in the length direction of the positive electrode sheet 11 , and the second region portion 162 b and the second groove edge 1522 b are located on the same side of the exposed groove 1521 in the length direction of the positive electrode sheet 11 .

[0069] Since the first positive electrode active layer 151 is provided with a tab groove 1511, and the second positive electrode active layer 152 is provided with an exposed groove 1521. In the process of forming the tab groove, the active material of the first positive electrode active layer 151 can be scraped off first to form the tab groove 1511, and then the active material of the second positive electrode active layer 152 can be scraped off to form the exposed groove 1521, and the scraped area of ​​the second positive electrode active layer 152 is larger than the scraped area of ​​the first positive electrode active layer 151, so that the orthographic projections of the two second groove edges 1522a and 1522b on the first positive electrode active layer 151 are respectively located outside the two first groove edges 1512a and 1512b, as shown in FIG. Figure 7 As shown in the figure, since the scraped areas on both sides of the positive electrode current collector 14 are different in area, it is possible to prevent the positive electrode current collector 14 from being repeatedly stressed at the same position and causing rupture.

[0070] refer to Figure 7 , each second groove edge has a transition zone between its orthographic projection on the first positive electrode active layer 151 and the first groove edge located on the same side of the tab groove 1511. Specifically, a transition zone 153a is formed between the orthographic projection of the second groove edge 1522a on the first positive electrode active layer 151 and the first groove edge 1512a, and a transition zone 153b is formed between the orthographic projection of the second groove edge 1522b on the first positive electrode active layer 151 and the first groove edge 1512b. Each transition zone has a size D2 in the length direction of the positive electrode sheet 11. Reference Figure 6B Each second region portion and the second groove edge located on the same side of the exposure groove 1521 may have a distance D3.

[0071] It is not advisable to punch holes in the transition areas 153a and 153b, otherwise the risk of powder falling may increase, thereby reducing the safety performance of the battery 100. In view of this, the size D1 can be greater than or equal to the size D2, so that the hole 16 in the first area 161 can be prevented from falling into the transition areas 153a and 153b, thereby reducing the risk of powder falling and improving the safety performance of the battery 100.

[0072] The relationship between the size D1 and the size D2 can satisfy: 1.1≤D1 / D2≤10, preferably, 1.13≤D1 / D2≤5. Alternatively, D1 / D2 can be 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5, 10. The ratio of D1 / D2 should not be too small. If D1 / D2 is less than 1.1, the hole 16 in the first area 161 will fall into the transition zone 153a, 153b, or be too close to the transition zone 153a, 153b. Both situations will increase the risk of powder loss. The ratio of D1 / D2 should not be too large. If D1 / D2 is greater than 10, it will increase the risk of lithium deposition on the edge of the pole ear. Selecting the ratio of D1 / D2 as 1.1≤D1 / D2≤10 can have both a lower risk of powder loss and a lower risk of lithium deposition on the edge of the pole ear.

[0073] More preferably, the dimensions D1, D2 and D3 may satisfy: 0.5mm≤D1≤15mm, 0.5mm≤D2≤5mm. 0.2mm≤D3≤10mm, preferably, 0.5mm≤D1≤7.5mm, 0.5mm≤D2≤1.5mm. 0.2mm≤D3≤5mm. Alternatively, D2 may be 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, and D3 may be 0.5mm, 1mm, 3mm, 5mm, 7mm, 9mm, 10mm. It has been proven that when the dimensions D1, D2 and D3 meet the above conditions, the risk of powder loss and the risk of lithium deposition on the side edge of the tab are relatively low, and the safety performance of the battery 100 is relatively high.

[0074] refer to Fig. 6A and Figure 7 , the first groove edge 1512a and the first area portion 161a located on the first side of the pole tab groove 1511 in the length direction of the positive electrode sheet 11 have a spacing D11, and the first groove edge 1512b and the first area portion 161b located on the second side of the pole tab groove 1511 in the length direction of the positive electrode sheet 11 have a spacing D12. The spacing D11 and the spacing D12 can satisfy: |D11-D12|≤10, preferably, |D11-D12|≤3. In other words, the spacing D11 and the spacing D12 are not required to be equal, and the difference between the two can be ±10mm. Reference Figure 6B, the second groove edge 1522a and the second area portion 162a located on the first side of the exposed groove 1521 in the length direction of the positive electrode sheet 11 have a spacing D31, and the second groove edge 1522b and the second area portion 162b located on the second side of the exposed groove 1521 in the length direction of the positive electrode sheet 11 have a spacing D32. Spacing D31 and spacing D32 can satisfy: |D31-D32|≤10, preferably, |D31-D32|≤5. In other words, spacing D31 and spacing D32 are not required to be equal, and the two can have a difference of ±10mm. Whether it is the difference between spacing D11 and spacing D12, or the difference between spacing D31 and spacing D32, it should not be too large or too small. If the difference is too small, higher manufacturing precision will be required, which will increase the manufacturing cost. If the difference is too large, it will cause the groove edge on one side to be too far from the corresponding area, while the groove edge on the other side will be too close to the corresponding area. As mentioned above, if the groove edge is too close to the corresponding area, the risk of powder falling will increase, thereby reducing the safety performance of the battery 100.

[0075] It should be noted that the spacing D11 may be the shortest distance between the first groove edge 1512a and the first area portion 161a, and the spacing D12 may be the shortest distance between the first groove edge 1512b and the first area portion 161b. Similarly, D31 may be the shortest distance between the second groove edge 1522a and the second area portion 162a, and D32 may be the shortest distance between the second groove edge 1522b and the second area portion 162b.

[0076] refer to Figure 5 and Fig. 6A , the positive electrode sheet 11 has a size W1 in the width direction, and the first region 161 has a size W2 in the width direction of the positive electrode sheet 11. The value range of size W2 can be: 2mm≤W2≤20mm, and size W1 and size W2 can satisfy: 1 / 35≤W2 / W1≤1 / 2. Alternatively, W2 can be 2mm, 4mm, 7mm, 10mm, 15mm, 20mm, and W2 / W1 can be 1 / 35, 1 / 30, 1 / 20, 1 / 10, 1 / 5, 1 / 2. If the size W2 and the ratio W2 / W1 are too large, the active material of the positive electrode active layer 15 will be reduced too much, which is not conducive to the energy density of the battery 100. If the size W2 and the ratio W2 / W1 are too small, it is difficult to effectively improve the lithium plating problem at the side edge of the pole ear. Selecting the value of the dimension W2 and the ratio W2 / W1 to be within the above range can improve lithium deposition at the edge of the tab without reducing the energy density of the battery 100 too much.

[0077] Continue to refer Fig. 6A, the first region 161 has a size W2 in the width direction of the positive electrode sheet 11, and the distance from the first region 161 to the active layer edge of the first positive electrode active layer 151 is D4. The value range of the distance D4 can be: 0.1mm≤D4≤10mm, preferably, 0.1mm≤D4≤5mm. Alternatively, D4 can be 0.5mm, 2mm, 4mm, 7mm. Here, the edge of the active layer is closer to the edge 111 of the first electrode sheet relative to the edge 112 of the second electrode sheet. In this way, it can be ensured that the edge of the electrode sheet is avoided when punching holes in the first positive electrode active layer 151, so as to avoid the edge of the electrode sheet being damaged to form burrs, and the problem of positive electrode sheet breakage during the later winding process. Furthermore, according to the above implementation method, the punching is performed so that the range of the area can cover the positive electrode edge corresponding to the lithium-prone area of ​​the negative electrode edge, thereby reducing the risk of lithium deposition at the negative electrode edge.

[0078] refer to Figure 8 , the positive electrode ear 19a can be welded together with the positive electrode current collector 14 to form at least one welding spot 191. The multiple first recesses can have a depth H1 (not shown in the figure), and the multiple first recesses have a spacing D5. The multiple welding spots 191 can have a welding spot depth H2 (not shown in the figure). It can be understood that the depths of the multiple first recesses can be the same, in which case H1 is the depth of any one of the first recesses. The depths of the multiple first recesses can also be different, in which case H1 can be the average depth. When calculating the average depth of the multiple first recesses, only the average depth of a portion of the multiple first recesses can be considered without including all the first recesses in the calculation. For example, H1 can be 10 cm close to the welding area. 2 The average depth of the first concave portion 16 in the region, H1 may also be the average depth of 10 adjacent first concave portions 16. Similarly, when calculating the weld depth H2 of the plurality of welds, only a portion of the welds 191 in the plurality of welds 191 may be considered. For example, H2 may be the depth of the welds located in the 6 cm region of the weld. 2The average depth of the solder joint 191 in the area, H2 can also be the average depth of 10 adjacent solder joints 191. The value range of the depth H1 can be: 5μm≤H1≤30μm. Alternatively, H1 can be 10μm, 15μm, 20μm, 25μm. The value range of the solder joint depth H2 can be: 30μm≤H2≤500μm. Alternatively, H2 can be 40μm, 60μm, 90μm, 100μm, 200μm, 300μm, 400μm. The depth H1 and the depth H2 can satisfy: 1≤H2 / H1≤100. The value range of the hole spacing D5 can be 100μm≤D5≤300μm. Alternatively, D5 can be 120μm, 150μm, 200μm, 250μm. The welding completed according to the above parameters is conducive to the combination of the tab and the current collector and the conductivity of the metal, and can avoid excessive internal resistance at the welding point, which causes heat accumulation during the charging and discharging process. In addition, according to the above implementation, there is no need to scrape off too much paste on the first positive electrode active layer 151, so while meeting the welding conditions, the capacity of the battery and the strength of the positive electrode sheet can also be guaranteed.

[0079] Continue to refer Figure 8 , τ1 refers to the number of first recesses 16 per unit area. τ2 refers to the number of solder joints 191 per unit area. The distribution density τ1 and the distribution density τ2 may satisfy: τ1 ≥ τ2. The value range of the distribution density τ1 may be: 9 pieces / mm 2 ≤τ1≤120pcs / mm 2 Alternatively, τ1 can be 20 pieces / mm 2 , 40 pieces / mm 2 , 60 pieces / mm 2 , 80 pieces / mm 2 , 100 pieces / mm 2 The distribution density τ2 can range from: 4 pieces / mm 2 ≤τ2≤64pcs / mm 2 Alternatively, τ1 can be 10 pieces / mm 2 , 20 pieces / mm 2 , 40 pieces / mm 2 , 60 pieces / mm 2 . The density of the tab welding point protrusion may be different from the density of the first recess 16. For example, the density of the welding point protrusion may be less than the density of the first recess 16. The density of the first recess 16 is relatively large, so that the positive electrode active layer after the first recess 16 is formed has a more uniform stress distribution. At the same time, since the electrolyte can be stored more in the first recess 16, the smoothness of lithium ion transmission can be improved, and the fast charging performance and long cycle performance of the battery can be enhanced.

[0080] refer to Fig.10The electrode assembly 10 may further include a first tape 171 attached to the positive electrode sheet 11, and the positive electrode tab 19a and the first region 161 may be partially covered by the first tape 171. The area of ​​the first region 161 covered by the first tape 171 is S1. The area S1 may satisfy: 0.1mm 2 ≤S1≤500mm 2 Alternatively, S1 can be 5 mm 2 , 40mm 2 、60mm 2 , 120mm 2 , 150mm 2 , 250mm 2 、300mm 2 , 400mm 2 , 450mm 2 According to the above implementation, the risk of short-circuiting the positive and negative electrode sheets after the metal burrs at the positive electrode tab pierce the diaphragm can be reduced, thereby ensuring the safety performance of the battery. In addition, after the electrode assembly 10 is hot-pressed, the first tape 171 covering the first recess 16 will sink into the first recess 16, thereby increasing the bonding strength between the positive electrode sheet 11 and the negative electrode sheet 12, while improving space utilization, thereby increasing the volume energy density.

[0081] It should be noted that the first tape 171 should cover the positive electrode as little as possible to ensure the amount of active lithium ions that can be exerted by the positive electrode and to ensure the capacity of the battery.

[0082] refer to Fig.9A , a receiving recess may be provided on the negative electrode active layer 122, and the receiving recess may be implemented as a receiving recess 123, and the positive projection of the positive electrode tab 19a of the positive electrode sheet 11 on the negative electrode sheet 12 may fall into the receiving recess 123, and the positive projection of the first region 161 on the negative electrode sheet 12 may fall outside the receiving recess 123. In this way, when the electrode assembly 10 is compressed in the width direction, the negative electrode active layer 122 can support the first positive electrode active layer 151, avoiding the paste on the first positive electrode active layer 151 from falling off, thereby affecting the viscosity of the first tape 171 of the tab.

[0083] The electrode assembly 10 may further include a second adhesive tape 172 adhered to the negative electrode sheet 12 to further reduce the risk of short-circuiting the positive and negative electrode sheets after metal burrs pierce the separator 13, thereby ensuring the safety performance of the battery.

[0084] As a way to achieve this, refer to Fig.9A , the second tape 172 can be completely located in the receiving recess 123. In this way, the orthographic projection of the second tape 172 on the positive electrode sheet 11 will not cover the first area 161, thereby not causing additional capacity loss.

[0085] As a possible implementation, refer to Fig. 9B , the second tape 172 may also be partially located outside the receiving recess 123. In this case, the orthographic projection of the portion of the second tape 172 located outside the receiving recess 123 on the positive electrode sheet 11 partially overlaps with the first area 161 and has an overlapping area S2. The value range of the overlapping area S2 is: 0.1 mm 2 ≤S2≤500mm 2 Alternatively, S2 can be 5 mm 2 , 40mm 2 、60mm 2 , 120mm 2 , 150mm 2 , 250mm 2 、300mm 2 , 400mm 2 , 450mm 2 In this value range, the second tape 172 will not cause excessive energy loss, and the existence of the receiving recess 123 can compensate for the energy loss caused by the positive electrode ear 19a.

[0086] Back to Figure 5 , at least one region may further include a third region 163 disposed in the first positive electrode active layer 151 and a fourth region 164 disposed in the second positive electrode active layer 152. The third region 163 may extend along the length direction of the positive electrode sheet 11, and the third region 163 may be close to the second electrode sheet edge 112, that is, the third region 163 is closer to the second electrode sheet edge 112 relative to the first electrode sheet edge 111. The fourth region 164 may extend along the length direction of the positive electrode sheet 11, and the fourth region 164 may be close to the second electrode sheet edge 112, that is, the fourth region 164 may be closer to the second electrode sheet edge 112 relative to the first electrode sheet edge 111. The multiple recesses 16 may further include at least one third recess and at least one fourth recess, at least one third recess is located in the third region, and at least one fourth recess is located in the fourth region. Since recesses 16 are provided in regions close to the first pole piece edge 111 and the second pole piece edge 112, and recesses 16 can store a portion of the electrolyte, this increases the residual liquid volume of the battery (i.e., the amount of electrolyte in the battery at the end), improves the cycle performance of the battery, and at the same time facilitates the migration of lithium ions, making it less likely for them to be enriched on the surface of the negative electrode, thereby reducing the risk of lithium precipitation.

[0087] refer to Fig. 9C and Fig.11, the electrode assembly 10 may further include a third tape 173 adhered to the positive electrode sheet 11. The positive projection of the negative electrode ear 19b of the negative electrode sheet 12 on the positive electrode sheet 11 falls on a corresponding area extending along the length direction of the positive electrode sheet 11. The corresponding area may be one of the first area 161, the second area 162, the third area 163 and the fourth area 164. The third tape 173 may be separated between the positive electrode sheet 11 and the negative electrode ear 19b, and the positive projection of the third tape 173 on the positive electrode sheet 11 overlaps with the positive projection of the negative electrode ear 19b on the positive electrode sheet 11, and the overlapping portion covers a portion of the corresponding receiving recess 123. In this way, it is possible to avoid the metal burrs of the negative electrode ear 19b from piercing the diaphragm 13 and directly short-circuiting with the positive electrode sheet 11, thereby affecting the safety performance of the battery. In addition, since the third tape 173 covers a portion of the first recess 16 on the first positive electrode active layer 151, after the electrode assembly 10 is hot-pressed, a portion of the third tape 173 will sink into the first recess 16, thereby increasing the bonding strength, improving the space utilization and the volume energy density.

[0088] Continue to refer Fig. 9C and Fig.11 , the third tape 173 may have a first tape edge 173a and a second tape edge 173b along the width direction of the positive electrode sheet 11, the first tape edge 173a may exceed the positive electrode sheet 11 outward in the width direction of the positive electrode sheet 11, and the second tape edge 173b may exceed the edge of the corresponding area in the width direction of the positive electrode sheet 11. The second tape edge 173b is spaced apart from the edge of the corresponding area by a distance D6. The value of the distance D6 may satisfy: D6≤20mm, preferably, D6≤5mm. Alternatively, D6 may be 18mm, 16mm, 14mm, 12mm, 10mm, 8mm, 6mm, 4mm, 2mm, or 1mm. In this way, it is possible to ensure that the third tape 173 covers the positive electrode sheet 11 as little as possible, thereby ensuring the number of active lithium ions that can be exerted by the positive electrode sheet 11 and ensuring the capacity of the battery.

[0089] It should be noted that the distance D6 is the shortest distance between the second tape edge 173b and the edge of the corresponding area.

[0090] refer to Figure 5 and Fig.12, the positive electrode sheet 11 may also include an arc segment located in the curved portion 181, and at least one region also includes a fifth region 165, and the fifth region 165 is at least partially provided in the arc segment. The multiple recesses 16 may also include at least one fifth recess, and at least one fifth recess is located in the fifth region. In the arc segment, the active material located on the inner side of the positive electrode sheet 11 is compressed, so that the content of active lithium is concentrated. According to the implementation method provided by an embodiment of the present invention, punching holes in the arc segment of the positive electrode sheet 11 can avoid the accumulation of active lithium ions in the arc segment, thereby reducing the risk of lithium precipitation. In addition, due to the presence of the fifth region 165, the stress on the inner side of the positive electrode sheet 11 can be released when winding the electrode sheet, avoiding excessive concentration of stress to cause powder loss, thereby causing local short circuit.

[0091] refer to Fig.12 , along the length direction of the positive electrode sheet 11, the two straight sections (the parts located in the flat portion 182) of the positive electrode sheet 11 are respectively connected to the two ends of the arc section (the part located in the curved portion 181), and the two edges of the fifth region 165 in the length direction of the positive electrode sheet 11 are respectively located in the two straight sections, that is, in the flat portion 182. The fifth region 165 on each arc section is at least partially located in the straight section 182, and the closer the arc section is to the outer circle, the less part of the fifth region 165 thereon is in the straight section 182. In this way, the amount of active lithium near the inner circle is less than the number of lithium insertion sites provided by the negative electrode sheet, thereby reducing the risk of lithium precipitation.

[0092] In some examples, reference Fig.13 , the holes 16 in the same area can be arranged nonlinearly, that is, the holes 16 are not arranged in rows or columns in the width direction and the length direction of the positive electrode sheet 11, that is, they are not arranged in a straight line. Reducing the arrangement requirements for the holes 16 can improve the process yield and avoid waste of resources. At the same time, the capillary effect of the holes 16 between different rows and columns can be increased by the misalignment of the holes 16, thereby increasing the wettability of the electrolyte to the positive electrode sheet 11, which is beneficial to the uniformity of the lithium ion transmission rate and avoids the local lithium ion enrichment causing lithium precipitation.

[0093] It should be noted that the spacing between adjacent rows or columns should not be too large, as too large a spacing will result in a weaker capillary effect. As an example, the offset distance may be less than 300 μm.

[0094] refer to Fig.14, the region extending in the length direction of the positive electrode sheet 11, that is, any one of the first region 161, the second region 162, the third region 163 and the fourth region 164, is divided into at least two sections arranged in the length direction of the positive electrode sheet 11 by at least one first stitching region 166. The region extending in the width direction of the positive electrode sheet 11, that is, the fifth region 165, is divided into at least two sections arranged in the width direction of the positive electrode sheet 11 by at least one second stitching region 167. The region extending in the length direction of the positive electrode sheet 11 and the region extending in the width direction of the positive electrode sheet 11 are separated by the third stitching region 168. By way of example only, the first stitching region 166 may have a size W3 along the length direction of the positive electrode sheet 11, the second stitching region has a size W4 along the width direction of the positive electrode sheet 11, and the third stitching region has a size W5 along the width direction of the positive electrode sheet 11, 0.1mm≤W3≤10mm, 0mm≤W4≤10mm, 0mm≤W5≤10mm. Preferably, 0.1mm≤W3≤3mm, 0mm≤W4≤3mm, 0mm≤W5≤3mm. Alternatively, W3 can be 0.5mm, 1mm, 3mm, 5mm, 7mm, 10mm; W4 can be 0.5mm, 1mm, 3mm, 5mm, 7mm, 10mm; W5 can be 0.5mm, 1mm, 3mm, 5mm, 7mm, 10mm. After the winding is completed, the paste on the outside of the arc segment in the negative electrode sheet 12 will be stretched, so that the thickness of the paste layer is lower than that of the inside, and the paste on the inside of the arc segment in the positive electrode sheet 11 will be compressed, so that the active lithium ions accumulate. According to the implementation method provided in the embodiment of the present invention, punching holes on the arc segment in the positive electrode sheet 11 can avoid the accumulation of active lithium ions, thereby reducing the risk of lithium precipitation. In addition, due to the presence of the splicing area, the stress on the inside of the positive electrode sheet 11 can be released when the electrode sheet is wound, avoiding excessive concentration of stress to cause powder loss, thereby causing local short circuit.

[0095] refer to Fig.15 , the negative electrode active layer 122 may be provided with a plurality of slots 124 arranged at intervals. For example, the plurality of slots 124 may extend along the length direction of the negative electrode sheet 12 and be spaced apart in the width direction of the negative electrode sheet 12. For another example, the plurality of slots 124 may also extend along the width direction of the negative electrode sheet 12 and be spaced apart in the length direction of the negative electrode sheet 12. By providing a plurality of slots 124 on the negative electrode active layer 122, the content of the residual electrolyte can be increased, thereby increasing the long cycle performance of the battery 100.

[0096] refer to Fig.15 and Fig.16, just by way of example, each groove 124 may have a groove depth H3, and two adjacent grooves 124 may have a spacing D7. The value range of the groove depth H3 may be 5μm≤H3≤30μm. The value range of the spacing D7 may be: 0.5mm≤D7≤5mm, preferably, 0.5mm≤D7≤1.5mm. Alternatively, D7 may be 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, H3 is the groove depth of the plurality of grooves 124, and D7 is the groove spacing of the plurality of grooves 124. By satisfying the above range of the groove depth H3 and the spacing D7, it is possible to ensure that lithium ions can be transmitted faster, while ensuring the number of lithium insertion sites of the negative electrode sheet 12 to avoid lithium precipitation.

[0097] In some possible examples, the material of the positive electrode active layer may include one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium titanate, ternary (lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide), lithium iron manganese phosphate, lithium-rich manganese-based materials, etc. The material of the negative electrode active layer includes: one or more of graphite and silicon-based materials. Graphite may include one or more of artificial graphite and natural graphite. Silicon-based materials may include one or more of silicon carbon, silicon oxygen, silicon element, and silicon alloy. In the case where the material of the negative electrode active layer contains silicon, the content of silicon element may be 3 to 30wt%. By doping with silicon element, the number of active sites where lithium ions can be embedded in the negative electrode sheet can be increased, and the battery capacity can be increased. At the same time, by setting the positive electrode to contain a recess, the lithium precipitation problem caused by the silicon negative electrode can be reduced.

[0098] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0099] Example 1

[0100] (1) Preparation of positive electrode sheet

[0101] Lithium cobalt oxide powder, polyvinylidene fluoride, acetylene black and carbon nanotubes are put into a vacuum mixer in a mass ratio of 96:2:1.5:0.5, and N-methylpyrrolidone (NMP) is added. They are fully mixed under vacuum stirring until a uniform and fluid positive electrode slurry is formed, in which the solid content is 55wt%; the above positive electrode slurry is evenly coated on a 12μm thick carbon-coated aluminum foil with a single-side surface density of 11mg / cm2. After drying and roller pressing, the active material thickness is controlled to 70μm, and then cut, scraped and laser punched to obtain a positive electrode sheet.

[0102] (2) Preparation of negative electrode sheet

[0103] The negative electrode main material (graphite, silicon carbon), styrene butadiene rubber, sodium carboxymethyl cellulose, and acetylene black were put into a vacuum mixer according to a mass ratio of 96.5:1:1:1.5, and deionized water was added. The mixture was fully mixed under the action of the vacuum mixer to finally form a uniform and fluid negative electrode slurry with a solid content of 45wt%. The negative electrode slurry was evenly coated on a copper foil with a thickness of 6μm, and the coating single-side surface density was 5mg / cm 2 After drying and roller pressing, the thickness of the active material is controlled to be 35 μm, cut and laser cleaned to obtain a negative electrode sheet with a silicon-based material content of 3.03 wt%.

[0104] (3) Preparation of electrolyte

[0105] In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and ethyl propionate (EP) are mixed evenly in a mass ratio of 2:9:9, and fully dried lithium hexafluorophosphate (LiPF6) and bis(fluorosulfonyl)imide lithium salt LiFSI are added thereto for stirring and dissolution. The mass proportions of LiPF6 and LiFSI are 6.5% and 10%, respectively, based on the total mass of the electrolyte. 2.5% of vinylene carbonate (VC) based on the total mass of the electrolyte is added, 0.5% of vinyl sulfite (ES), 0.5% of thiophene, and 0.5% of vinyl sulfate (DTD) based on the total mass of the electrolyte are added, and 1.0% of lithium difluorophosphate LiPO2F2 based on the total mass of the electrolyte is added, stirred evenly, and the electrolyte is obtained after passing the physical property test.

[0106] (4) Preparation of batteries

[0107] The positive electrode sheet obtained in step (2), the negative electrode sheet obtained in step (3) and the isolation film (PP) are wound to obtain a bare battery cell; the bare battery cell is welded with a pole ear and placed in a battery casing, and the electrolyte prepared in step (3) is injected into the dried and qualified battery cell, and a battery is obtained after standing, aging, formation, exhaust, aging, sorting and other processes.

[0108] Among them, the first region extends along the length direction of the positive electrode sheet 11 and the spacing D1 between the first region and the pole ear groove is 0.79mm, the dimension D2 of the transition zone between the orthographic projection of each second groove edge on the first positive electrode active layer and the first groove edge on the same side of the pole ear groove in the length direction of the positive electrode sheet 11 is 0.51mm, D1 / D2 is 1.549, the spacing D3 between the second region of the second positive electrode active layer and the exposed groove is 0.28mm, the distance D4 from the first region to the active layer edge of the first positive electrode active layer is 2.63mm, the dimension W1 of the positive electrode sheet in its width direction is 63mm, the dimension W2 of the first region in the width direction of the positive electrode sheet is 7.89mm, W2 / W1 is 1 / 8, the depth H1 of the first concave portion is 15.1μm, and the distribution density τ1 of the concave portion is 65 / mm 2 The depth H2 of the solder joint is 279 μm, H2 / H1 is 18.48, and the distribution density τ2 of the solder joint is 31 / mm 2 The area S1 of the first region covered by the first tape is 249.76 mm 2 The overlap area S2 of the orthographic projection of the part of the second tape outside the receiving recess on the positive electrode sheet and the first area is 250.78 mm 2 , the distance D6 between the edge of the second tape and its corresponding area on the positive electrode sheet is 3.4mm, the dimension W3 of the splicing area between the first areas along the length direction of the positive electrode sheet 11 is 0.17mm, the dimension W4 of the second splicing area between the fifth areas along the width direction of the positive electrode sheet 11 is 0.17mm, and the dimension W5 of the third splicing area between the first area and the fifth area along the width direction of the positive electrode sheet 11 is 0.17mm. The groove depth H3 of the groove on the negative electrode active layer is 5.3μm, and the groove spacing D7 is 0.5mm.

[0109] (5) Test battery

[0110] (i) Short-term autopsy

[0111] Use a battery cycle tester to perform charge and discharge cycles on the battery. The specific steps are as follows:

[0112] ①Let stand for 10 minutes;

[0113] ②0.2C discharge to voltage 3V, let stand for 10 minutes;

[0114] ③1C fully charged, cut off 0.05C, let stand for 10 minutes;

[0115] ④1C discharge to voltage 3V, let stand for 10min;

[0116] ⑤ Repeat steps ③ to ④ 20 times;

[0117] ⑥1C fully charged, to the cut-off current 0.05C.

[0118] After completing the above charge and discharge cycles, the battery is dissected. If the surface of the negative electrode is golden yellow, without black spots and no obvious color unevenness, it means that there is no lithium deposition. If there are obvious black spots on the surface of the negative electrode, it means that lithium deposition has occurred.

[0119] (ii) Battery capacity test

[0120] Use a battery capacity tester to charge and discharge the battery (charge and discharge at 0.2C, cut-off voltage is 4.4V), and the battery capacity test result obtained by the final instrument is the test result.

[0121] (iii) Welding tensile test

[0122] Use a universal mechanical testing machine to perform welding tensile tests on the pole lugs and pole pieces. The specific steps are as follows:

[0123] ① Remove the positive electrode sheet that has been welded and not affixed with protective glue at the welding station, and cut the positive electrode sheet with ceramic scissors. The cut sample is a square with a width greater than 24mm, and the positive electrode ear remains intact in the sample;

[0124] ② From the side where the positive ear is not welded, stick a 24±1mm transparent tape to the position where the projection of the positive ear is located. The width of the tape is 24±1mm. Align the tape with the positive ear on the side away from the edge of the positive electrode sheet to prevent the positive electrode sheet from being pulled off before the weld on the positive ear slot during the test;

[0125] ③Set the instrument lifting speed to 400mm / min;

[0126] ④ One end of the universal mechanical testing machine fixed frame clamps the exposed end of the positive electrode ear, and the other end clamps on the positive electrode sheet to ensure that the sample surface is flat;

[0127] ⑤ Start the test and stop when the positive ear and the positive plate are completely separated. The maximum tensile force displayed is the welding tensile force. If the tensile test result is: welding tensile force ≥ 15N, it means the battery is qualified.

[0128] Example 1-2

[0129] The difference from Example 1-1 is that the first region extends along the length direction of the positive electrode sheet 11 and the spacing D1 between the first region and the pole ear groove is 3.98 mm, the transition zone between the orthographic projection of each second groove edge on the first positive electrode active layer and the first groove edge on the same side of the pole ear groove has a dimension D2 of 1.45 mm in the length direction of the positive electrode sheet 11, D1 / D2 is 2.745, the spacing D3 between the second region of the second positive electrode active layer and the exposed groove is 2.53 mm, the dimension W3 of the splicing region between the first regions along the length direction of the positive electrode sheet 11 is 1.45 mm, the dimension W4 of the second splicing region between the fifth regions along the width direction of the positive electrode sheet 11 is 1.45 mm, and the dimension W5 of the third splicing region between the first region and the fifth region along the width direction of the positive electrode sheet 11 is 1.45 mm. The groove depth H3 of the groove on the negative electrode active layer is 16.4 μm, and the groove spacing D7 is 2.6 mm. The content of silicon-based material is 9.67wt%.

[0130] Examples 1-3

[0131] The difference from Example 1-1 is that the first region extends along the length direction of the positive electrode sheet 11 and the spacing D1 between the first region and the pole ear groove is 7.47 mm, the transition zone between the orthographic projection of each second groove edge on the first positive electrode active layer and the first groove edge on the same side of the pole ear groove has a dimension D2 of 2.50 mm in the length direction of the positive electrode sheet 11, D1 / D2 is 2.988, the spacing D3 between the second region of the second positive electrode active layer and the exposed groove is 4.97 mm, the dimension W3 of the splicing region between the first regions along the length direction of the positive electrode sheet 11 is 2.98 mm, the dimension W4 of the second splicing region between the fifth regions along the width direction of the positive electrode sheet 11 is 2.98 mm, and the dimension W5 of the third splicing region between the first region and the fifth region along the width direction of the positive electrode sheet 11 is 2.98 mm. The groove depth H3 of the groove on the negative electrode active layer is 29.7 μm, and the groove spacing D7 is 4.9 mm. The content of silicon-based material is 29.95wt%.

[0132] Examples 1-4

[0133] The difference from Example 1-1 is that the first region extends along the length direction of the positive electrode sheet 11 and the spacing D1 between the first region and the pole ear groove is 14.97 mm, the transition zone between the orthographic projection of each second groove edge on the first positive electrode active layer and the first groove edge on the same side of the pole ear groove has a dimension D2 of 4.99 mm in the length direction of the positive electrode sheet 11, D1 / D2 is 3.0, the spacing D3 between the second region of the second positive electrode active layer and the exposed groove is 9.97 mm, the dimension W3 of the splicing region between the first regions along the length direction of the positive electrode sheet 11 is 9.97 mm, the dimension W4 of the second splicing region between the fifth regions along the width direction of the positive electrode sheet 11 is 9.97 mm, and the dimension W5 of the third splicing region between the first region and the fifth region along the width direction of the positive electrode sheet 11 is 9.97 mm. The groove depth H3 of the groove on the negative electrode active layer is 7.8 μm, and the groove spacing D7 is 1.1 mm. The content of silicon-based material is 17.89wt%.

[0134] Examples 1-5

[0135] The difference from Example 1-1 is that the first region extends along the length direction of the positive electrode sheet 11 and the spacing D1 between the first region and the pole ear groove is 12.86 mm, the dimension D2 of the transition zone between the orthographic projection of each second groove edge on the first positive electrode active layer and the first groove edge on the same side of the pole ear groove in the length direction of the positive electrode sheet 11 is 2.89 mm, D1 / D2 is 4.45, the spacing D3 between the second region of the second positive electrode active layer and the exposed groove is 9.97 mm, the dimension W3 of the splicing region between the first regions along the length direction of the positive electrode sheet 11 is 19.78 mm, the dimension W4 of the second splicing region between the fifth regions along the width direction of the positive electrode sheet 11 is 19.78 mm, and the dimension W5 of the third splicing region between the first region and the fifth region along the width direction of the positive electrode sheet 11 is 19.78 mm. The groove depth H3 of the groove on the negative electrode active layer is 24.6 μm, and the groove spacing D7 is 4.1 mm. The content of silicon-based material is 24.46wt%.

[0136] Example 2-1

[0137] The difference from Example 1-2 is that the first region extends along the length direction of the positive electrode sheet 11 and the spacing D1 between the first region and the pole lug groove is 0.33 mm, the dimension D2 of the transition zone between the orthographic projection of each second groove edge on the first positive electrode active layer and the first groove edge on the same side of the pole lug groove in the length direction of the positive electrode sheet 11 is 0.15 mm, D1 / D2 is 2.2, and the spacing D3 between the second region of the second positive electrode active layer and the exposed groove is 0.18 mm.

[0138] Example 3-1

[0139] The difference from Example 1-2 is that the dimension D2 of the transition zone between the orthographic projection of each second groove edge on the first positive electrode active layer and the first groove edge on the same side of the electrode tab groove in the length direction of the positive electrode sheet 11 is 0.41 mm, D1 / D2 is 9.707, and the spacing D3 between the second area of ​​the second positive electrode active layer and the exposed groove is 3.57 mm.

[0140] Example 3-2

[0141] The difference from Example 1-2 is that D2 is 6.97 mm, D1 / D2 is 2.148, and the distance D3 between the second region of the second positive electrode active layer and the exposed groove is 8.0 mm.

[0142] Example 4-1

[0143] The difference from Example 1-2 is that D4 is 0.01 mm.

[0144] Example 4-2

[0145] The difference from Example 1-2 is that D4 is 0.17 mm.

[0146] Example 4-3

[0147] The difference from Example 1-2 is that D4 is 4.98 mm.

[0148] Example 4-4

[0149] The difference from Example 1-2 is that D4 is 7.15 mm.

[0150] Embodiment 4-5

[0151] The difference from Example 1-2 is that D4 is 9.83 mm.

[0152] Embodiment 4-6

[0153] The difference from Example 1-2 is that D4 is 11.07 mm.

[0154] Example 5-1

[0155] The difference from Example 1-2 is that W2 is 1.83 mm and W2 / W1 is 2 / 69.

[0156] Example 5-2

[0157] The difference from Example 1-2 is that W2 is 2.12 mm and W2 / W1 is 3 / 89.

[0158] Example 5-3

[0159] The difference from Example 1-2 is that W2 is 19.97 mm and W2 / W1 is 13 / 41.

[0160] Example 5-4

[0161] The difference from Example 1-2 is that W2 is 21.06 mm and W2 / W1 is 1 / 3.

[0162] Example 6-1

[0163] The difference from Example 1-2 is that H1 is 4.67 μm.

[0164] Example 6-2

[0165] The difference from Example 1-2 is that H1 is 5.01 μm.

[0166] Example 6-3

[0167] The difference from Example 1-2 is that H1 is 29.6 μm.

[0168] Example 6-4

[0169] The difference from Example 1-2 is that H1 is 31.4 μm.

[0170] Example 7-1

[0171] The difference from Example 1-2 is that H2 is 27.5 μm.

[0172] Example 7-2

[0173] The difference from Example 1-2 is that H2 is 30.4 μm.

[0174] Example 7-3

[0175] The difference from Example 1-2 is that H2 is 150 μm.

[0176] Example 7-4

[0177] The difference from Example 1-2 is that H2 is 499.6 μm.

[0178] Example 7-5

[0179] The difference from Example 1-2 is that H2 is 510.7 μm.

[0180] Example 8-1

[0181] The difference from Example 1-2 is that τ1 is 8 pieces / mm 2 .

[0182] Example 8-2

[0183] The difference from Example 1-2 is that τ1 is 10 pieces / mm 2 .

[0184] Example 8-3

[0185] The difference from Example 1-2 is that τ1 is 119 pieces / mm 2 .

[0186] Example 8-4

[0187] The difference from Example 1-2 is that τ1 is 134 pieces / mm 2 .

[0188] Example 9-1

[0189] The difference from Example 1-2 is that τ2 is 3 pieces / mm 2 .

[0190] Example 9-2

[0191] The difference from Example 1-2 is that τ2 is 5 pieces / mm 2 .

[0192] Example 9-3

[0193] The difference from Example 1-2 is that τ2 is 63 pieces / mm 2 .

[0194] Example 9-4

[0195] The difference from Example 1-2 is that τ2 is 71 pieces / mm 2 .

[0196] Example 10-1

[0197] The difference from Example 1-2 is that D5 is 98.1 μm.

[0198] Example 10-2

[0199] The difference from Example 1-2 is that D5 is 101.3 μm.

[0200] Example 10-3

[0201] The difference from Example 1-2 is that D5 is 299.7 μm.

[0202] Example 10-4

[0203] The difference from Example 1-2 is that D5 is 320.4 μm.

[0204] Example 11-1

[0205] The difference from Example 1-2 is that S1 is 499.84 mm 2 .

[0206] Example 11-2

[0207] The difference from Example 1-2 is that S1 is 510.7 mm 2 .

[0208] Example 11-3

[0209] The difference from Example 1-2 is that S1 is 0.01 mm 2 .

[0210] Example 12-1

[0211] The difference from Example 1-2 is that S2 is 0.03 mm 2 .

[0212] Example 12-2

[0213] The difference from Example 1-2 is that S2 is 499.65 mm 2 .

[0214] Example 12-3

[0215] The difference from Example 1-2 is that S2 is 520.11 mm 2 .

[0216] Example 13-1

[0217] The difference from Example 1-2 is that D6 is 4.97 mm.

[0218] Example 13-2

[0219] The difference from Example 1-2 is that D6 is 9.89 mm.

[0220] Example 13-3

[0221] The difference from Example 1-2 is that D6 is 19.69 mm.

[0222] Example 13-4

[0223] The difference from Example 1-2 is that D6 is 23.11 mm.

[0224] Comparative Example 1

[0225] The difference from Example 1-2 is that the first recess is not provided.

[0226] Comparative Example 2

[0227] The difference from Example 1-2 is that D1 is 0.03 mm, D2 is 0.01 mm, D1 / D2 is 3, and D3 is 0.02 mm. Table 1 Test results of the electrode assembly in the embodiment

[0228] It should be noted that before conducting short-term dissection and battery capacity testing, it is necessary to ensure that the batteries involved in the test are qualified batteries. If the batteries involved in the test do not meet this condition, short-term dissection and battery capacity testing will not be performed on them, which is reflected in Table 1 as no data, represented by “ / ”.

[0229] Several groups of embodiments are specifically described below: in Embodiment 2-1, the tab groove area of ​​the battery is easily broken, so the battery is unqualified; in Embodiment 4-1, the positive electrode sheet is severely broken, so the battery is unqualified; the welding tensile test result of the battery in Embodiment 7-1 is unqualified, so the battery is unqualified; in Embodiment 7-5, the tab is broken during welding, so the battery is unqualified; the welding tensile test result of the battery in Embodiment 9-1 is unqualified, so the battery is unqualified; in Embodiment 9-4, the tab is broken during welding, so the battery is unqualified; in Embodiment 11-3, the tab glue of some battery cells falls off; in Embodiment 12-1, the battery cell is short-circuited, so the battery is unqualified; the welding tensile test result of the battery in Comparative Example 2 is unqualified, so the battery is unqualified.

[0230] It should be understood that the term "including" and its variations used in the embodiments of the present invention are open inclusions, i.e., "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "plurality" means "more than one", which is intended to cover two, three or more situations.

[0231] It should be understood that although the terms "first" or "second" etc. may be used in embodiments of the present invention to describe various elements, for example, a first positive electrode active layer and a second positive electrode active layer, these elements are not defined by these terms, which are only used to distinguish one element from another. The protection scope of the embodiments of the present invention is not limited to the above embodiments. Any changes or substitutions that can be thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention. Therefore, the protection scope of the embodiments of the present invention should be based on the protection scope of the claims.

Claims

1. An electrode assembly, characterized in that: It includes a positive electrode sheet, a separator and a negative electrode sheet which are stacked and wound, the positive electrode sheet includes a positive electrode collector and a positive electrode active layer, the positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer which are arranged on opposite sides of the positive electrode collector in the thickness direction, the first positive electrode active layer is provided with a pole lug groove and at least one first recessed portion, the at least one first recessed portion is distributed in a first region of the first positive electrode active layer, a positive pole lug is arranged in the pole lug groove, the positive pole lug is electrically connected to the positive electrode collector, the positive electrode sheet has a first pole sheet edge and a second pole sheet edge in the width direction thereof, the pole lug groove, the first region and the first pole sheet edge are arranged on the same side in the width direction of the positive electrode sheet, the first region extends along the length direction of the positive electrode sheet and is spaced D1 from the pole lug groove, and D1≥0.2mm.

2. The electrode assembly according to claim 1, characterized in that: The second positive electrode active layer is provided with an exposed groove and at least one second recessed portion, the at least one second recessed portion is distributed in the second region of the second positive electrode active layer, the exposed groove, the second region and the first electrode sheet edge are arranged on the same side in the width direction of the positive electrode sheet, the pole tab groove has two first groove edges in the length direction of the positive electrode sheet, the exposed groove has two second groove edges in the length direction of the positive electrode sheet, the orthographic projections of the two second groove edges on the first positive electrode active layer are respectively located on the outsides of the two first groove edges, and each second groove edge has a transition zone between its orthographic projection on the first positive electrode active layer and the first groove edge located on the same side of the pole tab groove.

3. The electrode assembly according to claim 2, characterized in that: The transition zone has a dimension D2 in the length direction of the positive electrode sheet, wherein D1≥D2, preferably, 1.1≤D1 / D2≤10.

4. The electrode assembly according to claim 3, characterized in that: There is a distance D3 between the second area and the exposed groove, 0.5 mm≤D1≤15 mm, 0.5 mm≤D2≤5 mm, 0.2 mm≤D3≤10 mm.

5. The electrode assembly according to claim 2, characterized in that: A first groove edge of the electrode tab groove on a first side in the length direction of the positive electrode sheet is spaced from the first region by a distance D11, and a first groove edge of the electrode tab groove on a second side in the length direction of the positive electrode sheet is spaced from the first region by a distance D12, |D11-D12|≤10; and / or The second groove edge located on the first side of the exposed groove in the length direction of the positive electrode sheet has a distance D31 from the second area, and the second groove edge located on the second side of the exposed groove in the length direction of the positive electrode sheet has a distance D32 from the second area, |D31-D32|≤10.

6. The electrode assembly according to claim 1, characterized in that: 1 / 35≤W2 / W1≤1 / 2; and / or 2mm≤W2≤20mm; and / or 0.1mm≤D4≤10mm, Among them, W1 is the size of the positive electrode sheet in its width direction, W2 is the size of the first region in the width direction of the positive electrode sheet, and D4 is the distance from the first region to the edge of the active layer of the first positive electrode active layer, and the edge of the active layer is closer to the edge of the first electrode sheet than the edge of the second electrode sheet.

7. The electrode assembly according to claim 6, characterized in that: The positive electrode tab is welded to the positive electrode current collector and has a plurality of welding points, the at least one first recess includes a plurality of first recesses, and the plurality of welding points and the plurality of first recesses satisfy: 5μm≤H1≤30μm; and / or 30μm≤H2≤500μm; and / or 1≤H2 / H1≤100; and / or 100 μm ≤ D5 ≤ 300 μm; and / or τ1 ≥ τ2; and / or 9 pieces / mm 2 ≤τ1≤120pcs / mm 2 ; and / or 4pcs / mm 2 ≤τ2≤64pcs / mm 2 ; Among them, H1 is the depth of the multiple first recesses, H2 is the depth of the multiple solder joints, D5 is the spacing between the multiple first recesses, τ1 is the distribution density of the multiple first recesses, and τ2 is the distribution density of the multiple solder joints.

8. The electrode assembly according to claim 7, characterized in that: It also includes a first tape, which covers the positive electrode ear and part of the first region, and the area of ​​the first region covered by the first tape is S1, 0.1mm 2 ≤S1≤500mm 2 .

9. The electrode assembly according to claim 8, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer, the negative electrode active layer comprises a receiving recess, and the positive projection of the positive electrode tab on the negative electrode sheet at least partially overlaps with the receiving recess, The orthographic projection of the first region on the negative electrode sheet is located outside the receiving recess.

10. The electrode assembly according to claim 9, characterized in that: The negative electrode sheet further includes a second adhesive tape, wherein: The second adhesive tape is located in the receiving recess; or The second tape is partially located outside the receiving recess, and the orthographic projection of the portion of the second tape located outside the receiving recess on the positive electrode sheet partially overlaps with the first region and has an overlapping area S2, 0.1 mm 2 ≤S2≤500mm 2 .

11. The electrode assembly according to claim 1, characterized in that: The positive electrode sheet also includes a third tape, the orthographic projection of the negative electrode ear of the negative electrode sheet on the positive electrode sheet falls on the first area, the third tape is arranged at a position of the positive electrode sheet corresponding to the negative electrode ear, the orthographic projection of the third tape on the positive electrode sheet overlaps with the orthographic projection of the negative electrode ear on the positive electrode sheet, and the overlapping part covers a part of the first area.

12. The electrode assembly according to claim 11, characterized in that: The third tape has a first tape edge and a second tape edge along the width direction of the positive electrode sheet, the first tape edge extends outwardly beyond the positive electrode sheet in the width direction of the positive electrode sheet, the second tape edge extends inwardly beyond the corresponding area in the width direction of the positive electrode sheet, and the second tape edge has a spacing D6 with the corresponding area, D6≤20mm.

13. The electrode assembly according to claim 1, characterized in that ； The first positive electrode active layer is further provided with a third region, the third region is provided with at least one third recess, the third region extends along the length direction of the positive electrode sheet, and the third region is closer to the edge of the second electrode sheet than the edge of the first electrode sheet; and / or The second positive electrode active layer is further provided with a fourth region, in which at least one third recess is provided. The fourth region extends along the length direction of the positive electrode sheet, and the fourth region is closer to the edge of the second electrode sheet than the edge of the first electrode sheet.

14. The electrode assembly according to claim 1, characterized in that The electrode assembly has a flat portion and a curved portion, the positive electrode sheet includes an arc segment located in the curved portion, the positive electrode active layer is provided with a fifth region, at least one fifth recess is provided in the fifth region, and the fifth region is at least partially provided in the arc segment.

15. The electrode assembly according to claim 14, characterized in that: The positive electrode sheet also includes a straight section located in the flat portion, and the two straight sections are respectively connected to the two ends of the arc section along the length direction of the positive electrode sheet, and the two edges of the fifth region in the length direction of the positive electrode sheet are respectively located in the two straight sections.

16. The electrode assembly according to claim 14, characterized in that: The first region is divided into at least two sections arranged along the length direction of the positive electrode sheet by at least one first splicing region; and / or The fifth region is divided into at least two sections arranged along the width direction of the positive electrode sheet by at least one second splicing region; and / or The first area and the fifth area are separated by a third splicing area.

17. The electrode assembly according to claim 16, characterized in that: The first splicing area has a size W3 along the length direction of the positive electrode sheet, 0.1mm≤W3≤20mm; and / or The second splicing area has a size W4 along the width direction of the positive electrode sheet, 0mm≤W4≤20mm; and / or The third splicing area has a size W5 along the width direction of the positive electrode sheet, 0mm≤W5≤20mm.

18. The electrode assembly according to claim 1, characterized in that The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer which are stacked, and the negative electrode active layer is provided with a plurality of slots which are arranged at intervals.

19. The electrode assembly according to claim 18, characterized in that: 5μm≤H3≤30μm; and / or 0.5mm≤D7≤5mm, Among them, H3 is the groove depth of the plurality of grooves, and D7 is the groove spacing of the plurality of grooves.

20. The electrode assembly according to claim 1, characterized in that The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer which are stacked; the negative electrode active layer comprises a negative electrode active material, and the negative electrode active material comprises one or more of graphite and silicon-based materials. Preferably, the negative electrode active material comprises a silicon-based material, and the silicon-based material accounts for 3 to 30 wt % of the negative electrode active material.

21. A lithium ion secondary battery, characterized in that: The battery comprises the electrode assembly according to any one of claims 1 to 20.

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