Wound core structure and battery

Abstract

The present application discloses a wound core structure and a battery. In the wound core structure, a head wound layer of a positive electrode sheet comprises a first layer segment and a second layer segment, the first layer segment is located at the initial wound end of the positive electrode sheet, and the second layer segment is connected to the first layer segment and folded back relative to the first layer segment; a negative electrode sheet comprises a third layer segment located at the initial wound end of the negative electrode sheet, and the third layer segment is stacked between the first layer segment and the second layer segment; and the head of the third layer segment is provided with a single-sided coating area having a folded-back structure, the single-sided coating area comprises a first single-sided area and a second single-sided area, and an exposed current collector side surface in the first single-sided area and an exposed current collector side surface in the second single-sided area are stacked and in contact with each other. According to the present application, the single-sided coating area having the folded-back structure can ensure that the head of the negative electrode sheet is inserted into the deep bend of the head wound layer of the positive electrode sheet, and can achieve a good filling effect, thereby reducing the risk of fracture at the bending portion of the positive electrode sheet and improving the safety performance of the battery.

Description

A winding core structure and battery Technical Field

[0001] The present application relates to the technical field of battery manufacturing, and in particular to a winding core structure and a battery provided with the winding core structure.

[0002] Background of the Invention

[0003] Lithium-ion batteries are increasingly used in portable devices. As portable devices become more intelligent and multifunctional, batteries require higher energy density. In conventional spiral-wound batteries, the negative electrode sheet located in the innermost circle of the winding structure has a large portion that is not coated with active material, thus limiting the improvement of the battery's energy density. In contrast, spiral-wound batteries with a plug-in spiral structure are increasingly attracting attention because the negative electrode sheet in the innermost circle of the winding structure is double-sided coated, allowing the active material on both sides to be used.

[0004] However, the interleaved winding structure has significant drawbacks. As shown in Figure 1, in a wound battery with an interleaved winding structure, the innermost ring of the positive electrode sheet comprises a first layer segment 21' and a connected second layer segment 22'. The winding of the negative electrode sheet begins with a third layer segment 11' coated on both sides with active material. This third layer segment 11' comprises a current collector 11a and active material layers 11b on either side of the current collector 11a. This third layer segment 11' is located between the first layer segment 21' and the second layer segment 22'. Due to the high compaction density and brittleness of the positive electrode sheet, the head of the negative electrode sheet (i.e., the third layer segment 11') cannot be fully inserted into the deep bend where the first layer segment 21' and the second layer segment 22' of the positive electrode sheet meet, thereby forming a "cavity Q" (the cavity size L in Figure 1 is greater than zero). As a result, when the battery cell is hot-pressed, the position where the cavity Q is located is compressed to form a "sharp corner", and the curling stress of the positive electrode sheet becomes larger, resulting in easy breakage at the bend, causing the battery capacity to decrease. In addition, there are safety risks such as puncturing the diaphragm at the break, causing short circuit and even fire.

[0005] Summary of the Invention

[0006] In view of this, the purpose of the present application is to provide a winding core structure and a battery provided with the winding core structure, which can reduce the risk of fracture at the bending point of the positive electrode sheet and improve the safety performance of the battery.

[0007] The present application provides a winding core structure, including a positive electrode sheet and a negative electrode sheet, wherein the head coil layer of the positive electrode sheet includes a first layer segment and a second layer segment, the first layer segment is located at the initial end of the winding of the positive electrode sheet, and the second layer segment is connected to the first layer segment and folded back relative to the first layer segment; the negative electrode sheet includes a third layer segment located at the initial end of the winding of the negative electrode sheet, and the third layer segment is stacked between the first layer segment and the second layer segment; the head of the third layer segment is provided with a single-sided coating area with a folded structure, and the single-sided coating area includes a first single-sided area and a second single-sided area, and the exposed collector side of the first single-sided area and the exposed collector side of the second single-sided area are stacked and contacted.

[0008] Optionally, in the above-mentioned winding core structure, the second single-sided area is connected to the double-sided coated area of ​​the negative electrode sheet, and the X-direction dimension W2 of the second single-sided area is less than or equal to the X-direction dimension W of the head ring layer of the positive electrode sheet.

[0009] Optionally, in the above-mentioned winding core structure, the X-direction dimension W1 of the first single-sided area is less than or equal to the X-direction dimension W of the positive electrode sheet head layer; and / or, the X-direction dimension W1 of the first single-sided area is less than or equal to or greater than the X-direction dimension W2 of the second single-sided area.

[0010] Optionally, in the above-mentioned core structure, the third layer segment further includes a double-sided coating area connected to the second single-sided area.

[0011] Optionally, in the above-mentioned core structure, the junction of the first single-sided area and the second single-sided area constitutes a folding position, wherein: the gap distance between the head end of the single-sided area of ​​the first single-sided area away from the folding position and the active coating of the double-sided coating area is greater than or equal to zero; or, the first single-sided area partially overlaps with the double-sided coating area.

[0012] Optionally, the above-mentioned core structure further includes a filling layer, wherein the filling layer is located between the first single-sided area and the second single-sided area.

[0013] Optionally, in the above-mentioned core structure, the filling layer is a single-layer structure or a multi-layer folded structure.

[0014] Optionally, in the above-mentioned core structure, the filling layer includes any one or more combinations of adhesive paper, ceramic layer, rubber, and foam.

[0015] Optionally, the above-mentioned core structure further includes an insulating layer, which is located between the first layer segment and the third layer segment and is connected to the first layer segment; the projections of the single-sided area head end of the first single-sided area away from the folding position, and the junction of the double-sided coating area of ​​the third layer segment and the second single-sided area on the first layer segment all fall within the area where the insulating layer is located.

[0016] Optionally, in the above-mentioned core structure, the insulating layer includes a first side and a second side: the first side is located between the double-sided coating area of ​​the third layer segment and the first layer segment, and the distance M2 between the junction of the double-sided coating area and the second single-sided area and the first side is ≥0.5mm; and / or, the second side is located between the first single-sided area and the first layer segment, and the distance M3 between the head end of the single-sided area and the second side is ≥0.5mm.

[0017] Optionally, in the above-mentioned core structure, the insulating layer includes any one or more combinations of single-sided adhesive tape, double-sided adhesive tape, and ceramic coating.

[0018] Optionally, in the above-mentioned winding core structure, a groove is provided on the side of the first layer segment opposite to the insulating layer; the projections of the head end of the single-sided area and the junction of the double-sided coated area of ​​the negative electrode sheet and the second single-sided area on the first layer segment all fall within the groove.

[0019] Optionally, in the above winding core structure, the projection of the groove in the thickness direction of the first layer segment falls within the projection range of the insulating layer in the same direction.

[0020] Optionally, in the above winding core structure, in any direction perpendicular to the thickness direction of the first layer segment, a distance M1 between a side profile of the insulating layer and a notch profile of the groove is ≥0.1 mm.

[0021] Optionally, in the above-mentioned winding core structure, the depth D1 of the groove in the thickness direction of the pole piece is not greater than the thickness D of the single-sided active coating of the first layer segment.

[0022] Optionally, the third layer segment includes a first fold segment and a first extension segment, and the negative electrode sheet further includes a second fold segment, wherein the first fold segment, the first extension segment and the second fold segment are connected in sequence along the winding direction; the first fold segment is coated with a first active material layer on the side close to the positive electrode sheet; one end of the first fold segment is connected to the first extension segment, and the other end is located on the first side of the first extension segment; one end of the second fold segment is connected to the first extension segment, and the other end is located on the second side of the first extension segment.

[0023] Optionally, the length of the first folded section in the X direction is L2; ​​the total length of the first extension section and the second folded section in the X direction is L1; L1=(0.02-0.8)(L1+L2).

[0024] Optionally, the first layer segment includes a third extension segment, the second layer segment includes a third bend segment and a fourth extension segment, and the positive electrode sheet also includes a fourth bend segment, wherein the third extension segment, the third bend segment, the fourth extension segment and the fourth bend segment are connected in sequence along the winding direction; the third extension segment and the fourth extension segment are respectively located on the first side and the second side of the first extension segment; the third bend segment and the fourth bend segment are respectively located on the winding outside of the first bend segment and the second bend segment.

[0025] Optionally, a first insulating member is provided on a side of the fourth extension segment close to the first extension segment; and the projection of the head end of the negative electrode sheet on the fourth extension segment is located within a projection area of ​​the first insulating member in the same direction.

[0026] Optionally, the first fold back section is a single-sided coating structure, and the first extension section is a double-sided coating structure; the projection of the junction of the single-sided coating structure of the first fold back section and the double-sided coating structure of the first extension section on the fourth extension section is located within the projection area of ​​the first insulating part in the same direction.

[0027] Optionally, a gap distance L5 between the joint and the head end of the negative electrode sheet in the X direction is greater than or equal to zero.

[0028] Optionally, a gap between a projection of the first insulating member on the fourth extending segment and a projection of the third folded segment in the same direction is greater than or equal to zero.

[0029] Optionally, the head end and / or tail end of the negative electrode sheet is wrapped with a second insulating member.

[0030] Optionally, the second insulating member includes a coating area and an extension area, wherein: the coating area covers the first side and the second side of the negative electrode sheet, and the length of the coating area in the X direction is L4, L4 ≥ 1.5 mm; the extension area is located at the end of the negative electrode sheet and extends along the X direction, and the length of the extension area in the X direction is L3, L3 ≥ 0.2 mm.

[0031] Optionally, the winding core structure further includes a diaphragm; and the offset length between the winding starting end of the diaphragm and the second insulating member is less than or equal to 1 mm.

[0032] The present application also provides a battery provided with the winding core structure described in any of the above embodiments.

[0033] As can be seen from the above technical solution, in the winding core structure provided by the present invention, the first single-sided area and the second single-sided area at the head of the negative electrode sheet form a folded structure. On the one hand, this folded structure can increase the thickness of the negative electrode sheet head compared to the single-sided coated area of ​​the single-layer structure, thereby enhancing the filling effect on the inner side of the bend at the junction of the first and second layer sections of the positive electrode sheet. This helps to prevent the bend at the junction of the first and second layer sections of the positive electrode sheet from being compressed during hot pressing to form a "sharp corner", thereby avoiding the problem of excessive curling stress on the positive electrode sheet causing the bend to break. On the other hand, since the curved surface head end formed by the folding structure (i.e., the folding position at the head of the negative electrode sheet) is similar to the curved surface structure on the inner side of the bend at the connection between the first and second layers of the positive electrode sheet, it can enhance the filling effect on the inner side of the bend at the connection between the first and second layers of the positive electrode sheet. At the same time, it also facilitates the complete insertion of the head of the negative electrode sheet into the deep bend at the connection between the first and second layers of the positive electrode sheet, avoiding the formation of a cavity, which is conducive to avoiding the formation of a "sharp corner" at the connection between the first and second layers of the positive electrode sheet during hot pressing due to the pressure of the cavity, which in turn causes the positive electrode sheet to curl excessively and break at the bend. Moreover, since the above-mentioned "cavity" is avoided, the energy density of the battery can be improved.

[0034] In short, in the winding core structure provided by the present application, by setting a single-sided coating area with a folded structure at the head of the negative electrode sheet, it can be ensured that the head of the negative electrode sheet enters the sheet to the deep bending depth of the head layer of the positive electrode sheet, that is, the head of the negative electrode sheet is closer to the inner side of the bending angle at the connection between the first layer and the second layer of the positive electrode sheet, avoiding the formation of cavities, which is not only beneficial to prevent lithium deposition, but also can play a good filling role in the bending of the head layer of the positive electrode sheet, reduce the curling stress at the bending part of the positive electrode sheet, and avoid the problem of electrode breakage during hot pressing, thereby improving the safety performance of the battery.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] FIG1 is a schematic diagram of a conventional core winding structure with a plug-in structure, and an enlarged diagram of the structure of the initial end of the negative electrode sheet winding.

[0038] FIG2 is a schematic diagram of a partial structure of a winding core structure provided in the first specific embodiment of the present application.

[0039] FIG3 is a schematic diagram of the folded structure of the negative electrode head in the rectangular dotted area in FIG2 (the separator is omitted).

[0040] FIG4 is a schematic structural diagram of the negative electrode sheet in FIG3 when the head portion is not folded back.

[0041] FIG5 is a schematic diagram of a partial structure of a winding core structure provided in the second specific embodiment of the present application.

[0042] FIG6 is a schematic diagram of the electrode structure in the rectangular dotted area in FIG5 (the diaphragm is omitted).

[0043] FIG7 is a schematic diagram of the structure of a negative electrode sheet provided with a filling layer and provided in the third specific embodiment of the present application without the head being folded back.

[0044] FIG8 is a graph showing a long-term attenuation data curve of the K value formed by long-term monitoring of the K value of the winding core structure provided by an embodiment of the present application.

[0045] FIG9 is a schematic structural diagram of a winding core provided in a comparative example.

[0046] FIG10 is a schematic structural diagram of an innermost negative electrode sheet provided in a comparative example.

[0047] FIG11 is a schematic structural diagram of a winding core structure provided in another specific embodiment of the present application (the first folded section is a single-sided coating structure).

[0048] FIG12 is a schematic structural diagram of the innermost circle of the negative electrode sheet in FIG11 .

[0049] FIG13 is a schematic structural diagram of a winding core structure having a first insulating member provided in a specific embodiment of the present application.

[0050] FIG14 is a schematic structural diagram of a winding core structure provided in another specific embodiment of the present application (the first folded section is a double-sided coating structure);

[0051] FIG15 is a schematic structural diagram of a negative electrode sheet provided with a second insulating member at the starting end thereof in a specific embodiment of the present application.

[0052] FIG16 is a schematic structural diagram of a negative electrode sheet provided in a specific embodiment of the present application, in which second insulating members are respectively provided at both ends.

[0053] in:

[0054] 21 / 21'-first layer section, 22 / 22'-second layer section,

[0055] 11 / 11'-third layer section, 12 / 12'-fourth layer section,

[0056] 11a-current collector, 11b-active material layer,

[0057] Q-cavity, L-cavity size,

[0058] 101-single-side coating area, 102-double-side coating area,

[0059] 110-head end of single-sided area, 111-first single-sided area, 112-second single-sided area, 113-folding position,

[0060] 114-filling layer, 31-insulating layer, 210-groove, Y-connector area,

[0061] 1'-current collector, 10-negative electrode sheet, 20-positive electrode sheet, 30-separator, 50-first insulating member,

[0062] 60-second insulating member, 601-coating area, 602-extension area,

[0063] 100'-active material coating, 1010-first active material layer, 1020-second active material layer,

[0064] 1001-the first turning section, 1002-the first extension section,

[0065] 1003-The second turning section, 1004-The second extension section,

[0066] 2001-The third extension section, 2002-The third turn section,

[0067] 2003-The fourth extension section, 2004-The fourth turn section,

[0068] 2021-the starting point of the return, 2022-the end of the return,

[0069] A-single-sided coating structure, B-joining point, C-head cutting area.

[0070] Modes for Carrying Out the Invention

[0071] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0072] First specific embodiment

[0073] The first specific embodiment of the present application provides a roll core structure and a negative electrode sheet suitable for the roll core structure.

[0074] Please refer to FIG. 2 and FIG. 3 . The winding core structure provided in the first specific embodiment of the present application includes a positive electrode sheet and a negative electrode sheet.

[0075] The head coil layer of the positive electrode sheet includes a first layer segment 21 and a second layer segment 22. The first layer segment 21 is located at the initial end of the winding of the positive electrode sheet relative to the second layer segment 22. The second layer segment 22 is connected to the first layer segment 21 and folded back relative to the first layer segment 21.

[0076] The head coil layer of the negative electrode sheet includes a third layer segment 11 and a fourth layer segment 12. The third layer segment 11 is located at the initial end of the winding of the negative electrode sheet relative to the fourth layer segment 12 and is stacked between the first layer segment 21 and the second layer segment 22, and the first layer segment 21 is stacked between the third layer segment 11 and the fourth layer segment 12, thereby forming a plug-in structure.

[0077] In addition, the head of the third layer segment 11 is provided with a single-sided coating area 101 with a folded structure. Specifically, the single-sided coating area 101 includes a first single-sided area 111 and a second single-sided area 112. The exposed collector side of the first single-sided area 111 and the exposed collector side of the second single-sided area 112 are arranged in stacked contact, that is, the first single-sided area 111 is flipped 180° relative to the plane where the second single-sided area 112 is located to form a folded structure, and the folded position 113 formed at the junction of the first single-sided area 111 and the second single-sided area 112 is located on the inner side of the connection between the first layer segment 21 and the second layer segment 22.

[0078] It should be noted that the first single-sided area 111 can be flipped upward 180° relative to the plane where the second single-sided area 112 is located to form a folded structure (see Figures 2 to 7), or it can be flipped downward 180° to form a folded structure (see Figures 11 to 16). This application does not make any specific restrictions on this.

[0079] It should be noted that the "pole head" in this article refers to the inner end of the pole piece, that is, the starting end of the pole piece winding inside the winding core, and the "pole head layer" refers to the part of the pole piece that is located at the beginning of the winding of the pole piece on the inner side of the winding core (the starting position), which is also the layer where the pole piece head is located. Correspondingly, the "pole tail" refers to the outer end of the pole piece, that is, the end of the pole piece winding.

[0080] Furthermore, it should be noted that the “stacked arrangement” mentioned herein refers to a plurality of (at least two) sheet-like structures / side surfaces being stacked in layers in a substantially parallel manner to form a multi-layer structure.

[0081] In the winding core structure provided by this application, the first single-sided area 111 and the second single-sided area 112 at the head of the negative electrode sheet form a folded structure. On the one hand, this folded structure can increase the thickness of the negative electrode sheet head compared to the single-sided coated area of ​​the single-layer structure, thereby enhancing the filling effect on the inner side of the bend at the junction of the first layer segment 21 and the second layer segment 22 of the positive electrode sheet. This helps to prevent the bend at the junction of the first layer segment 21 and the second layer segment 22 of the positive electrode sheet from being compressed during hot pressing to form a "sharp corner", thereby avoiding the problem of excessive curling stress on the positive electrode sheet causing the bend to break. On the other hand, since the curved surface head end formed by the folding structure (i.e., the fold position 113 at the right end of the negative electrode sheet in FIG3 ) is similar to the curved surface structure on the inner side of the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, it can enhance the filling effect on the inner side of the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet. At the same time, it also facilitates the complete insertion of the negative electrode sheet head into the deep bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, avoiding the formation of the cavity Q in FIG1 , thereby helping to avoid the formation of a "sharp corner" at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet during hot pressing due to the pressure of the cavity, which in turn causes the positive electrode sheet to curl excessively and break at the bend. Moreover, since the above-mentioned "cavity" is avoided, the energy density of the battery can be improved.

[0082] In short, in the winding core structure provided by the present application, by setting a single-sided coating area 101 with a folded structure at the head of the negative electrode sheet, it can be ensured that the head of the negative electrode sheet enters the sheet to the deep bend of the head layer of the positive electrode sheet, that is, the head of the negative electrode sheet is closer to the inner side of the bend at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, avoiding the generation of the cavity Q in Figure 1, which is not only beneficial to prevent lithium deposition, but also can play a good filling role in the bend of the head layer of the positive electrode sheet, reduce the curling stress at the bend of the positive electrode sheet, and avoid the problem of electrode breakage during hot pressing, thereby improving the safety performance of the battery.

[0083] In a specific embodiment, referring to Figures 2 to 4 , the second single-sided region 112 is connected to the double-sided coated region 102 of the negative electrode sheet. The double-sided coated region 102 may be part of the third layer segment 11, i.e., the third layer segment 11 includes not only the single-sided coated region 101 but also the double-sided coated region 102 connected to the second single-sided region 112 in the single-sided coated region 101. Alternatively, in other specific embodiments, the double-sided coated region 102 may also be located in the fourth layer segment 12, i.e., the third layer segment 11 only includes the single-sided coated region 101.

[0084] Specifically, the X-direction dimension W2 of the second single-sided area 112 is less than or equal to the X-direction dimension W of the positive electrode sheet header coil layer, that is, 0<W2≤W; the X-direction dimension W1 of the first single-sided area 111 is less than or equal to the X-direction dimension W of the positive electrode sheet header coil layer, that is, 0<W1≤W. The X-direction dimension W1 of the first single-sided area 111 can be less than, equal to, or greater than the X-direction dimension W2 of the second single-sided area 112, that is, 0<W1≤W2, or 0<W2≤W1.

[0085] Specifically, the gap distance between the single-sided area head end 110 of the first single-sided area 111, which is away from the folding position 113, and the active coating layer of the double-sided coating area 102 is greater than or equal to zero. That is, the third layer section 11 includes the double-sided coating area 102 and the single-sided coating area 101. After the single-sided area head end 110 of the single-sided coating area 101 is folded back, it can exactly connect with the active coating layer of the double-sided coating area 102 as shown in Figure 3 (that is, the gap distance between the two is zero, specifically see the connection area Y in Figure 3), or it can maintain a gap distance greater than zero with the active coating layer of the double-sided coating area 102 (not shown in the figure). Alternatively, in other specific embodiments, the first single-sided area 111 can also partially overlap with the double-sided coating area 102, that is, the single-sided area head end 110 of the single-sided coating area 101 can cover the active coating layer of the double-sided coating area 102 after being folded back. In this case, the X-direction dimension W1 of the first single-sided area 111 is greater than the X-direction dimension W2 of the second single-sided area 112.

[0086] In summary, please refer to Figures 2 to 4. The negative electrode sheet with a new structure provided in the first specific embodiment of the present application includes a third layer segment 11 located at the initial end of the winding of the negative electrode sheet. The head of the third layer segment 11 is provided with a single-sided coating area 101 with a folded structure. The single-sided coating area 101 includes a first single-sided area 111 and a second single-sided area 112. The first single-sided area 111 can cover the exposed side of the collector of the second single-sided area 112 by folding back. The junction of the first single-sided area 111 and the second single-sided area 112 constitutes a folded position 113 of the folded structure.

[0087] It should be noted that, in the winding core structure provided in the present application, in addition to the above-mentioned positive and negative electrode sheets, a separator is also stacked between adjacent positive and negative electrode sheets.

[0088] Second specific embodiment

[0089] Please refer to Figures 5 and 6. The second specific embodiment of the present application provides a winding core structure and its negative electrode sheet, which differs from the above-mentioned first specific embodiment only in that: it also includes an insulating layer 31; further, a groove 210 is provided on the side of the first layer segment 21 opposite to the insulating layer 31.

[0090] Specifically, the insulating layer 31 is located between the first layer segment 21 and the third layer segment 11 and is connected to the first layer segment 21. The Z-direction projections (the projection direction can be seen from the arrow Z in FIG5 ) of the single-sided region head end 110 of the first single-sided region 111 away from the fold 113, and the junction of the double-sided coated region 102 of the third layer segment 11 and the second single-sided region 112 on the first layer segment 21 both fall within the projection range of the insulating layer 31 in the same direction, that is, fall on the insulating layer 31. As shown in FIG6 , the insulating layer 31 can cover the single-sided region head end 110 of the first single-sided region 111 near the double-sided coated region 102 of the negative electrode sheet (M3>0), and can also cover the junction of the double-sided coated region 102 of the negative electrode sheet and the second single-sided region 112 (M2>0). Therefore, the insulating layer 31 can ensure the insulation effect at its location, avoiding problems such as the surface of the joint area between the double-sided coating area 102 of the negative electrode sheet and the first single-sided area 111 being not smooth enough, resulting in increased bending stress during hot pressing of the first layer segment 21 of the positive electrode sheet and puncture of the diaphragm.

[0091] Specifically, the insulating layer 31 includes a first side 311 and a second side 312. The first side 311 is located between the double-sided coated area 102 of the third layer segment 11 and the first layer segment 21, and the distance M2 between the junction of the double-sided coated area 102 and the second single-sided area 112 and the first side 311 is ≥ 0.5 mm. Alternatively, the second side 312 is located between the first single-sided area 111 and the first layer segment 21, and the distance M3 between the single-sided area head end 110 and the second side 312 is ≥ 0.5 mm. The insulating layer 31 ensures good coverage of the junction area between the double-sided coated area 102 and the first single-sided area 111 of the negative electrode sheet.

[0092] In a specific implementation, the insulating layer 31 can be any one or more combinations of various insulating materials such as single-sided adhesive tape, double-sided adhesive tape, ceramic coating, etc.

[0093] Furthermore, a groove 210 is provided on the side of the first layer segment 21 opposite to the insulating layer 31. In addition, the Z-direction projection of the head end 110 of the single-sided area and the junction of the double-sided coated area 102 of the negative electrode sheet and the second single-sided area 112 on the first layer segment 21 (the projection direction can be seen from the arrow Z in Figure 5) all fall within the projection range of the groove 210 in the same direction, that is, fall within the groove 210. The main functions of the groove 210 are: first, to prevent the lithium deposition problem in the area when the "starting point" and "end point" of the single-sided coated area 101 of the negative electrode sheet do not overlap; second, to prevent the problem of excessive thickness in the area when the "starting point" and "end point" of the single-sided coated area 101 of the negative electrode sheet overlap, that is, the groove 201 helps to avoid the problem that the surface of the joint area between the double-sided coated area 102 of the negative electrode sheet and the first single-sided area 111 is not flat enough, resulting in increased bending stress during hot pressing of the first layer segment 21 of the positive electrode sheet.

[0094] In addition, an insulating layer 114 is provided outside the groove 210 to protect the area, further reduce the risk of lithium plating and short circuit, and improve the safety performance of the battery.

[0095] Specifically, the projection of the groove 210 in the thickness direction of the first layer segment 21 falls within the projection range of the insulating layer 31 in the same direction. Thus, the insulating layer 31 can cover the groove 210. As shown in Figure 6, assuming that the X-direction dimension and the Y-direction dimension of the insulating layer 31 are N1 and N3 respectively (not shown in the figure), and the X-direction dimension and the Y-direction dimension of the groove 210 are N2 and N4 respectively (not shown in the figure), then N1≥N2, N3≥N4. Among them, the Y-direction dimension N4≤N5 of the groove 210, N5 represents the Y-direction dimension of the positive electrode sheet, which is not shown in the figure. The X-direction dimension mentioned in this paragraph refers to the dimension in the length direction of the electrode sheet before the electrode sheet is wound; the Y-direction dimension mentioned in this paragraph refers to the dimension in the width direction of the electrode sheet before the electrode sheet is wound.

[0096] In a preferred embodiment, in any direction perpendicular to the thickness direction of the first layer segment 21 (see the Z direction shown in FIG5 ), the distance M1 between the side edge profile of the insulating layer 31 and the notch profile of the groove 210 is ≥ 0.1 mm. That is, the side edge of the insulating layer 31 protrudes radially outward from the notch edge of the positive electrode sheet groove 210 by at least 0.1 mm to ensure good coverage.

[0097] Specifically, the depth D1 of the groove 210 in the thickness direction of the pole piece (see the Z direction shown in FIG5 ) is not greater than the thickness D of the single-sided active coating of the first layer segment 21. Specifically, referring to FIG7 , the range of the depth D1 of the groove 210 in the thickness direction of the pole piece (see the Z direction shown in FIG5 ) is: D1 ≤ 1 / 2 (D-D0), where D is the thickness of the first layer segment 21 and D0 is the thickness of the current collector in the first layer segment 21.

[0098] Third specific embodiment

[0099] The third specific embodiment of the present application provides a winding core structure and a negative electrode sheet thereof, which is provided with a filling layer 114 on the basis of the above-mentioned first specific embodiment or the second specific embodiment, which is helpful to avoid the problem of excessive stress forming "sharp corners" after the negative electrode sheet is folded back, leading to the breakage of the negative electrode sheet.

[0100] Please refer to FIG. 7 for details. The filling layer 114 is located on the inner side of the fold of the single-sided coating area 101 , that is, the filling layer 114 is located between the first single-sided area 111 and the second single-sided area 112 .

[0101] Specifically, the filling layer 114 may be a single-layer structure or a multi-layer folded structure.

[0102] When the filling layer 114 is a single-layer structure, it can be first pasted to the side of the current collector of the first single-sided area 111 / the second single-sided area 112. When the first single-sided area 111 is folded back relative to the second single-sided area 112, the filling layer 114 is exactly located between the first single-sided area 111 and the second single-sided area 112, which can increase the thickness of the head of the negative electrode sheet, that is, the thickness of the folded structure of the single-sided coating area, and further avoid the problem of excessive curling stress at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, resulting in broken sheets at the bend.

[0103] When filling layer 114 has a two-layer, folded structure, it includes a first filling layer 1141 bonded to first single-sided area 111, and a second filling layer 1142 bonded to second single-sided area 112. When first single-sided area 111 folds back relative to second single-sided area 112, first filling layer 1141 folds back relative to second filling layer 1142, thereby forming a two-layer, folded filling layer. Specifically, the fold line where first single-sided area 111 folds back relative to second single-sided area 112 is located in the area where filling layer 114 is located, and filling layer 114 also folds back.

[0104] Alternatively, in other specific embodiments, the filling layer 114 can also be set as a multi-layer folded structure with more than two layers according to actual needs, so as to further increase the thickness of the head of the negative electrode sheet, that is, the thickness of the folded structure of the single-sided coating area, so as to avoid the problem of excessive curling stress at the connection between the first layer segment 21 and the second layer segment 22 of the positive electrode sheet, resulting in broken sheets at the bend.

[0105] In a specific implementation, the filling layer 114 can be any one or more material combinations of various materials such as adhesive tape, ceramic layer, rubber, foam, etc.

[0106] The following examples are given of the core structure and negative electrode sheet in several specific embodiments. The parameters of each core structure include: the core width (i.e., the Y-direction dimension of the core) is 59mm, the core thickness (i.e., the Z-direction dimension of the core) is 3.3mm, the positive electrode sheet width (i.e., the Y-direction dimension of the positive electrode sheet) is 75mm, the innermost circle width of the positive electrode sheet (i.e., the Y-direction dimension of the head circle of the positive electrode sheet) is 55.7mm, the positive electrode sheet thickness (i.e., the Z-direction dimension of the positive electrode sheet) is 99um, the positive electrode current collector thickness (i.e., the Z-direction dimension of the positive electrode current collector) is 9um, and the design capacity is 3490mAh. Among them:

[0107] (1) In a winding core structure using a conventional electrode-to-element structure, active material layers are provided on both surfaces of the negative electrode current collector, with no single-sided coating area. After winding, the single-layer length (i.e., the X-direction dimension) of the innermost circle of the negative electrode sheet is 53 mm. The negative electrode sheet does not extend deep into the first bend area of ​​the positive electrode sheet (i.e., deep inside the connection between the first layer segment 21 and the second layer segment 22 of the head layer of the positive electrode sheet), leaving a cavity Q with a cavity size L of approximately 2.7 mm.

[0108] (2) In the winding core structure provided in the first specific embodiment of the present application (see Figures 2 to 4), a single-sided coating area 101 is provided on one side of the negative electrode current collector, and the extended length of the single-sided coating area 101 (i.e., the X-direction dimension of the single-sided coating area 101 in the straight extended state before being folded back) is 17 mm (i.e., the sum of the X-direction dimensions of the first single-sided area 111 and the second single-sided area 112 in Figure 4 W1+W2=17 mm). After winding, the single-sided coating area 101 of the folded structure (see Figures 2 and 3) is located inside the winding core, and the folded length is 8.5 mm (i.e., the X-direction dimension W1 of the first single-sided area 111=8.5 mm). After folding back, the head end 110 of the single-sided area of ​​the negative electrode sheet is oriented in the same direction as the first short layer 21 of the positive electrode sheet located at the innermost part of the winding core.

[0109] (3) In the winding core structure provided in the second specific embodiment of the present application (see FIG. 7 ), a filling layer 114 is provided on the inner side of the fold of the negative electrode sheet's single-sided coating area 101. The filling layer 114 is adhesive tape. After winding and folding, the folding position 113 of the single-sided coating area 101 is located in the area covered by the filling layer 114, that is, the filling layer 114 is also folded. The filling layer 114 mainly plays a certain supporting role. After the filling layer is folded back, it plays a certain supporting role for the folded portion of the negative electrode sheet's single-sided coating area 101, thereby avoiding the problem of excessive stress causing the negative electrode sheet to break due to the formation of a "sharp corner" after the negative electrode sheet is folded back. In addition, the thickness of the folded portion of the negative electrode sheet's single-sided coating area 101 can be increased, which is beneficial to avoiding the problem of excessive stress causing the negative electrode sheet to break due to the formation of a "sharp corner" at the folded portion of the positive electrode sheet during hot pressing.

[0110] (4) In the winding core structure provided in the first specific embodiment of the present application, a groove 210 is provided at a position corresponding to the first layer segment 21 of the positive electrode sheet and the head end 110 of the single-sided area after folding back, and an insulating layer 114 is also provided outside the groove 210 (see Figures 5 and 6). The X-direction dimension N2 of the groove 210 is 9 mm, and the Y-direction dimension N4 of the groove 210 is the same as the Y-direction dimension N5 of the positive electrode sheet, both of which are 75 mm. The X-direction dimension N1 of the insulating layer 114 is 10 mm, and the Y-direction dimension N3 of the insulating layer 114 is 77 mm. The insulating layer 114 covers the notch of the groove 210, and its radially outward extension dimension M1 is 0.5 mm, and the groove depth D1 is 45 μm. The area occupied by the groove 210 on the first layer segment 21 of the positive electrode sheet is formed by cleaning off all the surface coating on one side of the positive electrode sheet in this area, exposing the positive electrode current collector. After the winding is completed, the head end 110 of the single-sided area of ​​the third layer section of the negative electrode sheet falls completely within the range of the groove 210 and the insulating layer 114. In addition, the measured end point position dimension M2 of the insulating layer 114 to the double-sided coating area 102 of the negative electrode sheet is 1.0 mm. The main functions of the groove 210 are: first, to prevent the problem of lithium plating in the area when the "starting point" and "end point" of the single-sided coating area 101 of the negative electrode sheet do not overlap; second, to prevent the problem of excessive thickness in the area when the "starting point" and "end point" of the single-sided coating area 101 of the negative electrode sheet overlap. At the same time, an insulating layer 114 is arranged outside the groove 210 to protect the area, further reduce the risk of lithium plating and short circuit, and improve the safety performance of the battery.

[0111] By comparing the process data in the table above, it is found that the actual capacity average of the battery cells in the two core structures with new negative electrode sheet structures (2) and (3) is basically consistent with the design value. However, in the core structure (1) with a conventional electrode sheet plug-in structure, the average capacity of the battery cells is lower. By conversion, it is basically one fold of the positive electrode sheet capacity different from (2) and (3). This shows that after the hot pressing of the battery cell in (1), the innermost positive electrode sheet is severely fractured.

[0112] Please refer to Figure 8. Through long-term monitoring of the K values ​​of the above-mentioned core structures, it was found that the K values ​​of the two core structures (2) and (3) with the new negative electrode sheet structure showed a trend of gradually decreasing over time, while the K value of the core structure (1) with the conventional electrode sheet plug-in structure fluctuated greatly. It was judged that this was because the positive electrode sheet broke at the first fold, resulting in aluminum foil leakage, causing part of the aluminum foil to pierce the diaphragm and cause a micro short circuit inside the battery cell, resulting in large long-term K value fluctuations. More seriously, it directly caused a short circuit, making its short circuit ratio higher than that of the new structure.

[0113] Referring to Figures 11 and 12 , embodiments of the present application further provide a winding core structure comprising a stacked negative electrode sheet 10 and a positive electrode sheet 20, with a separator 30 disposed between adjacent negative and positive electrode sheets 10 and 20. The third layer 11 comprises a first folded section 1001 and a first extended section 1002, and the negative electrode sheet further comprises a second folded section 1003. The first folded section 1001, the first extended section 1002, and the second folded section 1003 are sequentially connected along the winding direction.

[0114] Specifically, the winding starting section of the negative electrode sheet 10 includes, along the winding direction, a first folded section 1001, a first extension section 1002, a second folded section 1003, and a second extension section (also referred to as a fourth layer section) 1004, which are sequentially connected. The first folded section 1001 has one end connected to the first extension section 1002 and the other end located on a first side surface of the first extension section 1002; the second folded section 1003 has one end connected to the first extension section 1002 and the other end located on a second side surface of the first extension section 1002; and the first active material layer 1010 is coated on the side of the winding starting section (including the first folded section 1001) that is adjacent to the positive electrode sheet 20.

[0115] It can be seen that in this winding core structure, the winding starting section from the first fold section 1001 to the second fold section 1003 forms a folded winding structure similar to the letter "S" or the letter "Z" (where "S" and "Z" only indicate the folding direction and have nothing to do with the actual shape, size, fold angle, curvature, etc. of the winding structure). As a result, the side of the winding starting section close to the positive electrode sheet 20 can be completely coated with the first active material layer 1010 and can react with the positive electrode sheet 20 to generate current. Moreover, because the first fold section 1001 is coated with the first active material layer 1010 and does not contain a blank current collector, that is, there is no blank current collector at the head of the negative electrode sheet 10, the internal space of the winding core is highly utilized, which can improve the energy density of the winding core. Moreover, in the winding core structure, since the above-mentioned first fold section 1001 is provided at the innermost side of the winding core, it can ensure that the negative electrode sheet 10 can be inserted into the innermost bend of the positive electrode sheet 20, filling the innermost bend, which is beneficial to reduce the curling stress at the bend of the positive electrode sheet, avoid the risk of electrode breakage during hot pressing, and thus improve the safety performance of the battery.

[0116] In specific implementation, the first fold segment 1001 in the core structure can be a single-sided coating structure, specifically referring to A in Figures 11 and 12. The single-sided coating structure includes a current collector with a folded structure and a single-sided coating. In this case, the current collector is only provided with an active coating on the side close to the positive electrode sheet 20. Alternatively, in other embodiments, the first fold segment 1001 in the core structure can also be a double-sided coating structure. Specifically referring to Figure 14, the double-sided coating structure includes a current collector with a folded structure and a double-sided coating. In this case, the two sides of the current collector are respectively coated with active coatings. Alternatively, in other embodiments, the first fold segment 1001 in the core structure can also be composed of a single-sided coating structure and a double-sided coating structure, that is, the head end of the first fold segment 1001 is a single-sided coating structure, and the rest of the positions are double-sided coating structures. It can be seen that in the core structure provided by the present application, by significantly reducing the proportion of the single-sided coating area on the innermost side of the core, the active material coating area can be increased, thereby improving the battery energy density.

[0117] Referring to FIG. 12 , in some embodiments, assuming that the length of the first folded section 1001 in the X direction (i.e., the width / length direction of the core) is L2, and the total length of the first extension section 1002 and the second folded section 1003 in the X direction is L1, then L1 = (0.02-0.8)(L1+L2), i.e., the length of the first folded section 1001 in the X direction accounts for 2% to 80% of the size of the core in the X direction.

[0118] In other embodiments of the present application, the above-mentioned first layer segment 21 includes a third extension segment 2001, the second layer segment 22 includes a third return segment 2002 and a fourth extension segment 2003, and the positive electrode sheet also includes a fourth return segment 2004, wherein the third extension segment 2001, the third return segment 2002, the fourth extension segment 2003 and the fourth return segment 2004 are connected in sequence along the winding direction.

[0119] Specifically, referring to Figures 11 and 13, in some embodiments, the winding starting section of the positive electrode sheet 20 includes, along the winding direction, a third extending section 2001, a third return section 2002, a fourth extending section 2003, and a fourth return section 2004, which are connected in sequence. The third extending section 2001 and the fourth extending section 2003 are located on the first side and second side of the first extending section 1002, respectively; and the third return section 2002 and the fourth return section 2004 are located on the outer sides of the winding of the first return section 1001 and the second return section 1003, respectively.

[0120] Furthermore, in some embodiments, a first insulating member (also referred to as an insulating layer) 50 is provided on the side of the fourth extension section 2003 adjacent to the first extension section 1002, and the projection of the head end of the negative electrode sheet 10 on the fourth extension section 2003 is located within the projection area of ​​the first insulating member 50 in the same direction. In this case, the first folded section 1001 can have a single-sided coating structure (as shown in FIG. 13 ) or a double-sided coating structure.

[0121] When the first extension section 1002 has a double-sided coating structure and the first return section 1001 has a single-sided coating structure, the projection of the junction B (see FIG. 13 ) between the single-sided coating structure of the first return section 1001 and the double-sided coating structure of the first extension section 1002 on the fourth extension section 2003 is located within the projection area of ​​the first insulating member 50 in the same direction. Thus, the first insulating member 50 ensures good insulation between the junction B and the fourth extension section 2003 of the positive electrode sheet 20, and also helps ensure the flatness of this location, preventing the tip of the negative electrode sheet from scratching the positive electrode sheet.

[0122] Similarly, when the first folded section 1001 is a double-sided coating structure, the first insulating member 50 is also helpful in ensuring a smooth transition of the head end of the negative electrode sheet at this position, thereby preventing the head end of the negative electrode sheet from scratching the positive electrode sheet.

[0123] In a specific implementation, the first insulating member 50 may be made of any one or more combinations of insulating materials such as ceramics, single-sided adhesive tape, and double-sided adhesive tape.

[0124] Furthermore, a groove is provided on the side of the fourth extension section 2003 adjacent to the first extension section 1002. Specifically, the groove depth is less than or equal to the thickness of the coating on one side of the electrode sheet, and the groove length is less than or equal to the width of the positive electrode sheet 20 in the Z direction. That is, in the Y direction, the groove depth is less than or equal to the thickness of the coating on one side of the electrode sheet; in the Z direction, the groove length is less than or equal to the width of the electrode sheet.

[0125] Furthermore, the groove is located within the projection of the first insulating member 50 onto the fourth extension 2003. This groove structure improves the flatness of the negative electrode tip and the area surrounding the joint B, while also being completely covered by the first insulating member 50. Specifically, in the X direction, the width of the first insulating member 50 is greater than or equal to the groove width; and in the Z direction, which is perpendicular to the XY axis, the length of the first insulating member 50 is greater than or equal to the groove length.

[0126] Referring to Figure 13 , in some embodiments, the gap between the projection of the first insulating member 50 on the fourth extension 2003 and the projection of the third folded segment 2002 in the same direction is greater than or equal to zero, i.e., L6 ≥ zero in Figure 13 . In other words, the first insulating member 50 is close to the first folded segment 2001 of the positive electrode sheet, but does not extend beyond the end point 2022 of the first folded segment 2001 or the starting point 2021 of the first folded segment 2001. Furthermore, the groove on the fourth extension 2003 does not extend beyond the end point 2022 of the first folded segment 2001 or the starting point 2021 of the first folded segment 2001.

[0127] In some embodiments, the head end of the negative electrode sheet 10 is wrapped with a second insulating member 60 (as shown in FIG15 ). Alternatively, in some embodiments, the tail end of the negative electrode sheet 10 may also be wrapped with a second insulating member 60 (as shown in FIG16 ). Specifically, the second insulating member 60 is an insulating adhesive layer, and the types include: acrylic adhesive tape, rubber adhesive tape, etc. Therefore, the insulation of the end of the electrode sheet can be ensured by the second insulating member 60, and because the head and tail of the electrode sheet are completely wrapped in adhesive tape, the powder loss of the electrode sheet during cutting at the winding position can be reduced, thereby avoiding the impact of dust on the performance of the battery cell.

[0128] Specifically, referring to FIG15 , the second insulating member 60 generally includes a coating region 601 and an extension region 602. The coating region 601 covers the first and second side surfaces of the negative electrode sheet 10, and has a length L4 in the X direction, where L4 is ≥ 1.5 mm. The extension region 602 is located at the end of the negative electrode sheet 10 and extends along the X direction, and has a length L3 in the X direction, where L3 is ≥ 0.2 mm.

[0129] Specifically, at the innermost part of the winding core, the misalignment between the winding start of the separator 30 and the second insulating member 60 at the leading end of the negative electrode sheet is less than or equal to 1 mm. As shown in Figure 15 , at the leading cutting area C of the winding core, the second insulating member 60 and the cut end of the separator 30 are essentially flush, with a misalignment of ≤1.0 m in the X direction.

[0130] In addition, an embodiment of the present application also provides a battery, which is provided with the winding core structure described above, thereby having a higher energy density.

[0131] In summary, the embodiments of the present application also provide a comparative example and two test examples, and their specific parameters can be found in the table below.

[0132] Comparative Example

[0133] A conventional core structure with a core width of 60 mm and a core thickness of 3.5 mm.

[0134] The specific structure can be seen in Figures 9 and 10. The innermost circle of the negative electrode sheet of the core is composed of a current collector and an active material coating (also called an active material layer) 100'. After winding is completed: the head of the negative electrode is a blank current collector 1', and the blank current collector 1' includes a straight section 1000' and a first fold section 1001'; the first fold section 1001' is connected to the single-sided coating structure, and the outer side of the winding is provided with an active material coating 100', and the single-sided coating structure includes a first extension section 1002' and a second fold section 1003'. Thus, the first fold section 1001', the first extension section 1002', and the second fold section 1003' are connected in sequence, and are arranged in a "C-type" layout.

[0135] First Test Example

[0136] A new core structure with a core width of 60mm and a core thickness of 3.5mm.

[0137] There are multiple implementations of this novel winding core structure, and the specific structures can be seen in Figures 11 to 13.

[0138] As shown in Figures 11 to 13, the head of the negative electrode sheet 10 on the innermost side of the winding core is provided with a single-sided coating structure. The unrolled length of the single-sided coating structure is approximately 15 mm. The single-sided coating structure folds back at the head of the winding core to form a first folded section 1001. The length L2 of the first folded section 1001 in the X direction is approximately 7 mm. In other words, the first folded section 1001 is formed by folding back the single-sided coating structure. Furthermore, in this winding core structure, the first extension section 1002 connected to the first folded section 1001 has a length L2 in the X direction of approximately 49.5 mm.

[0139] Furthermore, the winding direction of the first folded section 1001 is opposite to that of the negative electrode sheet head in the comparative example. That is, in the first experimental example, the negative electrode sheet head, which is connected sequentially by the first folded section 1001, the first extension section 1002, and the second folded section 1003, forms an "S-shaped" layout; while the conventional negative electrode sheet head in the comparative example has a "C-shaped" layout, a significant difference between the two.

[0140] Referring to Figure 13 , after the single-sided coating structure at the head of the negative electrode sheet folds back to form the first fold segment 1001, a joint region is formed from the negative electrode sheet head end (i.e., the winding starting point) to the starting end of the negative electrode sheet's double-sided coating (i.e., the junction B between the single-sided coating structure and the double-sided coating structure shown in Figure 13 ). The width of this joint region (i.e., L5 in Figure 13 ) ranges from 0.3 mm to 2.0 mm, preferably 1 mm. A first insulating member 50 (e.g., adhesive tape) is provided on the side of the positive electrode sheet corresponding to this joint region. The width of the first insulating member 50 in the X direction is 6 mm. Furthermore, in the winding core thickness direction Y, the projection of this joint region falls entirely within the first insulating member 50.

[0141] Second Test Example

[0142] A new core structure with a core width of 60mm and a core thickness of 3.5mm.

[0143] This novel roll-up structure has multiple implementations, with the specific structure shown in Figure 15 . As shown in Figure 15 , the leading end of the negative electrode sheet 10 in this novel roll-up structure is wrapped with a second insulating member 60 (e.g., acrylic tape); as shown in Figure 16 , both the leading and trailing ends of the negative electrode sheet 10 in this novel roll-up structure are wrapped with a second insulating member 60 (e.g., acrylic tape).

[0144] Specifically, the negative electrode sheet 10 of the novel core structure is cut before winding. The negative electrode sheet is then stretched to a certain distance. Acrylic tape is applied to the upper and lower sides of the negative electrode sheet to form the coating area 601 of the second insulating member 60. During winding and cutting, the cutting position is located in the tape area, thereby forming an extension area 602 of the second insulating member 60. This produces two effects:

[0145] Effect 1): The head and tail of the negative electrode sheet of the core are completely wrapped in adhesive tape, which reduces the possibility of electrode powder falling during cutting at the winding position and avoids the impact of dust on battery performance. The length L4 of the coating area 601 in the X direction is 5 mm, and the length L3 of the extension area 602 (i.e., the pure adhesive tape area) in the X direction is 1.0 mm.

[0146] Effect 2): The edge of the coating area 601 located on the upper and lower sides of the pole piece in the head cutting area C is substantially flush with the diaphragm 30 located on the upper and lower sides of the pole piece, and the measured misalignment is ≤0.2 mm.

[0147] It can be seen from the data that the new winding core structure provided in this application has a certain improvement on the energy density (ED) of the battery cell. This is mainly because compared with the conventional structure, the new winding core structure has a greatly reduced proportion of the single-sided coating structure of the negative electrode sheet, and there is no empty current collector at the head, which has a high utilization rate of the internal space of the battery, thereby improving the energy density of the battery; the improvement of the structure of the head and tail glue wrapping of the negative electrode sheet is relatively small, mainly because the adhesive paper will occupy a certain thickness, and the relatively thick battery thickness affects the improvement of the battery ED.

[0148] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0149] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0150] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A winding core structure, comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The positive electrode sheet comprises a first layer segment (21) and a second layer segment (22), wherein the first layer segment (21) is located at the initial end of the winding of the positive electrode sheet, and the second layer segment (22) is connected to the first layer segment (21) and folded back relative to the first layer segment (21); The negative electrode sheet comprises a third layer segment (11) located at the initial end of the winding of the negative electrode sheet, and the third layer segment (11) is stacked between the first layer segment (21) and the second layer segment (22); The head of the third layer segment (11) is provided with a single-sided coating area (101) with a folded structure, and the single-sided coating area (101) includes a first single-sided area (111) and a second single-sided area (112), and the exposed collector side of the first single-sided area (111) and the exposed collector side of the second single-sided area (112) are arranged in stacked contact.

2. The winding core structure according to claim 1, characterized in that: The second single-sided area (112) is connected to the double-sided coating area (102) of the negative electrode sheet, and an X-direction dimension W2 of the second single-sided area (112) is less than or equal to an X-direction dimension W of the head ring layer of the positive electrode sheet.

3. The winding core structure according to claim 1 or 2, characterized in that: The X-direction dimension W1 of the first single-sided area (111) is less than or equal to the X-direction dimension W of the head ring layer of the positive electrode sheet; And / or, the X-direction dimension W1 of the first single-sided area (111) is smaller than, equal to, or larger than the X-direction dimension W2 of the second single-sided area (112).

4. The winding core structure according to any one of claims 1 to 3, characterized in that: The third layer section (11) further comprises a double-sided coating area (102) connected to the second single-sided area (112).

5. The winding core structure according to claim 4, characterized in that: The junction of the first single-sided area (111) and the second single-sided area (112) forms a folding position (113), wherein: The gap distance between the single-sided area head end (110) of the first single-sided area (111) away from the folding position (113) and the active coating of the double-sided coating area (102) is greater than or equal to zero; Alternatively, the first single-sided area (111) partially overlaps with the double-sided coating area (102).

6. The winding core structure according to any one of claims 1 to 5, characterized in that: It also includes a filling layer (114), wherein the filling layer (114) is located between the first single-sided area (111) and the second single-sided area (112).

7. The winding core structure according to claim 6, characterized in that: The filling layer (114) is a single-layer structure or a multi-layer folded structure.

8. The winding core structure according to claim 6 or 7, characterized in that: The filling layer (114) comprises any one or more combinations of adhesive tape, ceramic layer, rubber, and foam.

9. The winding core structure according to any one of claims 1 to 8, characterized in that: It also includes an insulating layer (31), wherein the insulating layer (31) is located between the first layer segment (21) and the third layer segment (11), and is connected to the first layer segment (21); The single-sided area head end (110) of the first single-sided area (111) away from the folding position (113), and the junction between the double-sided coated area (102) of the third layer segment (11) and the second single-sided area (112), all have their Z-direction projections on the first layer segment (21) falling on the insulating layer (31).

10. The winding core structure according to claim 9, characterized in that: The insulating layer (31) comprises a first side edge (311) and a second side edge (312): The first side edge (311) is located between the double-sided coating area (102) of the third layer segment (11) and the first layer segment (21), and a distance M2 between the junction of the double-sided coating area (102) and the second single-sided area (112) and the first side edge (311) is ≥0.5 mm; And / or, the second side edge (312) is located between the first single-sided area (111) and the first layer segment (21), and a distance M3 between the head end (110) of the single-sided area and the second side edge (312) is ≥0.5 mm.

11. The winding core structure according to claim 9 or 10, characterized in that: The insulating layer (31) comprises any one or more combinations of single-sided adhesive tape, double-sided adhesive tape and ceramic coating.

12. The winding core structure according to any one of claims 9 to 11, characterized in that: A groove (210) is provided on the side of the first layer segment (21) opposite to the insulating layer (31); The Z-direction projections of the head end (110) of the single-sided area and the junction of the double-sided coating area (102) of the negative electrode sheet and the second single-sided area (112) on the first layer segment (21) all fall within the groove (210).

13. The winding core structure according to claim 12, characterized in that: The projection of the groove (210) on the first layer segment (21) along the Z direction falls within the projection range of the insulating layer (31) in the same direction.

14. The winding core structure according to claim 13, characterized in that: In any direction perpendicular to the Z direction of the first layer segment (21), a distance M1 between a side profile of the insulating layer (31) and a notch profile of the groove (210) is ≥0.1 mm.

15. The winding core structure according to any one of claims 12 to 14, characterized in that: The depth D1 of the groove (210) in the Z direction is not greater than the thickness D of the single-sided active coating of the first layer section (21).

16. The winding core structure according to claim 1, characterized in that: The third layer segment (11) includes a first folded segment (1001) and a first extension segment (1002), and the negative electrode sheet further includes a second folded segment (1003), wherein the first folded segment (1001), the first extension segment (1002) and the second folded segment (1003) are sequentially connected along a winding direction; A first active material layer (1010) is coated on the side of the first folded section (1001) close to the positive electrode sheet (20); One end of the first folded section (1001) is connected to the first extension section (1002), and the other end is located on a first side surface of the first extension section (1002); One end of the second folded section (1003) is connected to the first extension section (1002), and the other end is located on the second side surface of the first extension section (1002).

17. The winding core structure according to claim 16, characterized in that: The length of the first folded section (1001) in the X direction is L2; The total length of the first extension section (1002) and the second folded section (1003) in the X direction is L1; L1 = (0.02 ~ 0.8) (L1 + L2).

18. The winding core structure according to claim 16 or 17, characterized in that: The first layer segment (21) includes a third extension segment (2001), the second layer segment (22) includes a third return segment (2002) and a fourth extension segment (2003), and the positive electrode sheet also includes a fourth return segment (2004), wherein the third extension segment (2001), the third return segment (2002), the fourth extension segment (2003) and the fourth return segment (2004) are sequentially connected along a winding direction; The third extension section (2001) and the fourth extension section (2003) are respectively located on a first side surface and a second side surface of the first extension section (1002); The third return section (2002) and the fourth return section (2004) are respectively located on the outer sides of the winding of the first return section (1001) and the second return section (1003).

19. The winding core structure according to claim 18, characterized in that: A first insulating member (50) is provided on the side of the fourth extension section (2003) close to the first extension section (1002); The projection of the head end of the negative electrode sheet (10) on the fourth extension section (2003) is located within the projection area of ​​the first insulating member (50) in the same direction.

20. The winding core structure according to claim 19, characterized in that: The first folded section (1001) is a single-sided coating structure, and the first extended section (1002) is a double-sided coating structure; The projection of the junction (B) of the single-sided coating structure of the first folded section (1001) and the double-sided coating structure of the first extension section (1002) on the fourth extension section (2003) is located within the projection area of ​​the first insulating member (50) in the same direction.

21. The winding core structure according to claim 20, characterized in that: A gap distance L5 between the joint (B) and the head end of the negative electrode sheet (10) in the X direction is greater than or equal to zero.

22. The winding core structure according to any one of claims 19 to 21, characterized in that: A gap between a projection of the first insulating member (50) on the fourth extension segment (2003) and a projection of the third folded segment (2002) in the same direction is greater than or equal to zero.

23. The winding core structure according to any one of claims 16 to 22, characterized in that: The head end and / or tail end of the negative electrode sheet (10) is wrapped with a second insulating member (60).

24. The winding core structure according to claim 23, characterized in that: The second insulating member (60) comprises a coating region (601) and an extension region (602), wherein: The coating area (601) covers the first side surface and the second side surface of the negative electrode sheet (10), and the length of the coating area (601) in the X direction is L4, and L4 is ≥ 1.5 mm; The extension area (602) is located at the end of the negative electrode sheet (10) and extends along the X direction. The length of the extension area (602) in the X direction is L3, and L3 is ≥ 0.2 mm.

25. The winding core structure according to claim 23 or 24, characterized in that: It also includes a diaphragm (30); the offset length between the winding start end of the diaphragm (30) and the second insulating member (60) is less than or equal to 1 mm.

26. A battery, characterized in that: A winding core structure according to any one of claims 1 to 25 is provided.

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