Roll core

Abstract

The utility model discloses a roll core. In the roll core, at least one side surface of a first pole piece current collector comprises a first region, a second region and a third region, the first region is provided with an active layer, the second region is provided with an insulating layer, and a connecting part of the insulating layer and the active layer is located in the third region; the second arc-shaped bending section of the first pole piece is provided with an insulating layer; and the connecting part is positioned at one end, far away from the tail end of the pole piece, of the second arc-shaped bent section in the direction opposite to the winding direction of the winding core, or is positioned at the second straight section connected with the end part. Therefore, the junction of the single face and the double faces of the original pole piece is coated with the insulating layer, the insulating layer is connected with the active layer, and the thickness change of the end of the active layer at the junction is slowed down through the insulating layer, so that pole piece fatigue caused by compaction at the position is relieved, the tensile strength of the pole piece at the position is improved, and the breakage risk of the pole piece is reduced.

Description

Technical Field

[0001] The present application relates to the field of new energy technologies, and particularly to a core roll. Background Art

[0002] Lithium-ion batteries are widely used as portable, mobile, and fixed energy storage devices due to their high energy conversion efficiency and high energy density, and their applications have brought earth-shaking changes to human society.

[0003] Currently, in order to pursue higher energy density in the battery industry, the compaction density of the electrode sheet is continuously increased. Under such an extreme system design, after the battery is cycled, due to the swelling of the battery core, the fracture phenomenon of the electrode sheet (especially the positive electrode sheet) frequently occurs at the junction of the active layer ends, resulting in the phenomenon of low capacity after the battery is cycled (i.e., the phenomenon of the battery capacity decreasing), and there are also safety risks at the same time. The "junction of the active layer ends" mentioned in this article includes the "single-sided and double-sided junction" and the "single-empty and double-sided junction". Among them, the "single-sided and double-sided junction" refers to the junction between the area where the active layer is provided on both sides of the electrode sheet and the area where the active layer is provided on one side of the electrode sheet, and the "single-empty and double-sided junction" refers to the junction between the area where the active layer is provided on one side of the electrode sheet and the area where there is no active layer on both sides of the electrode sheet (the two-side empty current collector area).

[0004] Therefore, how to reduce or even avoid the fracture phenomenon of the battery electrode sheet at the junction of the active layer ends is a technical problem that needs to be solved urgently by those skilled in the art. Utility Model Content

[0005] In view of this, the present application provides a core roll, which can improve the tensile strength of the electrode sheet at this junction and reduce the risk of electrode sheet fracture by setting an insulating layer connected to the active layer at the junction of the active layer ends of the electrode sheet.

[0006] In order to achieve the above application purpose, the present application provides the following technical solutions:

[0007] A core roll includes a first electrode sheet, a second electrode sheet, and a separator. Either the first electrode sheet or the second electrode sheet is a positive electrode sheet, and the other is a negative electrode sheet; the first electrode sheet includes a current collector, an active layer, and an insulating layer, where:

[0008] At least one side of the current collector includes a first region, a second region, and a third region located between the first region and the second region; the active layer is provided in the first region; the insulating layer is provided in the second region, and the thickness of the insulating layer is not greater than the thickness of the active layer; the connection part of the active layer and the insulating layer is located in the third region;

[0009] The first pole piece includes a second arc-shaped bending section, which is the third arc-shaped bending section close to the end of the pole piece in the direction opposite to the winding direction of the core, and the insulating layer is provided thereon;

[0010] The connecting portion is located at the second arc-shaped bending section or at the second straight section connected to one end of the second arc-shaped bending section away from the end of the pole piece in the direction opposite to the winding direction of the core.

[0011] Optionally, in the above-mentioned core, the first pole piece includes a first arc-shaped bending section, which is the first arc-shaped bending section close to the end of the pole piece in the direction opposite to the winding direction of the core, and the insulating layer is provided thereon.

[0012] Optionally, in the above-mentioned core, the insulating layer extends beyond the first arc-shaped bending section and reaches the end of the pole piece.

[0013] Optionally, in the above-mentioned core, the difference β between the distance a between the outer surface of the active layer in the connecting portion away from the current collector and the current collector and the thickness b of the active layer in the first region satisfies -10um ≤ β ≤ +10um.

[0014] Optionally, in the above-mentioned core, the difference δ between the thickness b of the active layer in the first region and the thickness c of the insulating layer in the second region satisfies -10um ≤ δ ≤ +10um;

[0015] The thickness b of the active layer in the first region ranges from 0 < b ≤ 100um;

[0016] The thickness c of the insulating layer in the second region ranges from 0 < c ≤ 100um.

[0017] Optionally, in the above-mentioned core, the thickness b of the active layer in the first region ranges from 0 < b ≤ 100um;

[0018] The thickness c of the insulating layer in the second region ranges from 0 < c ≤ 20um.

[0019] Optionally, in the above-mentioned core, the difference γ between the thickness d of the active layer in the connecting portion and the thickness b of the active layer in the first region satisfies -10um ≤ γ ≤ +10um.

[0020] Optionally, in the above-mentioned core, the active layer in the connecting portion is stacked on the side of the insulating layer away from the current collector.

[0021] Optionally, in the above-mentioned core, the length dimension S1 of the insulating layer in the connection part in the extending direction of the electrode tab ranges from 0 < S1 ≤ 50 mm;

[0022] and / or, the length dimension S2 of the insulating layer in the second region in the extending direction of the electrode tab ranges from 0 < S2 ≤ 300 mm.

[0023] Optionally, in the above-mentioned core, the insulating layer includes a ceramic layer, and the material composition of the ceramic layer includes at least one of silicon dioxide, aluminum oxide, boehmite, zirconia, magnesium oxide, magnesium hydroxide, and titanium oxide;

[0024] Alternatively, the insulating layer includes an adhesive layer, and the material composition of the adhesive layer includes at least one of polypropylene and polyethylene.

[0025] Optionally, in the above-mentioned core, it further includes:

[0026] A first adhesive tape that covers the surface of the connection part away from the current collector;

[0027] and / or, a second adhesive tape that is located on the surface of the current collector away from the connection part.

[0028] Optionally, in the above-mentioned core, the length L1 of the part of the first adhesive tape covering the active layer in the first direction ranges from 1 < L1 ≤ 10 mm;

[0029] The length L2 of the first adhesive tape in the second direction perpendicular to the first direction ranges from 6 < L2 ≤ 30 mm;

[0030] The thickness e of the first adhesive tape ranges from 5 μm < e ≤ 30 μm;

[0031] The projection of the second adhesive tape on the current collector is located within the projection area of the first adhesive tape on the current collector.

[0032] Optionally, in the above-mentioned core, raised structures are provided on the surfaces of the insulating layer and the active layer within a preset distance range on both sides of the connection part.

[0033] Optionally, in the above-mentioned core, the raised structure includes a plurality of strip-shaped protrusions arranged side by side in the extending direction of the electrode tab, and the protruding thickness L4 of the strip-shaped protrusions ranges from 0 < L4 ≤ 20 μm.

[0034] Optionally, in the above-mentioned core, the length S3 of the surface of the active layer provided with the raised structure extending in the extending direction of the electrode tab ranges from 0 < S3 ≤ 50 mm;

[0035] And / or, the length S4 of the surface of the insulating layer provided with the convex structure extending along the extending direction of the pole piece ranges from 0 < S4 ≤ 300 mm.

[0036] Compared with the prior art, in the core provided by the present application, an insulating layer is provided at the second arc-shaped bending section where the fracture problem is most likely to occur, and the insulating layer is connected to the end of the active layer, that is, an insulating layer is provided in the empty current collector area at the single-sided and double-sided junction of the original pole piece, and the insulating layer is connected to the active layer. Therefore, the insulating layer can slow down or even avoid the change in the thickness of the pole piece at the junction of the end of the active layer located in the second arc-shaped bending section or the second straight section connected thereto, and at the same time improve the tensile strength of the second arc-shaped bending section of the pole piece, relieve or even avoid the pole piece fatigue problem at the position where the junction of the end of the active layer is located due to the compaction of the core, thereby reducing or even avoiding the risk of pole piece fracture in the second arc-shaped bending section of the pole piece due to the change in the thickness of the end of the active layer and the compaction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0038] Figure 1 Schematic diagram of a core structure provided by an embodiment of the present application. (The arrow in the figure indicates the winding direction of the core)

[0039] Figure 2 Schematic diagram of a structure in which an insulating layer is provided at the junction of the ends of the active layer before the pole piece is cut in an embodiment of the present application.

[0040] Figures 3 to 8 Schematic diagrams of various pole pieces provided in different embodiments of the present application respectively.

[0041] Wherein:

[0042] 1 - pole piece, 3 - separator, 4 - adhesive tape, 5 - insulating layer,

[0043] 11 - current collector, 12 - active layer,

[0044] 41 - first adhesive tape, 42 - second adhesive tape,

[0045] 51 - first end region, 121 - second end region,

[0046] 61 - negative pole tab, 62 - positive pole tab,

[0047] 101 - first arc-shaped bending section, 102 - second arc-shaped bending section,

[0048] 103 - The first straight section, 104 - The second straight section,

[0049] 512 - The connecting part. Specific embodiments

[0050] It has been found through research that during the preparation of the battery cell, a cold rolling process is used to calender the electrode sheet. Due to the "step" structure caused by the thickness difference at the junction of the ends of the active layer of the electrode sheet, when pressure is applied to this junction, it will cause additional damage to the electrode sheet, resulting in a decrease in the tensile strength of the electrode sheet. For example, during the cold rolling process, the roller will cause greater damage to the electrode sheet at the junction of the ends of the active layer of the electrode sheet, making the tensile strength of the electrode sheet at this position lower than that at other positions. As a result, the junction of the ends of the active layer of the electrode sheet is prone to breakage due to the expansion of the battery cell, especially the third arc-shaped bending section (counting from the end of the electrode sheet) is most likely to have the phenomenon of electrode sheet breakage, followed by the first arc-shaped bending section (counting from the end of the electrode sheet) is also prone to have the phenomenon of electrode sheet breakage.

[0051] Based on this, the present application provides a structure in which an insulating layer (such as a ceramic layer) is connected to the active layer at the junction of the ends of the active layer of the electrode sheet (at least at the original single-sided and double-sided junction where cracking is most likely to occur), so as to improve the tensile strength of the electrode sheet at the corresponding position and reduce the risk of electrode sheet breakage.

[0052] It should be noted here that the end of the electrode sheet mentioned in this article refers to: the electrode sheet in the core is in a wound structure, the end located at the innermost part of the core is the head end of the electrode sheet, and the end located at the outermost side of the core is the end of the electrode sheet.

[0053] Next, the technical solutions in the embodiments of the present application will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0054] The first specific embodiment

[0055] Please refer to Figure 1 and Figure 3 , the first embodiment of the present application provides a core, which includes a first electrode sheet 1, a second electrode sheet 2 and a separator 3. Either the first electrode sheet 1 or the second electrode sheet 2 is a positive electrode sheet, and the other is a negative electrode sheet.

[0056] Among them, please refer to Figure 3, the first electrode tab 1 includes a current collector 11, an active layer 12, and an insulating layer 5, and: at least one side of the current collector 11 includes a first region, a second region, and a third region located between the first region and the second region; the first region is provided with the active layer 12; the second region is provided with the insulating layer 5, and the thickness of the insulating layer 5 is not greater than the thickness of the active layer 12; the joint portion 512 formed by the insulating layer 5 and the active layer 12 at their connection is located in the third region.

[0057] In addition, please refer to Figure 1 , the first electrode tab 1 includes a first arc-shaped bending section 101 and a second arc-shaped bending section 102. The first arc-shaped bending section 101 is the first arc-shaped bending section close to the end W of the electrode tab in the direction opposite to the winding direction of the core; the second arc-shaped bending section 102 is the third arc-shaped bending section close to the end W of the electrode tab in the direction opposite to the winding direction of the core, located radially inside the first arc-shaped bending section 101, and is provided with the insulating layer 5. Moreover, the joint portion 512 formed by the insulating layer 5 and the active layer 12 at their connection is located in the second arc-shaped bending section 102 (including inside the second arc-shaped bending section 102, and also including one end of the second arc-shaped bending section 102 in the direction away from / towards the end W of the electrode tab in the direction opposite to the winding direction of the core), or in the second straight section 104 connected to one end of the second arc-shaped bending section 102 in the direction opposite to the winding direction of the core and away from the end of the electrode tab.

[0058] It can be seen that in the core provided by the present application, the insulating layer 5 is provided in the second arc-shaped bending section 102 where the fracture problem is most likely to occur, and the ends of the insulating layer 5 and the active layer 12 are connected, that is, the insulating layer 5 is provided in the empty current collector area at the junction of the single and double sides of the original electrode tab, and the insulating layer 5 is connected to the active layer 12. Thus, the insulating layer 5 can slow down or even avoid the change in the thickness of the electrode tab at the junction of the ends of the active layer located in the second arc-shaped bending section 102 or its connected second straight section 104. At the same time, the tensile strength of the second arc-shaped bending section 102 of the electrode tab is improved, and the fatigue problem of the electrode tab caused by the compaction of the core at the location of the junction of the ends of the active layer is alleviated or even avoided, thereby reducing or even avoiding the risk of fracture of the second arc-shaped bending section 102 of the electrode tab due to the change in the thickness of the ends of the active layer and the compaction process.

[0059] Since the junction of the single-empty surface of the electrode tab, that is, the junction between the area where the active layer is provided on one side of the electrode tab and the area where there is no active layer on both sides of the electrode tab (the empty current collector areas on both sides), is generally located at the above-mentioned first arc-shaped bending section 102, and this single-empty surface junction is also a position where breakage is more likely to occur. Therefore, further, in some embodiments, an insulating layer 5 is also provided on the above-mentioned first arc-shaped bending section 101, and the connecting portion 512 formed by the insulating layer 5 and the active layer 12 at their connection is located on the first arc-shaped bending section 101 (including within the first arc-shaped bending section 101, and also including the end of the first arc-shaped bending section 101 that is away from / close to the electrode tab end W in the direction opposite to the winding direction of the core), or is located on the first straight section 103 connected to the end of the first arc-shaped bending section 101 that is away from the electrode tab end W in the direction opposite to the winding direction of the core. Further, the insulating layer 5 can also extend beyond the first arc-shaped bending section 101 and reach the electrode tab end; or the insulating layer 5 can be not provided on the side surface of the current collector between the first arc-shaped bending section 101 and the electrode tab end W, and only the empty current collector area of the electrode tab end W is fixed by the adhesive tape 4.

[0060] Thus, it can be seen that in this core, an insulating layer 5 is also provided on the first arc-shaped bending section 101 where breakage is more likely to occur, and the end of the insulating layer 5 is connected to the active layer 12. That is, an insulating layer 5 is provided in the empty current collector area at the original junction of the single-empty surface of the electrode tab, and the insulating layer 5 is connected to the active layer 12. Thus, through the insulating layer 5, the thickness change of the electrode tab at the junction of the ends of the active layer located on the first arc-shaped bending section 101 or the first straight section 103 connected thereto can be slowed down or even avoided, and at the same time, the tensile strength of the first arc-shaped bending section 101 of the electrode tab is improved, and the fatigue problem of the electrode tab caused by the compaction of the core at the position where the junction of the ends of the active layer is located is alleviated or even avoided, thereby reducing or even avoiding the risk of electrode tab breakage of the first arc-shaped bending section 101 of the electrode tab due to the thickness change of the ends of the active layer and the compaction process.

[0061] Please refer to Figure 3 , the difference β between the distance a between the outer surface of the active layer 12 away from the current collector 11 and the current collector 11 in the above-mentioned connecting portion 512 and the thickness b of the active layer 12 in the first region satisfies -10um ≤ β ≤ +10um. For example, β = 0 or ±1um or ±2um or ±3um or ±4um or ±5um or ±6um or ±7um or ±8um or ±9um, etc., any value within the range from -10um to +10um. That is, in the connecting portion 512, the distance a between the outer surface of the active layer 12 (one of the two side surfaces of the active layer 12 that is away from the current collector 11 is the outer surface) and the current collector 11 is the same as the thickness b of the active layer 12 in the first region, that is Figure 2The difference between a and b is very small, only within the error range, so it can be considered that a and b are basically equal. In other words, the thickness of the end of the active layer 12 connected to the insulating layer 5 is consistent with the thickness of the other active layers 12 located in the first region. Here, it should be noted that the so-called "being consistent" means that when the active layer 12 is coated on the current collector 11, the distance from the outer surface of the active layer 12 to the current collector 11 is basically within the same dimension range, and no thickening or thinning treatment is performed on the connecting portion 512. In a specific embodiment, the difference range between a and b is generally within ±10 μm. Moreover, it should also be noted that the "connecting portion 512" mentioned in this article can be Figure 2 , Figure 3 , Figure 5 , Figure 6 , Figure 8 , Figure 8 the seam structure formed at the connection by connecting in the transverse direction as shown in; or, it can also be Figure 4 the staggered connection structure formed by stacking and arranging in the longitudinal direction as shown in.

[0062] Thus, it can be seen that in the first pole piece 1 provided by the embodiment of the present application, an insulating layer 5 is coated on the current collector area at the junction of the original pole piece active layer end face and the empty current collector area, so that the insulating layer 5 is in contact with the active layer 12, so as to slow down the thickness change at the junction of the pole piece active layer end face through the insulating layer 5, relieve the pole piece fatigue caused by compaction at the junction of the pole piece active layer end face, thereby improving the tensile strength at the junction of the pole piece active layer end, and reducing the risk of pole piece fracture.

[0063] Please refer to Figure 2 and Figure 3 , in some embodiments, in the above-mentioned first pole piece 1, the difference δ between the thickness b of the active layer 12 located in the first region and the thickness c of the insulating layer 5 located in the second region satisfies -10um ≤ δ ≤ +10um, for example, δ = 0 or ±1um or ±2um or ±3um or ±4um or ±5um or ±6um or ±7um or ±8um or ±9um, etc., any value within the range from -10um to +10um. Moreover, the value range of the thickness b of the active layer 12 is 0 < b ≤ 100um, and the value range of the thickness c of the insulating layer 5 is 0 < c ≤ 100um. For example, b = 55um or 75um or 85um or 95um, etc., any value within 100um, c = 55um or 75um or 85um or 95um, etc., any value within 100um. Thus, as Figure 3As shown, the difference γ between the thickness d of the active layer 12 in the above-mentioned connecting portion 512 and the thickness b of the active layer 12 in the first region satisfies -10 μm ≤ γ ≤ +10 μm. For example, γ = 0 or ±1 μm or ±2 μm or ±3 μm or ±4 μm or ±5 μm or ±6 μm or ±7 μm or ±8 μm or ±9 μm, etc., any value within the range from -10 μm to +10 μm. That is, the thicknesses of the active layer 12 in the first region and the third region, and the thicknesses of the insulating layer 5 in the second region and the third region are basically the same. Thus, the risk of fracture caused by the change in the thickness of the electrode sheet is avoided to the greatest extent.

[0064] In some embodiments, the insulating layer 5 can be a ceramic layer, that is, the insulating layer 5 can be made of ceramic materials. Specifically, the material composition of the ceramic layer includes at least one of silicon dioxide, alumina, boehmite, and zirconia. However, it is not limited thereto, and in other embodiments, other materials with the same functional effects can be used instead. For example, the insulating layer 5 includes an adhesive layer, and the material composition of the adhesive layer includes at least one of polypropylene and polyethylene. When the insulating layer 5 is an adhesive layer, the thickness c of the adhesive layer can be set at 0 < c ≤ 20 mm. The present application does not make specific limitations in this regard. During specific implementation, the material particles of the insulating layer 5 are smaller than those of the active layer 12. During the cold rolling process of the electrode sheet, the insulating layer 5 with smaller particle size causes less damage to the electrode sheet, which is more conducive to reducing the damage of the roller to the electrode sheet, improving the tensile strength of the electrode sheet in the above-mentioned connecting portion 512, and avoiding the phenomenon of electrode sheet fracture.

[0065] During specific implementation, if the above-mentioned first electrode sheet 1 is a negative electrode sheet, the material of the active layer 12 includes at least one of graphite material, silicon-carbon material, and silicon-oxygen material; if the above-mentioned first electrode sheet 1 is a positive electrode sheet, the material of the active layer 12 includes at least one of LCO (abbreviation for lithium cobalt oxide, full name Lithium Cobalt Oxide) material, ternary material, and lithium iron phosphate material. Among them, the "ternary material" refers to a material as a whole composed of three chemical components (elements), components (simple substances and compounds), or parts (parts), including alloys, inorganic non-metallic materials, organic materials, polymer composite materials, etc. In the new energy industry, the ternary material usually refers to the positive electrode material of lithium nickel cobalt manganese oxide, which has advantages such as high voltage resistance, high specific capacity, and less cobalt content.

[0066] During specific implementation, before the process of cutting the electrode sheet, the above-mentioned insulating layer 5 can be provided in the empty current collector area of the electrode sheet, that is, on the side where the active layer 12 is not coated and the current collector 11 is exposed. Thus, a structure in which the insulating layer 5 and the active layer 12 are arranged at intervals on the side of the current collector 11 as shown in Figure 2 is formed. Among them, the insulating layer 5 can completely cover the exposed side of the current collector 11 (such as Figure 2As shown in [the figure], the problem of breakage caused by changes in the thickness of the electrode coating material can be completely eliminated. However, it is not limited to this. In other embodiments, the insulating layer 5 can also be connected only to the end of one side of the active layer 12 according to actual needs (not shown in the figure), as long as the electrode structure described above can be obtained by cutting.

[0067] Second specific embodiment

[0068] Please refer to Figure 4 , the second embodiment of the present application provides a core, which is only different from the core in the above first specific embodiment in that: the thickness b of the active layer 12 in the first region ranges from 0 < b ≤ 100 um, and the thickness c of the insulating layer 5 in the second region ranges from 0 < c ≤ 20 um. At this time, in the connection part 512: the interface between the insulating layer 5 and the active layer 12 is perpendicular to the side of the current collector; or, the angle between the interface between the insulating layer 5 and the active layer 12 and the side of the current collector is an acute angle. In this embodiment, although there is still a step structure caused by unequal thickness at the position of the connection part 512 between the insulating layer 5 and the active layer 12, the height difference of its step structure is much smaller than the height difference at the junction of the end of the active layer and the empty current collector area on the side of the current collector in the prior art. Therefore, the risk of the electrode breaking at this position can also be avoided to a great extent, and at the same time, it is beneficial to the weight reduction requirement of the battery cell.

[0069] Third specific embodiment

[0070] The third embodiment of the present application provides a core, which is only different from the core in the above second specific embodiment in the specific connection structure of the connection part 512. For details, please refer to Figure 5: The insulating layer 5 in the connecting portion 512 is referred to as the first end region 51, and the active layer 12 in the connecting portion 512 is referred to as the second end region 121. In the direction perpendicular to the side surface of the current collector, the second end region 121 covers the side surface of the first end region 51 that is away from the current collector 11. That is, the active layer in the connecting portion 512 is stacked on the side surface of the insulating layer 5 that is away from the current collector 11. That is to say, in the above-mentioned connecting portion 512: the insulating layer 5 covers the side surface of the current collector 11, and the active layer 12 covers the outer surface of the insulating layer 5 that is away from the current collector 11. Thus, in this connecting portion 512, the insulating layer 5 and the active layer 12 form a stacked structure in the direction perpendicular to the side surface of the current collector, and at the same time form an interleaved structure in the direction parallel to the side surface of the current collector. At this time, the range of the length dimension S1 of the insulating layer 5 (i.e., the first end region 51) in the connecting portion 512 in the extending direction can be set to 0 < S1 ≤ 50 mm; and / or, the range of the length dimension S2 of the other regions of the insulating layer 5 except the first end region 51 in the extending direction can be set to 0 < S2 ≤ 300 mm. Thus, it can be seen that in the first pole piece 1 of this core, since the insulating layer 5 is applied to the bottom at the junction of the active layer 12 and the empty current collector region (i.e., the connecting portion 512); and the material particles of the insulating layer 5 are smaller than those of the material of the active layer 12, therefore, during the cold rolling process of the pole piece, the small-particle insulating layer 5 causes less damage to the pole piece, which is beneficial to reducing the damage of the rolling mill to the pole piece, improving the tensile strength of the pole piece at the junction of the active layer 12 and the empty current collector region, and avoiding the phenomenon of pole piece fracture.

[0071] In summary, please refer to Figure 1 , in the core provided by this application, the position of the insulating layer 5 in the core at least includes the third arc-shaped bending section counted backwards along the direction opposite to the winding direction (i.e., Figure 1 the second arc-shaped bending section 102 shown by the bold arc in Figure 1 ), and further may include the first arc-shaped bending section located at the outermost side of the core and closest to the end of the pole piece (i.e.,

[0072] When the connecting portion 512 is located at one end of the second arc-shaped bending section 102 that is far from the end of the pole piece in the direction opposite to the winding direction of the core (i.e., the tangential connection position of the second arc-shaped bending section 102 and the second straight section 104), the insulating layer 5 can adopt an adhesive layer, and the adhesive layer covers the second arc-shaped bending section 102 and the first arc-shaped bending section 101 and extends to all empty current collector areas. Moreover, the thickness of the adhesive layer can be any value greater than zero and less than or equal to 20 mm. Since part of the reason for the pole piece breakage is that the negative pole piece expands during the cycling process, applying an outward force to the arc-shaped bending areas of each layer in the core. Therefore, adhesive layers are coated on the above two arc-shaped bending sections on the outermost side of the core, and then the two adhesive layers are compounded by a hot-melting method to jointly resist the outward expansion force of the pole piece, thereby being able to avoid the occurrence of pole piece breakage.

[0073] In some embodiments, the core may further include a structure with the tab in the middle and a multi-tab structure. Moreover, in some embodiments, the core battery further includes a first adhesive tape 41, as Figures 3 to 6 shown in [figure reference], the first adhesive tape 41 covers the surface of the connecting portion 512 far from the current collector 11. Further, in some embodiments, the core battery further includes a second adhesive tape 42, as Figure 6 shown in [figure reference], the second adhesive tape 42 is located on the surface of the current collector 11 far from the connecting portion 512. Specifically, the length L1 of the part of the first adhesive tape 41 covering the active layer 12 in the first direction (i.e., the length direction of the pole piece) ranges from 1 mm ≤ L1 ≤ 10 mm; the length L2 of the first adhesive tape 41 in the second direction (i.e., the width direction of the pole piece) perpendicular to the first direction ranges from 6 mm ≤ L2 ≤ 30 mm; the thickness e of the first adhesive tape 41 ranges from 5 μm ≤ e ≤ 30 μm. Moreover, the projection of the second adhesive tape 42 on the current collector 11 is located within the projection area of the first adhesive tape 41 on the current collector 11.

[0074] In addition, other adhesive tapes 4 are provided at other positions of the core battery. For example, the positions where the first tab 61 and the second tab 62 are located can be fixed and insulated by the adhesive tape 4, and for example, the end of the pole piece can be fixed by the adhesive tape 4.

[0075] In some embodiments, the surfaces of the insulating layer 5 and the active layer 12 within a preset distance range on both sides of the connecting portion 512 in the core battery are provided with embossed surfaces, that is, the surfaces are provided with a plurality of raised structures. For example, the above-mentioned second arc-shaped bending section 102 and the first arc-shaped bending section 101 are both provided with an insulating layer 5, and the junction or its vicinity of the second arc-shaped bending section 102 and the second straight section 104 is the connecting portion 512 where the active layer 12 and the insulating layer 5 are connected. Moreover, the above-mentioned second arc-shaped bending section 102 and the first arc-shaped bending section 101 are both embossed. Specifically, please refer to Figure 7 and Figure 8, the raised structures on the embossed surface include a plurality of strip-shaped protrusions arranged side by side along the extending direction of the electrode tab, that is, the embossing morphology is vertical strips parallel to the height direction of the core. Preferably, the protruding thickness L4 of the strip-shaped protrusion ranges from 0 < L4 ≤ 20 μm. Moreover, the length S3 of the embossed surface extending along the extending direction of the electrode tab on the surface of the active layer 12 ranges from 0 < S3 ≤ 50 mm; and / or, the length S4 of the embossed surface extending along the extending direction of the electrode tab on the surface of the insulating layer 5 ranges from 0 < S4 ≤ 300 mm.

[0076] During specific implementation, the cross-sectional morphology of the electrode tab after embossing treatment in the direction parallel to the long side of the electrode tab can be like Figure 7 shown in the figure as chain-shaped, or can be Figure 8 shown in the figure as W-shaped. Tests prove that the tensile strength of the electrode tab after embossing treatment does not decrease. During the cycling process of the battery cell, the electrode tab can buffer the acting force generated during the cyclic expansion of the battery cell (especially Figure 8 the shape of the electrode tab shown in the figure), thereby alleviating the fracture of the electrode tab.

[0077] Finally, it should also be noted that in this article, relational terms such as first and second are only used 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 term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed.

[0078] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0079] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A winding core, comprising a first pole piece (1), a second pole piece (2) and a separator (3), wherein either the first pole piece (1) or the second pole piece (2) is a positive pole piece and the other is a negative pole piece; the first pole piece (1) comprises a current collector (11) and an active layer (12), characterized in that: It also includes an insulating layer (5), wherein: At least one side of the current collector (11) comprises a first region and a second region, and a third region located between the first region and the second region; the first region is provided with the active layer (12); the second region is provided with the insulating layer (5), the thickness of the insulating layer (5) is not greater than the thickness of the active layer (12); the connection portion (512) between the active layer (12) and the insulating layer (5) is located in the third region; The first pole piece (1) comprises a second arc-shaped bending section (102), the second arc-shaped bending section (102) being the third arc-shaped bending section close to the pole piece tail end in a direction opposite to the winding direction of the winding core, and the second arc-shaped bending section (102) is provided with the insulating layer (5); The connecting portion (512) is located at the second arc-shaped bending section (102), or at the second straight section (104) connected to an end of the second arc-shaped bending section (102) away from the pole piece tail end in a direction opposite to the winding direction of the winding core.

2. The winding core according to claim 1, characterized in that: The first pole piece (1) comprises a first arc-shaped bending section (101), the first arc-shaped bending section (101) being the first arc-shaped bending section close to the pole piece tail end in a direction opposite to the winding direction of the winding core, and provided with the insulating layer (5).

3. The winding core according to claim 2, characterized in that: The insulating layer (5) exceeds the first arc-shaped bending section (101) and extends to the tail end of the pole piece.

4. The winding core according to claim 1, characterized in that: A difference β between a distance a between an outer surface of the active layer (12) in the connecting portion (512) away from the current collector (11) and the current collector (11) and a thickness b of the active layer (12) located in the first region satisfies -10um≤β≤+10um.

5. The winding core according to claim 1, characterized in that: A difference δ between a thickness b of the active layer (12) located in the first region and a thickness c of the insulating layer (5) located in the second region satisfies −10 um ≤ δ ≤ +10 um; The thickness b of the active layer (12) located in the first region is in the range of 0<b≤100 um; The thickness c of the insulating layer (5) located in the second region is in the range of 0<c≤100 um.

6. The winding core according to claim 1, characterized in that: The thickness b of the active layer (12) located in the first region is in the range of 0<b≤100 um; The thickness c of the insulating layer (5) located in the second region is in the range of 0<c≤20 um.

7. The winding core according to claim 5 or 6, characterized in that: A difference γ between a thickness d of the active layer (12) in the connecting portion (512) and a thickness b of the active layer (12) located in the first region satisfies −10 um ≤ γ ≤ +10 um.

8. The winding core according to claim 6, characterized in that: The active layer (12) in the connecting portion (512) is stacked and arranged on a side of the insulating layer (5) away from the current collector (11).

9. The winding core according to claim 8, characterized in that: The length dimension S1 of the insulating layer (5) in the connecting portion (512) in the extension direction of the pole piece is in the range of 0<S1≤50mm; And / or, the length dimension S2 of the insulating layer (5) in the second region in the extension direction of the pole piece is in the range of 0<S2≤300 mm.

10. The winding core according to claim 1, characterized in that: The insulating layer (5) comprises a ceramic layer, wherein the material composition of the ceramic layer comprises at least one of silicon dioxide, aluminum oxide, boehmite, zirconium oxide, magnesium oxide, magnesium hydroxide, and titanium oxide; Alternatively, the insulating layer (5) comprises an adhesive layer, and the material composition of the adhesive layer comprises at least one of polypropylene and polyethylene.

11. The winding core according to claim 1, characterized in that: Also includes: A first adhesive tape (41), the first adhesive tape (41) covering a surface of the connecting portion (512) away from the current collector (11); And / or, a second adhesive tape (42), wherein the second adhesive tape (42) is located on a surface of the current collector (11) away from the connecting portion (512).

12. The winding core according to claim 11, characterized in that: The length L1 of the portion of the first adhesive tape (41) covering the active layer (12) in the first direction is in the range of 1 mm ≤ L1 ≤ 10 mm; The length L2 of the first adhesive tape (41) in a second direction perpendicular to the first direction is in the range of 6 mm ≤ L2 ≤ 30 mm; The thickness e of the first adhesive tape (41) is in the range of 5 μm≤e≤30 μm; The projection of the second adhesive tape (42) on the current collector (11) is located within the projection area of ​​the first adhesive tape (41) on the current collector (11).

13. The winding core according to claim 1, characterized in that: The surfaces of the connecting portion (512) and the insulating layer (5) and the active layer (12) within a preset distance range on both sides thereof are provided with protruding structures.

14. The winding core according to claim 13, characterized in that: The protrusion structure includes a plurality of strip-shaped protrusions arranged side by side along the extension direction of the pole piece, and the protrusion thickness L4 of the strip-shaped protrusions is in the range of 0<L4≤20μm.

15. The winding core according to claim 13, characterized in that: The length S3 of the surface of the active layer (12) provided with the protruding structure extending in the extension direction of the pole piece is in the range of 0<S3≤50mm; And / or, the length S4 of the surface of the insulating layer (5) provided with the protruding structure extending along the extension direction of the pole piece is in the range of 0<S4≤300mm.

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