Roll core and battery

Abstract

The utility model provides a roll core and a battery, relates to the technical field of batteries, and is used for solving the problems of insufficient electrolyte infiltration and lithium precipitation in an arc region caused by pole piece interlayer extrusion in related technologies. A first active material layer and a second active material layer are arranged on two surfaces of the positive current collector; a plurality of first concave parts are arranged on the first active material layer, and a plurality of convex parts corresponding to the first concave parts are arranged on the second active material layer; the roll core comprises a straight area and an arc area, a plurality of second concave parts are further arranged on the first active material layer in the arc area, and the size of the vertical projection of the second concave parts in the thickness direction of the pole piece is smaller than that of the vertical projection of the first concave parts in the thickness direction of the pole piece. The convex part and the first concave part provide support for the contact of the diaphragm, so that the electrolyte has enough infiltration quantity; the second sunken part can reduce channels for lithium ions to be transmitted in the active material layer in the arc area, and lithium precipitation in the arc area is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium electronic batteries, and particularly to a winding core and a battery. BACKGROUND

[0002] With the rapid development of lithium ion battery technology, people have higher requirements for the energy density, cycle life and safety performance of lithium ion batteries.

[0003] During the charging and discharging process of a lithium ion battery, the negative electrode sheet will swell, and the layers of the electrode sheet will be squeezed; in particular, the winding structure of the winding type lithium ion battery has a large stress accumulation in the arc region, and the arc region itself has a squeeze between the electrode sheets; in addition, the negative electrode sheet will swell during the charging and discharging process, and the squeeze between the electrode sheets will be intensified; at the same time, the squeeze will also be transmitted from the arc region to the flat region. This interlayer squeeze will eventually lead to insufficient electrolyte and poor wetting between the layers, interface deterioration, even lithium precipitation in the negative electrode sheet, and affect the safety of the battery cell. CONTENT OF THE UTILITY MODEL

[0004] In view of the above problems, the present application provides a winding core and a battery to solve the problem of insufficient electrolyte wetting and lithium precipitation in the arc region caused by the squeeze between the electrode sheets of the winding core in the related art.

[0005] In order to achieve the above purpose, the embodiments of the present application provide the following technical solutions:

[0006] The present application provides a winding core, comprising: a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a first active material layer and a second active material layer, the positive electrode current collector having opposite first and second surfaces along the thickness direction of the positive electrode sheet, the first active material layer being arranged on the first surface, and the second active material layer being arranged on the second surface; a plurality of first recessed portions are arranged on the first active material layer, and a plurality of protruding portions corresponding to the first recessed portions are arranged on the second active material layer; the winding core comprises a flat region and arc regions located at opposite ends of the flat region, a plurality of second recessed portions are further arranged on the first active material layer in the arc regions, and the size of the vertical projection of the second recessed portions in the thickness direction of the positive electrode sheet is smaller than the size of the vertical projection of the first recessed portions in the thickness direction of the positive electrode sheet.

[0007] In an embodiment of the present application, the first recess comprises a first recess portion and a first root portion connecting the first recess portion and a surface of the first active material layer, the first root portion has a first vertical distance H1 from a lowest point of the first recess portion in the thickness direction of the positive electrode sheet; the protrusion portion comprises a protrusion portion and a second root portion connecting the protrusion portion and a surface of the second active material layer, the second root portion has a second vertical distance H2 from an apex of the protrusion portion in the thickness direction of the positive electrode sheet; and the first vertical distance H1 is greater than the second vertical distance H2.

[0008] In an embodiment of the present application, at least one second recess is arranged in each of the first recesses in the circular arc region.

[0009] In an embodiment of the present application, the second surface comprises an uncoated region, the first surface corresponding to the uncoated region is provided with the first active material layer; and the uncoated region is provided with a plurality of the first protrusion portions.

[0010] In an embodiment of the present application, the positive electrode sheet comprises a first recess region and a second recess region, the first recess region is provided with the plurality of first recesses, and the second recess region is provided with the plurality of second recesses; in the length direction of the positive electrode sheet, the ratio of the length of the first recess region to the length of the positive electrode sheet is 0.9-1; and / or, in the width direction of the positive electrode sheet, the ratio of the width of the first recess region to the width of the positive electrode sheet is 0.8-1; and / or, the ratio of the area of the first recess region to the area of the first active material layer is 0.75-1; and / or, in the length direction of the positive electrode sheet, the ratio of the length of the second recess region to the length of the positive electrode sheet is 0.2-0.5; and / or, in the width direction of the positive electrode sheet, the ratio of the width of the second recess region to the width of the positive electrode sheet is 0.8-1; and / or, the ratio of the area of the second recess region to the area of the second active material layer is 0.2-0.5.

[0011] In an embodiment of the present application, the second recess comprises a second recess portion and a third root portion connecting the second recess portion and a surface of the first active material layer, the third root portion has a third vertical distance H3 from a lowest point of the second recess portion in the thickness direction of the positive electrode sheet; the third vertical distance H3 is 1-50 μm; and / or, the first active material layer has a first thickness h1, the ratio of the third vertical distance H3 to the first thickness h1 is 0.1-0.2; and / or, the first vertical distance H1 is 1-30 μm; and / or, the first active material layer has a first thickness h1, the ratio of the first vertical distance H1 to the first thickness h1 is 0.4-1.

[0012] In an embodiment of the present application, the surface of the first active material layer close to the third root has a crack.

[0013] In an embodiment of the present application, the first recess has a first area S1 in the vertical projection in the thickness direction of the positive electrode sheet, the first area S1 is 0.15mm 2 ~ 20mm 2 ; and / or, the second recess has a third area S3 in the vertical projection in the thickness direction of the positive electrode sheet, the third area S3 is 0.002mm 2 ~ 0.2mm 2 ; and / or, the total area of the plurality of first recesses in the vertical projection in the thickness direction of the positive electrode sheet is a fifth area S5, the total area of the plurality of second recesses in the vertical projection in the thickness direction of the positive electrode sheet is a sixth area S6, and the ratio of the sixth area S6 to the fifth area S5 is 0.05 ~ 0.3.

[0014] In an embodiment of the present application, the plurality of first recesses and the plurality of second recesses are arranged in an array; the edges of two adjacent first recesses are spaced apart by a first distance p1, the first distance p1 is 0.5 ~ 5mm; and / or, the edges of two adjacent second recesses are spaced apart by a third distance p3, the third distance p3 is 100 ~ 500μm.

[0015] The embodiments of the present application also provide a battery comprising the winding core described above.

[0016] The winding core provided by the embodiments of the present application has the following technical effects:

[0017] The first recess and the protruding part corresponding to the first recess are machined on the positive electrode sheet by a special roller, the combination of the protruding part and the first recess provides support for the contact of the diaphragm, increases the micro-gap between the positive electrode sheet and the diaphragm, and these micro-gaps form a space that can accommodate electrolyte, so that the electrolyte has sufficient amount of wetting on the electrode sheet, and the abnormal situation of insufficient electrolyte between the electrode sheet and the diaphragm, poor wetting and even lithium precipitation of the negative electrode sheet caused by interlayer extrusion of the electrode sheet is avoided.

[0018] Meanwhile, a plurality of second recessed portions are provided on the active material layer of the positive electrode sheet in the circular arc region by means of laser drilling, the recessed directions of the second recessed portions and the first recessed portions are the same, the size of the vertical projection of the second recessed portions in the thickness direction of the positive electrode sheet is smaller than the size of the vertical projection of the first recessed portions in the thickness direction of the positive electrode sheet, the active material layer is composed of a plurality of active material particles, lithium ions need to pass through the gaps between the active material particles when transmitting in the active material layer, which leads to the bending of the transmission channel; therefore, the lithium ions transmitting in the electrolyte are faster and more uniform than the lithium ions transmitting in the active material layer. The second recessed portions provided in the active material layer of the circular arc region can reduce the transmission channel of the lithium ions in the active material layer, so that the lithium ions transmit in the electrolyte, avoid the accumulation of lithium ions in the circular arc region, and improve the lithium precipitation phenomenon in the circular arc region. BRIEF DESCRIPTION OF DRAWINGS

[0019] 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 needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0020] Figure 1 The structure schematic diagram of the winding core provided by the embodiments of the present application is shown in the figure;

[0021] Figure 2 The structure schematic diagram of the positive electrode sheet provided by the embodiments of the present application is shown in the figure Figure 1 ;

[0022] Figure 3 The structure schematic diagram of the first recessed portion on the positive electrode sheet provided by the embodiments of the present application is shown in the figure;

[0023] Figure 4 The structure schematic diagram of the second recessed portion on the positive electrode sheet provided by the embodiments of the present application is shown in the figure;

[0024] Figure 5 The enlarged view of part A in the figure Figure 2

[0025] Figure 6 The structure schematic diagram of the first recessed portion and the second recessed portion coinciding provided by the embodiments of the present application is shown in the figure;

[0026] Figure 7 The projection schematic diagram of the first recessed portion provided by the embodiments of the present application is shown in the figure;

[0027] Figure 8 The projection schematic diagram of the second recessed portion provided by the embodiments of the present application is shown in the figure;

[0028] Figure 9 ​Structure of the positive electrode sheet provided for the embodiments of the present application Figure 2 ;

[0029] Figure 10 Structure of the positive electrode sheet provided for the embodiments of the present application Figure 3 .

[0030] Reference signs:

[0031] 100 - positive electrode sheet;

[0032] 101 - positive electrode current collector; 102 - first active material layer; 103 - second active material layer;

[0033] 200 - negative electrode sheet;

[0034] 1021 - first recessed portion; 1022 - second recessed portion; 1031 - protruding portion; 1023 - third surface; 1032 - fourth surface;

[0035] 10211 - first recessed portion; 10212 - first root portion; 10311 - protruding portion; 10312 - second root portion; 10221 - second recessed portion; 10222 - third root portion;

[0036] 300 - tab;

[0037] S10 - flat area; S20 - circular arc area; S11 - first recessed area; S12 - second recessed area. DETAILED DESCRIPTION

[0038] The winding structure of the battery cell is formed by the electrode assembly through laminated winding, the cross section of the winding structure presents a flat elliptical structure, the two sides of the elliptical structure are circular arc areas, and the middle of the elliptical structure is a flat area; the negative electrode sheet will swell during the charging and discharging process of the lithium ion battery, the flat area can freely swell upward and downward, but the outward swelling of the circular arc area is restricted due to its structural characteristics and stress accumulation, resulting in interlayer extrusion of the electrode sheet in the circular arc area; the extrusion of the circular arc area will also be transmitted to the flat area, so that the interlayer extrusion of the electrode sheet also occurs in the flat area.

[0039] The interlayer extrusion of the electrode sheet will lead to poor electrolyte immersion and low electrolyte retention in the interlayer of the electrode sheet; which means that the region loses the transmission channel of lithium ions, so that the lithium ions of the positive electrode sheet cannot be extracted, the number of lithium ions embedded at the corresponding position of the negative electrode sheet is insufficient, and then purple spots appear, and finally the lithium ions of the negative electrode sheet cannot return to the positive electrode sheet, and finally deposit on the surface of the negative electrode sheet, i.e. lithium precipitation.

[0040] In addition, during the cycle process, due to the large swelling of the negative electrode sheet, the two side separators in contact with the negative electrode sheet are easily extruded, resulting in extrusion and deformation of the separator, so that the micropores of the separator are blocked, further increasing the risk of lithium precipitation in the circular arc area.

[0041] The winding core provided by the embodiment of the present application forms a positive plate after coating the active material layer on both sides of the positive current collector, and then processes a first recess and a protrusion corresponding to the first recess on the positive plate through a special roller. The combination of the protrusion and the first recess provides support for the contact of the diaphragm, increases the micro-gap between the positive plate and the diaphragm, and these micro-gaps form a space that can accommodate electrolyte, so that the electrolyte has sufficient wetting amount on the positive plate, avoiding the abnormal situation of insufficient electrolyte, poor wetting and even lithium precipitation of the negative plate caused by the interlayer extrusion of the positive plate.

[0042] Meanwhile, a plurality of second recesses are provided on the active material layer of the positive plate in the circular arc area by means of laser drilling, the recess directions of the second recesses and the first recesses are the same, the size of the vertical projection of the second recesses in the thickness direction of the positive plate is smaller than the size of the vertical projection of the first recesses in the thickness direction of the positive plate, and at least one second recess is arranged in each first recess in the circular arc area. The active material layer is composed of a plurality of active material particles, and lithium ions need to pass through the gap between the active material particles when transmitting in the active material layer, resulting in a curved transmission channel. Therefore, the lithium ions transmitting in the electrolyte are faster and more uniform than the lithium ions transmitting in the active material layer. The second recesses arranged in the active material layer in the circular arc area can reduce the transmission channel of the lithium ions in the active material layer, so that the lithium ions transmit in the electrolyte, avoid the accumulation of lithium ions in the circular arc area, and improve the lithium precipitation phenomenon in the circular arc area.

[0043] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not 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 labor are within the scope of protection of the present application.

[0044] In the embodiments of the present application, the thickness direction of the plate is also the z-axis shown in the figure; the length direction of the plate is also the x-axis shown in the figure; and the width direction of the plate is also the y-axis shown in the figure.

[0045] Reference Figure 1 The winding core provided by the embodiment of the present application includes a positive plate 100, a negative plate 200 and a diaphragm arranged between the positive plate 100 and the negative plate 200, and the positive plate 100, the diaphragm and the negative plate 200 are wound to form a winding core.

[0046] Reference Figure 2 And Figure 3The positive electrode sheet 100 includes a positive electrode current collector 101, a first active material layer 102, and a second active material layer 103. The positive electrode current collector 101 has opposite first and second surfaces in the positive electrode sheet thickness direction (z-axis shown in the figure). The first active material layer 102 is disposed on the first surface, and the second active material layer 103 is disposed on the second surface.

[0047] The first active material layer 102 is provided with a plurality of first recesses 1021 arranged in an array. The second active material layer 103 is provided with a plurality of protrusions 1031 corresponding to the first recesses 1021.

[0048] The correspondence between the first recesses 1021 and the protrusions 1031 means that the projection of the first recesses 1021 in the positive electrode sheet thickness direction (z-axis shown in the figure) covers the projection of the protrusions 1031 in the positive electrode sheet thickness direction.

[0049] The first recesses 1021 and the protrusions 1031 are respectively disposed on the first active material layer 102 and the second active material layer 103 coated on the two surfaces of the positive electrode current collector 101. This can provide support for the contact of the separator, increase the micro-gaps between the electrode sheet and the separator, and form spaces that can accommodate electrolyte. This allows the electrolyte to have sufficient wetting of the electrode sheet, and avoids the abnormal situation of insufficient electrolyte between the electrode sheet and the separator, poor wetting, or even lithium precipitation of the negative electrode sheet caused by interlayer extrusion of the electrode sheet.

[0050] Continuing to refer to Figure 1 and Figure 2 The core includes a flat area S10 and a circular arc area S20 located at opposite ends of the flat area S10. The first active material layer 102 in the circular arc area S20 is further provided with a plurality of second recesses 1022 arranged in an array. That is, the second recesses 1022 are only disposed in the circular arc area of the core, and the recess directions of the second recesses 1022 and the first recesses 1021 are the same.

[0051] The size of the vertical projection of the second recesses 1022 in the positive electrode sheet thickness direction (z-axis shown in the figure) is smaller than the size of the vertical projection of the first recesses 1021 in the positive electrode sheet thickness direction (z-axis shown in the figure).

[0052] The second recesses 1022 disposed in the first active material layer 102 in the circular arc area S20 can reduce the channel for lithium ion transmission in the first active material layer 102, so that lithium ion transmission in the electrolyte is achieved, lithium ion accumulation in the circular arc area S20 is avoided, and the lithium precipitation phenomenon in the circular arc area S20 is improved.

[0053] The plurality of second recessed portions 1022 are formed on the first active material layer 102 of the positive electrode sheet 100 in the arc region by means of laser drilling or mechanical hole making, and those skilled in the art can flexibly select the above two implementation manners according to actual conditions.

[0054] In the embodiment of the present application, at least one second recessed portion 1022 is arranged in each first recessed portion 1021 in the arc region. That is, in the arc region S20, there is an overlapping region of the first recessed portion 1021 and the second recessed portion 1022, and in the overlapping region, the number of the second recessed portions 1022 in the first recessed portion 1021 is at least one. The arrangement of at least one second recessed portion 1022 in the first recessed portion 1021 limits the arrangement density of the second recessed portion 1022 and ensures that the lithium precipitation phenomenon in the arc region can be improved.

[0055] Reference Figure 6 The number of the second recessed portions 1022 in the first recessed portion 1021 can also be 0-3.

[0056] If it is higher than 3, the stress in the overlapping region is too concentrated, the flexibility of the electrode sheet is poor, or the heat affected zone caused by the second recessed portion 1022 is stacked, resulting in more energy loss. If it is lower than 3, the improvement effect is not obvious.

[0057] Continuing to refer to Figure 3 In the embodiment of the present application, the first active material layer 102 has a third surface 1023, and the third surface 1023 is away from the positive electrode current collector 101; the first recessed portion 1021 includes a first recessed portion 10211 and a first root portion 10212 connecting the first recessed portion 10211 and the third surface 1023, and in the thickness direction of the positive electrode sheet (z-axis shown in the figure), the first root portion 10212 has a first vertical distance H1 from the lowest point of the first recessed portion 10211.

[0058] The second active material layer 103 has a fourth surface 1032, and the fourth surface 1032 is away from the positive electrode current collector 101; the protruding portion 1031 includes a protruding portion 10311 and a second root portion 10312 connecting the protruding portion 10311 and the fourth surface 1032, and in the thickness direction of the positive electrode sheet (z-axis shown in the figure), the second root portion 10312 has a second vertical distance H2 from the vertex of the protruding portion 10311.

[0059] The first vertical distance H1 is greater than the second vertical distance H2.

[0060] That is, when the first recessed portion 1021 is processed on the positive electrode sheet 100 by a special roller, the recessed degree of the first recessed portion 1021 decreases in the direction of the first active material layer 102 towards the second active material layer 103.

[0061] The decreasing degree of recess of the first recessed part 1021 can release stress generated when the first recessed part 1021 is formed, prevent the active material layer from being difficult to be delithiated due to the first recessed part 1021 being too compact, and further prevent the migration rate of lithium ions from being reduced, thereby avoiding the impedance of the roll core from being increased.

[0062] With reference to the foregoing Figure 3 In the embodiment, the first vertical distance H1 can be 1-30 μm; preferably, the first vertical distance H1 can be 5-25 μm.

[0063] The first vertical distance H1 is the depth of the first recessed part 1021 (or the height of the protruding part 1031). If the height of the protruding part 1031 is too small, the wettability effect cannot be met, and if the height of the protruding part 1031 is too large, the extrusion stress of the protruding part 1031 on the current collector 101 is large, which can easily cause the current collector 101 to be broken.

[0064] The first active material layer 102 has a first thickness h1, and the ratio of the first vertical distance H1 to the first thickness h1 is 0.4-1.

[0065] By limiting the relationship between the height of the protruding part 1031 and the thickness of the first active material layer 102, the wettability effect can be met, and the thickness of the roll core as a whole can be prevented from being too large.

[0066] With reference to the foregoing Figure 4 In the embodiment, the second recessed part 1022 includes a second recess 10221 and a third root 10222 connecting the second recess 10221 and the third surface 1023. In the thickness direction of the positive electrode sheet (z-axis shown in the figure), the third root 10222 and the lowest point of the second recess 10221 have a third vertical distance H3, the third vertical distance H3 is the depth of the second recessed part 1022, and the third vertical distance H3 is 1-50 μm; preferably, the third vertical distance H3 can be 10-40 μm.

[0067] The ratio of the third vertical distance H3 to the first thickness h1 is 0.1-0.2.

[0068] By limiting the depth of the second recessed part 1022, it can be ensured that the second recessed part 1022 can improve the lithium precipitation phenomenon in the circular arc area S20, and at the same time, the depth of the second recessed part 1022 can be prevented from being too large to cause the current collector to be easily exposed or the active material layer to be thick to increase the thickness of the battery.

[0069] With reference to the foregoing Figure 4In the embodiment of the present application, the vertical projection of the second recess 10221 of the second recessed portion 1022 in the thickness direction of the positive electrode sheet (z-axis shown in the figure) has a first size m1, and the first size m1 is 10-100 pm. The diameter of the second recessed portion 1022 is limited by the first size m1, thereby ensuring the effect of improving lithium precipitation in the circular arc area S20.

[0070] The lowest point of the second recess 10221 of the second recessed portion 1022 is in the shape of a circular arc, avoiding the lowest point of the second recess 10221 being too sharp.

[0071] In the embodiment of the present application, the third surface 1023 close to the third root 10222 has a crack, which forms a space for storing electrolyte on the surface of the active material layer, and at the same time exposes the coating inside the active material layer, thereby improving the infiltration rate of the electrolyte.

[0072] At the same time, the crack can extend in the diameter direction of the second recessed portion 1022.

[0073] In the embodiment of the present application, the second surface further comprises an uncoated area, and the first surface corresponding to the uncoated area is provided with a first active material layer 102 to form a single-sided area on the positive electrode sheet 100.

[0074] The uncoated area is also provided with a plurality of protrusions 1031; that is, when embossing the single-sided area, the first active material layer 102 is embossed from the positive electrode current collector 101, so that the first active material layer 102 forms a first recessed portion 1021, and the uncoated area forms a protrusion 1031 corresponding to the first recessed portion 1021.

[0075] By providing the first recessed portion 1021 and the protrusion 1031 in the single-sided area, the problem of wrinkling of the single-sided area sheet during battery production can be improved, the rate of winding failure can be reduced, and the flatness of the finished battery can be improved.

[0076] Continuing to refer to Figure 1 In the embodiment of the present application, the positive electrode sheet 100 has a first pit area S11, and a plurality of first recessed portions 1021 are arranged in the first pit area S11.

[0077] In the length direction of the positive electrode sheet (x-axis shown in the figure), the first pit area S11 has a first length L1, the positive electrode sheet 100 has a total length L, and the ratio L1 / L of the first length L1 to the total length L is 0.9-1.

[0078] In the width direction of the positive electrode sheet (y-axis shown in the figure), the first pit area S11 has a first width N1, the positive electrode sheet 100 has a total width N, and the ratio N1 / N of the first width N1 to the total width N is 0.8-1.

[0079] The first pit area S11 has a first pit area Q1, and the first active material layer 102 has a first active material area Q. The ratio Q1 / Q of the first pit area Q1 to the first active material area Q is 0.75-1.

[0080] By limiting the proportion of the first pit area S11 on the positive electrode sheet, it is ensured that the first pit area S11 can improve the electrolyte infiltration effect and increase the liquid retention amount under the premise of preventing the positive electrode sheet and the paste from deforming and powdering.

[0081] It should be noted that the position of the edge of the first recessed part 1021 closest to the edge of the positive electrode sheet is the boundary of the first pit area S11. For example, in the length direction of the positive electrode sheet, the positive electrode sheet has opposite first and second edges. The position of the edge of the first recessed part 1021 closest to the first edge is the first boundary, the position of the edge of the first recessed part 1021 closest to the second edge is the second boundary, and the line between the first boundary and the second boundary is the first length L1 of the first pit area S11.

[0082] Continuing to refer to Figure 2 and Figure 5 In the embodiment of the present application, the first pit area S11 further has a second pit area S12, and the second pit area S12 is provided with a plurality of second recessed parts 1022.

[0083] In the length direction of the positive electrode sheet (x-axis shown in the figure), the second pit area S12 has a second length L2, and the positive electrode sheet 100 has a total length L. The ratio L2 / L of the second length L2 to the total length L is 0.2-0.5.

[0084] In the width direction of the positive electrode sheet (y-axis shown in the figure), the second pit area S12 has a second width N2, and the positive electrode sheet 100 has a total width N. The ratio N2 / N of the second width N2 to the total width N is 0.8-1.

[0085] The second pit area S12 has a second pit area Q2, and the first active material layer 102 has a first active material area Q. The ratio Q2 / Q of the second pit area Q2 to the first active material area Q is 0.2-0.5.

[0086] By limiting the proportion of the second pit area S12 on the positive electrode sheet, it is ensured that the second pit area S12 can improve the lithium precipitation phenomenon in the arc area under the premise of preventing the positive electrode sheet and the paste from deforming and powdering.

[0087] It should be noted that the second pit area S12 is composed of a plurality of second recessed parts 1022 that do not overlap each other, and the edges of the outermost second recessed parts 1022 form the boundary of the second pit area S12.

[0088] It also needs to be explained that the two ends of the circular arc segment of the positive plate are respectively intersected with the flat segment, the second pit area S12 is located in the circular arc segment, and the boundary of the second pit area S12 overlaps with the intersection of the circular arc segment and the flat segment, thereby improving the improvement effect of the second pit area S12 on the lithium precipitation phenomenon in the circular arc area S20.

[0089] Reference Figure 7 and Figure 8 In the embodiment of the present application, the vertical projection of the first recessed part 1021 in the positive plate thickness direction (z-axis shown in the figure) has a first area S1, and the first area S1 is 0.15mm 2 ~20mm 2 .

[0090] By limiting the projection area of a single first recessed part 1021, the purpose of limiting the diameter of a single first recessed part 1021 is achieved, so as to meet the infiltration effect.

[0091] The vertical projection of the second recessed part 1022 in the positive plate thickness direction (z-axis shown in the figure) has a third area S3, and the third area S3 is 0.002mm 2 ~0.2mm 2 .

[0092] By limiting the projection area of a single second recessed part 1022, the diameter of a single second recessed part 1022 is limited, so as to ensure its effect of improving lithium precipitation in the circular arc area S20.

[0093] The total area of the vertical projection of the plurality of first recessed parts 1021 in the positive plate thickness direction (z-axis shown in the figure) is a fifth area S5, and the total area of the vertical projection of the plurality of second recessed parts 1022 in the positive plate thickness direction is a sixth area S6, and the ratio S6 / S5 of the sixth area S6 to the fifth area S5 is 0.05~0.3.

[0094] By limiting the area ratio of the plurality of first recessed parts 1021 and the plurality of second recessed parts 1022, it is ensured that at least one second recessed part 1022 is arranged in the first recessed part 1021, and it is ensured that the lithium precipitation phenomenon in the circular arc area can be improved.

[0095] In the embodiment of the present application, when the plurality of first recessed parts 1021 are arranged in an array, the edge distance between the adjacent two first recessed parts 1021 is a first distance p1, and the first distance p1 is 0.5~5mm.

[0096] By limiting the first distance p1, the distribution density of the plurality of first recessed parts 1021 is limited, so as to ensure that it can improve the infiltration amount of the electrolyte.

[0097] The edges of two adjacent second recesses 1022 are spaced apart by a third distance p3 when the plurality of second recesses 1022 are arranged in an array, and the third distance p3 is 100-500 μm.

[0098] By limiting the third distance p3 to limit the distribution density of the plurality of second recesses 1022, it is ensured that the lithium extraction in the arc region can be improved.

[0099] With reference to Figure 2 In the embodiments of the present application, in the width direction of the positive electrode sheet, the width of the second recessed area S12 satisfies the following relationship: Wn=a*π*H / 2.

[0100] Wherein, the two ends of the arc segment on the positive electrode sheet are connected with the flat segments respectively, H is the distance between the two ends of the arc segment, H1 is the distance between the two adjacent flat segments, H2 is the overall thickness of the battery, H1<H<H2, a is a coefficient for adjusting the width of the second recess 1022, 1≤a<10.

[0101] The above formula can ensure that the plurality of second recesses 1022 cover the arc region.

[0102] With reference to Figure 2 In the embodiments of the present application, the first active material layer 102 on the positive electrode sheet 100 has a head edge and a tail edge arranged oppositely along the length direction of the positive electrode sheet 100, and the tab 300 is arranged close to the head edge; the region where the positive electrode sheet 100 is bent for the first time is the first arc region, the region where the positive electrode sheet 100 is bent for the second time is the second arc region, and so on; each arc region is provided with a second recessed area S12; in the length direction of the positive electrode sheet 100, the distance between the center of each second recessed area S12 and the head edge of the first active material layer 102 satisfies the following relationship:

[0103] L n =L1+(n-1)*l+h1 / h2+(2n-3)*h3;

[0104] Wherein, 5 mm<L1<100 mm, h1=the height of the innermost circle of the roll core, h2=the height of the outermost circle of the roll core, n=the number of folds; h3=the thickness of the double-sided coated positive electrode sheet+the thickness of the double-sided coated negative electrode sheet+the thickness of the separator*2.

[0105] With reference to Figure 9 and Figure 10 In the embodiments of the present application, the vertical projection of the first recess 1021, the protruding portion 1031 and the second recess 1022 in the thickness direction of the positive electrode sheet (z-axis shown in the figure) can include a circle, a semicircle, an ellipse, a plum blossom shape, a polygon or a rhombus, etc.

[0106] The first recessed part 1021, the protruding part 1031 and the second recessed part 1022 have no sharp edges, so that the diaphragm is prevented from being punctured, and the positive and negative short circuit is prevented from causing the safety accident of the battery cell.

[0107] The application also provides a battery including the winding core.

[0108] The winding core provided by the application is described in detail below through specific examples, and the specific differences of different examples are shown in Table 1 and Table 2.

[0109] Example 1:

[0110] The battery preparation of the example includes the following steps:

[0111] 1. Preparation of the positive plate 100:

[0112] Lithium cobaltate, a conductive agent and PVDF are mixed in a mass ratio of 97.6:1.4:1, and then placed in NMP and stirred uniformly to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on the positive and negative surfaces of the current collector 101 to form the first active material layer 102 and the second active material layer 103 on the current collector 101, and the surface density of the coating is 0.01704 g / cm 2 ; after drying and rolling in sequence, the positive plate 100 is prepared.

[0113] The positive plate 100 is rolled using an embossing roller to form a plurality of first recessed parts 1021 on the first active material layer 102 and a plurality of protruding parts 1031 arranged opposite to the first recessed parts 1021 on the second active material layer 103.

[0114] A plurality of second recessed parts 1022 are arranged on the first active material layer 102 of the positive plate 100 in the arc region by means of laser drilling, and it is ensured that two second recessed parts 1022 are arranged in each first recessed part 1021.

[0115] The thickness of the first active material layer 102 is a first thickness h1 of 40 μm, the recessed depth of the first recessed part 1021 (the height of the protruding part 1031) is a first vertical distance H1 of 20 μm, the ratio of the first vertical distance H1 to the thickness of the first active material layer 102, i.e. H1 / h1, is 0.5, the recessed depth of the second recessed part 1022 is a third vertical distance H3 of 10 μm, and the ratio of the third vertical distance H3 to the thickness of the first active material layer 102, i.e. H3 / h1, is 0.25.

[0116] The area where the plurality of first recesses 1021 are located on the positive electrode sheet 100 is a first pit area S11, the first pit area S11 has a first pit area Q1, the first active material layer 102 has a first active material area Q, and the ratio Q1 / Q of the first pit area Q1 to the first active material area Q is 0.9.

[0117] The area where the plurality of second recesses 1022 are located on the positive electrode sheet 100 is a second pit area S12, the second pit area S12 has a second pit area Q2, and the ratio Q2 / Q of the second pit area Q2 to the first active material area Q is 0.3.

[0118] The area of the vertical projection of the first recess 1021 on the thickness direction of the positive electrode sheet (z-axis shown in the figure) is a first area S1, the first area S1 is 3.14mm 2 ; the area of the vertical projection of the second recess 1022 on the thickness direction of the positive electrode sheet is a third area S3, the third area S3 is 0.008mm 2 ; the total area of the vertical projection of the plurality of first recesses 1021 on the thickness direction of the positive electrode sheet is a fifth area S5, the total area of the vertical projection of the plurality of second recesses 1022 on the thickness direction of the positive electrode sheet is a sixth area S6, and the ratio S6 / S5 of the sixth area S6 to the fifth area S5 is 0.2.

[0119] 2. Preparation of negative electrode sheet 200:

[0120] The silicon-containing artificial graphite, conductive carbon black, butadiene rubber, and sodium carboxymethyl cellulose are placed in deionized water in a mass ratio of 97.2:0.5:1.3:1, and after stirring uniformly, a negative electrode slurry is prepared; among them, the content of silicon in the silicon-containing artificial graphite is 10%.

[0121] The negative electrode slurry is uniformly coated on the positive and negative surfaces of the negative electrode current collector, and after baking and rolling, a negative electrode sheet 200 is obtained, and a negative electrode tab is welded.

[0122] 3. Preparation of separator:

[0123] The separator is prepared by using a base material, ceramic, and rubber coating.

[0124] 4. Preparation of electrolyte:

[0125] The electrolyte includes lithium salt LiPF6 and solvent, and the solvent includes ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), wherein the molar ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) is DEC:EC:EMC=1:1:1.

[0126] 5. Assembly:

[0127] The positive electrode sheet 100, the separator and the negative electrode sheet 200 are wound to obtain a battery cell, and the battery cell is subjected to packaging, baking, liquid injection, formation, and two-sealing to obtain a battery.

[0128] Example 2:

[0129] Example 2 is performed according to Example 1, except that 4 second recessed portions 1022 are arranged in each first recessed portion 1021.

[0130] Example 3:

[0131] Example 3 is performed according to Example 1, except that 0.5 second recessed portions 1022 are arranged in each first recessed portion 1021.

[0132] Example 4:

[0133] Example 4 is performed according to Example 1, except that the first recessed portion 1021 has a recessed depth (height of the protruding portion 1031) first vertical distance H1 of 45 μm, and at the same time, the ratio H1 / h1 of the first vertical distance H1 to the thickness first thickness h1 of the first active material layer 102 is 1.125.

[0134] Example 5:

[0135] Example 5 is performed according to Example 1, except that the first recessed portion 1021 has a recessed depth (height of the protruding portion 1031) first vertical distance H1 of 2 μm, and at the same time, the ratio H1 / h1 of the first vertical distance H1 to the thickness first thickness h1 of the first active material layer 102 is 0.05.

[0136] Example 6:

[0137] Example 6 is performed according to Example 1, except that the second recessed portion 1022 has a recessed depth third vertical distance H3 of 55 μm, and at the same time, the ratio H3 / h1 of the third vertical distance H3 to the thickness first thickness h1 of the first active material layer 102 is 1.375.

[0138] Example 7:

[0139] Example 7 is performed according to Example 1, except that the second recessed portion 1022 has a recessed depth third vertical distance H3 of 0.5 μm, and at the same time, the ratio H3 / h1 of the third vertical distance H3 to the thickness first thickness h1 of the first active material layer 102 is 0.0125.

[0140] Comparative Example 1:

[0141] Comparative Example 1 was conducted with the difference that only a plurality of first recessed portions 1021 were formed on the first active material layer 102 by the embossing roller and a plurality of convex portions 1031 were formed on the second active material layer 103 opposite to the first recessed portions 1021 in Comparative Example 1; no second recessed portions 1022 were provided on the first active material layer 102 of the positive electrode sheet 100 in the circular arc region.

[0142] Comparative Example 2:

[0143] Comparative Example 2 was conducted with the difference that only a plurality of second recessed portions 1022 were formed on the first active material layer 102 of the positive electrode sheet 100 in the circular arc region by the laser punching method in Comparative Example 2, and no first recessed portions 1021 were provided.

[0144] Table 1:

[0145]

[0146] The related performances of the batteries in the above examples and comparative examples were tested, and the test results are recorded in Table 2, and the test methods are as follows:

[0147] 1. Liquid retention amount test

[0148] The liquid retention amount is the amount of electrolyte finally retained in the lithium ion battery. In order to ensure the consumption of electrolyte in the formation of lithium ion batteries, a certain amount of electrolyte is usually injected, and the excess electrolyte is extracted after formation; the injection amount m1 and the extracted electrolyte amount m2 are measured by weighing, and the liquid retention amount = m1-m2.

[0149] 2. Negative electrode sheet lithium precipitation

[0150] After the battery cell swelling rate test, the batteries obtained in the above examples and comparative examples were respectively fully charged, and the batteries were disassembled in a dry room environment to observe whether the negative electrode sheet appeared lithium precipitation and the degree of lithium precipitation. The degree of lithium precipitation was divided into slight lithium precipitation and severe lithium precipitation. When the interface appeared lithium precipitation, the lithium precipitation color was gray or gray-black, and when the interface was silver-white, the amount of lithium precipitation was large.

[0151] 3. Wettability improvement effect test

[0152] The battery was placed at room temperature (25°C) for 24h, and the wetting condition of the separator was observed. The wetted area size was estimated and compared, which was divided into three levels: significant (wetting area 60%-100%), medium (wetting area 30%-60%), and slight (wetting area 0%-30%). The unwetted area usually had irregular water streak boundaries, and the size difference could be directly observed.

[0153] Table 2:

[0154] Type Amount of liquid retained Infiltration improvement effect Lithium precipitation on negative electrode Example 1 8.27 Significant No lithium precipitation Example 2 8.24 Significant No lithium precipitation Example 3 8.25 Significant Slight lithium precipitation Example 4 8.26 Significant Slight lithium precipitation Example 5 8.11 Slight No lithium precipitation Example 6 8.25 Significant Slight lithium precipitation Example 7 8.11 Slight No lithium precipitation Comparative Example 1 8.17 Moderate Severe lithium precipitation Comparative Example 2 7.93 Slight Slight lithium precipitation

[0155] As shown in Table 1 and Table 2, the Comparative Example 1 has a certain amount of liquid retention, a moderate infiltration effect, and serious lithium precipitation in the arc region; the reason is that the Comparative Example 1 only forms a plurality of first recessed portions 1021 and protruding portions 1031 on the first active material layer 102 by the embossing roller, and does not set the second recessed portions 1022 in the arc region, resulting in serious lithium precipitation in the arc region. The liquid retention of the Comparative Example 2 is low, the infiltration effect is not obvious, and there is slight lithium precipitation in the arc region; the reason is that the Comparative Example 2 only sets a plurality of second recessed portions 1022 in the arc region, but does not set the first recessed portions 1021 on the positive electrode sheet, and the extrusion between the sheet layers results in insufficient electrolyte between the sheet and the separator.

[0156] The liquid retention of the Example 1 is higher than that of the Comparative Examples 1 and 2, and the Example 1 has no lithium precipitation; it is indicated that the first recessed portions 1021 and the protruding portions 1031 enable the electrolyte to have sufficient infiltration amount on the sheet, and the second recessed portions 1022 set on the arc region S20 solve the lithium precipitation phenomenon in the arc region S20.

[0157] It can be seen from the Example 2 and the Example 3 that when the number of the second recessed portions 1022 set in each first recessed portion 1021 located in the arc region is less than one, it is difficult to ensure that the lithium precipitation phenomenon in the arc region can be improved.

[0158] It can be seen from the Example 4 to the Example 7 that when the heights of the first recessed portions 1021 and the second recessed portions 1022 are high, the infiltration effect is obvious but it is easy to cause damage to the sheet and result in lithium precipitation; when the heights of the first recessed portions 1021 and the second recessed portions 1022 are low, the liquid retention is low and the infiltration effect is not obvious.

[0159] In summary, the application provides a winding core and a battery. The winding core comprises a positive electrode sheet 100, the positive electrode sheet 100 comprises a positive electrode current collector 101, a first active material layer 102 and a second active material layer 103, the positive electrode current collector 101 has opposite first and second surfaces along the positive electrode sheet thickness direction (z-axis shown in the figure), the first active material layer 102 is arranged on the first surface, and the second active material layer 103 is arranged on the second surface; a plurality of first recesses 1021 are arranged on the first active material layer 102, and a plurality of protrusions 1031 corresponding to the first recesses 1021 are arranged on the second active material layer 103; the winding core comprises a flat area S10 and a circular arc area S20 located at opposite ends of the flat area S10, and a plurality of second recesses 1022 are further arranged on the first active material layer 102 in the circular arc area S20; wherein the size of the vertical projection of the second recess 1022 on the positive electrode sheet thickness direction (z-axis shown in the figure) is smaller than the size of the vertical projection of the first recess 1021 on the positive electrode sheet thickness direction (z-axis shown in the figure).

[0160] By arranging the first recesses 1021 and the protrusions 1031 on the first active material layer 102 and the second active material layer 103 coated on the two surfaces of the positive electrode current collector 101 respectively, support can be provided for the contact of the separator, the micro-gap between the electrode sheet and the separator is increased, these micro-gaps form spaces that can accommodate electrolyte, so that the electrolyte has sufficient amount of infiltration to the electrode sheet, and abnormal conditions such as insufficient electrolyte and poor infiltration between the electrode sheet and the separator, and even lithium precipitation of the negative electrode sheet caused by interlayer extrusion of the electrode sheet are avoided.

[0161] Meanwhile, by arranging the second recesses 1022 on the first active material layer 102 in the circular arc area S20, the channel for lithium ion transmission in the first active material layer 102 in the circular arc area S20 is reduced, so that the lithium ion is transmitted in the electrolyte, the lithium ion accumulation in the circular arc area S20 is avoided, and the lithium precipitation phenomenon in the circular arc area S20 is improved.

[0162] In the specification, each embodiment or embodiment is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0163] It should be noted that the phrases "one embodiment", "embodiment", "exemplary embodiment", "some embodiments" and the like in the specification mean that the described embodiment can include a specific feature, structure or characteristic, but not necessarily every embodiment includes the specific feature, structure or characteristic. In addition, such phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure or characteristic is described in combination with an embodiment, it is within the knowledge of those skilled in the art to realize such feature, structure or characteristic in combination with other embodiments described explicitly or implicitly.

[0164] In general, terminology can be understood at least in part from usage in context. For example, terms, such as "one or more" as used herein, can be taken to describe any feature, structure, or characteristic in the singular or can be taken to describe a combination of features, structures or characteristics in the plural sense. Similarly, terms, such as "a" or "an," as used herein can be taken to convey a singular usage or a plural usage, depending at least in part on context.

[0165] It will be readily understood that the terms "on," "above," and "over," in the present disclosure, are to be interpreted in the broadest context possible so that "on" means not only "directly on" but also includes the meaning of "on" with intervening features or layers therebetween, and "above" or "over" includes not only the meaning of "above" or "over" but also can include the meaning of "above" or "over" without intervening features or layers therebetween (i.e., directly on).

[0166] In addition, spatially relative terms, such as "beneath", "below", "lower", "above", "upper", and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. The devices can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0167] Finally, it should be noted that the above-described embodiments are merely intended to illustrate the technical solutions of the present application, but not to limit the same; even though the present application has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions recorded in the above-described embodiments, or equivalent replacements can be made to some or all of the technical features thereof; and such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A type of winding core, characterized in that, include: Positive electrode plate, The positive electrode sheet includes a positive current collector, a first active material layer, and a second active material layer. The positive current collector has a first surface and a second surface opposite to each other along the thickness direction of the positive electrode sheet. The first active material layer is disposed on the first surface, and the second active material layer is disposed on the second surface. The first active material layer has a plurality of first recesses, and the second active material layer has a plurality of protrusions corresponding to the first recesses; The core includes a flat area and arc-shaped areas located at opposite ends of the flat area. The first active material layer located in the arc-shaped area is also provided with a plurality of second recesses. The size of the vertical projection of the second recesses in the thickness direction of the positive electrode sheet is smaller than the size of the vertical projection of the first recesses in the thickness direction of the positive electrode sheet.

2. The winding core according to claim 1, characterized in that, The first recess includes a first recess and a first root connecting the first recess and the surface of the first active material layer. In the thickness direction of the positive electrode sheet, the first root and the lowest point of the first recess have a first vertical distance H1. The protrusion includes a protrusion and a second root portion connecting the protrusion and the surface of the second active material layer. In the thickness direction of the positive electrode sheet, the second root portion and the vertex of the protrusion have a second vertical distance H2. Wherein, the first vertical distance H1 is greater than the second vertical distance H2.

3. The winding core according to claim 1, characterized in that, At least one second recess is provided in each of the first recesses located in the arc region.

4. The winding core according to claim 1, characterized in that, The second surface includes an uncoated area, and the first surface corresponding to the uncoated area is provided with the first active material layer; The uncoated area is provided with a plurality of the protrusions.

5. The winding core according to claim 1, characterized in that, The positive electrode includes a first pit region and a second pit region, wherein the first pit region is provided with the plurality of first recesses and the second pit region is provided with the plurality of second recesses. Along the length of the positive electrode sheet, the ratio of the length of the first recessed region to the length of the positive electrode sheet is 0.9 to 1; and / or, In the width direction of the positive electrode sheet, the ratio of the width of the first recessed area to the width of the positive electrode sheet is 0.8 to 1; and / or, The ratio of the area of ​​the first pit region to the area of ​​the first active material layer is 0.75 to 1; and / or, Along the length of the positive electrode sheet, the ratio of the length of the second recessed region to the length of the positive electrode sheet is 0.2 to 0.5; and / or, In the width direction of the positive electrode sheet, the ratio of the width of the second recessed region to the width of the positive electrode sheet is 0.8 to 1; and / or, The ratio of the area of ​​the second pit region to the area of ​​the second active material layer is 0.2 to 0.

5.

6. The winding core according to claim 2, characterized in that, The second recess includes a second recess and a third root connecting the surface of the second recess and the first active material layer. In the thickness direction of the positive electrode sheet, the third root has a third vertical distance H3 from the lowest point of the second recess. The third vertical distance H3 is 1–50 μm; and / or, The first active material layer has a first thickness h1, and the ratio of the third vertical distance H3 to the first thickness h1 is 0.4 to 1; and / or, The first vertical distance H1 is 1–30 μm; and / or, The first active material layer has a first thickness h1, and the ratio of the first vertical distance H1 to the first thickness h1 is 0.2 to 0.

5.

7. The winding core according to claim 6, characterized in that, The surface of the first active material layer near the third root has cracks.

8. The winding core according to claim 6, characterized in that, The area of ​​the first recess projected vertically along the thickness direction of the positive electrode sheet is the first area S1, and the first area S1 is 0.15 mm. 2 ~20mm 2 ; and / or, The area of ​​the second recess projected vertically along the thickness direction of the positive electrode sheet is the third area S3, and the third area S3 is 0.002 mm. 2 ~0.2mm 2 ; and / or, The total area of ​​the vertical projection of the plurality of first recesses in the thickness direction of the positive electrode sheet is the fifth area S5, and the total area of ​​the vertical projection of the plurality of second recesses in the thickness direction of the positive electrode sheet is the sixth area S6. The ratio of the sixth area S6 to the fifth area S5 is 0.05 to 0.

3.

9. The winding core according to claim 1, characterized in that, The plurality of first recesses and the plurality of second recesses are arranged in an array; The edges of two adjacent first recesses are spaced apart by a first distance p1, where p1 is 0.5–5 mm; and / or, The edges of two adjacent second recesses are spaced by a third distance p3, wherein the third distance p3 is 100 to 500 μm.

10. A battery, characterized in that, Includes the core as described in any one of claims 1-9.

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