Winding type battery cell and lithium ion battery

Abstract

The utility model relates to the field of lithium batteries, and discloses a winding type battery cell and a lithium ion battery, the winding type battery cell is characterized in that a first groove is formed in a bending section of a positive active material layer, second grooves are formed in two ends of the first groove, one end of each second groove extends to a straight section, and the other end of each second groove extends to the bending section; and the second groove is communicated with the first groove. The depth of the second groove is controlled to be greater than the depth of the first groove, so that the number of the positive active material layer in the area of the second groove is smaller, and protruding particles in the area are reduced. The second groove has fewer positive active material layers, so that the extrusion degree of the positive active material corresponding to the area where the second groove is located on the diaphragm can be reduced, and the K-value yield of the winding type battery cell can be improved.

Description

Technical Field

[0001] This application relates to the field of lithium batteries, and in particular to a wound cell and a lithium-ion battery. Background Technology

[0002] To improve the energy density of wound lithium-ion batteries, a thicker layer of active material can be coated onto the current collector. However, this also deteriorates the electrode kinetics, making lithium plating more likely to occur during fast charging. Especially in wound cells, the several folds and arcs inside the positive electrode are compressed and broken, the positive electrode becomes thicker, and the local NP ratio (the ratio of negative electrode capacity to positive electrode capacity) becomes extremely small, making lithium plating more likely to occur at the arcs of the negative electrode.

[0003] To address the lithium plating issue in wound cells, the active material layer can be thinned at the innermost bend of the positive electrode sheet to increase the NP ratio and thus resolve the lithium plating problem at the bend. However, after thinning at the innermost bend, the positive electrode sheet cannot be rolled further, resulting in an uneven surface of the active material layer. During subsequent pressure setting processes, numerous protruding particles emerge from both sides of the innermost bend, compressing the separator and leading to an extremely low K-value yield (below 50%) for the wound cell.

[0004] Therefore, how to solve the above-mentioned technical problems should be a key focus for those skilled in the art. Utility Model Content

[0005] The purpose of this application is to provide a wound cell and a lithium-ion battery to improve the K-value yield of the cell.

[0006] To solve the above-mentioned technical problems, this application provides a wound battery cell, comprising:

[0007] A positive electrode sheet, a separator, and a negative electrode sheet are sequentially stacked and wound together. The positive electrode sheet includes a positive current collector and a positive active material layer coated on the surface of the positive current collector.

[0008] Along the winding direction of the positive electrode sheet, the positive electrode active material layer includes a plurality of straight sections and bent sections connected in sequence. The first N bent sections are provided with a first groove. The positive electrode active material layer is also provided with a plurality of second grooves. The two ends of the first groove are respectively connected to the second groove. One end of the second groove extends to the straight section, and the other end of the second groove extends to the bent section and is connected to the first groove. N≥1.

[0009] The depth of the second groove is greater than the depth of the first groove.

[0010] Optionally, along the second direction, the positive electrode active material layer includes a first surface and a second surface. The first surface has a second groove. The end of the second groove away from the first groove is an inclined sidewall. The angle between the inclined sidewall and the first surface is in the range of 15° to 60°, and the inclined sidewall is inclined towards the adjacent straight section.

[0011] Optionally, it also includes:

[0012] An inactive layer, which at least covers the second groove.

[0013] Optionally, the inactive layer covers only the second groove;

[0014] Alternatively, the inactive layer extends from the second groove to the straight section;

[0015] Alternatively, the inactive layer covers the second groove and the first groove;

[0016] Alternatively, along the winding direction of the positive electrode sheet, the inactive layer covers the first groove of the first bending segment and the second grooves at both ends thereon, and the inactive layer extends to the second bending segment and covers the first groove of that bending segment.

[0017] Optionally, the inactive layer extends from the second groove to the straight section. Along the winding direction of the battery cell, the distance D between the two inactive layers is in the range of 0 < D ≤ (3.14 * d / 4) * 3 mm, where d is the arc diameter of the diaphragm corresponding to the bend section where the first groove is located.

[0018] Optionally, when the inactive layer covers the second groove and the first groove, the length of the inactive layer exceeding the sum of the lengths L3 of the first groove and the second groove along the winding direction of the battery cell is Q, which is 0 < Q ≤ 10 mm.

[0019] Optionally, the inactive layer may include a ceramic layer and / or an insulating layer.

[0020] Optionally, the inactive layer includes the insulating layer, wherein the edge of the insulating layer extends beyond the edge of the positive electrode sheet in a first direction; and / or, the inactive layer includes a ceramic layer, wherein the width of the ceramic layer is the same as the width of the positive electrode active material layer in a first direction.

[0021] Optionally, along the winding direction of the battery cell, the length L1 of the first groove is in the range of 3.14*d / 8≤L1≤3.14*d / 2, where d is the arc diameter of the diaphragm corresponding to the bend where the first groove is located;

[0022] And / or, the depth D1 of the first groove is in the range of D0 / 4≤D1<D0, where D0 is the thickness of the positive electrode active material layer corresponding to the straight section on the wound cell;

[0023] And / or, along the winding direction, the length L2 of the second groove is in the range of 2mm≤L2≤L0 / 2, where L0 is the length of the first fold of the positive electrode in the wound cell, and the first fold of the positive electrode is the positive electrode between the winding start end of the positive electrode and the middle of the first bending segment;

[0024] And / or, the depth D2 of the second groove is in the range of D1 < D2 ≤ 2 * D1, where D1 is the depth of the first groove.

[0025] Optionally, it also includes:

[0026] The raised block is located at the center inside the wound cell, and one end of the raised block is close to the innermost negative electrode sheet of the wound cell, at the first bend where a single-sided layer of negative electrode active material is coated from the starting end of winding.

[0027] Optionally, the thickness W of the raised block in the second direction is in the range of W1≤W≤W2, where W1 is the thickness of a positive electrode sheet with a double-sided positive active material layer, and W2 is the sum of the thicknesses of two positive electrode sheets with double-sided positive active material layers and two negative electrode sheets with double-sided negative active material layers.

[0028] And / or, the width of the shim block in the first direction is greater than the width of the negative electrode sheet;

[0029] And / or, the length L4 of the shim block in the third direction is L4 > d0 / 2, where d0 is the arc diameter of the diaphragm corresponding to the first bending segment in the wound cell;

[0030] And / or, on a plane perpendicular to the winding direction, the projection of the shim block does not overlap with the projection of the tab.

[0031] Optionally, in the first N bending segments, each bending segment is provided with the first groove, and the width of the first groove and the second groove along the first direction is equal to the width of the positive electrode sheet.

[0032] Optionally, in the first N bending segments, each bending segment is provided with at least two of the first grooves, and the first grooves are distributed at intervals along a first direction.

[0033] Optionally, the width of the gap between adjacent first grooves in the first direction is less than or equal to 20 mm.

[0034] This application also provides a lithium-ion battery, including any of the wound cells described above.

[0035] This application creates a first groove and a second groove on the positive electrode active material layer. One end of the second groove extends to a straight section, and the other end extends to a bent section. The depth of the second groove is controlled to be greater than the depth of the first groove, so that there is less positive electrode active material in the area where the second groove is located, thereby reducing the number of protruding particles in that area. In addition, since the second groove has less positive electrode active material, the pressure of the positive electrode active material on the separator in the area where the second groove is located can be reduced, thereby improving the K-value yield of the wound cell. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A partial schematic diagram of a wound battery cell provided in this application embodiment. Figure 1 ;

[0038] Figure 2 A schematic diagram of the structure of a wound battery cell provided in this application embodiment. Figure 1 ;

[0039] Figure 3 A partial schematic diagram of a wound battery cell provided in this application embodiment. Figure 2 ;

[0040] Figure 4 A schematic diagram of the structure of a wound battery cell provided in this application embodiment. Figure 2 ;

[0041] Figure 5 A partial schematic diagram of a wound battery cell provided in this application embodiment. Figure 3 ;

[0042] Figure 6 A schematic diagram of the structure of a wound battery cell provided in this application embodiment. Figure 3 ;

[0043] Figure 7 A partial schematic diagram of a wound battery cell provided in this application embodiment. Figure 4 ;

[0044] Figure 8 A schematic diagram of the structure of a wound battery cell provided in this application embodiment. Figure 4 ;

[0045] Figure 9 A partial schematic diagram of a wound battery cell provided in this application embodiment. Figure 5 ;

[0046] Figure 10 A partial schematic diagram of a wound battery cell provided in this application embodiment. Figure 6 ;

[0047] Figure 11 A schematic diagram of the structure of a wound battery cell provided in this application embodiment. Figure 5 ;

[0048] Figure 12 A schematic diagram showing the distribution of a groove structure at one of the bending centers of a positive electrode sheet, as provided in an embodiment of this application.

[0049] In the figure, 1 is the positive electrode sheet, 2 is the separator, 3 is the negative electrode sheet, 4 is the groove structure, 5 is the positive electrode tab, 6 is the negative electrode tab, 7 is the non-active layer, 8 is the raised block, 11 is the positive electrode active material layer, 12 is the positive electrode current collector, 31 is the negative electrode active material layer, 32 is the negative electrode current collector, 41 is the first groove, 42 is the second groove, 111 is the first surface, 112 is the second surface, S1 is the straight section, and S2 is the bent section. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0052] As described in the background section, in current wound cells, after the innermost bending position of the positive electrode sheet is thinned, it cannot be rolled again. The active material layer on the surface of the positive electrode sheet is uneven. In the subsequent pressure shaping process, there are many protruding particles on both sides of the innermost bending position. These particles squeeze the separator, resulting in an extremely low K-value yield of the wound cell.

[0053] In view of this, this application provides a wound battery cell, please refer to... Figures 1 to 2It can include:

[0054] A positive electrode 1, a separator 2, and a negative electrode 3 are sequentially stacked and wound together. The positive electrode 1 includes a positive current collector 12 and a positive active material layer 11 coated on the surface of the positive current collector 12.

[0055] Along the winding direction of the positive electrode sheet 1, the positive electrode active material layer 11 includes multiple straight sections S1 and bent sections S2 connected in sequence. The first N bent sections S2 are provided with a first groove 41. The positive electrode active material layer 11 is also provided with a second groove 42. The two ends of the first groove 41 are respectively connected to the second groove 42. One end of the second groove 42 extends to the straight section S1, and the other end of the second groove 42 extends to the bent section S2 and communicates with the first groove 41. The depth D2 of the second groove 42 is greater than the depth D1 of the first groove 41, and N≥1.

[0056] The first groove 41 and the second groove 42 form the groove structure 4.

[0057] It should be noted that the wound battery cell also includes a positive tab 5 and a negative tab 6. The positive tab 5 is connected to the positive electrode plate 1, and the negative tab 6 is connected to the negative electrode plate 3.

[0058] In a wound battery cell, positive electrode 1 and negative electrode 3 are alternately distributed, and separator 2 is located between positive electrode 1 and negative electrode 3.

[0059] The positive electrode 1 also includes a positive current collector 12. The positive active material layer 11 can be located on one surface (upper surface or lower surface) of the positive current collector 12, or simultaneously on two opposite surfaces (upper surface and lower surface) of the positive current collector 12.

[0060] The positive electrode current collector 12 can be aluminum foil, and the material of the positive electrode active material layer 11 can be lithium cobalt oxide, ternary nickel cobalt manganese material, ternary nickel cobalt aluminum material, lithium iron phosphate, lithium manganese iron phosphate, etc., which are not limited in this embodiment.

[0061] A positive electrode active material layer 11 is provided on the side of the positive electrode 1 corresponding to the negative electrode 3. That is, the positive electrode 1 located in the innermost or outermost layer of the wound cell is provided on the upper or lower surface of the positive current collector 12. When the positive electrode 1 is located in the middle of the wound cell, the positive electrode active material layer 11 is provided on both the upper and lower surfaces of the positive current collector 12.

[0062] The negative electrode 3 includes a negative electrode active material layer 31 and a negative electrode current collector 32. The negative electrode active material layer 31 can be located on one surface (upper surface or lower surface) of the negative electrode current collector 32, or simultaneously on two opposite surfaces (upper surface and lower surface) of the negative electrode current collector 32.

[0063] The negative electrode current collector 32 can be copper foil, and the material of the negative electrode active material layer 31 can be graphite, graphene, carbon, etc., which is not limited in this embodiment.

[0064] The negative electrode 3 is provided with a negative electrode active material layer 31 on the side corresponding to the positive electrode 1. That is, the negative electrode 3 located in the innermost or outermost layer of the wound cell is provided with a negative electrode active material layer 31 on the upper or lower surface of the negative electrode current collector 32. When the negative electrode 3 is located in the middle of the wound cell, the negative electrode active material layer 31 is provided on both the upper and lower surfaces of the negative electrode current collector 32.

[0065] N is a positive integer. It should be noted that the value of N is not limited in this embodiment and can be set by the user. For example, N = 1, 2, 3, 4, 5, etc.

[0066] In this embodiment, the depth D2 of the second groove 42 is greater than the depth D1 of the first groove 41. That is, more of the positive electrode active material layer 11 is removed in the area where the second groove 42 of the wound cell is located, which can reduce the degree of compression on the separator 2 at this point, thereby improving the K-value yield of the cell.

[0067] The depth D1 of the first groove 41 and the depth D2 of the second groove 42 are both less than the thickness of the positive electrode active material layer. It should be noted that in this embodiment, the specific values ​​of the depth D1 of the first groove 41 and the depth D2 of the second groove 42 are not limited and can be set by oneself.

[0068] It should also be noted that in this embodiment, the shape of the sidewall of the second groove 42 away from the first groove 41 is not limited.

[0069] As one possible implementation, the sidewall of the second groove 42 away from the first groove 41 can be vertical, such as... Figure 1 As shown.

[0070] As another possible implementation, the sidewall of the second groove 42 away from the first groove 41 can be inclined, and the inclination angle is not limited in this embodiment.

[0071] When the sidewall of the second groove 42 away from the first groove 41 is an inclined sidewall, it can make the transition between the groove structure 4 area on the positive electrode 1 and the normal area without grooves smooth, avoiding excessive sharp edges from squeezing the diaphragm 2.

[0072] Starting from the winding start point of the positive electrode 1, along the winding direction of the wound cell, the bending segment S2 can be sequentially referred to as the first bending segment, the second bending segment, ..., the Nth bending segment.

[0073] It should be noted that the number of groove structures 4 is not limited in this embodiment and can be set arbitrarily. For example, the number of groove structures 4 can be one. In this case, the groove structure 4 is located on the innermost positive electrode active material layer 11 of the wound cell. Correspondingly, the first groove 41 corresponds to the innermost bending segment S1 (i.e., the first bending segment S2) of the wound cell. Figure 2 As shown. Alternatively, there can be two groove structures 4. Accordingly, the first groove 41 can correspond to the innermost bending segment S2 (i.e., the first bending segment S1) and the second bending segment S2 in the wound cell.

[0074] The wound battery cell in this embodiment includes a positive electrode 1, a separator 2, and a negative electrode 3. The first N bending sections on the positive electrode active layer are provided with a first groove 41. The two ends of the first groove 41 are respectively connected to second grooves 42. One end of the second groove 42 extends to a straight section S1, and the other end extends to a bending section S2. Therefore, the positive electrode active material layer in the area where the second groove 42 is located can be reduced, which also reduces the number of protruding particles in this area. Furthermore, since the depth of the second groove 42 is greater than that of the first groove 41, there is less positive electrode active material layer 11 in the area where the second groove 42 is located. This reduces the pressure of the positive electrode active material 11 on the separator 2, thereby improving the K-value yield of the wound battery cell.

[0075] like Figure 3 As shown, based on the above embodiments, in one embodiment of this application, along the second direction (that is, the thickness direction of the positive electrode sheet 1), the positive electrode active material layer 11 includes a first surface 111 and a second surface 112. The first surface 111 has a second groove 42. The end of the second groove 42 away from the first groove 42 is an inclined sidewall. The angle between the inclined sidewall and the first surface 111 is in the range of 15°~60°, and the inclined sidewall is inclined towards the adjacent straight section S1.

[0076] For example, the angle between the inclined sidewall and the first surface 111 can be 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, etc.

[0077] If the angle between the inclined sidewall and the first surface 111 is too large, that is, the angle between the groove structure 4 on the positive electrode 1 and the area without grooves is too large, the compression on the separator 2 will be too large, affecting the improvement of the K-value yield. If the angle between the inclined sidewall and the first surface 111 is too small, the thinning length L5 of the positive electrode active material layer 11 corresponding to the angle will be too long, and more active material will be removed, which will lead to a reduction in battery capacity. Among them, the thinning length L5 is the horizontal projection length of the inclined sidewall of the second groove 42 near the straight section S1.

[0078] like Figures 4 to 8As shown, based on any of the above embodiments, in one embodiment of this application, the wound battery cell may further include:

[0079] The inactive layer 7 covers at least the second groove 42.

[0080] The inactive layer 7 can conduct ions. The thickness of the inactive layer 7 is not limited in this embodiment and depends on the specific circumstances.

[0081] By setting the inactive layer 7, the problem of particles on the positive electrode 1 squeezing the separator 2 can be solved on the one hand, and it can also play a filling role, reducing the gap between the positive electrode 1 and the negative electrode 3, and avoiding the negative electrode 3 from having excessive curvature, thereby avoiding the problem of capacity drop caused by interface abnormalities during cycle testing.

[0082] It should be noted that the position of the inactive layer 7 is not limited in this embodiment and can be set by oneself. Several possible settings are introduced below.

[0083] In one embodiment of this application, the non-active layer 7 covers only the second groove 42.

[0084] Both sides of the second groove 42 on the first groove 41 are covered with an inactive layer 7.

[0085] In one embodiment of this application, such as Figure 4 and Figure 5 As shown, the inactive layer 7 extends from the second groove 42 to the straight section S1. That is, the inactive layer 7 covers both sides of the second groove 42 of the first groove 41.

[0086] The two inactive layers 7 can be symmetrically distributed with the center of the bent section S2 as the axis, or they can be asymmetrically distributed. This application does not limit this.

[0087] As one possible implementation, when the inactive layer 7 extends from the second groove 42 to the straight section S1, along the winding direction of the battery cell, the distance D between the two inactive layers 7 is in the range of 0 < D ≤ (3.14 * d / 4) * 3 mm, where d is the arc diameter of the diaphragm 2 corresponding to the bending section S2 where the first groove 41 is located.

[0088] If the distance D between the two inactive layers 7 is too large, the inactive layer 7 may not be able to completely cover the second groove 42.

[0089] In one embodiment of this application, such as Figure 6 and Figure 7 As shown, the inactive layer 7 covers the second groove 42 and the first groove 41. That is, the first groove 41 and the second grooves 42 on both sides of the first groove 41 are covered with the inactive layer 7.

[0090] It should be noted that the length of the non-active layer 7 is not limited in this embodiment and depends on the situation.

[0091] As one possible implementation, when the inactive layer 7 covers the second groove 42 and the first groove 41, the length of the inactive layer 7 is equal to the length of the groove structure 4 along the winding direction. That is, the inactive layer 7 just covers the first groove 41 and the second groove 42 on both sides of the first groove 41, and the two ends of the inactive layer 7 are respectively aligned with the ends of the second groove 42 away from the first groove 41.

[0092] As another possible implementation, when the inactive layer 7 covers the second groove 42 and the first groove 41, the length of the inactive layer 7 exceeds the sum of the lengths L3 of the first groove 41 and the second groove 42 in the winding direction, where Q is 0 < Q ≤ 10 mm.

[0093] If the length of the non-active layer 7 exceeds the sum of the lengths of the first groove 41 and the second groove 42 by too much, it will affect the capacity utilization of the areas where the first groove 41 and the second groove 42 are not provided.

[0094] For example, the length range Q of the inactive layer 7, which exceeds the sum of the lengths of the first groove 41 and the second groove 42, can be 1 mm, 3 mm, 5 mm, 7 mm, 9 mm, 10 mm, etc.

[0095] Both ends of the inactive layer 7 extend beyond the ends of the groove structure 4, that is, both ends of the inactive layer 7 extend beyond the ends of the second groove 42 and are far away from the first groove 41, which can reduce the processing difficulty of the inactive layer 7.

[0096] In one embodiment of this application, such as Figure 8 As shown, the inactive layer 7 covers the second groove 42 and extends along the winding direction to the target position, and the inactive layer 7 covers at least the first two bends S2 starting from the winding start end; wherein, the target position is located behind the second bend of the positive electrode active material layer starting from the winding start end along the winding direction.

[0097] In this embodiment, the target location is not limited, but it needs to cover at least the first two bends S2 of the wound cell starting from the winding start end. In this embodiment, both the first groove 41 and the second groove 42 are covered with an inactive layer 7.

[0098] In this embodiment, the number of bends S2 covered by the inactive layer 7 is not limited and can be set arbitrarily. For example, the inactive layer 7 may cover the first two bends S2 or the first three bends S2 starting from the winding start end. The length of the inactive layer 7 is at least the length of the positive electrode 1 from the head of the wound cell to the end of the first bend S2, i.e. Figure 8The length between J and K.

[0099] In this embodiment, by providing a continuous inactive layer 7 within the range of at least the first two bending segments S2 starting from the winding start end, the processing of the wound battery cell can be facilitated, and the arc positioning problem can be avoided. At the same time, the inactive layer 7 can also block lithium dendrites from penetrating the separator 2, thus avoiding serious short circuits.

[0100] As one possible implementation, the non-active layer 7 includes, but is not limited to, a ceramic layer and / or an insulating layer.

[0101] The non-active layer 7 can be entirely ceramic, entirely insulating, or partly ceramic and partly insulating. The ceramic layer is coated onto the positive electrode 1, and the insulating layer is an adhesive film that can be directly adhered to the positive electrode 1.

[0102] When the non-active layer 7 includes a ceramic layer, in the first direction X, the width of the ceramic layer is equal to the width of the positive electrode 1 (i.e., the positive electrode active material layer 11).

[0103] When the non-active layer 7 includes an insulating layer, in the first direction X, the edge of the insulating layer extends beyond the edge of the positive electrode 1 to allow for processing capacity and facilitate the fabrication of the insulating layer. The extent by which the edge of the insulating layer extends beyond the edge of the positive electrode 1 can be greater than 0 and less than or equal to 2 mm, which facilitates processing while avoiding the use of excessive insulating layers and saving costs. The first direction X is the height direction of the wound cell.

[0104] Please refer to Figure 1 and Figure 9 Based on any of the above embodiments, in one embodiment of this application, along the winding direction, the length L1 of the first groove 41 is in the range of 3.14*d / 8≤L1≤3.14*d / 2, where d is the arc diameter of the diaphragm 2 corresponding to the bending segment S2 where the first groove 41 is located.

[0105] For example, the length L1 of the first groove 41 can be 3.14*d / 8, 3.14*d / 6, 3.14*d / 4, 3.14*d / 3, 3.14*d / 2, etc.

[0106] If the length L1 of the first groove 41 is too large, the first groove 41 will be distributed to the area where the second groove 42 is located, resulting in an increase in the positive electrode active material layer 11 corresponding to the area where the second groove 42 is located, which in turn leads to a limited improvement in K-value yield; if the length L1 of the first groove 41 is too small, the step structure formed by the different depths between the first groove 41 and the second groove 42 is not obvious, and the K-value yield cannot be improved.

[0107] Please refer to Figure 1Based on any of the above embodiments, in one embodiment of this application, the depth D1 of the first groove 41 is in the range of D0 / 4≤D1<D0, where D0 is the thickness of the positive electrode active material layer 11 corresponding to the straight section S1 of the wound cell.

[0108] For example, the depth D1 of the first groove 41 can be D0 / 4, D0 / 3, D0 / 2, etc.

[0109] If the depth D1 of the first groove 41 is too small, it cannot achieve the effect of thinning to reduce the lithium plating of the arc, and the equipment has difficulty controlling the depth D1 of the first groove 41, making the processing difficult.

[0110] Please refer to Figure 9 and Figure 2 Based on any of the above embodiments, in one embodiment of this application, along the winding direction of the battery cell, the length L2 of the second groove 42 is in the range of 2mm≤L2≤L0 / 2, where L0 is the length of the first fold positive electrode 1 in the wound battery cell, and the first fold positive electrode 1 is the positive electrode 1 between the winding start end of the positive electrode 1 and the middle of the first bending segment S1.

[0111] For example, the length L2 of the second groove 42 can be 2mm, 3mm, L0 / 2, etc.

[0112] like Figure 2 As shown, L0 is the length between A and B.

[0113] If the length L2 of the second groove 42 is too small, the yield improvement of K value will not be significant. If the length L2 of the second groove 42 is too large, too much of the positive electrode active material layer 11 will be removed, affecting the battery capacity.

[0114] Based on any of the above embodiments, in one embodiment of this application, the depth D2 of the second groove 42 is in the range of D1<D2≤2*D1, where D1 is the depth D1 of the first groove 41.

[0115] For example, the depth D2 of the second groove 42 can be 1.1*D1, 1.5*D1, 1.8*D1, 2*D1, etc.

[0116] Setting the depth D2 of the second groove 42 within the range of D1<D2≤2*D1 ensures that the step structure is formed by the depth difference between the first groove 41 and the second groove 42, thereby improving the K-value yield of the wound cell.

[0117] As one possible implementation, the length L1 of the first groove 41 can be 3.14*d / 4, the depth D1 of the first groove 41 can be D0 / 2, the length L2 of the second groove 42 can be 3.14*d / 4, and the depth D2 of the second groove 42 is 1.5*D1.

[0118] like Figure 10 and Figure 11 As shown, based on any of the above embodiments, in one embodiment of this application, the wound battery cell may further include:

[0119] The raised block 8 is located at the center inside the wound cell, and one end of the raised block 8 is close to the first bend S2 of the innermost negative electrode sheet of the wound cell, which is coated with a layer of negative electrode active material on one side from the starting end of winding.

[0120] It should be noted that in this embodiment, the position of the other end of the raised block 8 is not limited, but is determined according to the length of the raised block 8.

[0121] In this embodiment, the material of the raised block 8 is not limited and can be selected at will.

[0122] For example, the material of the raised block 8 can be a metal or a non-metal, preferably a metal. When the material of the raised block 8 is a metal, it can be Fe, Zn, or an alloy of Fe and Zn. In this case, the raised block 8 and the copper foil (negative electrode current collector 32) form a galvanic cell as a sacrificial anode to prevent corrosion of the copper foil.

[0123] By setting up the raised block 8, the problem of gaps between the positive electrode 1 and the negative electrode 3 caused by the excessive curvature of the negative electrode 3 can be avoided. This avoids the problem of interface abnormalities that easily occur during cycle testing, which can lead to a drop in capacity. At the same time, it avoids the problem of the local NP ratio being only 1 / 2 of the flat section S1 due to the collapse of the positive electrode 1, thereby solving the lithium plating problem caused by the extremely small local NP due to the collapse of the positive electrode 1.

[0124] It should be noted that the thickness of the shim block 8 is not limited in this embodiment and can be set by the user.

[0125] In one embodiment of this application, the thickness W of the shim block 8 in the second direction Y is in the range of W1≤W≤W2, where W1 is the thickness of a positive electrode sheet 1 with a double-sided positive active material layer 11, and W2 is the sum of the thicknesses of two positive electrode sheets 1 with double-sided positive active material layers 11 and two negative electrode sheets 3 with double-sided negative active material layers 31. The second direction Y is the thickness direction of the wound battery cell.

[0126] For example, the thickness of the raised block 8 can be the thickness of a positive electrode 1 with a double-sided positive active material layer 11, or the sum of the thickness of a positive electrode 1 with a double-sided positive active material layer 11 and the thickness of a negative electrode 3 with a double-sided negative active material layer 31, or the sum of the thickness of two positive electrode 1s with double-sided positive active material layers 11 and the thickness of two negative electrode 3s with double-sided negative active material layers 31, etc.

[0127] If the thickness of the shim block 8 is too small, it will not have the desired lifting effect. If the thickness of the shim block 8 is too large, it will affect the thickness of the wound cell, and thus the thickness of the battery.

[0128] It should be noted that the width of the raised block 8 is not limited in this embodiment and can be set by the user.

[0129] In one embodiment of this application, the width of the shim block 8 in the first direction X is greater than the width of the negative electrode sheet 3. During the hot pressing of the core, the edge of the negative electrode sheet 3 in the width direction may collapse. By setting the width of the shim block 8 to be greater than the width of the negative electrode sheet 3, it can provide some support for the edge of the negative electrode sheet 3, while also leaving some processing allowance and simplifying the manufacturing process.

[0130] As one possible implementation, on each side edge of the negative electrode 3 in the width direction, the length of the padding block 8 extending beyond the edge of the negative electrode 3 is greater than zero and less than or equal to 2 mm.

[0131] For example, the length of the raised block 8 extending beyond the edge of the negative electrode 3 can be 0.5mm, 1mm, 1.5mm, 2mm, etc.

[0132] If the length of the raised block 8 extending beyond the edge of the negative electrode 3 is too large, it will affect the size of the battery. Therefore, the length of the raised block 8 extending beyond the edge of the negative electrode 3 is controlled within 2mm.

[0133] In one embodiment of this application, the length L4 of the shim block 8 in the third direction Z is L4 > d0 / 2, where d0 is the arc diameter of the separator 2 corresponding to the first bend S2 in the wound cell. The third direction Z is the length direction of the wound cell.

[0134] The length L4 of the shim block 8 is in the range of L4 > d / 2, which can ensure that the shim block 8 has a shim effect in the bending section S1 near the innermost side of the wound cell.

[0135] In one embodiment of this application, the projection of the shim block 8 and the projection of the tab do not overlap on a plane perpendicular to the winding direction, to prevent the thickness of the shim block 8 and the tab from being superimposed, resulting in an excessively thick battery cell. The tab includes a positive tab 5 and a negative tab 6.

[0136] like Figure 1 and Figure 2 As shown, based on any of the above embodiments, in one embodiment of this application, in the first N bending segments S2, each bending segment S2 is provided with a first groove 41, and the width of the first groove 41 and the second groove 42 along the first direction X are both equal to the width of the positive electrode 1.

[0137] Figure 12 This is a schematic diagram showing the distribution of the groove structure 4 at one of the bending centers of the positive electrode sheet 1. Based on any of the above embodiments, in one embodiment of this application, each of the first N bending segments S2 is provided with at least two first grooves 41, and the first grooves 41 are distributed at intervals along the first direction X.

[0138] Since the first groove 41 is connected to the second groove 42 at both ends, the second groove 42 is distributed at intervals along the first direction X, that is, the groove structure is distributed at intervals along the first direction X.

[0139] In this embodiment, the number of groove structures 4 is not limited and depends on the situation. For example, the number of grooves can be 2, 4, 6, 8, 9, etc.

[0140] The area between adjacent groove structures 4 (that is, the area between adjacent first grooves 41) is called the interval area. In this embodiment, the groove structures 4 and the interval area are arranged alternately, which can reduce the capacity of the bending section S2 and slow down the lithium release; it can also minimize the capacity loss; and the interval area can provide support to prevent the diaphragm 2 from being directly squeezed by the loose particles of the groove structure 4.

[0141] It should be noted that in this embodiment, the width of the interval region in the first direction X is not limited and can be set by the user.

[0142] As one possible implementation, the width W4 of the gap between adjacent first grooves 41 in the first direction X is less than or equal to 20 mm, so as to avoid the gap being too large and causing local lithium plating.

[0143] For example, the width of the interval region W4 can be 1mm, 5mm, 10mm, 15mm, 20mm, etc.

[0144] The sum of the widths W5 of all the groove structures is greater than the sum of the widths W4 of all the interval areas.

[0145] The wound-type battery cells made with the positive electrode sheet without any treatment are used as the normal group; the wound-type battery cells made with the positive electrode sheet in the prior art (only the first groove is provided at the bending section) are used as the control group; the first groove and the second groove with a step are set in the present application as the experimental group 1; a ceramic layer is further coated on the basis of the positive electrode sheet in the prior art (only the first groove is provided at the bending section) as the experimental group 2; an insulating layer is further pasted on the basis of the positive electrode sheet in the prior art (only the first groove is provided at the bending section) to obtain the experimental group 3; no groove is provided on the positive electrode sheet, and only an insulating layer is pasted at the bending section as the experimental group 4; no groove is provided on the positive electrode sheet, and only a heightening body is provided at the center of the wound-type battery cell as the experimental group 5; only the first groove is provided at the bending section of the positive electrode sheet, and a heightening body is provided at the center of the wound-type battery cell as the experimental group 6; the first groove and the second groove with a step are set in the present application, and a heightening body is provided at the center of the wound-type battery cell as the experimental group 7; assuming that the wound-type battery cell has a total of 2M folds, and only the first M folds of the positive electrode sheet are coated with a ceramic layer as the experimental group 8, and a total of 10 experimental groups are obtained.

[0146] The lithium deposition situation at the bending section, the K-value yield, and the capacity retention rate after 800T cycles at 25 °C of each experimental group are respectively tested. Among them, the process of testing the lithium deposition situation is as follows: after the wound-type battery cell is cycled at room temperature for 100T according to the test specifications, it is disassembled when fully charged, and directly observe whether lithium is deposited at the bending position. Lithium deposition means that there is gray lithium deposition on the electrode sheet or the separator, or there is silver-white metallic lithium on the negative bending section.

[0147] The K-value test is carried out according to the OCV (Open Circuit Voltage) process. The test process is as follows: the battery is calibrated to 50% SOC (State Of Charge), left standing at 45 °C for 50h, and then left standing at 25 °C for 24h, and the battery voltage is measured as V1; then left standing at 25 °C for 72h (this step time is recorded as t), and the battery voltage is measured as V2, K = (V1 - V2) / t, and K ≤ 0.04 mV / h (millivolt per hour) is qualified, and the K-value yield is calculated accordingly.

[0148] The test process of the capacity retention rate after 800T cycles at 25 °C is as follows: the battery cell is cycled at room temperature according to the test specifications, and the capacity retention rate is calculated; if the capacity retention rate of the battery cell drops rapidly below 70% within 500T, it is defined as a dive. The test results are shown in Table 1.

[0149] Table 1

[0150] Group Lithium plating during bending K-value yield 25℃ Cycling 800T Capacity Retention Rate normal group Lithium plating 50% 78% control group Non-lithium plating 30.5% diving Experimental group 1 Non-lithium plating 81.4% diving Experimental group 2 Non-lithium plating 98.7% 80% Experimental group 3 Non-lithium plating 97.3% 82% Experimental group 4 Non-lithium plating 98.8% 82% Experimental group 5 Lithium plating reduction 98.2% 80% Experimental group 6 Non-lithium plating 78.0% 82% Experimental group 7 Non-lithium plating 93.2% 82% Experimental group 8 Lithium plating 98.5% 79%

[0151] As can be seen from the normal and control groups, thinning the bent section of the positive electrode can solve the lithium plating problem in the arc region, but it leads to a technical problem of extremely low K-value yield of the cell. However, as can be seen from the control group and experimental group 1, the stepped design of the first and second grooves of this invention can significantly improve the K-value yield of the cell. This is because the second groove has less positive active material layer, thereby reducing the compression of the separator by the positive active material in the area where the second groove is located, thus improving the K-value yield of the wound cell. As can be seen from experimental groups 1 and 7, placing a raised body in the center of the wound cell can further improve the K-value yield of the wound cell. In addition, the capacity retention rate of the cell is also significantly improved because the raised body can avoid gaps between the positive and negative electrodes caused by excessive curvature of the negative electrode. As seen in the control group and experimental groups 2-3, thinning the bent section of the positive electrode and then coating it with ceramic or attaching an insulating layer can significantly improve the K-value yield and capacity retention of the cell. This is because the ceramic or insulating layer can solve the problem of particles on the positive electrode compressing the separator, and it can also act as a filler, reducing the gap between the positive and negative electrodes. As seen in the normal group and experimental group 4, attaching an insulating layer to the bent section can also improve the K-value yield and capacity retention of the wound cell. As seen in the control group and experimental group 6, placing a raised element in the center of the wound cell can significantly improve the K-value yield and capacity retention of the wound cell. As seen in the normal group and experimental group 5, directly placing a raised element in the center of the wound cell can significantly improve the K-value yield and alleviate the lithium plating problem in the arc area. However, it can be seen from the normal group and experimental group 8 that applying a ceramic layer only to the M-fold in front of the positive electrode cannot solve the problem of lithium deposition in the arc region, but it can significantly improve the K-value yield of the wound cell.

[0152] This application also provides a lithium-ion battery, including the wound cell described in any of the above embodiments.

[0153] 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.

[0154] The wound battery cell and lithium-ion battery provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the solution and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of this application.

Claims

1. A wound battery cell, characterized in that, include: A positive electrode sheet, a separator, and a negative electrode sheet are sequentially stacked and wound together. The positive electrode sheet includes a positive current collector and a positive active material layer coated on the surface of the positive current collector. Along the winding direction of the positive electrode sheet, the positive electrode active material layer includes a plurality of straight sections and bent sections connected in sequence. The first N bent sections are provided with a first groove. The positive electrode active material layer is also provided with a plurality of second grooves. The two ends of the first groove are respectively connected to the second groove. One end of the second groove extends to the straight section, and the other end of the second groove extends to the bent section and is connected to the first groove. N≥1. The depth of the second groove is greater than the depth of the first groove.

2. The wound battery cell as described in claim 1, characterized in that, Along the second direction, the positive electrode active material layer includes a first surface and a second surface. The first surface has a second groove. The end of the second groove away from the first groove is an inclined sidewall. The angle between the inclined sidewall and the first surface is in the range of 15° to 60°, and the inclined sidewall is inclined towards the adjacent straight section.

3. The wound battery cell as described in claim 1, characterized in that, Also includes: An inactive layer, which at least covers the second groove.

4. The wound battery cell as described in claim 3, characterized in that, The inactive layer only covers the second groove; Alternatively, the inactive layer extends from the second groove to the straight section; Alternatively, the inactive layer covers the second groove and the first groove; Alternatively, along the winding direction of the positive electrode sheet, the inactive layer covers the first groove of the first bending segment and the second grooves at both ends thereon, and the inactive layer extends to the second bending segment and covers the first groove of that bending segment.

5. The wound battery cell as described in claim 4, characterized in that, The inactive layer extends from the second groove to the straight section. Along the winding direction of the battery cell, the distance D between the two inactive layers is in the range of 0 < D ≤ (3.14 * d / 4) * 3 mm, where d is the arc diameter of the diaphragm corresponding to the bend section where the first groove is located.

6. The wound battery cell as described in claim 4, characterized in that, When the inactive layer covers the second groove and the first groove, along the winding direction of the battery cell, the length of the inactive layer exceeds the sum of the lengths L3 of the first groove and the second groove, where Q is 0 < Q ≤ 10 mm.

7. The wound battery cell as described in claim 3, characterized in that, The inactive layer includes a ceramic layer and / or an insulating layer.

8. The wound battery cell as described in claim 7, characterized in that, The inactive layer includes the insulating layer, wherein, in a first direction, the edge of the insulating layer extends beyond the edge of the positive electrode sheet; and / or, the inactive layer includes a ceramic layer, wherein, in a first direction, the width of the ceramic layer is the same as the width of the positive electrode active material layer.

9. The wound battery cell as described in claim 1, characterized in that, Along the winding direction of the battery cell, the length L1 of the first groove is in the range of 3.14*d / 8≤L1≤3.14*d / 2, where d is the arc diameter of the diaphragm corresponding to the bend where the first groove is located; And / or, the depth D1 of the first groove is in the range of D0 / 4≤D1<D0, where D0 is the thickness of the positive electrode active material layer corresponding to the straight section on the wound cell; And / or, along the winding direction, the length L2 of the second groove is in the range of 2mm≤L2≤L0 / 2, where L0 is the length of the first fold of the positive electrode in the wound cell, and the first fold of the positive electrode is the positive electrode between the winding start end of the positive electrode and the middle of the first bending segment; And / or, the depth D2 of the second groove is in the range of D1 < D2 ≤ 2 * D1, where D1 is the depth of the first groove.

10. The wound battery cell as described in claim 1, characterized in that, Also includes: The raised block is located at the center inside the wound cell, and one end of the raised block is close to the innermost negative electrode sheet of the wound cell, at the first bend where a single-sided layer of negative electrode active material is coated from the starting end of winding.

11. The wound battery cell as described in claim 10, characterized in that, The thickness W of the raised block in the second direction is in the range of W1≤W≤W2, where W1 is the thickness of a positive electrode sheet with a double-sided positive active material layer, and W2 is the sum of the thicknesses of two positive electrode sheets with double-sided positive active material layers and two negative electrode sheets with double-sided negative active material layers. And / or, the width of the shim block in the first direction is greater than the width of the negative electrode sheet; And / or, the length L4 of the shim block in the third direction is L4 > d0 / 2, where d0 is the arc diameter of the diaphragm corresponding to the first bending segment in the wound cell; And / or, on a plane perpendicular to the winding direction, the projection of the shim block does not overlap with the projection of the tab.

12. The wound battery cell according to any one of claims 1 to 11, characterized in that, In the first N bending segments, each bending segment is provided with the first groove, and the width of the first groove and the second groove along the first direction are both equal to the width of the positive electrode sheet.

13. The wound battery cell according to any one of claims 1 to 11, characterized in that, In the first N bending segments, each bending segment is provided with at least two of the first grooves, and the first grooves are distributed at intervals along the first direction.

14. The wound battery cell as described in claim 13, characterized in that, The width of the gap between adjacent first grooves in the first direction is less than or equal to 20 mm.

15. A lithium-ion battery, characterized in that, Including the wound battery cell as described in any one of claims 1 to 14.

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