Battery cell and battery

Abstract

The utility model relates to the technical field of battery energy, in particular to a battery cell and a battery. The battery cell comprises a positive plate, a diaphragm and a negative plate, wherein the positive plate, the diaphragm and the negative plate are sequentially stacked and wound to form a straight section, a first arc section and a second arc section; the negative plate comprises a negative current collector, a first negative active layer and a second negative active layer, and an empty foil area is formed at the head of the negative current collector; one side, close to the first arc section, of the head of the first negative electrode active layer is bent towards the direction far away from the positive plate to form a first bent part, and on the plane where the straight section is located, the projection of the head of the positive plate is located outside the projection of the first bent part; the head of the second negative active layer extends to the first arc section, and the distance between the head of the second negative active layer and the first arc section is smaller than that between the head of the positive plate and the first arc section; a plurality of recesses are formed on the surface of the first negative electrode active layer and / or the second negative electrode active layer. And the problems of local over-thickness, over-voltage and over-large K value of the battery cell are not easy to occur.

Description

Technical Field

[0001] The present application relates to the field of battery energy technology, and in particular to a battery cell and a battery. Background Art

[0002] Battery is a widely used energy device. Using battery as an energy source can obtain stable voltage and current. The battery can provide stable power for a long time. The battery has a simple structure and is easy to carry. It is widely used in life.

[0003] At present, the battery cell includes a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence and then wound from the head to the tail to form a battery cell. After the positive electrode sheet and / or the negative electrode sheet are coated, a flat area and a thinned area at the end of the flat area are formed on the electrode sheet due to the fluidity of the slurry.

[0004] However, the battery cell is prone to problems such as local excessive thickness, overvoltage, and excessive K value. Utility Model Content

[0005] Based on this, the present application provides a battery to solve the problem in the related art that the battery cell is prone to local excessive thickness, overvoltage and excessive K value.

[0006] On the one hand, the present application provides a battery cell, including a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and wound to form a straight section and a first arc section and a second arc section located on both sides of the straight section;

[0007] The negative electrode sheet comprises a negative electrode current collector and a first negative electrode active layer and a second negative electrode active layer respectively located on opposite sides of the negative electrode current collector, wherein at least the first negative electrode active layer exceeds the second negative electrode active layer at the head of the negative electrode current collector and forms an empty foil area on the side of the negative electrode current collector away from the first negative electrode active layer;

[0008] The head of the first negative electrode active layer is bent at a side close to the first arc segment in a direction away from the positive electrode sheet to form a first bent portion, and on the plane where the straight segment is located, the projection of the head of the positive electrode sheet is located outside the projection of the first bent portion;

[0009] The head of the second negative electrode active layer extends to the first arc segment, and the distance between the head of the second negative electrode active layer and the first arc segment is smaller than the distance between the head of the positive electrode sheet and the first arc segment;

[0010] A plurality of recessed portions are formed on the surface of the first negative electrode active layer and / or the second negative electrode active layer.

[0011] In a possible implementation, the head of the second negative electrode active layer is bent on the side close to the first arc segment toward a direction away from the positive electrode sheet to form a second bent portion, and on the plane where the straight segment is located, the projection of the head of the positive electrode sheet is located outside the projection of the second bent portion.

[0012] In a possible implementation, along the length direction of the positive electrode sheet, the positive electrode sheet has a first coating termination end, a second coating termination end, and a first alignment end and a first misalignment end that are oppositely disposed;

[0013] Along the length direction of the negative electrode sheet, the negative electrode sheet has a third coating termination end, a fourth coating termination end, and a second alignment end and a second misalignment end that are oppositely arranged;

[0014] The first alignment end and the first coating termination end are located at the same end of the positive electrode sheet, the first misaligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second alignment end and the third coating termination end are located at the same end of the negative electrode sheet, and the second misaligned end and the fourth coating termination end are located at the same end of the negative electrode sheet; or,

[0015] The first misaligned end and the first coating termination end are located at the same end of the positive electrode sheet, the first aligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second misaligned end and the third coating termination end are located at the same end of the negative electrode sheet, and the second aligned end and the fourth coating termination end are located at the same end of the negative electrode sheet.

[0016] In a possible implementation, along the length direction of the positive electrode sheet, the positive electrode sheet has a first coating termination end, a second coating termination end, and a first alignment end and a first misalignment end that are oppositely disposed.

[0017] Along the length direction of the negative electrode sheet, the negative electrode sheet has a third coating termination end, a fourth coating termination end, and a second alignment end and a second misalignment end that are oppositely arranged;

[0018] The first aligned end and the first coating termination end are located at the same end of the positive electrode sheet, the first misaligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second misaligned end and the third coating termination end are located at the same end of the negative electrode sheet, and the second misaligned end and the fourth coating termination end are located at the same end of the negative electrode sheet; or,

[0019] The first misaligned end and the first coating termination end are located at the same end of the positive electrode sheet, the first aligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second aligned end and the third coating termination end are located at the same end of the negative electrode sheet, and the second misaligned end and the fourth coating termination end are located at the same end of the negative electrode sheet.

[0020] In one possible implementation, the first negative electrode active layer and the second negative electrode active layer both include a first layer and a second layer that are stacked, the first layer is located between the second layer and the negative electrode current collector, the first layer and the second layer both include graphite particles, and the average particle size of the graphite particles in the first layer is greater than the average particle size of the graphite particles in the second layer.

[0021] In a possible implementation, the ratio of the average particle size of the graphite particles in the second layer to the average particle size of the graphite particles in the first layer is 0.4-0.98; and / or,

[0022] The average particle size Dv501 of the graphite particles in the first layer, the average particle size Dv502 of the graphite particles in the second layer, the thickness H1 of the first layer and the thickness H2 of the second layer satisfy:

[0023]

[0024] In a possible implementation, the depth of the recess is less than the thickness of the second layer; and / or,

[0025] The slot width of the concave portion is greater than the slot bottom width of the concave portion, and the ratio X between the slot bottom width of the concave portion and the slot width of the concave portion, the thickness H1 of the first layer and the thickness H2 of the second layer satisfy the following:

[0026]

[0027] In a possible implementation, the recess is a linear groove, the linear groove extends along the width direction of the negative electrode sheet, and a plurality of linear grooves are sequentially spaced apart along the length direction of the negative electrode sheet; and / or

[0028] The recessed portion is a blind hole groove, and a plurality of blind hole grooves are arranged at intervals.

[0029] In a possible implementation, in the length direction of the negative electrode sheet, the distance between any linear groove or blind hole groove located at the edge and the edge of the adjacent negative electrode active layer is 2 mm-5 mm; and / or,

[0030] The ratio of the depth of the linear groove or the blind hole groove to the thickness of the negative electrode sheet is greater than or equal to 0.02 and less than or equal to 0.3.

[0031] In a possible implementation, the ratio of the thickness of the battery cell to the width of the battery cell is in a range of 0.1%-10%.

[0032] In a possible implementation, the negative electrode sheet further includes a negative electrode ear, which is electrically connected to the negative electrode current collector, and the positive electrode sheet includes two positive electrode ears.

[0033] In a possible implementation, the diaphragm includes a base film, a first ceramic layer and a first coating layer, the first ceramic layer is arranged on the side of the base film facing the positive electrode sheet, and the first coating layer is arranged on the side of the first ceramic layer away from the base film; the total thickness of the diaphragm is 5μm-10μm.

[0034] In a possible implementation, the thickness of the separator and the thickness of the negative electrode sheet satisfy:

[0035] 250≤H4×H≤1500.

[0036] In a possible implementation, the length of the first bent portion is less than or equal to 10 mm; and / or,

[0037] The length of the second bending portion is less than or equal to 3 mm.

[0038] On the other hand, the present application also provides a battery, comprising an electrolyte and the above-mentioned battery cell, wherein the electrolyte comprises ethyl difluoroacetate.

[0039] The battery provided in the present application comprises a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form a straight section and a first arc section and a second arc section located on both sides of the straight section. The negative electrode sheet comprises a negative electrode current collector and a first negative electrode active layer and a second negative electrode active layer located on opposite sides of the negative electrode current collector, respectively. The head of the negative electrode current collector is formed with an empty foil area, and the head of the first negative electrode active layer is bent toward a direction away from the positive electrode sheet on a side close to the first arc section to form a first bending portion, and on the plane where the straight section is located, the projection of the head of the positive electrode sheet is located outside the projection of the first bending portion. The first bending portion can make up for the thickness difference of the battery cell at the position between the head of the positive electrode sheet and the innermost first arc section, and at the same time, the first bending portion can avoid the thinning area of ​​the head of the first negative electrode active layer corresponding to the flat area of ​​the positive electrode active layer of the positive electrode sheet, thereby avoiding the problem of local excessive thickness of the battery cell and increased K value due to insufficient CB value at the head of the battery cell. A plurality of recesses are formed on the surface of the first negative electrode active layer and / or the second negative electrode active layer, and the recesses can drain the electrolyte, thereby preventing the electrolyte from accumulating on the empty foil area of ​​the negative electrode current collector head, making it less likely for copper oxide to appear on the empty foil area of ​​the negative electrode current collector head, thereby preventing the battery cell from self-discharging too much and reducing the K value of the battery cell. The recesses on the first negative electrode active layer and / or the second negative electrode active layer can also alleviate the problem of stress concentration at the recessed position, reduce pressure, and further prevent the battery cell from being too thick locally. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 A schematic diagram of the structure of a battery cell provided in an embodiment of the present application;

[0042] Figure 2 Schematic diagram of the structure of the negative electrode sheet provided in the embodiment of the present application Figure 1 ;

[0043] Figure 3 Schematic diagram of the structure of the positive electrode sheet provided in the embodiment of the present application Figure 1 ;

[0044] Figure 4 Schematic diagram of the structure of the positive electrode sheet provided in the embodiment of the present application Figure 2 ;

[0045] Figure 5 A cross-sectional view of the first negative electrode active layer provided in an embodiment of the present application;

[0046] Figure 6 Schematic diagram of the structure of the negative electrode sheet provided in the embodiment of the present application Figure 2 .

[0047] Description of reference numerals:

[0048] 100-positive electrode sheet; 110-positive electrode current collector; 120-first positive electrode active layer; 130-second positive electrode active layer; 141-first coating termination end; 142-second coating termination end; 150-positive electrode ear; 160-first thinning area; 171-first alignment end; 172-first misalignment end;

[0049] 200-negative electrode sheet; 210-negative electrode current collector; 220-first negative electrode active layer; 221-first bending portion; 230-second negative electrode active layer; 241-third coating termination end; 242-fourth coating termination end; 250-recess; 260-negative electrode ear; 270-second thinning area; 280-thickening area; 291-second alignment end; 292-second misalignment end;

[0050] 300-diaphragm;

[0051] 410 - straight section; 420 - first arc section; 430 - second arc section. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiment of the present application will be described in more detail below in conjunction with the drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar parts or parts with the same or similar functions. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. The embodiments of the present application are described in detail below in conjunction with the drawings.

[0053] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, or it can be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0054] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are orientations or positional relationships based on the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0055] The terms "first", "second" and "third" (if any) in the specification and claims of this application and the above drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0056] In addition, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or display comprising a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to such process, method, product, or display.

[0057] In the prior art, a battery includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. After the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, they are wound from the head to the tail to form a battery cell. After the positive electrode sheet and / or the negative electrode sheet are coated, a flattening area and a thinning area located at the end of the flattening area are formed on the electrode sheet due to the fluidity of the slurry. However, after the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, the thinning area of ​​the negative electrode active layer of the negative electrode sheet corresponds to the flattening area of ​​the positive electrode active layer of the positive electrode sheet, which easily leads to insufficient CB value in the head area of ​​the battery cell. After the positive electrode sheet and the negative electrode sheet are stacked and wound, there is a gap between the head of the positive electrode sheet and the innermost arc of the battery cell. In addition, the electrolyte is easily accumulated in the empty foil area of ​​the head of the negative electrode sheet, so that copper oxide appears in the empty foil area of ​​the head of the negative electrode sheet. The above reasons lead to local overvoltage and overthickness of the battery cell, and make the K value of the battery cell too large.

[0058] After repeated thinking and verification, the inventor found that if the relative position between the positive electrode sheet and the negative electrode sheet is adjusted so that the thinned area of ​​the negative electrode sheet is staggered with the flat area of ​​the positive electrode sheet, after the positive electrode sheet and the negative electrode sheet are stacked and wound, the head of the negative electrode active layer on one side of the negative electrode sheet that is longer is bent in a direction away from the positive electrode sheet to form a bent portion, which makes the thinned area of ​​the head of the negative electrode sheet away from the flat area of ​​the positive electrode sheet, ensuring the CB value of the head of the battery cell, and the bent portion can make up the gap between the head of the positive electrode sheet and the innermost arc, balancing the thickness of the battery cell, and the battery cell is not prone to local over-thickness and over-voltage, and the battery cell is not prone to excessive K value due to insufficient CB value of the head. A concave portion is provided on the negative active layer of the negative electrode sheet, which can drain the electrolyte and prevent the electrolyte from accumulating in the empty foil area at the head of the negative electrode sheet, so that copper oxide is not likely to appear on the empty foil area at the head of the negative electrode sheet, thereby preventing the battery cell from self-discharging too much and reducing the K value of the battery cell. In addition, the concave portion on the negative active layer can alleviate the problem of stress concentration at the location of the concave portion. In this way, the problems of local over-thickness, over-voltage and excessive K value of the battery cell can be effectively alleviated.

[0059] In view of this, the inventor has designed a battery, wherein the negative electrode sheet comprises a negative electrode current collector and a first negative electrode active layer and a second negative electrode active layer respectively located on opposite sides of the negative electrode current collector, and the battery cell comprises a straight section and a first arc section and a second arc section respectively located on both sides of the straight section. The head of the negative electrode current collector is formed with an empty foil area, the head of the first negative electrode active layer is bent toward a direction away from the positive electrode sheet on a side close to the first arc section to form a first bending portion, and on the plane where the straight section is located, the projection of the head of the positive electrode sheet is located outside the projection of the first bending portion. A plurality of recesses are arranged on the surface of the first negative electrode active layer and / or the second negative electrode active layer. The first bending portion is used to make up the gap between the head of the positive electrode and the first arc section, and the thinning area of ​​the head of the first negative electrode active layer is prevented from corresponding to the flat area of ​​the positive electrode active layer of the positive electrode sheet, and the electrolyte is drained through the recess and the stress concentration at the position of the recess is relieved. In this way, the problems of local over-thickness, over-voltage and excessive K value of the battery cell can be avoided.

[0060] The technical solutions of the battery cell and the battery provided in the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0061] Reference Figures 1 to 5 As shown, the battery cell provided in the embodiment of the present application includes a positive electrode sheet 100, a separator 300 and a negative electrode sheet 200, which are sequentially stacked and wound to form a straight section 410 and a first arc section 420 and a second arc section 430 located on both sides of the straight section 410. The negative electrode sheet 200 includes a negative electrode collector 210 and a first negative electrode active layer 220 and a second negative electrode active layer 230 located on opposite sides of the negative electrode collector 210, respectively. At the head of the negative electrode collector 210, at least the first negative electrode active layer 220 exceeds the second negative electrode active layer 230 and forms an empty foil area 211 on the side of the negative electrode collector 210 away from the first negative electrode active layer 220. The head of the first negative electrode active layer 220 is bent at a side close to the first arc segment 420 in a direction away from the positive electrode sheet 100 to form a first bent portion 221. On the plane where the straight segment 410 is located, the projection of the head of the positive electrode sheet 100 is located outside the projection of the first bent portion 221. The head of the second negative electrode active layer 230 extends to the first arc segment 420, and the distance between the head of the second negative electrode active layer 230 and the first arc segment 420 is smaller than the distance between the head of the positive electrode sheet 100 and the first arc segment 420. A plurality of recesses 250 are formed on the surface of the first negative electrode active layer 220 and / or the second negative electrode active layer 230.

[0062] It can be understood that the battery cell provided in the embodiment of the present application is a winding core, wherein the head of the pole piece is the starting end of the winding of the pole piece, and the tail of the pole piece is the ending end of the winding of the pole piece. After the pole piece is wound, the head of the pole piece is located inside the battery cell, and the tail of the pole piece is located outside the battery cell.

[0063] Indicatively, Figure 2 As shown, in the length direction of the negative electrode sheet 200, the size of the first negative electrode active layer 220 is greater than the size of the second negative electrode active layer 230. The head of the first negative electrode active layer 220 and the head of the second negative electrode active layer 230 are facing the inside of the battery cell, and the tail of the first negative electrode active layer 220 and the tail of the second negative electrode active layer 230 are facing the outside of the battery cell. It can be understood that the first negative electrode active layer 220 and the second negative electrode active layer 230 form a misaligned end at the head of the negative electrode sheet 200, and the first negative electrode active layer 220 and the second negative electrode active layer 230 form an aligned end at the tail of the negative electrode sheet 200.

[0064] like Figure 3 and Figure 4 As shown, the positive electrode sheet 100 includes a positive electrode current collector 110 and a first positive electrode active layer 120 and a second positive electrode active layer 130 respectively located on opposite sides of the positive electrode current collector 110, the head of the first positive electrode active layer 120 is aligned with the head of the second positive electrode active layer 130, and the tail of the first positive electrode active layer 120 exceeds the tail of the second positive electrode active layer 130. The head of the first positive electrode active layer 120 and the head of the second positive electrode active layer 130 face the inside of the battery cell, and the tail of the first positive electrode active layer 120 and the tail of the second positive electrode active layer 130 face the outside of the battery cell.

[0065] It can be understood that after the electrode is coated, due to the fluidity of the slurry, a thinning area is formed at the end of the active layer, and the thinning area is the area where the thickness of the end of the active layer gradually decreases. After the positive electrode sheet 100 and the negative electrode sheet 200 are stacked and wound, the first positive electrode active layer 120 of the positive electrode sheet 100 faces the first negative electrode active layer 220 of the negative electrode sheet 200, and the second positive electrode active layer 130 of the positive electrode sheet 100 faces the second negative electrode active layer 230 of the negative electrode sheet 200.

[0066] It can be understood that the empty foil area 211 is the portion of the negative electrode current collector 210 that is exposed at the position where the first negative electrode active layer 220 exceeds the second negative electrode active layer 230 at the head of the positive electrode sheet 100 and the side of the negative electrode current collector 210 that is away from the second negative electrode active layer 230. Preferably, copper foil can be used as the negative electrode current collector 210. In other embodiments, the negative electrode current collector 210 can also be made of other materials, such as aluminum foil or a composite current collector.

[0067] Among them, the number of the straight section 410, the first arc section 420 and the second arc section 430 are all multiple, which can be specifically set according to the number of turns of the positive electrode sheet 100 and the negative electrode sheet 200 stacked and wound. Multiple straight sections 410 are stacked, multiple first arc sections 420 are stacked on one side of the multiple straight sections 410, and multiple second arc sections 430 are stacked on the other side of the multiple straight sections 410. It can be understood that the first bending portion 221 is set at the head of the first negative electrode active layer 220, that is, the paste is folded at the head of the longer negative electrode active layer of the negative electrode sheet 200. It is worth mentioning that the head of the first negative electrode active layer 220 is bent on the side close to the first arc section 420 in the direction away from the first fold of the head of the positive electrode sheet 100 to form the first bending portion 221. The first bending portion 221 can make the second thinning area 270 of the head of the first negative electrode active layer 220 away from the flat area (that is, the normal thickness area) of the positive electrode active layer of the positive electrode sheet 100.

[0068] It is worth mentioning that, on the plane where the straight section 410 is located, the projection of the head of the positive electrode sheet 100 is located outside the projection of the first bent portion 221, that is, after the positive electrode sheet 100 and the negative electrode sheet 200 are stacked and wound, the thickness of the first bent portion 221 will not overlap with the thickness of the head of the positive electrode sheet 100 to cause the local thickness of the battery cell to be too thick. And the thickness of the first bent portion 221 can make up for the thickness of the battery cell at the gap position between the head of the positive electrode sheet 100 and the innermost first arc section 420.

[0069] The distance between the head of the second negative electrode active layer 230 and the first arc segment 420 is smaller than the distance between the head of the positive electrode sheet 100 and the first arc segment 420, that is, the head of the second negative electrode active layer 230 exceeds the head of the positive electrode sheet 100, ensuring the CB value of the battery cell at the head position of the positive electrode sheet 100.

[0070] It should also be noted that the head of the second negative electrode active layer 230 extends to the first arc segment 420, that is, the second negative electrode active layer 230 is located at the innermost end of the winding center and abuts against the first arc segment 420; of course, due to the error of the coating process in the actual production process, the head of the second negative electrode active layer 230 may also extend to no more than 2 mm on the first arc segment 420 or the distance from the first arc segment 420 is no more than 2 mm. The above can all be considered that the head of the second negative electrode active layer 230 extends to the first arc segment 420.

[0071] A plurality of recesses 250 may be formed on the surface of the first negative electrode active layer 220 and / or the second negative electrode active layer 230 by laser etching, and the number of recesses 250 is non-limiting and can be set by those skilled in the art as needed. The first negative electrode active layer 220 and / or the second negative electrode active layer 230 may contain electrolyte through the recesses 250 to achieve drainage of the electrolyte.

[0072] Optionally, the recess 250 may be disposed on the side of the first negative electrode active layer 220 and / or the second negative electrode active layer 230 away from the negative electrode current collector 210, and the thickness of the first negative electrode active layer 220 and / or the second negative electrode active layer 230 at the position of the recess 250 is less than the thickness at other positions. Exemplarily, the recess 250 may be punched out by laser on the side of the negative electrode active layer away from the negative electrode current collector 210, that is, the laser punches out the recess 250 in the thickness direction of the negative electrode sheet 200 from the side of the negative electrode active layer away from the negative electrode current collector 210 to the direction close to the negative electrode current collector 210. The recess 250 is disposed on the side of the negative electrode active layer away from the negative electrode current collector 210, so that the path of ions and electrons transmitted from the side of the corresponding negative electrode active layer away from the negative electrode current collector 210 to the negative electrode current collector 210 becomes shorter, and the transmission polarization is reduced, which is conducive to improving the charge and discharge capacity of the battery.

[0073] When the negative electrode sheet 200 expands, the recess 250 can release stress. The portion of the negative electrode active layer located at the edge of the recess 250 squeezes the recess 250 toward the middle, making the cross-sectional area of ​​the recess 250 smaller, thereby alleviating the stress concentration of the negative electrode sheet 200 at the position of the recess 250, which is beneficial to alleviating the expansion of the battery cell in the thickness direction.

[0074] The battery cell provided in this embodiment has a first bent portion 221 of the first negative active layer 220 of the negative electrode sheet 200 that can make up for the thickness difference of the battery cell at the position between the head of the positive electrode sheet 100 and the innermost first arc segment 420, and balance the thickness of the battery cell. At the same time, the first bent portion 221 can avoid the thinning area of ​​the head of the first negative active layer 220 to correspond to the flat area of ​​the positive active layer of the positive electrode sheet 100, and avoid the problem of local excessive thickness of the battery cell and increased K value due to insufficient CB value at the head of the battery cell. A plurality of recesses 250 are formed on the surface of the first negative active layer 220 and / or the second negative active layer 230, and the recesses 250 can play a role in draining the electrolyte, avoiding the electrolyte from accumulating on the empty foil area 211 of the head of the negative current collector 210, so that copper oxide is not easy to appear on the empty foil area 211 of the head of the negative current collector 210, avoiding excessive self-discharge of the battery cell, and reducing the K value of the battery cell. The recessed portion 250 on the first negative electrode active layer 220 and / or the second negative electrode active layer 230 can also alleviate the problem of stress concentration at the location of the recessed portion 250 , reduce pressure, and further avoid the situation where the battery cell is locally too thick.

[0075] In one embodiment, the head of the second negative electrode active layer 230 is bent toward the direction away from the positive electrode sheet 100 on the side close to the first arc segment 420 to form a second bent portion, and on the plane where the straight segment 410 is located, the projection of the head of the positive electrode sheet 100 is located outside the projection of the second bent portion.

[0076] That is, after the positive electrode sheet 100 and the negative electrode sheet 200 are stacked and wound, the head of the shorter negative active layer of the negative electrode sheet 200 is folded. The second folded portion makes the second thinned area 270 at the head of the second negative active layer 230 away from the flat area of ​​the positive active layer of the positive electrode sheet 100.

[0077] It can be understood that, on the plane where the straight section 410 is located, the projection of the head of the positive electrode sheet 100 is located outside the projection of the second bend. The head of the second negative electrode active layer 230 is bent on the side close to the first arc section 420 in a direction away from the first bend of the head of the positive electrode sheet 100 to form a second bend.

[0078] In this embodiment, a second bent portion is formed at the head of the second negative electrode active layer 230, which can ensure the CB value of the battery cell at the head of the second negative electrode active layer 230, and avoid the problem of local over-thickness, over-voltage and increased K value of the battery cell due to insufficient CB value at the head of the second negative electrode active layer 230. At the same time, the second bent portion can further make up for the thickness difference between the head of the positive electrode sheet 100 and the innermost first arc segment 420 of the battery cell, further balance the thickness of the battery cell, that is, further avoid local over-thickness of the battery cell.

[0079] In a possible implementation, the length of the first bending portion 221 is less than or equal to 10 mm.

[0080] That is to say, the length of the first bend portion 221 is greater than 0 mm and less than 10 mm. Exemplarily, the length of the battery cell at the gap position between the head of the positive electrode sheet 100 and the innermost arc of the battery cell is 2-10 mm. When the length of the first bend portion 221 is greater than 10 mm, the head of the first negative electrode active layer 220 extends to the position corresponding to the head of the positive electrode sheet 100, and the head of the first negative electrode active layer 220 is located on the side of the negative electrode collector 210 away from the positive electrode sheet 100, resulting in the thickening of the battery cell at the head of the first negative electrode active layer 220, forming stress extrusion, causing the electrode sheet to deform at the head of the first negative electrode active layer 220 in the later stage of the cycle, affecting the flatness of the battery cell. This embodiment does not limit the specific length of the first bend portion 221, and those skilled in the art can set it according to the length of the gap position between the head of the positive electrode sheet 100 and the innermost arc of the battery cell.

[0081] The above arrangement enables the first bent portion 221 to compensate for the thickness difference of the battery cell at the gap position, while preventing the battery cell from being thickened at a local position, thereby effectively ensuring the flatness of the battery cell.

[0082] Illustratively, the length of the second bending portion is less than or equal to 3 mm.

[0083] Among them, the 0mm-3mm position of the head of the second negative electrode active layer 230 is a region with greater thinning, and the thinning after 3mm can be controlled. When the length of the second bend portion is greater than 3mm, the second bend portion is easy to overlap with the head position of the first negative electrode active layer 220, resulting in thickness superposition, forming stress extrusion, causing the pole piece to deform at the overlapping position in the later stage of the cycle, and the thicker the battery cell, the more obvious the problem. Those skilled in the art can set the specific length of the second bend portion as needed, and it is not limited here.

[0084] With this structure, the second bent portion can effectively compensate for the thickness difference of the battery cell at the gap position, while avoiding the thickening of the battery cell at a local position, thereby effectively ensuring the flatness of the battery cell.

[0085] In one embodiment, Figure 2-Figure 4 As shown, along the length direction of the positive electrode sheet 100, the positive electrode sheet 100 has a first coating termination end 141, a second coating termination end 142, and a first alignment end 171 and a first misalignment end 172 disposed oppositely. Along the length direction of the negative electrode sheet 200, the negative electrode sheet 200 has a third coating termination end 241, a fourth coating termination end 242, and a second alignment end 291 and a second misalignment end 292 disposed oppositely.

[0086] The first alignment end 171 and the first coating termination end 141 are located at the same end of the positive electrode sheet 100, the first misaligned end 172 and the second coating termination end 142 are located at the same end of the positive electrode sheet 100, the second misaligned end 292 and the third coating termination end 241 are located at the same end of the negative electrode sheet 200, and the second misaligned end 292 and the fourth coating termination end 242 are located at the same end of the negative electrode sheet 200; or, the first misaligned end 172 and the first coating termination end 141 are located at the same end of the positive electrode sheet 100, the first alignment end 171 and the second coating termination end 142 are located at the same end of the positive electrode sheet 100, the second alignment end 291 and the third coating termination end 241 are located at the same end of the negative electrode sheet 200, and the second misaligned end 292 and the fourth coating termination end 242 are located at the same end of the negative electrode sheet 200.

[0087] The head of the first positive electrode active layer 120 and the head of the second positive electrode active layer 130 together form a first alignment end 171, and the tail of the first positive electrode active layer 120 and the tail of the second positive electrode active layer 130 together form a first misaligned end 172. The tail of the first negative electrode active layer 220 and the tail of the second negative electrode active layer 230 together form a second alignment end 291, and the head of the first negative electrode active layer 220 and the head of the second negative electrode active layer 230 together form a second misaligned end 292. In this embodiment, the positive electrode sheet 100 and the negative electrode sheet 200 have the same tape running mode. When the positive electrode sheet 100 is coated with head alignment, the negative electrode sheet 200 is also coated with head alignment; when the positive electrode sheet 100 is coated with tail alignment, the negative electrode sheet 200 is also coated with tail alignment. Here, it is defined that the coating starting end of the shorter active material layer on the pole piece on one side of the current collector is aligned with the coating terminating end of the longer active material layer on the other side of the current collector as head-aligned coating; the coating terminating end of the shorter active material layer on the pole piece on one side of the current collector is aligned with the coating starting end of the longer active material layer on the other side of the current collector as tail-aligned coating.

[0088] Take the example that the coating termination ends of the positive electrode sheet 100 and the negative electrode sheet 200 are both located at the aligned ends of the corresponding electrode sheets. Wherein, the positive electrode sheet 100 and the negative electrode sheet 200 are both coated in tail-aligned manner.

[0089] like Figure 3 and Figure 4 As shown, A1 is the coating start end of the first positive electrode active layer 120, A2 is the coating end end of the first positive electrode active layer 120, C1 is the coating start end of the second positive electrode active layer 130, C2 is the coating end end of the second positive electrode active layer 130, the coating start end of the first positive electrode active layer 120 and the coating end end of the second positive electrode active layer 130 together form the first aligned end 171 of the positive electrode sheet 100, and the coating end end of the first positive electrode active layer 120 and the coating start end of the second positive electrode active layer 130 together form the first misaligned end 172 of the positive electrode sheet 100. When coating the positive electrode sheet 100, the first positive electrode active layer 120 can be coated along A1 to A2 first, and then the second positive electrode active layer 130 can be coated along C1 to C2. C2 is the first coating termination end 141 of the positive electrode sheet 100 , which is located at the first alignment end 171 of the head of the positive electrode sheet 100 ; A2 is the second coating termination end 142 of the positive electrode sheet 100 , which is located at the first offset end 172 of the tail of the positive electrode sheet 100 .

[0090] like Figure 2As shown, A1 is the coating start end of the first negative electrode active layer 220, A2 is the coating end end of the first negative electrode active layer 220, C1 is the coating start end of the second negative electrode active layer 230, C2 is the coating end end of the second negative electrode active layer 230, the coating start end of the first negative electrode active layer 220 and the coating end end of the second negative electrode active layer 230 together form the second aligned end 291 of the negative electrode sheet 200, and the coating end end of the first negative electrode active layer 220 and the coating start end of the second negative electrode active layer 230 together form the second misaligned end 292 of the negative electrode sheet 200. When coating the negative electrode sheet 200, the first negative electrode active layer 220 can be coated along A1 to A2 first, and then the second negative electrode active layer 230 can be coated along C1 to C2. C2 is the third coating termination end 241 of the negative electrode sheet 200 , which is located at the second alignment end 291 at the tail of the negative electrode sheet 200 ; A2 is the fourth coating termination end 242 of the negative electrode sheet 200 , which is located at the second offset end 292 at the head of the negative electrode sheet 200 .

[0091] It is understood by those skilled in the art that after the negative electrode active layer is coated, the 0mm-3mm area at the end of the coating of the negative electrode active layer is a tailing area due to the influence of the slurry fluidity and the movement of the coating die head (from the appearance of the electrode sheet, it can be seen that the end of the coating of the negative electrode active layer is a sawtooth tail, which is different from the starting end of the coating, and the starting end of the coating is relatively smooth). After the positive electrode active layer is coated, the starting end of the coating of the positive electrode active layer forms a relatively obvious first thinning area 160 due to the influence of the slurry fluidity and the movement of the coating die head. For example, to ensure the CB value, the tailing area of ​​the negative electrode active layer needs to correspond to the first thinning area 160 of the positive electrode active layer.

[0092] In this embodiment, since the head of the first negative electrode active layer 220 forms the first bent portion 221, the first bent portion 221 compensates for the thickness difference of the battery cell at the position between the head of the positive electrode sheet 100 and the innermost first arc segment 420, and can avoid the thinning area of ​​the head of the first negative electrode active layer 220 corresponding to the flat area of ​​the positive electrode active layer of the positive electrode sheet 100, thereby avoiding the problem of local excessive thickness of the battery cell and increased K value due to insufficient CB value at the head of the battery cell. The positive electrode sheet 100 and the negative electrode sheet 200 are carried in the same way, so that the coating end end of the second negative electrode active layer 230 can correspond to the coating start end of the second positive electrode active layer 130, and the tailing area of ​​the coating end end of the second negative electrode active layer 230 can correspond to the coating start end of the second positive electrode active layer 130, ensuring the CB value of the battery cell at the coating end end position of the second negative electrode active layer 230, and avoiding the problem of the battery cell being too thick locally and the K value increasing due to insufficient CB value at the coating end end position of the second negative electrode active layer 230. In this way, the problem of the battery cell being too thick locally and the K value increasing can be effectively avoided.

[0093] In another embodiment, Figure 3 , Figure 4 and Figure 6 As shown, along the length direction of the positive electrode sheet 100, the positive electrode sheet 100 has a first coating termination end 141, a second coating termination end 142, and a first alignment end 171 and a first misalignment end 172 disposed oppositely. Along the length direction of the negative electrode sheet 200, the negative electrode sheet 200 has a third coating termination end 241, a fourth coating termination end 242, and a second alignment end 291 and a second misalignment end 292 disposed oppositely.

[0094] The first alignment end 171 and the first coating termination end 141 are located at the same end of the positive electrode sheet 100, the first misaligned end 172 and the second coating termination end 142 are located at the same end of the positive electrode sheet 100, the second misaligned end 292 and the third coating termination end 241 are located at the same end of the negative electrode sheet 200, and the second misaligned end 292 and the fourth coating termination end 242 are located at the same end of the negative electrode sheet 200; or, the first misaligned end 172 and the first coating termination end 141 are located at the same end of the positive electrode sheet 100, the first alignment end 171 and the second coating termination end 142 are located at the same end of the positive electrode sheet 100, the second alignment end 291 and the third coating termination end 241 are located at the same end of the negative electrode sheet 200, and the second misaligned end 292 and the fourth coating termination end 242 are located at the same end of the negative electrode sheet 200.

[0095] It can be understood that the tape running modes of the positive electrode sheet 100 and the negative electrode sheet 200 are inconsistent. When the positive electrode sheet 100 is coated with head alignment, the negative electrode sheet 200 is coated with tail alignment; when the positive electrode sheet 100 is coated with tail alignment, the positive electrode sheet 100 is coated with head alignment.

[0096] Take the first coating termination end 141 of the positive electrode sheet 100 at the alignment end and the third coating termination end 241 of the negative electrode sheet 200 at the misalignment end as an example. The negative electrode sheet 200 is coated in a head alignment manner, and the positive electrode sheet 100 is coated in a tail alignment manner.

[0097] like Figure 3 and Figure 4 As shown, A1 is the coating start end of the first positive electrode active layer 120, A2 is the coating end end of the first positive electrode active layer 120, C1 is the coating start end of the second positive electrode active layer 130, and C2 is the coating end end of the second positive electrode active layer 130. When coating the positive electrode sheet 100, the first positive electrode active layer 120 can be coated along A1 to A2 first, and then the second positive electrode active layer 130 can be coated along C1 to C2. C2 is the first coating end end 141 of the positive electrode sheet 100, and A2 is the second coating end end 142 of the positive electrode sheet 100.

[0098] like Figure 6As shown, A1 is the coating start end of the first negative electrode active layer 220, A2 is the coating end end of the first negative electrode active layer 220, C1 is the coating start end of the second negative electrode active layer 230, C2 is the coating end end of the second negative electrode active layer 230, the coating end end of the first negative electrode active layer 220 and the coating start end of the second negative electrode active layer 230 together form the second alignment end 291 of the negative electrode sheet 200, and the coating start end of the first negative electrode active layer 220 and the coating end end of the second negative electrode active layer 230 together form the second misaligned end 292 of the negative electrode sheet 200. When coating the negative electrode sheet 200, the first negative electrode active layer 220 can be coated along A1 to A2 first, and then the second negative electrode active layer 230 can be coated along C1 to C2. C2 is the third coating end end 241 of the negative electrode sheet 200, and A2 is the fourth coating end end 242 of the negative electrode sheet 200.

[0099] It can be understood by those skilled in the art that after the negative electrode active layer is coated, affected by the fluidity of the slurry and the movement of the coating die, the starting end of the negative electrode active layer coating forms a second thinning area 270 and a thickening area 280, and the thickening area 280 is located between the second thinning area 270 and the flattening area. Exemplarily, the size of the second thinning area 270 in the length direction of the negative electrode sheet 200 can be 0mm-3mm, the size of the thickening area 280 in the length direction of the negative electrode sheet 200 can be 3mm-10mm, and the thickness of the thickening area 280 exceeding the flattening area can be 0μm-20μm. Compared with the end end of the negative electrode active layer coating, the starting end of the negative electrode active layer coating can better control the thickening of the thickening area 280 to be 0μm-20μm, that is, the thickness is controllable. After the positive electrode active layer is coated, affected by the fluidity of the slurry and the movement of the coating die, a more obvious first thinning area 160 is formed at the starting end of the positive electrode active layer coating.

[0100] Through the above arrangement, after the positive electrode sheet 100 and the negative electrode sheet 200 are stacked and wound, since the first bending portion 221 is formed at the head of the first negative electrode active layer 220, when the coating starting end of the first negative electrode active layer 220 is located at the head of the first negative electrode active layer 220, the thickened area 280 at the head of the first negative electrode active layer 220 will not correspond to the head of the first positive electrode active layer 120. At the same time, the thickened area 280 at the head of the first negative electrode active layer 220 can effectively compensate for the thickness difference of the battery cell at the position between the head of the positive electrode sheet 100 and the innermost first arc segment 420. The coating starting end C1 of the second negative electrode active layer 230 corresponds to the coating starting end of the second positive electrode active layer 130, that is, the thickened area 280 on the second negative electrode active layer 230 corresponds to the first thinned area 160 on the second positive electrode active layer 130, so that the thickness of the positive electrode sheet 100 and the thickness of the negative electrode sheet 200 compensate each other, so that the thickness difference between the battery cell at the thinned area of ​​the positive electrode sheet 100 and the flat area of ​​the positive electrode sheet 100 is reduced, which is beneficial to reducing the stress in the thickness difference area, preventing stress deformation of the battery cell, and avoiding excessive local thickness of the battery cell.

[0101] It is worth mentioning that the structure of the positive electrode sheet 100 can be as follows Figure 4 As shown, since the first negative electrode active layer 220 has a first bent portion 221 at the head thereof, and the first bent portion 221 can make up for the thickness difference of the battery cell at the gap position between the head of the positive electrode sheet 100 and the innermost arc of the battery cell, and the thinned area of ​​the first positive electrode active layer 120 will not be opposite to the head of the first negative electrode active layer 220. After the positive electrode sheet 100 is coated, the first alignment end 171 can be cut off to a certain size, so that the thinned area at the first end A1 of the original first positive electrode active layer 120 does not exist, making the battery cell flatter and further preventing the battery cell from stress deformation.

[0102] In one possible implementation, the first negative electrode active layer 220 and the second negative electrode active layer 230 both include a first layer and a second layer that are stacked, the first layer is located between the second layer and the negative electrode current collector 210, the first layer and the second layer both include graphite particles, and the average particle size Dv501 of the graphite particles in the first layer is greater than the average particle size Dv502 of the graphite particles in the second layer.

[0103] Schematically, the negative electrode sheet 200 is coated with two layers, that is, two different graphites or graphite-doped silicon slurries are coated on the negative electrode current collector 210 at the same time to form a first layer and a second layer at the same time. Among them, the large-diameter graphite particles in the first layer, which is close to the negative electrode current collector 210, play a supporting role in improving the compaction of the negative electrode sheet 200, and the small-diameter graphite particles in the second layer play a role in increasing the porosity of the negative electrode sheet 200, improving the electrolyte wettability, and reducing the polarization of the negative electrode sheet 200.

[0104] It is worth mentioning that since the negative electrode active layer is two different layers of graphite or graphite-doped silicon materials coated at the same time, the average particle size and other parameters of the two layers of graphite particles are inconsistent, resulting in obvious differences in the particle size and casting performance of the two layers of slurry on the negative electrode collector 210. This makes it difficult to control the two layers on the negative electrode collector 210 to thicken or thin at the same time during coating. Therefore, the thinning size of the head and tail of the double-layer coating system negative electrode sheet 200 is quite different from the flat area in the middle of the electrode sheet when coating.

[0105] Optionally, the positive electrode sheet 100 and the negative electrode sheet 200 are coated in the same tape running mode, that is, when the positive electrode sheet 100 is coated in head alignment, the negative electrode sheet 200 is also coated in head alignment; when the positive electrode sheet 100 is coated in tail alignment, the negative electrode sheet 200 is also coated in tail alignment. The coating start end of the second positive electrode active layer 130 can be opposite to the coating end end of the second negative electrode active layer 230, effectively ensuring the CB value of the battery cell at the coating start end position of the second positive electrode active layer 130, and effectively avoiding the problem of local excessive thickness and increased K value of the battery cell due to insufficient local CB value.

[0106] In this structure, the negative active layer on the negative electrode sheet 200 has a stronger supporting effect on compaction, and at the same time, the polarization of the negative electrode sheet 200 is lower, and the electrode sheet dynamics of the negative electrode sheet 200 is higher. When the positive electrode sheet 100 and the negative electrode sheet 200 adopt the same tape running method during coating, the CB value of the battery cell at the coating start end position of the second positive active layer 130 can be effectively guaranteed, and the problem of local excessive thickness and increased K value of the battery cell due to insufficient local CB value can be effectively avoided.

[0107] In a possible implementation, the ratio of the average particle size Dv502 of the graphite particles in the second layer to the average particle size Dv501 of the graphite particles in the first layer is 0.4-0.98.

[0108] Specifically, 0.4≤Dv502 / Dv501≤0.98. Among them, the second layer can inhibit the expansion of the negative electrode active layer. When the ratio between the average particle size of the graphite particles in the second layer and the average particle size of the graphite particles in the first layer is less than 0.4, it indicates that the average particle size of the graphite particles in the second layer is too small or the average particle size of the graphite particles in the first layer is too large, and the negative electrode sheet 200 is prone to expansion after multiple cycles. When the ratio between the average particle size of the graphite particles in the second layer and the average particle size of the graphite particles in the first layer is greater than 0.98, it indicates that the average particle size of the graphite particles in the second layer is too large or the average particle size of the graphite particles in the first layer is too small. When the average particle size of the graphite particles in the second layer is too large, the polarization reduction of the negative electrode sheet 200 and the improvement of the electrode sheet dynamics are small. When the average particle size of the graphite particles in the first layer is too small, the improvement of the support effect on the compaction of the negative electrode sheet 200 is small. The above reasons will lead to a decrease in the capacity retention rate of the battery. Those skilled in the art can set the specific size of the ratio between the average particle size of the graphite particles in the second layer and the average particle size of the graphite particles in the first layer as needed, and no sole limitation is made here.

[0109] Through the above arrangement, the negative active layer on the negative electrode sheet 200 has a strong supporting effect on compaction, while ensuring that the polarization of the negative electrode sheet 200 is low and the electrode dynamics of the negative electrode sheet 200 are high, thereby ensuring the capacity retention rate of the battery.

[0110] Illustratively, the content of single graphite particles in the second layer is greater than the content of single graphite particles in the first layer.

[0111] Among them, the smaller the average particle size of the graphite particles in the second layer, the more single particles in the second layer of graphite particles or even all of them are single particles, the better the graphite rate performance, and the negative electrode active layer has a thinner second layer, which can significantly reduce the polarization of the negative electrode sheet 200 and improve the electrode sheet dynamics.

[0112] In a possible implementation, the average particle size Dv501 of the graphite particles in the first layer, the average particle size Dv502 of the graphite particles in the second layer, the thickness H1 of the first layer, and the thickness H2 of the second layer satisfy:

[0113]

[0114] Among them, when When the negative electrode sheet 200 is subjected to multiple cycles, it is easy to expand; when When the negative electrode sheet 200 is expanded, the polarization reduction and the improvement effect of the electrode sheet dynamics are small, or the support effect of the compaction of the negative electrode sheet 200 is small, resulting in a decrease in the capacity retention rate of the battery. That is, the above arrangement can effectively suppress the expansion of the negative electrode sheet 200 and ensure the capacity retention rate of the battery.

[0115] In a specific embodiment, the first layer further includes a silicon-containing compound, and the silicon doping amount of the first layer is greater than the silicon doping amount of the second layer.

[0116] Among them, the second layer may or may not include silicon-containing compounds, that is, the second layer may or may not be doped with silicon, and this is not the only limitation. Schematically, the total silicon-doping ratio of the negative electrode active layer is 1%-50%. It can be understood that by doping silicon in the negative electrode active layer, the energy density of the battery can be improved because the theoretical specific capacity of silicon is greater than that of graphite particles. The silicon particles with larger expansion are arranged on the side close to the negative electrode current collector 210, so that the graphite particles in the second layer can inhibit the expansion of the silicon particles. In other words, the above arrangement can effectively inhibit the expansion of the silicon-doped negative electrode sheet 200.

[0117] Schematically, the ratio W between the silicon doping amount of the first layer and the silicon doping amount of the corresponding negative electrode active layer, the thickness H1 of the first layer and the thickness H2 of the second layer satisfy:

[0118]

[0119] The greater the silicon content of the negative electrode active layer, the greater the proportion of the second layer in the thickness of the negative electrode active layer, that is, more second layers are needed to suppress the expansion of silicon particles. When , the amount of silicon doped in the first layer is small, and the improvement of battery energy density is small; when When the thickness of the second layer is small, the negative electrode sheet 200 is easy to expand after multiple cycles. In other words, the above arrangement can ensure the energy density of the battery and effectively inhibit the expansion of the negative electrode sheet 200.

[0120] In a possible implementation, the depth of the recess 250 is smaller than the thickness of the second layer.

[0121] Among them, the graphite particles with a smaller average particle size in the second layer can improve the electrode dynamics of the negative electrode 200, and only a smaller depth of the recess 250 is required to improve the battery's charge and discharge capabilities. In addition, when the depth of the recess 250 is greater than the thickness of the second layer, the negative electrode active layer loses more active material at the recess 250, resulting in a decrease in the energy density of the battery.

[0122] That is to say, the above arrangement can ensure the energy density of the battery while ensuring the charging and discharging capacity of the battery.

[0123] Schematically, the slot width of the recess 250 is greater than the slot bottom width of the recess 250 , and the ratio X between the slot bottom width of the recess 250 and the slot width of the recess 250 , the thickness H1 of the first layer and the thickness H2 of the second layer satisfy:

[0124]

[0125] Schematically, the cross-sectional shape of the recess 250 can be a trapezoid or a "U" shape, that is, the width of the notch of the recess 250 is greater than the bottom width. Among them, the smaller the thickness of the second layer, the better the rate performance of the second layer of graphite is, and the better the improvement effect on the dynamics of the pole piece. At this time, combined with the laser wire-making technology, only a smaller depth is needed to assist the second layer of graphite to improve the entire system, and vice versa. When , the ratio X between the groove bottom width and the groove opening width of the concave portion 250 is too small, which affects the energy density of the battery; when When the ratio X between the groove bottom width and the groove opening width of the concave portion 250 is too large, the concave portion 250 has a small effect on draining the electrolyte, relieving stress concentration, and improving the battery charge and discharge capacity. In other words, the above arrangement can ensure both the energy density of the battery and the drainage effect of the concave portion 250 on the electrolyte, so as to reliably reduce the K value of the battery cell.

[0126] It should be noted that in the battery cell on the high voltage platform (the upper limit of charging cut-off voltage is not less than 4.5V), the side reaction of the electrolyte is more intense. Since the recess 250 is formed on the negative electrode sheet 200 of the present application, on the one hand, although it has a certain drainage effect on the electrolyte, on the other hand, it increases the contact area with the electrolyte, resulting in the products of the side reaction with the electrolyte, such as hydrofluoric acid, which will corrode and destroy the conductive network and bonding network near the recess 250, thereby causing gas production, falling of negative electrode particles, etc., further causing the negative electrode particles to short-circuit with the head copper foil to form self-discharge, increasing the K value and forming copper oxide on the surface of the copper foil; further, it will also cause the negative electrode particles in the recess 250 to break into burrs, resulting in piercing the diaphragm 300, thereby causing the positive and negative electrode sheets 200 to contact and cause a short circuit, affecting the safety of the battery cell.

[0127] In this embodiment, That is, it ensures that the recess 250 can reliably drain the electrolyte, while preventing the contact area between the negative electrode active layer and the electrolyte from being too large, thereby effectively controlling the side reaction between the negative electrode active layer and the electrolyte, avoiding an increase in the K value of the battery cell while ensuring the safety of the battery cell.

[0128] In a specific embodiment, the recess 250 is a linear groove, which extends along the width direction of the negative electrode sheet 200 , and a plurality of linear grooves are sequentially spaced apart along the length direction of the negative electrode sheet 200 .

[0129] Specifically, the linear grooves can be continuous or discontinuous and formed by splicing multiple sections. A process error of ±1 mm is reserved at the interface between the two spliced ​​sections, so that the two spliced ​​sections are interconnected. Exemplarily, multiple linear grooves can be arranged at equal intervals along the length direction of the negative electrode sheet 200. The linear grooves extend along the width direction of the negative electrode sheet 200, so that the length of the linear grooves is small, which is convenient for setting the linear grooves on the negative electrode active layer.

[0130] The recess 250 is set as a linear groove, which can play a capillary role on the electrolyte, thereby improving the drainage effect of the recess 250 on the electrolyte. The electrolyte is not easy to accumulate in the empty foil area 211 at the head of the negative electrode current collector 210, so that copper oxide is not easy to appear on the empty foil area 211 at the head of the negative electrode current collector 210, thereby avoiding excessive self-discharge of the battery cell and reducing the K value of the battery cell.

[0131] In another specific embodiment, the recess 250 is a blind hole slot, and a plurality of blind hole slots are arranged at intervals.

[0132] That is, the concave portion 250 is formed as a hole that does not penetrate the negative electrode active layer. Exemplarily, the axis of the blind hole groove may extend along the thickness direction of the negative electrode active layer, and a plurality of blind holes may be arranged in multiple rows and columns on the negative electrode active layer.

[0133] The recess 250 is set as a blind hole groove, which can reduce the loss of active material of the negative electrode active layer at the position of the recess 250 and ensure the energy density of the battery cell.

[0134] In a specific embodiment, in the length direction of the negative electrode sheet 200, the distance between any linear groove or blind hole groove located at the edge and the edge of the adjacent negative electrode active layer is 2 mm-5 mm.

[0135] Specifically, in the length direction of the negative electrode active layer, there is a 2mm-5mm margin between the area where the linear groove or blind hole groove is opened on the negative electrode active layer and the edge of the negative electrode active layer. The above arrangement can avoid the linear groove or blind hole groove being opened in the area with uneven thickness on the negative electrode active layer, prevent the problem of mismatching the thinning area of ​​the positive and negative electrode sheets 200 from worsening, and ensure the CB value.

[0136] Optionally, the ratio of the depth of the linear groove or the blind hole groove to the thickness of the negative electrode sheet 200 is greater than or equal to 0.02 and less than or equal to 0.3.

[0137] When the ratio between the depth of the linear groove or blind hole groove and the thickness of the negative electrode sheet 200 is less than 0.02, the linear groove or blind hole groove has a small drainage effect on the electrolyte; when the ratio between the depth of the linear groove 250 and the thickness of the negative electrode sheet 200 is greater than 0.3, the negative electrode active layer loses more active materials at the position of the linear groove 250, resulting in a decrease in the energy density of the battery. In other words, the above-mentioned setting not only ensures the drainage effect of the linear groove or blind hole groove on the electrolyte to reliably reduce the K value of the battery cell, but also ensures the energy density of the battery.

[0138] In a specific embodiment, the ratio of the thickness of the battery cell to the width of the battery cell is in the range of 0.1%-10%.

[0139] It can be understood by those skilled in the art that when the ratio between the thickness of a battery cell and the width of the battery cell is in the range of 0.1%-10%, it is generally called a large and thin battery cell. Large and thin battery cells are easily squeezed and deformed by internal stress, usually manifesting as wave deformation or pot-lid deformation, and thus large and thin battery cells have higher requirements for flatness.

[0140] In this structure, since the head of the first active material layer of the negative electrode sheet 200 is formed with a first bent portion 221, the first bent portion 221 can make up for the thickness difference between the head of the positive electrode sheet 100 and the innermost first arc segment 420 of the battery cell, and at the same time, it can avoid the second thinning area 270 of the head of the first negative electrode active layer 220 corresponding to the flat area of ​​the positive electrode active layer of the positive electrode sheet 100, thereby ensuring the CB value of the head of the battery cell. The recess 250 on the negative electrode active layer can play a role in draining the electrolyte, and can also alleviate the problem of stress concentration. The K value of the battery cell is low, and the flatness of the battery cell is high, so the CB value of its head can be guaranteed, and the battery cell will not be locally too thick or over-voltage.

[0141] Optionally, the conveying method of the positive electrode sheet 100 of the battery cell is inconsistent with the conveying method of the negative electrode sheet 200 of the battery cell. When the positive electrode sheet 100 adopts head-aligned coating, the negative electrode sheet 200 adopts tail-aligned coating; when the positive electrode sheet 100 adopts tail-aligned coating, the positive electrode sheet 100 adopts head-aligned coating.

[0142] The positive electrode sheet 100 and the negative electrode sheet 200 of the battery cell adopt different tape conveying methods, and the thickness of the positive electrode sheet 100 of the battery cell and the thickness of the negative electrode sheet 200 compensate each other. The thickness difference between the thinning area of ​​the positive electrode sheet 100 and the flattened area of ​​the positive electrode sheet 100 is reduced, which is beneficial to reducing the stress in the thickness difference area, preventing the battery cell from stress deformation, avoiding excessive local thickness of the battery cell, and effectively ensuring the flatness of the battery cell.

[0143] like Figure 1As shown, the negative electrode sheet 200 further includes a negative electrode tab 260 , which is electrically connected to the negative electrode current collector 210 , and the positive electrode sheet 100 includes two positive electrode tabs 150 .

[0144] The negative electrode tab 260 is electrically connected to the negative electrode current collector 210, and the two positive electrode tabs 150 are electrically connected to the positive electrode current collector 110. For example, after the positive electrode sheet 100 and the negative electrode sheet 200 are stacked and wound, the negative electrode tab 260 is located between the two positive electrode tabs 150 in the width direction of the battery.

[0145] It is understandable that since the battery cell has one negative electrode tab 260 and two positive electrode tabs 150, the negative electrode impedance of the battery cell becomes a major factor hindering the charging capacity of the battery cell. If silicon is added to the negative electrode active layer, there will be more side reactions, the battery cell will generate more heat and expand more, the gap between graphite particles will increase, the polarization impedance of the negative electrode sheet 200 will worsen, and the problem of a higher CB value leading to a higher K value will easily occur.

[0146] The battery cell provided in this embodiment has one negative electrode tab 260 and two positive electrode tabs 150 , so compared with a battery cell having only one positive electrode tab 150 and one negative electrode tab 260 , the internal resistance of the battery cell is reduced and the charge and discharge rate of the battery cell is improved.

[0147] By providing the first bent portion 221 at the head of the first negative electrode active layer 220, the flatness of the battery cell is improved, and the problem of excessive thickness of the battery cell and increased K value due to insufficient CB value at the head of the battery cell is avoided. By providing the recess 250 on the negative electrode active layer, the recess 250 can be used to drain the electrolyte and relieve stress concentration, further avoiding excessive thickness of the local thickness of the battery cell and further reducing the K value of the battery cell.

[0148] Optionally, the battery cell provided in this embodiment has the same tape running mode for the positive electrode sheet 100 and the negative electrode sheet 200, so that the end end of the coating of the second negative electrode active layer 230 corresponds to the start end of the coating of the second positive electrode active layer 130, ensuring the CB value, avoiding the increase of the K value of the battery cell, the local excessive thickness of the battery cell, and the diaphragm being blocked. When the negative electrode active layer includes a second layer and a first layer stacked and the silicon doping amount of the first layer is greater than the silicon doping amount of the second layer, the graphite particles in the second layer can be consistent with the expansion of the silicon particles, thereby effectively inhibiting the expansion of the negative electrode sheet 200.

[0149] In one embodiment, Figure 1 As shown, the battery cell further includes a separator 300, which is disposed between the positive electrode sheet 100 and the negative electrode sheet 200. The separator 300 includes a base film, a first ceramic layer and a first glue layer, wherein the first ceramic layer is disposed on the side of the base film facing the positive electrode sheet 100, and the first glue layer is disposed on the side of the first ceramic layer facing away from the base film. The total thickness of the separator 300 is 5 μm-10 μm.

[0150] The diaphragm 300 further includes a second adhesive layer, which is located on the side of the base film away from the first ceramic layer. The diaphragm 300 may also include a second ceramic layer, which is located between the second adhesive layer and the base film. In other embodiments, the diaphragm 300 may also have only one ceramic layer, namely the first ceramic layer, which is not limited here.

[0151] It should be noted that the lithium deposition caused by unqualified coating thinning or mismatched positive and negative electrode thinning is different from conventional lithium deposition. The lithium deposition caused by unqualified thinning usually manifests as linear (lithium dendrites begin to accumulate along the unqualified thinning) protrusions. As the number of battery cycles increases, the protrusion height becomes larger and larger, and the diaphragm 300 is punctured to cause a large-scale short circuit problem.

[0152] In this embodiment, the base film of the separator 300 can effectively isolate the positive electrode sheet 100 and the negative electrode sheet 200, the first ceramic layer can improve the thermal stability of the separator 300, and effectively prevent the lithium dendrites caused by lithium precipitation from penetrating the separator 300, reducing the risk of short circuit, and the separator 300 can be reliably fixed between the positive electrode sheet 100 and the negative electrode sheet 200 through the first glue coating layer. The total thickness of the separator 300 can effectively prevent the lithium dendrite protrusions caused by linear lithium precipitation from piercing the separator 300 and causing a short circuit, while also ensuring the energy density of the battery.

[0153] In a specific embodiment, the thickness H4 of the separator 300 and the thickness H of the negative electrode sheet 200 satisfy:

[0154] 250≤H4×H≤1500.

[0155] The thinner the negative electrode sheet 200 is, the higher the proportion of the thickness of the thinned area is, the longer the thinned area is, and the more likely it is that the CB value is insufficient. When H4×H<250, it is easy for the lithium dendrite protrusions to pierce the diaphragm 300 due to linear lithium precipitation caused by insufficient CB value, resulting in a short circuit; when H4×H>1500, the thickness of the diaphragm 300 is relatively thick, which reduces the energy density of the battery.

[0156] The above arrangement can effectively prevent the lithium dendrite protrusions caused by linear lithium deposition from piercing the diaphragm 300 and causing a short circuit, reliably improve charging safety, and at the same time ensure the energy density of the battery.

[0157] The present application also provides a battery, comprising an electrolyte and the above-mentioned battery cell, wherein the electrolyte comprises ethyl difluoroacetate, and the depth H3 of the recess, the thickness H of the negative electrode sheet and the content B of ethyl difluoroacetate in the electrolyte satisfy:

[0158]

[0159] Thus, by adding ethyl difluoroacetate to the electrolyte, on the one hand, the anti-oxidation property of the electrolyte can be improved and the electrolyte can be improved in the infiltration of the negative electrode sheet, thereby reducing the side reaction between the electrolyte and the negative electrode material in the recess and facilitating Li+ conduction, while not reducing the infiltration performance of the electrolyte on the negative electrode sheet and reducing the side reaction of the negative electrode sheet recess, thereby improving the structural stability of the negative electrode sheet and avoiding the possibility of the electrode sheet falling during the charge and discharge cycle. On the other hand, ethyl difluoroacetate can form a stable SEI film on the surface of the recess, thereby improving the structural stability of the negative electrode sheet. In this way, the recess can reliably drain the electrolyte, while reducing the side reaction between the negative electrode active layer and the electrolyte, thereby reducing gas production and the falling of negative electrode particles, etc., and reliably reducing the K value of the battery cell.

[0160] Among them, when the depth of the linear groove 250 accounts for a smaller proportion in the thickness direction of the negative electrode sheet 200, it means that the thickness of the negative electrode active layer at the position of the linear groove 250 is greater, that is, the non-porous thickness under the linear groove 250 is greater, and the more it is necessary to increase the content of ethyl difluoroacetate in the electrolyte to increase the wettability of the electrolyte to the negative electrode sheet 200.

[0161] like This indicates that the content of ethyl difluoroacetate in the electrolyte is relatively high, which can easily lead to excessive fluorine and thus cause gas production;

[0162] like This indicates that the content of ethyl difluoroacetate in the electrolyte is too low and it cannot form a stable SEI film on the surface of the concave portion.

[0163] The battery of the present application is described in detail below through specific examples. The battery parameters of the following examples and comparative examples are recorded in Table 1 and Table 2.

[0164] Example 1

[0165] The battery preparation of this embodiment includes the following steps:

[0166] 1. Preparation of positive electrode sheet 100

[0167] The lithium cobalt oxide material is prepared into a positive electrode active layer slurry, which is coated on the surface of the positive electrode collector 110 by a tail-aligned tape method. After baking, rolling and slitting, the positive electrode sheet 100 is obtained. The positive electrode sheet 100 has two slots of fixed size. The aluminum electrode ear (positive electrode ear 150) is welded in the slot by laser or ultrasonic welding to obtain the positive electrode sheet 100 with two aluminum electrode ears.

[0168] 2. Preparation of negative electrode sheet 200

[0169] The amount of silicon-carbon particles accounts for 10% of the total graphite amount, 6% of which is mixed with graphite with a particle size of 13μm, and the remaining 4% of silicon-carbon is mixed with graphite with a particle size of 9μm to prepare negative electrode active layer slurries, and the negative electrode active layer slurries are simultaneously coated on the carbon-coated copper foil (negative electrode current collector 210) by tail-aligned belt conveying, wherein large-particle graphite doped with 6% silicon-carbon material (Dv501=13μm) is coated on 5μm carbon-coated copper foil, and small-particle graphite doped with 4% silicon-carbon material (Dv502=9μm) is coated on the surface of large-particle graphite doped with 6% silicon-carbon material, wherein the second layer thickness H2: the first layer thickness H1 is 0.1, and the silicon doping amount of the first layer accounts for the total silicon doping amount W=0.6. After baking, rolling and slitting, a double-layer coated negative electrode sheet 200 with a thickness H of 151 μm is obtained. A certain position of the negative electrode sheet 200 has a slot of fixed size, and a copper-plated nickel electrode tab (negative electrode tab 260) is welded in the slot by laser or ultrasonic welding;

[0170] A uniform concave portion 250 is punched on the surface of the negative electrode sheet 200 using a laser. The depth H3 of the concave portion 250 is 5 μm, and the ratio X between the width of the bottom of the concave portion 250 and the width of the notch of the concave portion 250 is 0.85.

[0171] 3. Assembly

[0172] After the positive and negative electrode sheets 200 are cut and sliced, they are wound with the separator 300 to obtain a battery cell with a width of 32 mm and a thickness of 5.2 mm. The total thickness H4 of the separator 300 used is 8 μm. The separator 300 includes a 5 μm thick base film, a 1 μm thick first ceramic layer and a 2 μm thick first adhesive layer. The first ceramic layer is located between the base film and the first adhesive layer. Among them, after winding, the head of the longer negative electrode active layer (the first negative electrode active layer 220) of the negative electrode sheet 200 is formed with a 3 mm long first bending portion 221, and the head of the shorter negative electrode active layer (the second negative electrode active layer 230) of the negative electrode sheet 200 is formed with a 3 mm long second bending portion.

[0173] The lithium-ion battery is then obtained through packaging, baking, liquid injection, formation, secondary sealing, sorting and OCV.

[0174] The electrolyte includes a lithium salt and an additive, wherein the lithium salt is LiFP6, the additive is ethyl difluoroacetate, and the content B of the additive is 3%.

[0175] Among them, the dimensions of the first bend 221 and the second bend can be measured using a steel ruler; the tape running mode can be judged based on the appearance of the active layer, the active layer is relatively smooth at the starting end of the coating, and the active layer forms a serrated tail at the ending end of the coating; the depth of the linear groove 250 can be measured by scanning the surface morphology of the negative electrode active layer using a 3D profile microscope.

[0176] Example 2

[0177] Example 2 is carried out with reference to Example 1, except that the width of the battery cell is 100 mm, the thickness is 2.87 mm, and the negative electrode active layer slurry is simultaneously coated on the negative electrode current collector 210 in a head-aligned tape-feeding manner.

[0178] Example 3

[0179] Example 3 is carried out with reference to Example 2, except that the negative electrode active layer slurry is simultaneously coated on the negative electrode current collector 210 in a tail-aligned belt conveying manner.

[0180] Example 4

[0181] Example 4 is carried out with reference to Example 1, except that the negative electrode active layer slurry is simultaneously coated on the negative electrode current collector 210 in a head-aligned belt-feeding manner.

[0182] Example 5

[0183] Example 5 is carried out with reference to Example 1, except that a second bending portion with a length of 5 mm is formed at the head of the second negative electrode active layer 230 .

[0184] Example 6

[0185] Example 6 is carried out with reference to Example 1, except that the head of the first negative electrode active layer 220 does not have the first bent portion 221 .

[0186] Example 7

[0187] Example 7 is carried out with reference to Example 1, except that the depth H3 of the recess 250 is 18 μm, and the ratio X between the width of the bottom of the recess 250 and the width of the notch of the recess 250 is 0.07.

[0188] Example 8

[0189] Example 8 is carried out with reference to Example 1, except that the depth H3 of the recess 250 is 35 μm, and the ratio X between the bottom width of the recess 250 and the notch width of the recess 250 is 0.04.

[0190] Example 9

[0191] Example 9 is carried out with reference to Example 1, except that the depth H3 of the recess 250 is 2 μm, and the ratio X between the width of the bottom of the recess 250 and the width of the notch of the recess 250 is 0.99.

[0192] Example 10

[0193] Example 10 is carried out with reference to Example 1, except that the second layer thickness H2 of the negative electrode active layer is 0.99 of the first layer thickness H1, and the silicon doping amount of the first layer accounts for W=0.51 of the total silicon doping amount.

[0194] Embodiment 11

[0195] Example 11 is carried out with reference to Example 1, except that the silicon doping amount of the first layer accounts for W=0.5 of the total silicon doping amount.

[0196] Example 12

[0197] Example 12 is carried out with reference to Example 1, except that the silicon doping amount of the first layer accounts for W=0.9 of the total silicon doping amount.

[0198] Example 13

[0199] Example 13 was carried out with reference to Example 1, except that the small-particle graphite Dv502=5 μm in the second layer of the negative electrode active layer.

[0200] Embodiment 14

[0201] Example 14 is carried out with reference to Example 1, except that the second layer thickness H2 of the negative electrode active layer is 0.12 of the first layer thickness H1, and the small-particle graphite Dv502 of the second layer of the negative electrode active layer is 5 μm.

[0202] Embodiment 15

[0203] Example 15 is carried out with reference to Example 1, except that the second layer thickness H2 of the negative electrode active layer is 0.9 of the first layer thickness H1, and the small and medium-sized graphite particles Dv502 of the second layer of the negative electrode active layer are 13 μm.

[0204] Example 16

[0205] Example 16 is carried out with reference to Example 1, except that the second layer thickness H2 of the negative electrode active layer is 0.98 of the first layer thickness H1, and the small particle graphite Dv502 of the second layer of the negative electrode active layer is 13 μm.

[0206] Embodiment 17

[0207] Example 17 is carried out with reference to Example 1, except that no recess 250 is provided on the surface of the negative electrode sheet 200, and the content B of the additive in the electrolyte is 20%.

[0208] Embodiment 18

[0209] Example 18 is carried out with reference to Example 1, except that the content of additive B in the electrolyte is 0.1%.

[0210] Embodiment 19

[0211] Example 19 is carried out with reference to Example 1, except that the thickness of the negative electrode sheet 200 is 98 μm, the content of the additive B in the electrolyte is 0.1%,

[0212] Embodiment 20

[0213] Example 20 is carried out with reference to Example 1, except that the thickness of the negative electrode sheet 200 is 98 μm, the content of the additive B in the electrolyte is 4%,

[0214] Embodiment 21

[0215] Example 21 is carried out with reference to Example 1, except that the thickness of the negative electrode sheet 200 is 98 μm, the content of the additive B in the electrolyte is 5%,

[0216] Comparative Example 1

[0217] Comparative Example 1 is carried out with reference to Example 1, except that the negative electrode active layer slurry is simultaneously coated on the negative electrode current collector 210 in a head-aligned tape-feeding manner, the first negative electrode active layer 220 is not provided with a first bent portion 221 , the total thickness H4 of the separator 300 is 4 μm, and no recess 250 is provided on the surface of the negative electrode sheet 200 .

[0218] Comparative Example 2

[0219] Comparative Example 2 is carried out with reference to Example 1, except that no recess 250 is provided on the surface of the negative electrode sheet 200 .

[0220] Comparative Example 3

[0221] Comparative Example 3 is carried out with reference to Example 1, except that the total thickness H4 of the separator 300 is 15 μm, and no recess 250 is provided on the surface of the negative electrode sheet 200 .

[0222] Table 1:

[0223]

[0224]

[0225]

[0226]

[0227]

[0228] Table 2:

[0229]

[0230]

[0231]

[0232]

[0233]

[0234]

[0235] The relevant performances of the batteries in the above embodiments and comparative examples were tested, and the test results are recorded in Table 3. The test method is as follows:

[0236] 1. Cycle 50T:

[0237] In a constant temperature room at 25℃, use 1.5C constant current and constant voltage to the upper limit voltage, 0.02C cut-off, leave it for 10 minutes and then discharge at 1C to 3.0V, test the first full-charge thickness, the first discharge capacity C0, after 50T cycles, test the thickness in the full-charge state, 50T discharge capacity C1, Swelling = (50T full-charge thickness - first full-charge thickness) / first full-charge thickness, Cap. (capacity retention rate) = C1 / C0.

[0238] 2. K value test after 50T cycle

[0239] After cycling for 50T using the above method, the battery is charged to 3.95V using a 0.2C constant current and constant voltage charge, with a cut-off of 0.02C. After standing in a constant temperature room at 25°C for 12h, the voltage V1 is tested. After standing for 48h-72h, the voltage V2 is tested. K = (V2-V1) / standing time.

[0240] 3. Extremely poor cell thickness:

[0241] The battery cell is scanned and imaged using a 3D profilometer to obtain the extreme thickness difference of the battery cell.

[0242] Table 3

[0243]

[0244]

[0245]

[0246] according to Figure 3It can be seen that compared with Comparative Examples 1 to 3, in Examples 1 to 21, since the surface of the negative electrode sheet 200 is provided with a recess 250, the recess 250 can drain the electrolyte and prevent the electrolyte from accumulating in the empty foil area 211 at the head of the negative electrode collector 210, so that copper oxide is not easy to appear on the empty foil area 211 at the head of the negative electrode collector 210, thereby preventing the battery cell from self-discharging too much, and the K value is smaller after the battery cell is cycled for 50T.

[0247] The ratio between the thickness of the battery cell and the width of the battery cell provided by Example 2 and Example 3 is 2.87%, that is, the battery cells used in Example 2 and Example 3 are both large and thin battery cells. Compared with Example 2, since the battery cell provided by Example 3 adopts a tape-feeding method in which the positive electrode sheet 100 and the negative electrode sheet 200 are inconsistent, the thickness of the positive electrode sheet 100 and the thickness of the negative electrode sheet 200 compensate each other, the thickness range of the battery cell is smaller, the battery cell is flatter, and it is less likely to have a local excessive thickness.

[0248] Compared with Example 4, since the battery cell provided in Example 1 adopts the same tape running method for the positive electrode sheet 100 and the negative electrode sheet 200, the tail area of ​​the coating termination end of the second negative electrode active layer 230 can correspond to the coating starting end of the second positive electrode active layer 130, thereby ensuring the CB value of the battery cell at the coating termination end of the second negative electrode active layer 230, and avoiding the problems of local excessive thickness of the battery cell, increased K value and lithium precipitation due to insufficient CB value at the coating termination end of the second negative electrode active layer 230.

[0249] Compared with Example 6, since the first bent portion 221 is formed at the head of the first negative electrode active layer 220 in Example 1, the first bent portion 221 can prevent the thinning area of ​​the head of the first negative electrode active layer 220 from corresponding to the flat area of ​​the positive electrode active layer of the positive electrode sheet 100, thereby avoiding the problem of local excessive thickness of the battery cell, lithium deposition and increased K value due to insufficient CB value at the head of the battery cell.

[0250] Comparing Example 1 with Examples 18 to 20, as the additive content B increases, the electrolyte has better infiltration into the negative electrode sheet 200, and the cycle 50T Cap. gradually increases.

[0251] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these 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 battery cell, characterized in that: It comprises a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and wound to form a straight section and a first arc section and a second arc section located on both sides of the straight section; The negative electrode sheet comprises a negative electrode current collector and a first negative electrode active layer and a second negative electrode active layer respectively located on opposite sides of the negative electrode current collector, wherein at least the first negative electrode active layer exceeds the second negative electrode active layer at the head of the negative electrode current collector and forms an empty foil area on the side of the negative electrode current collector away from the first negative electrode active layer; The head of the first negative electrode active layer is bent at a side close to the first arc segment in a direction away from the positive electrode sheet to form a first bent portion, and on the plane where the straight segment is located, the projection of the head of the positive electrode sheet is located outside the projection of the first bent portion; The head of the second negative electrode active layer extends to the first arc segment, and the distance between the head of the second negative electrode active layer and the first arc segment is smaller than the distance between the head of the positive electrode sheet and the first arc segment; A plurality of recessed portions are formed on the surface of the first negative electrode active layer and / or the second negative electrode active layer.

2. The battery cell according to claim 1, characterized in that: The head of the second negative electrode active layer is bent toward the direction away from the positive electrode sheet on the side close to the first arc segment to form a second bent portion, and on the plane where the straight segment is located, the projection of the head of the positive electrode sheet is located outside the projection of the second bent portion.

3. The battery cell according to claim 1, characterized in that: Along the length direction of the positive electrode sheet, the positive electrode sheet has a first coating termination end, a second coating termination end, and a first alignment end and a first misalignment end that are oppositely arranged; Along the length direction of the negative electrode sheet, the negative electrode sheet has a third coating termination end, a fourth coating termination end, and a second alignment end and a second misalignment end that are oppositely arranged; The first alignment end and the first coating termination end are located at the same end of the positive electrode sheet, the first misaligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second alignment end and the third coating termination end are located at the same end of the negative electrode sheet, and the second misaligned end and the fourth coating termination end are located at the same end of the negative electrode sheet; or, The first misaligned end and the first coating termination end are located at the same end of the positive electrode sheet, the first aligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second misaligned end and the third coating termination end are located at the same end of the negative electrode sheet, and the second aligned end and the fourth coating termination end are located at the same end of the negative electrode sheet.

4. The battery cell according to claim 1, characterized in that: Along the length direction of the positive electrode sheet, the positive electrode sheet has a first coating termination end, a second coating termination end, and a first alignment end and a first misalignment end that are oppositely arranged. Along the length direction of the negative electrode sheet, the negative electrode sheet has a third coating termination end, a fourth coating termination end, and a second alignment end and a second misalignment end that are oppositely arranged; The first aligned end and the first coating termination end are located at the same end of the positive electrode sheet, the first misaligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second misaligned end and the third coating termination end are located at the same end of the negative electrode sheet, and the second misaligned end and the fourth coating termination end are located at the same end of the negative electrode sheet; or, The first misaligned end and the first coating termination end are located at the same end of the positive electrode sheet, the first aligned end and the second coating termination end are located at the same end of the positive electrode sheet, the second aligned end and the third coating termination end are located at the same end of the negative electrode sheet, and the second misaligned end and the fourth coating termination end are located at the same end of the negative electrode sheet.

5. The battery cell according to claim 1, characterized in that: The first negative electrode active layer and the second negative electrode active layer both include a first layer and a second layer that are stacked, the first layer is located between the second layer and the negative electrode current collector, the first layer and the second layer both include graphite particles, and the average particle size of the graphite particles in the first layer is greater than the average particle size of the graphite particles in the second layer.

6. The battery cell according to claim 5, characterized in that: The ratio between the average particle size of the graphite particles in the second layer and the average particle size of the graphite particles in the first layer is 0.4-0.98; and / or, The average particle size Dv501 of the graphite particles in the first layer, the average particle size Dv502 of the graphite particles in the second layer, the thickness H1 of the first layer and the thickness H2 of the second layer satisfy:

7. The battery cell according to claim 5, characterized in that: The depth of the recess is less than the thickness of the second layer; and / or, The slot width of the concave portion is greater than the slot bottom width of the concave portion, and the ratio X between the slot bottom width of the concave portion and the slot width of the concave portion, the thickness H1 of the first layer, and the thickness H2 of the second layer satisfy:

8. The battery cell according to claim 1, characterized in that: The recess is a linear groove, the linear groove extends along the width direction of the negative electrode sheet, and a plurality of the linear grooves are sequentially spaced apart along the length direction of the negative electrode sheet; and / or The recessed portion is a blind hole groove, and a plurality of the blind hole grooves are arranged at intervals.

9. The battery cell according to claim 8, characterized in that: In the length direction of the negative electrode sheet, the distance between any linear groove or blind hole groove located at the edge and the edge of the adjacent negative electrode active layer is 2mm-5mm; and / or, The ratio of the depth of the linear groove or the blind hole groove to the thickness of the negative electrode sheet is greater than or equal to 0.02 and less than or equal to 0.

3.

10. The battery cell according to claim 1, characterized in that: The ratio of the thickness of the battery cell to the width of the battery cell is in the range of 0.1%-10%.

11. The battery cell according to claim 1, characterized in that: The negative electrode sheet further includes a negative electrode ear, which is electrically connected to the negative electrode current collector, and the positive electrode sheet includes two positive electrode ears.

12. The battery cell according to claim 1, characterized in that: The diaphragm includes a base film, a first ceramic layer and a first coating layer. The first ceramic layer is arranged on the side of the base film facing the positive electrode sheet, and the first coating layer is arranged on the side of the first ceramic layer away from the base film. The total thickness of the diaphragm is 5μm-10μm.

13. The battery cell according to claim 12, characterized in that: The thickness H4 of the separator and the thickness H of the negative electrode sheet satisfy: 250≤H4×H≤1500.

14. The battery cell according to claim 2, characterized in that: The length of the first bending portion is less than or equal to 10 mm; and / or, The length of the second bending portion is less than or equal to 3 mm.

15. A battery, characterized in that: The invention comprises an electrolyte and the battery core according to any one of claims 1 to 14, wherein the electrolyte comprises ethyl difluoroacetate.

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