Electrode assembly and battery cell

Abstract

The utility model provides an electrode assembly and a battery cell. The electrode assembly comprises a positive plate, a diaphragm and a negative plate which form a winding structure, the winding structure comprises a straight area and two bending areas connected to the two opposite ends of the straight area respectively. The positive plate comprises straight parts and bent parts which are alternately arranged along the winding direction, and the bent parts are positioned in the bent area; the bending part comprises a current collecting substrate and an active layer; in the winding direction, thinning grooves are formed in the surface of the active layer, located on the inner side of the current collecting base body, of the first N bending parts, and N is larger than or equal to 1 and smaller than or equal to 4. According to the electrode assembly and the battery cell provided by the invention, the thinning groove is formed in the inner side surface of the bending part of the positive plate, so that the thickness of the bending part can be reduced, and light transmission and breakage are not easy to occur when the bending part is extruded. Meanwhile, the thinning groove is formed in the active layer on the inner side of the bending part, so that the positive electrode active material at the bending part can be reduced, the CB value of the bending area is improved, and the risk of lithium precipitation is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrode assembly and a battery cell. BACKGROUND

[0002] In a lithium battery, an electrode assembly is arranged inside a shell of a battery cell, and the electrode assembly mainly has a winding structure and a laminated structure. However, the winding structure has higher preparation efficiency, and therefore the existing electrode assembly still mainly adopts the winding structure.

[0003] However, the applicant finds that the electrode assembly formed by winding the positive electrode sheet, the separator and the negative electrode sheet has the largest extrusion at the bending position of the inner circle (close to the winding center), and the electrode sheet is prone to brittle fracture, especially the positive electrode sheet with a large thickness. Once the electrode sheet is brittle fractured, the burr generated may pierce the separator, causing a safety risk and adversely affecting the electrical performance of the battery cell. Meanwhile, at the bending position of the inner circle, the bending radius of the negative electrode sheet on the inner side and the bending radius of the positive electrode sheet on the outer circle have a large difference, which may cause a small battery balance value (i.e., the ratio of the capacity of the negative electrode active material on the negative electrode sheet to the capacity of the positive electrode active material on the positive electrode sheet, or the CB value), and more easily cause lithium precipitation, further adversely affecting the safety and electrical performance of the battery cell. SUMMARY

[0004] Therefore, the present application aims to provide an electrode assembly and a battery cell to at least partially solve the problems of brittle fracture and lithium precipitation at the bending position of the inner circle.

[0005] To achieve the above purpose, the present application provides an electrode assembly in a first aspect, comprising a positive electrode sheet, a separator and a negative electrode sheet forming a winding structure; the winding structure comprises a flat area and two bending areas connected to opposite ends of the flat area, respectively; the positive electrode sheet comprises flat parts and bending parts alternately arranged along a winding direction, and the bending parts are located in the bending areas; one side of the bending part close to the flat area is an inner side; the bending part comprises a current collector substrate and an active layer at least coated on the inner side of the current collector substrate; the surface of the active layer on the inner side of the current collector substrate of the first N bending parts is provided with a thinning groove along the winding direction, and 1≤N≤4.

[0006] Optionally, the surface of the active layer on the inner side of the current collector substrate of the last M bending parts is provided with a thinning groove along the winding direction, and 1≤M≤4; in the positive electrode sheet, the total number of the bending parts is P, and P>M+N.

[0007] Optionally, P≥M+N+10.

[0008] Optionally, at least one end of the thinning groove extends to the flat part along the winding direction.

[0009] Optionally, the side of the bending part away from the flat area is an outer side, and the outer side of the current collecting substrate is also provided with the active layer; the surface of the active layer on the inner side of the current collecting substrate and the surface of the active layer on the outer side of the current collecting substrate are respectively provided with the thinning groove.

[0010] Optionally, the thinning groove comprises a first sub-groove arranged on the surface of the active layer, and a second sub-groove arranged on the bottom of the first sub-groove.

[0011] Optionally, along the winding direction, the slot width of the same thinning groove is greater than the bottom width.

[0012] Optionally, along the winding direction, the positive electrode sheet comprises a plurality of bending parts, and at least two of the plurality of bending parts are provided with the thinning groove; the width of the thinning groove arranged on the latter bending part is greater than the width of the thinning groove arranged on the former bending part.

[0013] Optionally, in the active layer arranged on one side of the current collecting substrate, the thickness of the area provided with the thinning groove is Y, and the thickness of the area not provided with the thinning groove is H.

[0014] When H is 90 microns to 105 microns, Y = (-2H) * X + 5.9H; wherein X is 2.55 to 2.7;

[0015] When H is 105 microns to 130 microns, Y = (-2H) * X + 5.8H; wherein X is 2.55 to 2.7;

[0016] When H is 130 microns to 140 microns, Y = (-2H) * X + 5.7H; wherein X is 2.55 to 2.7.

[0017] Based on the same inventive concept, the second aspect of the present application further provides an electric core comprising the electrode assembly of the first aspect.

[0018] Based on the above purpose, the present application provides an electrode assembly and an electric core. By arranging a thinning groove on the inner side active layer of the bending part of the positive electrode sheet, the thickness of the bending part can be reduced, so that a smaller bending radius can be achieved, and the bending part is not easy to appear light transmission and fracture when being extruded. At the same time, by arranging a thinning groove on the inner side active layer of the bending part, the positive active material at the bending part can be reduced, so as to improve the CB value of the bending area and reduce the risk of lithium precipitation. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in this application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are merely embodiments of this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 A schematic diagram of an electrode assembly according to an embodiment of the present application;

[0021] Figure 2 for Figure 1 A magnified schematic diagram of the first structure in part A;

[0022] Figure 3 for Figure 1 An enlarged schematic diagram of the first structure in part B;

[0023] Figure 4 for Figure 1 An enlarged schematic diagram of the second structure in part A;

[0024] Figure 5 for Figure 1 A magnified schematic diagram of the third structure in part A;

[0025] Figure 6 for Figure 1 A magnified schematic diagram of the fourth structure in part A.

[0026] Description of reference numerals:

[0027] 100, positive electrode sheet; 110, bent portion; 120, straight portion; 130, thinning groove; 131, groove wall; 132, first sub-groove; 133, second sub-groove; 140, active layer; 150, current collecting matrix;

[0028] 200, negative electrode sheet; 300, diaphragm; 400, bending area; 500, straight area. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of this application more clear, this application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0030] It should be noted that the relative arrangement of the components, the numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application unless specifically stated otherwise.

[0031] At the same time, it should be understood that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0032] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application or its application and uses.

[0033] It should be noted that the technical terms or scientific terms used in the embodiments of the present application should be understood as the general meaning understood by those skilled in the art to which the embodiments belong, unless otherwise defined. The terms "first", "second", and the like used in the embodiments of the present application do not represent any order, quantity or importance, but are only used to distinguish different components. The terms "include" or "contain" and the like mean that the elements or objects before the terms cover the elements or objects listed after the terms and their equivalents, and do not exclude other elements or objects. The terms "connected" or "connected" and the like are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to represent relative positional relationships, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0034] As Figure 1 , Figure 1 A schematic diagram of an electrode assembly is shown. The electrode assembly includes a positive electrode sheet 100, a separator 300, and a negative electrode sheet 200, which are stacked in sequence. The positive electrode sheet 100 and the negative electrode sheet 200 can be prevented from directly contacting each other by the separator 300. The positive electrode sheet 100, the negative electrode sheet 200, and the separator 300 are wound to form a wound structure, which includes a flat area 500 and two bending areas 400 connected to opposite ends of the flat area 500, respectively. The wound structure can include a plurality of winding layers. Except for the first winding layer and the last winding layer in the winding direction, each of the other winding layers passes through the two bending areas 400 and the flat area 500. For example, as shown in the structure and direction, one of the winding layers of the wound structure passes through the right bending area 400, the lower flat area 500, and the left bending area 400 in sequence from the upper flat area 500 (relative to the center of the wound structure). Then, the next winding layer covering the winding layer is formed. The adjacent winding layers are continuously arranged. Figure 1

[0035] Still taking Figure 1 ​The structure and direction shown are examples. In the same winding layer, the negative electrode sheet 200 is located on the inner side, and the positive electrode sheet 100 is located on the outer side. In the flat area 500, the surface size of the positive electrode sheet 100 and the negative electrode sheet 200 is the same; while in the bending area 400, especially in the inner coil winding layer close to the center of the winding structure, since the bending radius of the positive electrode sheet 100 is larger than that of the negative electrode sheet 200 and the difference is large, in the bending area 400, the surface area of the positive electrode sheet 100 in the same winding layer is larger than that of the negative electrode sheet 200, so that the amount of positive active material in the bending area 400 is more than the designed amount, so that the CB value of the bending area 400 is less than the preset value, and only part of the excess lithium ions provided by the positive electrode sheet 100 can be embedded in the negative electrode sheet 200, and the other part can only form a single metal lithium on the surface of the negative electrode sheet 200, that is, lithium precipitation occurs.

[0036] In addition, as the demand for energy density of the battery cell is higher and higher, the thickness of the electrode sheet in the electrode assembly, especially the positive electrode sheet 100, is larger and larger and the compaction density is increased, and the number of winding layers is also increased, so that the part of the winding layer close to the center position in the bending area 400 is close to folding, so that the positive electrode sheet 100 is more prone to brittle fracture, resulting in winding difficulty.

[0037] In order to solve the above problems, the applicant found that a certain amount of active material on the positive electrode sheet 100 in the inner coil winding layer can be reduced, so that the thickness of the positive electrode sheet 100 in the bending area 400 is thinned to reduce the risk of fracture; and the CB value of the bending area 400 can also be increased to reduce the risk of lithium precipitation.

[0038] Figure 2 The first structure of the A part of the embodiment is shown in the enlarged schematic view as shown in Figure 1 The first structure of the A part of the embodiment is shown in the enlarged schematic view as shown in Figure 1 And Figure 2 The electrode assembly provided by the embodiment of the present application, the positive electrode sheet 100 includes flat parts 120 and bending parts 110 arranged alternately along the winding direction, and the bending part 110 is located in the bending area 400; the side of the bending part 110 close to the flat area 500 is the inner side; along the winding direction, the surface of the active layer 140 of the first N bending parts 110 located on the inner side of the current collector substrate 150 is provided with a thinning groove 130, and 1≤N≤4.

[0039] For example, in the embodiment, the first bending part 110 is provided with a thinning groove 130; or the first and second bending parts 110 are both provided with a thinning groove 130; or the first, second and third bending parts 110 are all provided with a thinning groove 130; or the first, second, third and fourth bending parts 110 are all provided with a thinning groove 130.

[0040] For example, as shown in Figure 2The thinning grooves 130 are symmetrically arranged along the center line of the bending part 110 where the thinning grooves 130 are located (such as the transverse dash line in the figure) Figure 2

[0041] For example, the width (size along the winding direction) of the thinning groove 130 can be 3-8 cm, for example, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 8 mm.

[0042] For example, the active layer 140 of the positive electrode sheet 100 can include 89-99.1 wt% of a positive active main material, 0.4-4 wt% of a conductive agent, 0.5-5 wt% of a binder, and 0-2 wt% of a dispersing agent. The positive active main material can be mainly lithium iron phosphate. The conductive agent can be one or more of SP, conductive graphite KS-6, acetylene black, carbon fiber, ketjen black, carbon nanotube, and graphene. The binder can be one or more of polyvinylidene fluoride, vinylidene-hexafluoropropylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and ethylene-tetrafluoroethylene copolymer. Other additives such as lithium supplement, flexibility agent, and infiltration agent can also be added.

[0043] For example, the current collecting substrate 150 of the positive electrode sheet 100 can be an aluminum foil with a thickness of 5-20 microns, for example, the thickness of the aluminum foil can be 5 μm, 6 μm, 10 μm, 13 μm, 15 μm, 18 μm or 20 μm.

[0044] For example, the current collecting substrate 150 of the positive electrode sheet 100 can be a composite current collector with a thickness of 10-15 μm.

[0045] For example, the embodiment can form the thinning grooves 130 on the active layer 140 of the positive electrode sheet 100 by a laser thinning unit, a dust removal unit and a thickness measuring unit integrated on the winding machine. The laser thinning unit can drive the laser head by devices such as linear motors, so that the laser head can move to any preset position in the horizontal plane, thereby removing part of the material on the positive electrode sheet 100 by laser to form the thinning grooves 130. During the operation of the laser thinning unit, the depth of the thinning grooves 130 or the thickness of the positive electrode sheet 100 in the region provided with the thinning grooves 130 can be obtained in real time by the thickness measuring unit (for example, a laser thickness gauge, an ultrasonic thickness gauge or an X-ray thickness gauge), to assist in controlling the start and stop of the laser thinning unit. During the operation of the laser thinning unit, the dust removal unit can also be used to remove the dust generated, to avoid leaving dust in the electrode assembly and causing adverse effects.

[0046] ​In this embodiment, the thinning groove 130 is arranged on the active layer 140 of the bending part 110 of the positive electrode sheet 100, so that the thickness of the bending part 110 of the positive electrode sheet 100 is reduced. Accordingly, when the winding structure is formed, the bending part 110 of the positive electrode sheet 100 can achieve a smaller bending radius, and brittle fracture is less likely to occur.

[0047] At the same time, the arrangement of the thinning groove 130 substantially reduces the active material in the active layer 140, so that the positive electrode active material of the positive electrode sheet 100 in the bending area 400 is reduced, thereby improving the CB value of the bending area 400. After the total amount of lithium ions provided by the positive electrode sheet 100 is reduced, lithium precipitation is less likely to occur.

[0048] The electrode assembly provided in this embodiment can reduce the thickness of the bending part 110 by arranging the thinning groove 130 on the inner side of the active layer 140 of the bending part 110 of the positive electrode sheet 100, so that a smaller bending radius can be achieved, and the bending part 110 is less likely to be transparent and broken when it is pressed. At the same time, by arranging the thinning groove 130 on the inner side of the active layer 140 of the bending part 110, the positive electrode active material at the bending part 110 is reduced, thereby improving the CB value of the bending area 400 and reducing the risk of lithium precipitation.

[0049] As shown in Figure 3 , Figure 3 As shown in Figure 1 , the first structure of the B part in the middle is shown in an enlarged schematic view. In order to further reduce the risk of lithium precipitation, as shown in Figure 1 and Figure 3 , in some embodiments, along the winding direction, the surface of the active layer 140 on the inner side of the current collector substrate 150 of the last M bending parts 110 is provided with a thinning groove 130, 1≤M≤4; in the positive electrode sheet 100, the total number of bending parts 110 is P, P>M+N.

[0050] For example, in this embodiment, along the winding direction, at least one of the first to fourth bending parts 110 is provided with a thinning groove 130, and the last bending part 110 is provided with a thinning groove 130; or the last two bending parts 110 are respectively provided with a thinning groove 130; or the last three bending parts 110 are respectively provided with a thinning groove 130; or the last four bending parts 110 are respectively provided with a thinning groove 130.

[0051] It should be noted that, along the winding direction, in the positive electrode sheet 100, in addition to the first N and the last M bending parts 110, there are bending parts 110 between the first N and the last M bending parts 110 (hereinafter referred to as the intermediate bending parts 110, such as Figure 3The middle bending part 110 is not provided with the thinning groove 130. The thickness of the middle bending part 110 and the flat part 120 is uniform, which can make the middle bending part 110 provide greater support force to ensure that the winding structure does not locally collapse during extrusion, which helps to ensure that the appearance of the electrode assembly is good and improves the yield.

[0052] The thinning groove 130 provided in the M bending parts 110 behind in the winding direction has the same effect as the thinning groove 130 provided in the N bending parts 110 in front, which will not be repeated here.

[0053] In some embodiments, P≥M+N+10.

[0054] In this embodiment, the number of the middle bending parts 110 not provided with the thinning groove 130 is at least 10, which is greater than the N (1-4) bending parts 110 provided with the thinning groove 130 located in the inner ring and greater than the M (1-4) bending parts 110 provided with the thinning groove 130 located in the outer ring. Therefore, the support force provided by the middle bending part 110 is sufficient to offset the impact on the local strength of the winding structure caused by the provision of the thinning groove 130, which helps to ensure that the appearance of the electrode assembly is good and improves the yield.

[0055] As Figure 2 In some embodiments, the thinning groove 130 extends to the flat part 120 at least one end in the winding direction.

[0056] For example, when the thinning groove 130 extends to the flat part 120 at both ends in the winding direction, the thinning groove 130 can completely cover the bending part 110.

[0057] Extending the thinning groove 130 to the flat part 120 can make the thinning groove 130 cover a larger area or even the entire area in the bending area 400, which helps to make the distribution of the positive active material in the bending area 400 more uniform, so that more areas in the bending area 400 are not prone to lithium precipitation.

[0058] At the same time, the thinning groove 130 covers a larger area or even the entire area in the bending area 400, which can also reduce the thickness of a larger area of the bending part 110 to further reduce the bending radius that the positive plate 100 can reach and reduce the risk of plate fracture.

[0059] As Figure 4 , Figure 4 It is shown that Figure 1An enlarged schematic view of the second structure of the A part, in some embodiments, the outer side of the bending part 110 is away from one side of the flat area 500, and the outer side of the current collector substrate 150 is also provided with an active layer 140; the surface of the active layer 140 located on the inner side of the current collector substrate 150 and the surface of the active layer 140 located on the outer side of the current collector substrate 150 are respectively provided with thinning grooves 130.

[0060] For example, in the same bending part 110, the width of the thinning groove 130 on the inner side of the active layer 140 (hereinafter referred to as the inner width) and the width of the thinning groove 130 on the outer side of the active layer 140 (hereinafter referred to as the outer width) can be the same; or the inner width is smaller than the outer width; or the inner width is greater than the outer width.

[0061] For example, in the same bending part 110, the thinning groove 130 on the inner side of the active layer 140 and the thinning groove 130 on the outer side of the active layer 140 can be aligned or offset along the winding direction.

[0062] On the one hand, the thinning grooves 130 are arranged on the active layers 140 on both the inner and outer sides of the bending part 110, which can further reduce the thickness of the bending part 110. On the other hand, in the bending area 400, the thinning groove 130 on the inner side of the bending part 110 can make the CB value between the positive electrode sheet 100 and the negative electrode sheet 200 on the inner side tend to be closer to the preset value, and the thinning groove 130 on the outer side of the bending part 110 can also make the CB value between the positive electrode sheet 100 and the negative electrode sheet 200 on the outer side tend to be closer to the preset value, further reducing the risk of lithium precipitation and electrode sheet fracture.

[0063] As Figure 5 , Figure 5 It is shown that Figure 1 An enlarged schematic view of the third structure of the A part, in some embodiments, the thinning groove 130 includes a first sub-groove 132 arranged on the surface of the active layer 140, and a second sub-groove 133 arranged on the groove bottom of the first sub-groove 132.

[0064] For example, the width a' of the second sub-groove 133 can be 2-4 cm, for example, 2 mm, 3 mm or 4 mm. Along the winding direction, the distance a" between the groove wall 131 of the second sub-groove 133 and the groove wall 131 of the adjacent first sub-groove 132 can be 2-4 cm, for example, 2 mm, 3 mm or 4 mm.

[0065] By arranging the second sub-groove 133 at the groove bottom of the first sub-groove 132, the depth of the thinning groove 130 can be increased on the basis of the first sub-groove 132, so that the thickness of the bending part 110 is further reduced, the bending radius of the positive plate 100 at the bending area 400 can be further reduced, and the inner CB value of the bending area 400 tends to be closer to the preset value, thereby further reducing the risk of lithium precipitation and plate fracture.

[0066] As Figure 6 , Figure 6 As Figure 1 The fourth structure of the A part in the embodiment is shown in the enlarged schematic view. In some embodiments, the slot opening width of the same thinning groove 130 is greater than the groove bottom width in the winding direction.

[0067] For example, the groove wall 131 of the thinning groove 130 in the winding direction can be an inclined plane or an arc-shaped curved surface.

[0068] For example, the groove bottom width of the thinning groove 130 of the embodiment can be 3-5 cm, for example, 3 mm, 4 mm or 5 mm.

[0069] For example, the inclined angle of the groove wall 131 of the thinning groove 130 in the winding direction can be 45-75°, for example, 45°, 50°, 55°, 60°, 65°, 70° or 75°.

[0070] When the winding structure is formed, since the slot opening of the thinning groove 130 of the embodiment is large, the negative plate 200 near the slot opening side of the thinning groove 130 can be closer to the positive active material at the groove bottom of the thinning groove 130 through the slot opening with a larger width, so as to shorten the diffusion path of lithium ions and reduce the particle diffusion difficulty, thereby reducing the risk of lithium precipitation.

[0071] As Figure 1 In some embodiments, the positive plate 100 includes a plurality of bending parts 110 in the winding direction, and at least two of the plurality of bending parts 110 are provided with the thinning groove 130; the width of the thinning groove 130 arranged at the latter bending part 110 is greater than the width of the thinning groove 130 arranged at the former bending part 110.

[0072] For example, the groove bottom width of the thinning groove 130 of the thinning groove 130 of the embodiment can be 3-5 cm, for example, 3 mm, 4 mm or 5 mm. Figure 1The structure shown is used as an example to illustrate that, along the winding direction, when the first bending portion 110, the second bending portion 110, the third bending portion 110, and the fourth bending portion 110 are all provided with the thinning groove 130, the width of the thinning groove 130 on the first bending portion 110 (hereinafter referred to as the first thinning groove, and the like) is less than the width of the second thinning groove, the width of the second thinning groove is less than the width of the third thinning groove, and the width of the third thinning groove is less than the width of the fourth thinning groove. For example, the width of the first thinning groove can be 3 mm, the width of the second thinning groove can be 3.5 mm, the width of the third thinning groove can be 4 mm, and the width of the fourth thinning groove can be 5 mm.

[0073] As Figure 1 , along the winding direction, the bending radius of the positive electrode sheet 100 gradually increases, and then the width of the bending portion 110 along the winding direction gradually increases. If the width of the thinning groove 130 does not change, the influence of the thinning groove 130 on the bending radius of the positive electrode sheet 100 and the CB value in the bending area 400 will be reduced. Therefore, the width of the thinning groove 130 in this embodiment is also designed to gradually increase, so as to maintain that the thinning groove 130 can reduce the bending radius of the positive electrode sheet 100 and can make the CB value in the bending area 400 close to the preset value, thereby realizing the reduction of the risk of lithium precipitation and the risk of sheet fracture.

[0074] As Figure 2 , in some embodiments, in the active layer 140 provided on one side of the current collecting substrate 150, the thickness of the region provided with the thinning groove 130 is Y, and the thickness of the region not provided with the thinning groove 130 is H.

[0075] The single-sided (i.e., located on one side of the current collecting substrate 150) areal density of the active layer 140 of the positive electrode sheet 100 of this embodiment can be 250-350 g / m 2 , and the compaction density can be 2.55-2.7 g / cm 3 , specifically:

[0076] When the single-sided areal density of the active layer 140 is 250-275 g / m 2 , H is 90 microns to 105 microns, and Y = (-2H)*X+5.9H; wherein X is 2.55 to 2.7.

[0077] When the single-sided areal density of the active layer 140 is 275-325 g / m 2 , H is 105 microns to 130 microns, and Y = (-2H)*X+5.8H; wherein X is 2.55 to 2.7.

[0078] When the single-sided areal density of the active layer 140 is greater than 325 g / m 2H is 130 microns to 140 microns, and Y = (-2H)*X+5.7H; wherein X is 2.55 to 2.7.

[0079] It should be noted that when the single-sided area density of the active layer 140 of the positive electrode sheet 100 is less than 250 g / m 2 , the risk of brittle fracture of the bent portion 110 of the positive electrode sheet 100 is low. When the compacted density of the active layer 140 is less than 2.55 g / cm 3 , the risk of brittle fracture of the bent portion 110 of the positive electrode sheet 100 is also low. However, as the demand for the energy density of the battery cell is increasingly high, more and more products require the compacted density of the active layer 140 of the positive electrode sheet 100 to be 2.55-2.7 g / cm 3 . At this time, the risk of brittle fracture of the electrode sheet can be reduced by each of the above embodiments.

[0080] Specifically, when the thinning groove 130 is the first structure or the second structure described above, when the single-sided area density of the active layer 140 of the positive electrode sheet 100 is 250 g / m 2 , and the compacted density is 2.65 g / cm 3 , Y can be 56.4 microns. Along the winding direction, the widths of the thinning grooves 130 on the first four bent portions 110 can be 3 mm, 3.5 mm, 4 mm, and 5 mm, respectively.

[0081] When the thinning groove 130 is the second structure described above, when the single-sided area density of the active layer 140 of the positive electrode sheet 100 is 275 g / m 2 , and the compacted density is 2.65 g / cm 3 , Y can be 56.4 microns. Along the winding direction, the widths of the thinning grooves 130 on the first four bent portions 110 can be 3 mm, 3.5 mm, 4 mm, and 5 mm, respectively.

[0082] When the thinning groove 130 is the second structure described above, when the single-sided area density of the active layer 140 of the positive electrode sheet 100 is 300 g / m 2 , and the compacted density is 2.65 g / cm 3 , Y can be 56.6 microns. Along the winding direction, the widths of the thinning grooves 130 on the first four bent portions 110 can be 3 mm, 3.5 mm, 4 mm, and 5 mm, respectively.

[0083] When the thinning groove 130 is the second structure described above, when the single-sided area density of the active layer 140 of the positive electrode sheet 100 is 325 g / m 2 , and the compacted density is 2.65 g / cm 3When Y is 56.4 μm, the widths of the thinning grooves 130 on the first four bending portions 110 along the winding direction can be 3 mm, 3.5 mm, 4 mm, and 5 mm, respectively.

[0084] When the thinning groove 130 is the second structure, when the single surface density of the active layer 140 of the positive electrode sheet 100 is 325 g / m 2 , compacted density is 2.65g / cm 3 When Y is 61.3 μm, the widths of the thinning grooves 130 on the first four bends 110 along the winding direction can be 3 mm, 3.5 mm, 4 mm, and 5 mm, respectively. The widths of the thinning grooves 130 on the last two bends 110 can be 5.5 mm and 6 mm, respectively.

[0085] When the thinning groove 130 is the second structure, when the single surface density of the active layer 140 of the positive electrode sheet 100 is 350 g / m 2 , compacted density is 2.65g / cm 3 When Y is 52 μm, the widths of the thinning grooves 130 on the first four bends 110 along the winding direction can be 3 mm, 3.5 mm, 4 mm, and 5 mm, respectively. The widths of the thinning grooves 130 on the last four bends 110 can be 5.5 mm, 6 mm, 7 mm, and 8 mm, respectively.

[0086] When the thinning groove 130 is the fourth structure, when the single surface density of the active layer 140 of the positive electrode sheet 100 is 275 g / m 2 , compacted density is 2.65g / cm 3 Along the winding direction, the bottom widths of the thinning grooves 130 on the first four bending portions 110 can be 3 mm, 3.5 mm, 4 mm, and 5 mm, respectively, and the inclination angle of the groove wall 131 can be 55°.

[0087] When the thinning groove 130 is the third structure described above, when the single surface density of the active layer 140 of the positive electrode sheet 100 is 275 g / m 2 , compacted density is 2.65g / cm 3 The thickness of the active layer 140 corresponding to the first sub-groove 132 can be 85 μm, and the thickness of the active layer 140 corresponding to the second sub-groove 133 can be 62.3 μm. Along the winding direction, the widths of the thinning grooves 130 on the first four bending portions 110 can be 6 mm, 9 mm, 10.5 mm and 12 mm respectively.

[0088] Based on the same inventive concept and in combination with the description of the electrode assemblies of the above embodiments, this embodiment provides a battery cell having the corresponding technical effects of the electrode assemblies of the above embodiments, which will not be repeated here.

[0089] The embodiment provides an electric core, which comprises the electrode assembly according to the above various embodiments.

[0090] Based on the same inventive concept, in combination with the description of the electrode assembly and the electric core according to the above various embodiments, the embodiment provides a battery pack, which has the corresponding technical effects of the electrode assembly and the electric core according to the above various embodiments, and details are not repeated here.

[0091] The embodiment provides a battery pack, which comprises the electric core according to the above embodiment.

[0092] It should be noted that the above describes some embodiments of the application. Other embodiments are within the scope of the appended claims.

[0093] The embodiments in the present application are described in a progressive manner, and each embodiment mainly explains the difference from other embodiments. The same or similar parts of various embodiments can be understood by mutual reference.

[0094] The description of the present application is given for the purpose of illustration and description, and is not exhaustive or limiting to the form disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments are chosen and described in order to better illustrate the principles and practical application of the present application, and to enable those skilled in the art to understand the present application in order to design various embodiments with various modifications for specific purposes.

[0095] Those skilled in the art should understand that the discussion of any embodiment above is only exemplary, and is not intended to limit the scope (including claims) of the present application; the above embodiments or technical features in different embodiments can also be combined, and the steps can be implemented in any order, and there are many other changes of the aspects of the embodiments of the present application as described above, which are not provided in details for the sake of brevity.

[0096] Although the present application has been described in conjunction with specific embodiments thereof, many alternatives, modifications and variations will be apparent to those skilled in the art from the foregoing description.

[0097] The embodiments of the present application are intended to cover all such alternatives, modifications and variations as falling within the broad scope of the appended claims. Accordingly, any omission, modification, equivalent replacement, improvement, etc. made in the spirit and principle of the embodiments of the present application should be included in the protection scope of the present application.

Claims

1. An electrode assembly, characterized by, The electrode assembly comprises a positive electrode sheet, a separator and a negative electrode sheet, and forms a winding structure, which comprises a flat area and two bending areas respectively connected to opposite ends of the flat area; the positive electrode sheet comprises flat parts and bending parts arranged alternately along a winding direction, and the bending parts are located in the bending areas; The bending part has an inner side close to the flat area and an outer side away from the flat area; the bending part comprises a current collector substrate and an active layer at least on the inner side of the current collector substrate; the surface of the active layer on the inner side of the current collector substrate of the first N bending parts along the winding direction is provided with a thinning groove, and 1≤N≤4.

2. The electrode assembly of claim 1, wherein, The surface of the active layer on the inner side of the current collector substrate of the last M bending parts along the winding direction is provided with a thinning groove, and 1≤M≤4; the total number of the bending parts in the positive electrode sheet is P, and P>M+N.

3. The electrode assembly of claim 2, wherein, P≥M+N+10.

4. The electrode assembly of claim 1, wherein, The thinning groove extends to the flat part at least at one end along the winding direction.

5. The electrode assembly of claim 1, wherein, The bending part has an inner side close to the flat area and an outer side away from the flat area; the bending part comprises a current collector substrate and an active layer at least on the inner side of the current collector substrate; the surface of the active layer on the inner side of the current collector substrate of the first N bending parts along the winding direction is provided with a thinning groove, and 1≤N≤4.

6. The electrode assembly of claim 1, wherein, The thinning groove comprises a first sub-groove on the surface of the active layer and a second sub-groove on the bottom of the first sub-groove.

7. The electrode assembly of claim 1, wherein, The slot width of the same thinning groove is greater than the groove bottom width along the winding direction.

8. The electrode assembly of claim 1, wherein, The positive electrode sheet comprises a plurality of bending parts along the winding direction, and at least two of the plurality of bending parts are provided with the thinning groove; the width of the thinning groove provided in the latter bending part is greater than the width of the thinning groove provided in the former bending part.

9. The electrode assembly of claim 1, wherein, In the active layer provided on one side of the current collector substrate, the thickness of the area provided with the thinning groove is Y, and the thickness of the area not provided with the thinning groove is H; When H is 90-105 microns, Y=(-2H)*X+5.9H; wherein X is 2.55-2.7; When H is 105-130 microns, Y=(-2H)*X+5.8H; wherein X is 2.55-2.7; When H is 130-140 microns, Y=(-2H)*X+5.7H; wherein X is 2.55-2.

7.

10. An electric cell characterized by The electrode assembly comprises a positive electrode sheet, a separator and a negative electrode sheet, and forms a winding structure, which comprises a flat area and two bending areas respectively connected to opposite ends of the flat area; the positive electrode sheet comprises flat parts and bending parts arranged alternately along a winding direction, and the bending parts are located in the bending areas;

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