Wound electrode assembly and lithium ion secondary battery

Abstract

The embodiment of the utility model provides a winding type electrode body and a lithium ion secondary battery. The wound electrode body comprises a positive plate, a negative plate and a diaphragm which are arranged in a laminated manner. The positive electrode sheet and the negative electrode sheet are wound into a wound electrode body having a flat portion and a curved portion with a separator interposed therebetween. The positive plate is provided with a straight section positioned at the flat part and an arc section positioned at the bent part; the positive plate comprises a positive current collector and a positive active layer arranged on the positive current collector; the positive electrode active layer is provided with a plurality of concave portions and / or a plurality of convex portions arranged dispersedly. The positive electrode active layer is further provided with at least one groove part, at least one first groove part is at least partially arranged in the arc section, and the thickness of the positive electrode active layer in the arc section is smaller than that of the positive electrode active layer in the straight section. Therefore, a plurality of liquid storage positions can be formed between the adjacent concave parts of the arc section of the positive plate, and the first groove part can further solve the problems of lithium separation and black spot generation caused by ion migration blocking due to the fact that the bent part is not easy to store the electrolyte and the electrolyte is lost.

Description

TECHNICAL FIELD

[0001] The utility model relates to a battery field especially, relates to a kind of winding electrode body and lithium ion secondary battery. BACKGROUND

[0002] The cell of lithium ion secondary battery is composed of positive electrode, negative electrode, electrolyte and separator. During charging and discharging, lithium ions shuttle between the two electrodes: during charging, lithium ions are extracted from the positive electrode, embedded in the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharging, it is the opposite.

[0003] Some lithium ion secondary batteries, such as soft pack batteries, have flat winding electrode bodies (also known as winding cores). Along the width direction, the flat electrode body includes two curved portions arranged opposite to each other and a flat portion located between them.

[0004] With the increase of the number of charging and discharging of the battery, the curved portion of the flat electrode body has the problem of lithium precipitation. SUMMARY

[0005] Therefore, the utility model embodiment provides a winding electrode body and a lithium ion secondary battery having the same to solve the problem of lithium precipitation in the curved portion of the flat electrode body.

[0006] In one aspect, the utility model embodiment provides a winding electrode body. The winding electrode body includes positive electrode sheets, negative electrode sheets and separators arranged in layers. The positive electrode sheets and the negative electrode sheets are wound into a winding electrode body with a flat portion and a curved portion through the separators. The positive electrode sheet has a flat section located in the flat portion and a circular arc section located in the curved portion. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector. The positive electrode active layer is provided with a plurality of recesses and / or a plurality of protrusions arranged dispersedly. The positive electrode active layer is also provided with at least one first groove portion, which is at least partially arranged in the circular arc section. The thickness of the positive electrode active layer in the circular arc section is less than the thickness of the positive electrode active layer in the flat section.

[0007] Additionally or alternatively, the positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer arranged oppositely on both sides of the positive electrode current collector along the thickness direction of the positive electrode sheet. The first positive electrode active layer is arranged on the side of the positive electrode current collector facing the winding center, and the second positive electrode active layer is arranged on the side of the positive electrode current collector away from the winding center. The first positive electrode active layer is provided with a plurality of recesses and at least one first groove portion.

[0008] Additionally or alternatively, the second positive electrode active layer is provided with at least one first groove portion and a plurality of protrusions, and the plurality of protrusions are at least partially located in the circular arc section, and / or the plurality of recesses are at least partially located in the circular arc section.

[0009] Additionally or alternatively, the plurality of recesses and / or the plurality of protrusions are also partially located in the flat section.

[0010] Additionally or alternatively, the plurality of recesses or the plurality of protrusions satisfy:

[0011] 0.5 mm≤R≤2.5 mm;

[0012] 10 μm≤T1≤90 μm; and

[0013] 1 mm≤D1≤5 mm,

[0014] Here, R is a diameter of a circumscribed circle of the recess or the protrusion, T1 is a dimension of the recess or the protrusion in a thickness direction of the positive electrode sheet, and D1 is a distance between any two adjacent recesses or protrusions.

[0015] Additionally or alternatively, a surface of the at least one first groove portion is provided with a part of the plurality of recesses or a part of the plurality of protrusions.

[0016] Additionally or alternatively, a length direction of the at least one first groove portion is perpendicular to a length direction of the positive electrode sheet, the at least one first groove portion includes a first side wall and a second side wall located at opposite ends in the length direction, and the first side wall and the second side wall are each in a slope shape.

[0017] Additionally or alternatively, the first side wall forms an angle α1 with the positive electrode current collector, the second side wall forms an angle α2 with the positive electrode current collector, and the angle α1 and the angle α2 each have a value in a range of 35° to 80°.

[0018] Additionally or alternatively, each of the at least one first groove portion includes a plurality of first grooves, the first grooves each have a width S, the first grooves each have a depth T2, and adjacent two of the first grooves each have a pitch D2, the width S has a value in a range of 0.005 mm to 2 mm, the depth T2 has a value in a range of 1 μm to 35 μm, and the pitch D2 has a value in a range of 0.005 mm to 2 mm.

[0019] Additionally or alternatively, each of the at least one first groove portion includes a plurality of first grooves, a length direction of the plurality of first grooves is perpendicular to a length direction of the positive electrode sheet, and the at least one first groove portion is located at least in the circular arc section.

[0020] Additionally or alternatively, the at least one first groove portion is parallel to the length direction of the positive electrode sheet, the wound electrode body has a thickness H, the at least one first groove portion has a dimension W1 in the length direction of the positive electrode sheet, and the thickness H and the dimension W1 satisfy: 3.14×H / 2-2 mm≤W1≤3.14×H / 2+2 mm.

[0021] Supplementarily or alternatively, each of the at least one first groove portion includes one first groove, the jelly-roll electrode body has a thickness H, the first groove has a width W2 along a length direction of the positive electrode sheet, and the thickness H and the width W2 satisfy: 3.14xH / 2-2 mm≤W2≤3.14xH / 2+2 mm.

[0022] Supplementarily or alternatively, a surface of the at least one first groove portion comprises a rough surface.

[0023] Supplementarily or alternatively, the rough surface has a height difference between a highest point and a lowest point in a range of 2x2 mm 2 of 1 μm to 10 μm.

[0024] Supplementarily or alternatively, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and a silicon content A in a negative electrode active material of the negative electrode active material layer is 1 wt% to 20 wt%.

[0025] Supplementarily or alternatively, a ratio of a value of the depth T2 of the first groove portion to a value of A satisfies T2 / A=0.06 to 0.5.

[0026] In another aspect, the utility model embodiment further provides a lithium ion secondary battery. The lithium ion secondary battery comprises the jelly-roll electrode body.

[0027] According to the jelly-roll electrode body and the lithium ion secondary battery provided by the utility model embodiment, the positive electrode active layer is provided with a plurality of recesses and / or protrusions arranged in a scattered manner at least in the circular arc segment. Therefore, a plurality of liquid storage positions can be formed between adjacent recesses and / or protrusions of the circular arc segment of the positive electrode sheet, so that the liquid storage amount of the region is increased, and the transmission rate of lithium ions is further increased, and the side reaction and lithium precipitation problem caused by electrolyte loss are reduced. At the same time, the recesses, the gaps between the recesses, and the gaps between the protrusions can provide a gap for the circular arc segment, so as to provide space for the expansion of the negative electrode active material, avoid the negative electrode active material from extruding the separator, and cause the problems of hole blocking and electrolyte extrusion of the separator.

[0028] In addition, the first groove portion is arranged in the circular arc segment, which is equivalent to a thinning treatment of the positive electrode active layer of the circular arc segment of the positive electrode sheet. That is, the positive electrode active material of the circular arc segment of the positive electrode sheet is reduced, and the N / P ratio of the bending part of the jelly-roll electrode body is increased, so that the lithium precipitation problem caused by the insufficient N / P ratio of the bending part of the jelly-roll electrode body is solved. In addition, the first groove portion arranged in the positive electrode active layer can also play a role in facilitating the storage of electrolyte, and further improve the problems of lithium precipitation and black spot caused by the ion migration obstruction caused by the electrolyte loss due to the difficulty of the bending part of the jelly-roll electrode body in storing electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1A schematic view of lithium ion migration when the positive active layer at the arc portion is located outside the negative active layer.

[0030] FIG. 2 A schematic view of lithium ion migration when the positive active layer at the arc portion is located inside the negative active layer.

[0031] FIG. 3 A schematic view of a winding electrode body according to an embodiment of the present application.

[0032] FIG. 4 A schematic view of a winding electrode body according to an embodiment of the present application. FIG. 3 A sectional view of the winding electrode body along D-D.

[0033] FIG. 5 A schematic view of a winding electrode body according to an embodiment of the present application.

[0034] FIG. 6 A schematic view of a positive electrode sheet according to an embodiment of the present application.

[0035] FIG. 7 A schematic view of a positive electrode sheet according to an embodiment of the present application. FIG. 6 A top view of the positive electrode sheet.

[0036] FIG. 8 A schematic view of a positive electrode sheet according to another embodiment of the present application.

[0037] FIG. 9 A schematic view of a positive electrode sheet according to another embodiment of the present application. FIG. 6 A schematic view of an arc segment structure of the positive electrode sheet.

[0038] FIG. 10 A schematic view of an arc segment structure of the positive electrode sheet. FIG. 9 An enlarged structural schematic view of a first groove portion of the F region.

[0039] FIG. 11 An enlarged structural schematic view of an arc segment structure of the positive electrode sheet. FIG. 10 A local enlarged structural schematic view of the G region.

[0040] FIG. 12 A schematic view of a positive electrode sheet according to another embodiment of the present application.

[0041] FIG. 13 A schematic view of a positive electrode sheet according to another embodiment of the present application. FIG. 12 A top view of the positive electrode sheet.

[0042] FIG. 14 An enlarged schematic view of a recess portion of the I region. FIG. 12 A local enlarged schematic view of a recess portion of the J region.

[0043] FIG. 15 A local enlarged schematic view of a recess portion of the J region. FIG. 14 A local enlarged schematic view of a recess portion of the J region.

[0044] FIG. 16This is a partial cross-sectional schematic diagram of a wound electrode body according to another embodiment of the present invention.

[0045] FIG. 17 This is a schematic diagram of a negative electrode sheet according to one embodiment of the present invention.

[0046] FIG. 18 for FIG. 17 A cross-sectional view of the negative electrode along CC.

[0047] FIG. 19 This is a schematic diagram of a lithium-ion secondary battery according to one embodiment of the present invention.

[0048] FIG. 20 This is a schematic diagram of a lithium-ion secondary battery according to another embodiment of the present invention.

[0049] Figure Labels

[0050] 1000, Lithium-ion secondary battery;

[0051] 100. Winded electrode body; 101. Bending portion; 101a. First bending portion; 101b. Second bending portion; 102. Flat portion;

[0052] 10. Positive electrode sheet; 11. Positive electrode active layer; 11a. First positive electrode active layer; 11b. Second positive electrode active layer; 111. First groove / first groove; 111a. First first groove; 111n. Nth first groove; 1111. First sidewall; 1112. Second sidewall; 12. Positive electrode current collector; 13. Straight section of positive electrode sheet; 14. Arc section of positive electrode sheet; 151. Recess; 152. Convex;

[0053] 20. Negative electrode sheet; 21. Negative electrode active layer; 22. Negative electrode current collector; 23. Second groove / second groove;

[0054] 200. Shell;

[0055] 30. Diaphragm. Detailed Implementation

[0056] With the rapid development of lithium-ion battery technology, higher demands are being placed on the energy density, fast charging capability, and charge / discharge rate of lithium-ion batteries. Fast-charging lithium batteries are also a development trend in consumer lithium-ion batteries. However, the development of fast-charging technology has also brought about safety issues related to lithium-ion batteries.

[0057] For example, the lithium ion secondary battery including the flat wound electrode body, as the number of charge and discharge of the battery increases, the inventors find that the lithium precipitation easily occurs in the bending part of the wound electrode body under the condition of fast charging, which further causes the problems of the cycle performance degradation of the lithium battery and the swelling failure caused by the corrugation of the bending part of the cell, greatly reducing the service life of the lithium battery.

[0058] The wound electrode body includes the positive electrode sheet, the negative electrode sheet and the separator arranged in a stack, and the positive electrode sheet and the negative electrode sheet are wound with the separator to form the wound electrode body having the flat part and the bending part. In the conventional wound electrode body, the positive active layer thicknesses at the straight section and the circular arc section of the positive electrode sheet are the same. The inventors find through research that the main reason for the lithium precipitation in the bending part of the wound electrode body is that the bending part has a certain curvature, which causes the NP of the negative electrode and the positive electrode to be small.

[0059] Specifically, referring to FIG. 1 and FIG. 2 , when the negative electrode B is located at the outer circular arc and the positive electrode A is located at the inner circular arc (as shown in FIG. 2 ), the lithium ions stripped from the positive electrode side during charging migrate to the negative electrode B in a divergent state. At this time, the lithium ions are dispersed on the surface of the negative electrode B, and in this case, the NP of the negative electrode and the positive electrode is large, and lithium precipitation is not easy. When the negative electrode B is located at the inner circular arc and the positive electrode A is located at the outer circular arc (as shown in FIG. 1 ), the lithium ions stripped from the positive electrode side during charging migrate to the negative electrode B in a convergent state. At this time, the lithium ions are gathered on the surface of the negative electrode B, and in this case, the NP of the negative electrode and the positive electrode is small, and lithium precipitation is more likely to occur. Therefore, lithium precipitation and black spots occur in the bending part.

[0060] To solve the above problems, the embodiment of the utility model provides a kind of wound electrode body 100 and battery 1000. Below, the wound electrode body 100 and battery 1000 of the embodiment of the utility model are described in conjunction with FIG. 3 to FIG. 18 .

[0061] For the convenience of description, the "width direction", "thickness direction" and "length direction" of the electrode body 100 and the electrode sheet are mentioned in the embodiment of the utility model. The width direction of the wound electrode body 100 refers to the direction from one bending part to another bending part, indicated by arrow U in the figure;The length direction of the wound electrode body 100 refers to the direction parallel to the winding axis E, indicated by arrow R in the figure;The thickness direction of the wound electrode body 100 refers to the direction perpendicular to the width direction and the length direction, indicated by arrow V in the figure.

[0062] In addition, this article will also mention the length, width, and thickness directions of each electrode. The length direction of the electrode refers to the direction from the starting end of the winding to the ending end, indicated by arrow X in the diagram; the width direction of the electrode is perpendicular to the length direction, that is, from one edge of the electrode to the other edge, indicated by arrow Y in the diagram; the thickness direction of the electrode is perpendicular to both the length and thickness directions, indicated by arrow Z in the diagram. After the electrode is wound, its length direction is the winding direction.

[0063] Exemplary jelly-roll electrode body

[0064] See 3 to FIG. 18 The wound electrode body 100 may include a positive electrode 10, a negative electrode 20, and a separator 30 arranged in a stacked manner. For example... FIG. 3 and FIG. 4 As shown, the positive electrode 10 and the negative electrode 20 are wound together with a separator 30 to form a wound electrode body 100 having a flat portion 102 and two curved portions 101a and 101b. The two curved portions 101a and 101b are distributed along the width direction at opposite ends of the flat portion 102. The two curved portions 101a and 101b are collectively referred to as curved portion 101.

[0065] The positive electrode 10 includes a positive current collector 12 and a positive active layer 11 disposed thereon, wherein the two positive active layers 11 may be located on opposite sides of the positive current collector 12 in the thickness direction. The negative electrode 20 may include a negative current collector 22 and a negative active layer 21 disposed thereon, wherein the two negative active layers 21 may be located on opposite sides of the negative current collector 22 in the thickness direction.

[0066] By way of example only, the positive electrode current collector 12 can be a strip of metal foil, and the positive electrode active layer 11 can contain a positive electrode active material capable of reversibly absorbing and releasing charge carriers. Furthermore, they can further include conductive materials, binders, and various additives. By way of example only, the metal foil mentioned here can be aluminum foil, the positive electrode active material can be lithium nickel cobalt manganese composite oxide, lithium cobalt oxide, or other lithium transition metal composite oxides, the conductive material can be carbon-based materials such as acetylene black, and the binder can be polyvinylidene fluoride, etc.

[0067] By way of example only, the negative electrode current collector 22 can be a strip of metal foil, and its active material layer can contain a negative electrode active material capable of reversibly absorbing and releasing charge carriers, a binder, a dispersant, and various additives. By way of example only, the metal foil mentioned here can be copper foil, the negative electrode active material can be a carbon-based material such as graphite, the binder can be a rubber such as styrene-butadiene rubber, and the dispersant can be a cellulose such as carboxymethyl cellulose.

[0068] The separator 30 is a member that insulates the positive electrode sheet 10 and the negative electrode sheet 20. As some examples, the separator 30 can be a porous resin tape made of a polyolefin resin such as polyethylene, polypropylene, or the like. Of course, it is also possible for the separator 30 to be made of other materials.

[0069] In the length direction, the positive electrode sheet 10 includes a plurality of circular arc segments 14, and the plurality of straight segments 13 and the plurality of circular arc segments 14 are alternately arranged. After winding, the circular arc segments 14 of the positive electrode sheet 10 are located in the curved portion 101 of the jelly-roll electrode body 100, and the straight segments 13 of the positive electrode sheet 10 are located in the flat portion 102 of the jelly-roll electrode body 100.

[0070] Reference FIG. 3 to FIG. 16 The positive active layer 11 can be provided with a plurality of recesses 151 and / or a plurality of protrusions 152 arranged in a dispersed manner, that is, the positive active layer 11 can be provided with a plurality of recesses 151 or a plurality of protrusions 152 arranged in a dispersed manner, or both a plurality of recesses 151 and a plurality of protrusions 152. The positive active layer 11 is further provided with at least one first groove portion 111, which is at least partially arranged in the circular arc segment 14, so that the thickness of the positive active layer 11 in the circular arc segment 14 is less than the thickness thereof in the straight segment 13. Here, the recess 151 refers to a depression of no fixed shape on the positive active layer 11, and the first groove portion 111 refers to a groove on the positive active layer 11.

[0071] In this way, a plurality of liquid storage positions can be formed between adjacent recesses 151, adjacent recesses 152 of the circular arc segment 14 of the positive electrode sheet 10, so as to increase the amount of liquid stored in this region, thereby improving the transmission rate of lithium ions and reducing the side reactions and lithium precipitation problems caused by the lack of electrolyte. At the same time, the recesses 151 and the spaces between them, the protrusions 152 and the spaces between them can provide gaps for the circular arc segment 14, so as to provide space for the expansion of the negative active material and avoid the problem of the negative active material expanding and pressing the separator, which leads to the problem of the separator being blocked and the electrolyte being squeezed out.

[0072] In addition, the first groove portion 111 provided in the circular arc segment 14 is equivalent to a thinning process of the positive active layer 11 of the circular arc segment 14 of the positive electrode sheet 10. That is, the positive active material of the circular arc segment 14 of the positive electrode sheet 10 is reduced, thereby improving the N / P ratio of the curved portion of the jelly-roll electrode body 100, and the problem of lithium precipitation caused by the insufficient N / P ratio of the curved portion 14 of the jelly-roll electrode body 100 can be solved. Then, the first groove portion 111 provided in the positive active layer 11 can also play a role in facilitating the storage of electrolyte, and further improve the problem of lithium precipitation and the generation of black spots caused by the lack of electrolyte, which leads to the problem of ion migration being blocked due to the curved portion of the jelly-roll electrode body 100 being difficult to store electrolyte.

[0073] Reference FIG. 5 to FIG. 16In some embodiments, the positive electrode active layer 11 can include a first positive electrode active layer 11a and a second positive electrode active layer 11b arranged on opposite sides of the positive electrode current collector 12 along the thickness direction of the positive electrode sheet 10, the first positive electrode active layer 11a being arranged on the side of the positive electrode current collector 12 facing the winding center, and the second positive electrode active layer 11b being arranged on the side of the positive electrode current collector 12 facing away from the winding center. That is, in the wound electrode body 100, the first positive electrode active layer 11a is arranged on the inner side of the positive electrode current collector 12, and the second positive electrode active layer 11b is arranged on the outer side of the positive electrode current collector 12. The first positive electrode active layer 11a is provided with a plurality of recesses 151 and at least one first groove portion 111, and the plurality of recesses 151 are at least partially located in the circular arc segment 14.

[0074] The second positive electrode active layer 11b is also provided with the at least one first groove portion 111 and a plurality of protrusions 152, and the plurality of protrusions 152 are at least partially located in the circular arc segment 14.

[0075] Further, the plurality of recesses 151 and / or the plurality of protrusions 152 are also partially located in the flat segment 13.

[0076] It should be noted that the positive electrode sheet 10 has a plurality of circular arc segments 14, the first positive electrode active layer 11a can be provided with a plurality of recesses 151, and the plurality of recesses 151 can be arranged in the first positive electrode active layer 11a corresponding to the plurality of circular arc segments 14 of the positive electrode sheet 10 respectively, and the second positive electrode active layer 11b can be provided with a plurality of protrusions 152, and the plurality of protrusions 152 can be arranged in the second positive electrode active layer 11b corresponding to the plurality of circular arc segments 14 of the positive electrode sheet 10 respectively. That is, each recess 151 is at least partially located in a corresponding circular arc segment 14, and each protrusion 152 is at least partially located in a corresponding circular arc segment 14.

[0077] For example, the positive electrode sheet 10 also has a plurality of flat segments 13, and the plurality of recesses 151 can be distributed in the first positive electrode active layer 11a of the plurality of flat segments 13 simultaneously, and the plurality of protrusions 152 can be distributed in the second positive electrode active layer 11b of the plurality of flat segments 13 simultaneously. For example, in some examples, the plurality of recesses 151 and the plurality of protrusions 152 extend from the circular arc segment 14 to the flat segment 13 of the positive electrode sheet 10; in other examples, the plurality of recesses 151 and the plurality of protrusions 152 extend through the circular arc segment 14 and the flat segment 13 of the positive electrode sheet 10. Herein, when describing the plurality of recesses 151, it is for any one of the plurality of recesses 151; similarly, when describing the plurality of protrusions 152, it is for any one of the plurality of protrusions 152.

[0078] Reference FIG. 11 and FIG. 15Further, the plurality of recesses 151 and the plurality of protrusions 152 satisfy: 0.5 mm≤R≤2.5 mm, optionally, R is 1 mm, 1.5 mm, or 2 mm, etc., 10 μm≤T1≤90 μm, optionally, T1 is 20 μm, 40 μm, 60 μm, or 80 μm, etc., preferably, 0.8 mm≤R≤2.0 mm, for example, 1.2 mm, 1.4 mm, or 1.8 mm, etc.; 20 μm≤T1≤50 μm, for example, 25 μm, 35 μm, or 45 μm, etc.; and 1 mm≤D1≤5 mm, optionally, D1 is 2 mm, 3 mm, or 4 mm, etc. Here, R is the diameter of the recess 151 or the protrusion 152; T1 is the size of the recess 151 or each protrusion 152 in the thickness direction of the positive electrode sheet 10, for example, the depth of the recess 151, or the height of the protrusion 152; and D1 is the distance between any two adjacent recesses 151 or any two adjacent protrusions 152.

[0079] The plurality of recesses 151 preferably have the shape of irregular polygonal depressions, and the plurality of protrusions 152 preferably have the shape of irregular polygonal islands.

[0080] It should be noted that the shape of the recess 151 is not limited to the shape of an irregular polygonal depression, and the shape of the protrusion 152 is not limited to the shape of an irregular polygonal island. The shapes of the recess 151 and the protrusion 152 can also be set to other shapes, such as circular, square, diamond, and elliptical, according to the needs of specific application scenarios. Correspondingly, when the recess 151 and the protrusion 152 have other shapes, R is the diameter of the circumscribed circle of each polygonal portion 15.

[0081] In this way, a plurality of liquid storage positions can be formed between adjacent protrusions 152 of the second positive electrode active layer 11b, and a plurality of liquid storage portions can be formed between adjacent recesses 151 of the first positive electrode active layer 11a, so as to increase the liquid storage amount of the positive electrode sheet 10, thereby increasing the transmission rate of lithium ions, reducing side reactions and lithium precipitation problems caused by electrolyte loss.

[0082] At the same time, the recesses 151 and the gaps therebetween and the gaps between the protrusions 152 can provide gaps for the circular arc segments 14, so as to provide space for the expansion of the negative electrode active material, thereby avoiding the problem of the negative electrode active material expanding and pressing the separator, causing the separator to be blocked and the electrolyte to be squeezed out.

[0083] In addition, the protrusions 152 are arranged in the first positive electrode active layer 11a inside the positive electrode current collector 12, so as to increase the N / P ratio of the curved portion of the wound electrode body 100, and increase the margin of the capacity of the positive electrode facing the negative electrode (i.e., the N / P ratio: the capacity of the unit area negative electrode / the capacity of the unit area positive electrode) of the curved portion 101 of the wound electrode body 100 under the same conditions in the same stage, thereby effectively solving the problem of lithium precipitation caused by the insufficient N / P ratio of the curved portion 101 of the wound electrode body 100.

[0084] As described above, in some examples, the surface of the at least one first groove portion 111 is provided with a portion of the plurality of recesses 151 or a portion of the plurality of protrusions 152. That is, the surface of the first groove portion 111 on the first positive active layer 11a is provided with the recess 151, and the surface of the first groove portion 111 on the second positive active layer 11b is provided with the protrusion 152.

[0085] It should be noted that the positive electrode sheet 10 has a plurality of circular arc segments 14, and in each circular arc segment 14, one groove portion 111 can include a plurality of first grooves 111. That is, in each circular arc segment 14, a first first groove 111a to an Nth first groove 111n can be provided. Herein, when describing the first groove portion 111, it is directed to any one of the plurality of circular arc segments 14.

[0086] In this way, the first groove portion 111 is combined with the recess 151 or the protrusion 152, which can further increase the liquid storage amount of the positive electrode sheet 10, thereby improving the transmission rate of lithium ions, reducing the side reaction and lithium precipitation problem caused by the lack of electrolyte.

[0087] Reference FIG. 6 , FIG. 7 and FIG. 9 to FIG. 15 The length direction of the at least one first groove portion 111 is perpendicular to the length direction of the positive electrode sheet 10, the at least one first groove portion 111 includes a first side wall 1111 and a second side wall 1112 located at opposite ends of the length direction, and the first side wall 1111 and the second side wall 1112 are both in a slope shape. The first side wall 1111 forms an angle α1 with the positive electrode current collector 12, and the second side wall 1112 forms an angle α2 with the positive electrode current collector 12, and the angle α1 and the angle α2 are in a range of 35° to 80°, for example, 40°, 50°, 60° or 70°, etc.

[0088] Reference FIG. 9 and FIG. 10 In some examples, each of the at least one first groove portion 111 can include a plurality of first grooves 111, for example, a first first groove 111a to an Nth first groove 111n.

[0089] That is, the positive active layer 11 can be provided with a plurality of first groove portions 111 arranged at intervals, each of the first groove portions 111 can include a plurality of first grooves 111, for example, a first first groove 111a to an Nth first groove 111n, and the plurality of first grooves 111 can be at least partially located in the circular arc segment of the positive electrode sheet 10, so that the thickness of the positive active layer 11 in the circular arc segment of the positive electrode sheet 10 is less than the thickness of the positive active layer 11 in the flat segment 13 of the positive electrode sheet 10.

[0090] In this way, the positive active layer 11 of the arc segment 14 of the positive electrode sheet 10 is thinned. The positive active material of the arc segment 14 of the positive electrode sheet 10 is reduced, thereby increasing the N / P ratio of the bending portion 101 of the wound electrode body 100, and the problem of lithium precipitation caused by an insufficient N / P ratio of the bending portion 101 of the wound electrode body 100 can be solved. In addition, the plurality of first groove portions 111 arranged at intervals in the positive active layer 11 can also function to facilitate the storage of electrolyte, thereby further improving the problem of lithium precipitation and black spot generation caused by the difficulty of the bending portion 101 of the wound electrode body 100 in storing electrolyte and the difficulty of ion migration caused by the lack of electrolyte.

[0091] It should be noted that the positive electrode sheet 10 has a plurality of arc segments 14, and a plurality of first grooves 111 can be arranged in each arc segment 14. That is, a first first groove 111a to an Nth first groove 111n can be arranged in each arc segment 14. Herein, the plurality of first grooves 111 are described with respect to any one of the plurality of arc segments 14.

[0092] Each first groove 111 can include a first side wall 1111 and a second side wall 1112 opposite in the length direction of the positive electrode sheet 10. The first side wall 1111 of the first first groove 111a and the second side wall 1112 of the Nth first groove 111n can each be ramp-shaped. In this way, the groove walls of the plurality of first grooves 111 can transition more gently to the surface of the other part of the positive active layer 11, avoiding the problem of positive and negative short circuits caused by the vertical groove walls pressing the separator 30 and causing the separator 30 to break. The bottom of each first groove 111 can be a flat surface.

[0093] Continuing to refer to FIG. 9 and FIG. 10 Further, the first side wall 1111 of the first first groove 111a can form an angle a1 with the positive current collector 12, and the second side wall 1112 of the Nth first groove 111n can form an angle a2 with the positive current collector 12. The angle a1 and the angle a2 are greater than 0° and less than 90°, and can alternatively be 40°, 50°, 60°, or 70°, etc.

[0094] The first side wall 1111 of the first first groove 111a and the second side wall 1112 of the Nth first groove 111n can each be ramp-shaped, and the values of the angle a1 and the angle a2 are set to the above range, which can avoid the problem of positive and negative short circuits caused by the vertical groove walls pressing the separator 30 and causing the separator 30 to break, while also avoiding the risk of excessive loss of positive active material and excessive loss of energy density.

[0095] It can be understood that the other side wall of the first first slot 111a, the other side wall of the Nth first slot 111n, and the first and second side walls 1111, 1112 of the other first slots 111 therebetween can be vertical (i.e. perpendicular to the thickness direction of the positive current collector 12) or can be ramped, preferably ramped, to facilitate storage of electrolyte.

[0096] With reference to FIG. 12 and FIG. 14 In some examples, each of the at least one first slot portion 111 can include one first slot 111, which can include first and second side walls 1111, 1112 opposite along the length direction of the positive plate 10, and the first and second side walls 1111, 1112 can each be ramped. In this way, the slot wall of one first slot can transition more gently to the surface of other parts of the positive active layer 11, such as the parts located at the circular arc segment 14, avoiding the problem of vertical slot wall pressing the separator 30, leading to the positive and negative short circuit caused by the rupture of the separator 30.

[0097] With reference to FIG. 14 Further, the first side wall 1111 can form an angle α1 with the positive current collector 12, and the second side wall 1122 can form an angle α2 with the positive current collector 12. The angle α1 and the angle α2 are greater than 0° and less than 90°, and can be 20°, 30°, 35°, 40°, 50°, 60°, 70° or 85°, etc. Within this angle range, the problem of vertical slot wall pressing the separator 30, leading to the positive and negative short circuit caused by the rupture of the separator 30 can be avoided, while the risk of excessive loss of positive active material, leading to excessive loss of energy density, can also be avoided.

[0098] With reference to FIG. 6 to FIG. 11, each of the at least one first groove portion 111 can include a plurality of first grooves 111, the first grooves 111 can have a width S, the grooves 111 can have a depth T2, and two adjacent first grooves 111 can have a pitch D2. The width S can be in a range of 0.005 mm to 2 mm, and can alternatively be 0.008 mm, 0.01 mm, 0.10 mm, 0.15 mm, 0.2 mm, 0.3 mm, 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 1.5 mm, or 1.8 mm, etc.; the depth T2 can be in a range of 1 pm to 35 pm, and can alternatively be 5 pm, 10 pm, 15 pm, 20 pm, 25 pm, or 30 pm, etc.; and the pitch D2 can be in a range of 0.005 mm to 2 mm, and can alternatively be 0.008 mm, 0.01 mm, 0.10 mm, 0.15 mm, 0.2 mm, 0.3 mm, 0.5 mm, 0.7 mm, 0.9 mm, 1 mm, 1.5 mm, or 1.8 mm, etc., to ensure that the N / P ratio of the bending portion is improved to avoid lithium precipitation there, while the energy density is taken into account. Meanwhile, the depth T2 is controlled in this range, which can ensure that the specific depth of the long groove bottom to the positive current collector 12 is 2 pm to 5 pm, thereby preventing damage to the positive current collector 12 during the manufacture of the first grooves 111, which can cause the belt to break during production.

[0099] With reference to FIG. 6 , FIG. 7 and FIG. 9 to FIG. 11 , in some embodiments, each of the at least one first groove portion 111 can include a plurality of first grooves 111, the length direction of the plurality of first grooves 111 can be perpendicular to the length direction of the positive electrode sheet 10, and the at least one first groove portion 111 is located at least at the circular arc segment.

[0100] In this way, the N / P ratio of the bending portion of the wound electrode body 100 can be improved, the problem of lithium precipitation caused by insufficient N / P ratio of the bending portion can be solved, and the loss of positive active material is avoided, thereby preventing excessive loss of energy density.

[0101] In some alternative embodiments, with reference to FIG. 8 , the at least one first groove portion 111 is parallel to the length direction of the positive electrode sheet 10, the wound electrode body 100 has a thickness H, each of the at least one first groove portion 111 has a dimension W1 in the length direction of the positive electrode sheet 10, and the thickness H and the width W1 satisfy: 3.14 x H / 2 - 2 mm < W1 < 3.14 x H / 2 + 2 mm.

[0102] With reference to FIG. 8At least one first slot part 111 includes a plurality of first slots 111 parallel to the length direction of the positive electrode sheet 10, and the plurality of first slots 111 are located on at least the circular arc segment 14. The positive electrode sheet can include a plurality of circular arc segments 14, and each first slot part 111 is arranged one-to-one with the plurality of circular arc segments 114.

[0103] In some embodiments, referring back to FIG. 4 to FIG. 10 The wound electrode body 100 has a thickness H, and each of the plurality of first slot parts 111 has a size (i.e., a width) W1 in the length direction of the positive electrode sheet 10.

[0104] When the length direction of the first slot part 111 is perpendicular to the length direction of the positive electrode sheet 10, W1 is the total width of all the first slots 111 in the plurality of first slots 111, i.e., the distance between the first side wall 1111 of the first first slot 111a and the second side wall 1112 of the Nth first slot 111n. When the length direction of the first slot part 111 is parallel to the length direction of the positive electrode sheet 10, W1 is the length of one first slot 111 in the plurality of first slots 111, such as the length of the longest first slot 111 in one first slot part 111, the length from left to right of one first slot part 111, or the average of the lengths of all the first slots 111 in one first slot part 111, etc.

[0105] The thickness H of the wound electrode body 100 and the width W1 of the first slot part 111 in the length direction of the positive electrode sheet 10 can satisfy: 3.14×H / 2-2mm≤W1≤3.14×H / 2+2mm.

[0106] In this way, when the face scanning is performed to form a long slot to thin the circular arc segment of the positive active material, the entire circular arc segment can be covered. When less than the lower limit value, the face scanning width cannot cover the entire circular arc segment 14, and the bending part 101 will also be prone to lithium precipitation. When greater than the upper limit value, the face scanning width will be too large, the positive active material will be lost too much, and the energy density will be lost too much.

[0107] Referring back to FIG. 12 to FIG. 16 In some embodiments, each of the at least one first slot part 111 can include one first slot 111, and the wound electrode body 100 can have a thickness H, and the one first slot 111 can have a width W2 in the length direction of the positive electrode sheet 10. The thickness H and the width W2 can satisfy: 3.14×H / 2-2mm≤W2≤3.14×H / 2+2mm.

[0108] In this way, when the positive active material is formed by the face sweep to form the first groove portion 111 to thin the circular arc segment 114, the entire circular arc segment 114 can be covered. When less than the left end value, the face sweep width cannot cover the entire circular arc segment 114, and the bending portion 101 can also cause lithium precipitation. When greater than the left end value, the face sweep width is too large, the positive active material is lost too much, and the energy density is lost too much.

[0109] Reference FIG. 3 to FIG. 16 In some embodiments, the surface (including the bottom surface and the side wall) of each first groove portion 111 can be a rough surface to increase the porosity of the region to facilitate the storage of the electrolyte.

[0110] Further, with reference to FIG. 13 , the rough surface is in the range of 4 mm2, i.e., in the range of 2 mm x 2 mm ( FIG. 13 , the height difference between the highest point and the lowest point is in the range of 1 μm to 10 μm. Further, the bottom surface of each long groove is in the range of 4 mm2, i.e., in the range of 2 mm x 2 mm, the height difference between the highest point and the lowest point is in the range of 1 μm to 10 μm, and optionally, 3 μm, 5 μm, 7 μm, or 9 μm, etc. The side wall is in the range of 0.04 mm2, i.e., in the range of 0.2 mm x 0.2 mm ( FIG. 13 , the height difference between the highest point and the lowest point is in the range of 1 μm to 10 μm, and optionally, 3 μm, 5 μm, 7 μm, or 9 μm, etc. When the value is less than 1 μm, it is not conducive to the further storage of the electrolyte, and may, in the later stage of the cycle, cause the risk of lithium precipitation. When the value is greater than 10 μm, the higher protruding points can pierce the separator 30 to cause the risk of short circuit of the battery 1000.

[0111] Reference FIG. 17 and FIG. 18 In some examples, the negative electrode sheet 20 includes a negative electrode current collector 22 and a negative electrode active layer 21 disposed on the negative electrode current collector 22. The silicon content A in the negative electrode active material of the negative electrode active layer 21 is 1 wt% to 20 wt%. The silicon can be included in a silicon-carbon material in the negative electrode active material. Exemplarily, the silicon-carbon material includes one or more of elemental silicon, a silicon-based alloy, a silicon oxide, and a silicon-carbon composite material.

[0112] The ratio of the depth T2 of the first groove portion to the value of A satisfies T2 / A = 0.03 to 0.57, such as 0.04, 0.045, 0.05, 0.1, 0.2, 0.3, or 0.4, etc., and preferably 0.06 to 0.5.

[0113] T2 can increase with the increase of A. In this way, the depth of the first groove portion 23 can be adjusted according to the silicon content to better alleviate the negative electrode expansion pressure and provide electrolyte storage space. It should be noted that the vertical and parallel mentioned herein are not absolute vertical or parallel, and appropriate errors, such as ± 10%, should be covered.

[0114] It should also be noted that the wound electrode body of the present application can be realized by one or more combinations between the above embodiments, or based on their variants.

[0115] Exemplary lithium-ion secondary battery

[0116] On the other hand, as FIG. 19 and 20 indicated, the present application embodiment also provides a lithium ion secondary battery 1000. The lithium ion secondary battery 1000 includes the above-mentioned wound electrode body 100.

[0117] Referring to FIG. 19 and 20 , the lithium ion secondary battery 1000 can include the wound electrode body 100 and a housing 200. The housing 200 can be provided with a receiving cavity, and one or more wound electrode bodies 100 can be received in the receiving cavity.

[0118] As shown in FIG. 19 , in some embodiments, the housing 200 can be square. That is, the battery 1000 can be a square battery 1000. The material of the housing 200 can be the same as that used in the past, and is not particularly limited. For example, the housing 200 can be made of metal, in particular, can be made of aluminum (alloy) or iron (alloy) and the like.

[0119] As shown in FIG. 20 , in some embodiments, the housing 200 is flat and is made of a relatively soft material, such as an aluminum plastic film. That is, in this embodiment, the lithium ion secondary battery 1000 can be a soft pack lithium ion secondary battery 1000.

[0120] It can be foreseen that in other examples of the present application embodiment, the battery 1000 can also be realized as other types in addition to the square lithium ion secondary battery 1000 and the soft pack lithium ion secondary battery 1000.

[0121] It should be noted that other aspects of the lithium ion secondary battery 1000 can be the same as the structure of the conventional lithium ion secondary battery 1000, and for the purpose of brevity, the present application embodiment will not be described in detail.

[0122] The lithium ion secondary battery 1000 provided by the embodiment of the present application has the corresponding effects of the above-mentioned wound electrode body 100, and specific reference can be made to the above, and no further description is made herein.

[0123] It should be noted that in the present application, the "battery" refers to a storage device capable of repeated charging and discharging, which can be interpreted as the concept of "secondary battery". In the embodiment of the present application, the concept of "secondary battery" can include lithium ion secondary battery and the like.

[0124] It should be understood that the term "comprising" and its variants used in the embodiments of the present application are open and inclusive, i.e. "including but not limited to". The term "according to" is "at least partially according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "multiple" means "more than one", which means to cover the cases of two, three or more.

[0125] It should be understood that although the terms "first" or "second" and the like can be used to describe various elements in the embodiments of the present application, for example, the first side wall and the second groove part, these elements are not provided by these terms, and these terms are only used to distinguish one element from another.

[0126] The protection scope of the embodiments of the present application is not limited to the above-mentioned embodiments, and any person skilled in the art can think of changes or replacements within the technical range disclosed by the embodiments of the present application, which should be covered within the protection scope of the embodiments of the present application. Therefore, the protection scope of the embodiments of the present application should be subject to the protection scope of the claims.

[0127] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the embodiments of the present application.

[0128] The materials, reagents and the like used in the following embodiments can be obtained from commercial channels unless otherwise specified. The processing process and technology involved are conventional technical means unless otherwise specified.

[0129] The present application will be described in detail below in combination with specific embodiments, which are used for understanding rather than limiting the present application.

[0130] Example 1-1

[0131] The positive active material lithium cobaltate, polyvinylidene fluoride and acetylene black are mixed in a mass ratio of 97.2:1.3:1.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed until the mixed system becomes a uniform flowable positive electrode slurry; the positive electrode slurry is uniformly coated on a positive current collector 11 (aluminum foil) with a thickness of 10 μm; the coated aluminum foil is dried, rolled, and cut to obtain a positive electrode sheet 10, and a laser is used to form a concave portion 151 on the first positive active layer 11a of the positive electrode sheet 10 and a convex portion 152 on the second positive active layer 11b. Here, the R of the concave portion 151 and the convex portion 152 is 0.51 mm, the T1 is 45.3 μm, and the D1 is 3.12 mm. The first groove portion 111 is formed on the positive active layer 11 (see FIG. 8 ), the width W1 of the first groove portion 111 is 7.56 mm, the height difference between the highest point and the lowest point of the bottom rough surface of each first groove of the first groove portion 111 in a range of 2x2 mm2is 4.8 μm, the height difference between the highest point and the lowest point of the side wall rough surface in a range of 0.2x0.2 mm2is 4.8 μm, the included angle α1 between the first side wall 1113 and the positive current collector 12 is 35.6°, and the included angle α2 between the second side wall 1114 and the positive current collector 12 is 35.3°. The pitch D2 of adjacent first grooves is 0.006 mm, the first groove depth T2 is 1.2 μm, and the first groove width S is 0.007 mm.

[0132] The negative active material is a combination of artificial graphite and silicon-carbon material, wherein the mass ratio of artificial graphite to silicon-carbon is 7:3, and the silicon content in the silicon-carbon material is 4 wt%, single-walled carbon nanotubes, conductive carbon black, and butadiene rubber are mixed in a mass ratio of 95.9:0.1:1:3, deionized water is added, and stirring is performed until the mixed system becomes a uniform flowable negative electrode slurry; the negative electrode slurry is uniformly coated on a negative current collector 21 (copper foil) with a thickness of 6 μm; the coated copper foil is dried, rolled, and cut to obtain a negative electrode sheet 20. The depth T3 of the second groove portion 23 is 2 μm.

[0133] The prepared positive electrode sheet 10, separator 30, and negative electrode sheet 20 are stacked and wound to form a wound electrode body 100, which is then packaged, baked, injected with electrolyte, formed, double-sealed, sorted, and OCV to obtain a lithium ion secondary battery 1000. Here, the thickness H of the wound electrode body is 4.75 mm.

[0134] The electrolyte is a commercially available conventional electrolyte, and the lithium salt therein is LiFP6.

[0135] It should be noted that other forming processes of the positive electrode sheet 10 and the negative electrode sheet 20 are conventional means in the art, and the materials involved are commercially available conventional materials, which will not be described here.

[0136] It should be noted that other forming processes of the positive electrode sheet 10 and the negative electrode sheet 20 and the materials involved are conventional technical means in the art, which will not be described here.

[0137] It should be noted that a1, a2, roughness, size of the groove, size of the concave and convex parts can be controlled by processing parameters, such as laser forming parameters (e.g. laser power, etc.).

[0138] Example 1-2

[0139] The difference from Example 1-1 is that R is 1.63 mm, the angle a1 of the first side wall 1113 with the positive current collector 12 is 54.9°, and the angle a2 of the second side wall 1114 with the positive current collector 12 is 54.8°. The distance D2 between adjacent first grooves is 1.1 mm, the first groove depth T2 is 17.8 μm, the first groove width S is 1.04 mm, and the silicon content in the silicon-carbon material is 35 wt%.

[0140] Example 1-3

[0141] The difference from Example 1-1 is that R is 2.49 mm, the angle a1 of the first side wall 1113 with the positive current collector 12 is 79.6°, and the angle a2 of the second side wall 1114 with the positive current collector 12 is 79.4°. The distance D2 between adjacent first grooves is 1.98 mm, the first groove depth T2 is 34.9 μm, the first groove width S is 1.97 mm, and the silicon content in the silicon-carbon material is 95 wt%.

[0142] Example 1-4

[0143] The difference from Example 1-1 is that the first groove part 111 is arranged as shown in FIG. 7 , that is, the first groove part 111 is perpendicular to the length direction of the positive electrode sheet 10.

[0144] Example 1-5

[0145] The difference from Example 1-2 is that the first groove part 111 is arranged as shown in FIG. 7 .

[0146] Example 1-6

[0147] The difference from Example 1-3 is that the first groove part 111 is arranged as shown in FIG. 7 .

[0148] Example 1-7

[0149] The difference from Example 1-1 is that the first groove part 111 is arranged as shown in FIG. 9 , that is, in the circular arc segment, at least one first groove part 111 is a groove 111, and the groove 111 is perpendicular to the length direction of the positive electrode sheet 10.

[0150] Example 1-8

[0151] The difference from Example 1-2 is that the first groove portion 111 is provided as seen in FIG. 9 .

[0152] Example 1-9

[0153] The difference from Example 1-3 is that the first groove portion 111 is provided as seen in FIG. 9 .

[0154] Example 2-1

[0155] The difference from Example 1-2 is that R is 0.43 mm.

[0156] Example 2-2

[0157] The difference from Example 1-2 is that R is 2.97 mm.

[0158] Example 3-1

[0159] The difference from Example 1-2 is that T1 is 10.3 μm.

[0160] Example 3-2

[0161] The difference from Example 1-2 is that T1 is 89.7 μm.

[0162] Example 3-3

[0163] The difference from Example 1-2 is that T1 is 8.9 μm.

[0164] Example 3-4

[0165] The difference from Example 1-2 is that T1 is 101.2 μm.

[0166] Example 4-1

[0167] The difference from Example 1-2 is that D1 is 1.05 mm.

[0168] Example 4-2

[0169] The difference from Example 1-2 is that D1 is 4.98 mm.

[0170] Example 4-3

[0171] The difference from Example 1-2 is that D1 is 0.87 mm.

[0172] Example 4-4

[0173] The difference from Example 1-2 is that D1 is 5.89 mm.

[0174] Example 5-1

[0175] The difference from Example 1-2 is that a1 and a2 are 2.9°.

[0176] Example 5-2

[0177] The difference from Example 1-2 is that a1 and a2 are 86.7°.

[0178] Example 6-1

[0179] The difference from Example 1-2 is that the roughness of the first groove bottom and side is 1.3 μm.

[0180] Example 6-2

[0181] The difference from Example 1-2 is that the roughness of the first groove bottom and side is 9.6 μm.

[0182] Example 6-3

[0183] The difference from Example 1-2 is that the roughness of the first groove bottom and side is 12.8 μm.

[0184] Example 6-4

[0185] The difference from Example 1-2 is that the roughness of the first groove bottom and side is 0.5 μm.

[0186] Example 7-1

[0187] The difference from Example 1-2 or 1-5 is that W1 is 5.61 mm.

[0188] Example 7-2

[0189] The difference from Example 1-2 or 1-5 is that W1 is 9.38 mm.

[0190] Example 7-3

[0191] The difference from Example 1-2 or 1-5 is that W1 is 3.87 mm.

[0192] Example 7-4

[0193] The difference from Example 1-2 or 1-5 is that W1 is 13.45 mm.

[0194] Example 8-1

[0195] The difference from Example 1-8 is that W1 is 6.61 mm.

[0196] Example 8-2

[0197] The difference from Examples 1-8 is that W1 is 9.38 mm.

[0198] Example 8-3

[0199] The difference from Examples 1-8 is that W1 is 3.87 mm.

[0200] Example 8-4

[0201] The difference from Examples 1-8 is that W1 is 13.45 mm.

[0202] Comparative Example 1

[0203] The difference from Examples 1-2 is that the recess 151 is not provided.

[0204] Comparative Example 2

[0205] The difference from Examples 1-2 is that the first groove portion 111 is not provided.

[0206] Comparative Example 3

[0207] The difference from Examples 1-2 is that the recess 151 and the first groove portion 111 are not provided.

[0208] The batteries of the examples and comparative examples were tested according to the following test methods.

[0209] Test conditions and evaluation criteria for lithium precipitation: using a charge-discharge device, the batteries prepared in the above examples and comparative examples were charged and discharged 800 times at a 2C rate under constant temperature conditions of 25°C ± 3°C, and after 800 charge-discharge cycles, the batteries were disassembled and observed for lithium precipitation. Lithium precipitation and black spot area accounting for more than 70% of the circular arc area was defined as very severe lithium precipitation, lithium precipitation and black spot area accounting for 50% to 70% of the circular arc area was defined as severe lithium precipitation, lithium precipitation and black spot area accounting for 30% to 50% of the circular arc area was defined as lithium precipitation, lithium precipitation and black spot area accounting for less than 30% of the circular arc area was defined as slight lithium precipitation, and 0% was defined as no lithium precipitation.

[0210] Test conditions and evaluation criteria for separator rupture: the batteries were charged and discharged 100 times at a 2C rate under constant temperature conditions of 25°C ± 3°C, and after 100 charge-discharge cycles, the batteries were disassembled and observed for separator rupture. If the separator ruptured, a burning point would appear on the negative electrode sheet. The larger the area of the burning point, the more severe the rupture. A burning point with an inscribed circle diameter of 0.01 mm to 0.1 mm was defined as slight rupture, a burning point with an inscribed circle diameter of 0.1 mm to 0.3 mm was defined as rupture, and a burning point with an inscribed circle diameter greater than 0.3 mm was defined as severe rupture.

[0211] Test condition and evaluation standard of the fracture of the electrode plate: the battery was charged and discharged at 2C rate for 800 times at constant temperature of 25°C±3°C, and the fracture of the negative electrode plate was observed after disassembling at 800 times of full charge. No crack of the negative electrode plate means no fracture.

[0212] Table 1 is the test results of each example and the comparative example.

[0213] Table 1 test results

[0214]

[0215]

[0216] As can be seen from the test results, the recess 151 is arranged in the positive active layer of the positive electrode plate, and the groove portion 111 is arranged in the circular arc segment, which can better reduce and avoid lithium precipitation.

Claims

1. A jelly-roll type electrode body, characterized by comprising: The positive electrode sheet, the negative electrode sheet and the separator are arranged in a stack, the positive electrode sheet and the negative electrode sheet are wound into the wound electrode body having flat portions and curved portions with the separator interposed therebetween, the positive electrode sheet has a flat section located at the flat portion and a circular arc section located at the curved portion, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector, the positive electrode active layer is provided with a plurality of recesses and / or a plurality of protrusions arranged in a dispersed manner, and the positive electrode active layer is further provided with at least one first groove portion, the at least one first groove portion is at least partially arranged in the circular arc section, and the thickness of the positive electrode active layer in the circular arc section is less than the thickness of the positive electrode active layer in the flat section.

2. The jelly-roll electrode body according to claim 1, characterized by The positive electrode active layer comprises a first positive electrode active layer and a second positive electrode active layer arranged on both sides of the positive electrode current collector in the thickness direction of the positive electrode sheet, the first positive electrode active layer is arranged on the side of the positive electrode current collector facing the winding center, and the second positive electrode active layer is arranged on the side of the positive electrode current collector away from the winding center, and the first positive electrode active layer is provided with the plurality of recesses and the at least one first groove portion.

3. The jelly-roll electrode body according to claim 2, characterized by The second positive electrode active layer is provided with the at least one first groove portion and the plurality of protrusions, and the plurality of protrusions are at least partially located in the circular arc section and / or the plurality of recesses are at least partially located in the circular arc section.

4. The jelly-roll electrode body according to claim 3, characterized by The plurality of recesses and / or the plurality of protrusions are also at least partially located in the flat section.

5. The jelly-roll electrode body according to claim 3, characterized by The plurality of recesses or the plurality of protrusions satisfy: 0.5mm≤R≤2.5mm; 10μm≤T1≤90μm; and 1mm≤D1≤5mm, wherein R is the diameter of the circumscribed circle of the recess or the protrusion, T1 is the size of the recess or the protrusion in the thickness direction of the positive electrode sheet, and D1 is the distance between any two adjacent recesses or protrusions.

6. The jelly-roll electrode body according to claim 3, characterized by The surface of the at least one first groove portion is provided with part of the plurality of recesses or part of the plurality of protrusions.

7. The jellyroll of claim 1, wherein The length direction of the at least one first groove portion is perpendicular to the length direction of the positive electrode sheet, the at least one first groove portion comprises a first side wall and a second side wall located at opposite ends of the length direction, and the first side wall and the second side wall are both in a slope shape.

8. The jelly-roll electrode body according to claim 7, characterized by The first side wall forms an angle α1 with the positive electrode current collector, the second side wall forms an angle α2 with the positive electrode current collector, and the values of the angle α1 and the angle α2 are in the range of 35° to 80°.

9. The jellyroll of claim 1, wherein Each of the at least one first groove portion comprises a plurality of first grooves, each first groove has a width S, each first groove has a depth T2, and any two adjacent first grooves have a spacing D2, the width S is in the range of 0.005mm to 2mm, the depth T2 is in the range of 1μm to 35μm, and the spacing D2 is in the range of 0.005mm to 2mm.

10. The jelly-roll electrode body according to claim 9, characterized by Each of the at least one first groove portion comprises a plurality of first grooves, the length direction of the plurality of first grooves is perpendicular to the length direction of the positive electrode sheet, and the at least one first groove portion is at least located in the circular arc section.

11. The jelly-roll electrode body according to claim 9, characterized by The at least one slot portion is parallel to the length direction of the positive electrode sheet, the jelly-roll electrode body has a thickness H, the at least one first slot portion has a size W1 in the length direction of the positive electrode sheet, and the thickness H and the size W1 satisfy 3.14xH / 2-2mm≤W1≤3.14xH / 2+2mm.

12. The jellyroll of claim 1, wherein Each of the at least one first slot portion includes one first slot, the jelly-roll electrode body has a thickness H, the first slot has a width W2 in the length direction of the positive electrode sheet, and the thickness H and the width W2 satisfy 3.14xH / 2-2mm≤W2≤3.14xH / 2+2mm.

13. The jellyroll of any one of claims 1 to 12, wherein A surface of the at least one first slot portion includes a rough surface.

14. The jellyroll of claim 13, wherein The rough surface has a height difference between the highest points and the lowest points in the range of 2 x 2 mm 2 1 μm to 10 μm.

15. The jellyroll of any one of claims 1 to 12, wherein The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on the negative electrode current collector, and a content A of silicon in a negative electrode active material of the negative electrode active layer is 1 wt% to 20 wt%.

16. The jellyroll of claim 15, wherein A ratio of a depth T2 of the first slot portion to a value of A satisfies T2 / A=0.06 to 0.

5.

17. A lithium-ion secondary battery, characterized by comprising: A jelly-roll electrode body according to any one of claims 1 to 16.

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