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 active layer is provided with a sunken part at least partially located in the arc section, and the thickness of the positive active layer in the arc section is smaller than that of the positive active layer in the straight section. The concave part comprises a first side wall and a second side wall which are opposite to each other in the length direction of the positive plate, and the first side wall and the second side wall are in slope shapes. Therefore, the positive active material of the arc section of the positive plate is reduced, and the N / P ratio of the bending part is improved. And the sunken part can also play a role in conveniently storing the electrolyte. In addition, the first side wall and the second side wall are slope-shaped, so that the diaphragm can be prevented from being extruded by the vertical groove wall.

Description

TECHNICAL FIELD

[0001] The utility model relates to the field of battery, in particular, relate 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 are inserted and de-inserted between two electrodes: when charging, lithium ions are de-inserted from the positive electrode, inserted into the negative electrode through electrolyte, and the negative electrode is in a lithium-rich state; when 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 with 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, which includes positive electrode sheets, negative electrode sheets and separators arranged in a stacked and wound manner. The positive electrode sheets and the negative electrode sheets are wound into a winding electrode body with flat portions and curved portions 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 recess portion located at least partially in the circular arc section. The thickness of the positive electrode active layer in the circular arc section is less than that in the flat section. The recess portion includes first and second side walls opposite along the length direction of the positive electrode sheet, and both the first and second side walls are in a slope shape.

[0007] Additionally or alternatively, the winding electrode body has a thickness H, and the recess portion has a width W along the length direction of the positive electrode sheet. Here, the thickness H and the width W satisfy: 3.14×H / 2-2mm≤W≤3.14×H / 2+2mm.

[0008] Additionally or alternatively, the surface of the recess portion includes a rough surface.

[0009] Additionally or alternatively, the rough surface has a height difference between the highest point and the lowest point within a range of 2*2mm 2 of 1 μm to 10 μm.

[0010] Supplementarily or alternatively, the first side wall forms an angle a1 with the positive current collector, and the second side wall forms an angle a2 with the positive current collector, the angle a1 and the angle a2 are 35° to 80°.

[0011] Supplementarily or alternatively, the negative tab has a flat section in the flat part and a circular arc section in the curved part, the negative tab comprises a negative current collector and a negative active layer arranged thereon, the negative active layer is provided with at least one groove, and the at least one groove is at least partially located in the circular arc section of the negative tab.

[0012] Supplementarily or alternatively, each groove has a width S, each groove has a depth T, two adjacent grooves have a spacing D1, and the lowest part of each groove has a spacing D2 from the negative current collector. Here, the width S is 50 μm to 250 μm, the depth T is 5 μm to 35 μm, the spacing D1 is 0.5 mm to 5 mm, and the spacing D2 is 3 μm to 10 μm.

[0013] Supplementarily or alternatively, the length direction of each groove is parallel to the length direction of the negative tab; and / or

[0014] The at least one groove extends along the winding direction of the wound electrode body and ends in the circular arc section or the flat section.

[0015] Supplementarily or alternatively, the recess has a width W along the length direction of the positive tab, and the at least one groove has a length L1. Here, the width W and the length L1 satisfy: W≤L1≤W+10 mm.

[0016] Supplementarily or alternatively, the at least one groove extends through the circular arc section and the flat section.

[0017] Supplementarily or alternatively, along the length direction of the negative tab, the distance between the two ends of the at least one groove is L3, and the negative active layer has a length L2. Here, the distance L3 and the length L2 satisfy: L2-5 mm≤L3≤L2-1 mm.

[0018] Supplementarily or alternatively, each groove comprises a plurality of groove sections arranged along the length direction of the negative tab, wherein:

[0019] The plurality of groove sections are connected end to end; or,

[0020] The plurality of groove sections are staggered along the width direction of the negative tab; or,

[0021] The plurality of groove sections are arranged at intervals along the length direction of the negative tab, and two adjacent groove sections have a spacing D3, and the spacing D3 is 0.2 mm to 10 mm.

[0022] Supplementarily or alternatively, along the winding direction of the wound electrode body, the end of each groove section is located in the flat section of the negative tab.

[0023] On the other hand, this utility model embodiment provides a lithium-ion secondary battery, which includes the above-mentioned wound electrode body.

[0024] According to the spiral-wound electrode body and lithium-ion secondary battery provided in this embodiment of the present invention, the positive electrode active layer has a recessed portion located at least partially in the arc segment. Therefore, the thickness of the positive electrode active layer in the arc segment of the positive electrode sheet is less than its average thickness in the straight segment of the positive electrode sheet. In other words, the positive electrode active layer in the arc segment of the positive electrode sheet is thinned. In this way, the positive electrode active material in the arc segment is reduced, thereby increasing the capacity margin of the opposite negative electrode super-positive electrode in the curved portion of the spiral-wound electrode body under the same stage and conditions (i.e., N / P ratio: negative electrode capacity per unit area / positive electrode capacity per unit area), thus effectively solving the lithium plating problem caused by insufficient N / P ratio in the curved portion of the spiral-wound electrode body. In addition, the multiple recessed portions arranged at intervals in the positive electrode active layer can also facilitate the storage of electrolyte, further improving the problems of lithium plating and black spots caused by the lack of electrolyte due to the difficulty in storing electrolyte in the curved portion of the spiral-wound electrode body and the resulting hindered ion migration. Due to the presence of the sloping first and second sidewalls, the groove wall of the recessed portion can transition more smoothly to the surface of other parts of the positive electrode active layer, such as the part located in the arc segment, avoiding the vertical groove wall from squeezing the diaphragm and causing the diaphragm to rupture and resulting in a short circuit between the positive and negative electrodes. Attached Figure Description

[0025] FIG. 1 This is a schematic diagram of lithium-ion migration when the positive electrode active layer at the arc portion is located outside the negative electrode active layer.

[0026] FIG. 2 This is a schematic diagram of lithium-ion migration when the positive electrode active layer at the arc portion is located inside the negative electrode active layer.

[0027] FIG. 3 This is a schematic diagram of a positive electrode sheet according to an embodiment of the present invention.

[0028] FIG. 4 for FIG. 3 An enlarged schematic diagram of the recessed part.

[0029] FIG. 5 for FIG. 3 Top view.

[0030] FIG. 6 This is a schematic diagram of a negative electrode sheet according to an embodiment of the present invention.

[0031] FIG. 7 for FIG. 6 A cross-sectional view of the negative electrode along CC.

[0032] FIG. 8 This is a schematic diagram of a negative electrode sheet according to an embodiment of the present invention.

[0033] FIG. 9 This is a schematic diagram of a negative electrode sheet according to another embodiment of the present invention.

[0034] FIG. 10 This is a schematic diagram of a negative electrode sheet according to another embodiment of the present invention.

[0035] FIG. 11 This is a schematic diagram of a negative electrode sheet according to another embodiment of the present invention.

[0036] FIG. 12 This is a three-dimensional schematic diagram of a wound electrode body according to an embodiment of the present invention.

[0037] FIG. 13 for FIG. 12 A cross-sectional view along DD of the medium-wound electrode body.

[0038] FIG. 14 This is a schematic diagram of a battery according to an embodiment of the present invention.

[0039] FIG. 15 This is a schematic diagram of a lithium-ion secondary battery according to another embodiment of the present invention.

[0040] Figure label:

[0041] 1000, Lithium-ion secondary battery;

[0042] 100. Winded electrode body; 101a. First curved portion; 101b. Second curved portion; 102. Flat portion;

[0043] 10. Positive electrode sheet; 11. Positive electrode active layer; 111. Recessed portion; 1113. First sidewall; 1114. Second sidewall; 12. Positive electrode current collector; 13. Straight section of the positive electrode sheet; 14. Arc section of the positive electrode sheet;

[0044] 20. Negative electrode sheet; 21. Negative electrode active layer; 211. Groove; 22. Negative electrode current collector; 23. Straight section of negative electrode sheet; 24. Arc section of negative electrode sheet;

[0045] 200. Shell;

[0046] 30. Diaphragm. Detailed Implementation

[0047] With the rapid development of lithium-ion battery technology, higher demands have been 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.

[0048] For example, the 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 problem of the bending part of the wound electrode body is prone to occur under the condition of fast charging, and further brings the problems of the cycle performance decline of the lithium battery and the swelling failure caused by the corrugation of the bending part of the cell, which greatly reduces the service life of the lithium battery.

[0049] The wound electrode body includes a positive electrode sheet, a negative electrode sheet and a separator arranged in a stack, and the positive electrode sheet and the negative electrode sheet are wound with the separator to form a wound electrode body having a flat part and a bending part. In the conventional wound electrode body, the positive active layer thicknesses at the straight sections and the circular arc sections of the positive electrode sheet are the same. The inventors have found through research that the main reason for the lithium precipitation of the bending part of the wound electrode body is that the bending part has a certain curvature, which leads to the existence of a small NP ratio of the negative electrode to the positive electrode.

[0050] 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 released 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 ratio of the negative electrode to 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 released 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 ratio of the negative electrode to the positive electrode is small, and lithium precipitation is more likely to occur. Therefore, lithium precipitation and black spots occur in the bending part.

[0051] To solve the above problems, the embodiments of the present application provide a wound electrode body 100 and a battery 1000. In the following, the wound electrode body 100 and the battery 1000 will be described in conjunction with FIG. 3 to FIG. 15 .

[0052] It should be understood that the implementation manner of the present application can be various, and should not be interpreted as being limited to the embodiments set forth herein, and the embodiments set forth herein are only for a more thorough and clear understanding of the present disclosure.

[0053] For the convenience of description, the embodiments of the present application refer to the "width direction", "thickness direction" and "length direction" of the wound electrode body 100. The width direction of the wound electrode body 100 refers to the direction from one bending part to another bending part, which is indicated by the arrow U in the figure; the length direction of the wound electrode body 100 refers to the direction parallel to the winding axis E, which is indicated by the arrow R in the figure; and the thickness direction of the wound electrode body 100 refers to the direction perpendicular to both the width direction and the length direction, which is indicated by the arrow V in the figure.

[0054] Furthermore, the length direction, the width direction, and the thickness direction of each tab will be mentioned herein. The length direction of the tab is the direction from the winding start end to the winding end, indicated by an arrow X in the drawings. The width direction of the tab is the direction perpendicular to the length direction, that is, the direction from one side edge to the other side edge of the tab, indicated by an arrow Y in the drawings. The thickness direction of the tab is the direction perpendicular to both the length direction and the width direction, indicated by an arrow Z in the drawings. After the tab is wound, the length direction becomes the winding direction.

[0055] Exemplary jelly-roll electrode body

[0056] Referring to FIGS. 3 to FIG. 13 The wound electrode body 100 can include the positive tab 10, the negative tab 20, and the separator 30 arranged in layers. The positive tab 10 and the negative tab 20 are wound with the separator 30 therebetween to form the wound electrode body 100 having the flat portion 102 and two curved portions 101a and 101b. The two curved portions 101a and 101b are distributed in the width direction at opposite ends of the flat portion 102. The two curved portions 101a and 101b are collectively referred to as the curved portion 101.

[0057] The positive tab 10 can include the positive current collector 12 and the positive active layer 11 disposed thereon, and two positive active layers 11 can be located on opposite sides in the thickness direction of the positive current collector 12. The negative tab 20 can include the negative current collector 22 and the negative active layer 21 disposed thereon, and two negative active layers 21 can be located on opposite sides in the thickness direction of the negative current collector 22.

[0058] By way of example only, the positive current collector 12 can be a metal foil in a strip shape, and the positive active layer 11 can contain a positive active material capable of reversibly absorbing and releasing charge carriers, and can further include a conductive material, a binder, and various additive ingredients, etc. By way of example only, the metal foil mentioned herein can be an aluminum foil, the positive active material mentioned can be a lithium nickel cobalt manganese composite oxide, a lithium transition metal composite oxide such as lithium cobaltate, the conductive material mentioned can be a carbon-based material such as acetylene black, and the binder mentioned can be polyvinylidene fluoride, etc.

[0059] By way of example only, the negative current collector 22 can be a metal foil in a strip shape, and the active material layer can contain a negative active material capable of reversibly absorbing and releasing charge carriers, a binder, a dispersant, and various additive ingredients, etc. By way of example only, the metal foil mentioned herein can be a copper foil, the negative active material mentioned can be a carbon-based material such as graphite, a silicon-containing negative electrode material, the binder mentioned can be a rubber-based material such as styrene butadiene rubber, and the dispersant mentioned can be a cellulose-based material such as carboxymethyl cellulose.

[0060] The separator 30 is a component that insulates the positive electrode 10 and the negative electrode 20. As some examples, the separator 30 can be a porous strip made of resin composed of polyolefin resins such as polyethylene and polypropylene. Of course, other materials can also be used to construct the separator 30.

[0061] Along its length, the positive electrode 10 includes multiple arc segments 14 and multiple straight segments 13, which are arranged alternately. After winding, the arc segments 14 of the positive electrode 10 are located in the curved portion 101 of the wound electrode body 100, and the straight segments 13 of the positive electrode 10 are located in the flat portion 102 of the wound electrode body 100. Correspondingly, along its length, the negative electrode 20 includes multiple arc segments 24 and multiple straight segments 23, which are arranged alternately. After winding, the arc segments 24 of the negative electrode 20 are located in the curved portion 101 of the wound electrode body 100, and the straight segments 23 of the positive electrode 10 are located in the flat portion 102 of the wound electrode body 100.

[0062] like FIG. 3 to FIG. 5 As shown, the positive electrode active layer 11 may have a recess 111, which may be at least partially located in the arc segment of the positive electrode sheet 10, so that the thickness of the positive electrode active layer 11 in the arc segment 14 is less than its thickness in the straight segment 14. The recess 111 may include a first sidewall 1113 and a second sidewall 1114 opposite to each other along the length direction of the positive electrode sheet 10, and both the first sidewall 1113 and the second sidewall 1114 may be sloped. That is, in the unfolded state of the positive electrode sheet 10, the first sidewall 1113 and the second sidewall 1114 form an angle greater than 0 degrees and less than 90 degrees with the positive electrode current collector 12.

[0063] In this way, the positive active layer 11 of the arc segment of the positive electrode 10 is thinned, thereby reducing the positive active material in the arc segment of the positive electrode 10, and thus improving the N / P ratio of the curved portion of the wound electrode body 100. This can solve the lithium plating problem caused by insufficient N / P ratio in the curved portion of the wound electrode body 100. In addition, the recessed portion 111 provided in the positive active layer 11 can also facilitate the storage of electrolyte, further improving the problem of lithium plating and black spots caused by the lack of electrolyte due to the difficulty in storing electrolyte in the curved portion of the wound electrode body 100 and the resulting ion migration obstruction. Due to the presence of the sloping first sidewall 1113 and second sidewall 1114, the groove wall of the recessed portion 111 can transition more smoothly to the surface of other parts of the positive active layer 11, such as the part located in the arc segment 14, avoiding the problem of positive and negative electrode short circuit caused by the vertical groove wall pressing the separator 30 and causing the separator 30 to rupture.

[0064] It should be noted that the positive plate 10 has a plurality of circular arc segments, and the positive active layer 11 can be provided with a plurality of recesses 111. The plurality of recesses 111 can respectively correspond to the plurality of circular arc segments 14 of the positive plate 10. That is, each recess 111 is at least partially located in a corresponding circular arc segment 14.

[0065] Further, as shown in FIG. 4 , the first side wall 1113 can form an angle α1 with the positive current collector 12, and the second side wall 1114 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°, for example, 10°, 20°, 35°, 40°, 50°, 60°, 70° or 85°, etc.

[0066] The first side wall 1113 and the second side wall 1114 of the recess 111 are arranged as slopes, and the angles between them and the positive current collector 12 are controlled within this range of angles, which can avoid the problem of positive and negative short circuit caused by the vertical slot wall extruding the separator 30 and causing the separator 30 to break, and also avoid the risk of excessive loss of positive active material, resulting in excessive loss of energy density.

[0067] Referring to FIG. 3 to FIG. 5 and FIG. 13 , the wound electrode body 100 can have a thickness H, and the recess 111 can have a width W in the length direction of the positive plate 10. The thickness H and the width W can satisfy: 3.14*H / 2-2mm≤W≤3.14*H / 2+2mm. In this way, when the positive active material of the circular arc segment is thinned by forming a recess by face scanning, the entire circular arc segment 14 can be substantially covered. When less than the left end value, the face scanning width cannot substantially cover the entire circular arc segment, and the bending part will also be lithiumized. When greater than the right end 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.

[0068] As shown in FIG. 4 and FIG. 5 , the surface (including the bottom surface and the side wall) of the recess 111 can be a rough surface with concave and convex, which can increase the porosity of the area and be more conducive to the storage of electrolyte.

[0069] Further, the height difference between the highest point and the lowest point of the rough surface in the range of 2*2mm 2 ( FIG. 5 ) is 3μm to 10μm. Further, the height difference between the highest point and the lowest point of the bottom surface of the recess in the range of 2*2mm 2 is 1μm to 10μm, and the height difference between the highest point and the lowest point of the side wall in the range of 0.2*0.2mm 2 ( FIG. 5The height difference between the highest point and the lowest point within the range of the B region (as shown in the example) is in the range of 1 pm to 10 pm, for example, 2 pm, 4 pm, 6 pm, or 8 pm, etc. When the value is less than 1 pm, it is not conducive to the further storage of electrolyte, and may cause lithium precipitation risk in the later stage of the cycle. When the value is greater than 10 pm, the higher protruding point can pierce the separator 30, causing a short circuit risk of the battery 1000.

[0070] With reference to FIG. 6 to FIG. 11 The negative active layer 21 can be provided with at least one groove 211 arranged at intervals, and the at least one groove 211 is at least partially located in the circular arc segment 24 of the negative tab 20. In this way, the storage amount of electrolyte can be improved, thereby improving the transmission rate of lithium ions and reducing side reactions and lithium precipitation problems caused by electrolyte loss.

[0071] In some embodiments, with reference to FIG. 8 to FIG. 10 The length direction of each groove 211 can be substantially parallel to the length direction of the negative tab 20, that is, substantially parallel to the winding direction, for example, the deviation between the length direction of each groove 211 and the length direction of the negative tab 20 can be ±5% to ±10%. In this way, the electrolyte in this area can be well locked and not squeezed out of the circular arc segment 24, further increasing the electrolyte content in this area to improve the lithium precipitation problem.

[0072] With reference to FIG. 8 and FIG. 11 In some embodiments, along the winding direction of the wound electrode body 100, the at least one groove 211 ends at the circular arc segment 24 or the straight segment 24. That is, the at least one groove 211 only covers the circular arc segment 24 of the negative tab 20 and does not cover the straight segment 23 of the negative tab 20.

[0073] Further, with reference to FIG. 8 and FIG. 11 The at least one groove 211 can have a length L1. The size W and the length L1 can satisfy: W≤L1≤W+10 mm. With reference to FIG. 3 and FIG. 8 / FIG. 11 In this way, after winding, the orthographic projection of the recess 114 on the negative tab 20 will fall within the at least one groove 211, ensuring that the at least one groove 211 wraps around the recess 114, which can better receive lithium ions from the positive electrode, improve the negative electrode reaction kinetics in the interface region to facilitate the reception of lithium ions and improve the lithium precipitation problem.

[0074] It should be noted that, here, the length L1 can be the distance between the leftmost and rightmost of the at least one groove 211 when the line connecting the endpoints of the left end and the right end of the at least one groove 211 is a straight line; when the line connecting the endpoints of the left end and the right end of the at least one groove 211 is not a straight line, the length L1 can also be the average distance, the maximum distance or the minimum distance between the left end and the right end, etc., which is not limited in the present application.

[0075] In some alternative embodiments, as shown in FIGS. 1A and 1B, the at least one groove 211 can extend through the circular arc segment 24 and the flat segment 23. That is, the at least one groove 211 covers both the circular arc segment 23 of the negative electrode sheet 20 and the flat segment 23 of the negative electrode sheet 20, which can further better receive lithium ions from the positive electrode and improve the negative electrode reaction kinetics of the interface region. FIG. 9 FIG. 10 In some alternative embodiments, as shown in FIGS. 1A and 1B, the at least one groove 211 can extend through the circular arc segment 24 and the flat segment 23. That is, the at least one groove 211 covers both the circular arc segment 23 of the negative electrode sheet 20 and the flat segment 23 of the negative electrode sheet 20, which can further better receive lithium ions from the positive electrode and improve the negative electrode reaction kinetics of the interface region.

[0076] Further, each groove 211 can include a plurality of groove segments 212 arranged along the length direction of the negative electrode sheet 20.

[0077] For example, in some examples, the plurality of groove segments 212 can be connected end to end, facilitating segmented laser forming of the groove segments 212.

[0078] For another example, in some other examples, the plurality of groove segments 212 are staggered along the width direction of the negative electrode sheet 20, which can more evenly improve the storage capacity of the electrolyte and improve the negative electrode reaction kinetics.

[0079] For another example, in some other examples, the plurality of groove segments 212 are arranged at intervals along the length direction of the negative electrode sheet 20.

[0080] In the case where the plurality of groove segments 212 are arranged at intervals along the length direction of the negative electrode sheet 20, the two adjacent groove segments 212 have a spacing D3, and the spacing D3 has a value in the range of 0.2mm to 10mm, such as 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm or 9mm, etc.

[0081] Of course, it can also be a combination of these several setting modes, for example, the plurality of groove segments 212 are connected end to end and staggered along the width direction and / or the length direction of the negative electrode sheet 20, or the plurality of groove segments 212 are arranged at intervals along the length direction of the negative electrode sheet 20 and staggered along the width direction and / or the length direction of the negative electrode sheet 20.

[0082] Further, along the winding direction of the jelly-roll electrode body 100, the end of each groove segment 212 is located in the flat segment 23 of the negative electrode sheet 20, so as to avoid the connection position between the two groove segments 212 falling into the circular arc segment 24 of the negative electrode sheet 20, which helps to further reduce the risk of lithium precipitation.

[0083] ​Reference FIG. 9 and FIG. 10 , along the length direction of the negative electrode sheet 20, the distance between the two ends of the at least one groove 211 is L3, and the negative electrode active layer 21 can have a length L2. The distance L3 and the length L2 can satisfy: L2-5mm≤L3≤L2-1mm. For example, when the at least one groove 211 is discontinuously arranged along the length direction of the negative electrode sheet 20 (as shown in FIG. 10 ), L3 is the distance between the left end of the leftmost groove segment 212 and the right end of the rightmost groove segment 212, and when the groove 211 is continuously arranged along the length direction (as shown in FIG. 9 ), L1 is the distance between the left end and the right end of one groove. In this way, the edge of the groove 211 is away from the edge of the negative electrode active material layer 21 by a certain distance, which can avoid the problem of exceeding the coating when the negative electrode sheet 20 is provided with the groove, and the problem of damaging the foil to cause the foil to break.

[0084] It should be noted that when the at least one groove 211 covers the arc segment 23 of the negative electrode sheet 20, here, when the line connecting the left end and the right end of the at least one groove 211 is a straight line, the length L3 can be the distance between the leftmost and the rightmost of the at least one groove 211; when the line connecting the left end and the right end of the at least one groove 211 is not a straight line, the maximum distance between the left end and the right end.

[0085] In some alternative embodiments, as shown in FIG. 11 , the length direction of each groove 211 can be substantially perpendicular to the length direction of the negative electrode sheet 20, that is, substantially perpendicular to the winding direction, which is convenient for laser forming the groove. For example, the deviation of the length direction of each groove 211 from the direction perpendicular to the length direction of the negative electrode sheet 20 is ±5% to ±10%. Referring to FIG. 3 and FIG. 10 , at this time, the extension direction of the groove 211 is parallel to the direction of the recess 111, which is convenient for the electrolyte to flow between the two.

[0086] Referring to FIG. 6 to FIG. 11 , each groove 211 can have a V-shaped cross-sectional shape, that is, the opening of the V-shaped groove can face upward. The V-shaped side wall increases the surface area of the negative electrode for receiving lithium ions, which can receive lithium ions from the positive electrode faster, can further facilitate the storage of electrolyte, receive lithium ions from the positive electrode at a faster speed, provide lithium ion transmission speed, and further improve the kinetic performance of the negative electrode arc segment. A large amount of lithium ions from the positive electrode can be received in a short time, which prevents the problem of lithium precipitation caused by the aggregation of lithium ions on the surface of the negative electrode.

[0087] Further, as shown in FIG. 7As shown, each groove 211 has a width S, each groove 211 has a depth T, two adjacent grooves 211 have a pitch D1, the lowest part of each groove 211 has a pitch D2 with the negative current collector 22, the width S can be 50 μm to 250 μm, and can be 70 μm, 100 μm, 130 μm, 160 μm, 190 μm or 220 μm, etc., the depth T can be 5 μm to 35 μm, and can be 7 μm, 10 μm, 13 μm, 16 μm, 19 μm, 22 μm, 28 μm or 33 μm, etc., the pitch D1 can be 0.5 mm to 5 mm, and can be 0.8 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.5 mm, 3.5 mm or 4.5 mm, etc., and the pitch D2 can be 3 μm to 10 μm, and can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm or 9 μm, etc. In this way, the storage amount of the electrolyte is increased while the N / P ratio is ensured. Meanwhile, the depth T is controlled in the range, so that the distance between the bottom of the groove 211 and the negative current collector 22 is not less than 5 μm to 35 μm, so as to avoid damage to the negative current collector 22 during preparation of the groove 211, thereby preventing the problem of fracture of the negative current collector 22.

[0088] It should be noted that the wound electrode body of the present application can be realized by one or more of the above embodiments in combination, or based on variants thereof.

[0089] Exemplary lithium-ion secondary battery

[0090] On the other hand, as shown in FIG. 14 and 15 The present application also provides a lithium ion secondary battery 1000. The lithium ion secondary battery 1000 includes the wound electrode body 100 described above.

[0091] Referring to FIG. 14 and 15 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.

[0092] As shown in FIG. 14 In some embodiments, the housing 200 can be square. That is, the lithium ion secondary battery 1000 can be a square lithium ion secondary 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) or the like.

[0093] As shown in FIG. 15As shown, in some embodiments, the case 200 is flat and made of a relatively soft material, such as an aluminum laminate film. That is, in this embodiment, the lithium-ion secondary battery 1000 can be a soft-pack lithium-ion secondary battery 1000.

[0094] It can be envisaged that, in other examples of the embodiments of the present application, the lithium-ion secondary battery 1000 can also be implemented as other types of lithium-ion secondary battery 1000 other than the square lithium-ion secondary battery 1000 and the soft-pack lithium-ion secondary battery 1000.

[0095] It should be noted that other aspects of the lithium-ion secondary battery 1000 can be the same as those of the conventional battery 1000, and for the purpose of brevity, the embodiments of the present application will not be described in detail.

[0096] The lithium-ion secondary battery 1000 according to the embodiments of the present application has the corresponding effects of the above-described wound electrode body 100, and specific reference is made to the foregoing, and will not be described in detail here.

[0097] It should be noted that, in the present disclosure, the "battery" refers to a power storage device capable of repeated charging and discharging, which can be interpreted as the concept of "secondary battery". In the embodiments of the present application, the concept of "secondary battery" can include lithium-ion secondary batteries and the like.

[0098] 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.

[0099] The scope of protection of the embodiments of the present application is not limited to the above-described embodiments, and any person skilled in the art can think of changes or substitutions within the technical scope disclosed by the embodiments of the present application, which should be covered within the scope of protection of the embodiments of the present application. Therefore, the scope of protection of the embodiments of the present application should be subject to the scope of protection of the claims.

[0100] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application.

[0101] The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified. The processing processes and techniques involved are conventional technical means unless otherwise specified.

[0102] The present application will be described in detail below with reference to specific embodiments, which are used to understand rather than limit the present application.

[0103] Example 1-1

[0104] Lithium cobalt oxide, polyvinylidene fluoride, and acetylene black, the positive electrode active materials, were mixed in a mass ratio of 97.2:1.3:1.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred until a homogeneous and fluid positive electrode slurry was formed. This positive electrode slurry was uniformly coated onto a 10 μm thick positive electrode current collector 11 (aluminum foil). The coated aluminum foil was dried, rolled, and slit to obtain a positive electrode sheet 10. A recess 111 was formed on the positive electrode active layer 11 of the positive electrode sheet 10 using a laser. The width W of the recess 111 was 5.5 mm, and the bottom roughness of the recess 111 was 2*2 mm. 2 The height difference between the highest and lowest points within the range is 5 μm, and the sidewall roughness is 0.2*0.2 mm. 2 The height difference between the highest and lowest points within the range is 5 μm. The angle α1 between the first sidewall 1113 and the positive current collector 12 is 35°, the angle α2 between the second sidewall 1114 and the positive current collector 12 is 34.9°, and the thickness of the single-sided positive active layer is 15.3 μm.

[0105] A negative electrode active material (a combination of artificial graphite and silicon carbon, wherein the mass ratio of artificial graphite to silicon carbon is 7:3), single-walled carbon nanotubes, conductive carbon black, and styrene-butadiene rubber are mixed in a mass ratio of 95.9:0.1:1:3. Deionized water is added, and the mixture is stirred until a homogeneous and fluid negative electrode slurry is formed. This negative electrode slurry is uniformly coated onto a negative electrode current collector 21 (copper foil) with a thickness of 6 μm. The coated copper foil is dried, rolled, and slit to obtain a negative electrode sheet 20. A groove 211 is formed on the negative electrode active material 21 using a laser. The width S of the groove 211 is 50 μm, and the depth T is 5 μm. The spacing D1 between adjacent grooves 211 is 0.5 mm (see...). FIG. 7 , FIG. 8 and FIG. 11 The length L1 of the groove 211 is 6.7 mm, the distance D2 between the lowest point of the groove 211 and the negative electrode current collector 21 is 10 μm, the groove 211 is mainly distributed in the arc segment 24 of the negative electrode sheet 20; the thickness of the single-sided negative electrode active layer is 15 μm.

[0106] The prepared positive electrode 10, separator 30, and negative electrode 20 are stacked and wound to form a wound electrode body 100. Then, through encapsulation, baking, electrolyte injection, formation, secondary sealing, sorting, and OCV, a lithium-ion secondary battery 1000 is obtained. Here, the thickness H of the wound electrode body is 4.71 mm.

[0107] The electrolyte is a commercially available conventional electrolyte, and the lithium salt in it is LiFP6.

[0108] It should be noted that other forming processes of the positive sheet 10 and the negative sheet 20 are conventional means in the art, and the materials involved are conventional materials available on the market, which will not be described here.

[0109] Example 1-2

[0110] The difference from Example 1-1 is that the width W of the recess 111 on the positive sheet 10 is 8.3 mm, the included angle a1 of the first side wall 1113 with the positive current collector 12 is 49.8°, the included angle a2 of the second side wall 1114 with the positive current collector 12 is 49.7°, and the thickness of the single-sided positive active layer 11 is 25.1 μm; on the negative sheet 20, the width S of the groove 211 is 150 μm, the depth T is 20 μm, the distance D1 between adjacent grooves 211 is 2.51 mm, the length L1 of the groove 211 is 13.2 mm, and the distance D2 between the lowest part of the groove 211 and the negative current collector 21 is 5 μm; the thickness of the single-sided negative active layer 21 is 25 μm.

[0111] Example 1-3

[0112] The difference from Example 1-1 is that the width W of the recess 111 on the positive sheet 10 is 9.2 mm, the included angle a1 of the first side wall 1113 with the positive current collector 12 is 80°, the included angle a2 of the second side wall 1114 with the positive current collector 12 is 79.6°, and the thickness of the single-sided positive active layer 11 is 39.9 μm; on the negative sheet 20, the width S of the groove 211 is 249 μm, the depth T is 35 μm, the distance D1 between adjacent grooves 211 is 5 mm, the length L1 of the groove 211 is 19.2 mm, and the distance D2 between the lowest part of the groove 211 and the negative current collector 21 is 4.98 μm; the thickness of the single-sided negative active layer 21 is 40 μm.

[0113] Example 1-4

[0114] The difference from Example 1-1 is that the grooves 211 on the negative sheet 20 are distributed on the straight section 23 and the circular arc section 24 at the same time (see FIG. 9 and FIG. 10 ), and the distance D3 between adjacent groove sections is 0.35 mm. The distance L3 (the length sum of the groove sections) is 1380.4 mm, so that the edge of the groove is kept away from the edge of the negative active material layer, and the length L2 of the negative active layer is 1385.1 mm.

[0115] Example 1-5

[0116] The difference from Example 1-2 is that the grooves 211 on the negative sheet 20 are distributed on the straight section 23 and the circular arc section 24 at the same time (see FIG. 9 and FIG. 10), the interval D3 of the adjacent groove segments is 5.13 mm. The time interval L3 (the length of the plurality of groove segments and) is 1250.3 mm. The length L2 of the negative electrode active layer is 1253.4 mm so as to keep the edge of the groove away from the edge of the negative electrode active material layer.

[0117] Examples 1-6

[0118] The difference from Example 1-3 is that, on the negative electrode tab 20, the grooves 211 are distributed on both the flat section 23 and the circular arc section 24 (see FIG. 9 and FIG. 10 ), the interval D3 of the adjacent groove segments is 9.97 mm. The time interval L3 (the length of the plurality of groove segments and) is 1339.8 mm. The length L2 of the negative electrode active layer is 1341.2 mm so as to keep the edge of the groove away from the edge of the negative electrode active material layer.

[0119] Example 2-1

[0120] The difference from Example 1-2 is that, on the positive electrode tab 10, the width W of the recessed part 111 is 16 mm, and on the negative electrode tab 20, the length L1 of the groove is 40 mm.

[0121] This group of examples (Examples 3-1 to 3-3) is used to verify the influence brought by the change of "the height difference between the highest point and the lowest point of the rough surface of the bottom of the recessed part 111 within the range of 2*2 mm 2 ", and "the height difference between the highest point and the lowest point of the rough surface of the side wall of the recessed part 111 within the range of 0.2*0.2 mm 2 ".

[0122] This group of examples is implemented with reference to Example 1-2, except that the height difference between the highest point and the lowest point of the rough surface is regulated by controlling the "scanning parameters (such as laser power, etc.) when the recessed part 111 is formed by laser".

[0123] Example 3-1

[0124] The difference from Example 1-2 is that the height difference between the highest point and the lowest point of the rough surface of the bottom of the recessed part 111 within the range of 2*2 mm 2 is 1 μm, and the height difference between the highest point and the lowest point of the rough surface of the side wall within the range of 0.2*0.2 mm 2 is 1 μm.

[0125] Example 3-2

[0126] The difference from Example 1-2 is that the height difference between the highest point and the lowest point of the rough surface of the bottom of the recessed part 111 within the range of 2*2 mm 2 is 10 μm, and the height difference between the highest point and the lowest point of the rough surface of the side wall within the range of 0.2*0.2 mm 2The height difference between the highest point and the lowest point in the range is 10 pm.

[0127] Example 3-3

[0128] The difference from Example 1-2 is that the bottom rough surface of the recess 111 is 2*2 mm 2 The height difference between the highest point and the lowest point in the range is 12 pm, and the height difference between the highest point and the lowest point in the range is 12 pm. 2 The height difference between the highest point and the lowest point in the range is 12 pm.

[0129] The present group of examples (Examples 4-1 and 4-2) is to verify the influence brought by the change of the angles a1 and a2 of the first side wall 1113 and the second side wall 1114 of the recess 111 with the positive current collector 12, respectively.

[0130] The present group of examples is carried out with reference to Example 1-2, except that a1 and a2 are regulated by controlling “the scanning parameters (such as laser power) when laser forming the recess 111, etc.”

[0131] Example 4-1

[0132] The difference from Example 1-2 is that the angle a1 of the first side wall 1113 with the positive current collector 12 is 2°, and the angle a2 of the second side wall 1114 with the positive current collector 12 is 2°.

[0133] Example 4-2

[0134] The difference from Example 1-2 is that the angle a1 of the first side wall 1113 with the positive current collector 12 is 86.9°, and the angle a2 of the second side wall 1114 with the positive current collector 12 is 87.1°.

[0135] The present group of examples is carried out with reference to Example 1-2, except that L1 is regulated by controlling “the scanning parameters (such as scanning length) when laser forming the recess 111, etc.”

[0136] Example 5-1

[0137] The difference from Example 1-2 is that the length L1 of the groove 211 is 8.34 mm.

[0138] Example 5-2

[0139] The difference from Example 1-2 is that the length L1 of the groove 211 is 18.1 mm.

[0140] Example 5-3

[0141] The difference from Example 1-2 is that the length L1 of the groove 211 is 6.9 mm.

[0142] Comparative Example 1

[0143] The difference from Examples 1-2 is that the recess 111 is not provided.

[0144] Comparative Example 2

[0145] The difference from Examples 1-2 is that the width W of the recess 111 is 7 mm.

[0146] Comparative Example 3

[0147] The difference from Examples 1-2 is that the angle a1 of the first side wall 1113 of the recess 111 with the positive current collector 12 is 90°, and the angle a2 of the second side wall 1114 with the positive current collector 12 is 90°.

[0148] The batteries of the examples and comparative examples were tested according to the following test methods.

[0149] 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 rate of 2C 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 with a precipitation area accounting for more than 70% of the circular arc area was defined as very severe lithium precipitation, a precipitation area accounting for 50% to 70% of the circular arc area was defined as severe lithium precipitation, a precipitation area accounting for 30% to 50% of the circular arc area was defined as lithium precipitation, a precipitation 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.

[0150] Test conditions and evaluation criteria for separator rupture: the batteries were charged and discharged 100 times at a rate of 2C 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, and 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.

[0151] Test conditions and evaluation criteria for electrode fracture: the batteries were charged and discharged 800 times at a rate of 2C under constant temperature conditions of 25°C ± 3°C, and after 800 charge-discharge cycles, the batteries were disassembled and observed for negative electrode fracture. No cracks in the negative electrode indicated that the negative electrode had not fractured.

[0152] Table 1 is the test results of each example and comparative example.

[0153] Table 1 Test Results

[0154]

[0155]

[0156] As can be seen from Table 1, the recess is arranged at the arc segment of the positive plate, the lithium precipitation at the bending part can be well relieved and avoided, and the first side wall and the second side wall are arranged in a slope shape, so that the diaphragm can be avoided from being cut.

Claims

1. A wound electrode body, characterized in that, The electrode body comprises a positive electrode sheet, a negative electrode sheet, and a separator arranged in a stacked and wound manner. The positive electrode sheet and the negative electrode sheet are wound together with the separator to form a wound electrode body having a flat portion and a curved portion. The positive electrode sheet has a straight section located in the flat portion and an arcuate section located in the curved portion. The positive electrode sheet includes a positive current collector and a positive active layer disposed on the positive current collector. The positive active layer has a recess located at least partially in the arcuate section. The thickness of the positive active layer in the arcuate section is less than its thickness in the straight section. The recess includes a first sidewall and a second sidewall opposite to each other along the length direction of the positive electrode sheet. Both the first sidewall and the second sidewall are sloped.

2. The wound electrode body according to claim 1, characterized in that, The wound electrode body has a thickness H, and the recessed portion has a width W along the length direction of the positive electrode sheet. The thickness H and the width W satisfy: 3.14×H / 2-2mm≤W≤3.14×H / 2+2 mm.

3. The wound electrode body according to claim 1, characterized in that, The surface of the recess includes a rough surface.

4. The wound electrode body according to claim 3, characterized in that, The rough surface is 2×2 mm 2 The height difference between the highest and lowest points within the range is 1 μm to 10 μm.

5. The wound electrode body according to claim 1, characterized in that, The first sidewall forms an angle α1 with the positive current collector, and the second sidewall forms an angle α2 with the positive current collector, wherein the angles α1 and α2 are between 35° and 80°.

6. The wound electrode body according to any one of claims 1 to 5, characterized in that, The negative electrode sheet has a straight section located in the flat portion and an arc section located in the curved portion. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed thereon. The negative electrode active layer is provided with at least one groove, and the at least one groove is located at least partially in the arc section of the negative electrode sheet.

7. The wound electrode body according to claim 6, characterized in that, Each slot has a width S, each slot has a depth T, adjacent slots have a spacing D1, and the lowest point of each slot has a spacing D2 with the negative current collector. The width S ranges from 50 μm to 250 μm, the depth T ranges from 5 μm to 35 μm, the spacing D1 ranges from 0.5 mm to 5 mm, and the spacing D2 ranges from 3 μm to 10 μm.

8. The wound electrode body according to claim 6, characterized in that, The length direction of each slot is parallel to the length direction of the negative electrode sheet; and / or The at least one groove extends along the winding direction of the wound electrode body and ends in the arc segment or the straight segment.

9. The wound electrode body according to claim 8, characterized in that, The recessed portion has a width W along the length direction of the positive electrode sheet, and the at least one groove has a length L1. The width W and the length L1 satisfy: W≤L1≤W+10mm.

10. The wound electrode body according to claim 8, characterized in that, The at least one groove extends through the arc segment and is located in the straight segment.

11. The wound electrode body according to claim 10, characterized in that, Along the length direction of the negative electrode sheet, the distance between the two ends of the at least one groove is L3, the negative electrode active layer has a length L2, and the distance L3 and the length L2 satisfy: L2-10 mm≤L3≤L2.

12. The wound electrode body according to claim 10, characterized in that, Each slot includes multiple slot segments arranged along the length of the negative electrode sheet, wherein: The multiple slot segments are connected end-to-end; or... The plurality of groove segments are staggered along the width direction of the negative electrode sheet; or, The plurality of slots are arranged at intervals along the length of the negative electrode sheet, and two adjacent slots have a spacing D3, the value of which ranges from 0.2 mm to 10 mm.

13. The wound electrode body according to claim 12, characterized in that, Along the winding direction of the wound electrode body, the end of each groove segment is located in the straight section of the negative electrode sheet.

14. A lithium-ion secondary battery, characterized in that, Includes a wound electrode body according to any one of claims 1 to 13.

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