Battery

Abstract

The invention relates to the technical field of batteries, and discloses a battery which comprises a battery cell, a pole piece, a diaphragm and a negative pole piece, a protective layer is preferentially arranged on a positive pole current collector at a first positive pole arc section, a groove is formed in the corresponding position of the protective layer, the two ends of the groove extend to the two edges of the pole piece in the width direction, and the ratio of H2 to H1 is controlled to meet the following conditions: 0.12 H1 < = H2 < = 0.3 H1 and H2 = h1 + h2, h1 > = 0 [mu] m, and h2 > 0 [mu] m; 25 [mu] m < = H1 < = 60 [mu] m, and the risks of short circuit and self-discharge of the battery can be reduced.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to batteries. Background Technology

[0002] With the rapid development of new energy technologies, batteries are increasingly widely used in electronic devices, electric vehicles, and other fields, leading to increasingly higher requirements for their energy density and safety. Traditional wound lithium-ion batteries suffer from limited thickness due to the presence of a single-sided negative electrode area at the winding start and the presence of multiple ineffective separators designed to meet safety and manufacturability requirements. This restricts further improvements in battery energy density. To address this issue, researchers proposed an interlocking wound structure, which effectively improves the space utilization of the cell thickness by removing the ineffective thickness stacking at the winding start. However, during implementation, the first positive electrode arc segment experiences increased stress due to its larger curvature, increasing the risk of powder shedding from the positive electrode active layer. Once powder shedding produces tiny particles, these particles can easily puncture the adhesive tape and separator, triggering a micro-short circuit and causing self-discharge, ultimately negatively impacting battery safety. Summary of the Invention

[0003] Based on this, the present invention provides a battery to solve the problems of short circuit and self-discharge caused by stress accumulation in the first positive electrode arc segment of a wound battery cell.

[0004] In a first aspect, the present invention provides a battery, comprising: a battery cell, the battery cell including a positive electrode sheet, a separator, and a negative electrode sheet sequentially stacked and wound, the battery cell including a flat region and an arcuate region connected to both ends of the flat region; the positive electrode sheet including a first positive electrode flat segment, a first positive electrode arcuate segment, and a second positive electrode flat segment sequentially arranged along its winding starting direction, the end of the first positive electrode flat segment away from the first positive electrode arcuate segment being the positive electrode winding starting end of the positive electrode sheet; the negative electrode sheet including a first negative electrode flat segment located in the flat region, the first negative electrode flat segment being located between the first positive electrode flat segment and the second positive electrode flat segment along a first direction, the end of the first negative electrode flat segment facing the first positive electrode arcuate segment being the negative electrode winding starting end of the negative electrode sheet; the positive electrode sheet including a positive electrode current collector and a first positive electrode active layer disposed on a first surface of the positive electrode current collector, the first surface being close to the center of the battery cell, The first surface is provided with a protective layer, and the first positive electrode active layer includes a groove located in the first positive electrode arc segment, the bottom surface of the groove being the protective layer or the first positive electrode active layer; the projection of the groove along the thickness direction of the positive electrode sheet at least partially overlaps with the projection of the protective layer along the thickness direction of the positive electrode sheet; along the winding axis of the cell, both ends of the groove extend to the two edges of the positive electrode sheet respectively; the battery satisfies the following relationships: 0.12H1≤H2≤0.3H1, H2=h1+h2, h1≥0μm, h2>0μm; 25μm≤H1≤60μm; where h2 is the thickness of the protective layer along the thickness direction of the positive electrode sheet; h1 is the dimension between the bottom surface of the groove and the surface of the protective layer away from the positive electrode current collector along the thickness direction of the positive electrode sheet; H1 is the thickness of the first positive electrode active layer along the thickness direction of the positive electrode sheet.

[0005] In some embodiments, along the winding axis of the battery cell, both ends of the protective layer extend to the two edges of the positive electrode sheet; and / or, h1 > 0 μm, 0.01h2 ≤ h1 ≤ 0.5h2.

[0006] In some embodiments, the protective layer is a conductive coating or an insulating coating; and / or, 3μm≤h2≤15μm.

[0007] In some embodiments, insulating tape is provided in the groove; or, when the protective layer is an insulating coating, insulating tape may not be provided in the groove.

[0008] In some embodiments, the orthographic projection of the insulating tape onto the thickness direction of the positive electrode sheet and the orthographic projection of the groove onto the thickness direction of the positive electrode sheet have at least a partially non-overlapping area.

[0009] In some embodiments, the projections of the two ends of the insulating tape along the winding direction of the battery cell onto the first direction are respectively located on the first negative electrode straight section; preferably, the projections of the two ends of the insulating tape along the winding direction of the battery cell onto the first direction are staggered, and the stagger distance is D1, 1mm≤D1≤3mm, and / or; the protective layer is an insulating coating, and along the winding direction of the battery cell, the projections of the two ends of the protective layer onto the first direction are located on the first negative electrode straight section; preferably, the projections of the two ends of the protective layer along the winding direction of the battery cell onto the first direction are staggered, and the stagger distance is D2, 1mm≤D2≤3mm.

[0010] In some embodiments, a protrusion is provided at the junction of the groove and the outer surface of the first positive electrode active layer, and on the outer surface of the first positive electrode active layer. The height of the protrusion is F, 1μm≤F≤10μm; the distance between the protrusion and the end near the protective layer along the winding direction of the cell is W, 0mm≤W≤1mm; preferably, there are two protrusions, which are located on both sides of the groove, and the projections of the two protrusions in the first direction are both located on the straight section of the first negative electrode; the projections of the two protrusions in the first direction overlap, or the projections of the two protrusions in the first direction are staggered, and the stagger distance is D3, 1mm≤D3≤3mm.

[0011] In some embodiments, a protrusion is provided at the junction of the groove and the outer surface of the first positive electrode active layer or on the outer surface of the first positive electrode active layer. There are two protrusions. Along the first direction, the first negative electrode straight section is located between the two protrusions. The distance between each protrusion and the first negative electrode straight section is less than or equal to 1 mm.

[0012] In some embodiments, the groove is provided with insulating tape, and the end of the insulating tape is spaced apart from the protrusion along the winding direction of the battery cell.

[0013] In some embodiments, the distance between either end of the insulating tape and the adjacent protrusion is E, where 1mm ≤ E ≤ 5mm.

[0014] In some embodiments, along the winding axis of the battery cell, the positive current collector has notches at both edges of the first positive arc segment, and the two notches correspond to the two ends of the groove along the winding axis of the battery cell; along the winding direction of the positive electrode sheet, the width of the notch is greater than the width of the groove.

[0015] Compared with the prior art, the technical solution of the present invention has at least the following advantages: (1) A protective layer is first set on the positive current collector at the first positive arc segment, and a groove is set at the corresponding position of the protective layer. The two ends of the groove extend to the two edges of the electrode in the width direction. This setting can make the thickness transition of this area more gradual during the winding and bending process of the cell, which alleviates the problem of stress concentration and powder shedding caused by the thickness difference between the groove edge and the groove body area, thereby improving the self-discharge phenomenon of the battery. In addition, since the protective layer is pre-covered on the current collector, when the active material is subsequently removed by laser to form the groove, even if the laser action area extends to the edge of the electrode in the width direction, the protective coating can also serve as an effective buffer and protection layer to prevent the high-energy laser from directly damaging the edge of the current collector. This solves the problem that the laser scanning to the edge can easily damage the current collector and generate burrs in the prior art, and can further reduce the probability of battery micro short circuit.

[0016] (2) Controlling the ratio of H2 to H1 within the above range can ensure that the coating in this area has a certain thickness to absorb laser energy, thus avoiding damage to the foil by the laser and the generation of burrs; at the same time, it can also prevent the total thickness H2 of the protective coating (protective layer and possible residual active layer) from being too large, thus avoiding the generation of new bending stress when the protective coating is bent, thereby preventing the protective coating from being excessively squeezed and losing powder, thereby further reducing the risk of short circuit and self-discharge of the battery. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a cross-sectional view of a battery cell according to an embodiment of the present invention; Figure 2 This is a partially enlarged schematic diagram of the battery cell according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the positive electrode sheet according to an embodiment of the present invention; Figure 4 for Figure 3 A partially enlarged schematic diagram of the positive electrode plate; Figure 5 This is a partially enlarged schematic diagram of the positive electrode sheet according to another embodiment of the present invention; Figure 6 This is a top view of the positive electrode sheet according to an embodiment of the present invention; Figure 7 This is a schematic diagram of a positive electrode sheet according to another embodiment of the present invention; Figure 8 for Figure 7 A partially enlarged schematic diagram of the positive electrode plate; Figure 9 This is a schematic diagram of a positive electrode sheet according to another embodiment of the present invention; Figure 10 This is a schematic diagram of the positive electrode sheet according to another embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures: 10-Cell; 10a-Straight region; 10b-Circular arc region; 11-Positive electrode sheet; 11A-Starting end; 101-Positive current collector; 102-First positive active layer; 103-Groove; 104-Protrusion; 105-Notch; 111-First positive straight section; 112-First positive circular arc section; 113-Second positive straight section; 12-Negative electrode sheet; 12A-Negative winding starting end; 121-First negative straight section; 20-Protective layer; 30-Insulating tape; Y-Wound axis direction; Z-First direction; X-Length direction. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Traditional wound lithium-ion batteries have negative and positive electrodes wound in the same direction, with the initial section of the negative electrode being a single-sided negative electrode area. Furthermore, for safety manufacturing considerations of isolation and buffering, multiple layers of separators are often pre-installed at the beginning of the cell. These "ineffective" areas occupy valuable internal thickness space within the cell, directly reducing the battery's volumetric energy density. Moreover, this mechanically weak single-sided negative electrode area is prone to bending and coiling during the winding process and subsequent cycle expansion, potentially increasing the risk of separator damage and internal short circuits. To address this, researchers have proposed an interlocking wound cell structure. In this structure, the positive and negative electrodes begin winding from opposite sides of the winding axis, with their initial sections spatially interlocked and staggered. This design eliminates the "single-sided negative electrode area" of the traditional structure, allowing the negative electrode current collector to be symmetrically coated with active material on both sides along its winding direction; that is, the entire effective area of ​​the negative electrode is a "double-sided area." This design not only significantly improves the space utilization of electrode materials and battery energy density, but also eliminates the hidden dangers of bending and rolling caused by mechanical defects in the single-sided area, thereby simultaneously improving the safety and energy density of the battery.

[0022] In the winding head of a plug-in battery cell, because the starting end of the negative electrode faces the first positive electrode arc segment, adhesive tape is usually applied to the surface of the positive active layer of the first positive electrode arc segment to prevent lithium plating at this location and reduce the amount of lithium ions released. However, during the battery winding process, the first positive electrode arc segment is subjected to a huge accumulation of mechanical stress. This stress can easily cause microcracks or even peeling of the positive active material coating, producing fine active material particles. These detached particles may form sharp foreign objects during subsequent winding and compaction, which can not only pierce the adhesive tape that is supposed to provide protection, but may also further pierce the separator, thereby establishing a local electronic conductive channel between the positive and negative electrodes, forming a micro-short circuit that is difficult to detect. This micro-short circuit will cause continuous and unstable self-discharge of the battery, resulting in irreversible capacity decay and reduced cycle life, and also poses a potential safety hazard.

[0023] Research has shown that using a laser to remove part or all of the positive electrode active material in the first arc segment of the positive electrode reduces the thickness of the positive electrode active layer at the first arc, thereby reducing the problem of powder shedding caused by excessive compression of the active material during bending. However, due to the presence of laser radiation energy, the electrode edge is easily damaged, resulting in burrs that can further cause micro-short circuits. Therefore, to solve the problem of burrs at the electrode edge, an un-thinned area is usually set at the edge of the electrode when removing the active material at the first arc of the positive electrode. However, there will be a thickness difference between the edge of the groove and the main body of the groove. In actual applications, the presence of an un-thinned positive electrode active material layer at this location will further lead to stress accumulation. During winding and bending, the coating of the positive electrode at this location will be squeezed, making it easier to shed powder and generate free particles. These particles can puncture the separator and cause safety problems such as battery short circuits.

[0024] To address these issues, the following will be discussed in conjunction with... Figures 1 to 10 The following describes embodiments of the present invention.

[0025] According to an embodiment of the present invention, a battery is provided, including a cell 10, the cell 10 including a positive electrode 11, a separator (not shown) and a negative electrode 12 sequentially stacked and wound. Although the separator is not shown in the figure, it can be understood that a separator is sandwiched between each layer of positive electrode 11 and negative electrode 12, thereby preventing positive and negative short circuits.

[0026] The battery cell 10 includes a flat region 10a and an arc region 10b connecting the two ends of the flat region 10a. The positive electrode 11 includes a first positive electrode flat section 111, a first positive electrode arc section 112 and a second positive electrode flat section 113 arranged sequentially along its winding starting direction. The end of the first positive electrode flat section 111 away from the first positive electrode arc section 112 is the positive electrode winding starting end 11A of the positive electrode 11.

[0027] The negative electrode 12 includes a first negative electrode straight section 121 located in the straight region 10a. Along the first direction Z, the first negative electrode straight section 121 is located between the first positive electrode straight section 111 and the second positive electrode straight section 113. The end of the first negative electrode straight section 121 facing the first positive electrode arc section 112 is the negative electrode winding starting end 12A of the negative electrode 12, thus the cell 10 constitutes a plug-in wound cell. It can be understood that the first negative electrode straight section 121 and the first positive electrode straight section 111 extend in opposite directions. The first direction Z can be the thickness direction of the battery, i.e., the direction perpendicular to the large surface area of ​​the battery.

[0028] The positive electrode 11 includes a positive current collector 101 and a first positive active layer 102 disposed on a first surface of the positive current collector 101. The first surface is close to the center of the cell and has a protective layer 20. The first surface located on the first positive arc segment 112 faces the negative electrode winding start end 12A. The protective layer 20 is at least partially located on the first surface of the first positive arc segment 112. The protective layer 20 may extend beyond the first positive arc segment 112 into a straight section. Alternatively, the protective layer 20 may not extend beyond the first positive arc segment 112. The protective layer 20 can be applied to the first surface by coating. The X direction represents the length direction X of the cell.

[0029] The first positive electrode active layer 102 includes a groove 103 located in the first positive electrode arc segment 112. The bottom surface of the groove 103 is either the protective layer 20 or the first positive electrode active layer 102. When the bottom surface of the groove 103 is the protective layer 20, there is no residual first positive electrode active layer 102 in the groove 103. When the bottom surface of the groove 103 is the first positive electrode active layer 102, the bottom surface is a residual portion of the first positive electrode active layer 102. The groove 103 can be formed on the surface of the first positive electrode active layer 102 by laser surface scanning. During laser surface scanning, a portion of the first positive electrode active layer 102 can be retained to form the bottom surface of the groove, or the first positive electrode active layer 102 can be omitted, and the exposed protective layer 20 forms the bottom surface of the groove. It can be explained that the groove 103 can also be implemented in other ways, such as reducing the amount of active material coated in the arc region.

[0030] Along the winding axis Y of the cell 10, both ends of the groove 103 extend to the two edges of the positive electrode 11. That is, along the winding axis Y of the cell 10, the length of the groove 103 is equal to the width of the positive electrode 11. The winding axis Y of the cell 10 can be parallel to the width direction of the cell 10. The groove 103 can be formed on the surface of the first positive electrode active layer 102 by laser scanning.

[0031] The projection of the groove 103 along the thickness direction R of the positive electrode 11 at least partially overlaps with the projection of the protective layer 20 along the thickness direction R of the positive electrode 11, reducing the risk of burning the positive electrode current collector during laser surface scanning. This can be understood as the protective layer 20 covering part of the groove 103, or covering all of the groove 103. Preferably, the protective layer 20 covers all of the groove 103, further reducing the risk of burning the positive electrode current collector during laser surface scanning.

[0032] Therefore, when the groove 103 is formed on the first positive electrode active layer 102 by laser surface scanning, the protective layer 20 can absorb some of the laser energy, preventing the laser from burning the positive electrode current collector 101 and effectively protecting the positive electrode current collector 101. If the laser burns the positive electrode current collector 101, it will cause microcracks in the positive electrode current collector 101. These microcracks are prone to breakage of the positive electrode current collector 101 after being subjected to the battery cycle expansion stress. The broken positive electrode current collector 101 can easily puncture the separator and cause safety problems such as battery short circuit. When the first positive electrode active layer 102 remains in the groove 103, the remaining first positive electrode active layer 102 can protect both the protective layer 20 and the positive electrode current collector 101, thus providing double protection for the positive electrode current collector 101, further reducing the risk of breakage of the positive electrode current collector 101, thereby preventing battery short circuit. By extending both ends of the groove 103 along the winding axis Y of the cell 10 to the two edges of the positive electrode 11, i.e., through-scanning, this design eliminates the problem that the coating of the positive electrode is squeezed and more prone to powdering when winding and bending, caused by the thickness difference between the groove edge and the main groove area when the un-thinned area is set near the two edges of the positive electrode 11. This design can further improve safety issues such as battery short circuit caused by free particles piercing the separator.

[0033] The battery satisfies the following relationships: 0.12H1≤H2≤0.3H1, H2=h1+h2, h1≥0μm, h2>0μm; 25μm≤H1≤60μm; where h2 is the thickness of the protective layer 20 along the thickness direction R of the positive electrode sheet; h1 is the dimension between the bottom surface of the groove 103 and the surface of the protective layer 20 away from the positive electrode current collector 101 along the thickness direction R of the positive electrode sheet; H1 is the thickness of the first positive electrode active layer 102 along the thickness direction R of the positive electrode sheet.

[0034] H1 can be 25μm, 30μm, 40μm, 50μm, 60μm, or within any two of the above values.

[0035] H2 can be 0.12H1, 0.15H1, 0.2H1, 0.25H1, 0.3H1, or within any two of the above values.

[0036] Figure 4 This shows the case where h1 is greater than 0 μm. Figure 5This shows the case where h1 equals 0 μm.

[0037] By ensuring that H1 and H2 satisfy the above relationship, it can be ensured that the coating in this area has a certain thickness to absorb laser energy, avoiding damage to the foil caused by the laser and the generation of burrs; at the same time, it can also prevent the total thickness H2 of the protective coating (protective layer and possibly residual active layer) from being too large, avoiding the generation of new bending stress when the protective coating is bent, thereby preventing the protective coating from being excessively squeezed and losing powder, thereby further reducing the risk of short circuit and self-discharge of the battery.

[0038] In this invention, the test method for the dimension h1 between the bottom surface of the groove 103 and the surface of the protective layer 20 that is away from the positive current collector 101 includes: taking a cross-section of the electrode at that position, taking three samples at different positions, measuring their dimensions using SEM, and taking the average value.

[0039] In some embodiments, along the winding axis Y of the cell 10, both ends of the protective layer 20 extend to the two edges of the positive electrode 11. That is, the length of the protective layer 20 is equal to the width of the positive electrode 11.

[0040] When the laser channel forms the groove 103 on the first positive electrode active layer 102, the two edges of the positive electrode current collector 101 are easily burned by the laser, producing burrs. These burrs can easily puncture the separator, leading to a micro-short circuit, causing self-discharge, and affecting the cycle life of the battery. By extending from both ends of the protective layer 20 to the two edges of the positive electrode sheet 11, when the laser scan forms the groove 103 on the first positive electrode active layer 102, the protective layer 20 can effectively protect the two edges of the positive electrode sheet 11, preventing burns and burr formation on the edges of the positive electrode sheet 11, thus avoiding puncture of the separator and subsequent self-discharge.

[0041] In some embodiments, h1 > 0 μm, and 0.01h2 ≤ h1 ≤ 0.5h2.

[0042] h1 is greater than 0 μm. The groove 103 has a residual positive electrode active layer. The residual first positive electrode active layer 102 can protect the protective layer 20 and the positive electrode current collector 101, so that the positive electrode current collector 101 is protected by a double layer, further reducing the risk of breakage of the positive electrode current collector 101, thereby preventing the battery from short-circuiting.

[0043] h1 should not be too small, as it will not effectively protect the protective layer 20 and the positive electrode current collector 101. At the same time, it should not be too large, as this will still cause the positive electrode active layer to be squeezed and shed powder. The particles generated by this powder shedding can easily puncture the separator, leading to battery short circuits and self-discharge. Therefore, it is necessary to control h1 to be 0.01h2 ≤ h1 ≤ 0.5h2.

[0044] In some embodiments, the protective layer 20 is a conductive coating or an insulating coating.

[0045] The protective layer 20 may contain at least one of the following metal oxides: silicon dioxide, titanium dioxide, magnesium oxide, zirconium oxide, aluminum oxide, boehmite, cobalt tetroxide, etc.; the protective layer 20 may also contain at least one of the following polymers: polyethylene, phenolic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyimide (PI), polyacrylic acid (PAA) resin, etc.; the protective layer 20 may also contain at least one of the following adhesives: PVDF, PMMA, polyacrylic acid, fluorosulfonamide polymer, etc.

[0046] When the protective layer 20 is a conductive coating, the conductive coating may contain at least one of conductive carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes. The conductive coating may contain 60-80% metal oxide, 20-30% binder, and 5-10% conductive agent.

[0047] In some embodiments, 3μm≤h2≤15μm. h2 can be 3μm, 5μm, 8μm, 10μm, 12μm, 13μm, 15μm, or within any two of the above values.

[0048] When h2 is too large, the rigidity of the protective layer 20 is too high, and it is prone to brittleness during battery winding and battery cycle expansion, resulting in failure to protect the positive current collector 101 and easy breakage of the positive current collector 101. When h2 is too small, the protective layer 20 is too thin, and when the groove 103 is formed on the first positive active layer 102 by laser surface scanning, it is not enough to absorb more laser radiation heat, resulting in the positive current collector 101 being burned and easy to break. Therefore, it is necessary to control 3μm≤h2≤15μm.

[0049] In some embodiments, the groove 103 is provided with insulating tape 30. The insulating tape 30 can prevent the risk of short circuit with the first positive arc segment 112 caused by burrs or displacement that may exist at the negative electrode winding start end 12A; in addition, when there is residual positive electrode active layer in the groove 103, the insulating tape 30 can also prevent the residual positive electrode active layer from shedding powder, which would lead to battery self-discharge.

[0050] In some embodiments, when the protective layer 20 is an insulating coating, the groove 103 may not be provided with insulating tape 30. That is, the groove 103 may or may not be provided with insulating tape 30.

[0051] The protective layer 20 is an insulating coating. Even if the groove 103 does not contain insulating tape 30, it can still prevent a short circuit between the negative electrode winding start end 12A and the first positive electrode arc segment 112. It can also reduce costs, reduce space occupation, and help improve the volumetric energy density of the battery. Furthermore, the bottom surface of the groove 103 is the protective layer 20.

[0052] The protective layer 20 is an insulating coating. When the groove 103 is provided with insulating tape 30, and the bottom surface of the groove 103 is the positive electrode active layer, it can also prevent the positive electrode active layer from shedding powder, which would cause the battery to self-discharge.

[0053] In some embodiments, the orthographic projection of the insulating tape 30 on the thickness direction R of the positive electrode sheet and the orthographic projection of the groove 103 on the thickness direction R of the positive electrode sheet have at least a partially non-overlapping area. That is, the insulating tape 30 may be entirely located within the groove 103. Alternatively, a portion of the insulating tape 30 may be located within the groove 103.

[0054] When the insulating tape 30 is entirely located within the groove 103, the portion of the insulating tape 30 that does not cover the bottom surface of the groove 103 corresponds to the non-overlapping area. When a portion of the insulating tape 30 is located within the groove 103 and a portion is adhered to the surface of the first positive electrode active layer 102, the overlapping area between the insulating tape 30 and the surface of the first positive electrode active layer 102 corresponds to the non-overlapping area.

[0055] In one example, along the length of the positive electrode, when the width of the groove 103 is relatively large, for example, approximately equal to the width of the first positive electrode arc segment 112, or between 11mm and 25mm, the groove 103 has sufficient area for reliable adhesion of the insulating tape 30, ensuring bonding strength and preventing the insulating tape 30 from falling off. In this case, the width of the insulating tape 30 can be smaller than the width of the groove 103, and the insulating tape 30 is entirely located within the groove 103. Figure 7 As shown in the figure, this setting can avoid the insulation tape 30 being pasted on the positive electrode active layer, which would increase the total thickness of the cell and reduce the energy density, thus helping to improve the space utilization and energy density of the battery.

[0056] In another example, along the length of the positive electrode sheet, when the width of the groove 103 is small, for example, between 5mm and 10mm, the bonding area between the bottom surface of the groove 103 and the insulating tape 30 is small, which is not conducive to improving the bonding strength and makes it easy for the insulating tape 30 to fall off. In this case, it is preferable that the width of the insulating tape 30 is greater than the width of the groove 103, so that part of the insulating tape 30 is bonded inside the groove 103 and part is bonded to the surface of the first positive electrode active layer 102. Figure 9 As shown in the figure, this setting can prevent the insulating tape 30 from falling off, which could lead to a short circuit and self-discharge of the battery.

[0057] In some embodiments, refer to Figure 2 The projections of the two ends of the insulating tape 30 along the winding direction of the battery cell onto the first direction Z are respectively located on the first negative electrode straight section 121. That is, both ends of the insulating tape 30 along the winding direction of the battery cell extend to the straight section 10a.

[0058] This configuration ensures that the insulating tape 30 covers the first positive electrode arc segment 112, further preventing battery micro-short circuits caused by coating powder peeling due to stress accumulation in the first positive electrode arc segment.

[0059] Preferably, the two ends of the insulating tape 30 along the winding direction of the battery core are misaligned in the projection of the two ends in the first direction Z, and the misalignment distance is D1, where 1mm≤D1≤3mm. D1 can be 1mm, 1.5mm, 2mm, 2.5mm, 3mm, or within any two of the above values.

[0060] D1 should not be too large. If it is too large, one end of the insulating tape 30 may not cover the first positive electrode arc segment 112, which may lead to lithium plating and cause a short circuit in the battery. Therefore, it is necessary to have 1mm ≤ D1 ≤ 3mm.

[0061] The protective layer 20 is an insulating coating. Along the winding direction of the battery cell, the projections of both ends of the protective layer 20 in the first direction Z lie on the straight section 121 of the first negative electrode. This arrangement ensures that the protective layer 20 covers the arc section 112 of the first positive electrode, preventing high-energy laser damage to the edge of the current collector, thereby reducing burrs and microcracks and improving battery self-discharge.

[0062] Preferably, the projections of the two ends of the protective layer 20 along the winding direction of the battery cell onto the first direction Z are staggered, and the stagger distance is D2, where 1mm≤D2≤3mm. D2 can be 1mm, 1.5mm, 2mm, 2.5mm, 3mm, or within any two of the above values.

[0063] D2 should not be too large. If it is too large, one end of the protective layer 20 may not cover the first positive electrode arc segment 112, which may lead to lithium plating and cause a short circuit in the battery. Therefore, it is necessary to have 1mm ≤ D2 ≤ 3mm.

[0064] In some embodiments, a protrusion 104 is provided at the junction of the sidewall of the groove 103 and the first positive electrode active layer or on the outer surface of the first positive electrode active layer 102. The height of the protrusion 104 is F, where 1μm ≤ F ≤ 10μm, and F can be 1μm, 2μm, 3μm, 5μm, 7μm, 8μm, 10μm, or any two of the above values. The distance between the protrusion 104 and the end near the protective layer 20 along the winding direction of the battery cell is W, where 0mm ≤ W ≤ 1mm, and W can be 0mm, 0.2mm, 0.4mm, 0.5mm, 0.7mm, 0.8mm, 1mm, or any two of the above values. The height F of the protrusion 104 is the vertical distance between the highest point of the protrusion 104 and the surface of the first positive electrode active layer 102 along the thickness direction of the positive electrode sheet 11. When W is greater than 0, the distance W between the protrusion 104 and the end near the protective layer 20 is the minimum spacing distance between the protrusion 104 and the end near the protective layer 20 along the length direction of the positive electrode sheet; when W is equal to 0, the projection of the protrusion 104 on the thickness direction R of the positive electrode sheet overlaps with the end of the protective layer 20.

[0065] Preferably, there are two protrusions 104, which correspond to the two ends of the protective layer 20 along the winding direction of the battery cell. The projections of the two protrusions 104 in the first direction Z are both located on the straight section 121 of the first negative electrode. The projections of the two protrusions 104 in the first direction Z overlap, or the projections of the two protrusions 104 in the first direction Z are staggered, and the stagger distance is D3, where 1mm≤D3≤3mm. D3 can be 1mm, 1.5mm, 2mm, 2.5mm, 3mm, or within any two of the above values.

[0066] Preferably, along the first direction Z, the first negative electrode straight section 121 is located between two protrusions 104, and the distance between each protrusion 104 and the first negative electrode straight section 121 is less than or equal to 1 mm.

[0067] During the battery cycle expansion process, the protrusion 104 can clamp the first negative electrode straight section 121 and limit the first negative electrode straight section 121 to prevent the negative electrode winding start end 12A from shifting and causing it to puncture the separator and come into contact with the first positive electrode arc section 112, thus causing a battery short circuit.

[0068] In some embodiments, an insulating tape 30 is provided in the groove 103, and the end of the insulating tape 30 is spaced apart from the protrusion 104 along the winding direction of the battery cell. When there are two protrusions 104, one end of the insulating tape 30 is spaced apart from the adjacent protrusion 104, or both ends of the insulating tape 30 are spaced apart from the corresponding protrusion 104.

[0069] With this configuration, the insulating tape 30 avoids the protrusion 104, preventing the smooth surface of the insulating tape 30 from covering the protrusion 104 and affecting the limiting effect of the protrusion 104 on the first negative electrode straight section 121.

[0070] The distance between either end of the insulating tape 30 and the adjacent protrusion 104 is E, where 1mm ≤ E ≤ 5mm. E can be 1mm, 2mm, 3mm, 4mm, 5mm, or any two of these values. If E is too small, the insulating tape 30 may stretch and cover the protrusion 104 as the battery expands during cycling, affecting the limiting effect of the protrusion 104 on the straight section 121 of the first negative electrode. If E is too large, the bonding area between the insulating tape 30 and the bottom surface of the groove 103 may be insufficient, affecting the bonding strength. Therefore, 1mm ≤ E ≤ 5mm is required.

[0071] In some embodiments, refer to Figure 10 Along the winding axis Y of the battery cell, the positive current collector 101 has notches 105 on both edges of the first positive arc segment 112. The two notches 105 correspond to the two ends of the groove 103 along the winding axis Y of the battery cell. Along the winding direction of the positive electrode sheet, the width of the notch 105 is greater than the width of the groove 103.

[0072] The notch 105 can further eliminate the burrs on the edge of the positive electrode 11, preventing the burrs from piercing the separator and causing safety problems such as short circuits.

[0073] The shape of the notch 105 is preferably elliptical or semi-circular to avoid the risk of stress concentration caused by right-angle corners leading to electrode tearing.

[0074] Example 1: Battery preparation: (1) Preparation of positive electrode Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and conductive carbon (SuperP) are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 98:1:1 and stirred evenly to form a positive electrode slurry. This slurry is then uniformly coated onto both sides of the positive electrode current collector (aluminum foil) along its thickness direction. After drying and rolling, a positive electrode sheet 11 is formed. Before coating the positive electrode slurry, a protective layer 20 (polyvinylidene fluoride) is pre-coated onto the positive electrode current collector at the first arc of the positive electrode sheet, starting from the starting end of the winding of the positive electrode sheet. A portion of the positive electrode active material on the protective layer is removed by laser to form a groove 103. Along the width direction of the positive electrode sheet, both ends of the groove 103 extend to the two edges of the positive electrode sheet, and insulating adhesive paper 30 is adhered in the groove 103.

[0075] (2) Preparation of negative electrode Silicon-carbon composite material, graphite, conductive carbon black, polyacrylic acid, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 45:52:0.5:1.2:0.4:0.9, and then mixed evenly with deionized water to form a negative electrode slurry. This slurry is then evenly coated on both sides of the negative electrode current collector (copper foil) along its thickness direction to form a negative electrode active layer. After drying and rolling, the negative electrode sheet 12 is formed.

[0076] (3) Preparation of electrolyte The non-aqueous organic solvents were: 1M lithium hexafluorophosphate (LiPF6) as the lithium salt; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:1:1; a mixture of carboxylic acid ester solvents (ethyl propionate (EP) and propyl propionate (PP) in a mass ratio of 2:1:1, and fluoroethylene carbonate in a mass ratio of 10% based on the total amount of electrolyte); and fluoroethylene carbonate.

[0077] (4) Preparation of the diaphragm PP diaphragm is used.

[0078] (5) Battery assembly The positive electrode sheet prepared in step (1), the separator prepared in step (4), and the negative electrode sheet prepared in step (2) are stacked in sequence. The first straight section of the positive electrode sheet and the first straight section of the negative electrode sheet are wound in opposite directions to form a cell with a plug-in structure. The cell is then placed in a casing, and the electrolyte prepared in step (3) is injected into the dried and qualified cell. After processes such as standing, aging, formation, degassing, aging, and sorting, a lithium-ion battery is obtained. The structural parameters are shown in Table 1.

[0079] Other embodiments and comparative examples were prepared in accordance with Example 1, with different specific parameters as shown in Table 1, which will not be detailed here.

[0080] The difference between Comparative Example 3 and Example 1 is that no protective layer is provided on the positive current collector at the first arc.

[0081] The difference between Comparative Example 4 and Example 1 is that a portion of the positive electrode active material on the protective layer is removed by laser to form a groove. Along the width direction of the positive electrode sheet, the two ends of the groove do not extend to the two edges of the positive electrode sheet.

[0082] Test case 1. Short-term K-value testing method: At 25℃±2℃, discharge to the lower limit voltage at 0.2C, charge to 50% SOC at 0.7C, and then place at a high temperature of 45℃±3℃ for 2 days. Then place at room temperature of 25℃±3℃ for 2 days. The first voltage is measured with a voltmeter and recorded as V1 in mV, and the test time is recorded as T1. Then place at room temperature of 25℃±3℃ for 3 days and measure the second voltage V2 with a voltmeter in mV, and the test time is recorded as T2. The formula for calculating the short-term K value is K=V1-V2 / (T2-T1), with the unit being mV / H.

[0083] 2. Voltage drop ΔV test method (self-discharge): Under the environment of 25℃±2℃, discharge to the lower limit voltage at 0.2C, charge to the upper limit voltage at 0.7C (cut off at 0.025C), and record the voltage value V1 after standing in the Blue Electric test cabinet for 24 hours (1min sampling). Then, after standing for another 7 days, record the voltage value V2. Then the voltage drop ΔV = V1 - V2.

[0084] Table 1

[0085] As can be seen from the analysis in Table 1, by setting a protective layer on the positive current collector at the first positive arc segment, and setting a groove at the corresponding position of the protective layer, with both ends of the groove extending to the two edges of the electrode in the width direction, and controlling the ratio of H2 to H1 within the protection range, the risk of short circuit and self-discharge of the battery can be reduced.

[0086] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A battery, characterized in that, include: A battery cell, comprising a positive electrode, a separator, and a negative electrode arranged in sequence and wound together, the battery cell comprising a flat region and an arc region connected to both ends of the flat region; The positive electrode sheet includes a first positive electrode straight section, a first positive electrode arc section and a second positive electrode straight section arranged sequentially along its winding starting direction, and the end of the first positive electrode straight section away from the first positive electrode arc section is the positive electrode winding starting end of the positive electrode sheet. The negative electrode sheet includes a first negative electrode straight section located in the straight region. Along the first direction, the first negative electrode straight section is located between the first positive electrode straight section and the second positive electrode straight section. The end of the first negative electrode straight section facing the first positive electrode arc section is the negative electrode winding start end of the negative electrode sheet. The positive electrode sheet includes a positive current collector and a first positive active layer disposed on a first surface of the positive current collector. The first surface is close to the center of the cell and has a protective layer. The first positive active layer includes a groove located in the first positive arc segment, and the bottom surface of the groove is the protective layer or the first positive active layer. The projection of the groove along the thickness direction of the positive electrode sheet at least partially overlaps with the projection of the protective layer along the thickness direction of the positive electrode sheet. Along the winding axis of the cell, the two ends of the groove extend to the two edges of the positive electrode sheet, respectively. The battery satisfies the following relationships: 0.12H1≤H2≤0.3H1, H2=h1+h2, h1≥0μm, h2>0μm; 25μm≤H1≤60μm; where h2 is the thickness of the protective layer along the thickness direction of the positive electrode sheet; h1 is the dimension between the bottom surface of the groove and the surface of the protective layer away from the positive electrode current collector along the thickness direction of the positive electrode sheet; and H1 is the thickness of the first positive electrode active layer along the thickness direction of the positive electrode sheet.

2. The battery according to claim 1, characterized in that, Along the winding axis of the battery cell, both ends of the protective layer extend to the two edges of the positive electrode sheet; and / or, h1>0μm, 0.01h2≤h1≤0.5h2.

3. The battery according to claim 1, characterized in that, The protective layer is a conductive coating or an insulating coating; and / or, 3μm≤h2≤15μm.

4. The battery according to claim 3, characterized in that, The groove is provided with insulating tape; or, When the protective layer is an insulating coating, the groove may not contain insulating tape.

5. The battery according to claim 4, characterized in that, The orthographic projection of the insulating tape onto the thickness direction of the positive electrode sheet and the orthographic projection of the groove onto the thickness direction of the positive electrode sheet have at least a partially non-overlapping area.

6. The battery according to claim 4, characterized in that, The projections of the two ends of the insulating tape along the winding direction of the battery cell onto the first direction are respectively located on the straight section of the first negative electrode; preferably, the projections of the two ends of the insulating tape along the winding direction of the battery cell onto the first direction are staggered, and the stagger distance is D1, 1mm≤D1≤3mm, and / or; The protective layer is an insulating coating. Along the winding direction of the battery cell, the projections of the two ends of the protective layer in the first direction are located on the straight section of the first negative electrode. Preferably, the projections of the two ends of the protective layer along the winding direction of the battery cell in the first direction are staggered, and the stagger distance is D2, 1mm≤D2≤3mm.

7. The battery according to any one of claims 1-6, characterized in that, The groove has a protrusion at the junction of its sidewall and the outer surface of the first positive electrode active layer, or on the outer surface of the first positive electrode active layer. The height of the protrusion is F, where 1 μm ≤ F ≤ 10 μm. The distance between the protrusion and the end near the protective layer along the winding direction of the battery cell is W, where 0 mm ≤ W ≤ 1 mm. Preferably, there are two protrusions, located on opposite sides of the groove along the winding direction of the battery cell. The projections of the two protrusions in the first direction are both located on the straight section of the first negative electrode. The projections of the two protrusions in the first direction overlap, or the projections of the two protrusions in the first direction are staggered, with a stagger distance of D3, where 1 mm ≤ D3 ≤ 3 mm. And / or... The groove has two protrusions at the junction of its sidewall and the outer surface of the first positive electrode active layer or on the outer surface of the first positive electrode active layer. The first negative electrode straight section is located between the two protrusions along the first direction. The distance between each protrusion and the first negative electrode straight section is less than or equal to 1 mm.

8. The battery according to claim 7, characterized in that, The groove is provided with insulating tape, and the end of the insulating tape is spaced apart from the protrusion along the winding direction of the battery cell.

9. The battery according to claim 8, characterized in that, The distance between either end of the insulating tape and the adjacent protrusion is E, where 1mm ≤ E ≤ 5mm.

10. The battery according to claim 1, characterized in that, Along the winding axis of the battery cell, the positive current collector has notches on both edges of the first positive arc segment, and the two notches correspond to the two ends of the groove along the winding axis of the battery cell; along the winding direction of the positive electrode sheet, the width of the notch is greater than the width of the groove.

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