Pole piece for forming wound electrode assembly and wound electrode assembly of secondary battery

Abstract

The application relates to a pole piece for forming a wound electrode assembly and a wound electrode assembly of a secondary battery. The pole piece comprises a current collector layer and an active substance layer, wherein the active substance layer is coated on at least one surface of the current collector layer; the active material layer comprises at least two target areas, the target areas correspond to the bent parts of the winding type electrode assembly, each target area comprises a plurality of grooves formed in the active material layer, the grooves extend in the width direction of the pole piece, each groove is provided with a top end and a bottom end, and the top ends and the bottom ends are arranged in the grooves. And the section width of the groove in the thickness direction of the pole piece is gradually reduced from the top end to the bottom end. According to the pole piece, the grooves are formed in the target area of the active material layer, so that the extrusion stress of the active material layer in the bending area after winding is reduced, the fracture risk in the hot pressing process can be reduced, and the problem of light transmission is avoided.

Description

Technical Field

[0001] This application relates to the field of secondary batteries, and more specifically to an electrode assembly for forming a wound electrode assembly and a secondary battery. Background Technology

[0002] Rechargeable batteries play a crucial role in today's energy storage field, widely used in various electronic devices and electric vehicles. In the manufacturing process of rechargeable batteries, the winding and hot-pressing process has a significant impact on battery performance and quality. However, within this process, as the coating density increases, the compaction design also becomes increasingly demanding. During the manufacturing of wound cells, after hot pressing, the inner ring of the wound cell may become translucent or break, which has a serious impact on cell safety.

[0003] Furthermore, there are certain limitations in the selection of materials and the manufacturing process of positive electrode sheets. To achieve both high energy density and high rate capability, while increasing the areal density of the electrode sheet, its thickness must also be further controlled, which leads to a continuous increase in compaction density. As a result, problems such as cracking and wrinkling can easily occur during the winding and hot pressing process, leading to light transmission.

[0004] These problems not only affect the finished product quality and appearance of secondary batteries, but may also cause a series of serious consequences such as increased internal resistance, accelerated capacity decay, and reduced safety, which greatly limit the improvement of secondary battery performance and the expansion of its application scope. Utility Model Content

[0005] This application addresses the problem of light transmission caused by easy breakage during the hot pressing process of battery winding. It proposes a winding electrode assembly for forming electrode sheets of a winding electrode assembly and a secondary battery, which can solve and alleviate the problem of breakage of the inner ring electrode sheet of the winding core during hot pressing.

[0006] The technical solution adopted in this application to solve the above-mentioned technical problems is an electrode sheet for forming a wound electrode assembly, comprising: a current collector layer and an active material layer, wherein the active material layer is coated on at least one surface of the current collector layer; the active material layer includes at least two target regions, the target regions corresponding to the bent portions of the wound electrode assembly, the target regions including a plurality of grooves formed in the active material layer, the grooves extending along the width direction of the electrode sheet, the grooves having a top end and a bottom end, and the cross-sectional width of the grooves in the thickness direction of the electrode sheet gradually decreasing from the top end to the bottom end.

[0007] In one embodiment of this application, a thinning portion is provided between two adjacent grooves, the thickness of which is less than or equal to the coating thickness of the active material layer.

[0008] In one embodiment of the present application, the thinning portion has a bottom close to the current collector layer and a top far from the current collector layer, and the cross-sectional width of the thinning portion in the thickness direction of the electrode sheet gradually increases from the top to the bottom.

[0009] In one embodiment of the present application, there is a spacing between the plurality of grooves, and the plurality of spacings are equal or unequal.

[0010] In one embodiment of the present application, from the middle of the target area to both sides, the spacing gradually increases or decreases.

[0011] In one embodiment of the present application, the bottom end is located on the current collector layer or on the active material layer.

[0012] In one embodiment of the present application, the top end of the groove has a first cross-sectional width W1 in the thickness direction of the electrode sheet, and there is a spacing W3 between adjacent grooves, where 0 < W1 ≤ 2 mm, and / or, 0 < W3 ≤ 5 mm.

[0013] In one embodiment of the present application, W1 = W3, or, W1 < W3.

[0014] In one embodiment of the present application, the bottom end of the groove has a second cross-sectional width W2 in the thickness direction of the electrode sheet, where W2 = 0, and W1 = W3.

[0015] The present application also provides a wound electrode assembly for a secondary battery to solve the above technical problems. The wound electrode assembly is wound by the electrode sheet as described above. The wound electrode assembly includes a bending portion. Among them, the active material layer located on the inner circle is separated by the groove in the bending portion to form a plurality of gaps, and the width of the gap is greater than or equal to 0.

[0016] For the electrode sheet used to form the wound electrode assembly in the present application, by providing grooves in the target area of the active material layer, the extrusion stress in the bending area after the active material layer is wound is reduced, the fracture risk in the hot pressing process can be reduced, and thus the occurrence of light transmission problems can be avoided. The cross-sectional width of the groove gradually decreases from the top end to the bottom end, which is beneficial to cleaning the waste generated by grooving and ensuring the battery performance. The wound electrode assembly of the present application is wound by the electrode sheet of the present application, which can improve the electrochemical performance and cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To make the above objects, features, and advantages of the present application more obvious and understandable, the following detailed description of the specific embodiments of the present application is provided in conjunction with the accompanying drawings, where:

[0018] Figure 1 is a schematic diagram of an electrode sheet according to an embodiment of the present application;

[0019] Figure 2 yes Figure 1 A magnified cross-sectional view of region A along line BB;

[0020] Figure 3 This is a partial schematic diagram of a wound electrode assembly according to an embodiment of this application after the electrode sheet has been wound;

[0021] Figures 4-6 Partial cross-sectional views of the electrode sheet in three embodiments of this application are shown respectively. Detailed Implementation

[0022] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein, and therefore this application is not limited to the specific embodiments disclosed below.

[0024] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0025] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0026] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. In addition, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of this description. Moreover, this application should be understood not only through the actual terms used, but also through the meaning implied by each term.

[0027] The embodiments of this application are described below based on the accompanying drawings. However, the embodiments shown below are examples of electrode sheets used to embody the technical concept of this application, and the electrode sheets of this application are not specifically defined as follows. Furthermore, in order to facilitate understanding of the scope of the claims, the components corresponding to the components shown in the embodiments are assigned numbers to the components shown in the "Claims" and "Utility Model Content" columns. However, the components shown in the claims are not intended to be specific to the components of the embodiments. In particular, the dimensions, materials, shapes, and relative arrangements of the constituent components described in the embodiments are not intended to limit the scope of this application unless specifically stated otherwise, but are merely illustrative examples.

[0028] However, the dimensions or positional relationships of the components shown in the accompanying drawings are sometimes exaggerated for clarity. Therefore, in the following description, detailed descriptions of the same names and symbols representing the same or homogeneous components are appropriately omitted. Furthermore, the elements constituting this application may be multiple elements composed of the same components, thus allowing one component to function as multiple elements; conversely, multiple components may share the function of one component. Additionally, the content described in some embodiments and implementations can be applied to other embodiments and implementations. Furthermore, in this specification, "upper" is not limited to the case of being formed in contact with an upper surface, but also includes the case of being formed separately on top, and also includes the meaning of an intermediate layer between layers.

[0029] The electrode sheets of this application are suitable for forming secondary batteries, including but not limited to nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid (or lead-acid) batteries, lithium-ion batteries, polymer lithium-ion batteries, etc. The secondary batteries have wound electrode assemblies, also known as cores, made by winding the electrode sheets.

[0030] Figure 1 This is a schematic diagram of an electrode sheet according to an embodiment of this application. Figure 2 yes Figure 1 An enlarged cross-sectional view of region A along line BB. (Reference) Figure 1 and Figure 2As shown, the electrode tab 100 includes a current collector layer 110 and an active material layer 120, and the active material layer 120 is coated on at least one surface of the current collector layer 110. The active material layer 120 includes at least two target regions 210 corresponding to the bending portions of the wound electrode assembly, and the target regions 210 include a plurality of grooves 220 formed in the active material layer 120. The grooves 220 extend along the width direction D1 of the electrode tab 100. The grooves 220 have a top end 221 and a bottom end 222, and the cross-sectional width of the grooves 220 in the thickness direction D3 of the electrode tab 100 gradually decreases from the top end 221 to the bottom end 222.

[0031] As Figure 2 shown, the current collector layer 110 is a layered or sheet-like structure. The surface of the current collector layer 110 includes opposite first and second surfaces 111 and 112. The current collector layer 110 can be aluminum foil, copper foil or a composite current collector. The active material layer 120 is coated on the first surface 111. In some embodiments, the active material layer 120 is coated on the first surface 111 and the second surface 112. The active material layer 120 is generally coated on the surface of the current collector layer 110 with a uniform thickness. As Figure 2 shown, the coating thickness of the active material layer 120 is W4. In the thickness direction D3 of the electrode tab 100, the opening of the groove 220 has the characteristic of being larger at the top and smaller at the bottom. Specifically, in the cross-sectional view as Figure 2 shown, the top end 221 of the groove 220 has a first cross-sectional width W1 in the thickness direction D3 of the electrode tab 100, and the bottom end 222 of the groove 220 has a second cross-sectional width W2 in the thickness direction D3 of the electrode tab 100, and W1 > W2. In Figure 2 the shown embodiment, the cross-sectional shape of the groove 220 is an inverted trapezoid, that is, the opening size gradually decreases from the top end 221 to the bottom end 222.

[0032] It should be noted that using the cross-sectional width to represent the opening size of the groove 220 does not limit the specific shape of the groove 220. W1 > W2 can indicate that the opening area of the groove 220 at the top end 221 is larger than the opening area of the groove 220 at the bottom end 222. Figure 2

[0033] In some embodiments, 0 < W1 ≤ 2 mm. W1 is not equal to 0. In one embodiment, the maximum value of W1 is equal to 500 μm. For example, the value of W1 is 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1 mm, 1.5 mm, 2 mm, etc.

[0034] ​In some embodiments, the grooves 220 in the active material layer 120 are formed by laser grooving. By setting the cross-sectional shape of the grooves 220 to be larger at the top and smaller at the bottom, it is beneficial for the waste generated during laser grooving to be cleaned out of the grooves 220 and not to accumulate in the grooves 220. If there is waste in the grooves 220, after the core is formed, the presence of waste will cause internal short circuits or uneven local lithium intercalation, which will have an adverse effect on battery performance and battery life. Therefore, according to the electrode 100 of this application, the waste in the grooves can be easily cleaned, thereby helping to avoid the problems caused by waste.

[0035] like Figure 1 As shown, the electrode 100 also includes an empty foil region 130. The empty foil region 130 can be used directly as the electrode tab of the battery cell, or the empty foil region 130 can be die-cut to form an electrode tab. Figure 1 The diagram shows the width direction D1 and length direction D2 of the electrode 100. During the winding process to form the cell, the electrode 100 is wound along its length direction D2. Figure 3 This is a partial schematic diagram of a wound electrode assembly according to an embodiment of this application, after the electrode sheet has been wound. Figure 3 The structure of the electrode 100 after one winding is shown only, including the bent portion 310 and the planar portion 320. It is assumed that the first surface 111 of the current collector layer 110 is in the inner circle after bending, and the second surface 112 is in the outer circle. For an electrode without the groove 220, the active material layer 120a in the inner circle is compressed after bending. After the hot-pressing process of the battery cell is performed, the active material layer 120a in the inner circle may break or wrinkle, leading to light transmission. For multi-layer wound batteries, the active material layer 120a in the innermost circle experiences the greatest compressive stress.

[0036] In the embodiments of this application, such as Figure 3 As shown, the active material layer 120a on the first surface 111 has grooves 220a. This application creates multiple grooves 220a in the target area 210 of the electrode 100 corresponding to the bending portion 310, so that after the electrode 100 is wound, the active material layer 120a between adjacent grooves 220a is squeezed into the space of the groove 220a, and can even fill the space of the groove 220a. Due to the space provided by the grooves 220a, the compressive stress of the active material layer 120a after winding is reduced, which can reduce the risk of breakage during the hot pressing process, thereby avoiding light transmission problems.

[0037] based on Figure 3It is understood that after multiple windings, the bend 310 comprises an alternating stacked structure of multiple current collector layers 110 and active material layers 120. It is understood that the position of the target region 210 on the electrode 100 can be determined according to the number of winding layers, so that all the grooves 220 after winding correspond to the bend 310 of the core.

[0038] refer to Figure 3 As shown, in an embodiment where active material layers 120 are coated on both surfaces of the current collector layer 110, the active material layer 120b on the second surface 112 is located on the outer ring after being wound. This active material layer 120b is subject to tensile stress, which may cause it to break and shed powder during hot pressing. In some embodiments, by creating grooves 220b on the active material layer 120b on the second surface 112, the tensile stress is released more evenly, thereby avoiding the problem of breakage and powder shedding.

[0039] This application does not impose any restrictions on the positional and numerical relationships between the grooves 220a of the active material layer 120 on the first surface 111 and the grooves 220b of the active material layer 120b on the second surface 112. The position, spacing, and number of grooves 220a and 220b in the target area 210 can be determined through experiments to achieve the best stress relief effect.

[0040] In some embodiments, a thinning portion 230 is provided between two adjacent grooves 220, and the thickness of the thinning portion 230 is less than or equal to the coating thickness of the active material layer 120. Here, the coating thickness is... Figure 2 W4, as shown, represents the original thickness of the active material layer 120 when it is coated on the current collector layer 110.

[0041] exist Figure 2 In the embodiment shown, the thickness of the thinned portion 230 is equal to the coating thickness W4.

[0042] refer to Figure 2 As shown, in some embodiments, the thinning portion 230 has a bottom 232 near the current collector layer 110 and a top 231 away from the current collector layer 110, and the cross-sectional width of the thinning portion 230 in the thickness direction D3 of the electrode 100 gradually increases from the top 231 to the bottom 232.

[0043] In some embodiments, the groove 220 and the thinned portion 230 may be formed simultaneously in a single laser process.

[0044] refer to Figure 2 As shown, in some embodiments, W2=0. That is, the cross-sectional shape of the groove 220 is a triangle with the sharp corners pointing downwards, and the bottom 232 of the adjacent thinned portions 230 are almost continuous.

[0045] refer to Figure 2 As shown, there is a spacing W3 between adjacent grooves 220, and multiple spacings W3 can be equal or unequal. The spacing W3 can be the center-to-center spacing of two adjacent grooves 220, or the spacing between corresponding position points in two adjacent grooves 220. In some embodiments, 0 < W3 ≤ 5 mm. For example, the value of W3 is 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1 mm, 1.5 mm, 2 mm, 3 mm, 4 mm, 5 mm, etc. In some embodiments, 0 < W1 ≤ 2 mm, and 0 < W3 ≤ 5 mm.

[0046] As Figure 2 shown, in some embodiments, W1 < W3. According to these embodiments, for a substrate of the same length, it is equivalent to a relatively sparse opening density of the grooves 220, with fewer opening numbers, and more active substances can be retained to increase the battery capacity. In some other embodiments, W3 can also be less than W1. It is equivalent to a relatively dense opening density of the grooves 220, which is suitable for regions with a large degree of bending. In some embodiments, at the center of the bending portion, W3 < W1 can be set, and at both ends of the bending portion, W1 < W3 can be set. In this way, while avoiding breakage caused by winding, as much active substance as possible can be retained.

[0047] In some embodiments, W2 = 0, and W1 = W3. According to these embodiments, the cross-sectional shape of the groove 220 and the cross-sectional shape of the thinning portion 230 are basically complementary, and since W2 = 0, it is beneficial for adjacent thinning portions 230 to completely fit after winding, thus filling the space provided by the groove 220. In some embodiments, the width of the top 231 of the thinning portion 230 is greater than 0, and the cross-sectional shape of the thinning portion 230 is trapezoidal. In some embodiments, the width of the top 231 of the thinning portion 230 is also equal to 0, so that the groove 220 and the thinning portion 230 are completely complementary. At this time, the cross-sectional shape of the thinning portion 230 is triangular. Combining Figure 3 , where the cross-sectional shape of the thinning portion 2301 is basically trapezoidal, and the cross-sectional shapes of the thinning portions 2302 and 2303 are triangular.

[0048] In some embodiments, W1 = W3, and W2 > 0. According to these embodiments, the cross-sectional shape of the groove 220 and the cross-sectional shape of the thinning portion 230 are basically complementary. After winding, adjacent thinning portions 230 partially fit, and there is still a certain gap between them. This gap can provide space for the expansion of active substances during subsequent charge and discharge processes, which is beneficial to improving the electrochemical performance and cycle life of the battery.

[0049] Figure 3This also indicates that, on the same active material layer 120, the shape and size of each thinning section 230 can be designed according to its location after winding. The shape and size of each thinning section 230 can be different.

[0050] The electrode 100 of this application has multiple grooves 220 formed in the target region 210, that is, a portion of the active material layer 120 is retained in the target region 210, i.e., the thinned portion 230. Compared with the embodiment that completely removes all the active material layer 120 in the target region 210, the embodiment with multiple grooves 220 can retain more active material layer and improve the battery capacity.

[0051] refer to Figure 2 As shown, in some embodiments, the bottom end 222 of the groove 220 is located on the current collector layer 110. That is, the bottom of the groove 220 is the current collector layer 110 corresponding to the location of the groove 220. It should be noted that the depth of the groove 220 can be determined by controlling the parameters of the laser. For example, controlling the power of the laser; the higher the power, the deeper the groove 220. Another example is controlling the duration for which the laser stays at the groove 220; the longer the duration, the deeper the groove 220.

[0052] It should be noted that the process of forming the groove 220 on the electrode 100 of this application can be incorporated into the winding process. At this time, the electrode 100 continuously travels along its length direction D1, and the laser equipment is set at the corresponding station. By setting the laser's moving speed and optical power, grooves 220 can be formed on the electrode 100 during its movement. Figure 1 The groove 220 shown extends along the width direction D1.

[0053] In some embodiments, such as Figure 1 As shown, the groove 220 extends through the active material layer 120 along the width direction D1. In other embodiments, the extension length of the groove 220 along the width direction D1 is less than the length of the active material layer 120 along the width direction D1.

[0054] Combination Figure 3 As shown, in some embodiments, the spacing W3 gradually increases or decreases from the center of the target region 210 towards both sides. (See reference...) Figure 3As shown, the center of the target region 210 corresponds to the center of the bending portion 310, i.e., the region with the largest bending curvature. The two sides of the target region 210 correspond to the two sides of the bending portion 310, with smaller bending curvatures. According to these embodiments, for the inner ring active material layer 120a, the spacing gradually decreases from the center to both sides. This is because the space in the center is smaller or the length is shorter, so the spacing is larger, and the number of grooves 220a and thinning portions 230 is less; while the space on both sides is larger or the length is longer, so the spacing is smaller, and the number of grooves 220a and thinning portions 230 is more. For the outer ring active material layer 120b, the spacing gradually increases from the center to both sides. This is because the active material layer 120b in the center is subjected to greater tensile stress, so the spacing is smaller, i.e., the number of grooves 220b can be more, thus releasing more stress; while the active material layers 120b on both sides are subjected to less tensile stress, so the spacing is larger, i.e., the number of grooves 220b is less, thus releasing less stress. This ensures that the stress released by the bending section 310 is uniform throughout the whole.

[0055] Figures 4-6 Partial cross-sectional views of the electrode sheet in three embodiments of this application are shown respectively. Figures 4-6 perspective and Figure 2 Same. Reference Figure 4 As shown, in this embodiment, the coating thickness of the active material layer 120 is W41, and the thickness W42 of the thinned portion 230 is less than W41. (Comparison) Figure 2 and Figure 4 ,form Figure 4 The method for thinning the thinned portion 230 can be to reduce the spacing W3 to W31. When the spacing is reduced, the laser beams forming adjacent grooves 220 are closer together, thereby allowing the thinned portion 230 to be further etched. Figure 4 In the embodiment shown, due to the smaller spacing W31, more grooves 220 can be formed in the target area 210.

[0056] exist Figure 5 In the embodiment shown, the spacing W32 is greater than Figure 4 The spacing W31 in the middle means that the number of grooves 220 and thinning portions 230 formed in the same target area 210 is relatively small.

[0057] Figure 4 and Figure 5 The cross-sectional shape of the thinned portion 230 shown is triangular.

[0058] exist Figure 6In the illustrated embodiment, the bottom end 222 of the groove 220 is located within the active material layer 120. According to this embodiment, the groove 220 has a relatively shallow depth, allowing for the use of a lower-power laser device for grooving, thus reducing equipment costs. Furthermore, the thickness W42 of the active material layer 120 is less than... Figure 5 W41. This is because the groove 220 is relatively shallow, allowing the active material layer 120 below the bottom 222 of the groove 220 to be retained. The total volume of the active material layer 120 is related to the battery capacity. Since part of the active material layer 120 is retained at the bottom of the groove 220, the coating thickness of the active material layer 120 can be reduced to W42 in order to obtain the same battery capacity.

[0059] for Figures 4-6 In the embodiments shown, the laser grooving process can be matched to the production site of the core during the production process. By controlling parameters such as the speed and power of the laser, the grooving process will not affect the die-cutting time of the electrode 100 and the core, and will not affect the core efficiency.

[0060] According to the electrode 100 of this application, the problem of light transmission at the inner corner bend after hot pressing of the wound cell is solved by forming a groove 220 in the active material layer 120. By precisely controlling the laser, the groove 220 and the thinning portion 230 can be formed and matched with the winding process, improving battery performance without affecting production efficiency.

[0061] This application also proposes a wound electrode assembly for a secondary battery, formed by winding the electrode sheets described above. The following references... Figure 3 This describes the wound electrode assembly. Although... Figure 3 Only a partial structure of one turn of the wound electrode assembly is shown, but based on Figure 3 The description can be used to explain the entire wound electrode assembly. For example... Figure 3 As shown, the wound electrode assembly includes a bent portion 310, wherein the active material layer 120a located in the inner ring is separated by grooves 220a in the bent portion 310 to form a plurality of gaps 240, the width of which is greater than or equal to 0. It should be noted that the gaps 240 are not the same as the grooves 220a. This is because the grooves 220a are a structural feature on the electrode 100, while the gaps 240 are a structural feature of the wound electrode assembly. After the electrode 100 is wound, the spacing between the active material layers 120a on both sides of the grooves 220a, i.e., the thinned portions 230, is compressed to form the gaps 240. It can be understood that when the gap is equal to 0, it is equivalent to the active material layers 120a between adjacent grooves 220a being in contact; when the gap is greater than 0, it indicates that the active material layers 120a between adjacent grooves 220a are not in contact.

[0062] It should be noted that after multiple charge-discharge cycles, the active material in a secondary battery expands, thus affecting the battery's electrochemical performance and cycle life. In embodiments with a gap greater than 0, space is provided for the expansion of the active material, which can improve the battery's electrochemical performance and cycle life.

[0063] While the foregoing disclosure has discussed various embodiments that are currently considered useful, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments. Rather, the claims are intended to cover all modifications and equivalent combinations that conform to the spirit and scope of the embodiments of this application. For example, although the system components described above can be implemented by hardware devices, they can also be implemented solely by software solutions, such as installing the described system on existing servers or mobile devices.

[0064] Similarly, it should be noted that, in order to simplify the description of the present application and thus aid in the understanding of one or more embodiments, the foregoing description of the embodiments of the present application sometimes combines multiple features into a single embodiment, drawing, or description thereof. However, this disclosure method does not imply that the subject matter of the present application requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of the single embodiments disclosed above.

[0065] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of scope in some embodiments of this application are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

Claims

1. An electrode sheet for forming a wound electrode assembly, characterized in that, Comprising: A current collector layer and an active material layer, the active material layer being coated on at least one surface of the current collector layer; The active material layer includes at least two target regions corresponding to the bent portions of the wound electrode assembly. The target regions include a plurality of grooves formed in the active material layer, the grooves extending along the width direction of the electrode tab. The grooves have a top end and a bottom end, and the cross-sectional width of the grooves in the thickness direction of the electrode tab gradually decreases from the top end to the bottom end.

2. The electrode sheet as described in claim 1, characterized in that, There is a thinning portion between two adjacent grooves, and the thickness of the thinning portion is less than or equal to the coating thickness of the active material layer.

3. The electrode sheet as described in claim 2, characterized in that, The thinning portion has a bottom portion close to the current collector layer and a top portion away from the current collector layer, and the cross-sectional width of the thinning portion in the thickness direction of the electrode tab gradually increases from the top portion to the bottom portion.

4. The electrode sheet as described in claim 1, characterized in that, There is a spacing between the plurality of grooves.

5. The electrode sheet as described in claim 4, characterized in that, From the middle of the target region to both sides, the spacing gradually increases or decreases.

6. The electrode sheet as described in claim 1, characterized in that, The bottom end is located on the current collector layer or in the active material layer.

7. The electrode sheet as described in claim 1, characterized in that, The top end of the groove has a first cross-sectional width W1 in the thickness direction of the electrode tab, and there is a spacing W3 between adjacent grooves, where 0 < W1 ≤ 2 mm, and / or, 0 < W3 ≤ 5 mm.

8. The electrode sheet as described in claim 7, characterized in that, W1 = W3, or, W1 < W3.

9. The electrode sheet as described in claim 7, characterized in that, The bottom end of the groove has a second cross-sectional width W2 in the thickness direction of the electrode tab, where W2 = 0, and W1 = W3.

10. A wound electrode assembly for a secondary battery, characterized in that, Wound from the electrode tab according to any one of claims 1-9, the wound electrode assembly includes a bent portion, wherein, The active material layer located on the inner circle is separated by the grooves at the bent portion to form a number of gaps, and the width of the gaps is greater than or equal to 0.

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