Cathode sheet, electrochemical device, and electronic device

Abstract

This application discloses a cathode sheet, an electrochemical device, and an electronic device. The cathode sheet includes a current collector, a first active material layer, and a second active material layer. The first active material layer is disposed on the current collector and includes a plurality of first material portions and a plurality of second material portions alternately distributed along a second direction. Each first material portion has a first groove, and each second material portion has a second groove. The compaction density at the bottom of the first groove is C1, and the compaction density at the bottom of the second groove is C2, where C2 < C1. The second active material layer is disposed on a second base surface. The cathode sheet is used to form a wound battery cell. The first material portions are located in the straight section of the cathode, and the second material portions are located inside the curved section of the cathode. This increases the contact area between the active material of the cathode sheet and the electrolyte, reduces the risk of cracking or detachment of the active material, thereby reducing the risk of short circuit in the electrochemical device and improving the cycle performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a cathode plate, an electrochemical device, and an electronic device. Background Technology

[0002] In some technologies, the energy density of electrochemical devices such as batteries is improved by compacting the active material. Furthermore, grooves are formed on the active material layer using an embossing process to increase the contact area between the cathode active material and the electrolyte, thereby improving lithium plating. However, the embossed grooves can lead to excessive compaction density of the active material at the bottom of the groove. When this is located in the corner area of ​​a wound cell, the stress concentration on the inner side of the corner can easily cause the active material to crack or detach. This not only increases the risk of short circuits in the electrochemical device but also affects its cycle performance. Utility Model Content

[0003] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a cathode sheet that can be used in electrochemical devices. By increasing the contact area between the active material of the cathode sheet and the electrolyte, it can reduce the risk of cracking or detachment of the active material, thereby reducing the risk of short circuit in the electrochemical device and improving the cycle performance of the electrochemical device.

[0004] This application also proposes an electrochemical device including the aforementioned cathode plate.

[0005] This application also proposes an electronic device including the above-described electrochemical device.

[0006] The cathode sheet according to the first aspect of this application includes a current collector, a first active material layer, and a second active material layer.

[0007] The current collector has two first base surfaces and a second base surface that are opposite to each other in a first direction, the first direction being parallel to the thickness direction of the cathode sheet;

[0008] The first active material layer is disposed on the first base surface. The active material layer includes a plurality of first material portions and a plurality of second material portions alternately distributed along a second direction, which is parallel to the length direction of the cathode sheet. The first material portion has a first groove, and the second material portion has a second groove. The compaction density at the bottom of the first groove is C1, and the compaction density at the bottom of the second groove is C2, where C2 < C1. The second active material layer is disposed on the second base surface. The cathode sheet is used to be wound together with the anode sheet and the separator to form a wound cell with a straight region and a corner region. The cathode sheet is formed into a straight cathode section located in the straight region and a bent cathode section located in the corner region. The first material portion is located in the straight cathode section, and the second material portion is located inside the bent cathode section.

[0009] The cathode sheet according to the embodiments of this application has at least the following beneficial effects:

[0010] In this embodiment, the compaction density at the bottom of the first groove is C1, and the compaction density at the bottom of the second groove is C2, where C2 < C1. When the cathode sheet of this embodiment is used to wind a battery cell, the second material portion is located inside the bent section of the cathode, meaning the compaction density inside the bent section is smaller, and the gaps between particles in the active material are larger. Therefore, stress can be effectively released when compressed, thereby effectively suppressing the cracking and shedding of the active material inside the corner area. Thus, using the cathode sheet of this embodiment in an electrochemical device can reduce the risk of cracking or shedding of the active material by increasing the contact area between the active material of the cathode sheet and the electrolyte, thereby reducing the risk of short circuits in the electrochemical device and improving the cycle performance of the electrochemical device.

[0011] According to some embodiments of this application, the compaction density at the edge of the second groove is greater than the compaction density at the edge of the first groove.

[0012] According to some embodiments of this application, a direction parallel to the width direction of the cathode sheet is defined as a third direction, the first groove extends along the third direction and penetrates the first material portion, and / or,

[0013] The second groove extends along a third direction and penetrates the second material portion.

[0014] According to some embodiments of this application, each of the second material portions has a plurality of second grooves spaced apart along the second direction, wherein the dimension of the second groove in the second direction is defined as the width, and the dimension in the first direction is defined as the depth.

[0015] In the second direction, the width of the plurality of second grooves distributed from the middle to both sides of each second material part gradually decreases.

[0016] According to some embodiments of this application, the second groove is formed by material removal processing, and in the second direction, the thickness of the plurality of second grooves distributed from the middle to both sides of each second material part gradually increases.

[0017] According to some embodiments of this application, the second active material layer includes a plurality of third material portions and a plurality of fourth material portions alternately distributed along the second direction. When the electrode is applied to a wound cell, the third material portions are located on the straight section of the cathode, and the fourth material portions are located on the outside of the curved section of the cathode.

[0018] The third material part has a third groove, the fourth material part has a fourth groove, the compaction density at the bottom of the three grooves is C3, the compaction density at the bottom of the fourth groove is C4, and C4 < C3.

[0019] According to some embodiments of this application, the first groove is a groove formed by embossing on the first material portion, and the second groove is a groove formed by laser processing on the second material portion.

[0020] According to some embodiments of this application, in the first direction, the size of the first groove is H1, the size of the second groove is H2, and 3≤H1 / H2≤25.

[0021] An electrochemical device according to a second aspect of this application includes: an anode sheet, a separator, and a cathode sheet according to a first aspect. The cathode sheet, the separator, and the anode sheet are stacked and wound to form a wound structure. The wound structure includes a straight region and corner regions located on both sides of the straight region. The straight region includes a cathode straight section formed by the cathode sheet, and the corner regions include a cathode curved section formed by the cathode sheet. A first material portion is located in the cathode straight section, and a second material portion is located inside the cathode curved section.

[0022] The electrochemical device according to the embodiments of this application has at least the following beneficial effects:

[0023] The cathode sheet using the first aspect embodiment has a first material portion with a first groove and a second material portion with a second groove. The compaction density at the bottom of the first groove is C1, and the compaction density at the bottom of the second groove is C2, where C2 < C1. The second material portion is located inside the bent section of the cathode, meaning the compaction density inside the bent section is lower, and the gaps between particles in the active material are larger. Therefore, it can effectively release stress when compressed, thereby effectively suppressing the cracking and shedding of the active material inside the corner area. Therefore, compared to conventional technologies, this solution can reduce the risk of cracking or shedding of the active material while increasing the contact area between the active material and the electrolyte, thereby reducing the risk of short circuits in the electrochemical device and improving the cycle performance of the electrochemical device.

[0024] An electronic device according to a third aspect of this application includes an electrochemical device according to a second aspect of this application.

[0025] The electronic device according to the embodiments of this application has at least the following beneficial effects:

[0026] The electrochemical device of the second aspect embodiment has higher safety and better cycle performance, thereby making the electronic device of this embodiment safer and longer service life.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The present application will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0029] Figure 1 This is a cross-sectional view of a first structure of a cathode sheet according to a first aspect embodiment of this application;

[0030] Figure 2 This is a cross-sectional view of a second structure of the cathode sheet according to the first aspect of this application;

[0031] Figure 3 This is a schematic diagram of a third structure of the cathode sheet according to the first aspect of this application;

[0032] Figure 4 This is a cross-sectional view of a fourth structure of the cathode sheet according to the first aspect of this application.

[0033] Figure 5 This is a schematic diagram of the structure of the battery cell in the electrochemical device according to the second aspect of this application;

[0034] Figure 6 for Figure 5 A magnified view of area A in the middle.

[0035] Figure label:

[0036] Current collector 100, first base plane 110, second base plane 120;

[0037] First active material layer 200, first material portion 210, first groove 211, first bottom 212, first edge 213, second material portion 220, second groove 221, second bottom 222, second edge 223;

[0038] Second active material layer 300, third material part 310, third groove 311, third bottom 312, fourth material part 320, fourth groove 321, fourth bottom 322;

[0039] The straight section is 400°, and the cathode straight section is 410°.

[0040] Corner area 500, cathode bending section 510. Detailed Implementation

[0041] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0042] In the description of this application, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and 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. Therefore, they should not be construed as limitations on this application.

[0043] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0044] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0045] Definitions:

[0046] Cell Balance (CB) is a core design parameter, essentially the ratio of the capacity of the negative electrode active material to that of the positive electrode active material under the same stage and conditions. A CB value that is too low may lead to lithium plating on the negative electrode, and lithium dendrites may puncture the separator, causing a short circuit; a CB value that is too high will result in wasted negative electrode material and a decrease in energy density. Furthermore, a reasonable CB value can alleviate stress concentration during cycling.

[0047] In some technologies, the energy density of electrochemical devices such as batteries is improved by compacting the active material. Based on this, grooves are formed on the active material layer through embossing to increase the contact area between the cathode active material and the electrolyte, thereby reducing lithium plating. However, the grooves formed by embossing can lead to excessive compaction density of the active material at the bottom of the grooves. The cathode active material is formed by coating a mixture of active particles (such as ternary materials and lithium iron phosphate), binders (such as PVDF), and conductive agents (such as carbon black) onto a metal current collector. Compaction reduces the gaps between particles and between particles and the current collector through mechanical force, increasing density to optimize conductivity and energy density. However, it also reduces the space occupied by the binder. Higher compaction density results in less elastic space for the binder and a higher proportion of rigid contact between particles, transforming the entire active material layer from a "slightly deformable flexible structure" into a "rigid structure with weak deformation resistance." When it is located in the corner area of ​​a wound cell, the inner area of ​​the corner is subjected to stress concentration, which can easily cause the active material to crack or fall off. This not only increases the risk of short circuit in the electrochemical device, but also affects the cycle performance of the electrochemical device.

[0048] In view of the above background, this application proposes a cathode sheet that can be used in an electrochemical device to reduce the risk of powder shedding in the corner area 500, thereby reducing the risk of short circuit in the electrochemical device and improving the cycle performance of the electrochemical device.

[0049] Reference Figure 1 and Figure 5 The cathode sheet of the first aspect of this application is used to be wound together with the anode sheet and the separator to form a wound battery cell. The wound battery cell includes a flat region 400 and corner regions 500 located on both sides of the flat region 400. Specifically, the cathode sheet, the separator, and the anode sheet are stacked sequentially and wound together by a winding device to form a wound battery cell (e.g., ...). Figure 5 As shown in the diagram, the straight region 400 is the portion of the stacked structure in the wound cell that maintains parallel extension, and the corner region 500 is the arc-shaped region formed at the bend of the wound cell. The cathode sheet of this embodiment includes a current collector 100 and an active material. The cathode sheet of this embodiment includes a current collector 100, a first active material layer 200, and a second active material layer 300.

[0050] The current collector 100 can be a metal foil or a composite current collector 100. For example, as a metal foil, it can be aluminum with a silver-plated surface, stainless steel with a silver-plated surface, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel, or titanium, etc. The composite current collector 100 can include a polymer material base layer and a metal layer. The composite current collector 100 can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.). The current collector 100 has a first base surface 110 and a second base surface 120 facing away from each other in a first direction, the first direction being parallel to the thickness direction of the cathode sheet. A first active material layer 200 is disposed on a first base surface 110, and a second active material layer 300 is disposed on a second base surface 120. Both the first active material layer 200 and the second active material layer 300 are formed by coating and rolling with a positive electrode active material. The first active material layer 200 and the second active material layer 300 can be the same material or different materials. The positive electrode active material includes one or more of lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. Examples of lithium phosphates include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds.

[0051] The first active material layer 200 includes a plurality of first material portions 210 and a plurality of second material portions 220 alternately distributed along a second direction parallel to the length direction of the cathode sheet. Each first material portion 210 has a first groove 211, which can be any shape, such as circular, square, or triangular, and can also be arranged in an array along the second and third directions. Each second material portion 220 has a second groove 221, which can also be any shape, such as circular, square, or triangular, and can also be arranged in an array along the second and third directions. The compaction density at the bottom of the first groove 211 is C1, and the compaction density at the bottom of the second groove 221 is C2, where C2 < C1. For clarity, the positive electrode active material at the bottom of the first groove 211 is defined as the first bottom 212, and the positive electrode active material at the bottom of the second groove 221 is defined as the second bottom 222, and these are separately labeled in the accompanying drawings. For example, the first groove 211 is formed by an embossing process, and the second groove 221 is formed by laser processing. Both embossing and laser processing are common processing methods in the present invention, and this embodiment does not make any improvements to them. During the embossing process, the positive electrode active material can be squeezed so that the compaction density of the positive electrode active material at the bottom of the first groove 211 is greater than that of other areas. However, laser processing does not squeeze the positive electrode active material, so that the compaction density of the positive electrode active material at the bottom of the second groove 221 is the same as that of other areas, thereby achieving the goal of C2 < C1. In addition, by selecting different support platforms (the platform used to place the cathode sheet in this embodiment during embossing), the flatness of the surface of the second active material layer 300, which is set opposite to the first active material layer 200, can be achieved. For example, when the support platform is rigid, the surface of the second active material layer 300 is flat; if a support platform with a certain degree of flexibility is used, a protrusion can be formed on the second active material layer 300 during embossing, thereby increasing the contact area between the second active material layer 300 and the electrolyte. The second groove is formed by laser processing. Laser processing removes some of the positive electrode active material. When this material is used to wind the battery cell, it can increase the CB value of this area, thereby improving the lithium plating situation.

[0052] Specifically, in this embodiment, the cathode sheet is used to be wound together with the anode sheet and the separator to form a wound battery cell having a straight region 400 and a corner region 500. The cathode sheet forms a straight cathode section 410 located in the straight region 400 and a bent cathode section 510 located in the corner region 500. The first material portion 210 is located in the straight cathode section 410, and the second material portion 220 is located inside the bent cathode section 510 (the side of the bent section 510 closer to the winding center is the inside side; in the following embodiment, the outside side is the side of the bent section 510 facing away from the winding center). Since the compaction density at the bottom of the first groove 211 is C1 and the compaction density at the bottom of the second groove 221 is C2, C2 < C1. Therefore, when the cathode sheet of this embodiment is used to wind a battery cell, the second material portion 220 is located inside the bent cathode section 510, that is, the compaction density inside the bent cathode section 510 is smaller, which means the gap between particles in the active material is larger. Therefore, using the cathode sheet of this embodiment in an electrochemical device can reduce the risk of cracking or falling off of the active material by increasing the contact area between the active material of the cathode sheet and the electrolyte, thereby reducing the risk of short circuit in the electrochemical device and improving the cycle performance of the electrochemical device.

[0053] It should be noted that the rectangular structure of the first groove 211 and the second groove 221 in the attached drawings should not be interpreted as the only limitation of this embodiment. The first groove can be any shape, such as circular, square, or triangular, and can also be distributed in rows along the second and third directions. Similarly, the second groove 221 can be any shape, such as circular, square, or triangular, and can also be distributed in rows along the second and third directions, as long as the compaction density of the second bottom 222 is less than the compaction density of the first bottom 212.

[0054] Reference Figure 2 In some embodiments, the compaction density at the edge of the second groove 221 is greater than that at the edge of the first groove 211. Specifically, during the manufacturing process of lithium battery winding cells, due to the geometric deformation of the material (inner layer shrinkage, outer layer stretching tendency is limited) and the radial component concentration of the winding tension in the corner region 500, stronger compression occurs between the layers in the corner region 500. That is, when the cathode sheet of the embodiment is used for winding the cell, the curved section located in the corner region 500 will be subjected to greater compression by the separator. The higher compaction density at the edge of the second groove 221 can effectively resist external compression, thereby reducing the risk of positive electrode active material falling off at the edge of the second groove 221, further reducing the risk of short circuit in the electrochemical device and improving the cycle performance of the electrochemical device.

[0055] To illustrate this more clearly, the positive electrode active material in the edge region of the first groove 211 is defined as the first edge 213, and the positive electrode active material in the edge region of the second groove 221 is defined as the second edge 223, and they are separately labeled in the accompanying drawings.

[0056] Reference Figure 3 In some embodiments, the direction parallel to the width direction of the cathode sheet is defined as the third direction. The first groove 211 extends along the third direction and penetrates the first material portion 210. Therefore, when the cathode sheet of this embodiment is used in an electrochemical device, the electrolyte can enter the first groove 211 from the side of the first material portion 210, thereby improving the electrolyte wetting efficiency. Similarly, in some embodiments, the second groove 221 extends along the third direction and penetrates the second material portion 220.

[0057] Reference Figure 4 In some embodiments, each second material portion 220 has a plurality of second grooves 221 spaced apart along a second direction. The dimension of the second groove 221 in the second direction is defined as its width, and its dimension in the first direction is defined as its depth. In the second direction, the width of the plurality of second grooves 221 distributed from the middle to both sides of each second material portion 220 gradually decreases. Specifically, during the winding of the battery cell, after winding, the winding needle needs to be removed and hot-pressed for shaping. Since the winding needle has a certain thickness, a semi-elliptical structure is formed in the bending area after the winding needle is removed. Therefore, for the bending section, the radius of curvature in the middle region is smaller and gradually increases towards both sides. Based on this, in the second direction, the width of the second groove 221 in the middle is larger, which facilitates providing a larger stress buffer space in the middle region with a larger curvature, thereby reducing the risk of the positive electrode active material falling off.

[0058] Reference Figure 4 In some embodiments, the second groove 221 is formed by laser processing or machining. In the second direction, the thickness of the multiple second grooves 221 distributed from the middle to both sides of each second material part 220 gradually increases, thereby making the area of ​​the inner wall surface of each second groove 221 nearly uniform. On the other hand, this allows for a uniform distribution of the wetting area of ​​the electrolyte in each groove, improving the uniformity of ion transport efficiency. Furthermore, making the volume of each second groove 221 nearly uniform, which is equivalent to making the removal of positive electrode active material nearly uniform, ensures the CB value of the entire bending section, thereby improving the lithium plating situation in the bending section.

[0059] It should be noted that laser processing or machining are common processing methods in the present invention, and this embodiment does not make any improvements to them.

[0060] Reference Figure 1In some embodiments, the second active material layer 300 includes a plurality of third material portions 310 and a plurality of fourth material portions 320 alternately distributed along a second direction. When the cathode sheet is applied to a wound cell, the third material portions 310 are located on the straight section 410 of the cathode, and the fourth material portions 320 are located outside the curved section 510 of the cathode. The third material portions 310 have a third groove 311, and the fourth material portions 320 have a fourth groove 321. The compaction density at the bottom of the third groove 311 is C3, and the compaction density at the bottom of the fourth groove 321 is C4, where C4 < C3. Exemplarily, the third groove 311 is formed by embossing on the third material portion 310, and the fourth groove 321 is formed by laser processing of the fourth material portion 320.

[0061] Specifically, the positive electrode active material is formed by coating a mixture of active particles (such as ternary materials and lithium iron phosphate), binders (such as PVDF), and conductive agents (such as carbon black) onto a metal current collector 100. During compaction, mechanical force reduces the gaps between particles and between particles and the current collector 100, increasing density to optimize conductivity and energy density. However, it also reduces the space occupied by the binder. The higher the compaction density, the smaller the elastic space of the binder, and the higher the proportion of rigid contact between particles. The entire active material layer changes from a "flexible structure that can be slightly deformed" to a "rigid structure with weak resistance to deformation." In the wound cell, the back side of the bent section is subjected to a certain tensile stress. Due to the insufficient flexibility of the binder and the disappearance of gaps between particles, the compacted active material layer cannot disperse stress through small deformations, resulting in tensile stress concentrated in a local area on the back side. When the concentrated stress exceeds the bonding strength between active particles (or the tensile strength of the particles themselves), the bonding interface between particles will break, leading to the fracture of the active material layer. In this embodiment, the compaction density C4 at the bottom of the fourth groove 321 is lower than the compaction density C3 at the bottom of the third groove 311, which effectively releases the stress on the active material at the bottom of the fourth groove 321. This reduces the risk of the second active material layer 300 breaking in the bending section, improving the cycle life and safety of the battery cell. Meanwhile, the higher compaction density C3 at the bottom of the third groove 311 ensures the energy density of the electrochemical device. Therefore, when the cathode sheet of this embodiment is used in an electrochemical device, it can effectively alleviate the problem of cracking of the active material layer caused by stress concentration during the winding process while ensuring the energy density of the electrochemical device.

[0062] To illustrate this more clearly, the positive electrode active material in the bottom region of the third groove 311 is defined as the third bottom 312, and the positive electrode active material in the bottom region of the fourth groove 321 is defined as the fourth bottom 322, and they are separately labeled in the accompanying drawings.

[0063] In some embodiments, the compaction density at the edge of the third groove 311 is greater than the compaction density at the edge of the fourth groove 321. This is based on the same principle as the compaction density at the edge of the second groove 221 being greater than the compaction density at the edge of the first groove 211, and will not be elaborated further here.

[0064] Furthermore, in some embodiments, the first active material layer 200 and the second active material layer 300 have the same structure, that is, each fourth material portion 320 has a plurality of fourth grooves 321 spaced apart along the second direction. In the second direction, the width of the plurality of fourth grooves 321 distributed from the middle to the sides of each fourth material portion 320 gradually decreases. The fourth grooves 321 are formed by laser processing or machining. In the second direction, the thickness of the plurality of fourth grooves 321 distributed from the middle to the sides of each fourth material portion 320 gradually increases, and the principle is similar to that of the first active material layer 200, which will not be repeated here. It should be noted that the identical structure does not mean that the first active material layer 200 and the second active material layer 300 are symmetrically arranged about the current collector 100. The first active material layer 200 and the second active material layer 300 may have different dimensions in the second direction.

[0065] In some embodiments, the first groove 211 is a groove formed by embossing on the first material portion 210, and the second groove 221 is a groove formed by laser processing on the second material portion 220. In the first direction, the size of the first groove 211 is H1, and the size of the second groove 221 is H2, where 3 ≤ H1 / H2 ≤ 25. Specifically, when the depth of the embossed first groove 211 is too large and the depth of the laser-processed second groove 221 is small, and the depth of the embossed first groove 211 is too large, a high protrusion will be formed on the back side of the first groove 211, thereby affecting the overall fit of the cathode sheet after winding in this embodiment, and thus affecting the energy density of the electrochemical device. When the depth of the first groove 211 is too small, the gap in the corner area of ​​the cell is too small, increasing the risk of lithium plating. When the depth of the first groove 211 is too small and the depth of the second groove 221 is too large, the contact area between the electrolyte and the electrode sheet is insufficient, resulting in high cell impedance and affecting the improvement of corner lithium plating. Based on this, in this embodiment, 3≤H1 / H2≤25 is set, and the depth of the first groove 211 and the depth of the second groove 221 are set within a suitable range, so that the electrochemical device has a high energy density, while reducing the resistance during lithium ion transport and reducing the risk of lithium plating at the anode corner.

[0066] Further, in some embodiments, the total cross-sectional area of ​​the second groove 221 of each second material part 220 along a third direction is S, that is, each second material part 220 has only one second groove 221, and S is the area of ​​the cross-section of one second groove 221. When each second material part 220 has multiple second grooves 221, S is the total cross-sectional area of ​​the multiple second grooves 221. The first active material layer 200 has a dimension D in the first direction, a dimension W in the second direction, and a dimension L in the third direction, that is, the thickness of the first active material layer 200 is D, the length is W, the width is L, and 1% ≤ (S×L) / (D×W×L) ≤ 3%. Specifically, S×L is the volume of positive electrode active material removed by laser cleaning, and D×W×L is the total volume of the first active material layer 200. Removing too much positive electrode active material will lead to a decrease in the energy density of the electrochemical device; removing too little will not effectively relieve stress. Based on this, in this embodiment, 1% ≤ (S×L) / (D×W×L) ≤ 3% is set so that the volume ratio of the removed active material is within a reasonable range, which can effectively release stress, inhibit crack propagation, and maintain the integrity of the electrode structure and energy density to the maximum extent.

[0067] To verify the above effects, the following experiment was conducted. The total cross-sectional area S of the second groove 221 of each second material part 220 along the third direction was 0% to 5%, and the parts were divided into 5 groups. Coronavirus sheets were prepared for each group, and 1000 cells were produced for each group. The lithium-ion soft-pack cell production process was carried out normally, including liquid injection, formation, capacity testing, secondary sealing, and voltage testing. During the winding process, 10 cells from each group were disassembled to observe whether powder was falling off at the corners of the cathode sheet. After secondary sealing, 3 cells from each group were taken, charged and discharged at 0.5C for 600 cycles, and then fully charged and disassembled to observe whether lithium was deposited at the anode corners. The experimental results are shown below:

[0068] Example 1 2％ 8.57 5074 14.2 no no Example 2 1％ 8.57 5082 14.4 no no Example 3 3％ 8.57 5063 13.9 no no Example 4 2％ 5 5072 14.1 no no Example 5 2％ 25 5073 14.0 no no Comparative Example 1 0％ 8.57 5081 15.3 yes yes Comparative Example 2 5％ 8.57 5044 14.1 no no Comparative Example 3 2％ 1 5070 15.4 no yes Comparative Example 4 2％ 40 5069 15.1 no yes

[0069] As can be seen from Examples 1-3 and Comparative Examples 1-2, when the total S percentage of the cross-section of the second groove 221 of each second material part 220 along the third direction is between 1% and 3%, the cathode bending section 510 of the cell does not shed powder, and after 600 cycles, the long-cycle anode corner position does not deposit lithium, and the corresponding cell impedance is also relatively small. This proves that when 1% ≤ (S×L) / (D×W×L) ≤ 3%, the cathode sheet powder shedding situation can be effectively improved, the lithium ion transport path can be shortened, and the risk of lithium deposition at the anode corner corresponding to this position can be reduced.

[0070] As can be seen from Examples 1, 4-5, and Comparative Examples 3-4, when the ratio H1 / H2 of the depth of the first groove 211 and the depth of the second groove 221 is in the range of 3 to 25, the cell impedance is small and no lithium plating occurs after long cycling. However, when the ratio of H1 / H2 is outside the range of 3 to 25, the impedance increases and lithium plating occurs. This proves that when 3 ≤ H1 / H2 ≤ 25, the lithium ion transport path can be shortened and the risk of lithium plating at the corresponding anode corner can be reduced.

[0071] Reference Figure 5 and Figure 6 The electrochemical device according to the second aspect of this application includes any device in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy. Specific, non-limiting examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0072] The electrochemical device of this embodiment includes an anode sheet, a separator, and a cathode sheet according to the first aspect embodiment. The cathode sheet, separator, and anode sheet are stacked and wound to form a wound structure. The wound structure includes a straight region 400 and corner regions 500 located on both sides of the straight region 400. The straight region 400 includes a cathode straight section 410 formed by the cathode sheet, and the corner region 500 includes a cathode curved section 510 formed by the cathode sheet. A first material portion 210 is located in the cathode straight section 410, and a second material portion 220 is located inside the cathode curved section 510. The first material portion 210 of the cathode sheet has a first groove 211, and the second material portion 220 has a second groove 221. The compaction density at the bottom of the first groove 211 is C1, and the compaction density at the bottom of the second groove 221 is C2, where C2 < C1. The second material section 220 is located inside the cathode bending section 510, meaning the compaction density inside the cathode bending section 510 is lower and the gaps between particles in the active material are larger. Therefore, it can effectively release stress when compressed, thereby effectively suppressing the cracking and detachment of the active material inside the corner region 500. Therefore, compared to conventional technology, this embodiment can reduce the risk of cracking or detachment of the active material while increasing the contact area between the cathode active material and the electrolyte, thereby reducing the risk of short circuits in the electrochemical device and improving the cycle performance of the electrochemical device. It should be noted that since this embodiment adopts all the technical features of the first aspect embodiment, it possesses all the beneficial effects brought by the first aspect embodiment.

[0073] The electronic device according to the third aspect of this application can be any electronic device known in the prior art, including but not limited to mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robotic dogs, industrial robots, and android robots. The electronic device includes the electrochemical device of the second aspect embodiment. Because electrochemical devices offer higher safety and superior cycle performance, the electronic device of this embodiment has higher safety and a longer service life.

[0074] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of this application. Furthermore, in the description of this application, the reference to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., means that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A cathode plate, characterized in that, include: The current collector has a first base surface and a second base surface facing away from each other in a first direction, the first direction being parallel to the thickness direction of the cathode sheet; A first active material layer is disposed on the first base surface. The active material layer includes a plurality of first material portions and a plurality of second material portions that are alternately distributed along a second direction. The second direction is parallel to the length direction of the cathode sheet. The first material portion has a first groove, and the second material portion has a second groove. The compaction density at the bottom of the first groove is C1, and the compaction density at the bottom of the second groove is C2, where C2 < C1. A second active material layer is disposed on the second base surface; The cathode sheet is used to be wound together with the anode sheet and the separator to form a wound cell having a straight region and a corner region, and the cathode sheet forms a straight cathode section located in the straight region and a bent cathode section located in the corner region. The first material part is located in the straight cathode section and the second material part is located inside the bent cathode section.

2. The cathode sheet according to claim 1, characterized in that, The compaction density at the edge of the second groove is greater than that at the edge of the first groove.

3. The cathode sheet according to claim 1, characterized in that, A direction parallel to the width direction of the cathode sheet is defined as the third direction, and the first groove extends along the third direction and penetrates the first material portion, and / or, The second groove extends along a third direction and penetrates the second material portion.

4. The cathode sheet according to claim 1, characterized in that, Each of the second material portions has a plurality of second grooves spaced apart along the second direction, wherein the dimension of the second groove in the second direction is defined as the width, and the dimension in the first direction is defined as the depth; In the second direction, the width of the plurality of second grooves distributed from the middle to both sides of each second material part gradually decreases.

5. The cathode sheet according to claim 4, characterized in that, The second groove is formed by material removal processing, and in the second direction, the thickness of the multiple second grooves distributed from the middle to both sides of each second material part gradually increases.

6. The cathode sheet according to claim 1, characterized in that, The second active material layer includes a plurality of third material portions and a plurality of fourth material portions that are alternately distributed along the second direction. When the cathode sheet is applied to the wound cell, the third material portions are located on the straight section of the cathode, and the fourth material portions are located on the outside of the curved section of the cathode. The third material part has a third groove, the fourth material part has a fourth groove, the compaction density at the bottom of the three grooves is C3, the compaction density at the bottom of the fourth groove is C4, and C4 < C3.

7. The cathode plate according to any one of claims 1 to 6, characterized in that, The first groove is formed by embossing on the first material part, and the second groove is formed by laser processing on the second material part.

8. The cathode sheet according to claim 7, characterized in that, In the first direction, the size of the first groove is H1, the size of the second groove is H2, and 3 ≤ H1 / H2 ≤ 25.

9. An electrochemical device, characterized in that, include: Anode plate; Separating membrane; The cathode sheet according to any one of claims 1 to 8 is stacked and wound with the separator and the anode sheet to form a wound structure, the wound structure including a straight region and corner regions located on both sides of the straight region, the straight region including a cathode straight section formed by the cathode sheet, the corner region including a cathode curved section formed by the cathode sheet, the first material part being located in the cathode straight section, and the second material part being located inside the cathode curved section.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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