Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device.The electrochemical device comprises a positive electrode, a negative electrode and an isolating membrane located between the positive electrode and the negative electrode, the first face of the positive electrode is provided with an inwards-concave area, the second face of the positive electrode is provided with a protruding area corresponding to the inwards-concave area, and a gap is formed between the positive electrode and the negative electrode through the protruding area; and a gap is formed between the first surface of the anode and the cathode through the concave area.

Description

[0001] This application is a divisional application of application number 202280007758.0, filed on July 29, 2022, entitled "Electrochemical Device and Electronic Device". Technical Field

[0002] Embodiments of this disclosure relate to the field of electrochemical technology, and particularly to an electrochemical device and an electronic device. Background Technology

[0003] Electrochemical devices, such as ion batteries, have advantages such as good rate performance, light weight, long cycle life, no memory effect, and good stability, and are widely used. However, electrochemical devices typically expand during use, especially the negative electrode, which may lead to a reduction in cycle life. Summary of the Invention

[0004] This application proposes an electrochemical device and an electronic device that, by creating a gap between the positive and negative electrodes to reserve expansion space for the negative electrode, releases the cyclic expansion force and improves the cycle performance.

[0005] Some embodiments of this application propose an electrochemical device comprising: a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. The first surface of the positive electrode has a concave region, and the second surface of the positive electrode has a convex region corresponding to the concave region. A gap is formed between the second surface of the positive electrode and the negative electrode through the convex region; alternatively, a gap is formed between the first surface of the positive electrode and the negative electrode through the concave region. By buffering the expansion of the negative electrode through the gap between the positive and negative electrodes, the expansion force during the negative electrode cycling process is released, thereby preventing deformation of the electrochemical device and improving the cycling performance. Furthermore, the concave region of the first surface of the positive electrode and the gap can absorb electrolyte, increasing the amount of electrolyte between layers and improving electrolyte retention, which also benefits the cycling performance of the electrochemical device.

[0006] In some embodiments of this application, the thickness h0 of the negative electrode before formation and the thickness h1 of the negative electrode after formation are respectively. The height h2 of the protrusion region extending beyond the peripheral region of the positive electrode in the thickness direction Y is given. The expansion rate of the negative electrode is δ, satisfying: h2 ≥ h0 × δ. The expansion rate δ is related to the properties of the negative electrode active material, such as graphite, which is generally 8% to 12%. After formation, the thickness h1 of the negative electrode and the height h2 of the protrusion region extending beyond the peripheral region of the positive electrode in the thickness direction satisfy 0.01h1 ≤ h2 ≤ 0.03h1. In some embodiments, the height h2 of the protrusion region extending beyond the peripheral region of the positive electrode in the thickness direction satisfies 0.01h1 ≤ h2 ≤ 0.02h1. In some embodiments, the thickness h1 of the negative electrode is 100 μm to 180 μm. In some embodiments, the height h2 of the protrusion region extending beyond the peripheral region of the positive electrode in the thickness direction is 2 μm to 40 μm.

[0007] A positive electrode, a negative electrode, and a separator are wound to form a wound structure. The wound structure includes a main body and curved portions located on both sides of the main body. In some embodiments, in the main body, a raised area on the second surface protrudes beyond the peripheral region of the raised area on the second surface by a height h2. In some embodiments, in the curved portions, the height h2 of the raised area protruding beyond the peripheral region of the raised area in the thickness direction of the positive electrode is 2 μm to 30 μm. In some embodiments, the height of the raised area in the curved portion protruding beyond the peripheral region of the raised area in the thickness direction of the positive electrode is 4 to 10 times that of the height of the raised area in the main body protruding beyond the peripheral region of the raised area in the thickness direction of the positive electrode. In some embodiments, within the above range, the cyclic expansion force of the electrochemical device can be effectively released, preventing deformation of the electrochemical device. In some embodiments of this application, the height of the raised area protruding beyond the peripheral region of the raised area in the thickness direction Y of the positive electrode is 2 μm to 20 μm.

[0008] In some embodiments of this application, in the main body portion, the height h2 of the protrusion extending beyond the peripheral region of the protrusion region in the thickness direction of the positive electrode is 2 μm to 10 μm. In some embodiments, in the main body portion, the height h2 of the protrusion region extending beyond the peripheral region of the protrusion region in the thickness direction of the positive electrode is 2 μm to 5 μm. In some embodiments, in the curved portion, the height h2 of the protrusion region extending beyond the peripheral region of the protrusion region in the thickness direction of the positive electrode is 5 μm to 30 μm. In some embodiments, in the curved portion, the height h2 of the protrusion region extending beyond the peripheral region of the protrusion region in the thickness direction of the positive electrode is 10 μm to 30 μm.

[0009] In some embodiments of this application, the separator surface has a ceramic layer, thereby improving safety. In some embodiments of this application, the separator comprises at least one of polypropylene, polyethylene, or a composite film of polypropylene and polyethylene. In some embodiments of this application, the thickness h3 of the separator is 3 μm to 30 μm, thereby ensuring safety and ion conduction efficiency. In some embodiments of this application, the peel strength between the separator and the positive electrode is less than 0.5 N / m, thereby protecting the separator. In some embodiments of this application, the peel strength between the separator and the positive electrode is 0 N / m.

[0010] In some embodiments of this application, the density of the raised areas on the second surface is 7 per cm. 2 Up to 60 per cm 2 In some embodiments of this application, in the main body, the density of the protrusions on the second surface is 8 per cm. 2 Up to 50 per cm 2 In some embodiments, in the curved portion, the density of the protrusions on the second surface is 8 per cm. 2 Up to 40 per cm 2In some embodiments, in the main body, the density of the protrusions on the second surface is 8 per cm². 2 Up to 30 per cm 2 In some embodiments, in the main body, the density of the protrusions on the second surface is 8 per cm². 2 Up to 20 per cm 2 .

[0011] In some embodiments of this application, the number of raised areas is at least two, and the raised areas are evenly distributed on the second surface, thereby reducing stress concentration. In some embodiments of this application, the shape of the raised areas is dot-shaped, strip-shaped, or polygonal. In some embodiments of this application, the positive electrode, negative electrode, and separator are wound to form a wound structure; the wound structure includes a main body and curved portions located on both sides of the main body. In the main body, the surface of the negative electrode facing the positive electrode is planar, and in the curved portions, the surface of the negative electrode facing the positive electrode is arc-shaped, thereby reducing the probability of the separator being damaged.

[0012] In some embodiments of this application, an electronic device is also proposed, comprising any of the electrochemical devices described above.

[0013] In some embodiments of this application, the first surface of the positive electrode of the electrochemical device has a concave region, and the second surface of the positive electrode has a convex region corresponding to the concave region. A gap is formed between the positive electrode and the negative electrode through the convex region, or the first surface of the positive electrode forms a gap with the negative electrode through the concave region. By reserving expansion space for the negative electrode, the cyclic expansion force is released, the deformation caused by cyclic expansion is reduced or avoided, the liquid retention is increased, and the cyclic performance is improved. Attached Figure Description

[0014] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. Throughout the drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the originals and elements are not necessarily drawn to scale.

[0015] Figure 1 These are membrane structure diagrams of electrochemical devices in some embodiments.

[0016] Figure 2 This is a schematic diagram of the first side of the positive electrode of the electrochemical device in some embodiments.

[0017] Figure 3 This is a schematic diagram of the second side of the positive electrode of the electrochemical device in some embodiments.

[0018] Figure 4 These are schematic diagrams of electrochemical devices in some embodiments.

[0019] Figure 5 These are membrane structure diagrams of electrochemical devices in some embodiments.

[0020] Figure 6 These are schematic diagrams of the winding structure in the electrochemical device in some embodiments.

[0021] Figure 7 These are diagrams of the membrane structure of the curved portion in some embodiments.

[0022] Figure 8 These are schematic diagrams of the expansion process of the electrochemical device in some embodiments.

[0023] Figure 9 These are test results diagrams of the raised and recessed areas in some embodiments.

[0024] Figure 10 This is a schematic diagram of some embodiments testing the height of the protrusion region protruding from the peripheral region of the protrusion region in the thickness direction of the positive electrode.

[0025] Figure 11 This is a schematic diagram of the density test of the raised area on the second surface in some embodiments.

[0026] Figure 12 These are schematic diagrams illustrating the core manufacturing process of the electrochemical device in some embodiments.

[0027] Figure 13 These are schematic diagrams of the overall and partial structures of the core of the electrochemical device in some embodiments.

[0028] Figure 14 These are schematic diagrams of the expansion process in some existing electrochemical devices.

[0029] Figure 15 These are test diagrams of the electrochemical device before cycling in some embodiments.

[0030] Figure 16 These are test images of the positive electrode after disassembly following the expansion of the negative electrode in some embodiments of the electrochemical device.

[0031] Figure 17 This is a cross-sectional schematic diagram of the electrochemical devices of Example 1 and Comparative Example 1 after cycling.

[0032] Figure 18 This is a graph showing the test results of the height of the raised area at different stages in Example 1. Detailed Implementation

[0033] The following embodiments are intended to enable those skilled in the art to fully understand this application, but do not limit this application in any way.

[0034] Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0035] The embodiments of this application will be described in detail below. However, this application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided to provide a thorough and detailed understanding of this application to those skilled in the art.

[0036] Additionally, for brevity and clarity, the dimensions or thicknesses of various components and layers may be enlarged in the accompanying drawings. Throughout the text, the same numerical values ​​refer to the same elements. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more of the associated enumerated items. Furthermore, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0037] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0038] The technical terms used herein are for the purpose of describing particular embodiments and are not intended to limit this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It should be further understood that the term "comprising," as used in this specification, means the presence of the described features, values, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.

[0039] Spatial terms, such as "above," may be used herein for convenience in describing the relationship between one element or feature and another element (or feature) or feature (or feature) illustrated in the figures. It should be understood that, in addition to the directions depicted in the figures, spatial terms are intended to include different orientations of the device or apparatus during use or operation. For example, if the device in the figure is flipped, an element described as "above" or "on" other elements or features would be oriented "below" or "under" other elements or features. Therefore, the exemplary term "above" can include both above and below orientations. It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, a first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0040] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on its differences from other embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other technical solutions obtained by those skilled in the art are within the scope of protection of this application. It should be noted that, in the specific embodiments of this application, a lithium-ion battery can be used as an example of an electrochemical device to explain this application; however, the electrochemical device of this application is not limited to lithium-ion batteries.

[0041] In some embodiments of this application, an electrochemical device and an electronic device are proposed that, by creating a gap between the positive and negative electrodes to reserve expansion space for the negative electrode, thereby releasing the cycle expansion force, reducing battery cost, and improving cycle performance.

[0042] An electrochemical device is proposed in some embodiments of this application, such as Figure 1As shown, the electrochemical device includes: a positive electrode 1, a negative electrode 2, and a separator 3 located between the positive electrode 1 and the negative electrode 2. The positive electrode 1 may include a positive electrode current collector 13 and a positive electrode active material layer 14 located on one or both sides of the positive electrode current collector 13. The positive electrode current collector 13 may be, for example, aluminum foil. The positive electrode active material layer 14 may contain a positive electrode active material, such as lithium cobalt oxide, lithium nickel oxide, or lithium manganese oxide. The negative electrode 2 may include a negative electrode current collector 21 and a negative electrode active material layer 22 located on one or both sides of the negative electrode current collector 21. The negative electrode current collector 21 may be, for example, copper foil. The negative electrode active material layer may contain a negative electrode active material, such as graphite or silicon-containing materials. The first surface 11 of the positive electrode 1 has a concave region 111, and the second surface 12 of the positive electrode 1 has a protruding region 121 corresponding to the concave region 111 and protruding toward the negative electrode 2. A gap 4 is formed between the second surface 12 of the positive electrode 1 and the negative electrode 2 through the protruding region 121. In some embodiments, the positive electrode 1 and the separator 3 may or may not be in contact, and the separator 3 and the negative electrode 2 may or may not be in contact. In some embodiments, when the separator 3 is attached to the negative electrode 2, the gap 4 between the positive electrode 1 and the negative electrode 2 may refer to the gap between the second surface 12 of the positive electrode 1 and the separator 3; when the separator 3 is attached to the second surface 12 of the positive electrode 1, the gap 4 between the positive electrode 1 and the negative electrode 2 may refer to the gap between the separator 3 and the negative electrode 2.

[0043] In some embodiments, such as Figure 1 and Figure 2 As shown, the first surface 11 of the positive electrode 1 is concave to form a concave region 111. In some embodiments, a portion of the surface of the first surface 11 of the positive electrode 1 is concave towards the second surface 12 of the positive electrode 1 to form the concave region 111. The concave region 111 and the protruding region 121 can correspond one-to-one, or they may not correspond one-to-one. In some embodiments, such as... Figure 1 (A) to Figure 1 As shown in (C), the electrochemical device can be a wound electrochemical device, with the X direction being the winding direction. Along the winding direction, the positive electrode 1 and the negative electrode 2 will be bent. The X direction can be, for example, the length direction of the positive electrode current collector 13. The Z direction is a direction perpendicular to both X and Y, and can be the width direction of the positive electrode current collector 13. The Y direction is the thickness direction of the positive electrode 1, which is perpendicular to the positive electrode current collector. The concave region 111 and the corresponding protruding region 121 can overlap or partially overlap in the thickness direction Y of the positive electrode 1. In some embodiments, since the protruding region 121 protrudes from the peripheral region 122 of the protruding region 121 on the second surface 12, the peripheral region 122 of the protruding region 121 can be at least the region surrounding the protruding region 121 when viewed from the Y direction. Therefore, the top of the protruding region 121 will be closer to the negative electrode 2 than the peripheral region 122 of the protruding region on the second surface 12 of the positive electrode 1. In some embodiments, such as Figure 1 As shown in (B), the raised area 121 may press against the separator 3, causing the top of the raised area 121 to embed into the separator 3. This increases the contact area between the separator 3 and the raised area 121. When the negative electrode 2 expands, the separator 3 applies a more uniform compressive force to the raised area 121, preventing stress concentration that could cause cracks in the positive electrode active material layer 14. In some embodiments, there can be multiple raised areas 121, forming a gap 4 between the second surface 12 of the positive electrode 1 and the negative electrode 2. In some embodiments, such as... Figure 1 As shown in (A) to (G), the size of the concave region 111 on the first surface 11 and the size of the convex region 121 on the second surface 12 can be the same or different, such as... Figure 1 As shown in (D), the dimensions of the recessed areas 111 at different locations can be different. For example, the depth h3 and width W2 of the recessed areas 111 at different locations can be different. This reduces manufacturing difficulty. In some embodiments, the dimensions of the recessed areas 111 are different, so the amount of electrolyte stored in the different recessed areas 111 is different. Therefore, the size of the recessed areas 111 that are farther away from the edge of the positive electrode active material layer 14 in the X or Y direction can be set to be larger. This is beneficial for the recessed areas 111 closer to the center region of the positive electrode active material layer 14 to better retain electrolyte, which is beneficial for cycle performance. The dimensions of the protruding areas 121 at different locations can also be different. For example, the height h2 and width W1 of the protruding areas 121 at different locations can be different. In some embodiments, when the heights of the raised regions 121 are different, different raised regions 121 can not contact the separator 3 simultaneously, thereby reducing the resistance to electrolyte flow and providing a flow channel for electrolyte flow, ensuring the wettability of the electrolyte to the positive electrode active material layer 14. In some embodiments, the closer the raised region 121 is to the edge of the positive electrode active material layer 14 in the X or Y direction, the smaller its height h2. This avoids the raised regions 121 near the edge of the positive electrode active material layer blocking the electrolyte from flowing into the central region of the positive electrode active material layer, which is beneficial to cycle performance. In some embodiments, when the size of the concave region 111 is different from the size of the raised region 121, such as... Figure 1 As shown in (D), the size of the concave region 111 can be larger than the size of the convex region 121. For example, the depth h3 of the concave region 111 can be greater than the height h2 of the convex region 121, and the width W2 of the concave region 111 can be greater than the width W1 of the convex region 121. When the convex region 121 is compressed and contracts due to the expansion of the negative electrode 2, the size of the concave region 111 will also decrease. Because the size of the concave region 111 is greater than the size of the convex region 121, when the convex region 121 is compressed due to the expansion of the negative electrode 2, the concave region 111 can prevent the first surface 11 from bulging out due to the compression of the convex region 121. In other embodiments, such as... Figure 1As shown in (E), the size of the concave region 111 can be smaller than the size of the convex region 121. For example, the depth h3 of the concave region 111 can be smaller than the height h2 of the convex region 121, and the width W2 of the concave region 111 can be smaller than the width W1 of the convex region 121. In this case, the expansion of the negative electrode can also be buffered. In some embodiments, the depth difference between different concave regions 111 can be less than 3 μm, and in some embodiments, the height difference between different convex regions 121 can be less than 3 μm. Figure 1 (G) shows Figure 1 (A) is a schematic diagram of the electrochemical device after cycling, showing that the dimensions of the protruding region 121 and the concave region 111 decrease after cycling. This is because the expansion of the negative electrode 2 compresses the protruding region 121 on the positive electrode 1, reducing the height h2 of the protruding region 121 and pushing it inward to compress the concave region 111, thus reducing the internal space of the concave region 111. Because the height h2 of the protruding region 121 decreases, the gap between the positive electrode 1 and the negative electrode 2 decreases, thereby buffering the expansion generated during the cycling process. In some embodiments, Figure 4 The following are schematic diagrams showing the disassembled electrochemical devices in some embodiments of this application. Figure 2 A schematic diagram of the first surface 11 of the positive electrode 1 is shown, as follows: Figure 2 As shown, a concave region 111 is formed on the first surface 11 of the positive electrode. The cross-section of the concave region 111 along the first surface 11 can be hemispherical, striped, triangular, square, or polygonal. The shape of the concave region 111 is not limited to this. The shape of the cross-section of the concave region 111 along the first surface 11 can be the same as the shape of the cross-section of the protruding region 121 along the second surface 12. Figure 3 The diagram shown is a schematic of the second surface 12 of the positive electrode, illustrating the shape of the protruding region 121. The shape of the protruding region 121 can be compared with... Figure 2 The shape of the concave region 111 is similar, such as Figure 3 As shown, the cross-section of the protrusion 121 along the first surface 11 can also be hemispherical, striped, triangular, square, or polygonal, but is not limited thereto.

[0044] In other embodiments of this application, such as Figure 5As shown, the electrochemical device includes: a positive electrode 1, a negative electrode 2, and a separator 3 located between the positive electrode 1 and the negative electrode 2. The positive electrode 1 may include a positive electrode current collector 13 and a positive electrode active material layer 14 located on one or both sides of the positive electrode current collector 13. The positive electrode active material layer 14 may contain a positive electrode active material, such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, etc. The negative electrode 2 may include a negative electrode current collector 21 and a negative electrode active material layer 22 located on one or both sides of the negative electrode current collector 21. The negative electrode active material layer may contain a negative electrode active material, such as graphite, silicon-containing materials, etc. The first surface 11 of the positive electrode 1 has a concave region 111, and the second surface 12 of the positive electrode 1 has a protruding region 121 corresponding to the concave region 111. The protruding region 121 protrudes away from the negative electrode 2, and a gap 4 is formed between the first surface 11 of the positive electrode 1 and the negative electrode 2 through the concave region 111. In some embodiments, when the separator 3 is attached to the negative electrode 2, the gap 4 between the positive electrode 1 and the negative electrode 2 can refer to the gap between the positive electrode 1 and the separator 3, for example, it can be the gap formed between the concave region 111 and the separator 3. When the separator 3 is attached to the first surface 11 of the positive electrode 1 facing the negative electrode 2, the gap 4 between the positive electrode 1 and the negative electrode 2 can refer to the gap between the separator 3 and the negative electrode 2.

[0045] In some embodiments, Figure 5 In the electrochemical device shown, the second surface 12 of the positive electrode 1 away from the negative electrode 2 has a raised region 121, and the first surface 11 of the positive electrode 1 facing the negative electrode 2 has a concave region 111. The concave region 111 corresponds to the raised region 121. Since the concave region 111 is recessed within the first surface 11 of the positive electrode 1, all other areas on the first surface 11 except for the concave region 111 are partially or entirely closer to the negative electrode 2 than the concave region 111. Therefore, a gap 4 is formed between the positive electrode 1 and the negative electrode 2. The gap 4 can be the internal space of the concave region 111. In some embodiments, such as... Figure 5 (A) and Figure 5 As shown in (B), the concave region 111 and the convex region 121 can overlap or partially overlap in the thickness direction Y of the positive electrode 1. This way, when the convex region 121 is compressed and contracts, the size of the concave region 111 will decrease without causing the first surface 11 to bulge. In some embodiments, such as... Figure 5 As shown in (A) to (F), the dimensions of the concave region 111 on the first surface 11 and the convex region 121 on the second surface 12 can be the same or different. For example, the depth h3 of the concave region 111 can be the same as or different from the height h2 of the convex region 121, and the width W2 of the concave region 111 can be the same as or different from the width W1 of the convex region 121. Figure 5As shown in (C), the size of the recessed area 111 at different locations can be different. For example, the depth h3 of the recessed area 111 at different locations can be different, and the width W2 of the recessed area 111 can be different. This can reduce the manufacturing difficulty. In some embodiments, the size of the recessed area 111 is different, so the amount of electrolyte stored in the different recessed areas 111 is different. Therefore, the size of the recessed area 111 that is farther away from the edge of the positive electrode active material layer 14 in the X or Y direction can be set to be larger, which is beneficial for the recessed area 111 near the center region of the positive electrode active material layer 14 to better retain electrolyte and improve cycle performance. The dimensions of the raised areas 121 at different locations can also be different. For example, the height h2 and width W1 of the raised areas 121 at different locations can be different. In some embodiments, when the heights of the raised areas 121 are different, the different raised areas 121 reduce the resistance to electrolyte flow, provide a flow channel for electrolyte flow, and ensure the wettability of the electrolyte to the positive electrode active material layer 14. In some embodiments, the closer the raised areas 121 are to the edge of the positive electrode active material layer 14 in the X or Y direction, the smaller their height h2. This avoids the raised areas 121 near the edge of the positive electrode active material layer blocking the electrolyte from flowing into the central region of the positive electrode active material layer, which is beneficial to cycle performance. In some embodiments, when the dimensions of the concave area 111 are different from the dimensions of the raised areas 121, such as... Figure 5 As shown in (D), the size of the protruding area 121 can be larger than the size of the concave area 111. For example, the height h2 of the protruding area 121 can be larger than the depth h3 of the concave area 111, and the width W1 of the protruding area 121 can be larger than the width W2 of the concave area 111. When the protruding area 121 is compressed and contracts due to the expansion of the negative electrode 2, the size of the concave area 111 will also decrease. Because the size of the concave area 111 is larger than the size of the protruding area 121, when the protruding area 121 is compressed due to the expansion of the negative electrode 2, the concave area 111 can prevent the first surface 11 from bulging out due to the compression of the protruding area 121. Figure 5 As shown in (E), the size of the raised region 121 can be smaller than the size of the recessed region 111. For example, the height h2 of the raised region 121 can be smaller than the depth h3 of the recessed region 111, and the width W1 of the raised region 121 can be smaller than the width W2 of the recessed region 111. This can also buffer the expansion of the negative electrode 2. In some embodiments, the difference in depth h3 between different recessed regions 111 can be less than 3 μm. In some embodiments, the difference in height h2 between different raised regions 121 can be less than 3 μm. Figure 5 (F) shows a schematic diagram after the electrochemical device has been cycled, in which it can be seen that after the electrochemical device has been cycled, the size of the raised region 121 and the concave region 111 decreases, the height h2 of the raised region 121 and the depth h3 of the concave region 121 decrease, thereby buffering the expansion generated during the cycle.

[0046] In some embodiments of this application, such as Figure 6 As shown, the positive electrode 1, the negative electrode 2, and the separator 3 are wound together to form a wound structure; the wound structure includes a main body 10 and curved portions 20 located on both sides of the main body 10. Figure 1 and Figure 5 What is shown can be a membrane structure diagram of the main body 10. For the curved portion 20, its membrane structure diagram can be as follows: Figure 7 As shown, Figure 7 As shown, in the bent portion, the positive electrode 1, the negative electrode 2, and the separator 3 are in a bent state. In some embodiments, Figure 1 It can be Figure 6 A schematic diagram of region R1 in the main body 10. Figure 5 This could be a schematic diagram of region R2 in the curved section 20.

[0047] In some embodiments, such as Figure 8 As shown, in some embodiments of this application, the electrochemical device, during cycling, Figure 8 (a) and Figure 8 (b) Demonstrates the changes in the membrane structure of the main body 10 before and after cycling. Figure 8 (c) and Figure 8 (d) illustrates the changes in the membrane structure of the curved section 20 before and after cycling. For example... Figure 8 As shown in (a), during the initial stage of the formation cycle charge-discharge, a pressure F (0.02 MPa to 2 MPa) can be applied. At this time, the negative electrode 2 has not yet expanded. Figure 8 In (a), positive electrodes 1 are provided on both sides of the negative electrode 2. For the positive electrode 1 on one side of the negative electrode 2 ( Figure 8 (a) Positive electrode 1 above negative electrode 2), the side of positive electrode 1 facing negative electrode has a raised area 121, and the side of positive electrode 1 away from negative electrode 2 has a concave area 111, for the positive electrode 1 on the other side of negative electrode 2 ( Figure 8 (a) The positive electrode 1 below the negative electrode 2 has a concave region 111 on the side facing the negative electrode and a convex region 121 on the side of the positive electrode 1 away from the negative electrode 2. During the formation process, the expansion force of the negative electrode 1 is released, such as... Figure 8As shown in (b), when the negative electrode 2 expands due to cyclic charging and discharging, for the positive electrode 1 on one side of the negative electrode 2, the protruding area 121 will be compressed by the negative electrode 2 during the expansion of the negative electrode 2, causing the height h2 of the protruding area 121 protruding from the peripheral area 122 of the protruding area on the second surface 12 to decrease, thereby reducing the gap 4 between the positive electrode 1 and the negative electrode 2. The increased thickness on the negative electrode 2 side is approximately equal to the decrease in height of the protruding area 121. The compressed protruding area 121 moves away from the negative electrode 2. If there were no concave area 111, the compression of the protruding area 121 might cause the side of the positive electrode 1 away from the negative electrode to bulge out. Since the concave area 111 is perpendicular to the thickness direction of the positive electrode 1... The overlap or partial overlap means that when the protruding area 121 is compressed, the depth and other dimensions of the concave area 111 will gradually decrease, thereby reducing or preventing the side of the positive electrode 1 away from the negative electrode 2 from protruding. This releases the internal stress generated by the expansion of the negative electrode 2 and reduces or prevents deformation of the electrochemical device. For the positive electrode on the other side of the negative electrode 2, when the negative electrode 2 expands, the positive electrode 1 is compressed, and the protruding area 121 on the surface of the positive electrode 1 away from the negative electrode 2 may contact the housing or other components of the electrochemical device, thereby reducing the height h2 of the protruding area 121. The concave area 111 corresponding to the protruding area 121 prevents the side of the positive electrode 1 facing the negative electrode 2 from protruding. For the electrochemical device with the curved portion 20, similar to the main body 10, as... Figure 8 As shown in (c), before the negative electrode 2 expands, a gap 4 is formed between the negative electrode 2 and the positive electrode 1 through the protruding region 121 and the concave region 111. After the negative electrode expands due to cycling or other reasons, the protruding region 121 is squeezed towards the positive electrode, causing the concave region 111 to decrease, thereby reducing the gap 4. Since the gap 4 is reduced, it provides a buffer space for the expansion of the negative electrode 2. That is, in some embodiments of this application, the expansion of the negative electrode 2 is buffered by the concave region 111 and the protruding region 121, releasing the expansion force during the negative electrode cycling process, thereby reducing or avoiding the deformation of the electrochemical device and improving the cycling effect. In addition, the gap between the positive electrode 1 and the negative electrode 2 can absorb electrolyte, increase the amount of electrolyte between layers, improve the electrolyte retention between layers, and also benefit the cycling performance of the electrochemical device.

[0048] Please refer to some embodiments of this application. Figure 1 and Figure 5The height h2 of the protrusion 121 protruding from the peripheral region 122 in the thickness direction Y of the positive electrode 1 is 2 μm to 40 μm. In some embodiments, the height h2 of the protrusion 121 protruding from the peripheral region 122 in the thickness direction of the positive electrode 1 can refer to the average of the maximum heights of the protrusion 121 protruding from the peripheral region 122. Ten protrusions 121 can be selected and their maximum heights tested, and then the average value can be calculated to obtain the height h2 of the protrusion 121. In some embodiments, when the height h2 of the protrusion 121 is in the range of 2 μm to 40 μm, it can reduce or avoid deformation of the electrochemical device while having a high volumetric energy density. In some embodiments, h2 can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or 35 μm.

[0049] In some embodiments of this application, the height h2 of the raised area 121 and the depth h3 of the recessed area 111 may be different, and the depth h3 of the recessed area 111 may be greater than the height h2 of the raised area 121. For example, 1.2 h2 ≥ h3 ≥ 1.08 h2. Figure 9 Images (a) and (b) show the test results for the height h2 of the raised area 121 in a selected region on the main body 10 of the positive electrode 1. Figure 9 Images (c) and (d) show the test results for the depth h3 of the concave region 111 in the selected area. It can be seen that the depth h3 of the concave region 111 is greater than the height h2 of the convex region 121. In some embodiments, such as... Figure 9 As shown in (a), the image of the sample is first tested using a 3D imager. Then, a straight line passing through the center of the raised area is drawn in the image, and the height at each position on the line is measured, as shown in (a). Figure 9 As shown in (b), then find the peak on the straight line, and connect the two sides of the peak's base with a connecting line. The distance between the peak's top and the connecting line is the height h2 of the raised area 121. The method for testing the depth h3 of the concave area 111 is the same, as follows: Figure 9 As shown in (c), the image of the sample is first tested using a 3D imager. Then, a straight line passing through the center of the concave region is drawn in the image, and the height at each position on the line is measured, as shown in (c). Figure 9 As shown in (d), then find the valley on the straight line, connect the two sides of the valley top with a connecting line, and the distance between the valley bottom and the connecting line is the depth h3 of the concave area 111.

[0050] In some embodiments of this application, in the main body 10, the height of the protrusion 121 protruding from the peripheral region 122 of the protrusion region in the thickness direction Y of the positive electrode 1 is different from that in the curved portion 20, the height of the protrusion 121 protruding from the peripheral region 122 of the protrusion region in the thickness direction Y of the positive electrode 1 is different.

[0051] In some embodiments of this application, in the main body 10, the height h2 of the protrusion region 121 protruding from the peripheral region 122 of the protrusion region 121 in the thickness direction of the positive electrode 1 is 2 μm to 20 μm. In some embodiments, the height h2 of the protrusion region 121 protruding from the peripheral region 122 of the protrusion region 121 in the thickness direction of the positive electrode 1 decreases during the expansion of the negative electrode 2. That is, the height h2 decreases as the number of cycles of the electrochemical device increases. Therefore, in some embodiments, the height h2 of the protrusion region 121 protruding from the peripheral region 122 of the protrusion region 121 in the thickness direction of the positive electrode 1 decreases, but the height h2 of the protrusion region 121 can always be greater than zero. This ensures that there is always a certain gap 4 between the positive electrode 1 and the negative electrode 2, thereby always storing a certain amount of electrolyte, which is beneficial to cycle performance.

[0052] In some embodiments of this application, in the curved portion 20, the height h2 of the protrusion 121 protruding from the peripheral region 122 in the thickness direction Y of the positive electrode 1 is 2 μm to 30 μm, for example, h2 can be 5 μm, 10 μm, 15 μm, 20 μm or 25 μm. In some embodiments, the height of the protrusion 121 in the curved portion 20 protruding from the peripheral region 122 in the thickness direction Y of the positive electrode 1 is 4 to 10 times that of the height of the protrusion 121 in the main body 10 protruding from the peripheral region 122 in the thickness direction Y of the positive electrode 1, for example, it can be 5 times, 6 times, 7 times, 8 times or 9 times. In some embodiments, the pressure generated by the expansion of the curved portion 20 is relatively smaller than that of the main body 10, so the reduction in height of the protrusion 121 when the negative electrode 2 expands is smaller, meaning that the height of the protrusion 121 in the curved portion 20 is higher than the height of the protrusion 121 in the main body 10.

[0053] In some embodiments of this application, the thickness h0 of the negative electrode 2 before formation is h0, and the thickness of the negative electrode 2 after formation is h0. 1，The height h2 of the protruding region 121 in the thickness direction Y of the positive electrode 1 protruding beyond the peripheral region 122 of the protruding region is 121. The expansion rate of the negative electrode 2 is δ, satisfying: h2 ≥ h0 × δ. The expansion rate δ is related to the properties of the negative electrode active material, such as graphite, which is generally 8% to 12%. After formation, the thickness of the negative electrode 2 and the thickness h1 of the protruding region satisfy 0.01h1 ≤ h2 ≤ 0.03h1. In some embodiments, h0 × δ represents the increase in thickness of the negative electrode 2 due to expansion. The height h2 of the protruding region 121 in the bending part is not less than the increase in thickness of the negative electrode 2 due to expansion, thus ensuring the release of internal stress generated by the expansion of the negative electrode 2 and avoiding deformation of the electrochemical device. In some embodiments, the thickness of the negative electrode is h1, and the height h2 of the protruding region 121 protruding beyond the peripheral region 122 of the protruding region 121 in the thickness direction Y of the positive electrode 1 is 0.01h1 ≤ h2 ≤ 0.02h1. The thickness h1 of the negative electrode 2 is 100 μm to 180 μm. In some embodiments, the thickness h1 of the negative electrode 2 is the thickness of the negative electrode 2 after formation in the electrochemical device. The thickness h1 of the negative electrode 2 is related to the amount of cyclic expansion of the negative electrode 2. The greater the thickness of the negative electrode 2, the greater the amount of cyclic expansion, and the higher the requirement for the height h2 of the protrusion region 121. Therefore, controlling the thickness of the negative electrode 2 to be between 100 μm and 180 μm can avoid the height h2 of the protrusion region 121 being too high and reduce the processing difficulty.

[0054] In some embodiments, the height h2 of the protrusion region 121 of the main body and the curved portion protruding from the peripheral region 122 of the protrusion region in the thickness direction Y of the positive electrode 1 is measured in the following manner: the electrochemical device is disassembled, and samples of the positive electrode measuring 4cm × 4cm are taken from three different locations (e.g., three different locations in the width direction) of the positive electrode 1, such as... Figure 10 As shown, the sample is placed under a 3D imager to test any position, and the thickness of the raised area 121 is ( Figure 10 The height h2 of the convex mark is represented by a uniform convex point. The height h2 can be obtained by comparing the highest position of the convex point with the position of the surrounding plane. Then, the average value is calculated as the height h2 of the convex area 121.

[0055] In some embodiments of this application, the surface of the separator 3 may have an adhesive, including at least one selected from polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In other embodiments of this application, the surface of the separator 3 may not have an adhesive. In some embodiments, because the deformation problem caused by the expansion of the negative electrode 2 is solved, it is not necessary to use a separator 3 with an adhesive, and it is not necessary to suppress the deformation of the electrochemical device through the separator 3. By using a separator 3 without an adhesive, the cost of the electrochemical device can be reduced.

[0056] In some embodiments of this application, the surface of the separator 3 has a ceramic layer. In some embodiments, the ceramic layer on the separator 3 can improve the insulation of the separator 3, prevent lithium dendrites from piercing the separator 3, and increase product life. The ceramic layer can be a porous ceramic layer, thereby retaining electrolyte, increasing electrolyte retention, and thus benefiting the cycle performance of the electrochemical device. The ceramic layer can be selected from at least one of alumina (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate.

[0057] In some embodiments of this application, the separator 3 includes at least one of polypropylene, polyethylene, or a composite film of polypropylene and polyethylene.

[0058] In some embodiments of this application, the thickness h3 of the isolation membrane 3 is 3 μm to 30 μm.

[0059] In some embodiments of this application, the peel strength between the separator 3 and the positive electrode 1 is less than 0.5 N / m, and in some embodiments, the peel strength between the separator 3 and the positive electrode 1 is 0 N / m. In some embodiments, the surface of the separator 3 does not have an adhesive, so the peel strength between the separator 3 and the positive electrode 1 is small, which reduces the probability of damage caused by the expansion of the negative electrode 2 and the contraction of the protrusion area 121. In some embodiments, the peel strength between the separator 3 and the positive electrode 1 can be measured by taking a 3mm×3mm composite sheet, which is a stack of the positive electrode 1 and the separator 3, and performing a mechanical tensile test on it. The separator 3 is bonded and fixed on a platform, the mechanical tensile tester is connected to the positive electrode 1, and a tensile force is applied to separate the positive electrode 1 and the separator 3. The tensile force is recorded as the peel strength between the separator 3 and the positive electrode 1. In some embodiments, the peel strength between the separator 3 with adhesive and the positive electrode 1 is greater than 3 N / m, and the peel strength of the separator 3 without adhesive is less than 0.5 N / m, close to 0 N / m. In some embodiments of this application, the number of raised areas 121 is at least two, and the raised areas 121 are evenly distributed on the second surface 12. In some embodiments, the even distribution of the raised areas 121 reduces the probability of stress concentration, which may damage the isolation membrane 3.

[0060] In some embodiments of this application, the density of the raised areas 121 on the second surface is 7 per cm. 2 Up to 60 per cm 2In some embodiments, when the density of the raised area 121 is too low, it may become concave due to stress during the manufacturing process of the electrochemical device, making it impossible to effectively form the gap 4. Conversely, when the density of the raised area 121 is too high, it may cause difficulties in manufacturing the embossing roller, increasing the manufacturing complexity, and may also lead to cracks in the positive electrode 1. In some embodiments, in the main body 10, the density of the raised area 121 on the second surface is 8 units / cm². 2 Up to 50 per cm 2 。 In some embodiments, in the curved portion, the density of the protrusions 121 on the second surface 12 is 8 per cm. 2 Up to 40 per cm 2 In some embodiments, in the main body 10, the density of the protrusions 121 on the second surface 12 is 8 per cm. 2 Up to 30 per cm 2 In some embodiments, in the main body 10, the density of the protrusions 121 on the second surface 12 is 8 per cm. 2 Up to 20 per cm 2 This ensures that the gap 4 between the positive electrode 1 and the negative electrode 2 matches the space required for the expansion of the negative electrode 2, and better releases the expansion force.

[0061] In some embodiments, the density of the raised area 121 on the second surface 12 can be tested as follows: A 40mm × 40mm positive electrode sample is placed on a 3D Profile stage. A clamp is used to press the sample onto the positive electrode to ensure it is flat and wrinkle-free. Using a 3D Profile measurement system with a magnification of ×12, automatic focusing is performed. The plane is confirmed and scanned. The contour function is activated to display the size, shape, and number of the raised area 121 measured on the sample. In some embodiments, the test results of the positive electrode sample are as follows: Figure 11 As shown, the density of the protrusion 121 on the second surface 12 is calculated by reading the number of protrusions 121 and the area of ​​the test area of ​​the positive electrode sample in the test results.

[0062] In some embodiments of this application, the shape of the raised area 121 is dot-shaped, strip-shaped, or polygonal. The shape of the raised area 121 refers to the cross-sectional shape obtained by taking a section of the raised area along a direction parallel to the second surface 12. The shape of the raised area 121 can also be other shapes, which can be set as needed.

[0063] In some embodiments of this application, the positive electrode 1, the negative electrode 2, and the separator 3 are wound to form a wound structure. The wound structure includes a main body 10 and curved portions 20 located on both sides of the main body 10. In the main body 10, the surface of the negative electrode 2 facing the positive electrode 1 is flat, and in the curved portions 20, the surface of the negative electrode 2 facing the positive electrode 1 is curved. In some embodiments, the surface of the negative electrode 2 opposite to the positive electrode 1 is flat or curved, thus avoiding the problem of uneven stress distribution in various regions due to unevenness of the negative electrode 2 surface. In some embodiments, the flat or curved surface may have certain undulations; for example, when the undulation on the flat surface is no greater than 1 μm, it can be considered a flat surface.

[0064] In some embodiments, the raised area 121 or the concave area 111 may be deformed under force. The number of raised areas 121 and concave areas 111 may be no less than two. Therefore, the shapes of different raised areas 121 and different concave areas 111 may be different. After the raised area 121 is deformed under force, its raised top may become a plane, or it may become a curved surface with reduced curvature. Correspondingly, the inner bottom of the concave area 111 may also become a plane or a curved surface with reduced curvature.

[0065] In some embodiments, the sizes of the raised area 121 and the recessed area 111 may not be exactly the same. In some embodiments, the size of the recessed area 111 of the first surface 11 may be larger than the size of the raised area 121 of the corresponding second surface 12. In some embodiments, the size of the recessed area 111 of the first surface 11 may be smaller than the size of the raised area 111 of the second surface 12.

[0066] In some embodiments, the size of the protrusion 121 may include the height h2 of the protrusion 121 in the thickness direction of the positive electrode 1 and the width W1 of the protrusion 121 in the direction parallel to the positive electrode 1, and the size of the concave region 111 may include the depth h3 of the concave region 111 in the thickness direction of the positive electrode 1 and the width W2 of the concave region 111 in the direction parallel to the positive electrode 1.

[0067] In some embodiments of this application, the positive electrode 1 can be prepared in the following manner, such as... Figure 12 As shown, an embossing process is used to create raised grooves of a certain thickness on the positive electrode 1. An embossing roller and a rubber roller are used to roll the positive electrode 1 under a pressure of 0.02 MPa to 0.9 MPa. Before winding, the positive electrode 1 forms a raised area 121 with raised grooves of a certain thickness. The height h2 of the raised area 121 can be 2 μm to 40 μm, preferably 2 μm to 20 μm. The positive electrode 1, negative electrode 2, and separator 3 are then wound to form a core. In some embodiments, the positive electrode 1, negative electrode 2, and separator 3 can be stacked together. A schematic diagram of the prepared core and a partial view of the core are shown below. Figure 13 As shown, Figure 1 and Figure 5 The diagram in the diagram can be Figure 13 The schematic diagram of a portion selected from the core shows that a gap is formed between the positive electrode 1 and the negative electrode 2.

[0068] In some embodiments of this application, the positive electrode 1 has a raised area 121 of a certain thickness, thereby forming a gap 4 between the positive electrode 1 and the negative electrode 2. During the charging and discharging process, the negative electrode 2 can release the internal expansion force, solving the problem of deformation of the electrochemical device. Therefore, a non-adhesive layer separator 3 can be used, thereby reducing costs. The gap can additionally retain electrolyte, which can increase the interlayer electrolyte wetting, improve long-cycle performance, and achieve a gain effect.

[0069] In this embodiment, the negative electrode 2 includes a negative electrode current collector and a negative electrode active material layer located within the negative electrode current collector. The negative electrode active material layer includes a negative electrode material. The negative electrode material includes at least one of graphite, silicon, silicon-based materials, silicon-carbon composites, or metals. In some embodiments, the negative electrode active material layer may further include a conductive agent and a binder. In some embodiments, the conductive agent in the negative electrode active material layer may include at least one of conductive carbon black, Ketjen black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the negative electrode material, conductive agent, and binder in the negative electrode active material layer may be (78 to 98.5):(0.1 to 10):(0.1 to 10). The negative electrode material may be a mixture of silicon-based materials and other materials. It should be understood that the above description is merely an example, and any other suitable materials and mass ratios can be used. In some embodiments, the negative electrode current collector can be at least one of copper foil, nickel foil, or carbon-based current collector.

[0070] In some embodiments, the positive electrode 1 includes a positive electrode current collector 13 and a positive electrode active material layer 14 disposed on the positive electrode current collector 13. The positive electrode active material layer 14 may include a positive electrode material. In some embodiments, a concave region 111 may be located in the positive electrode active material layer 14; in some embodiments, a convex region 121 may be located in the positive electrode active material layer 14; in some embodiments, the positive electrode current collector 13 may also have a concave region 111; in some embodiments, the positive electrode current collector may also have a convex region 121. In some embodiments, the positive electrode material includes at least one of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadium oxide phosphate, sodium vanadium oxide phosphate, lithium vanadate, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, or lithium nickel cobalt aluminum oxide. In some embodiments, the positive electrode active material layer may also include a conductive agent. In some embodiments, the conductive agent in the positive electrode active material layer 14 may include at least one of conductive carbon black, Ketjen black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the positive electrode active material layer 14 may further include a binder, which may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the positive electrode material, conductive agent, and binder in the positive electrode active material layer 14 may be (80 to 99):(0.1 to 10):(0.1 to 10). In some embodiments, the thickness of the positive electrode active material layer 14 may be from 10 μm to 500 μm. It should be understood that the above description is merely an example, and the positive electrode active material layer 14 may employ any other suitable material, thickness, and mass ratio.

[0071] In some embodiments, the current collector 13 of the positive electrode can be an Al foil, or other current collectors commonly used in the art can be used. In some embodiments, the thickness of the current collector 13 of the positive electrode can be from 1 μm to 50 μm. In some embodiments, the positive electrode active material layer 14 can be coated only on a portion of the current collector 13 of the positive electrode.

[0072] In some embodiments of this application, the electrochemical device is of the wound type. In some embodiments, the positive and / or negative electrodes of the electrochemical device can be multilayer structures formed by winding, or they can be single-layer structures consisting of a single-layer positive electrode, a separator, and a single-layer negative electrode wound together.

[0073] In some embodiments, the electrochemical device includes a lithium-ion battery, but this application is not limited thereto. In some embodiments, the electrochemical device may also include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution, wherein the electrolyte solution includes a lithium salt and a non-aqueous solvent. The lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. For example, LiPF6 is selected as the lithium salt. The non-aqueous solvent may be a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.

[0074] Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. Examples of fluorinated carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0075] Examples of carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, methyl formate, or combinations thereof.

[0076] Examples of ether compounds are dibutyl ether, tetraethylene dimethyl ether, diethylene dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0077] Examples of other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.

[0078] In some embodiments of this application, taking a lithium-ion battery as an example, the positive electrode 1, the separator 3, and the negative electrode 2 are sequentially wound into an electrode assembly, then encapsulated in, for example, an aluminum-plastic film, and injected with electrolyte. The assembly is then formed and encapsulated to produce a lithium-ion battery. The prepared lithium-ion battery is then subjected to performance testing.

[0079] Those skilled in the art will understand that the methods for preparing the electrochemical devices (e.g., lithium-ion batteries) described above are merely examples. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

[0080] Embodiments of this application also provide electronic devices including the electrochemical devices described above. The electronic devices in the embodiments of this application are not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, drones, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0081] In existing electrochemical devices (such as lithium-ion batteries), the separator typically has an adhesive layer. The strong adhesion of this adhesive layer prevents the negative electrode from deforming after expansion. However, using an adhesive layer on the separator increases costs by about 4% compared to separators without an adhesive layer. Furthermore, to ensure that the electrochemical device does not deform in the later stages of cycling, external pressure needs to be applied, further increasing costs.

[0082] However, if a release liner without an adhesive layer is used directly, such as Figure 14 (a) As shown in the figure, before formation, positive electrode 1, negative electrode 2, and separator 3 are stacked and an external force F is applied. After formation, as shown in the figure... Figure 10 (b) As shown in the figure, negative electrode 2 expands. As the cycle continues, as... Figure 14 As shown in (c), due to the lack of an adhesive layer, after the internal stress of the negative electrode 2 is released, there is no additional space to absorb the expansion force of the negative electrode 2, resulting in obvious wrinkles on the negative electrode 2. After unloading the external force F after formation is completed, as shown in (c)... Figure 14As shown in (d), the overall deformation of the electrochemical device leads to a deterioration in cycle performance. In contrast, the electrochemical device proposed in this application has a gap formed between the positive electrode 1 and the negative electrode 2 through the protrusion region 121. By reserving expansion space for the negative electrode 2, the deformation caused by cycle expansion is released, the liquid retention is increased, and the cycle performance is improved.

[0083] In some embodiments of this application, such as Figure 15 and Figure 16 As shown, Figure 15 and Figure 16 These are test images of the positive electrode before and after the expansion of the negative electrode in the electrochemical device. Figure 15 In (a), three regions (square regions) were selected on the positive electrode 1, and the heights of the protrusions 121 in these three regions were measured to be 22 μm, 21 μm, and 19 μm, respectively. Figure 16 As shown, the electrochemical device was disassembled after cycling (after the expansion of negative electrode 2). Figure 16 (a) shows a schematic diagram of positive electrode 1. Figure 13 (b) is for Figure 13 The height change test was conducted on the area selected in (a), and the test results are as follows: Figure 13 As shown in (c), it can be seen that after the negative electrode expands, the height of the protrusion region 121 decreases to 3μm to 4μm. This is because the expansion of the negative electrode 2 during the cycle causes compression on the protrusion region 121, resulting in a decrease in the height of the protrusion region 121.

[0084] To further demonstrate the technical effects of this application, the electrochemical device proposed in this application is compared with the electrochemical device of the comparative example below.

[0085] Example 1:

[0086] Cathode preparation:

[0087] Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride were mixed evenly in a ratio of 96:2.8:1.2. An appropriate amount of N-methylpyrrolidone was added and stirred thoroughly to prepare a uniform slurry. This slurry was coated onto an Al foil (positive electrode current collector), and then dried and cold-pressed to obtain a positive electrode sheet with a thickness of 187 μm.

[0088] Anode preparation:

[0089] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed evenly in a weight ratio of 97:2:1. After adding an appropriate amount of deionized water and stirring thoroughly, a uniform slurry was prepared and coated onto a Cu foil (negative electrode current collector). After drying and cold pressing, a negative electrode sheet with a thickness of 139 μm was obtained.

[0090] Lithium-ion battery fabrication: A 20μm polypropylene (PP) film is used as the separator. The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, and tabs are welded on. After rolling and winding, the electrode assembly is obtained. The electrode assembly is placed in a packaging shell, electrolyte is injected, and it is encapsulated to obtain a lithium-ion battery. Then, formation is performed at a formation pressure of 0.3MPa.

[0091] During the rolling process, an embossing roller is used: the pressure is set to 0.3 MPa, and a raised area with a height of 30 μm is created on the side of the positive electrode sheet facing the negative electrode sheet, and a corresponding concave area is created on the other side.

[0092] Comparative Example 1

[0093] The only difference between Comparative Example 1 and Example 1 is that no embossing roller was used during the rolling process, and there are no raised or recessed areas on the positive electrode sheet.

[0094] Loop testing:

[0095] In an environment of 25℃, the first charge and discharge cycle was performed. The battery was charged at a constant current of 1C until it reached 3.65V, and then charged at a constant voltage of 3.65V until it reached 0.05C. After resting for 10 minutes, the battery was discharged at a constant current of 1C until the final voltage reached 2.58V. After resting for 10 minutes, the discharge capacity of the first cycle was recorded. The above steps were then repeated for 500 charge and discharge cycles. After the cycle was completed, the lithium-ion battery was disassembled and the electrode components were observed for wrinkles.

[0096] In some embodiments, Figure 17 (a) and Figure 17 (b) shows a cross-sectional schematic diagram of the electrode assembly in the electrochemical device of Example 1 and Comparative Example 1. Figure 17 (a) shows a cross-sectional schematic diagram of the electrochemical device of Example 1, wherein, Figure 17 (a) The spiral-wound electrode assembly shown is merely an application example and does not impose any limitation on this application. The shape of the electrode assembly in this application is not limited to that of the present application. Figure 14 The shape in the image indicates that the electrode assembly in this application may not have... Figure 17 The curved part in the middle, from Figure 17 As can be seen from (a) and (b), when the electrochemical device proposed in this application is used, the electrode assembly hardly deforms because the stress of the negative electrode expansion is absorbed through the gap between the positive and negative electrodes. When a non-adhesive separator is used directly instead of the electrochemical device proposed in this application, the electrode assembly expansion is not buffered by the absence of raised and recessed areas. Figure 17As shown in (b), the electrode assembly of Comparative Example 1 exhibits significant deformation. Parallel experiments were conducted to test the height of the protrusion area in the lithium-ion battery of Example 1 after preparation, formation, and after 500 cycles. The test results are as follows: Figure 18 As shown in (a), the height of the protrusion area before formation after the lithium-ion battery fabrication is 30 μm, as Figure 18 As shown in (b), the height of the bump area after lithium-ion battery formation is 10 μm, as Figure 18 As shown in (c), the height of the bulge region is 3 μm after 500 cycles of the lithium-ion battery. The reduction in the height of the bulge region buffers the expansion of the lithium-ion battery.

[0097] The above description is merely a selection of preferred embodiments of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. An electrochemical device, wherein, include: A positive electrode, a negative electrode, and a separator membrane located between the positive electrode and the negative electrode; the positive electrode, the negative electrode, and the separator membrane are wound to form a wound structure; the wound structure includes a main body portion and curved portions located on both sides of the main body portion; The first surface of the positive electrode has a concave region, and the second surface of the positive electrode has a convex region corresponding to the concave region. The second surface of the positive electrode forms a gap with the negative electrode through the convex region, or the first surface of the positive electrode forms a gap with the negative electrode through the concave region. The height by which the convex region in the curved portion protrudes beyond the peripheral region of the convex region in the thickness direction of the positive electrode is 4 to 10 times the height by which the convex region in the main body portion protrudes beyond the peripheral region of the convex region in the thickness direction of the positive electrode.

2. The electrochemical device according to claim 1, wherein, The thickness of the negative electrode is h1, and the height h2 of the protrusion area protruding from the peripheral region of the protrusion area in the thickness direction of the positive electrode is 0.01h1≤h2≤0.03h1.

3. The electrochemical device according to claim 1, wherein, The thickness of the negative electrode is h1, and the height h2 of the protrusion area protruding from the peripheral area of ​​the protrusion area in the thickness direction of the positive electrode is 0.01h1≤h2≤0.02h1.

4. The electrochemical device according to claim 2, wherein, The thickness of the negative electrode is h1, which is 100 μm to 180 μm.

5. The electrochemical device according to claim 1, wherein, The height h2 of the protrusion area protruding from the peripheral region of the protrusion area in the thickness direction of the positive electrode is 2μm to 40μm.

6. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of the following: (a) In the main body portion, the height h2 of the protrusion region protruding from the peripheral region of the protrusion region in the thickness direction of the positive electrode is 2 μm to 20 μm. (b) In the curved portion, the height h2 of the protrusion area protruding from the peripheral region of the protrusion area in the thickness direction of the positive electrode is 2 μm to 30 μm.

7. The electrochemical device according to claim 6, wherein, In the main body, the height h2 of the protrusion area protruding from the peripheral region of the protrusion area in the thickness direction of the positive electrode is 2 μm to 10 μm.

8. The electrochemical device according to claim 6, wherein, In the main body, the height h2 of the protrusion area protruding from the peripheral region of the protrusion area in the thickness direction of the positive electrode is 2 μm to 5 μm.

9. The electrochemical device according to claim 6, wherein, In the curved portion, the height h2 of the protrusion area protruding from the peripheral region of the protrusion area in the thickness direction of the positive electrode is 5 μm to 30 μm.

10. The electrochemical device according to claim 6, wherein, In the curved portion, the height h2 of the protrusion area protruding from the peripheral region of the protrusion area in the thickness direction of the positive electrode is 10 μm to 30 μm.

11. The electrochemical device according to claim 1, wherein, It satisfies at least one of the following: (a) The surface of the isolation membrane has a ceramic layer; (b) The separator comprises at least one of polypropylene, polyethylene, or a composite film of polypropylene and polyethylene; (c) The thickness h3 of the isolation membrane is 3 μm to 30 μm.

12. The electrochemical device according to claim 1, wherein, The peel strength between the separator and the positive electrode is 0 N / m.

13. The electrochemical device according to claim 1, wherein, The number of raised areas is at least two, and the raised areas are evenly distributed on the second surface.

14. The electrochemical device according to claim 1, wherein, The density of the protrusions on the second surface is 7 per cm. 2 Up to 60 per cm 2 .

15. The electrochemical device according to claim 6, wherein, In the main body, the density of the protrusions on the second surface is 8 per cm. 2 Up to 50 per cm 2 .

16. The electrochemical device according to claim 6, wherein, In the curved portion, the density of the protrusions on the second surface is 8 per cm. 2 Up to 40 per cm 2 .

17. The electrochemical device according to claim 6, wherein, In the main body, the density of the protrusions on the second surface is 8 per cm. 2 Up to 30 per cm 2 .

18. The electrochemical device according to claim 6, wherein, In the main body, the density of the protrusions on the second surface is 8 per cm. 2 Up to 20 per cm 2 .

19. The electrochemical device according to claim 1, wherein, The shape of the raised area can be dot-shaped, strip-shaped, or polygonal.

20. The electrochemical device according to claim 1, wherein, The positive electrode, the negative electrode, and the separator are wound together to form a wound structure; the wound structure includes a main body and curved portions located on both sides of the main body; In the main body, the surface of the negative electrode facing the positive electrode is a plane; In the curved section, the surface of the negative electrode facing the positive electrode is an arc surface.

21. An electronic device comprising an electrochemical device according to any one of claims 1 to 20.

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