Electrochemical apparatus, and electronic apparatus using electrochemical apparatus

Abstract

Provided are an electrochemical apparatus, and an electronic apparatus using the electrochemical apparatus. The electrochemical apparatus comprises a positive electrode sheet, a negative electrode sheet and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive-electrode current collector, and a positive-electrode active layer provided on at least one side of the positive-electrode current collector, wherein the positive-electrode active layer comprises a central region, and an edge region arranged around the periphery of the central region, and the width of the edge region ranges from 2 mm to 10 mm, and the periphery of the edge region is the periphery of the positive-electrode active layer. Under the condition that an SOC is 100%, the difference value between the delithiation amount of the central region and the delithiation amount of the edge region ranges from 0.1% to 2%, such that the stability of the edge region is enhanced and the escalation of oxidation side reactions is suppressed, thereby facilitating an improvement in the overall cycling stability of the electrochemical apparatus.

Description

Electrochemical device and electronic device using the same Technical Field

[0001] The present application relates to the field of electrochemical energy supply, and in particular to an electrochemical device and an electronic device using the electrochemical device. Background Art

[0002] Electrochemical devices, especially lithium-ion batteries, offer advantages such as high energy density, high power, and long cycle life, making them widely used in consumer electronics. However, as their application continues to expand, particularly in electric bicycles and electric vehicles, the performance requirements for electrochemical devices are also increasing. Therefore, ensuring or improving the overall performance of electrochemical devices is a current challenge.

[0003] Summary of the Invention

[0004] In view of the above situation, an electrochemical device is provided that improves overall performance by reducing the difference between the amount of lithium depleted in the central region and the amount of lithium depleted in the edge region, and an electronic device using the electrochemical device.

[0005] In a first aspect, the present application provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active layer comprises a central region and an edge region disposed around the outer periphery of the central region. The width of the edge region is 2 mm to 10 mm, and the outer periphery of the edge region is the outer periphery of the positive electrode active layer. Under 100% SOC conditions, the difference between the amount of lithium depletion in the central region and the amount of lithium depletion in the edge region is 0.1% to 2%.

[0006] In an electrochemical device, the electric field strength at the edge of each electrode is higher than that at the center. Due to the lack of differentiation between the edge and center regions of the electrode in the prior art, the edge region has a fast delithiation rate and a high amount of delithiation, while the center region has a slow delithiation rate and a low amount of delithiation. This results in a high over-delithiation potential at the edge region, which can easily lead to structural instability and an increase in oxidative side reactions in the electrochemical device, worsening the cycling stability of the electrochemical device. In the electrochemical device of the present application, by designing the difference between the delithiation amount at the center region and the delithiation amount at the edge region, it is beneficial to improve the stability of the edge region and to control the increase in oxidative side reactions, thereby improving the overall cycling stability of the electrochemical device.

[0007] Based on the first aspect, in some possible embodiments, under 100% SOC conditions, the difference between the amount of delithiation in the central area and the amount of delithiation in the edge area is 0.1% to 1.5%, which is beneficial to further improve the stability of the edge area and to control the increase of oxidation side reactions, thereby helping to improve the overall cycle stability of the electrochemical device.

[0008] Based on the first aspect, in some possible embodiments, the edge region includes a first positive electrode active material, the first positive electrode active material including at least one of lithium cobalt oxide with a coating amount or doping amount of 0.81 wt% to 5.0 wt%, lithium nickel cobalt manganese oxide with a cobalt content of 5% to 20%, or lithium iron phosphate. The central region includes a second positive electrode active material, the second positive electrode active material including at least one of lithium cobalt oxide with a coating amount or doping amount of 0.05 wt% to 0.8 wt%, lithium nickel cobalt manganese oxide with a cobalt content of 21% to 33%, or lithium manganese oxide.

[0009] In the above possible implementation manner, the edge region uses an active material with lower kinetic performance and higher stability than that of the central region, which is beneficial to reducing the phenomenon of excessive delithiation of the edge region compared to the central region and improving the stability of the edge region, so as to narrow the difference in kinetic performance between the central region and the edge region, and thus help improve the overall cycle stability of the electrochemical device.

[0010] Based on the first aspect, in some possible embodiments, the edge area also includes a first adhesive, the center area also includes a second adhesive, the ratio of the swelling rate of the first adhesive to the swelling rate of the second adhesive is 1:3 to 1:1.1, and the swelling rate of the first adhesive is 1% to 10%.

[0011] Since the edge region of the electrode is easily exposed to free electrolyte, the binder in the active layer swells when immersed in the electrolyte, which reduces the bonding effect and easily causes the active layer to fall off due to repeated expansion and contraction during the cycle of the electrochemical device, thereby deteriorating the cycle performance of the electrochemical device. In the above possible embodiment, by designing the swelling rate of the first binder in the edge region to be lower than the swelling rate of the second binder in the center region, it is beneficial to reduce the impact of the swelling of the first binder on the edge region, thereby reducing the risk of loosening or even falling off in the edge region to improve the stability of the edge region, and further improving the overall cycle stability of the electrochemical device. The above-mentioned first binder with a specific swelling rate and the second binder with a specific ratio range to the swelling rate of the first binder are beneficial to ensure that the entire positive electrode active layer is not easy to loosen while reducing the difference between the edge region and the center region caused by swelling, thereby improving the overall cycle stability of the electrochemical device.

[0012] Based on the first aspect, in some possible implementations, the first binder is a polyacrylic acid binder, and the molecular weight of the first binder is 100,000 to 1,000,000.

[0013] In the above possible implementation manner, the above first binder has a lower swelling rate, which is beneficial to reducing the impact of the swelling of the first binder on the edge area, thereby reducing the risk of the edge area loosening or even falling off, thereby improving the stability of the edge area, and further helping to improve the overall cycle stability of the electrochemical device.

[0014] Based on the first aspect, in some possible embodiments, the content of the first binder in the edge region is 0.5wt% to 5.0wt%, and the content of the first binder in the edge region is greater than the content of the second binder in the central region, and the difference is 0.1wt% to 1.0wt%.

[0015] In the above possible embodiments, based on the fact that the edge region of the electrode is easily exposed to the free electrolyte, under the condition of the same degree of swelling, the use of a first binder with a higher content in the edge region is beneficial to improving the bonding force between the edge region and the positive electrode current collector, thereby reducing the risk of loosening or even falling off of the edge region to improve the stability of the edge region, thereby improving the stability of the overall cycle of the electrochemical device. Furthermore, by designing the edge region to use a higher binder content and the center region to use a lower binder content, the second binder in the center region is reduced compared to the first binder in the edge region. The interface transport barrier of lithium ions is improved to improve the kinetic performance, thereby narrowing the difference in kinetic performance between the center region and the edge region, thereby improving the overall capacity of the electrochemical device and improving the overall performance of the electrochemical device. In addition, the first binder within the above-mentioned specific content range and the second binder having a content with a specific difference range from the first binder content are beneficial to ensuring the bonding force between the edge area and the center area and the positive electrode current collector, that is, it is beneficial to ensuring the bonding force between the positive electrode active layer and the positive electrode current collector, while also beneficial to improving the kinetic performance of the entire positive electrode active layer, thereby being beneficial to the stability of the positive electrode sheet structure while also beneficial to improving the overall kinetic performance of the electrochemical device, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0016] Based on the first aspect, in some possible embodiments, the edge area also includes a first conductive agent, and the central area also includes a second conductive agent. The content of the first conductive agent in the edge area is 0.2 wt% to 2.0 wt%, and the ratio of the content of the first conductive agent in the edge area to the content of the second conductive agent in the central area is 1:2 to 1:1.05.

[0017] In the above possible embodiments, by designing the edge region to have a lower conductive agent content and the center region to have a higher conductive agent content, it is beneficial to improve the electron transport capacity of the center region compared to the edge region, thereby improving the kinetic performance of the center region compared to the edge region, thereby helping to narrow the kinetic performance difference between the edge and center regions, and further helping to improve the overall capacity of the electrochemical device, thereby improving the overall performance of the electrochemical device. The above-mentioned specific content of the first conductive agent and the second conductive agent having a content within a specific ratio range with the content of the first conductive agent are beneficial to ensuring the electron transport capacity of the positive electrode sheet and giving the positive electrode sheet higher kinetic performance, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0018] Based on the first aspect, in some possible embodiments, the first conductive agent includes conductive carbon black, carbon nanotubes and vapor-grown carbon fibers in a weight ratio of (3.3 to 9): (3.3 to 0.5): (3.4 to 0.5), and the second conductive agent includes conductive carbon black, carbon nanotubes and vapor-grown carbon fibers in a weight ratio of (0.5 to 3.3): (9 to 3.3): (0.5 to 3.4).

[0019] In the above possible embodiments, the composition of the first conductive agent in the edge area contains a lower content of high-conductivity materials than the composition of the second conductive agent in the central area, which is beneficial to reducing the electron transmission capacity of the edge area to reduce the kinetic performance, and further beneficial to narrowing the difference between the edge area and the central area, which is beneficial to improving the overall cycle stability of the electrochemical device.

[0020] Based on the first aspect, in some possible implementations, the electrochemical device further includes an electrolyte, the electrolyte contains a nitrile additive, and the content of the nitrile additive in the electrolyte is 0.1 wt % to 3 wt %.

[0021] In the above possible implementation manner, the electrolyte contains the above specific content of nitrile additives, which is conducive to forming a stable interface film on the surface of the positive electrode plate, thereby facilitating the improvement of the overall cycle stability of the electrochemical device.

[0022] Based on the first aspect, in some possible implementations, the tortuosity of the edge region is 3 to 8, the tortuosity of the central region is smaller than that of the edge region, and the difference is 1 to 3.

[0023] In the above possible embodiments, by designing the tortuosity of the edge region to be greater than that of the central region, it is beneficial to improve the liquid phase transport barrier of lithium ions in the edge region compared to the central region, thereby helping to reduce the kinetic performance of the edge region to reduce the amount of lithium desorption in the edge region, thereby helping to reduce the risk of lithium deposition in the electrochemical device and improve the stability of the overall cycle of the electrochemical device. In addition, the edge region having a tortuosity within the above range and the central region having a specific difference range in tortuosity from the edge region are beneficial to reducing the amount of lithium desorption in the edge region and narrowing the difference between the edge region and the central region while ensuring the overall energy density of the electrochemical device.

[0024] A second aspect of the present application provides an electronic device comprising a main body and the electrochemical device described above, the electrochemical device being electrically connected to the main body for powering the main body. In the electronic device described above, by designing the difference between the amount of lithium depleted in the central region and the amount of lithium depleted in the edge region, the stability of the edge region is improved and the increase in oxidative side reactions is controlled, thereby improving the stability of the overall cycle of the electrochemical device and, in turn, improving the power supply performance of the electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a schematic structural diagram of an electrochemical device according to one embodiment of the present application.

[0026] FIG2 is a schematic cross-sectional view of an electrochemical device according to one embodiment of the present application.

[0027] FIG3 is a schematic cross-sectional view of a positive electrode sheet according to an embodiment of the present application, taken along a direction perpendicular to the thickness.

[0028] FIG4 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

[0029] Description of main component symbols

[0030] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0031] The following specific embodiments illustrate the implementation of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Although the description of the present application will be introduced in conjunction with the embodiments, this does not mean that the features of this application are limited to this implementation. On the contrary, the purpose of introducing the application in conjunction with the implementation is to cover other options or modifications that may be extended based on the claims of the present application. In order to provide an in-depth understanding of the present application, the following description will contain many specific details. The present application can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present application, some specific details will be omitted in the description.

[0032] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0033] Hereinafter, if used, the terms "first," "second," etc., are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature qualified as "first," "second," etc. may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0034] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0035] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to 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.

[0036] The following describes the embodiments of the present application in conjunction with the accompanying drawings. Unless otherwise specified, the data range values ​​recorded in this application should include the end values.

[0037] The energy density of lithium-ion batteries is usually improved by increasing the capacity and voltage of the active materials in the electrodes and increasing the content of the active materials in the electrodes. Among them, increasing the compaction density of the active materials and preparing thicker electrode active layers can increase the content of the active materials.

[0038] In lithium-ion batteries, there are differences in electric field strength, potential and polarization between the edge and center areas of the electrode, resulting in uneven electrochemical reactions between the edge and main areas of the electrode. This uneven electrochemical reaction phenomenon becomes more obvious with the increase of active layer thickness and active layer compaction density, thereby deteriorating the overall performance of the battery (including but not limited to affecting cycle life, causing thermal safety issues, etc.) and restricting a substantial increase in active layer thickness and compaction density.

[0039] In view of this, embodiments of the present application provide an electrochemical device and an electronic notification using the electrochemical device.

[0040] Please refer to Figure 1, which shows an electrochemical device 100 according to an embodiment of the present application. Please refer to Figure 2, which shows the electrochemical device 100 including a positive electrode sheet 10, a negative electrode sheet 30, and a separator 50. The separator 50 is disposed between the positive electrode sheet 10 and the negative electrode sheet 30. As shown in Figure 2, the positive electrode sheet 10, the separator 50, and the negative electrode sheet 30 can be alternately stacked in the thickness direction X to form a laminated electrode assembly A, or the positive electrode sheet 10, the separator 50, and the negative electrode sheet 30 can be stacked in sequence and then wound to form a wound electrode assembly (not shown). Below, the laminated electrode assembly A will be used as an example for subsequent description.

[0041] The electrochemical device 100 also includes a housing 20 and an electrolyte 60. The electrolyte 60 and the electrode assembly A are contained within the housing 20, and the positive electrode sheet 10, the negative electrode sheet 30, and the separator 50 in the electrode assembly A are in contact with the electrolyte 60. The housing 20 can be a packaging bag formed using a packaging film, such as, but not limited to, an aluminum-plastic film. That is, the electrochemical device can be a soft-pack battery. The housing 20 can also be, but is not limited to, those disclosed in the prior art, such as steel-cased batteries and aluminum-cased batteries.

[0042] The positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active layer 13 disposed on at least one surface of the positive electrode current collector 11. In this embodiment, as shown in FIG2 , the positive electrode active layer 13 may be disposed on only one side of the positive electrode current collector 11, or may be disposed on two opposite surfaces of the positive electrode current collector 11.

[0043] The positive electrode current collector 11 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0044] Please refer to Figure 3 . The positive electrode active layer 13 includes a central region 131 and an edge region 133 disposed around the outer periphery of the central region 131. When the positive electrode sheet 10 forms a laminated electrode assembly A, as shown in Figure 3 , when viewed along the thickness direction X, the edge region 133 is annular (a rectangular ring as shown in Figure 3 ) surrounding the central region 131. When the positive electrode sheet 10 forms a wound electrode assembly, when the positive electrode sheet 10 is laid out, i.e., not wound, when viewed along the thickness direction of the positive electrode sheet 10, the edge region 133 is annular (a rectangular ring as shown in Figure 3 ) surrounding the central region 131. When the positive electrode sheet 10 is wound to form a wound electrode assembly, the edge region 133 includes the starting and ending ends of the positive electrode active layer 13, as well as two ends of the positive electrode active layer 13 disposed opposite each other along the central axis of the winding.

[0045] In this embodiment, the width of the edge region 133 may be 2 mm to 10 mm, for example, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, or any specific value between any two adjacent values. The outer periphery of the edge region 133 is the outer periphery of the positive electrode active layer 13. The width of the edge region 133 refers to the distance from any position on the outer periphery of the edge region 133 to the closest point where the adjacent edge region 133 connects to the inner periphery of the central region 131.

[0046] Under 100% SOC conditions, the amount of lithium removed from the edge region 133 is greater than the amount of lithium removed from the center region 131, and the difference is 0.1% to 2%, for example, 0.1%, 0.25%, 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75%, 2%, or any specific value between any two adjacent values ​​mentioned above. In the electrochemical device, the electric field strength of the edge region of each electrode is higher than that of the center region. Since the edge region and the center region of the electrode are designed in the same way in the prior art, the delithiation rate of the edge region is fast and the amount of lithium removed is large, while the delithiation rate of the center region is slow and the amount of lithium removed is small, resulting in a high over-delithiation potential in the edge region, which can easily lead to structural instability and increase the oxidative side reactions in the electrochemical device, thereby deteriorating the cycle stability of the electrochemical device. However, the present application designs the difference between the delithiation amount of the center region and the delithiation amount of the edge region, which is beneficial to improving the stability of the edge region and controlling the increase of the oxidative side reactions, thereby improving the overall cycle stability of the electrochemical device. In some embodiments, under a 100% SOC condition, the difference between the amount of delithiation in the edge region 133 and the amount of delithiation in the central region 131 may be 0.1% to 1.5%.

[0047] The edge region 133 includes a first positive electrode active material, and the center region 131 includes a second positive electrode active material. The first positive electrode active material and the second positive electrode active material each include a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the first positive electrode active material and the second positive electrode active material each may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the first positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or lithium iron phosphate (LiFePO4). The second positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5Mn 1.5 O4) or lithium iron phosphate (LiFePO4) and the like.

[0048] Furthermore, in this embodiment, the first positive electrode active material may include at least one of lithium cobalt oxide with a coating or doping amount of 0.81wt% to 5.0wt%, lithium nickel cobalt manganese oxide with a cobalt content of 5% to 20%, or lithium iron phosphate; the central region includes a second positive electrode active material, and the second positive electrode active material may include at least one of lithium cobalt oxide with a coating or doping amount of 0.05wt% to 0.8wt%, lithium nickel cobalt manganese oxide with a cobalt content of 21% to 33%, or lithium manganese oxide. Furthermore, the first positive electrode active material may be composed of at least one of lithium cobalt oxide with a coating or doping amount of 0.81wt% to 5.0wt%, lithium nickel cobalt manganese oxide with a cobalt content of 5% to 20%, or lithium iron phosphate; the second positive electrode active material may be composed of at least one of lithium cobalt oxide with a coating or doping amount of 0.05wt% to 0.8wt%, lithium nickel cobalt manganese oxide with a cobalt content of 21% to 33%, or lithium manganese oxide. The edge region 133 uses an active material with lower kinetic performance and higher stability than that of the central region 131, which is beneficial to reducing the phenomenon of excessive delithiation of the edge region 133 compared to the central region 131 and improving the stability of the edge region 133, thereby narrowing the difference in kinetic performance between the central region 131 and the edge region 133, and further beneficial to improving the overall cycle stability of the electrochemical device.

[0049] In the present application, the coating or doping of lithium cobalt oxide is the common coating and doping of lithium cobalt oxide in the industry, wherein the doping element can generally be but not limited to at least one of B, Al, Mg, Cr or Ni, and the coating can generally be formed by at least one of TiO2, MgO, Al2O3 or ZnO to form a coating layer, but not limited to the specific doping method and coating method are not specifically limited in this application.

[0050] Because the positive electrode active layer 13 undergoes a lamination process during its formation, the outer edge of the central region 131 and the inner edge of the edge region 133, which are adjacent or connected to each other before lamination, merge with each other after lamination to form a transition region 135. That is, the positive electrode active layer 13 also includes the transition region 135, which connects the inner periphery of the edge region 133 and the outer periphery of the central region 131.

[0051] In addition, since the positive electrode active layer 13 undergoes a lamination process during its formation, the thickness of each region varies before and after lamination. The edge region 133 may extend away from the center region 131. However, since the center region 131 is surrounded by the edge region 133, the movable space of the center region 131 during lamination is limited by the edge region 133. Therefore, the thickness of the center region 131 is generally greater than that of the edge region 133. In some embodiments, the difference between the thickness of the center region 131 and the thickness of the edge region 133 may be less than 1 micron, which is beneficial for improving the flatness of the electrode assembly formed by the positive electrode sheet 10 and the negative electrode sheet 30, thereby improving the overall flatness of the electrochemical device.

[0052] In some embodiments, the tortuosity of the edge region 133 may be 3 to 8, and the tortuosity of the central region 131 may be less than the tortuosity of the edge region 133, and the difference may be 1 to 3, so as to improve the liquid-phase transport barrier of lithium ions in the edge region 133 compared to the central region 131, thereby helping to reduce the difference in kinetic properties of the edge region 133 to reduce the amount of lithium removed from the edge region 133, thereby helping to reduce the risk of lithium deposition in the electrochemical device and improve the stability of the overall cycle of the electrochemical device. In addition, the edge region 133 having a tortuosity within the above range and the central region 131 having a specific difference range in tortuosity from the edge region 133 are conducive to reducing the amount of lithium removed from the edge region 133 and reducing the difference between the edge region 133 and the central region 131 while ensuring the overall energy density of the electrochemical device. In some embodiments, the difference between the tortuosity of the edge region 133 and the tortuosity of the central region 131 can be 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, or any specific value between any two adjacent values ​​mentioned above.

[0053] The edge region 133 further includes a first binder for bonding the first positive electrode active material particles to facilitate film formation and improve the bonding strength between the edge region 133 and the positive electrode current collector 11. The central region 131 further includes a second binder for bonding the second positive electrode active material particles to facilitate film formation and improve the bonding strength between the central region 131 and the positive electrode current collector 11.

[0054] The first binder and the second binder may respectively include but are not limited to at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyacrylic resin (PAA), styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0055] In some embodiments, the swelling rate of the first binder may be lower than that of the second binder. Because the edge regions of the positive electrode sheets are easily exposed to free electrolyte, the binder in the positive electrode active layer swells when immersed in the electrolyte, reducing the bonding effect. This can easily cause the active layer to fall off due to repeated expansion and contraction during the cycling of the electrochemical device, thereby deteriorating the cycling performance of the electrochemical device. By designing the swelling rate of the first binder in the edge region 133 to be lower than that of the second binder in the center region 131, the impact of the first binder swelling on the edge region 133 is reduced, thereby reducing the risk of loosening or even falling off of the edge region 133, improving the stability of the edge region 133, and ultimately improving the overall cycling stability of the electrochemical device. Specifically, the ratio of the swelling rate of the first binder to the swelling rate of the second binder can be 1:3 to 1:1.1, for example, 1:3, 1:2.75, 1:2.5, 1:2.25, 1:2, 1:1.75, 1:1.5, 1:1.35, 1:1.1, or any specific ratio between any two adjacent ratios. In some embodiments, the swelling rate of the first binder can be 1% to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any specific ratio between any two adjacent ratios. The first binder having the above-mentioned specific swelling rate and the second binder having a specific ratio range with respect to the swelling rate of the first binder are beneficial for ensuring that the entire positive electrode active layer is not easily loosened while reducing the difference between the edge region 133 and the center region 131 caused by swelling, thereby improving the overall cycling stability of the electrochemical device.

[0056] Furthermore, in some embodiments, the first binder may be, but is not limited to, a polyacrylic acid adhesive, and the molecular weight of the first binder may be between 100,000 and 1,000,000, for example, 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, or any specific value between any two adjacent values. The first binder has a low swelling rate, thereby reducing the impact of swelling of the first binder on the edge region, thereby reducing the risk of loosening or even falling off the edge region, improving the stability of the edge region, and thereby improving the overall cycling stability of the electrochemical device.

[0057] The content of the first binder in the edge region 133 can be greater than the content of the second binder in the center region 131. Because the edge region of the positive electrode sheet is easily exposed to free electrolyte, using a higher content of the first binder in the edge region 133, given the same degree of swelling, can improve the bonding between the edge region 133 and the positive electrode current collector 11, thereby reducing the risk of loosening or even falling off the edge region 133 and improving the stability of the edge region 133, thereby improving the overall cycling stability of the electrochemical device. Furthermore, by designing a higher binder content in the edge region 133 and a lower binder content in the center region 131, the second binder in the center region 131 is less likely to hinder the interfacial transport of lithium ions than the first binder in the edge region 133, thereby improving the kinetic performance of the center region 131 compared to the edge region 133. This reduces the difference in kinetic performance between the center region 131 and the edge region 133, thereby improving the overall capacity of the electrochemical device and enhancing the overall performance of the electrochemical device.

[0058] Specifically, the content of the first binder in the edge region 133 may be 0.5 wt % to 5.0 wt %, for example, 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 3.5 wt %, 4.0 wt %, 4.5 wt %, 5.0 wt %, or any specific value between any two adjacent values ​​thereof. In some embodiments, the difference between the content of the first binder in the edge region 133 and the content of the second binder in the central region 131 may be 0.1 wt % to 1.0 wt %, for example, 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1.0 wt %, or any specific value between any two adjacent values ​​thereof. The first binder within the above-mentioned specific content range and the second binder having a content within a specific difference range from the first binder are beneficial to ensuring the bonding force between the edge region 133 and the central region 131 and the positive electrode current collector 11, that is, it is beneficial to ensuring the bonding force between the positive electrode active layer 13 and the positive electrode current collector 11, while also beneficial to improving the kinetic performance of the entire positive electrode active layer 13, thereby being beneficial to the stability of the positive electrode sheet structure while also beneficial to improving the overall kinetic performance of the electrochemical device, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0059] The edge region 133 may further include a first conductive agent, and the center region 131 may further include a second conductive agent. The content of the second conductive agent in the center region 131 may be greater than the content of the first conductive agent in the edge region 133. By designing the edge region 133 to have a lower conductive agent content and the center region 131 to have a higher conductive agent content, the electron transport capability of the center region 131 is improved compared to the edge region 133, thereby improving the kinetic performance of the center region 131 compared to the edge region 133. This, in turn, reduces the difference in kinetic performance between the edge region 133 and the center region 131, thereby increasing the overall capacity of the electrochemical device and improving the overall performance of the electrochemical device.

[0060] Specifically, the ratio of the first conductive agent content in the edge region 133 to the second conductive agent content in the central region 131 can be 1:2 to 1:1.05, for example, 1:2, 1:1.9, 1:1.8, 1:1.7, 1:1.6, 1:1.5, 1:1.4, 1:1.3, 1:1.2, 1:1.05, or any specific ratio between any two adjacent ratios. In some embodiments, the first conductive agent content in the edge region can be 0.2 wt % to 2.0 wt %, for example, 0.2 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.8 wt %, 1.0 wt %, 1.2 wt %, 1.4 wt %, 1.5 wt %, 1.6 wt %, 1.8 wt %, 2.0 wt %, or any specific ratio between any two adjacent ratios. The above-mentioned specific content of the first conductive agent and the second conductive agent whose content has a specific ratio range with the content of the first conductive agent are beneficial to ensuring the positive electrode's ability to transmit electrons and making the positive electrode have higher kinetic performance, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0061] The first conductive agent and the second conductive agent may include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, conductive carbon black (SP), carbon nanotubes (CNTs), acetylene black, Ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0062] In this embodiment, the first conductive agent may include SP, CNT and vapor-grown carbon fiber (VGCF), and the ratio of SP:CN:VGCF by weight may be (3.3-9):(3.3-0.5):(3.4-0.5). The second conductive agent may include SP, CNT and vapor-grown carbon fiber (VGCF), and the ratio of SP:CN:VGCF by weight may be (0.5-3.3):(9-3.3):(0.5-3.4). Furthermore, the first conductive agent may be composed of SP, CNT and VGCF, and the second conductive agent may also be composed of SP, CNT and VGCF. The composition of the first conductive agent in the edge region 133 is lower than that of the second conductive agent in the central region 131, which is conducive to reducing the electron transport capacity of the edge region 133 to reduce the kinetic performance, thereby helping to narrow the difference between the edge region 133 and the central region 131, and helping to improve the stability of the overall cycle of the electrochemical device.

[0063] The negative electrode sheet 30 includes a negative current collector 31 and a negative active layer 33 disposed on at least one surface of the negative current collector 31. In this embodiment, as shown in FIG3 , the negative active layers 33 may be disposed on two opposite surfaces of the negative current collector 31, respectively.

[0064] The negative electrode current collector 31 can be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil or a carbon-based current collector, or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0065] The negative electrode active layer 33 includes a negative electrode active material, which can be any known negative electrode active material capable of reversible deintercalation of active ions, and is not limited in this application. For example, it can include, but is not limited to, at least one of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. The graphite can be selected from at least one of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0066] The negative electrode active layer 33 also includes a binder to bind the negative electrode active material particles to facilitate film formation and improve the bonding between the negative electrode active layer and the negative electrode current collector. In some embodiments, the binder in the negative electrode active layer 33 may include, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic resin, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0067] The isolation membrane 50 comprises a porous film layer, and its material may include at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene may include at least one of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in improving short circuits and can enhance the stability of the electrochemical device 100 through a shutdown effect.

[0068] The electrolyte 60 may be in one or more of a gel state, a solid state, and a liquid state. The liquid electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt can be selected from but is not limited to one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2, tris(trifluoromethylsulfonyl)methyl lithium (LiC(SO2CF3)3), lithium bisoxalatoborate (LiBOB) and lithium difluorophosphate (LiPO2F2). For example, the lithium salt is selected from LiPF6 because it can give high ionic conductivity and improve cycle characteristics. The non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, Compounds, nitrile compounds, other organic solvents or combinations thereof. Examples of carbonate compounds may include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), 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 and combinations thereof.

[0069] In some embodiments, the electrolyte 60 may also include nitrile additives, wherein the content of the nitrile additives in the electrolyte may be 0.1 wt% to 3 wt%, for example, 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt% or any specific value between any two adjacent values ​​mentioned above, which is beneficial to forming a stable interface film on the surface of the positive electrode sheet, thereby helping to improve the overall cycle stability of the electrochemical device.

[0070] The nitrile additive can be selected from but is not limited to at least one of succinonitrile, glutaronitrile, adiponitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarboxylic acid nitrile, 1,2,3-tris(cyanoethoxy)propane or 1,5-dicyanopentane.

[0071] 4 , the electrochemical device 100 can be applied to an electronic device 200. The electronic device 200 further includes a body 201, and the electrochemical device 100 is electrically connected to the body 201 for powering the body 201. The electronic device 200 may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, lighting fixtures, toys, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0072] The present application is described in detail below through comparative examples and examples. It is understood that the parameters in the present application are not limited to those described in the comparative examples and examples, and can be selected according to actual needs.

[0073] According to the table, laminated lithium-ion batteries corresponding to Examples 1-27 and Comparative Examples 1-3 were prepared. The parameters of the lithium-ion batteries corresponding to Examples 1-27 and Comparative Examples 1-3 were the same except for the parameters in the table.

[0074] Example 1

[0075] Preparation of positive electrode sheet:

[0076] The positive electrode active material lithium cobalt oxide (coating amount or doping amount 0.5wt%), binder PVDF (homopolymer, molecular weight M 中 1.27 million, swelling rate ESR 中 The conductive agent SP, the conductive agent CNT, and the conductive agent VGCF are added to N-methylpyrrolidone (NMP) in a ratio of 97.0:1.5:0.43:0.86:0.21, mixed and dispersed to prepare a first slurry (solid content of 75%), and the first slurry is extruded onto an aluminum foil current collector with a thickness of 9 microns and dried to form a first electrode sheet. The first slurry is correspondingly cured to form a first active layer (corresponding to the central area).

[0077] The positive electrode active material lithium cobalt oxide (coating amount or doping amount 1.2wt%), binder PAA (molecular weight M 边 500,000, swelling rate ESR 边The conductive agent SP, the conductive agent CNT and the conductive agent VGCF are added into NMP in a ratio of 97.0:2.0:0.57:0.29:0.14, mixed and dispersed to prepare a second slurry (solid content of 75%), and the second slurry is coated outwardly on the outer periphery of the first active layer of the first electrode sheet by gravure, and the second electrode sheet is formed after drying. The second slurry is correspondingly cured to form a second active layer (corresponding to the edge area).

[0078] The cold pressed positive electrode (the tortuosity of the edge area is 5 and the tortuosity of the center area is 3.5) is formed by cold pressing at a pressure of 80t and a speed of 20m / min, and then die-cut to form the positive electrode sheet. 过渡 The width of the edge area is 0.2mm. 边 The thickness of the center area is 0.5 microns greater than that of the edge area, that is, △Tk is 0.5 microns, and the thickness of the edge area Tk 边 The size of the positive electrode sheet is approximately 70mm*80mm.

[0079] Preparation of negative electrode sheet:

[0080] A negative electrode slurry (48% solids content) was prepared by mixing and dispersing the negative electrode active material graphite, binder SBR, and binder CMC in deionized water at a ratio of 97.4:1.4:1.2. The slurry was then extrusion-coated onto a 6-micron copper current collector and dried to form a negative electrode sheet. The negative electrode slurry also formed the negative electrode active layer. The thickness of the negative electrode active layer was 120 microns. The dimensions of the negative electrode sheet were approximately 72mm by 82mm.

[0081] Preparation of lithium-ion batteries:

[0082] The positive electrode sheets, separator (a PE film with a thickness of 5 microns and a porosity of approximately 35%), and the negative electrode sheets are alternately stacked in sequence to form a laminated electrode assembly. After welding the tabs, the assembly is placed in a battery case and an electrolyte (1M LiPF6in EC:DEC:EMC:adiponitrile = 32.83:32.83:32.83:1.51) is injected. The assembly is then packaged and formed to form a lithium-ion battery, i.e., an electrochemical device.

[0083] At 100% SOC, the difference in the amount of lithium depletion between the edge area and the center area is 1%.

[0084] Lithium removal XRD characterization method: ① The first slurry was applied to a 35µm copper foil surface using a 200µm scraper and then dried at 110°C to form a coated electrode. This was then cold-pressed at 80t pressure and 20m / min to form a cold-pressed positive electrode. The positive electrode was then assembled against the lithium sheet to form a button half-cell (using a specific button half-cell mold with a top window to allow X-ray transmission and ensure sealing). ② The button cell assembled in step 1 was charged at a constant current rate of 0.1C to a cutoff voltage of 4.47V. This was then charged at a constant voltage of 4.47V to a cutoff current of 50µA. After 5 minutes of rest, the cell was discharged at a constant current rate of 0.1C to 3.0V. This charge and discharge procedure was repeated three times. Simultaneously test XRD during the charge and discharge process; ③ Model the XRD 003 crystal plane interlayer spacing d tested in step ② and the amount of lithium cobalt oxide delithiation x during the charge and discharge process (the ratio of the charge or discharge capacity at different voltage states to the rated capacity) to form a linear equation d = -0.7372x + 5.2329; ④ Fully charge the battery cell, disassemble it to obtain the edge area and the middle area, and test XRD separately; ⑤ Substitute the d obtained in step ④ into the corresponding relationship in step ③ to obtain the delithiation amount of the edge area and the middle area, and the difference between the two is the difference in delithiation amount.

[0085] Comparative Example 1

[0086] Comparative Example 1 differs from Example 1 in the preparation of the positive electrode sheet: The positive electrode active material, lithium cobalt oxide (coating or doping amount 1.2 wt%), the binder PVDF (homopolymer, molecular weight 1.27 million, swelling ratio 10%), the conductive agents SP, CNT, and VGCF, were mixed and dispersed in NMP at a ratio of 97.0:2.0:0.57:0.29:0.14 to prepare a positive electrode slurry (solid content 75%). The slurry was extrusion-coated onto a 9-micron-thick aluminum foil current collector and dried to form a positive electrode active layer. The slurry was then cold-pressed at a pressure of 80 tons and a speed of 20 m / min to form a cold-pressed positive electrode (tortuosity 5), which was then die-cut to form positive electrode sheets. The thickness of the positive electrode active layer was 100 microns.

[0087] Laminated lithium-ion batteries corresponding to Examples 2-27 were prepared according to the steps of Example 1 and Tables 1-4 and 6-8 below. Laminated lithium-ion batteries corresponding to Comparative Examples 2-3 were prepared according to the steps of Comparative Example 1 and Table 3 above. The lithium-ion batteries corresponding to Examples 1-27 and Comparative Examples 1-3 had the same parameters except for the steps described above and the parameters in the tables.

[0088] The following performance tests were conducted on each of the above examples and comparative examples: 25°C capacity retention @ 500 cls and 45°C capacity retention @ 500 cls. The test results are recorded in Tables 1-3 and 5-8. The specific methods for each performance test are described below.

[0089] 25℃ Capacity Retention @ 500cls: The lithium-ion battery is charged at 0.2C constant current to the cutoff voltage at 25℃. Then, it is charged at constant voltage at the cutoff voltage until the current is less than 0.05C. After 5 minutes of rest, it is discharged at 0.2C DC to the cutoff voltage. The ratio of the 0.2C DC capacity at the 500th cycle to the 0.2C DC capacity at the first cycle is the 25℃ Capacity Retention @ 500cls. A larger ratio indicates better cycling performance.

[0090] 45℃ Capacity Retention @ 500cls: The lithium-ion battery is charged at 0.2C constant current at 45℃ to the cutoff voltage. Then, it is charged at constant voltage at the cutoff voltage until the current is less than 0.05C. After 5 minutes of rest, it is discharged at 0.2C DC to the cutoff voltage. The ratio of the 0.2C DC capacity at the 500th cycle to the 0.2C DC capacity at the first cycle is the 45℃ Capacity Retention @ 500cls. A larger ratio indicates better cycling performance.

[0091] Table 1

[0092] Table 2

[0093] Table 3

[0094] Table 4 (in the table, △ω 粘 represents the difference between the binder content in the second slurry and the binder content in the first slurry, ω 粘- 边 Indicates the content of binder in the second slurry, ω 导-边 represents the content of the total conductive agent in the second slurry)

[0095] Table 5

[0096] Table 6 (ω in the table 导-边 Represents the content of the total conductive agent in the second slurry, ω 导-中represents the content of the total conductive agent in the first slurry)

[0097] Table 7

[0098] Table 8

[0099] From the data of Examples 1-27 and Comparative Examples 1-3 in Tables 1 to 8, it can be seen that by reducing the difference between the amount of lithium removed from the central region 131 and the amount of lithium removed from the edge region 133 in the positive electrode sheet 10, the capacity retention rate of the lithium-ion battery is improved, that is, the cycle life of the lithium-ion battery is extended and the cycle stability of the lithium-ion battery is improved. Further, from the data of Examples 1-5 in Table 1, it can be seen that the wider the edge region 133 of the positive electrode sheet 10, the more conducive it is to reducing the difference between the amount of lithium removed from the central region 131 and the amount of lithium removed from the edge region 133, thereby being more conducive to improving the capacity retention rate of the lithium-ion battery and improving the cycle stability of the lithium-ion battery. From the data of Examples 1 and 6-9 in Table 2, it can be seen that increasing the coating amount or doping amount of the positive electrode active material in the positive electrode sheet 10 is conducive to reducing the difference between the amount of lithium removed from the central region 131 and the amount of lithium removed from the edge region 133 in the positive electrode sheet 10, thereby being conducive to improving the capacity retention rate of the lithium-ion battery and improving the cycle stability of the lithium-ion battery. From the data in Table 3 comparing Example 1 and Comparative Example 1, Example 10 and Comparative Example 3, and Example 11 and Comparative Example 2, it can be seen that even for positive electrode active materials of different materials, reducing the difference between the amount of lithium depleted in the central region 131 and the amount of lithium depleted in the edge region 133 of the positive electrode sheet 10 can improve the capacity retention rate of the lithium-ion battery, that is, the cycle life of the lithium-ion battery can be extended and the cycle stability can be improved. From the data in Tables 4 and 5 for Example 1 and Examples 12-13, it can be seen that the lower the ratio of the swelling rate of the binder in the edge region 133 of the positive electrode sheet 10 to the swelling rate of the binder in the central region 131, the more conducive it is to reducing the difference between the amount of lithium depleted in the central region 131 and the amount of lithium depleted in the edge region 133 of the positive electrode sheet 10, thereby improving the capacity retention rate of the lithium-ion battery and improving the cycle stability of the lithium-ion battery. As can be seen from the data in Tables 4 and 5 for Examples 1 and 14-15, a higher swelling rate of the binder in the edge region 133 of the positive electrode sheet 10 is more conducive to reducing the difference between the amount of lithium removed from the central region 131 and the amount of lithium removed from the edge region 133 of the positive electrode sheet 10, thereby being more conducive to improving the capacity retention rate of the lithium-ion battery and thus improving the cycling stability of the lithium-ion battery. As can be seen from the data in Tables 4 and 5 for Examples 1 and 16-17, a higher binder content in the edge region 133 of the positive electrode sheet 10 and a greater difference in the binder content from the central region 131 are more conducive to reducing the difference between the amount of lithium removed from the central region 131 and the amount of lithium removed from the edge region 133 of the positive electrode sheet 10, thereby being more conducive to improving the capacity retention rate of the lithium-ion battery and thus improving the cycling stability of the lithium-ion battery.As can be seen from the data of Example 1 and Examples 18-19 in Table 6, a lower ratio of the conductive agent content in the edge region 133 to the central region 131 of the positive electrode sheet 10 is more conducive to reducing the difference between the amount of lithium depleted in the central region 131 and the amount of lithium depleted in the edge region 133 of the positive electrode sheet 10, thereby being more conducive to improving the capacity retention rate of the lithium-ion battery and thus improving the cycling stability of the lithium-ion battery. As can be seen from the data of Example 1 and Examples 20-21 in Table 6, a higher content of SP in the edge region 133 of the positive electrode sheet 10 is more conducive to reducing the amount of lithium depleted in the edge region 133 and thus reducing the difference between the amount of lithium depleted in the central region 131 and the amount of lithium depleted in the edge region 133 of the positive electrode sheet 10, thereby being more conducive to improving the capacity retention rate of the lithium-ion battery and thus improving the cycling stability of the lithium-ion battery. As shown in Table 6 for Example 1 and Examples 22-23, a higher CNT content in the central region 131 of the positive electrode sheet 10 is more conducive to reducing the difference between the amount of lithium removed from the central region 131 and the amount of lithium removed from the edge region 133 of the positive electrode sheet 10, thereby improving the capacity retention rate of the lithium-ion battery and thus improving the cycling stability of the lithium-ion battery. As shown in Table 7 for Example 1 and Examples 24-25, an increase in the content of nitrile additives in the electrolyte is conducive to reducing the difference between the amount of lithium removed from the central region 131 and the amount of lithium removed from the edge region 133 of the positive electrode sheet 10, thereby improving the capacity retention rate of the lithium-ion battery and thus improving the cycling stability of the lithium-ion battery. From the data of Example 1 and Examples 26-27 in Table 8, it can be seen that the higher the tortuosity of the edge area 133 of the positive electrode sheet 10 and the greater the difference in tortuosity with the central area 131, the more conducive it is to reducing the difference in the amount of lithium desorption between the central area 131 and the amount of lithium desorption in the edge area 133 in the positive electrode sheet 10, and thus the more conducive it is to improving the capacity retention rate of the lithium-ion battery and thus improving the cycle stability of the lithium-ion battery.

[0100] In addition, those skilled in the art can make various other corresponding changes and modifications based on the technical concept of this application, and all these changes and modifications should fall within the scope of protection of this application.

Claims

1. An electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one side of the positive electrode current collector, wherein: The positive electrode active layer includes a central area and an edge area arranged around the outer periphery of the central area, the width of the edge area is 2mm to 10mm, and the outer periphery of the edge area is the outer periphery of the positive electrode active layer, and under 100% SOC conditions, the difference between the delithiation amount of the central area and the delithiation amount of the edge area is 0.1% to 2%.

2. The electrochemical device according to claim 1, wherein Under 100% SOC conditions, the difference between the delithiation amount of the central region and the delithiation amount of the edge region is 0.1% to 1.5%.

3. The electrochemical device according to claim 1, wherein The edge area includes a first positive electrode active material, which includes at least one of lithium cobalt oxide with a coating amount or doping amount of 0.81wt% to 5.0wt%, lithium nickel cobalt manganese oxide with a cobalt element content of 5% to 20%, or lithium iron phosphate; the central area includes a second positive electrode active material, which includes at least one of lithium cobalt oxide with a coating amount or doping amount of 0.05wt% to 0.8wt%, lithium nickel cobalt manganese oxide with a cobalt element content of 21% to 33%, or lithium manganese oxide.

4. The electrochemical device according to claim 3, wherein: The edge region further includes a first adhesive, and the central region further includes a second adhesive. The ratio of the swelling rate of the first adhesive to the swelling rate of the second adhesive is 1:3 to 1:1.1, and the swelling rate of the first adhesive is 1% to 10%.

5. The electrochemical device according to claim 4, wherein: The first binder is a polyacrylic acid binder, and the molecular weight of the first binder is 100,000 to 1,000,000.

6. The electrochemical device according to claim 4, wherein: The content of the first binder in the edge region is 0.5 wt % to 5.0 wt %, and the content of the first binder in the edge region is greater than the content of the second binder in the central region, and the difference is 0.1 wt % to 1.0 wt %.

7. The electrochemical device according to claim 3, wherein: The edge region also includes a first conductive agent, and the central region also includes a second conductive agent, the content of the first conductive agent in the edge region is 0.2wt% to 2.0wt%, and the ratio of the content of the first conductive agent in the edge region to the content of the second conductive agent in the central region is 1:2 to 1:1.

05.

8. The electrochemical device according to claim 7, wherein: The first conductive agent includes conductive carbon black, carbon nanotubes and vapor-grown carbon fibers in a weight ratio of (3.3-9): (3.3-0.5): (3.4-0.5), and the second conductive agent includes conductive carbon black, carbon nanotubes and vapor-grown carbon fibers in a weight ratio of (0.5-3.3): (9-3.3): (0.5-3.4).

9. The electrochemical device according to claim 1, wherein: The electrochemical device further includes an electrolyte solution, wherein the electrolyte solution contains a nitrile additive, and the content of the nitrile additive in the electrolyte solution is 0.1 wt % to 3 wt %.

10. The electrochemical device according to claim 1, wherein The tortuosity of the edge region is 3 to 8, the tortuosity of the central region is smaller than the tortuosity of the edge region, and the difference is 1 to 3.

11. An electronic device, comprising a body, wherein the electronic device further comprises an electrochemical device as claimed in any one of claims 1 to 10, and the electrochemical device is electrically connected to the body for supplying power to the body.

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