Electrochemical devices and electronic devices using the same

Abstract

An electrochemical device includes a positive electrode sheet, a negative electrode sheet, and a separator film between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one side of the positive electrode current collector, the positive electrode active layer including a central region and an edge region disposed around an 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. The difference between the delithiation amount of the central region and the delithiation amount of the edge region is 0.1% to 2% under 100% SOC conditions, thereby facilitating the stability of the edge region and the control of the increase of the oxidation side reaction, and further facilitating the stability of the overall cycle of the electrochemical device. The application also provides an electronic device using the above electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical power supply, and more particularly to an electrochemical device and an electronic device using the electrochemical device. Background Technology

[0002] Electrochemical devices, especially lithium-ion batteries, possess advantages such as high energy density, high power, and long cycle life, leading to their widespread use in consumer electronics. However, as their applications continue to expand, particularly in electric bicycles and electric vehicles, the performance requirements for electrochemical devices are constantly increasing. Therefore, ensuring or improving the overall performance of electrochemical devices is a current challenge. Summary of the Invention

[0003] In view of the above, an electrochemical device is provided that improves overall performance by reducing the difference between the amount of lithium delithiation in the central region and the amount of lithium delithiation in the edge region, and an electronic device using the electrochemical device is provided.

[0004] This application provides an electrochemical device including a positive electrode, a negative electrode, and a separator, the separator being located between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer includes a central region and an edge region surrounding 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 active layer. Under 100% SOC conditions, the difference between the amount of lithium delithiation in the central region and the edge region is 0.1% to 2%.

[0005] In electrochemical devices, the electric field strength at the edge region of each electrode is higher than that at the center region. Due to the lack of differentiation between the edge and center regions in existing technologies, the edge region exhibits a faster delithiation rate and greater delithiation amount, while the center region suffers from a slower delithiation rate and less delithiation amount. This results in a higher excessive delithiation potential at the edge region, which can easily lead to structural instability and increased oxidation side reactions in the electrochemical device, thus deteriorating its cycle stability. However, in the electrochemical device described in this application, by designing a difference in the delithiation amount between the center and edge regions, the stability of the edge region is improved, and the increase in oxidation side reactions is controlled, thereby enhancing the overall cycle stability of the electrochemical device.

[0006] Based on the first aspect, in some possible implementations, under 100% SOC conditions, the difference between the amount of lithium removed from the central region and the amount of lithium removed from the edge region is 0.1% to 1.5%, which is beneficial to further improve the stability of the edge region and to control the increase of oxidation side reactions, thereby improving the overall cycle stability of the electrochemical device.

[0007] Based on the first aspect, in some possible embodiments, the edge region includes a first positive electrode active material, which includes at least one of lithium cobalt oxide with a coating 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, which includes at least one of lithium cobalt oxide with a coating 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.

[0008] In the above possible implementations, the edge region uses an active material with lower kinetic performance and higher stability than the central region. This helps to reduce the phenomenon of excessive delithiation in the edge region compared to the central region and improve the stability of the edge region, thereby narrowing the difference in kinetic performance between the central and edge regions and thus improving the overall cycle stability of the electrochemical device.

[0009] Based on the first aspect, in some possible implementations, the edge region further includes a first adhesive, and the central region further includes a second adhesive, wherein 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%.

[0010] Because the electrode edge region is easily exposed to free electrolyte, the binder in the active layer swells under electrolyte immersion, reducing the bonding effect and making the active layer prone to detachment due to repeated expansion and contraction during electrochemical device cycling, thus deteriorating the cycling performance of the electrochemical device. In the above possible embodiments, by designing the swelling rate of the first binder in the edge region to be lower than that 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 detachment of the edge region and improving the stability of the edge region, which in turn helps to improve the overall cycling stability of the electrochemical device. Furthermore, the aforementioned first binder with a specific swelling rate and the second binder with a specific ratio range to the swelling rate of the first binder help to ensure that the entire positive electrode active layer is not easily loosened while reducing the difference between the edge region and the center region caused by swelling, thereby improving the overall cycling stability of the electrochemical device.

[0011] Based on the first aspect, in some possible implementations, the first adhesive is a polyacrylic acid adhesive, and the molecular weight of the first adhesive is between 100,000 and 1,000,000.

[0012] In the above possible implementations, the first adhesive has a low swelling rate, which helps to reduce the impact of the swelling of the first adhesive on the edge region, thereby reducing the risk of loosening or even falling off the edge region and improving the stability of the edge region, which in turn helps to improve the overall cycle stability of the electrochemical device.

[0013] Based on the first aspect, in some possible implementations, the content of the first adhesive in the edge region is 0.5 wt% to 5.0 wt%, and the content of the first adhesive in the edge region is greater than the content of the second adhesive in the center region, with a difference of 0.1 wt% to 1.0 wt%.

[0014] In the above possible implementations, since the electrode edge region is easily exposed to the free electrolyte, using a higher content of the first binder in the edge region, under the same degree of swelling, helps to improve the adhesion between the edge region and the positive electrode current collector. This reduces the risk of loosening or even detachment of the edge region, thereby improving its stability and ultimately enhancing the overall cycle stability of the electrochemical device. Furthermore, by designing a higher binder content in the edge region and a lower binder content in the central region, the interfacial transport barrier of the second binder in the central region compared to the first binder in the edge region is reduced, improving kinetic performance. This narrows the difference in kinetic performance between the central and edge regions, thereby enhancing the overall capacity utilization of the electrochemical device and improving its overall performance. In addition, the first binder with a specific content range and the second binder with a content difference range from the first binder content are beneficial to ensuring the bonding force between the edge region and the central region and the positive electrode current collector. This is beneficial to ensuring the bonding force between the positive electrode active layer and the positive electrode current collector, while also improving the kinetic performance of the entire positive electrode active layer. This is beneficial to the stability of the positive electrode structure and also to improving the overall kinetic performance of the electrochemical device, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0015] Based on the first aspect, in some possible implementations, the edge region further includes a first conductive agent, and the central region further includes a second conductive agent. The content of the first conductive agent in the edge region is 0.2 wt% to 2.0 wt%, 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.

[0016] In the above possible implementations, by designing a lower conductive agent content in the edge region and a higher conductive agent content in the central region, it is beneficial to improve the electron transport capability of the central region compared to the edge region, thereby improving the kinetic performance of the central region compared to the edge region. This helps to reduce the difference in kinetic performance between the edge and central regions, and thus helps to improve the overall capacity of the electrochemical device, thereby improving the overall performance of the electrochemical device. Furthermore, the specific content of the first conductive agent and the second conductive agent, whose content has a specific ratio range to the first conductive agent, help to ensure the electron transport capability of the positive electrode and give the positive electrode higher kinetic performance, thus facilitating the improvement of the overall performance of the electrochemical device.

[0017] Based on the first aspect, in some possible embodiments, the first conductive agent comprises 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 comprises 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).

[0018] In the above possible implementations, the composition of the first conductive agent in the edge region has a lower content of high conductivity material compared to the composition of the second conductive agent in the center region. This helps to reduce the electron transport capability of the edge region and reduce the kinetic performance, thereby helping to reduce the difference between the edge region and the center region and improving the overall cycle stability of the electrochemical device.

[0019] Based on the first aspect, in some possible embodiments, the electrochemical device further includes an electrolyte containing nitrile additives in an amount of 0.1 wt% to 3 wt%.

[0020] In the above possible implementations, the electrolyte contains the aforementioned specific amount of nitrile additives, which is beneficial for forming a stable interfacial film on the surface of the positive electrode, thereby improving the overall cycle stability of the electrochemical device.

[0021] Based on the first aspect, in some possible implementations, the tortuosity of the edge region is 3 to 8, and the tortuosity of the central region is less than that of the edge region, with a difference of 1 to 3.

[0022] In the above possible implementations, by designing the tortuosity of the edge region to be greater than that of the central region, it is beneficial to increase the lithium-ion liquid phase transport resistance in the edge region compared to the central region. This helps to reduce the kinetic performance of the edge region, thereby reducing the amount of lithium delithiation in the edge region. Consequently, it helps to reduce the risk of lithium plating in the electrochemical device and improve the overall cycle stability of the electrochemical device. Furthermore, an edge region with the aforementioned range of tortuosity and a central region with a specific range of tortuosity difference from the edge region help to reduce the amount of lithium delithiation in the edge region and minimize the difference between the edge and central regions while ensuring the overall energy density of the electrochemical device.

[0023] A second aspect of this application provides an electronic device, including a body and an electrochemical device as described above, wherein the electrochemical device is electrically connected to the body for supplying power to the body. In the aforementioned electronic device of this application, by designing the difference between the amount of lithium removal in the central region and the amount of lithium removal in the edge region, it is beneficial to improve the stability of the edge region and to control the increase of oxidation side reactions, thereby improving the overall cycle stability of the electrochemical device and thus enhancing the power supply performance of the electronic device. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of an electrochemical device according to one embodiment of this application.

[0025] Figure 2 This is a cross-sectional schematic diagram of an electrochemical device according to an embodiment of this application.

[0026] Figure 3 This is a cross-sectional view of the positive electrode sheet of one embodiment of this application, perpendicular to the thickness direction.

[0027] Figure 4 This is a schematic diagram of the structure of an electronic device according to one embodiment of this application.

[0028] Explanation of main component symbols

[0029] Electrochemical device 100 Positive electrode sheet 10 Negative electrode sheet 30 Separating membrane 50 Thickness direction X Electrode assembly A case 20 electrolyte 60 Positive current collector 11 Positive electrode active layer 13 Central area 131 Edge area 133 Transition area 135 Negative current collector 31 Negative electrode active layer 33 Electronic devices 200 Ontology 201

[0030] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0031] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Although the description of this application is presented in conjunction with embodiments, this does not mean that the features of this application are limited to this embodiment. On the contrary, the purpose of describing the application in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of this application. To provide a thorough understanding of this application, many specific details will be included in the following description. This application may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of this application, some specific details will be omitted in the description.

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0033] In the following description, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0034] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0035] 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.

[0036] The embodiments of this application are described below with reference to the accompanying drawings. Unless otherwise specified, the data range values ​​recorded in this application shall include the end values.

[0037] The energy density of lithium-ion batteries is usually increased by improving the capacity and voltage of the active materials in the electrode and by increasing the content of active substances in the electrode. Increasing the compaction density of the active materials and preparing a thicker electrode active layer can both increase the content of active substances.

[0038] In lithium-ion batteries, the electric field strength, potential, and polarization differ between the edge and center regions of the electrode, resulting in uneven electrochemical reactions between the edge and main regions. This uneven electrochemical reaction becomes more pronounced with increasing active layer thickness and compaction density, thereby deteriorating the overall battery performance (including but not limited to affecting cycle life and causing thermal safety issues) and limiting significant improvements 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 see Figure 1 This is an electrochemical device 100 according to an embodiment of this application. Please refer to [the relevant documentation]. Figure 2 The electrochemical device 100 includes a positive electrode 10, a negative electrode 30, and a separator 50. The separator 50 is disposed between the positive electrode 10 and the negative electrode 30. Figure 2 As shown, the positive electrode 10, the separator 50, and the negative electrode 30 can be alternately stacked along the thickness direction X to form a stacked electrode assembly A, or the positive electrode 10, the separator 50, and the negative electrode 30 can be stacked in sequence and then wound to form a wound electrode assembly (not shown in the figure). The following will use the stacked electrode assembly A as an example for further explanation.

[0041] The electrochemical device 100 also includes a housing 20 and an electrolyte 60. The electrolyte 60 and the electrode assembly A are housed within the housing 20, and the positive electrode 10, negative electrode 30, and separator 50 in the electrode assembly A are in contact with the electrolyte 60. The housing 20 may be a packaging bag encapsulated with an encapsulation film, such as, but not limited to, aluminum-plastic film; that is, the electrochemical device may be a pouch battery. The housing 20 may also be, but is not limited to, housings disclosed in the prior art such as steel-cased batteries and aluminum-cased batteries.

[0042] The positive electrode 10 includes a positive current collector 11 and a positive active layer 13 disposed on at least one surface of the positive current collector 11. In this embodiment, as... Figure 2 As shown, the positive electrode active layer 13 can be provided on only one side of the positive electrode current collector 11, or the positive electrode active layer 13 can be provided on the two opposite surfaces of the positive electrode current collector 11 respectively.

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

[0044] Please refer to the following: Figure 3The positive electrode active layer 13 includes a central region 131 and an edge region 133 surrounding the outer periphery of the central region 131. When the positive electrode sheet 10 is used to form a stacked electrode assembly A, as shown in the figure... Figure 3 As shown, when viewed along the thickness direction X, the edge region 133 appears to be annular (e.g., Figure 3 The rectangular ring shown surrounds the central region 131. When the positive electrode 10 is formed as a wound electrode assembly, and when the positive electrode 10 is laid flat (i.e., not wound), the edge region 133 appears ring-shaped when viewed along the thickness direction of the positive electrode 10 (as shown). Figure 3 The rectangular ring shown surrounds the central region 131; and when the positive electrode 10 is wound to form a wound electrode assembly, the edge region 133 includes the starting end and the ending end of the winding of the positive active layer 13, as well as the two ends of the positive active layer 13 that are arranged opposite to each other along the winding central axis.

[0045] In this embodiment, the width of the edge region 133 can be from 2mm to 10mm, for example, it can be 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, or any specific value between any two adjacent values ​​mentioned above. 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 nearest 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 that from the central region 131, with a difference of 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 electrochemical devices, the electric field strength of the edge region of each electrode is higher than that of the central region. Due to the lack of difference between the edge and central regions of electrodes in existing technologies, the edge region has a faster lithium removal rate and a larger amount of lithium removed, while the central region has a slower lithium removal rate and a smaller amount of lithium removed. This results in a higher excessive lithium removal potential in the edge region, which easily leads to structural instability and an increase in oxidation side reactions in the electrochemical device, thus deteriorating the cycle stability of the electrochemical device. This application, by designing the difference between the lithium removal amount in the central region and the edge region, is beneficial to improving the stability of the edge region and controlling the increase of oxidation side reactions, thereby improving the overall cycle stability of the electrochemical device. In some implementations, under 100% SOC conditions, the difference between the amount of delithiation in the edge region 133 and the amount of delithiation in the central region 131 can be 0.1% to 1.5%.

[0047] The edge region 133 includes a first positive electrode active material, and the central region 131 includes a second positive electrode active material. The first and second positive electrode active materials each comprise compounds that reversibly insert and deintercalate lithium ions (i.e., lithiation intercalation compounds). In some embodiments, the first and second positive electrode active materials may each comprise a lithium transition metal composite oxide. This 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 materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 The second positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNiO4). 0.5 Mn 1.5 At least one of the following: O4 or lithium iron phosphate (LiFePO4).

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

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

[0050] Since the positive electrode active layer 13 requires a pressing process during its formation, the outer edges of the adjacent or connected central region 131 and the inner edges of the edge region 133 are mixed together after pressing 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] Furthermore, since the positive electrode active layer 13 requires a pressing process during formation, the thickness of each region changes before and after pressing. The edge region 133 can extend away from the central region 131, and because the central region 131 is surrounded by the edge region 133, the movable space of the central region 131 is restricted by the edge region 133 during pressing. Therefore, the thickness of the central region 131 is usually greater than the thickness of the edge region 133. In some embodiments, the difference between the thickness of the central region 131 and the thickness of the edge region 133 can be less than 1 micrometer, which is beneficial to improving the flatness of the electrode assembly composed of the positive electrode 10 and the negative electrode 30, thereby improving the overall flatness of the electrochemical device.

[0052] In some embodiments, the tortuosity of the edge region 133 can be 3 to 8, and the tortuosity of the central region 131 is less than that of the edge region 133, with a difference of 1 to 3. This is beneficial for improving the lithium-ion liquid phase transport resistance of the edge region 133 compared to the central region 131, thereby reducing the difference in kinetic performance of the edge region 133 and decreasing the amount of lithium delithiation in the edge region 133. This, in turn, helps to reduce the risk of lithium plating in the electrochemical device and improve the overall cycle stability of the electrochemical device. Furthermore, the tortuosity of the edge region 133 within the aforementioned range and the central region 131 having a specific difference in tortuosity from the edge region 133 are beneficial for reducing the amount of lithium delithiation in the edge region 133 and minimizing the difference between the edge region 133 and the central region 131 while ensuring the overall energy density of the electrochemical device. In some implementations, the difference between the tortuosity of the edge region 133 and the tortuosity of the center 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 also includes a first binder for bonding the first positive electrode active material particles to facilitate the formation of a film layer, and also to improve the bonding force between the edge region 133 and the positive electrode current collector 11. The central region 131 also includes a second binder for bonding the second positive electrode active material particles to facilitate the formation of a film layer, and also to improve the bonding force between the central region 131 and the positive electrode current collector 11.

[0054] The first adhesive and the second adhesive 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, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyacrylic acid 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 less than that of the second binder. Since the edge region of the positive electrode sheet is easily exposed to free electrolyte, the binder in the positive electrode active layer swells under electrolyte immersion, reducing the bonding effect and making the active layer prone to detachment due to repeated expansion and contraction during electrochemical device cycling, thus 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 central region 131, the impact of the swelling of the first binder on the edge region 133 is reduced, thereby reducing the risk of loosening or even detachment of the edge region 133 and improving its stability, which in turn improves 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 from 1:3 to 1:1.1, for example, it can be 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 mentioned above. In some embodiments, the swelling rate of the first binder can be from 1% to 10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any specific value between any two adjacent values ​​mentioned above. The aforementioned specific swelling rate of the first binder and the second binder having a specific ratio range with the swelling rate of the first binder are beneficial in ensuring that the entire positive electrode active layer is not easily loosened, while reducing the difference between the edge region 133 and the central region 131 caused by swelling, thereby improving the overall cycle stability of the electrochemical device.

[0056] Furthermore, in some embodiments, the first adhesive may be, but is not limited to, a polyacrylic acid adhesive, and the molecular weight of the first adhesive may be from 100,000 to 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 ​​mentioned above. The aforementioned first adhesive has a low swelling rate, which helps to reduce the impact of the swelling of the first adhesive on the edge region, thereby reducing the risk of loosening or even detachment of the edge region and improving the stability of the edge region, thus contributing to improving the overall cycle stability of the electrochemical device.

[0057] The content of the first binder in the edge region 133 can be greater than that of the second binder in the central region 131. Since the edge region of the positive electrode sheet is more easily exposed to free electrolyte, under the same degree of swelling, using a higher content of the first binder in the edge region 133 helps improve the adhesion between the edge region 133 and the positive current collector 11, thereby reducing the risk of loosening or even detachment of the edge region 133 and improving its stability. This, in turn, improves the overall cycle stability of the electrochemical device. Furthermore, by designing a higher binder content in the edge region 133 and a lower binder content in the central region 131, the interfacial transport barrier of the second binder in the central region 131 compared to the first binder in the edge region 133 is reduced, thus improving the kinetic performance of the central region 131 compared to the edge region 133. This narrows the difference in kinetic performance between the central region 131 and the edge region 133, thereby enhancing the overall capacity of the electrochemical device and improving its overall performance.

[0058] Specifically, the content of the first adhesive in the edge region 133 can be from 0.5 wt% to 5.0 wt%, for example, it can be 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 ​​mentioned above. In some embodiments, the difference between the content of the first adhesive in the edge region 133 and the content of the second adhesive in the central region 131 can be from 0.1 wt% to 1.0 wt%, for example, it can be 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 ​​mentioned above. The first binder with a specific content range and the second binder with a content difference range from the first binder content are beneficial to ensuring the bonding force between the edge region 133 and the central region 131 and the positive electrode current collector 11. This is beneficial to ensuring the bonding force between the positive electrode active layer 13 and the positive electrode current collector 11, while also improving the kinetic performance of the entire positive electrode active layer 13. This is beneficial to the stability of the positive electrode structure and also 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 central region 131 may further include a second conductive agent. The content of the second conductive agent in the central 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 use a lower conductive agent content and the central region 131 to use a higher conductive agent content, the electron transport capability of the central region 131 compared to the edge region 133 is improved, thereby enhancing the kinetic performance of the central region 131 compared to the edge region 133. This reduces the difference in kinetic performance between the edge region 133 and the central region 131, thereby improving the overall capacity utilization of the electrochemical device and enhancing its overall performance.

[0060] Specifically, the ratio of the content of the first conductive agent in the edge region 133 to the content of the second conductive agent in the central region 131 can be from 1:2 to 1:1.05, for example, it can be 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 mentioned above. In some embodiments, the content of the first conductive agent in the edge region can be from 0.2wt% to 2.0wt%, for example, it can be 0.2wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2.0wt%, or any specific value between any two adjacent values ​​mentioned above. The aforementioned specific content of the first conductive agent and the second conductive agent having a specific ratio range with the content of the first conductive agent help ensure the electron transport capability of the positive electrode and enable the positive electrode to have high kinetic performance, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0061] The first and second conductive agents may include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, synthetic graphite, conductive carbon black (SP), carbon nanotubes (CNTs), acetylene black, Ketjen black, carbon fibers, or any combination thereof. In some embodiments, 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, CNTs, and vapor-grown carbon fiber (VGCF), and the weight ratio of SP:CN:VGCF may be (3.3-9):(3.3-0.5):(3.4-0.5). The second conductive agent may include SP, CNTs, and VGCF, and the weight ratio of SP:CN:VGCF may be (0.5-3.3):(9-3.3):(0.5-3.4). Further, the first conductive agent may be composed of SP, CNTs, and VGCF, and the second conductive agent may also be composed of SP, CNTs, and VGCF. Compared with the composition of the second conductive agent in the central region 131, the composition of the first conductive agent in the edge region 133 has a lower content of high conductivity materials, which is beneficial to reduce the electron transport capability of the edge region 133 and reduce the kinetic performance, thereby reducing the difference between the edge region 133 and the central region 131 and improving the overall cycle stability of the electrochemical device.

[0063] The negative electrode sheet 30 includes a negative electrode current collector 31 and a negative electrode active layer 33 disposed on at least one surface of the negative electrode current collector 31. In this embodiment, as... Figure 3 As shown, negative electrode active layers 33 can be respectively disposed on the two opposite surfaces of the negative electrode current collector 31.

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

[0065] The negative electrode active layer 33 includes a negative electrode active material, which is a known negative electrode active material capable of reversible intercalation and deintercalation of active ions, and this application is not limited thereto. For example, it may include, but is not limited to, at least one of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Among them, graphite may be selected from at least one of artificial graphite, natural graphite, and modified graphite; silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials may 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 for bonding the negative electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force 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, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid resin, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0067] The separator 50 includes a membrane layer with a porous structure, and its material may include at least one selected from polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene may include at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene, in particular, have a good effect on improving short circuits and can improve the stability of the electrochemical device 100 through a turn-off effect.

[0068] The electrolyte 60 can be in one or more of the following states: gel, solid, and liquid. Liquid electrolytes include lithium salts and non-aqueous solvents. The lithium salt may 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 bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tri(trifluoromethanesulfonyl)methyllithium (LiC(SO2CF3)3), lithium dioxolaneborate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, LiPF6 is selected as the lithium salt because it can provide high ionic conductivity and improve cycling characteristics. The non-aqueous solvent may be a carbonate compound, a carboxylic acid ester compound, or an ether. 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), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butyl 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 further include nitrile additives, wherein the content of the nitrile additives in the electrolyte may be from 0.1wt% to 3wt%, for example, 0.1wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, or any specific value between any two adjacent values ​​mentioned above, which is beneficial for forming a stable interface film on the surface of the positive electrode, thereby improving the overall cycle stability of the electrochemical device.

[0070] The nitrile additive may be selected from, but is not limited to, at least one of butadionitrile, glutaronitrile, adiponitrile, trans-butenedionitrile, trans-hexenedionitrile, 1,2-di(cyanoethoxy)ethane, 1,3,6-hexanetricarbonitrile, 1,2,3-tri(cyanoethoxy)propane, or 1,5-dicyanopentane.

[0071] Please see Figure 4The electrochemical device 100 described above can be applied to the electronic device 200. The electronic device 200 also includes a body 201, to which the electrochemical device 100 is electrically connected for supplying power. The electronic device 200 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, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

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

[0073] The stacked lithium-ion batteries corresponding to Examples 1-27 and Comparative Examples 1-3 were prepared according to the table. Except for the parameters in the table, the lithium-ion batteries corresponding to Examples 1-27 and Comparative Examples 1-3 had the same parameters.

[0074] Example 1

[0075] Preparation of the positive electrode sheet:

[0076] The positive electrode active material is lithium cobalt oxide (coating or doping amount 0.5wt%), and the binder is PVDF (homogeneous type, molecular weight M). 中 The value is 1.27 million, and the swelling ratio (ESR) is 1.27 million. 中 A first slurry (with a solid content of 75%) was prepared by mixing and dispersing N-methylpyrrolidone (NMP) with conductive agent SP, conductive agent CNT, and conductive agent VGCF in a ratio of 97.0:1.5:0.43:0.86:0.21. The first slurry was then extruded and coated onto an aluminum foil current collector with a thickness of 9 micrometers, and dried to form a first electrode sheet. The first slurry was then cured to form a first active layer (corresponding to the central region).

[0077] The positive electrode active material is lithium cobalt oxide (coating or doping amount 1.2wt%), and the binder PAA (molecular weight M) is added. 边 The value is 500,000, and the swelling ratio (ESR) is [missing information]. 边A second slurry (with a solid content of 75%) is prepared by mixing and dispersing NMP with conductive agent SP, conductive agent CNT, and conductive agent VGCF in a ratio of 97.0:2.0:0.57:0.29:0.14. The second slurry is then coated outward from the outer periphery of the first active layer of the first electrode sheet using a gravure printing plate. After drying, the second electrode sheet is formed, and the second slurry is cured to form the second active layer (corresponding to the edge region).

[0078] Cold-pressed positive electrode (with a tortuosity of 5 in the edge region and 3.5 in the center region) is formed under a pressure of 80t and a speed of 20m / min, and then die-cut to form a positive electrode sheet. The width W of the transition region in the positive electrode sheet is... 过渡 The width W of the edge area is 0.2mm. 边 The thickness is 4.0 mm, and the thickness of the central region is 0.5 micrometers greater than that of the edge region, i.e., ΔTk is 0.5 micrometers. The thickness Tk of the edge region is... 边 It is 100 micrometers. The size of the positive electrode is approximately 70mm*80mm.

[0079] Preparation of negative electrode sheet:

[0080] A negative electrode slurry (solid content 48%) was prepared by mixing and dispersing graphite (anode active material), SBR (solid-bound polymer), and CMC (cement-bound polymer) in deionized water at a ratio of 97.4:1.4:1.2. The slurry was then extruded and coated onto a 6-micron copper current collector, followed by drying to form a negative electrode sheet. The negative electrode slurry correspondingly forms the negative electrode active layer, which has a thickness of 120 microns. The negative electrode sheet has an approximate size of 72mm x 82mm.

[0081] The fabrication of lithium-ion batteries:

[0082] The above-mentioned positive electrode, separator (PE film with a thickness of 5 micrometers and a porosity of about 35%) and negative electrode are sequentially and alternately stacked to form a stacked electrode assembly. After welding the tabs, the assembly is placed in the battery case and injected with electrolyte (1M LiPF6 in EC∶DEC∶EMC∶adiponitrile = 32.83∶32.83∶32.83∶1.51). After encapsulation and formation, a lithium-ion battery, i.e., an electrochemical device, is formed.

[0083] At 100% SOC, the difference ΔB between the amount of lithium removed from the edge region and the center region is 1%.

[0084] XRD characterization method for lithium removal: ① The first slurry was coated onto a 35µm copper foil surface using a 200µm doctor blade and dried at 110℃ to form a coated electrode. The electrode was then cold-pressed at 80t pressure and 20m / min speed to form a cold-pressed positive electrode. The positive electrode was then assembled into a coin cell with a lithium foil (using a specific coin cell mold with a viewing window at the top to allow X-rays to pass through while ensuring sealing). ② The coin cell assembled in step ① was charged at a constant current rate of 0.1C to a cutoff voltage of 4.47V, then charged at a constant voltage of 4.47V until a cutoff current of 50µA was reached. After resting for 5 minutes, it was discharged at a constant current rate of 0.1C to 3.0V. This charge-discharge cycle was repeated three times. ③ Simultaneously test XRD during charging and discharging; ④ Model the XRD 003 crystal interlayer spacing d obtained in step ② with the amount of lithium cobalt oxide delithiation x during charging and discharging (the ratio of charging or discharging capacity to rated capacity under different voltage states) to form a linear equation d = -0.7372x + 5.2329; ⑤ Fully charge the cell, disassemble it to obtain the edge region and the middle region, and test XRD for each; ⑥ Substitute the d obtained in step ④ into the correspondence in step ③ to obtain the amount of lithium delithiation in the edge region and the middle region. The difference between the two is the difference in the amount of lithium delithiation.

[0085] Comparative Example 1

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

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

[0088] The performance tests for each of the above embodiments and comparative examples were performed as follows: 25℃ capacity retention@500cls and 45℃ capacity retention@500cls. 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 charged at constant voltage until the current <0.05C. After resting for 5 minutes, it is discharged at 02C DC to the cutoff voltage. This charge-discharge cycle is repeated. The ratio of the 02C DC capacity of the 500th cycle to the 02C DC capacity of the 1st cycle is the 25℃ capacity retention@500cls. The higher the ratio, the better the cycle performance of the lithium-ion battery.

[0090] 45℃ capacity retention@500cls: The lithium-ion battery is charged at 0.2C constant current to the cutoff voltage at 45℃, then charged at constant voltage until the current <0.05C. After resting for 5 minutes, it is discharged at 02C DC to the cutoff voltage. This charge-discharge cycle is repeated. The ratio of the 02C DC capacity of the 500th cycle to the 02C DC capacity of the 1st cycle is the 45℃ capacity retention@500cls. The higher the ratio, the better the cycle performance of the lithium-ion battery.

[0091] Table 1

[0092]

[0093] Table 2

[0094]

[0095]

[0096] Table 3

[0097]

[0098] Table 4 (Using △ω in the table) 粘 ω represents the difference between the binder content in the second slurry and the binder content in the first slurry. 粘 - 边 Indicates the binder content in the second slurry, ω 导-边 (This indicates the total conductive agent content in the second slurry)

[0099]

[0100]

[0101] Table 5

[0102] △B 25℃capacity retention@500cls 45℃capacity retention@500cls Example 1 1.00％ 90％ 85％ Example 12 1.70％ 87％ 81％ Example 13 0.50％ 91.5％ 87.5％ Example 14 1.90％ 85％ 80％ Example 15 0.20％ 92％ 88％ Example 16 1.85％ 85％ 80％ Example 17 0.20％ 92％ 88％ Comparative Example 1 3.00％ 70％ 60％

[0103] Table 6 (ω in the table) 导-边 ω represents the total conductive agent content in the second slurry. 导-中 (This indicates the total conductive agent content in the first slurry)

[0104]

[0105]

[0106] Table 7

[0107]

[0108] Table 8

[0109]

[0110] As shown in Tables 1 to 8, using data from Examples 1-27 and Comparative Examples 1-3, by reducing the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10, the capacity retention rate of the lithium-ion battery is improved, meaning the cycle life and cycle stability of the lithium-ion battery are extended. Furthermore, as shown in Table 1, using data from Examples 1-5, a wider edge region 133 of the positive electrode 10 is more conducive to reducing the difference between the amount of lithium delithiation in the central region 131 and the edge region 133, thus improving the capacity retention rate and cycle stability of the lithium-ion battery. As shown in Table 2, using data from Examples 1 and 6-9, increasing the coating or doping amount of the positive active material in the positive electrode 10 helps to reduce the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10, thereby improving the capacity retention rate and cycle stability of the lithium-ion battery. Data from Table 3 between Example 1 and Comparative Example 1, Example 10 and Comparative Example 3, and Example 11 and Comparative Example 2 show that, even for different positive electrode active materials, reducing the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10 can improve the capacity retention of the lithium-ion battery, that is, extend the cycle life and improve the cycle stability. Data from Tables 4 and 5 for Examples 1 and Examples 12-13 show that a lower ratio of the swelling rate of the binder in the edge region 133 to the central region 131 of the positive electrode 10 is more conducive to reducing the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10, thereby improving the capacity retention and 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 10 is more conducive to reducing the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10, thereby improving the capacity retention rate of the lithium-ion battery and enhancing its cycle stability. 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 10, and a larger difference between the binder content in the edge region 133 and the central region 131, is more conducive to reducing the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10, thereby improving the capacity retention rate of the lithium-ion battery and enhancing its cycle stability.As shown in Table 6, the lower the ratio of the conductive agent content in the edge region 133 to the central region 131 of the positive electrode 10, the more beneficial it is to reduce the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10, thus improving the capacity retention rate of the lithium-ion battery and enhancing its cycle stability. As shown in Table 6, the higher the SP content in the edge region 133 of the positive electrode 10, the more beneficial it is to reduce the amount of lithium delithiation in the edge region 133, thus reducing the difference between the amount of lithium delithiation in the central region 131 and the edge region 133 of the positive electrode 10, thus improving the capacity retention rate of the lithium-ion battery and enhancing its cycle stability. As shown in Table 6, the higher the CNT content in the central region 131 of the positive electrode 10, the more beneficial it is to reduce the difference between the amount of lithium delithiation in the central region 131 and the amount of lithium delithiation in the edge region 133 of the positive electrode 10, thus improving the capacity retention rate and cycle stability of the lithium-ion battery. As shown in Table 7, the higher the content of nitrile additives in the electrolyte, the more beneficial it is to reduce the difference between the amount of lithium delithiation in the central region 131 and the amount of lithium delithiation in the edge region 133 of the positive electrode 10, thus improving the capacity retention rate and cycle stability of the lithium-ion battery. As can be seen from the data in Examples 1 and 26-27 in Table 8, the higher the tortuosity of the edge region 133 of the positive electrode 10 and the greater the difference between the tortuosity of the edge region 133 and the center region 131, the more beneficial it is to reduce the difference between the amount of lithium delithiation in the center region 131 and the amount of lithium delithiation in the edge region 133 of the positive electrode 10, and thus more beneficial to improve the capacity retention rate of the lithium-ion battery and improve the cycle stability of the lithium-ion battery.

[0111] Furthermore, those skilled in the art can make various other corresponding changes and modifications based on the technical concept of this application, and all such changes and modifications should fall within the protection scope of this application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive electrode and the negative electrode, the positive electrode comprising a positive current collector and a positive active layer disposed on at least one side of the positive current collector, wherein, The positive electrode active layer includes a central region and an edge region surrounding 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 removed from the central region and the amount of lithium removed from the edge region is 0.1% to 2%.

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

3. The electrochemical device as described in claim 1, wherein, The edge region includes a first positive electrode active material, which includes at least one of lithium cobalt oxide with a coating 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, which includes at least one of lithium cobalt oxide with a coating 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.

4. The electrochemical device as described in claim 3, wherein, The edge region further includes a first adhesive, and the central region further includes a second adhesive, wherein 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 as described in claim 4, wherein, The first adhesive is a polyacrylic acid adhesive, and the molecular weight of the first adhesive is between 100,000 and 1,000,000.

6. The electrochemical device as claimed in claim 4, wherein, The first adhesive has a content of 0.5 wt% to 5.0 wt% in the edge region, and the content of the first adhesive in the edge region is greater than the content of the second adhesive in the center region, with a difference of 0.1 wt% to 1.0 wt%.

7. The electrochemical device as claimed in claim 3, wherein, The edge region further includes a first conductive agent, and the central region further includes a second conductive agent. The content of the first conductive agent in the edge region is 0.2 wt% to 2.0 wt%, 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 as claimed in claim 7, wherein, The first conductive agent comprises 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 comprises 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 as claimed in claim 1, wherein, The electrochemical device further includes an electrolyte containing nitrile additives, the nitrile additives being present in an amount of 0.1 wt% to 3 wt% in the electrolyte.

10. The electrochemical device as claimed in claim 1, wherein, The tortuosity of the edge region is 3 to 8, and the tortuosity of the central region is less than that of the edge region, with a difference of 1 to 3.

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

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