Electrochemical devices and electronic devices using the same

Abstract

An electrochemical device includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector. The positive electrode active layer includes a center region and an edge region disposed around a periphery of the center region, the edge region including a first positive electrode active material and the center region including a second positive electrode active material. The first positive electrode active material has a solid-phase diffusion coefficient of 10 ‑15 cm 2 / s to 10 ‑5 cm 2 / s, and a ratio of the solid-phase diffusion coefficient of the first positive electrode active material to the solid-phase diffusion coefficient of the second positive electrode active material is 1:3 to 1:1.05. The electrochemical device described above is advantageous in reducing 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. The present application also provides an electronic device using the electrochemical device described above.

Description

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 same. BACKGROUND

[0002] Electrochemical devices, especially lithium ion batteries, have the advantages of high energy density, high power, long cycle life, etc., and are widely used in the field of consumer electronics. With the continuous expansion of its application range, especially in electric bicycles and electric vehicles, the performance requirements of electrochemical devices are also increasing. Therefore, how to guarantee or improve the overall performance of electrochemical devices is a problem currently faced. SUMMARY

[0003] In view of the above, it is necessary to provide an electrochemical device that improves the overall performance by reducing the kinetic performance difference between the center region and the edge region of the positive electrode, and an electronic device using the same.

[0004] The first aspect of the present application provides an electrochemical device, comprising a positive electrode, a negative electrode and an electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode active layer arranged on at least one surface of the positive electrode current collector. The positive electrode active layer comprises a center region and an edge region arranged around the outer periphery of the center region, the edge region comprises a first positive electrode active material, and the center region comprises a second positive electrode active material. The solid-phase diffusion coefficient of the first positive electrode active material is 10 -15 cm 2 / s to 10 -5 cm 2 / s, and the ratio of the solid-phase diffusion coefficient of the first positive electrode active material to the solid-phase diffusion coefficient of the second positive electrode active material is 1:3 to 1:1.05.

[0005] In the electrochemical device, the electric field intensity of the edge region of each electrode sheet is higher than that of the center region, and due to the lack of differentiation between the edge region and the center region of the electrode sheet in the prior art, the edge region has a high delithiation rate and a large delithiation amount, while the center region has a low delithiation rate and a small delithiation amount, resulting in a decrease in the overall capacity of the electrochemical device and poor overall kinetic performance. In the electrochemical device described above, the edge region and the center region of the positive electrode are designed differently, the second positive electrode active material with a lower solid-phase diffusion coefficient is used in the edge region, and the first positive electrode active material with a higher solid-phase diffusion coefficient is used in the center region, which is conducive to improving the solid-phase diffusion rate of lithium ions in the center region compared to the edge region to improve the kinetic performance of the center region compared to the edge region, thereby narrowing the kinetic performance difference between the center region and the edge region, narrowing the difference in delithiation amount between the edge region and the center region, and further improving the overall capacity of the electrochemical device to improve the overall performance of the electrochemical device. In addition, the solid-phase diffusion rate of lithium ions of the first positive electrode active material with the above range of solid-phase diffusion coefficients is conducive to the intercalation and deintercalation of lithium ions, and is conducive to improving the overall kinetic performance of the electrochemical device, and the specific ratio of the above-mentioned solid-phase diffusion coefficients is also conducive to narrowing the difference between the two regions and avoiding causing reverse differences while improving the overall kinetic performance of the electrochemical device.

[0006] Based on the first aspect, in some possible implementations, the ratio of the solid-phase diffusion coefficient of the first positive electrode active material to the solid-phase diffusion coefficient of the second positive electrode active material is 1:2.8 to 1:1.5, which is conducive to further narrowing the difference between the two regions and avoiding causing reverse differences while improving the overall kinetic performance of the electrochemical device.

[0007] Based on the first aspect, in some possible implementations, the compaction density of the edge region is 2.0 g / cc to 4.35 g / cc, the compaction density of the edge region is greater than that of the center region, and the difference is 0.03 g / cc to 0.5 g / cc.

[0008] In the above possible implementations, by designing the edge region with a higher compaction density and the center region with a lower compaction density, the liquid-phase diffusion capacity of lithium ions in the center region compared to the edge region is improved, the kinetic performance of the center region compared to the edge region is improved, thereby narrowing the difference in kinetic performance between the center region and the edge region, and further improving the overall capacity of the electrochemical device to improve the overall performance of the electrochemical device. Furthermore, the edge region with the above range of compaction densities and the center region with a specific difference range in compaction density from the edge region are conducive to improving the overall volume energy density of the electrochemical device, thereby further improving the overall performance of the electrochemical device.

[0009] In some possible implementation manners based on the first aspect, the ratio of the porosity of the edge region to the porosity of the center region is 1:2 to 1:1.1, and the porosity of the edge region is 10% to 45%.

[0010] In the above possible implementation manners, by designing the center region with a higher porosity and the edge region with a lower porosity, the lithium ion liquid-phase diffusion capacity of the center region compared with the edge region is improved, so as to improve the kinetic performance of the center region compared with the edge region, thereby reducing the difference in kinetic performance between the center region and the edge region, and further improving the overall capacity of the electrochemical device, so as to improve the overall performance of the electrochemical device. If the porosity of the edge region is too large, the volume energy density of the electrochemical device cannot be guaranteed, and if the porosity of the edge region is too small, the kinetic performance of the electrochemical device is poor, which is not conducive to guaranteeing the overall performance of the electrochemical device. In addition, if the porosity ratio is too small, it is not easy to reduce the difference in kinetic performance between the center region and the edge region, and if the porosity ratio is too large, the difference between the center region and the edge region is too large, which is likely to cause a reverse difference, which is also not conducive to improving the overall performance of the electrochemical device.

[0011] In some possible implementation manners based on the first aspect, the width of the edge region is 2 mm to 10 mm.

[0012] In some possible implementation manners based on the first aspect, the positive active layer further comprises a transition region, the transition region connecting the inner periphery of the edge region and the outer periphery of the center region. The width of the transition region is 0.02 mm to 0.5 mm.

[0013] In some possible implementation manners based on the first aspect, the thickness of the center region is greater than the thickness of the edge region, and the difference is less than 1 micron. The thickness of the edge region is 50 microns to 1000 microns.

[0014] In the above possible implementation manners, the thickness difference of the edge region of the center region is less than 1 micron, which is conducive to improving the flatness of the electrode assembly composed of the positive electrode and the negative electrode, thereby improving the overall flatness of the electrochemical device. In addition, the thickness range of the edge region and the difference range between the center region and the edge region are conducive to avoiding the influence of purple stains or lithium precipitation caused by flatness on the overall performance of the electrochemical device.

[0015] In some possible implementation manners based on the first aspect, the thickness of the edge region is 100 microns to 500 microns.

[0016] In some possible implementations of the first aspect, a ratio of the particle size Dv50 of the first positive electrode active material to the particle size Dv50 of the second positive electrode active material is 1.1:1 to 2:1, and the particle size Dv50 of the first positive electrode active material is 1.0 microns to 25 microns.

[0017] In the above possible implementations, by designing the edge region to use the active material with a larger particle size and the center region to use the active material with a smaller particle size, the solid-phase transport distance of lithium ions in the active material in the center region compared to the edge region is reduced, so as to improve the kinetic performance in the center region compared to the edge region, thereby reducing the difference in kinetic performance between the center region and the edge region, and further improving the overall capacity of the electrochemical device, so as to improve the overall performance of the electrochemical device. The first positive electrode active material with the specific particle size range and the second positive electrode active material with the specific ratio range to the first positive electrode active material are conducive to achieving a higher tap density and a higher kinetic electrode assembly, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0018] In some possible implementations of the first aspect, the edge region further comprises a first binder, and the center region further comprises a second binder. The content of the second binder in the edge region is 0.4wt% to 4.0wt%, and a ratio of the content of the second binder in the center region to the content of the first binder in the edge region is 1:1.02 to 1:2.

[0019] In the above possible implementations, by designing the edge region to use a higher content of the binder and the center region to use a lower content of the binder, the interface transport resistance of lithium ions of the second binder in the center region compared to the first binder in the edge region is reduced, so as to improve the kinetic performance in the center region compared to the edge region, thereby reducing the difference in kinetic performance between the center region and the edge region, and further improving the overall capacity of the electrochemical device, so as to improve the overall performance of the electrochemical device. Furthermore, the second binder with the above content and the first binder with the content in the specific ratio range to the content of the second binder are conducive to ensuring the bonding force between the edge region and the center region and the positive electrode current collector, that is, the bonding force between the positive electrode active layer and the positive electrode current collector, while improving the kinetic performance of the entire positive electrode active layer, so as to facilitate the improvement of the overall performance of the electrochemical device while ensuring the stability of the positive electrode structure and improving the overall kinetic performance of the electrochemical device.

[0020] In some possible implementation manners of the first aspect, the edge region further comprises a first conductive agent, and the center region further comprises a second conductive agent. The content of the second conductive agent in the center region is 0.2 wt% to 4.0 wt%, and the content of the second conductive agent in the center region is greater than the content of the first conductive agent in the edge region, and the difference is 0.1 wt% to 2.0 wt%.

[0021] In the possible implementation manners described above, by designing the edge region to have a lower content of the conductive agent and the center region to have a higher content of the conductive agent, the electron transport capability of the center region is improved compared with that of the edge region, so that the kinetic performance of the center region is improved compared with that of the edge region, thereby the kinetic performance difference between the edge region and the center region is reduced, and the overall capacity of the electrochemical device is improved, so that the overall performance of the electrochemical device is improved. The second conductive agent with the specific content and the first conductive agent with the content having a specific difference range from the content of the second conductive agent are beneficial to guarantee the electron transport capability of the positive electrode and make the positive electrode have higher kinetic performance, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0022] In some possible implementation manners of the first aspect, under the condition of 100% SOC, the delithiation amount of the first positive electrode active material in the edge region is greater than the delithiation amount of the second positive electrode active material in the center region, and the difference is 0.1% to 2%.

[0023] In the possible implementation manners described above, the difference between the electrochemical reaction of the edge region and the electrochemical reaction of the center region is reduced, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0024] A second aspect of the present application provides an electronic device comprising a body and an electrochemical device as described above, and the electrochemical device is electrically connected with the body for supplying power to the body. In the above-mentioned electronic device of the present application, the edge region and the center region of the positive electrode are designed differently, by using a positive electrode active material with a lower solid-phase diffusion coefficient in the edge region and a positive electrode active material with a higher solid-phase diffusion coefficient in the center region, the solid-phase diffusion rate of lithium ions in the center region is improved compared with that in the edge region, so that the kinetic performance of the center region is improved compared with that of the edge region, thereby reducing the kinetic performance difference between the center region and the edge region, reducing the difference in delithiation amount between the edge region and the center region, and further improving the overall capacity of the electrochemical device, so as to improve the overall performance of the electrochemical device, and further improve the power supply performance of the electronic device. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 FIG. 1 is a structural schematic diagram of an electrochemical device according to an embodiment of the present application.

[0026] Figure 2A cross-sectional view of an electrochemical device according to an embodiment of the present application.

[0027] Figure 3 A cross-sectional view of a positive electrode according to an embodiment of the present application.

[0028] Figure 4 A schematic view of an electronic device according to an embodiment of the present application.

[0029] Explanation of main element symbols

[0030]

[0031]

[0032] The following detailed description will further describe the present application with reference to the above drawings. DETAILED DESCRIPTION

[0033] The following will describe embodiments of the present application by way of specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in the specification. Although the description of the present application will be introduced in conjunction with the examples, it does not mean that the features of the present application are limited to the examples. On the contrary, the purpose of introducing the present application in conjunction with the examples is to cover other alternatives or modifications that can be extended based on the claims of the present application. In order to provide a deep understanding of the present application, many specific details will be included in the following description. The present application can also be implemented without using these details. In addition, in order to avoid confusion or obscure the present application, some specific details will be omitted in the description.

[0034] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0035] Hereinafter, the terms "first", "second", and the like are used only for the purpose of description and should not be construed as indicating or implying relative importance or implying the number of the technical features indicated. Therefore, the features defined with "first", "second", and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise stated, the meaning of "plurality" is two or more.

[0036] Further, when describing the embodiments of the present application, "may" means "one or more embodiments of the present application".

[0037] The specific terminology used herein is for the purpose of describing embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0038] The embodiments of the present application are described below in conjunction with the accompanying drawings of embodiments of the present application. The data range values described in the present application should include the end values unless otherwise specified. The electrochemical device of the present application is illustrated by taking lithium ion battery as an example to illustrate its effect.

[0039] The energy density of lithium ion battery is usually improved by increasing the capacity and voltage of active material in the electrode and increasing the content of active material in the electrode, wherein increasing the compaction density of active material and preparing thicker active layer of electrode can increase the content of active material.

[0040] In lithium ion battery, the electric field intensity, electric potential and polarization of the edge region and the center region of the electrode sheet are different, which leads to the electrochemical reaction of the edge region and the main body region of the electrode sheet being non-uniform, and the above-mentioned electrochemical reaction non-uniform phenomenon will be more obvious with the increase of the thickness of the active layer and the increase of the compaction density of the active layer, thereby deteriorating the overall performance of the battery (including but not limited to affecting the cycle life, causing thermal safety problems, etc.) and restricting the substantial increase of the thickness and compaction density of the active layer.

[0041] In view of this, the embodiments of the present application provide an electrochemical device and an electronic device applying the same.

[0042] Please refer to Figure 1 , an electrochemical device 100 of the embodiments of the present application. Please refer to Figure 2 , the electrochemical device 100 includes a positive electrode 10, a negative electrode 30 and a separator 50. The separator 50 is arranged between the positive electrode 10 and the negative electrode 30. As Figure 2 shown, the positive electrode 10, the separator 50 and the negative electrode 30 can be alternately stacked in sequence along the thickness direction X to form a laminated electrode assembly A, or the positive electrode 10, the separator 50 and the negative electrode 30 are stacked in sequence and then wound around the center axis to form a wound electrode assembly (not shown in the figure). In the following, the laminated electrode assembly A will be taken as an example for subsequent description.

[0043] The electrochemical device 100 further includes a case 20 and an electrolyte 60, and the electrolyte 60 and the electrode assembly A are housed in the case 20. The case 20 can be a packaging bag obtained by packaging with a packaging film such as, but not limited to, an aluminum laminate film, i.e., the electrochemical device can be a pouch battery. The case 20 can also be, but is not limited to, a steel case battery, an aluminum case battery, and the like disclosed in the prior art.

[0044] The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active layer 13 provided on at least one surface of the positive electrode current collector 11. In the present embodiment, as shown in FIG. 1, 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 both opposite surfaces of the positive electrode current collector 11. Figure 2

[0045] The positive electrode current collector 11 can be made of an aluminum foil or a 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.

[0046] Please refer to FIG. 1, the positive electrode active layer 13 includes a central region 131 and an edge region 133 provided around the outer periphery of the central region 131. When the positive electrode 10 corresponds to a laminated electrode assembly A, as shown in FIG. 1, viewed in the thickness direction X, the edge region 133 is annular (e.g., a rectangular ring as shown in FIG. 2) around the central region 131. When the positive electrode 10 corresponds to a jelly-roll electrode assembly, when the positive electrode 10 is laid flat, i.e., not wound, viewed in the thickness direction of the positive electrode 10, the edge region 133 is annular (e.g., a rectangular ring as shown in FIG. 3) around the central region 131; and when the positive electrode 10 is wound to form a jelly-roll electrode assembly, the edge region 133 includes the start end and the end of the winding of the positive electrode active layer 13 and the two ends of the positive electrode active layer 13 disposed opposite to each other along the winding central axis. Figure 3 Figure 3 Figure 3 Figure 3

[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 ratio of the solid-phase diffusion coefficient (Ds1) of the first positive electrode active material to the solid-phase diffusion coefficient (Ds2) of the second positive electrode active material is 1:3 to 1:1.05, and the solid-phase diffusion coefficient of the first positive electrode active material is 10 -15 cm 2 / s to 10 -5 cm 2 ​​​​​ / s. The edge region 133 is formed by the first positive electrode active material with a lower solid-phase diffusion coefficient, and the center region 131 is formed by the second positive electrode active material with a higher solid-phase diffusion coefficient, which differentiates the design of the edge region 133 and the center region 131 of the positive electrode 10. The lithium ion solid-phase diffusion rate of the center region 131 is higher than that of the edge region 133, which improves the kinetic performance of the center region 131 compared to the edge region 133, thereby reducing the kinetic performance difference between the center region 131 and the edge region 133, reducing the difference in lithium extraction amount between the edge region 133 and the center region 131, and further improving the overall capacity of the electrochemical device, thereby improving the overall performance of the electrochemical device. In some embodiments, the solid-phase diffusion coefficient Ds1 of the first positive electrode active material can be 10 - 15 cm 2 / s, 10 -14 cm 2 / s, 10 -12 cm 2 / s, 10 -10 cm 2 / s, 10 -9 cm 2 / s, 10 -7 cm 2 / s, 10 -5 cm 2 / s, or any specific value between any two adjacent values of the foregoing. Ds1:Ds2 can be 1:3, 1:2.75, 1:2.5, 1:2, 1:7.5, 1:1.5, 1:1.05, or any specific ratio between any two adjacent ratios of the foregoing. The lithium ion solid-phase diffusion rate of the first positive electrode active material with the above range of solid-phase diffusion coefficients facilitates lithium ion intercalation and extraction, and is beneficial to improving the overall kinetic performance of the electrochemical device 100. The specific ratio of the above solid-phase diffusion coefficients is also beneficial to reducing the difference between the two regions and avoiding the reverse difference while improving the overall kinetic performance of the electrochemical device 100. In some embodiments, Ds1:Ds2 can be 1:2.8 to 1:1.5. Under 100% SOC conditions, the lithium extraction amount of the first positive electrode active material in the edge region 133 is greater than that of the second positive electrode active material in the center region 131, and the difference is 0.1% to 2%, for example, it can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.7%, 2%, or any specific value between any two adjacent values of the foregoing, thereby reducing the difference between the electrochemical reactions of the edge region and the electrochemical reactions of the center region, which is beneficial to improving the overall performance of the electrochemical device.

[0048] The particle size Dv50 of the first positive electrode active material can be greater than the particle size Dv50 of the second positive electrode active material. By designing the edge region 133 to use a larger particle size active material and the center region 131 to use a smaller particle size active material, the solid phase transport distance of lithium ions in the active material in the center region 131 compared to the edge region 133 is reduced to improve the kinetic performance of the center region 131 compared to the edge region 133, thereby reducing the difference in kinetic performance between the center region 131 and the edge region 133, and thereby improving the overall capacity of the electrochemical device to improve the overall performance of the electrochemical device. Specifically, the ratio of the particle size Dv50 of the first positive electrode active material to the particle size Dv50 of the second positive electrode active material can be 1.1:1 to 2:1, such as 1.1:1, 1.3:1, 1.5:1, 1.7:1, 1.9:1, 2:1, or any specific ratio between any two adjacent ratios. In some embodiments, the particle size Dv50 of the first positive electrode active material can be 1.0 microns to 25 microns, such as 1.0 microns, 5.0 microns, 7.0 microns, 10.0 microns, 14.0 microns, 15.0 microns, 17.0 microns, 25 microns, or any specific value between any two adjacent values. The first positive electrode active material having the above specific particle size range and the second positive electrode active material having a specific ratio range with the first positive electrode active material are beneficial for achieving higher compaction density and higher kinetic electrode assembly, thereby facilitating the improvement of the overall performance of the electrochemical device 100.

[0049] 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 can 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 can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel manganate (LiNi 0.5 Mn 1.5 O4), or lithium iron phosphate (LiFePO4), etc. The second positive electrode active material can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel manganate (LiNi 0.5 Mn 1.5 O4), or lithium iron phosphate (LiFePO4), etc.

[0050] In some embodiments, the width of the edge region 133 can 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 of the foregoing. The width refers to the distance from any position of the outer periphery of the edge region 133, i.e., any position of the outer periphery of the entire positive active layer 13, to the nearest position of the inner periphery of the center region 131 where the adjacent edge region 133 connects the center region 131.

[0051] Since the positive active layer 13 needs to undergo a pressing process when formed, the outer edge of the center region 131 and the inner edge of the edge region 133 arranged adjacently or in contact before pressing will be mixed with each other to form a transition region 135 after pressing. That is, the positive 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 center region 131. In some embodiments, the width of the transition region 135 can be 0.02 mm to 0.5 mm, for example, 0.02 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or any specific value between any two adjacent values of the foregoing.

[0052] In addition, since the positive active layer 13 needs to undergo a pressing process when formed, the thickness of each region will change before and after pressing. Among them, the edge region 133 can extend away from the center region 131, and since the center region 131 is surrounded by the edge region 133, the movable space of the center region 131 is limited by the edge region 133 during pressing, so the thickness of the center region 131 is usually greater than the thickness 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 can be less than 1 micron, which is beneficial to improve the flatness of the electrode assembly composed of the positive electrode 10 and the negative electrode 30, thereby improving the flatness of the entire electrochemical device. In some embodiments, the thickness of the edge region can be 50 microns to 1000 microns. The above thickness range of the edge region 133 and the difference range between the center region 131 and the edge region 133 are beneficial to avoid the influence of purple stains or lithium precipitation caused by flatness on the overall performance of the electrochemical device. Further, the thickness of the edge region can be 100 microns to 500 microns, for example, 100 microns, 200 microns, 300 microns, 400 microns, 500 microns, or any specific value between any two adjacent values of the foregoing.

[0053] In some embodiments, the compaction density of the edge region 133 can be greater than that of the center region 131. By designing a higher compaction density of the edge region 133 and a lower compaction density of the center region 131, the lithium ion liquid phase diffusion capability of the center region 131 compared to the edge region 133 is improved to improve the kinetic performance of the center region 131 compared to the edge region 133, thereby reducing the difference in kinetic performance between the center region 131 and the edge region 133, and further improving the overall capacity of the electrochemical device to improve the overall performance of the electrochemical device. Specifically, the difference between the compaction density of the edge region 133 and the compaction density of the center region 131 can be 0.03 g / cc to 0.5 g / cc, for example, it can be 0.03 g / cc, 0.06 g / cc, 0.1 g / cc, 0.2 g / cc, 0.3 g / cc, 0.4 g / cc, 0.5 g / cc, or any specific value between any two adjacent values of the foregoing. In some embodiments, the compaction density of the edge region 133 can be 2.0 g / cc to 4.35 g / cc, for example, it can be 2.0 g / cc, 2.3 g / cc, 2.6 g / cc, 3.0 g / cc, 3.35 g / cc, 3.5 g / cc, 4.0 g / cc, 4.35 g / cc, or any specific value between any two adjacent values of the foregoing. The edge region 133 having the above range of compaction density, and the center region 131 having a specific difference range of compaction density from the edge region 133, are beneficial to improve the overall volumetric energy density of the electrochemical device 100, thereby further improving the overall performance of the electrochemical device 100.

[0054] In some embodiments, the porosity of the edge region 133 can be less than that of the center region 131. By designing a higher porosity center region 131 and a lower porosity edge region 133, the lithium ion liquid diffusion capability of the center region 131 compared to the edge region 133 is improved to improve the kinetic performance of the center region 131 compared to the edge region 133, thereby reducing the difference in kinetic performance between the center region 131 and the edge region 133, and further improving the overall capacity of the electrochemical device to improve the overall performance of the electrochemical device. Specifically, the ratio of the porosity of the edge region 133 to the porosity of the center region 131 can be 1:2 to 1:1.1, for example, can be 1:2, 1:1.85, 1:1.75, 1:1.5, 1:1.3, 1:1.2, 1:1.1, or any specific value between any two adjacent values of the foregoing. In some embodiments, the porosity of the edge region 133 can be 10% to 45%, for example, can be 10%, 14%, 15%, 18%, 20%, 23%, 25%, 29%, 30%, 35%, 38%, 41%, 45%, or any specific value between any two adjacent values of the foregoing. The above-mentioned range of porosity and the ratio of porosity are beneficial to reducing the difference between the center region 131 and the edge region 133 while ensuring the kinetic performance of the electrochemical device.

[0055] The edge region 133 also includes a first binder for binding 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 center region 131 also includes a second binder for binding the second positive electrode active material particles to facilitate the formation of a film layer, and also to improve the bonding force between the center region 131 and the positive electrode current collector 11.

[0056] The content of the second binder in the central region 131 can be less than the content of the first binder in the edge region 133. By designing the edge region 133 to have a higher binder content and the central region 131 to have a lower binder content, the interface transport resistance of lithium ions of the second binder in the central region 131 compared to the first binder in the edge region 133 is reduced to improve the kinetic performance of the central region 131 compared to the edge region 133, thereby reducing the kinetic performance difference between the central region 131 and the edge region 133, and thereby improving the overall capacity of the electrochemical device to improve the overall performance of the electrochemical device. Specifically, the ratio of the content of the second binder in the central region 131 to the content of the first binder in the edge region 133 can be 1:1.02 to 1:2, for example, 1:1.02, 1:1.25, 1:1.5, 1:1.75, 1:2, or any specific ratio between any two adjacent ratios. In some embodiments, the content of the second binder in the edge region 133 can be 0.4wt% to 4.0wt%, for example, 0.4wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, or any specific value between any two adjacent values. The above-mentioned content of the second binder and the content of the first binder having a specific ratio range with the content of the second binder are beneficial to ensure the bonding force between the edge region 133 and the central region 131 and the positive current collector 11, i.e., the bonding force between the positive active layer 13 and the positive current collector 11, while also improving the kinetic performance of the entire positive active layer 13, thereby facilitating the improvement of the overall performance of the electrochemical device 100 while facilitating the improvement of the overall kinetic performance of the electrochemical device 100, thereby facilitating the improvement of the overall performance of the electrochemical device 100.

[0057] The first binder and the second binder can each include, but are not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylidene fluoride (PVDF), polyethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc. The first binder and the second binder can be the same or different.

[0058] The edge region 133 can further include a first conductive agent, and the center region 131 can further include a second conductive agent. The content of the second conductive agent in the center region 131 can 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 content of the conductive agent and the center region 131 to have a higher content of the conductive agent, the electron transport capability of the center region 131 is improved compared to the edge region 133, the kinetic performance of the center region 131 is improved compared to the edge region 133, the kinetic performance difference between the edge region 133 and the center region 131 is reduced, and the overall capacity of the electrochemical device is improved, thereby improving the overall performance of the electrochemical device. Specifically, the difference between the content of the second conductive agent in the center region 131 and the content of the first conductive agent in the edge region 133 can be 0.1 wt% to 2.0 wt%, for example, 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, or any specific value between any two adjacent values of the foregoing. In some embodiments, the content of the second conductive agent in the center region 131 can be 0.2 wt% to 4.0 wt%, for example, 0.2 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, or any specific value between any two adjacent values of the foregoing. The specific content of the second conductive agent and the first conductive agent having a specific difference range in content from the content of the second conductive agent are beneficial to ensuring the electron transport capability of the positive electrode 10 and making the positive electrode 10 have higher kinetic performance, thereby facilitating the improvement of the overall performance of the electrochemical device 100.

[0059] The first conductive agent and the second conductive agent can each include, but are not limited to, a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material can include, but is not limited to, natural graphite, artificial graphite, carbon black (SP), carbon nanotubes (CNT), acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based material can include, but is not limited to, metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative. The first conductive agent and the second conductive agent can be the same or different.

[0060] The negative electrode 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 the present embodiment, as shown in FIG. 1, the negative electrode current collector 31 has two opposite surfaces, and the negative electrode active layer 33 is disposed on each of the two opposite surfaces of the negative electrode current collector 31. Figure 3 As shown in FIG. 1, the negative electrode current collector 31 has two opposite surfaces, and the negative electrode active layer 33 is disposed on each of the two opposite surfaces of the negative electrode current collector 31.

[0061] The negative current collector 31 can use at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, and can be 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.

[0062] The negative active layer 33 includes a negative active material, and can use any negative active material known in the art that can reversibly deintercalate active ions. For example, the negative active material can include, but is not limited to, at least one of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, a silicon-based material, a tin-based material, lithium titanate, or other metals that can form an alloy with lithium.

[0063] The negative active layer 33 also includes a binder to bind the negative active material particles to facilitate the formation of a film layer and to improve the adhesion between the negative active layer and the negative current collector. In some embodiments, the binder in the negative active layer 33 can include, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber (SBR), acrylated styrene butadiene rubber, epoxy resin, or nylon.

[0064] The separator 50 includes a film layer having a porous structure, and can include at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene can include at least one of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Among them, polyethylene and polypropylene have a good effect on improving short circuit and can improve the stability of the electrochemical device 100 through the shutdown effect.

[0065] The state of the electrolyte 60 can be one or more of a gel state, a solid state, and a liquid state. The liquid electrolyte includes a lithium salt and a nonaqueous solvent. The lithium salt is selected from 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 bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2, lithium tris(trifluoromethylsulfonyl)methide (LiC(SO2CF3)3), lithium bisoxalatoborate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, the lithium salt is selected as LiPF6because it can give a high ionic conductivity and improve the cycle characteristics. The nonaqueous solvent can be a carbonate compound, a carboxylic ester compound, an ether compound, a nitrile compound, other organic solvents, or a combination thereof. Examples of the carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), 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 a combination thereof.

[0066] Referring to Figure 4 The above-described 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 supplying power to the body 201. The electronic device 200 can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a home-use large storage battery, and a lithium-ion capacitor, etc.

[0067] The application will be specifically illustrated by the following examples and comparative examples. It can be understood that the parameters in the application are not limited to the contents described in the examples and comparative examples, and can be selected according to actual needs.

[0068] Example 1

[0069] Preparation of the positive electrode:

[0070] The positive electrode active material lithium cobaltate (the solid-phase diffusion coefficient Ds2 is 2*10 -5 cm 2 / s, D V 50 is 16.7 microns, i.e. D V 50 中 ), the binder PVDF, the conductive agent SP and the conductive agent CNT are added into N-methyl pyrrolidone (NMP) in a ratio of 97.5:1.0:1.0:0.5 to prepare a first slurry (the solid content is 75%), and the first slurry is coated on an aluminum foil current collector with a thickness of 9 microns by extrusion, and dried to form a first electrode sheet, and the first slurry corresponds to a first active layer (corresponding to the central region) formed after solidification.

[0071] The positive electrode active material lithium cobaltate (the solid-phase diffusion coefficient Ds1 is 1*10 -5 cm 2 / s, D V 50 is 25 microns, i.e. D V 50 边 ), the binder PVDF, the conductive agent SP and the conductive agent CNT are added into N-methyl pyrrolidone (NMP) in a ratio of 97.75:1.25:0.5:0.5 to prepare a second slurry (the solid content is 75%), and the second slurry is coated on the outer periphery of the first active layer of the first electrode sheet by gravure with a width of 2 mm, and dried to form a second electrode sheet, and the second slurry corresponds to a second active layer (corresponding to the edge region) formed after solidification.

[0072] The cold-pressed positive electrode (the compaction density of the edge region is 4.35 g / cc and the porosity is 10%, and the compaction density of the central region is 4.25 g / cc and the porosity is 15%) is formed by cold pressing under a pressure of 80 t and a speed of 20 m / min, and die-cut to form a positive electrode. The width W 过渡 of the transition region in the positive electrode is 0.2 mm, the width W 边 of the edge region is 4.0 mm, the thickness of the central region is 0.5 microns larger than the thickness of the edge region, i.e. △Tk is 0.5 microns, and the thickness Tk 边 of the edge region is 100 microns. The size of the positive electrode is approximately 70 mm*80 mm.

[0073] Preparation of the negative electrode:

[0074] The negative active material graphite, the binder SBR, and the binder CMC were added into deionized water in a ratio of 97:1.6:1.4, mixed and dispersed to prepare a negative slurry (solid content of 48%), and the negative slurry was coated on a 6-micron copper current collector by extrusion, dried to form a negative electrode, and the negative slurry correspondingly formed a negative active layer. The thickness of the negative active layer was 120 microns. The size of the negative electrode was approximately 72 mm*82 mm.

[0075] Preparation of a lithium ion battery:

[0076] The above positive electrode, a separator (a PE film with a thickness of 5 microns and a porosity of about 35%), and the above negative electrode were alternately stacked to form a laminated electrode assembly, and after the tab was welded, it was placed in a battery shell and injected with an electrolyte (1M LiPF6 in EC:DEC:EMC=1:1:1) and then packaged and formed into a lithium ion battery, i.e., an electrochemical device.

[0077] At 100% SOC, the difference in lithium extraction amount between the edge region and the center region was 1%.

[0078] Lithium extraction amount XRD characterization method: ① The above first slurry was coated on the surface of a 35-um copper foil using a 200-um doctor blade, then dried at 110°C to form a coated electrode, and then cold-pressed at a pressure of 80 t and a speed of 20 m / min to form a cold-pressed positive electrode; the positive electrode was assembled with a lithium sheet to form a coin-type half-cell (a special coin-type half-cell mold was used, which had a viewing window on the top to allow X-ray transmission while ensuring sealing); ② The coin-type battery assembled in step ① was charged at a rate of 0.1C to a cutoff voltage of 4.47V, then charged at a constant voltage of 4.47V until the cutoff current was 50uA, then rested for 5 min, and then discharged at a rate of 0.1C to 3.0V. The above charging and discharging steps were repeated 3 times. XRD was tested synchronously during the charging and discharging process; ③ A linear equation d=-0.7372x+5.2329 was formed based on the XRD 003 interlayer spacing d and the lithium extraction amount x of lithium cobalt oxide (the ratio of the charging or discharging capacity at different voltages to the rated capacity) tested in step ②; ④ The cell was fully charged, then disassembled to obtain the edge region and the center region, and XRD was tested for each region; ⑤ The d obtained in step ④ was input into the corresponding relationship in step ③ to obtain the lithium extraction amount of the edge region and the center region, and the difference between the two was the lithium extraction amount difference.

[0079] Comparative Example 1

[0080] Comparative Example 1 differs from Example 1 in the preparation of the positive electrode: the positive active material lithium cobalt oxide (the solid-phase diffusion coefficient Ds1 was 1*10 -5 cm 2 / s, D V50 25 micrometers), adhesive PVDF, conductive agent SP and conductive agent CNT were added into mixed dispersion NMP in a ratio of 97.75:1.25:0.5:0.5 to prepare positive electrode slurry (solid content of 75%), and the positive electrode slurry was coated on an aluminum foil current collector with a thickness of 9 micrometers by extrusion coating, dried to form a positive electrode active layer, and then cold-pressed under a pressure of 80 t and a speed of 20 m / min to form a cold-pressed positive electrode (the compaction density of each region of the positive electrode active layer was 4.35 g / cc and the porosity was 10%), and die-cut to form a positive electrode. The thickness of the positive electrode active layer was 100 micrometers.

[0081] The lithium ion batteries corresponding to Examples 2-33 and Comparative Examples 2-3 were prepared according to the above steps and the following tables, and the lithium ion batteries corresponding to Examples 1-33 and Comparative Example 1-3 were prepared according to the above steps and Table 9, except that the parameters in the tables were different.

[0082] The following performance tests were carried out on each of the above examples and comparative examples: DC-rate@1C, CC / (CC+CV)capacity@1C and -20℃ DC-rate@0.2C. The test results are shown in Tables 1-8 and Table 10. The methods for each performance test are described in detail as follows.

[0083] DC-rate@1C: At 25℃, constant current charging to the cut-off voltage at 0.2C rate, constant voltage charging to the current ≤0.05C to make the battery reach the full charge state, after 5 min, constant current discharging to the cut-off voltage at 0.2C rate, the discharge capacity is D0; after 5 min, constant current charging to the cut-off voltage at 0.2C rate, constant voltage charging to the current ≤0.05C to reach the full charge state again, after 5 min, constant current discharging to the cut-off voltage at 1C rate, the discharge capacity is D1, wherein the ratio of D1 to D0 is the capacity retention rate of DC-rate@1C.

[0084] CC / (CC+CV)capacity@1C: At 25℃, constant current charging to the cut-off voltage at 1C rate, constant voltage charging to the current ≤0.05C to make the battery reach the full charge state, the capacity in the constant current stage is C CC ; the capacity in the constant voltage stage is C CV , wherein the ratio of C CC to (C CC +C CV ) is the CC / (CC+CV)capacity@1C.

[0085] -20℃ DC-rate @ 0.2C: charge at 0.2C rate to the cut-off voltage at 25℃, constant voltage charge to the cut-off voltage after the current is less than or equal to 0.05C to make the cell reach the full charge state, after 5min rest, discharge at 0.2C to the cut-off voltage, the discharge capacity is D0; after 5min rest, adjust the temperature to -20℃, after 5min rest, charge at 0.2C rate to the cut-off voltage, constant voltage charge to the cut-off voltage after the current is less than or equal to 0.05C to reach the full charge state again, after 5min rest, discharge at 0.2C to the cut-off voltage, the discharge capacity is D1, wherein the ratio of D1 to D0 is the capacity retention rate of -20℃ DC-rate @ 0.2C.

[0086] Table 1

[0087]

[0088] Table 2

[0089]

[0090]

[0091] Table 3

[0092]

[0093] Table 4

[0094]

[0095]

[0096] Table 5

[0097]

[0098] Table 6

[0099]

[0100] Table 7

[0101]

[0102]

[0103] Table 8

[0104]

[0105] Table 9

[0106]

[0107]

[0108] Table 10

[0109]

[0110] As can be seen from the data of Examples 1-33 and Comparative Examples 1-3 in Tables 1-10, by differentiating the edge region 133 and the center region 131 of the positive electrode 10, the lithium ion battery can have reduced lithium loss, improved rate performance, and thus improved overall kinetic performance, and also improved capacity, i.e., improved overall performance. Further, as can be seen from the data of Examples 1-5 in Table 1, the wider the edge region 133 of the positive electrode 10, the smaller the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data of Examples 1 and 6-9 in Table 1, when the ratio of the solid-phase diffusion coefficients between the edge region 133 and the center region 131 of the positive electrode 10 is between 1:1.5 and 1:2.8, the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133 can be maintained within a small range, and the lithium ion battery can have better overall kinetic performance and higher charge-discharge performance. As can be seen from the data of Examples 1 and 10-13 in Table 2, the smaller the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133 of the positive electrode 10, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data of Examples 1 and 14-17 in Table 3, the smaller the porosity ratio between the center region 131 and the edge region 133 of the positive electrode 10, the smaller the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data of Examples 1 and 18-19 in Table 4, the narrower the width of the transition region of the positive electrode 10, the smaller the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data of Examples 1 and 20-21 in Table 5, the smaller the thickness difference between the center region 131 and the edge region 133, the smaller the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data of Examples 1 and 22-23 in Table 5, the smaller the thickness of the positive electrode active layer 13, the smaller the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data of Examples 1 and 24-25 in Table 6, the larger the particle size ratio of the positive electrode active material between the edge region 133 and the center region 131, the smaller the lithium loss difference and the kinetic performance difference between the center region 131 and the edge region 133, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance.As can be seen from the data of Example 1 and Examples 26-27 in Table 7, the greater the ratio of the content of the binder between the edge region 133 and the center region 131, the smaller the difference in the amount of lithium extraction between the center region 131 and the edge region 133, the smaller the difference in the kinetic performance, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data of Example 1 and Examples 28-29 in Table 8, the greater the difference in the content of the conductive agent between the center region 131 and the edge region 133, the smaller the difference in the amount of lithium extraction between the center region 131 and the edge region 133, the smaller the difference in the kinetic performance, the higher the overall kinetic performance of the lithium ion battery, and the better the charge-discharge performance. As can be seen from the data between Example 1 and Comparative Example 1, between Example 30 and Comparative Example 2, and between Example 32 and Comparative Example 3 in Table 9, even for different materials of the positive electrode active material, the differential design of the edge region 133 and the center region 131 of the positive electrode 10 can also improve the overall kinetic performance and capacity of the lithium ion battery. As can be seen from the data of Example 1 and Examples 30-33 in Table 9, the lithium ion battery with different materials of the positive electrode active material has a good kinetic performance and capacity after the differential design of the edge region 133 and the center region 131 of the positive electrode 10.

[0111] In addition, for those skilled in the art, other various corresponding changes and modifications can be made according to the technical concept of the present application, and all these changes and modifications shall belong to the protection scope of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein, The positive electrode active layer includes a center region and an edge region disposed around a periphery of the center region, the edge region includes a first positive electrode active material, the center region contains a second positive electrode active material, a solid phase diffusion coefficient of the first positive electrode active material is 10 -15 cm 2 / s to 10 -5 cm 2 / s, and a ratio of the solid phase diffusion coefficient of the first positive electrode active material to the solid phase diffusion coefficient of the second positive electrode active material is 1:3 to 1:1.

05.

2. The electrochemical device of claim 1, wherein, The ratio of the solid phase diffusion coefficient of the first positive electrode active material to the solid phase diffusion coefficient of the second positive electrode active material is 1:2.8 to 1:1.

5.

3. The electrochemical device of claim 1, wherein, The compaction density of the edge region is 2.0 g / cc to 4.35 g / cc, the compaction density of the edge region is greater than the compaction density of the center region, and the difference is 0.03 g / cc to 0.5 g / cc.

4. The electrochemical device of claim 1, wherein, The ratio of the porosity of the edge region to the porosity of the center region is 1:2 to 1:1.1, and the porosity of the edge region is 10% to 45%.

5. The electrochemical device of claim 1, wherein, The width of the edge region is 2 mm to 10 mm.

6. The electrochemical device of claim 1, wherein, The positive electrode active layer further comprises a transition region, the transition region connects the inner periphery of the edge region and the outer periphery of the center region, and the width of the transition region is 0.02 mm to 0.5 mm.

7. The electrochemical device of claim 1, wherein, The thickness of the center region is greater than the thickness of the edge region, and the difference is less than 1 micron, and the thickness of the edge region is 50 microns to 1000 microns.

8. The electrochemical device of claim 7, wherein, The thickness of the edge region is 100 microns to 500 microns.

9. The electrochemical device of claim 1, wherein, The ratio of the particle size Dv50 of the first positive electrode active material to the particle size Dv50 of the second positive electrode active material is 1.1:1 to 2:1, and the particle size Dv50 of the first positive electrode active material is 1.0 micron to 25 microns.

10. The electrochemical device of claim 1, wherein, The edge region further comprises a first binder, the center region further comprises a second binder, the content of the second binder in the edge region is 0.4 wt% to 4.0 wt%, and the ratio of the content of the second binder in the center region to the content of the first binder in the edge region is 1:1.02 to 1:

2.

11. The electrochemical device of claim 1, wherein, The edge region further comprises a first conductive agent, the center region further comprises a second conductive agent, the content of the second conductive agent in the center region is 0.2 wt% to 4.0 wt%, and the content of the second conductive agent in the center region is greater than the content of the first conductive agent in the edge region, and the difference is 0.1 wt% to 2.0 wt%.

12. The electrochemical device of claim 1, wherein, Under 100% soc conditions, the amount of lithium extraction of the first positive electrode active material in the edge region is greater than the amount of lithium extraction of the second positive electrode active material in the center region, and the difference is 0.1% to 2%.

13. An electronic device comprising a body, wherein the electronic device further comprises an electrochemical device as claimed in any one of claims 1 to 12, the electrochemical device being electrically connected to the body for powering the body.

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