Electrochemical apparatus, and electronic apparatus using electrochemical apparatus

Abstract

An electrochemical apparatus, comprising a positive electrode sheet, a negative electrode sheet, and a separator, which is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive-electrode current collector and a positive-electrode active layer, wherein the positive-electrode active layer comprises a central region, and an edge region surrounding the periphery of the central region. The separator comprises a first region, and second regions which are connected to the periphery of the first region and surround same, wherein the second regions overlap with the edge region in a first direction, and in any direction perpendicular to the first direction, the second regions go beyond the edge region; and the ionic conductivity of the second region ranges from 0.1 mS / cm to 0.625 mS / cm, and the ratio of the ionic conductivity of the second region to the ionic conductivity of the first region ranges from 1:5 to 1:1.2, such that the lithium-ion migration capability in the second region is reduced relative to that in the first region, thus reducing the difference value between the delithiation amount of the edge region and the delithiation amount of the central region, and improving the thermal stability and high-temperature storage performance of the electrochemical apparatus. Further provided in the present application is an electronic apparatus.

Description

Electrochemical device and electronic device using the same Technical Field

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

[0002] Lithium-ion batteries, with their high energy density, high power, and long cycle life, are widely used in consumer electronics. As their applications continue to expand, particularly in electric bicycles and electric vehicles, the performance requirements for lithium-ion batteries are also increasing. However, lithium-ion batteries generate heat during use, so ensuring or improving their thermal safety is a current challenge.

[0003] Summary of the Invention

[0004] In view of the above situation, it is necessary to provide an electrochemical device that is conducive to improving thermal safety and an electronic device using the electrochemical device.

[0005] In a first aspect, the present application provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive current collector and a positive active layer, wherein the positive active layer comprises a central region and an edge region arranged around the outer periphery of the central region. The separator comprises a first region and a second region arranged around the outer periphery connected to the first region, wherein the second region and the edge region are stacked in a first direction, and in any direction perpendicular to the first direction, the second region extends beyond the edge region. The ionic conductivity of the second region is 0.1 mS / cm to 0.625 mS / cm, and the ratio of the ionic conductivity of the second region to the ionic conductivity of the first region is 1:5 to 1:1.2.

[0006] In an electrochemical device, the electric field strength in the edge region of each electrode is higher than that in the central region. Due to the indifferent design between the edge region and the central region of the electrode in the prior art, the delithiation rate in the edge region is fast and the amount of delithiation is large, while the delithiation rate in the central region is slow and the amount of delithiation is small, resulting in a high over-delithiation potential in the edge region, which can easily lead to structural instability and increase oxidative side reactions in the electrochemical device, deteriorating the thermal stability and high-temperature storage performance of the electrochemical device. In the above-mentioned electrochemical device of the present application, the ionic conductivity of the second region of the edge region of the separator corresponding to the positive electrode electrode is less than the ionic conductivity of the first region of the central region of the separator corresponding to the positive electrode electrode, which is beneficial to reducing the migration ability of the second region corresponding to the edge region for lithium ions compared to the first region corresponding to the central region, thereby helping to narrow the difference in kinetic performance between the central region and the edge region, and reducing the difference in the amount of delithiation between the edge region and the central region, thereby helping to improve the overall thermal stability and high-temperature storage performance of the electrochemical device. Furthermore, an ionic conductivity within the aforementioned range for the second region can help reduce the degree of excessive delithiation in the edge region, thereby improving the stability of the edge region. Ionic conductivity within the aforementioned specific ratio range can help reduce the difference between the two regions while improving the overall performance of the electrochemical device. When the ionic conductivity ratio is greater than 1:1.2, it is difficult to reduce the difference in delithiation between the central and edge regions, thereby improving the overall performance of the electrochemical device. When the ionic conductivity ratio is less than 1:5, the difference between the central and edge regions can be excessively large, leading to a reverse difference, which is also detrimental to improving the overall performance of the electrochemical device.

[0007] Based on the first aspect, in some possible embodiments, the ratio of the ionic conductivity of the second region to the ionic conductivity of the first region is 1:4 to 1:2. In the above possible embodiments, the overall thermal stability and high-temperature storage performance of the electrochemical device are further improved.

[0008] Based on the first aspect, in some possible embodiments, the ratio of the ionic conductivity of the second region to the ionic conductivity of the first region is 1:4 to 1:3. In the above possible embodiments, the overall thermal stability and high-temperature storage performance of the electrochemical device are further improved.

[0009] Based on the first aspect, in some possible embodiments, the edge region includes a first positive electrode active material, and the center region includes 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.

[0010] In the above possible embodiment, the edge region and the central region of the positive electrode are designed differently. By using a first positive electrode active material with a lower solid-phase diffusion coefficient in the edge region and a second positive electrode active material with a higher solid-phase diffusion coefficient in the central region, it is beneficial to improve the solid-phase diffusion rate of lithium ions in the central region compared to the edge region to improve the kinetic performance of the central region compared to the edge region, thereby helping to narrow the difference in kinetic performance between the central region and the edge region, and narrowing the difference in the amount of lithium desorption between the edge region and the central region, thereby helping to improve the thermal stability and high-temperature storage performance of the electrochemical device. In addition, the solid-phase diffusion rate of lithium ions of the first positive electrode active material having a solid-phase diffusion coefficient in the above range is beneficial to the insertion and extraction of lithium ions, and is beneficial to improving the overall kinetic performance of the electrochemical device. The above-mentioned specific ratio of the solid-phase diffusion coefficients is also beneficial to improving the overall kinetic performance of the electrochemical device while narrowing the difference between the two regions. Secondly, when the ratio of the above-mentioned solid-phase diffusion coefficients is greater than 1:1.05, it is not easy to narrow the difference in kinetic performance between the central area and the edge area. When the ratio of the above-mentioned solid-phase diffusion coefficients is less than 1:3, it is easy to make the difference between the central area and the edge area too large, and thus easily cause a reverse difference, which is also not conducive to improving the overall performance of the electrochemical device.

[0011] Based on the first aspect, in some possible implementations, the porosity of the second region of the isolation membrane is 30% to 45%, and the porosity of the first region of the isolation membrane is greater than that of the second region of the isolation membrane, and the difference is 2% to 10%.

[0012] In the above possible embodiments, by designing the porosity of the first region of the separator to be greater than the porosity of the second region of the separator, it is beneficial to reduce the lithium ion diffusion capacity of the second region of the separator compared to the first region of the separator, thereby reducing the difference in the amount of lithium depletion between the edge region of the positive electrode sheet corresponding to the second region and the center region of the positive electrode sheet corresponding to the first region, that is, it is beneficial to reduce the degree of excessive lithium depletion in the edge region of the positive electrode sheet, narrowing the difference in kinetic performance between the center region and the edge region, and thus improving the thermal stability and high-temperature storage performance of the electrochemical device. The above-mentioned second region of the separator having a specific porosity and the first region of the separator having a porosity within a specific difference range from the porosity of the second region of the separator are beneficial to narrowing the difference between the center region and the edge region while ensuring the overall lithium ion migration capacity of the electrochemical device, thereby benefiting the overall performance of the electrochemical device.

[0013] Based on the first aspect, in some possible embodiments, the Gurley value of the second region of the isolation membrane is 4s / 100cc to 8s / 100cc, and the ratio of the Gurley value of the second region of the isolation membrane to the Gurley value of the first region of the isolation membrane is 1:1.2 to 1:2.

[0014] In the above possible embodiment, by designing the air permeability (i.e., Gurley value) of the second region of the separator to be lower than the air permeability of the first region of the separator, it is beneficial to reduce the lithium ion diffusion capacity of the second region of the separator compared to the first region of the separator, thereby reducing the difference in the amount of lithium depletion between the edge region of the positive electrode sheet corresponding to the second region and the center region of the positive electrode sheet corresponding to the first region, that is, it is beneficial to reduce the degree of excessive lithium depletion in the edge region of the positive electrode sheet, narrowing the difference in kinetic performance between the center region and the edge region, and thus helping to improve the thermal stability and high-temperature storage performance of the electrochemical device. The above-mentioned second region of the separator having a specific Gurley value, and the first region of the separator having a specific ratio range of Gurley value to the second region of the separator, are beneficial to narrowing the difference between the center region and the edge region while ensuring the overall lithium ion migration capacity of the electrochemical device, thereby benefiting the overall performance of the electrochemical device.

[0015] Based on the first aspect, in some possible embodiments, the isolation film includes a substrate layer, a first coating layer, and a second coating layer, wherein the first coating layer and the second coating layer are disposed on opposite sides of the substrate layer in a first direction. The first region of the isolation film includes the first coating layer and a portion of the substrate layer corresponding to the first coating layer, and the second region of the isolation film includes the second coating layer and a portion of the substrate layer corresponding to the second coating layer. The first coating layer includes a first adhesive and first ceramic particles dispersed in the first adhesive, and the second coating layer includes a second adhesive and second ceramic particles dispersed in the second adhesive.

[0016] In the above possible implementation manner, since the isolation membrane includes the first ceramic particles and the second ceramic particles, it is beneficial to improve the high-temperature stability of the isolation membrane, thereby facilitating the improvement of the high-temperature stability of the entire electrochemical device.

[0017] Based on the first aspect, in some possible embodiments, the average particle size Dv50 of the second ceramic particles is 0.3 μm to 1.0 μm, the particle size Dv50 of the second ceramic particles is greater than the particle size Dv50 of the first ceramic particles, and the difference is 0.1 μm to 0.5 μm.

[0018] In the above possible embodiment, the particle size Dv50 of the second ceramic particles in the second region of the separator is greater than the particle size Dv50 of the first ceramic particles in the first region of the separator, which is beneficial to reducing the lithium ion diffusion capacity of the second region of the separator compared to the first region of the separator, thereby helping to reduce the difference in the amount of lithium depletion between the edge region of the positive electrode sheet corresponding to the second region and the central region of the positive electrode sheet corresponding to the first region, that is, helping to reduce the degree of excessive lithium depletion in the edge region of the positive electrode sheet, narrowing the difference in kinetic performance between the central region and the edge region, and thus helping to improve the thermal stability and high-temperature storage performance of the electrochemical device. The above-mentioned second ceramic particles with a specific particle size and the first ceramic particles with a specific difference in particle size from the second ceramic particles are beneficial to narrowing the difference between the central region and the edge region while ensuring the overall lithium ion migration capacity of the electrochemical device, thereby benefiting the overall performance of the electrochemical device.

[0019] Based on the first aspect, in some possible embodiments, the content of the second adhesive in the second coating layer is 10 wt % to 15 wt %, and the ratio of the content of the second adhesive in the second coating layer to the content of the first adhesive in the first coating layer is 1.1:1 to 2:1.

[0020] In the above possible embodiment, by designing the content of the second adhesive in the second region of the separator to be higher than the content of the first adhesive in the first region of the separator, it is beneficial to improve the interfacial transport barrier of lithium ions in the second region of the separator compared to the first region of the separator, thereby reducing the difference in the amount of lithium depletion between the edge region of the positive electrode sheet corresponding to the second region and the central region of the positive electrode sheet corresponding to the first region, that is, it is beneficial to reduce the degree of excessive lithium depletion in the edge region of the positive electrode sheet, narrow the difference in kinetic performance between the central region and the edge region, and thus is beneficial to improving the thermal stability and high-temperature storage performance of the electrochemical device. The above-mentioned content of the second adhesive and the first adhesive having a content within a specific ratio range with respect to the content of the second adhesive are beneficial to ensuring the bonding force between the first coating layer and the second coating layer in the separator and the substrate layer, that is, it is beneficial to ensuring the structural stability of the separator while also ensuring the overall kinetic performance of the electrochemical device, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0021] Based on the first aspect, in some possible embodiments, the first positive electrode active material includes at least one of lithium cobalt oxide with a coating amount or doping amount of 0.81 wt% to 5.0 wt%, lithium nickel cobalt manganese oxide with a cobalt content of 5% to 20%, or lithium iron phosphate. The second positive electrode active material includes at least one of lithium cobalt oxide with a coating amount or doping amount of 0.05 wt% to 0.8 wt%, lithium nickel cobalt manganese oxide with a cobalt content of 21% to 33%, or lithium manganese oxide.

[0022] In the above possible implementation manner, the edge region uses an active material with lower kinetic performance and higher stability than that of the central region, which is beneficial to reducing the phenomenon of excessive delithiation of the edge region compared to the central region and improving the stability of the edge region, so as to narrow the difference in kinetic performance between the central region and the edge region, and thus is beneficial to improving the thermal stability and high-temperature storage performance of the electrochemical device.

[0023] Based on the first aspect, in some possible implementations, the porosity of the edge region is 10% to 45%, and the ratio of the porosity of the edge region to the porosity of the central region is 1:2 to 1:1.1.

[0024] In the above possible embodiments, by designing a central region with higher porosity and an edge region with lower porosity, it is beneficial to improve the liquid phase diffusion capacity of lithium ions in the central region compared to the edge region to improve the kinetic performance of the central region compared to the edge region, thereby helping to narrow the difference in kinetic performance between the central region and the edge region, and thus helping to enhance the overall capacity of the electrochemical device, so as to enhance the overall performance of the electrochemical device (such as thermal stability and high temperature storage performance). Among them, the porosity of the edge region is too large, which is not conducive to ensuring the volume energy density of the electrochemical device, while the porosity of the edge region is too small, and the kinetic performance of the electrochemical device is poor, which is not conducive to ensuring the overall performance of the electrochemical device. In addition, if the porosity ratio is too small, it is not easy to narrow the difference in kinetic performance between the central region and the edge region, and if the porosity ratio is too large, it is easy to make the difference between the central region and the edge region too large, which is easy to cause a reverse difference, which is also not conducive to improving the overall performance of the electrochemical device.

[0025] Based on the first aspect, in some possible embodiments, the ratio of the particle size Dv50 of the first positive active material to the particle size Dv50 of the second positive active material is 1.1:1 to 2:1, and the particle size Dv50 of the first positive active material is 1.0 micron to 25 microns.

[0026] In the above possible embodiments, by designing the edge region to use an active material with a larger particle size and the center region to use an active material with a smaller particle size, it is beneficial to reduce the solid-phase transmission distance of lithium ions in the active material in the center region compared to the edge region to improve the kinetic performance of the center region compared to the edge region, thereby helping to narrow the difference in kinetic performance between the center region and the edge region, and thus helping to improve the overall capacity of the electrochemical device, thereby improving the overall performance of the electrochemical device. The first positive electrode active material in the above-mentioned specific particle size range and the second positive electrode active material having a specific ratio range with the first positive electrode active material are conducive to achieving a higher compaction density and a higher kinetic electrode assembly, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0027] Based on the first aspect, in some possible implementations, the width of the second region of the isolation film is 5 mm to 13 mm, and the width of the edge region is 2 mm to 10 mm.

[0028] Based on the first aspect, in some possible embodiments, the isolation membrane includes multiple first regions and multiple second regions, each second region corresponding to a first region is connected to form a stacking region, and in the first direction, each stacking region is located between adjacent positive pole pieces and negative pole pieces. The isolation membrane also includes at least one connecting region, and each connecting region connects two adjacent stacking regions.

[0029] The second aspect of the present application provides an electronic device, comprising a main body and an electrochemical device as described above, wherein the electrochemical device is electrically connected to the main body for supplying power to the main body. In the above-mentioned electronic device of the present application, the first and second regions of the separator are designed to be differentiated. By having the second region corresponding to the edge region of the positive electrode sheet have a lower ionic conductivity and the first region corresponding to the center region of the positive electrode sheet have a higher ionic conductivity, it is beneficial to reduce the migration of lithium ions in the second region corresponding to the edge region compared to the first region corresponding to the center region, thereby facilitating the reduction of the difference in kinetic performance between the center region and the edge region, and reducing the difference in the amount of lithium desorption between the edge region and the center region, thereby facilitating the improvement of the overall thermal stability and high-temperature storage performance of the electrochemical device, and thereby facilitating the improvement of the high-temperature resistance and service life of the electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic structural diagram of an electrochemical device according to one embodiment of the present application.

[0031] FIG2 is a schematic cross-sectional view of an electrochemical device according to one embodiment of the present application.

[0032] FIG3 is a schematic cross-sectional view of a positive electrode according to an embodiment of the present application, taken along a direction perpendicular to the thickness.

[0033] FIG4 is a top view of an isolation film according to an embodiment of the present application, taken along a direction perpendicular to the thickness.

[0034] FIG5 is an enlarged schematic diagram of a partial cross-section along the thickness direction of an electrochemical device according to one embodiment of the present application.

[0035] FIG6 is a schematic cross-sectional view of an electrode assembly according to another embodiment of the present application.

[0036] FIG7 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

[0037] Description of main component symbols

[0038] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0039] The following specific embodiments illustrate the implementation of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Although the description of the present application will be introduced in conjunction with the embodiments, this does not mean that the features of this application are limited to this implementation. On the contrary, the purpose of introducing the application in conjunction with the implementation is to cover other options or modifications that may be extended based on the claims of the present application. In order to provide an in-depth understanding of the present application, the following description will contain many specific details. The present application can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present application, some specific details will be omitted in the description.

[0040] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0041] Hereinafter, if used, the terms "first," "second," etc., are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature qualified as "first," "second," etc. may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0042] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0043] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of the described features, values, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0044] The following describes the embodiments of the present application in conjunction with the accompanying drawings. Unless otherwise specified, the data range values ​​recorded in this application should include the end values.

[0045] The energy density of lithium-ion batteries is usually improved by increasing the capacity and voltage of the active materials in the electrodes and increasing the content of the active materials in the electrodes. Among them, increasing the compaction density of the active materials and preparing thicker electrode active layers can both increase the content of the active materials.

[0046] In lithium-ion batteries, there are differences in electric field strength, potential and polarization between the edge and center areas of the electrode, resulting in uneven electrochemical reactions between the edge and main areas of the electrode. This uneven electrochemical reaction phenomenon becomes more obvious with the increase of active layer thickness and active layer compaction density, thereby deteriorating the overall performance of the battery (including but not limited to affecting cycle life, causing thermal safety issues, etc.) and restricting a substantial increase in active layer thickness and compaction density.

[0047] In view of this, embodiments of the present application provide an electrochemical device and an electronic notification using the electrochemical device.

[0048] Please refer to Figure 1, which shows an electrochemical device 100 according to an embodiment of the present application. Please refer to Figure 2, the electrochemical device 100 includes a positive electrode sheet 10, a negative electrode sheet 30, and a separator 50. The separator 50 is disposed between the positive electrode sheet 10 and the negative electrode sheet 30. As shown in Figure 2, the positive electrode sheet 10, the separator 50, and the negative electrode sheet 30 can be alternately stacked in sequence along the thickness direction X, i.e., the first direction, to form a laminated electrode assembly A, or the positive electrode sheet 10, the separator 50, and the negative electrode sheet 30 can be stacked in sequence and then wound around a central axis to form a wound electrode assembly (not shown). Below, the laminated electrode assembly A will be used as an example for subsequent description.

[0049] The electrochemical device 100 also includes a housing 20 and an electrolyte 60. The electrolyte 60 and the electrode assembly A are contained within the housing 20. The housing 20 can be a packaging bag formed using a packaging film, such as, but not limited to, an aluminum-plastic film. That is, the electrochemical device can be a soft-pack battery. The housing 20 can also be, but is not limited to, those disclosed in the prior art, such as steel-cased batteries and aluminum-cased batteries.

[0050] The positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active layer 13 disposed on at least one surface of the positive electrode current collector 11. In this embodiment, as shown in FIG2 , the positive electrode active layer 13 may be disposed on only one side of the positive electrode current collector 11, or may be disposed on two opposite surfaces of the positive electrode current collector 11.

[0051] The positive electrode current collector 11 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0052] Please refer to Figures 2 and 3 in conjunction. The positive electrode active layer 13 includes a central region 131 and an edge region 133 disposed around the outer periphery of the central region 131. When the positive electrode sheet 10 forms a laminated electrode assembly A, as shown in Figure 3 , when viewed along the thickness direction X, the edge region 133 is annular (as shown in Figure 3 ) surrounding the central region 131. When the positive electrode sheet 10 forms a wound electrode assembly, when the positive electrode sheet 10 is laid out, i.e., not wound, when viewed along the thickness direction of the positive electrode sheet 10, the edge region 133 is annular (as shown in Figure 3 ) surrounding the central region 131. When the positive electrode sheet 10 is wound to form a wound electrode assembly, the edge region 133 includes the starting and ending ends of the positive electrode active layer 13, as well as two ends of the positive electrode active layer 13 disposed opposite each other along the central axis of the winding.

[0053] In some embodiments, the width of the edge region 133 may be 2 mm to 10 mm, for example, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, or any specific value between any two adjacent values ​​mentioned above. The width refers to the distance from any position of the outer periphery of the edge region 133 away from the central region 131, that is, any position of the outer periphery of the entire positive electrode active layer 13, to the closest point where the adjacent edge region 133 connects to the inner periphery of the central region 131.

[0054] Because the positive electrode active layer 13 undergoes a lamination process during its formation, the outer edge of the central region 131 and the inner edge of the edge region 133, which are adjacent or connected to each other before lamination, merge with each other after lamination to form a transition region 135. That is, the positive electrode active layer 13 also includes a transition region 135, which connects the inner periphery of the edge region 133 and the outer periphery of the central 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 ​​mentioned above.

[0055] In addition, because the positive electrode active layer 13 undergoes a lamination process during its formation, the thickness of each region varies before and after lamination. The edge region 133 may extend away from the center region 131. However, since the center region 131 is surrounded by the edge region 133, the movable space of the center region 131 during lamination is limited by the edge region 133. Therefore, the thickness of the center region 131 is generally greater than 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 may be less than 1 micron, which helps improve the flatness of the electrode assembly formed by the positive electrode sheet 10 and the negative electrode sheet 30, thereby improving the overall flatness of the electrochemical device. In some embodiments, the thickness of the edge region may be between 50 microns and 1000 microns. Furthermore, the thickness of the edge region may be between 100 microns and 500 microns, for example, 100 microns, 200 microns, 300 microns, 400 microns, 500 microns, or any specific value between any two adjacent values ​​mentioned above.

[0056] Referring to FIG. 2 and FIG. 4 , the separator 50 includes a first region 50a and a second region 50b disposed around an outer periphery connected to the first region 50a. The second region 50b overlaps with the edge region 133 of the positive electrode tab 10 in the thickness direction X, and extends beyond the edge region 133 in any direction perpendicular to the thickness direction X. In other words, the second region 50b also overlaps with at least a portion of the central region 131 or at least a portion of the transition region 135 of the positive electrode tab 10 in the thickness direction X. In some embodiments, the width of the second region 50b of the separator 50 is between 5 mm and 13 mm, for example, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, or any specific value between any two adjacent values ​​thereof.

[0057] In this embodiment, the ionic conductivity of the second region 50b is lower than the ionic conductivity of the first region 50a, which is beneficial to reducing the migration of lithium ions in the second region 50b corresponding to the edge region 133 compared to the first region 50a corresponding to the center region 131, thereby helping to narrow the difference in kinetic performance between the center region 131 and the edge region 133, and reducing the difference in lithium desorption between the edge region 133 and the center region 131, which is beneficial to improving the overall thermal stability and high-temperature storage performance of the electrochemical device. Specifically, the ionic conductivity of the second region 50b is 0.1 mS / cm to 0.625 mS / cm, for example, 0.1 mS / cm, 0.15 mS / cm, 0.2 mS / cm, 0.25 mS / cm, 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm, 0.625 mS / cm, or any specific value between any two adjacent values ​​of the foregoing. To reduce the degree of excessive delithiation in the edge region 133 and thereby improve the stability of the edge region 133, the ratio of the ionic conductivity of the second region 50b to the ionic conductivity of the first region 50a is 1:5 to 1:1.2, such as 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, 1:1.2, or any specific ratio between any two adjacent ratios, which helps to reduce the difference between the two regions while improving the overall performance of the electrochemical device 100. When the ionic conductivity ratio is greater than 1:1.2, it is difficult to reduce the difference in the amount of delithiation between the central region 131 and the edge region 133, thereby improving the overall performance of the electrochemical device. When the ionic conductivity ratio is less than 1:5, the difference between the central region 131 and the edge region 133 is likely to be too large, which can easily lead to a reverse difference, which is also not conducive to improving the overall performance of the electrochemical device 100. In some embodiments, the ratio of the ionic conductivity of the second region 50b to the ionic conductivity of the first region 50a is 1:4 to 1:2.

[0058] As shown in FIG2 , when the electrode assembly A includes a plurality of positive electrode sheets 10 and a plurality of negative electrode sheets 30 , the separators 50 between any adjacent positive electrode sheets 10 and negative electrode sheets 30 are independently designed.

[0059] In some embodiments, the porosity of the first region 50a of the isolation membrane 50 is greater than the porosity of the second region 50b of the isolation membrane 50, which is beneficial to reducing the lithium ion diffusion capacity of the second region 50b of the isolation membrane 50 compared to the first region 50a of the isolation membrane 50, thereby helping to reduce the difference in the amount of lithium desorption between the edge region 133 of the positive electrode plate 10 corresponding to the second region 50b and the central region 131 of the positive electrode plate 10 corresponding to the first region 50a, that is, helping to reduce the degree of excessive lithium desorption in the edge region 133 of the positive electrode plate 10, narrowing the difference in kinetic performance between the central region 131 and the edge region 133, and thus helping to improve the thermal stability and high-temperature storage performance of the electrochemical device 100.

[0060] Specifically, the difference between the porosity of the first region 50a of the isolation membrane 50 and the porosity of the second region 50b of the isolation membrane 50 may be 2% to 10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any specific value between any two adjacent values ​​thereof. In some embodiments, the porosity of the second region 50b of the isolation membrane 50 may be 30% to 45%, for example, 30%, 32%, 34%, 35%, 37%, 39%, 40%, 42%, 45%, or any specific value between any two adjacent values ​​thereof. The second region 50b of the isolation membrane 50 having a specific porosity and the first region 50a of the isolation membrane 50 having a porosity within a specific difference range from the porosity of the second region 50b of the isolation membrane are beneficial for reducing the difference between the central region 131 and the edge region 133 while ensuring the overall lithium ion migration capability of the electrochemical device, thereby benefiting the overall performance of the electrochemical device 100.

[0061] In some embodiments, the permeability of the second region 50b of the isolation membrane 50 is lower than the permeability of the first region 50a of the isolation membrane 50, which is beneficial to reducing the lithium ion diffusion capacity of the second region 50b of the isolation membrane 50 compared with the first region 50a of the isolation membrane 50, thereby helping to reduce the difference in the amount of lithium desorption between the edge region 133 of the positive electrode plate 10 corresponding to the second region 50b and the central region 131 of the positive electrode plate 10 corresponding to the first region 50a, that is, it is beneficial to reduce the degree of excessive lithium desorption in the edge region 133 of the positive electrode plate 10, narrow the difference in kinetic performance between the central region 131 and the edge region 133, and thus help to improve the thermal stability and high-temperature storage performance of the electrochemical device 100.

[0062] Specifically, the ratio of the Gurley value of the second region 50 b of the isolation film 50 to the Gurley value of the first region 50 a of the isolation film 50 may be 1:1.2 to 1:2, for example, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, or any specific ratio between any two adjacent ratios. In some embodiments, the Gurley value of the second region 50 b of the isolation film 50 may be 4 s / 100 cc to 8 s / 100 cc, for example, 4 s / 100 cc, 5 s / 100 cc, 6 s / 100 cc, 7 s / 100 cc, 8 s / 100 cc, or any specific ratio between any two adjacent ratios. The second region 50b of the isolation membrane 50 having a specific Gurley value, and the first region 50a of the isolation membrane 50 having a specific ratio range of Gurley value to the second region 50b of the isolation membrane 50, are beneficial for reducing the difference between the central region 131 and the edge region 133 while ensuring the overall lithium ion migration capability of the electrochemical device, thereby benefiting the overall performance of the electrochemical device 100.

[0063] In some embodiments, referring to FIG. 5 , the isolation film 50 may include a substrate layer 51 , a first coating layer 53 a and a second coating layer 53 b , wherein the first coating layer 53 a and the second coating layer 53 b are disposed on opposite sides of the substrate layer 51 in the thickness direction X.

[0064] The substrate layer 51 may be, but is not limited to, a porous non-woven fabric, membrane, or composite membrane. Its material may include, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. The polyethylene may include at least one of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in improving short circuits and can enhance the stability of the electrochemical device 100 through a shutdown effect.

[0065] The first region 50a of the isolation membrane 50 includes a first coating layer 53a and a portion of the substrate layer 51 corresponding to the first coating layer 53a, and the second region 50b of the isolation membrane 50 includes a second coating layer 53b and a portion of the substrate layer 51 corresponding to the second coating layer 53b. The first coating layer 53a may include a first adhesive and first ceramic particles dispersed in the first adhesive, and the second coating layer 53b may include a second adhesive and second ceramic particles dispersed in the second adhesive. Ceramics (first ceramic particles and second ceramic particles) have excellent high temperature resistance, heat shrinkage resistance, and puncture strength, which are beneficial to improving the high temperature stability of the isolation membrane 50, thereby improving the overall high temperature stability of the electrochemical device 100, and further improving the safety performance of the electrochemical device 100. In some embodiments, the first ceramic particles and the second ceramic particles may include, but are not limited to, aluminum oxide particles.

[0066] The particle size Dv50 of the second ceramic particles can be larger than the particle size Dv50 of the first ceramic particles, which is beneficial to reducing the lithium ion diffusion capacity of the second region of the isolation membrane compared with the first region of the isolation membrane, thereby helping to reduce the difference in the amount of lithium desorption between the edge region 133 of the positive electrode plate 10 corresponding to the second region 50b and the central region 131 of the positive electrode plate 10 corresponding to the first region 50a, that is, it is beneficial to reduce the degree of excessive lithium desorption in the edge region 133 of the positive electrode plate 10, narrow the difference in kinetic performance between the central region 131 and the edge region 133, and thus help to improve the thermal stability and high-temperature storage performance of the electrochemical device 100.

[0067] Specifically, the difference between the particle size Dv50 of the second ceramic particles and the particle size Dv50 of the first ceramic particles can be 0.1 μm to 0.5 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or any specific value between any two adjacent values ​​thereof. In some embodiments, the average particle size Dv50 of the second ceramic particles can be 0.3 μm to 1.0 μm, for example, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, or any specific value between any two adjacent values ​​thereof. The second ceramic particles having a specific particle size and the first ceramic particles having a specific particle size difference with the second ceramic particles described above are beneficial for reducing the difference between the central region 131 and the edge region 133 while ensuring the overall lithium ion mobility of the electrochemical device 100, thereby improving the overall performance of the electrochemical device 100.

[0068] The content of the second adhesive in the second coating 53b may be greater than the content of the first adhesive in the first coating 53a. By designing the content of the second adhesive in the second region 50b of the isolation membrane 50 to be higher than the content of the first adhesive in the first region 50a of the isolation membrane 50, it is beneficial to improve the interface transport barrier of lithium ions in the second region 50b of the isolation membrane 50 compared with the first region 50a of the isolation membrane 50, thereby helping to reduce the difference in the amount of lithium desorption in the edge region 133 of the positive electrode plate 10 corresponding to the second region 50b compared with the central region 131 of the positive electrode plate 10 corresponding to the first region 50a, that is, it is beneficial to reduce the degree of excessive lithium desorption in the edge region 133 of the positive electrode plate 10, narrow the difference in kinetic performance between the central region 131 and the edge region 133, and thus help to improve the thermal stability and high-temperature storage performance of the electrochemical device 100.

[0069] Specifically, the ratio of the second adhesive content in the second coating layer to the first adhesive content in the first coating layer can be 1.1:1 to 2:1, for example, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, or any specific ratio between any two adjacent ratios. In some embodiments, the second adhesive content in the second coating layer can be 10 wt % to 15 wt %, for example, 10 wt %, 11 wt %, 12 wt %, 13 wt %, 14 wt %, 15 wt %, or any specific ratio between any two adjacent ratios. The aforementioned second binder content and the first binder content within a specific ratio range to the second binder content are beneficial for ensuring the bonding strength between the first coating layer 53a and the second coating layer 53b in the separator and the substrate layer 51, respectively. This helps ensure the structural stability of the separator 50 while also ensuring the overall dynamic performance of the electrochemical device 100, thereby improving the overall performance of the electrochemical device 100. In some embodiments, the first coating layer may be composed of the first binder and first ceramic particles, and the second coating layer may be composed of the second binder and second ceramic particles.

[0070] As shown in FIG6 , in some embodiments, when the electrode assembly A includes multiple positive electrode sheets 10 and multiple negative electrode sheets 30, the electrode assembly A may include a separator 50 that is generally serpentine-shaped and sequentially wound around both sides of the positive electrode sheet 10 and / or both sides of the negative electrode sheet 30. Specifically, the separator 50 may include multiple first regions 50a and multiple second regions 50b, each second region 50b corresponding to a first region 50a connected to form a stacking region 50c. Each stacking region 50c is located between adjacent positive electrode sheets 10 and negative electrode sheets 30. The separator 50 may further include at least one connecting region 50d, each connecting region 50d connecting two adjacent stacking regions 50c.

[0071] Referring to Figures 2 and 3, the edge region 133 includes a first positive electrode active material, and the center region 131 includes a second positive electrode active material. The ratio of the solid phase diffusion coefficient of the first positive electrode active material (which can be recorded as Ds1) to the solid phase diffusion coefficient of the second positive electrode active material (which can be recorded as Ds2) can be 1:3 to 1:1.05, for example, 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 mentioned above. Furthermore, in some embodiments, the solid phase diffusion coefficient of the first positive electrode active material can be 10 -15 cm 2 / s to 10 -5 cm 2 / s, for example, 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 ​​mentioned above. By using a first positive electrode active material with a lower solid-phase diffusion coefficient in the edge region 133 and a second positive electrode active material with a higher solid-phase diffusion coefficient in the center region 131 to form a differentiated design of the edge region 133 and the center region 131 of the positive electrode sheet 10, the solid-phase diffusion rate of lithium ions in the center region 131 is improved compared to the edge region 133, thereby improving the kinetic performance of the center region 131 compared to the edge region 133, thereby reducing the difference in kinetic performance between the center region 131 and the edge region 133, reducing the difference in lithium desorption between the edge region 133 and the center region 131, and thereby improving the thermal stability and high-temperature storage performance of the electrochemical device 100. In addition, the solid-phase diffusion rate of lithium ions of the first positive electrode active material with a solid-phase diffusion coefficient in the above range is conducive to the insertion and extraction of lithium ions, which is conducive to improving the overall kinetic performance of the electrochemical device 100, and the above-mentioned specific ratio of the solid-phase diffusion coefficients is also conducive to reducing the difference between the two regions while improving the overall kinetic performance of the electrochemical device 100. Secondly, when the ratio of the solid-phase diffusion coefficients is greater than 1:1.05, it is difficult to reduce the difference in kinetic performance between the central region 131 and the edge region 133. When the ratio of the solid-phase diffusion coefficients is less than 1:3, the difference between the central region 131 and the edge region 133 is likely to be too large, which may easily lead to a reverse difference, which is also not conducive to improving the overall performance of the electrochemical device 100.

[0072] The particle size Dv50 of the first positive electrode active material may be greater than the particle size Dv50 of the second positive electrode active material. By designing the edge region 133 to use an active material with a larger particle size and the center region 131 to use an active material with a smaller particle size, the solid-phase transmission distance of lithium ions in the active material in the center region 131 is reduced compared to that in the edge region 133 to improve the kinetic performance of the center region 131 compared to the edge region 133, thereby narrowing the difference in kinetic performance between the center region 131 and the edge region 133, thereby improving the overall capacity of the electrochemical device, thereby improving the overall performance of the electrochemical device (such as thermal stability and high-temperature storage performance). 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 may be 1.1:1 to 2:1, for example, 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 mentioned above. In some embodiments, the particle size Dv50 of the first positive electrode active material may be 1.0 μm to 25 μm, for example, 1.0 μm, 5.0 μm, 7.0 μm, 10.0 μm, 14.0 μm, 15.0 μm, 17.0 μm, 25 μm, or any specific value between any two adjacent values ​​thereof. The first positive electrode active material within the above-mentioned specific particle size range and the second positive electrode active material having a specific ratio range to the first positive electrode active material are conducive to achieving a higher compaction density and a higher kinetic electrode assembly, thereby facilitating the improvement of the overall performance of the electrochemical device.

[0073] The first positive electrode active material and the second positive electrode active material each include a compound that can reversibly intercalate and deintercalate 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 include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the first positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or lithium iron phosphate (LiFePO4). The second positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or lithium iron phosphate (LiFePO4) and the like.

[0074] Furthermore, in this embodiment, the first positive electrode active material may include at least one of lithium cobalt oxide with a coating or doping amount of 0.81wt% to 5.0wt%, lithium nickel cobalt manganese oxide with a cobalt content of 5% to 20%, or lithium iron phosphate; the central region includes a second positive electrode active material, and the second positive electrode active material may include at least one of lithium cobalt oxide with a coating or doping amount of 0.05wt% to 0.8wt%, lithium nickel cobalt manganese oxide with a cobalt content of 21% to 33%, or lithium manganese oxide. Furthermore, the first positive electrode active material may be composed of at least one of lithium cobalt oxide with a coating or doping amount of 0.81wt% to 5.0wt%, lithium nickel cobalt manganese oxide with a cobalt content of 5% to 20%, or lithium iron phosphate; the second positive electrode active material may be composed of at least one of lithium cobalt oxide with a coating or doping amount of 0.05wt% to 0.8wt%, lithium nickel cobalt manganese oxide with a cobalt content of 21% to 33%, or lithium manganese oxide. The edge region 133 uses an active material with lower kinetic performance and higher stability than that of the central region 131, which is beneficial to reducing the phenomenon of excessive delithiation of the edge region 133 compared to the central region 131 and improving the stability of the edge region 133, thereby narrowing the difference in kinetic performance between the central region 131 and the edge region 133, and further beneficial to improving the overall cycle stability of the electrochemical device 100.

[0075] In the present application, the coating or doping of lithium cobalt oxide is the common coating and doping of lithium cobalt oxide in the industry, wherein the doping element can generally be but not limited to at least one of B, Al, Mg, Cr or Ni, and the coating can generally be formed by at least one of TiO2, MgO, Al2O3 or ZnO to form a coating layer, but not limited to the specific doping method and coating method are not specifically limited in this application.

[0076] In some embodiments, the porosity of the edge region 133 may be less than the porosity of the central region 131. By designing a central region 131 with a higher porosity and an edge region 133 with a lower porosity, the liquid-phase diffusion capacity of lithium ions in the central region 131 is improved compared to the edge region 133 to improve the kinetic performance of the central region 131 compared to the edge region 133, thereby narrowing the difference in kinetic performance between the central region 131 and the edge region 133, thereby improving the overall capacity of the electrochemical device and improving the overall performance of the electrochemical device (such as thermal stability and high-temperature storage performance). Specifically, the ratio of the porosity of the edge region 133 to the porosity of the central region 131 may be 1:2 to 1:1.1, for example, 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 ​​​​forementioned. In some embodiments, the porosity of the edge region 133 may be between 10% and 45%, for example, 10%, 14%, 15%, 18%, 20%, 23%, 25%, 29%, 30%, 35%, 38%, 41%, 45%, or any specific value between any two adjacent values. If the porosity of the edge region 133 is too large, it is not conducive to ensuring the volumetric energy density of the electrochemical device 100. If the porosity of the edge region 133 is too small, the kinetic performance of the electrochemical device 100 is poor, which is not conducive to ensuring the overall performance of the electrochemical device 100. In addition, if the porosity ratio is too small, it is not easy to reduce the difference in kinetic performance between the central region 131 and the edge region 133. If the porosity ratio is too large, it is easy to increase the difference between the central region 131 and the edge region 133, which can easily lead to a reverse difference, which is also not conducive to improving the overall performance of the electrochemical device 100.

[0077] The positive electrode active layer 13 also includes a binder to bind the positive electrode active material particles to facilitate film formation, and to improve the bonding strength between the positive electrode active layer 13 and the positive electrode current collector 11. In some embodiments, the binder in the positive electrode active layer 13 may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylidene fluoride (PVDF), a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0078] The positive electrode active layer 13 also includes a conductive agent, which may include but is not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black (SP), carbon nanotubes (CNTs), acetylene black, Ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based material may include but is not limited to metal powder or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0079] The negative electrode sheet 30 includes a negative current collector 31 and a negative active layer 33 disposed on at least one surface of the negative current collector 31. In this embodiment, as shown in FIG3 , the negative active layers 33 may be disposed on two opposite surfaces of the negative current collector 31, respectively.

[0080] The negative electrode current collector 31 can be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil or a carbon-based current collector, or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0081] The negative electrode active layer 33 includes a negative electrode active material, which can be any known negative electrode active material capable of reversible deintercalation of active ions, and is not limited in this application. For example, it can include, but is not limited to, at least one of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. The graphite can be selected from at least one of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0082] The negative electrode active layer 33 also includes a binder to bind the negative electrode active material particles to facilitate film formation and improve the bonding between the negative electrode active layer and the negative electrode current collector. In some embodiments, the binder in the negative electrode active layer 33 may include, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0083] 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 non-aqueous 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 bis(trifluoromethanesulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2, tris(trifluoromethylsulfonyl)methyl lithium (LiC(SO2CF3)3), lithium bis(oxalatoborate) (LiBOB) and lithium difluorophosphate (LiPO2F2). For example, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2, tris(trifluoromethylsulfonyl)methyl lithium (LiC(SO2CF3)3), lithium bis(trifluoromethylsulfonyl)methyl lithium (LiC(SO2CF3)3), lithium bis(trifluoromethylsulfonyl)methyl lithium (LiBOB) and lithium difluorophosphate (LiPO2F2). LiPF6 is used because it can give high ionic conductivity and improve cycle characteristics. The non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, other organic solvents or a combination thereof. Examples of carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2- trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

[0084] 7 , the electrochemical device 100 can be applied to an electronic device 200. The electronic device 200 further includes a body 201, and the electrochemical device 100 is electrically connected to the body 201 for powering the body 201. The electronic device 200 may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, lighting fixtures, toys, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0085] The present application is described in detail below through comparative examples and examples. It is understood that the parameters in the present application are not limited to those described in the comparative examples and examples, and can be selected according to actual needs.

[0086] Example 1

[0087] Preparation of positive electrode sheet:

[0088] The positive electrode active material lithium cobalt oxide (coating amount or doping amount 0.5wt%, particle size Dv50 13.3 microns, solid phase diffusion coefficient 2*10 -5 cm 2 / s), binder PVDF (homopolymer, molecular weight of 1.27 million, swelling rate of 10%), conductive agent SP, conductive agent CNT, conductive agent VGCF are added to N-methylpyrrolidone (NMP) in a ratio of 97.5:1.0:0.43:0.86:0.21, mixed and dispersed to prepare a first slurry (solid content of 75%), and the first slurry is extruded onto an aluminum foil current collector with a thickness of 9 microns and dried to form a first electrode sheet. The first slurry is correspondingly cured to form a first active layer (corresponding to the central area).

[0089] The positive electrode active material lithium cobalt oxide (coating amount or doping amount 1.2wt%, particle size Dv50 20 microns, solid phase diffusion coefficient 1*10 -5 cm 2 / s), binder PAA (molecular weight of 500,000, swelling rate of 5%), conductive agent SP, conductive agent CNT, and conductive agent VGCF are added to NMP in a ratio of 97.5:1.5:0.57:0.29:0.14, mixed and dispersed to prepare a second slurry (solid content of 75%), and the second slurry (width 4 mm) is coated outward on the outer periphery of the first active layer of the first electrode sheet through a gravure, and a second electrode sheet is formed after drying. The second slurry is correspondingly cured to form a second active layer (corresponding to the edge area).

[0090] Cold-pressed positive electrodes (with a porosity of 10% in the edge region and 15% in the center region) are formed by cold pressing at a pressure of 80 tons and a speed of 20 m / min. These electrodes are then die-cut to form positive electrode sheets. The width of the transition region is 0.2 mm, the width of the edge region is 4.0 mm, the thickness of the center region is 0.5 μm greater than that of the edge region, and the thickness of the edge region is 100 μm. The dimensions of the positive electrode sheet are approximately 70 mm by 80 mm.

[0091] Preparation of negative electrode sheet:

[0092] A negative electrode slurry (48% solids content) was prepared by mixing and dispersing the negative electrode active material graphite, binder SBR, and binder CMC in deionized water at a ratio of 97.4:1.4:1.2. The slurry was then extrusion-coated onto a 6-micron copper current collector and dried to form a negative electrode sheet. The negative electrode slurry also formed the negative electrode active layer. The thickness of the negative electrode active layer was 120 microns. The dimensions of the negative electrode sheet were approximately 72mm by 82mm.

[0093] Preparation of isolation membrane:

[0094] A first coating slurry was prepared by mixing and dispersing ceramic alumina (particle size Dv50:0.3 μm) and a polyacrylic acid resin (PAA) adhesive at a mass ratio of 92:8. This first coating slurry was then gravure coated onto a 5-μm-thick PE film serving as a substrate layer and dried. The first coating slurry then solidified to form a first coating layer. The thickness of the first coating layer was 2 μm.

[0095] Ceramic boehmite (particle size Dv50 is 0.6 microns) and adhesive PAA are mixed and dispersed in a mass ratio of 88:12 to form a second coating slurry. The second coating slurry is coated on the PE film around the outer periphery of the first coating layer by gravure with a coating width of 7 mm, and then dried to obtain an isolation membrane. The second coating slurry is cured to form a second coating layer. The thickness of the second coating layer is 2 microns. The ionic conductivity of the first area corresponding to the first coating layer in the isolation membrane is 0.75 mS / cm, the porosity is 45%, and the Gurley permeability is 9 s / 100 cc. The ionic conductivity of the second area corresponding to the second coating layer in the isolation membrane is 0.25 mS / cm, the porosity is 40%, and the Gurley permeability is 6 s / 100 cc.

[0096] Preparation of lithium-ion batteries:

[0097] The positive electrode sheets, separators, and negative electrode sheets are alternately stacked in sequence to form a laminated electrode assembly. After the tabs are welded, they are placed in a battery case and injected with an electrolyte (1M LiPF6in EC:DEC:EMC:adiponitrile = 32.83:32.83:32.83:1.51). After packaging and formation, a lithium-ion battery, i.e., an electrochemical device, is formed.

[0098] Comparative Example 1

[0099] The difference between Comparative Example 1 and Example 1 lies in the preparation of the positive electrode sheet and the separator:

[0100] Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide (coating amount or doping amount 0.5wt%, particle size Dv50 13.3 microns, solid phase diffusion coefficient 2*10 -5 cm 2 / s), binder PVDF (homopolymer, molecular weight 1.27 million, swelling rate 10%), conductive agent SP, conductive agent CNT, and conductive agent VGCF are added to N-methylpyrrolidone (NMP) in a ratio of 97.5:1.0:0.43:0.86:0.21 and mixed and dispersed to prepare a positive electrode slurry (solid content 75%). The positive electrode slurry is then extruded onto a 9-micron thick aluminum foil current collector and dried to form a positive electrode active layer. It is then cold-pressed at a pressure of 80t and a speed of 20m / min to form a cold-pressed positive electrode (porosity 15%), and die-cut to form a positive electrode sheet. The thickness of the positive electrode active layer is 100 microns. The size of the positive electrode sheet is approximately 70mm*80mm.

[0101] Preparation of the separator: Ceramic alumina (particle size Dv50, 0.3 μm) and a polyacrylic acid resin (PAA) binder were mixed and dispersed in a mass ratio of 92:8 to form a coating slurry. This coating slurry was then gravure coated onto a 5-μm-thick PE film serving as the substrate layer and dried. The coating slurry then solidified to form a coating layer with a thickness of 2 μm. The separator membrane had an ionic conductivity of 0.75 mS / cm, a porosity of 45%, and a Gurley permeability of 9 s / 100 cc.

[0102] Laminated lithium-ion batteries corresponding to Examples 2-19 were prepared according to the steps of Example 1 and Tables 1 and 3-7 below. Laminated lithium-ion batteries corresponding to Comparative Examples 2-3 were prepared according to the steps of Comparative Example 1 and Table 5 above. The lithium-ion batteries corresponding to Examples 1-19 and Comparative Examples 1-3 had the same parameters except for the steps described above and the parameters in the tables.

[0103] In addition, Example 20 was prepared, wherein the positive electrode plate of the lithium ion battery in Example 20 was the positive electrode plate prepared in Comparative Example 1, and the other structures of the lithium ion battery in Example 20 (isolation membrane, negative electrode plate and electrolyte) were consistent with the corresponding structures in the lithium ion battery in Example 1.

[0104] Each of the above examples and comparative examples was subjected to the following performance tests: Hotbox maximum temperature, storage swelling at 60°C for 30 days, and storage swelling at 85°C for 24 hours. The test results are reported in Tables 2 and 4-8. The methods for each performance test are described in detail below.

[0105] To pass the hotbox maximum temperature test: Charge at a constant current rate of 0.7C to the cutoff voltage at 20°C (±5°C), then charge at a constant voltage rate to 0.025°C at the cutoff voltage. Before testing, inspect the appearance and take photos. Place the sample vertically in a hotbox and heat it at a rate of 5±2°C to the target temperature ±2°C, maintaining the temperature for 60 minutes. After the test, inspect the appearance and take photos. If the battery does not ignite or explode at the target temperature, it passes the test. The highest temperature it can pass is the hotbox maximum temperature.

[0106] storage swelling@60℃30D: At a temperature of 25℃, the battery was charged at a constant current rate of 0.5C to 4.48V (cut-off voltage), and then charged at a constant voltage rate of 0.025C to the cut-off voltage. The test battery thickness was recorded as T1; after storage at 60℃ for 30D (i.e. 30 days), the test battery thickness was recorded as T2. The storage swelling rate of the battery = (T2-T1) / T1.

[0107] storage swelling@85℃24H: At a temperature of 25℃, charge the battery at a constant current rate of 0.5C to 4.48V (cut-off voltage), and then charge the battery at the cut-off voltage to 0.025C. The test cell is recorded as T1'; after storing at 85℃ for 24 hours (i.e., 24 hours), the cell is tested at T2'. The storage swelling rate of the battery = (T2'-T1') / T1'.

[0108] Table 1

[0109] Table 2

[0110] Table 3

[0111] Table 4

[0112] Table 5 (The solid-phase diffusion coefficient of the edge area is marked as Ds1, and the solid-phase diffusion coefficient of the central area is marked as Ds2)

[0113] Table 6

[0114] Table 7

[0115] Table 8

[0116] The data in Tables 1 to 8 demonstrate that differential design of the edge region 133 and central region 131 of the positive electrode sheet 10, as well as differential design of the first region 50a and second region 50b of the separator 50, can improve the thermal stability and high-temperature storage performance of the lithium-ion battery. The data in Table 8 demonstrate that simply differential design of the first region 50a and second region 50b of the separator 50 can also improve the thermal stability and high-temperature storage performance of the lithium-ion battery, but the improvement is not as significant as differential design of both the edge region 133 and central region 131 of the positive electrode sheet 10, as well as the first region 50a and second region 50b of the separator 50.

[0117] In addition, those skilled in the art can make various other corresponding changes and modifications based on the technical concept of this application, and all these changes and modifications should fall within the scope of protection of this application.

Claims

1. An electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet comprises a positive current collector and a positive active layer, wherein: The positive electrode active layer includes a central area and an edge area arranged around the outer periphery of the central area, the isolation membrane includes a first area and a second area arranged around the outer periphery connected to the first area, the second area and the edge area are stacked in a first direction, and in any direction perpendicular to the first direction, the second area exceeds the edge area; the ionic conductivity of the second area is 0.1mS / cm to 0.625mS / cm, and the ratio of the ionic conductivity of the second area to the ionic conductivity of the first area is 1:5 to 1:1.

2.

2. The electrochemical device according to claim 1, wherein The ratio of the ionic conductivity of the second region to the ionic conductivity of the first region is 1:4 to 1:

2.

3. The electrochemical device according to claim 1, wherein The ratio of the ionic conductivity of the second region to the ionic conductivity of the first region is 1:4 to 1:

3.

4. The electrochemical device according to claim 1, wherein The edge region includes a first positive electrode active material, the central region includes a second positive electrode active material, 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, 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.

5. The electrochemical device according to any one of claims 1 to 4, wherein: The porosity of the second region of the isolation film is 30% to 45%, and the porosity of the first region of the isolation film is greater than the porosity of the second region of the isolation film, and the difference is 2% to 10%.

6. The electrochemical device according to any one of claims 1 to 4, wherein: The Gurley value of the second region of the isolation film is 4s / 100cc to 8s / 100cc, and the ratio of the Gurley value of the second region of the isolation film to the Gurley value of the first region of the isolation film is 1:1.2 to 1:

2.

7. The electrochemical device according to any one of claims 1 to 4, wherein: The isolation film includes a substrate layer, a first coating layer and a second coating layer, wherein the first coating layer and the second coating layer are both arranged on opposite sides of the substrate layer in the first direction, the first region of the isolation film includes the first coating layer and a portion of the substrate layer corresponding to the first coating layer, and the second region of the isolation film includes the second coating layer and a portion of the substrate layer corresponding to the second coating layer; the first coating layer includes a first adhesive and first ceramic particles dispersed in the first adhesive, and the second coating layer includes a second adhesive and second ceramic particles dispersed in the second adhesive.

8. The electrochemical device according to claim 7, wherein: The particle size Dv50 of the second ceramic particles is 0.3 micrometers to 1.0 micrometers, and the particle size Dv50 of the second ceramic particles is greater than the particle size Dv50 of the first ceramic particles, and the difference is 0.1 micrometers to 0.5 micrometers.

9. The electrochemical device according to claim 7, wherein: The content of the second adhesive in the second coating layer is 10wt% to 15wt%, and the ratio of the content of the second adhesive in the second coating layer to the content of the first adhesive in the first coating layer is 1.1:1 to 2:

1.

10. The electrochemical device according to claim 4, wherein The first positive electrode active material includes at least one of lithium cobalt oxide with a coating amount or doping amount of 0.81wt% to 5.0wt%, lithium nickel cobalt manganese oxide or lithium iron phosphate with a cobalt element content of 5% to 20%; the second positive electrode active material includes at least one of lithium cobalt oxide with a coating amount or doping amount of 0.05wt% to 0.8wt%, lithium nickel cobalt manganese oxide or lithium manganese oxide with a cobalt element content of 21% to 33%.

11. The electrochemical device according to any one of claims 1 to 4, wherein: The porosity of the edge region is 10% to 45%, and the ratio of the porosity of the edge region to the porosity of the central region is 1:2 to 1:1.

1.

12. The electrochemical device according to claim 4, 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 micrometer to 25 micrometers.

13. The electrochemical device according to claim 1, wherein The width of the second region of the isolation film is 5 mm to 13 mm, and the width of the edge region is 2 mm to 10 mm.

14. The electrochemical device according to claim 1, wherein The isolation film includes a plurality of the first regions and a plurality of the second regions, each of the second regions corresponding to a first region is connected around to form a stacking region, and in the first direction, each of the stacking regions is located between adjacent positive electrode sheets and negative electrode sheets, and the isolation film also includes at least one connecting region, each of the connecting regions connects two adjacent stacking regions.

15. An electronic device, comprising a body, wherein the electronic device further comprises an electrochemical device as claimed in any one of claims 1 to 14, and the electrochemical device is electrically connected to the body for supplying power to the body.

Images