Electrochemical device and electronic device using same

Abstract

An electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer; and the negative electrode active layer comprises a central region and an edge region arranged around the outer periphery of the central region. The ionic impedance of the edge region is 30 Ohm to 54.5 Ohm, and the ratio of the ionic impedance of the edge region to the ionic impedance of the central region is 1:1.1-1:2, so that the liquid-phase transmission capability of the edge region for lithium ions can be improved compared with the central region, thereby improving the safety and cycle stability of the electrochemical device, and guaranteeing the overall energy density of the electrochemical device. Also provided is an electronic device using the electrochemical device.

Description

Electrochemical device and electronic device using the same Technical Field

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

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

[0003] Summary of the Invention

[0004] In view of the above situation, it is necessary to provide an electrochemical device that is conducive to improving overall performance 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 positioned between the positive and negative electrode sheets. The negative electrode sheet comprises a negative current collector and a negative active layer, wherein the negative active layer comprises a central region and an edge region disposed around the outer periphery of the central region. The ionic impedance of the edge region is 30 ohms to 54.5 ohms, and the ratio of the ionic impedance of the edge region to the ionic impedance of the central region is 1:1.1 to 1:2.

[0006] In an electrochemical device, the electric field strength of the edge region of each electrode is higher than that of the central region and the edge region is easily contacted by the electrolyte. Due to the indifferent design between the edge region and the central region of the electrode in the prior art, the lithium desorption rate and the amount of lithium desorption in the edge region of the positive electrode are greater than the lithium desorption rate and the amount of lithium desorption in the central region of the positive electrode, resulting in the number of lithium ions that the edge region of the negative electrode needs to accept per unit time being greater than the number of lithium ions that the central region of the negative electrode needs to accept per unit time, thereby making the edge region of the negative electrode prone to lithium deposition, affecting the safety and cycle stability of the electrochemical device. In the above-mentioned electrochemical device of the present application, the edge region and the central region of the negative electrode are designed to be differentiated. By designing the ionic impedance of the edge region of the negative electrode is lower than the ionic impedance of the central region of the negative electrode, it is beneficial to improve the liquid phase transmission capacity of the edge region for lithium ions compared to the central region without affecting the corresponding energy density of the central region, thereby improving the lithium insertion capacity of the edge region compared to the central region, reducing the risk of lithium deposition in the edge region of the negative electrode, and thus improving the safety and cycle stability of the electrochemical device. The edge region having the above-mentioned specific range of ionic impedance and the central region having a specific ratio range of ionic impedance to the ionic impedance of the edge region are beneficial for ensuring the overall energy density of the electrochemical device while ensuring the kinetic performance of the electrochemical device, so as to achieve improved kinetic performance while ensuring a higher energy density of the electrochemical device, thereby improving the overall performance of the electrochemical device.

[0007] Based on the first aspect, in some possible embodiments, the ratio of the ionic impedance of the edge region to the ionic impedance of the central region is 1:1.2 to 1:2, which is beneficial to further reduce the risk of lithium plating in the edge region of the negative electrode, so as to further improve the safety and cycle stability of the electrochemical device.

[0008] Based on the first aspect, in some possible embodiments, the separator includes a first region and a second region disposed around an outer periphery connected to the first region, the second region and the edge region overlapping in a first direction, and the second region extends beyond the edge region in any direction perpendicular to the first direction. The ionic conductivity of the second region is 0.1 mS / cm to 0.4 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.

[0009] In the above possible embodiment, the ionic conductivity of the second region of the separator corresponding to the edge region of the negative electrode sheet is less than the ionic conductivity of the first region of the separator corresponding to the center region of the negative electrode sheet, which is beneficial to reducing the migration capacity of the second region for lithium ions compared to the first region while ensuring the overall ionic conductivity of the separator, that is, reducing the number of lithium ions that diffuse from the positive electrode sheet to the edge region of the negative electrode sheet, thereby reducing the risk of lithium plating in the edge region of the negative electrode sheet, thereby improving the safety and cycle stability of the electrochemical device while ensuring the capacity of the electrochemical device. The second region having the ionic conductivity in the above specific range and the first region having an ionic conductivity within a specific ratio range to the ionic conductivity of the second region can make the separator have a higher ionic conductivity as a whole while reducing the risk of lithium plating in the edge region, thereby making the electrochemical device have a higher capacity while having better safety and cycle stability, thereby improving the overall performance of the electrochemical device.

[0010] Based on the first aspect, in some possible embodiments, the puncture resistance of the second region of the isolation membrane is 0.03 kgf to 0.1 kgf, and the ratio of the puncture resistance of the second region of the isolation membrane to the puncture resistance of the first region of the isolation membrane is 1.2:1 to 3:1.

[0011] In the above possible implementation, based on the fact that lithium deposition is prone to occur in the edge area of ​​the negative electrode sheet, by designing the puncture strength of the second area of ​​the separator to be greater than the puncture strength of the first area of ​​the separator, it is beneficial to avoid the lithium dendrites formed by lithium deposition from piercing the second area of ​​the separator corresponding to the edge area of ​​the negative electrode sheet under the premise of controlling costs and ensuring the overall conductivity of the separator, thereby facilitating the improvement of the overall safety and cycle stability of the electrochemical device. The second area of ​​the separator having a puncture strength within the above range, and the first area of ​​the separator having a puncture strength within a specific ratio range to the puncture strength of the second area of ​​the separator, can help the separator as a whole have a higher ionic conductivity while reducing the risk of lithium deposition in the edge area, thereby helping the electrochemical device have a higher capacity while having better safety and cycle stability, thereby improving the overall performance of the electrochemical device.

[0012] Based on the first aspect, in some possible embodiments, after keeping warm at 150 degrees Celsius for 1 hour, the thermal shrinkage ratio of the second area of ​​the isolation membrane is 3% to 16.4%, and the ratio of the thermal shrinkage ratio of the second area of ​​the isolation membrane to the thermal shrinkage ratio of the first area of ​​the isolation membrane is 1:1.1 to 1:5.

[0013] In the above possible embodiments, the second region of the separator having a specific thermal shrinkage ratio is beneficial for improving the shrinkage resistance of the second region of the separator corresponding to the edge region of the negative electrode sheet at high temperatures to reduce the risk of short circuit or self-discharge caused by separator shrinkage under high temperature conditions, thereby improving the high-temperature cycling stability of the electrochemical device. The differentiated design of the thermal shrinkage ratio of the second region of the separator and the thermal shrinkage ratio of the first region of the separator is beneficial for simultaneously ensuring the electrical conductivity of the first region to ensure the capacity of the electrochemical device. The thermal shrinkage ratio of the second region of the separator and the thermal shrinkage ratio of the first region of the separator within the above specific ratio range is beneficial for ensuring that the electrochemical device has a higher capacity while having better safety and cycling stability, thereby improving the overall performance of the electrochemical device.

[0014] Based on the first aspect, in some possible embodiments, the electrolyte wettability of the second region of the isolation membrane is 50 mm / min to 90 mm / min, the electrolyte wettability of the second region of the isolation membrane is greater than the electrolyte wettability of the first region of the isolation membrane, and the difference is 5 mm / min to 20 mm / min.

[0015] In the above possible embodiments, the electrolyte wettability of the second region of the isolation membrane in the above specific range is beneficial to improving the liquid retention capacity between the second region of the isolation membrane and the edge region of the corresponding negative electrode plate, thereby helping to avoid the risk of lithium plating of the negative electrode plate due to insufficient electrolyte, and further helping to improve the safety and cycle stability of the electrochemical device.

[0016] 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.

[0017] In the above possible implementation manner, since the isolation membrane contains the first ceramic particles and the second ceramic particles, it is beneficial to improve the high-temperature stability of the isolation membrane, and to increase the puncture resistance of the isolation membrane to reduce the risk of the isolation membrane being punctured by lithium dendrites formed due to lithium precipitation, thereby improving the high-temperature stability, safety and cycle stability of the electrochemical device.

[0018] Based on the first aspect, in some possible implementations, the aspect ratio of the second ceramic particles is 5 to 50, and the ratio of the aspect ratio of the second ceramic particles to the aspect ratio of the first ceramic particles is 1.1:1 to 5:1.

[0019] In the above possible embodiments, the film layer formed by the ceramic particles with a larger aspect ratio, that is, the flatter they are, has a stronger resistance to puncture and thermal shrinkage, while the path through which lithium ions pass is more tortuous, which is not conducive to the rapid transmission of lithium ions. By designing the second region of the separator to use second ceramic particles that are flatter than the first ceramic particles in the first region of the separator, it is beneficial to improve the puncture resistance and thermal shrinkage resistance of the second region of the separator while ensuring the transmission capacity of the first region of the separator for lithium ions, thereby helping to improve the overall safety and cycle stability of the electrochemical device while ensuring the overall capacity of the electrochemical device. The above-mentioned second ceramic particles with an aspect ratio within a specific range and the first ceramic particles with an aspect ratio within a specific ratio range to the aspect ratio of the second ceramic particles are beneficial to improving the puncture resistance and thermal shrinkage resistance of the second region of the separator while ensuring that the transmission of lithium ions by the separator as a whole is not too low, thereby helping to improve the overall safety and cycle stability of the electrochemical device while ensuring the overall capacity of the electrochemical device, thereby improving the overall performance of the electrochemical device.

[0020] Based on the first aspect, in some possible embodiments, the content of the second ceramic particles in the second coating is 70 wt % to 95 wt %, and the content of the second ceramic particles in the second coating is greater than the content of the first ceramic particles in the first coating, and the difference is 0.5% to 20%.

[0021] In the above possible embodiments, the second region of the separator has a relatively high content of the second ceramic particles, which helps improve the puncture resistance and thermal shrinkage resistance of the second region of the separator, thereby improving the overall safety and cycling stability of the electrochemical device. The differentiated design of the ceramic particle content in the second coating and the first coating helps ensure the overall puncture resistance and thermal shrinkage resistance of the separator while also ensuring the overall lithium ion transmission of the separator. This helps to improve the overall safety and cycling stability of the electrochemical device while maintaining the capacity of the electrochemical device, thereby improving the overall performance of the electrochemical device.

[0022] Based on the first aspect, in some possible implementations, the tortuosity of the edge region is 1.04 to 3, and the ratio of the tortuosity of the edge region to the tortuosity of the central region is 1:1.05 to 1:3.

[0023] In the above possible embodiments, by reducing the tortuosity of the edge region to reduce the barrier to liquid-phase transport of lithium ions in the edge region, the lithium insertion capacity of the edge region is improved, which in turn helps reduce the risk of lithium deposition in the edge region and improves the overall safety and cycle stability of the electrochemical device. The tortuosity within the above specific range of the edge region can help ensure the lithium insertion capacity of the edge region, and the specific ratio range of the tortuosity between the edge region and the central region is conducive to improving the lithium insertion capacity of the edge region while ensuring the overall energy density of the electrochemical device.

[0024] Based on the first aspect, in some possible embodiments, the edge region includes a first negative electrode active material, and the central region includes a second negative electrode active material. The first negative electrode active material has an OI value of 6 to 15, and the second negative electrode active material has an OI value greater than the OI value of the first negative electrode active material, and the difference is 1 to 5.

[0025] The OI value characterizes the arrangement direction of the active material particles of the electrode along the current collector of the electrode, and refers to the ratio of the current collector direction parallel to the electrode to the current collector direction perpendicular to the electrode. In the negative electrode, the smaller the OI value, the easier it is for lithium ions to be embedded. In the above possible implementation, the first negative electrode active material is designed to have an OI value in a specific range to ensure the lithium embedding ability of the edge area, thereby facilitating the reduction of the risk of lithium precipitation. The differentiated design of the OI value between the second negative electrode active material and the first negative electrode active material is conducive to ensuring the overall capacity of the electrochemical device while ensuring the overall energy density of the electrochemical device, which is conducive to improving the overall performance of the electrochemical device.

[0026] Based on the first aspect, in some possible embodiments, the edge region includes a first negative electrode active material, and the central region includes a second negative electrode active material. The first negative electrode active material has a core-shell structure, including a first core and a first shell encapsulating the first core, with the first shell comprising 0.5 wt% to 20 wt% of the first negative electrode active material. The second negative electrode active material has a core-shell structure, including a second core and a second shell encapsulating the second core, with the ratio of the first shell to the second shell in the first negative electrode active material being 1.1:1 to 3:1.

[0027] In the above possible embodiments, the core-shell structure of the first negative electrode active material and the second negative electrode active material can enhance the lithium insertion capacity. By designing the content of the first shell in the first negative electrode active material so that the first negative electrode active material has an OI value within a specific range, the lithium insertion capacity of the edge area is guaranteed, thereby reducing the risk of lithium plating. The differentiated design of the shell content between the second negative electrode active material and the first negative electrode active material is conducive to ensuring the overall capacity of the electrochemical device while ensuring the overall energy density of the electrochemical device, thereby improving the overall performance of the electrochemical device.

[0028] Based on the first aspect, in some possible implementations, the width of the second region of the separator is 5 mm to 13 mm, and the width of the edge region of the positive electrode active layer is 4 mm to 12 mm.

[0029] 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.

[0030] The second aspect of the present application provides an electronic device, comprising a body and an electrochemical device as described above, the electrochemical device being electrically connected to the body for powering the body. In the above-mentioned electronic device of the present application, the edge area and the central area of ​​the negative electrode plate are designed differently. By designing the ionic impedance of the edge area of ​​the negative electrode plate to be lower than the ionic impedance of the central area of ​​the negative electrode plate, it is beneficial to improve the liquid phase transmission capacity of the edge area for lithium ions compared to the central area without affecting the corresponding energy density of the central area, thereby improving the lithium insertion capacity of the edge area compared to the central area, reducing the risk of lithium plating in the edge area of ​​the negative electrode plate, and thus helping to improve the safety and cycle stability of the electrochemical device. The edge area with the above-mentioned specific range of ionic impedance and the central area with a specific ratio range of ionic impedance to the ionic impedance of the edge area are beneficial to ensuring the overall energy density of the electrochemical device while ensuring the kinetic performance of the electrochemical device, so as to achieve improved kinetic performance under the premise of ensuring a higher energy density of the electrochemical device, thereby improving the overall performance of the electrochemical device. By improving the overall performance (including energy density, safety and cycle stability) of the electrochemical device, the safety and service life of the electronic device using the electrochemical device are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a schematic structural diagram of an electrochemical device according to one embodiment of the present application.

[0032] FIG2 is a schematic cross-sectional view of an electrochemical device according to one embodiment of the present application.

[0033] FIG3 is a schematic cross-sectional view of a negative electrode sheet according to an embodiment of the present application, taken along a direction perpendicular to the thickness.

[0034] 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.

[0035] 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.

[0036] FIG6 is a schematic cross-sectional view of an electrode assembly according to another embodiment of the present application.

[0037] FIG7 is a schematic structural diagram of an electronic device according to an embodiment of the present application.

[0038] Description of main component symbols

[0039] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0044] 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.

[0045] 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.

[0046] The electrochemical device of the present application is described by taking a lithium-ion battery as an example to illustrate its effects.

[0047] The energy density of lithium-ion batteries is usually improved by increasing the capacity and voltage of the active materials in the electrodes and increasing the content of the active materials in the electrodes. Among them, increasing the compaction density of the active materials and preparing thicker electrode active layers can increase the content of the active materials.

[0048] 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.

[0049] In view of this, embodiments of the present application provide an electrochemical device and an electronic device using the electrochemical device.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The positive electrode active layer 13 includes a positive electrode active material, which includes a compound that can reversibly intercalate and deintercalate lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the 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 At least one of lithium phosphate (LiFePO4), lithium iron phosphate (LiFePO4), etc. In some embodiments, the positive electrode active material (the aforementioned materials) may be further modified by doping or coating.

[0055] Doping modification can be cation doping, anion doping or anion-cation composite doping. The purpose of doping modification is to dope some cations, anions or composite ions in the positive electrode active material lattice to suppress the mixing of cations, which helps to reduce the first irreversible capacity, especially to make the layered structure of NCM more complete, the stability of the crystal structure higher, and the probability of particle breakage and crystal structure damage lower, which is beneficial to improving the cycle performance and thermal stability of lithium-ion batteries. The specific method of doping modification is not limited. Wet doping can be performed in the precursor co-precipitation stage, or dry doping can be performed in the sintering stage. In some embodiments, the cation doping element may include but is not limited to one or more of Al, Zr, Ti, B, Mg, V, Cr, Zn, Y, etc. The anion doping element may include but is not limited to one or more of F, P, S, etc., wherein F can not only promote the sintering of the positive electrode active material and make the structure of the positive electrode active material more stable, but also stabilize the interface between the positive electrode active material and the electrolyte during the cycle, which is beneficial to improving the cycle performance of the lithium-ion battery.

[0056] Coating modification is to form a coating layer on the surface of the positive electrode active material, which plays the role of isolating the electrolyte from direct contact with the positive electrode active material. This can greatly reduce the side reactions between the electrolyte and the positive electrode active material, reduce the dissolution of transition metals, and improve the electrochemical stability of the positive electrode active material. The presence of the coating layer can also reduce the collapse of the crystal structure of the positive electrode active material during repeated charge and discharge, reduce the probability of particle breakage and crystal structure damage, and thus improve the cycle performance of lithium-ion batteries. The specific method of coating modification is not limited, and wet coating can be performed in the precursor co-precipitation stage, or dry coating can be performed in the sintering stage. In some embodiments, the coating layer can be selected from but is not limited to one or more of a carbon layer, a graphene layer, an oxide layer, an inorganic salt layer, or a conductive polymer layer. Among them, the oxide may be but is not limited to oxides formed by one or more elements of Al, Ti, Mn, Zr, Mg, Zn, Ba, Mo, and B; the inorganic salt may be but is not limited to one or more of Li2ZrO3, LiNbO3, Li4Ti5O12, Li2TiO3, LiTiO2, Li3VO4, LiSnO3, Li2SiO3, LiAlO2, AlPO4, and AlF3; the conductive polymer may be but is not limited to one or more of polypyrrole (PPy), poly 3,4-ethylenedioxythiophene (PEDOT), or polyamide (PI).

[0057] 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.

[0058] 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 (e.g., vapor-grown 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.

[0059] 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 FIG2 , the negative active layers 33 may be disposed on two opposite surfaces of the negative current collector 31, respectively.

[0060] 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.

[0061] Referring to Figures 2 and 3 , the negative electrode active layer 33 includes a central region 331 and an edge region 333 disposed around the outer periphery of the central region 331. However, when the negative electrode sheet 30 forms a laminated electrode assembly A, as shown in Figure 3 , when viewed along the thickness direction X, the edge region 333 is annular (as shown in Figure 3 ) surrounding the central region 331. When the negative electrode sheet 30 forms a wound electrode assembly, when the negative electrode sheet 30 is flattened, i.e., unwound, when viewed along the thickness direction of the negative electrode sheet 30, the edge region 333 is annular (as shown in Figure 3 ) surrounding the central region 331. When the negative electrode sheet 30 is wound to form a wound electrode assembly, the edge region 333 includes the starting and ending ends of the winding of the negative electrode active layer 33, as well as two ends of the negative electrode active layer 33 that are oppositely disposed along the central axis of the winding.

[0062] In some embodiments, the width of the edge region 333 may be 4 mm to 12 mm, for example, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, or any specific value between any two adjacent values. This width refers to the distance from any location on the outer periphery of the edge region 333 facing away from the center region 331, that is, from any location on the outer periphery of the entire negative electrode active layer 33, to the closest point where the adjacent edge region 333 connects to the inner periphery of the center region 331.

[0063] Because the negative electrode active layer 33 undergoes a lamination process during its formation, the outer edge of the central region 331 and the inner edge of the edge region 333, which are adjacent or connected before lamination, merge into a transition region 335 after lamination. Specifically, the negative electrode active layer 33 also includes the transition region 335, which connects the inner periphery of the edge region 333 and the outer periphery of the central region 331. In some embodiments, the width of the transition region 335 may be 0.02 mm to 0.5 mm.

[0064] In addition, because the negative electrode active layer 33 undergoes a lamination process during its formation, the thickness of each region varies before and after lamination. Specifically, the edge region 333 may extend away from the center region 331. However, since the center region 331 is surrounded by the edge region 333, the movable space of the center region 331 is limited by the edge region 333 during lamination. Therefore, the thickness of the center region 331 is generally greater than the thickness of the edge region 333. In some embodiments, the difference between the thickness of the center region 331 and the thickness of the edge region 333 may be less than 1 micron, which is beneficial for improving the flatness of the electrode assembly formed by the positive electrode sheet 10 and the negative electrode sheet 30, thereby improving the overall flatness of the electrochemical device.

[0065] In this embodiment, the ionic impedance of the edge region 333 is less than the ionic impedance of the central region 331. In an electrochemical device, the electric field strength in the edge region of each electrode is higher than that in the central region, and the edge region is easily contacted by the electrolyte. Due to the indistinguishable design between the edge and central regions of the electrode in the prior art, the lithium desorption rate and amount in the edge region of the positive electrode electrode are greater than the lithium desorption rate and amount in the central region of the positive electrode electrode. As a result, the number of lithium ions that the edge region of the negative electrode electrode needs to accept per unit time is greater than the number of lithium ions that the central region of the negative electrode electrode needs to accept per unit time. As a result, lithium deposition is easily generated in the edge region of the negative electrode electrode, affecting the safety and cycle stability of the electrochemical device. The edge area 333 and the center area 331 of the above-mentioned negative electrode plate 30 are designed differently. By designing the ionic impedance of the edge area 333 of the negative electrode plate 30 to be lower than the ionic impedance of the center area 331 of the negative electrode plate 30, it is beneficial to improve the liquid phase transmission capacity of the edge area 333 for lithium ions compared with the center area 331 without affecting the corresponding energy density of the center area 331, thereby helping to improve the lithium insertion capacity of the edge area 333 compared with the center area 331, reducing the risk of lithium plating in the edge area 333 of the negative electrode plate 30, and further helping to improve the safety and cycle stability of the electrochemical device 100. Specifically, the ratio of the ionic impedance of the edge region 333 to the ionic impedance of the central region 331 is 1:1.1 to 1:2, and the ionic impedance of the edge region 333 is 30 Ohms to 54.5 Ohms, which is beneficial for ensuring the kinetic performance of the electrochemical device 100 while also ensuring the overall energy density of the electrochemical device 100, thereby improving the kinetic performance while ensuring a high energy density of the electrochemical device 100, thereby improving the overall performance of the electrochemical device 100. In some embodiments, the ratio of the ionic impedance of the edge region 333 to the ionic impedance of the central region 331 can be selected from 1:1.1, 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, or any specific ratio between any two adjacent ratios thereof. The ionic impedance of the edge region 333 can be selected from 30 Ohms, 35 Ohms, 40 Ohms, 50 Ohms, 54.5 Ohms, or any specific value between any two adjacent values ​​thereof. In some embodiments, the ratio of the ionic impedance of the edge region 333 to the ionic impedance of the central region 331 is 1:1.2 to 1:2.

[0066] In some embodiments, the tortuosity of the edge region 333 may be less than the tortuosity of the central region 331. While ensuring the energy density corresponding to the central region 331, the tortuosity of the edge region 333 is reduced to reduce the liquid phase transmission barrier of lithium ions in the edge region 333, thereby improving the lithium insertion capacity of the edge region 333, thereby reducing the risk of lithium deposition in the edge region 333 and improving the overall safety and cycle stability of the electrochemical device. Specifically, the ratio of the tortuosity of the edge region 333 to the tortuosity of the central region 331 may be 1:1.05 to 1:3. In some embodiments, the tortuosity of the edge region 333 may be 1.04 to 3. The tortuosity of the edge region 333 in the above-mentioned specific range can be conducive to ensuring the lithium insertion capacity of the edge region 333, and the specific ratio range of the tortuosity between the edge region 333 and the central region 331 is conducive to improving the lithium insertion capacity of the edge region 333 while ensuring the overall energy density of the electrochemical device 100. In some embodiments, the ratio of the tortuosity of the edge region 333 to the tortuosity of the central region 331 can be selected from 1:1.05, 1:1.1, 1:1.5, 1:2, 1:2.5, 1:3, or any specific ratio between any two adjacent ratios thereof. The tortuosity of the edge region 333 can be selected from 1.04, 1.08, 1.1, 1.5, 1.8, 2, 2.3, 2.5, 2.7, 3, or any specific ratio between any two adjacent ratios thereof.

[0067] The edge region 333 includes a first negative electrode active material, and the central region 331 includes a second negative electrode active material. In some embodiments, the OI value of the first negative electrode active material may be 6 to 15, for example, it can be selected from 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or any specific value between any two adjacent values ​​​​mentioned above. The OI value characterizes the arrangement direction of the active material particles of the electrode along the current collector of the electrode, which refers to the ratio of the current collector direction parallel to the electrode to the current collector direction perpendicular to the electrode. In the negative electrode, the smaller the OI value, the easier it is for lithium ions to be embedded. By designing the first negative electrode active material to have an OI value in a specific range, the lithium insertion ability of the edge region 333 is guaranteed, thereby facilitating the reduction of the risk of lithium plating.

[0068] The OI value of the second negative electrode active material may be greater than the OI value of the first negative electrode active material. In some embodiments, the difference between the OI value of the second negative electrode active material and the OI value of the first negative electrode active material may be 1 to 5, for example, selected from 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any specific value between any two adjacent values ​​of the foregoing. The differentiated OI value design between the second negative electrode active material and the first negative electrode active material is beneficial for ensuring the overall capacity of the electrochemical device 100 while also ensuring the overall energy density of the electrochemical device 100, thereby improving the overall performance of the electrochemical device 100.

[0069] The first negative electrode active material is in a granular form and may have a core-shell structure. Specifically, the first negative electrode active material includes a first core and a first shell coating the first core. The first core may include, but is not limited to, graphite, and the first shell may include, but is not limited to, amorphous carbon. The graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite. The content of the first shell in the first negative electrode active material may be 0.5 wt% to 20 wt% to ensure that the first negative electrode active material has an OI value within a specific range to ensure the lithium insertion capacity of the edge region 333, thereby reducing the risk of lithium plating. In some embodiments, the content of the first shell in the first negative electrode active material may be selected from 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 18 wt%, 20 wt%, or any specific value between any two adjacent values ​​mentioned above.

[0070] The second negative electrode active material is in a granular form and may have a core-shell structure. Specifically, the second negative electrode active material includes a second core and a second shell coating the first core. The second core may include, but is not limited to, graphite, and the second shell may include, but is not limited to, amorphous carbon. The graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite. The content of the first shell in the first negative electrode active material may be greater than the content of the second shell in the second negative electrode active material. In some embodiments, the ratio of the content of the first shell in the first negative electrode active material to the content of the second shell in the second negative electrode active material may be 1.1:1 to 3:1, for example, selected from 1.1:1, 1.25:1, 1.5:1, 1.75:1, 2:1, 2.3:1, 2.5:1, 2.7:1, 3:1, or any specific ratio between any two adjacent ratios described above. The differentiated design of the shell content between the second negative electrode active material and the first negative electrode active material is beneficial for ensuring the overall capacity of the electrochemical device 100 while ensuring the overall energy density of the electrochemical device 100, thereby improving the overall performance of the electrochemical device 100.

[0071] The edge region 333 includes a first binder for bonding the first negative electrode active material particles to facilitate film formation. The center region 331 includes a second binder for bonding the second negative electrode active material particles to facilitate film formation. The first binder and the second binder can also improve the bonding strength between the negative electrode active layer 33 and the negative electrode current collector 31. In some embodiments, the first binder and the second binder may each include, but are not limited to, one or more of 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.

[0072] Referring to FIG. 2 and FIG. 4 , the separator 50 may include 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 333 of the negative electrode tab 30 in the thickness direction X, and extends beyond the edge region 333 in any direction perpendicular to the thickness direction X. In other words, the second region 50b also overlaps with a portion of the central region 331 of the negative electrode tab 30 or at least a portion of the transition region 335 in the thickness direction X. In some embodiments, the width of the first region 50a of the separator 50 may be 5 mm to 13 mm.

[0073] 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.

[0074] In some embodiments, the ionic conductivity of the second region 50b is less than the ionic conductivity of the first region 50a, which is beneficial to reducing the migration ability of the second region 50b for lithium ions compared to the first region 50a while ensuring the overall ionic conductivity of the isolation membrane 50, that is, reducing the number of lithium ions diffused from the positive electrode sheet 10 to the edge region 333 of the negative electrode sheet 30, thereby helping to reduce the risk of lithium plating in the edge region 333 of the negative electrode sheet 30, and further helping to improve the safety and cycle stability of the electrochemical device 100 while ensuring the capacity of the electrochemical device 100.

[0075] Specifically, the ionic conductivity of the second region 50b can be 0.1 mS / cm to 0.4 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, or any specific value between any two adjacent values ​​thereof. The ratio of the ionic conductivity of the second region 50b to the ionic conductivity of the first region 50a can be 1:5 to 1:1.2, for example, 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 thereof. The second region 50b having the ionic conductivity within the above-mentioned specific range and the first region 50a having an ionic conductivity within a specific ratio range to the ionic conductivity of the second region 50b can enable the isolation membrane 50 as a whole to have a higher ionic conductivity while reducing the risk of lithium deposition in the edge region 333, thereby helping the electrochemical device 100 to have a higher capacity while having better safety and cycle stability, thereby improving the overall performance of the electrochemical device 100.

[0076] In some embodiments, based on the fact that lithium deposition is prone to occur in the edge region 333 of the negative electrode sheet 30 corresponding to the second region 50b of the separator 50, the puncture resistance of the second region 50b of the separator 50 may be greater than the puncture resistance of the first region 50a of the separator 50. This is beneficial for preventing lithium dendrites formed by lithium deposition from piercing the second region 50b of the separator 50 corresponding to the edge region 333 of the negative electrode sheet 30 while controlling costs and ensuring the overall electrical conductivity of the separator 50, thereby improving the overall safety and cycle stability of the electrochemical device 100. Specifically, the ratio of the puncture resistance of the second region 50b of the separator 50 to the puncture resistance of the first region 50a of the separator 50 may be 1.2:1 to 3:1. In some embodiments, the puncture resistance of the second region 50b of the separator 50 may be 0.03kgf to 0.1kgf. The second region 50b of the isolation membrane 50 having a puncture resistance within the above-mentioned range, and the first region 50a of the isolation membrane having a puncture resistance strength within a specific ratio range to the puncture resistance strength of the second region 50b of the isolation membrane 50, can help the isolation membrane 50 as a whole have a higher ionic conductivity while reducing the risk of lithium deposition in the edge region 333, thereby helping the electrochemical device 100 have a higher capacity while having better safety and cycle stability, thereby improving the overall performance of the electrochemical device 100.

[0077] In some embodiments, the thermal shrinkage ratio of the second region 50b of the separator 50 may be 3% to 16.4%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 13%, 16.4%, or any specific value between any two adjacent values. The second region 50b of the separator 50 having such a specific thermal shrinkage ratio helps improve the shrinkage resistance of the second region 50b of the separator 50 corresponding to the edge region 333 of the negative electrode sheet 30 at high temperatures, thereby improving the cycling stability of the electrochemical device 100. In some embodiments, the thermal shrinkage ratio of the second region 50b of the separator 50 may be less than the thermal shrinkage ratio of the first region 50a of the separator 50. The differentiated design of the thermal shrinkage ratios of the second region 50b of the separator 50 and the first region 50a of the separator 50 helps to simultaneously maintain the electrical conductivity of the first region 50a, thereby maintaining the capacity of the electrochemical device 100. Specifically, the ratio of the thermal shrinkage ratio of the second region 50b of the separator 50 to the thermal shrinkage ratio of the first region 50a of the separator 50 can be 1:1.1 to 1:5, which is beneficial for enabling the electrochemical device 100 to have a higher capacity while also having better safety and cycling stability, thereby improving the overall performance of the electrochemical device 100. In some embodiments, the ratio of the thermal shrinkage ratio of the second region 50b of the separator 50 to the thermal shrinkage ratio of the first region 50a of the separator 50 can be selected from 1:1.1, 1:1.5, 1:2, 1:3, 1:4, 1:5, or any specific ratio between any two adjacent ratios of the foregoing.

[0078] In some embodiments, the electrolyte wettability of the second region 50b of the separator 50 may be 50 mm / min to 90 mm / min, for example, 50 mm / min, 55 mm / min, 60 mm / min, 65 mm / min, 70 mm / min, 75 mm / min, 80 mm / min, 85 mm / min, 90 mm / min, or any specific value between any two adjacent values ​​thereof. In some embodiments, the electrolyte wettability of the second region 50b of the separator 50 may be greater than the electrolyte wettability of the first region 50a of the separator 50. Specifically, the difference between the electrolyte wettability of the second region 50b of the separator 50 and the electrolyte wettability of the first region 50a of the separator 50 may be 5 mm / min to 20 mm / min, for example, 5 mm / min, 7 mm / min, 10 mm / min, 13 mm / min, 15 mm / min, 18 mm / min, 20 mm / min, or any specific value between any two adjacent values ​​thereof. The electrolyte wettability of the second region 50b of the isolation membrane 50 in the above-mentioned specific range is beneficial to improving the liquid retention capacity between the second region 50b of the isolation membrane 50 and the corresponding edge region 333 of the negative electrode plate 30, thereby helping to avoid the risk of lithium plating due to insufficient electrolyte in the negative electrode plate 30, and further helping to improve the safety and cycle stability of the electrochemical device 100.

[0079] 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.

[0080] 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.

[0081] 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. At the same time, it is also beneficial to increase the puncture resistance of the isolation membrane 50 to reduce the risk of the isolation membrane 50 being punctured by lithium dendrites formed by lithium precipitation, thereby improving the high temperature stability, safety performance, and cycle stability 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, for example, may be selected from but are not limited to pure aluminum oxide particles, boehmite particles, etc.

[0082] The aspect ratio of the second ceramic particles can be greater than that of the first ceramic particles. The larger the aspect ratio, that is, the flatter the ceramic particles, the stronger the puncture resistance and thermal shrinkage resistance of the film layer formed, while the more tortuous the path for lithium ions to pass through, the less conducive it is to the rapid transmission of lithium ions. Therefore, by designing the second region 50b of the separator 50 to use second ceramic particles that are flatter than the first ceramic particles in the first region 50a of the separator 50, it is beneficial to improve the puncture resistance and thermal shrinkage resistance of the second region 50b of the separator 50 while ensuring the transmission capacity of the first region 50a of the separator 50 for lithium ions, thereby improving the overall safety and cycle stability of the electrochemical device 100. Specifically, the ratio of the aspect ratio of the second ceramic particles to the aspect ratio of the first ceramic particles can be 1.1:1 to 5:1, for example, 1.1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any specific ratio between any two adjacent values ​​thereof. In some embodiments, the aspect ratio of the second ceramic particles can be 5 to 50, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or any specific ratio between any two adjacent values ​​thereof. The above-mentioned second ceramic particles having an aspect ratio within a specific range and the first ceramic particles having an aspect ratio within a specific ratio range with the aspect ratio of the second ceramic particles are beneficial to improving the puncture resistance and thermal shrinkage resistance of the second region 50b of the isolation membrane 50 while ensuring that the overall transmission of lithium ions by the isolation membrane 50 is not too low, thereby helping to improve the overall safety and cycle stability of the electrochemical device 100 while ensuring the overall capacity of the electrochemical device 100, thereby improving the overall performance of the electrochemical device 100.

[0083] In some embodiments, the second ceramic particles may comprise 70 wt% to 95 wt% in the second coating layer 53b, such as 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or any specific value between any two adjacent values. A higher content of the second ceramic particles in the second region 50b of the separator 50 may improve the puncture resistance and thermal shrinkage resistance of the second region 50b of the separator 50, thereby improving the overall safety and cycling stability of the electrochemical device 100. The second ceramic particles may comprise a greater content in the second coating layer 53b than in the first coating layer 53a. Specifically, the difference between the content of the second ceramic particles in the second coating layer 53b and the content of the first ceramic particles in the first coating layer 53a may be 0.5% to 20%, such as 0.5 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%, 17 wt%, 20 wt%, or any specific value between any two adjacent values. The differentiated design of the ceramic particle content in the second coating 53b and the first coating 53a is beneficial to ensuring the overall puncture resistance and thermal shrinkage resistance of the isolation membrane 50 while also ensuring the overall transmission of lithium ions by the isolation membrane 50, thereby ensuring the capacity of the electrochemical device 100 while improving the overall safety and cycle stability of the electrochemical device 100, thereby improving the overall performance of the electrochemical device 100.

[0084] The types and contents of the first adhesive and the second adhesive are not particularly limited and can be selected according to actual needs.

[0085] 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.

[0086] The electrolyte 60 may be in one or more of a gel state, a solid state, and a liquid state. The liquid electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt 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 LiPF6 because it can provide high ionic conductivity and improve cycle characteristics. The non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, Compounds, nitrile compounds, other organic solvents or combinations thereof. Examples of carbonate compounds 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), vinylethylene 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.

[0087] 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.

[0088] 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.

[0089] Example 1

[0090] Preparation of negative electrode sheet:

[0091] The negative electrode active material graphite (the coating amount of amorphous carbon is 2.5wt%, the OI value is 12), the binder SBR, and the binder CMC are added to deionized water in a mass ratio of 97.4:1.4:1.2, mixed and dispersed to prepare a first negative electrode slurry (solid content is 48%), and the first negative electrode slurry is extrusion-coated on a 6-micron copper current collector and dried to form a first electrode sheet. The first negative electrode slurry corresponds to forming a first active layer (corresponding to the central area).

[0092] The negative electrode active material graphite (the coating amount of amorphous carbon is 5wt%, and the OI value is 9), the binder SBR, and the binder CMC are added to deionized water in a mass ratio of 97.4:1.4:1.2, and mixed and dispersed to prepare a second negative electrode slurry (solid content is 48%). The second negative electrode slurry is coated outward from the outer periphery of the first active layer of the first electrode sheet through a gravure plate, and the second electrode sheet is formed after drying. The second negative electrode slurry is correspondingly solidified to form a second active layer (corresponding to the edge area).

[0093] The cold pressed negative electrode is formed at a pressure of 20t and a speed of 20m / min (the tortuosity of the edge area is 2 and the ionic resistance is 30Ohm; the tortuosity of the center area is 4 and the ionic resistance is 60Ohm), and then die-cut to form the negative electrode sheet. The width W of the transition area in the negative electrode sheet is 过渡 The width of the edge area is 0.2mm. 边 The thickness of the center area is 0.5 microns greater than that of the edge area, that is, △Tk is 0.5 microns, and the thickness of the edge area Tk 边 The negative electrode sheet is approximately 72mm*82mm in size.

[0094] Preparation of positive electrode sheet:

[0095] The positive electrode active material lithium cobalt oxide, binder PVDF, conductive agent SP, conductive agent CNT and conductive agent VGCF (i.e., vapor-grown carbon fiber) are added to N-methylpyrrolidone (NMP) in a mass ratio of 97.0:1.5:0.43:0.86:0.21, mixed and dispersed to prepare a positive electrode slurry (solid content of 75%), and the positive electrode slurry is extrusion-coated on an aluminum foil current collector with a thickness of 9 microns and dried to form an electrode sheet, wherein the positive electrode slurry forms a corresponding positive electrode active layer.

[0096] Cold-pressed electrodes are formed using a pressure of 80 tons and a speed of 20 m / min, and then die-cut into positive electrode sheets. The thickness of the positive electrode active layer is 100 microns, and the dimensions of the positive electrode sheets are approximately 70 mm by 80 mm.

[0097] Preparation of isolation membrane:

[0098] Ceramic boehmite (aspect ratio of 3.3) and a polyacrylic acid resin (PAA) adhesive were mixed and dispersed in a mass ratio of 80:20 to form a first coating slurry. This first coating slurry was then gravure coated onto a PE film (5 microns thick) 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 microns.

[0099] Ceramic boehmite (aspect ratio of 10) and adhesive PAA are mixed and dispersed in a mass ratio of 90:10 to form a second coating slurry, and 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 dried to obtain an isolation membrane. The second coating slurry is correspondingly 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 0.75mS / cm, the puncture resistance is 0.04kgf, the thermal shrinkage ratio is 18%, and the EL wettability is 60mm / min. The ionic conductivity of the second area corresponding to the second coating layer in the isolation membrane is 0.25mS / cm, the puncture resistance is 0.06kgf, the thermal shrinkage ratio is 6%, and the EL wettability is 70mm / min.

[0100] Preparation of lithium-ion batteries:

[0101] 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.

[0102] Comparative Example 1

[0103] The differences between Comparative Example 1 and Example 1 are 1) preparation of the negative electrode sheet and 2) preparation of the separator.

[0104] 1) Preparation of Negative Electrode Sheets: Graphite (amorphous carbon coating of 2.5 wt% and an OI of 12), SBR (binder SBR), and CMC (binder CMC) were mixed and dispersed in deionized water at a mass ratio of 97.4:1.4:1.2 to prepare a negative electrode slurry (solids content 48%). The slurry was then extrusion-coated onto a 6-micron copper current collector and dried to form a negative electrode active layer. The negative electrode was then cold-pressed at a pressure of 20 tons and a speed of 20 m / min to form a cold-pressed negative electrode (tortuosity of each region of the negative electrode active layer was 4 and ionic resistance was 60 ohms). The negative electrode sheets were then die-cut. The thickness of the negative electrode active layer was 120 microns.

[0105] 2) Preparation of the Isolator: Ceramic boehmite (aspect ratio of 10) and a polyacrylic acid resin (PAA) adhesive were mixed and dispersed in a mass ratio of 80:20 to form a coating slurry. The coating slurry was gravure coated onto a PE film (5 μm thick) serving as a substrate layer and dried to produce the Isolator. The coating slurry formed a coating layer having a thickness of 2 μm. The Isolator exhibited an ionic conductivity of 0.75 mS / cm, a puncture resistance of 0.04 kgf, a thermal shrinkage ratio of 18%, and an EL wettability of 60 mm / min.

[0106] According to the steps of the above embodiments and the following Tables 1-4 and 6-10, laminated lithium-ion batteries corresponding to Examples 1-18 were prepared. According to the steps of Comparative Example 1 and the above Table 1, laminated lithium-ion batteries corresponding to Comparative Example 2 were prepared. The lithium-ion batteries corresponding to Examples 1-18 and Comparative Example 1-2 had the same parameters except for the parameters in the table.

[0107] The following performance tests were conducted on each of the above examples and comparative examples: 25°C lithium deposition window, 25°C capacity retention (i.e., capacity retention) @ 500 cls, and 45°C capacity retention @ 500 cls. The test results are summarized in Tables 1-2 and 5-10. The methods for each performance test are described in detail below.

[0108] 25℃ lithium plating window: Lithium-ion battery is charged at 25℃ with constant current of nC (target rate) to the cut-off voltage, then charged at constant voltage at the cut-off voltage until the current is less than 0.05C, and then discharged at 02C DC to the cut-off voltage after standing for 5 minutes. Cycle 10 times according to the above charge and discharge process. Then charge at constant current of nC (target rate) to the cut-off voltage, then charge at constant voltage at the cut-off voltage until the current is less than 0.05C, and then disassemble the battery cell after standing for 5 minutes to observe whether there is lithium plating on the anode surface. Maximum rate without lithium plating n max C is the lithium deposition window.

[0109] 25℃ Capacity Retention @ 500cls: The lithium-ion battery is charged at 0.2C constant current to the cutoff voltage at 25℃. Then, it is charged at constant voltage at the cutoff voltage until the current is less than 0.05C. After 5 minutes of rest, it is discharged at 0.2C DC to the cutoff voltage. The ratio of the 0.2C DC capacity at the 500th cycle to the 0.2C DC capacity at the first cycle is the 25℃ Capacity Retention @ 500cls. A larger ratio indicates better cycling performance.

[0110] 45℃ Capacity Retention @ 500cls: The lithium-ion battery is charged at 0.2C constant current at 45℃ to the cutoff voltage. Then, it is charged at constant voltage at the cutoff voltage until the current is less than 0.05C. After 5 minutes of rest, it is discharged at 0.2C DC to the cutoff voltage. The ratio of the 0.2C DC capacity at the 500th cycle to the 0.2C DC capacity at the first cycle is the 45℃ Capacity Retention @ 500cls. A larger ratio indicates better cycling performance.

[0111] Table 1

[0112] Table 2

[0113] Table 3

[0114] Table 4

[0115] Table 5

[0116] Table 6

[0117] Table 7

[0118] Table 8

[0119] Table 9

[0120] Table 10

[0121] As can be seen from the data in Table 1, by differentially designing the edge area 333 and the central area 331 of the negative electrode plate 30, the lithium plating of the lithium-ion battery can be improved, the risk of lithium plating can be reduced, and the capacity retention rate of the lithium-ion battery can be improved, thereby improving the safety and cycle stability of the lithium-ion battery. As can be seen from the data in Table 2, the wider the width of the edge area 333 of the negative electrode plate 30, the more conducive it is to reducing the risk of lithium plating of the lithium-ion battery, and the more conducive it is to improving the capacity retention rate of the lithium-ion battery, thereby improving the safety and cycle stability of the lithium-ion battery. As can be seen from the data in Tables 3 to 7, by differentially designing the first area 50a and the second area 50b of the isolation membrane 50, the lithium plating of the lithium-ion battery can be improved, the risk of lithium plating can be reduced, and the capacity retention rate of the lithium-ion battery can be improved, thereby improving the safety and cycle stability of the lithium-ion battery. Among them, it can be seen from the data in Table 6 that the larger the ratio of the aspect ratio of the ceramic particles in the second region 50b of the separator 50 to the aspect ratio of the ceramic particles in the first region 50a, the more conducive it is to reducing the risk of lithium plating in the lithium-ion battery, and the more conducive it is to improving the capacity retention rate of the lithium-ion battery, and thus the more conducive it is to improving the safety and cycle stability of the lithium-ion battery. And from the data in Table 7, it can be seen that the larger the difference in the content of the ceramic particles in the second region 50b and the first region 50a of the separator 50, the more conducive it is to reducing the risk of lithium plating in the lithium-ion battery, and the more conducive it is to improving the capacity retention rate of the lithium-ion battery, and thus the more conducive it is to improving the safety and cycle stability of the lithium-ion battery. From the data in Table 8, it can be seen that the smaller the ratio of the tortuosity between the edge region 333 and the central region 331 of the negative electrode sheet 30, the more conducive it is to reducing the risk of lithium plating in the lithium-ion battery, and the more conducive it is to improving the capacity retention rate of the lithium-ion battery, and thus the more conducive it is to improving the safety and cycle stability of the lithium-ion battery. As can be seen from the data in Table 9, a greater difference in the OI value of the negative electrode active material between the central region 331 and the edge region 333 of the negative electrode sheet 30 is more conducive to reducing the risk of lithium plating in the lithium-ion battery, and is more conducive to improving the capacity retention rate of the lithium-ion battery, thereby improving the safety and cycling stability of the lithium-ion battery. As can be seen from the data in Table 10, a greater ratio of the amount of negative electrode active material coated between the central region 331 and the edge region 333 of the negative electrode sheet 30 is more conducive to reducing the risk of lithium plating in the lithium-ion battery, and is more conducive to improving the capacity retention rate of the lithium-ion battery, thereby improving the safety and cycling stability of the lithium-ion battery.

[0122] 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 negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer, wherein: The negative electrode active layer includes a central region and an edge region arranged around the outer periphery of the central region, the ionic impedance of the edge region is 30 Ohm to 54.5 Ohm, and the ratio of the ionic impedance of the edge region to the ionic impedance of the central region is 1:1.1 to 1:

2.

2. The electrochemical device according to claim 1, wherein The ratio of the ionic resistance of the edge region to the ionic resistance of the central region is 1:1.2 to 1:

2.

3. The electrochemical device according to claim 1, wherein The isolation membrane includes a first region and a second region arranged around the outer periphery connected to the first region, 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 exceeds the edge region; the ionic conductivity of the second region is 0.1mS / cm to 0.4mS / 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.

4. The electrochemical device according to claim 3, wherein: The puncture resistance of the second region of the isolation film is 0.03 kgf to 0.1 kgf, and a ratio of the puncture resistance of the second region of the isolation film to the puncture resistance of the first region of the isolation film is 1.2:1 to 3:

1.

5. The electrochemical device according to claim 3, wherein: After keeping warm at 150 degrees Celsius for 1 hour, the heat shrinkage ratio of the second area of ​​the isolation film is 3% to 16.4%, and the ratio of the heat shrinkage ratio of the second area of ​​the isolation film to the heat shrinkage ratio of the first area of ​​the isolation film is 1:1.1 to 1:

5.

6. The electrochemical device according to claim 3, wherein: The electrolyte wettability of the second region of the isolation membrane is 50 mm / min to 90 mm / min, and the electrolyte wettability of the second region of the isolation membrane is greater than the electrolyte wettability of the first region of the isolation membrane, and the difference is 5 mm / min to 20 mm / min.

7. The electrochemical device according to claim 3, 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 aspect ratio of the second ceramic particles is 5 to 50, and the ratio of the aspect ratio of the second ceramic particles to the aspect ratio of the first ceramic particles is 1.1:1 to 5:

1.

9. The electrochemical device according to claim 7, wherein: The content of the second ceramic particles in the second coating layer is 70wt% to 95wt%, and the content of the second ceramic particles in the second coating layer is greater than the content of the first ceramic particles in the first coating layer, and the difference is 0.5% to 20%.

10. The electrochemical device according to claim 1, wherein The tortuosity of the edge region is 1.04 to 3, and the ratio of the tortuosity of the edge region to the tortuosity of the central region is 1:1.05 to 1:

3.

11. The electrochemical device according to claim 1, wherein: The edge region includes a first negative electrode active material, and the central region includes a second negative electrode active material. The OI value of the first negative electrode active material is 6 to 15, and the OI value of the second negative electrode active material is greater than the OI value of the first negative electrode active material, and the difference is 1 to 5.

12. The electrochemical device according to claim 1, wherein The edge region includes a first negative electrode active material, and the central region includes a second negative electrode active material, wherein the first negative electrode active material is a core-shell structure, including a first core body and a first shell covering the first core body, and the content of the first shell in the first negative electrode active material is 0.5wt% to 20wt%, and the second negative electrode active material is a core-shell structure, including a second core body and a second shell covering the second core body, and the ratio of the content of the first shell in the first negative electrode active material to the content of the second shell in the second negative electrode active material is 1.1:1 to 3:

1.

13. The electrochemical device according to claim 3, wherein: The width of the second region of the separator is 5 mm to 13 mm, and the width of the edge region of the positive electrode active layer is 4 mm to 12 mm.

14. The electrochemical device according to any one of claims 3 to 7, 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.

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