Electrochemical device, preparation method thereof and electric equipment

Abstract

The invention discloses an electrochemical device, a preparation method thereof and electric equipment. An electrochemical device includes an electrode assembly. The electrode assembly includes a cathode tab including a cathode current collector, a first material layer, a second material layer, and a cathode active material layer. The first material layer and the second material layer are arranged on the first surface of the cathode current collector in a stacked mode and located between the cathode current collector and the cathode active material layer, the first material layer comprises first ceramic insulation particles, the second material layer comprises a cathode active material and second ceramic insulation particles, the thickness of the first material layer is h, the thickness of the second material layer is H, and the thickness of the second material layer is H; 1 < = h / H < = 3.

Description

Technical Field

[0001] The present application relates to the field of energy storage devices, and in particular to an electrochemical device and a preparation method thereof and electrical equipment. Background Art

[0002] Electrochemical devices can convert chemical energy into electrical energy, have stable voltage and current, reliable performance, simple structure, and are easy to carry. They have become the main power source for various consumer electronic products and electric products, and are widely used in all aspects of people's production and life. In recent years, the market has put forward higher and higher requirements on the performance of electrochemical devices. How to make electrochemical devices have both high safety performance and cycle performance has become a technical problem that needs to be overcome urgently. Summary of the invention

[0003] The present application provides an electrochemical device and a preparation method thereof, aiming to enable the electrochemical device to have both high safety performance and cycle performance.

[0004] The first aspect of the present application provides an electrochemical device, including an electrode assembly. The electrode assembly includes a cathode electrode sheet, and the cathode electrode sheet includes a cathode current collector, a first material layer, a second material layer, and a cathode active material layer. The first material layer and the second material layer are stacked on the first surface of the cathode current collector and are located between the cathode current collector and the cathode active material layer. The first material layer includes first ceramic insulating particles, the second material layer includes cathode active material and second ceramic insulating particles, the thickness of the first material layer is h, the thickness of the second material layer is H, and 1≤h / H≤3.

[0005] The electrochemical device provided by the present application is configured with a first material layer and a second material layer, which can separate the cathode current collector and the anode material layer when mechanical abuse such as nail penetration occurs, thereby reducing the risk of short circuit between the cathode current collector and the anode material layer and improving safety performance; and introducing ceramic insulating particles into the first material layer and the second material layer can further improve the safety performance of the electrochemical device, and introducing cathode active materials into the second material can improve the cycle performance of the electrochemical device; in addition, the ratio of the thickness of the first material layer to the thickness of the second material layer is limited to 1 to 3, and when the energy density remains unchanged, the first material layer and the second material layer can have suitable thicknesses, thereby enabling the electrochemical device to have good safety performance and good cycle performance.

[0006] Based on the first aspect, in some embodiments, 1.5≤h / H≤2.5. When h / H is within the above range, the thicknesses of the first material layer and the second material layer are more appropriate, so that the electrochemical device has better cycle performance while ensuring safety performance.

[0007] Based on the first aspect, in some embodiments, 0.7 μm ≤ h ≤ 1 μm, 0.43 μm ≤ H ≤ 0.7 μm. When h satisfies the above range, the electrochemical device can have both good safety performance and high volume energy density. When H satisfies the above range, the electrochemical device can have both good cycle performance and high volume energy density.

[0008] Based on the first aspect, in some embodiments, the first material layer is disposed on the first surface, and the second material layer is located between the first material layer and the cathode active material layer, which better achieves a balance between safety performance and cycle performance.

[0009] Based on the first aspect, in some embodiments, the second material layer is disposed on the first surface, and the first material layer is located between the second material layer and the cathode active material layer.

[0010] Based on the first aspect, in some embodiments, the cathode electrode sheet further includes a third material layer and a fourth material layer, the third material layer and the fourth material layer are stacked on the second surface of the cathode current collector, the third material layer includes a first ceramic insulating particle, the fourth material layer includes a cathode active material and a second ceramic insulating particle, the thickness of the third material layer is h', the thickness of the fourth material layer is H', along the thickness direction of the electrode assembly, the first surface is closer to the geometric center of the electrode assembly than the second surface, h'>h, h' / H'>h / H. Under the condition of unchanged energy density, when the above conditions are met, the thickness of the third material layer located on the outside of the electrode assembly is greater, and the thickness of the second material layer located on the inside of the electrode assembly is greater, which is more conducive to the electrochemical device having good safety performance and good cycle performance.

[0011] Based on the first aspect, in some embodiments, based on the mass of the first material layer, the mass percentage of the first ceramic insulating particles is 80% to 90%; and / or, based on the mass of the second material layer, the mass percentage of the second ceramic insulating particles is 10% to 30%, and the mass percentage of the cathode active material is 70% to 98%. When the content of the first ceramic insulating particles is within the above range, the first material layer can have a suitable puncture resistance and have less impact on the impedance of the electrochemical device, thereby improving the safety performance and cycle performance of the electrochemical device. When the content of the second ceramic insulating particles is within the above range, the second material layer can have a certain puncture resistance and have less impact on the impedance of the electrochemical device. When the content of the cathode active material is within the above range, the contact resistance between the cathode current collector and the cathode active material layer can be reduced, thereby improving the cycle performance and safety performance of the electrochemical device.

[0012] Based on the first aspect, in some embodiments, the first ceramic insulating particles and the second ceramic insulating particles each independently include one or more of boehmite, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide, and zinc oxide.

[0013] Based on the first aspect, in some embodiments, the cathode active material includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate.

[0014] The second aspect of the present application provides a method for preparing an electrochemical device, characterized in that it includes: coating a first coating on the first surface of a cathode current collector, wherein the first coating includes a first material layer and a second material layer stacked, the first material layer includes first ceramic insulating particles, the second material layer includes second ceramic insulating particles and a cathode active material, the coating weight of the first material layer is A, the coating weight of the second material layer is B, 1≤A / B≤3; coating the cathode active material layer on the surface of the first coating to obtain a cathode electrode. When A / B is within the above range, the first material layer and the second material layer can have a suitable thickness, so that the electrochemical device has good safety performance and good cycle performance.

[0015] Based on the second aspect, in some embodiments, the first material layer and the second material layer are rolled while the rolling pressure is controlled to be constant. When the rolling pressure is controlled to be constant, the thickness of the first material layer and the second material layer can be adjusted by adjusting the coating weight of the first material layer and the second material layer.

[0016] Based on the second aspect, in some embodiments, A is 2g / 1540.25mm 2 ~3g / 1540.25mm 2 , B is 1g / 1540.25mm 2 ~2g / 1540.25mm 2 When A meets the above range, the thickness of the first material layer is appropriate, so that the electrochemical device has good safety performance and a high volume energy density. When B meets the above range, the thickness of the second material layer is appropriate, so that the electrochemical device has good cycle performance and a high volume energy density.

[0017] Based on the second aspect, in some embodiments, a second coating is applied to the second surface of the cathode current collector, wherein the second coating comprises a third material layer and a fourth material layer stacked, the third material layer comprises a first ceramic insulating particle, and the fourth material layer comprises a cathode active material and a second ceramic insulating particle, wherein the coating weight of the third material layer is A', and the coating weight of the fourth material layer is B', and along the thickness direction of the electrochemical device, the first surface is closer to the geometric center of the electrochemical device than the second surface, A'>A, A' / B'>A / B; the rolling pressure is controlled to remain unchanged, and the first material layer, the second material layer, the third material layer and the fourth material layer are rolled. In the case of unchanged energy density, when the above conditions are met, the thickness of the third material layer located on the outside of the electrode assembly is greater, and the thickness of the second material layer located on the inside of the electrode assembly is greater, which is more conducive to the electrochemical device having good safety performance and good cycle performance.

[0018] A third aspect of the present application provides an electrical device, comprising any one of the above-mentioned electrochemical devices, or comprising an electrochemical device prepared according to any one of the above-mentioned preparation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the structure of an electrochemical device provided in one embodiment of the present application.

[0020] Figure 2 A schematic diagram of the structure of an electrode assembly provided in one embodiment of the present application.

[0021] Figure 3 For along Figure 2 Schematic cross-sectional view at point A.

[0022] Figure 4 A schematic cross-sectional view of a cathode electrode provided in accordance with an embodiment of the present application.

[0023] Figure 5 A schematic diagram of the structure of an electrical device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0024] The technical scheme in the embodiment of the present application is described clearly and in detail below. Obviously, the described embodiment is a part of the embodiment of the present application, rather than all the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0025] Hereinafter, embodiments of the present application will be described in detail. However, the present application may be embodied in many different forms and should not be construed as being limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided so that the present application is thoroughly and in detail communicated to those skilled in the art.

[0026] As used herein, the terms "and / or", "with and / or" include any and all combinations of one or more of the associated listed items. In addition, it should be understood that when element A is referred to as being "connected to" element B, element A can be directly connected to element B, or there may be an intervening element C and element A and element B can be indirectly connected to each other.

[0027] It should be understood that although the terms first, second, third, etc. can be used to describe various elements, components, regions, layers and / or parts herein, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part without departing from the teaching of the exemplary embodiment.

[0028] It should be noted that, in the present application, the term "geometric center" refers to the geometric center of the position of the electrode assembly distributed in the thickness direction.

[0029] Further, the use of “may” when describing embodiments of the present application refers to “one or more embodiments of the present application”.

[0030] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit the present application. As used herein, the singular form is intended to also include the plural form, 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 narrated 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.

[0031] It should be noted that the electrochemical device includes any device that generates an electrochemical reaction, such as all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. Secondary batteries may include nickel-hydrogen batteries, nickel-cadmium batteries, lead-acid (or lead storage) batteries, lithium secondary batteries, sodium secondary batteries, zinc secondary batteries, etc. Lithium secondary batteries may include lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries.

[0032] See also Figure 1An embodiment of the present application provides an electrochemical device 100, including a housing 10, an electrode assembly 20, and an electrode terminal 30. The electrode assembly 20 is accommodated in the housing 10, and the electrode terminal 30 is connected to the electrode assembly 20 and extends from the housing 10 to connect to external components. In this example, the number of electrode terminals 30 is two, namely a cathode terminal and an anode terminal, and the two electrode terminals 30 extend from the same side of the housing 10. In other embodiments, the number of electrode terminals 30 may be greater than two, and multiple electrode terminals 30 may extend from different sides of the housing 10.

[0033] The housing 10 may be any known housing suitable for the electrochemical device 100. For example, the housing 10 may be a packaging bag obtained by packaging film, such as aluminum-plastic film, steel-plastic film, etc.; or, the housing 10 may be a metal housing, such as a steel shell, an aluminum shell, etc.

[0034] See also Figure 2 , the electrode assembly 20 includes a cathode electrode sheet 21, an anode electrode sheet 22 and a separator 23. The separator 23 is disposed between the cathode electrode sheet 21 and the anode electrode sheet 22. In this embodiment, the electrode assembly 20 has a winding structure, specifically, the electrode assembly 20 is formed by stacking the cathode electrode sheet 21, the separator 23 and the anode electrode sheet 22 in sequence and then winding them. In another embodiment, the electrode assembly 20 has a laminated structure, specifically, the electrode assembly 20 is formed by stacking the cathode electrode sheet 21, the separator 23 and the anode electrode sheet 22 in sequence alternately.

[0035] See also Figure 3 The anode electrode 22 includes an anode current collector 221 and an anode material layer 222. The anode material layer 222 can be disposed on two opposite surfaces of the anode current collector 221, or only on one surface of the anode current collector 221, which is not limited in the present application. The anode current collector 221 is electrically connected to the anode terminal. The anode current collector 221 can be any known current collector, for example, copper foil, copper alloy foil or a composite current collector. The anode material layer 222 includes an anode material, and the anode material can include one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxides, silicon carbon composites, lithium titanate or metals that can form alloys with lithium.

[0036] The separator 23 may be any known separator. For example, the separator 23 may be a film made of one or more materials selected from polyethylene, polypropylene, non-woven fabric, and polyfiber.

[0037] See also Figure 3, the cathode electrode sheet 21 includes a cathode current collector 211 and a first cathode active material layer 213. The cathode current collector 211 includes a first surface 211A and a second surface 211B opposite to each other, and the first cathode active material layer 213 is arranged on the side where the first surface 211A is located. In some embodiments, the cathode electrode sheet 21 also includes a second cathode active material layer 215, and the second cathode active material layer 215 is arranged on the side where the second surface 211B is located. The cathode current collector 211 is electrically connected to the cathode terminal. The cathode current collector 211 can be any known current collector, such as aluminum foil, aluminum alloy foil or a composite current collector. The first cathode active material layer 213 and the second cathode active material layer 215 both include cathode active materials, and the material of the first cathode active material layer 213 and the material of the second cathode active material layer 215 can be the same or different. In some embodiments, the cathode active material of the first cathode active material layer 213 and the cathode active material of the second cathode active material layer 215 can each include one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium manganese-rich material, lithium nickel cobalt aluminum oxide, and combinations thereof.

[0038] See also Figure 3 , the cathode plate 21 also includes a first coating 212. The first coating 212 is located between the cathode current collector 211 and the first cathode active material layer 213. In some embodiments, the first coating 212 is provided on the first surface 211A, and the first cathode active material layer 213 is provided on the surface of the first coating 212 away from the cathode current collector 211. The first coating 212 can isolate the cathode current collector 211 and the anode material layer 222 when mechanical abuse such as nailing occurs, reduce the risk of contact short circuit between the cathode current collector 211 and the anode material layer 222, and improve safety performance. The first coating 212 includes a first material layer 2121 and a second material layer 2122 arranged in a stacked manner. The first material layer 2121 includes first ceramic insulating particles. The second material layer 2122 includes second ceramic insulating particles and cathode active materials. The introduction of ceramic insulating particles into the first material layer 2121 and the second material layer 2122 can improve the puncture resistance of the cathode plate 21, thereby improving the safety risks caused by needle puncture and heavy object impact of the electrochemical device 100. Introducing cathode active material into the second material layer 2122 can reduce the contact resistance between the cathode current collector and the cathode active material layer, which is beneficial to improving the cycle performance of the electrochemical device 100 .

[0039] Along the thickness direction T of the electrode assembly 100, the thickness of the first material layer 2121 is h, and the thickness of the second material layer 2122 is H, 1≤h / H≤3. For example, h / H can be 1, 1.2, 1.5, 1.8, 2, 2.5, 3, or a range consisting of any two values ​​therein. Under the condition of a certain volume energy density, when h / H is within the above range, the first material layer 2121 and the second material layer 2122 can have a suitable thickness, thereby enabling the electrochemical device 100 to have good safety performance and good cycle performance.

[0040] In some embodiments, 1.5≤h / H≤2.5. Under the condition of constant volume energy density, when h / H is within the above range, the thickness of the first material layer 2121 and the second material layer 2122 is more appropriate, and the electrochemical device 100 can have better cycle performance while ensuring safety performance.

[0041] In some embodiments, h is 0.7 μm to 1 μm. For example, h can be 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or a range consisting of any two of these values. When h satisfies the above range, the thickness of the first material layer 2121 is appropriate, so that the electrochemical device 100 has good safety performance and a high volume energy density.

[0042] In some embodiments, H is 0.43 μm to 0.7 μm. For example, H can be 0.43 μm, 0.5 μm, 0.6 μm, 0.7 μm, or a range consisting of any two of these values. When H satisfies the above range, the thickness of the second material layer 2122 is appropriate, so that the electrochemical device 100 has good cycle performance and a high volume energy density.

[0043] In some embodiments, the cathode electrode sheet 21 further includes a second coating 214. The second coating 214 is located between the cathode current collector 211 and the second cathode active material layer 215. The second coating 214 can isolate the cathode current collector 211 and the anode material layer 222 when mechanical abuse such as nail penetration occurs, reduce the risk of contact short circuit between the cathode current collector 211 and the anode material layer 222, and improve safety performance.

[0044] In some embodiments, the second coating layer 214 is disposed on the second surface 211B, and the second cathode active material layer 215 is disposed on the surface of the second coating layer 214 away from the cathode current collector 211. The second coating layer 214 includes a third material layer 2141 and a fourth material layer 2142 that are stacked. The third material layer 2141 includes first ceramic insulating particles, and the fourth material layer 2142 includes second ceramic insulating particles and cathode active materials. The introduction of ceramic insulating particles into the third material layer 2141 and the fourth material layer 2142 is conducive to improving the safety performance of the electrochemical device 100; the introduction of cathode active materials into the fourth material layer 2142 is conducive to improving the cycle performance of the electrochemical device 100.

[0045] Along the thickness direction T of the electrode assembly 100, the thickness of the third material layer 2141 is h', and the thickness of the fourth material layer 2142 is H'. In some embodiments, 1≤h' / H'≤3. For example, h' / H' can be 1, 1.2, 1.5, 1.8, 2, 2.5, 3, or a range consisting of any two of these values. Under the condition of a certain volume energy density, when h' / H' is within the above range, the third material layer 2141 and the fourth material layer 2142 can have a suitable thickness, thereby enabling the electrochemical device 100 to have good safety performance while having good cycle performance.

[0046] In some embodiments, 1.5≤h' / H'≤2.5. Under the condition of constant volume energy density, when h' / H' is within the above range, the thickness of the third material layer 2141 and the third material layer 2142 is more appropriate, and the electrochemical device 100 can have better cycle performance while ensuring safety performance.

[0047] In some embodiments, h' is 0.7 μm to 1 μm. When h' satisfies the above range, the thickness of the third material layer 2141 is appropriate, so that the electrochemical device 100 has good safety performance and high volume energy density.

[0048] In some embodiments, H' is 0.43 μm to 0.7 μm. When H' satisfies the above range, the thickness of the fourth material layer 2142 is appropriate, so that the electrochemical device 100 has good cycle performance and high volume energy density.

[0049] In some embodiments, along the thickness direction T of the electrode assembly 20, the first surface 211A is closer to the geometric center of the electrode assembly 20 than the second surface 211B, wherein h'>h, h' / H'>h / H. The outer side of the electrode assembly 20 has higher requirements for safety performance than the inner side of the electrode assembly 20. When the energy density remains unchanged and the above conditions are met, the thickness of the third material layer 2141 located on the outer side of the electrode assembly 20 can be made larger, and the thickness of the second material layer located on the inner side of the electrode assembly can be made larger, which is more conducive to the electrochemical device 100 having good safety and good cycle performance.

[0050] In some embodiments, see Figure 3 , the first material layer 2121 is disposed on the first surface 211A, the second material layer 2122 is located between the first material layer 2121 and the first cathode material layer 213; the third material layer 2141 is disposed on the second surface 211B, and the fourth material layer 2142 is located between the third material layer 2141 and the second cathode material layer 215. In other embodiments, please refer to Figure 4 , the second material layer 2122 is disposed on the first surface 211A, and the first material layer 2121 is located between the second material layer 2122 and the first cathode material layer 213; the fourth material layer 2142 is disposed on the second surface 211B, and the third material layer 2141 is located between the fourth material layer 2142 and the second cathode material layer 215. Compared with the case where the second material layer 2122 and the fourth material layer 2142 are disposed on the surface of the cathode current collector 211, the first material layer 2121 and the third material layer 2141 are disposed on the surface of the cathode current collector 211, which can reduce the impedance of the electrochemical device 100 and improve the safety performance and cycle performance.

[0051] In some embodiments, the first material layer 2121, the second material layer 2122, the third material layer 2141, and the fourth material layer 2142 all include an adhesive, and the adhesive is used to bond the component particles in each material layer together. The adhesives in each material layer may be the same or different. The adhesive may include one or more of polyfluoroolefins, polyacrylates, polyacrylic acids, polyurethanes, silicone resins, epoxy resins, and cellulose-derived adhesives.

[0052] In some embodiments, the first material layer 2121, the second material layer 2122, the third material layer 2141, and the fourth material layer 2142 all include a conductive agent, which is used to improve the conductive properties of the coating. The conductive agents in each material layer may be the same or different. The conductive agent may include one or more of conductive carbon black, carbon nanotubes, carbon fibers, or graphene.

[0053] In some embodiments, based on the mass of the first material layer 2121, the mass percentage of the first ceramic insulating particles is 80% to 90%. For example, the mass percentage of the first ceramic insulating particles can be 80%, 82%, 85%, 87%, 90%, or a range consisting of any two of these values. When the content of the first ceramic insulating particles is within the above range, the first material layer 2121 can have a suitable puncture resistance and have a small impact on the impedance of the electrochemical device 100, thereby improving the safety performance and cycle performance of the electrochemical device 100.

[0054] In some embodiments, based on the mass of the third material layer 2141, the mass percentage of the first ceramic insulating particles is 80% to 90%. For example, the mass percentage of the first ceramic insulating particles can be 80%, 82%, 85%, 87%, 90%, or a range consisting of any two values ​​therein. When the content of the first ceramic insulating particles is within the above range, the third material layer 2141 can have a suitable puncture resistance and have a small effect on the impedance of the electrochemical device 100, thereby improving the safety performance and cycle performance of the electrochemical device 100.

[0055] In some embodiments, based on the mass of the second material layer 2122, the mass percentage of the second ceramic insulating particles is 10% to 30%, and the mass percentage of the cathode active material is 60% to 80%. For example, the mass percentage of the second ceramic insulating particles can be 10%, 15%, 20%, 25%, 30% or a range consisting of any two values ​​therein, and the mass percentage of the cathode active material can be 60%, 65%, 70%, 75%, 80% or a range consisting of any two values ​​therein. When the content of the second ceramic insulating particles is within the above range, the second material layer 2122 can have a certain puncture resistance and have less impact on the impedance of the electrochemical device 100; when the content of the first cathode active material is within the above range, the contact resistance between the cathode current collector 211 and the cathode active material layer 215 can be reduced, thereby improving the cycle performance and safety performance of the electrochemical device 100.

[0056] In some embodiments, based on the mass of the fourth material layer 2142, the mass percentage of the second ceramic insulating particles is 10% to 30%, and the mass percentage of the cathode active material is 60% to 80%. For example, the mass percentage of the second ceramic insulating particles can be 10%, 15%, 20%, 25%, 30% or a range consisting of any two values ​​therein, and the mass percentage of the cathode active material can be 60%, 65%, 70%, 75%, 80% or a range consisting of any two values ​​therein. When the content of the second ceramic insulating particles is within the above range, the fourth material layer 2142 can have a certain puncture resistance and have less impact on the impedance of the electrochemical device 100; when the content of the cathode active material is within the above range, the contact resistance between the cathode current collector 211 and the cathode active material layer 215 can be reduced, thereby improving the cycle performance and safety performance of the electrochemical device 100.

[0057] In some embodiments, the first ceramic insulating particles and the second ceramic insulating particles each independently include one or more of boehmite, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide, and zinc oxide.

[0058] In some embodiments, the cathode active material and the second include at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium iron manganese phosphate.

[0059] An embodiment of the present application also provides a method for preparing an electrochemical device, comprising the following steps: (a) coating a first coating on a first surface of a cathode current collector, the first coating comprising a first material layer and a second material layer stacked; (b) coating a second coating on a second surface of the cathode current collector, the second coating comprising a third material layer and a fourth material layer stacked; (c) coating a first cathode active material layer on the surface of the first coating, and coating a second cathode active material layer on the surface of the second coating to obtain a cathode electrode sheet; (d) forming an electrode assembly by combining the cathode electrode sheet, a separator and an anode electrode sheet; and (e) placing the electrode assembly in a shell to obtain an electrochemical device.

[0060] In some embodiments, the method for preparing an electrochemical device further comprises the following steps: controlling the rolling pressure to remain constant, and rolling the first material layer, the second material layer, the third material layer, the fourth material layer, the first cathode active material layer, and the second cathode active material layer. Specifically, the cathode electrode sheet obtained in step (c) is transferred to a rolling device for rolling, wherein the rolling pressure is maintained constant during the rolling process. When the rolling pressure is controlled to remain constant, the thickness of the first material layer and the second material layer can be regulated by adjusting the coating weight of the first material layer, the second material layer, the third material layer, and the fourth material layer.

[0061] In step (a), the coating weight of the first material layer is A, the coating weight of the second material layer in the second coating layer is B, and 1≤A / B≤3. For example, A / B can be 1, 1.2, 1.5, 1.8, 2, 2.5, 3, or a range consisting of any two of these values. Under the condition of a certain volume energy density, when A / B is within the above range, using the same rolling pressure, the first material layer and the second material layer can have a suitable thickness, thereby enabling the electrochemical device to have good safety performance and good cycle performance.

[0062] In step (b), the coating weight of the third material layer is A', the coating weight of the fourth material layer in the second coating layer is B', and 1≤A' / B'≤3. For example, A' / B' can be 1, 1.2, 1.5, 1.8, 2, 2.5, 3 or a range consisting of any two of these values. Under the condition of a certain volume energy density, when A' / B' is within the above range, using the same rolling pressure, the third material layer and the fourth material layer can have a suitable thickness, thereby enabling the electrochemical device to have good safety performance and good cycle performance.

[0063] In some embodiments, along the thickness direction of the electrochemical device, the first surface is closer to the geometric center of the electrochemical device than the second surface, A'>A, A' / B'>A / B. The outer side of the electrode assembly has higher requirements for safety performance than the inner side of the electrode assembly. When the energy density remains unchanged and the rolling pressure is constant, when the above conditions are met, the thickness of the third material layer located on the outer side of the electrode assembly is greater, and the thickness of the second material layer located on the inner side of the electrode assembly is greater, which is more conducive to ensuring the safety performance of the electrochemical device while having good cycle performance.

[0064] In some embodiments, A is 2 g / 1540.25 mm 2 ~3g / 1540.25mm 2 , B is 1g / 1540.25mm 2 ~2g / 1540.25mm 2 When A meets the above range, the same rolling pressure can be used to make the thickness of the first material layer appropriate, so that the electrochemical device has good safety performance and a high volume energy density. When B meets the above range, the same rolling pressure can be used to make the thickness of the second material layer appropriate, so that the electrochemical device has good cycle performance and a high volume energy density.

[0065] In some embodiments, A' is 2g / 1540.25mm 2 ~3g / 1540.25mm 2 , B' is 1g / 1540.25mm 2~2g / 1540.25mm 2 When A' meets the above range, the same rolling pressure can be used to make the thickness of the third material layer appropriate, so that the electrochemical device has good safety performance and a high volume energy density. When B' meets the above range, the same rolling pressure can be used to make the thickness of the fourth material layer appropriate, so that the electrochemical device has good cycle performance and a high volume energy density.

[0066] In some embodiments, step (a) includes: coating a first material layer on a first surface of the cathode current collector, and coating a second material layer on a surface of the first material layer to obtain a first coating layer. In other embodiments, step (a) includes: coating a second material layer on a first surface of the cathode current collector, and coating a first material layer on a surface of the second material layer to obtain a first coating layer.

[0067] In some embodiments, step (b) includes: coating a third material layer on the second surface of the cathode current collector, and coating a fourth material layer on the surface of the third material layer to obtain a second coating layer. In other embodiments, step (b) includes: coating a fourth material layer on the second surface of the cathode current collector, and coating a third material layer on the surface of the fourth material layer to obtain a second coating layer.

[0068] See also Figure 5 In one embodiment of the present application, an electric device 200 is provided, comprising the electrochemical device 100. The electric device 200 may be, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic 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 TV, 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, a car, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0069] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein a lithium-ion battery is used as an example.

[0070] Example 1

[0071] Preparation of cathode electrode:

[0072] The first ceramic insulating particles (boehmite particles), the binder (polyvinylidene fluoride), and the conductive agent (conductive carbon black) are dissolved in an N-methylpyrrolidone solution at a weight ratio of 85:7.5:7.5 to obtain a first material layer slurry. The cathode active material (lithium iron phosphate), the second ceramic insulating particles (boehmite particles), the binder (polyvinylidene fluoride), and the conductive agent (conductive carbon black) are dissolved in an N-methylpyrrolidone solution at a weight ratio of 70:20:5:5 to form a second material layer slurry.

[0073] Aluminum foil is used as the current collector. The first material layer slurry is coated on the first surface and the second surface of the aluminum foil to form the first material layer and the third material layer. The second material layer slurry is coated on the surface of the first material layer and the third material layer to form the second material layer and the fourth material layer. The coating weight of the first material layer, the second material layer, and the third material layer is 2g / 1540.25mm 2 .

[0074] The active material (lithium cobalt oxide), binder (polyvinylidene fluoride), and conductive agent (conductive carbon black) are dissolved in N-methylpyrrolidone solution at a weight ratio of 97:1.5:1.5 to form a cathode slurry with a solid content of 70%. The cathode slurry is applied to the surface of the first coating to obtain a first cathode active material layer, and the cathode slurry is applied to the surface of the second coating to obtain a second cathode active material layer. The current collector coated with the first material layer, the second material layer, the third material layer, the fourth material layer, the first cathode active material layer, and the second cathode active material layer is rolled, and the rolling pressure is controlled to remain unchanged during the rolling process. The cathode electrode sheet is then cut.

[0075] Preparation of anode electrode:

[0076] 97.7wt% graphite, 1.3wt% sodium carboxymethyl cellulose, 1.0wt% styrene-butadiene rubber and an appropriate amount of deionized water are mixed to form an anode slurry. The anode slurry is applied to the surface of the primer layer and dried to obtain an anode material layer. Subsequently, the anode pole piece is obtained by cold pressing and cutting.

[0077] Preparation of diaphragm: Polyethylene film is selected as the diaphragm.

[0078] Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) are mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent, and then fully dried lithium salt LiPF 6 The electrolyte is obtained by mixing with an organic solvent in a weight ratio of 8:92.

[0079] Preparation of lithium-ion battery: stack the cathode electrode sheet, separator, and anode electrode sheet in order, place the separator between the cathode electrode sheet and the anode electrode sheet, and wind them to obtain an electrode assembly; place the electrode assembly in an aluminum-plastic film, inject liquid, and form a lithium-ion battery. The first surface is closer to the geometric center of the electrode assembly than the second surface.

[0080] Embodiment 2-7

[0081] The difference from Example 1 is that at least one of the thickness h of the first material layer, the thickness H of the second material layer, h / H, the thickness h' of the third material layer, the thickness H' of the fourth material layer, and h' / H' is different. The thickness of the first material layer, the second material layer, the third material layer, and the fourth material layer is controlled by controlling the coating weight of the first material layer, the second material layer, the third material layer, and the fourth material layer.

[0082] Comparative Example 1

[0083] The difference from Example 1 is that only the first material layer and the third material layer are coated on the surface of the current collector, while the second material layer and the fourth material layer are not coated.

[0084] Comparative Example 2

[0085] The difference from Example 1 is that only the second material layer and the fourth material layer are coated on the surface of the current collector, while the first material layer and the third material layer are not coated.

[0086] Comparative Examples 3-4

[0087] The difference from the first embodiment is that at least one of the thickness h of the first material layer, the thickness H of the second material layer, h / H, the thickness h' of the third material layer, the thickness H' of the fourth material layer, h' / H' is different.

[0088] The test methods for various parameters of this application are described below.

[0089] (1) Thickness test method:

[0090] The cathode electrode piece is cut in a cross section in the thickness direction, and a CCD detection device (charge coupled device image sensor camera) is used to measure the thickness of the first material layer, the second material layer, the third material layer and the fourth material layer in the cross section to obtain thickness values.

[0091] (2) Volume energy density test:

[0092] The lithium-ion battery was placed in a 25°C thermostat for 30 minutes to allow the lithium-ion battery to reach a constant temperature. The lithium-ion battery that reached a constant temperature was charged at a constant current of 0.5C to a voltage of 4.53V, then charged at a constant voltage of 4.53V to a current of 0.05C, and discharged at 0.2C to a voltage of 3.0V, and the discharge capacity and platform voltage were recorded.

[0093] Volume energy density = discharge capacity × platform voltage / (length × width × thickness of lithium-ion battery).

[0094] (3) Nail penetration test:

[0095] Under the test environment of 20±5℃, place the lithium-ion battery on the test table, and use a 4mm diameter steel nail to pierce the lithium-ion battery along the thickness direction of the electrode assembly at a speed of 30mm / s. The judgment standard for passing the nail penetration test is: no fire, no explosion. Test 100 lithium-ion batteries, the number of batteries that pass the test is X, and the test pass rate is X / 100.

[0096] (4) Cyclic performance test:

[0097] At room temperature (25°C), the lithium-ion battery is charged to 4.53V at a constant current of 2C, then charged to 0.02C at a constant voltage, then left to stand for 5 minutes, and then discharged to 3V at a constant current of 0.7C. This is a charge and discharge cycle, and the discharge capacity is recorded as the discharge capacity of the first cycle of the lithium-ion battery. The lithium-ion secondary battery is subjected to 1000 cycles of charge and discharge tests according to the above method, and the discharge capacity of each cycle is recorded. The capacity retention rate after 1000 cycles (%) = discharge capacity of the 1000th cycle / discharge capacity of the first cycle × 100%.

[0098] Table 1 lists the parameters and evaluation results of various embodiments and comparative examples.

[0099] Table 1

[0100]

[0101]

[0102] As can be seen from Table 1, compared with Comparative Examples 1-4, Examples 1-7 can have both a higher puncture pass rate and a higher cycle capacity retention rate by configuring the first material layer (third material layer) and the second material layer (fourth material layer), and limiting the ratio of the thickness of the first material layer (third material layer) to the thickness of the second material layer (fourth material layer) to 1 to 3. This is because the introduction of ceramic insulating particles in the first material layer (third material layer) can improve the safety performance of lithium-ion batteries, and the introduction of cathode active materials in the second material layer (fourth material layer) can improve the cycle performance of lithium-ion batteries. Under the condition of constant energy density, in comparative example 1, only the first material layer (third material layer) is configured, and its puncture pass rate is the highest, but the cycle capacity retention rate is the lowest; in comparative example 2, only the second material layer (fourth material layer) is configured, and its puncture pass rate is the lowest, but the cycle capacity retention rate is the highest; in comparative example 3, the ratio of the thickness of the first material layer (third material layer) to the thickness of the second material layer (fourth material layer) h / H (h' / H') is less than 1, and the thickness of the first material layer (third material layer) is small, resulting in a small puncture pass rate; in comparative example 4, the ratio of the thickness of the first material layer (third material layer) to the thickness of the second material layer (fourth material layer) is greater than 3, and the thickness of the second material layer (fourth material layer) is small, resulting in a small cycle capacity retention rate. Examples 2-4 and 6-7 meet 1.5≤h / H≤2.5 and 1.5≤h' / H'≤2.5, and have a high puncture pass rate to ensure safety performance, and at the same time have a high cycle capacity retention rate.

[0103] It can be seen from Examples 6 and 7 that when h' / H'>h / H is satisfied, the puncture pass rate is higher. This is because when the above conditions are satisfied, the thickness of the third material layer located on the outside is greater, which is conducive to improving the puncture pass rate.

[0104] Embodiment 8-16

[0105] The difference from Example 4 is that the thickness h of the first material layer, the thickness H of the second material layer, and h / H are different, see Table 2 for details. Wherein, h'=h, H'=H, the lithium ion battery in Example 8 has a length of 97 mm, a width of 66 mm, and a thickness of 4.2 mm.

[0106] Table 2

[0107]

[0108] It can be seen from Examples 4, 8-12 that as the thickness h of the first material layer increases, the puncture pass rate tends to increase, the cycle capacity retention rate remains roughly unchanged, and the energy density tends to decrease. Examples 9-11 satisfy 0.7μm≤h≤1μm, and have both high puncture pass rate and energy density. In Example 8, h<0.7μm, although the energy density is high, the puncture pass rate is small; in Examples 4 and 12, h>1μm, although the puncture pass rate is large enough, the energy density is small.

[0109] It can be seen from Examples 11, 13-16 that as the thickness H of the second material layer increases, the puncture pass rate remains roughly unchanged, the cycle capacity retention rate shows an increasing trend, and the energy density shows a decreasing trend. Examples 11, 14-15 satisfy 0.43μm≤H≤0.7μm, and have both high cycle capacity retention rate and energy density. In Example 13, H<0.43μm, although the energy density is high, the cycle capacity retention rate is small; in Example 16, H>0.7μm, although the cycle capacity retention rate is large, the energy density is small.

[0110] Examples 17-24

[0111] The difference from Example 3 is that at least one of the content of the first ceramic insulating particles, the content of the second ceramic insulating particles and the content of the cathode active material is different, see Table 3 for details. In each example, h=1 μm, H=0.5 μm, h'=h, H'=H.

[0112] Table 3

[0113]

[0114]

[0115] It can be seen from Examples 3 and 17-20 that as the content of the first ceramic insulating particles in the first material layer increases, the puncture pass rate tends to increase, and the cycle capacity retention rate tends to decrease. This is because, as the content of the first ceramic insulating particles increases, the puncture resistance of the first material layer increases, thereby increasing the puncture pass rate, but the impedance of the lithium-ion battery will also increase, thereby reducing the cycle capacity retention rate. In Examples 3 and 18-19, the content of the first ceramic insulating particles in the first material layer is 80wt% to 90wt%, which has both a high puncture pass rate and a cycle capacity retention rate. In Example 17, the content of the first ceramic insulating particles is less than 80wt%, and the puncture pass rate is relatively small; in Example 20, the content of the first ceramic insulating particles is greater than 90wt%, and the puncture pass rate is large enough, but the cycle capacity retention rate is relatively small.

[0116] It can be seen from Examples 3 and 21-24 that as the content of the cathode active material in the second material layer increases, the puncture pass rate tends to decrease, and the cycle capacity retention rate tends to increase. This is because as the content of the cathode active material increases, the content of the second ceramic insulating particles decreases, which reduces the puncture resistance of the second material layer and reduces the impedance of the lithium-ion battery, thereby reducing the puncture pass rate and increasing the cycle capacity retention rate; and as the content of the first cathode active material increases, the second material layer can provide a larger capacity, thereby improving the cycle capacity retention rate. In Examples 3, 22-23, the content of the second ceramic insulating particles in the second material layer is 10wt%-30wt%, and the content of the cathode active material is 60wt%-80wt%, which has both a high puncture pass rate and a cycle capacity retention rate.

[0117] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the present application. Therefore, equivalent changes made according to the present application are still within the scope covered by the present application.

Claims

1. An electrochemical device, comprising an electrode assembly, wherein the electrode assembly comprises a cathode electrode sheet, wherein the cathode electrode sheet comprises a cathode current collector and a cathode active material layer, wherein: The cathode electrode sheet also includes a first material layer and a second material layer, which are stacked on the first surface of the cathode current collector and located between the cathode current collector and the cathode active material layer, the first material layer includes first ceramic insulating particles, the second material layer includes second ceramic insulating particles and cathode active material, the thickness of the first material layer is h, the thickness of the second material layer is H, 1≤h / H≤3.

2. The electrochemical device according to claim 1, characterized in that 1.5≤h / H≤2.

5.

3. The electrochemical device according to claim 1, characterized in that 0.7μm≤h≤1μm, 0.43μm≤H≤0.7μm.

4. The electrochemical device according to claim 1, characterized in that The first material layer is disposed on the first surface, and the second material layer is located between the first material layer and the cathode active material layer.

5. The electrochemical device according to claim 1, characterized in that The second material layer is disposed on the first surface, and the first material layer is located between the second material layer and the cathode active material layer.

6. The electrochemical device according to claim 1, characterized in that The cathode electrode sheet also includes a third material layer and a fourth material layer, and the third material layer and the fourth material layer are stacked on the second surface of the cathode current collector, the third material layer includes the first ceramic insulating particles, and the fourth material layer includes the cathode active material and the second ceramic insulating particles. The thickness of the third material layer is h', and the thickness of the fourth material layer is H'. Along the thickness direction of the electrode assembly, the first surface is closer to the geometric center of the electrode assembly than the second surface, h'>h, h' / H'>h / H.

7. The electrochemical device according to claim 1, characterized in that Based on the mass of the first material layer, the mass percentage of the first ceramic insulating particles is 80% to 90%; and / or, based on the mass of the second material layer, the mass percentage of the second ceramic insulating particles is 10% to 30%, and the mass percentage of the cathode active material is 60% to 80%.

8. The electrochemical device according to claim 1, characterized in that The first ceramic insulating particles and the second ceramic insulating particles each independently include one or more of boehmite, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide, and zinc oxide.

9. The electrochemical device according to claim 1, characterized in that The cathode active material includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate.

10. A method for preparing an electrochemical device, characterized in that: include: Coating a first coating layer on a first surface of a cathode current collector, wherein the first coating layer comprises a first material layer and a second material layer stacked, the first material layer comprises a first ceramic insulating particle, the second material layer comprises a cathode active material and a second ceramic insulating particle, the coating weight of the first material layer is A, the coating weight of the second material layer is B, and 1≤A / B≤3; A cathode active material layer is coated on the surface of the first coating layer to obtain a cathode electrode sheet.

11. The method for preparing an electrochemical device according to claim 10, characterized in that: The rolling pressure is controlled to remain unchanged, and the first material layer and the second material layer are rolled.

12. The method for preparing an electrochemical device according to claim 10, characterized in that: include: A second coating is applied on the second surface of the cathode current collector, wherein the second coating comprises a third material layer and a fourth material layer which are stacked, the third material layer comprises the first ceramic insulating particles, and the fourth material layer comprises the cathode active material and the second ceramic insulating particles, wherein the coating weight of the third material layer is A', the coating weight of the fourth material layer is B', and along the thickness direction of the electrochemical device, the first surface is closer to the geometric center of the electrochemical device than the second surface, A'>A, A' / B'>A / B; The rolling pressure is controlled to remain unchanged, and the first material layer, the second material layer, the third material layer and the fourth material layer are rolled.

13. An electrical equipment, characterized in that: The invention comprises the electrochemical device according to any one of claims 1 to 9, or comprises the electrochemical device prepared by the method for preparing the electrochemical device according to any one of claims 10 to 12.

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