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 including a cathode tab including a cathode current collector, a first material layer, a second material layer, a first cathode active material layer, and a second cathode active material layer. The first material layer is arranged on the surface of the cathode current collector and located between the cathode current collector and the first cathode active material layer, the second material layer is arranged on the surface of the cathode current collector and located between the cathode current collector and the second cathode active material layer, the first material layer comprises first ceramic insulating particles, and the second material layer comprises second ceramic insulating particles; the thickness of the first material layer is larger than that of the second material layer, and the second material layer is closer to the geometric center of the electrode assembly than the first material layer in the thickness direction of the electrode assembly.

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 volume energy density 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 volume energy density.

[0004] In a first aspect, the present application provides an electrochemical device, including an electrode assembly, the electrode assembly including a cathode electrode sheet, the cathode electrode sheet including a cathode current collector, a first material layer, a second material layer, a first cathode active material layer, and a second cathode active material layer. The first material layer is disposed on a first surface of the cathode current collector and between the cathode current collector and the first cathode active material layer, the second material layer is disposed on a second surface of the cathode current collector and between the cathode current collector and the second cathode active material layer, the first material layer includes first ceramic insulating particles, the second material layer includes second ceramic insulating particles, the thickness of the first material layer is greater than the thickness of the second material layer, and along the thickness direction of the electrode assembly, the second material layer is closer to the geometric center of the electrode assembly than the first material layer.

[0005] In the present application, by configuring the first material layer and the second material layer, when mechanical abuse such as nail penetration occurs, the cathode current collector can be separated from the anode material layer, reducing the risk of short circuit between the cathode current collector and the anode material layer, thereby improving safety performance; and the thickness of the first material layer is greater than the thickness of the second material layer, and the first material layer with a larger thickness is configured on the outside of the electrode assembly, which is beneficial to improving the safety performance of the electrochemical device; the second material layer with a smaller thickness is configured on the inside of the electrode assembly, which is beneficial to improving the volume energy density. Therefore, the electrochemical device can have both high safety performance and high volume energy density.

[0006] Based on the first aspect, in some embodiments, the thickness of the first material layer is h, 2.5 μm≤h≤3 μm. When h is within the above range, the thickness of the first material layer is appropriate, so that the electrochemical device has good safety performance and high volume energy density.

[0007] Based on the first aspect, in some embodiments, the thickness of the second material layer is H, 1<h / H≤10. When h / H is within the above range, the first material layer and the second material layer can have suitable thicknesses, thereby making the electrochemical device have good safety performance and high volume energy density.

[0008] Based on the first aspect, in some embodiments, 1.25≤h / H≤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 a higher volume energy density while ensuring safety performance.

[0009] Based on the first aspect, in some embodiments, 0.3 μm≤H≤2 μm. When H is within the above range, the thickness of the second material layer is appropriate, so that the electrochemical device has good safety performance and high volume energy density.

[0010] Based on the first aspect, in some embodiments, the mass percentage of the first ceramic insulating particles in the first material layer is 80% to 90%, and / or the mass percentage of the second ceramic insulating particles in the second material layer is 80% to 90%. When the contents of the first ceramic insulating particles and the second ceramic insulating particles are within the above range, the first material layer and the second material layer can have 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.

[0011] 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.

[0012] The second aspect of the present application provides a method for preparing an electrochemical device, including: coating a first material layer on a first surface of a cathode current collector; coating a first cathode active material layer on the surface of the first material layer; coating a second material layer on a second surface of the cathode current collector, wherein the coating weight of the second material layer is less than the coating weight of the first material layer, and along the thickness direction of the electrochemical device, the second material layer is closer to the geometric center of the electrochemical device than the first material layer; coating a second cathode active material layer on the surface of the second material layer to prepare a cathode electrode sheet. The coating weight of the first material layer is greater than the coating weight of the second material layer, and the first material layer with a larger coating weight is arranged on the outer side of the electrode assembly, which is beneficial to improving the safety performance of the electrochemical device; the second material layer with a smaller coating weight is arranged on the inner side of the electrode assembly, which is beneficial to improving the volume energy density.

[0013] Based on the second aspect, in some embodiments, the coating weight of the first material layer is A, the coating weight of the second material layer is B, and 1<A / B≤4.5. When A / B is within the above range, the first material layer and the second material layer can have suitable thicknesses so that the electrochemical device has good safety performance and high volume energy density.

[0014] Based on the second aspect, in some embodiments, A is 4g / 1540.25mm 2 ~4.5g / 1540.25mm 2 , B is 1g / 1540.25mm 2 When A and B meet the above ranges, the electrochemical device can have a high volume energy density while having good safety performance.

[0015] 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

[0016] Figure 1 A schematic diagram of the structure of an electrochemical device provided in one embodiment of the present application.

[0017] Figure 2 A schematic diagram of the structure of an electrode assembly provided in one embodiment of the present application.

[0018] Figure 3 For along Figure 2 Schematic cross-sectional view at point A.

[0019] Figure 4 A schematic diagram of the structure of an electrical device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Further, the use of “may” when describing embodiments of the present application refers to “one or more embodiments of the present application”.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] See also Figure 3The cathode electrode sheet 21 includes a cathode current collector 211, a first cathode active material layer 213 and a second cathode active material layer 215. The cathode current collector 211 includes a first surface 211A and a second surface 211B opposite to each other, the first cathode active material layer 213 is arranged on the side where the first surface 211A is located, 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.

[0034] See also Figure 3 , the cathode electrode sheet 21 further includes a first material layer 212 and a second material layer 214. The first material layer 212 is provided on the first surface 211A and is located between the cathode current collector 211 and the first cathode active material layer 213. The second material layer 214 is provided on the second surface 211B and is located between the cathode current collector 211 and the second cathode active material layer 215. The thickness h of the first material layer 212 is greater than the thickness H of the second material layer 214. By configuring the first material layer 212 and the second material layer 214, the cathode current collector 211 can be separated from the anode material layer 222 when mechanical abuse such as nail penetration occurs, reducing the risk of short circuit between the cathode current collector 211 and the anode material layer 222, thereby improving safety performance. The first material layer 212 and the second material layer 214 have different thicknesses. The first material layer 212 with a larger thickness can be arranged on the side of the cathode electrode 21 with a higher requirement for safety performance, which is beneficial to improving the safety performance of the electrochemical device 100. The second material layer 214 with a smaller thickness can be arranged on the side of the cathode electrode 21 with a lower requirement for safety performance, which is beneficial to improving the volume energy density of the electrochemical device 100. Therefore, the electrochemical device 100 can have both higher safety performance and higher volume energy density.

[0035] In some embodiments, along the thickness direction T of the electrode assembly 20, the second surface 211B is closer to the geometric center of the electrode assembly 20 than the first surface 211A, and the second material layer 214 is closer to the geometric center of the electrode assembly 20 than the first material layer 212. Configuring the thicker first material layer 212 on the outside of the electrode assembly 20 is beneficial to improving the safety performance of the electrochemical device 100; configuring the thinner second material layer 214 on the inside of the electrode assembly 20 is beneficial to improving the volume energy density.

[0036] In some embodiments, 1<h / H≤10. For example, h / H can be 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two values ​​therein. When h / H is within the above range, the first material layer 212 and the second material layer 214 can have a suitable thickness so that the electrochemical device 100 has good safety performance and a high volume energy density.

[0037] In some embodiments, 1.25≤h / H≤5. When h / H is within the above range, the thicknesses of the first material layer 212 and the second material layer 214 are more appropriate, so that the electrochemical device 100 has a higher volume energy density while ensuring safety performance.

[0038] In some embodiments, the first material layer 212 includes first ceramic insulating particles, and the second material layer 214 includes second ceramic insulating particles. Introducing ceramic insulating particles into the first material layer 212 and the second material layer 214 can reduce the risk of the first material layer 212 and the second material layer 214 being punctured and short-circuited when the electrochemical device 100 is punctured by a needle or impacted by a heavy object, thereby improving the safety performance of the electrochemical device 100.

[0039] 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.

[0040] In some embodiments, the first material layer 212 and the second material layer 214 both include a binder, and the binder of the first material layer 212 and the binder of the second material layer 214 can each independently include one or more of polyfluoroolefins, polyacrylates, polyacrylic acids, polyurethanes, silicones, epoxy resins, and cellulose-derived binders. In some embodiments, the first material layer 212 and the second material layer 214 both include a conductive agent, and the conductive agent can include one or more of conductive carbon black, carbon nanotubes, carbon fibers, or graphene.

[0041] In some embodiments, the mass percentage of the first ceramic insulating particles in the first material layer 212 is 80% to 90%, and the mass percentage of the second ceramic insulating particles in the second material layer 214 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, and the mass percentage of the second ceramic insulating particles is 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 first material layer 212 can have a suitable anti-short circuit performance 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. When the content of the second ceramic insulating particles is within the above range, the second material layer 214 can have a suitable anti-short circuit performance 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.

[0042] In some embodiments, 2.5 μm ≤ h ≤ 3 μm. For example, h can be 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or a range consisting of any two of these values. When h satisfies the above range, the thickness of the first material layer 212 is appropriate, so that the electrochemical device 100 has a high volume energy density while having good safety performance.

[0043] In some embodiments, 0.3 μm ≤ H ≤ 2 μm. For example, H may be 0.3 μm, 0.8 μm, 1.3 μm, 1.8 μm, 2 μm, or a range consisting of any two of these values. When H satisfies the above range, the electrochemical device 100 may have a high volume energy density while having good safety performance.

[0044] One embodiment of the present application also provides a method for preparing an electrochemical device, comprising the following steps: (a) coating a first material layer on a first surface of a cathode current collector, and coating a first cathode active material layer on the surface of the first material layer; (b) coating a second material layer on a second surface of the cathode current collector, and coating a second cathode active material layer on the surface of the second material layer to obtain a cathode electrode sheet, wherein the coating weight of the second material layer is less than the coating weight of the first material layer, and along the thickness direction of the electrochemical device, the second material layer is closer to the geometric center of the electrochemical device than the first material layer; (c) forming an electrode assembly from the cathode electrode sheet, the separator and the anode electrode sheet; (d) placing the electrode assembly in a housing to obtain an electrochemical device. The coating weight of the first material layer is greater than the coating weight of the second material layer, and the first material layer with a larger coating weight is arranged on the outer side of the cathode electrode sheet with a higher requirement for safety performance, which is conducive to improving the safety performance of the electrochemical device, and the second material layer with a smaller coating weight is arranged on the inner side of the cathode electrode sheet with a lower requirement for safety performance, which is conducive to improving the volume energy density of the electrochemical device.

[0045] 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 first cathode active material layer, and the second cathode active material layer. Specifically, the cathode electrode sheet obtained in step (b) 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 controlled by adjusting the coating weight of the first material layer and the second material layer.

[0046] In some embodiments, the coating weight of the first material layer is A, the coating weight of the second material layer is B, and 1<A / B≤4.5. For example, A / B can be 1.2, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, or a range consisting of any two values ​​therein. 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 so that the electrochemical device has good safety performance and a high volume energy density.

[0047] In some embodiments, A is 4 g / 1540.25 mm 2 ~4.5g / 1540.25mm 2 , B is 1g / 1540.25mm 2 ~4g / 1540.25mm 2 When A and B meet the above ranges, the same rolling pressure can be used to make the thickness of the first material layer and the second material layer appropriate, thereby making the electrochemical device have a high volume energy density while having good safety performance.

[0048] See also Figure 4 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.

[0049] 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.

[0050] Example 1

[0051] Preparation of cathode electrode:

[0052] Ceramic insulating particles (boehmite particles), binder (polyvinylidene fluoride), and conductive agent (conductive carbon black) are dissolved in N-methylpyrrolidone solution at a weight ratio of 80:10:10 to obtain a slurry. Aluminum foil is used as a current collector, and the slurry is coated on the first surface and the second surface of the aluminum foil to form a first material layer and a second material layer. The coating weight of the first material layer is 4.3g / 1540.25mm 2 , the coating weight of the second material layer is 4g / 1540.25mm 2 .

[0053] The active material (lithium cobalt oxide), the binder (polyvinylidene fluoride), and the conductive agent (conductive carbon black) are dissolved in an 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 material layer to obtain a first cathode active material layer, and the cathode slurry is applied to the surface of the second material layer to obtain a second cathode active material layer. The current collector coated with the first material layer, the second 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.

[0054] Preparation of anode electrode:

[0055] 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.

[0056] Preparation of diaphragm: Polyethylene film is selected as the diaphragm.

[0057] 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.

[0058] Preparation of lithium-ion battery: stack the cathode electrode sheet, separator, and anode electrode sheet in order, so that the separator is 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. Among them, the second material layer is closer to the geometric center of the electrode assembly than the first material layer. The length of the lithium-ion battery is 97mm, the width is 66mm, and the thickness is 4.2mm.

[0059] Embodiment 2-10

[0060] 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, and the content of ceramic insulating particles is different. The thickness of the first material layer and the second material layer is controlled by controlling the coating weight of the first material layer and the second material layer.

[0061] Comparative Example 1-2

[0062] The difference from Embodiment 1 is that the thickness of the first material layer is the same as the thickness of the second material layer.

[0063] The test methods for various parameters of this application are described below.

[0064] (1) Thickness test method:

[0065] 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 and the second material in the cross section to obtain thickness values.

[0066] (2) Volume energy density test:

[0067] 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.

[0068] Volume energy density = discharge capacity × platform voltage / (length × width × thickness of lithium-ion battery).

[0069] (3) Nail penetration test:

[0070] 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 test is: no fire, no explosion. Test 10 lithium-ion batteries, the number of batteries that pass the test is X, and the test pass rate is X / 100.

[0071] (4) Cyclic performance test:

[0072] At room temperature, 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 charged and discharged 1000 times 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%.

[0073] Table 1 lists the parameters and evaluation results of various embodiments and comparative examples.

[0074] Table 1

[0075]

[0076] As can be seen from Table 1, compared with Comparative Example 1, Examples 1-5 satisfy h>H, and the first material layer with a larger thickness is arranged on the outside of the electrode assembly, so that the puncture pass rate is increased and the safety performance is improved. Compared with Comparative Example 2, Example 1 satisfies h>H, and the second material layer with a smaller thickness is arranged on the inside of the electrode assembly, which increases the volume energy density, and the puncture pass rate does not decrease significantly.

[0077] It can be seen from Examples 1-5 that as the thickness h of the first material layer increases, the puncture pass rate increases and the volume energy density decreases. Example 2-4 satisfies 2.5 μm≤h≤3 μm, and has both high puncture pass rate and energy density.

[0078] It can be seen from Examples 6-10 that as the thickness H of the first material layer increases, the puncture pass rate increases and the volume energy density decreases. Example 4 and Examples 7-9 satisfy 0.3 μm ≤ H ≤ 2 μm, and have both high puncture pass rate and energy density.

[0079] It can be seen from Examples 1-10 that when 1<h / H≤10 is satisfied, the first material layer and the second material layer have appropriate thicknesses, a high puncture pass rate and a high volume energy density. In Example 6, h / H>10, the thickness of the second material layer is small, and the puncture pass rate is low. Examples 2-5 and 8-9 satisfy 1.25≤h / H≤5, which have a high puncture pass rate to ensure safety performance, and at the same time have a high energy density.

[0080] Examples 11-14

[0081] The difference from Example 4 is that the content of ceramic insulating particles is different, see Table 3 for details. In the table, the content of ceramic insulating particles refers to the content of first ceramic insulating particles in the first material layer and the content of second ceramic insulating particles in the second material layer.

[0082] Table 2

[0083]

[0084] It can be seen from Table 2 that as the content of ceramic insulating particles increases, the puncture pass rate tends to increase, and the cycle capacity retention rate tends to decrease. This is because, as the content of ceramic insulating particles increases, the puncture resistance of the first material layer and the second 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 4, 12, and 13, the content of ceramic insulating particles is 80wt% to 90wt%, which has both a high puncture pass rate and a cycle capacity retention rate. In Example 11, the content of ceramic insulating particles is less than 80wt%, and the puncture pass rate is relatively small; in Example 14, the content of ceramic insulating particles is greater than 90wt%, and the puncture pass rate is large enough, but the cycle capacity retention rate is relatively small.

[0085] 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 first cathode active material layer disposed on a first surface of the cathode current collector and a second cathode active material layer disposed on a second surface of the cathode current collector, characterized in that: The cathode electrode sheet also includes a first material layer and a second material layer, the first material layer is arranged on the first surface of the cathode current collector and is located between the cathode current collector and the first cathode active material layer, the second material layer is arranged on the second surface of the cathode current collector and is located between the cathode current collector and the second cathode active material, the first material layer includes first ceramic insulating particles, the second material layer includes second ceramic insulating particles, the thickness of the first material layer is greater than the thickness of the second material layer, and along the thickness direction of the electrode assembly, the second material layer is closer to the geometric center of the electrode assembly than the first material layer.

2. The electrochemical device according to claim 1, characterized in that The thickness of the first material layer is h, 2.5 μm≤h≤3 μm.

3. The electrochemical device according to claim 2, characterized in that The thickness of the second material layer is H, 1<h / H≤10.

4. The electrochemical device according to claim 3, characterized in that 1.25≤h / H≤5.

5. The electrochemical device according to claim 3, characterized in that 0.3μm≤H≤2μm.

6. The electrochemical device according to claim 1, characterized in that The mass percentage of the first ceramic insulating particles in the first material layer is 80% to 90%, and / or the mass percentage of the second ceramic insulating particles in the second material layer is 80% to 90%.

7. The electrochemical device according to claim 6, 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.

8. A method for preparing an electrochemical device, characterized in that: include: Coating a first material layer on a first surface of the cathode current collector; Coating a first cathode active material layer on the surface of the first material layer; Coating a second material layer on a second surface of the cathode current collector, wherein the coating weight of the second material layer is less than the coating weight of the first material layer, and along the thickness direction of the electrochemical device, the second material layer is closer to the geometric center of the electrochemical device than the first material layer; A second cathode active material layer is coated on the surface of the second material layer to obtain a cathode electrode sheet.

9. The method for preparing an electrochemical device according to claim 8, characterized in that: The rolling pressure is controlled to remain unchanged, and the first material layer and the second material layer are rolled.

10. An electrical device, characterized in that: The invention comprises the electrochemical device according to any one of claims 1 to 7, or comprises the electrochemical device prepared by the method for preparing the electrochemical device according to any one of claims 8 to 9.

Images