Electrochemical device and electric equipment
By setting gaps and conductive layers in the positive electrode active material layer in the bending region and setting a groove coating in the substrate layer, the problems of uneven lithium-ion deposition and thermal runaway caused by stress concentration in electrochemical devices are solved, thereby improving the uniformity of current density and cycle performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG LIWINON ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-03-31
- Publication Date
- 2026-06-05
AI Technical Summary
In existing wound electrochemical devices, the active material layer at the bending part of the positive electrode is prone to peeling or uneven lithium ion deposition due to stress concentration, which can lead to lithium plating problems. In addition, the gap setting causes a sharp increase in current density, and heat cannot be dissipated quickly, which increases the risk of thermal runaway and affects cycle performance.
Several gaps are set on the second positive electrode active material layer in the bending region, and a conductive layer is filled in the gaps. At the same time, a coating is set on the substrate layer towards one side of the positive electrode sheet. The coating has an array of grooves to promote the transport of electrons and lithium ions, improve the uniformity of current density, and reduce excessive local current and temperature rise.
Effective regulation of electron transport paths and lithium-ion flux distribution can avoid excessive local current, reduce the risk of thermal runaway, and improve the cycle performance and safety of electrochemical devices.
Smart Images
Figure CN122158663A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of electrochemical energy storage technology, specifically to an electrochemical device and an electrical device. Background Technology
[0002] Existing wound electrochemical devices (such as wound batteries) generally include a casing and a core and electrolyte placed inside the casing. The core is usually formed by stacking and winding a positive electrode, a separator, and a negative electrode in sequence. The positive electrode located at the bending part of the core is prone to stress concentration, which can lead to the peeling of the active material layer or uneven lithium ion deposition, thus causing lithium plating problems. Although the stress can be relieved by setting gaps in the second positive electrode active material layer, the following defects still exist: (1) The setting of gaps will cause the local current density of the electrochemical device to increase sharply under fast charging or high temperature, and the heat cannot be dissipated quickly, thus increasing the risk of thermal runaway of the electrochemical device; (2) The electric field distortion at the edge of the gap will intensify ion aggregation, accelerate side reactions, and affect the cycle performance of the electrochemical device.
[0003] In view of the above, this application is hereby submitted. Summary of the Invention
[0004] Based on the deficiencies of existing technologies, the purpose of this application is to provide an electrochemical device and an electrical device. This application provides a plurality of gaps on the second positive electrode active material layer located in the bending region, a conductive layer is disposed within the gaps, and a coating is disposed on one side of the positive electrode sheet on the substrate layer. The coating includes a plurality of grooves distributed in an array, which can promote the transport of electrons and lithium ions, improve the uniformity of current density distribution, avoid excessive local current and excessive local lithium insertion / deintercalation, reduce the temperature rise of the electrochemical device during cyclic charging and discharging, thereby reducing the risk of thermal runaway of the electrochemical device and improving the cycle performance of the electrochemical device.
[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: In a first aspect of this application, an electrochemical device is provided, including a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the positive electrode and the negative electrode, and the negative electrode, the separator, and the positive electrode are sequentially stacked and wound to form a wound structure, wherein the wound structure includes a straight region and a bent region, and the bent region is connected to an adjacent straight region. The positive electrode sheet includes a positive current collector, and a first positive active material layer is disposed on at least one side surface of the positive current collector. A second positive active material layer is disposed on the side surface of the first positive active material layer opposite to the positive current collector. The second positive active material layer located in the bending region is provided with a plurality of gaps arranged at intervals along the length direction of the positive electrode sheet, and the gaps are filled with a conductive layer. The separator includes a substrate layer, and a coating is provided on the side of the substrate layer facing the positive electrode. The coating includes a plurality of grooves arranged in an array, and the material of the coating includes at least one of alumina, silicon carbide, titanium dioxide, and zirconium oxide.
[0006] In a second aspect of this application, an electrical device is provided, including the aforementioned electrochemical device. Attached Figure Description
[0007] The embodiments described in this application are not limited to the figures described below, which are only some of the embodiments described in this application. Those skilled in the art can obtain figures of other embodiments based on the content of this application.
[0008] Figure 1 A partial cross-sectional view of the positive electrode sheet provided in this application; Figure 2 A partial cross-sectional view of the diaphragm provided in this application; Figure 3 This is a partial schematic diagram of the winding structure provided in this application in the bending region.
[0009] In the figure, 1 is the positive electrode sheet, 11 is the positive current collector, 12 is the first positive active material layer, 13 is the second positive active material layer, 14 is the conductive layer, 2 is the separator, 21 is the substrate layer, 22 is the groove, 23 is the coating, and 3 is the negative electrode sheet. Detailed Implementation
[0010] To better illustrate the purpose, technical solution, and advantages of this application, the following description, in conjunction with embodiments, aims to provide a detailed understanding of the content of this application, rather than to limit it. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application.
[0011] The technical features described in this application in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions.
[0012] It should be understood that, unless otherwise specified, the numerical ranges involved in this application are considered continuous, including the minimum and maximum values of the range, and every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the maximum and minimum values of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any or all of the subranges to which they are included.
[0013] In this application, the terms "first" and "second" are used only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or implicitly indicating the order of the technical features indicated.
[0014] In this application, the terms "some embodiments," "examples," etc., refer to specific features, structures, materials, or characteristics described in connection with the embodiment or example that are included in at least one embodiment or example of this application. In this application, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0015] It should be understood that this application does not impose any particular restrictions on the specific dispersion or mixing methods.
[0016] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.
[0017] In the first aspect of this application, please refer to Figures 1-3 This application provides an electrochemical device, including a positive electrode 1, a negative electrode 3 and a separator 2. The separator 2 is disposed between the positive electrode 1 and the negative electrode 3. The negative electrode 3, the separator 2 and the positive electrode 1 are sequentially stacked and wound to form a wound structure. The wound structure includes a straight region and a bent region. The bent region is connected to the adjacent straight region. The positive electrode 1 includes a positive current collector 11. A first positive active material layer 12 is respectively disposed on two opposite surfaces of the positive current collector 11. A second positive active material layer 13 is disposed on the side of the first positive active material layer 12 facing away from the positive current collector 11. The second positive active material layer 13 located in the bending area is provided with a plurality of gaps arranged at intervals along the length direction of the positive electrode 1. The gaps are filled with a conductive layer 14. The separator 2 includes a substrate layer 21, and a coating 23 is disposed on the side of the substrate layer 21 facing the positive electrode 1. The coating is provided with a plurality of grooves 22 arranged in an array. The material of the coating includes at least one of alumina, silicon carbide, titanium dioxide, and zirconium oxide.
[0018] This application provides several gaps on the second positive electrode active material layer located in the bending region, a conductive layer within the gaps, and a coating layer on the substrate layer facing the positive electrode sheet. The coating layer has several arrayed grooves, which can promote the transport of electrons and lithium ions, improve the uniformity of current density distribution, avoid excessive local current and excessive local lithium insertion / deintercalation, reduce the temperature rise of the electrochemical device during cyclic charging and discharging, thereby reducing the risk of thermal runaway of the electrochemical device and improving the cycle performance of the electrochemical device.
[0019] Specifically, this application sets several gaps on the second positive electrode active material layer located in the bending region, and sets a conductive layer in the gaps. The conductive layer acts as a thermal channel and charge bridge, which can effectively regulate the electron transport path and lithium ion flux distribution on the positive electrode surface, avoid excessive local current and excessive local lithium insertion / deintercalation, thereby delaying rapid capacity decay. It can also indirectly make the lithium deposition on the negative electrode more uniform. The conductive layer can divert the current in the gap region to other regions, improve the uniformity of current density distribution, avoid the sharp increase in local current density in the electrochemical device under fast charging or high temperature, accelerate heat dissipation, and thus reduce the temperature rise of the electrochemical device during cyclic charging and discharging, reducing the risk of thermal runaway of the electrochemical device.
[0020] This application provides a coating on one side of the positive electrode sheet at the substrate level. The coating has an array of grooves, which provide rigid support for the substrate layer of the separator and can effectively reduce the thermal shrinkage rate of the separator. The grooves can serve as micro-reservoirs to ensure a stable supply and distribution of electrolyte during charging and discharging. The array of grooves helps to form a more uniform and efficient ion transport channel, avoiding a sudden increase in resistance and severe local heating due to local lack of liquid, and reducing the formation of lithium dendrites on the negative electrode. Compared with the irregularly distributed pore structure in traditional separators, it can more effectively reduce ion transport resistance, thereby helping to improve the cycle performance of the electrochemical device.
[0021] In some embodiments, the conductive layer includes at least one of a nitrogen-containing conductive polymer and a carbon-based conductive filler. The nitrogen-containing conductive polymer includes at least one of polypyrrole, polyaniline, and polythiophene, and the carbon-based conductive filler includes at least one of carbon nanotubes, graphene, and carbon fibers.
[0022] In some embodiments, the conductive layer comprises a nitrogen-containing conductive polymer and a carbon-based conductive filler, wherein the nitrogen-containing conductive polymer has a mass percentage of 60-80% and the carbon-based conductive filler has a mass percentage of 20-40%, based on the sum of the masses of the nitrogen-containing conductive polymer and the carbon-based conductive filler.
[0023] For example, based on the sum of the masses of the nitrogen-containing conductive polymer and the carbon-based conductive filler, the mass percentage of the nitrogen-containing conductive polymer can be any one or a combination of two of the following: 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%. The mass percentage of the carbon-based conductive filler can be any one or a combination of two of the following: 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%.
[0024] In some embodiments, the diameter of the groove is 0.1~0.5μm, and the distribution density of the groove is 10. 5 ~10 6 pcs / cm 2 .
[0025] For example, the diameter of the groove is within the range of any one or a combination of two of 0.1μm, 0.2μm, 0.3μm, 0.4μm, and 0.5μm. The distribution density of the groove is 10. 5 pcs / cm 2 2×10 5 pcs / cm 2 3×10 5 pcs / cm 2 4×10 5 pcs / cm 2 5×10 5 pcs / cm 2 6×10 5 pcs / cm 2 7×10 5 pcs / cm 2 8×10 5 pcs / cm 2 9×10 5 pcs / cm 2 10 6 pcs / cm 2 The range consisting of any one or both of them.
[0026] In some embodiments, the thickness of the coating is 50~500 nm.
[0027] For example, the thickness of the coating may be any or a combination of any two of the following: 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, and 500nm.
[0028] In this application, the method for preparing the coating includes, but is not limited to, the following methods: (1) A coating is prepared on one side surface of the substrate layer by magnetron sputtering; (2) The coating is etched by a picosecond ultraviolet laser to form a coating consisting of an array of grooves.
[0029] The magnetron sputtering process conditions are as follows: the sputtering power source is an RF power source with a sputtering power of 50~200W, the sputtering atmosphere is an argon atmosphere with a pressure of 0.1~1Pa, the deposition rate is 0.1nm / min, and the target material is at least one of alumina, silicon carbide, zirconium oxide, and silicon oxide.
[0030] The etching process conditions are as follows: ultraviolet laser wavelength is 355nm, pulse width is 10~15ps, and single pulse energy is 20~30μJ.
[0031] In some embodiments, the thickness of the substrate layer is 5~10 μm.
[0032] For example, the thickness of the substrate layer can be any or a combination of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm.
[0033] In some embodiments, the substrate layer includes at least one of polyethylene, polypropylene, polyamide, and aramid.
[0034] In some embodiments, the distance between any two adjacent gaps in the longitudinal direction of the positive electrode is 0.5 to 2 mm.
[0035] For example, in the length direction of the positive electrode sheet, the spacing between any two adjacent gaps can be any one or a combination of any two of the following: 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, and 2.0mm.
[0036] In some embodiments, the conductive layer has a dimension of 0.5 to 3 mm along the length of the positive electrode.
[0037] For example, the dimension of the conductive layer in the length direction of the positive electrode sheet can be any one or a combination of any two of the following: 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm, and 3.0mm.
[0038] In some embodiments, the thickness of the conductive layer is equal to the thickness of the second positive electrode active material layer, and the thickness ratio of the first positive electrode active material layer to the second positive electrode active material layer is 0.5 to 2. When this condition is met, the overall performance of the electrochemical device is better.
[0039] For example, the thickness ratio of the first positive electrode active material layer to the second positive electrode active material layer can be any one or a combination of two of the following: 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.25, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.
[0040] In some embodiments, the thickness of the first positive electrode active material layer is 5~20 μm.
[0041] For example, the thickness of the first positive electrode active material layer can be any or a combination of any two of the following: 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 19μm, and 20μm.
[0042] In some embodiments, the thickness of the second positive electrode active material layer is 7.5~15 μm.
[0043] For example, the thickness of the second positive electrode active material layer can be any or a combination of 7.5 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm.
[0044] In some embodiments, the first positive electrode active material layer includes a first positive electrode active material, a first positive electrode conductive agent, and a first positive electrode binder, wherein the mass ratio of the first positive electrode active material, the first positive electrode conductive agent, and the first positive electrode binder is (94~98.12):(1~3):(0.88~3).
[0045] The second positive electrode active material layer includes a second positive electrode active material, a second positive electrode conductive agent, and a second positive electrode binder, wherein the mass ratio of the second positive electrode active material, the second positive electrode conductive agent, and the second positive electrode binder is (94~98.12):(1~3):(0.88~3).
[0046] Specifically, the first positive electrode active material and the second positive electrode active material each independently include LiC. O At least one of the following: O2, LiNiO2, LiNixMnyO2, Li1+zNixMnyCo1-x-yO2, LiNixCoyAlzO2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, and LiMnPO4, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.
[0047] This application does not impose any particular restrictions on the positive current collector, as long as it can achieve the purpose of this application. The positive current collector can be aluminum foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof, each independently.
[0048] The first and second positive electrode conductive agents can each independently comprise conductive agents conventional in the battery field, and any conductive material can be used as long as it does not cause a chemical change. For example, the first and second positive electrode conductive agents can each independently comprise at least one of conductive carbon black, conductive graphite, graphene, carbon nanotubes, and carbon fibers.
[0049] The first and second positive electrode binders may each independently comprise binders conventional in the battery industry. For example, the first and second positive electrode binders may each independently comprise at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), and sodium alginate.
[0050] In some embodiments, the negative electrode sheet includes a negative electrode current collector, and at least one side surface of the negative electrode current collector is provided with a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material, which may further include natural graphite, artificial graphite, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), tin-based materials, silicon-based materials, and lithium titanate (Li4Ti5O).12 The tin-based material includes at least one of the following: Sn, SnO2, SnO, and tin alloys; the silicon-based material includes at least one of Si, silicon-nitrogen composite material, and silicon-oxygen composite material.
[0051] In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent and a negative electrode binder, wherein the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is (90~97.7):(1~5):(1.3~5).
[0052] Specifically, this application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector can be at least one of copper foil, aluminum foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and composite current collector.
[0053] The negative electrode conductive agent may include conductive agents conventional in the field of electrochemical devices, such as at least one of conductive carbon black, conductive graphite, graphene, carbon nanotubes, and carbon fibers.
[0054] The negative electrode binder is used to improve the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material layer and the negative electrode current collector. The negative electrode binder may include binders conventional in the field of electrochemical devices. For example, the first anode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyacrylate, polyolefin, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), and polyimide (PI).
[0055] In some embodiments, the electrochemical device includes any apparatus in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy, and specific, non-limiting examples include all kinds of primary electrochemical devices, secondary electrochemical devices, fuel electrochemical devices, solar electrochemical devices, or capacitors. In particular, the electrochemical device is a lithium secondary electrochemical device, including lithium metal secondary electrochemical devices, lithium-ion secondary electrochemical devices, lithium polymer secondary electrochemical devices, or lithium-ion polymer secondary electrochemical devices.
[0056] In some embodiments, the electrochemical device further includes an electrolyte, which may include liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, etc., which may be used in the production of the electrochemical device, but are not limited thereto.
[0057] In some embodiments, the liquid electrolyte may include a non-aqueous solvent and a lithium salt.
[0058] The lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalate) phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalate) borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).
[0059] The concentration of lithium salt in the liquid electrolyte is 0.5~1 mol / L.
[0060] The non-aqueous solvent can be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.
[0061] Specifically, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.
[0062] The chain carbonate compound may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC).
[0063] The cyclic carbonate compound may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), and vinyl ethylene carbonate (VEC).
[0064] The fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.
[0065] The carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.
[0066] The ether compound may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.
[0067] Optionally, the non-aqueous solvent may further include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.
[0068] In some embodiments, the outer casing of the electrochemical device can be a rigid casing, such as a hard plastic casing, an aluminum casing, or a steel casing. The outer casing of the electrochemical device can also be a flexible package, such as a pouch-type flexible package. For example, the material of the flexible package can be plastic, aluminum-plastic film, etc., wherein the plastic includes, but is not limited to, at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate, and the aluminum-plastic film comprises a three-layer composite structure of a PP layer, an Al layer, and a nylon layer.
[0069] In a second aspect of this application, an electrical device is provided, including the aforementioned electrochemical device.
[0070] The electrical equipment includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.
[0071] In this application, thickness refers to the thickness in the following context: Figure 1 or Figure 2 The dimension in the H direction, the length refers to, for example Figure 1 or Figure 2 The dimension in the L direction.
[0072] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments.
[0073] Unless otherwise specified, all experimental reagents and instruments used in this application are commonly used and ordinary reagents and instruments. Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this application are commercially available, and the raw materials used in each parallel experiment are the same.
[0074] Example 1 This embodiment provides a secondary battery, the structure of which is as follows: Figures 1-3As shown. The secondary battery includes a casing and a cell assembly housed within the casing. The cell assembly includes a positive electrode 1, a negative electrode 3, and a separator 2. The separator 2 is disposed between the positive electrode 1 and the negative electrode 3. The negative electrode 3, the separator 2, and the positive electrode 1 are sequentially stacked and wound to form a winding structure. The winding structure includes a straight region and a bent region, and the bent region connects to the adjacent straight region.
[0075] The positive electrode 1 includes a positive current collector 11. A first positive active material layer 12 is respectively disposed on two opposite surfaces of the positive current collector 11. A second positive active material layer 13 is disposed on the side of the first positive active material layer 12 facing away from the positive current collector 11. The second positive active material layer 13 located in the bending region is provided with a plurality of gaps arranged at intervals along the length direction of the positive electrode 1. The gaps are filled with a conductive layer 14.
[0076] The conductive layer comprises a nitrogen-containing conductive polymer, a carbon-based conductive filler, and a dispersant, sodium dodecylbenzenesulfonate. The selection of the nitrogen-containing conductive polymer and the carbon-based conductive filler, as well as their respective mass ratios, are shown in Table 1. The mass of the dispersant is 3% of the mass of the carbon-based conductive filler. The thickness of the conductive layer is equal to the thickness of the second positive electrode active material layer. The thicknesses of the first positive electrode active material layer, the second positive electrode active material layer, and their ratio are shown in Table 1.
[0077] The separator 2 includes a substrate layer 21. A coating 23 is disposed on the side of the substrate layer 21 facing the positive electrode 1. The coating is provided with a plurality of grooves 22 arranged in an array. The thickness of the coating 23, the diameter of the grooves 22 and the distribution density are shown in Table 1.
[0078] The method for preparing the secondary battery includes the following steps: S1. Preparation of the positive electrode: S11. The positive electrode active material lithium cobalt oxide (LiCoO2), conductive agent acetylene black, conductive carbon nanotubes (CNTs) and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of LiCoO2:acetylene black:CNT:PVDF=97.6:0.5:0.6:1.3 and then added to N-methylpyrrolidone. The mixture is fully dispersed and uniformly dispersed to obtain a positive electrode slurry with a solid content of 70%. Carbon-based filler and dispersant sodium dodecylbenzenesulfonate were added to N-methylpyrrolidone and ultrasonically treated at 500W for 30 minutes. Then polypyrrole was added and ultrasonic treatment was continued for another 30 minutes to obtain a conductive paste with a solid content of 25%. S12. The positive electrode slurry is coated onto the two opposite sides of the current collector aluminum foil, then dried, and a positive electrode active material layer is formed on the surface of the positive electrode current collector by rolling. Laser etching is performed in a predetermined area of the positive electrode active material layer to form a first positive electrode active material layer and a second positive electrode active material layer with a gap (the thickness of the second positive electrode active material layer is the depth of the gap, which is also equal to the thickness of the conductive layer). S13. The conductive paste is filled into the gap, dried, and a conductive layer is formed in the gap. Finally, the positive electrode sheet is obtained by rolling and cutting. S2, Preparation of the negative electrode: Graphite, conductive carbon black SP, and binder SBR are mixed in a mass ratio of 97.7:1.1:1.2, added to deionized water, and fully dispersed to obtain a negative electrode slurry with a solid content of 70%. The negative electrode slurry is coated on two opposite surfaces of the negative electrode current collector copper foil, and then dried, rolled, and cut to obtain the negative electrode sheet. S3. Preparation of the diaphragm: S31. Select a commercially available PE polyethylene film with a thickness of 8μm as the substrate layer; S32. A coating is formed on one side surface of the substrate layer by magnetron sputtering. The magnetron sputtering target is an Al2O3 target, the sputtering power source is an RF power source, the sputtering power is 90W, the sputtering atmosphere is an argon atmosphere, the gas pressure is 0.1Pa, the argon flow rate is 20sccm, and the deposition rate is 0.1nm / min to form the coating. S33. The coating is etched using a picosecond ultraviolet laser with a wavelength of 355nm, a pulse width of 12ps, and a single pulse energy of 25μJ to form a coating consisting of several groove arrays. S4. Preparation of electrolyte: Fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), propyl propionate (PP), and dimethyl malonate (MA) were mixed in a volume ratio of FEC:EMC:PP:MA = 1.5:3:3:2.5 to obtain a mixed organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte. The concentration of lithium salt LiPF6 in the electrolyte was 1 mol / L. S5. Preparation of secondary batteries: The positive electrode, separator, and negative electrode are stacked in sequence and wound in the same direction to form a wound cell; then, an aluminum-plastic film is used for encapsulation, electrolyte is injected, and the cell is vacuum-sealed, formed, and shaped to obtain a secondary battery.
[0079] Examples 2-20 and Comparative Examples 1-4 The difference between Examples 2-4 and Example 1 is that the mass ratios of the nitrogen-containing conductive polymer and carbon-based conductive filler in the conductive layer of Examples 2-4 are shown in Table 1.
[0080] The difference between Example 5 and Example 1 is that the conductive layer of Example 5 does not contain carbon-based conductive filler, as shown in Table 1.
[0081] The difference between Example 6 and Example 1 is that the conductive layer of Example 6 does not contain nitrogen-containing conductive polymers, as shown in Table 1.
[0082] The difference between Examples 7 and 8 and Example 1 is that the types of nitrogen-containing conductive polymers and carbon-based conductive fillers used in Examples 7 and 8 are shown in Table 1.
[0083] The difference between Examples 9-12 and Example 1 is that the thickness of the second positive electrode active material layer, the spacing between any two adjacent gaps, and the size of the gaps in the length direction of the positive electrode sheet are shown in Table 1.
[0084] The difference between Examples 13 and 14 and Example 1 is that the materials of the coatings in Examples 13 and 14 are as shown in Table 2.
[0085] The difference between Examples 15-18 and Example 1 is that the coating thickness, groove diameter, and distribution density in Examples 15-18 are shown in Table 2.
[0086] The difference between Examples 19 and 20 and Example 1 is that the thickness of the first positive electrode active material layer in Examples 19 and 20 is shown in Table 1.
[0087] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not have a coating (as shown in Table 2) and did not perform steps S32 and S33.
[0088] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the conductive paste was not filled into the gaps in step S13 and no conductive layer was provided, as shown in Table 1.
[0089] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 did not perform laser etching in step S12, did not fill conductive paste in step S13, and did not set gaps and conductive layers, as shown in Table 1.
[0090] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 did not perform step S33, which resulted in a coating without a groove structure, as shown in Table 2.
[0091] The secondary batteries obtained according to the above embodiments and comparative examples were tested as follows: (1) Temperature rise during 5C fast charging: The battery was left to stand for 1 hour at 25±2℃. Before charging and discharging, thermocouples or infrared thermometers were attached to the center and edge of the large surface of the cell. The battery was charged at 5C constant current to 100% SOC (charging cut-off voltage is 4.2V). Then it was immediately discharged at 0.33C constant current to 2.5V. During the charging and discharging process, the temperature change was recorded in real time, and the temperature rise ΔT was calculated: ΔT = maximum temperature - initial temperature.
[0092] (2) Lithium deposition in bending areas: The battery was left to stand for 1 hour at 25±2℃, then charged and discharged 5 times at 1C (to activate the battery), and charged at 5C constant current to 100% SOC. The battery was then disassembled in an argon glove box and the core was removed. The positive electrode sheet in the bending area was scanned by SEM to observe the lithium metal deposition morphology. Ten bending areas were randomly selected, and the area percentage of lithium dendrites was calculated (%).
[0093] (3) Cyclic performance: At 25℃, the secondary battery was charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V until the current was less than 0.05C, and then discharged at a constant current of 1C to 2.5V. The initial discharge capacity C0 was recorded. The battery was placed in a constant temperature chamber at 45±2℃ and the following cycles were repeated: ① Charging: Charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V until the current was less than 0.05C; ② Discharging at a constant current of 1C to 2.5V; The discharge capacity C after 1000 cycles was recorded. n The discharge capacity retention rate is calculated using the following formula: Discharge capacity retention rate = (C n / C0) × 100%.
[0094] The results of the above performance tests are shown in Table 3.
[0095] Table 1 Table 2 Table 3 As can be seen from Tables 1-3, each embodiment of this application sets several gaps on the second positive electrode active material layer located in the bending region, sets a conductive layer in the gaps, and sets a coating on the substrate layer facing the positive electrode sheet. Under the action of the conductive layer and the coating, the risk of thermal runaway of the electrochemical device can be reduced, the cycle performance of the electrochemical device can be improved, the temperature rise of the secondary battery during the charging and discharging process is not greater than 35.2°C, the area ratio of lithium dendrites in the bending region is not greater than 2.15%, and the capacity retention rate is greater than 85% after 1000 cycles.
[0096] Compared to the embodiments, Comparative Example 1 did not have a coating on the substrate layer of the diaphragm (as shown in Table 2). Compared with the embodiments, Comparative Example 2 did not have a conductive layer in the gap of the second positive electrode active material layer, and Comparative Example 3 did not have a gap and a conductive layer in the second positive electrode active material layer. This significantly increased the temperature rise of the secondary battery during the charging and discharging process, significantly increased the area of lithium dendrites in the bending region, and significantly reduced the cycle performance.
[0097] Compared with the embodiments, Comparative Example 4 did not have a groove structure in the coating, which increased the measured temperature rise and the area of lithium dendrites in the bending zone, and also reduced the cycle performance.
[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.
Claims
1. An electrochemical device, characterized in that, The device includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the positive electrode and the negative electrode. The negative electrode, the separator, and the positive electrode are sequentially stacked and wound to form a wound structure. The wound structure includes a straight region and a bent region. The bent region is connected to an adjacent straight region. The positive electrode sheet includes a positive current collector, and a first positive active material layer is disposed on at least one side surface of the positive current collector. A second positive active material layer is disposed on the side surface of the first positive active material layer opposite to the positive current collector. The second positive active material layer located in the bending region is provided with a plurality of gaps arranged at intervals along the length direction of the positive electrode sheet, and the gaps are filled with a conductive layer. The separator includes a substrate layer, and a coating is provided on the side of the substrate layer facing the positive electrode. The coating is provided with a plurality of grooves arranged in an array. The material of the coating includes at least one of alumina, silicon carbide, titanium dioxide, and zirconium oxide.
2. The electrochemical device as described in claim 1, characterized in that, The conductive layer includes at least one of a nitrogen-containing conductive polymer and a carbon-based conductive filler. The nitrogen-containing conductive polymer includes at least one of polypyrrole, polyaniline, and polythiophene. The carbon-based conductive filler includes at least one of carbon nanotubes, graphene, and carbon fibers.
3. The electrochemical device as described in claim 1, characterized in that, The thickness of the conductive layer is equal to the thickness of the second positive electrode active material layer.
4. The electrochemical device as described in claim 1, characterized in that, The diameter of the groove is 0.1~0.5μm, and the distribution density of the groove is 10. 5 ~10 6 pcs / cm 2 .
5. The electrochemical device as described in claim 1, characterized in that, The thickness of the coating is 50~500nm.
6. The electrochemical device as claimed in claim 1, characterized in that, The thickness of the substrate layer is 5~10μm.
7. The electrochemical device as claimed in claim 1, characterized in that, Along the length of the positive electrode, the distance between any two adjacent gaps is 0.5~2mm.
8. The electrochemical device as claimed in claim 1, characterized in that, The conductive layer has a dimension of 0.5~3mm along the length of the positive electrode sheet.
9. The electrochemical device as claimed in claim 1, characterized in that, The thickness ratio of the first positive electrode active material layer to the second positive electrode active material layer is 0.5~2.
10. An electrical appliance, characterized in that, Includes the electrochemical device as described in any one of claims 1 to 9.