Electrochemical apparatus and electronic device

Abstract

The present application discloses an electrochemical apparatus and an electronic device. The electrochemical apparatus comprises a negative electrode sheet and an electrolyte. The negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material. On the basis of the mass of the negative electrode active material, the mass percentage content of a silicon element in the silicon-based material is Z1%, wherein 0.1<Z1<15. The electrolyte comprises a compound of formula I and a substance A, and the substance A is selected from at least one of ethylene sulfite, ethylene sulfate, vinyl ethylene sulfite, trifluoromethyl phenyl sulfide, and methylene methanedisulfonate. On the basis of the mass of the electrolyte, the mass percentage content of the compound of formula I is a%, and the mass percentage content of the substance A is b%, wherein 0.5≤a / b≤20 and 0.5≤a≤20. The electrochemical apparatus of the present application has small volume expansion and low impedance growth during room-temperature cycling.

Description

Electrochemical devices and electronic equipment Technical Field

[0001] This application relates to the field of electrochemical technology, and more particularly to an electrochemical device and an electronic device. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, high operating voltage, long cycle life, and environmental friendliness, making them widely used in portable electronic devices such as mobile phones, laptops, and cameras. They are also the preferred power source for future electric and hybrid vehicles. Currently, to improve the energy density of lithium-ion batteries, high-specific-capacity electrode materials are mainly used. Silicon-based materials, as a type of alloyed anode material, can provide ultra-high specific capacities up to 4200 mAh / g. However, silicon anodes undergo drastic volume expansion and contraction during lithium-ion insertion / extraction, leading to increased impedance. Summary of the Invention

[0003] In view of this, this application provides an electrochemical device and an electronic device, wherein the negative electrode of the electrochemical device is a silicon-containing negative electrode and the electrolyte of the electrochemical device contains a compound of formula I and substance A. By adjusting the types and contents of the three substances appropriately, the three substances can work together to suppress the volume expansion and impedance increase of the electrochemical device during room temperature cycling.

[0004] In a first aspect, this application provides an electrochemical device, which includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode active material, which contains a silicon-based material. Based on the mass of the negative electrode active material, the mass percentage of silicon element in the silicon-based material is Z1%, where 0.1 < Z1 < 15. The electrolyte includes a compound of formula I.

[0005] R is selected from fluorinated or unsubstituted C2-C6 alkyl groups, fluorinated or unsubstituted C6-C6 alkyl groups. 12 Nitrogen-containing heterocyclic groups, fluorine-substituted or unsubstituted C6-C 12The electrolyte also includes substance A, which is selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methane disulfonate. Based on the mass of the electrolyte, the mass percentage of compound I is a%, the mass percentage of substance A is b%, and 0.5 ≤ a / b ≤ 20, 0.5 ≤ a ≤ 20. Preferably, substance A is selected from at least two of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methane disulfonate and contains at least vinyl sulfate. This application improves the volume expansion and impedance growth of silicon-containing anode electrochemical devices during room temperature cycling by controlling the silicon content in the silicon-based material within the above range, and simultaneously synergistically controlling the electrolyte to include compound I and substance A, with the type and content of compound I and substance A also within the above range. The inventors discovered that by regulating the electrolyte to contain compound I and substance A within the above-mentioned range, a relatively stable interface layer can be formed on the surface of the electrolyte and the mixed silicon-carbon anode, thereby reducing the side reactions of the electrolyte on the anode surface during cycling, thus suppressing the volume expansion and impedance growth of the battery during room temperature cycling.

[0006] In some embodiments, the compound of formula I includes at least one of the following compounds:

[0007] When the above-mentioned compounds of formula I are combined with substance A and an appropriate amount of silicon, they are more effective in suppressing the volume expansion and impedance increase of the battery during room temperature cycling.

[0008] In some embodiments, at least one of the following conditions is satisfied: (1) 0.1 ≤ a / Z1 ≤ 6, (2) 0.3 ≤ b ≤ 8. Preferably, 4 ≤ Z1 ≤ 5, 0.5 ≤ b ≤ 4. More preferably, 1 ≤ b ≤ 3, 2 ≤ a / Z1 ≤ 3. This application further regulates the values ​​of silicon element content, compound I content, and substance A content within the above ranges, which can further improve the cycle performance of the electrochemical device at room temperature.

[0009] In some embodiments, the silicon-based material includes at least one of silicon, silicon suboxide, silicon-carbon, or silicon-oxygen-carbon ceramic particles. The silicon-carbon particles include a carbon skeleton, amorphous silicon dispersed in the carbon skeleton, and a protective layer located on at least a portion of the surface of the carbon skeleton. The material of the protective layer includes amorphous carbon, and the carbon skeleton material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, or hard carbon.

[0010] In some embodiments, the electrolyte comprises fluoroethylene carbonate and / or vinylene carbonate, wherein the mass percentage of fluoroethylene carbonate is c1% and the mass percentage of vinylene carbonate is c2% based on the mass of the electrolyte, satisfying: 12≤(c1+c2×60)≤25, 0.5≤(c1+c2×60) / Z1≤10. Preferably, 2.4≤(c1+c2×60) / Z1≤4.8. Adjusting the electrolyte further includes fluoroethylene carbonate and / or vinylene carbonate, and their content relationship is within the above range. This not only suppresses the volume expansion of the electrochemical device during room temperature cycling but also further improves its storage performance at high temperatures, especially suppressing its storage volume expansion at high temperatures.

[0011] In some embodiments, the electrolyte includes a dinitrile compound selected from at least one of succinic anhydride, adiponitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, or 1,4-dicyano-2-butene. The mass percentage of the dinitrile compound is d%, 0.1 ≤ d ≤ 5, based on the mass of the electrolyte. Adding a dinitrile compound to the electrolyte, and ensuring that the type and content of the dinitrile compound are within the scope of this application, facilitates further improvement of the storage performance of the electrochemical device at high temperatures.

[0012] In some embodiments, the electrolyte includes a trinitrile compound selected from at least one of 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, 1,3,5-pentanetricarbononitrile, or tricyanobenzene. The mass percentage of the trinitrile compound is e% based on the mass of the electrolyte, with 1 ≤ d / e ≤ 2. Preferably, 1 ≤ d ≤ 5. Further adjusting the electrolyte to include a trinitrile compound, and ensuring the content of the trinitrile compound is within the above range, improves the high-temperature storage performance of the electrochemical device.

[0013] In some embodiments, the electrolyte further includes substance B and ethylene carbonate. Substance B is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, or ethyl propionate. Based on the mass of the electrolyte, the mass percentage of substance B is f%, 25 ≤ f ≤ 50, and the mass percentage of ethylene carbonate is g%, 10 ≤ g ≤ 20. The presence of substance B of the aforementioned type in the electrolyte, and the content of substance B being within the scope of this application, allows substance B and an appropriate amount of ethylene carbonate to further improve the overall performance of the electrochemical device, particularly by providing superior capacity retention at both room temperature and high temperature, as well as a lower volume expansion rate during high-temperature storage. Preferably, 0.5 ≤ f / g ≤ 3.

[0014] Secondly, this application provides an electronic device that includes the electrochemical device in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good room temperature performance.

[0015] The electrochemical device provided in the first aspect of this application exhibits small volume expansion and low impedance growth during room temperature cycling. Therefore, the electronic device provided in the second aspect of this application also exhibits small volume expansion and low impedance growth during room temperature cycling. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0017] It should be noted that, in the specific embodiments of this application, lithium-ion secondary batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion secondary batteries.

[0018] Lithium-ion secondary batteries

[0019] It includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative current collector and a negative active material disposed on at least one surface of the negative current collector. The negative active material contains a silicon-based material. Based on the mass of the negative active material, the mass percentage of silicon element in the silicon-based material is Z1, where 0.1 < Z1 < 15. The electrolyte includes a compound of formula I.

[0020] R is selected from fluorinated or unsubstituted C2-C6 alkyl groups, fluorinated or unsubstituted C6-C6 alkyl groups. 12 Nitrogen-containing heterocyclic groups, fluorine-substituted or unsubstituted C6-C 12The electrolyte also includes substance A, which is selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methane disulfonate. Based on the mass of the electrolyte, the mass percentage of compound I is a%, the mass percentage of substance A is b%, and the mass percentages are 0.5 ≤ a / b ≤ 20, 0.5 ≤ a ≤ 20, 0.1 ≤ a / z1 ≤ 6, and 0.3 ≤ b ≤ 8. Preferably, substance A is selected from at least two of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methane disulfonate, and contains at least vinyl sulfate. This application improves the volume expansion and impedance growth of the electrochemical device under ambient temperature cycling by appropriately controlling the silicon content in the silicon-based material and controlling the electrolyte to include compound I and substance A, with the contents of compound I and substance A within the above-mentioned ranges. For example, the value of 'a' can be 0.5, 1, 2, 5, 6, 8, 10, 12, 14, 15, 17, 18, 20, or a range of any two of the above values. For example, the value of 'a / b' can be 0.5, 1.3, 3.2, 4.4, 5.2, 7.2, 8.5, 9.9, 11.4, 13.9, 14.4, 16.1, 17.1, 19.4, 20, or a range of any two of the above values. For example, the value of 'a / Z1' can be 0.1, 0.2, 0.8, 1.1, 1.4, 1.9, 2.0, 2.7, 2.8, 3, 3.4, 3.7, 4.1, 4.5, 4.7, 5, 6, or a range of any two of the above values. For example, the value of b can be 0.3, 0.5, 1.0, 1.3, 1.6, 2.0, 2.5, 2.7, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.6, 4.9, 5, 5.5, 6, 6.5, 7.5, 8, or a range of any two of the above values. For example, the value of Z1 can be 4, 4.3, 4.5, 4.6, 4.8, 5, or a range of any two of the above values.

[0021] In some embodiments, the compound of formula I includes at least one of the following compounds:

[0022] The aforementioned compounds of Formula I are more conducive to synergistically improving the volume expansion and impedance growth of electrochemical devices during ambient temperature cycling with other substances.

[0023] In some embodiments, the electrolyte comprises fluoroethylene carbonate and / or vinylene carbonate, wherein the mass percentage of fluoroethylene carbonate is c1% and the mass percentage of vinylene carbonate is c2% based on the mass of the electrolyte, satisfying: 12 ≤ (c1 + c2 × 60) ≤ 25, 2.4 ≤ (c1 + c2 × 60) / Z1 ≤ 4.8. The presence of fluoroethylene carbonate and / or vinylene carbonate in the electrolyte, with the content of fluoroethylene carbonate and / or vinylene carbonate within the aforementioned range, can better mitigate the volume expansion of the electrochemical device at room temperature while maintaining a low impedance increase. Exemplarily, the value of (c1 + c2 × 60) can be 12, 12.4, 13.4, 14.8, 16.0, 16.7, 17.0, 18.3, 19.7, 20.4, 21.6, 22.6, 23.0, 24.7, 25, or a range consisting of any two of the above values. For example, the value of (c1+c2×60) / Z1 can be 0.5, 1.5, 2.4, 2.6, 2.8, 3, 3.2, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 6, 8.5, 10 or a range of any two of the above values.

[0024] In some embodiments, the electrolyte includes a dinitrile compound selected from at least one of succinic anhydride, adiponitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, or 1,4-dicyano-2-butene. The mass percentage of the dinitrile compound is d%, 0.1 ≤ d ≤ 5, based on the mass of the electrolyte. The presence of the aforementioned types and amounts of dinitrile compounds in the electrolyte is beneficial for further improving the high-temperature storage performance of the electrochemical device. Exemplarily, the value of d can be 0.1, 0.3, 0.6, 1.1, 1.3, 1.6, 2.2, 2.5, 2.8, 3.4, 3.6, 4, 4.4, 5, or a range consisting of any two of the above values.

[0025] In some embodiments, the electrolyte includes a trinitrile compound selected from at least one of 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, 1,3,5-pentanetricarbononitrile, or tricyanobenzene. The mass percentage of the trinitrile compound is e% based on the mass of the electrolyte, with a mass ratio of 1 ≤ d / e ≤ 2. The presence of the above-mentioned types and amounts of trinitrile compounds in the electrolyte further improves the high-temperature storage performance of the electrochemical device. Exemplarily, the value of d / e can be 1, 1.1, 1.3, 1.5, 1.8, 2, or a range consisting of any two of the above values.

[0026] In some embodiments, the electrolyte further includes substance B and ethylene carbonate, wherein substance B is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, or ethyl propionate, and the mass percentage of substance B is f% based on the mass of the electrolyte (25 ≤ f ≤ 50), and the mass percentage of ethylene carbonate is g% (10 ≤ g ≤ 20). In this case, the overall performance of the electrochemical device is superior, i.e., it is superior in room temperature cycling, high temperature cycling, and high temperature storage. Exemplarily, the value of f can be 25, 28, 30, 32, 35, 38, 40, 45, 50, or a range of any two of the above values. Exemplarily, the value of g can be 10, 12, 13, 15, 18, 19, 20, or a range of any two of the above values. For example, the value of f / g can be 0.5, 0.6, 0.8, 0.9, 1.2, 1.3, 1.5, 1.8, 2.0, 2.1, 2.3, 2.4, 2.8, 2.9, 3, or a range of any two of the above values.

[0027] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector can be 5 μm to 12 μm. This application also does not impose any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can contain copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors, etc.

[0028] The negative electrode material layer may also include a binder and a thickener. This application does not impose any particular restrictions on the types of binders and thickeners, as long as they can achieve the purpose of this application. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0029] The negative electrode material layer may also include a conductive agent. This application does not particularly limit the type of conductive agent, as long as it achieves the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, metallic materials, or conductive polymers. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode active layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved. Optionally, the negative electrode sheet may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active layer. This application does not particularly limit the composition of the conductive layer, and it can be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. This application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the conductive agent and binder in the aforementioned negative electrode active layer.

[0030] other

[0031] The lithium-ion secondary battery also includes a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., a composite current collector with a metal layer disposed on the surface of a polymer layer).

[0032] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be from 5 μm to 13 μm.

[0033] The positive electrode active material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may contain one or more lithium-containing composite metal oxides selected from the group consisting of cobalt, manganese, and nickel, or one or more lithium-containing olivine-type phosphates selected from iron, cobalt, nickel, and manganese. These positive electrode active materials can be used individually or in combination.

[0034] Suitable examples of such lithium composite metal oxides include, for instance, those selected from LiCoO2, LiMn2O4, LiNiO2, and LiCo. 1-x Ni x O2(0.01 <x<1)、LiNi x MnyCo z O2 (x+y+z=1), solid solutions of Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe, etc.), LiNi 1 / 2 Mn 3 / 2 O4, LiFePO4, LiMnPO4, and LiMn1-x Fe x One or more of PO4 (0.01 < x < 1), more preferably two or more. A part of these composite metal oxides with lithium or lithium-containing olivine-type phosphates can be replaced by other elements, or a part of cobalt, nickel, manganese, and iron can be replaced by one or two or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or coated with a compound containing these other elements or a carbon material. The present application does not particularly limit the thickness of the positive electrode active material layer, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm.

[0035] The positive electrode active material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNT), carbon fibers, Ketjen black, graphene, metal materials, or conductive polymers. The binder may include, but is not limited to, at least one of polyacrylic acid, polyacrylates, acrylate polymers, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, or vinylidene fluoride-hexafluoropropylene copolymer.

[0036] The present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer. Those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved.

[0037] The lithium ion secondary battery further includes a separator, which is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and does not affect the progress of the electrochemical charge and discharge process. The present application does not particularly limit the separator, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendared film, or a spun film.

[0038] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0039] In this application, the pore size of the separator is from 0.01 μm to 1 μm, and the thickness is from 5 μm to 50 μm. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0040] The electrochemical device of this application also includes a packaging bag for containing the positive electrode, the separator, the negative electrode, and the electrolyte, as well as other components known in the art in the electrochemical device. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0041] Lithium-ion secondary batteries can be prepared according to conventional methods in the art. Exemplarily, the above-mentioned positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes to obtain an electrode assembly. Alternatively, the electrode assembly can be obtained by winding. The electrode assembly is placed in a packaging shell, electrolyte is injected, and the shell is sealed to obtain a secondary battery. There are no particular limitations on the structure of lithium-ion secondary batteries; coin-shaped batteries, cylindrical batteries, prismatic batteries, or pouch batteries with single or multiple separators can be used.

[0042] The application of the lithium-ion secondary battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the lithium-ion battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0043] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Unless otherwise stated, all parts, percentages, and ratios listed are based on mass.

[0044] Example 1-1

[0045] (I) Preparation of Lithium-ion Batteries

[0046] <Preparation of Negative Electrode Sheets>

[0047] Si / C composite material (carbon nanopore-loaded Si), artificial graphite, lithium polyacrylate (PAA-Li) anode binder, and carbon nanotubes anode conductive agent were mixed in a mass ratio of 20:70:7:3. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain an anode slurry with a solid content of 30 wt%. The anode slurry was uniformly coated on one side of a copper foil anode current collector with a thickness of 12 μm and dried at 120 °C to obtain a single-sided coated anode electrode with a coating thickness of 143 μm. The above steps were repeated on the other side of the copper foil to obtain a double-sided coated anode electrode. After cold pressing and slitting, a 78 mm × 875 mm anode electrode was obtained. The silicon content in the silicon-based material is shown in Table 1 based on the mass of the anode active material.

[0048] <Preparation of the positive electrode>

[0049] Lithium cobalt oxide (LiCoO2), a positive electrode active material, Super P, and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred evenly in a vacuum mixer to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector and dried at 85°C to obtain a single-sided coated positive electrode sheet with a coating thickness of 110 μm. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After coating, the positive electrode sheet was cold-pressed and cut into 74 mm × 867 mm dimensions for later use. The compaction density of the positive electrode layer after cold pressing was 4.15 g / cm³. 3 .

[0050] <Preparation of Electrolyte>

[0051] In an argon-atmospheric glove box with a water content of less than 10 ppm, propylene carbonate (PC), propyl propionate (PP), and diethyl carbonate (DEC) were mixed in a mass ratio of 2:3:5 to obtain a base solvent. Then, Formula I-1 (Compound I), vinyl sulfate (Substance A), and lithium hexafluorophosphate were added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium hexafluorophosphate was 12.5%. The contents of Compound I and Substance A are shown in Table 1, with the remainder being the base solvent.

[0052] <Septum>

[0053] A porous polyethylene (PE) membrane with a thickness of 5 μm was used.

[0054] <Preparation of Lithium-ion Batteries>

[0055] The prepared positive electrode, separator, negative electrode, and separator are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, shaping, and capacity testing.

[0056] Examples 1-2 to 1-39

[0057] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0058] Examples 2-1 to 2-7

[0059] Based on the electrolytes of Examples 1-6, the substances in Table 2 were added to the base solvent during the preparation process, with the remainder being the base solvent, and the rest being the same as in Examples 1-6.

[0060] Examples 3-1 to 3-5

[0061] Based on the electrolytes of Examples 2-7, the substances listed in Table 3 were added to the base solvent during the preparation process, with the remainder being the base solvent, and the rest being the same as in Examples 1-1.

[0062] Comparative Examples 1 to 7

[0063] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0064] (II) Test Methods

[0065] 1. Testing of silicon content

[0066] A lithium-ion battery discharged at 0.5C to 3.0V was disassembled, and the negative electrode sheet was removed. It was then soaked in dimethyl carbonate (DMC) for 20 minutes, followed by rinsing with DMC and acetone respectively. The negative electrode sheet was then placed in an oven and baked at 80℃ for 12 hours to obtain the negative electrode sheet. The negative electrode sheet was then placed in a vacuum oven and dried at 100℃ for 24 hours. One gram of powdered negative electrode material layer was scraped off from the negative electrode sheet with a blade, and the mass percentage of silicon in the negative electrode material layer was determined using an ICP (Inductively Coupled Plasma) analyzer.

[0067] 2. Cyclic performance test

[0068] The lithium-ion battery was placed in a 25℃ / 45℃ constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 0.5C to 4.45V, followed by constant voltage charging to a current of 0.025C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V. This initial discharge capacity was recorded as C1, the initial thickness as D1, and the initial impedance as I1. This process was repeated 500 times. After 500 cycles, the discharge capacity C2, thickness D2, and impedance I2 were recorded. The cycle capacity retention rate of the lithium-ion battery was then calculated.

[0069] Capacity retention during ambient / high temperature cycling = C2 / C1 × 100%

[0070] The volume expansion rate during room temperature cycling is calculated as D2 / D1 × 100%, and the impedance growth rate during room temperature cycling is calculated as I2 / I1 × 100%.

[0071] 3. High-temperature storage test

[0072] The lithium-ion battery was placed in a constant temperature environment of 25℃ and left to stand for 30 minutes to reach the constant temperature state. It was then charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.025C. The thickness of the lithium-ion battery at this point was recorded as the initial thickness H0. The lithium-ion battery was then transferred to a constant temperature chamber at 60℃ and stored for 30 days. During this period, the thickness of the lithium-ion battery was measured and recorded every 6 days. The measured thickness recorded after 30 days was recorded as the storage thickness H1.

[0073] High-temperature storage volume expansion rate = (H1-H0) / H0×100%.

[0074] Table 1 Note: " / " in the table indicates that there are no relevant parameters.

[0075] Referring to Table 1, compared with Example 1-1, the mass ratio (a / b) of Compound I and Substance A in the electrolytes of Comparative Examples 1 to 7 is not within a suitable range; the content 'a' of Compound I in the electrolyte of Comparative Example 3 is not within a suitable range; the silicon content in the negative electrode sheets of Comparative Examples 4 to 5 is not within a suitable range; the electrolyte of Comparative Example 6 does not contain Substance A; and the electrolyte of Comparative Example 7 does not contain Compound I. As can be seen from Table 1, the room temperature performance of the lithium-ion batteries corresponding to Comparative Examples 1 to 7 is inferior to that of the lithium-ion batteries of Example 1-1. In particular, the volume expansion rate of the lithium-ion batteries of Comparative Examples 1 to 7 at room temperature is all above 17.9%, reaching a maximum of 23.3%, and their impedance growth rate at room temperature is also as high as 76.4%, reaching a maximum of 85.3%. The lithium-ion battery of Example 1-1 has a suitable silicon content and contains appropriate types and mass proportions of Formula I compound and substance A in the electrolyte. Its volume expansion rate at room temperature is only 14.3%, and the impedance growth rate is reduced to 74.8%.

[0076] In particular, further regulating the silicon content in the silicon-based material and the content of compound I and substance A in the electrolyte within the preferred range is beneficial to the synergistic effect among the three, and can further suppress the volume expansion and impedance growth of the electrochemical device at room temperature.

[0077] Table 2

[0078] As can be seen from Table 2, by further adding fluoroethylene carbonate and / or vinylene carbonate to the electrolyte containing compound I and substance A, and controlling the content of fluoroethylene carbonate and / or vinylene carbonate within the above range, it is possible to further improve the high-temperature performance of lithium-ion batteries while taking into account their room temperature cycle performance, especially to suppress their storage volume expansion at high temperatures.

[0079] In particular, when the electrolyte further contains dinitrile and trinitrile compounds, and the types and contents of dinitrile and trinitrile compounds are appropriate, the effect of improving the room temperature and high temperature performance of lithium-ion batteries is even better. In particular, it can further suppress the volume expansion rate under room temperature cycling and improve the storage volume expansion rate under high temperature.

[0080] Table 3

[0081] According to Table 3, when an appropriate amount of substance B is added to the electrolyte, and an appropriate amount of ethylene carbonate is added in combination, the overall performance of the electrochemical device is better, and the improvement in room temperature cycling capacity rate, high temperature cycling capacity rate and high temperature storage volume expansion rate is more obvious.

[0082] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a negative electrode and an electrolyte; The negative electrode sheet includes a negative electrode active material, which contains silicon-based material. Based on the mass of the negative electrode active material, the mass percentage of silicon element in the silicon-based material is Z1%, where 0.1 < Z1 < 15. The electrolyte includes a compound of formula I; Wherein, R is selected from fluorinated or unsubstituted C2-C6 alkyl groups, fluorinated or unsubstituted C6-C6 alkyl groups. 12 Nitrogen-containing heterocyclic groups, fluorine-substituted or unsubstituted C6-C 12 Aryl; The electrolyte also includes substance A, which is selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methane disulfonate. Based on the mass of the electrolyte, the mass percentage of compound I is a%, the mass percentage of substance A is b%, 0.5 ≤ a / b ≤ 20, and 0.5 ≤ a ≤ 20.

2. The electrochemical device according to claim 1, characterized in that, The compound of formula I includes at least one of the following compounds:

3. The electrochemical device according to claim 1, characterized in that, At least one of the following conditions must be met: (1) 0.1 ≤ a / Z1 ≤ 6; (2)0.3≤b≤8。 4. The electrochemical device according to any one of claims 1 to 3, characterized in that, The electrolyte comprises fluoroethylene carbonate and / or vinylene carbonate; Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is c1%, and the mass percentage of the vinylene carbonate is c2%, satisfying: 12≤(c1+c2×60)≤25.

5. The electrochemical device according to claim 4, characterized in that, 0.5≤(c1+c2×60) / Z1≤10.

6. The electrochemical device according to claim 4, characterized in that, The electrolyte includes dinitrile compounds; The dinitrile compound is selected from at least one of butadionitrile, adiponitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether or 1,4-dicyano-2-butene; Based on the mass of the electrolyte, the mass percentage of the dinitrile compound is d%, 0.1≤d≤5.

7. The electrochemical device according to claim 6, characterized in that, The electrolyte includes trinitrile compounds; The trinitrile compound is selected from at least one of 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, 1,3,5-pentanetricarbonitrile, or tricyanobenzene; Based on the mass of the electrolyte, the mass percentage of the trinitrile compound is e%, 1≤d / e≤2.

8. The electrochemical device according to any one of claims 1 to 3, characterized in that, The electrolyte also includes substance B and ethylene carbonate; The substance B is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, or ethyl propionate. Based on the mass of the electrolyte, the mass percentage of substance B is f%, 10≤f≤50, and the mass percentage of ethylene carbonate is g%, 10≤g≤20.

9. The electrochemical device according to claim 8, characterized in that, 0.5≤f / g≤3.

10. An electronic device, characterized in that, The electronic device includes the electrochemical device according to any one of claims 1 to 9.

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