Electrolyte solution, electrochemical device including same, and electronic device

Abstract

The present application provides an electrolyte comprising a compound of formula I and fluoroethylene carbonate, # imgabs0 # R1 is selected from a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group, and a substituted or unsubstituted C1-C2 alkenyl group, and # imgabs0 # R2 is selected from a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group, and a substituted or unsubstituted C1-C2 alkenyl group. R1 is selected from a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group and a substituted or unsubstituted C1-C2 alkenyl group, R2 is selected from O, a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group and a substituted or unsubstituted C1-C2 alkenyl group, R3 is selected from a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group and a substituted or unsubstituted C1-C2 alkenyl group, and on the basis of the total weight of the electrolyte, R1 is selected from a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group and a substituted or unsubstituted C1-C2 alkenyl group, and R2 is selected from a substituted or unsubstituted C1-C2 alkoxy group and a substituted or unsubstituted C1-C2 alkenyl group. The content W1 of the compound in the formula I is 10-40 wt%, and the content W2 of the fluoroethylene carbonate is 2-10 wt%. The invention also provides an electrochemical device and an electronic device comprising the electrolyte.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage, and particularly to an electrolyte and an electrochemical device including the same. Background Art

[0002] Electrochemical devices, such as lithium-ion batteries, are widely used in consumer electronics (such as mobile phones, laptops, cameras, etc.), energy storage products (home energy storage, energy storage power stations, UPS power supplies, etc.), new energy vehicles and other fields and industries due to their advantages of high energy density, high working voltage platform, low self-discharge, long service life and environmental friendliness. The electrolyte is an important component of lithium batteries and is regarded as the "blood" of the battery. The electrolyte of lithium-ion batteries mainly consists of lithium salts, solvents and additives, among which the mass ratio of the solvent exceeds 80%. Since 1994, the commercial electrolyte solvent system has hardly changed, and carbonate compounds are generally used. However, recent studies have shown that the electrolyte plays an important role in the initiation, exacerbation and final eruption of lithium battery thermal runaway. There is evidence that the heat in the electrolyte mainly comes from the interaction between the cyclic ethylene carbonate EC solvent and the positive electrode material. In addition, the EC solvent forms a loose organic SEI film on the surface of negative electrodes such as graphite and silicon, which cannot prevent the continuous corrosion of the negative electrode by the electrolyte, thereby causing the attenuation of the battery life.

[0003] Therefore, there is a need in the art for an electrolyte with low heat, weak film-forming activity and no negative impact on battery performance. Summary of the Invention

[0004] In a first aspect of the present application, the present application provides an electrolyte, which comprises a compound of Formula I and fluoroethylene carbonate,

[0005]

[0006] R1 is selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy and substituted or unsubstituted C1-C2 alkenyl, R2 is selected from O, substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy and substituted or unsubstituted C1-C2 alkenyl, R3 is selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy and substituted or unsubstituted C1-C2 alkenyl,

[0007] Wherein, based on the total weight of the electrolyte, the content W1 of the compound of Formula I is 10% by weight to 40% by weight, and the content W2 of the fluoroethylene carbonate is 2% by weight to 10% by weight.

[0008] The compound of formula I according to the present invention has a high boiling point, a low melting point, a moderate viscosity, a large polarity, and a reduced heat generation of interaction with the positive electrode, and the active material in the positive electrode is, for example, LiNi m Co n A (1-m-n) O2, where A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium, and tungsten, 0.7 ≤ m ≤ 1, 0 ≤ n ≤ 0.3, and m + n ≤ 1. In addition, the compound of formula I according to the present invention has very stable electrochemical activity during battery cycling. Compared with the interfacial film (CEI / SEI) generated by the decomposition of ethylene carbonate (EC) solvent, the compound of formula I rarely decomposes on the surfaces of the positive and negative electrodes. Therefore, it can reduce the consumption of the electrolyte, lower the interfacial impedance of the battery, and improve the kinetic performance of the electrode material at the same time.

[0009] Thus, by using the compound of formula I according to the present invention in the electrolyte, the heat generation of interaction between the electrolyte and the positive electrode material can be effectively reduced. At the same time, the gas generation during battery cycling can be reduced, and the interfacial side reactions between the electrolyte and the positive and negative electrodes can be inhibited, thereby significantly improving the cycling performance of the battery.

[0010] The electrolyte according to the present invention further contains fluoroethylene carbonate (FEC). By using the compound of formula I and FEC in combination to form a solid electrolyte interfacial film CEI / SEI with a high content of inorganic compounds (such as LiF) on the surface of the active material layer, the interfacial impedance of lithium ion transmission at the battery positive and negative electrode interfaces can be reduced, the stability of the interfacial films of the battery positive and negative electrodes can be improved, and the side reactions on the surface of the electrode sheet can be reduced, thereby prolonging the battery life and improving the rate performance of the battery.

[0011] In some embodiments, R1 is a fluorine-substituted alkyl group, and / or R2 is a fluorine-substituted alkyl group.

[0012] In some embodiments, when W1 is too high and W2 is too low, the solubility of the lithium salt will be reduced and the cycling performance of the battery will deteriorate. When W1 is too low and W2 is too high, the heat of interaction between the electrolyte and the positive electrode cannot be effectively reduced. Therefore, 0 wt% ≤ W1 - 2W2 ≤ 30 wt% is set.

[0013] In some embodiments, W1 is 20 wt% to 40 wt%. In some embodiments, W2 is 5 wt% to 10 wt%. In some embodiments, 0 wt% ≤ W1 - 2W2 ≤ 10 wt%. Thus, more excellent stability (such as a lower thickness change rate) and cycling performance are obtained.

[0014] In some embodiments, the electrolyte further comprises lithium bis(fluorosulfonyl)imide (LiFSI), and based on the total weight of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 5 wt% to 20 wt%. LiFSI has higher solubility and conductivity compared to conventionally used lithium salts (such as LiPF6). When LiFSI is used in the electrolyte according to the present invention, since the compound of formula I has a particularly strong dissociation ability for LiFSI, the combined use of LiFSI and the compound of formula I can particularly provide excellent ionic conductivity for the electrolyte.

[0015] In some embodiments, the electrolyte further includes cyclic carbonates. Based on the total weight of the electrolyte, the content of cyclic carbonates in the electrolyte is below 10 wt%, and the cyclic carbonates include at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and hexylene carbonate, thereby reducing the interaction heat between the electrolyte and the positive electrode.

[0016] Thus, even if the lithium salt in the electrolyte according to the present invention forms an interfacial film on the surface of the electrode sheet, such an interfacial film is much denser than the interfacial film formed by the decomposition of EC. The interfacial film formed by the decomposition of EC is relatively loose and cannot prevent the contact between the electrolyte and the electrode active material, which will lead to the continuous occurrence of side reactions and continuous gas generation, especially serious at high temperatures. Significantly different, the dense interfacial film formed by the lithium salt in the electrolyte of the present invention can effectively prevent the continued contact between the electrolyte and the active material in the electrode sheet, thereby inhibiting gas generation.

[0017] In some embodiments, the compound of formula I comprises a compound of formula I'.

[0018]

[0019] Wherein, R4 is selected from a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group, and a substituted or unsubstituted C1-C2 alkenyl group.

[0020] In some embodiments, the compound of formula I includes at least one of the following:

[0021]

[0022] In some embodiments, the compound of formula I includes formula I-3.

[0023] In some embodiments, the electrolyte further includes a chain carbonate, and wherein, based on the total weight of the electrolyte, the content of the chain carbonate is 35 wt% to 70 wt%, and the chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate.

[0024] In some embodiments, the electrolyte further includes an additive, and based on the total weight of the electrolyte, the content of the additive is 1 wt% to 5 wt%, and the additive includes at least one of vinylene carbonate, ethylene vinylene carbonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, and cyclic sulfonate.

[0025] In some embodiments, the electrolyte further includes a non-sulfonylimide lithium salt, and based on the total weight of the electrolyte, the content of the non-sulfonylimide lithium salt is 2 wt% to 10 wt%, and the non-sulfonylimide lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiOTf), lithium bis(oxalato)borate (LiBOB), lithium bis(fluoromalonate)borate (LiBFMB), and lithium difluoro(oxalato)borate (LiDFOB).

[0026] In some embodiments, the electrolyte further contains lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, ethyl methyl carbonate, and vinylene carbonate, wherein based on the total weight of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 5 wt% to 15 wt%, the content of lithium hexafluorophosphate is 2 wt% to 10 wt%, the content of ethyl methyl carbonate is 35 wt% to 65 wt%, and the content of vinylene carbonate is 1 wt% to 5 wt%.

[0027] In a second aspect of the present application, the present application provides an electrochemical device, which includes the electrolyte according to the first aspect of the present application.

[0028] In a third aspect of the present application, the present application provides an electronic device, which includes the electrochemical device according to the second aspect of the present application. Detailed Description

[0029] Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the scope of the claims of the present application. Unless otherwise expressly specified, the following terms used herein have the meanings set forth below.

[0030] As used herein, the term "about" is used to describe and account for small variations. When used in conjunction with an event or circumstance, the term can refer to instances where the event or circumstance occurs precisely as well as instances where it occurs approximately. For example, when used in conjunction with a numerical value, the term can refer to a range of variation of plus or minus 10% of the numerical value, such as plus or minus 5%, plus or minus 4%, plus or minus 3%, plus or minus 2%, plus or minus 1%, plus or minus 0.5%, plus or minus 0.1%, or plus or minus 0.05%. Additionally, sometimes quantities, ratios, and other numerical values are presented herein in a range format. It should be understood that such range formats are for convenience and brevity and should be interpreted flexibly to include not only the explicitly specified numerical values that are range limitations, but also all individual numerical values or sub-ranges subsumed within the range as if each numerical value and sub-range were explicitly specified.

[0031] In the detailed description and claims, a list of items joined by the term "one of" can mean any one of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0032] In the detailed description and claims, a list of items joined by the term "at least one of", "at least one kind of", or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" or "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" or "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0033] In the detailed description and claims, for expressions regarding the number of carbon atoms, i.e., the number following the capital letter "C", such as "C1-C 10 ", "C3-C 10 ", etc., the numbers following "C" such as "1", "3", or "10" represent the number of carbon atoms in a specific functional group. That is, the functional groups can include 1 - 10 carbon atoms and 3 - 10 carbon atoms respectively. For example, "C1-C4 alkyl" or "C1-4 "Alkyl" refers to an alkyl group having 1 to 4 carbon atoms, such as CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, CH3CH2CH(CH3)-, or (CH3)3C-.

[0034] As used herein, the term "alkyl" refers to a straight-chain saturated hydrocarbon structure having 1 to 10 carbon atoms. "Alkyl" is also expected to be a branched or cyclic hydrocarbon structure having 3 to 10 carbon atoms. For example, the alkyl group can be an alkyl group having 1 - 10 carbon atoms, an alkyl group having 1 - 8 carbon atoms, an alkyl group having 1 - 6 carbon atoms, or an alkyl group having 1 - 4 carbon atoms. When specifying an alkyl group with a specific number of carbons, all geometric isomers with that number of carbons are expected to be covered; thus, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; "propyl" includes n-propyl, isopropyl, and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc. Additionally, the alkyl group can be optionally substituted.

[0035] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group that can be straight-chain or branched and has at least one, and usually 1, 2, or 3 carbon-carbon double bonds. Unless otherwise defined, the alkenyl group generally contains 2 - 10 carbon atoms, and can be, for example, an alkenyl group having 2 - 8 carbon atoms, an alkenyl group having 2 - 6 carbon atoms, or an alkenyl group having 2 - 4 carbon atoms. Representative alkenyl groups include (for example) vinyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, etc. Additionally, the alkenyl group can be optionally substituted.

[0036] When the above substituents are substituted, unless otherwise specified, they are substituted with one or more halogens.

[0037] I. Electrochemical Device

[0038] The electrochemical device of the present application includes any device that undergoes an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery or a sodium secondary battery, including a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, a lithium-ion polymer secondary battery, a sodium-ion secondary battery, a sodium polymer secondary battery, or a sodium-ion polymer secondary battery.

[0039] In some embodiments, the electrochemical device of the present application includes an electrolyte, a positive electrode, a negative electrode, and a separator.

[0040] Electrolyte

[0041] The electrolyte according to the present application contains the compound of Formula I and fluoroethylene carbonate.

[0042]

[0043] R1 is selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, and substituted or unsubstituted C1-C2 alkenyl.

[0044] R2 is selected from O, substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, and substituted or unsubstituted C1-C2 alkenyl.

[0045] R3 is selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, and substituted or unsubstituted C1-C2 alkenyl.

[0046] Wherein, based on the total weight of the electrolyte, the content W1 of the compound of Formula I is 10% by weight to 40% by weight, and the content W2 of the fluoroethylene carbonate is 2% by weight to 10% by weight.

[0047] In some embodiments, W1 is, for example, 10% by weight, 15% by weight, 20% by weight, 25% by weight, 30% by weight, 35% by weight, or any range formed by them. In some embodiments, W2 is, for example, 2% by weight, 4% by weight, 6% by weight, 8% by weight, 10% by weight, or any range formed by them.

[0048] In some embodiments, W1 - 2W2 is, for example, 5% by weight, 10% by weight, 15% by weight, 20% by weight, 25% by weight, or any range formed by them.

[0049] In some embodiments, the electrolyte further includes cyclic carbonate. Based on the total weight of the electrolyte, the content of the cyclic carbonate is below 10% by weight, for example, below 9% by weight, below 8% by weight, below 7% by weight, below 6% by weight, below 5% by weight, below 4% by weight, below 3% by weight.

[0050] In some embodiments, the electrolyte further includes linear carbonate. Based on the total weight of the electrolyte, the content of the linear carbonate is 35% by weight to 70% by weight, for example, 35% by weight, 40% by weight, 45% by weight, 50% by weight, 55% by weight, 60% by weight, 65% by weight, 70% by weight, or any range formed by them.

[0051] In some embodiments, the electrolyte further contains lithium bis(fluorosulfonyl)imide. Based on the total weight of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 5 wt% to 20 wt%, such as 5 wt%, 10 wt%, 15 wt%, 20 wt%, or any range composed of them.

[0052] In some embodiments, the electrolyte further includes a non-sulfonylimide lithium salt. Based on the total weight of the electrolyte, the content of the non-sulfonylimide lithium salt is 2 wt% to 10 wt%, such as 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt%, or any range composed of them.

[0053] The non-sulfonylimide lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, lithium bis(fluoromalonate)borate, and lithium difluoro(oxalato)borate.

[0054] In some embodiments, the electrolyte further includes an additive. Based on the total weight of the electrolyte, the content of the additive is 1 wt% to 5 wt%, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any range composed of them.

[0055] The additive includes at least one of vinylene carbonate, ethylene vinylene carbonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, and cyclic sulfonate.

[0056] The electrolyte used in the electrochemical device of the present application is any of the above electrolytes of the present application.

[0057] Positive electrode

[0058] In some embodiments, the positive electrode includes a current collector and a positive electrode active material layer located on the current collector. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer further includes a binder and optionally includes a conductive material. The binder improves the binding between the positive electrode active material particles and also improves the binding between the positive electrode active material and the current collector.

[0059] In some embodiments, the current collector can be aluminum, but is not limited thereto.

[0060] In some embodiments, the positive electrode active material includes at least one selected from lithium nickel transition metal oxides. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in the formula LiNi m Co n A (1-m-n)As shown in O2, where A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium, and tungsten, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in the formula LiNi m Co n A (1-m-n) O2, where A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium, and calcium, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1.

[0061] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM523, NCM622, NCM811, Ni90 (i.e., NCM90), Ni92 (i.e., NCM92), or Ni95 (i.e., NCM900).

[0062] In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in the formula LiNi m Co n A (1-m-n) O2, where A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium, and tungsten, 0.7 ≤ m ≤ 1, 0 ≤ n ≤ 0.3, and m + n ≤ 1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in the formula LiNi m Co n A (1-m-n) O2, where A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium, and calcium, 0.7 ≤ m ≤ 1, 0 ≤ n ≤ 0.3, and m + n ≤ 1.

[0063] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM811, Ni90, Ni92, or Ni95.

[0064] Negative electrode

[0065] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0066] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector, such as copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0067] In some embodiments, the negative electrode active material includes, but is not limited to: lithium metal, structured lithium metal, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithiated TiO2-Li4Ti5O with a spinel structure 12 , Li-Al alloy, or any combination thereof. The silicon-carbon composite refers to a material that contains at least about 5% by mass of silicon based on the mass of the silicon-carbon negative electrode active material.

[0068] In some embodiments, the negative electrode active material contains at least one of artificial graphite, natural graphite, hard carbon, soft carbon, silicon carbide compound, and silicon oxide compound.

[0069] In some embodiments, the negative electrode active material layer further includes a binder, and in some embodiments, the negative electrode active material layer further includes a conductive agent.

[0070] In some embodiments, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. The silicon-based material includes at least one of silicon, silicon alloy, silicon oxide compound, and silicon carbide compound. In some embodiments, the silicon-based material includes a silicon oxide compound and / or a silicon carbide compound. In some embodiments, the negative electrode active material further includes a carbon-based material, and the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotube, and graphene.

[0071] In some embodiments, based on the mass of the negative electrode active material, the mass content g% of the silicon-based material satisfies: 8 ≤ g ≤ 100. In some embodiments, g is 10, 12, 14, 16, 18, 20, 22, 25, 28, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or a range formed by any two of these values. In some embodiments, 10 ≤ g ≤ 50. In other embodiments, 12 ≤ g ≤ 35.

[0072] Separator

[0073] In some embodiments, a separator is provided between the positive electrode and the negative electrode in the electrochemical device of the present application to prevent short circuit. There are no particular limitations on the material and shape of the separator used in the electrochemical device of the present application, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer, an inorganic substance, etc. formed of a material stable to the electrolyte of the present application.

[0074] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.

[0075] In some embodiments, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In some embodiments, the separator includes a porous substrate and a coating layer, and the coating layer includes inorganic particles and a binder.

[0076] II. Electronic Device

[0077] The electronic device of the present application can be any device using the electrochemical device of the present application.

[0078] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, energy storage systems, etc. In order to meet the device's requirements for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

[0079] In other embodiments, the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0080] In order to achieve the above object and enable those skilled in the art to understand the solution of the present application, the following gives examples of the specific implementation schemes adopted by the present application. It should be noted that the described embodiments are only partial embodiments of the present application, rather than all embodiments.

[0081] III. Test Method

[0082] 1. Test of the interaction heat between the electrolyte and the positive electrode

[0083] First, charge the battery cell to 4.25V and then disassemble it. Take out the positive electrode plate and scrape the powder on the surface of the positive electrode plate; then soak these powders three times with a dimethyl carbonate solvent to thoroughly remove the lithium salt on the surface, and then dry it. Finally, add the obtained positive electrode powder and the electrolyte to a high-pressure crucible in a glove box at a ratio of 6mg:3mg and perform a DSC test. The temperature range is from 25°C to 450°C, and the DSC heating rate is 5°C / min. The heat generated by the electrolyte and the positive electrode powder is the area of the peak obtained from the test, and the specific value can be directly read in the DSC test software.

[0084] 2. DCR test after battery formation

[0085] The battery cell is discharged at a constant current of 1C to the cut-off voltage (3.0V), left to stand for 1h at 20±2℃, then charged at a current of 1C for 18min to adjust the SOC to 30%, left to stand for 1h, then charged at 3C for 1.5min, left to stand for 1h, then discharged at 9C for 0.5min, left to stand for 1h, and then charged at 1C for 6min to adjust the SOC to 40%, left to stand for 1h. Such cycles are repeated until the SOC reaches 70%, and the DCR value is obtained through the calculation formula R = ΔU / ΔI.

[0086] 3. Capacity Retention Rate Test

[0087] 25℃ 1C / 1C cycle 500: Under the condition of 25℃, the above lithium-ion battery is charged at a constant current and constant voltage of 1C to 4.25V, and then discharged at a constant current of 1C to 2.5V. After 500 charge-discharge cycles, calculate the capacity retention rate after the 500th cycle at 25℃ according to the following formula: Discharge capacity after the 500th cycle / Discharge capacity of the first cycle × 100%.

[0088] 25℃ 2C / 2C cycle 300: Under the condition of 25℃, the above lithium-ion battery is charged at a constant current and constant voltage of 2C to 4.25V, and then discharged at a constant current of 2C to 2.5V. After 300 charge-discharge cycles, calculate the capacity retention rate after the 300th cycle at 25℃ according to the following formula: Discharge capacity after the 300th cycle / Discharge capacity of the first cycle × 100%.

[0089] 4. Thickness Change Rate Test

[0090] The battery is discharged at 0.5C to 3.0V at 25℃, then charged at 0.5C to 4.45V, and charged at a constant voltage of 4.45V until the current is 0.05C. The thickness of the battery is measured at this time using a PPG soft-pack battery thickness gauge and recorded as a. The battery is placed in an oven and stored at a constant voltage of 4.45V at 45℃ for 30 days, and the thickness after 30 days is measured and recorded as b. The calculation formula for the thickness expansion rate is: (b - a) / a × 100%.

[0091] Example 1

[0092] Preparation of the negative electrode: The negative electrode active material silicon-graphite composite (where the ratio of artificial graphite and silicon-based material (SiOx, 0.5≤x≤1.5) is 14:86), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickener sodium carboxymethyl cellulose, and polyacrylic acid are mixed in a weight ratio of 96:2:1.5:1:0.5, and deionized water is added and stirred to obtain the negative electrode slurry; the negative electrode slurry is evenly coated on an 8μm negative electrode current collector copper foil; the coated copper foil is dried at 85℃, and then after cold pressing, slicing, and slitting, it is dried in a vacuum at 120℃ for 12 hours to obtain the negative electrode.

[0093] Preparation of the positive electrode: Mix the positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2, the conductive materials carbon nanotubes, acetylene black, and the binder polyvinylidene fluoride in a mass ratio of 95:2:1:2, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer to obtain a positive electrode slurry; uniformly coat the positive electrode slurry on a 12-μm positive electrode current collector aluminum foil; dry the coated aluminum foil at 85°C, and then after cold pressing, slicing, and slitting, dry it under vacuum conditions at 85°C for 4 hours to obtain the positive electrode.

[0094] Preparation of the electrolyte: In a dry argon atmosphere glove box, based on the total weight of the electrolyte, mix 8 wt% of LiPF6, 10 wt% of LiFSI (lithium bis(fluorosulfonyl)imide), 20 wt% of the compound of formula I, 55 wt% of EMC (ethyl methyl carbonate), and 2 wt% of VC (vinylene carbonate) evenly to obtain the electrolyte.

[0095] Preparation of the separator: A PP / PE / PP three-layer composite separator.

[0096] Assembly of the lithium-ion battery: Stack the positive electrode, separator, and negative electrode in sequence, with the separator between the positive and negative electrode sheets, then after winding and welding the tabs, place them in an outer packaging aluminum-plastic film, inject the above-mentioned electrolyte, let it stand at 45°C for 48 h, and then perform high-temperature jig formation (formation conditions: pressure 210 kgf, charge at 0.05C current to 4.2V, stand for 60 min, then charge at 0.1C to 4.2V, and then discharge at 0.2C to 3.0V, repeat twice, the formation temperature is provided in Table 1), and then after secondary sealing, perform conventional grading.

[0097] Examples 2-9 and Comparative Examples 1-8

[0098] Examples 2-9 and Comparative Examples 1-8 were carried out with reference to Example 1, except that the contents of the compound of formula I, cyclic carbonate, FEC, and EMC were selected according to Table 1.

[0099] Table 1

[0100]

[0101] Note: " / " indicates non-existence.

[0102] The contents of each component in Table 1 are calculated based on the total weight of the electrolyte.

[0103] Although the illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as a limitation of the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principles, and scope of the present application, and these changes, substitutions, and modifications also fall within the protection scope of the present application.

Claims

1. An electrolyte, characterized in that, The electrolyte contains a compound of Formula I and fluoroethylene carbonate, R1 is selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, and substituted or unsubstituted C1-C2 alkenyl, R2 is selected from O, substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, and substituted or unsubstituted C1-C2 alkenyl, R3 is selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, and substituted or unsubstituted C1-C2 alkenyl, wherein, based on the total weight of the electrolyte, the content W1 of the compound of Formula I is 10% by weight to 40% by weight, and the content W2 of the fluoroethylene carbonate is 2% by weight to 10% by weight.

2. The electrolyte according to claim 1, characterized in that, R1 is a fluorine-substituted alkyl, and / or R2 is a fluorine-substituted alkyl.

3. The electrolyte according to claim 1, characterized in that, 0% by weight ≤ W1 - 2W2 ≤ 30% by weight.

4. The electrolyte according to claim 1, characterized in that, The electrolyte further contains lithium bis(fluorosulfonyl)imide, and based on the total weight of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 5% by weight to 20% by weight.

5. The electrolyte according to claim 1 or 2, characterized in that, The compound of Formula I contains a compound of Formula I', wherein, R4 is selected from substituted or unsubstituted C1-C2 alkyl, substituted or unsubstituted C1-C2 alkoxy, and substituted or unsubstituted C1-C2 alkenyl.

6. The electrolyte according to claim 1, characterized in that, Satisfy at least one of the following: (a) W1 is 20% by weight to 40% by weight; (b) W2 is 5% by weight to 10% by weight; (c) 0% by weight ≤ W1 - 2W2 ≤ 10% by weight.

7. The electrolyte according to claim 1, characterized in that, The compound of Formula I includes at least one of the following:

8. The electrolyte according to claim 1, characterized in that, Satisfy at least one of the following: (i) The electrolyte further includes a cyclic carbonate, and based on the total weight of the electrolyte, the content of the cyclic carbonate is below 10% by weight; (ii) The electrolyte further includes a linear carbonate, and based on the total weight of the electrolyte, the content of the linear carbonate is 35% by weight to 70% by weight; (iii) The electrolyte further includes an additive, and based on the total weight of the electrolyte, the content of the additive is 1% by weight to 5% by weight; (iv) The electrolyte further includes a non-sulfonylimide lithium salt, and based on the total weight of the electrolyte, the content of the non-sulfonylimide lithium salt is 2% by weight to 10% by weight.

9. The electrolyte according to claim 8, characterized in that, The cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and hexenylene carbonate; The linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate; The additive includes at least one of vinylene carbonate, ethylene vinyl ether carbonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, and cyclic sulfonate; The non-sulfonylimide lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, lithium bis(fluoromalonate)borate, and lithium difluoro(oxalato)borate.

10. The electrolyte according to claim 1, characterized in that, The electrolyte further comprises lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, ethyl methyl carbonate and vinylene carbonate, wherein based on the total weight of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 5 wt% to 15 wt%, the content of lithium hexafluorophosphate is 2 wt% to 10 wt%, the content of ethyl methyl carbonate is 35 wt% to 65 wt%, and the content of vinylene carbonate is 1 wt% to 5 wt%.

11. An electrochemical device, characterized in that, The electrochemical device comprises the electrolyte according to any one of claims 1 to 10.

12. An electronic device, characterized in that, The electronic device comprises the electrochemical device according to claim 11.

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