Electrolyte solution, electrochemical device and electronic device

Abstract

An electrolyte solution, an electrochemical device and an electronic device. The electrolyte solution comprises at least two of an additive I, an additive II and an additive III. The additive I is selected from at least one additive in a group consisting of a compound as represented by formula 1a below, a compound as represented by formula 1b, and lithium difluorophosphate; the additive II is selected from at least one additive in a group consisting of lithium fluorosulfonate, bis(fluorosulfonyl)imide, and bis(trifluoromethanesulfonyl)imide; and the additive III is selected from at least one additive in a group consisting of lithium difluoro(oxalato)borate, lithium bis(oxalato)borate and lithium tetrafluoroborate. The electrolyte solution can improve the low-temperature characteristics, impedance and thickness swelling rate of an electrochemical device.

Description

Electrolytes, electrochemical devices, and electronic devices Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and in particular to electrolytes, electrochemical devices, and electronic devices. Background Art

[0002] Electrochemical devices (e.g., lithium-ion batteries) have the advantages of high energy storage density, high open-circuit voltage, low self-discharge rate, long cycle life, and good safety. With the widespread use of electronic devices, research on electrochemical devices with high energy density as power sources has been actively carried out.

[0003] Conventional non-aqueous electrolyte solutions struggle to achieve good low-temperature output characteristics and high-temperature stability due to the formation of a non-uniform solid electrolyte interface (SEI) film. Furthermore, when electrolyte additives are included in the electrolyte, side reactions caused by the additives can occur, leading to an increase in the irreversible capacity of the electrochemical device.

[0004] Summary of the Invention

[0005] The present application provides an electrolyte, the electrolyte comprising at least two of additives I, II, and III. Additive I is selected from at least one additive in the group consisting of a compound represented by Formula 1a, a compound represented by Formula 1b, or lithium difluorophosphate.

[0006] Additive II is at least one selected from the group consisting of lithium fluorosulfonate, bisfluorosulfonimide, and bistrifluoromethanesulfonimide; and Additive III is at least one selected from the group consisting of lithium difluorooxalatoborate, lithium bisoxalatoborate, and lithium tetrafluoroborate. The electrolyte additive provided herein can form a uniform solid electrolyte interface (SEI) film and positive electrode electrolyte (CEI) film, exhibiting good low-temperature performance, low impedance, and low thickness expansion.

[0007] In some embodiments, Additive I comprises a compound represented by Formula 1a, and Additive II comprises lithium fluorosulfonate. In some embodiments, Additive I comprises a compound represented by Formula 1a, and Additive II comprises bisfluorosulfonyl imide. In some embodiments, Additive I comprises a compound represented by Formula 1a, and Additive II comprises bistrifluoromethanesulfonyl imide. In some embodiments, Additive I comprises a compound represented by Formula 1a, and Additive III comprises lithium difluorooxalatoborate. In some embodiments, Additive I comprises a compound represented by Formula 1a, and Additive III comprises lithium bisoxalatoborate. In some embodiments, Additive I comprises a compound represented by Formula 1a, and Additive III comprises lithium tetrafluoroborate. In some embodiments, Additive I comprises a compound represented by Formula 1b, and Additive II comprises lithium fluorosulfonate. In some embodiments, Additive I comprises a compound represented by Formula 1b, and Additive II comprises bisfluorosulfonyl imide. In some embodiments, Additive I comprises a compound represented by Formula 1b, and Additive II comprises bistrifluoromethanesulfonyl imide. In some embodiments, Additive I comprises a compound represented by Formula 1b, and Additive III comprises lithium difluorooxalatoborate. In some embodiments, Additive I comprises a compound represented by Formula 1b, and Additive III comprises lithium bisoxalatoborate. In some embodiments, additive I includes a compound represented by formula 1b, and additive III includes lithium tetrafluoroborate. In some embodiments, additive I includes lithium difluorophosphate, and additive II includes lithium fluorosulfonate. In some embodiments, additive I includes lithium difluorophosphate, and additive II includes bisfluorosulfonyl imide. In some embodiments, additive I includes lithium difluorophosphate, and additive II includes bistrifluoromethanesulfonyl imide. In some embodiments, additive I includes lithium difluorophosphate, and additive III includes lithium difluorooxalatoborate. In some embodiments, additive I includes lithium difluorophosphate, and additive III includes lithium bisoxalatoborate. In some embodiments, additive I includes lithium difluorophosphate, and additive III includes lithium tetrafluoroborate. Conventional additive ingredients may not be fully decomposed under low or high temperature conditions, and the electrolyte including the above-mentioned additives can ensure that the electrochemical device has good low temperature performance, low impedance and low thickness expansion rate.

[0008] In some embodiments, the mass content of additive I in the electrolyte is a, where 0.01% ≤ a ≤ 5%. In some embodiments, the mass content of additive II in the electrolyte is b, where 0.01% ≤ b ≤ 5%. In some embodiments, the mass content of additive III in the electrolyte is c, where 0.01% ≤ c ≤ 5%. In some embodiments, a is 0.1%, 0.2%, 0.3%, 1%, 1.6%, 2.5%, 3%, 3.2%, or a range between any two of these values. In some embodiments, b is 0.05%, 0.1%, 0.2%, 0.3%, 1%, 1.3%, 2%, or a range between any two of these values. In some embodiments, c is 0.05%, 0.1%, 0.2%, or a range between any two of these values. When the additive content in the electrolyte is within the above range, the low-temperature capacity retention of the electrochemical device can be significantly improved through the multi-component SEI and CEI membranes, and the impedance and thickness expansion rate can be further reduced.

[0009] In some embodiments, when the electrolyte includes additive I and additive II, 0.1≤a / b≤50. In some embodiments, when the electrolyte includes additive II and additive III, 0.1≤b / c≤50. In some embodiments, when the electrolyte includes additive I and additive III, 0.1≤a / c≤50. In some embodiments, when the electrolyte includes additive I and additive II, 0.1≤a / b≤40. In some embodiments, when the electrolyte includes additive II and additive III, 0.1≤b / c≤40. In some embodiments, when the electrolyte includes additive I and additive III, 0.5≤a / c≤45. Electrolyte additive components that satisfy the above content relationship can further avoid the occurrence of side reactions, and the SEI and CEI film thicknesses are moderate, thereby improving the cycle performance of the electrochemical device and reducing impedance.

[0010] In some embodiments, the electrolyte further includes an organic solvent, wherein the organic solvent includes at least one of ethyl propionate or propyl propionate. In some embodiments, the ethyl propionate content of the electrolyte is 20% to 60% by weight. In some embodiments, the propyl propionate content of the electrolyte is 32% to 47% by weight. Electrolytes meeting the above conditions can effectively inhibit the dissociation and dissolution of transition metals and reduce performance fluctuations of electrochemical devices at different temperatures.

[0011] In some embodiments, the electrolyte further comprises an additive IV as shown in Formula 2,

[0012] Where X1 is CH or N, R a is substituted or unsubstituted C1-C 20 alkyl.

[0013] In some embodiments, the electrolyte contains additive IV in an amount ranging from 0.01% to 4% by weight. In some embodiments, the electrolyte contains additive IV in an amount ranging from 1.2% to 1.9% by weight. Additive IV has excellent low- and high-temperature stability, providing positive effects without increasing electrolyte viscosity, thereby further reducing impedance. In some embodiments, the electrolyte further comprises at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8.

[0014] The present application also provides an electrochemical device comprising the above-mentioned electrolyte.

[0015] The present application also provides an electronic device comprising the above-mentioned electrochemical device.

[0016] The electrolyte provided in the present application can improve the effect of forming a solid electrolyte interface (SEI) on the positive electrode surface and the negative electrode surface, thereby enhancing the interfacial passivation effect, and has good stability under both low and high temperature conditions, which can improve the low-temperature characteristics, impedance and thickness expansion rate of the electrochemical device. DETAILED DESCRIPTION

[0017] The following embodiments may enable those skilled in the art to more fully understand the present application, but do not limit the present application in any way.

[0018] The present application provides an electrolyte comprising at least two of additives I, II, and III. In some embodiments, additive I is selected from at least one additive in the group consisting of a compound represented by formula 1a, a compound represented by formula 1b, or lithium difluorophosphate.

[0019] In some embodiments, Additive II is selected from at least one additive selected from the group consisting of lithium fluorosulfonate, bisfluorosulfonimide, and bistrifluoromethanesulfonimide. In some embodiments, Additive III is selected from at least one additive selected from the group consisting of lithium difluorooxalatoborate, lithium bisoxalatoborate, and lithium tetrafluoroborate. By using at least two of Additives I, II, and III in the electrolyte, the formation of a solid electrolyte interface (SEI) on the positive and negative electrode surfaces can be improved, thereby enhancing interfacial passivation, thereby improving the low-temperature characteristics, impedance, and thickness expansion rate of the electrochemical device.

[0020] In some embodiments, the electrolyte includes additive I and additive II, additive I includes a compound represented by formula 1a, and additive II includes lithium fluorosulfonate. In some embodiments, the electrolyte includes additive I and additive II, additive I includes a compound represented by formula 1a, and additive II includes bisfluorosulfonyl imide. In some embodiments, the electrolyte includes additive I and additive II, additive I includes a compound represented by formula 1a, and additive II includes bistrifluoromethanesulfonyl imide. In some embodiments, the electrolyte includes additive I and additive III, additive I includes a compound represented by formula 1a, and additive III includes lithium difluorooxalatoborate. In some embodiments, the electrolyte includes additive I and additive III, additive I includes a compound represented by formula 1a, and additive III includes lithium bisoxalatoborate. In some embodiments, the electrolyte includes additive I and additive III, additive I includes a compound represented by formula 1a, and additive III includes lithium tetrafluoroborate. In some embodiments, the electrolyte includes additive I and additive II, additive I includes a compound represented by formula 1b, and additive II includes lithium fluorosulfonate. In some embodiments, the electrolyte includes additives I and additives II, additive I includes a compound represented by formula 1b, and additive II includes bisfluorosulfonyl imide. In some embodiments, the electrolyte includes additives I and additives II, additive I includes a compound represented by formula 1b, and additive II includes bistrifluoromethanesulfonyl imide. In some embodiments, the electrolyte includes additives I and additives III, additive I includes a compound represented by formula 1b, and additive III includes lithium difluorooxalatoborate. In some embodiments, the electrolyte includes additives I and additives III, additive I includes a compound represented by formula 1b, and additive III includes lithium bisoxalatoborate. In some embodiments, the electrolyte includes additives I and additives III, additive I includes a compound represented by formula 1b, and additive III includes lithium tetrafluoroborate. In some embodiments, the electrolyte includes additives I and additives II, additive I includes lithium difluorophosphate, and additive II includes lithium fluorosulfonate. In some embodiments, the electrolyte includes additives I and additives II, additive I includes lithium difluorophosphate, and additive II includes bisfluorosulfonyl imide. In some embodiments, the electrolyte comprises Additive I and Additive II, Additive I comprising lithium difluorophosphate, and Additive II comprising bistrifluoromethanesulfonimide. In some embodiments, the electrolyte comprises Additive I and Additive III, Additive I comprising lithium difluorophosphate, and Additive III comprising lithium difluorooxalatoborate. In some embodiments, the electrolyte comprises Additive I and Additive III, Additive I comprising lithium difluorophosphate, and Additive III comprising lithium bisoxalatoborate. In some embodiments, the electrolyte comprises Additive I and Additive III, Additive I comprising lithium difluorophosphate, and Additive III comprising lithium tetrafluoroborate.The above additive combination can enhance film formation stability, improve interface passivation effect, further reduce the occurrence of side reactions, and is beneficial to improving the low-temperature characteristics, impedance and thickness expansion rate of electrochemical devices.

[0021] In some embodiments, the mass content of Additive I in the electrolyte is a, where 0.01% ≤ a ≤ 5%. In some embodiments, the mass content of Additive II in the electrolyte is b, where 0.01% ≤ b ≤ 5%. In some embodiments, the mass content of Additive III in the electrolyte is c, where 0.01% ≤ c ≤ 5%. By controlling the mass content of Additive I, Additive II, and Additive III within the above ranges, the stability of the electrochemical device can be improved, as well as the low-temperature characteristics, impedance, and thickness expansion ratio of the electrochemical device.

[0022] In some embodiments, the mass content of additive I in the electrolyte is a, and a is 0.1%, 0.2%, 0.3%, 1%, 1.6%, 2.5%, 3%, 3.2%, or a range between any two of these values. In some embodiments, the mass content of additive II in the electrolyte is b, and b is 0.05%, 0.1%, 0.2%, 0.3%, 1%, 1.3%, 2%, or a range between any two of these values. In some embodiments, the mass content of additive III in the electrolyte is c, and c is 0.05%, 0.1%, 0.2%, or a range between any two of these values. By regulating the mass content of additive I, additive II, or additive III within the above ranges, different additives can be made to work synergistically to form SEI and CEI films with diverse and uniform compositions, thereby providing an electrochemical device with better low-temperature characteristics, impedance, and thickness expansion rate.

[0023] In some embodiments, when the electrolyte includes Additive I and Additive II, 0.1≤a / b≤50. By limiting the mass content of Additive I and Additive II to the above ratio, the low-temperature characteristics, impedance, and thickness expansion rate of the electrochemical device are improved. In some embodiments, when the electrolyte includes Additive II and Additive III, 0.1≤b / c≤50. By limiting the mass content of Additive II and Additive III to the above ratio, the low-temperature characteristics, impedance, and thickness expansion rate of the electrochemical device are improved. In some embodiments, when the electrolyte includes Additive I and Additive III, 0.1≤a / c≤50. By limiting the mass content of Additive I and Additive III to the above ratio, the low-temperature characteristics, impedance, and thickness expansion rate of the electrochemical device are improved. In some embodiments, when the electrolyte includes Additive I and Additive II, 0.1≤a / b≤40. In some embodiments, when the electrolyte includes Additive II and Additive III, 0.1≤b / c≤40. In some embodiments, when the electrolyte includes Additive I and Additive III, 0.5≤a / c≤45. By limiting the mass contents of Additive I, Additive II, and Additive III to the above ratios, the low-temperature characteristics, impedance, and thickness expansion ratio of the electrochemical device are further improved.

[0024] In some embodiments, the electrolyte further comprises an organic solvent, wherein the organic solvent comprises at least one of ethyl propionate (EP) or propyl propionate (PP). In some embodiments, the mass content of ethyl propionate in the electrolyte is 20% to 60%. In some embodiments, the mass content of propyl propionate in the electrolyte is 32% to 47%. By limiting the mass content of ethyl propionate or propyl propionate in the electrolyte to the above range, the low-temperature characteristics, impedance, and thickness expansion rate of the electrochemical device can be improved.

[0025] In some embodiments, the electrolyte further comprises an additive IV as shown in Formula 2,

[0026] Where X1 is CH or N, R a is substituted or unsubstituted C1-C 20Alkyl. In some embodiments, the alkyl group can be a straight chain or branched chain alkyl group. Non-limiting examples of straight chain alkyl groups include substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted butyl, substituted or unsubstituted pentyl, substituted or unsubstituted hexyl, substituted or unsubstituted heptyl, substituted or unsubstituted octyl, substituted or unsubstituted nonyl, substituted or unsubstituted decyl, substituted or unsubstituted dodecyl, etc. Non-limiting examples of branched chain alkyl groups include substituted or unsubstituted isopropyl, substituted or unsubstituted sec-butyl, substituted or unsubstituted isobutyl, substituted or unsubstituted neopentyl, substituted or unsubstituted isopentyl, etc. In addition, the substituted alkyl group can be a fluorine-substituted alkyl group. The substituted alkyl group can be substituted in the middle of the alkyl group or at the end of the alkyl group. That is, the substituted alkyl group is an alkyl group in which at least one hydrogen is replaced by fluorine, for example, -(CF2) n -CF3 (n is an integer from 0 to 20).

[0027] In some embodiments, a specific example of Formula 2 may be Formula 2a or Formula 2b as shown below:

[0028] The additive IV shown in Formula 2 can decompose to form a stable passivation film on the surface of the negative electrode, which has improved lithium ion transport performance and is stable under low-temperature and room-temperature storage, thereby suppressing gas generation and showing improved expansion performance.

[0029] In some embodiments, the weight content of Additive IV in the electrolyte is 0.01% to 4%. By regulating the weight content of Additive IV within this range, the low-temperature characteristics and impedance of the electrochemical device can be significantly improved, and the thickness expansion rate of the electrochemical device can be reduced. In some embodiments, the weight content of Additive IV in the electrolyte is 1.2% to 1.9%. In this case, the impedance and thickness expansion rate of the electrochemical device are further improved.

[0030] In some embodiments, the electrolyte further comprises an ionizable lithium salt, and the ionizable lithium salt comprises at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8. The concentration of the ionizable lithium salt in the electrolyte is not particularly limited, but is preferably 0.5 mol / L or more, more preferably 0.8 mol / L or more, and even more preferably 1.0 mol / L or more. In addition, it is preferably 3 mol / L or less, more preferably 2 mol / L or less, even more preferably 1.8 mol / L or less, and particularly preferably 1.6 mol / L or less. If the concentration of these ionizable lithium salts is too low, the conductivity of the electrolyte may be insufficient. On the other hand, if the concentration of these ionizable lithium salts is too high, the viscosity of the electrolyte may increase, thereby reducing the conductivity, which may lead to reduced performance of the electrochemical device.

[0031] In some embodiments, the electrolyte further comprises at least one of a fluoroether, a fluoroethylene carbonate, or an ether nitrile. In some embodiments, the electrolyte further comprises a non-aqueous solvent. The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.

[0032] The carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0033] Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), or combinations thereof. Examples of fluorocarbonate compounds are 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, trifluoromethylethylene carbonate, or combinations thereof.

[0034] Examples of the carboxylic acid ester compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0035] Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0036] Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid esters or combinations thereof.

[0037] The present application also provides an electrochemical device comprising the above-described electrolyte. In some embodiments, the electrochemical device further comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet and the negative electrode sheet are separated by the separator disposed therebetween. In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed thereon, the positive electrode active material layer comprising a positive electrode active material; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed thereon, the negative electrode active material layer comprising a negative electrode active material.

[0038] In some embodiments, the negative electrode plate may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may be disposed on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be at least one of copper foil, nickel foil, or a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be 1 μm to 200 μm. In some embodiments, the negative electrode active material layer may be coated only on a partial area of ​​the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and other suitable thicknesses may be used.

[0039] In some embodiments, as described above, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative electrode active material includes at least one of natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon oxide, a silicon carbon compound, or a silicon alloy.

[0040] In some embodiments, the negative electrode active material layer may further include a negative electrode conductor and / or a negative electrode binder. The negative electrode conductor may include at least one of carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the negative electrode binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate, polyvinyl pyrrolidone, polyimide, polysiloxane, or styrene-butadiene rubber. It should be understood that the materials disclosed above are only exemplary, and the negative electrode active material layer may be made of any other suitable material. In some embodiments, the mass ratio of the negative electrode active material, the negative electrode conductor, and the negative electrode binder in the negative electrode active material layer may be (80-99): (0.5-10): (0.5-10). It should be understood that this is only exemplary and is not intended to limit the present application.

[0041] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer may be located on one side or both sides of the positive electrode current collector. In some embodiments, the positive electrode current collector may be made of aluminum foil. Of course, other positive electrode current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 200 μm. In some embodiments, the positive electrode active material layer may be coated only on a partial area of ​​the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and other suitable thicknesses may be used.

[0042] In some embodiments, as described above, the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive electrode active material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide, and the above positive electrode active materials may be doped and / or coated.

[0043] In some embodiments, the positive electrode active material layer also includes a positive electrode binder and a positive electrode conductor. In some embodiments, the positive electrode binder may include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene at least one. In some embodiments, the positive electrode conductor may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes or carbon fibers. In some embodiments, the mass ratio of the positive electrode active material, positive electrode conductor and positive electrode binder in the positive electrode active material layer may be (80-98): (0.5-10): (0.5-10). It should be understood that the above is only an example, and the positive electrode active material layer may adopt any other suitable material, thickness and mass ratio.

[0044] In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in preventing short circuits and can improve battery safety through a shutdown effect. In some embodiments, the separator has a thickness ranging from approximately 3 μm to 500 μm.

[0045] In some embodiments, the surface of the isolation membrane may further include a porous layer, the porous layer being disposed on at least one surface of the isolation membrane, the porous layer comprising at least one of inorganic particles or a binder, the inorganic particles being selected from at least one of aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the isolation membrane have a diameter in the range of approximately 0.01 μm to 1 μm. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the electrode.

[0046] In some embodiments, the electrochemical device is a lithium-ion battery, but the present application is not limited thereto.

[0047] In some embodiments of the present application, taking lithium-ion batteries as an example, the positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, which is then encapsulated in a shell such as an aluminum-plastic film, and the electrolyte is injected, formed, and packaged to make a lithium-ion battery.

[0048] The embodiments of the present application also provide an electronic device including the above-mentioned electrochemical device. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium ion capacitor, etc.

[0049] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein a lithium-ion battery is used as an example.

[0050] Preparation of lithium-ion batteries

[0051] Preparation of the positive electrode sheet: The positive electrode active material, lithium cobalt oxide, the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 96.6:1.5:1.9. N-methylpyrrolidone (NMP) was added and stirred evenly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was evenly coated on one surface of a 10 μm thick positive electrode current collector aluminum foil and dried at 120°C to obtain a positive electrode sheet coated with an 80 μm thick positive electrode active material layer on one side. The above steps were repeated on the other side of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. The sheet was then cold pressed, cut, and slit to obtain a positive electrode sheet with a size of 470 mm × 92 mm.

[0052] Preparation of the negative electrode sheet: Artificial graphite (negative electrode active material), conductive carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed in a weight ratio of 96.5:1.5:1:1. Deionized water was added and the mixture was stirred uniformly in a vacuum mixer to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was evenly applied to one surface of a negative electrode current collector copper foil and dried at 120°C to obtain a negative electrode sheet coated with a 90 μm thick negative electrode active material layer on one side. The above steps were repeated on the other side of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. The sheet was then cold pressed, cut, and slit to obtain a negative electrode sheet with a size of 476 mm × 93.5 mm.

[0053] Preparation of isolation membrane: A 10 μm thick polyethylene (PE) microporous membrane was selected as the isolation membrane.

[0054] Preparation of the electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), and diethyl carbonate (abbreviated as DEC) are mixed in a mass ratio of 1:1:1 to obtain a base solvent, and then lithium salt LiPF6 and additives are added to the above base solvent and mixed evenly to obtain an electrolyte, wherein the mass percentage of LiPF6 based on the mass of the electrolyte is 12.5%. The difference between the various embodiments lies in the different types and / or contents of the additives used in the electrolyte. The specific types of additives and the mass percentages in the electrolyte are shown in Tables 1 to 4 below. The content of the additives is the mass percentage calculated based on the total mass of the electrolyte. The abbreviations of some of the additives are as follows: lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium fluorosulfonate (LiSO3F), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), and lithium bis(fluorosulfonyl imide) (LiFSI).

[0055] Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets to act as an isolater, and then wind them to obtain an electrode assembly. After welding the tabs, the electrode assembly is placed in an outer packaging aluminum-plastic film. After dehydration at 80°C, the above-mentioned electrolyte is injected. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, a lithium-ion battery is obtained.

[0056] The test method is as follows:

[0057] (1) -10℃ low temperature cycle test:

[0058] Place the lithium-ion battery in a -10°C thermostat and let it sit for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge the lithium-ion battery to 4.5V at a constant current of 0.2C at -10°C, charge it to 0.05C at a constant voltage at 4.5V, let it sit for 5 minutes, then discharge it to 3.0V at a constant current of 0.2C and let it sit for 5 minutes. Test the initial capacity (C11). Then charge it to 4.2V at a constant current of 0.5C, charge it to 0.3C at a constant voltage at 4.2V, then charge it to 4.25V at a constant current of 0.3C, then charge it to 0.05C at a constant voltage at 4.5V, let it sit for 5 minutes, then discharge it to 3.0V at a constant current of 0.2C and let it sit for 5 minutes. This constitutes one charge and discharge cycle. Repeat this charge / discharge cycle, and test the discharge capacity (C12) of the lithium-ion battery after 200 cycles. Calculate the capacity retention rate of the lithium-ion battery after 200 cycles.

[0059] Capacity retention after 200 cycles at -10°C = C12 / C11×100%.

[0060] (2) DC resistance (DCR) test:

[0061] At 25°C, the lithium-ion battery was charged at a constant current of 0.7C to 4.48V, then charged at a constant voltage of 4.48V to a current of 82.5mAh, and then discharged at a constant current of 0.2C for 4h to make the lithium-ion battery state of charge (SOC) of 20%. After the lithium-ion battery cycle was completed, the lithium-ion battery was discharged to 20% SOC according to the same charge and discharge steps as above, and the DC internal resistance (DCR) was tested respectively.

[0062] Test method: Discharge at 0.1C for 10 seconds to obtain voltage V0; discharge at 1C for 1 second to obtain voltage V1. DCR = (V0 - V1) / 0.1C.

[0063] The DCR change rate at 20% SOC after 1000 cycles at 25°C is: (DCR (1000 cycles at 25°C) / DCR (initial state at 25°C) - 1) × 100%.

[0064] (3) Storage thickness expansion rate test:

[0065] Place the lithium-ion battery in a 25°C constant temperature oven and let it rest for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge the lithium-ion battery at a constant current of 0.7C to a voltage of 4.48V, then charge it at a constant voltage of 4.48V to a current of 82.5mA. Measure the thickness of the lithium-ion battery and record it as T0. Place the battery in an 85°C oven for 8 hours, cool it for 1 hour, and measure its thickness as T1. Monitor the thickness of the lithium-ion battery in the oven in real time. The thickness expansion rate of the lithium-ion battery after 6 hours of storage at 85°C = (T1-T0) / T0×100%.

[0066] Table 1 shows various parameters and evaluation results of Examples 1 to 8 and Comparative Examples 1 to 10.

[0067] Table 1 Wherein, “-” means that the substance is not added.

[0068] Additive I forms a robust SEI on both the positive and negative electrodes, improving the low-temperature characteristics, impedance, and thickness expansion rate of the electrochemical device. Additive II improves the low-temperature characteristics of the electrolyte. Additive III also improves the low-temperature characteristics of the electrolyte. Comparison of Examples 1 to 8 with Comparative Examples 1 to 10 demonstrates that the addition of at least two of Additives I, II, and III to the electrolyte significantly improves the low-temperature cycle capacity retention, cycle impedance growth rate, and thickness expansion rate of lithium-ion batteries, compared to the absence of Additives I, II, and III, or the addition of only one of Additives I, II, and III.

[0069] Table 2 shows various parameters and evaluation results of Examples 9 to 19 and Comparative Examples 11 to 25.

[0070] Table 2 Wherein, “-” means that the substance is not added.

[0071] By comparing Comparative Examples 11 to 16, it can be seen that with the increase in the mass content of the additive I in the electrolyte, the capacity retention of the lithium ion battery first increases and then decreases, the cycle impedance growth rate first decreases and then increases, and the thickness expansion first decreases and then increases. By comparing Comparative Examples 17 to 21, it can be seen that with the increase in the mass content of the additive II in the electrolyte, the capacity retention of the lithium ion battery first increases and then decreases, the cycle impedance growth rate first decreases and then increases, and the thickness expansion first decreases and then increases. By comparing Comparative Examples 22 to 25, it can be seen that with the increase in the mass content of the additive III in the electrolyte, the capacity retention of the lithium ion battery first increases and then decreases, the cycle impedance growth rate first increases and then decreases and then increases again, and the thickness expansion first increases and then decreases and then increases again.

[0072] By comparing Examples 9 to 13, it can be seen that as a / b increases, the capacity retention of the lithium-ion battery first increases and then decreases, the cycle impedance growth rate first decreases and then increases, and the thickness expansion first decreases and then increases. By comparing Examples 14 to 16, it can be seen that as b / c increases, the capacity retention of the lithium-ion battery first increases and then decreases, the cycle impedance growth rate first decreases and then increases, and the thickness expansion first decreases and then increases. By comparing Examples 17 to 19, it can be seen that as a / c increases, the capacity retention of the lithium-ion battery first increases and then decreases, the cycle impedance growth rate first decreases and then increases, and the thickness expansion first decreases and then increases.

[0073] Table 3 shows various parameters and evaluation results of Examples 20 to 34. In Examples 20 to 34, an organic solvent EP or PP was additionally added.

[0074] Table 3 Wherein, “-” means that the substance is not added.

[0075] The low-temperature capacity retention rate, cycle impedance growth rate and thickness expansion rate of lithium-ion batteries can be further improved by introducing organic solvents ethyl propionate or propyl propionate.

[0076] Table 4 shows various parameters and evaluation results of Examples 35 to 42. In Examples 35 to 42, Additive IV was additionally added.

[0077] Table 4 Wherein, “-” means that the substance is not added.

[0078] The introduction of Additive IV can further improve the low-temperature capacity retention, cycle impedance growth rate, and thickness expansion rate of lithium-ion batteries. This is because Additive IV decomposes to form a stable passivation film on the surface of the negative electrode. This passivation film has good lithium-ion transport properties and is stable under low and high temperature conditions, thereby suppressing gas generation and showing improved cycle performance and expansion performance.

[0079] The above description is merely a preferred embodiment of the present application and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application is not limited to technical solutions formed by a specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalents. For example, a technical solution formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises at least two of additive I, additive II and additive III: The additive I is at least one additive selected from the group consisting of a compound represented by the following formula 1a, a compound represented by the following formula 1b, or lithium difluorophosphate, The additive II is at least one additive selected from the group consisting of lithium fluorosulfonate, bis(fluorosulfonyl)imide and bis(trifluoromethanesulfonyl)imide; The additive III is at least one additive selected from the group consisting of lithium difluorooxalatoborate, lithium bisoxalatoborate and lithium tetrafluoroborate.

2. The electrolyte according to claim 1, characterized in that At least one of the following is met: (1) The additive I comprises a compound represented by formula 1a, and the additive II comprises lithium fluorosulfonate; (2) the additive I comprises a compound represented by formula 1a, and the additive II comprises bis(fluorosulfonyl)imide; (3) The additive I includes a compound represented by formula 1a, and the additive II includes bistrifluoromethanesulfonimide.

3. The electrolyte according to claim 1, characterized in that At least one of the following is met: (4) the additive I comprises a compound represented by formula 1a, and the additive III comprises lithium difluorooxalatoborate; (5) The additive I comprises a compound represented by formula 1a, and the additive III comprises lithium bis(oxalatoborate); (6) The additive I includes a compound represented by formula 1a, and the additive III includes lithium tetrafluoroborate.

4. The electrolyte according to claim 1, characterized in that At least one of the following is met: (7) The additive I comprises a compound represented by formula 1b, and the additive II comprises lithium fluorosulfonate; (8) The additive I comprises a compound represented by formula 1b, and the additive II comprises bis(fluorosulfonyl)imide; (9) The additive I includes a compound represented by formula 1b, and the additive II includes bistrifluoromethanesulfonimide.

5. The electrolyte according to claim 1, characterized in that At least one of the following is met: (10) The additive I comprises a compound represented by formula 1b, and the additive III comprises lithium difluorooxalatoborate; (11) The additive I comprises a compound represented by formula 1b, and the additive III comprises lithium bis(oxalatoborate); (12) The additive I includes a compound represented by formula 1b, and the additive III includes lithium tetrafluoroborate.

6. The electrolyte according to claim 1, characterized in that At least one of the following is met: (13) The additive I includes lithium difluorophosphate, and the additive II includes lithium fluorosulfonate; (14) The additive I includes lithium difluorophosphate, and the additive II includes bis(fluorosulfonyl)imide; (15) The additive I includes lithium difluorophosphate, and the additive II includes bistrifluoromethanesulfonimide.

7. The electrolyte according to claim 1, characterized in that At least one of the following is met: (16) The additive I includes lithium difluorophosphate, and the additive III includes lithium difluorooxalatoborate; (17) The additive I includes lithium difluorophosphate, and the additive III includes lithium bis(oxalatoborate); (18) The additive I includes lithium difluorophosphate, and the additive III includes lithium tetrafluoroborate.

8. The electrolyte according to claim 1, characterized in that At least one of the following is met: (1) The mass content of the additive I in the electrolyte is a, 0.01%≤a≤5%; (2) The mass content of the additive II in the electrolyte is b, 0.01%≤b≤5%; (3) The mass content of the additive III in the electrolyte is c, 0.01%≤c≤5%.

9. The electrolyte according to claim 8, characterized in that At least one of the following is met: (1) a is 0.1%, 0.2%, 0.3%, 1%, 1.6%, 2.5%, 3%, 3.2%, or a range between any two of these values; (2) b is 0.05%, 0.1%, 0.2%, 0.3%, 1%, 1.3%, 2% or a range between any two of these values; (3) c is 0.05%, 0.1%, 0.2% or a range between any two of these values.

10. The electrolyte according to claim 1, characterized in that At least one of the following is met: (1) When the electrolyte includes the additive I and the additive II, 0.1≤a / b≤50; (2) When the electrolyte includes the additive II and the additive III, 0.1≤b / c≤50; (3) When the electrolyte includes the additive I and the additive III, 0.1≤a / c≤50.

11. The electrolyte according to claim 1, characterized in that At least one of the following is met: (1) When the electrolyte includes the additive I and the additive II, 0.1≤a / b≤40; (2) When the electrolyte includes the additive II and the additive III, 0.1≤b / c≤40; (3) When the electrolyte includes the additive I and the additive III, 0.5≤a / c≤45.

12. The electrolyte according to claim 1, characterized in that The electrolyte also includes an organic solvent, and the organic solvent includes at least one of ethyl propionate and propyl propionate, wherein the mass content of ethyl propionate in the electrolyte is 20% to 60%, and the mass content of propyl propionate in the electrolyte is 32% to 47%.

13. The electrolyte according to claim 1, characterized in that The electrolyte further comprises an additive IV as shown in Formula 2, Where X1 is CH or N, R a is substituted or unsubstituted C1-C 20 alkyl; The mass content of the additive IV in the electrolyte is 0.01% to 4%, preferably 1.2% to 1.9%.

14. An electrochemical device comprising the electrolyte according to any one of claims 1 to 13.

15. An electronic device comprising the electrochemical device according to claim 14.

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