Electrolyte, electrochemical device, and electronic device

Abstract

The application discloses an electrolyte, an electrochemical device and an electronic device, the electrolyte comprises an organic solvent, lithium bisfluorosulfonylimide, a compound of formula I and an additive; the additive comprises fluoroethylene carbonate and a compound of formula II; the special solvation structure in the electrolyte is conducive to the formation of a LiF-rich SEI film derived from the anion of lithium bisfluorosulfonylimide, the LiF-rich SEI film has high mechanical strength and can adapt to the large volume change of a silicon-based material, and the additive in the electrolyte is conducive to the improvement of the flexibility of the SEI film, so that the stability of the whole SEI film can be improved, and the cycle stability of the electrochemical device is improved.

Description

Technical Field

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

[0002] Silicon has a theoretical specific capacity of approximately 4200 mAh / g, which is much higher than that of graphite (approximately 372 mAh / g). Therefore, it has become the preferred negative electrode active material for developing high-energy-density lithium-ion batteries. However, silicon exhibits significant volume expansion (approximately 300%) during charge and discharge. Consequently, the strength of the solid electrolyte interphase (SEI) film formed on the negative electrode surface by ordinary electrolytes is insufficient to accommodate such large volume changes. It is necessary to explore electrolytes that can form a higher-strength SEI film on the negative electrode surface. Summary of the Invention

[0003] This application provides an electrolyte, an electrochemical device, and an electronic device to improve the cycle performance of the electrochemical device.

[0004] In a first aspect, this application provides an electrolyte comprising an organic solvent, lithium bis(fluorosulfonyl)imide, a compound of formula I, and additives. The additives include fluoroethylene carbonate and a compound of formula II.

[0005]

[0006] R1 to R6 are each independently selected from hydrogen, fluorine, fluorinated or unfluorinated C1-C. 12 Alkyl, fluorinated or unfluorinated C1-C 12 The alkyl group, wherein two adjacent groups in R1 to R6 are optionally linked to form a ring, and at least one of R1 to R6 contains fluorine. R7 to R 10 Each is independently selected from substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C1-C 12 Oxyalkyl, substituted or unsubstituted C2-C 12 Groups containing unsaturated carbon-carbon double bonds, substituted or unsubstituted C2-C 12 Groups containing unsaturated carbon-carbon triple bonds, and R7 to R 10 At least one of them includes an unsaturated carbon-carbon double bond or an unsaturated carbon-carbon triple bond; when substituted, the substituents include halogens.

[0007] The electrolyte in this application, due to its special solvation structure, allows the anionic FSI in lithium bis(fluorosulfonyl)imide (LiFSI) to... - Being at a lower LUMO level and a higher HOMO level is advantageous for FSI. -During charging and discharging, it participates in redox reactions, forming a LiF-rich SEI film and a positive electrode electrolyte interphase (CEI) film on the surfaces of the positive and negative electrodes. This enhances the mechanical strength of the protective film, helps it adapt to large volume changes at the negative electrode, improves the ionic conductivity of the protective film, reduces polarization during cycling, and thus improves the cycle performance of the electrochemical device. Compound I exhibits good wettability and strong oxidation resistance. Adding it to the electrolyte can form a locally high-salt electrolyte, reducing the electrolyte viscosity. Furthermore, compound I can be reduced and defluorinated at the negative electrode, further promoting the formation of the LiF-rich SEI film, which is beneficial for improving the kinetic and cycle performance of the electrochemical device. Simultaneously, the introduced fluoroethylene carbonate can be reduced at the negative electrode, thereby reacting with FSI... - The combined effect forms a stable outer organic and inner inorganic SEI film, increasing the overall stability of the SEI film. Furthermore, the silicon functional groups in compound II can undergo coupling reactions with the -OH groups on the negative electrode surface to form strong Li-O-Si chemical bonds. The unsaturated groups in compound II, after polymerization, exhibit good compatibility with the organic components in the SEI film, thereby improving the bonding force between the organic and inorganic layers on the negative electrode surface. This results in a more flexible SEI film that can adapt to larger volume changes at the negative electrode, further enhancing the cycle stability of the electrochemical device.

[0008] In some embodiments, the compound of formula II includes at least one of the following compounds:

[0009]

[0010]

[0011] In some embodiments, the compound of formula I includes at least one of the following compounds:

[0012]

[0013]

[0014] In some embodiments, based on the mass of the electrolyte, the mass percentage of the compound of formula I is denoted as a, the mass percentage of the organic solvent is denoted as b, the mass percentage of the lithium bis(fluorosulfonyl)imide is denoted as c, the mass percentage of the fluoroethylene carbonate is denoted as x, and the mass percentage of the compound of formula II is denoted as y, satisfying at least one of the following conditions: (1) 25% ≤ c / (b+c) ≤ 60%; (2) 25% ≤ a / (a+b+c) ≤ 70%; (3) 15% ≤ b ≤ 50%; (4) 8% ≤ c ≤ 50%. A suitable ratio of lithium salt and organic solvent is beneficial for reducing the content of free solvent, thereby reducing the HOMO energy level of the solvent, increasing the LUMO energy level, and broadening the electrochemical window of the electrolyte. At this time, FSI... - Being at a higher HOMO level and a lower LUMO level is advantageous for FSI. - It participates in redox reactions, forming a LiF-rich SEI / CEI protective film, thereby improving the mechanical stability of the protective film and increasing its ionic conductivity, reducing polarization during cycling; the appropriate content of Formula I compound is beneficial to increasing the wettability of the electrolyte, reducing the overall viscosity of the electrolyte, thereby improving the conductivity, which is beneficial to improving the long-cycle stability of the electrochemical device.

[0015] In some embodiments, 0.1% ≤ x ≤ 5%. An appropriate amount of fluoroethylene carbonate can form a stable SEI film with an outer organic and inner inorganic layer on the negative electrode surface, thereby increasing the overall stability of the SEI film and improving the cycle performance of the electrochemical device. In some embodiments, 0.5% ≤ x ≤ 3%.

[0016] In some embodiments, 0.02 ≤ x / b ≤ 0.25. By controlling the ratio x / b of the mass percentage of FEC to the mass percentage of organic solvent within the above range, it is more beneficial for FEC to promptly repair defects caused by SEI membrane rupture during cycling, thereby improving the cycling performance of the electrochemical device. In some embodiments, 0.02 ≤ x / b ≤ 0.15.

[0017] In some embodiments, 0.01% ≤ y ≤ 5%. An appropriate amount of Formula II compound is beneficial for improving the bonding force between the organic and inorganic layers on the negative electrode surface, resulting in greater flexibility of the SEI film, thereby improving the cycle stability and thermal box safety performance of the electrochemical device. In some embodiments, 0.3% ≤ y ≤ 2%.

[0018] In some embodiments, 0.02 ≤ y / (x+y) ≤ 0.75. In some embodiments, 0.1 ≤ y / (x+y) ≤ 0.5.

[0019] In some embodiments, at least one of the following conditions is met: (1) 27% ≤ c / (b+c) ≤ 56%; (2) 30% ≤ a / (a+b+c) ≤ 55%; (3) 20% ≤ b ≤ 40%; (4) 15% ≤ c ≤ 35%. In this case, FSI is more favorable. - It participates in redox reactions, promotes the formation of LiF-rich SEI and CEI films, further enhances the mechanical strength and ion conductivity of the protective film, and improves the cycle performance of the electrochemical device.

[0020] In some embodiments, the organic solvent includes at least one of carbonate or carboxylic acid ester.

[0021] In some embodiments, the carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dipropyl carbonate, or methyl propyl carbonate.

[0022] In some embodiments, the carboxylic acid ester includes at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate.

[0023] In some embodiments, the additive further includes a compound of formula III;

[0024] M-(Q) x Formula III

[0025] Wherein, M is selected from any one of C1-C5 alkyl, C1-C5 alkylene, and the group shown in formula c;

[0026]

[0027] Q is independently selected from any one of the groups shown in formula d;

[0028] * -OR 17 -CN formula d

[0029] Among them, R 17Each compound is independently selected from any one of C1 to C3 alkylene groups; x is selected from any value of 1, 2, and 3. All compounds of Formula III are ether nitrile additives. Ether nitrile additives can absorb moisture in the electrochemical device, forming amides and reducing the impact of moisture on the device. Simultaneously, the cyano group can complex with transition metals on the surface of the positive electrode active material, adsorbing onto the surface and reducing the dissolution of transition metals, thus improving the high-temperature cycling performance of the electrochemical device. However, the addition of large amounts of ether nitrile additives can damage the SEI film and deteriorate the room-temperature cycling performance. The presence of silane additives, on the one hand, can improve the adhesion of the organic layer on the negative electrode surface, making the SEI film more flexible; on the other hand, it can reduce the damage to the SEI film caused by the addition of ether nitrile additives, ensuring the room-temperature cycling performance of the electrochemical device.

[0030] In some embodiments, the compound of formula III includes at least one selected from 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(2-cyanoethoxy)propane, 3-isopropoxypropionitrile, 3-ethoxypropionitrile, or 2-ethoxyacetonitrile.

[0031] In some embodiments, the mass percentage of the compound of formula III, denoted as z, is based on the mass of the electrolyte and satisfies the following condition: 0.02% ≤ z ≤ 5%. The addition of appropriate amounts of ether nitrile additives is beneficial for improving the high-temperature cycling performance of the electrochemical device.

[0032] In some embodiments, 0.17 ≤ z / (z+y) ≤ 0.86.

[0033] In some embodiments, the electrolyte further includes lithium difluorophosphate. The mass percentage of lithium difluorophosphate, denoted as d, is based on the mass of the electrolyte and satisfies the condition: 0.01 ≤ d / c ≤ 0.3. The addition of lithium difluorophosphate can reduce the risk of lithium bis(fluorosulfonyl)imide corroding the aluminum foil. Simultaneously, controlling the amount of lithium difluorophosphate added within the aforementioned range, without affecting the original solvation structure, helps improve the oxidation resistance and overall stability of the electrolyte, thereby improving the cycle performance and thermal box safety performance of the electrochemical device.

[0034] Secondly, this application provides an electrochemical device, the electrochemical device comprising a negative electrode sheet and an electrolyte; the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material; the electrolyte being any of the electrolytes described above.

[0035] In some embodiments, the silicon-based material has a mass percentage content of 40% to 90% based on the mass of the negative electrode active material. The electrolyte described in this application is suitable for negative electrodes with a high silicon-based material content.

[0036] Thirdly, this application provides an electronic device that includes the aforementioned electrochemical device. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0038] electrolyte

[0039] A first aspect of this application provides an electrolyte comprising an organic solvent, lithium bis(fluorosulfonyl)imide, a compound of formula I, and additives; the additives include fluoroethylene carbonate and a compound of formula II.

[0040]

[0041] For compounds of formula I, R1 to R6 are each independently selected from hydrogen, fluorine, fluorinated or unfluorinated C1-C. 12 Alkyl, fluorinated or unfluorinated C1-C 12 The alkyl group R1 to R6 may optionally be a ring, and at least one of R1 to R6 may contain fluorine. Optionally, in some embodiments, R1 to R6 are each independently selected from hydrogen, fluorine, fluorinated or unfluorinated C1-C6 alkyl groups, and fluorinated or unfluorinated C1-C6 alkyl groups. Further optionally, in some embodiments, R1 to R6 are each independently selected from hydrogen, fluorine, fluorinated or unfluorinated C1-C3 alkyl groups, and fluorinated or unfluorinated C1-C3 alkyl groups.

[0042] For compounds of formula II, where R7 to R 10 Each is independently selected from substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C1-C 12 Oxyalkyl, substituted or unsubstituted C2-C 12 Groups containing unsaturated carbon-carbon double bonds, substituted or unsubstituted C2-C 12 Groups containing unsaturated carbon-carbon triple bonds, and R7 to R 10 At least one of them includes an unsaturated carbon-carbon double bond or an unsaturated carbon-carbon triple bond; when substituted, the substituent includes a halogen. Optionally, in some embodiments, R7 to R 10Each group is independently selected from substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 oxyalkyl groups, substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon double bonds, and substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon triple bonds. Further optionally, in some embodiments, R7 to R... 10 Each group is independently selected from substituted or unsubstituted C1-C3 alkyl groups, substituted or unsubstituted C1-C3 oxyalkyl groups, substituted or unsubstituted C2-C3 groups containing unsaturated carbon-carbon double bonds, and substituted or unsubstituted C2-C3 groups containing unsaturated carbon-carbon triple bonds.

[0043] The electrolyte in this application, due to its special solvation structure, allows the anionic FSI in lithium bis(fluorosulfonyl)imide (LiFSI) to... - Being at a lower LUMO level and a higher HOMO level is advantageous for FSI. - During charge and discharge, it participates in redox reactions, forming LiF-rich SEI and CEI films on the surfaces of the positive and negative electrodes. This enhances the mechanical strength of the protective films, helps them adapt to large volume changes at the negative electrode, improves the ionic conductivity of the protective films, reduces polarization during cycling, and thus improves the cycle performance of the electrochemical device. Compound I exhibits good wettability and strong oxidation resistance. Adding it to the electrolyte can form a locally high-salt electrolyte, reducing the electrolyte viscosity. Furthermore, compound I can be reduced and defluorinated at the negative electrode, further promoting the formation of the LiF-rich SEI film, which is beneficial for improving the kinetic and cycle performance of the electrochemical device. Simultaneously, the introduced fluoroethylene carbonate can be reduced at the negative electrode, thereby reacting with FSI... - The combined effect forms a stable outer organic and inner inorganic SEI film, increasing the overall stability of the SEI film. Furthermore, the silicon functional groups in compound II can undergo coupling reactions with the -OH groups on the negative electrode surface to form strong Li-O-Si chemical bonds. The unsaturated groups in compound II, after polymerization, exhibit good compatibility with the organic components in the SEI film, thereby improving the bonding force between the organic and inorganic layers on the negative electrode surface. This results in a more flexible SEI film that can adapt to larger volume changes at the negative electrode, further enhancing the cycle stability of the electrochemical device.

[0044] In some embodiments, the compound of formula I includes at least one of the following compounds:

[0045]

[0046] In some embodiments, based on the mass of the electrolyte, the mass percentage of the compound of formula I is denoted as a, the mass percentage of the organic solvent is denoted as b, the mass percentage of the lithium bis(fluorosulfonyl)imide is denoted as c, the mass percentage of the fluoroethylene carbonate is denoted as x, and the mass percentage of the compound of formula II is denoted as y, satisfying at least one of the following conditions: (1) 25% ≤ c / (b+c) ≤ 60%; (2) 25% ≤ a / (a+b+c) ≤ 70%; (3) 15% ≤ b ≤ 50%; (4) 8% ≤ c ≤ 50%. A suitable ratio of lithium salt and organic solvent is beneficial for reducing the content of free solvent, thereby reducing the HOMO energy level of the solvent, increasing the LUMO energy level, and broadening the electrochemical window of the electrolyte. At this time, FSI... - Being at a higher HOMO level and a lower LUMO level is advantageous for FSI. - It participates in redox reactions, forming a LiF-rich SEI / CEI protective film, thereby improving the mechanical stability of the protective film and increasing its ionic conductivity, reducing polarization during cycling; the appropriate content of Formula I compound is beneficial to increasing the wettability of the electrolyte, reducing the overall viscosity of the electrolyte, thereby improving the conductivity, which is beneficial to improving the long-cycle stability of the electrochemical device.

[0047] In some embodiments, c / (b+c) can be 25%, 30%, 35%, 40%, 45%, 50%, 60%, or a range of any two values ​​therein. In some embodiments, a / (a+b+c) can be 25%, 30%, 35%, 40%, 45%, 50%, 60%, 65%, 70%, or a range of any two values ​​therein. In some embodiments, b can be 15%, 20%, 25%, 30%, 35%, 40%, 50%, or a range of any two values ​​therein. In some embodiments, c can be 8%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, or a range of any two values ​​therein.

[0048] Optionally, in some embodiments, at least one of the following conditions is satisfied: (1) 27% ≤ c / (b+c) ≤ 56%; (2) 30% ≤ a / (a+b+c) ≤ 55%; (3) 20% ≤ b ≤ 40%; (4) 15% ≤ c ≤ 35%.

[0049] In some embodiments, 0.1% ≤ x ≤ 5%. An appropriate amount of fluoroethylene carbonate can form a stable SEI film with an outer organic and inner inorganic layer on the negative electrode surface, thereby increasing the overall stability of the SEI film and improving the cycle performance of the electrochemical device. For example, x can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range of any two of these values. Optionally, in some embodiments, 0.5% ≤ x ≤ 3%.

[0050] In some embodiments, 0.02 ≤ x / b ≤ 0.25. By controlling the ratio x / b of the mass percentage of FEC to the mass percentage of organic solvent within the above range, it is more beneficial for FEC to promptly repair defects caused by SEI membrane rupture during cycling, thereby improving the cycling performance of the electrochemical device. For example, x / b can be 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, or a range of any two of these values. Optionally, in some embodiments, 0.02 ≤ x / b ≤ 0.15.

[0051] In some embodiments, 0.01% ≤ y ≤ 5%. An appropriate amount of the Formula II compound is beneficial for improving the adhesion between the organic and inorganic layers on the negative electrode surface, resulting in greater flexibility of the SEI film, thereby improving the cycle stability and thermal box safety performance of the electrochemical device. For example, y can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range of any two of these values. Optionally, in some embodiments, 0.3% ≤ y ≤ 2%.

[0052] In some embodiments, 0.02 ≤ y / (x+y) ≤ 0.75. By controlling the mass percentage content of compound II within the above range, the bonding force between the organic and inorganic layers on the negative electrode surface can be further improved, resulting in greater flexibility of the SEI film and thus improving the long-cycle stability of the electrochemical device. For example, y / (x+y) can be 0.02, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.35, or a range of any two of these values. Optionally, in some embodiments, 0.1 ≤ y / (x+y) ≤ 0.5.

[0053] In some embodiments, the organic solvent includes at least one of carbonate or carboxylic acid ester.

[0054] In some embodiments, the carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dipropyl carbonate, or methyl propyl carbonate.

[0055] In some embodiments, the carboxylic acid ester includes at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate.

[0056] In some embodiments, the additive further includes a compound of formula III;

[0057] M-(Q) x Formula III

[0058] Wherein, M is selected from any one of C1-C5 alkyl, C1-C5 alkylene, and the group shown in formula c;

[0059]

[0060] Q is independently selected from any one of the groups shown in formula d;

[0061] * -OR 17 -CN formula d

[0062] Among them, R 17 Each is independently selected from any one of the C1 to C3 alkylene groups; x is selected from any value of 1, 2, or 3.

[0063] Compound III is an ether nitrile additive. Ether nitrile additives can absorb moisture in the electrochemical device, forming amides and reducing the impact of moisture on the device. Simultaneously, the cyano group can complex with transition metals on the surface of the positive electrode active material, adsorbing onto the surface and reducing transition metal dissolution, thus improving the high-temperature cycling performance of the electrochemical device. However, the addition of large amounts of ether nitrile additives can damage the SEI film, deteriorating its room-temperature cycling performance. In contrast, the presence of silane additives (compound II) can, on the one hand, improve the adhesion of the organic layer on the negative electrode surface, giving the SEI film greater flexibility; on the other hand, it can reduce the damage to the SEI film caused by the addition of ether nitrile additives, ensuring the room-temperature cycling performance of the electrochemical device.

[0064] In some embodiments, the compound of formula III includes at least one selected from 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(2-cyanoethoxy)propane, 3-isopropoxypropionitrile, 3-ethoxypropionitrile, or 2-ethoxyacetonitrile.

[0065] In some embodiments, the mass percentage of the compound of formula III, denoted as z, is based on the mass of the electrolyte and satisfies the condition: 0.02% ≤ z ≤ 5%. For example, z can be 0.02%, 0.05%, 0.1%, 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range of any two of these values. Optionally, in some embodiments, 0.1% ≤ z ≤ 3%.

[0066] In some embodiments, the mass percentage of the compound of formula III, denoted as z, is based on the mass of the electrolyte and satisfies: 0.17 ≤ z / (z+y) ≤ 0.86. For example, z / (z+y) can be 0.17, 0.2, 0.3, 0.4, 0.5, 0.7, 0.86, or a range of any two of these values. Optionally, in some embodiments, 0.5 ≤ z / (z+y) ≤ 0.7.

[0067] In some embodiments, the electrolyte further includes lithium difluorophosphate. The mass percentage of lithium difluorophosphate, denoted as d, is based on the mass of the electrolyte and satisfies the condition: 0.01 ≤ d / c ≤ 0.3. The addition of lithium difluorophosphate can reduce the risk of lithium bis(fluorosulfonyl)imide corroding the aluminum foil. Simultaneously, controlling the amount of lithium difluorophosphate added within the aforementioned range, without affecting the original solvation structure, helps improve the oxidation resistance and overall stability of the electrolyte, thereby improving the cycle performance and thermal box safety performance of the electrochemical device. For example, d / c can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or a range consisting of any two of these values. Optionally, in some embodiments, 0.1 ≤ d / c ≤ 0.25.

[0068] Electrochemical device

[0069] A second aspect of this application provides an electrochemical device, including a positive electrode, a negative electrode, a separator, and the electrolyte described in the first aspect.

[0070] The positive electrode 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 achieves 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). This application does not impose any particular limitation on the thickness of the positive current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive current collector is 5 μm to 12 μm. The positive active material layer includes a positive active material. This application does not impose any particular limitation on the positive active material, as long as it achieves the purpose of this application. For example, the positive active material may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, or lithium manganese iron phosphate. This application does not impose any particular limitation on the thickness of the positive active material layer, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm. The positive electrode active material layer may also include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve 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. The binder may include, but is not limited to, at least one of polyacrylic acid, polyacrylate, acrylate polymers, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, or polyvinylidene fluoride-hexafluoropropylene copolymer. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0071] The negative electrode includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative active material layer includes a negative active material, which may be a silicon-based material. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (e.g., a composite current collector with a metal layer disposed on the surface of a polymer layer). This application does not impose any particular limitation on the thickness of the negative current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative current collector may be 5 μm to 12 μm. In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon-oxygen composite materials, or silicon-carbon composite materials. In some embodiments, the negative active material may also include other negative active materials known in the art besides the aforementioned silicon-based materials. For example, other negative active materials known in the art may include, but are not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, or Li-Al alloy. In some embodiments, the silicon-based material comprises 40% to 90% by mass, based on the mass of the negative electrode active material. The negative electrode active material layer may also include a binder and a thickener. This application does not impose any particular limitation on the types of binders and thickeners, as long as they 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. The negative electrode active material layer may also include a conductive agent. This application does not impose any particular limitation on the types of conductive agents, as long as they achieve 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 impose any particular limitation on the mass ratio of the negative electrode active material, binder, conductive agent, and thickener in the negative electrode active material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0072] This application does not impose any particular restrictions on the separator membrane; any known porous separator membrane with electrochemical and chemical stability can be selected.

[0073] The electrochemical device of this application may include any device in which an electrochemical reaction occurs, and specific examples include all types of primary or secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0074] electronic devices

[0075] The electronic devices described in this application include any of the electrochemical devices described above. These electronic devices may include, but are not limited to, mobile phones, laptops, e-book players, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, electronic notebooks, calculators, portable recorders, radios, backup power supplies, electric vehicles, electric motorcycles, electric bicycles, lighting fixtures, toys, game consoles, clocks, power tools, cameras, and large household batteries, etc.

[0076] 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 weight.

[0077] Example 1-1

[0078] Preparation of positive electrode sheet

[0079] Lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2, polyvinylidene fluoride (PVDF) binder, and Super-P conductive agent are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 and mixed evenly to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto a 12 μm thick aluminum foil used as a positive electrode current collector and dried at 120°C to obtain a positive electrode sheet with a single-sided coating of the positive electrode active material layer. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode active material layer. This positive electrode sheet is then compacted and slit to obtain the final positive electrode sheet.

[0080] Preparation of negative electrode sheet

[0081] A negative electrode active material, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber were dissolved in water at a mass ratio of 96:2:2 and thoroughly mixed to obtain a negative electrode slurry. The negative electrode active material was a mixture of graphite and silicon-based material SiO at a mass ratio of 40:60, with an average particle size of 7 μm for the silicon-based material. The negative electrode slurry was uniformly coated onto a 12 μm thick copper foil used as a negative electrode current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material. This was then compacted and slit to obtain the final negative electrode sheet.

[0082] Preparation of electrolyte

[0083] Compound of Formula I (Formula I-5), organic solvent (diethyl carbonate), and lithium bis(fluorosulfonyl)imide were mixed uniformly at a mass ratio of 55:22.6:22.4 to obtain a basic electrolyte. Fluoroethylene carbonate (FEC) and compound of Formula II (Formula II-2) were then added to the basic electrolyte to obtain the final electrolyte. The mass percentage of FEC was 2%, and the mass percentage of compound of Formula II was 0.05%, based on the mass of the electrolyte. Specific substances and their proportions are shown in Table 1.

[0084] Preparation of lithium-ion batteries

[0085] A 10μm porous polypropylene film was used as the separator. The positive electrode, separator, and negative electrode were stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked material was then wound into an electrode assembly. The electrode assembly was placed in an aluminum-plastic film packaging bag, baked at 80°C to remove moisture, and then injected with the aforementioned electrolyte. After vacuum sealing, settling, formation, and shaping, the lithium-ion battery was successfully manufactured.

[0086] Examples 1-2 to Examples 1-30

[0087] Unlike Example 1-1, the types of substances and their proportions were adjusted during the preparation of the electrolyte, as detailed in Table 1.

[0088] Comparative Example 1-1

[0089] Unlike Example 1-1, the types of substances and their proportions were adjusted during the preparation of the electrolyte, as detailed in Table 1.

[0090] Performance testing:

[0091] (1) High-temperature cycling performance test

[0092] The lithium-ion battery was charged to 4.25V at a constant current of 0.5C at 45℃, left to rest for 30 minutes, and then discharged to 3.0V at a constant current of 0.5C. The discharge capacity of this discharge cycle was recorded as the first discharge capacity. The above charge-discharge cycle was repeated 500 times, and the discharge capacity of the 500th cycle was recorded.

[0093] 45℃ cycle capacity retention rate (%) = discharge capacity after 500 cycles / discharge capacity after first cycle × 100%.

[0094] (2) Room temperature cycling performance test

[0095] The lithium-ion battery was charged to 4.25V at a constant current of 0.5C at 25℃, left to rest for 30 minutes, and then discharged to 3.0V at a constant current of 0.5C. The discharge capacity of this discharge cycle was recorded as the first discharge capacity. The above charge-discharge cycle was repeated 500 times, and the discharge capacity of the 500th cycle was recorded.

[0096] 25℃ cycle capacity retention rate (%) = discharge capacity after 500 cycles / discharge capacity after first cycle × 100%.

[0097] (3) Hot box test

[0098] Take 10 lithium-ion batteries and charge them to 4.25V at a constant current of 0.5C at 25℃. Place the fully charged lithium-ion batteries in a constant temperature chamber and heat them to 132℃ at a rate of 5℃ / min. Maintain the temperature at 132℃ for 1 hour and monitor the lithium-ion batteries. If the lithium-ion batteries do not catch fire or explode, the test is considered passed.

[0099] Hot box test pass rate = number of tests passed / 10.

[0100] The test results of Examples 1-1 to 1-30 and Comparative Example 1-1 are shown in Table 1.

[0101] Table 1

[0102]

[0103]

[0104] As shown in Table 1, the lithium-ion batteries of Examples 1-1 to 1-30 with added Formula II compounds exhibit significantly improved high-temperature and room-temperature cycle performance, as well as thermal safety performance, compared to Comparative Example 1-1 without added Formula II compounds. This may be because fluoroethylene carbonate can react with the FSI anion in lithium bis(fluorosulfonyl)imide. - The two layers work together to form an outer organic and inner inorganic SEI film on the surface of the negative electrode active material. However, the bonding between the two is relatively weak. By further adding compound II, the silicon functional groups in compound II can undergo a coupling reaction with the -OH on the negative electrode surface to form a strong Li-O-Si chemical bond. Moreover, the unsaturated groups in compound II have good compatibility with the organic components in the SEI film after polymerization, thereby improving the bonding force between the organic and inorganic layers on the negative electrode surface. This makes the SEI film more flexible and better able to adapt to the large volume changes of the negative electrode, thus significantly improving the long-cycle stability of lithium-ion batteries.

[0105] A comparison of Examples 1-15 to 1-30 shows that the examples satisfying 27% ≤ c / (b+c) ≤ 56% and 30% ≤ a / (a+b+c) ≤ 55% exhibit further improved cycle stability and hot box safety performance. This may be because a better ratio of lithium salt to organic solvent can reduce the content of free solvent, lower the HOMO energy level of the solvent, raise the LUMO energy level, and broaden the electrochemical window of the electrolyte. At this point, FSI- is at a higher HOMO energy level and a lower LUMO energy level, which is beneficial for FSI- to participate in redox reactions, forming a LiF-rich SEI / CEI protective film, thereby improving the mechanical strength of the protective film and increasing its ionic conductivity, reducing polarization during cycling. Simultaneously, a suitable content of Formula I compound helps increase the wettability of the electrolyte, reduce the overall viscosity of the electrolyte, and thus improve conductivity, further enhancing the long-cycle stability of the lithium-ion battery.

[0106] Examples 2-1 to 2-12

[0107] Unlike Examples 1-3, compounds of Formula III (ether nitrile additives) shown in Table 2 were added to the electrolytes of Examples 1-3, while keeping the ratio of c / (b+c) and a / (a+b+c) in the electrolyte constant. The types and amounts of Formula III compounds are shown in Table 2, and the test results are also shown in Table 2.

[0108] Table 2

[0109]

[0110]

[0111] Compared to Examples 1-3, Examples 2-1 to 2-12 show that the addition of ether nitrile additives can further improve the cycle performance and thermal safety performance of lithium-ion batteries. This is because ether nitrile additives are excellent positive electrode protective additives. The -CN group in their molecules has a strong complexing effect with the transition metals on the surface of the positive electrode active material, which can inhibit the dissolution of the transition metals and thus inhibit the structural phase transition of the positive electrode active material and the side reactions with the electrolyte. Moreover, their solvation effect with lithium ions is relatively small. When an appropriate amount of such additives is added, it can ensure the formation of a LiF-rich CEI film by anion derivation and further reduce the influence of transition metals on the SEI film, thereby improving the cycle performance of lithium-ion batteries. However, the addition of a large amount of ether nitrile additives can lead to the destruction of the SEI film and deteriorate the room temperature cycle performance. The presence of silane additives can, on the one hand, improve the adhesion of the organic layer on the negative electrode surface, making the SEI film more flexible, and on the other hand, reduce the damage to the SEI film caused by the addition of ether nitrile additives, ensuring the room temperature cycle performance of lithium-ion batteries. A comparison of Examples 2-1 to 2-6 shows that controlling the content of ether nitrile additives within the range of z / (y+z) of 0.17 to 0.86 is beneficial for simultaneously improving the high-temperature cycle performance and room-temperature cycle performance of lithium-ion batteries.

[0112] Examples 3-1 to 3-3

[0113] Unlike Example 1-1, the composition of the electrolyte was further adjusted. Lithium difluorophosphate was added to the electrolyte of Example 1-1 to replace part of the lithium difluorosulfonylimide. The amount of lithium difluorophosphate is shown in Table 3, and the test results are also shown in Table 3.

[0114] Table 3

[0115]

[0116]

[0117] Compared with Example 1-1, Examples 3-1 to 3-3, by controlling the amount of lithium difluorophosphate added to meet 0.01≤d / c≤0.3, improves the oxidation resistance and overall stability of the electrolyte without affecting the original solvation structure, thereby further improving the cycle performance and thermal safety performance of the lithium-ion battery.

[0118] 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 electrolyte, characterized in that, The electrolyte comprises an organic solvent, lithium difluorosulfonylimide, a compound of formula I, and additives; The additives include fluoroethylene carbonate and compounds of formula II; Formula I Formula II wherein R1to R6are each independently selected from hydrogen, fluorine, C1-C 12 alkyl, C1-C4fluorosubstituted or non-fluorosubstituted alkyl, C1-C4 12 oxygenated alkyl, it being possible for two of R1to R6adjacent groups to be linked into a ring, and at least one of R1to R6being fluorine-containing; R7 to R 10 Each is independently selected from substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C1-C 12 Oxyalkyl, substituted or unsubstituted C2-C 12 Groups containing unsaturated carbon-carbon double bonds, substituted or unsubstituted C2-C 12 Groups containing unsaturated carbon-carbon triple bonds, and R7 to R 10 At least one of them includes an unsaturated carbon-carbon double bond or an unsaturated carbon-carbon triple bond; when substituted, the substituents include halogens; Based on the mass of the electrolyte, the mass percentage of the compound of formula II is denoted as y; The additive also includes compounds of formula III; Formula III Wherein, M is selected from any one of C1~C5 alkyl, C1~C5 alkylene, and the group shown in formula c; Formula c Q is independently selected from any one of the groups shown in formula d; Formula d Among them, R 17 Each is independently selected from any one of the C1-C3 alkylene groups; x is selected from any value among 1, 2, and 3; Based on the mass of the electrolyte, the mass percentage of the compound of formula III is denoted as z, which satisfies: 0.1%≤z≤3%; 0.17≤z / (z+y)≤0.86; The electrolyte includes lithium difluorophosphate, the mass percentage of which is denoted as d, and the mass percentage of which is lithium difluorosulfonylimide is denoted as c. Based on the mass of the electrolyte, the following condition is met: 0.01 ≤ d / c ≤ 0.

3.

2. The electrolyte according to claim 1, characterized in that, The compound of formula II includes at least one of the following compounds: Formula II-1 Formula II-2 Formula II-3 Formula II-4 Formula II-5 Formula II-6.

3. The electrolyte according to claim 1, characterized in that, The compound of formula I includes at least one of the following compounds: Equation I-1, Equation I-2, Formula I-3, Formula I-4, Formula I-5, Formula I-6, Formula I-7, Formula I-8, Equation I-9, Formula I-10, Formula I-11, Formula I-12, Formula I-13, Formula I-14, Formula I-15, Formula I-16, Formula I-17, Formula I-18, Formula I-19, Formula I-20, Formula I-21, Formula I-22.

4. The electrolyte according to claim 1, characterized in that, Based on the mass of the electrolyte, the mass percentage of the compound of formula I is denoted as a, the mass percentage of the organic solvent is denoted as b, the mass percentage of the lithium bis(fluorosulfonyl)imide is denoted as c, and the mass percentage of the fluoroethylene carbonate is denoted as x, satisfying at least one of the following conditions (1) to (9): (1) 25%≤c / (b+c)≤60%; (2)25%≤a / (a+b+c)≤70%; （3）15%≤b≤50%； （4）8%≤c≤50%； （5）0.1%≤x≤5%； (6) 0.02 ≤ x / b ≤ 0.25; （7）0.01%≤y≤5%； (8)0.02≤y / (x+y)≤0.75; (9) The organic solvent includes at least one of carbonate or carboxylic acid ester.

5. The electrolyte according to claim 4, characterized in that, At least one of the following conditions (1) to (10) must be met: (1) 27%≤c / (b+c)≤56%; (2)30%≤a / (a+b+c)≤55%; （3）20%≤b≤40%； （4）15%≤c≤35%； （5）0.5%≤x≤3%； (6) 0.02 ≤ x / b ≤ 0.15; （7）0.3%≤y≤2%； (8) 0.1≤y / (x+y)≤0.5; (9) The carbonate includes at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dipropyl carbonate or methyl propyl carbonate; (10) The carboxylic acid ester includes at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate.

6. The electrolyte according to claim 1, characterized in that, The compound of Formula III includes at least one of 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(2-cyanoethoxy)propane, 3-isopropoxypropionitrile, 3-ethoxypropionitrile, or 2-ethoxyacetonitrile.

7. An electrochemical device, characterized in that, It includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; the electrolyte is the electrolyte according to any one of claims 1 to 6.

8. An electronic device comprising the electrochemical device of claim 7.

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