Electrolyte, electrochemical device using same, and electronic device

Abstract

An electrolyte, an electrochemical device using same, and an electronic device. The electrolyte comprises a first compound, a second compound, and a compound of formula (IV). The first compound comprises at least one of a compound of formula (I), a compound of formula (II), or a compound of formula (III). The second compound comprises at least one of the following compounds: ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, diamyl carbonate, ethyl isobutyl carbonate, methyl isopropyl carbonate, dibutyl carbonate, diisopropyl carbonate or propyl carbonate. On the basis of the mass of the electrolyte, the mass percentage of the first compound is 41.6%-79%, the mass percentage of the second compound is 4.2%-41.6%, and the mass percentage of the compound of formula (IV) is 4%-15%. Using the electrolyte can significantly improve the energy density, the high-temperature cycle performance and the rate capability of the electrochemical device under a high voltage.

Description

Electrolyte and electrochemical device and electronic device using the same

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on September 28, 2023, with application number 202311277650.6 and invention name “Electrolyte and electrochemical device and electronic device using the same”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to an electrolyte and an electrochemical device and an electronic device using the electrolyte. Background Art

[0003] Electrochemical devices (e.g., lithium-ion batteries) are widely used in consumer electronics due to their high specific energy, lightweight, and long cycle life. As electronic products become thinner and more portable, demands for higher battery energy density, lifespan, and safety are increasing.

[0004] In order to further improve the energy density of lithium-ion batteries, doping can be performed in the positive and negative electrodes, but doping with higher capacity materials generally leads to a deterioration in cycle life. In order to improve the cycle life, elements such as Mn and Al can be doped in the positive electrode active material, but doping with Mn and Al elements will lead to a loss of capacity. The energy density can also be increased by increasing the amount of lithium removed from the material by increasing the charge cut-off voltage. However, under high voltage, the positive and negative electrodes, the separator and the electrolyte are prone to redox reactions and are in an unstable state, which greatly deteriorates the cycle performance of the battery. In addition, in order to increase the charging speed (i.e. Li + High electrolyte conductivity is often required to achieve high transfer speeds. Increasing the carboxylate content can enhance electrolyte fluidity and conductivity, but carboxylate esters are often prone to side reactions at the positive and negative electrodes, deteriorating high-temperature cycling performance.

[0005] In view of this, it is indeed necessary to provide an effective strategy to improve the energy density, high-temperature cycling performance and rate performance of electrochemical devices at high voltage.

[0006] Summary of the Invention

[0007] The present application attempts to solve at least one problem existing in the related art to at least some extent by providing an electrolyte and an electrochemical device and an electronic device using the electrolyte.

[0008] According to one aspect of the present application, the present application provides an electrolyte comprising a first compound, a second compound and a compound of formula (IV), wherein:

[0009] The first compound includes at least one of the compound of formula (I), the compound of formula (II), or the compound of formula (III), and the structural formulas of the compound of formula (I), the compound of formula (II), the compound of formula (III), and the compound of formula (IV) are as follows:

[0010] wherein R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, F, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, fluorine-substituted C1-C5 alkyl, fluorine-substituted C2-C5 alkenyl, fluorine-substituted C2-C5 alkynyl, sulfonic acid group-substituted C2-C5 alkyl or cyano group-substituted C2-C5 alkyl; at least one of R1 and R2 contains at least one fluorine atom; at least one of R3 and R4 contains at least one fluorine atom; at least one of R5 and R6 contains at least one fluorine atom; at least one of R7 and R8 contains at least one fluorine atom; the second compound comprises at least one of the following compounds: ethylene carbonate, propylene carbonate ester, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, dioctyl carbonate, dipentyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, dibutyl carbonate, diisopropyl carbonate or propyl carbonate; and, based on the mass of the electrolyte, the mass percentage of the first compound is A% and 41.6≤A≤79, the mass percentage of the second compound is B% and 4.2≤B≤41.6, and the mass percentage of the compound of formula (IV) is M% and 4≤M≤15. In the present application, R7 and R8 each independently represent one or more groups, and the above groups can be selected from H, F, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, fluorine-substituted C1-C5 alkyl, fluorine-substituted C2-C5 alkenyl, fluorine-substituted C2-C5 alkynyl, sulfonic acid-substituted C2-C5 alkyl or cyano-substituted C2-C5 alkyl.

[0011] According to an embodiment of the present application, the first compound includes at least one of the following compounds:

[0012] According to an embodiment of the present application, the compound of formula (IV) includes at least one of the following compounds:

[0013] According to an embodiment of the present application, 45.8≤A≤74.9 and 8.3≤B≤37.4.

[0014] According to an embodiment of the present application, 49.9≤A≤74.9 and 8.3≤B≤33.3.

[0015] According to an embodiment of the present application, the electrolyte further contains a nitrile compound. Based on the mass of the electrolyte, the mass percentage content of the nitrile compound is C%, where 0 < C ≤ 7 and 0 < 100C / A ≤ 12.0.

[0016] According to an embodiment of the present application, the nitrile compound includes at least one of a compound having two cyano groups or a compound having three or more cyano groups, where: the compound having two cyano groups includes at least one of the following compounds: malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, terephthalonitrile, tetradecanedinitrile, azomalononitrile, methylglutaronitrile or glutaconitrile; and the compound having three or more cyano groups includes at least one of the following compounds: nonanenitrile, 1,3,5-benzenetricarbonitrile, 2,4,6-trifluorobenzene-1,3,5-tricarbonitrile, 2-bromobenzene-1,3,5-tricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,2,6-hexanetricarbonitrile or a compound of formula (V), and the compound of formula (V) includes at least one of the following compounds:

[0017] According to an embodiment of the present application, the electrolyte further contains a compound of formula (VI):

[0018] where: R9, R 10 and R 11 are each independently selected from H, F, a substituted or unsubstituted C1-C5 alkyl group, a C1-C5 alkoxy group, a C2-C5 alkenyl group or a C2-C5 alkynyl group. When substituted, the substituent is selected from at least one of F, an aldehyde group or a cyano group; R 12 is selected from O or -CH(R a )-; and R a is selected from H, F, a substituted or unsubstituted C1-C5 alkyl group or a C1-C5 alkoxy group. When substituted, the substituent is selected from at least one of F, an aldehyde group or a cyano group;

[0019] And based on the mass of the electrolyte, the mass percentage content of the compound of formula (VI) is D%, and D is from 0.01 to 3.

[0020] According to an embodiment of the present application, the compound of formula (VI) includes at least one of the following compounds:

[0021] According to an embodiment of the present application, the electrolyte further includes a first additive. The first additive includes at least one of 1,3-propane sultone, ethylene sulfate or vinylene carbonate, and based on the mass of the electrolyte, the mass percentage content of the first additive is less than or equal to 5%.

[0022] According to an embodiment of the present application, the electrolyte also includes a third compound, which includes at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate or butyl butyrate, and based on the mass of the electrolyte, the mass percentage of the third compound is less than or equal to 20%.

[0023] According to another aspect of the present application, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator and the electrolyte described in the present application.

[0024] According to yet another aspect of the present application, the present application provides an electronic device, which includes the electrochemical device according to the present application.

[0025] The present application can significantly improve the energy density, high temperature cycle performance and rate performance of the electrochemical device at high voltage by using an electrolyte containing a first compound, a second compound and a compound of formula (IV) in a specific content and type.

[0026] Additional aspects and advantages of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0027] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0028] In the detailed description and claims, a list of items linked by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can contain a single element or multiple elements. Item B can contain a single element or multiple elements. Item C can contain a single element or multiple elements.

[0029] As used herein, the term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having 1 to 20 carbon atoms. "Alkyl" is also intended to be a branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms. When specifying an alkyl group with a specific carbon number, it is intended to encompass all geometric isomers with that carbon number; therefore, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Alkyl examples include, but are not limited to methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc.

[0030] As used herein, the term "alkenyl" refers to a monovalent unsaturated hydrocarbon group which may be straight or branched and has at least one, and typically 1, 2, or 3, carbon-carbon double bonds. Unless otherwise defined, such alkenyl groups typically contain from 2 to 20 carbon atoms and include, for example, -C 2-4 Alkenyl, -C 2-6 Alkenyl and -C 2-10 Representative alkenyl groups include, for example, ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like.

[0031] As used herein, the term "alkynyl" refers to a monovalent unsaturated hydrocarbon group which may be straight or branched and has at least one, and typically one, two, or three, carbon-carbon triple bonds. Unless otherwise defined, such alkynyl groups typically contain from 2 to 20 carbon atoms and include, for example, -C 2-4 Alkynyl, -C 3-6 Alkynyl and -C 3-10 Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like.

[0032] As used herein, "alkoxy" refers to an alkyl group (-O-alkyl) that is connected to the parent structure by an oxygen atom. When a cycloalkyl group is connected to the parent structure by an oxygen atom, the group may also be referred to as a cycloalkoxy group. Examples include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, butoxy, sec-butoxy, tert-butoxy, pentyloxy, cyclohexyloxy, etc. "perhaloalkoxy" is expected to be a perhaloalkyl group connected to the parent structure by oxygen, such as group -O-CF .

[0033] Electrochemical devices (e.g., lithium-ion batteries) have been widely used in various fields due to their superior performance, and people have increasingly higher requirements for their performance, such as energy density, cycle performance, and rate performance. The energy density of electrochemical devices can usually be improved by doping in the positive and negative electrodes, for example, by doping Ni elements in the positive electrode active material LiCoO2. However, doping in the positive and negative electrodes usually deteriorates the cycle performance of the electrochemical device, especially the cycle life at high temperatures. Further doping elements such as Mn or Al in the positive electrode active material LiCoO2 can improve the cycle life of the electrochemical device, but these elements will lead to capacity loss of the electrochemical device. The energy density can also be increased by increasing the amount of lithium removed from the material by increasing the charge cut-off voltage. However, under high voltage, the positive and negative electrodes, the separator and the electrolyte are prone to redox reactions and are in an unstable state, which greatly deteriorates the cycle performance of the electrochemical device. In addition, increasing the content of carboxylates can enhance the fluidity of the electrolyte and improve the conductivity, thereby increasing the charging speed (i.e., Li + However, carboxylates are often prone to react at the positive and negative electrodes, which can deteriorate high-temperature cycling performance.

[0034] In order to solve the above problems, the present application provides an electrolyte comprising a first compound, a second compound and a compound of formula (IV), wherein:

[0035] The first compound includes at least one of the compound of formula (I), the compound of formula (II), or the compound of formula (III). The structural formulas of the compound of formula (I), the compound of formula (II), the compound of formula (III), and the compound of formula (IV) are as follows:

[0036] wherein R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, F, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, fluorine-substituted C1-C5 alkyl, fluorine-substituted C2-C5 alkenyl, fluorine-substituted C2-C5 alkynyl, sulfonic acid-substituted C2-C5 alkyl or cyano-substituted C2-C5 alkyl; at least one of R1 and R2 contains at least one fluorine atom; at least one of R3 and R4 contains at least one fluorine atom; at least one of R5 and R6 contains at least one fluorine atom; at least one of R7 and R8 contains at least one fluorine atom;

[0037] the second compound comprises at least one of the following compounds: ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, dioctyl carbonate, diamyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, dibutyl carbonate, diisopropyl carbonate, or propyl carbonate; and

[0038] Based on the mass of the electrolyte, the mass percentage of the first compound is A% and 41.6≤A≤79, the mass percentage of the second compound is B% and 4.2≤B≤41.6, and the mass percentage of the compound of formula (IV) is M% and 4≤M≤15.

[0039] When the first compound is added to the electrolyte, the electrochemical device can achieve better cycle performance. At the same time, since there is no need to add excessive additives to continuously repair the interface, the active lithium consumed at the interface is reduced, thereby improving the energy density of the electrochemical device. In addition, the addition of the second compound to the electrolyte can increase the dissociation of the lithium salt, thereby improving the rate performance of the electrochemical device and significantly reducing the charging time, thereby further improving the high-temperature cycle performance of the electrochemical device. Adding the compound of formula (IV) to the electrolyte can preferentially reduce the negative electrode to form a passivation layer, reducing the consumption of active lithium at the negative electrode, but it is easy to approach the surface of the negative electrode and react with dehydrogenation at the negative electrode to form HF, which continuously etches the positive electrode interface. When the contents of the first compound, the second compound, and the compound of formula (IV) in the electrolyte meet specific ranges, the first compound reacts preferentially, and the resulting interface component contains a large amount of LiF, which gives the interface higher mechanical strength and corrosion resistance. Therefore, the electrochemical device still has excellent high-temperature cycle performance at high voltage. At the same time, the presence of the second compound can avoid the significant increase in charging time caused by insufficient dissociation of the lithium salt, thereby improving the rate performance of the electrochemical device. Adding the first compound, the second compound and the compound of formula (IV) in the above-mentioned amounts to the electrolyte can continuously repair the interface, significantly improve the energy density, high-temperature cycle performance and rate performance of the electrochemical device at high voltage, thereby improving the overall performance of the electrochemical device.

[0040] In some embodiments, 45.8 ≤ A ≤ 74.9. In some embodiments, 49.9 ≤ A ≤ 74.9. In some embodiments, A is 45.8, 49.9, 55, 60, 65, 70, 74.9, or a value within a range formed by any two of the foregoing values. When the content of the first compound in the electrolyte is within the foregoing range, the energy density, high-temperature cycling performance, and rate performance of the electrochemical device at high voltage can be further improved, thereby enhancing the overall performance of the electrochemical device.

[0041] In some embodiments, 8.3 ≤ B ≤ 37.4. In some embodiments, 8.3 ≤ B ≤ 33.3. In some embodiments, B is 8.3, 10, 12, 15, 18, 20, 25, 30, 33.3, 37.4, or a value within a range formed by any two of the foregoing values. When the content of the second compound in the electrolyte is within the foregoing range, the energy density, high-temperature cycling performance, and rate performance of the electrochemical device at high voltage can be further improved, thereby enhancing the overall performance of the electrochemical device.

[0042] In some embodiments, the first compound includes at least one of the compounds of the following formula:

[0043] In some embodiments, the compound of formula (IV) includes at least one of the compounds of the following formula:

[0044] In some embodiments, the electrolyte further contains a nitrile compound.

[0045] In some embodiments, the nitrile compound includes at least one of a compound having two cyano groups or a compound having three or more cyano groups. A compound having two cyano groups can be abbreviated as dinitrile, a compound having three cyano groups can be abbreviated as trinitrile, and a compound having more cyano groups can be abbreviated as polynitrile.

[0046] In some embodiments, the compound having two cyano groups includes at least one of the following compounds: malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, terephthalonitrile, tetradecanedinitrile, azomalononitrile, methylglutaronitrile or pentenedinitrile.

[0047] In some embodiments, the compound having three or more cyano groups includes at least one of the following compounds: nonanetricarbonitrile, 1,3,5-benzenetricarbonitrile, 2,4,6-trifluorobenzene-1,3,5-tricarbonitrile, 2-bromobenzene-1,3,5-tricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,2,6-hexanetricarbonitrile or the compound of formula (V), and the compound of formula (V) includes at least one of the following compounds:

[0048] In some embodiments, based on the mass of the electrolyte, the mass percentage content of the nitrile compound is C%, where 0 < C ≤ 7 and 0 < 100C / A ≤ 12.0. In some embodiments, C is 0.5, 1, 2, 3, 4, 5, 6, 7 or a value within the range formed by any two of the above values. In some embodiments, 100C / A is 0.5, 1, 3, 5, 8, 10, 12.0 or a value within the range formed by any two of the above values.

[0049] The nitrile compound can bind to the transition metal on the surface of the positive electrode, and the first compound and the nitrile compound form a coating layer of an inorganic compound or an organic composition containing F and cyano groups, which has the antioxidant property of the first compound, can reduce the side reactions of the electrolyte, and at the same time has a strong complexing effect of the nitrile compound on the transition metal, making the structure of the positive electrode material more stable. Thus, the cycle performance and high-temperature storage performance of the electrochemical device under high temperature and high pressure can be further improved.

[0050] In some embodiments, the electrolyte further comprises a compound of formula (VI):

[0051] Among them: R9, R 10 and R 11 R is independently selected from H, F, substituted or unsubstituted C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl or C2-C5 alkynyl, and when substituted, the substituent is selected from at least one of F, aldehyde or cyano; 12 Selected from O or -CH(R a )-; and R a is selected from H, F, substituted or unsubstituted C1-C5 alkyl or C1-C5 alkoxy, and when substituted, the substituent is selected from at least one of F, aldehyde or cyano.

[0052] In some embodiments, the compound of formula (VI) comprises at least one of the following compounds:

[0053] In some embodiments, the mass percentage of the compound of formula (VI) based on the mass of the electrolyte is D%, and D is 0.01 to 3. In some embodiments, D is 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, or a value within a range formed by any two of the foregoing values.

[0054] The compound of formula (VI) easily reacts with the nitrile compound at the negative electrode, which can effectively improve the effects of the first compound and the nitrile compound on the negative electrode and significantly improve the stability of the negative electrode interface, thereby significantly improving the cycle performance of the electrochemical device under high temperature and high pressure and enhancing its thermal stability such as hot box performance.

[0055] In some embodiments, the electrolyte further includes a first additive, the first additive including at least one of 1,3-propane sultone (PS), diethyl thiosulfate (DTD), or vinylene carbonate (VC).

[0056] In some embodiments, the weight percentage of the first additive based on the weight of the electrolyte is less than or equal to 5%. In some embodiments, the weight percentage of the first additive based on the weight of the electrolyte is 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1%, 5%, or a value within a range formed by any two of the foregoing values.

[0057] When the electrolyte contains a certain amount of the first additive, the cycle performance of the electrochemical device under high temperature and high pressure can be further improved.

[0058] In some embodiments, the electrolyte further includes a second additive, and the second additive includes at least one of lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, or lithium difluorophosphate.

[0059] In some embodiments, the weight percentage of the second additive is less than or equal to 5% based on the weight of the electrolyte. In some embodiments, the weight percentage of the second additive is 1%, 2%, 3%, 4%, 5%, or a value within a range formed by any two of the above values ​​based on the weight of the electrolyte.

[0060] When the electrolyte contains a certain amount of the second additive, the interface film formed based on the second additive has better stability, thereby improving the cycle performance of the electrochemical device under high temperature and high pressure.

[0061] In some embodiments, the electrolyte further includes a third compound comprising at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, or butyl butyrate.

[0062] In some embodiments, the weight percentage of the third compound is less than or equal to 20% based on the weight of the electrolyte. In some embodiments, the weight percentage of the third compound is 1%, 5%, 10%, 15%, 20%, or a value within a range formed by any two of the foregoing values, based on the weight of the electrolyte.

[0063] Adding the third compound to the electrolyte helps reduce the viscosity of the electrolyte, thereby accelerating lithium ion transport. When the electrolyte contains the third compound in the above-mentioned amount, it helps further improve the cycling performance of the electrochemical device under high temperature and high pressure.

[0064] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of LiPF6, LiTFSI, LiFSI, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3 or Li2SiF6.

[0065] In some embodiments, the lithium salt comprises 8% to 20% by weight of the electrolyte. In some embodiments, the lithium salt comprises 8%, 10%, 12%, 15%, 18%, 20% by weight of the electrolyte, or a value within a range formed by any two of the foregoing values. When the lithium salt content in the electrolyte is within the foregoing range, the overall performance of the electrochemical device can be further improved.

[0066] The present application also provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator and the electrolyte described in the present application.

[0067] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, and the positive electrode material layer includes a positive electrode active material. In the present application, the above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0068] In some embodiments, the positive electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. For example, the binder may include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride. The present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer. Those skilled in the art can select it according to actual needs as long as the purpose of the present application can be achieved.

[0069] This application does not impose any particular restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 15 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm. This application does not impose any particular restrictions on the thickness of the positive electrode sheet, as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode sheet is 50 μm to 250 μm.

[0070] The present application does not impose any particular restrictions on the preparation method of the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the preparation method of the positive electrode active material may include but is not limited to the following steps: LiCoO2 (CAS No.: 12190-79-3) is mixed evenly with a nickel-containing compound and then heat-treated in an air atmosphere to obtain a positive electrode active material. The present application does not impose any particular restrictions on the temperature, time, and heating rate of the above-mentioned heat treatment, as long as the purpose of the present application can be achieved. For example, the heat treatment temperature is 650°C to 850°C, the time is 22h to 26h, and the heating rate is 2°C / min to 8°C / min. The present application does not impose any particular restrictions on the mass ratio of LiCoO2 to the nickel-containing compound, as long as the purpose of the present application can be achieved.

[0071] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. In this application, the "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector surface, or it can be a partial area of ​​the negative electrode current collector surface. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0072] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). The negative electrode current collector can be a metal plate without through holes, or a porous metal plate with through holes.

[0073] In some embodiments, the negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys.

[0074] In some embodiments, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not particularly limit the types of the conductive agent, binder, and thickener, as long as the purpose of this application can be achieved. For example, the conductive agent and binder can be at least one of the above-mentioned conductive agents and binders, and the thickener can include but is not limited to at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0075] This application does not impose any particular restrictions on the thickness of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 150 μm. This application does not impose any particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 12 μm. This application does not impose any particular restrictions on the thickness of the negative electrode pole piece, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode pole piece is 50 μm to 250 μm.

[0076] The isolation membrane in the electrochemical device is used to separate the positive electrode plate and the negative electrode plate, prevent the internal short circuit of the electrochemical device, allow the electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the isolation membrane, as long as the purpose of the present application can be achieved. For example, the material of the isolation membrane may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. Exemplarily, polyethylene includes at least one of high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene. The type of isolation membrane may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0077] In some embodiments, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. For example, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited and may, for example, include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited and may, for example, be at least one of the above binders. The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0078] The preparation process of the electrochemical device of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device. In addition, as needed, an overcurrent protection element, a guide plate, etc. may be placed in the packaging bag to prevent pressure rise and overcharging and discharging inside the electrochemical device. The packaging bag is a packaging bag known in the art and is not limited in the present application.

[0079] In some embodiments, the electrochemical device may include an electrode assembly. In some embodiments, the electrode assembly is a wound electrode assembly or a stacked electrode assembly. In some embodiments, the electrochemical device of the present application includes, but is not limited to, all types of primary batteries, secondary batteries, or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In some embodiments, the electrochemical device is a sodium ion battery.

[0080] The present application further provides an electronic device, which includes the electrochemical device described in the present application.

[0081] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type 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 television, a portable cleaner, a portable CC machine, 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, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0082] The preparation of lithium-ion batteries is described below using lithium-ion batteries as an example and in combination with specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0083] Example

[0084] The following describes the performance evaluation of the lithium-ion battery according to the embodiments and comparative examples of the present application.

[0085] 1. Preparation of lithium-ion batteries

[0086] 1. Preparation of positive electrode

[0087] The positive electrode active material, lithium cobalt oxide (LiCoO2), the conductive agent, carbon nanotubes (CNTs), and the binder, polyvinylidene fluoride, were mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added as a solvent and stirred in a vacuum mixer until a uniform positive electrode slurry with a solids content of 75 wt% was formed. The positive electrode slurry was evenly coated on one surface of a 12 μm thick positive electrode current collector aluminum foil, dried at 85°C, and cold pressed to produce a positive electrode sheet with a 100 μm thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode material layer. The positive electrode sheet was cut into 74 mm x 867 mm dimensions and welded to the tabs before use.

[0088] 2. Preparation of negative electrode

[0089] The negative electrode active materials, artificial graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC), were mixed in a mass ratio of 95:2:3. Deionized water was then added as a solvent to create a slurry with a solids content of 70 wt%, which was then stirred thoroughly. The slurry was evenly coated on one surface of an 8μm-thick copper foil, dried at 110°C, and cold-pressed to produce a single-sided negative electrode sheet with a 150μm-thick negative electrode material layer. The above steps were repeated on the other surface of the copper foil to produce a double-sided negative electrode sheet. The negative electrode sheet was cut into 75mm x 867mm dimensions and the tabs were welded before use.

[0090] 3. Preparation of isolation membrane

[0091] A polyethylene porous polymer film with a thickness of 15 μm (manufacturer: Celgar C Separator Co., Ltd., USA) was used as a separator.

[0092] 4. Preparation of electrolyte

[0093] In an argon atmosphere glove box with a water content of less than 10 ppm, the components were uniformly mixed with 0.3% LiBOB and 12.5% ​​lithium hexafluorophosphate (LiPF6) according to the settings of the following examples and comparative examples to obtain an electrolyte.

[0094] 6. Preparation of lithium-ion batteries

[0095] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound and placed in an aluminum-plastic film packaging bag. The bag is then dehydrated at 80°C and filled with the prepared electrolyte. The battery is vacuum packaged, allowed to stand, formed, and shaped to produce a lithium-ion battery. The upper limit of the formation voltage is 4.15V, the formation temperature is 70°C, and the formation standing time is 2 hours.

[0096] 2. Test Method

[0097] 1. Test method for discharge capacity of lithium-ion batteries

[0098] Preparation of lithium-ion button cells: In a glove box, the negative electrode shell, gasket, lithium metal sheet, separator, positive electrode sheet, spring, and positive electrode shell were assembled in sequence and packaged on a packaging machine. After the gasket, lithium metal sheet, separator, and positive electrode sheet were placed, electrolyte was dripped onto each to wet them. The positive electrode sheet, separator, and electrolyte described above were those used in the Examples or Comparative Examples. The diameter of the positive electrode sheet was 14 mm, the diameter of the lithium metal sheet was 16 mm, and the diameter of the separator was 16.5 mm.

[0099] At 25°C, the prepared lithium-ion button cell was charged at a rate of 0.2C until the voltage reached 4.5V. It was then charged at a constant voltage of 4.5V until the current was less than 0.05C, reaching a fully charged state at 4.5V. The cell was then discharged at a constant current rate of 0.2C until the voltage reached 3.0V. The discharge capacity of the lithium-ion cell was measured as follows: discharge capacity in grams of the lithium-ion cell = discharge capacity / mass of the positive electrode active material. The mass of the positive electrode active material can be calculated based on the size of the positive electrode sheet and the formulation of the positive electrode sheet prepared in each embodiment or comparative example.

[0100] 2. Test method for high temperature cycle performance of lithium-ion batteries

[0101] At 45°C, charge the lithium-ion battery at a constant current of 0.7C to 4.52V, then charge at a constant voltage of 4.52V to a current of 0.05C, and then discharge at a constant current of 1C to 3.0V. This is one charge and discharge cycle, and record the discharge capacity of the lithium-ion battery in the first cycle. Charge and discharge the lithium-ion battery 500 times according to the above method, and record the discharge capacity of the 500th cycle. Calculate the discharge capacity retention rate of the lithium-ion battery using the following formula:

[0102] Discharge capacity retention rate=discharge capacity at the 500th cycle / discharge capacity at the 1st cycle×100%.

[0103] The high-temperature cycle performance of lithium-ion batteries can be evaluated by the discharge capacity retention rate. The higher the discharge capacity retention rate, the better the high-temperature cycle performance of the lithium-ion battery; the lower the discharge capacity retention rate, the worse the high-temperature cycle performance of the lithium-ion battery.

[0104] 3. Test method for rate performance of lithium-ion batteries

[0105] The lithium-ion battery was charged at a constant current of 0.7C to 4.52V, and then charged at a constant voltage to a current of 0.05C. After standing for 10 minutes, it was discharged at a constant current of 0.5C to 3V, and the discharge capacity D0 was recorded. After standing for 15 minutes, the lithium-ion battery was again charged at a constant current of 0.7C to 4.52V, and then charged at a constant voltage to a current of 0.05C. After standing for 10 minutes, it was discharged at a constant current of 2C to 3V, and the discharge capacity D1 was recorded. The 2C rate of the lithium-ion battery is calculated by the following formula:

[0106] 2C magnification=D1 / D0×100%.

[0107] 4. Test method for high temperature storage performance of lithium-ion batteries

[0108] At 25°C, the thickness of a half-charged lithium-ion battery is measured and recorded as C1. The lithium-ion battery is then charged to 4.5V at a constant current of 0.7C, then charged to a current of 0.05C at a constant voltage, and allowed to stand for 10 minutes. The fully charged battery is then left at 85°C for 8 hours, and the thickness measured at 25°C is recorded as C2. The high-temperature storage thickness expansion rate of a lithium-ion battery is calculated using the following formula:

[0109] High temperature storage thickness expansion ratio = (C2 / C1-1) x 100%.

[0110] 5. Hot box test method for lithium-ion batteries

[0111] The lithium-ion battery was discharged at 0.5C constant current to 3.0V at 25°C, then charged at 0.5C constant current to 4.5V. At 4.5V, it was charged to 0.05C constant voltage. The battery was placed in a 132°C high-temperature furnace for 1 hour. After the test, the battery was observed to see if it ignited. If it did not ignite, it was considered to have passed. Ten samples were tested for each example, and the pass rate of the hot box test was calculated.

[0112] 3. Test Results

[0113] Table 1 shows the effects of the first compound and the second compound in the electrolyte and their contents on the gram capacity, rate performance and high-temperature cycle performance of lithium-ion batteries at high voltage.

[0114] Table 1

[0115] Note: "EC" stands for ethylene carbonate, "PC" stands for propylene carbonate, "DEC" stands for diethyl carbonate, "EMC" stands for ethyl methyl carbonate, and "Ⅳ-1" stands for fluoroethylene carbonate. " / " indicates that it is not added or does not exist.

[0116] As shown in the comparative examples, when the electrolyte contains only two of the compound of formula (IV), the first compound, and the second compound, the lithium-ion battery has poor gram capacity, rate performance, and high-temperature cycle performance at high voltage. When the electrolyte contains too high a content of the second compound, the lithium-ion battery has poor gram capacity, rate performance, and high-temperature cycle performance at high voltage.

[0117] As shown in the examples, when the electrolyte contains 41.6% to 79% by mass of the first compound, 4.2% to 41.6% by mass of the second compound, and 4% to 15% by mass of the compound of formula (IV), the specific capacity, 2C rate, and discharge capacity retention rate of the lithium-ion battery can be significantly improved, thereby significantly improving the specific capacity, rate performance, and high-temperature cycling performance of the lithium-ion battery at high voltages. When the content of the first compound in the electrolyte is 45.8% - 74.9%, especially 49.9% - 74.9%, and the content of the second compound is 8.3% - 37.4%, especially 8.3% - 33.3%, the improvement effect is particularly obvious.

[0118] Table 2 shows the effects of nitrile compounds and their contents in the electrolyte on the cycling performance and high-temperature storage performance of lithium-ion batteries under high temperature and high pressure. Except for the parameters listed in Table 2, the other parameters of Examples 2-1 to 2-16 are the same as those of Example 1-4. The addition amounts of the newly added substances in Table 2 compared with Example 1-4 are obtained by reducing the content of the second compound in Example 1-4 by the corresponding mass percentage, so that the sum of the contents of all substances in the electrolyte is equal to 100%.

[0119] Table 2

[0120] Note: " / " indicates not added or does not exist.

[0121] The results show that further adding a nitrile compound to the electrolyte containing 41.6% to 79% by mass of the first compound, 4.2% to 41.6% by mass of the second compound, and 4% to 15% by mass of the compound of formula (IV) such that its mass percentage C (wt%) satisfies 0 < C ≤ 7 and 0 < 100C / A ≤ 12.0 can further improve the discharge capacity retention rate of the lithium-ion battery and significantly reduce the high-temperature storage thickness expansion rate of the lithium-ion battery.

[0122] Table 3 shows the effects of the compound of formula VI and its content in the electrolyte on the cycling performance and safety of lithium-ion batteries under high temperature and high pressure. Except for the parameters listed in Table 3, the other parameters of Examples 3-1 to 3-6 are the same as those of Example 2-16. The addition amounts of the newly added substances in Table 3 compared with Example 2-16 are obtained by reducing the content of the second compound in Example 2-16 by the corresponding mass percentage, so that the sum of the contents of all substances in the electrolyte is equal to 100%.

[0123] Table 3

[0124] Note: " / " indicates not added or does not exist.

[0125] The results show that further adding 0.01% to 3% by mass of the compound of formula VI to the electrolyte comprising 41.6% to 79% by mass of the first compound, 4.2% to 41.6% by mass of the second compound, 4% to 15% by mass of the compound of formula (IV) and not more than 7% by mass of the nitrile compound can further improve the discharge capacity retention rate of the lithium-ion battery and significantly improve its hot box test pass rate, that is, improve its safety.

[0126] Table 4 shows the effects of the third compound and its content, as well as the first additive and its content, in the electrolyte on the cycling performance of lithium-ion batteries under high temperature and high pressure. Aside from the parameters listed in Table 4, the other parameters of Examples 4-1 to 4-8 are consistent with those of Example 1-4. The amounts of the additional substances in Table 4 compared to Example 1-4 are obtained by reducing the content of the second compound in Example 1-4 by the corresponding percentage by mass, so that the sum of the contents of all substances in the electrolyte equals 100%.

[0127] Table 4

[0128] Note: "VC" stands for vinylene carbonate, "PS" stands for 1,3-propane sultone, and "DTD" stands for vinyl sulfate. " / " indicates that it is not added or does not exist.

[0129] The results show that further adding no more than 20% of the third compound and / or no more than 5% of the first additive to the electrolyte comprising 41.6% to 79% by mass of the first compound, 4.2% to 41.6% by mass of the second compound and 4% to 15% by mass of the compound of formula (IV) can further improve the discharge capacity retention rate of the lithium-ion battery.

[0130] References throughout this specification to "an embodiment," "part of an embodiment," "one embodiment," "another example," "an example," "a specific example," or "a portion of an example" mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as, "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "an example," are not necessarily references to the same embodiment or example in this application. In addition, the specific features, structures, materials, or characteristics described herein may be combined in any suitable manner in one or more embodiments or examples.

[0131] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. An electrolyte, which comprises a first compound, a second compound and a compound of formula (IV), wherein: The first compound comprises at least one of the compound of formula (I), the compound of formula (II) or the compound of formula (III), and the structural formulas of the compound of formula (I), the compound of formula (II), the compound of formula (III) and the compound of formula (IV) are as follows: wherein: R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from H, F, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, fluorine-substituted C1-C5 alkyl, fluorine-substituted C2-C5 alkenyl, fluorine-substituted C2-C5 alkynyl, sulfonic acid group-substituted C2-C5 alkyl or cyano-substituted C2-C5 alkyl; at least one of R1 and R2 contains at least one fluorine atom; at least one of R3 and R4 contains at least one fluorine atom; at least one of R5 and R6 contains at least one fluorine atom; at least one of R7 and R8 contains at least one fluorine atom; the second compound comprises at least one of the following compounds: ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, dipentyl carbonate, ethyl isobutyl carbonate, methyl isopropyl carbonate, dibutyl carbonate, diisopropyl carbonate or propyl carbonate; and, based on the mass of the electrolyte, the mass percentage content of the first compound is A% and 41.6 ≤ A ≤ 79, the mass percentage content of the second compound is B% and 4.2 ≤ B ≤ 41.6, and the mass percentage content of the compound of formula (IV) is 4% to 15%.

2. The electrolyte according to claim 1, wherein the first compound comprises at least one of the following compounds: The compound of formula (IV) includes at least one of the following compounds:

3. The electrolyte according to claim 1, wherein 45.8 ≤ A ≤ 74.9 and 8.3 ≤ B ≤ 37.

4.

4. The electrolyte according to claim 1, wherein 49.9 ≤ A ≤ 74.9 and 8.3 ≤ B ≤ 33.

3.

5. The electrolyte according to any one of claims 1 to 4, wherein the electrolyte further comprises a nitrile compound, and based on the mass of the electrolyte, the mass percentage content of the nitrile compound is C%, 0 < C ≤ 7 and 0 < 100C / A ≤ 12.

0.

6. The electrolyte according to claim 5, wherein the nitrile compound comprises at least one of a compound having two cyano groups or a compound having three or more cyano groups, wherein: the compound having two cyano groups comprises at least one of the following compounds: malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, terephthalonitrile, tetradecanedinitrile, azomalononitrile, methylglutaronitrile or pentenedinitrile; and The compound having three or more cyano groups includes at least one of the following compounds: nonanetrinitrile, 1,3,5-benzenetrinitrile, 2,4,6-trifluorobenzene-1,3,5-trinitrile, 2-bromobenzene-1,3,5-trinitrile, 1,3,6-hexanetrinitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,2,6-hexanetricarbonitrile or a compound of formula (V), wherein the compound of formula (V) includes at least one of the following compounds:

7. The electrolyte according to claim 5, wherein the electrolyte further comprises a compound of formula (VI): in: R9, R 10 and R 11 Each is independently selected from H, F, substituted or unsubstituted C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl or C2-C5 alkynyl, and when substituted, the substituent is selected from at least one of F, aldehyde or cyano; R 12 Selected from O or -CH(R a )-; and R a is selected from H, F, substituted or unsubstituted C1-C5 alkyl or C1-C5 alkoxy, and when substituted, the substituent is selected from at least one of F, aldehyde or cyano; and based on the mass of the electrolyte, the mass percentage content of the compound of formula (VI) is D%, and D is 0.01 to 3.

8. The electrolyte according to claim 7, wherein the compound of formula (VI) comprises at least one of the following compounds:

9. The electrolyte according to claim 1, wherein the electrolyte further comprises a first additive, the first additive comprises at least one of 1,3-propane sultone, vinylene sulfate or vinylene carbonate, and based on the mass of the electrolyte, the mass percentage content of the first additive is less than or equal to 5%.

10. The electrolyte according to claim 1, wherein the electrolyte further comprises a third compound, the third compound comprising at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate or butyl butyrate, and the mass percentage of the third compound based on the mass of the electrolyte is less than or equal to 20%. 11 . An electrochemical device comprising a positive electrode, a negative electrode, a separator and the electrolyte according to claim 1 .

12. An electronic device comprising the electrochemical device according to claim 11.

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