Electrolyte and electrochemical device comprising the same

Abstract

The application provides an electrolyte and an electrochemical device containing the electrolyte, wherein the electrolyte contains a compound of formula I; wherein R 1 , R 2 , R 3 , R 4 and R 5 are each independently selected from any one of a fluorine atom, a trifluoromethyl group, a C1-C3 alkyl group, a cyano group, a nitro group, a vinyl group and an ethynyl group. Based on the above technical solution provided in the application, the cycle and storage performance of the battery cell can be significantly improved.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and particularly relates to the field of lithium-ion battery technology, specifically to an electrolyte and an electrochemical device containing the electrolyte. Background Technology

[0002] Electrochemical devices, especially lithium-ion batteries, are increasingly used in portable electronic products. This is because electrochemical devices, particularly lithium-ion batteries, offer advantages such as high energy density, high operating voltage, light weight, low self-discharge rate, long cycle life, no memory effect, and environmental friendliness. Beyond smart electronic products (including mobile phones, laptops, cameras, etc.) and energy storage products, there is growing demand in higher-power electronic products such as electric vehicles, power tools, drones, and electric ships. Simultaneously, the performance requirements for electrochemical devices are becoming increasingly stringent. Therefore, developing electrochemical devices, especially lithium-ion batteries, with relatively low impedance and excellent cycle and storage performance is particularly important. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte and an electrochemical device comprising the electrolyte to improve the storage and cycling performance of battery cells. The specific solution is as follows:

[0004] According to a first aspect of this application, an electrolyte is provided, the electrolyte comprising: a compound of formula I;

[0005]

[0006] Among them, R 1 R 2 R 3 R 4 and R 5 Each is independently selected from any one of fluorine atom, trifluoromethyl, C1-C3 alkyl, cyano, nitro, vinyl, and ethynyl.

[0007] In the technical solution provided in this application, by adding a compound of formula I to the electrolyte, on the one hand, at the positive electrode interface, the lone pair electrons of the nitrogen atom on the pyridine of the compound of formula I can coordinate with the transition metal atoms at the positive electrode interface; on the other hand, at the negative electrode interface, the pyridine ring of the compound of formula I can form π-π interactions with the π electrons on the graphite of the negative electrode. Based on this, the lone pair electrons on the nitrogen atom and the electron vacancies on the graphite form new chemical bonds. Therefore, the compound of formula I can be stably adsorbed at the positive and negative electrode interfaces, playing a role in stabilizing the interface. In addition, the sulfonate group of the compound of formula I can preferentially undergo electrochemical redox reactions at the interface before the electrolyte, forming an interface film rich in nitrogen, sulfur, and fluorine elements, improving the cycle and storage performance of the battery cell. At the same time, this application has found that adding nitrogen heterocyclic substances and substances containing sulfonate groups or sulfur separately can have adverse effects on the negative electrode interface, resulting in a relatively high impedance. However, by adding an appropriate amount of the compound of formula I provided in this application to the electrolyte, the impedance is not worsened, and the storage performance is also improved. In particular, the compound of formula I provided in this application exhibits better film-forming properties due to the following structure: (1) The nitrogen heterocycle is a pyridine ring, which has a better electron distribution than the five-membered ring, and thus can be uniformly adsorbed at the interface, resulting in better film uniformity; while the electron distribution of the five-membered ring is oriented, which leads to poor uniformity of film-forming product distribution at the interface during film formation, affecting the improvement effect of cycling and storage performance. (2) The sulfonate group on the compound of formula I is connected to the C phase on the N heterocycle (pyridine ring) through O. By using this method to connect the pyridine ring and the sulfonate group, the reaction can be preferentially carried out at the active sites at the positive and negative electrode interfaces, so that the decomposition products cover the active sites, inhibiting the occurrence of side reactions and improving the cycling and storage effect. The spatial effect of the five-membered ring structure affects the reaction at the interface, and the adsorption effect of the compound of formula I provided in this application at the interface is stronger.

[0008] In some embodiments of this application, based on the total mass of the electrolyte, the mass content of the compound of formula I is A, where A satisfies: 0.01% ≤ A ≤ 10%; preferably, A satisfies: 0.01% ≤ A ≤ 5%. Further adjusting the mass content A of the compound of formula I within the above range can further improve the cycle and storage performance of the battery cell. If the mass content of the compound of formula I is lower than the above range, a complete protective film cannot be formed on the interface. If the mass content of the compound of formula I is higher than the above range, the impedance of the formed interface film will increase significantly, deteriorating the cycle performance.

[0009] In some embodiments of this application, the compound of formula I includes at least one of the compounds shown in formulas I-1 to I-12:

[0010]

[0011]

[0012] In a further technical solution of this application, the compound of formula I is selected from at least one of the compounds of formula I-1 to formula I-12, which can further improve the storage and cycle performance of the battery cell.

[0013] In some embodiments of this application, the electrolyte further includes cyclic carbonates. In this application, an appropriate amount of cyclic carbonate is further introduced into the electrolyte as an additive. The cyclic carbonate can polymerize at the negative electrode interface to form a polycarbonate-rich film layer, which can effectively encapsulate nitrogen and sulfur elements and distribute them uniformly on the negative electrode interface, promoting the effect of compound I and further improving the cycle performance of the battery cell.

[0014] In some embodiments of this application, the electrolyte further includes cyclic carbonates. Based on the total mass of the electrolyte, the mass content of the cyclic carbonates is F, where F satisfies: 0.01% ≤ F ≤ 10%; preferably, F satisfies: 0.1% ≤ F ≤ 5%. Controlling the mass content F of the cyclic carbonates in the electrolyte within the above range can further improve the cycle performance of the battery cell. When the mass content of the cyclic carbonates is too low, it cannot have a significant improvement effect; when the mass content is too high, the cyclic carbonates are prone to decomposition and gas generation at high temperatures, thereby deteriorating high-temperature storage performance and failing to achieve the corresponding performance improvement effect.

[0015] In some embodiments of this application, the cyclic carbonate includes at least one selected from vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate. In further technical solutions provided in this application, when the cyclic carbonate is selected from at least one selected from vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate, the cycle performance of the battery cell can be further improved.

[0016] In some embodiments of this application, based on the total mass of the electrolyte, the ratio A / F of the mass content A of the compound of formula I to the mass content F of the cyclic carbonate satisfies the following relationship: 0.01 ≤ A / F ≤ 50; preferably, A / F satisfies the following relationship: 0.1 ≤ A / F ≤ 50. Further adjusting the ratio A / F of the mass content A of the compound of formula I to the mass content F of the cyclic carbonate within the above range can further improve film-forming performance and further improve cell cycle life.

[0017] In some embodiments of this application, the electrolyte further includes a polynitrile compound. By adding a polynitrile compound to the electrolyte, the cyano group of the compound can combine with the transition metal atoms at the positive electrode interface, stabilizing the interface. Simultaneously, its alkyl chain can be stably cross-linked at the positive electrode interface, further promoting the adsorption and film-forming reaction of the compound of formula I at the positive electrode interface, thereby reducing side reactions in the electrolyte and further improving the storage stability of the battery cell.

[0018] In some embodiments of this application, the electrolyte further includes a polynitrile compound, the polynitrile compound comprising formula 1 to

[0019] At least one of the compounds shown in Formula 15:

[0020]

[0021]

[0022] In a further technical solution of this application, when the polynitrile compound is further selected from at least one of the above compounds (1)-(15), a better effect of improving the cell storage stability can be achieved.

[0023] In some embodiments of this application, the electrolyte further includes a polynitrile compound. Based on the total mass of the electrolyte, the mass content of the polynitrile compound is N, where N satisfies the following condition: 0.05% ≤ N ≤ 5%. Polycyano compounds exhibit poor reduction stability at the negative electrode, leading to instability at the negative electrode interface and thus deteriorating the cell's cycle performance. Further controlling the mass content N of the polynitrile compound in the electrolyte within the aforementioned range can improve the adsorption of Compound I at the positive electrode interface while reducing excessive cyano reduction at the negative electrode, achieving further improvement.

[0024] In some embodiments of this application, the electrolyte further includes a polynitrile compound. Based on the total mass of the electrolyte, the ratio N / A of the mass content N of the polynitrile compound to the mass content A of the compound of formula I satisfies: 0.005 ≤ N / A ≤ 10. Further controlling the ratio N / A of the mass content N of the polynitrile compound to the mass content A of the compound of formula I within the above range can improve the adsorption of the compound of formula I at the positive electrode interface while reducing excessive reduction of cyano groups at the negative electrode, thereby further improving high-temperature storage and cycling performance.

[0025] In some embodiments of this application, the electrolyte further includes cyclic sulfur oxides. The addition of cyclic sulfur oxides to the electrolyte allows them to synergistically participate in the solvation structure of lithium ions with the compound of Formula I, promoting the uniform adsorption of the compound of Formula I at both the positive and negative electrodes. Simultaneously, the cyclic sulfur oxides themselves can also participate in the formation of the interfacial film, further improving storage performance.

[0026] In some embodiments of this application, the electrolyte further includes cyclic sulfur oxides, which include at least one selected from 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, vinyl sulfate, and vinyl sulfite. The selection of cyclic sulfur oxides from at least one of 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, vinyl sulfate, and vinyl sulfite can further improve storage performance.

[0027] In some embodiments of this application, the electrolyte further includes a cyclic sulfur oxide compound. Based on the total mass of the electrolyte, the mass content of the cyclic sulfur oxide compound is S, where S satisfies: 0.05% ≤ S ≤ 5%. By controlling the mass content S of the cyclic sulfur oxide compound in the electrolyte within the above range, the cyclic sulfur oxide compound can be more rationally combined with the compound of Formula I. The two compounds adsorb at the positive electrode interface through competitive reactions, which can further increase the reaction probability of the compound of Formula I at the negative electrode interface, thereby better protecting the positive and negative electrode surfaces and further improving storage performance.

[0028] In some embodiments of this application, the electrolyte further includes a cyclic sulfur oxide compound. Based on the total mass of the electrolyte, the ratio S / A of the mass content A of the compound of formula I to the mass content S of the cyclic sulfur oxide compound satisfies the following relationship: 0.005 ≤ S / A ≤ 10. When the ratio S / A of the mass content A of the compound of formula I to the mass content S of the cyclic sulfur oxide compound is controlled within the above range, storage can be further improved with minimal impact on impedance.

[0029] According to a second aspect of this application, this application also provides an electrochemical device comprising the electrolyte described in any one of the first aspects of this application. The electrochemical device comprising the above-described electrolyte exhibits excellent high-temperature storage and cycling performance. Detailed Implementation

[0030] The technical solutions of this application are further illustrated below through specific embodiments. These specific embodiments do not represent a limitation on the scope of protection of this application. Any non-essential modifications and adjustments made by others based on the concept of this application still fall within the scope of protection of this application.

[0031] It should be noted that, in the following explanation, lithium-ion batteries are used as an example of secondary batteries to illustrate this application. However, the secondary batteries in this application are not limited to lithium-ion batteries, but can be any other suitable secondary batteries, such as lithium metal secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0032] I. Electrolyte

[0033] According to a first aspect of this application, an electrolyte is provided, the electrolyte comprising: a compound of formula I;

[0034]

[0035] Among them, R 1 R 2 R 3 R 4 and R 5 Each is independently selected from any one of fluorine atom, trifluoromethyl, C1-C3 alkyl, cyano, nitro, vinyl, and ethynyl.

[0036] Specifically, the chemical formula of the "fluorine atom" is -F. The "trifluoromethyl" group is a group formed by one carbon atom (C) and three fluorine atoms (F) covalently bonded together, with the chemical formula -CF3. The "C1-C3 alkyl" refers to a hydrocarbon group formed by removing one hydrogen atom from an alkane molecule with 1 to 3 carbon atoms, usually represented by "-R", also called an R group. The "cyano" group refers to a group in which a carbon atom and a nitrogen atom are connected by a triple bond, with the chemical formula -CN. The "nitro" group refers to the group remaining after removing one hydroxyl group from a nitric acid molecule, with the chemical formula -NO2. The "vinyl" group is obtained by removing one hydrogen atom from an ethylene molecule, with the chemical formula -HC=CH2. The "ethynyl" group is equivalent to the group formed by removing one hydrogen atom from an acetylene molecule, with the chemical formula CH≡C-. Specifically, the "fluorocarboxylic acid ester" is a class of carboxylic acid ester compounds containing fluorine atoms, with the chemical formula CnF2n+1COOR.

[0037] In the technical solution provided in this application, by adding a compound of formula I to the electrolyte, on the one hand, at the positive electrode interface, the lone pair electrons of the nitrogen atom on the pyridine of the compound of formula I can coordinate with the transition metal atoms at the positive electrode interface; on the other hand, at the negative electrode interface, the pyridine ring of the compound of formula I can form π-π interactions with the π electrons on the graphite of the negative electrode. Based on this, the lone pair electrons on the nitrogen atom and the electron vacancies on the graphite form new chemical bonds. Therefore, the compound of formula I can be stably adsorbed at the positive and negative electrode interfaces, playing a role in stabilizing the interface. In addition, the sulfonate group of the compound of formula I can preferentially undergo electrochemical redox reactions at the interface before the electrolyte, forming an interface film rich in nitrogen, sulfur, and fluorine elements, improving the cycle and storage performance of the battery cell. At the same time, this application has found that adding nitrogen heterocyclic substances and substances containing sulfonate groups or sulfur separately can have adverse effects on the negative electrode interface, resulting in a relatively high impedance. However, by adding an appropriate amount of the compound of formula I provided in this application to the electrolyte, the impedance is not worsened, and the storage performance is also improved. In particular, the compound of formula I provided in this application exhibits better film-forming properties due to the following structure: (1) The nitrogen heterocycle is a pyridine ring, which has a better electron distribution than the five-membered ring, thus it can be uniformly adsorbed at the interface, resulting in better film uniformity; while the electron distribution of the five-membered ring is oriented, which leads to poor uniformity of film-forming product distribution at the interface during film formation, affecting the improvement effect of cycling and storage performance. (2) The sulfonate group on the compound of formula I is connected to the C phase on the N heterocycle (pyridine ring) through O. By using this method to connect the pyridine ring and the sulfonate group, the reaction can preferentially occur at the active sites at the positive and negative electrode interfaces, thereby covering the decomposition products at the active sites, inhibiting the occurrence of side reactions, and improving the cycling and storage effect. The spatial effect of the five-membered ring structure affects the reaction at the interface, and the adsorption effect of the compound of formula I provided in this application at the interface is stronger.

[0038] In some embodiments of this application, the mass content of the compound of formula I is A, based on the total mass of the electrolyte, where A satisfies: 0.01% ≤ A ≤ 10%. Specifically, in some embodiments of this application, the mass content A of the compound of formula I, based on the total mass of the electrolyte, can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, or 2.2%. The percentages are 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, or a range consisting of any two of the above values. Preferably, A satisfies: 0.01% ≤ A ≤ 5%. When the mass content A of compound I is further controlled within the above range, the cycle and storage performance of the cell can be further improved. If the mass content of compound I is lower than the above range, a complete protective film cannot be formed on the interface. If the mass content of compound I is higher than the above range, the impedance of the formed interface film will increase significantly, deteriorating the cycle performance.

[0039] In some embodiments of this application, the compound of formula I includes at least one of the compounds shown in formulas I-1 to I-12:

[0040]

[0041] In a further technical solution of this application, the compound of formula I is selected from at least one of the compounds shown in formulas I-1 to I-12 above, which can further improve the storage and cycle performance of the battery cell.

[0042] In some embodiments of this application, the electrolyte further includes cyclic carbonates. In most prior art solutions, carbonates are used as solvents, primarily to dissociate lithium salts or reduce electrolyte viscosity. However, in this application, cyclic carbonates are further introduced as additives into the electrolyte. Cyclic carbonates can polymerize at the negative electrode interface to form a polycarbonate-rich film, effectively encapsulating nitrogen and sulfur elements and distributing them uniformly on the negative electrode interface, thus promoting the effect of Formula I compounds and further improving the cycle performance of the battery cell.

[0043] In some embodiments of this application, the electrolyte further includes cyclic carbonates. Based on the total mass of the electrolyte, the mass content of the cyclic carbonates is F, where F satisfies: 0.01% ≤ F ≤ 10%. Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the mass content F of the cyclic carbonates can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, or 2.2%. The percentages are 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, or a range consisting of any two of the above values. Preferably, F% satisfies: 0.1% ≤ F ≤ 5%. By controlling the mass content F of cyclic carbonate in the electrolyte within the above range, the cycle performance of the battery cell can be further improved. When the mass content of cyclic carbonate is too low, it cannot have a significant improvement effect. When the mass content is too high, the cyclic carbonate is prone to decomposition and gas generation at high temperatures, which will deteriorate the high-temperature storage performance and fail to achieve the corresponding performance improvement effect.

[0044] In some embodiments of this application, the cyclic carbonate includes at least one selected from vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate. In further technical solutions provided in this application, when the cyclic carbonate is selected from at least one selected from vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate, the cycle performance of the battery cell can be further improved.

[0045] In some embodiments of this application, based on the total mass of the electrolyte, the ratio A / F of the mass content A of the compound of formula I to the mass content F of the cyclic carbonate satisfies the following relationship: 0.01≤A / F≤50. Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the ratio A / F of the mass content A of the compound of formula I to the mass content F of the cyclic carbonate can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 The values ​​are 0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or a range consisting of any two of the above values. Preferably, A / F satisfies the following relationship: 0.1 ≤ A / F ≤ 50. By further controlling the ratio A / F of the mass content A of the Formula I compound to the mass content F of the cyclic carbonate within the above range, the mass content of the Formula I compound and the cyclic carbonate added to the electrolyte can be controlled within a reasonable range, which can further improve film formation performance and further improve cell cycle.

[0046] In some embodiments of this application, the electrolyte further includes a polynitrile compound. By adding a polynitrile compound to the electrolyte, the cyano group of the compound can combine with the transition metal atoms at the positive electrode interface, stabilizing the interface. Simultaneously, its alkyl chain can be stably cross-linked at the positive electrode interface, further promoting the adsorption and film-forming reaction of the compound of formula I at the positive electrode interface, thereby reducing side reactions in the electrolyte and further improving the storage stability of the battery cell.

[0047] In some embodiments of this application, the electrolyte further includes a polynitrile compound, which includes at least one of compounds of formula 1 to formula 15:

[0048]

[0049] When the polynitrile compound is further selected from at least one of the compounds of Formula 1 to Formula 15 above, a better effect can be achieved in improving the storage stability of the battery cell.

[0050] In some embodiments of this application, the electrolyte further includes a polynitrile compound, and the mass content of the polynitrile compound is N, based on the total mass of the electrolyte, where N satisfies: 0.05% ≤ N ≤ 5%. Specifically, in some embodiments of this application, the mass content N of the polynitrile compound, based on the total mass of the electrolyte, can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, etc. The concentrations are 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or any combination of two of the above values. Polycyanate compounds exhibit poor reduction stability at the negative electrode, leading to instability at the negative electrode interface and thus deteriorating the cell's cycle performance. Further controlling the mass content (N) of the polycyanate compound within the above range can improve the adsorption of Compound I at the positive electrode interface while reducing excessive cyano group reduction at the negative electrode, achieving further improvement.

[0051] In some embodiments of this application, the electrolyte further includes a polynitrile compound, and based on the total mass of the electrolyte, the ratio N / A of the mass content N of the polynitrile compound to the mass content A of the compound of formula I satisfies: 0.005 ≤ N / A ≤ 10. Specifically, in some embodiments of this application, the ratio N / A of the mass content N of the polynitrile compound to the mass content A of the compound of formula I can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7%, 0.8, 0.9, 1.0, 1.1, 1.2%, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or 2. 1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any range of two of the above values. Further adjusting the ratio N / A of the mass content N of the polynitrile compound to the mass content A of the compound of Formula I within the above range can improve the adsorption of the compound of Formula I at the positive electrode interface while reducing excessive reduction of cyano groups at the negative electrode, thereby further improving high-temperature storage and cycling performance.

[0052] In some embodiments of this application, the electrolyte further includes cyclic sulfur oxides. The addition of cyclic sulfur oxides to the electrolyte allows them to synergistically participate in the solvation structure of lithium ions with the compound of Formula I, promoting the uniform adsorption of the compound of Formula I at both the positive and negative electrodes. Simultaneously, the cyclic sulfur oxides themselves can also participate in the formation of the interfacial film, further improving storage performance.

[0053] In some embodiments of this application, the electrolyte further includes cyclic sulfur oxides, which include at least one selected from 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, vinyl sulfate, and vinyl sulfite. The selection of cyclic sulfur oxides from at least one of 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, vinyl sulfate, and vinyl sulfite can further improve storage performance.

[0054] In some embodiments of this application, the electrolyte further includes cyclic sulfur oxides. Based on the total mass of the electrolyte, the mass content of the cyclic sulfur oxides is S, where S satisfies: 0.05% ≤ S ≤ 5%. Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the mass content S of the cyclic sulfur oxides can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%. The percentages are 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, or any combination of two of the above values. By controlling the mass content S of the cyclic sulfur oxides within the above range, the cyclic sulfur oxides can be more rationally combined with the compound of Formula I. Through competitive reactions, they adsorb at the positive electrode interface, further increasing the reaction probability of the compound of Formula I at the negative electrode interface, thus better protecting the positive and negative electrode surfaces and further improving storage performance.

[0055] In some embodiments of this application, the electrolyte further includes cyclic sulfur oxides. Based on the total mass of the electrolyte, the ratio S / A of the mass content A of the compound of formula I to the mass content S of the cyclic sulfur oxides satisfies the following relationship: 0.005 ≤ S / A ≤ 10. Specifically, in some embodiments of this application, the ratio S / A of the mass content A of the compound of formula I to the mass content S of the cyclic sulfur oxides can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7%, 0.8, 0.9, 1.0, 1.1, 1.2%, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2 The values ​​are 1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or any two of the above values. When the ratio S / A of the mass content A of the compound of Formula I to the mass content S of the cyclic sulfur oxide is controlled within the above range, storage can be further improved with minimal impact on impedance.

[0056] In some embodiments of this application, the electrolyte provided may also contain other components, including but not limited to: diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or dimethyl carbonate (DMC). In some embodiments of this application, other components may include ether solvents, including but not limited to: at least one of 1,3-dioxapentane (DOL) and dimethyl glycol ether (DME).

[0057] In some embodiments of this application, the electrolyte provided may further include lithium salts as the electrolyte. The lithium salts in the electrolyte include, but are not limited to: LiClO4, LiAsF6, LiPF6, LiSbF6, LiSO3F, LiN(FSO2)2, LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium bis(oxalate)borate, lithium tri(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, or lithium tetrafluoro(oxalate)phosphate. Furthermore, one of the above lithium salts may be used alone, or two or more may be used simultaneously. In some embodiments, the lithium salt includes LiPF6. In some embodiments, the mass content of the lithium salt in the electrolyte is 10% to 20% based on the total mass of the electrolyte. Specifically, based on the total mass of the electrolyte, the mass content of lithium salt in the electrolyte is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of the above values.

[0058] In some embodiments of this application, the preparation method of the electrolyte provided in this application is not limited and can be prepared in accordance with conventional electrolyte preparation methods. In some embodiments, the electrolyte of this application can be prepared by mixing the components.

[0059] II. Electrochemical Device

[0060] According to a second aspect of this application, this application also provides an electrochemical device comprising the electrolyte described in any one of the first aspects of this application. The electrochemical device comprising the above-described electrolyte exhibits excellent high-temperature storage and cycling performance.

[0061] In some embodiments of this application, the electrochemical device includes, but is not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In some embodiments of this application, the electrochemical device is a lithium secondary battery. In some embodiments of the present invention, the lithium secondary battery includes, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0062] In some embodiments of this application, the electrochemical device of this application may also be a negative electrode-free battery system.

[0063] 1. Positive electrode

[0064] In some embodiments of this application, the electrochemical device further includes a positive electrode, which comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The specific type of positive electrode active material in the positive electrode active material layer is not specifically limited and can be selected according to requirements. In some embodiments of this application, the positive electrode active material includes lithium transition metal composite oxides. In some embodiments, the positive electrode active material is selected from at least one of the following: lithium cobalt oxide, lithium nickel manganese cobalt ternary materials, lithium manganese oxide, lithium nickel manganese oxide (or lithium iron phosphate).

[0065] In some embodiments of this application, the positive electrode active material layer further includes a binder. The binder can improve the bonding between the positive electrode active material particles and the bonding between the positive electrode active material and the positive electrode current collector. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon, etc.

[0066] In some embodiments of this application, the positive electrode active material layer further includes a conductive agent to impart conductivity to the electrode. The conductive agent may include any conductive material, as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0067] In some embodiments of this application, the positive current collector is a metal, such as aluminum foil.

[0068] In some embodiments of this application, the structure of the positive electrode is a positive electrode structure known in the art that can be used in secondary batteries.

[0069] In some embodiments of this application, the method for preparing the positive electrode is a well-known method in the art for preparing positive electrodes for secondary batteries. For example, the positive electrode can be obtained by mixing a positive electrode active material, a conductive agent, and a binder in a solvent to prepare a positive electrode active material slurry, coating the positive electrode active material slurry onto a positive electrode current collector, drying, and cold pressing to form a positive electrode active material layer. In some embodiments, the solvent may include water, N-methylpyrrolidone, etc., but is not limited thereto.

[0070] 2. Negative electrode

[0071] In some embodiments of this application, the electrochemical device further includes a negative electrode, which comprises a negative electrode current collector and a negative polar material layer located on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, which is any material capable of electrochemically adsorbing and releasing metal ions such as lithium ions. In some embodiments of this application, the negative electrode active material includes carbonaceous materials (graphite), silicon materials, hard carbon materials, or lithium metal materials. In some embodiments of this application, the negative electrode active material includes one or more of the above-mentioned materials.

[0072] In some embodiments of this application, the negative electrode active material layer further includes a conductive agent to improve electrode conductivity. Any conductive material can be used as the conductive material, as long as it does not cause a chemical change. Examples of conductive agents include, but are not limited to: carbon-based materials, such as carbon black, acetylene black, Ketjen black, carbon fibers, etc.; metal-based materials, such as metal powders or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof.

[0073] In some embodiments of this application, the negative electrode active material layer further includes a thickener. The thickener may be selected from sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVDF).

[0074] In some embodiments of this application, the negative electrode active material layer further includes an adhesive, which may include various adhesive polymers such as polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0075] In some embodiments of this application, the negative electrode current collector includes, but is not limited to: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and any combination thereof. In some embodiments, the negative electrode current collector is copper foil.

[0076] In some embodiments of this application, the structure of the negative electrode can be a negative electrode structure known in the art that can be used in electrochemical devices.

[0077] In some embodiments of this application, the method for preparing the negative electrode is a method known in the art for preparing negative electrodes that can be used in electrochemical devices. Exemplarily, the negative electrode can be obtained by mixing a negative electrode active material, a conductive agent, and a binder in a solvent, and heating a thickener as needed to prepare a negative electrode active material slurry, coating the negative electrode active material slurry onto a negative electrode current collector, drying, and cold pressing to form a negative electrode active material layer. In some embodiments, the solvent may include, but is not limited to, water and N-methylpyrrolidone.

[0078] 3. Separating membrane

[0079] In some embodiments of this application, the electrochemical device further includes a separator membrane to prevent short circuits. The material and shape of the separator membrane are not particularly limited and can be any technology disclosed in the prior art. For example, in some embodiments, the separator membrane includes a substrate layer, which is a nonwoven fabric, membrane, or composite membrane with a porous structure. The material of the substrate layer can be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, the material of the substrate layer can be selected from at least one of polypropylene porous membrane, polyethylene porous membrane, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite membrane. At least one surface of the substrate layer is provided with a surface treatment layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by a mixture of polymers and inorganic materials. Specifically, the inorganic layer comprises inorganic particles and a binder. The inorganic particles may be selected from one or more of the following: alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder may be selected from one or more of the following: polyvinylidene fluoride, a polymer of polyvinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0080] III. Electronic Equipment

[0081] The electrolyte according to this application enables electrochemical devices to have good high-temperature storage and cycling performance, making the electrochemical devices manufactured therefrom suitable for electronic devices in various fields.

[0082] The application of the electrochemical device in this application is not particularly limited, and it can be used for any purpose known in the prior art. In one embodiment, the electrochemical device of this application can be used in, but is not limited to: laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc. Furthermore, the electrochemical device provided in this application is applicable not only to the electronic devices exemplified above, but also to energy storage power stations, marine transport vehicles, and air transport vehicles, including air transport vehicles within and outside the atmosphere.

[0083] Example

[0084] The following describes the implementation of this application in more detail through specific embodiments and comparative examples.

[0085] The test methods used in the following examples and comparative examples are as follows:

[0086] (1) Lithium-ion battery DC resistance (DCR) test

[0087] Place the lithium-ion battery in a 0℃ constant temperature environment and let it stand for 5 minutes to allow the lithium-ion battery to reach a constant temperature. Record the lithium-ion battery voltage at this time as U1. Discharge it at a constant current of 0.1C for 10 minutes and record the lithium-ion battery voltage at this time as U2. The impedance DCR of the lithium-ion battery at 0℃ is (U1-U2) / 0.1C.

[0088] (2) High-temperature gas generation performance test of lithium-ion batteries

[0089] The lithium-ion battery was placed in a constant temperature environment of 25℃ and left to stand for 30 minutes to reach the 25℃ constant temperature state. It was then charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.025C. The thickness of the lithium-ion battery at this point was recorded as the initial thickness H0. The lithium-ion battery was then transferred to a constant temperature chamber at 60℃ and stored for 30 days. During this period, the thickness of the lithium-ion battery was measured and recorded every 6 days. The measured thickness after 30 days was recorded as the storage thickness H1. The high-temperature storage thickness expansion rate = (H1 - H0) / H0 × 100%.

[0090] (3) Lithium-ion battery cycle performance test

[0091] The lithium-ion battery was placed in a constant temperature environment of 25°C and allowed to stand for 30 minutes to reach the 25°C constant temperature state. It was then charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.025C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V. The initial discharge capacity was recorded as C0. This charge-discharge cycle was repeated 500 times, and the discharge capacity after 100 cycles was recorded as C1. Cycle capacity retention = C1 / C0 × 100%.

[0092] Example 1-1

[0093] (1) Preparation of the positive electrode

[0094] The positive electrode active material LiCoO2, conductive agent Super P, and binder polyvinylidene fluoride were mixed in a weight ratio of 97:1.4:1.6, and then added to N-methylpyrrolidone (NMP) solvent. The mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto the positive electrode current collector aluminum foil. The coated aluminum foil was dried at 85°C, and then cold-pressed, cut, and slit. Finally, it was dried under vacuum at 85°C for 4 hours to obtain the positive electrode.

[0095] (2) Preparation of negative electrode

[0096] Artificial graphite (negative electrode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed in a weight ratio of 96:2:0.8:1.2. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry with a solid content of 54 wt%. The negative electrode slurry was further prepared according to the following formula: negative electrode active material areal density 7.8 mg / cm³. 2 The coating is uniformly applied to the copper foil of the negative electrode current collector; the coated copper foil is dried at 85°C, and then cold-pressed, cut, and slit before being dried under vacuum at 120°C for 12 hours to obtain the negative electrode.

[0097] (3) Electrolyte preparation

[0098] In a dry (water content <10ppm) argon atmosphere glove box, the solvent was mixed in a mass ratio of EC:DEC:EMC = 30:40:30. Then, fully dried lithium salt LiPF6 (1mol / kg, abbreviated as 1M) was added, dissolved, and stirred thoroughly. Then, compound I (Formula I-1) was added and mixed evenly to obtain the electrolyte. The mass content of compound I (Formula I-1) was 0.01%, the mass content of LiPF6 was 12.5%, and the balance was the solvent composed of EC, DEC, and EMC.

[0099] (4) Preparation of the separating membrane

[0100] A 9μm thick polyethylene (PE) separator membrane was selected. After coating with PVDF slurry and inorganic particles (flaky boehmite and Al2O3 in a mass ratio of 70:30) and drying, the final separator membrane was obtained with a coating thickness of 3μm and a membrane porosity of 55%.

[0101] (5) Preparation of lithium-ion batteries

[0102] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. Then, they are wound to obtain a bare cell. After welding the tabs, the bare cell is placed in an outer packaging foil aluminum-plastic film and injected with the prepared electrolyte. Then, it undergoes vacuum sealing, settling, formation (0.02C constant current charging to 3.3V, then 0.1C constant current charging to 3.8V), shaping, and capacity testing to obtain a soft-pack lithium-ion battery.

[0103] Examples 1-2 to 1-22

[0104] Except for the specific category and mass content parameters of the compound of Formula I as specified in Table 1, the remaining parameters of Examples 1-2 to 1-22 are the same as those of Example 1-1.

[0105] Comparative Examples 1-1 to 1-4

[0106] Except for the specific categories and mass content parameters of the compounds in Formula I as adjusted according to Table 1, the remaining parameters of Comparative Examples 1-1 to 1-4 are the same as those of Example 1-1.

[0107] The impedance DCR (mΩ), high-temperature storage thickness expansion rate (%), and cycle capacity retention rate (%) of the lithium-ion batteries prepared by Examples 1-1 to 1-22 and Comparative Examples 1-1 to 1-4 were tested according to the above test methods. The results are shown in Table 1.

[0108] Table 1

[0109]

[0110] According to the results presented in Table 1, adding compound of formula I to the electrolyte can significantly improve the cycle performance of lithium-ion batteries. Furthermore, by adopting the technical solution provided in this application, while improving the cycle performance of lithium-ion batteries, the lithium-ion batteries also possess good impedance performance and high-temperature storage performance.

[0111] Examples 2-1 to 2-14

[0112] Based on the results in Table 1, the corresponding examples further investigated the effects of other components and amounts on the impedance, high-temperature storage, and cycle performance of lithium-ion batteries. Except for adjusting the specific type and mass content of Formula I compound and cyclic carbonate according to Table 2, the other parameters of Examples 2-1 to 2-14 were the same as those of Examples 1-5.

[0113] Comparative Examples 2-1 to 2-4

[0114] Based on the results in Table 1, the corresponding examples further investigated the effects of other components and amounts on the impedance, high-temperature storage, and cycle performance of lithium-ion batteries. Except for adjusting the specific types and mass contents of Formula I compounds and cyclic carbonates according to Table 2, the other parameters of Comparative Examples 2-1 to 2-4 were the same as those of Examples 1-5.

[0115] The impedance DCR (mΩ), high-temperature storage thickness expansion rate (%), and cycle capacity retention rate (%) of the lithium-ion batteries prepared by Examples 2-1 to 2-14 and Comparative Examples 2-1 to 2-4 were tested according to the above test methods. The results are shown in Table 2.

[0116] Table 2

[0117]

[0118] The results presented in Table 2 show that by further adding cyclic carbonates to the electrolyte, the cycle performance of lithium-ion batteries can be further improved, and the lithium-ion batteries can simultaneously possess good impedance performance and high-temperature storage performance.

[0119] Examples 3-1 to 3-24

[0120] Based on the results in Table 1, the corresponding examples further explored the effects of other components and dosages on the impedance, high-temperature storage, and cycle performance of lithium-ion batteries. Except for adjusting the specific types and mass contents of cyclic carbonates, polynitrile compounds, and cyclic sulfur oxides according to Table 3, the remaining parameters of Examples 3-1 to 3-24 were the same as those of Examples 1-5.

[0121] Comparative Examples 3-1 to 3-8

[0122] Based on the results in Table 1, the corresponding examples further investigated the effects of other components and amounts on the impedance, high-temperature storage, and cycle performance of lithium-ion batteries. Except for adjusting the specific types and mass contents of cyclic carbonates, polynitrile compounds, and cyclic sulfur oxides according to Table 3, the other parameters of Comparative Examples 3-1 to 3-8 were the same as those of Examples 1-5.

[0123] The impedance DCR (mΩ), high-temperature storage thickness expansion rate (%), and cycle capacity retention rate (%) of the lithium-ion batteries prepared by Examples 3-1 to 3-24 and Comparative Examples 3-1 to 3-8 were tested according to the above test methods. The results are shown in Table 3.

[0124] Table 3

[0125]

[0126]

[0127] According to the results presented in Table 3, adding polynitrile compounds and cyclic sulfur oxides to the electrolyte can further improve the cycle performance of lithium-ion batteries, and also enable lithium-ion batteries to have good impedance performance and high-temperature storage performance.

[0128] It is understood that this application has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the scope of this application. Furthermore, based on the teachings of this application, these features and embodiments can be modified to adapt to specific situations and materials without departing from the scope of this application. Therefore, this application is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are protected by this application.

Claims

1. An electrolyte, wherein, The electrolyte comprises: a compound of formula I; Among them, R 1 R 2 R 3 R 4 and R 5 Each compound is independently selected from any one of fluorine, trifluoromethyl, C1-C3 alkyl, cyano, nitro, vinyl, and ethynyl groups; based on the total mass of the electrolyte, the mass content of the compound of formula I is A, where A satisfies: 0.01% ≤ A ≤ 10%; The electrolyte further includes a polynitrile compound; the polynitrile compound includes at least one of the compounds shown in Formulas 1 to 15:

2. The electrolyte according to claim 1, wherein, A satisfies: 0.01% ≤ A ≤ 5%.

3. The electrolyte according to claim 1, wherein, The compound of formula I includes at least one of the compounds shown in formulas I-1 to I-12:

4. The electrolyte according to claim 1, wherein, The electrolyte also includes cyclic carbonates; based on the total mass of the electrolyte, the mass content of the cyclic carbonates is F, where F satisfies: 0.01% ≤ F ≤ 10%.

5. The electrolyte according to claim 4, wherein, F satisfies: 0.1% ≤ F ≤ 5%.

6. The electrolyte according to claim 4, wherein, The cyclic carbonate is selected from at least one of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate.

7. The electrolyte according to any one of claims 4-6, wherein, Based on the total mass of the electrolyte, the ratio A / F of the mass content A of the compound of formula I to the mass content F of the cyclic carbonate satisfies the following relationship: 0.01≤A / F≤50.

8. The electrolyte according to any one of claims 4-6, wherein, A / F satisfies the following relationship: 0.1≤A / F≤50.

9. The electrolyte according to claim 1, wherein, The electrolyte satisfies at least one of the following conditions (1) to (2): (1) Based on the total mass of the electrolyte, the mass content of the polynitrile compound is N, where N satisfies: 0.05% ≤ N ≤ 5%; (2) Based on the total mass of the electrolyte, the ratio N / A of the mass content N of the polynitrile compound to the mass content A of the compound of formula I satisfies: 0.005≤N / A≤10.

10. The electrolyte according to claim 1, wherein, The electrolyte satisfies at least one of the following conditions (3) to (6): (3) The electrolyte also includes cyclic sulfur oxides; (4) The electrolyte further includes cyclic sulfur oxides, which include at least one of 1,3-propane sulpholactone, 2,4-butane sulpholactone, vinyl sulfate, and vinyl sulfite. (5) The electrolyte also includes cyclic sulfur oxides. Based on the total mass of the electrolyte, the mass content of the cyclic sulfur oxides is S, where S satisfies: 0.05% ≤ S ≤ 5%. (6) The electrolyte also includes cyclic sulfur oxides. Based on the total mass of the electrolyte, the ratio S / A of the mass content A of the compound of formula I to the mass content S of the cyclic sulfur oxides satisfies the following relationship: 0.005≤S / A≤10.

11. An electrochemical device, wherein, The electrochemical device includes the electrolyte according to any one of claims 1 to 10.

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