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 and a fluorinated carboxylic acid ester; 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; the mass content of the compound of formula I is A and the mass content of the fluorinated carboxylic acid ester is S based on the total mass of the electrolyte, wherein A satisfies 0.01%≤A≤5%; S satisfies 5%≤S≤80%; and A / S satisfies 0.001≤A / S≤1. Through the technical scheme provided by the application, the kinetic performance of the electrolyte can be improved and the storage and cycle performance of the battery cell can be 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 requirements for high-temperature gas generation and safety performance of electrochemical devices are becoming increasingly stringent. Therefore, developing electrochemical devices, especially lithium-ion batteries, with relatively low impedance and the ability to balance high-temperature storage and cycle performance is particularly important. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte and an electrochemical device containing 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, this application provides an electrolyte comprising: a compound of formula I and a fluorocarboxylic acid ester;

[0005]

[0006] 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, and the mass content of the fluorocarboxylic acid ester is S, wherein A satisfies: 0.01% ≤ A ≤ 5%; S satisfies: 5% ≤ S ≤ 80%; and A / S satisfies: 0.001 ≤ A / S ≤ 1.

[0007] Fluorinated carboxylic esters, when used as solvents in electrolytes, can further improve the oxidation resistance and stability of the electrolyte at the positive electrode interface. However, fluorinated carboxylic esters have the drawback of significantly reducing electrolyte kinetics. Therefore, this application has found that introducing compound I into an electrolyte containing fluorinated carboxylic esters can further improve the electrolyte's kinetic performance, thereby improving cell storage and cycle performance. By introducing compound I into an electrolyte containing fluorinated carboxylic esters, on the one hand, due to the structural characteristics of compound I itself, such as pyridine and sulfonate structures, it can participate in the solvation of lithium ions in the electrolyte, improving the electrolyte's kinetic performance; on the other hand, compound I migrates to the positive and negative electrode interfaces through solvation to participate in redox reactions, generating interfacial components rich in sulfur, fluorine, and nitrogen structures, thus improving cell storage and cycle performance. Meanwhile, this application has found that adding nitrogen-containing heterocyclic substances and sulfonic acid-containing or sulfur-containing substances separately can have adverse effects on the negative electrode interface and result in relatively high impedance. However, adding the compound of formula I provided in this application does not worsen the impedance and also improves the storage performance. Furthermore, compared to substances containing N-heterocyclic structures disclosed in the prior art, the lone pair electrons in the nitrogen atom of the pyridine structure in the compound of formula I provided in this application can complex with transition metal elements and preferentially adsorb at the positive electrode interface, promoting the film-forming reaction of the sulfonate structure at the positive electrode interface. In addition, the structure of the pyridine conjugated ring can form π-π conjugation with the large π bond of graphite, thereby promoting the reduction and decomposition of the sulfonate at the negative electrode interface to form a negative electrode protective film. Moreover, the decomposition products of pyridine and sulfonate have high heat resistance, which can significantly improve the performance of the battery cell at high temperatures. Simultaneously, the stable interface components formed can improve the cycle performance of the battery cell. Furthermore, this application found in its research that the amount of Compound I and fluorocarboxylic acid ester added also significantly affects the improvement of the corresponding performance. For example, excessive addition of Compound I can lead to impedance deterioration, and excessive addition of fluorocarboxylic acid ester can lead to a negative impact on electrolyte kinetics. Further adjusting the ratio of the amount of Compound I and fluorocarboxylic acid ester within the above-mentioned range can further improve the kinetic performance of the electrolyte and achieve better cell storage and cycle performance improvement.

[0008] In some embodiments of this application, the mass content A of the compound of formula I in the electrolyte satisfies: 0.05% ≤ A ≤ 5%. By further adjusting the mass content A of the compound of formula I in the electrolyte to the above range, the defect of increased impedance caused by excessive participation of the compound of formula I in film formation can be reduced, thereby achieving further improvement in cell storage, impedance, and cycle performance.

[0009] In some embodiments of this application, the ratio A / S of the mass content A of the compound of formula I in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 0.001 ≤ A / S ≤ 0.5; preferably, A / S satisfies: 0.001 ≤ A / S ≤ 0.1. By further adjusting the dosage relationship between the compound of formula I and the fluorocarboxylic acid ester within the above range, the deterioration of high-temperature storage performance caused by excessive use of the compound of formula I and the negative impact of the fluorocarboxylic acid ester on interfacial composition and kinetics can be further reduced, thereby achieving better improvement in the kinetic performance of the electrolyte and the improvement in cell storage and cycling performance.

[0010] In some embodiments of this application, the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 10% ≤ S ≤ 50%. By further adjusting the mass content S of the fluorocarboxylic acid ester in the electrolyte to within the above range, the kinetic performance of the electrolyte and the storage and cycling performance of the battery cell can be further improved. For example, when the amount of fluorocarboxylic acid ester is lower than the above range, the effect on improving storage is not obvious. When the amount of fluorocarboxylic acid ester is higher than the above range, the kinetics of the electrolyte will decrease significantly, leading to an increase in the impedance of the battery cell and further affecting the improvement effect of the corresponding performance.

[0011] 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:

[0012]

[0013] In the technical solution provided in this application, when the compound of Formula I is selected from at least one of the above compounds, the kinetic performance of the electrolyte and the cell storage and cycling performance can be further improved.

[0014] In some embodiments of this application, the fluorocarboxylic acid ester includes at least one of the compounds shown in Formulas 1 to 8:

[0015]

[0016] In the technical solution provided in this application, when the fluorocarboxylic acid ester is selected from at least one of the above-mentioned compounds, the kinetic performance of the electrolyte and the cell storage and cycling performance can be further improved.

[0017] In some embodiments of this application, the electrolyte further includes carbonate compounds, including at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. As mentioned above, the use of fluorocarboxylic acid esters in the electrolyte can reduce the electrolyte kinetics to some extent. This application has found that further introducing carbonate compounds into an electrolyte containing fluorocarboxylic acid esters can improve the dissociation of lithium salts, thereby further improving the kinetic performance of the electrolyte. Since carbonate compounds participate in redox reactions, especially at high voltages, they can cause severe gas production problems. However, when combined with a compound of formula I, the compound of formula I can significantly improve interfacial stability, thereby reducing the oxidative decomposition of carbonate compounds and reducing the deterioration of high-temperature performance.

[0018] In some embodiments of this application, the electrolyte further includes carbonate compounds. Based on the total mass of the electrolyte, the mass content of the carbonate compounds in the electrolyte is C, where C satisfies: 10% ≤ C ≤ 30%. Further controlling the mass content C of the carbonate compounds in the electrolyte within the above range can further improve the kinetic performance of the electrolyte and enhance the storage and cycling performance of the battery cell.

[0019] In some embodiments of this application, the ratio C / A of the mass content C of the carbonate compound in the electrolyte to the mass content A of the compound of formula I in the electrolyte satisfies the following relationship: 20 ≤ C / A ≤ 120. Further limiting the ratio C / A of the mass content C of the carbonate compound in the electrolyte to the mass content A of the compound of formula I in the electrolyte within the above range can reduce the excessive decomposition of the carbonate compound at the interface, which can affect the film-forming effect of the compound of formula I and further improve storage performance.

[0020] In some embodiments of this application, the ratio C / S of the mass content C of the carbonate compound in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies the following relationship: 0.15 ≤ C / S ≤ 5. Further controlling the ratio C / S of the mass content C of the carbonate compound in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte within the above range ensures sufficient kinetics in the electrolyte and further stabilizes the cycle performance.

[0021] According to a second aspect of this application, an electrochemical device is also provided, the electrochemical device comprising the electrolyte described in any one of the first aspects of this application. The electrochemical device comprising the above-described electrolyte has relatively low impedance and good high-temperature storage and cycling performance. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] I. Electrolyte

[0025] According to a first aspect of this application, this application provides an electrolyte comprising: a compound of formula I and a fluorocarboxylic acid ester;

[0026]

[0027] 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, and the mass content of the fluorocarboxylic acid ester is S, wherein A satisfies: 0.01% ≤ A ≤ 5%; S satisfies: 5% ≤ S ≤ 80%; and A / S satisfies: 0.001 ≤ A / S ≤ 1.

[0028] 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.

[0029] Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the mass content A of the compound of formula I 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%, 3.0%, 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 a range consisting of any two of the above values. Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the mass content S of the fluorocarboxylic acid ester can be 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%, or 39%. 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or a range consisting of any two of the above values. Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the ratio A / S of the mass content A of the compound of formula I to the mass content S of the fluorocarboxylic acid ester can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 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, or a range consisting of any two of the above values.

[0030] Fluorinated carboxylic esters, when used as solvents in electrolytes, can further improve the oxidation resistance and stability of the electrolyte at the positive electrode interface. However, fluorinated carboxylic esters also significantly reduce electrolyte kinetics. Therefore, this application has found that introducing compound I into an electrolyte containing fluorinated carboxylic esters can further improve the electrolyte's kinetic performance, thereby improving cell storage and cycle performance. By introducing compound I into an electrolyte containing fluorinated carboxylic esters, on the one hand, due to the structural characteristics of compound I itself, such as pyridine and sulfonate structures, it can participate in the solvation of lithium ions in the electrolyte, improving the electrolyte's kinetic performance; on the other hand, compound I migrates to the positive and negative electrode interfaces through solvation to participate in redox reactions, generating interfacial components rich in sulfur, fluorine, and nitrogen structures, thus improving cell storage and cycle performance. Meanwhile, this application has found that adding nitrogen-containing heterocyclic substances and sulfonic acid-containing or sulfur-containing substances separately can have adverse effects on the negative electrode interface and result in relatively high impedance. However, adding the compound of formula I provided in this application does not worsen the impedance and also improves the storage performance. Furthermore, compared to substances containing N-heterocyclic structures disclosed in the prior art, the lone pair electrons in the nitrogen atom of the pyridine structure in the compound of formula I provided in this application can complex with transition metal elements and preferentially adsorb at the positive electrode interface, promoting the film-forming reaction of the sulfonate structure at the positive electrode interface. In addition, the structure of the pyridine conjugated ring can form π-π conjugation with the large π bond of graphite, thereby promoting the reduction and decomposition of the sulfonate at the negative electrode interface to form a negative electrode protective film. Moreover, the decomposition products of pyridine and sulfonate have high heat resistance, which can significantly improve the performance of the battery cell at high temperatures. Simultaneously, the stable interface components formed can improve the cycle performance of the battery cell. Furthermore, this application found in its research that the amount of Formula I compound and fluorocarboxylic acid ester added also significantly affects the improvement of the corresponding performance. For example, adding too much Formula I compound will lead to impedance deterioration, and adding too much fluorocarboxylic acid ester will lead to a negative impact on electrolyte kinetics. Further, by controlling the ratio of the amount of Formula I compound and fluorocarboxylic acid ester within the above range, the kinetic performance of the electrolyte can be further improved, as well as the cell storage and cycle performance can be improved.

[0031] In some embodiments of this application, the mass content A of the compound of formula I in the electrolyte satisfies: 0.05% ≤ A ≤ 5%; preferably, the mass content A of the compound of formula I in the electrolyte satisfies: 0.1% ≤ A ≤ 5%; more preferably, the mass content A of the compound of formula I in the electrolyte satisfies: 0.2% ≤ A ≤ 5%; more preferably, the mass content A of the compound of formula I in the electrolyte satisfies: 0.5% ≤ A ≤ 5%. By further adjusting the range of the mass content A of the compound of formula I in the electrolyte, the defect of increased impedance caused by excessive participation of the compound of formula I in film formation can be further reduced, thereby achieving further improvements in cell storage, impedance, and cycle performance.

[0032] In some embodiments of this application, the ratio A / S of the mass content A of the compound of formula I in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 0.001 ≤ A / S ≤ 0.5; in some embodiments of this application, the ratio A / S of the mass content A of the compound of formula I in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 0.001 ≤ A / S ≤ 0.1. By further adjusting the dosage relationship between the compound of formula I and the fluorocarboxylic acid ester within the above range, the deterioration of high-temperature storage performance caused by excessive use of the compound of formula I and the negative impact of the fluorocarboxylic acid ester on interfacial composition and kinetics can be reduced, thereby further improving the kinetic performance of the electrolyte and the storage and cycling performance of the battery cell.

[0033] In some embodiments of this application, the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 10% ≤ S ≤ 50%. By further adjusting the mass content S of the fluorocarboxylic acid ester in the electrolyte to within the above range, the kinetic performance of the electrolyte and the storage and cycling performance of the battery cell can be further improved. For example, when the amount of fluorocarboxylic acid ester is lower than the above range, the effect on improving storage is not obvious. When the amount of fluorocarboxylic acid ester is higher than the above range, the kinetics of the electrolyte will decrease significantly, leading to an increase in the impedance of the battery cell and further affecting the improvement effect of the corresponding performance.

[0034] 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:

[0035]

[0036] In the technical solution provided in this application, when the compound of Formula I is selected from at least one of the above compounds, the kinetic performance of the electrolyte and the cell storage and cycling performance can be further improved.

[0037] In some embodiments of this application, the fluorocarboxylic acid ester includes at least one of the compounds shown in Formulas 1 to 8:

[0038]

[0039] In the technical solution provided in this application, when the fluorocarboxylic acid ester is selected from at least one of the above-mentioned compounds, the kinetic performance of the electrolyte and the cell storage and cycling performance can be further improved.

[0040] In some embodiments of this application, the electrolyte further includes carbonate compounds, including at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. As mentioned above, the use of fluorocarboxylic acid esters in the electrolyte can reduce the electrolyte kinetics to some extent. This application has found that further introducing carbonate compounds into an electrolyte containing fluorocarboxylic acid esters can improve the dissociation of lithium salts, thereby further improving the kinetic performance of the electrolyte. Since carbonate compounds participate in redox reactions, especially at high voltages, they can cause severe gas production problems. However, when combined with a compound of formula I, the compound of formula I can significantly improve interfacial stability, thereby reducing the oxidative decomposition of carbonate compounds and reducing the deterioration of high-temperature performance.

[0041] In some embodiments of this application, the electrolyte further includes carbonate compounds. Based on the total mass of the electrolyte, the mass content of the carbonate compounds is C, where C satisfies: 10% ≤ C ≤ 30%. Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the mass content C of the carbonate compounds can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range consisting of any two of the above values. Further controlling the mass content C of the carbonate compounds in the electrolyte within the above range can further improve the kinetic performance of the electrolyte and the cell storage and cycling performance.

[0042] In some embodiments of this application, the ratio C / A of the mass content C of the carbonate compound in the electrolyte to the mass content A of the compound of formula I in the electrolyte satisfies the following relationship: 20 ≤ C / A ≤ 120. Specifically, in some embodiments of this application, the ratio C / A of the mass content C of the carbonate compound in the electrolyte to the mass content A of the compound of formula I in the electrolyte can be 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, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 6 5, 66, 67, 68, 69%, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, or a range consisting of any two of the above values. By further limiting the ratio C / A of the mass content C of carbonate compounds in the electrolyte to the mass content A of the compound of formula I in the electrolyte to the above range, excessive decomposition of carbonate compounds at the interface can be reduced, which can affect the film-forming effect of the compound of formula I and further improve storage performance.

[0043] In some embodiments of this application, the ratio C / S of the mass content C of the carbonate compound in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies the following relationship: 0.15 ≤ C / S ≤ 5. Specifically, in some embodiments of this application, the ratio C / S of the mass content C of the carbonate compound in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte can be 0.15, 0.16, 0.17, 0.18, 0.19, 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 The values ​​are 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, 3.0, 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 two of the above values. Further controlling the ratio C / S of the mass content C of the carbonate compound in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte within the above range ensures sufficient kinetics in the electrolyte and further stabilizes the cycle performance.

[0044] 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).

[0045] 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.

[0046] 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.

[0047] II. Electrochemical Device

[0048] According to a second aspect of this application, an electrochemical device is also provided, the electrochemical device comprising the electrolyte described in any one of the first aspects of this application. The electrochemical device comprising the above-described electrolyte has relatively low impedance and good high-temperature storage and cycling performance.

[0049] 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.

[0050] In some embodiments of this application, the electrochemical device of this application may also be a negative electrode-free battery system.

[0051] 1. Negative electrode

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 2. Positive electrode

[0056] 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 a lithium transition metal composite oxide. 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.

[0057] 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.

[0058] 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.

[0059] 3. Separating membrane

[0060] 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.

[0061] III. Electronic Equipment

[0062] The electrolyte according to this application enables electrochemical devices to have relatively low impedance and good high-temperature storage and cycling performance, making the electrochemical devices manufactured thereby suitable for electronic devices in various fields.

[0063] 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 the atmosphere and air transport vehicles outside the atmosphere.

[0064] Example

[0065] The following describes the implementation of this application in more detail through specific embodiments and comparative examples.

[0066] The test methods used in the following examples and comparative examples are as follows:

[0067] (1) Lithium-ion battery DC resistance (DCR) test

[0068] 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.

[0069] (2) High-temperature gas generation performance test of lithium-ion batteries

[0070] 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 4.3V, and then charged at a constant voltage of 4.3V 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%.

[0071] (3) Lithium-ion battery cycle performance test

[0072] 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 4.3V, and then charged at a constant voltage of 4.3V to a current of 0.025C. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 2.8V. The initial discharge capacity was recorded as C0. This charge-discharge cycle was repeated 500 times, and the discharge capacity after 150 cycles was recorded as C1. Cycle capacity retention = C1 / C0 × 100%.

[0073] Example 1-1

[0074] (1) Preparation of the positive electrode

[0075] The positive electrode active material NCM811, 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.

[0076] (2) Preparation of negative electrode

[0077] 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.

[0078] (3) Electrolyte preparation

[0079] 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) and fluorocarboxylic acid ester (Formula 1) were added and mixed evenly to obtain the electrolyte. The mass content of compound I (Formula I-1) was 0.1wt%, the mass content of fluorocarboxylic acid ester (Formula 1) was 5wt%, and the mass content of LiPF6 was 12.5wt%, based on the total mass of the electrolyte.

[0080] (4) Preparation of the separating membrane

[0081] 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%.

[0082] (5) Preparation of lithium-ion batteries

[0083] 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.

[0084] Examples 1-2 to 1-26

[0085] Except for the specific categories and mass content parameters of Compound I and fluorocarboxylic acid esters as adjusted according to Table 1, the remaining parameters of Examples 1-2 to Examples 1-26 are the same as those of Example 1-1.

[0086] Comparative Examples 1-1 to 1-17

[0087] Except for the specific categories and mass content parameters of Compound I and fluorocarboxylic acid esters as adjusted according to Table 1, the remaining parameters of Comparative Examples 1-1 to 1-17 are the same as those of Example 1-1.

[0088] 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 1-26 and Comparative Examples 1-1 to 1-17 were tested according to the above test methods. The results are shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] According to the results presented in Table 1, the simultaneous addition of Compound I and fluorocarboxylic acid ester to the electrolyte can significantly improve the cycle performance of lithium-ion batteries. Furthermore, by further adjusting the amount of Compound I and fluorocarboxylic acid ester in the electrolyte, the impedance and high-temperature storage performance of lithium-ion batteries can be further improved.

[0093] Examples 2-1 to 2-12

[0094] 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 type and mass content of carbonate compounds and the mass content of compound I according to Table 2, the remaining parameters of Examples 2-1 to 2-12 are the same as those of Examples 1-13.

[0095] The impedance DCR (mΩ), high-temperature storage thickness expansion rate (%), and cycle capacity retention rate (%) of the lithium-ion batteries prepared in Examples 2-1 to 2-12 were tested according to the above test methods. The results are shown in Table 2.

[0096] Table 2

[0097]

[0098]

[0099] The results presented in Table 2 indicate that the impedance performance, high-temperature storage, and cycle performance of lithium-ion batteries can be further improved by adding carbonate compounds to the electrolyte.

[0100] 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 and a fluorocarboxylic acid ester; 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, and the mass content of the fluorocarboxylic acid ester is S, wherein A satisfies: 0.01% ≤ A ≤ 5%; S satisfies: 5% ≤ S ≤ 80%; and A / S satisfies: 0.001 ≤ A / S ≤ 1. The fluorocarboxylic acid esters include at least one of the compounds shown in (Formula 1) to (Formula 8):

2. The electrolyte according to claim 1, wherein, The mass content A of the compound of formula I in the electrolyte satisfies the following condition: 0.05% ≤ A ≤ 5%.

3. The electrolyte according to claim 1, wherein, The ratio A / S of the mass content A of the compound of formula I in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 0.001≤A / S≤0.

5.

4. The electrolyte according to claim 1, wherein, The ratio A / S of the mass content A of the compound of formula I in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 0.001≤A / S≤0.

1.

5. The electrolyte according to claim 1, wherein, The mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies: 10% ≤ S ≤ 50%.

6. 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:

7. The electrolyte according to claim 1, wherein, The electrolyte also includes carbonate compounds, and the mass content of the carbonate compounds is C based on the total mass of the electrolyte, wherein C satisfies: 10% ≤ C ≤ 30%.

8. The electrolyte according to claim 7, characterized in that, The ratio C / A of the mass content C of the carbonate compound in the electrolyte to the mass content A of the compound of formula I in the electrolyte satisfies the following relationship: 20≤C / A≤120.

9. The electrolyte according to claim 7, characterized in that, The ratio C / S of the mass content C of the carbonate compound in the electrolyte to the mass content S of the fluorocarboxylic acid ester in the electrolyte satisfies the following relationship: 0.15≤C / S≤5.

10. An electrochemical device comprising the electrolyte according to any one of claims 1 to 9.

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