Electrochemical device and electric equipment

Abstract

The invention provides an electrochemical device and electric equipment. Electrolyte of the electrochemical device comprises a chain carboxylic ester compound and a dinitrile compound. Based on the total mass of the electrolyte, the mass ratio a of the chain carboxylic ester compound is 20%-50%, the mass ratio b of the dinitrile compound is 0.01%-7%, the binding force between the negative active material layer of the negative plate and the negative current collector is peel strength, and the peel strength F N / m is 5N / m-20N / m; the mass ratio a of the chain carboxylic ester compound, the mass ratio b of the dinitrile compound and the peel strength F meet the following relational expression: (100b + F) / 100a is more than or equal to 0.14 and less than or equal to 1.35. The electrochemical device provided by the invention has relatively good charging speed, high-temperature cycle performance, hot box performance and high-temperature full-charge storage stability.

Description

Technical Field

[0001] The present application relates to the technical field of electrochemical devices, and in particular to an electrochemical device and an electrical equipment. Background Art

[0002] Rechargeable electrochemical devices are considered to be one of the most attractive energy storage systems due to their high energy density, relatively simple reaction mechanism, high operating voltage, long life, and environmental friendliness. Nowadays, electrochemical devices such as lithium-ion batteries have been widely used in various fields such as wearable devices, smartphones, drones, and laptops.

[0003] As the application fields of electrochemical devices continue to expand, the market has higher and higher performance requirements for electrochemical devices. For example, in the field of smartphones, electrochemical devices are developing towards fast charging and high performance. On the one hand, electrochemical devices need to have high dynamics to meet the increasingly fast charging speed; on the other hand, smartphones will generate a lot of heat when running in a high power consumption state, requiring electrochemical devices to have good high temperature performance. Summary of the invention

[0004] The purpose of this application is to provide an electrochemical device and electrical equipment to improve the charging speed, high temperature cycle performance, hot box performance and high temperature full charge storage stability of the electrochemical device. The specific technical solution is as follows:

[0005] The first aspect of the present application provides an electrochemical device, which includes a positive electrode sheet, an electrolyte and a negative electrode sheet, wherein the electrolyte includes a chain carboxylic acid ester compound and a dinitrile compound, and the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. Based on the total mass of the electrolyte, the mass proportion a of the chain carboxylic acid ester compound is 20% to 70%, the mass proportion b of the dinitrile compound is 0.01% to 7%, the bonding force between the negative electrode active material layer and the negative electrode current collector is the peel strength, and the peel strength FN / m is 5N / m to 20N / m; the mass proportion a of the chain carboxylic acid ester compound, the mass proportion b of the dinitrile compound, and the peel strength FN / m satisfy the following relationship: 0.14≤(100b+F) / 100a≤1.35.

[0006] In the electrochemical device provided in the present application, the chain carboxylic acid ester compound (in which the ester group does not form a ring) can reduce the viscosity of the electrolyte system and improve the dynamics of the electrochemical device to a certain extent, but has a certain swelling effect on the binder in the negative electrode sheet, thereby affecting the peel strength of the negative electrode sheet and reducing the bonding strength between the negative electrode active material layer and the negative electrode current collector, thereby affecting the effective transfer of electrons and affecting the fast charging performance. Therefore, the peel strength of the negative electrode sheet and the chain carboxylic acid ester compound are limited within the above range, which can make the negative electrode active material layer and the negative electrode current collector in closer contact, so that the fast charging performance can be satisfied to a certain extent; in addition, the high temperature performance of the chain carboxylic acid ester compound is relatively poor, and the introduction of dinitrile compounds can effectively improve the high temperature performance, and the dinitrile compound can improve the bonding of the negative electrode sheet, thereby further improving the fast charging performance of the electrochemical device. Therefore, in the present application, the mass proportion a of the chain carboxylic acid ester compound (a is 20% to 70%), the mass proportion b of the dinitrile compound (b is 0.01% to 7%), and the peel strength FN / m (FN / m is 5N / m to 20N / m) satisfy the following relationship: 0.14≤(100b+F) / 100a≤1.35, which can make the electrochemical device have better charging speed, high temperature cycle performance, hot box performance and high temperature full charge storage stability.

[0007] In some embodiments of the present application, a is 21% to 49%, which can further improve the charging speed of the electrochemical device while maintaining good high-temperature cycle performance and high-temperature full-charge storage stability of the electrochemical device.

[0008] In some embodiments of the present application, b is 1.1% to 4.9%, which can further improve the high-temperature cycle performance and high-temperature full-charge storage stability of the electrochemical device.

[0009] In some embodiments of the present application, FN / m is 7.1 N / m to 15.5 N / m, which can further increase the charging speed of the electrochemical device and improve the high-temperature cycle performance of the electrochemical device.

[0010] In some embodiments of the present application, a is 36% to 43%, which can further improve the charging speed of the electrochemical device while maintaining good high-temperature cycle performance and high-temperature full-charge storage stability of the electrochemical device.

[0011] In some embodiments of the present application, b is 2.1% to 4.1%, which can further improve the high-temperature cycle performance and high-temperature full-charge storage stability of the electrochemical device.

[0012] In some embodiments of the present application, FN / m is 8.2 N / m to 13.7 N / m, which can further increase the charging speed of the electrochemical device and improve the high-temperature cycle performance of the electrochemical device.

[0013] In some embodiments of the present application, a, b, and FN / m satisfy the relationship: 0.21≤(100b+F) / 100a≤0.39, which can further improve the high temperature performance of the electrochemical device.

[0014] In some embodiments of the present application, a, b, and FN / m satisfy the relationship: 0.23≤(100b+F) / 100a≤0.33, which can further improve the high temperature performance of the electrochemical device.

[0015] In some embodiments of the present application, the chain carboxylate compound includes at least one of ethyl acetate, methyl propionate, isopropyl formate, ethyl propionate, propyl acetate, isopropyl acetate, methyl butyrate, methyl isobutyrate, propyl propionate, isopropyl propionate, ethyl butyrate, ethyl isobutyrate, butyl acetate, isobutyl acetate and their fluorine-substituted products.

[0016] In some embodiments of the present application, the dinitrile compound includes at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 2-methyleneglutaronitrile, dipropylmalononitrile and 1,2-bis(cyanoethoxy)ethane.

[0017] In some embodiments of the present application, the electrolyte includes succinonitrile and adiponitrile. By adding the above compounds in combination, the capacity retention rate of the electrochemical device can be further improved, and the charging speed and the hot box temperature can be balanced.

[0018] In some embodiments of the present application, the electrolyte includes adiponitrile and 1,2-bis(cyanoethoxy)ethane. By adding the above compounds in combination, the capacity retention rate of the electrochemical device can be further improved, and the charging speed and the hot box temperature can be balanced.

[0019] In some embodiments of the present application, the electrolyte includes ethyl acetate and adiponitrile. By adding the above compounds in combination, the capacity retention rate of the electrochemical device can be further improved, and the charging speed and the hot box temperature can be balanced.

[0020] In some embodiments of the present application, the electrolyte further comprises a compound of formula I, and based on the total mass of the electrolyte, the mass proportion c of the compound of formula I is 0.04% to 0.8%, and satisfies the relationship with a: 0.01≤10c / a≤0.2. The structural formula of the compound of formula I is:

[0021] Wherein, R1, R2, R3 and R4 are each independently selected from N or C-R5; R5 is each independently selected from hydrogen, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C2-10 alkenyl, substituted or unsubstituted C2-10 alkynyl, substituted or unsubstituted C6-10 aryl, substituted or unsubstituted C3-10 alicyclic hydrocarbon, substituted or unsubstituted C2-10 heterocyclic, substituted or unsubstituted C1-10 alkoxy; and, when substituted, the substituent is selected from halogen.

[0022] By adding compounds satisfying the above general formula, the capacity retention rate of the electrochemical device can be further improved, and its content can be controlled to balance the charging speed and the hot box temperature.

[0023] In some embodiments of the present application, the compound of formula I includes at least one of the following chemical formulas:

[0024]

[0025] By selecting the above compounds, the effects of improving the high temperature cycle performance and hot box performance of the electrochemical device are excellent.

[0026] In some embodiments of the present application, the electrolyte further includes a trinitrile compound, and based on the total mass of the electrolyte, the mass proportion d of the trinitrile compound is 0.01% to 5%, and d and b satisfy the relationship: 0.0014≤d / b≤3. By adding the trinitrile compound, the high temperature cycle performance and high temperature full charge storage stability are further improved, and its mass proportion is controlled to balance the overall impedance of the electrochemical device.

[0027] In some embodiments of the present application, the trinitrile compound includes at least one of 1,3,5-pentanetricarboxylic acid nitrile, 1,3,6-hexanetricarboxylic acid nitrile, 1,2,6-hexanetricarboxylic acid nitrile, and 1,2,3-tris(2-cyano)propane. By selecting the above compounds, the high temperature cycle performance and high temperature full charge storage stability of the electrochemical device are further improved.

[0028] In some embodiments of the present application, the electrolyte further comprises lithium difluorophosphate, and the mass proportion e of lithium difluorophosphate is 0.01% to 1% based on the mass of the electrolyte. Lithium difluorophosphate can participate in the formation of SEI film at the negative electrode sheet and participate in the formation of CEI film at the positive electrode sheet to form a stable solid electrolyte interface rich in F, inhibit the oxidation reaction of chain carboxylic acid ester compounds and dinitrile compounds at the positive electrode sheet, and co-embed at the negative electrode sheet, and lithium difluorophosphate can inhibit the decomposition of lithium hexafluorophosphate by affecting the hydrolysis reaction balance of lithium hexafluorophosphate, reduce the acidity of the electrolyte, and reduce the corrosion of the negative electrode current collector, thereby ensuring the peeling strength of the negative electrode sheet, thereby further improving the charging speed of the electrochemical device.

[0029] In some embodiments of the present application, the negative electrode active material layer includes a negative electrode material, a binder and a conductive agent, the negative electrode material includes graphite, and the specific surface area f of the graphite is 1m 2 / g~6m 2 / g. The liquid retention amount of the negative electrode sheet can be made more reasonable, so that the swelling of the binder in the negative electrode sheet by the electrolyte can be controlled, so as to further improve the high-temperature cycle performance and high-temperature full-charge storage stability of the electrochemical device.

[0030] In some embodiments of the present application, the negative electrode active material layer includes a negative electrode material, a binder and a conductive agent, and the binder includes at least one of styrene-butadiene rubber, fluorinated rubber, polyacrylonitrile, polyacrylic acid, polyacrylate, polyvinyl alcohol, polytetrafluoroethylene or polyolefin, which can make the negative electrode sheet have better bonding performance and higher peel strength.

[0031] The second aspect of the present application provides an electrical device, which includes the electrochemical device in any of the above embodiments. Therefore, the electrical device provided by the present application has good performance. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme, and advantages of the present application more clearly understood, the present application is further described in detail with reference to the following embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field belong to the scope of protection of the present application.

[0033] The present application provides an electrochemical device, which includes a positive electrode sheet, an electrolyte and a negative electrode sheet, wherein the electrolyte includes a chain carboxylic acid ester compound and a dinitrile compound, and the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. Based on the total mass of the electrolyte, the mass proportion a of the chain carboxylic acid ester compound is 20% to 70%, the mass proportion b of the dinitrile compound is 0.01% to 7%, the bonding force between the negative electrode active material layer and the negative electrode current collector is the peeling strength, and the peeling strength FN / m is 5N / m to 20N / m; the mass proportion a of the chain carboxylic acid ester compound, the mass proportion b of the dinitrile compound, and the peeling strength F satisfy the following relationship: 0.14≤(100b+F) / 100a≤1.35.

[0034] Among them, chain carboxylic acid ester compounds contain ester groups: The ester group does not form a ring, and the chain carboxylic acid ester compound is not a lactone, lactide, etc. It should be noted that: the present application does not mean that a lactone compound, lactide compound, etc. cannot be added to the solvent, and a lactone compound solvent, a lactide compound solvent, etc. can be further added on the basis of adding the chain carboxylic acid ester compound (ester group does not form a ring) of the present application.

[0035] Chain carboxylic acid ester compounds (in which the ester group does not form a ring) can reduce the viscosity of the electrolyte system and improve the kinetic performance of the electrochemical device to a certain extent, but have a certain swelling effect on the binder in the negative electrode sheet, thereby affecting the peel strength of the negative electrode sheet and reducing the bonding strength between the negative electrode active material layer and the negative electrode current collector, which will affect the effective transfer of electrons and lead to the fast charging performance. Therefore, the peel strength of the negative electrode sheet and the chain carboxylic acid ester compounds are limited within the above range, which can make the negative electrode active material layer and the negative electrode current collector in closer contact, so that the fast charging performance can be satisfied to a certain extent; in addition, the high temperature performance of chain carboxylic acid ester compounds is relatively poor. The introduction of dinitrile compounds can effectively improve the high temperature performance, and the dinitrile compounds can improve the bonding of the negative electrode sheet, thereby further improving the fast charging performance of the electrochemical device. Therefore, in the present application, the mass proportion a of the chain carboxylic acid ester compound (a is 20% to 70%), the mass proportion b of the dinitrile compound (b is 0.01% to 7%), and the peel strength F (F is 5N / m to 20N / m) satisfy the following relationship: 0.14≤(100b+F) / 100a≤1.35, which can make the electrochemical device have better charging speed, high temperature cycle performance, hot box performance and high temperature full charge storage stability.

[0036] As an example, based on the total mass of the electrolyte, the mass proportion a of the chain carboxylic acid ester compound (ester group does not form a ring) is 20%, 21%, 25%, 30%, 35%, 36%, 40%, 43%, 45%, 49% or 50%; Optionally, the mass proportion a of the chain carboxylic acid ester compound (ester group does not form a ring) is 21% to 49%, which can further improve the charging speed of the electrochemical device, and the high temperature performance of the electrochemical device is moderate. Optionally, the mass proportion a of the chain carboxylic acid ester compound (ester group does not form a ring) is 36% to 43%, which can further improve the charging speed of the electrochemical device, and the high temperature performance of the electrochemical device is moderate.

[0037] In some embodiments, the chain carboxylic acid ester compound (the ester group does not form a ring) includes ethyl acetate, methyl propionate, isopropyl formate, ethyl propionate, propyl acetate, isopropyl acetate, methyl butyrate, methyl isobutyrate, propyl propionate, isopropyl propionate, ethyl butyrate, ethyl isobutyrate, butyl acetate, isobutyl acetate and at least one of their fluorine-substituted products.

[0038] For example, the chain carboxylic acid ester compounds (ester groups do not form a ring) include at least one of ethyl acetate, fluorinated products of ethyl acetate, methyl propionate, fluorinated products of methyl propionate, isopropyl formate, fluorinated products of isopropyl formate, ethyl propionate, fluorinated products of ethyl propionate, propyl acetate, fluorinated products of propyl acetate, isopropyl acetate, fluorinated products of isopropyl acetate, methyl butyrate, fluorinated products of methyl butyrate, methyl isobutyrate, fluorinated products of methyl isobutyrate, propyl propionate, fluorinated products of propyl propionate, isopropyl propionate, fluorinated products of isopropyl propionate, ethyl butyrate, fluorinated products of ethyl butyrate, ethyl isobutyrate, fluorinated products of ethyl isobutyrate, butyl acetate, fluorinated products of butyl acetate, isobutyl acetate, and fluorinated products of isobutyl acetate. The fluorinated products refer to at least one hydrogen atom in the chain carboxylic acid ester compounds being replaced by a fluorine atom.

[0039] For example, the fluorine-substituted product of the chain carboxylic acid ester compound may be at least one of methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate and 2,2,2-trifluoroethyl trifluoroacetate.

[0040] Optionally, the chain carboxylic acid ester compound (the ester group does not form a ring) includes at least one of ethyl acetate, methyl propionate, ethyl propionate, propyl acetate, methyl butyrate, propyl propionate, ethyl butyrate and butyl acetate. Selecting the above chain carboxylic acid ester compounds can effectively improve the charging speed.

[0041] In other embodiments, the electrolyte in the present application may further include other non-aqueous solvents, and the other non-aqueous solvents include at least one of cyclic carboxylates, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers and aromatic fluorine-containing solvents.

[0042] The cyclic carboxylic acid ester includes one or both of γ-butyrolactone and γ-valerolactone. Some hydrogen atoms of the cyclic carboxylic acid ester may be substituted by fluorine atoms.

[0043] The cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate.

[0044] The linear carbonate may include, but is not limited to, at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, or di-n-propyl carbonate.

[0045] The cyclic ether may include, but is not limited to, at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl1,3-dioxolane, 4-methyl1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, or dimethoxypropane.

[0046] The chain ether may include, but is not limited to, at least one of dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, or 1,2-ethoxymethoxyethane.

[0047] The aromatic fluorine-containing solvent may include, but is not limited to, at least one of fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene and trifluoromethylbenzene.

[0048] As an example, based on the total mass of the electrolyte, the mass proportion b of the dinitrile compound is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.1%, 2%, 2.1%, 3%, 4%, 4.1%, 4.9%, 5%, 6% or 7%; Optionally, the mass proportion b of the dinitrile compound is 1.1% to 4.9%, which can further improve the high temperature cycle performance and high temperature full charge storage stability of the electrochemical device. Optionally, the mass proportion b of the dinitrile compound is 2.1% to 4.1%, which can further improve the high temperature cycle performance and high temperature full charge storage stability of the electrochemical device.

[0049] In some embodiments, the dinitrile compound includes at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 2-methyleneglutaronitrile, dipropylmalononitrile, and 1,2-bis(cyanoethoxy)ethane.

[0050] Furthermore, the dinitrile compound includes at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 2-methyleneglutaronitrile and dipropylmalononitrile. The selection of the above dinitrile compounds can effectively improve the high temperature cycle performance and high temperature full charge storage stability of the electrochemical device.

[0051] As an example, the peel strength FN / m between the negative electrode active material layer and the negative electrode current collector is 5N / m, 7.1N / m, 8N / m, 8.2N / m, 10N / m, 12N / m, 13.7N / m, 15N / m, 15.5N / m, 18N / m or 20N / m; optionally, the peel strength FN / m between the negative electrode active material layer and the negative electrode current collector is 7.1N / m to 15.5N / m, which can further improve the charging speed of the electrochemical device and improve the high temperature cycle performance and charging speed of the electrochemical device. Optionally, the peel strength FN / m between the negative electrode active material layer and the negative electrode current collector is 8.2N / m to 13.7N / m, which can further improve the charging speed of the electrochemical device and improve the high temperature cycle performance and charging speed of the electrochemical device.

[0052] As an example, the mass proportion a of the chain carboxylic acid ester compound (ester group does not form a ring), the mass proportion b of the dinitrile compound, and the peel strength FN / m are (100b+F) / 100a, and the value of (100b+F) / 100a can be 0.14, 0.2, 0.21, 0.23, 0.25, 0.3, 0.33, 0.39, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 or 1.35. Optionally, the mass proportion a of the chain carboxylic acid ester compound (ester group does not form a ring), the mass proportion b of the dinitrile compound, and the peel strength FN / m satisfy the relationship: 0.21≤(100b+F) / 100a≤0.39, which can further improve the high temperature performance of the electrochemical device. Optionally, the mass proportion a of the chain carboxylic acid ester compound (the ester group does not form a ring), the mass proportion b of the dinitrile compound, and the peel strength F satisfy the relationship: 0.23≤(100b+F) / 100a≤0.33, which can further improve the high temperature performance of the electrochemical device.

[0053] In some embodiments, the electrolyte includes succinonitrile and adiponitrile, which can further improve the capacity retention rate of the electrochemical device and balance the charging speed and the hot box temperature.

[0054] In some embodiments, the electrolyte includes adiponitrile and 1,2-bis(cyanoethoxy)ethane, which can further improve the capacity retention of the electrochemical device and balance the charging speed and the hot box temperature.

[0055] In some embodiments, the electrolyte includes ethyl acetate and adiponitrile, which can further improve the capacity retention rate of the electrochemical device and balance the charging speed and the hot box temperature.

[0056] In some embodiments, the electrolyte further comprises a compound of formula I, and based on the total mass of the electrolyte, the mass proportion c of the compound of formula I is 0.04% to 0.8%, and satisfies the relationship with a: 0.01≤10c / a≤0.2. The structural formula of the compound of formula I is:

[0057] Wherein, R1, R2, R3 and R4 are each independently selected from N or C-R5, and the remaining group is C-R5; R5 is each independently selected from hydrogen, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C2-10 alkenyl, substituted or unsubstituted C2-10 alkynyl, substituted or unsubstituted C6-10 aryl, substituted or unsubstituted C3-10 alicyclic hydrocarbon, substituted or unsubstituted C2-10 heterocyclic, substituted or unsubstituted C1-10 alkoxy; and, when substituted, the substituent is selected from halogen.

[0058] By adding compounds satisfying the above general formula, the capacity retention rate of the electrochemical device can be further improved, and its content can be controlled to balance the charging speed and the hot box temperature.

[0059] For example: R1 in the structural formula of the above-mentioned compound of formula I is N, and the remaining groups (R2, R3 and R4) are all C-R5; the R5 groups in R2, R3 and R4 are independently selected from hydrogen, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C2-10 alkenyl, substituted or unsubstituted C2-10 alkynyl, substituted or unsubstituted C6-10 aryl, substituted or unsubstituted C3-10 alicyclic hydrocarbon, substituted or unsubstituted C2-10 heterocyclic group, substituted or unsubstituted C1-10 alkoxy; and, when substituted, the substituent is selected from halogen. In other embodiments, the R5 group may also contain heteroatoms, and the heteroatoms include at least one of O, S, N, B, P, and Si.

[0060] For another example: R2 in the structural formula of the above-mentioned compound of formula I is N, and the remaining groups (R1, R3 and R4) are all C-R5; the R5 groups in R1, R3 and R4 are each independently selected from hydrogen, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C2-10 alkenyl, substituted or unsubstituted C2-10 alkynyl, substituted or unsubstituted C6-10 aryl, substituted or unsubstituted C3-10 alicyclic hydrocarbon, substituted or unsubstituted C2-10 heterocyclic, substituted or unsubstituted C1-10 alkoxy; and, when substituted, the substituent is selected from halogen. In other embodiments, the R5 group may also contain heteroatoms, and the heteroatoms include at least one of O, S, N, B, P, and Si.

[0061] For another example: R1 and R2 in the structural formula of the above-mentioned compound of formula I are N, and the remaining groups (R3 and R4) are all C-R5; the R5 groups in R3 and R4 are independently selected from hydrogen, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C2-10 alkenyl, substituted or unsubstituted C2-10 alkynyl, substituted or unsubstituted C6-10 aryl, substituted or unsubstituted C3-10 alicyclic hydrocarbon, substituted or unsubstituted C2-10 heterocyclic, substituted or unsubstituted C1-10 alkoxy; and, when substituted, the substituent is selected from halogen. In other embodiments, the R5 group may also contain heteroatoms, and the heteroatoms include at least one of O, S, N, B, P, and Si.

[0062] In the above-mentioned compound of formula I structure, the anhydride part can neutralize the alkalinity of the surface of the positive electrode sheet and inhibit the decomposition effect of the alkalinity of the metal oxide on the carboxylic acid ester; on the other hand, the unsaturated ring part of the compound of formula I structure can form a film on the positive electrode sheet and the negative electrode sheet to form a stable CEI and SEI, thereby improving the high temperature performance of the electrochemical device. Based on the total mass of the electrolyte, the mass proportion c of the compound of formula I structure is 0.04% to 0.8%. Within this mass proportion range, it can not only significantly improve the high temperature cycle performance and high temperature full charge storage stability of the electrochemical device, but also has a moderate effect on the impedance of the electrochemical device; the mass proportion c of the compound of formula I structure and the mass proportion a of the chain carboxylic acid ester compound satisfy the relationship: 0.01≤10c / a≤0.2. If this relationship is satisfied, the compound of formula I structure can effectively improve the high temperature problem caused by the chain carboxylic acid ester compound, and the chain carboxylic acid ester compound can effectively improve the high impedance problem caused by the compound of formula I structure, further improving the comprehensive performance of the electrochemical device.

[0063] As an example, based on the total mass of the electrolyte, the mass proportion c of the compound of formula 1 is 0.04%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%; and c and a satisfy the relationship: the value of 10c / a is 0.01, 0.02, 0.03, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18 or 0.2. Optionally, based on the total mass of the electrolyte, the mass proportion c of the compound of formula I is 0.3% to 0.5%, and satisfies the relationship with a: 0.08≤10c / a≤0.13.

[0064] In some embodiments, the compound of formula I comprises at least one of the following chemical formulas:

[0065]

[0066]

[0067] By selecting the above compounds, the effects of improving the high temperature cycle performance and hot box performance of the electrochemical device are excellent.

[0068] In some embodiments, the electrolyte further includes a trinitrile compound, and based on the total mass of the electrolyte, the mass proportion d of the trinitrile compound is 0.01% to 5%, and d and b satisfy the relationship: 0.0014≤d / b≤3. By adding the trinitrile compound, the high temperature performance and hot box performance are further improved, and other properties of the electrochemical device can be maintained to a certain extent.

[0069] As an example, based on the total mass of the electrolyte, the mass proportion d of the trinitrile compound is 0.01%, 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4% or 5%, d and b satisfy the relationship: d / b value is 0.0014, 0.01, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5 or 3. Optionally, based on the total mass of the electrolyte, the mass proportion d of the trinitrile compound is 1% to 2.5%, d and b satisfy the relationship: 0.5≤d / b≤1.25.

[0070] In some embodiments, the trinitrile compound includes at least one of 1,3,5-pentanetricarboxylic acid nitrile, 1,3,6-hexanetricarboxylic acid nitrile, 1,2,6-hexanetricarboxylic acid nitrile, and 1,2,3-tris(2-cyano)propane. By selecting the above compounds, the high temperature cycle performance and high temperature full charge storage stability of the electrochemical device are further improved.

[0071] In some embodiments, the electrolyte further includes lithium difluorophosphate, and based on the mass of the electrolyte, the mass proportion e of lithium difluorophosphate is 0.01% to 1%. Lithium difluorophosphate can participate in the formation of SEI film at the negative electrode sheet, participate in the formation of CEI film at the positive electrode sheet, form a stable solid electrolyte interface rich in F, inhibit the oxidation reaction of chain carboxylic acid ester compounds and dinitrile compounds at the positive electrode sheet, and co-embed at the negative electrode sheet, and lithium difluorophosphate can inhibit the decomposition of lithium hexafluorophosphate by affecting the hydrolysis reaction balance of lithium hexafluorophosphate, reduce the acidity of the electrolyte, and reduce the corrosion of the negative electrode current collector, thereby ensuring the peeling strength of the negative electrode sheet, thereby further improving the charging speed of the electrochemical device. As an example, based on the mass of the electrolyte, the mass proportion e of lithium difluorophosphate is 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%. Optionally, based on the mass of the electrolyte, the mass proportion e of lithium difluorophosphate is 0.3% to 0.6%.

[0072] Based on the total mass of the electrolyte, the mass proportion of lithium salt is 10% to 20%. In addition to lithium difluorophosphate, the lithium salt may include but is not limited to inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, and LiWF7; lithium tungstates such as LiWOF5; HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2L i and other carboxylic acid lithium salts; FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li and other sulfonic acid lithium salts; LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethanebissulfonyl imide lithium, cyclic 1,3-perfluoropropane bissulfonyl imide lithium, LiN (CF3SO2) (C4F9SO2) and other imide lithium salts; LiC (FSO2) 3, LiC (CF3SO2) 3, LiC (C2F5SO2) 3 and other methylated lithium salts; bis (malonate) borate lithium salts, difluoro (malonate) borate lithium salts and other (malonate) borate lithium salts; tri (malonate) phosphate lithium, difluorobis (malonate) phosphate lithium, tetrafluoro (malonate) phosphate lithium salts and other (malonate) phosphate lithium salts; and LiPF4 (CF3) 2, LiPF4 (C2 F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2 and other fluorine-containing organic lithium salts; lithium oxalate borate salts such as lithium difluorooxalatoborate and lithium bis(oxalate)borate; at least one of lithium oxalate phosphate salts such as lithium tetrafluorooxalato phosphate, lithium difluorobis(oxalato)phosphate and lithium tris(oxalato)phosphate.

[0073] In this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or can be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. There is no special limitation in this application, as long as the purpose of this application can be achieved.

[0074] The negative electrode active material layer includes a negative electrode material, a binder, and a conductive agent. The negative electrode active material layer can be one layer or multiple layers, and each layer in the multiple negative electrode active material layers can include the same or different negative electrode materials. The negative electrode material is any substance that can reversibly intercalate and deintercalate active ions such as lithium ions. The negative electrode material can include, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiOx (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy, metallic lithium, and at least one of the like. The binder includes, but is not limited to, at least one of styrene-butadiene rubber, fluororubber, polyacrylonitrile, polyacrylic acid, polyacrylate, polyvinyl alcohol, polytetrafluoroethylene, or polyolefin, which can make the bonding performance of the negative electrode sheet better and the peel strength higher. The conductive agent includes, but is not limited to, at least one of carbon-based materials, metal-based materials, and conductive polymers. Exemplarily, the carbon-based materials can include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof, the metal-based materials can include metal powder, metal fiber, copper, nickel, aluminum, silver; the conductive polymer can include polyphenylene derivatives. There is no special limitation on the mass ratio of the negative electrode material, conductive agent, and binder in the negative electrode active material layer in this application, and those skilled in the art can select according to actual needs as long as the purpose of this application can be achieved.

[0075] In some embodiments, the negative electrode material includes graphite, and the specific surface area f of the graphite is 1 m 2 / g to 6 m 2 / g. This can make the liquid retention amount of the negative electrode sheet more reasonable, so that the swelling of the binder in the negative electrode sheet by the electrolyte can be controlled, in order to further improve the high-temperature cycling performance and high-temperature full charge storage stability of the electrochemical device.

[0076] As an example, the specific surface area f of the graphite is 1 m 2 / g, 1.5 m 2 / g, 2 m 2 / g, 2.5 m 2 / g, 3m 2 / g, 3.5m 2 / g, 4m 2 / g, 4.5m 2 / g, 5m 2 / g, 5.5m 2 / g or 6m 2 / g.

[0077] In some embodiments, the negative electrode active material layer may further include a thickener. The type of the thickener is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickener may include but is not limited to sodium carboxymethyl cellulose.

[0078] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or composite current collector. In the present application, there is no particular restriction on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6μm to 10μm, and the thickness of the negative electrode active material layer is 30μm to 120μm. In the present application, there is no particular restriction on the thickness of the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode sheet is 50μm to 150μm. The negative electrode sheet may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active material layer. The composition of the conductive layer is not particularly limited, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0079] In some embodiments, the negative electrode current collector can be copper foil, copper alloy foil or copper foam, and the dinitrile compound can be complexed with the copper ions in the negative electrode current collector to form a protective film on the surface of the copper-containing negative electrode current collector, so that the surface of the copper-containing negative electrode current collector has more bonding sites, and cooperates with the binder to make the bonding performance between the negative electrode current collector and the negative electrode active material layer better, thereby improving the fast charging performance of the electrochemical device. In addition, if a trinitrile compound is added to the electrolyte, although the product of the complexation of the trinitrile compound with the copper ions will dissolve in the electrolyte, there is a risk of corroding the copper-containing negative electrode current collector, but because the dinitrile compound is added to the present application, the protection of the dinitrile compound on the copper-containing negative electrode current collector can prevent the copper-containing negative electrode current collector from being corroded, so that the dinitrile compound and the trinitrile compound can be coordinated to further improve the high temperature cycle performance, high temperature full charge storage stability and hot box temperature of the electrochemical device.

[0080] In the present application, the positive electrode sheet includes 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 above-mentioned "positive electrode active material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or a partial area of ​​the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0081] The positive electrode active material layer includes a positive electrode material, and the positive electrode material includes a substance that can reversibly embed and extract active ions such as lithium ions. The positive electrode active material layer can be one or more layers, and each layer in the multi-layer positive electrode active material layer can include the same or different positive electrode materials. The present application has no particular restrictions on the positive electrode material, as long as the purpose of the present application can be achieved. For example, the positive electrode material may include but is not limited to lithium nickel cobalt manganese oxide (such as common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. At least one of.

[0082] In some embodiments, the surface of the positive electrode material may be attached with a substance different from its composition. For example, the substance attached to the surface may include but is not limited to at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, lithium carbonate, calcium carbonate, magnesium carbonate or carbon. By attaching the above substances on the surface of the positive electrode material, the oxidation reaction of the electrolyte on the surface of the positive electrode material can be suppressed, and the service life of the electrochemical device can be improved. The present application has no particular restrictions on the shape of the positive electrode material particles, as long as the purpose of the present application can be achieved. For example, the shape of the positive electrode material particles may include but is not limited to at least one of block, polyhedron, spherical, ellipsoidal, plate-like, needle-like or columnar. The present application has no particular restrictions on the particles of the positive electrode material, as long as the purpose of the present application can be achieved. For example, the positive electrode material particles may include but are not limited to primary particles, secondary particles or a combination thereof.

[0083] The positive electrode active material layer also includes a conductive agent and a binder. The present application does not particularly limit the types of conductive agents and binders, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, polyvinylidene fluoride, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon; the conductive agent may include but is not limited to at least one of carbon-based materials, metal-based materials and conductive polymers. Exemplarily, the carbon-based material may include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof, and the metal-based material may include metal powder, metal fiber, copper, nickel, aluminum, silver; the conductive polymer may include polyphenylene derivatives. The present application does not particularly limit the mass ratio of the positive electrode material, conductive agent and binder in the positive electrode active material layer, and those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0084] The present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to aluminum foil, aluminum alloy foil or composite current collector (such as aluminum-carbon composite current collector). The present application has no special restrictions on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 6μm to 12μm, and the thickness of the positive electrode active material layer is 30μm to 120μm. The present application has no special restrictions on the thickness of the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode sheet is 50μm to 150μm.

[0085] In the present application, the electrochemical device also includes an isolation membrane to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the electrochemical device, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the isolation membrane, as long as the purpose of the present application can be achieved. For example, the material of the isolation membrane may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of isolation membrane may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0086] For example, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, for example, they may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is not particularly limited, for example, it may be at least one of the above-mentioned binders. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).

[0087] The electrochemical device of the present application also includes a packaging bag for containing a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the field of electrochemical devices, and the present application does not limit the above-mentioned other components. The present application does not specifically limit the packaging bag, and it can be a packaging bag known in the art, as long as it can achieve the purpose of the present application.

[0088] The electrochemical device of the present application is not particularly limited, and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The electrochemical device may also be a sodium ion battery (lithium salt in the electrolyte is replaced with sodium salt), a potassium ion battery (lithium salt in the electrolyte is replaced with potassium salt), etc.

[0089] The preparation process of the electrochemical device of the present application is well known to those skilled in the art, and the present application has no particular limitation. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain an electrochemical device; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain an electrochemical device. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent pressure rise and overcharge and discharge inside the electrochemical device.

[0090] The present application also provides an electrical device, which includes the electrochemical device in any of the above embodiments. Therefore, the electrical device provided by the present application has good performance.

[0091] The electrical equipment of the present application is not particularly limited, and it can be any electrical equipment known in the prior art. In some embodiments, the electrical equipment may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0092] Example

[0093] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0094] Test methods and equipment:

[0095] Negative electrode peel strength test:

[0096] Cut a piece of double-sided tape (width: 20mm, length: 60 to 70mm) and stick it on the steel plate; cut the negative electrode sheet to be tested and stick it on the double-sided tape surface along the thickness direction, away from the current collector (the negative electrode sheet is longer than the double-sided tape and the width is completely covered); roll with a 2kg roller to ensure that the tape fits the test surface; use a tensile testing machine to stretch the current collector for a peel strength test, and use the tensile test result when the current collector is peeled off as the bonding force F between the bonding layer and the negative electrode current collector.

[0097] High temperature cycle performance test:

[0098] Place the lithium-ion battery in a 45℃ constant temperature box, charge at a constant current of 4.5C to 4.48V, charge at a constant voltage of 0.05C at 4.48V, and then discharge at a constant current of 1.0C to 3.0V. This is a charge and discharge cycle process. Record the first discharge capacity as C1. Perform 800 charge and discharge cycles in the above manner, and record the discharge capacity after the 800th cycle as C 800 .

[0099] The cycle capacity retention rate of lithium-ion batteries = (C 800 / C1)×100%.

[0100] Charging speed test:

[0101] After the lithium-ion battery is left to rest at 25°C for 30 minutes, the initial time t1 is recorded, and then it is charged at 4.5C to 4.2V, then 3.5C to 4.35V, then 2.5C to 4.4V, then 2C to 4.48V, and then constant voltage charging to 0.05C, at which time the end time t2 is recorded.

[0102] Charging speed t=t2-t1.

[0103] High temperature storage performance test:

[0104] The lithium-ion battery was charged at room temperature (25°C) at a constant current of 1.5C to 4.48V, and at a constant voltage of 4.48V to 0.05C, and the initial thickness L1 was recorded; then placed in an 85°C oven for 4 hours, and then the thickness L2 of the lithium-ion battery was thermally measured.

[0105] High temperature storage volume expansion rate = (L2 / L1-1) × 100%.

[0106] Hot box test:

[0107] The battery is charged at room temperature at a constant current of 1.5C to ~4.48V, and at 4.48V at a constant voltage of ~0.05C; then the temperature is raised to ~T℃±2℃ in a high temperature furnace at a rate of 5℃ / min±2℃ / min, and maintained for 60min (T is the set test temperature); each time 5ea cells are tested, those that do not catch fire are considered to have passed the hot box test at that temperature.

[0108] Specific surface area test:

[0109] The lithium-ion battery is disassembled after discharge, and the negative electrode active material layer of the disassembled negative electrode sheet is scraped off and soaked in solvent NMP (N-methylpyrrolidone) to wash out the binder in the negative electrode active material layer to obtain a powder material. The specific surface area of ​​the material is measured based on the adsorption of nitrogen by the powder material. Instrument model: TriStar II 3020.

[0110] Example 1-1

[0111] <Preparation of positive electrode material>

[0112] The lithium source material Li2CO3 and the transition metal source material Co(NO3)2 are used as raw materials, and their mass ratio is controlled to be 11:26. The above raw materials are dispersed in anhydrous ethanol, and the solid content in the dispersion is adjusted to 35%, and ground evenly. The ground solution is dried at 60°C to obtain a powder, and the above powder is subjected to a first heat treatment at 600°C, and the first heat treatment is carried out in an air atmosphere for 3h. After the first heat treatment, a transition metal oxide is obtained; the transition metal oxide and the doping element source material Mg(NO3)2 are mixed evenly according to a mass ratio of 1639:1, and a second heat treatment is carried out at a temperature of 1000°C in a nitrogen atmosphere to obtain a positive electrode material doped with Mg metal element.

[0113] <Preparation of positive electrode sheet>

[0114] The positive electrode material, acetylene black and polyvinylidene fluoride prepared above are mixed in a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid mass ratio of 75%. After vacuum stirring, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 90°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer coated with a coating thickness of 100 μm. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer. After drying at 90°C, cold pressing is performed, and then cutting and welding of the pole ears are performed to obtain a positive electrode sheet with a specification of 74mm×867mm for standby use.

[0115] <Preparation of negative electrode sheet>

[0116] Artificial graphite, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97.2:1.4:1.4, and deionized water is added as a solvent to prepare a slurry with a solid content of 45%. After being stirred evenly by a vacuum mixer, a negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 10 μm, and dried at 90°C to obtain a negative electrode sheet with a single-sided negative electrode active material layer coated with a coating thickness of 100 μm. Then the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode active material layer coated. After drying at 90°C, cold pressing is performed, and then the sheet is cut and the pole ears are welded to obtain a negative electrode sheet with a specification of 78 mm × 875 mm for standby use.

[0117] <Preparation of Electrolyte>

[0118] In an argon atmosphere glove box with a water content of less than 10ppm, ethyl propionate (EP), ethylene carbonate (EC), and propylene carbonate (PC) are mixed evenly in a mass ratio of 1:1:1, and then the fully dried lithium salt LiPF6 is dissolved in the above non-aqueous solvent to form a basic electrolyte; adiponitrile is added to the obtained basic electrolyte, and the electrolyte is obtained after mixing evenly. Among them, based on the total mass of the electrolyte, the mass proportion of ethyl propionate is 20%, the mass proportion of LiPF6 is 12.5%, the mass proportion of adiponitrile is 2%, and the mass proportion of other non-aqueous solvents (obtained by mixing PC and EC in a mass ratio of 1:1) is 65.5%.

[0119] <Preparation of Separator Film>

[0120] A porous polyethylene film with a thickness of 7 μm (provided by Celgard Company) was used.

[0121] <Preparation of lithium-ion batteries>

[0122] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging foil, and moisture is removed at 80°C, and the prepared electrolyte is injected, and a lithium-ion battery is obtained after vacuum packaging, standing, forming, shaping and other processes.

[0123] The parameters of the electrochemical devices in different embodiments and comparative examples are shown in Table 1.

[0124] Table 1 Parameters of the electrochemical device

[0125]

[0126]

[0127] The performance of the electrochemical devices provided in the above embodiments and comparative examples is shown in Table 2.

[0128] Table 2 Performance of electrochemical devices

[0129]

[0130]

[0131] Combining Table 1 and Table 2, it can be seen that in Comparative Example 1-1, the amount of ethyl propionate added is too little, and the value of (100b+F) / 100a is too high, so that the charging speed of the electrochemical device is very low (23.2 min); in Comparative Example 1-2, the amount of ethyl propylene added is too high, so that the high temperature performance of the electrochemical device is poor, especially the hot box temperature is very low (124° C.); in Comparative Example 1-3, the content of adiponitrile is too high, so that the charging speed of the electrochemical device is very low (21.8 min); in Comparative Example 1-4, the peel strength of the negative electrode sheet is too low, and the value of (100b+F) / 100a is too low, so that the capacity retention rate of the electrochemical device is very low; in Comparative Example 1-5, the value of (100b+F) / 100a is too low, so that the high temperature performance of the battery is poor, its capacity retention rate is low, its high temperature storage stability is poor, and the hot box temperature is also low.

[0132] In Examples 1-1 to 1-36, the comprehensive performance of the electrochemical device is good, and can to a certain extent take into account the charging speed of the electrochemical device, high-temperature cycle performance (high capacity retention rate of 45°C cycle), high-temperature full-charge storage stability (low volume expansion rate after storage at 85°C for 4 hours after full charge) and hot box performance (higher hot box temperature).

[0133] From the comparison of Examples 1-1 to 1-7, it can be seen that based on the total mass of the electrolyte, the mass proportion a of the chain carboxylic acid ester compound (for example, ethyl propionate) is in the range of 21% to 49%, which can further improve the charging speed of the electrochemical device, and the high temperature performance of the electrochemical device is moderate.

[0134] From the comparison of Examples 1-12 to 1-15, it can be seen that, based on the total mass of the electrolyte, the mass proportion b of the dinitrile compound (for example, adiponitrile) is in the range of 1.1% to 4.9%, which can further improve the high temperature performance of the electrochemical device while maintaining the charging speed of the electrochemical device, so that the high temperature cycle performance, high temperature full charge storage stability and hot box performance of the electrochemical device are better.

[0135] From the comparison of Examples 1-19 to 1-23, it can be seen that the peel strength of the negative electrode sheet is in the range of 7.1 N / m to 15.5 N / m, which can satisfy the fast charging performance of the electrochemical device to a certain extent, and the high-temperature cycle performance is good and the hot box temperature is high.

[0136] From the comparison between Example 1-7 and Example 1-18 to Example 1-30, it can be seen that 0.21≤(100b+F) / 100a≤0.39, which can significantly improve the high temperature performance of the electrochemical device, and make the high temperature cycle performance, high temperature full charge storage stability and hot box performance of the chemical device better.

[0137] From the comparison of Example 1-21, Example 1-31 to Example 1-32, and Example 1-34, it can be seen that the chain carboxylic acid ester compound (the ester group does not form a ring) in the present application is selected as ethyl propionate, ethyl acetate, propyl propionate or ethyl trifluoropropionate, and satisfies a in the range of 20% to 70%, 0.14≤(100b+F) / 100a≤1.35, which can improve the comprehensive performance of the electrochemical device to a certain extent.

[0138] From the comparison between Example 1-21 and Example 1-33 to Example 1-34, it can be seen that the dinitrile compound is selected as adiponitrile, succinonitrile or 2-methyleneglutaronitrile, and b is in the range of 0.01% to 7%, and 0.14≤(100b+F) / 100a≤1.35, which can improve the comprehensive performance of the electrochemical device to a certain extent.

[0139] Example 2-1

[0140] Example 2-1 is an improvement on Example 1-21, and the difference between Example 2-1 and Example 1-21 is that Example 2-1 further adds a compound of Formula I. The specific selection and addition amount of the compound of Formula I are shown in Table 3.

[0141] Table 3 Specific selection of compounds of formula I and the amount of addition and the performance of the electrochemical device

[0142]

[0143]

[0144] Note: " / " in Table 3 indicates that there is no corresponding substance or parameter; the selection of compounds of formula I in Table 3 (I-1 to I-5 refer to structural formulas I-1 to I-5 in the specific implementation methods of the specification, respectively).

[0145] It can be seen from Table 3 that if an additive (a compound of formula I) is added to the electrolyte, based on the total mass of the electrolyte, the mass proportion c of the compound of formula I is 0.04% to 0.8%, and satisfies the relationship with a: 0.01≤10c / a≤0.2, the comprehensive performance of the electrochemical device can be improved, especially the high temperature performance of the electrochemical device can be improved (high temperature cycle performance and hot box temperature are both higher).

[0146] From the comparison of Examples 2-1 to 2-9, it can be seen that based on the total mass of the electrolyte, the mass proportion c of the compound with structure I (for example, the compound with structure I-1) is 0.3% to 0.5%, and satisfies the relationship with a: 0.08≤10c / a≤0.13, which can improve the high temperature performance of the electrochemical device.

[0147] By comparing Example 2-1 and Example 2-10 to Example 2-13, it can be seen that the compound with the structure of Formula I is the compound with the structure of Formula I-3, which can accelerate the charging speed of the electrochemical device; the compound with the structure of Formula I is the compound with the structure of Formula I-4, which can improve the high-temperature performance of the electrochemical device.

[0148] Example 3-1

[0149] Example 3-1 is an improvement on Example 1-21, and Example 3-8 is an improvement on Example 1-12. Examples 3-1 and 3-8 further add a trinitrile compound. The specific selection and addition amount of the trinitrile compound are shown in Table 4.

[0150] Table 4 Specific selection of trinitrile compounds and addition amount and performance of electrochemical device

[0151]

[0152] Note: “ / ” in Table 4 means there is no corresponding substance or parameter.

[0153] It can be seen from Table 4 that if a trinitrile compound is added to the electrolyte, based on the total mass of the electrolyte, the mass proportion d of the trinitrile compound is 0.01% to 3%, and d and b satisfy the relationship: 0.0014≤d / b≤3, the comprehensive performance of the electrochemical device can be improved, especially the high temperature performance of the electrochemical device can be improved (high temperature cycle performance and hot box temperature are both higher).

[0154] From the comparison of Examples 3-1 to 3-8, it can be seen that based on the total mass of the electrolyte, the mass proportion d of the trinitrile compound is 1% to 2.5%, and d and b satisfy the relationship: 0.5≤d / b≤1.25, which can make the high temperature performance of the electrochemical device better and the charging speed will not be greatly affected.

[0155] By comparing Example 3-1 and Example 3-9 to Example 3-11, it can be seen that the trinitrile compound is 1,2,6-hexanetricarboxylic acid nitrile, which can make the charging speed of the electrochemical device faster; the trinitrile compound is 1,2,3-tris(2-cyano)propane, which can make the high-temperature performance of the electrochemical device better.

[0156] Example 4-1

[0157] Example 4-1 is an improvement on Example 1-21, and lithium difluorophosphate is further added to Example 4-1. The amount of lithium difluorophosphate added is shown in Table 5.

[0158] Table 5 Lithium difluorophosphate addition amount and performance of electrochemical device

[0159]

[0160] Note: “ / ” in Table 5 means there is no corresponding substance or parameter.

[0161] It can be seen from Table 5 that if lithium difluorophosphate is added to the electrolyte, and the mass proportion e of lithium difluorophosphate based on the total mass of the electrolyte is 0.01% to 1%, the comprehensive performance of the electrochemical device can be improved, especially the charging speed of the electrochemical device can be accelerated.

[0162] From the comparison of Example 4-1 to Example 4-5, it can be seen that based on the total mass of the electrolyte, the mass proportion of lithium difluorophosphate is 0.3% to 0.6%, which can make the charging speed of the electrochemical device faster while the high temperature performance will not be greatly affected.

[0163] Example 5-1

[0164] Example 5-1 is an improvement on Example 1-19. The difference between Example 5-1 and Example 1-19 is that the specific surface area of ​​the negative electrode material artificial graphite is different, as shown in Table 6 for details.

[0165] Table 6 Specific surface area of ​​artificial graphite and performance of electrochemical device

[0166]

[0167] It can be seen from Table 6 that if the specific surface area of ​​the artificial graphite in the negative electrode material is 1m 2 / g~6m 2 / g range, the comprehensive performance of the electrochemical device can be higher. The higher the specific surface area of ​​artificial graphite, the faster the charging speed of the electrochemical device; the lower the specific surface area of ​​artificial graphite, the better the high temperature performance of the electrochemical device.

[0168] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application claimed for protection, but only represents selected embodiments of the present application.

Claims

1. An electrochemical device, characterized in that: The invention comprises a positive electrode sheet, an electrolyte and a negative electrode sheet, wherein the electrolyte comprises a chain carboxylic acid ester compound and a dinitrile compound, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; Based on the total mass of the electrolyte, the mass proportion a of the chain carboxylic acid ester compound is 20% to 70%, the mass proportion b of the dinitrile compound is 0.01% to 7%, the bonding force between the negative electrode active material layer and the negative electrode current collector is the peel strength, and the peel strength FN / m is 5N / m to 20N / m; the mass proportion a of the chain carboxylic acid ester compound, the mass proportion b of the dinitrile compound, and the peel strength FN / m satisfy the following relationship: 0.14≤(100b+F) / 100a≤1.

35.

2. The electrochemical device according to claim 1, characterized in that The electrochemical device satisfies at least one of the following conditions: a) a is 21% to 49%, preferably, a is 36% to 43%; b) b is 1.1% to 4.9%, preferably, b is 2.1% to 4.1%; c) the FN / m is 7.1 N / m to 15.5 N / m, preferably, the FN / m is 8.2 N / m to 13.7 N / m; d) a, b, and F satisfy the relationship: 0.21≤(100b+F) / 100a≤0.39, preferably, 0.23≤(100b+F) / 100a≤0.

33.

3. The electrochemical device according to claim 1, characterized in that The electrochemical device satisfies at least one of the following conditions: e) the chain carboxylate compound comprises at least one of ethyl acetate, methyl propionate, isopropyl formate, ethyl propionate, propyl acetate, isopropyl acetate, methyl butyrate, methyl isobutyrate, propyl propionate, isopropyl propionate, ethyl butyrate, ethyl isobutyrate, butyl acetate, isobutyl acetate and fluorine-substituted products thereof; f) The dinitrile compound includes at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 2-methyleneglutaronitrile, dipropylmalononitrile and 1,2-bis(cyanoethoxy)ethane.

4. The electrochemical device according to claim 1, characterized in that The electrochemical device satisfies at least one of the following conditions: g) the electrolyte comprises succinonitrile and adiponitrile; h) the electrolyte comprises adiponitrile and 1,2-bis(cyanoethoxy)ethane; i) The electrolyte comprises ethyl acetate and adiponitrile.

5. The electrochemical device according to any one of claims 1 to 4, characterized in that: The electrolyte further comprises a compound of formula I. Based on the total mass of the electrolyte, the mass proportion c of the compound of formula I is 0.04% to 0.8%, and satisfies the relationship with a: 0.01≤10c / a≤0.2; the structural formula of the compound of formula I is: Wherein, R1, R2, R3 and R4 are each independently selected from N or C-R5; R5 is each independently selected from hydrogen, substituted or unsubstituted C1-10 alkyl, substituted or unsubstituted C2-10 alkenyl, substituted or unsubstituted C2-10 alkynyl, substituted or unsubstituted C6-10 aryl, substituted or unsubstituted C3-10 alicyclic hydrocarbon, substituted or unsubstituted C2-10 heterocyclic, substituted or unsubstituted C1-10 alkoxy; and, when substituted, the substituent is selected from halogen.

6. The electrochemical device according to claims 1 to 4, characterized in that: The compound of formula I includes at least one of the following chemical formulas:

7. The electrochemical device according to any one of claims 1 to 4, characterized in that: The electrolyte also includes a trinitrile compound. Based on the total mass of the electrolyte, the mass proportion d of the trinitrile compound is 0.01% to 5%, and d and b satisfy the relationship: 0.0014≤d / b≤3; the trinitrile compound includes at least one of 1,3,5-pentanetricarboxylic acid nitrile, 1,3,6-hexanetricarboxylic acid nitrile, 1,2,6-hexanetricarboxylic acid nitrile, and 1,2,3-tris(2-cyano)propane.

8. The electrochemical device according to claims 1 to 4, characterized in that: The electrolyte further comprises lithium difluorophosphate, and based on the mass of the electrolyte, the mass proportion e of the lithium difluorophosphate is 0.01% to 1%.

9. The electrochemical device according to any one of claims 1 to 4, characterized in that: The negative electrode active material layer includes a negative electrode material, a binder and a conductive agent, and the electrochemical device satisfies at least one of the following conditions: i) The negative electrode material comprises graphite, and the specific surface area f of the graphite is 1 m 2 / g~6m 2 / g; j) The binder comprises at least one of styrene-butadiene rubber, fluorinated rubber, polyacrylonitrile, polyacrylic acid, polyacrylate, polyvinyl alcohol, polytetrafluoroethylene or polyolefin.

10. An electronic device, characterized in that: The invention comprises the electrochemical device according to any one of claims 1 to 9.

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