CN108242556B - Electrolyte and secondary battery - Google Patents

Abstract

The present invention provides an electrolyte and a secondary battery. The electrolyte includes an electrolyte salt, an organic solvent, and an additive. The organic solvent includes a carboxylate compound. The additives include dinitrile compounds, aromatic compound overfill additives, and fluoroethylene carbonate and/or vinylene carbonate. When the electrolyte is applied to the secondary battery, the rate performance, normal temperature cycle performance, high temperature storage performance and overcharge safety performance of the secondary battery can be improved.

Description

Electrolyte and secondary battery

technical field

The present invention relates to the technical field of batteries, in particular to an electrolyte and a secondary battery.

Background technique

In the rapidly developing information age, the demand for electronic products such as mobile phones, notebooks, cameras, etc. is increasing year by year. Secondary batteries, especially lithium-ion secondary batteries, as the working power supply of electronic products, have the characteristics of high energy density, no memory effect, and high working voltage, and are gradually replacing traditional Ni-Cd and MH-Ni batteries. However, with the expansion of market demand for electronic products and the development of power and energy storage equipment, people's requirements for secondary batteries are constantly increasing, and it is imperative to develop secondary batteries with high energy density and fast charging and discharging. At present, the effective methods are to improve the voltage, compaction density of the electrode active material and select the appropriate electrolyte.

At present, electrolytes widely used in lithium ion secondary batteries include electrolytes using lithium hexafluorophosphate as electrolyte salt and mixtures of cyclic carbonates and chain carbonates as organic solvents. However, the above electrolytes have many deficiencies, especially However, at high voltage, the cycle performance, high temperature storage performance, safety performance and rate performance of the secondary battery are poor.

SUMMARY OF THE INVENTION

In view of the problems existing in the background technology, the purpose of the present invention is to provide an electrolyte and a secondary battery, when the electrolyte is applied to the secondary battery, the rate performance, normal temperature cycle performance, and high temperature storage of the secondary battery can be improved. performance and overcharge safety.

In order to achieve the above object, in one aspect of the present invention, the present invention provides an electrolyte solution, which includes: an electrolyte, an organic solvent and an additive. The organic solvent includes a carboxylate compound. The additives include dinitrile compounds, aromatic compound overfill additives, and fluoroethylene carbonate and/or vinylene carbonate.

In another aspect of the present invention, the present invention provides a secondary battery including the electrolyte according to an aspect of the present invention.

Compared with the prior art, the beneficial effects of the present invention include, but are not limited to:

When the electrolyte of the present invention is applied to a secondary battery, the rate performance, normal temperature cycle performance, high temperature storage performance and overcharge safety performance of the secondary battery can be improved.

Detailed ways

The electrolyte solution and the secondary battery according to the present invention will be described in detail below.

First, the electrolyte solution according to the first aspect of the present invention will be described.

The electrolytic solution according to the first aspect of the present invention includes an electrolyte salt, an organic solvent, and an additive. The organic solvent includes a carboxylate compound. The additives include dinitrile compounds, aromatic compound overfill additives, and fluoroethylene carbonate and/or vinylene carbonate.

In the electrolyte according to the first aspect of the present invention, the carboxylate compound is used to improve the rate capability of the secondary battery, but when the carboxylate compound is applied to a secondary battery of a high voltage system, it is easily oxidized In addition, when a secondary battery using a carboxylate compound is used in a high temperature environment, the capacity loss of the secondary battery after multiple cycles is severe, and the high temperature storage performance of the secondary battery is severely deteriorated. The dinitrile compound can be complexed with the positive electrode of the secondary battery, which reduces the interfacial side reaction at high temperature and also reduces the kinetic performance of the secondary battery. The obtained electrons undergo a reduction reaction, and the products obtained by the reduction are unstable and can be deposited on the negative electrode, thereby affecting the normal temperature cycle performance and rate performance of the secondary battery. Fluorinated ethylene carbonate and/or vinylene carbonate can preferentially form a film on the surface of the negative electrode, inhibit the reduction of the carboxylate compound and the side reaction of the dinitrile compound, thereby improving the normal temperature cycle performance of the secondary battery. Ester will generate HF on the surface of the positive electrode with high voltage, and vinylene carbonate will oxidize on the surface of the positive electrode, both of which will increase the gas production of the secondary battery and deteriorate the high-temperature storage performance of the secondary battery. The aromatic compound overcharge additive can improve the overcharge safety performance of the secondary battery, but when its content increases, the viscosity of the electrolyte will increase and the kinetic performance of the secondary battery will be deteriorated. When carboxylate compound, dinitrile compound, aromatic compound overcharge additive and fluoroethylene carbonate and/or vinylene carbonate are added to the electrolyte at the same time, under the synergistic effect of the above substances, the secondary battery can be improved at the same time. excellent rate performance, high temperature storage performance, normal temperature cycle performance and overcharge safety performance.

In the electrolyte solution according to the first aspect of the present invention, the carboxylate compound is selected from one or more of the compounds represented by Formula 1. In Formula 1, R ₁ and R ₂ are each independently selected from the group consisting of an alkane group having 1 to 10 carbon atoms and a halogenated alkane group having 1 to 10 carbon atoms. Wherein, the halogen atom in the halogenated alkane group is selected from one or more of F, Cl, Br, and I.

In the electrolyte solution according to the first aspect of the present invention, the alkane group having 1 to 10 carbon atoms may be a chain alkane group or a cyclic alkane group. Among them, the chain alkane group also includes straight chain alkane group and branched chain alkane group. In addition, the cyclic alkane group may or may not contain a substituent. In the alkane group, the preferable lower limit of the number of carbon atoms may be 1, 2, and 3, and the preferable upper limit of the number of carbon atoms may be 4, 5, 6, 7, 8, 9, and 10. Preferably, R ₁ and R ₂ are each independently selected from a chain alkane group having 1 to 6 carbon atoms or a cyclic alkane group having 3 to 8 carbon atoms. More preferably, R ₁ and R ₂ are each independently selected from a chain alkane group having 1 to 4 carbon atoms or a cyclic alkane group having 5 to 7 carbon atoms.

Specifically, the alkane group having 1 to 10 carbon atoms can be selected from methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, Cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, 2,2 dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methyl Butyl, n-hexyl, isohexyl, 2-hexyl, 3-hexyl, cyclohexyl, 2-methylpentyl, 3-methylpentyl, 1,1,2-trimethylpropyl, 3,3 -Dimethylbutyl, n-heptyl, 2-heptyl, 3-heptyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, isoheptyl, cycloheptyl, n-octyl , one of cyclooctyl, nonyl and decyl.

In the electrolyte according to the first aspect of the present invention, the number of substitutions of halogen atoms in the haloalkane group with 1 to 10 carbon atoms and the substitution positions thereof are not particularly limited, and can be selected according to actual needs. Specifically, the number of halogen atoms may be 1, 2, 3 or 4. When the number of halogen atoms is two or more, the kinds of halogen atoms may be the same, completely different, or partially the same. The haloalkane group may be a chain haloalkane group or a cyclic haloalkane group. The chain haloalkane group also includes straight chain haloalkane groups and branched chain haloalkane groups. The cyclic halogenated alkane group may or may not have a substituent. In the halogenated alkane group, the preferable lower limit of the number of carbon atoms may be 1, 2, and 3, and the preferable upper limit of the number of carbon atoms may be 4, 5, 6, 7, 8, 9, and 10. Preferably, R ₁ and R ₂ are each independently selected from a chain halogenated alkane group having 1 to 6 carbon atoms or a cyclic halogenated alkane group having 3 to 8 carbon atoms. More preferably, R ₁ and R ₂ are each independently selected from a chain haloalkane group having 1 to 4 carbon atoms or a cyclic haloalkane group having 5 to 7 carbon atoms.

Specifically, the halogenated alkane group having 1 to 10 carbon atoms is selected from chloromethyl, dichloromethyl, trichloromethyl, 1-chloroethyl, 1,2-dichloroethyl, and 2-chloro-n-propyl , 2,2-dichloro-n-propyl, 1-chloroisopropyl, monochlorocyclopropyl, 1-chloro-n-butyl, 2-chloroisobutyl, monochlorocyclobutyl, 1-chloro-n-pentyl yl, 2-chloro-n-pentyl, 1-chloroisopentyl, 2,2-dichloromethylpropyl, monochlorocyclopentyl, 3-chloro-2,2-dimethylpropyl, 1-chloro -1-ethylpropyl, 1-chloro-1-methylbutyl, 2-chloro-2-methylbutyl, 2-chloro-n-hexyl, monochlorocyclohexyl, 2-chloromethylpentyl, 3 - One of chloro-3-methylpentyl, 2-chloro-1,1,2-trimethylpropyl, 4-chloro-3,3-dimethylbutyl, 2-chloro-n-heptyl . In the above-mentioned groups, the Cl atom in the halogenated alkane group can also be partially or completely substituted by one or more of F, Br, and I.

In the electrolyte according to the first aspect of the present invention, the carboxylate compound can be selected from methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, propionic acid Ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, amyl propionate, isoamyl propionate, ethyl isopropionate, ethyl butyrate, ethyl isobutyrate, butyl butyrate Ester, butyl isobutyrate, amyl butyrate, isoamyl butyrate, ethyl valerate, ethyl isovalerate, propyl valerate, propyl isovalerate and the aforementioned carboxylate compounds are F, Cl , Br, one or more of the partially substituted or fully substituted compounds of one or more of the compounds. Preferably, the carboxylate compound is selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and the aforementioned carboxylate compounds are compounded by F, Cl, Br, One or more of the partially substituted or fully substituted compounds in I.

In the electrolyte according to the first aspect of the present invention, the dinitrile compound is selected from one or more of the compounds represented by formula 2. In formula 2, R ₃ is selected from an alkylene group having 1 to 20 carbon atoms, a halogenated alkylene group having 1 to 20 carbon atoms, an alkyleneoxy group having 1 to 20 carbon atoms, a carbon atom One of the halogenated alkeneoxy groups with 1 to 20 carbon atoms, the alkenylene group with 2 to 20 carbon atoms, and the halogenated alkene groups with 2 to 20 carbon atoms, wherein the halogen atom is selected from F , one or more of Cl, Br, and I.

NC-R ₃ -CN type ₂

In the electrolyte solution according to the first aspect of the present invention, preferably, R ₃ is selected from an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, Alkyleneoxy group having 1 to 10 carbon atoms, halogenated alkyleneoxy group having 1 to 10 carbon atoms, alkenylene group having 2 to 10 carbon atoms, halogenated alkenylene group having 2 to 10 carbon atoms One of them, wherein the halogen atom is selected from one or more of F, Cl, and Br.

In the electrolyte solution according to the first aspect of the present invention, the number of oxygen atoms in the alkyleneoxy group and the halogenated alkyleneoxy group may be one, two or more.

In the electrolyte according to the first aspect of the present invention, the dinitrile compound is selected from malononitrile, succinonitrile, 2-methylsuccinonitrile, tetramethylsuccinonitrile, glutaronitrile, 2- Methylglutaronitrile, Adiponitrile, Fumaronitrile, 2-methyleneglutaronitrile, 3,5-dioxa-pimelonitrile, ethylene glycol bis(2-cyanoethyl) ether, Diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, 1,2-diethylene glycol (2-cyanoethoxy)ethane, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5-bis(2-cyanoethoxy)butane 2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl) ether, 1,6-dicyanohexane, 1,2-dibromo-2,4-dicyanobutyl One or more of the alkanes.

In the electrolyte according to the first aspect of the present invention, the aromatic compound overcharge additive is selected from one of biphenyl, cyclohexylbenzene, toluene, xylene, fluorobenzene, tert-butylbenzene, and tert-amylbenzene species or several.

In the electrolyte solution according to the first aspect of the present invention, the volume of the carboxylate compound is 5% to 50% of the total volume of the organic solvent. Preferably, the volume of the carboxylate compound is 10% to 40% of the total volume of the organic solvent. Further preferably, the volume of the carboxylate compound is 20% to 35% of the total volume of the organic solvent.

In the electrolytic solution according to the first aspect of the present invention, the content of the dinitrile compound is 0.5% to 10% of the total weight of the electrolytic solution. Preferably, the content of the dinitrile compound is 1% to 5% of the total weight of the electrolyte.

In the electrolyte according to the first aspect of the present invention, the content of the aromatic compound overcharge additive is 0.5% to 15% of the total weight of the electrolyte. Preferably, the content of the aromatic compound overcharge additive is 1% to 5% of the total weight of the electrolyte.

In the electrolyte according to the first aspect of the present invention, the total content of fluoroethylene carbonate and/or vinylene carbonate is 0.05% to 12% of the total weight of the electrolyte.

In the electrolyte according to the first aspect of the present invention, preferably, the content of the fluoroethylene carbonate is 0.5% to 10% of the total weight of the electrolyte. Further preferably, the content of the fluoroethylene carbonate is 1% to 5% of the total weight of the electrolyte.

In the electrolyte solution according to the first aspect of the present invention, preferably, the content of the vinylene carbonate is 0.05% to 5% of the total weight of the electrolyte solution. Further preferably, the content of the vinylene carbonate is 0.2% to 1% of the total weight of the electrolyte.

In the electrolyte according to the first aspect of the present invention, the electrolyte salt may be selected from lithium salts, sodium salts or zinc salts, depending on the secondary battery to which the electrolyte is applied.

In the electrolyte solution according to the first aspect of the present invention, the content of the electrolyte salt is 6.2% to 25% of the total weight of the electrolyte solution. Preferably, the content of the electrolyte salt is 6.25% to 18.8% of the total weight of the electrolyte. Further preferably, the content of the electrolyte salt is 10% to 15% of the total weight of the electrolyte solution.

In the electrolyte according to the first aspect of the present invention, the specific type of the organic solvent is not particularly limited, and can be selected according to actual needs. Preferably, non-aqueous organic solvents are used. The non-aqueous organic solvent may include any kind of carbonates and halogenated compounds of carbonates. The carbonates may include cyclic carbonates and chain carbonates. Specifically, the organic solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, amylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC) , one or more of dipropyl carbonate, ethyl methyl carbonate (EMC), γ-butyrolactone (BL) and tetrahydrofuran (THF).

In the electrolytic solution according to the first aspect of the present invention, the electrolytic solution may be prepared by a conventional method, for example, each material in the electrolytic solution may be uniformly mixed.

Next, the secondary battery according to the second aspect of the present invention will be explained.

A secondary battery according to the second aspect of the present invention includes the electrolytic solution according to the first aspect of the present invention.

In the secondary battery according to the second aspect of the present invention, the secondary battery further includes: a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode film sheet disposed on the positive electrode current collector, and the positive electrode film sheet includes a positive electrode active material, a binder and a conductive agent. The negative electrode sheet includes a negative electrode current collector and a negative electrode film sheet disposed on the negative electrode current collector, and the negative electrode film sheet includes a negative electrode active material, a binder, and may also include a conductive agent. The separator is spaced between the positive electrode sheet and the negative electrode sheet.

In the secondary battery according to the second aspect of the present invention, the separator may be any separator material used in existing secondary batteries, such as polyethylene, polypropylene, polyvinylidene fluoride and multilayers thereof composite membranes, but not limited to these.

In the secondary battery according to the second aspect of the present invention, the secondary battery may be a lithium ion secondary battery, a sodium ion secondary battery, or a zinc ion secondary battery.

When the secondary battery is a lithium ion secondary battery, the electrolyte salt may be selected from lithium salts, and the lithium salt may be selected from LiPF ₆ , LiBF ₄ , LiFSI, LiTFSI, LiClO ₄ , LiAsF ₆ , LiBOB, LiDFOB, LiPO One or more of ₂ F ₂ , LiTFOP, LiN(SO ₂ RF) ₂ , and LiN(SO ₂ F)(SO ₂ RF), wherein RF=C _n F _2n+1 , representing a saturated perfluoroalkyl group , n is an integer within 1-10. Preferably, the lithium salt is LiPF ₆ .

When the secondary battery is a lithium ion secondary battery, the positive electrode active material may be selected from lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), spinel-type LiMn ₂ O ₄ , olivine-type One of LiMPO ₄ , ternary cathode material LiNi _x A _y B _(1-xy) O ₂ and Li _1-x' (A'_y'B'_z' C _1-y'-z' )O ₂ or several. Wherein, in the olivine-type LiMPO ₄ , M is selected from one or more of Co, Ni, Fe, Mn, V; in the ternary positive electrode material LiNi _x A _y B _(1-xy) O ₂ , A and B are each independently selected from one of Co, Al and Mn, and A and B are different, 0<x<1, 0<y<1 and x+y<1; in the ternary cathode material Li _{1 In -x'} (A'_y'B'_z' C _1-y'-z' )O ₂ , A', B', C are each independently selected from one of Co, Ni, Fe, Mn, 0 <x'<1, 0≤y'<1, 0≤z'<1 and y'+z'<1, and A', B', and C are different.

When the secondary battery is a lithium ion secondary battery, the negative electrode active material may be selected from metallic lithium. The negative electrode active material can also be selected from materials that can intercalate lithium when <2V (vs. Li/Li ⁺ ), specifically, the negative electrode active material can be selected from natural graphite, artificial graphite, mesophase microcarbon spheres ( Abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO ₂ , lithiated TiO ₂ -Li ₄ with spinel structure One or more of Ti ₅ O ₁₂ and Li-Al alloys.

When the secondary battery is a sodium ion secondary battery or a zinc ion secondary battery, it is only necessary to change the corresponding positive electrode active material, negative electrode active material, and electrolyte salt.

The present application will be further described below with reference to the embodiments. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. In the examples, only the case where the secondary battery is a lithium ion secondary battery is shown, but the present invention is not limited to this.

In the following examples, the materials, reagents and instruments used can be purchased from commercial sources unless otherwise specified.

For the convenience of description, the additives used in the following examples are abbreviated as follows:

A1: Ethyl propionate

A2: Propionate

B1: Adiponitrile

B2: Succinonitrile

C1: Biphenyl

C2: tert-butylbenzene

D1: Fluoroethylene carbonate

D2: vinylene carbonate

The lithium ion secondary batteries in Examples 1-17 and Comparative Examples 1-15 were prepared according to the following methods.

(1) Preparation of positive electrode sheet

The positive active material lithium cobalt oxide (LiCoO ₂ ), the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed according to the weight ratio of 96:2:2, and N-methylpyrrolidone (NMP) is added. Under the action of a vacuum mixer Stir until the system becomes uniform and transparent to obtain a positive electrode slurry; evenly coat the positive electrode slurry on the positive electrode current collector aluminum foil with a thickness of 12 μm; after drying the aluminum foil at room temperature, transfer it to a 120 ℃ oven for drying for 1 hour, and then undergo cold pressing , and cut to obtain a positive electrode sheet.

(2) Preparation of negative electrode sheet

The negative active material artificial graphite, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber are mixed according to the weight ratio of 97:1:2, added to deionized water, and stirred by a vacuum mixer. Obtain the negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector copper foil with a thickness of 8 μm; after drying the copper foil at room temperature, transfer it to a 120 ℃ oven to dry for 1 hour, and then cold-press and cut to obtain a negative electrode sheet .

(3) Electrolyte preparation

In an argon atmosphere glove box with water content <10ppm, EC, PC, DEC were mixed according to the volume ratio of EC:PC:DEC=1:1:1, and then fully dried lithium salt LiPF ₆ was dissolved in mixed organic In the solvent, carboxylate compound, dinitrile compound, aromatic compound overcharge additive and fluoroethylene carbonate and/or vinylene carbonate are added, and the electrolyte is obtained after mixing uniformly. Among them, the content of LiPF ₆ is 12.5% of the total weight of the electrolyte. The specific types and contents of carboxylate compound, dinitrile compound, aromatic compound overcharge additive, fluoroethylene carbonate and vinylene carbonate used in the electrolyte are shown in Table 1. In Table 1, the content of the carboxylate compound is the volume percentage calculated based on the total volume of the organic solvent, and the content of the dinitrile compound, aromatic compound overcharge additive, fluoroethylene carbonate, and vinylene carbonate is based on the electrolyte solution. The weight percent calculated from the total weight.

(4) Preparation of separator

A polypropylene separator with a thickness of 16 μm (type C210, provided by Celgard) was used.

(5) Preparation of lithium ion secondary battery

The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, so that the separator is placed between the positive and negative electrode sheets for isolation, and then rolled to obtain a bare cell; the bare cell is placed in the outer packaging foil, and the battery After the core is placed at a high temperature of 75 °C for 24 hours, after the moisture meets the specifications, the above-prepared electrolyte is injected into the dried bare cell, and after vacuum packaging, standing, chemical formation, shaping and other processes, the lithium ion secondary battery is obtained. secondary battery.

Table 1 Parameters of Examples 1-17 and Comparative Examples 1-15

Note: "-" means not added.

Next, the test procedure of the lithium ion secondary battery will be described.

(1) Rate performance test of lithium ion secondary battery

At 25°C, charge the lithium-ion secondary battery with a constant current of 1C (nominal capacity) to a voltage of 4.3V, then charge it with a constant voltage of 4.3V until the current is ≤0.05C, and discharge it with a constant current of 0.2C after leaving it for 5 minutes. When the cut-off voltage is 3V, the actual discharge capacity is recorded as D0.

Then charge the lithium-ion secondary battery with a constant current of 1C to a voltage of 4.3V, and then charge it with a constant voltage of 4.3V until the current is ≤ 0.05C. After leaving it for 5 minutes, discharge it with a constant current of 2C to a cut-off voltage of 3V. The discharge capacity at this time is Record it as D1.

Lithium-ion secondary battery 2C/0.2C rate capability=D1/D0×100%. 15 lithium-ion secondary batteries were tested in each group, and the average value was taken.

(2) Normal temperature cycle performance test of lithium ion secondary battery

At 25°C, the lithium-ion secondary battery was charged at a constant current of 1C to a voltage of 4.3V, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3.0V, this is a charge-discharge cycle process, the discharge capacity of this time is the discharge capacity of the first cycle. The lithium ion secondary battery was charged/discharged for 300 cycles according to the above method, and the discharge capacity of the 300th cycle was detected.

Capacity retention rate (%) of lithium ion secondary battery after 300 cycles at 25°C = (discharge capacity after 300 cycles of lithium ion secondary battery/discharge capacity after first cycle of lithium ion secondary battery)×100%. 15 lithium-ion secondary batteries were tested in each group, and the average value was taken.

(3) High temperature storage performance test of lithium ion secondary battery

At 25°C, charge the lithium-ion secondary battery with a constant current of 0.5C to a voltage of 4.3V, and then charge it with a constant voltage of 4.3V to a current of 0.05C, test the thickness of the lithium-ion secondary battery and record it as h ₀ ; After that, the lithium ion secondary battery was put into a constant temperature box at 60° C., and taken out after being stored for 30 days. The thickness of the lithium ion secondary battery was measured and recorded as h ₁ .

Thickness expansion ratio of lithium ion secondary battery after storage at 60° C. for 30 days=[(h ₁ −h0)/h0]×100%. 15 lithium-ion secondary batteries were tested in each group, and the average value was taken.

(4) Overcharge safety performance test of lithium ion secondary battery

At 25°C, the lithium-ion secondary battery was charged at a constant current of 3C (nominal capacity) to a voltage of 7.5V, and then continued to be charged at a constant voltage of 7.5V for 5 hours to observe the state of the lithium-ion secondary battery. The pass rate of the lithium ion secondary battery is calculated based on the criteria of no fire, no combustion and no explosion.

Table 2 Test results of Examples 1-17 and Comparative Examples 1-15

From the relevant data analysis in Table 2, it can be known that after the electrolyte of the present invention is applied to a lithium ion secondary battery, the normal temperature cycle performance, high temperature storage performance, rate performance and overcharge safety performance of the lithium ion secondary battery can be simultaneously improved .

In Comparative Example 2, when only the carboxylate compound was added, the rate performance of the lithium ion secondary battery was improved, but the normal temperature cycle performance and the high temperature storage performance were deteriorated. In Comparative Example 3, only adding a dinitrile compound can improve the high-temperature storage performance, but slightly deteriorate the rate performance and normal temperature cycle performance. In Comparative Example 4, only adding the aromatic compound overcharge additive can improve the overcharge safety performance, but other properties are deteriorated. The addition of fluoroethylene carbonate in Comparative Example 5 can improve the normal temperature cycle performance, but deteriorate the high temperature storage performance. In Comparative Example 6, adding a carboxylate compound and a dinitrile compound at the same time can improve the rate performance and improve the high temperature storage performance, but the room temperature cycle performance deteriorates. In Comparative Example 7, adding the carboxylate compound and the aromatic compound overcharge additive at the same time can take both the rate performance and the overcharge safety performance into consideration, but the normal temperature cycle performance and the high temperature storage performance are deteriorated. In Comparative Example 8, adding carboxylate compound and fluoroethylene carbonate at the same time can improve the rate performance and normal temperature cycle performance, but will deteriorate the high temperature storage performance. In Comparative Example 9, adding dinitrile compound and aromatic compound overcharge additive at the same time can improve high temperature storage performance and overcharge safety performance, but rate performance and normal temperature cycle performance deteriorate. In Comparative Example 10, adding dinitrile compound and fluoroethylene carbonate at the same time can improve the high temperature storage performance and normal temperature cycle performance, but the rate performance is poor. In Comparative Example 11, adding an aromatic compound overcharge additive and fluoroethylene carbonate at the same time can improve the normal temperature cycle performance and overcharge safety performance, but will deteriorate the high temperature storage performance. In Comparative Example 12, adding carboxylate compound, dinitrile compound and aromatic compound overcharge additives at the same time can improve the rate performance, high temperature storage performance and overcharge safety performance, but the room temperature cycle performance deteriorates. In Comparative Example 13, the simultaneous addition of carboxylate compound, dinitrile compound and fluoroethylene carbonate can improve the rate performance, high temperature storage performance and normal temperature cycle performance, but the lithium ion secondary battery cannot pass the overcharge test. In Comparative Example 14, the simultaneous addition of carboxylate compound, aromatic compound overcharge additive and fluoroethylene carbonate can improve rate performance, overcharge safety performance and normal temperature cycle performance, but deteriorate high temperature storage performance. In Comparative Example 15, the simultaneous addition of dinitrile compound, aromatic compound overcharge additive and fluoroethylene carbonate can improve high temperature storage performance, overcharge safety performance and normal temperature cycle performance, but rate performance deteriorates.

Claims (13)

1. An electrolyte, comprising: Electrolyte salt; organic solvents; and additive; It is characterized in that, The organic solvent includes a carboxylate compound; The additives include: Dinitrile compounds; Aromatic compound overfill additives; and Fluoroethylene carbonate and/or vinylene carbonate; The volume of the carboxylate compound is 5% to 20% of the total volume of the organic solvent; The content of the dinitrile compound is 0.5% to 10% of the total weight of the electrolyte; The content of the aromatic compound overcharge additive is 0.5% to 15% of the total weight of the electrolyte; The total content of the fluoroethylene carbonate and/or vinylene carbonate is 0.05% to 12% of the total weight of the electrolyte. 2. The electrolyte according to claim 1, wherein the carboxylate compound is selected from one or more of the compounds shown in formula 1;

in, R ₁ and R ₂ are each independently selected from the group consisting of an alkane group having 1 to 10 carbon atoms and a halogenated alkane group having 1 to 10 carbon atoms; The halogen atom in the halogenated alkane group is selected from one or more of F, Cl, Br, and I. 3. The electrolyte according to claim 2, wherein the carboxylate compound is selected from methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, propyl acetate Ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, amyl propionate, isoamyl propionate, ethyl isopropionate, ethyl butyrate, ethyl isobutyrate, butyric acid Butyl, butyl isobutyrate, amyl butyrate, isoamyl butyrate, ethyl valerate, ethyl isovalerate, propyl valerate, propyl isovalerate and the aforementioned carboxylate compounds are treated by F, One or more of the partially substituted or fully substituted compounds of one or more of Cl, Br, and I. 4. electrolyte according to claim 3, is characterized in that, described carboxylate compound is selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate And one or more of the compounds in which the aforementioned carboxylate compound is partially or fully substituted by one or more of F, Cl, Br, and I. 5. The electrolyte according to claim 1, wherein the dinitrile compound is selected from one or more of the compounds shown in formula 2; NC-R ₃ -CN formula 2 in, R ₃ is selected from the group consisting of an alkylene group having 1 to 20 carbon atoms, a halogenated alkylene group having 1 to 20 carbon atoms, an alkyleneoxy group having 1 to 20 carbon atoms, and an alkylene group having 1 to 20 carbon atoms. One of the halogenated alkyleneoxy group, the alkenylene group with 2 to 20 carbon atoms, the halogenated alkene group with 2 to 20 carbon atoms, and the halogen atom is selected from F, Cl, Br, I one or more of them. 6. The electrolyte according to claim 5, wherein the dinitrile compound is selected from malononitrile, succinonitrile, 2-methylsuccinonitrile, tetramethylsuccinonitrile, glutaronitrile, 2-Methylglutaronitrile, Adiponitrile, Fumaronitrile, 2-Methyleneglutaronitrile, 3,5-dioxa-pimelonitrile, ethylene glycol bis(2-cyanoethyl) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, 1,2 -Bis(2-cyanoethoxy)ethane, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5- bis(2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl) ether, 1,6-dicyanohexane, 1,2-dibromo-2,4-dicyano One or more of the base butanes. 7. The electrolyte according to claim 1, wherein the aromatic compound overcharge additive is selected from biphenyl, cyclohexylbenzene, toluene, xylene, fluorobenzene, tert-butylbenzene, tert-amylbenzene one or more of them. 8. electrolyte according to claim 1, is characterized in that, The content of the dinitrile compound is 1% to 5% of the total weight of the electrolyte; The content of the aromatic compound overcharge additive is 1% to 5% of the total weight of the electrolyte. 9 . The electrolyte solution according to claim 1 , wherein the content of the electrolyte salt is 6.2% to 25% of the total weight of the electrolyte solution. 10 . 10 . The electrolyte solution according to claim 9 , wherein the content of the electrolyte salt is 6.25% to 18.8% of the total weight of the electrolyte solution. 11 . 11 . The electrolyte solution according to claim 10 , wherein the content of the electrolyte salt is 10% to 15% of the total weight of the electrolyte solution. 12 . 12. The electrolyte according to claim 1, wherein the organic solvent also comprises ethylene carbonate, propylene carbonate, butylene carbonate, amylene carbonate, dimethyl carbonate, diethyl carbonate , one or more of dipropyl carbonate, ethyl methyl carbonate, γ-butyrolactone and tetrahydrofuran. 13. A secondary battery, comprising the electrolyte according to any one of claims 1-12.