CN108242556A - Electrolyte solution and secondary battery - Google Patents

Abstract

The invention provides an electrolytic solution and a secondary battery. The electrolyte includes electrolyte salt, organic solvent and additives. The organic solvent includes carboxylate compounds. Such additives include dinitrile compounds, aromatic compound overcharge additives, and fluoroethylene carbonate and/or vinylene carbonate. When the electrolyte solution 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 invention relates to the technical field of batteries, in particular to an electrolyte solution and a secondary battery.

Background technique

In the rapidly developing information age, the demand for mobile phones, notebooks, cameras and other electronic products is increasing year by year. As the working power source of electronic products, secondary batteries, especially lithium-ion secondary batteries, 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 continue to increase, and the development of secondary batteries with high energy density and fast charging and discharging has become a top priority. At present, the effective methods are to increase the voltage and compaction density of the electrode active materials and to select the appropriate electrolyte.

At present, the electrolytes widely used in lithium-ion secondary batteries include those with lithium hexafluorophosphate as the electrolyte salt and a mixture of cyclic carbonates and chain carbonates as organic solvents. However, the above-mentioned electrolytes have many deficiencies, especially Especially under high voltage, the cycle performance, high temperature storage performance, safety performance and rate performance of the secondary battery are poor.

Contents 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 a secondary battery, it can improve the rate performance, normal temperature cycle performance, and high temperature storage of the secondary battery. performance and overcharge safety performance.

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

In another aspect of the present invention, the present invention provides a secondary battery comprising the electrolytic solution according to the 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 solution 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 electrolytic solution and the secondary battery according to the present invention will be described in detail below.

First, the electrolytic 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 additives. The organic solvent includes carboxylate compounds. Such additives include dinitrile compounds, aromatic compound overcharge additives, and fluoroethylene carbonate and/or vinylene carbonate.

In the electrolyte solution according to the first aspect of the present invention, the carboxylate compound is used to improve the rate performance 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 the secondary battery using the carboxylate compound is used in a high-temperature environment, the capacity loss of the secondary battery is serious after repeated cycles, and the high-temperature storage performance of the secondary battery is seriously deteriorated. The dinitrile compound can be complexed with the positive electrode of the secondary battery, which reduces the kinetic performance of the secondary battery while reducing the interface side reaction at high temperature. The electrons are obtained and a reduction reaction occurs, and the product obtained by the reduction is unstable and may be deposited on the negative electrode, thereby affecting the normal temperature cycle performance and rate performance of the secondary battery. Fluoroethylene carbonate and/or vinylene carbonate can preferentially form a film on the surface of the negative electrode, inhibit the reduction of carboxylate compounds and the side reactions of dinitrile compounds, thereby improving the normal temperature cycle performance of the secondary battery, but the fluoroethylene carbonate Ester will generate HF on the surface of the positive electrode at 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, thereby deteriorating the kinetic performance of the secondary battery. 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 simultaneously. 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 shown in Formula 1. In Formula 1, R ₁ and R ₂ are each independently selected from one 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, I.

In the electrolytic 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. Wherein, chain alkane groups include straight chain alkane groups and branched alkane groups. In addition, the cycloalkane group may have a substituent or may not contain a substituent. In the alkane group, the preferable lower limit of the number of carbon atoms may be 1, 2 or 3, and the preferable upper limit of the number of carbon atoms may be 4, 5, 6, 7, 8, 9 or 10. Preferably, R ₁ and R ₂ are each independently selected from a chain alkane group with 1 to 6 carbon atoms or a cyclic alkane group with 3 to 8 carbon atoms. More preferably, R ₁ and R ₂ are each independently selected from a chain alkane group with 1 to 4 carbon atoms or a cyclic alkane group with 5 to 7 carbon atoms.

Specifically, the alkane group with 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 solution according to the first aspect of the present invention, the substitution number and substitution position of the halogen atoms in the halogenated alkane group having 1 to 10 carbon atoms 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 types of the halogen atoms may be the same, completely different, or partly the same. The haloalkane group may be a chain haloalkane group or a cyclic haloalkane group. The chain haloalkane group further includes straight chain haloalkane group and branched chain haloalkane group. The cyclic haloalkane 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, or 3, and the preferable upper limit of the number of carbon atoms may be 4, 5, 6, 7, 8, 9, or 10. Preferably, R ₁ and R ₂ are each independently selected from a chain haloalkane group having 1 to 6 carbon atoms or a cyclic haloalkane 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 with 1 to 10 carbon atoms is selected from chloromethyl, dichloromethyl, trichloromethyl, 1-chloroethyl, 1,2-dichloroethyl, 2-chloro-n-propyl , 2,2-dichloro-n-propyl, 1-chloroisopropyl, 1-chlorocyclopropyl, 1-chloro-n-butyl, 2-chloroisobutyl, 1-chlorocyclobutyl, 1-chloro-n-pentyl Base, 2-chloro-n-pentyl, 1-chloroiso-pentyl, 2,2-dichloromethylpropyl, 1-chlorocyclopentyl, 3-chloro-2,2-dimethylpropyl, 1-chloro -1-ethylpropyl, 1-chloro-1-methylbutyl, 2-chloro-2-methylbutyl, 2-chloro-n-hexyl, a chlorocyclohexyl, 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 groups, the Cl atom in the haloalkane group can also be partially or fully substituted by one or more of F, Br, and I.

In the electrolyte solution according to the first aspect of the present invention, the carboxylate compound may 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, pentyl propionate, isoamyl propionate, ethyl isopropionate, ethyl butyrate, ethyl isobutyrate, butyl butyrate Esters, butyl isobutyrate, pentyl butyrate, isoamyl butyrate, ethyl valerate, ethyl isovalerate, propyl valerate, propyl isovalerate and the aforementioned carboxylate compounds are covered by F, Cl , Br, I in one or more partially substituted or fully substituted compounds in one or more. 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 replaced by F, Cl, Br, One or more of the partially substituted or fully substituted compounds in I.

In the electrolyte solution according to the first aspect of the present invention, the dinitrile compound is selected from one or more of the compounds shown in Formula 2. In Formula 2, _R3 is selected from the group consisting of alkylene groups with 1 to 20 carbon atoms, halogenated alkylene groups with 1 to 20 carbon atoms, alkyleneoxy groups with 1 to 20 carbon atoms, carbon atom One of halogenated alkyleneoxy groups with 1 to 20 carbon atoms, alkenylene groups with 2 to 20 carbon atoms, and halogenated alkenylene groups with 2 to 20 carbon atoms, wherein the halogen atom is selected from F , Cl, Br, I in one or more.

NC-R ₃ -CN formula ₂

In the electrolyte solution according to the first aspect of the present invention, preferably, _R3 is selected from the group consisting of alkylene groups with 1 to 10 carbon atoms, halogenated alkylene groups with 1 to 10 carbon atoms, Alkyleneoxy group with 1 to 10 carbon atoms, halogenated alkyleneoxy group with 1 to 10 carbon atoms, alkenylene group with 2 to 10 carbon atoms, halogenated alkenylene group with 2 to 10 carbon atoms One of them, wherein the halogen atom is selected from one or more of F, Cl, Br.

In the electrolytic solution according to the first aspect of the present invention, the number of oxygen atoms in the alkyleneoxy group and the halogenated alkylene group group can be 1, 2 or more.

In the electrolyte solution 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-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-dicyanobutyl One or more of alkanes.

In the electrolyte solution 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 electrolytic solution according to the first aspect of the present invention, the volume of the carboxylate compound is 5%-50% of the total volume of the organic solvent. Preferably, the volume of the carboxylate compound is 10%-40% of the total volume of the organic solvent. Further preferably, the volume of the carboxylate compound is 20%-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%-10% of the total weight of the electrolytic solution. Preferably, the content of the dinitrile compound is 1%-5% of the total weight of the electrolyte.

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

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

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

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

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

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

In the electrolyte solution 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. Carbonates may include cyclic carbonates and chain carbonates. Specifically, the organic solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, pentylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC) , dipropyl carbonate, ethyl methyl carbonate (EMC), γ-butyrolactone (BL), tetrahydrofuran (THF) in one or more.

In the electrolyte solution according to the first aspect of the present invention, the electrolyte solution can be prepared by a conventional method, for example, all materials in the electrolyte solution can be mixed uniformly.

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

A secondary battery according to a 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 membrane disposed on the positive electrode collector, and the positive electrode membrane includes a positive electrode active material, a binder and a conductive agent. The negative electrode sheet includes a negative electrode collector and a negative electrode membrane disposed on the negative electrode collector, and the negative electrode membrane 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 can be any separator material used in existing secondary batteries, such as polyethylene, polypropylene, polyvinylidene fluoride and their multilayer 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 , 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 can 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 kinds. Wherein, in olivine-type LiMPO ₄ , M is selected from one or more of Co, Ni, Fe, Mn, V; in ternary cathode 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 -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 at <2V (vs. Li/Li ⁺ ), specifically, the negative electrode active material can be selected from natural graphite, artificial graphite, mesophase microcarbon spheres ( MCMB for short), 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.

Below in conjunction with embodiment, further elaborate the present application. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. In the embodiment, only the case where the secondary battery is a lithium ion secondary battery is shown, but the present invention is not limited thereto.

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

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

A1: ethyl propionate

A2: Propyl 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

Mix the positive electrode active material lithium cobaltate (LiCoO ₂ ), the binder polyvinylidene fluoride, and the conductive agent acetylene black according to the weight ratio of 96:2:2, add N-methylpyrrolidone (NMP), and under the action of a vacuum mixer Stir until the system becomes uniform and transparent to obtain the positive electrode slurry; evenly coat the positive electrode slurry on the aluminum foil of the positive electrode current collector with a thickness of 12 μm; dry the aluminum foil at room temperature and transfer it to an oven at 120°C for 1 hour to dry, then cold press , Slitting to obtain the positive electrode sheet.

(2) Negative sheet preparation

Negative electrode active material artificial graphite, thickener sodium carboxymethylcellulose (CMC), and binder styrene-butadiene rubber are mixed according to the weight ratio of 97:1:2, added to deionized water, and stirred under the action of a vacuum mixer Obtain the negative electrode slurry; apply the negative electrode slurry evenly on the copper foil of the negative electrode current collector with a thickness of 8 μm; dry the copper foil at room temperature and transfer it to an oven at 120°C to dry for 1 hour, and then cold press and cut to obtain the negative electrode sheet .

(3) Electrolyte preparation

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

(4) Preparation of separator

A 16 μm thick polypropylene isolation film (model C210, provided by Celgard) was selected.

(5) Preparation of lithium-ion secondary battery

Stack the positive electrode, separator, and negative electrode in order, so that the separator is between the positive and negative electrodes to play a role of isolation, and then wind up to get the bare cell; put the bare cell in the outer packaging foil, and the battery After the core was left standing at a high temperature of 75°C for 24 hours, after the water content met the specifications, the above-mentioned prepared electrolyte was injected into the dried bare cell, and after vacuum packaging, standing, chemical formation, shaping and other processes, the lithium-ion secondary cell was obtained. secondary battery.

Table 1 The parameters of Examples 1-17 and Comparative Examples 1-15

Note: "-" means not included.

Next, a 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 to a current ≤0.05C, and then discharge it at a constant current of 0.2C after leaving it aside for 5 minutes Until the cut-off voltage is 3V, record the actual discharge capacity as D0 at this time.

Then charge the lithium-ion secondary battery with a constant current of 1C to a voltage of 4.3V, then charge it with a constant voltage of 4.3V to a current ≤0.05C, and then discharge it at a constant current of 2C to a cut-off voltage of 3V. Denote it as D1.

Lithium-ion secondary battery 2C/0.2C rate performance=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, charge the lithium-ion secondary battery at a constant current of 1C to a voltage of 4.3V, then charge at a constant voltage to a current of 0.05C, and then discharge at a constant current of 1C to a voltage of 3.0V. This is a charge-discharge cycle process, the discharge capacity this time is the discharge capacity of the first cycle. The lithium-ion secondary battery was subjected to 300 cycle charge/discharge tests according to the above method, and the discharge capacity of the 300th cycle was detected.

Capacity retention (%) of the lithium ion secondary battery after 300 cycles at 25°C=(discharge capacity of the lithium ion secondary battery after 300 cycles/discharge capacity of the lithium ion secondary battery after the first cycle)×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, 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 _h0 ; Afterwards, the lithium-ion secondary battery was put into a thermostat at 60° C., stored for 30 days, and then taken out. The thickness of the lithium-ion secondary battery was measured and recorded as h ₁ .

The thickness expansion rate of the 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 lithium-ion secondary batteries is calculated by taking no fire, no combustion, and no explosion as the judging criteria.

The test result of table 2 embodiment 1-17 and comparative example 1-15

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

In Comparative Example 2, only the carboxylate compound was added, and the rate performance of the lithium-ion secondary battery was improved, but the normal temperature cycle performance and high temperature storage performance deteriorated. Only adding dinitrile compound in Comparative Example 3 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 performances are all deteriorated. The addition of fluoroethylene carbonate in Comparative Example 5 can improve the normal temperature cycle performance, but it will deteriorate the high temperature storage performance. In Comparative Example 6, adding carboxylate compound and dinitrile compound at the same time can improve the rate performance and high-temperature storage performance, but the normal-temperature cycle performance deteriorates. In Comparative Example 7, carboxylate compounds and aromatic compound overcharge additives were added at the same time, which can take into account the rate performance and overcharge safety performance, but the normal temperature cycle performance and high temperature storage performance deteriorated. Adding carboxylate compound and fluoroethylene carbonate at the same time in Comparative Example 8 can improve the rate performance and normal temperature cycle performance, but it 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 the high-temperature storage performance and overcharge safety performance, but the 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 the aromatic compound overcharge additive and fluoroethylene carbonate at the same time can improve the normal temperature cycle performance and overcharge safety performance, but it will deteriorate the high temperature storage performance. In Comparative Example 12, adding carboxylate compound, dinitrile compound and aromatic compound overcharge additive can improve the rate performance, high temperature storage performance and overcharge safety performance, but the normal temperature cycle performance deteriorates. Adding carboxylate compound, dinitrile compound and fluoroethylene carbonate at the same time in Comparative Example 13 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, adding carboxylate compound, aromatic compound overcharge additive and fluoroethylene carbonate can improve the rate performance, overcharge safety performance and normal temperature cycle performance, but it will deteriorate the high temperature storage performance. In Comparative Example 15, 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 the rate performance deteriorates.

Claims (10)

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 overcharge additives; and Fluoroethylene carbonate and/or vinylene carbonate. 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 one of alkane groups with 1 to 10 carbon atoms and halogenated alkane groups with 1 to 10 carbon atoms; The halogen atoms in the haloalkane group are selected from one or more of F, Cl, Br, and I. 3. The electrolytic solution 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, pentyl butyrate, isopentyl butyrate, ethyl valerate, ethyl isovalerate, propyl valerate, propyl isovalerate and the aforementioned carboxylate compounds are referred to as F, One or more of one or more partially substituted or fully substituted compounds in Cl, Br, I, preferably, the carboxylate compound is selected from methyl acetate, ethyl acetate, propyl acetate, Methyl propionate, ethyl propionate, propyl propionate and one or more of the aforementioned carboxylate compounds are partially substituted or fully substituted by one or more of F, Cl, Br and I. 4. electrolyte solution according to claim 1, is characterized in that, described dinitrile compound is selected from one or more in the compound shown in formula 2; NC-R ₃ -CN formula 2 in, _R3 is selected from alkylene groups with 1 to 20 carbon atoms, halogenated alkylene groups with 1 to 20 carbon atoms, alkyleneoxy groups with 1 to 20 carbon atoms, and alkylene groups with 1 to 20 carbon atoms. One of the halogenated alkylene groups, the alkylene group with 2 to 20 carbon atoms, and the halogenated alkylene group with 2 to 20 carbon atoms, and the halogen atom is selected from F, Cl, Br, and I one or more of. 5. electrolytic solution according to claim 4, is characterized in that, described 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 butanes. 6. 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. 7. electrolyte solution according to claim 1, is characterized in that, The volume of the carboxylate compound is 5% to 50% of the total volume of the organic solvent, preferably 10% to 40%, more preferably 20% to 35%; The content of the dinitrile compound is 0.5% to 10% of the total weight of the electrolyte, preferably 1% to 5%; The content of the aromatic compound overcharge additive is 0.5% to 15% of the total weight of the electrolyte, preferably 1% to 5%; The total content of the fluoroethylene carbonate and/or vinylene carbonate is 0.05%-12% of the total weight of the electrolytic solution. 8. The electrolyte solution according to claim 1, characterized in that, 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%-18.8% of the total weight of the electrolyte, and more preferably, the content of the electrolyte salt is 10%-15% of the total weight of the electrolyte. 9. electrolytic solution according to claim 1, is characterized in that, described organic solvent also comprises ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate , dipropyl carbonate, ethyl methyl carbonate, γ-butyrolactone, tetrahydrofuran or one or more. 10. A secondary battery, characterized by comprising the electrolyte solution according to any one of claims 1-9.