CN114583264A

CN114583264A - Electrolyte additive, electrolyte and lithium ion battery

Info

Publication number: CN114583264A
Application number: CN202011375916.7A
Authority: CN
Inventors: 谢泽中; 王圣; 任建新; 陶蒙
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2020-11-30
Filing date: 2020-11-30
Publication date: 2022-06-03

Abstract

The application provides an electrolyte additive comprising at least one compound as shown in formula (I), formula (II), formula (III) and formula (IV):

wherein R is₁、R₂、R₁' and R₂' is independently selected from halogen atom, carboxyl, hydroxyl, cyano, isothiocyanato, ester group, amido, amine group, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstitutedOne or more of aryl groups; r₃And R₃' is independently selected from

And a substituted structure thereof, wherein n is an integer from 1 to 5. The electrolyte additive can form a solid electrolyte interface film on both the positive electrode and the negative electrode so as to simultaneously protect the positive electrode and the negative electrode of the battery, inhibit gas generation of the battery, complex with positive electrode transition metal ions, reduce the damage of dissolution of the positive electrode transition metal ions to the negative electrode and improve the cycle performance of the battery. The application also provides an electrolyte containing the electrolyte additive and a lithium ion battery.

Description

Electrolyte additive, electrolyte and lithium ion battery

Technical Field

The application relates to the technical field of battery electrolyte, in particular to an electrolyte additive, electrolyte and a lithium ion battery.

Background

With the development of economy and science and technology, energy storage devices with higher energy density and better cycle performance are urgently needed in the industries of portable electronic devices (mobile phones, tablet computers and the like), unmanned planes, electric vehicles and the like. However, in these battery systems, the problem of dissolution of transition metal elements is easily caused in the positive electrode material, and the dissolved transition metal ions are reduced in the negative electrode, which damages an SEI (solid electrolyte interface) film formed on the surface of the negative electrode, thereby seriously affecting the cycle performance of the battery.

Among them, adding a film-forming additive to the electrolyte of a lithium ion battery becomes an effective means for improving the cycle performance of the battery. However, the conventional negative electrode film forming additive, Vinylene Carbonate (VC), and additives capable of forming films on both the surfaces of the positive and negative electrodes, such as Propylene Sulfite (PS) and vinyl sulfate (DTD), do not achieve a good effect of suppressing elution of the positive electrode-side transition metal element.

Disclosure of Invention

In view of this, the application provides an electrolyte additive, which can form a film on both a positive electrode and a negative electrode, and also has a certain complexing effect on transition metal ions, so that the damage of the transition metal ions dissolved out from the positive electrode to the negative electrode can be reduced, and the cycle performance of the battery can be improved.

Specifically, the present application provides, in a first aspect, an electrolyte additive comprising at least one compound represented by formula (i), formula (ii), formula (iii), and formula (iv):

in the formula (I), R₁、R₂、R₁' and R₂' is independently selected from one or more of halogen atoms, carboxyl groups, hydroxyl groups, cyano groups, isothiocyanates, ester groups, amide groups, amine groups, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, and substituted or unsubstituted aryl groups; r is₃And R₃' is independently selected from

And a substituted structure thereof, wherein n is an integer from 1 to 5.

The electrolyte additive contains at least one compound shown in a formula (I) to a formula (IV), the compounds contain sulfuryl (-S (═ O) -) or sulfoxide (-S (═ O) -), and two arms of the sulfuryl and the sulfoxide are respectively connected with an S atom. On one hand, the sulfone group or the sulfoxide group is used as a strong electron-withdrawing group in the compounds, so that the Lowest Unoccupied Molecular Orbital (LUMO) energy of the compounds can be reduced, the reduction potential of the compounds is further improved, and the compounds can generate an SEI film on the surface of a negative electrode before a carbonate and carboxylic ester electrolyte solvent; these negative electrode SEI films may contain Li in addition to some organic substances₂O、Li₂The inorganic substance component with high S plasma conductivity and high-temperature stability improves the high-temperature stability of the battery, and enables the formed SEI film to be more compact and the interface impedance to be lower. In addition, when the compound is reduced in a negative electrode, S-S bonds are easy to break to generate free radicals, and further free radical polymerization is easy to generate substances such as polythioether and the like, so that the SEI film has certain elasticity, and the damage of negative electrode (especially silicon negative electrode) particle expansion to the SEI film is reduced. Therefore, the negative electrode SEI film containing both organic matters and inorganic matters can effectively prevent the side reaction of the electrolyte and the surface of the negative electrode,meanwhile, the interface impedance is greatly reduced, the high-temperature cycle performance of the battery is improved, and the service life of the battery is prolonged.

On the other hand, the four compounds represented by the formulae (I) to (IV) may form an SEI film on the positive electrode, and LiS may be formed in the SEI film on the positive electrode₂O₃And lithium alkyl sulfonate, etc. can protect the positive electrode and inhibit the gas generation of the electrolyte caused by the positive electrode material. In addition, the compounds are deposited or dispersed in the SEI film of the positive electrode, sulfur atoms connected to two sides of a sulfone group or a sulfoxide group in the compounds have more lone-pair electrons, and the sulfur atoms with the lone-pair electrons can also have a certain complexing effect on transition metal ions, so that the dissolution of the transition metal ions such as manganese ions and cobalt ions of the positive electrode to damage the negative electrode can be inhibited, and the cycle performance of the battery is improved.

In this application, R₁、R₂、R₁' and R₂' is independently selected from one or more of halogen atom, carboxyl group, hydroxyl group, cyano group, isothiocyanic group, ester group (-COOR), amide group (-NHCOR), amine group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, and substituted or unsubstituted aryl group. Wherein the halogen atom comprises chlorine atom (Cl), bromine atom (Br) and iodine atom (I). The amine group may include a primary amino group (-NH)₂) Secondary amino (otherwise known as alkylamino, -NHR), tertiary amino (otherwise known as dialkylamino, -NRR').

Alternatively, the substituted group in the substituted alkyl group and the substituted alkenyl group comprises at least one of a halogen atom, a carboxyl group, a hydroxyl group, a cyano group, an isothiocyanic group, and an ether bond (-O-). For example, an alkyl group substituted with a halogen atom may be referred to as a "haloalkyl group", an "alkoxy group" may be referred to as an alkyl group substituted with an ether bond, and a "haloalkoxy group" may be referred to as an alkyl group simultaneously substituted with an ether bond and a halogen atom. Similarly, an alkenyl group substituted with a halogen atom may be referred to as a "haloalkenyl group", an "alkenyloxy group" may be regarded as an alkenyl group substituted with an ether bond, and a "haloalkenyloxy group" may be regarded as an alkenyl group simultaneously substituted with an ether bond and a halogen atom.

Optionally, the substituent group in the substituted aryl group includes at least one of a halogen atom, a carboxyl group, a hydroxyl group, a cyano group, an isothiocyanate group, an ester group, an amide group, an amine group, and a substituted or unsubstituted alkyl group, a cycloalkyl group, and an alkenyl group. The aryl group can be a monocyclic aryl group (e.g., phenyl) or a polycyclic aryl group (e.g., biphenyl, terphenyl, triphenylene, or naphthyl, and the like).

In some embodiments of the present application, R₁、R₂、R₁' and R₂' is independently selected from one or more of halogen atom, carboxyl, hydroxyl, cyano, isothiocyanic group, ester group, amide group, amine group, alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, alkenyl, halogenated alkenyl, alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy and halogenated aryloxy.

Optionally, the number of carbon atoms of the alkyl, haloalkyl, alkoxy, haloalkoxy is 1-20; the carbon atoms of the alkenyl, the halogenated alkenyl, the alkenyloxy and the halogenated alkenyloxy are 2-20; the number of carbon atoms of the aryl, halogenated aryl, aryloxy and halogenated aryloxy is 6-20.

In the embodiments of the present application, the above

The substituted structure of (b) means a structure obtained by substituting a halogen atom, an alkyl group, a cycloalkyl group, or the like.

In some embodiments of the present application, R is₁、R₂、R₁' and R₂' independently contain a cyano group. The cyano-containing group is more beneficial to the complexation of the compounds of the formulas (I) and (IV) with transition metal ions at the positive electrode, and the inhibition effect on the dissolution of the transition metal ions is enhanced.

In some embodiments of the present application, R is₃And R₃' is

At this time, radicals of the compounds of formula (i) to (iv) broken by S — S are more likely to form a polymer film at the electrode interface, increasing the elasticity of the SEI film.

Specifically, the electrolyte additive may include at least one compound represented by the following formulas (a) to (h):

wherein the CAS number of the compound represented by the formula (a) is 1208-20-4, and the Chinese name is phenylthiosulfinylbenzene. The CAS number of the compound of formula (b) is 108677-61-8. The CAS number for the compound of formula (c) is 13686-82-3. The CAS number for the compound of formula (d) is 13686-74-3. The CAS number of the compound of formula (e) is 36264-19-4. The CAS number of the compound of formula (f) is 209208-05-9. The CAS number of the compound of formula (g) is 59318-20-6. The CAS number of the compound of formula (h) is 1170318-61-2.

In the present application, the electrolyte additive may include only at least one compound satisfying the above formula (i), formula (ii), formula (iii) and formula (iv), and may further include at least one compound satisfying the above formula (i), formula (ii), formula (iii) and formula (iv), and other additives. Wherein the other additives may include one or more of Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), phenyl ethylene carbonate (PhEC), styrene ethylene carbonate (PhVC), fluoroethylene carbonate (FEC), Catechol Carbonate (CC), Alkenylphenyl Methyl Carbonate (AMC), vitamin a (va), and 2-hydro furan (CN-F), but are not limited thereto.

According to the electrolyte additive provided by the first aspect of the application, an SEI film is formed on the surface of a negative electrode, so that the damage of an electrolyte solvent to the structure of a negative electrode material is inhibited, and the effect of protecting the negative electrode is achieved; and after the positive electrode is formed into a film, the electrolyte additive has a certain complexing effect on transition metal ions, so that the damage of the transition metal ions dissolved out from the positive electrode to the negative electrode is inhibited, and the cycle performance, particularly the high-temperature cycle performance, of the battery is improved.

A second aspect of the present application provides an electrolyte comprising a lithium salt, an organic solvent and an electrolyte additive as described in the first aspect of the present application.

Optionally, the electrolyte additive according to the first aspect of the present application is 0.1% to 10% by mass in the electrolyte. The appropriate amount of the electrolyte additive can prevent the film from being too thick to increase the impedance of the battery on the premise of ensuring that the electrolyte additive can form films on the surfaces of the positive electrode and the negative electrode and reducing the dissolution of transition metal ions of the positive electrode, thereby ensuring that the cycle performance of the battery is better improved.

In the electrolyte of the present application, the lithium salt may include lithium hexafluorophosphate (LiPF)₆) Lithium difluoride imide (LiFSI), lithium bistrifluoromethylsulfonyl imide (LiTFSI), lithium tetrafluoroborate (LiBF)₄) Lithium hexafluoroarsenate (LiAsF)₆) Lithium hexafluoroantimonate (LiSbF)₆) Lithium perchlorate (LiClO)₄) Lithium bistrifluoromethylsulfonyl imide (LiTFSI), lithium dioxalate borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium triflate (LiCF)₃SO₃) Lithium perfluorobutylsulfonate (LiC)₄F₉SO₃) Lithium bis (trifluoromethylsulfonyl) imide (Li (CF)₃SO₂)₂N), lithium bis (perfluoroethylsulfonyl) imide (Li (C)₂F₅SO₂)₂N) is selected. The content of the lithium salt in the electrolyte is not particularly limited, and may be determined by the conventional amount in the art. For example, the concentration of the lithium salt in the electrolyte may be 0.1 to 5mol/L, preferably 0.5 to 4 mol/L.

In the electrolyte of the present application, the organic solvent may include one or more of carbonate, carboxylate and derivatives thereof, but is not limited thereto. The carbonate may be cyclic and/or linear, and the carboxylate may be linear and/or branched. Exemplary organic solvents may include one or more of Ethylene Carbonate (EC), Propylene Carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), ethyl propyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, ethyl butyrate, and the like, but are not limited thereto. Optionally, the mass of the organic solvent accounts for 10% -90% of the mass of the electrolyte. Preferably, the organic solvent is a carbonate. At this time, the electrolyte additive has good compatibility with a carbonate solvent, and is soluble with the carbonate solvent, and the addition of the electrolyte additive does not affect physicochemical properties such as viscosity of the matrix electrolyte.

In a third aspect, the present application provides a lithium ion battery, in which the electrolyte according to the first aspect of the present application is embedded. The battery containing the electrolyte has good normal-temperature cycle performance and excellent high-temperature cycle performance.

Specifically, the lithium ion battery comprises a battery shell, and a battery core and an electrolyte, which are accommodated in the battery shell, wherein the battery core comprises a positive plate, a negative plate and a diaphragm located between the positive plate and the negative plate, and the electrolyte is as described in the first aspect of the present application.

The preparation method of the lithium ion battery comprises the following steps: and sequentially stacking the positive plate, the diaphragm and the negative plate to form a battery core, accommodating the battery core in a battery shell, injecting the electrolyte, and sealing the battery shell to obtain the lithium ion battery.

The negative plate, the positive plate and the diaphragm are all conventional choices in the battery field. For example, the positive electrode sheet includes a current collector and a positive electrode material layer disposed on the current collector, wherein the positive electrode material layer includes a positive electrode active material, a positive electrode binder, and optionally a conductive agent. The negative electrode sheet includes a current collector and a negative electrode material layer disposed on the current collector, wherein the negative electrode material layer may include a negative electrode active material, a negative electrode binder, and optionally a conductive agent. The diaphragm comprises modified polyethylene felt, modified polypropylene felt, superfine glass fiber felt, vinylon felt, or a composite film formed by welding or bonding nylon felt and a wettable polyolefin microporous film.

Advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Drawings

FIG. 1 is a plot of the linear sweep voltammetry test for the pull-out with the electrolyte of example 1 versus the pull-out with the electrolyte of comparative example 1;

FIG. 2 is a plot of the cyclic voltammetry tests for the pull-out with the electrolyte of example 1 versus the pull-out with the electrolyte of comparative example 1.

Detailed Description

The examples of the present application are further illustrated below in various examples.

Example 1

30g of Ethylene Carbonate (EC) and 70g of Ethyl Methyl Carbonate (EMC) were mixed to obtain a mixed solvent, and 14.4g of lithium hexafluorophosphate (LiPF) was added to the mixed solvent₆) After stirring, 1.15g of phenylthiosulfinyl benzene was added as an additive and dispersed sufficiently to obtain an electrolyte solution designated as E1. In this electrolyte E1, the mass percent of phenylthiosulfinylbenzene was 1%.

A method of making a lithium ion battery, comprising:

A) preparing a negative plate: mixing 100 parts of graphite material, 2 parts of conductive agent super-p, 2 parts of sodium carboxymethylcellulose (CMC) and 3 parts of Styrene Butadiene Rubber (SBR) in water, uniformly stirring to obtain negative electrode slurry, coating the negative electrode slurry on copper foil serving as a negative electrode current collector, and drying for 24 hours at 80 ℃ in vacuum to obtain a negative electrode sheet; B) preparing a positive plate: mixing 100 parts of positive active material (specifically, lithium cobaltate, LCO), 2 parts of Carbon Nano Tube (CNT) and 2 parts of polyvinylidene fluoride (PVDF) in N-methyl pyrrolidone to obtain positive slurry, uniformly coating the positive slurry on an aluminum foil serving as a positive current collector, and drying for 24 hours at 80 ℃ in vacuum to obtain a positive plate; C) assembling the battery: in a glove box, the positive plate, the diaphragm and the negative plate are stacked in sequence and wound into a cell, the cell is arranged in a battery shell and welded, then 1.2g of electrolyte E1 is injected into the battery shell, and the battery shell is sealed to obtain the LCO/graphite soft package full battery with the model number of CSL492430, which is recorded as a battery S1 and used for cycle performance testing.

Before the electrochemical performance test of the soft package battery, the battery cell needs to be formed to form an SEI film. The formation process of the full cell comprises the following steps: charging the full cell to 1.9V at a current of 25mA (0.05C), and keeping the voltage at 1.9V for 10h to fully wet the electrode plates of the cell; after the constant voltage was completed, the battery was charged with a current of 5mA (0.01C) for 10h to form a stable and dense SEI film, and then charged to 4.4V with a current of 50mA (0.05C), followed by discharging to 2.75V.

Example 2

An electrolyte was prepared in the same manner as in example 1, except that the additive was 2.33g of phenylthiosulfinyl benzene, to obtain electrolyte E2 in which the additive was present in an amount of 2% by mass.

According to the method for producing a full cell provided in example 1, the electrolyte E2 was prepared to obtain a cell S2.

Example 3

An electrolyte was prepared in the same manner as in example 1, except that the additive was 6g of phenylthiosulfinylbenzene, to obtain an electrolyte E3 in which the additive was 5% by mass.

According to the preparation method of the full cell provided in example 1, the electrolyte E3 was prepared to obtain a cell S3.

Example 4

An electrolyte E4 was prepared in the same manner as in example 1, except that the composition of the mixed solvent was 30g of Ethylene Carbonate (EC) and 70g of dimethyl carbonate (DMC).

According to the method for producing a full cell provided in example 1, the electrolyte E4 was prepared to obtain a cell S4.

Example 5

Electrolyte E5 was prepared according to the method of example 1, except that: the additive was 1.15g of the compound represented by the formula (b).

Example 6

Electrolyte E6 was prepared according to the method of example 1, except that: the additive was 1.15g of the compound represented by the formula (d).

Example 7

Electrolyte E6 was prepared according to the method of example 1, except that: the additive was 1.15g of the compound represented by the formula (f).

Example 8

Electrolyte E6 was prepared according to the method of example 1, except that: the additive was 1.15g of the compound represented by the formula (h).

To highlight the advantageous effects of the examples of the present application, the following comparative examples 1 to 3 are provided.

Comparative example 1

Electrolyte RE1 was prepared according to the method of example 1 except that no additives were present. According to the preparation method of the full cell provided in example 1, the electrolyte RE1 is prepared to obtain a cell RS 1.

Comparative example 2

Electrolyte RE2 was prepared according to the method of example 1, except that: the additive was 1.15g of Vinylene Carbonate (VC). According to the preparation method of the full cell provided in example 1, the electrolyte RE2 is prepared to obtain a cell RS 2.

Comparative example 3

Electrolyte RE3 was prepared according to the method of example 1, except that: the additive was 1.15g of 1, 3-Propane Sultone (PS). According to the preparation method of the full cell provided in example 1, the electrolyte RE3 is prepared to obtain a cell RS 3.

Performance testing

1. Reduction potential and oxidation potential tests of additives

The reduction potential and the oxidation potential of each electrolyte are obtained by carrying out volt-ampere test on the corresponding button cell. For example, the reduction potential of the electrolyte E1 is obtained by testing the CR2016 type button half cell assembled by the negative electrode sheet and the metal lithium sheet in example 1, and the injection amount of the electrolyte E1 in the button cell is about 0.1 g. The oxidation potential of the electrolyte E1 is obtained by testing the button half cell assembled by the stainless steel sheet and the metal lithium sheet. Wherein, the sweep rate of the volt-ampere test is 0.2mV/s, the sweep range is 0.005V-3V, the test equipment is an Autolab electrochemical workstation, and the test results are summarized in the following table 1.

TABLE 1 summary of film formation potentials of respective electrolytes

Wherein, the linear sweep voltammetry test curves of the charging of the electrolyte E2 containing example 1 and the charging of the electrolyte RE1 containing comparative example 1 are shown in FIG. 1, and the cyclic voltammetry test curve is shown in FIG. 2.

As can be seen from fig. 1, the phenylthiosulfinyl benzene in example 1 exhibited an oxidation peak at around 4V, whereas the electrolyte of comparative example 1 exhibited no oxidation peak at this potential. As can be seen from fig. 2, the phenylthiosulfinyl benzene in example 1 exhibited an oxidation peak at 1.41V, whereas the electrolyte of comparative example 1 exhibited no reduction peak at this potential. This indicates that the thiophenylsulfinyl benzene provided in the examples of the present application can form a film on the positive electrode and the negative electrode at the same time.

In addition, as can be seen from table 1, the reduction potential of the additive of the embodiment of the present invention to lithium is between 1.3V and 1.7V, which is higher than the film formation potential (0.8V) of ethylene carbonate as a solvent, so that the additive provided by the present application can form a film on a negative electrode in preference to the solvent. The reduction voltage of the additive of the embodiment of the application is higher than that of the VC additive of the comparative example 2 and that of the PS additive of the comparative example 3, which further shows that the additive of the embodiment of the application is easier to form a film on a negative electrode than the existing additive.

2. High temperature cycling test of batteries

The full cells in each example and comparative example (10 full cells each, the results of which were averaged) were placed in an incubator at 60 ℃ and connected to a cell performance tester (which may be a blue CT2001C test system, in particular) through an outgoing line, and were cycled 120 times at a current of 500mA (1C) for each full cell between 2.75V and 4.4V. The discharge capacity at the 120 th cycle was divided by the initial discharge capacity at the 1 st cycle to obtain a ratio as a capacity retention rate of each battery at 60 ℃ for 120 cycles of high temperature cycles, and the result of the capacity retention rate of each battery is shown in table 2.

3. Battery transition metal ion dissolution test

The full cells in each example and comparative example (10 full cells each, the results were averaged) were subjected to 2.75V to 4.5V (accelerated dissolution of transition metal ions under 4.5V overcharge conditions)The current of 500mA (1C) is circulated for 120 times. And then discharging the battery to 2.75V, disassembling the battery, taking out the negative plate, cleaning the negative plate by using DMC, and drying the negative plate. Then taking 10cm²The DMC-cleaned negative electrode pieces of the sizes were pickled with 1mL of a 3M nitric acid solution to dissolve the transition metal deposited on the negative electrode into transition metal ions, and the concentrations of the transition metal ions were measured by an Inductively Coupled Plasma (ICP) instrument, and the results are summarized in table 2.

TABLE 2 high-temperature capacity retention ratio and metal ion eluted from negative electrode of each battery

As can be seen from table 2, the batteries of comparative examples 1 to 3 have a large amount of cobalt ions eluted from the negative electrode after being cycled for a plurality of times, which indicates that the elution inhibition effect of both the additives VC and PS on the cobalt ions is not significant, whereas the additives of examples 1 to 8 of the present invention have significant inhibition effect on the elution of transition metal ions. In particular, the lowest concentration of cobalt ions eluted in examples 5 and 8 indicates that when the additive of the present application contains a cyano group, a better effect of inhibiting elution of transition metal ions can be achieved.

In addition, the high-temperature capacity retention rate of the batteries of examples 1 to 8 of the present application is higher than that of comparative examples 1 to 3. This indicates that the additives provided herein are advantageous for improving the high temperature cycle performance of the battery. The high-temperature cycle retention of the batteries of examples 5 and 8 is particularly outstanding, and it is shown that the additive containing a cyano group can inhibit the dissolution of transition metal ions and can also better inhibit the damage of the dissolved transition metal ions to the negative electrode in the cycle process, thereby improving the high-temperature cycle performance of the batteries.

The foregoing is illustrative of the present application and it will be appreciated by those skilled in the art that various modifications and adaptations can be made without departing from the principles of the application and are intended to be within the scope of the application.

Claims

1. An electrolyte additive comprising at least one compound represented by formula (i), formula (ii), formula (iii), and formula (iv):

wherein R is₁、R₂、R₁' and R₂' is independently selected from one or more of halogen atoms, carboxyl groups, hydroxyl groups, cyano groups, isothiocyanates, ester groups, amide groups, amine groups, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, and substituted or unsubstituted aryl groups; r₃And R₃' is independently selected from

And a substituted structure thereof, wherein n is an integer from 1 to 5.

2. The electrolyte additive of claim 1 wherein R is₁、R₂、R₁' and R₂' independently contain a cyano group.

3. The electrolyte additive of claim 1 wherein R is₃And R₃' are all

4. An electrolyte comprising a lithium salt, an organic solvent, and the electrolyte additive according to any one of claims 1 to 3.

5. The electrolyte of claim 4, wherein the electrolyte additive is present in the electrolyte in an amount of 0.1% to 10% by mass.

6. The electrolyte of claim 4, wherein the organic solvent comprises one or more of a carbonate, a carboxylate, and derivatives thereof.

7. The electrolyte of claim 6, wherein the organic solvent comprises one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, propyl methyl carbonate, propyl ethyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, and ethyl butyrate.

8. The electrolyte of claim 4, wherein the concentration of the lithium salt in the electrolyte is 0.1 to 5 mol/L.

9. The electrolyte of claim 4, wherein the lithium salt comprises one or more of lithium hexafluorophosphate, lithium difluorobenzimide, lithium bistrifluoromethylsulfonyl imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium perchlorate, lithium dioxalate borate, lithium difluorooxalato borate, lithium trifluoromethylsulfonate, lithium perfluorobutylsulfonate, lithium bis (trifluoromethylsulfonyl) imide and lithium bis (perfluoroethylsulfonyl) imide.

10. A lithium ion battery having the electrolyte according to any one of claims 4 to 9 incorporated therein.