阅读说明：本技术 一种多功能高电压电解液及其在锂离子电池中的应用 (Multifunctional high-voltage electrolyte and application thereof in lithium ion battery ) 是由 洪波 赖延清 刘方岩 黄泽彧 张智 白茂辉 张治安 周言根 方静 于 2021-08-02 设计创作，主要内容包括：本发明公开了一种多功能高电压电解液及其在锂离子电池中的应用。添加了同时包含硼基(-B-)和腈基(-C≡N)功能基团的硼腈类化合物功能添加剂的锂离子电池电解液,利用硼腈类化合物中硼基和腈基的协同作用,在锂离子电池首次充放电过程中在正极表面形成一层致密稳定的CEI膜,以提高正极和电解液之间的界面稳定性,避免电解液与正极活性物质的直接接触,同时抑制了电解液在高电压下的氧化分解,使得电解液具有高氧化电位,进而能匹配高电压正极材料,因此,利用包含硼腈类化合物功能添加剂的电解液可以获得在高电压(≥4.5V)下具有优异循环性能和倍率性能的锂离子电池。(The invention discloses a multifunctional high-voltage electrolyte and application thereof in a lithium ion battery. The electrolyte of the lithium ion battery added with the functional additive of the boron nitrile compound simultaneously containing the functional groups of boron group (-B-) and nitrile group (-C ≡ N) forms a layer of compact and stable CEI film on the surface of the anode in the first charge-discharge process of the lithium ion battery by utilizing the synergistic action of the boron group and the nitrile group in the boron nitrile compound so as to improve the interface stability between the anode and the electrolyte, avoid the direct contact of the electrolyte and an anode active substance, and inhibit the oxidative decomposition of the electrolyte under high voltage so that the electrolyte has high oxidation potential and can be matched with a high-voltage anode material, therefore, the lithium ion battery with excellent cycle performance and high multiplying power performance under high voltage (more than or equal to 4.5V) can be obtained by utilizing the electrolyte containing the functional additive of the boron nitrile compound.)

1. A multifunctional high-voltage electrolyte is characterized in that: functional additives comprising boronitrile compounds;

the boronitrile compound has a structure shown in formula I:

wherein the content of the first and second substances,

R₁、R₂and R₃Independently selected from an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a cyano-substituted aliphatic hydrocarbon group or a cyano-substituted aromatic hydrocarbon group;

and R is₁、R₂And R₃At least one of which is a cyano-substituted aliphatic hydrocarbon group or a cyano-substituted aromatic hydrocarbon group.

2. The multifunctional high-voltage electrolyte of claim 1, wherein:

the aliphatic hydrocarbon group is C₁～C₁₀An aliphatic hydrocarbon group of (a);

the aromatic hydrocarbon group is C₆～C₁₀Aromatic hydrocarbon group ofClustering;

the cyano-substituted aliphatic hydrocarbon group is a cyano-substituted C₁～C₁₀An aliphatic hydrocarbon group of (a);

the aromatic hydrocarbon group containing a cyano substituent is C containing a cyano substituent₆～C₁₀An aromatic hydrocarbon group of (1).

3. The multifunctional high-voltage electrolyte of claim 1, wherein: the mass percentage concentration of the boron nitrile compound in the electrolyte is 0.1-10%.

4. The multifunctional high-voltage electrolyte of claim 1, wherein: the electrolyte also includes a carbonate solvent and a conductive lithium salt.

5. The multifunctional high voltage electrolyte of claim 4, wherein: the carbonate solvent is composed of a cyclic carbonate solvent and a linear carbonate solvent according to a volume ratio of 1 (1-3).

6. The multifunctional high voltage electrolyte of claim 5, wherein: the cyclic carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and vinylene carbonate.

7. The multifunctional high voltage electrolyte of claim 5, wherein: the chain carbonate solvent comprises at least one of diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and dimethyl carbonate.

8. The multifunctional high voltage electrolyte of claim 4, wherein: the concentration of the conductive lithium salt in the electrolyte is 0.6-1.5 mol/L.

9. The multifunctional high voltage electrolyte of claim 8, wherein: the conductive lithium salt comprises at least one of lithium bis (trifluoromethanesulfonylimide), lithium bis (fluorosulfonylimide), lithium trifluoromethanesulfonate, lithium difluorooxalato borate, lithium bis (oxalato) borate, lithium difluorobis (oxalato) phosphate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate and lithium perchlorate.

10. The multifunctional high-voltage electrolyte as claimed in any one of claims 1 to 9, which is used as an electrolyte for a lithium ion battery.

Technical Field

The invention relates to an electrolyte, in particular to a multifunctional high-voltage electrolyte containing a functional additive of a boron nitrile compound, and also relates to application of the multifunctional high-voltage electrolyte in a lithium ion battery, belonging to the technical field of lithium ion batteries.

Background

With the development of economy and the progress of science and technology, the requirements of the fields of electronic products, electric automobiles, medical equipment, aerospace and the like on energy storage devices are increasingly improved, and the lithium ion battery has the advantages of high energy density, high working voltage, small volume, long cycle life and the like, so that the lithium ion battery is widely applied. At present, the anode materials of commercial lithium ion batteries mainly comprise lithium manganate, lithium iron phosphate, lithium cobaltate and ternary materials, and the charge cut-off voltage of the lithium ion batteries is generally not more than 4.2V. Increasing the charge cut-off voltage is an effective method for increasing the actual discharge capacity of the anode material, and is a promising strategy for realizing a lithium ion battery with higher energy density.

However, as the voltage increases, the electrochemical performance of the battery also decreases. The electrolyte can be continuously decomposed under a higher working voltage, and the anode is continuously corroded, so that the structure of the anode is damaged; in addition, decomposition products of the electrolyte may be non-uniformly deposited on the surface of the positive electrode, increasing interfacial resistance and polarization of the battery. Therefore, effective improvement of the interface between the positive electrode and the electrolyte is the focus of current research.

The addition of small amounts of electrolyte additives with specific functional groups is the most economical and straightforward way to improve the stability of the positive electrode/electrolyte interface. Among the numerous additives, boron-based additives and nitrile-based additives are very popular high voltage electrolyte additives. The boron-based additive has lower oxidation potential than a carbonate solvent, can be preferentially oxidized and decomposed on the surface of the positive electrode to form a compact and stable CEI film, and inhibits the decomposition of electrolyte on the surface of the positive electrode, thereby showing excellent electrochemical performance. For example, patent CN 105633464 a discloses a high-voltage functional electrolyte containing trimethyl borate additive, which optimizes the surface film of the positive electrode and reduces the resistance between the positive electrode and the electrolyte, so that the cycle performance of the lithium ion battery containing the electrolyte additive is improved under 3-4.5V. However, if the charge cut-off voltage is further increased, the stability of the positive electrode structure is deteriorated, and the service life of the battery is significantly shortened. Nitrile groups (-C ≡ N) in the nitrile group additive can be coordinated with transition metal ions in the anode, so that the nitrile groups are effectively inhibited from being dissolved into electrolyte, side reactions are reduced, and the stability of the anode structure under high voltage is improved. For example, patent CN 109473721 a provides a high voltage electrolyte additive containing heterocyclic nitrile compounds, which can significantly broaden the electrochemical window when used in lithium ion batteries, but the cycling stability needs to be further improved.

In summary, the boron-based additive or the nitrile-based additive commonly used in the prior art has a single function, and cannot well solve various problems of the lithium ion battery under high voltage, if the boron-based additive and the nitrile-based additive are added simultaneously, the modification effect is mutually inhibited, the synergistic modification effect cannot be achieved, and the effect of improving the cycle stability of the lithium ion battery under high voltage is limited.

Therefore, there is an urgent need in the art to develop a multifunctional high-voltage electrolyte additive, which is of great significance for further improving the energy density of lithium ion batteries.

Disclosure of Invention

The invention aims to solve the technical problems of low specific discharge capacity, poor cycle performance, low energy density and the like of a lithium ion battery under high voltage caused by the defects of the lithium ion battery electrolyte in the prior art, and the first purpose of the invention is to provide the electrolyte containing the functional additive of the boron nitrile compound, wherein the functional additive of the boron nitrile compound in the electrolyte can form a compact and stable CEI film on the surface of a positive electrode material of the lithium ion battery, so that the stability of an interface between a positive electrode and the electrolyte is improved, the oxidative decomposition of the electrolyte is effectively inhibited, and the dissolution corrosion of the electrolyte to the positive electrode material is reduced.

The second purpose of the invention is to provide the application of the multifunctional high-voltage electrolyte in the lithium ion battery, and the lithium ion battery adopting the electrolyte has good cycle performance and rate capability under high voltage (more than or equal to 4.5V).

In order to achieve the above technical objects, the present invention provides a multifunctional high voltage electrolyte comprising a functional additive of a borated compound;

the boronitrile compound has a structure shown in formula I:

wherein the content of the first and second substances,

R₁、R₂and R₃Independently selected from an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a cyano-substituted aliphatic hydrocarbon group or a cyano-substituted aromatic hydrocarbon group;

and R is₁、R₂And R₃At least one of which is a cyano-substituted aliphatic hydrocarbon group or a cyano-substituted aromatic hydrocarbon group.

As a preferred embodiment, the aliphatic hydrocarbon group is C₁～C₁₀An aliphatic hydrocarbon group of (1). The aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group, specifically, an alkanyl group including a straight-chain alkanyl group, a branched-chain alkanyl group or a cyclic alkanyl group; the aliphatic hydrocarbon group may also be an unsaturated aliphatic hydrocarbon group, specifically, an alkenyl and/or alkynyl-containing aliphatic hydrocarbon group, the number of the alkenyl and alkynyl groups may be one or more, the position of the alkenyl and/or alkynyl group is not limited, and when a plurality of alkenyl and/or alkynyl groups are present, the alkenyl and/or alkynyl groups may be present independently or may be present in a conjugated form.

As a preferred embodiment, the aromatic hydrocarbon group is C₆～C₁₀An aromatic hydrocarbon group of (a); said aromatic hydrocarbon groupSelected from phenyl, phenyl derivatives, naphthyl or naphthyl derivatives, the phenyl derivatives being phenyl containing common substituents such as C₁～C₅Alkyl, halogen substituents, etc., the position of the substituent is not limited, the number of the substituents may be one or more, and the naphthyl derivative is a naphthyl derivative containing a common substituent on the naphthyl, such as C₁～C₅Alkyl, halogen substituents, etc., and the position of the substituents is not limited, and the number may be one or more, and halogen substituents such as fluorine substituents, chlorine substituents, bromine substituents, etc.

As a preferable mode, the cyano-substituted aliphatic hydrocarbon group is a cyano-substituted C₁～C₁₀An aliphatic hydrocarbon group of (1). The aliphatic hydrocarbon group in the cyano-substituent-containing aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group, specifically, an alkanyl group including a straight-chain alkanyl group, a branched-chain alkanyl group or a cyclic alkanyl group; the aliphatic hydrocarbon group may also be an unsaturated aliphatic hydrocarbon group, specifically, an alkenyl and/or alkynyl-containing aliphatic hydrocarbon group, the number of the alkenyl and alkynyl groups may be one or more, the position of the alkenyl and/or alkynyl group is not limited, and when a plurality of alkenyl and/or alkynyl groups are present, the alkenyl and/or alkynyl groups may be present independently or may be present in a conjugated form. The cyano groups in the cyano-substituted aliphatic hydrocarbon groups may be present as terminal groups or as pendant groups, and the number thereof may be one or more, and usually one or two cyano groups are present. In addition, the aliphatic hydrocarbon group containing a cyano substituent may further contain some common substituent groups, such as halogen substituent groups, and the position of the halogen substituent group is not limited. Halogen substituents such as fluoro substituents, chloro substituents, bromo substituents and the like.

As a preferred embodiment, the cyano-substituted aromatic hydrocarbon group is a cyano-substituted C₆～C₁₀An aromatic hydrocarbon group of (1). The aromatic hydrocarbon group in the aromatic hydrocarbon group containing the cyano substituent is selected from phenyl, phenyl derivative, naphthyl or naphthyl derivative, the phenyl derivative is phenyl containing common substituent, and the substituent is C₁～C₅Alkyl, halogen substituents, etc., the position of the substituent is not limited, and the number may be oneOr more than one naphthyl derivative is naphthyl with common substituent groups such as C₁～C₅Alkyl, halogen substituents, etc., and the position of the substituents is not limited, and the number may be one or more, and halogen substituents such as fluorine substituents, chlorine substituents, bromine substituents, etc. The cyano groups in the cyano-substituted aromatic hydrocarbon group are mainly substituted on the benzene ring or the naphthalene ring, and the number thereof may be one or more, and usually one or two cyano groups are contained.

As a more preferred embodiment, R in the boranitriles of formula I₁、R₂And R₃Independently selected from an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a cyano-substituted aliphatic hydrocarbon group or a cyano-substituted aromatic hydrocarbon group; and R is₁、R₂And R₃At least two of which are cyano-substituted aliphatic hydrocarbon groups or cyano-substituted aromatic hydrocarbon groups. As a further preferred variant, R in the boranitriles of the formula I₁、R₂And R₃Independently selected from a cyano-substituted aliphatic hydrocarbon group or a cyano-substituted aromatic hydrocarbon group. A large number of experiments show that when the boronitrile compound contains 3 aliphatic hydrocarbon groups containing cyano substituents or aromatic hydrocarbon groups containing cyano substituents, the boronitrile compound has better film-forming property and stability when added into an electrolyte, can better improve the cycle performance and rate capability of a lithium ion battery under high voltage, and has the effect that the effect is better than that of the boronitrile compound containing 2 aliphatic hydrocarbon groups containing cyano substituents or aromatic hydrocarbon groups containing cyano substituents and is far better than that of the boronitrile compound containing 1 aliphatic hydrocarbon group containing cyano substituents or aromatic hydrocarbon groups containing cyano substituents.

The key point of the multifunctional high-voltage electrolyte is that a functional additive of a boron nitrile compound is used, the boron nitrile compound simultaneously contains two functional groups of boron group and nitrile group, the two functional groups show obvious synergistic action in a charge-discharge system with the cut-off voltage of more than or equal to 4.5V and endow the multifunctional high-voltage electrolyte with better film-forming performance and stability under high voltage, so that a stable and compact CEI film with a protection function and lower impedance is formed on the surface of a positive electrode, on one hand, the oxidative decomposition of the electrolyte under high voltage is inhibited, and the interface stability between the positive electrode and the electrolyte is improved; on the other hand, the structural stability of the anode material is maintained, and the cycle performance and the rate capability of the high-voltage lithium ion battery can be improved simultaneously.

Preferably, the mass percentage concentration of the boron nitrile compound in the electrolyte is 0.1-10%. The mass percentage concentration of the cyanoboran compound in the electrolyte is more preferably 0.5 to 1.5%. If the addition amount of the cyanoborate compound in the electrolyte is too low, the effect of improving the electrochemical performance cannot be achieved; if the addition amount is too high, on one hand, the viscosity of the electrolyte is too high, the comprehensive performance is influenced, and on the other hand, the production cost of the electrolyte is increased.

As a preferable mode, the electrolyte further includes a carbonate solvent and a conductive lithium salt.

Preferably, the carbonate solvent is composed of a cyclic carbonate solvent and a linear carbonate solvent according to a volume ratio of 1 (1-3). The cyclic carbonate solvent and the linear carbonate solvent can well dissolve the conductive lithium salt within the preferable proportion range, the viscosity of the system cannot be increased, and the comprehensive performance of the lithium ion battery can be improved.

In a preferred embodiment, the cyclic carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and vinylene carbonate.

As a preferable mode, the chain carbonate solvent includes at least one of diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, and dimethyl carbonate.

Preferably, the concentration of the conductive lithium salt in the electrolyte is 0.6-1.5 mol/L. The viscosity of the solution system is increased due to the excessively high concentration of the conductive lithium salt, the cost is greatly increased, and the concentration of lithium ions in the system is reduced due to the excessively low concentration of the lithium salt, so that the ionic conductivity is reduced, and the performance of the lithium ion battery is deteriorated.

As a preferable aspect, the conductive lithium salt includes at least one of lithium bistrifluoromethanesulfonimide, lithium trifluoromethanesulfonate, lithium difluorooxalato borate, lithium bisoxalato borate, lithium difluorobis (oxalato) phosphate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, and lithium perchlorate. These lithium salts are lithium salts commonly used in lithium ion electrolytes.

The invention also provides application of the multifunctional high-voltage electrolyte as a lithium ion battery electrolyte.

The preparation method of the multifunctional high-voltage electrolyte comprises the following steps:

(1) mixing a cyclic carbonate solvent and a chain carbonate solvent at room temperature, purifying and removing impurities, and removing water;

(2) adding conductive lithium salt into the mixed solvent obtained in the step (1), and stirring and dissolving to obtain a basic electrolyte;

(3) and (3) adding a high-voltage electrolyte additive containing boron nitrile compounds into the basic electrolyte obtained in the step (2) to obtain the multifunctional high-voltage electrolyte.

The method for preparing the lithium ion battery by using the multifunctional high-voltage electrolyte comprises the following steps:

(1) sequentially compounding the positive electrode, the diaphragm and the negative electrode into a battery cell; the positive electrode comprises a positive electrode current collector and a positive electrode material compounded on the surface of the positive electrode current collector; the positive electrode material is obtained by solidifying slurry of a positive electrode active material, a conductive agent and a binder; the mass ratio of the positive electrode active material to the conductive agent to the binder is 7-9.5: 0.5-2: 1; the positive active material is NCA, NCM111, NCM523, NCM622, NCM811, lithium iron phosphate, lithium cobaltate, lithium-rich manganese base, lithium nickelate, lithium manganate, lithium nickel manganate, lithium vanadium phosphate or lithium vanadium fluorophosphate; the conductive agent is at least one of Surpe P, acetylene black, KS-6, CNT or graphene; the binder is at least one of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene and sodium carboxymethylcellulose; the negative electrode is graphite, silicon-carbon compound, lithium metal, lithium alloy or lithium titanate; the diaphragm is at least one of polypropylene, polyethylene and glass fiber;

(2) the battery core is arranged in a battery shell, and multifunctional high-voltage electrolyte is injected into the battery shell;

(3) and then packaging the battery to obtain the lithium ion battery.

Compared with the prior art, the technical scheme of the invention has the following advantages:

the functional additive of the boronitrile compound is rich in boron-oxygen bonds (-B-O-) and nitrile groups (-C ≡ N), and the two groups can act synergistically to improve the interface of a positive electrode/electrolyte, stabilize the structure of a positive electrode material and improve the electrochemical oxidation window. Compared with the electrolyte additive with a single functional group, the functional additive of the boron nitrile compound can obviously improve the electrochemical performance of the battery. In addition, the electrolyte with the functional additive of the boron nitrile compound can effectively inhibit the oxidative decomposition of the electrolyte because the functional additive of the boron nitrile compound can form a compact and stable CEI film on the surface of a positive electrode material, so that the cycle performance and the rate capability of a lithium ion battery prepared from the multifunctional high-voltage electrolyte adopting the functional additive of the boron nitrile compound under high voltage (more than or equal to 4.5V) are effectively improved.

Drawings

FIG. 1 is a graph comparing the rate capability of the lithium ion batteries of example 1 and comparative example 1;

FIG. 2 is a first three-cycle charge-discharge curve diagram of the lithium ion battery of comparative example 2 at a voltage range of 2.75-4.7V; FIG. 3 is a graph showing the first three-cycle charging and discharging curves of the lithium ion battery of example 5 at a voltage of 2.75-4.7V.

Detailed Description

The following examples are intended to further illustrate the present invention and are not intended to limit the scope of the claims of the present invention.

In the following embodiments, the boronitriles used have the following structures (A-D), and these are commercially available or are prepared by reference to the prior art:

the production method of the cyanoboran compound can be referred to in the literature (Journal of Power Sources 503(2021) 230033): 4-hydroxybenzonitrile reacts with trimethyl borate in ethyl ether, the generated white substance is washed by ethyl ether and then dried in a vacuum chamber overnight, the compound is refined by crystallization, and the synthesis method of other compounds is similar and only needs to replace raw materials.

Example 1

Preparing multifunctional high-voltage electrolyte:

(1) mixing a cyclic carbonate solvent Ethylene Carbonate (EC), a chain carbonate solvent diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) according to the volume ratio of EC to DEC to EMC of 1:1, and purifying and removing impurities and water by adopting a molecular sieve, calcium hydride and lithium hydride;

(2) dissolving 1.0mol/L conductive lithium salt lithium hexafluorophosphate in the mixed solvent obtained in the step (1), and uniformly stirring to obtain a basic electrolyte;

(3) the consumption of the boron nitrile compound A in the basic electrolyte prepared in the step (2) is 1 percent of the mass of the basic electrolyte; the multifunctional high-voltage electrolyte solution of the benzonitrile compound a of the present example was obtained.

(II) application in lithium ion batteries:

(1) preparation of the positive electrode: mixing lithium cobaltate, acetylene black and PVDF according to the mass ratio of 8:1:1, adding a proper volume of N-methylpyrrolidone (NMP), placing the mixture into a homogenizer, and stirring for 15min at the rotating speed of 15kr/min to form stable and uniform anode slurry. The slurry was coated on aluminum foil with a spatula and placed in an oven at 60 ℃ for 12h until the NMP was completely volatilized.

(2) Assembling the battery: and punching the prepared positive plate into a circular plate with the diameter of 10mm, in an argon atmosphere, taking metal lithium as a negative electrode, selecting a polypropylene microporous membrane with the model of Celgard 2320 as a diaphragm, injecting the multifunctional high-voltage electrolyte into the battery, and assembling the battery (CR2025) in sequence.

(3) The battery was completely sealed to obtain the lithium ion battery of this example.

(III) electrochemical Performance testing

And (3) carrying out charge-discharge cycle test on a blue test charge-discharge tester under the test condition of charge-discharge cycle under the multiplying power of 1C, setting the charge cut-off voltage to be 4.5V and setting the test temperature to be 25 ℃. The test results obtained are shown in Table 1.

Example 2

The other conditions were the same as in example 1 except that the multifunctional high-voltage electrolyte in this example was obtained by adding the boron nitrile compound B to the base electrolyte. The test results obtained are shown in Table 1.

Example 3

The other conditions were the same as in example 1 except that the multifunctional high-voltage electrolyte in this example was obtained by adding the boron nitrile compound C to the base electrolyte. The test results obtained are shown in Table 1.

Example 4

The other conditions were the same as in example 1, except that the multifunctional high-voltage electrolyte in this example was obtained by adding the boron nitrile compound D to the base electrolyte. The test results obtained are shown in Table 1.

Example 5

The other conditions were the same as in example 1 except that a lithium ion battery was assembled by selecting NCM811 as a positive electrode active material in this example, and the charge cut-off voltage of the test was set to 4.7V. The test results obtained are shown in Table 1.

Example 6

The other conditions were the same as in example 1, except that the multifunctional high-voltage electrolyte in this example was obtained by adding 0.1 mass% of the boron nitrile compound a to the base electrolyte. The test results obtained are shown in Table 1.

Example 7

The other conditions were the same as in example 1, except that the multifunctional high-voltage electrolyte in this example was obtained by adding 10 mass% of the boron nitrile compound a to the base electrolyte. The test results obtained are shown in Table 1.

Example 8

Other conditions were the same as in example 1, except that in this example, a cyclic carbonate solvent of Ethylene Carbonate (EC) and a chain Ethyl Methyl Carbonate (EMC) were mixed at a volume ratio of EC to EMC of 3 to 7, purification and impurity removal were performed, water was removed, a conductive lithium salt of lithium hexafluorophosphate having a concentration of 1mol/L was dissolved in the mixed solvent, and the mixture was stirred uniformly to obtain a base electrolyte of this example. The test results obtained are shown in Table 1.

Example 9

Other conditions were the same as in example 1 except that in this example, a cyclic carbonate solvent of Ethylene Carbonate (EC), a chain carbonate solvent of diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) were mixed at a volume ratio of EC: DEC: EMC of 1:1, purified to remove impurities and water, and a conductive lithium salt of lithium tetrafluoroborate was dissolved in a mixed solvent at a concentration of 0.6mol/L, and the mixture was stirred uniformly to obtain a base electrolyte of this example. The test results obtained are shown in Table 1.

Example 10

The other conditions were the same as in example 1 except that in this example, a cyclic carbonate solvent of Ethylene Carbonate (EC), a chain carbonate solvent of diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) were mixed at a volume ratio of EC: DEC: EMC of 1:1, purified to remove impurities and water, a conductive lithium salt of lithium bistrifluoromethanesulfonimide was dissolved in a mixed solvent at a concentration of 1.5mol/L, and the mixture was stirred uniformly to obtain a base electrolyte of this example. The test results obtained are shown in Table 1.

Comparative example 1

The other conditions were the same as in example 1, except that the electrolyte in this example did not contain the boron nitrile compound a. The test results obtained are shown in Table 1.

Comparative example 2

The other conditions were the same as in example 1 except that the electrolyte in this example did not contain the boron nitrile compound a and the lithium ion battery was assembled with NCM811 as the positive electrode active material, and the charge cut-off voltage of the test was set to 4.7V. The test results obtained are shown in Table 1.

TABLE 1 results of performance test of examples and comparative examples

According to analysis of test results, the compound containing the boron nitriles is added into the electrolyte as a multifunctional high-voltage electrolyte additive, and the interface stability between the anode and the electrolyte can be obviously improved through the synergistic effect of boron groups and nitrile groups, and meanwhile, the room-temperature cycle performance of the battery under high voltage (not less than 4.5V) can be obviously improved.

The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.