CN118063359B - Binary asymmetric organic lithium salt, electrolyte and lithium battery - Google Patents

Abstract

The invention provides a binary asymmetric organic lithium salt, an electrolyte and a lithium battery, wherein the binary asymmetric organic lithium salt has a structural general formula A; wherein M ⁺ is Li ⁺,R₁ and R ₂ are selected from fluorine atoms, trifluoromethyl or fluorine-containing phenyl, R ₁ and R ₂ are different, R ₃ is selected from hydrogen atoms, C1-C3 alkyl, methyl acetate group, ethyl acetate group or propyl acetate group, and X is selected from methine or nitrogen atoms. The characteristic halogenated aromatic anion structure contained in the binary asymmetric organic lithium salt structure provided by the invention can be used for in-situ construction of a solid electrolyte interface layer rich in lithium halide, has high Young modulus and high surface energy, can be used for homogenizing lithium ion flux and reducing lithium ion diffusion energy barrier, so that interface stability is improved, and further performances such as electrochemical cycle of a lithium battery are effectively improved.

Description

Binary asymmetric organic lithium salt, electrolyte and lithium battery

Technical Field

The invention relates to the field of lithium batteries, in particular to a binary asymmetric organic lithium salt, electrolyte and a lithium battery.

Background

Considering that the future lithium battery has obvious high nickel and high voltage trend, the index requirements on the safety, energy density and the like of the lithium battery are gradually improved, but the current common lithium hexafluorophosphate (LiPF ₆) is applied to the lithium battery, and the problems that the heat stability is poor, the lithium hexafluorophosphate is easy to hydrolyze, the capacity of the battery is easy to quickly attenuate, potential safety hazards are brought, and harmful gas hydrogen fluoride is easily absorbed, decomposed and released are still present, and the requirements may not be satisfied in the future.

The novel electrolyte solute lithium salt has higher thermal stability, thermodynamic stability and high-low temperature discharge performance, has physical and chemical properties superior to those of LiPF ₆, and can better meet the development trend of lithium batteries. The application of the novel lithium salt to the lithium battery can widen the service temperature of the battery, improve the cycle life and the safety, and is an important direction of future development under the demand environment of high energy density and high safety of the power battery. Of these new lithium salts, lithium bis-fluorosulfonyl imide (LiFSI) is one of the lithium salts with a clear prospect of development. However, liFSI has higher cost and is unfavorable for battery commercialization, and more LiFSI is used as an additive in electrolyte at present, and the additive amount is generally less than or equal to 3wt%; the electrolyte is not compatible with the anode material after being added, gas is not easy to decompose at high temperature, the conductivity is good at low temperature, the dissolubility is good, and the performances in all aspects are relatively good. Lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) has been very important, and can improve the conductivity of the electrolyte, and a small amount of lithium bis (trifluoromethylsulfonyl) imide can improve the low-temperature performance of the electrolyte when used as an additive, but the lithium bis (trifluoromethylsulfonyl) imide has no obvious help to the high-temperature performance. With the advent of the alternative LiFSI, the mass production of LiTFSI was largely invisible in lithium battery electrolytes, whereas LiTFSI is widely used as a single conductive lithium salt in polymer electrolytes, mainly thanks to its highly delocalized anions and the consequent high ionic conductivity.

Currently, research on novel lithium fluorosulfonyl imide salts has focused on monobasic fluorosulfonimides (i.e., containing only one coordinated lithium cation in the molecule), such as LiTFSI and LiFSI described above, but still remains to be improved in performance and cost.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a binary asymmetric organic lithium salt, electrolyte and a lithium battery.

There are few reports on the research of binary or multi-element fluorine-containing sulfonimide lithium salt, especially the application of the binary or multi-element fluorine-containing sulfonimide lithium salt as an electrolyte component in a secondary lithium battery. Therefore, the binary or multi-element fluorine-containing sulfimide lithium salt, the preparation method and the application exploration thereof have extremely high application prospect.

To achieve the above object, in a first aspect, an embodiment of the present invention provides a binary asymmetric organolithium salt having a general structural formula of formula a:

Formula A;

Wherein M ⁺ is Li ⁺,R₁ and R ₂ are selected from fluorine atoms, trifluoromethyl or fluorine-containing phenyl, R ₁ and R ₂ are different, R ₃ is selected from hydrogen atoms, C1-C3 alkyl, methyl acetate group, ethyl acetate group or propyl acetate group, and X is selected from methine or nitrogen atoms. The C1-C3 alkyl comprises alkyl groups with the carbon number of 1,2 and 3, namely methyl, ethyl, n-propyl and isopropyl.

Preferably, R ₁ is selected from 3-fluoro-4-bromophenyl, 3,4, 5-trifluorophenyl or 4-bromo-3, 5-difluorophenyl, R ₂ is selected from fluorine atom, trifluoromethyl or 3-trifluoromethyl-4-bromophenyl, R ₃ is selected from methyl or methyl acetate.

In the organic lithium salt structure shown in the formula A of the embodiment of the invention, M ⁺ is lithium ion, and R ₁ and R ₂ which are respectively connected with two sulfonyl groups have different fluorine-containing group structures, namely a binary asymmetric structure, which can also be called as binary asymmetric organic lithium salt. The fluorine-containing group may be a fluorine atom (F), a trifluoromethyl group (-CF ₃) or a fluorine-containing phenyl group including substituted phenyl groups containing one or more fluorine groups such as phenyl groups substituted with monofluorine at the 3-position, 4-position or 5-position, 3-fluoro-4-bromophenyl groups, 3, 5-difluoro-4-bromo-phenyl groups, 3,4, 5-trifluorophenyl groups, 3-trifluoromethyl-4-bromophenyl groups and the like.

Preferably, at least one of R ₁ and R ₂ is a fluorine-containing phenyl group. And X is selected from a methine group (-CH) or a nitrogen atom (N), and R ₃ to which it is attached may be a hydrogen atom (H), a methyl group (-CH ₃) or a methyl acetate group (-CH ₂COOCH₃) or the like.

The binary asymmetric organic lithium salt provided by the embodiment of the invention has larger anion radius, so that lithium ions are easier to dissociate when a small amount of electrolyte is added, the ion transmission selectivity is enhanced, the migration number of lithium ions is improved, and the concentration polarization phenomenon is relieved. Meanwhile, electrochemical reduction decomposability of a characteristic halogenated aromatic anion structure contained in some structures is enhanced, so that the lithium halide aromatic anion structure can be decomposed on the surface of a lithium negative electrode preferentially, a Solid Electrolyte Interface (SEI) layer rich in lithium fluoride LiF and lithium bromide LiBr is constructed in situ, wherein lithium ion flux is uniform due to high Young modulus and high surface energy of LiF, liBr has a lower lithium ion diffusion energy barrier in the SEI layer, interface stability is improved, and performances such as electrochemical circulation and the like of a lithium battery are further effectively improved.

In a preferred embodiment of the present invention, the binary asymmetric organolithium salt is selected from at least one of the formulae I to IX, wherein the independent single bond "—" in the following structural formulae represents methyl;

The compound of the formula I, The compound of the formula II is shown in the specification,The compound of the formula III,The compound of the formula IV,

The characteristic of the V-shaped alloy is that,A compound of the formula VI,

The compound of the formula VII,The catalyst of formula VIII,Formula IX.

The embodiment of the invention provides a preparation method of binary asymmetric organic lithium salt, which comprises the following steps:

Carrying out substitution reaction on the binary sulfimide compound and a lithium source to obtain binary asymmetric organic lithium salt shown in a formula A; the binary sulfimide compound has a structural general formula B:

Formula B;

Wherein R ₁ and R ₂ are selected from fluorine atoms, trifluoromethyl or fluorine-containing phenyl, R ₁ and R ₂ are different, R ₃ is selected from hydrogen atoms, C1-C3 alkyl groups, methyl acetate groups, ethyl acetate groups or propyl acetate groups, and X is selected from methine groups or nitrogen atoms.

The synthetic routes in some examples of the invention are shown below, but are not limiting of the preparation methods provided by the invention:

。

Specifically, in the embodiment of the invention, two sulfonamide monomers and a dichloro monomer are subjected to nucleophilic substitution reaction to prepare a binary sulfimide compound with a structure shown in a formula B, and the intermediate is subjected to substitution reaction with a lithium source to obtain the binary asymmetric organic lithium salt.

Wherein, R ₁、R₂、R₃ and X groups in the monomer structure are consistent with the previous description; the nucleophilic substitution reaction is carried out in an ice bath (such as-10-0 ℃) in the presence of a catalyst; the lithium source for substitution reaction with the intermediate includes, but is not limited to, lithium hydroxide. In addition, the reactions in the synthesis method are all carried out in an organic solvent under the condition of protective atmosphere. The method for preparing the binary asymmetric organic lithium salt is simple, convenient and feasible, and is suitable for large-scale production.

Compared with the prior art, the binary asymmetric organic lithium salt prepared by the embodiment of the invention is used as an electrolyte additive, has larger anion radius, so that lithium ions are easier to dissociate, and therefore, the binary asymmetric organic lithium salt has excellent solubility in the electrolyte; the lithium ion transfer rate can be effectively improved, the conductivity of the electrolyte is increased, and the concentration polarization phenomenon under high multiplying power is relieved when the lithium ion transfer rate is used as an additive. Meanwhile, electrochemical reduction decomposability of a characteristic halogenated aromatic anion structure contained in some structures is enhanced, so that the LiF and LiBr-rich SEI passivation layer can be preferentially decomposed on the surface of a lithium negative electrode, in-situ construction is carried out, liF shows high Young modulus and high surface energy, lithium ion flux can be homogenized, liBr shows extremely low lithium ion diffusion barrier in the SEI layer, therefore, lithium ions can be rapidly and stably transmitted at an interface, the stability of a lithium negative electrode-electrolyte interface is remarkably improved, growth of lithium dendrites caused by nonuniform deposition of lithium is effectively avoided, and the electrochemical performance of a lithium battery is effectively improved.

In a second aspect, an embodiment of the present invention provides an electrolyte comprising a lithium salt, a nonaqueous organic solvent, and an additive, wherein the additive is a binary asymmetric organolithium salt as described above. Wherein the additive may be referred to as a binary asymmetric organolithium salt additive having the structure of formula a; based on the performance of the additive, the electrolyte provided by the invention is used in a lithium ion battery, and the electrochemical performance of the electrolyte can be improved.

Further, the lithium salt is at least one selected from lithium hexafluorophosphate (LiPF ₆), lithium perchlorate (LiClO ₄), lithium tetrafluoroborate (LiBF ₄), lithium bisoxalato borate (LiBOB); more preferably LiPF ₆, lithium hexafluorophosphate performs better in performance and cost.

The embodiment of the invention mainly provides a nonaqueous electrolyte containing the additive, and the nonaqueous organic solvent can be one or more selected from an ester solvent and an ether solvent.

Further, the ester solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, methyl trifluoroethyl carbonate and di (2, 2-trifluoroethyl) carbonate; the ether solvent is dimethyl ether, diethyl ether, methylethyl ether 1, 2-tetrafluoroethyl-2, 3-tetrafluoropropyl ether and 1H, 5H-at least one of octafluoropentyl-1, 2-tetrafluoroethyl ether.

In addition to using the binary asymmetric organolithium salt as an additive, the electrolyte preferably also includes auxiliary additives including a positive film-forming additive and/or a resistance-reducing additive.

Further, the auxiliary additive includes ethylene carbonate, ethylene sulfate, ethylene bissulfate, propylene sulfate, 1, 3-propane sultone, 1, 3-propenesulfonic acid sultone, 1, 4-butanesulfonic acid lactone, 2, 4-butanesulfonic acid lactone, phenyl methanesulfonate, methylene methanesulfonate, N-phenylbis (trifluoromethanesulfonyl) imide, triallyl phosphate, tris (trimethylsilane) phosphate, trimethyl phosphite, triphenyl phosphite, tetramethylene diphosphate, propargyl phosphate, (2-allylphenoxy) trimethyl silane, tris (trimethylsilane) borate, 1,3, 5-triallyl isocyanurate, isocyanatoethyl methacrylate, hexamethylene diisocyanate, terephthalyl diisocyanate, 2, 4-toluene diisocyanate, adiponitrile, succinonitrile, glutaronitrile, 1,3, 6-hexanetrinitrile and 1, 2-bis (cyanoethoxy) ethane, lithium bistrifluoromethylsulfonimide, lithium difluorooxalate and lithium difluoroborate, lithium monofluorophospholate, and the like.

In some embodiments, the binary asymmetric organolithium salt additive of the present invention primarily optimizes the negative electrode film-forming function, preferably in combination with other electrolyte additives such as positive electrode film-forming additives, impedance-reducing additives, to achieve optimal battery performance.

Preferably, the lithium salt accounts for 10-15% of the weight of the electrolyte, and further 11-13%.

Preferably, the nonaqueous organic solvent accounts for 80-87% of the weight of the electrolyte, and is further 81.8% -86.8%.

Preferably, the binary asymmetric organic lithium salt additive with the structure of formula A accounts for less than 2% of the weight of the electrolyte, and is further 0.1-2%; the sum of the mass of the additive and the mass of the auxiliary additive accounts for within 6 percent of the weight of the electrolyte, and is further 1.3 to 5.5 percent.

The third aspect of the embodiment of the invention also provides a lithium battery, which comprises a positive electrode, a negative electrode, a diaphragm and the non-aqueous electrolyte; the lithium battery containing the nonaqueous electrolyte provided by the embodiment of the invention has good electrochemical performance. The lithium battery comprises a lithium ion secondary battery and a lithium metal secondary battery, and in some embodiments, the lithium metal secondary battery is mainly used.

Further, the active material of the positive electrode is selected from lithium cobaltate, lithium manganate, ternary nickel cobalt manganese lithium, lithium nickel manganate, lithium iron phosphate and lithium manganese iron phosphate; preferably, ternary nickel cobalt manganese lithium (NCM 811) is selected and commercially available. The positive electrode is a conventional component and generally includes an active material, a conductive agent such as carbon black, a carbon nanomaterial, and a binder, mainly polyvinylidene fluoride (PVDF).

Further, the active material of the negative electrode is selected from any one of graphite (including artificial graphite and natural graphite), lithium titanate, lithium metal, silicon oxide and silicon carbon composite material; preferably, metallic lithium is selected as the negative electrode.

Further, the membrane is a polyolefin membrane and can be selected from a polypropylene membrane or a polyethylene membrane; preferably, a polyethylene separator is selected.

The nonaqueous electrolyte is adopted to prepare a lithium battery (no special requirement is imposed on components such as a diaphragm) according to a conventional process, and the electrochemical performance such as the cycle life is better; the method is characterized in that the quick charge performance and the overall cycle life of the prepared NCM811 Li battery in a voltage range of 3.0-4.25V are greatly improved.

Detailed Description

In order to enable those skilled in the art to better understand the technical solution of the present invention, the following further describes the objects, technical solutions and advantageous effects of the present invention by means of specific examples, but does not constitute any limitation of the present invention. Those not explicitly stated in the examples may be performed under conventional conditions or conditions suggested by the manufacturer. The reagents or apparatus used were conventional products available commercially without the manufacturer's attention.

Example 1

The preparation of the compound (I) comprises the following specific steps:

；

To a clean, dry, three-neck 500 mL flask equipped with a magnetic rotor under nitrogen atmosphere was added 200 mL anhydrous Tetrahydrofuran (THF), then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃, 3-fluoro-4-bromobenzenesulfonamide (12.65 g,50.00 mmol) and sulfamoyl fluoride (4.95 g,50.00 mmol) were slowly added, then sodium hydride (NaH) was slowly added in three portions (1.44 g,60.00 mmol), and stirring was continued for 30 min. To the resulting solution was slowly added 100 mL of anhydrous THF solution pre-frozen to 0 ℃ with 1, 3-dichloro-2-methylpropane (13.86 g,110.00 mmol) using a constant pressure dropping funnel over 30min, after the addition was completed the ice water bath was removed and the resulting mixture was stirred at room temperature 12 h. The mixture was then quenched with 50 mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with n-hexane/methanol (volume ratio 95:5) and rotary evaporation to remove the solvent to give the binary sulfonimide intermediate 1, yield 81.3%.TOF-SIMS (m/z): calcd. for C₁₀H₁₃N₂O₄S₂BrF₂ [M+1]⁺, 405.95, found 405.97.

To a clean, dry, three-necked 500 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 1 (20.30 g,50 mmol) and lithium hydroxide (2.63 g,110 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (I) with the yield 75.6%.TOF-SIMS (m/z): calcd. for C₁₀H₁₁N₂O₄S₂BrF₂Li₂ [M+1]⁺, 417.96, found 418.13.

The electrolyte 1 sample was prepared as follows:

In an argon glove box with water oxygen content less than or equal to 0.1 ppm, uniformly mixing Ethylene Carbonate (EC), propylene Carbonate (PC), fluoroethylene carbonate (FEC) and Ethyl Methyl Carbonate (EMC) according to a volume ratio of 5:10:15:70 to obtain an organic solvent, slowly adding lithium hexafluorophosphate (LiPF ₆) into the organic solvent, adding 1, 3-Propane Sultone (PS), lithium difluorophosphate (LiPO ₂F₂) and an organic lithium salt compound (I) after complete dissolution, and uniformly stirring to obtain an electrolyte 1, wherein the use amounts of the LiPF ₆, the organic solvent, the PS, the LiPO ₂F₂ and the compound (I) are respectively 12.5%, 84%, 2%, 0.5% and 1% of the total mass of the electrolyte.

The experimental battery 1 sample was prepared as follows:

Preparation of a positive plate: and weighing and mixing 8-series nickel cobalt lithium manganate (NCM 811), carbon black (SuperP) serving as a conductive agent and a carbon nano tube (CNT, 5% mass fraction of methyl pyrrolidone (NMP) solution) serving as a binder of polyvinylidene fluoride (PVDF, 5% mass fraction of NMP solution), adding an appropriate amount of NMP after the mixing is finished to control the theoretical solid content to be 65%, homogenizing by using a vacuum defoaming machine to obtain positive electrode slurry, uniformly coating the positive electrode slurry on an aluminum foil with the thickness of 13 mu m, and drying, rolling and cutting to obtain a positive electrode sheet.

Preparation of the separator: the polyethylene diaphragm is used as a separation membrane, and the separation membrane is placed in a drying room with a dew point of minus 35 ℃ for 72 hours before use.

Preparing a negative plate: and rolling the metal lithium to two sides of the copper foil with the thickness of 10 mu m by a physical rolling mode to obtain the composite anode, wherein the thickness of a single-sided lithium layer is 40 mu m. After cutting, the mixture is transferred into an argon glove box for storage.

Preparation of the battery: manufacturing a battery in an argon atmosphere glove box with water oxygen value less than or equal to 0.1 ppm, sequentially stacking and placing a positive plate, a diaphragm and a composite negative plate in sequence, adhering an adhesive tape for fixing, welding a tab, then placing in an aluminum plastic film, vacuum baking at 90 ℃ for 12 hours, cooling, injecting the prepared electrolyte 1, and finally vacuum packaging, high Wen Jinrun, formation, aging, secondary sealing and capacity division to obtain the experimental battery 1 with the capacity of about 1 Ah.

Example 2

The preparation of compound (II) comprises the following specific steps:

；

To a clean, dry, three-neck 500 mL flask equipped with a magnetic rotor under nitrogen atmosphere was added 200 mL anhydrous THF, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃,3, 4, 5-trifluorobenzenesulfonamide (10.55 g,50.00 mmol) and sulfamoyl fluoride (4.95 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100mL anhydrous THF solution of 1, 3-dichloro-2-methylpropane (13.86 g,110.00 mmol) pre-frozen to 0 ℃ using a constant pressure dropping funnel over 30min, after the addition was completed the ice water bath was removed and the resulting mixture was stirred at room temperature 12 h. The mixture was then quenched with 50 mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with n-hexane/methanol (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 2 in yield 78.3%.TOF-SIMS (m/z): calcd. for C₁₀H₁₂N₂O₄S₂F₄ [M+1]⁺, 364.02, found 364.05.

To a clean, dry, three-necked 250 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 2 (20.02 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100 mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (II) with the yield 77.8%.TOF-SIMS (m/z): calcd. for C₁₀H₁₀N₂O₄S₂F₄Li₂ [M+1]⁺, 376.03, found 376.04.

Electrolyte 2 and experimental battery 2 were prepared as in example 1, except that the solvents in electrolyte 2 were FEC and EMC at a volume ratio of 25:75, and the additives added were PS, tris (trimethylsilane) phosphate (TMSP) and compound (II), wherein LiPF ₆, the organic solvent, PS, TMSP and compound (II) were used in amounts of 13%, 84.7%, 1%, 0.3% and 1% of the total mass of the electrolyte, respectively.

Example 3

The preparation of compound (III) comprises the following specific steps:

；

To a clean, dry, three-necked 500-mL flask equipped with a magnetic rotor under nitrogen atmosphere, 200 mL of anhydrous THF was added, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃,3, 5-difluoro-4-bromobenzenesulfonamide (13.55 g,50.00 mmol) and 3-trifluoromethyl-4-bromobenzenesulfonamide (15.15 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100 mL anhydrous THF solution of 1, 3-dichloro-2-methylpropane (13.86 g,110.00 mmol) pre-frozen to 0 ℃ using a constant pressure dropping funnel over 30 min, after the addition was completed the ice water bath was removed and the resulting mixture was stirred at room temperature 12h. The mixture was then quenched with 50 mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with a hexane/methanol mixture (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 3 in yield 80.4%.TOF-SIMS (m/z): calcd. for C₁₇H₁₅Br₂N₂O₄S₂F₅ [M+1]⁺, 627.88, found 628.15.

To a clean, dry, three-necked 500 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 3 (34.53 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100 mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (III) with the yield 79.2%.TOF-SIMS (m/z): calcd. for C₁₇H₁₃Br₂N₂O₄S₂F₅Li₂[M+1]⁺,639.89, found 640.01.

Electrolyte 3 and experimental battery 3 were prepared as in example 1, except that additives added to electrolyte 3 were PS, succinonitrile (ADN), hexamethylene Diisocyanate (HDMI), and compound (III), and LiPF ₆, organic solvent, PS, ADN, HDMI, and compound (III) were used in amounts of 13%, 82.7%, 1%, 2%, 0.5%, and 0.8% of the total mass of the electrolyte, respectively.

Example 4

The preparation of compound (IV) comprises the following specific steps:

；

To a clean, dry, three-neck 500mL flask equipped with a magnetic rotor under nitrogen atmosphere was added 200 mL anhydrous THF, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃, 3-fluoro-4-bromobenzenesulfonamide (12.65 g,50.00 mmol) and trifluoromethanesulfonamide (7.45 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100 mL anhydrous THF solution pre-frozen to 0 ℃ in dichloromethyl-methyl amine (13.97 g,110.00 mmol) using a constant pressure dropping funnel over 30 min, after the addition was completed the ice water bath was removed and the resulting mixture was stirred at room temperature 12 h. The mixture was then quenched with 50 mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with a hexane/methanol mixture (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 4 in yield 84.7%.TOF-SIMS (m/z): calcd. for C₁₀H₁₂BrN₃O₄S₂F₄ [M+1]⁺, 456.94, found 457.08.

To a clean, dry, three-necked 500 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 4 (25.13 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100 mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (IV) with the yield 81.9%.TOF-SIMS (m/z): calcd. for C₁₀H₁₀BrN₃O₄S₂F₄Li₂ [M+1]⁺, 468.96, found 469.07.

Electrolyte 4 and experimental battery 4 were prepared as in example 1, except that PS, propargyl phosphate (TPP), lithium difluorodioxalate borate (LiODFB) and compound (IV) were added to the electrolyte 4, and the amounts of LiPF ₆, organic solvent, PS, TPP, liODFB and compound (IV) used were 15%, 81.8%, 1%, 0.2%, 1% and 1% of the total mass of the electrolyte, respectively.

Example 5

The preparation of compound (V) comprises the following specific steps:

；

To a clean, dry, three-neck 500 mL flask equipped with a magnetic rotor under nitrogen atmosphere was added 200 mL anhydrous THF, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃,3,4, 5-trifluorobenzenesulfonamide (10.55 g,50.00 mmol) and sulfamoyl fluoride (4.95 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100 mL anhydrous THF solution pre-frozen to 0 ℃ in dichloromethyl-methyl amine (13.97 g,110.00 mmol) using a constant pressure dropping funnel over 30 min, after the addition was completed the ice water bath was removed and the resulting mixture was stirred at room temperature 12 h. The mixture was then quenched with 50mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with a hexane/methanol mixture (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 5 in yield 79.8%.TOF-SIMS (m/z): calcd. for C₉H₁₁N₃O₄S₂F₄ [M+1]⁺, 365.01, found 365.03.

To a clean, dry, three-necked 500mL flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, then the flask was placed in a low temperature reactor, intermediate 5 (20.08 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours after the addition was completed. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (V) with the yield 80.3%.TOF-SIMS (m/z): calcd. for C₉H₉N₃O₄S₂F₄Li₂ [M+1]⁺, 377.03, found 377.05.

Electrolyte 5 and experimental battery 5 were prepared as in example 1, except that lithium salt added in electrolyte 5 was LiPF ₆ and lithium bisoxalato borate (LiBOB), and additives were PS, vinyl sulfate (DTD) and compound (V), wherein the amounts of LiPF ₆, liBOB, organic solvent, PS, DTD and compound (V) used were 8%, 4%, 85%, 1% and 1% of the total mass of the electrolyte, respectively.

Example 6

The preparation of compound (VI) comprises the following specific steps:

；

To a clean, dry, three-neck 500 mL-flask equipped with a magnetic rotor under nitrogen atmosphere was added 200 mL anhydrous THF, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃,3, 5-difluoro-4-bromobenzenesulfonamide (13.55 g,50.00 mmol) and sulfamoyl fluoride (4.95 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100mL anhydrous THF solution pre-frozen to 0 ℃ in dichloromethyl-methyl amine (13.97 g,110.00 mmol) using a constant pressure dropping funnel over 30 min, after the addition was completed the ice water bath was removed and the resulting mixture was stirred at room temperature 12 h. The mixture was then quenched with 50mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with a hexane/methanol mixture (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 6 in yield 83.1%.TOF-SIMS (m/z): calcd. for C₉H₁₁BrN₃O₄S₂F₃ [M+1]⁺, 424.93, found 425.92.

To a clean, dry, three-necked 500 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 6 (23.37 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100 mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (VI) with the yield 83.6%.TOF-SIMS (m/z): calcd. for C₉H₉BrN₃O₄S₂F₃Li₂ [M+1]⁺, 436.95, found 437.96.

Electrolyte 6 and experimental cell 6 were prepared as in example 1, except that the organic solvent in electrolyte 6 was FEC, 1, 2-tetrafluoroethyl-2, 3-tetrafluoropropyl ether (HFE), EMC, methyltrifluoroethyl carbonate (FEMC), the volume ratio was 25:10:45:20, and the additives were 1, 3-propenesulfonic acid lactone (PST), vinyl sulfate (DTD), and compound (VI), wherein LiPF ₆, the organic solvent, PST, DTD, and compound (VI) were used in amounts of 12%, 85.8%, 0.2%, 1% of the total mass of the electrolyte, respectively.

Example 7

The preparation of compound (VII) comprises the following specific steps:

；

To a clean, dry, three-necked 500-mL flask equipped with a magnetic rotor under nitrogen atmosphere, 200 mL of anhydrous THF was added, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃, 3-fluoro-4-bromobenzenesulfonamide (12.65 g,50.00 mmol) and sulfamoyl fluoride (4.95 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100mL anhydrous THF solution of bis (chloromethyl) (methylcarboxyethyl) amine (20.35 g,110.00 mmol) pre-chilled to 0 ℃ using a constant pressure dropping funnel over 30min, after the addition was complete the ice water bath was removed and the resulting mixture was stirred at room temperature for 12 h. The mixture was then quenched with 50 mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with a hexane/methanol mixture (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 7 in yield 84.0%.TOF-SIMS (m/z): calcd. for C₁₁H₁₄BrN₃O₆S₂F₂ [M+1]⁺, 464.95, found 465.08.

To a clean, dry, three-necked 500 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 7 (25.57 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100 mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (VII) with the yield 82.7%.TOF-SIMS (m/z): calcd. for C₁₁H₁₂BrN₃O₆S₂F₂Li₂[M+1]⁺, 476.96, found 476.99.

Electrolyte 7 and experimental battery 7 were prepared as in example 1, except that lithium salt added in electrolyte 7 was LiPF ₆ and lithium perchlorate (LiClO ₄), and additives were PS, tris (trimethylsilane) borate (TMSB) and compound (VII), wherein LiPF ₆、LiClO₄, organic solvent, PS, TMSB and compound (VII) were used in amounts of 8%, 5%, 84.5%, 1%, 0.5% and 1% of the total mass of the electrolyte, respectively.

Example 8

The preparation of compound (VIII) comprises the following specific steps:

；

To a clean, dry, three-neck 500 mL flask equipped with a magnetic rotor under nitrogen atmosphere was added 200 mL anhydrous THF, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃,3, 4, 5-trifluorobenzenesulfonamide (10.55 g,50.00 mmol) and sulfamoyl fluoride (4.95 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100 mL anhydrous THF solution of bis (chloromethyl) (methylcarboxyethyl) amine (20.35 g,110.00 mmol) pre-chilled to 0 ℃ using a constant pressure dropping funnel over 30 min, after the addition was complete the ice water bath was removed and the resulting mixture was stirred at room temperature for 12 h. The mixture was then quenched with 50mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with a hexane/methanol mixture (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 8 in yield 81.6%.TOF-SIMS (m/z): calcd. for C₁₁H₁₃N₃O₆S₂F₄ [M+1]⁺, 423.02, found 423.05.

To a clean, dry, three-necked 500 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 8 (23.27 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated until the volume is reduced by half, then 100 mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (VIII) with the yield 79.9%.TOF-SIMS (m/z): calcd. for C₁₁H₁₁N₃O₆S₂F₄Li₂ [M+1]⁺, 435.03, found 435.07.

Electrolyte 8 and experimental battery 8 were prepared as in example 1, except that the organic solvent in electrolyte 8 was FEC, EMC, 1h,5 h-octafluoropentyl-1, 2-tetrafluoroethyl ether (F-EAE), the volume ratio was 30:50:20, and the additives were PS, 1,3, 5-triallyl isocyanurate (TAIC) and compound (VIII), wherein LiPF ₆, the organic solvent, PS, TAIC, and compound (VIII) were used in amounts of 11%, 86.8%, 1%, 0.2%, and 1% of the total mass of the electrolyte, respectively.

Example 9

The preparation of compound (IX) is carried out as follows:

；

To a clean, dry, three-neck 500 mL-flask equipped with a magnetic rotor under nitrogen atmosphere was added 200mL anhydrous THF, then the flask was placed in a low temperature reactor, stirring was turned on, after THF was reduced to-10 ℃, 3, 5-difluoro-4-bromobenzenesulfonamide (13.55 g,50.00 mmol) and sulfamoyl fluoride (4.95 g,50.00 mmol) were slowly added, then NaH (1.44 g,60.00 mmol) was slowly added in three portions, and stirring was continued for 30 min. To the resulting solution was slowly added 100mL anhydrous THF solution of bis (chloromethyl) (methylcarboxyethyl) amine (20.35 g,110.00 mmol) pre-chilled to 0 ℃ using a constant pressure dropping funnel over 30 min, after the addition was complete the ice water bath was removed and the resulting mixture was stirred at room temperature for 12 h. The mixture was then quenched with 50 mL ammonium chloride solution and extracted three times with ethyl acetate (200 mL x 3), the organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel with a short pad eluting with a hexane/methanol mixture (volume ratio 95:5) and solvent was removed by rotary evaporation to give the binary sulfonimide intermediate 9 in yield 82.3%.TOF-SIMS (m/z): calcd. for C₁₁H₁₃BrN₃O₆S₂F₃ [M+1]⁺, 482.94, found 483.04.

To a clean, dry, three-necked 500 mL-necked flask equipped with a magnetic rotor under nitrogen atmosphere, 120 mL absolute ethanol and 120 mL ethyl acetate were added, stirring was started, the flask was placed in a low-temperature reactor, intermediate 9 (26.56 g,55 mmol) and lithium hydroxide (2.88 g,120 mmol) were added to the solution after cooling to about 0 ℃ and reacted for 12 hours. After the reaction is finished, the reaction solution is distilled under reduced pressure and concentrated to reduce the volume by half, then 100 mL anhydrous dichloromethane is added into the reaction solution, the solid is filtered and taken out, and then 40 mL anhydrous dichloromethane is used for washing and drying, thus obtaining the white powdery target organic lithium salt compound (IX) with the yield 83.1%.TOF-SIMS (m/z): calcd. for C₁₁H₁₁BrN₃O₆S₂F₃Li₂ [M+1]⁺, 494.95, found 495.03.

Electrolyte 9 and experimental battery 9 were prepared as in example 1, except that lithium salts added to electrolyte 9 were lithium tetrafluoroborate (LiBF ₄) and LiPF ₆, and additives were PS, DTD, and compound (IX), wherein the amounts of LiBF ₄、LiPF₆, organic solvent, PS, DTD, and compound (IX) used were 4%, 8%, 85%, 1% of the total mass of the electrolyte, respectively.

Example 10

Electrolyte 10 and experimental cell 10 were prepared as in example 1, except that PS and compound (VI) were added as additives, and the amounts of LiPF ₆, organic solvent, PS, and compound (VI) used were 13%, 83%, 2%, and 2% of the total mass of the electrolyte, respectively.

Example 11

Electrolyte 11 and experimental cell 11 were prepared as in example 1, except that PS and compound (VI) were added as additives, and the amounts of LiPF ₆, organic solvent, PS, and compound (VI) used were 13%, 84.9%, 2%, and 0.1% of the total mass of the electrolyte, respectively.

Comparative example 1

Electrolyte 12 and experimental cell 12 were prepared as in example 1, except that additives added to electrolyte 12 were PS and LiTFSI, and the amounts of LiPF ₆, organic solvent, PS, liTFSI used were 13%, 83%, 2% of the total mass of the electrolyte, respectively.

Comparative example 2

Electrolyte 13 and experimental cell 13 were prepared according to the method of example 1, except that additives added to electrolyte 13 were PS and LiFSI, and the amounts of LiPF ₆, organic solvent, PS, liFSI used were 13%, 83%, 2% of the total mass of the electrolyte, respectively.

The compositions and contents of the electrolytes of examples 1 to 11 and comparative examples 1 to 2 are shown in table 1.

The lithium batteries prepared in examples 1 to 11 and comparative examples 1 to 2 were subjected to a normal temperature cycle performance test, a rate cycle performance test, and the like, respectively, under the following test conditions:

battery normal temperature cycle test

The prepared lithium metal battery is charged to the cut-off current of 0.05C at the constant current of 1C and the voltage of 4.25V in a constant temperature room with the ambient temperature of 25 ℃, then is discharged to the voltage of 3V at the constant current of 1C, and is circulated for 500 weeks, the recording capacity retention rate and the nth cycle capacity retention rate (%) = (the nth cycle discharge specific capacity/the first cycle discharge specific capacity) are 100%.

Battery rate cycle test

The prepared lithium metal battery is charged to the cut-off current of 0.05C at constant current and constant voltage in a constant temperature room with the ambient temperature of 25 ℃ at the current of 5C and the voltage of 4.25V, then is discharged to the voltage of 3V at constant current of 1C, and is circulated for 500 weeks, wherein the recording capacity retention rate and the nth cycle capacity retention rate (%) = (nth cycle discharge specific capacity/first cycle discharge specific capacity) are 100%.

Direct current impedance (DCR) test

The prepared lithium metal battery is fully charged after 500 circles are circulated, then the battery is discharged with a constant current of 1C for 30min, the SOC is adjusted to be 50%, after the battery is placed for 2 hours, a voltage value V0 is recorded, then the battery is discharged with a constant current of 3C (the actual value is recorded and is recorded as I0) for 10 seconds, and voltage values V1 and DCR (3C, 10 s) = (V0-V1)/I0 are recorded.

The electrolyte solutions prepared in examples 1-11 and comparative examples 1-2 are used for preparing lithium batteries, and battery performance test results are shown in table 1, and it can be seen that the binary asymmetric organolithium salt additive compound prepared by the invention is applied to the electrolyte solution, so that an excellent effect is obtained, and the prepared lithium metal battery shows excellent electrochemical long cycle life. In addition, compared with comparative examples 1-2, the DCR values of examples 1-11 were lower, indicating that the battery interface resistance was at a lower level, so that lithium ions can be normally and rapidly extracted and inserted between the positive and negative electrodes under the high-current charge and discharge conditions, thereby exhibiting stronger rapid charging performance.

From the above examples, it can be seen that the use of the binary asymmetric organic lithium salt of the formula a according to the embodiment of the present invention as an additive can be attributed to the fact that the lithium salt additive provided by the present invention can preferentially generate a low-impedance lithium halide-rich SEI film on the surface of a lithium metal negative electrode in situ, thereby passivating the surface of an active lithium metal negative electrode, and the passivation layer exhibits a higher young modulus and a higher surface energy to homogenize the lithium ion flux, thereby inhibiting the growth of lithium dendrites during the cycle, and further improving the electrochemical cycle life and the fast charge performance of the battery.

Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.

Claims (11)

1. A binary asymmetric organolithium salt characterized by a general structural formula of formula a:

Formula A;

Wherein M ⁺ is Li ⁺,R₁ and R ₂ are selected from fluorine atom, trifluoromethyl, 3-fluoro-4-bromophenyl, 3, 5-difluoro-4-bromophenyl, 3-trifluoromethyl-4-bromophenyl or 3,4, 5-trifluorophenyl, R ₁ and R ₂ are different, R ₃ is selected from hydrogen atom, C1-C3 alkyl, methyl acetate group, ethyl acetate group or propyl acetate group, and X is selected from methine or nitrogen atom.

2. The binary asymmetric organolithium salt according to claim 1, wherein R ₁ is selected from 3-fluoro-4-bromophenyl, 3,4, 5-trifluorophenyl or 3, 5-difluoro-4-bromophenyl, R ₂ is selected from a fluorine atom, trifluoromethyl or 3-trifluoromethyl-4-bromophenyl, and R ₃ is selected from methyl or methyl acetate.

3. The binary asymmetric organolithium salt of claim 2, wherein the binary asymmetric organolithium salt is selected from at least one of formulas I-IX:

The compound of the formula I, The compound of the formula II is shown in the specification,

The compound of the formula III,The compound of the formula IV,

The characteristic of the V-shaped alloy is that,A compound of the formula VI,

The compound of the formula VII,The catalyst of formula VIII,

Formula IX.

4. A method of preparing the binary asymmetric organolithium salt of any of claims 1-3, comprising:

Carrying out substitution reaction on the binary sulfimide compound and a lithium source to obtain binary asymmetric organic lithium salt shown in a formula A; the binary sulfimide compound has a structural general formula B:

Formula B;

Wherein R ₁ and R ₂ are selected from fluorine atoms, trifluoromethyl, 3-fluoro-4-bromophenyl, 3, 5-difluoro-4-bromophenyl, 3-trifluoromethyl-4-bromophenyl or 3,4, 5-trifluorophenyl, R ₁ and R ₂ are different, R ₃ is selected from hydrogen atoms, C1-C3 alkyl groups, methyl acetate groups, ethyl acetate groups or propyl acetate groups, and X is selected from methine groups or nitrogen atoms.

5. An electrolyte comprising a lithium salt, a nonaqueous organic solvent and an additive, wherein the additive is a binary asymmetric organolithium salt according to any one of claims 1 to 3.

6. The electrolyte according to claim 5, wherein the lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, and lithium bisoxalato borate.

7. The electrolyte according to claim 5, wherein the nonaqueous organic solvent is selected from one or more of an ester solvent and an ether solvent; the nonaqueous organic solvent accounts for 80-87% of the weight of the electrolyte.

8. The electrolyte of claim 5 further comprising an auxiliary additive selected from the group consisting of ethylene carbonate, ethylene sulfate, ethylene bis-sulfate, propylene sulfate, 1, 3-propane sultone, 1, 3-propenesulfonic acid lactone, 1, 4-butanesulfonic acid lactone, 2, 4-butanesulfonic acid lactone, phenyl methanesulfonate, methylene methane disulfonate, N-phenyl bis (trifluoromethanesulfonyl) imide, triallyl phosphate, tris (trimethylsilane) phosphate, trimethyl phosphite, triphenyl phosphite, tetramethylene diphosphate, propargyl phosphate, (2-allylphenoxy) trimethyl silane, tris (trimethylsilane) borate, 1,3, 5-triallyl isocyanurate, isocyanatoethyl methacrylate, hexamethylene diisocyanate, terephthalyl diisocyanate, 2, 4-toluene diisocyanate, adiponitrile, succinonitrile, glutaronitrile, 1,3, 6-hexane tri-nitrile and 1, 2-bis (ethoxy) lithium bis (fluoroethane) sulfinate, lithium bis (lithium) bis (fluoroethane) lithium (lithium) oxalate, lithium bis (fluoroethane) or lithium bis (fluoroethane) oxalate.

9. The electrolyte of claim 8, wherein the lithium salt comprises 10-15% by weight of the electrolyte, the additive comprises less than 2% by weight of the electrolyte, and the sum of the additive and the auxiliary additive comprises less than 6% by weight of the electrolyte.

10. A lithium battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte of claim 5.

11. The lithium battery of claim 10, wherein the active material of the negative electrode is selected from one or more of graphite, lithium titanate, lithium metal, silicon oxide, and silicon carbon composite; the separator is selected from polyolefin-based separators.