CN113871698A

CN113871698A - Electrolyte and lithium battery containing same

Info

Publication number: CN113871698A
Application number: CN202111027264.2A
Authority: CN
Inventors: 白岩; 刘心同; 周世波; 郑军华
Original assignee: Svolt Energy Technology Co Ltd
Current assignee: Svolt Energy Technology Co Ltd
Priority date: 2021-09-02
Filing date: 2021-09-02
Publication date: 2021-12-31
Anticipated expiration: 2041-09-02
Also published as: CN113871698B

Abstract

The invention relates to the technical field of lithium ion batteries, and particularly provides an electrolyte and a lithium battery containing the same.

Description

Electrolyte and lithium battery containing same

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte and a lithium battery containing the electrolyte.

Background

The development of high voltage positive electrode materials is one of the important routes for the development of high energy density batteries. However, the conventional electrolyte is easy to generate side reaction on the surface of the positive electrode, and influences the exertion of the high-voltage positive electrode material. The high voltage electrolyte needs to satisfy a wide electrochemical stability window, high ionic conductivity, nonflammability, good compatibility with the negative electrode, and the like. At present, two main methods for realizing high voltage electrolyte pressurization are available: improving the oxidation resistance of the solvent: by design, the HOMO value of solvent molecules is reduced by methods such as substitution, grafting and the like, and the electrochemical stability window of the solvent molecules is widened; using an electrolyte additive: film forming additive: the additive is superior to carbonate, loses electrons, is oxidized, forms a protective film on the surface of the anode, inhibits the dissolution of transition metal ions, and prevents the reaction of electrolyte and an electrode; adsorption type additive: the additive is complexed with metal ions on the surface of the electrode, so that the charge balance on the surface of the electrode is ensured, and the catalytic active sites are passivated, thereby stabilizing the system.

The development of high-voltage and high-capacity cathode materials ensures that the upper limit of the charging voltage of the materials exceeds the electrochemical stability limit (more than 4.5V) of carbonate and organic electrolyte, and in addition, the carbonate solvent is volatile and easy to burn, the service temperature range of the battery is reduced, and potential safety hazards are brought to the battery.

The room temperature ionic liquid is a novel solvent which is composed of anions and cations and is liquid at room temperature. Ionic liquids are of great interest because of their low vapor pressure, low melting point, high boiling point, high specific heat capacity, nonflammability, high ionic conductivity, and high chemical stability. However, the reduction potential of the anion of the ionic liquid is high, and the corresponding cation can be reversibly deintercalated between graphite layers to destroy the stability of the graphite structure; the defects of high viscosity, low conductivity and the like can cause poor cycle stability and rate capability; the ionic liquid has high price, and the commercial application of the ionic liquid is restricted.

Therefore, how to improve the cycle stability of the lithium battery is a technical problem that research and development personnel need to solve urgently at present.

Disclosure of Invention

Therefore, the present invention is directed to overcome the defect of poor cycle stability of the lithium battery in the prior art, and to provide an electrolyte and a lithium battery containing the same.

The invention provides an electrolyte, which comprises a fluorine-containing lithium salt and an additive composition, wherein the additive composition comprises a dinitrile compound, pentafluoro (phenoxy) cyclotriphosphazene (PFPN) and lithium bis (oxalato) borate (LiBOB).

Further, the fluorine-containing lithium salt is selected from lithium hexafluorophosphate (L)iPF₆) And/or lithium tetrafluoroborate.

Further, the dinitrile compound is selected from at least one of Suberonitrile (SUN), succinonitrile, adiponitrile.

Further, the molar concentration of the lithium bis (oxalato) borate in the electrolyte is 1.0-1.5 mol/L.

Further, the molar concentration of the fluorine-containing lithium salt in the electrolyte is 1.0-1.1 mol/L.

Further, the volume ratio of the dinitrile compound to the pentafluoro (phenoxy) cyclotriphosphazene is 1:1 to 1: 5.

Furthermore, the electrolyte also comprises 5-20 vt% of ethylene carbonate and/or 5-20 vt% of propylene carbonate.

The invention also provides a preparation method of the electrolyte, which comprises the following steps:

mixing the fluorine-containing lithium salt, the dinitrile compound, the pentafluoro (phenoxy) cyclotriphosphazene and the lithium bis (oxalato) borate to obtain the lithium borate. Mixing can be carried out according to conventional methods, such as stirring and mixing at room temperature, with a rotation speed of 200-300 rpm.

The invention also provides a lithium battery which comprises the electrolyte or the electrolyte prepared by the preparation method.

Further, the positive electrode material of the lithium battery is selected from at least one of lithium nickel manganese oxide material, lithium nickel oxide material, lithium cobalt oxide material, lithium nickel cobalt oxide material and lithium nickel manganese cobalt oxide material.

Further, the diaphragm is characterized by being selected from at least one of polyacrylonitrile diaphragm, polyvinylidene fluoride diaphragm and ethylene terephthalate diaphragm.

Generally, substituents with strong electron withdrawing property, such as fluorine substituents, sulfone functional groups (-SO2-), and nitrile functional groups (-CN), are introduced into molecules to effectively reduce the electron cloud density of the substituted molecules, enhance the dipole moment, anode stability and dielectric constant of the molecules, and make valence electrons in the molecules difficult to be abstracted by the anode SO as to improve the oxidation resistance potential of the molecules. Common fluorinated solvents include fluorinated carbonate solvents such as fluoroethylene carbonate (FEC) and trifluoropropylene carbonate (TFPC). The XPS technology finds that the high-concentration C-F group in the CEI film in a fluorinated solvent system is beneficial to the interface stability of the anode, and meanwhile, the reduction of the LiF content can reduce the interface resistance. A small amount of fluoro solvent molecules are reduced and decomposed at a carbon cathode interface, so that the SEI film structure of the cathode can be optimized, and the compatibility of the electrolyte and the cathode material can be improved. The fluoro-solvent has a certain flame-retardant effect, and can effectively improve the thermal stability and safety of the electrolyte. However, fluorine has a strong electron withdrawing effect, and decreases the dn (Donor number) value of the solvent, thereby decreasing the dissolving power for the lithium salt. The sulfone solvent based on the sulfone functional group is found to have an electrochemical window of 5.0-5.9V (vs Li +/Li). Then most sulfones have the problems of high melting point, high viscosity, poor compatibility with graphite and the like, and the use of the sulfones as a high-voltage electrolyte solvent is limited. Proper substituent groups are required to be introduced to reduce the symmetry of the molecular structure and optimize the characteristics of the molecules; improving the alkyl functional group of the sulfone can also improve the compatibility with the graphite cathode.

The cyano compound usually has adsorption phenomenon on the surface of transition metal, and the stability of different adsorption configurations has great difference. A surface complex can be formed between the cyano functional group and the cobalt atom on the surface of the electrode, so that the thermal stability of the material can be remarkably improved. Nitriles have a certain inhibitory effect on corrosion of aluminum current collectors at high potential. However, nitrile solvents are poor in compatibility with graphite or lithium metal and the like at a low lithium removal potential, polymerization reaction is easy to occur on the surface of a negative electrode, and raw polymers can organize Li + de-intercalation, so that the nitrile solvents are limited to be used as single solvents.

The use of electrolyte additives is an economical and effective method for improving the high-voltage stability of the electrolyte. Among a plurality of additives, the lithium bis (oxalato) borate does not contain fluorine and phosphorus and has higher stability; particularly, the surface of the graphite negative electrode can directly participate in the formation of an SEI film, so that the co-intercalation of PC in a graphite layer can be effectively inhibited even in a pure PC electrolyte, and the stripping of graphite is inhibited. Lithium bis (oxalato) borate may also participate in the formation of the positive electrode interface film, where oxidative decomposition to boric acid or oxalic acid functional compounds may occur under high pressure. However, the lithium bis (oxalato) borate has low solubility in carbonate solvents, and the low concentration and conductivity of the lithium bis (oxalato) borate cannot meet the requirements of industrialization and increasing energy density.

The research of the invention finds that the dinitrile compound, the pentafluoro (phenoxy) cyclotriphosphazene and the lithium bis (oxalato) borate are matched for use, so that various performances of the electrolyte can be greatly improved.

The technical scheme of the invention has the following advantages:

1. according to the electrolyte provided by the invention, the additive composition comprising the dinitrile compound, the pentafluoro (phenoxy) cyclotriphosphazene and the lithium bis (oxalato) borate is matched with the fluorine-containing lithium salt for use, so that a synergistic effect is exerted, the side reaction of the battery can be effectively inhibited, the electrochemical polarization rate is reduced, an effective CEI interface film is formed, the stability of the material structure of the positive electrode material in the high-voltage circulation process is greatly improved, and the circulation performance of the battery is improved.

2. According to the electrolyte provided by the invention, the ionic conductivity of the electrolyte can be further increased and the rate performance of the battery can be improved by controlling the molar concentration of lithium bis (oxalato) borate in the electrolyte to be 1.0-1.5 mol/L.

3. According to the electrolyte provided by the invention, the dinitrile compound is selected from at least one of octanedionitrile, succinonitrile and adiponitrile, and the octanedionitrile and other additives are preferably matched for use, so that the ionic conductivity of the electrolyte can be further increased, and the rate capability of the battery can be improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a molecular structural diagram of octanedionitrile and lithium bis (oxalato) borate;

FIG. 2 is a molecular structure diagram of a pentafluoro (phenoxy) cyclotriphosphazene;

FIG. 3 is a graph of the conductivity of the electrolyte of example 1 of the present invention as a function of temperature;

FIG. 4 is a first charge-discharge curve of the positive electrode material in the electrolyte of example 1 in Experimental example 1 of the present invention;

FIG. 5 is a cycle curve of the positive electrode material in Experimental example 1 of the present invention in the electrolyte of example 1;

FIG. 6 is a charge and discharge curve of the positive electrode material in Experimental example 1 of the present invention after different cycle times of the electrolyte in example 1;

FIG. 7 is a charge and discharge curve of 4.5 to 3.9V in Experimental example 2 of the present invention;

FIG. 8 is a charge and discharge curve of 4.5 to 3.9V in Experimental example 3 of the present invention;

FIG. 9 is a graph showing the median voltage after different numbers of cycles in Experimental example 4 of the present invention;

FIG. 10 is an SEM image of the lithium ion battery of example 4 of the invention after 500 cycles of charge-discharge experiment at a current density of 140 mAh/g;

FIG. 11 is an SEM image of a lithium ion battery of comparative example 1 of the present invention after 500 cycles of a charge-discharge experiment at a current density of 140 mAh/g;

FIG. 12 is an SEM image of a lithium ion battery of comparative example 3 of the present invention after 500 cycles of a charge-discharge experiment at a current density of 140 mAh/g;

FIG. 13 is a TEM image of 500 cycles of a charge-discharge experiment performed on the lithium ion battery of example 4 in Experimental example 5 of the present invention at a current density of 140 mAh/g;

FIG. 14 is a TEM image of a lithium ion battery of comparative example 1 of experimental example 5 of the present invention after 500 cycles of a charge-discharge experiment at a current density of 140 mAh/g;

FIG. 15 is a TEM image of a lithium ion battery of comparative example 3 of experimental example 5 of the present invention after 500 cycles of a charge-discharge experiment at a current density of 140 mAh/g;

FIG. 16 is a charge-discharge curve of a lithium battery of example 4 in Experimental example 6 of the present invention;

fig. 17 is a cycle curve of the lithium battery of example 4 in experimental example 6 of the present invention at a rate of 0.5C.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents or instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.

Example 1

This example provides an electrolyte comprising 1.0mol/L lithium hexafluorophosphate, 1.0mol/L lithium bis (oxalato) borate, 25 vt% octanedionitrile and 75 vt% pentafluoro (phenoxy) cyclotriphosphazene.

The preparation method of the electrolyte comprises the following steps: 500mL of octanedionitrile (4A molecular sieve for removing water) and 1500mL of pentafluoro (phenoxy) cyclotriphosphazene are mixed to obtain a mixed solution 1, 2mol of lithium bis (oxalato) borate is dissolved in the mixed solution 1 to obtain a mixed solution 2, and 2mol of lithium hexafluorophosphate is dissolved in the mixed solution 2 to obtain an electrolyte.

The conductivity of the electrolyte was measured at different temperatures and the results are shown in figure 3, with the conductivity increasing with increasing temperature.

Example 2

This example provides an electrolyte comprising 1mol/L lithium hexafluorophosphate, 1.0mol/L lithium bis (oxalato) borate, 25 vt% succinonitrile and 75 vt% pentafluoro (phenoxy) cyclotriphosphazene.

The preparation method of the electrolyte comprises the following steps: 500mL of succinonitrile (4A molecular sieve for removing water) and 1500mL of pentafluoro (phenoxy) cyclotriphosphazene are mixed to obtain a mixed solution 1, 2mol of lithium bis (oxalato) borate is dissolved in the mixed solution 1 to obtain a mixed solution 2, and 2mol of lithium hexafluorophosphate is dissolved in the mixed solution 2 to obtain the electrolyte.

Example 3

This example provides an electrolyte comprising 1.0mol/L lithium tetrafluoroborate, 1.5mol/L lithium bis oxalato borate, 45 vt% octanedionitrile, 45 vt% pentafluoro (phenoxy) cyclotriphosphazene, and 10 vt% ethylene carbonate.

The preparation method of the electrolyte comprises the following steps: 900mL of octanedionitrile (4A molecular sieve with water removed), 900mL of pentafluoro (phenoxy) cyclotriphosphazene and 200mL of ethylene carbonate were mixed to obtain a mixed solution 1, 3mol of lithium bis (oxalato) borate was dissolved in the mixed solution 1 to obtain a mixed solution 2, and 2mol of lithium tetrafluoroborate was dissolved in the mixed solution 2 to obtain an electrolyte.

Example 4

This example provides a battery, which was prepared by mixing a lithium cobaltate positive electrode material (available from tungsten corporation, type: CC-01, nominal voltage: 4.2-4.5V), carbon black and NMP solution having a solid content of 20% PVDF at a mass ratio of 1:1:2, coating, baking, rolling, and cutting. And then respectively assembling button half batteries, wherein the negative electrode is lithium metal, the diaphragm is a PE diaphragm, and the electrolyte adopts the electrolyte in the embodiment 1 to obtain the lithium ion batteries.

Examples 5 and 6

Examples 5 and 6 each provide a battery whose raw material composition and production method are substantially the same as those of example 4 except that the electrolyte is different, the battery of example 5 employs the electrolyte obtained in example 2, and the battery of example 6 employs the electrolyte obtained in example 3.

Comparative example 1

This example provides an electrolyte solution of ethylene carbonate containing 1.0mol/L lithium hexafluorophosphate.

The preparation method of the electrolyte comprises the following steps: 1mol of lithium hexafluorophosphate was dissolved in 1L of ethylene carbonate to prepare an electrolyte. A battery was fabricated by the method of example 4 using the electrolyte of this comparative example.

Comparative example 2

This example provides an electrolyte comprising 1.0mol/L lithium hexafluorophosphate, 45 vt% octanedionitrile and 55 vt% ethylene carbonate.

The preparation method of the electrolyte comprises the following steps: 450mL of octanedionitrile (4A molecular sieve with water removed) and 550mL of ethylene carbonate were mixed to obtain a mixed solution 1, and 1mol of lithium hexafluorophosphate was dissolved in the mixed solution 1 to obtain an electrolyte solution. A battery was fabricated by the method of example 4 using the electrolyte of this comparative example.

Comparative example 3

This example provides an electrolyte solution of ethylene carbonate containing 1.0mol/L of lithium hexafluorophosphate and 1.5mol/L of lithium bis (oxalato) borate.

The preparation method of the electrolyte comprises the following steps: 1.5mol of lithium bis (oxalato) borate and 1mol of lithium hexafluorophosphate were dissolved in 1L of ethylene carbonate to prepare an electrolyte. A battery was fabricated by the method of example 4 using the electrolyte of this comparative example.

Comparative example 4

This example provides an electrolyte of 45 vt% pentafluoro (phenoxy) cyclotriphosphazene and 55 vt% ethylene carbonate containing 1.0mol/L lithium hexafluorophosphate.

The preparation method of the electrolyte comprises the following steps: 450mL of pentafluoro (phenoxy) cyclotriphosphazene and 550mL of ethylene carbonate were mixed to obtain a mixed solution 1, and 1mol of lithium hexafluorophosphate was dissolved in 1000mL of the mixed solution 1 to obtain an electrolyte. A battery was fabricated by the method of example 4 using the electrolyte of this comparative example.

Experimental example 1

The lithium ion batteries of examples 4 to 6 and comparative examples 1 to 4 were subjected to a charge/discharge experiment at a current density of 14mAh/g at room temperature, and the first charge/discharge capacity, the coulombic efficiency, and the charge/discharge cycle retention rate of 500 cycles were tested. The results are shown in Table 1.

Table 1 table of charge and discharge experimental results

As can be seen from fig. 4-6 and the above table, the lithium cobaltate material continuously increases with the cycle, and the discharge curve changes toward a low voltage direction, which indicates that the working voltage of the lithium cobaltate material gradually declines and the energy density of the battery decreases during the cycle. When lithium bis (oxalato) borate, octanedionitrile and pentafluoro (phenoxy) cyclotriphosphazene are used as combined additives, the material has a smaller polarization rate and optimal electrochemical stability. Therefore, the composite additive of the lithium bis (oxalato) borate, the octanedionitrile and the pentafluoro (phenoxy) cyclotriphosphazene is beneficial to maintaining the voltage platform of the lithium cobaltate material, so that the cycling stability is greatly improved, the addition of the composite additive can be reacted, and the stability of the material structure of the lithium cobaltate material in the high-voltage cycling process can be improved.

Experimental example 2

Taking a high-potential lithium cobaltate positive electrode material (purchased from tungsten of Xiamen, model: CB-06), mixing carbon black and an NMP solution with solid content of 20% PVDF according to the mass ratio of 1:1:2, coating, baking, rolling and cutting into pieces to prepare the positive electrode. And then, respectively assembling button half batteries, wherein the negative electrode is lithium metal, the diaphragm is a PE diaphragm, and the electrolyte adopts the electrolyte in example 1 to obtain a lithium cobaltate/Li button battery (the nominal voltage is 4.5V). And (3) charging and discharging the lithium cobaltate/Li button cell for two weeks at a voltage interval of 3.9-4.5V at a current density of 14mAh/g, then charging to 4.5V at a current density of 140mAh/g, charging for 4h at 4.5V, and taking out the anode material in a glove box after the charging is finished.

As shown in FIG. 7, it can be seen from FIG. 7 that the charging and discharging performance was good in the voltage range of 3.9 to 4.5V, indicating that the cycle stability was good.

Experimental example 3

Taking a lithium cobaltate positive electrode material (purchased from tungsten of Xiamen, model: CD-05), mixing carbon black and a NMP solution with solid content of 20 percent of PVDF according to the mass ratio of 1:1:2, coating, baking, rolling and cutting into pieces to prepare the positive electrode. And then, respectively assembling button half batteries, wherein the negative electrode is lithium metal, the diaphragm is a PE diaphragm, and the electrolyte adopts the electrolyte in example 1 to obtain a lithium cobaltate/Li button battery (the nominal voltage is 3.9V). And (3) after the lithium cobaltate/Li button cell is charged and discharged for two circles at a current density of 14mAh/g, the 500 th circle is charged and discharged at a current density of 140mAh/g, the discharge is stopped after the discharge reaches 3.9V, and the anode material is taken out.

As shown in FIG. 8, it can be seen from FIG. 8 that the charge/discharge characteristics were good in the voltage range of 3.9 to 4.5V, indicating that the cycle stability was good.

Experimental example 4

Taking a high-potential lithium cobaltate positive electrode material (purchased from tungsten of Xiamen, model: SC-02), mixing carbon black and an NMP solution with solid content of 20% PVDF according to a mass ratio of 1:1:2, coating, baking, rolling and cutting into pieces to prepare the positive electrode. And then, respectively assembling button half batteries, wherein the negative electrode is lithium metal, the diaphragm is a PE diaphragm, and the electrolyte adopts the electrolyte in example 1 to obtain a lithium cobaltate/Li button battery (the nominal voltage is 4.5V). And (3) charging and discharging the lithium cobaltate/Li button cell for two weeks at a voltage interval of 3.0-4.5V at a current density of 14mAh/g, then charging to 4.5V at a current density of 140mAh/g, charging for 4h at 4.5V, and taking out the anode material in a glove box after the charging is finished.

Referring to fig. 9, it can be seen from fig. 9 that the median voltage is above 3.8V, indicating good cycling stability.

Experimental example 5

Taking a high-potential lithium cobaltate positive electrode material (purchased from tungsten of Xiamen, model: CB-06), mixing carbon black and an NMP solution with solid content of 20% PVDF according to the mass ratio of 1:1:2, coating, baking, rolling and cutting into pieces to prepare the positive electrode. And then, respectively assembling the button half-cells, wherein the negative electrode is lithium metal, the diaphragm is a PE diaphragm, and the electrolytes respectively adopt the electrolytes of example 1 and comparative examples 1 and 3 to obtain three groups of lithium cobaltate/Li button cells (the nominal voltage is 4.5V). Three groups of lithium cobaltate/Li button batteries are respectively charged and discharged for two weeks at a voltage interval of 3.9-4.5V at a current density of 14mAh/g, then charged to 4.5V at a current density of 140mAh/g and charged for 4h at 4.5V, and after the charge and discharge experiment is cycled for 500 circles, the anode material is taken to be subjected to scanning electron microscope shooting and transmission electron microscope shooting, as shown in figures 10-15.

In the standard electrolysis, the surface of the electrode is covered by a layer of decomposition product which is uniformly distributed and thick due to continuous oxidation and decomposition of the electrolyte, and the surface of the electrode has agglomerated particles. In the single additive system of lithium bis (oxalato) borate, a layer of uniform and compact surface film is formed on the surface of the electrode, and particularly in the combined solvent system of lithium bis (oxalato) borate, octanedionitrile and pentafluoro (phenoxy) cyclotriphosphazene, the surface film almost covers the whole surface of the electrode. Therefore, the composition of the lithium bis (oxalato) borate, the octanedionitrile and the pentafluoro (phenoxy) cyclotriphosphazene is more favorable for forming a uniform and dense surface film, thereby effectively inhibiting the oxidative decomposition of the electrolyte. Further contributes to the stability of the material structure and the improvement of the cycling stability.

The observation is clearer from a TEM picture, the positive electrode which is not dipped in the electrolyte is a smooth and clean interface, and the interface film is covered by a layer of interface film after the circulation of the conventional electrolyte, while the interface film after the circulation is more compact and reliable in the mixed additive of lithium bis (oxalato) borate, octanedionitrile and pentafluoro (phenoxy) cyclotriphosphazene.

Experimental example 6

High-voltage Lithium Nickel Manganese Oxide (LNMO) (purchased from Capacity technology, model XC-86), a conductive agent and a binder (PVDF) according to a mass ratio of 8: 1:1 to obtain a mixture, adding NMP 2 times the mass of the mixture to stir for 8 hours, then coating on an aluminum foil, and drying in a vacuum drying oven at 80 ℃ for 12 hours to prepare a positive electrode, a lithium sheet as a negative electrode, Celgard K2045(PE) as a separator, and assembling a battery (nominal voltage of 4.7V) using the electrolyte prepared in example 1. After the battery is assembled, the battery is stood for 12 hours to fully soak the electrolyte, and then the electrochemical performance of the battery is tested. Constant current discharge experiments of the batteries were performed on a test cabinet. The voltage range is 3.5-5.0V (vs Li +/Li). The cyclic voltammetry curve of the cell is carried out on an electrochemical workstation, the scanning voltage range is 3.5-5.0V, and the scanning speed is 0.1 mv/s. EIS tests were also performed on electrochemical workstations at frequencies ranging from 0.01Hz to 100 KHZ.

As a result, as shown in FIG. 16, the gram capacity of the material was 140mAh/g under the action of the high voltage electrolyte, the voltage plateau was stable, and the capacity exhibited was excellent. Under the multiplying power of 0.5C, the capacity is still maintained at 136mAh/g after 100 weeks of circulation.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. An electrolyte comprising a fluorine-containing lithium salt and an additive composition comprising a dinitrile compound, pentafluoro (phenoxy) cyclotriphosphazene, and lithium bis (oxalato) borate.

2. The electrolyte of claim 1, wherein the lithium salt comprising fluorine is selected from lithium hexafluorophosphate and/or lithium tetrafluoroborate; and/or, the dinitrile compound is selected from at least one of suberonitrile, succinonitrile, adiponitrile.

3. The electrolyte according to claim 1 or 2, wherein the molar concentration of lithium bis (oxalato) borate in the electrolyte is 1.0 to 1.5 mol/L.

4. The electrolyte of any one of claims 1 to 3, wherein the molar concentration of the fluorine-containing lithium salt in the electrolyte is 1.0 to 1.1 mol/L.

5. The electrolyte of any one of claims 1-4, wherein the volume ratio of dinitrile compound to pentafluoro (phenoxy) cyclotriphosphazene is in the range of 1:1 to 1: 5.

6. The electrolyte according to any one of claims 1 to 5, wherein the electrolyte further comprises 5 to 20 vt% by volume of ethylene carbonate and/or 5 to 20 vt% by volume of propylene carbonate.

7. A method of preparing the electrolyte of any one of claims 1 to 6, comprising mixing a fluorine-containing lithium salt, a dinitrile compound, pentafluoro (phenoxy) cyclotriphosphazene and lithium bis (oxalato) borate.

8. A lithium battery comprising the electrolyte according to any one of claims 1 to 6 or the electrolyte obtained by the production method according to claim 7.

9. The lithium battery of claim 8, wherein the positive electrode material of the lithium battery is selected from at least one of a lithium nickel manganese oxide material, a lithium nickel oxide material, a lithium cobalt oxide material, a lithium nickel cobalt oxide material, and a lithium nickel manganese cobalt oxide material.

10. The lithium battery according to claim 8 or 9, wherein the separator of the lithium battery is at least one selected from a polyacrylonitrile separator, a polyvinylidene fluoride separator, and a polyethylene terephthalate separator.