Electrolyte for lithium metal battery, preparation method of electrolyte and lithium metal battery

Abstract

The invention discloses an electrolyte for a lithium metal battery, a preparation method of the electrolyte and the lithium metal battery. The electrolyte comprises electrolyte lithium salt, a carbonic ester organic solvent, a phosphate ester organic solvent and nitrate ionic liquid. A nitrate ionic liquid is added into the electrolyte as an additive, and a phosphate ester solvent is doped into the electrolyte as a cosolvent, so that the solubility of nitrate radicals in the carbonate ester electrolyte is improved, a stable and tough SEI film can be formed on a metal lithium negative electrode, and the growth of lithium dendrites is inhibited; the side reaction caused by direct contact between the electrolyte and the metal lithium is reduced, and the cycle life and the safety of the lithium metal battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and in particular relates to an electrolyte for a lithium metal battery and a preparation method thereof, and also relates to a lithium metal battery containing the electrolyte. Background Art

[0002] Lithium metal battery refers to a lithium-ion battery that uses metallic lithium as the negative electrode, in which the metallic lithium in the negative electrode can provide a higher specific capacity (up to 3860mA / hg) and a lower redox potential (-3.04V relative to the standard hydrogen electrode). Therefore, lithium metal batteries occupy an important position in future energy storage systems.

[0003] However, lithium metal batteries currently face some defects that hinder their commercial prospects: one is the growth of lithium dendrites during repeated charge / discharge, which poses a safety hazard due to high surface area and possible internal short circuits; the other is the low Coulomb efficiency, which leads to a short cycle life of the battery. One of the effective ways to protect the lithium metal anode is to use a combination of various salts / solvents / additives in the electrolyte to prepare an in-situ formed stable solid-electrolyte interface (SEI) between the electrolyte and the metal lithium anode.

[0004] Among them, lithium nitrate has good ionic conductivity, can provide high ion transport, can improve the charge and discharge efficiency of the battery, and lithium nitrate has high electrochemical stability and a wide electrochemical window, which can be used in high voltage and high temperature working environments. More importantly, it can induce regular Li deposition morphology and produce a conductive SEI layer rich in nitrogen-containing species. Therefore, lithium nitrate has significant advantages in regulating Li deposition uniformity and SEI stability. But LiNO 3 The low solubility in carbonate solvents limits its direct application in traditional ester-based electrolytes.

[0005] By introducing additional additives or co-solvents into the electrolyte to increase the LiNO 3 The solubility of lithium metal anodes can be improved by introducing additional Lewis acid sites and co-solvents with high donor numbers into the electrolyte. However, it should be noted that the use of high-valent cations can cause metal deposition and lead to battery short circuits, and high-solubility solvents are often highly corrosive to lithium metal anodes due to their strong catastrophic reactivity, which will eventually damage the long-term cycle stability of lithium metal batteries and affect their practical applications.

[0006] As an important transport medium in lithium metal batteries, electrolyte plays a key role in the overall performance of lithium metal batteries. Therefore, the development of a safe, efficient and electrochemically high performance lithium metal battery electrolyte is of great significance to the development of lithium metal batteries. Summary of the invention

[0007] In view of this, the primary purpose of the present invention is to provide an electrolyte for a lithium metal battery, in which a class of nitrate ionic liquids is added as an additive, and a phosphate solvent is added as a co-solvent, thereby increasing the solubility of nitrate ions in carbonate electrolytes. The electrolyte can form a stable and strong SEI film on the metallic lithium negative electrode, inhibit the growth of lithium dendrites, and reduce side reactions caused by direct contact between the electrolyte and metallic lithium, thereby increasing the cycle life and safety of the lithium metal battery.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention firstly provides an electrolyte for a lithium metal battery, comprising an electrolyte lithium salt, a carbonate organic solvent, a phosphate organic solvent and a nitrate ion liquid.

[0010] In a further embodiment, the anion of the nitrate ionic liquid is nitrate, and the cation is a pyrazolium cation, a triazole cation, a pyrrolidine cation or an amino acid ester cation.

[0011] In a further embodiment, the nitrate ionic liquid is one or a combination of two or more of N-propyl-N-methylpyrrolidine nitrate ionic liquid, 1-butyl-2,3,5-trimethylpyrazole nitrate ionic liquid, L-proline butyl ester nitrate ionic liquid, L-leucine methyl ester nitrate ionic liquid, glycine methyl ester nitrate ionic liquid, and 1-alkyl-4-amino-1,2,4-triazole nitrate ionic liquid.

[0012] In a further embodiment, in the electrolyte, the concentration of the nitrate ionic liquid is 0.3 mol / L to 1 mol / L.

[0013] In a further embodiment, the electrolyte lithium salt is LiPF 6 、LiAsF 6 , LiBF 4 、LiClO 4 、LiCF 3 SO 3 、LiPO 2 F 2 、LiN 4 C 6 F 3 , LiBC 2 O 4 F 2 , LiBF 3 Cl、LiP(CO 2 CO 2 ) 3 、LiPF 4 (CO2 CO 2 )、LiB(C 2 O 4 ) 2 and LiN(C x F 2x+1 SO 2 )·(C y F 2y+1 SO 2 ), wherein x and y are independently an integer from 0 to 5.

[0014] In a further embodiment, the total concentration of the electrolyte lithium salt is 0.5 mol / L to 2.5 mol / L.

[0015] In a further embodiment, the carbonate organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0016] In a further embodiment, the phosphate ester organic solvent is at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, and toluene diphenyl phosphate.

[0017] In a further embodiment, the volume percentage of the phosphate organic solvent in the electrolyte is 10% to 30%.

[0018] The present invention further provides a method for preparing the electrolyte for a lithium metal battery as described above, comprising the following steps:

[0019] Under the condition of isolating water and oxygen, the carbonate organic solvent and the electrolyte lithium salt are mixed evenly to obtain an electrolyte base liquid;

[0020] Evenly mixing the nitrate ionic liquid and the phosphate organic solvent to obtain a mixed solution;

[0021] The mixed solution is added into the electrolyte base solution and mixed evenly.

[0022] The present invention further provides the use of the electrolyte for lithium metal batteries as described above or the electrolyte for lithium metal batteries prepared by the preparation method described above in the preparation of lithium metal batteries.

[0023] The present invention further provides a lithium metal battery, comprising the lithium metal battery electrolyte as described above or the lithium metal battery electrolyte prepared by the preparation method described above.

[0024] Beneficial effects of the present invention:

[0025] The electrolyte for lithium metal batteries of the present invention adds a type of nitrate ion liquid, and simultaneously incorporates a phosphate solvent as a co-solvent, thereby solving the problem of low solubility of nitrate ions in carbonate electrolytes. The electrolyte of the present invention can form a stable and strong SEI film on the negative electrode of metallic lithium, inhibit the growth of lithium dendrites, and reduce side reactions caused by direct contact between the electrolyte and metallic lithium, thereby improving the cycle life and safety of lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The SEM characterization results of the metal lithium negative electrode of the lithium metal battery assembled with the electrolyte in Example 1 after cycling 200 times at room temperature 25°C.

[0027] Figure 2 This is the SEM characterization result of the metal lithium negative electrode of the lithium metal battery assembled with the electrolyte in Comparative Example 3 after cycling 200 times at room temperature 25°C. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0030] A first aspect of the present invention provides an electrolyte for a lithium metal battery, comprising an electrolyte lithium salt, a carbonate organic solvent, a phosphate organic solvent and a nitrate ionic liquid.

[0031] The present invention improves the solubility of nitrate in the electrolyte by adding a class of nitrate ionic liquids into a carbonate electrolyte and simultaneously doping a phosphate organic solvent as a co-solvent. A tough, high-conductivity electrolyte interface (SEI) film is formed on the surface of a lithium metal battery through the synergistic effect of nitrate anions, ionic liquid cations and phosphate organic solvents. The SEI film can effectively isolate the electrolyte and the electrode, reduce the reduction and decomposition of the electrolyte, inhibit the formation of metal lithium dendrites, and improve the safety and cycle life of the lithium metal battery.

[0032] The various components of the electrolyte for lithium metal batteries in the present invention will be described in detail below.

[0033] Electrolyte lithium salt

[0034] The electrolyte lithium salt described herein is an inorganic lithium salt or an organic lithium salt conventionally used in the art for lithium-ion battery electrolytes and capable of providing and transporting lithium ions. Specific examples include lithium hexafluorophosphate (LiPF4 6 ) lithium hexafluoroarsenate (LiAsF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 )Lithium difluorophosphate (LiPO 2 F 2 ), 2-trifluoromethyl-4,5-dicyanoimidazole lithium (LiN 4 C 6 F 3 ), lithium difluorooxalate borate (LiBC 2 O 4 F 2 ), lithium chlorotrifluoroborate (LiBF 3 Cl), lithium trioxalophosphate (LiP(CO 2 CO 2 ) 3 ), lithium tetrafluorooxalate phosphate (LiPF 4 (CO 2 CO 2 ))、LiB(C 2 O 4 ) 2 )、LiN(C x F 2x+1 SO 2 )·(C y F 2y+1 SO 2 ), wherein x and y are independently integers of 0 to 5, but are not limited thereto. In some specific embodiments of the present invention, the electrolyte lithium salt is lithium hexafluorophosphate (LiPF 6 ), which is the most commonly used electrolyte lithium salt in commercial lithium-ion batteries.

[0035] Furthermore, in the electrolyte, the concentration of the electrolyte lithium salt is not particularly limited, and the electrolyte lithium salt concentration known or commonly used in the art can be adopted. In the present invention, the total concentration of the electrolyte lithium salt is 0.5 mol / L to 2.5 mol / L, for example, it can be any concentration of 0.5 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, and 2.5 mol / L. In some preferred embodiments of the present invention, the concentration of the electrolyte lithium salt is 1 mol / L.

[0036] Carbonate organic solvents

[0037] The carbonate organic solvent described in this article is a kind of organic solvent commonly used in lithium-ion battery electrolytes, which are usually divided into cyclic carbonates and chain carbonates. Among them, cyclic carbonates have high dielectric constants and high ion conductivity, but high viscosity; while chain carbonates have low dielectric constants and low viscosity, and stable electrochemical properties. Therefore, usually, chain carbonates and cyclic carbonates are mixed for use to better ensure the performance of the electrolyte.

[0038] Specific examples of carbonate organic solvents described in the present invention include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or any combination thereof, but are not limited thereto. In some preferred embodiments of the present invention, the carbonate organic solvent used is a mixture of cyclic carbonate and linear carbonate, such as a mixture of EC and DEC, a mixture of EC and EMC, etc.

[0039] Phosphate ester organic solvents

[0040] The phosphate organic solvent described in this article refers to a class of organic compounds that can be used in lithium-ion battery electrolytes and contain phosphate groups in their structures. Specific examples include, but are not limited to, at least one of trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), trioctyl phosphate (TOP), and toluene diphenyl phosphate (CDP).

[0041] In the present invention, the phosphate organic solvent acts as a common solvent, and synergistically with the nitrate anion and the ionic liquid cation to improve the performance of the electrolyte. Therefore, the amount of the phosphate organic solvent added should not be too much, and preferably, the volume percentage of the phosphate organic solvent in the electrolyte is 10% to 30%, for example, it can be any value among 10%, 12%, 15%, 17%, 20%, 24%, 28%, and 30%.

[0042] Nitrate Ionic Liquids

[0043] The nitrate ionic liquid described herein is a special type of ionic liquid with nitrate as anion. In the present invention, its cation may be a pyrazolium cation, a triazole cation, a pyrrolidine cation or an amino acid ester cation.

[0044] Specific examples that can be mentioned include one or a combination of two or more of N-propyl-N-methylpyrrolidine nitrate ionic liquid, 1-butyl-2,3,5-trimethylpyrrolidine nitrate ionic liquid, L-proline butyl ester nitrate ionic liquid, L-leucine methyl ester nitrate ionic liquid, glycine methyl ester nitrate ionic liquid, and 1-alkyl-4-amino-1,2,4-triazole nitrate.

[0045] In the present invention, the concentration of the nitrate ionic liquid in the electrolyte is 0.3 mol / L to 1 mol / L, for example, it can be any value among 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, and 1 mol / L.

[0046] The second aspect of the present invention provides a method for preparing the electrolyte for a lithium metal battery as described above, which can be prepared by a preparation method well known in the art, and the components can be fully mixed. Preferably, in some specific embodiments of the present invention, the preparation of the electrolyte includes the following steps:

[0047] Under the condition of isolating water and oxygen, the carbonate organic solvent and the electrolyte lithium salt are mixed evenly to obtain an electrolyte base liquid;

[0048] Evenly mixing the nitrate ionic liquid and the phosphate organic solvent to obtain a mixed solution;

[0049] The mixed solution is added into the electrolyte base solution and mixed evenly.

[0050] Among them, in the present invention, the isolation of water and oxygen means that the content of water and oxygen is respectively below 10 ppm, and more preferably below 0.1 ppm, which is usually achieved in a glove box filled with protective gas (such as nitrogen or rare gases such as argon, helium, etc.).

[0051] The present invention further provides the use of the electrolyte for lithium metal batteries as described above or the electrolyte for lithium metal batteries prepared by the preparation method described above in the preparation of lithium metal batteries.

[0052] The present invention further provides a lithium metal battery, comprising the lithium metal battery electrolyte as described above or the lithium metal battery electrolyte prepared by the preparation method described above.

[0053] It is understandable that the lithium metal battery described in the present invention also includes materials such as positive electrode, negative electrode and separator, which can all adopt conventional or known material types in the art, wherein the negative electrode is lithium metal or a lithium alloy with a content of more than 50%.

[0054] It is understandable that the lithium metal battery described in this article has the same advantages or beneficial effects as the electrolyte described above, so they will not be elaborated here one by one.

[0055] The present invention is described below by means of specific examples. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0056] Example 1

[0057] This embodiment provides an electrolyte for a lithium metal battery, wherein the electrolyte lithium salt LiPF 6 The concentration of is 1 mol / L, the concentration of the nitrate ionic liquid N-propyl-N-methylpyrrolidine nitrate is 0.5 mol / L, the volume percentage of triethyl phosphate is 20%, and the carbonate organic solvent is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a mass ratio of 1:1.

[0058] This embodiment further provides a method for preparing the above-mentioned lithium metal electrolyte, and the specific steps are as follows:

[0059] The electrolyte was prepared in a glove box with a water and oxygen content of less than 0.1 ppm at room temperature (25°C). Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1, sealed and placed in a refrigerator. After cooling to -10°C, it was transferred to a glove box and LiPF was added. 6 Allow it to fully dissolve to obtain an electrolyte base solution;

[0060] Adding N-propyl-N-methylpyrrolidine nitrate to triethyl phosphate, mixing well, and obtaining a mixed solution;

[0061] The mixed solution was added to the electrolyte base solution and stirred for 24 hours to obtain an electrolyte solution containing 1 mol / L LiPF 6 , 0.5 mol / L N-propyl-N-methylpyrrolidine nitrate, and the volume percentage of triethyl phosphate is 20%.

[0062] Example 2

[0063] This embodiment provides another electrolyte for lithium metal batteries, and its composition is the same as that of Example 1, except that the nitrate ionic liquid is 1-butyl-2,3,5-trimethylpyrazole nitrate. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0064] Example 3

[0065] This embodiment provides an electrolyte for a lithium metal battery, and its composition is the same as that of Embodiment 1, except that the nitrate ionic liquid is a glycine methyl ester nitrate ionic liquid. The other compositions and preparation of the electrolyte are the same as those of Embodiment 1.

[0066] Example 4

[0067] This embodiment provides an electrolyte for lithium metal batteries, and its composition is the same as that of embodiment 1, except that the nitrate ionic liquid is L-leucine methyl ester nitrate ionic liquid. The other compositions and preparation of the electrolyte are the same as those of embodiment 1.

[0068] Example 5

[0069] This embodiment provides an electrolyte for lithium metal batteries, and its composition is the same as that of embodiment 1, except that the phosphate organic solvent is toluene diphenyl phosphate. The other compositions and preparation of the electrolyte are the same as those of embodiment 1.

[0070] Example 6

[0071] This embodiment provides an electrolyte for lithium metal batteries, the composition of which is the same as that of Example 1, except that the concentration of the nitrate ionic liquid is 0.3 mol / L. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0072] Example 7

[0073] This embodiment provides an electrolyte for lithium metal batteries, the composition of which is the same as that of Example 1, except that the concentration of the nitrate ionic liquid is 1 mol / L. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0074] Example 8

[0075] This embodiment provides an electrolyte for lithium metal batteries, and its composition is the same as that of Example 1, except that the volume percentage of the phosphate organic solvent is 10%. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0076] Example 9

[0077] This embodiment provides an electrolyte for lithium metal batteries, the composition of which is the same as that of Example 1, except that the volume percentage of the phosphate organic solvent is 30%. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0078] Example 10

[0079] This embodiment provides an electrolyte for a lithium metal battery, and its composition is the same as that of Example 1, except that: the electrolyte lithium salt is LiClO 4 The other compositions and preparation of the electrolyte are the same as those in Example 1.

[0080] Embodiment 11

[0081] This embodiment provides an electrolyte for a lithium metal battery, and its composition is the same as that of Example 1, except that: the electrolyte lithium salt is LiPF 4 (CO 2 CO 2 ). The other compositions and preparation of the electrolyte are the same as those in Example 1.

[0082] Example 12

[0083] This embodiment provides an electrolyte for lithium metal batteries, the composition of which is the same as that of Example 1, except that the carbonate organic solvent is EC:EMC=1:1 (mass ratio). The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0084] Embodiment 13

[0085] This embodiment provides an electrolyte for lithium metal batteries, the composition of which is the same as that of Example 1, except that the carbonate organic solvent is EC:DMC=1:1 (mass ratio). The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0086] Comparative Example 1

[0087] This comparative example provides an electrolyte for a lithium metal battery, the composition of which is the same as that of Example 6, except that triethyl phosphate is not added. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0088] Comparative Example 2

[0089] This comparative example provides an electrolyte for a lithium metal battery, the composition of which is the same as that of Example 6, except that no nitrate ionic liquid is added. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0090] Comparative Example 3

[0091] This comparative example provides an electrolyte for a lithium metal battery, the composition of which is the same as that of Example 6, except that no nitrate ionic liquid and triethyl phosphate are added. The other compositions and preparation of the electrolyte are the same as those of Example 1.

[0092] Table 1 Composition of the electrolyte in Examples 1-13 and Comparative Examples 1-3

[0093]

[0094]

[0095] Note: “-” in Table 1 means that the substance is not added.

[0096] Performance Testing

[0097] The electrolytes in the examples and comparative examples were assembled into lithium metal batteries according to the following method:

[0098] Positive electrode: The positive electrode active material Li(Ni 0.8 Co 0.1 Mn 0.1 ) 2 , binder PVDF, and conductive agent SP were mixed in a mass ratio of 8:1:1, N-methylpyrrolidone was added, and the mixture was stirred in a high-speed vibration ball mill until it was stable and uniform to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on an aluminum foil and transferred to a 55°C blast oven for drying for 2 hours, and then cold pressed and cut to obtain a positive electrode sheet with a diameter of 14 mm, each with a capacity of about 2 mAh. The positive electrode sheet was transferred to a vacuum drying oven at 55°C for vacuum drying for 24 hours for use.

[0099] Negative electrode: A metallic lithium disc with a diameter of 15.6 mm and a thickness of 0.45 mm was used as the negative electrode.

[0100] Diaphragm: Punch the polyethylene diaphragm into a disc with a diameter of 16 mm and use it as a diaphragm.

[0101] Take Li(Ni 0.8 Co 0.1 Mn 0.1 ) 2 As the positive electrode, metallic lithium as the negative electrode, and the configured electrolyte are used to assemble a CR2032 button battery.

[0102] The lithium metal battery was tested using the Arbin BT2000 test system, with a charge and discharge voltage range of 2.8 to 4.3 V. At room temperature (25°C), the battery was activated at a rate of 0.1C for three cycles and then cycled at a rate of 1C; the capacity retention rate after 200 cycles was the ratio of the discharge capacity at the 200th cycle to the discharge capacity at the third cycle. The results are shown in Table 2.

[0103] Table 2 Performance test results of lithium metal batteries

[0104]

[0105] It can be seen from the results in Table 2 that, compared with the electrolyte to which only a single nitrate ionic liquid or a single phosphate organic solvent is added and no additives are added, the electrolyte to which the nitrate ionic liquid and the phosphate organic solvent are added in the present invention can effectively improve the first cycle coulomb efficiency and cycle life of the battery. This is due to the synergistic effect of nitrate ions, ionic liquid cations and phosphate esters, which promotes the Li-rich electrolyte on the lithium metal side. X The SEI film of N is formed, and the SEI film has high conductivity, thereby improving the first-cycle coulombic efficiency and cycle life of lithium metal batteries.

[0106] At the same time, the batteries in Example 1 and Comparative Example 3 after 200 cycles at room temperature of 25°C were disassembled, and the metal lithium negative electrodes were taken out and their morphologies were characterized by scanning electron microscopy (SEM). Figure 1 (Example 1) and Figure 2 (Comparative Example 3) It can be seen that the lithium metal battery with the addition of nitrate ionic liquid and phosphate organic solvent has a more complete and uniform morphology of the metal lithium negative electrode, and no lithium dendrites are generated. This shows that the scheme in the present invention can inhibit the growth of lithium dendrites, thereby significantly improving the safety of lithium metal batteries.

[0107] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An electrolyte for a lithium metal battery, characterized in that: It includes electrolyte lithium salt, carbonate organic solvent, phosphate organic solvent and nitrate ionic liquid.

2. The electrolyte for lithium metal battery according to claim 1, characterized in that The anion of the nitrate ionic liquid is nitrate, and the cation is a pyrazolium cation, a triazole cation, a pyrrolidine cation or an amino acid ester cation; Preferably, the nitrate ionic liquid is one or a combination of two or more of N-propyl-N-methylpyrrolidine nitrate ionic liquid, 1-butyl-2,3,5-trimethylpyrazole nitrate ionic liquid, L-proline butyl ester nitrate ionic liquid, L-leucine methyl ester nitrate ionic liquid, glycine methyl ester nitrate ionic liquid, and 1-alkyl-4-amino-1,2,4-triazole nitrate ionic liquid.

3. The electrolyte for lithium metal battery according to claim 1 or 2, characterized in that In the electrolyte, the concentration of the nitrate ionic liquid is 0.3 mol / L to 1 mol / L.

4. The electrolyte for lithium metal battery according to claim 1, characterized in that The electrolyte lithium salt is LiPF6, LiAsF6, LiBF4, LiClO4, LiCF3SO3, LiPO2F2, LiN4C6F3, LiBC2O4F2, LiBF3Cl, LiP(CO2CO2)3, LiPF4(CO2CO2), LiB(C2O4)2 and LiN(C x F 2x+1 SO2)·(C y F 2y+1 SO2) or a combination of two or more thereof, wherein x and y are independently integers of 0 to 5.

5. The electrolyte for lithium metal battery according to claim 1 or 4, characterized in that The total concentration of the electrolyte lithium salt is 0.5 mol / L to 2.5 mol / L.

6. The electrolyte for lithium metal battery according to claim 1, characterized in that The carbonate organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate and ethyl propyl carbonate.

7. The electrolyte for lithium metal battery according to claim 1, characterized in that The phosphate ester organic solvent is at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, and toluene diphenyl phosphate; Preferably, the volume percentage of the phosphate organic solvent in the electrolyte is 10% to 30%.

8. A method for preparing the electrolyte for a lithium metal battery according to any one of claims 1 to 7, characterized in that: The following steps are involved: Under the condition of isolating water and oxygen, the carbonate organic solvent and the electrolyte lithium salt are mixed evenly to obtain an electrolyte base liquid; Evenly mixing the nitrate ionic liquid and the phosphate organic solvent to obtain a mixed solution; The mixed solution is added into the electrolyte base solution and mixed evenly.

9. Use of the electrolyte for lithium metal batteries according to any one of claims 1 to 7 or the electrolyte for lithium metal batteries prepared by the preparation method according to claim 8 in the preparation of lithium metal batteries.

10. A lithium metal battery, characterized in that: Contains the electrolyte for a lithium metal battery as described in any one of claims 1 to 7 or the electrolyte for a lithium metal battery prepared by the preparation method according to claim 8.

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