Ether-ester mixed electrolyte, lithium battery and preparation method thereof

Abstract

The present invention discloses an ether-ester mixed electrolyte, a lithium battery, and a preparation method thereof. The electrolyte comprises the following components: a halogen lithium salt, a lithium imide salt, lithium nitrate, lithium hexafluorophosphate, a cyclic ether, a chain ether, a cyclic ester, and a chain ester. The preparation method comprises: dissolving the halogen lithium salt, the lithium nitrate, and the lithium imide salt in a mixed ether solvent composed of the cyclic ether and the chain ether to obtain an ether-containing mixture; dissolving the lithium hexafluorophosphate in a mixed ester solvent composed of the cyclic ester and the chain ester to obtain an ester-containing mixture; and mixing the ether-containing mixture and the ester-containing mixture to obtain the ether-ester mixed electrolyte. The present invention can effectively improve the poor cycle performance of high-nickel ternary lithium batteries, resulting in high-nickel ternary lithium batteries with superior performance.

Description

Technical Field

[0001] The present invention relates to the technical field of high-nickel ternary lithium batteries, and in particular to the technical field of electrolytes for high-nickel ternary lithium batteries containing halogen lithium salts. Background Art

[0002] Lithium-ion batteries (LIBs) have been extensively studied and successfully applied in a variety of fields, including portable consumer electronics, new energy vehicles, and storage systems, due to their high energy density, long service life, stable operating voltage, light weight, and environmental friendliness. In recent years, with the rapid development of new energy electric vehicles, society's demand for high-energy-density power batteries has also increased. However, the actual capacity of lithium-ion batteries with graphite as the negative electrode has approached the theoretical capacity limit. Lithium metal batteries with high-nickel ternary materials have attracted more attention due to their advantages such as low cost and high capacity. However, they have the significant disadvantage of poor cycling stability.

[0003] High-nickel ternary lithium batteries are composed of three core materials: electrolyte, positive electrode material, and negative electrode material. The electrolyte not only directly connects the positive and negative electrodes, but also serves as a medium for lithium ion transport in redox reactions, affecting and controlling interfacial reactions and battery safety. The main reasons for the poor cycle performance of high-nickel ternary lithium batteries include the side reactions between metallic lithium and existing electrolytes, which lead to excessive consumption of metallic lithium and further the phenomenon of "dead lithium" during the cycle. To address this problem, solid electrolyte membranes are a better solution due to their blocking effect on side reactions. However, existing technologies still lack solid electrolytes with ideal performance that can be applied to high-nickel ternary lithium batteries. Summary of the Invention

[0004] In view of the defects of the prior art, the purpose of the present invention is to provide a new electrolyte and the resulting high-nickel ternary lithium battery, and to provide a preparation method thereof. The new electrolyte can solve the shortcomings of the prior art high-nickel ternary lithium battery, such as the irreversible consumption of the metal lithium negative electrode in the long cycle and the non-dense and non-uniform solid electrolyte interface generated between the metal lithium and the electrolyte during the charge and discharge process. It can form a solid electrolyte interface with a higher inorganic component content, a denser and more stable structure at a low cost, thereby effectively improving the capacity and cycle performance of the high-nickel ternary lithium battery.

[0005] The present invention first provides the following technical solutions:

[0006] The ether-ester mixed electrolyte comprises the following components: halogen lithium salt, imide lithium salt, lithium nitrate, lithium hexafluorophosphate, cyclic ether, chain ether, cyclic ester and chain ester.

[0007] According to some preferred embodiments of the present invention, the mass ratio of the halogen lithium salt, the lithium nitrate, the imide lithium salt, and the lithium hexafluorophosphate is (0.1-1): (0.1-1): (0.1-3): (0.1-3).

[0008] According to some preferred embodiments of the present invention, the volume ratio of the cyclic ether, chain ether, cyclic ester and chain ester is (0.1-1):(0.1-1):(0.1-1):(0.1-1).

[0009] According to some preferred embodiments of the present invention, the volume of the cyclic ether accounts for 10-90% of the total volume of the cyclic ether and the chain ether. More preferably, the volume of the cyclic ether accounts for 50% of the total volume of the cyclic ether and the chain ether.

[0010] According to some preferred embodiments of the present invention, the volume of the cyclic ester accounts for 10-90% of the total volume of the cyclic ester and the chain ester. More preferably, the volume of the cyclic ester accounts for 50% of the total volume of the cyclic ester and the chain ester.

[0011] According to some preferred embodiments of the present invention, the mass ratio of the halogen lithium salt, the lithium nitrate, the imide lithium salt, and the lithium hexafluorophosphate is 26:8:32:32.

[0012] According to some preferred embodiments of the present invention, the halogen lithium salt is selected from one or more of lithium fluoride, lithium bromide, and lithium iodide. More preferably, the halogen lithium salt is selected from lithium fluoride.

[0013] According to some preferred embodiments of the present invention, the lithium imide salt is selected from lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

[0014] According to some preferred embodiments of the present invention, the cyclic ether is selected from 1,3-dioxolane and / or tetrahydrofuran.

[0015] According to some preferred embodiments of the present invention, the chain ether is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0016] According to some preferred embodiments of the present invention, the cyclic ester is selected from ethylene carbonate and / or propylene carbonate.

[0017] According to some preferred embodiments of the present invention, the chain ester is selected from dimethyl carbonate and / or ethyl methyl carbonate.

[0018] The present invention further provides a method for preparing the above-mentioned ether-ester mixed electrolyte, which comprises:

[0019] dissolving the halogen lithium salt, the lithium nitrate, and the imide lithium salt in a mixed ether solvent consisting of the cyclic ether and the chain ether under an inert atmosphere to obtain an ether-containing mixture;

[0020] dissolving the lithium hexafluorophosphate in a mixed ester solvent of the cyclic ester and the chain ester under an inert atmosphere to obtain an ester-containing mixture;

[0021] mixing the ether-containing mixture and the ester-containing mixture under an inert atmosphere to obtain a total mixture;

[0022] The total mixture is fully mixed under an inert atmosphere until it is completely dissolved to obtain the ether-ester mixed electrolyte.

[0023] According to some preferred embodiments of the present invention, the volume of the ether-containing mixture accounts for 10% to 90% of the volume of the total mixture. More preferably, the volume of the ether-containing mixture accounts for 10% of the volume of the total mixture.

[0024] According to some preferred embodiments of the present invention, the inert atmosphere is an argon atmosphere, the water content of which is less than 1 ppm, and the oxygen content of which is less than 1 ppm.

[0025] According to some preferred embodiments of the present invention, the mixing temperature in step (4) is 20-30° C., i.e., mixing at room temperature.

[0026] The present invention further provides a high-nickel ternary lithium battery containing the above-mentioned ether-ester mixed electrolyte and / or the ether-ester mixed electrolyte prepared according to the above-mentioned preparation method, and a preparation method thereof.

[0027] According to some preferred embodiments of the present invention, the method for preparing the high-nickel ternary lithium battery includes:

[0028] obtaining the ether-ester mixed electrolyte;

[0029] Obtaining the high-nickel ternary lithium battery positive electrode material and lithium sheet;

[0030] The high-nickel ternary lithium battery positive electrode material, the lithium sheet and the ether-ester mixed electrolyte are packaged to obtain the high-nickel ternary lithium battery.

[0031] Among them, the positive electrode material can be further preferably such as: high nickel ternary positive electrode material LiNi 0.6 Co 0.2 Mn 0.2 and / or LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0032] The present invention can obtain a new type of ether-ester mixed electrolyte of high-concentration halogen lithium salt and lithium nitrate, which can be successfully applied to high-nickel ternary lithium batteries. The organic and inorganic components in the solid electrolyte membrane formed by the present invention can fully modify the solid electrolyte membrane (SEI) of the high-nickel ternary lithium battery in the prior art.

[0033] In the electrolyte of the present invention, inorganic lithium salts such as halogen lithium salts (such as lithium fluoride) and lithium nitrate help to form a more stable, uniform and dense solid electrolyte membrane. Among them, halogen lithium salts such as lithium fluoride have the characteristics of low cost, small molecules and good wettability to the electrode surface, but they have the defects of being difficult to dissolve in other organic solvents. By dissolving lithium fluoride in an ether mixed solvent and then mixing ether and ester organic solvents, the lithium fluoride can be fully and uniformly added to the electrolyte system to obtain a stable and uniform solid electrolyte membrane.

[0034] The present invention further has the following beneficial effects:

[0035] The present invention addresses the disadvantages of high nickel ternary lithium batteries, which have the advantages of high specific capacity and low cost, but poor cycle performance and poor thermal stability. By adopting a mixture of ether and ester, high concentrations of lithium fluoride and lithium nitrate are used to adjust the composition structure of the solid electrolyte membrane, thereby achieving high stability cycle of high nickel ternary lithium batteries.

[0036] In some preferred embodiments, the lithium fluoride used in the present invention has the advantages of low price, low viscosity, high solvent oxidation stability, and good wettability for electrodes and separators. It works synergistically with lithium nitrate to facilitate the modification of solid electrolyte membranes. However, lithium fluoride is slightly soluble in water, soluble in acid, and poorly soluble in alcohol and other organic solvents. The present invention solves the problem of lithium fluoride and lithium nitrate being insoluble in ester solvents by using an ether-ester mixture, achieving a uniform and dense solid electrolyte membrane and stabilizing the metallic lithium anode. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Comparison of the charge and discharge curves of the lithium battery with high concentration of lithium salt in Example 1 and low concentration of lithium salt in Example 2 at 0.1C

[0038] Figure 2 This is a comparison of the charge and discharge curves of lithium batteries with different lithium salt components at 0.1C in Example 3.

[0039] Figure 3 This is a comparison of the charge and discharge curves of lithium batteries with different ether and ester components at 0.1C in Example 4.

[0040] Figure 4This is a comparison chart of the charge and discharge curves of a lithium battery containing an ether-ester mixed electrolyte obtained by mixing the mixed ether solvent containing different volumes of cyclic ethers and the mixed ester solvent containing different volumes of cyclic esters in Example 5 at 0.1C.

[0041] Figure 5 This is a comparison chart of charge and discharge curves of lithium batteries containing electrolytes obtained by containing different volumes of mixed ether solvents in the total ether-ester mixed electrolyte in Example 6 at 0.1C.

[0042] Figure 6 、 7 The coulombic efficiency curve at 0.2C and the symmetrical battery curve of the lithium battery using the electrolyte obtained in Example 1 in Example 7 are shown.

[0043] Figure 8 、 9 The coulombic efficiency curve at 0.2C and the symmetrical battery curve of the lithium battery using the electrolyte obtained in Example 2 in Example 7 are shown. DETAILED DESCRIPTION

[0044] The present invention is described in detail below with reference to the embodiments and accompanying drawings. However, it should be understood that the embodiments and accompanying drawings are merely exemplary descriptions of the present invention and do not constitute any limitation on the scope of protection of the present invention. All reasonable variations and combinations within the scope of the inventive concept of the present invention fall within the scope of protection of the present invention.

[0045] According to the technical solution of the present invention, some specific methods for preparing ether-ester mixed electrolytes include:

[0046] (1) In an inert atmosphere such as argon, a halogen lithium salt, lithium nitrate, and an imide lithium salt are weighed in sequence and dissolved in a mixed ether solvent of a cyclic ether and a chain ether to obtain an ether-containing mixture, wherein the volume of the cyclic ether accounts for 10% to 90% of the volume of the mixed ether solvent.

[0047] (2) In an inert atmosphere such as argon, lithium hexafluorophosphate is weighed and dissolved in a mixed ester solvent of cyclic ester and chain ester to obtain an ester-containing mixture, wherein the volume of the cyclic ester accounts for 10% to 90% of the volume of the mixed ester solvent.

[0048] (3) Weighing the ether-containing mixture and the ester-containing mixture in an inert atmosphere such as argon to obtain a total mixture, wherein the volume of the ether-containing mixture accounts for 10% to 90% of the volume of the total mixture.

[0049] (4) Stir the total mixture in an inert atmosphere such as argon atmosphere until dissolution is complete.

[0050] in,

[0051] The argon atmosphere is preferably argon gas with a water content of less than 1 ppm and an oxygen content of less than 1 ppm. The stirring temperature is preferably 20 to 30° C., the stirring pressure is preferably 0.1 to 1.0 MPa, and the stirring time is preferably 10 to 30 minutes.

[0052] The mass ratio of the halogen lithium salt, lithium nitrate, lithium imide salt, and lithium hexafluorophosphate is preferably 0.1 to 1 g: 0.1 to 1 g: 0.1 to 3 g: 0.1 to 3 g.

[0053] The lithium imide salt is preferably lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide.

[0054] The cyclic ether is preferably 1,3-dioxolane and / or tetrahydrofuran.

[0055] The chain ether is preferably one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0056] The cyclic ester is preferably ethylene carbonate and / or propylene carbonate.

[0057] The chain ester is preferably dimethyl carbonate and / or ethyl methyl carbonate.

[0058] Furthermore, the obtained electrolyte is assembled with a lithium-ion battery positive electrode material such as NCM622 and a negative electrode material such as a lithium sheet to obtain the lithium-ion battery.

[0059] The present invention is further illustrated below with reference to specific embodiments:

[0060] Example 1

[0061] The ether-ester mixed electrolyte is prepared by the following process:

[0062] (1) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium fluoride, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of the cyclic ether 1,3-dioxolane and 2 ml of the linear ether ethylene glycol dimethyl ether, wherein the volume of the cyclic ether accounted for 50% of the total ether solvent;

[0063] (2) In an argon atmosphere with a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in 4 ml of a mixed ester solvent of cyclic ester ethylene carbonate and linear ester dimethyl carbonate, wherein the volume of the cyclic ester accounted for 50% of the total ester solvent;

[0064] (3) in an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (1) and (2) are weighed and mixed in sequence to obtain an ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% of the volume of the total ether-ester mixed solution;

[0065] (4) Stirring the ether-ester mixed solution in an argon atmosphere at a stirring temperature of 20 to 30° C., a stirring pressure of 0.1 to 1.0 MPa, and a stirring time of 10 to 30 minutes until the solvent is completely dissolved to obtain an ether-ester mixed electrolyte containing a high concentration of lithium salt.

[0066] Example 2

[0067] The ether-ester mixed electrolyte is prepared by the following process:

[0068] (1) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 0.04 g of lithium fluoride, 0.08 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of the cyclic ether 1,3-dioxolane and 2 ml of the linear ether ethylene glycol dimethyl ether, wherein the volume of the cyclic ether accounted for 50% of the total ether solvent;

[0069] (2) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in a mixed ester solvent of 4 ml of cyclic ester ethylene carbonate and 4 ml of linear ester dimethyl carbonate, wherein the volume of the cyclic ester accounted for 50% of the total ester solvent;

[0070] (3) in an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (1) and (2) are weighed and mixed in sequence to obtain an ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% of the volume of the total ether-ester mixed solution;

[0071] (4) Stirring the above ether-ester mixed solution in an argon atmosphere at a stirring temperature of 20 to 30° C., a stirring pressure of 0.1 to 1.0 MPa, and a stirring time of 10 to 30 minutes until the solvent is completely dissolved to obtain an ether-ester mixed electrolyte with a low concentration of lithium salt.

[0072] Example 3

[0073] The ether-ester mixed electrolyte is prepared by the following process:

[0074] (1) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium fluoride, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of cyclic ether 1,3-dioxolane and 2 ml of linear ether ethylene glycol dimethyl ether, wherein the volume of the cyclic ether accounted for 50% of the total volume of the ether solvent;

[0075] (2) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium bromide, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(fluorosulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of cyclic ether 1,3-dioxolane and 2 ml of linear ether ethylene glycol dimethyl ether, wherein the volume of the cyclic ether accounted for 50% of the total volume of the ether solvent;

[0076] (3) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in a mixed ester solvent of 4 ml of cyclic ester ethylene carbonate and 4 ml of linear ester dimethyl carbonate, wherein the volume of the cyclic ester accounted for 50% of the total ester solvent;

[0077] (4) in an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (1) and (3) are weighed and mixed in sequence to obtain a first ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% by volume of the total ether-ester mixed solution;

[0078] (5) in an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (2) and (3) are weighed and mixed in sequence to obtain a second ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% by volume of the total ether-ester mixed solution;

[0079] (6) Stirring the ether-ester mixed solutions of steps (4) and (5) in an argon atmosphere, respectively, at a stirring temperature of 20 to 30° C., a stirring pressure of 0.1 to 1.0 MPa, and a stirring time of 10 to 30 minutes until the solvent is completely dissolved, thereby obtaining the first and second ether-ester mixed electrolytes containing different lithium salt components.

[0080] Example 4

[0081] The ether-ester mixed electrolyte is prepared by the following process:

[0082] (1) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium fluoride, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of cyclic ether 1,3-dioxolane and 2 ml of linear ether ethylene glycol dimethyl ether, wherein the volume of the cyclic ether accounted for 50% of the total volume of the ether solvent;

[0083] (2) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium fluoride, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of cyclic ether tetrahydrofuran and 2 ml of linear ether diethylene glycol dimethyl ether, wherein the volume of the cyclic ether accounted for 50% of the total ether solvent;

[0084] (3) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in 4 ml of a mixed ester solvent of cyclic ester ethylene carbonate and 4 ml of linear ester dimethyl carbonate, wherein the volume of the cyclic ester accounted for 50% of the total ester solvent;

[0085] (4) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in 4 ml of a mixed ester solvent of a cyclic ester, propylene carbonate, and 4 ml of a linear ester, methyl ethyl carbonate, wherein the volume of the cyclic ester accounted for 50% of the total ester solvent;

[0086] (5) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (1) and (3) are weighed in sequence and mixed to obtain a third ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% of the volume of the total ester-ether mixed solution.

[0087] (6) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (2) and (4) are weighed in sequence and mixed to obtain a fourth ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% of the volume of the ester-ether mixed solution.

[0088] (7) Stirring the ether-ester mixed solutions of steps (5) and (6) in an argon atmosphere at a stirring temperature of 20 to 30° C., a stirring pressure of 0.1 to 1.0 MPa, and a stirring time of 10 to 30 minutes, respectively, until the solvent is completely dissolved, thereby obtaining third and fourth ether-ester mixed electrolytes containing different ester and ether components.

[0089] Example 5

[0090] The ether-ester mixed electrolyte is prepared by the following process:

[0091] (1) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium fluoride, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of the cyclic ether 1,3-dioxolane and 2 ml of the cyclic chain ether diethylene glycol dimethyl ether, wherein the volume of the cyclic ether solvent accounted for 10% of the total ether solvent.

[0092] (2) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium fluoride, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide were weighed in sequence and dissolved in a mixed ether solvent of 2 ml of the cyclic ether 1,3-dioxolane and 2 ml of the linear ether diethylene glycol dimethyl ether, wherein the volume of the cyclic ether solvent accounted for 50% of the total ether solvent.

[0093] (3) In an argon atmosphere with a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in 4 ml of a mixed ester solvent of cyclic ester ethylene carbonate and 4 ml of linear ester dimethyl carbonate, wherein the volume of the cyclic ester accounted for 10% of the total ester solvent.

[0094] (4) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in a mixed ester solvent of 4 ml of cyclic ester ethylene carbonate and 4 ml of linear ester dimethyl carbonate, wherein the volume of the cyclic ester accounted for 50% of the total ester solvent.

[0095] (5) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (1) and (2) are weighed in sequence and mixed to obtain a fifth ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% of the total volume.

[0096] (6) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent obtained in steps (3) and (4) are weighed in sequence and mixed to obtain a sixth ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% of the total volume.

[0097] (7) The ether-ester mixed solutions of steps (5) and (6) are stirred in an argon atmosphere at a temperature of 20 to 30° C., a pressure of 0.1 to 1.0 MPa, and a time of 10 to 30 minutes until the solvent is completely dissolved, thereby obtaining the fifth and sixth ether-ester mixed electrolytes containing different volumes of cyclic ether and cyclic ester.

[0098] Example 6

[0099] The ether-ester mixed electrolyte is prepared by the following process:

[0100] (1) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1 g of lithium fluoride or lithium bromide, 0.28 g of lithium nitrate, and 1.14 g of lithium bis(trifluoromethanesulfonyl)imide are weighed in sequence and dissolved in a mixed ether solvent of 2 ml of cyclic ether 1,3-dioxolane and 2 ml of linear ether ethylene glycol dimethyl ether, wherein the volume of the cyclic ether accounts for 10% of the total volume of the mixed ether solvent;

[0101] (2) In an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, 1.2 g of lithium hexafluorophosphate was weighed and dissolved in 4 ml of a mixed ester solvent of cyclic ester ethylene carbonate and 4 ml of linear ester dimethyl carbonate, wherein the volume of the cyclic ester accounted for 10% of the total volume of the mixed ester solvent;

[0102] (3) in an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent in steps (1) and (2) are weighed and mixed in sequence to obtain a seventh ether-ester mixed solution, wherein the mixed ether solvent accounts for 10% of the total volume;

[0103] (4) in an argon atmosphere having a water content of less than 1 ppm and an oxygen content of less than 1 ppm, the mixed ether solvent and the mixed ester solvent in steps (1) and (2) are weighed and mixed in sequence to obtain an eighth ether-ester mixed solution, wherein the mixed ether solvent accounts for 90% of the total volume;

[0104] (5) Stirring the ether-ester mixed solutions of steps (3) and (4) separately in an argon atmosphere, with a stirring temperature of 20 to 30° C., a stirring pressure of 0.1 to 1.0 MPa, and a stirring time of 10 to 30 minutes until the solvent is completely dissolved, thereby obtaining the seventh and eighth ether-ester mixed electrolytes containing different volumes of mixed ether solvents.

[0105] Example 7

[0106] The lithium battery is prepared by the following process:

[0107] (1) NCM622 positive electrode material was prepared by high-temperature solid-phase sintering and other methods.

[0108] (2) NCM622 positive electrode material, 50-120 μL of any one of the electrolytes in Examples 1-6, and a 150 μm lithium sheet were sequentially placed into a button battery, and sealed with a sealing machine at a pressure of 0.5-1 MPa to obtain a lithium-ion button battery.

[0109] The prepared button battery was placed in a constant temperature box and charged and discharged at a rate of 0.1C at 25°C. The voltage window was 2.8-4.2V. Figures 1 to 5 Comparison of charge and discharge curves.

[0110] in, Figure 1 The comparison results of lithium salts of different concentrations in Examples 1 and 2 show that the combination of high-concentration halogen lithium salts and lithium nitrate with lithium bis(trifluoromethanesulfonyl)imide in Example 1 has significant advantages over the low-concentration halogen lithium salts in Example 2 in the ether-ester mixed solvent.

[0111] Figure 2 This is the comparison result of the first and second ether-ester mixed electrolytes in Example 3, where pattern 1 corresponds to the lithium battery using the first ether-ester mixed electrolyte, and pattern 2 corresponds to the lithium battery using the second ether-ester mixed electrolyte. It can be seen that the lithium battery using the first ether-ester mixed electrolyte has a smoother discharge platform and a higher capacity.

[0112] Figure 3 The figures are the comparison results of the third and fourth ether-ester mixed electrolytes in Example 4, where pattern 1 corresponds to the lithium battery using the third ether-ester mixed electrolyte, and pattern 3 corresponds to the lithium battery using the fourth ether-ester mixed electrolyte. It can be seen that the lithium battery using the third ether-ester mixed electrolyte has a smoother discharge platform and a higher capacity.

[0113] Figure 4 This is the comparison result of the fifth and sixth ether-ester mixed electrolytes in Example 5, where pattern 1 corresponds to the lithium battery of the fifth ether-ester mixed electrolyte, and pattern 4 corresponds to the lithium battery of the sixth ether-ester mixed electrolyte. It can be seen that the lithium battery using the fifth ether-ester mixed electrolyte with a volume ratio of 1:1 between cyclic and chain solvents has better performance, and its electrolyte lithium ion mobility, viscosity, etc. are better, and its performance is better.

[0114] Figure 5 This is the comparison result of the seventh and eighth ether-ester mixed electrolytes in Example 6, wherein pattern 1 corresponds to the lithium battery of the seventh ether-ester mixed electrolyte, and pattern 5 corresponds to the lithium battery of the eighth ether-ester mixed electrolyte. It can be seen that the lithium battery using the seventh ether-ester mixed electrolyte in which the volume of the mixed ether solvent accounts for 10% of the volume of the total ether-ester mixed solvent has better performance.

[0115] The lithium battery using the ether-ester mixed electrolyte obtained in Example 1 and the lithium battery using the ether-ester mixed electrolyte obtained in Example 2 were subjected to a 0.2C charge-discharge cycle test and a symmetrical battery curve test, and the results were as follows: Figure 6 The 0.2C coulombic efficiency curve of the lithium battery corresponding to Example 1 shown, Figure 7 The symmetrical battery curve diagram of the lithium battery corresponding to Example 1 shown in FIG. Figure 8The 0.2C coulombic efficiency curve of the lithium battery corresponding to Example 2 shown, Figure 9 The symmetrical battery curve diagram of the lithium battery corresponding to Example 2 shown in FIG. Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 From the comparison, it can be seen that the lithium battery using the electrolyte of Example 1 has better performance.

[0116] In summary, the optimal electrolyte combination includes: high concentration lithium fluoride and lithium nitrate dissolved in the cyclic ether 1,3-dioxolane and the chain ether ethylene glycol dimethyl ether in a volume ratio of 1:1; lithium hexafluoroborate dissolved in the cyclic ester ethylene carbonate and the chain ester dimethyl carbonate in a volume ratio of 1:1; the volume ratio of mixed ether and mixed ester in the electrolyte is 1:9.

[0117] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. Ether-ester mixed electrolyte, characterized in that: The invention comprises the following components: halogen lithium salt, imide lithium salt, lithium nitrate, lithium hexafluorophosphate, cyclic ether, chain ether, cyclic ester and chain ester; wherein the mass ratio of the halogen lithium salt, the lithium nitrate, the imide lithium salt and the lithium hexafluorophosphate is (0.1-1): (0.1-1): (0.1-3): (0.1-3); the volume ratio of the cyclic ether, chain ether, cyclic ester and chain ester is (0.1-1): (0.1-1): (0.1-1): (0.1- 1); wherein the imide lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide; the cyclic ether is selected from 1,3-dioxolane and / or tetrahydrofuran; the chain ether is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; the cyclic ester is selected from ethylene carbonate and / or propylene carbonate; the chain ester is selected from dimethyl carbonate and / or ethyl methyl carbonate; the halogen lithium salt is selected from lithium fluoride; the volume of the cyclic ether accounts for 10 to 90% of the total volume of the cyclic ether and the chain ether; the volume of the cyclic ester accounts for 10 to 90% of the total volume of the cyclic ether and the chain ether.

2. The ether-ester mixed electrolyte according to claim 1, characterized in that The mass ratio of the halogen lithium salt, the lithium nitrate, the imide lithium salt, and the lithium hexafluorophosphate is 26:8:32:

32.

3. The ether-ester mixed electrolyte according to claim 1, characterized in that: in, The volume of the cyclic ether accounts for 50% of the total volume of the cyclic ether and the chain ether; and / or the volume of the cyclic ester accounts for 50% of the total volume of the cyclic ester and the chain ester.

4. The method for preparing the ether-ester mixed electrolyte according to any one of claims 1 to 3, characterized in that: include: (1) dissolving the halogen lithium salt, the lithium nitrate, and the imide lithium salt in a mixed ether solvent consisting of the cyclic ether and the chain ether under an inert atmosphere to obtain an ether-containing mixture; (2) dissolving the lithium hexafluorophosphate in a mixed ester solvent of the cyclic ester and the chain ester under an inert atmosphere to obtain an ester-containing mixture; (3) mixing the ether-containing mixture and the ester-containing mixture under an inert atmosphere to obtain a total mixture; (4) fully mixing the total mixture at room temperature under an inert atmosphere until it is completely dissolved to obtain the ether-ester mixed electrolyte; The volume of the ether-containing mixture accounts for 10-90% of the volume of the total mixture.

5. The preparation method according to claim 4, characterized in that: The volume of the ether-containing mixture accounts for 10% of the volume of the total mixture.

6. A high-nickel ternary lithium battery comprising the ether-ester mixed electrolyte according to any one of claims 1 to 3 and / or the ether-ester mixed electrolyte prepared by the preparation method according to claim 4 or 5.

7. The method for preparing a high-nickel ternary lithium battery according to claim 6, characterized in that: include: obtaining the ether-ester mixed electrolyte; Obtaining the high-nickel ternary lithium battery positive electrode material and lithium sheet; The high-nickel ternary lithium battery positive electrode material, the lithium sheet and the ether-ester mixed electrolyte are packaged to obtain the high-nickel ternary lithium battery.

Images