Lithium ion battery multi-element deep eutectic electrolyte and preparation method thereof

Abstract

The invention provides a multi-element deep eutectic electrolyte for a lithium ion battery and a preparation method of the multi-element deep eutectic electrolyte. The multi-element deep eutectic electrolyte for the lithium ion battery can comprise a hydrogen bond donor and a hydrogen bond acceptor, the hydrogen bond donor is a nitrile compound, and the hydrogen bond acceptor is at least two of a carbonate compound, a sulfonyl compound, a sulfate compound and a sulfonate compound. The preparation method comprises the following steps: mixing the hydrogen bond donor and the hydrogen bond acceptor, uniformly stirring, and adding the lithium salt to obtain the multi-element deep eutectic electrolyte of the lithium ion battery. The anti-oxidation potential of the prepared multi-element deep eutectic electrolyte reaches 4.6 V or above, and the high voltage resistance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and more specifically, to a multi-element deep eutectic electrolyte for lithium ion batteries and a preparation method thereof. Background Art

[0002] The electrolyte is an important component of metal ion batteries. It plays the role of forming the electrode-electrolyte membrane (SEI membrane and CEI membrane) and carrying the metal ions in the battery. Currently, the solvent of commercial electrolytes usually adopts a combination of cyclic carbonates and linear carbonates, controls the different volume ratios and molar ratios of the solvents, and then adds the corresponding metal ion salts and additives to form the electrolyte. However, it has the disadvantages of low antioxidant potential and flammability when exposed to open flames. Summary of the invention

[0003] In view of the deficiencies in the prior art, one of the purposes of the present invention is to solve one or more problems in the prior art. For example, one of the purposes of the present invention is to provide an electrolyte that improves the high voltage resistance and flame retardancy of lithium-ion batteries.

[0004] One aspect of the present invention provides a multi-element deep eutectic electrolyte for a lithium-ion battery, which may include a hydrogen bond donor and a hydrogen bond acceptor, wherein the hydrogen bond donor is a nitrile compound and the hydrogen bond acceptor is at least two of a carbonate compound, a sulfonyl compound, a sulfate compound and a sulfonate compound.

[0005] Furthermore, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor may be 1:(9-11).

[0006] Further, the nitrile compound may include one or more of succinonitrile, adiponitrile, adiponitrile, terephthalonitrile, p-trifluoromethylphenylacetonitrile and p-fluorophenylacetonitrile.

[0007] Further, the carbonate compound may include one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate and difluoroethylene carbonate;

[0008] Further, the sulfonyl compound may include one or more of methylsulfonylmethane, di(3,4-dimethylbenzene)sulfonyl, bis(ethylenesulfonyl)ethane and tetrahydrothiophenesulfonyl;

[0009] Further, the sulfite compound includes one or more of ethylene sulfite, propylene sulfite, dimethyl sulfite, and diethyl sulfite;

[0010] Furthermore, the thioane compound includes one or more of 1,3-dithiane, 1,4-dithiane, 1,3,5-trithiane, and 2-methyl-1,3-dithiane;

[0011] Further, the sulfate ester compound may include one or more of vinyl sulfate, propylene sulfate, butylene sulfate, diethyl sulfate and dimethyl sulfate;

[0012] Further, the sulfonate compound may include one or more of 1,3-propane sultone, 1,4-butane sultone, vinyl propane sultone, 2,4-butane sultone, phenyl methanesulfonate and cyanomethyl p-toluenesulfonate.

[0013] Furthermore, the electrolyte may further include a lithium salt, and the molar concentration of the lithium salt in the electrolyte may be 1 mol / L to 5 mol / L.

[0014] Further, the lithium salt may include one or more of lithium hexafluorophosphate, lithium bis(fluoromethyl)sulfonyl imide, lithium bis(trifluoromethyl)sulfonyl imide, lithium tetrafluoroborate and lithium difluorooxalatoborate.

[0015] Furthermore, the electrolyte may further include an additive, and the additive may be one or more of lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorobis(oxalatophosphate) and bis(trifluoromethyl)ethyl methyl carbonate.

[0016] Another aspect of the present invention provides a method for preparing a multi-component deep eutectic electrolyte for a lithium ion battery, which may include the following steps: mixing a hydrogen bond donor and a hydrogen bond acceptor and stirring them evenly, adding a lithium salt, and obtaining a multi-component deep eutectic electrolyte for a lithium ion battery.

[0017] Furthermore, the preparation process is carried out in an environment where the water content and the oxygen content are both below 0.01 ppm.

[0018] Another aspect of the present invention provides a lithium-ion battery, which may include the lithium-ion battery multi-element deep eutectic electrolyte described above, as well as a positive electrode, a negative electrode and a separator.

[0019] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0020] (1) Compared with conventional commercial carbonate electrolytes, which undergo intense decomposition at 4.23 V and experience a rapid decrease in capacity when used with high-voltage positive electrode materials, the multi-element deep eutectic electrolyte prepared in the present invention has an antioxidant potential of 4.6 V or above, which can improve the high-voltage resistance of lithium-ion batteries.

[0021] (2) The multi-element deep eutectic electrolyte of the present invention is non-flammable when exposed to open flames, thereby improving the flame retardant properties of lithium-ion batteries.

[0022] (3) The multi-element deep eutectic electrolyte of the present invention improves the room temperature and high temperature cycle performance of high voltage layered oxide positive electrode full cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects and features of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0024] Figure 1 This is the cycling performance diagram of the multi-element deep eutectic electrolyte prepared in Example 1.

[0025] Figure 2 Figure 2 shows the cycling performance of commercial carbonate electrolytes.

[0026] Figure 3 This is a comparison chart of the cycling performance of the multi-element deep eutectic electrolyte prepared in Example 3 and the industrial carbonate electrolyte at 1C rate.

[0027] Figure 4 This is a comparison chart of the cycling performance of the multi-component deep eutectic electrolyte and the binary deep eutectic electrolyte prepared in Example 4 at a 0.3C rate.

[0028] Figure 5 This is a comparison chart of the cycling performance of the multi-component deep eutectic electrolyte and the binary deep eutectic electrolyte prepared in Example 5 at 60°C.

[0029] Figure 6 This is the Raman spectrum of the multi-element deep eutectic electrolyte prepared in Example 5.

[0030] Figure 7 Linear sweep voltammetry test comparison of the multi-element deep eutectic electrolyte prepared in Example 1, the commercial carbonate electrolyte and the electrolyte prepared in Comparative Example 1.

[0031] Figure 8 Impedance test comparison of the multi-element deep eutectic electrolyte prepared in Example 1, the commercial carbonate electrolyte and the electrolyte prepared in Comparative Example 1.

[0032] Fig. 9 is the lithium ion migration number (t Li + )Test results.

[0033] Fig.10 is the lithium ion transference number of commercial carbonate electrolyte (t Li + )Test results. DETAILED DESCRIPTION

[0034] Hereinafter, a multi-element deep eutectic electrolyte for a lithium-ion battery and a preparation method thereof according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0035] Specifically, on the one hand, ethylene carbonate is the earliest solvent used in lithium-ion battery electrolytes, but because the melting point (35 ° C) is higher than room temperature, it cannot be used alone as a solvent on a large scale; on the other hand, sulfur-containing substances such as vinyl sulfate, propylene sulfate, thiodiglycol anhydride, vinyl sulfite, 1,3-dithiane are often used as film-forming additives in the alkali metal ion battery electrolyte industry, but due to their high melting points (> 50 ° C), they cannot be used as solvents; on the other hand, nitrile substances with high HOMO energy levels are also often used as high-voltage resistant additives and are not prepared for use as solvents. The inventors found that when nitrile substances are used directly as solvents, the cyano groups contained in the nitrile substances can complex the transition metal ions of the positive electrode material, alleviate the dissolution in the electrolyte, and thus weaken the crosstalk effect on the negative electrode, but due to the strong electron-withdrawing effect of the cyano group, the surface electron distribution of the hydrogen atoms connected to the adjacent carbon is affected, and the α hydrogen activity is significantly enhanced. Therefore, when nitrile molecules are used as solvents, as the dosage increases, during the cycle, the α hydrogen of the nitrile will be strongly reduced at the negative electrode, and the formed hydrogen radicals will continue to attack the negative electrode material, causing the structural collapse of the negative electrode and the uncontrollable polymerization of the nitrile. Sulfates, sulfites, thioanes, sulfonyls, etc. with sulfur-oxygen double bonds and carbonates with carbon-oxygen double bonds are typical hydrogen bond acceptor compounds, which can form strong hydrogen bonds with the α hydrogen of nitriles, significantly weakening the activity of α hydrogen, and hydrogen bonds further change the intermolecular forces, affecting the arrangement of molecules, so that the melting point of their mixture drops below -10 ° C. Therefore, the present invention uses a mixture of hydrogen bond donors and hydrogen bond acceptors as an electrolyte, which can improve the defects of using only nitrile substances as solvents.

[0036] Moreover, the current research on deep eutectic electrolytes is limited to the use of binary deep eutectic electrolytes (using solvent systems composed of no more than two molecules), which has led to limitations in the development of deep eutectic electrolytes. However, the multicomponent deep eutectic electrolyte system proposed in the present invention uses more than two hydrogen bond donor compounds and hydrogen bond acceptor compounds after mixing, and the hydrogen bond network formed between the multicomponent solvents is richer, which can be seen from the Raman spectra of the formed multicomponent deep eutectic solvents and the single component (such as Figure 6 The rich hydrogen bond network causes the stretching vibration peak of the molecular functional group to shift significantly. In addition, the multi-element deep eutectic electrolyte has a lower impedance than the binary deep eutectic electrolyte (as shown in Figure 8 ), corresponding to a higher ionic conductivity.

[0037] One aspect of the present invention provides a multi-element deep eutectic electrolyte for a lithium-ion battery, which may include a hydrogen bond donor and a hydrogen bond acceptor. The hydrogen bond donor may be a nitrile compound. The hydrogen bond acceptor may be at least two of a carbonate compound, a sulfonyl compound, a sulfate compound, a sulfite compound, a thioane compound, and a sulfonate compound. For example, the hydrogen bond acceptor may be composed of a carbonate compound, a sulfonyl compound, a sulfate compound, and a sulfonate compound.

[0038] In some embodiments, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor can be 1:(9-11). For example, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor can be 1:10. For hydrogen bond acceptors composed of different substances, the molar ratio between the different substances can be any. For example, if the hydrogen bond acceptor is composed of a sulfonyl compound and a sulfate compound, the sulfonyl compound and the sulfate compound can be in any molar ratio. For another example, if the hydrogen bond acceptor is composed of a sulfonyl compound, a sulfate compound and a sulfonate compound, the molar ratio of the sulfonyl compound, the sulfate compound and the sulfonate compound can be 1:1:1.

[0039] In some embodiments, the nitrile compound may include one or more of succinonitrile, adiponitrile, adiponitrile, terephthalonitrile, p-trifluoromethylphenylacetonitrile, and p-fluorophenylacetonitrile.

[0040] In some embodiments, the carbonate compound may include one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate;

[0041] In some embodiments, the sulfonyl compound may include one or more of methylsulfonylmethane, di(3,4-dimethylbenzene)sulfonyl, bis(ethylenesulfonyl)ethane, and tetrahydrothiophenesulfonyl;

[0042] In some embodiments, the sulfate ester compound may include one or more of vinyl sulfate, propylene sulfate, butylene sulfate, diethyl sulfate, and dimethyl sulfate;

[0043] In some embodiments, the sulfonate compound may include one or more of 1,3-propane sultone, 1,4-butane sultone, vinyl propane sultone, 2,4-butane sultone, phenyl methanesulfonate, and cyanomethyl p-toluenesulfonate.

[0044] In some embodiments, the electrolyte may further include a lithium salt. The molar concentration of the lithium salt in the electrolyte may be 1 mol / L to 5 mol / L. For example, the molar concentration of the lithium salt in the electrolyte may be 2 mol / L to 4 mol / L. For another example, the molar concentration of the lithium salt in the electrolyte may be 3 mol / L.

[0045] In some embodiments, the lithium salt may include one or more of lithium hexafluorophosphate, lithium bis(fluoromethylsulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

[0046] In some embodiments, the electrolyte may further include an additive, which may be one or more of lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorobis(oxalatophosphate), and bis(trifluoromethyl)methylethyl carbonate.

[0047] In some embodiments, the electrolyte of the present invention is particularly suitable for lithium-ion batteries using high-voltage layered oxide cathode materials.

[0048] Another aspect of the present invention provides a method for preparing a multi-element deep eutectic electrolyte for a lithium-ion battery, which may include the following steps: mixing a hydrogen bond donor and a hydrogen bond acceptor and stirring them evenly, adding a lithium salt, and obtaining a multi-element deep eutectic electrolyte for a lithium-ion battery. For example, the preparation method may include:

[0049] Step 1, mixing a hydrogen bond donor and a hydrogen bond acceptor;

[0050] Step 2, continuously stirring the mixture obtained in step 1 at 60° C. to obtain a clear transparent liquid;

[0051] Step 3, adding lithium salt to the obtained clear and transparent liquid, and continuously stirring to obtain a multi-element deep eutectic electrolyte.

[0052] In some embodiments, the preparation process of step 1, step 2 and step 3 can be carried out in an environment where the water content and the oxygen content are both below 0.01 ppm.

[0053] Another aspect of the present invention provides a lithium-ion battery, which may include the lithium-ion battery multi-element deep eutectic electrolyte described above, as well as a positive electrode, a negative electrode and a separator.

[0054] In some embodiments, the positive electrode can be made of one or more ternary layered structure positive electrode materials such as lithium nickel oxide, lithium nickel manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0055] In some embodiments, the negative electrode can be made of one or more of metallic lithium, graphite, silicon negative electrode, silicon-carbon negative electrode, and lithium titanate.

[0056] In some embodiments, the diaphragm can be any one of polyethylene, polypropylene, PP / PE / PP three-layer composite diaphragm, nano-alumina-coated PP diaphragm, GF / A glass fiber diaphragm, GF / C glass fiber diaphragm and GF / D glass fiber diaphragm.

[0057] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0058] Example 1

[0059] A multi-element deep eutectic electrolyte for a lithium-ion battery and a preparation method thereof, which may specifically include the following steps:

[0060] Step 1, uniformly mix succinonitrile, ethylene carbonate and ethylene sulfate in a molar ratio of 1:3:7, and continuously stir to obtain a clear and transparent solution.

[0061] Step 2: Add 0.5 mol of LiTFSI and 0.5 mol of LiBF4 to prepare a multi-element deep eutectic electrolyte with a lithium ion concentration of 2.5 mol / L.

[0062] The prepared electrolyte was subjected to conductivity test and electrochemical window test, and applied to Ni 0.98 Co 0.01 Mn 0.01 In a button-type graphite lithium-ion full battery with O2 as the positive electrode, an electrochemical test was performed, and the electrochemical window was 2.8V to 4.5V. This example uses a binary deep eutectic electrolyte (succinonitrile and vinyl sulfate are mixed in a molar ratio of 1:10, the type and amount of lithium salt are the same as in Example 1, and the lithium ion concentration is 2.5mol / L) and a commercial carbonate electrolyte (ethylene carbonate and ethyl methyl carbonate are mixed in a molar ratio of 3:7, and 1mol / L LiPF6 is added) as a comparison.

[0063] Figure 1 This is the electrolyte cycle performance diagram prepared in this embodiment, Figure 7 The linear sweep voltammetry test results show that the room temperature electrochemical oxidation potential of this embodiment is 4.65V, while the antioxidant potentials of the binary deep eutectic electrolyte and the commercial carbonate electrolyte are 4.28V and 4.23V, respectively, indicating that the multi-element deep electrolyte prepared in this embodiment has a higher antioxidant potential and is not easily decomposed under high voltage. In addition, the room temperature ionic conductivity of the multi-element deep eutectic electrolyte is 2.8×10 -3 S / cm, while the ionic conductivity of the binary deep eutectic electrolyte is 2.32×10 -3 The initial discharge capacity of the graphite full battery using the electrolyte of this embodiment at room temperature is 232 mAh / g, while the initial discharge capacity of the commercial carbonate electrolyte is 180 mAh / g. Figure 2 As shown, it is much smaller than the multi-element deep eutectic electrolyte prepared in Example 1. Figure 8 As shown, the impedance test comparison of the multi-component deep eutectic electrolyte, commercial carbonate electrolyte and binary deep eutectic electrolyte prepared in Example 1 is shown. Figure 8It shows that the electrolyte prepared in Example 1 has a small impedance. The smaller the impedance, the higher the ion conductivity and the better the lithium ion transfer kinetics.

[0064] Example 2

[0065] A multi-element deep eutectic electrolyte for a lithium-ion battery and a preparation method thereof, which may specifically include the following steps:

[0066] Step 1, terephthalonitrile, dimethyl sulfite and dimethyl carbonate are uniformly mixed in a molar ratio of 1:3.5:6.5, and stirred to obtain a low eutectic solvent.

[0067] Step 2: Add 0.5 mol of LiTFSI and 0.5 mol of LiDFOB to prepare a low eutectic electrolyte with a lithium ion concentration of 3 mol / L.

[0068] The prepared multi-element deep eutectic electrolyte was subjected to conductivity test and electrochemical window test, and applied to LiNi 0.8 Co 0.1 Mn 0.1 In the button-type graphite full battery with O2 as the positive electrode, the graphite full battery was electrochemically tested, and the electrochemical window was 2.8-4.3V. The deep eutectic electrolyte had a discharge capacity of 200mAh / g at room temperature, and a capacity retention rate of 96% after 200 cycles.

[0069] Example 3

[0070] A multi-element deep eutectic electrolyte for a lithium-ion battery and a preparation method thereof, which may specifically include the following steps:

[0071] Step 1, adiponitrile, ethyl methyl carbonate and di(3,4-dimethylbenzene)sulfonyl are uniformly mixed in a molar ratio of 1:3:7, and stirred to obtain a low eutectic solvent.

[0072] Step 2: Add 0.8 mol of LiTFSI and 0.2 mol of LiDFOB to prepare an electrolyte with a lithium ion concentration of 2.7 mol / L.

[0073] The multi-element deep eutectic electrolyte prepared above was applied to a graphite metal battery with ultra-high nickel layered oxide as the positive electrode, and electrochemical tests were performed, and the electrochemical window was 2.8-4.3V. Figure 3 As shown, the test results show that the deep eutectic electrolyte has a specific capacity of 215 mAh / g at 1C rate at room temperature, and a capacity retention rate of 91% after 100 cycles, while the capacity retention rate of the commercial carbonate electrolyte after 100 cycles is 82%.

[0074] Example 4

[0075] A multi-element deep eutectic electrolyte for a lithium-ion battery and a preparation method thereof, which may specifically include the following steps:

[0076] Step 1, terephthalonitrile, propylene sulfate and vinyl sulfate are uniformly mixed in a molar ratio of 1:3:7, and stirred to obtain a low eutectic solvent.

[0077] Step 2: Add 1 mol of LiFSI to prepare a low-melting electrolyte with a lithium ion concentration of 3.5 mol / L.

[0078] The multi-element deep eutectic electrolyte prepared above was applied to Ni 0.98 Co 0..01 Mn 0.01 In the graphite full battery with O2 as the positive electrode, electrochemical tests were carried out and the electrochemical window was 2.8-4.4V. Figure 4 As shown, the test results show that the capacity retention rate of the multi-element deep eutectic electrolyte after 100 cycles at 0.3C rate is 92%, while the capacity retention rate of the battery using the binary deep eutectic electrolyte after 100 cycles is 81%. The binary deep eutectic electrolyte is composed of terephthalonitrile and vinyl sulfate in a molar ratio of 1:10, and 3.5 mol / L of LiFSI is added.

[0079] Example 5

[0080] A multi-element deep eutectic electrolyte for a lithium-ion battery and a preparation method thereof, which may specifically include the following steps:

[0081] Step 1, uniformly mixing succinonitrile, vinyl sulfate and diethyl carbonate in a molar ratio of 1:5:5, and stirring to obtain a deep eutectic solvent.

[0082] Step 2: Add 1 mol of LiDFOB to prepare a deep eutectic electrolyte with a lithium ion concentration of 2.8 mol / L.

[0083] The prepared multi-element deep eutectic electrolyte was applied to a graphite full battery with ultra-high nickel layered oxide as the positive electrode for electrochemical testing at a temperature of 60°C and an electrochemical window of 2.8-4.3V. Figure 5 As shown, the electrochemical test results show that the first-cycle discharge specific capacity of the deep eutectic electrolyte is 230mAh / g under a high temperature environment of 60°C, while the first-cycle discharge specific capacity of the binary deep eutectic electrolyte under the same conditions is only 200mAh / g, and the specific capacity has an obvious downward trend. The binary deep eutectic electrolyte is composed of succinonitrile and diethyl carbonate in a ratio of 1:10, with 2.8 mol / L of LiDFOB added. Figure 6 This is the Raman spectrum of the multi-element deep eutectic solvent prepared in Example 5. Figure 6It can be seen that the formation of hydrogen bonds, due to the formation of a rich hydrogen bond network between the multi-components, affects the chemical properties of the hydrogen bond donor and hydrogen bond acceptor molecular functional groups, so there will be obvious peak shifts in the Raman spectrum. In addition, the lithium ion migration number of the electrolyte of this embodiment and the commercial carbonate electrolyte was tested. Fig. 9 As shown in FIG. 1 , the lithium ion migration number of the embodiment reaches 0.52. Fig.10 As shown, the migration number of the commercial carbonate electrolyte is only 0.43, indicating that the electrolyte prepared in this example has faster lithium ion transmission power.

[0084] Example 6

[0085] A multi-element deep eutectic electrolyte for a lithium-ion battery and a preparation method thereof, which may specifically include the following steps:

[0086] Step 1, uniformly mix p-fluorophenylacetonitrile, tetrahydrothiophenesulfonyl and 1,4-butanesulfonate in a molar ratio of 1:4.2:5.8, and stir to obtain a deep eutectic solvent.

[0087] Step 2: Add 1 mol of LiDFOB to prepare a multi-element deep eutectic electrolyte with a lithium ion concentration of 2.9 mol / L.

[0088] The deep eutectic electrolyte prepared above was applied to LiNi 0.8 Co 0.1 Mn 0.1 Electrochemical tests were conducted in a graphite full battery with O2 as the positive electrode, and the electrochemical window was 2.8-4.3 V. The test results showed that the multi-element deep eutectic electrolyte had a discharge capacity of 200 mAh / g at room temperature and a capacity retention rate of 90% after 100 cycles.

[0089] The electrochemical data of all embodiments and comparative examples are summarized in Table 1.

[0090] Table 1 Electrochemical data of Examples 1-6

[0091]

[0092] Although the present invention has been described above by combining with exemplary embodiments, it will be apparent to those skilled in the art that various modifications and changes may be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined in the claims.

Claims

1. A multi-element deep eutectic electrolyte for lithium-ion batteries, characterized in that: It comprises a hydrogen bond donor and a hydrogen bond acceptor, wherein the hydrogen bond donor is a nitrile compound, and the hydrogen bond acceptor is at least two of carbonate compounds, sulfonyl compounds, sulfate compounds, sulfite compounds, thiane compounds, amide compounds and sulfonate compounds.

2. The multi-element deep eutectic electrolyte for lithium-ion batteries according to claim 1, characterized in that: The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(9-11).

3. The multi-element deep eutectic electrolyte for lithium-ion batteries according to claim 1 or 2, characterized in that: The nitrile compound includes one or more of succinonitrile, adiponitrile, adiponitrile, terephthalonitrile, p-trifluoromethylphenylacetonitrile and p-fluorophenylacetonitrile; The carbonate compound includes one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate and difluoroethylene carbonate; The sulfonyl compounds include one or more of methylsulfonylmethane, di(3,4-dimethylbenzene)sulfonyl, bis(ethylenesulfonyl)ethane and tetrahydrothiophenesulfonyl; The sulfate ester compounds include one or more of vinyl sulfate, propylene sulfate, butyl sulfate, diethyl sulfate and dimethyl sulfate; The sulfite compounds include one or more of ethylene sulfite, propylene sulfite, dimethyl sulfite, and diethyl sulfite; Thiane compounds include one or more of 1,3-dithiane, 1,4-dithiane, 1,3,5-trithiane, and 2-methyl-1,3-dithiane; The sulfonate compounds include one or more of 1,3-propane sultone, 1,4-butane sultone, vinyl propane sultone, 2,4-butane sultone, phenyl methanesulfonate and cyanomethyl p-toluenesulfonate.

4. The multi-element deep eutectic electrolyte for lithium-ion batteries according to claim 1 or 2, characterized in that: It also includes lithium salt, and the molar concentration of the lithium salt in the electrolyte is 1 mol / L to 5 mol / L.

5. The multi-element deep eutectic electrolyte for lithium-ion batteries according to claim 4, characterized in that: The lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluoromethylsulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium tetrafluoroborate (LiBF4) and lithium difluorooxalatoborate (LiDFOB).

6. The multi-element deep eutectic electrolyte for lithium-ion batteries according to claim 1, 2 or 4, characterized in that: The invention also includes additives, which are one or more of lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorobis(oxalatophosphate) and bis(trifluoromethyl)ethyl methyl carbonate.

7. A method for preparing a multi-element deep eutectic electrolyte for a lithium-ion battery according to any one of claims 1 to 6, characterized in that: The following steps are involved: The hydrogen bond donor and the hydrogen bond acceptor are mixed and stirred evenly, and lithium salt is added to obtain a multi-element deep eutectic electrolyte for lithium-ion batteries.

8. The method for preparing a multi-element deep eutectic electrolyte for lithium-ion batteries according to claim 7, characterized in that: The preparation process is carried out in an environment where the water content and oxygen content are both below 0.01 ppm.

9. A lithium ion battery, characterized in that: An electrolyte comprising the multi-element deep eutectic electrolyte for lithium-ion batteries as described in any one of claims 1 to 6 or the electrolyte prepared by the method for preparing the multi-element deep eutectic electrolyte for lithium-ion batteries as described in claim 7 or 8, as well as a positive electrode, a negative electrode and a separator.

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