Lithium metal battery electrolyte and lithium metal battery

Abstract

The invention discloses a lithium metal battery electrolyte and a lithium metal battery. The electrolyte comprises a lithium salt, a main solvent and a cosolvent, wherein the molar concentration of the lithium salt in the main solvent is more than 0.5 mol / L; the cosolvent is a chlorinated ether-based solvent. Compared with the prior art, the electrolyte has the advantages that (1) when the electrolyte is used for the lithium metal battery, ultrahigh energy density can be realized, stable SEI derived from anions is formed, the lithium metal deposition / stripping efficiency reaches 99.9%, and the electrolyte is very stable to metal lithium, so that stable circulation of the high-voltage / high-energy-density lithium metal battery is realized; and (2) due to the addition of the cosolvent, the viscosity of the electrolyte is reduced, so that the reactivity of the lithium metal and the electrolyte cannot be hindered due to the excessive viscosity of the electrolyte even in the lithium salt electrolyte in a saturated state.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a novel electrolyte for lithium-ion batteries, in particular to a lithium metal battery electrolyte and a lithium metal battery. Background Art

[0002] High energy density lithium metal batteries are a new generation of energy storage battery systems that can significantly increase the driving time of electric vehicles. The energy density of commercial lithium-ion batteries with graphite as the negative electrode is close to its theoretical limit. In order to obtain lithium batteries with higher energy density, lithium metal batteries using metallic lithium as the negative electrode will be the key technology to break through the bottleneck of lithium battery energy density. However, as an alkali metal with the lowest electrode potential (-3.04V relative to the standard hydrogen electrode), side reactions will inevitably occur between lithium metal and the electrolyte to form an electrode electrolyte interface film (SEI). Continuous side reactions, lithium dendrite growth, and the formation of dead lithium will greatly damage the cycle life of lithium metal batteries.

[0003] In the prior art, how to regulate the electrolyte and electrode interface reaction mechanism to improve the stability of active positive and negative electrodes has always attracted much attention from academia and industry. For example, Chinese patent application CN114421014A discloses a chloroether electrolyte and its application, and specifically discloses that chlorine atoms are used to replace the hydrogen atoms at the terminal β carbon position of common ether molecules to obtain chloroether as an electrolyte solvent. Due to the strong electronegativity and steric hindrance effect of chlorine atoms, the electrolyte forms a solvation structure dominated by anion and cation aggregates, thereby deriving a stable interface rich in inorganic components. At the same time, chlorine can effectively capture free radicals generated during the combustion process, so the antioxidant capacity and flame retardant capacity of the developed chloroether solvent molecules are effectively improved. In addition, a diluent can also be added to the electrolyte of the prior art, and its role is to facilitate the formation of a protective layer. However, in the embodiment of the prior art, a chlorinated ether solvent is directly used as the main solvent, and even in a local high-concentration electrolyte system with a diluent added, satisfactory stability to the lithium negative electrode cannot be shown. And the low boiling point of the fluorinated ether diluent itself will still have a large application limitation.

[0004] Chinese patent application CN118554018A discloses lithium-ion battery electrolyte and lithium-ion battery, and specifically discloses monofluoroether-based molecules as co-solvents for high-voltage lithium metal batteries, the main purpose of which is to change the dominant role in the electrolyte from the coordination of lithium ions in lithium salts and main solvent molecules to the hydrogen bonding of difluoromethyl in the co-solvent and main solvent molecules, thereby improving the antioxidant properties of the solvent molecules, while inhibiting the main solvent molecules from being embedded in the graphite interlayers together with lithium ions, thereby achieving high-voltage and high-coulomb efficiency cycles, and significantly improving the performance of the battery. From the perspective of those skilled in the art, combined with the effects of the prior art, the technical solution cannot achieve effective utilization of lithium metal negative electrodes. Summary of the invention

[0005] Technical problem to be solved: In order to overcome the shortcomings of the prior art, a lithium metal battery having excellent stability to lithium metal and capable of forming a stable SEI derived from anions, achieving a high lithium deposition and stripping efficiency, thereby enabling the lithium metal battery to have a good cycle life; in view of this, the present invention provides a lithium metal battery electrolyte and a lithium metal battery.

[0006] Technical solution: A lithium metal battery electrolyte, the electrolyte comprising a lithium salt, a main solvent and a co-solvent; wherein the molar concentration of the lithium salt in the main solvent is above 0.5-16 mol / L; and the co-solvent is a chloroether-based solvent.

[0007] Preferably, the molar concentration of the lithium salt in the main solvent is 8-16 mol / L.

[0008] Preferably, the lithium salt is in a supersaturated state in the main solvent.

[0009] Preferably, the volume ratio of the main solvent to the co-solvent is 1:5-10.

[0010] Preferably, the lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalatoborate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0011] Preferably, the main solvent is at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethyl ether, propyl ether, butyl ether, tetrahydrofuran, tetrahydropyran, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0012] Preferably, the co-solvent is at least one of chloromethyl ethyl ether, chloromethyl propyl ether, 2-chloroethyl methyl ether, chloromethyl isopropyl ether, 2-chloroethyl chloromethyl ether, 2-chloropropyl methyl ether, 2,2-dichloroethyl ether, 1,2-dichloroethoxyethane, 1-chloro-1-ethoxyethane, 1,7-dichloro-4-oxaheptane, and 2-ethoxychloroethane.

[0013] The lithium metal battery electrolyte is prepared by the following method: after the solvent and the co-solvent are uniformly mixed in proportion, lithium salt is added and stirred until it is completely dissolved, thereby obtaining the lithium metal battery electrolyte.

[0014] Use of any of the above lithium metal battery electrolytes in the preparation of lithium metal batteries.

[0015] Preferably, the negative electrode of the lithium metal battery is metallic lithium or a lithium alloy, and the positive electrode is a layered nickel-cobalt-manganese-based ternary oxide. Among them, the layered nickel-cobalt-manganese-based ternary oxide is LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.9 Co 0.05 Mn 0.05 At least one of O2. The battery separator is polyethylene or polypropylene.

[0016] Preferably, the lithium metal battery is a button cell or a soft pack cell.

[0017] The working principle of the lithium metal battery electrolyte of the present invention is that the chlorinated ether-based co-solvent of the present invention cannot dissolve lithium salt alone, but can be miscible with the main solvent; that is, the chlorinated ether-based co-solvent is introduced into the ether-based or ester-based high-concentration lithium salt electrolyte, thereby achieving the purpose of ultra-high concentration lithium salt solubility. Furthermore, the chlorinated ether-based co-solvent in the electrolyte system promotes the combination of lithium ions and anions to form a tighter small solvation structure cluster dominated by anions, promotes the complete decomposition of lithium salts, forms a SEI with good stability, and inhibits the reactivity of lithium metal and electrolyte.

[0018] Beneficial effects: (1) The electrolyte of the present invention can achieve ultra-high energy density when used in lithium metal batteries, form a stable SEI derived from anions, and make the lithium metal deposition / stripping efficiency reach 99.9%. It is very stable to metallic lithium, thereby achieving stable circulation of high-voltage / high-energy-density lithium metal batteries; (2) The addition of the co-solvent reduces the viscosity of the electrolyte. Therefore, even in a supersaturated lithium salt electrolyte, the reactivity of lithium metal and the electrolyte will not be hindered due to the excessive viscosity of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The test results of the lithium metal battery electrolyte prepared in Example 1 in a Li||Cu battery;

[0020] Figure 2 The lithium metal battery electrolyte prepared in Example 1 is Li||LiNi 0.8 Co 0.1 Mn 0.1 Test results in O2 cells;

[0021] Figure 3This is the test result of the lithium metal battery electrolyte prepared in Comparative Example 1 in a Li||Cu battery;

[0022] Figure 4 The lithium metal battery electrolyte prepared in Comparative Example 1 is Li||LiNi 0.8 Co 0.1 Mn 0.1 Test results in O2 cells;

[0023] Figure 5 This is the test result of the lithium metal battery electrolyte prepared in Comparative Example 2 in a Li||Cu battery;

[0024] Figure 6 The lithium metal battery electrolyte prepared in Comparative Example 2 is Li||LiNi 0.8 Co 0.1 Mn 0.1 Test results in O2 cells. DETAILED DESCRIPTION

[0025] The following examples further illustrate the content of the present invention, but should not be construed as limiting the present invention. Without departing from the spirit and essence of the present invention, modifications and substitutions made to the method, steps or conditions of the present invention all belong to the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0026] Example 1

[0027] The main solvent and the co-solvent are mixed in a volume ratio of 1:7, and after mixing evenly, lithium salt is added and completely dissolved to obtain an electrolyte with a lithium salt concentration of 2 mol / L, which is equivalent to a molar concentration of lithium salt in the main solvent of 16 mol / L.

[0028] Among them, the main solvent is any one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethyl ether, propyl ether, butyl ether, tetrahydrofuran, tetrahydropyran, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0029] The co-solvent is any one of chloromethyl ethyl ether, chloromethyl propyl ether, 2-chloroethyl methyl ether, chloromethyl isopropyl ether, 2-chloroethyl chloromethyl ether, 2-chloropropyl methyl ether, 2,2-dichloroethyl ether, 1,2-dichloroethoxyethane, 1-chloro-1-ethoxyethane, 1,7-dichloro-4-oxaheptane, and 2-ethoxychloroethane.

[0030] The lithium salt is any one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0031] The electrolyte prepared in this example is used in Li||Cu battery and Li||LiNi 0.8 Co 0.1 Mn 0.1 O2 battery, and conduct performance tests, the results are as follows Figure 1 , 2 The electrolyte is used in Li||Cu batteries and the performance is tested ( Figure 1 ), the coulombic efficiency of lithium metal deposition and stripping can reach 99.9%, indicating that the electrolyte is very stable to lithium metal. The electrolyte is used for Li||LiNi 0.8 Co 0.1 Mn 0.1 O2 battery and conduct performance tests ( Figure 2 ), the unit area capacity is 3.8 mAh / cm 2 The negative electrode is 20μm lithium metal foil, the charge and discharge voltage range is 2.8-4.3V, 0.2C charge / 1C discharge, and the capacity retention rate after 350 cycles is 80%, indicating that the electrolyte has good performance on lithium metal negative electrode and high-load high-voltage LiNi 0.8 Co 0.1 Mn 0.1 The O2 positive electrode also has excellent compatibility.

[0032] Example 2

[0033] The difference from Example 1 is that the volume ratio of the main solvent to the co-solvent in the electrolyte is 1:6, and the electrolyte with a lithium salt concentration of 2 mol / L is obtained by complete dissolution, which is equivalent to a molar concentration of the lithium salt in the main solvent of 14 mol / L.

[0034] The electrolytes obtained in this example are used for Li||Cu batteries and Li||LiNi 0.8 Co 0.1 Mn 0.1 O2 battery, and conducted performance tests, the results showed that the coulombic efficiency of lithium metal deposition and stripping can reach 99.8%, Li||LiNi 0.8 Co 0.1 Mn 0.1 The capacity retention rate of the O2 battery after 300 cycles is 80%.

[0035] Example 3

[0036] The difference from Example 1 is that the volume ratio of the main solvent to the co-solvent in the electrolyte is 1:5, and the electrolyte with a lithium salt concentration of 2.5 mol / L is obtained by complete dissolution, which is equivalent to a molar concentration of the lithium salt in the main solvent of 15 mol / L.

[0037] The electrolytes obtained in this example are used for Li||Cu batteries and Li||LiNi0.8 Co 0.1 Mn 0.1 O2 battery, and conducted performance tests, the results showed that the coulombic efficiency of lithium metal deposition and stripping can reach 99.8%, Li||LiNi 0.8 Co 0.1 Mn 0.1 The capacity retention rate of the O2 battery was 80% after 280 cycles.

[0038] Comparative Example 1

[0039] The difference from Example 1 is that no co-solvent is added, that is, the electrolyte with a lithium salt concentration of 2 mol / L.

[0040] like Figure 3 , 4 As shown, the electrolyte prepared in this comparative example is used in Li||Cu batteries and Li||LiNi 0.8 Co 0.1 Mn 0.1 O2 battery and conduct performance test. Figure 3 It is shown that the Coulombic efficiency of lithium metal deposition and stripping can reach 99.24% in Li||Cu batteries, indicating that the electrolyte is relatively stable to lithium metal; Figure 4 The unit area capacity is 3.8 mAh / cm 2 The negative electrode is 20μm lithium metal foil, the charge and discharge voltage range is 2.8-4.3V, 0.2C charge / 1C discharge, and the capacity retention rate after 23 cycles is 80%. This shows that the electrolyte has high load and high voltage LiNi 0.8 Co 0.1 Mn 0.1 Stable cycling is not possible in O2 batteries.

[0041] Comparative Example 2

[0042] The difference from Example 2 is that no co-solvent is added, that is, the electrolyte with a lithium salt concentration of 10 mol / L.

[0043] like Figure 5 , 6 As shown, the electrolyte prepared in this comparative example is used in Li||Cu batteries and Li||LiNi 0.8 Co 0.1 Mn 0.1 O2 battery and conduct performance test. Figure 5 It is shown that the Coulombic efficiency of lithium metal deposition and stripping can reach 99.34% in Li||Cu batteries, indicating that the electrolyte is relatively stable to lithium metal; Figure 6 The unit area capacity is 3.8 mAh / cm 2The negative electrode is 20μm lithium metal foil, the charge and discharge voltage range is 2.8-4.3V, 0.2C charge / 1C discharge, and the capacity retention rate after 61 cycles is 80%, indicating that the electrolyte has good performance in high-load and high-voltage LiNi 0.8 Co 0.1 Mn 0.1 Stable cycling is not possible in O2 batteries.

Claims

1. A lithium metal battery electrolyte, characterized in that: The electrolyte comprises a lithium salt, a main solvent and a co-solvent; wherein the molar concentration of the lithium salt in the main solvent is above 0.5 mol / L; and the co-solvent is a chloroether-based solvent.

2. The lithium metal battery electrolyte according to claim 1, characterized in that The molar concentration of the lithium salt in the main solvent is 0.5-16 mol / L.

3. The lithium metal battery electrolyte according to claim 1, characterized in that The lithium salt is in a supersaturated state in the main solvent.

4. The lithium metal battery electrolyte according to claim 1, characterized in that The volume ratio of the main solvent to the co-solvent is 1:5-10.

5. The lithium metal battery electrolyte according to claim 1, characterized in that The lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalatoborate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

6. The lithium metal battery electrolyte according to claim 1, characterized in that The main solvent is at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethyl ether, propyl ether, butyl ether, tetrahydrofuran, tetrahydropyran, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

7. The lithium metal battery electrolyte according to claim 1, characterized in that The co-solvent is at least one of chloromethyl ethyl ether, chloromethyl propyl ether, 2-chloroethyl methyl ether, chloromethyl isopropyl ether, 2-chloroethyl chloromethyl ether, 2-chloropropyl methyl ether, 2,2-dichloroethyl ether, 1,2-dichloroethoxyethane, 1-chloro-1-ethoxyethane, 1,7-dichloro-4-oxaheptane, and 2-ethoxychloroethane.

8. Use of the lithium metal battery electrolyte according to any one of claims 1 to 7 in the preparation of lithium metal batteries.

9. The use according to claim 8, characterized in that: The negative electrode of the lithium metal battery is metallic lithium or a lithium alloy, and the positive electrode is a layered nickel-cobalt-manganese-based ternary oxide.

10. The use according to claim 8, characterized in that: The lithium metal battery is a button battery or a soft pack battery.

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