Multifunctional electrolyte and lithium metal battery

Abstract

The invention relates to the technical field of lithium batteries, and discloses a multifunctional electrolyte and a lithium metal battery, the electrolyte comprises an organic solvent, an active additive and a lithium salt, and the active additive comprises a leveling additive, a film-forming additive and a brightening additive. According to the active additive composed of the three components, the three additives interact, the leveling additive can generate characteristic adsorption on the surface of a metal electrode, then the film forming additive and the brightening additive are induced to generate self-assembly on the surface of the metal electrode through chemical adsorption, and a stable surface molecular layer is formed. The materials used in the invention are all commercially purchased, the operation is simple and convenient, the production cost is low, and large-scale industrial production is facilitated.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high voltage, high capacity, low consumption, no memory effect, small size, low internal resistance, low self-discharge, and high cycle times, making them one of the most promising high-energy secondary rechargeable battery systems. However, the unstable lithium metal anode / electrolyte interface leads to short battery cycle life and safety issues. Therefore, it is imperative to construct a stable SEI film to efficiently and long-term protect the lithium metal surface.

[0003] Electrolyte additives are considered to be the most feasible, economical and effective way to improve the electrochemical performance of lithium batteries. They usually do not participate in the electrode reaction of the cycle process, but can improve the lithium electrolyte interface and the SEI film of the lithium metal electrode, reduce the side reactions of the lithium interface, reduce the interface impedance, and improve the coulombic efficiency. Existing electrolyte additives have limited improvement on the electrochemical performance of batteries and cannot completely and effectively solve a series of problems existing in lithium negative electrodes, such as many side reactions and uncontrollable growth of dendrites, as well as the resulting short life and safety issues. Summary of the invention

[0004] Based on this, the present invention provides a multifunctional electrolyte and a lithium metal battery to solve the problem that the electrolyte additives in the prior art cannot completely and effectively solve the poor stability of lithium and the resulting short life.

[0005] To achieve the above object, the present invention provides a multifunctional electrolyte for lithium metal batteries, which includes an organic solvent, an active additive and a lithium salt, wherein the active additive consists of a leveling additive, a film-forming additive and a brightening additive;

[0006] The leveling additive is at least one of coumarin and saccharin sodium having a carbonyl group;

[0007] The film-forming additive is at least one of lithium nitrate, vinyl ethylene carbonate, tris(pentafluorophenyl)borane, fluoroethylene carbonate, ethyl 2,2,2-trifluoroacetate, difluoroacetic anhydride, heptafluorobutyrylimidazole, potassium perfluorobutylsulfonate, trifluoroacetamide, N,N-dimethyltrifluoroacetamide, vinyl sulfate, dimethyl sulfate, 1,3-propane sultone, triallyl phosphate, tris(trimethylsilyl)phosphite, tert-butyldiphenylsilyl trifluoromethanesulfonate, N,O-bis(trimethylsilyl)trifluoroacetamide, and 1,3-divinyltetramethyldisiloxane, and the film-forming additive satisfies: the LUMO orbital energy of the film-forming additive is less than the LUMO orbital energy of any solvent in a blank electrolyte without any active additive added;

[0008] The brightening additive is at least one of hexadecyltrimethylammonium chloride and octylphenol polyoxyethylene ether having a high molecular weight long chain.

[0009] As a further preferred technical solution of the present invention, the lithium salt includes at least one of LiPF6, LiBF4, LiCH3SO3, LiCF3SO3, LiAsF6, LiClO4, LiBOB, and LiN(CF3SO2)2.

[0010] As a further preferred technical solution of the present invention, in the multifunctional electrolyte, the lithium salt concentration is 0.1-2.0M.

[0011] As a further preferred technical solution of the present invention, the organic solvent is at least one of dimethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and ethylene glycol dimethyl ether.

[0012] As a further preferred technical solution of the present invention, in the multifunctional electrolyte, the concentration of the leveling additive is 0.05-50.0 mM, the concentration of the film-forming additive is 0.05-100.0 mM, and the concentration of the brightening additive is 0.05-50.0 mM.

[0013] According to another aspect of the present invention, the present invention provides a lithium metal battery using the above-mentioned multifunctional electrolyte, which can be a button battery.

[0014] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0015] 1) The present invention proposes an active additive composed of three components: a leveling additive, a film-forming additive and a brightening additive. The three additives interact with each other. The leveling additive will be characteristically adsorbed on the surface of the metal electrode, and then the film-forming additive and the brightening additive will be induced to self-assemble on the surface of the metal electrode through chemical adsorption to form a stable surface molecular layer. In the subsequent cycle process, the leveling additive can be adsorbed on the lithium negative electrode and inhibit electrodeposition, so the surface leveling effect can be achieved, and the adhesion of the SEI film on the metal lithium negative electrode can be improved. The film-forming additive can be consumed in the reaction of the metal lithium negative electrode, participate in the construction of the SEI film, and improve the mechanical properties and ion conduction of the SEI film. The polymer brightening additive remains stable, and the dense deposition of metal lithium is efficiently regulated in each cycle process, dendrites are suppressed, and the SEI film is ensured to be intact and not broken after multiple cycles, thereby greatly improving the cycle life (breaking through 200 weeks) of ultra-high specific energy metal lithium batteries (500Wh / Kg), and promoting the progress of its commercial application.

[0016] 2) The materials used in the present invention are all purchased commercially, and the operation is simple, the production cost is low, and it is convenient for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] Figure 1 The scanning electron microscope images of the lithium surface of the electrolytes of Comparative Example 1 and Example 1 are shown;

[0019] Figure 2 The constant current charge and discharge curves of the lithium ion batteries assembled based on Example 1 and Comparative Examples 1-4.

[0020] Figure 3 The scanning electron microscope images of the lithium surface of the electrolytes according to Comparative Example 5 and Example 2 are shown;

[0021] Figure 4 The constant current charge and discharge curves of the lithium-ion batteries assembled based on Example 2 and Comparative Examples 5-8.

[0022] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0024] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by technicians in the field to which the present invention belongs. The test reagents used in the following examples are conventional biochemical reagents unless otherwise specified; the experimental methods are conventional methods unless otherwise specified. The parameters of the batteries assembled in the following examples and comparative examples are the same, and all use Li / Li button-type symmetrical mold full batteries with a lithium foil diameter of 1 cm.

[0025] Comparative Example 1:

[0026] The electrolyte of the lithium metal battery is composed of an organic solvent (ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:1 volume ratio) and LiPF6 (concentration of 1.0M).

[0027] Comparative Example 2:

[0028] The lithium metal battery electrolyte consists of an organic solvent (ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:1 volume ratio), LiPF6 (concentration of 1.0 M), and sodium saccharin leveling additive (concentration of 1.0 mM).

[0029] Comparative Example 3:

[0030] The lithium metal battery electrolyte consists of an organic solvent (ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:1 volume ratio), LiPF6 (concentration of 1.0 M), and tert-butyldiphenylsilyl trifluoromethanesulfonate film-forming additive (concentration of 2.0 mM).

[0031] Comparative Example 4:

[0032] The lithium metal battery electrolyte consists of an organic solvent (ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:1 volume ratio), LiPF6 (concentration of 1.0M), and hexadecyltrimethylammonium chloride brightener (concentration of 0.5mM).

[0033] Embodiment 1:

[0034] The electrolyte of the lithium metal battery consists of an organic solvent (ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:1 volume ratio), LiPF6 (concentration of 1.0M), and active additives (sodium saccharin, tert-butyldiphenylsilyl trifluoromethanesulfonate and hexadecyltrimethylammonium chloride).

[0035] The concentration of saccharin sodium was 1.0 mM, the concentration of tert-butyldiphenylsilyl trifluoromethanesulfonate was 2.0 mM, and the concentration of hexadecyltrimethylammonium chloride was 0.5 mM.

[0036] Comparative Example 5:

[0037] The lithium metal battery electrolyte consists of an organic solvent (1,3-dioxolane:ethylene glycol dimethyl ether=1:1 volume ratio) and lithium bis(trifluoromethanesulfonyl)imide (concentration of 1.0 M).

[0038] Comparative Example 6:

[0039] The lithium metal battery electrolyte consists of an organic solvent (1,3-dioxolane:ethylene glycol dimethyl ether=1:1 volume ratio), lithium bis(trifluoromethanesulfonyl)imide (concentration of 1.0 M), and a coumarin leveling additive (concentration of 0.5 mM).

[0040] Comparative Example 7:

[0041] The lithium metal battery electrolyte consists of an organic solvent (1,3-dioxolane:ethylene glycol dimethyl ether=1:1 volume ratio), lithium bis(trifluoromethanesulfonyl)imide (concentration of 1.0 M), and a 1,3-divinyltetramethyldisiloxane film-forming additive (concentration of 2.5 mM).

[0042] Comparative Example 8:

[0043] The lithium metal battery electrolyte consists of an organic solvent (1,3-dioxolane:ethylene glycol dimethyl ether=1:1 volume ratio), lithium bis(trifluoromethanesulfonyl)imide (concentration of 1.0M), and octylphenol polyoxyethylene ether brightener (concentration of 0.5mM).

[0044] Embodiment 2:

[0045] The lithium metal battery electrolyte consists of an organic solvent (1,3-dioxolane:ethylene glycol dimethyl ether = 1:1 volume ratio), lithium bis(trifluoromethanesulfonyl)imide (concentration of 1.0M), and active additives (coumarin, 1,3-divinyltetramethyldisiloxane, and octylphenol polyoxyethylene ether).

[0046] The concentration of coumarin was 0.5 mM, the concentration of 1,3-divinyltetramethyldisiloxane was 2.5 mM, and the concentration of octylphenol polyoxyethylene ether was 0.5 mM.

[0047] The electrolytes prepared in Examples 1 and 2 and Comparative Examples 1-8 were assembled into batteries and their electrochemical performance was tested. The specific operation is illustrated by Example 1:

[0048] Take a Li / Li button-type symmetrical battery and inject 0.1 mL of the electrolyte prepared in Example 1 into it at 1 mA cm -2 The current density and 3 mAh cm -2 Lithium-to-lithium deposition stripping tests were performed at a deposition amount of .

[0049] Figure 1 The scanning electron microscope images of the lithium sheet surface after the lithium-on-lithium deposition stripping test was completed by the battery assembled with the electrolyte without active additives in Comparative Example 1 and the electrolyte in Example 1 are given. Figure 1 It can be clearly seen that the surface of the lithium sheet in the electrolyte without active additives is uneven and has a large number of dendrites, while the surface of the lithium sheet with the addition of three-component active additives (sodium saccharin, tert-butyldiphenylsilyl trifluoromethanesulfonate and hexadecyltrimethylammonium chloride) is flat.

[0050] Figure 2The constant current charge and discharge curves of the lithium ion batteries assembled in Example 1 and Comparative Examples 1-4 are given. It can be seen from the figure that, compared with lithium ion batteries without additives and single additive electrolytes, lithium ion batteries using three-component active additives show excellent long cycle life in the electrochemical test of lithium-to-lithium deposition and stripping, and the cycle life exceeds 200 weeks. This is mainly due to the synergistic effect of the three-component electrolyte additives. The carbonyl group on the leveling additive sodium saccharin will interact with the metal lithium electrode and undergo characteristic adsorption in the concave part of the metal lithium electrode to achieve the effect of leveling the metal lithium electrode. At the same time, the carbonyl group will chemically react with the film-forming additive tert-butyldiphenylsilyl trifluoromethanesulfonate and the brightening additive hexadecyltrimethylammonium chloride and adsorb them on the surface of the metal lithium electrode. The brightening additive is induced to self-assemble around the film-forming additive through chemical adsorption to form a stable and uniform surface molecular layer. In the subsequent cycle process, since the LUMO orbital energy of the film-forming additive is smaller than the LUMO orbital energy of any solvent in the blank electrolyte, the surface molecular layer is stable and uniform. The presence of leveling additives can improve the adhesion of SEI film to the metal lithium electrode, and enhance the mechanical properties and ion conductivity of SEI film. Brightening additives with long polymer chains can ensure the stability of SEI film, effectively regulate the dense deposition of metal lithium in each cycle, inhibit dendrites, and ensure that SEI film is intact and not broken after multiple cycles, thereby greatly improving the cycle life (exceeding 200 weeks) and safety of ultra-high specific energy metal lithium batteries.

[0051] Figure 3 The scanning electron microscope images of the lithium sheet surface after the lithium-on-lithium deposition stripping test was completed by the battery assembled with the electrolyte without active additives of Comparative Example 5 and the electrolyte of Example 2 are given. Figure 3 It can be clearly seen that the surface of the lithium sheet in the electrolyte without active additives is uneven and has a large number of dendrites, while the surface of the lithium sheet with the addition of three-component active additives (coumarin, 1,3-divinyltetramethyldisiloxane and octylphenol polyoxyethylene ether) is flat.

[0052] Figure 4The constant current charge and discharge curves of the lithium ion batteries assembled in Example 2 and Comparative Examples 5-8 are given. It can be seen from the figure that, compared with lithium ion batteries without additives and single additive electrolytes, lithium ion batteries using three-component active additives show excellent long cycle life in the electrochemical test of lithium-to-lithium deposition and stripping, and the cycle life exceeds 200 weeks. This is mainly due to the synergistic effect of the three-component electrolyte additives. The carbonyl group on the leveling additive coumarin will interact with the metal lithium electrode and undergo characteristic adsorption in the concave part of the metal lithium electrode to achieve the effect of leveling the metal lithium electrode. At the same time, the carbonyl group will chemically react with the film-forming additive 1,3-divinyltetramethyldisiloxane and the brightening additive octylphenol polyoxyethylene ether and adsorb them on the surface of the metal lithium electrode, and induce the brightening additive to self-assemble around the film-forming additive through chemical adsorption to form a stable and uniform surface molecular layer; in the subsequent cycle process, since the LUMO orbital energy of the film-forming additive is smaller than the LUMO orbital energy of any solvent in the blank electrolyte The amount of leveling additives can be reduced and decomposed preferentially on the metal lithium electrode and form a stable SEI film together with the brightening additive, which protects the lithium negative electrode on the one hand and the electrolyte from being consumed on the other hand; the presence of the leveling additive can improve the adhesion of the SEI film on the metal lithium electrode, and enhance the mechanical properties and ion conductivity of the SEI film. The brightening additive with a long polymer chain can ensure the stability of the SEI film, efficiently regulate the dense deposition of metal lithium during each cycle, inhibit dendrites, and ensure that the SEI film is intact and not broken after multiple cycles, thereby greatly improving the cycle life (exceeding 200 weeks) and safety of ultra-high specific energy metal lithium batteries.

[0053] In summary, the three-component electrolyte additive can effectively improve the surface of the lithium electrode, regulate the dense deposition of metallic lithium, inhibit the growth of lithium dendrites, maintain the smoothness of the electrode surface, improve the mechanical properties of the SEI film, solve safety problems such as battery short circuit, and the corresponding battery cycle life has also been greatly improved.

[0054] The present invention aims at the short battery cycle life and safety problems caused by the unstable lithium negative electrode / electrolyte interface of the current lithium metal battery, and proposes a solution of using three-component electrolyte additives to collaboratively construct a stable SEI film to efficiently and long-term protect the lithium metal surface. The three additives interact with each other, and the leveling additive will undergo characteristic adsorption on the metal electrode surface, and then induce the film-forming additive and the brightening additive to self-assemble on the metal electrode surface through chemical adsorption to form a stable surface molecular layer. In the subsequent cycle process, the leveling additive can be adsorbed on the lithium negative electrode and inhibit electrodeposition, so that the surface leveling effect can be achieved, and the adhesion of the SEI film on the metal lithium negative electrode can be improved. The film-forming additive can be consumed in the reaction of the metal lithium negative electrode, participate in the construction of the SEI film, and improve the mechanical properties and ion conduction of the SEI film. The polymer brightening additive remains stable, and the dense deposition of metal lithium is efficiently regulated in each cycle process, dendrites are inhibited, and the SEI film is ensured to be intact and not broken after multiple cycles, thereby greatly improving the cycle life (breaking through 200 weeks) of ultra-high specific energy metal lithium batteries (500Wh / Kg), and greatly promoting the progress of its commercial application.

[0055] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A multifunctional electrolyte for lithium metal batteries, characterized in that: It includes an organic solvent, an active additive and a lithium salt, wherein the active additive is composed of a leveling additive, a film-forming additive and a brightening additive; The leveling additive is at least one of coumarin and saccharin sodium having a carbonyl group; The film-forming additive is at least one of lithium nitrate, vinyl ethylene carbonate, tri(pentafluorophenyl)borane, fluoroethylene carbonate, ethyl 2,2,2-trifluoroacetate, difluoroacetic anhydride, heptafluorobutyrylimidazole, potassium perfluorobutylsulfonate, trifluoroacetamide, N,N-dimethyltrifluoroacetamide, vinyl sulfate, dimethyl sulfate, 1,3-propane sultone, triallyl phosphate, tri(trimethylsilyl)phosphite, tert-butyldiphenylsilyl trifluoromethanesulfonate, N,O-bis(trimethylsilyl)trifluoroacetamide, and 1,3-divinyltetramethyldisiloxane, and the film-forming additive satisfies: the LUMO orbital energy of the film-forming additive is less than the LUMO orbital energy of any solvent in a blank electrolyte without any active additive added; The brightening additive is at least one of hexadecyltrimethylammonium chloride and octylphenol polyoxyethylene ether having a high molecular weight long chain.

2. The multifunctional electrolyte for lithium metal batteries according to claim 1, characterized in that: The lithium salt includes at least one of LiPF6, LiBF4, LiCH3SO3, LiCF3SO3, LiAsF6, LiClO4, LiBOB, and LiN(CF3SO2)2.

3. The multifunctional electrolyte for lithium metal batteries according to claim 1, characterized in that: In the multifunctional electrolyte, the lithium salt concentration is 0.1-2.0M.

4. The multifunctional electrolyte for lithium metal batteries according to claim 1, characterized in that: The organic solvent is at least one of dimethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and ethylene glycol dimethyl ether.

5. The multifunctional electrolyte for lithium metal batteries according to any one of claims 1 to 4, characterized in that: In the multifunctional electrolyte, the concentration of the leveling additive is 0.05-50.0 mM, the concentration of the film-forming additive is 0.05-100.0 mM, and the concentration of the brightening additive is 0.05-50.0 mM.

6. A lithium metal battery, characterized in that: A multifunctional electrolyte for a lithium metal battery according to any one of claims 1 to 5.

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