Local high-concentration electrolyte added with difunctional diluent as well as preparation method and application of local high-concentration electrolyte

Abstract

The invention provides a local high-concentration electrolyte added with a difunctional diluent as well as a preparation method and application of the local high-concentration electrolyte. The electrolyte contains a conductive lithium salt, an organic solvent for dissolving the lithium salt and a difunctional diluent, wherein the difunctional diluent is a fluorine-containing compound with nitryl. On one hand, nitryl of the difunctional diluent has relatively high redox potential, so that the electrochemical window of the electrolyte can be widened, the electrochemical stability of the electrolyte can be improved, a stable solid electrolyte interface (SEI) membrane can be formed, the mechanical strength can be enhanced, and the growth of lithium dendrites can be inhibited; and on the other hand, fluorine in the difunctional diluent can form SEI rich in lithium fluoride (LiF) on the surface of an electrode, good ionic conductivity and low electronic conductivity are achieved, the ion flux can uniformly pass through, and the interface resistance is reduced, so that the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of chemical power sources, in particular to a type of locally high-concentration electrolyte added with a bifunctional diluent, a preparation method thereof, and an application thereof. Technical Background

[0002] With the continuous growth of the global economy, the global energy consumption has gradually increased. To alleviate the rapid depletion of fossil fuels and environmental problems, it is urgent to find sustainable alternative energy sources. Although lithium-ion batteries dominate the market, they still have limitations in high specific energy applications. Developing new energy storage systems with higher energy density is particularly important. Lithium-sulfur batteries stand out due to their theoretically high energy density (up to 2600 Wh / kg), and they also have the characteristics of environmental friendliness and economic feasibility. Sulfur resources are abundant, inexpensive, and environmentally harmless, making lithium-sulfur batteries a strong candidate for the next-generation energy storage solution.

[0003] The electrolyte is the medium for lithium ions to move between the positive and negative electrodes in a lithium battery. In common electrolytes, the content of lithium salts is generally low, and problems such as shortened battery life cycles, slow electrode reaction kinetics, and poor safety performance limit the application of the batteries. High-concentration lithium salt electrolytes (HCEs) (i.e., the concentration of lithium salts in the electrolyte reaches above 3 mol / L) are widely used in high-energy density battery systems, which can increase the high ion transference number, prevent the corrosion of aluminum current collectors, and effectively inhibit lithium dendrites. However, the cost is relatively high, and there are huge challenges in large-scale commercial promotion and application. By adding an "inert" diluent to HCE to form LHCE, the diluent itself means having a similar or wider electrochemical window to the high-concentration electrolyte, being insoluble in salts but miscible with solvents, forming a ((Li + -solvent) diluent) state. It does not affect the original salt-solvent coordination in HCE, but can significantly reduce the salt content per unit volume, thereby reducing the cost of salts, while retaining or even enhancing the unique properties of HCE, which is more in line with practical applications. By carefully selecting suitable lithium salts, solvents, and diluents and experimentally adjusting the ratio of the three, a "low-concentration, low-cost" high-concentration electrolyte can be realized for application in secondary batteries.

[0004] In response to this, the present invention proposes a type of locally high-concentration electrolyte added with a bifunctional diluent. This electrolyte contains a conductive lithium salt, an organic solvent capable of dissolving the lithium salt, and a bifunctional diluent. The diluent is a fluorine compound with a nitro group that is insoluble in lithium salts but miscible with solvents. By adding a new diluent, a new type of locally high-concentration electrolyte is obtained. This electrolyte maintains a low viscosity and good wettability of the separator without changing the original solvation structure in the high-concentration electrolyte, while improving problems such as limited working voltage and serious side reactions in traditional low-concentration electrolytes. In addition, this locally high-concentration electrolyte can further improve the cycle life and rate performance of the battery. Summary of the Invention

[0005] In order to solve the technical problems existing in the above-mentioned background art, the present invention provides a kind of local high-concentration electrolyte added with a bifunctional diluent, a preparation method thereof, and an application thereof.

[0006] The present invention adopts the following technical solutions: a kind of local high-concentration electrolyte added with a bifunctional diluent, comprising: an organic solvent, a bifunctional diluent, and a lithium salt;

[0007] Wherein, the organic solvent is any one or a combination of at least two of: 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), dimethyl carbonate (DMC), tris(2,2,2-trifluoroethyl) phosphate (TFEP), triethyl phosphate (TEP), acetonitrile (AN), sulfolane (TMS), 2-methyltetrahydropyran, 2,5-dimethyltetrahydrofuran, ethylene glycol bis(propionitrile) ether (DENE), triethylene glycol dimethyl ether (G3), and diethylene glycol dimethyl ether (DG);

[0008] The bifunctional diluent is a fluorine-containing compound with a nitro group.

[0009] In a further embodiment, the bifunctional diluent includes: fluorinated ether compounds containing nitro groups, fluorinated ester compounds containing nitro groups, fluorinated hydrocarbon compounds containing nitro groups, and fluorinated aromatic compounds containing nitro groups.

[0010] In a further embodiment, the lithium salt includes: any one or a combination of at least two of: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0011] In a further embodiment, a local high-concentration electrolyte is formed by adding a lithium salt, and the concentration is 1.0 - 8.0 mol / L.

[0012] In a further embodiment, the volume ratio of the organic solvent to the bifunctional diluent is 1:1 - 1:10.

[0013] A preparation method for preparing the above-mentioned local high-concentration electrolyte includes the following steps:

[0014] Mix an appropriate proportion of an organic solvent and a bifunctional diluent capable of dissolving a lithium salt evenly, and add the lithium salt to form a local high-concentration electrolyte suitable for a lithium metal battery.

[0015] A type of locally high-concentration electrolyte added with a bifunctional diluent as described above is applied to a lithium metal battery.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) The nitro group of the bifunctional diluent in this patent has a relatively high redox potential, which can broaden the electrochemical window of the electrolyte, improve the electrochemical stability of the electrolyte, form a stable solid electrolyte interface (SEI) film, enhance the mechanical strength, and also inhibit the growth of lithium dendrites. In addition, the relatively high polarity can enhance the ionic conductivity of the electrolyte.

[0018] (2) Fluorine in the bifunctional diluent can form an SEI rich in lithium fluoride (LiF) on the electrode surface, which has good ionic conductivity and low electronic conductivity. The ionic flux can uniformly pass through and reduce the interfacial resistance, thereby improving the cycle life of the battery.

[0019] (3) The advantage of the method of the locally high-concentration electrolyte with a bifunctional diluent containing a nitrofluoride compound in this patent is that it is simple and easy to operate, convenient for large-scale use. Therefore, it is beneficial to the actual deployment of this strategy at the industrial level and helps the lithium metal battery to achieve commercialization. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of a bifunctional diluent with a nitrofluoride compound.

[0021] Figure 2 It is the discharge curve of the battery. Detailed Embodiments

[0022] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in combination with preferred experimental examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0023] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0024] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0025] A type of locally high-concentration electrolyte added with a bifunctional diluent includes: an organic solvent, a bifunctional diluent, and a lithium salt;

[0026] Among them, the organic solvent is any one or a combination of at least two of: 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), dimethyl carbonate (DMC), tris(2,2,2-trifluoroethyl) phosphate (TFEP), triethyl phosphate (TEP), acetonitrile (AN), sulfolane (TMS), 2-methyltetrahydropyran, 2,5-dimethyltetrahydrofuran, ethylene glycol bis(propionitrile) ether (DENE), triglyme (G3), and diglyme (DG);

[0027] The bifunctional diluent is a fluorinated compound with a nitro group.

[0028] In a further embodiment, the bifunctional diluent includes: fluorinated ether compounds containing nitro groups, fluorinated ester compounds containing nitro groups, fluorinated hydrocarbon compounds containing nitro groups, and fluorinated aromatic compounds containing nitro groups. As Figure 1 shown.

[0029] In a further embodiment, the lithium salt includes any one or a combination of at least two of: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0030] In a further embodiment, a locally high-concentration electrolyte is formed by adding a lithium salt, and the concentration is 1.0 - 8.0 mol / L.

[0031] In a further embodiment, the volume ratio of the organic solvent to the bifunctional diluent is 1:1 - 1:10.

[0032] A preparation method for preparing the locally high-concentration electrolyte as described above includes the following steps:

[0033] Mix an appropriate proportion of the organic solvent of the soluble lithium salt and the bifunctional diluent evenly, and add the lithium salt to form a locally high-concentration electrolyte suitable for lithium metal batteries.

[0034] A locally high-concentration electrolyte of the type described above with a bifunctional diluent added is applied to lithium metal batteries.

[0035] Example 1

[0036] In this embodiment, the composition of the locally high-concentration electrolyte with a bifunctional diluent includes the following steps: The organic solvent capable of dissolving lithium salts is selected as ethylene glycol bis(propionitrile) ether (DENE), and the diluent is selected as 2,2,3,3-tetrafluorobutane-1,4-diol dinitrate (AFA). 5.61 g of lithium bis(fluorosulfonyl)imide (LiFSI) is dissolved in 1.24 mL of ethylene glycol bis(propionitrile) ether (DENE), and 2.48 mL of 2,2,3,3-tetrafluorobutane-1,4-diol dinitrate (AFA) is added to obtain a locally high-concentration electrolyte of 5 M LiFSI / DENE / AFA. After stirring evenly, a locally high-concentration electrolyte is formed. The electrolyte combination is prepared in a glove box, and the actual oxygen content in the glove box is <0.1 ppm, and the moisture content is <0.1 ppm. Then, a battery test is assembled using the locally high-concentration electrolyte of 5 M LiFSI / DME / AFA, a lithium metal negative electrode, a carbon-sulfur composite positive electrode, and a polypropylene (PP) separator. At a 3C rate, the discharge specific capacity of the material is 583 mAh / g. When returning to the initial condition of 0.1C rate again, the discharge specific capacity is 1240.6 mAh / g. It is beneficial for rapid Li + transport, and the lithium-sulfur battery has good rate performance.

[0037] Example 2

[0038] In this embodiment, the composition of the locally high-concentration electrolyte with a bifunctional diluent includes the following steps: The organic solvent capable of dissolving lithium salts is selected as 1,2-dimethoxyethane (DME), and the diluent is selected as 5-nitro-bis(2,2,2-trifluoroethyl) ester. 5.23 g of lithium bis(oxalato)borate (LiBOB) is dissolved in 1.5 mL of 1,2-dimethoxyethane (DME), and 4.5 mL of bis(2,2,2-trifluoroethyl) 4-methyl-4-nitroheptanedioate (BTFN) is added to obtain a locally high-concentration electrolyte of 4.5 M LiBOB / DME / BTFN. After stirring evenly, a locally high-concentration electrolyte is formed. The electrolyte combination is prepared in a glove box, and the actual oxygen content in the glove box is <0.1 ppm, and the moisture content is <0.1 ppm. Then, an assembly test is carried out using the 4.5 M LiBOB / DME / BTFN locally high-concentration electrolyte, a lithium metal negative electrode, a carbon-sulfur composite positive electrode, and a polypropylene (PP) separator. As Figure 2 shown, at a current density of 0.5C, the specific capacity is 1188.4 mAh / g, and after 200 cycles, 84% of the capacity (998.3 mAh / g) is still maintained, showing excellent stability.

Claims

1. A locally high-concentration electrolyte added with a bifunctional diluent, characterized in that, Comprising: an organic solvent, a bifunctional diluent, and a lithium salt; wherein the organic solvent is any one or a combination of at least two of: 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), dimethyl carbonate (DMC), tris(2,2,2-trifluoroethyl) phosphate (TFEP), triethyl phosphate (TEP), acetonitrile (AN), sulfolane (TMS), 2-methyltetrahydropyran, 2,5-dimethyltetrahydrofuran, ethylene glycol bis(propionitrile) ether (DENE), triglyme (G3), and diglyme (DG); the bifunctional diluent is a fluorinated compound with a nitro group.

2. The locally high-concentration electrolyte with a bifunctional diluent added according to claim 1, characterized in that, The bifunctional diluent includes: a fluorinated ether compound containing a nitro group, a fluorinated ester compound containing a nitro group, a fluorinated hydrocarbon compound containing a nitro group, and a fluorinated aromatic compound containing a nitro group.

3. The local high-concentration electrolyte with a bifunctional diluent added according to claim 1, wherein The lithium salt includes: any one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

4. The local high-concentration electrolyte added with a bifunctional diluent according to claim 1, wherein By adding a lithium salt, a locally high-concentration electrolyte solution is formed, with a concentration of 1.0 to 8.0 mol / L.

5. The local high-concentration electrolyte added with a bifunctional diluent according to claim 1, wherein The volume ratio of the organic solvent to the bifunctional diluent is 1:1 - 1:

10.

6. A method for preparing the locally high-concentration electrolyte according to any one of claims 1 to 5, characterized in that, Including the following steps: Mix an appropriate proportion of an organic solvent and a bifunctional diluent that can dissolve the lithium salt evenly, and add a lithium salt to form a locally high-concentration electrolyte solution suitable for a lithium metal battery.

7. A kind of local high-concentration electrolyte added with a bifunctional diluent as described in any one of claims 1 to 5, characterized in that, Applied to a lithium metal battery.

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