Wide-temperature-range electrolyte of lithium-sulfur battery as well as preparation method and application of wide-temperature-range electrolyte

Abstract

The invention provides a wide-temperature-range electrolyte of a lithium-sulfur battery as well as a preparation method and application of the wide-temperature-range electrolyte. The electrolyte comprises a lithium salt, a high-boiling-point low-freezing-point organic solvent and an additive. Wherein an organic solvent in the wide-temperature-range electrolyte system has an extremely wide liquid temperature range, does not generate obvious phase change at low temperature and high temperature, has good chemical stability, and does not excessively decompose at high temperature and high voltage; secondly, the selected lithium salt is not easy to decompose at a high temperature, and can provide high ionic conductivity at a low temperature; the additive has good film-forming property and can form stable CEI and SEI on a positive and negative electrode interface so as to improve the cycling stability of the lithium ion battery. The three components are mutually influenced in a battery system to generate a synergistic effect, and the wide temperature range performance of the lithium ion battery is jointly improved.

Description

Technical Field

[0001] The present invention belongs to the field of chemical power sources, and in particular relates to a wide-temperature-range electrolyte for lithium-sulfur batteries, a preparation method thereof, and applications thereof. Technical Background

[0002] Lithium-ion batteries, the dominant secondary battery type in the energy storage market, have been used in nearly every aspect of life over the past few decades, from handheld electronic devices to all-electric vehicles and even micro-smart grids. However, due to their limited energy density (400Wh / kg), lithium-ion batteries cannot meet the high energy storage demands of the future. Lithium-sulfur (Li-S) batteries, with their high energy density (2600Wh / kg), low cost, and environmental friendliness, have become a candidate for next-generation energy storage systems and have become a research hotspot in recent years.

[0003] However, the performance of lithium-ion batteries will be greatly degraded at high and low temperatures, making it impossible to work stably in extreme environments. When the temperature rises, the LiPF6 in the commercial electrolyte will decompose rapidly to produce hydrofluoric acid, which will cause corrosion of the internal structure of the battery and damage to the positive and negative electrode interface films. The harmful byproducts produced by the continuous decomposition of the electrolyte at the interface cannot form the SEI and CEI films that can effectively passivate the positive and negative electrode interfaces, causing the internal resistance to continue to increase, which in turn leads to rapid degradation of the battery capacity and even thermal runaway. When the battery works at low temperatures, the viscosity of the electrolyte increases sharply and the ionic conductivity decreases, resulting in Li + The transmission rate in the liquid phase becomes lower, and the electron transfer rate at the electrode-electrolyte interface also decreases sharply. Lithium will be deposited in large quantities at the interface to form lithium dendrites, which may cause the diaphragm to be punctured and the battery to short-circuit.

[0004] In this regard, this patent proposes a composition of a wide temperature range (-60°C) electrolyte for lithium-sulfur batteries. The organic solvent of the wide temperature range electrolyte system has an extremely wide liquid temperature range, does not undergo obvious phase change at low and high temperatures, and has good chemical stability and will not decompose excessively at high temperatures and high voltages. Secondly, the selected lithium salt should not be easily decomposed at high temperatures and can provide high ionic conductivity at low temperatures. The additive has good film-forming properties and can form stable CEI and SEI at the positive and negative electrode interfaces to improve the cycle stability of lithium-ion batteries. These three interact with each other in the battery system to produce a synergistic effect, jointly improving the wide temperature range performance of lithium-ion batteries. Summary of the Invention

[0005] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a wide-temperature range electrolyte for lithium-sulfur batteries and a preparation method and application thereof.

[0006] The present invention adopts the following technical solution: a wide-temperature-range electrolyte for lithium-sulfur batteries, where the wide temperature range is -60°C to [temperature value not provided in the original]; including: an organic solvent, an additive, and a lithium salt;

[0007] Among them, the organic solvent has a high boiling point and a low freezing point.

[0008] In a further embodiment, the organic solvent includes any one or at least two of 2-methyltetrahydropyran, 3-methyltetrahydropyran, dipropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,3-dimethoxy-2,2-difluoropropane, 2,5-dimethyltetrahydrofuran, cyclopentyl methyl ether (CPME), ethylene glycol bis(propionitrile) ether (DENE), triethylene glycol dimethyl ether (G3), and diethylene glycol dimethyl ether (DG).

[0009] In a further embodiment, the additive includes a film-forming additive (fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS)), a flame retardant additive (such as trimethyl phosphate (TMP), triethyl phosphate (TEP), propyl acetate (PA), methyl acetate (MA), methyl propionate (MP)), and a multifunctional additive ((N-trifluoromethanesulfonylimide trifluoromethanesulfonamide (NTSA), ethylene sulfate (SN), succinic anhydride (SA), thionyl chloride (SOCl2), tris(trimethylsilyl) phosphate) any one or at least two of them).

[0010] In a further embodiment, the lithium salt includes: any one or 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, the high boiling point and low freezing point are greater than 90°C.

[0012] In a further embodiment, the mass percentage content of the organic solvent in the solvent is 40 - 90 wt%; the mass percentage content of the additive is 0.1 - 10 wt%; the mass percentage content of the lithium salt is 1 - 45 wt%.

[0013] A preparation method for the wide-temperature-range electrolyte for lithium-sulfur batteries as described above includes the following steps: mixing an appropriate proportion of the organic solvent evenly, and adding the additive and the lithium salt.

[0014] The wide-temperature-range electrolyte for lithium-sulfur batteries as described above is applied to lithium-sulfur batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) The wide-temperature-range electrolyte in this patent can maintain good performance and stability within a wide temperature range (-60°C to 80°C). The selected organic solvent has an extremely wide liquid temperature range, does not undergo obvious phase changes at low and high temperatures, and has good chemical stability; the selected lithium salt should not be easily decomposed at high temperatures and can provide high ionic conductivity at low temperatures; the additive has good film-forming properties and can form stable CEI and SEI at the positive and negative electrode interfaces to improve the cycle stability of the lithium-ion battery.

[0017] (2) The composition method in this patent has the advantages of being easy to operate and convenient for large-scale use. Therefore, it is beneficial to the actual deployment of this strategy at the industrial level and helps the lithium-sulfur battery to achieve commercialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the discharge curve of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0020] Unless otherwise defined, all the technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical 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.

[0021] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0022] A wide-temperature-range electrolyte for a lithium-sulfur battery, the wide temperature range being -60°C to 80°C; comprising: an organic solvent, an additive, and a lithium salt;

[0023] Among them, the organic solvent has a high boiling point and a low freezing point.

[0024] In a further embodiment, the organic solvent includes any one or at least two of 2-methyltetrahydropyran, 3-methyltetrahydropyran, dipropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,3-dimethoxy-2,2-difluoropropane, 2,5-dimethyltetrahydrofuran, cyclopentyl methyl ether (CPME), ethylene glycol bis(propionitrile) ether (DENE), triethylene glycol dimethyl ether (G3), and diethylene glycol dimethyl ether (DG).

[0025] In a further embodiment, the additives include film-forming additives (fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS)), flame retardant additives (such as trimethyl phosphate (TMP), triethyl phosphate (TEP), propyl acetate (PA), methyl acetate (MA), methyl propionate (MP)), and multifunctional additives (any one or at least two of (N-trifluoromethanesulfonyl imide trifluoromethanesulfonamide (NTSA), vinyl sulfate (SN), succinic anhydride (SA), thionyl chloride (SOCl2), tris(trimethylsilyl) phosphate)).

[0026] In a further embodiment, the lithium salts include any one or 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).

[0027] In a further embodiment, the high boiling point and low freezing point are greater than 90 °C.

[0028] In a further embodiment, the mass percentage content of the organic solvent in the solvent is 40 - 90 wt%; the mass percentage content of the additive is 0.1 - 10 wt%; and the mass percentage content of the lithium salt is 1 - 45 wt%.

[0029] A method for preparing the wide-temperature-range electrolyte for a lithium-sulfur battery as described above includes the following steps: mixing appropriate proportions of organic solvents uniformly, and adding additives and lithium salts.

[0030] The wide-temperature-range electrolyte for a lithium-sulfur battery as described above is applied to a lithium-sulfur battery.

[0031] Example 1

[0032] In this embodiment, the composition of the electrolyte for a lithium-sulfur battery with a wide temperature range (-60 °C in the embodiment) includes the following steps: The organic solvents are most preferably bis(propionitrile)ether (DENE) and 2,5-dimethyltetrahydrofuran, with mass percentages of 30 wt% and 53 wt% respectively; the additives are fluoroethylene carbonate (FEC) and propyl acetate (PA), with mass percentages of 5 wt% and 5 wt% respectively; the lithium salts are dissolved in the organic solvents, and lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiODFB) have mass percentages of 3 wt% and 4 wt% respectively; after stirring evenly, it is used as the basic electrolyte. The electrolyte combination is prepared in a glove box, where the actual oxygen content in the glove box is <0.1 ppm and the moisture content is <0.1 ppm. This electrolyte has the functions of withstanding high voltage, high temperature and low temperature, can perform good electronic matching with the electrode material at the molecular level, form a stable passivation film, and reduce the occurrence of side reactions. At a current density of 0.1 C, at -50 °C, it has a specific capacity of 441.83 mAh / g, and after 100 cycles, it still maintains 82.9% of its capacity (366.28 mAh / g), showing excellent low-temperature stability.

[0033] Example 2

[0034] In this embodiment, the composition of the electrolyte for a lithium-sulfur battery with a wide temperature range (-60 °C in the embodiment) includes the following steps: The organic solvents are most preferably diglyme (DG) and 2-methyltetrahydropyran, with mass percentages of 35 wt% and 45 wt% respectively; the additives are trimethyl phosphate (TMP) and thionyl chloride (SOCl2), with mass percentages of 6 wt% and 4 wt% respectively; the lithium salts are dissolved in the organic solvents, and lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4) have mass percentages of 4 wt% and 6 wt% respectively; after stirring evenly, it is used as the basic electrolyte. The electrolyte combination is prepared in a glove box, where the actual oxygen content in the glove box is <0.1 ppm and the moisture content is <0.1 ppm. This electrolyte has the functions of withstanding high voltage, high temperature and low temperature, can perform good electronic matching with the electrode material at the molecular level, form a stable passivation film, and reduce the occurrence of side reactions. At a current density of 0.1 C, at 80 °C, it has a specific capacity of 945.6 mAh / g, and after 100 cycles, it still maintains 84% of its capacity (794.3 mAh / g), showing excellent high-temperature stability.

Claims

1. A wide-temperature-range electrolyte for a lithium-sulfur battery, characterized in that, The wide temperature range is -60. It is characterized in that it includes: organic solvents, additives and lithium salts; Among them, the organic solvent has a high boiling point and a low freezing point.

2. The wide-temperature-range electrolyte for a lithium-sulfur battery according to claim 1, wherein The organic solvent includes any one or at least two of 2-methyltetrahydropyran, 3-methyltetrahydropyran, dipropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,3-dimethoxy-2,2-difluoropropane, 2,5-dimethyltetrahydrofuran, cyclopentyl methyl ether (CPME), ethylene glycol bis(propionitrile) ether (DENE), triethylene glycol dimethyl ether (G3), and diethylene glycol dimethyl ether (DG).

3. The wide-temperature-range electrolyte for a lithium-sulfur battery according to claim 1, wherein The additives include film-forming additives (fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS)), flame retardant additives (such as trimethyl phosphate (TMP), triethyl phosphate (TEP), propyl acetate (PA), methyl acetate (MA), methyl propionate (MP)), and multifunctional additives (any one or at least two of (N-trifluoromethanesulfonylimide trifluoromethanesulfonamide (NTSA), vinyl sulfite (SN), succinic anhydride (SA), thionyl chloride (SOCl2), tris(trimethylsilyl) phosphate)).

4. The wide-temperature-range electrolyte for a lithium-sulfur battery according to claim 1, characterized in that, The lithium salts include: any one or 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).

5. The wide-temperature-range electrolyte for a lithium-sulfur battery according to claim 1, wherein The high boiling point and low freezing point are greater than 90.

6. The wide-temperature-range electrolyte for a lithium-sulfur battery according to claim 1, wherein The mass ratio content of the organic solvent in the solvent is 40-90 wt%; the mass ratio content of the additive is 0.1-10 wt%; the mass ratio content of the lithium salt is 1-45 wt%.

7. A preparation method for a wide-temperature-range electrolyte of a lithium-sulfur battery as described in any one of claims 1 to 6, characterized in that, It includes the following steps: Mix an appropriate proportion of organic solvents evenly, and add additives and lithium salts.

8. The wide-temperature-range electrolyte for lithium-sulfur batteries according to any one of claims 1 to 6, characterized in that It is applied to lithium-sulfur batteries.

Images