Recently, researchers from Hyundai Motor Company found that sulfone based electrolyte can effectively improve the capacity and reversible capacity retention rate of lithium sulfur battery. At the 2014 SAE World Congress, Hyundai Motor Company reported the above new findings in detail. Compared with ordinary electrolytes, the capacity of lithium sulfur batteries can be effectively improved by using sulfone based electrolytes, with a capacity increase of 52.1% to 715 mAh/g; The reversible capacity retention rate increased by 63.1% to 72.6%.

As a new material battery with energy density exceeding that of lithium ion battery, lithium sulfur battery has larger battery capacity, and the pure electric range of electric vehicles equipped with the battery will also be longer. The theoretical energy density of lithium sulfur battery system reaches 2600 watt hours/kg, but its low reversible capacity retention rate is a well-known problem. At the same time, lithium sulfur batteries also have problems such as polysulfide compounds (pS) dissolved in electrolyte and solid lithium sulfide and other insoluble precipitates on the cathode during discharge.

Shin et al., a researcher of Hyundai Motor Corporation, said that the reaction mechanism of lithium sulfur battery is that the cathode metal lithium loses electrons and becomes lithium ions during discharge, and the positive sulfur reacts with lithium ions and electrons to generate polysulfides (polysulfide pS is a compound containing polysulfide ions, wherein the specific reaction process is S8→ Li2S8→ Li2S6→ Li2S4→ Li2S). The potential difference between the positive and negative electrode reactions is the discharge voltage supplied by the lithium sulfur battery. Under the application of applied voltage, the positive and negative electrode reactions of lithium sulfur battery go in reverse, namely, the charging process, in which a reversible reaction occurs. In the reaction process of polysulfide, Li2S6 and Li2S4 can be dissolved in electrolyte. Polysulfides play an important role in improving the sulfur utilization rate of lithium sulfur battery and the reversible cycle utilization rate of battery.

Because of its good polysulfide solubility and high chemical stability, ether type solvent is considered as the best electrolyte choice for lithium sulfur batteries. In addition, dissolved polysulfides will cause redox reaction, which will reduce the coulomb efficiency of the battery, shorten the reversible cycle retention rate, and lead to self discharge. Therefore, the important purpose of this research and development work is to develop a new electrolyte to reduce the redox reaction and improve the reversible cycle retention rate of the battery.https://www.nxbtx.com/other_im/

In the research process of Hyundai Motor Company, the researchers used five groups of monobasic ether electrolytes (DME, DEGDME, Triglyme, TEGDME and DIOX) One group of binary ether electrolytes (TEGDME and dioxane DIOX mixture) and three groups of ternary ether electrolytes (TEGDME: dioxane DIOX: sulfolane mixed electrolyte with the mixing ratio of 1:1:1, 1:1:2 and 1:1:3 respectively) were compared.

The lithium sulfur battery in the experiment conducted by researchers of Hyundai Motor Company adopts sulfur cathode and lithium metal foil anode, and polyethylene diaphragm is used between the two electrodes. The electrochemical experiment of lithium sulfur battery was carried out at room temperature of 20 ℃, and the working voltage was controlled between 1.5 V and 2.65 V.

In the experiment of monoether electrolyte, DME electrolyte system has the highest energy density, reaching 878 mAh/g; The energy density of diethylene glycol dimethyl ether (DEGDME) electrolyte system was the second, reaching 857 mAh/g. However, the battery capacity of DME electrolyte system declined obviously after the sixth working cycle; However, in the diethylene glycol dimethyl ether DEGDME electrolyte system, after the second working cycle, the battery capacity decreased significantly. In the first working cycle, the energy density of dioxane DIOX electrolyte system reached 1040 mAh/g, while in the 12th working cycle, the energy density rapidly decreased to 640 mAh/g. The dioxane DIOX electrolyte system has a very high initial energy density. However, after the 12th working cycle, its energy density also shows a very obvious battery capacity degradation. The initial energy density of TEGDME electrolyte system was low, reaching only 200 mAh/g, but there was no obvious battery capacity degradation in its subsequent working cycle.

In the experiment of binary ether electrolyte, the experimenter obtained the binary ether electrolyte by mixing triethylene glycol dimethyl ether TEGDME and dioxane DIOX in 1:1 ratio. The purpose of this experiment is to comprehensively utilize the good reversible cycle retention rate of TEGDME and the high energy density of dioxane DIOX. The experiment shows that the initial energy density of the binary ether electrolyte system reaches 1057 mAh/g, and after 20 working cycles, the energy density is 470 mAh/g. Compared with the monobasic ether electrolyte, the binary ether electrolyte has a good reversible cycle retention rate. However, after the first working cycle, the binary ether electrolyte system still has obvious battery capacity degradation. At the same time, after 20 working cycles, the reversible cycle retention rate of the binary ether electrolyte system is low, only 44.5%.

In the experiment of binary ether electrolyte, the experimenter also added a glass membrane changing filter between the two electrodes of the lithium sulfur battery, which aims to suppress the high impedance around the electrode of the lithium sulfur battery. Glass membrane changing filter can attract electrolyte, so the possibility of electrolyte shortage around the electrode can be effectively reduced by adding glass membrane changing filter. By using the glass membrane exchange filter, the initial energy density of the binary ether electrolyte system has been reduced, while the retention rate of the reversible cycle has been improved. After 20 working cycles, the energy density can reach 605 mAh/g.