Schemes of new solution treatment technology for sulfide SEs. Credit: Toyohashi University of Technology

Research group in the doctoral program of the Department of Electrical and Electronic Information Engineering of the University of Toyohashi, which includes doctoral student Hirotada Gama and specially appointed associate professor Jin Nishida, specially appointed associate professor Atsushi Nagai, associate professor Kazuhira Hishimano, professor of technology7P3S11 solid electrolytes for solid lithium-ion secondary batteries.

This method involves adding an excessive amount of sulfur (S) along with Li2C and P2S5Lee’s source materials7P3S11, to a solvent containing a mixture of acetonitrile (ACN), tetrahydrofuran (THF) and a small amount of ethanol (EtOH). It helped cut back reaction time from 24 hours and more to just two minutes. The final product obtained by this method is high purity lithium7P3S11 without the impurity phase, which showed a high ionic conductivity of 1.2 mSm see-1 at 25 ° C. These results allow us to produce large quantities sulfide solid electrolytes for all-solid state batteries at a low price. The results of the study were published online Advanced research in energy and sustainable development April 28, 2022


It is expected that solid state batteries will be the next generation of batteries for electric vehicles (EV), because they are very safe and allow you to move to high energy density and high power output. Sulfide solid electrolytes, which exhibit good ionic conductivity and ductility, are being actively developed for use in fully solid-state EV batteries. However, at the level of commercialization, no large-scale technology for the production of sulfide solid electrolytes has been created, as sulfide solid electrolytes are unstable in the atmosphere and the process of their synthesis and processing requires atmospheric control. For this reason, there is an urgent need to develop liquid-phase technology for the production of sulfide solid electrolytes, which provides low cost and high scalability.

Lee7P3S11 solid electrolytes exhibit high ionic conductivity and are therefore one of the candidates for solid electrolytes for fully solid state batteries. Liquid-phase synthesis of Li7P3S11 usually occurs in solvent acetonitrile reaction (ACN) through precursors, including insoluble compounds. Conventional reaction processes, such as this one, are time consuming as they go through a kinetically unfavorable reaction from an insoluble starting material to an insoluble intermediate. What is worse, it is possible that the insoluble intermediate creates unevenness through the complex phase, leading to increased costs for large-scale production.

Against this background, the research team worked on the development of technology for liquid-phase production of high-ionic Li7P3S11 solid electrolytes through homogeneous solutions of precursors. It has been shown that a newly developed method allows to obtain a homogeneous solution of the precursor containing soluble lithium polysulfide (Li2Sx) in just two minutes, adding Li2C and P2S5Lee’s source materials7P3S11, and an excessive amount of S to a solvent containing a mixture of ACN, THF and a small amount of EtOH. The key to rapid synthesis in this method is the formation of lithium polysulfide through the addition of a small amount of EtOH or an excessive amount of S.

To determine the mechanism of the reaction in this method, ultraviolet (UV-Vis) spectroscopy was used to study the chemical stability of Li2Sx with and without EtOH. The study found that the presence of EtOH made Li2Sx more chemically stable. Therefore, the reaction in this method will take the following steps. First, lithium ions are strongly coordinated with EtOH, a highly polar solvent. Further, shielding polysulfide ions from lithium ions stabilizes highly reactive S3radical anions, which are a type of polysulfide. Generated C3 attacks P2S5, violation of cell design P2S5 and elicits a reaction to progress. The reaction produces lithium thiophosphate, which is soluble in a mixed solvent containing ACN and THF solvents. This may have helped to obtain homogeneous solutions of the precursors very quickly. The final product, Li7P3S11could be cooked in two hours without the need for ball crushing or high energy processing during the reaction.

Ionic conductivity Li7P3S11 obtained by this method was 1.2 ms see-1 at 25 ° C, higher than Li7P3S11 synthesized using the usual method of liquid-phase synthesis (0.8 mSm see-1) or ball milling (1.0 ms cm)-1). The method offers a new pathway for the synthesis of sulfide solid electrolyte and achieves large-scale production technology with low cost.

Prospects for the future

The research team believes that low-cost technologies for large-scale production of sulfide solid electrolytes for fully solid-state batteries proposed in this study may be important in the commercialization of EVs equipped with fully solid-state batteries. The study focused on Lee7P3S11 for use as a solid sulfide electrolyte. We also want to apply this technology to the synthesis of sulfide solid electrolytes other than Li7P3S11.

Influence of solvent on liquid-phase synthesis of lithium solid electrolytes

Additional information:
Hirotada Gamo et al., Treatment of solutions with dynamic sulfide radical anions for sulfide solid electrolytes, Advanced research in energy and sustainable development (2022). DOI: 10.1002 / aesr.202200019

Citation: The development of a new large-scale technology for the production of sulfide solid electrolytes (2022, May 13) was obtained on May 13, 2022 from html

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