Policy recommendations of the electrification of the vehicles have been issued all over the world in these years. Energy density is one of the important keywords for realizing such policies. Several novel systems have been investigated, and Li-S system is quite promising among them. Leading research organizations and start-up companies have manufactured the trial prototype Li-S cell with energy density of 300-400 Wh/kg. And Li-S batteries application is not limited to vehicles.

We have tried to innovate the conventional Li-S battery using metal polysulfides like a-TiS₄^1,2, Li₈FeS₅ ^{3, 4}, VS₄ ⁵, and so on in RISING2 (Research and Development Initiative for Scientific Innovation of New Generation Batteries 2) project. Sulfur is connected to metal atom and dissolution of Li polysulfides into the electrolyte was greatly suppressed. Quite recently 8 Ah cell was constructed and energy density of more than 310 Wh/kg was confirmed. Project target is to confirm 500 Wh/kg by prototype cell for innovative batteries in the end of FY2020. In the presentation, RISING2 activity, state of the art of the Li-S and our recent progress will be introduced.

Acknowledgement

This work was financially supported by RISING2 project by NEDO and METI.

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