Revealing the Electrochemistry of Solid-State Li-SeS 2 Battery via In-Situ Transmission Electron Microscopy.

Se x S y is considered as a promising cathode material as it can deliver higher energy density than selenium (Se) and offer improved conductivity and enhanced reaction kinetics compared with S. However, the electrochemistry of the Li-SeS 2 all-solid-state battery (ASSB) has not been well understood to date. Herein the electrochemistry of Li-SeS 2 battery was revealed by in-situ transmission electron microscopy. The charge products were phase-separated Se and S, rather than the widely believed SeS 2 . Among the various Se x S y cathodes, SeS 2 achieved the best electrochemical performance. The Li-SeS 2 ASSB delivered a high reversible capacity of 1052 mAh g -1 at 1 A g -1 over 350 cycles, and a high areal capacity of 4 mAh cm -2 was also achieved with a high cathode mass loading of 7.6 mg cm -2 . These results represent the best performance achieved to date in the Li-SeS 2 ASSB and brings us one step closer toward its practical applications.