Insights into evolution processes and degradation mechanisms of anion-tunable interfacial stability in all-solid-state lithium-sulfur batteries

Abstract Among the all-solid-state lithium metal batteries, it is remarkably of importance to realize the superior compatibility and stability of electrode/electrolyte solid-solid interface. A direct viewer of microevolution will induce an in-depth fundamental insight into the reaction mechanisms and interfacial regulations during the cycling operation. Herein, using in situ electrochemical atomic force microscopy combined with optical microscope imaging techniques, we present a dynamic observation of interfacial processes and structural evolution of solid-state electrolyte mediated by lithium salts in a working all-solid-state lithium-sulfur battery (ASSLSB) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl) imide (LiFSI) and LiTFSI-LiFSI binary-salts. The in-situ monitoring shows that the binary-anion polymer-rich composite electrolytes could well achieve self-regulation in the interfacial compatibility and the side reaction of dissolved polysulfides in enabling ASSLSBs. Moreover, it indicates the anion dependence of ion transportation, interphasial wettability and labile decomposition of electrolytes for ASSLS systems, which determines the dynamic evolution and systematically proposes the corresponding interfacial degradation mechanisms. The in situ visualization provides a direct understanding of ASSLS electrochemical reaction mechanisms and interphasial properties, which will efficiently guide one to explore strategies to develop the optimum all-solid-state systems.