Redox mediators for lithium sulfide cathodes in all-solid-state Li-S batteries: Recent advantages and future perspective

Abstract

All-solid-state Li-S batteries (ASSLSBs) are more attractive owing to their achievable superior energy density at a reasonable cost and the solid electrolyte (SE) utilization mitigating the widely recognized polysulfide shuttle problem. While the volume expansion (∼80%) that occurs during the initial transformation of sulfur to lithium sulfide induces mechanical stress, this can be avoided by using Li2S as a cathode, which also permits the anode-free cell design. However, the high oxidation energy barrier of Li2S cathode during the charging step limits its application in commercial devices. Redox mediators have been extensively used to reduce the oxidation energy barrier of Li2S to the sulfur conversation and boost the reversible kinetics of the conversion reaction. In this review, we have summarized the available redox mediators for Li2S cathode in ASSLSBs and its working mechanism. Moreover, we have proposed novel strategies and guidelines for designing effective redox mediators to boost the reversible conversion reaction. © 2024 Science Press