Multi-electron redox in alkali-rich sulfides

Abstract

Multi-electron cathode materials for Li-ion batteries bypass the restrictions imposed by conventional intercalation chemistries limited to 1 e- for each transition metal. Li-rich phases like the Li_2MO_3 phases studied by Goodenough and later Tarascon support oxidn. of >1 e- per transition metal, bypassing the paradigm imposed by conventional intercalation chem. In the oxide phases, the oxidn. profile changes significantly from the first to second cycle suggesting issues with reversibility. In an effort to develop structure-property relationships assocd. with multi-electron redox, we have prepd. structurally analogous alkali-rich sulfide phases. The sulfides phases benefit from a lower voltage window thereby eliminating detrimental electrolyte decompn. that obfuscates the electrochem. Sulfides also allow us to probe the behavior of technol. relevant 3d transition metals. We will discuss the redox mechanisms assocd. with the sulfide phases from a structural point of view and the differences in reversibility compared to the oxides.