Direct visualization of complex mechanisms in lithium tellurium batteries.

Many studies on lithium-sulfur batteries have been conducted with respect to reaction mechanisms and performance improvements. Despite the high electronic conductivity and volumetric capacity of tellurium, research on lithium-tellurium batteries remains relatively limited. Herein, we shed light on the unique reaction mechanism of lithium-tellurium batteries: a solid-liquid-solid-liquid-solid pathway mediated by the solid Li2Te6 intermediate, as revealed by operando analyses, in contrast to the simpler solid-liquid-solid mechanism of lithium-sulfur and lithium-selenium batteries. Moreover, we demonstrate that Li2Te6 morphology and size are path-dependent: long-chain lithium polytellurides during discharge yield small cubic-like Li2Te6 that dissolve completely, whereas short-chain lithium polytellurides during charge form larger Li2Te6 that do not fully dissolve and enable subsequent tellurium growth. Surprisingly, path-dependency causes residual Li2Te6 to persist in subsequent cycles, thereby degrading battery performance. To address this limitation, we propose tailored charge protocols to control Li2Te6 crystal growth, guided by the reaction mechanisms revealed in this study.