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.