Reversible Lithium Intercalation into the Three‐Dimensional Cluster Network Structure of Ta₆Cl₁₅

Abstract

Abstract A crystalline powder of Ta 6 Cl 15 was synthesized through solid state reaction of Ta powder, and TaCl 5 at 700 °C. The structure contains [Ta 6 Cl 12 ] 3+ clusters which are three‐dimensionally interconnected by Cl bridges, leaving cavities which are shown to be suitable for lithium insertion. Reversible lithium intercalation into Ta 6 Cl 15 involves 1 mol of lithium per formula unit under equilibrium conditions, when cells are discharged between 3 and 1.8 V, leading to the upper composition LiTa 6 Cl 15 . Although capacity values within this reversible voltage range are small (ca. 25 Ah·kg −1 ), the cycle life of such Li/Ta 6 Cl 15 cells is excellent, and the initial capacity value is maintained over 1500 cycles. On the other hand, a maximum of 15 moles of lithium can be reacted with one mole Ta 6 Cl 15 when lithium cells were deep‐discharged. This process is likely due to the complete and irreversible reduction of the parent by lithium.