Electrochemical Zinc-Ion Intercalation Properties and Crystal Structures of ZnMo6S8 and Zn2Mo6S8 Chevrel Phases in Aqueous Electrolytes

The crystal structures and electrochemical properties of ZnxMo6S8 Chevrel phases (x = 1, 2) prepared via electrochemical Zn2+-ion intercalation into the Mo6S8 host material, in an aqueous electrolyte, were characterized. Mo6S8 [trigonal, R3, a = 9.1910(6) A, c = 10.8785(10) A, Z = 3] was first prepared via the chemical extraction of Cu ions from Cu2Mo6S8, which was synthesized via a solid-state reaction for 24 h at 1000 °C. The electrochemical zinc-ion insertion into Mo6S8 occurred stepwise, and two separate potential regions were depicted in the cyclic voltammogram (CV) and galvanostatic profile. ZnMo6S8 first formed from Mo6S8 in the higher-voltage region around 0.45–0.50 V in the CV, through a pseudo two-phase reaction. The inserted zinc ions occupied the interstitial sites in cavities surrounded by sulfur atoms (Zn1 sites). A significant number of the inserted zinc ions were trapped in these Zn1 sites, giving rise to the first-cycle irreversible capacity of ∼46 mAh g–1 out of the discharge capacity o...