Dehydration Pathway of CoF2·4H2O Revisited by Integrated Ex Situ and In Situ Calorimetric and Structural Studies

Cobalt (II) fluoride (α-CoF2) has potential for application as a high performance electrode material in lithium ion batteries. α-CoF2 is synthesized by the thermal heat treatment of CoF2·4H2O, commonly synthesized in an aqueous environment. There exists disagreement in the literature upon the mechanism, intermediate hydration states, and temperatures of reaction. Here, we resolve this discontinuity by using integrated structural, thermogravimetric, and calorimetric analyses to elucidate the dehydration pathway of CoF2·4H2O in both ex situ and in situ experimental conditions. Specifically, the decomposition of CoF2·4H2O to α-CoF2 has been investigated using isothermal thermogravimetry (ex situ TG), thermogravimetry (TG) – differential scanning calorimetry (DSC), kinetic analysis, and ex situ and in situ X-ray diffraction (XRD). We deduce that in two irreversible steps CoF2·4H2O completely decomposes to α-CoF2, with an amorphous intermediary phase of CoF2·0.5H2O. Under DSC condition with a heating rate of 1...