Conversion reaction mechanism of cobalt telluride-carbon composite microspheres synthesized by spray pyrolysis process for K-ion storage

Abstract

Owing to its similarity to lithium and sodium, potassium has been increasingly used to fabricate potassium ion batteries (KIBs). Following vigorous attempts to identify highly efficient electrode materials, transition metal chalcogenide materials have been identified as promising candidates. In this study, the performance of metal telluride (cobalt telluride) as new anode material for KIBs is investigated. Cobalt telluride-C (CoTe2-C) composite microspheres are synthesized using spray pyrolysis. Thereafter, a facile one-step post-treatment process results in the formation of pure-phase CoTe2-C composite microspheres with uniform composition, owing to the direct embedding of Te within the composite microspheres. Conversely, tellurization via application of H2Te gas results in inhomogeneous CoTe2-C composite microspheres, arising from crystal growth of CoTe2, owing to Ostwald ripening. The conversion reaction mechanism of CoTe2-C microspheres for K-ion storage has been examined using in-situ and ex-situ measurements and the reversible reaction mechanism from the second cycle of the reaction of CoTe2 with K ions, described by the reaction: 2Co + K5Te3 + K2Te ↔ 2CoTe + 2Te + 7 K+ + 7e−. Additionally, at a current density of 0.5 A g−1, the discharge capacity of the CoTe2-C composite was 189.5 mA h g−1 for the 100th cycle.