Reaction Mechanism and Kinetic Analysis of the Solid-State Reaction to Synthesize Single-Phase Li<sub>2</sub>Co<sub>2</sub>O<sub>4</sub>Spinel
Kingo Ariyoshi, Kazuki Yuzawa, Yusuke Yamada
Abstract
Lithium cobalt oxide has two polymorphs that display different electrochemical properties despite their identical redox reactions: a high-temperature phase having a layered structure (LiCoO2; HT-LCO) and a low-temperature phase with a spinel framework (Li2Co2O4; LT-LCO). The synthetic conditions of the single-phase LT-LCO were determined by thermogravimetric analysis performed on the solid-state reaction of Li2CO3 and Co3O4. The results revealed that LCO synthesis was a second-order reaction with an activation energy of Ea = 150 kJ mol–1 and a pre-exponential factor of A = 9.2 × 107 s–1. XRD studies indicated that low-temperature synthesis below 350 °C is necessary to obtain the single-phase LT phase because the HT phase fraction increased with increasing synthesis temperature. Virtually single-phase LT-LCO obtained by calcining at 325 °C for 240 h exhibited zero-strain lithium insertion. These results contribute toward the establishment of a synthetic method for novel materials with reduced spinel structure.