Kinetically Enhanced Reaction Pathway to Form Highly Crystalline Layered LiCoO2 at Low Temperatures Below 300 °C.

Abstract

Layered LiCoO2 is usually synthesized after a prolonged sintering process at high temperatures (≥800 °C) for 10-20 h. This study developed a "hydroflux process" to obtain highly crystalline and layered LiCoO2 at a low temperature of 300 °C within 30 min. Molten mixed hydroxide-containing water molecules significantly accelerated the formation of LiCoO2, which showed a highly reversible capacity of 120 mAh g-1 without postannealing. The reaction mechanism study showed fast growth of LiCoO2 crystals, suggesting that the excess molten hydroxides containing water dissolve the cobalt species of HCoO2-. Consequently, the accelerated LiCoO2 formation suppresses the competing reaction of Co3O4 formation, leading to spinel LiCoO2 formation at low temperatures. Excess water in the starting materials further accelerated the crystal growth of LiCoO2, forming large particles (>1 μm). Moreover, the layered LiCoO2 began to form at 150 °C. This study is the first experimental demonstration that proves the thermodynamic stability of layered LiCoO2 at low temperatures (150-300 °C) under ambient pressure. This novel process offers significant energy savings in the production process of LiCoO2 and other ceramics materials.