Investigation of Ca Insertion into α-MoO₃ Nanoparticles for High Capacity Ca-Ion Cathodes

Calcium-ion batteries (CIBs) are a promising alternative to lithium-ion batteries (LIBs) due to the low redox potential of calcium metal and high abundance of calcium compounds. Due to its layered structure, α-MoO₃ is regarded as a promising cathode host lattice. While studies have reported that α-MoO₃ can reversibly intercalate Ca ions, limited electrochemical activity has been noted, and its reaction mechanism remains unclear. Here, we re-examine Ca insertion into α-MoO₃ nanoparticles with a goal to improve reaction kinetics and clarify the storage mechanism. The α-MoO₃ electrodes demonstrated a specific capacity of 165 mA h g^-1 centered near 2.7 V vs Ca²⁺/Ca, stable long-term cycling, and good rate performance at room temperature. This work demonstrates that, under the correct conditions, layered oxides can be a promising host material for CIBs and renews prospects for CIBs.