Synthesis Process of CoSeO₃ Microspheres for Unordinary Li-ion Storage Performances and Mechanism of Their Conversion Reaction with Li ions

Multicomponent materials with various double cations have been studied as anode materials of lithium-ion batteries (LIBs). Heterostructures formed by coupling different-bandgap nanocrystals enhance the surface reaction kinetics and facilitate charge transport because of the internal electric field at the heterointerface. Accordingly, metal selenites can be considered efficient anode materials of LIBs because they transform into metal selenide and oxide nanocrystals in the first cycle. However, few studies have reported synthesis of uniquely structured metal selenite microspheres. Herein, synthesis of high-porosity CoSeO₃ microspheres is reported. Through one-pot oxidation at 400 °C, CoSe_x–C microspheres formed by spray pyrolysis transform into CoSeO₃ microspheres showing unordinary cycling and rate performances. The conversion mechanism of CoSeO₃ microspheres for lithium-ion storage is systematically studied by cyclic voltammetry, in situ X-ray diffraction and electrochemical impedance spectroscopy, and transmission electron microscopy. The reversible reaction mechanism of the CoSeO₃ phase from the second cycle onward is evaluated as CoO + xSeO₂ + (1 − x)Se + 4(x + 1)Li⁺+ 4(x + 1)e⁻ ↔ Co + (2x + 1)Li₂O + Li₂Se. The CoSeO₃ microspheres show a high reversible capacity of 709 mA h g⁻¹ for the 1400th cycle at a current density of 3 A g⁻¹ and a high reversible capacity of 526 mA h g⁻¹ even at an extremely high current density of 30 A g⁻¹.