Electrochemical reaction mechanism of amorphous iron selenite with ultrahigh rate and excellent cyclic stability performance as new anode material for lithium-ion batteries

Metal selenite materials have unique advantages from forming metal oxide and selenide heterostructure nanocrystals, which assist in accelerating electron and lithium-ion transportation and providing more active sites via interfacial coupling, during the first cycle. In this study, synthesis of amorphous iron selenite materials derived via oxidation at a low temperature of 250 °C of crystalline iron selenide was firstly researched in detail, and their composite (FeSeO–C–CNT) with carbon materials was applied as an anode material for lithium-ion batteries. The reversible reaction mechanism of iron selenite with Li ions is described by the reaction: Fe₂O₃ + FeSe₂ + xSeO₂ + (1 − x)Se + (4x + 12)Li⁺ + (4x + 12)e⁻ ↔ 3Fe + (2x + 3)Li₂O + 3Li₂Se. FeSeO–C–CNT composite electrode showed high reversible capacities of 617 mA h g⁻¹ for the 1800th cycle even at an extremely high current density of 30 A g⁻¹, which surprisingly indicated that FeSeO–C–CNT is enabled to fully charge in a very short time of 72 s. This study demonstrated that amorphous iron selenite materials could be excellent candidates for new anode compositions with high capacities and fast electrochemical kinetics properties.