Lithium ion storage mechanism exploration of copper selenite as anode materials for lithium-ion batteries

Copper-based materials as electrode materials have been attracted attention for their various merits such as nature abundance, low-cost, easy preparation, chemical stability, high theoretical specific capacity, and environmental friendliness. Metal selenite materials transforming into heterostructured metal oxide and selenide during the first cycle was considered as efficient anode materials for lithium-ion batteries. Herein, copper selenite microspheres were synthesized by applying facile spray pyrolysis process and for the first time, their conversion reaction mechanism with lithium-ions was systematically comprehended by various in-situ and ex-situ analysis. The selenization of spray pyrolysis product (Cu nitrate-polyvinylpyrrolidone composite) yielded cooper selenide (Cu_xSe)-C composite. Subsequently, partial oxidation process produced carbon-free hollow cooper selenite (Cu₂O(SeO₃)) microspheres. Through the various technical measurements, the following reversible reaction mechanism of Cu₂O(SeO₃) phase could be confirmed from the second cycle onward: CuO + CuSe + 4Li⁺ + 4e⁻ ↔ 2Cu + Li₂O + Li₂Se. Moreover, hollow Cu₂O(SeO₃) microspheres showed excellent cycling and rate performances. The discharge capacity of Cu₂O(SeO₃) for 500th cycle at a current density of 3.0 A g⁻¹ is 645 mA h g⁻¹ and exhibited a stable reversible capacity even at extremely high current density of 30 A g⁻¹.