Exploring the effects of temperature-driven phase transition on supercapacitive performance of cobalt diselenide

Recently, doping-induced phase transition of cobalt diselenide have been explored extensively for applications in the electrocatalysis, lithium-ion batteries, and sodium-ion batteries, however, there are very few works on understanding of the relationship between phase transition and supercapacitor performance up to now. Herein, we report a temperature-driven phase transformation strategy to synthesize metastable orthorhombic o-CoSe2 and stable c-CoSe2 by the thermal induced in-situ reaction of cobalt precursor and selenium powder. The o-CoSe2 shows a higher specific capacity (244.2 mAh g−1 at 1.0 A g−1), while c-CoSe2 shows a better cycling stability (103.0% capacity retention after 2000 cycles at 10.0 A g−1). Combing density functional theory (DFT) calculations and experimental results, we explain the unique effects of phase structure on supercapacitive performance. Furthermore, a hybrid supercapacitor of o-CoSe2//AC delivers a high energy density of 79.1 Wh kg−1 at a power density of 850.0 W kg−1, which suggests the prospects of practical application as energy storage device. Our work provides useful guidance for the design of cobalt diselenide based materials for supercapacitors.