In situ X-ray diffraction investigation of CoSe2 anode for Na-ion storage: Effect of cut-off voltage on cycling stability

Owing to their high specific capacity, transition metal chalcogenides (TMCs) based materials attract enormous attentions for energy storage, yet the performance decay observed in TMCs anodes are strongly depended on the host material and working conditions. Here we report CoSe2 nanorods as a promising alternative for sodium-ion batteries (SIBs), which are fabricated by a facile hydrothermal strategy. At upper cut-off voltage of 0.4 V, the as-prepared sample can demonstrate improved sodiation capacity, rate capability, and cycling stability (a high capacity of 386 mAh g(-1) at 5 A g(-1) even after 2000 cycles). In situ XRD and ex situ TEM measurements are utilized to investigate phase transition behavior of CoSe2 nanorods in the initial 9 sodiation/desodiation cycles. The high electrochemical reversibility of CoSe2 nanorods within the potential window of 0.4-3.0 V is ascribed to that the deep conversion reaction below 0.4 V is effectively avoided, thus the volume expansion and pulverization of CoSe2 nanorods are efficiently suppressed. It convinces that applying suitable and optimal cut-off voltage is a useful approach to regulate the reactions progress for TMCs anode, improving their cycling and structure stability. (C) 2017 Elsevier Ltd. All rights reserved.