Nontopotactic Reaction in Highly Reversible Sodium Storage of Ultrathin Co9Se8/rGO Hybrid Nanosheets

Transition metal chalcogenide with tailored nanosheet architectures with reduced graphene oxide (rGO) for high performance electrochemical sodium ion batteries (SIBs) are presented. Via one-step oriented attachment growth, a facile synthesis of Co9Se8 nanosheets anchored on rGO matrix nanocomposites is demonstrated. As effective anode materials of SIBs, Co9Se8/rGO nanocomposites can deliver a highly reversible capacity of 406 mA h g−1 at a current density of 50 mA g−1 with long cycle stability. It can also deliver a high specific capacity of 295 mA h g−1 at a high current density of 5 A g−1 indicating its high rate capability. Furthermore, ex situ transmission electron microscopy observations provide insight into the reaction path of nontopotactic conversion in the hybrid anode, revealing the highly reversible conversion directly between the hybrid Co9Se8/rGO and Co nanoparticles/Na2Se matrix during the sodiation/desodiation process. In addition, it is experimentally demonstrated that rGO plays significant roles in both controllable growth and electrochemical conversion processes, which can not only modulate the morphology of the product but also tune the sodium storage performance. The investigation on hybrid Co9Se8/rGO nanosheets as SIBs anode may shed light on designing new metal chalcogenide materials for high energy storage system.