Designed hybrid nanostructure with catalytic effect: Beyond the theoretical capacity of SnO₂ anode material for lithium ion batteries

Transition metal cobalt (Co) nanoparticle was designed as catalyst to promote the conversion reaction of Sn to SnO₂ during the delithiation process which is deemed as an irreversible reaction. The designed nanocomposite, named as SnO₂/Co₃O₄/reduced-graphene-oxide (rGO), was synthesized by a simple two-step method composed of hydrothermal (1 st step) and solvothermal (2nd step) synthesis processes. Compared to the pristine SnO₂/rGO and SnO₂/Co₃O₄ electrodes, SnO₂/Co₃O₄/rGO nanocomposites exhibit significantly enhanced electrochemical performance as the anode material of lithium-ion batteries (LIBs). The SnO₂/Co₃O₄/rGO nanocomposites can deliver high specific capacities of 1038 and 712 mAh g^-1 at the current densities of 100 and 1000 mA g^-1, respectively. In addition, the SnO₂/Co₃O₄/rGO nanocomposites also exhibit 641 mAh g^-1 at a high current density of 1000 mA g^-1 after 900 cycles, indicating an ultra-long cycling stability under high current density. Through ex-situ TEM analysis, the excellent electrochemical performance was attributed to the catalytic effect of Co nanoparticles to promote the conversion of Sn to SnO₂ and the decomposition of Li₂O during the delithiation process. Based on the results, herein we propose a new method in employing the catalyst to increase the capacity of alloying-dealloying type anode material to beyond its theoretical value and enhance the electrochemical performance.