Synthesis of cambered nano-walls of SnO₂/rGO composites using a recyclable melamine template for lithium-ion batteries

Graphene and graphene/metal oxide composite materials have attracted considerable interest for use as energy materials due to their excellent electrochemical performances. Here, we propose using melamine as a template for the synthesis of cambered nano-walls of SnO₂/rGO materials. Melamine powder can effectively absorb SnO₂/GO from the solution to form a core-shell structure of melamine@SnO₂/GO. After thermal reduction of GO at 200 °C to form the melamine@SnO₂/rGO, melamine was dissolved in hot water at 80 °C, leaving behind the cambered SnO₂/rGO nano-walls. Melamine is recyclable since it precipitates when its solution cools to room temperature. The thickness of the SnO₂/rGO nano-walls can be easily controlled by adjusting the mass ratio of melamine to SnO₂/GO. When the mass ratio was set to ten, cambered walls of SnO₂/rGO with a thickness of about 100-200 nm were achieved. The resulting SnO₂/rGO delivered an initial reversible capacity of 998 mA h g^-1 at a current density of 100 mA g^-1 and a capacity of 855 mA h g^-1 after 100 discharge-charge cycles in a potential range between 0.02 and 3.0 V vs. Li/Li⁺. It also showed good rate performance with a reversible capacity of 460 mA h g^-1 at 1 A g^-1. These high capacities can be linked to the special cambered nano-walls which ensure fast solid diffusion in addition to providing an effective liquid-channel and buffer-volume in the electrode. The proposed synthesis method is easily scalable and should be applicable to many other graphene based energy materials.