One-Step Hydrothermal Synthesis of SnO₂@Carbon Composites with Super Lithium Ions Storage Performances

Tin oxide (SnO₂) based anode materials for lithium ion batteries (LIBs) have drawn much attention for their high theoretical capacity and energy density, but suffer from a large volume change and resulting a rapid capacity fading during charging/discharging cycles. To optimize the status, herein, SnO₂/carbon composites are synthesized using SnCl₄ · 5H₂O and glucose with different mass ratio as raw materials via a simple one-step hydrothermal process, following calcination under Ar gas atmosphere. As comparison, pure SnO₂ is synthesized as the same as SnO₂/carbon composites without glucose and calcination in air. The electrochemical impedance spectroscopy (EIS) measurements were used to investigate the lithium ions storage behavior in pure SnO₂ and the SnO₂@carbon composites. The EIS results indicate that pure SnO₂ has much larger electronic transfer resistance and smaller diffusion coefficient of Li⁺ resulting worst electrochemical performances, while carbon can substantially enhance the electronic conductivity of the composites and resulting better cycle stability and rate capability of the composite anodes. Moreover, the stability and capacity of the composites are different from each other due to diverse carbon content, surface area and particle size, in which, SnO₂-24%C exhibits better lithium storage performances. The initial discharge/charge capacities are up to 1650 and 890 mAh g^-1 at the current density of 0.2 A g^-1, and the reversible capacity even still maintains at 800 mAh g^-1 after 60 cycles. The super electrochemical performances are attributed to that the proper content of carbon clusters as a support can buffer volume expansion of SnO₂ during cycling, enhance the electrode conductivity and accelerate the diffusion of Li⁺ ions in the composite. The results implying that the composite with proper carbon content has a wide application prospect for anode material of LIBs.