Superior and Reversible Lithium Storage of SnO₂/Graphene Composites by Silicon Doping and Carbon Sealing

The poor cycle stability and reversibility seriously hinder the widespread application of SnO₂ materials as anodes for lithium-ion batteries (LIBs). A novel sandwich-architecture composite of Si-doped SnO₂ nanorods and reduced graphene oxide with carbon sealing (Si-SnO₂@G@C) is engineered and fabricated by a facile two-step hydrothermal process and subsequent annealing treatment, which exhibit not only extraordinary rate performance and ultrahigh reversible capacity but also excellent cycle stability and high electrical conductivity as the anode of LIBs. The Si-doped SnO₂ nanoparticles on the surface of graphene were firmly wrapped in the C-coating and formed a porous sandwich structure, which can efficiently prevent the Sn nanoparticles from aggregation and provide more extra space for accommodating the volume variations and more active sites for reactions. The carbon layer also blocks the direct contact of the SnO₂ nanorods with electrolyte and prevents the graphene nanosheets from the restacking. More importantly, the reversibility of lithiation/delithiation reactions can be remarkably improved by the doping silicon. The doped Si not only accelerates the diffusion of Li⁺ but also brings a significant increase in the specific capacity. As a consequence, the Si-SnO₂@G@C nanocomposite can maintain a high capacity of 654 mAh/g at 2 A/g even after 1200 cycles with negligible capacity loss and excellent reversibility with a Coulombic efficiency retention over 99%, which can be capable of the alternative to commercial graphite anodes. This work provides a new strategy for the reasonable design of advanced anode materials with superior and reversible lithium storage capacity.