Nano-Sn embedded in expanded graphite as anode for lithium ion batteries with improved low temperature electrochemical performance

Highlights: • Nano-Sn embedded in interlayers of expanded graphite is fabricated. • The graphene/nano-Sn/graphene stacked structure promotes cycling stability of Sn. • The Sn/EG shows improved low temperature electrochemical performance. • Chemical diffusion coefficients of the Sn/EG are obtained by GITT. • The Sn/EG exhibits faster Li-ion intercalation kinetics than graphite. - Abstract: Metallic tin (Sn) used as anode material for lithium ion batteries has long been proposed, but its low temperature electrochemical performance has been rarely concerned. Here, a Sn/C composite with nano-Sn embedded in expanded graphite (Sn/EG) is synthesized. The nano-Sn particles (∼30 nm) are uniformly distributed in the interlayers of expanded graphite forming a tightly stacked layered structure. The electrochemical performance of the Sn/EG, particularly at low temperature, is carefully investigated compared with graphite. At -20 °C, the Sn/EG shows capacities of 200 mAh g⁻¹ at 0.1C and 130 mAh g⁻¹ at 0.2C, which is much superior to graphite (<10 mAh g⁻¹). EIS measurements suggest that the charge transfer impedance of the Sn/EG increases less rapidly than graphite with decreasing temperatures, which is responsible for the improved low temperature electrochemical performance. The Li-ion chemical diffusion coefficients of the Sn/EG obtained by GITT are an order of magnitude higher at room temperature than that at -20 °C. Furthermore, the Sn/EG exhibits faster Li-ion intercalation kinetics than graphite in the asymmetric charge/discharge measurements, which shows great promise for the application in electric vehicles charged at low temperature.