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

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 (similar to 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 degrees 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 degrees 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. (C) 2015 Elsevier Ltd. All rights reserved.