Tin-Containing Graphite for Sodium-Ion Batteries and Hybrid Capacitors

Abstract

The limited Na-storage capacity of graphite anodes for sodium-ion batteries (∼110 mAh g−1) is significantly enhanced by the incorporation of nanosized Sn (17 wt%). The composite (SntGraphite), prepared by simple annealing of graphite with SnCl2, shows a specific capacity of 223 mAh g−1 (at 50 mA g−1) combined with excellent cycle life (i. e., 96 % of capacity retention after 2,200 cycles at 1 A g−1) and initial Coulomb efficiency (90 %). The combined storage of sodium in graphite (by solvent co-intercalation) and Sn (by alloy formation) is followed by in situ X-ray diffraction and in situ electrochemical dilatometry (ECD). While the additional tin almost doubles the electrode capacity, its contribution to the electrode expansion (∼3 %) is surprisingly small. The use of SntGraphite as anode for sodium-ion hybrid capacitors with activated carbon as cathode provides a maximum energy and power density of ∼93 Wh kg−1 and 7.8 kW kg−1, with a capacity retention of ∼80 % after 8,000 cycles.