Abstract
AbstractThe 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.
Highlights
The limited Na-storage capacity of graphite anodes for sodiumion batteries (~ 110 mAh g 1) is significantly enhanced by the incorporation of nanosized Sn (17 wt%)
An important challenge faced by SIBs is applicable to sodium-ion hybrid capacitors (SIHCs) as well, i. e., finding a suitable anode material that provides high capacities at very high rates over many cycles
This process is done to facilitate the interaction of graphite with the Sn-precursor
Summary
The synthesis of SntGraphite is sketched in Scheme 1 and described in the experimental section. Graphite was mildly oxidized by thermal treatment at 630 °C in air atmosphere. The typical graphite reflections are found in all samples indicating that the major fraction of graphite maintains its graphitic structure during the synthesis This result means that the turbostratic disorder observed by TEM is more located at the particle surface, i. E. the thermal activation leads to oxidation of the graphite surface. This is in line with N2 physisorption measurements which show only a moderate increase in Brunauer-Emmett-Teller (BET) surface area for tGraphite (~ 4 m2 g 1) compared to graphite (~ 1 m2 g 1), see Figure S3. The total Sn content in SntGraphite was deterBatteries & Supercaps 2020, 3, 1 – 11 www.batteries-supercaps.org mined as 17 wt% using TGA analysis (Figure S4) and the BET specific surface area of SntGraphite was ~ 3 m2 g 1 (Figure S3)
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