Surface-driven sodium ion energy storage in nanocellular carbon foams.

Sodium ion (Na(+)) batteries have attracted increased attention for energy storage due to the natural abundance of sodium, but their development is hindered by poor intercalation property of Na(+) in electrodes. This paper reports a detailed study of high capacity, high rate sodium ion energy storage in functionalized high-surface-area nanocellular carbon foams (NCCF). The energy storage mechanism is surface-driven reactions between Na(+) and oxygen-containing functional groups on the surface of NCCF. The surface reaction, rather than a Na(+) bulk intercalation reaction, leads to high rate performance and cycling stability due to the enhanced reaction kinetics and the absence of electrode structure change. The NCCF makes more surface area and surface functional groups available for the Na(+) reaction. It delivers 152 mAh/g capacity at the rate of 0.1 A/g and a capacity retention of 90% for over 1600 cycles.