Abstract
Efficient Na ion intercalation/deintercalation in the semigraphitic lattice of a hard carbon derived from the walnut shell is demonstrated. High-temperature (1000 °C) pyrolysis of walnut shells under an inert atmosphere yields a hard carbon with a low surface area (59 m(2) g(-1)) and a large interplanar c axis separation of 0.39-0.36 nm as compared to 0.32 nm for graphite, suitable for Na ion intercalation/deintercalation. A stable reversible capacity of 257 mAh g(-1) is observed at a current density of 50 mA g(-1) for such nutshell-derived carbon (NDC) with an impressive rate performance. No loss of electrochemical performance is observed for high current cycling (100 mA g(-1) → 2 A g(-1) → 100 mA g(-1)). Additionally, the NDC shows remarkably stable electrochemical performance up to 300 charge-discharge cycles at 100 mA g(-1) with a minimal drop in capacity.