Hard carbon derived from hazelnut shell with facile HCl treatment as high-initial-coulombic-efficiency anode for sodium ion batteries

Hard carbon is an extremely promising anode material for Na-ion batteries owing to its low cost and low operating potential plateau. However, the practical use of hard carbon materials in sodium-ion batteries (SIBs) is greatly constrained by their low initial coulombic efficiency (ICE). Biomass as carbon sources are a good choice due to the abundance of resources and natural microstructure. Regrettably, biomass contains many impurities that lower its electrochemical performance. Here, by facile synthesis methods, we prepare a hard carbon with a high reversible capacity of 342 mA h g −1 and a high ICE of 91%. The hard carbon is obtained by carbonizing a low-cost biomass hazelnut shell under hydrochloric acid treatment. Hydrochloric acid treatment removes impurities and change microstructure such as interlayer spacing and active sites. The results reveal that the active site and interlayer spacing of the hard carbon material was raised with hydrochloric acid treatment. Therefore, the reversible capacity of hard carbon was greatly improved by the hydrochloric acid treatment.