Kelp-derived hard carbons as advanced anode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) have received much attention for scalable electrical energy storage because of the abundance and wide availability of sodium resources. However, it is still unclear whether carbon anodes can realize large-scale commercial application in SIBs as in lithium-ion batteries. Recently, great attention has been devoted to hard carbon which has been treated as a promising choice. Herein, we observe that the turbostratic lattice of kelp-derived hard carbon (KHC) is repeatedly expandable and shrinkable upon cycling, where the interlayer distance varies between 3.9 and 4.3 angstrom. Such interlayer spacing dilation is highly reversible, giving rise to high rate capability (a stable capacity of 96 mA h g(-1) at 1000 mA g(-1)) and excellent cycling performance (205 mA h g(-1) after 300 cycles at 200 mA g(-1)). Furthermore, kelp-derived hard carbon exhibits a good specific capacity at potentials higher than 0.05 V, which make it an essentially dendrite-free anode for SIBs.