Hierarchical porous hard carbon derived from rice husks for high-performance sodium ion storage

Hard carbon is one of the most promising anodic materials for sodium ion batteries (SIBs) because of its low charge/discharge voltage platform, high specific surface area and higher layer spacing. However, the disadvantages of its unsatisfied sodium storage capacity and high cost owing to low carbonization yield of precursors frustrate its practical use. In this paper, we have developed a hierarchical porous hard carbon derived from rice husks (HCRH) synthesized via NaOH solution impregnation method combined with reflux and carbonization at different temperature. This kind of hard carbon kept the natural porous structure of rice husk, and the rich porous structure increased the active site of Na+, shortened the diffusion distance of Na+, and promoted the transport of electrolyte. As an anode for SIBs, the HCRH carbonization at 1200 degrees C (HCRH-1200) with a suitable graphite layer spacing (0.382 nm)delivered the highest capacity of 328.4 mAh g-1 after 100 cycles at 25 mA g- 1. This study could provide a simple method to prepare high performance anode materials for sodium ion batteries using biomass rice husk as carbon source, and this design strategy could be extended to other biomass-based carbon materials.