Sustainable Balsa wood-derived high-rate hard carbon anodes for sodium-ion hybrid capacitors

Biomass -derived hard carbons have broad prospects toward commercialized sodium -ion batteries because of their advantages of low cost, renewability, and the diversity of precursors. Although hard carbon materials have advantages such as considerable specific capacity and good stability, the application of hard carbon materials in sodium -ion hybrid capacitors (SIHCs) is still limited by their low -rate capability. In this work, a direct carbonization method is used to prepare hard carbons derived from Balsa woods (BHCs). The best rate capability of BHCs is obtained by an optimized carbonization temperature of 1400 degrees C. The prepared hard carbon shows a smaller closed pore size (1.77 nm) compared to most recently reported hard carbons, which ensures their high rate capability. At the carbonization temperature of 1400 degrees C, BHC achieves the highest capacity of 296 mAh g -1 . BHC-1400 also exhibits a high capacity retention of 54.9 % at a current density of 5 A g -1 . The excellent electrochemical properties indicate that the BHCs have potential in the application of high -rate SIHCs.