Structure-dependent sodium ion storage mechanism of cellulose nanocrystal-based carbon anodes for highly efficient and stable batteries

We herein report the preparation of SIBs using carbon anodes based on spray-dried cellulose nanocrystals (CNCs) carbonized over a wide temperature range (i.e., 800–2500 °C). The structural variations in the CNC-based carbon anodes are correlated with the sodiation mechanism by investigating the galvanostatic voltage profiles, and it is found that Na ion adsorption takes place in the less-ordered carbonaceous structures followed by intercalation into the more ordered internal carbon structure with an average interlayer spacing of >0.37 nm. Among the various anodes examined, the CNCs carbonized at 1500 °C (C1500) deliver the highest reversible specific capacity of 311 mA h g−1 at a current density of 10 mA g−1, and exhibit an outstanding rate capability (273 mA h g−1 at 400 mA g−1). In addition, they also possess an excellent specific capacity retention of 92.3% even after 400 cycles at 100 mA g−1, along with an initial coulombic efficiency of 85%. Density functional theory (DFT) calculation exhibits that the energy barrier for Na ion intercalation of C1500 (0.20 eV) is almost a half that of the CNCs carbonized at 2500 °C (0.39 eV). [Display omitted] •Carbonized cellulose nanocrystals are used to prepare Na ion battery.•Structure development of carbonized CNC plays a critical role on Na storage mechanism.•Optimally carbonized CNCs exhibit stable and excellent electrochemical performance.