A comparative study of cellulose derived structured carbons on the electrochemical behavior of lithium metal-based batteries

Cellulose nanomaterials with different structures (i.e., cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC)) were carbonized to investigate the effect of morphology and crystallinity of cellulose-derived carbon nanomaterials on the overall electrochemical reactions in Li metal-based batteries. Carbonized CNF (c-CNF) and carbonized CNC (c-CNC) were coated separately on either a Cu current collector or a polypropylene (PP) separator for electrochemical tests. The resulting carbon derived from the amorphous region of CNF contributes to increasing the specific capacity of a cell but decreasing the overall electrical conductivity of the electrode. The c-CNF electrode delivered a relatively high capacity of 412 mAh g−1 at a low current density (0.2 A g−1) in comparison with the c-CNC (370 mAh g−1). In contrast, the c-CNC exhibited better rate capability than the c-CNF. When PP separators modified with c-CNF and c-CNC were employed in Li/Cu cells, it has shown remarkable improvements in Coulombic efficiency and cycle stability (over 120 cycles). This effect is ascribed to the substantially decreased local current density and the improved Li-ion storage in additional c-CNF and c-CNC layers. In addition, Li/LiFePO4 full-cell study tested with modified membranes further demonstrated the beneficial effect of cellulose-derived carbon nanomaterials on electrochemical reactions. Throughout this study, we explored the material characteristics of c-CNF and c-CNC, revealing the strong influence of the resulting carbon originated from the amorphous region of CNF on the electrochemical behaviors in Li-ion and Li-metal batteries.