Synthesizing higher-capacity hard-carbons from cellulose for Na- and K-ion batteries

Non-graphitizable hard carbons are synthesized through carbonization of glucose, sucrose, maltose, cellulose, glycogen, and amylopectin. Cellulose-derived carbon delivers superior reversible sodiation capacity, and optimal carbonization for a higher capacity Na-ion battery is found to be two-step heating of cellulose at 275 °C and 1300–1500 °C in air and argon, respectively. The hard carbon delivers a higher reversible capacity of 353 mA h g−1 in a Na cell. The 275 °C heating is important to regulate dehydration and cross-linkage degrees of cellulose, which affect the nano-scale structure of hard carbons. The cellulose-derived carbons deliver 523 and 290 mA h g−1 in Li and K cells, respectively.