Cellulose-derived carbons as a high performance anodic material for Na-ion battery

A facile and easily scalable method for producing disordered carbons as active materials for sodium ion (Na-ion) battery anode has been developed. The materials were synthesized by two-step pyrolysis of microcrystalline cellulose at the final temperature in the range of 950 to 1250 °C, followed by pyrolytic carbon (PC) coating. The effect of heat-treatment temperature (HTT) and PC process on heteroatom content (elemental analysis), porous texture (N2 and CO2 adsorption), and electrochemical performance (coin-type half-cell) was analyzed. Increasing HTT results in remarkable decrease of oxygen content, from 4.4 to 1.4 wt.%, and the surface area accessible for N2 molecules (microporosity), from 502 to 114 m2 g−1, while the carbonization degree, expressed as the H/C atomic ratio and the area probed by CO2 (ultramicropores) are only slightly reduced. Elevating carbonization temperature gradually decreases the irreversible Cirr and increases the reversible Crev capacities in the first charge/discharge cycle. PC coating, applied to 1000 °C, seems to be less effective in improving electrochemical properties than HTT factor despite strong reduction of porosity and surface chemistry. Simple heat treatment at 1200 °C seems to be optimal to produce anodic material with the best electrochemical performance in a wide range of current load: coulombic efficiency of 0.78 and Crev of 306 or 261 mAh g−1 at 20 or 500 mA g−1, respectively.