Effect of Carbonization Behaviour of Cotton Biomass in Electrodes for Sodium-Ion Batteries

Free-standing hard carbon electrodes are produced from cotton biomass using a low-cost, one-step pathway. The free-standing feature of the electrode eliminates the use of binders and toxic solvents. The electrochemical performance of the electrodes is tested to study the correlation between Na storage and the structural properties of the hard carbon material. A remarkable specific capacity of 272 mAh g(-1) at a current density of 50 mA g(-1) is obtained with a high initial Coulombic efficiency of 75 % for the cotton fabric (CF) sample pyrolyzed at 1000 degrees C for 5 min (CF5 min). The excellent performance of the free-standing electrode is attributed to a large interlayer spacing between the graphene layers, and a high number of oxygen-containing functional groups on the surface. X-ray photoelectron spectroscopy (XPS) surface characterisation shows that a thin and uniformly distributed SEI (solid electrolyte interphase) layer, mainly composed of NaF and Na2O, is formed on the CF5 min surface, whereas a thick SEI layer with a long Na+ diffusion pathway is formed on the sample pyrolyzed at 1000 degrees C for 10 h (CF10 h), which leads to slower reaction kinetics and poor electrochemical performance. This work proposes a scalable and economically feasible strategy to produce sodium ion anode materials with a focus on environmental sustainability and value addition to waste streams.