Investigation of structural & interfacial properties of hard carbon electrodes from cotton snippets toward sustainable sodium-ion batteries

Hard carbon electrodes are produced from cotton snippets through carbonization at different temperatures and isothermal hold times. The electrochemical performance of the electrodes is evaluated to understand the correlation between Na storage and the micro/nanostructure, texture, and surface functionality of the hard carbon samples. The sample CSC5 (carbonized at 1200 °C with an isothermal hold time of 5 min) shows a significant specific capacity of 270 mAh g−1 at a current density of 50 mA g−1 and a high initial coulombic efficiency of 82%. This can be attributed to a large interlayer spacing, low specific surface area, and low porosity of the sample. Additionally, ex-situ MAS (magic angle spinning) NMR (nuclear magnetic resonance) spectroscopy on the solid electrolyte interphase (SEI) layer of the sample revealed a lesser amount of conductive SEI layer on the surface of this sample, mainly composed of NaF and an additional FSI-derived Na complex. This is interpreted as a thinner SEI layer which led to a shorter Na+ diffusion pathway, faster Na + reaction kinetics, and a better electrochemical performance overall. This work proposes a strategy to utilize cotton textiles as a biomass source along with a mechanistic insight for further optimization toward sustainable hard carbon anodes for sodium-ion batteries.