Abstract
The implementation of sodium-ion batteries for renewable energy storage requires the development of sustainable electrode materials. Usually, these materials are produced through complex energy-intensive processes that are challenging to scale and involve expensive and/or toxic reagents. In this study, sustainable hard carbon materials, some doped with iron, synthesized from sucrose using a simple, fast, and cost-effective two-step eco-friendly process, are investigated as anodes for sodium-ion batteries. The influence of physicochemical and structural material properties on electrode reversible capacity, cycling stability, and efficiency is analyzed. The SC900 material, which exhibits a certain development of graphite-like structure, though not strictly graphitic, showed the best electrochemical performance, providing discharge capacities exceeding 100 mAh g(-1) after 400 cycles with excellent cycling stability and high coulombic efficiency. The capacity of the materials increases as d(002) decreases, (i.e., as the degree of structural order increases), to the optimum value of ~0.3700 nm. However, a further decrease in d(002) to values characteristic of quasi-graphitic materials, as a consequence of the catalytic effect of iron, hinders Na(+)-ion storage, which, in addition to the low electrochemical activity of the iron oxides present, leads to much lower capacities.