Electrochemical performance of peat-derived hard carbon: Impact of textural properties, catalytic pyrolysis, and electrolyte chemistry

Peat-derived hard carbons were prepared by catalyst-assisted pyrolysis using Fe and Fe/B species and evaluated as anodes for sodium-ion batteries in carbonate and ionic liquid-based electrolytes. Catalyst treatment significantly altered the pore structure, reducing microporosity and increasing mesoporosity, especially in Peat@Fe/B-10%. The electrochemical behavior strongly depended on the electrolyte. In 1 M NaPF 6 in EC:PC, Peat@Fe showed the best performance, delivering 192 mAh /g with an initial coulombic efficiency of 67.0%, which is attributed to its relatively low surface area and moderated mesoporosity that limit excessive SEI formation. In contrast, the ionic liquid electrolyte (NaFSI:C 3 mpyrFSI, 1:1) favored the more mesoporous Peat@Fe/B-10% electrode, which showed the highest capacity, the best rate capability, and the lowest charge-transfer resistance (14.1 Ω). Cyclic voltammetry indicated mainly surface-controlled sodium storage with b-values of 0.54–0.73, while impedance analysis confirmed improved interfacial and charge-transfer kinetics in the catalyst-treated carbons. The superior performance of Peat@Fe/B-10% in the ionic liquid electrolyte is linked to its high mesopore fraction (72.4%), low microporosity (19%), and improved local structural ordering, which together enhance electrolyte access and Na⁺ transport. These results show that the sodium storage performance of peat-derived hard carbon depends strongly on both its pore structure and the electrolyte used.