Unlocking the potential of sodium-ion batteries: Synthesizing sodium iron silicate cathodes using aliphatic diols

Nanostructured Na₂FeSiO₄ (NFS) cathodes are synthesized using diol-assisted hydrothermal processing followed by calcination, employing 1,2-ethanediol, 1,4-butanediol, and 1,6-hexanediol serving as both solvents and carbon sources. The morphology, crystal structure, and electrochemical properties are tuned by systematically varying the diol carbon chain length and the calcination temperature. The synthesized nanosheet architecture incorporates defective nanocarbon and features varying thicknesses and surface areas. The coordination environments and oxidation states of Fe²⁺/Fe³⁺ link phase evolution with coordinated water removal and hydroxyl group transformations during thermal treatment. Electrochemical tests demonstrate the superior rate capability and cycling stability of the optimized cathode, with an initial discharge capacity of 141.4 and 88.5 mAh g⁻¹ and a capacity retention of 89.3 % and 98.6 % after 150 cycles at 0.1C and 0.4C, respectively. At a high rate of 7C, this cathode also achieves an initial capacity of 56.5 mAh g⁻¹ and retains 77.1 % of it over 600 cycles. Such enhanced performance is attributed to optimized crystallinity, reduced charge-transfer resistance, improved sodium-ion diffusion, and interfacial charge storage. These findings underscore the potential of NFS as a high-rate, long-cycle cathode for sodium-ion batteries and provide a framework for the rational design of next-generation energy-storage materials.