Electrochemical evaluation of Na<sub>2</sub>FeP<sub>2</sub>O<sub>7</sub>/C positive electrodes prepared via simple solid-state synthesis for sodium-ion batteries

Na2FeP2O7 cathode materials for sodium-ion batteries were synthesized from NaH2PO4 and Fe2O3 raw materials using a simple solid-state synthesis method involving mechanical milling and calcination. Specifically, four types of active materials were prepared via carbon compositing with the calcined raw materials, followed by additional calcination. Electrode slurries were fabricated by adding conductive additives and binders to the active materials, which were then assembled into coin cells and evaluated through electrochemical tests. According to the results, the electrode that underwent the solid-state synthesis process, followed by carbon compositing and subsequent re-calcination, exhibited the highest diffusion coefficient. The discharge capacities measured at 0.1, 10, and 30 C-rates were 87.8, 59.8, and 15.9 mAh g−1, respectively. The electrode also exhibited excellent capacity retention, maintaining 99.9 % of its initial capacity (81.6 mAh g−1) after 200 cycles at 1 C-rate, demonstrating good battery performance.