Charge–Discharge Characteristics of Fe‐Doped NaMnO Cathodes with Na ₃ PO ₄ Aqueous Electrolytes: A High‐Temperature Stable and Eco‐Friendly Energy Storage Technology

This work develops an eco‐friendly Na‐ion battery using NaMnO and Fe‐doped NaMnO cathodes synthesized via solid‐state reaction, paired with a C‐based anode and H 2 O‐based Na 3 PO 4 electrolyte. Material analyses (X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman) show Fe doping mitigates the Jahn–Teller effect, enhancing cathode structural stability. Electrochemical tests indicate that the Fe‐doped cathode delivers robust specific capacity and retains superior cycling stability, particularly under elevated temperatures (55 °C). This stability arises from the synergy of Fe doping, which reduces the dissolution of active materials, and the nonflammable Na 3 PO 4 electrolyte, which poses no threat of hazardous leakage or byproducts. Electrochemical tests indicate that the Fe‐doped cathode delivers robust specific capacity and retains superior cycling stability, particularly under elevated temperatures (55 °C). Specifically, the HSLF800 sample achieves a discharge specific capacity of 23.58 mAh g −1 with a 72.02% retention rate at room temperature and 27.53 mAh g −1 with 67.86% retention at 55 °C, outperforming the undoped counterpart (HS800). Overall, the use of earth‐abundant elements and a nonflammable H 2 O‐based Na 3 PO 4 electrolyte ensures that this system provides stable, high‐temperature electrochemical performance without generating harmful pollutants.