Fig. 4: Na-ion storage mechanism in the NaFeMnF-based positive electrode.

a In situ XRD and corresponding charge-discharge profiles of PTCDI||NaFeMnF in the modified electrolyte at 50 mA g⁻¹ and 25 °C. b Unit cell structural changes of NaFeMnF during three phase transitions. c Ex situ Raman measurement of fully discharged cathodes in the blank electrolyte and modified electrolyte. The blue peaks correspond to Fe²⁺–C≡N–Mn²⁺ vibrational modes, and the red peaks correspond to Fe²⁺–C≡N–Mn³⁺ vibrational modes. d Ex situ EPR measurements of fully discharged cathodes in the blank electrolyte and modified electrolyte. PTCDI||NaFeMnF was subjected to 300 cycles at 0.5 A g⁻¹ at 25 °C before collection and ex situ Raman and ex situ EPR measurements of the positive electrodes.