Fig. 2: Electrochemical measurements of NaFe[O₃PCH(OH)CO₂] in Na half-cells.

a Galvanostatic charge-discharge curves at 12 mA g^–1. b Galvanostatic charge-discharge curves for 50 cycles at different current densities of 12, 24, 36, 48 and 60 mA g^–1. c Rate performance under different current densities. d CV curves in different cycles at a scan rate of 0.5 mV s⁻¹. e Cycling performance at 240 mA g^–1 for 1000 cycles. f CV curves of NaFe[O₃PCH(OH)CO₂] at scan rate of 0.05-3 mV s^–1, respectively. g The fitting curves between the peak current (I_P) and the square root of the scan rate (ν^1/2). h Na⁺ diffusion coefficient calculated from GITT curve as a function of voltage.