Fig. 2

Electrochemical profiles of both samples. a Rate capability of both samples from 0.1 C to 20 C. The inset is the cycling stability at low current density (0.05 C). b Cyclic voltammetry (CV) curves for the first 5 cycles of NFPP-E electrode (scan rate 0.05 mV s⁻¹). c Charge-discharge curves at different rates for both samples. d Cycling stability of NFPP-E electrodes over 250 cycles at 0.2 C and 430 cycles at 0.5 C. e Long-term cycling stability (4400 cycles) at high rate (20 C) for both NFPP-E and NFPP-C electrodes. f Galvanostatic intermittent titration technique (GITT) curves of NFPP-E material for both charge and discharge processes. The inset is the chemical diffusion coefficient of Na⁺ ions as a function of voltage calculated from the GITT profile (after 30 cycles, current density: 0.05 C). g The calculated capacitance contribution (shadowed area) to the CV curve of NFPP-E at the scan rate of 0.3 mV s⁻¹