Fig. 3
Air stability, low/high-temperature performance, and full cell performance. a XRD comparison of NFPP-E powder in the fresh state and after exposure to air for three months (Cu Kα radiation, λ = 1.5406 Å). b Fe 2p, C 1s, and P 2p XPS fitted spectra of NFPP-E powder in the fresh state and after exposure to air for three months. c EIS spectra of NFPP-E powder in the fresh state and after exposure to air for three months. d HRTEM image of the powder after exposure to air for three months. The inset is the fast Fourier transform (FFT) pattern of the marked area. e C-rate capability of NFPP-E electrodes: fresh, exposed to air for three months, and fresh at both −20 °C and 50 °C. f Cycling performances of the four electrodes in e. g Charge/discharge curves of polypyrrole (PPy)-coated Fe3O4 at various current densities. The insets are (top) SEM image of as-prepared Fe3O4 nanospheres and (bottom) the cycling performance. h Voltage profiles of the all-iron-based Na4Fe3(PO4)2(P2O7)//Fe3O4 full cell for the first five cycles. i Cycling stability of the Na4Fe3(PO4)2(P2O7)//Fe3O4 full cell. The specific capacities of the full cell were all based on the anodes. Scale bars: 10 nm (d); 200 nm (g, inset)
