RESEARCH / A0272
Reduced Bond Covalency and Anisotropic Lattice Distortion Enable High Fe–Mn Redox Activation in a Mixed-Polyanionic Cathode
Read the original paper · 10.1021/acsnano.5c12007 ↗
Source figures may contain other techniques and soft X-ray spectra. C, N and O measurements are outside our current hard-XAFS testing range.
Figure 1. Crystal structure and composition of the materials. (a) XRD patterns of the NMFPP and NFPP. Inset illustrates the partial Mn substitution in Fe sites. (b) Rietveld refinement of the XRD pattern of the NMFPP powder. The fitting result is satisfactory, with Rwp = 2.82% and Rp = 1.71%. The inset illustration of the crystal structure of NMFPP, where the pink, brown, blue polyhedrons represent [MnO6], [FeO6], and [PO4] units, respectively, and the yellow balls represent Na ions. (c) The EXAFS spectra of Fe in NFPP and Fe and Mn in NMFPP. (d) The FTIR spectra of NMFPP. (e) HR-TEM images of the NMFPP material. The inset is the corresponding fast Fourier transform (FFT) pattern (bottom) and the enlarged lattice image (up). (f) Elemental mapping images of the NMFPP particle.
Figure 6. Reaction kinetics and crystal structure variation during the sodium storage process. (a) In situ EIS and the corresponding equivalent circuit diagram. (b) Variation of Rct during the in situ EIS test. (c) Warburg coefficients, which are inversely proportional to Naion diffusion coefficients, are calculated based on the in situ EIS. (d) Ex situ Mn k-edge XANES spectra of NMFPP electrodes at different charge/discharge states. (e) Ex situ Fe k-edge XANES spectra of NMFPP electrodes at different charge/discharge states. (f) The ex situ Mn EXAFS spectra of NMFPP electrodes. (g) The ex situ Fe EXAFS spectra of NMFPP electrodes. (h) In situ XRD pattern of the NMFPP cathode and the charge/discharge curve. (i) Corresponding contour maps of the in situ XRD pattern. (j) Variations of lattice parameters and unit cell volume during the sodium storage process.