Configuration-Interaction Full-Multiplet Calculation to Analyze the Electronic Structure of a Cyano-Bridged Coordination Polymer Electrode

To understand the electronic-structure changes of electrode materials during the charge/discharge processes is one of the most important fundamental aspects to improve the battery performance. Soft X-ray, absorption spectroscopy (XAS) was used to study a bimetallic NiFe Prussian blue analogue electrode. XA spectra were obtained during the charge/discharge and were analyzed by the configuration interaction full-multiplet (CIEM) calculation, in which the strong charge transfer due to the sigma/pi-donation and back donation of cyanide was taken into account. The CIFM calculation revealed that the metal-to-ligand charge transfer (MLCT) played an important role in the electronic state of Ni-N bond: The Fe3+-FC bond in the charged state is dominated by both the MLCT and ligand-to-metal charge transfer (LMCT), whereas only the MLCT strongly affects the Fe2+-C bond in the discharged state.