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 (CIFM) calculation, in which the strong charge transfer due to the σ/π-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⁺-C 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.