Two-electron reaction without structural phase transition in nanoporous cathode material

Abstract

We investigated the charge/discharge properties, valence states, and structural properties of a nanoporous cathode material Li xMn[Fe(CN) 6] 0.83 · 3.5H 2O. The film-type electrode of Li xMn[Fe(CN) 6] 0.83 3.5 · H 2O exhibited a high charge capacity (=128 mAh g -1) and a good cyclability (87% of the initial value after 100 cycles) and is one of the promising candidates for Li-ion battery cathode. X-ray absorption spectra near the Fe and Mn K-edges revealed that the charge/discharge process is a two-electron reaction; that is, Mn II -NC- Fe II, Mn II -NC- Fe III, and Mn III -NC- Fe III. We further found that the crystal structure remains cubic throughout the charge/discharge process. The lattice constant slightly increased during the [Fe II(CN) 6] 4- [Fe III(CN) 6] 3- oxidization reaction while decreased during the Mn II Mn III oxidization reaction. The two-electron reaction without structural phase transition is responsible for the high charge capacity and the good cyclability. © 2012 Tomoyuki Matsuda and Yutaka Moritomo.