XAFS Studies on Charging-Discharging Processes in Molecular Cluster Batteries

Introduction Recently, much attention has been focused on the creation of new energy systems, such as highperformance rechargeable batteries, as a solution to the global energy and environmental crises. Redox active molecular materials are good candidates for a highperformance cathode active material. To achieve both high capacity and fast charging/discharging, we have previously proposed the use of polynuclear metal complex clusters (molecular clusters that are small aggregates of metal ions connected by organic ligands) that undergo multi-step redox reactions as a cathode active material for lithium batteries In our previous paper, we reported the fabrication of a molecular cluster battery (MCB) in which the cathode active material is [Mn12O12(CH3COO)16(H2O)4] (abbreviated as Mn12Ac). Here we carried out ex situ XAFS analyses on the charging/discharging processes of the Mn12-MCBs to reveal the microscopic mechanisms of their battery performance. XAFS analysis is an appropriate technique for observing valence changes and local structures of nanoscale or highly disordered compounds such as battery active materials.