Manganese oxides (MnOx) have a long history as charge-storing materials in electrochemical devices, ranging from electrolytic MnO2 in primary alkaline batteries to spinel-type Li-MnOx compositions that serve as high-performance cathodes in Li-ion batteries. More recently the application of this class of oxides has extended to aqueous-electrolyte electrochemical capacitors (ECs) in which nanostructured MnOx–based materials enable pulse-power capabilities via fast pseudocapacitance charge-storage mechanisms. The ability of MnOx to alternately express battery-like and capacitor-like functionality offers intriguing prospects to design electrode materials and corresponding devices that deliver both high energy content and rapid charge/discharge response. We are exploring such opportunities with electrode architectures comprising nanoscale MnOx coatings affixed to porous carbon frameworks [1,2,3]. By varying such factors as the oxide crystal structure (layered birnessite MnOx vs. cubic spinel LiMn2O4) and the composition of the contacting electrolyte (mixtures of Na+, Li+, and/or Zn2+), the resulting electrodes exhibit either battery- or capacitor-like behavior as well as combinations thereof. We are also developing electroanalytical protocols to deconvolve the complex electrochemical response of such systems in terms of both time scale and current–potential profile.
1. A.E. Fischer, K.A. Pettigrew, D.R. Rolison, R.M. Stroud, and J.W. Long, Nano Letters 2007, 7, 281–286.
2. J.W. Long, M.B. Sassin, A.E. Fischer, and D.R. Rolison, J. Phys. Chem. C 2009, 113, 17595–17598.
3. M.B. Sassin, S.G. Greenbaum, P.E. Stallworth, A.N. Mansour, B.P. Hahn, K.A. Pettigrew, D.R. Rolison, and J.W. Long, J. Mater. Chem. A 2013, 1, 2431–2440.