Optimization of MnO2 Cathodes for Aqueous Battery Applications

Monday, 25 May 2015: 08:20
Continental Room A (Hilton Chicago)


Grid-level energy storage demands a low-cost, safe, long cycle life battery chemistry. The Zn-MnO2 alkaline battery chemistry hits the first two targets. This type of battery has high energy density (comparable to that of a Li-ion battery) and low cost per kilowatt-hour.  However, their rechargeability is limited by phase transformations which occur in the MnO2 cathode during discharge of close to one electron, which transforms it into an spinel phase, generally considered to be electrochemically inert. As a result, depth of discharge is limited to no more than 70% of the 1e- capacity of MnO2 at best, and in a large format cell typically no more than 0.5 e-.

We have extensively studied the MnO2 alkaline system and have developed a variety of techniques to extend this depth of discharge window, improving the capacity and cyclability of the cell dramatically. We have also developed novel nanostructured forms of MnO2 for use as a cathode material in this system. Using these techniques, we have achieved capacities of over 350 mAh/g (1.2 e-) for more than 150 cycles. In this presentation, we will discuss the various failure modes of the MnO2 alkaline system, and the techniques our group has developed to overcome them. We will describe the crystal structure and electrochemical performance of the nanomaterials we have synthesized, as well as the structural changes occurring during their use as an electrode material as characterized via synchrotron radiation and other techniques.  

With further development, this material, combined with either a zinc anode or an earth abundant, insoluble anode such as Fe or Cd, may allow for over 1000 cycles at a cost of less that $100/kWhr for a packed out cell.

Figure: a) MnO2 electrode before cycling; b) MnO2 electrode after 1st-electron discharge; c) MnO2 electrode after full discharge; d) MnO2 electrode after full recharge; e) MnO2 electrode after 3 cycles (discharged state); f) MnO2 electrode after 15 cycles (discharged state)