April 2015

Rechargeable metal–air (or more precisely metal–oxygen) batteries with aprotic electrolytes are very attractive energy stores as they potentially combine low-cost components and very high energy densities. The reality of this type of battery, however, is complex and fundamental issues still need to be overcome in order to make any application feasible. The lithium–oxygen battery clearly is the frontrunner in recent worldwide research efforts, but recently it was found that replacing lithium by sodium can enable a much more controlled cell reaction by forming sodium superoxide during discharging. In a joint study from the Justus-Liebig-University Gießen and BASF SE, Conrad L. Bender et al. show that the capacity and cycle life of the sodium–oxygen battery can be improved by using technically processed, free-standing electrodes based on commercial carbon nanotubes. Deep discharging delivers a capacity of 1530 mAh/g for a few cycles, but a lifetime of more than 140 cycles is observed for shallow cycling. The results are superior in comparison to earlier studies on conventional carbon electrodes. The picture of the month shows the cell design and images of the carbon nanotube electrode before and after discharge. The discharge product (NaO2) crystallizes in the form of large cubic particles. More information can be found in the recently published work: http://onlinelibrary.wiley.com/doi/10.1002/ente.201402208/abstract(Picture submitted by Conrad L. Bender.)