A High Temperature Lithium Metal-Air Primary Battery Based on Solid Electrolytes and Molten Salt

Developing metal-oxygen batteries with a high specific energy (gravimetric energy density) is a significant challenge due to the highly reactive nature of active materials used as the negative electrode, such as Li, Al, or Mg. In addition, the metal-oxide discharge products are highly stable and passivating to many oxygen-reduction catalysts. Here we present an alterative way of utilizing the high specific energy lithium metal-oxygen reaction by combining both cation and anion transport in a single device, operated at 550°C. To do this, we combined a Li6.4La2.8Al0.2Zr1.4Ta0.6O12 (LLZO) cation solid electrolyte, yttria stabilized zirconia oxygen ion conductor, and KCl-LiCl eutectic salt as an interlayer between the two solid electrolytes. We find that the constructed battery shows an open circuit voltage consistent with the thermodynamic value predicted for the Li-O2 reaction at 550°C. Furthermore, we found that the cell could be discharged at 20 mA, showing no significant passivation of the reaction until all of the lithium metal was depleted. However, we were unable to re-deposit the lithium metal electrochemically, possibly due to parasitic reduction of the LLZO tube upon charging. This work presents a unique device which may inspire other high temperature electrochemical devices in the field.