Timm Lohmann

Overview of LiO2 Battery Systems, with a Focus on Oxygen Handling Requirements and Technologies

The reactions of Li and O2 to form Li2O2, and of Li, O2, and H2O to form LiOH·H2O, have exceptional energy content but are adversely affected by components of air such as CO2 (for both cases) and H2O (for the Li2O2 case). Hence, a method is required to supply O2 while excluding contaminants. In this chapter we focus on O2 supply for both a closed system (in which tanks store pure O2 at pressures up to 350 bar) and an open system (in which CO2 and possibly H2O are removed through a series of unit operations). In particular, we consider the implications of the O2 supply method on the specific energy and energy density at the system level, as well as other system attributes such as cost. For the closed (tank) system we find that with the use of a carbon fiber tank, for the reaction forming Li2O2, the specific energy is twice that of a comparison cell (one pairing Li metal with an advanced intercalation metal oxide), but the energy density is about 30 % lower. For the reaction forming LiOH·H2O, the specific energy is about 40 % above that of a Li/metal oxide cell, but the energy density is 50 % lower. A unique challenge for the closed system is the need for high-pressure compression. An open system may be enabled through the combined use of several gas separation steps (including a membrane and solid adsorption) as well as a compressor to drive the air. The required purity of an O2 supply stream remains unclear, but for a reduction of CO2 and H2O to levels of 1 ppm, the mass and volume of the O2 supply equipment for the open system is comparable to that of the closed system. A unique challenge for the open system is safely charging in closed environments where the O2 emitted does not quickly dissipate. For both types of systems, handling any volatile cell components (e.g., solvents) may be a challenge (for the closed system they may enter the high-pressure O2 tanks, while in the open system they may be lost to the atmosphere), and potential technologies to address volatiles are not included in this analysis. We encourage Li/O2 researchers to investigate sets of nonvolatile materials that may improve the robustness of the cell chemistry to the presence of air contaminants.