Round-Trip Efficiency Enhancement Of Hybrid Li-Air Battery Enables Efficient Power Generation From Low-Grade Waste Heat

The superior energy density renders hybrid Li-air batteries (HLABs) promising candidate energy storage systems to enhance the sustainability of power grids. Nevertheless, HLABs operated at ambient temperature struggle to meet power and cycle life performance requirements for commercial application. At the same time, low-grade heat is abundantly available from industrial processes as well as from solar-thermal or geothermal sources, but there is a blatant lack of technologies to efficiently convert low-grade waste heat into valuable electrical energy. We find that cells operated with an anolyte of tetraethylene glycol dimethyl ether and 1 M aqueous lithium hydroxide as the catholyte achieve a marked decrease in cell polarization with an increasing operation temperature of up to 80 degrees C. Therefore, the energy efficiency, eta, can be increased significantly. While the increase from eta(RT) = 90% at room temperature to eta(353K) = 98% efficiency at a reference current density 0.03 mA cm(-2) may appear gradual, the increase in efficiency becomes rapidly more prominent with increasing current density (e.g., from eta(RT) = 59% to eta(353K) = 84% at 0.5 mA cm(-2)). The additional electrical energy that can be drawn from a HLAB heated by low-grade waste heat leads to a highly attractive heat-to-power conversion efficiency.