Li-O₂ flow batteries with high mass loading and energy density

Li[sbnd]O₂ and Li-air batteries are promising energy storage technologies due to their high theoretical energy density. However, their achievable energy densities are much lower due to the low mass loading of electrodes and low electrode utilization rates. This study designed Li[sbnd]O₂ flow batteries that actively circulate liquid electrolytes through the porous positive electrode, enabling high utilization rates for the electrodes with high mass loading. The experimental tests and model simulations in this study demonstrated the advantages of the flow battery design. Using commercially available carbon electrodes and 1 M LiTFSI in tetraethylene glycol dimethyl ether (TEGDME), this scalable battery concept achieved an energy density of 773 Wh/kg at 0.25 mA/cm² and 436.6 Wh/kg at 0.5 mA/cm² at room temperature. In comparison, using the same electrodes and electrolytes, traditional Li[sbnd]O₂ batteries without electrolyte flow only obtained 294 Wh/kg at 0.25 mA/cm² and 239.7 Wh/kg at 0.5 mA/cm². In addition, the flow battery demonstrated better cyclability compared to the traditional battery. The flow battery completed 23 cycles at a current density of 0.25 mA/cm² and a cut-off capacity of 1 mAh/cm², whereas the traditional passive battery completed only 8 cycles under the same conditions. The model simulation quantitatively showed that convection of the electrolyte significantly improved mass transfer and material utilization of the positive electrode. The energy consumption to circulate the electrolyte was measured to be only 1.3 % of the discharged energy. Comparable improvements in energy density were observed when 1 M LiTFSI in dimethyl sulfoxide (DMSO) was utilized as the electrolyte. This design opens up opportunities for new research to develop scalable batteries with exceptionally high energy density, far surpassing current state-of-the-art Li-ion batteries, while maintaining relatively high power density.