Fumisato Ozawa

Lithium-air batteries (LABs) develop high-energy-density battery storages, but the low-rate capabilities limit their practical applications. This study demonstrates an innovative approach for enhancing the power of LABs by integrating a highly porous carbon nanotube (CNT) air-electrode with a low-viscosity amide-based electrolyte. CNT air-electrodes with high surface area enable high-rate discharges, and increasing the electrode porosity allows for sustained discharges at high rates. Amide-based electrolytes with low viscosity, such as 1 M lithium nitrate (LiNO3) dissolved in N,N-dimethylacetamide (DMA) having a one-sixth viscosity of typical LAB electrolytes based on tetraethyleneglycol dimethylether (TEG) solvent, decreased cathode resistance by half by facilitating oxygen transport, enabling an ever-high current density discharge of 4.0 mA cm(-2) to provide a capacity of 4.6 mAh cm(-2) under dry air, i.e., similar to 21 % oxygen atmosphere. Cell assembly suppressing electrolyte solvent evaporation produced high-power rechargeable LAB cells with a power density of 447 W kg(-1), providing 447 Wh kg(-1) of energy with respect to the total cell weight. This represents the first case of discharge-charge cycles of LABs with high power output specifically focused on drone hovering. The high-power, high-energy density LABs demonstrated in this study pave the way for developing ultra-lightweight aircraft batteries.

Abstract Redox mediators (RMs) suppress the charging overpotential to enhance the cycle performance of lithium-air batteries (LABs), but inappropriate RM incorporation can adversely shorten cycle life. In this study, three typical organic RMs; tetrathiafulvalene (TTF), 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), and 10-methylphenothiazine (MPT), were incorporated into the air-electrode (AE) of the LAB (RM-on-AE), rather than dissolving them in the electrolyte (RM-in-EL), to maximize the RM effect throughout the cycle life. The discharge/charge cycle test confirmed that the cells with RM-on-AE prevented the reductive decomposition of RM with the lithium anode, deriving the RM effect for a longer cycle life than the cells with RM-in-EL. The measurement of AE deposits revealed that the TTF- and TEMPO-on-AE cells failed to generate a quantitative amount of Li2O2 discharge product. In contrast, the MPT-on-AE provided a 96% yield of Li2O2 after the first discharge because of the reductive tolerance of the MPT as organic RM. The quantitative analysis also revealed an accumulation of Li2CO3 on the AEs, along with the generation of carboxylate, as the side products of irrelevant battery reactions. This study provides a practical methodology for selecting RMs and their incorporation for developing long-life LABs.