齋藤 守弘

Lithium–air batteries (LABs) have an energy density of 500–1000 Wh kg ⁻¹ , which exceeds that of current lithium-ion batteries. However, their practical application is currently limited by poor cycle life and safety risks associated with unstable lithium metal anodes, such as sudden ignition caused by short circuits or contact with water. Alloying lithium with magnesium (Li–Mg) is a promising solution as it incorporates the Li source within the alloy lattice. This study evaluated Li–Mg alloys containing 10 wt% (Li-0.1 Mg) and 20 wt% (Li-0.2 Mg) magnesium as an alternative to pure lithium anodes. Lithium dissolution and plating in pure oxygen revealed that the alloy anodes exhibited enhanced cycling stability, with the Li-0.1 Mg alloy demonstrating the lowest overpotential. LAB cells with carbon cathodes and Li-0.1 Mg anodes exhibited performance comparable to that of cells with pure Li anodes. SEM analysis confirmed considerable dendrite suppression. Stack-type LAB cells with Li-0.1 Mg anodes achieved a capacity of 0.51 Ah and an energy density of 530 Wh kg ⁻¹ in dry air. The reduced reactivity of Li–Mg alloy anodes with water further enhances safety without compromising the cell’s light weight and capacity. These findings provide new guidelines for designing safe and durable metal anodes for practical LABs.

Lithium–air batteries (LABs) are a promising technology for high‐energy‐density battery storage. However, their open‐cell structure for oxygen exchange leads to electrolyte evaporation, which limits cycling performance under ambient conditions. Herein, volatile amide‐based electrolytes for LABs using gravimetric analysis are evaluated. The cell weight change during discharge–charge cycles confirms the two‐electron oxygen reduction/evolution reactions while also revealing that electrolyte evaporation correlates with the solvent vapor pressure. This behavior significantly compromises the cycle performance of low‐viscosity amide electrolyte cells. Despite this, rate‐dependent cycling experiments demonstrate the superior cyclability of the low‐viscosity amide electrolyte cells at high current rates (0.8 mA cm⁻² or higher), conditions under which cells with a conventional tetraethylene glycol dimethyl ether (TEG)‐based LAB electrolyte fail. Scanning electron microscopy and X‐ray diffraction analyses show that these cells exhibit improved rechargeability at high‐rate cycles, with discharge product morphology changing to a more easily decomposable form. This electrolyte design strategy marks a significant advancement toward developing high‐power, high‐energy rechargeable LABs.