東 翔太

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.

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.

Visible-light responsive photoanodes for water splitting into hydrogen and oxygen were fabricated via NiTi-layered double hydroxide (NiTi-LDH, [Ni_1-xTi_x(OH)₂]^2x+(A^n-)_2x/n・mH₂O]) and NiTi-LDH/graphene composite prepared by homogeneous precipitation methods. The NiTi-LDH and NiTi-LDH/graphene films were formed on transparent fluorine-doped tin oxide (FTO) glass substrates by electrophoretic deposition (EPD). The EPD films showed the pattern of hydrotalcite structure under x-ray diffraction, indicating that NiTi-LDH has been deposited on FTO by EPD without degradation. NiTi-LDH powder was obtained from formic acid intercalated LDH by homogeneous precipitation in formamide with hexamethylenetetramine, and NiTi-LDH/graphene composite was obtained from graphene and NiTi-LDH aqueous suspension with urea. The formed NiTi-LDH and NiTi-LDH/graphene composite films have different morphologies. Both NiTi-LDH and NiTi-LDH/graphene films prepared showed photovoltage of 15-55 mV under visible-light irradiation. Their photoelectrochemical properties were affected by the film morphology.