Optimizing LiMn 1.5 M 0.5 O 4 cathode materials for aqueous photo-rechargeable batteries.

Spinel oxides are promising for high-potential cathode materials of photo-rechargeable batteries. However, LiMn 1.5 M 0.5 O 4 (M = Mn) shows a rapid degradation during charge/discharge under the illumination of UV-visible light. Here, we investigate various spinel-oxide materials by modifying the composition (M = Fe, Co, Ni, Zn) to demonstrate photocharging in a water-in-salt aqueous electrolyte. LiMn 1.5 Fe 0.5 O 4 exhibited a substantially higher discharge capacity compared to that of LiMn 2 O 4 after long-term photocharging owing to enhanced stability under illumination. This work provides fundamental design guidelines of spinel-oxide cathode materials for the development of photo-rechargeable batteries.