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Spinel oxides are promising for high-potential cathode materials of photo-rechargeable batteries. However, LiMn1.5M0.5O4 (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. LiMn1.5Fe0.5O4 exhibited a substantially higher discharge capacity compared to that of LiMn2O4 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. [ABSTRACT FROM AUTHOR]

We present a method for obtaining a three-dimensional quantitative hydrogen distribution in a Ni–MH battery cathode using laser-induced breakdown spectroscopy (LIBS) and demonstrate that the reaction distribution in the cathode can be interpreted based on a state-of-charge (SOC) distribution converted from the hydrogen distribution. In this method, we measured the hydrogen emission-line intensities at 656.28 nm for a model cathode cycled five times at 2.3 mA cm−2 and a commercial Ni–MH battery cathode cycled 1000 times at 1C under a 3000 Pa helium atmosphere. Our results show that the average SOC in the SOC distributions of the cathodes agreed with those evaluated from X-ray diffraction and charge–discharge curves and that the overcharged areas exhibited SOC values above 100%. The present LIBS method will allow us to understand the deterioration mechanism of a Ni–MH battery and improve its cycle life and capacity. [ABSTRACT FROM AUTHOR]

Photocharging of high-potential spinel LiMn2O4 is demonstrated by using a water-in-salt electrolyte and TiO2 nanoparticles. In a developed half-cell system with an electron acceptor, Li extraction from LiMn2O4 proceeds under the illumination of UV-visible light at an estimated rate of ∼23 mA g−1. This work paves the way for high-potential cathode materials in photo-rechargeable batteries. [ABSTRACT FROM AUTHOR]

Spinel MgCo 2 O 4 oxide, expected as a cathode material candidate for magnesium rechargeable battery, undergoes spinel-to-rocksalt transition accompanied with Mg insertion. Upon scanning-transmission-electron-microscopy observation, cations located at the tetrahedral sites readily migrate to the adjacent octahedral sites due to electron irradiation (without any Mg insertion), so that the spinel structure changes to a defect rocksalt structure with cation disorder. This together with first-principles calculations demonstrates that there is little energetic preference for Mg cation between the tetrahedral and octahedral sites, accounting for the feasibility of the Mg insertion into the spinel MgCo 2 O 4 cathode via intercalation and push-out process of Mg cation. Unlabelled Image [ABSTRACT FROM AUTHOR]