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Nano-scale Al-rich layers on the surface of LiNi0.92Al0.08O2 and substituted-Al in the crystal suppress both the surface degradation and bulk degradation, resulting in the excellent cycling performance Ni-rich electrode material.

Oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) on glassy-carbon-supported platinum electrodes (Pt/GCs), which are partially immersed in alkaline electrolytes, are investigated as a model of the triple phase boundary (TPB) in air electrodes for metal-air secondary batteries. ORR currents are measured with changing the vertical position of Pt/GCs, and OER currents are measured by linear sweep voltammetry. Based on the electrochemical results, it is found that thin liquid film on Pt/GCs effectively serves to expand TPB regions for ORR, but the liquid film hardly increases OER currents. Therefore, we conclude that the most effective TPB form are determined by the electrode reactions (ORR or OER), which are corresponding to discharge and charge processes for metal-air secondary batteries. In practice, it is strongly necessary to control the wettability of electrode inside, in order to construct high-performance bifunctional air electrodes.

Elucidating reaction inhomogeneity of composite electrodes is key to improve the performances of batteries such as rate capability and durability. Because the reaction inhomogeneity often disappears after a certain relaxation period, operando analytical techniques are indispensable. We hereby propose that operando optical analysis as a common lab method can be applied to visualize the reaction inhomogeneity of LiFePO 4 composite electrodes for lithium-ion batteries with sufficient space and time resolutions. The results indicate that the brightness of the charged phase was higher than that of the discharged phases, which can be used to separate the phases and thus to elucidate the reaction inhomogeneity in the cross section of the composite electrode. A metastable phase Li 3/4 FePO 4 was also captured at a low temperature with the optical analysis.