Recently, Cu element has been introduced into layered sodium transition metal oxides (NaxTMO2) as cathode materials for sodium ion batteries to engineer rate and cycling performance. To study the unique role provided by Cu, we designed, synthesized and tested four different compositions of P2-type Nax(MnyFezCo1-y-z)O2 and three compositions of P2-type Nax(MnyFezCu1-y-z)O2 cathode materials. When cycled in the full voltage range of 1.5∼4.5 V under different rates 0.1 C, 1 C and 10 C, the cyclability of MnFeCu-based compounds is better than that of MnFeCo-based ones. Using X-ray diffraction, we observed the P2 to O2-like phase transition of MnFeCu-based materials upon charging and studied its influence on battery performance. Limiting the P2-O2 phase transition delivers less capacity, but improves cyclability. By DFT simulations, we showed that different Na diffusivity and site preference in the high voltage phase contribute to the difference in the electrochemical performances of these cathode materials.

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.