In the last few decades, there are some exciting developments in the field of lithium (Li)-ion batteries from small portable devices to large power system such as electric vehicles (EVs). However, the maximum energy density of lithium-ion batteries is insufficient for the extended range of EVs propulsion. On the other hand, metal-air batteries have a greater power storage capacity, a few times more than the best performing lithium-ion batteries. Mechanically rechargeable zinc (Zn)-, magnesium (Mg)-, and aluminum (Al)-air batteries are receiving increasing attention, due to the advantages of using safe, low cost and abundant materials. If successfully developed, these batteries could provide an energy source for EVs comparing that of gasoline in terms of usable energy density. Nevertheless, there are still numerous scientific and technical challenges that must be overcome, if this alluring promise can be turned into reality. This paper provides a comprehensive overview of recent advances and challenges of metal air batteries from various elements, including air cathode, electrolyte, and anode. In addition, this review outlines the fundamental principles and understanding of the electrochemical reactions in the areas of lithium-air batteries. Finally, a summary of future research directions in the field of the metal-air batteries is provided.

Despite the high theoretical capacity of Si anodes, the electrochemical performance of Si anodes is hampered by severe volume changes during lithiation and delithiation, leading to poor cyclability and eventual electrode failure. Nanostructured silicon and its nanocomposite electrodes could overcome this problem holding back the deployment of Si anodes in lithium‐ion batteries (LIBs) by providing facile strain relaxation, short lithium diffusion distances, enhanced mass transport, and effective electrical contact. Here, the recent progress in nanostructured Si‐based anode materials such as nanoparticles, nanotubes, nanowires, porous Si, and their respective composite materials and fabrication processes in the application of LIBs have been reviewed. The ability of nanostructured Si materials in addressing the above mentioned challenges have been highlighted. Future research directions in the field of nanostructured Si anode materials for LIBs are summarized.

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Separation of single-walled carbon nanotubes (SWNTs) according to their handedness has been attracting growing interest. Our methodology to separate the enantiomers of SWNTs is based on molecular recognition with chiral diporphyrin nanotweezers. Herein, we report novel nanotweezers 1 consisting of two chiral porphyrins and phenanthrene in between. These nanotweezers 1 are rationally designed to discriminate diameter and handedness simultaneously by taking into account the relationship between the (n, m) selectivity and the structures of previously reported chiral nanotweezers. Owing to the relatively narrow cleft made by two porphyrins, the nanotweezers 1 showed high selectivity toward (6,5)-SWNTs possessing the smallest diameter among the major components of CoMoCAT-SWNTs. In addition, the chiral diporphyrin 1 discriminated the left- and right-handed structures of (6,5)-SWNTs, providing high enantiomeric excess (67% ee on the basis of the (6,5)-SWNTs with high optical purity recently reported by Weisman). In conclusion, only the single stereoisomer of (6,5)-SWNTs was highly enriched through the extraction of CoMoCAT-SWNTs with phenanthrene-bridged chiral diporphyrin nanotweezers 1.