Na-ion batteries are an attractive alternative to Li-ion batteries for large-scale energy storage systems because of their low cost and the abundant Na resources. This Review provides a comprehensive overview of selected anode materials with high reversible capacities that can increase the energy density of Na-ion batteries. Moreover, we discuss the reaction and failure mechanisms of those anode materials with a view to suggesting promising strategies for improving their electrochemical performance.

A new polyanion‐based compound, Na3.12M2.44(P2O7)2 (M = Fe, Fe0.5Mn0.5, Mn) is synthesized and examined as a cathode for Na ion batteries. Off‐stoichiometric synthesis induces the formation of a Na‐rich phase, Na3.32Fe2.34(P2O7)2 ‐ a member of the solid solution series Na4‐αFe2+α/2(P2O7)2 (2/3 ≤ α ≤ 7/8) ‐ which delivers a reversible capacity of about 85 mA h g−1 at ca. 3 V vs. Na/Na+ and exhibits very stable cycle performance. Above all, it shows fast kinetics for Na ions, delivering an almost constant 72% reversible capacity at rates between C/10 and 10C without the necessity for nanosizing or carbon coating. We attribute this to the spacious channel size along the a‐axis, along with a single phase transformation upon de/sodiation.

Recent studies demonstrate roles for activation of caspases and cleavage of cellular proteins within neurons of the Alzheimer's disease (AD) brain. To determine whether a similar role for caspases also occurs within glial cells in AD, we designed a site-directed caspase-cleavage antibody specific to glial fibrillary acidic protein (GFAP), a cytoskeleton protein specifically expressed in astrocytes. In vitro characterization of this antibody using both a cell-free system and a cell model system of apoptosis demonstrated that the antibody (termed GFAP caspase-cleavage product antibody or GFAP-CCP Ab) immunolabeled the predicted caspase-cleavage fragment, but not full-length GFAP, by Western blot analysis. To determine whether caspases cleave GFAP in vivo, tissue sections from control and AD brains were examined by immunohistochemistry using the GFAP-CCP Ab. Two prominent features of staining were evident: immunolabeling of degenerating astrocytes in proximity to blood vessels and staining within plaque-rich regions of the AD brain. Furthermore, co-localization of the GFAP-CCP Ab and an antibody specific to active caspase-3 was demonstrated within damaged astrocytes of the AD brain. These data suggest that the activation of caspases and cleavage of cellular proteins such as GFAP may contribute to astrocyte injury and damage in the AD brain.

We clarified the failure mechanism of Li–O2batteries with a redox mediator.

Mild‐acid Zn‐MnO2 batteries have been considered a promising alternative to Li‐ion batteries for large scale energy storage systems because of their high safety. There have been remarkable improvements in the electrochemical performance of Zn‐MnO2 batteries, although the reaction mechanism of the MnO2 cathode is not fully understood and still remains controversial. Herein, the reversible dissolution/deposition (Mn2+/Mn4+) mechanism of the MnO2 cathode through a 2e− reaction is directly evidenced using solution‐based analyses, including electron spin resonance spectroscopy and the designed electrochemical experiments. Solid MnO2 (Mn4+) is reduced into Mn2+ (aq) dissolved in the electrolyte during discharge. Mn2+ ions are then deposited on the cathode surface in the form of the mixture of the poorly crystalline Zn‐containing MnO2 compounds through two‐step reactions during charge. Moreover, the failure mechanism of mild‐acid Zn‐MnO2 batteries is elucidated in terms of the loss of electrochemically active Mn2+. In this regard, a porous carbon interlayer is introduced to entrap the dissolved Mn2+ ions. The carbon interlayer suppresses the loss of Mn2+ during cycling, resulting in the excellent electrochemical performance of pouch‐type Zn‐MnO2 cells, such as negligible capacity fading over 100 cycles. These findings provide fundamental insights into strategies to improve the electrochemical performance of aqueous Zn‐MnO2 batteries.