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Following the fundamental research conducted by J. B. Goodenough, the important role of electron localization induced by elemental substitution is studied. The size and electron negativity of host and substituting ions are two important factors in tuning material properties such as local structure and transition metal (TM) oxygen covalency. However, another factor, electron localization, which is widely studied in catalyst research but largely overlooked for battery materials, deserves systematic studies. A combined investigation using synchrotronbased X‐ray spectroscopy and theoretical calculations is carried out on the Li‐Co‐Mn‐O model system in which the substituting cation Mn4+, with its 3d3 electronic structure, is used as a promoter for electron localization. Results indicate that electron localization greatly influences the CoO bond by making it less covalent, which increases the delithiation voltage. It is also found that during charge/discharge, electron localization tends to make TM K‐edge X‐ray absorption near edge spectroscopy (XANES) spectra show a more "rigid shift" behavior while electron delocalization makes the XANES exhibit a "shape change." It clearly explains why the K‐edge XANES data of some TM oxides show no "rigid shift" while the nominal valence states changed. This work highlights the importance of electron localization with guidance for XANES interpretation. [ABSTRACT FROM AUTHOR]

Exceptional cycling performance of graphite anode in K-ion batteries is demonstrated with a reversible capacity of 246 mAh g-1 and 89% retention of the initial capacity after 200 cycles. Although the graphite anode experiences huge volume change and worse kinetics during K intercalation/deintercalation, the cycling stability delivered in K-ion batteries is comparable to that of Li-ion batteries using the same graphite anode. The combination of excellent electrochemical performance, the abundance and wide availability of K in earth's crust, and the well-developed technology of the graphite anode make the K-ion battery very attractive for offering a low cost battery chemistry for large-scale energy storage applications. [ABSTRACT FROM AUTHOR]

A copper-stabilized sulfur-microporous carbon (MC-Cu-S) composite is synthesized by uniformly dispersing 10% highly electronically conductive Cu nanoparticles into microporous carbon (MC), followed by wet-impregnating S. In the MC-Cu-S composite, the MC host that physically confines S/polysulfides provides free space to accommodate volumetric expansion of S during lithiation, while the Cu nanoparticles that are anchored in the MC further chemically interact with S/polysulfides through bonding between Cu and S/polysulfides. The Cu loading allows the S content to increase from 30 to 50% in the carbon-S cathode material without scarifying the electrochemical performance in a low-cost carbonate electrolyte. At a current density of 100 mA g-1, the MC-Cu-S cathode shows that Coulumbic efficiency is close to 100% and capacity maintains more than 600 mAh g-1 with progressive cycling up to more than 500 cycles. In addition, the Cu nano-inclusins also enhance the electronic conductivity of the MC-Cu-S composite, remarkably increasing the rate capabilities. Even the current density increases 10.0 A g-1, the MC-Cu-S cathode can still deliver a capacity of 200 mAh g-1. This strategy of stabilization of S with small amount of metal nanoparticles anchored in MC provides an effective approach to improve the cycling stability, Coulumbic efficiency, and S loading for Li-S batteries. [ABSTRACT FROM AUTHOR]