Potassium tetratitanate (K2Ti4O9) has been synthesized by solid state method using K2CO3 and TiO2, and studied as an anode material for potassium ion batteries for the first time. A discharge capacity of 80 mAh g−1 has been obtained at a current density of 100 mA g−1 (0.8 C rate) and 97 mAh g−1 at 30 mA g−1 (0.2 C rate), initially. The discharge capacity is stable at low rates of cycling. The uptake of K+ on charging K2Ti4O9 electrodes is quantitatively studied. The proposed mechanism of charging involves reduction of two Ti ions from 4+ oxidation state to 3+ oxidation state, which facilitates insertion of two K+ ions per formula unit. The rate capability experiments suggest that K2Ti4O9 is capable of undergoing charge-discharge cycling at high rates (up to 15 C rate), but with a low discharge capacity. Thus K2Ti4O9 is a promising anode material for future K-ion batteries.

Sodium-ion batteries are a promising battery technology for their cost and sustainability. This has led to increasing interest in the development of new sodium-ion batteries and new analytical methods to non-invasively, directly visualise battery chemistry. Here we report operando 1 H and 23 Na nuclear magnetic resonance spectroscopy and imaging experiments to observe the speciation and distribution of sodium in the electrode and electrolyte during sodiation and desodiation of hard carbon in a sodium metal cell and a sodium-ion full-cell configuration. The evolution of the hard carbon sodiation and subsequent formation and evolution of sodium dendrites, upon over-sodiation of the hard carbon, are observed and mapped by 23 Na nuclear magnetic resonance spectroscopy and imaging, and their threedimensional microstructure visualised by 1 H magnetic resonance imaging. We also observe, for the first time, the formation of metallic sodium species on hard carbon upon first charge (formation) in a full-cell configuration.

rGO wrapped MoO3 NPs were successfully synthesized via simple and scalable steps as potential anode materials for Li-ion batteries.