In situ 7Li and ex situ 6Li nuclear magnetic resonance (NMR) spectroscopy is applied to monitor lithium mobility in a LiNiO2 cathode during Li-ion (de)­intercalation. In situ X-ray absorption spectroscopy and galvanostatic intermittent titration are also used to capture changes during the Li-ion deintercalation process. A considerable line broadening was first found by 7Li NMR spectroscopy. The Jahn–Teller distortion hinders the Li diffusion, thus broadening the NMR signal. The observed NMR shifts are compared to Li/vacancy ordering patterns described earlier by Arroyo y de Dompablo et al. Coupled motions of electrons and Li ions are also discovered by both in situ 7Li and ex situ 6Li NMR spectroscopy for the first time. They result in local Li environments with an enhanced number of Ni3+ neighbors at highly charged states. This opens a new perspective for understanding the highly delithiated structure.

The magnesium-sulfur (Mg-S) battery has attracted considerable attention as a candidate of post-lithium battery systems owing to its high volumetric energy density, safety, and cost effectiveness. However, the known shuttle effect of the soluble polysulfides during charge and discharge leads to a rapid capacity fade and hinders the realization of sulfur-based battery technology. Along with the approaches for cathode design and electrolyte formulation, functionalization of separators can be employed to suppress the polysulfide shuttle. In this study, a glass fiber separator coated with decavanadate-based polyoxometalate (POM) clusters/carbon composite is fabricated by electrospinning technique and its impacts on battery performance and suppression of polysulfide shuttling are investigated. Mg-S batteries with such coated separators and non-corrosive Mg[B(hfip) 4 ] 2 electrolyte show significantly enhanced reversible capacity and cycling stability. Functional modification of separator provides a promising approach for improving metal-sulfur batteries.

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