New Insights into Lithium Hopping and Ordering in LiNiO2 Cathodes during Li (De)intercalation

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.