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.