Operando NMR of NMC811/Graphite Lithium-Ion Batteries: Structure, Dynamics, and Lithium Metal Deposition

Lithium-ion batteries (LIBs) are of tremendous importance for our society, but their limited lifetime still poses a great challenge. For a better understanding of battery cycling and degradation, operando analytical measurements are invaluable. In this work, we demonstrate that operando ⁷Li nuclear magnetic resonance (NMR) spectroscopy can be applied to full LIBs. We exemplify this on LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811)/graphite cells, which are typical high-energy LIBs. Employing industry-standard electrodes, our operando cells show realistic cycling performance at practical rates, which allows us to conduct experiments at different rates and temperatures and to draw conclusions on the performance of LIBs. The NMR experiments monitor processes in both electrodes individually, including Li-ion mobility and its changes with temperature. Moreover, Li metal deposition on graphite is observed at low temperature, which is an important degradation mechanism in LIBs and a severe safety hazard. Our experiments offer unique insights into this Li metal deposition process under different charging conditions.