Lithiation and Delithiation Dynamics of Different Li Sites in Li-Rich Battery Cathodes Studied by Operando Nuclear Magnetic Resonance

Li in Li-rich cathodes mostly resides at octahedral sites in both Li layers (Li Li ) and transition metal layers (Li TM ). Extraction and insertion of Li Li and Li TM are strongly influenced by surrounding transition metals. pjMATPASS and operando Li nuclear magnetic resonance are combined to achieve both high spectral and temporal resolution for quantitative real time monitoring of lithiation and delithiation at Li Li and Li TM sites in Li 2 MnO 3, Li 1.2 Ni 0.2 Mn 0.6 O 2, and Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 cathodes. The results have revealed that Li TM are preferentially extracted for the first 20% of charge and then Li Li and Li TM are removed at the same rate. No preferential insertion or extraction of Li Li and Li TM is observed beyond the first charge. Ni and Co promote faster and more complete removal of Li TM . The recovery of the removed Li is <60% for Li TM and >80% for Li Li upon first discharge. The study sheds light on the activity of Li Li and Li TM during electrochemical processes as well as their respective contributions to cathode capacity.