Lithiation and Delithiation Dynamics of Different
Li Sites in Li-Rich Battery Cathodes Studied by <i>Operando</i> Nuclear Magnetic Resonance
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Abstract
Li
in Li-rich cathodes mostly resides at octahedral sites in both
Li layers (Li<sub>Li</sub>) and transition metal layers (Li<sub>TM</sub>). Extraction and insertion of Li<sub>Li</sub> and Li<sub>TM</sub> are strongly influenced by surrounding transition metals. pjMATPASS
and <i>operando</i> 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<sub>Li</sub> and Li<sub>TM</sub> sites in Li<sub>2</sub>MnO<sub>3</sub>, Li<sub>1.2</sub>Ni<sub>0.2</sub>Mn<sub>0.6</sub>O<sub>2</sub>, and Li<sub>1.2</sub>Ni<sub>0.13</sub>Mn<sub>0.54</sub>Co<sub>0.13</sub>O<sub>2</sub> cathodes. The results have revealed that Li<sub>TM</sub> are
preferentially extracted for the first 20% of charge and then Li<sub>Li</sub> and Li<sub>TM</sub> are removed at the same rate. No preferential
insertion or extraction of Li<sub>Li</sub> and Li<sub>TM</sub> is
observed beyond the first charge. Ni and Co promote faster and more
complete removal of Li<sub>TM</sub>. The recovery of the removed Li
is <60% for Li<sub>TM</sub> and >80% for Li<sub>Li</sub> upon
first discharge. The study sheds light on the activity of Li<sub>Li</sub> and Li<sub>TM</sub> during electrochemical processes as well as
their respective contributions to cathode capacity
