Dynamics of Lithium Microstructure at Lithium Metal and Graphite Anodes Probed with in Operando Pulse EPR

Abstract

Lithium microstructure formation is the limiting factor preventing the application of lithium metal anodes and, to some degree, fast-charging of graphite anodes, because of enhanced cell degradation and risks of short-circuits. To improve mechanistic understanding and develop prevention strategies, a complementary analytical tool set is necessary.Contributing to non-invasive in operando techniques, we present pulse electron paramagnetic resonance (pEPR) with a practical sampling rate of 100 microseconds, providing a global view on lithium microstructure formation and evolution.[1] pEPR experiments offer an estimate of the dimension and size distribution of the morphology that is in line with post-test SEM characterization. For lithium metal anodes, the sampling rate is sufficient to observe dynamic morphology changes that evolve for several seconds after fresh lithium deposition, attributed to surface smoothening, comparable to recently observed heating-induced healing of dendrites.[2] For graphite anodes, lithium plating can be followed at C-rates up to 18C. Quantitative measurements reveal an exponential increase of deposited lithium mass upon galvanostatic charge. The plating onset is pinpointed to the characteristic voltage drop well below 0 V vs. Li/Li+.[3] After stopping the charge at intermediate states of charge, the partial intercalation of lithium can be monitored at OCV, identifying two kinetic domains and the amount of remaining dead lithium.[1] C. Szczuka, J. Ackermann, P. Philipp, M. Schleker, P. Jakes, R.-A. Eichel, J. Granwehr, Commun. Mater. 2021, 2, 20.[2] L. Li, S. Basu, Y. Wang, Z. Chen, P. Hundekar, B. Wang, J. Shi, Y. Shi, S. Narayanan, N. Koratkar, Science. 2018, 359, 1513–1516.[3] C. Uhlmann, J. Illig, M. Ender, R. Schuster, E. Ivers-Tiffée, J. Power Sources 2015, 279, 428–438. Figure 1