There is significant interest in solid-state batteries (SSBs) as an alternative to traditional Li-ion batteries, as they can potentially eliminate the flammable liquid electrolyte and enable Li-metal anodes. However, manufacturing of SSBs with Li metal anodes poses a significant challenge, owing to the highly reactive nature of Li metal. Therefore, there has been a recent increase in interest in “anode-free” configurations, where the Li metal anode is formed in situ using the pre-existing inventory in the cathode. In addition to manufacturing considerations, anode-free configurations also enhance energy density compared to batteries with excess Li metal in the anode. However, compared to pre-formed Li metal/solid electrolyte interfaces, the nucleation, growth, and stripping of Li metal in anode-free SSBs has not been widely studied, and poses unique electro-chemo-mechanical phenomena.

To probe the dynamic interfacial evolution of anode-free SSBs, in this study, I will present results using a complimentary set of in situ/operando methodologies. First, I will describe the morphological evolution of Li nucleation and growth at garnet LLZO solid electrolytes, using a newly developed platform for operando 3-D video microscopy [1]. In particular, the influence of mechanical stresses on both the thermodynamic and kinetic properties of Li will be discussed, and unique electrochemical signatures of anode-free plating will described. A mechanistic framework for these electro-chemo-mechanics will be presented, which results in design rules for improving the homogeneity of Li plating during anode formation.

To compliment this morphological information, I will also present results using operando x-ray photoelectron spectroscopy (XPS) on sulfide solid electrolytes. This allows for direct observation of SEI formation during in situ anode formation. In particular, we observe a transition in reaction pathways from SEI formation to nucleation of Li metal, which is a function of both the charging protocol and the presence of interlayer coatings [2-3]. Finally, these results will be compared and contrasted to anode-free Li plating in liquid electrolytes, and a discussion will be presented on how to optimize plating morphology and reversibility.

[1] E. Kazyak, M. Wang, K. Lee, S. Yadavalli, A. J. Sanchez, M. D. Thouless, J. Sakamoto, N. P. Dasgupta, Submitted (2022).

[2] A. L. Davis, R. Garcia-Mendez, K. N. Wood, E. Kazyak, K.-H. Chen, G. Teeter, J. Sakamoto, N. P. Dasgupta, J. Mater. Chem. A 8, 6291 (2020).

[3] A. L. Davis, E. Kazyak, D. W. Liao, K. N. Wood, N. P. Dasgupta, J. Electrochem. Soc. 168, 070557 (2021).