Impact of Solid Electrolyte Interphase (SEI) Stiffness on Lithium Dendrite Growth

Abstract

Extensive research is being conducted for the successful implementation of lithium metal anodes (Li) in next generation lithium ion batteries (LIBs) due to its very low potential and large specific capacity. However, growth of dendritic protrusions during continuous charge-discharge cycles, and subsequent shorting of the cell, is considered as the largest bottleneck preventing its commercial implementation [1]. In spite of substantial research over the last decade, no strategy has yet been devised that can completely suppress the growth of Li dendrites over thousands of cycles. Computational modeling tools are presently being used for developing a better understanding of the growth of dendritic protrusions, and constructing new strategies for preventing its growth. Some of the computational models developed till date to understand the growth of dendritic protrusions took the effect of solid electrolyte interphase (SEI) layer into account [2], whereas, some others completely neglected SEI layers owing to its very small thickness [3]. Earlier computational models of dendrite growth with SEI layer considered only the transport resistances exerted by the interphase layer [4]. Very recently the impact of mechanical stiffness of the SEI layer on dendrite growth have been incorporated into the computational models [5]. Since the lithium metal and SEI layers are in contact, both displacement and force at the Li/SEI interface must be continuous. However, all the computational studies capture only the continuity of displacement at the Li/SEI interface [5]. The normal force equilibrium at Li/SEI interface has not been studied by any researcher. In the present study, a computational model has been developed that can capture the formation and growth of Li dendritic nuclei. The impact of SEI layers has been appropriately taken into account by ensuring continuity of displacement, as well as force equilibrium, at the Li/SEI interface. The initial phase of the Li dendrite is modeled, which has been characterized as the “nucleus”. It has been assumed that non-uniform transport through a damaged SEI layer is the main cause of Li dendrite growth. Figure 1 depicts a phase map demonstrating the variation in protrusion height, as the applied current density (Iapp) and SEI stiffness (GSEI) changes. Larger magnitudes of applied current density increase the non-uniformity in lithium deposition, and help the Li nucleus to grow. However, due to the mechanical equilibrium at the Li/SEI interface, higher elastic modulus of the SEI layer helps to prevent the growth of dendrites. In the present research, impact of SEI thickness, and various transport properties (such as, conductivity, diffusivity, etc.) of Li through the SEI, on the formation of a dendritic protrusion, will be investigated. Extension of this particular model, for elucidating the impact of protective layers (PLs) on the lithium dendrite growth process, will also be demonstrated. [1] X. B. Cheng et al. Chemical Reviews (2017) 117 10403 – 10473. [2] G. Yoon et al. Chemistry of Materials (2018) 30, 19, 6769 – 6776. [3] D. R. Ely and R. E. Garcia. Journal of the Electrochemical Society (2013) 160 (4) A662 – A668. [4] P. Arora et al.Journal of the Electrochemical Society (1999) 146 (10) 3543 – 3553. [5] G. Liu and W. Lu. Journal of the Electrochemical Society (2017) 164 (9) A1826 – A1833. Figure 1