Roles of Ionic Transport in Dendrite Growth through Solid State Electrolytes at the Critical Current Density

Abstract

Lithium metal anodes hold the promise to significantly increase the energy density of current Li-ion batteries by replacing the bulkier graphite anode. However, these batteries have low cycling efficiency and internal short circuiting due to metal dendrites. A strategy to prevent dendritic growth is using a stiff solid electrolyte that can mechanically block their growth, while in reality, penetration through the tough solid electrolytes by soft Li metal filaments still occurs at a relatively low critical current density.Inspired by the dendrite initiation at the system-specific limiting current in liquid electrolytes, we explore the possibility in this study that dendrite growth in solid state electrolytes at the critical current density (CCD) is a transport limited phenomenon determined by ionic conduction. Previous studies have used galvanostatic cycling [1] as the basis for measuring the CCD, however cycling presents problems of interfacial stripping and delamination leading to a reduction in contact surface area and high localized current densities. Here we use linear sweep voltammetry (LSV) with the implementation of stack pressure to mitigate these effects to initially determine the CCD and develop a model connected to the ionic conduction. With the experimentally determined CCD, we then investigate the penetration time at various higher-than-CCD constant current densities to uncover a Sand’s time-like behavior, which offers insights on the transport dynamics consistent with our previous work [2]. Operando and postmortem analyses were also performed to complement the electrochemical characterization toward a self-consistent comprehensive understanding. In conclusion, our new method allows us to understand the growth mechanism of dendrites in solid electrolytes, while still connecting microstructural and interfacial aspects from previous published works[3][4], to present a unified approach to understanding the metal dendrite initiation at the CCD.References E. Kazyak, R. Garcia-Mendez, W.S. LePage, A. Sharafi, A.L. Davis, A.J. Sanchez, K.-H. Chen, C. Haslam, J. Sakamoto and N.P. Dasgupta. Li Penetration in Ceramic Solid Electrolytes: Operando Microscopy Analysis of Morphology, Propagation, and Reversibility. Matter 2, 1025-1048, (2020).P. Bai, J. Li, F.R. Brushett and M.Z. Bazant. Transition of lithium growth mechanisms in liquid electrolytes. Energ Environ Sci 9, 3221-3229, (2016).L. Porz, T. Swamy, B.W. Sheldon, D. Rettenwander, T. Frömling, H.L. Thaman, S. Berendts, R. Uecker, W.C. Carter and Y.-M. Chiang. Mechanism of Lithium Metal Penetration through Inorganic Solid Electrolytes. Advanced Energy Materials 7, 1701003-n/a, (2017).T. Krauskopf, H. Hartmann, W.G. Zeier and J. Janek. Toward a Fundamental Understanding of the Lithium Metal Anode in Solid-State Batteries—An Electrochemo-Mechanical Study on the Garnet-Type Solid Electrolyte Li6.25Al0.25La3Zr2O12. ACS Applied Materials & Interfaces 11, 14463-14477, (2019). Figure 1