Direct Mechanical and Electrochemical Analysis of Dendrites in Solid-State Electrolytes

Although solid-state batteries with metal anodes promise to enable safer, higher energy density batteries, metal protrusions (dendrites) short-circuit the cell when charging faster than a critical current density.1,2It is generally believed that dendrites grow when the strain energy available for crack extension (the strain energy release rate, ) exceeds that required for fracture of the solid-electrolyte..2-4 We test this hypothesis using operando birefringence microscopy5 to directly observe dendrite-induced stresses. The strain energy release rate is determined by fitting the experimentally measured stress distribution to that which is expected in the vicinity of an internally loaded crack (detailed in Fig. 1).6 These operando experiments, combined with cryogenic scanning transmission electron microscopy (STEM) characterization of the dendrite tip, enable studies of electrochemical and mechanical phenomena underlying dendrite growth in ceramic electrolytes. All experiments were conducted on the most electrochemically stable Li-ion conducting solid electrolyte (tantalum-doped lithium lanthanum zirconium oxide). References: Sudworth, J. L., Hames, M. D., Storey, M. A., Azim, M. F. & Tilley, A. R. An analysis and laboratory assessment of Two Sodium Sulfur Cell Designs. Power Sources 4, 1–18 (1972). Sharafi, A. S. et al. Characterizing the Li–Li7La3Zr2O12 interface stability and kinetics as a function of temperature and current density. J. Power Sources 302, 135–139 (2016). Fincher, C. D. et al. Controlling dendrite propagation in solid-state batteries with engineered stress. Joule 6, 2794-2809 (2022). Porz†, L., Swamy†, T. et al. Mechanism of lithium metal penetration through inorganic solid electrolytes. Adv. Energy Mater. 7, 1701003 (2017). Athanasiou†, C. E., Fincher†, C. D. et al. Operando measurements of dendrite-induced stresses in ceramic electrolytes using photoelasticity. Matter (2023). Fincher C. D., et al. In prep. Figure 1: Operando birefringence imaging enables direct measurement of dendrite-induced stresses in solid-electrolytes. Pixel-by-pixel computational analysis allows measurement of the mechanical driving force for crack growth, (the strain energy release rate).6 (a) Dendrites are grown through the plane of a thin LLZO solid electrolyte which was mechanically thinned to the point of translucency. A microscope is used to collect (b) polarized light images of dendrite propagation, and (c) spatially resolved measurements of the max shear stress in the solid electrolyte. The stress measurements in (c) correspond to the region enclosed by the dashed black box in (b). The strain energy release rate is determined by fitting the experimentally determined stress field (c) to that expected analytically (d), using as a fitting parameter. (e) The stress distribution measured along a line profile starting at the crack tip and ending at a point 45° (in red) and 90° (in blue) from the propagation direction. The solid and dashed lines series represent data from the experimental and computed analytic stress fields in c and d, respectively. The end points of the 45° and 90° profiles are shown as red and blue “X” symbols in c and d, respectively. Figure 1