The Effect of Pore Connectivity on Li Dendrite Propagation within Llzo Electrolytes Observed with Synchrotron X-Ray Tomography

Abstract

Li7La3Zr2O12 (LLZO) is a garnet type material that demonstrates promising characteristics for all solid-state battery applications due to its high Li-ion conductivity and its compatibility with Li metal1,2. The primary limitation of LLZO is the propensity for short-circuiting at low current densities3. Microstructure features such as grain boundaries, pore character, and density all contribute to this shorting phenomenon. Toward the goal of understanding structure-processing relationships for practical design of solid electrolytes, the present study tracks structural transformations in solid electrolytes processed at three different temperatures (1000, 1050 and 1150 °C) using synchrotron x-ray tomography4. A sub volume of 300 μm3 captures the heterogeneity of the solid electrolyte microstructure while minimizing the computational intensity associated with 3D reconstructions. While the porosity decreases with increasing temperature, the underlying connectivity of the pore region increases. Solid electrolytes with interconnected pores short circuit at lower critical current densities than samples with less connected pores. [1]Thompson, Travis, et al. "Tetragonal vs. cubic phase stability in Al–free Ta doped Li 7 La 3 Zr 2 O 12 (LLZO)." Journal of Materials Chemistry A 2.33 (2014): 13431-13436. [2] Sharafi, Asma, et al. "Characterizing the Li–Li 7 La 3 Zr 2 O 12 interface stability and kinetics as a function of temperature and current density." Journal of Power Sources 302 (2016): 135-139. [3] Cheng, Eric Jianfeng, Asma Sharafi, and Jeff Sakamoto. "Intergranular Li metal propagation through polycrystalline Li 6.25 Al 0.25 La 3 Zr 2 O 12 ceramic electrolyte." Electrochimica Acta 223 (2017): 85-91. [4] Hatzell, Kelsey B., et al. "Direct observation of active material interactions in flowable electrodes using X-ray tomography." Faraday discussions 199 (2017): 511-524. Figure 1