Oxychloride antiperovskite Li conductors represent compelling candidates for battery solid electrolytes (SEs), owing to their stability vs. Li and ductility. However, the influence of synthesis route and resulting microstructure on transport behavior remains incompletely studied. We prepared Li2OHCl in 3 ways: a) cold-pressing of solid-state-synthesized orthorhombic and cubic Li2OHCl powders, b) sintering of these powders into pellets, and c) reactive sintering of high-energy ball-milled LiCl and LiOH reagents. We studied the impedance spectra for route a) at 25 °C, for route b) from ∼25–270 °C, and for route c) during the reactive sintering process to form the cubic phase, coupled to in-situ XRD. Cold-pressed powders typically exhibited a single impedance arc, while ex-situ sintered pellets exhibited an offset resistance with lower activation energy (∼0.44–0.48 eV) >60 °C and an arc with higher activation energy (∼0.6–1.2 eV). With increasing temperature, the offset feature increasingly dominated the impedance spectra, and its associated conductivity (1.9 × 10−3 Scm−1) was in good agreement with the total conductivity magnitude (1.3 × 10−3 Scm−1) and activation energy (0.42 eV) measured during reactive sintering of reagents once the cubic phase was obtained (>160 °C). Spectra were simulated using the brick layer model corresponding to the microstructure observed by SEM and varied specific conductivities and permittivities. Based on the above results, we attribute the offset feature to grains and the arc to blocking grain boundaries. A signature of possible proton transport in adsorbed H2O layers was observed in non-Arrhenius behavior below ∼60 °C, rendering separation of grain and grain boundary Li transport challenging at room temperature.
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