PNNL

Abstract

In the pursuit of urgently-needed, energy dense solid-state batteries for electricvehicle and portable electronics applications, halide solid electrolytes offer a promisingpath forward with exceptional compatibility against high-voltage oxide electrodes,tunable ionic conductivities, and facile processing. For this family of compounds, synthesisprotocols strongly affect cation site disorder and modulate Li+ mobility. Inthis work, we reveal the presence of a high concentration of stacking faults in thesuperionic conductor Li3YCl6 and demonstrate a method of controlling its Li+ conductivityby tuning the defect concentration with synthesis and heat treatments atselect temperatures. Leveraging complementary insights from variable temperaturesynchrotron X-ray diffraction, neutron diffraction, cryogenic transmission electron microscopy,solid-state nuclear magnetic resonance, density functional theory, and electrochemicalimpedance spectroscopy, we identify the nature of planar defects and the roleof nonstoichiometry in lowering Li+ migration barriers and increasing Li site connectivityin mechanochemically-synthesized Li3YCl6. We harness paramagnetic relaxationenhancement to enable 89Y solid-state NMR, and directly contrast the Y cation sitedisorder resulting from different preparation methods, demonstrating a potent tool forother researchers studying Y-containing compositions. With heat treatments at temperaturesas low as 333 K (60°C), we decrease the concentration of planar defects,demonstrating a simple method for tuning the Li+ conductivity. Findings from thiswork are expected to be generalizable to other halide solid electrolyte candidates andprovide an improved understanding of defect-enabled Li+ conduction in this class ofLi-ion conductors.