The Role of Anti-Phase Domains in Enhancing Ionic Conductivity of Na-based Solid-State Battery Electrolytes

All-solid-state batteries (ASSBs) are a promising alternative to current Li-ion systems, with the potential for significantly improved safety and energy density. Solid electrolytes require high ionic and low electronic conductivity, as well as electro-chemical and mechanical compatibility with electrodes. Both requirements remain a critical bottleneck for practical applications. Recently, our collaborators discovered that substituting Y3+ in Na3YCl6 with Zr4+ to form Na3-xY1-xZrxCl6 (NYZCx) enhances Na+ conductivity by two orders of magnitude, while simultaneously preventing electrochemical decomposition when paired with a NaCrO2 cathode.

We used Bragg Coherent Diffractive Imaging (CDI) on several NYZCx stoichiometries, which allowed us to directly image electrolyte nanocrystals in 3D. Our data showed an abundance of anti-phase domains in these materials, and further analysis revealed that higher density of anti-phase domain boundaries correlated with an increase in ionic conductivity. These findings demonstrate the importance of nanoscale defects on the performance of battery materials, and call for defect engineering as a pathway for progress in the field.