All Solid State Batteries Based on Sodium Electrochemistry

Solid-state batteries have gained significant attention in recent years as they have the potential to be the leading next-generation energy storage devices, offering improved safety, higher energy densities, and longer cycle life. For grid-level energy storage, where having an accessible supply of battery materials and low cost per kilowatt-hour is important, sodium solid-state batteries are a promising technology. Within the past five years, halide-based solid electrolyte materials have become increasingly popular due to their superior oxidation stability, excellent deformability, and moderate ionic conductivities. As such, they are ideal catholytes for enabling high-voltage-coating-free cathode materials. However, to improve sluggish solid-state battery kinetics, it is still necessary to enhance their ionic conductivity, especially for sodium systems, which calls for new approaches to materials design. I will talk about a novel approach towards synthesizing nanocrystalline and amorphous chlorides for use as <i>superionic</i> conductors in sodium all-solid-state batteries. Our concept is based on the tendency of chlorides to form these phases by adjusting the composition of the system, as demonstrated using the NaCl−YCl₃−ZrCl₄ phase composition diagram as an example. We show that by controlling the molar amount of NaCl, electrolytes with low sodium concentrations and nanocrystalline or amorphous nature can be obtained. The structural amorphization, along with an increase in free volume, and preferential population of prismatic Na⁺ local environments, leads to an exceptional ionic conductivity at room temperature. Our approach has the potential to be applied universally to other halide-based systems, leading to a shift in the design of future solid electrolytes for high-performance all-solid-state batteries operating at ambient temperatures.