Synergistic In-Silico Design and Electrochemical Characterization of Solid-State Electrolytes with Fully Earth Abundant Chemical Compositions for Na/K-Metal Batteries

The concept of corner-sharing frameworks is fundamental to the design of oxide solid-state electrolytes with superionic conductivity for alkali-metal ions such as Li⁺ and Na⁺. These structures are composed of a highly covalent skeleton of corner-sharing polyhedra, allowing alkali-metal ions to diffuse through interconnected and highly metastable interstitial positions within the framework.In this study, our focus is on a class of earth-abundant rock silicates as solid-state electrolytes (SSE) for Na/K-metal batteries. Through a synergistic approach involving in-silico design and electrochemical characterization, we investigated the relationship between structural features—such as migration energy barriers for Na⁺ and K⁺, bottleneck pathways in the skeleton structure, polyhedron packing ratio, and continuous symmetry measure—with SSE performance indicators such as ionic conductivity and phase stability under ambient conditions. Our preliminary investigations indicate that a high Continuous Symmetry Measure value in Na/K-polyhedra, along with a low packing ratio of the skeleton structure, are key features in achieving fast kinetic transport for Na⁺ and K⁺. Experimental results demonstrate that by applying this hypothesis, it is possible to achieve Na⁺/K⁺ ionic conductivity levels in the range of 10-0.1 mS/cm at 50 °C, using a fully earth-abundant chemical composition without relying on rare-earth or multi-valent transition metal ions. An SSE based on the Na-Mg-Al-Ca-Si-O oxide system was fabricated into thin, self-standing tape-cast layers under ambient conditions. These thin, self-standing layers, in a symmetrical cell configuration of Na/SSE/Na, cycled for more than 50 cycles up to 1 mA/cm2 at 50 °C. The utilization of earth-abundant rock silicates as SSE, demonstrated through synergistic in-silico design and experimental characterization, offers a promising avenue for the development of high-performance and sustainable solid-state batteries, showcasing significant potential in achieving enhanced ionic conductivity and phase stability without relying on rare-earth or multi-valent transition metal ions.