Substitution Tuning of Na-Ion Solid Electrolytes: A First-Principles Perspective

Chi-Hsuan Lee^1*, Chun-Wei Pao¹

¹Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan

* Presenter:Chi-Hsuan Lee, email:frankreichparis@gmail.com

All-solid-state batteries (ASSBs) are among the most promising technologies for next-generation energy storage, offering significant advantages in safety and energy density over conventional liquid-based systems. Central to the performance of ASSBs is the development of solid-state electrolytes (SSEs) that exhibit high room-temperature ionic conductivity, broad electrochemical stability windows, and favorable interfacial compatibility. In parallel, sodium-ion batteries (SIBs) have attracted increasing attention as a more sustainable and cost-effective alternative to lithium-ion systems, owing to the natural abundance and low cost of sodium.

In this study, we present a computational design framework based on density functional theory (DFT) to evaluate Na-based halide SSEs through systematic isovalent cation and anion substitutions. Thermodynamic stability is evaluated by constructing mixing energy landscapes, and sodium-ion diffusion behavior is assessed via ab initio molecular dynamics (AIMD) simulations, further accelerated by active machine learning techniques for efficient sampling. We find that halogen mixing strongly influences phase stability, whereas isovalent substitutions introduce local lattice distortions that effectively modulate Na-ion activation barriers and enhance ion mobility.

Our results highlight a set of promising Na-based SSE candidates with both thermodynamic robustness and favorable diffusion pathways. The insights from this work provide practical guidance for the experimental development of high-performance solid electrolytes for sodium ASSBs and contribute to the broader understanding of structure–diffusion interplay in halide-based ionic conductors.

Keywords: Solid Electrolyte, Density functional theory, Ionic conductivity