Anionic polymerization strategy for improving ionic conductivity in solid hydroborate electrolytes: the anion paddle-wheel effect

Abstract

Owing to their wide electrochemical stability window and enhanced ionic conductivity, conjuncto‑type hydroborates are promising candidates for high-voltage solid-state electrolytes. However, despite experimental evidence of improved performance as electrolytes compared with Na2B12H12 with a single B12H12 cage, the mechanisms driving these changes remain unexplored systematically. In this study, first-principles calculations were employed to investigate the electronic properties, electrochemical stability, ionic conductivity properties, and mechanical properties of the conjuncto-type hydroborates Nan+1B12nH11n+1 (n=2, 3, 4). The polymerization strategy of [B12H12]2- anions can effectively reduce diffusion barriers and strengthen the anion paddle-wheel effect to enhance the ionic conductivity while preserving the electronic insulation and electrochemical stability of conjuncto-type hydroborate electrolytes. Moreover, the polymerized long-chain anions exhibit more flexibility, further improving the interfacial compatibility and mechanical processability. Our work provides insights into the design of advanced hydroborate electrolytes, highlighting the significant influence of anionic polymerization on both ion conductivity and mechanical properties.