Boosting Potassium-Ion Conductivity through Heteroatom Effect and Neutral Ligand Coordination for Solid-State Potassium Batteries

Abstract The limited availability of solid electrolytes that simultaneously exhibit high ionic conductivity and robust interface compatibility is acknowledged as a critical barrier to the practical implementation of all-solid-state potassium-ion batteries. In this study, three potassium carbolide isomers and their coordinated complexes were designed and fabricated to enhance the potassium ion conductivity through employing the synergy of heteroatom (nitrogen) and neutral ligand coordination effects. Among them, the new crystal structures of β-potassium carbolide (β-KNCZ for short) and its tetrahydrofuran (THF) complex (β-KNCZ-1.0THF for short) were successfully determined. Upon modulating the position of the nitrogen atom and the content of ligand THF, β-KNCZ-0.75THF exhibited an ionic conductivity of 0.22 mS cm–1 at 60 °C with an activation energy of as low as 0.19 eV, indicating its potential as a competitive ion conductor. Further optimizing the type and content of ligand, β-KNCZ-0.70EDA (EDA: ethylenediamine) achieved an ionic conductivity of 1.3 mS cm–1 at 100 °C, which exhibits exceptional performance under the elevated temperature conditions (Table S1). Furthermore, both β-KNCZ-0.75THF and β-KNCZ-0.70EDA demonstrated favorable stability and interface compatibility with a K2S electrode during hundred hours electrochemical cycles with a low overpotential.