Stable solid-state potassium metal batteries enabled by a KB11H14·2Me3NBH3 complex electrolyte

Solid-state potassium metal batteries have increasingly gained attention as promising alternatives in large-scale energy storage due to their safety and low cost. However, these batteries usually suffer from a lack of suitable K⁺ conducting solid electrolytes. Herein, a new KB₁₁H₁₄·2Me₃NBH₃ complex electrolyte with high ionic conductivity and relative stability against K metal is reported. The crystal structure was solved as a monoclinic P2₁/c lattice. The density functional theory (DFT) calculations confirm significantly enhanced K-ion diffusion in the structure. High K-ion conductivities of 2.63 × 10⁻⁶ S cm⁻¹ at 25 °C and 3.25 × 10⁻⁴ S cm⁻¹ at 75 °C are achieved, putting it among the leading K⁺ solid conductors. Moreover, it reveals favorable interfacial stability against the K metal anode precoated by NH₃B₃H₇. Batteries coupling the TiS₂ cathode deliver long-term cycling stability. This work opens a new group of K-ion solid-state electrolytes for safe potassium metal batteries.