Facile Synthesis of Potassium Decahydrido-Monocarba-closo-Decaborate Imidazole Complex Electrolyte for...

All-solid-state potassium metal batteries have caught increasing interest owing to their abundance, cost-effectiveness, and high energy/power density. However, their development is generally constrained by the lack of suitable solid-state electrolytes. Herein, we report a new complex KCB₉H₁₀ ⋅ 2C₃H₄N₂, synthesized by grinding and heating the mixture of potassium decahydrido-monocarba-closo-decaborate (KCB₉H₁₀) and imidazole (C₃H₄N₂) under mild conditions, to achieve the K-ion superionic solid-state electrolyte. The crystal structure was revealed as an orthorhombic lattice with the space group of Pna2₁ by FOX software. The diffusion properties for K⁺ in the crystal structure were calculated using the climbing image nudged elastic band (CI-NEB) method. KCB₉H₁₀ ⋅ 2C₃H₄N₂ exhibited a high ionic conductivity of 1.3×10^-4 S cm^-1 at 30 °C, four orders of magnitude higher than that of KCB₉H₁₀. This ionic conductivity is also the highest value of hydridoborate-based K⁺ conductors reported. Moreover, KCB₉H₁₀ ⋅ 2C₃H₄N₂ demonstrated a K⁺ transference number of 0.96, an electrochemical stability window of 1.2 to 3.2 V vs. K/K⁺, and good stability against the K metal coated by a layer of potassium imidazolate (KIm). These great performances make KCB₉H₁₀ ⋅ 2C₃H₄N₂ a promising K-ion solid-state electrolyte.