Synthesis, Structure, and Ion Conduction of Potassium Carbazolides for Potassium Ion Solid‐State Electrolytes

Abstract Potassium ion batteries gradually have aroused worldwide interest due to the limited lithium resource. However, the research on the solid‐state potassium‐ion batteries is at its very early stage. The lack of electrolytes with high ionic conductivity and interfacial stability is the major obstacle. In this work, a new phase of potassium carbazolide (KC 12 H 8 N, β ‐KCZ) is synthesized and expected to be less rigid in the stacking layers than the reported α ‐KCZ, indicating weaker cation−π interactions. Upon complexing KCZ with THF, a new type of potassium solid‐state electrolyte is successfully developed (K x CZ‐yTHF), particularly, an optimal composition K 0.9 CZ‐0.7THF reveals an ionic conductivity as high as 4.2 × 10 −4 S cm −1 at 100 °C, which is among the top K + conductors at this temperature. Furthermore, K x CZ‐yTHF also demonstrates a remarkable electrochemical stability window of 3.1 V, as well as outstanding interfacial stability and compatibility against K 2 S electrode during a 400‐h electrochemical cycling test. Other advantages of this electrolyte include cold pressing for molding, ease for scaling up, and high safety upon exposure to air. To the best of the knowledge, this is the first report that a potassium organic compound is employed as potassium solid‐state electrolyte.