Molecular Design of Crystalline Potassium Pyridonate Electrolytes for All-Solid-State Potassium Metal Batteries

All-solid-state potassium metal batteries (PMBs) emerge as promising alternatives to lithium batteries owing to their natural abundance and high theoretical energy density. Nevertheless, the advancement of efficient PMBs is still hindered by the lack of suitable electrolytes. Therefore, exploring solid-state electrolytes (SSEs) for PMBs is critical. Compared with inorganic SSEs, research on developing pristine organic potassium salt-based SSEs remains extremely sparse. Herein, a "Heteroaromatic-Assisted Migration" approach was employed to design crystalline organic potassium salts (i.e., potassium pyridonates) as SSEs by incorporating a nitrogen atom into the phenoxide ring. Specifically, through tuning the position of N, the isomer of "K-deficient" meta-KOC₅H₄N achieves an ionic conductivity of 0.22 mS cm^-1 at 90 °C with an ion transference number (t_i) higher than 0.99, ranking among the highest conductivity reported. Meanwhile, it demonstrates outstanding thermal stability (>240 °C), air tolerance, and low Young's modulus, which enable high stability, scalable synthesis, and ease of molding. The crystal structure of meta-KOC₅H₄N is determined as a monoclinic lattice with the space group of P2₁/m (no. 11), where unsaturated K-ion coordination and flexible layered structure are observed. We successfully demonstrated the first all-solid-state PMB prototype using this organic salt. Both experimental and first-principles calculations reveal that ion diffusion occurs via defect-mediated mechanisms within the layered flexible lattice. Compared with the inorganic SSEs, the present study opens up a new avenue for fabricating safe and facile organic electrolyte materials.