N‑Substitution‑Directed Molecular Engineering of Organic Solid‑State Electrolytes for Potassium Ion Conduction

ABSTRACT

As a potential alternative and complement to lithium‐ion batteries (LIBs), potassium‐ion batteries (PIBs) draw global attention. However, the lack of high‐performance potassium solid‐state ion conductors is the core bottleneck impeding the practical application of all‐solid‐state PIBs. In this work, we employ an N‐substitution strategy at a molecular level on potassium carbazolide (KCZ), where four N‐substituted structural isomers are rationally fabricated. Among them, δ ‐potassium carbolinide ( δ ‐KNCZ) demonstrates an ionic conductivity of 2.8 × 10 ⁻⁴ S cm ⁻¹ at 120°C with a transference number of 0.98, while the unsubstituted KCZ and other isomers ( α‐, β‐ , and γ ‐KNCZ) do not exhibit any detectable ionic conductivity. Crystal structure analysis reveals that δ ‐KNCZ crystallizes in an orthorhombic system with the space group of Pna2 ₁ (No. 33), in which K ⁺ occupies a conduction‐favorable planar quadrilateral coordination center with an elongated K─N ionic bond. Theoretical calculations further demonstrate that the K ⁺ hops between tetra‐coordinated centers with an energy barrier consistent with experimental results. Both experimental and theoretical results indicate that N‐substitution at appropriate positions in organic substrates can tailor the coordination environment of K ⁺ and weaken K─N ionic bonds, thereby facilitating potassium ion conduction. This study provides new insights into the design and development of organic solid‐state ionic conductors.