Tailoring Lithium-Ion Coordination in Metal-Organic Frameworks via d-Orbital Control for Fast Ion Conduction

The development of solid-state electrolytes (SSEs) is fundamentally constrained by the intrinsic trade-off between ionic transport efficiency and interfacial stability. While previous design strategies have enhanced lithium-ion conduction kinetics, the rational engineering of high-performance SSEs remains challenged by insufficient atomic-level insights into Li⁺ coordination microenvironments. Herein, we present a dynamic electronic-structure engineering approach utilizing π-conjugated two-dimensional metal-organic frameworks (M-4PyCN) with precisely modulated d-orbital occupation states. Through precision modulation of transition-metal centers, we achieve targeted charge density redistribution in cyanide ligands while leveraging abundant cyano groups to construct high-density coordination networks within subnanoscale channels. The pronounced ligand-to-metal charge transfer (LMCT) mediated by π-d orbital hybridization induces charge delocalization effects that enables the synergistic regulation of the interfacial microenvironment and Li⁺ coordination. This synergy facilitates rapid Li⁺ desolvation and directional migration through coordinated hopping pathways. The obtained π-conjugated two-dimensional MOF (M-4PyCN) SSE simultaneously exhibits an exceptional ionic conductivity of 3.2 mS cm^-1 and an ultralow electronic conductivity of 10^-8-10^-9 S cm^-1 at room temperature, along with stable Li||Li symmetric cell cycling exceeding 4000 h. This work establishes a universal framework that bridges atomic-scale coordination environments with macroscopic ion-transport dynamics, demonstrating potential applicability to alkali-metal anodes and multivalent ion conductor systems.