Molten Guest-Mediated Metal-Organic Frameworks Featuring Multi-Modal Supramolecular Interaction Sites for Flame-Retardant Superionic Conductor in All-Solid-State Batteries.

Abstract

The development of solid-state electrolytes (SSEs) with outstanding comprehensive performance is currently a critical challenge for achieving high energy density and safer solid-state batteries (SSBs). In this study, a strategy of nano-confined in situ solidification is proposed to create a novel category of molten guest-mediated metal-organic frameworks, named MGM-MOFs. By embedding the newly developed molten crystalline organic electrolyte (ML₂₀) into the nanocages of anionic MOF-OH, MGM-MOF-OH, characterized by multi-modal supramolecular interaction sites and continuous negative electrostatic environments within nano-channels, is achieved. These nanochannels promote ion transport through the successive hopping of Li⁺ between neighbored negative electrostatic environments and suppress anion movement through the chemical constraint of the hydroxyl-functionalized pore wall. This results in remarkable Li⁺ conductivity of 7.1 × 10^-4 S cm^-1 and high Li⁺ transference number of 0.81. Leveraging these advantages, the SSBs assembled with MGM-MOF-OH exhibit impressive cycle stability and a high specific energy density of 410.5 Wh kg_{anode + cathode + electrolyte} ^-1 under constrained conditions and various working temperatures. Unlike flammable traditional MOFs, MGM-MOF-OH demonstrates high robustness under various harsh conditions, including ignition, high voltage, and extended to humidity.