Anion Immobilization from Quasi-Icosahedron to Cubo-Octahedron Enhances the Lithium Ion Transference Number in Solid-State Electrolytes

Herein, we report the self-assembly of a D3-symmetric quasi-icosahedron 4 based on a desymmetrized terpyridine ligand. The participant triflimide (NTf2-) interacts with a rectangular aperture, templating the generation of 4. With the addition of the other smaller anions (50-90 Å3) into 4, supramolecular conversion to highly symmetric (O) cuboctahedron 5 can be observed due to optimizing the binding capabilities between anions and apertures of metallo-organic cages. This supramolecular conversion enables selective tight and multiple anion bindings with a clear binding mechanism and has been utilized to facilitate the dissociation of lithium-anion pairs and immobilization of anions in lithium metal batteries. Introducing 4 into solid polymer electrolytes can increase the lithium ion transference number t+ to 0.78, significantly enhancing the lithium ion conductivity within the electrolyte and enriching the lithium ion flux for transport. Consequently, the composite electrolyte exhibits excellent lithium ion transport kinetics, thereby endowing lithium metal batteries with superior electrochemical performance.