Enhancing ionic conductivity in solid electrolyte by relocating diffusion ions to under-coordination sites

Solid electrolytes are highly important materials for improving safety, energy density, and reversibility of electrochemical energy storage batteries. However, it is a challenge to modulate the coordination structure of conducting ions, which limits the improvement of ionic conductivity and hampers further development of practical solid electrolytes. Here, we present a skeleton-retained cationic exchange approach to produce a high-performance solid electrolyte of Li₃Zr₂Si₂PO₁₂ stemming from the NASICON-type superionic conductor of Na₃Zr₂Si₂PO₁₂. The introduced lithium ions stabilized in under-coordination structures are facilitated to pass through relatively large conduction bottlenecks inherited from the Na₃Zr₂Si₂PO₁₂ precursor. The synthesized Li₃Zr₂Si₂PO₁₂ achieves a low activation energy of 0.21 eV and a high ionic conductivity of 3.59 mS cm^-1 at room temperature. Li₃Zr₂Si₂PO₁₂ not only inherits the satisfactory air survivability from Na₃Zr₂Si₂PO₁₂ but also exhibits excellent cyclic stability and rate capability when applied to solid-state batteries. The present study opens an innovative avenue to regulate cationic occupancy and make new materials.