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 Li ₃ Zr ₂ Si ₂ PO ₁₂ stemming from the NASICON-type superionic conductor of Na ₃ Zr ₂ Si ₂ PO ₁₂ . The introduced lithium ions stabilized in under-coordination structures are facilitated to pass through relatively large conduction bottlenecks inherited from the Na ₃ Zr ₂ Si ₂ PO ₁₂ precursor. The synthesized Li ₃ Zr ₂ Si ₂ PO ₁₂ achieves a low activation energy of 0.21 eV and a high ionic conductivity of 3.59 mS cm ⁻¹ at room temperature. Li ₃ Zr ₂ Si ₂ PO ₁₂ not only inherits the satisfactory air survivability from Na ₃ Zr ₂ Si ₂ PO ₁₂ 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.