Tuning Site Energy by XO6 Units in LiX2(PO4)3 Enables High Li Ion Conductivity and Improved Stability

Solid-state electrolytes (SSEs) with high ion conductivity are necessary for all-solid-sate lithium ion batteries. Here, a less studied NASICON-type LiZr₂(PO₄)₃ (LZP) is screened out from seven LXP compounds (LiX₂(PO₄)₃, X = Si, Ge, Sn, Ti, Zr, Hf, and Mo), which combines the electrochemical stability with high Li conductivity. The bond valence site energy (BVSE), climbing image nudged elastic band (Cl-NEB) method, and electrochemical phase diagram prove LZP has a lower Li migration barrier and the largest electrochemical stability window. The underlying reason for high Li conductivity is analyzed from the structural features to the electronic structures. Furthermore, the XO₆ unit mixed frameworks Li_1.667Ca_0.333Zr_1.667(PO₄)₃ (LCZP) and Li_1.667Mg_0.333Zr_1.667(PO₄)₃ (LMZP) exhibit high Li ion conductivity associated with a very low Li migration barrier (∼0.20 eV). This work opens a new avenue of broad compositional spaces in LXP for SSEs.