Al─N Co-Doped LLZO Solid Electrolytes via One-Step Sintering: Toward High Ionic Conductivity

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid electrolyte for solid-state lithium batteries owing to its relatively high ionic conductivity and wide electrochemical window. However, its conductivity still needs further improvement to meet practical application requirements. Herein, we propose for the first time a cation-anion co-doping strategy to synthesize Al─N co-doped LLZO via a one-step sintering process, achieving a high ionic conductivity of 2.19 × 10^-3 S cm^-1. Nudged elastic band (NEB) calculations reveal that Al─N co-doping reduces the energy barrier for Li⁺ migration, thereby enhancing ionic transport. Remarkably, the Li|LLZO-Al_0.50N_0.50|Li symmetric cell demonstrates stable lithium plating/stripping cycling over 600 h at 0.1 mA cm^-2, and the LiFePO₄| LLZO-Al_0.50N_0.50|Li full cell retains 82.6% of its initial capacity after 200 cycles at 0.3 C. This work confirms Al─N co-doping as an effective strategy for improving the ionic conductivity of LLZO, offering a viable route toward high-performance garnet-type solid electrolytes.