Optimized Lithium Ion Coordination via Chlorine Substitution to Enhance Ionic Conductivity of Garnet‐Based Solid Electrolytes

Abstract Garnet‐type solid‐state electrolytes attract abundant attentions due to the broad electrochemical window and remarkable thermal stability while their poor ionic conductivity obstructs their widespread application in all‐solid‐state batteries. Herein, the enhanced ionic conductivity of garnet‐type solid electrolytes is achieved by partially substituting O 2− sites with Cl − anions, which effectively reduce Li + migration barriers while preserving the highly conductive cubic phase of garnet‐type solid‐state electrolytes. This substitution not only weakens the anchoring effect of anions on Li + to widen the size of Li + diffusion channel but also optimizes the occupancy of Li + at different sites, resulting in a substantial reduction of the Li + migration barrier and a notable improvement in ionic conductivity. Leveraging these advantageous properties, the developed Li 6.35 La 3 Zr 1.4 Ta 0.6 O 11.85 ‐Cl 0.15 (LLZTO‐0.15Cl) electrolyte demonstrates high Li + conductivity of 4.21×10 −6 S cm −1 . When integrated with LiFePO 4 (LFP) cathode and metallic lithium anode, the LLZTO‐0.15Cl electrolyte enables the solid‐state battery to operate for more than 100 cycles with a high capacity retention of 76.61% and superior Coulombic efficiency of 99.48%. This work shows a new strategy for modulating anionic framework to enhance the conductivity of garnet‐type solid‐state electrolytes.