Ionic Conductivity Enhancement of Li2ZrCl6 Halide Electrolytes via Mechanochemical Synthesis for All-Solid-State Lithium–Metal Batteries

Superionic halides have returned to the spotlight of solid electrolytes because of their satisfactory ionic conductivity, soft texture, and stability toward high-voltage electrode materials. Among them, Li₂ZrCl₆ has aroused interests since abundant Zr element can reduce the cost of large-scale synthesis. However, the related research is very limited, including the detailed parameters during synthesis and the possible strategies for enhancing ionic conductivity. In this work, we have systematically investigated the effects of synthesis parameters on the structure and ionic conductivity of Li₂ZrCl₆ during the ball-milling annealing process. It is found that mild heat treatment (100 °C) can largely enhance the ionic conductivity of ball-milled electrolytes by 2-3 times, which has not been previously reported. Such enhancement is mainly attributed to the network-like micromorphology composed of nanorods, nanowires, or nanoballs, which is beneficial for lithium ion migration. Finally, the modified Li₂ZrCl₆ (4.46 × 10^-4 S cm^-1 @ RT) is also proved to be applicable in LiNi_0.8Mn_0.1Co_0.1O₂/ Li₂ZrCl₆/ Li₆PS₅Cl/Li-In all-solid-state lithium metal batteries (ASSLMBs). It presents high initial charge capacity of 176.4 mAh g^-1 and satisfactory cycle stability since a discharge capacity of 90.8 mAh g^-1 is maintained after 40 cycles at 0.1 C. The Li₂ZrCl₆ electrolytes synthesized via the mechanochemical method is promising to be applied in the high-voltage ASSLMBs, and its ionic conductivity can be enhanced by the strategies provided in our work.