High-Conductivity Li2ZrCl6 Electrolytes via an Optimized Two-Step Ball-Milling Method for All-Solid-State Lithium–Metal Batteries

The combined advantages of good mechanical deformability, high Li+ conductivity, and strong compatibility with 4 V-class cathodes make halide solid-state electrolytes promising candidates for high-energy all-solid-state lithium–metal batteries (ASSLMBs). Among these, the cost-effective Li2ZrCl6 has garnered significant attention due to the non-inclusion of rare-earth metals. However, the conventional one-step ball-milling synthesized Li2ZrCl6 always exhibits an ionic conductivity lower than 5 × 10–4 S cm–1 in most literature. Here, a simple optimized two-step ball-milling strategy is adopted to achieve a high Li+ conductivity of nearly 1 × 10–3 S cm–1 at 30 °C for Li2ZrCl6. Simultaneously, the effects of rotational speed and ball-to-powder mass ratio on the structure and ionic conductivity of Li2ZrCl6 are investigated. The Li+ migration pathways in electrolytes are also studied by bond valence site energy (BVSE) calculations. Moreover, the application potential of the modified Li2ZrCl6 electrolyte in ASSLMBs assembled with the LiCoO2 cathode and the lithium–indium alloy anode has been studied. The ASSLMBs exhibit an initial discharge capacity of 123.4 mA h g–1 at room temperature (0.1 C) and a capacity retention of 71% after 50 cycles. Therefore, this study introduces an effective strategy for synthesizing high-performance halide electrolytes, thus facilitating the practical implementation of halide-based ASSLMBs.