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

Abstract

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 Li 2 ZrCl 6 has garnered significant attention due to the non-inclusion of rare-earth metals. However, the conventional one-step ball-milling synthesized Li 2 ZrCl 6 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 Li 2 ZrCl 6 . Simultaneously, the effects of rotational speed and ball-to-powder mass ratio on the structure and ionic conductivity of Li 2 ZrCl 6 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 Li 2 ZrCl 6 electrolyte in ASSLMBs assembled with the LiCoO 2 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.

Effect of Cation Disorder on Lithium Transport in Halide Superionic Conductors

“…Some of the halide conductors contain low-abundance metals (e.g., Sc/Y/Tb/Lu). In addition, many of the interesting halides are unstable in ambient conditions and their ionic conductivity significantly degrades by exposure to moisture. , Recently, the Zr-based compounds (e.g., Li 2 ZrCl 6 , LZC) and their doped variants have demonstrated the potential to overcome these challenges. ,− LZC exhibits distinct polymorphism with its structure depending on the synthesis method, as summarized in Figure a. The mechanochemical synthesis produces α h -LZC (hexagonal close-packed anions, hcp), whereas the β c -LZC (cubic close-packed anions, ccp) can form by annealing α h -LZC at temperatures above 260 °C.…”