Aliovalent substitution of Al3+ in Li2ZrCl6 solid electrolyte towards large-scale application

Halide solid electrolytes, known for their stability to 4 V-class cathodes and deformability, emerge as promising candidates for high-performance all-solid-state batteries. Unfortunately, their synthesis often involves expensive elements, limiting mass production and cost-effectiveness. In this study, aliovalent-substituted Li2ZrCl6 with Al3+ is fabricated by one-step ball milling, exhibiting lower cost, higher ionic conductivity and a wider electrochemical window. The cost is reduced by approximately 13.4% through a 25% aliovalent substitution. Li+ conductivity of Li2+xZr1-xAlxCl6 increases from 0.12 mS/cm (x = 0) to a peak of 1.13 mS/cm (x = 0.25) at 25°C, and activation energy (Ea) reduces from 0.43 eV to 0.29 eV, which is attributed to the extension of Li+ migration pathways along intra- and inter- ab-plane around Al sites as revealed by AIMD and BVSE calculations. Both experimental result and calculation indicate that the substitution of Al3+ improves the oxidation potential from 4.1 V in Li2ZrCl6 to 4.3 V in Li2.25Zr0.75Al0.25Cl6. Furthermore, the excellent electrochemical performance of all-solid-state batteries is demonstrated using Al-substituted Li2ZrCl6 and commercial LiNi0.8Co0.1Mn0.1O2. The unravelled multifaceted effects of Al3+ aliovalent substitution in Li2ZrCl6 solid electrolyte endow it highly advantageous for future applications in halide-based all-solid-state lithium batteries.