Mechanically compliant and cost-effective 1.4Li2O-0.75ZrCl4-0.25AlCl3 solid electrolyte for all-solid-state batteries with improved cycling stability

Although Li-ion conductivity has been the primary focus during decades of solid-electrolyte research, the mechanical compliance is equally important. For most state-of-the-art solid electrolytes, the mechanical compliance is characterized by the hardness above 1 GPa and Young's modulus above 15 GPa. Here, we report a particularly compliant solid electrolyte, 1.4Li₂O-0.75ZrCl₄-0.25AlCl₃, whose hardness and Young's modulus reach 0.22 and 1.41 GPa, respectively. Meanwhile, it shows an ionic conductivity of 2.55 mS cm^-1 at 25 °C and an estimated cost of $43.70 L^-1, considerably lower than that of the Li₂ZrCl₆ solid electrolyte known for cost-effectiveness ($140.01 L^-1). The improved mechanical compliance and fast Li-ion transport in 1.4Li₂O-0.75ZrCl₄-0.25AlCl₃ enable decent cell performance. With high positive electrode active material loading above 20 mg cm^-2, these two types of cells achieve areal capacities of 3.62 mAh cm^-2 (85.78% capacity retention) and 3.92 mAh cm^-2 (90.11% capacity retention), respectively, after 100 cycles under 0.1 C at 25 °C. The simultaneous achievement of highly competitive mechanical compliance, Li-ion conductivity, and cost-effectiveness in 1.4Li₂O-0.75ZrCl₄-0.25AlCl₃ have the potential to pave the way for the realization of commercial, practical all-solid-state Li batteries.