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

## TL;DR

A new solid electrolyte for all-solid-state batteries is developed that is mechanically compliant, cost-effective, and improves battery cycling stability.

## Contribution

The development of a solid electrolyte with low hardness and Young’s modulus, high ionic conductivity, and lower cost compared to existing options.

## Key findings

- The new electrolyte has a hardness of 0.22 GPa and Young’s modulus of 1.41 GPa, much lower than typical solid electrolytes.
- It achieves an ionic conductivity of 2.55 mS cm−1 at 25 °C and a cost of $43.70 L−1, significantly lower than Li2ZrCl6.
- Cells using this electrolyte retain over 85% of their capacity after 100 cycles with high electrode material loading.

## Abstract

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.

The mechanical properties of inorganic solid electrolytes for Li batteries are typically characterised by a high Young’s modulus above 15 GPa and hardness above 1 GPa. Here, authors develop a cost-effective and mechanically compliant inorganic solid electrolyte, with reduced Young’s modulus and hardness of 1.41 and 0.22 GPa, respectively, for practical all-solid-state Li batteries.