A high-entropy Al-based halide electrolyte enables cost-effective, high-performance all-solid-state batteries

Rare-earth halides are promising solid electrolytes (SEs) because of their comprehensively superior ionic conductivity, excellent electrochemical oxidative stability, and mechanical softness. However, their application is limited by their reliance on rare earth and expensive elements. While chloroaluminates offer an economical alternative, they typically suffer from low ionic conductivities. This study reports a high-entropy aluminum (Al)-based halide SE, Li1.245Al0.745(ZrPSiB)0.0636O0.7Cl3.1, synthesized from inexpensive precursors using a high-entropy strategy. Rietveld refinement with an internal standard reveals that mechanical milling produces this composition with ∼39.7% amorphous content alongside a monoclinic LiAlCl4 phase. X-ray photoelectron spectroscopy elucidates the competitive roles of non-bridging oxygen and bridging oxygen within the modified halide framework. This structural modification results in a tenfold increase in ionic conductivity (0.2 mS cm−1 at 25 °C) compared to pristine LiAlCl4. All-solid-state batteries (ASSBs) employing the Li1.245Al0.745(ZrPSiB)0.0636O0.7Cl3.1 as a catholyte with single-crystalline LiNi0.8Co0.1Mn0.1O2 cathodes demonstrate excellent cycling stability over 200 cycles at upper cutoff potentials of 4.2 and 4.3 V vs Li/Li+. This work highlights the potential of high-entropy chloroaluminates as cost-effective solid electrolytes for ASSBs.