A Highly Conductive Halospinel Cathode for All-Solid-State Batteries.

High-power lithium-ion batteries (LIBs) rely on highly ionically and electronically conductive cathode active materials (CAMs). While oxospinels meet these criteria and are therefore widely employed in state-of-the-art LIBs, we demonstrate that halospinels offer greatly enhanced transport properties and enable the incorporation of earth-abundant transition metals, such as iron. Using spinel-type Li2-x FeCl4 (0 < x ≤ 1, LFC) as a model CAM in an all-solid-state battery (ASSBs), we show that its intrinsically high ionic-electronic conductivity enables the fabrication of cathodes composed of micron-sized CAM particles with high areal capacity (>2 mA h cm-2) at practical current densities (0.5 mA cm-2) over 200 cycles. Our findings position LFC as a promising CAM, paving the way for cost-effective, high-performance ASSBs.