To meet the growing demands of modern energy storage, cathode active materials (CAMs) in Li-ion batteries (LIBs) not only need to offer high energy density, but also enable fast charge and discharge.^[1] To this end, CAMs must facilitate both rapid electronic and ionic transport at the lattice scale, since chemical diffusion will be rate‑limited by the slower species (Figure a, b). 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(Figure c, d).^[2] Using Li_2-xFeCl₄ (0<x≤1, LFC) as a model system, we show that its intrinsically high ionic-electronic conductivity allows for all-solid-state batteries (ASSBs) with micron-sized CAM particles, achieving exceptional areal capacity (>2 mA h cm^‑2) at practical current densities (0.5 mA cm^‑2) and extended cycle life of 200 cycles (Figure e). Our findings position LFC as a commercially viable CAM, paving the way for cost-effective, high-performance ASSBs.

[1]       Y. Liu, Y. Zhu, Y. Cui, Nat. Energy 2019, 4, 540.

[2]       J. F. Baumgärtner, D. Isler, Q. H. Nguyen, M. Klimpel, C. Černe, J. Šivavec, D. Chernyshov, W. van Beek, D. Rettenwander, K. V. Kravchyk, M. V. Kovalenko, in Review 2025.