Breaking the Conductivity‐Capacity Trade‐Off in MCl 6 Anionic Framework: Amorphous Oxyhalide Cathode Materials Enable ≈1100 Wh Kg −1 at Cathode‐Level in All‐Solid‐State Lithium Batteries

Halide cathode active materials (CAMs) with high ionic conductivities have attracted significant attention. However, their capacity and energy density are limited by the large molar weight of the Li⁺ transport-dependent MCl₆ anionic framework. In this study, a low-cost amorphous iron-based oxyhalide LFFOC-0.5 CAM is introduced that overcomes the conductivity-capacity trade-off between high ionic conductivity and low discharge capacity associated with the MCl₆ framework. LFFOC-0.5 CAM achieves dual breakthroughs, exhibiting an impressive ionic conductivity of 0.26 mS cm^-1 at 25 °C, and a high specific capacity of 586 mAh g^-1 via an intercalation-conversion reaction at 60 °C. Due to its superior ionic conductivity and capacity, LFFOC-0.5 CAM enables a catholyte-free electrode to achieve an exceptional energy density of ≈1100 Wh kg^-1 _cathode and a power density of 2185 W kg^-1 _cathode at 60 °C, surpassing reported halide- and oxide-based CAMs by 1.5 to 3 times. Additionally, LFFOC-0.5 CAM is highly cost-effective ($9.3 kg^-1) and exhibits remarkable humidity stability, retaining 100% of its capacity after 12 h of exposure to 5 ± 1% humidity. The multifunctional iron-based oxyhalide CAMs open new avenues for advancing high-performance all-solid-state lithium batteries.