Embedding Fe‐Based Redox Chemistry Into Low‐Cost Oxyhalide Solid Electrolytes for High‐Performance All‐Solid‐State Batteries

ABSTRACT Halide solid electrolytes (SEs) with excellent ionic conductivity and wide electrochemical stability windows are promising for next‐generation all‐solid‐state batteries (ASSBs). However, their intrinsic electrochemical inertness and high cost significantly constrain the attainable energy density and large‐scale applicability of ASSBs. Here, we integrate Fe 2 O 3 into Li 2 ZrCl 6 (LZC) to construct an electrochemically active and cost‐effective oxyhalide SE (Li 1.6 ZrFe 0.8 O 1.2 Cl 5.6 , denoted LiZrFeOCl‐1604), which enables Fe‐based redox chemistry while preserving cost‐effectiveness. Benefiting from its amorphous framework comprising interconnected Zr─O/Cl, Fe─O/Cl, and Li─Cln ( n ≤ 6) polyhedra,LiZrFeOCl‐1604 exhibits a high ionic conductivity of 2.55 mS cm −1 and a pronounced reversible capacity of 163 mAh g −1 . Coupled with LiFePO 4 (LFP) cathode, the composite electrode delivers a high capacity of 321.6 mAh g −1 and an energy density of 982.1 Wh kg −1 (based on LFP mass), representing a 101.8% enhancement over electrochemically inactive LZC. Moreover, the ASSBs retain 92.7% of its initial capacity (205.7 mAh g −1 ) over 800 cycles at 1C rate. Notably, this asynchronous charge–discharge behavior not only boosts the practical energy density but also mitigates safety risks associated with overcharge and overdischarge of ASSBs.