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

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 Fe₂O₃ into Li₂ZrCl₆ (LZC) to construct an electrochemically active and cost-effective oxyhalide SE (Li_1.6ZrFe_0.8O_1.2Cl_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 LiFePO₄ (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.