Modulating the Structure of Interlayer/Layer Matrix on δ-MnO₂ via Cerium Doping-Engineering toward High-Performance Aqueous Zinc Ion Batteries

δ-MnO₂ has been vigorously developed as an ideal cathode material for rechargeable aqueous zinc-ion batteries (AZIBs) due to its spacious layer spacing suitable for ion storage. However, poor intrinsic conductivity, structural collapse, and sluggish reaction kinetics are major limitations restricting their battery performance. Doping engineering has been proven to be an effective strategy for modifying the structure, conductivity, and electronic properties of Mn-based oxides. Here, a series of δ-MnO₂ hierarchical flowers with different cerium-doped sites are proposed as high-performance cathodes for AZIBs, revealing the effects of various Ce doping sites on the MnO₂ layer-by-layer structure and battery performance. Chemical analysis and theoretical calculations indicate that δ-MnO₂ with both in-layer and interlayer Ce doping (Ce_in/inter-MnO₂) allows for sufficient Zn²⁺ storage sites, higher conductivity, and enhanced reaction kinetics due to enlarged interlayer spacing, increased oxygen defects, and reduced Coulombic repulsion between zinc ions and manganese oxide hosts. As a result, Ce_in/inter-MnO₂ with extended ion transfer channels and sturdy structure delivers a superior capacity of 348.8 mAh g⁻¹ at a current density of 300 mA g⁻¹ over 100 cycles, and a high retention rate of ≈100% at a current density of 3000 mA g⁻¹ over 2000 cycles.