<p>Manganese-based cathodes for aqueous zinc-ion batteries often suffer from structural degradation caused by the Jahn–Teller effect. Herein, a Mo⁶⁺-modified MgCO₃–Na₂Mn₈O₁₆ composite cathode is fabricated via a hydrothermal-calcination strategy. Mo⁶⁺ doping induces anisotropic lattice distortion and a mixed Mn³⁺/Mn⁴⁺ valence state in Na₂Mn₈O₁₆, thereby enhancing its intrinsic electronic conductivity. Meanwhile, the in situ-formed MgCO₃ phase establishes strong interfacial chemical coupling with the manganese oxide framework through Mo–O–Mn/Mg bonds, forming a stable three-dimensional heterostructure. Benefiting from this synergistic design, the optimized cathode delivers a high reversible capacity of 418.25 mAh g⁻¹ at 50&#xa0;mA&#xa0;g⁻¹, along with superior rate capability and cycling stability. First-principles calculations reveal that the MgCO₃/Na₂Mn₈O₁₆ interface exhibits a high binding energy and optimized Mn-3d/O-2p orbital hybridization, which facilitate charge transfer and help maintain structural integrity during cycling. This work provides an effective strategy that combines heteroatom doping and interfacial engineering for developing high-performance cathode materials for zinc-ion batteries.</p>