Magneto-Electrodeposition and Field-Enhanced Ion Transport in Zn-MnO₂ Batteries

Aqueous zinc-ion batteries (AZIBs) are promising alternatives to lithium-ion systems for safe and low-cost energy storage; however, their practical application is limited by poor cyclability, cathode degradation, and sluggish kinetics. Here, we introduce a magnetic-field-assisted electrodeposition strategy, termed magneto-electrodeposition (MED), to fabricate MnO₂ cathodes. The applied magnetic field induces Lorentz-force-driven magnetohydrodynamics, enhancing Mn²⁺ ion transport and enabling the formation of uniform and robust MnO₂ coatings with enhanced δ-MnO₂ character. Structural analyses confirm that, through the MED approach, MnO₂ depositions with higher Mn content (14.6%) and mass loading (26.6%) are obtained compared to conventional electrodeposited cathodes. Electrochemical characterization revealed improved charge-transfer kinetics, with ∼95% reduced interfacial resistance (R_ct). The optimized MED MnO₂ cathode delivered an initial areal capacity of 0.62 mAh cm^{- 2}, nearly twice the conventionally electrodeposited cathode, with 73% capacity retention after 100 cycles. Introducing an internal magnetic field during operation further enhances performance, with 10 mT being optimal for improving Zn^{2 +} transport. Consequently, the Zn-MnO₂ cell employing the MED cathode delivers stable cycling for ∼315 cycles, outperforming the conventionally electrodeposited cathode, which fails after ∼130 cycles. This work demonstrates that coupling magneto-electrodeposition with in-operando magnetic-field-assistance provides a scalable strategy to engineer cathodes and regulate ion transport for high-performance AZIBs.