Prolonged slow cycling in aqueous Zn-MnO₂ batteries

iiiAbstractThe global transition toward renewable energy has increased the need for safe and cost-effective batteries capable of multi-hour discharge. Among alternatives to the dominant lithium-ion chemistry, aqueous zinc manganese dioxide (Zn-MnO₂) batteries are attractive for their nonflammable design and abundance of raw materials. Yet, under grid-relevant cycling (C-rate ≤ 1C) in mildly acidic electrolytes, Zn electrodeposition, proton-coupled Mn redox, pH evolution, and precipitation reactions are strongly coupled, leading to passivation, hydrogen evolution, transport limitation, and variable lifetime.This thesis investigates strategies that stabilize the Zn−Mn−pH−precipitation system during slow cycling. First, an H₂SO₄ polishing protocol modifies Zn foil toward basal plane exposure, resulting in reduced polarization and dendritic growth. Symmetric Zn||Zn cells cycle beyond ~ 1200 h at 0.5 mA cm⁻² and 1 mAh cm⁻², with improved stability under higher rate stress protocols.Second, replicated coin cell datasets, coulombic efficiency, and survival analysis show that cathode architecture strongly governs durability as porous urchin MnO₂, with radially oriented rods, improves ionic access, reduces transport losses, shifts failure distributions, and extends time to failure relative to non-urchin morphologies.Third, an ambient-pressure synthesis route is demonstrated for urchin γ-MnO₂. Late-stage acid-assisted treatment tunes defect chemistry and architecture to produce a higher performing cathode. At ~ 4 mg cm⁻² active loading, the acid-treated urchin cathode sustains ~ 1300 cycles at C/4 in 2 M ZnSO₄ with ~ 75% capacity and energy retention, corresponding to ~ 136 mAh g⁻¹ and ~ 184 Wh kg⁻¹. Voltage signatures, operando pH tracking, impedance spectroscopy, and post-mortem characterization identify two degradation regimes: (i) a largely reversible zinc hydroxide sulfate (ZHS)-regulated regime, and (ii) a ZHS-accumulating regime associated with progressive transport restriction.Finally, a scenario-based techno-economic model benchmarks Zn-MnO₂ against LFP/graphite for containerized storage and shows that delivered energy competitiveness depends primarily on cycle life and round-trip efficiency, with a break-even target of 5 × 10³ cycles at ~ 80% depth ivof discharge. Together, these results connect electrode design, mechanistic diagnostics, and deployment targets for Zn-MnO₂ batteries under grid-relevant conditions. Under comparable cycling conditions, the achieved slow rate durability falls among the stronger coin cell demonstrations reported for aqueous Zn-MnO₂.