Enhancing Proton Reaction Chemistry of Aqueous Zn─MnO₂ Battery by Phosphate Proton Reservoir

Aqueous rechargeable Zn─MnO₂ batteries have emerged as promising candidates for grid-scale energy storage due to their low cost, high safety, natural abundance, and high working potential. However, their widespread application is hindered by rapid capacity degradation and sluggish reaction kinetics. In this study, we introduce Zn₃(PO₄)₂ 4H₂O (ZPH) as a proton reservoir to significantly enhance the electrochemical performance of MnO₂ by optimizing proton reaction chemistry. Specifically, ZPH stores protons during charging and releases them during discharging, creating a localized H⁺-rich environment that facilitates proton intercalation of Mn⁴⁺/Mn³⁺ and the two-electron transfer reaction of Mn⁴⁺/Mn²⁺. Leveraging the proton storage capability of ZPH, the layered MnO₂ cathode demonstrates exceptional rate performance (219.2 mA h g^-¹ at 3 A g^-¹), high specific capacity (347.3 mA h g^-¹ at 0.1 A g^-¹), and remarkable cycling performance (1500 cycles at 2 A g^-¹). This work provides a scalable and electrolyte-compatible pathway to optimize proton-involved reaction dynamics in aqueous Zn─MnO₂ batteries.