Structural instability and slow reaction kinetics restrict the application of MnO₂ cathode in aqueous zinc-ion batteries. This research proposes a guest cation screening principle, identifying Sr²⁺ as the promising intercalation ion. As demonstrated, it enables in situ forming customized SrSO₄ CEI that suppresses Mn dissolution and boosts the de-solvation of hydrated zinc ions, yet stabilizes the MnO₂ host structure.

Abstract

Intrinsic structural instability and sluggish reaction kinetics at the electrode/electrolyte interface are two critical concerns that block the application of MnO₂ cathode in high-performance aqueous zinc-ion batteries. This work proposes a theoretical screening principle to select the compatible guest cation for MnO₂ host, not only to strengthen the structure but also customize high-efficiency cathode/electrolyte interphase (CEI). As identified, Sr²⁺ is selected as the suitable intercalation ion that enable in situ forming the SrSO₄ CEI after partial release upon charge process. Moreover, density functional theory calculation and multiple characterization research indicate that such SrSO₄ interphase shows an electronic insulation to stabilize the interfacial pH, inhibit the Mn dissolution, and promote the efficient de-solvation of hydrated zinc ions. Benefited from the self-optimizing cathode/electrolyte interface chemistry, the 2.5% Sr-MnO₂ one exhibits higher specific capacity (304.1 mAh g⁻¹ at 0.5 A g⁻¹), better rate capability (115 mAh g⁻¹ at 10 A g⁻¹), as well as higher capacity retention of 87.9% after 1000 cycles at 2 A g⁻¹, when compared with pure δ-MnO₂ electrode. This study provides a new insight on understanding the functions of ion intercalation engineering to design robust layered cathode for high-performance aqueous zinc-ion batteries and beyond.