Synergistic yolk-shell engineering and electrochemical activation of MnO@C nanoplates for stable aqueous zinc-ion batteries

Manganese(II) oxide (MnO) is a promising cathode for aqueous zinc-ion batteries (AZIBs) but suffers from poor conductivity, sluggish kinetics, and an unclear energy storage mechanism. Herein, we report a yolk-shell structured N-doped carbon-coated MnO nanoplate (MnO@C-YS) synthesized via co-precipitation combined with polydopamine coating and pyrolysis. The optimized yolk-shell architecture features a MnO-rich core (400–500 nm) encapsulated within a conformal N-doped carbon shell with an interstitial void of 50–100 nm. This unique nanostructure synergistically buffers volume changes, facilitates ion transport, enhances electronic conductivity, and suppresses Mn dissolution. The resulting MnO@C-YS cathode delivers a high discharge capacity of 270 mAh g⁻¹ at 0.1 A g⁻¹, enhanced rate capability (113 mAh g⁻¹ at 5 A g⁻¹), and long-term cycling stability (97% retention after 1000 cycles at 1 A g⁻¹; 73% after 4000 cycles at 5 A g⁻¹). Ex situ characterizations reveal an activation mechanism wherein rock-salt MnO undergoes gradual in situ transformation into layered Mn₇O₁₃·5H₂O, which serves as the true host for reversible Zn²⁺/H⁺ co-intercalation. The work enriches the fundamental comprehension of AZIBs and sheds light on modifing MnO electrodes for performance enhancement.