Mn²⁺ Ion-Mediated Zn Dendrite Suppression and Reversible Stripping in Aqueous Zn-Ion Batteries as Revealed by In Situ Liquid-Cell TEM

Achieving uniform Zn deposition and its reversible dissolution at the anode remains a major challenge in aqueous zinc-ion batteries (AZIBs), where dendrite growth and interfacial instability limit the cycling life. Herein, we employ in situ electrochemical liquid-phase transmission electron microscopy (EC-LPTEM) to mimic a battery operation and directly visualize Zn electrodeposition in the presence of MnSO₄ in an aqueous ZnSO₄ electrolyte. Real-time observations reveal that Mn²⁺ ions regulate interfacial nucleation, suppress dendritic elongation, and promote uniform plating, while facilitating nearly complete Zn dissolution during stripping. Post-deposition analyses using transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) show that Mn²⁺ ions are incorporated into chemically labile Zn-Mn-O-S interfacial deposits. Ex situ electrochemical measurements confirm that Mn²⁺ ions improve Zn anode stability and extend cycling performance. These findings provide direct nanoscale insights into additive-regulated Zn deposition and highlight Mn²⁺ ion-mediated interfacial modulation as an effective strategy for controlling Zn deposit morphology and enhancing AZIB durability.