Pre‐Intercalation of Zn Ions to Enlarge and Stabilize Hierarchical Structure of ZnxMn1‐xSe Cathode for Flexible Zn‐Ion Capacitor

Abstract Zn‐ion capacitors (ZICs) assembled from cathodes with diffusion‐controlled behaviors and capacitive anodes have attracted increasing interest thanks to their satisfactory and balanced energy and power densities. However, currently, only two cathode materials of this type, MnO 2 and V 2 O 5 , are applied to ZICs. MnSe is increasingly being reported to exhibit diffusion‐controlled characteristics in metal‐ion batteries and supercapacitors, yet its insufficient interlayer spacing and unstable structure lead to poor energy storage capacity. Herein, Zn x Mn 1‐x Se microflowers with nanosheets can be in situ pre‐intercalated with Zn ions to enlarge and stabilize the interlayer spacing of hierarchical porous structure, demonstrating to be a superior cathode for ZICs. During the charging/discharging process of Zn 0.14 Mn 0.86 Se electrode, a redox couple at ≈0.6/0.3 V on cyclic voltammetry profile, and a potential plateau appearing at ≈0.2 V on discharge curve is detected, corresponding to the insertion/extraction of Zn ions. Thus, a long discharge time realizes on the discharge curve of flexible ZIC assembled from polyacrylamide gel electrolyte and activated carbon anode, achieving a superb areal capacitance of 2,038.2 mF cm −2 at 1 mA cm −2 . This work offers an exemplary effort to unlock fresh cathodes for ZICs.