Pre-Intercalation of Zn Ions to Enlarge and Stabilize Hierarchical Structure of Zn_xMn_1-xSe Cathode for Flexible Zn-Ion Capacitor

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, MnO₂ and V₂O₅, 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_xMn_1-xSe 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_0.14Mn_0.86Se 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.