A mild one-step synthesis of sodium pre-intercalated δ-MnO2@CC for flexible high-performance supercapacitors with ultralong cycle life

Cation ion intercalated δ-MnO2 has been considered as a promising candidate for flexible energy storage devices. Herein, we fabricated Na ion pre-intercalated δ-MnO2 immobilized on flexible carbon cloth (CC) for symmetric supercapacitors via a mild one-step cyclic voltammetry (CV) electrodeposition method. Compared to that of NaxMnO2–32 without NH4+additive, NaxMnO2–32-N with NH4+ additive obtained a larger Cs (1208 mF·cm−2) with a 40 % increase and a maintained Cm (208 F·g−1 at 1 mA·cm−2). In addition, NaxMnO2–32-N exhibited more remarkable capacitive behavior and better rate capability. Based on the XPS, BET, TEM and SEM results, the increase of specific surface area, Na+ ion pre-embedded content and deposition mass were deduced to be the dominant role in optimizing electrochemical properties of δ-MnO2. A flexible symmetric supercapacitor was assembled by NaxMnO2–32-N electrodes to evaluate its applications and demonstrated a high energy density of 117.74 μW·h·cm−2 (at a power density of 225 μW·cm−2) and power density of 3375 μW·cm−2 (at an energy density of 12.35 μW·h·cm−2) with good flexibility. Furthermore, it showed excellent capacity retention rate (97 %) and coulomb efficiency (105 %) after 80,000 long-term charging/recharging cycles.