Hierarchical MnO2/NiS–MnS with Rich Electro-Microstructural Physiognomies for Highly Efficient All-Solid-State Hybrid Supercapacitors

Abstract

To revolutionize the charge storage efficiency of electrode materials for their utilizations in high Ragone efficient electrochemical energy storage devices, herein, a slow-precipitation-induced material growth approach has been innovated to design a hetero oxide–sulfide [MnO2/NiS–MnS (MnO2/Ni–Mn–S)] material with smaller crystallite size, ultrathin assembled-sheet-like microstructure, and perceptible phase physiognomies (α-MnO2, MnS, and α-NiS). The electroredox assessment of MnO2/Ni–Mn–S illustrates high pseudocapacitive energy storage efficiency, significant redox reversibility, lowly constrained bulk accessibility of the OH– ions at higher rate electrochemical reaction conditions, dominance of semi-infinite diffusion-controlled electrochemical processes, and extremely low charge-transfer resistance (∼1.45 Ω), total series resistance (∼0.51 Ω) and diffusion (Warburg) resistance. A fabricated 1.8 V MnO2/Ni–Mn–S||nitrogen-doped reduced graphene oxide (N-rGO) all-solid-state hybrid supercapacitor (ASSHSC) device with N-rGO as the negative electrode material delivers high area and mass specific capacitance/capacity, ∼100% Columbic efficiency at high-rate operating conditions, and very low charge-transfer and Warburg resistance. The MnO2/Ni–Mn–S||N-rGO ASSHSC device also delivers excellent Ragone efficiency (ED = 31.5 W h kg–1 at PD = 937.5 W kg–1 and ED = 15.5 W h kg–1 at PD = 2767.5 W kg–1) and ∼97.6% retention of charge storage after 11,000 uninterrupted charge–discharge cycles. The significantly improved supercapacitive charge storage efficacy of MnO2/Ni–Mn–S is ascribed to the cohesive redox activity of Ni2+, Ni3+, Mn2+, and Mn3+ and nonstoichiometric Ni2±δ, Ni3±δ, Mn2±δ, and Mn3±δ ions, rich ion-disseminating bulk, S2– vacancy-induced electronic conductivity, and suitable electro-microstructural physiognomies for the electrochemical processes.