Acid–Alkaline Electrolyte for the Development of High-Energy Density Zn-Ion Batteries through Structural Modification of MoS2 by MnO2

Aqueous rechargeable Zn-ion batteries (ZiBs) are of low cost and high safety but suffer from a narrow electrochemical stability window, leading to the low-energy density. The battery performance is impeded because of the sluggish intercalation kinetics associated with the Zn2+ ion at the cathode in the aqueous electrolyte. An asymmetric-bipolar ZiB ("H" cell) consisting of an acid–alkaline dual electrolyte separated by an ion-exchange membrane is proposed. The MoS2@δ-MnO2 cathode and the Zn anode operated at different pHs of the electrolyte, leading to a high cell voltage of 2.48 V. The efficiency of Zn2+ accepting the host is enhanced through structural modification of the MoS2 layer by MnO2. The deposition/dissolution and insertion/extraction charge storage mechanisms in "H" cells were investigated through ex situ field-emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-dependent activation energy calculation, and distribution relaxation time studies. The "H" cell delivered ∼464 mAh g–1 specific capacity and ∼348 Wh kg–1 energy density at 0.2 A g–1 current density with ∼99.9% Coulombic efficiency and exhibited superior cycling stability with ∼74% capacity retention after 5000 charge–discharge cycles.