Unlocking the Critical Role of Cations Doping in MnO2 Cathode with Enhanced Reaction Kinetics for Aqueous Zinc Ion Batteries

Abstract

MnO₂-based cathode aqueous rechargeable zinc-ion batteries (ZIBs) have favorable sustainability characteristics and are considered potential candidates for low-cost effective, high-safety energy storage systems. Nevertheless, the development of them has been hampered by unstable electrode structures and ambiguous charge storage mechanisms. Herein, the role of doping Fe³⁺ and Co²⁺ into δ-MnO₂ cathode materials (FMO, CMO) is comprehensively probed and the working mechanism of Zn//FMO, Zn//CMO batteries are studied using in situ and ex situ characterization, electrochemical analysis, and theoretical calculations. Metal cations can partially replace Mn to form M─O bonds and enhance the structural stability as well as redox activity of MnO₂. It is found that Fe doping effectively modulates the interaction between Zn²⁺/H⁺ and the MnO₂ structure and inhibits the formation of ZnMn₂O₄ (ZMO) by-products and Co doping confers the fast diffusion ability of Zn²⁺. The charge storage reactions of FMO and CMO are mainly via H⁺/Zn²⁺ intercalation/deintercalation accompanied by OTF-base-like double hydroxide Zn_x(OTF)_y(OH)_2x-y-nH₂O (Z-LDH) deposition/dissolution. This research enriches the fundamental comprehension of rechargeable ZIBs and reveals the way to modify electrodes for performance enhancement.