Construction of δ-MnO 2 /rGO Cathode via In-situ Oil-water Interface Reaction for Enhancing Electrochemical Performance of Aqueous Zinc-Ion Batteries

Abstract

Abstract：MnO 2 -based cathodes normally suffer from poor electric conductivity, severe dissolution, and agglomeration in aqueous zinc-ion batteries (AZIBs), and rGO species are utilized to resolve these issues due to its large surface area and superior electrical conductivity. Nevertheless, the undesired composite structured styles of MnO 2 and rGO significantly restrains the Zn 2+ storage capability towards cathode materials, which are mainly determined by the synthesis method.Herein, we innovatively proposed an oil-water interface reaction to in-situ grow δ-MnO 2 on the GO substrates, and the subsequent thermal reduction was applied to obtain the δ-MnO 2 /rGO composites (in-MG-2). Compared with samples prepared by the simple physical blending and in-situ growing δ-MnO 2 on the rGO substrates, the as-prepared in-MG-2 samples demonstrate favorable features, including well-dispersed δ-MnO 2 nanosheets, expanded (001) crystal planes, and the forming Mn-O-C bonds, which can enhance diffusion rates of Zn 2+ , accelerate the interface charge transfer and reduce de-solvation energy barrier. Therefore, the as-assembled Zn//in-MG-2 cell exhibits higher capacity of 351.17 mAh g -1 at 0.2 A g -1 and 142.8 mAh g -1 at 4.0 A g -1 , and enhanced stability of 97.6% capacity retention after 500 cycles at 1.0 A g -1 .Moreover, the Zn//in-MG-2 pouch cell can also power a smartphone and exhibit superior cycling stability. Meanwhile, the storage mechanism of cooperative insertion of H + /Zn 2+ has been revealed in the in-MG-2 cathode. This work not only provides a promising cathode in AZIBs, but exploits a new oil-water interface reaction to grow other transition metal compounds on the GO substrates.