Investigating the physical-chemical effects of reduced graphene oxide-covered manganese oxide on ammonium-ion batteries

Aqueous ammonium-ion batteries have attracted more attentions. Electrodeposited manganese oxide (MnOx) electrodes stand out electrochemical behaviors for storing NH4+. However, the unsatisfied conductivity and dissolution of MnOx impede electrochemical properties of MnOx for applying in ammonium-ion batteries. In this work, electrochemical coverage of reduced graphene oxide (rGO) layers on MnOx was carried out to improve the properties of MnOx as a positive electrode of ammonium-ion batteries. The improvements are attributed to three functions of rGO additives to engage as conductive layers (fast electron transportation), blocking layers (inhibition of Mn2+ diffusion) and capacitive behaviors (adsorption of Mn2+ and NOx−), which makes sure the excellent rate capability (109 mAh g−1 at 5 A g−1) and cycling stability (92.6% after 1000 cycles) of rGO60/MnOx. In addition, we also studied the redox of NH4+ on rGO layers to investigate the stability of electrolyte, and the redox of NH4+ on rGO layers is highly reversible and low active, which implies that the rGO is suitable to be a functionalized component for improving the properties of MnOx to apply in ammonium-ion batteries. This work provides a new thought to design electrodes with comprehensive strategies for ammonium-ion batteries.