Oxygen-Deficient β-MnO₂@Graphene Oxide Cathode for High-Rate and Long-Life Aqueous Zinc Ion Batteries

Recent years have witnessed a booming interest in grid-scale electrochemical energy storage, where much attention has been paid to the aqueous zinc ion batteries (AZIBs). Among various cathode materials for AZIBs, manganese oxides have risen to prominence due to their high energy density and low cost. However, sluggish reaction kinetics and poor cycling stability dictate against their practical application. Herein, we demonstrate the combined use of defect engineering and interfacial optimization that can simultaneously promote rate capability and cycling stability of MnO₂ cathodes. β-MnO₂ with abundant oxygen vacancies (V_O) and graphene oxide (GO) wrapping is synthesized, in which V_O in the bulk accelerate the charge/discharge kinetics while GO on the surfaces inhibits the Mn dissolution. This electrode shows a sustained reversible capacity of ~ 129.6 mAh g^-1 even after 2000 cycles at a current rate of 4C, outperforming the state-of-the-art MnO₂-based cathodes. The superior performance can be rationalized by the direct interaction between surface V_O and the GO coating layer, as well as the regulation of structural evolution of β-MnO₂ during cycling. The combinatorial design scheme in this work offers a practical pathway for obtaining high-rate and long-life cathodes for AZIBs.