Ag doped urchin-like α-MnO2 toward efficient and bifunctional electrocatalysts for Li-O2 batteries

Abstract

Rechargeable Li-O2 batteries (LOBs) have been receiving intensive attention because of their ultra-high theoretical energy density close to the gasoline. Herein, Ag modified urchin-like α-MnO2 (Ag-MnO2) material with hierarchical porous structure is obtained by a facile one-step hydrothermal method. Ag-MnO2 possesses thick nanowires and presents hierarchical porous structure of mesopores and macropores. The unique structure can expose more active sites, and provide continuous pathways for O2 and discharge products as well. The doping of Ag leads to the change of electronic distribution in a-MnO2 (i.e., more oxygen vacancies), which play important roles in improving their intrinsic catalytic activity and conductivity. As a result, LOBs with Ag-MnO2 catalysts exhibit lower overpotential, higher discharge specific capacity and much better cycle stability compared to pure α-MnO2. LOBs with Ag-MnO2 catalysts exhibit a superior discharge specific capacity of 13,131 mAhg−1 at a current density of 200 mAg−1, a good cycle stability of 500 cycles at the capacity of 500 mAhg−1. When current density is increased to 400 mAg−1, LOBs still retain a long lifespan of 170 cycles at a limited capacity of 1,000 mAhg−1.