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

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 α-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 mA·h·g^-1 at a current density of 200 mA·g^-1, a good cycle stability of 500 cycles at the capacity of 500 mA·h·g^-1. When current density is increased to 400 mA·g^-1, LOBs still retain a long lifespan of 170 cycles at a limited capacity of 1,000 mA·h·g^-1.