Fig. 4. Discharge profiles of Li–O₂ batteries with RuO₂ or Li_xRuO₂ cathode at a current density of (a) 100 mA g⁻¹ and (b) 200 mA g⁻¹. The first-cycle charge–discharge curve (c), terminal discharge voltages and corresponding capacity (d) and cycling stability (e) of Li–O₂ batteries with RuO₂ or Li_xRuO₂ cathode at 100 mA g⁻¹ with a limited capacity of 500 mA h g⁻¹.