Stable Voltage Cutoff Cycle Cathode with Tunable and Ordered Porous Structure for Li‐O 2 Batteries

Ordered porous RuO 2 materials with various pore structure parameters are prepared via a hard‐template method and are used as the carbon‐free cathodes for Li‐O 2 batteries under the voltage cutoff cycle mode. The influences of pore structure parameters of porous RuO 2 on electrochemical performance are systematically studied. Results indicate that specific surface area and pore size determine the specific capacity and round‐trip efficiency of Li‐O 2 batteries. Too small pores cause pore blockage and hinder the diffusion pathways of Li + and O 2 , thereby causing small specific capacity and high overpotentials. Too large pores weaken the mechanical property of porous RuO 2 , thereby causing the rapid decrease in capacity during electrochemical reaction. The Li‐O 2 battery based on the RuO 2 cathode with an average pore size of 16 nm (RuO 2 ‐16) exhibits a high round‐trip efficiency of ≈75.6% and an excellent cycling stability of up to 70 cycles at 100 mA g −1 with a voltage window of 2.5–4.0 V. The superior performance of RuO 2 ‐16 can be attributed to its optimal pore structure parameters. Furthermore, the in situ differential electrochemical mass spectrometry test demonstrates that RuO 2 can effectively reduce parasitic reactions compared with carbon materials.