Ordered porous RuO2 materials with various pore structure parameters are prepared via a hard-template method and are used as the carbon-free cathodes for Li-O2 batteries under the voltage cutoff cycle mode. The influences of pore structure parameters of porous RuO2 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-O2 batteries. Too small pores cause pore blockage and hinder the diffusion pathways of Li+ and O2 , thereby causing small specific capacity and high overpotentials. Too large pores weaken the mechanical property of porous RuO2 , thereby causing the rapid decrease in capacity during electrochemical reaction. The Li-O2 battery based on the RuO2 cathode with an average pore size of 16 nm (RuO2 -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 RuO2 -16 can be attributed to its optimal pore structure parameters. Furthermore, the in situ differential electrochemical mass spectrometry test demonstrates that RuO2 can effectively reduce parasitic reactions compared with carbon materials.
Keywords: cathode; lithium-O2 batteries; ordered porous materials; voltage cutoff cycle.
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.