The Pore Size Effect of Ordered Mesoporous Carbon in Li-O2 Batteries
The carbon materials helped to increase capacity, but failed to decrease the OER potential due to the low electronic conductivity of Li2O2. To increase the capacity and decrease the OER potential simultaneously, several metal (oxide) catalyst and carbon composite material was used for the cathode of Li-O2 cells. By using a catalyst, it was possible to lower the charging potential under 4 V corresponding overpotential of 1.1 V.
In spite of this, to the best of our knowledge, there has been no attempt to decrease the charging potential of Li-O2 cells by changing the morphology of the carbon materials. Furthermore, there has not been an approach that solves the low rate capability due to the low electrical conductivity of Li2O2.
Among the various carbon materials, ordered mesoporous carbon with pore sizes ranging from 2 to 50 nm can be a potential candidate electrode material because of the high surface area, various pore sizes and structures. Other authors have already applied the mesoporous carbon as an oxygen electrode for Li-O2 cells, but it was difficult to directly observe the lithium peroxide by transmission electron microscopy (TEM) after discharge due to the various pore sizes and disordered pore distributions of mesoporous carbon.
In this work, we used two different highly ordered mesoporous carbons with a pore size of 6 nm (OMC-6) and 17 nm (OMC-17) for an oxygen electrode without catalyst. By using the OMC material as an oxygen electrode, it was demonstrated that the charge potential can be lowered while improving the rate capability compared with super P carbon. The morphology of the discharge product that formed on the OMC material was found to be different from that of super P.
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