U of Western Ontario researchers find nitrogen-doped graphene nanosheet cathodes significantly increase performance of Li-oxygen batteries; 11,660 mAh g-1 at 75 mA g-1
|Voltage profiles of GNS and N-GNS electrodes at various current densities. Yi et al. Click to enlarge.|
Researchers at the University of Western Ontario (Canada) report that using nitrogen-doped graphene nanosheets as cathode materials significantly increases the performance of a non-aqueous lithium-oxygen battery, even compared to the use of the high-performance pristine graphene nanosheets they had developed earlier. (Earlier post.)
In a paper accepted for publication in the journal Electrochemistry Communications, Yongliang Li and his colleagues found that their nitrogen-doped graphene nanosheet (N-GNS) cathode materials delivered a discharge capacity of up to 11,660 mAh g-1; the pristine graphene nanosheets (GNSs) had shown a capacity of up to 8,706 mAh g-1—at that time, the highest capacity of any carbon-based materials in lithium-oxygen batteries reported, according to the team.
In their new study, they found that the electrocatalytic activity of N-GNSs for oxygen reduction in the non-aqueous electrolyte is 2.5 times that of GNSs. They attributed the excellent electrochemical performance of N-GNSs to the defects and functional groups as active sites introduced by nitrogen doping.
Recent studies reported that nitrogen-doped carbon powder and carbon nanotubes showed higher discharge capacities than the pristine counterparts, however, there is no report on nitrogen-doped graphene nanosheets (N-GNSs) as cathode materials for lithium-oxygen batteries. In this study, for the first time, N-GNSs were employed in lithium-oxygen batteries, and it was found that they show excellent electrocatalytic activity for oxygen reduction, therefore, increasing about 40% of the discharge capacity compared to GNSs. This finding not only shows that N-GNSs are promising electrode materials, but also gives a rational direction to modify other carbon materials for application in lithium-oxygen batteries.—Yi et al.
In the current study, Yi et al. prepared both GNS and N-GNS cathodes; findings included:
The initial discharge capacity of the GNS electrode was 8,530 mAh g-1 at a current density of 75 mA g-1, while the N-GNS electrode delivered 11,660 mAh g-1 for N-GNSs—about 37% higher.
As current densities increased, the discharge capacities of both samples decreased: 5,333 and 3,090 mAh g-1 for GNS and 6,640 and 3,960 mAh g-1 for N-GNS at current densities of 150 and 300 mA g-1, respectively.
The research was supported by Natural Sciences and Engineering Research Council of Canada, Canada Research Chair Program, Canada Foundation for Innovation, Ontario Early Researcher Award and the University of Western Ontario.
Yongliang Li, Jiajun Wang, Xifei Li, Dongsheng Geng, Mohammad N. Banis, Ruying Li, Xueliang Sun (2012) Nitrogen-doped Graphene Nanosheets as Cathode Materials with Excellent Electrocatalytic Activity for High Capacity Lithium-oxygen Batteries. Electrochem. Commun. doi: 10.1016/j.elecom.2012.01.023