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
06 February 2012
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| 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.
Resources
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
http://www.electrochem.org/dl/ma/206/pdfs/0333.PDF
Typical(like today's Leaf): 180 mAh/g are obtained for Li[Ni1/3Co1/3Mn1/3]O2
vs
Li-oxygen batteries(this article): 11,660 mAh g-1
is a factor of ~65 times higher capacity.
Any questions?
Posted by: kelly | 06 February 2012 at 02:13 PM
Well, you are not including the anode, separator, casing, or any specialized support equipment. Also the standard Li-ion batteries can produce 1C to 10C output, that is about 1 amp/g, where as this is about 1/10, so you would need a battery 10 times larger than the Leaf battery to get the same acceleration.
This is an intriguing development, but hardly the holy grail.
Posted by: Roy_H | 06 February 2012 at 07:29 PM
There are many metrics that must be met for a successful EV battery. mAh/g is just one of many. There is usually a trade off with other specs - like squeezing a balloon.
Posted by: TM | 06 February 2012 at 09:45 PM
I have always found the researchers in the Li-air area to be very disingenuous when it comes to reporting energy densities. They never account for the dead space and distribution of oxygen. They typically report only active material capacities. The air batteries are much more like fuel cells in that there needs to be an air distribution system, and this is essentially ignored in the reports. The question they should answer, but never do, is what is the energy density of a cell or module. They probably don't know. However simply reporting the capacity of the active material is not fair. The active material must be supported on a porous substrate and there is a huge amount of empty volume. You have to have a way of flowing oxygen in also. So sure, maybe the active material mass goes down, but what has to be added, and in the end have you gained anything. Perhaps overall mass goes down, but I find it hard to believe that the batteries would be more energy dense on a volume basis. You know, some evidence would be helpful.
Posted by: Brotherkenny4 | 07 February 2012 at 08:11 AM
Good question BK4. The complete unit energy density could be about 1/10 the individual element energy capacity given above. If so, it could still be a 4X improvement over current technologies.
Posted by: HarveyD | 07 February 2012 at 08:45 AM
None of the hedging noted can fully cover a factor of 65.
Posted by: kelly | 07 February 2012 at 11:56 AM
Rechargeable lithium air batteries are still a decade or more away, if they can really do them at all. It they could get them viable it would be a breakthrough in capacity and range.
Posted by: SJC | 07 February 2012 at 01:25 PM
I always assumed that if they fixed the Li-air issues with cycle life (and presumably cost) then they would have a hard time getting the power densities needed...at least for the first few generations.
So we would probably see some type of "hybrid Li battery". Maybe 50kg of A123 cells or Toshiba SCiB cells providing the power and regen braking and the Li-Air batteries acting as a range extender.
Let both batteries focus on what their good at.
Posted by: DaveD | 07 February 2012 at 09:57 PM
DaveD,
That seems like the idea. The recharge cycles are the big issue with lithium air. They can get them to recharge, but not for 1000s of cycles, right now it is dozens of cycles.
Posted by: SJC | 08 February 2012 at 09:02 AM