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Univ. of Western Ontario researchers develop graphene nanosheet electrodes with high energy capacity for non-aqueous Li-air batteries

Li
Discharge–charge performance of lithium-oxygen batteries with (a) GNSs, (b) BP-2000, and (c) Vulcan XC-72 cathodes at a current density of 75 mA g-1. Li et al. Click to enlarge.

Researchers from the Nanomaterials and Energy Group at the University of Western Ontario, Canada, report the development of graphene nanosheet (GNS) cathode materials for non-aqueous lithium-oxygen (Li-air) batteries that show a capacity of 8,705.9 mAh g-1—the highest capacity of any carbon-based materials in lithium-oxygen batteries reported so far, according to the team. Their paper appears in the RSC journal Chemical Communications.

Non-aqueous Li-air batteries are one of the promising systems being explored for “beyond Li-ion” energy storage solutions for electric vehicles (EVs) because of their extremely high theoretical energy density. The porosity of the air electrode is one of the critical factors in Li-air battery performance, because insoluble products are deposited in the electrode, which block O2 from diffusing to the reaction sites.

Other work, notes the team, also shows that the oxygen reduction reaction (ORR) in the carbon electrode signficantly affects performance.

Therefore, it is important to develop new carbon electrodes to improve the kinetics and enhance the energy capacity. Graphene nanosheets (GNSs) have attracted great attention for energy storage applications. Especially, they have been widely used as catalyst supports or non-noble catalysts for fuel cells.

Recently, Yoo and Zhou examined the GNSs as air electrodes in lithium-air batteries with a hybrid electrolyte and found that GNSs showed good electrocatalytic activity for ORR in an aqueous electrolyte, resulting in high performance. They also developed an idea of applying a graphene-like thin film on a ceramic state electrolyte in a lithium-air battery.

However, to the best of our knowledge, no research on GNSs as a cathode for nonaqueous lithium-oxygen batteries has been reported. Herein, for the first time, we employed GNSs as cathode active materials in nonaqueous lithium-oxygen batteries and found that GNSs delivered an extremely high discharge capacity.

—Li et al.

The research team, led by Professor Xueliang (Andy) Sun, believes that the superior capacity is due to the unique structures of the synthesized GNSs, which provides ideal porosity suitable for the electrolyte wetting and O2 diffusion, thereby significantly improving the discharge capacity.

The team also pointed out that the edge sites of the GNSs which contained a large amount of unsaturated atoms were highly active in reaction with oxygen and form oxygen-containing groups, contributing to the battery performance.

Although the detailed mechanism for the oxygen reduction reaction on GNSs in a nonaqueous electrolyte is unclear, it has [been] revealed that GNSs can deliver an extremely high discharge capacity, showing promising applications in lithium-oxygen batteries

—Xueliang Sun

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, Ruying Li and Xueling Sun (2011) Superior energy capacity of graphene nanosheets for a nonaqueous lithium-oxygen battery. Chem. Commun., 47, 9438–9440 doi: 10.1039/c1cc13464g

Comments

HarveyD

Another potential application of graphene electrodes to eventually get much higher energy storage performance. What are the fall backs? Toyota (battery group) has been working on a similar solid state battery approach for a long time but the results are not published.

HealthyBreeze

Lithium-air batteries have problems with moisture, and need ventilation systems which add back in some weight and bulk. Graphene...anybody know how to make it in volume?

DaveD

There have been a couple of breakthroughs recently on cheap graphene production (I'll have to go dig up the links).

But eyballing the graph, looks like about 7,000mAh/g at 2.6V would be 18.2kWh/kg in the cathode. That doesn't include the rest of the weight of a cell or a pack, but it's a hell of a start towards a high energy density battery.

Of course, now we have to ask:
Cycle life? Power density? COST!?, safety? shelf life? COST? did I mention COST??? :-)

ExDemo

Lithium ion energey density makes EVs and EREVs possible. But it will take the next generation of battery chemisties to make them practical.

Li-Air is one of thoe battery chenmistries. However it islekly htta they won't be availble commerciallly for another decade.

Bob Wallace

EVs and PHEVs are practical right now for a very large segment of drivers.

Most households which have two vehicles could quite easily make one of them an EV. Not that many people drive more than 100 miles very often. No doubt there are many people who use public transportation (planes and trains) for trips greater than a few miles.

Almost any driver who can get by with a smaller vehicle, who doesn't need to haul more than four-five passengers or tons of luggage, can easily use a PHEV like the Chevy Volt. There is no range restriction when you can tank up on long trips.

The current generation of batteries should bring us affordable EVs and PHEVs as soon as economy of scale kicks in. The generation after should increase EV range to the point where many more people will find EVs fit their needs.

The battery developments we're reading about today will likely mean the end of the internal combustion engine for personal transportation later on. When a very affordable battery can last more than ten years and hold 400-500 miles of cheap electricity then the days of gas stations are over.

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