Researchers show nitrogen- or born-doped graphene can serve as high-power and high-energy anodes for Li-ion batteries
03 July 2011
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| Ragone plots for the pristine graphene, N-doped graphene, B-doped graphene, graphene oxide (GO), and GO500 based cells with lithium metal as the counter/reference electrode. The calculation of gravimetric energy and power density was based on the active material mass of a single electrode. Credit: ACS, Wu et al. Click to enlarge. |
Researchers at the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences have shown that nitrogen- or boron-doped graphene can be used as an anode material for high-power and high-energy lithium-ion batteries under high-rate charge and discharge conditions.
The doped graphene shows a high reversible capacity of >1040 mAh g–1 at a low rate of 50 mA g–1. Also, it can be quickly charged and discharged in a very short time of 1 h to several tens of seconds together with high-rate capability and excellent long-term cyclability. As an example, the team achieved a very high capacity of 199 and 235 mAh g–1 for the N-doped graphene and B-doped graphene at 25 A g–1 (about 30 s to full charge).
These results, Wu et al. noted in a paper in the journal ACS Nano, are superior to those of chemically derived graphene and other carbonaceous materials, indicating the potential of N- and B-doped graphene as high-performance LIB anode materials.
It is generally believed that lithium ion batteries (LIBs) using a bulk material such as layered graphite or metal oxide as an anode are capable of achieving a high energy density by storing charges in the bulk of the material, but suffer from a low power density compared to another important electrochemical storage device, electrochemical capacitors (ECs). The power capability of a LIB depends critically on the speed at which Li+ ions and electrons migrate through the electrolyte and bulk electrode.
...Graphene, a one-atom-thick two-dimensional (2D) carbon material, is expected to be a good candidate as a high-power and high-energy electrode material due to its intrinsically superior electrical conductivity, excellent mechanical flexibility, remarkable thermal conductivity, and high surface area, as well as the open and flexible porous structure of graphene powders.
...Here we report an electrode with extremely high rate and large capacity made by heteroatom (N, B)-doped chemically derived graphene.
—Wu et al.
The team synthesized graphene by oxidation and thermal exfoliation of natural flake graphite powder at 1050 °C in an Ar flow, followed by H2 reduction at 450 °C in a gas flow of H2 and Ar (“pristine graphene” in the paper). They carried out further heat treatment of the pristine graphene in N- and B-containing gases for N and B doping, respectively.
The team suggested that the unique two-dimensional structure of the doped graphenes, their disordered surface morphology, heteroatomic defects, better electrode/electrolyte wettability, increased intersheet distance, improved electrical conductivity, and thermal stability are beneficial to rapid surface Li+ absorption and ultrafast Li+ diffusion and electron transport, and thus make the doped materials superior to those of pristine chemically derived graphene and other carbonaceous materials.
We believe that the high power and energy capabilities as well as the low cost and easy large-scale preparation of doped graphene electrodes open up an opportunity to develop high-performance electrochemical storage devices for powering HEVs, plug-in HEVs, and EVs at high rates of several minutes to tens of seconds.
—Wu et al.
Resources
Zhong-Shuai Wu, Wencai Ren, Li Xu, Feng Li, Hui-Ming Cheng (2011) Doped Graphene Sheets As Anode Materials with Superhigh Rate and Large Capacity for Lithium Ion Batteries ACS Nano Article ASAP doi: 10.1021/nn200624
Fine tuned graphene electrodes may eventually become the path to 600 Wh/Kg to 1000 Wh/Kg batteries for highway BEVs.
Let's hope that it (and/or other technologies) can do it by 2020 at an affordable price.
Posted by: HarveyD | 03 July 2011 at 09:27 AM
This appears to be about on par with an earlier article:
http://www.greencarcongress.com/2011/05/chang-20110521.html
One may be easier to manufacture than the other. One thing common with these (and Nazar's cathode http://www.greencarcongress.com/2009/05/researchers-develop-electrode-materials-for-highcapacity-lis-battery-cells.html#more) is poor performance at high power. This article is the first that I have seen that gives specifications at very high power, although the performance drops down to regular Li-ion capacity.
As these designs stand, since they are power limited, they will only be useful for cars if they are very large packs. i.e. at C/10 to draw 100 amps at about 400 volts = 400kwh. This would be huge (1500-2000 lbs?) but would be well over 1000 miles range. These are very promising designs, but work must be done to increase their power density.
Posted by: Roy_H | 04 July 2011 at 01:35 AM
Could the high power required for acceleration and hill climbing be supplied by complementary Super-Caps and extended e-range (and super caps recharge) by very high energy density batteries?
Such combo could be electronically controlled to suit changing requirements and/or variable driving aggressiveness.
Posted by: HarveyD | 04 July 2011 at 09:13 AM
Yes, some combination of super caps or even LiFePO4 batteries could be workable. Caps are horrifically expensive and thus would be limited to a few seconds of surge power such as needed for passing. Conventional batteries could provide 10 minutes or more and be useful for hill climbing but not mountain climbing.
Posted by: Roy_H | 04 July 2011 at 06:13 PM
A good compromise, until the ideal battery is produced.
Posted by: HarveyD | 05 July 2011 at 08:43 AM