Adding Graphene to Metal Oxides Significantly Improves Li-ion Electrode Specific Capacity at High Charge/Discharge Rates
24 September 2009
| Specific capacities of two TiO2-FGS (functionalized graphene sheets) hybrids at different charge / discharge rates compared to control TiO2. Credit: ACS, Wang 2009. Click to enlarge. |
Researchers at the US Department of Energy’s (DOE) Pacific Northwest National Laboratory have found that adding graphene—sheets made up of single carbon atoms—to titanium dioxide (TiO2) results in lithium-ion electrode materials that significantly outperform standard titanium dioxide materials. They presented the results of their work on these hybrid TiO2-graphene systems earlier this week at the Micro Nano Breakthrough Conference in Portland, Oregon.
As attractive as Li-ion batteries are for application in electric vehicles and renewable energy applications, many potential electrode materials are limited by slow Li-ion diffusion, poor electron transport in electrodes, and increased resistance at the interface of electrode/electrolyte at high charge. One avenue researchers are exploring to improve that performance is to introduce hybrid nanostructured electrodes that interconnect nanostructured electrode materials with conductive additive material.
While the hybrids or nanocomposites offer significant advantages, some of the candidate materials to improve the conductivity, such as RuO2 and CNTs [carbon nanotubes], are inherently expensive. In addition, conventional carbon additives at high loading content (20 wt% or more) are still needed to ensure good electron transport in fabricated electrodes. To improve high-rate performance and reduce cost of the electrochemically active materials, it is important to identify high surface area, inexpensive, and highly conductive nanostructured materials that can be integrated with electrochemical active materials at nanoscale.
—Wang et al.
TiO2 is an attractive electrode material. It is abundant, low cost, and environmentally benign. It is also structurally stable during the insertion and extraction of lithium ions, and is intrinsically safe by avoiding lithium electrochemical deposition. Graphene has excellent electronic conductivity and mechanical properties, and may be the ideal conductive additive for hybrid nanostructured electrodes, the researchers suggested.
We demonstrate the use of graphene as a conductive additive in self-assembled hybrid nanostructures to enhance high rate performance of electrochemical active materials. We choose metal oxide TiO2 as a model electrochemical active oxide material, but this method can be applied to other materials as well.
—Wang et al.
The PNNL team developed a one-step synthesis approach for the self-assembly of the metal oxide-graphene hybrid nanostructures. They found that the hybrid materials showed enhanced Li-ion insertion/extraction kinetics, with specific capacity more than doubled at high charge rates, as compared with the pure TiO2 material. The high rate performance is important for applications where fast charge and discharge is needed, such as in load leveling utility applications.
The attributed the improved capacity at high charge-discharge rate to increased electrode conductivity in the presence of the percolated graphene network embedded into the metal oxide electrodes.
The high rate properties obtained from the graphene nanocomposite materials are comparable to some of the best results reported in the literature using RuO2 or carbon nanotubes with a higher carbon (Super P) additive content. The simple self-assembly approach, and the potential low manufacturing cost of graphene may provide a new pathway for large scale applications of novel hybrid nanocomposite materials for energy storage.
...we expect that the self-assembly approach discussed here can be applied to other metal oxide-graphene hybrid nanostructures to study synergetic properties and improve the performance of oxide electrodes in electrochemical energy storage and conversion.
—Wang et al.
Resources
Donghai Wang, Daiwon Choi, Juan Li, Zhenguo Yang, Zimin Nie, Rong Kou, Dehong Hu, Chongmin Wang, Laxmikant V. Saraf, Jiguang Zhang, Ilhan A. Aksay and Jun Liu (2009) Self-Assembled TiO2–Graphene Hybrid Nanostructures for Enhanced Li-Ion Insertion. ACS Nano, 3 (4), pp 907–914 doi: 10.1021/nn900150y
Is the significant improvement for the first cycle only?
Posted by: kelly | 24 September 2009 at 06:00 AM
http://www.sciencedaily.com/releases/2009/09/090922160058.htm
Where do the graphs show "..containing graphene outperformed the standard titanium dioxide by up to three times."?
Posted by: kelly | 24 September 2009 at 06:39 AM
Doubling or thripling the natural discharge/charge rates will extend the overall duration (life) + percentage of useable charge of most lithium batteries could be a huge step forward. If life expectation + useable charge + charge/discharge rates can be increased while reducing cost, lithium batteries may have another chance to make it to mass production for PHEVs and BEVs. This is the type of breakthrough take Toyota may have been waiting for.
Long life, quick deeper charges/discharges and reduced cost e-storage units are essential for affordable future highway BEVs.
There is no doubt that many more inovations will be made to improve the performance of e-storage units during the next decade.
It would be interesting to know where we will be at by 2020.
Posted by: HarveyD | 24 September 2009 at 07:50 AM
@kelly
Look carefully at the graphs on this page. You'll see quite clearly that the addition of Graphene substantially improves the specific charge at high rates of charge/discharge. I could explain it here but all you really need to do is look cloesely at the charts
This seems like a huge advance. It appears, from these graphs, that the cycle life of lithium-titanate batteries could be substantially prolonged WHILE increasing the usable charge. It has always been my opinion that increasing the cycle life such that a vehicle's battery would be good for ~250,000 miles would be key. Said batteries could attract large scale investment from pension funds, energy companies, and private investors who would purchase the batteries and then rent them out to end users/consumers.
Posted by: GreenPlease | 24 September 2009 at 12:32 PM
Improved battery technology is not needed to get electric cars on the road. Smaller cheaper cars that are plug-in-hybrids will get lots of cars on the road.
GM is introducing a 13 kW (20 hp) car in India but continues to foist the development of the VOLT on US taxpayers. Lets have an EDISON or STEINMETZ or WESTINGHOUSE that could just be the Indian car with proper lights, brakes and testing and a 7 kw or less engine range extender. ..HG..
Posted by: Henry Gibson | 24 September 2009 at 12:47 PM
Amen, Henry.
A little EV (size of a mini or suzuki sx4) that can get 50+ miles AND price around $15K would be a huge hit.
-
People might still want an ICE for trips, but for groceries, taking kids to soccer, etc. the EV would be first choice.
Posted by: danm | 24 September 2009 at 01:53 PM
@GreenPlease,
Now I see the 2X+ improvement above the 20C rate and 30th cycle.
If the durability can improve by a magnitude or two and if it's economic - we got a winner.
Can oil firms buy a DOE patent?
Posted by: kelly | 25 September 2009 at 07:10 AM
HG:
Agree with you that first generation BEVs could be ZENN type city small cars. The world could use a few million of them while e-storage units mature to the level required for larger highway type BEVs. The $110K sport Tesla is not the solution for everybody.
As an interim solution, affordable highway capable PHEVs, with optional battery and genset size, could be a viable solution and be complementary to current improved HEVs for the next 10-15 years.
By 2020, affordable, quick charge, extended range highway type BEVs will be mass produced in many countries. HEVs and PHEVs will be progressively phased out. ICE will quickly become museum pieces.
Posted by: HarveyD | 25 September 2009 at 11:51 AM
Improved battery technology IS needed to get electric cars on the road in any significant number. Smaller cheaper EVs that will be available soon (we hope) will get lots of cars on the road.
So will larger cheaper EVs.
Face it – there is almost always no market for these autos you wish were imported, but aren't.
When a little foreign auto will sell, someone will bring it in.
Will the few people who want these little-little cars to be available, bring them here? NO. The market will bring them.
BEVs are coming - the technology will bring them – a FEW wanting what is now available elsewhere, but not desired by most here, will not.
Posted by: ToppaTom | 26 September 2009 at 08:08 AM
TT:
Free market PR convinced 50% + of the American population that 5000+ lbs ICE monsters were essential to drive to work, go shopping, drive the kid to school, to impress the neighbours etc.
Higher gas prices + higher registration fees + higher road usage fees + reversed PR could convince many that 2000 lbs BEVs could do the same job much more efficiently.
Free Market alone cannot do it fast enough, specially when it is not it their interest to do so. A helping hand is required. That's why we have responsible governments.
Posted by: HarveyD | 27 September 2009 at 10:30 AM
Since the free market can't do it fast enough HarveyD has the answer. Higher taxes, more legislation, and increased bureaucracy will save the day. Malinvestment is definitely the solution.
Posted by: Mannstein | 27 September 2009 at 11:10 AM
Mannstein:
If USA leaves the transition in the hands of the national free market, up to 80% may still be driving Hummer style ICE monsters in 2050 because we are convinced that Big is beautiful. Crude oil price may have to go all the way to $200+/barrel.
It seems that effective ways to accellerate the transition process may be with States/Fed legislations + incentives, + subsidies to retool and automate manufacturing facilities. Progressive much higher gas tax + higher fees/tariffs will be required to pay for the transition program. Nobody else but the national population will pay for it unless we borrow more $T from abroad. That too has limits.
Many (the majority) will not like to pay for it and will loudly resist as usual.
If a major transition program is not implemented soon, future mass produced affordable electrified vehicles may very have to be imported. Closing most existing car plants would soon follow.
Every industrial country has to do whatever is required to mainntain a strong national industrial base. This is specially true when major technological changes are being implemented.
Free market industries don't have the same goals as industrial nations. They just keep moving where production can be done at lower cost, regardless of the impacts on USA's industrial base.
Have a look at what happened (or is happening) to the cotton, clothing, Radio-TV-Telephone, computer, printer, batteries, tools, car parts, tires, paper, wood products etc industries and you may see what is going to happen to the EV battery + electrified vehicle industry in the next decade.
Faith in the current Big-3 management and UAW union to do what is best for USA's industrial base may not give the expected results.
Posted by: HarveyD | 30 September 2009 at 09:31 AM