3D Porous Silicon Shows Promise as High-Performance Li-ion Anode Material
20 November 2008
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| SEM images of the 3D porous c-Si particles after etching. Click to enlarge. Credit: Angewandte Chemie |
A research team led by Dr. Jaephil Cho at Hanyang University in Korea has developed a new silicon material for lithium-ion battery anodes—three-dimensional porous bulk silicon particles—that can accommodate large strains without pulverization after 100 cycles and maintain a charge capacity of greater than 2,800 mAh g-1 at a rate of 1 C. A report on their work is a “hot paper” published online in the journal Angewandte Chemie International Edition.
The use of silicon as a next-generation high capacity anode material has attracted a great deal of research interest. (Earlier post, earlier post.) Silicon has a theoretical lithium capacity of approximately 4,200 mAh g-1 corresponding to Li4.4Si. This is 10-11 times greater than that of graphite (ca. 372 mAh g-1) and much larger than various nitride and oxide materials. However, practical application of silicon anode materials has been problematic.
Lithium-ion batteries produce current by moving lithium ions. While the battery is being charged, lithium ions migrate into the anode. When the battery is being discharged, these ions migrate back to the cathode. An anode material with significantly greater capacity than the commonly used graphite could thus significantly improve the capacity of the cells.
Although silicon offers that greater capacity, its volume changes by up to 400% upon the insertion and extraction of lithium ions during charge/discharge cycles (the alloying and de-alloying process to form LixSi and reform Si, respectively). This results in pulverization, in turn resulting in electrically disconnected smaller particles and rapid capacity fading.
Numerous studies have tackled reducing this volume change by using a variety of approaches, including developing composites with an inactive carbon phase and the development of silicon nanowires.
Cho, for example, also published a paper in October in the ACS journal Nanoletters (Kim 2008b) reporting on the development of mesoporous Si@carbon core-shell nanowires for use as an anode material in Li-ion batteries. This effort resulted in an initial capacity of 3,163 mAh g-1 and capacity retention after 80 cycles of 87%. Other nanowire efforts have returned somewhat similar results in terms of capacity, but have been hampered by capacity retention.
Cho’s team has now developed a new method for the production of a porous silicon anode that can withstand the strain. They annealed silicon dioxide nanoparticles with silicon particles whose outermost silicon atoms have short hydrocarbon chains attached to them at 900° C under an argon atmosphere. The silicon dioxide particles were removed from the resulting mass by etching. What remained were carbon-coated silicon crystals in a continuous, three-dimensional, highly porous structure.
Anodes made of this highly porous silicon have a high charge capacity for lithium ions. In addition, the lithium ions are rapidly transported and stored, making rapid charging and discharging possible. A high specific capacity is also attained with high current. The changes in volume that occur upon charging and discharging cause only a small degree of swelling and shrinking of the pore walls, which have a thickness of less than 70 nm.
In addition, the first charging cycle results in an amorphous (noncrystalline) silicon mass around residual nanocrystals in the pore walls. Consequently, even after 100 cycles, the stress in the pore wall is not noticeable in the material.
The present work demonstrates that 3D, porous Si particles that consist of bulk sizes greater than 20 µm can be prepared by simple thermal annealing of SiO2 and butyl-capped Si particles at 900° C under an Ar stream. Since this method does not require the use of a sealed ampoule, the reduction is easy to scale up. These particles facilitate faster transport and better intercalation kinetics of lithium ions; the ordered arrangement guarantees that a rapid charge–discharge process can be completed in a very short time, which results in a high specific capacity even with a high charge–discharge current.
—Kim et al. (2008b)
Resources
Hyunjung Kim, Byunghee Han, Jaebum Choo, Jaephil Cho (2008a) Three-Dimensional Porous Silicon Particles for Use in High-Performance Lithium Secondary Batteries. Angew. Chem. Int. Ed. 47, 1 doi: 10.1002/anie.200804355
Hyesun Kim and Jaephil Cho (2008b) Superior Lithium Electroactive Mesoporous Si@Carbon Core-Shell Nanowires for Lithium Battery Anode Material. Nanoletters Vol. 8, No. 11 3688-3691 doi: 10.1021/nl801853x
Extreme mid to long term potential.
This technology could eventually represent about a 10:1 energy density improvement over current lithium batteries.
It's almost too good to believe what a 1000 Wh/Kg battery pack could do to future PHEV and BEV performance. Even a 500 Wh/Kg pack would give a huge boost to e-vehicles development.
It will be interesting to see what other technologies will appear in the next 5 to 7 years.
Posted by: HarveyD | 20 November 2008 at 09:28 AM
Sounds like technology out of a Firefly lead-acid battery
Posted by: mo | 20 November 2008 at 10:19 AM
LiSi: 1000Wh/kg utilized at 90% TTW efficiency
compared to
Gasoline :12,800Wh/kg utilized at 30% TTW efficiency
The LiSi is still only ~1/3 as dense but then you have to consider the phenomenal power and torque densities of electric motors.
Posted by: GreenPlease | 20 November 2008 at 10:29 AM
"This technology could eventually represent about a 10:1 energy density improvement over current lithium batteries."
Only if you ignore the cathode.
Posted by: | 20 November 2008 at 10:59 AM
greenplease:
I agree with you. Only about 12.6% to 15.6% of the gasoline energy is delivered to the wheels vs about 85% to 95% with high efficiency e-motors.
Batteries and super-caps may never reach the energy density of liquid fuel but e-motors will be much cheper to build, are much lighter, more efficient, require less maintenance and will last much longer than ICE + less GHG etc.
Posted by: HarveyD | 20 November 2008 at 11:11 AM
It appears that the next geenration battery chemsitry will not have to deaprt from Li-Ion. so the investments in technology fro thea tcjemsitry will not be wasted.
It si encouraging to see the progress toward the Electrificationof Ground Trsnport continue to develop.
The era of petroleum price shakedowns and dependence on unreliable Mid-East regimes is finally after 35 years, drawing to a close.
It's not here yet, but a decade from now, the last obstacles to a rich developed lifestyle for all humanity will be assured. The future certainly looks bright.
Posted by: stas peterson | 20 November 2008 at 12:46 PM
quote :
"LiSi: 1000Wh/kg utilized at 90% TTW efficiency
compared to
Gasoline :12,800Wh/kg utilized at 30% TTW efficiency"
So multiplying this out you get 900 Wh/kg versus about 3,800 Wh/kg (done in my head). But then also factor in that you no longer need an ICE in your car, and can instead use that space / weight for batteries, and the comparison gets even better. Maybe you're up to 1/2, which is getting pretty d**n close!
Posted by: Mark_BC | 20 November 2008 at 03:56 PM
Well, it's not like we haven't seen better results for cathodes reported here too. A quick search yielded:
http://www.greencarcongress.com/2008/03/argonne-license.html
^^
Lithiated Nickle/Manganese/Cobalt Oxide @ 250-ish mAh/g
It's better than what we're using now...
Posted by: rob | 20 November 2008 at 05:17 PM
One thing to consider, assuming the cathodes can be made cheaply, is swapping the cathodes out after ~100 cycles while leaving the anode in place. The Si could simply be recycled.
Posted by: GreenPlease | 20 November 2008 at 06:30 PM
Forget about any swapping scheme. It is unworkable and impractical.
If you consider the weight of the transmission, radiator, coolants, pumps, transfer case, axle and differential, catalytic convertor, carb, alt, oil system, etc., I bet the specific energy density of a Si-Li battery will exceed that of an equivalent ICE system. - to the point that it could be used in aircraft, where weight is a lot more critical than for a vehicle.
Saudis extract oil at $3 and sell at $55. This is a disgusting %1733 profit margin. Compare that to a 15% profit margin to an honest business practice in a competitive market.
The lefties who claim that we are exploiting the M.E. and colonizing it and stealing oil are a bunch of douchebag ignorants who failed Economics in school. Obviously its the oil producing monopolies that are milking us dry.
Posted by: Mohsen | 20 November 2008 at 07:41 PM
One thing to consider though:
Yes this is a great announcement, but what no one in these comments has considered yet is charging times. It takes the volt ~3 hours to charge at 240 volts, simply because of the current limits of the circuit. How long would it take to charge a full battery capable of going the distances current gasoline cars go without ruining the battery chemistry by overheating, assuming you have an electrical system capable of providing said energy.
This is one area ultracapacitors still have an edge on, but I still have yet to see anything concrete from the major players in the ultracapacitor market.
Posted by: George Furey | 20 November 2008 at 11:09 PM
George Fureu
There are limits for fast charging. Currently there are developed chargers 250 kW. This would charge 35 kWh within 10 min. This amount of energy would allow travelling from 280 km to 800 km depending on speed, car size and auxiliaries in use.
Posted by: | 21 November 2008 at 12:57 AM
I think the point George is making is about charging at home. Most homes can't support more than 80 amps at 240v without doing a serious wiring upgrade of the entire house. A friend of mine got a quote for doing an electrical upgrade of his home and was quoted several thousand dollars to trench from his circuit breaker to the street to lay a new mainline and a whole bunch more money to put in a larger capacity circuit breaker and wiring.
You generally don't want to load a home circuit at more than 80%, so 240v * 60 amps = 14.4 kw. That's PLENTY for an average EV, but it still means that full charges for high capacity EV's are measured in hours, not minutes. For charging on the road, you'd need a heavy-duty commercial charging station with the capability for very high voltage, like 2000 volts at 200 amps or so. That would give 400 kw charging, so a 100kw/h battery could be recharged in 15-20 minutes depending on thermal control and how depleted it was.
Posted by: Sid Hoffman | 21 November 2008 at 09:24 AM
quote:
"Most homes can't support more than 80 amps at 240v without doing a serious wiring upgrade of the entire house."
Yes but at home, almost by definition, you will have a few hours to charge your car. When you need a fast charge is when you're out on the road, in which case you go to a fast charge station.
quote:
"The lefties who claim that we are exploiting the M.E. and colonizing it and stealing oil are a bunch of douchebag ignorants who failed Economics in school. Obviously its the oil producing monopolies that are milking us dry."
I think it is a combination of oil producing monopolies and western oil corporations, who are milking us all dry. Corruption, inefficiency, and waste presents itself at both ends of the political spectrum.
Posted by: Mark_BC | 21 November 2008 at 03:14 PM
Sid, there's no reason (aside from cost) that your charger couldn't accumulate 30 or 40kWh in it's own batteries and then quickly dump that into the car when you connect it. It'd be expensive, but you could also earn some back by offering dispatch service to the grid 24/7.
Granted, once you charged the car you couldn't quick-charge it again from the same charger for several hours.
Posted by: rob | 21 November 2008 at 06:50 PM
@Rob:
Nor would you need to.
Posted by: gr | 22 November 2008 at 12:47 AM
stas:
Your point is well taken.
With the required efforts, USA could rid itself from imported oil, within a few years.
Transport vehicles and HVAC electrification + non-food agro-fuel production is the way to do it.
USA could do both quickly.
Posted by: HarveyD | 22 November 2008 at 03:37 PM
Sid:
Fully electric homes in our area (90 + %) are already equipped with 200 Amps (small houses) or 400 Amps (larger houses) main distribution panel.
That much power is required for electric heating during very cold days. However, since programmable e-thermostats lower the heat required at night (i.e. from 22h-23h to 06h) there is plenty of power freed for e-car night charging without upgrading the electrical system.
A simple programmable ($40) 4000 watt e-thermostat can be used to activate the e-car battery charger exactly when required.
Posted by: HarveyD | 23 November 2008 at 10:02 AM
Anno:
....only if you ignore the cathode.....
Please read what Prof. Jaephil Cho and his team at the Hanyang University of South Korea has done with cathode (8x) efficiency.
Improvements in Anode, Cathode and Separator will lead to much higher energy density batteries within 3 to 5 years.
Practical affordable PHEVs and specially BEVs will be possible when those improved batteries are mass produced.
Nissan may be on the right track with BEVs instead of PHEVs for 2012/13+.
Posted by: HarveyD | 24 November 2008 at 10:52 AM
rates of charge and discharge have to be considered,
how much power can go in/come out for how long, self discharge, Si tends to shatter at high C/D rates, ie, pulverize, turn into powder, albeit its energy density is the highest known, and a lot of other things need to be known before claims can be made, then comes manufacturing, engineering, costs and so on...be careful, so far technology has done nothing but destroy the planet, fast, very fast
Posted by: rose | 12 December 2008 at 01:31 PM