PNNL Researchers Developing High-Capacity Silicon Anode Material Using Micrometer-sized Particles with Nanopore Structure; 1600 mAh/g After 40 Cycles
12 October 2010
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| transmission electron microscopic (TEM) images of silicon anode morphologies: a) original porous silicon and b) porous silicon coated with nano layer of carbon. Source: PNNL. Click to enlarge. |
Scientists at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a silicon-based anode material for Li-ion batteries using micrometer-sized silicon particles with a nanopore structure. The material shows reversible capacity of more than 1,600 mAh/g after 40 charging/discharging cycles.
With a theoretical capacity some 10 times that of graphite, silicon anodes could contribute to a doubling of the capacity of graphite-anode Li-ion batteries. However, a silicon anode experiences a large volume expansion during lithium-ion insertion and a consequent shrinkage during extraction; this leads to severe particle pulverization, resulting in quick failure of the electrode structure and resulting capacity fade with cycling. Accordingly, a numerous efforts are underway to devise a structure and a material resistant to those changes.
Dr. Jason Zhang and the PNNL research team are addressing that challenge by designing a silicon particle architecture that would maintain structural integrity. The porous structure of the Si helps accommodate the large volume variations that occur during the Li insertion/extraction processes.
Chemical vapor deposition (CVD) of carbon coatings and highly elastic Ketjen Black (KB) carbon were used to improve the electrical conductivity throughout all cycling stages. The team placed these anodes between graphene—planar sheets of bonded carbon atoms—to maintain strong electrical contact between silicon particles.
The combination of the nanopore structure, CVD-coated carbon on the Si surface, and the elastic carbon (KB) among the silicon particles provides a cost-effective approach to utilize the large micrometer-sized Si particles in Li-ion batteries.
—Xiao et al.
The PNNL research team continues to improve the performance and long-term stability of the silicon anodes from 40 to 50 charging/discharging cycles today to a goal of about 500 cycles in the future. One solution may be the development of a better binder that can maintain improved mechanical and electrical contact. This method has potential for much greater cyclability while maintaining high energy density.
Resources
Xiao J, W Xu, D Wang, D Choi, W Wang, X Li, GL Graff, J Liu, and J Zhang (2010) Stabilization of Silicon Anode for Li-Ion Batteries. Journal of The Electrochemical Society, doi: 10.1149/1.3464767
A promising technology and one more positive step towards future improved energy density rechargeable batteries.
Posted by: HarveyD | 12 October 2010 at 07:20 AM
Assuming they are talking the usual ~3.6V from a typical lithium chemistry, that could lead to a BEV with a 350 mile range with batteries weighing only 13.8kg.
That is incredibly energy dense. Of course, you would have to have a matching anode to really get that density but even if it's up around 100kg total for the battery pack then it is incredible.
And they would have to get it closer to that 500 cycle number. If they could, then an 80kWh battery would give you ~175,000 miles...better than most ICE engines are going to last you today.
But at what price? :-)
Great lab work, but it will take time to see what real world stuff comes out the back end.
Posted by: DaveD | 12 October 2010 at 07:59 AM
We've seen this before - another high density anode. It's always good news, but what is needed is a high energy density cathode. The anode typically takes up only 20 % of the mass of the Li-Ion battery. So if you can reduce the anode by 99%, you still have a battery that weighs only 20 % less for the same energy storage.
Posted by: Zhukova | 12 October 2010 at 02:30 PM
Agree with you, Zhukova. But if a 20% mass reduction can be achieved, it is also a tremendous improvement.
On the other side, if the anode capacity can be improve to be 5 times higher that present graphite, the mass load of cathode should be 5 times higher than present level. As to my perspective, it is impossible to make the cathode film by using present technique.
Posted by: Account Deleted | 12 October 2010 at 08:37 PM
This is true. Actually a 20% reduction in mass corresponds to a 25% increase in gravimetric capacity per kilogram. Used for a traction motor in an EV, this results in 25% more range per charge, which is very significant.
If the anode capacity is improved ten times and the fabrication cost is 3 times (for example) over carbon anodes, this could bring down the cost of the battery a little. We still have to keep hoping for a breakthrough in cathode development.
Posted by: Zhukova | 13 October 2010 at 10:02 AM