Making Super Lithium-Ion Batteries with Silicon NanotubesResearchers from Stanford University and Hanyang University in Ansan, Korea, in collaboration with LG Chem (makers of the Chevy Volt battery), have made a breakthrough that could change the future of electric cars. It's too early to know for sure, but what we know so far is very promising. They have shown that by replacing the conventional graphite electrodes in lithium-ion batteries with silicon nanotube electrodes (silicon nanotubes, not the more common carbon nanotubes), 10 times more charge could be stored. This could not only greatly extend the range of electric cars, but it would also make gasoline-electric hybrids more efficient by allowing them to run in electric mode for longer periods.
Here is the abstract of the Nano Letters paper titled Silicon Nanotube Battery Anodes:
We present Si nanotubes prepared by reductive decomposition of a silicon precursor in an alumina template and etching. These nanotubes show impressive results, which shows very high reversible charge capacity of 3247 mA h/g with Coulombic efficiency of 89%, and also demonstrate superior capacity retention even at 5C rate (=15 A/g). Furthermore, the capacity in a Li-ion full cell consisting of a cathode of LiCoO2 and anode of Si nanotubes demonstrates a 10 times higher capacity than commercially available graphite even after 200 cycles.
Jaephil Cho, the associate professor of applied chemistry at Hanyang University who led the research on nanotube anodes, says that this technology could boost the capacity of a hybrid car's battery between 6 and 8 times.
Technology Review writes: "Silicon anodes have a higher energy-storage capacity than conventional graphite because the material can take up 10 times more lithium by weight than graphitic carbon. In fact, silicon takes up so much lithium--increasing in volume by as many as four times--that it can be a disadvantage. The mechanical strain on the brittle material is so great that silicon anodes tend to crack after they're charged and discharged only a few times. So researchers, including [Jaephil Cho] and Stanford materials scientist Yi Cui, have been developing nanostructured silicon designed to better withstand these stresses. They've made silicon nanowire anodes and nanoporous silicon anodes. Now they've collaborated to develop silicon nanotube anodes, whose storage capacity is better than those of other nanostructured silicon materials, says Cho."
Challenges AheadBefore electric cars (and trucks and buses) can benefit from high-performance lithium-ion batteries with silicon nanotubes anodes, some technical difficulties will need to be addressed.
Among other things, the anodes will need to prove that they can still hold (and release) power after thousands of charges. The silicon nanotube anode has been demonstrated up to around 200 charges, but that's not enough. Another problem will be pairing the high-performance anode with a cathode that can match it, so if the new Si-nanotube anode can store 10x more charge, a cathode that can also store 10x more charge will be required.
Above is the GM Volt battery. Is it possible that GM made a deal with LG Chem because, among other things, they saw preliminary data on this Si-nanotube research? Who knows...
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