Building Better Batteries

Plug-in hybrid electric vehicles and pure electric vehicles are better for the planet. They generate less pollution and less greenhouse gas emissions. So why don't we see more of them on the roads? Blame the battery. The lithium-ion versions currently used simply don't have the capacity that drivers want. A Nissan Leaf, for example, can travel only 100 miles on a single charge. At UW, Canada Research Chair Linda Nazar is turning her attention to lithium-sulfur (Li-S) and lithium-oxygen (Li-O2) batteries. Because of their energy density, they have the potential to achieve a far higher energy density than their lithium-ion counterparts. In Li-S batteries, the electrons and lithium are stored at the positive electrode by reacting them with sulfur to form lithium sulfide (Li2S). The process is reversible, so directing the flow of electrons the other way regenerates the sulfur, creating a rechargeable cell. Li-O2 batteries rely on similar chemistry, except that storage is in the form of Li2O2. Although Li-S cells are further along in development, there are two main hurdles to commercialization. One is keeping the sulfur - or the discharge product, Li2S - in intimate contact with a conductive material in the cathode. The other is preventing the soluble polysulfide intermediates from getting "lost" into the electrolyte, thus reducing the capacity of the batteries with each cycle.

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