| Title | Scientists Explore Paths to Better Batteries | |
| Date | Monday March 02 2015, @02:34AM | |
| Author | janrinok | |
| Topic | ||
| from the this-story-brought-to-you-by-Torchy-the-battery-boy dept. | ||
Battery technology advances seem to come every other month, all of them seem to be the proverbial 5 years away. But by and large, these developments are simply nibbling around the edges of current battery technology, making minor improvements.
ArsTechnica reports that at the recent meeting of the American Association for the Advancement of Science, scientists explain that what is needed to make battery technology suitable for use in motor vehicles and grid storage is to triple capacity, AND cut price by nearly 70%. This would require raising the energy density of batteries from its present 200 W-hr/kg to about 600 W-hr/kg.
The way forward is to step out side the familiar battery chemistry we've been working with.
Electrodes play a key role in batteries in that they're where charge carriers—lithium in today's batteries—are held. Their ability to store lithium therefore becomes a key determinant of the storage density of a battery. Right now, carbon electrodes require six atoms of carbon for each lithium atom stored. Elements further down that column in the periodic table, like silicon and germanium, however, have a more complicated electronic structure, which can interact with more lithium atoms. As a result, you can store 4.4 lithium atoms for each silicon atom—a significant boost in capacity.
The article goes on to explain the issues with silicon. Lithium atoms cause silicon to expand, damaging the battery. Using, amorphous silicon beads and a polymer they've achieved 360 W-hr/kg version working in the lab. Still far short of the goal.
Jumping beyond silicon, the scientists explored Lithium-sulfur batteries, which have a theoretical capacity of 2,500 W-hr/kg. This would be an ideal material for electrodes, because it is cheap and plentiful. The article explains the struggle to get sulfur to remain where its needed. It has a nasty habit of forming polysulfides that can leak away from the electrode and undergo reactions elsewhere in the battery. A couple of different approaches to solving the wandering sulfur problem appear to be promising, yielding batteries in the lab that exhibit charge-discharge cycle counts comparable with today's lithium technology.
Are they ready for market yet? Of course not. In fact the researchers aren't even sure these chemistries are the right approach. Costs of production may still be too high. But the results are good enough to demonstrate that the major jumps in battery energy density are possible, and we may be able to blow right by the the goal of tripling energy density.
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