Friday, November 27, 2015         


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Lithium looks elemental to our energy revolution

By Richard Brill


Lithium ion batteries are the hottest thing in portable energy.

Their high energy density, as well as their ability to hold a charge and withstand many recharge cycles, have led to their use in many applications where light weight and long life are important.

There is little doubt that some form of lithium battery will power electric cars over the next few decades.

A stream of improvements in energy density, durability, cost and intrinsic safety of the batteries is flowing from intense research under way in both the public and private sectors.

Why lithium?

Lithium is the lightest metal, and the lightest element after hydrogen and helium. It is very reactive and sits atop the electromotive series, a numerical scale of the relative ability of different atoms to hold onto electrons.

Batteries take advantage of this difference with an anode and a cathode made of two different materials that exchange ions and electrons. When the electrons go one way, the battery charges up; when they go the other way, the battery releases its charge.

Charging a battery involves reversing the flow of electrons using a slightly higher voltage than that which the battery produces.

Lithium compounds are especially finicky. Minute differences in the charging voltage and chemistry make a big difference in how lithium ion batteries heat up and otherwise behave during recharge.

Over multiple charge and discharge cycles, microscopic dendrite fibers of lithium form on the carbon anodes of the batteries, causing short circuits, overheating and other problems.

Because they hold so much promise, there are several notable areas of research aimed at producing better lithium batteries.

One research group developed a synthetic molecule that sponges up electrons to keep the battery from charging too quickly.

Another lab developed a stainless-steel anode covered in silicon nanowires to replace the traditional graphite anode.

Silicon can store 10 times more lithium than graphite. This produces a greater energy density on the anode, while the large surface area of the nanowires allows for fast charging and discharging.

A team at MIT made a cathode out of layers of carbon nanotubes to produce a similar effect.

Perhaps the most promising technology is the lithium air battery, which uses oxygen as the cathode and lithium as the anode. There is no material cathode other than a foamy catalyst that extracts oxygen from the air and drastically reduces the weight of the battery.

The lithium air battery can store five to 10 times the energy density of lithium ion batteries, which makes it comparable to the energy density of gasoline.

Because it will be 10 to 20 years before the lithium air battery is in production, research continues briskly on other methods to improve existing lithium ion battery technology as automakers, universities and independent labs examine various chemistries to maximize the efficacy of lithium batteries of all kinds.

The obstacles are formidable, and it will require innovations in materials science, chemistry and engineering to replace our thirst for gasoline with a hunger for lithium.

Think of the implications for geopolitics, economics, resource development and environmental impacts if we craved lithium ores instead of petroleum.

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