Protective carbon nanosphere coating overcomes lithium problems, pointing the way to improved capacity

A team of Stanford University researchers, including former Energy Secretary Steven Chu, believes it has achieved the “holy grail” of lithium battery design: an anode of pure lithium that could boost the range of an electric car to 300 miles.

Lithium-ion batteries are one of the most common types of rechargeable batteries on the market today. But most of the batteries—found in technologies like smartphones and electric cars—use an anode made of graphite or silicon.

The lithium in a lithium-ion battery today is found in the electrolyte. The electrons in the electrolyte flow to the anode during recharging, and if the anode were also made of lithium, the battery would be able to generate much more power and weigh much less.

Until now, however, lithium anodes have been unusable. The material expands during charging, opening fissures on the surface that release lithium ions and form messy, hairlike growths called dendrites that reach out and short-circuit the battery. Lithium anodes are also highly chemically reactive with the lithium electrolyte and can overheat to the point of fire or even explosion.

The potential flammability of lithium-ion batteries has come under scrutiny after three electric cars made by Tesla Motors Inc. crashed and caught fire last year after hitting road debris (Greenwire, Nov. 8, 2013).

The Stanford team thinks it has solved these problems with a protective layer of tiny carbon domes, called nanospheres, that form a flexible honeycomb-styled shield over the anode. The nanosphere wall, just 20 nanometers thick, is strong and flexible enough to move up and down as the anode expands and contracts during the battery’s charge-discharge cycle.



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