Monday, April 25, 2016

Nanowires Dramatically Increase Lithium Ion Battery Life

Battery life is of critical concern to car makers and energy storage companies. All of today’s lithium ion batteries degrade over time. The more times they are charged and discharged, the shorter their lifespan. Researchers at the University of California at Irvine (UCI) say they have discovered how to increase the tensile strength of nanowires. That breakthrough could be used to make lithium ion batteries that last virtually forever. Here’s the story.
Nanowire battery
UCI doctoral candidate Mya Le Thai holds a nanowire device. Credit: Steve Zylius/UCI
Researchers have tried using nanowires in batteries for years because the filaments, which are thousands of times thinner than a human hair, are highly conductive and have a large surface area for the storage and transfer of electrons. The problem is that nanowires are also extremely fragile. They don’t hold up well to repeated discharging and recharging, known as “cycling.” For example, in a typical lithium-ion battery, they expand and grow brittle, which leads to cracking.
The researchers, led by doctoral candidate Mya Le Thai, found a way to make nanowires less brittle. They coated a gold nanowire in a manganese dioxide shell and encased it in an electrolyte made of a Plexiglas-like gel called propylene carbonate. Capacitors made with uncoated nanowires have a useful life of between 2000 and 8000 cycles. Those with the coating are able to function through 200,000 cycles.
Reginald Penner, chairman of UCI’s chemistry department, says, “Mya was playing around, and she coated this whole thing with a very thin gel layer and started to cycle it. She discovered that just by using this gel, she could cycle it hundreds of thousands of times without losing any capacity. That was crazy because these things typically die in dramatic fashion after 5,000 or 6,000 or 7,000 cycles at most.”
The researchers believe the gel plasticizes the metal oxide in the battery and gives it flexibility, preventing cracking. Thai, the study’s leader, cycled the nanowire-enhanced electrode up to 200,000 times over three months without detecting any loss of capacity or power and without fracturing any nanowires. “All nanowire capacitors can be extended from 2000 to 8000 cycles to more than 100,000 cycles, simply by replacing a liquid electrolyte with a… gel electrolyte,” the researchers wrote in their paper.
“The coated electrode holds its shape much better, making it a more reliable option,” Thai said in a statement. “This research proves that a nanowire-based battery electrode can have a long lifetime and that we can make these kinds of batteries a reality.” If the research can be translated into viable commercial products, the result could be commercial batteries that last a lifetime in computers, smartphones, appliances, cars and spacecraft.
Source: Computerworld

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