Developing better batteries


The scientists' research paper, published on the online edition of The Journal of the American Chemical Society, showed how lithium-ion batteries with anodes built with what the research team calls PEFM can store 30% more power than those made with the more common aggregated carbon particles. Previous research from the team had produced PFM, the predecessor of PEFM. The Berkeley Lab scientists' work follows similar developments launched at the 26th EU PVSEC in Hamburg in 2011.

Gao Liu, who was a co-lead author of the paper, said, "In addition to developing this binder, we developed a method to engineer and test ways to improve it. We are continuing to use those tools, and now we are approaching an ideal design."

In their paper, Liu and Wanli Yang explained how they and their team modified the original binder to increase its capacity to transport positively-charged lithium ions. The performance limits of the original polymer binder had been determined by its less-than-ideal transport of lithium ions.

During a charging cycle, lithium ions are transported within the binder to the embedded silicon particles through electrolyte uptake, which consists mainly of organic solvents filled with lithium ions in solution. As a result of the improved ion flow, the specific capacity of the silicon anode made with the new binder rose from 2,100 mAh/g to 3,750 mAh/g.

"It means we are using 100% of the silicon particles embedded in the conducting polymer binder," said Liu. "That makes it pretty close to the ‘ideal' binder."

Liu said his team will continue to fine-tune its conducting polymer binders. The next goal is to find materials that offer comparable performance at lower cost. Significant testing will determine whether batteries made with the new silicon composite anodes are as durable as those made with graphite.

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The team’s work was funded by the Office of Vehicle Technologies of the U.S. Department of Energy, under the Batteries for Advanced Transportation Technologies (BATT) program, and by a University of California Discovery Grant.

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