Silicon Nanopores Breakthrough Could Boost Lithium-Ion Battery Anode Capacity by 10x

Photo: Jeff Fitlow/Rice University
Nanotubes, Nanopores... The Future's Happening on a Small Scale
Last year, I wrote about a battery tech breakthrough by researchers at Stanford and Hanyang University in Ansan, South-Korea. By using silicon nanotubes, they boosted the capacity of a lithium-ion battery's anode by a factor of about 10. Building on that work, a team of Rice University and Lockheed Martin scientists has done something that similar, but they instead used silicon nanopores. Their solution could actually be easier to implement and more robust, potentially changing the portable electronics and electric vehicle landscape! Read on for more details.
Photo: Biswal Lab/Rice University

"The anode, or negative, side of today's batteries is made of graphite, which works. It's everywhere," Wong said. "But it's maxed out. You can't stuff any more lithium into graphite than we already have."

Silicon has the highest theoretical capacity of any material for storing lithium, but there's a serious drawback to its use. "It can sop up a lot of lithium, about 10 times more than carbon, which seems fantastic," Wong said. "But after a couple of cycles of swelling and shrinking, it's going to crack."

Other labs have tried to solve the problem with carpets of silicon nanowires that absorb lithium like a mop soaks up water, but the Rice team took a different tack.

They found that adding micron-sized pores ("nanopores") to the surface of a silicon wafer gives the material sufficient room to expand. While common lithium-ion batteries hold about "300 milliamp hours per gram of carbon-based anode material, they determined the treated silicon could theoretically store more than 10 times that amount."

Quite a big step forward if it can be commercialized. Even without improvements on the same scale in the cathode, it would increase the total capacity of lithium-ion batteries significantly.

Photo: Biswal Lab/Rice University

Nanopores are simpler to create than silicon nanowires, Biswal said. The pores, a micron wide and from 10 to 50 microns long, form when positive and negative charge is applied to the sides of a silicon wafer, which is then bathed in a hydrofluoric solvent. "The hydrogen and fluoride atoms separate," she said. "The fluorine attacks one side of the silicon, forming the pores. They form vertically because of the positive and negative bias."

The straightforward process makes it highly adaptable for manufacturing, she said. "We don't require some of the difficult processing steps they do -- the high vacuums and having to wash the nanotubes. Bulk etching is much simpler to process.

This also increases the lifetime of the batteries compared to nanowire ones, which is also important for portable electronics and electric vehicles (you can extend the life of batteries by managing their cycles in clever ways, but it's always better to have a long-lived battery to start with).

Via EurekAlert, Futurepundit
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Tags: Electric Cars | Electric Vehicles


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