After Gutenberg

This blog has tracked Silicon nano-structured battery anodes development, e.g.,

• 3D Porous Silicon
• Carbon-Silicon Core-Shell Nanowires
• Optimized, Nano-structured Silicon Anode
• A Better Binder by Battelle

When researchers from Stanford University and Hanyang University in Ansan, South-Korea, in collaboration with LG Chem (makers of the Chevy Volt battery), replaced conventional graphite electrodes in lithium-ion batteries with silicon nanotube electrodes, Ottawa, Canada Treehugger Michael Graham Richard deemed it a breakthrough battery technology.

He now reports on a team of Rice University and Lockheed Martin scientists. Silicon nanotubes, not the more common carbon nanotubes, can store 10 times more charge. The problem with silicon is that “after a couple of cycles of swelling and shrinking, it’s going to crack. Whereas other labs have tried to solve the problem with carpets of silicon nanowires that absorb lithium like a mop soaks up water,” the Rice team took a different tack: silicon nanopores.

Photo: Biswal Lab/Rice University

“The straightforward process makes it highly adaptable for manufacturing,” says Sibani Lisa Biswal, assistant professor in the Department of Chemical and Biomolecular Engineering at Rice University. “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.

The Rice team is Mahduri Thakur, a post-doctoral researcher in Rice’s Chemical and Biomolecular Engineering Department; Mark Isaacson of Lockheed Martin; Biswal, Wong and Sinsabaugh.

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

The Rice team also say that their approach increases the lifetime of the batteries, even when compared to nanowire anodes.

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.”