Porous Silicon Anode Could Triple Battery Capacity

Researchers at the University of Southern California say anodes made of porous silicon nanoparticles could help next-generation lithium-ion batteries recharge in 10 minutes and hold three times the energy of current designs.

Porous silicon isn't new. Until now, however, using it in anodes was tricky because the material could be pulverized by expansion and contraction as lithium ions are inserted and extracted during charging and discharging.

Last year, the research team led by Prof. Chongwu Zhou at USC's Viterbi School of Engineering demonstrated that porous silicon nanowires could handle expansion and contraction without breaking. The material showed a capacity of more than 1,000 milliamp-hours per gram with a current of 4 amps/gram for 2,000 cycles.

But the microscopic wires are difficult to produce. Now the scientists are testing micro-etched silicon spheres they say are cheaper and easier to make in high volume. The spheres coated with boron, then etched with silver nitrate and hydrofluoric acid.

So far the spheres have revealed capacities of 1,400 mA-h/g at a current of 1 A/g and 1,000 mA-h/g at 2 A/g for 200 cycles.

The team published reports on both technologies in recent editions of Nano Letters.