Researchers produce silicon 'sponge' battery components

17 July 2012

The team from Rice University in Texas and defence company Lockheed Martin believes porous silicon could replace graphite anodes in rechargeable lithium-ion batteries because it expands as it soaks up the ions and so can absorb up to 10 times more of them.

The researchers found that the electrochemical etching process used to create the pores in the silicon can also separate the sponge from the substrate on which it is grown, further increasing the amount of lithium it can store and allowing the substrate to be reused.

At least four films of silicon can be drawn from a standard 250-micron-thick wafer, according to the team led by Rice research associate Madhuri Thakur and assistant professor of chemical and biomolecular engineering Sibani Lisa Biswal.

The researchers also found a way to make the silicon pores 50 microns deep — up from the 12 microns achieved by a previous Rice/Lockheed project.

After being lifted from the wafer, the sponges were then enhanced for conductivity by soaking them in a conductive polymer binder, pyrolysed polyacrylonitrile (PAN).

This produced a tough film that could be attached to a current collector made from a thin layer of titanium on copper and placed in a battery configuration to create a device with a discharge capacity of 1,260 milliamp-hours per gram. The team said this should lead to batteries that last longer between charges.

The research was supported by the Lockheed Martin Advanced Nanotechnology Center of Excellence at Rice University and was published in the journal Chemistry of Materials.