The key to a long-lasting, more powerful lithium-ion battery might be the inclusion of a small amount of silicon.

Researchers at Rice University and Lockheed Martin have found that Swiss cheese-like silicon "sponges" can store more than four times their weight in lithium, ten times the amount that can be absorbed by graphite.

They have devised a way to craft multiple high-performance anodes from a single silicon wafer. They can get at least four thin-film silicone anodes from a standard 250-micron-thick wafer.

A normal lithium-ion battery expands and contracts with each charge-discharge cycle. This causes the battery material to degrade and over time it loses its ability to store energy. Because silicon expands as it absorbs lithium ions, the sponge-like configuration gives it room to grow internally without degrading the battery's performance.

Assistant professor of chemical and biomolecular engineering Sibani Lisa Biswal, research scientist Madhuri Thakur and professor of chemical and biomolecular engineering, Michael Wong and Lockheed Martin Fellow Steven Sinsabaugh first worked with the silicon sponges in 2010.

The silicon sponges had pores a micron wide and 12 microns deep and they discovered that the electrochemical etching process used to create the pores can also separate the sponge from the main wafer which can then be reused to make more.

The team also found a way to make the pores 50 microns deep. Once lifted from the wafer, the songes, now open at the top and bottom, were enhanced for conductivity by soaking in a conductive polymer binder known as pyrolyzed polyacrylonitrile.

The result was a tough film that could be attached to a current collector and placed in a battery configuration.

The teams working lithium-ion battery created this way has a discharge capacity of 1,260 milliamp-hours per gram, a capability that should lead to batteries that last longer between charges. The best recorded by the researchers was 20 cycles.

They are continuing their work to increase the number of charge and discharge cycles that they can get using this material. The work was supported by the Lockheed Martin Advanced Nanotechnology Center of Excellence at Rice. – EcoSeed Staff