Packing peanuts for lithium batteries

US researchers have found a new use for the polystyrene and starch-based beads - so-called packing peanuts - used to package delicate goods in various boxes. They have found a way to convert this waste material into high-performance carbon electrodes for rechargeable lithium-ion batteries that work better - charging faster and with higher "specific capacity" than standard graphite electrodes.

Vilas Pol and his team at Purdue University reported to the Denver meeting of the American Chemical Society how they can fabricate carbon-nanoparticle and microsheet anodes from these waste materials Recycling expanded polystyrene, Styrofoam, at plastics processing plants is not cost effective in terms of transportation and other factors, such as its low density, so re-use is a much eco-friendly alternative to simply sending the waste to landfill. Even starch-based packing peanuts represent a problem because they usually contain additives.

The new processing method involves "simply" heating the packing peanuts to a temperature between 500 and 900 degrees Celsius in a furnace under an inert atmosphere with or without a transition metal salt catalyst. It avoids the need for pressurization, making it scalable and relatively inexpensive. The product of this treatment can then be shaped into an anode.

"The process is inexpensive, environmentally benign and potentially practical for large-scale manufacturing," says Etacheri. "Microscopic and spectroscopic analyses proved the microstructures and morphologies responsible for superior electrochemical performances are preserved after many charge-discharge cycles." Moreover, given that the particles comprising the anode are a tenth the size of those in conventional anodes, the lithiation process that takes place during charging is faster because the distances the lithium ions need to diffuse under an electric current are so much shorter. Additionally, these thin, porous materials provided better contact with the liquid electrolyte in the battery.

The team reports that their electrodes show much higher lithium-ion storage performance compared to commercially available graphite anodes. The researchers demonstrated a maximum specific capacity of 420 milliamp hours per gram (mAh/g) as opposed to the theoretical capacity of graphite (372 mAh/g).

"Long-term electrochemical performances of these carbon electrodes are very stable," Etacheri says. "We cycled it 300 times without significant capacity loss. These carbonaceous electrodes are also promising for rechargeable sodium-ion batteries." He suggests that the next step will be to improve performance still further by activation to increase the surface area and pore size.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".