When a new lab was recently being set up at Purdue University in Indiana, a lot of the equipment arrived in boxes full of protective packing "peanuts." Unfortunately, few facilities exist for recycling the little pieces of foam, so they typically end up sitting in (or getting blown around) landfills for several decades. A team of Purdue researchers, however, discovered that they could find use in better-performing lithium-ion batteries.
When a lithium-ion battery is charging, the lithium ions are stored in one of its two electrodes, known as the anode. Ordinarily, anodes are made out of graphite. Led by Prof. Vilas Pol, the Purdue scientists instead set out to create a new type of anode made from carbon.
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They started by heating packing peanuts (which were made from polystyrene or were starch-based) to a temperature of between 500 and 900 ºC (932 to 1,652 ºF). They did so in an inert atmosphere, in either the presence or absence of a transition metal salt catalyst. Depending on the peanut material and the approach taken, the result was either carbon nanoparticles or carbon microsheets. In both cases, they made excellent anodes.
This was partially because they were about one tenth the thickness of graphite anodes, allowing for quicker charging times. Additionally, they exhibited less electrical resistance than graphite. In more precise terms, they demonstrated a maximum specific capacity of 420 mAh/g (milliamp hours per gram), as opposed to the theoretical 372 mAh/g maximum for graphite anodes.
What's more, the carbon anodes stood up to 300 charging cycles without a significant loss in that capacity.
The microsheets were particularly effective, as their porous structure allowed for more contact area between the anode and the battery's ion-carrying liquid electrolyte. That said, the researchers are now working on making them even more porous, to further enhance their electrochemical performance.
According to Purdue, the packing peanut conversion process is inexpensive, environmentally-friendly, and should be practical for large-scale battery production.
Source: Purdue UniversityView gallery - 2 images