In a scientific breakthrough that would be the envy of George Washington Carver himself, scientists may have come up with the most ingenious use of the peanut yet. But these are not the popular legume that Carver fashioned into foods, dyes and cosmetics—they are packing peanuts. A team of chemical engineers at Purdue University has now developed a fascinating way of reusing packing peanuts for the manufacture of carbon anodes, a component of rechargeable batteries that outperform competitive batteries in the market.
Packing peanuts have proven to be incredibly helpful in ensuring the safe arrival of bulky parcels with negligible added weight. However, they are a devil to dispose of. Because they take up so much space and are expensive to transport, many curbside recycling services no longer accept peanuts. As a result, only a fraction of packing peanuts are properly recycled.
The remaining majority gets dumped in landfills where they can pose a significant environmental threat. In addition to taking multiple generations to decompose, polystyrene (Styrofoam being the common brand) based peanuts contain chemicals that are believed to be carcinogenic. In response to criticism of these harmful environmental effects, manufacturers introduced non-toxic starch based, biodegradable peanuts. Yet, the researchers at Purdue claim that this “green” alternative may also contain potentially hazardous chemicals that are used to “puff up” these peanuts.
Vilas Pol, an associate professor at Purdue’s School of Chemical Engineering and lead author of the study, says his inspiration for the project came while ordering materials for his new experimental battery research lab. “We were getting a lot of equipment and chemicals contained in many boxes all full of packing peanuts, and at some point I realized that all these peanuts were going to waste,” says Pol. “We wanted to do something that was good for society and the environment.”
Lithium-ion batteries primarily consist of a positive electrode (cathode) made of a lithium-based substance, a negative electrode (anode) made of carbon, a polymeric membrane separating them and an electrolyte fluid substance that can carry charge through the membrane. When the battery charges, positive lithium ions move from the positive cathode to the negative anode and are stored on the carbon. Conversely, when the battery is in use, the lithium ions flow in the opposite direction, generating electricity.
After an initial analysis revealed that the primary components of packing peanuts are carbon, hydrogen and oxygen, the team sought to develop a process that could utilize the carbon to create an anode for a lithium ion battery. By heating the peanuts under specific conditions, the team was able to isolate the carbon, taking special care to dispose of the oxygen and hydrogen through the formation of water vapor, so as not to create a by-product that was hazardous to the environment. The team then applied additional heat to the remaining carbon, molding it into very thin sheets capable of serving as an anode for their battery.
Surprisingly, the new “upcycled” battery vastly exceeded the scientists’ expectations—storing more overall charge, by about 15 percent, and charging faster than other comparable lithium-ion batteries. It turns out that the team’s unique manufacturing process inadvertently altered the structure of the carbon to their advantage. Further investigation revealed that when water was released from the starch, it produced small pores and cavities—increasing the overall surface area capable of holding the lithium charge. Pol and his colleagues also discovered that their process increased the spacing between the carbon atoms—facilitating a faster charge by allowing the lithium ions more efficient access to each carbon atom. “It’s like you have a bigger door for lithium to travel through,” says Pol. “And this bigger space motivates lithium to move faster.”
In addition to the inherent positive environmental impact of reusing peanuts that would otherwise crowd landfills, the isolation of pure carbon from the peanuts requires minimal energy (only 1,100 degrees Fahrenheit). By contrast, the temperature required to produce conventional carbon used for battery anodes is between 3,600 degrees and 4,500 degrees Fahrenheit and takes several days, states Pol.
The researchers have applied for a patent for their new technology, in hopes of bringing it to market in the next two years, and plan to investigate other uses for the carbon, as well. “This is a very scalable process,” says Pol. And “these batteries are only one of the applications. Carbon is everywhere.