Packaging peanuts make high-performing Li-ion anodes

Batteries have two electrodes, called an anode and a cathode. The anodes in most of today's lithium-ion batteries are made of graphite. Lithium ions are contained in a liquid called an electrolyte, and these ions are stored in the anode during recharging. Now, researchers have shown how to manufacture carbon-nanoparticle and microsheet anodes from polystyrene and starch-based packing peanuts, respectively.

“We were getting a lot of packing peanuts while setting up our new lab,” recalled postdoctoral research associate Vinodkumar Etacheri. “Professor Vilas Pol suggested a pathway to do something useful with these peanuts.”

This simple suggestion led to a potential eco-friendly application for the packaging waste. Research findings indicate that the anodes can charge faster and deliver higher specific capacity compared to commercially available graphite anodes, Pol said.

The findings were presented during the 249th American Chemical Society& National Meeting & Exposition, Denver, 22^nd to 26^th March 2015. The work was performed by Vinodkumar Etacheri and Vilas Pol, alongside undergraduate chemical engineering student Chulgi Nathan Hong.

“Although packing peanuts are used worldwide as a perfect solution for shipping, they are notoriously difficult to break down, and only about 10% are recycled,” Pol said. “Due to their low density, huge containers are required for transportation and shipment to a recycler, which is expensive and does not provide much profit on investment. Consequently, packing peanuts often end up in landfills, where they remain intact for decades. Although the starch-based versions are more environmentally friendly than the polystyrene peanuts, they do contain chemicals and detergents that can contaminate soil and aquatic ecosystems, posing a threat to marine animals.”

The new method “is a very simple, straightforward approach,” Pol continued. “Typically, the peanuts are heated between 500 and 900°C in a furnace under inert atmosphere in the presence or absence of a transition metal salt catalyst.”

The resulting material is then processed into the anodes.

“The process is inexpensive, environmentally benign and potentially practical for large-scale manufacturing,” Etacheri added. “Microscopic and spectroscopic analyses proved the microstructures and morphologies responsible for superior electrochemical performances are preserved after many charge-discharge cycles.”

Commercial anode particles are about 10 times thicker than the new anodes and have higher electrical resistance, which increase charging time. Because the sheets are thin and porous, they allow better contact with the liquid electrolyte in batteries.

“In our case, if we are lithiating this material during the charging of a battery it has to travel only 1μm distance, so you can charge and discharge a battery faster than your commercially available material,” explained Pol. “These electrodes exhibited notably higher lithium-ion storage performance compared to the commercially available graphite anodes.”

Packing-peanut-derived carbon anodes demonstrated a maximum specific capacity of 420mAh/g, which is higher than the theoretical capacity of graphite (372mAh/g), Etacheri said.

“Long-term electrochemical performance of these carbon electrodes are very stable,” he said. “We cycled it 300 times without significant capacity loss. These carbonaceous electrodes are also promising for rechargeable sodium-ion batteries. Future work will include steps to potentially improve performance by further activation to increase the surface area and pore size to improve the electrochemical performance.”

The researchers acknowledge funding from Purdue, the university's School of Chemical Engineering and a Kirk Endowment grant from the Birck Nanotechnology Center. Purdue’s Office of Technology Commercialisation filed a U.S. patent application on the technology in 2014.

Image: "Foam Peanuts" by Gabriel Herrera is licensed under CC BY 2.0.