Degradable battery ditches the metals

The lithium-ion batteries that power small electronics are rarely recycled. These materials also use significant amounts of cobalt, which is in short supply and sometimes mined using unethical practices. Jodie Lutkenhaus, Karen Wooley, and coworkers at Texas A&M University have now built a battery that avoids these problems. Their metal-free battery uses an organic polypeptide backbone for its electrodes, which the scientists can degrade with acid into amino acids for potential reuse (Nature 2021, DOI: 10.1038/s41586-021-03399-1).

The design is a step toward a circular battery life cycle, in which batteries could be degraded and rebuilt without entering the waste stream. This offers an improvement over batteries made from nondegradable organic polymers, another approach for eliminating metals from batteries. These organic polymer batteries would likely have the same fate as other plastics, Wooley says. “More than 90% of the plastics that could be recycled are not.”

To make a battery that could reliably store charge without metals, the scientists had to completely rethink the chemistry, Lutkenhaus says. The team started with l-glutamic acid polypeptide chains. They attached 2,2,6,6-tetramethyl-4-piperidine-1-oxyl (biTEMPO) to make the cathode and 4,4′-bipyridine derivatives (viologen) to make the anode. A radical-based mechanism shuttled electrons between the two. The degradable battery performed about one-third as well as a Li-ion battery but about as well as other organic polymer batteries.

To test the battery’s degradation, the team added hydrochloric acid and used mass spectrometry to watch the compound fall apart into l-glutamic acid, n-hexylamine, and other hydrolysis products. Even if these batteries don’t make it to a recycling center, Wooley says, they would still break down naturally in the environment into these compounds.

The authors’ design of a polypeptide organic battery that can degrade to its raw materials fills a need for biodegradable pathways, chemistry that’s lacking in current technologies, says Natia Frank, an organic materials chemist at the University of Nevada, Reno.