Chem. Mater. http://doi.org/bckw (2016)

Nickel manganese cobalt oxide (NMC) is a class of lithium intercalation compound that is widely used as a cathode material in lithium-ion batteries, which power electric cars. A single electric car with a typical 24 kWh battery pack contains >38 kg of nanoscale cathode material and it is estimated that by 2020 there will be 20 million vehicles on the road. These numbers suggest that nanoscale metal oxide could be an emerging environmental contaminant if these batteries are disposed into landfills. Christy Haynes, Robert Hamers and colleagues at the University of Wisconsin, Madison and the University of Minnesota now report that NMC can impair the growth and respiration of a soil and sediment bacterium, Shewanella oneidensis.

The researchers prepared thin sheets of lithium NMC and added different concentrations of the material to cultures of S. oneidensis, which is a gram-negative bacteria known for cycling metals in the environment. At 5 mg l−1 NMC, bacteria growth and respiration were inhibited. Experiments using inductively coupled plasma optical emission spectroscopy and X-ray photoelectron spectroscopy showed that NMC nanoparticles in aqueous medium preferentially released lithium, nickel and cobalt ions into solution, while leaving behind nanoparticles enriched in manganese. When nickel and cobalt ions were introduced to the bacterium culture, similar toxic effects were seen as when they were exposed to NMC nanoparticles, suggesting that toxicity is arising from the released transition metal ions rather than the remaining manganese-enriched nanoparticles. These preliminary results suggest that NMC may be a source of toxic nickel and cobalt ions, and that further efforts are needed to develop effective recycling strategies for these batteries.