Nanotoxicity of Emerging NMC-Family Energy Storage Nanomaterials

Abstract

The increasing use of metal oxide materials has met with equal concern as regards associated health risks and environmental transference. NMC-family (LiNi_xCo_yMn_zO₂, where x+y+z=1) energy storage materials are complex transition metal oxides that are being rapidly deployed as replacements to the conventional lithium-ion batteries (LiBs) in the electric vehicle industry. Sustainable catalysis is another area of increasing study since multi-component oxides have a high propensity for cleaving strong chemicals such as the carbon-fluorine bond. NMC materials are mostly synthesized through different thermomechanical processes, with the final composition depending on the required properties in the derived nanostructures. The biological impact of NMC-type materials has been found to be dependent not just on the overall mass, but also on the mass distribution which could be in the form of micro or nanostructures. This study therefore assesses the toxicity effect of NMC-family nanoscale material for energy storage and catalysis, with a view to determining possible safety levels as regards the composition of constituent materials. Preliminary toxicity studies were conducted on inoculated S. oneidensis, B. subtilis and D. magna substrates exposed to NMC materials for time intervals ranging from 0 to 72h and found a direct relationship between the ease of release of Ni and Co ions and cellular respiration and growth. The chemical transformation of NMC nanomaterials was however found to favor an ion release of the order Li > Ni > Co > Mn, although this is an entirely slow process. Altering the configuration of NMC materials through Mn enrichment was also found to significantly reduce its dissolution and could be an important approach to preventing its release into the environment.