N-Methylpryrrolidone (NMP) is of the most commonly used solvents in battery production, however its health risks have led to increasingly restrictive policies regarding its use. Due to these risks and regulations, it is clear that battery makers will have to start searching for other options. Not only is NMP a danger to manufacturing plant workers, it also largely contributes to the carbon footprint of lithium-ion batteries. Until now, there have not been viable alternatives to NMP because of the need to dissolve fluorinated polymers in the electrode slurry.
As of 2020, NMP is already regulated in the EU with exposure thresholds in place and it is currently on the REACH restricted substances list. Substances added to this list are reviewed by the European Chemical Agency (ECHA) and are determined to have an unacceptable risk to human health or the environment. Also, in 2020 the U.S. Environmental Protection Agency, (EPA) conducted a risk evaluation for NMP which determined it poses a significant health threat and is a proven developmental toxicant with human exposure. More recently in December of 2022 the EPA announced their plans to propose a rule to regulate NMP so that it no longer presents an unreasonable risk of health.
NMP is a member of the nitrogen heterocyclic compound family. It has been used in battery production for years in order to break down the fluorinated binders used in conventional manufacturing. Other benefits include low volatility and good stability.
Safety concerns have been known for many years with respect to NMP. First and foremost, it’s an irritant to exposed areas and is linked to a number of serious health issues.
Not only is NMP a hazard to factory workers, but it is also a main driver in energy consumption in battery manufacturing and therefore CO2 emissions. NMP makes the drying stage of the electrode coating process significantly more energy intensive. This is because the solvent’s low vapor pressure and high boiling point make it difficult to dry.
Neocarbonix at the Core technology replaces NMP with other solvents like water or alcohols and is estimated to reduce drying energy consumption by 75% and total cell manufacturing energy consumption by 25%. That is roughly 500MM Tonnes CO2 per year per gigafactory. By designing with Neocarbonix, battery makers can instantly comply with NMP restrictions and prepare for upcoming CO2 thresholds in the EU.
In short, NMP is hazardous for humans and is a main driver in the CO2 footprint of battery manufacturing. Limiting NMP use is necessary to comply with upcoming policies and to protect battery makers' health and our planet.