Water Determination in NMP by Density

In the process of coating the electrodes for batteries, N-methyl-2-pyrrolidone (NMP) is used as a solvent. Polyvinylidene fluoride (PVDF), the most popular substance used to bond both the anodes and cathodes in the creation of Li, Ni, Mg and Co batteries, is easily dissolved by NMP. When water is present, it reacts with the electrolyte salt to produce aggressive degradation products that limit performance. This makes thorough testing for water in all functional components of a lithium-ion battery essential for quality control. Hence, the importance to assess water content also in NMP.

This application note describes the indirect determination of water content in NMP relying on the relationship between density and water content. The use of density determinations and NMP-water calibration curves obtained with Karl Fischer titration allow determining this important physicochemical parameter.

This method can be used for quality assurance, to speed up quality control, and manufacturing process optimization. The density approach, when applied, offers the following advantages:

• At-line: the instrument can be conveniently placed close to the production. Direct liquid suction from the process is also possible, even in a bypassed form.
• Fast: no sample preparation or dilution is needed. The sample is measured “as it is”. Measurement time is reduced.
• Chemicals-free: no reagents or chemical reactions are involved in the analysis. No additional waste is produced.
• Simple operation: calibration curve calculations are built-in the instrumentation. Tolerance checks deliver automatic pass/fail results. Together with autosample solutions, fully automatic, unattended measurements are carried out.