γ-Valerolactone: An Alternative Solvent for Manufacturing of Lithium-Ion Battery Electrodes

Currently, cathode manufacturing for lithium-ion batteries requires N-methyl-2-pyrrolidone (NMP) as a coating solvent. With concerns over its petrochemical origins and increasing scrutiny due to its undesirable toxicological profile, there is market demand for application-specific, less-regulated alternatives. Here, we evaluate y-valerolactone (GVL), a promising green-candidate based on its closeness to NMP in the Hansen Solubility Space. It has successfully dissolved polyvinylidene fluoride (PVDF) at a temperature of 60 degrees C. We also show that the handling of lithium nickel cobalt manganese oxide (NCM I I I) coating slurry prepared using GVL at 60 degrees C is comparable to NMP-based slurry at 25 degrees C. Cathode sheets (with dry mass loadings: 18 and 25 mg/cm(2)) were manufactured by blade coating and drying (gas temperatures: 80 and 120 degrees C) in a custom-built batch coater with a convective drying unit. Adhesion and cell tests were performed to compare the resulting sheets. NMP-based films generally have higher adhesion strength than their GVL counterpart. We also report comparable resistance and columbic efficiency (after 1 cycle) for all cathodes, with slightly higher resistance for GVL dried harshly (i.e., 120 degrees C). Also, thinner NMP-based cathodes had better specific capacity during cycling than their GVL counterparts, irrespective of the drying temperature. However, thicker cathodes dried under higher throughput conditions (temperature of 120 degrees C) have comparable specific capacity after 100 cycles. Through this study, we highlight that GVL is a promising candidate currently available that merits further investigation.

Automated summary

The study evaluates GVL as a potential alternative to NMP for cathode manufacturing in lithium-ion batteries, showing its promise as a sustainable green candidate. Although GVL exhibits lower adhesion strength compared to NMP, it performs similarly in terms of resistance, coulombic efficiency, and specific capacity, highlighting its potential as a substitute.