γ‑Valerolactone:\nAn Alternative Solvent\nfor Manufacturing of Lithium-Ion Battery Electrodes

Abstract

Currently, cathode manufacturing\nfor lithium-ion batteries requires <i>N</i>-methyl-2-pyrrolidone\n(NMP) as a coating solvent. With\nconcerns over its petrochemical origins and increasing scrutiny due\nto its undesirable toxicological profile, there is market demand for\napplication-specific, less-regulated alternatives. Here, we evaluate\nγ-valerolactone (GVL), a promising green-candidate based on\nits closeness to NMP in the Hansen Solubility Space. It has successfully\ndissolved polyvinylidene fluoride (PVDF) at a temperature of 60 °C.\nWe also show that the handling of lithium nickel cobalt manganese\noxide (NCM 111) coating slurry prepared using GVL at 60 °C is\ncomparable to NMP-based slurry at 25 °C. Cathode sheets (with\ndry mass loadings: 18 and 25 mg/cm²) were manufactured\nby blade coating and drying (gas temperatures: 80 and 120 °C)\nin a custom-built batch coater with a convective drying unit. Adhesion\nand cell tests were performed to compare the resulting sheets. NMP-based\nfilms generally have higher adhesion strength than their GVL counterpart.\nWe also report comparable resistance and columbic efficiency (after\n1 cycle) for all cathodes, with slightly higher resistance for GVL\ndried harshly (i.e., 120 °C). Also, thinner NMP-based cathodes\nhad better specific capacity during cycling than their GVL counterparts,\nirrespective of the drying temperature. However, thicker cathodes\ndried under higher throughput conditions (temperature of 120 °C)\nhave comparable specific capacity after 100 cycles. Through this study,\nwe highlight that GVL is a promising candidate currently available\nthat merits further investigation.