Alternatives assessment of polyvinylidene fluoride-compatible solvents for N-methyl pyrrolidone substitution in lithium-ion battery cathodes

Abstract

Lithium-ion batteries (LIBs) are central to electrification yet, to increase the efficiency and scalability of electric systems, energy storage technologies must integrate sustainability concepts into their design. Notably, the incumbent LIB technology uses the reprotoxic solvent N-methyl pyrrolidone (NMP) to dissolve polyvinylidene fluoride (PVdF) as a binder. This solvent, of concern to human and ecological health, must be replaced with less toxic alternatives. Accordingly, the objective of this study was to determine which potential solvents, compatible with PVdF binder within the cathode processing of LIBs, could replace NMP. This study followed the U.S. National Research Council’s Framework to Guide Selection of Chemical Alternatives, and thus assembled and compared data concerning ecological and human hazards, performance, and cost. Five solvents were assessed as alternatives to NMP, derived from an analysis of 948 cells of data (708 cells of hazard data, 54 cells of performance data, and 186 cells of cost data). Triethyl phosphate (TEP) and N-N’-dimethylpropyleneurea (DMPU) are found to exhibit reprotoxic properties, and dimethylsulfoxide (DMSO) raised concerns in all three data categories studied. The most promising alternatives to NMP were dihydrolevoglucosenone (Cyrene) and γ-valerolactone (GVL). With demand for sustainable energy storage growing, the results of this study aim to guide research and innovation of LIB technologies while avoiding regrettable substitutions in developing NMP-free LIBs.