Researcher(s)
- Daniel Chaykin, Chemistry, SUNY Stony Brook University
Faculty Mentor(s)
- Koffi Pierre Yao, Mechanical Engineering, University of Delaware
Abstract
Li-ion batteries are a prevalent form of energy storage in modern technology but involve manufacturing methods that are receiving increasing scrutiny. In particular, Li-ion battery electrodes are commonly prepared using the solvent N-methyl-2-pyrrolidone (NMP) which increases costs through its drying process and is toxic in nature. Therefore, it is necessary to investigate alternative solvents to NMP which are safer and less expensive without sacrificing its electrochemical performance. This study investigates four potential candidates to replace NMP based on having similar Hansen Solubility parameters: cyrene, cyrene blended with 2-methyltetrahydrofuran (2-MeTHF), cyrene blended with γ-valerolactone (GVL), and dimethyl isosorbide (DMI). Each solvent is evaluated based on its ability to dissolve the main binding agent used in cathode processing, polyvinylidene fluoride (PVDF), and electrochemical performance compared to NMP. Using optical microscopy, all four solvent candidates were found to be capable of dissolving PVDF at room temperature which is in-line with NMP. Furthermore, each solvent could form a coating slurry using LiNi0.6Mn0.2Co0.2O2 (NMC 622) cathode material with DMI being the most comparable to NMP. However, scanning electron microscopy (SEM) images of the coated electrodes demonstrate thin film crack formation for all the alternative solvents. In addition, coin cells were prepared using each of the five solvents and then studied using electrochemical impedance spectroscopy (EIS) and galvanostatic cycling. The three variations of cyrene exhibited less favorable performance than the standard of NMP, such as an initial specific capacity range between 122-148 mAh/g compared to the NMP reading of 179 mAh/g at a C/3 current rate. Conversely, cells assembled using DMI failed to surpass one cycle of usage. Overall, we find that cyrene and its two blends can be used in Li-ion cathode fabrication but need further investigation to improve electrochemical performance, while DMI requires a solution that resolves its struggle in electronic applications.