(Invited) High Throughput Solvent-Free Manufacturing of Battery Electrodes

Abstract

Research into the manufacturing of LIB electrodes is constantly evolving with new active materials, improved binders, and improved drying techniques to more efficiently produce high-quality electrodes. However, the one constant in all these endeavors is that electrode research and manufacture still generally rely on a slurry-coating process, where large amounts of potentially toxic solvents are necessary for slurry production. As such, solvent-free, also known as dry-process (DP), electrode processing has been proposed to solve the conventional lithium-ion battery electrodes fabrication disadvantages, such as high equipment costs for solvent reclamation, currently seen in industry. Currently, the solvent-free, state-of-the-art electrodes use polytetrafluoroethylene (PTFE) as a binder and the PTFE is fibrillized and dispersed in the dry powder mixture using a jet mill. One key solvent-free electrode shortcoming is that PTFE is not electrochemically stable for the anode, traditionally resulting in initial capacity losses of greater than 30% and poor mechanical strength, effectively limiting solvent-free processing to cathodes. A second shortcoming is that solvent-free electrodes generally require the addition of fibrillization promoters or processing steps that add cost and detract from performance by limiting active material content in the final electrodes. In a recent development, Navitas and its internal partners of Cabot, Arkema, the University of Tennessee, Knoxville, and Oak Ridge National Laboratory have shown the capability to produce both solvent-free anodes and cathodes utilizing an advanced dry-electrode process (ADEP) that also enables high-throughput production of next generation battery electrodes. These electrodes have improved mechanical strength, sufficient to withstand roll-to-roll manufacturing, and the anodes demonstrate an initial capacity loss of less than 15%. The group has demonstrated roll-to-roll production of solvent-free electrodes at quasi-industry standard active material compositions (90-92%) without the reliance of previously used fibrillization promoters, even at reduced PTFE concentrations in the formulation. Navitas has recently demonstrated the large format lamination of the initially formed, or “free-standing,” electrodes after they have been produced in roll-to-roll manufacturing and the integration of solvent-free electrodes in dual-layer and multi-layer pouch cells using typical industry tooling and cell production techniques. Key words: solvent-free, dry-process, fibrillization, next generation lithium-ion batteries (NGLB), advanced dry-electrode process (ADEP), initial capacity loss, free-standing, roll-to-roll, pouch cell