Development of continuous coating technology for lithium-ion electrodes

The production of lithium-ion cells is highly amenable to a continuous coating process for both anodes and cathodes with their respective thin metal foil current collectors serving as a web. Yardney Technical Products, Inc. has improved lithium-ion technology by using a prismatic cell design in which both the cathode and the anode are coated on the front and back side. This accomplishment was achieved using an extrusion die coating method that allows the simultaneous coating on each side of the current collector. This results in reduced labor costs, improved electrode uniformity and increased production yields. The outcome is cell integration into battery packs which are easier to charge and balance leading to long battery cycle life. Important process variables have been identified and optimized to obtain slurries of desired rheological characteristics, coat quality, adhesion, coatability, stability, manufacturability and cell performance. Mixing methods using a twin screw continuous mixer, ultrasonification, dry powder blending and ball milling were examined. Slurry formulation variables investigated included evaluation of several types of graphites, carbon blacks and binders. Processes to improve the extrusion die process emphasized the optimization of fluid delivery system dynamics, correct pump selection and establishment of precise delivery/metering flow control parameters. Other coating methods evaluated included knife over plate, knife over roller and slot die. Cells manufactured from extruded cathode materials will be evaluated to establish a database of cell performance information.