- March 26, 2012, Mark Miller
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With the advent of car battery technology moving into the mainstream for consumer vehicles, the need for advanced battery technology has skyrocketed. As with any consumer-based technology, the need to have a competitive edge financially is important. To obtain the competitive edge, battery manufacturing companies are asking process engineers to look throughout the process and find the efficiency improvement areas, and guess where they land—the coating step.
In the multi-tiered process of advanced battery manufacturing, there are many areas to develop improvements. Mixing of the anode and cathode slurries, curing speeds, defect reduction, and calendaring efficiencies can all be improved. However, nowhere in the battery-making process can the slurry meet the substrate with more effectiveness than the coating head. The most utilized equipment for coating the anode and cathode slurries is a slot die.
While a fixed geometry slot die head can be used, with the current state of battery slurry chemistry, there are some advantages to using flexible slot die geometry. Namely, having the ability to adjust for viscosity differences in the battery slurry throughout a coating production run is very important.
So what can a battery manufacturer do to improve efficiency? Because the final structure of the battery allows for a single foil to have slurry coated and cured on both sides of the substrate, it is advantageous to simultaneously coat the cathode on both sides of the aluminum foil or the anode on both sides of the copper foil. The trick is to determine how to process two wet coatings on one substrate without damaging the slurry prior to curing the system. With different physical arrangements, different process considerations are presented. The slot die process engineer needs to think about whether a direct coating method, with a precision roll, is ideal or whether a free span coating method, without a roll, will provide the most process capability.
The assembled battery configuration also dictates the coating width of the slurry. While most economy-of-scale arguments would require one large width slot die to be equipped with shims to coat the slurry in lanes, there are equally strong arguments for obtaining foil the width most conducive for the final battery cell configuration and coating to this width. Of course, handling, converting, and other financial impacts need to be considered before determining the optimum equipment installation for the manufacturing process.
Another concept to consider in the coating efficiency of battery slurries is “patch coating.” Patch coating is the starting and stopping of fluid coating through the coating head while the substrate moves along at a constant speed. The benefit to patch coating is the rectangular shape of slurry coated on the substrate can reduce the converting requirements on the back end of assembling the battery cell. Patch coating is not a simple process step, however, and coating expertise needs to be developed to handle the complexities of intermittent coating.
While dual sided coating, economy-of-scale, and patch coating are running though the heads of coating process engineers in the battery industry, I am sure that new developments will lead the way for battery operated vehicles in the near future. Though three process improvements have carried the battery manufacturing into an improved stage of production, I doubt we have reached entitlement with these coated products. Similar to other coated consumer products, line speeds need to increase and quality needs to constantly keep pace with production. Battery manufacturing is definitely a developing industry.
Roll-to-roll coating industry expert Mark Miller, owner of Coating Tech Service, has 14+ years of slot die coating experience and troubleshooting. Contact him at 612-605-6019; firstname.lastname@example.org; www.coatingtechservice.com.