By Allison Proffitt
July 30, 2020 | The closing day of the International Battery Seminar was again packed with sessions covering battery design and application for consumer electronics, the grid, and much more.
Avetik Harutyunyan presented Honda’s flexible batteries for wearable applications (no mention of EVs). Honda wanted to use a thin sheet of carbon nanotubes—buckypapers—but found that the conventional method for obtaining carbon nanotube-based composite sheets densified the carbon nanotube arrays, creating brittle sheets. Instead, Harutyunyan explained, the team developed a patented process to create nanotube-based composite electrodes using pristine nanotubes to completely avoid the wet chemistry step and eliminate metal current collectors, binders and additives. The resulting electrodes are conductive and flexible with high capacity retention, and the completed cells are undisturbed when subjected to mechanical stress.
Mark Hersam, Northwestern University, shared his group’s advances creating graphene-encapsulated cathodes: much thinner, denser, mechanically flexible cathodes that have high chemical stability, high electrical conductivity, and higher volumetric capacity. The group started with LMO cells, hoping that the graphene coating could mitigate manganese dissolution into the electrolyte. The graphene-LMO did suppress Mn dissolution, minimized voltage fade, and reduced capacity loss on cycling. Now, Hersam said, the group is testing the technique on NMC and NCA cells and is finding that graphene still enhances capacity and rate for nickel-rich cathodes.
And John Wozniak outlined the consumer battery opportunities. Though many manufacturers have left the 3C battery space because of decreasing profitability, he sees opportunities for battery innovation in home cleaning products, wearable devices, drones, and security devices. In security devices, for instance, he highlighted smart doorbells like the Ring. Some doorbells are hardwired to the house; others are battery powered, but with all that these devices do—connect to WiFi, have motion sensors, transmit videos and images, support two-way voice—batteries are essential in both types. In addition, the batteries need to stand up to outdoor climate conditions.
But more batteries and more use cases aren’t our only innovation challenges. Steve Tolen with Indie Power Systems explored the opportunities for secondary use batteries. It’s ecologically responsible to recycle batteries, he said, but acknowledged that it’s expensive and challenging. He focused on reusing EV batteries, which can decrease the total cost of ownerships for EVs, thus increasing value and marketability. But real progress in battery re-use will require some design concessions. He called for common-sense reform of battery labeling and transport regulations, and challenged battery manufactures to include design elements conducive to reuse including mechanical fasteners on packs (don’t weld it shut!) and direct-to-rack pack designs. But a big part of progress will be more openness in OEM battery management systems allowing for managing different capacities and efficient balancing.