The team led by Yuan Yang, assistant professor of materials science and engineering in the department of applied physics and mathematics at Columbia Engineering developed a prototype with a thick, rigid segment that stores energy by winding the electrodes (“vertebrae”) around a thin, flexible part (“marrow”) that connects the vertebra-like stacks of electrodes together.
“The energy density of our prototype is one of the highest reported so far,” said Yang. “We’ve developed a simple and scalable approach to fabricate a flexible spine-like lithium ion battery that has excellent electrochemical and mechanical properties. Our design is a very promising candidate as the first-generation, flexible, commercial lithium-ion battery.”
“We are now optimizing the design and improving its performance. As the volume of the rigid electrode part is significantly larger than the flexible interconnection, the energy density of such a flexible battery battery can be greater than 85 percent of a battery in standard commercial packaging. Because of the high proportion of the active materials in the whole structure, our spine-like battery shows very high energy density–higher than any other reports we are aware of. The battery also successfully survived a harsh dynamic mechanical load test because of our rational bio-inspired design.”
Yang’s team cut the conventional anode/separator/cathode /separator stacks into long strips with multiple branches extending out from a backbone. Then they wrapped each branch around the backbone to form thick stacks for storing energy, like vertebrae in a spine. With this design, the battery’s energy density is limited only by the longitudinal percentage of vertebra-like stacks compared to the whole length of the device, which can easily reach over 90 percent.
The battery shows stable capacity upon cycling, as well as a stable voltage profile no matter how it is flexed or twisted. After cycling, the team found that the positive electrode was intact with no obvious cracking or peeling from the aluminum foil, confirming the mechanical stability of the design.
Even when the cell was continuously flexed and twisted during the whole discharge, the voltage profile remained and the battery in the flexed state was also cycled at higher current densities, with the capacity retention remaining at 84% at 3C, the charge in 1/3 of an hour.
“Our spine-like design is much more mechanically robust than are conventional designs,” said Yang. “We anticipate that our bio-inspired, scalable method to fabricate flexible Li-ion batteries could greatly advance the commercialization of flexible devices.”