Layered Composites from Branched Nanofibers for Lithium Ion Batteries

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High-capacity, high-discharge rate batteries are essential for many technologies but their use has been hampered by troublesome safety and longevity records. These problems stem from the growth of dendrites that pierce ion conducting membranes and cause short-circuits leading to capacity fade, overheating, and fires. Dendrites are microscale branched metallic protrusions shaped as fern leaves forming on the surface of electrodes. They have numerous sharp nanoscale tips that exert large pressure on the membranes. Attempts to inhibit dendritic growth have met with limited success and highlight the fact that materials properties needed for safe high-performance batteries are fundamentally difficult to obtain. Resolution of this materials engineering problem will make possible a marked improvements in the performance of batteries without sacrificing their safety. This project will be focused on materials engineering of ion-conducting membranes (ICMs) aimed at making them strong, tough, and resilient to high temperatures. A new method will be employed for constructing ion-conductors and a new nanoscale component. The new generation of ICMs will be made using layer-by-layer assembly (LBL) that affords nanoscale precision in construction of composites. Branched aramid nanofibers (ANFs) discovered recently at the University of Michigan will be utilized as the ultrastrong component during the layered manufacturing of the membranes. The membranes will be made from ANF and ion-conducting polymers and systematically investigated for suppression of lithium dendrites. The prototypes of high capacity charge storage cells will be prepared and tested for performance and safety.