Project Details

Description

TECHNICAL SUMMARY

Polymer electrolytes are safer, cleaner, and more flexible than liquid electrolytes currently used in Li batteries. They are an attractive possibility for use with Li metal electrodes because they are stiffer than liquid electrolytes. For this purpose, PEO-based electrolytes are not stiff enough to prevent dendrite formation, which limits use of Li metal. They also do not have high enough conductivity to be practical. Unfortunately, stiffness and conductivity are inversely related because Li motion is coupled to polymer motion, and any attempt to improve conductivity through faster polymer motion results in decreased stiffness. This project is based on the idea that tunnel-like polymer/salt structures promote fast Li motion, recently demonstrated using single-crystal electrolytes. It will harness this motion with a set of high aspect ratio nanofillers based on cellulose nanowhiskers, which are hypothesized to promote the tunnel structures. These fillers offer controllable surface chemistry, degree of functionalization and aspect ratio, thus forming an ideal model system. Building on prior work, particular attention will be paid to the eutectic composition, at which improved electrical conductivity and mechanical properties are established in metal alloys. At this composition, the analogous metal alloys form large-scale structures with the two crystal phases in alternating lamellae. The formation of such structures for polymer electrolytes has not been investigated. The project will use cyclic thermal treatments as a means to produce similar patterns in polymer/salt eutectics, which will extend the tunnel-like structures further from the filler surface. The ideal electrolyte would have fillers, and thus Li conduction pathways, aligned along the direction normal to the electrodes. It is established that cellulose nanowhiskers can be aligned using magnetic fields, electric fields, and shear, and the project will investigate all three for effectiveness at alignment without disrupting polymer/salt pattering extending from the filler surface. The project will promote understanding of the roles of surface chemistry and aspect ratio on interaction of nanoscale fillers with polymer/salt systems, the factors controlling polymer eutectic structures, and the best ways to control filler alignment in polymer/salt mixtures.

NON-TECHNICAL SUMMARY

Polymer electrolytes are safer, cleaner, and more flexible than liquid electrolytes currently used in the Li batteries in cell phones and laptop computers. They are an attractive possibility for use in vehicles, where Li ion battery technology is already used. Polymer electrolytes are attractive for this application because they allow technical advancements that extend the charge lifetime from 100 to 400 miles per charge. Polymer electrolytes are not currently feasible with these technical advancements, nor can they attain power discharge sufficient for vehicle applications. These two required improvements are currently mutually exclusive: attempts to enable longer charge lifetime will reduce power and vice versa. The science in this project will decouple the objectives of long lifetime and high power. It is based on unique features of polymer/Li salt mixtures that occur near inorganic surfaces. It will use very small fillers, which provide more surface area, and alter the surface chemistry and filler alignment to obtain optimal results. The results of this work will allow scientists to work on increasing power and lifetime independently, thus promoting advancement of the alternative energy technology of Li ion batteries. The U.S. is a world leader in scientific research, yet struggles to fill jobs in the sciences, technology, engineering and mathematics. The United InnoWorks Academy is a national organization that seeks to narrow this disconnect by introducing STEM concepts in a fun way to kids in the critical period where they are deciding what they like and what they are good at. The program is specifically designed towards students who, at age 11, may have already decided that they are not good at math and science. InnoWorks is a student-run organization in which professors, graduate students and undergraduate students raise funds, develop curriculum, and prepare and run summer camps. This project will start a Penn State Chapter, thus showing kids that science is fun.

StatusFinished
Effective start/end date6/1/135/31/17

Funding

  • National Science Foundation: $480,000.00

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