ABSTRACT

Rechargeable lithium ion batteries support the development of sustainable energy systems by storing electricity generated by renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. Lithium ion batteries that use lithium metal as the anode have much higher energy storage capacity than conventional carbon anodes. A fundamental reliability issue with experimental lithium ion batteries that use lithium metal electrodes is the formation of lithium metal whiskers within the battery during recharging, which ultimately shorts out the battery, creating a potential fire hazard and reducing battery life. This project will develop new solid polymer electrolytes to address this problem. The key innovation is that a hybrid mixture of organic and silicon- based polymer materials will be developed to impede lithium metal whisker formation while providing high conductivity for movement of lithium metal ions across the battery. The educational activities associated with this project include new modules for a polymer science course at Drexel University that focus on polymer materials for sustainable energy applications, and hands-on outreach on battery topics to high school students from diverse backgrounds in the Philadelphia area, coordinated through The Summer Engineering Experience @ Drexel program.

Rechargeable lithium ion batteries that use lithium metal as the anode have much higher electrochemical energy storage capacity than carbon-based anodes currently in use. However, imperfections on the metal surface serve as nucleation sites for the deposition of lithium metal dendrites. These microscopic projections grow upon repeated cycling and ultimately pierce the separator, touch the cathode, and short out the device. The goal of this research is to develop a new class of cross-linked hybrid network of solid polymer electrolytes with inorganic polyhedral oligomeric silsesquioxane as the cross-linker, and polyethylene glycol as the lithium ion solvating polymer. The hypothesis is that the hybrid network structure of two intertwined crosslinked polymers will resist dendrite growth and provide both high mechanical strength and lithium ion conductivity. The research plan will design, synthesize and test a series of solid polymer electrolyte network structures through four objectives. The first objective is to understand the fundamental mechanisms of lithium dendrite growth within solid polymer electrolyte hybrid networks. The second objective is to improve the lithium dendrite resistance of the hybrid network by introducing a series of double network structures. The third objective is to correlate the electrochemical performance to the nanostructure and morphology of the hybrid network, and the fourth objective is to fabricate and test the stability and performance of lithium metal batteries which contain the solid polymer electrolyte polymer networks. The fabrication will be made compatible with scalable roll-to-roll battery manufacturing processes.

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