The use of advanced lithium-ion batteries for vehicle transport and renewable electricity grid storage applications could improve domestic energy security, but their use is limited by high cost and limited battery lifetime. The main cause of battery failure is undesirable chemical side reactions within the device that are difficult to quantify and to understand. Because of this lack of fundamental understanding, engineers are less able to design materials and devices that can withstand side reactions for longer times. In advanced battery designs such as hybrid lithium batteries, gel electrolytes have been favored because they allow high liquid-like conductivities of conventional electrolytes yet favorable mechanical properties and enhanced safety like solid polymer electrolytes. This CAREER project will conduct fundamental research on polymer processing methods to efficiently deposit gel electrolytes inside a battery's porous electrode to form thin protective coatings that improve resistance to unwanted side reactions and provide structural stability. Beyond electrochemical energy storage applications, these studies will enable scalable, rapid polymer depositions that have general relevance in many other applications such as corrosion protection coatings, barrier and dielectric layers, and optical coatings. As educational benefits, this project will train student researchers in critical thinking skills, and in the disciplines of reaction engineering, polymer science, advanced semiconductor processing, and electrochemical energy storage. The PI has also partnered with the Rochester City Public District to introduce chemical engineering principles to high school students using interactive service-learning inspired projects.
The polymer chemical vapor deposition (CVD) process in this project is based on heterogeneous cationic polymerizations. The central hypothesis is that strong acid molecules, which are introduced into the deposition chamber as vapor-phase precursors, react with surface-adsorbed vinyl monomers, generating carbenium ions that then undergo polymerization. The overarching research objective is to understand the fundamental transport and reaction processes that constitute cationic polymer CVD in order to establish synthetic and morphological control of polymer gel electrolytes deposited within porous lithium ion battery electrodes. This project is divided into two thrusts, where the first thrust seeks to establish the reaction mechanism and understand the material properties of the deposited films. The second thrust will research the processing conditions that effectively balance the rate of surface reaction with mass transport to achieve conformal coatings inside porous structures. Novel gel electrolyte materials will be synthesized within electrode porosity using cationic CVD. These two thrusts are highly integrated and will be conducted in concert to discern structure-property relationships and the effects of processing conditions in these novel gel materials. To establish foundational understanding of the gels' electrochemical behavior in relevant lithium ion battery cells, electrochemical characterization of the gels is emphasized including Li ion transport and oxidative stability. Initially, the gel electrolyte composition will be based on crosslinked poly(vinyl pyrrolidone) swollen in conventional alkyl carbonate liquid electrolytes. Over a longer term as both the project and energy storage field advance, additional novel gel compositions will be developed to address material challenges in future lithium battery technologies.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
