Collaborative Research: Effect of Cyclic Mechanical Stress on Ionic Conduction in Composite Polymer Electrolytes for Solid-State Batteries

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This grant will investigate how cyclic mechanical stress affects ionic conductivity in ceramic-in-polymer composite electrolytes for solid-state batteries. Solid-state electrolytes are receiving increasing attention as safer alternatives to conventional organic liquid electrolytes, which are flammable and prone to overheating. Several composite polymer electrolytes have been developed to balance high ionic conductivity and mechanical toughness. However, solid-state batteries tend to suffer performance degradation with an increased number of cycles. Internal stresses develop during charging and discharging cycles, as lithium ions move back and forth between dissimilar electrodes. Although degradation of electrodes has been studied extensively, very little is known about mechanical and microstructural changes within the electrolyte. This lack of knowledge limits the full development of safe and high-performance energy storage systems for diverse U.S. industry sectors ranging from electric vehicles, portable electronics, and biomedical devices. A more complete understanding of how dispersed rigid particles affect the mechanical behavior of polymer composites may further contribute to advances in other applications such as fuel cells, photovoltaics, biomaterials, and flexible electronics. The collaboration supported by this grant will engage and connect faculty and students at a primarily undergraduate institution and at a PhD-granting research university, both of which are Hispanic-serving institutions.Mechanical behavior of ceramic-in-polymer electrolytes is especially intriguing because it involves a very large difference in material properties between rigid particles and a viscoelastic matrix, highly coupled interaction between mechanical stresses and electrochemical ion transport, and a functionally critical space-charge region at the interface between ceramic particles and polymer chains. The central hypothesis of the project is that a limiting factor for long-range battery performance (e.g., capacity fade) is viscoelastic remodeling of composite microstructure. The project is organized along three objectives: (1) determine how composite microstructure affects mechanical behavior, (2) interrelate dynamic stresses and device-level electrochemical performance, and (3) determine how nanoscale contact stresses affect interfacial ionic conduction. Using complementary macroscale and nanoscale experiments, this investigation will develop, interrogate, and validate a multiphysics model of the interdependencies among mechanical properties, microstructure, and electrochemical performance.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.