Electrochemically-Induced Fracture of Ionic Conductors: Electrolyzers and Batteries

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NON-TECHNICAL DESCRIPTION: Many technological and consumer applications involve use of electrochemical devices such as batteries. For the next generation automobiles, one fuel choice is hydrogen which is often made by high temperature electrolysis. These devices are subject to failure during operation. Even more dramatic are recent failures of lithium batteries that have led to fires. Numerous instances of fires caused by failed batteries in laptops, cell phones, skate boards, and airplanes have been reported. Even though electrolyzers do not catch fire, they are still subject to failure. Much of the reported research has been on attributing failures to effects such as electrode cracking, changes in microstructures, and defective electrodes. Theoretical research demonstrates that the key component that undergoes failure is often the electrolyte itself. The electrochemical transport (ionic current) through the electrolyte under certain situations can cause failure due to the electrochemical-mechanical coupling, which causes electrochemically-induced fracture of the electrolyte and device. Theoretical and experimental work is conducted to investigate the fundamental reasons of battery and electrolyzer failures. Understanding electrochemical fracture also helps design more durable batteries and minimize the propensity to accidental fires. Experimental work is conducted on lithium and oxygen ion conductors. Theoretical work is conducted on understanding the origin of electrochemical fracture and the rate of crack growth. The project supports one graduate student working towards a PhD and one undergraduate student. Students will be trained for employment in academia and battery companies. TECHNICAL DETAILS: Although numerous instances of fires due to lithium batteries have been reported, understanding of fundamental causes of failures has been elusive. Electrolyzers are known to fail under certain conditions. The common thread is that they fail during operation. This project investigates electrochemically induced fracture of the electrolyte which leads to the ultimate device failure, both theoretically and experimentally. Theoretical work examines occurrence of crack growth during the passage of current which leads to fracture under internally generated load. Experimental work is conducted on lithium and oxygen ion conductors. Metallic probes are embedded inside the electrolyte with terminals protruding out. Electrochemically induced fracture is initiated by testing the samples in electrolytic mode. The measurement of current and generated Nernst potential gives information on local pressure and onset of crack growth. Measurement of impedance spectra gives kinetics of electrochemically induced crack growth. Solution to coupled electrical-mechanical problem gives a quantitative approach to investigating fundamentals of electrolyte failures, which have important implications concerning battery fires. The work is timely as larger batteries are needed for handheld electronics and automobiles with added urgency to minimize propensity to fires. Understanding of electrolyte failures under electrochemical operation has the potential to lead to safer batteries.