Thin-Film Formation of Insoluble Discharging Products at the Reaction Interface of Li-Air Batteries

University Of California-Irvine, Irvine CA

Investigators

Abstract

PI: Wang, Yun Proposal Number: 1336873 Institution: University of California-Irvine Title: Thin-Film Formation of Insoluble Discharging Products at the Reaction Interface of Li-Air Batteries Lithium-air (Li-air) batteries show great potential for high capacity of energy storage. Their unique feature is that the cathode active material, oxygen, is not stored in the batteries, but obtained from the ambient environment. In addition, Lithium metal is used rather than the Li intercalated graphite (LiC6) as that in Li-ion batteries. The theoretical specific energy of Li-air batteries reaches 11,680 Wh/kg, comparable to that of gasoline (13,000 Wh/kg). Despite the great promise, they face scientific and technical challenges: one is their discharge capability limited by insoluble products formation in cathode electrodes. It has been observed that precipitation of insoluble discharging products forms a nano-scale film on the reaction surface, hampering electrochemical activity and eventually leading to significant voltage/capability loss. The underlying physics are, however, poorly understood at present. This project examines the thin-film formation at the reaction surface and its effects on Li-air battery performance, with the ultimate goal to eliminate its adverse effects. This project hypothesizes that the thin-film formation of insoluble discharging products exhibits heterogeneous structures depending on operating conditions, and thus delineating the heterogeneity is crucial to understand the underlying physics of discharging voltage and capacity losses. The first objective is to explore the film growth modes at typical surface morphologies, and understand the thin-film structure, i.e. the spatial variation of film properties; the second objective is to explore the effects of film formation on battery?s voltage loss following an approach newly developed in PEM fuel cells for subfreezing operation: product water in fuel cells freezes with ice forming at the reaction surface and hampering electrochemical activities, which is similar to the film formation of insoluble discharging products in Li-air batteries. In the first, three surface morphologies will be analyzed: planar, cylindrical, and spherical shapes. The PI will also directly measure the thin-film?s spatially varying properties, including chemical composition, porosity, and electric resistance. In the latter, the PI will analyze the capacity and discharging voltage loss due to film formation, following that of ice formation in PEM fuel cells. Diagnostics methods such as cyclic voltammeter (CV) and impedance will be applied to measure reaction surface loss, and the reaction and oxygen transport resistances. The project is anticipated to develop fundamental knowledge regarding thin-film formation, its physical properties, chemical composition, and effects on electrochemical reaction activities, significant to Li-air battery development. The outcomes also benefit other research areas, such as the biological reactors, other battery systems, PEM fuel cells, high-temperature fuel cells (tar formation in the anode), nano film growth, and electron tunneling. Li-air battery technology has the potential to overcome the major technical hurdle for electrical vehicles, i.e. the insufficient storage capability. Outreach efforts include: 1) Multidisciplinary learning experiences for graduate and undergraduate students; 2) a renewable energy outreach program which emphasizes hands-on engineering experience for high school students and teachers, participating alongside undergraduate students.