ChBE Seminar Series: David L. Jacobson
Tuesday, March 24, 2015
11:00 a.m.-12:15 p.m.
Room 2108, Chemical and Nuclear Engineering Building
Professor Chunsheng Wang
Imaging In Situ the Distribution of Lithium and Hydrogen in Energy Storage Devices with Neutrons
David L. Jacobson
Physical Measurement Laboratory
National Institute of Standards and Technology
Both low temperature polymer electrolyte membrane fuel cells (PEMFCs) and lithium ion batteries have been the subject of intense study in recent years for use as power sources in electric vehicles. To fully characterize and understand these devices there is a strong need for in situ measurement technology that can experimentally validate models of device operation. One technique that has been developed towards this end has been neutron imaging. Neutrons are able to non-destructively penetrate the components of PEMFCs and batteries and remain sensitive to hydrogen or lithium. This talk will provide a basic introduction to the technique of neutron radiography along with examples of how it has been applied to understand both PEMFCs and batteries. For PEMFCs neutrons can directly measure the water distribution throughout the device in situ. These devices require a balance of water to allow the proton conducting membrane to function yet too much water can result in flooding and degradation of the catalyst layer, clogging of the gas diffusion media, and blocking the flow channels. Under freezing conditions ice formed will plug the cell and damage the components. Neutron imaging provides a way to validate models of PEMFC operation and to directly measure the impact on water transport due to changing material properties such as thermal conductivity and water contact angle of components. Neutrons are also uniquely sensitive to the isotope lithium-6 (7.5 % natural abundance). Because of this neutrons have recently been used to measure the lithium distribution in Lithium Iron Phosphate (LFP) pouch cell battery at various states of charge (SOC) and discharge. Measuring the distribution of lithium v.s. SOC is important to models of the battery performance and to understand degradation mechanisms such as the formation of dendrites. Finally new diffraction contrast imaging methods will be discussed that allow one to look at the spatial distribution of crystalographic d-spacings and measure changes in mechanical stress states will also be discussed as well as a new neutron microscopy method aimed at improving the current spatial resolution of 10 micrometers to 1 micrometer.