(Invited, Digital Presentation) Multiscale Measurements and Characterization of Thermal Transport in Materials and across Interfaces in Li-Ion Cells

Abstract

Li-ion cells are used universally for energy conversion and storage. Key application areas include electric vehicles, grid energy storage, air/space vehicles and consumer electronics. Overheating of Li-ion cells is a well-known problem, with serious concerns related to thermal runaway and fire. Additionally, Li-ion cells also under-perform at low temperatures, which is a particularly important problem for automotive and space applications. Advances in battery materials are needed to mitigate these concerns and improve the performance and safety of Li-ion cells. This talk will summarize research advances in understanding and optimizing thermal transport in Li-ion cell and battery pack materials. Measurement of thermal conductivity of cylindrical Li-ion cells, indicating the highly anisotropic nature of thermal conduction will be described. This will be followed by discussion of measurement of thermal properties of individual cell materials, such as the separator, as well as thermal contact resistance at the cathode-separator interface. This contact resistance will be shown to play a rate-limiting role in determining overall thermal transport properties of the cell, and is, in particular, responsible for anisotropic thermal conduction. Experiments to mitigate this thermal resistance through molecular bridging at the interface will be described. Good agreement with molecular dynamics simulations will be demonstrated. Challenges associated with practical implementation of such techniques will be discussed. Finally, numerical simulations to understand the nature of thermal transport in battery packs will be described, with the goal of minimizing thermal runaway propagation. These measurements and modeling techniques contribute towards a fundamental understanding of multiscale thermal transport in Li-ion cell materials, and may help optimize and improve thermal performance of practical energy conversion and storage devices.