(383a) Nonequilibrium Phase Stability of Ion Intercalation Materials—Nonisothermal Effects

The calendar and cycle life of lithium-ion batteries is significantly affected by the coupling of reaction and diffusion phenomena under non-isothermal conditions that take place during battery operation [1]. In particular, driven electrochemical reactions, such as ion intercalation, lead to heat generation and thus to temperature increase, which consequently affects the reactions themselves as well as other transport processes, e.g. liquid electrolyte and solid-state diffusion. Battery materials such as lithium iron phosphate, graphite, and lithium cobalt oxide, are phase separating by nature. It is known that the interplay of heat and mass transfer determines the stability of phase-separating systems, which contain many electrode materials. Here, we develop the nonequilibrium thermodynamic framework of non-isothermal open driven systems and predict the nonequilibrium phase stability of the active materials in Li-ion batteries during their operation.

By performing linear stability under (dis)charging conditions, we characterize the phase stability of the system as a function of the heat transfer Dahmkohler number, which compares the reaction to heat generation rates. Additionally, we identify the effects of different ion intercalation reaction mechanisms and demonstrate the importance of the limiting current as a result of electron transfer limitations to both the heat generation and nonequilibrium phase stability of the system. Finally, we discuss the implications of our findings on the design of Li-ion batteries, and speculate their application on other open driven systems, such as photocatalysis and electrodeposition.

[1] Waldmann, Thomas, et al. Journal of Power Sources 262 (2014): 129-135.