Influence of state of health and individual aging mechanisms on the thermal conductivity of lithium-ion cells

Battery aging strongly influences the inner structure of the cell whereby the through-plane thermal conductivity is altered. Despite being of high interest for thermal management design, only few information about the correlation between thermal conductivity and aging can be found in literature. Therefore, 14 cells are extracted from sophisticated aging test cycles to emulate aging in the field. Furthermore, the individual aging mechanisms of electrolyte loss, lithium plating and gas formation are isolated in sample cells by tailored cell cycling. Following, the temperature-and SOC-dependent thermal conductivity of all sample cells is measured whereby the effect of the SOH on the thermal conductivity as well as the impact of individual aging mechanisms can be characterized first-ever.It is found that a reduced state of health results in a linearly declining thermal conductivity of up to -40% which strongly affects the design of thermal management systems for aged lithium-ion cells. Furthermore, electrolyte loss strongly reduces the thermal conductivity while the thermal conductivity of fully dry cells does not show any temperature dependency. Gas formation also reduces the thermal conductivity without permanently changing the active material's thermal conductivity while lithium plating only moderately affects the thermal conductivity.