Anisotropic thermal characterisation of large-format lithium-ion pouch cells

TL;DR

This paper develops new methods to measure the anisotropic thermal properties of large lithium-ion pouch cells, providing essential data for accurate thermal modeling crucial for safety and performance.

Contribution

It introduces innovative experimental approaches to quantify heat capacity and anisotropic thermal conductivity of lithium-ion pouch cells, including inverse modelling techniques.

Findings

Heat capacity at 100% SOC is 541 J/K.

In-plane thermal conductivity is 26.6 W/(mK).

Through-plane thermal conductivity is 0.52 W/(mK).

Abstract

Temperature strongly impacts battery performance, safety and durability, but modelling heat transfer requires accurately measured thermal properties. Herein we propose new approaches to characterise the heat capacity and anisotropic thermal-conductivity components for lithium-ion pouch cells. Heat capacity was estimated by applying Newton's law of cooling to an insulated container within which the cell was submerged in warmed dielectric fluid. Thermal conductivity was quantified by heating one side of the cell and measuring the opposing temperature distribution with infra-red thermography, then inverse modelling with the anisotropic heat equation. Experiments were performed on commercial 20 Ah lithium iron phosphate (LFP) pouch cells. At 100% state-of-charge (SOC), the heat capacity of a 489 g, 224 mL pouch cell was 541 J/K. The through-plane and in-plane thermal conductivities were respectively 0.52 and 26.6 W/(mK). Capturing anisotropies in conductivity is important for accurate thermal simulations. State-of-charge dependence was also probed by testing at 50% SOC: the heat capacity dropped by 6% and thermal conductivity did not significantly change.