Measurement of the temperature-dependent cross-plane thermal conductivity of the Li-ion battery pouch cell

Abstract

Due to the lamella structure of Li-ion batteries, their cross-plane thermal conductivity is substantially lower than the in-plane conductivity. This leads to pronounced anisotropy, which complicates the accurate measurement of thermal conductivity, underscoring the importance of precise temperature monitoring to better understand and manage thermal behavior within the battery. This study presents an effective approach for precisely measuring the cross-plane thermal conductivity of Lithium Iron Phosphate (LFP) pouch cell by utilizing a guarded-hot-plate (GHP) method. We minimized edge effects and promoted one-dimensional heat flow by strategically determining the size of the main and guide plates of the GHP device. Calibration experiments resulted in a measurement uncertainty of about 2%. Notably, our measurements showed that the cross-plane thermal conductivity of LFP pouch cell is strongly temperature-dependent, changing from $0.128\pm 0.005$ Wm⁻¹K⁻¹ at 21.7 °C to $0.199\pm 0.006$ Wm⁻¹K⁻¹ at 44 °C (i.e., 55% increase). It is also shown that the thermal conductivity of two LFP pouch cells, despite their identical specifications, display noticeable discrepancies, which is due to their different SOC levels of 79.6% and 87.1%. This research provides a detailed framework for evaluating the cross-plane thermal conductivity of Li-ion batteries, offering critical insights into their thermal behavior at different temperatures and contributing to developing their improved thermal management strategies.