A thorough understanding of the thermal transport characteristics of Li-ion batteries is critical for the development of accurate thermal models and the enhancement of thermal management strategies. In this study, the cross-plane thermal conductivity ( \(k_{\perp }\) ) of a commercial 20 Ah Li-ion pouch cell was systematically measured across a broad range of state-of-charge (SOC) levels and temperatures (20.6 to 43.3 \(^{\circ }\) C) using a custom-designed guarded hot plate apparatus. The results indicate that at room temperature (27.3 \(^{\circ }\) C), \(k_{\perp }\) decreases with increasing SOC, reaching a minimum near \(\text {SOC}=80\%\) , followed by a marked increase at \(\text {SOC}=100\%\) . Furthermore, at \(\text {SOC}=100\%\) , \(k_{\perp }\) increased by approximately 0.188 \(\hbox {Wm}^{-1}\) \(\hbox {K}^{-1}\) (80% enhancement) as the temperature rose from 20.6 to 43.3 \(^{\circ }\) C. The observation shows that \(k_{\perp }\) consistently increases with temperature across all SOC levels, exhibiting nearly consistent slopes. To elucidate these trends, various contributing factors were systematically examined.
