Impact of state-of-charge and temperature on the cross-plane thermal conductivity of a Li-ion pouch cell

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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi> <mml:mo>⊥</mml:mo></mml:msub> </mml:math> ) 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mrow></mml:mrow> <mml:mo>∘</mml:mo></mml:mmultiscripts> </mml:math> C) using a custom-designed guarded hot plate apparatus. The results indicate that at room temperature (27.3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mrow></mml:mrow> <mml:mo>∘</mml:mo></mml:mmultiscripts> </mml:math> C), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi> <mml:mo>⊥</mml:mo></mml:msub> </mml:math> decreases with increasing SOC, reaching a minimum near <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>SOC</mml:mtext> <mml:mo>=</mml:mo> <mml:mn>80</mml:mn> <mml:mo>%</mml:mo></mml:mrow> </mml:math> , followed by a marked increase at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>SOC</mml:mtext> <mml:mo>=</mml:mo> <mml:mn>100</mml:mn> <mml:mo>%</mml:mo></mml:mrow> </mml:math> . Furthermore, at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>SOC</mml:mtext> <mml:mo>=</mml:mo> <mml:mn>100</mml:mn> <mml:mi>\%</mml:mi></mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi> <mml:mo>⊥</mml:mo></mml:msub> </mml:math> increased by approximately 0.188 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>Wm</mml:mtext> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mtext>K</mml:mtext> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:math> (80% enhancement) as the temperature rose from 20.6 to 43.3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow></mml:mrow> <mml:mrow></mml:mrow> <mml:mo>∘</mml:mo></mml:mmultiscripts> </mml:math> C. The observation shows that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>k</mml:mi> <mml:mo>⊥</mml:mo></mml:msub> </mml:math> consistently increases with temperature across all SOC levels, exhibiting nearly consistent slopes. To elucidate these trends, various contributing factors were systematically examined.