Thermal Conductivity in Aged Li-Ion Cells under Various Compression Conditions and State-of-Charge

Abstract

Thermal conductivity (TC) is a parameter, which significantly influences the spatial temperature gradients of lithium ion batteries in operative or abuse conditions. It affects the dissipation of the generated heat by the cell during normal operation or during thermal runaway propagation from one cell to the next after an external short circuit. Hence, the thermal conductivity is a parameter of great importance, which concurs to assess the safety of a Li-ion battery. In this work, an already validated, non-destructive measurement procedure was adopted for the determination of the evolution of the through-plane thermal conductivity of 41 Ah commercially available Li-ion pouch cells (LiNiMnCoO2-LiMn2O4/Graphite) as function of battery lifetime and state of charge (SOC). Results show a negative parabolic behaviour of the thermal conductivity over the battery SOC-range. In addition, an average decrease of TC in thickness direction of around 4% and 23% was measured for cells cycled at 60 °C with and without compression, respectively. It was shown that pretension force during cycling reduces battery degradation and thus minimises the effect of ageing on the thermal parameter deterioration. Nevertheless, this study highlights the need of adjustment of the battery pack cooling system due to the deterioration of thermal conductivity after certain battery lifetime with the aim of reducing the risk of battery overheating after certain product life.

Meta-analysis of experimental results for heat capacity and thermal conductivity in lithium-ion batteries: A critical review

“…In addition, electrolyte consumption and gas development due to the electrolyte reduction could lead to a decrease in 𝑘 ⊥ . The results of Vertiz et al [101] and Kovachev et al [129] show a significant decrease in 𝑘 ⊥ with SOH, which is reflected in a poorer thermal performance of the cell, since the heat development also increases with SOH. However, more research is needed to confirm the correlation between 𝑘 ⊥ and SOH for cylindrical and prismatic cells.…”

“…The reason for this significant decrease was not discussed by Vertiz et al [101]. Kovachev et al [129] cycled three pouch cells at 60°C with different electrical currents (1C to 3C) and pretension between 0 and 0.56 MPa.…”

“…The decrease in SOH caused an average decrease in 𝑘 ⊥ between 23% and 4% (Figure 6 b)). Kovachev et al [129] explained the SOH dependence of 𝑘 ⊥ with an additional thermal resistance on the anode side caused by the SEI growth. In addition, electrolyte consumption and gas development due to the electrolyte reduction could lead to a decrease in 𝑘 ⊥ .…”

“…Then these changes in battery states are linked to seven underlying mechanisms leading to five primary effects considered in Equation ( 10) and porous media theory such as Krischer [50]. For example, 1) a change in thermal conductivity in the liquid phase could result from electrolyte consumption [129] if the electrolyte is replaced by gases with low thermal conductivity. 2) The thermal conductivity of the solid phase depends on the phonon and electron conduction, which are influenced by the crystal lattice parameters [133].…”

The Application of Fuel-Cell and Battery Technologies in Unmanned Aerial Vehicles (UAVs): A Dynamic Study

“…At the current stage, the suggested integrated systems of batteries and fuel cells are not able to provide the required power for huge passenger planes [5], but they can generate the needed electricity to run small-sized planes (around 100 kW to 300 kW); hence, the objective of the current study was related to the domain of unmanned aerial vehicles (UAVs). UAVs are designed to fulfill long and high-altitude flight missions without any people on board [6].…”