In a study published in the Journal of Power Sources, researchers from the Karlsruhe Institute of Technology (KIT) have quantitatively demonstrated that there are significant changes to the thermal transport properties of both the anode and cathode dependent on the aging conditions.

Marconnet et al.

While battery researchers often focus on optimizing device performance to improve, for example, battery capacity or charging rate, thermal effects have often been relegated to a secondary concern. The evolution of the thermal properties with aging and cycling impacts the temperatures within the battery cell and, in turn, the performance and reliability of the battery cell. This work focuses on quantifying the change in thermophysical properties of lithium-ion battery cells subject to various aging conditions.

—Marconnet et al.

Generally, the researchers said, heat removal from a Li-ion battery is limited to convection or conduction at the outer surface;, conduction within the cell must allow efficient heat transport to the casing. However, increased heat removal from outside or increased heat release within the cell (e.g., due to fast charging) leads to increasing temperature gradients within the cell that can only be limited by sufficiently large values of the cell’s effective thermal conductivity.

Effective heat dissipation is necessary to prevent the cell from overheating which leads to faster aging as well as suboptimal performance and may even result in catastrophic thermal runaways.

The effective thermal diffusivity of the electrode stack and thermal conductivity of the active materials are significantly impacted by the aging conditions, while the volumetric heat capacity remains relatively constant, they said.

Aging below room temperature results in relatively stable thermal transport, while aging above room temperature degrades thermal transport by up to ∼75% after 8200 equivalent full cycles at 50 °C.

For the cathode, the reduction in transport properties corresponds to visual observation of breakage of the particles. For the anode, solvent co-intercalation and exfoliation, along with growth of the solid electrolyte interphase (SEI) and loss of contact between active particles, may explain the reduction, they suggested.

Ultimately, the changes in thermophysical properties with aging will increase temperatures and reduce the electrochemical performance and reliability.

Resources

• Amy Marconnet, Sabrina Herberger, Sabine Paarmann, Philipp Seegert, Thomas Wetzel (2024) “Impact of aging on the thermophysical properties of lithium-ion battery electrodes,” Journal of Power Sources, Volume 603, doi: 10.1016/j.jpowsour.2024.234367