In a study published in the Journal of Power Sources, researchers from the Karlsruhe Institute of Technology (KIT) have demonstrated that there are significant changes to the thermal transport properties of battery anodes and cathodes dependent on the aging conditions.
The effective thermal diffusivity of the electrode stack and thermal conductivity of the active materials are significantly affected by the aging conditions, while the volumetric heat capacity remains relatively constant, the researchers said. Aging below room temperature results in relatively stable thermal transport, while aging above room temperature degrades thermal transport by up to 75% after 8,200 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.
“Generally, the 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,” said the researchers. “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.”
Source: Journal of Power Sources
