What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells

March 11, 2024

Researchers at the University of Illinois Urbana-Champaign have developed a novel technique to study the chemical properties of lithium-ion battery cells using the Peltier effect, where electrical current induces heat transfer. Published in Physical Chemistry Chemical Physics, this method enabled them to measure a critical thermodynamic feature, the entropy of the lithium-ion electrolyte.
The Peltier effect remains largely unexplored in ionic systems like lithium electrolytes for the smaller temperature differences created by Peltier heating and cooling compared to other effects. To overcome this barrier, the researchers used a measurement system capable of resolving one hundred-thousandth of a degree Celsius, allowing researchers to measure the heat between the two ends of the cell and use it to calculate the entropy of the lithium-ion electrolyte in the cell.
The researchers explored how the Peltier heat flow changed with the concentration of lithium ions, solvent type, electrode material and temperature. In all cases, they observed that the heat flow ran opposite to the ionic current in the solution, implying that the entropy from the dissolution of lithium ions is less than the entropy of solid lithium.
The ability to measure the entropy of lithium-ion electrolyte solutions can provide important insights into the ions' mobility, governing the battery's recharging cycle, and how the solution interacts with the electrodes, an important factor in the battery's lifetime.

From: EurekAlert!