Local in-Operando Temperature Measurements Across the Interfaces of a Lithium Ion Battery Cell Using Microscopic Thermography

The predicted widening of applications for lithium ion batteries is still lagging behind due to several disadvantages mostly concerning safety and reliability hazards caused by the heat evolution during rapid charging and discharging. For targeted material development, design optimization and battery management a detailed and fundamental knowledge of the heat evolution mechanisms and the heat transfer on the micro and macro scale is obligatory.

Most of the investigations published in literature focus on the heat evolution in lithium ion batteries and dealing with integral measurement techniques at commercially available systems. The interpretability of the measurements is rather difficult due to the complexity of the multi composite system.

For a detailed and fundamental research on the heat evolution mechanisms in the individual battery components cathode, separator/electrolyte and anode the authors developed a special electrochemical cell for microscopic in-operando thermography. Using a thermography system with high spatial and temperature resolution we were able to measure the spatially resolved temperature evolution across the interfaces of anode/separator/cathode.

Differences in the heat evolution rates of cathode, separator and anode depending on the electrochemical reactions, the state of charge and the applied electric current density are identified by the experiments. The heat evolution was investigated depending on the charging-discharging rate. The main heat evolution mechanisms are:

·         the superiority of reversible heat effects due to the electrode reactions for near equilibrium conditions

·         the dominating effect of Joule heating for high charging-discharging rates.

In the investigated battery setup the LiCoO₂ cathode can be identified as the most decisive component for the overall heat evolution in the cell according to the ohmic resistance and remarkable high reversible heat effects.