A Standardised Potentiometric Method for the Effective Parameterisation of Reversible Heating in a Lithium-Ion Cell

Abstract

Lithium-ion batteries generate heat, degrading faster and becoming unsafe at high temperature. Yet many battery models do not consider the contribution of reversible, entropic heating when evaluating the rate of heat generation from a cell or battery pack. This leads to temperature prediction errors in battery management systems, increased safety risk, and reduced lifetime of the battery pack. Here, a standardised potentiometric method is proposed, allowing anyone with access to a typical battery lab to reliably and accurately extract the entropy coefficient for any electrochemical cell, the key parameter for the inclusion of reversible heating in a battery model. The proposed method takes 7.4 days to complete, representing a reduction of 90% compared to some methods proposed in the literature. Results highlight the importance of moving away from the multiple temperature steps, and the temperature step increases that dominate the existing literature. These arguments are justified through the observation and introduction of voltage relaxation following both kinetic and thermal excitation. These phenomena are termed post-kinetic-potentialisation and post-thermalisation-potentialisation. Post-thermalisation-potentialisation is not discussed in any published literature yet represents an important behavioural trait for any lithium-ion cell with a non-negligible length scale and thermal diffusivity.