Non-invasive accurate time resolved inverse battery calorimetry

Abstract

Precise knowledge of the battery heat generation rate and the internal temperature rise allows accurate thermal regulation required for enabling fast charging while minimizing side reactions and avoiding thermal runaway. With the necessity of high energy density, the size of batteries is constantly increasing. Because of poor thermal conduction, the thermal lag in large batteries is significant resulting in a considerable temperature gradient within the cell. Existing calorimetry methods only account for the external heat flow measurement and the external temperature rise and therefore cannot account for the thermal lag inside the cell. Additionally, with these methods, the temporal (time-resolved) information of the heat generation rate is compromised, which makes observation and attribution of electrochemical- thermal signatures impossible. As a potential solution, various intrusive techniques such as embedded thermal sensors have been proposed in the literature. However, these techniques are limited in scope. To enable accurate measurement of time-resolved heat flux measurement in commercial batteries, we instead propose a new battery calorimetry approach by combining state-of-the-art commercial calorimetry with an inverse heat transfer algorithm. This inverse calorimetry is completely non-intrusive with no change to commercial calorimeters. The inverse calorimetry reduces the error in heat generation rate to within 10% of the actual heat generation rate compared to 50% from the lumped capacitance method (best existing method). This method enables time resolved observation of electrochemical-thermal signatures such as a negative heat generation rate due to entropy change, which could not be observed from existing calorimetry methods.