Electrothermal characterization of batteries using high-speed high-resolution (HH) calorimetry

Abstract

This thesis presents a high-speed and high-resolution (HH) calorimetric method for electro-thermal characterization of batteries. The electrical and thermal response of a battery to a sequence of square current pulses in an isothermal environment is analyzed to determine the entropy variations and the internal ohmic resistance as a function of state-of charge. The proposed method's measurement duration is reduced compared to the conventional calorimetry methods by optimizing the rest time between the square current pulses in the sequence. An exponential-regression-based approach is adopted to estimate the exchanged heat energy between the battery and the external environment, which allows reduction in the waiting time due to the slow thermal relaxation of the battery after each current pulse. The heat flux measurements are performed using an in-house developed calorimetry device that incorporates flexible thermoelectric sensors for a compact design. The ohmic (DC) resistance and the entropy-variations profiles of two pouch cells of 340 and 650mAh rated capacities were extracted over the entire range of states of charge with resolution as low as 2.5%.