Thermal Modelling of Battery Characterization Techniques

Abstract

The goal of this master’s thesis was to calibrate a calorimeter in a vacuum environment and quantify its potential benefits compared to air. The motivation for the project was to record the heat from a cylindrical cell with high accuracy. Peltier elements were used to record the heat flow of the samples’ cubical enclosure, each side with a heat sink to maintain a stable cold-side reference. The initial testing proved unstable and problematic to replicate, motivating four iterations of the setup. Vacuum conditions proved stable, yet time-consuming, requiring 6 hours to reach a steady state, compared to under 2 hours in air. The sensitivity of the Peltier elements was found to be 50-100 mW, yet the full system could only achieve a stable calibration coefficient from 1 W, found to be 19.93 and 19.85 W/V for air and vacuum, respectively. The main challenges with the calorimeter in vacuum were the high correlation to the surrounding lab temperature and the resulting radiation onto the setup. The added isolation proved to be inefficient. The heat sink’s surface was heated up by radiation, corrupting the heat flow signal. The recorded voltage was corrected using a reference cell and baseline voltage. The digital-twin model reached a 7% deviation, which helped locate the parasitic convection through the power cables, accounting for around 21% of the applied power. It also quantified 170-190 mW of radiative heating onto the heat sinks and 30-80 mW of conductive heat from the plastic stand. Ultimately, the vacuum environment proved challenging with no significant benefit over air. Although convective heat transfer was successfully removed, further changes could potentially improve the sensitivity and stability.