Meaning
Rate of thermal energy transfer per unit area through a surface. Quantifying heat flux allows engineers to determine the intensity of heat generation during rapid discharge cycles in lithium ion cells. The value is expressed in watts per square metre.
Sensors placed on the cell skin capture the temperature gradient across a material of known thermal conductivity to derive this figure.
Measurement Method
Differential sensors or thin film transducers provide the primary data for this specific calculation. Measuring the heat flux requires a sensor placed directly against the battery skin. This setup ensures that surface contact resistance does not skew the resulting data points.
Thermal Management
Cooling system efficiency relies on the accurate mapping of heat dissipation across different load profiles. High heat flux at the terminal connections often indicates electrical resistance issues that passive cooling cannot resolve. Designers use these metrics to size heat sinks or liquid cooling plates for large scale battery packs.
Effective extraction of heat prevents the acceleration of chemical degradation within the electrolyte.
Design Implication
Surface area to volume ratios dictate how easily a cell sheds heat during operation. A large prismatic cell faces different challenges than a cylindrical counterpart because the internal heat flux must travel further to reach a cooling interface. Localised spikes in thermal transfer can lead to internal hotspots.
These temperature variances shorten the cycle life of the pack by causing uneven aging across the series strings.
