Application Note BATT1024
Introduction
The primary function of separators in Li-ion batteries is to prevent contact between anode and cathode while facilitating Li-ion transport through fine pores. The separators require dimensional stability within the operating temperature range and a shutdown function that collapses the pores to prevent thermal runaway. Thermomechanical Analysis (TMA) and Differential Scanning Calorimetry (DSC) are applied to characterize this performance.
Thermal analysis
- Analysis: Separator material
- Analysis method: Melting, Expansion/Shrinkage
- Use: Evaluation of thermal stability
- Analyzed materials: Three-layer separator
DSC revealed endothermic peaks corresponding to the melting of polypropylene and polyethylene at 132°C and 165°C, respectively. The melting of porous polyethylene triggers the shutdown function.
With TMA, we can identify shrinkage around the polyethylene melting temperature in the A direction, while elongation occurs above the polypropylene melting temperature in the B direction.
Conclusion
TMA and DSC allow us to evaluate the thermal shrinkage and shutdown temperature of separators. These analyses are valuable for evaluating separator thermal stability and guiding material selection.
