Author: Christoph Drießen, University Assistant and PhD Candidate, Vehicle Safety Institute, Graz University of Technology

A range of mechanical, thermal, and electrical abuse tests are conducted to simulate potential real-world hazards. The analysis of the battery responses under these conditions allows examining various failure mechanisms and collecting data for developing models and algorithms for protective safety measures. Insights gained from abuse testing contribute to the design of safer batteries and help reduce the risk of fire, explosion, or other safety-critical incidents in real-life applications.

Abuse test in NEMO

As part of the NEMO project, one of the key tasks of the Vehicle Safety Institute at TU Graz is to develop a data-driven State-of-Safety estimator that can predict safety-critical events in the short and long term.

At first, the focus has been placed on mechanical loads, which simulate the deformation that a battery cell might experience during a side impact in a collision or crash. These experiments, conducted under controlled conditions, apply significantly higher mechanical loads than those typically seen in real-world crash scenarios, with the aim of establishing a high safety margin of resistance.

We have conducted some mechanical abuse tests – more specifically, local mechanical deformation tests – to determine the mechanical load limits of the cells. Such internal short circuits can trigger the hazardous event known as thermal runaway.

The parameters evaluated in these tests serve as a baseline for further experiments in which cells are deformed without triggering an internal short circuit. These follow-up tests involve taking electrical measurements and using them to predict the defined states of deformation. This enables early identification of safety-critical battery cell states.

Stressing the cells

In the video below, the battery cell is placed on a steel plate and deformed at its center with a hemispherical impactor in an out-of-plane direction, which is the weakest side of the cell under local impact. The test is conducted at 75% state of charge (SoC), with the deforming impactor moving at 0.1 mm/s (accelerated in the video) until an internal short circuit (ISC) – indicated by a voltage drop – occurs. The ISC then triggers a thermal runaway, visible as an explosion and fire.

Our investigations have helped define the mechanical safety limits of the cells, specifically the deformation depths and forces that can lead to internal short circuits and trigger thermal runaway.

Building on this, we have conducted an additional experimental series, namely local stepwise mechanical deformation tests in combination with electrical impedance spectroscopy (EIS) measurements.

Looking ahead in the project, TU Graz plans to perform thermal load tests as well, offering new insights into battery safety under real-world conditions.

The Vehicle Safety Institute (VSI) is a research group at the Graz University of Technology, focused on the crash behavior of energy storage systems and materials. Within the NEMO project, VSI is responsible for three main tasks: developing a mechanical swelling model, creating a data-driven estimator to assess the battery’s safety status, and coordinating the testing and demonstration activities to make sure the developed solutions work in practice.