Assessing thermal runaway propagation in battery modules and packs requires systematic experimental methodologies to evaluate safety risks and mitigation strategies. The following approaches focus on characterization techniques to measure heat generation, propagation pathways, and the effectiveness of containment designs.

Calorimetry techniques provide quantitative data on heat release during thermal runaway. Accelerating rate calorimetry measures the self-heating rate of cells under adiabatic conditions, determining the onset temperature of thermal runaway and total energy release. Bomb calorimetry evaluates the complete energy content of battery materials by combusting samples in a controlled oxygen environment. For module-level testing, large-scale calorimeters with capacities exceeding 1000 liters capture the total heat flux from multiple cells undergoing cascading failure. These systems measure parameters including peak heat generation rate, total energy output, and gas production volumes. Differential scanning calorimetry analyzes material-level exothermic reactions but requires coupling with larger-scale tests for pack-level validation.

Infrared imaging tracks surface temperature distributions during propagation events. High-speed infrared cameras with frame rates above 100 Hz and thermal resolutions under 0.1°C map thermal gradients across cell surfaces and intercell regions. This identifies hot spots where propagation initiates and quantifies heat transfer coefficients between adjacent cells. Emissivity corrections account for varying surface materials, while synchronized visible-light cameras correlate thermal data with physical deformation. Stationary and robotic-mounted systems provide both overview and localized monitoring of pack behavior. Post-processing algorithms calculate propagation velocities between cells by analyzing temperature front movement across predefined regions of interest.

Temperature sensor placement follows strategic patterns to capture critical thermal pathways. Type K or T thermocouples with response times under 500 ms attach to cell casings at predetermined intervals, typically every second cell in large modules. Fiber Bragg grating sensors offer distributed measurements along the entire length of battery strings with millimeter-scale spatial resolution. Sensors position at three key locations: cell-to-cell interfaces, thermal barrier surfaces, and structural weak points in the pack design. Data acquisition systems sample at minimum 10 Hz to resolve rapid temperature spikes during runaway events. Complementary heat flux sensors quantify energy transfer through conduction paths in busbars and cooling plates.

Test protocols for containment designs involve controlled initiation of single-cell thermal runaway. Resistive heaters or nail penetration triggers the initial failure while instrumentation records propagation timing. Containment effectiveness evaluates through three metrics: time delay before adjacent cell ignition, maximum external surface temperature, and structural integrity post-event. Phase change materials undergo testing with standardized heat pulses matching thermal runaway profiles, measuring absorption capacity and duration of temperature stabilization. Containment layers such as ceramic blankets or intumescent materials face repeat testing to assess degradation after multiple exposures.

Propagation delay measurements require synchronized temperature and voltage monitoring across all cells in the test pack. The time difference between trigger cell failure and subsequent cell voltage collapse provides the primary delay metric. Secondary indicators include temperature crossover points where adjacent cells exceed their thermal runaway thresholds. Statistical analysis across multiple trials establishes minimum safe spacing requirements and validates computational models. High-speed pressure sensors complement these measurements by detecting venting events that precede thermal escalation.

Abuse testing protocols standardize initiation methods and environmental conditions. State of charge levels fix at 100% for worst-case scenarios unless testing partial charge effects. Thermal propagation tests conduct in both open atmosphere and enclosed chambers to evaluate different ventilation conditions. Repeat testing under varying ambient temperatures from -20°C to +60°C characterizes environmental influences on propagation rates. Forced convection cooling during tests assesses whether active systems can arrest propagation if detection occurs during early stages.

Gas analysis forms a critical component of propagation studies. Fourier-transform infrared spectroscopy identifies gas species composition during venting, while particulate filters collect ejected solids for mass quantification. Gas volume measurement occurs through displacement apparatus or flow meters in sealed test chambers. These data inform pressure relief requirements and toxicity risks in confined spaces. Synchronization with thermal data reveals correlations between gas release timing and secondary cell ignitions.

Mechanical testing evaluates propagation risks from structural deformation. Crush tests apply progressive loading to packs while monitoring internal short circuits via impedance changes. Vibration tables simulate transportation stresses prior to thermal testing, identifying whether mechanical fatigue lowers propagation thresholds. Post-test X-ray computed tomography scans reveal internal damage patterns that influence heat transfer pathways.

Data acquisition systems for propagation studies require high channel counts and robust synchronization. Minimum specifications include 16-bit resolution, 100 kS/s aggregate sampling, and galvanic isolation for safety. Time-aligned data streams from thermal, electrical, mechanical, and gas sensors enable comprehensive event reconstruction. Automated triggering systems initiate data capture upon detecting predefined voltage drops or temperature thresholds.

Validation testing follows a tiered approach from single cells to full packs. Small modules of 3-5 cells establish baseline propagation characteristics before scaling to larger configurations. Full pack tests verify whether localized protections sufficiently isolate damaged sections. Statistical significance requires multiple trials under identical conditions to account for cell-to-cell variations. Control experiments without mitigation measures provide reference benchmarks for evaluating new designs.

Standardized reporting formats ensure comparability across test programs. Key parameters include propagation speed (cells/minute), maximum achieved temperature, total energy released, and failure containment percentage. Secondary metrics cover gas emission rates, pressure buildup dynamics, and post-event insulation resistance. These datasets feed into safety ratings and inform regulatory test requirements for different battery applications.

The methodologies described enable objective comparison of thermal runaway propagation risks across battery designs. By focusing on measurable physical phenomena rather than material properties, these experimental approaches provide actionable data for improving pack safety architectures. Continuous refinement of test protocols remains essential as battery technologies evolve toward higher energy densities and new form factors.