Thermal Runaway Testing for New Energy Vehicle Batteries: Standards, Methods, and Requirements

Thermal runaway testing is one of the most critical safety evaluations for lithium-ion power batteries used in new energy vehicles (NEVs), verifying that cells, modules, and packs do not catch fire or explode under abuse conditions. Performed by accredited third-party laboratories in accordance with standards such as GB 38031, IEC 62660-3, SAE J2464, and UL 2580, these tests characterize thermal runaway triggering, temperature rise behavior, gas venting, and cell-to-cell thermal propagation. This article explains the applicable standards, sample requirements, test items, methods, and typical applications of NEV battery thermal runaway testing.

Technical Overview

Thermal runaway is a self-accelerating exothermic failure process in lithium-ion batteries. It typically begins with the decomposition of the solid electrolyte interphase (SEI) layer at approximately 90–120 °C, followed by separator shrinkage or melting, chemical reactions between the anode and electrolyte, cathode material decomposition with oxygen release, and finally combustion of the vented flammable gases. Once initiated, thermal runaway can propagate from a single cell to neighboring cells, resulting in fire or explosion of the entire battery pack.

Thermal runaway testing simulates internal and external abuse conditions in a controlled laboratory environment to determine how easily a battery enters thermal runaway, how violently it releases energy, and whether thermal propagation can be contained. In China, GB 38031-2020 is the mandatory national standard for electric vehicle power battery safety. It requires that, after thermal runaway is triggered, the battery provides a warning signal at least five minutes before any fire or explosion occurs, allowing occupants to evacuate safely. The revised GB 38031-2025 standard further tightens the requirement to no fire and no explosion after thermal runaway is triggered, with an extended observation period.

Internationally, thermal runaway and thermal propagation requirements are addressed in standards and regulations including UN Regulation No. 100, IEC 62660-3, UL 2580, SAE J2464, and ISO 6469-1. Accredited third-party laboratories conduct these tests to support type approval, research and development validation, and post-incident failure analysis.

Testing Samples

Battery Cells

Single lithium-ion cells in cylindrical, prismatic, or pouch formats, covering mainstream chemistries such as lithium iron phosphate (LFP) and nickel-cobalt-manganese (NCM/NMC). Cell-level testing determines the fundamental thermal runaway characteristics, including onset temperature, maximum surface temperature, temperature rise rate, and venting behavior. Cells are typically tested at 100% state of charge (SOC) as required by GB 38031.

Battery Modules

Modules consisting of multiple cells assembled with busbars, cell-to-cell thermal barriers, and thermal management interfaces. Module-level testing evaluates how thermal runaway initiated in one cell propagates through the module structure and whether inter-cell insulation materials, aerogel pads, or cooling plates effectively delay or prevent propagation.

Battery Packs

Complete battery packs including the battery management system (BMS), housing, coolant circuits, venting channels, and safety devices. Pack-level thermal propagation testing is the key compliance item for GB 38031, because it verifies system-level protective design under realistic installation conditions with all control and warning functions active.

Testing Items

Core thermal runaway related test items include:

• Cell thermal runaway trigger testing (nail penetration, external heating, and overcharge triggering methods)
• Thermal runaway characteristic parameter measurement (onset temperature, trigger time, maximum temperature, temperature rise rate dT/dt)
• Thermal propagation testing at module and pack level
• Overcharge and forced discharge abuse testing
• External short circuit testing
• Thermal abuse (heating) testing
• Crush and mechanical abuse testing related to internal short circuit initiation
• Vented gas composition and volume analysis (hydrogen, carbon monoxide, carbon dioxide, methane, electrolyte vapors)
• Material-level thermal stability evaluation using adiabatic calorimetry (ARC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA)
• Post-test teardown inspection and failure analysis

Testing Methods

Sample Conditioning and Instrumentation

Samples are charged to 100% SOC in accordance with the manufacturer's specified procedure and stabilized at ambient temperature, typically 25 ± 2 °C. Thermocouples are attached to cell surfaces, busbars, and module housings; voltage monitoring lines are connected to each cell; and gas sensors, pressure transducers, and high-speed cameras are installed. All tests are performed inside a blast-resistant, ventilated test chamber with remote data acquisition, explosion-proof lighting, and exhaust gas treatment to protect laboratory personnel.

Thermal Runaway Trigger Methods

GB 38031 permits several trigger methods, and the laboratory selects the method that most reliably initiates thermal runaway for the specific cell design. Nail penetration uses a steel nail of defined diameter driven into the cell at a controlled speed to create an internal short circuit. The heating method uses film heaters or heating rods to raise the cell temperature beyond the decomposition onset point. The overcharge method drives the cell far beyond its specified charge limit until thermal runaway occurs. Trigger success is verified by the detection criteria described below.

Thermal Runaway Detection Criteria

Thermal runaway is considered triggered when one or more of the following criteria are met: a rapid collapse of cell voltage (for example, a voltage drop rate exceeding approximately 1 V/s), a surface temperature rise rate dT/dt of at least 1 °C/s measured by thermocouple, or the cell surface temperature exceeding the maximum operating temperature specified by the manufacturer. The exact moment of triggering is recorded together with venting, smoking, jet flame, and pressure release events.

Thermal Propagation Evaluation

In the propagation test, thermal runaway is triggered in a single cell, usually selected at the most thermally vulnerable location within the pack. Engineers continuously monitor the temperatures of adjacent cells, gas concentrations inside the pack enclosure, BMS warning signals, and any visible fire, explosion, or smoke. Under GB 38031-2020, the pack must remain free of fire and explosion for at least five minutes after issuing a warning signal to the vehicle occupants. Under GB 38031-2025, the strengthened requirement is no fire and no explosion after triggering, verified over the specified observation window. A complete test report documents trigger conditions, propagation timelines, temperature distribution, gas evolution, and video records.

Applications

Thermal runaway testing supports multiple engineering and compliance objectives across the NEV industry:

• Mandatory type approval and market access for electric vehicles in China under GB 38031
• International homologation and export certification under UN R100, IEC 62660-3, and UL 2580
• Research and development validation of cell chemistry, separator materials, thermal insulation layers, and pack venting design
• Verification of BMS thermal warning functions and thermal management system performance
• Supplier quality control, incoming inspection, and batch safety consistency evaluation
• Forensic investigation of field incidents, root cause analysis, and recall support
• Safety assessment for battery transport, storage, and second-life applications

FAQ

Which standards govern thermal runaway testing of new energy vehicle batteries?

In China, GB 38031-2020 is the mandatory national standard, and the upgraded GB 38031-2025 version further requires no fire and no explosion after thermal runaway. Related international references include UN Regulation No. 100, IEC 62660-3, UL 2580, SAE J2464, and ISO 6469-1. Accredited third-party laboratories can advise on the correct standard combination for a target market.

At what state of charge are samples tested?

Thermal runaway and thermal propagation tests under GB 38031 are conducted at 100% SOC, which represents the most energetic and worst-case condition. Some development-oriented studies additionally evaluate lower SOC levels to characterize the relationship between stored energy and runaway severity.

How is thermal runaway confirmed during a test?

Thermal runaway confirmation relies on objective detection criteria: a sharp voltage drop, a surface temperature rise rate of at least 1 °C/s, or the surface temperature exceeding the manufacturer's specified maximum, supplemented by visual evidence such as venting, smoke, or flame.

What are the pass criteria for the thermal propagation test?

Under GB 38031-2020, the battery must provide a thermal event warning at least five minutes before any fire or explosion, with no fire or explosion within five minutes after the warning. The revised GB 38031-2025 standard eliminates the five-minute allowance and requires no fire and no explosion after thermal runaway is triggered.

How many samples are required and how long does testing take?

Sample quantities depend on the test level and standard requirements, typically covering multiple cells plus one or more modules or packs for propagation evaluation. After sample conditioning and instrumentation, a single propagation test is usually completed within one to several days, while a full test program including reporting generally takes several weeks. Accredited third-party laboratories provide project-specific schedules.

What safety precautions are taken in the laboratory?

Tests are conducted in reinforced explosion-proof chambers with controlled ventilation, exhaust gas scrubbing, fire suppression systems, fully remote instrumentation, and dedicated emergency response procedures, ensuring that even violent thermal runaway events are contained safely.