How to Enhance Battery Safety by Evaluating Materials’ Thermal Stability

From fast-charging phones to long-distance electric vehicles, battery innovations are continuously improving various aspects of daily life. However, battery research is beholden to one critical factor: safety.

Lithium-ion batteries are especially prone to thermal runaway events, which can be caused through mechanical, thermal, or electrical abuses. For example, if a battery pack’s thermal management system fails and the cell overheats, its temperature can rise beyond safe conditions, leading to thermal runaway and pressure increases that can trigger an explosion and/or fire. Or a chemicals reaction inside the battery can release significant amounts of heat to further an exothermic reaction, potentially causing unwanted reactions and thermal runaway.

In order to ensure end-use safety, battery developers need to be able to answer: When my battery heats up, what reactions happen at what temperature? What gasses are released?

Battery researchers utilize two material analysis techniques to analyze battery reactions and prevent safety issues: Differential Scanning Calorimetry and Thermogravimetric Analysis with Evolved Gas Analysis.

Differential Scanning Calorimetry (DSC) measures temperatures and heat flows associated with thermal transitions in a material. In battery safety testing, DSC is a critical technique for assessing:

• Thermal stability of battery materials
• Onset of exothermic reactions
• Heat of reactions and transitions (enthalpy)
• Specific heat capacity
• Safety across different states of charge

Battery materials can be tested in sealed, high-pressure DSC capsules, which capture the full heat of the decomposition or chemical reaction. In the example below, a lithium nickel manganese cobalt (NMC) cathode and graphite anode were tested in a high-pressure capsule at 100% state-of-charge (SOC).

Source: Safety Evaluation of Lithium-ion Battery Cathode and Anode Materials Using Differential Scanning Calorimetry

Both the NMC cathode and graphite anode have exothermic reactions taking place, but the energy difference and the character of the exotherms are quite different. The difference in peak locations indicated different on reaction mechanisms. The anode has about 300 J/g of energy released. The cathode has 1.6 kJ/g of energy released, with three separate exotherms revealing three separate decomposition events. The cathode is releasing more energy and driving thermal runaway.

The high sensitivity and excellent baseline flatness on the Discovery DSC reveals that the anode material actually begins to decompose first. At around 82 °C, the anode has an onset of exothermic activity, which is the degradation of the solid electrolyte interface (SEI). Even though the cathode material has more energy release and a more complex transition, it’s the degradation of the SEI early on in the anode which initiates these reactions.

Researchers from Sandia National Laboratory and University of Maryland use a Discovery DSC to assess heat flow of battery components and combinations of components¹ as well as determine the onset temperature of exothermic reactions, heat flow, and the total heat released.² Their studies are facilitated by the Discovery DSC’s high sensitivity to detect onset temperatures and accurate heat flows.

Thermogravimetric Analysis (TGA) measures weight change (loss or gain) and the rate of weight change as a function of temperature, time, and atmosphere. TGA traditionally measures weight loss during a heating ramp, capturing the onset of degradation, quantifying total loss of degradation byproducts, and characterizing relative thermal stability between samples. Battery research benefits from TGA’s assessment of the:

• Thermal and oxidative stability of materials
• Decomposition kinetics
• Off-gasses produced

In the example below, the thermal degradation of three NMC cathode materials were studied at different states of charge under high temperatures. TGA measured their weight change, shown as a percentage of weight lost, and the derivative of the weight change is shown. To understand how both state-of-charge (SOC) and NMC decomposition mechanisms influence thermal stability of the cathode, TGA was coupled with mass spectrometry (MS).

Source: Thermal Degradation and Evolved Gas Analysis of Lithium-Ion Battery Cathode Materials at Different States of Charge

Simultaneously with the heating ramp, MS measured the oxygen released from the sample. The chart shows that NMC at 100-SOC has a weight loss derivative correlating with high oxygen release, indicating that the loss of oxygen from the NMC sample is a large factor in the observed weight loss over the whole thermal degradation.

The large amount of oxygen release from the high SOC battery will act as fuel for a battery fire. The production of these gases is a major reason why battery fires are difficult to extinguish. Battery developers need this information to understand and mitigate such safety risks.

Researchers used a TA Instruments TGA to assess their new electrolyte and separator for high temperature battery operation.³ Their system was shown to operate at 120 °C with excellent cyclability, which is significantly above the operation temperature of a traditional lithium-ion battery. Their work illustrates the importance of carefully studying new battery formats’ safety under high temperatures.

Despite its advantages, TGA comes with some challenges when testing battery materials due to their sensitivity, which historically necessitated placing the entire TGA in a glovebox to maintain sample integrity. New TGA Smart Seal Pans allow researchers to load moisture- or air-sensitive samples within a glovebox and then run tests on a benchtop-installed Discovery TGA, where the sealed pan will automatically open at around 55°C.

As the examples above illustrate, DSC and TGA are essential techniques to characterize battery safety. DSC’s insights into heat flow and thermal stability support safety predictions and operating condition recommendations, while TGA supports decomposition assessment and off-gas analysis when coupled with MS. Many battery researchers combine DSC and TGA to gain a complete understanding of their battery’s safety and reaction mechanisms.

For more information and detailed analysis, watch Applications Scientist Gray Slough’s battery safety webinar. Learn more about TA Instruments’ battery characterization solutions, find the right technique for you in our selection guide, or contact TA Instruments’ experts for personalized recommendations to enhance your battery safety testing.

1. Johnson, N. B.; Bhargava, B.; Chang, J.; Zaman, S.; Schubert, W.; Albertus, P. Assessing the Thermal Safety of a Li Metal Solid-State Battery Material Set Using Differential Scanning Calorimetry. ACS Applied Materials & Interfaces 2023. https://doi.org/10.1021/acsami.3c13344.
2. Wang, Z.; Bhargava, B.; Johnson, N. B.; Bates, A. M.; Torres-Castro, L.; Petracci, M. F.; McKee, M. G.; Schubert, W.; Zaman, S.; Albertus, P. Early-Stage Thermal Safety Evaluation of the NMC811/LLZO/Li Solid-State Battery Chemistry Using Calorimetry and Characterization Methods. ACS Applied Materials & Interfaces 2025. https://doi.org/10.1021/acsami.5c13030.
3. Kohlmeyer, R. R.; Horrocks, G. A.; Blake, A. J.; Yu, Z.; Maruyama, B.; Huang, H.; Durstock, M. F. Pushing the Thermal Limits of Li-Ion Batteries. Nano Energy 2019, 64, 103927. https://doi.org/10.1016/j.nanoen.2019.103927.