How Dynamic Mechanical Analysis Ensures Battery Safety, from Thin Film Separators to Solid Electrolytes

As lithium-ion batteries evolve to meet demands for increased energy density, safety, and form factor versatility, one component remains central to their capacity and reliability: the separator. Whether in conventional liquid electrolyte systems or emerging architectures such as gel polymer electrolytes and solid electrolytes, these thin film materials’ thermal stability and mechanical resilience play a critical role in battery performance.

Researchers are pushing the boundaries of battery design with new thinner and lighter separators, but these pose new challenges in mechanical strength and safety. This blog will explore the unique testing considerations for new electrolyte designs and how mechanical analysis supports cutting-edge battery development.

Separators are critical to battery function, serving as the physical barrier between electrodes while allowing ions to pass through for charge and discharge cycles. Put simply, the entire battery’s electrochemical reaction revolves around the separator fulfilling its function as a semi-porous membrane.

Thin film separators offer three major advantages, identified by Zong et. al.: high energy density, low internal resistance, and low material cost.¹ While all separators are prone to shrinking and deforming under elevated temperatures, thinner separators have reduced mechanical strength and puncture strength, increasing the likelihood of a mechanical failure that can lead to a short circuit. Additionally, separators interact with the liquid electrolyte, which can alter their mechanical behavior. Solvents and salts can plasticize the separator material, reducing its stiffness and increasing its susceptibility to deformation.² Therefore, separators need to be evaluated both independently and in solution for complete characterization.

Another approach to improving battery energy density is replacing the flammable liquid electrolyte and separator with solid electrolytes in solid-state batteries (SSBs). This technology offers numerous benefits, including the potential for a wider operating temperature, increased safety, higher energy density, and faster charging than traditional Li-ion batteries. The majority of failures in SSBs are due to mechanical failure, highlighting the importance of considering the mechanical response to strain.³ Gel polymer electrolytes are a hybrid material where a polymer matrix contains a liquid electrolyte, often referred to as semi-solid-state batteries. Gel polymer electrolytes similarly offer advantages in performance as well as mechanical flexibility in bending.⁴

Ensuring thin separator efficacy and safety requires predicting how they will deform under application-relevant conditions. Enter Dynamic Mechanical Analysis (DMA), a thermal analysis technique that measures how materials respond to stress, stain, and temperature over time.

DMA is the ideal technique to simulate battery operating temperatures and mechanical loads, helping researchers assess whether a separator will maintain its integrity or fail. Battery researchers use DMA to measure the following separator properties:

• Storage and Loss Moduli: Measure materials stiffness and energy dissipation or damping
• Glass Transition Temperature (Tg): The temperature at which the separator transitions from rigid to rubbery
• Creep and Stress Relaxation: Time-dependent mechanical properties of materials under applied load or stain
• Fatigue: Determining how a product responds to a repeated (cyclic) load

Thin films, including thin separator materials, can be loaded in a tensile clamp on a TA Instruments DMA, measuring mechanical properties as the samples are heated to predict the separator behavior under extreme conditions as demonstrated by Yan et. al.⁵

Separators can also be evaluated in solution on a TA Instruments DMA, as demonstrated by Sheidaei et. al.⁶ Testing in solution is especially important since research demonstrates that electrolyte solutions have a significant impact on the mechanical properties of submersed separators.

DMA also measures tensile strength and Young’s modulus, both of which predict the mechanical strength of the separator by evaluating the deformation (yield) point and breakage point.⁶ Storage modulus is another important measurement from DMA, as it indicates softening and melting under elevated temperatures.⁷

TA Instruments offers three instruments suitable for DMA testing of novel separators and solid electrolytes:

The DMA 850 is frequently used by battery scientists focused on modulus, viscoelastic profiling, and routine mechanical testing. Dynamic mechanical analyzers offer a comprehensive view of separators’ mechanical and thermal properties, helping researchers ensure their thin film materials are ready to perform under realistic application conditions.

The RSA-G2 is a high-precision instrument for the mechanical analysis of solids. Its dual-head design enables precise control of deformation and stress measurement, delivering purer mechanical data. This instrument is suited for researchers focused on complex mechanical simulations, as it was used by Ihuaenyi et. al for testing separators in a solvent bath.³ The RSA-G2 also offers dielectric thermal analysis (DETA) for simultaneous electrical and mechanical characterization of materials.

Another option is the Discovery Hybrid Rheometer: a versatile, high-precision instrument that measures materials’ flow and deformation. In addition to DMA mode, hybrid rheometers are excellent for optimizing electrode slurries including simultaneous rheological and electrical measurements with the Rheo-Impedance and dielectric accessory. It is ideal for studying gel polymer electrolytes’ viscoelastic properties under shear, tension and compression.

As battery technology advances with thinner separators and innovative electrolytes, mechanical integrity becomes more critical than ever. Thin film separators enable higher energy density but are more prone to mechanical and thermal degradation. Solid-state batteries introduce rigid interfaces that are susceptible to cracking and delamination, while gel polymer electrolytes offer flexibility but require careful viscoelastic profiling.

Researchers use TA Instruments to simulate real-world battery conditions—such as elevated temperatures, mechanical stress, and electrolyte exposure—and quantify how these materials respond, ensuring they meet safety and performance standards. DMA offers a robust, reliable method to evaluate separator performance under realistic conditions, ensuring that innovation in battery energy density does not sacrifice safety or performance.

Instruments like the TA Instruments DMA 850, RSA-G2, and Hybrid Rheometer with DMA mode offer high-precision capabilities tailored to battery research. Whether assessing mechanical strength during cycling or predicting softening and failure, DMA empowers scientists to design robust separators and solid electrolyte systems that support the next generation of high-performance, safer batteries.

1. Zhong, S.; Yuan, B.; Guang, Z.; Chen, D.; Li, Q.; Dong, L.; Ji, Y.; Dong, Y.; Han, J.; He, W. Recent progress in thin separators for upgraded lithium ion batteries. Energy Storage Materials 2021, 41. https://doi.org/10.1016/j.ensm.2021.07.028
2. Ihuaenyi, R.C.; Deng, J.; Bae, C.; Xiao, X. A Coupled Nonlinear Viscoelastic–Viscoplastic Thermomechanical Model for Polymeric Lithium-Ion Battery Separators. Batteries 2023, 9, 475. https://doi.org/10.3390/batteries9090475
3. Castillo, J.; Santiago, A.; Judez, X.; Garbayo, I.; Clemente, J. A. C.; Morant-Miñana, M. A.; Villaverde, A.; González-Marcos, J.A.; Zhang, H.; Armand, M.; Li, C. Safe, Flexible, and High-Performing Gel-Polymer Electrolyte for Rechargeable Lithium Metal Batteries. Chemistry of Materials 2021 33 (22), 8812-8821. https://doi.org/10.1021/acs.chemmater.1c02952
4. Yan, S.; Deng, J.; Bae, C.; Xiao, X. Thermal expansion/shrinkage measurement of battery separators using a dynamic mechanical analyzer. Polymer Testing 2018 71, 65-71. https://doi.org/10.1016/j.polymertesting.2018.08.028
5. Sheidaei, A.; Xiao, X.; Huang, X.; Hitt, J. Mechanical behavior of a battery separator in electrolyte solutions. Journal of Power Sources 2011 196, 20, 8728-8734. https://doi.org/10.1016/j.jpowsour.2011.06.026
6. Browne, J. Thermal Analysis of Battery Separator Film. Waters TA Instruments 2023. https://www.tainstruments.com/applications-notes/thermal-analysis-of-battery-separator-film/
7. Vail, J.; Janisse, A.; Dennis, K.; Lau, H. Battery Separator Film Development: Impact of Coating. Waters TA Instruments 2023. https://www.tainstruments.com/applications-notes/battery-separator-film-development-impact-of-coating/