IEST In‑Situ Gas Evolution Solution Quantifies Thermal Stability of High‑Safety Solid Polymer Electrolytes (AEM 2024)

1. Preface

In 2024, a research team led by Professors Dong-Liang Peng and Qingshui Xie from Xiamen University, in collaboration with Professor Jun Lu’s group from Zhejiang University, published a study in Advanced Energy Materials entitled “Deep Eutectic Solvent-Based Solid Polymer Electrolytes for High-Voltage and High-Safety Lithium Metal Batteries.” This work addresses the critical challenges of flammable electrolytes, unstable interfaces, and restricted ion transport in high‑voltage, high‑safety lithium metal batteries, and proposes a solid polymer electrolyte system based on deep eutectic solvents. The team in‑situ encapsulated a succinonitrile‑based deep eutectic solvent within an ETPTA polymer network, constructing a DES‑ETPTA solid polymer electrolyte that combines high ionic conductivity, favorable lithium metal interfacial stability, and excellent flame‑retardant properties. Further cyanoacrylate copolymerization modification enhanced its oxidative stability in high‑voltage LiCoO₂ cathode systems.

Notably, during the battery safety verification phase, the research team employed the IEST GVM2200 in-situ gas and volume monitor to perform in-situ, continuous, and quantitative monitoring of pouch cell volume changes under high-temperature conditions, providing key evidence for evaluating the solid polymer electrolyte’s ability to suppress thermally induced gas evolution and swelling behavior.

2. Research Background: Why Solid Polymer Electrolytes Need In-Situ Gas Evolution Monitoring

Lithium metal anodes offer compelling theoretical specific capacity (~3,860 mAh g⁻¹) and the lowest electrochemical potential (−3.04 V vs. SHE) of any anode material, making them a central target for next-generation high-energy-density batteries. However, conventional liquid electrolytes pose fundamental safety limitations: flammability, electrolyte decomposition at high temperatures, and gas evolution during thermal abuse or extended cycling all contribute to pouch cell swelling, internal pressure build-up, and potential safety failure.

Solid polymer electrolytes (SPEs) represent a promising pathway to address these safety concerns by replacing flammable liquid electrolytes with mechanically and thermally more stable alternatives. However, objectively characterizing the thermal stability improvement that SPEs provide — specifically, whether and to what degree they suppress thermal-induced gas generation — requires more than combustion tests or post-mortem cell disassembly.

The critical technical gap is clear: conventional observation approaches can only confirm whether a pouch cell has swollen — they cannot answer when gas generation began, at what rate gas accumulated, or how much total volume change occurred. Without this quantitative data, comparing thermal stability across different electrolyte systems remains largely qualitative. This gap is precisely where in-situ volume change measurement becomes indispensable.

3. The DES-ETPTA Solid Polymer Electrolyte: Design and Key Properties

The research team designed the DES-ETPTA solid polymer electrolyte by in-situ encapsulating a succinonitrile (SN)-based deep eutectic solvent within an ethoxylated trimethylolpropane triacrylate (ETPTA) polymer network. This dual-component architecture simultaneously addresses the three principal limitations of existing solid polymer electrolyte systems:

• Ionic conductivity: The deep eutectic solvent component provides ionic transport channels within the polymer matrix, achieving sufficient conductivity for room-temperature operation without liquid plasticizers that would reintroduce flammability risk.
• Lithium metal interface stability: The ETPTA polymer network forms a mechanically stable solid electrolyte interphase (SEI) layer that suppresses lithium dendrite growth during repeated plating and stripping cycles.
• Flame retardancy: By replacing carbonate-based liquid electrolytes with the non-flammable DES component, the DES-ETPTA system substantially reduces electrolyte combustion risk — a key requirement for high-safety lithium metal battery electrolyte design.

To extend the DES-ETPTA electrolyte’s operational voltage window for compatibility with high-voltage LiCoO₂ cathodes (charging to 4.5 V vs. Li/Li⁺), the team incorporated cyanoacrylate copolymerization modification, improving the electrolyte’s oxidative stability at the cathode interface and enabling stable high-voltage LiCoO₂ solid-state battery cycling.

Figure 1. In-situ polymerization of DES-ETPTA solid polymer electrolyte forming stable electrode/electrolyte interfaces for high-voltage, high-safety lithium metal batteries (Xiamen & Zhejiang University, AEM 2024)

3. Liquid Electrolyte vs. Solid Polymer Electrolyte vs. DES-ETPTA: Performance Comparison

4. How IEST GVM2200 In-Situ Gas Evolution Monitoring Provided the Key Evidence

The thermal stability validation phase of the study posed a measurement challenge that conventional characterization methods could not fully resolve. The research team assembled pouch cells using both conventional liquid electrolyte and DES-ETPTA solid polymer electrolyte, then subjected both to controlled high-temperature conditions. Visual observation of the pouch cell exterior (Figures 2a–d) confirmed that the liquid electrolyte cell swelled while the DES-ETPTA cell remained flat — but visual inspection could not answer the quantitative questions that determine scientific and practical value:

• At exactly what temperature or time point does gas evolution begin?
• Is gas accumulation gradual or does it occur in discrete events?
• What is the total volume change, and how large is the difference between the two electrolyte systems?
• Can the safety improvement be expressed as a reproducible, instrument-verifiable number?

To convert these qualitative observations into quantitative, publishable evidence, the research team employed the IEST GVM2200 in-situ gas evolution monitor, which continuously records real-time volume-versus-time curves based on the Archimedes buoyancy principle. This approach transformed the binary question of “did the cell swell?” into a parametric volume change curve, enabling direct, numerical comparison of thermal stability between the liquid and solid electrolyte systems.

The GVM2200 measurement results (Figure 2e) showed clearly that the conventional liquid electrolyte pouch cell exhibited progressive volume increase under high-temperature conditions — consistent with electrolyte thermal decomposition and gas release. In contrast, the DES-ETPTA solid polymer electrolyte pouch cell maintained near-constant volume throughout the same thermal protocol, providing quantitative, instrument-validated evidence that the DES-ETPTA electrolyte effectively suppresses thermal-induced gas generation and cell swelling.

Figure 2. High-temperature pouch cell swelling comparison: liquid electrolyte vs. DES-ETPTA solid polymer electrolyte — visual observation (panels a–d) and in-situ volume change curves measured by IEST GVM2200 (panel e). The DES-ETPTA cell shows near-zero volume change throughout the thermal test.

5. IEST GVM2200: From Qualitative Swelling Observation to Quantitative Volume Change Data

Figure 3. IEST GVM2200 in-situ gas evolution volume monitoring instrument — Archimedes buoyancy principle, continuous real-time pouch cell volume change measurement for battery safety research.

The GVM2200 addresses the measurement gap between “visual observation” and “quantitative safety data” that the Xiamen/Zhejiang University study exemplifies. Applicable test scenarios where the GVM2200 provides irreplaceable quantitative data include:

• High-temperature storage: Continuous pouch cell volume monitoring to identify gas evolution onset temperature and rate during thermal soak tests.
• Overcharge abuse: Real-time tracking of electrolyte decomposition and gas release during voltage overshoot protocols.
• Next-generation anode systems: Gas evolution characterization for silicon-based anodes (volume expansion + SEI gas), high-nickel cathodes (oxygen release), lithium metal batteries, and all-solid-state cells.
• Electrolyte and additive system comparison: Side-by-side quantitative thermal stability evaluation of liquid electrolytes, solid polymer electrolytes, and semi-solid hybrid systems — as demonstrated in this AEM 2024 study.
• Material-to-cell validation: In-situ volume change evaluation from electrode material development stage through pouch cell verification, enabling early-stage safety screening.

6. Summary

The AEM 2024 study from Xiamen University and Zhejiang University demonstrates that deep eutectic solvent-based solid polymer electrolytes represent a credible pathway toward high-safety, high-voltage lithium metal batteries. The DES-ETPTA electrolyte system delivers simultaneous improvements across the critical safety dimensions: it suppresses thermal gas evolution, maintains stable lithium metal interfaces, reduces flammability, and extends operational voltage to 4.5 V for LiCoO₂ compatibility.

The IEST GVM2200 in-situ gas evolution monitoring instrument provided the quantitative experimental foundation for the thermal safety comparison in this study — converting the observation “DES-ETPTA does not swell” from a qualitative visual impression into a parametric volume-time curve with clear numerical differentiation from the liquid electrolyte baseline. As solid polymer electrolyte research advances and increasingly subtle safety improvements need to be distinguished between candidate materials, in-situ volume change monitoring with quantitative, continuous measurement capability becomes not a supplementary technique but a primary characterization method.

7. Original Article

C. Zhang, H. Zheng, L. Lin, J. Wen, S. Zhang, X. Hu, D. Zhou, B. Sa, L. Wang, J. Lin, Q. Xie, D.-L. Peng, J. Lu, Deep Eutectic Solvent-Based Solid Polymer Electrolytes for High-Voltage and High-Safety Lithium Metal Batteries. Adv. Energy Mater.2024, 14, 2401324. 

8. FAQs