Determination of Gas Evolution from Thermal Decomposition of Solid-State Electrolytes: Methods, Stan

Gas evolution during thermal decomposition is a critical safety and quality parameter for solid-state electrolytes used in next-generation lithium batteries. This article outlines professional laboratory approaches—including TG-MS evolved gas analysis, sealed-vessel manometry, and GC-MS quantification—for measuring total gas release and identifying decomposition products such as H2S, SO2, CO2, CO, and light hydrocarbons. It covers sample types, testing items, methodologies, applicable standards frameworks, and practical applications in battery safety assessment.

Technical Overview

Solid-state electrolytes (SSEs), including sulfide, oxide, polymer, and halide material families, are enabling the development of all-solid-state lithium batteries with improved energy density and intrinsic safety. However, when these materials are exposed to elevated temperatures—whether from external abuse, internal short circuits, or thermal runaway propagation—they can undergo decomposition reactions that release gaseous products. Sulfide electrolytes may generate highly toxic H2S even at ambient temperature upon contact with moisture, while polymer and composite systems can release flammable hydrocarbons, CO, and hydrogen at higher temperatures. Quantifying the total gas volume and its composition is therefore essential for hazard classification, vent-gas prediction, cell and pack design, and comparative material screening.

Determination of thermal decomposition gas evolution is typically performed by accredited third-party laboratories and battery research institutions using coupled thermal analysis and gas measurement techniques. Results are expressed as total gas volume normalized to sample mass (mL/g at STP or mmol/g) together with a temperature-resolved profile of each detected gas species. Because no single international standard is dedicated exclusively to SSE gas evolution, laboratories apply validated procedures aligned with established thermal analysis and battery safety standards, including ASTM E1131, ASTM E2550, ISO 11358-1, IEC 62133-2, IEC 62660-3, UL 9540A, and GB 38031.

Testing Samples

Sulfide Solid Electrolytes

Sulfide-based materials such as argyrodite Li6PS5Cl, Li10GeP2S12 (LGPS-type), Li3PS4, and Li7P3S11 glass-ceramics are the most gas-sensitive SSE family. Testing evaluates both moisture-triggered H2S release at ambient conditions and high-temperature decomposition gases such as SO2, COS, and CS2. Samples are handled and sealed under inert atmosphere (glovebox with water and oxygen content below 1 ppm) to prevent uncontrolled pre-reaction.

Oxide Solid Electrolytes

Garnet-type LLZO (Li7La3Zr2O12), NASICON-type LATP and LAGP, and perovskite LLTO ceramics are chemically stable and generate minimal gas. Testing focuses on decomposition of surface lithium carbonate or residual organics, typically releasing CO2, and confirms the low gas signature that qualifies these materials for high-temperature applications.

Polymer and Composite Electrolytes

PEO-LiTFSI, PVDF-based, PAN-based, and ceramic-polymer composite membranes undergo chain scission and side reactions on heating, releasing H2O, CO2, CO, ethylene, methane, light hydrocarbons, and in fluorinated systems potentially HF. Sample films are tested as received or after controlled conditioning.

Halide and Emerging Electrolytes

Materials such as Li3InCl6 and Li3YCl6 combine moderate thermal stability with strong hygroscopicity, and testing addresses moisture-driven HCl-bearing gas release as well as high-temperature decomposition behavior.

Cell-Level and Composite Specimens

Cathode-electrolyte composites, bilayer separators, and small-format prototype cells or cell fragments can be tested to capture gas generation from interfacial side reactions that powder-level testing cannot reproduce.

Testing Items

Core measurable parameters delivered in a standard test report include:

• Total gas evolution volume (mL/g at STP or mmol/g) over a defined temperature program
• Gas species identification and quantitative breakdown (H2S, SO2, COS, CS2, CO2, CO, H2, CH4, C2H4, C2H6, H2O, HF, HCl)
• Onset temperature of gas release and peak gas evolution temperature
• Temperature-resolved gas evolution rate profiles
• Sealed-vessel pressure rise (kPa or MPa) under adiabatic or programmed heating
• Ambient-temperature H2S release upon controlled humidity exposure (for sulfides)
• Mass loss curve and residue yield by thermogravimetric analysis

Testing Methods

Thermogravimetric Analysis Coupled with Mass Spectrometry (TG-MS)

A small sample (typically 10–100 mg) is heated at 5–10 °C/min under flowing argon or nitrogen from room temperature to 600–800 °C. Evolved gases are transferred through a heated capillary to a quadrupole mass spectrometer, which monitors characteristic mass-to-charge fragments in real time. This method simultaneously yields mass loss (per ASTM E1131 and ISO 11358-1 conventions) and temperature-resolved identification of evolved species, making it the primary screening technique for thermal stability per ASTM E2550.

Sealed-Vessel Manometric (Volumetric) Method

A larger sample charge (0.5–5 g) is sealed in a pressure-rated stainless-steel or Hastelloy-type autoclave fitted with a calibrated pressure transducer and thermocouple. The vessel is heated under a programmed or adiabatic profile, and the pressure increase is converted to total moles of gas via the ideal gas law with thermal expansion correction and blank subtraction. This closed-system approach reproduces confined-cell conditions and provides the most direct measurement of total gas quantity.

Gas Chromatography and GC-MS Analysis of Collected Gases

Gas accumulated in the sealed vessel or captured in inert gas sampling bags is analyzed by gas chromatography with thermal conductivity, flame ionization, sulfur chemiluminescence, or mass spectrometric detection. Certified calibration gas mixtures enable quantification of permanent gases (H2, CO, CO2, CH4, C2H4) and sulfur species (H2S, SO2, COS, CS2) down to low ppm levels.

Targeted H2S and Corrosive Gas Quantification

Because of its toxicity, H2S from sulfide electrolytes is specifically quantified using electrochemical sensors, colorimetric detector tubes, or absorption into buffered solution followed by ion chromatography or spectrophotometric sulfide determination. Complementary FTIR or non-dispersive infrared analysis is used for CO2, CO, SO2, and moisture.

Accelerating Rate Calorimetry with Gas Collection

Adiabatic calorimetry following the philosophy of UL 9540A and IEC 62660-3 thermal abuse testing determines self-heating onset temperature, thermal runaway trigger temperature, and maximum temperature and pressure rise, with vent gas collected for subsequent compositional analysis.

Quality Assurance

All procedures incorporate instrument calibration with certified gas standards, blank and reference-material runs, duplicate testing for repeatability verification, and full chain-of-custody documentation for moisture-sensitive samples prepared under inert atmosphere.

Applications

Gas evolution data from thermal decomposition testing supports the full lifecycle of solid-state battery development:

• Comparative screening and selection of sulfide, oxide, halide, and polymer electrolytes by inherent gas hazard
• Safety assessment and abuse testing of all-solid-state cells in the context of IEC 62133-2, IEC 62660-3, UL 9540A, and GB 38031 compliance programs
• Thermal runaway modeling, vent-gas prediction, and pressure-relief or packaging design for modules and packs
• Manufacturing process safety, including dry-room H2S exposure limits and ventilation engineering controls
• Batch-to-batch quality control and incoming material release for electrolyte production
• Root-cause investigation of field failures, storage degradation, and transport incidents
• Research into interfacial stability between electrolytes and electrode active materials

FAQ

Why is gas evolution measurement important if solid-state batteries contain no flammable liquid electrolyte?

Although SSEs eliminate volatile organic solvents, they are not gas-inert. Sulfide electrolytes can release highly toxic H2S with even trace moisture, and polymer binders or composites can generate flammable gases during thermal abuse. Quantifying this gas release is essential for genuine safety claims, ventilation design, and regulatory compliance.

What gases are typically detected?

Sulfide systems predominantly release H2S, SO2, COS, and CS2; polymer systems release H2O, CO2, CO, H2, methane, and light hydrocarbons, with HF possible from fluorinated polymers; oxide ceramics typically show only minor CO2 from surface carbonate decomposition.

How much sample is required?

TG-MS screening requires roughly 10–100 mg, while sealed-vessel manometric and GC-based quantification typically uses 0.5–5 g per test to ensure measurable pressure rise and sufficient gas volume for compositional analysis.

What temperature range and heating rates are used?

Standard programs cover room temperature to 600 °C at 5–10 °C/min under inert purge; adiabatic calorimetry follows self-heating to beyond 800 °C or until cell destruction, depending on the safety question being addressed.

How are moisture-sensitive sulfide samples protected during testing?

Samples are loaded inside argon-filled gloveboxes, sealed in gas-tight transfer vessels or hermetic pans, and never exposed to ambient humidity before the test begins, ensuring that measured gas generation reflects true thermal decomposition rather than uncontrolled hydrolysis.

What is the difference between open (flowing-gas) and closed (sealed-vessel) testing?

Open-system TG-MS provides the richest compositional and temperature-resolved information but can underrepresent total volume for condensable species; closed-vessel manometry gives the most accurate total gas quantity and pressure behavior under confined conditions. A combined test program delivers the most complete safety picture.

How are results reported?

Reports present total gas volume normalized to sample mass, quantitative composition of each detected species, onset and peak gas evolution temperatures, pressure rise curves, thermogravimetric mass loss, instrumentation and calibration details, and interpretation relative to the client's safety or design objectives.