Quantitative Analysis of Gases Released from Thermal Decomposition of Solid-State Electrolytes

Quantitative analysis of gases released during the thermal decomposition of solid-state electrolytes is essential for evaluating the safety of next-generation solid-state batteries. Using hyphenated evolved gas analysis techniques such as TGA-MS, TGA-FTIR, and pyrolysis-GC/MS, accredited third-party laboratories can identify gas species, determine onset temperatures, and precisely quantify gas volumes across sulfide, oxide, polymer, and halide electrolyte systems. This article outlines the sample types, testing items, analytical methods, and applications of solid-state electrolyte thermal decomposition gas quantification for battery R&D, safety assessment, and regulatory compliance.

Technical Overview

Solid-state electrolytes (SSEs), spanning sulfide, oxide, polymer, and halide chemistries, are central to the development of next-generation lithium batteries with higher energy density and improved safety margins. Although these materials eliminate the flammable carbonate solvents found in conventional liquid electrolytes, they are not chemically inert under thermal stress. When heated to elevated temperatures, or when a cell enters thermal runaway, solid-state electrolytes can decompose and release significant quantities of toxic, corrosive, or flammable gases.

The gas-release profile differs sharply by chemistry. Sulfide electrolytes such as argyrodite Li6PS5Cl and Li10GeP2S12 are particularly gas-active, evolving hydrogen sulfide (H2S), sulfur dioxide (SO2), and carbonyl sulfide (COS) upon heating, and even upon exposure to trace moisture. Polymer and composite electrolytes depolymerize to yield CO, CO2, methane, ethylene, and heavier hydrocarbon fragments. Halide electrolytes may release chlorine- or bromine-containing corrosive species, while oxide ceramics such as LLZO remain largely stable, emitting only trace gases at extreme temperatures. Quantifying these emissions is therefore a prerequisite for toxicity assessment, flammability evaluation, and thermal runaway propagation modeling.

Quantitative evolved gas analysis (EGA) couples thermogravimetric analysis (TGA) with mass spectrometry (MS), Fourier-transform infrared spectroscopy (FTIR), or gas chromatography-mass spectrometry (GC/MS) to identify each gas species, determine onset temperatures, and measure cumulative gas volumes. Testing is typically performed by accredited third-party laboratories in accordance with internationally recognized frameworks such as ISO 11358, ASTM E1131, and ASTM E2105, and supports compliance with battery safety standards including GB 38031, IEC 62660-3, and UL-based certification schemes.

Testing Samples

Sulfide Solid Electrolytes

Argyrodite-type Li6PS5Cl, LGPS-type Li10GeP2S12, glass-ceramic Li7P3S11, and Li3PS4 systems represent the highest-priority samples for toxic gas quantification. These materials are highly moisture-sensitive, so samples are sealed under inert atmosphere and transferred via glovebox handling to prevent pre-test hydrolysis and uncontrolled H2S generation.

Oxide Solid Electrolytes

Garnet-type Li7La3Zr2O12 (LLZO), NASICON-type LATP and LAGP, and perovskite-type LLTO are supplied as powders, sintered pellets, or thin films. Testing establishes the baseline thermal stability of these ceramics and detects trace O2, CO2, and H2O released from surface carbonates, adsorbed moisture, and residual organics from processing.

Polymer and Composite Solid Electrolytes

PEO-lithium salt complexes, PVDF-, PAN-, and PMMA-based systems, as well as ceramic-in-polymer and polymer-in-ceramic composites, are analyzed for organic decomposition products. Decomposition of the polymer matrix and lithium salts such as LiTFSI can release hydrocarbon fragments, CO, CO2, SO2, and fluorinated compounds at moderate temperatures.

Halide Solid Electrolytes

Emerging halide systems including Li3InCl6, Li3YCl6, and Li3YBr6 are strongly hygroscopic. Quantitative gas testing characterizes both moisture-driven hydrolysis products and thermally induced release of chlorine- and bromine-containing corrosive species.

Sample Forms and Preparation

Acceptable sample forms include powders, pressed pellets, freestanding membranes, coated separators, and materials harvested from fresh, aged, cycled, or abuse-tested cells. Typical sample mass is 5–50 mg per run, with larger formats sub-sampled to ensure representativeness. All moisture- and oxygen-sensitive materials are documented for storage history and atmosphere exposure.

Testing Items

A comprehensive quantitative gas analysis program for solid-state electrolyte thermal decomposition delivers the following measurable results:

• Qualitative identification of evolved gas species, including H2, H2O, O2, CO, CO2, CH4, C2H4, H2S, SO2, COS, CS2, HF, HCl, NH3, and hydrocarbon fragments
• Quantitative determination of instantaneous gas concentration (ppm to vol%) and cumulative release volume (mL/g or mmol/g)
• Onset temperature and peak release temperature for each detected gas species
• Gas evolution rate profiles as a function of temperature and time
• Simultaneous mass loss curve, decomposition stages, and residual mass from TGA measurement
• Moisture-triggered H2S release quantification for sulfide systems at ambient temperature and controlled humidity
• Comparative testing under inert (N2 or Ar) versus air or oxygen-containing atmospheres
• Toxicity and flammability screening of the aggregate evolved gas mixture for hazard classification

Testing Methods

TGA-MS (Thermogravimetry Coupled with Mass Spectrometry)

The sample is heated at a controlled rate, typically 5–10 °C/min from room temperature to 600–1000 °C, while evolved gases transfer through a heated capillary to a quadrupole mass spectrometer. Characteristic ions (m/z 2–200) are monitored in real time with ppm-level sensitivity. Quantification is achieved through calibration with certified standard gas mixtures, making TGA-MS the preferred method for tracking permanent gases such as H2, CO, CO2, and H2S and for constructing kinetic release profiles.

TGA-FTIR (Thermogravimetry Coupled with Infrared Spectroscopy)

Evolved gases flow into a heated gas cell and are analyzed by FTIR, producing time-resolved infrared spectra and Gram-Schmidt release profiles. This technique is highly effective for identifying CO2, CO, SO2, COS, HF, and hydrocarbon species, and for resolving overlapping mass spectral fragments. ASTM E2105 provides the recognized practice framework for this hyphenated configuration.

Pyrolysis-GC/MS and Micro-GC

Rapid pyrolysis or temperature-programmed decomposition is followed by chromatographic separation and MS identification of complex organic products. Micro-GC with TCD and FID detectors provides absolute quantification of permanent gases and light hydrocarbons. This combination is essential when decomposition generates dozens of co-eluting organic species that cannot be resolved by MS or FTIR alone.

Thermal Runaway Simulation with Gas Collection

Accelerating rate calorimetry (ARC) or sealed pressure-reactor tests replicate self-heating and thermal runaway conditions representative of cell abuse scenarios. Total gas volume is measured directly, and collected gas bags are analyzed offline by GC/MS and ion chromatography, aligning with gas composition evaluation requirements referenced in GB 38031 and IEC 62660-3 abuse test protocols.

Calibration and Data Quality

Quantitative accuracy relies on certified reference gas mixtures, multi-point external calibration curves, and instrument-specific response factors. Blank runs, replicate testing, and heated transfer-line verification are performed to prevent condensation losses and ensure reproducibility. Results are reported in accordance with ISO 11358 and ASTM E1131 conventions, including complete documentation of the temperature program, atmosphere, and calibration traceability.

Applications

Quantitative gas release data from solid-state electrolyte decomposition directly supports safety engineering, materials development, and regulatory compliance across the battery value chain:

• Thermal runaway hazard assessment, including gas generation budgeting and propagation modeling for solid-state cells and packs
• Comparative material selection, ranking candidate electrolytes by gas-release onset temperature, species toxicity, and total volume
• Cell and module engineering inputs for vent sizing, pressure management, and gas diffusion barrier design
• Regulatory and certification support, providing data packages consistent with GB 38031, IEC 62660-3, and UL-based certification schemes
• R&D and mechanistic studies of decomposition pathways, enabling evaluation of stabilization strategies such as doping, surface coating, and binder modification
• Incoming material quality control and batch consistency verification for electrolyte manufacturers and cell makers
• Failure analysis of field-returned or abuse-damaged cells, using gas signatures to reconstruct the thermal event history
• Environmental, health, and safety assessment of H2S and corrosive gas exposure risks during manufacturing, handling, and recycling operations

FAQ

What gases are released during thermal decomposition of sulfide solid electrolytes?

H2S is typically the dominant species, accompanied by SO2, COS, CS2, and various phosphorus-sulfur fragments. Notably, moisture exposure alone can generate H2S at room temperature, so comprehensive testing programs often include controlled humidity challenge protocols in addition to thermal ramp experiments.

How is the amount of released gas quantified?

MS ion currents and FTIR absorbance signals are converted into gas concentrations using certified calibration gas standards, then integrated over the entire test to yield cumulative release volumes in mL/g or mmol/g. GC analysis of collected gas bags from reactor or ARC tests provides absolute quantification as an independent verification step.

What sample size and form are required?

Typically 5–50 mg of powder, pellet, membrane, or film per analytical run. Larger components are sub-sampled at multiple locations. Moisture-sensitive sulfide and halide samples are prepared and transferred under glovebox conditions with water and oxygen levels controlled to parts-per-million levels.

What temperature range and heating rates are used?

Standard screening covers room temperature to 1000 °C, most commonly 25–600 °C at 5–10 °C/min under inert gas. Isothermal hold steps, staged ramps, and rapid-heating or ARC protocols are added to simulate specific processing, storage, or abuse conditions.

How do the results support battery safety certification?

Gas species and volume data feed hazard classification, vent design verification, and the abuse-test documentation required under GB 38031, IEC 62660-3, and UL-based product certification schemes. Reports issued by accredited third-party laboratories are accepted by regulators, certification bodies, and OEM procurement teams.

Can electrolytes extracted from finished cells be tested?

Yes. Materials harvested from fresh, aged, cycled, or abuse-tested cells can be analyzed to correlate degradation state with gas-release behavior. This supports failure analysis, warranty investigation, and end-of-life safety studies for solid-state battery products.