Meaning
Gaseous compound release inside a sealed cell accumulates in the void volume above the active materials. Measuring headspace outgassing allows engineers to identify volatile organic compounds and gaseous degradation products generated during formation or under abuse conditions. This helps in mapping the safety and stability profiles of the cell.
Volatile Analysis
Gas chromatographs coupled with mass spectrometers process the vapor extracted from the cell package. During the headspace outgassing test, the cell is held at a specific temperature to partition volatile species into the gas phase before sampling. This allows for the identifying of carbon dioxide, carbon monoxide and various hydrocarbon species.
These gases are often generated by the decomposition of carbonate solvents in the electrolyte.
Sourcing Safety
Battery pack designers rely on this quantitative data to size vent valves and design gas-handling systems. Sourcing teams compare the headspace outgassing rates of different cell suppliers to choose the chemistry that is least prone to thermal runway and swelling. A cell with lower gas emission rates under overcharge test conditions requires less robust mechanical containment.
This saves mass and reduces the cost of the overall enclosure.
Analytical Limitation
Condensable species present a challenge because they can return to the liquid phase before reaching the analyzer. If high-boiling point solvents condense on the extraction needle or inside the transfer lines, the calculated headspace outgassing volume will be lower than the actual volume produced. To minimize this error, heated transfer lines and high-temperature sampling valves are mandatory.
Sourcing specs must detail the temperature profile of the sampling apparatus.
