This master thesis focuses on the early detection of the thermal runaway of lithium-ion batteries. For the early detection, gases are detected which outgas from the battery already before the thermal runaway. To make this possible, four gas sensors are installed, which detect carbon monoxide, carbon dioxide, general hydrocarbons, and hydrogen. The work deals with the construction of a test facility as well as the programming of software for data logging. The software is also used to warn users of possible a thermal runaway. Nickel-manganese-cobalt-oxide batteries are used for the experiments and different states of charge are investigated. The gas detection takes place at different vertical distances from the batteries.