Oxygen, hydrogen, ethylene and CO2 development in lithium-ion batteries

Gas evolution has been examined for different types of battery-related electrode materials via in situ differential electrochemical mass spectrometry (DEMS). Besides standard graphite also a novel silicon-based negative electrode was examined and it was shown that the evolution of hydrogen and ethylene is considerably reduced on this material compared to graphite. Oxygen evolution was proven to happen on the oxidative reaction of a Li2O2 electrode, besides a certain oxidation of the electrolyte. The 4.5 V plateau upon the oxidation of Li[Ni0.2Li0.2Mn0.6]O2 was likewise proven to be linked to oxygen evolution. Also in this case electrolyte oxidation was shown to be a side reaction. Layered positive electrode materials Li(Ni,Co,Al)O2 and Li(Ni,Mn,Co)O2 were also examined. The influence of different parameters on the CO2 evolution in lithium-ion batteries was shown up. The amount of CO2 formation is increased by high temperatures and cell voltages, while the addition of vinylene carbonate (VC) decreases it. Li(Ni,Mn,Co)O2 shows much less CO2 evolution than Li(Ni,Co,Al)O2.