show that dimethyl ether is a decomposition product of the 2G electrolyte in SIBs at these potentials. Gasses that are formed at potentials around 3.3 V for cells cycled to 4.25 V can be suppressed by lowering the upper cut-off to 3.8 V. This suggests that the species reacting at these lower potentials are formed at higher potentials in the preceding cycle. The H2 formation is presumably caused by cross-talk of protic species. These form at the NaMNO electrode during charging (oxidation) and then diffuse to the counter electrode where they are reduced. The measurements also indicate that Na2CO3 impurities from the synthesis of the NaMNO decompose when charged to 4.25 V but several cycles are required when cycling up to 3.8 V.