CH4 and dimethyl ether in the case of 2G evolve at potentials above 3.9 V, so they should be products of the electrolyte oxidation at high potentials. The peaks of these gases increase from cycle to cycle, so intermediates need to be formed first or the surface reactivity of the electrode towards the decomposition increases over cycling. Another reason might be the particle cracking, which leads to an increasing reactive surface area.