Redox shuttle electrolyte additives (RSAs) can be applied for reversible overcharge protection of batteries. Their successful operation involves their oxidation at the cathode and reduction at the anode. The most common anodes in lithium-ion batteries are graphite or amorphous carbon, which are normally covered with a solid electrolyte interphase (SEI). The reduction of RSAs at these anodes is in apparent contradiction with the common understanding of the SEI, which is thought to be electronically insulating. In this communication the reduction behaviour of ferrocene and 2,5-di-tert-butyl-1,4-dimethoxybenzene is studied at un-filmed and SEI-filmed electrodes. It is found that it depends strongly on the type of RSA and/or composition of the SEI. The rotating ring-disc electrode (RRDE) is introduced as a powerful diagnostic tool to study the reaction mechanism of RSAs in general and the influence of the SEI in particular.