2,5-Di-tert-butyl-1,4-dimethoxybenzene is a redox shuttle for overcharge protection of LiFePO4-based lithium-ion batteries with a working potential lower than 4.2V versus Li+/Li. However, an irreversible decomposition occurs when the working potential is higher than 4.2V versus Li+/Li. 2,3,5,6-Tetrafluoro-1,4-di-tert-butoxybenzene was also investigated as a model molecule to further understand the possible degradation pathway of 2,5-di-tert-butyl-1,4-dimethxybenzene. The experimental results strongly suggest that the irreversible reaction be related to the decomposition of OC bond in alkoxy substitution groups.