3,5-di-tert-butyl-1,2-dimethoxybenzene (DBDB) has been synthesized as a new redox shuttle additive for overcharge protection of lithium-ion batteries. DBDB can easily dissolve in carbonate-based electrolytes, which facilitates its practical use in lithium-ion batteries; however, it has poor electrochemical stability compared to 2,5-di-tert-butyl-1,4-dimethoxybenzene (DDB). The structures of DBDB and DDB were investigated using X-ray crystallography and density functional calculations. The structures differ in the conformations of the alkoxy bonds probably due to the formation of an intramolecular hydrogen bond in the case of DBDB. We investigated reaction energies for decomposition pathways of neutral DBDB and DDB and their radical cations and found little difference in the reaction energies, although it is clear that kinetically, decomposition of DBDB is more favorable.