Various organic compounds with heteroatoms (N, O, F, Si, P, S) were tested as overcharge protection additives for 4-V class lithium cells. It was found that trimethyl-3,5-xylylsilane exhibited preferable oxidation potential (E ox) as overcharge protection additive, and charge–discharge cycling efficiency (Eff) of lithium anode in electrolyte with arylsilanes was as high as tolyladamantanes, reported previously by us. From room temperature to 60°C, E ox of trimethyl-3,5-xylylsilane decreased only 0.07V. Difference in E ox among regioisomers of tolyltrimethylsilanes is smaller than that among tolyladamantanes. 1H NMR and UV spectra suggest the steric repulsion between tolyl group and trimethylsilyl group in o-tolyltrimethylsilane is smaller than that of the related substituents of o-tolyladamantane.