The electrochemical characterization and application of silicon phthalocyanine µ-oxo oligomers to symmetric, slurry redox flow batteries are reported. Electrolytes comprising (C6H13)3-Si-O-Si(Pc)-O-Si(C6H13)3, (C6H13)3-Si-O-Si(Pc)-O-Si(Pc)-O-Si(C6H13)3, (C6H13)3Si-O-Si(Pc)-O-Si(Pc)-O-Si(Pc)-O-Si(C6H13)3, Ketjenblack EC-600JD carbon, and TBAPF6 in propylene carbonate exhibit near-unity Coulombic efficiencies and near to greater than 60% energy efficiencies. Notably, (C6H13)3Si-O-Si(Pc)-O-Si(Pc)-O-Si(Pc)-O-Si(C6H13)3 exhibits negligible capacity fade over two weeks of charge-discharge cycling at 50% state of charge. The unique multi-electron oxidative stability of higher-order oligomers is rationalized through a combination of time-dependent density functional theory (TDDFT) and ab initiocalculations. These materials provide a promising class of multi-electron transfer reagents for use in semi-solid, non-aqueous redox flow batteries.