||Increasing demand for scalability, redox flow batteries (RFBs) are one of the most promising decoupled energy and power and excellent scalability energy storage system. In the case of commonly used aqueous vanadium RFB, operating cells at a potential higher than 1.23V results in loss of electrolyte due to solvent degradation, in which case the aqueous electrolyte has a limitation in operating voltage. In addition, at high current density, the excessive cell polarization causes a decrease in energy density. To solve these problems, we used 2,2,6,6-tetramethyl-1-piperidinyloxy as an active material to ensure high voltage and energy density and carbon fiber type electrodes with a high surface area and high electrical conductivity to reduce high polarization. In this study, carbon felt containing numerous redox-active heteroatoms was fabricated by following pyrolysis process. We showed optimal reactivity between heteroatom-doped carbon felt and various electrolytes with additives.