Carbon felt, which is a textile material that consists of randomly oriented short carbon fibers, has been used as an electrode material of vanadium redox flow batteries owing to its high electrical conductivity, large specific surface area, and chemical stability. Despite these advantages, the inert surface of the carbon felt has been a critical drawback, leading to low electrode performance. The heat-treatment method has been principally proposed as one of the methods for activating the carbon felt surface. However, the heat-treatment method causes local damage on the carbon felt surface. In this study, glucose is selected as a coating material to protect the carbon felt during the heat treatment and provide abundant functional groups as active sites in the redox reaction. We confirm that the glucose-based carbon-coating layer on the carbon felt exhibits a higher crystalline graphitic structure than heat-treated carbon felt and promotes electrochemical properties such as electron-transfer kinetics and reversibility of the redox reaction. The carbon felt with a glucose-based carbon-coating layer exhibits an energy efficiency of 82.79% at 100 mA cm−2, which is 2.0% higher than that of a neat carbon felt.