Recently, the demand for renewable energy has raised with the increase of environmental issues and exhaustion of crude oil. To acquire efficient utilization of the renewable energy, large-scale energy storage systems (ESSs) are necessary that balance the discrepancy between production of and the time required to consume renewable energy. Li-ion batteries have been considered as candidates for large-scale ESSs because they provide high energy density and a long cycle life. However, due to the lack of Li reserves in the Earth and the corresponding growing cost problems, Na-ion batteries have been received great attention as alternative candidates for Li-ion batteries. The Na-ion batteries can replace the Li-ion batteries in the aspects of abundant Na resources, low cost, and easily accessible reserves. Furthermore, the similarity of the electrochemical reaction mechanisms of Na-ion batteries to that of Li-ion batteries has accelerated the development of the Na-ion batteries; thus, various research studies have been conducted to find proper electrode materials for Na-ion batteries. Among various cathode materials of sodium-ion batteries for large-scale applications, NASICON-Na3V2(PO4)3 is an attractive candidate for the cathode material of Na-ion batteries due to its thermal and structural stabilities. Also, Na3V2(PO4)3 shows 117.6 mAh·g-1 theoretical capacity at 3.4 V vs. Na/Na+ using the V3+/4+ redox couple. However, the operating voltage of Na3V2(PO4)3 should be improved to replace the conventional Li-ion battery cathode materials. If V4+/5+ redox reaction, which utilizes higher operating voltage, can be employed in this material, higher operating voltage could be achieved. Herein, we suggest a simple method to enhance the operating voltage of Na3V2(PO4)3. In this work, non-transition metal ions are substituted for V-ions in Na3V2(PO4)3 to utilize V4+/5+ redox reaction. During the (de)intercalation of Na-ions, the oxidation state of the non-transition metal ions is not changed. Hence, some V3+ ions in Na3V2(PO4)3 should be oxidized until V5+ instead of non-transition metal ions while two Na-ions are extracted. Therefore, some part of capacity reacts at 3.4 V using V3+/4+ redox couple and the other part reacts at voltage higher than 3.4 V using V4+/5+ redox couple. Through the tuning of V redox couple, not only the enhancement of energy density of the cathode material but the cost reduction of expensive V source also is possible. The figure shows the initial charge profiles of Na3V2(PO4)3/C and metal-ion substituted Na3V1.5M0.5(PO4)3/C. In case of Na3V1.5M0.5(PO4)3/C, a high voltage V4+/5+ redox reation was clearly observed as the cell was charged above 3.5 V vs. Na/Na+. In the presentation, the detailed structural analyses and electrochemical performance of the materials will be shown. Figure 1