Activating Vanadium's Highest Oxidation State in the NASICON Structure

The capacity and energy density of Na3V2(PO4)3 cathode material, for sodium ion batteries, was enhanced by partial substitution of iron in the octahedral vanadium site. Through this process, we show for the first time that the V4+/V5+ redox couple can be utilized in rhombohedral NASICON at above 4.0V vs. Na/Na+. At this juncture, we discovered that iron is unique in its ability to easily activate vanadium's highest oxidation state. Furthermore, an additional 12% capacity is realized due to the increased sodium concentration in the synthesized compound.