Abstract
Natrium superionic conductor (NASICON) compounds have emerged as a rising star in the field of sodium-ion batteries (SIBs) owing to their stable framework structure and high Na(+) ionic conductivity. The NASICON-structured Na(2)VTi(PO(4))(3) manifests significant potential as Na(+) storage material, characterized by decent rate capability and cyclability. However, the low redox potential of Ti(3+)/Ti(4+) and undesirable energy density limit its practical applications. We developed a NASICON-structured Na(3)Co(2/3)V(2/3)Ti(2/3)(PO(4))(3) (NCTVP) cathode material by doping an appropriate amount of cobalt into Na(2)VTi(PO(4))(3). Cobalt doping introduces a Co(3+)/Co(2+) redox couple at ~4.1 V and activates the V(5+)/V(4+) redox at ~3.9 V, resulting in significantly increased medium discharge voltage and capacity. NCTVP demonstrates a high capacity of over 160 mAh g(-1) at 20 mA g(-1). With a medium discharge voltage of ~2.7 V, the energy density of NCTVP reaches 432.0 Wh kg(-1). NCTVP also demonstrates desirable cycling stability (87.4% retention for 100 cycles at 50 mA g(-1)). In situ X-ray diffraction discloses a solid solution reaction mechanism for NCTVP, while the galvanostatic intermittent titration technique demonstrates fast Na(+) diffusion kinetics. NCTVP also demonstrates high capacity and good cyclability in full cells. This contribution demonstrates an effective approach for the construction of NASICON materials for SIBs.