Emerging high voltage V/V redox reactions in NaV(PO)-based cathodes for sodium-ion batteries

Na 3 V 2 (PO 4 ) 3 (NVP) cathode materials with the advantages of long cycle life and superior thermal stability have been considered promising cathode candidates for SIBs. However, the unsatisfactory energy density derived from low theoretical capacity and operating voltage (3.35 V vs. Na + /Na, based on the V 3+ /V 4+ redox couple) inevitably limits their practical application. Therefore, the activation of the V 4+ /V 5+ redox couple (∼4.0 V vs. Na + /Na) in NVP-based cathode materials to boost the energy density of SIBs has attracted extensive attention. Herein, we first analyze the challenges of activation of the V 4+ /V 5+ redox couple in NVP-based cathode materials. Subsequently, the recent achievement of NVP-based cathode materials with activated V 4+ /V 5+ redox reactions for SIBs is overviewed. Finally, further research directions of high voltage V 4+ /V 5+ redox reactions in NVP-based cathodes are proposed. This review provides valuable guidance for developing high energy density NVP-based cathode materials for SIBs. In this review, we will focus on NVP-based cathodes which achieve reversible activation of the V 4+ /V 5+ redox couple and improve the energy density of SIBs.