Optimizing Vanadium Redox Reaction in Na 3 V 2 (PO 4 ) 3 Cathodes for Sodium-Ion Batteries by the Synergistic Effect of Additional Electrons from Heteroatoms.

Na 3 V 2 (PO 4 ) 3 (NVP) is one of the most potential cathode materials for sodium-ion batteries (SIBs), but its actual electrochemical performance is limited by the defects of large electron and ion transfer resistance. Multicomponent design is considered an effective method to optimize the conductivity of NVP electrodes. Therefore, Cr and Si are added in NVP to form a multielement component of Na 3 V 1.9 Cr 0.1 (PO 4 ) 2.9 (SiO 4 ) 0.1 (NVP-CS). It is confirmed that 3d electrons of Cr are beneficial for improving the conductivity and increasing the average potential by activating V 4+ /V 5+ . Theoretical calculations show that the introduction of Si changes the electronic structure of V and O, thus promoting the electrochemical reaction of V 3+ /V 4+ to exert higher capacity. Due to the coordination of the two elements, a lower migration barrier is obtained in NVP-CS. Specifically, NVP-CS retains the advantages of single-doped electrodes very well (capacity retention of 90% after 300 cycles at 1 C and a high capacity of 94.1 mA h g -1 at 5 C, compared to NVP with only 82.6% capacity retention at 1 C and 59.4 mA h g -1 at 5 C). The excellent electrochemical performance results show that NVP can be successfully optimized by the introduction of Cr and Si. This work can provide some inspiration for multicomponent material research of cathode materials.