Creating multi-electron reactions in NASICON-type Na 7 V 4 (P 2 O 7) 4 (PO 4 ) cathode for sodium-ion battery by activating reversible V 4+ /V 5+ redox reactions

Abstract

Na 7 V 4 (P 2 O 7 ) 4 (PO 4 ), which serves as a cathode for sodium-ion batteries, has a high operating voltage and is thus ideal for high energy density sodium-ion batteries. However, its practical application is limited by low capacity and electronic conductivity. To address this issue, the Na 7 V 4 (P 2 O 7 ) 4 (PO 4 )@NSC-x composite material was successfully synthesized by constructing an N/S co-doping carbon layer coating. N/S co-doping introduces abundant defects and active sites in carbon, boosting electronic conductivity. The formation of the C-S-V bond activates the V 4+ /V 5+ redox process, which creates a multi-electron reaction and enhances capacity. The composite shows 113.8 mAh•g -1 at 0.1 C, and remains 80.8 mAh•g -1 even at 30 C. The symmetric full battery retained 73.5% of its capacity after 1000 cycles at 5 C. These results confirm the feasibility of N/S co-doping for NASICON-type cathodes, providing a modification strategy for subsequent research on exploiting the multielectron reaction characteristics of such NASICON cathodes.