Outstanding electrochemical performance of N/S co-doped carbon/Na3V2(PO4)3 hybrid as the cathode of a sodium-ion battery

Abstract Na3V2(PO4)3 is a typical NASICON-structure material that possesses 3D channels for sodium-ion migration. It is considered a promising cathode material for sodium-ion batteries due to its high energy density and thermal stability. However, the low innate conductivity of unmodified Na3V2(PO4)3 has restricted its utilization. In this paper, we prepared a hybrid of Na3V2(PO4)3 and nitrogen/sulfur (N/S) co-doped carbon (NVP-C-NS) as the cathode of a sodium-ion battery via a simple sol-gel method. NVP-C-NS demonstrates excellent sodium storage properties in comparison to the hybrid of unmodified carbon and Na3V2(PO4)3 (NVP-C). The discharge capacity of NVP-C-NS reached 115.7 and 98.2 mAh g-1 at 50 and 1000 mA g-1, which were 9.4 mAh g-1 and 63.6 mAh g-1 larger than that exhibited by NVP-C. In addition, NVP-C-NS exhibited high cyclic stability in long-cycling tests. After 500 cycles at 200 mA g-1, NVP-C-NS delivered a discharge capacity of 74.2 mAh g-1 and maintained 83.4% of the initial discharge capacity. The enhanced performance of the NVP-C-NS hybrid is mainly due to the improved electrical conductivity, the formation of surface defects, and improved dispersion. The excellent electrochemical performance of NVP-C-NS indicates that N/S co-doped carbon compositing is a valid and efficient method for raising the performance of Na3V2(PO4)3 electrodes in sodium-ion batteries.