N-Doped Carbon-Layer-Modified Na3V2(PO4)3 as a High-Performance Cathode Material for Sodium-Ion Batteries

Sodium super ion conductor (NASICON)-type Na3V2(PO4)3 (NVP) has been seen as an extremely potential cathode material in sodium-ion batteries (SIBs) because it owns many prominent merits, like an open three-dimensional channel, high-voltage platform, structural stability, etc. Nevertheless, NVP is difficult to obtain excellent electrochemical performance at high rates with the defect of low electronic conductivity, which leads to the restriction of practical application. In this paper, a nitrogen-doped carbon layer-coated Na3V2(PO4)3 composite material (NVP/NC) was synthesized by a simple sol–gel method using urea as a nitrogen source. The further test proved that NVP/NC has a better rate performance compared to NVP/C. The initial reversible capacity of NVP/NC can reach 109.18 mAh g–1 at 1 C, and the discharge specific capacity can reach 88.3 mAh g–1, even when the ultrahigh current density is 50 C. In addition, NVP/NC has excellent long cycle stability (the capacity retention rate reaches 72.89% at 50 C after 8000 cycles, and the capacity reduction rate per revolution is only about 0.0034%). Because the N-doped carbon layer provides a surface channel for electron transmission of NVP, the electronic conductivity is greatly enhanced, making NVP/NC a better composite material for SIBs. Hence, this work offers a practical process to solve the poor electronic conductivity issue of NVP.