Constructing sandwich structure of Nb-substituted Na3V2(PO4)3/C nanoparticles enwrapped on three-dimensional graphene with superior sodium storage property

Abstract

Poor intrinsic conductivity has been a principal limiting factor for Na3V2(PO4)3 (NVP) cathode material. Herein, a synergistic strategy of Nb5+ substitution and constructing with three-dimensional rGO lamella is proposed for the first time to optimize the characteristics of NVP. The introduction of Nb5+ generates beneficial carriers and vacancies that optimize the electronic structure of NVP system. Meanwhile, rGO substrate can construct an effective conductive network for the facilitated electronic transportation and form a stabilized SEI layer after cycling to protect the active particles from being collapsed. This double treatment significantly improves the kinetic characteristics of NVP. Moreover, theoretical calculations indicate that beneficial Nb5+ doping can effectively reduce the band gap between conductive and valence bands, as well as decline the energy barrier of migration for Na+. Notably, the modified Nb0.15-NVP/C@rGO exhibits impressive electrochemical performance. It delivers a capacity of 107.9 mAh g−1 and keeps a value of 102.6 mAh g−1 after 500 cycles at 2C with a high retention of 95.35%. It submits a capacity value of 97.2 mAh g−1 at 20C, 82.92% reversible capacity (80.6 mAh g−1) could be retained after 2000 cycles. Even at 120 and 300C, this material still performs high values of 84.9 and 71.3 mAh g−1, indicating the superior rate capability.