Simultaneous modified Na2.9V1.9Zr0.1(PO4)3/C@rGO as a superior high rate and ultralong lifespan cathode for symmetric sodium ion batteries

Na3V2(PO4)3(NVP), a promising cathode candidate for sodium ion batteries (SIBs), is restricted by the poor intrinsic conductivity and sever volumetric shrinkage. Herein, we report a feasible dual strategy to optimize the crystal structure and conductive characteristics of NVP. The substitution of Zr4+ is favorable to broaden the ionic channel and stabilize the structural framework due to its larger ionic radius. Meanwhile, vacancies are generated with Zr4+ doping, dramatically facilitating the internal electronic conduction. The coated carbon layer and rGO construct an efficient carbon matrix for electronic and ionic transportation. Moreover, the layered rGO nanosheet benefits to inhibit the growth of the sintered grains, reducing the particle size to provide shortened pathway for Na+ migration, facilitating the kinetic characteristics sufficiently. Consequently, the optimized Na2.9V1.9Zr0.1(PO4)3/C@rGO (Zr0.1-NVP/C@rGO) reveals an outstanding rate capability (81.3 mAh g-1 at 120C) and long cyclic stability (retention of 74.3% at 200C after 3000 cycles) in a half cell. Moreover, the symmetric full cell presents competitive electrochemical property and potential applicability. Multiple measurements demonstrate the superior kinetic characteristics of Zr0.1-NVP/C@rGO, in which GITT illuminates the variation rule of DNa+ value definitely. Such a facile and beneficial design supplies an effective strategy for other materials with high-quality in SIBs.