Insights into the enhanced sodium storage property and kinetics based on the Zr/Si codoped Na3V2(PO4)3/C cathode with superior rate capability and long lifespan

Abstract

Na3V2(PO4)3(NVP) is a promising cathode material. However, the poor intrinsic conductivity and sever volumetric shrinkage constrain the applications of NVP. Herein, we propose a remarkable Si/Zr co-doped Na3V2-xZrx(PO4)3-x(SiO4)x/C composite. The optimized co-doped sample exhibits superior rate and cycling performance resulting from the improved ionic conductivity. The synergetic effects of Si/Zr co-doping on the crystal structural stability and Na+ migration capability are significant, leading to superior electrochemical performance for the co-doped composites. Moreover, the Na3V2-xZrx(PO4)3-x(SiO4)x/C possess an extra high voltage plateau at 3.7 V, corresponding to the V4+/V5+ reaction. The optimized Na3V1.97Zr0.03(PO4)2.97(SiO4)0.03/C reveals an initial capacity of 109.6 mA h g−1 at 0.1 C. It performs a capacity retention of 87.7% at 6 C after 500 cycles. At a higher density of 12 C, the initial capacity is 95.7 mA h g−1, and it retains a value of 68.3 mA h g−1 after 2000 cycles, corresponding to a low decay of 0.014% per cycle. Due to the high potential platform and superior capacity value, it delivers an energy density of 403.5 Wh kg−1, surpassing the theoretical one (397.8 Wh kg−1). The kinetic behavior is explored by GITT, and the lowest diffusion coefficients appeared at 3.4 V and 3.7 V conforms to the electrochemical tests.