Improved Electrochemical Performance of Na₃V_2−xZr_x(PO₄)₃/C Through Electronic and Ionic Conductivities Regulation

Electronic and ionic conductivities are two key parameters in determining the electrochemical performance of lithium/sodium ion batteries, and element-doping is an effective way to regulate the conductivity of an active material. In this work, we attempt to modify the electronic and ionic conductivities of Na₃V₂(PO₄)₃/C cathode through a proper content of Zr-doping and the two kinds of conductivities are distinguished by an ion-blocking measurement method. All Zr-doped samples display significant increase of the electronic conductivity and the x = 0.1 sample possesses the highest value of the electronic conductivity. The ionic conductivity shows a similar variation trend, but the variation value is far smaller than that of the electronic conductivity. The increase of the electronic conductivity is about one order larger than that of the ionic conductivity as x increases from 0 to 0.1. The enhanced electronic and ionic conductivities can considerably improve the cycling and rate performance of the sodium ion batteries using Na₃V₂(PO₄)₃/C cathode, especially the rate performance. The x = 0.1 electrode exhibits a much higher capacity in the whole cycling process after 1000 cycles at 10 C rate and its capacity at 50 C is about 5 times larger than that of the pristine sample.