Na$_{4}$Co$_{3}$(PO$_{4}$)$_{2}$P$_{2}$O$_{7}$/NC composite as a negative electrode for sodium-ion batteries

Abstract

In recent years, the mixed phosphates based polyanionic electrode materials have attracted great attention in sodium-ion batteries due to their structural stability during cycling and open framework for ion diffusion. Here, we report the electrochemical performance of Na4Co3(PO4)2P2O7/nitrogen doped carbon (NCPP/NC) composite as a negative electrode (anode) for sodium ion batteries in the working potential range of 0.01-3.0 V. It delivers a reversible discharge capacity of 250 mAhg −1 at 0.5 C current rate, which corresponds to the insertion/extraction of four sodium ions. The rate capability study indicates the reversible mechanism and highly stable capacity (61 mAhg −1 ) even at high rate up to 5 C as compared to pristine NCPP. The incorporation of the N doped carbon spheres in the composite is expected to enhance the electronic/ionic conductivity, which plays an important role in improving the performance and stability up to 400 cycles at 1 C rate. Intriguingly, the analysis of cyclic voltammetry data measured at different scan rates confirm the capacitive/diffusive controlled mechanism and the extracted diffusion coefficient is found to be around 10 −10 cm 2 s −1 . Our results demonstrate that the NCPP/NC composite is also a potential candidate as anode in sodium-ion batteries due to its three dimensional framework, cost effectiveness, enhanced specific capacity as well as further possibility of improving the stability.