High rate performance of a NaTi2(PO4)3/rGO composite electrode via pyro synthesis for sodium ion batteries

Abstract

The present study reports on a highly rate capable NASICON-structured NaTi₂(PO₄)₃/reduced graphene oxide (NTP/rGO) composite electrode synthesized by polyol-assisted pyro synthesis for Na-ion batteries (NIBs). X-ray diffraction (XRD) studies confirmed the presence of a rhombohedral NaTi₂(PO₄)₃ phase in the composite while Raman spectroscopy studies helped to identify the existence of rGO in the composite. Electron microscopy studies established that NaTi₂(PO₄)₃ nanoparticles of average sizes ranging between 20 and 30 nm were uniformly distributed and embedded in the GO sheets. When tested for sodium storage properties, the obtained NTP/rGO composite electrode registered high rate capacities (95 mA h g⁻¹ at 9.2C and 78 mA h g⁻¹ at 36.8C) when compared to that of the NTP/C electrode (∼1 mA h g⁻¹ at 9.2 and 36.8C). Further, the NTP/rGO composites delivered a reversible capability of 62 mA h g⁻¹ at 20C after 1000 cycles. The enhanced performance of the composite electrode can be attributed to the nano-sized NaTi₂(PO₄)₃ particles with shorter diffusion path lengths. These particles embedded in the rGO sheets with enhanced electrolyte/electrode contact areas ultimately lead to an improvement in the electrical conductivity at high current densities. Ex situ XANES studies confirmed reversible Na-ion intercalation/de-intercalation into/from NTP/rGO. The study thus demonstrates that the NaTi₂(PO₄)₃/rGO nanocomposite electrode is a promising candidate for the development of high power/energy density anodes for NIBs.