The Na2FeP2O7-carbon nanotubes composite as high rate cathode material for sodium ion batteries

Among the viable positive electrode materials recently proposed for Na-ion secondary batteries, Na2FeP2O7 was investigated thanks to its facile preparation, the use of highly abundant and low cost raw materials, and the highest thermal stability among all others cathode materials. In the present work the electrochemical features of the Na2FeP2O7 are improved by synthesizing a Na2FeP2O7-carbon nanotubes composite with prominent high-rate performances. The material shows a reversible specific capacity of 86 mAh g-1 for 140 cycles at 1C and 68 mAh g-1 at 10C. An in depth investigation about the Na+ diffusion rates inside the material was conducted by electrochemical impedance spectroscopy.