Electrochemical studies on Lagerstroemia speciosa based hard carbon anode for sodium ion batteries

Biomass derived hard carbon (HC) was prepared from Lagerstroemia speciosa using carbonization method at three different temperatures vis 1000 degrees C, 1200 degrees C and 1400 degrees C respectively. The amorphous nature of the material was confirmed through X-ray diffraction (XRD) with decrease in interlayer spacing on increasing carbonization temperature. The Fourier transform infra red (FTIR) spectrum showed the characteristic of HC and the defect sites was analyzed by the Id/Ig ratio from Raman spectrum. Further the scanning electron microscope (SEM) images showed the presence of irregular morphology for all the samples. Also, the elemental presence was confirmed through X-ray photoelectron spectroscopy (XPS) and the surface area studies signify the presence of nanovoids and graphitic domains. All the three samples were employed as anode in Na ion battery and their performance was analysed. It is seen that among all the samples, HC prepared at 1200 degrees C showed an initial columbic efficiency of 70.7 % with excellent capacity of 397 mAhg- 1. The cyclic stability test had a retention rate of 85% after 100 cycles. This is attributed to the presence of more graphitic domains and nanovoids on the HC1200 samples. Further possible insights on the mechanism of charge storage were highlighted.