Modified Graphene Oxide for Long Cycle Sodium-Ion Batteries

Hummer's process was modified to produce gram levels of 2-dimensional nanosheets of graphene oxide (GO) with varying degree of exfoliation and chemical functionalization. This was achieved by varying the weight ratios and reaction times of oxidizing agents used in the process. Based on Raman and Fourier transform infra red spectroscopy we show that potassium permanganate (KMnO$_{\mathrm{4}})$ is the key oxidizing agent while sodium nitrate (NaNO$_{\mathrm{3}})$ and sulfuric acid (H$_{\mathrm{2}}$SO$_{\mathrm{4}})$ play minor role during the exfoliation of graphite. Tested as working electrode in sodium-ion half-cell, the GO nanosheets produced using this optimized approach showed high rate capability and exceptionally high energy density of \textasciitilde 500 mAh/g for up to at least 100 cycles, which is among the highest reported for sodium/graphite electrodes. The average Coulombic efficiency was approximately 99 {\%}.