Expanded graphitic materials prepared from micro- and nanometric precursors as anodes for sodium-ion batteries

• Micro (ESGs) and nano (EGNFs) expanded graphitic materials were used as anodes for SIBs.
• ESGs provided better electrochemical performances due to lower surface area and porosity.
• A material oxygen content of 12–25 wt.% was found to be optimal for this application.
• Crev ∼150 mA h g−1 at 37 mA g−1 and ∼110 mA h g−1 at 100 mA g−1 were attained.
• Up to 50% of initial Crev at 19 mA g−1 was kept at 372 mA g−1 (∼86 mA h g−1).

A series of expanded graphitic materials are prepared from two different precursors: micrometric synthetic graphite and graphitized carbon nanofibers, and tested as anodes for sodium-ion batteries. The materials preparation involves the oxidation of the precursors followed by partial thermal reduction. Overall, the expanded synthetic graphite materials show better electrochemical performance as anode than the expanded graphite nanofibers, providing higher specific capacity, leading to lower capacity losses in the first discharge-charge cycle and exhibiting outstanding cycling stability. Specific capacities of ∼150 mA h g−1 at 37 mA g−1 and ∼110 mA h g−1 at 100 mA g−1 are attained, and up to 50% of the initial capacity at 19 mA g−1 is kept at 372 mA g−1. Unexpectedly, higher capacity losses are measured for the nanostructured electrodes by progressively increasing the current density. These differences are attributed to the lower surface area and porosity of expanded synthetic graphite materials which favors the formation of thinner and more stable SEI, thus reducing the electrode resistance and enhancing the accessibility of Na+ ions to surface oxygen-containing functional groups with the consequent increase of the surface capacity which was found to be the main contribution to the total specific capacity.

Specific capacities > 100 mA h g−1 were provided by the expanded graphitic materials prepared after 200 cycles at 100 mA g−1.Figure optionsDownload as PowerPoint slide