Sodium naphthalene-2,6-dicarboxylate : an anode for sodium batteries

Abstract

The conjugated dicarboxylate, sodium naphthalene-2,6-dicarboxylate (Na2NDC), has been prepared by a low energy consumption reflux method and its performance as a negative electrode for sodium-ion batteries evaluated in electrochemical cells. The structure of Na2NDC was solved for the first time (monoclinic P21/c) from powder X-ray diffraction data and consists of π-stacked naphthalene units separated by sodium-oxygen layers. Through an appropriate choice of binder and conducting carbon additive Na2NDC exhibits a reversible two electron sodium insertion at around 0.4 V vs. Na+/Na with remarkably stable capacities of ca. 200 mA h g-1 at a rate of C/2 and good rate capability (~133 mA h g-1 at 5C). In parallel the high thermal stability of the material is demonstrated by HT-X-ray diffraction, the framework remaining intact to above 500 °C.