Sodium naphthalene-2,6-dicarboxylate: an Anode for Sodium Batteries.

The conjugated dicarboxylate sodium naphthalene-2,6-dicarboxylate (Na2NDC) was prepared by a low-energy-consumption reflux method, and its performance as a negative electrode for sodium-ion batteries was evaluated in electrochemical cells. The structure of Na2NDC was solved for the first time (monoclinic P2(1)/c) from powder XRD data and consists of pi-stacked naphthalene units separated by sodium-oxygen layers. Through an appropriate choice of binder and conducting carbon additive, Na2NDC exhibited a reversible two electron sodium insertion at approximately 0.4 V (vs. Na+/Na) with remarkably stable capacities of approximately 200 mAh g(-1) at a rate of C/2 and good rate capability (approximate to 133 mAh g(-1) at 5 C). In parallel, the high thermal stability of the material was demonstrated by high-temperature XRD: the framework remained intact to above 500 degrees C.