Density Functional Theory (DFT) calculations were performed to explore the electrochemical properties of two organic molecules that show promise to serve as affordable and safe anode materials in aqueous sodium-ion batteries. Upon sodium insertion, N,N’ –bis(methyl)- 1,4,5,8-naphthalene diimide (NDMe) appears to share sodium atoms with three surrounding molecules in the crystal lattice in so called Triple Binding Spots (TBS). Until a sodiation fraction of 0.5, it shows a voltage plateau at 1.78 V versus Na/Na$^+$. For increasing sodiation fractions a voltage plateau of roughly 0.4 V versus Na/Na$^+$ is predicted. The second organic molecule N,N’ –bis(p-tolyl)- 1,4,5,8-naphthalene diimide (NDTo) appears to share sodium atoms between in two or four molecules, forming Dual Binding Spots (DBS) or Quartet Binding Spots (QBS). After Van der Waals corrections, the voltage profile of NDTo shows a sloping voltage between 2.05 V and 1.2 V till a sodiation fraction of 0.5, followed by a rather low voltage plateau at 0.24V versus Na/Na$^+$ until full sodiation.

It is found to be of crucial importance to include a Van der Waals correction in the DFT calculations for NDMe and NDTo. Without Van der Waals corrections, the outcomes of the DFT calculations without exceptions show large deviations from experimental data in all cell parameters. For NDTo, the Van der Waals corrections show more significance for an increasing fraction of sodiation.

Both organic crystals show extreme lattice distortions upon sodiation. NDMe shows a volumetric change of 14,73\% upon full sodiation with changes in vector lengths up to 50,13\%. NDTo shows a volumetric change of 8,24\% upon full sodiation with changes in vector lengths up to 10,41\%. These large lattice distortions demand for the crystal structure to have an exceptionally high flexibility in order to prevent material degradation when applied as anode material in a sodium-ion battery. For this reason a revaluation of NDMe and NDTo as robust anode materials is suggested, based on computational findings as presented here.

Solutions with different concentrations of sodium perchlorate (NaClO$_4$) have been tested in a three-electrode open test-cell to find evidence for an enlarged electrochemical stability window compared to that of distilled water. At a concentration of 10M, close to the saturation limit, the solution shows a stability window between -1.29 V and 1,762 V versus Ag/AgCl, effectively offering a stability window of 3.05 V. In order to test its applicability with an organic anode material, NDMe has been obtained and tested in 10M NaClO$_4$ versus a titanium counter electrode. To proof the open test-cell design to be suitable for yielding reliable results, two easy to synthesize inorganic electrodes that are elaborately described in previous studies have been selected and tested as reference electrode materials.

NDMe shows redox potentials that are well within the improved stability window, suggesting safe use as anode material in aqueous batteries. However, capacity fading was observed upon the first cycles, which could not be quantified. Due to the open test-cell, dissolved oxygen can easily react, and is replenished by atmospheric oxygen. A new type of test-cell that is air tight is strongly recommended. Future research may now look beyond the limitations of the traditional narrow aqueous stability window, by identifying and testing aqueous battery chemistries that approach 3.0 V full cell potentials.