Divulging the Hidden Capacity and Sodiation Kinetics of Na_xC₆Cl₄O₂: A High Voltage Organic Cathode for Sodium Rechargeable Batteries

Abstract

In the current emerging sustainable organic battery field, quinones are seen as one of the prime candidates for application in rechargeable battery electrodes. Recently, C6Cl4O2, a modified quinone, has been proposed as a high voltage organic cathode. However, the sodium insertion mechanism behind the cell reaction remained unclear due to the nescience of the right crystal structure. Here, the framework of the density functional theory (DFT) together with an evolutionary algorithm was employed to elucidate the crystal structures of the compounds Na x C6Cl4O2 (x = 0.5, 1.0, 1.5 and 2). Along with the usefulness of PBE functional to reflect the experimental potential, also the importance of the hybrid functional to divulge the hidden theoretical capacity is evaluated. We showed that the experimentally observed lower specific capacity is a result of the great stabilization of the intermediate phase Na1.5C6Cl4O2. The calculated activation barriers for the ionic hops are 0.68, 0.40, and 0.31 eV, respectively, for NaC6Cl4O2, Na1.5C6Cl4O2, and Na2C6Cl4O2. These results indicate that the kinetic process must not be a limiting factor upon Na insertion. Finally, the correct prediction of the specific capacity has confirmed that the theoretical strategy used, employing evolutionary simulations together with the hybrid functional framework, can rightly model the thermodynamic process in organic electrode compounds.

Computational Studies of Electrode Materials in Sodium‐Ion Batteries

“…The commonly used LDA and GGA functionals neglect the long‐range vdW interactions . For the materials systems commonly studied for NIBs, the long‐range vdW interactions are important to properly describe the structures and energies of layered materials and organic molecular materials . A number of vdW corrections, including semiempirical corrections (e.g., DFT‐D, DFT‐D2, DFT‐D3) and vdW functionals (e.g., vdW‐DF, vdW‐DF2, and vdW‐optPBE), have been developed for the DFT computation scheme.…”

“…The vdW‐DF method instead determines the dispersion interactions directly from the electron density: nonlocal, long‐range correlations from vdW interactions were added into the semi‐local correlation functionals. The vdW corrections show significant improvements in reproducing the lattice parameters and the formation energies of layered materials (e.g., graphite and polysilane) and organic molecular materials (e.g., Na x C 6 O 6 and Na x C 6 Cl 4 O 2 ). In addition, the energies of adsorption and intercalation, e.g., in graphite and phosphorene, are also improved by the use of vdW corrections.…”

“…In particular, C 6 Cl 4 O 2 was demonstrated in their experiments with good electrochemical performances. Araujo et al studied the crystal structures of Na x C 6 Cl 4 O 2 using the USPEX structure prediction algorithm and reproduced the experimental voltage profile. They also found that hybrid functional calculations provided more accurate energies for these organic compounds.…”

Boosting Rechargeable Batteries R&D by Multiscale Modeling: Myth or Reality?

“…The calculated voltages involving this new phase were found to be consistent with the experimental result within approximately ±0.2 V accuracy. Recently, the sodium insertion mechanism in the tetrasubstituted quinone C 6 Cl 4 O 2 was also studied 174 within the framework of DFT combined with the evolutionary algorithm, USPEX. The crystal structures of the compound Na x C 6 Cl 4 O 2 ( x = 0.5, 1.0, 1.5, and 2) were thus elucidated, and the results have highlighted great structural changes upon sodium insertion reaction with a volume change going to about 14% when x varies from 0 to 2 (in the PBE+D2 approach).…”

Structure–property relationships in organic battery anode materials: exploring redox reactions in crystalline Na- and Li-benzene diacrylate using combined crystallography and density functional theory calculations

“…Largely employed in the field of organic electronics, density functional theory (DFT) calculations have become appealing for the organic battery field as a mean to assess properties and processes which are not so easily reachable by experimental tools. [24][25][26][27][28][29][30][31][32] Despite the fact that molecular level calculations can give a good insight into the materials' electrochemical performance, some aspects can only be unveiled by considering the intrinsic environment present in the solid-state structure. Some studies have adopted to this approach by utilizing the experimental crystal structure, 31 or by starting with the experimental structure for the pristine materials and evaluating the ion diffusion through nudged elastic band methods and thereafter evaluating the most probable site for ion insertion by computing the binding energy.…”