Benzenediacrylates as organic battery electrode materials : Na versus Li

This paper discusses investigations of a novel Na-based organic battery electrode material, disodium benzenediacrylate (Na(2)BDA) in comparison with its Li-ion homologue. Li(2)BDA has previously shown promising battery properties, such as stable cycling and good capacity retention. Na(2)BDA and Li(2)BDA are here successfully synthesized and characterized, and investigated as anode materials in prototype Na- and Li-ion battery cells. Moreover, different electrolytes are screened for the Na-battery material, and a useful operating voltage window is explored. Na(2)BDA is shown to possess a higher initial coulombic efficiency (91%) than the Li-homologue, which is uncommon for sodiated organic electrode materials. The Na-compound shows an initial capacity of 177.7 mA h g(-1), which however decreases to ca. 50 mA h g(-1) after 20-100 cycles depending on the cycling rate; a significantly lower capacity retention then that observed for Li(2)BDA. The capacity loss can primarily be explained by a decomposition mechanism of the Na(2)BDA compound

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

Organic-based materials are potential candidates for a new generation of sustainable and environmentally friendly battery technologies, but insights into the structural, kinetic and thermodynamic properties of how these compounds lithiate or sodiate are currently missing. In this regard, benzenediacrylates (BDAs) are here investigated for application as low-potential electrodes in Na-ion and Li-ion batteries. Aided by a joint effort of theoretical and experimental frameworks, we unveil the structural, electronic and electrochemical properties of the Na(2)BDA and Li(2)BDA compounds. The crystal structure of these systems in their different sodiated and lithiated phases have been predicted by an evolutionary algorithm interplayed with density functional theory calculations. Due to difficulties in obtaining useful single crystals for the BDA salts, other methods have been explored in combination with the computational approach. While the predicted structure of the pristine Na(2)BDA compound has been experimentally confirmed through the 3D Electron Diffraction (3DED) technique, the hydrated version of Li(2)BDA is analysed through single crystal X-ray diffraction. The calculated cell voltages for the sodiation (0.63 V vs. Na/Na+) and lithiation (1.12 V vs. Li/Li+) processes display excellent quantitative agreement with experimental findings. These results validate the developed theoretical methodology. Moreover, fundamental aspects of the electronic structures and their relationship with the reaction thermodynamics are discussed. The results suggest a possible disproportionation between the sodiated phases of Na(2)BDA, supporting a two-electron process, and also unveil major differences for the two employed cations: Na+ and Li+