Comparative computational study of lithium and sodium insertion in van der Waals and covalent tetracyanoethylene (TCNE) -based crystals as promising materials for organic lithium and sodium ion batteriesWednesday (28.09.2016) 12:15 - 12:30 Part of:
Organic electrodes are a way to achieve high rate and environment-friendly batteries. A promising class of organic electrode materials is tetracyanides. TCNQ has been used as an organic cathode while TCNE molecules were predicted to have high specific capacity and voltages more suited for anodic operation.
Here, we present a comparative dispersion-corrected density functional theory (DFT) computational study of the possibilities of Li and Na storage in TCNE-based molecular (vdW) and covalent crystals. Specifically, we confirm the previously reported XRD structure of Li-TCNE and predict the existence of a covalent Na-TCNE crystal. In the molecular/covalent TCNE crystals, insertion sites are identified with the binding energy of Li and Na up to 2.7/1.8 and 2.6/1.8 eV stronger than Li and Na cohesive energy, respectively, in dilute concentrations. Up to 6/2.5 and 3/2 Li and Na atoms per TCNE unit can be inserted in the molecular/covalent crystals, respectively, while preserving the structure, with maximum voltages, respectively, 3.5/2.2 and 3.3/2.7 V. Significantly, up to capacity of 416 mAh/g for both Li and Na in the molecular crystal and 197 mAh/g for Li and 176 mAh/g for Na in the covalent crystal, the insertion of Li and Na would not lead to reactions with common electrolytes. Therefore, we conclude that TCNE-based molecular and covalent crystals could become an efficient organic cathode and anode material, respectively, for both Li and Na ion batteries.