Theoretical investigation of a tetrazine based covalent organic framework as a promising anode material for sodium/calcium ion batteries

Abstract

Nowadays, great attention is being directed towards the development of promising electrode materials for non-lithium rechargeable batteries such as sodium and calcium ion batteries (SIBs and CIBs), due to their large abundance, storage capacity and charge/discharge rate. Using density functional theory (DFT) based computations we have predicted that the recently synthesized bilayer s-tetrazine based covalent organic framework (bilayer TZACOF) may be a promising anode material for sodium and calcium ion batteries. The electronic band structure calculations suggest that the bilayer TZACOF is an indirect band gap semiconductor with a band gap of 0.95 eV. The sodium and calcium atoms are adsorbed on the bilayer TZACOF at the most energetically favorable adsorption sites with adsorption energies of −1.37 eV and −2.27 eV, respectively. Moreover, the diffusion energy barriers for the migration of sodium and calcium atoms on the bilayer TZACOF are 0.19 eV and 0.63 eV, respectively, which indicates the fast ion mobility and charge/discharge rate. The theoretical specific capacity (TSC) of the bilayer TZACOF as the electrode material for SIBs and CIBs is 618.69 and 412.46 mA h g⁻¹, respectively. Furthermore, the average voltage of the bilayer TZACOF as the electrode material for SIBs and CIBs is found to be 0.96 and 1.13 V, respectively. Based on the results of rich electronic properties, low diffusion barriers, high storage capacity, and low average voltage, we can reach at the conclusion that the bilayer TZACOF may be a suitable candidate for use as an anode material for sodium and calcium ion batteries (SIBs and CIBs).