Terephthalate-based covalent organic framework as high-performance anode material for sodium-ion storage and full cell

Abstract

Carboxylate-based anode materials have substantial application potential for sodium-ion batteries (SIBs) used for large scale electrochemical energy storage owing to their advantages of high specific capacity, cost-effective and sustainability. Covalent organic frameworks (COFs) are able to improve the cycling stability and rate performance of small organic compound due to their designable compositions and stable porous structures. Herein, terephthalic acid (TPA) was reacted with hexachlorocyclotriphosphazene (HCCP) via polycondensation to prepare TPA-HCCP COF. The prepared COF anode exhibits a low discharge potential of 0.26 V, high reversible specific capacity of 120 mA h g⁻¹ and good rate performance due to its stable microporous framework with abundant accessible active sites. Sodium-ion storage kinetics of the COF is a combination process of diffusion and capacitance due to the electroactive sites of CO and coordinate sites of N for sodium-ions. Full cell was fabricated using Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) as cathode material to evaluate the practical application potential of the COF anode at wide operation temperature. The NFPP||COF full cell exhibited a high mean voltage of 3.0 V and delivered a specific discharge capacity of 118 mA h g⁻¹. This research provides an effective strategy of designing and preparing terephthalate-based COF anode material and validates its practical application potential for SIBs.