A Naphthalene Diimide Covalent Organic Framework: Comparison of Cathode Performance in Lithium-Ion Batteries with Amorphous Cross-linked and Linear Analogues, and Its Use in Aqueous Lithium-Ion Batteries

We report a two-dimensional (2D) imine-linked covalent organic framework (COF) containing naphthalene diimide (NDI) redox groups, TAPB-NDI COF. Lithium-ion batteries (LIBs) with TAPB-NDI COF-based electrodes exhibited >95% of their theoretical capacity at a C/20 charge/discharge rate, among the highest faradaic efficiency of a NDI-COF electrode. The pores of TAPB-NDI COF are among the largest reported and presumably facilitate efficient Li+ ion transport. An amorphous cross-linked network (TAPB-NDI Amp) and a linear polymer (PD-NDI Lp) with similar chemical structures demonstrated lower capacities than the COF at C/20 current rate. However, PD-NDI Lp exhibited an overall higher gravimetric capacity and superior specific capacity retention at higher discharge rates compared to the TAPB-NDI COF. The COF is stable in neutral aqueous solutions, allowing its use as an electrode in neutral aqueous LIBs, which exhibited better rate performances than those in coin-cell set ups. Importantly, the cathodes did not suffer from a competitive hydrogen evolution reaction in aqueous LIBs. This opens up opportunities for using NDI moieties in neutral aqueous batteries and other energy-storage devices. Aqueous devices have been largely limited to "quinone-hydroquinone"-based redox couples, which are, however, operable only in acidic media.