A Porous Azatruxene Covalent Organic Framework as Positive Electrode Materials in Li- and Mg-based Batteries

Covalent-organic frameworks (COFs) containing well-defined redox-active groups have become competitive materials for next-generation batteries. Although a high rate performance can be expected, only few examples of p-type COFs have been reported for charge storage to date, with even fewer examples showing the use of COFs in multivalent ion batteries. Herein, we report the synthesis of an azatruxene-based COF and its application as positive electrode material in Li- and Mg-based batteries. Through solvothermal condensation a highly porous and crystalline COF was obtained, as confirmed by N2 adsorption and powder X-ray diffraction (PXRD). The electron-rich azatruxene monomer shows up to three reversible one-electron oxidations making it an attractive material for anion storage. When this material is utilized in Li-based cells as a COF/CNT electrode, an average discharge potential of 3.9 V is obtained with discharge capacities of up to 70 mA h g−1 at a 2C rate. In Mg batteries using a tetrakis(hexafluoroisopropyloxy) borate electrolyte cycling proceeds with an average discharge voltage of 2.9 V. Even at a fast current rate of 5C, the capacity retention amounts to 84% over 1000 cycles, and the cells deliver an energy density of 112 W h kg−1.