Cobalt(II)-Hexaazatriphenylene Hexacarbonitrile Coordination Compounds Based Cathode Materials with High Capacity and Long Cycle Stability

Organic cathode materials are plagued by their low cycle stability and poor electronic conductivity, even though they have attracted increasing attention in the context of lithium-ion batteries (LIBs). Herein, a coordination polymer cobalt-hexaazatriphenylene hexacarbonitrile (Co(HAT-CN)) is prepared via a facile solvothermal method, which is composed of the redox-active HAT-CN linker and the Co(II) ion center. The fabricated material shows excellent structural stability and high conductivity. Moreover, graphene oxide (GO) is introduced as a substrate, and in-situ loading of Co(HAT-CN) on its surface shows enhanced cycling stability. For Co(HAT-CN)/GO, a high specific capacity of 204 mAh g(-1) can be retained even after 200 cycles at a current density of 40 mA g(-1) in a voltage window of 1.2-3.9 V. Ex situ and in situ analyses are applied to probe the reversibility of the pyrazine redox-active center during the cycling process and the lithium storage process. Density functional theory calculations reveal that the high conductivity of Co(HAT-CN) should be ascribed to the narrow LUMO-HOMO gap (0.61 eV), and strong binding of lithiated molecules.