Copper porphyrin within graphene hosts for high-performance lithium-ion battery cathodes

Redox-active organic electrode materials have emerged as a promising alternative to inorganic counterparts in view of their low cost and easily tunable chemical/electrical/mechanical properties. However, practical issues of using these materials remain as a consequence of their electrically insulating character, limited specific capacity and cyclability. Porphyrin, a highly conjugated macrocyclic organic compound, is an appealing candidate due to its multi-electron transfer mechanism and its small energy barrier for rapid electron transfer. Here, a new class of copper(II) meso-tetra(4-pyridyl) porphyrin (CuTPyP) was obtained by introducing copper ions into free-base H 2 TPyP for regulation of redox activity and prevention of material dissolution, and was further hosted on conducting reduced graphene oxide (rGO) to enhance the redox activity. The resultant CuTPyP/rGO composites hence demonstrated a high reversible discharge capacity of 152 mAh g −1 after 200 cycles, with a capacity retention rate of 84.5 % at 0.5 C, vastly superior to the bare CuTPyP (113 mAh g −1 ) and free-base H 2 TPyP (62 mAh g −1 ). A deep insight into the chemical states showed that electron-donating N atoms in the tetrapyridyl subunits behaved as the main charge storage sites during the charge and discharge state along with part contribution from the Cu(II)/Cu(I) conversion center. The high and stable electrochemical performance makes porphyrins a potential choice for real-use cathodes for long-term organic alkali metal batteries.