Multifunctional Polymeric Phthalocyanine-Coated Carbon Nanotubes for Efficient Redox Mediators of Lithium-Sulfur Batteries

Metal phthalocyanine (Pc) complexes are considered to be promising functional organic materials owing to their tunable properties and unique pi-electron structure. Despite these advantages, the application of polymeric metal Pc into lithium-sulfur (Li-S) batteries has yet to be explored. Herein, this work demonstrates a molecular design of multifunctional polymeric cobalt Pc with triethylene glycol linkers (TCP) that provide a redox mediating capability for the Co ion in the center of the Pc, a strong polar interaction of N atoms with Li, and the lithiophilic sites of crown ether mimicking linkers for highly efficient Li-S batteries. As verified by electrochemical and theoretical analyses, the cooperative redox mediating and lithiophilic effects of TCP coated onto multiwalled carbon nanotube (TCP/MC) are attributed to the facilitated conversion reaction kinetics of S cathodes for the high utilization efficiency of S and the inhibition of polysulfide shuttling. Consequently, the S@TCP/MC delivers high discharge capacity of 1392.8 mA h g(-1) and high-rate capacity of 667.9 mA h g(-1) at 5.0 C. Moreover, this cathode achieves a high capacity retention of 81.5% over 200 cycles, along with a high areal capacity of 6.83 mA h cm(-2) at 0.2 C with a high S loading of 6.6 mg cm(-2).

Automated summary

In this study, a multifunctional polymeric cobalt phthalocyanine (TCP) material was designed and applied in lithium-sulfur batteries, showing promising performance. The TCP coating on multiwalled carbon nanotubes exhibited cooperative redox mediating and lithiophilic effects, leading to improved conversion reaction kinetics of S cathodes, enhanced utilization efficiency of S, and inhibition of polysulfide shuttling. As a result, the S@TCP/MC cathode achieved high discharge capacity, high-rate capacity, high capacity retention, and high areal capacity.