Cobalt(II) Tetraaminophthalocyanine‐modified Multiwall Carbon Nanotubes as an Efficient Sulfur Redox Catalyst for Lithium–Sulfur Batteries

An efficient Li–S redox catalyst consisting of MWCNTs covalently modified by cobalt(II) tetraaminophthalocyanines (TaPcCo‐MWCNTs) is developed. Effective lithium polysulfide (LiPS) capturing is enabled by the lithiophilic N‐containing phthalocyanine rings and the sulfiphilic Co central atoms. This adsorption geometry utilizes the Co unoccupied d‐orbitals as electron super‐exchange highways. Elevated kinetics of LiPSs reactions in the liquid phase as well as liquid–solid transitions were revealed by electrochemical measurements and density functional theory calculations. Uniform deposition of Li2S films was also observed, which preserves cathode integrity and sulfur utilization during cell cycling. The catalyzed sulfur redox is also significantly facilitated by the fast electron and Li‐ion transport to and from the reaction sites through the conductive MWCNT skeletons and the lithiophilic substituent amino groups on TaPcCo. With 6 wt % addition of TaPcCo‐MWCNT in the cathode coatings, high sulfur utilization is achieved with areal sulfur loadings of up to 7 mg cm−2. Stable long‐term cycling is achieved at 1 C at a sulfur loading of 5 mg cm−2, with an initial areal capacity of 4.4 mAh cm−2 retention of 3.5 mAh cm−2 after 500 cycles. Considering the high structural diversity of phthalocyanines macromolecules, this study provides opportunities for a new class of Li–S catalysts. Transport geometry: Multiwalled carbon nanotubes covalently modified by cobalt(II) tetraaminophthalocyanines are developed as a highly efficient catalyst for Li–S redox in the liquid phase and during liquid–solid transitions. This is enabled by the appropriate polysulfide binding geometry as well as fast electron and Li‐ion transport to and from the reaction sites. Outstanding Li–S battery performance is obtained at high sulfur contents and areal loadings.