Fluorinated quinone derived organosulfur copolymer cathodes for long-cycling, thermostable and flexible lithium–sulfur batteries

Organosulfur copolymers are promising cathode materials in lithium–sulfur batteries because of adjustable molecular structure, tunable electrochemical properties and excellent processability. However, conventional organosulfur copolymers suffer from poor electronic/ionic conductivity and low sulfur content, which limit rate capability and energy density. Herein, fluorinated quinone-derived organics are copolymerized with sulfur via convenient nucleophilic aromatic substitution (SNAr) reaction. The homogeneous distribution of sulfur over poly(tetrafluorohydroquinone)-sulfur (PTFHQS) at molecular level endows excellent Li+ ion diffusivity and fast redox kinetics. The abundant semi-ionic C–F bonds with polar characteristic have strong interactions with polysulfides, thus diminishing the shuttle effect. In result, flexible PTFHQS cathode with ~ 71 wt% sulfur content exhibits high discharge capacity of 643 mAh gtotal–1 (906 mAh gsulfur–1) at 0.5C, stable Coulombic efficiency (>99%), good rate performance of 307 mAh gtotal–1 (432 mAh gsulfur–1) 2.0C, excellent cycling stability (capacity retention of 87% for 600cycles), and functions normally at elevated working temperature (80 °C). Compared to another copolymer of sulfurized tetrafluoro-p-benzoquinone monomer (TFBQS), molecular structure characterization and electrochemical analysis verifies that pre-polymerized skeleton of PTFHQS is conducive to the homogeneous distribution and efficient utilization of sulfur species. We expect this work will bring inspiration to exploit organosulfur compounds with rational molecular structures and convenient synthesis routes for lithium–sulfur batteries.