Polymer-Capped Sulfur Copolymers as Lithium–Sulfur Battery Cathode: Enhanced Performance by Combined Contributions of Physical and Chemical Confinements

Flexible polymers show high potential applications in rechargeable lithium–sulfur (Li–S) batteries for their capability of confining sulfur diffusion and tolerance to large volume expansion during lithiation. Herein, sulfur is copolymerized with 3-butylthiophene via radical polymerization by heating the mixture of both components at controlled temperatures. Further capping of the thus-synthesized copolymer CP­(S3BT) with highly conductive PEDOT:PSS thin film substantially enhances the electrical conductivity. With the resulting polymer hybrids as the cathode material, a Li–S battery is constructed which shows an initial discharge capacity of 1362 mA h g–1 at 0.1 C and a reversible capacity of 631 mA h g–1 even at 5 C. Moreover, the polymer cathode exhibits a high capacity of 682 mA h g–1 after 500 charge–discharge cycles at 1 C with 99.947% retention per cycle. The remarkable performance is attributed to the synergetic effects of (i) high conductivity resulting from both the conducting blocks of poly­(3-butylthiophene) (P3BT) and PEDOT:PSS capping layer, (ii) physical confinement of polysulfides by P3BT segments and PEDOT:PSS capping layers, and (iii) chemical confinement resulting from the high density of chemical bonds between sulfur and 3-butylthiophene. The results may offer a new paradigm in the development of efficient and stable polymer cathodes for high performance Li–S batteries.