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.