Development of lithium/sulfur (Li/S) batteries is limited by their low Coulombic efficiency and low cycle life, which are mainly due to active mass loss and polysulfide dissolution into the electrolyte solution. Here we report a new approach to overcome these drawbacks by employing a novel composite polymer electrolyte that not only facilitates rapid transport of lithium ions for electrochemical reactions with sulfur, resulting in improved capacity of the battery, but also prevents the generated polysulfides from shuttling between the electrodes during cycling of the battery. Improved performance of the battery was achieved: An initial discharge capacity of 1648 mA h g sulfur − 1 and reversible capacity of 1143 mA h g sulfur − 1 were obtained after 100 cycles at 0.2 C (1 C = 1672 mA h g−1), which could be among the highest reversible capacities reported for Li/S batteries so far.