Provided is a rechargeable alkali metal-sulfur cell comprising an anode layer, an electrolyte and a porous separator, a cathode layer, and a discrete anode-protecting layer disposed between the anode layer and the separator and/or a discrete cathode-protecting layer disposed between the separator and the cathode active material layer; wherein the anode-protecting layer or cathode-protecting layer comprises a conductive sulfonated elastomer composite having from 0.01% to 50% by weight of a conductive reinforcement material dispersed in a sulfonated elastomeric matrix material and the protective layer has a thickness from 1 nm to 50 μm, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10−7 S/cm to 5×10−2 S/cm, and an electrical conductivity from 10−7 S/cm to 100 S/cm. This battery exhibits an excellent combination of high sulfur content, high sulfur utilization efficiency, high energy density, and long cycle life.