Lithium-selenium battery containing an electrode-protecting layer and method for improving cycle-life

A lithium-selenium secondary battery comprising a cathode, an anode, and a porous separator or electrolyte disposed between said cathode and said anode, comprising:

• (a) an anode active material layer, comprising a layer of lithium or lithium alloy, in a form of a foil, coating, or multiple particles aggregated together, as an anode active material, and an optional anode current collector supporting said anode active material layer;
• (b) a cathode active material layer, comprising a selenium-containing material as a cathode active material, selected from selenium, a selenium-carbon hybrid, a selenium-graphite hybrid, a selenium-graphene hybrid, a conducting polymer-selenium hybrid, a metal selenide, a Se alloy or mixture with Sn, Sb, Bi, S, or Te, a selenium compound, or a combination thereof, and an optional cathode current collector supporting said cathode active material layer;
• (c) an electrolyte and a porous separator layer;
• and
• (d) a discrete anode-protecting layer disposed between said anode active material layer and said porous separator and/or a discrete cathode-protecting layer disposed between the porous separator and the cathode active material layer;
• wherein said 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 said layer of conductive sulfonated elastomer composite has a thickness from 1 nm to 100 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 when measured at room temperature.