Cathode-supported solid polymer electrolyte with solvate ionic liquid and polysulfide modification for rechargeable lithium metal batteries

To overcome the application bottlenecks of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) related to low ionic conductivity and unstable interface chemistry at both electrodes, Li+-conductive solvate ionic liquid (SIL) and soluble long-chain polysulfide (Li2S6) were introduced into the SPE as a liquid plasticizer and functional additive, respectively. Additionally, an integrated structure with a cathode-supported SPE was adopted to enhance interface contact. The modified PEO-based SPE exhibited excellent comprehensive properties, including high ionic conductivity, Li-ion transfer number, oxidation potential and Li metal compatibility. In particular, the moderate addition of Li2S6 was found to not only decrease the PEO crystallinity through strong interaction and uniform dispersion but also effectively stabilized the Li surface and suppressed dendrite growth via chemical reduction. The synergistic effect of the two functional agents and the integrated design endowed the Li metal battery with high reversible capacity and superior cycle stability when operated at room temperature.