Driven by the continually accelerating demand for energy storage, the development of batteries with high energy, high power, low cost, and high safety is an endless goal and eternally inspires researchers to pursue advanced energy storage technologies. Battery systems based on non-aqueous chemistry of lithium and sulfur have garnered overwhelming attention in the past decade. So far, many significant progresses have been made through rigorous research over the past decade. However, this battery technology still confronts considerably critical challenges. Due to their unique charge-discharge mechanism, electrochemical processes of a Li–S cell experience the formation of a sequence of soluble intermediate products existing in a variety form of polysulfides dissolved in the non-aqueous liquid electrolyte. Under the operating conditions of a Li-S cell, the solvated polysulfide species have a tendency to migrate from the positive electrode through the conventional porous separator to react with Li-metal anode. The shuttle of polysulfide can severely degrade the cell performance, lowers the cycling efficiency, and induces capacity fade during cycling. On the other hand, use of a lithium-metal anode in Li-S batteries would unavoidably lead to the additional persistent problem of Li dendrite with can easily penetrate a conventional porous separator and short the cell. These two problems — the polysulfide shuttle and lithium dendrites — are the most critical challenges for Li–S battery development. To overcome the above two issues, we present here a lithiated polymer membrane (as pictured in Figure 1a) which is developed from agarose (AG, with a unit molecular structure as displayed in Figure 1b) as a cation-selective electrolyte for Li–S batteries to suppress the polysulfide diffusion and to reduce the formation Li dendrite. Preliminary results of a Li ǁ AG ǁ Li symmetric cell showed that the membrane could sustain high-current-density operation with low overpotential (Figure 1c). The AG membrane exhibited amorphous structure (Figure 1d) and nonporous feature (Figure 1e). Our ongoing work includes the evaluation of dendrite-suppression capability and polysulfide-shuttle-inhibition function of the AG-based membrane, as well as the electrochemical performance of Li-S batteries with the AG membrane. In addition, ionic transport mechanism in the AG-based membrane will be presented as well.