Li-Ion-Permeable and Electronically Conductive Membrane Comprising Garnet-Type Li₆La₃Ta_1.5Y_0.5O₁₂ and Graphene Toward Ultrastable and High-Rate Lithium Sulfur Batteries

State-of-the-art lithium sulfur (Li-S) batteries suffer from serious systemic issues, which are mainly derived from polysulfide shuttling effect, poor sulfur utilization, and low Coulombic efficiency. These fundamental challenges impede the practical use of sulfur cathode in commercial battery, albeit its higher theoretical storage capacity compared to intercalation electrodes based Li ion batteries, including graphite-LiCoO₂, graphite-LiFePO₄, and graphite-Li(Ni,Mn,Co)O₂ cells. In this Article, we designed a multifunctional membrane, comprising a graphene nanosheet and Li-stuffed garnet solid-state electrolyte (SSE) composite, to synergistically enhance both cycle stability and rate capability of general sulfur cathode in a facile and effective way. With the synergistic contribution of graphene nanosheet and SSE, the sulfur cathode exhibited a superior capacity of 1165 mAh g^-1 at 0.5 C and retained an excellent discharge capacity of 947.03 mAh g^-1 (81% of initial capacity) over 200 cycles when a Gr/SSE-separator was employed. In addition, the sulfur cathode with a Gr/SSE-separator delivered a remarkable discharge capacity of 643 mAh g^-1 even at 4 C. These results are attributed to three main benefits of Gr/SSE layer: (a) synergistically enhanced electrical and Li-ion conductivity of interlayer, (b) improved electrolyte wettability, and (c) well-entangled architecture of graphene nanosheet and SSE powder.