IntroductionAs the most popular energy storage devices, lithium-ion batteries (LIBs) enjoy the merits of relatively high energy densities, good reliability, and stability. However, LIBs are still expensive and nearing their ceiling performance. Currently, lithiumsulfur (Li-S) battery has spurred a great deal of attention and hold potential to serve as next-generation energy storage system due to its unique characteristics. Based on the complete reduction of elemental S to Li 2 S, the Li-S battery has a high theoretical energy density of 2600 W h kg −1 , 3-5 times higher than those conventional Li-ion battery cathode materials, such as layered LiCoO 2 and olivine LiFePO 4 . [1,2] Furthermore, sulfur as abundant, economical, and environment-friendly, are all in line with current public transportation and health priorities. The past years have also witnessed unprecedented improvements made by the research groups worldwide. [2][3][4][5][6][7] However, its practical application is still hinged on several tough challenges, such as the inherent poor electronic conductivity of sulfur and its insoluble discharging products (i.e., Li 2 S/Li 2 S 2 ), large volume variation (over 80%) due to the density difference between sulfur and Li 2 S/Li 2 S 2 . More importantly, the shuttle phenomenon caused by the dissolution and migration of long-chain polysulfides (Li 2 S n , 4 ≤ n ≤ 8) lead to the fast capacity decay, self-discharge, and low coulombic efficiency, which further exacerbate the serious problem.In order to address these problems, various hierarchical structured carbonaceous materials, such as porous carbons, [8,9] carbon nanotubes (CNTs), [10,11] and graphene, [12,13] have been thoroughly explored to host sulfur and confine lithium polysulfides (LiPSs). Moreover, they could offer intrinsic high conductivity for charge transport and cushion volume expansion. However, the interactions between the nonpolar hydrophobic carbonaceous materials and polar hydrophilic LiPSs are weak, [14] leading to the out-diffusion, thus deteriorating the battery performance. Electrode modification, such as the addition Freestanding cathode materials with sandwich-structured characteristic are synthesized for high-performance lithium-sulfur battery. Sulfur is impregnated in nitrogen-doped graphene and constructed as primary active material, which is further welded in the carbon nanotube/nanofibrillated cellulose (CNT/NFC) framework. Interconnected CNT/NFC layers on both sides of active layer are uniquely synthesized to entrap polysulfide species and supply efficient electron transport. The 3D composite network creates a hierarchical architecture with outstanding electrical and mechanical properties. Synergistic effects generated from physical and chemical interaction could effectively alleviate the dissolution and shuttling of the polysulfide ions. Theoretical calculations reveal the hydroxyl functionization exhibits a strong chemical binding with the discharge product (i.e., Li 2 S). Electrochemical measurements suggest that the rationally d...
