To obtain soft electronics, it is essential to develop high-performance and mechanically flexible energy storage at the industry level. Herein, we report flexible high-energy-density lithium-sulfur (Li–S) batteries based on all-fibrous sulfur cathodes and separators. To implement free-standing and flexible sulfur cathodes, electrically conductive single-walled carbon nanotubes (CNTs) are impregnated with cellulose nanofibers. This fibrous structure forms a 3D porous electrode with a large surface area to improve redox kinetics and achieve a high sulfur loading content without the use of a metal collector, which can then be applied in high-energy-density batteries. These flexible sulfur cathodes are combined with a commercial glass fiber separator coated with a CNT layer through a cost-effective solution process to suppress the shuttle effects of lithium–polysulfide, thereby exhibiting robust cycling stability. The prepared Li–S batteries exhibit high capacities of 940 mAh g−1 at a charge current density of 1.57 mA cm−2 and at 25 °C, and the Coulombic efficiency exceeds 90% even after 50 charge/discharge cycles. Moreover, Li-S batteries with a high gravimetric energy density of 443 Wh kg−1 per cell is achieved, and these batteries demonstrate excellent reliability in regard to electrochemical performance even under severe mechanical stress conditions for over 100 cycles.

The widespread adoption of Li‐ion batteries is currently limited by their unstable electrochemical performance and high flammability under mechanical deformation conditions and a relatively low energy density. Herein, high‐energy‐density lithium–sulfur (Li–S) batteries are developed for applications in next‐generation flexible electronics and electric vehicles with long cruising distances. Freestanding high‐S‐loading carbon nanotubes cathodes are assembled with a phosphorus (P)‐doped carbon interlayer coated on commercial separators. Strategies for the active materials and structural design of both the electrodes and separators are highly efficient for immobilizing the lithium polysulfides via multimodal capturing effects; they significantly improve the electrochemical performance in terms of the redox kinetics and cycling stability. The foldable Li–S cells show stable specific capacities of 850 mAh g−1 over 100 cycles, achieving high gravimetric and volumetric energy densities of 387 Wh kgcell−1 and 395 Wh Lcell−1, respectively. The Li–S cells show highly durable mechanical flexibilities under severe deformation conditions without short circuit or failure. Finally, the Li–S battery is explored as a light‐weight and flexible energy storage device aboard airplane drones to ensure at least fivefold longer flight times than traditional Li‐ion batteries. Nanocarbon‐based S cathodes and P‐doped carbon interlayers offer a promising solution for commercializing rechargeable Li–S batteries.

Unlike commercial lithium‐ion batteries, the high cost and low ionic conductivity of solid electrolytes (SEs) continues to be a big hurdle in commercially available all‐solid‐state batteries (ASSBs). Rather than the conventional dry‐process and high‐energy ball milling processes, the productive solution synthesis of bulk‐type SEs is the most crucial issue in the successful application of high‐energy‐density ASSBs. In this study, the way is paved to overcome the hurdle for commercial lithium phosphorus sulfide chloride (LPSCl) SEs via a readily processable bulk‐type solution‐based synthesis without acquiring any high‐energy ball‐milling processes. By incorporating an elemental sulfur additive during the preparation process, Li2S and S form a polysulfide, and P2S5 is induced to react readily to provide LPSCl with excellent ion conductivity as high as 1.8 mS cm−1. Surprisingly, the purity of bulk type precursors does not affect the final composition and ionic conductivity of sulfide electrolytes, which show the same electrochemical characteristics of ASSB cells with a high discharge capacity of 185.6 mA h g−1. The study offers a promising strategy for saving the production cost of sulfide SEs, possibly up to 92%, and their commercial ASSBs are expected to be achieving a competitive cost per energy density of ≈0.46 $ W−1.

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