The future wearable/portable electronics need flexible power sources with higher storage capability. Lithium-sulfur (Li-S) battery is very promising for the development of next-generation high-energy battery due to its ultra-high theoretical capacity. However, lithium-sulfur battery manufacturing still encounters several roadblocks, including low sulfur utilization, severe capacity fading, poor cycling life and bad Coulombic efficiency, which can be ascribed to the insulating nature of sulfur (~5×10^-30 S cm^-1 at 25 ℃), the “shuttle effect” of soluble reaction intermediates (polysulfides), as well as the uncontrolled side reaction at lithium anode. To date, various strategies have been explored to push up the potential of Li-S systems, which indeed help reaching an encouraging practical capacity (~550 mAh g^-1), more than twice of the state of the art lithium-ion batteries (~180 mAh g^-1) [1,2]. Obviously, Li-S batteries hold great promise for the development of next-generation flexible power sources because of their superior energy density. However, the development of flexible Li-S batteries are still bothered by its fast capacity decay and lack of suitable flexible substrates. Our previous studies have demonstrated that the activated cotton textile (ACT) converted from cotton textile could be an excellent platform for constructing flexible energy systems (e.g. flexible supercapacitors and flexible lithium-ion batteries) due to their excellent conductivity and eminent flexibility [3-5]. However, to the best of our knowledge, ACTs have not been explored for flexible Li-S batteries.

Herein, a conductive activated cotton textile (ACT) with porous tubular structure was first derived from natural cotton textile to load sulfur, which was further wrapped with partially reduced graphene oxide (ACT/S-rGO) to immobilize lithium polysulfides. Meanwhile, the partially reduced graphene oxide nanosheets could be served as a conductive coating, which further mitigated the poor conductivity of sulfur and enabled fast electron transportation along ACT fibers. Furthermore, a KOH-activated ACT with micropore size distribution was inserted between cathode and separator to mitigate the “shuttle effect” of polysulfides. Finally, the assembled ACT/S-rGO cathode with porous ACT interlayer exhibited an exceptional rate capability and durable cyclic performance (with a well-retained capacity of ~1016 mAh g⁻¹even after 200 cycles). A flexible Li-S cell with ACT/S-rGO as a cathode was also assembled to demonstrate its superior potential as flexible power sources for future wearable electronic devices.

References:

1. Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. Li–O₂ and Li–S Batteries with High Energy Storage. Nat. Mater. 2011, 11, 172–172.
2. Manthiram, A.; Fu, Y.; Su, Y. S. Challenges and Prospects of Lithium-Sulfur Batteries. Acc. Chem. Res. 2013, 46, 1125–1134.
3. Gao, Z.; Song, N.; Zhang, Y.; Li, X. Cotton Textile Enabled, All-Solid-State Flexible Supercapacitors. RSC Adv. 2015, 5, 15438–15447.
4. Gao, Z.; Song, N.; Li, X. Microstructural Design of Hybrid CoO@NiO and Graphene Nano-Architectures for Flexible High Performance Supercapacitors. J. Mater. Chem. A 2015, 3 (28), 14833–14844.
5. Gao, Z.; Song, N.; Zhang, Y.; Li, X. Cotton-Textile-Enabled, Flexible Lithium-Ion Batteries with Enhanced Capacity and Extended Lifespan. Nano Lett. 2015, 15, 8194–8203.

Acknowledgements

Financial support for this study was provided by the U.S. National Science Foundation (CMMI-1418696 and CMMI-1358673) and the i6 Virginia Innovation Partnership.