Abstract
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.
Highlights
Some pioneering companies have launched innovative mobile smart devices, such as the Samsung Galaxy Z Flip and Huawei Mate X, which are foldable 5 G smartphones
We propose flexible Li–S batteries based on the fibrous composition of sulfur cathodes that consist of a cellulose nanofiber (CNF) framework and electronically conductive carbon nanotubes (CNTs) additives
A sulfur layer with a nanoscale thickness conformably formed on the surface of the one-dimensional structure of the multiwalled carbon nanotubes (MWCNTs)
Summary
Some pioneering companies have launched innovative mobile smart devices, such as the Samsung Galaxy Z Flip and Huawei Mate X, which are foldable 5 G smartphones. These foldable phones are not mainstream devices, this technological trend will be maintained further and is expected to be accelerated by the development of new materials and components. Lithium-ion batteries (LIBs) have been widely used for portable electronic devices and electric vehicles owing to their high energy density (~300 Wh kg−1), high operating voltage, and long cycling lifetime. The high capacity and charge/discharge cycling performance of these materials results from their two-electron system during the electrochemical reaction. Li-S batteries can exhibit a specific energy density of ~ 2500 Wh kg−1, which is five- to tenfold higher than that of LIBs7,13–16
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