High areal capacity flexible sulfur cathode based on multi-functionalized super-aligned carbon nanotubes

Rational design of a robust carbon matrix has a profound impact on the performance of flexible/wearable lithium/sulfur batteries. Herein, we demonstrate a freestanding three-dimensional super-aligned carbon nanotube (SACNT) matrix reinforced with a multi-functionalized carbon coating for flexible, high-areal sulfur loading cathode. By employing the sulfur/nitrogen co-doped carbon (SNC) "glue", the joints in the SACNT scaffold are tightly welded together so that the overall mechanical strength of the electrode is significantly enhanced to withstand the repeated bending as well as the volume change during operation. The SNC also shows intriguing catalytic effect that lowers the energy barrier of Li ion transport, propelling a superior redox conversion efficiency. The resulting binder-free and current collector-free sulfur cathode exhibits a high reversible capacity of 1, 079 mAh·g^-1 at 1 C, a high-rate capacity of ~ 800 mAh·g^-1 at 5 C, and an average capacity decay rate of 0.037% per cycle at 2 C for 1, 500 cycles. Impressively, a large-areal flexible Li/S pouch cell based on such mechanically robust cathode exhibits excellent capacity retention under arbitrary bending conditions. With a high areal sulfur loading of 7 mg·cm^-2, the large-areal flexible cathode delivers an outstanding areal capacity of 6.3 mAh·cm^-2 at 0.5 C (5.86 mA·cm^-2), showing its promise for realizing practical high energy density flexible Li/S batteries.