Oriented outperforms disorder: Thickness-independent mass transport for lithium-sulfur batteries

Abstract

Extreme fast charging in a thick electrode film is critical for high rate lithium sulfur batteries. However, the high ion-path tortuosity of most carbon/sulfur cathodes dramatically hinder their mass transport, thus leading to poor rate performance. This situation goes worse with increasing the electrode thickness. Here, we report a binder-free vertically-aligned carbon nanotube/sulfur (VACNT/S) cathode with an excellent thickness-independent mass transport and high-rate performance. Compared with a conventional disordered carbon nanotube/sulfur electrode, the highly conductive VACNTs provide directional paths for the ultrafast transfer of both lithium ions and electrons, leading to improved kinetics and a stable redox activity. The VACNT/S electrode shows an extremely high initial specific capacity of 894 mA h g−1 at a 5 C rate, and very stable charge/discharge performance with a capacity of 486.1 mA h g−1 after 400 cycles and a low capacity decay rate of 0.1% per cycle. This work demonstrates an efficient pathway for the design of electrodes for high-rate lithium sulfur batteries.