The oxygen-doped self-supporting functional carbon nanotube sponge realized the synergistic enhancement of lithium ion transport and lithium polysulfide reaction

Abstract

Lithium-sulfur (Li-S) batteries are one of the most promising energy storage systems, in which the severe shuttle effect causes the loss of the sulfur active species and unacceptable capacity and cycling stability. Here, a self-supporting functional carbon nanotube sponge (FCNTS), electrostatically repelling polysulfide anions and allowing Li+ to pass through, is synthesized by etching channels and introducing enriched anions on CNTs based on the “Donnan effect”. The experimental results confirmed that FCNTS accelerated the Li-ion transport, that is, the Li+ transfer rates of the FCNTS materials were 8.226 (Li2S4 reduction) and 3.627 times (Li2S oxidation) that of the CNTs blank samples, respectively. Meanwhile, defects and O-group modified FCNTS regulated the local charge density of carbon-based materials, which enriched the reduction current response of the soluble Li2S4 and the oxidation current of Li2S2/Li2S around the cathode more than 1.9 and 1.6 times that of the CNTs blank samples, respectively. This significantly improved the kinetics and suppressed the overpotential. Thus, the cells assembled by S@FCNTS achieved a high-rate performance (866.9 mAh∙g−1 at 2 C), excellent stability (fading rate of only 0.035% per cycle after 500 cycles at 2 C), and a high area capacity of 13.2 mAh∙cm−2 at a high sulfur load of 10.9 mA∙cm−2. This work demonstrates a dynamic polysulfide-interception strategy to facilitate the utilization of polysulfides and provides a promising idea for the design of multi-functional sulfur storage electrode materials for high-load LSBs.