RESUMO
Due to the shuttle effect and low conductivity of sulfur (S), it has been challenging to realize the application of lithium-sulfur (Li-S) batteries with high performance and long cyclability. In this study, a high catalytic active CNTs@FeOOH composite is introduced as a functional interlayer for Li-S batteries. Interestingly, the existence of oxygen vacancy in FeOOH functions electrocatalyst and promotes the catalytic conversion of intercepted lithium polysulfides (LiPS). As a result, the optimized CNTs@FeOOH interlayer contributed to a high reversible capacity of 556 mAh g-1 at 3,200 mA g-1 over 350 cycles. This study demonstrates that enhanced catalytic effect can accelerate conversion efficiency of polysulfides, which is beneficial of boosting high performance Li-S batteries.
RESUMO
Li-metal batteries are the preferred candidates for the next-generation energy storage, due to the lowest electrode potential and high capacity of Li anode. However, the dangerous Li dendrites and serious interface reaction hinder its practical application. In this work, we construct a difunctional protecting layer on the surface of the Li anode (the AgNO3-modified Li anode, AMLA) for Li-S batteries. This stable protecting layer can hinder the corrosion reaction with intermediate polysulfides (Li2Sx, 4 ≤ x ≤ 8) and suppress the Li dendrites by regulating Li metal nucleation and depositing Li under the layer uniformly. The AMLA can cycle more than 50 h at 5 mA cm-2 with the steady overpotential of lower than 0.2 V and show high capacity of 666.7 mAh g-1 even after 500 cycles at 0.8375 mA cm-2 in Li-S cell. This work makes great contribution to the protection of the Li anode and further promotes the practical application.
RESUMO
Nanocarbon-based materials, such as carbon nanotubes (CNTs) and graphene have been attached much attention by scientific and industrial community. As two representative nanocarbon materials, one-dimensional CNTs and two-dimensional graphene both possess remarkable mechanical properties. In the past years, a large amount of work have been done by using CNTs or graphene as building blocks for constructing novel, macroscopic, mechanically strong fibrous materials. In this review, we summarize the assembly approaches of CNT-based fibers and graphene-based fibers in chronological order, respectively. The mechanical performances of these fibrous materials are compared, and the critical influences on the mechanical properties are discussed. Personal perspectives on the fabrication methods of CNT- and graphene-based fibers are further presented.
RESUMO
Supercapacitors with porous electrodes of graphene macroscopic assembly are supposed to have high energy storage capacity. However, a great number of "close pores" in porous graphene electrodes are invalid because electrolyte ions cannot infiltrate. A quick method to prepare porous graphene electrodes with reduced "close pores" is essential for higher energy storage. Here we propose a wet-spinning assembly approach based on the liquid crystal behavior of graphene oxide to continuously spin orientational graphene hydrogel films with "open pores", which are used directly as binder-free supercapacitor electrodes. The resulting supercapacitor electrodes show better electrochemical performance than those with disordered graphene sheets. Furthermore, three reduction methods including hydrothermal treatment, hydrazine and hydroiodic acid reduction are used to evaluate the specific capacitances of the graphene hydrogel film. Hydrazine-reduced graphene hydrogel film shows the highest capacitance of 203 F g(-1) at 1 A g(-1) and maintains 67.1% specific capacitance (140 F g(-1)) at 50 A g(-1). The combination of scalable wet-spinning technology and orientational structure makes graphene hydrogel films an ideal electrode material for supercapacitors.