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[Display omitted] Carbon nanotubes (CNTs) are often used to settle down the sluggish reaction kinetics in lithium–sulfur batteries (LSBs). However, the self-aggregation of CNTs often makes them fail to effectively inhibit the shuttling effect of soluble lithium polysulfide (LiPS) intermediates. Herein, a type of ultra-stable carbon micro/nano-scale interconnected "carbon cages" has been designed by incorporating polar acid-treated carbon fibers (ACF) into three-dimensional (3D) CNT frameworks during vacuum filtration processes. Results show that the ACF-CNT composite frameworks possess a reinforced-concrete-like structure, in which the ACFs can well work as the main mechanical supporting frames for the composite electrodes, and the oxygen-containing functional groups (OFGs) formed on them as cross linker between ACFs and CNTs. Benefitted from this design, the ACF-CNT/S cathodes deliver an excellent rate capability (retain 72.6% at 4C). More impressively, the ACF-CNT/S cathodes also show an ultrahigh cycling stability (capacity decay rate of 0.001% per cycle over 350 cycles at 2C). And further optimization suggests that the suitable treatment on CFs could balance the chemical adsorption (OFGs) and physical confinement (carbon cages), leading to fast and durable electrochemical reaction dynamics. In addition, the assembled soft-pack LSBs further show a high dynamic bending stability. [ABSTRACT FROM AUTHOR]

It was demonstrated that the electrochemical performance enhancements in KOH-activated carbon materials should be mainly due to the created polar oxygen-containing functional groups (OFGs, such as such as C–O, C O, –OH, and O–C O), while the role of each OFGs on the electrochemical enhancements is still unclear. In this work, KOH activation treatments were systematically conducted on carbon nanotubes (CNTs) to explore the role of each OFG on the performance enhancements of Li–S batteries (LSBs). Results showed that the capacity of activated-CNT-sulfur (a-CNT-S) cathodes is 33% higher than that of the pristine CNT-S cathodes, and their rate capability and cycling stability are also enhanced. And the electrochemical analysis combining with Fourier transform infrared spectroscopy indicated that the formed C–O bonds are the real factor for the enhanced electrochemical performances of a-CNT-S cathodes. Furthermore, the optimal activation conditions on CNT-based cathodes for LSBs were optimized to be 10 min at 700 °C. Image 1 • KOH activated CNTs (a-CNTs) were used as the sulfur hosts for Li-S batteries. • FTIR tests indicated a-CNT-S cathodes' performances are linearly dependent on the C−O bonds. • The optimal activation conditions on CNT hosts were determined (10 min, 700 °C). [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) and their related hybrids grown by chemical vapor deposition (CVD) method have been frequently used as energy-storage electrode materials. In most cases, the tips of CNTs are almost well closed, which often limits the utilization efficiency of their tubular structure in storage of charges. In this work, the authors have designed a type of tip-open CNT/CNF hierarchical hybrids via KOH activation on the CVD-grown Al/Fe-catalyzed CNT/CNF precursors. Results showed that the CNT hierarchies' tips can be fully opened via KOH activation at 700–750 °C for 90 min. As expected, the tip-open CNT-CNF hybrids show a highly improved specific capacitance, which increases by 3.3 times that of the pristine ones. Moreover, sweep analysis indicated that the diffusion-type capacitance increases by 3.7 times while the Helmholtz-type capacitance increases only by 1.5 times, indicating that the tip-open CNTs contribute to ∼30% of the increase in double-layer capacitance. Further optimization on activation time and temperature indicated that activation at 700 °C for 90 min is suitable for opening the tips of CNT hierarchies and protecting the CNTs' tubular structure. This research would give some useful advice for the preparation of high-performance CNT-related electrode materials for energy storage. Image 1 [ABSTRACT FROM AUTHOR]