A Typha Angustifolia-like MoS2/carbon nanofiber composite for high performance Li-S batteries

A Typha Angustifolia-like MoS2/carbon nanofiber composite as both a chemically trapping agent and redox conversion catalyst for lithium polysulfides has been successfully synthesized via a simple hydrothermal method. Cycling performance and coulombic efficiency have been improved significantly by applying the Typha Angustifolia-like MoS2/carbon nanofiber as the interlayer of a pure sulfur cathode, resulting in a capacity degradation of only 0.09% per cycle and a coulombic efficiency which can reach as high as 99%

Airborne topological acoustics

Advances in topological acoustics are leading to potential development for noise attenuation, ultrasonic imaging, sound manipulation, and information delivering, etc. Recently, ideas and methodologies from condensed-matter physics, such as the quantum Hall effect (QHE), the quantum spin Hall effect (QSHE), and the quantum valley Hall effect (QVHE), combined with configurations of sonic crystals and metamaterials, have been investigated in manipulating acoustic transmissions in the form of one-way edge modes and defect-immune protected acoustics. However, many related studies are still in their infancy and mostly rely on bulky, noisy, overly complicated, untunable and narrow-band-effective facilities, and so it is highly desirable but challenging to design more practical topological acoustic systems, with backscattering immune, tunable, broadband and miniaturized topological acoustic properties. This thesis investigates novel modulation mechanisms, versatile configurable lattice structures, and microscale acoustic transmission mechanisms to solve the aforementioned airborne topological acoustic challenges. Starting with the rotating modified spiral springs configuration adjusting the inner radius without altering the external lattice structure, a gapless topologically protected acoustic flow-free resonator system based on the QVHE in reconfigurable sonic crystals is designed to realize backscattering immune, tunable and broadband functional acoustic applications. Then, based on the acoustic analogue of the QHE, to replace the generating mechanism of the noisy fan-induced airflow, a new method using heat-induced natural convection coupled with an acoustic circulator is proposed to realize robust nonreciprocal acoustic propagation. This strategy is more feasible because of its dynamic control and versatile topological structures in the absence of moving parts. To further promote the topological acoustics into a more practical stage, based on the QSHE, a temperature modulation scheme is designed to demonstrate that the Floquet topological insulators with thermal-induced impedance matching can realize robust topological acoustic propagation, which is especially useful for noiseless and miniaturized airborne acoustics. Thermal modulation enables miniaturized topological airborne acoustics to the millimeter scale or even smaller. Additionally, a theoretical model with a second-order slip boundary to iii describe acoustic wave propagation in micro- and nanochannels is proposed to investigate the miniaturized topological acoustic transmission mechanism. Based on the molecular-based direct simulation Monte Carlo (DSMC) method, this model provides an analytical solution beneficial for topological acoustics in ultrasonic or in miniaturized structures