Room-temperature sodium-sulfur (RT Na-S) batteries are arousing great interest in recent years. Their practical applications, however, are hindered by several intrinsic problems, such as the sluggish kinetic, shuttle effect, and the incomplete conversion of sodium polysulfides (NaPSs). Here a sulfur host material that is based on tungsten nanoparticles embedded in nitrogen-doped graphene is reported. The incorporation of tungsten nanoparticles significantly accelerates the polysulfides conversion (especially the reduction of Na 2 S 4 to Na 2 S, which contributes to 75% of the full capacity) and completely suppresses the shuttle effect, en route to a fully reversible reaction of NaPSs. With a host weight ratio of only 9.1% (about 3-6 times lower than that in recent reports), the cathode shows unprecedented electrochemical performances even at high sulfur mass loadings. The experimental findings, which are corroborated by the first-principles calculations, highlight the so far unexplored role of tungsten nanoparticles in sulfur hosts, thus pointing to a viable route toward stable Na-S batteries at room temperatures.

Lithium-sulfur (Li-S) batteries, as part of the post-lithium-ion batteries (post-LIBs), are expected to deliver significantly higher energy densities. Their power densities, however, are today considerably worse than that of the LIBs, limiting the Li-S batteries to very few specific applications that need low power and long working time. With the rapid development of single cell components (cathode, anode, or electrolyte) in the last few years, it is expected that an integrated approach can maximize the power density without compromising the energy density in a Li-S full cell. Here, this goal is achieved by using a novel biomass porous carbon matrix (PCM) in the anode, as well as N-Co 9 S 8 nanoparticles and carbon nanotubes (CNTs) in the cathode. The authors' approach unlocks the potential of the electrodes and enables the Li-S full pouch cells with unprecedented power densities and energy densities (325 Wh kg −1 and 1412 W kg −1 , respectively). This work addresses the problem of low power densities in the current Li-S technology, thus making the Li-S batteries a strong candidate in more application scenarios.

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Smooth and fully relaxed highly boron-doped germanium layers were grown directly on Si(001) substrates using carbon-mediated epitaxy. A doping level of N 1.1 10 cm A 20 3 »´was measured by several methods. Using high-resolution x-ray diffraction we observed different lattice parameters for intrinsic and highly boron-doped samples. A lattice parameter of a Ge:B = 5.653 Å was calculated using the results obtained by reciprocal space mapping around the (113) reflection and the model of tetragonal distortion. The observed lattice contraction was adapted and brought in accordance with a theoretical model developed for ultra-highly boron-doped silicon. Raman spectroscopy was performed on the intrinsic and doped samples. A shift in the first order phonon scattering peak was observed and attributed to the high doping level. A doping level of 1.28 0.19 10 cm 20 3 ´-() was calculated by comparison with literature. We also observed a difference between the intrinsic and doped sample in the range of second order phonon scattering. Here, an intense peak is visible at 544.8 cm 1 for the doped samples. This peak was attributed to the bond between germanium and the boron isotope 11 B.

Epitaxial Ge films were grown on Si(001) substrates by molecular beam epitaxy. During epitaxial growth, two carbon interlayers were deposited at varying substrate temperatures (140−620°C) and with varying C quantity (0−1.5monolayers). The influence of the second carbon interlayer on in-plane strain was investigated using high-resolution x-ray diffraction and transmission electron microscopy (TEM). All samples exhibited compressive strain, which was attributed to substitutional incorporation of carbon atoms. In-plane strain decreases with increasing substrate temperature during carbon deposition, indicating that enhanced surface mobility of carbon adatoms leads to formation of carbon clusters. This was confirmed by cross-sectional TEM investigations. Variation of C quantity at 180°C reveals maximum strain at an intermediate quantity of 0.8 monolayers. Omission of the second C interlayer results in much lower strain, indicating a mismatch between the two Ge layers separated by a C interlayer. This could be used to enforce dislocation filtering following the principle of strained layer superlattices. An upper estimate of 1×10−3 was found for the mismatch strain, resulting in a critical thickness for dislocation filtering of hc=153nm. A sample just exceeding hc exhibited a clear dislocation reduction effect as shown by TEM.