Sulfur (S) is an attractive cathode material with advantages including high theoretical capacity and low cost. However, issues such as the lithium polysulfide shuttle effect and its insulating properties greatly limit the future applications of lithium‐sulfur (Li‐S) batteries. Here, a viscous aqueous ink with nanoscale S uniformly decorated on the polar, metallically conductive titanium carbide MXene nanosheets (S@Ti3C2Tx) is reported to address these issues. Importantly, it is observed that the conductive Ti3C2Tx mediator efficiently chemisorbs the soluble polysulfides and converts them into thiosulfate/sulfate. The in situ formed sulfate complex layer acts as a thick protective barrier, which significantly retards the shuttling of polysulfides upon cycling and improves the sulfur utilization. Consequently, the binder‐free, robust, highly electrically conductive composite film exhibits outstanding electrochemical performance, including high capacities (1244–1350 mAh g‐1), excellent rate handling, and impressive cycling stability (0.035–0.048% capacity loss per cycle), surpassing the best MXene‐S batteries known. The fabrication of a pouch cell based on the freestanding S@Ti3C2Tx film is also reported. The prototype device showcases high capacities and excellent mechanical flexibility. Considering the broad family of MXenes and their unique roles in immobilizing the polysulfides, various S@MXene composites can be similarly fabricated with promising Li+ storage capability and long lifetime performance.
High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite (SG) as the attenuating agent were fabricated through hot-pressing sintering. The SG maintains its three-dimensional (3D) morphology within the sintered bodies, which considerably impedes the sintering of the composites to some extent but slightly influences on the growth of AlN grains. The addition of SG reduces the strength of the composites, but provides a moderate toughening effect at the optimal addition amount (3.8 MPa·m1/2 at 4 wt% SG). Benefiting from the low anisotropy, high thermal conductivity, and the 3D morphology of SG, the composites exhibit a relatively higher thermal conductivity (76.82 W·m−1·K−1 at 10 wt% SG) compared with composites added with non-spherical attenuating agent. The dielectric constant and loss (8.2–12.4 GHz) increase remarkably as the amount of SG added increases up to 8 wt%, revealing that the incorporation of SG improves the dielectric property of the composite. The composite with 7 wt% SG exhibits the best absorption performance with a minimum reflection loss of −13.9 dB at 12.4 GHz and an effective absorbing bandwidth of 0.87 GHz. The excellent overall properties of the SG/AlN microwave attenuating composites render them as a promising material for various applications. Moreover, SG has a great potential as an attenuating agent for microwave attenuating composites due to its strong attenuation upon integration, high thermal conductivity, and low anisotropy.
SiC-AlN multiphase ceramics with 10 wt. %Y2O3-BaO-SiO2 additives were fabricated by pressureless sintering in a nitrogen atmosphere. The effects of SiC contents and sintering temperatures on the sinterability, microstructure, thermal conductivity and high-frequency dielectric properties were characterized. In addition to 6H-SiC and AlN, the samples also contained Y3Al5O12 and Y4Al2O9. SiC-AlN ceramics sintered with 50 wt. % SiC at 2173 K exhibited the best thermal diffusivity and thermal conductivity (26.21 mm2·s−1 and 61.02 W·m−1·K−1, respectively). The dielectric constant and dielectric loss of the sample sintered with 50 wt. % SiC and 2123 K were 33–37 and 0.4–0.5 at 12.4–18 GHz. The dielectric constant and dielectric loss of the samples decreased as the frequency of electromagnetic waves increased from 12.4–18 GHz. The dielectric thermal conductivity properties of the SiC-AlN samples are discussed.