Advancements in Microwave Absorption Motivated by Interdisciplinary Research.

Microwave absorption materials (MAMs) are originally developed for military purposes, but have since evolved into versatile materials with promising applications in modern technologies, including household use. Despite significant progress in bench-side research over the past decade, MAMs remain limited in their scope and have yet to be widely adopted. This review explores the history of MAMs from first-generation coatings to second-generation functional absorbers, identifies bottlenecks hindering their maturation. It also presents potential solutions such as exploring broader spatial scales, advanced characterization, introducing liquid media, utilizing novel toolbox (machine learning, ML), and proximity of lab to end-user. Additionally, it meticulously presents compelling applications of MAMs in medicine, mechanics, energy, optics, and sensing, which go beyond absorption efficiency, along with their current development status and prospects. This interdisciplinary research direction differs from previous research which primarily focused on meeting traditional requirements (i.e., thin, lightweight, wide, and strong), and can be defined as the next generation of smart absorbers. Ultimately, the effective utilization of ubiquitous electromagnetic (EM) waves, aided by third-generation MAMs, should be better aligned with future expectations.

An Ultrastrong and Antibacterial Silver Nanowire/Aligned Cellulose Scaffold Composite Film for Electromagnetic Interference Shielding.

Constructing multifunctional electromagnetic interference (EMI) shielding films with superior mechanical strength has sparked a lot of interest in the fields of wearable electronics. In this work, the conductive silver nanowires (AgNWs) were synthesized and impregnated into the highly aligned cellulose scaffold (CS) fabricated by wood delignification followed by hot-pressing and polydimethylsiloxane (PDMS) dipping processes to obtain the outstanding EMI shielding cellulosic film (d-AgNWs@CS-PDMS). The consecutively conductive pathway of AgNWs was constructed in the microchannels of the CS as a result of the hydrogen bonding between AgNWs and cellulose fibers, which is conducive to the reflection of incident EM waves. The higher degree of nanofiber alignment and the compact conductive network were improved by densification upon hot pressing, which endows the composite film with striking mechanical properties (maximum tensile strength of 511.8 MPa) and superb EMI shielding performance (shielding effectiveness value of 46 dB with a filler content of 21.6 wt %) at the X band (8.2-12.4 GHz). Moreover, the existence of an intensive AgNWs network and the introduction of the PDMS layer improve the hydrophobicity and antibacterial activity of the composite film, avoiding serious health concerns in the long-term wearing. These results demonstrate that the obtained d-AgNWs@CS-PDMS composite film has high potential as an EMI shielding material used for wearable devices.

Spinel-Layered Intergrowth Composite Cathodes for Sodium-Ion Batteries.

The vital challenge of a layered manganese oxide cathode for sodium-ion batteries is its severe capacity degradation and sluggish ion diffusion kinetics caused by irreversible phase transitions. In response to this problem, the spinel-layered manganese-based composite with an intergrowth structure is ingeniously designed by virtue of an interesting spinel-to-layered transformation in the delithiated LiMn2O4 under Na+ insertion. This unique spinel-layered intergrowth structure is strongly confirmed by combining multiple structure analysis techniques. The layered component can provide more reversible capacity, while the spinel component is crucial for the stabilized crystal structure and accelerated ion diffusion kinetics. As an appealing cathode for sodium-ion batteries, the layered-spinel composite delivers a high reversible capacity of 180.9 mAh g-1, excellent cycling stability, and superior rate capability with 55.7 mAh g-1 at 12 C. Furthermore, the reaction mechanism upon Na+ extraction/insertion is revealed in detail by ex situ X-ray diffraction and X-ray photoelectron spectroscopy, indicating that Na+ ions can be accommodated by the layered structure at a low voltage and by the spinel at a high voltage. This study will provide a new idea for the rational design of an advanced cathode for sodium-ion batteries.

Morphology Design of Co-electrospinning MnO-VN/C Nanofibers for Enhancing the Microwave Absorption Performances.

To enhance microwave loss abilities, constructing composites with one-dimensional (1D) structure is an excellent scheme. In this work, a high-efficiency microwave absorber of MnO nanograins decorated vanadium nitride/carbon nanofibers (MnO-VN/C NFs) was successfully prepared for the first time via co-electrospinning technology and subsequent nitriding treatment. Studying in detail the specific relationship between nitriding time and the morphology of the as-prepared NFs, the precipitations of MnO nanoparticles with tailored structures were attached on the surface of VN/C NFs to optimize their electromagnetic parameters. When the nitriding time was 2.0 h at 600 °C, the MnO-VN/C NFs displayed good microwave absorption performances: the minimum reflection loss (RL) value was -63.2 dB at 8.8 GHz, and the bandwidth of RL < -10 dB was up to 6.4 GHz from 11.6 to 18 GHz at the thickness of 2.8 mm. Meanwhile, the absorption bandwidth (RL< -10 dB) could cover the whole X and Ku band by adjusting the thickness, respectively. The outstanding performances could be attributed to the good impedance matching and various loss pathways including conductive loss and interfacial and dipole polarizations. In these regards, MnO-VN/C NFs are likely to be utilized as a high-efficiency microwave absorber. And the strategy in this work can provide great help to design other 1D structural microwave absorbers with a broader absorbing band.