LaCr0.7Fe0.3O3-NiMn2O4 supported NTC composite ceramics with a sandwich-like structure

A novel sandwich-like structure was first proposed to adjust the electrical properties of NTC thermistors. The LaCr_0.7Fe_0.3O₃-NiMn₂O₄ supported composite ceramics with sandwich-like structure were initially fabricated via traditional solid-state reaction and uniaxial pressing methods, which allowed for the advantages of each component to be integrated into one material. X-Ray diffraction analysis indicates the ceramics mainly consisting of orthorhombic perovskite LaCr_0.7Fe_0.3O₃ and cubic spinel NiMn₂O₄ phases. SEM images manifest that the three layers adhered well to each other and exhibited high density. For electrical properties, the ρ_25°C was expanded to a wide range of 1182–110,233 Ω?cm and could be adjusted to the desired values by tuning the volume ratio of two basic layers, the B value was enhanced from 3358 K to 4167 K by NiMn₂O₄, and the thermal stability was improved by LaCr_0.7Fe_0.3O₃ with a resistance shift less than 0.55 % after annealing at 150 °C for 1500 h.     

Partial self-sacrificing templates synthesis of sandwich-like mesoporous CN@Fe3O4@CN hollow spheres for high-performance Li-ion batteries

Integrating carbonaceous materials onto nano-scaled porous metal oxides to form shell-core-shell hollow structure has good prospects in the development of high-performance electrode materials for Li-ion battery, but it still remains challenging. Herein, with Fe₃O₄ hollow nanospheres as partial self-templates, we construct sandwich-like double nitrogen-doped C-shelled porous Fe₃O₄ hollow spheres by pyrolyzing polypyrrole (PPY) which is in situ polymerized on the interior and the exterior shells of Fe₃O₄ hollow spheres. And the polymerization time of PPY have important influence on thickness of carbon layer in the composites and further change their electrochemical performance. The shell-core-shell hollow structure offers highly contact between carbon and porous Fe₃O₄ and provides amount of volume stress buffer nanospaces during electrochemical processes, which promotes electron transport effectively and keeps good structural stability. The obtained sandwich-like double N-doped C-shelled porous Fe₃O₄ hollow spheres (CN@Fe₃O₄@CN HSs) are prepared as Li-ion battery anode and show an ultrahigh reversible specific capacity, high rate capability, remarkable cycle stability, excellent capacity retention (high capacity of 1048 mA h g⁻¹ after 300 cycles at 0.1 A g⁻¹, which is about 99.1% of the capacity in the 2nd cycle) and high coulombic efficiency (about 99% over 300 cycles). This research shows great potential of the sandwich-like shell-core-shell hollow structure in Li-ion batteries.     

A simple spray assisted method to fabricate high performance layered graphene/silicon hybrid anodes for lithium-ion batteries

Incorporating silicon (Si) in anodes has shown great promise for the development of high capacity Li-ion batteries (LIBs). Moreover, it is a safe and environmentally benign material, and hence suitable for large-scale manufacturing. However, volumetric expansion of Si particles upon lithiation causes irreversible damage to the anode structure and promotes an unstable solid electrolyte interface (SEI), that cause a rapid capacity drop. The architecture of successful Si-based anodes, therefore, needs to cater to the large volumetric expansion such that the high specific capacity of Si can be taken advantage of without having to worry about the detrimental effects of expansion. In this study, we introduce a simple and cost-effective spray-drying method to fabricate a layered (sandwich-like) anode structure using synthesized Si nanoparticles (NPs) and thermally reduced graphene oxide (rGO). The Si NPs are obtained by the magnesiothermic reduction of SiO₂ nanoparticles. Using an original, scalable, and simplistic spraying/drying method, we embedded Si NPs between two coats of strong yet flexible rGO sheets. The sandwich-like structure, which successfully contains the expansion of Si particles, protects the anode from detrimental conditions. With this new and uncomplicated production technique, the rGO-Si-rGO anode after 50 cycles, shows a high specific capacity of 1089 mAhg⁻¹ at 1C with 97% coulombic efficiency and a stable cycling performance at current densities up to 5C.     

Fe3O4-intercalated reduced graphene oxide nanocomposites with enhanced microwave absorption properties

Fe₃O₄-intercalated reduced graphene oxide (Fe₃O₄-rGO) nanocomposites were synthesized by an in situ reduction process. The results of XRD and XPS analyses suggested the successful formation of a Fe₃O₄ crystal phase within the rGO sheets. The SEM and TEM images demonstrated that Fe₃O₄ was flaky and was inserted stably within the rGO layers to form a typical sandwich-like structure. The hysteresis loops revealed the superparamagnetic behavior of the Fe₃O₄-rGO nanocomposites at room temperature. The electromagnetic parameters revealed that Fe₃O₄-rGO nanocomposites exhibited multiple dielectric relaxation and magnetic resonance. The reflection loss revealed that the maximum loss was −49.53 dB at 6.32 GHz for a thickness of 3.4 mm while the highest effective absorption bandwidth was 2.96 GHz.     

Super-thin LiV3O8 nanosheets/graphene sandwich-like nanostructures with ultrahigh lithium ion storage properties

With the thickness less than 5?nm, super-thin LiV₃O₈ nanosheets have already been successfully synthesized by transformation from super-thin V₂O₅·xH₂O nanosheets, moreover, super-thin LiV₃O₈ nanosheets@graphene (LVO/G) sandwich-like layer-by-layer nanostructures were successfully obtained via a facile self-assembly method and annealing treatment. Such interesting LVO/G nanostructures as cathodes for lithium ion batteries not only show high capacity up to 397.2?mA?h?g^?1 and outstanding rate capabilities (171?mA?h?g^?1 at 10?C, 112?mA?h?g^?1 at 15?C), but also present super-long cycle performance (301.2?mA?h?g^?1 after 500 cycles at 1?C). As far as we known, the LVO/G cathodes exhibit ultrahigh lithium storage performances even much higher than those of previously reported literatures of LiV₃O₈, which demonstrates that such sandwich-like layer-by-layer LVO/G nanostructures is a potential candidate cathode material for the next generation of batteries.     

High-performance asymmetric supercapacitors based on reduced graphene oxide/polyaniline composite electrodes with sandwich-like structure

The sandwich-like structure of reduced graphene oxide/polyaniline(RGO/PANI) hybrid electrode was prepared by electrochemical deposition. Both the voltage windows and electrolytes for electrochemical deposition of PANI and RGO were optimized. In the composites, PANI nanofibers were anchored on the surface of the RGO sheets, which avoids the re-stacking of neighboring sheets. The RGO/PANI composite electrode shows a high specific capacitance of 466 F/g at 2 m A/cm~2 than that of previously reported RGO/PANI composites. Asymmetric flexible supercapacitors applying RGO/PANI as positive electrode and carbon fiber cloth as negative electrode can be cycled reversibly in the high-voltage region of 0–1.6 V and displays intriguing performance with a maximum specific capacitance of 35.5 m F cm~(-2). Also, it delivers a high energy density of 45.5 m W h cm~(-2) at power density of 1250 m W cm~(-2). Furthermore, the asymmetric device exhibits an excellent long cycle life with 97.6% initial capacitance retention after 5000 cycles.Such composite electrode has a great potential for applications in flexible electronics, roll-up display,and wearable devices.     

One-pot solvothermal synthesis of sandwich-like graphene nanosheets/Fe3O4 hybrid material and its microwave electromagnetic properties

A novel sandwich-like graphene nanosheets (GNs)/Fe₃O₄ hybrid material was synthesized through a facile one-pot solvothermal method using FeCl₃ as iron source, ethylene glycol as the reducing agent and graphene nanosheets as templates. The Fe₃O₄ nanoparticles, with the average diameters of ca. 40 nm, were self-assembled on the graphene nanosheets through electrostatic attraction and formed sandwich-like nanostructure. The ferromagnetic signature emerged with the saturated magnetization of ~ 72.3 emu g^− 1, and the coercive force of ~ 196.1 Oe at 300 K. The magnetic loss was caused mainly by natural resonance which is in agreement with the Kittel equation. The novel electromagnetic hybrid material is believed to have potential applications in the microwave absorbing performances.