Hierarchical structures of graphene@Fe3O4@SiO2@NiO nanosheets were prepared by combining the versatile sol-gel process with a hydrothermal reaction. Graphene@Fe3O4 composites were first synthesized by the reduction reaction between FeCl3 and diethylene glycol (DEG) in the presence of GO. Then, graphene@Fe3O4 was coated with SiO2 to obtain graphene@Fe3O4@SiO2. Finally, NiO nanosheets were grown perpendicularly on the surface of graphene@Fe3O4@SiO2 and graphene@Fe3O4@SiO2@NiO nanosheet hierarchical structures were formed. Moreover, the microwave absorption properties of both graphene@Fe3O4 and graphene@Fe3O4@SiO2@NiO nanosheets were investigated between 2 and 18 GHz microwave frequency bands. The electromagnetic data demonstrate that graphene@Fe3O4@SiO2@NiO nanosheet hierarchical structures exhibit significantly enhanced microwave absorption properties compared with graphene@Fe3O4, which probably originate from the unique hierarchical structure with a large surface area and high porosity.

a conventional battery, such as good electrochemical performance, affordable price, and high safety.A conventional full cell LIB is a complicated device, composed of a current collector, a cathode, an anode, a separator, an electrolyte, and a proper packaging. To fabricate a stretchable full cell, we need to replace all these components with materials that can provide simultaneously the appropriate electrochemical functionalities as well as the intrinsic mechanical stretchability. Many components that could potentially be used in a stretchable battery have been presented in the literature. For example, several approaches have been reported for fabricating stretchable electrodes by incorporating rigid electrode materials within a porous framework, with a wavy design, or with helically coiled spring configuration. [6] However, these structures are usually complicated and costly to produce and scale-up, and, due to the use of polydimethylsiloxane (PDMS) or other substrates, the cells are thick and heavy. [7] Also, stretchable composite conductors for applications in electronics have been widely investigated. [8] However, there are only very few reports targeting battery current collectors. [7,9] The sheet resistances of the reported materials range from around 150 to 200 Ω □ −1 in the unstretched states and get much higher when stretched, producing significant internal resistance. Polymer gel electrolytes (PGEs) composed of poly(vinylidene fluoride) (PVDF), [10] poly(ethylene glycol) (PEG), [11] poly(ethylene oxide) (PEO), [12] or poly(ionic liquid) [13] are widely accepted as promising solution for flexible LIBs due to their advantageous flexibility, safety, and packaging behavior compared to the liquid electrolytes with a porous separator. Unfortunately, PGEs usually show quite a low room temperature ionic conductivity that ranges from 10 −4 to 10 −3 S cm −1 . Since 2015, "water-in-salt" (WiS) aqueous electrolytes containing extremely concentrated lithium salt have been investigated. [14] Some of these WiS-based gel electrolytes have also been reported to show better safety and robustness compared with the conventional PGE. [15] However, none of these materials exhibited mechanical stretchability.It is interesting to note that although so many stretchable battery components have been reported, their processing into full cells is rarely described, and even in these cases, usually not all the LIB components were made stretchable. [7,16] The reason for this is the diffculty in obtaining robust conductive interfaces between the battery components enabling efficient ion and A solid-state lithium-ion battery, in which all components (current collector, anode and cathode, electrolyte, and packaging) are stretchable, is introduced, giving rise to a battery design with mechanical properties that are compliant with flexible electronic devices and elastic wearable systems. By depositing Ag microflakes as a conductive layer on a stretchable carbon-polymer composite, a current collector with a low sheet resistance of ≈2.7 Ω ...

A general method for preparing nano-sized metal oxide nanoparticles with highly disordered crystal structure and their processing into stable aqueous dispersions is presented. With these nanoparticles as building blocks, a series of nanoparticles@reduced graphene oxide (rGO) composite aerogels are fabricated and directly used as high-power anodes for lithium-ion hybrid supercapacitors (Li-HSCs). To clarify the effect of the degree of disorder, control samples of crystalline nanoparticles with similar particle size are prepared. The results indicate that the structurally disordered samples show a significantly enhanced electrochemical performance compared to the crystalline counterparts. In particular, structurally disordered Ni FeO @rGO delivers a capacity of 388 mAh g at 5 A g, which is 6 times that of the crystalline sample. Disordered Ni FeO @rGO is taken as an example to study the reasons for the enhanced performance. Compared with the crystalline sample, density functional theory calculations reveal a smaller volume expansion during Li insertion for the structurally disordered Ni FeO nanoparticles, and they are found to exhibit larger pseudocapacitive effects. Combined with an activated carbon (AC) cathode, full-cell tests of the lithium-ion hybrid supercapacitors are performed, demonstrating that the structurally disordered metal oxide nanoparticles@rGO||AC hybrid systems deliver high energy and power densities within the voltage range of 1.0-4.0 V. These results indicate that structurally disordered nanomaterials might be interesting candidates for exploring high-power anodes for Li-HSCs.

Microporous nitrogen-rich carbon fibers (HAT-CNFs) are produced by electrospinning a mixture of hexaazatriphenylene-hexacarbonitrile (HAT-CN) and polyvinylpyrrolidone and subsequent thermal condensation. Bonding motives, electronic structure, content of nitrogen heteroatoms, porosity, and degree of carbon stacking can be controlled by the condensation temperature due to the use of the HAT-CN with predefined nitrogen binding motives. The HAT-CNFs show remarkable reversible capacities (395 mAh g −1 at 0.1 A g −1 ) and rate capabilities (106 mAh g −1 at 10 A g −1 ) as an anode material for sodium storage, resulting from the abundant heteroatoms, enhanced electrical conductivity, and rapid charge carrier transport in the nanoporous structure of the 1D fibers. HAT-CNFs also serve as a series of model compounds for the investigation of the contribution of sodium storage by intercalation and reversible binding on nitrogen sites at different rates. There is an increasing contribution of intercalation to the charge storage with increasing condensation temperature which becomes less active at high rates. A hybrid sodium-ion capacitor full cell combining HAT-CNF as the anode and salt-templated porous carbon as the cathode provides remarkable performance in the voltage range of 0.5-4.0 V (95 Wh kg −1 at 0.19 kW kg −1 and 18 Wh kg −1 at 13 kW kg −1 ).

Na‐ion hybrid capacitors are an emerging class of inexpensive and sustainable devices that combine the high energy of batteries with the high power of capacitors. However, their development is strongly impeded by a limited choice of electrode materials that display good electrochemical kinetics and long‐term cyclability. Here, a reduced graphene oxide–Zn0.25V2O5·nH2O nanobelt composite is introduced as a high power anode for Na‐ion batteries and Na‐ion hybrid capacitors. The composite material possesses fast Na‐ion intercalation kinetics, high electronic conductivity, and small volume change during Na‐ion storage, which lead to outstanding rate capability and cycling stability in half‐cell tests. Pairing it with a hard salt–templated, highly ordered mesoporous carbon as a high‐performance capacitive cathode results in a Na‐ion hybrid capacitor, which delivers a high energy density (88.7 Wh kg−1 at 223 W kg−1), a high power density (12552 W kg−1 with 13.2 Wh kg−1 retained), and an impressive cycling performance (31.7 Wh kg−1 (i.e., 87%) retained after 2000 cycles at 1 A g−1). This work explores zinc vanadate, a typical example of a layered metal vanadate, as an intercalation anode material with high pseudocapacitance for Na‐ion hybrid capacitors, which may open a promising direction for high‐rate Na‐ion storage.