Flexible Nickel Research Articles

Flexible nickel–cobalt double hydroxides micro-nano arrays for cellular secreted hydrogen peroxide in-situ electrochemical detection

It is critical to detect cellular secreted hydrogen peroxide (H2O2) in situ for clinical diagnosis, biomedical research and cancer treatment. Herein, the electrochemical determination of H2O2 released by cancer cells grown on the surface of carbon cloth supported NiCo-DH/AuPt micro-nano arrays to elevate the capability of in situ signal collection was achieved. NiCo-DH/AuPt @CC was successfully prepared using the cobalt based metal–organic framework (Co-MOF) as a presoma after in situ etching growth onto the CC and electrodeposition of gold and platinum nanoparticles (AuPt NPs). Under the optimal conditions, owing to the excellent catalytic efficiency of NiCo-DH and AuPt NPs, the designed sensor performs a relatively wider linear range to H2O2 concentration from 10 μM to 22.08 mM, and the limit of detection is 0.145 μM. Accordingly, the as-prepared sensing system was also applied to determine H2O2 secreted by living cells which grown on the surface of NiCo-DH/AuPt @CC with satisfactory consequences. In possession of the superior sensitivity, selectivity, reproducibility, the NiCo-DH/AuPt @CC is a luciferous platform for the real time detection of H2O2 in the area of biomedical and clinical diagnosis.

Flexible nickel Prussian blue analogue films for electrochromic and H2O2 sensing

We showed that nickel Prussian blue analogue (NiPBA) films were electrochemically deposited onto a conducting transparent indium tin oxide coated with polyethylene terephthalate electrodes. The flexible NiPBA films were characterized by means of scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS), X-ray photoelectronspectroscopy technique and X-ray diffraction analyses. Electrochromic performance of the flexible NiPBA films was investigated using cyclic voltammetry, chronoamperometry and chronocoulometry methods. The coloration, bleaching times and reversibility of the NiPBA film were calculated as 5.8 s, 2.7 s, and 97.37% in KCl liquid electrolyte medium, respectively. Electrocatalytic behavior of the NiPBA film towards H2O2 sensor was also evaluated by chronoamperometry technique. The flexible NiPBA film showed a linear response to H2O2 in concentration range of 3.92 to 15.68 mM (R2 = 0.9906), sensitivity of 1.6272 µAmM−1 cm−2. After performing repeated bended cycle tests, the flexible NiPBA films showed good mechanical stability in terms of both electrochromic and H2O2 sensing properties. The presented results can promote its potential application in wearable devices, displays, which are flexible states for monitoring.

A multi-dimensional and level-by-level assembly strategy for constructing flexible and sandwich-type nanoheterostructures for high-performance electromagnetic interference shielding.

To shield against massive electromagnetic pollution and meet increasing demand in portable electronics, the development of flexible, lightweight and high-performance electromagnetic interference (EMI) shielding materials with good environmental friendliness is an urgent but still challenging need. Herein, a creative multi-dimensional and level-by-level assembly strategy is proposed to construct free-standing and sandwich-type nanoheterostructures consisting of flexible cotton-derived carbon fibers (CFs), magnetic and conductive nickel nanoparticles (Ni NPs) and highly conductive and large-surface-area dandelion-like graphene (DLG), via a high-precision combination technology of magnetron sputtering-plasma enhanced chemical vapor deposition. The multiple spatial-scale DLG/Ni NPs/CF composites achieve a remarkable conductivity of 625 S m-1 and an outstanding EMI shielding effectiveness of ∼50.6 dB in the X-band (8.2-12.4 GHz) which can be classified as attenuation levels of "AAAA" for professional use. The dielectric loss from multiple polarizations is principally responsible for the electromagnetic loss of the composites. Besides, the large surface area of heterogeneous interfaces and defects in DLG contribute to enhancing the amount of polarization. In addition, the ultrathin and ultralight composites (d = 0.65 mm, ρ = 113 mg cm-3) can be bent, twisted and folded, revealing their excellent processability for commercial uses. More importanly, this novel structural design concept opens up an interesting promising research field of novel next-generation EMI shielding materials.

Flexible integrated metallic glass-based sandwich electrodes for high-performance wearable all-solid-state supercapacitors

The design and preparation of nanoporous metal (NPM)/metallic oxides (or hydroxides) electrodes with good flexibility as well as high energy storage performance has become a great challenge for applications in wearable electronic products. Herein, we report a novel strategy to synthesize flexible nickel oxide/hydroxide coated nanoporous nickel (np-NiOxHy@Ni) electrode containing metallic glass (MG) interlayer (np-NiOxHy@Ni/MG/np-NiOxHy@Ni sandwich) by one-step dealloying of Ni40Zr20Ti40 MG ribbons. Benefiting from the ductile MG interlayer, the sandwich-like electrode presents excellent flexibility, which has not been reported for other dealloyed porous ribbons. Electrochemical measurements show that the electrode is essentially a battery-type material while it also exhibits pseudocapacitive behavior. Due to an integrated sandwich structure and np-NiOxHy@Ni shell@core network, the electrode displays an enhanced capacitance of 778 F cm−3 at 1 A cm−3 in KOH solutions (achieves 3536.01 F cm−3 when just considering the volume of the dealloyed layer) and a remarkable rate performance (80.3 % retention when the current density increase by 128-fold), as well as an outstanding cycle stability (100 % capacitance retention after 8000 cycles). Furthermore, the cable-like all-solid-state flexible supercapacitor (CAFS) device assembled by this flexible electrode can bear a bending of 0–180° without significant performance change. The highest volumetric energy density of 28.52 mW h cm−3 with a power density of 0.10 W cm−3 is obtained, which far exceeds commercially available supercapacitors (<1 mW h cm−3) and thin-film lithium batteries (0.3–10 mW h cm−3). Moreover, a wearable system by the integration of the CAFS device with an electronic watch is achieved, which amazingly runs for more than 25 min. The introduction of MG into NPM composites greatly improves the flexibility, which harnesses the promise for applying dealloyed materials in advanced wearable devices.

Annealing temperature effect on 3D hierarchically porous NiO/Ni for removal of trace hexavalent chromium

Three-dimensional (3D) hierarchically porous NiO/Ni composites were fabricated by hydrothermal method combined with subsequent annealing process. First, nickel hydroxide (Ni(OH)2) nanosheets were synthesized on flexible and porous nickel foam to form Ni(OH)2/Ni. Second, 3D porous nickel oxide (NiO) nanosheets grown on nickel substrate, named NiO/Ni, were obtained by thermal decomposition of Ni(OH)2/Ni in air at 400–650 °C for 3 h. The prepared samples were applied as adsorbents for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions and characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption and desorption to analyze their structures and compositions. NiO nanosheets grow on the 3D nickel foam provide more active sites and the large connected macropores are favorable to flow of solution. Numerous mesopores and micropores emerged on NiO nanosheets after thermal calcination, leading to high surface area favorable to adsorption of Cr(VI) ions. The results show that NiO/Ni annealed at 400 °C provides the maximum specific surface area (22 m2 g−1) and best removal capacity (25.94 mg g−1) at pH 4 with excellent recyclling performance. The pseudo-first-order kinetic fitting suggests the physical adsorption of Cr(VI) on NiO/Ni surface and the possible adsorption mechanism was investigated. Moreover, the effect of contact time, initial concentration of Cr(VI), pH, and matrix anion were studied in detail.

Polymorphic Structure of 1T´-Mo6Te6 Nanoplates and Few-atomic-layered 2H-MoTe2 for Efficient Pseudocapacitor

Te-based transitional metal dichalcogenides (TMDs) as supercapacitors are gaining substantial attention with a few reports. The integration of 1T´-Mo6Te6 nanoplates (NPs) into few-atomic-layered two dimensional (2D) 2H-MoTe2 thin film has not been realized in supercapacitive studies. Herein, we demonstrate the growth of 1T´-Mo6Te6 NP/2H-MoTe2 thin film polymorphic structure through metal organic chemical vapor deposition (MOCVD) on Si/SiO2 and thereby, the successful transfer of these polymorphic structure on a flexible nickel (Ni) foam current collector by simple chemical etching protocol for high performance supercapacitors. A layer by layer study of the Mo6Te6/MoTe2 polymorphic structure is carried out by varying the number of transfer layers on the Ni foam. The resultant supercapacitors demonstrate a three-fold enhancement in areal capacitance (1542 mFcm-2 at 10 mVs-1) compared to a single layer transferred electrode, together with remarkable electrochemical stability (96%) and high energy density (140.36 mWcm-2 at 4 mA). These supercapacitors outperform the TMD-based (Te-based) supercapacitors presented in the past, demonstrating the high potential for their application in energy conversion devices. Keywords: 2D TMD, 1T´ phase, molybdenum ditelluride, 1D/2D polymorphic structure, supercapacitor

Electrodeposited Stable Binder‐Free Organic Ni(OH)2 Flexible Nanohybrid Electrodes for High‐Performance Supercapacitors

Organic–inorganic hybrid materials with nanoscale morphologies gain significant attention as a potential candidate for energy storage applications. Herein, nickel hydroxide (Ni(OH)2) and benzo[2,1,3]selenadiazole (BSe)‐capped dipeptide amphiphiles are electrodeposited over flexible nickel foam (NF) substrates to fabricate organic–inorganic nanohybrids. The in situ electrochemical deposition of organic–inorganic nanohybrids is investigated by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, energy dispersive‐electron microscopy, and elemental mapping. The nanostructured morphology of the nanohybrid material is investigated by field‐emission scanning electron microscopy and transmission electron microscopy. The electrochemical performance and supercapacitor properties are examined in 1 m KOH aqueous solution. Aromatic diphenylalanine (FF)‐based nanohybrid BSeFF/Ni(OH)2 deposited on the NF electrode exhibit a specific capacitance of 1250 F g−1, whereas dileucine (LL)‐based nanohybrids BSeLL/Ni(OH)2 show a specific capacitance of 689 F g−1 at a current density of 2 A g−1.

Flexible nickel aluminate (NiAl2O4) based dual-band double negative metamaterial for microwave applications

Development and analysis of materials having flexibility, low dielectric constant and tangent losses are greatly demandable in the field of wireless technology. The purpose of this paper is introducing new flexible metamaterials design based on nickel aluminate (NiAl2O4) substrate material for microwave applications. Commercially available electromagnetic simulator computer simulation technology are utilised in this investigation. The Nicolson-Ross-Weir method is used to investigate the double negative characteristics of the designed flexible metamaterial structures. At 36% concentration of nickel based flexible substrate shows measured resonances at 8.34 GHz, 12.78 GHz and 14.32 GHz. As well as for nickel 42% concentration with different design, the measured resonance shows at 11.21 GHz. The developed flexible metamaterials are suitable for modern radar and satellite application.

Fabrication of Nickel Coating on Polyethylene Terephthalate Substrate Modified with Primer: Effect of Surface Roughness on Structural Properties of Plated Coating

Fabrication of nickel coating on polyethylene terephthalate substrate via primer modification combined with PdCl2 activation and electroless nickel plating is researched. The effect of surface roughness on structural properties of the plated coating was investigated. The modified substrate could adsorb Sn2+ and Pd2+, which can catalyze the electroless nickel plating. Increasing the SiO2 content in the primer could enhance surface roughness of primer coating, adsorbed capacity of Sn2+ and Pd2+, crystallinity and adhesive force of nickel-plated coating. The nickel-plated film was compact, as SiO2 particles were uniformly dispersed and well bonded with nickel coating. When the average roughness was about 18 μm, the plated coating presented thickness of 2 μm, a low resistivity of 6.6 × 10−5 Ω cm and good adhesive strength of 5B. In addition, selective and flexible nickel patterns could be obtained successfully after laser etching.

Nickel Particle-Based Compact Flexible Antenna for Modern Communication Systems

A flexible antenna is a significant part of the new generation of wireless communication systems. Conventional antennas are typically fabricated on available FR-4 and RT/Duroid dielectric materials, where the dielectric constant cannot be selected arbitrarily and the degrees of freedom in designing the antenna are limited, whereas our flexible substrate offers moderate dielectric values by changing the concentration of the raw materials. Synthesised nickel particle-based flexible nickel aluminate (NiAl2O4) is utilized as a substrate material to make an effective antenna for microwave applications. The nickel aluminate substrate was made with 42% concentration of nickel, and has a dielectric constant of 4.979 and a thickness of 1 mm. The fabricated flexible antenna shows measured bandwidth from 6.50–8.85 GHz. On the other hand, the maximum measured gain and efficiency was 4.75 dBi and 91%, respectively. Finally, that antenna has directional radiation patterns and the presented antenna has a novelty where the nickel aluminate substrate was used for the first time. Thus the compactness of the antenna and its performance with a flexible nature makes it a worthy one to be used in the C-band application.

The effects of sodium tartrate concentration on the properties of CdTe thin films prepared by electrodeposition

In this paper, we successfully fabricate compact and uniform cadmium telluride (CdTe) films on flexible nickel foils using simple electrodeposition technique and sintering in a nitrogen atmosphere. The effect of the concentration of sodium tartrate on the structures and properties of the deposited CdTe thin films are studied. Various test techniques are used to characterize the results. The results of XRD analysis show that the highest crystallinity film is obtained when the added sodium tartrate concentration is 0.05 M. With the increase of sodium tartrate concentration, the composition of the film gradually changes from Te-rich to Cd-rich, and the thickness of the film becomes thin gradually. We also find that the CdTe thin film prepared under 0.05 M sodium tartrate shows the best optical and optoelectronic properties. Thus, a moderate amount of sodium tartrate is added into an acidic solution as surfactant for CdTe thin film fabrication. Moreover, sodium tartrate is easily volatilized from the film during the annealing process because of its small molecular weight, which can prevent the carbon precipitation.

Roll‐to‐Roll Hot Embossing of 1D and 2D Photonic Nanostructures

Roll‐to‐roll hot embossing is exploited for the fabrication of 1D nanogratings and 2D nanopillar arrays. Critical structure diameters as low as 150 nm and distances down to 50 nm are replicated in a polystyrene foil using flexible nickel shims, which are made using electron beam lithography and subsequent electroplating. The high quality of the as‐fabricated structures is proven by their application in two key nanophotonic components. After evaporation of 250 nm of Alq3:DCM on 1D nanogratings using grating periods between 375 and 415 nm, we can realize tunable organic DFB lasers emitting between 604 and 665 nm. 2D nanopillar arrays are covered with a thermally evaporated Au layer and integrated in microfluidic chips for surface‐enhanced Raman measurements. High and homogeneous enhancement of the Raman signal is achieved using rhodamine 6G as exemplary analyte. For polystyrene nanopillar arrays with pillar diameters of 190 nm, a spacing of 50 nm, and a height of 100 mm coated with a 70 nm thick Au layer, an analytical enhancement factor of ≈4.3 × 104 is demonstrated. The presented work shows the versatility of roll‐to‐roll hot embossing for the low‐cost and large‐area fabrication of nanostructures.

Facilely Synthesized NiCo2O4/NiCo2O4 Nanofile Arrays Supported on Nickel Foam by a Hydrothermal Method and Their Excellent Performance for High-Rate Supercapacitance

NiCo2O4 nanoleaf arrays (NCO NLAs) and NiCo2O4/NiCO2O4 nanofile arrays (NCO/NCO NFAs) material was fabricated on flexible nickel foam (NF) using a facile hydrothermal approach. The electrochemical performance, including the specific capacitance, charge/discharge cycles, and lifecycle of the material after the hydrothermal treatment, was assessed. The morphological and structural behaviors of the NF@NCO NLAs and NF@NCO/NCO NFAs electrodes were analyzed using a range of analysis techniques. The as-obtained nanocomposite of the NF@NCO/NCO NFAs material delivered outstanding electrochemical performance, including an ultrahigh specific capacitance (Cs) of 2312 F g−1 at a current density of 2 mA cm−2, along with excellent cycling stability (98.7% capacitance retention after 5000 cycles at 5 mA cm−2). These values were higher than those of NF@NCO NLAs (Cs of 1950 F g−1 and 96.3% retention). The enhanced specific capacitance was attributed to the large electrochemical surface area, which allows for higher electrical conductivity and rapid transport between the electrons and ions as well as a much lower charge-transfer resistance and superior rate capability. These results clearly show that a combination of two types of binary metal oxides could be favorable for improving electrochemical performance and is expected to play a major role in the future development of nanofile-like composites (NF@NCO/NCO NFAs) for supercapacitor applications.

Efficient supercapacitor based on polymorphic structure of 1T′-Mo6Te6 nanoplates and few-atomic-layered 2H-MoTe2: A layer by layer study on nickel foam

Te-based transitional metal dichalcogenides (TMDs) as supercapacitors are gaining substantial attention with a few reports. The integration of 1T′-Mo6Te6 nanoplates (NPs) into few-atomic-layered two dimensional (2D) 2H-MoTe2 thin film has not been realized in supercapacitive studies. Herein, we demonstrate the growth of 1T′-Mo6Te6 NP/2H-MoTe2 thin film polymorphic structure through metal organic chemical vapor deposition (MOCVD) on Si/SiO2 and thereby, the successful transfer of these polymorphic structure on a flexible nickel (Ni) foam current collector by simple chemical etching protocol for high performance supercapacitors. A layer by layer study of the Mo6Te6/MoTe2 polymorphic structure is carried out by varying the number of transfer layers on the Ni foam. The resultant supercapacitors demonstrate a three-fold enhancement in areal capacitance (1542 mFcm−2 at 10 mVs−1) compared to a single layer transferred electrode, together with remarkable electrochemical stability (96%) and high energy density (140.36 mWcm−2 at 4 mA). These supercapacitors outperform the TMD-based (Te-based) supercapacitors presented in the past, demonstrating the high potential for their application in energy conversion devices.

Fabrication of Hierarchical NiMoO4/NiMoO4 Nanoflowers on Highly Conductive Flexible Nickel Foam Substrate as a Capacitive Electrode Material for Supercapacitors with Enhanced Electrochemical Performance

Hierarchical NiMoO4/NiMoO4 nanoflowers were fabricated on highly conductive flexible nickel foam (NF) substrates using a facile hydrothermal method to achieve rapid charge-discharge ability, high energy density, long cycling lifespan, and higher flexibility for high-performance supercapacitor electrode materials. The synthesized composite electrode material, NF/NiMoO4/NiMoO4 with a nanoball-like NF/NiMoO4 structure on a NiMoO4 surface over a NF substrate, formed a three-dimensional interconnected porous network for high-performance electrodes. The novel NF/NiMoO4/NiMoO4 nanoflowers not only enhanced the large surface area and increased the electrochemical activity, but also provided an enhanced rapid ion diffusion path and reduced the charge transfer resistance of the entire electrode effectively. The NF/NiMoO4/NiMoO4 composite exhibited significantly improved supercapacitor performance in terms of a sustained cycling life, high specific capacitance, rapid charge-discharge capability, high energy density, and good rate capability. Electrochemical analysis of the NF/NiMoO4/NiMoO4 nanoflowers fabricated on the NF substrate revealed ultra-high electrochemical performance with a high specific capacitance of 2121 F g−1 at 12 mA g−1 in a 3 M KOH electrolyte and 98.7% capacitance retention after 3000 cycles at 14 mA g−1. This performance was superior to the NF/NiMoO4 nanoball electrode (1672 F g−1 at 12 mA g−1 and capacitance retention 93.4% cycles). Most importantly, the SC (NF/NiMoO4/NiMoO4) device displayed a maximum energy density of 47.13 W h kg−1, which was significantly higher than that of NF/NiMoO4 (37.1 W h kg−1). Overall, the NF/NiMoO4/NiMoO4 composite is a suitable material for supercapacitor applications.

Organic solvent free in situ growth of flower like Co-ZIF microstructures on nickel foam for glucose sensing and supercapacitor applications

Flower like microstructures of cobalt zeolitic imidazolate framework (FLCo-ZIF) was grown on flexible nickel foam (NF) when water was used as a solvent using Co-salt and imidazole as precursors. No such flower like microstructures was formed when ethanol or methanol was used as a solvent. Interestingly, no microstructures were grown on NF in the presence of DMF or DMSO. The microstructure growth was optimized with respect to the mole ratio of 2-methylimidazole (2-MI) and Co salt, solvent and immersion time. The scanning electron microscopy (SEM) images confirmed the formation of FLCo-ZIF on NF with an average framework size of 5 μm from 1:2 mole ratio in water at an immersion time of 3 h. Here, water acted as a green solvent and structure-directing agent to favour Co2+ nuclei to interact with the smaller building units of 2-MI to form FLCo-ZIF microstructures on NF. The cyclic voltammogram of FLCo-ZIF showed two redox waves corresponding to Co and Ni. Further, the FLCo-ZIF fabricated on NF was directly used as a binder free electrocatalyst for glucose oxidation and supercapacitor electrode. When the concentration of glucose increases the amperometric current was increased linearly from 2 μM to 1 mM in 0.1 M NaOH and the limit of detection (LOD) was found to be 0.42 μM (S/N = 3) with a sensitivity of 2.981 mA/(mM cm2). The clinical application of the present method was evaluated by determining glucose in human blood serum samples and the results were validated with the commercial glucometer. Besides, NF modified with FLCo-ZIF was also used for supercapacitor application. It showed a specific capacitance (C) of 87 F g−1 at the current density of 0.5 A g−1 and good stability for 2000 cycles. Thus, the FLCo-ZIF formed on NF from a green solvent shown here is a potential candidate for not only non-enzymatic sensing of glucose but also supercapacitor application.

Flexible and self-standing nickel ferrite-PVDF-TrFE cast films: promising candidates for high-end magnetoelectric applications.

Polymer-based magnetoelectrics are identified as a newly emerging area of research due to their profound potential applications centered on spintronic technology. In line with this, we have developed a novel, flexible nickel ferrite (NiFe2O4)-PVDF-TrFE (NF-PVDF-TrFE) polymer based magnetoelectric film, with excellent magnetoelectric coupling at room temperature. Nanocomposite films were prepared by the solution cast method, in which the nickel ferrite nanoparticles with different weight percentages (2, 4, 8 and 16%) were incorporated in the electroactive PVDF-TrFE polymer matrix. The ferroelectric β-crystalline phase of PVDF-TrFE was confirmed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Raman studies. Dielectric and thermal properties of the composite films were found to be substantially improved with the addition of magnetic nanoparticles. Ferroelectric and magnetic characteristics of the composite films were also considerably improved with an increase in NiFe2O4 concentration. A magnetic saturation (Ms) of 4.81 emu g-1 and a ferroelectric maximum polarization of 18.9 μC cm-2 were shown by the composite film at room temperature for 16 wt% loading of NF nanoparticles. Besides these functionalities, ac and dc magnetoelectric coupling coefficients of 69 mV cm-1 Oe-1 and 90 mV cm-1 Oe-1 were obtained for 16NF-PVDF-TrFE along with excellent mechanical stability. These flexible and self-standing magnetoelectric composite films with enhanced magnetoelectric coupling coefficients at room temperature could be suitable candidates for the development of ultramodern information storage devices, memory devices, signal processing devices etc.

“Carbon‐Glue” Enabled Highly Stable and High‐Rate Fe3O4 Nanorod Anode for Flexible Quasi‐Solid‐State Nickel–Copper//Iron Alkaline Battery

AbstractThe practical application of iron oxide anode in rechargeable alkaline batteries is greatly hampered by the poor electrochemical stability and low rate capability. In addition, flexible solid‐state iron anode‐based rechargeable batteries with distinctive counter electrode coupling are quite lacking. Herein, an interesting “carbon glue” penetration strategy toward Fe3O4 nanorod film anode is proposed. This design not only immobilizes the nanorods and maintains strong adhesion with the current collector but also ensures continuous electrically conductive pathway, resulting in dramatically increased stability (≈99% capacity retention after 1000 cycles) and excellent rate performance (1.2 min charging with ≈70.6% initial capacity kept). By pairing with a new‐type Ni0.49Cu0.51O nanowire array cathode, a unique 1.2 V flexible rechargeable nickel–copper//iron alkaline battery is further assembled, which stores energy based on redox electrochemistry of transition metal ions. It delivers high volumetric energy and power densities (7.21 mWh cm−3; 299.30 mW cm−3), and demonstrates outstanding stability up to 5000 cycles. In particular, with the utilization of quasi‐solid‐state electrolyte, the device still maintains good performance upon substantially bending and twisting. This work presents a new concept to design high stability iron anode‐based alkaline batteries and further pushes forward the development of emerging flexible energy storage systems.

Left-handed metamaterial inspired by joint T-D geometry on flexible NiAl2O4 substrate

In this paper, we introduce a new compact left-handed tunable metamaterial structure, inspired by a joint T-D shape geometry on a flexible NiAl2O4 substrate. The designed metamaterial exhibits an extra-large negative refractive index bandwidth of 6.34 GHz, with an operating frequency range from 4 to 18 GHz. We demonstrate the effects of substrate material thickness on the effective properties of metamaterial using two substrate materials: 1) flame retardant 4 and 2) flexible nickel aluminate. A finite integration technique based on the Computer Simulation Technology Microwave Studio electromagnetic simulator was used for our design, simulation, and investigation. A finite element method based on an HFSS (High Frequency Structure Simulator) electromagnetic simulator is also used to simulate results, perform verifications, and compare the measured results. The simulated resonance peaks occurred at 6.42 GHz (C-band), 9.32 GHz (X-band), and 16.90 GHz (Ku-band), while the measured resonance peaks occurred at 6.60 GHz (C-band), 9.16 GHz (X-band) and 17.28 GHz (Ku-band). The metamaterial structure exhibited biaxial tunable properties by changing the electromagnetic wave propagation in the y and z directions and the left-handed characteristics at 11.35 GHz and 13.50 GHz.

Enhanced Cycling Stability of SiOx/Si/Nickel Foam Thin Film Anodes for Lithium Ion Batteries

Silicon has been known as the next generation anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity (4200 mA h g-1). However silicon anodes face the challenge of large volume change over 400 % during lithiation/delithiation cycles, leading to the pulverization of the silicon based electrodes. In this study, radio frequency (RF) magnetron sputtering is used to deposit amorphous silicon thin films on nickel foam current collectors. This flexible three-dimensional structure is found to relieve stress caused by the volume expansion. Furthermore, SiOx is coated on the previously fabricated silicon anodes as a buffer layer. The oxygen contents and the thickness of the SiOx are controlled by depositing under different Ar/O2 ratios, and depositing times. The electrochemical behaviors of the SiOx/Si/nickel foam electrodes toward lithium are studied. It is found that the SiOx/Si/nickel foam electrodes with optimized oxygen contents and thickness of SiOx films exhibit high cycling stability and coulombic efficiency. The results are attributed to the stress relaxation effect provided by the flexible nickel foams and the SiOx buffer layers.