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The low capacitance utilization and capacitance fading of manganese dioxide (MnO2) is mainly due to poor electro-conductivity and irreversible phase transform. This work proposes a new method of designing hierarchical and binder-free electrode based on MnO2 material for stable supercapacitor with high specific capacitance. Herein, we fabricated the self-standing electrode of MnO2 on nitrogen-doped graphene and single wall carbon nanotubes (SWCNTs) self-standing film (NGCF) by electrochemical deposition. As a result, as-prepared MnO2/NGCF cathode showed excellent electrochemical performance of 489.7 F g-1 at 1 A g-1. Assembled symmetric aqueous supercapacitor (SC) manifests high voltage of 2.4 V and presents excellent high energy density of 106.7 Wh kg-1 at 1200 W kg-1 and outstanding long-life stability without no decay after 10 000 charge-discharge circuits. This work proposes a new view of designing hierarchical and binder-free electrode with high energy density and long cycling stability based on MnO2 material for stable symmetric supercapacitor.

Spark-assisted chemical engraving (SACE) is suitable to machine hard and brittle insulating materials such as quartz glass; however, the processing efficiency is quite low for achieving good machin...

In this work, the time-delay effect on device operation caused by capacitance is studied in terms of phase-change memory (PCM) integrated with an ovonic threshold switch (OTS) selector. The capacitance studied in this work is the intrinsic capacitance associated with capacitive reactance of the PCM itself. The capacitance of the PCM in the amorphous state was measured, and it presents an exponential dependence on voltage bias. Through the simulation model of an OTS-PCM integrated device that considering the measured capacitance behavior, the time-delay characteristics of the integrated device for the SET process with various pulses were investigated. Results indicate that the onset of the threshold switching (TS) is delayed in the PCM but occurs early in the OTS with capacitance in the integrated device. In addition, it is found that the variable capacitance behavior can not only minimize the delay effect, but also accelerate the SET operation under certain conditions in the integrated device. Our results can provide practical guidance for the design of fast operating devices.

Adopting the sidewall-insulated hollow electrode (SIHE) is an ideal approach to achieve electrolyte-refresh and stray corrosion inhibition functions in micro electrochemical machining (ECM) processes. Most of the traditional SIHEs are made of metal substrate and non-metal thin films. The insulating film has poor durability, and the preparation approach of the traditional SIHE is complex and has limited repeatability. This research presents a novel structure of a SIHE with an insulated substrate and an internal conductive film. The machining performance of the novel SIHE is primarily verified by a potential distribution analysis in the numerical simulation. According to the concept of the novel SIHE, a silver-plated glass tube electrode (SPGTE) is presented: the glass tube acts as the insulated substrate, and the plated silver layer acts as the working cathode. Then, a fabrication process for the SPGTE is proposed. Silver layers are tightly bonded on the glass tube surface by electroless plating. The thickness of the silver layer is approximately 3.5 μm, and its electrical resistivity is approximately 5 × 10−5 Ω cm. In micro ECM experiments, microstructures with steep sidewalls with taper angles of

Polymer nanocomposite coatings have attracted great interest in the anticorrosion fields due to their excellent properties. Nanofillers are necessary to achieve high anticorrosion performance of the polymer coating. Herein, we report a wet-chemical template strategy to prepare large-size ZrO2 nanosheets, in which the Zr4+ ions are anchored on the surface of a graphene oxide template via electrostatic adsorption, followed by a thermal treatment process to remove graphene. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images show that the size and thickness of as-prepared ZrO2 nanosheets are more than 2 μm and ~ 4.5 nm, respectively. The micron-scale ultrathin two-dimension (2D) ZrO2 nanosheets, for the first time, are utilized as the anticorrosive fillers in the epoxy coating to reduce the porosity, consequently promoting the gas and water barrier properties of the composite coating. The polymer coating containing 1.0 wt% ZrO2 nanosheets shows a high initial impedance (89.1 GΩ·cm2) that can protect the metal substrate from being corroded during long-term immersion (60 days), which is better than that of the reduced graphene oxide (rGO)-incorporated coating and the ZrO2 nanoparticles-incorporated coating. This work offers valuable insights into the design and preparation of novel and efficient 2D electric-inert nanofillers for anticorrosion coatings.

In this letter, we fabricated a C-doped GeTex Ovonic threshold switching (OTS) selector in a via-hole structure. The material composition is simple without toxic element doping. Performance of the GeTex-based selector is improved to be comparable to commercial GeSe-based selectors through C doping. A selector with advantages of low off-current (2 nA), low threshold voltage (1.26 V) accompanying with a big voltage window (0.55 V), high selectivity ( $> 4.2\times 10 ^{4}$ ), satisfactory endurance (> 107 cycles with 2 mA on-current), low cycle-to-cycle $\text{V}_{{\mathrm {th}}}$ variation and fast operating speed (8.5 ns) was fabricated. Besides, selector with self-limited on-current character was found. Next, reasons behind off-current reduction and consistency improvement by using C doping were studied by First-principles calculations.

We present a finite-element model for the confined-structure device integrating a phase change memory (PCM) and an ovonic threshold switch (OTS) selector. In this model, the threshold switching (TS) characteristics of the PCM and OTS were described by an embedded numerical model to simulate the operation of the integrated device. Both the SET and RESET processes have been well implemented in the integrated device by simulating. The electronic properties of the integrated device with various OTS material parameters have been investigated by simulating. Based on the simulated results, a moderate set-pulse has been obtained by optimizing only the OTS conductivity at a high-conductivity state. Further simulations for multilevel storage have been carried out in the integrated device based on the optimized OTS. The results indicate the confined-structure device with a larger length–diameter ratio will result in a more flexible operation window for multilevel storage. Particularly, when the length–diameter ratio of the confined-structure is 2:1 in the integrated device, five levels of device resistance could be obtained in the simulations of multilevel storage by applying multiple set-pulse or reset-pulse. This could guide further studies on the multilevel storage.

The defects including halide vacancies and uncoordinated Pb in perovskite films caused by the cracking of Pb–I bonds in the thermal annealing process are responsible for the degradation of the photovoltaic performance and long-term stability of perovskite solar cells (PSCs). Passivation of halide vacancies and uncoordinated Pb defects and construction of high quality perovskite films are vital to promote carrier lifetime and reduce non-radiative recombination losses. Herein, we develop a facile and broadly applicable surface passivation strategy for various compositional perovskite films, in which cadmium bromide (CdBr2) is selected and adopted to passivate the halide vacancies and uncoordinated Pb defects of the perovskite films owing to the stronger bond energies of Cd–I and Pb–Br than that of Pb–I. CdBr2 modification is found to be able to prolong carrier lifetime and decrease defect amount together with improving film quality of the typical compositional perovskites i.e. MAPbI3, Cs0.15FA0.85PbI3 and CsPbI2Br, as evidenced by spectral and photoelectrochemical measurements. As a result, the photovoltaic performance and ambient, photo and thermal stability of perovskite devices are greatly promoted, with a high efficiency of 16.05% achieved by the CdBr2-modified PSCs with the architecture of ITO/SnO2/MAPbI3/carbon, exceeding the previous highest PCE record for carbon-based MAPbI3 PSCs.

In this study, a novel self-healing material with a dual-network composed of a cross-linked structure by Diels–Alder (DA) chemistry interconnected with self-assembled π-conjugated polymer nanofibrils was developed for application in electromagnetic interference (EMI) shielding. A poly(caprolactone-co-furfuryl glycidyl ether)-block-hydrogenated polybutadiene-block-poly(caprolactone-co-furfuryl glycidyl ether) copolymer (PCLF–HPB–PCLF) was synthesized and used as the primary molecular skeleton for incorporating graphene nanosheets (GNS). This was followed by the addition of poly(3-hexylthiophene) (P3HT) as the dispersant, which effectively promoted the dispersion of GNS through π–π interactions. Through an aging process, P3HT progressively self-organized into nanofibrils, forming an interpenetrating network that effectively prevented the GNS from restacking. Moreover, 1,1′-(methylenedi-4,1-phenylene)bismaleimide (BMI) was added to the hybrid. Within the multicomponent system, the different diene/dienophile pairs of furan/maleimide, graphene/furan, and graphene/maleimide underwent multiple DA reactions, resulting in a cross-linked structure that was interconnected with the nanofibrillar P3HT network. This dual-network structure facilitated the enhancement of GNS dispersion, thereby improving the uniformity of the internal structure of the material system and endowing it with sufficient plasticity through the triggering of the retro-DA reaction. Specifically, the nanocomposite (containing 5 wt% GNS and 10 wt% P3HT) with a dual-network structure exhibited excellent self-healing and reprocessing abilities. By contrast, the composite (containing 5 wt% GNS) with a single-network structure by DA chemistry exhibited poor self-repairing and remolding properties. In addition, the dual-network hybrid had excellent electrical properties, with a conductivity of 303.6 S m−1 and an EMI shielding effectiveness of 24.4 dB in the X-band frequency range. These results clearly demonstrate the synergistic effect of the self-assembled π-conjugated polymer network in enhancing the dispersion of GNS in a DA cross-linked system. The present findings provide a promising direction for the development of novel multifunctional durable materials, showing potential for future electromagnetic applications.

Conductive bridge threshold switching (CBTS) selector is a selector candidate for large-scale 3D crosspoint memory. In spite of its high selectivity, the generally low current density (JON) of

Sputtering with copper indium gallium selenide (CIGS) ceramic targets could produce smooth CIGS thin films that are preferred for preparing two-terminal tandem devices. However, grain sizes prepared in this way are small and device efficiency was low. To increase the grain size, in this report, an Ag layer was pre-sputtered beneath CIGS. The Ag doping layer increased the grain size and improved the crystalline alignment. Consequently, the Ag-doped films exhibited improved charge mobility. From X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy characterizations, we obtained an optimized Ag thickness of 15 nm. Short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) were all improved after doping with 15-nm Ag. Increasing the annealing temperature from 550 °C to 575 °C, the grains was enlarged further, with the power conversion efficiency (PCE) increasing to 14.33% and VOC to 545 mV. Upon the smooth CIGS film, a thin conformal perovskite layer was fabricated without polishing. This work demonstrates a simple way to fabricate smooth and highly-crystalline CIGS films that can be used for tandem solar cells.

Micro electrochemical machining (ECM) is practicable for machining micro holes with internal features by adjusting machining parameters along with machining depths. However, it is difficult to maintain the shape accuracy due to dramatically varied electrolyte temperature (T) and gas void fraction (vol) caused by the parameter variations. Taking the reverse tapered hole as an example, this research presents a multiphysics model to investigate the effects of machining parameters on T and vol and further optimize parameters for shape accuracy improvement. Firstly, the rules of current efficiency with various pulse-on times are measured from dissolution experiments. The gas fluxes are calculated from the Faraday current, and then multiphysics models coupling electric field, electrolyte flow, gas transport, and heat transfer are established by COMSOL software. The effects of the machining voltage, pulse-on time, duty ratio, and inlet pressure are investigated. Simulation results indicate that T and vol increase with the machining voltage or duty ratio and decrease with the inlet pressure. By using a smaller duty ratio or a higher inlet pressure, the sidewall dissolution region expands in a larger range. Increasing the inlet pressure is beneficial for reducing the negative influence of rising T and vol. However, excessive inlet pressure causes undesired material dissolution. The optimal inlet pressures are obtained from simulation results of the electrolyte vortex area. Micro ECM experiments are carried out to verify the simulation results and optimize the parameters. Micro reverse tapered holes with sidewall straightness of 8.6 μm are machined, and the shape accuracy is significantly improved.

Spark assisted chemical engraving (SACE) has the advantages of less contact stress and little/no tool electrode wear, and it is expected to achieve damage-free processing on dielectric workpieces. The key factors of electrolyte depths and machining gaps play an important role in the SACE process, especially for a micro-SACE process. Currently, there is still no convenient method for forming a thin and stable electrolyte depth in a scanning process of micro-SACE, and the existing methods are difficult to specify a micron-level machining gap between a tool electrode and a workpiece. In order to solve these problems, a scanning process of micro-SACE based on the thin laminar flow electrolyte and the narrow machining gap was proposed. This research focuses on the experiments to obtain the controllable rules of a stable thin film of electrolyte for concentrating the processing energy and restricting the processing locality. A novel method of indirect electric contact was presented for measuring workpiece surface height and then precisely leveling the workpiece surface before the scanning process. A micro-feed contact method with CCD (charge coupled device) vision was used to give a narrow machining gap. In experiments, the leveling accuracy of workpiece surface can reach ± 0.1 μm/mm, and the adjusting resolution of micro-machining gaps can be down to a precise scale of ± 0.5 μm. As a result, a micro-structure of 1.2 × 1.2 mm with a depth removal resolution down to ~ 2 μm was achieved on the surface of ZrO2 workpiece with the flow layer electrolyte as thin as 165 ± 5 μm.

Ge-Sb-Te (GST)-based phase-change memory (PCM) excels in the switching performance but remains insufficient of the operating speed to replace cache memory (the fastest memory in a computer). In this work, a novel approach using Sb2Te3 templates is proposed to boost the crystallization speed of GST by five times faster. This is because such a GST/Sb2Te3 heterostructure changes the crystallizing mode of GST from the nucleation-dominated to the faster growth-dominated one, as confirmed by high-resolution transmission electron microscopy, which captures the interface-induced epitaxial growth of GST on Sb2Te3 templates in devices. Ab initio molecular dynamic simulations reveal that Sb2Te3 templates can render GST sublayers faster crystallization speed because Sb2Te3's "sticky" surface contains lots of unpaired electrons that may attract Ge atoms with less antibonding interactions. Our work not only proposes a template-assisted PCM with fast speed but also uncovers the hidden mechanism of Sb2Te3's sticky surface, which can be used for future material selection.

As a non-traditional machining process, spark assisted chemical engraving (SACE) can machine hard, brittle, and non-conducting materials. The spark discharges on tool-electrode sidewall result in e...

Zirconium dioxide (ZrO2) is a ceramic material used in a wide range of applications. However, the mechanical properties of ZrO2 ceramics, such as brittleness, high hardness, and high temperature resilience, make it challenging to machine. SACE (spark assisted chemical engraving) is an advanced technology for machining ZrO2 ceramics that has also been used successfully in glass machining. However, the sidewall of the SACE tends to generate spark discharges, which not only waste energy but also affect machining accuracy. In a set of exploratory SACE experiments, it was found that a large percentage of discharges occur at the end of the tool electrode under certain conditions. It is believed that the sharp square edge of the tool-electrode end is conducive to the end discharges by large. Therefore, a cylindrical notched tool electrode with an increased number of sharp edges to improve discharge constraint is proposed in the SACE process. SACE scanning experiments were conducted on ZrO2 ceramics using the proposed tool electrode and found that it significantly improved machining efficiency and accuracy.

Stray corrosion and electrolytic products deposition in the machining gap are major influence factors seriously restricting the application of micro electrochemical machining (ECM). Currently, one technical bottleneck is preparing thin and durable insulating films on electrode sidewall to restrain the stray corrosion. In previous work, we proposed an anisotropically-etched silicon electrode for micro ECM, on which silicon dioxide and silicon nitride are deposited as insulating films. The heavily doped silicon electrode body has good electrical conductivity, and the silicon-based films have excellent insulating property. The anisotropically-etched silicon electrode on (1 0 0) crystal plane has an isosceles trapezoid cross section. To get better machining performance compared with cylindrical electrode, the silicon electrode is rapidly rotated on a spindle in micro ECM process. The periodically varying lateral gap has a special effect on the electrolyte flow characteristics. A simulation model of electrolyte flow and discrete phase distribution is established by Fluent software. Simulation results indicate that the normal flow rate of electrolyte with silicon electrode is 50 times higher than that with cylindrical electrode, which is benefit for removing solid electrolytic products smoothly. The maximum concentration and residual ratio of solid electrolytic products are decreased with the rotating speed increasing. When the rotating speed is higher than 1200 rpm, the residual ratio is reduced to 13%. ECM experimental results indicate that electrolytic products on the workpiece machined by a silicon electrode are much fewer than that by cylindrical electrode. Silicon electrodes with trapezoidal cross section have a distinct advantage for reducing electrolytic products deposition.

Phase change memory is an excellent candidate for next-generation memory technologies with a high operation speed, but the memory capacity is not very satisfactory, due to which engineers have to add the 3D stacking technology (3D XPoint) for new products. Alternatively, multi-level storage is an easy approach to enable large data density and probably future neuromorphic computing. Lately, K2Sb8Se13 has attracted considerable attention as a multi-level phase change material because it exhibits an interesting amorphous-to-amorphous (polyamorphic) transformation before crystallization, and these two polyamorphic states as well as the crystalline phase show distinct resistances, adding a new data state to the existing “0” and “1”. Understanding and stabilizing this new amorphous state is the key to the application of this material; here, we have investigated these two amorphous states through ab initio simulations. We found that these two states showed obvious differences in the local structures, and the void concentration revealed by the low-electron-density areas indicated stronger interactions between the atomic clusters in the denser phase. The density of states and electron localization function were analyzed and we confirmed that adding electronic holes were largely responsible for the decrease in resistance. In this work, we have discovered the origin of multi-level resistance states in K2Sb8Se13, paving the way for the design of new phase change memory devices based on this material.

3D scanning (or milling) micro electrical discharge machining (EDM) can machine 3D microstructures with free-form surfaces on metal/alloy materials. The novel process of servo scanning 3D micro EDM (SS-3D micro EDM) provides a practical solution for the real-time online compensation of micro tool-electrode wear. However, the key parameters of servo scanning are difficult to be optimized by a large number of trial-and-error experiments. This causes the unstable and destructive process of frequent short circuit, less cutting, and collision of tool electrode and workpiece because the optimization still lacks theoretical basis. In this research, considering the actual influence of delay response time of a machining system, we analyzed the process of servo control of machining gap according to threshold control method and the matching effect with scanning speed. Boundary models were established for providing the theoretical basis of the servo control speed and its reasonable matching with the scanning speed. Furthermore, the optimization procedures with the proposed boundary models for the reasonable matching of these parameters were proposed and verified by machining experiments.

Fast hole electrical discharge machining (EDM) is widely used in drilling circular holes with sub-millimeter diameters on metal alloy materials. As a kind of non-contact machining process, the discharge gap between tool electrode and workpiece significantly affects the machining efficiency. Ordinarily, this process can achieve high machining efficiency based on large discharge energy and high pressure inner flush. However, in case of demanding high shape precision and surface quality, such as film cooling holes, the discharge energy needs to be reduced. Thus the electrode wear ratio is increased and the removal of machining debris becomes more difficult. Consequently, the control of discharge gap gets hard and then the machining efficiency is significantly decreased. In this research, a nonlinear velocity controller based on sliding mode control (SMC) method is proposed to improve servo control of discharge gap in precise fast hole EDM. The dynamic model of fast hole EDM is firstly established to provide the physical basis for the controller design. Then a sliding mode algorithm is designed based on Lyapunov stability theory to improve the anti-interference of the control system, and the dynamic characteristics are analyzed through simulations based on the state equation and control algorithm. Furthermore, the performance of the proposed method is discussed by comparing the tool electrode movement, gap average voltage and utilization ratio of pulses measured in experiments. The experimental results showed that the proposed method can increase machining efficiency by 38.1%.

In the lithography-based fabrication process of microstructures on microfluidic chip molds, the shortcoming of limited substrate materials seriously shortens the service lifetime of the mold. This research focuses on a profile shaping and surface finishing process of micro electrochemical machining (ECM) for microstructures with targeted dimensional and geometrical characteristics on the mold steel S136H. The effects of parameters on the material removal region and single-layer depth are firstly investigated. The sidewall taper of the machined groove increases with the machining voltage and decreases with the scanning velocity. Besides, the bottom surface quality is improved with increasing path spans. Then, the mathematical models of the material removal region and single-layer depth are analyzed, which are regarded as guidance for path planning and parameter optimization. In ECM experiments, a relatively higher machining voltage (20 V) is utilized to rapidly machine basic profiles of the designed flow resistor in the profiles shaping procedure. Sloping sidewalls and rough surfaces are finished by using a lower machining voltage (14 V) and a higher scanning velocity (500 μm s−1) in the surface finishing procedure. As a result, the specially designed flow resistor with a dimensional deviation < 10 μm, and surface roughness Ra < 500 nm is obtained. The proposed ECM process is proved to machine microstructures with high precision and curve profiles on the mold steel.

To obtain high performance supercapacitors suitable for tiny, compact and portable electronic devices, a new type of electrode with high energy density, high speed performance and long cycling-stability is essential. In practical applications, both volumetric capacitance and gravimetric capacitance should be regarded as equally important parameters. Due to their high open surface structures, high compressibility and high conductivity, low-density three-dimensional (3D) carbon scaffolds hold great promise for excellent electrochemical performance, high diffusion rates and low ion transport resistance. Here, a new 3D elastic sponge composed of single-walled carbon nanotubes/graphene (SWNT-rGO-S) was successfully prepared by a superfast and facile flame burning method in an open environment within 20 s. Moreover, the hierarchical NiCo2O4 nanosheets were deposited on the SWNT-rGO-S scaffold through the hydrothermal method and the annealing treatment. Due to the 3D open pore and compositional features, the compressed NiCo2O4/SWNT-rGO-S electrode exhibits a high gravimetric capacitance of 2050 F g−1 and a volumetric capacitance of 1200 F cm−3, together with a high cycling stability with 115.3% capacitance retention after 6800 cycles at the current density of 20 A g−1 and a high rate performance of 73.2% capacitance retention with the current density being increased from 2 to 80 A g−1. Additionally, a high performance asymmetric supercapacitor was fabricated by using NiCo2O4/SWNT-rGO-S as the positive electrode and activated polyaniline derived carbon (APDC) as the negative electrode, presenting high gravimetric and volumetric energy densities of 53.5 Wh kg−1 and 26.9 Wh L−1, respectively, and exhibiting a very high 83.5% capacitance retention after 10,000 cycles.

Diffuser shaped film cooling holes are increasingly being applied in the turbine blades of advanced aeroengines. It is a difficult problem to machine this kind of cooling holes due to their complicated shape and superalloy material. Currently, die-sinking electrical discharge machining (EDM) is regarded as an available process for machining the diffuser holes. However, the change of tool electrode shape caused by the electrode wear and difficult renew of dielectric fluid affect the processing precision. The worn tool electrode has to be replaced with a fresh one after machining one or several holes. The replacing procedure is time consuming to break the machining process. In the previous work, a novel block divided EDM process was proposed to efficiently machine the diffuser holes, but the machining accuracy needs to be further improved. In this research, the block divided EDM process firstly is analyzed and simulated in detail to know the key factor affecting the machined accuracy. Furthermore, a self-repair method and a profile error compensation method of the tool electrode wear are proposed for improving the processing accuracy. The self-repair method is to plan and control the rotation motion of the tool electrode for maintaining its shape. The profile error compensation method is to modify the Z coordinate of the tool electrode for decreasing the machining error. Machining experiments verified that the proposed methods can meet the accuracy requirements of the film cooling holes with diffusion angle error

In this work, hydrophobic magnetic nanoparticles (MNPs) were successfully synthesized by the one-pot solvothermal reaction at the presence of surface modifier for the first time and characterized by SEM, EDS, TEM, WAXD, TGA, FTIR, and XPS. The fabrication of the magnetic superhydrophobic melamine sponge was realized by the deposition of the as-synthesized hydrophobic MNPs on the melamine sponge using a simple drop-coating method with the aid of silicone adhesive to achieve a firm attachment. The resultant surface-modified durable melamine sponge exhibited not only the high absorption capacities for different oil and organic solvent ranging from 39.8 g/g to 78.7 g/g but also the good reusability for absorption even after 14 absorbing-squeezing cycles. The oil absorption ability of the magnetic superhydrophobic highly-porous melamine sponge was much better than that of the magnetic superhydrophobic polyurethane sponge with relatively low porosity. Moreover, it could be found from the demonstrating experiments that the as-prepared magnetic superhydrophobic melamine sponge had the abilities to (1) remove the floating peanut oil from water followed by convenient magnetic recovery, (2) separate CH2Cl2 from water as a filter only driven by gravity, (3) absorb and collect peanut oil continuously from water surface assisted by a vacuum pump. We believe that the as-prepared magnetic superhydrophobic melamine sponge should have great potential in the effective oil-water separation.

Dielectric fluids affect not only the discharge status but also the structure and composition of recast layer in the electrical discharge machining (EDM) process. In order to reduce the thickness of recast layer and improve the surface quality of film cooling holes of nickel alloy, in this paper, the effects of four different types of dielectric fluids on surface integrity of the recast layer formed during high speed EDM drilling process were investigated; the formation mechanism of the recast layer on nickel alloy was discussed by comparing the surface characters of the bulk and those of the recast layer using various characterization methods. The dielectric fluids with larger electric conductivity (emulsion and water solution) were found to have higher sensitivity to the single pulse discharge energy. With the increase in electric conductivity of dielectric fluids, the recast layer became thicker accordingly. The thickness of the recast layer when using kerosene fluid was the smallest (4.8 μm), which was nearly one third of the that of using water-based fluid. The cooling rate of the dielectric fluid affected the microstructure of the recast layer, where the surface of recast layer was apt to form fine grain zone and the bottom formed columnar grain.

Phase change memory is an emerging nonvolatile memory technology, recently becoming the center of attention to bridge the speed gap between fast dynamic random access memory and slow flash-based solid-state drives. Lately, CrGeTe3 has been investigated as a special phase change material with an inverse resistance and density change. This material has excellent properties such as good thermal stability, ultralow-energy glass formation process and almost zero mass-density change upon crystallization. Here, we analyzed the amorphous structure of this abnormal material in detail through ab initio simulations and discovered that the metallic-like tight atomic packing is the origin of the high carrier concentration and high mass density in the amorphous phase. Furthermore, the bonding analysis confirms that it is the short Cr–Cr bonds that lead to high packing efficiency in the amorphous local order. Our results discovered the material gene of the amorphous CrGeTe3, paving the way for the design of high-performance memory devices based on this material.

The thermal conductivities of GeTe/Bi2Te3 superlattice-like materials are calculated based on density functional perturbation theory (DFPT) and measured using a 3ω method. The calculated results show that the lattice thermal conductivity or thermal diffusivity of GeTe/Bi2Te3 superlattice-like materials significantly decrease due to the effects of interfaces and Bi atoms in Bi2Te3. Our measured results are in line with the theoretical calculations, and reach an extremely low thermal conductivity at 0.162 W mK−1 compared with published work on Ge–Sb(Bi)–Te, indicating the effectiveness of modulating the thermal properties of phase change materials by using Bi-based GeTe/Bi2Te3 superlattice-like materials. Our findings give a calculation method to modify the thermal characteristics of superlattice-like materials and confirm Bi-based GeTe/Bi2Te3 superlattice-like materials as promising candidates for phase change materials with lower thermal conductivity.

High-quality inorganic red-emitting phosphors are widely used in white light-emitting diodes to realize excellent white light emission. Tungstate is one of the most popular materials for phosphors due to their great chemical stability and unique luminescent properties. However, the quantum efficiency of tungstate-based phosphor is still not high enough for commercial application. In this study, we synthesized a series of α-La2W2O9: Eu3+ phosphors by a modified high-temperature solid-state reaction method. The prepared phosphors crystallized well in triclinic structure. Eu3+ ion mainly substituted La3+ ion in La (1) site of low local symmetry as C1, thus the phosphors showed a strong red emission at 618 nm by 5D0→7F2 transition. When Eu3+ doping concentration is 3%, α-La2W2O9: 3%Eu3+ presents maximum luminescent intensity, longest lifetime (0.651 ms) and highest quantum yield (77%). Furthermore, the mechanism of concentration quenching is discussed and indicates that electric dipole-dipole interaction is the dominant mechanism. Our study demonstrates a high-quality red-emitting phosphor based on α-La2W2O9: 3%Eu3+, which is potential for commercial white light-emitting diodes applications.

In order to reduce the thickness of recast layer and improve the surface quality of film cooling holes, a novel high speed self-adjusting electrical discharge machining (EDM)/ electrochemical machining (ECM) approach was developed by applying two independent flushing systems that were able to switch automatically in the machining process. The new flushing systems used different work-liquids and online dynamically changing discharge parameters. With the change in gap distance and the depth of the hole drilled, the dominant machining mechanism is graduated changed from EDM to electrochemical discharge machining (ECDM) and ECM. The formation mechanism of the recast layer on nickel alloy was investigated by comparing the surface characters of the bulk material and those of the recast layer using transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). The results from comparison experiments, in which different discharge parameters and sustaining time were applied, show that this new flushing systems would ensure much better flushing continuity of the working fluid and improve the discharge gap status. In addition, low voltage and current would benefit the ECM process and the removal of recast layer.

Plastic pollution has inspired the preparation of environmentally friendly bio-based plastics that can replace petroleum-based plastics. Herein, a composite film with oxygen and water resistant properties was prepared by a fluidized bed method, employing bio-based cellulose acetate (CA) as raw material, glycerol as a plasticizer, and chitosan and silica as additives. The addition of 15% chitosan greatly reduced the oxygen transmission rate of the CA film by 83.5%, and increased the tensile stress and tensile strain of the composite membrane, reaching 26.5 MPa and 22.2%, respectively. The deposition of silica particles is able to compensate for the undesired increase in the hydrophilicity caused by the addition of chitosan, and tune the hydrophilic nature of the surface of the CA/CS films to the hydrophobic nature, which is desirable for water-resistant applications. The prepared composite film displays good oxygen and water resistant properties and can be used for food packaging and related applications.

Sb-Based phase-change materials have exhibited tremendous advantages in both data storage and reconfigurable photonic devices. Despite the intensive studies on their structures and properties in the crystalline state, the widely used amorphous phase remains elusive. Here, we investigate amorphous Sb2Te3, Sb2Se3, and Sb2S3 through ab initio calculations to link their unique properties to the local structure and bonding nature. We discover that Sb forms shorter and stronger bonds with Se and S than Te, and the average bonding angles of Se (92.0°) and S (94.1°) show larger distortion than that of Te (91.5°). This leads to larger Peierls-like distortion in Sb2Se3 and Sb2S3. On the other hand, more charge transfer and void fraction are presented, opening band gaps and leading to different electronic and optical properties. In contrast, Sb2Te3, due to its semiconducting behavior and low thermal stability, enables its application in phase-change memory. Our results reveal the physics of vastly different electronic and optical properties induced by S, Se, and Te alloying, providing an effective strategy for materials design.

Microstructures determine flow properties of microfluidic chip. Micromold forming is an effective method to realize mass manufacturing of microfluidic chips. This requires to machine some kind of special microstructure of high surface quality on a metal/alloy workpiece. Micro V-shaped grooves are the typical microstructures of the chip micromolds used for controlling microfluid or weld packaging. In this research, a scanning micro-electrochemical machining (ECM) process of V-shaped grooves is proposed using a tool electrode fabricated by micro–electrical discharge machining (EDM) on-machine. Theoretical and experimental research was conducted for achieving the V-shaped grooves with a given angle on die steel. A long-distance V-shaped groove with the given angle of 67 deg and the depth of 125 μm was successfully machined.

Nickel cobalt sulfur is attracting more attention due to its great electrical conductivity and high specific capacitance for faraday pseudo-capacitors. Here, by evaporation-induced drying, heterostructure NiS2/NiCo2S4 nanosheets on self-supporting substrate of nitrogen-doped single-walled carbon nanotubes sponge (NSCS) are obtained with the sponge volume significantly being reduced. With the electrode film thickness being 80 μm, the as-prepared heterostructure NiS2/NiCo2S4/NSCS electrode shows outstanding areal/gravimetric/volumetric capacitance of 10.5 F cm−2/2905 F g−1/1307.2 F cm−3 at 1 A g−1. With the increase of current density from 1 to 60 A g−1, the current retention rate maintains at 61%. When the active material loading is increased to 14 mg cm−2, the gravimetric capacitance can still maintain at 1725 F g−1, indicating the high ratio performance. After 10,000 cycles, the capacity retention still remains 83% at current density of 10 A g−1. In addition, an asymmetric supercapacitor (ASC) delivers have high gravimetric/volumetric energy density of 58.1 W h kg−1/52.3 W h L−1 with excellent cycle stability after 20,000 cycles. Therefore, the electrode material with high loading and high rate performance can be realized by this method.

Traditional machining processes are usually unworkable for ZrO 2 ceramics due to the mechanical properties of fragility, high hardness and high-temperature resistance. The process of spark assisted chemical engraving (SACE) has been explored for machining ZrO 2 ceramics, but up to now the processing mechanism has not been clearly understood yet. To understand the microscopic mechanism, the phase transition paths of ZrO 2 ceramics under various physical and chemical conditions were analyzed. A backstepping approach based on structures and components of SACE processed products was proposed to verify the physical and chemical mechanisms. According to the crystal phase composition of the processed debris resulting from Raman spectrum analysis, it was found that the debris exhibited crystalline and amorphous forms which provided the evidence of physical crushing and chemical reactions. Furthermore, the chemical removal mechanism was proven by the nearly saturated concentration of Zr ion in the processed solution according to the ICP-OES assay of SACE electrolyte. The quantitative proportion of physical and chemical effect can be successfully determined by distinguishing and analyzing two kinds of debris with different crystal phase compositions which yield distinctly identifiable appearances under an optical microscope.

We demonstrate a CuS/GeSe dual-layer selector with excellent performance. This CuS/GeSe dual-layer selector exhibits ultrahigh selectivity ( $\text {1.25}\times \text {10}^{\text {9}}$ ), high on-current drive ( $600~\mu \text{A}$ ), ultralow off current (~100 fA), and extremely steep switching slope (

Stray current always causes undesired material dissolution in micro electrochemical machining (ECM). The preparation of reliable insulating films on micro electrodes is a critical technique to restrict the stray current, and then improves the machining localization. To meet the requirements for insulating films like good insulation property, thin & uniform thickness and good adhesive strength, a novel method of silicon-based tool electrode is proposed. Heavily doped monocrystalline silicon is used as the electrode body. Silicon dioxide and silicon nitride are deposited on electrode sidewall as insulating films. Through simulations of electrode conductivity, the feasibility of the silicon-based tool electrode is preliminarily verified. Then, a fabrication process of the silicon-based tool electrode is presented. The electrode body is fabricated by wet etching and insulating films are deposited by low pressure chemical vapour deposition (LPCVD). Consequently, the electrodes with section size of 91 × 52 μm, 1–2 mm length and 800 nm-thick insulating films are obtained. As the silicon-based electrode is installed on a rotating head in ECM experiments, the electrode with non-circular cross section not only achieves the same effect with a cylindrical electrode, but also is beneficial to removing electrolytic products through the turbulent electrolyte flow. In experimental results, micro grooves with steep sidewall and smooth undersurface (Ra 0.42 μm) are machined. Micro holes with inlet diameter of 146 μm and taper angle of 0.58° are obtained. They indicate the feasibility of silicon-based tool electrodes and the effect of insulating films on stray corrosion restriction.

In order to increase the energy density of supercapacitor, a new kind electrode material with excellent structure and outstanding electrochemical performance is highly desired. In this article, a new type of three-dimensional (3D) nitrogen-doped single-wall carbon nanotubes (SWNTs)/graphene elastic sponge (TRGN−CNTs−S) with low density of 0.8 mg cm −3 has been successfully prepared by pyrolyzing SWNTs and GO coated commercial polyurethane (PU) sponge. In addition, high performance electrode of the honeycomb-like NiCo 2 O 4 @Ni(OH) 2 /TRGN-CNTs-S with core-shell structure has been successfully fabricated through hydrothermal method and then by annealing treatment and electrochemical deposition method, respectively. Benefited from 3D structural feature, the compressed NiCo 2 O 4 @Ni(OH) 2 /TRGN-CNTs-S electrode exhibits high gravimetric and volumetric capacitance of 1810 F g −1 , 847.7 F cm −3 at 1 A g − 1 . The high rate performance and long-term stability was also obtained. Furthermore, an asymmetric supercapacitor using NiCo 2 O 4 @Ni(OH) 2 /TRGN-CNTs-S cathode and NGN/CNTs anode delivered high gravimetric and volumetric energy density of 54 Wh kg −1 at 799.9 W kg −1 and 37 Wh L −1 at 561.5 W L −1 . In summary, an excellent electrochemical electrode with new elastic 3D SWNTs/graphene supports and binder free pseudocapacitive materials was introduced.

Diffuser shaped film cooling holes are more and more used on the hot side blade of advanced aeroengines or gas turbines. The machining of diffuser holes is a key problem for its complicated shapes and Ni base superalloy. Currently die-sinking electrical discharge machining (EDM) is still considered to be an available process for the machining of diffuser holes. However, the tool electrode shape changes after each process due to electrode wear in EDM, therefore traditional die-sinking EDM process can not meet the requirements of shape precision and machining efficiency for film cooling holes. In this study, a novel EDM process named block divided EDM is proposed. In this process, the space of the complex shape of the hole is divided into several blocks. A slender rod electrode with simple cross-section is employed to form the blocks, each of which can be processed by feeding once. When the tip shape of the electrode changes due to electrode wear, it can be repaired efficiently because of the simple electrode shape. In order to analyze the machining error caused by electrode wear under different machining parameters, a geometry simulation model of the block division EDM process is established. In this simulation model, the shapes of electrode and workpiece are represented by three-dimensional matrix. The electrode motion, the spark gap, and the electrode wear ratio are taken into account. Finally, confirmatory experiments are carried out. It is shown that laidback fan-shaped holes, one type of diffuser shaped film cooling holes can be efficiently formed by the proposed process.

The tunable disorder of vacancies upon annealing is an important character of crystalline phase-change material Ge2Sb2Te5 (GST). A variety of resistance states caused by different degrees of disorder can lead to the development of multilevel memory devices, which could bring a revolution to the memory industry by significantly increasing the storage density and inspiring the neuromorphic computing. This work focuses on the study of disorder-induced carrier localization which could result in multiple resistance levels of crystalline GST. To analyze the effect of carrier localization on multiple resistant levels, the intrinsic field effect (the change in surface conductance with an applied transverse electric field) of crystalline GST was measured, in which GST films were annealed at different temperatures. The field effect measurement is an important complement to conventional transport measurement techniques. The field effect mobility was acquired and showed temperature activation, a hallmark of carrier localization. Based on the relationship between field effect mobility and annealing temperature, we demonstrate that the annealing shifts the mobility edge towards the valence-band edge, delocalizing more carriers. The insight of carrier transport in multilevel crystalline states is of fundamental relevance for the development of multilevel phase change data storage.

To investigate the influence of passivation behavior on electrochemical machining (ECM) performance, electrochemical behavior and passive film properties of S136H in neutral solutions composed of NaClO3 and NaNO3 were investigated by potentiodynamic measurements, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and auger electronic spectrometry. The results demonstrated that the corrosion resistance of the passive film increased with increasing NaNO3 concentration. The passive film formed in NaNO3 was more stable than that in NaClO3, which was attributed to the larger thickness, higher Fe2+/Fe3+ ratio and higher Cr2O3/Cr(OH)3 ratio of the passive film formed in NaNO3. From the ECM experimental results, the material removal rate and radial overcut area both decreased with increasing NaNO3 concentration because the area of the broken-down passive film was smaller than that in NaClO3. Additionally, a larger local corrosion area was formed on the workpiece in NaNO3 because some pores were generated in the passive film instead of the decomposition of the passive film. Therefore, compared with the NaNO3 electrolyte, using a NaClO3 electrolyte can improve the material removal rate and profile accuracy of microstructures on S136H steel.

Organic solvent nanofiltration (OSN) membranes suffer from separation performance inconformity (SPI) after the OSN application process in industry. In this work, a membrane and an indicator are proposed to solve this problem. Briefly, an adamantane (AD) structure is introduced into the active layer via 3-amino-1-adamantanol (AAMO) interfacial polymerization with acyl chloride to build a semi adamantane-amide active layer (SAAAL) on the aramid substrate. The substrate is also enhanced by the introduction of a certain amount of AAMO. The TFC membrane with SAAAL exhibits an “onion ring” surface morphology, lowered water contact angle, increased surface energy (γS) and acceptable OSN performance, in which the pure methanol (MeOH) permeance reaches 29.5 L·m−2·h−1·bar−1 and the removal ability toward fast green FCF (FCF) approaches 84.4%. In addition, a novel concept named the SPI index is proposed here to estimate the level of the SPI phenomena. According to the evaluation results based on five dyes in three solvents, the as-developed SAAAL-covered membranes show lower SPI indices compared to conventional aromatic polyamide layer (APAL)-covered membranes in the nanofiltration (NF) range. Long-term stability operation results also identify the potential of the AD structure in fabricated membranes showing both excellent OSN performance and mitigation of SPI phenomena.

Conical surfaces can be applied in the valves of liquid seal. In the fuel injection unit of a diesel engine, an outer conical surface at the tip of a slender needle works with an inner conical surface as injector-body seat to realize the switching and sealing of a fuel passage. So far, the conical surfaces are usually machined by mechanical grinding. The small grinding wheels 100,000 RPM have to be utilized for achieving enough circumferential speed. The inner conical surface is located in a small and deep bore, so the insufficient stiffness of the grinding tool is easy to cause machining errors. In this research, the process of wire electro discharge grinding (WEDG) by using a line-segment wire discharge (called line-segment WEDG in this paper) was explored for machining such conical surfaces. The emphasis was focused on the effect of wire alignment error on the accuracy of the conical surfaces. By the line-segment WEDG, an outer conical surface, or a conical tool electrode, can be machined directly and whereby an inner conical surface can be machined by die-sinking electro discharge machining (EDM). Machining experiments achieved some promising results including the outer conical surfaces with a total height of waviness profile Wt < 2.5 μm and surface roughness of R a0.4μm, the inner conical surfaces with Wt < 1.5 μm and R a0.2 μm, and all cone-angle errors are less than 0.1∘.

Nano electro discharge machining (nano EDM), as a frontier processing method in the research stage of exploration, has an important application prospect in the machining of metal and alloy materials for achieving nanoscale removal resolution. A pulsed power supply used in nano EDM is expected to limit a single pulse energy to nJ order of magnitude for improving the removal resolution of single pulsed discharge even to nanoscale. One developing direction is to decrease pulsewidth of the pulsed power supply. Conventional pulsed power supplies hardly output a single pulse and continuous pulses with nanosecond (ns) pulsewidth, resulting in too large single pulsed energy of μJ order of magnitude usually. In this research, a novel pulsed power supply is designed for realizing the ns-pulsewidth with controllable pulsewidth and peak voltage. The key novelty lies in a cascaded circuit with two triodes working in the state of ultra-fast avalanche conduction, where pF capacitors are applied to adjust the pulsewidth and pulsed energy precisely. Performance tests verified that a single pulse of 5 ns pulsewidth or continuous pulses up to 9 MHz can be outputted. Furthermore, nano EDM experiments of single pulsed discharge are carried out under the conditions of nanometer (nm) discharge gap and nm-tip tool electrode based on an atomic force microscope (AFM) system. The special results are achieved: a single pulsed energy can reach down to 1.75 nJ by outputting a pulsewidth of 10 ns, and a nano-EDM crater is only about 182 nm in diameter with regular shape and little recasting. Those results verify the possibility of AFM-tip-based nano EDM for machining nanostructures.

In this paper, we present a multiple layer device for investigating the impact of electric field on the conductance switching of GeTe phase change material excluding the contribution from Joule heat. The device includes a dielectric layer with excellent current-blocking which can result in a large electric field generated in the amorphous GeTe film and almost no current. With the generated electric field far beyond its threshold value for the conductance switching, our experimental data indicate that the conductance switching has not happened in the GeTe film. This indicates that the ovonic threshold switching (OTS) could not be induced by the purely electric field in amorphous chalcogenide film. Meanwhile, a modified thermal-assist model based on the Poole–Frenkel (PF) mechanism has been proposed to verify the thermal assistance is indispensable in the OTS process. And the modified model is well applied on the GeTe devices with different scales, which further supports the current experimental conclusion. This contributes to the further study of the OTS mechanism and application of the phase-change memory (PCM).

Compared with traditional methods for elaborately tailoring the active layer of thin-film composite (TFC) membranes, this study focused on building novel substrates for potential applications in developing organic solvent nanofiltration (OSN) membranes. One kind of “three-parts” hierarchically structured interface with nanospheres and macro surface pores was successfully prepared via Michael addition and Schiff's base (MS (2) glycerite-NAE-A silane (GNAS) nanospheres; and (3) the substrate surface. These phenomena also resulted in better surface hydrophilicity. All types of organic solvents, including harsh solvents, such as tetrahydrofuran (THF) and N,N-dimethylformamide (DMF), had stable permeability within the substrate, as did apolar n-hexane and isopar™ G. Therefore, the as-prepared TFC OSN membrane, which had an extremely short polymerization time, retained broad-spectrum solvent stability and had the highest solvent permeance in acetonitrile (24.5 ± 0.4 L m−2 h−1·bar−1). In addition, the resultant TFC membrane almost completely rejected the popular macrolide antibiotic azithromycin (AZM, 748.98 g mol−1) in ethanol, which is used to treat COVID-19.

To get micro holes with high aspect ratio on metal alloys by electrochemical machining (ECM) process, the mutual restricted problems between machining localization and efficiency are researched. By analyzing the thickening process of passive film, the mechanism of gas inhibition and dissolution promotion (GIDP) is explored. Thereby, a three-electrode pulse power supply (PPS) is designed to acidize on the workpiece/solution interface, for both better machining localization and efficiency. Micro ECM experiments, using the three-electrode PPS in neutral salt solution as electrolyte, are carried out on 304 stainless steel and 18CrNi8 alloy, in which a micro hollow electrode is used to flush electrolyte under high-pressure supply. It is found that the material removal rate (MRR) is increased by at least 80% and surface roughness R a is dropped by 40%, compared to those of two-electrode PPS. Micro array holes with diameter of about 175 μm are machined through metallic plates with thickness of 0.5 and 1.1 mm respectively. The micro array holes obtained have high consistent precision, good surface quality, and aspect ratio up to 6.5. Experimental results show the feasibility of micro ECM techniques proposed for micro hole with high aspect ratio.

Flexible nanoporous nitrogen-doped graphene film ( PNGF) prepared by facile hydrothermal ammonia reaction of nanoporous graphene oxide film (PGOF) is reported. The specific capacitance of the PNGF are 468 F g−1 at a scan rate of 2 mV s−1. The capacity retention after 10,000 charge/discharge cycles at a current density of 1 A g−1 is more than 81%. Two-electrode symmetric supercapacitor in a 6 M KOH aqueous electrolyte solution was fabricated, delivering a maximum power density of 5000 W kg−1 (at the energy density of 4.17 W h kg−1) and the maximum energy density of 6.43 W h kg−1 (at the power density of 150 W kg−1). The enhanced electrochemical performance can be attributed to nitrogen doped and the unique graphene film nanostructure. The expansion nanoporous structure of layer by layer plays the role of an “ion-buffering” reservoir, offering nano-channels for liquid electrolyte penetration by enlarging the specific surface area of PNGF efficiently. This flexible nanoporous gaphene film significantly suggests a broad range of application for fabricating high performance and novel energy storage devices.

Phase-change materials, the highly promising candidate for nonvolatile data recording, present a different phase-change property when film thickness shrinks to very deep submicron scale. The local structure of amorphous GeTe ultrathin films, which contributes to the characteristics of phase change, is examined using X-ray absorption measurements. Ge atoms are found to be low-coordinated when the film thickness decreases. Ge atoms are linked to neighbor atoms by covalent bond, and the weaker Ge–Te bonds are more easily broken, which suggests that Ge atoms are located in the defective Ge2Te3 local arrangement. The mixture of sp3/sp2 hybridization and 3-coordinated Ge found in ab initio molecular dynamics simulations also supports this local motif. The exponential rise of crystallization temperatures of ultrathin films with decreasing film thickness, which is a vital parameter for phase change process, can be well explained by the proposed defective GeTe local arrangement.

To increase the volumetric and gravimetric capacitances of supercapacitors, a new class of electrode materials with high electrochemical activity and favorable structures is extremely desired. In this work, a hollow novel nitrogen-doped 3D elastic single-walled carbon nanotube sponge (NSCS) which is ultra lightweight with the lowest density of 0.8 mg cm−3, and has a high open surface structure for electrolyte accessibility and excellent compressible properties as the electrode scaffold has been successfully fabricated by the pyrolysis method which could produce the carbon nanotube sponge easily on a large scale without high-cost and time-consuming processes. Moreover, a NiCo2O4 nanosheet supported on the NSCS has been successfully fabricated. The highest volumetric and gravimetric capacitance of this electrode is 790 F cm−3 at 1.43 g cm−3 and 1618 F g−1 at 0.54 g cm−3 with excellent cycling stability. The density of NiCo2O4/NSCS electrode was adjusted by mechanical compression and the most favorable density of the film for both high volumetric and gravimetric capacitances obtained was 1.21 g cm−3. The thick NiCo2O4/NSCS film of 72 μm has been fabricated at this favorable density, presenting both high volumetric and gravimetric capacitances of 597 F cm−3 and 1074 F g−1 at 1 A g−1, respectively, indicating that the structure of the NSCS is extremely feasible for obtaining a thick film electrode with excellent volumetric and gravimetric capacitances. Furthermore, an asymmetric supercapacitor of NiCo2O4/NSCS//NGN/CNTs was fabricated, exhibiting a high gravimetric energy density of 47.65 W h kg−1 at 536 W kg−1 and a volumetric energy density of 33.44 W h L−1 at 376.16 W L−1.

Developing flexible and lightweight energy storage systems for miniaturized electronic equipment and high volumetric performance is arousing increasing interest. For practical applications, the parameters of gravimetric and volumetric performance should both be taken into account and given the same importance. Here, a novel hierarchical structure of free-standing, binder-free electrodes of corrugated NiCo2O4 nanosheets on nitrogen doped graphene/carbon nanotubes (NGN/CNTs) film has been designed for use in high-performance supercapacitors. This unique lightweight electrode structure achieved extremely high electrochemical performance, with a volumetric capacitance of 482.7 F cm−3, a gravimetric capacitance of 2292.7 F g−1 at 5 A g−1, and very long-term cycle stability (125% capacitance retention after 10 000 circles at 30 A g−1). Optimal supercapacitive performance was also achieved in our fabricated asymmetric supercapacitor (ASC) by using NiCo2O4/NGN/CNTs as the cathode and NGN/CNTs as the anode. The device exhibited high gravimetric energy densities of 42.71 W h kg−1 at 775 W kg−1 and of 24.69 W h kg−1 at a high gravimetric power density of 15 485 W kg−1; it even demonstrated a high volumetric energy density of 25.90 W h L−1 and a high volumetric power density of 9389 W L−1. This strategy provides a new method to design flexible high-performance electrodes for a new generation of energy storage applications.