Flexible Energy Devices Research Articles

Charge Capturing Effects of Boron Nitride Nanosheets on Enhanced Triboelectric Properties of Polyimide Nanocomposite Films in a Conductor-to-Dielectric Mode

Dielectric composite materials play a crucial role in the performance of triboelectric nanogenerators (TENGs) by influencing charge storage and transfer capabilities. In this study, we investigate the influence of boron nitride nanosheets (BNNS) on the triboelectric properties of polyimide (PI)-based dielectric nanocomposite films within a TENG setup employing a conductor-to-dielectric configuration and a contact-separation mode. To achieve this, we manufactured PI/BNNS nanocomposite films containing 1-10wt% BNNS with a thickness of ~14.67nm via a solution casting method, followed by thermal imidization. Thermogravimetric characterization revealed that the thermal stability of the nanocomposites improved with increasing BNNS content. Additionally, the triboelectric performance of the PI/BNNS films, used as the negative friction layer, was enhanced due to the electron-trapping capabilities at the BNNS-PI interface. Among the samples, the nanocomposite film containing 5wt% BNNS exhibited the most significant triboelectric output, generating a voltage of ~4.0V and a current of ~426.4nA. Moreover, the triboelectric AC output generated by the TENG using PI/BNNS nanocomposite films was successfully rectified into DC signals and subsequently stored in microcapacitors. This capability highlights the significant potential of PI/BNNS nanocomposite films for energy harvesting and storage applications, further supporting their suitability for integration into advanced flexible energy devices.

Fabrication of flexible pressure sensor for human detection by direct-write printing concave surface

Flexible pressure sensor plays an important role in the field of human-computer interaction area due to its high flexibility and sensitivity. Convex surface of flexible electrodes provide an efficient way to enhance the sensitivity of flexible pressure sensors. However, facilely preparing controllable convex surface of flexible electrodes is still a challenge for obtaining high sensitive flexible pressure sensors. In this paper, direct-write print technique was utilized to prepare a concave structure surface with viscoelastic substrate, which could be used to prepare convex structure flexible electrode for fabricating highly sensitive flexible pressure sensors. Interaction between ink droplet and substrate was explored to generate a concave template, which could be controlled in spacing and diameter with printing spacing and nozzle diameter. Convex structure flexible surface could be prepared with the concave template, and then the convex structure flexible electrode could be realized with the evaporation of metallic silver on the surface. Furthermore, flexible pressure sensor was assembled with an interlocking structure by stacking two convex structure flexible electrodes in a face-to-face way, which could efficiently enhance flexibility and electrical property. The flexible pressure sensor presents a high sensitivity, a fast response/recovery time (<100 ms) and excellent flexibility (more than 10,000 cycles of bending), which could be applied in monitor physiological signals such as pulse detection, sound vibration, finger bending and so on. Therefore, this work provides an efficient method for preparing controllable structured surface, which has a great potential in the fabrication of flexible sensors, wearable electronics and energy devices.

Electrodeposited polyaniline modified CNT fiber as efficient counter electrode in flexible dye-sensitized solar cells

Carbon-based electrodes played a significant role toward the development of wearable and flexible photovoltaic energy devices in an efficient and affordable manners. Here, all-carbon-based electrodes composed of carbon nanotubes fiber (CNTF) have been used to fabricate a flexible wire shaped dye-sensitized solar cell (DSSC). A facile electrodeposited approach has been adopted to modify a CNTF with polyaniline (PANI) under acidic conditions. Both photoanode (TiO2@CNTs) and counter electrode (PANI@CNTs) twisted around each other, acted as electrons and hole collectors in the presence of redox couple (iodide/triiodide) as electrolyte. Scanning electron microscopy (SEM) images demonstrated the successful growth of TiO2 nanoparticles and conducting polyaniline (PANI) over the surface of CNTs fibers, as photoanode and counter electrode, respectively. Cyclic voltammetric (CV) measurements and electrochemical impedance spectroscopy (EIS), examined the reduction of triiodide and resistance of charge transfer. While the current-voltage measurements were carried out to check the performance of fabricated device when illuminated under simulated light source. With APNI modified counter electrode, device exhibited higher photoelectric conversion efficiency (3.57 %) under optimal conditions as compared to pristine CNTs fiber-based device with lower efficiency (2.26 %). The improved performance of modified counter electrode further confirmed by the lower peak separation (ΔEp= 0.42 V) and charge transfer resistance (RCE =19.28 Ω) in cyclic voltammetry and impedance spectroscopy, respectively. These fabricated electrodes could be promising alternate for metal-based electrodes in dye-sensitized solar cells due to its facile fabrication process, low cost, and higher chemical stability.

Recent development on the design, preparation, and application of stretchable conductors for flexible energy harvest and storage devices

AbstractThe intensifying energy crisis has made it urgent to develop robust and reliable next‐generation energy systems. Except for conventional large‐scale energy sources, the imperceptible and randomly distributed energy embedded in daily life awaits comprehensive exploration and utilization. Harnessing the latent energy has the potential to facilitate the further evolution of soft energy systems. Compared with rigid energy devices, flexible energy devices are more convenient and suitable for harvesting and storing energy from dynamic and complex structures such as human skin. Stretchable conductors that are capable of withstanding strain (≫1%) while sustaining stable conductive pathways are prerequisites for realizing flexible electronic energy devices. Therefore, understanding the characteristics of these conductors and evaluating the feasibility of their fabrication strategies are particularly critical. In this review, various preparation methods for stretchable conductors are carefully classified and analyzed. Furthermore, recent progress in the application of energy harvesting and storage based on these conductors is discussed in detail. Finally, the challenges and promising opportunities in the development of stretchable conductors and integrated flexible energy devices are highlighted, seeking to inspire their future research directions.

Laser‐Induced Graphene Toward Flexible Energy Harvesting and Storage Electronics

AbstractEnergy harvesting and storage devices play an increasingly important role in the field of flexible electronics. Laser‐induced graphene (LIG) with hierarchical porosity, large specific surface area, high electrical conductivity, and mechanical flexibility is an ideal candidate for fabricating flexible energy devices which supply power for other electronic components. Through a simple laser irradiation process with designable routes, abundant precursors (or substrates) rapidly transform into patterned LIG without any other treatments. The structure and physicochemical properties of LIG can be regulated by controlling the processing strategies and parameters, enabling the optimization of device performance. The laser scribing method, as a non‐contact and in situ technique, proves to be efficient in integrating different LIG‐based devices, resulting in all‐in‐one flexible power platforms. Here, a systematic summary of recent advancements in LIG‐based flexible energy electronics is presented. The controllable synthesis of LIG, functional LIG, and 3D architectures are described by elucidating corresponding mechanisms and processing strategies. An overall review of flexible energy conversion and storage devices based on LIG is presented. Eventually, the challenges and opportunities of LIG‐based materials in flexible energy conversion and storage are briefly discussed.

Enhancing piezoelectric properties of PVDF-HFP composite nanofibers with cellulose nanocrystals

With the increasing interest in flexible self-powering energy devices, piezoelectric polymers such as poly(vinylidene fluoride) (PVDF), PVDF-trifluoroethylene (PVDF-TrFE and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) have garnered substantial research attention. Among these, PVDF-HFP has demonstrated immense research potential in harvesting mechanical energy and converting it to electric energy. It is also particularly attractive due to its low cost compared to some other PVDF co-polymers. In this study, PVDF-HFP nanofibers were produced by electrospinning with cellulose nanocrystal (CNC) employed as a filler to improve their piezoelectric performance. Smooth and bead-free fibers were obtained with up to 1 wt% of CNC in the solution. The inclusion of CNC increased the uniformity of fiber diameter and improved thermal stability. Higher CNC concentration (2–3 wt%) engendered agglomeration and adversely impacted the conversion of non-polar phase to electroactive phase for PVDF-HFP molecules. At the optimal CNC concentration of 1 wt%, the voltage and current sensitivities for 1 cm2 samples were obtained as 0.146±0.048 mV/mN and 0.009±0.003 nA/mN, respectively. The open-circuit voltage output of 2.69±1.11 V was achieved under an average impact force of 40 N, and this increased with increased magnitude and frequency of the applied force. The mechanical properties of composite nanofibers maximized at 0.5 wt% CNC with tensile strength of 37.85±4.35 MPa, elastic modulus of 124.96±42.17 MPa, and strain at failure of 82.32±14.84 %. The improved piezoelectric and mechanical properties of the CNC-aided electrospun PVDF-HFP fibers will open new pathways for flexible energy harvesting systems.

Advancing low-dimensional flexible energy devices for wearable technology

This perspective article discusses the research, issues, and prospects of flexible batteries and supercapacitors in terms of one- and two-dimensions, as well as their stretchable, bendable, and twistable properties.

Ab Initio Molecular Dynamics Study on Self-Healing Solid Polymer Electrolyte for Lithium Metal Batteries

Lithium metal batteries (LMBs) have generally become potential candidates for energy storage devices because of their high energy density. However, the practical applications of LMBs have been limited due to the low safety of liquid electrolytes. Compared to liquid electrolytes, solid-state polymer electrolytes (SPEs) have excellent mechanical strength. However, there is room for improvement because traditional PEO-based SPEs need more mechanical properties and electrode contacts for flexible energy device applications. Self-healing solid polymer electrolytes (SHSPEs) have excellent flexibility and healing ability and can also suppress dendrite formation to increase the safety of LMBs. In this study, a novel SHSPE is designed by a combination of the zwitterionic copolymer, SBMA ([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide)-co-BA (Butyl Acrylate), and a lithium salt, LiTFSI. We explored their solvation structures and reactivity on the Li metal anode using Density functional theory (DFT) and ab initio molecular dynamics (AIMD) methods. Besides, we also studied the reactivity of the considered SHSPE on the Cu (100) surface to explore the SEI formation mechanisms. The cationic NR4 + and anionic SO3 - groups of SBMA interact electrostatically and form cross-linked network structures within the electrolyte framework, providing the designed SHSPE with prominent self-healing capacity. The decomposition reactions of SHSPE on the Li metal anode are explored, and the resultant decomposition products that contribute to the formation of the solid electrolyte interphase (SEI) are identified. Furthermore, AIMD results indicate that highly concentrated SO3 - groups in the SHSPE promote Li ion diffusion, which increases Li ionic conductivity. The present findings provide design criteria for developing highly conductive self-healing SPEs.

Robust conductive nanocomposite hydrogels with an interpenetrating network based on polyaniline for flexible supercapacitors

AbstractConductive polyacrylic acid/polyaniline/SiO2 (PAA/PANI/SiO2) nanocomposite hydrogels as electrolytes for a high‐performance flexible supercapacitor were prepared by combining in situ radical polymerization of anionic monomer acrylic acid, in situ sol–gel reaction of vinyltriethoxysilane (VTES), and oxidative polymerization of conductive monomer aniline (ANI). In the nanocomposite hydrogel, vinyl‐SiO2 nanoparticles served as analogous covalent crosslinkers, while the reversible noncovalent interactions (such as hydrogen bonds, electrostatic interactions, and chain entanglements) between the PAA/SiO2 and PANI networks acted as physical crosslinkers. The interconnected PANI and PAA/SiO2 networks thus constructed an interpenetrating three‐dimensional network that improved the movement of electrons and ions while also enhancing the mechanical properties of the hydrogel. At a volume ratio of ANI to VTES of 50:200, the compressive strength and conductivity of PAA/PANI/SiO2 hydrogels were as high as 1505 kPa and 4.42 S/m, respectively. Moreover, the flexible supercapacitors based on the nanocomposite hydrogel electrolyte exhibited high specific capacitance (574.7 F/g), energy density (19.6 Wh/kg), and power density (1.4 kW/kg) at a current density of 0.05 A/g. Meanwhile, these supercapacitors exhibit exceptional flexibility and mechanical stability, and can be repeatedly bent without degrading performance. This nanocomposite hydrogel has considerable potential for use in other flexible energy devices and electronics due to its excellent mechanical and electrochemical properties.Highlights Conductive nanocomposite hydrogel have good conductivity and mechanical properties. Conductive hydrogels are used as electrolytes for flexible supercapacitors. Vinyl‐SiO2 served as analogous covalent crosslinkers for the hydrogel. Noncovalent bonds between PAA/SiO2 and PANI acted as physical crosslinkers. Interconnected PANI and PAA/SiO2 networks formed an interpenetrating network.

Lignin‐Based Encapsulation of Liquid Metal Particles for Flexible and High‐Efficiently Recyclable Electronics

AbstractRoom‐temperature liquid metals (RTLMs) have excellent shape reconfiguration capabilities, which make them ideal for flexible electrodes, sensors, and energy devices. However, due to the high surface tension and weak adhesion of RTLM, the types of printing substrates, patterning, and recovery processes are limited. It is essential to develop advanced encapsulation techniques for the patterning of RTLMs. Lignin has great potential for promotion as nanodispersants and nanocarriers because of its abundant hydroxyl groups and good self‐assembly properties. In this work, a green and facile encapsulation method using industrial lignin is reported for stable, uniform, and reproducible patterning of eutectic gallium–indium (EGaIn). Lignin‐encapsulated EGaIn particles exhibit good stability and can be patterned on the surface of various substrates with a simple ballpoint pen. The electrical resistance of the conductive tracks shows little change under bending and twisting (720°) conditions. More importantly, the lignin‐encapsulated system can be easily dissolved and regenerated, which is also supported by molecular dynamics simulations and density functional theory calculations. 96.9% of the EGaIn can be recovered from the system. These characteristics make it very environmentally friendly throughout the preparation process and find applications in flexible sensors, transient circuits, and many other areas.

Enhanced dielectric and photocatalytic properties of TiO2-decorated rGO/PANI hybrid composites synthesized by in-situ chemical oxidation polymerization route

In this research, we synthesized composites of TiO2-decorated rGO surface, encapsulated in PANI matrix by using a facile in-situ chemical oxidation polymerization route. Different nanocomposites are prepared by varying concentration of rGO from 0.1 to 0.7% to PANI/TiO2 hybrid. The resulting composites were characterized by fourier transform infrared (FT-IR) spectroscopy, X-rat diffraction (XRD) analysis, Scanning electron microscopty (SEM), thermogravimetric analysis (TGA) and UV–visible spectroscopy. FT-IR and XRD analysis shows no change in the structure of any composite components and all the three phases retain their structure in the composite. But the dielectric properties of the material enhanced with the gradual increase in dielectric constant with the increase in concentration of rGO in the PANI/TiO2 matrix. The percolation threshold for dielectric constant was found to be 0.7 % rGO contents in PANI/TiO2 hybrid composite and is explained by the Maxwell-Wagner model. Further, this novel composite also presents enhanced photocatalytic properties with the remarkable red shift in the ability of visible light absorption and a narrow band gap in comparison to TiO2. Its hydrogen production ability by water splitting under irradiation is also investigated. The results show low electron-hole pair recombination property of the composite material by the much higher hydrogen production with excellent stability value of the critical composite in comparison to TiO2. Thus, this synthetic strategy provides a scalable approach to enhance the dielectric as well as the photocatalytic properties of the polymer-based inorganic composite for their application in flexible electrical appliances and energy devices.

Subsegmental approaches to S7: anatomic laparoscopic transdiaphragmatic and nonanatomic robotic transthoracic.

Minimally invasive liver surgery of postero-superior segments (S4a, S7, S8) remains a challenge. The caudal view, an increased distance between trocars and the operative field, and the liver fulcrum limiting the view, contribute to the difficulty [1, 2]. We and other groups have previously reported the use of intercostal trocars to access subdiaphragmatic tumors (transdiaphragmatic approach) [3-5], only few reports on a laparoscopic total transthoracic approach, none (to our knowledge) dynamic manuscripts of a total transthoracic robotic approach, and none (to our knowledge) that use preoperative port site and anatomic modelling exist. Further, we developed a total transthoracic (thoracoscopic) approach to avoid a hostile abdomen, while bringing viewing axis and instruments close to the target [6-10]. In this context, this report details the advantages of a laparoscopic vs. robotic transthoracic approach. According to institutional protocol, reports of individual cases in print or video format do not require institutional review board approval. A 68-year-old male on peritoneal dialysis with left colon adenocarcinoma and a single synchronous liver metastasis in S6-7 close to the root of the right hepatic vein underwent a laparoscopic transdiaphragmatic metastasectomy. Two years later, the patient developed a recurrent 1.5cm liver metastasis in S7, which lend itself to a robotic transthoracic approach. Following 3-D modelling and virtual port placement planning, the first metastasectomy was performed laparoscopically using a transdiaphragmatic approach. The recurrence was managed transthoracically due to more apical, subdiaphragmatic location. For this operation, a robotic approach was optimal as robotic wrist articulation facilitates manipulation via the limited intercostal space. This was particularly helpful during the diaphragmatic reconstruction. Total transthoracic liver surgery is certainly an advanced procedure requiring superior MIS liver skills. Recommendations for starting with a total transthoracic approach are not unlike from starting a standard, none-transthoracic liver surgery. Early on in the experience we recommend advanced liver MIS skills, and single, small, subdiaphragmatic tumors away from major vessels. Nonetheless, when these recommendations are followed a total transthoracic approach may be safer and result in less access trauma, than traversing a hostile abdomen to reach the posterior-superior liver. Both laparoscopic and robotic transthoracic approaches can facilitate the resection of subdiaphragmatic tumors, especially in patients with hostile abdomens. While the laparoscopic approach has advantages due to a broader spectrum of available surgical tools (flexible tip camera, parenchymal dissection, and energy devices), the robotic wrist articulation facilitates manipulation via the restricted intercostal space.

A More Controllable Laser Reduction of Graphene Oxide Membrane for Electrode Applications

Reduced graphene oxide (rGO) has attracted significant attention as an active electrode material for sensors and flexible energy devices due to its high electric conductivity and large surface area. rGO is usually obtained from graphene oxide(GO) through a thermal, chemical, photochemical, and electrochemical reduction process. Compared to the other reduction strategy, laser reduction is a single-step, precise, low cost, and chemical-free processing that can be directly applied on the GO membrane at room temperature in an ambient condition.The laser irradiation parameter, such as laser source, power, speed, and frequency, plays an important role in reduction optimization. In general, the quality of the rGO is not as high as that of pristine graphene because of incomplete reduction, and oxygenated defects involved in the reduction process.The not fully removed oxygenated function group not only influence the sensitivity and selectivity of the electrode, but also influences response time and recovery time during sensing and the electrochemical window of the supercapacitor made with those rGO electrode.This study aims to develop reduced graphene oxide (rGO) through laser irradiation for application in supercapacitors and electrochemical sensors as electrodes. GO membranes were fabricated with a layer-by-layer assembly process first then further reduced through conventional CO2 laser reduction. The laser irradiation parameters including intensity, frequency, and scan speed will be optimized to achieve the reduction up to maximi, C/O ratio. The effects of the reduction will be characterized and evaluated using scanning electron microscope (SEM), Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD)spectroscopy, and four-point probe station. The influence of the humidity on the impedance of the rGO electrode and the capacitance of the planar supercapacitor made with rGO electrode will also be analyzed for potential application of as-prepared rGO electrodes in supercapacitors and humidity sensors.

Multi-functional zeolitic imidazolate framework-67 (ZIF-67) for solid-state fiber energy harvesting and storage devices

Wearable electronic devices using energy device-based smart fibers have brought changes in Internet of Things (IoT) technology paradigms. Since electric power is essential to drive all current electronic devices, a flexible energy device is essential to construct a wearable energy systems. Herein, two different types of the fiber-based energy devices were manufactured using ZIF-67, which can improve catalytic properties. First of all, it was confirmed that ZIF-67 was adsorbed on the electrodes of the solid-state fiber-shaped supercapacitor (SS-FSC) and the catalytic property was enhanced, thereby improving the specific capacitance. Second, it was verified that ZIF-67 was adsorbed on the surface of Pt wire, which is the counter electrode (CE) of the solid-state fiber dye-sensitized solar cell (SS-FDSSC), to improve the catalytic properties, resulting in the improvement of the power conversion efficiency (PCE) of the SS-FDSSCs. The optimized SS-FDSSC demonstrated enhanced electrocatalytic activity, with a PCE of up to 7.03%, which is about 40% greater than that of the pristine Pt wire electrode (5.02%). Therefore, the fiber-based energy devices functionalized with ZIF-67 with excellent catalytic properties and high surface area have been identified as having great potential for producing novel and efficient power sources for wearable electronic devices to be utilized in IoT applications.

Stretchable and self-healable conductive hydrogel-based multifunctional triboelectric nanogenerator for energy harvesting and dance motion sensing

Hydrogels with the integrated characteristics of adhesion, self-healing, deformability, and conductivity hold enormous potential for the design of next-generation flexible human body posture sensor and energy device. Here, we proposed a double-network hybrid polyacrylamide/poly(acrylic acid)/MXene/PEDOT:PET (PPMP) hydrogel with excellent flexibility, self-healing capabilities, and stability. Furthermore, the proposed PPMP conductive hydrogel with MXene/PDMS encapsulation layer can play the role of a wearable strain sensor that can be used to detect various dance movement postures, including those of facial expressions, blinking, and elbow joints. Additionally, the proposed PPMP hydrogel with MXene/PDMS encapsulation layer can function as a flexible and stretchable triboelectric nanogenerator (FS-TENG) to harvest human motion energy. The FS-TENG can obtain an open-circuit voltage (Voc) of 169.2 V and a short-circuit current (Isc) of 9.6 µA. Moreover, the electric energy generated by these FS-TENGs can be used to drive hygrothermographs. This research offers a feasible strategy to design self-powered strain sensors for use in dance posture monitoring and energy harvesting in human motion.

Ionic Liquid Cross-linked Poly(N-isopropylacrylamide) Hydrogel Electrolytes for Self-Protective Flexible Separator-Free Supercapacitors

Thermoresponsive sol–gel transitions of poly(N-isopropylacrylamide) (PNIPAm) aqueous electrolytes have been explored to endow smart overheating self-protection for energy devices, but sol-state electrolytes are not suitable for flexible or wearable energy devices. It has remained challenging to explore PNIPAm hydrogels as smart electrolytes and separators in flexible energy devices. Herein, PNIPAm hydrogels cross-linked by ionic liquids were designed and prepared with gel–gel transitions for flexible supercapacitors, working both as the smart electrolyte and separator. The assembled supercapacitors exhibited desired specific capacitance and long-term stability at room temperature, and the capacitance suddenly dropped to almost zero at 60 °C to switch to self-protection of the supercapacitors. The reversible overheating protections were both obtained in both unbending and bending supercapacitors. The ionic liquid cross-linker played an important role to achieve effective overheating protections by confining more ions in the aggregated PNIPAm phase at high temperatures. Consequently, the ionic liquid cross-linked PNIPAm hydrogel electrolytes here demonstrated the advanced shutdown function of electrochemical performance compared with conventional thermoresponsive electrolytes. This work will inspire a more rational design of thermoresponsive hydrogel electrolytes in the perspective of polymers and aqueous electrolytes to achieve overheating protections.

Investigation of the reliability of nano-nickel/niobium oxide-based multilayer thin films deposited on polymer substrates for flexible electronic applications

Novel fracture/fatigue resistant nickel–niobium oxide (crystalline–amorphous) sandwich nanolayers on a polyimide (PI) substrate as a potential candidate for electrodes or interconnects for flexible electronic or energy devices.

Ultrastable 2D material-wrapped copper nanowires for high-performance flexible and transparent energy devices

Wrapping metallic nanomaterials with two-dimensional (2D) materials can significantly improve the physical properties required for various electronic and catalytic applications. However, synthesizing 2D material-wrapped metal nanowires with highly organized shell morphology is still difficult because of their large surface area and high aspect ratio. We propose a simple and practical method for synthesizing 2D material-wrapped copper nanowires (CuNWs) with highly organized shell morphology by using 2D quantum dot (QD) assembly and flash light irradiation under low temperature and non-vacuum conditions. A uniform and thin layer of QDs comprising 2D material such as graphene or hexagonal boron nitride is constructed on the CuNW by using a solution process. The 2D QD-wrapped CuNW is then subjected to flash light irradiation to realize highly organized shell morphology. Microstructural observations showed that the flash light irradiation reconstructs the shell structure and improves crystal quality without structural deformation. The 2D material-wrapped CuNWs were used to fabricate transparent conducting electrodes (TCEs) exhibited outstanding oxidation stability, chemical stability, and mechanical durability. These TCEs were applied to realize high-performance transparent supercapacitors and heaters. In particular, the transparent supercapacitors based on the graphene-wrapped CuNW TCE demonstrated excellent capacitive behavior under acidic electrolyte conditions. They showed the highest areal capacitance (18.97 mF cm−2) compared to other metal nanowire-based transparent supercapacitors. Finally, a novel method for fabricating carbon and boron nitride nanotubes by wet-etching the core CuNW of the 2D material-wrapped CuNWs was successfully developed.

Opportunities of Flexible and Portable Electrochemical Devices for Energy Storage: Expanding the Spotlight onto Semi-solid/Solid Electrolytes.

The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

Black Phosphorus/Carbon Nanoframes for Efficient Flexible All-Solid-State Supercapacitor.

A flexible all-solid-state supercapacitor with fast charging speed and high power density is a promising high-performance energy storage and sensor device in photovoltaic systems. Two-dimensional black phosphorus (BP) is a prospective electrode nanomaterial, but it struggles to fully exert its properties limited by its self-stacking. Herein, by embedding carbon nanoparticles into the interlayer of BP microplates, the designed BP/carbon nanoframe (BP/C NF) forms a certain nano-gap on the substrate for promoting the orderly transport of charges. The corresponding supercapacitor BP/C SC has a capacity of 372 F g−1, which is higher than that constructed from BP microplates (32.6 F g−1). Moreover, the BP/C SC exhibits good stability with a ca. 90% of capacitance retentions after 10,000 repeated bending and long-term cycles. Thus, the proposed strategy of using BP/carbon nanoframes is feasible to develop exceptional flexible energy devices, and it can guide the design of relevant two-dimensional nanocomposites.