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The miniaturization of the electronic devices requires smaller packaged chips, and the distance between the chip and the substrate becomes smaller, which make it necessary to introduce the nano-silica in the filler for advanced packaging. However, the nano-silica is easy to settle in the underfill and block the packing, because it tends to agglomerate due to its large specific area. Unfortunately, the addition of nano-silica in the underfill could also largely improve the viscosity, giving rise to the unacceptable low flowability. Therefore, it is necessary to investigate the key factors that could influence the dispersion of nano-silica in the epoxy resin. In this paper, the time domain nuclear magnetic resonance spectrometer (NMR) technique was used to study the dispersion of silica fillers. This research studied the nano-silica particle size impact and the surface modification impact on the dispersion of nano-silica in epoxy resin. The shape and size distribution of three types of particles were characterized before studying the relaxation property. The three types of particles were then modified with silane coupling agents. The results of time domain NMR relaxation rate showed that the surface modified nano-silica particles have lower relaxation time, meaning the better dispersity in the epoxy. Meanwhile, after surface modification, larger fillers obtained better dispersity compared with smaller fillers, which result in the uniform dispersion in the resin.

In this study, a flexible asymmetrical solid-state filter paper-based supercapacitor was fabricated. Common laboratory filter paper (FP) provides toughness and flexibility to the whole device. Simply, traditional electroless Ni plating and electro-deposition were introduced to change the electrical conductivity of FP as a flexible and conductive substrate material. Then, the electrochemical active material Co(OH)2 and active carbon (AC) were respectively coated on the conductive Ni paper through electro-deposition and physical coating methods to prepare Ni/Co(OH)2-FP as a positive electrode and Ni/AC-FP as a negative electrode. Moreover, they were separated by a piece of FP coated with an ionic gel electrolyte to assemble the flexible asymmetrical solid-state supercapacitors. This supercapacitor exhibits superior flexibility, large volume energy density (0.64 mW h cm−3), and good bending cycle performance (95.89% capacitance retention after 500 bending cycles). It has been demonstrated that the assembled supercapacitor can still power a red light-emitting diode (LED) indicator normally regardless of the bending state and bending frequency. This study may provide promising insights for the design and fabrication of a flexible asymmetrical solid-state supercapacitor in a flexible power supply for wearable and portable applications.

A compressible supercapacitor is a promising energy storage device for wearable flexible electronic devices. In this study, a compressible electrode material of MF/Ni(II)–Co(OH)2 based on melamine foam (MF) for all-solid supercapacitors was fabricated by an electroless plating and electrodeposition method. The electrode of MF/Ni(I) was prepared by electroless plating on commercial MF, and the subsequent step of electrodeposition was introduced to fabricate MF/Ni(II) and MF/Ni(II)–Co(OH)2. The electrochemical results show that the obtained compressible electrode material exhibits exceptional capacitive behavior (volumetric capacitance of 8.82 F cm−3 at 3 mA cm−3), cycling stability (80.95% capacitance retention after 1000 cycles at 10 mA cm−3), and superior compression stability (93.81% capacitance retention even under 50% compression). Then, a compressible asymmetrical all-solid supercapacitor was fabricated with MF/Ni(II)–Co(OH)2 as the positive electrode and Ni/carbon (Ni/C) as the negative electrode, separated by laboratory filter paper and KOH–poly(vinyl alcohol) (PVA) electrolyte. Such a compressible supercapacitor displays good capacitive behavior, exceptional compression stability (84.21% capacitance retention even under 50% compression) and cycling stability (94.44% capacitance retention after 1000 cycles at 10 mA cm−3). It has been shown that the assembled compressible supercapacitor can be used as a power source to drive a light-emitting diode (LED) and it can work properly under different compression conditions. These favorable results demonstrate that MF/Ni(II)–Co(OH)2 is an appropriate electrode material for compressible supercapacitors.

In order to develop a low cost, sustainable, and eco-friendly energy storage device, we demonstrated an all solid state symmetric flexible supercapacitor based on the office waste paper fibers-reduced graphene oxide-manganese dioxide (PF-RGO-MnO2) which acts as both the positive and negative electrodes. With the assistance of facile solution phase assembly and vacuum filtration method, the flexible PF-RGO-MnO2 electrodes with high physical flexibility and excellent mechanical strength were fabricated directly without any binder agents. Furthermore, owing to the advantages of the lager surface area and microfibers of the each single paper fiber, the PF-based hybrid flexible electrodes show high specific capacitance of 410 F g− 1 at 0.8 A g− 1 and retain 93% capacitance over 5000 cycles, indicating outstanding electrochemical performance. In addition, the assembled solid-state symmetric supercapacitors exhibit high energy density (19.6 Wh kg− 1 at 400 W kg− 1) and excellent cycling stability of 85.3% retention even after 2000 folding and bending cycles. These results propose a renewable way to turn “waste” into wealth, and provide a new method to fabricate the sustainable and freestanding paper-based supercapacitor for application in the flexible energy storage devices.

Direct printing techniques have generated significant research interest in fabricating flexible and scalable micro-supercapacitors (MSCs). In this study, we report a facile and cost-effective way to synthesize water soluble reduced graphene oxide (WSG) with a high concentration by decoration with aminobenzenesulfonic acid (ABS) and reduction with ascorbic acid. The WSG possesses excellent electrical conductivity (360 S m−1), good water dispersion stability as well as a high zeta potential value (−62 mV at pH 11), and the concentration of the as-prepared WSG could reach 5 mg mL−1, nearly as great as the highest value from previous reports. Then, using this high-concentration WSG dispersion directly as an electrochemically active ink material, micro-supercapacitor electrodes could be facilely fabricated via a direct printing technique on common printing paper, and the all-solid-state flexible MSCs could be further assembled. The results show that these flexible MSCs exhibit high area and volume specific capacitances of 2.67 mF cm−2 and 6.75 F cm−3, maintaining 94.8% of their initial specific capacitance after 5000 cycles at a scan rate of 50 mV s−1. More importantly, the capacitance and potential can be expanded by connecting a WSG-MSC device in parallel and in series, and the assembled devices are further demonstrated to be capable of lighting a liquid crystal display with three WSG-MSCs in series. These findings not only provide a simple way to synthesize WSG with a high concentration, but also facilitate its applications in printable and flexible MSCs with high performance.

Compared with other mechanical energy collectors, triboelectric nanogenerators have the advantages of large output, high efficiency and good stability. However, they can produce stretching, twisting, bending in the process of collecting mechanical energy generated by human motion. Maintaining good stability under deformation becomes one of the great challenges of triboelectric nanogenerators. This work offers effective and simple method to fabricate a triboelectric nanogenerator that can work well under deformation. By spin-coating AgNWs on the pre-stretched PDMS surface to make a flexible electrode. Due to the materials used are silicone and silver nanowires, the device also has good transparency.

A flexible all-solid-state asymmetric supercapacitor (FAAS) was prepared via a low-cost method with commonly used paper fibers as the substrate and a modified polymer-based hydrogel as the electrolyte. In the designed structure of the positive electrode, a three dimensional network of stacked thin film based on paper fibers (PFs), chemically reduced graphene oxide (RGO) and the electro-polymerization of polyaniline (PANI) nanorods was prepared via an extended filtration assisted method. The fabricated PF–RGO–PANI electrodes exhibit large specific capacitance of 587 F g−1 at the current density of 0.8 A g−1 and excellent cycling stability (99.6% retention of initials specific capacitance even after 5000 cycles). PF–RGO film was introduced as the negative electrode for the designed asymmetric supercapacitor. During the preparation process of FAAS, a glutaraldehyde (GA) cross-linked PVA–H2SO4 hydrogel was not only used as the electrolyte but also explored as a separator and external packaging material prepared by a fast layer-by-layer assembly technique within one minute. The resulted FAAS exhibits a maximum energy density and power density of 175 W h kg−1 and 9200 W kg−1. Moreover, superior mechanical stability of the FAAS has been demonstrated by testing its bending and folding performance, which retains over 84% of its original specific capacitance even after 2000 cycles of bending and folding. The simple and low-cost preparation process of electrodes, the ultra-fast flexible supercapacitor assembling and the efficient packaging technique proposed in this study provide a good contribution to the development of FAAS for the next generation flexible energy storage devices.

In this study, the oxygen-rich functional groups grafted carbon fiber cloth electrode (OCC) was successfully fabricated by activating carbon fiber cloth (CC) in strongly corrosive and oxidative environment, and the content of oxygen functional groups on surface of OCC can be easy controlled through different activation time. Surprisingly, the OCC electrode possesses an ultra wide potential range of −1.2 − 1.2 V in neutral electrolyte that is impossible to achieve in acidic or alkaline aqueous electrolyte, and the assembled symmetric supercapacitor device (SSD) exhibits a large operating voltage of 2.2 V. What's more, SSD presents high energy density of 0.87 mW·h cm−3 at power density of 5.5 mW cm−3 and superior cycling stability (86.8% of capacitance retention after 10,000 cycles). This study may provide a facile and available method for fabricating and designing flexible electrode with high performance.

Designing and fabricating the electrochemical active materials with outstanding electrochemical performance is crucial for supercapacitors in applications of energy storage devices. In this study, a structure of ultrathin manganese dioxide (MnO2) nanosheets deposited on the surface of mesoporous carbon hollow spheres (MCHSs) is designed and fabricated through a simple method. MCHSs are served as both substrate materials for growth of MnO2 nanosheets and electrical conductive layer for improving the poor electrical conductivity of MnO2, thus obtaining MCHS/MnO2 with good electrochemical performance. What’s more, the synergy of pseudocapacitance and electrical double-layer capacitance (EDLC) in asymmetrical configuration plays a crucial role in enhancing energy density of assembled supercapacitors. The obtained results exhibit that asymmetrical MCHS/MnO2//MCHS supercapacitor displays large specific capacitance (116.4 F/g at 0.1 A/g) and superior cycling stability (90.3% of capacitance retention after 6000 c...

The piezoelectric nanogenerator (PENG) is an important landmark in the development nanotechnology. The PENG, conventing mechanical energy to electrical energy in nanoscale, relies on the coupling of piezoelectric and semiconducting properties of nanomaterials. This approach offers a potential solution for harvesting energy from the environment for self-powered nanotechnology. How to improve the conversion efficiency is still one of the most factors for current PENG. Here, based on the fundamental research of piezoelectric nanogenerators, we propose a simple, robust, and scalable approach for fabricating a nanowire nanogenerator in which, ZnO nanowires is grown on the micro-pyramid textured surface of the silicon wafer and then a nanogenerator is fabricated by simply combine two substrates with ZnO nanowires face-to-face. The proposed geometry allows the nanogenerator to collect multi-faceted mechanical energy. This pyramid structure of the ZnONWs nanogenerators can generate piezoelectric current with an average signal about 3nA when the device was drove by ultrasonic waves at 40 kHz.

In this paper, a flexible supercapacitor electrode with high electrochemical performance was fabricated via a electroless plating-electrodeposition combined method which was facile and efficient. The low-cost and available cellulose paper (CP) was employed as flexible substrate loaded highly conductive current collect materials and electrochemical active materials. Results indicate that the as-fabricated electrode is sandwich-structured and flexible and the electrode itself is easy to be bended, twisted and rolled. The electrochemical data showed that the as-fabricated composite electrode displays excellent areal specific capacitance (2485 mF/cm2 at scan rate of 5 mV/s) and the series resistance of the electrode was about 2.2 Ω, which is relatively low enough to be used.