A strong and sticky hydrogel electrolyte for flexible supercapacitors

With the rapid development of flexible supercapacitors (SCs), there is increasing demand for high-performance solid electrolyte to replace the conventional liquid electrolyte. Hydrogel electrolyte is one of the promising candidates, which possesses solid state but contains plenty of water within its highly porous structure. In this paper, a strong and sticky hydrogel has been synthesized using bacterial cellulose (BC) and poly (acrylic acid) (PAA). The results of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy shows that two components are well combined. Scanning electron microscopy (SEM) test shows that BC/PAA has a highly porous structure, which is modified by the interaction between BC nanofibers and acrylic acid monomer. Double network created by BC and PAA not only enhances the mechanical property of PAA but also improves the anti-compression ability of BC. Moreover, a sticky property is recognized within BC/PAA due to PAA, which can prevent the spilt of two flexible electrodes. The high ionic strength makes PAA shrink in 1M Na2SO4. However, the swelling ratio of BC/PAA could still reach to approximately 500% and its ionic conductivity is about 0.06 S·cm-1. This prepared BC/PAA hydrogel electrolyte has a great potential to be used in flexible SCs. © 2016 Author(s)

A strong and sticky hydrogel electrolyte for flexible supercapacitors

With the rapid development of flexible supercapacitors (SCs), there is increasing demand for high-performance solid electrolyte to replace the conventional liquid electrolyte. Hydrogel electrolyte is one of the promising candidates, which possesses solid state but contains plenty of water within its highly porous structure. In this paper, a strong and sticky hydrogel has been synthesized using bacterial cellulose (BC) and poly (acrylic acid) (PAA). The results of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy shows that two components are well combined. Scanning electron microscopy (SEM) test shows that BC/PAA has a highly porous structure, which is modified by the interaction between BC nanofibers and acrylic acid monomer. Double network created by BC and PAA not only enhances the mechanical property of PAA but also improves the anti-compression ability of BC. Moreover, a sticky property is recognized within BC/PAA due to PAA, which can prevent the spilt of two flexible electrodes. The high ionic strength makes PAA shrink in 1M Na2SO4. However, the swelling ratio of BC/PAA could still reach to approximately 500% and its ionic conductivity is about 0.06 S·cm-1. This prepared BC/PAA hydrogel electrolyte has a great potential to be used in flexible SCs. © 2016 Author(s)

A moving least square immersed boundary method for SPH with thin-walled structures

This paper presents a novel method for smoothed particle hydrodynamics (SPH) with thin-walled structures. Inspired by the direct forcing immersed boundary method, this method employs a moving least square method to guarantee the smoothness of velocity near the structure surface. It simplifies thin-walled structure simulations by eliminating the need for multiple layers of boundary particles, and improves computational accuracy and stability in three-dimensional scenarios. Supportive three-dimensional numerical results are provided, including the impulsively started plate and the flow past a cylinder. Results of the impulsively started test demonstrate that the proposed method obtains smooth velocity and pressure in the, as well as a good match to the references results of the vortex wake development. In addition, results of the flow past cylinder test show that the proposed method avoids mutual interference on both side of the boundary, remains stable for three-dimensional simulations while accurately calculating the forces acting on structure.Comment: 15 pages,11 figure

Polyaniline/reduced graphene oxide hydrogel film with attached graphite current collector for flexible supercapacitors

Reduced graphene oxide (RGO) hydrogel films possess a low specific capacitance and have no flexible current collectors, which limit their use in flexible supercapacitors. To solve these problems, a novel polyaniline (PANI) modified RGO hydrogel film with an attached graphite current collector (PANI/RGO/G) was prepared. Based on this film, a flexible supercapacitor device was fabricated and characterized. PANI/RGO/G film demonstrates good flexibility and electron transport. The graphite current collector highly reduces the internal resistance of the device. It shows a high specific capacitance of 478 F g−1 at a current density of 2 mA cm−2 based on the mass of one electrode and a good cycling stability (86.5% retention after 5000 cycles). Moreover, during the fabrication of the device, a modified design was adopted to solve the problem of low extension of PANI/RGO/G hydrogel film. The obtained device also exhibits a good flexibility; its capacitance hardly changes after 500 cycles of bending at an angle of 90°. © 2017, Springer Science+Business Media, LLC, part of Springer Nature.LO1504, NPU, Northwestern Polytechnical University; 15520720500, STCSM, Science and Technology Commission of Shanghai Municipality; IGA/CPS/2015/008, ERDF, European Regional Development Fund; CZ.1.05/2.1.00/19.0409, ERDF, European Regional Development Fund; IGA/CPS/2016/003, ERDF, European Regional Development Fund; LTACH17015, MoE, Ministry of Education, Government of the People's Republic of Bangladesh; ERDF, European Regional Development Fund; Research and DevelopmentMinistry of Education, Youth, and Sports of the Czech Republic [LTACH17015]; NPU Program I [LO1504]; Operational Program Research and Development for Innovations - European Regional Development Fund (ERDF); national budget of the Czech Republic within the framework of the CPS-strengthening research capacity [CZ.1.05/2.1.00/19.0409]; Internal Grant Agency from Tomas Bata University in Zlin, Czech Republic [IGA/CPS/2015/008, IGA/CPS/2016/003]; Shanghai Municipality Research Project [15520720500

Nano storage-boxes constructed by the vertical growth of MoS2 on graphene for high-performance Li-S batteries

In order to accelerate the reaction kinetics of lithium-sulfur batteries, the introduction of electro catalysis and proper structural control of the sulfur cathode is urgently needed. MoS2 nano sheets was selectively grown vertically (V-MoS2) on the microwave-reduced graphene (rGO) sheets through chemical coupling to construct a self-supporting sulfur cathode with a nano storage-box structure (V-MoS2 as the wall and rGO as the bottom). RGO, which has a high conductivity of 37 S cm−1, greatly accelerates the transfer of electrons from the active sites on the edge of the layer to the solution. The introduction of carbon tubes can connect the abundant pores in the foam and act as a long-range conductive path. The 2D-orthogonal-2D structure maximally exposes the edge active sites of MoS2, and together with graphene form a nano reactor of sulfur, intermediate lithium polysulfides and discharge product Li2S(2). The effective combination of the microstructure confinement of the nano storage-boxes and the efficient synchronous catalytic mechanism of V-MoS2 greatly improves the electrochemical performance of the lithium-sulfur batteries. As a result, the assembled lithium-sulfur battery displays a high initial discharge capacity of 1379 mAh g−1, good cycle stability (86% capacity retention after 500 cycles at 0.1C) and superior rate performance. © 2021 Science PressNational Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21875065, 51673064]; International Science & Technology Cooperation Program of China [2016YFE0131200]National Natural Science Foundation of China, NSFC: 21875065, 51673064; International Science and Technology Cooperation Programme, ISTCP: 2016YFE013120

A novel poly(vinyl carbonate-co-butyl acrylate) quasi-solid-state electrolyte as a strong catcher for lithium polysulfide in Li–S batteries

Lithium-sulfur batteries show great potential in the field of energy storage because of their high-energy density, but the shuttle effect of lithium polysulfide has seriously hindered their practical process. Quasi-solid-state electrolyte (QPE) is considered to be a promising alternative to traditional liquid electrolyte, which can improve the safety and cycling performance of lithium-sulfur batteries. Herein, a novel poly(vinyl carbonate-co-butyl acrylate) QPE with 3D crosslinked network (PEGDA-P(VCA-co-BA)) is designed to capture lithium polysulfide through a chemical adsorption of abundant ester groups. The PEGDA-P(VCA-co-BA) QPE exhibits high ionic conductivity of 2.9 mS cm−1. In order to synergize the beneficial effect of the PEGDA-P(VCA-co-BA) QPE, the nitrogen-doped carbon nanotube film-supported sulfur/Li cells are assembled with the QPE. As-assembled lithium-sulfur batteries show high initial capacity of 1080 mAh g−1 at 0.1 C, long cycle life (capacity retention of 715 mAh g−1 after 500 cycles) and superior rate performance. © 2019 Elsevier LtdNational Natural Science Foundation of ChinaNational Natural Science Foundation of China [21875065, 51673064]; International Science & Technology Cooperation Program of China [2016YFE0131200

Alkali-Resistant Quasi-Solid-State Electrolyte for Stretchable Supercapacitors

Research on stretchable energy-storage devices has been motivated by elastic electronics, and considerable research efforts have been devoted to the development of stretchable electrodes. However, stretchable electrolytes, another critical component in stretchable devices, have earned quite little attention, especially the alkali-resistant ones. Here, we reported a novel stretchable alkali-resistant electrolyte made of a polyolefin elastomer porous membrane supported potassium hydroxide–potassium polyacrylate (POE@KOH–PAAK). The as-prepared electrolyte shows a negligible plastic deformation even after 1000 stretching cycles at a strain of 150% as well as a high conductivity of 0.14 S cm^–1. It also exhibits excellent alkali resistance, which shows no obvious degradation of the mechanical performance after immersion in 2 M KOH for up to 2 weeks. To demonstrate its good properties, a high-performance stretchable supercapacitor is assembled using a carbon-nanotube-film-supported NiCo₂O₄ (CNT@NiCo₂O₄) as the cathode and Fe₂O₃ (CNT@Fe₂O₃) as the anode, proving great application promise of the stretchable alkali-resistant electrolyte in stretchable energy-storage devices

A facile prestrain-stick-release assembly of stretchable supercapacitors based on highly stretchable and sticky hydrogel electrolyte

A facile prestrain-stick-release assembly strategy for the stretchable supercapacitor device is developed based on a novel Na2SO4-aPUA/PAAM hydrogel electrolyte, saving the stretchable rubber base conventionally used. The Na2SO4-aPUA/PAAM hydrogel electrolyte exhibits high stretchability (>1000%), electrical conductivity (0.036 S cm-1) and stickiness. Due to the unique features of the hydrogel electrolyte, the carbon nanotube@MnO2 film electrodes can be firmly stuck to two sides of the prestrained hydrogel electrolyte. Then, by releasing the hydrogel electrolyte, homogenous buckles are formed for the film electrodes to get a full stretchable supercapacitor device. Besides, the high stickiness of the hydrogel electrolyte ensures its strong adhesion with the film electrodes, facilitating ion and electronic transfer of the supercapacitor. As a result, excellent electrochemical performance is achieved with the specific capacitance of 478.6 mF cm-2 at 0.5 mA cm-2 (corresponding to 201.1 F g-1) and capacitance retention of 91.5% after 3000 charging-discharging cycles under 150% strain, which is the best for the stretchable supercapacitors. © 2015 Elsevier B.V. All rights reserved.National Natural Science Foundation of China [51173042]; Shanghai Municipal Science and Technology Commission [12nm0504102]; Fundamental Research Funds for the Central Universities; Czech-Chinese Cooperation [LH14273

A Novel Flexible Supercapacitor Based on Cross-Linked PVDF-HFP Porous Organogel Electrolyte and Carbon Nanotube Paper@π-Conjugated Polymer Film Electrodes

High energy density and safety are the goals in the pursuit of flexible energy storage devices. Herein, we report a novel flexible supercapacitor (SC) fabricated with a cross-linked poly­(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (PVDF-HFP) porous organogel electrolyte and carbon nanotube paper@poly­(1,5-diaminoanthraquinone) (CNT@PDAA) film electrodes. The PVDF-HFP/tetraethylammonium tetrafluoroborate-acetonitrile (Et₄NBF₄-AN) organogel electrolyte, featured with a highly porous structure and chemical cross-linking, exhibits nonflammability, a broad electrochemical stable window, and high ionic conductivity of 14.4 × 10^–3 S cm^–1, as well as improved solvent resistance. The CNT@PDAA electrode displays good pseudocapacitive performance in a broad potential window due to p- and n-doping characteristics. Because of this rational design, the as-prepared flexible SC device achieves an excellent volumetric capacitance of 5.2 F cm^–3 and a high energy density of 5.16 mWh cm^–3 (41.4 Wh kg^–1) at a power density of 0.051 W cm^–3 (0.41 kW kg^–1). More importantly, a unit of as-assembled SC is shown to drive a commercially available product even in a bent state

A self-healable and easily recyclable supramolecular hydrogel electrolyte for flexible supercapacitors

Although research on polymer hydrogel electrolytes has achieved great progress, their practical application is restricted due to their vulnerability and non-recyclability problems caused by covalent cross-linking effects. Herein, we report a ferric ion cross-linked supramolecular PAA hydrogel electrolyte (KCl-Fe3+/PAA), in which the ionic bond and hydrogen bond endow the KCl-Fe3+/PAA hydrogel electrolyte with favorable self-healing ability and easy-recyclability. In addition, considering the eco-friendly and cost effective properties of both ferric ion and polyacrylic acid, there would be great potential for this KCl-Fe3+/PAA hydrogel electrolyte to be broadly applied. Meanwhile, the hydrogel electrolyte maintained good mechanical performance (extensibility &gt; 700%, and stress &gt; 400 kPa) and excellent conductivity (0.09 S cm-1), which completely satisfy the demands of flexible supercapacitors. After being assembled with graphene foam supported polypyrrole electrodes, the electrochemical performance of this flexible supercapacitor is comparable to that of its liquid electrolyte counterpart. © 2016 The Royal Society of Chemistry.51173042, NSFC, National Natural Science Foundation of ChinaShanghai Municipality Research Project [15520720500]; National Natural Science Foundation of China [51173042]; Czech-Chinese Cooperation Project by the Ministry of Education, Youth and Sports of the Czech Republic [LH14273