Chitin and chitin-cellulose composite hydrogels prepared by ionic liquid-based process as the novel electrolytes for electrochemical capacitors

This paper reports on the preparation and electrochemical performance of chitin- and chitin-cellulose-based hydrogel electrolytes. The materials were prepared by a casting solution technique using ionic liquid-based solvents. The method of chitin dissolution in ionic liquid with the assistance of dimethyl sulfoxide co-solvent was investigated. The obtained membranes were soaked with 1-M lithium sulfate aqueous solution. The prepared materials were preliminarily characterized in terms of structural and physicochemical properties. Further, the most promising biopolymer membranes were assembled with activated carbon cloth electrodes in symmetric electrochemical capacitor cells. The electrochemical performances of these devices were studied in a 2-electrode system by commonly known electrochemical techniques, such as cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The devices operated at a maximum voltage of 0.8 V. All the investigated materials have shown high efficiency in terms of specific capacitance, power density, and cyclability. The studied capacitors exhibited specific capacitance values in the range of 92–98 F g⁻¹, with excellent capacitance retention (ca. 97–98%) after 20,000 galvanostatic charge and discharge cycles. Taking into account the above information and the eco-friendly nature of the biopolymer, it appears that the prepared chitin- and chitin-cellulose-based hydrogel electrolytes can be promising components for green electrochemical capacitors.

     

Formulation of Ionic‐Liquid Electrolyte To Expand the Voltage Window of Supercapacitors

An effective method to expand the operating potential window (OPW) of electrochemical capacitors based on formulating the ionic‐liquid (IL) electrolytes is reported. Using model electrochemical cells based on two identical onion‐like carbon (OLC) electrodes and two different IL electrolytes and their mixtures, it was shown that the asymmetric behavior of the electrolyte cation and anion toward the two electrodes limits the OPW of the cell and therefore its energy density. Also, a general solution to this problem is proposed by formulating the IL electrolyte mixtures to balance the capacitance of electrodes in a symmetric supercapacitor.     

高性能硫化物基全固态锂电池设计：从实验室到实用化

全固态锂电池因其优异的安全性和高能量密度成为储能领域的重点研究内容。硫化物电解质因其高离子电导率、良好电极/电解质界面兼容性及易加工性,有力推动了硫化物基全固态锂电池的发展。本文首先从实验室研究阶段出发,从正极/电解质界面、硫化物电解质自身及负极/电解质界面三方面阐述了硫化物基全固态锂电池现阶段面临的主要问题,并介绍了相关的解决策略。随后从硫化物基全固态锂电池的实用化生产角度出发,介绍了电极/电解质膜的制膜工艺、软包电池的装配相关问题、高载正极的设计及硫化物电解质的大规模、低成本制备。最后展望了硫化物基全固态锂电池的未来研究方向和发展趋势。     

Combination of Organic and Inorganic Electrolytes for Composite Membranes Toward Applicable Solid Lithium Batteries

To meet the demand for long-range electric vehicles with high-energy-density batteries,the solid-state batteries(SSBs)have attracted ever-increasing attention due to their enormous potential in affording the energy density greater than 400 W·h/kg.As the key materials,the solid electrolytes can be classified as inorganic electrolyte and organic electrolyte.The former usually has high ionic conductivity,good stability and mechanical properties,whereas being heavy and brittle.The latter is usually flexible,light and easy to mass produce,nevertheless has poor ionic conductivity and stability.Thus,the combination of the organic and the inorganic electrolytes for the composite membranes has become the inevitable trend to achieve the high energy density and safety of lithium batteries.From the perspective of practical application,this paper discusses how to construct the ideal organic-inorganic composite solid electrolyte with low areal specific resistance,thin texture,wide electrochemical window and high safety for applicable SSBs.Furthermore,the critical challenges and future development directions are prospected for the composite solid electrolytes.     

Application of a novel binder for activated carbon-based electrical double layer capacitors with nonaqueous electrolytes

In this work, we have fabricated activated carbon electrodes using the binder LA135 and assembled electrical double layer capacitors with nonaqueous electrolytes of 1 M tetraethyl ammonium tetrafluoroborate (Et₄NBF₄) in propylene carbonate (PC), 1 M Et₄NBF₄ in acetonitrile (AN), and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) ionic liquid, respectively. The main chemical compositions of the binder are polyacrylonitrile and styrene–butadiene rubber. Scanning electron microscope images show that the conductive agents have been uniformly dispersed on the activated carbons in the electrode. The thermal stabilities of electrodes using different binders are studied by thermogravimetric analysis. The electrochemical properties of cells in different nonaqueous electrolytes are characterized by cyclic voltagramms, electrochemical impedance spectra, galvanostatic charge–discharge, leakage current, and cycle life measurements. The capacitor in Et₄NBF₄/AN has the lowest internal resistance and superior high-rate capability, and the one in Et₄NBF₄/PC has the smallest leakage current. The capacitor in EMIMBF₄ has the energy density as high as 35.4 Wh?kg^?1 at a current density of 0.2 A g^?1 (based on the total mass of active materials), which is 1.6 times higher than that of capacitor in PC electrolyte. Besides, the electrochemical properties of capacitors with different binders are comparatively studied. The capacitor using LA135 has the highest specific capacitance and moderate internal resistance comparing with the ones using poly(tetrafluoroethylene), sodium carboxymethyl cellulose + styrene–butadiene rubber or poly (vinylidene fluoride).     

Effect of solvated ionic liquids on the ion conducting property of composite membranes for lithium ion batteries

We prepared the polyethylene oxide (PEO)-based composite membrane electrolytes which contained the specialized ionic liquids and the inorganic filler of Li₇La₃Zr₂O₁₂ (LLZO). Mixtures of ionic liquids and tetragonal inorganic fillers were used as additives to prepare composite electrolytes for an application of all solid-state lithium ion batteries (ASLBs). In order to improve the ionic conductivity of composite membranes, we studied the structural change and the electrochemical behaviors as a function of the amounts of solvated ionic liquids (ILs). The addition effect of solvated ILs showed the higher ionic conductivity such as 10^?4 S/cm at 55 °C by reducing the crystalline character of polymer based composite, resulting in the enhanced ion conducting property. The hybrid composite membranes were successfully made in flexible form, and have an excellent thermal and electrochemical stability. Finally, the electrochemical performance of the half-cell was evaluated, and it was confirmed that the ion-conducting characteristics were influenced and controlled by the effect of ILs.     

New ceramic-carbon composites for electrodes for electrochemical capacitors

A new class of composite materials is introduced. Fine powders of silica, titania, Y-modified zirconia, and three types of alumina were pressed and sintered to form porous monoliths with relatively uniform pore structure. Carbon was then deposited in the pores of such monoliths by thermal decomposition of dichloromethane, cyclohexene, and glucose. The structure of the carbon deposit was studied by low-temperature nitrogen adsorption and by thermal analysis. The composite materials were used as electrodes in electrochemical capacitors with 1-ethyl-3-methylimidazolium trifluoromethylsulfonate (a low-temperature ionic liquid) as the electrolyte. High capacitances were observed for glucose-derived materials, which had high specific surface areas.     

Nanocrystalline cellulose-reinforced composite mats for lithium-ion batteries: electrochemical and thermomechanical performance

Nanocrystalline cellulose (NCC)-reinforced poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) composite mats have been prepared by electrospinning method. Polymer electrolytes formed by activating the composite mats with 1 M lithium bis(trifluoromethanesulfonyl)imide/1-butyl-3-methypyrrolidinium bis(trifluoromethanesulfonyl)imide electrolyte solution. The addition of 2 wt% NCC in PVdF-HFP improved the electrolyte retention and storage modulus of the separator by 63 and 15 %, respectively. The developed electrolyte demonstrated high value of ionic conductivity viz. 4?×?10^?4?S?cm^?1 at 30 °C. Linear scan voltammetry revealed a wide electrochemical stability of the composite mat separator up to 5 V (vs. Li⁺/Li). Cyclic voltammetry of the polymer electrolyte with a graphite electrode in 2.5 to 0 V (vs. Li⁺/Li) potential range showed a reversible intercalation/de-intercalation of Li⁺ ions in the graphite. No peaks were observed related to the reduction of the electrolyte on the anode.     

Cross-linking copolymers of acrylates’ gel electrolytes with high conductivity for lithium-ion batteries

The cross-linking gel copolymer electrolytes containing alkyl acrylates, triethylene glycol dimethacrylate, and liquid electrolyte were prepared by in situ thermal polymerization. The gel polymer electrolytes containing 15 wt% polymer content and 85 wt% liquid electrolyte content with sufficient mechanical strength showed the high ionic conductivity around 5?×?10^?3 Scm^?1 at room temperature. The gel electrolytes containing different polymer matrices were prepared, and their physical observation and conductivity were discussed carefully. The cross-linking copolymer gel electrolytes of alkyl acrylates with other monomers were designed and synthesized. The results showed that copolymerization can improve the mechanical properties and ionic conductivities of the gel electrolytes. The polymer matrices of gels had excellent thermal stability and electrochemical stability. The scanning electron microscope analysis showed the gel electrolyte was the homogeneous structure, and the cross-linking polymer host was the porous three-dimensional network structure, which demonstrated the high conductivity of the gel electrolytes. The gel polymer Li-ion battery was prepared by this in situ thermal polymerization. The cell exhibited high charge-discharge efficiency at 0.1 C. The results of LiFePO4-PEA-Li cell and graphite-PEA-Li cell showed that gel polymer electrolytes have good compatibility with the battery electrodes materials.     

碳化聚丙烯腈多孔材料在电化学电容器中的应用研究

聚丙烯腈 (PAN)及其共聚物是常用的高分子材料 ,在纺织和膜技术方面倍受重视 .聚丙烯腈纤维经氧化、碳化后 ,可制成具有高强度、高模量、能导电的碳纤维 .随着电子、信息、环保事业的发展和对新能源需求的提高 ,电化学电容器的研究成了一个热点 ,聚丙烯腈及其共聚物也开拓了它们的新应用领域 .电化学电容器是一类新型电子元件 ,其能量密度及功率密度介于电池及普通电容器之间 ,在低负荷场合可广泛应用于移动电话、录像机和笔记本电脑等电子产品 ,在高的功率负荷场合可与电池匹配 ,用于电动汽车 .从上世纪 80年代中后期开始 ,相关研究活跃…     

On the interaction of carbon electrodes and non conventional electrolytes in high-voltage electrochemical capacitors

This study is essentially based on innovative electrolytes such as the organic salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr₁₄BF₄) dissolved in propylene carbonate (PC) and the pure ionic liquid (N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄TFSI) and its solution in PC. Activated carbon cloths were used as self-standing binder-free electrodes. It is found that the presence of impurities in carbon electrodes may lead to electrolyte decomposition and electrode degradation which notably affect the electrochemical double-layer capacitor (EDLC) performance. Such processes greatly depend on the composition of both the electrode and the electrolyte, being much less significant with solvent-containing electrolytes. By raising the operation temperature to 60 °C, the EDLC performance in the ionic liquid Pyr₁₄TFSI is notably improved due to a relevant decrease in the viscosity and increase in ionic conductivity. By contrast, the presence of impurities, e.g., Zn and Al, in the electrodes remarkably reduces the electrolyte stability and a thick layer of decomposition products completely covers the carbon fibers after cycling at high temperature. The ionic liquid in solution maintains the high maximum operative voltage of the net ionic liquid whereas its viscosity and ionic conductivity are close to those of the conventional Et₄NBF₄/PC. Furthermore, the presence of propylene carbonate as solvent prevents to some extent the ionic liquid degradation.     

Electroanalysis based on stand-alone matrices and electrode-modifying films with silica sol-gel frameworks: a review

Silica sol-gel matrices and its organically modified analogues that contain aqueous electrolytes, ionic liquids, or other ionic conductors constitute stand-alone solid-state electrochemical cells when hosting electrodes or serve as modifying films on working electrodes in conventional cells. These materials facilitate a wide variety of analytical applications and are employed in various designs of power sources. In this review, analytical applications are the focus. Solid-state cells that serve as gas sensors, including in chromatographic detectors of gas-phase analytes, are described. Sol-gel films that modify working electrodes to perform functions such as hosting electrochemical catalysts and acting as size-exclusion moieties that protect the electrode from passivation by adsorption of macromolecules are discussed with emphasis on pore size, structure, and orientation. Silica sol-gel chemistry has been studied extensively; thus, factors that control its general properties as frameworks for solid-state cells and for thin films on the working electrode are well characterized. Here, recent advances such as the use of dendrimers and of nanoscale beads in conjunction with electrochemically assisted deposition of silica to template pore size and distribution are emphasized. Related topics include replacing aqueous solutions as the internal electrolyte with room-temperature ionic liquids, using the sol-gel as an anchor for functional groups and modifying electrodes with silica-based composites.

     

Polyethylene oxide-based nanocomposite polymer electrolytes for redox capacitors

In this work, the use of a polyethylene oxide-based nanocomposite polymer electrolyte (NCPE) in a redox capacitor with polypyrrole electrodes has been studied. To the best of our knowledge, not much work has been reported in the literature on redox capacitors fabricated using NCPEs. The composition of the polyethylene oxide (PEO)-based NCPE was fine tuned to obtain films with the highest ionic conductivity. They were mechanically stable to handle for any purpose without damaging the film. The optimized composition was {[(10PEO:NaClO₄) molar ratio]: 75 wt.% propylene carbonate (PC)}: 5 wt.% TiO₂. This electrolyte film showed an ambient temperature ionic conductivity of 5.42 × 10^?3 S cm^?1. It was employed in a redox capacitor with polypyrrole electrodes polymerized in the presence of sodium perchlorate in non-aqueous medium. Performance of the redox capacitors were observed using cycling voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge discharge test. It was possible to observe a satisfactory capacitive behavior in the range 58–83 F/g. Further, the redox capacitors had the ability to retain for continuous charge discharge processes.     

Synthesis and electrochemical properties of activated carbons and Li4Ti5O12 as electrode materials for supercapacitors

New activated nanoporous carbons, produced by carbonization of mixtures of coal tar pitch and furfural with subsequent steam activation, as well as electrochemically active oxide Li₄Ti₅O₁₂, prepared by thermal co-decomposition of oxalates, were tested and characterized as electrode materials for electrochemical supercapacitors. The phase composition, microstructure, surface morphology and porous structure of the materials were studied. Pure carbon electrodes as well as composite electrodes based on these materials obtained were fabricated. Two types of supercapacitor (SC) cells were assembled and subjected to charge–discharge cycling study at different current rates: (1) symmetric sandwich-type SC cells with identical activated carbon electrodes and different organic electrolytes, and (2) asymmetric hybrid SC cell composed by activated graphitized carbon as a negative electrode and activated carbon–Li₄Ti₅O₁₂ oxide composite as a positive electrode, and an organic electrolyte (LiPF₆–dimethyl carbonate/ethylene carbonate (DMC/EC). Four types of carbons with different specific surface area (1,000–1,600 m² g^?1) and texture parameters, as well as three types of organic electrolytes: Et₄NBF₄–propylene carbonate (PC), LiBF₄–PC and LiPF₆–DMC/EC in the symmetric SC cell, were tested and compared with each other. Capacitance value up to 70 F g^?1 for the symmetric SC, depending on the electrolyte microstructure and conductivity of the carbon material used, and capacitance of about 150 F g^?1 for the asymmetric SC cell, with good cycleability for both supercapacitor systems, were obtained.     

Recent Progress in High-Performance Lithium Sulfur Batteries: The Emerging Strategies for Advanced Separators/Electrolytes Based on Nanomaterials and Corresponding Interfaces

Lithium-sulfur (Li−S) batteries, possessing excellent theoretical capacities, low cost and nontoxicity, are one of the most promising energy storage battery systems. However, poor conductivity of elemental S and the “shuttle effect” of lithium polysulfides hinder the commercialization of Li−S batteries. These problems are closely related to the interface problems between the cathodes, separators/electrolytes and anodes. The review focuses on interface issues for advanced separators/electrolytes based on nanomaterials in Li−S batteries. In the liquid electrolyte systems, electrolytes/separators and electrodes system can be decorated by nano materials coating for separators and electrospinning nanofiber separators. And, interface of anodes and electrolytes/separators can be modified by nano surface coating, nano composite metal lithium and lithium nano alloy, while the interface between cathodes and electrolytes/separators is designed by nano metal sulfide, nanocarbon-based and other nano materials. In all solid-state electrolyte systems, the focus is to increase the ionic conductivity of the solid electrolytes and reduce the resistance in the cathode/polymer electrolyte and Li/electrolyte interfaces through using nanomaterials. The basic mechanism of these interface problems and the corresponding electrochemical performance are discussed. Based on the most critical factors of the interfaces, we provide some insights on nanomaterials in high-performance liquid or state Li−S batteries in the future.     

Electrochemical characterization of composite membranes based on crown-ethers intercalated into montmorillonite

Oxyethylene macrocyclic compounds (crown-ethers) act as ligands of intracrystalline cations of certain layered silicates as montmorillonites. Stable intercalation materials are formed which are used to prepare organic-inorganic membranes by encapsulating these intercalation compounds with a poly-butadiene thin coating. Electrochemical Impedance Spectroscopy (EIS) is used to study the resulting composite membranes in contact with aqueous electrolytes. From the impedance plots, the ionic resistance of the membranes is obtained. The thickness of the polybutadiene coating is an important factor determining the ability of ions to pass across the membrane. Marked differences in the ionic resistance are observed as a function of the nature of the interlayer macrocyclic compound. For non-intercalated montmorillonite membranes, the ionic resistance is strongly reduced, whereas for some crown-ether intercalated materials such as 18-crown-6 and dibenzo 24-crown-8, iono-selective membranes are obtained. Concerning the nature of the electrolyte, cations exhibiting greater hydration energies show higher difficulties to pass through the membrane and, consequently, the ionic resistance increases.     

PEO-LiClO_4-ZSM5复合聚合物电解质II.ZSM-5对离子电导率的影响

通过XRD ,DSC ,FT IR和SEM等方法对PEO LiClO4 ZSM5复合电解质进行了研究 ,结果表明ZSM 5可以有效地降低PEO LiClO4 ZSM5复合电解质中PEO的结晶度和玻璃化温度 ,从而提高其低温区域的离子电导率 .温度高于PEO的结晶熔融温度后 ,复合电解质离子电导率的提高则是由于在ZSM 5表面形成了有利于Li离子迁移的导电通道所引起的 .较高的离子电导率和较宽的电化学稳定窗口表明PEO LiClO4 ZSM5复合电解质在全固态锂离子二次电池领域具有良好的应用前景 .     

Water-in-salt electrolytes for high voltage aqueous electrochemical energy storage devices

If were not by their low electrochemical stability, aqueous electrolytes would be the preferred alternative to be used in electrochemical energy storage devices. Their abundance and nontoxicity are key factors for such application, especially in large scale. The development of highly concentrated aqueous electrolytes, so-called water-in-salt electrolytes, has expanded the electrochemical window of aqueous electrolyte up to 3.0 V (whereas salt-in-water electrolytes normally shows up to 1.6 V), showing that water can be an alternative after all. Many devices, ranging from metal-ion batteries to electrochemical capacitors, have been reported recently, making use of such wider electrochemical stability and enhancing devices energy density. Different salts have also been proposed not only to gain in costs but also to improve physicochemical properties.     

Study of the role of ceramic filler in composite gel electrolytes based on microporous polymer membranes

The presented contribution aims at reconsidering the role of filler in affecting the ionic transport in composite gel electrolytes for Li-ion cells based on microporous polymer membranes. The gels have been prepared by swelling thin PVdF/HFP membranes either with conventional liquid electrolyte or with pure propylene carbonate solvent. The membranes contained dispersed submicron-size modified silica filler added in a wide range of weight ratios. The effect of filler content on the kinetics of liquid phase absorption and evaporation from the composite membranes, as well as on the conductivity of the corresponding gel electrolytes, has been studied and discussed in terms of the “colloidal” and “soggy sand” electrolyte concepts. It has been found that conductivity increase of composite gels is not directly correlated with the liquid electrolyte uptake. On this basis it is concluded that important part of ionic transport in this type of composite gel polymer electrolytes is realized on the filler grain boundaries, through overlapping space charge layers of the silica grains.     

Improving electrochemical performance of poly(vinyl butyral)-based electrolyte by reinforcement with network of ceramic nanofillers

This study has concerned the development of polymer composite electrolytes based on poly(vinyl butyral) (PVB) reinforced with calcinated Li/titania (CLT) for use as an electrolyte in electrochemical devices. The primary aim of this work was to verify our concept of applying CLT-based fillers in a form of nano-backbone to enhance the performance of a solid electrolyte system. To introduce the network of CLT into the PVB matrix, gelatin was used as a sacrificial polymer matrix for the implementation of in situ sol–gel reactions. The gelatin/Li/titania nanofiber films with various lithium perchlorate (LiClO₄) and titanium isopropoxide proportions were initially fabricated via electrospinning, and ionic conductivities of electrospun nanofibers were then examined at 25 °C. In this regard, the highest ionic conductivity of 2.55 × 10⁻⁶ S/cm was achieved when 10 wt% and 7.5 wt% loadings of LiClO₄ and titania precursor were used, respectively. The nanofiber film was then calcined at 400 °C to remove gelatin, and the obtained CLT film was then re-dispersed in solvated PVB-lithium bis(trifluoromethanesulfonyl)imide (PVB-LiTFSI) solution before casting to obtain reinforced composite solid electrolyte film. The reinforced composite PVB polymer electrolyte film shows high ionic conductivity of 2.22 × 10⁻⁴ S/cm with a wider electrochemical stability window in comparison to the one without nanofillers.