Stable Voltage Window Research Articles

3D Prussian blue decorated porous carbon composite electrode for advanced asymmetric supercapacitor applications

Irrational use of fossil fuels led to global warming and pollution. Therefore, the newer technologies should be sustainable and eco-friendly to combat climate change. In this context, supercapacitors (SCs) are demonstrated with carbon materials derived from natural biomaterials. The utilization of biomass-derived materials in energy storage not only converts biowaste material to value-added products but also reduces the production cost. Although SCs exhibit high power density, they are not considered a primary energy source due to their poor energy density. By taking advantage of the present work's asymmetric configuration, the operating voltage window and energy density of aqueous SCs are significantly enhanced. An asymmetric SC is developed by combining a porous 3D cubical-shaped Prussian blue (PB) decorated carbon derived from tamarind seeds (ACTS-800) (PB/ACTS-800) positive electrode with ACTS-800 negative electrode and aqueous 3 M KNO3 electrolyte. The resulting ACTS-800//PB/ACTS-800 (1:2) asymmetric SC demonstrated a broad electrochemical stable voltage window of 2.2 V in the aqueous medium. Impressively, a high energy density of 60 Wh/kg @ 551 W/kg realized is much superior to most of the carbon/carbon SCs operated in an aqueous medium.

(Digital Presentation) Elucidating the Charge Storage Mechanism on Ti3C2 MXene through in-Situ/Operando Raman Spectroelectrochemistry

Current climate issues we face can be partially remedied through the inclusion of renewable energy sources. However, these energy sources suffer from the need for highly efficient energy storage systems. To this end, studies have been conducted on developing energy storage materials that can provide high energy and power densities. Two-dimensional (2D) carbide and nitride MXenes have the potential to provide both if their mechanism of charge storage is known. Here, we use in-situ/operando Raman spectroelectrochemistry to investigate the charge storage mechanism of the benchmark Ti3C2 MXene in acidic and neutral media (0.1M HCl and 0.5M NaSO4, respectively). We found that overcharging of the MXene electrode occurs during electrochemical charging, which draws positively charged ions towards the MXene’s surface to enable a pseudocapacitive process or Faradaic redox process. The material then undergoes reversible redox processes accompanied by reversible structural changes within its stable voltage window during electrochemical charge storage. I will show density functional theory (DFT) calculation results that corroborate these findings. Ultimately, these fundamental insights can be used to design electrode materials with both high energy and power densities.

Decoupled aqueous batteries using pH-decoupling electrolytes.

Aqueous batteries have been considered as the most promising alternatives to the dominant lithium-based battery technologies because of their low cost, abundant resources and high safety. The output voltage of aqueous batteries is limited by the narrow stable voltage window of 1.23 V for water, which theoretically impedes further improvement of their energy density. However, the pH-decoupling electrolyte with an acidic catholyte and an alkaline anolyte has been verified to broaden the operating voltage window of the aqueous electrolyte to over 3 V, which goes beyond the voltage limitations of the aqueous batteries, making high-energy aqueous batteries possible. In this Review, we summarize the latest decoupled aqueous batteries based on pH-decoupling electrolytes from the perspective of ion-selective membranes, competitive redox couples and potential battery prototypes. The inherent defects and problems of these decoupled aqueous batteries are systematically analysed, and the critical scientific issues of this battery technology for future applications are discussed.

Magnesium ion conducting free-standing biopolymer blend electrolyte films for electrochemical device application

Solid polymer blend electrolyte films composed of 70 wt.% of chitosan (CS) and 30 wt.% of methylcellulose (MC) were prepared with different weight percentages of MgCl2 by solution casting method. FTIR analysis demonstrated the interactions between blend and MgCl2, XRD study revealed the amorphous nature of the films. Thermogravimetric analysis (TGA) was carried out to study the thermal stability. Electrical impedance spectroscopy (EIS) study showed that the bulk resistance decreased with increasing salt concentration and is due to the influence of carrier concentration. From EIS measurement, the highest value of DC conductivity at ambient temperature (30 °C) was found to be 2.75 × 10−3 Scm−1 for the sample containing 30 wt.% of MgCl2. The voltage stability window of the highest conducting film was found to be 3.86 V. The total ionic transference number was found to be 0.98. Finally, the highest conducting polymer electrolyte was employed to construct a primary magnesium ion battery.

Potassium Polyacrylate-Based Gel Polymer Electrolyte for Practical Zn-Ni Batteries.

Because of their high theoretical value of volumetric energy density, excellent rate performance, and high level of safety, zinc-nickel batteries (ZNBs) show potential applications for uninterrupted power supply (UPS) systems. However, despite all the advantages of ZNBs, the commercial application of ZNBs has been prevented by their short lifetime caused by the shape change, the corrosion, and the dendrite formation of the Zn anode. In this work, we proposed a flexible and durable potassium polyacrylate (PAAK)-KOH gel polymer electrolyte (GPE) prepared in a very simple way to solve the above problems of the Zn anode. The obtained highly porous gel electrolyte showed higher water retention, satisfying ionic conductivity (0.918 S cm-1), and a broad electrochemical stable voltage window. By providing a stable and homogeneous electrode/electrolyte interface for the Zn anode, the gel electrolyte can inhibit the uneven deposition and dendrite formation. As a result, the gel electrolyte greatly prolonged the cycling life to 776 h. In addition, because of the considerably batter corrosion resistance of the Zn anode in the PAAK-KOH GPE, the ZNB with gel electrolyte also exhibited a superior shelf life of more than 431 h and a superior cycling performance under float charge for more than 400 h at 60 °C. This work demonstrates that the gel electrolyte with a simple preparation method is suitable for large-scale practical production and can be successfully used in Zn-Ni batteries as an electrolyte exhibiting excellent performance.

An Ion‐Dipole‐Reinforced Polyether Electrolyte with Ion‐Solvation Cages Enabling High–Voltage‐Tolerant and Ion‐Conductive Solid‐State Lithium Metal Batteries (Adv. Funct. Mater. 5/2022)

High-Performance Polymer Electrolytes In article number 2107764, Xinran Wang, Ying Bai, Chuan Wu, and co-workers develop a hyperbranched polyether electrolyte for solid-state Li metal batteries. The existing ion-solvation structures allow for fast Li+ migration (1.26 × 10−4 S cm−1, 25 °C), a wide stable voltage window (up to 4.6 V), and Li dendrite suppression, overcoming the insufficiencies encountered by polymer electrolytes. The ion-dipole-reinforced solid electrolyte yields sustainable Li stripping/platting and interfacial stability, thus enabling high cycle stability and capacity retention in NCM811|Li solid-state cells.

Deoxygenated porous carbon with highly stable electrochemical reaction interface for practical high-performance lithium-ion capacitors

Metal-ion capacitors, especially lithium-ion capacitors (LICs), are promising energy storage devices with much higher energy density than conventional electrochemical double-layer capacitors (EDLC). While compared with the EDLCs, the stable voltage window of the cathode in LICs is much narrower than that in EDLCs because of the different energy storage mechanisms, which restricts the energy density of LICs. In this work, the porous carbon (D-HAC) with an ultra-low oxygen element content of 0.973 wt.% is synthesized by heating the starch-based porous carbon (HAC) in the hydrogen-argon mixing atmosphere. The specific capacitance of D-HAC reaches up to 106.7 F g−1 at 50 mA g−1. Owing to high specific capacitance of D-HAC, LIC constructed with D-HAC cathode and soft carbon anode can provide a high energy density of 123.5 Wh kg−1. More importantly, the D-HAC//SC LIC shows excellent capacity retention of 96.77% after 10 000 cycles at a high rate of 50 C due to the stable electrochemical interface of D-HAC. This work provides a simple and efficient method to remove the unstable oxygen element of the porous carbon materials and shows a promising approach to develop advanced metal-ion capacitors with high energy density and long cycle life.

Maximizing Energy Density of Nanostructured Electrochemical Capacitors: From Proof of Concept to Reliable Manufacturing

Currently, portable energy storage devices are lacking in the overall performance characteristics needed to meet desired energy and power density performance demands. Furthermore, these performance demands for long-lasting energy storage devices for portable electronics continue to constantly increase. Batteries remain the main source of portable energy storage, but they generally lack the pulsed-power delivery capability required by many applications, as well as have limited cycle life. Thus, improvements in devices that show a high operational cycle life in addition to delivering high energy and power densities are extremely desirable over a wide range of physical sizes, footprints, and power delivery capabilities. Conventional electrostatic capacitors provide some of these benefits compared to batteries, including high power density and extended cycle life, but are lacking in the energy density capability required to replace batteries in many applications.Electrochemically-based double-layer capacitors (EDLCs) or ultracapacitors offer a promising solution to bridging the gap between maintaining the high-power density capability of electrostatic capacitors while providing a path to improving the energy density to be comparable to batteries –significantly broadening their applicability. An EDLC’s power density and energy density are based on the highly reversible surface charge adsorption-based mechanism of energy storage. This provides benefits in terms of high frequency responses as well as providing a route to supply power for longer duration pulses. Additionally, since the stored capacity is based on the surface charge adsorption-based energy storage, it provides an essentially indefinite lifespan as long as the materials do not degrade. However, current EDLC technologies still provide significantly lower energy density than is available from batteries. This energy density gap must be narrowed if the EDLCs are going to make further inroads toward replacing batteries.The capacitance and energy density are driven by the electrode’s available solution-accessible surface area. Thus, our approach to increasing the energy density of electrochemical capacitors is through the development of carbon nanotube-based electrode structures with a precise, highly controlled and ordered nanostructured porosity. To further improve power and energy density, these electrode structures are used in combination with an ionic liquid electrolyte with high voltage window, thus providing an increased operating voltage. While traditional electrode materials are generally comprised of randomly ordered porous structures, we have developed electrodes with an adjustable and highly controlled pore structure that provide very high surface area. These electrodes are produced using a nanotemplated approach that allows for preparation of high surface area aligned and vertically oriented carbon nanotube (CNT)-based electrodes. The templated approach has the added benefit of a achieving a greater areal CNT density than available in traditional carpet-grown CNT forests as well as providing more uniform and controllable CNT outer and inner diameters. The ability to control these dimensions allows for tailoring the electrode geometry for a specific electrolyte.Ionic liquids are becoming increasingly popular in a variety of applications as a result of their unique properties and highly tailorable chemistry. In electrochemical applications, their large voltage stability window, low vapor pressure, excellent thermal stability at temperatures above most organic solvents’ boiling points, and lower temperature conductivity make them an excellent electrolyte choice. Ionic liquids are ideal for use in higher temperature electronics applications, especially in small-scale microelectronics formats where confined spaces make efficient heat removal very difficult. By making use of ionic liquid electrolytes and optimizing the interaction of the electrolyte with our templated CNT electrodes, we have developed an energy storage technology with high-energy density and high-power density.In this talk, we will discuss the challenges and solutions to scaling up the fabrication and testing of reproducible, nanostructured electrodes from 3.14 cm2 or smaller single-sided lab cells to multiple 200 cm2 electrodes on both sides of an aluminum current collector. We will discuss the electrode fabrication scale-up and performance validation from small coin or disc cells tested in a glove box to larger area sealed pouch cells with integration of an optimized ionic liquid electrolyte. We discuss cell fabrication challenges and solutions including verifying the performance of the electrodes as they are scaled up, and the cell fabrication including ensuring the electrode and separator are reliably wetted with the ionic liquid electrolyte. The challenges of optimizing the practical tradeoff of electrode active depth and minimizing the current collector thickness as we move the electrode and overall cell design to a fully packaged cell while maintaining the optimized electrochemical performance characteristics will be discussed.[DISTRIBUTION STATEMENT A. Approved for public release; Distribution is unlimited 412TW-PA-21154]

Accessing the 2 V VV/VIV redox process of vanadyl phosphate cathode for aqueous batteries

Rechargeable aqueous batteries using zinc metal anode offer high safety and low cost. However, the narrow electrochemically stable voltage window of water and lack of high voltage cathode materials limit the energy density. Herein, we demonstrate a high voltage polyanion cathode and realize its reversible deep charge in Na–Zn hybrid aqueous batteries. The exfoliated layered VOPO 4 ·2H 2 O cathode contains partially reduced vanadium centers and presents a high open circuit voltage of 1.8 V ( vs. Zn). The effective oxidation of V IV to V V is realized in the water-in-tri-salt electrolyte of 0.5 m Zn(ClO 4 ) 2 /16 m NaClO 4 /3 m NaOTf as confirmed by electrochemical analysis, X-ray diffraction, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, as well as density of state calculations. The process retrieves more V V /V IV redox centers for energy storage and provides an extra reversible capacity of 38 mAh g −1 at 2 V. The electrode delivers an overall capacity of 140 mAh g −1 with excellent stability and coulombic efficiency. Further analysis demonstrates that Na + is the major active cation in the cathode reaction, while Zn 2+ de/intercalation provides additional capacity. Our work reveals the energy storage mechanism of vanadyl phosphate cathode and proposes an efficient strategy towards high performance Na–Zn hybrid batteries. • A vanadyl phosphate cathode is demonstrated for Na–Zn hybrid aqueous batteries. • The deep charge of vanadyl phosphate is enabled by a water-in-tri-salt strategy. • The V V /V IV redox couple is responsible for the 2 V voltage plateau. • The cathode delivers a high capacity of 140 mAh g −1 and excellent stability. • Reversible Na + /Zn 2+ co-de/intercalation mechanism is demonstrated.

All-solid-state Na+ ion supercapacitors using Na3Zr2Si2PO12-polymer hybrid films as electrolyte

We report all-solid-state Na+ ion electrical double layer capacitors (EDLCs) for the first time in this study. These are fabricated using a novel Na+ ion solid polymer electrolyte (SPE) and high surface area (877 m2-g−1) activated carbon electrodes. Using salt (NaI), polyethylene oxide (PEO) and nano particles of Na3Zr2Si2PO12 (NZSP), hybrid electrolyte films with compositions 10NaI-90[PEO1-xNZSPx], where 0 ≤ x ≤ 0.7 are synthesized by a novel milling assisted route. The freestanding flexible film for x = 0.7 exhibits a maximum ionic conductivity of ~ 10−4 Ω−1 cm−1 at room temperature. The 2032 type EDLC with graphite current collector and polymer electrolyte film of composition x = 0.4 exhibits notably high value of specific capacitance (~ 104 F-g−1), and specific energy (~ 44 Wh-Kg−1) with a voltage stability window of ~ 2 volts. The NZSP content in the electrolyte influence the EDLC performance. The EDLCs with graphite sheet as current collector offer superior performance as compared to copper. Galvanostatic charge-discharge studies suggest stability of these supercapacitors at least upto ~ 400 cycles.

(Invited) Operando Characterization of Transient Material Changes in Battery Cathode Materials By X-Ray Diffraction and Spectroscopy

Operando characterization of battery materials provides several benefits. For example it eliminates the chance that materials are oxidized or further transformed during removal from the cell and sample preparation, and increases the odds that short-lived material changes and intermediate species can be observed and correlated to electrochemical data. Receiving adequate experimental signal from complicated electrochemical cells can be problematic, and the use of synchrotron light is one solution. X-rays with high brightness, flux, or energy can provide data that is adequately temporally (and sometimes spatially) resolved to correlate material changes with cycling data. This talk will present characterization by both X-ray diffraction and X-ray absorption spectroscopy, which provide information about long-range and short-range structural order respectively.The first example is that of a sulfide all solid-state cathode that is a composite of FeS2, conductive carbon, and Li6.6Ge0.6Sb0.4S5I solid electrolyte (SE).1 Voltage stability window of sulfide SEs is a critical issue, and we directly observe crystal structure distortion of the SE that occurs during discharge. This occurs in the cathode but not elsewhere in the cell, and is reversible provided a minimum potential limit is not passed (see Figure 1). Given the air and moisture sensitivity of the SE, experiments had to be performed within the sealed cell, under significant applied pressure. Operando energy-dispersive x-ray diffraction (EDXRD) allowed data to be collected from buried locations in the bulk of intact and sealed batteries during cycling.2 The second example is that of a rechargeable alkaline Bi-modified MnO2 cathode, in which both Bi and Mn are electrochemically active and provide cycled capacity. The mechanism of MnO2 cycling is complex, first involving insertion of cations into the layered structure, followed by conversion to a new structure. By using rapid collection of X-ray absorption near edge structure (XANES) data at the Mn K-edge and Bi LIII-edge, an interaction between Mn and Bi was identified during early stages of the charging step.3 This gives insight into the cycling mechanism that makes rechargeability possible. Acknowledgments This work was supported by the U.S. Department of Energy (DOE) Office of Electricity Delivery and Energy Reliability, Dr. Imre Gyuk, Energy Storage Program Manager. We also acknowledge financial support from the National Science Foundation under Award Number CBET-ES-1924534. References Sun, X.; Stavola, A.M.; Cao, D.; Bruck, A.M.; Wang, Y.; Zhang, Y.; Luan, P.; Gallaway, J.W.; Zhu, H., Advanced Energy Materials,2020, 2002861.Marschilok, A. C.; Bruck, A.; Abraham, A.; Stackhouse, C.; Takeuchi, K. J.; Takeuchi, E. S.; Croft, M.; Gallaway, J.W., Physical Chemistry Chemical Physics, 2020, 22, 20972-20989.Bruck, A.M.; Kim, M.A.; Ma, L.; Ehrlich, S.N.; Okasinski, J.S.; and Gallaway, J.W., Journal of the Electrochemical Society, 2020, 167, 110514. Figure 1

Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

Summary O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

A 2.7 V Aqueous Supercapacitor Using a Microemulsion Electrolyte**

AbstractThe use of aqueous electrolytes in energy storage devices is traditionally limited by the voltage stability window of water at 1.23 V. Here, we present the use of a microemulsion based electrolyte which, although mostly water by mass, has a voltage stability window of up to 5 V. This allows the cost and safety benefits of aqueous electrolytes to finally be realised in high voltage systems. Supercapacitors constructed using this electrolyte were able to achieve and maintain a capacitance of ∼40 Fg−1 and an energy density of ∼40 Wh kg−1 with a Coulombic efficiency of 99 % for over 10,000 cycles on activated carbon.

Deep eutectic solvent-based supramolecular gel polymer electrolytes for high-performance electrochemical double layer capacitors

Gel polymer electrolytes (GPEs) can avoid the electrolyte leakage risk of electrochemical double layer capacitors (EDLCs). But aqueous GPEs often suffer from narrow electrochemical windows. Herein, a series of deep eutectic solvent (DES)-based supramolecular GPEs are firstly developed for carbon-based EDLCs with wide voltage windows. The as-fabricated DES-based GPE shows an ionic conductivity of ~58 mS cm−1, which makes the stable voltage window of a carbon-based EDLC reach 2.4 V. The carbon-based EDLC exhibits a specific capacitance of 32.1 F g−1, an energy density of 24.6 Wh kg−1 and a capacitance retention of ~90% after 15,000 charge-discharge cycles. Moreover, when quinhydrone is added into the DES-based GPE, the specific capacitance and energy density of the corresponding EDLC can be further expanded to 60 F g−1 and 43.6 Wh kg−1, respectively. Therefore, our work may present a universal strategy to prepare novel supramolecular GPEs for high-performance EDLCs with wide voltage windows.

Correction to: Ion transport, dielectric and electrochemical properties of sodium ion-conducting polymer nanocomposite: application in EDLC

The present paper reports the investigation of structural, electrical, dielectric, and transport properties of the polyethylene oxide (PEO)-based polymer nanocomposite (PNC), with sodium hexafluorophosphate (NaPF6) salt and barium titanate (BaTiO3) as nanofillers. The PNC has been prepared via standard solution casting technique. The structural investigation has been investigated by X-ray diffraction and evidence the enhancement in amorphous content. The presence of polymer–ion and ion–ion interaction has been confirmed by the Fourier transform infrared spectra (FTIR) and evidences the PNC formation. The impedance spectroscopy has been performed to evaluate the ionic conductivity in the temperature range 40–100 °C. The increase of conductivity is obtained with the addition of nanofiller and temperature-dependent conductivity follows Arrhenius behavior. The PNC film having the highest conductivity exhibits low activation energy and indicates the fast ion migration. The ion transference number is close to unity and the voltage stability window is within the desirable limit. The complex permittivity and complex conductivity have been obtained and the plot has been fitted in the whole frequency window. The fitted plot is in perfect agreement with experimental data. The PNC having the highest conductivity has high dielectric strength and low relaxation time. It confirms the nanofiller role in enhancing ion migration. The ion transport parameters (n, μ, D) are also in correlation with impedance and dielectric analysis. The optimized PNC films have been used to prepare the Electric double-layer capacitors (EDLC) and it demonstrates the improved performance which may be attributed to the effective role played by nanofiller in boosting ion dynamics.

Nanofiller-assisted Na+-conducting polymer nanocomposite for ultracapacitor: structural, dielectric and electrochemical properties

We report the preparation of ZrO2 nanofiller-incorporated polymer nanocomposite electrolyte based on the PEO-NaPF6 matrix via standard solution cast method. The structure and morphology of polymeric films have been examined with X-ray diffraction and field emission scanning electron microscopy. Different interactions between the polymer, salt and nanofiller have been examined by Fourier transform infrared technique. The temperature-dependent (40–100 °C) electrical conductivity has been examined from complex impedance spectroscopy (CIS). The highest ionic conductivity is exhibited by 5 wt% nanofiller-based electrolyte and recorded ~ 2 × 10–4 S cm−1 at 100 °C. The voltage stability window of polymeric film checked from linear sweep voltammetry is about ~ 4 V, and ion transference number close to unity confirms the major contribution from ion conduction. The dielectric properties have been explored in terms of complex permittivity, loss tangent and complex conductivity. The dielectric plots have been further fitted with an associated equation to evaluate principal dielectric parameters. The optimized polymer electrolyte possesses the lowest relaxation time and the highest dielectric constant that suggests the highest ionic conductivity, which is in good correlation with impedance results. The dc conductivity is also highest for the optimum system, and relaxation time decreases with an increase in temperature. The thermal stability of polymer electrolytes is about 200 °C, as examined by thermogravimetric analysis (TGA). The ion transport parameters n, μ, D have been evaluated via FTIR, impedance spectroscopy and Bandara and Mellander (B–M) approach. Finally, the optimized polymer nanocomposite film has been used as an electrolyte-cum-separator for the fabrication of a solid-state symmetric supercapacitor. The electrochemical parameters specific capacitance, energy density, power density have been examined from cyclic voltammetry and galvanostatic charge–discharge technique. It may be concluded that nanofiller incorporation is an effective strategy to enhance the properties of electrolyte and has the potential to adopt as an electrolyte-cum-separator for ultracapacitor.

A supramolecular hydrogel electrolyte for high-performance supercapacitors

With the development of flexible supercapacitors, aqueous gel polymer electrolytes with high ionic conductivity, wide voltage window, good mechanical performance and enough security are drawing great attention. Herein, a series of novel supramolecular hydrogel electrolytes are proposed and fabricated by a facile process at room temperature. They show good elongation at break and moderate ultimate tensile strength. The optimum hydrogel electrolyte exhibits an ionic conductivity of 81.27 mS cm−1, which endows a carbon-based supercapacitor with a stable voltage window of 2 V. The carbon-based supercapacitor can deliver a specific capacitance of 24.0 F g−1, a specific energy of 12.6 Wh kg−1 and a capacitance retention of 110% after 5000 charge-discharge cycles. After introducing a redox additive into the hydrogel electrolyte, the specific capacitance and specific energy of the resultant supercapacitor can be further increased to 32.7 F g−1 and 18.2 Wh kg−1, respectively. This work may provide a universal strategy to explore aqueous gel polymer electrolytes with high voltage window for applications in flexible energy storage devices.

High-Performance Solid-State Hybrid Supercapacitors Based on One-Dimensional Nickel Sulfide Nano-Arrays and Commercial Activated Carbon

Nano-materials with ordered structures exhibit the valuable application in the domain of supercapacitors due to the internal structural advantages. Herein, one-dimensional nickel sulfide nano-arrays were prepared by a one-pot solvothermal method. When applied as the binder-free electrodes of supercapacitors, one-dimensional nickel sulfide nano-arrays can achieve superior electrochemical properties. It is particularly important that solidstate hybrid supercapacitors based on one-dimensional nickel sulfide nano-arrays and commercial activated carbon can achieve the areal energy density of 0.355 mWh cm–2 and stable voltage window of 0–1.6 V. In the meantime, the current hybrid supercapacitors can deliver the outstanding working lifetimes and the higher practical value. Such exciting results demonstrates that one-dimensional nickel sulfide nano-arrays have the wide application prospects in the field of small, lightweight, and mobile electronic products.

Ion transport, dielectric, and electrochemical properties of sodium ion-conducting polymer nanocomposite: application in EDLC

The present paper reports the investigation of structural, electrical, dielectric, and transport properties of the polyethylene oxide (PEO)-based polymer nanocomposite (PNC), with sodium hexafluorophosphate (NaPF6) salt and barium titanate (BaTiO3) as nanofillers. The PNC has been prepared via standard solution casting technique. The structural investigation has been investigated by X-ray diffraction and evidence the enhancement in amorphous content. The morphology has been examined by Field emission scanning electron microscopy technique and confirms the composite formation. The presence of polymer–ion and ion–ion interaction has been confirmed by the Fourier transform infrared spectra (FTIR) and evidences the PNC formation. The impedance spectroscopy has been performed to evaluate the ionic conductivity in the temperature range 40–100 °C. The increase of conductivity is obtained with the addition of nanofiller and temperature-dependent conductivity follows Arrhenius behavior. The PNC film having the highest conductivity exhibits low activation energy and indicates the fast ion migration. The ion transference number is close to unity and the voltage stability window is within the desirable limit. The complex permittivity and complex conductivity have been obtained and the plot has been fitted in the whole frequency window. The fitted plot is in perfect agreement with experimental data. The PNC having the highest conductivity has high dielectric strength and low relaxation time. It confirms the nanofiller role in enhancing ion migration. The ion transport parameters (n, μ, D) are also in correlation with impedance and dielectric analysis. The optimized PNC films have been used to prepare the Electric double-layer capacitors (EDLC) and it demonstrates the improved performance which may be attributed to the effective role played by nanofiller in boosting ion dynamics.

Understanding the Role of Solvents on the Morphological Structure and Li-Ion Conductivity of Poly(vinylidene fluoride)-Based Polymer Electrolytes

Polymer-based solid-state electrolytes (SSEs) are promising candidates to enhance the performances of current lithium-ion batteries (LiBs), as they possess advantages of facile processing and flexibility over ceramic SSEs. However, polymer SSEs such as poly(ethylene oxide) (PEO) suffer from low ionic conductivity, a limited voltage stability window, and thermal stability. Poly(vinylidene fluoride) (PVDF)-based polymer electrolytes (PPEs) with lean solvent confinement provide improved ionic conductivity and outstanding chemical/electrochemical stability. In this study, we report the effects of different solvents on the morphological structure and ionic conductivity of PPEs. We demonstrate that solvents with relatively high boiling points (dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-Methyl-2-pyrrolidone (NMP), and dimethylacetamide (DMA)) can be trapped in PPEs, and they all have positive effects on the ionic conductivity. The ionic conductivity is related to the quantity of the trapped solvent; for a PPE with DMF retention of ∼20%, the ionic conductivity is about 0.1 mS cm−1. Increasing the amount of lithium salt was found to improve the solvent retention but at the cost of membranes’ mechanical property. It is also possible to introduce a low boiling point co-solvent in order to reduce the production cost and drying duration for manufacturing PPEs.