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Hybrid polymers combining P2S5 moieties with oligoether spacers have been prepared, and the conductivities and glass transition temperatures of their solutions of lithium salts have been examined. The materials are highly viscous but mostly not rubbery. A high ambient temperature conductivity of 10−3.9 S cm−1 was obtained with LiTFSI dissolved in the sulfide–PEO matrix. The decoupling of Li+ motion from the polymer segmental motion is demonstrated, suggesting that, in certain cases, the transport number for Li+ ion in the sulfide–PEO matrix will be much higher than in a typical PEO-based salt-in-polymer system.
Gaining insight into the effects of pulse charging on the performances of energy storage devices is very important for the practical applications of triboelectric nanogenerators (TENGs). In this work, the effects of pulse charging on lithium-ion batteries (LIBs) are investigated. Energy efficiency of the pulse power source coupled with a LIB at different pulse charge voltages is examined. A peak value efficiency of 22.9% is observed at a pulse charging voltage of 8.0 V mode. All-atom classical molecular dynamics simulations suggest that the different diffusion coefficients of Li ion in electrolyte under different applied voltage may be responsible for the different energy efficiencies. Moreover, the cycle performances of the LIBs with intermittent and continuous pulse charging were also investigated. Bad cycling performance of LIBs at pulse charging modes is ascribed to the pulverization of electrode particles arising from the larger strain during cycling, which is corroborated by the software simulation. Based on these results, we further designed a better procedure by combining galvanostatic charge-discharge (GCD) mode with pulse charging mode to improve the battery performance.
Spinel-type FexCo3−xO4 thin films with x = 0, 1, 2 and 3 were prepared, on stainless steel supports, using the thermal decomposition method at 400 °C. The X-ray diffraction patterns show the presence of a spinel-type structure with a low crystallinity. The electrochemical behaviour was investigated in 1 M KOH, using open-circuit-potential measurements and cyclic voltammetry. The studies allowed to observe the redox reactions occurring at the FexCo3−xO4 (x = 1 and 2) oxide surface, namely Fe3O4/Fe(OH)2 or Fe3O4/Fe2O3, Co3O4/CoOOH, Co(OH)2/CoOOH and CoO2/CoOOH by comparing the experimental data with those obtained for the Co3O4 and Fe3O4 films as well as with those referred to in the literature. The results show that iron ions play the major role in the solid-state surface redox transitions in the negative potential range, whereas the cobalt ions are the key species in the positive potential range. However, the contribution of each component, although small, has to be considered in both potential regions.
This work investigates the capacitive capabilities of Li-ion pouch and cylindrical cells in respect to the provision of Frequency Response services and a potential for reduction in battery ageing effects. This is achieved using Electrochemical Impedance Spectroscopy (EIS) and a novel method of identifying and defining the threshold frequency between pseudo-capacitive and diffusion processes of the cell. It is found that this threshold frequency is independent of current intensity up to 1 C, showing that even at high power, pseudo-capacitance has significant impact. However, a severe dependency upon relative cell surface area and State of Charge (SoC) is identified. Symmetrical charge-discharge pulses of up to 10 s utilise primarily cell capacitance. Literature indicates, that this level of utilisation reduces the electrochemical ageing impact significantly. This article displays a method to identify and isolate these processes for any given cell and to allow enhancement of conventional ageing modelling.
Lithium salts based on perfluorinated sulfonimide anions (PSAs) are promising new electrolyte components for application in next-generation lithium batteries. Several typical symmetric ([(n-C m F2m+1SO2)2N]−, m = 0, 1, 2, 3, and 4) and asymmetric ([(FSO2) (n-C m F2m+1SO2)N], m = 1, 2, 4, 6, and 8) PSAs have been extensively investigated in recent years. Yet little is known about the role of asymmetry in the physicochemical and electrochemical properties at the molecular level. Here we use first-principle density functional theory calculations to thoroughly examine such fundamental structure-activity relationship. Compared to symmetric PSAs, asymmetric isomers show intrinsically better internal flexibility of the S─N bond, lower dissociation energy of Li+ cation, and thereby they can be promising candidates for polymer electrolytes. We also observe that more than four C atoms in the perfluorinated chain results in negligible improvements in terms of dissociation energy, thermal stability, and anodic stability. These results provide an in-depth understanding of the impact of the molecular structure on PSAs, helping design new robust anions for lithium batteries in the future.
The possibility of producing electrical power from chemical energy with biological catalysts has induced the development of biofuel cells as viable energy sources for powering portable and implanted electronic devices. These power sources employ biocatalysts, called enzymes, which are highly specific and catalytic towards the oxidation of a biofuel and the reduction of oxygen or hydrogen peroxide. Enzymes, on one hand, are promising candidates to replace expensive noble metal-based catalysts in fuel cell research. On the other hand, they offer the exciting prospect of a new generation of fuel cells which harvest energy from body fluids. Biofuel cells which use glucose as a fuel are particularly interesting for generating electricity to power electronic devices inside a living body. Hydrogen consuming biofuel cells represent an emerging alternative to platinum catalysts due to comparable efficiencies and the capability to operate at lower temperatures. Currently, these technologies are not competitive with existing commercialised fuel cell devices due to limitations including insufficient power outputs and lifetimes. The advantages and challenges facing glucose biofuel cells for implantation and hydrogen biofuel cells will be summarised along with recent promising advances and the future prospects of these exotic energy-harvesting devices.
The electrochemistry of the electrolyte plays a significant role in the performance of lithium ion batteries. In order to further investigate the effect of combining an ionic liquid with a conventional electrolyte, a hybrid electrolyte (HE) based on a mixture of 38% N-methyl-N-propyl-pyrrolidinium bis(trifluromethanesulfonyl) imide in an electrolyte consisting of LiPF6 in Ethylene Carbonate: Diethyl Carbonate (1:1) was studied and compared with the properties of a standard organic electrolyte in this work. Thermal measurements reveal that the addition of the ionic liquid improves the thermal stability of the hybrid electrolyte. The interfacial behavior was studied in lithium symmetric cells and it was found that the combined effects of the ionic liquid and the conventional electrolyte results in lower interfacial resistance. The charge-discharge behaviour of LiFePO4 / Li cells was investigated; at the end of 100 cycles, the discharge capacity of the cell with LP30, HE and [C3mpyr][TFSI] was 141 mAh/g, 148 mAh/g and 45mAh/g, respectively. Analysis of the separator recovered from Li/LiFePO4 cells that had been stored for 30 days at 20°C shows iron dissolution from the cathode into the LP30 electrolyte, but not into the hybrid electrolyte. Posthumous studies of the cycled electrodes were carried out using FTIR, XRD, FEG-SEM and HR-TEM analyses, show that the HE forms a permeable interface on the cathode material which prevents metal dissolution from the cathode structure, leading to better cyclic performance.
LiFePO4 is a practically used cathode material for lithium-ion batteries due to a high theoretical capacity, high cycle capability and the high-rate performance. The metastable Li x FePO4 (L x FP) phase with an intermediate composition appears in the non-equilibrium state at high-rate condition. However, the formation process of the metastable L x FP phase and its impact to the electrochemical property are still unclear. In order to elucidate these points, we directly observed the phase transition behavior by applying operando XRD during 10C charge-discharge. L x FP phase does not form in charge reaction but preferentially forms in discharge reaction. The phase transition from L x FP to Li-rich phase is less likely to proceed in the end of discharge reaction. The asymmetric phase transition between LiFePO4 and FePO4 results in decreasing the discharge capacity and increasing the irreversible capacity at high-rate conditions.
Aggregated control of electrical loads in a large cluster of buildings has been a challenge due to the complexity of the system involving generators, grid constraints, load serving entities complex load models, and people behavior. This paper introduces a novel load aggregation method in an electricity distribution system with Model Predictive Controlled (MPC) loads. This method closes the control loop from power generation to people behavior, resulting in a more stable and efficient integrated buildings-to-grid system. A behavior-driven price-based MPC is introduced for a residential building energy management system, which controls the air conditioner (AC), electric vehicle (EV), water heater, and battery energy storage system. A nodal pricing method is introduced representing power generation and distribution costs, which is mathematically proven to stabilize the system with MPC controlled loads. The method is tested in a 342-node residential building distribution network with 15,000 buildings which is inverse sampled from hundreds of actual smart meter data. The results show a 21% reduction in generation cost, 17% reduction in peak load, and reduced nodal voltage drop from the coordinated control system.
Oropharyngeal dysphagia (OD) is a disorder that can have devastating and long lasting effects on a person’s medical, mental and psychosocial well-being, thus negatively impacting quality of life. There is currently no validated dysphagia-specific quality of life instrument in Norway. This project aims to evaluate the psychometric properties of the culturally adapted Norwegian version of SWAL-QOL (Nor-SWAL-QOL).
High cost and technical immaturity of bulk (multi-hour) electricity storage (BES) systems are often cited as major hurdles to increasing the penetration of intermittent renewables. We use a simple model to assess the economics of BES under carbon emissions constraints. Size and dispatch of a green-field generation fleet is optimized to meet a variable load at a 15 minute time resolution. Electricity supply options are wind, gas turbine, BES, and a generic dispatchable-zero-carbon (DZC) source as a proxy for fossil fuel plants with carbon capture or nuclear plants. We review the cost of selected BES technologies and parameterize the performance of storage, focusing on the energy- and power-specific capital costs. We examine sensitivity of the electricity cost to storage performance under a range of emissions constraints. Availability of inexpensive BES systems in general and particularly electrochemical technologies has a small impact on the overall cost of decarbonization. Proportional reductions in capital costs of wind and DZC lower decarbonization costs far more. We find no economic justification for seasonal storage. Intermittent renewables can be used to decarbonize the electricity supply with a proportionally small requirement for BES because gas provides much of the intermittency management even when the carbon emissions intensity is cut to less than 30% of today's U.S. average. Substantial BES is required only when emissions are constrained to nearly zero and DZC is not allowed.
Thin-film LiCoO2 batteries using the Lipon electrolyte exhibit excellent cycleability up to 4.4V. With the enhanced voltage limit for repeatable cycling, the thin-film cathode delivers a specific capacity of 170mAh/g, which is 22% higher than that for previous LiCoO2 cathodes cycled to 4.2V. No evidence of grain fracture was detected by transmission electron microscopy (TEM) in the cathode layer after cycling to 4.4V. When cycled to >4.4V, capacity fades and cell resistance increases more rapidly, attributed to the onset of a phase transition at >4.4V. Fracture of grains was observed by TEM in the cathode layer after cycling to 5V. Nanocrystalline films show better cycleability to 5V than films with a larger grain size.
Lithium manganese orthosilicate is an attractive cathode material providing high theoretical specific capacity (ca. 330 mAhg−1) and reasonably high potential; however, it suffers from rapid capacity/voltage decay upon cycling. The origin of the poor cyclability is closely related to the structural instability of Li2MnSiO4 polymorphs, including layer exfoliation and pulverization during extended cycling. To address these problems, a gradient Na substitution method was developed to prepare Li2MnSiO4 cathode materials with a Na+-enriched surface pillaring layer and a moderately Na+-substituted core material. The results shows that the pillaring layer can effectively suppress the occurrence of layer exfoliation/collapse during delithiation/lithiation and prevent particle pulverization upon extended cycling. This corresponds to a high initial Coulombic efficiency (89.8%) and improved cyclability with a capacity retention (81.3%) after 200 cycles in Na-substituted materials. The gradient Na substitution process also results in improved Li+ diffusivity and rate performance in Na-substituted materials by shortening LiLi distances. This gradient Na-doping method can be further applied to other structure-unstable polyanion-type cathode materials, such as phosphates, fluorophosphates and borates.
(Pentafluorophenyl)diphenylphosphine (PFPDPP) is studied as an effective dual-functional additive for high-voltage LiNi0.5Mn1.5O4 (LNMO) cathodes. The additive can stabilize the LiPF6 salt and form a good cathode–electrolyte interphase (CEI). Hydrolysis of LiPF6 in the electrolyte is investigated by 19F and 31P nuclear magnetic resonance spectroscopy, which reveal that PFPDPP suppresses the decomposition of LiPF6 into LiF, PO3F2−, and PO2F2 −. Cyclic voltammetry results reveal that PFPDPP is anodically decomposed at 3.5 V vs. Li/Li+ prior to the oxidation of carbonate electrolytes to form a CEI film. The results of scanning electron microscopy, transmission electron microscopy, and AC impedance analyses show that PFPDPP forms a thin CEI film with low impedance. X-ray photoelectron spectroscopy results also confirm that the addition of PFPDPP suppresses the formation of LiF in the CEI film. Furthermore, the Li|1.0 M LiPF6-EC/DEC (1:1, v/v)|LNMO cell with 0.2 wt% PFPDPP shows a retention capacity of 71% after 300 cycles at a charge–discharge rate of 2C between 3.0 and 5.0 V, whereas the cell without the additive shows a retention capacity of only 53.4% after 300 cycles. Furthermore, self-discharge of the battery is suppressed upon the addition of PFPDPP.
The effect of composition on the voltage fade phenomenon was probed using combinatorial synthesis methods. In compositions that have the general formula, (Li2MnO3)a(LiNiO2)b(LiMnO2)c(LiCoO2)d, where 0 ≤ a≤0.83, 0.15 ≤ b ≤ 0.42, 0 ≤ c ≤ 0.85, and 0 ≤ d ≤ 0.30 (a + b + c + d = 1), the dependence of features in the x-ray diffraction pattern and of voltage fade on composition were identified and mapped. The observed values of voltage fade indicated that it displayed some sensitivity to composition, but that the sensitivity was not large. The values of voltage fade were found to be amenable to statistical modeling. The model indicated that it may be possible to lower the value of voltage fade below 0.01% by adjusting the composition of the system; however, the composition is not expected to have the layered–layered structure.
The paper investigates monetary policy in Brazil following a shift to a floating exchange rate alongside inflation targeting adoption. The benchmark reaction function reveals that the Central Bank behaves according to the Taylor principle by raising the overnight Selic policy interest rate more than the amount by which expected inflation exceeds the target. The investigation also considers a data-rich environment via an excess policy response containing information from a panel of 45 economic time series. The excess policy response carries a positive and significant coefficient in the reaction function including only an inflation gap variable.
Polyindole nanofiber is prepared using electrospinning technique for the first time and evaluated as cathode active material for application in lithium ion battery. Surface morphology of the cathode is studied using scanning electron microscope. It shows porous structure constructed by nanofibers with diameter ranged from 347 nm to 180 nm. Electrochemical evaluation of the Li/polyindole nanofiber battery shows good cycling properties as well as fast charge and discharge properties. The battery achieves about 3.0 V electromotive force with discharge capacity of 83 mAh g−1 which is about 99% of theoretical value. There is slow capacity fading during cycling and the discharge capacity drops to 72% of theoretical capacity after 500 cycles at discharge current density of 40 mA g−1. At higher discharge current density like 200 mA g−1 and 400 mA g−1, the cell still can deliver stable discharge capacity of 79 mAh g−1 and 70 mAh g−1. Temperature performances test of the Li/polyindole nanofiber battery shows that the discharge capacity of the Li/polyindole nanofiber battery increases with temperature increasing. In summary, the test results have proved that polyindole nanofiber is a good candidate as cathode material for lithium ion battery.
Uniform Fe3O4/PPy composite nanospheres (FPCNs) with Fe3O4 nanoparticles embedded in PPy nanospheres (∼200nm) were prepared by a hydrothermal process followed by an ultrasonication assisted polymerization. For the first time, FPCNs were used as anode for lithium ion batteries, demonstrating enhanced electrochemical performance with high reversible capacity (544mAhg−1 after 300 cycles), remarkable capacity retention (98% of the initial capacity after 300 cycles), as well as good rate capability (332 mAh g−1 at 2000mAg−1). The spherical PPy matrix in FPCNs possesses three functions: 1) buffering the structural variation of Fe3O4 nanoparticles during charging/discharging process; 2) preventing the aggregation of Fe3O4 nanoparticles; 3) avoiding the direct contact between Fe3O4 nanoparticles and the electrolyte. The results observed in this study may shed some light on the investigation of MOx/polymer composite electrode materials.
Dipyrido[3,2-a:2′,3′-c]-phenazine (L) was employed as a selectively fluorescent chemosensor for Hg2+ in DMF solution under buffered conditions with its fluorescence being strongly increased. The fluorescence increasing was attributed to the formation of L–Hg2+ by 1:1 complex ratio (K=3.7×105 M−1), which constitutes the basis for the determination of Hg2+ with the prepared chemosensor. The experiment results also show that the response behavior of L to Hg2+ is pH independent in the range of pH 6.0–9.0 and show excellent sensitivity and selectivity for Hg2+ over other examined metal ions.
Hexagonal boron nitride (hBN) monolayers have attracted considerable interest as atomically thin sp2-hybridized sheets that are readily synthesized on various metal supports. They complement the library of two-dimensional materials including graphene and open perspectives for van der Waals heterostructures. In this review, we discuss the surface science of hBN including its growth, the hBN/metal interface and its application as template for adsorbates. We mainly focus on experimental studies on hBN/metal single crystals under ultra-high vacuum conditions. The interfaces are classified regarding their geometric structure - ranging from planar to strongly corrugated overlayers - and their electronic properties - covering weakly and strongly interacting systems. The main part of this review deals with hBN/metal substrates acting as supports for adsorbates such as individual atoms, metal clusters, organic molecules, metal-organic complexes and networks. We summarize recent surface science studies that reveal the unique role of the hBN/metal interfaces in tailoring characteristic properties of such adsorbates. Central aspects include templating and self-assembly, catalytic activity and on-surface reactions, electronic and magnetic structure. As many of the resulting systems feature superstructures with periodicities in the nanometer range, a length scale also reflecting the size of adsorbates, scanning probe microscopy is one of the most common techniques employed. In short, the goal of this review is to give an overview on the experimental and complementary theoretical studies on hBN templates available to date and to highlight future perspectives.
Sulfonated polyimide (SPI) interpenetrating polymer network (IPN) (IXSPI)–silica (SiO2) nanocomposite membranes were fabricated as proton conducting solid electrolytes for fuel cells. Urethane acrylate non-ionomers (UANs) were used as dispersants to homogeneously distribute nanosized SiO2 and, simultaneously, as crosslinkers to induce IPN structure formation. IXSPI–SiO2 nanocomposite membranes showed high proton conductivity and hydrolytic stability, and low methanol permeability as compared with those of pristine SPI. Interestingly, the casting solvent for membrane fabrication influenced membrane performances, especially proton conductivity. In particular, dimethyl sulfoxide exhibited a strong interaction with sulfonic acid groups in the polymer matrix, which hindered them from spontaneously releasing protons and reduced the proton conductivity and electrochemical performances of the resulting membranes. Crosslinkers with long polyethylene oxide chains also contributed to improved proton conductivity and increased single cell performances.
The high redox potential of LiMnPO4, ∼4.0 vs. (Li+/Li), and its high theoretical capacity of 170mAhg−1 makes it a promising candidate to replace LiCoO2 as the cathode in Li-ion batteries. However, it has attracted little attention because of its severe kinetic problems during cycling. Introducing iron into crystalline LiMnPO4 generates a solid solution of LiFe x Mn1−x PO4 and increases kinetics; hence, there is much interest in determining the Fe-to-Mn ratio that will optimize electrochemical performance. To this end, we synthesized a series of nanoporous LiFe x Mn1−x PO4 compounds (with x =0, 0.05, 0.1, 0.15, and 0.2), using an inexpensive solid-state reaction. The electrodes were characterized using X-ray diffraction and energy-dispersive spectroscopy to examine their crystal structure and elemental distribution. Scanning-, tunneling-, and transmission-electron microscopy (viz., SEM, STEM, and TEM) were employed to characterize the micromorphology of these materials; the carbon content was analyzed by thermogravimetric analyses (TGAs). We demonstrate that the electrochemical performance of LiFe x Mn1−x PO4 rises continuously with increasing iron content. In situ synchrotron studies during cycling revealed a reversible structural change when lithium is inserted and extracted from the crystal structure. Further, introducing 20% iron (e.g., LiFe0.2Mn0.8PO4) resulted in a promising capacity (138mAhg−1 at C/10), comparable to that previously reported for nano-LiMnPO4.