Concentrated Electrolyte Solutions Research Articles

Statistical optimization of treatment conditions for the electrochemical oxidation of PAN-based carbon fiber by response surface methodology: Application to carbon fiber/epoxy composite

In the current study, the effect of three independent variables; electrochemical oxidation time along with concentration and temperature of an acidic electrolyte solution on the oxygen content of surface groups (O/C ratio) and tensile strength of PAN-based carbon fiber have been investigated. The electrochemical oxidation process of carbon fibers is carried out in nitric acid solution (as the electrolyte) with a constant potential oxidation, obtained from a cyclovoltammetric method. Box–Behnken design, which is subset of the response surface methodology, has been employed to present mathematical models as the function of physical factors for prediction of O/C ratio and tensile strength behavior of the electrochemically oxidized carbon fibers and also optimizing mentioned surface chemistry and mechanical properties of carbon fiber. Overally, 17 experiments with 5 replicates at the center point were designed. The minimum and maximum values of O/C ratio were 0.0107 wt% and 0.7339 wt% which occurred in design runs 11 and 13, respectively. A also, the maximum and minimum values for tensile strength were 3087 MPa and 2221 MPa which occurred in design runs 17 and 8, respectively. The optimization results, obtained using the optimization part of design expert software, showed that the most optimal O/C ratio and tensile strength were to be 0.5045 wt% and 2574 MPa, respectively, and achieved at 15 wt% of the electrolyte concentration, oxidation time of 10 min and temperature oxidation of 20 °C. However, preparing and testing five replicate samples and taking the average gave 0.4912 wt% and 2565 MPa for O/C ratio and tensile strength, respectively. In addition, electrochemical oxidation caused a roughening of the fibers surface and decrease of their tensile strength. Change in adhesion between the epoxy matrix and the carbon fiber was measured by ILSS (interlaminar shear strength).

Characterization of Skeletonema costatum intracellular organic matter and study of nanomechanical properties under different solution conditions

In the current investigation, a rigorous characterization of the high molecular weight (HMW) compounds of Skeletonema costatum (SKC) intracellular organic matter (IOM), including nanomechanical properties, was conducted. HMW SKC-IOM was characterized as a mixture of polysaccharides, proteins, and lipids. Atomic force microscopy (AFM) provided crucial information of this isolate at a nanoscale resolution. HMW SKC-IOM showed highly responsive to solution chemistry: fully extended chains at low ionic strength, and compressing structures with increasing electrolyte concentration in solution. Interestingly, two regions of different nanomechanical properties were observed: (a) Region #1: located farther from the substrate and showing extended polymeric chains, and (b) Region #2: located <10nm above the substrate and presenting compressed structures. The polymer length, polymer grafting density, and compressibility of these two regions were highly influenced by solution conditions. Results suggest that steric interactions originating from HMW SKC-IOM polymeric structure would be a dominant interacting mechanism with surfaces. The current investigation has successfully applied models of polymer physics to describe the complex HMW SKC-IOM structural conformation at different solution conditions. The detailed methodology presented provides a tool to characterize and understand biopolymers interactions with surfaces, including filtration membranes, and can be extended to other environmentally relevant organic compounds.

Strategy and method for nanoporous cladding formation on silica optical fiber.

We demonstrate the proof of an innovative concept of fabricating nanostructured aluminum oxide cladding on silica optical fiber. Our fabrication strategy entails freeze-coating aluminum on silica fiber and its subsequent anodization, resulting in the formation of anodized aluminum oxide (AAO) cladding with highly organized nanopore channels vertically aligned to the fiber axis. We show that the structure (diameter of pore channels and the porosity) of AAO cladding can be controlled by varying anodization conditions such as the type and concentration of electrolyte solutions and applied voltage. The versatility of AAO as a cladding with tunable structural and optical characteristics and/or a host of other functional nanostructures within the pore channels has the potential to enable a new class of specialty optical fiber for new sensor architecture and applications.

Propylene Carbonate-Based Highly Concentrated Electrolyte Solutions for LiNi0.5Mn1.5O4 Positive Electrodes of Lithium Ion Batteries

High-potential positive electrodes, such as LiNi0.5Mn1.5O4 and LiCoPO4, are promising to enhance the energy density of lithium-ion batteries. However, at the high potentials of ca. 4.7 V vs. Li/Li+, conventional electrolyte solutions are thermodynamically unstable to be decomposed oxidatively. Highly concentrated electrolyte solutions, including solvate ionic liquids, have been reported to offer many unique features, including a wide potential window owing to enhanced reductive and oxidative stability. 1,2 These effects are particularly noted for ether-based concentrated electrolyte solutions, while not so remarkable for carbonate ester-based ones.3 In the present work, propylene carbonate (PC)-based concentrated electrolyte solutions were used to suppress the oxidative decomposition on LiNi0.5Mn1.5O4positive electrodes. Here PC was employed as a solvent because PC dissolves a larger amount of Li salts than EC or EC-based solvents. When 4.45 mol kg-1 LiPF6 /PC (nearly saturated) was used, the initial irreversible capacity decreased to 14 mhA g-1 and the discharge capacity increased to 130 mAh g-1, compared to those obtained for 0.83 mol kg-1 (ca. 1 mol dm-3) LiPF6 /PC. These results clearly indicate that the oxidative decomposition of electrolyte solution was effectively suppressed, and that the initial charge/discharge performance of LiNi0.5Mn1.5O4 positive electrodes was significantly improved by employing highly concentrated electrolyte solutions. However, the discharge capacity decreased rapidly to 124 mAh g-1 in the first 4 cycles, and then decreased gradually to 112 mAh g-1 at the 50th cycle. This value was higher than those obtained in 0.83 mol kg-1 LiPF6 /PC, but the capacity retention (85.6%) was lower. Thus, the oxidative stability of the electrolyte solution was improved with increasing concentration, but the capacity fading was more marked than those in 0.83 mol kg-1 LiPF6 /PC. We hence assumed that either the conductive additive of acetylene black or the binder is degraded. To prove this assumption, we used a graphitized Ketjenblack conductor, which was heat-treated at 2200 oC and has a high oxidative stability, in place of the acetylene black conductor. As a result, the cycleability of LiNi0.5Mn1.5O4 was greatly improved when Ketjenblack was used as a conductor in 4.27 mol kg-1 LiPF6 /PC (Fig.1a); the discharge capacity of 123 mAh g-1 was obtained even at the 50th cycle, corresponding to 92.3 % of the initial capacity (Fig.1b). In the concentrated electrolyte solution, the oxidative decomposition of solvent molecules was greatly suppressed, and hence the degradation of the carbon conductor became a more critical factor for cycleability. In the present study, it was found that the decomposition of solvent molecules can be effectively suppressed by the use of concentrated electrolyte solutions without free PC molecules. However, not only the stability of the electrolyte solution, but also the stability of the other components such as carbon conductor, binder, separator, etc. against oxidation is also important for realizing practical 5-V lithium-ion batteries. Acknowledgments: The authors wish to thank Ms. Hidemi Inoue, Ms. Hiroe Nakagawa, and Dr. Tokuo Inamasu in GS Yuasa International Ltd. for their helpful discussions. This research is partially supported by “the Super Cluster Program” from MEXT and JST and “Kyoto Regional Scientific Innovation Hub” from MEXT.

Modeling of Conductivity of Lithium Salt in Electrolytes for Lithium-Ion Batteries

The lithium ion battery is the most competitive power source for electric vehicles needed in the future, thus attracting extensive interest. The performance of a lithium ion battery depends to a great extent on the conductivity of electrolyte solution, because the conductivity of electrolyte solution is related to transport process and play an important role in field of lithium batteries as knowledge of the conductivity is necessary for the design of Li cells [1]. The conductivity provides also useful insights on ion solvation and association. We present in this work a comparative study on experimental values of conductivity of several formulated electrolytes (pure solvents, binary or ternary systems involving a lithium salt) with calculated values by modelling. At first, by using different well-known equations based on Stock-Einstein, Jones-Dole and Bjerrum theories and of the solvent-solvent and solvent-salt interactions a model of conductivity ionic had been developed. The relative permittivity values of the electrolytes as well as the B- coefficients of the Jones-Dole equation for the relative viscosity of concentrated electrolyte solutions have been determined as a function of the temperature. Finally, the calculated values were then compared with experimental data of conductivity to evaluate the predictive capability of the model. Excellent agreements were obtained between calculations and experimental data electrolytes as a function of temperature with deviations up to (4 and 10) %. Results obtained by modeling during this work will guide the formulation of safer electrolytes able to improve the performances of lithium-ion batteries of lithium-ion batteries and the lifetime [1] F.Blanchard, B. Carré, P.Willmann, D. Lemordant, Journal of power sources. 109 (2002) 203-213.

Can sodium NMR provide more than a tracer for brine in petrophysics?

Sodium has been suggested as a tracer for brine in reservoir formations, where sodium ions are found exclusively in the aqueous phase, and can be detected by time-domain nuclear magnetic resonance (NMR). To date, petrophysical applications of sodium-23 NMR have focused on concentrated NaCl electrolyte solutions where the nuclear spin relaxation time is related to ion concentration. Therefore, a measure of brine volume is achieved directly from the sodium signal amplitude and relaxation time, available in a single measurement. However, real reservoir formation or injection brines contain many different ionic moieties. Sodium-23 relaxation times and diffusion coefficients are measured using time-domain NMR and pulsed field gradient (PFG) NMR techniques, respectively, and shown to depend strongly on the ions present in solution. Correlations between sodium-23 relaxation times and sodium ion concentration are found to differ depending on the cations and other anions present in the brine. However, consistent correlations are obtained for sodium-23 relaxation times and diffusion coefficient, and brine viscosity, regardless of the ionic content of the brine. In general, sodium-23 NMR remains a qualitative technique for monitoring changes in sodium concentration or brine volume (at constant salinity) in reservoir formations. However, if knowledge of the brine chemistry is available, then sodium-23 NMR offers a non-invasive and quantitative method of robustly measuring brine volume and viscosity in petrophysical applications.

Concentrated LiPF6/PC electrolyte solutions for 5-V LiNi0.5Mn1.5O4 positive electrode in lithium-ion batteries

Charge and discharge properties of spinel LiNi0.5Mn1.5O4 positive electrodes were investigated using propylene carbonate (PC)-based concentrated electrolyte solutions in the range of 0.83 (ca. 1moldm−3) to 4.45 (nearly saturated) molkg−1. The solvation state of PC in the concentrated electrolyte solution was studied by Raman spectroscopy. The HOMO energy of PC in Li+(PC)n was evaluated by first-principle calculation to assess the oxidative stability of PC molecules solvating lithium ion. Charge and discharge measurements revealed that the irreversible capacity due to solvent decomposition decreased with increasing the concentration of LiPF6, while discharge capacity increased. In addition, cycle performance of LiNi0.5Mn1.5O4 positive electrodes was remarkably improved by the use of graphitized Ketjenblack as a conductive additive.

Gibbsite Solubility in Hanford Nuclear Waste Approached from above and below Saturation

Liquid Hanford nuclear wastes are highly concentrated caustic aqueous electrolyte solutions. They contain elevated dissolved aluminum concentrations compared to simple NaOH(aq) solutions in equilibrium with gibbsite [γ-Al(OH)3]. The reason for this elevated solubility has been debated for years, with slow gibbsite precipitation kinetics or various unverified thermodynamic factors being historically offered as explanations. The present study determines whether there is a kinetic or thermodynamic explanation. Here, dissolved aluminum in real tank waste was equilibrated with excess gibbsite, approached from both above and below saturation at 40 °C. In both cases, the samples equilibrated to an aluminum concentration up to four times higher than in pure NaOH(aq) solutions of the same hydroxide concentration. However, in one case, when all of the gibbsite dissolved during heating, no measurable precipitation was observed from the supersaturation direction when gibbsite seed was unavailable for nucleation. Thes...

Removal of Cadmium and Zinc Contaminations in Landfill Leachate by Using Electrocoagulation Process

The research works involve the study of removal of cadmium and zinc contaminations in landfill leachate by electrocoagulation process. This project focused on leachate landfill from Pulau Burung, Nibong Tebal, Penang as an electrolyte solution. Heavy metals are the main factor contributing to pollution in leachate landfill. Types of electrodes used in this study were aluminium (grade 5052) and Stainless Steel (grade 316). The ranges of initial pH applied were pH (3, 4, 5, 6 and 7) and voltages applied were 1.5V, 2.0V and 2.5V. At the end of electrocoagulation process, the solutions were stored and analysed usingatomic absorption spectroscopy (AAS) to determine the final concentration of electrolyte solution. It was found difference electrodes have difference effectiveness in removing heavy metals, relies on the types of electrodes (aluminium or stainless steel) and also types of heavy metals that were being treated. The initial pH also gives the significant effect to removal of heavy metal and the maximum voltages give higher removal of heavy metal. Removal of cadmium and zinc by stainless steel electrode was more effective than aluminium electrodes at voltage of 2.5V. The removal using stainless steel was 22.45% and 97.54% respectively. For removal using aluminium electrodes 18.37% and 92.12% respectively. It was found that the maximum voltages give higher removal of heavy metal for all removal of cadmium and zinc. The removal maximum when the applied voltage was 2.5V and minimum at 1.5V.

Low Potential Asymmetrical Functionalization of Conductive Micro- and Nanowires By Closed Bipolar Electrochemistry

Bipolar electrochemistry occurs when faradaic reactions are driven on electronic conductor not directly connected to an electrical power source, but in contact with a dielectric (typically a solution) which is polarized under the influence of an applied electric field. Bipolar electrochemical cells can be designed according to two configurations: open bipolar electrochemical cells (OBPECs) 1-3 and closed bipolar electrochemical cells (CBPECs) 4,5. In OBPEC, the bipolar electrode (BPE) is a conductor immersed in an electrolyte solution. When a voltage is applied between two driving electrodes (not in direct contact with the BPE), a potential difference between the two poles of the BPE and the electrolyte solution is generated by the polarization of the latter. The extent of polarization at the two ends of the BPE is directly proportional to the intensity of the electric field and inversely proportional to the critical dimension (e.g. length) of the BPE. As a consequence, for performing open bipolar electrochemical depositions on micro or nanosized substrates, the applied electric fields must be of the order of tens kV/m. 6-7 In CBPECs, the BPE can be a whole conductive object or a composite material in which conductive particles are embedded in an insulating matrix. The main advantage of closed bipolar electrochemistry is the possibility to perform bipolar electrochemistry experiments by applying low intensity electric fields, and to operate even in concentrated electrolyte solutions. Furthermore, the cell is composed of two separated compartments, so that it is possible to use two electrolyte solution with different chemical composition and operating in distinct experimental conditions (e.g. temperature, pH, viscosity etc.). Therefore the use of CBPECs allows one to couple electrochemical reactions and to apply experimental conditions inaccessible via OBPECs. We demonstrate here the possibility to apply closed bipolar electrochemistry for the asymmetrical deposition of metals and metal oxides on bipolar electrodes of decreasing dimensions, down to nanosize by applying a potential difference between the driving electrodes as low as 1 V. In particular, we focus on the asymmetrical deposition of semiconducting oxides (TiO2, Cu2O and Co2O3) and Pt metal at the two opposite ends of carbon-microwires and gold-nanowires (30 nm diameter). The optimization of the process is studied using a 4-electrode voltammetric cell.8 Scanning electron microscopy and energy dispersive X-ray spectroscopy confirm the achievement of the desired deposition. Electron backscatter diffraction is applied to perform the crystallographic analysis identifying cuprite in all the Cu2O deposits. The deposited materials are chosen on the basis of their photochemical, photoelectrochemical and electrocatalytic properties, moreover they require deposition conditions which are hardly applicable in OBPECs. The results achieved demonstrate that closed bipolar electrochemistry can be successfully applied to obtain the Janus-like nanosized objects containing two different hetero-junctions of the kind: semiconductor 1/metal nanowire/ semiconductor 2.

Alternating electric field actuated oscillating behavior of liquid metal and its application

As a class of newly emerging functional material, Gallium based liquid metals have attracted increasing attentions in many fields, such as chip cooling, printed electronics and microfluidics, etc. Particularly, the motion control of liquid metal droplet has been recently tried for its importance in microelectromechanical system (MEMS), microfluidics and potential use in micro-machine or reconfigurable soft robot. This paper is dedicated to explore the motion behavior of liquid metal droplet under AC electric field. The quickly induced oscillation phenomena of liquid metal droplet and surrounding electrolyte solution were observed and the major factors to influence such behaviors are theoretically interpreted and experimentally investigated, including the size of the liquid metal droplet, electrode voltage, electrolyte solution concentration and AC signal frequency etc. Moreover, some typical features to distinguish AC filed actuation with DC field are observed, such as intensive fluid waving induced by the resonance stimulation, and the efficient inhibition of solution electrolysis. Finally, two important applications of adopting AC induced surface oscillation of liquid metal droplet to develop solution mixer as well as fluidic pump were demonstrated which successfully avoid gas generation inside electrolyte environment. The bulk oscillation effects of liquid metal as clarified here could be very useful in a variety of areas such as solution disturbance and mixing, and fluid oscillator or pump etc.

Theoretical estimation of conductivity of ion-exchange membranes taking into account to spatial orientation of conducting phases

The conductivity of ion-exchange membranes are theoretically assessed in a wide range of concentration of equilibrium electrolyte solutions with the use of the power equation of the two-phase model of conduction. A relationship is revealed between the parameter characterizing the spatial orientation of membrane’s conducting phases and the solution concentration range allowing the adequate description of membrane conductivity. The approach proposed is checked based on experimental concentration dependences of the conductivity of ion-exchange membranes of different structural types.

Complex Formation of Divalent Cations with Carboxylic Acid Resins as a Factor Determining Different Stationary States of Their Swelling

ABSTRACTThree samples of carboxylic acid gel-type cross-linked polyelectrolytes were examined by registering the extent and kinetics of their volume change depending on the temperature, concentration, and nature of external electrolyte solutions, as well as the initial state (ionic form, water content) of the bead. It is found that in some systems the swelling of the bead (as a result of lowering the temperature) proceeds much more slowly than the preceding shrinking (as a result of the increase of temperature). Moreover, the initial volume of the bead is not restored, and a new stationary state of swelling is established. By means of optical dilatometry, it is found that in the systems in which the differences in the stationary states of swelling are found, the beads display plasto-elastic properties, whereas in the absence of such differences the beads show elastic properties. It is found that different stationary states of swelling are also established when the beads of copolymer of methacrylic acid cross-linked with divinylbenzene in Na+ form in the dry state and in the NaCl solution-swollen state are placed into a solution of a divalent cation salt. The difference in the stationary states of swelling reaches 12% in 4 N NiCl2 solution. The substantial differences in the swelling behavior and viscoelastic properties of the resins in their Na+, Mg2+, Ca2+, and Ni2+ forms are interpreted in terms of formation of different kinds of complexes of functional groups of the polymer with Ca2+ and Ni2+ ions.

An assessment of the basic medication safety practices in Khartoum State hospitals

PurposeTo assess the presence of medication safety practices in Khartoum State hospitals.MethodsA previously used questionnaire was used to evaluate medication safety practices. The main practices evaluated were the presence of...

Mobile nanostructures (cybotactic groups) as a basis of generalised phenomenological model of aqueous electrolyte solutions

In this paper, we briefly review our researches into concentrated electrolyte solutions by means of a proposed phenomenological model. Electrolyte solutions are complex systems with a multitude of interactions. However, totality of interactions in solution is reflected in its constitution. The description of solution structure includes all parameters that define short-range ordering of particles, a full description of all possible coexistent vibrationally averaged structures (V-structures). We believe that information about the presence of the concentration ranges with different dominant structures and boundaries may be derived from the solubility polytherm (phase diagram) of the water-salt system. The boundary concentration corresponds to the eutectic composition (EC). In the range of pre-eutectic concentrations the dominant structure is the proper structure of water, and ion hydration is the major type of interaction between components. A crystalline hydrate or anhydrous salt crystallises at reduced temperatures from solutions with post-eutectic concentrations; hence, the dominant solute included V-structures are the structures of corresponding crystalline hydrate or quasi-crystalline fragments of anhydrous salt. For above-discussed spatial ordering of particles we used Stewart's term 'cybotactic group' (CG), which is a nanodimensional mobile V-structure that corresponds to the unit cell of a solid phase, which crystallises from solution under freezing. Analysis of concentration dependences of structural-sensitive properties (parameters) serve as information source about structural changes in solution, and 'special points' or singularities as the concentration boundaries of structural changes in solution correspond to eutectic and peritectics on solubility diagram. We proposed a new method of sounding to probe some peculiarities and differences in the solution structure. This method consists of monitoring of structural and dynamical features of new micro components introduced into the system under investigation. As such micro components one can use small additives of salts of transition and rare-earth metals. The structure of solution has a pronounced effect on the condition of complex-forming cations, which are presented as additives. If dominant structure (CG) has changed, there are alterations in structural and dynamical parameters of micro components, thus indicating that their behaviour 'obeys' the overall structural rearrangement in the solution. Such alterations of micro components can serve for probing some differences in the dominant structure of the supporting solution.

Plasmonic gold nanoparticles for ZnO-nanotube photoanodes in dye-sensitized solar cell application.

Surface modification of nanostructured metal oxides with metal nanoparticles has been extensively used to enhance their nanoscale properties. The unique properties of metal nanoparticles associated with their controllable dimensions allow these metal nanoparticles to be precisely engineered for many applications, particularly for renewable energy. Here, a simple electrodeposition method to synthesize gold nanoparticles (GNPs) on electrochemically grown ZnO nanotubes (NTs) is reported. The size distribution and areal density of the GNPs can be easily controlled by manipulating the concentration of AuCl3 electrolyte solution, and the deposition time, respectively. An excellent enhancement in the optical properties of ZnO NTs surface-decorated with GNPs (GNP/ZnO-NT), especially in the visible region, is attributed to their surface plasmon resonance. The plasmonic effects of GNPs, together with the large specific surface area of ZnO NTs, can be used to significantly enhance the dye-sensitized solar cell (DSSC) properties. Furthermore, the Schottky barrier at the Au/ZnO interface could prevent electron back transfer from the conduction band of ZnO to the redox electrolyte and thus could substantially increase electron injection in the ZnO conduction band, which would further improve the overall performance of the constructed DSSCs. The GNP/ZnO-NT photoanode has been found to increase the efficiency of the DSSC significantly to 6.0% from 4.7% of the pristine ZnO-NT photoanode, together with corresponding enhancements in short-circuit current density from 10.4 to 13.1 mA cm(-2) and in fill factor from 0.60 to 0.75, while the open-circuit voltage remain effectively unchanged (from 0.60 to 0.61 V). Surface decoration with GNPs therefore provides an effective approach to creating not only a high specific surface area for superior loading of dye molecules, but also higher absorbance capability due to their plasmonic effect, all of which lead to excellent performance enhancement for DSSC application.

Electrocoagulation Process by Using Aluminium and Stainless Steel Electrodes to Treat Total Chromium, Colour and Turbidity

The research works involve the study of removal of Total Chromium, Colour and Turbidity contaminations in landfill leachate by electrocoagulation process. This project focused on leachate landfill from Pulau Burung, Nibong Tebal, Penang as an electrolyte solution. Heavy metals are the main factor contributing to pollution in leachate landfill. Leachate is the main pollution factors from landfill sites and must be treated before it is released into the environment1. Landfill leachate contain high amount of heavy metals that can cause serious health problems to human, if the wastewater that contained heavy metals is not treated properly2. This project tried to reduce and treat the heavy metal that contain in the landfill leachate. Types of electrodes used in this study were Aluminium (grade 5052) and Stainless Steel (grade 316). The ranges of initial pH applied were pH (3, 4, 5, 6 and 7) and voltages applied were 1.5V, 2.0V and 2.5V. At the end of electrocoagulation process, the solutions were stored and analysed using Atomic Absorption Spectroscopy (AAS) to determine the final concentration of electrolyte solution. It was found that, the difference electrodes have different effectiveness in removing Total Chromium, colour and turbidity, relies on the types of electrodes (Aluminium or Stainless Steel). Based on the result, can be concluded that Aluminium Electrodes are best for removal of turbidity and colour. Stainless Steel Electrodes is best for removal Total Chromium. The initial pH also gives the significant effect to removal of heavy metal and the maximum voltages give higher removal of heavy metal.

LiBF4-Based Concentrated Electrolyte Solutions for Suppression of Electrolyte Decomposition and Rapid Lithium-Ion Transfer at LiNi0.5Mn1.5O4/Electrolyte Interface

Charge and discharge properties of spinel LiNi0.5Mn1.5O4 positive electrodes were investigated using concentrated LiBF4/propylene carbonate (PC) electrolyte solutions in the range of 0.833 (ca. 1 mol dm−3) to 7.25 (nearly saturated) mol kg−1. The irreversible decomposition of electrolyte solution was effectively suppressed with an increase in concentration. In addition, the polarization in charge/discharge reactions remained small in the nearly saturated 7.25 mol kg−1 LiBF4/PC even though the viscosity was very high and the ionic conductivity was low. The rate capability was higher than that obtained with nearly saturated 4.3 mol kg−1 LiPF6/PC. The structure, viscosity, and ionic conductivity of the concentrated LiBF4/PC were investigated. Based on the experimental results, the rapid charge/discharge reactions at LiNi0.5Mn1.5O4 electrodes were discussed.

Spectroscopic and electrochemical investigations of lead–lead dioxide glasses and vitroceramics with applications for rechargeable lead–acid batteries

A new class of glass and vitroceramic electrodes with applications for rechargeable batteries was obtained by a melt quenching method. The structural characterization of the samples having the xPb·(100−x)PbO2 composition, where x=0, 10, 20, 30, 40 and 50mol% Pb, was performed by UV–vis and FTIR spectroscopies investigations.UV–vis and FTIR data reveal that the excess of lead content in the host matrix generates the transformation and/or disintegration of [PbO6] octahedral structural units into [PbO4] structural units or Pb2+ ions and non-bonding oxygen ions centers.The electrochemical performances of the glass and vitroceramics electrodes were investigated by cyclic voltammetry. The shapes of the cyclic voltammograms and redox peaks depend on the electrolyte solution concentration and the lead content in host matrix. Differences between these waves are determined by the type of electrochemically active species existing in the glass or glass ceramics. The improved performance of the vitroceramic electrodes is attributed to the presence of the lead metallic phase that seems to offer an easier route for the charge process of the electrodes. Thus, the presence of these phases generates more electrochemically active species, inhibits the secondary reactions implying PbO, takes up the ionic conduction of the larger electrolyte solution and increases the charge/discharge rate of the electrochemical processes.

Enhancing Cycle Stability of Lithium Iron Phosphate in Aqueous Electrolytes by Increasing Electrolyte Molarity

Aqueous lithium ion batteries (ALIBs) exhibit great potential to reduce the cost and improve the safety of rechargeable energy storage technologies. Lithium iron phosphate (LFP) cathodes have become a material of choice for many conventional, high power LIBs. However, experimental studies on LFP in aqueous lithium (Li) ion electrolytes are limited. Here, results of systematic studies are shown where it is demonstrated that the Li salt concentration of the aqueous electrolyte can significantly improve discharge capacity retention while minimally impacting rate capability, for electrodes made with a typical commercial sub‐micron sized LFP powder. Based on the postmortem analysis and the results of electrochemical characterization it is proposed that undesirable side reactions of aqueous electrolytes with LFP induce electrochemical separation of individual particles within the electrode, leading to the observed capacity fading. Increasing the salt concentration in aqueous solutions effectively reduces the concentration of water molecules in the electrolyte, which are mostly responsible for these undesirable side reactions. Similar trends observed with other cathode materials suggest that the use of concentrated aqueous electrolyte solutions offers an effective route to improve stability of aqueous Li ion batteries.