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In this communication, flower-like tetragonal ZnMn2O4 superstructures are synthesized by a facile low temperature solvothermal process. Characterizations show that these ZnMn2O4 superstructures are well crystallized and of high purity. The product exhibits an initial electrochemical capacity of 763mAhg−1 and retains stable capacity of 626mAhg−1 after 50 cycles. Its stable capacity is significantly higher than that of nanocrystalline ZnMn2O4 synthesized by a polymer-pyrolysis method. It is found that the higher capacity retention can be attributed to three-dimensional superstructural nature of the as-prepared flower-like ZnMn2O4 material. This study suggests that the solvothermally synthesized flower-like ZnMn2O4 is a promising anode material for lithium-ion batteries.
Highly crystalline β-type strontium hydrogen phosphate (β-SrHPO4) nanosheets were prepared by a hydrothermal method and used for the immobilization of lead ions (Pb2+) from acidic aqueous solution. The effects of various parameters on the immobilization process, including solution pH value, contact time, initial ion concentrations, and coexistent competing cations, were studied to optimize the conditions for maximum immobilization. The β-SrHPO4 nanosheets exhibited a capacity of (1,120 ± 22) mg/g toward Pb2+ in acidic solution (pH value is 3.0), and the equilibrium was achieved within 8 min. The competing cations such as Cu2+, Zn2+, Cd2+, and Co2+ affected slightly on the selective immobilization of Pb2+. The results revealed that the removal mechanism of Pb2+ by the β-SrHPO4 nanosheets was the dissolution/precipitation process in the acidic solution.
Titanium-based layered oxides (TLOs) are one of the most promising electrode material families for sodium-ion batteries (NIBs) due to their smooth charge/discharge profiles and excellent cycle performance. However, the reaction mechanism of these materials, especially the reason for the disappearance of multiple voltage plateaus, is still not clear. Herein, two representative TLOs (Na2/3Ni1/3Ti2/3O2 and Na2/3Co1/3Ti2/3O2) with the same P2 crystal structure have been studied to scrutinize those unexplained issues. In situ synchrotron high-energy X-ray diffraction revealed a solid solution reaction mechanism for both, suggesting the absence of rigid phase transitions upon electrochemical cycling. An interesting “spring effect” of the TiO6 octahedron, i.e., the reversible vibration of the central Ti atom inside the local octahedron upon electrochemical redox, was demonstrated by advanced X-ray absorption spectroscopy and theoretical calculations. Such an effect could suppress the rigid phase transitions, and result in smooth charge/discharge profiles and enhanced cycle stability. This work not only accounts for the disappearance of multiple voltage plateaus of TLOs for NIBs, but also provides an effective local-structure viewpoint to increase the cycle stability of electrode materials for other advanced battery systems.
The rechargeable lithium-sulfur battery is recognized as a next-generation lithium-ion battery due to its exceptionally high energy density and low cost. Unfortunately, the high dissolution of polysulfides and the low conductivity of sulfur and lithium sulfide lead to a fast capacity decay and a poor specific capacity of the sulfur cathode, which impedes the further development of lithium-sulfur batteries. To overcome these issues, we propose a 3D binder-free collector via in situ-grown polar TiO2 nanowires on carbon-nanofibers, which can successfully suppress the “shuttle effect” of polysulfides and improve the electron conductivity of the sulfur cathode. The prepared TiO2-nanowires arrays provide a large surface area for sulfur loading and a convenient path for electron transfer. These characteristics result in a high ion diffusion capacity of up to 699 mA h g−1 with an excellent coulombic efficiency, higher than 98.5% after 300 cycles at 1.0 C, and a capacity decay as low as 0.075% per cycle. In addition, the strong chemical binding interaction between the polysulfides and TiO2 was directly observed by in situ UV/Vis spectroscopy.
A comprehensive roadmap describing the current density- and size-dependent dendrite growth mechanisms is presented. Based on a thermodynamically consistent theory, the combined effects of chemical diffusion, electrodeposition, and elastic and plastic deformation kinetics are analyzed to rationalize their contributions to experimentally observable morphologies. A critical current density, î* = ziliml(ΔGΩκi), in the tσ < t < tSand range, results in plastic flow at the tips, dendrite bifurcation, and bent and kinked morphologies. Three dendrite growth mechanisms are observed: (1) electrochemical shielding, where there is practically no electrodeposition/electrodissolution; (2) stress-induced electrodissolution and electrodeposition on those interfaces directly facing each other, generating a self-sustained overpotential that pushes the dendrites towards the counter electrode; and (3) local, lateral plastic extrusion in those side branches experiencing non-hydrostatic stresses. Six regimes of lithium electrodeposit growth are identified: (i) thermodynamic suppression regime, (ii) incubation regime, (iii) base-controlled regime, (iv) tip-controlled regime, (v) mixed regime, and (vi) Sand's regime.
In this work, nonaqueous electrolyte-based Li-air batteries with an O2-selective membrane have been developed for operation in ambient air of 20–30% relative humidity (RH). The O2 gas is continuously supplied through a membrane barrier layer at the interface of the cathode and ambient air. The membrane allows O2 to permeate through while blocking moisture. Such membranes can be prepared by loading O2-selective silicone oils into porous supports such as porous metal sheets and Teflon (PTFE) films. It was found that the silicone oil of high viscosity shows better performance. The immobilized silicone oil membrane in the porous PTFE film enabled the Li-air batteries with carbon black air electrodes to operate in ambient air (at 20% RH) for 16.3 days with a specific capacity of 789mAhg−1 carbon and a specific energy of 2182Whkg−1 carbon. Its performance is much better than a reference battery assembled with a commercial, porous PTFE diffusion membranes as the moisture barrier layer on the cathode, which only had a discharge time of 5.5 days corresponding to a specific capacity of 267mAhg−1 carbon and a specific energy of 704Whkg−1 carbon. The Li-air battery with the present selective membrane barrier layer even showed better performance in ambient air operation (20% RH) than the reference battery tested in the dry air box (<1% RH).
The electrical conductivity of disperse electrolytes was systematically measured as a function of temperature (0°C to 60°C) and filler content for different types of fillers with a range of pore geometry, pore structure and specific surface area. As fillers mesoporous silicas SBA-15, MCM-41 and KIT-6 with pore ranges between 3nm and 15nm were dispersed in commercially available liquid lithium electrolytes. As electrolytes 1M of lithium hexafluorophosphate (LiPF6) in a mixture of ethylene carbonate (EC) and diethylene carbonate (DEC) at the ratio 3:7 (wt/wt) and the same solvent mixture with 0.96M lithium bis(trifluoromethanesulfon)imide (LiTFSI) were used. No conductivity enhancement could be observed, but with respect to safety aspects the highly viscous disperse pastes might be useful. The conductivity decrease varied considerably for the different fillers.
The stability of electrolyte at high voltage is important to the development of Li-ion battery that required by the high energy density and high security. However, the decomposition of commercial electrolyte at high voltage limits its practical application. Herein, we introduce a “localized concentrated high-concentration electrolyte” which indicates underlying prospect in high voltage batteries. The “localized concentrated high-concentration electrolyte” can be achieved by adding 1,1,1,3,3,3-hexafluoroisopropyl methyl ether into traditional dimethyl carbonate and fluoroethylene carbonate solvents. The electrolyte (3 mol L−1 LiPF6 DMC/FEC/HFPM 6/1/3) exhibits excellent flame retardant, low viscosity, wide electrochemical window and superior wettability. The Li‖LiNi0.5Mn1.5O4 and Li‖Li1.144Mn0.544Ni0.136Co0.136O2 coin cells with this electrolyte display splendid discharge capacity of 122.2 mAh g−1 after 400 cycles and 221.0 mAh g−1 after 100 cycles at 0.5 C, respectively. While 100.1 mAh g−1 after 35 cycles and 194.8 mAh g−1 after 100 cycles are obtained in commercial electrolyte, respectively. Further analysis shows that stability of high voltage cathodes is mainly contributed to the fluoride protective layer. This method offers a novel pathway for high-concentration electrolyte to improve the performance of Li-ion batteries.
The flavin adenine dinucleotide (FAD) modified zinc oxide films have been prepared using repeated cyclic voltammetry to investigate both the deposition process and the films’ electrocatalytic properties. This paper describes the successful loading of electrochemically active molecules into ZnO by electrochemical method. The cyclic voltammograms recorded the direct deposition of the FAD/zinc oxide films over different scanning potential ranges from the mixed aqueous Zn2+ ions and FAD. In addition to the cyclic voltammetry, an electrochemical quartz crystal microbalance, UV–visible absorption spectroscopy, and the stopped-flow method were used to study the growth mechanism and their properties of the FAD/zinc oxide films. The results showed that the Zn2+ ions and FAD reacted by an electrochemical process to form a self-assembly FAD modified zinc oxide film. The FAD/zinc oxide films exhibited a single redox couple that included both the electron and proton transfer, with a formal potential that demonstrated a proton effect in acidic and basic solutions. The electrocatalytic reduction of NAD+ employing the FAD/zinc oxide films was investigated by cyclic voltammetry and UV–visible absorption spectroscopy methods. The electrocatalytic reduction of S 4 O 6 2 - , SO 5 2 - , S 2 O 8 2 - , ClO 3 - , BrO 3 - , and IO 3 - ions using a FAD/zinc oxide film occurred in neutral aqueous solutions.
Urinary incontinence (UI) is experienced by an estimated 51% of women in the U.S. and often results from impaired function or weakening of the pelvic floor muscles. Pelvic floor muscle training (PFMT) is a frontline nonsurgical treatment, yet a number of symptomatic individuals cannot accurately perform a pelvic floor muscle contraction with simple verbal or written instruction. Long-term adherence to PFMT regimens is often a barrier to resolution of symptoms. Various biofeedback tools have been utilized to aid correct pelvic floor muscle performance and adherence. One novel device, the leva® Pelvic Digital Health System, utilizes an intravaginal probe embedded with MEMS accelerometer sensors that allow real-time visualization of the shape and motion of the vagina during PFMT. Early positive results with this device prompted design of a wearable version. The purpose of this study was to design a wearable, wireless clinical research device to optimize MEMS accelerometer sensor placement to detect maximal movement during a pelvic floor muscle exercise (PFME) and to test the form factor for retention and user acceptability. The device comprised a ring designed to sit at the fornix with an extension following the length of the vagina. This paper presents design components and results from clinical testing of 10 subjects. It was determined that a ring form factor alone, similar to other vaginal rings (pessaries, estrogen rings) provided less accurate visual information about PFME performance. By contrast, we determined that a ring with an extension allowed for device retention and improved real-time detection of vaginal shape and motion during PFMT.
The electrochemical behavior of zinc in strong alkaline solutions containing 8.5M of potassium hydroxide (KOH) and polymeric organic inhibitors was evaluated. The concentrations of the organic inhibitors studies were in the range of 400–4000ppm and included polyethylene glycol (PEG), with a molecular weight of 600, and polyoxyethylen alkyl phosphate ester acid form (GAFAC RA600). The electrochemical studies included anodic, cathodic, and linear polarization along with potentiostatic studies. It was found that the inhibition properties of PEG, in the strong alkaline solution, are by far much more efficient than the inhibition capability of GAFAC RA600. Surface analysis obtained with the use of high resolution scanning electron microscopy (HRSEM) revealed different morphology characteristic developed at the zinc surface in the presence of the two inhibitors. A methodology employing electrochemical tests is proposed to quickly and conveniently evaluate inhibitors for Zn in alkaline media.
A proton exchange membrane fuel cell (PEMFC) cogeneration system that provides high-quality electricity and hot water has been developed. A specially designed thermal management system together with a microcontroller embedded with appropriate control algorithm is integrated into a PEM fuel cell system. The thermal management system does not only control the fuel cell operation temperature but also recover the heat dissipated by FC stack. The dynamic behaviors of thermal and electrical characteristics are presented to verify the stability of the fuel cell cogeneration system. In addition, the reliability of the fuel cell cogeneration system is proved by one-day demonstration that deals with the daily power demand in a typical family. Finally, the effects of external loads on the efficiencies of the fuel cell cogeneration system are examined. Results reveal that the maximum system efficiency was as high as 81% when combining heat and power.
A new type of sodium–nickel chloride batteries using NaSICON solid electrolytes (Na1+xZr2SixP3−xO12) was successfully investigated at much lower operation temperature of 195°C compared with that of conventional Zebra batteries adapting same electrochemistry. The gradual phase transition in NaSICON from monoclinic to rhombohedral was perceived at 100–180°C by high temperature XRD investigation. From symmetrical Na/NaSICON/Na cell test, the abrupt increase of cell resistance was observed at 177–180°C, which reveals the change of ionic conduction mechanism in NaSICON solid electrolytes due to phase transformation. The sintered NaSICON solid electrolytes exhibit full densified morphology but somewhat lower average flexural strength of ~98MPa compared with that reported for the β″-Alumina solid electrolytes commercially available. The low temperature electrochemical performances of sodium–nickel chloride batteries were compared by using NaSICON and β″-Alumina solid electrolytes at 195°C. The lower internal resistances of the cell using NaSICON were confirmed by impedance spectroscopy and cyclic voltammetry tests. Also proto-type cell tests revealed the clear advantages of NaSICON cell (N-Cell) over β″-Alumina cell (β-Cell) at low temperature performances below 200°C due to high Na+ ionic conductivity.
In this work, the high voltage LiMn1.5Ni0.5O4 cathode material has been synthesized as octadecahedron crystals with a disordered spinel structure and has been coated with a carbon layer from two different precursors (sucrose and Xerogel carbon) to improve its performance in Li-ion batteries. The effect of carbon coating on the physical and electrochemical properties of the crystals has been evaluated using X-ray diffraction (XRD), Infrared (IR) and Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental and surface area (BET) analyses and battery cycling at different charge/discharge rates and temperatures. It was found that the amount of carbon, present as a thin layer (5–10 nm) and estimated at <1 w.t.%, causes an increase in electronic conductivity with no effect on crystal structure. Battery results of the cathode material in half cells show that carbon coating greatly improves the discharge capacity, rate capability at room temperature and 60 °C as well as cycling stability. Moreover, the material coated from Xerogel carbon shows the highest capacity at 10 C rate and 60 °C.
The applications of vanadium oxide bronzes as cathode materials for rechargeable lithium-ion batteries are hindered by inferior cyclability and insufficient rate capability, which arised from weak structural stability and sluggish electrochemical kinetics. To address this issue, we incorporate alkaline-earth metals as interlayer materials within the vanadium oxide layered framework, leading to a whole new family of potential Li+ intercalated materials with a general formula MV6O16·nH2O (M=Mg, Ca, Sr, Ba). In these bronze-hydrated compounds, interlayer water can serve as pillars pinning the V–O layers together, coupled with the enhanced divalent cation pillars, maintaining substantial structure stability and leading to excellent long-term stability. Additionally, the interlayer spacing can be further expanded by intercalation of water molecules, offering enhanced Li+ diffusion channel and leading to high rate capability. In this family, we fabricate and study the first such candidate, ultralong metahewettite CaV6O16·3H2O nanoribbons. When evaluated as cathode materials, for the first time, they exhibit high-rate kinetics (103, 78mAhg−1 at 6 and 10Ag−1, respectively) and excellent long-term cyclability (83.6%, 89.5% capacity retention after 1000 cycles at 2 and 6Ag−1, respectively). The electrode shows optimal cycling stability for vanadate-based cathode materials for LIBs ever reported.
We have characterized a ternary mixture of N-methyl-(n-butyl)pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI)+0.5M LiTFSI+ y poly(ethylene glycol) dimethyl ether (PEGDME) (y =kg PEGDME/kg PYR14TFSI) as an electrolyte in Li metal/S cells. The presence of PYR14TFSI in the mixture resulted in a significant improvement of the thermal stability and the ionic conductivity (σ) of the mixture with increasing PEGDME contents (for example, σ =4.2×10−3 Scm−1 at 29°C for y =2.0). These improvements are most significant at low temperatures, which is probably due to a lowering of the viscosity of the mixture with higher amounts of PEGDME. It is found that the mixture has good compatibility with respect to Li metal as demonstrated by time-dependent interfacial impedance and galvanostatic Li stripping/deposition measurements. We found that a Li/S cell with PYR14TFSI+0.5M LiTFSI+ y PEGDME (y =2.0) can deliver about 1300mAhg−1-sulfur at 0.054mAcm−2 at ambient temperature at the first cycle. A better charge/discharge cyclability of the Li/S cell in PYR14TFSI+0.5M LiTFSI+ y PEGDME was found at higher PEGDME contents, and a Li/S cell with the mixture having y =2.0 exhibited a capacity fading rate of 0.42% per cycle over 100 cycles at 0.054mAcm−2 at 40°C. Consequently the PYR14TFSI+LiTFSI+PEGDME mixture is a promising electrolyte for Li/S cells.
In this work, silicon@reduced graphene oxide/pyrolytic carbon nanofibers (Si@RGO/C NFs) composite with double modified layer is prepared through electrospinning, stabilization and carbonization. In this composite, polyethylene oxide–polypropylene oxide–polyethylene oxide (P123, a non-ionic surfactant) is introduced as the dispersant, which can make silicon nanoparticles evenly dispersed in electrospinning solution to prevent it from agglomeration. Graphene modified layer can buffer the volumetric expansion of silicon nanoparticles, prevent direct contact between silicon and electrolyte as well as enhance the electrical conductivity. Moreover, carbon fibers synthesized by electrospinning can encapsulate silicon@graphene composite internally to form a double modified layer. This composite with double modified layer can further alleviate the volume change of silicon nanoparticles and avoid direct contact between silicon and electrolyte to form a stable interface. Owing to the above-mentioned merits, the Si@RGO/C NFs composite exhibits excellent cyclic stability and superior rate performance. Particularly, it maintains a specific capacity of 929 mA h g−1 with the retention ratio of 83.1% after 100 cycles at 0.5 A g−1 and delivers an outstanding rate capability of 1003 mA h g−1 at 2 A g−1.
The present study concerns the electrochemical behavior of catechol and 4-methylcatechol in the presence of 2-mercapto-5-methyl-1,3,4-thiadiazole (MMT) in aqueous medium on the surface of the glassy carbon electrode by means of cyclic voltammetry and controlled-potential coulometry. The oxidation mechanism was deduced from voltammetric and spectrophotometric data. The electro-generation of quinoid intermediates and their subsequent Michael-type reaction with MMT has been investigated as a clean and convenient strategy for the synthesis of corresponding reaction products. In addition, electro-synthesis of Michael addition products has been successfully accomplished by controlled-potential coulometry in a divided H-type cell in mild conditions that can be considered as a green procedure. The reaction products were characterized by spectrophotometric, 1H and 13C NMR, and mass spectrometric methods.
High-quality metal oxides hetero-structured nanoarrays have been receiving great attention in electrochemical energy storage application. Self-supported TiO2/NiO core/shell nanorod arrays are prepared on carbon cloth via the combination of hydrothermal synthesis and electro-deposition methods. The obtained core/shell nanorods consist of nanorod core and interconnected nanoflake shell, as well as hierarchical porosity. As cathode materials for pseudo-capacitors, the TiO2/NiO core/shell nanorod arrays display impressive electrochemical performances with both high capacitance of 611 F g−1 at 2 A g−1, and pretty good cycling stability with a retention of 89% after 5000 cycles. Besides, as compared to the single NiO nanoflake arrays on carbon cloth, the TiO2/NiO core/shell nanorod arrays exhibit much better electrochemical properties with higher capacitance, better electrochemical activity and cycling life. This enhanced performance is mainly due to the core/shell nanorods architecture offering fast ion/electron transfer and sufficient contact between active materials and electrolyte.
In this work, we develop a two-dimensional, transient model to investigate the mechanisms of ion-transport through a porous separator in VRFBs and their effects on battery performance. Commercial-available separators with pore sizes of around 45 nm are particularly investigated and effects of key separator design parameters and operation modes are explored. We reveal that: i) the transport mechanism of vanadium-ion crossover through available separators is predominated by convection; ii) reducing the pore size below 15 nm effectively minimizes the convection-driven vanadium-ion crossover, while further reduction in migration- and diffusion-driven vanadium-ion crossover can be achieved only when the pore size is reduced to the level close to the sizes of vanadium ions; and iii) operation modes that can affect the pressure at the separator/electrode interface, such as the electrolyte flow rate, exert a significant influence on the vanadium-ion crossover rate through the available separators, indicating that it is critically important to equalize the pressure on each half-cell of a power pack in practical applications.