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The crystallization and morphology of brookite and anatase titania (TiO2) were controlled using the urea-mediated hydrolysis/precipitation route in the presence of the Ti3+ ions. Without the strong complexing agents and the non-hydrothermal conditions, simple alterations to the urea concentration led to the synthesis from brookite nanorods to anatase nanoflowers at a low temperature below 100°C, whereas the BET specific surface area evolved from 102 to 268m2 g−1, respectively. A possible formation mechanism was also proposed for these TiO2 nanostructures. The excellent reversible capacity and rate capability were achieved for the anatase nanoflowers because of the small crystallite size and significantly large surface area.
The carbon-coated LiMn0.8Fe0.2PO4 (LMFP) mesocrystal, composed of ~40-nm-sized nanocrystallites, was designed to be favorable for the fast charge transport kinetics. The carbon-coated LMFP mesocrystal exhibited good electrochemical properties (i.e., high specific capacity and superior rate capability), ensuring that the LMFP mesocrystal is a proper model system to study the reaction mechanism upon the battery cycling. In order to investigate the electronic-structure effects of each transition metal (Mn and Fe) on the electrochemical performance, we performed synchrotron-based soft and hard x-ray absorption spectroscopy (sXAS and XAS), and quantitatively analyzed the changes of the transition-metal redox states in the carbon-coated LMFP electrodes during the electrochemical reaction. We believe that our comprehensive as well as complementary analyses using ex situ sXAS and in situ XAS can provide clear experimental evidence on the reaction mechanism of LiMn0.8Fe0.2PO4 electrodes during battery operation.
Yttrium-doped mixed oxides, Li(Ni0.7−y Y y Co0.3)O2, y=0.00–0.05 have been synthesized and characterized. Their cathodic behavior has been examined in cells with lithium metal as anode. The limit for Y solubility is ≤0.05. The beneficial effect of Y is evident by way of increased capacity — retention during charge–discharge cycling, up to 100 cycles at 0.2C rate and up to 50 cycles at 1C rate. Cyclic voltammograms indicate that the phase transitions which usually occur in LiNiO2 during cycling, are suppressed by Co- and Y-doping but not completely eliminated. A reduced hysteresis in the anodic and cathodic peak voltages observed for y=0.05 is an indication of excellent reversibility of the electrode. Thermal stability of the charged cathode is not, however, improved by Y-doping.
Defect and N-activated electronic engineering are of paramount importance for developing highly active carbon-based electrocatalysts toward oxygen reduction reaction (ORR) because the binding affinity of the carbon matrix can be efficiently tuned and thus promote the electrocatalytic activity. Herein, we present a facile and general strategy for fabricating pyridinic-N dominated and defect-enriched graphene-like nanocarbon material (ND-GLC) involving in-situ alkaline activation of cellulose and ammonia injection. The ND-GLC material has a superior and enhanced ORR activity and stability compared to commercial Pt/C catalyst in both rotating disk electrode measurements and Zn-air battery applications. Experimental and theoretical studies describe that the high electrocatalytic activity of ND-GLC mainly originates from the synergetic effect of edges/defects and pyridinic-N dopants. Importantly, our concept is demonstrated to be universal for other carbon-based nanomaterials (i.e., graphite nanoplates, carbon nanotubes, carbon nanospheres, graphene nanosheets).
A relationship between physical properties and local structure of 20Li2O·10Fe2O3·xWO3·(70–x)V2O5 glass, abbreviated as xLFWV glass (x = 0 − 25 in mol%), was investigated by 57Fe-Mössbauer spectroscopy, Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), leaching test using 20 vol% HCl and DC two- or four-probe method. 57Fe-Mössbauer spectra of xLFWV glass showed an increase of quadrupole splitting (Δ) from 0.67 to 0.73±0.02 mm s − 1 and a constant isomer shift (δ) of 0.39±0.01 mm s − 1 with an increase of ‘x’ from 0 to 25. This suggests that FeIIIO4 tetrahedra gradually increase their local distortion along with a substitution of WO3 for V2O5. DTA of xLFWV glass showed an increase in glass transition temperature (Tg) from 252 to 298
A new class of divalent cation incorporated materials, Li1+x Ni0.75Co0.25Mg x O2(1+x), corresponding to Li(Ni0.75Co0.25)1−y Mg y O2 (y=x/(1+x)), have been successfully synthesized and electrochemically characterized. Good cyclability, high voltage durability (up to 4.4 V during charging) and high capacity (>150 mA h/g) are the main characteristics of this class of materials. The successful introduction of the divalent cations alone on the transition metal sites helps to attain these characteristics while also maintaining a large nominal capacity of the material without the interference of the aliovalent cations on the Li sites. Good cycling behavior at high voltages is probably due to the prevention of overcharging of the material caused by the overoxidation of the transition metal as well as the presence of divalent cations on the transition metal site. The presence of the overoxidized transition metal as well as divalent cations on the transition metal site not only increases the cycling voltage but also enhances the phase stability of the materials during cycling.
To improve the electrochemical characteristics of the natural graphite (NG-3) negative electrode in the LiCl saturated AlCl3-1-ethyl-3-methylimizadolium chloride+thionyl chloride (SOCl2) melt as the electrolyte for non-flammable lithium-ion batteries, we examined the influence of the binder types on its electrochemical characteristics. The cyclic voltammograms showed that the reduction current at 1.2–3.2V vs. Li/Li(I) was repressed using polyacrylic acid (PAA) as the binder. The charge–discharge tests showed that the discharge capacity and the charge–discharge efficiency of the NG-3 electrode coated with the PAA binder at the 1st cycle were 322.8mAhg−1 and 65.6%, respectively. Compared with the NG-3 electrode using the conventional poly(vinylidene fluoride) binder, it showed considerably a better cyclability with the discharge capacity of 302.1mAhg−1 at the 50th cycle. Li(I) ion intercalation into the graphite layers could be improved because the NG-3 electrode coated with the PAA binder changed to a golden-yellow color after the 1st charging, and the formation of first stage LiC6 was demonstrated by X-ray diffraction (XRD) measurement. In addition, the XRD and X-ray photoelectron spectroscopy indicated that one of the side reactions during charging was the formation of LiCl on the graphite surface regardless of the binder types.
Impulsivity is a multi-dimensional construct, and it is plausible that distinct brain networks contribute to its different aspects. Here the authors identify distinct cortical and subcortical networks underlying cognitive, clinical and genetic dimensions of impulsivity in a large sample of adolescents.
Magnesium (Mg) is an attractive metallic anode material for next-generation batteries owing to its inherent dendrite-free electrodeposition, high capacity and low cost. Here we report a new class of Mg batteries based on both elemental selenium (Se) and selenium-sulfur solid solution (SeS2) cathode materials. Elemental Se confined into a mesoporous carbon was used as a cathode material. Coupling the Se cathode with a metallic Mg anode in a non-nucleophilic electrolyte, the Se cathode delivered a high initial volumetric discharge capacity of 1689 mA h cm−3 and a reversible capacity of 480 mA h cm−3 was retained after 50 cycles at a high current density of 2 C. The mechanistic insights into the electrochemical conversion in Mg-Se batteries were investigated by microscopic and spectroscopic methods. The structural transformation of cyclic Se8 into chainlike Sen upon battery cycling was revealed by ex-situ Raman spectroscopy. In addition, the promising battery performance with a SeS2 cathode envisages the perspective of a series of SeSn cathode materials combining the benefits of both selenium and sulfur for high energy Mg batteries.
Polyethylene (PE) separator grafted with 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (siloxane) was newly prepared by electron beam irradiation. The degree of grafting and morphology of the grafted separators were characterized by FT-IR and scanning electron microscopy (SEM). The polymer electrolytes based on the grafted separators were prepared by immersing the separators in the electrolyte containing 1M LiPF6 in EC/DMC (1:1 by volume). The ionic conductivity of the grafted separators was changed with the degree of grafting and showed the highest value of 7×10−4 Scm−1 at the degree of grafting of 6%. The electrochemical stability limit of the grafted separator with the degree of grafting of 6% was increased to 5.2V. The Li ion cell using the grafted separator also showed an improved performance, suggesting that the grafted separator is a good candidate for the separator of lithium batteries at high voltage operation.
Photovoltaic (PV) is one of the promising solar energy applications. Measured data can give the realistic performance of PV systems under actual operating environments for product selection and system design. This paper studies a grid-connected PV system installed in an institutional building. Technical data including available solar radiation and output energy generated were systematically recorded and analyzed. The performance of the PV system is elaborated in terms of energy, environmental and financial aspects. Feed-in-tariff (FIT) schemes with high electricity selling price can encourage the deployment of PV system. The monetary payback period (MPBP) for the PV system was computed to be 72.4years when the electricity buying price is equal to the electricity selling price. If carbon trading was considered, the payback was shortened to 61.4years. The embodied energy payback period (EEPBP) was estimated to be 8.9years. The findings would be useful for planning grid-connected PV installations and applicable to other spaces with similar architectural layouts.
In this paper the electrochemical impedance response of phase transition materials is investigated within the Cahn–Hilliard framework. The application of regular perturbation techniques allows the determination of analytical expressions for stable perturbations around constant initial condition. If the initial condition corresponds to a steady state configuration with coexistence of two phases on the sample, then approximate analytical expressions can be found by suitable modification of the boundary conditions. In particular, the impedance response of a particle being synchronously charged/discharged on both sides (reflective conditions), featuring two phases and a phase transition region, is equivalent to the impedance response of a particle of smaller size allowing current go through (absorbing conditions).
To improve the utilization of the active materials and the cyclic performance of the lithium sulfur (Li-S) battery, we designed a sulfur-salt composite cathode that was prepared by the simplest ball-milling method and employed lithium bis(trifluoromethane) sulfonamide (LiTFSI) as one of the cathode components. It is found that the presence of LiTFSI salt plays an important role in increasing the lithium ionic conductivity, enlarging the ion exchange area of the aggregation insulating sulfur particles, and promoting the electrochemical reaction kinetic performance to optimize the utilization of active materials. As a result, the as-prepared cathode shows a pronounced high capacity of 1342mAhg−1 and excellent coulombic efficiency of nearly 100%. Additionally, the scanning electron microscopy (SEM) images confirmed the alleviated loss of active materials in the resultant sulfur-salt cathode. Furthermore, the high–capacity retention and improved electrochemical kinetic performance were validated by charging and discharging tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This effective and simple method provides a new methodology for attaining high-energy Li-S batteries via electrode materials preparation without complex chemical synthesis procedures.
Solid polymer electrolytes based on a novel comb-like copolymer, polyethylene glycol-grafted sulfonated polyether ether ketone (SPEEK-g-PEG), was designed and synthesized through the reaction between partially hydroxyl-functionalized sulfonated polyether ether ketone (SPEEK) and epoxy-functionalized PEG. The resulting SPEEK-g-PEG was fully characterized by FTIR, 1H NMR, TGA, and DSC. All data proved the successful grafting of PEG onto the SPEEK main chain. The resulting comb-like structure effectively inhibited the crystallization of PEG. After doping with a lithium salt, the obtained SPEEK-g-PEG polymer electrolyte membrane showed an improved ionic conductivity. The effects of chain length and PEG grafting ratio on the ionic conductivity of SPEEK-g-PEG were also investigated by electrochemical impedance spectroscopy (EIS). Moreover, the effect of this comb-like structure on increasing the ionic conductivity is higher than that of SPEEK/PEG blends, making these comb-like SPEEK-g-PEG copolymers attractive for an application in LIBs.
The uniform distribution of nano-sized conductive fillers in conductive papers is still a big challenge. Herein, we report a novel cycled film-liquid interface culture (CFLIC) method to produce flexible, ultra-strong, and highly conductive papers based on bacterial cellulose (BC) and graphene (GE). During this biosynthesis process, the GE nanosheets uniformly dispersed in the culture medium are closely bundled by growing BC nanofibers, which leads to a sophisticated multilayered GE/BC nanocomposite. The as-prepared GE/BC paper shows greatly improved tensile strength (93% improvement) and electrical conductivity (10 orders of improvement) over bare BC paper while still retaining the excellent flexibility of BC paper. The strategy is versatile, facile, and scalable and the resultant paper shows promise in numerous fields such as energy storage and electromagnetic interference shielding.
Evidence of the genetic correlates of inhibitory control is scant. Two previously studied dopamine-related polymorphisms, COMT rs4680 and the SLC6A3 3′ UTR 40-base-pair VNTR (rs28363170), have been associated with response inhibition, however with inconsistent findings. Here, we investigated the influence of these two polymorphisms in a large healthy adult sample (N = 515) on a response inhibition battery including the antisaccade, stop-signal, go/no-go and Stroop tasks as well as a psychometric measure of impulsivity (Barratt Impulsiveness Scale) (Experiment 1). Additionally, a subsample (N = 144) was studied while performing the go/no-go, stop-signal and antisaccade tasks in 3T fMRI (Experiment 2). In Experiment 1, we did not find any significant associations of COMT or SLC6A3 with inhibitory performance or impulsivity. In Experiment 2, no association of COMT with BOLD was found. However, there were consistent main effects of SLC6A3 genotype in all inhibitory contrasts: Homozygosity of the 10R allele was associated with greater fronto–striatal BOLD response than genotypes with at least one 9R allele. These findings are consistent with meta-analyses showing that the 10R allele is associated with reduced striatal dopamine transporter expression, which in animal studies has been found to lead to increased extracellular dopamine levels. Our study thus supports the involvement of striatal dopamine in the neural mechanisms of cognitive control, in particular response inhibition.
Thin microfibrous substrates were built using a low cost, high speed, wet lay papermaking process with nickel and copper microfibers. High quality microfiber sheets with designed thickness and void volumes were fabricated at the Center for Microfibrous Materials Manufacturing at Auburn University. Products include thin microfibrous nickel and copper substrates with or without suitable expanded metal meshes, either sandwiched inside or on the backside. An improved method for fabrication of zinc electrodes was accomplished by electro-depositing active zinc material on 6 and/or 9μm diameter microfibrous copper substrates. These zinc electrodes with various additives were examined for shape change and tested for performance. A new structure of electrode design was employed using an accordion-fold cell. By using five individual segments sintered onto an expanded metal mesh, an accordion-fold cell (670mAh rated capacity) was assembled and had 98.0% coulomb efficiency, 88.6% energy efficiency at 72% depth-of-discharge (DOD) and 73.2% state-of-recharge (SOR) in the 79th cycle. A Ni–Zn cell consisting of one thick nickel and one thick zinc electrode was tested for rate performance in comparison with the 670mAh accordion-fold cell. The accordion-fold cell (1279mAh rated capacity) was scaled-up and tested for 835 cycles at 38% DOD at a 0.3C charge and discharge rates, and continuously operated at 38% DOD until the 1050th cycle was finished at 0.16C charge/discharge rates. A 7115mAh accordion-fold demonstration cell was tested at 0.28C charge and discharge rates for 608 cycles and still had a 4.7Ah capacity at a 0.08C discharge rate.
The electrochemical performance of the sulfurized polyacrylonitrile (SPAN)/Li cell affected by the Li2SiO3 particles that added between cathode and separator in the assembly process is studied. Fast capacity decay happens to the base SPAN/Li cell without Li2SiO3 due to deactivation of sulfur and side reactions etc.. However, the decay is obviously mitigated in the presence of Li2SiO3. Reversible capacity retention of 79% can be achieved after 100 cycles at 0.5C, while it is less than 10% for its counterpart. XPS and TEM measurements are conducted and the result indicates a positive effect of Li2SiO3 on the inhibition of side reactions, because Li2SiO3 can hold the dissociated sulfur substances and consume PF5/HF in the carbonate electrolyte.
Li3PO4, with a Li ion conductivity of 8.62 × 10−8 S cm−1, is considered as a matrix material in this study to improve the cyclability of tin anodes. Toward this goal, a well-crystallized NASICON-structured LiSn2(PO4)3 using nano-SnO2 as a precursor has been prepared at 900 °C using a solid-state reaction. Compared to SnO2, this material exhibits better cycling performance, with a capacity of 320 mAh g−1 after 50 cycles. Additionally, the insertion/extraction mechanism of LiSn2(PO4)3 is investigated through ex-situ X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) measurements. The apparent diffusion coefficient (D Li ) is studied using cyclic voltammetry (CV) experiments employing a powder microelectrode. In addition, differential scanning calorimetry (DSC) measurements are employed to investigate the thermal stability of LiSn2(PO4)3.
Highly ion-conductive gel polymer electrolyte (GPE) with mechanical flexibility is developed by incorporating liquid electrolyte into polymer films that are fabricated by initiator-free photopolymerization of poly(ethylene glycol) dimethacrylate (acrylate monomer) and pentaerythritol tetrakis (3-mercaptopropionate) (thiol monomer) blend. When UV is irradiated on the blend, the thiol monomers themselves produce radicals to initiate the polymerization. GPEs with 40–50wt.% of thiol monomer content show mechanically free standing characteristics with sufficient flexibility. The ionic conductivity of the GPE reaches1.1×10−3 Scm−1 at 25°C and is thus high enough to be applied for lithium secondary batteries. The GPE is electrochemically stable up to 4.4V versus Li/Li+ and the unit cells consisting of LiCoO2/GPE/lithium metal show good cycling performance. This GPE is thus considered a good electrolyte candidate for future flexible and wearable lithium secondary batteries.
Mechanical degradation of electrode active materials (“electrochemical shock”) contributes to impedance growth of battery electrodes, but relatively few design criteria have been developed to mitigate fracture. Using micromechanical models and in situ acoustic emission experiments, we demonstrate and explain C-rate independent electrochemical shock in polycrystalline electrode materials with anisotropic Vegard coefficients. We conclude that minimizing the principal shear strain, rather than minimizing net volume change as previously suggested, is an important new design criterion for crystal chemical engineering of electrode materials for mechanical reliability. Polycrystalline particles of anisotropic Li-storage materials should be synthesized with primary crystallite sizes smaller than a material-specific critical size to avoid fracture along grain boundaries. Finally, we revise the electrochemical shock map construction to incorporate the material-specific critical microstructure feature sizes for C-rate independent electrochemical shock mechanisms, providing a simple tool for designing long-lived battery electrodes.
In high temperature electrical generators such as thermal batteries, the molten salt electrolyte needs to be retained by a binder, e.g. MgO. We have pointed out that the magnesia volume fraction was a more accurate parameter than the usually used weight fraction. Moreover, based on our technique measurements, we defined a magnesia volume fraction range (27–30vol.%) where the electrolyte retention could be considered as efficient whatever its nature. And finally, we proposed a microstructure description of the retained electrolyte.
Li–CO2 batteries are considered promising approaches for reducing the “greenhouse effect” and taking advantage of the abundant CO2 in the atmosphere for use in energy storage devices, due to the molecule's reversible reaction with Li. However, Li–CO2 batteries suffer from several setbacks, such as poor rechargeability and low Coulombic efficiency. Designing and fabricating a highly efficient cathode is one of the key components to improving the electrochemical performance. For the first time, we demonstrate a transient, in situ thermal shock method combined with a three-dimensional cross-linked structure derived from CO2 gasification to produce a high dispersion of ultrafine Ru nanoparticles on activated carbon nanofibers to serve as an efficient cathode in Li–CO2 batteries. The interconnected channels, numerous pores, ultrafine nanoparticles, and highly crystalline structure promote the diffusion of CO2 and the permeation of electrolyte, enhancing the catalytic decomposition of discharge products in Li–CO2 batteries. These devices exhibit not only impressive cycling performance with a limited capacity of 1000 mA h g−1, but also a low overpotential due to the sufficient number of active sites on the cathode. The electrode displays a low overpotential of 1.43 V after 50 cycles at 0.1 A g−1. Furthermore, low overpotentials of 1.79 and 1.81 V can be achieved even at elevated current densities of 0.8 and 1.0 A g−1, respectively. In comparison, the previously reported overpotentials were up to 1.95 and 1.90 V at low current densities of 0.1 and 0.2 A g−1, respectively, indicating the Ru nanoparticles on the carbon nanofibers display excellent catalytic performance towards the reaction of Li and CO2. Therefore, this approach offers a new pathway to high performance Li–CO2 batteries and may spur further applications in catalysis and other renewable energy storage technologies.
A methodology is developed for assessing the durability of friction pairs with solid lubrication coatings (SLCs) having different compositions functioning under the conditions of the reverse motion based on adjusting the durability values obtained for unidirectional sliding friction by reduction to a unified temperature mode using the thermocorrelational dependences of the durability on the friction temperature and conversion factors for a decrease in durability.