20th Cycle Research Articles

Impedance Informed, High Frequency Pulse Charging As Method to Enable Stable Low Temperature Li-Ion Battery Operation

Low temperature cycling of Li-ion batteries can have two major complications: incomplete intercalation in the anode and lithium metal deposition.1-2 These complications lead to a loss in capacity and cell instability caused by lithium deposits inside the cell. Instability within the cell can cause the battery to begin an exothermic reaction and go into thermal runaway, resulting in a potentially hazardous reaction. Herein we use a pulse charging technique to overcome the limitations associated with low temperature cycling. Commercial 18650 cells were cycled 50 times at 25°C (ambient), 0°C, and at 0°C using a pulse charging technique. The parameters of pulse charge were determined using a single point impedance technique.3 Electrochemical impedance spectroscopy (EIS) was acquired at 10% increments of state of charge (SOC). The frequency least dependent on state of charge indicates a time constant of ion movement where the solid electrolyte interface (SEI) at the anode is least inhibiting to ion flow. Therefore, this frequency was imitated with a square-wave, current pulse to ameliorate the sluggish SEI kinetics often blamed for onset of lithium deposition in low temperature charging. The magnitude of current was prescribed by the cell manufacturer and square pulses were applied until the voltage cutoff was reached. The charge was then topped off with a CV step and constant current discharged in the same manner as the conventionally charged 25°C and 0°C controls. The cells cycled at 25°C remained stable across 50 cycles: staying around 2.6A with 98% capacity retention. The pulsed cell and the cold cell begin with a capacity deficit due to enhanced cell impedance at the cold conditions. The capacity of the cold cell starts to fade, and at the 20th cycle a large drop in capacity is apparent. The drop off in capacity is due to plating of lithium within the cell, which is illustrated in the differential capacity assessment and computed tomography renderings of the cells after charging. The pulses cell does not exhibit fade like the cold cell, maintains a constant capacity, and has an impressive 99% capacity retention at the 50th cycle, which is comparable to the ambient cell. Figure 1. Charge/discharge behavior over 50 cycles for (a) constant current at 25°C (ambient), (b) pulsed charging at 0°C, and (c) constant current charging at 0°C. (d) Capacity retention over 50 cycles for the three charging and temperature conditions. Love, C.; Dubarry, M.; Reshetenko, T.; Devie, A.; Spinner, N.; Swider-Lyons, K.; Rocheleau, R., Lithium-Ion Cell Fault Detection by Single-Point Impedance Diagnostic and Degradation Mechanism Validation for Series-Wired Batteries Cycled at 0 °C. Energies 2018, 11 (4), 834.Love, C. T.; Baturina, O. A.; Swider-Lyons, K. E., Observation of Lithium Dendrites at Ambient Temperature and Below. Ecs Electrochem Lett 2015, 4 (2), A24-A27.Love, C. T.; Virji, M. B. V.; Rocheleau, R. E.; Swider-Lyons, K. E., State-of-health monitoring of 18650 4S packs with a single-point impedance diagnostic. Journal of Power Sources 2014, 266, 512-519. Figure 1

Development of Polymer Blend Electrolyte Membranes Based on Chitosan: Dextran with High Ion Transport Properties for EDLC Application.

Solid polymer blend electrolyte membranes (SPBEM) composed of chitosan and dextran with the incorporation of various amounts of lithium perchlorate (LiClO4) were synthesized. The complexation of the polymer blend electrolytes with the salt was examined using FTIR spectroscopy and X-ray diffraction (XRD). The morphology of the SPBEs was also investigated using field emission scanning electron microscopy (FESEM). The ion transport behavior of the membrane films was measured using impedance spectroscopy. The membrane with highest LiClO4 content was found to exhibit the highest conductivity of 5.16 × 10−3 S/cm. Ionic (ti) and electronic (te) transference numbers for the highest conducting electrolyte were found to be 0.98 and 0.02, respectively. Electrochemical stability was estimated from linear sweep voltammetry and found to be up to ~2.3V for the Li+ ion conducting electrolyte. The only existence of electrical double charging at the surface of electrodes was evidenced from the absence of peaks in cyclic voltammetry (CV) plot. The discharge slope was observed to be almost linear, confirming the capacitive behavior of the EDLC. The performance of synthesized EDLC was studied using CV and charge–discharge techniques. The highest specific capacitance was achieved to be 8.7 F·g−1 at 20th cycle. The efficiency (η) was observed to be at 92.8% and remained constant at 92.0% up to 100 cycles. The EDLC was considered to have a reasonable electrode-electrolyte contact, in which η exceeds 90.0%. It was determined that equivalent series resistance (Resr) is quite low and varies from 150 to 180 Ω over the 100 cycles. Energy density (Ed) was found to be 1.21 Wh·kg−1 at the 1st cycle and then remained stable at 0.86 Wh·kg−1 up to 100 cycles. The interesting observation is that the value of Pd increases back to 685 W·kg−1 up to 80 cycles.

Capsule-like Co3O4 nanocage@Co3O4 nanoframework/TiO2 nodes as anode material for lithium-ion batteries

Co3O4 nanoparticles-assembled 3-dimension mesoporous nanoframework with TiO2 spheres as framework nodes was successfully synthesized in Co3O4 nanocage, forming a unique nanocapsule with large specific surface area and abundant mesopores. As anode material for lithium ion batteries, the nanocapsules exhibited high specific capacity (1409 mAh g−1 at 200 mA g−1 at the 19th cycle), good cycling performance and rate capability. The superior lithium storage performance was attributed to the unique capsule structure. It increased electrochemical activity and stability of Co3O4.

Cyclic durability of calcium carbonate materials for oxide/water thermo-chemical energy storage

Calcium oxide/water reaction is a promising thermochemical energy storage system owing to its high reaction enthalpy, wide availability at low cost, and favorable reaction temperature. In this research work, a calcium carbonate material was developed, featuring nano-order diameter with a silane coupling agent on the surface, and was kinetically evaluated for use in calcium oxide/water thermochemical energy storage. The kinetics analysis of the material was conducted and compared with other conventional calcium carbonate materials in which particle diameter was 2–3 μm as a reference material. Calcium oxide materials prepared through a decarbonation of calcium dioxide were used for 20 repeated cycle operations. In comparison with the conventional calcium carbonate material, the developed material showed high durability for the cycle operation and maintained its reaction conversion as almost 100% between the 8th and 20th cycle. The presence of silicate produced from the thermal decomposition of the silane coupling agent on the material surface could prevent particle aggregation. It maintained vapor diffusivity between the particles, and enhanced cyclic reaction durability of the developed material. The reaction conversion directly affects thermochemical energy storage performance, and these results indicated that the developed material had sufficient performance compared to conventional calcium carbonate materials as a thermochemical energy storage material.

Dual electrolyte additives of potassium hexafluorophosphate and tris (trimethylsilyl) phosphite for anode-free lithium metal batteries

Potassium hexafluorophosphate and tris (trimethylsilyl) phosphite are applied as electrolyte additives to enhance electrochemical performance of an anode-free lithium metal battery (AFLMB) based on a Cu‖NMC cell configuration. The synergistic effect of the dual additives has been investigated using a commercial carbonate electrolyte (1 M LiPF6-EC/DEC (1:1 vol%)). Herein, we report that an electrolyte with dual additive of 2 wt% KPF6 - 2 vol% TMSP significantly improves the charge/discharge capacity, average coulombic efficiency and retention capacity of a Cu‖NMC cell configuration. An AFLMB cell with 2 wt% KPF6 - 2 vol% TMSP additives retained 48% of its initial capacity at the 20th cycle, while the reference cell with the commercial electrolyte in the absence of additives reached only 14%. The enhanced performance using the prepared electrolyte is attributed to the self-healing electrostatic shielding (SHES) effect of KPF6 to prevent dendrite growth and the removal of hydrofluoric acid (HF) produced from the commercial LiPF6 carbonate electrolytes by the reaction of phosphorus pentafluoride (PF5) with water using TMSP. This study provides a broader vision in developing functional electrolyte additives for an anode-free lithium metal battery.

Effects of yttrium substitution for magnesium on the electrochemical performances of La2Mg1−xYxNi8.8Co0.2 hydrogen storage alloys

The effects of yttrium substitution for magnesium in the La2Mg1−xYxNi8.8Co0.2 hydrogen storage alloys on the electrochemical properties are investigated in this paper. Yttrium substitution in the alloys can significantly improve the cycle stability, although the discharge capacity was decreased. The capacity and retention capacity after 20th cycle of the La2Mg0.9Y0.1Ni8.8Co0.2 alloys achieved values above 370mAh/g and 95%, respectively, which already exceed those of most hydrogen storage alloys with A2B7 or AB3 structure. The charge-transfer resistance also reached the lowest when x was 0.1 in the La2Mg1−xYxNi8.8Co0.2 alloy, resulting in the highest charge transfer rate.

Improved iron oxide oxygen carriers for chemical looping hydrogen generation using colloidal crystal templated method

Abstract Iron oxide has been widely studied in chemical looping hydrogen generation (CLHG) process as an oxygen carrier, but fast decline of its activity in redox cycles due to sintering and agglomeration is one of the main drawbacks. In this work, the colloidal crystal templated (CCT) method was applied to synthesize Fe2O3/CeO2 oxygen carrier and the mole ratio of Fe/Ce was 8:2, aiming to inhibit adjacent grains from agglomerating and improve the contact between the fuel gas and the oxygen carrier. The redox performances were evaluated with CO as fuel in a batch fixed bed reactor for 20 redox cycles, with oxygen carriers prepared by co-precipitation (CP) and sol-gel (SG) methods as references. X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), and H2-temperature programmed reduction (H2-TPR) were used for characterization. The results showed that the calcination temperature lower than 750 °C was suitable for the CCT. The redox experiments showed that the H2 yield and the redox stability for the oxygen carrier prepared by CCT were higher than those by co-precipitation and sol-gel methods. The H2 yield of CCT oxygen carrier kept stable from the 3rd cycle and was 8.5 mmol/gOC in the 20th cycle. The pore structures resulting from CCT were different from another two oxygen carriers before and after the cycles, but maintained well through SEM images, leading to high activity and stability during redox cycles. The crystallite sizes of Fe2O3 and CeO2 before and after redox cycles were the smallest for the CCT oxygen carrier from XRD patterns. In addition, H2-TPR demonstrated that CCT oxygen carrier exhibited the highest reactivity.

Biodegradation of crude oil hydrocarbons by a newly isolated biosurfactant producing strain

New bacterial strain BN66 was isolated by selective enrichment, identified as Bacillus cereus and proved to degrade crude oil, together with biosurfactant synthesis. Free and cryogel immobilized Bacillus cereus cells were involved in a crude oil degradation process. The studied strain degraded 93% of the aliphatic fraction for 48 h. We immobilized cells in two types of cryogels synthesized from high molar mass polyacrylamide or acrylamide precursors and explored the degradation capability and possibility for re-use of the preparations. Reusability tests revealed that the oil degradation ability of immobilized cells was stable after 47 days (28 °C and shaker speed 120 rpm) and the degradation rate of immobilized cells was maintained at a high level up to the 20th cycle of operation. The matrices obtained from high molar mass polyacrylamide appeared to be more suitable due to their ability to keep the cells within the carrier. The cells immobilized in cryogels exhibited more effective degradation for 22 active cycles at semicontinuous mode of operation compared to only three cycles performed by free cells.

Al3+ ion intercalation in MoO3 for aqueous aluminum-ion battery

While addressing the question of Al3+ ion intercalation/deintercalation in MoO3, we unravel that Al3+ ion preferentially intercalates in MoO3 in certain aqueous electrolytes. The Al3+ ion electrochemistry in MoO3 shows stark contrasting characteristics in different aqueous electrolytes. Although very high initial Al3+ ion storage capacity of 680 mAhg−1 is observed, a stable discharge capacity of approximately 170 mAhg−1 is attained after 20th cycle over the measured time (350th cycle) at a specific current of 2.5 Ag-1 (5 mA cm−2) in AlCl3 aqueous electrolyte. AlCl3 aqueous electrolyte exhibits superior benefits than Al2(SO4)3 and Al(NO3)3 aqueous electrolytes in terms of offering higher Al3+ ion storage capacity, long-term stability, capacity retention and minimized polarization.

State-of-charge estimation method of lithium-ion batteries based on long-short term memory network

This paper presents a method to estimate the state-of-charge (SOC) of lithium-ion batteries based on long-short term memory network (LSTM). The method is mainly composed of two parts: (1) A linear neural network is used to identify the parameters of second-order equivalent circuit model. (2) A LSTM network is built to estimate the SOC of lithium-ion battery. The linear neural network is trained using the American Dynamic Stress Test Condition (DST) dataset of battery (1st cycle), while the LSTM network is trained using the Chinese Standard Operating Condition (QCT) datasets of battery (1st, 10th and 20th cycle). After that, the trained LSTM network is tested using DST datasets of the batteries and QCT datasets under different temperatures. The results show that the LSTM network can accurately estimate the SOC of lithium battery under different temperatures, different working conditions and lifespan.

Carbon-enhanced centrifugally-spun SnSb/carbon microfiber composite as advanced anode material for sodium-ion battery

Antimony tin (SnSb) based materials have become increasingly attractive as a potential anode material for sodium-ion batteries (SIBs) owing to their prominent merit of high capacity. However, cyclic stability and rate capability of SnSb anodes are currently hindered by their large volume change during repeated cycling, which results in severe capacity fading. Herein, we introduce carbon-coated centrifugally-spun SnSb@carbon microfiber (CMF) composites as high-performance anodes for SIBs that can maintain their structural stability during repeated charge-discharge cycles. The centrifugal spinning method was performed to fabricate SnSb@CMFs due to its high speed, low cost, and large-scale fabrication features. More importantly, extra carbon coating by chemical vapor deposition (CVD) has been demonstrated as an effective method to improve the capacity retention and Coulombic efficiency of the SnSb@CMF anode. Electrochemical test results indicated that the as-prepared SnSb@CMF@C anode could deliver a large reversible capacity of 798 mA h∙g−1 at the 20th cycle as well as a high capacity retention of 86.8% and excellent Coulombic efficiency of 98.1% at the 100th cycle. It is, therefore, demonstrated that SnSb@CMF@C composite is a promising anode material candidate for future high-performance SIBs.

Optimised cycling stability of sorption enhanced chemical looping steam reforming of acetic acid in a packed bed reactor

The cycling stability of reactor bed materials during the production of enhanced high purity hydrogen in the sorption enhanced chemical looping steam reforming (SE-CLSR) of acetic acid was studied and compared with the conventional steam reforming process. A packed bed reactor was used at 1 atm with a nickel catalyst supported on calcium aluminate intimately mixed with CaO in the role of high temperature CO2 sorbent. Twenty cycles of SE-CLSR were conducted under combined NiO-reduction/HAc steam reforming at 650 °C, at feed molar steam to carbon ratio of 3 and WHSV of 1.18 h−1, cyclically alternating with air feed to perform the coupled Ni-oxidation and CaCO3 calcination at 850 °C. Sustained and consistent reforming was achieved in excess of 80% of HAc conversion across all 20 SE-CLSR cycles; this was accompanied by hydrogen yield efficiencies exceeding 78% when compared to equilibrium values at same conditions. However, by the end of the 20th cycle, the extent of CaO carbonation had dropped to about 50% of that observed in the first cycle. Five SE-CLSR cycles were run using steam hydration at 250 °C prior to the fuel feed with the aim of improving sorbent conversion. A higher hydrogen yield was observed with an increase in fuel conversion. The sorbent conversion was also stable across all 5 SE-CLSR cycles when performed with sorbent pre-hydration using steam. This was attributed to an increased carbonation rate during the sorbent’s pre-breakthrough period. Enhanced auto-reduction of the NiO catalyst resulting from sorption of the CO2 product was also observed, and an improved sorbent conversion outlook over the cycles was investigated. TEM and SEM images indicated that carbon formed during the fuel-feed stage was eliminated during the cyclic oxidation step.

Peculiarities of the geomagnetic field secular variations at the 20th solar activity cycle

The decrease of solar and; correspondingly; geomagnetic activities at the 20th cycle has reflected on the secular variations of the geomagnetic field. On the continental magnetic observatories of the Earth north hemisphere (Europe and North America) the effect was positive and maximal amplitude was observed at the region of geomagnetic and magnetic poles. If the latitudes of the observatories diminishes amplitude of the effect also decreased and was about zero at the latitudes less 45°. At the Asia; the effect was negative and its maximal amplitude was observed at the observatory IRT. The sign of the effect changes at longitudes 60° (observatory KZN) and 150°—180° (observatory CWE; BRW). At the african and south America observatories the effect was not observed. The most probably; it was result of total variations from external and internal sources and the nearness of observatories to the geomagnetic equator. At Earth’s south hemisphere; the most of the observatories are costal or are placed on the is-lands. The effect was not observed at these observatories. Maybe the induction current of ocean flows compensates the external variations. At the Antarctic continent the little amplitude effect was observed at the south magnetic pole region (DRV).

Interfacial Impedance Growth in Si-Alloy/Graphite Blended Electrodes

Active material blended electrodes are comprised of physical mixtures of two or more lithium insertion compounds. Blended electrodes can have superior balanced performance compared to electrodes with an individual active compound.1 For instance, Si and Si-based materials have been successfully blended into graphite electrodes in lithium-ion batteries.2,3 Si-alloy/graphite blended electrodes result in higher cell energy density than graphite electrodes and pure Si-alloy electrodes and also have higher capacity retention than pure Si-alloy electrodes.3 Some properties of active material blended electrodes are difficult to predict simply from the individual active materials, such as cell lifetime.4 Electrochemical impedance spectroscopy (EIS) provides diagnostic information concerning the state of health of electrodes and properties of the solid-electrolyte interphase (SEI).5 The electrode/electrolyte interfacial impedance growth of Si-alloy/graphite electrodes will be discussed here. Figure 1 (a-c) shows measured Nyquist plots of graphite, Si-alloy, and graphite/Si-alloy blended electrodes at different cycles. The interfacial resistance (Rir) is highest for the graphite and Si-alloy electrodes and is lowest for the graphite/Si blended alloy electrode. Changes in Rir for these electrodes are not monotonic and do not at first seem related. The trends in Rir as a function of cycle number for these electrodes are summarized in Figure 1 (d), where the Rir data were normalized with respect to the first cycle. After normalization relationships between the coatings appear. For all three electrodes, Rir increases from the 1st cycle to the 5th cycle and then decreases from cycle 5 to 10. After 10 cycles, Rir increases for graphite electrodes, while Si-alloy and the blended electrodes have a constant Rir. The relative Rir values of the graphite/Si-alloy blended electrodes have very similar behavior to the pure Si-alloy electrode. Therefore, it appears that the Si-alloy component is dominant with regard to the behavior of Rir. To verify this, the relative Rir at the 20th cycle of electrodes with various ratios of Si-alloy/graphite blended electrodes are shown in Figure 2. All blended electrodes have relative Rir values that are different from pure graphite, but have similar relative Rir values to pure Si-alloy electrodes, regardless of the graphite content. In this presentation, an explanation of this behavior in the interfacial resistance of graphite/alloy blended electrodes will be proposed. Reference S. B. Chikkannanavar, D. M. Bernardi, and L. Liu, J. Power Sources, 248, 91–100 (2014).R. Petibon et al., J. Electrochem. Soc., 163, A1146–A1156 (2016).V. L. Chevrier et al., J. Electrochem. Soc., 161, A783–A791 (2014).H. Kitao, T. Fujihara, K. Takeda, N. Nakanishi, and T. Nohma, Electrochem. Solid-State Lett., 8, A87 (2005).M. Galeotti, L. Cinà, C. Giammanco, S. Cordiner, and A. Di Carlo, Energy, 89, 678–686 (2015). Figure 1 Nyquist plots for (a) graphite, (b) Si-alloy, and (c) Si-alloy/graphite (60:28 wt/wt) blended electrodes measured at different cycles. (d) the relative interfaical resistance vs. cycle number of these three electrodes. Relative interfaical resistance values were measured as the diameter of the semicircles in the Nyquist plots, normalized on the basis of first cycle interfacial resistance. The error bars were calculated as the range of two samples. The cells were cycled at 30.0 ± 0.1 ºC and EIS spectra were measured at 10 ºC. Figure 2 The relative interfaical resistances of graphite/Si-alloy blended electrodes with various compositions, measured at 20th cycle. The error bars were calculated as the range of two samples.The cells were cycled at 30.0 ± 0.1 ºC and EIS spectra were measured at 10 ºC. Figure 1

Improving the Performance of MoSx/r-GO Cathode Materials for Lithium-Ion Battery Via an in-Situ Electrochemical Method

While lithium-ion batteries (LIBs) with high energy density, long lifetime, and high operating voltage are widely used not only for portable devices but also for large scale devices and facilities, present LIBs have an insufficient energy density due to the use of large and heavy lithium metal oxide cathodes (100 ~ 200 Wh kg-1). Hence, sulfur is being proposed as a new cathode material due to about 5 times higher energy density (500 Wh kg-1) as well as lower cost than the commercial cathode materials. However, lithium-sulfur (Li-S) batteries have rapid initial capacity fading induced by dissolution of highly ordered polysulfide (Li2Sx, 8≥x>6) and large volume expansion (~80 %). Metal sulfides, such as MoS2, can directly form Li2S without the formation of intermediate products in a Li-S battery. In particular, the reversible reaction between Li2S and S at a voltage of over 2.2 V is notable for the use as new cathode material. Herein, we hypothesized that an increase of S content in the metal sulfide compound can expand the operating voltage window over 2 V such as S cathode. Therefore, we prepared molybdenum-sulfide compound with a higher content of S (MoSx, x>2) than MoS2 for use as a cathode instead of S. Moreover, we attached the MoSx on the oxygen functional group of graphene oxide (GO) to strongly anchor the MoSx and GO was partially changed to reduced GO (r-GO) in this process. In this study, we introduce an improved MoSx/r-GO cathode using an in-situ electrochemical method (named as “in-situ electrochemical pulverization”). The nano-sized material shows high kinetic performance and low volume expansion due to a short ion diffusion path and a large surface to volume ratio. Therefore, to improve the performance and stability of the prepared electrode, we pulverize bulk MoSx into nano-sheets by repetitive full lithiation/delithiation cycles. Moreover, the pulverized nano sheets are securely anchored by the oxygen functional group in partially reduced GO, so that they are not separated from the electrode. In addition, to enhance the stability more, a nano-scaled SEI layer is formed on the in-situ pulverized nano sheets by controlling the initial potential. As shown in Fig. 1a, the capacity rapidly decreased from 2680 to 561 mAh g-1 over the 20th cycle (step 1) presumably due to S dissolution. Then, the performance was recovered to 1627 mAh g-1 over the following 110th cycle (step 2) and it was maintained at that level for subsequent cycles (1606 mAh g-1 for the 250th cycle at 0.5 A g-1). To elucidate the behavior underlying this observed gradual increase in capacity during step 2, we studied the morphology of the electrode by HR-TEM at the uncycled state, 60th, and 100th cycles. As shown in Fig 1b, the uncycled electrode shows a micro-sized layer structure along the r-GO surface. However, the repetitive electrochemical reaction (step 2 of Fig. 1a) induced a continuous pulverization of the bulk sheets into nano sheets with a size of 5.0 nm for the 100th cycle (Fig. 1c-d). This TEM behavior is in good agreement with the cyclic performance of Fig. 1a. Moreover, in Fig. 2a thin film with a thickness of 0.9 – 1.0 nm, formed by controlling the potential, covered the pulverized sheets. Additionally, in XPS surface analysis of the electrode after the 100th cycle, peaks of 285, 286.5, and 290 – 291.5 eV associated with carbonate compounds were identified. (Fig. 2b). These compounds correspond to the SEI layer. Although the SEI layer is an insulator, it can protect the active material from side reaction with the electrolyte and dissolution in the solution itself. Thus, the formation of a thin SEI on the pulverized sheets led to maintenance of capacity of above 1500 mAh g-1 after the 110th cycle. Based on the above results, it is concluded that the in-situ electrochemical pulverization of the MoSx/r-GO can improve electrochemical performances by forming nano-sized sheets which are securely anchored on r-GO. Also, the formation of a thin SEI layer can support the stability of the pulverized nano sheets. Figure 1

Enhanced electrochemical lithium storage performance of Mg2FeH6 anode with TiO2 coating

Light-weight metal hydrides are potential high-capacity conversion anode materials for lithium-ion batteries, but the poor reaction reversibility and cyclic stability of hydride anodes need to be improved. In this work, the ternary hydride Mg2FeH6 was composited with the graphite (G) by ball-milling, and the Mg2FeH6-G composite electrode was further coated with amorphous TiO2 film by magnetron sputtering. The resultant Mg2FeH6-G/TiO2 electrode exhibited a stable charge capacity of 412 mAh g−1 over 100 cycles, which is much higher than 46 mAh g−1 at 20th cycle for the pure Mg2FeH6 electrode, or 185 mAh g−1 at 100th cycle for the Mg2FeH6-G electrode. There is only little capacity degradation after 20 cycles for the Mg2FeH6-G/TiO2 electrode and the charge capacity retention is 84.7% after 100 cycles. The remarkable improvement in the cyclic stability of Mg2FeH6-G/TiO2 electrode is mainly attributed to the dense TiO2 coating that maintains the structural integrity of electrode during cycling. The TiO2 coating also prevents the direct contact of high active LiH/MgH2 with the liquid electrolyte, and thus ensures the high reversibility of conversion reaction of MgH2 during cycling.

Hysteretic behaviour of high strength S690 steel materials under low cycle high strain tests

This paper describes a detailed experimental investigation into structural behaviour of S690 steel materials under both monotonic and cyclic loading conditions. In addition to 6 monotonic tensile tests, which were conducted to establish basic mechanical properties, 36 cyclic tests were then carried out in order to examine hysteretic behaviour of the S690 steel materials under various target strains and loading frequencies. The experimental arrangements used for the monotonic and the cyclic tests are described, and a detailed account of the test results is provided. The monotonic tests showed that all the S690 steel specimens satisfied the ductility requirements stipulated in current European provisions which are typically based solely on monotonic behaviour. In the cyclic tests, most specimens were able to complete 20 cycles with target strain amplitudes of ±2.5%, ±5.0%, ±7.5%, and ±10.0%, under loading frequencies of 0.1, 0.5, 1.0 and 2.0 Hz. However, some specimens fractured at the 20th cycle when the target strains were ±10.0% irrespective of the loading frequency. Additionally, significant strength enhancement due to strain hardening was observed and quantified in the cyclic tests, depending on the level of target strains. The results additionally illustrated the importance of using actual instantaneous cross-sectional diameters for evaluating true stresses in order to obtain actual representative hysteretic curves.In general, the study highlights the importance of establishing seismic ductility requirements based on cyclic tests, particularly for high strength steel materials. It also provides a detailed assessment of the hysteretic characteristics, which can be directly employed to develop reliable constitutive models for high strength S690 steel materials under seismic loading conditions.

Functionalization of Moringa oleifera gum for use as Hg2+ ions adsorbent

Modification of biomass or natural polymers is an attractive strategy to develop efficient bioadsorbents for toxic metal ions removal from polluted water as these have inherent biodegradability after use. In the present study, Moringa oleifera gum (MOG), a natural stem exudate was modified via acryloylation reaction to nano-polyacryloyl MOG (NPAMG). The latter was characterized by different techniques (FTIR, FE-SEM, EDX, XRD, TEM, AFM and particle size analysis) and evaluated as adsorbent for Hg2+ ions as a function of contact time, temperature, pH and initial ion concentration. NPAMG has been observed to be an efficient adsorbent with the maximum adsorption capacity of 840.34 mg g−1 calculated by applying the Langmuir model. The high desorption tendency was also observed as reusability study was carried out for 20 repeated cycles with adsorption capacity of 71.25 mg g−1 after 20th cycle and cumulative 1606.25 mg g−1 of Hg2+ ions were adsorbed with the same dosage of adsorbent. Langmuir model fitted the equilibrium adsorption data better than Freundlich isotherm model. Adsorption kinetic data were best fitted by pseudo-second order kinetic model as confirmed by high correlation coefficients (0.9995) and low chi-square values (0.0009).

Essential features of long-term changes of areas and diameters of sunspot groups in solar activity cycles 12–24

We analyze the Greenwich catalog data on areas of sunspot groups of last thirteen solar cycles. Various parameters of sunspots are considered, namely: average monthly smoothed areas, maximum area for each year and equivalent diameters of groups of sunspots. The first parameter shows an exceptional power of the 19th cycle of solar activity, which appears here more contrastively than in the numbers of spots (that is, in Wolf’s numbers). It was found that in the maximum areas of sunspot groups for a year there is a unique phenomenon: a short and high jump in the 18th cycle (in 1946–1947) that has no analogues in other cycles. We also studied the integral distributions for equivalent diameters and found the following: (a) the average value of the index of power-law approximation is 5.4 for the last 13 cycles and (b) there is reliable evidence of Hale's double cycle (about 44 years). Since this indicator reflects the dispersion of sunspot group diameters, the results obtained show that the convective zone of the Sun generates embryos of active regions in different statistical regimes which change with a cycle of about 44 years.

TiO2-CNTs grown on titanium as an anode layer for lithium-ion batteries

TiO2 has recently been attracted for use as anode material in lithium ion batteries (LIBs). However, its drawbacks are poor electrical conductivity and low intrinsic diffusivity of Li ions. In this work, a TiO2-carbon nanotubes (CNTs) anode layer was grown on a titanium thin plate via micro-arc oxidation (MAO) technique by incorporating CNTs into the electrolyte. Material characterization and electrochemical measurement were carried to the obtained Ti/TiO2-CNTs composite. Experimental results show that the obtained TiO2-CNTs layer was found to coexist micro- and nano-TiO2 in morphology with evenly dispersed CNTs. By serving the Ti/TiO2-CNTs composite as the anode, the assembled coin cell increases its discharge capacity to 201 mAh/g measured after the 20th cycle at a discharge rate of 0.2 C, as opposed to the value of 69 mAh/g when without the addition of CNTs. This indicates that the CNTs network contributes to the increase its electrochemical properties.