Mahr Research Articles

One‐pot hydrothermal synthesis of porous anatase TiO2 nanotube formed bundles for lithium ion battery anodes

AbstractAnatase phase of TiO2 nanomaterial has been deemed a potential anode material for lithium ion battery (LIB) applications because of its remarkable electrochemical properties. However, TiO2 anodes always suffer from intrinsic poor electrical conductivity and slow ion kinetics, which would restrict their practical usage. To address this issue, efficient control and design of the anatase crystal structure of TiO2 material with desirable morphology is one of the critical approaches. In this work, a good lithium storage capability of 181 mA hr g−1 at rate of 0.2C, high rate performance of 70 mA hr g−1 at 20C, and excellent cyclability of 117 mA hr g−1 with a capacity retention of 93% at 1C after 100 cycles and 84 mA hr g−1 at 10C after 1,000 cycles are observed in an optimized porous anatase TiO2 one‐dimensional nanotube bundle nanomaterial fabricated through a simple hydrothermal process with post calcination treatment. These excellent electrochemical properties of the product can be ascribed to its anatase crystal phase, 1D nanostructure, and porous framework with a large surface area, which provide it with an efficient electrode/electrolyte contact area and a faster ion/electron diffusion pathway.

A Visible Light-Near-Infrared Dual-Band Smart Window with Internal Energy Storage

Summary The integration of electrochromic smart windows with energy storage is an appealing concept for green building development. Herein, we report a dual-band electrochromic energy storage (DEES) window capable of independent control of visible light (VIS) and near-infrared (NIR, solar heat) transmittance with a high internal charge storage. The key design feature is the use of composition-optimized Ta-doped nano-TiO2 nanocrystals as a multifunctional active material to deliver a high charge-storage capability concurrently with high bistability and long-cycle-life electrochromism in three distinct operating modes: (1) the VIS and NIR transparent “bright” mode; (2) the VIS transparent and NIR opaque “cool” mode; and (3) the completely opaque “dark” mode. The independent control of VIS (sunlight) and NIR (solar heat) modulation was successfully demonstrated in a DEES prototype with a high charge-storage capacity of 466.5 mA hr m−2 at 150 mA m−2 of current density.

Yolk-Shell Germanium@Polypyrrole Architecture with Precision Expansion Void Control for Lithium Ion Batteries

SummaryThe key properties of yolk-shell architecture in improving electrochemical performance lies in its uniformity and the appropriate void space, which can expand/contract freely upon lithium alloying and leaching without damaging the outer shell, while being achievable with minimal sacrifice of volumetric energy density. Therefore, we developed a highly controllable strategy to fabricate a uniform porous germanium@polypyrrole (PGe@PPy) yolk-shell architecture with conformal Al2O3 sacrificial layer by atomic layer deposition (ALD) process. The PGe@PPy yolk-shell anode fabricated with 300 ALD cycles delivers excellent electrochemical performance: high reversible capacity (1,220 mA hr g−1), long cycle performance (>95% capacity retention after 1,000 cycles), and excellent rate capability (>750 mA hr g−1 at 32 A g−1). Electrodes with high areal capacity and current density were also successfully fabricated, opening a new pathway to develop high-capacity electrode materials with large volume expansion.

Deciphering the Modulation Essence of p Bands in Co-Based Compounds on Li-S Chemistry

Summary Despite the fact that metal-based compounds have been extensively used as sulfur cathode additives, large variations in electrochemical performance have been commonly observed from one material to another, which cannot be simply explained by the adsorption capability. Herein, we have systematically studied the kinetic behaviors of Li-S chemistry on Co-based compounds with fixed metal cation and varied non-metal anions, and deciphered the intrinsic modulation essence of the anions. Among the Co-based compounds, CoP exhibits the lowest overpotential for polysulfide transformation. Even at 40.0 C, S@CoP/rGO still delivers a high capacity of 417.3 mA hr g−1 and an unprecedented power density of 137.3 kW kg−1, representing the best rate performance. DFT analysis reveals that the performance variations mainly originate from the shift of p band centers, which modulate the interfacial electron transfer dynamics. This work could unlock the potential of band engineering for Li-S batteries and beyond.

Scalable Room-Temperature Synthesis of Multi-shelled Na3(VOPO4)2F Microsphere Cathodes

Summary The large-scale application of rechargeable batteries in electric vehicles and energy-storage systems is still hindered by their high cost, particularly from the active materials. Here we proposed a concept of integration of extraction-separation and materials-preparation to further reduce the materials' cost. The power of this concept was demonstrated by the large-scale room-temperature synthesis (150 g per batch) of multi-shelled Na3(VOPO4)2F microspheres based on in situ generated bubbles as soft templates. The as-prepared Na3(VOPO4)2F shows superior rate capability with discharge capacity of 81 mAh g−1 at 15 C current rate and capacity retention of 70% after 3,000 cycles. Ex situ UV-vis was first employed to characterize the variation of oxidation state for vanadium during the charging and discharging process. This is the first report of a rapid and facile large-scale room-temperature controllable synthesis of Na3(VOPO4)2F microspheres, and this approach could be extended to synthesize other similar compounds.

MOF-derived Cobalt Sulfide Grown on 3D Graphene Foam as an Efficient Sulfur Host for Long-Life Lithium-Sulfur Batteries

SummaryLithium-sulfur (Li-S) batteries are an appealing candidate for advanced energy storage systems because of their high theoretical energy density and low cost. However, rapid capacity decay and short cycle life, mainly resulting from polysulfide dissolution, remains a great challenge for practical applications. Herein, we present a metal-organic framework (MOF)-derived Co9S8 array anchored onto a chemical vapor deposition (CVD)-grown three-dimensional graphene foam (Co9S8-3DGF) as an efficient sulfur host for long-life Li-S batteries with good performance. Without polymeric binders, conductive additives, or metallic current collectors, the free-standing Co9S8-3DGF/S cathode achieves a high areal capacity of 10.9 mA hr cm−2 even at a very high sulfur loading (10.4 mg cm−2) and sulfur content (86.9 wt%). These results are attributed to the unique hierarchical nanoarchitecture of Co9S8-3DGF/S. This work is expected to open up a promising direction for the practical viability of high-energy Li-S batteries.

Understanding High-Energy-Density Sn4P3 Anodes for Potassium-Ion Batteries

Summary Phosphorus-based anodes for alkali metal-ion batteries are attractive due to their high theoretical-specific capacity. However, their poor electrochemical performance caused by relatively large volume variations during cycling, low electrical conductivity, and severe electrolyte decomposition due to highly reactive phosphide surface hinder their potential applications. Herein, we confine Sn4P3 in N-doped carbon fibers as anode for potassium-ion batteries with enhanced cycling stability and high rate capability (160.7 mA hr g−1 after 1,000 cycles at 500 mA g−1). The Sn4P3 anodes undergo a sequential conversion (P to K3P11, K3P) and alloying (Sn to KSn) reactions with synergistic K-storage mechanisms. Also, the electrolyte with potassium bis(fluorosulfonyl)imide salt can effectively suppress the dendrite growth in K stripping/plating, stabilize the solid-electrolyte interphase (SEI) layer, and avoid excessive side reactions, thus enhancing the electrode stability. This work provides a feasible approach to overcome the durability bottlenecks of K-ion batteries through regulating dendrite growth and SEI formation.

Room-Temperature Aluminum-Sulfur Batteries with a Lithium-Ion-Mediated Ionic Liquid Electrolyte

Summary Aluminum-sulfur (Al-S) chemistry is attractive for the development of future-generation electrochemical energy storage technologies. However, to date, only limited reversible Al-S chemistry has been demonstrated. This paper demonstrates a highly reversible room-temperature Al-S battery with a lithium-ion (Li + -ion)-mediated ionic liquid electrolyte. Mechanistic studies with electrochemical and spectroscopic methodologies revealed that the enhancement in reversibility by Li + -ion mediation is attributed to the chemical reactivation of aluminum polysulfides and/or sulfide by Li + during electrochemical cycling. The results obtained with X-ray photoelectron spectroscopy and density functional theory calculations suggest the presence of a Li 3 AlS 3 -like product with a mixture of Li 2 S- and Al 2 S 3 -like phases in the discharged sulfur cathode. With Li + -ion mediation, the cycle life of room-temperature Al-S batteries is greatly improved. The cell delivers an initial capacity of ∼1,000 mA hr g −1 and maintains a capacity of up to 600 mA hr g −1 after 50 cycles.

Reversible Mg-Ion Insertion in a Metastable One-Dimensional Polymorph of V2O5

Summary The Li-ion paradigm of battery technology is constrained by the monovalency of the Li ion. A straightforward solution is to transition to multivalent-ion chemistries, where Mg 2+ is the most obvious candidate because of its size and mass. The realization of Mg batteries has faced myriad obstacles, including a sparse selection of cathode materials demonstrating the ability to reversibly insert divalent ions. Here, we provide evidence of reversible topochemical and electrochemical insertion of Mg 2+ into a metastable one-dimensional polymorph of V 2 O 5 up to a capacity of 0.33 Mg 2+ per formula unit. An electrochemical capacity of 90 mA hr g −1 was retained after 100 cycles with an average operating potential of 1.65 V versus Mg 2+ /Mg 0 . Not only does ζ-V 2 O 5 represent a rare addition to the pantheon of functional Mg battery cathode materials, but it is also distinctive in exhibiting a combination of high stability, high specific capacity, and moderately high operating voltage.

Self-Standing Hierarchical P/CNTs@rGO with Unprecedented Capacity and Stability for Lithium and Sodium Storage

Summary Red phosphorus (P) suffers from large volume variation and poor conductivity as anodes for lithium and sodium ion batteries. Moreover, the currently used evaporation-condensation preparation method raises serious safety concerns, and ball-milled P/C also gives poor performance because of interparticle adhesion. Here, we present a mild solution synthesis of unique hierarchical P/CNTs@rGO, which not only achieves maximum conductivity in red P agglomerates but also provides volume variation space to relieve the pulverization issues. Even at a high P content of 70 wt %, P/CNTs@rGO still exhibits a specific capacity of 2,189.1 mA hr g −1 for lithium-ion batteries and 2,112.9 mA hr g −1 for sodium-ion batteries. These values are very close to the theoretical specific capacity. More importantly, it achieves an unprecedented gravimetric capacity of 1,532.4 mA hr g −1 on the basis of the mass of the whole electrode, as well as excellent cycling performance for 500 cycles, representing the best Li-storage performance among red-P-based electrodes to date.

Designing Lithium-Sulfur Cells with Practically Necessary Parameters

Summary In the pursuit of high-energy-density batteries, there is tremendous appetite for developing the lithium-sulfur technology with high sulfur loading and content while keeping the electrolyte/sulfur (E/S) ratio low to be competitive with or surpass the current lithium-ion technology. However, very limited studies have focused on keeping these parameters at practically desirable ranges. Here, we present a lithium-sulfur cell with a coaxial-graphene-coated cotton-carbon (CGCC) cathode that displays excellent performance with high sulfur loading (57.6 mg cm −2 ), high sulfur content (75 wt %), and low E/S ratio (4.2 μL mg −1 ) simultaneously. The cell exhibits high areal capacity (31 mA hr cm −2 ) and areal energy density (66 mW hr cm −2 ) that exceed the areal capacity (4 mA hr cm −2 ) and areal energy density (10 mW hr cm −2 ) of a commercial LiCoO 2 cathode with a high capacity-retention rate of 68% over 200 cycles.

Crumpled Graphene Balls Stabilized Dendrite-free Lithium Metal Anodes

Summary With its high theoretical capacity and low electrochemical potential, Li metal itself would be the ideal anode for Li-ion batteries. However, practical use of the Li anode has been hindered by its tendency for dendritic growth, which leads to unstable solid electrolyte interphase, volume fluctuation during cycling, and even shorting of the battery. This problem can be solved by employing a conducting, lightweight, and lithiophilic scaffold that can stabilize high loading of Li during cycling and avoid its dendritic filament growth. Here we report that crumpled paper ball-like graphene particles can readily assemble to yield a scaffold with scalable Li loading up to 10 mA hr cm −2 within tolerable volume fluctuation. High Coulombic efficiency of 97.5% over 750 cycles (1,500 hr) was achieved. Plating/stripping Li up to 12 mA hr cm −2 on crumpled graphene scaffold does not experience dendrite growth.

The Study of the financial effects of divorce on Iran's Law

Cancellation of contract primarily causes the loss of all relations arising from it, but in the case of married couples, the financial relations continue in cases even after the cancellation. Methodology: This article evaluates the financial impact of divorce in Iranian law with library method. Of the Law Concerning divorce reform enacted in 1992, it obliges the man who is seeking a divorce to pay financial rights of women included the wages, Nahla, and up to half of the assets, inheritance, alimony and mahr and dowry. Results: Nahla is establishing rights that were entered Iranian law by the law amending the provisions of the divorce. However, in accordance with Article (336) of the Civil Code, nothing is unpaid, but obligation of man to pay the works of women at home is subject to conditions in the year 1992. Conclusion: In the absence of financial condition during the marriage, the wage should be calculated based on the work that women do at home of the husband.

Differential Voltage Analysis of Composite Silicon Anodes for Lithium Ion Cells

1. Introduction Silicon remains as an attractive but challenging anode material for lithium ion cell anodes. It has a high capacity compared to graphite (3579 : 372 mA hr g-1), but significantly greater expansion when fully lithiated (280 : 10 %). Significant advances in the understanding of the lithiation in silicon process have been made through techniques like in situ and ex situ NMR [1]. The initial crystalline silicon is converted into amorphous silicon clusters, then discrete silicon atoms, and then finally crystalline Li15Si4. Information from these spectroscopic techniques can be used to interpret data from more routine cycling methods, during the development of silicon electrodes.Differential voltage analysis has been applied to various lithium ion cells, to study degradation reactions as a function of cycle number [2, 3]. Standard cycling data is used to calculate either dQ / dV or dV / dQ, which is then plotted against the voltage. In dQ / dV plots, the peaks represent phase equilibria, whereas in dV / dQ plots, the peaks represent phase transitions. This report uses differential voltage analysis to investigate composite silicon electrodes under different test conditions. 2. Results Composite silicon anodes were prepared using a 3 mm silicon powder, with partially neutralised poly acrylic acid as binder. Silicon half cells were cycled at fixed lithiation capacities (1200 and 1800 mA hr g-1), and also at full capacity down to 0.005 V. Figure 1 shows a typical result for full capacity cycling, and Figure 2 the corresponding differential dQ / dV plot. The peak at 0.1 V / 0.3 V was barely present at 1200 mA hr g-1, and declined steadily at higher capacities. The 0.1 V peak is associated with the formation of isolated silicon atoms, via small clusters e.g. Si2 dumb-bells. The peak at 0.2 V is from an earlier stage of the reaction, when amorphous silicon is converted to an extended network, and then larger clusters. Cycling at full capacity causes more expansion than the binder can withstand. In turn, this leads to a relatively rapid decline in capacity, and a corresponding increase in the cycling rate. The disappearance of the 0.1 V lithiation peak is associated with a much more rapid drop in electrode voltage. The delithiation peak initially at 0.3 V declines, and the peak voltage drifts to higher values. From approximately 35 cycles onwards, the delithiation voltage jumps straight to 0.5 V. The lithiation and hence subsequent delithiation reactions are rate dependent [1], which may explain the results observed here. Further results with three electrode cells will be presented at the conference. 3 Conclusions Silicon electrodes in practical cells at realistic current densities show similar multi-stage electrochemical processes as those observed in specialised spectroscopy cells at low current densities. Using dQ / dV analysis in half cells and three electrode cells allows the peaks in simple two electrode full cells to be interpreted.

Studies of Anomalous Diffusion in Composite Silicon Anodes

1. Introduction The diffusion coefficient is an important parameter of active materials for lithium ion batteries, particularly in higher rate applications like electric vehicles. It is useful to know the diffusion coefficient as a function of state of charge, and other parameters like temperature. Silicon has a very high lithiation capacity (3579 mA hr g-1), but a correspondingly large expansion when fully lithiated (> 270 %). On the first charge, crystalline silicon is converted to amorphous LixSi, and then to crystalline Li15Si4 at full lithiation. The diffusion coefficient in a-LixSi will have an important influence on the movement of these two phase boundaries, which in turn will impact upon the performance and operating life of the electrode. The two main techniques used to measure diffusion coefficients are a. c. impedance, via the Warburg coefficient, and galvanostatic intermittent titration technique (GITT). This report describes the use of both of these methods on composite silicon anodes. 2. Results Electrodes were prepared using 3 µm silicon powder, with partially neutralised poly acrylic acid as binder and conductive carbon. Following a slow formation cycle (C/20), impedance spectra were recorded in two electrode half cells, at different states of charge. Figure 1 shows typical results at lithiation capacities of 300, 600, 900 and 1200 mA hr g-1. The data was fitted to equivalent circuits, with a series resistance, two resistor // CPE parallel combinations, and a low frequency constant phase element (CPE) tail. Apart from the fully delithiated anode, the tail was always at a much steeper angle than the standard Warburg value of 45o (power term = 0.5). Figure 2 shows plots of the fitted power term {n in Z = (iw)-n C-1}, at three different states of charge, during cycling. 3. Discussion One explanation for the steeper gradient is that the diffusion is anomalous or non-Fickian [1]. This can occur for charge carrier movement in amorphous solids, like LixSi. After each hop, the charge carrier can wait “for a period drawn from a broad power law distribution” [1], reducing the overall rate of diffusion. Interestingly, a recent theoretical study has calculated a wide range of activation energies for lithium hopping in amorphous silicon (0.1 to 2.4 eV [2]). The difference in the power term at 600 mA hr g-1 during lithiation and delithiation implies a structural hysteresis, which may match the voltage hysteresis observed with silicon anodes. Further results, including GITT experimental data and analysis, will be presented at the conference.

LiMn2O4@Au Particles as Cathodes for Li-Ion Batteries

LiMn2O4 (LMO) particles were coated with a Au shell by a simple and scalable electroless deposition for use as Li-ion battery cathodes. The Au shell was intended to limit the capacity fade commonly seen with LMO cathodes. Characterization by SEM, TEM, EELS, and AFM showed that the Au shell was approximately 3 nm thick. The Au shell prevented much of the Mn from dissolving in the electrolyte with 82% and 88% less dissolved Mn in the electrolyte at room temperature and 65°C, respectively, as compared to the uncoated LMO. Electrochemical performance studies with half cells showed that the Au shell maintained a higher discharge capacity over 400 cycles by nearly 30% with 110 mA hr g−1 for the 400th cycle as compared to a commercial LMO at 85 mA hr g−1. Similarly, the capacity fade was reduced in full cells, where the coated LMO had 47% greater capacity after 400 cycles over the control.

Potassium barium hexacyanoferrate – A potential cathode material for rechargeable calcium ion batteries

Potassium barium hexacyanoferrate (K2BaFe(CN)6) was investigated as a cathode material for reversible Ca2+ ion insertion/extraction type rechargeable battery using non-aqueous electrolytes. The electrochemical performance of K2BaFe(CN)6was evaluated using cyclic voltammetry and galvanic cycling at ambient temperature. It is shown that addition of water led to significant enhancement in intercalation and de-intercalation of Ca2+ ions, leading to improved charge/discharge capacity. The enhancement in performance is attributed to formation of solvation spheres around the intercalating Ca2+ ions which provide screening from the electrostatic charges of the BaFe(CN)6 lattice. A reversible capacity of 55.8 mA hr g−1 and a coulombic efficiency of 93.8% was demonstrated at the end of 30 charge/discharge cycles.

Rheological phase synthesis and electrochemical performances of LiVMoO6 as a high-capacity anode material for lithium ion batteries

Research for new anode materials has been stimulated by the development of lithium ion batteries since the introduction of carbon as a negative material in 1990 by Sony Energetics Inc. Some metal oxides and metalbased composite oxides [1, 2], nitrides [3, 4] and intermetallics [5, 6], which capacities are comparable or superior to those of graphitized carbon (theoretical maximum capacity of 372 mA hr g−1 [7, 8]), were considered as possible candidates for next generation of anode materials. Recently, several vanadium composite oxides exhibited their high-capacity and high-rate performance as negative electrode materials due to their open structure and interesting characteristics from a standpoint of the variety of oxidation states [9–12]. LiMoVO6 crystallizes with the ThTi2O6 branneritetype structure [13] and its electrochemical properties as a positive electrode material for lithium secondary batteries have been investigated [14–16]. But the performance of LiMoVO6 as negative electrode material was seldom reported. In this work, brannerite-type LiMoVO6 powder was obtained by rheological phase reaction method [17]. The result of electrochemical tests showed that the obtained LiMoVO6 as a novel anode material was also feasible and demonstrated very high energy density. The precursor was prepared by rheological phase reaction method. Analytical reagent grade chemicals, LiOH·H2O, NH4VO3 and (NH4)6Mo7O24·4H2O, were used as the starting materials and fully mixed by grinding in a 1:1:1 molar ratio. A proper amount of water was added to get a rheological body and the mixture was sealed in a closed container for 8 hr at 80 ◦C. After drying under vacuum at 80 ◦C for several hours, the precursor was pyrolyzed at 550 ◦C for 10 hr in air, and soft yellow powder LiMoVO6 was obtained. Thermogravimetry and differential thermal analysis (TG/DTA) of the precursor were performed by the Netzsch STA 449 thermal analysis system at a heating rate of 10 ◦C/min in air. The X-ray diffraction (XRD) measurements of the sample were carried out by Shimadzu XRD-6000 diffractometer with CuKα1 radiation (λ = 1.54056 A). The particle sizes and morphological features were observed by a scanning electron microscope (Hitachi SEM X-650).

Rheological phase synthesis and electrochemical performances of LiVMoO6 as a high-capacity anode material for lithium ion batteries

Research for new anode materials has been stimulated by the development of lithium ion batteries since the introduction of carbon as a negative material in 1990 by Sony Energetics Inc. Some metal oxides and metalbased composite oxides [1, 2], nitrides [3, 4] and intermetallics [5, 6], which capacities are comparable or superior to those of graphitized carbon (theoretical maximum capacity of 372 mA hr g−1 [7, 8]), were considered as possible candidates for next generation of anode materials. Recently, several vanadium composite oxides exhibited their high-capacity and high-rate performance as negative electrode materials due to their open structure and interesting characteristics from a standpoint of the variety of oxidation states [9–12]. LiMoVO6 crystallizes with the ThTi2O6 branneritetype structure [13] and its electrochemical properties as a positive electrode material for lithium secondary batteries have been investigated [14–16]. But the performance of LiMoVO6 as negative electrode material was seldom reported. In this work, brannerite-type LiMoVO6 powder was obtained by rheological phase reaction method [17]. The result of electrochemical tests showed that the obtained LiMoVO6 as a novel anode material was also feasible and demonstrated very high energy density. The precursor was prepared by rheological phase reaction method. Analytical reagent grade chemicals, LiOH·H2O, NH4VO3 and (NH4)6Mo7O24·4H2O, were used as the starting materials and fully mixed by grinding in a 1:1:1 molar ratio. A proper amount of water was added to get a rheological body and the mixture was sealed in a closed container for 8 hr at 80 ◦C. After drying under vacuum at 80 ◦C for several hours, the precursor was pyrolyzed at 550 ◦C for 10 hr in air, and soft yellow powder LiMoVO6 was obtained. Thermogravimetry and differential thermal analysis (TG/DTA) of the precursor were performed by the Netzsch STA 449 thermal analysis system at a heating rate of 10 ◦C/min in air. The X-ray diffraction (XRD) measurements of the sample were carried out by Shimadzu XRD-6000 diffractometer with CuKα1 radiation (λ = 1.54056 A). The particle sizes and morphological features were observed by a scanning electron microscope (Hitachi SEM X-650).

Danish law and the practice of mahr among Muslim Pakistanis in Denmark

Cet article se penche sur la transmission des biens a la femme en cas de veuvage ou de divorce au sein de la communaute Pakistanaise du Danemark. Designee sous le nom de mahr, cette pratique est egalement examinee sous l'angle des attitudes adoptees par le droit et les tribunaux danois a son egard