High Discharge Potential Research Articles

Oxidation rate of Fe and electrochemical performance of Fe–air solid oxide rechargeable battery using LaGaO3 based oxide ion conductor

Effects of oxidation rate of Fe powder in Fe–air solid oxide rechargeable battery on discharge potential and capacity were studied. From the measurement of PO2 in Fe set chamber and AC impedance for electrode reaction, oxidation rate of Fe, i.e., formation rate of H2, was an important parameter for discharge performance of Fe–air solid oxide battery. Slow oxidation rate of Fe, namely, low current density, shows high discharge potential, however, caused sintering of Fe powder resulting in the decreased discharge capacity and so decreased usage efficiency of Fe powder. On the other hand, larger capacity (1145 mAh gFe−1), which is close to the theoretical capacity, can be achieved at higher discharge rate of 30 mA cm−2 at 873 K. Therefore, higher current density seems to be suitable for larger discharge capacity. Concentration overpotential is negligibly small at initial stage of discharge, however, with discharge period, diffusion overpotential became significantly enlarged caused by the slow oxidation rate of Fe. Sintering of Fe powder was observed after discharge at 5 mA cm−2 by SEM and TEM observations and so fast oxidation rate at larger current density can be assigned to bulk oxidation of Fe powder with small particle size sustained during discharge.

Effect of Sn on Microstructure and Electrochemical Properties of Mg Alloy Anode Materials

Abstract Morphologies, microstructure and composition distribution of the magnesium anode materials were studied by metallographic microscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The corrosion behavior and electrochemical properties of Mg alloy were also investigated by constant current method, potential polarization, and drainage. The results show that Sn and Pb can restrain β-Mg 17 Al 12 phase precipitation along the grain boundary and Mg-Al-Pb-Sn magnesium alloys have uniform and fine grain size. With the content of tin increasing, the content of particle Mg 2 Sn phase increases. After uniform heat treatment, most of β-Mg 17 Al 12 phase dissolve, while most of Mg 2 Sn and Mg 2 Pb do not dissolve. The tin can improve self-corrosion potential and reduce release hydrogen rate. Magnesium anode has high discharge potential and current efficiency with 2wt% tin. With the current density increasing, the release hydrogen rate improves, owing to negative variance effect of magnesium alloys. The current efficiency is up to 88% at 10 mA/cm 2 . The main composition of the corrosion products are Mg(OH) 2 , SnO 2 and MgSnO 3 that are easier to peel off, which leads to more negative and stable work potential and can accelerate reaction continuously.

Enhanced electrochemical properties of LiFe1−xMnxPO4/C composites synthesized from FePO4·2H2O nanocrystallites

The high discharge potential of LiMnPO4, 4.1 V vs. Li/Li+, and its theoretical capacity of 170 mAh g−1 make it a promising candidate as a cathode material in lithium-ion batteries. But extremely low electronics conductivity, slow lithium diffusion kinetics, and the Jahn-Teller effect of Mn3+ limit the electrochemical performances of LiMnPO4. In this work, the pre-synthesized and defined FePO4·2H2O nanocrystallites are used as one of the raw materials to synthesize LiFe1−xMnxPO4/C (x = 0.85, 0.75, 0.65) composites via solid-state reactions. The synthesized LiFe1−xMnxPO4 samples show well-crystallized structures and have enhanced electrochemical properties. There exist two plateaus around 3.5 and 4.1 V on both of their charge and discharge curves. Among the samples, the Fe0.25Mn0.75PO4 one exhibits the longest high-voltage charge/discharge plateau at 4.10 V/4.05 V, and has an average discharge voltage of ∼3.78 V vs. Li/Li+ and a discharge capacity of ∼130 mAh g−1 at 0.05 C rate. For the Fe0.25Mn0.75PO4 sample, the noticeable improvement of its electrochemical performances is mainly attributed to iron substitution, the appropriate Mn/Fe ratio, and the well-ordered crystal structure forming by using FePO4·2H2O nanocrystallites as one of the raw materials.

Ni foam as the current collector for high capacity C–Si composite electrode

Si electrode is very promising as the anode material for next generation lithium ion batteries requiring high capacity and energy because of its high theoretical capacity (4200mAhg−1 compared to 372mAhg−1 for graphite) and low discharge potential (∼0.5V vs. Li/Li+). However, fast capacity fading of Si electrode is suffered from huge volume expansion and contraction during charging and discharging. Although many methods, including nanostructured electrode, thin film and composite electrode, have been proposed to overcome the capacity fading problem, high synthesis cost and/or poor effects prevent them from being used in the commercial applications. In this study, 3-dimensional (3D) Ni foam is adopted as the current collector for high capacity C–Si composite electrode. The results show that Ni foam can effectively suppress the electrode expansion and greatly improve the cycle life of Si electrode due to the 3D structure. Electrochemical impedance spectroscopy also shows that the electrode with Ni foam show much lower impedance after cycling. Therefore, adopting Ni foam as the current collector provides a new way to incorporate the electrode materials with large volume expansion.

ChemInform Abstract: Fabrication and Electrochemical Characteristics of LiFePO4 Powders for Lithium‐Ion Batteries

AbstractReview: 154 refs.

Influences of Rapid Quenching on the Structures and Electrochemical Performances of La<sub>0.7</sub>Mg<sub> 0.3</sub>Co<sub>0.45</sub>Ni<sub> 2.55-x</sub>Fe<sub>x</sub> (x = 0-0.4) Electrode Alloys

The influences of rapid quenching on the structures and electrochemical behaviors of La-Mg-Ni system (PuNi3-type) La0.7Mg0.3Co0.45Ni2.55-xFex (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys were systemically investigated. The results show that the rapid quenching, instead of changing the phase structures of the alloys, leads to c axis enlarged and the a axis and cell volumes of the LaNi5 and (La, Mg)Ni3 major phases decreased slightly. The morphologies of the as-quenched alloys exhibit a massive structure, which differ from that of the as-quenched AB5-type alloy. The rapid quenching clearly impairs some electrochemical performances of the alloys, involving discharge capacity, high rate discharge ability (HRD) and discharge potential, but it significantly prolongs the cycle life of the alloy. With an increase in the quenching rate from 0 (As-cast was defined as quenching rate of 0 m/s) to 30 m/s, the discharge capacity of the alloy (x = 0.4) decreases from 351.06 to 313.36 mAh/s, the HRD from 69.36 to 50.54%, whereas its cycle life increases from 106 to 166 cycles at a charging discharging current density of 600 mA/g.

Effect of Tin on Microstructure and Electrochemistrical Properties of Mg-Al-Sn-Zn Magnesium Alloys Anodic Materials

Morphologies, microstructure and composition distribution of the magnesium anodic materials were studied by metallographic microscopy, x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The corrosion behavior and electrochemical properties of Mg alloy were also investigated by constant current method, potential polarization, collecting gas through drainage. The results show that tin restrained β-Mg17Al12 phase precipitation along the grain boundary. With the content of tin increasing, granular Mg2Sn phase was improved. After uniform heat treatment, most of β-Mg17Al12 phase was dissolved, but most of Mg2Sn was not dissolved. Tin could improve self-corrosion potential and release hydrogen rate. Magnesium alloy anode with 1% tin content had high discharge potential and current efficiency. With the current density increasing, the release hydrogen rate augmented. The current efficiency reached 82 % at 20mA/cm2. The main composition of the corrosion products were MgO and Al2O3 which were easily peeled off. As a result, more negative and stable work potential was produced and the reaction was accelerated continuously.

Molybdenum nitride based hybrid cathode for rechargeable lithium–O2 batteries

Molybdenum nitride/nitrogen-doped graphene nanosheets (MoN/NGS) are synthesized and used as an alternative O(2) electrode for Li-O(2) batteries. In comparison with electrocatalysts proposed previously, this hybrid cathode exhibits a high discharge potential (around 3.1 V) and a considerable specific capacity (1490 mA h g(-1), based on carbon + electrocatalyst).

Fabrication and Electrochemical Characteristics of LiFePO<sub>4</sub> Powders for Lithium-Ion Batteries

Novel powder fabrication technologies provide opportunities to develop high-performance, low-cost cathode materials for rechargeable lithium-ion batteries. Among various energy storage technologies, rechargeable lithium-ion batteries have been considered as effective solution to the increasing need for high-energy density electrochemical power sources. Rechargeable lithium-ion batteries offer energy densities 2–3 times and power densities 5–6 times higher than conventional Ni-Cd and Ni-MH batteries, and as a result, they weigh less and take less space for a given energy delivery. However, the use of lithium-ion batteries in many large applications such as electric vehicles and storage devices for future power grids is hindered by the poor thermal stability, relatively high toxicity, and high cost of lithium cobalt oxide (LiCoO2) powders, which are currently used as the cathode material in commercial lithium-ion batteries. Recently, lithium iron phosphate (LiFePO4) powders have become a favorable cathode material for lithium-ion batteries because of their low cost, high discharge potential (around 3.4 V versus Li/Li+), large specific capacity (170 mAh/g), good thermal stability, and high abundance with the environmentally benign and safe nature. As a result, there is a huge demand for the production of high-performance LiFePO4 powders. However, LiFePO4 also has its own limitation such as low conductivity (∼10−9 S/cm), which results in poor rate capability. This can be addressed by modifying the powder structure using novel fabrication technologies. This paper presents an overview of recent advances in the fabrication of high-performance LiFePO4 powders for lithium-ion batteries. The LiFePO4 powder fabrication methods covered include: solid-state synthesis, mechanochemical activation, carbothermal reduction, microwave heating, hydrothermal synthesis, sol-gel synthesis, spray pyrolysis, co-precipitation, microemulsion drying, and others. The impacts of these fabrication methods on the structure and performance of LiFePO4 powders are discussed. In addition, the improvement of the conductivity of LiFePO4 powders through novel powder technologies is addressed.

Reconstructing morphological and depositional characteristics in subsurface sedimentary systems: An example from the Maastrichtian–Danian Ormen Lange system, Møre Basin, Norwegian Sea

Understanding large-scale sediment distribution patterns and morphological characteristics in subsurface sedimentary systems is highly challenging and generally requires regional seismic and well coverage. Here, we test a method that aims to predict first-order morphological characteristics and type of sedimentary transport system in ancient source-to-sink systems based on trends observed in submodern (Pliocene–Holocene) depositional environments. An example from the Paleocene Ormen Lange system (More Basin, Norwegian Sea) demonstrates the application of the method, and several descriptive parameters are estimated for this ancient subsurface system. In the Ormen Lange system, basin-floor fan and distal-slope parameters are well constrained from seismic and well control. However, knowledge of the morphology and relationships between upper slope, shelf, and catchment characteristics and their relationships to deep-water systems is poor, and these are the parameters that are discussed in this study. Estimated parameters of catchment size derived from this technique are in good agreement with preserved remnants of fluvial valleys located onshore. Predicted sediment transport characteristics are also comparable to the depositional mechanisms interpreted from cores and well logs, suggesting a small tectonically active system with high fluvial discharge and low sediment storage potential in the catchment and shelf subenvironments. The discussed method is thus capable of predicting first-order segment characteristics in subsurface sedimentary systems with an uncertainty of one to two orders of magnitude. This information can be used to increase the understanding of unexplored basins or to add data and uncertainty ranges to well-known petroleum systems.

Mechanochemical Synthesis of Carbon Fluorides

Synthesis of electrochemically active carbon fluorides was achieved through the high-energy milling of graphite or carbon black with CoF 3 at room temperature. The carbon fluorides were characterized by elemental analysis, X-ray diffraction, IR, and X-ray photoelectron spectroscopy. The results for the carbon fluoride powder prepared from graphite are reported here. This material, with the formula C 1.6 F, appears to have both semi-ionic and covalent CF bonds and demonstrates many of the characteristics of low-temperature carbon fluorides. The material has a high discharge potential of 3.2 V vs Li/Li + and a discharge capacity in the range of 450-500 mAh/g to 2.0 V.

Influences of the substitution of Fe for Ni on structures and electrochemical performances of the as-cast and quenched La 0.7Mg 0.3Co 0.45Ni 2.55− xFe x ( x = 0–0.4) electrode alloys

In order to improve the cycle stability of the La–Mg–Ni system PuNi 3-type hydrogen storage electrode alloys, Ni in the alloy was partially substituted by Fe. The La 0.7Mg 0.3Co 0.45Ni 2.55− x Fe x ( x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the substitution of Fe for Ni on the structures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results of the electrochemical measurement indicate that the substitution of Fe for Ni obviously decreases the discharge capacity, high rate discharge capability (HRD) and discharge potential of the as-cast and quenched alloys, but it significantly improves their cycle stabilities, and its positive impact on the cycle life of as-quenched alloy is much more significant than on that of the as-cast one. The microstructure of the alloys analyzed by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure which is composed of two major phases (La, Mg)Ni 3 and LaNi 5 as well as a residual phase LaNi 2. The substitution of Fe for Ni helps the formation of a like amorphous structure in the as-quenched alloy. With the increase of Fe content, the grain sizes of the as-quenched alloys significantly reduce, and the lattice constants and cell volumes of the alloys obviously increase.

Synthesis and physicochemical properties of LiAl 0.05Mn 1.95O 4 cathode material by the ultrasonic-assisted sol–gel method

Spinel LiAl 0.05Mn 1.95O 4 has been successfully synthesized by a new ultrasonic-assisted sol–gel (UASG) method. The structure and physicochemical properties of this as-prepared powder compared with the pristine LiMn 2O 4 and LiAl 0.05Mn 1.95O 4 synthesized by the traditional sol–gel method were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), and galvanostatic charge–discharge testing in detail. The results show that all samples have high phase purity, and ultrasonic process plays an important role in controlling morphology; LiAl 0.05Mn 1.95O 4 has higher Mn oxidation state, and the absorption peak of Mn(III) O and Mn(IV) O bonds has blue shift because of the doped Al. CV confirms that the LiAl 0.05Mn 1.95O 4 sample (UASG) has a good reversibility and its structure is very advantageous for the transportation of lithium ions. The charge–discharge tests indicate that LiAl 0.05Mn 1.95O 4 (UASG) has nearly equal initial capacity with LiMn 2O 4 (sol–gel) at 1 C discharge rate, but LiAl 0.05Mn 1.95O 4 (UASG) has higher discharge potential than that of LiMn 2O 4 (sol–gel). In addition, LiAl 0.05Mn 1.95O 4 (UASG) has higher discharge potential and capacity than that of LiAl 0.05Mn 1.95O 4 (sol–gel) at 1 C discharge rate, and LiAl 0.05Mn 1.95O 4 (UASG) has high capacity retention at C/3 and 1 C discharge rate among three samples after 50 cycles, which reveals that the sample obtained via UASG method, has the best electrochemical performance among three samples.

Surface modification of nickel hydroxide particles by micro-sized cobalt oxide hydroxide and properties as electrode materials

Surface modification of nickel hydroxide particles by directly coating micro-sized cobalt (III) oxide hydroxide was studied. The XRD and SEM characterized the structure and morphology of surface coatings. The surface coating had a beta-phase rhombohedral structure with a space group of R3m. The electrochemical properties of coated and uncoated nickel hydroxide electrodes were investigated and compared. The results showed that the nickel hydroxide modified by 3–5 wt.% cobalt (III) oxide hydroxide coatings with a sheet-like structure exhibited high utilization, discharge potential, rate-capacity properties and cycling durability.

Structure and Electrochemical Performance of Mn-substituted Nickel Hydroxide

The Mn-substituted Ni(OH)(2) samples were prepared by a coprecipitation method, and their structure was characterized by X-ray diffraction (XRD). Their electrochemical performance was also investigated by various electrochemical techniques. The results of XRD indicated that the Ni(OH)(2) samples with Mn contents less than 20% mainly consist of beta-phase, and the sample with a pure a structure can be obtained when the Mn content reaches 28.3%. The results of the electrochemical experiments showed that the Mn-substituted Ni(OH)(2) samples manifest high electrochemical cycling stability, and the samples with lower manganese contents exhibit larger discharge capacity and higher discharge potential. It was also found that the doping of Mn obviously increases the oxygen evolution potential and leads to the formation of proton deficiency.

Cathodic performance of VOPO 4 with various crystal phases for Li ion rechargeable battery

Cathodic performance of six different VOPO 4 phases for Li ion rechargeable battery was investigated. It was found that VOPO 4 exhibits a high flat discharge potential of 3.7 V for Li ion electrochemical intercalation and de-intercalation excepting for β- and ε-types. On the other hand, slightly higher flat discharge potential of 3.9 and 3.8 V was observed for β- and ε-types. Capacity for Li intercalation is strongly related with the crystal structure of VOPO 4. In particular, δ-phase exhibits the largest reversible capacity of ca. 130 mAh/g among the examined VOPO 4. High capacity for Li intercalation in δ-phase VOPO 4 hardly decreased over 30 times of charge and discharge cycles. Although the reversible capacity decreased with increasing the current density for charge and discharge, large capacity of 80 mAh/g was still sustained at 0.4 mA/cm 2 for δ-type VOPO 4.

First Principles Study of H-insertion in MnO2

We present an extensive First Principles study on proton intercalation in the pyrolusite and ramsdellite forms of MnO2. It is shown that protons are always covalently bonded to an oxygen atom in MnO2. In ramsdellite, the proton prefers the pyramidal oxygen to the planar coordinated oxygen as that site is farther away from the Mn cations. In both pyrolusite and manganite, the octahedral sites are unstable, but the two local minima on each side of the octahedron are connected by a barrier of only about 25 meV, so that protons may rapidly exchange between these sites. Proton diffusion in pyrolusite occurs by hopping along the 1×1 open tunnels with an activation barrier that increases from about 575 meV at the beginning of discharge to about 1eV at high H concentration. Diffusion in ramsdellite takes place along the 2×1 open tunnels and occurs with much lower activation energy (respectively, 200 and 400 meV, at low and high H concentrations). Introduction of twinning defects has a large adverse effect on the proton diffusivity. Results indicate that direct H–H interactions are not that significant compared to oxygen-mediated-interactions. Experimental and calculated ramsdellite discharge curves deviate significantly at early stages of the reduction process. The calculations on defected structures indicate that a significant source of this discrepancy may be due to presence of proton-compensated Mn vacancies in real MnO2, which create local sites with higher discharge potential. The calculations suggest that the ordered phase, observed in experiments at mid-reduction (groutellite, MnOOH0.5), is due to the lattice remaining coherent during intercalation.

Preparation and electrochemical characteristics of a new Li-Mn-V-O system formed from heat-treatment of a MnO2, NH4VO3 and LiNO3 mixture

New quarternary oxides (Li2O) x · MnO2 · yV2O5 (x = 0.125 ∼ 0.25, y = 0.125 ∼ 0.25), formed by heating mixtures of MnO2, NH4VO3 and LiNO3 at various Li/Mn and V/Mn atomic ratios and at different temperatures (300 ∼ 400 °C in air, have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy (ESCA) and infrared spectroscopy. The quarternary oxide with x = 0.25 and y = 0.25 showed a discharge capacity of 220 A h (kg oxide)−1 and an energy density of ca. 600 W h (kg oxide)−1 at a current density of 0.20 mA cm−1 in 1 m LiClO4-propylene carbonate at 25 °C. When charge-discharge cycling with the (Li2O) · MnO2 · 0.25V2O5 electrode was performed at a constant capacity of 30 A h (kg oxide)−1 and at a constant current density of 0.10 0.20 mA cm−2, the electrode sustained over 100 cycles at a high mean discharge potential of ca. 3 V vs Li/Li+.

Polycarbofluorides for lithium sources of current with nonaqueous electrolyte

Fluorinated carbon used as a cathode substance in lithium cells with a high and stable discharge potential is of great practical and theoretical importance. Its electrochemical activity has been reported earlier [l-3] to be determined in many respects by the nature of fluorinated substance, degree of fluorination, particle size and crystal lattice parameters. The latter two factors are of paramount importance and can be controlled in technological conditions of fluorination. We have studied 25 types of fluorocarbon substances which differ both in nature, initial substances and the conditions of fluorination.

Preparation and electrochemical characteristics of new LiMnVO system as positive materials for rechargeable lithium batteries

New quaternary spinels, Li n Mn 2O 4·χV 2O 5 ( n=0.5–1.5, x=0–0.7), which were formed by heating mixtures of MnCO 3, NH 4VO 3 and LiNO 3 at various Li:Mn and V:Mn atomic ratios and at different temperatures (300 to 400 °C) in air, have been characterized by X-ray diffraction method, X-ray photoelectron spectroscopy (ESCA) and infrared spectroscopy. The amount of Li + ions inserted into the crystal lattice of the quaternary oxide by using an electrochemical method increased with decreasing n-value and reaches ∼2Li/mole of the oxide at n=0.5 in Li n Mn 2O 4·0.5V 2O 5. But the amount of Li + ions inserted into several LiMn 2O 4·χV 2O 5 (χ=0.25–0.7) with different x-values were almost constant, being ∼2Li/mole of the oxide, which is double of that for ternary spinel LiMn 2O 4 not containing V 2O 5. When the charge/discharge cyclings with the Li n Mn 2O 5·0.5V 2O 5 electrode were performed in the n-value range between 0.5 and 0.8 and at a current density of 0.20 mA cm −2, the electrode could be cycled over 50 cycles at a high mean discharge potential ∼3.5 V versus Li/Li +.