Charge Curves Research Articles

High Sulfur Loading of Cathodes for Li-S Batteries

Lithium sulfur batteries have attracted the most attention owing to their high energy density (2600Wh/kg), while the specific capacity and capacity retention of sulfur electrodes play a crucial role on increasing the energy density of lithium sulfur batteries. Many researches focus on the materials with very high specific capacity per gram of sulfur but very low sulfur content and cells with very low sulfur loading of cathodes [1-3]. In this work, the cells with much higher sulfur loading of electrodes (4.34mg S/cm2, named as S-L and 7.24mg S/cm2, named as S-H) show better electrochemical performance.Fig. 1(a) shows the first discharge/charge potential curves of lithium sulfur batteries with S-L and S-H as cathodes. Two plateaus (about 2.35V and 2.10V) in the discharge curve and one plateaus (about 2.20-2.40V) in the charge curve are observed, which agree well with the previous work [4]. Comparison of cycling performance between S-L and S-H cathode was shown in Fig. 1(b). S-L cathode shows an initial specific capacity of 845mAh/g at 50mA/g between 1.50-2.80V, which exhibits a discharge capacity of 763mAh/g after 45 cycles with a capacity retention of 90.3%. Moreover, the cell with S-H cathode delivers 836mAh/g and 754mAh/g at the first cycle and the 25th cycle, respectively. The excellent electrochemical performance of high sulfur loading of electrodes makes the development of high energy Li-S batteries possible.Fig. 1 (a) The first discharge/charge potential curves of lithium sulfur batteries with S-L and S-H as cathode between 1.50-2.80V; (b) Comparison of cycling performance between S-L and S-H cathode.Reference:[1] F. F. Zhang, X. B. Zhang, Y. H. Dong, L. M. Wang, J. Mater. Chem., 2012, 22, 11452.[2] S. Evers, L. F. Nazar, Chem. Commun., 2012, 48, 1233.[3] G. Zheng, Y. Yang, J.J. Cha, S. S. Hong, Yi Cui, Nano Lett., 2011, 11, 4462.[4] L. Xiao, Y. Cao, J. Xiao, B. Schwenzer, M. H. Engelhard, L. V. Saraf, Z. Nie, G. J. Exarhos, J. Liu, Adv. Mater., 2012, 24, 1176.

Effect of Current Density on the Heat Generation of Lithium-Sulphur Batteries during Charge and Discharge

The investigations of thermal effects of charging, discharging and storage of batteries is important to solve the fundamental and applied problems of energy conversion in electrochemical systems. They are especially significant to develop and design batteries on the base of electrochemical systems with high energy density (for example Li-S).The thermal effects of charging and discharging batteries include several components: (1) the thermal effects of the electrochemical reactions, (2) the thermal effects of the processes accompanying the electrochemical reactions, (3) Joule heat.In contrast to the batteries with solid active materials (Li-Ion batteries) when lithium-sulphur batteries charging and discharging the complex multistep processes occur and include:- the electrochemical reactions;- the chemical reactions (corrosion, disproportion reactions of lithium polysulphides);- the reactions of solvation/desolvation and complexing of lithium polysulphide generated in solutions;- the phase transformations (dissolution, precipitation, sorption, desorption).All these processes effect on the efficiency of conversion chemical energy to electrical in lithium-sulphur batteries.When changing of conditions of charge/discharge cycling of lithium-sulphur batteries the contribution of different process are changing therefore energy conversion efficiency can be increased or reduced. The effect of current density on the heat generation of lithium-sulphur batteries was studied in this work by special designed and built instrument “Electrochemical calorimeter”The Electrochemical calorimeter simultaneously records thermal and electric characteristics of planar cells under/without polarisation. The instrument includes calorimetric block, potentiostat and control block. The measurements of thermal effects are carried out in isoperibol mode. The accuracy of temperature stabilization is ± 5∙10-4K. The temperature range is -20 – +90 °C. The measurement accuracy of heat flow is 50 µW.The relative error of current stabilization is 0.1 %. The voltage measurement error is 10 μV.The test objects were the lithium-sulphur pouch cells. Lithium foil (99.9%) with a thickness of 100 μm was used as negative electrodes. The working electrodes were sulphur electrodes (70% of Sulphur, 10% of Carbon and 20% of poly(ethylene oxide)). One layer of micro porous membrane Celgard 3501 was used as a separator. The electrolyte was 1M solution of LiCF3SO3in sulfolane.To get reproducible results 10 form cycles were done before study of influence of current density on the heat generation of the lithium-sulphur cells.The study shows that the shape of curves of heat generation is similar in the investigated range of current density (Fig.).When charging the lithium-sulphur cells there are few characteristic segments at the curve of heat generation. I. At the initial stages of charging (Q< 30 mAh g-1(S)) there is a maximum of heat generation and it is linear increasing with the current density increase. For the same charge state there is a maximum of overvoltage at the charging curves and it is also increasing with the current density increase. It allows concluding that this maximal of heat generation is caused by Joule heat. II. The voltage and heat generation is continuously increasing with the further charging of lithium-sulphur cell (low voltage plateau). III. There is a minimum at the curve of heat flow and it corresponds to the transition between low and high voltage plateau. This minimum is increasing with current density increase. IV. The heat generation of lithium-sulphur batteries is much greater at the high voltage plateau of charging curve than at the low voltage curve. It should be noted it is linear increasing with current increase.The shapes of heat generation are different at charging and discharging of lithium-sulphur cell (Fig.). The heat generation curve can be divided in several characteristic segments (Fig. d): I. At the initial stage of discharging the intensive heat generation is observed. Its fast decrease correlates to reducing of overvoltage at the discharging. II. There is a maximum at the heat generation curve corresponding to the high voltage curve of discharging. This maximum is linear increasing and shifting to the large discharge capacity with current density increase. III. At the transition between high and low voltage plateau at discharge curve there are two inflections at the heat generation curve. They are also shifting to the higher discharge capacity with increasing of current density. IV. The heat generation of lithium-sulphur cell changes insignificantly at the low voltage discharge curve. The overvoltage and the heat generation increase with current density increasing.Also it should be noted that heat generation is greater at discharging of lithium-sulphur cell then at charging.The analysis of data shows that there are maximum at the dependences of efficiency of energy conversion on the current density for charging and discharging of lithium-sulphur batteries. The current density affects stronger on the efficiency of energy conversion at charging than at discharging (especially for high voltage plateau). The reported study was partially supported by RFBR, research projects No 13-00-14056 and 14-03-31399.

Electrochemical performance of All-Solid-State Lithium-Oxygen Batteries

Introduction The lithium-air batteries have attracted much more attentions because of its high theoretical energy density, which is over 3500 Wh kg-1. However the lithium-air batteries still have a lot of problems and the problem related with the decomposition of organic liquid electrolytes is the most serious and one of the main research topics in the present stage. Thus, we have developed all-solid-state lithium-air batteries using the inorganic solid electrolytes, which are more stable than the liquid electrolytes. The application of the solid electrolytes to the lithium-air batteries can solve not only the decomposition of electrolytes but also the safety problem and some other problems specific to the liquid such as leakage and volatilization. In this study, an all-solid-state cell consisting of Li anode, Li1+xAlyGe2-y(PO4)3 (LAGP) solid electrolyte, and LAGP-carbon nanotube (CNT) composite cathode was operated in the pure oxygen atmosphere (so-called Li-O2 cell) and the fundamental electrochemical performance was examined. Experimental The all-solid-state Li-O2 cells were fabricated. The LAGP solid electrolyte was synthesized by the conventional solid-phase method. The air electrode was composed of LAGP and multi-walled CNT particles. The composite electrode was fabricated on the LAGP pellet by sintering and Li anode was fused on another side of the LAGP pellet. Li anode was sealed by the plastic film. The cell was put into the bottles connecting to the oxygen gas flow channel. Results and discussion The electrochemical properties of the solid-state lithium-oxygen battery were examined. First of all, the potential for the electrochemical reactions in the Li / LAGP / LAGP-CNT-O2 cell was investigated using cyclic voltammetry (CV) as shown in Fig. 1a. The measurement was conducted at a scan rate of 10 mV s-1 at room temperature in the O2 atmosphere. The cell showed the cathodic peak at the potential less than 3 V and anodic peak between 3.1 V and 4.0 V. Then the cell was discharged and charged under the constant current density of 10 mA g-1 in the voltage range of 2.0 - 4.8 V at room temperature (Fig. 1b). The cell showed the voltage of 2.4 V at the beginning of discharge and then the discharge voltage gradually decreased to 2.0 V. The discharge capacity was about 1420 mAh g-1 and the recharge capacity of about 1130 mAh g-1 was obtained in the cell charged up to 4.8 V. It is noteworthy that the charge process starts from 3.0 V and proceeds in the voltage below 4.2 V. This voltage profile in the constant current condition matches the result obtained by CV measurement.Fig. 1c shows the cycle performance under the current density of 10 mA g-1 at room temperature in the voltage region of 1.6 - 4.8 V. The measurement was conducted with the capacity limit of 500 mAh g-1. Although the discharge voltage decreased with the cycling, the discharge capacity was retained during 10 cycles. The charge capacity was smaller than the discharge capacity and efficiencies of all cycles were 80 ~ 90 %. It results in increasing the amount of remained discharge products after charging, which would caused the decrease of the discharge voltage with cycling.The redox potentials in the all-solid-state Li-O2 cells are consistent with the potentials for the oxygen reduction reaction and oxygen evolution reaction reported by many researchers. Especially, the cell using the glyme electrolyte, which are well-known as relatively stable liquid electrolytes, shows similar CV results [1]. In addition, the all-solid-state cell showed the repeatedly same charge curve and the rise at the end of the charging. It means that the continuous decomposition of electrolyte and electrode materials does not occur in this voltage region. Therefore, it can be stated that the solid electrolyte is quite stable in the all-solid-state Li-O2 cells.

Anomalous Voltage Change in Charge and Discharge Curves for Electrode Materials Showing Plateau-like Behavior

Recently T. Sasaki et al. 1 reported on a phenomenon of an anomalous voltage change that occurs when electrode materials showing a plateau-like behavior (during charge/discharge) are partially charged and/or discharged. They studied the anomalous voltage change in lithium iron phosphate (LiFePO4) as well as in lithium titanate (Li4Ti5O12). The anomalous voltage change was referred to as ‘voltage bump’ which appears already after only one cycle of partial charge and discharge. The voltage bump was explained in connection to a particle-by-particle charge/discharge model. The reported electrochemical tests were performed at room temperature in two-electrode coin-type or three-electrode cells with Li-metal as reference and counter electrode (half cell).In this work, partial charge/discharge experiments (Fig. 1) were used to study the effect of temperature on the anomalous voltage change. The investigations were carried out on commercially available large-format cells based on LiFePO4/graphite system (full cell). Increasing the number of partial cycles leads to an interference of single voltage bumps, but the voltage rise was observed to saturate at a given voltage level (Fig. 2). An increased voltage bump was observed at smaller temperature, while an opposite effect was obtained at higher temperature (Fig. 2). Resulting voltage bumps in the range of up to 20 mV were observed, depending on temperature. The observed behavior is discussed in view of the particle-by-particle model and kinetic effects. Such a slight voltage change can lead to substantial miscalculations in estimating the state of charge of cells and batteries. 1Tsuyoshi Sasaki, Yoshio Ukyo, Petr Novák, Nature Materials, published online: 14 April 2013, DOI: 10.1038/NMAT3623.

Microwave (MW) Assisted Electro-Active Tempo Functionalized Single Walled Carbon Nanotube (SWNT) Electrodes for Li-Ion Batteries

The ever-increasing demand for high-performing, light weight, economical, and safe power storage for high–tech portable devices and electric vehicles leads to augmented research efforts in the field of organic or organic/hybrid materials for energy storage devices.With the aim of performing a balance between battery (charge producing system) and capacitor (charge storing system), Carbon Nanotubes (CNTs) can work as a template that can be functionalized with stable electro-active redox group. Since both capacitors and batteries can provide limited usability, an electrode material that hosts both properties will be more rewarding for the development of battery technology. Owing to the electrical and physical properties, CNTs are challenging material for the energy storage devices. There are some noticeable works about producing Carbon Nanotube thin electrodes to fabricate paper battery [1-3]In the light of these investigations, rapid microwave (MW) assisted functionalization of Single Walled Carbon Nanotubes (SWNTs) with electro-active TEMPO group was successfully performed with one step nitrene insertion reaction without using any harshly oxidative methods which are uncontrollable and destructive for SWNT. Their role of Functionalized SWNT samples (f-SWNTs) were characterized as a host for Li storage and their performance as electro-active cathode material were investigated.f-SWNTs were easily dispersed in solvents and they can form stable dispersions during 1 month where as non-functionalized SWNTs coagulate immediately. This can be considered as an indication of a successful surface functionalization. Depending on the degree of functionalization of SWNTs (without losing its electrical properties) their dispersibility in H2O and NMP (N-Methyl-2-pyrrolidone) and free standing paper electrode forming possibilities increase (Fig.1). Output Open Circuit Voltage (O.C.V) of cells with SWNT and functionalized SWNT (f-SWNT) samples changes between 2.5-3.0V vs. Li metal. The Cyclic Voltammetry study of the TEMPO functionalized f- SWNT 1 sample vs. Li metal is seen in Fig. 2.The constructed 2016-size button cell of f-SWNT 1 displayed an initial specific capacity of 441 mAh/g which decreased to 127 mAh/g in the second cycle of charge- discharge (Fig. 3). This large first cycle irreversible capacity loss could be attributed to various causes such as the irreversible reduction of oxygenated functional groups that may be originally present on the CNT surface as well as the attached nitroxide radical functional group to its amine oxide form. This electrochemical reduction was known to be an irreversible process in non-aqueous carbonate electrolyte systems and may be responsible for the reduction in the charge capacity. In the fifth cycle it dropped to 54 mA/g and after tenth and fifteenth cycles this value was reduced to 35 and 28 mAh/g, repectively. The reversibility of nitroxide radical group of TEMPO under basic conditions may provide an opportunity for battery systems which is under investigation.The f-SWNT 1 was subjected to charge and discharge cycles between 3 and 4V vs. Li (Figure 4). The charge curve plateau between 3.6 and 3.7 V can be ascribed to irreversible electrochemical oxidation of nitroxide radicals to oxoammonium species. The charging capacity suddenly faded from 140 mAh/g to 20 mAh/g in 15 charge discharge cycles.

The Electrochemical Properties of Low-crystallinity TiO2(B)-Carbon Composite as an Anode Material in Lithium Ion Battery

We have prepared two types TiO2(B)-carbon composites from Lepidocrocite-type compounds (K0.86Li0.26Ti1.72O4) heated at 700 and 900°C under presence of carbon nanotube (CNT) and glucose as carbon sources. The XRD data shows that it contains a single phase of TiO2(B) and the existence of carbon was confirmed by Raman spectra. TEM image confirms that TiO2(B) primary particles and carbon nanotube are scattered randomly and contact tightly in the composite. Carbon content in the composite was found to be 5 - 8% and CNT is the major carbonaceous material. The charge and discharge curves of TiO2(B)-carbon composite prepared from precursor heated at 700°C resemble with that of amorphous TiO2. The calculated discharge capacity of the composite is 323mAhg−1 at a cut off voltage of 0.9V, which is higher than that of bare TiO2(B). It is suggested that the electrochemical performance of this material is strongly influenced by both the operating temperature and cut off voltage. The discharge capacity can reach 198mAhg−1 at 4.5C rate at a cut off voltage 1.3V and the coulombic efficiency is over 99.8% after 10th cycles.

Potentiometry up to 275 °C: Example of pH titrations of cobalt ferrite particles

HypothesisHigh temperature potentiometry (or pH-metry) is needed for specific hydrothermal applications such as acid–base titration of metallic oxides particles to predict their reactivity toward dissolved species, or to describe the surface charge mechanisms. We present here a specific set-up, operational up to 300°C, H2-free and compatible with oxidizing conditions. ExperimentsAn autoclave in Hastelloy with a zirconia pH probe has been used to titrate a suspension of cobalt ferrite (CoFe2O4), a typical corrosion product found in cooling circuit, up to 275°C. The technical choices of autoclave material and pH probe type were based on the objective of a high versatility of the set-up. Thus, reducible particles can be titrated thanks to the absence of H2 required in hydrogen electrode, and higher temperatures than those possible using Teflon-lined autoclaves can be reached. FindingsThe charge vs. pH curve has been determined at 120, 200 and 275°C and was found to be consistent with a surface complexation model (1-pK/constant capacitance model). To model the curves, the values of point of zero charge previously determined by mass titration were used and the capacitance was the only adjustable parameter. Its value was found to increase from 0.27 to 0.42Fm−2, from 25°C to 200°C, respectively, then decrease to 0.25Fm−2 at 275°C. These results show the possibility of such a set-up to determine chemical properties of mineral–solution interfaces or any else properties of aqueous fluid at elevated temperature.

Data-driven method based on particle swarm optimization and k-nearest neighbor regression for estimating capacity of lithium-ion battery

Reliability of lithium-ion (Li-ion) rechargeable batteries used in implantable medical devices has been recognized as of high importance from a broad range of stakeholders, including medical device manufacturers, regulatory agencies, physicians, and patients. To ensure Li-ion batteries in these devices operate reliably, it is important to be able to assess the battery health condition by estimating the battery capacity over the life-time. This paper presents a data-driven method for estimating the capacity of Li-ion battery based on the charge voltage and current curves. The contributions of this paper are three-fold: (i) the definition of five characteristic features of the charge curves that are indicative of the capacity, (ii) the development of a non-linear kernel regression model, based on the k-nearest neighbor (kNN) regression, that captures the complex dependency of the capacity on the five features, and (iii) the adaptation of particle swarm optimization (PSO) to finding the optimal combination of feature weights for creating a kNN regression model that minimizes the cross validation (CV) error in the capacity estimation. Verification with 10years’ continuous cycling data suggests that the proposed method is able to accurately estimate the capacity of Li-ion battery throughout the whole life-time.

A facile method to prepare bi-phase lithium vanadate as cathode materials for Li-ion batteries

Bi-crystal lithium vanadate is synthesized with starting materials of V2O5 and LiF by one-step solid-state reaction. Since fluorine reacts with crucible made of silica, Li0.3V2O5-liked and LiV3O8-liked phases without F coexist in the produces. The stoichiometric proportion of two phases depends on the amount of dopant LiF. These are confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and transmission electron microscopy (TEM). Charge and discharge curves of bi-crystal materials present better reversibility of voltage plateaus than that of pure V2O5. The initial discharge capacity of Li0.3V2O5-liked phase dominated bi-crystal material is higher than pure V2O5. LiV3O8-liked phase dominated bi-crystal material has lower initial discharge capacity but delivers better cycling performance. Electrochemical impedance spectroscopy (EIS) measurements are performed to evaluate electrochemical kinetics of the bi-crystal materials. The results indicate that bi-crystal phase benefit the transfer resistance, interior diffusion resistance, and structure stability. Cathodes with different bi-phase structures have variable charge transfer resistance and lithium-ion diffusion speed due to this special structure.

Synthesis and electrochemical behavior of LiFePO4/C with an air–electrode in an aqueous lithium ion battery

This study investigated the intercalation of lithium ions for carbon-coated LiFePO4 (LiFePO4/C) in an aqueous rechargeable lithium-ion battery. LiFePO4/C was obtained using a sol–gel method, with citric acid as the chelating agent. The phase structures and morphologies confirmed the orthorhombic crystal structure of LiFePO4 surrounded by the carbon layer. The electrochemical behavior of LiFePO4/C vs. an air–electrode as the counter electrode was investigated in a 5M LiNO3 solution. The well-defined flat plateaus in the charge and discharge curves showed that the intercalation of lithium ions and the reduction of oxygen occurred simultaneously within the electrochemical stability window of water. The LiFePO4/C system showed good rate capabilities even at a higher current density (5C) with a small capacity loss. The rate capability of the LiFePO4/C system was also compared with the rate capability of a platinum counter electrode; the air–electrode still showed better cycling behavior.

Truly wearable display comprised of a flexible battery, flexible display panel, and flexible printed circuit

AbstractIn an effort to create a truly flexible and wearable display having a flexible battery as well as a flexible organic light‐emitting diode panel and a flexible printed circuit, a flexible lithium‐ion battery has been developed, and a prototype wrist‐wearable or arm‐wearable display has been fabricated. Owing to improvements in the internal structure and exterior of the lithium‐ion battery, no remarkable changes in charge and discharge curves and the internal state of the electrodes were observed even after conducting a 10,000‐cycle bending test. Therefore, this flexible lithium‐ion battery prototype demonstrated remarkable bending resistance. Thus, we succeeded in fabricating a truly flexible and wearable display comprised of a flexible organic light‐emitting diode panel, a flexible printed circuit, and a flexible battery.

Enhanced electrochemical performance of LiMnPO4 by Li+-conductive Li3VO4 surface coatings

By a simple wet ball-milling method, Li3VO4-coated LiMnPO4 samples were prepared successfully for the first time. The thin Li3VO4 coating layer with a three-dimensional Li+-ion transport path and high mobility of Li+-ion strongly adhered to the LiMnPO4 material reduces Mn dissolution and increases the Li+ flux through the surface of the LiMnPO4 itself by preventing formation of phases on the surface that would normally block Li+ as well as Li+-ion permeation into the surface of the LiMnPO4 electrode and therefore improve the rate capability as well as the cycling stability of LiMnPO4 materials. The electrochemical testing shows that the 5% Li3VO4-coated LiMnPO4 sample shows a clear voltage plateau in the charge curves and a much higher reversible capacity at different discharge rates compared with the pristine LiMnPO4. EIS results also show that the surface charge transfer resistance and Warburg impedance of the Li3VO4-coated LiMnPO4 samples significantly decreased. The surface charge transfer resistance and Warburg impedance for the pristine LiMnPO4 are 955.1Ω and 400.3Ω, respectively. While, for the 5% Li3VO4-coated LiMnPO4, the value are only 400.2Ω and 283.6Ω, respectively. The surface charge transfer resistance decreases more than half. All of the improved performance will be favorable for application of the LiMnPO4 in high-power lithium ion batteries.

The Calorimetric Study of Electrochemical Process in the Lithium-Sulphur Cells

The studies of thermal effects of cycling and storage of lithium-sulphur cells have significant value to development of energy storage systems on the base of new electrochemical systems with high specific energy. One of the most promising electrochemical systems is lithium-sulphur system.The mechanisms of electrochemical, physicochemical and chemical processes occurring in the lithium-sulphur cells during cycling significantly differ from the mechanisms of processes in lithium-ion cells. Electrochemical conversion of sulphur and products of its reduction is multi-step process including electrochemical and chemical reactions, also phase transformations (dissolution, precipitation, crystallization, sorption, desorption).To study of thermal effects of electrochemical cells we designed and built specialized instrument “Electrochemical calorimeter”. It simultaneously records thermal and electric characteristics of planar cells under polarisation. The instrument includes calorimetric block, potentiostat and control block. The measurements of thermal effects are carried out in isoperibol mode. The accuracy of temperature stabilization is ± 5∙10-4K. The temperature range is 253-363 K. The measurement accuracy of heat flow is 50 µW. The relative error of current stabilization is 0.1 %. The voltage measurement error is 10 μV.We studied the thermal effects of charging and discharging of the lithium-sulphur cells by designed instrument.The test subjects were the lithium-sulphur pouch cells. Lithium foil (99.9%) with a thickness of 100 μm was used as negative electrodes. The working electrodes were sulphur electrodes (70% of Sulphur, 10% of Carbon and 20% of poly(ethylene oxide)). One layer of micro porous membrane Celgard® 3501 was used as a separator. The electrolyte was 1M solution of LiCF3SO3in sulfolane.There are two maximums of heat generation during discharging of lithium-sulphur cell (Fig. 1). The first maximum has complex shape and correlates to the transition between high and low voltage plateaus of discharge curve. The second maximum is observed at the end of discharging.The comparison between curves of heat generation (Fig. 1c) and internal resistance (Fig. 1b) during discharging of lithium-sulphur cells makes it possible to conclude that first maximum is caused by polarization heat and Joule heat and thermal effects of chemical and electrochemical reactions. The second maximum is caused by the polarization heat and Joule heat.The heat flow curve correlated to the charging of lithium sulphur-cell (Fig. 2c) has more complex shape than the curve correlated to the discharging (Fig. 1c).The analysis of heat flow, internal resistance and charge curves allows to conclude that first maximum of heat generation is caused by the polarization heat and Joule heat. The heat absorption corresponding to the transition between high and low voltage plateaus of charge curve is possible to be caused by physicochemical and chemical process accompany the electrochemical oxidation of low ordered lithium polysulphides. The intensive heat generation is likely to be caused by chemical reaction of sulphur or high ordered lithium polysulphides and metallic lithium at the end of charging of lithium-sulphur cell.

Effects of Doping on XLi2MnO3•(1-x)LiNi1/3Mn1/3Co1/3O2 Prepared Via Spray Pyrolysis

LixMO2 (M= Mn, Ni, Co) materials with layered structures have received attention as high-capacity, low cost and safer cathode materials for lithium-ion batteries [1]. Various synthesis methods have been developed for the production of these materials, including co-precipitation, solid state synthesis and ball milling [2-4]. Recently a spray pyrolysis synthesis method has been developed by this group for producing cathode materials with porous morphologies [5]. Spray pyrolysis has certain advantages compared to other methods: the short residence time in the reactor allows large throughput; the process is scalable, no further post-synthesis purification steps are required, the product is inherently purified throughout the synthesis. Most importantly, each particle is synthesized with precise stoichiometry because each droplet behaves as a mini-reactor. This allows for accurate control of dopant levels in the product. The layered lithium-nickel-manganese-cobalt oxides, such as 0.5Li2MnO3•0.5LiNi1/3Mn1/3Co1/3O2 are known to demonstrate a voltage fade over cycling. This effect has been attributed to a layered-spinel transformation [6-7]. Many studies have suggested that voltage fade can potentially be eliminated via doping. Therefore, this study will focus on doping xLi2MnO3•(1-x)LiNi1/3Mn1/3Co1/3O2using trace level dopants and exploring their effects on voltage fade and cycling stability.Figure 1 shows a typical SEM result of lithium excess material prepared via spray pyrolysis, demonstrating the uniform and spherical morphology. Figure 2 compares the charge and discharge profile for xLi2MnO3•(1-x)LiNi1/3Mn1/3Co1/3O2 materials annealed at 900°C for 2 hours when x is 0.5 and less than 0.5. Voltage fade is typically observed as a shift in the charge and discharge curves as a result of the structural transformation [6]. It is clearly present for x=0.5 (black line in Fig.2), however the effect is almost overcome for lower x values. Initial results indicated a significant drop in capacity values, which are expected to be overcome by optimization of synthesis conditions. Figure 3 compares the cycling results of the materials with and without Al doping. The material doped with Al clearly demonstrates a better cycling stability after 100 cycles. The Al doped sample retains 99.4% of it’s capacity between cycle 5 and 100, compared to 91.5% for the undoped sample. Acknowledgements: The authors are grateful to the NSF and X-tend Energy LLC for support. RLA and Washington University may receive income based on a license of related technology by the University to X-tend Energy LLC.

Optimal charge control strategies for stationary photovoltaic battery systems

Battery systems coupled to photovoltaic (PV) modules for example fulfill one major function: they locally decouple PV generation and consumption of electrical power leading to two major effects. First, they reduce the grid load, especially at peak times and therewith reduce the necessity of a network expansion. And second, they increase the self-consumption in households and therewith help to reduce energy expenses. For the management of PV batteries charge control strategies need to be developed to reach the goals of both the distribution system operators and the local power producer. In this work optimal control strategies regarding various optimization goals are developed on the basis of the predicted household loads and PV generation profiles using the method of dynamic programming. The resulting charge curves are compared and essential differences discussed. Finally, a multi-objective optimization shows that charge control strategies can be derived that take all optimization goals into account.

Surface complexation modeling of arsenate adsorption by akagenéite (β-FeOOH)-dominant granular ferric hydroxide

A surface complexation model has been set up for the first time with akaganéite (β-FeOOH), a major compound of granular ferric hydroxide (GFH) used in groundwater purification units worldwide for arsenic and other toxic pollutant removal. Unlike the situation for the α-FeOOH polymorph goethite, there is yet no published surface complexation model to predict competing oxyanion effects. This is due to a linked bulk-surface reactivity by which excess protons released in an unknown amount from tunnel sites hamper quantification of surface protonation by acid titration. The measured proton uptake thus exceeds what can be expected from OH groups active in surface protonation. However, chloride ions are co-sorbed in 1:1 stoichiometry and co-released with the protons from tunnel sites albeit with slow kinetics. Because of this kinetics, dynamic acid-base titrations using automatic titrators are not feasible for reliable estimation of surface charge vs. pH curves. We propose to precisely monitor the chloride exchange during batch titrations with at least one day batch equilibration times. The thus obtained chloride data were used to correct for the pH-dependent bulk proton exchange and to reconstruct the true surface potential vs. pH curves, and thus to reliably parameterize a CD-MUSIC surface complexation model for arsenate adsorption.

Load shift potential of electric vehicles in Europe

Many governments highly encourage electric mobility today, aiming at a high market penetration. This development would bring forth an impact on the energy system, which strongly depends on the driving and charging behavior of the users. While an uncontrolled immediate charging might strain the local grid and/or higher peak loads, there are benefits to be gained by a controlled charging. We examine six European mobility studies in order to display the effects of controlled and uncontrolled unidirectional charging. Taking into account country-specific driving patterns, we generate for each country a charging load curve corresponding to uncontrolled charging and consider the corresponding parking time at charging facilities in order to identify load shift potentials. The main results are that besides the charging power of the vehicles, the possibility to charge at the work place has a significant influence on the uncontrolled charging curve. Neither national nor regional differences are as significant. When charging is only possible at home, the vehicle availability at charging facilities during the day for all countries is at least 24%. With the additional possibility to charge at work, at least 45% are constantly available. Accordingly, we identified a big potential for load shifting through controlled charging.

A novel bifunctional catalyst of Ba0.9Co0.5Fe0.4Nb0.1O3−δ perovskite for lithium–air battery

Ba0.9Co0.5Fe0.4Nb0.1O3 (BCFN) perovskite has been synthesized by a solid-state reaction method, and characterized by XRD, SEM, BET. This oxide has a porous structure and a specific surface area of 10.24 m2 g−1 after ball-milled 24 h. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the ORR mainly favors a direct four electron pathway, and a maximum cathodic current density of −5.70 mA cm−2 at 2500 rpm was obtained, which is close to that of Pt/C (20 wt.% Pt on carbon) electrocatalyst in the same testing conditions. Compared with behaviors of pure C and Pt/C electrode, a lower onset potential of BCFN for OER is observed, and a bigger anodic current at the same applied potential is obtained. Considering small surface area of the BCFN catalyst, a big overpotential is given in the discharge–charge curves. However, the outputs of 2032 coin Li–air batteries in a dry gas mixture composed of 80 vol.% pure N2 and 20 vol.% pure O2 demonstrated that BCFN could be a potential bifunctional catalyst for the Li–air battery.

Enhanced storage capability and kinetic processes by pores- and hetero-atoms- riched carbon nanobubbles for lithium-ion and sodium-ion batteries anodes

Efficient electrodes with impressive storage capability and fast kinetic processes are urgently needed in meeting the demand for high energy and large rate powering devices. Through a simple silica templated ionic liquids (ILs) impregnating method and an annealing process, nitrogen and oxygen co-doped carbon nanobubbles are synthesized. The fabricated carbon nanobubbles feature multiscale nanopores and abundant few-layer graphitic zones in the thin shells of several nanometers. When used as anodes for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), the nanobubbles not only exhibit excellent storage capability and rate performance, but also achieve enhancing cyclibility in the long-term cycles. Further analysis on the charging curves and the electrochemical impedance spectroscopy (EIS) reveal the enhancing cyclibility and storage capability might depend on the interfacial capacitance derived from quasi-connection between Li+ or Na+ and the hetero-atom evolving dissociative groups, while the superior rate performance might be attributed to the low interfacial charge-transfer resistance in the carbon nanobubbles electrode.

基于蒙特卡洛模拟的电动汽车充电负荷预测

本文主要对未来各类电动汽车大规模充电时所造成的电网负荷进行预测。基于现有中国电动汽车的发展趋势，根据用途不同，分为电动公交车、电动出租车、电动公务车、电动私家车；讨论不同类型电动汽车充电时对应的充电方式及充电时段，采用蒙特卡洛模拟法抽取起始荷电状态、起始充电时间；计算四种电动汽车的充电负荷，应用C++语言仿真模拟对应负荷特性曲线，并计算得到总体负荷曲线；通过分析曲线特征，总结未来电动汽车充电负荷主要影响因素，为电动汽车的充电设备建设提供指导型意见。 The charging load of a large number of electric vehicles is predicted in this paper. Based on the trends of electric vehicles in China, the electric vehicles are divided into electric buses, electric taxis, electric officer’s car and electric private car according to different use. The charging mode and time of different kinds of electric vehicles are discussed. The Monte Carlo simulation method is applied to determine the starting state of charge (SOC) and the initial charging point. The charging loads of four kinds of electric vehicles are calculated. The corresponding four charging curves and the total curves are obtained via simulation. Through analyzing the character of the curves, the influence factors of electric vehicles charging load in future are summarized and the suggestion for charging equipment building is provided.