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Novel colloidal pseudocapacitors are designed using commercially available MnCl2 salts as starting materials and KOH as electrolyte, where the colloids synthesis and subsequently integrating into practical electrode structures occur at the same spatial and temporal scale. Highly electroactive Mn7O13·5H2O colloids are formed in-situ by electric field assisted chemical coprecipitation in KOH solution. The highly efficient Faradaic redox reactions involving Mn3+ ↔ Mn4+ and Mn2+ ↔ Mn3+ are confirmed in electroactive Mn7O13·5H2O pseudocapacitors, which can deliver high specific capacitance of 2518 F/g based on active Mn cations at current density of 5 A/g. The present results show that instead of one-electron Faradaic reaction, Mn cations in our designed system can lead to two-electron Faradaic reactions. The colloidal pseudocapacitor system involving Mn-based colloids is a novel route to engineer electrochemical performances of inorganic pseudocapacitors.
Pyrrolidinium-based ionic liquids (ILs), such as PYR13TFSI, PYR14TFSI, and PYR1(2O1)TFSI, exhibit high thermal and electrochemical stability with wide electrochemical windows as electrolytes for application to rechargeable Li–O2 batteries. In this work, several fundamental properties of three ILs are measured: the ionic conductivity, oxygen solubility, and oxygen diffusion coefficient. The oxygen electro-reduction kinetics is characterized using cyclic voltammetry. The performances of Li–O2 batteries with these IL electrolytes are also investigated using electrochemical impedance spectroscopy and galvanostatic discharge–charge tests. The results demonstrate that the PYR1(2O1)TFSI electrolyte battery has a higher first-discharge voltage than the PYR13TFSI electrolyte and PYR14TFSI electrolyte batteries. Both PYR13TFSI- and PYR1(2O1)TFSI-based batteries exhibit higher first-discharge capacities and better cycling stabilities than the PYR14TFSI-based battery for 30 cycles. A theoretical analysis of the experimental results shows that the diffusion coefficient and solubility of oxygen in the electrolyte remarkably affect the discharge capacity and cycling stability of the batteries. Particularly, the oxygen diffusion coefficient of the IL electrolyte can effectively facilitate the electrochemical oxygen electro-reduction reaction and oxygen concentration distribution in the catalyst layers of air electrodes. The oxygen diffusion coefficient and oxygen solubility improvements of IL electrolytes can enhance the discharge–charge performances of Li–O2 batteries.
Mechanical stress is generated in electrode particles of a Lithium ion Polymer Battery (LiPB) during charge and discharge. The stress can cause cracks and fractures in the solid particles over time when cells are cycled, which leads to a disorder and a fracture of the electrodes. In order to understand the mechanism, a stress model for a pouch type high power LiPB is developed based on electrochemical and thermal model, where the stress induced by the ion concentration in the electrode particles is considered. The stress in the particles causes changes in the electrode volumes and leads to changes in the thickness of a battery cell, which is measured using a device designed with two linear voltage displacement transducers (LVDT). This model is validated against experimental data obtained from a pouch cell. Analysis shows that the magnitude of stress depends upon locations and C rate, while the thickness of a single cell is mainly affected by the state of charge (SOC), but not C rate.
The electrolytic conductivities and charge–discharge characteristics of lithium electrode are examined in propylene carbonate (PC)- and ethylene carbonate (EC) tetrahydrofurans, such as 2-methyltetrahydrofuran (2-MeTHF) and 2,5-dimethyltetrahydrofuran (2,5-DMeTHF), binary solvent electrolytes containing lithium bis[1,2-benzenediolato(2-)-O,O′]borate (LBBB), lithium bis[2,3-naphthalenediolato(2-)-O,O′]borate (LBNB), lithium bis[2,2′-biphenyldiolato(2-)-O,O′]borate (LBBPB) and lithium bis[salicylato(2-)]borate (LBSB). The order of specific conductivities in PC- and EC-based equimolar binary solutions containing these organoborates is LBBB≥LBNB>LBSB>LBBPB. The conductivity in LBNB electrolyte with higher viscosity than that in LBSB electrolyte becomes high. The PC–2-MeTHF and PC–2,5-DMeTHF equimolar binary solutions containing LBSB and a mixed electrolyte (LBBPB+LiPF6) show very high cycling efficiencies more than 90% at a higher range of cycle number. The EC–THF and EC–2-MeTHF equimolar binary solutions are moderate electrolytes with about 80% cycling efficiencies. It is found by using scanning electron microscope (SEM) that the films formed on the electrode in PC–2-MeTHF and PC–2,5-DMeTHF electrolytes with higher cycling efficiencies have a homogeneous surface with uniform grain size.
Electrochemical characteristics of spinel cubic LiFeTiO4 are evaluated through Density Functional Theory (DFT) study. Li+ intercalation/de-intercalation behavior of LiFeTiO4 is studied in accordance to the electrochemical relation; LiFeTiO4+Li → Li2FeTiO4 and LiFeTiO4−0.5Li → Li0.5FeTiO4 respectively. Effect of Li+ ion exchange on geometrical and electronic structure in terms of volume strain and density of states are respectively studied. It is found that there would be 4% volume strain in charge-discharge cycle accompanying 1.5 Li+ ions exchange per cycle producing high structural rigidity and hence electrochemical safety. The intercalation/de-intercalation voltages are estimated to be 2.6 V and 3.7 V respectively, and are in accordance with earlier experimental reports. The redox active couple corresponding to the intercalation reaction is identified to be Fe+3/Fe+2 while those corresponds to the de-intercalation reaction are identified to be Fe+3/Fe+(3+δ) and O−2/O−2+γ. The electrochemical capacity is estimated to be 230 mA h g−1 per cycle enabling 1.5 Li+ exchange.
A large variety of energy storage systems are currently investigated for using surplus power from intermittent renewable energy sources. Typically, these energy storage systems are compared based on their Power-to-Power reconversion efficiency. Such a comparison, however, is inappropriate for energy storage systems not providing electric power as output. We therefore present a systematic environmental comparison of energy storage systems providing different products. As potential products, we consider the reconversion to power but also mobility, heat, fuels and chemical feedstock. Using life cycle assessment, we determine the environmental impacts avoided by using 1 MW h of surplus electricity in the energy storage systems instead of producing the same product in a conventional process. Based on data for several countries including the United States, Brazil, Japan, Germany and the United Kingdom, our analysis determines the highest reduction of global warming and fossil depletion impact for using surplus power in heat pumps with hot water storage and battery electric vehicles. Third highest environmental benefits are achieved by electrical energy storage systems (pumped hydro storage, compressed air energy storage and redox flow batteries). Environmental benefits are also obtained if surplus power is used to produce hydrogen but the benefits are lower. Our environmental assessment of energy storage systems is complemented by determination of CO2 mitigation costs. The lowest CO2 mitigation costs are achieved by electrical energy storage systems.
La0.7Sr0.3MnO3-coated 5 V spinel LiNi0.5Mn1.5O4 as cathode is prepared by mixing LiNi0.5Mn1.5O4 powders and the sol–gel-drived La0.7Sr0.3MnO3 matrix, followed by high-temperature calcinations. The effect of La0.7Sr0.3MnO3-coating on the electrochemical performances of LiNi0.5Mn1.5O4 cells, especially at elevated temperature, is investigated systematically by the charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. Compared to pristine LiNi0.5Mn1.5O4, La0.7Sr0.3MnO3-coated material has much lower surface and charge-transfer resistances and shows a higher lithium diffusion rate. The results of electrochemical experiments demonstrate that the modified material exhibits remarkably enhanced electrochemical reversibility and stability at elevated temperature. The La0.7Sr0.3MnO3-coating layer protected the surface of the active materials from HF in the electrolyte during electrochemical cycling. As a result, the electrochemical cycling stability is improved.
Until now, there is no internationally accepted guideline for the measurement, data exchange and analysis of PV–Wind Hybrid Systems. As there is a need for such a tool, so as to overcome the barrier that the lack of confidence due to the absence of reliability means for the development of the market of Hybrid Systems, an effort has been made to suggest one tool for PV–Wind Hybrid Systems. The suggested guidelines presented in this work are based on the existing guidelines for PV Systems, as a PV–Wind Hybrid system can be roughly thought of as a PV System to which wind generation has been added. So, the guidelines for PV Systems are valid for the PV–Wind System, and only the part referred to wind generation should be included. This has been the process followed in this work. The proposed method is applied to a case study, the CICLOPS Project, a 5kW PV, 7.5kW Wind Hybrid system installed at the Isolated Wind Systems Test Site that CIEMAT owns in CEDER (Soria, Spain). This system has been fully monitored through a year and the results of the monitoring activity, characterizing the long-term performance of the system are shown in this work.
In real-time energy management of a converter-based microgrid, it is difficult to determine optimal operating points of a storage system in order to save costs and minimise energy waste. The complexity arises due to time-varying electricity prices, stochastic energy sources and power demand. Many countries have imposed real-time electricity pricing to efficiently control demand side management. This paper presents a particle swarm optimisation (PSO) for the application of real-time energy management to find optimal battery controls of a community microgrid. The modification of the PSO consists in altering the cost function to better model the battery charging/discharging operations. As optimal control is performed by formulating a cost function, it is suitably analysed and then a dynamic penalty function is proposed in order to obtain the best cost function. Several case studies with different scenarios are conducted to determine the effectiveness of the proposed cost function. The proposed cost function can reduce operational cost by 12% as compared to the original cost function over a time horizon of 96 h. Simulation results reveal the suitability of applying the regularised PSO algorithm with the proposed cost function, which can be adjusted according to the need of the community, for real-time energy management.
Background Hypothermia is a common battlefield trauma occurrence. This study compared the effectiveness of the hypothermia, environmental, exposure, and trauma (HEET) garment (Trident Industries, Beaufort, SC) with and without thermal inserts with a control group of two wool blankets in the prevention of hypothermia in a treated hypovolemic porcine model. Materials and methods Five female swine (Sus scrofa-Yorkshire cross) were assigned to each of three groups: HEET with thermal inserts (n=5); HEET without thermal inserts (n=5); or control (n=5). After the animals were anesthetized and stabilized for 30min, the swine were hemorrhaged to a mean arterial pressure (MAP) of 30mm Hg, simulating a battlefield injury. Hetastarch 6% (500mL) was rapidly administered, simulating initial field resuscitation. One hour later, the animals' shed blood was reinfused, simulating transfusion at a field medical facility. The investigators moved the animal into a cooler set at 10°C±0.5°C. A pulmonary artery catheter was used to monitor core body temperature over a 6-h period. Results A repeated measures ANOVA and Tukey's post hoc test were used to analyze the data. There was a significant difference between the groups. At the end of 6h, the mean core temperature for the HEET with inserts group was 32.69°C±1.5; the HEET without inserts, 31.02°C±1.8; and control, 34.78°C±1.2 (P<0.05). While all groups became hypothermic, the wool blanket group was most effective in maintaining body temperature closer to normothermia. Conclusion The HEET garments with and without heaters are ineffective in preventing hypothermia.
Thermal decomposition of cadmium formate, Cd(HCOO)2, was studied in dynamic helium and air atmosphere by means of simultaneous TGA, DTA and MS analysis. It was found that the cadmium formate decomposes at about 210°C to metallic cadmium and cadmium carbonate which next decomposes with formation of cadmium oxide. In helium cadmium melts, evaporates and the reaction residue consists of CdO and a small amount of elementary carbon formed in result of pyrolysis of formate groups. In air cadmium oxidizes and the final solid product of decomposition is CdO. The gaseous products of cadmium formate decomposition are: carbon dioxide, water, carbon monoxide, formaldehyde, methyl alcohol and methyl formate.
Energy storage can help integrate local renewable generation, however the best deployment level for storage remains an open question. Using a data-driven approach, this paper simulates 15-min electricity consumption for households and groups them into local communities of neighbors using real locations and the road network in Cambridge, MA. We then simulate PV for these households and use this framework to study battery economics in a high PV adoption, high electricity cost scenario, in order to demonstrate significant storage adoption. We compare the results of storage adoption at the level of individual households to storage adoption on the community level using the aggregated community demands. Under the simulated conditions, we find that the optimum storage at the community level was 65% of that at the level of individual households and each kWh of community battery installed was 64–94% more effective at reducing exports from the community to the wider network. Therefore, given the current increasing rates of residential battery deployment, our research highlights the need for energy policy to develop market mechanisms which facilitate the deployment of community storage.
Here, we demonstrate how the oxidation level of graphene oxide, pH, temperature and duration of hydrothermal process affects the physicochemical and electrochemical characteristics of resulting 3D graphene hydrogels as electrode material in supercapacitors. Two graphene oxide samples are prepared using Hummers and Tour methods to follow the influences of oxidation level and the type of oxygenated functional groups on the electrochemical and morphological characteristics of resulting 3D graphene hydrogels. The optimized conditions for the hydrothermal process are determined with respect to achieving samples with the highest capacitive characteristics. Hydrogels obtained using Tour's graphene oxide has a hierarchical and interconnected porous framework and provides the best electrochemical characteristics. It also exhibits specific surface area of 921 m2 g−1, ionic conductivity of 0.44 S cm−1 and double layer capacitance of 200 F g−1 at 5 mV s−1 in 6 M KOH, which are about 12%, 5% and 7% higher than that achieved for the best sample prepared based on Hummers' graphene oxide, respectively. The assembled symmetric supercapacitor prepared based on this hydrogel exhibits a remarkable gravimetric capacitance of 245 F g−1 at 0.5 A g−1 and an excellent cyclic stability with 78% capacitance retention at high current density of 50 A g−1.
There is much reason to believe that fleets of service vehicles of many organizations will transform their vehicles that utilize alternative fuels that are more sustainable. The electric vehicle (EV) is a good candidate for this transformation, especially which “refuels” by exchanging its spent batteries with charged ones. This paper discusses some new logistical issues that must be addressed by such EV fleets, principally the issues related to the limited driving range of each EV's set of charged batteries and the possible detouring for battery exchanges. In particular, the paper addresses (1) the routing and scheduling of the fleet, (2) the locations of battery-exchange stations, and (3) the sizing of each facility. An overview of the literature on the topic is provided and some initial results are presented.
The increasing interest in gel polymer electrolyte for the lithium battery is attributed to its excellent plasticity, enhanced safety and significantly improved electrochemical stability. Herein, on account of the two-phase structure of thermoplastic polyurethane (TPU) consisting of soft and hard segments, the cellulose/TPU with ether bond composite gel polymer electrolyte (CGPE) was fabricated and investigated for applications in lithium batteries. This study demonstrated that the CGPE possessed preeminent comprehensive properties such as sufficient ionic conductivity (4.8×10−4 Scm−1) at 80°C, high lithium ion transport number (t+ =0.68) and improved electrochemical stability. Moreover, the assembled LiFePO4/Li battery using CGPE exhibitedoutstanding rate capacity and remarkable cycle performance at the elevated temperature of 80°C. Notably, the discharge capacity was still 128.2mAhg−1 after 200 cycles, 95% of the capacity retention at a charge/discharge rate of 2C. These findings suggest that CGPE is a very prospective polymer electrolyte for high-performance lithium batteries.
The closed and open carbon nanotube electrodes have been studied as a function of frequency and the open circuit cell potential. A comparison of these spectra reveals different behaviors depending on the form of the carbon nanotubes: for the closed carbon nanotubes the impedance spectra consists of only one arc in the high frequency, for the open carbon nanotubes the impedance spectra consists of two separated semicircles in the high frequency. Analysis based on plausible equivalent circuit models for the carbon nanotubes lead to evaluation the kinetic parameters for the various physicochemical processes occurring at the electrode/electrolyte interface.
The electrochemical property of graphene can be significantly enhanced due to the incorporating of heteroatoms into graphene. In this article, the ternary nitrogen-doped graphene/nickel ferrite/polyaniline (NGNP) nanocomposite is synthesized by a facile two-step approach and its electrochemical properties as electrodes for supercapacitors are studied by various electrochemical measurements. The specific capacitance of NGNP is 645.0 F g−1 at 1 mV s−1 and 667.0 F g−1 at 0.1 A g−1 in a three- and two-electrode system, respectively, much higher than other binary electrodes. In a two-electrode symmetric system, the energy density of the NGNP electrode is 92.7 W h kg−1 at a power density of 110.8 W kg−1, moreover, that of the supercapacitor based on NGNP can also reach 23.2 W h kg−1 at a power density of 27.7 W kg−1. In addition, the capacitance loses only 5% after repeating test for 5000 cycles, and about 10% after 10,000 cycles at a high current density 5 A g−1. The results demonstrate the novel ternary NGNP electrode produced by the current economical method will gain promising applications in supercapacitors and other devices by virtue of its outstanding characteristics (high specific capacitance, high power and energy density, excellent cycle life).
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Lithium-rich layered oxides (LRLO) are among the leading candidates for the next-generation cathode material for energy storage, delivering 50% excess capacity over commercially used compounds. Despite excellent prospects, voltage fade has prevented effective use of the excess capacity, and a major challenge has been a lack of understanding of the mechanisms underpinning the voltage fade. Here, using operando three-dimensional Bragg coherent diffractive imaging, we directly observe the nucleation of a mobile dislocation network in LRLO nanoparticles. The dislocations form more readily in LRLO as compared with a classical layered oxide, suggesting a link between the defects and voltage fade. We show microscopically how the formation of partial dislocations contributes to the voltage fade. The insights allow us to design and demonstrate an effective method to recover the original high-voltage functionality. Our findings reveal that the voltage fade in LRLO is reversible and call for new paradigms for improved design of oxygen-redox active materials.
LiFePO4 has been considered a promising battery material in electric vehicles. However, there are still a number of technical challenges to overcome before its wide-spread applications. In this article, the structure and electrochemical performance of LiFePO4 are reviewed in light of the major technical requirements for EV batteries. The rate capability, capacity density, cyclic life and low-temperature performance of various LiFePO4 materials are described. The major factors affecting these properties are discussed, which include particle size, doping, carbon coating, conductive carbon loading and synthesis techniques. Important future research for science and engineering is suggested.
Electric vehicles, including both PEVs and PHEVs have been recently interested to a large extent in global markets due to their capabilities. These plug-in vehicles are able to absorb/inject power from/to the electric grid that turns them into an interesting solution for the power systems. However, large numbers of such plug-in vehicles can be a threaten to power systems. In this regard, it seems necessary to investigate the problems caused by the uncertain driving nature of such electric vehicles. On the other hand, the opportunities provided by the presence of a large fleet of plug-in vehicles as mobile storage/load should be discussed. For this end, this paper reviews the challanges and the problems caused by charging/discharging of PHEV/PEVs in large numbers and investigates their capabilities as a solution to integrate the RESs and demand response programs in power systems.
The synthesis and characterization of core/shell-type Co3O4/C nanocapsules for application as anode material in lithium ion batteries are reported in this paper. The synthesis process involves the preparation of Co/C nanocapsules using a modified arc-discharge method and the annealing of the Co/C nanocapsules at 300°C for 2h in air. The as-synthesized products show a spherical shape and a core/shell-type structure in which a Co3O4 nanoparticle core of diameter 10–30nm is encapsulated by an onion-like carbon shell of thickness approximately 1nm. The Co/C nanocapsules can be stable below 130°C, and be oxidized above 205°C in air. The Co3O4/C nanocapsules deliver an initial discharge capacity of 1467.6mAhg−1 at 0.5C and maintain a high reversible capacity of 1026.9mAhg−1 after 50 charge–discharge cycles, much higher than the Co3O4 nanoparticles (471.5mAhg−1). A postmortem analysis of the Co3O4 and Co3O4/C anodes subjected to prolonged cycling reveals the existence of a lower degree of surface cracking and particle breakage in the Co3O4/C anode than the Co3O4 anode. The improved electrochemical performance and structural stability in the Co3O4/C nanocapsules are attributed to the enhanced electrical conductivity and structural buffering provided by the onion-like carbon shell.