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An Equivalent Circuit Model (ECM) of a lithium ion (Li-ion) battery is an empirical, linear dynamic model and the bandwidth of the input current signal and level of non-linearity in the voltage response are important for the model’s validity. An ECM is, however, generally parametrised with a pulse current signal, which is low in signal bandwidth (Part 1) and any non-linear dependence of the voltage on the current due to transport limitations is ignored. This paper presents a general modelling methodology which utilises the higher bandwidth and number of signal levels of a pulse-multisine signal to estimate the battery dynamics and non-linear characteristics without the need of a 3D look-up table for the model parameters. In the proposed methodology a non-parametric estimate of the battery dynamics and non-linear characteristics are first obtained which assists in the model order selection, and to assess the level of non-linearity. The new model structure, termed as the Non-linear ECM (NL-ECM), gives a lower Root Mean Square (RMS) and peak error when compared to an ECM estimated using a pulse data set.
Here we reported an effective method to prepare TiO2/C core–shell nanocomposites as active anode materials for lithium ion batteries with markedly ameliorated electrochemical performance. At first, a precursor, polyacrylonitrile coated nano-TiO2 particles, was formed by emulsion polymerization. Then the precursor was heat-treated under argon atmosphere to achieve the nanocomposites. The conductive carbon shell enveloped TiO2 nanoparticles and suppressed the aggregation of nanoparticles during cycling. Meanwhile, it combined closely with the nanocores, significantly enhanced kinetics of lithium intercalation and de-intercalation and diffusion coefficient of lithium ion. This provides a good way to improve the cycling and kinetics of nanoanode materials.
Silicon oxycarbide/nano-silicon composites (SiOC/nSi) are prepared by mixing of nano-sized silicon, either crystalline (nSi_c) or amorphous (nSi_a), with commercially available polyorganosiloxane RD-684a and subsequent pyrolysis. The influence of the type of nano-silicon, namely crystalline vs. amorphous, on the electrochemical properties and performance is analyzed and correlated with the corresponding composite microstructure. In the case of crystalline nano-silicon, a high reversible capacity of 905 mAh g−1 is registered, whereas that for amorphous nano-silicon embedment reaches 704 mAh g−1. However, regarding the cycling stability, SiOC/nSi_c shows a significant capacity fading upon continuous cycling, related to SiOC matrix failure. The host phase is not able to accommodate the arising mechanical stresses upon Si grain expansion and contraction when alloying/dealloying with Li. SiOC/nSi_a on the contrary, demonstrates a stable cycling performance for up to 100 cycles. This excellent performance is explained by the enhanced matrix integrity of the compound, rationalized by a smaller size of the embedded crystallized Si grains and an intrinsically enhanced electrical conductivity due to the formation of SiC.
ABSTRACT Lithium-ion capacitors (LICs) are assembled with activated carbon (AC) cathode and pre-lithiated hard carbon (HC) anode. Two kinds of HC materials with different physical and electrochemical behaviors have been investigated as the negative electrodes for LIC. Compared with spherical HC, the irregular HC shows a distinct lithium ion intercalation plateau in the charge–discharge process. The existence of lithium ion intercalation plateau for irregular HC greatly affects the electrochemical behavior of HC negative electrode and AC positive electrode. The effect of working potential range on the electrochemical performance of LIC-SH and LIC-IH is investigated by the galvanostatic charging–discharging, electrochemical impedance tests and cycle performance testing. The charge–discharge potential range of the irregular HC negative electrode is lower than the spherical HC electrode due to the existence of lithium ion intercalation plateau, which is conducive to the sufficient utilization of the AC positive electrode. The working potential range of LIC should be controlled to realize the optimization of electrochemical performance of LIC. LIC-IH at the working potential range of 2.0-4.0V exhibits the optimal electrochemical performance, high energy density up to 85.7Whkg−1 and power density as high as 7.6kWkg−1 (based on active material mass of two electrodes), excellent capacity retention about 96.0% after 5000 cycles.
The anthropogenic silver cycle shows the global material flows of silver on an annual basis. Beginning with mine supply the silver flows in various end use sectors. It is either stored as part of the above ground silver reserves or gets consumed and recycled or dissipates on landfills or with sewage. The article discusses supply–demand scenarios of silver. The study is methodically based on an analysis of resource specific factors like exploration rates, reserves and resources and regional distribution of exploration areas. Among the numerous application areas for silver the one with the greatest growth potential is discussed in detail. Solar energy sector is a fast growing area which is analysed quantitatively in detail to obtain information on potential future bottlenecks in material availability. Due to its' high electrical conductivity silver is used in silicon photovoltaic technology and Grätzel cells to form the electrical contacts. In concentrated solar power applications silver is the material of choice as the coating of the mirror because of its' high optical reflectivity. Both concerns about climate change as well as questions related to energy resources and energy security stress the importance of renewable energy technologies. This has resulted in several future scenarios with partly very ambitious goals for the construction of the new energy infrastructure. The scenarios are discussed in the light of known silver resources.
With the retirement of a massive amount of end-of-life lithium ion batteries (LIBs), proper disposal of the hazardous wastes and cost-effective valorization of useful materials have become increasingly pressing and have attracted extensive attention worldwide. The state-of-the-art recycling technologies, which are generally based on chemical leaching methods, have critical issues like enormous consumption of chemicals and secondary pollution, and generally involve tedious procedures. Here, we report an innovative approach in light of a redox targeting-based process and demonstrate the operation for the recycling of spent LiFePO4. With 0.20 M [Fe(CN)6]3− solution as a selective and regenerative redox mediator, LiFePO4 is readily broken down into FePO4 and Li+via the redox-targeting reaction between the redox mediator and the material, with a recycling efficiency for lithium removal up to 99.8% at room temperature. The reacted redox species are instantaneously regenerated on the electrode for subsequent rounds of reaction while Li+ is separated from the counter electrode compartment. Consequently, the consumption of chemicals is drastically minimized and secondary pollutants are eliminated. By virtue of the new process, high purity LiOH (99.90%) and FePO4 (99.97%) have been obtained. We envisage that this cost-effective and environment-friendly approach can be extended to other materials and promote the sustainability of LIB technologies.
The accuracy for positional alignment of the positive electrode vs. the negative electrode is of great importance for the quality of assembly of lithium ion cells. Area-oversized negative electrodes increase the tolerance for electrode alignment. In this study, the impact of area-oversizing of the negative electrode on the specific capacity losses during charge/discharge cycling is systematically investigated by using electrochemical and analytical methodologies. It is shown, that with a higher degree of area-oversizing more active lithium is kinetically trapped in the outer negative electrode areas (“overhang”), causing performance-deteriorating losses in usable specific capacity. Nevertheless, most of this “lost” specific capacity is of reversible nature as the trapped active lithium can be electrochemically recovered, which is analytically proven by inductively coupled plasma-optical emission spectrometry (ICP-OES) and laser ablation-inductive coupled plasma-mass spectrometry (LA-ICP-MS). Given this relation, a periodic application of a short constant voltage step after discharge results in a significant performance increase. In contrast, holding the cell in the charged state is detrimental for cells with area oversized negative electrodes as the amount of reversible and irreversible trapped active lithium increases. Based on the obtained insights, the influence of variations of the electrochemical conditions on charge/discharge cycling performance is discussed.
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Anodes containing spherical natural graphite (SNG12) and cathodes containing LiFePO4, both from HydroQuebec, were prepared with aqueous-based polyacrylic acid (PAAH), its neutralized derivatives polyacrylic acid (PAAX) (X=Li, Na, and K), and with conventional poly(vinylidene difluoride) (PVDF) binders. A comparison of electrode performance was made between these three binder systems. The electrodes were optimized by adding elastic styrene butadiene rubber (SBR) and conductive vapor grown carbon fiber (VGCF) in the place of some of the PAAX. Initially, SNG12 and LiFePO4 electrodes were characterized in half cells with Li as the counter electrode. The electrochemistry results show that the use of PAAX binders can significantly improve the initial coulombic efficiency, reversible capacity, and cyclability of SNG12 anodes and LiFePO4 cathodes as compared to that of electrodes based on a PVDF binder. By using an optimized composition for the anode and cathode, SNG12/LiFePO4 full cells with PAALi binder cycled 847 times with 70% capacity retention, which was a significant improvement over the electrodes with PVDF (223 cycles). This study demonstrates the possibility of manufacturing Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like NMP, thereby improving performance, reducing cost, and protecting the environment.
Since Li-ion batteries made of Li-rich layered materials might work at extreme environments, understanding the low temperature properties of Li-rich layered materials is of great importance. In this article, the low temperature properties and corresponding mechanism of Li-rich layered materials with a great amount of activated Li2MnO3 are unraveled through a comparison of the low temperature characteristics of Li-rich layered materials with a small amount of activated Li2MnO3 versus the former. Our findings indicate that in the electrode with a large amount of activated Li2MnO3, the sluggish kinetics of the electrode reaction at low temperatures suppresses greatly the Mn4+/Mn3+ reduction reaction, leading to much smaller initial discharge capacity and much better cyclic performance compared with situations at room temperature. Moreover, the increasingly suppressed Mn4+/Mn3+ reduction reaction stop the discharge voltage fading, which might mitigate the layered-to-spinel phase transformation.
The solvothermal method has been employed to synthesize cuprous oxide (Cu2O) nanowires using a precursor of cupric acetate monohydrate (CuAc2) and ethylene glycol (EG) as the solvent. By optimizing the reaction temperature and reaction time, we have prepared Cu2O nanowires with a diameter of approximately 7nm and a length of several nanometers. The UV–visible absorption spectrum of the nanowires shows obvious blueshift compared to the bulk Cu2O, which arises from the quantum confinement effect of the excitonic transition expected for Cu2O nanowires. Here we also report the role of different excitation energies on the photoluminescence (PL) properties of the Cu2O nanowires by steady-state and time-resolved PL spectroscopy. The decay times vary from nanoseconds to picoseconds. Decay kinetics indicates that the average lifetime 〈τ〉 of the nanowires increases with increasing excitation energy. The current–voltage (I–V) curves of the nanowires give the photocurrent density 16 times larger than the dark current density.
A facile and potentially scalable synthesis route to obtain SnO2–carbon composites was developed. SnO2 nanoparticles were deposited on the surface of two types of graphitic carbon: (a) commercial porous graphite (HG) and (b) graphitic carbon nanostructures. The synthesis procedure consists of two simple steps: (i) room temperature formation/deposition of SnO2 nanocrystals and (ii) thermal treatment at 350 °C to generate SnO2 nanoparticles (size ~3.5 nm) over the carbon surface. The electrochemical performance of the graphitic carbons and the SnO2–carbon composites as anode materials in Li-ion rechargeable batteries was investigated. In all cases, tape casting electrode fabrication allowed almost full active material utilization. Good cyclabilities were achieved, with HG and HG–SnO2 showing capacities of 356 and 545 mAh g−1, respectively after 50 cycles.
To improve the performances of Nickel–Metal Hydride batteries, an important step is the understanding of the corrosion processes that take place in the electrode material. In particular, the present study focuses for the first time on the model (La, Mg)2Ni7 system. The calendar corrosion in 8.7 M KOH medium was investigated from 6 h to 16 weeks immersion. By a unique combination of structural and elemental characterisations, the corrosion products are evidenced in those systems. In particular, we demonstrate that Ni and Mg combine in a pseudo-binary hydroxide Mg1−xNix(OH)2 whereas La corrodes into nanoporous La(OH)3 needles with inner hollow nanochannels.
This paper uses a physics-based battery model to develop a generic framework to solve optimal charging strategies. The study will also provide insight into the interplay between optimized charging strategies and the battery internal electrochemical kinetics. With a physics-based battery model, a multi-objective optimal control problem is proposed to investigate the charging strategies that optimally trade off the temperature rise, charging time, and loss. First, a fast-charging strategy (minimum time) with the sole purpose of reducing charging time is presented and experimentally validated. The fast-charging strategy can significantly reduce the charging time but causes a high-temperature rise and charging loss. Next, the interplays between temperature rise and charging time, charging loss, and charging time are investigated, respectively. It is found that, in order to reduce the battery temperature during charging, high-current charging at the initial stage should be avoided. Finally, a balanced charging strategy, which considers temperature rise, charging time, and charging loss simultaneously, is developed and analyzed. Experimental results show that the balanced charging strategy has a similar temperature rise as 4C CC/CV charging, but the charging time is reduced by 24.8% and the charging loss is reduced by 56.4%.
In an effort to fabricate highly conductive, stable solid-state polymer electrolyte membranes (PEM), polyethylene glycol bis-carbamate (PEGBC) was synthesized via condensation reaction between polyethylene glycol diamine and ethylene carbonate. Subsequently, dimethacrylate groups were chemically attached to both ends of PEGBC to afford polyethylene glycol-bis-carbamate dimethacrylate (PEGBCDMA) precursor having crosslinking capability. The melt-mixed ternary mixtures consisting of PEGBCDMA, succinonitrile plasticizer, and lithium trifluorosulphonyl imide salt were completely miscible in a wide compositional range. Upon photo-crosslinking, the neat PEGBCDMA network was completely amorphous exhibiting higher tensile strength, modulus, and extensibility relative to polyethylene glycol diacrylate (PEGDA) counterpart. Likewise, the succinonitrile-plasticized PEM network containing PEGBCDMA remained completely amorphous and transparent upon photo-crosslinking, showing superionic conductivity, improved thermal stability, and superior tensile properties with improved capacity retention during charge/discharge cycling as compared to the PEGDA-based PEM.
The melting process and the solidifying process of phase change material (PCM) are usually considered symmetrical in the traditional PCM heat transfer models, but there are inevitable calculation errors using these models. In this paper, a new heat transfer model of PCM based on the energy asymmetry was built, and it was validated by experimental data. It was found that the two main reasons for the energy asymmetry of the PCM were the melting temperature range and the solidifying temperature range were not the same and the supercooling problem during the cooling process. No matter for only one thermal cycle or for the multiple thermal cycles, the results from the asymmetrical model and the symmetrical model were different. Apparently, compared with the symmetrical model, the asymmetrical model had higher accuracy, and the heating/cooling process in the asymmetrical model was more consistent with the real heating/cooling process of the PCM.
Energy storage units have become important components in residential micro-cogeneration (MCG) systems. As MCG systems are often connected to single residences or buildings in a wide variety of settings, they are frequently unique and highly customized. Lithium-ion batteries have recently gained some profile as energy storage units of choice, because of their good capacity, high efficiency, robustness and ability to meet the demands of typical residential electrical loads. In the present work, modeled scenarios are explored which examine the performance of a MCG system with an internal combustion engine, photovoltaic input and a Li-ion storage battery. An electricity demand profile from new data collected in Ottawa, Canada is used to provide a full year energy use context for the analyses. The demands placed on the battery are examined to assess the suitability of the battery size and performance, as well as control related functionalities which reveal significantly varying battery use, and led to a quantitative expression for equivalent cycles. The energy use simulations are derived from electrochemical fundamentals adapted for a larger battery pack. Simulation output provides the basis for techno-economic commentary on how to assess large-scale Li-ion batteries for effective electrical storage purposes in MCG systems, and the impact of the nature of the control strategy on the battery service life.
Background Distressing ‘psychotic-like’ or unusual experiences (UEDs) signify increased mental health risk in the general population, including greater likelihood and severity of co-occurring non-psychotic mental health problems, and, from fourteen years of age, increased risk of a future psychotic illness. Healthcare guidelines for under eighteens recommend psychological intervention for UEDs, to reduce current distress and adverse functional impact, and, potentially, future mental health risk. Children tend not to report UEDs unless directly asked, indicating a need for routine screening. We report on the feasibility of a routine screening methodology, and screening outcomes, in Child and Adolescent Mental Health Services (CAMHS) in South East London, United Kingdom. Method Four general community CAMHS teams were invited to screen, by adding a nine-item self-report UED measure to their routine assessment battery. Screening data were collected over 18months from 02/2015 to 07/2016. Results All but one team agreed to screen. Each team saw around 300 accepted referrals during the audit period (total: 900); 768 of these (85%) were successfully screened; of those screened, 68% (n =524) self-reported UEs, 60% (n =461) with associated distress/adverse functional impact. Screening was acceptable to clinicians, children and families. Conclusions Assessing UEDs routinely in CAMHS is feasible, and suggests that around two thirds of assessed referrals could potentially benefit from interventions targeting UEDs. Additional training may be required for the CAMHS workforce to address this need.
Nickel–copper metallic foams were electrodeposited from an acidic electrolyte, using hydrogen bubble evolution as a dynamic template. Their morphology and chemical composition was studied by scanning electron microscopy and related to the deposition parameters (applied current density and deposition time). For high currents densities (above 1 A cm−2) the nickel–copper deposits have a three-dimensional foam-like morphology with randomly distributed nearly-circular pores whose walls present an open dendritic structure. The nickel–copper foams are crystalline and composed of pure nickel and a copper-rich phase containing nickel in solid solution. The electrochemical behaviour of the material was studied by cyclic voltammetry and chronopotentiometry (charge–discharge curves) aiming at its application as a positive electrode for supercapacitors. Cyclic voltammograms showed that the Ni–Cu foams have a pseudocapacitive behaviour. The specific capacitance was calculated from charge–discharge data and the best value (105 F g−1 at 1 mA cm−2) was obtained for nickel–copper foams deposited at 1.8 A cm−2 for 180 s. Cycling stability of these foams was also assessed and they present a 90 % capacitance retention after 10,000 cycles at 10 mA cm−2.
This paper reports the successful preparation of catalytic electrodes based on carbon-fiber paper modified with dendrimer-encapsulated platinum nanoparticles. The metallic nanoparticles were first synthesized from solution within generation-four hydroxyl-terminated PAMAM dendrimers, which serve as a carrier for their subsequent immobilization on the solid substrates. The carbon-fiber surfaces were activated by means of three alternative anodic pretreatments and then loaded with the dendrimer-metal nanocomposites by cycling of the carbon-electrode potential. The degree of oxidation of the carbon surface affects the anchoring of the dendritic material, the coverage of which is indicated by the electroactive area of the encapsulated platinum. The modified carbon-fiber surfaces pretreated by cyclic polarization are found to be electrocatalytic for the oxygen reduction reaction, presenting a good exchange-current density at low platinum loading.
Undoped Mn3O4 shows relatively poor performance as a possible anode material on reversible reaction with lithium. A dramatic increase in cyclability is obtained on partial substitution of Mn by Co. Data are presented for the composition Mn2.6Co0.4O4, which, after the first cycle, shows essentially constant capacity of 400mAhg−1 at ∼0.6V.
Porous copper was electrodeposited using hydrogen bubble dynamic template. Various electrolytes having CuSO4 and H2SO4 in fixed molar ratio approximately equal to 0.3 and at temperature 18°C were utilized for potentiostatic electrodeposition at various cathodic potentials. After electrodeposition, electrochemical impedance spectroscopy studies were conducted in 2.5M NaCl solution at room temperature for determining electrochemically active true surface area. The surface morphologies of the deposits were analyzed using scanning electron microscope. Electrolyte with composition 0.12M CuSO4 and 0.4M H2SO4 resulted in maximum electrochemically active true surface area due to more open structure with thick dendrite branches which was correlated to high hydrogen evolution rate.