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Recent experiments showed, that in contrast to traditional opinion, if the cathode was protected by anode limitation the capacity fade of Rechargeable Alkaline Manganese Dioxide Zinc (RAM™) cells was not caused by the EMD cathode, but by the gelled zinc anode. The key is the electrolyte. The cathode competition for the electrolyte and the increasing requirement of chemically formed ZnO for more electrolyte caused an electrolyte deficiency at the front face of the anode and finally caused precipitation of zincate and passivation of zinc. The crust is a mixed material of precipitation and passivation products. The low solubility ZnO is formed by decomposition of electrochemically generated zincate ions [Zn(OH)4]2− and also by recombination of zinc with oxygen during overcharge. The progressively thickened “crust” at the front face of the anode increases the resistance, then finally causes the cell to fade. The crusting is a redistribution of active material and electrolyte between the front and rear of the cylindrical gelled zinc anode. More electrolyte and proper charging can delay such a “crusting” phenomenon.
A new class of mesomorphic polymer electrolytes (side group liquid crystalline polyethers) is described whose members exhibit significant ionic conductivity in both liquid crystalline and glassy states. It is suggested that the pendent side groups effectively “jacket” the ethylene oxide backbones, and prevent the ethylene oxide units from adopting a close-packed structure during cooling. The resulting open structure and multiplicity of ion sites is probably the origin of the decoupling process which permits ion migration even below T g. This could be a widespread phenomenon in polymer electrolytes.
This paper presents a topology to passively balance two types of lithium-ion cells without using additional active electrical components or employing any algorithm based balancing management systems. We connect nickel-metal hydride or nickel-zinc cells in parallel to lithium-ion cells. The hydrogen/oxygen recombination process of the nickel-based cells can be used to balance lithium-ion cells. Two serially connected lithium iron phosphate cells, combined each with two serially connected nickel-zinc cells, show a successful balancing of 8% of the lithium iron phosphate cell's initial capacity. A lithium titanate cell connected in parallel to two nickel-metal hydride cells can be fully charged without suffering from over-voltage effects by constant current charging.
Novel electrolyte materials, room temperature ionic liquids (RTILs) were applied to the Li battery system and their characteristics in Li-metal batteries are discussed, partly reviewing authors work in the past. Quaternary ammonium (QA) cation-imide RTIL was focused on because of the excellent stability in cathodic environment of Li. Li/LiCoO2 cell performance and Li cycling efficiency using the selected QA-imide RTIL was almost satisfactory. In addition, thermal stability of selected QA-imide RTIL with the charged positive electrode and Li was the advantage for Li battery. On the other hand, further improvement in the conducting properties is required with balanced approach for both electrochemical stability and thermal stability in order to use the RTIL electrolyte practically in batteries.
The submicron single crystals of LiCoPO4 with 500 nm diameter are prepared by solvothermal method. The carbon coated sample is obtained using sucrose as carbon source under 650 °C subsequently. It is investigated that the solvent composition has an effect on the morphology and the electrochemical performance of the cathode material. The as-prepared samples are characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopic, dynamic light scattering, and Fourier transform infrared spectra. The electrochemical performance is evaluated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. The LiCoPO4/C cathode can reach an initial discharge capacity of 123.8 mA h g−1 at 0.1C, with a retention of 83% after 100 cycles. A discharge capacity of 84.9 mA h g−1 is still attainable when the rate is up to 2C. The good cycling performance and rate capability are contributed to the decrease of particle size along with the lower antisite defect concentration in the LCP crystals, and uniform carbon coating.
Modification of graphene has been undertaken in many research contexts in order to improve its properties. In this study, we examine Ni-nanoparticles decoration on graphene and its effect on sodium-ion battery performance. A definite trend is observed on the relationship between Ni-nanoparticles concentration (and hence size) and battery performance. Comparable capacities on the order of 420mAhg−1 after 20 cycles at 100mAg−1 is observed for the 3 relatively high Ni-concentration samples NiC10, NiC40, and NiC80. As the Ni:C ratio decreases, a decreasing trend is observed in the measured capacity, with NiC200, NiC500, and NiC1000 producing capacities of 350mAhg−1, 380mAhg−1, and 300mAhg−1 respectively after 20 cycles at the same rate. Ex situ energy dispersive X-ray spectroscopy, scanning, and transmission electron microscopy shows the morphology of the Ni-nanoparticles decorated graphene and assists in quantifing their sodium content, emphasizing the increasing sodium content with increasing Ni-nanoparticles concentration. This systematic study details how Ni-nanoparticles concentration on graphene surfaces can be manipulated to enhance electrochemical performance, and that higher concentrations up to NiC10 favour better performance. For a compromise between performance and cost (Ni cost), the best composition is NiC500 which favors best performance with the least Ni decoration.
Commercial carbon cloth made of PAN-based carbon fibres was used as free-standing anode for lithium intercalation. The role of surface functional groups on the specific irreversible charge loss and reversible charge during the intercalation and de-intercalation of lithium ions into carbon cloth has been investigated. Oxygen groups have been introduced by nitric acid vapour treatment and subsequently gradually removed by thermal treatment at different temperatures in He or H2 atmosphere as confirmed by X-ray photoelectron spectroscopy. A clear correlation between the amount of surface-bound oxygen groups and the irreversible specific charge was observed. Three irreversible processes were distinguished during the first cathodic scan: (i) reduction of oxygen groups, (ii) formation of the solid electrolyte interphase (SEI) and (iii) presumably exfoliation. The latter one was only observed for samples with low surface oxygen concentration, and its contribution to the irreversible capacity was small due to the low graphitization degree of the samples. An increased specific reversible charge upon increasing the amount of oxygen-containing groups was observed with the main improvement above 1.5V.
The electrochemical behavior at low temperatures of anatase TiO2 electrodes for Lithium ion batteries have been evaluated by galvanostatic cycles in the temperature range 20 to −30°C. Two different manufacturing processes have been used to prepare anatase anodes containing water soluble sodium carboxymethyl cellulose (CMC) or poly(vinilydene fluoride) (PVDF) as binder. The low temperature performances at different charge/discharge rates of TiO2/CMC and TiO2/PVDF electrodes are compared and discussed in terms of irreversible capacity loss (ICL) at the first cycle, capacity retention and reversible capacity. The kinetics of the electrodes containing CMC or PVDF is evaluated by Electrochemical Impedance Spectroscopy.
This work reported controllable synthesis of TiO2/graphene nanocomposites with various morphologies by a one-pot one-step solvothermal method and tested their lithium storage performance. In the absence of glucose, TiO2 nanolayers grafted graphene with low crystallinity were obtained. In the presence of glucose at a low content, TiO2/graphene was composed with well-dispersed nanoparticles and has high crystallinity of TiO2, while at a high content of glucose, TiO2/graphene was a mixture of hierarchical TiO2 microspheres and graphene covered with amorphous carbon. As a result, these TiO2/graphene nanocomposites went through different mechanisms of lithium ions insertion/extraction due to their different particle sizes and crystal structures. Compared with the ultrathin layers and microspheres morphologies, TiO2 nanoparticles/graphene demonstrated high reversible capacity (>260mAhg−1 at 0.1C, C=168mAg−1), long-term cycling ability at 1C (1000 cycles, retention 83%) and superior rate capability from 0.1C to 10C, and still delivers a high capacity of 154mAhg−1 after 1000 cycles even at 2C. The superiority of TiO2 nanoparticles/graphene benefits from the combination of small particle size (<10nm), high dispersion, mesoporous structure, and improved electronic conductivity. The findings in this work will advance the design of functional materials for energy storage.
Electricity generated from renewable sources, which has shown remarkable growth worldwide, can rarely provide immediate response to demand as these sources do not deliver a regular supply easily adjustable to consumption needs. Thus, the growth of this decentralized production means greater network load stability problems and requires energy storage, generally using lead batteries, as a potential solution. However, lead batteries cannot withstand high cycling rates, nor can they store large amounts of energy in a small volume. That is why other types of storage technologies are being developed and implemented. This has led to the emergence of storage as a crucial element in the management of energy from renewable sources, allowing energy to be released into the grid during peak hours when it is more valuable. The work described in this paper highlights the need to store energy in order to strengthen power networks and maintain load levels. There are various types of storage methods, some of which are already in use, while others are still in development. We have taken a look at the main characteristics of the different electricity storage techniques and their field of application (permanent or portable, long- or short-term storage, maximum power required, etc.). These characteristics will serve to make comparisons in order to determine the most appropriate technique for each type of application.
Existing computer tools for ergonomic design are unable to assist designers with higher level advice within design processes. Thus, design engineers need to rely on their own knowledge and experience when making crucial decisions relating to products’ ergonomic parameters. An intelligent decision support system has been developed in order to overcome this bottleneck. This paper presents a knowledge base, containing ergonomic design knowledge specific for hand tool design. A pneumatic hammer handle design is used as a case study in order to show how ergonomic design knowledge built within this system is used to improve the ergonomic value of a product. Relevance to industry Engineers in small and medium-size enterprises (SME's) or young designers are in an unenviable position as their knowledge domains and experiences are minimal. When applying decision support system discussed here, even SME's could appear on the market with optimal designed products with relatively minor influence on development budget. Consequently their role on the market will be aggrandised.
Macroporous carbon foams (Cfoams) were synthesized by the replication process from mesophase pitch precursor and then characterized for electrochemical sensing and electrosynthetic applications. Scanning electron and optical microscopies revealed a uniform macropore size distribution, replicating the characteristics of the leachable NaCl particles used as templating agent. Nitrogen adsorption/desorption isotherms revealed the absence of meso- or microporosity, and the specific surface area was measured to be 0.38 m2 g−1. Mercury intrusion porosimetry offered similar results for the specific surface area, and the pore size distribution was deduced to be in the interval of 80 nm–200 µm. X-ray photoelectron spectroscopy allowed concluding that the pore surface exhibited poor oxygenated functionalization. Cyclic voltammetry depicted a wide potential window for the oxidation and reduction of water, with small pseudo-capacitive process. The electrochemical behaviour of outer-sphere reversible redox couples provided a standard rate constant k° of ca. 0.7 cm s−1, which is slightly superior to that shown using a conventional glassy carbon electrode. Biomolecules such as ascorbic acid, uric acid and dopamine were also examined to shed some light on sensing applications. The viability of regenerating the coenzyme nicotinamide adenine dinucleotide using a rhodium redox complex has also been addressed in order to explore electrosynthetic potentialities.
Gold nanoparticles and nanostructures were electrodeposited on transparent ITO electrodes in the presence of l-cysteine. When the deposition potential was shifted from −0.5V (vs. Ag|AgCl) to 0.0V (deposition time: 60s), the gold nanoparticles changed from spheres to larger and bumpy structures, resulting in a redshift of the absorption peak based on localized surface plasmon resonance (LSPR) from 630nm to 710nm. Prolonged deposition at −0.5V increased the size as well as the absorption and scattering of the spherical nanoparticles. At 0.0V, elongated deposition increased the size of the bumpy nanoparticles, and finally yielded more complicated three-dimensional structures including dendritic structures, which gave low scattering and intense absorption. The electrodeposited gold nanoparticles were applied to a LSPR sensor for refractive index with controllable working wavelength and sensitivity.
Sugar crystallizers deliver a slurry where the sugar grains are suspended in the so called mother liquor. The batch centrifuges are the units in charge of mechanically separating the former from the latter guaranteeing the quality and efficiency of the process. A realistic first principles model of a batch sugar centrifuge is described in the context of a Sugar House object oriented generic library, specially designed for the training of control room personnel. The challenges posed by the hybrid continuous–discrete character of the model are particularly addressed.
The International Congress on Membranes and Membrane Processes 2011 (ICOM 2011) is scheduled to be held on 23–29 July 2011 in Amsterdam, The Netherlands.
NaOH-neutralized poly(acrylic acid) is examined as a binder for Si-based negative electrodes in rechargeable Li-ion batteries. To better understand the influence of polymer binder characteristics, the impact of neutralization degree (ND) of poly(acrylic acid) (PAH) on electrode performance of a Si–graphite composite is studied. The electrode performance of the Si-based composites is remarkably improved by appropriate neutralization of PAH because the NDs highly influence rheological properties of a slurry and thus the electrode morphology, such as porosity. It is found that 80% neutralized PAH provides the moderate porous structure inside the composite electrode with 10 wt% binder content because of a unique rheological property during the drying process after casting the slurry onto a current collector. The self-formed porous structure by the partially neutralized PAH is beneficial to buffer volume expansion caused by lithiation of Si. Therefore, an excellent capacity retention for a 100 cycle test with a high reversible capacity of approximately 1000 mA h g−1 is achieved with the 80% neutralized PAH as a binder for Si-based composite electrodes.
To test the hypotheses that (i) electroencephalograms (EEGs) are largely made up of oscillations at many frequencies and (ii) that the peaks in the power spectra represent oscillations, we applied a new method, called the period specific average (PSA) to a wide sample of EEGs. Both hypotheses can be rejected. Although the principal peaks in the two spectra agree most of the time, quite often a peak in the power spectrum accompanies no periodicity peak and some periodicity peaks have no power spectral peak. The Fourier spectrum is not a reliable indication of rhythms. EEG samples from patients during waking, sleeping and seizure states, and volunteer healthy subjects doing cognitive tasks quite often show no significant rhythms, on an arbitrary, common sense definition. When clear rhythms are seen, they involve one or two, rarely up to four or five simultaneous non-harmonically related frequencies. Rhythms are special cases; most of the power spectrum most of the time is nonrhythmic. “Good” rhythms usually have quite narrow peaks, with frequency modulation of <5%, strengths of >2.5 up to >10 times the expectation from chance, and they often show fine structure by being quite local and brief. Most rhythms are quasisinusoidal but others are sharp-cornered recurrent events with <50% duty cycle. In the face of wide variability, we do not report any systematic differences in periodicity among EEGs from different parts of the brain or different brain states or species; it will take many more exemplars of each state, species or brain part to establish characteristic features. The PSA method may be the best so far proposed to demonstrate and quantify periodicity in wide-band time series with noise, but it has serious limitations. Discussion leads to the conclusion that it is time for a new paradigm or metaphor for brain waves.
The layered complex cathode has attracted much interest recently due to its high capacity, which exceeds 250mAhg−1. On the other hand, it also shows large voltage hysteresis which causes energy loss when applied as a practical battery material. It has been reported that the hysteresis is an intrinsic bulk property, and the phenomenological model due to the migration of transition metal has been also proposed. Then, it is considered that to study the hysteresis for various compositions of transition metal is valuable to clarify the phenomenon. In this work, the layered complex cathode of 0.5Li2MnO3-0.5LiNi1/3Co1/3Mn1/3O2 was investigated. The results are discussed in comparison with the previous reports for 0.5Li2MnO3-0.5LiMn0.5Ni0.5O2. Investigating dQ/dV profilesrevealed that redox peaks at around 3.75V showed small dependency on composition of transition metal, while it seemed that a reduction peak at 3.26V was independent on the composition. Precise measurement of open circuit potential vs. capacity characteristics demonstrated that the energy dissipation during a cycle was abut 26kJmol−1.
A novel composite of highly-crystalline ultrathin Li4Ti5O12 (LTO) nanosheets and Ag nanocrystals (denoted as LTO NSs/Ag) as an anode material for Li-ion batteries (LIBs) is prepared by hydrothermal synthesis, post calcination and electroless deposition. The characterizations of structure and morphology reveal that the LTO nanosheets have single-crystal nature with a thickness of about 10 nm and highly dispersed Ag nanocrystals have an average diameter of 5.8 nm. The designed LTO NSs/Ag composite takes advantage of both components, thereby providing large contact area between the electrolyte and electrode, low polarization of voltage difference, high electrical conductivity and lithium ion diffusion coefficient during electrochemical processes. The evaluation of its electrochemical performance demonstrates that the prepared LTO NSs/Ag composite has superior lithium storage performance. More importantly, this unique composite has an ability to deliver high reversible capacities with superlative cyclic capacity retention at different current rates, and exhibit excellent high-rate performance at a current rate as high as 30 C. Our results improve the current performance of LTO based anode material for LIBs.
To access the full performance potential of advanced batteries, electrodes and electrolytes must be designed to facilitate ion transport at all applicable length scales. Here, we perform electrodynamic measurements on single electrode particles of ~6 nAh capacity, decouple bulk and interfacial transport from other pathways and show that Li intercalation into LiNi0.33Mn0.33Co0.33O2 (NMC333) is primarily impeded by interfacial kinetics when using a conventional LiPF6 salt. Electrolytes containing LiTFSI salt, with or without LiPF6, exhibit about 100-fold higher exchange current density under otherwise identical conditions. This anion group effect is explained using molecular dynamics simulations to identify preferred solvation structures, density functional theory calculations of their binding energies and Raman spectroscopy confirmation of solvation structure. We show that TFSI− preferentially solvates Li+ compared to PF6−, and yet its preferred solvation structures provide a lower Li+ binding energy, suggesting a lower desolvation energy consistent with ultrafast interfacial kinetics.
A phase field model is developed to investigate the silicon nanowire behaviors in lithium-ion battery electrode during its lithiation process. The coupling effect among lithium ion diffusion/insertion process, structure deformation and local stress/strain evolution are established. Modeling demonstrates that such coupling effect can significantly influence electrochemical performance of silicon composite electrode. On a 2D silicon nanowire geometry, Cahn-Hilliard equation and Ginzberg-Landau equations are developed and solved by finite element method. The developed model has nearly the same prediction on volumetric expansion ratio of silicon NW in comparison with the published experimental observation and can capture the a − L i η S i / c − S i phase boundary during lithiation. Numerical results show that large local stress exists in the outer region of silicon NW and could negatively influence the fast charging performance of silicon composite electrode. Results also show that small lithium mobility can limit the lithiation depth of silicon electrode during the charging process, and can result in reduced charge capacity of silicon composite electrode. By simulating different silicon NW structures, it is found that silicon NW structure can significantly influence the local stress distribution and evolution in silicon composite electrode. It is also found that porous silicon NW has potential structure degradation around the core region during its lithiation process. These obtained results can provide insights into the dynamic process of silicon electrode degradation and can assist in developing applicable high performance silicon electrode for future lithium ion batteries.
LiCoO2 thin films have been prepared on aluminium substrate with RF sputtering using a bias effect combined with a moderate post-annealing treatment at 500 °C and their electrochemical properties investigated in liquid electrolyte by cyclic voltammetry, galvanostatic experiments in various voltage windows, and ac impedance spectroscopy. The positive effect of bias is shown allowing to minimize the presence of the cubic LiCoO2 phase. The lithium extraction process is highly reversible in the biased LiCoO2 films with charge–discharge curves which really superimpose at C/10 rate. A 450 nm thin film is shown to exhibit an initial charge capacity of ≈60 μAh cm−2 μm−1 at C/10 and a high discharge capacity of ≈50 μAh cm−2 μm−1. The rate capability study demonstrates the film can easily sustain high charge–discharge rates and exhibits good cycling properties with capacity retention of 90% after 50 cycles up to a 2C rate and still 73% of the maximum capacity is recovered at 8C in the 4.2 V–3 V potential window. This constitutes remarkable performances both in terms of rate capability and cycling stability. The charge–discharge behaviour as a function of the film thickness in the range 0.25–3.6 μm is investigated and indicates an efficient and homogeneous electrochemical activity with a linear increase of the capacity with thickness. As a consequence an optimization of the capacity is proposed with the use of the thickest deposit of 3.6 μm leading to the value of 200 μAh cm−2, the best one available for a LiCoO2 film in liquid electrolyte.