Dual active material composite cathode structures for Li-ion batteries

The efficacy of composite Li-ion battery cathodes made by mixing active materials that possessed either high-rate capability or high specific energy was examined. The cathode structures studied contained carbon-coated LiFePO₄ and either Li[Li_0.17Mn_0.58Ni_0.25]O₂ or LiCoO₂. These active materials were arranged using three different electrode geometries: fully intermixed, fully separated, or layered. Discharge rate studies, cycle-life evaluation, and electrochemical impedance spectroscopy studies were conducted using coin cell test structures containing Li-metal anodes. Results indicated that electrode configuration was correlated to rate capability and degree of polarization if there was a large differential between the rate capabilities of the two active material species.     

A low complexity hardware architecture of K-means algorithm for real-time satellite image segmentation

Multimedia Tools and Applications - The Real time monitoring of forest area, coastal regions, sea, river basins, nation borders etc. helps in quick determination of devastations caused by natural...     

Microstructure and pitting corrosion of partially melted zones of A356 Al-Si alloy welds

The corrosion behaviour of weld metal, partially melted zones and heat affected zones of gas tungsten arc welds in A356 Al-Si alloy with different prior thermal tempers has been studied. Continuous and pulsed current gas tungsten arc welding techniques were used. Potentiodynamic polarization testing was carried out to determine the corrosion resistance. Optical and scanning electron microscopy studies were carried out to determine the corrosion mechanism. The partially melted zone of the welds was found to be attacked severely. A pulsing technique was found to decrease the severity of corrosion damage in the partially melted zone. The prior thermal condition of the alloys was found to influence the corrosion of heat affected zones of welds.     

Implications of the first cycle irreversible capacity on cell balancing for Li2MnO3-LiMO2 (M = Ni, Mn, Co) Li-ion cathodes

Much of the research on lithium-ion cathodes consisting of layered solid solutions of Li₂MnO₃-LiMO₂ (M = Mn, Co, Ni) has focused on identifying the causes of the irreversible capacity loss on the first cycle. However, a key issue that must be addressed is whether the high irreversible capacity observed seen on the first cycle is associated with intercalated lithium at the anode, or if it is associated with irretrievable capacity (i.e., film formation, and/or decomposition reactions). To this end, we have quantified the amount of utilizable lithium that is made available for the anodes when employing Li₂MnO₃-LiMO₂ as cathodes. Using a MoS₂ anode lithiation plateau transition as a reference point to the amount of lithium transferred to the anode during charge, it has been shown that almost none of the cathode irreversible charge capacity resulted in lithiation of the anode. Further, by reacting charged graphitic anodes that were retrieved from C anode-Li_1.2Ni_0.175Co_0.1Mn_0.52O₂ cathode cells with water to generate H₂ gas to measure the active amount of lithium in the anode, we confirmed the results with the MoS₂ titration experiments, demonstrating that lithium released from the cathode during the first charge is not proportionate to the cathode charge capacity.     

Gel polymer electrolyte lithium-ion cells with improved low temperature performance

For a number of NASA's future planetary and terrestrial applications, high energy density rechargeable lithium batteries that can operate at very low temperature are desired. In the pursuit of developing Li-ion batteries with improved low temperature performance, we have also focused on assessing the viability of using gel polymer systems, due to their desirable form factor and enhanced safety characteristics. In the present study we have evaluated three classes of promising liquid low-temperature electrolytes that have been impregnated into gel polymer electrolyte carbon-LiMn₂O₄-based Li-ion cells (manufactured by LG Chem. Inc.), consisting of: (a) binary EC + EMC mixtures with very low EC-content (10%), (b) quaternary carbonate mixtures with low EC-content (16–20%), and (c) ternary electrolytes with very low EC-content (10%) and high proportions of ester co-solvents (i.e., 80%). These electrolytes have been compared with a baseline formulation (i.e., 1.0 M LiPF₆ in EC + DEC + DMC (1:1:1%, v/v/v), where EC, ethylene carbonate, DEC, diethyl carbonate, and DMC, dimethyl carbonate). We have performed a number of characterization tests on these cells, including: determining the rate capacity as a function of temperature (with preceding charge at room temperature and also at low temperature), the cycle life performance (both 100% DOD and 30% DOD low earth orbit cycling), the pulse capability, and the impedance characteristics at different temperatures. We have obtained excellent performance at low temperatures with ester-based electrolytes, including the demonstration of >80% of the room temperature capacity at −60 °C using a C/20 discharge rate with cells containing 1.0 M LiPF₆ in EC + EMC + MB (1:1:8%, v/v/v) (MB, methyl butyrate) and 1.0 M LiPF₆ in EC + EMC + EB (1:1:8%, v/v/v) (EB, ethyl butyrate) electrolytes. In addition, cells containing the ester-based electrolytes were observed to support 5C pulses at −40 °C, while still maintaining a voltage >2.5 V at 100 and 80% state-of-charge (SOC).     

Organic cathode materials in sodium batteries

In order to circumvent the corrosion problems prevalent in many existing electrochemical couples using the Na/-alumina half cell, a new class of high energy density organic materials was studied as cathode materials. In particular, one material tetracyanoethylene (TCNE), has favourable electrochemical characteristics with a potential >3.0 V against Na⁺/Na and energy density 620 Wh kg^–1. Adopting a cell designed to permit sealing the anode half cell, the performance of TCNE was evaluated under various experimental conditions, that is, at different concentrations of TCNE in the catholyte and with different current collectors. The electrochemical behaviour of the TCNE cathode and the kinetics of TCNE reduction were examined. The kinetic parameters, exchange current density and diffusion coefficient, were determined from different a.c. and d.c. electrochemical techniques and evaluated with respect to the changes in TCNE concentrations in the catholyte. A chemical transformation occurring in the cell operating conditions which does not reduce the electrochemical activity of TCNE was identified from FTIR spectra. Finally, possible approaches to the use of TCNE or other organic materials in sodium or lithium rechargeable batteries are outlined.     

Electrochemical performance and kinetics of Li1+x(Co1/3Ni1/3Mn1/3)1−xO2 cathodes and graphite anodes in low-temperature electrolytes

Lithium-ion batteries have started replacing the conventional aqueous nickel-based battery systems in space applications, such as planetary landers, rovers, orbiters and satellites. The reasons for such widespread use of these batteries are the savings in mass and volume of the power subsystems, resulting from their high gravimetric and volumetric energy densities, and their ability to operate at extreme temperatures. In our pursuit to further enhance the specific energy as well as low-temperature performance of Li-ion batteries, we have been investigating various layered lithiated metal oxides, e.g., LiCoO₂, LiNi_0.8Co_0.2 and LiNi_0.8Co_0.15Al_0.05O₂, as well as different low-temperature electrolytes, including ternary and quaternary carbonate mixtures with various co-solvents. In this paper, we report our recent studies on Li_1+x(Co_1/3Ni_1/3Mn_1/3)_1−xO₂ cathodes, combined with three different low-temperature electrolytes, i.e.: (1) 1.0 M LiPF₆ in EC:EMC (20:80), (2) 1.2 M LiPF₆ in EC:EMC (20:80) and (3) 1.2 M LiPF₆ in EC:EMC (30:70). Electrical performance characteristics were determined in laboratory glass cells at different discharge rates and different temperatures. Further, individual electrode kinetics of both Li_1+x(Co_1/3Ni_1/3Mn_1/3)_1−xO₂ cathodes and MCMB graphite anodes were determined at different temperatures, using dc micropolarization, Tafel polarization and electrochemical impedance spectroscopy (EIS). Analysis of these data has led to interesting trends relative to the effects of solvent composition and salt concentration, on the electrical performance and on the kinetics of cathode and anode.     

DerainGAN: Single image deraining using wasserstein GAN

Multimedia Tools and Applications - Rainy weather greatly affects the visibility of salient objects and scenes in the captured images and videos. The object/scene visibility varies with the type of...     

Passive films on magnesium anodes in primary batteries

The characteristics of the passive films over Mg anodes, which essentially govern the voltage delay of the latter, have been determined non-destructively from an analysis of the transient and steady-state response of the electrode potential to low-amplitude galvanostatic polarization under various experimental conditionsviz., with different corrosion inhibitor coatings on Mg, after various periods of ageing of anode in solutions containing corrosion inhibitors, at various low temperatures etc. Using these parameters, the kinetics of film build-up or dissolution under these conditions have been monitored. The morphology of the anode film has been predicted from a combination of potential-time transients at low c.d.s and delay-time curves during ageing and verified with scanning electron microscopy. Similar transients at low temperatures point out a steep rise in the film resistivity which is essentially responsible for the severe voltage delay. Finally, possible application of this technique in secondary Li batteries to improve cycling characteristics of the Li anode has been pointed out.