Chemically Etched Silicon Nanowires As Anodes for Lithium-Ion Batteries
Abstract not provided.
Publications
LiS Pouch Cell Fabrication and Cathode Prototyping
Abstract not provided.
Composition and manufacturing effects on electrical conductivity of Li/FeS2 thermal battery cathodes
Journal of the Electrochemical Society
Electrical conductivity is key to the performance of thermal battery cathodes. In this work we present the effects of manufacturing and processing conditions on the electrical conductivity of Li/FeS2 thermal battery cathodes. We use finite element simulations to compute the conductivity of three-dimensional microcomputed tomography cathode microstructures and compare results to experimental impedance spectroscopy measurements. A regression analysis reveals a predictive relationship between composition, processing conditions, and electrical conductivity; a trend which is largely erased after thermally-induced deformation. The trend applies to both experimental and simulation results, although is not as apparent in simulations. This research is a step toward a more fundamental understanding of the effects of processing and composition on thermal battery component microstructure, properties, and performance.
Understanding performance limitations to enable high performance magnesium-ion batteries
Journal of the Electrochemical Society
A mathematical model was developed to investigate the performance limiting factors of Mg-ion battery with a Chevrel phase (MgxMo6S8) cathode and a Mg metal anode. The model was validated using experimental data from the literature [Cheng et al., Chem. Mater., 26, 4904 (2014)]. Two electrochemical reactions of the Chevrel phase with significantly different kinetics and solid diffusion were included in the porous electrode model, which captured the physics sufficiently well to generate charge curves of five rates (0.1C-2C) for two different particle sizes. Limitation analysis indicated that the solid diffusion and kinetics in the highervoltage plateau limit the capacity and increase the overpotential in the Cheng et al.'s thin (20-μm) electrodes. The model reveals that the performance of the cells with reasonable thickness would also be subject to electrolyte-phase limitations. The simulation also suggested that the polarization losses on discharge will be lower than that on charge, because of the differences in the kinetics and solid diffusion between the two reactions of the Chevrel phase.
Measuring Li+ inventory losses in LiCoO2/graphite cells using raman microscopy
Journal of the Electrochemical Society
The contribution from loss of Li+ inventory to capacity fade is described for slow rates (C/10) and long-term cycling (up to 80 cycles). It was found through electrochemical testing and ex-situ Raman analysis that at these slow rates, the entirety of capacity loss up to 80 cycles can be explained by loss of Li+ inventory in the cell. The Raman spectrum of LiCoO2 is sensitive to the state of lithiation and can therefore be leveraged to quantify the state of lithiation for individual particles. With these Raman derived estimates, the lithiation state of the cathode in the discharged state is compared to electrochemical data as a function of cycle number. High correlation is found between Raman quantifications of cycleable lithium and the capacity fade. Additionally, the linear relationship between discharge capacity and cell overpotential suggests that the loss of capacity stems from an impedance rise of the electrodes, which based on Li inventory losses, is caused by SEI formation and repair.
Conductivity Degradation of Polyvinylidene Fluoride Composite Binder during Cycling: Measurements and Simulations for Lithium-Ion Batteries
Journal of the Electrochemical Society
The polymer-composite binder used in lithium-ion battery electrodes must both hold the electrodes together and augment their electrical conductivity while subjected to mechanical stresses caused by active material volume changes due to lithiation and delithiation. We have discovered that cyclic mechanical stresses cause significant degradation in the binder electrical conductivity. After just 160 mechanical cycles, the conductivity of polyvinylidene fluoride (PVDF):carbon black binder dropped between 45-75%. This degradation in binder conductivity has been shown to be quite general, occurring over a range of carbon black concentrations, with and without absorbed electrolyte solvent and for different polymer manufacturers. Mechanical cycling of lithium cobalt oxide (LiCoO2 ) cathodes caused a similar degradation, reducing the effective electrical conductivity by 30-40%. Mesoscale simulations on a reconstructed experimental cathode geometry predicted the binder conductivity degradation will have a proportional impact on cathode electrical conductivity, in qualitative agreement with the experimental measurements. Finally, ohmic resistance measurements were made on complete batteries. Direct comparisons between electrochemical cycling and mechanical cycling show consistent trends in the conductivity decline. This evidence supports a new mechanism for performance decline of rechargeable lithium-ion batteries during operation - electrochemically-induced mechanical stresses that degrade binder conductivity, increasing the internal resistance of the battery with cycling.
In situ XANES and EXAFS Analysis of Redox Active Fe Center Ionic Liquids
Electrochimica Acta
In situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques are applied to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Determination of the extent of reduction under negative bias on the working electrode and the extent of oxidation are determined after pulse voltammetry to quiescence. While the ionic liquid undergoes full oxidation, it undergoes only partial reduction, likely due to transport issues on the timescale of the experiment. Nearest neighbor Fe-O distances in the fully oxidized state match well to expected values for similarly coordinated solids, but reduction does not result in an extension of the Fe-O bond length, as would be expected from comparisons to the solid phase. Instead, little change in bond length is observed. We suggest that this may be due to a more complex interaction between the monodentate ligands of the metal center anion and the surrounding charge cloud, rather than straightforward electrostatics between the metal center and the nearest neighbor grouping.
The role of polymer composite binder on mechanics and performance of lithium ion battery electrodes
Abstract not provided.
The role of polymer composite binder on mechanics and performance of lithium ion battery electrodes
Abstract not provided.
Mesoscale Modeling and Simulation of Composition Manufacturing and Microstructure Effects on Electrical Conduction in Thermal Battery Cathodes
Abstract not provided.
Etched Silicon Nanowires as Anodes
Abstract not provided.
Performance of a MgS battery using Grignard Based Electrolytes
Abstract not provided.
Steps towards in-situ studies of the mechanical degradation of Li-Ion Batteries Using Fluorescence Confocal Microscopy
Abstract not provided.
Performance of a MgS battery using Grignard Based Electrolytes
Abstract not provided.
Mesoscale modeling and simulation of composition, manufacturing, and microstructure effects on electrical conduction in thermal battery cathodes
ECS Transactions
Li/FeS2 thermal batteries provide a stable, robust, and reliable power source capable of long-term electrical energy storage without performance degradation. These systems rely on the electrical conductivity of FeS2 cathodes for critical performance parameters such as power and lifetime, and on permeability of the electrolyte through the solid FeS2 particles for ion transfer. The effects of component composition, manufacturing conditions, and the mechanical deformation on conductivity and permeability have not been studied. We present simulation results from a finite element computer model compared with impedance spectroscopy electrical conductivity experiments. Our methods elucidate the combined effects of slumping, particle size distribution, composition, and pellet density on properties related to electrical conduction in Li/FeS2 thermal battery cathodes.
Degradation of Thin Film Pb(ZrTi)O3 in H2SO4
Abstract not provided.
Electrochemical Fabrication of Energetic Thin Films
Abstract not provided.
Lithium Thiophosphate Compounds as Stable High Rate Li-Ion Separators
Battery separators based upon lithium thiophosphate (LiPS4) have previously been demonstrated at UC Boulder, but the thickness of the separators was too high to be of practical use in a lithium ion battery. The separators are solid phase, which makes them intrinsically less prone to thermal runaway and thereby improves safety. Results of attempting to develop sputtered thin film layers of this material by starting with targets of pure Li, Li2S, and P2S5 are reported. Sputtering rates and film quality and composition are discussed, along with efforts to use Raman spectroscopy to determine quantitative film composition. The latter is a rate limiting step in the investigation of these films, as they are typically thin and require long times to get to sufficient thickness to be analyzed using traditional methods, whereas Raman is particularly well suited to this analysis, if it can be made quantitative. The final results of the film deposition methods are reported, and a path towards new films is discussed. Finally, it should be noted that this program originally began with one graduate student working on the program, but this student ultimately chose to not continue with a PhD. A second student took over in the middle of the effort, and a new program has been proposed with a significantly altered chemistry to take the program in a new direction.
Synthesis and Characterization of Alkali Metal Ion Battery Cathode Materials from Novel Single-source Metal Alkoxides
Abstract not provided.
Scaling effects in Nasicon thin films prepared via chemical solution deposition
Abstract not provided.
Synthesis and characterization of alkali metal ion battery cathode materials from novel single-source metal alkoxides
Abstract not provided.
Nanocathode precursors for lithium ion batteries
Abstract not provided.
Synthesis of a Family of Lithium Iron Double Aryloxide Precursors for Nano-LiFeO2 Cathode Materials
European Journal of Inorganic Chemistry
Abstract not provided.
Examining the effects of charge defects on domain switching in thin film PZT via controlled neutron irradiation
Abstract not provided.
The Price of Small: Power at the Microscale
Abstract not provided.
Results 26–50 of 84