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Inhomogeneity in Li(ion) Battery Electrodes: Causes and Effects
No full textThe environmental and climate change concerns are calling for rapid energy transition by the use of more green resources and zero emission solutions. This requires development of mature energy storage systems like rechargeable batteries. For instance, the Li-ion battery technology was first commercialized in 1985, but still is under research and development to increase energy density and cycle life beyond the state-of-the-art. The search for energy dense active-materials like high nickel content transition metal oxides, the use of solid electrolytes or the strive for enabling dendrite-free lithium metal anodes all aim to tackle the limitations of today’s technology. Another strategy is to ensure that the battery is manufactured authentically, devoid of defects and inhomogeneities. These inhomogeneities might exist at different length scales from nanoscale to macroscale or in other words from active-material level to cell pack level. The focus of this thesis is to investigate the causes and effects of inhomogeneities in the cells, especially at the electrode level, like poor carbon distribution or insufficient electrolyte wetting in the electrodes. Such flaws can interfere with electronic and ionic transport in the battery porous electrodes and possibly cause reduced performance, non-uniform degradation and accelerated aging.
The first chapter presents a brief review of Li-ion battery technology, porous electrode model, battery aging mechanisms and an introduction to inhomogeneities at different length scales. In the second chapter, we study LiNi0.6Mn0.2Co0.2O2 slurries prepared via different methods and characterize their viscoelastic behavior and dis/charge behavior of electrodes made thereof. We observed disparities among the dis/charge behavior, and ascribed it to the local variations in carbon-binder domain porosity and thickness. In chapter 3, we fabricated bilayer electrodes with a disparity among the two layers as inhomogeneity of porous electrodes. In our system, we had a carbon-deficient or carbon-rich layer near the electrode current collector. The results showed that the former can have a destructive effect on rate performance and aging while the latter appeared to have a constructive effect. Chapter 4 investigates possible aging mechanism in porous NMC electrodes in the presence of heterogeneity in the electrode structure. We observed frequent reductions in the charge transfer resistance of the electrodes during long term cycling of the electrodes which is correlated to the fracture of active-material particles. This hypothesis was further elaborated by cross-sectional imaging as well as observation of an unusual energy recovery which could be explained by intergranular fracture. Finally in chapter 5, we looked at the inhomogeneity in-plane of the battery electrodes. Large format lithium electrodes were made and tested in a home-made setup in symmetric configuration where both working and counter electrodes were lithium. The spatial distribution of degradation over the surface of large electrodes was correlated to non-uniform distribution of current density in-plane of the battery electrodes
Poly(ethylene disulfide)/graphene oxide nanocomposites: Dynamic-mechanical and electrochamical properties
No full textPoly(ethylene disulfide)/graphene oxide nanocomposites: Dynamic-mechanical and electrochemical properties
No full textIn this work, dynamic-mechanical and electrochemical properties of polyethylene disulfide and polyethylene disulfide/graphene oxide (GO) nanocomposites are investigated to explore their possible application in rechargeable batteries. The crude polyethylene disulfide, as well as GO and sodium dodecylbenzenesulfonate (SDBS) modified-GO loaded nanocomposites are synthesized through the in situ interfacial polymerization. The GO loaded nanocomposite presents a glass transition temperature of 4.5 °C and a high storage modulus of 115 MPa at 25 °C, which is 17% and 155% higher than that for the crude polyethylene disulfide and the SDBS-modified-GO loaded nanocomposite, respectively. Although the electrical conductivity of the 2 GO loaded nanocomposite is slightly higher than other two materials (due to the slightly higher electrical conductivity of GO nanosheets), the electrical conductivity of all polysulfide materials is very close and in the range of 10-6 and 10-4 S/m at low (10 Hz) and high frequencies (10 6 Hz), respectively. Notably, the polyethylene disulfide/GO nanocomposite presents a Coulombic efficiency of 97% in a lithium cell with a conventional liquid-electrolyte
Toward a synergistic optimization of porous electrode formulation and polysulfide regulation in lithium-sulfur batteries
No full textThe use of functional materials is a popular strategy to mitigate the polysulfide-induced accelerated aging of lithium-sulfur (Li-S) batteries. However, deep insights into the role of electrode design and formulation are less elaborated in the available literature. Such information is not easy to unearth from the existing reports on account of the scattered nature of the data and the big dissimilarities among the reported materials, preparation protocols, and cycling conditions. In this study, model functional materials known for their affinity toward polysulfide species, are integrated into the porous sulfur electrodes at different quantities and with various spatial distributions. The electrodes are assembled in 240 lithium-sulfur cells and thoroughly analyzed for their short- and long-term electrochemical performance. Advanced data processing and visualization techniques enable the unraveling of the impact of porous electrodes' formulation and design on self-discharge, sulfur utilization, and capacity loss. The results highlight and quantify the sensitivity of the cell performance to the synergistic interactions of catalyst loading and its spatial positioning with respect to the sulfur particles and carbon-binder domain. The findings of this work pave the road for a holistic optimization of the advanced sulfur electrodes for durable Li-S batteries.
This research seeks to offer key insights into optimizing advanced electrodes for lithium-sulfur batteries. The study emphasizes the critical role of optimal catalyst quantity and strategic placement near sulfur particles or the carbon-binder domain. These factors notably impact capacity retention and rate-capability, governing the local balance between the conversion and migration rates of polysulfides.imag
Theoretical and Experimental Insights into Dendrite Growth in Lithium-Metal Electrode
Full text linkA stable lithium-metal electrode can enable the shift from the Li-ion batteries to the next generation chemistries such as Li-S and Li-O2 with significant gains in the energy density and sustainability. This transition, however, is hindered by the dendrite formation, high chemical reactivity, and volume changes of the Li electrode. Although recent advancements in computational and experimental research have deepened our understanding of these issues, the primary obstacles to the commercialization of the lithium-metal batteries (LMBs) still persist. To address these challenges, a synergistic approach that combines computational and experimental strategies shows great promise. In this regard, this paper reviews the current experimental and theoretical understanding of the lithium-metal electrodes in view of the initiation and growth mechanisms of the lithium dendrites and interface instability. Leveraging the strengths of both approaches can offer a holistic insight into the LMB performance and guide the development of innovative designs for electrolytes and electrodes that can enhance the stability and performance of the LMBs
Synergistic interactions between the charge‐transport and mechanical properties of the ionic‐liquid‐based solid polymer electrolytes for solid‐state lithium batteries
Full text linkH2020 LEIT Advanced Materials, Grant/Award Number: 87555
Probing Charge Transport and Microstructural Attributes in Solvent- versus Water-Based Electrodes with a Spotlight on Li-S Battery Cathode
No full textIn the quest for environmentally benign battery technologies, this study examines the microstructural and transport properties of water-processed electrodes and compares them to conventionally formulated electrodes using the toxic solvent, N-Methyl-2-pyrrolidone (NMP). Special focus is placed on sulfur electrodes utilized in lithium-sulfur batteries for their sustainability and compatibility with diverse binder/solvent systems. The characterization of the electrodes by X-ray micro-computed tomography reveals that in polyvinylidene fluoride (PVDF) Lithium bis(trifluoromethanesulfonyl)imide/NMP, sulfur particles tend to remain in large clusters but break down into finer particles in carboxymethyl cellulose-styrene butadiene rubber (CMC-SBR)/water and lithium polyacrylate (LiPAA)/water dispersions. The findings reveal that in the water-based electrodes, the binder properties dictate the spatial arrangement of carbon particles, resulting in either thick aggregates with short-range connectivity or thin films with long-range connectivity among sulfur particles. Additionally, cracking is found to be particularly prominent in thicker water-based electrodes, propagating especially in regions with larger particle agglomerates and often extending to cause local delamination of the electrodes. These microstructural details are shown to significantly impact the tortuosity and contact resistance of the sulfur electrodes and thereby affecting the cycling performance of the Li-S battery cells. The choice of solvent and binder is crucial in determining particle surface charge, which directly influences active material dispersion and carbon-binder arrangement within the battery porous electrodes. This, in turn, affects ionic and electronic transport properties, ultimately impacting electrochemical performance. Meticulous engineering of the slurry to control these factors is essential for efficient and sustainable water-based electrode processing. imageThis work was supported by SIM (Strategic Initiative Materials in Flanders)and VLAIO (Flemish Government Agency Flanders Innovation and En-trepreneurship) within the SBO project “FuGels” (Grant HBC.2021.0016)under the SIM research program “SIMBA—Sustainable and InnovativeMaterials for Batteries.” Additional support was provided by the FaradayInstitution (www.faraday.ac.uk; EP/S003053/1) through the Lithium SulfurTechnology Accelerator (LiSTAR) program (FIRG014, FIRG058). The au-thors would also like to thank S.Sallard for helpful discussions on binderpreparation, A. Ethirajan and B. Luyck for facilitating Zeta Potential mea-surements, and R. S. Young for developing a software tool to maximizephase contrast using X-ray C
Revisiting the Importance of Sulfur Electrode-Current-Collector Interface in Lithium-Sulfur Batteries
No full textThe authors are grateful for financial support to FWO-Vlaanderen and the Special Research Fund BOF of Hasselt University. A.C.R. is a PhD research fellow of the Research Foundation Flanders (FWO Vlaanderen). The authors are also grateful for the work and contribution of Hide Pellears concerning the preparation and treatment of the numerous samples used in this work
Demystifying charge transport limitations in the porous electrodes of lithium-ion batteries
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