1,720,983 research outputs found
Effect of Surface Modifications on Electrochemical Performance of NMC811
Get PDFThe benefits of all-solid-state batteries(ASSBs) like safety, energy density, etc. are often touted but rarely realized. The biggest bottleneck in achieving high energy density is on the cathode side. High nickel-content cathode materials are now considered the most promising candidates for achieving the energy requirements, but they still have many shortcomings including poor cycling stability, especially when cycled at high voltage vs Li/Li+. Through this work, the author hopes to encourage the commercialization of energy-dense Li-ion batteries via the development of surface coatings to enhance the electrochemical properties of and protect the cathode material during cycling in an all-solid-state cell.
First, we utilized a nanometer layer coating of a lithium-ion conducting solid electrolyte, lithium phosphorus oxynitride (LiPON) by using RF-magnetron sputtering. The LiPON layer provides interfacial stability at high voltages, suppresses the growth of impedance with cycling, and improves the rate capability. Thicker coatings showed a negative impact on the performance of the cells owing to the increase in electronic resistance with increasing thickness of the LiPON layer.
To further progress our work, the problem of electrolyte decomposition was tackled by reducing the amount of conductive additive in the cathode composite and compensating for the loss in electronic conductivity by applying an amorphous polyacrylonitrile (PAN) coating on the surface of NMC811 followed by a simple heat treatment in air. The electrochemical properties and cycling performance of the cathode were improved by the mixed conducting nature of the cyclized PAN and its ability to coat the active materials due to its polar nature. Lastly, the heat treatment of PAN was further optimized by introducing oxygen gas during the stabilization of PAN coating via heat treatment. High initial discharge capacity was achieved with this work along with improvement in cyclability. The author expects this work to have a broad impact on the battery community and may pave the way for the eventual commercialization of the all-solid-state Li-ion cell.</p
Effect of Surface Modifications on Electrochemical Performance of NMC811
Get PDFThe benefits of all-solid-state batteries(ASSBs) like safety, energy density, etc. are often touted but rarely realized. The biggest bottleneck in achieving high energy density is on the cathode side. High nickel-content cathode materials are now considered the most promising candidates for achieving the energy requirements, but they still have many shortcomings including poor cycling stability, especially when cycled at high voltage vs Li/Li+. Through this work, the author hopes to encourage the commercialization of energy-dense Li-ion batteries via the development of surface coatings to enhance the electrochemical properties of and protect the cathode material during cycling in an all-solid-state cell.
First, we utilized a nanometer layer coating of a lithium-ion conducting solid electrolyte, lithium phosphorus oxynitride (LiPON) by using RF-magnetron sputtering. The LiPON layer provides interfacial stability at high voltages, suppresses the growth of impedance with cycling, and improves the rate capability. Thicker coatings showed a negative impact on the performance of the cells owing to the increase in electronic resistance with increasing thickness of the LiPON layer.
To further progress our work, the problem of electrolyte decomposition was tackled by reducing the amount of conductive additive in the cathode composite and compensating for the loss in electronic conductivity by applying an amorphous polyacrylonitrile (PAN) coating on the surface of NMC811 followed by a simple heat treatment in air. The electrochemical properties and cycling performance of the cathode were improved by the mixed conducting nature of the cyclized PAN and its ability to coat the active materials due to its polar nature. Lastly, the heat treatment of PAN was further optimized by introducing oxygen gas during the stabilization of PAN coating via heat treatment. High initial discharge capacity was achieved with this work along with improvement in cyclability. The author expects this work to have a broad impact on the battery community and may pave the way for the eventual commercialization of the all-solid-state Li-ion cell.</p
Isolation, Transfer and Characterisation of 2D Halide Organo-Metallic Perovskites
Get PDFOrganometallic halide perovskites have shown so much promise as solar cell materials and muchof this promise is attributed to high-performance metrics which are tuned with morphological variations. Since the advent of layered halide perovskites, much discussion has broken out on the properties of exfoliated/2D layers over the bulk or spin-coated counterparts of the same species. While previous literature has explored the structure-property dependence of different phases of the same molecularity, it is hoped that adapting accessible methods such as mechanical exfoliation can yield good quality few-layer materials with unique properties. This thesis covers a new set of parameters developed for isolating monolayer (PEA)2PbI4 and (PEA)2PbBr4 perovskites, and discusses the validation of these methods with Atomic Force Microscopy.
Extensive research is being done on the sensitivities of these halide perovskites to degradation in ambient conditions. The ultimate goal is to develop exfoliation and transfer methods to study the unique properties of these 2D halide perovskites. This paper examines the application of dl/dV measurements and scanning microwave microscopy to novel materials. This thesis aims to establish that this material shows unique properties in its single/few-layer forms when compared to the bulk state.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Finite Size Effects in Near Field Radiative Heat Transfer
Get PDFRadiative heat transfer is an extremely important area of study as it is the only mode of heat transfer which can occur is the absence of a medium. When radiative heat transfer occurs at a distance d which is smaller than the characteristic wavelength of radiative heat transfer it has been extensively studied that the Stefan-Boltzmann law of radiative heat transfer cannot predict the heat flux between two bodies due quantum effects such as photon tunneling. Hence in the near field the radiative heat flux is several orders of magnitude greater than the corresponding black body radiation. This gives rise to extremely interesting applications of radiative heat transfer at the nanoscale and heat flux enhancement. Current analytical solutions to solve near field radiative heat transfer between two parallel plates overestimate the radiative heat flux between the two surfaces as the analytical solutions do not consider energy loss due to escaping electromagnetic waves. This is because the parallel surfaces are considered to be infinitely long when compared to the distance between the surfaces. But as science progresses and object sizes become smaller and smaller the assumption that surfaces are infinitely larger than the distance between them can no longer hold true. Therefore this thesis focuses on studying the near field radiative heat transfer between surfaces than can be considered finite sized and establish the difference between the analytical heat flux and simulated heat flux to establish these finite size effects and understand the energy loss due to finite sizes. In particular, this thesis studies the finite size effects due to change in length and width of the two parallel and change in gap size d between two surfaces. For analytical studies this thesis uses the semi-infinte parallel plane approach and uses a multiphysics software known as SCUFFEM which uses the fluctuating surface current approach alongside boundary element method to calculate temperature independent generalized flux which can in turn be used to calculate the energy transfer between two surfaces.</p
Design of Compact Optically Pumped Vector Magnetometer
Get PDFThe Svenja and Regal research groups are collaboratively advancing the development of scalar and vector magnetometers, including integrated vector-scalar systems. This thesis focuses on designing a compact optically pumped vector magnetometer (COPVM) that measures the orientation of the magnetic field through Rabi frequencymeasurements driven by a microwave field, serving as an electromagnetic vector reference, across multiple atomic transitions. We transformed a large optical table setup for the vector magnetometer, designed by Cindy's group, into a 20 cm by 10 cm rectangular optical breadboard, designing and fabricating essential components like optical mounts, a microwave cavity, a thermal oven, Kapton heaters, and photodiode electronics to meet the dimensional constraints of COPVMs. To improve temperature uniformity in the vapor cell, we propose a novel cylindrical oven design supported by thermal simulations and in-situ experimental measurements of the vapor cell's heating temperature. We also designed a low-magnetic polyimide heater to mitigate magnetic field interference caused by conventional electrical heating elements. Additionally, we developed a compact cubic dielectric cavity (15 x 15 x 15 mm) with feeding loop antennas as a microwave source to drive various hyperfine 87Rb transitions (σ± and π). This project analyzes miniaturization challenges for the compact physics package (CPP) and its impact on size, weight, and power (SWaP), aiming to maintain optimal functionality. Components like optics mounts and microwave cavities are fabricated from nonmetallic materials using advanced techniques such as selective laser sintering (SLS) and CNC machining, which reduce magnetic interference and enhance structural alignment. This approach also allows for customization and rapid adjustments, supporting flexible prototyping and optimization. This thesis provides a roadmap for designing a compact optically pumped vector magnetometer, addressing key challenges and laying the foundation for future advancements in miniaturized atomic sensors.</p
Finite Size Effects in Near Field Radiative Heat Transfer
Get PDFRadiative heat transfer is an extremely important area of study as it is the only mode of heat transfer which can occur is the absence of a medium. When radiative heat transfer occurs at a distance d which is smaller than the characteristic wavelength of radiative heat transfer it has been extensively studied that the Stefan-Boltzmann law of radiative heat transfer cannot predict the heat flux between two bodies due quantum effects such as photon tunneling. Hence in the near field the radiative heat flux is several orders of magnitude greater than the corresponding black body radiation. This gives rise to extremely interesting applications of radiative heat transfer at the nanoscale and heat flux enhancement. Current analytical solutions to solve near field radiative heat transfer between two parallel plates overestimate the radiative heat flux between the two surfaces as the analytical solutions do not consider energy loss due to escaping electromagnetic waves. This is because the parallel surfaces are considered to be infinitely long when compared to the distance between the surfaces. But as science progresses and object sizes become smaller and smaller the assumption that surfaces are infinitely larger than the distance between them can no longer hold true. Therefore this thesis focuses on studying the near field radiative heat transfer between surfaces than can be considered finite sized and establish the difference between the analytical heat flux and simulated heat flux to establish these finite size effects and understand the energy loss due to finite sizes. In particular, this thesis studies the finite size effects due to change in length and width of the two parallel and change in gap size d between two surfaces. For analytical studies this thesis uses the semi-infinte parallel plane approach and uses a multiphysics software known as SCUFFEM which uses the fluctuating surface current approach alongside boundary element method to calculate temperature independent generalized flux which can in turn be used to calculate the energy transfer between two surfaces.</p
Isolation, Transfer and Characterisation of 2D Halide Organo-Metallic Perovskites
Get PDFOrganometallic halide perovskites have shown so much promise as solar cell materials and muchof this promise is attributed to high-performance metrics which are tuned with morphological variations. Since the advent of layered halide perovskites, much discussion has broken out on the properties of exfoliated/2D layers over the bulk or spin-coated counterparts of the same species. While previous literature has explored the structure-property dependence of different phases of the same molecularity, it is hoped that adapting accessible methods such as mechanical exfoliation can yield good quality few-layer materials with unique properties. This thesis covers a new set of parameters developed for isolating monolayer (PEA)2PbI4 and (PEA)2PbBr4 perovskites, and discusses the validation of these methods with Atomic Force Microscopy.
Extensive research is being done on the sensitivities of these halide perovskites to degradation in ambient conditions. The ultimate goal is to develop exfoliation and transfer methods to study the unique properties of these 2D halide perovskites. This paper examines the application of dl/dV measurements and scanning microwave microscopy to novel materials. This thesis aims to establish that this material shows unique properties in its single/few-layer forms when compared to the bulk state.</p
Thermal Modeling and Cryogenic Testing of Low-Cost Insulating Foam for a Next Generation Electron Electric Dipole Moment Experiment
Get PDFThe standard model of particle physics has been very successful in explaining many phenomenon, but we know it is incomplete. Observing a finite electron electric dipole moment (eEDM) would be of particular interest for extensions to the standard model. To improve upon the current eEDM sensitivity limit set by our experiment at JILA using HfF+, we are switching to a new molecule, ThF+. The latter promises longer coherence times than the former, because the eEDM sensitive state in ThF+ is the ground state. However, the coherence of this quantum state is readily destroyed by room temperature black body radiation. In order to realize any advantage, the experiment must be kept at cryogenic temperatures of about 200 K. This thesis investigates the feasibility of using low-cost household foam as cryogenic insulation for the setup.</p
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