Development and Application of a ReaxFF Reactive Force Field for Solid Electrolyte Interphase Study in Silicon Based Li-ion Batteries
Development and Application of a ReaxFF Reactive Force Field for Solid Electrolyte Interphase Study in Silicon Based Li-ion Batteries

Author: Mahdi Khajeh Talkhoncheh

Publisher:

Published: 2024

Total Pages: 0

ISBN-13:

DOWNLOAD EBOOK

The amount of energy required to satisfy the demands of the human population may not be able to be supplied solely by fossil fuels as the world population continues to rise and the supply of fossil fuels starts to decline. Lithium-ion batteries (LIBs), since being suggested as commercialized energy storage systems by Sony company in the 1990s, have been considered an important device in alternative energy solutions owing to their high energy density, wide working voltage, long cycling life, and low self-discharge rate. Improvement of the performance of these high energy chemical systems is directly linked to the understanding and improving the complex physical and chemical phenomena and exchanges that take place at their different interfaces. Surfaces or interfaces, which means structures built between dissimilar media such as liquids and solids, and interphases, which means structures formed within these dissimilar media, present significant challenges for their study and understanding since these are the regions where myriad events such as electron transfer, ion transfer and migration, reactions, and solvation/desolvation processes occur and significantly alter their configuration. A detailed understanding of battery chemistry, especially the formation of a solid electrolyte interphase (SEI)--a thin passivation layer which is generated during the first charge cycle due to the reduction of electrolytes--is still elusive. It is well known that the SEI has a strong influence on the battery performance characteristics, such as irreversible capacity, safety, and cycle life, when the SEI is a thin layer between the liquid electrolytes and anode surfaces formed by the electrochemical reductive decomposition reaction of the electrolyte during the initial few cycles. A stable SEI with full surface coverage over the electrode is important for achieving optimal electrochemical performances of Li-ion batteries. Understanding the SEI is quite challenging due to its complicated and amorphous structure. In order to investigate the physical and chemical interactions at the interfaces of energy storage devices such as Li-ion batteries a, we used ReaxFF reactive molecular dynamics simulations in the following two research areas: 1. In the last decade silicon has attracted significant attention as a potential next generation anode material for Li-ion batteries (LIBs) due to its high theoretical specific capacity (3579 mAh/g (Li15Si4)) compared to that of the commonly used graphite (372 mAh/g). However, despite the apparent attractiveness of Si in view of its application in LIBs, it is known to suffer from severe degradation problems which lead to performance losses of Si-based anodes, and the electrochemical outcome of the degradation is well documented in the literature: rapid capacity fading of the anode accompanied by the increased internal resistance of the cell. Full utilization of silicon's potential as an anode material is thus prevented by incomplete understanding of the degradation mechanisms and the resulting inability to implement effective mitigation tactics. To study the Si anode degradation at the anode/electrolyte interface, we have developed a ReaxFF reactive force field simulation protocol. In this protocol, a delithiation algorithm is employed. This novel systematic delithiation algorithm helps to capture the effect of different delithiation rates, which plays an important role in the irreversible structural change of delithiated Si. Besides, the fundamental of degradation was investigated by analyzing the relationship between the depth of discharge and corresponding volume and structural changes at different rates. 2. The SEI (solid-electrolyte interphase) is important for protecting silicon anodes in batteries from losing both silicon and electrolyte through side reactions. A major issue with this technology is SEI breakdown caused by cracking in silicon particles. A strategy is presented for creating a self-sealing SEI that automatically covers and protects the cracked surface of silicon microparticle anodes by bonding an ion pair to the silicon surface. The cations in the bond prevent silicon-electrolyte reactions while the anions migrate to the cracked surface and decompose more easily than the electrolyte. The SEI formed in this way has a double layer structure with a high concentration of lithium fluoride in the inner layer. To study the electrode electrolyte reactions at the anode/electrolyte interface, we have developed ReaxFF reactive force field parameter sets to organic electrolyte species such as ethylene carbonate, N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI), LiPF6 salt and lithium-Silicon oxygen electrode. Density Functional Theory (DFT) data describing Li-associated initiation reactions for the organic electrolytes and bonding energies of Li-electrolyte structures were generated and added to ReaxFF training data and subsequently, we trained the ReaxFF parameters with the aim to find the optimal reproduction of the DFT data. This force field is capable of distinguishing Li interaction with electrolyte in presence of self-sealing layer. Moreover, these findings provide a new way to design a stable SEI at the highly dynamic electrode-electrolyte interface. In addition to this battery work, we also studied halogen interaction with platinum surfaces, a system that has received considerable attention in catalysis and semiconductor mannufacturing. These halogen gases are applied as platinum mobilizers in both deposition and corrosion or etching processes since PtCl4 adsorption from an electrolyte and subsequent reduction to metallic Pt clusters is an electrochemical pathway for obtaining highly dispersed, catalytically active Pt surfaces. A novel ReaxFF reactive force field has been developed to understand the size and shape-dependent properties of platinum nanoparticles for the design of nanoparticle-based applications. The ReaxFF force field parameters are fitted against a quantum mechanical (QM) training set containing the adsorption energy of Cl and dissociative HCl on Pt (100) and Pt (111), the energy-volume relations of PtCl2 crystals, and Cl diffusion on Pt (100) and Pt (111). ReaxFF accurately reproduces the QM training set for structures and energetics of small clusters and PtClx crystals. The predictive capacity of the force field was manifested in molecular dynamics simulations of the Cl2 and HCl molecules interactions on the (100) and)111(surfaces of c-Pt crystalline solid slabs. The etching ratio between HCl and Cl2 are compared to experimental results, and satisfactory results are obtained, indicating that this ReaxFF protocol provides a useful tool for studying the atomistic-scale details of the etching process.

ReaxFF And EReaxFF Reactive Force Field Development And Applications To Energy Storage Interfaces
ReaxFF And EReaxFF Reactive Force Field Development And Applications To Energy Storage Interfaces

Author: Md Jamil Hossain

Publisher:

Published: 2021

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

The depletion of fossil fuels necessitates alternate and clean energy sources. Lithium-ion batteries and solid oxide electrocatalysis devices are some of the most popular candidates. However, further improvements of these energy storage devices are essential in order to meet the ever-increasing global energy demand. Improvement of the performance of these high energy chemical systems is directly linked to the understanding and improving the complex physical and chemical phenomena and exchanges that take place at their different interfaces. Surfaces or interfaces, structures created between dissimilar media, such as liquids and solids, and interphases, structures arising in between these dissimilar media, present great challenges for their study and understanding since these are the regions where myriad events such as electron transfer, ion transfer and migration, reactions, and solvation/desolvation processes take place and significantly alter their landscape. In order to investigate the physical and chemical interactions at the interfaces of energy storage devices such as Li-ion batteries and solid oxide electrocatalysis devices, we used ReaxFF and eReaxFF reactive molecular dynamics simulations in the following research areas: 1) In the electrode/electrolyte interface of a typical lithium-ion battery a solid electrolyte interphase layer is formed as a result of electrolyte decomposition during the initial charge/discharge cycles. Electron leakage from anode to the electrolyte reduces the Li+-ion and makes them more reactive resulting in decomposition of the organic electrolyte. To study the Li-electrolyte solvation, solvent exchange and subsequent solvent decomposition reactions at the anode/electrolyte interface, we have extended existing ReaxFF reactive force field parameter sets to organic electrolyte species such as ethylene carbonate, ethyl methyl carbonate, vinylene carbonate and LiPF6 salt. Density Functional Theory (DFT) data describing Li-associated initiation reactions for the organic electrolytes and binding energies of Li-electrolyte solvation structures were generated and added to existing ReaxFF training data and subsequently, we trained the ReaxFF parameters with the aim to find the optimal reproduction of the DFT data. In order to discern the characteristics of Li neutral and cation, we have introduced a second Li parameter set to describe Li+-ion. ReaxFF is trained for Li-neutral and Li+-cation to have similar solvation energies but unlike the neutral Li, Li+ will not induce reactivity in the organic electrolyte. Solvent decomposition reactions are presumed to happen once Li+-ions are reduced to Li-atoms, which can be simulated using a Monte-Carlo type atom modification within ReaxFF. This newly developed force field is capable of distinguishing between a Li-atom and a Li+-ion properly. Moreover, it is found that the solvent decomposition reaction barrier is a function of the number of EC molecules solvating the Li-atom. 2) Graphene, a 2D material arranged in an sp2-bonded hexagonal network, is one of the most promising materials for lithium-ion battery anodes due to its superior electronic conductivity, high surface area for lithium intercalation, fast ionic diffusivity and enhanced specific capacity. A detailed atomistic modeling of electronic conduction and non-zero voltage simulations of graphitic materials require the inclusion of an explicit electronic degree of freedom. To enable large length and time scale simulations of electron conduction in graphitic anodes, we developed an eReaxFF force field describing graphitic materials with an explicit electron concept. The newly developed force field, verified against quantum chemistry-based data describing, amongst others, electron affinities and equation of states, reasonably reproduces the behavior of electron conductivity in pristine and imperfect graphitic materials at different applied temperatures and voltages. Our eReaxFF description is capable of simulating leakage of excess electrons from graphene which are captured by exposed lithium ions; a common behavior at the anode/electrolyte interface of a lithium-ion battery. Finally, the initiation of Li-metal-plating observed at the graphene surface reveals the eReaxFF force field's potential for the future development of Li-graphene interactions with explicit electrons. 3) Electrocatalysis results in the change of the rate of an electrochemical reaction occurring on an electrode surface by varying the electrical potential. Electrocatalysis can be used in hydrogen generation and the generated hydrogen can be stored for future use in fuel cells for clean electricity. The use of solid oxide in electrocatalysis specially in hydrogen evolution reaction is promising. To enable large length and time scale atomistic simulations of solid oxide electrocatalysis for hydrogen generation, we developed an eReaxFF force field for barium zirconate doped with 20 mol% of yttrium (BZY20). All parameters for the eReaxFF were optimized to reproduce quantum mechanical (QM) calculations on relevant condensed phase and cluster systems describing oxygen vacancies, vacancy migrations, water adsorption, water splitting and hydrogen generation on the surfaces of the BZY20 solid oxide. Using the developed force field, we performed zero-voltage molecular dynamics simulations to observe water adsorption and the eventual hydrogen production. Based on our simulation results, we conclude that this force field sets a stage for the introduction of explicit electron concept in order to simulate electron conductivity and non-zero voltage effects on hydrogen generation. Overall, the work described in this dissertation demonstrate how atomistic-scale simulations can enhance our understanding of processes at interfaces in energy storage materials.

ReaxFF Reactive Force-field Modeling of High-capacity Electrodes in Lithium Ion Batteries and Two Dimensional Materials
ReaxFF Reactive Force-field Modeling of High-capacity Electrodes in Lithium Ion Batteries and Two Dimensional Materials

Author: Alireza Ostadhossein

Publisher:

Published: 2016

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

1. Development and application of ReaxFF for Energy Storage Materials Energy storage as a key aspect of assimilating renewable energy sources in power grids made the development of high capacity batteries an important technical challenge. The proliferation of portable electronics, hybrid electric vehicles (HEVs), and large scale energy storage has drawn significant attention toward the development of new generation-Lithium ion batteries (LIBs). Currently, most of commercial LIBs use graphitic anodes due to its long cycle life, high conductivity, abundance, and relatively low cost. However, the low specific charge capacity "(375 mAh" "g" ^"-1" ")" of graphite caused researchers to dedicate extensive attempts to find better alternative anode materials. Among all potential anodes, Silicon (Si), which can host a large amount of Lithium (Li) - each silicon atom can host up to 4.4 lithium atoms - is the most promising candidate. Nevertheless, associated with its large charge capacity of" 4200 mAh" "g" ^"-1" , insertion of lithium into silicon causes a large volumetric expansion of up to" 300%" , resulting in mechanical degradation and fracture. On the other side of the battery, the cathode, which mainly controls the voltage of LIB, should be tailored so that it can react with Li in a reversible manner. Sulfur (S) has been identified as one of most promising cathode materials for its high theoretical capacity, five times higher than that of the LiCoO2/graphite system. However, since the capacity of sulfur and its intermediate lithium polysulfide products rapidly decay due to the dissolution of intermediate polysulfides into the electrolytes, the commercialization of Li/S has been hindered. In this thesis study, systematic Molecular Dynamics (MD) simulations have been performed using ReaxFF reactive potentials to study the atomistic mechanisms governing the chemo-mechanical degradation in high-energy density anode and cathode materials. Our modeling results have shed light on the electrochemical insertion process of Li into the new high-capacity electrodes and have provided fundamental guidance to the rational designs of the next generation high capacity electrode materials with enhanced capacity retention and durability. 2. Application of ReaxFF for tow-dimensional materialsWhile the first part of this thesis covers battery applications, the second part of this thesis is devoted to the application and development of ReaxFF to model two-dimensional (2D) materials. The discovery of graphene in 2004 was the moment of the birth of an emerging research realm of 2D materials. Due to its exceptional electronic, optoelectronic and chemo-mechanical properties, graphene became ushers in the field of nano-transistors, photovoltaics, light emitting devices, optical sensors and topological field effect transistors. However, the ever increasing demands of semiconductor industry to utilize novel materials with a wider band-gap and superior structural, thermal and electrical properties has stimulated extensive scientific efforts to develop and synthesis of new generation of graphene-liked 2D-materials. Of the various proposed materials, transition metal dichalcogenides (TMDCs), such as MoS2 and WS2 have been recognized as promising candidates. It is well established that mechanical strain and geometry changes could dramatically affect the band structure and in turn electronic properties of 2D materials and in turn affect the performance and workability of the nano-transistors made of these materials. In this study, we present the development of a new ReaxFF reactive potential which can accurately describe the thermodynamic and structural properties of MoS2 sheets. Extensive Density Functional Theory (DFT) simulations are carried out to produce the required data-set for optimization of the new empirical potential parameters. This force field is able to accurately predict the mechanical properties and elastic constants of single layer MoS2. The newly developed potential is also successfully applied to estimate the formation energies of various types of point-defects (5 different vacancy types) along with the vacancy migration barriers and transition of 2H (semiconducting) 1T (metallic) phases. The energetics of ripplocations, a recently observed defect in van der Waals layers, is examined and the interplay between these defects and sulfur (S) vacancies is studied. As strain-engineering of MoS2 sheets is as an effective way to manipulate the electronic and optical properties of this material, the new ReaxFF description can provide a comprehensive insight about the morphological changes under various conditions of loading and defects to further tuning the band-gap properties in these 2D-structures. Recent experimental advances however confirm the possibility of further tuning the electronic properties of MoS2 through the fabrication of single-layer heterostructures consisting of semiconducting (2H) and metallic (1T) MoS2 phases. However, despite of technological and scientific interests, there exist limited information concerning the mechanical properties of these systems. Consequently, this investigation aims to provide a general vision regarding the mechanical properties of all-MoS2 single-layer structures at room temperature. This goal was achieved by performing extensive classical molecular dynamics simulations using a recently developed RexFF forcefield. We first studied the chirality dependent mechanical properties of defect-free 2H and 1T phases. Our atomistic modeling results for pristine 2H MoS2 were found to agree fairly well with the experimental tests. We finally discussed the mechanical response of 2H/1T single layer heterostructures. Our atomistic results suggest all-MoS2 heterostructures as suitable candidates to reach a strong and flexible material with tunable electronic properties.

Reactive Molecular Dynamics Simulations of Lithium Secondary Batteries - Interfaces and Electrodes
Reactive Molecular Dynamics Simulations of Lithium Secondary Batteries - Interfaces and Electrodes

Author: Md Mahbubul Islam

Publisher:

Published: 2016

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

Over the last two decades, lithium-based batteries have revolutionized the energy storage technologies. Li-ion batteries have found widespread use in portable electronics and electric vehicle applications. However, a detailed understanding of the battery chemistry, especially the formation of a solid electrolyte interphase (SEI)a thin passivation layer which is generated during the first charge cycle due to the reduction of electrolytesis still elusive. The mass scale commercialization of electric vehicles requires the storage capacity beyond the conventional Li-ion batteries, which spurred research interests towards Li-S technologies. Li-S batteries are attractive for their very high capacity and energy density, but their commercial application has been thwarted due to several critical limitations stemming from electrolyte dissociation chemistry and electrode material properties. To investigate the current issues associated with the Li-ion and Li-S batteries and to find possible countermeasures, we used both a newly developed computational tool eReaxFF and the standard ReaxFF reactive molecular dynamics simulations in the following research areas:1) We developed a computational method, eReaxFF, for simulating explicit electrons within the framework of the standard ReaxFF reactive force field method. We treat electrons explicitly in a pseudoclassical manner that enables simulation several orders of magnitude faster than quantum chemistry (QC) methods, while retaining the ReaxFF transferability. We describe in this thesis the fundamental concepts of the eReaxFF method, and the integration of the Atom-condensed Kohn-Sham DFT approximated to second order (ACKS2) charge calculation scheme into the eReaxFF. We trained our force field to capture electron affinities (EA) of various species. As a proof-of-principle, we performed a set of molecular dynamics (MD) simulations with an explicit electron model for representative hydrocarbon radicals. We establish a good qualitative agreement of EAs of various species with experimental data, and MD simulations with eReaxFF agree well with the corresponding Ehrenfest dynamics simulations. The standard ReaxFF parameters available in literature are transferrable to the eReaxFF method. The computationally economic eReaxFF method will be a useful tool for studying large-scale chemical and physical systems with explicit electrons as an alternative to computationally demanding QC methods. 2) A detailed understanding of the mechanism of the formation of SEI is crucial for designing high capacity and longer lifecycle lithium-ion batteries. The anode side SEI is primarily comprised of the reductive dissociation products of the electrolyte molecules. Any accurate computational method to study the reductive decomposition mechanism of electrolyte molecules is required to possess an explicit electronic degree of freedom. In this study, we employed our newly developed eReaxFF method to investigate the major reduction reaction pathways of SEI formation with ethylene carbonate (EC) based electrolytes. In the eReaxFF method, a pseudo-classical treatment of electrons provides the capability to simulate explicit electrons in a complex reactive environment. Our eReaxFF predicted simulation results of the EC decomposition reactions are in good agreement with the quantum chemistry data available in literature. Our MD simulations capture the mechanism of the reduction of the EC molecule due to the electron transfer from lithium, ring opening of the EC to generate EC-/Li+ radicals, and subsequent radical termination reactions. Our results indicate that the eReaxFF method is a useful tool for large-scale simulations to describe redox reactions occurring at electrode-electrolyte interfaces where quantum chemistry based methods are not viable due to their high computational requirement.3) Li-S batteries still suffer several formidable performance degradation issues that impede their commercial applications. The lithium negative electrode yields high anodic capacity, but it causes dendrite formation and raises safety concerns. Furthermore, the high reactivity of lithium is accountable for electrolyte decomposition. To investigate these issues and possible countermeasures, we used ReaxFF reactive molecular dynamics simulations to elucidate anode-electrolyte interfacial chemistry and utilized an ex-situ anode surface treatment with Teflon coating. In this study, we employed Li/SWCNT (single-wall carbon nanotube) composite anode instead of lithium metal and tetra (ethylene glycol) dimethyl ether (TEGDME) as electrolyte. We find that at a lithium rich environment of the anode-electrolyte interface, electrolyte dissociates and generates ethylene gas as a major reaction product, while utilization of Teflon layer suppresses the lithium reactivity and reduces electrolyte decomposition. Lithium discharge from the negative electrode is an exothermic event that creates local hot spots at the interfacial region and expedites electrolyte dissociation reaction kinetics. Usage of Teflon dampens initial heat flow and effectively reduces lithium reactivity with the electrolyte. 4) Sulfur cathodes of Li-S batteries undergo a noticeable volume variation upon cycling, which induces stress. In spite of intensive investigation of the electrochemical behavior of the lithiated sulfur compounds, their mechanical properties are not very well understood. In order to fill this gap, we developed a ReaxFF interatomic potential to describe Li-S interactions and performed MD simulations to study the structural, mechanical, and kinetic behavior of the amorphous lithiated sulfur (a-LixS) compounds. We examined the effect of lithiation on material properties such as ultimate strength, yield strength, and Youngs modulus. Our results suggest that with increasing lithium content, the strength of lithiated sulfur compounds improves, although this increment is not linear with the lithiation. The dependence of the mechanical properties and failure behavior on the loading rate of the amorphous lithiated sulfur compositions was also studied. The diffusion coefficients of both lithium and sulfur were computed for the a-LixS system at various stages of Li-loading. A Grand canonical Monte Carlo (GCMC) scheme was used to calculate the open circuit voltage (OCV) profile during cell discharge. The calculated OCV is consistent with prior experimental results. Our ReaxFF potentials also reproduced experimentally observed volume expansion of a-LixS phases upon lithiation. The Li-S binary phase diagram was constructed using genetic algorithm based tools. These simulation results provide insight into the behavior of sulfur-based cathode materials that are needed for developing high-performance lithium-sulfur batteries.

Proceedings of 22nd International Conference and Expo on Nanoscience and Molecular Nanotechnology 2017
Proceedings of 22nd International Conference and Expo on Nanoscience and Molecular Nanotechnology 2017

Author: ConferenceSeries

Publisher: ConferenceSeries

Published: 2017-10-31

Total Pages: 102

ISBN-13:

DOWNLOAD EBOOK

Nov 06-08, 2017 Frankfurt, Germany Key Topics : Nanomedicine & Nanobiotechnology,Nanoparticles, Nanomaterials- production, synthesis and processing, Nanoengineering, Computation, Simulation & Modeling of Nanostructures, Nano systems & devices, Bio-Nanomaterials and biomedical devices, applications, Nano photonics, Nano Imaging, Spectroscopy & Plasmonic devices, Nanoelectronics and nanometrology, Nanotechnology & Energy, Micro/ Nano-fabrication, Nano patterning, Nano Lithography & Nano Imprinting, Nanotechnology: Environmental effects and Industrial safety, Future prospects of Nanotechnologies and commercial viability, Graphene and Applications, Other Related research, Dna Nanoelectronics,

A Reactive Force Field Study of Li/C Systems for Electrical Energy Storage
A Reactive Force Field Study of Li/C Systems for Electrical Energy Storage

Author:

Publisher:

Published: 2015

Total Pages: 11

ISBN-13:

DOWNLOAD EBOOK

Graphitic carbon is still the most ubiquitously used anode material in Li-ion batteries. In spite of its ubiquity, there are few theoretical studies that fully capture the energetics and kinetics of Li in graphite and related nanostructures at experimentally relevant length, time-scales, and Li-ion concentrations. In this paper, we describe the development and application of a ReaxFF reactive force field to describe Li interactions in perfect and defective carbon-based materials using atomistic simulations. We develop force field parameters for Li-C systems using van der Waals-corrected density functional theory (DFT). Grand canonical Monte Carlo simulations of Li intercalation in perfect graphite with this new force field not only give a voltage profile in good agreement with known experimental and DFT results but also capture the in-plane Li ordering and interlayer separations for stage I and II compounds. In defective graphite, the ratio of Li/C (i.e., the capacitance increases and voltage shifts) both in proportion to the concentration of vacancy defects and metallic lithium is observed to explain the lithium plating seen in recent experiments. We also demonstrate the robustness of the force field by simulating model carbon nanostructures (i.e., both 0D and 1D structures) that can be potentially used as battery electrode materials. Whereas a 0D defective onion-like carbon facilitates fast charging/discharging rates by surface Li adsorption, a 1D defect-free carbon nanorod requires a critical density of Li for intercalation to occur at the edges. Our force field approach opens the opportunity for studying energetics and kinetics of perfect and defective Li/C structures containing thousands of atoms as a function of intercalation. As a result, this is a key step toward modeling of realistic carbon materials for energy applications.

Practical Aspects of Computational Chemistry V
Practical Aspects of Computational Chemistry V

Author: Jerzy Leszczynski

Publisher: Springer Nature

Published: 2021-10-21

Total Pages: 292

ISBN-13: 3030832449

DOWNLOAD EBOOK

This book presents contributions on a wide range of computational research applied to fields ranging from molecular systems to bulk structures. This volume highlights current trends in modern computational chemistry and discusses the development of theoretical methodologies, state-of-the-art computational algorithms and their practical applications. This volume is part of a continuous effort by the editors to document recent advances by prominent researchers in the area of computational chemistry. Most of the chapters are contributed by invited speakers and participants to International annual conference “Current Trends in Computational Chemistry”, organized by Jerzy Leszczynski, one of the editors of the current volume. This conference series has become an exciting platform for eminent theoretical and computational chemists to discuss their recent findings and is regularly honored by the presence of Nobel laureates. Topics covered in the book include reactive force-field methodologies, coarse-grained modeling, DNA damage radiosensitizers, modeling and simulation of surfaces and interfaces, non-covalent interactions, and many others. The book is intended for theoretical and computational chemists, physical chemists, material scientists and those who are eager to apply computational chemistry methods to problems of chemical and physical importance. It is a valuable resource for undergraduate, graduate and PhD students as well as for established researchers.

The Role of Surface Reactions and Solid Electrolyte Interphase in Silicon Electrodes for Lithium-ion Batteries
The Role of Surface Reactions and Solid Electrolyte Interphase in Silicon Electrodes for Lithium-ion Batteries

Author: Kjell William Schroder

Publisher:

Published: 2015

Total Pages: 350

ISBN-13:

DOWNLOAD EBOOK

In order to utilize renewable energy sources to avoid adverse climate change caused by fossil fuel use, economical, efficient, and long-cycling energy storage means are needed for grid power applications and electric vehicles. Lithium-ion batteries (LIBs) are promising electrochemical energy storage devices for these applications, but capacity, cycle life, and device energy density need to be improved to meet these challenges. Silicon, as a lithium alloy, promises high gravimetric and volumetric charge capacities as a negative electrode in the next generation of LIBs. However silicon has a lithiation potential outside the window of stability of common non-aqueous liquid electrolytes (e.g., lithium hexafluorophosphate in ethylene carbonate and diethyl carbonate mixtures). Consequently, parasitic side reactions occur during continued lithiation and delithiation (cycling) of silicon. However, these side reactions (including electro-reduction and thermal decomposition) form insoluble products that make a solid electrolyte interphase (SEI), passivating an electrode’s surface. Cycling silicon electrodes can entail incomplete passivation (via unstable SEI species) and newly exposed surfaces (due to mechanical wear) and thus continued side reactions that lead to thermal runaway, capacity loss, and cell failure. By understanding interfacial electrode chemistry, it is hoped that novel design suggestions for addressing these problems will be uncovered. Model silicon electrodes studied by X-ray Photoelectron Spectroscopy (XPS), and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) were used to explore the effects of surface layer conductivity and electrolyte additives on SEI composition and structure. Anhydrous and anoxic techniques showed better reproducibility and accuracy in characterizing the SEI over previous studies of composite electrodes exposed to ambient conditions. By comparing silicon oxide and etched silicon surfaces, electrode conductivity was studied as well as how the co-solvent additive fluoroethylene carbonate (FEC) affects the SEI. Both the etched silicon surface and FEC produced SEI species like lithium fluoride that improved stability by resisting further electro-reduction. However, questions about the oxidative stability of some SEI species were raised (namely lithium oxide), suggesting a more stable artificial SEI could be manufactured compared to those formed during naive device operation.

DESIGN STABLE SOLID-ELECTROLYTE INTERPHASE FOR ANODES IN RECHARGEABLE LITHIUM BATTERIES.
DESIGN STABLE SOLID-ELECTROLYTE INTERPHASE FOR ANODES IN RECHARGEABLE LITHIUM BATTERIES.

Author: Yue Gao

Publisher:

Published: 2018

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

Solid-electrolyte interphase (SEI) is a nanoscale composite layer of organic and inorganic lithium (Li) salts formed on the electrode surface by electrolyte decomposition. It is ionically conductive and electrically insulating, thus allowing facile Li-ion transport and preventing further electrolyte decomposition. Owing to these features, SEI stability is crucial to the performance of rechargeable Li batteries. Unfortunately, SEI layer are unstable for most advanced battery materials, including high-capacity anodes materials (e.g., silicon (Si) and Li) in liquid electrolyte and Li anodes in solid electrolytes (e.g., Li10GeP2S12 (LGPS)). An unstable SEI layer may cause poor battery performance including consumption of active materials and electrolyte, capacity fading, resistance increase., etc. The structure and property of SEI have generally eluded rational control since its formation and growth processes involve a series of complex and competitive electrochemical reactions. The main efforts to addressing this issue have been made on the development of new electrolyte systems to form alternative SEI layers and preformed artificial SEI layers on the electrode surface to replace the electrolyte-derived SEI.This dissertation focuses on intrinsically regulating the chemical composition and nanostructure of SEI for advanced battery materials in conventional electrolyte systems, which enables not only optimized chemical and physical properties of SEI but improved battery performance. This is realized by developing chemical and electrochemical reactive materials and allowing them to participate in the SEI formation. These materials can contribute functional components in the SEI layer and therefore alter the structure and property of the SEI deliberately. The design of functional material is based on the requirement of SEI layers for different anodes. In Chapters 2 and 3, I presented approaches to manipulating the formation process, chemical composition, and morphology of SEI for nano-sized and micro-sized Si anodes, respectively. The SEI layers were fabricated through a covalent anchoring of multiple functional components onto the Si surface, followed by electrochemical decomposition of the functional components and conventional electrolyte. We showed that to covalently bond organic oligomeric species at the surface of nano-sized Si anodes can effectively increase its SEI flexibility and realized an intimate contact between SEI and Si surface (Chapter 2). In the case of micro-sized Si anodes, we reported that to covalently bond a functional salt, N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI), at the surface of micro-sized Si anodes can effectively stabilize the interface and SEI (Chapter 3). In Chapters 4 and 5, we designed chemically and electrochemically active organic polymer, namely poly((N-2,2-dimethyl-1,3-dioxolane-4-methyl)-5-norbornene-exo-2,3-dicarboximide), and polymeric composite containing poly(vinylsulfonyl fluoride-ran-2-vinyl-1,3-dioxolane) and graphene oxide (GO) nanosheets to alter SEI formation process and regulate the composition and nanostructure of SEI for Li metal anodes. The reactive organic polymer and polymeric composite can generate stable SEI layers in situ by reacting with Li to occupy surface sites and then electrochemically decomposing to form nanoscale SEI components. The formed SEI layers presented excellent surface passivation, homogeneity, and mechanical strength. Using the polymer, we can implant polymeric ether species in the electrolyte-derived SEI, enabling improved SEI flexibility and homogeneity. In the case of polymeric composite, the SEI is mainly generated by the composite instead of electrolyte. In this way, we realized an intrinsic control of SEI structure and property. The formed SEI presented excellent homogeneity, mechanical strength, ionic conductivity, and surface passivation.In Chapter 6, we reported a novel approach based on the use of a nanocomposite consisting of organic elastomeric salts (LiO-(CH2O)n-Li) and inorganic nanoparticle salts (LiF, -NSO2-Li, Li2O), which serve as an interphase to protect Li10GeP2S12 (LGPS), a highly conductive but reducible SSE. The nanocomposite is formed in situ on Li via the electrochemical decomposition of a liquid electrolyte, therefore possessing excellent chemical and electrochemical stability, affinity for Li and LGPS, and limited interfacial resistance. We concluded this dissertation work in Chapter 7 and briefly discussed the possible future work.

Classical And Quantum Dynamics In Condensed Phase Simulations: Proceedings Of The International School Of Physics
Classical And Quantum Dynamics In Condensed Phase Simulations: Proceedings Of The International School Of Physics

Author: Bruce J Berne

Publisher: World Scientific

Published: 1998-06-17

Total Pages: 881

ISBN-13: 9814496057

DOWNLOAD EBOOK

The school held at Villa Marigola, Lerici, Italy, in July 1997 was very much an educational experiment aimed not just at teaching a new generation of students the latest developments in computer simulation methods and theory, but also at bringing together researchers from the condensed matter computer simulation community, the biophysical chemistry community and the quantum dynamics community to confront the shared problem: the development of methods to treat the dynamics of quantum condensed phase systems.This volume collects the lectures delivered there. Due to the focus of the school, the contributions divide along natural lines into two broad groups: (1) the most sophisticated forms of the art of computer simulation, including biased phase space sampling schemes, methods which address the multiplicity of time scales in condensed phase problems, and static equilibrium methods for treating quantum systems; (2) the contributions on quantum dynamics, including methods for mixing quantum and classical dynamics in condensed phase simulations and methods capable of treating all degrees of freedom quantum-mechanically.