Multiwall carbon nanotubes (CNTs) were synthesized by catalytic chemical vapor deposition of acetylene and used as templates to prepare CNT-Sb and CNT-SnSb₀.₅ nanocomposites via the chemical reduction of SnCl₂ and SbCl₃ precursors. SEM and TEM imagings show that the Sb and SnSb₀.₅ particles were uniformly dispersed in the CNT web and on the outside surface of CNTs. These CNT-metal composites are active anode materials for lithium ion batteries, showing improved cyclability compared to unsupported Sb and SnSb particles; and higher reversible specific capacities than CNTs. The improvement in cyclability may be attributed to the nanoscale dimensions of the metal particles and CNT’s role as a buffer in containing the mechanical stress arising from the volume changes in electrochemical lithium insertion and extraction reactions. / Singapore-MIT Alliance (SMA)

The report deals with energy conservation, mainly in the field of portable energy, which is asubject that today raises questions around the world. This report describes the design and theimplementation of a Battery Management System on the platform NI ELVIS II+ managed bythe software Labview. The first aim has been on finding information about the design of theBattery Management System that corresponds to the choice of the battery itself. The systemwas designed completely independent with different charging methods, simulations ofdischarge, and its own cell balancing, as a 3 cells battery pack was used. The battery chosenwas the lithium-ion technology that has the most promising battery chemistry and is the fastestgrowing. Several experimentations and simulations have been done, with and without cellbalancing that permited to highlight that the cell balancing is mandatory in a Batterymanagement System. Furthermore, a simulation of use of the battery in an Electrical Vehiclewas made, which can lead to conclude that the Lithium-Ion battery must be manageddifferently to be used in the application of an Electrical Vehicle.

Polymer nanocomposites are used in a variety of applications due to their good mechanical properties. Specifically, better performance of lithium ion batteries and thermal interface material can be obtained by using conductive materials and polymer composites. In the case of lithium ion batteries, electrochemical properties of batteries can be improved by adding conductive additives and conducting polymer into the cathode. Several samples, to which different conductive additives and conducting polymer were added, were prepared and their electrical resistance and discharge capacity measured. In the thermal interface material case, also, thermal properties can be enhanced by polymer nanocomposites. In order to confirm the thermal conductivity enhancement, samples were synthesized using different filler, polymer and methods, and their thermal conductivity measured. The influence of polymer nanocomposites and results are discussed and future plan are presented. In addition, reasons of thermal conductivity changing in each case are discussed.

Nowadays personal small electronic devices like cellphones are more and more popular, but the various batteries in need of charging become a problem. This thesis aims to explain a Lithium-ion charger which can control the current and voltage so that it can charge most kinds of popular batteries. More specifically, Li-ion battery charging is presented. The charging circuit design, simulation and the measurements will also be included.

Li-ion batteries are widely used in electronics and automotives. Despite their success, improvements in cost, safety, cycle life, and energy density are necessary. One way to enhance the energy density is to find advanced cathodes such as Li-rich layered oxides, which are similar to the commonly layered oxide cathodes (e.g., LiCoO2), except there are additional Li ions in the transition-metal layer, due to their higher charge-storage capacity. Another way of advancing is to design new battery chemistries, such as those involving multivalent-ion systems (e.g., Mg2+ and Zn2+) as they could offer higher charge-storage capacities and/or cost advantages. Li-rich layered oxides have a complex first charge-discharge cycle, which affects their other electrochemical properties. Ru doping was expected to improve the performance of Li-rich layered oxides due to its electroactivity and overlap of the Ru4+/5+:4d band with the O2-:2p band, but it unexpectedly decreased the capacity due to the reduction in oxygen loss behavior. Preliminary evidence points to the formation of Ru-Ru dimers, which raises the Ru4+/5+:4d band, as the cause of this behavior. Li-rich layered oxides suffer from declining operating voltage during cycling, and it is a huge challenge to employ them in practical cells. Raising the Ni oxidation state was found to reduce the voltage decay and improve the cyclability; however, it also decreased the discharge capacity. Increasing the Ni oxidation state minimized the formation of Mn3+ ions during discharge and Mn dissolution, which led to the improvements in voltage decay and cyclability. Extraction of lithium from spinel oxides such as LiMn2O4 with acid was found to follow a Mn3+ disproportionation mechanism and depend on the Mn3+ content. Other common dopants like Cr3+, Fe3+, Co3+, or Ni2+/3+ did not disproportionate, and no ion-exchange of Li+ with H+ occurred in the tetrahedral sites of the spinel oxides. Extraction with acid of Mg and Zn from spinel oxides, such as MgMn2O4 and ZnMn2O4, were also found to follow the same mechanism as Li-spinels. The Mg-spinels, however, do experience ion exchange when Mg ions are in the octahedral sites. Chemical extraction of Mg or Zn with an oxidizing agent NO2BF4 in acetonitrile medium, however, failed due to the electrostatic repulsion felt by the migrating divalent ions. In contrast, extraction with acid was successful as Mn dissolution from the lattice opened up favorable pathways for extraction. / text

Lithium-ion (Li-ion) batteries are critically important for portable electronics, electric vehicles, and grid-level energy storage. The development of next-generation Li-ion batteries requires high-capacity electrodes with a long cycle life. However, the high capacity of Li storage is usually accompanied by large volume changes, dramatic morphological evolution, and mechanical failures in the electrodes during charge and discharge cycling. To understand the degradation of electrodes and resulting loss of capacity, this thesis aims to develop mechanistic-based models for predicting the chemo-mechanical processes of lithiation and delithiation in high-capacity electrode materials. To this end, we develop both continuum and atomistic models that simulate mass transport, interface reaction, phase and microstructural evolution, stress generation and damage accumulation through crack or void formation in the electrodes. The modeling studies are tightly coupled with in-situ transmission electron microscopy (TEM) experiments to gain unprecedented mechanistic insights into electrochemically-driven structural evolution and damage processes in high-capacity electrodes. Our models are successfully applied to the study of the two-phase lithiation and associated stress generation in both crystalline and amorphous silicon anodes, which have the highest known theoretical charge capacity, as well as the lithiation/sodiation-induced structural changes and mechanical failures in silicon-based multilayer electrodes. The modeling studies have uncovered unexpected electrochemical reaction mechanisms and revealed novel failure modes in silicon-based nanostructured anodes. Our modeling research provides insights into how to mitigate electrode degradation and enhance capacity retention in Li-ion batteries. More broadly, our work has implications for the design of nanostructured electrodes in next-generation energy storage systems.

This thesis investigates the mechanical behavior of electrodes in Li-ion batteries. Each electrode in a Li-ion battery consists of host atoms and guest atoms (Li atoms). The host atoms form a framework, into which Li atoms are inserted via chemical reactions. During charge and discharge, the amount of Li in the electrode varies substantially, and the host framework deforms. The deformation induces in an electrode a field of stress, which may lead to fracture or morphological change. Such mechanical degradation over lithiation cycles can cause the capacity to fade substantially in a commercial battery. We study fracture of elastic electrodes caused by fast charging using a combination of diffusion kinetics and fracture mechanics. A theory is outlined to investigate how material properties, electrode particle size, and charging rate affect fracture of electrodes in Li-ion batteries. We model an inelastic host of Li by considering diffusion, elastic-plastic deformation, and fracture. The model shows that fracture is averted for a small and soft host—an inelastic host of a small feature size and low yield strength. We present a model of concurrent reaction and plasticity during lithiation of crystalline silicon electrodes. It accounts for observed lithiated silicon of anisotropic morphologies. We further explore the microscopic deformation mechanism of lithiated silicon based on first-principles calculations. We attribute to the microscopic mechanism of large plastic deformation to continuous Li-assisted breaking and reforming of Si-Si bonds. In addition, we model the evolution of the biaxial stress in an amorphous Si thin film electrode during lithiation cycle. We find that both the atomic insertion driven by the chemomechanical load and plasticity driven by the mechanical load contribute to reactive flow of lithiated silicon. In such concurrent process, the lithiation reaction promotes plastic deformation by lowering the stress needed to flow. Li-ion battery is an emerging field that couples electrochemistry and mechanics. This thesis aims to understand the deformation mechanism, stresses and fracture associated with the lithiation reaction in Li-ion batteries, and hopes to provide insight on the generic phenomenon that involves interactive chemical reactions and mechanics. / Engineering and Applied Sciences

The main goal of this research was to apply first-principles electronic structure calculations to investigate atomic motions in several condensed materials. This thesis consists of five separate but related topics that are classified into two main categories: structure of materials under pressure and Li ion dynamics in lithium battery materials. The atomic structure of liquid gallium was investigated in order to resolve a controversy about an anomalous structural feature observed in the x-ray and neutron scattering patterns. We explored the pressure effect when modifying the liquid structure close to the solid-liquid melting line. The atomic trajectories obtained from first-principles molecular dynamics (FPMD) calculations were examined. The results clarified the local structure of liquid gallium and explained the origin of a peculiar feature observed in the measured static structure factor. We also studied the structure of a recently discovered phase-IV of solid hydrogen over a broad pressure range near room temperature. The results revealed novel structural dynamics of hydrogen under extreme pressure. Unprecedented large amplitude fluxional atomic dynamics were observed. The results helped to elucidate the complex vibrational spectra of this highly-compressed solid. The atomic dynamics of Li ions in cathode, anode, and electrolyte materials - the three main components of a lithium ion battery - were also studied. On LiFePO4, a promising cathode material, we found that in addition to the commonly accepted one-dimensional diffusion along the Li channels in the crystal structure, a second but less obvious multi-step Li migration through the formation of Li-Fe antisites was identified. This discovery confirms the two-dimensional Li diffusion model reported in several Li conductivity measurements and illustrates the importance of the distribution of intrinsic defects in the enhancement of Li transport ability. The possibility of using type-II clathrate Si136 as an anode material was investigated. It was found that lithiated Si-clathrates are intrinsic metals and their crystal structures are very stable. Calculations revealed the charge and discharge voltages are very low and almost independent of the Li concentrations, an ideal property for an anode material. Significantly, migration pathways for Li ions diffusing through the cavities of the clathrate structures were found to be rather complex. Finally, the feasibility of a family of Li3PS4 crystalline and nanoporous cluster phases were studied for application as solid electrolytes. It was found that the ionic conductivity in the nanocluster is much higher than in crystalline phases. It is anticipated that the knowledge gained in the study of battery materials will assist in future design of new materials with improved battery charge and discharge performance.

No description available.

Lithium-ion batteries are of great importance for today's society. The state-of-the-art batteries that are used today use a fluorinated electrolyte that contains the salt LiPF6 and acts as both a safety hazard and an environmental issue due to its ability to form the toxic gas hydrogen fluoride (HF). This project aims to find a fluorine-free electrolyte that can be used in silicon-based lithium-ion batteries to make them more environmentally friendly without detriment to the electrochemical performance. To do so, an additive that may form a solid electrolyte interphase (SEI) stable enough to allow a fluorine-free electrolyte to replace the ones used today is sought for. The salt of interest is lithium  bis(oxalato)borate (LiBOB). Based on previous research electrolytes using LiBOB in either the solvent γ-Butyrolactone (GBL) or a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are examined. The additives used are vinylene carbonate (VC) and 1,3,2-dioxathiolane 2,2-dioxide (DTD). Techniques used are cyclic voltammetry, linear sweep voltammetry, galvanostatic charge and discharge, X-ray photoelectron spectroscopy and scanning electron microscopy.  The cells using GBL as solvent have cycled very poorly during this project while LiBOB in EC:EMC + VC shows the most promising results, with highest capacity retention and less amount of degraded LiBOB during the first charge. It is also to be noted that both EC:EMC based electrolytes provide the formation of a passivating solid electrolyte interface (SEI) and are of interest for further investigation based on the results obtained during this project.