The demand for high performance Lithium-ion batteries (LIBs) is increasing due to widespread use of portable devices and electric vehicles. Silicon (Si) is one of the most attractive candidate anode materials for the next generation LIBs because of its high theoretical capacity (3,578 mAh/g) and low operation potential (~0.4 V vs Li+/Li). However, the high volume change (>300%) during Lithium ion insertion/extraction leads to poor cycle life. The goal of this work is to improve the electrochemical performance of Si/C composite anode in LIBs. Two strategies have been employed: to explore spatial arrangement in micro-sized Si and to use Si/graphene nanocomposites. A unique branched microsized Si with carbon coating was made and demonstrated promising electrochemical performance with a high active material loading ratio of 2 mg/cm2, large initial discharge capacity of 3,153 mAh/g and good capacity retention of 1,133 mAh/g at the 100th cycle at 1/4C current rate. Exploring the spatial structure of microsized Si with its advantages of low cost, easy dispersion, and immediate compatibility with the prevailing electrode manufacturing technology, may indicate a practical approach for high energy density, large-scale Si anode manufacturing. For Si/Graphene nanocomposites, the impact of particle size, surface treatment and graphene quality were investigated. It was found that the electrochemical performance of Si/Graphene anode was improved by surface treatment and use of graphene with large surface area and high defect density. The 100 nm Si/Graphene nanocomposites presented the initial capacity of 2,737 mAh/g and good cycling performance with a capacity of 1,563 mAh/g after 100 cycles at 1/2C current rate. The findings provided helpful insights for design of different types of graphene nanocomposite anodes.

The Li-ion field of battery research has in the latest decades made substantial progress and is seen to be the most promising battery technology due to the high volume and specific energy densities of Li-ion batteries. However, in order to achieve a battery capable of competing with the energy density of a combustion engine, further research into new electrode materials is required. As the cathode materials are the limiting factor in terms of capacity, this is the main area in need of further research. The introduction of 3-D electrodes brought new hope as the ion transportpath is decreased as well as an increased electrode area leading to an increased capacity. This thesis work has focused on the development of aluminium 3-D current collectors in order to improve the electrode area and shorten the Li-ion transportpath. By using a template assisted electrodeposition technique, nanorods of controlled magnitude and order can be synthesized. Furthermore, the electrodeposition brings excellent possibilities of upscaling for future industrial manufacturing of the batterycells. A polycarbonate template material which showed interesting properties,was used in the electrodeposition of aluminium nanorods. As the template pores were nonhomogeneously ordered a number of nonordered nanorods were expected to arise during the deposition. However, a surplus of nanorods in reference to the template pores was acquired. This behavior was investigated and a hypothesis was formed as to the mechanism of the nanorod formation. In order to achieve acomplete cathode electrode, a coating of an ion host material on the nanorods isneeded. Due to its high capacity and voltage, vanadium oxide was selected. Based on previous work with electrodeposition of V2O5 on platinum, a series of experiments were performed to mimic the deposition on an aluminium sample. Unfortunately, the deposition was unsuccessful as the experimental conditions resulted in aluminium corrosion which in turn made deposition of the cathode material impossible. The pH dependence of the deposition was evaluated and the conclusion was drawn, that electrodeposition of vanadium oxide on aluminium is not possible using this approach.

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Electric Vehicles (EVs) have gained acceptance as low or zero emission means of transportation. This thesis deals with the design of a battery cell testing platform and Lithium-Ion (Li-Ion) battery modeling for EVs. A novel regenerative cell testing platform is developed for cell cycling applications. A 300 W - 5 V cell cycler consisting of a buck and a boost converter is designed. Furthermore, a novel battery modeling approach is proposed to accurately predict the battery performance by dynamically updating the model parameters based on the battery temperature and State of Charge (SOC). The comparison between the experimental and the model simulation results of an automotive cell under real-world drive-cycle illustrates 96.5% accuracy of the model. In addition, the model can be utilized to assess the long-term impact of battery impedance on performance of EVs under real-world drive-cycles.

Electric Vehicles (EVs) have gained acceptance as low or zero emission means of transportation. This thesis deals with the design of a battery cell testing platform and Lithium-Ion (Li-Ion) battery modeling for EVs. A novel regenerative cell testing platform is developed for cell cycling applications. A 300 W - 5 V cell cycler consisting of a buck and a boost converter is designed. Furthermore, a novel battery modeling approach is proposed to accurately predict the battery performance by dynamically updating the model parameters based on the battery temperature and State of Charge (SOC). The comparison between the experimental and the model simulation results of an automotive cell under real-world drive-cycle illustrates 96.5% accuracy of the model. In addition, the model can be utilized to assess the long-term impact of battery impedance on performance of EVs under real-world drive-cycles.

<p>The predicted growth in demand for electric vehicles (EVs) has given rise to increasing use of lithium-ion batteries (LIBs), which are the source of energy used in all EVs. Recycling of spent LIBs not only can supply more materials to manufacturing new LIBs, but also can mitigate haz-ardous waste disposal in the environment. Direct recycling focuses on separating cathode materials to be re-purposed or remanufactured. Delamination of cathode materials is the necessary first step; however, it is fraught with difficulties due to the strong adhesive forces provided by the polyvi-nylidene fluoride (PVDF) binder that is widely used in LIBs. The widely accepted delamination methods are N-Methyl-2-pyrrolidone (NMP) solvent dissolution and direct calcination, which are not desirable due to either environmental and health concerns or high energy consumption.</p> <p>The lithium chemical systems (LiCl, LiNO₃, and LiOH) and their binary eutectic systems, were systematically studied to recover heterogeneous cathode active materials (NMC 111 and LMO) from spent LIBs of EVs. The LiOH-LiNO₃ eutectic system showed 98.3% peel-off effi-ciency under preferable conditions. The recycled products were characterized using ICP-OES, XPS, SEM, and XRD. There were minimal changes in chemical composition, morphology, or crystal structure of the recycled cathode materials after LiOH-LiNO3 eutectic treatment, compared with those recycled with an AlCl₃-NaCl eutectic molten salt treatment that introduces more Al contamination and morphological defects.  </p> <p>In order to avoid corrosive chemicals and minimize particle agglomeration, additional lith-ium salts were investigated, including LiOAc (lithium acetate), Li₂CO₃, and Li₂SO₄. A peel-off efficiency of up to 98.5% was achieved at a LiOAc to LiNO₃ molar ratio of 3:2, salt to cathode mass ratio of 10:1, temperature of 300° C, and a holding time of 30 minutes. To validate the effect of the cations, the recycled products from the molten sodium salt system (NaOAc-NaNO3) were tested. The lithium salt system achieved separation at a lower temperature. Use of LiOAc-LiNO₃ minimized morphological changes compared with direct calcination.</p> <p>The effective separation in LiOH-LiNO3 or LiOAc-LiNO3 molten salt systems was based on promotion of PVDF decomposition, and these two systems may be feasible for recycling other typical cathodes (LCO and LFP) where PVDF is used as the binder. Use of molten lithium salts as alternatives to direct calcination or use of other solvents, may help facilitate recycling of spent LIBs, and even achieve a way for closed loop direct recycling of materials.</p> <p> Additionally, a chemical-free pressure washing system was studied to overcome the adhe-sion provided by PVDF. Although the pressure washing system was not able to remove PVDF from the cathode materials, nearly instant separation from the aluminum backing was achieved when the shear stress and normal stress provided by the impacting of high-pressure waterjet was stronger than the binding forces. Factors investigated included water pressure, distance between the nozzle and cathode, the incident angle of the water jet, and the nozzle type (sprayer angle). A 34-1 fractional factorial design was used to evaluate the parameters and find the optimal operating conditions. A small amount of Al and consistent morphology (of nearly pristine cathode active materials) were detected. Three kinds of recycled cathode materials (NMC&LMO, LCO, and LFP) were used as inputs to investigate a sulfuric acid leaching process, indicating high leaching effi-ciencies (lithium > 90% and cobalt > 85%).</p> <p>The degradation of cathode active materials or PVDF affects the adhesion force between cathode materials layer and Al current collector. Because delamination replies on inactivation of bonding forces provided by PVDF, it is believed that the storage environment (air, O₂ or H_{<strong>2</strong>}O) will affect the performances of delamination to some extent. Three representative methods (direct cal-cination, solvent extraction, and pressure washing system) of delamination were selected to eluci-date the effect from air exposure time. Direct calcination was barely influenced and stably sepa-rated CAMs in terms of peel-off efficiency. The pressure washing system or solvent extraction exhibited high peel-off efficiency using control samples, but the performance regarding either Al contamination or separation efficiency  significantly worsened after long air exposure time. This hypothesis could explain lack of reproducibility of some results in different studies and highlight the importance of strict storage condition of spent LIBs to direct recycling technology. </p> <p>Overall, this thesis examines innovative delamination methods for the development of cost-efficient and environmentally friendly direct recycling of spent LIBs. Application of the eutectic molten lithium salt system (LiOH-LiNO₃ and LiOAc-LiNO₃) or pressure washing system indicates promising benefits to reduce toxic gas emission and energy consumption, and accelerate the cir-cular economy.</p>

Thesis advisor: Dunwei Wang / When their electrodes are made of nanomaterials or materials with nanoscale features, devices for energy conversion and energy storage often exhibit new and improved properties. One of the main challenges in material science, however, is to synthesize these nanomaterials with designed functionality in a predictable way. This thesis presents our successes in synthesizing TiSi₂ nanostructures with various complexities using a chemical vapor deposition (CVD) method. Attention has been given to understanding the chemistry guiding the growth. The governing factor was found to be the surface energy differences between various crystal planes of orthorhombic TiSi₂ (C54 and C49). This understanding has allowed us to control the growth morphologies and to obtain one-dimensional (1D) nanowires, two-dimensional (2D) nanonets and three-dimensional (3D) complexes with rational designs by tuning the chemical reactions between precursors. Among all these morphologies, the 2D nanonet, which is micrometers wide and long but only approximately 15 nm thick, has attracted great interest because it is connected by simple nanostructures with single-crystalline junctions. It offers better mechanical strength and superior charge transport while preserving unique properties associated with the small-dimension nanostructure, which opens up the opportunity to use it for various energy related applications. In this thesis we focus on its applications in lithium ion batteries. With a unique heteronanostructure consisting of 2D TiSi₂ nanonets and active material coating, we demonstrate the performances of both anode and cathode of lithium ion batteries can be highly improved. For anode, Si nanoparticles are deposited as the coating and at a charge/discharge rate of 8400 mA/g, we measure specific capacities >1000 mAh/g with only an average of 0.1% decay per cycle over 100 cycles. For cathode, V₂O₅ is employed as an example. The TiSi₂/V₂O₅ nanostructures exhibit a specific capacityof 350 mAh/g, a power rate up to 14.5 kW/kg, and 78.7% capacity retention after 9800 cycles. In addition, TiSi₂ nanonet itself is found to be a good anode material due to the special layer-structure of C49 crystals. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Dunwei Wang / The performance of advanced energy storage devices is intimately connected to the designs of electrodes. To enable significant developments in this research field, we need detailed information and knowledge about how the functions and performances of the electrodes depend on their chemical compositions, dimensions, morphologies, and surface properties. This thesis presents my successes in synthesizing and characterizing electrode materials for advanced electrochemical energy storage devices, with much attention given to understanding the operation and fading mechanism of battery electrodes, as well as methods to improve their performances and stabilities. This dissertation is presented within the framework of two energy storage technologies: lithium ion batteries and lithium oxygen batteries. The energy density of lithium ion batteries is determined by the density of electrode materials and their lithium storage capabilities. To improve the overall energy densities of lithium ion batteries, silicon has been proposed to replace lithium intercalation compounds in the battery anodes. However, with a ~400% volume expansion upon fully lithiation, silicon-based anodes face serious capacity degradation in battery operation. To overcome this challenge, heteronanostructure-based Si/TiSi2 were designed and synthesized as anode materials for lithium ion batteries with long cycling life. The performance and morphology relationship was also carefully studied through comparing one-dimensional and two-dimensional heteronanostructure-based silicon anodes. Lithium oxygen batteries, on the other hand, are devices based on lithium conversion chemistries and they offer higher energy densities compared to lithium ion batteries. However, existing carbon based electrodes in lithium oxygen batteries only allow for battery operation with limited capacity, poor stability and low round-trip efficiency. The degradation of electrolytes and carbon electrodes have been found to both contribute to the challenges. The understanding of the synergistic effect between electrolyte decomposition and electrode decomposition, nevertheless, is conspicuously lacking. To better understand the reaction chemistries in lithium oxygen batteries, I designed, synthesized, and studied heteronanostructure-based carbon-free inorganic electrodes, as well as carbon electrodes whose surfaces protected by metal oxide thin films. The new types of electrodes prove to be highly effective in minimizing parasitic reactions, reducing operation overpotentials and boosting battery lifetimes. The improved stability and well-defined electrode morphology also enabled detailed studies on the formation and decomposition of Li2O2. To summarize, this dissertation presented the synthesis and characterization of inorganic nanostructured materials for advanced energy storage. On a practical level, the new types of materials allow for the immediate advancement of the energy storage technology. On a fundamental level, it helped to better understand reaction chemistries and fading mechanisms of battery electrodes. / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Lithium-ion battery (LIB) is widely utilized in many modern applications as energy sources. Numerous efforts have been dedicated to increasing electrochemical performances, but improvement on battery safety remains a visible challenge. While new electrode materials have been developed, advancement in new separator for LIB has remained relatively slow. Separator is the polymeric porous material that physically separates electrodes and allows free flow of ions through its structure. It is electrochemically inactive but essential for avoiding thermal runaway conditions. Besides its crucial functions, separator has been known as the mechanically weakest component. Structural battery is a new approach that employs multifunctional material concept to use LIB as load-bearing material to minimize the weight of the complete system and maximize the efficiency. Separator materials are required to have good thermal stability, battery chemistry, and mechanical performance. This work aims at creating electrospun membranes with improved thermal resistance, structural integrity and moderate ionic conductivity as the next generation LIB separators. Electrospinning process is known as a versatile and straightforward technique to fabricate continuous fibers at nano- and micro- scales. The electrospinning process employs an electrostatic force to control the production of fibers from polymer solutions. Solution and process parameters, including type of polymer and solvent system, concentration of polymer solution, acceleration voltage, and solution feed rate, have been studied to achieve the desirable membrane properties. In this report, the electrospinning parameters affecting morphology and corresponding properties of electrospun membranes, electrospun polymer composite and polymer-metal oxide composite membranes for structural battery applications will be discussed.

The demand for electrical energy storage has increased tremendously in recent years, especially in the applications of portable electronic devices, transportation and renewable energy. The performances of lithium-ion and sodium-ion batteries depend on their electrode materials. In commercial Li-ion batteries with graphite anodes the intercalation potential of lithium in graphite is close to the reversible Li/Li⁺ half-cell potential. The proximity of the potentials can result in unintended electroplating of metallic instead of intercalation of lithium in the graphite anode and frequently leads to internal shorting and overheating, which constitute unacceptable hazards, especially when the batteries are large, as they are in cars and airplanes. Moreover, graphite cannot be readily used as the anode material of Na-ion batteries, because electroplating of metallic sodium on graphite is kinetically favored over sodium intercalation in graphite. This dissertation examines safer Li-ion and Na-ion battery anode materials. / text