Browsing by Subject "Anode"

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Alkali metal anodes for next generation, high-energy density rechargeable batteries
(2020-05) Rodriguez, Rodrigo, Ph. D.; Mullins, C. B.; Heller, Adam; Hwang, Gyeong S; Yu, Guihua
In order to progress beyond the state-of-the-art lithium-ion batteries (LIBs), it is necessary to replace the graphitic electrode with an anode of higher energy density. Lithium metal’s ultra-high gravimetric capacity (3860 mAh g⁻¹), coupled with currently used metal oxide cathode materials could increase the gravimetric energy density of LIBs by approximately 35%. However, the well-known problem of lithium’s poor plating/stripping efficiency and dendrite formation has stalled its commercialization. The low cycling efficiency and formation of dendritic deposits is largely a consequence of the solid electrolyte interphase (SEI). This SEI forms promptly when the highly reducing lithium metal contacts the liquid organic electrolyte (LOE). It is composed of organic and inorganic reaction products. This SEI can be engineered by meticulously selecting electrolyte components (salts, solvents, and additives) which yield passivating and dendrite inhibiting constituents. A series of electrolyte compositions was surveyed and it was found that a concentrated LiNO₃ electrolyte could yield dendrite-free lithium deposits. Further optimization of this electrolyte yielded a much higher capacity retention and retained the dendrite-free deposition behavior in the visualization cell. The scarcity of lithium in the earth’s crust brings to question its sustainability as the ultimate anode choice for high-energy density, rechargeable batteries. Akin to lithium, sodium metal anodes have a high gravimetric charge capacity. However, the deposition of sodium is poorly understood compared to lithium. Sodium electrodeposits from ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) electrolytes were shown to generate large volumes of gas and yielded fragile, porous dendrites. The use of fluoroethylene carbonate (FEC) was shown to improve SEI passivation and mitigate gas evolution. Formation of sodium dendrites would be avoided by electrodepositing on the molten metal anode; however, this requires an operating temperature higher than the melting point of sodium. Formation of a room temperature sodium-potassium (NaK) liquid alloy has recently been proposed as a solution to address the operating temperature and dendrite challenges. However, visualization cell electrodepositions revealed that the NaK alloy deposits dendritically akin to solid sodium anodes in LOEs. However, when sodium was deposited on a potassium-rich alloy, dendrite formation was reduced but not completely avoided.
Alloy-type and conversion-type anode materials for enhanced performance as lithium ion battery anode materials
(2015-12) Klavetter, Kyle Christopher; Mullins, C. B.; Heller, Adam; Ellison, Chris; Hwang, Gyeong; Humphrey, Simon
Charge storage in the contemporary lithium-ion battery is at an energy density too low to support the function of long-range electric vehicles and other electronically powered technologies. To obtain up to two times or greater higher energy density than what is available by intercalation of lithium ions into graphite, the prevalent anode material in commercial batteries, materials with a higher storage density of lithium may be used, including materials that alloy with lithium or undergo a reversible conversion reaction to form lithium oxide. In this work, several such materials are considered – Ge, SnO2, Co3O4, and Ge0.1Se0.9 – and focus is directed to first demonstrating significantly enhanced cycling stability and capacity retention at variable charge/discharge rates and, second, to explaining the electrochemical performance in terms of key physical and chemical properties. Particular attention is given to assessing the formation of the solid electrolyte interphase (SEI) formed upon the anode material during charge/discharge cycling by means of microscopy and chemical characterization.
Chemical modification of nanocolumnar semiconductor electrodes for enhanced performance as lithium and sodium-ion battery anode materials
(2014-08) Abel, Paul Robert; Mullins, C. B.
Chemical Engineering
Computational, theoretical investigation of materials for a sustainable energy future
(2016-08) Stauffer, Shannon Kaylie; Henkelman, Graeme; Mullins, Charles B; Crooks, Richard; Hwang, Gyeong; Milliron, Delia
Over the past several decades there has been significant progress in electronic structure theory, statistical sampling algorithms and computational resources which can be leveraged to calculate fundamental properties of materials and estimate rates of relevant chemical reactions. In the following dissertation, I use computational methods to address the materials problem of a sustainable energy future. Energy storage technologies have played a vital role in the mobile-technology revolution and the transition to utilize more sustainable energy sources; however improvements to the energy density, charge/discharge rate, and safety of rechargeable batteries are needed to realize the ambitious goals of fully electric vehicles and on-grid storage in areas with intermittent, renewable power sources. Li-ion batteries, in general, have a potential to fulfill these demands. In the following work, a new, high energy density electrode material with little capacity loss is considered. Additionally, the complex interaction between an electrode/electrolyte model system is considered in a potential dependent computational framework. Having a sustainable energy future also means utilizing energy-efficient processing in industrial scale applications. Separation processes use roughly 12% of all energy consumed in the United States due to energy-intensive thermal separation techniques. A final study looks at an alloy catalysts for the separation of ethylene from ethane/ethylene mixtures. A unique selectivity property was discovered that may help design catalysts to replace thermal separation of gases.
Development of electrode materials with matched thermal expansion for solid oxide fuel cells
(2018-07-09) Lai, Ke-Yu; Manthiram, Arumugam; Goodenough, John B.; Kovar, Desiderio; Hwang, Gyeong S.
Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices with a conversion efficiency of over 50 % from fuel to electricity. Their high operation temperature (600 - 1000 °C) enables SOFCs to directly utilize hydrocarbon fuels without an external fuel reforming system or precious-metal catalyst. However, several critical electrode challenges impede the mass commercialization, such as high thermal stress, electrode material decomposition, unwanted reactions between neighboring components, and impurity poisoning. A rapid SOFC failure during operation is mainly caused by the mismatch of thermal expansion coefficients (TECs) among device components. Unfortunately, few electrode materials with suitable TECs and adequate electrochemical activities have been reported. With the aim of achieving high phase stability and enhancing catalytic activity, new anode and cathode materials with compatible TECs are developed. YBaCo₄O₇-based swedenborgite oxides with Y-site dopants (In³⁺ and Ca²⁺) and Co-site dopants (Ga³⁺, Al³⁺, and Fe³⁺) are investigated as cathode materials in intermediate-temperature SOFCs (600 - 800 °C). The high-spin state of the Co cation in a tetrahedral coordination prevents spin transition at elevated temperatures and makes the TECs of YBaCo₄O₇-based materials much lower than those of Co-containing perovskite oxides. However, YBaCo₄O₇-based materials may decompose at > 600 °C. Hence, the cation doping effect on the long-term phase stability is examined with 50 compositions. The electrical conductivity, TECs, thermal behavior, catalytic activity toward the oxygen reduction reaction, and SOFC performance and stability are comprehensively evaluated. A Co-doped chromite perovskite oxide with self-regenerating Co-Fe nanoparticles is utilized as a catalytically-active anode. The moderate TEC of the chromite perovskite oxide is slightly higher than the TECs of common electrolyte materials. Unlike the conventional Ni - electrolyte cermet anode, the oxide anode exhibits high redox phase stability without irreversible performance degradation during a reduction and oxidation (redox) cycle. The performance is significantly enhanced with exsolved Co-Fe nanocatalysts. The sulfur impurity tolerance and coking resistance are evaluated with an electrolyte-supported single cell by various fuels. Meanwhile, the self-regeneration behavior of exsolved nanoparticles on the oxide surface is described by carefully observing the surface evolution during a redox cycle at 700 and 800 °C.
Effect of anode properties on the performance of a direct methanol fuel cell
(2010-12) Garvin, Joshua Joseph; Meyers, Jeremy P.; Hidrovo, Carlos
This thesis is an investigation of the anode of a direct methanol fuel cell (DMFC) through numerical modeling and simulation. This model attempts to help better understand the two phase flow phenomena in the anode as well as to explain some of the many problems on the anode side of a DMFC and show how changing some of the anode side properties could alleviate these problems. This type of modeling is important for designing and optimizing the DMFC for specific applications like portable electronics. Understanding the losses within the DMFC like removable of carbon dioxide, conversion losses, and methanol crossover from the anode to the cathode will help the DMFC become more commercially viable. The model is based on two phase flow in porous media combined with equilibrium between phases in a porous media with contributions from a capillary pressure difference. The effect of the physical parameters of the fuel cell like the thickness, permeability, and contact angle as well as the operating conditions like the temperature and methanol feed concentration, have on the performance of the DMFC during operation will be investigated. This will show how to remove the gas phase from the anode while enabling methanol to reach the catalyst layer and minimizing methanol crossover.
Fast-charging lithium metal batteries enabled by engineering tetrahydrofuran-based electrolytes
(2024-05) Paul-Orecchio, Austin; Mullins, C. B.; David Mitlin, Hang Ren, Michael Aubrey; Michael Aubrey; Hang Ren
There has been significant interest from academic and industrial sectors to use lithium metal anodes in energy storage devices due to their superior energy density (3860 mAh/g) compared with conventional, graphite-based counterparts. However, the safety and inefficiency concerns arising from dendritic lithium formation prohibit their widespread adoption. This dissertation focuses on preventing dendrites by engineering a tetrahydrofuran-based electrolyte mixture (LiFSI-THFMix) with alloying M-nitrate (M: Ag, Bi, Ga, In, Zn) additives. Through a simple in situ solution, lithium metal anodes can withstand stable lithium metal plating during fast-charging conditions. Notably, Zn-protected cells achieve the lowest overpotential (156 mV) and longest cycle stability (140 cycles) during ultra-fast 10.0 mA cm⁻² Li||Li cycling. Additionally, C/2 Li||LFP full cells demonstrate the highest capacity (134 mAh g⁻¹) and capacity retention (89.2%) after 400 cycles. Their success was attributed to a robust passivation layer (LiF, Li₃N, LiNₓOᵧ) and lithiophilic alloy (LiZn), enhancing Li⁺ diffusion and plating. Overall, this dissertation highlights tetrahydrofuran-based electrolyte mixtures and alloying nitrate additives as promising solutions enabling next-generation lithium metal batteries.
First principles study of silicon-based nanomaterials for lithium ion battery anodes
(2014-05) Chou, Chia-Yun Ph. D.; Hwang, Gyeong S.; Mullins, Charles B; Manthiram, Arunmugam; Ekerdt, John G; Stevenson, Keith
Silicon (Si)-based materials have recently emerged as a promising candidate for anodes in lithium-ion batteries because they exhibit much higher energy-storage capacities than the conventional graphite anode. However, the practical use of Si is hampered by its poor cycleability; during lithiation, Si forms alloys with Li and undergoes significant structural and volume changes, which can cause severe cracking/pulverization and consequent capacity fading arising from the loss of electrical contacts. To overcome these drawbacks, many innovative approaches have been explored with encouraging results; however, many fundamental aspects of the lithiation behavior remain ambiguous. Hence, the focus of this work is to develop a better understanding of the lithiation process at the atomistic scale using quantum mechanical calculations. In addition, based on the improved understanding, we attempt to address the fundamental mechanisms behind the successful approaches to enhance the anode performance. To lay a foundation for the investigation of alloy-type anodes, in Chapter 3, we first examine how lithiation occurs in Si and the formation of crystalline and amorphous LixSi alloys (0 ≤ x ≤ 4); followed by assessing the lithiation-induced changes in the energetics, atomic structure, electronic and mechanical properties, and Li diffusivity. The same approach is then extended to analyze the lithiation behavior of germanium (Ge) and tin (Sn) for developing a generalized understanding on the Group IV alloy-type anodes. Along this comparative study, we notice a few distinguishing features pertain only to Si (or Ge), such as the facile Li diffusion in Ge and facet-dependent lithiation in Si, which are discussed in Chapter 4. Beyond the fundamental research, we also look into factors that may contribute to the improved anode performance, including (i) finetuning of the oxidation effects in Si-rich oxides, [alpha] -SiO [subscript 1/3] (Chapter 5), (ii) maximizing the surface effects through nano-engineered structures (Chapters 6 & 7), and finally (iii) the role of interface in Si-graphene (carbon) composites (Chapter 8).
High-stability lithium metal batteries enabled by a tetrahydrofuran-based electrolyte mixture
(2022-05-11) Paul-Orecchio, Austin; Mullins, C. B.
There has been significant interest from academic and industrial sectors to use lithium metal anodes in energy storage devices due to their much higher energy density (3860 mAh/g) compared with conventional, graphite-based counterparts. However, the safety and inefficiency concerns arising from lithium dendrite formation on these anodes during operation have prohibited their widespread adoption. This study focuses on reducing the dendritic tendencies on lithium anodes by forming an in situ, LiF-rich surface layer on the lithium metal, designed specifically to facilitate uniform lithium diffusion and nucleation. The LiF-rich solid electrolyte interphase (SEI) is a result of the employment of a low salt concentration electrolyte mixture (1.0 M LiFSI -THFMix). Remarkably, Li||Li symmetric cells with this type of electrolyte show stable cycling over 1700+ hours at a current density of 0.5 mA cm⁻². To understand the influence of electrolyte on the chemical composition of the SEI a combination of time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS) were applied. This work demonstrates a low concentration electrolyte mixture to significantly suppress dendritic growth in lithium metal batteries and identifies the key mechanisms for this beneficial effect.
Insights into constructing energy dense battery electrodes with lightweight carbon materials
(2020-05-07) Pender, Joshua Paul; Mullins, C. B.; Heller, Adam (Professor of chemical engineering); Rose, Michael; Roberts, Sean T
The lithium-ion battery (LIB) has revolutionized modern society, powering the wireless world of portable electronics and emerging as the battery-of-choice for electric vehicles (EVs) and electrical grid storage. Although LIBs offer superior energy density to other commercial battery technologies, they are also often a limiting factor: in portable electronics, LIBs often occupy significant weight/volume and limit device form factor, while EVs are currently restricted by either the short driving range or the high cost of the large LIB packs and maintenance systems. Batteries of higher energy density would alleviate these limitations and greatly expand the possibilities of LIB-powered devices. Increasing battery energy density is complicated by several factors and has motivated significant effort over the past 30 years to develop higher performing LIBs. As an emerging class of materials for advanced battery electrodes, porous carbons are attractive due to their production from inexpensive feedstocks, high electrical conductivity, and tunable surface chemistry and textural properties. The use of porous materials in commercial batteries has traditionally been hindered by their low packing density and weak mechanical properties that restrict processing into energy-dense electrodes. To address these limitations, a series of reduced graphene oxide (rGO) aerogels were synthesized, characterized, processed, and electrochemically tested as lightweight electrode scaffolds in LIBs. Initial efforts focused on correlating various parameters of commercially available LIB electrode materials supported on thermally crosslinked rGO-poly (acrylic acid) (PAA) aerogels. By switching from conventional metal foil electrode supports to the lightweight aerogel systems, a 25% increase in energy density of commercial battery electrodes can be realized. Furthermore, the prospect of using structural control to enable mechanically durable, PAA-free rGO aerogels is discussed. Another route to higher energy density can be realized by replacing the standard graphite anode with new materials capable of storing more lithium per unit weight and volume. A templating method was developed for tuning the surface chemistry and textural properties of nanostructured, nitrogen-doped carbons. The proposed mechanism and characterization provide guidelines for fabricating materials capable of storing two-to-three times more lithium than graphite with little degradation over 2000 charge-discharge cycles.
Silicon nanowires : synthesis and use as lithium-ion battery anodes
(2014-12) Bogart, Timothy Daniel; Korgel, Brian Allan, 1969-; Mullins, C. Buddie; Ekerdt, John G.; Chelikowsky, James R.; Manthiram, Arumugam
As the power demands of mobile technologies continue to increase, lithium-ion batteries are needed with greater power and energy density. Silicon anodes offer an alternative to commercial graphite with much greater gravimetric and volumetric Li storage. Si nanowires are particularly compelling anode materials because they provide short Li diffusion paths due to their narrow diameter combined with long continuous paths for electron transport down their length. To achieve reasonable battery performance in Si nanowire anodes, conductive carbon particles must be added to provide sufficient electrical conductivity through the anode layer. This lowers the capacity of the anode, but more importantly the carbon particles can segregate in the electrode layer during processing or as a result of mechanical stresses during cycling, leading to unreliable performance. Better performance can be achieved by altering the structure of the Si nanowire to improve electrical conductivity. Si nanowires with a conductive carbon coating were synthesized in a supercritical organic solvent using an organometallic tin precursor to seed growth. The coating eliminated the need for additional conductive additives and improved Si nanowire anode performance. In situ TEM experiments showed that the coated nanowires exhibit higher lithiation rates than bare Si nanowires, but the coating restricts volume expansion limiting the amount of Li storage. Nanowires with a crystalline Si core and amorphous Si shell were also synthesized. The thickness of the core and shell were controlled by altering the Si:Sn precursor ratio. Sn was found to incorporate strongly within the crystalline core, but not at all in the amorphous shell, creating nanowires with varying conductivity. The addition of tin improved Si nanowire performance in Li-ion batteries, eliminating the need for conductive additives. Lastly, the low-temperature limit on the solution synthesis of Si nanowires via in situ seeding was explored using tin, gallium, and indium seeds.
Synthesis and characterization of nanocomposite alloy anodes for lithium-ion batteries
(2012-05) Applestone, Danielle Salina; Manthiram, Arumugam; Goodenough, John; Mullins, Charles; Stevenson, Keith; Meyers, Jeremy
Lithium-ion batteries are most commonly employed as power sources for portable electronic devices. Limited capacity, high cost, and safety problems associated with the commercially used graphite anode materials are hampering the use of lithium-ion batteries in larger-scale applications such as the electric vehicle. Nanocomposite alloys have shown promise as new anode materials because of their better safety due to higher operating potential, increased energy density, low cost, and straightforward synthesis as compared to graphite. The purpose of this dissertation is to investigate and understand the electrochemical properties of several types of nanocomposite alloys and to assess their viability as replacement anode materials for lithium-ion batteries. Tin and antimony are two elements that are active toward lithium. Accordingly, this dissertation is focused on tin-based and antimony-based nanocomposite alloy materials. Tin and antimony each have larger theoretical capacities than commercially available anodes, but the capacity fades dramatically in the first few cycles when metallic tin or antimony is used as the anode in a lithium-ion battery. This capacity fade is largely due to the agglomeration of particles in the anode material and the formation of a barrier layer between the surface of the anode and the electrolyte. In order to suppress agglomeration, the active anode material can be constrained by an inactive matrix of material that makes up the nanocomposite. By controlling the surface of the particles in the nanocomposite via methods such as the addition of additives to the electrolyte, the detrimental effects of the solid-electrolyte interphase layer (SEI) can be minimized, and the capacity of the material can be maintained. Moreover, the nanocomposite alloys described in this dissertation can be used above the voltage where lithium plating occurs, thereby enhancing the safety of lithium-ion batteries. The alloy anodes in this study are synthesized by high-energy mechanical milling and furnace heating. The materials are characterized by X-ray diffraction, scanning and transmission electron microscopies, and X-ray photoelectron spectroscopy. Electrochemical performances are assessed at various temperatures, potential ranges, and charge rates. The lithiation/delithiation reaction mechanisms for these nanocomposite materials are explored with ex-situ X-ray diffraction. Specifically, three different nanocomposite alloy anode materials have been developed: Mo3Sb7-C, Cu2Sb-Al2O3-C, and Cu6Sn5-TiC-C. Mo3Sb7-C has high gravimetric capacity and involves a reaction mechanism whereby crystalline Mo3Sb7 disappears and is reformed during each cycle. Cu2Sb-Al2O3-C with small particles (2 - 10 nm) of Cu2Sb dispersed in the Al2O3-C matrix is made by a single-step ball milling process. It exhibits long cycle life (+ 500 cycles), and the reversibility of the reaction of Cu2Sb-Al2O3-C with lithium is improved when longer milling times are used for synthesis. The reaction mechanism for Cu2Sb-Al2O3-C appears to be dependent upon the size of the crystalline Cu2Sb particles. The coulombic efficiency of Cu2Sb-Al2O3-C is improved through the addition of 2 % vinylethylene carbonate to the electrolyte. With a high tap density of 2.2 g/cm3, Cu6Sn5-TiC-C exhibits high volumetric capacity. The reversibility of the reaction of Cu6Sn5-TiC-C with lithium is improved when the material is cycled above 0.2 V vs. Li/Li+.
Synthesis and electrochemical characterization of novel electroactive materials for lithium-ion batteries
(2017-10-02) Kreder, Karl Joseph, III; Manthiram, Arumugam; Goodenough, John B; Yu, Guihui; Hwang, Gyeong S; Ferreira, Paulo J
Lithium-ion batteries (LIBs) have become ubiquitous as energy storage devices for mobile electronics, electric vehicles, and are beginning to be used for electric grid-scale energy storage. Lithium-ion batteries offer higher efficiencies, energy density, and longer life compared to incumbent technologies such as lead-acid and nickel metal hydride. Applications in which LIBs are used are continuing to demand better performing batteries at lower cost, which requires improvement in electroactive materials. This dissertation investigates the low temperature synthesis and modification of LiCoPO₄ as a potential high-voltage and therefore higher energy density polyanion cathode material for LIBs, as well as a new class of interdigitated metal foil anodes which promises to be an inexpensive, higher energy density, alternative to graphite. Chapter 1 is a brief introduction to lithium-ion batteries and the principle of operation of intercalation type electrochemical energy storage devices. The components of lithium ion batteries are introduced, specifically the anode, cathode, separator, and electrolyte. Some of the shortfalls of the current technologies are discussed and areas of research interest are highlighted. Chapter 2 is a brief overview of the various experimental methods that are generally applicable to more than one of the subsequent chapters. Methods which are specific to a given study are discussed in their respective chapters. Chapter 3 presents work on the low temperature microwave-assisted solovthermal synthesis (MW-ST) of three unique polymorphs of LiCoPO₄, specifically the polymorphs belonging to the Pnma, Cmcm, and Pn2₁a space groups. Prior to this work, only the Pnma polymorph had been reported via MW-ST method, and electrochemistry had not yet been reported for either the Pn2₁a or Cmcm polymorph. The dependence of the polymorphs on both the water content, and ammonium hydroxide content of the solvent was shown. Although, the electrochemistry of both the Pn2₁a and Cmcm polymorphs was found to be inferior to the Pnma polymorph, the ability to synthesize phase pure materials was crucial to conducting the work presented in chapters 4 and 5. Chapter 4 presents the aliovalent substitution of V³⁺ for Co²⁺ in LiCoPO₄ via a low-temperature MW-ST process. Substitution of up to 7% vanadium for cobalt was demonstrated and verified by changes in the lattice parameters with vanadium content. Both the ionic and electronic conductivity of LiCoPO₄ was enhanced with increasing vanadium substitution, which was attributed to the introduction of both charge carriers as well as inter-tunnel cobalt vacancies. Finally, the first cycle capacity was enhanced (from 69 mAh/g to 115 mAh/g) as well as the capacity retention over cycling. Chapter 5 demonstrates a novel technique of MW-ST assisted coating of a thin (2-5nm) conformal coating of LiFePO₄ on vanadium substituted LiCoPO₄. Although the vanadium substitution was able to independently increase the performance of LiCoPO₄, the materials still suffers from severe side reactions with the electrolyte. The coating of LiFePO₄ effectively raises the Fermi energy of the cathode material above the high occupied molecular orbital (HOMO) of the electrolyte preventing side reactions and increase the coulombic efficiency to nearly 100%. Chapter 6 introduces a novel method of producing high surface area, electrically conductive, metal nanofoams via a MW-ST process. Nickel, copper, and silver metal nanofoams are made via an inexpensive yet scalable process whereby metal acetates are reduced by polyglycol under microwave irradiation. The nanofoams were characterized via BET, SEM, XRD, EDS, and TEM. The nanofoams have potential uses in many clean energy applications, particularly lithium-ion batteries. Chapter 7 introduces a new framework for making a new class of high capacity, low-cost alloying anodes for lithium ion batteries. A novel interdigitated metal foil anode (IMFA) in which a nanosized active material, such as tin, is interdigitated with an electrically conductive matrix, such as aluminum, is presented. The foils are formed by the rolling of a eutectic Al-Sn alloy into a foil, which is an extremely cheap and scalable process. The anodes demonstrate an approximately 70% increase in capacity compared to graphite over 100 cycles, at reasonably fast rates (C/5), and high coulombic efficiency (>99%). Finally, Chapter 8 gives a brief overview of the results of the prior work and proposes areas for future research.