Browsing by Subject "Battery"

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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.
Coordination complex design for applications in thin films and electrochemical energy storage
(2020-12-11) Hall, Justin Walker; Jones, Richard A., 1954-; Que, Emily; Rose, Michael; Ekerdt, John G; Campion, Alan
Several applications of d-block organometallic chemistry will be presented, spanning chemical vapor deposition precursors, lithium ion battery electrode materials, and redox flow battery electrolytes. In the first chapter, the coordination chemistry of phosphine (PH3) with Ruthenium will be explored in the context of attempts to design a carbon-free Ru(P) thin film chemical vapor deposition precursor. In the second chapter, a novel application of organometallic proton exchange to the synthesis of amorphous Li-ion battery electrodes with the goal of increased capacity retention will be demonstrated. In the third chapter, the identity and electrochemistry of the redox active species in a novel redox flow battery system will be elucidated.
Design and analysis of precursors for CVD of Ru thin films and Li-ion batteries with MoP₄ anode materials
(2013-08) De Pue, Lauren Joy; Jones, Richard A., 1954-
The chemical vapor deposition growth of amorphous metallic alloys is currently of interest for potential uses in electronic devices. We have explored the use of ligands having Ru-H, Ru-N, and Ru-P bonds to study the effects of ligand selection. The synthesis and design of novel Ru dinuclear complexes using volatile ligands such as 3,5-bis-trifluoromethylpyrazolate and trimethylphosphine will be presented as well as materials characterization studies on grown films. Another class of functional materials of interest is the transition metal phosphides (TMPs) which have found applications in Li-ion batteries. Current research on TMPs is focused on obtaining materials with improved or new compositions and morphologies and on improving Li insertion/de-insertion reactions and charge carrying capacities. Traditional routes to these materials involve the use of high temperatures and pressures. The work presented here will focus on a synthetic route which employs relatively mild conditions. Surface analysis studies and the electrochemical performance of mesoporous MoP₄ for use as anode materials in Li-ion batteries will be described.
A dynamic model-based estimate of the potential value of a vanadium redox flow battery for energy arbitrage and frequency regulation in Texas
(2012-08) Fares, Robert Leo; Webber, Michael E., 1971-; Meyers, Jeremy P.
Large-scale electrochemical energy storage is a technology that is uniquely suited to integrate intermittent renewable energy sources with the electric grid on a large scale. Grid-based energy storage also has the potential to reduce costs associated with periods of peak electric demand. For these reasons, this work describes the potential applications for grid-based energy storage, and then reviews large-scale energy storage technology innovations since the development of the lead-acid battery. The potential value of grid-based battery energy storage is discussed in the context of restructured electricity markets; then, a dynamic model-based economic optimization routine is developed to gauge the potential value of a vanadium redox flow battery (VRFB) operating for wholesale energy arbitrage and frequency regulation in Texas. Based on this analysis, the relative value of a VRFB in various regions of Texas for energy arbitrage and frequency regulation is examined. It is shown that frequency regulation is an appealing application for a grid-based VRFB, with a VRFB utilized for frequency regulation service in Texas potentially worth approximately $1500/kW. Finally, the effect of a VRFB’s characteristics on its value for frequency regulation and energy arbitrage are compared, and the operational insight developed in this work is used to glean how policies to integrate a large-scale energy storage with the electricity market might be crafted.
Efficient models and algorithms for mass conservation and morphology evolution in lithium metal batteries
(2023-04-19) Jang, Taejin; Subramanian, Venkat R.; Manthiram, Arumugam; Mitlin, David; Hwang, Gyeong S.; Roberts, Scott A.
The demand for energy storage devices with high energy density, coulombic efficiency, long-term stability, and high capacity while ensuring safety has never been higher. However, the efforts towards carbon neutrality and exploration of next-generation batteries for electric vehicles and mobile applications are still insufficient to meet the demands. The development of Lithium-ion batteries is a giant leap in achieving the utilization of lithium, which has high reactivity, mobility, and superior energy density along with high output voltage. However, there is one major area of improvement to advance the conventional lithium-ion batteries: the anode electrode. Lithium metal has the highest energy density among the other potential candidates for anodes, ahead of conventional graphite electrodes which are based on the intercalation of lithium ions. Despite the early research interests, the metal anode was not commercially successful due to safety concerns and inferior cyclability. Even today, those defects are challenging and need further research. Thus, to resolve the above-mentioned difficulties, there is a significant need for a fundamental understanding of the morphology changes during the deposition and stripping, specifically, the anomalies in the microscale, such as the formation of dendrites, local cavitation, and initial surface defects. These translate into macroscale as dendrite growth, depletion of the electrolyte by the continuous solid-electrolyte interface (SEI) layer growth, and formation of isolated regions called 'dead lithium'. This thesis focuses on the physics-based models and algorithms at different scales and varying complexity of the system to simulate the evolution of the anode surface in lithium metal batteries. This includes continuum, mesoscale and multiscale models conserving the system's total mass. The different approaches, such as coordinate transformation and phase-field model, are discussed with proper mathematical reformulation. Lastly, an effective algorithm for fast and accurate simulation is proposed with selected examples.
Electrochemical transport simulation of 3D lithium-ion battery electrode microstructures
(2015-10-21) Trembacki, Bradley Louis; Murthy, Jayathi; Moser, Robert D; Roberts, Scott A; Duoss, Eric B; Chen, Dongmei
Lithium-ion batteries are commonly modeled using a volume-averaged formulation (porous electrode theory) in order to simulate battery behavior on a large scale. These methods utilize effective material properties and assume a simplified spherical geometry of the electrode particles. In contrast, a particle-scale (non-porous electrode) simulation applied to resolved electrode geometries predicts localized phenomena. Complete simulations of batteries require a coupling of the two scales to resolve the relevant physics. A central focus of this thesis is to develop a fully-coupled finite volume methodology for the simulation of the electrochemical equations in a lithium-ion battery cell at both the particle scale and using volume-averaged formulations. Due to highly complex electrode geometries at the particle scale, the formulation employs an unstructured computational mesh and is implemented within the MEMOSA software framework of Purdue’s PRISM (Prediction of Reliability, Integrity and Survivability of Microsystems) center. Stable and efficient algorithms are developed for full coupling of the nonlinear species transport equations, electrostatics, and Butler-Volmer kinetics. The model is applied to synthetic electrode particle beds for comparison with porous electrode theory simulations and to evaluate numerical performance capabilities. The model is also applied to a half-cell mesh created from a real cathode particle bed reconstruction to demonstrate the feasibility of such simulations. The second focus of the thesis is to investigate 3D battery electrode architectures that offer potential energy density and power density improvements over traditional particle bed battery geometries. A singular feature of these geometries is their interpenetrating nature, which significantly reduces diffusion distance. Advancement of micro-scale additive manufacturing techniques has made it possible to fabricate these electrode microarchitectures. A fully-coupled finite volume methodology for the transport equations coupled to the relevant electrochemistry is implemented in the PETSc (Portable, Extensible Toolkit for Scientific Computation) software framework which allows for a straightforward scalable simulation on orthogonal hexahedral meshes. Such scalability becomes important when performing simulations on fully resolved microstructures with many parameter sweeps across multiple variables. Using the computational model, a variety of 3D battery electrode geometries are simulated and compared across various battery discharge rates and length scales in order to quantify performance trends and investigate geometrical factors that improve battery performance. The energy density and power density of the 3D battery microstructures are compared in several ways, including a uniform surface area to volume ratio comparison as well as a comparison requiring a minimum manufacturable feature size. Significant performance improvements over traditional particle bed electrode designs are observed, and electrode microarchitectures derived from minimal surfaces are shown to be superior under a minimum feature size constraint. An average Thiele modulus formulation is presented to predict the performance trends of 3D microbattery electrode geometries. As a natural extension of the 3D battery particle-scale modeling, the third and final focus of the thesis is the development and evaluation of a volume-averaged porous electrode theory formulation for these unique 3D interpenetrating geometries. It is necessary to average all three material domains (anode, cathode, and electrolyte) together, in contrast to traditional two material volume-averaging formulations for particle bed geometries. This model is discretized and implemented in the PETSc software framework in a manner similar to the particle-scale implementation and enables battery-level simulations of interpenetrating 3D battery electrode architectures. Electrode concentration gradients are modeled using a characteristic diffusion length, and results for plate and cylinder electrode geometries are compared to particle-scale simulation results. Additionally, effective diffusion lengths that minimize error with respect to particle-scale results for gyroid and Schwarz P electrode microstructures are determined, since a theoretical single diffusion length is not easily calculated. Using these models, the porous electrode formulation for these 3D interpenetrating geometries is shown to match the results of particle-scale models very well.
Environmental impacts of onshoring lithium and lithium-ion battery production
(2022-07-06) Harner, Zakariah Quinton; Childress, Tristan M.; Chuchla, Richard J. (Richard Julian)
Life cycle assessment was conducted to quantify prospective environmental impacts of a transition to onshore supply of lithium battery materials and onshore production of lithium-ion battery cells in the United States. Life cycle assessments were compiled for current lithium raw materials and lithium-ion battery cell supply chain pathways, dominated by a Chinese midstream monopoly on refinement and lithium-ion battery component production, and compared with prospective American-based supply chain pathways. Differences in global warming potential (GWP) (kg of carbon dioxide equivalents), water consumption, and land use of differing supply chain pathways were the primary environmental impacts under comparison and analysis. Both “Traditional” (current) and prospective American supply chain pathways were developed for lithium carbonates, lithium hydroxides, nickel-cobalt-aluminum (NCA) based battery cells, and lithium-iron-phosphate (LFP) based battery cells. Each product was modeled from cradle-to-gate, meaning from raw material extraction through transportation to point of sale. Transition from Traditional lithium carbonate supply chain pathways to American-based pathways resulted in a 66% reduction in the GWP of transportation of refined materials, thanks largely to elimination of the need for cross-Pacific freight shipping. Transition from Traditional supply chain pathways to American-based lithium hydroxide pathways resulted in a 49% reduction in the GWP of electricity usage during refinement when transitioning from Chinese and Japanese electricity grids to United States counterparts, due largely to lower amounts of coal-based electricity generation within the United States electricity grid. During the simulated production of 100 kWh of NCA and LFP-based lithium-ion battery cells, NCA cells were found to produce 11% less GWP than LFP equivalents on average. Utilizing lithium raw materials sourced from the Americas, American based production of NCA and LFP cells was found to produce an average of 13% less GWP than Traditional supply chain pathway counterparts
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.
Li-ion and Na-ion battery anode materials and photoanodes for photochemistry
(2015-08) Dang, Hoang Xuan; Mullins, C. B.; Heller, Adam; Hwang, Gyeong S.; Fan, Donglei; Korgel, Brian A.
The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance. The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance.
Modernizing commercial rate design to align the private benefits of distributed energy storage with system and social welfare
(2020-05-05) Haley, Matthew Thomas; Beach, Fred Charles, 1959-
The adoption of Distributed Energy Resources (DER) – such as battery energy storage and rooftop solar - are revolutionizing the topology and operation of the electric grid. When paired with smart control and communication technologies, DERs transform traditional electricity customers into providers of (potentially zero-emission) energy and grid services. Electricity rates - the policies that govern the retail use cases for these technologies – however, lag the technological advances of the modern grid. Retail rates designed in a less technically complex era – such as demand charges – do not send price signals that align customer behavior with either grid or social benefits. In this research we investigate the retail rate incentives for the commercial segment of energy customers in Texas. Texas provides an interesting test case for commercial investment in energy storage for two reasons: first, low energy prices driven by cost declines in renewables and natural gas has caused commercial and industrial energy use in Texas to grow compared to other states, second, retail restructuring in Texas has diversified the types of rates a commercial customer can choose from. In this analysis, we formulate a linear program to optimize commercial DER behavior over a variety of increasingly time-responsive commercial rate designs. We then utilize four years of historical data from ERCOT and 15 commercial building load profiles to investigate how each retail rate design aligns with system and social objectives including emission reductions. I find that time invariant rates – such as demand charges - often provide perverse incentives to some classes of commercial DER applications that increase system-wide costs and can increase emissions. In comparison I find that exposing commercial DER customers to dynamic prices that better reflects real-time system needs decreases overall costs and decreases emissions.
Operation and control strategies for battery energy storage systems to increase penetration levels of renewable generation on remote microgrids
(2013-08) Such, Matthew Clayton; Masada, Glenn Y.
A critical requirement of any remote microgrid is its capability to control the balance between electric generation and load within the confines of the microgrid itself. The integration of significant amounts of “as available” renewable generation to any electric grid (macro or micro) makes it more difficult to maintain this balance and can result in large frequency deviations on a microgrid. Ancillary services provide the resources required to maintain the instantaneous and ongoing balance between generation and load. Battery energy storage systems (BESS) can provide regulating reserves, a type of ancillary service, by modulating active power for frequency control, referred to as load frequency control (LFC), to reduce frequency deviations caused by sudden changes in renewable generation. Historically, the most common methodology for reducing frequency disturbances exacerbated by wind plants with BESS systems is ramp rate control and more recently lead compensation. This thesis proposed a modified lead compensator for use in microgrid applications. A PSS®E microgrid model, based upon existing validated models, was developed to test the effectiveness of the LFC controllers used to dispatch the BESS as a regulating resource to allow increased wind energy penetration levels on remote microgrids. A model of the remote microgrid of the island of Maui, Hawaii was chosen as the basis for the designs. Daily wind power data from 2012 was classified and indexed on an hourly basis by severity of variation. The worst hour for power variation from the wind plants was identified from this indexing and used as the basis for simulating the LFC controllers. The results compared the effectiveness of droop, ramp rate, lead compensation, and modified lead compensation controllers in reducing the variability in the grid frequency caused by changes in wind power generation. An RMS of variation with respect to an average over different time windows was used as the comparison metric. The combined modified lead compensator with ramp rate control showed the best performance of the overall system behavior.
Polymorphs of lithium transition-metal phosphates : synthesis and characterization
(2015-08) Assat, Gaurav; Manthiram, Arumugam; Yu, Guihua
Lithium transition-metal phosphates, LiMPO₄ (M = Mn, Fe, Co, and Ni) have gained significant research interest over the past two decades as an important class of lithium-ion battery cathode materials. However, almost all of the investigations thus far have focused on the olivine polymorph which exists in orthorhombic Pnma space group. In this report, a distinct orthorhombic but non-olivine polymorph of LiMPO₄, described by a Cmcm space group symmetry, has been synthesized with M = Mn, Fe, Co, and Ni. Of these, LiMPO₄ in the Cmcm space group had never been reported before. A rapid microwave-assisted solvothermal (MW-ST) heating process with tetraethylene glycol (TEG) as the solvent and transition-metal oxalates as precursors facilitate the synthesis of these materials. The peak reaction temperatures and pressures, respectively, were below 300 °C and 30 bar, which is several orders of magnitude lower than the previously reported high pressure (GPa) method. The physiochemical and electrochemical properties of the synthesized materials are characterized with several techniques. X-ray diffraction (XRD) confirms the crystal structure with Cmcm space group and scanning electron micrographs (SEM) indicate a sub-micron thin platelet like morphology. The synthesis process conditions have been optimized to obtain impurity-free samples with correct stoichiometry, as characterized with XRD and inductively coupled plasma - optical emissions spectroscopy (ICP-OES). Upon heat treatment to higher temperatures, the transformation of the Cmcm polymorphs into olivine is observed with XRD and Fourier transform infrared spectroscopy (FTIR). Although the electrochemical activity of these polymorphs as lithium-ion cathodes turns out to be poor, the facile synthesis under mild conditions has enabled easy access to these materials, some of which were not even possible before.
Sodium layered-oxide cathodes for lithium-free and cobalt-free batteries
(2022-07-01) Lamb, Julia; Manthiram, Arumugam; Hwang, Gyeong; Yu, Guihua; Korgel, Brian
Sodium-ion batteries (SIBs) are gaining attention as alternatives to lithium-ion batteries (LIBs), particularly in the field of building-scale and grid-scale energy storage systems. The natural abundance and affordability of sodium relative to lithium makes the SIB a good contender for large-scale storage applications where battery cost is a more critical parameter than battery size and weight. At the cathode side of the battery, sodium layered-oxide materials are of great interest due to their similarities with the standard lithium layered oxide, and their high theoretical capacity of 240 mA h g ⁻¹. However, in practice, a high-energy sodium-ion cell is difficult to achieve, and their poor surface stability leads to rapid degradation in contact with both air and electrolyte. This dissertation begins with a comprehensive study to evaluate the various degradation routes of a sodium layered oxide. This evaluation is used to guide the future modification projects which aim to stabilize the material. A sodium phosphate coating applied post-calcination is found to greatly stabilize the cathode surface in both air and during cycling. The coating acts as a stable, artificial surface layer during cycling and protects the material from degradation on exposure to air due to moisture and CO₂. An alternative approach to surface stabilization is examined with the molten-salt synthesis method. In the molten salt, the particles preferentially grow parallel to the sodium diffusion channels, forming a micron-scale plate-like morphology. The edge planes, where reactivity and degradation are most severe, are highly narrow. The small surface area of the edge planes helps minimize surface reactions and subsequent capacity loss. Furthermore, the molten-salt synthesis method has benefits over the industrial coprecipitation technique and may be a practical method for large-scale synthesis of layered-oxide materials. Finally, the primary source of capacity fade during cycling is addressed at the electrolyte. The standard carbonate electrolytes degrade into an unstable, organic surface layer on the cathode surface. The electrolyte also causes transition-metal dissolution and its migration and attack on the anode. Two new classes of electrolytes are found to form a stable surface layer with minimal degradation of the bulk layered oxide. Together, the methods presented herein provide practical solutions to stabilizing layered-oxide cathode materials that can be applied either alone or in combination.
Studies of electrode materials for lithium and sodium metal batteries
(2020-07-31) Meyerson, Melissa Lynn; Mullins, C. B.; Heller, Adam; Henkelman, Graeme; Humphrey, Simon
There is a need for higher capacity batteries to address the increasing energy demand for electric vehicles and portable technologies. With more than ten times the capacity of current graphite anodes, Li metal is an ideal replacement; however, it suffers from safety and efficiency problems that have so far prevented it from being commercialized. In particular, Li metal has a tendency to form dendritic structures during electrodeposition, which not only present a high surface area leading to excess electrolyte consumption, but may also cause short circuit leading to thermal runaway and battery fires. The causes for dendrite nucleation on metallic Li are numerous and complex making determination of an exact cause for dendrite growth difficult. In this work, the mechanisms for dendrite growth are examined by exploring the relationship between the anode chemistry, topography, and solid electrolyte interphase. Based on the findings, mitigation techniques are proposed and tested; specifically, the used of artificial coatings to homogenize Li electrodeposition on Li metal anodes. While Li may be an ideal anode in terms of its capacity and redox potential, from a practical standpoint it is geographically limited and therefore less desirable for commercial production. Sodium is less expensive and more abundant than Li making it a potential alternative for high capacity batteries. High capacity cathodes are needed to pair with Na anodes, and S is an ideal candidate. However, similar to Li-S batteries, Na-S batteries experience rapid capacity fade due to polysulfide shuttling. The final portion of this work explores a sulfur equivalent cathode material, MoS [subscript 5.6], with the aim of creating a high-capacity, stable Na-S battery.
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+.
Understanding the electrochemistry and reaction mechanisms of solid-state sulfides with application to the lithium-sulfur battery system
(2017-05) Klein, Michael James; Manthiram, Arumugam; Goodenough, John B; Ferreira, Paulo J; Yu, Guihua; Hwang, Gyeong S
The lithium-sulfur (Li-S) battery is a highly promising technology for next-generation high energy density storage. This high energy density has its roots in the conversion chemistry of the Li-S system, which also imparts numerous challenges to the realization of practically viable cells. This dissertation focuses on improving the performance and understanding of insulating solid-state lithium sulfides, which are the source of many of the challenges inherent to Li-S batteries. First, a facile strategy is presented to generate a manganese sulfide surface layer on Li₂S particles, which dramatically improves cycling performance. Analysis of this reaction mechanism demonstrates how surface layers with limited conductivity but high electrochemical stability and facile charge transfer can profoundly improve the solid Li₂S charge mechanism. The role of solid sulfur-sulfur bonding in the cycling mechanism was then analyzed by direct chemical synthesis and isolation of insoluble sulfur-sulfur bonded species (i.e., Li₂S₂-type species). While these syntheses are shown not to generate Li₂S₂ separate from Li₂S, the insoluble polysulfide species were isolated from the soluble polysulfides. These isolated insoluble sulfides are used to demonstrate that solid-state sulfur-sulfur bonds can be reduced in the absence of soluble polysulfides, and the formation of Li₂S₂ is thus not inherently limiting to the capacity of Li-S batteries. To further clarify the fundamental limitation of Li₂S thickness on Li-S battery rate performance, a system was built to sputter-deposit air-sensitive lithium sulfide films of arbitrary thickness. It is shown that while the deposition initially generates a novel sulfide structure containing polymer-like Li₂S units, highly pure crystalline films of Li₂S can be generated with annealing. These Li₂S films are used to systematically determine the maximum thickness of Li₂S that can be charged at a practical rate is approximately 40 nm at a local charge density of 1 μA cm-2. This systematic approach additionally identified the appearance of the activation overpotential when charging Li₂S to be associated with the generation of soluble polysulfide species. Finally, these results are used to develop a model for the rational design of Li-S cathodes by tailoring the conductive pore structure around the local charge density and total sulfur content.