Browsing by Subject "Cathodes"
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Item Chemical, structural, and electrochemical characterization of 5 V spinel and complex layered oxide cathodes of lithium ion batteries(2007) Tiruvannamalai Annamalai, Arun Kumar; Manthiram, ArumugamLithium ion batteries have revolutionized the portable electronics market since their commercialization first by Sony Corporation in 1990. They are also being intensively pursued for electric and hybrid electric vehicle applications. Commercial lithium ion cells are currently made largely with the layered LiCoO₂ cathode. However, only 50% of the theoretical capacity of LiCoO₂ can be utilized in practical cells due to the chemical and structural instabilities at deep charge as well as safety concerns. These drawbacks together with the high cost and toxicity of Co have created enormous interest in alternative cathodes. In this regard, spinel LiMn₂O₄ has been investigated widely as Mn is inexpensive and environmentally benign. However, LiMn₂O₄ exhibits severe capacity fade on cycling, particularly at elevated temperatures. With an aim to overcome the capacity fading problems, several cationic substitutions to give LiMn[subscript 2-y]M[subscript y]O₄ (M = Cr, Fe, Co, Ni, and Cu) have been pursued in the literature. Among the cation-substituted systems, LiMn[subscript 1.5]Ni[subscript 0.5]O₄ has become attractive as it shows a high capacity of ~ 130 mAh/g (theoretical capacity: 147 mAh/g) at around 4.7 V. With an aim to improve the electrochemical performance of the 5 V LiMn[subscript 1.5]Ni[subscript 0.5]O₄ spinel oxide, various cation-substituted LiMn[subscript 1.5-y]Ni[subscript 0.5-z]M[subscript y+z]O₄ (M = Li, Mg, Fe, Co, and Zn) spinel oxides have been investigated by chemical lithium extraction. The cation-substituted LiMn[subscript 1.5-y]Ni[subscript 0.5-z]M[subscript y+z]O₄ spinel oxides exhibit better cyclability and rate capability in the 5 V region compared to the unsubstituted LiMn[subscript 1.5]Ni[subscript 0.5]O₄ cathodes although the degree of manganese dissolution does not vary significantly. The better electrochemical properties of LiMn[subscript 1.5-y]Ni]subscript 0.5-z]M[subscript y+z]O₄ are found to be due to a smaller lattice parameter difference among the three cubic phases formed during the chargedischarge process. In addition, while the spinel Li[subscript 1-x]Mn[subscript 1.58]Ni[subscript 0.42]O₄ was chemically stable, the spinel Li[subscript 1-x]Co₂O₄ was found to exhibit both proton insertion and oxygen loss at deep lithium extraction due to the chemical instability arising from a overlap of the Co[superscript 3+/4+]:3d band on the top of the O[superscript 2-]:2p band. The irreversible oxygen loss during the first charge and the consequent reversible capacities of the solid solutions between Li[Li[subscript 1/3]Mn[subscript 2/3]]O₂ and Li[Co[subscript 1-y]Ni[subscript y]]O₂ has been found to be determined by the amount of lithium in the transition metal layer of the O3 type layered structure. The lithium content in the transition metal layer is, however, sensitively influenced by the tendency of Ni[superscript 3+] to get reduced to Ni[superscript 2+] and the consequent volatilization of lithium during synthesis. Moreover, high Mn4+ content causes a decrease in oxygen mobility and loss. In addition, the chemically delithiated samples were found to adopt either the parent O3 type structure or the new P3 or O1 type structures depending upon the composition and synthesis temperature of the parent samples and the proton content inserted into the delithiated sample. In essence, the chemical and structural stabilities and the electrochemical performance factors of the layered (1-z) Li[Li[subscript 1/3]Mn[subscript 2/3]]O₂ · (z) Li[Co[subscript 1-y]Ni[subscript y]]O₂ solid solution cathodes are found to be maximized by optimizing the contents of the various ions.Item Crystal chemistry, chemical stability, and electrochemical properties of layered oxide cathodes of lithium ion batteries(2006) Choi, Jeh Won; Manthiram, ArumugamLithium ion batteries are now widely used as power sources in mobile electronics due to their high energy density. Layered LiCoO2 is currently employed as the cathode material in commercial lithium ion batteries, but its reversible capacity is limited to only 50 % of its theoretical capacity. Co is also relatively expensive and toxic. In this regard, layered LiNi1-y-zMnyCozO2 cathodes have become appealing recently as they offer higher capacity, lower cost, and enhanced safety compared to the LiCoO2 cathode. This dissertation explores the chemical and structural factors and instabilities that control and limit the electrochemical performance parameters such as the capacity, cyclability, and rate capability of various layered LiNi1-y-zMnyCozO2 cathodes. A quantitative determination of proton contents in various chemically delithiated oxide cathodes using Prompt Gamma Ray Activation Analysis (PGAA) indicates that while the delithiated layered Li1-xCoO2, Li1-xNi1/3Mn1/3Co1/3O2, and Li1- xNi1/2Mn1/2O2 have a significant amount of proton in the lattice at deep lithium extraction, orthorhombic Li1-xMnO2, spinel Li1-xMn2O4, and olivine Li1-xFePO4 do not encounter such proton insertion. The results are complemented by mass spectrometric and thermogravimetric analysis data. The differences are attributed to the differences in the chemical instability of the various cathodes. From a systematic investigation of three series of layered LiNi1-y-zMnyCozO2 compositions (LiNi0.5-yMn0.5-yCo2yO2, LiCo0.5-yMn0.5-yNi2yO2, LiNi0.5-yCo0.5-yMn2yO2), those around LiNi1/3Mn1/3Co1/3O2 are found to have optimized electrochemical performances with high reversible capacity, good cyclability, and good rate capability. The results are explained on the basis of chemical instability in the Co-rich compositions, lithium deficiency and concurrent cation disorder in the Ni-rich compositions, and existence of the impurity phase Li2MnO3 in the Mn-rich compositions. The electrochemical rate capability is found to bear a clear relationship to the chemical lithium extraction rate, which decreases with decreasing Co content due to an increasing cation disorder. Additionally, the lithium extraction rate is found to influence the structure of the chemically delithiated end members HxNi0.5-yMn0.5- yCo2yO2; the structure changes from P3 to O1 to O3 with decreasing Co content 2y. A comparison of the chemical stability of the Na0.75-xCoO2 system shows that it maintains the theoretical value of the oxidation state of cobalt during chemical sodium extraction to low sodium contents of (0.75-x) ≈ 0.3, while Li1-xCoO2 incorporates protons for (1-x) < 0.5. The differences between two systems are discussed based on the crystal structure and the position of Co3+/4+:3d band relative to the top of the O2-:2p band.Item Development of alternative cathodes for intermediate temperature solid oxide fuel cells(2009-08) Kim, Junghyun; Manthiram, ArumugamItem Development of perovskite and intergrowth oxide cathodes for intermediate temperature solid oxide fuel cells(2006-05) Lee, Ki-tae, 1971-; Manthiram, ArumugamSolid oxide fuel cells (SOFC) offer the advantage of using less expensive oxide catalysts and hydrocarbon fuels directly, but chemical reactivity and thermal expansion mismatch at the conventional operating temperature of ~ 1000 o C pose serious problems. These difficulties have generated considerable interest in intermediate temperature (500-800 o C) SOFC, but the lower temperature leads to poor oxygen reduction reaction kinetics with the conventional cathode material, La1- xSrxMnO3. To address this issue, this dissertation focuses on the synthesis and characterization of alternative cathode materials based on Ln1-xSrxCoO3-δ perovskites and La3-xSrxFe2-yCoyO7-δ and LaSr3Fe3-yCoyO10-δ intergrowth oxides. Both the electrical conductivity and the oxide ion vacancy concentration decrease from Ln = La to Gd in Ln1-xSrxCoO3-δ, which leads to a decrease in the electrocatalytic activity for the oxygen reduction reaction. However, the thermal expansion coefficient (TEC) decreases from Ln = La to Gd due to a decreasing ionicity of the Ln-O bond and a suppression of the tendency to lose oxygen from the lattice. Therefore, Nd1-xSrxCoO3-δ with an intermediate size lanthanide ion offers a tradeoff between electrocatalytic activity and TEC, with the x = 0.4 sample exhibiting the highest catalytic activity without any interfacial reaction. The substitution of Fe or Mn for Co in Nd0.6Sr0.4CoO3-δ leads to a decrease in the oxygen non-stoichiometry, TEC, electrical conductivity, and electrocatalytic activity, but the decrease in catalytic activity is rapid with the Mn-doped system due to a faster decrease in the oxide ion and electronic conductivities. Interestingly, the incorporation of metallic Ag into porous Nd0.6Sr0.4Co0.5Fe0.5O3-δ improves the electrochemical performance due to an increased electronic conductivity and enhanced electrocatalytic activity. The electrical conductivity, oxygen vacancy concentration, TEC, and electrocatalytic activity increase with increasing Co content in the perovskite-related intergrowth oxide systems, LaSr3Fe3-yCoyO10-δ and Sr3-xLaxFe2-yCoyO7-δ. The increase in catalytic activity is due to an increase in the electronic and oxide ion conductivities. The intergrowth LaSr3Fe3-yCoyO10-δ cathodes offer electrochemical performances comparable to that of the well-known La0.6Sr0.4CoO3-δ cathode, but with an important advantage of significantly lower TEC.Item Hydrogen determination in chemically delithiated lithium ion battery cathodes by prompt gamma activation analysis(2007-08) Alvarez, Emilio, 1981-; Manthiram, Arumugam; Landsberger, SheldonLithium ion batteries, due to their relatively high energy density, are now widely used as the power source for portable electronics. Commercial lithium ion cells currently employ layered LiCoO₂ as a cathode but only 50% of its theoretical capacity can be utilized. The factors that cause the limitation are not fully established in the literature. With this perspective, prompt gamma-ray activation analysis (PGAA) has been employed to determine the hydrogen content in various oxide cathodes that have undergone chemical extraction of lithium (delithiation). The PGAA data is complemented by data obtained from atomic absorption spectroscopy (AAS), redox titration, thermogravimetric analysis (TGA), and mass spectroscopy to better understand the capacity limitations and failure mechanisms of lithium ion battery cathodes. As part of this work, the PGAA facility has been redesigned and reconstructed. The neutron and gamma-ray backgrounds have been reduced by more than an order of magnitude. Detection limits for elements have also been improved. Special attention was given to the experimental setup including potential sources of error and system calibration for the detection of hydrogen. Spectral interference with hydrogen arising from cobalt was identified and corrected for. Limits of detection as a function of cobalt mass present in a given sample are also discussed. The data indicates that while delithiated layered Li[subscript 1-x]CoO₂, Li[subscript 1-x]Ni[subscript 1/3]Mn[subscript 1/3]Co[subscript 1/3]O₂, and Li[subscript 1-x]Ni[subscript 0.5]Mn[subscript 0.5]O₂ take significant amounts of hydrogen into the lattice during deep extraction, orthorhombic Li[subscript 1-x]MnO₂, spinel Li[subscript 1-x]Mn₂O₄, and olivine Li[subscript 1-x]FePO₄ do not. Layered LiCoO₂, LiNi[subscript 0.5]Mn[subscript 0.5]O₂, and LiNi[subscript 1/3]Mn[subscript 1/3]Co[subscript 1/3]O₂ have been further analyzed to assess their relative chemical instabilities while undergoing stepped chemical delithiation. Each system takes increasing amounts of protons at lower lithium contents. The differences are attributed to the relative chemical instabilities of the various cathodes that could be related to the position of the transition metal band and the top of the O²-:2p band. Chemically delithiated layered Li[Li[subscript 0.17]Mn[subscript 0.33]Co[subscript0.5-y]Ni[subscript y]]O₂ cathodes have also been characterized. The first charge and discharge capacities decrease with increasing nickel content. The decrease in the capacity with increasing nickel content is due to a decrease in the lithium content present in the transition metal layer and a consequent decrease in the amount of oxygen irreversibly lost during the first charge.Item Lifetime performance parameter measurement of a low power closed drift thruster(Texas Tech University, 2004-08) Foster, Gregory WNot availableItem Low thermal expansion transition metal oxides for reduced temperature solid oxide fuel cell cathodes(2014-12) West, Matthew David; Manthiram, ArumugamSolid oxide fuel cells (SOFCs) are power generation devices that offer many great advantages compared to lower temperature fuel cells; for example, they are able to operate at high efficiencies without the use of expensive precious metal catalysts, and are also able to directly utilize hydrocarbon fuels without the need of an external reformer. Unfortunately, the conventional high operating temperature of these devices (T ≈ 1000 °C) requires the use of expensive, specialized materials that can withstand these high temperatures. This issue has generated considerable interest in reducing the operating temperature of these devices to the intermediate-temperature (600 – 800 °C) to allow for the use of less-expensive materials, such as stainless steel. However, the conventionally utilized SOFC cathode materials exhibit poor electrochemical performance at these reduced temperatures. Currently considered alternative intermediate temperature cathodes, such as Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ (BSCF), offer improved performance, but have a large thermal expansion coefficient (TEC), leading to cell failure. In light of these issues, this dissertation focuses on the development of low TEC cathodes for intermediate temperature SOFCS (IT-SOFCs). The primary focus of this dissertation is on the swedenborgite-type RBaCo₃MO₇₊δ (R = Y, In, and Ca; M = Zn and Fe) series of cathodes. Due to their tetrahedrally-coordinated M site, the cobalt ions in these materials do not undergo a spin-state transition, and have TECs similar to conventional SOFC electrolyte materials. The long-term phase stability of these materials was addressed, and it was discovered that a slight In substitution significantly promoted phase stability. In the Y₁₋[subscript x] In [subscript x] BaCo₃ZnO₇₊δ series, it was observed that x = 0.1 successfully stabilized the phase without observable degradation of performance. Similarly, a high-Ca content material (Y₀.₅In₀.₁Ca₀.₄BaCo₃ZnO₇₊δ) was successfully stabilized, though Ca is known to destabilize the phase; furthermore, this compound showed improved performance compared to YBaCo₃ZnO₇₊δ. Lastly, the replacement of the performance-inhibiting Zn with Fe was investigated, and the Y₀.₉In₀.₁BaCo₃Zn₀.₆Fe₀.₄O₇₊δ sample showed low temperature performance rivaling BSCF. Other work in this dissertation focuses on the application of functional silver materials for use in SOFCs, with good performance; these materials were easily manufactured, and they showed performance drastically greater than the conventionally utilized platinum.Item Manganese oxide cathodes for rechargeable batteries(2002) Im, Dongmin; Manthiram, ArumugamManganese oxides are considered as promising cathodes for rechargeable batteries due to their low cost and low toxicity as well as the abundant natural resources. In this dissertation, manganese oxides have been investigated as cathodes for both rechargeable lithium and alkaline batteries. Nanostructured lithium manganese oxides designed for rechargeable lithium cells have been synthesized by reducing lithium permanganate with methanol or hydrogen in various solvents followed by firing at moderate temperatures. The samples have been characterized by wet-chemical analyses, thermal methods, spectroscopic methods, and electron microscopy. It has been found that chemical residues in the oxides such as carboxylates and hydroxyl groups, which could be controlled by varying the reaction medium, reducing agents, and additives, make a significant influence on the electrochemical properties. The Li/Mn ratio in the material has also been found to be a critical factor in determining the rechargeability of the cathodes. The optimized samples exhibit a high capacity of close to 300 mAh/g with good cyclability and charge efficiency. The high capacity with a lower discharge voltage may make these nanostructured oxides particularly attractive for lithium polymer batteries. The research on the manganese oxide cathodes for alkaline batteries is focused on an analysis of the reaction products generated during the charge/discharge processes or by some designed chemical reactions mimicking the electrochemical processes. The factors influencing the formation of Mn3O4 in the two-electron redox process of d-MnO2 have been studied with linear sweep voltammetry combined with X-ray diffraction. The presence of bismuth, the discharge rate, and the microstructure of the electrodes are found to affect the formation of Mn3O4, which is known to be electrochemically inactive. A faster voltage sweep and a more intimate mixing of the manganese oxide and carbon in the cathode are found to suppress the formation of Mn3O4. Bismuth has also been found to be beneficial in the one-electron process of gMnO2 when incorporated into the cathode. The results of a series of chemical reactions reveal that bismuth is blocking some reaction paths leading to the unwanted birnessite or Mn3O4. Barium is also found to play a similar role, but it is less effective than bismuth for the same amount of additive. Optimization of the additives has the potential to make the rechargeable alkaline cells based on manganese oxides to successfully compete with other rechargeable systems due to their low cost, environmental friendliness, and excellent safety features.Item Manufacturing of intermediate-temperature solid oxide fuel cells using novel cathode compositions(2007-05) Torres Garibay, Claudia Isela, 1972-; Kovar, DesiderioItem Manufacturing of intermediate-temperature solid oxide fuel cells using novel cathode compositions(2007) Torres Garibay, Claudia Isela; Kovar, DesiderioThe development of intermediate temperatures solid oxide fuel cells (IT-SOFC) with YSZ electrolytes imposes a double requirement in their manufacturing. First, the electrolyte has to be kept as thin as possible to minimize ohmic polarization losses. Second, the cathode compositions used must exhibit an adequate catalytic activity at the operating temperature (600 – 800 ºC). Current methods to manufacture thin YSZ electrolytes require complex processes, and sometimes costly equipment. Cathode compositions traditionally used for high temperature solid oxide fuel cells, such as (La,Sr)MnO3 do not exhibit good catalytic properties at intermediate temperatures. These challenges present areas of opportunity in the development of original manufacturing techniques and new cathode compositions. This study presents a low-cost fabrication procedure for IT-SOFC using tape casting, co-firing and screen printing. The electrochemical performance of the cells is evaluated using a known cathode composition for IT-SOFC, such as La0.6Sr0.4CoO3-δ (LSC), novel perovskite oxides, such as Nd0.6Sr0.4CoO3-δ (NSC), and perovskite-related intergrowth oxides compositions, like Sr0.7La0.3Fe1.4Co0.6O7-δ (SLFCO7) and LaSr3Fe1.5Co1.5O10-δ (LSFCO10). The impact of conductivity is studied by substituting Fe for Co in the case of the perovskite oxides, with compositions such as La0.6Sr0.4Co0.5Fe0.5O3-δ (LSCF), and Nd0.6Sr0.4Co0.5Fe0.5O3-δ (NSCF) and by infiltration of NSCF with silver. The effect of the cathode sintering temperature is studied using LSC and LSCF cathodes. It is found that there is generally a correlation between cell performance and conductivity. However, the microstructure of the cathode is also important in determining cell performance by tailoring the cathode sintering temperature. IT-SOFC with SLFCO7 cathodes show a performance comparable to cells with LSFC cathode. In the case of LSFCO10, the performance loss associated with its lower conductivity compared to LSC can be more than offset by tailoring the microstructure.Item Optimization of dispenser cathodes for operation in hydrogen(Texas Tech University, 1990-05) Kennedy, Murray JamesNot availableItem Perovskite-related and trigonal RBaCo₄O₇-based oxide cathodes for intermediate temperature solid oxide fuel cells(2011-12) Kim, Young Nam, 1974-; Manthiram, Arumugam; Kovar, Desiderio; Wheat, Harovel G.; Ferreira, Paulo J.; Mullins, Charles B.Solid oxide fuel cells (SOFCs) offer the advantages of (i) employing less expensive catalysts compared to the expensive Pt catalyst used in proton exchange membrane fuel cells and (ii) directly using hydrocarbon fuels without requiring external fuel reforming due to the high operating temperature. However, the conventional high operating temperatures of 800 - 1000 °C lead to interfacial reactions and thermal expansion mismatch among the components and limitations in the choice of electrode and interconnect materials. These problems have prompted a lowering of the operating temperature to an intermediate range of 500 - 800 °C, but the poor oxygen reduction reaction kinetics of the conventional La[subscript 1-x]Sr[subscript x]MnO₃ perovskite cathode remains a major obstacle for the intermediate temperature SOFC. In this regard, cobalt-containing oxides with perovskite or perovskite-related structures have been widely investigated, but they suffer from large thermal expansion coefficient (TEC) mismatch with the electrolytes. With an aim to lower the TEC and maximize the electrochemical performance, this dissertation focuses on perovskite-related and trigonal RBaCo₄O₇-based oxide cathode materials. First, the effect of M = Fe and Cu in the perovskite-related layered LnBaCo₂₋xMxO₊[delta] (Ln = Nd and Gd) oxides has been investigated. The Fe and Cu substitutions lower the polarization resistance and offer fuel cell performance comparable to that of La[subscript 1-x]Sr[subscript x]CoO₃₋[delta] perovskite due to improved chemical stability with the electrolyte and a better matching of the TEC with those of standard electrolytes. Second, the perovskite-related intergrowth oxides Ln(Sr,Ca)₃Fe₁.₅Co₁.₅O₀ and La₁.₈₅Sr₁.₁₅Cu[subscript 2-x]Co[subscript x]O[subscript 6 +delta] and their composites with gadolinia-doped ceria (GDC) have been investigated. The electrical conductivity, TEC, and catalytic activity increase with increasing Co content. The composite cathodes exhibit enhanced electrochemical performance due to lower TEC and increased triple-phase boundary. Third, RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) oxides with a trigonal structure and tetrahedral-site Con+ ions have been investigated. The chemical instability normally encountered with this class of oxides has been overcome by appropriate cationic substitutions as in (Y₀.₅Ca₀.₅)Ba(Co₂.₅Zn₁.₅)O₇ and (Y₀.₅In₀.₅)BaCo₃ZnO₇. With an ideal matching of TEC with those of standard electrolytes, the RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) + GDC composite cathodes exhibit low polarization resistance and electrochemical performance comparable to that of perovskite oxides.Item Soft chemistry synthesis and structure-property relationships of lithium-ion battery cathodes(2001-08) Choi, Seungdon; Manthiram, ArumugamLithium-ion batteries have become attractive for portable electronic devices due to their higher energy density. While the commercial lithium-ion cells presently use the layered LiCoO2 as the cathode, there is enormous interest to develop alternative inexpensive and environmentally benign cathodes for next generation cells. In this regard, design of novel synthesis procedures to obtain metastable phases that are otherwise inaccessible by conventional methods and a fundamental understanding of the factors that control the electrochemical properties – cell voltage, capacity, and cyclability – play a key role. This dissertation explores the use of soft chemistry procedures to obtain new electrode materials and investigates the structureproperty relationship of some lithium-ion battery cathodes. Oxidation reactions of transition metal ions in solutions are used to synthesize oxide cathodes based on Mn, Fe, Co, Ni, and Cu. For example, the metastable spinel Li2Mn4O9-d and the layered LiNi1-xCoxO2 synthesized by such an approach show capacities of, respectively, 130 and 165 mAh/g with good cyclability. On the other hand, nanocrystalline LixCu1-yFeyOz synthesized, for the first time, shows a high initial capacity of 340 mAh/g, but declining to 220 mAh/g after 40 cycles. This system is attractive as both Fe and Cu are inexpensive and environmentally benign. Nanocrystalline LixCu1-yFeyOz as well as some amorphous manganese oxides having high capacities are also investigated for use in polymer electrolyte cells. An investigation of the influence of synthesis conditions on the phase relationships of the system LixMn3-xO4+d indicates that the lithium-rich spinel phases with x > 1 are more stable at intermediate firing temperatures T » 600 oC compared to LiMn2O4. A systematic investigation of the layered to spinellike phase transition in chemically synthesized Li0.5MO2 (M = Mn, Co and Ni) reveals that the ease of transformation decreases in the order Mn > Ni > Co. Presence of mixed cations in the transition metal ion plane is found to be effective to suppress such a transition and impart better structural stability. A closer look at the origin of the high voltage (> 4.5 V) capacity in some of the spinel series of materials suggests that the high voltage capacity is due to the oxidation of primarily the oxide ions.Item Structural and chemical characterizations of delithiated layered oxide cathodes of lithium-ion cells(2004) Sivaramakrishnan, Venkatraman; Manthiram, ArumugamItem Structural and electrochemical characterization and surface modification of layered solid solution oxide cathodes of lithium ion batteries(2008-05) Wu, Yan, 1977-; Manthiram, ArumugamLithium ion batteries are widely used to power portable electronic devices such as cell phones and laptop computers due to their high energy density. However, the currently used layered LiCoO2 cathode could deliver only 50 % of its theoretical capacity in practical lithium ion cells (140 mAh/g) due to the chemical and structural instabilities at deep charge with (1-x) < 0.5 in Li1-xCoO2. Also, cobalt is relatively expensive and toxic. These difficulties have generated enormous interest in alternative cathode hosts. In this regard, solid solutions between layered Li[Li1/3Mn2/3]O2 (commonly designated as Li2MnO3) and LiMO2 (M = Mn, Ni, Co)) have become appealing as some of them exhibit much higher capacity (~ 250 mAh/g on charging to 4.8 V) with lower cost and better safety compared to LiCoO2. This dissertation investigates the (1-z) Li[Li1/3Mn2/3]O2 - (z) Li[Mn0.5-yNi0.5-yCo2y]O2 (y = 1/12, 1/6 and 1/3 and 0.25 ≤ z ≤ 0.75) layered oxide cathodes, which belong to a solid solution series between layered Li[Li1/3Mn2/3]O2 and Li[Mn0.5-yNi0.5-yCo2y]O2, with an aim to develop a better understanding of the chargedischarge mechanisms and optimize the electrochemical performance of these materials. To accomplish this, the structural and electrochemical characterization of the (1- z) Li[Li1/3Mn2/3]O2 - (z) Li[Mn0.5-yNi0.5-yCo2y]O2 cathodes is carried out. It is found that the amount of oxygen loss is related to the lithium content in the transition metal layer, and the Co and Mn4+ contents play a role in influencing the electrochemical behavior. In addition, the chemically delithiated samples are found to transform to O1 or P3 structure with a vanishing of the superlattice reflections arising from cationic ordering in the transition metal layer due to the incorporation of protons from the chemical delithiation medium, while the electrochemically charged samples retain the initial O3 structure. These layered solid solution oxides exhibit high irreversible capacity (IRC) loss (difference between first charge and discharge capacity) values (up to 100 mAh/g), which have been reduced significantly by modifying the cathode surface with other materials like Al2O3, AlPO4, and F- . For example, compared to an IRC of 75 mAh/g and a first discharge capacity of 253 mAh/g for the pristine Li[Li0.2Mn0.54Ni0.13Co0.13]O2 (y = 1/6 and z = 0.4), the 3 wt. % Al2O3 modified sample exhibits a lower IRC of 41 mAh/g and a higher first discharge capacity of 285 mAh/g, which is two times higher than that achieved with the LiCoO2 cathode. A careful and systematic analysis of the experimentally observed capacity and IRC values suggest that part of the oxide ion vacancies created during first charge is retained in the layered lattice in contrast to the idealized model (elimination of all oxide ion vacancies) proposed in the literature. The surface modification helps to retain even more number of oxide ion vacancies in the lattice, which leads to a lower IRC and higher discharge capacity values. Additionally, bulk cationic and anionic substitutions of Al3+ and F- in Li[Li0.17Mn0.58Ni0.25]O2 (y = 0 and z = 0.5) are found to sensitively decrease the amount of oxygen loss from the lattice.Item Understanding the capacity fade mechanisms of spinel manganese oxide cathodes and improving their performance in lithium ion batteries(2007) Choi, Won Chang, 1975-; Manthiram, ArumugamLithium ion batteries have been successful in portable electronics market due to their high energy density, adopting the layered LiCoO₂ as the cathode material in commercial lithium ion cells. However, increasing interest in lithium ion batteries for electric vehicle and hybrid electric vehicle applications requires alternative cathode materials due to the high cost, toxicity, and limited power capability of the layered LiCoO₂ cathode. In this regard, spinel LiMn₂O₄ has become appealing as manganese is inexpensive and environmentally benign, but LiMn₂O₄ is plagued by severe capacity fade at elevated temperatures. This dissertation explores the factors that control and limit the electrochemical performance of spinel LiMn₂O₄ cathodes and focuses on improving the performance parameters such as the capacity, cyclability, and rate capability of various spinel cathodes derived from LiMn₂O₄. From a systematic investigation of a number of cationic and anionic (fluorine) substituted spinel oxide compositions, the improvements in electrochemical properties and performances are found to be due to the reduced manganese dissolution and suppressed lattice parameter difference between the two cubic phases formed during the charge-discharge process. Investigations focused on fluorine substitution reveal that spinel LiMn[subscript 2-yz]LiyZnzO[subscript 4-eta]F[subscript eta] oxyfluoride cathodes synthesized by solid-state reactions at 800 °C employing ZnF₂ as a raw material and spinel LiMn[subscript 2-y-z]Li[subscript y]Ni[subscript z]O[subscript 4-eta]F[subscript eta] oxyfluoride cathodes synthesized by firing the cation-substituted LiMn[subscript 2-y-z]LiyNi[subscript z]O₄ oxides with NH₄HF₂ at a moderate temperature of 450 °C show superior cyclability, increased capacity, reduced Mn dissolution, and excellent storage performance compared to the corresponding oxide analogs and the conventional LiMn₂O₄. Spinel-layered composite cathodes are found to exhibit better electrochemical performance with graphite anode when charged to 4.7 V in the first cycle followed by cycling at 4.3-3.5 V compared to the normal cycling at 4.3 - 3.5 V. The improved performance is explained to be due to the trapping of trace amounts of protons that may be present in the electrolyte within the layered oxide lattice during the first charge to 4.7 V and the consequent reduction in Mn dissolution. Electrochemical performances of 3 V spinel Li₄Mn₅O₁₂ cathodes are also improved by fluorine substitution due to the suppression of the disproportionation of Li4Mn5O12 during synthesis and the formation of the Li₂MnO₃ phase.Item Understanding the electrochemical properties and safety characteristics of spinel cathodes for lithium-ion batteries(2013-05) Chemelewski, Katharine Rose; Manthiram, ArumugamManganese spinel cathodes LiMn₂O₄ offer the advantage of a strong, edge-shared octahedral framework with fast, 3-dimensional Li⁺-ion conduction. To better understand the safety of these materials, the thermal stability characteristics of spinel oxide and oxyfluoride cathodes Li[subscript 1.1]Mn[subscript 1.9-y]M[subscript y]O₄[subscript-z]F[subscript z] (M = Ni and Al, 0 ≤ y ≤ 0.3, and 0 ≤ z ≤ 0.2) have been investigated systematically. The thermal characteristics are assessed in terms of the onset temperature and reaction enthalpy for the exothermic reaction. The thermal stability increases with decreasing lithium content in the cathode in the charged state. High-voltage spinel cathodes LiMn[subscript 1.5]Ni[subscript 0.5]O₄ are promising candidates for electric vehicles and stationary storage of electricity produced by renewable energies due to their high power capability. However, widespread adoption of this high-voltage spinel cathode is hampered by severe capacity fade resulting from aggressive reaction with the electrolyte to form a thick solid-electrolyte interphase (SEI) layer. The synthesis conditions of the co-precipitation method are found to influence the microstructure and morphology through nucleation and growth of crystals in solution. Two samples prepared by similar wet-chemical routes have been characterized by microscopy and electrochemical methods to determine the role of microstructure and morphology on the electrochemical performance. It is found that the surface crystal planes play a key role in the capacity retention and rate performance. In order to achieve consistent electrochemical properties essential for the commercialization of the high-voltage spinel cathode LiMn[subscript1.5]Ni[subscript 0.5]O₄, the relationship between cation ordering, presence of impurity phase, and particle morphology must be elucidated. Accordingly, comparison of the stoichiometric LiMn[subscript1.5]Ni[subscript 0.5]O₄ cathodes with a Mn/Ni ratio of 3.0 prepared by different methods having varying morphologies and degrees of cation ordering is presented. It is found that although an increase in the degree of cation ordering decreases the rate capability, the crystallographic planes in contact with the electrolyte have a dominant effect on the electrochemical properties. To examine the effect of cation substitution on morphology, an investigation of the nucleation and growth of doped co-precipitated mixed-metal hydroxide precursor particles and the resulting stabilization of preferred crystallographic surface planes in the final spinel samples are presented. It is found that doping with certain cations stabilizes the growth of low-energy (111) surface planes, facilitating a long cycle life and fast high-rate performance. With an aim to develop a better understanding of the factors influencing the electrochemical properties, a systematic investigation of LiMn[subscript 1.5]Ni[subscript0.5-x]M[subscript x]O₄ (M = Cu and Zn and x = 0.08 and 0.16), in which Ni²⁺ ions are substituted by divalent Cu2+ and Zn2+ ions, is presented. It is found that although both Zn and Cu are divalent with ionic radii similar to that of Ni2+, they behave quite differently with respect to cation ordering and site occupancy, and higher levels of doping leads to distinct differences in cycling and rate performances.