There is considerable interest in ESs as they have huge potential in energy storage devices, play a key role in advanced power systems, and have the potential to revolutionize hybrid vehicles and electronics. SCs are known for their hybrid power and energy density, fast charge and discharge rates, and long-term cycling stability. The performance of SCs depend largely on the specific capacitance of their electrodes. Among various cathode materials, unitary transition metal oxides (TMOs), especially manganese oxide, are favored due to their multiple oxidation states, excellent redox properties, abundant availability, simple synthesis, and cost-effectiveness. The low intrinsic conductivity of manganese oxide can be significantly enhanced by adding conductive additives such as multi-walled carbon nanotubes (CNTs). We are developing a novel colloid processing technique to synthesize MnOx-CNT nanocomposites with enhanced electronic conductivity. Our research involves the use of advanced capping agents and co-dispersants to fabricate MnOx-CNTs nanocomposite electrodes that exhibit superior performance and bypass the lengthy activation process commonly cited in our previous results. Testing results indicate that functional catechol-based molecules, including quercetin (QC), rhamnolipid (RL), tetrahydroxy-1,4-quinone (TQ), catechin (CT) and gallocyanine (GA), have excellent dispersion properties for MnOx and CNTs. These compounds form uniform and stable suspensions that improve the nanostructure and electrochemical performance of the electrodes. They also serve as capping agents for Mn3O4 synthesis, reducing agglomeration and improving morphology. Additionally, murexide was tested as a co-dispersant and capping agent due to its chelating properties, forming a tridentate bond with Mn atoms and adsorbing onto the carbon rings of CNTs. As a capping agent, murexide can promote electrostatic dispersion by forming strong tridentate bonds with Mn3O4 particle surfaces, thereby reducing agglomeration and improving composite morphology. In addition, binary (MnFe2O4) or ternary (La0.65Sr0.35MnO3(LSM)) metal oxides can overcome the limitations of single metal oxides through the synergistic effect between metal ions, improve capacitive performance and expand the potential window. These compounds are promising candidates as ES electrode materials. High-energy ball milling (HEBM) helps reduce particle size, enhance electrolyte contact with active material surfaces, achieve high capacitance at high active mass loading, and produce high-performance supercapacitors (SCs). / Thesis / Candidate in Philosophy / There is considerable interest in ESs as they have huge potential in energy storage devices, play a key role in advanced power systems, and have the potential to revolutionize hybrid vehicles and electronics. SCs are known for their hybrid power and energy density, fast charge and discharge rates, and long-term cycling stability. The performance of SCs depend largely on the specific capacitance of their electrodes. Among various cathode materials, unitary transition metal oxides (TMOs), especially manganese oxide, are favored due to their multiple oxidation states, excellent redox properties, abundant availability, simple synthesis, and cost-effectiveness. The low intrinsic conductivity of manganese oxide can be significantly enhanced by adding conductive additives such as multi-walled carbon nanotubes (CNTs). We are developing a novel colloid processing technique to synthesize MnOx-CNT nanocomposites with enhanced electronic conductivity. Our research involves the use of advanced capping agents and co-dispersants to fabricate MnOx-CNTs nanocomposite electrodes that exhibit superior performance and bypass the lengthy activation process commonly cited in our previous results. Testing results indicate that functional catechol-based molecules, including quercetin (QC), rhamnolipid (RL), tetrahydroxy-1,4-quinone (TQ), catechin (CT) and gallocyanine (GA), have excellent dispersion properties for MnOx and CNTs. These compounds form uniform and stable suspensions that improve the nanostructure and electrochemical performance of the electrodes. They also serve as capping agents for Mn3O4 synthesis, reducing agglomeration and improving morphology. Additionally, murexide was tested as a co-dispersant and capping agent due to its chelating properties, forming a tridentate bond with Mn atoms and adsorbing onto the carbon rings of CNTs. As a capping agent, murexide can promote electrostatic dispersion by forming strong tridentate bonds with Mn3O4 particle surfaces, thereby reducing agglomeration and improving composite morphology. In addition, binary (MnFe2O4) or ternary (La0.65Sr0.35MnO3(LSM)) metal oxides can overcome the limitations of single metal oxides through the synergistic effect between metal ions, improve capacitive performance and expand the potential window. These compounds are promising candidates as ES electrode materials. High-energy ball milling (HEBM) helps reduce particle size, enhance electrolyte contact with active material surfaces, achieve high capacitance at high active mass loading, and produce high-performance supercapacitors (SCs).

This work presents the preparation and physical properties of spinel nanoparticles and nanocomposites. All nanocomposites in diamagnetic matrix like chromites CoCr2O4, CuCr2O4, NiCr2O4, ZnCr2O4 and ferrite MgFe2O4 were prepared using sol-gel method. On the other hand, isolated nanoparticles such as MgCr2O4, MnCr2O4, CuCr2O4, NiCr2O4, and FeCr2O4, were prepared using autocombustion a co-precipitation methods. CoFe2O4 and MgFe2O4 were prepared by microemulsion alkoxide method. This microemulsion method was used for the spinel nanoparticles preparation for the first time. This work describes the influence of heat treatment temperature on the final particle size and influence of particle size on physical properties of material. The study of the influence of twovalent cationt in the spinel structure on the magnetic properties of chromites was also carried out. The final samples were characterized by XRD powder diffraction, Mössbauer spectroscopy, infrared and Raman spectroscopy, and HRTEM. The dependence of magnetization on applied magnetic field at constant temperature and ZFC (zero-field cooling) - FC (field cooling) measurement was carried out on the prepared sample.

No description available.

none

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Physics and Astronomy." Includes bibliographical references.

Thesis (Ph. D.)--Miami University, Dept. of Geology, 2001. / Title from title page of PDF document. Document formatted into pages; contains vii, 114 p. : ill. Includes bibliographical references.

Lithium 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. / text

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains vii, 42 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 40-42).

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

No description available.