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The Origins of the Rate Enhancement in LiNi0.4Co0.2-yAlyMn0.4O2 (0<y<_0.2) Cathode Materials

Description: Recently, much research has been directed towards finding a replacement cathode material for LiCoO{sub 2} combining high performance with lower cost and toxicity. One promising candidate material is the mixed transition metal oxide LiNi{sub 0.4}Co{sub 0.2}Mn{sub 0.4}O{sub 2}, which delivers 180 mAh/g below 4.4 V versus Li/Li{sup +} (1, 2). However, in this material, there is 4% anti-site cation mixing, which hinders the mobility of lithium within the lattice, adversely affecting its rate performance in lithium batteries. Ongoing work in our lab has shown that partial or full substitution of cobalt with aluminum, LiNi{sub 0.4}Co{sub 0.2}Mn{sub 0.4}O{sub 2} (0 &lt; y {le} 0.2), can lead to significant improvements in rate performance (3). In particular, LiNi{sub 0.4}Co{sub 0.2}Mn{sub 0.4}O{sub 2} shows greatly improved rate capability with almost no sacrifice in the overall capacity delivered at low rates between 2.0 and 4.3V (Figure 1). The smaller ionic radius of Al{sup 3+} in octahedral coordination (0.535 {angstrom}) compared to Li{sup +} (0.76 {angstrom}) creates a strong driving force for the formation of a more lamellar structure in the aluminum containing materials (4, 5). XRD experiments and subsequent Rietveld refinement (Figure 2) reveal a significant decrease in anti-site defect concentration upon aluminum substitution, dropping from {approx}4% at y=0 to {approx}2.5% at y=0.2. Concurrently, there is an increase in the lithium slab dimension from 2.6 {angstrom} to 2.63 {angstrom}. This expansion allows for a reduced activation energy and improved lithium diffusivity through the crystal lattice (6). Interestingly, the pressed pellet conductivities of Al-substituted compounds are lower than that of the parent as determined by AC impedance measurements. This lends further credence to the hypothesis that structural effects resulting in improved lithium diffusivity are responsible for the rate enhancement, rather than changes in the electronic structure. Further experiments to understand the effect of structural changes induced ...
Date: May 29, 2008
Creator: Doeff, Marca M; Wilcox, James & Doeff, Marca M.
Partner: UNT Libraries Government Documents Department

Co-synthesis of LiFePO4 and Carbon Nanotubes

Description: The rate capabilities of LiFePO{sub 4} composites are dependent on the structure of the carbon that coats the powders, formed during co-calcination with carbon containing precursors. The addition of readily decomposed pyromellitic acid and graphitization catalysts such as ferrocene during synthesis results in coatings with low D/G (disordered/graphene) ratios, while maintaining the carbon content of the powders below 2 wt. %. This is important to avoid adversely affecting the tap density. The good correlation between the pressed pellet conductivities of the LiFePO{sub 4}/C composites and their rate capability in lithium cells is further confirmation of the importance of the carbon structure, because graphitic carbons generally have higher conductivities than disordered ones.
Date: May 26, 2006
Creator: Wilcox, James & Doeff, Marca M.
Partner: UNT Libraries Government Documents Department

Batteries: Overview of Battery Cathodes

Description: The very high theoretical capacity of lithium (3829 mAh/g) provided a compelling rationale from the 1970's onward for development of rechargeable batteries employing the elemental metal as an anode. The realization that some transition metal compounds undergo reductive lithium intercalation reactions reversibly allowed use of these materials as cathodes in these devices, most notably, TiS{sub 2}. Another intercalation compound, LiCoO{sub 2}, was described shortly thereafter but, because it was produced in the discharged state, was not considered to be of interest by battery companies at the time. Due to difficulties with the rechargeability of lithium and related safety concerns, however, alternative anodes were sought. The graphite intercalation compound (GIC) LiC{sub 6} was considered an attractive candidate but the high reactivity with commonly used electrolytic solutions containing organic solvents was recognized as a significant impediment to its use. The development of electrolytes that allowed the formation of a solid electrolyte interface (SEI) on surfaces of the carbon particles was a breakthrough that enabled commercialization of Li-ion batteries. In 1990, Sony announced the first commercial batteries based on a dual Li ion intercalation system. These devices are assembled in the discharged state, so that it is convenient to employ a prelithiated cathode such as LiCoO{sub 2} with the commonly used graphite anode. After charging, the batteries are ready to power devices. The practical realization of high energy density Li-ion batteries revolutionized the portable electronics industry, as evidenced by the widespread market penetration of mobile phones, laptop computers, digital music players, and other lightweight devices since the early 1990s. In 2009, worldwide sales of Li-ion batteries for these applications alone were US$ 7 billion. Furthermore, their performance characteristics (Figure 1) make them attractive for traction applications such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (EVs); a market ...
Date: July 12, 2010
Creator: Doeff, Marca M
Partner: UNT Libraries Government Documents Department

Electrode Materials with the Na0.44MnO2 Structure: Effect ofTitanium Substitution on Physical and Electrochemical Properties

Description: The physical and electrochemical properties of LixMnO2 and LixTi0.11Mn0.89O2 synthesized from precursors made by glycine-nitrate combustion (GNC) and solid-state synthesis methods (SS) are examined in this paper. The highest specific capacities in lithium cells are obtained for SS-LixMnO2 electrodes at low current densities, but GNC-LixTi0.11Mn0.89O2 electrodes show the best high rate performance. These results can be explained by changes in the voltage characteristics and differences in the particle morphologies induced by the Ti-substitution and synthesis method. Ti-substitution also results in a decrease in the electronic conductivity, but greatly improves the thermal properties and imparts dissolution resistance to the electrode. For these reasons, it is preferable to use LixTi0.11MnO0.89O2 in lithium battery configurations rather than LixMnO2. Suggestions for improving the electrochemical performance of the Ti-substituted variant are given based on the results described herein.
Date: March 10, 2008
Creator: Doeff, Marca M; Saint, Juliette A.; Doeff, Marca M & Wilcox, James D.
Partner: UNT Libraries Government Documents Department

Effect of Structure on the Storage Characteristics of ManganeseOxide Electrode Materials

Description: Eleven types of manganese-containing electrode materialswere subjected to long-term storage at 55oC in 1M LiPF6 ethylenecarbonate/dimethyl carbonate (EC/DMC) solutions. The amount of manganesedissolution observed depended upon the sample surface area, the averageMn oxidation state, the structure, and substitution levels of themanganese oxide. In some cases, structural changes such as solvateformation were exacerbated by the high temperature storage, andcontributed to capacity fading upon cycling even in the absence ofsignificant Mn dissolution. The most stable materials appear to beTi-substituted tunnel structures and mixed metal layered oxides with Mnin the +4 oxidation state.
Date: January 31, 2006
Creator: Park, Yong Joon & Doeff, Marca M.
Partner: UNT Libraries Government Documents Department

Factors Influencing the Quality of Carbon Coatings onLiFePO4

Description: Several LiFePO4/C composites were prepared and characterizedelectrochemically in lithium half-cells. Pressed pellet conductivitiescorrelated well with the electrochemical performance in lithiumhalf-cells. It was found that carbon structural factors such as sp2/sp3,D/G, and H/C ratios, as determined by Raman spectroscopy and elementalanalysis, influenced the conductivity and rate behavior strongly. Thestructure of the residual carbon could be manipulated through the use ofadditives during LiFePO4 synthesis. Increasing the pyromellitic acid (PA)content in the precursor mix prior to calcination resulted in asignificant lowering of the D/G ratio and a concomitant rise in thesp2/sp3 ratio of the carbon. Addition of both iron nitrate and PAresulted in higher sp2/sp3 ratios without further lowering the D/Gratios, or increasing carbon contents. The best electrochemical resultswere obtained for LiFePO4 processed with both ferrocene and PA. Theimprovement is attributed to better decomposition of the carbon sources,as evidenced by lower H/C ratios, a slight increase of the carbon content(still below 2 wt. percent), and more homogeneous coverage. A discussionof the influence of carbon content vs. structural factors on thecomposite conductivities and, by inference, the electrochemicalperformance, is included.
Date: October 11, 2006
Creator: Wilcox, James D.; Doeff, Marca M.; Marcinek, Marek & Kostecki,Robert
Partner: UNT Libraries Government Documents Department

Characterization and Electrochemical Performance of SubstitutedLiNi0.4Co0.2-yAlyMn0.4O2 (0&lt;_y&lt;_0.2) Cathode Materials

Description: A complete series of LiNi0.4Co0.2-yAlyMn0.4O2 (0&lt;_y&lt;_0.2) materials have been synthesized and investigated as cathode materials for lithium ion batteries. When cycled between 2.0 and 4.3 V vs. Li/Li+ at a current density of 0.1 mA/cm2, stable capacities of ~;;160 mAh/g for y=0 to ~;;110 mAh/g for y=0.2 are achieved. Upon increasing the current density, it is found that all materials containing aluminum show reduced polarization and improved rate performance. The optimal performance at all current densities was found for the compound with y=0.05. The effect of aluminumsubstitution on the crystal structure of the host is discussed.
Date: November 28, 2007
Creator: Wilcox, James D. & Doeff, Marca M.
Partner: UNT Libraries Government Documents Department

Comparison of LiMnPO4 made by Combustion and Hydrothermal Syntheses

Description: Among the olivine-structured metal phosphate family, LiMnPO{sub 4} exhibits a high discharge potential (4V), which is still compatible with common electrolytes, making it interesting for use in the next generation of Li ion batteries. The extremely low electronic conductivity of this material severely limits its electrochemical performance, however. One strategy to overcome this limitation is to make LiMnPO{sub 4} nanoparticulate to decrease the diffusion distance. Another is to add a carbon or other conductive coating in intimate contact with the nanoparticles of the main phase, as is commonly done with LiFePO{sub 4}. The electrochemical performance of LiFePO{sub 4} is highly dependent on the quality of the carbon coatings on the particles [1-2], among other variables. Combustion synthesis allows the co-synthesis of nanoparticles coated with carbon in one step. Hydrothermal synthesis is used industrially to make LiFePO{sub 4} cathode materials [3] and affords a good deal of control over purity, crystallinity, and particle size. A wide range of olivine-structured materials has been successfully prepared by this technique [4], including LiMnPO{sub 4} in this study. In this paper, we report on the new synthesis of nano-LiMnPO{sub 4} by a combustion method. The purity is dependent upon the conditions used for synthesis, including the type of fuel and precursors that are chosen. The fuel to nitrate ratio influences the combustion temperature, which determines the type and amount of carbon found in the LiMnPO{sub 4} composites. This can further be modified by use of carbon structural modifiers added during a subsequent (optional) calcination step. Figure 1 shows a transmission electron microscopy (TEM) image of the spherical nano-sized LiMnPO{sub 4} particles typically formed by combustion synthesis. The average particle size is around 30 nm, in agreement with values obtained by the Rietveld refinement of XRD patterns. The small size of the particles cause the peak ...
Date: May 15, 2008
Creator: Chen, Jiajun; Doeff, Marca M. & Wang, Ruigang
Partner: UNT Libraries Government Documents Department

Comparison of LiMnPO4 made by Combustion and Hydrothermal Syntheses

Description: Among the olivine-structured metal phosphate family, LiMnPO{sub 4} exhibits a high discharge potential (4V), which is still compatible with common electrolytes, making it interesting for use in the next generation of Li ion batteries. The extremely low electronic conductivity of this material severely limits its electrochemical performance, however. One strategy to overcome this limitation is to make LiMnPO{sub 4} nanoparticulate to decrease the diffusion distance. Another is to add a carbon or other conductive coating in intimate contact with the nanoparticles of the main phase, as is commonly done with LiFePO{sub 4}. The electrochemical performance of LiFePO{sub 4} is highly dependent on the quality of the carbon coatings on the particles, among other variables. Combustion synthesis allows the co-synthesis of nanoparticles coated with carbon in one step. Hydrothermal synthesis is used industrially to make LiFePO{sub 4} cathode materials and affords a good deal of control over purity, crystallinity, and particle size. A wide range of olivine-structured materials has been successfully prepared by this technique, including LiMnPO{sub 4} in this study. In this paper, we report on the new synthesis of nano-LiMnPO{sub 4} by a combustion method. The purity is dependent upon the conditions used for synthesis, including the type of fuel and precursors that are chosen. The fuel to nitrate ratio influences the combustion temperature, which determines the type and amount of carbon found in the LiMnPO{sub 4} composites. This can further be modified by use of carbon structural modifiers added during a subsequent (optional) calcination step. Figure 1 shows a transmission electron microscopy (TEM) image of the spherical nano-sized LiMnPO{sub 4} particles typically formed by combustion synthesis. The average particle size is around 30 nm, in agreement with values obtained by the Rietveld refinement of XRD patterns. The small size of the particles cause the peak broadening evident in ...
Date: October 12, 2008
Creator: Chen, Jiajun; Doeff, Marca M. & Wang, Ruigang
Partner: UNT Libraries Government Documents Department

The Origins of the Rate Enhancement in LiNi0.4Co0.2-yAlyMn0.4O2 (0&lt;y&lt;_0.2) Cathode Materials

Description: Recently, much research has been directed towards finding a replacement cathode material for LiCoO{sub 2} combining high performance with lower cost and toxicity. One promising candidate material is the mixed transition metal oxide LiNi{sub 0.4}Co{sub 0.2}Mn{sub 0.4}O{sub 2}, which delivers 180 mAh/g below 4.4 V versus Li/Li{sup +}. However, in this material, there is 4% anti-site cation mixing, which hinders the mobility of lithium within the lattice, adversely affecting its rate performance in lithium batteries. Ongoing work in our lab has shown that partial or full substitution of cobalt with aluminum, LiNi{sub 0.4}Co{sub 0.2-y}Al{sub y}Mn{sub 0.4}O{sub 2} (0 &lt; y {le} 0.2), can lead to significant improvements in rate performance. In particular, LiNi{sub 0.4}Co{sub 0.15}Al{sub 0.05}Mn{sub 0.4}O{sub 2} shows greatly improved rate capability with almost no sacrifice in the overall capacity delivered at low rates between 2.0 and 4.3V (Figure 1). The smaller ionic radius of Al{sup 3+} in octahedral coordination (0.535 {angstrom}) compared to Li{sup +} (0.76 {angstrom}) creates a strong driving force for the formation of a more lamellar structure in the aluminum containing materials. XRD experiments and subsequent Rietveld refinement (Figure 2) reveal a significant decrease in anti-site defect concentration upon aluminum substitution, dropping from {approx}4% at y=0 to {approx}2.5% at y=0.2. Concurrently, there is an increase in the lithium slab dimension from 2.6 {angstrom} to 2.63 {angstrom}. This expansion allows for a reduced activation energy and improved lithium diffusivity through the crystal lattice. Interestingly, the pressed pellet conductivities of Al-substituted compounds are lower than that of the parent as determined by AC impedance measurements. This lends further credence to the hypothesis that structural effects resulting in improved lithium diffusivity are responsible for the rate enhancement, rather than changes in the electronic structure. Further experiments to understand the effect of structural changes induced by Al substitution on ...
Date: October 12, 2008
Creator: Doeff, Marca M. & Wilcox, James D.
Partner: UNT Libraries Government Documents Department

Direct synthesis of LiNi1/3Co1/3Mn1/3O2 from nitrateprecursors

Description: Two novel methods for synthesis of the title compound directly from metal nitrates are described. Phase-pure materials are produced when precursors are calcined between 600 and 1000 C, with little to no ion mixing exhibited for products heated to 900 C or above. The electrochemical characteristics of these materials depended upon calcination temperature and synthesis method, with results comparable to a commercial sample for the materials made at high temperatures in a one-step process without combustion. The sample prepared by combustion also exhibited very stable capacity retention upon cycling.
Date: April 28, 2004
Creator: Patoux, Sebastien & Doeff, Marca M.
Partner: UNT Libraries Government Documents Department

Optimization of Carbon Coatings on LiFePO4

Description: The electrochemical performance of LiFePO{sub 4} in lithium cells is strongly dependent on the structure (disordered/graphene or D/G ratio) of the in situ carbon produced during synthesis from carbon-containing precursors. Addition of pyromellitic acid (PA) prior to final calcination results in lower D/G ratios, yielding a higher-rate material. Further, improvements in electrochemical performance are realized when graphitization catalysts such as ferrocene are also added during LiFePO{sub 4} preparation, although overall carbon content is still less than 2 wt.%.
Date: July 14, 2005
Creator: Doeff, Marca M.; Wilcox, James D.; Kostecki, Robert & Lau, Grace
Partner: UNT Libraries Government Documents Department

Synthesis and Electrochemistry of Li3MnO4: Mn in the +5 OxidationState

Description: Computational and experimental work directed at exploringthe electrochemical properties of tetrahedrally coordinated Mn in the +5oxidation state is presented. Specific capacities of nearly 700 mAh/g arepredicted for the redox processes of LixMnO4 complexes based on twotwo-phase reactions. One is topotactic extractionof Li from Li3MnO4 toform LiMnO4 and the second is topotactic insertion of Li into Li3MnO4 toform Li5MnO4. In experiments, it is found that the redox behavior ofLi3MnO4 is complicated by disproportionation of Mn5+ in solution to formMn4+ and Mn7+ and byother irreversible processes; although an initialcapacity of about 275 mAh/g in lithiumcells was achieved. Strategiesbased on structural considerations to improve the electrochemicalproperties of MnO4n- complexes are given.
Date: June 19, 2007
Creator: Saint, Juliette.A.; Doeff, Marca M. & Reed, John
Partner: UNT Libraries Government Documents Department

Conductive Carbon Coatings for Electrode Materials

Description: A simple method for optimizing the carbon coatings on non-conductive battery cathode material powders has been developed at Lawrence Berkeley National Laboratory. The enhancement of the electronic conductivity of carbon coating enables minimization of the amount of carbon in the composites, allowing improvements in battery rate capability without compromising energy density. The invention is applicable to LiFePO{sub 4} and other cathode materials used in lithium ion or lithium metal batteries for high power applications such as power tools and hybrid or plug-in hybrid electric vehicles. The market for lithium ion batteries in consumer applications is currently $5 billion/year. Additionally, lithium ion battery sales for vehicular applications are projected to capture 5% of the hybrid and electric vehicle market by 2010, and 36% by 2015 (http://www.greencarcongress.com). LiFePO{sub 4} suffers from low intrinsic rate capability, which has been ascribed to the low electronic conductivity (10{sup -9} S cm{sup -1}). One of the most promising approaches to overcome this problem is the addition of conductive carbon. Co-synthesis methods are generally the most practical route for carbon coating particles. At the relatively low temperatures (&lt;800 C) required to make LiFePO{sub 4}, however, only poorly conductive disordered carbons are produced from organic precursors. Thus, the carbon content has to be high to produce the desired enhancement in rate capability, which decreases the cathode energy density.
Date: July 13, 2007
Creator: Doeff, Marca M.; Kostecki, Robert; Wilcox, James & Lau, Grace
Partner: UNT Libraries Government Documents Department

Combustion Synthesis of Nanoparticulate LiMgxMn1-xPO4 (x=0, 0.1, 0.2) Carbon Composites

Description: A combustion synthesis technique was used to prepare nanoparticulate LiMgxMn1-xPO4 (x=0, 0.1,0.2)/carbon composites. Powders consisted of carbon-coated particles about 30 nm in diameter, which were partly agglomerated into larger secondary particles. The utilization of the active materials in lithium cells depended most strongly upon the post-treatment and the Mg content, and was not influenced by the amount of carbon. Best results were achieved with a hydrothermally treated LiMg0.2Mn0.8PO4/C composite, which exhibited close to 50percent utilization of the theoretical capacity at a C/2 discharge rate.
Date: December 14, 2009
Creator: Doeff, Marca M; Chen, Jiajun; Conry, Thomas E.; Wang, Ruigang; Wilcox, James & Aumentado, Albert
Partner: UNT Libraries Government Documents Department

Effect of Titanium Substitution on the Compatiblity of Electrodeswith Pyrrolidinium-Based Ionic Liquid Electrolytes

Description: The quest for the development of rechargeable lithium-metal batteries has attracted vigorous worldwide research efforts because this system offers the highest theoretical specific energy [1]. For this to be achieved, the repetitive deposition and stripping of lithium must be close to fully reversible. Thus, alternative electrolytes have been investigated, such as the room-temperature ionic liquid (RTILs). Lithium can be cycled with a high degree of reversibility with efficiencies exceeding 99% using systems based on N-methyl N-alkyl pyrrolidinium (P{sub 1X}{sup +}) combined with the TFSI anion [2]. More recent efforts have been directed towards systems based on P{sub 1X}{sup +} cations with the FSI anion and appear to be even more promising [3,4]. In this work, we discuss to what extent RTILs based on P{sub 1X}{sup +} cations with TFSI or FSI anions can be used as electrolytes for rechargeable Li batteries. In particular, their physical and chemical properties are thoroughly discussed so as to explain the difference observed in their electrochemical behavior. Although these two systems seem to be stable against lithium, their compatibilities with cathode materials require full assessment as well. Thus, various manganese oxide cathodes are investigated in this study. Strategies to minimize cathode dissolution are also debated, such as the substitution of part of the manganese for titanium.
Date: May 16, 2007
Creator: Saint, Juliette A.; Shin, Joon-Ho; Best, Adam; Hollenkamp,Anthony; Kerr, John & Doeff, Marca M.
Partner: UNT Libraries Government Documents Department

Impact of Carbon Structure and Morphology on the ElectrochemicalPerformance of LiFePO4/C Composites

Description: The electrochemical performance of LiFePO{sub 4}/C composites in lithium cells is closely correlated to pressed pellet conductivities measured by AC impedance methods. These composite conductivities are a strong function not only of the amount of carbon, but of its structure and distribution. Ideally, the amount of carbon in composites should be minimal (less than about 2 wt. %) so as not to decrease the energy density unduly. This is particularly important for plug-in hybrid electric vehicle applications (PHEVs) where both high power and moderate energy density are required. Optimization of the carbon structure, particularly the sp{sup 2}/sp{sup 3} and D/G (disordered/graphene) ratios, improves the electronic conductivity while minimizing the carbon amount. Manipulation of the carbon structure can be achieved via the use of synthetic additives including iron-containing graphitization catalysts. Additionally, combustion synthesis techniques allow co-synthesis of LiFePO{sub 4} and carbon fibers or nanotubes, which can act as 'nanowires' for the conduction of current during cell operation.
Date: August 7, 2007
Creator: Doeff, Marca M.; Wilcox, James D.; Yu, Rong; Aumentado, Albert; Marcinek, Marek & Kostecki, Robert
Partner: UNT Libraries Government Documents Department

Synthesis and Electrochemical Characterization of M2Mn3O8 (M=Ca,Cu) Compounds and Derivatives

Description: M{sub 2}Mn{sub 3}O{sub 8} (M=Ca{sup 2+}, Cu{sup 2+}) compounds were synthesized and characterized in lithium cells. The M{sup 2+} cations, which reside in the van der Waal's gaps between adjacent sheets of Mn{sub 3}O{sub 8}{sup 4-}, may be replaced chemically (by ion-exchange) or electrochemically with Li. More than 7 Li{sup +}/Cu{sub 2}Mn{sub 3}O{sub 8} may be inserted electrochemically, with concomitant reduction of Cu{sup 2+} to Cu metal, but less Li can be inserted into Ca{sub 2}Mn{sub 3}O{sub 8}. In the case of Cu{sup 2+}, this process is partially reversible when the cell is charged above 3.5 V vs. Li, but intercalation of Cu{sup +} rather than Cu{sup 2+} and Li{sup +}/Cu{sup +} exchange occurs during the subsequent discharge. If the cell potential is kept below 3.4 V, the Li in excess of 4Li{sup +}/Cu{sub 2}Mn{sub 3}O{sub 8} can be cycled reversibly. The unusual mobility of +2 cations in a layered structure has important implications both for the design of cathodes for Li batteries and for new systems that could be based on M{sup 2+} intercalation compounds.
Date: August 25, 2005
Creator: Park, Yong Joon & Doeff, Marca M.
Partner: UNT Libraries Government Documents Department

Evaluation of sulfur-doped aluminum-substituted manganese oxidespinels for lithium ion battery applications

Description: Spinels with nominal composition Li{sub 1.02}Al{sub 0.25}Mn{sub 1.75}O{sub 3.97}S{sub 0.03}, Li{sub 1.02}Al{sub 0.25}Mn{sub 1.75}O{sub 4} and Li{sub 1.02}Al{sub 0.15}Mn{sub 1.85}O{sub 3.96}S{sub 0.04} have been evaluated for their suitability as positive electrode materials in rechargeable lithium ion batteries for electric (EV) and hybrid electric vehicle (HEV) applications. {sup 7}Li magic angle spinning (MAS) NMR, XRD, and EDS experiments indicate that sulfur is most likely present as a trace impurity on the surface of the spinel particles rather than substituting for oxygen ions in the bulk, so it is unlikely to account for the previously reported enhanced cyclability of this material. Rather, the unusual particle morphology produced during calcination of some samples in the presence of sulfur compounds appears to impede (but does not completely prevent) conversion to the tetragonal phase that occurs at 3V vs. Li, and ameliorates the capacity fading associated with it. These materials exhibit reduced rate capability and capacity at 4 V, making them unsuitable for high energy density (EV) or high power density applications (HEV).
Date: September 10, 2002
Creator: Doeff, Marca M.; Hollingsworth, Joel; Shim, Joongpyo; Lee, YoungJoo; Striebel, Kathryn; Reimer, Jeffrey et al.
Partner: UNT Libraries Government Documents Department