Lithium Transition Metal Oxides as Article Review
- Length: 20 pages
- Sources: 15
- Subject: Chemistry
- Type: Article Review
- Paper: #32701294
Excerpt from Article Review :
The energy it stores (?180 Wh kg?1) at an average voltage of 3.8 V is only a factor of 5 higher than that stored by the much older lead -- acid batteries. This may seem poor in the light of Moore's law in electronics (according to which memory capacity doubles every 18 months), but it still took a revolution in materials science to achieve it. Billions of lithium-ion cells are produced for portable electronics, but this is not sustainable as cobalt must be obtained from natural resources (it makes up 20 parts per million of Earth's crust). (Armand & Tarascon, 2008, p. 653).
Fu investigated the lithium-ion conductivities of glasses and glass-ceramics in the LI2O-AlO3-TiO2P2O5 system. Fu's samples revealed high conductivity, albeit when Abrahams and Hadzifejzovic similarly investigated the LI2O-AlO3-TiO2P2O5 glass and glass-ceramic systems, their findings revealed "a maximum room temperature conductivity of 3.98 x 10-6 S/cm in their crystallized cast-gas pellet sample. When Fu later investigated the incorporation of a number of other M2O3 type constituents where M = Y, Dy, Gd, and LA to extend the research, Fu found that the parent glass' ionic conductivity basically remained consistent with increasing ionic radium of M3+. The ionic conductivities of the glass-ceramics, albeit, significantly decreased while the ionic radius of the M3+. atom increased (Lee & Komarneni, 2005).
Table one depicts characteristics of the primary processes planned for ceramic membranes use.
Table 1: Ceramic Membranes Main Characteristics Processes (Lee & Komarneni, 2005 p. 631).
Nature of Feed/Strip
Origin of selectivity
Clarification, debacterization, separation
1 nm-0.1 µm
Clarification, purification, concentration
Sieving + specific interactions with the membrane
Purification, water softening, separation, concentration
Liquid/gas <2 nm
Sieving + additional specific interaction
Gas filtration Gas separation
50 nm-<2 nm
Sieving + additional specific interaction
0.1-5 bars 0.1-50 bars
Separation, extraction, Purification
Ionic conduction of O2- by oxides p (O2)
Air separation, transport of O2
Figure 3 portrays typical representative cathode crystal structures: (a): rhombohedra R3m; (b) monoclinic C2/m; (c) spinel Fd3m; (d) orthorhombic Pmmm. Figure 2 also relates ceramic materials for lithium-ion battery applications.
Figure 3: Typical Representative Cathode Crystal Structures (Lee & Komarneni, 2005, p. 669).
Lithium Oxide, Li2O, a highly undissolvable thermally stable Lithium source, is best suited for ceramic, glass and optic applications. The article, "Lithium Oxide," (2010) published by American Elements, a prominent manufacturer of engineered and advanced material products, explains that "Oxide compounds are not conductive to electricity. However, certain perovskite structured oxides are electronically conductive finding application in the cathode of solid oxide fuel cells and oxygen generation systems" (¶ 1). These particular compounds contain one oxygen anion and one metallic cation.
Lithium transition metal oxides, compounds with phenomenal intercalation, exhibit a variety of captivating electronic and phase phenomena. Gholamabbas Nazri and Gianfranco Pistoia (2004) assert in the book, Lithium batteries: Science and technology, that lithium possesses the ability to "undergo large variation in lithium concentration, often without suffering irreversible changes" (p. 42). This makes lithium transition metal oxides, which consist of metal oxide host "with a crystal structure in which lithium ions occupy a relatively open network of interstitial sites" (Ibid.) ideal electrodes for rechargeable lithium batteries. Lithium transition metal oxides prove to be somewhat instrumental as an anode in rechargeable lithium batteries, however, they are more suited as a cathode because they display high voltage. "In a rechargeable lithium battery, lithium ions are shuttled between an anode and a cathode, whereby lithium ions are removed from and inserted into the electrodes" (Nazri & Pistoia, 2004, p. 42). In the deintercalation of a lithium metal oxide, open spaces are made on the lithium portions of the host, during intercalation, lithium refills these portions.
Inserting and removing lithium ions may cause a remarkable phenomena that could increasingly affect the electrochemical properties of a compound. Differences in the concentration of lithium can change the electronic properties of the transition metal oxide host. "The valence electron of each lithium ion is generally donated to the host where it can either the valence state of the transition metal ion and/or alter the nature of the bonds between the transition metal and the oxygen ions" (Nazri & Pistoia, 2004, p. 43). At the same time, removing lithium from the host may cause the structure of the metal oxide to become unstable or stimulate the order-disorder phase transitions between lithium and vacancies following the attainment of a critical vacancy concentration. At times, these phenomena may significantly affect the voltage characteristic or the lattice parameters of the compound.
Typically, lithium transition metal oxides are not water soluble. They are, however, extremely stable which makes them particularly complementary to ceramic structures. "Metal oxide compounds are basic anhydrides and can therefore react with acids and with strong reducing agents in redox reactions. Lithium Oxide is also available in pellets, pieces, sputtering targets, tablets and nanopowder" (Lithium Oxide, 2010, ¶ 1). Lithium, part of the alkali group of metals, has the maximum specific heat of any other material and the highest electrochemical potential.
In ceramic processing, the first step involves preparing the ceramic powder, while the second step comprises molding (forming). In the publication, "Ceramic materials - forming methods and properties of final element, "Magdalena Gizowska (N.d.) purports that a myriad of methods for forming ceramics exists; albeit they primarily depend on the product's ultimate desired shape. Most widespread methods for forming dense ceramics may be characterized into a number of groups. Well-known are also methods of designing porous ceramic materials.
The third step in ceramic processing sintering, depicts a process that heating causes, material consolidation. "The temperature of sintering is between 2/3-4/5 of melting point of the predominant component in the ceramic material. The visible sign of sintering is the shrinkage of the material (Ibid.). Figure 4 portrays the significant structural changes that occur during fabrication of ceramic products in ceramic processing.
Figure 4: Ceramic Processing Structural Changes (Lee & Komarneni, 2005, p. 669).
Advantages of Lithium Transition Metal Oxides
The low costs of cathode materials of advanced lithium batteries with their perceived thermodynamic and kinetic stability make them particularly attractive (Whittingham, Song, Lutta, Zavalij & Chernova, 2005). Two separate categories of cathode materials exist; layered compounds containing anion tightly packed lattice and vanadium oxides, which have more open structures. Guozhong Cao and Jeffery Brinker (2008) assert in the book, Annual review of nano research, volume 2 "one is layered compounds with anion close-packed lattice; transition metal cations occupy alternative layers between the anion sheets and lithium ions are intercalated into remaining empty layers" (p. 550). LiTiS2, LiCo2, LiNit-xCoxO2, and LiNixMnxMnxCo1-2xO2are compounds that are in the first group, which are layered compounds.
The spinels with the transition metal cations ordered in all the layers can be considered to be in this group as well (Cao & Brinker, 2008, p. 550). This class of materials have the inherent advantage of higher energy density (energy per unit of volume) owning to their more compact lattices. The other group of cathode materials has more open structures, such as vanadium oxides, the tunnel compounds of manganese oxides, and transition metal phosphates (e.g., the olivine LiFePO4). The materials generally provide the advantages of better safety and lower cost compared to the first group (Cao & Brinker, 2008, p. 551).
Manganese oxides have been investigated because of their low cost and non-toxicity. Many crystalline, amorphous, and aerogel forms of manganese oxides have been studied; each one has advantages and disadvantages. Spinel structures of manganese oxides have particularly been investigated for battery applications, but so far they have exhibited lower intercalation capacity and poorer cycling performance than LiCoO2. At voltages of 4 V, cubic spinel LixMn2O4 can sufficiently cycle 0.4 Li. Though cubic spinel may intercalate up to 1.0 Li at 4 V with minimal isotropic expansion of the crystal lattice, dissolution of Mn3+ and oxidation of electrolyte causes gradual capacity loss upon cycling (Capozzi & Xu, Introduction section, ¶ 4, 2002).
Most cell phones and laptop computers use batteries that contain a LiCoO2 cathode. Michael P. Kocher, PhD (2008), Arizona State University, asserts in the journal article, "The electronic structure of Lithium transition metal oxides," that the low abundance of cobalt, thermal instability and environmental concerns has stimulated and intensified efforts to find an alternative material for portable energy sources. The electronic structure of Lix Mn1/2 Ni1/2 O2 and Lix Mn1/3, Ni1/3, Co1/3 O2 can be calculated by the use of Density Functional Theory (DFT) to comprehend the essential uniqueness in terms of the molecular activity. The calculations show the characteristics of the molecules effect when integrating the Li into the molecule regarding its spin density and molecular spherical integration charge, and angular momentum projected density…