Lithium transition metal oxides as battery cathodes

Lithium Transition Metal Oxides as Battery Cathode

"Although the basics of electricity were established in 600 B.C. By the Greek philosopher

Thales of Miletus and then refined by scientist William Gilbert of England in 1600,

the first battery actually dates back to the 18th century"

(Millard, N.d., p.2).

Modern Miniaturization

Contrary to the contemporary trend to supersize fast food portions, which Jennifer O. Fisher and Tanja V.E. Kral (2007) note in the article, "Super-size me...," manufacturers routinely reduce the size of electronic components. As this practice of downsizing electronic components contributed to improvements in integrated circuit technology and fabrication processes, it simultaneously led to electronic devices and related peripherals becoming miniaturized. According to Burtrand Insung Lee and Sridhar Komarneni (2005) in the book, Chemical Processing of Ceramics, "the consumer market has readily embraced the miniaturization of products and manufacturers have continuously come up with new products and marketing concepts. All… ubiquitous miniaturized devices… need…efficient, lightweight, and rechargeable power sources" (p. 668). The bulk lithium-ion battery depicts one power source that matches each of these particular requirements that the contemporary consumer craves.

The lithium-ion battery, initially introduced as replacement for the heavier, older nickel-metal hydride (NiMH) battery, provided superior energy density and weighed less than the NiMH. As the lithium-ion battery technology has spread through the consumer electronic field, one finds the lithium-ion battery ubiquitous. A traditional lithium battery contains a lithium anode, a cathode made of a transition metal oxide and an organic electrolyte that contains lithium ions. Transition metal oxides, electrode materials, prove useful in various types of batteries, including rechargeable and lithium. In the journal article, "Vanadium-doped manganese oxides as cathode materials for rechargeable lithium batteries," Charles J. Capozzi and Jun John Xu (2002), both with the Department of Ceramic and Materials Engineering, Rutgers University, explain that in the past, researchers believed "the reaction of lithium metal and a transition metal oxide yielded lithium oxide due to reduction of the transition metal oxide. However, emf values were not consistent with thermodynamically expected values" (Introduction section, ¶ 1). Some studies, according to Capozzi and Xu report, conclude that lithium intercalated into the transition metal oxide structure by expanding the volume of the transition metal oxide structure. Through the examination of related literature, the researcher relates a number of advantages, disadvantages, future prospects, fabrication methods and challenges for lithium transition metal oxide, one type ceramic, as a battery cathode and simultaneously introduces the lithium transition metal oxides as the battery cathode.

Time Refines Batteries

Count Alessandro Volta of Italy developed the first battery, according to the article, "Battery power," (2008). In a paper Volta submitted to the Royal Society in 1799, he described his battery, which "comprised alternating discs of zinc and copper with pieces of cardboard soaked in brine between the metals" ("Battery power," ¶ 2). In time, this battery became known as Volta's pile. A number of individuals introduced and manufactured additional various cell chemistries. During 1836, John Frederic Daniell, a British chemist, invented the Daniell cell (Ibid.). In the article "Gassner, Carl," Cutler J. Cleveland and Tom Lawrence (2008) report that Carl Gassner, a German scientist, invented the first commercially successful dry cell battery in1881. Gassner's battery became the contemporary, general-purpose, carbon-zinc battery. Gassner added zinc chloride to the electrolyte. This significantly increased the cell's useful life and reduced the corrosion of zinc when the cell idled. In1899, Waldmar Jungner, a Swede, developed the first nickel-cadmium (NiCd) battery (Ibid.). Figure 1 depicts the chemistry of the Daniell cell.

Figure 1: The Daniell Cell's Chemistry (Battery Power, 2010, Further Reading Section).

When the circuit is complete, electrons flow from the zinc to the copper, owing to the electrical potential. Conventional current flows from the positive (anode) to the negative (cathode): this is the opposite to the direction of electron flow.

The porous separator prevents bulk mixing of the electrolytes but allows aqueous ions to pass through to maintain the ionic balance.

Anode: Zn(s) Zn2+(aq) + 2e-

Cathode: Cu2+(aq) + 2e- Cu(s)

For a copper-zinc cell under standard conditions (25°C, 1 mol dm-3, 1 atmosphere) the cell voltage may be calculated from the oxidation and reduction half reactions.

Zn(s) 1/2 Zn2+ | Cu2+(aq) 1/2 Cu(s)

E Zn2++ 2e- Zn E = -0.76V

E Cu2+ + 2e- Cu E = +0.34V

E for the cell = +0.34 - (-0.76) = 1.10V. (Battery Power, 2010, Further Reading Section)

Batteries consist of three separate parts, an anode (-) which comprises that negative side, a cathode (+) positive side, and the electrolyte. In a traditional battery, the cathode and anode connect to an electrical circuit. The Northwestern State University article, "How do batteries work?"(2010), explains that "the chemical reactions in the battery causes a buildup of electrons at the anode. This results in an electrical difference between the anode and the cathode. & #8230;[One may] think of this difference as an unstable build-up of the electrons" (¶ 3). As a result the electrons rearrange themselves by repelling each other and finding a place with fewer electrons.

In batteries, these electrons can only travel to the cathode, as the electrolyte stops the electrons from reaching the anode and end up at the cathode. "When the circuit closes (a wire connects the cathode and the anode) the electrons will be able to get to the cathode. In the picture above, the electrons go through the wire, lighting the light bulb along the way" (How do batteries…, 2010, ¶ 4). Electrochemical processes changes the chemicals in the cathode and anode to ensure they do not supply electrons, this explains why there is limited power available from batteries. When recharging a battery, the flow of electrons is reversed by using a different power source, perhaps solar panels, allowing the anode and cathode to be restored to their full power. Figure 2 depicts this process.

Figure 2: Depicts Currency of a Battery (How do batteries…, 2010).

A myriad of items, including, but not limited to, cars; cell phones; computers; microchips; etc. may use energy batteries provide. M. Armand and J.-M. Tarascon (2008), with the Universite de Picardie Jules Verne, Amiens, France, assert in the journal article, "Building better batteries," that variations of the combustion reaction fueled the past few centuries' technological revolution. During the majority of the 20th century, several generations of disposable dry cell batteries as well as Jungner's rechargeable nickel-cadmium served as the primary power sources for portable electric and electronic equipment. A number of inherent problems challenged the dry cell batteries and the nickel cadmium batteries as they not only contained lead, mercury and cadmium, they proved to have high toxicity when individuals disposed them. The nickel-cadmium batteries also became known for "memory effect." When one charged one of these batteries prior to it being completely expended, the battery would only hold the charge from the point the individual charged it. In regard to the lithium ion battery,

Metallic lithium, which is used in lithium primary cells, is unsuitable for rechargeable cells owing to dendritic crystal growth of the metal in the recharge phase which can damage the cell. Instead lithiated graphite is used as the anode.

Anode: Lithiated graphite (LiC6)

Cathode: LiCoO2

Electrolyte: LiPF6 in aprotic solvent

Overall reaction: Li 1-x CoO2 + CLix LiCoO2 + CE = 3.7V

Lithium atoms in the lithiated graphite are intercalated between the hexagonal layer molecular structure of the graphite and are free to move around. On discharge these atoms migrate from the graphite to the lithium cobalt oxide. This technology was developed by the British company AEA Technology and commercialised by Sony under licence from AEA. Currently Quallion in the U.S. uses this technology in microbatteries (the size of a grain of rice) in medical implants for neurological disorders. The batteries have a 10-year life. (Battery Power, 2010, Secondary Cells Section, ¶ 12).

In 1980, Mizushima et al. initially examined LiCoO2. At that time, a number of researchers projected LiCoO2 to comprise a potential positive electrode for lithium-ion rechargeable batteries. Sony Corporation commercialized the first lithium-ion battery in 1991. Sony used lithium cobalt oxide for the positive electrode and graphite (carbon) for the negative electrode. Since 1991, manufactures have generally used LiCoO2 as the primary cathode in commercial lithium-ion batteries. LiCoO2 continues to claim a significant stance as a cathode material. Lithium oxide used as a flux in ceramic glaze, also serves as a replacement for lithium cobalt oxide as the cathode in the lithium ion batteries used ... lithium (element, metal -- in chemistry Merriam Webster Dictionary defines "flux' (2010) as a substance used to promote fusion (as of metals or minerals); especially: one (as rosin) applied to surfaces to be joined by soldering, brazing, or welding to clean and free them from oxide and promote their union" (p. 1).

Lee and Komarneni (2005) assert that currently, manufacturers use three intercalation materials as positive electrode materials to produce commercial lithium-ion rechargeable batteries: LiCoO2, LiNiO2, and LiMn2O4. Armand and Tarascon (2008) explain:

The lithium-ion battery, first commercialized by Sony in 1991, owes its name to the exchange of the Li+ ion between the graphite (LixC6) anode and a layered-oxide (Li1?xTMO2) Cathode2, with TM being a transition metal (usually cobalt but sometimes nickel or manganese). 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).

Process

Nature of Feed/Strip

Pore size

Origin of selectivity

Pressure Gradient

Elemental Operation

Microfiltration

0.1-10µm

Sieving effect

1-3 bars

Clarification, debacterization, separation

Ultrafiltration

Liquid/liquid

1 nm-0.1 µm

Sieving effect

3-10 bars

Clarification, purification, concentration

Nanofiltration

Sieving + specific interactions with the membrane

10-40bars

Purification, water softening, separation, concentration

Pervaporation

Liquid/gas

Sieving + additional specific interaction

1 bar

Separation

Gas filtration Gas separation

Gas/gas

100 µm

50 nm-

Sieving effect

Sieving + additional specific interaction

0.1-5 bars 0.1-50 bars

Separation, dusting

Separation, extraction, Purification

Gas separation

Dense

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 states. The integrated charge density characteristics remained independent of the concentration of the Li added showing the Ni maintained its same charge state. The electron density revealed the hybridized p orbital of the O. correlated near the Fermi level constitutes the essential component for the charge compensation mechanism. Evidence interpreted from the analysis reveals O. is essential in charge regulation the addition of the Li and prevents Ni from converting to either Ni2+ to Ni4+. EELS analysis, on the density of states from the previous analysis, were conducted to validate the results ( Kocher, 2008).

Using the DFT and DFT+U methods, the electronic structure of LiFePO4 and FePO4 were determined and the observations revealed a minimal dependency of the concentration of Li regarding the spherically integrated spin and charge densities. The expected density of states demonstrates an increase in the p orbital of O. And the d orbital of Fe hybridization states when the Li is removed, signifying the essential component regarding the charge compensation mechanism is the covalent bonds (Kocher, 2008, ¶ 3).

Byoungwoo Kang and Gerbrand Ceder (2009), both with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, assert in the journal article, "Battery materials for ultrafast charging and discharging," "Supercapaciotors are essential to achieve high power rates in electrochemical systems, where high power is exchanged to low energy density since energy can only be stored by the reactions of surface adsorption of charged molecules on an electrode material. Testing reveals that batteries attain ultrahigh discharge rates comparable of the supercapacitors due to the storing of the charge within the bulk of the batteries material that allows it to gather high energy density. This is demonstrated by a material constructed of high lithium bulk motility, LiFePO4, which was analyzed using a fast ion-conducting surface phase through controlled off-stoichiometry. In respect to the discharge of a full battery, the capability rate of 10- 20 seconds was achievable (p 190).

LiFePO4 reacts like any lithium battery material in reference to the extracting and then re-inserting of Li ions and electron and the energy absorbed and released by these reactions. Migration of the Li ions and electrons in to the active electrode material by way of the composite electrode structure and electrolytes will be dependent of the rate of migration in calculating the power capacity. The need to raise the LiFePO4's low performance rate is being analyzed by usage of nano-sized materials to reduce the path length the ions have to travel and increasing the electron transport on the surface of the material or in the bulk component.

Results determined that increased diffusion can increase rate capability by the exchange of LiFePO4 molecules with the surface electrolytes since Li ions move one direction which is to the bulk of crystal. Li transport carries equivalent importance with regards to electron transport (Kang & Ceder, 2009, p. 190).

A source of good, stable Li conduction can be realized in glassy lithium phosphates and when treated with transition metals achieve electronic conduction. To achieve significant high performance rate, a coating of lithium phosphate was applied to the surface area of nanoscale LiFePO4. High phosphorus composites situated on the binary edge of Li 2O -- P2O5 can be excellent formers of glass resulting in high Li conductivity. The addition of nitrogen treated Li3PO4 to the mixture represent a competent solid state lithium electrolyte. Under normal conditions, there would be a decrease in lithium conductivity and ability for the formation of glass with Li2O present, but glasses will dissolve transition metal ions and extenuate the electronic conductivity. Certain optimal compositions for coating that contain good lithium conductivity are essential to eliminate any potential problems (Kang & Ceder, 2009, p. 190).

To maintain the high rate of energy required, all components involved in the Li electron path form the anode to the cathode must contain the capability of maintaining the rate needed. Carbon black inserted into the system will bring about the transport of the materials actively involved to the collector. Testing performed contained 65% by weight concentration of carbon.

Normally this high concentration of carbon would be excessive in real batteries; however it helped establish the active materials accurate rate capacity and is common in analyzing high rate nanomaterials. In reporting the results of their findings, Kang and Ceder state, "at a 200C rate (corresponding to an 18-s total discharge) more than 100 mAh g21 can still be achieved, and a capacity of 60 mAh g21 is obtained at a 400C rate (9 s to full discharge)" (p 191). These findings show that in relation to the lithium ion batteries currently in use as of 1999, the active materials in their studies achieved a magnitude of two orders higher (Kang & Ceder, 2009, p. 191).

The only drawback is the larger amount of carbon used in testing the theory reduces volumetric energy density of the electrodes used. Development of electrode structures that contain good electronic conductivity and percolation but optimize the energy-storing active components volume fraction are essential to enable the systems to work efficiently. Changes regarding lifestyle and the advent of new technology could enhance the time needed to charge and discharge batteries from hours to mere seconds (Kang & Ceder, 2009, p. 192).

Lithium Transition Metal Oxides Disadvantages

Air electrodes and metal -- air battery technologies have already been used in primary systems such as fuel cells, but the use of lithium instead of zinc as the metal will increase the energy output eightfold. An oxygen electrode proceeding in tandem with lithium according to the reaction 2Li + O2 ? Li2O2 can deliver a capacity of 1,200 mAh g?1. The first lithium -- air cell was successfully assembled and discharged in 1996, but attractive rechargeability was demonstrated only recently. It could be argued that such a system unites within the same device the two most prominent failures of battery and fuel-cell technologies, namely the inability to master lithium and oxygen electrodes. These perceived issues have prevented the practical use of lithium -- air batteries (Armand & Tarascon, 2008, p. 654).

Ying Wang and Guozhong Cao (2008), both with the Department of Materials Science and Engineering, University of Washington, assert in the journal article, "Developments in nanostructured cathode materials for high performance lithium-ion batteries," at present, lithium-ion batteries are efficient, light-weight, and rechargeable power sources for consumer electronics such as laptop computers, digital cameras, and cellular phones. Moreover, they have been intensively studied for use as power supplies of electric vehicles (EVs) and hybrid electric vehicles (HEVs), which require high energy and power densities Lithium-ion batteries are attractive power-storage devices owning to their high energy density; however, their power density is relatively low because of a large polarization at high charge -- discharge rates. This polarization is caused by slow lithium diffusion in the active material and increases in the resistance of the electrolyte when the charging -- discharging rate is increased. To overcome these problems, it is important to design and fabricate nanostructured electrode materials that provide high surface area and short diffusion paths for ionic transport and electronic conduction (p. 2252).

Nanomaterials offer unusual mechanical, electrical, and optical properties endowed by confining the dimensions of such materials, and the overall behaviors of nanomaterials exhibit combinations of bulk and surface properties. Thus, nanostructured materials are drawing a tremendous amount of attention because of their novel properties, and because of their potential applications in a variety of nanodevices, such as field-effect transistors (FETs), chemical and biological sensors, nanoprobes, and nanocables. Reports on the processing, properties, and applications of nanomaterials are appear rapidly, on a daily basis. Many synthesis methods have been reported for the synthesis of nanostructured electrode materials. Among them, solution-based methods are well-known for their advantages in tailoring the size and morphology of the nanostructures. It is the uncomplicated sol -- gel processing (soft chemistry) method in combination with template synthesis or hydrothermal treatment that produces the most desirable nanostructures with remarkable reliability, efficiency, selectivity, and variety (Wang & Cao, 2008, p. 2252).

It should be noted that the nanoparticulate forms of lithium transition metal oxides such as LiCoO2, LiNiO2, or their solid solutions can react with the electrolyte and lead to safety problems. In the case of LiMn2O4, the use of nanoparticles causes undesirable dissolution of Mn. Significant efforts have been made to increase the stability of these nanocrystalline lithium metal oxides. Better stability can be achieved by coating the electrode materials with a nanosized stabilizing surface layer that alleviates these problems. As for LiCoO2, coatings of various phosphates and oxides have been studied and significant improvements in capacity retention have been demonstrated. Kim et al. made an extensive study on the effect of the MPO4 (M1/4Al, Fe, SrH, and Ce) nanoparticle coatings on LiCoO2 cathode materials. They found that the extent of the coating coverage is affected by the nanoparticle size and morphology despite the same coating concentration and annealing temperature (Wang & Cao, 2008, p. 2260).

Lei Wang, Thomas Maxisch, and Gerbrand Ceder (2006), all with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, assert in the journal article, "Oxidation energies of transition metal oxides within the GGA+U framework," Oxidation and reduction reactions play a key role in many technological and environmental processes, such as corrosion, combustion, metal refining, electrochemical energy generation and storage, photosynthesis, and metabolism. The ability to correctly predict the reaction energy and electrochemical potentials of such reactions with first-principles methods is therefore important. Although the local density approximation _LDA_ and generalized gradient approximation _GGA_, two standard approximations to density functional theory _DFT_, are rather crude approximations to the many-body electron problems, their successes in accurately predicting materials properties are in large part due to the cancellation of errors in energy differences (p. 1).

The energy of a large number of oxidation reactions of 3d transition metal oxides is computed using the generalized gradient approach _GGA_ and GGA+U methods. Two substantial contributions to the error in GGA oxidation energies are identified. The first contribution originates from the overbinding of GGA in the O2 molecule and only occurs when the oxidant is O2. The second error occurs in all oxidation reactions and is related to the correlation error in 3d orbitals in GGA. Strong self-interaction in GGA systematically penalizes a reduced state _with more d electrons_ over an oxidized state, resulting in an overestimation of oxidation energies (Wang, Maxisch & Ceder, 2006, p. 1).

The constant error in the oxidation energy from the O2 binding error can be corrected by fitting the formation enthalpy of simple nontransition metal oxides. Removal of the O2 binding error makes it possible to address the correlation effects in 3d transition metal oxides with the GGA+U method. Calculated oxidation energies agree well with experimental data for reasonable and consistent values of U (Wang, Maxisch & Ceder, 2006, p. 1).

Future Prospects of Lithium transition metal oxides

M. Stanley Whittingham, Oxford University, United Kingdom, Yanning Song, Shanghai Jiaotong University, Shanghai, China, Samuel Lutta, State University of New York at Binghamton, Peter Zavalij, L'viv National University, Ukraine and Natasha A. Chernova (2005), M.V. Lomonosov Moscow State University, assert in the journal article, "Some transition metal (oxy)phosphates and vanadium oxides for lithium batteries," iron and vanadium oxides have a rich structural chemistry when combined with phosphate groups; the transition metal most commonly in an octahedral coordination. The inductive effect increases the potential difference between Fe3+/Fe2+ and Li/Li + couples in phosphate lattices relative to the pure iron oxides; a similar behavior is found for the corresponding vanadium compounds. Of the iron phosphates, the olivine phase LiFePO4 has high thermal and chemical stability, even when lithium-free; the challenges of low electronic conductivity are being overcome, but data is lacking on the true lithium diffusion behavior. The all-ferric lipscombite-type phase, Fe1.33PO4OH, shows the highest capacity of the iron phosphates for lithium intercalation (p. 3362).

The e-VOPO4 material, formed by the oxidative de-intercalation of protons from H2VOPO4, can reversibly react with two lithium atoms in two steps. The face- and edge-sharing transition metal octahedra lead to a range of interesting and structurally revealing magnetic interactions. A number of vanadium oxide phases are known, with those containing VO6 octahedra showing the greatest stability when undergoing redox reactions. Such structures have been synthesized using xerogel, hydrothermal and electrochemical methods. The double-sheet delta structures show reversible lithium intercalation of up to one lithium ion per vanadium, leading to the highest storage capacities. However, the large potential width of discharge and the apparent low reaction rates will minimize their use unless improved (Whittingham, Song, Lutta, Zavalij & Chernova, 2005, p. 3362).

It is difficult to measure the diffusion coefficient by standard cathode methods because there is no compositional variation so what is measured is the movement of the LiFePO 4/FePO4 interface. One experimental study suggests a diffusion coefficient of 2-6 10214 cm2 s21 for LiFePO4,23 and another 24 on LiCoPO4 found values varying from 10211 to 10212 cm2 s21 depending on the electrolyte suggesting that these are "system" diffusion coefficients rather than the true bulk value for the phosphate. Franger et al. have reported 15 a value of around 10213 -- 10214 cm2 sec21 over the whole range of composition for LiFePO4. These values are consistent with conductivity values of less than 1029 S. cm21 for pure compounds. A measurement of the intrinsic ionic conductivity would be desirable, probably using the methods appropriate for a solid electrolyte (Whittingham, Song, Lutta, Zavalij & Chernova, 2005, p. 3366).

Binod Kumara (2010), Metals and Ceramics Division, University of Dayton Research Institute, et al., assert in the journal article, "A solid-state, rechargeable, long cycle life lithium -- air battery," the lithium ion battery business has grown into a multibillion dollar global industry, and a robust growth is anticipated in the future. The state-of-the-art lithium ion batteries employ many variations in cell components and chemistries. Most of them use a graphitic carbon anode _negative electrode_, a liquid electrolyte comprised of lithium salts dissolved in organic solvents, a microporous polymer separator, and a lithiumintercalated transition-metal oxide cathode _positive electrode_. The small lithium ion cells and battery packs made from them have gained worldwide consumer acceptance. Larger lithium ion batteries for hybrid and electric vehicles are yet to be developed, tested, and accepted. A few safety incidents and recalls of lithium ion cells produced by major manufacturers have also drawn significant attention (p. 157).