Lithium oxides, layered structures

An example of a layer structure mixed conductor is provided by the cathode material L CoC used in lithium batteries. In this solid the ionic conductivity component is due to the migration of Li+ ions between sheets of electronically conducting C0O2. The production of a successful mixed conductor by doping can be illustrated by the oxide Cei-jPxx02- Reduction of this solid produces oxygen vacancies and Pr3+ ions. The electronic conductivity mechanism in these oxides is believed to be by way of electron hopping between Pr4+ and Pr3+, and the ionic conductivity is essentially vacancy diffusion of O2- ions. 

In ternary oxides AMO3 the second class of structures arises when A and M are the same size and the size is suitable for octahedral co-ordination. These adopt structures in which both ions are 6-coordinate. An example is the lithium nio-bate structure, which contains hexagonally packed anion layers (Figure 11.6(d)). Surprisingly, no known fluoride adopts such a structure. 

Figure 1. Layered structure of LiTiSj, LiVSe2, LiCo02, LiNi02, and LiNi Mn/Hoi-2/32, showing the lithium ions between the transition-metal oxide/sulfide sheets. The actual stacking of the metal oxide sheets depends on the transition metal and the anion.

Another vanadium oxide that has received much attention is LiVaOs, which has a layer structure composed of octahedral and trigonal bipyramidal ribbons that can be swelled just like other layered compounds and can intercalate lithium. Here again, the method of preparation is important to its electrochemical characteristics. West et al. made a systematic study of the impact of synthesis technique on capacity and cycling and showed that amorphous material increased the capacity above 2 V from 3—4 lithium per mole of LiVsOs at low current drains, 6—200 fiAlcm. ... 

Figure 1. Schematic description of a (lithium ion) rocking-chair cell that employs graphitic carbon as anode and transition metal oxide as cathode. The undergoing electrochemical process is lithium ion deintercalation from the graphene structure of the anode and simultaneous intercalation into the layered structure of the metal oxide cathode. For the cell, this process is discharge, since the reaction is spontaneous.

The mineralized core of ferritin can be modeled by mixed valence species such as [Fe 4-Fe g02(0Me)i8(02CMe)6]-4.67MeCN, whose 3D close-packed layer structure mimics ferritin. This compound can be prepared by oxidizing a methanolic solution of iron(II) acetate and lithium methoxide with a slow stream of dioxygen it can be reduced to give [Fe 2Fe o02-(0Me)i8(02CMe)g]2-.i ... 

LiNi02 has a structure consisting of cubic close-packed 02 ions with Ni3+ ions occupying alternate layers of octahedral sites between adjacent close-packed oxide layers, while Li+ ions occupy the other set of octahedral sites between the oxide layers. The variation of the voltage of the Li(1 Ni02 electrode is shown in Fig. 7.17 as a function of lithium... 

In the structure of lithium oxide, Li20, as shown in Figure 6.11, there is a ccp (3P) framework of oxide ions with Li+ ions filling both T layers (T+ and T ) between P layers. The very close T+ and T layers (above and below each P layer) are clearly shown. There is no problem with all T sites occupied for a ccp arrangement because the T sites are staggered (A, B, and C). Each oxide ion is at the center of a cube formed by eight Li+ ions. This structure is the reference structure for many related tetrahedral structure involving partial occupancy of T and/or P layers. 

The layered lithium insertion cobalt and nickel oxides are materials of industrial importance [126]. The layered structure provides two-dimensional paths for lithium insertion, during which a charge transfer occurs involving the reduction of M" to... 

Transition metal compounds are important materials for electrochemistry due to their ability to exist in various valence states. Several transition metal oxides (M0O3, V2O5, Mn02, etc.) have gained additional attention in the field of secondary lithium batteries due to their layered structure. These layers can be propped open by intercalated species such as solvated lithium and sodium ions, as well as larger molecules [5]. The layered structure intercalates lithium while the mixed valence transition metal centers allow for electron transfer. 

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