Framework Structures The Family of Spinel Compounds

Lifl fiV2 -04 H2O has a layered structure in which sheets of VO, square pyramids sandwich the water molecules (Fig. 10a). Half of the square pyramids in one sheet point towards one hydrated layer the other half point in the opposite direction, towards an adjacent layer. Neutron diffraction data have suggested that the lithium ions are distributed over various sites, (i) between the water molecules, (ii) at the base of the VO, square pyramids, and (iii) in some vanadium sites. The Lio V2 -O4.. H2O structure can be dehydrated removal of water shifts the sheets of VO, square pyramids so that the oxygens at the peak of each pyramid occupy the sites where the water oxygens had resided in the hydrated phase (Fig. 10b). Electrochemical data obtained from anhydrous Lio Vj, -04 y electrodes have shown that all the lithium can be de-intercalated from the structure on an initial charge on subsequent discharge and charge, 1.4 Li can be inserted into, and removed from, the structure in a reversible manner [94]. 

Electrode materials with a spinel-type structure, A[B2]X4, have become the subject of intensive research over the past 10 years. This interest is partly due to the fact that many spinel compounds exist in nature, and are therefore intrinsically stable materials. Furthermore, the family of spinels encompasses a vast number of compositions because it is possible to vary not only the type and valency of the A and B cations within the A[B2]X4 structure, but also the type and valency of the X ani- 

1 The Structural Stahility of Transition Metal Oxide Insertion Electrodes for Lithium Batteries 

When or-Fe203 was used as the positive electrode in high-temperature lithium cells, the introduction of a small amount of lithium into the corundum-type structure caused the hexagonal-close-packed oxygen array to shear irreversibly to cubic-close packing which generated a defect /-Li FCjOj (spinel-type) structure. Further lithiation resulted in the formation of LiFe,Ojj thereafter, the reaction followed the same sequence as that shown in reactions (4), (5) and (6) [100]. The stability of the spinel structures at elevated temperatures, as well as the ability of the cubic close-packed oxygen array to accommodate lithium at the expense of 

Two important observations were made in this study of magnetite [lOl]. Firstly, the [Fe2]04 spinel framework remained intact during the lithiation process, and secondly, the interstitial space of 8a tetrahedra and 16c octahedra provided a three- 

Co304 with an excess of n-butyl lithium results in further lithiation of the oxide particles, but with a concomitant extrusion of very finely divided transition metal from the rock salt structure. Highly lithiated iron oxide particles are pyrophoric if exposed to air [100]. 

Unfortunately, Fe304, Co304, and Mn304 are unattractive insertion electrodes because the large and bulky transition metal ions in the interstitial space of 

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