Manganese oxides with layer structures

Most of the Mn(IV) oxide minerals listed in table 8.3 occur in weathered continental rocks, and often constitute important manganese ore deposits. However, several of the minerals, notably todorokite, bimessite, vemadite and, perhaps, buserite and asbolane, are major constituents of seafloor hydrothermal crusts near spreading centres and in manganese nodule deposits. 

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In this section, we have chosen to present the two alternatives to layered oxides currently commercialized (1) the manganese oxides with spinel structure that make a less expensive alternative to batteries requiring a limited lifespan and (2) the olivine LiFeP04 which by its development at the nanoscale overthrew all the concepts that had previously been established and thus opened the way to an entire field of research into new polyanionic materials with poor electronic conducting properties. 

Unlike cobalt and nickel, manganese does not form a stable, pure LiMn02 phase and forms the spinel structure instead, named after the mineral of spinel (Table 1.3) with the composition of Lio.5Mn02, conunonly expressed as LiMn204. Manganese-based cathode materials are attractive mainly due to their low cost compared to cobalt and nickel. A wide variety of the hthiated manganese oxides with multiple structures and compositions (Li Mn 0 ratios) exist and many of these compounds can reversibly intercalate lithium, but amongst these materials, spinel materials and the layered derivatives are the most mature, to the point of commercial availability. Spinel-stractured materials will be discussed separately in the next part of this chapter. 

Thus lithiated manganese oxides with a substantial amount of nickel and other elements could play a crucial role in stabilizing the layered crystal structure, thereby improving the electrochemical characteristics. 

An efficient oxidation catalyst, OMS-1 (octahedral mol. sieve), was prepared by microwave heating of a family of layered and tunnel-structured manganese oxide materials. These materials are known to interact strongly with microwave radiation, and thus pronounced effects on the microstructure were expected. Their catalytic activity was tested in the oxidative dehydrogenation of ethylbenzene to styrene [25]. 

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