Degradation lithiated carbons

From the lithium chemistry point of view, the carbon-fluorine bond cannot be considered as a carbon-halogen bond because alkyl or aryl fluorides are not adequate starting materials in lithiation processes, due to the fact that this bond is the strongest that carbon can form . On the other hand, a possible reductive defluorination process could be important from an environmental point of view due to the difficult degradation of fluoro derivatives in nature . 

As in the previous section, electrophilic attack at carbon has only been mentioned in connection with the 8-azapurine system. The iodo-compound (77a) is lithiated by butyllithium and the subsequent metalated derivative undergoes normal reactions with electrophiles to give compounds (78a and b) (Scheme 2). Under the same conditions of lithiation, the chloro compound (77b) is degraded to 5-amino-4-cyano-l-phenyltriazole (79) <91CPB2793>. 

The two types of high temperature fuel cell are quite different from each other (Table 6). The molten carbonate fuel cell, which operates at 650°C, has a metal anode (nickel), a conducting oxide cathode (e.g. lithiated NiO) and a mixed Li2C03/K2C03 fused salt electrolyte. Sulphur attack of the anode, to form liquid nickel sulphide, is a severe problem and it is necessary to remove H2S from the fuel gas to <1 ppm or better. However, CO is not a poison. Other materials science problems include anode sintering and degradation, corrosion of cell components and evaporation of the electrolyte. Work continues on this fuel cell in U.S.A. and there is some optimism that the problem will be solved within 10 years. 

The volume of a fuUy lithiated Li-Si alloy can be 3-4 times larger than the unalloyed silicon volume. This is much larger than the volume change seen in carbon anodes. As a consequence of such expansion and contraction, which on each cycle causes mechanical degradation of the silicon material and electrical isolation of sections, the electrodes can have a short cycle life (47). 

In addition to the stabilizing effect of cathode particles on the electrolyte solutions at elevated temperatures, graphite-like carbon electrodes (anodes) were also foimd to reduce the thermal decomposition of bulk LiPFe electrolyte solutions. However, the reduction of bulk electrolyte decomposition coincided with reactions of the electrolyte with the anode. The surface of the carbon electrode was covered with the products of the electrolyte reduction, which formed a protective solid electrolyte interface (SEl) layer [35-37], The stabilizing effect of these anodes (e.g., based on lithiated mesocarbon microbeads, MCMB) on the electrolyte was proposed to relate to the degradation of the solid-electrolyte interphase (SEl) in LiPFe-based electrolytes at elevated temperatures [32,38], The loss of capacity and power from lithium-ion cells undergoing accelerated aging experiments has been attributed to the presence of thermal decomposition products of the electrolyte in the anode SEl [32],... 

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