Electrochemical Behavior of Samples in Lithium Cells

Because of its relevance to batteries, the mechanism of lithium insertion into anatase Ti02 has been extensively studied. The electrochemical insertion/extraction of Li is believed to be driven by the accumulation of electrons in Ti02 electrodes in contact with Li -containing electrolytes, and the overall cell reaction can be written as 

The crystalline structure of anatase is tetragonal (s.g. IT /amd] and contains distorted TiOg octahedra, which define a series of octahedral and tetrahedral vacant sites. These sites allow lithium uptake of 0.5 Li per formula unit, corresponding to a theoretical capacity of 168 mAh g [81]. A two-phase mechanism has been suggested to describe the electrochemical insertion of lithium 

Values for layers of 600 nm length onto Si substrates and Ti foils. 

Strongly chemisorbed water [35] or bound water [40]. The difference in the irreversible capacity can be explained by the fact that an annealing treatment removes structural and chemical defects in the amorphous phase that act as Li ion traps. 

Other possible reasons for the high experimental capacity values are the high surface area and highly organized ID structure of titania nanotube layers. When a rate of 100 pA cm (2.5C) is used, the reversible and irreversible capacities are lower than at a rate of 5 pA cm, but the capacity retention for crystalline is around 96% (close and star-shaped symbols in Fig. 5.13c Table 5.1). 

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