Electrical conductivity and 6,7Li NMR studies of Li1 + yCoO2

✍ Scribed by M. Carewska; S. Scaccia; Fausto Croce; S. Arumugam; Y. Wang; S. Greenbaum

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 819 KB
• Volume: 93
• Category: Article
• ISSN: 0167-2738
• DOI: 10.1016/s0167-2738(96)00545-0

✦ Synopsis

The battery cathode material LiCoO, was synthesized with a deliberate excess of Li, according to Li, +,CoOz, where y = 0.08 and 0.35 (nominally). The effect of divalent doping with Mg" was also explored for some samples, with y values of 0.0 (stoichiometric) and 0.08. Electrical conductivity measurements of the stoichiometric material, without Mg, as functions of oxygen partial pressure and temperature exhibit p-type semiconducting behaviour and suggest that the defects primarily responsible for the generation of holes are cobalt ion vacancies. Excess Li increases the electrical conductivity, while the incorporation of Mg leads to a more dramatic enhancement in conductivity, the latter interpreted as a transition to metallic behaviour. NMR spectroscopic measurements of both 6S7Li isotopes suggest that only a small fraction ( < 20%) of the excess, Li in the y = 0.35 material enters the structure ionically while reducing the formal Co valence. Most of the excess consists of L&CO, and possibly other impurity phases, the former also having been identified by X-ray diffraction. Another small portion of the excess Li (about 10%) appears to enter interstitial sites in close proximity to paramagnetic Co'+ ions.