Chemical extraction of lithium from layered LiCoO2

Chemical extraction of lithium from LiCoO2 has been investigated with various oxidizing agents - Cl-2, Br-2, and I-2 - and with dilute sulfuric acid. A considerable amount of lithium could be extracted with both chlorine and acid to give a final lithium content(1 - x) approximate to 0.3 in Li1-xCoO2. The stronger oxidizing power of Cl-2, and the relative instability associated with the Li-extracted samples lead to the dissolution of a considerable amount of the sample during chlorine oxidation. A deeper lithium extraction with chlorine also leads to the occurrence of oxygen vacancies in Li1-xCoO2-delta. Lithium extraction with acid proceeds predominantly by a disproportionation of Co3+ to Co2+ and Co4+ analogous to that in the spinel LiMn2O4 with a small degree of ion exchange of Li+ by H+. However, the results of both chlorine oxidation and acid treatment are strongly influenced by the nature of the initial material. An Li/Co ratio < 1 and/or a disorder between Li and Co in the initial Li1-xCo1-zO2 result in a competition of Co extraction from Li planes with Li extraction as evidenced by the Li/Co ratio in the filtrate as well as the changes in the relative intensities of the (003) and (104) reflections. Extraction of Co from Li planes by this process might prove to be useful to obtain improved electrode materials for lithium batteries. The degree of lithium extraction that can be achieved with different oxidizing agents follows the trend in their oxidation potential. In addition, the literature data that Na can be extracted more easily from NaCoO2 than Li from LiCoO2 is explained on the basis of the relative energies of the Co-3+/4+ redox couple in the two compounds. (C) 1996 Academic Press, Inc.