in the early 1990s [1].Desirable characteristics, such as high energy density, low auto-discharge rate, and high potential difference, made these batteries preferable to the typical Ni–Cd and Ni–MH batteries for many applications.
Moreover, Li-ion batteries are less harmful to the environment. For Li-ion batteries, the main materials used are LiCoO2 in the cathode and carbon in the anode [2]. High potentials obtained with these batteries (approximately 3.70V) hinder the utilization of aqueous electrolytes so that a mixture of lithium organic solvents and inorganic salts is usually required.
Li-ion battery production has been continually increasing since the 1990s, accompanying the consumption growth of portable devices (e.g., cellular phones, microcomputers, and toys). World production of Li-ion batteries increased from 250 to 700 million units between 1998 and 2004 [3]. Residues generated by Li-ion batteries remained at 200–500 tons year−1 from 2002 to 2006. Cobalt constitutes between 5 and 20% (m/m) of this residue,while lithium constitutes 2–5% (m/m) of it [3]. The price of cobalt increased from $15 to $54 per kilogram between 2003 and 2004 [4]. Li-ion battery recycling is of great importance for environmental protection;