Journal of Power Sources 185 (2008) 549–553 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Electrodeposition of cobalt from spent Li-ion battery cathodes by the electrochemistry quartz crystal microbalance technique E.M. Garcia a , J.S. Santos b , E.C. Pereira b , M.B.J.G. Freitas a,∗ a Universidade Federal do Espírito Santo, Av. Fernando Ferrari 514, Goiabeiras, Vitória, ES, CEP 29075-910, Brazil b Universidade Federal de São Carlos, Rod. Washington Luís (SP-310), Km 235, São Carlos, SP, CEP 13565-905, Brazil article info Article history: Received 14 May 2008 Received in revised form 5 July 2008 Accepted 7 July 2008 Available online 17 July 2008 Keywords: Cobalt Cobalt electrodeposition Li-ion batteries Recycling abstract Information about the cobalt electrodeposition mechanism at different pH values was obtained using an electrochemistry quartz crystal microbalance (EQCM) technique as well as potentiodynamic and potentio- static techniques. Potentiodynamic and potentiostatic electrodeposition of ionic cobalt at pH 5.40 occurs via a direct reduction mechanism. The mass/charge relation was found to be 33.00 g mol -1 . At pH 2.70, electrodeposition under potentiodynamic conditions occurs via a mechanism of cobalt reduction with the formation of adsorbed hydrogen. Potentiostatic analysis verified that cobalt reduction occurs simultane- ously via direct reduction and with the formation of adsorbed hydrogen. The ratio mass/charge (M/z) is 13.00 g mol -1 for potentiodynamic conditions and 26.00 g mol -1 for potentiostatic conditions and poten- tiodynamic conditions. The cobalt electrodissolution occurs directly to Co 2+ in pH 2.7 and through of the intermediary Co + that is oxidized to Co 2+ in pH 5.4. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Li-ion batteries were brought onto the consumer market by Sony Corp. in the early 1990s [1]. Desirable characteristics, such as high energy density, low auto-discharge rate, and high potential dif- ference, made these batteries preferable to the typical Ni–Cd and Ni–MH batteries for many applications. Moreover, Li-ion batter- ies are less harmful to the environment. For Li-ion batteries, the main materials used are LiCoO 2 in the cathode and carbon in the anode [2]. High potentials obtained with these batteries (approxi- mately 3.70 V) 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 bat- teries 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 $54 per kilogram between 2003 and 2004 [4]. Li-ion bat- tery recycling is of great importance for environmental protection; ∗ Corresponding author. Tel.: +55 27 33352486; fax: +55 27 33352460. E-mail address: marcosbj@hotmail.com (M.B.J.G. Freitas). however, economic factors should also be considered. In the USA, Japan, France, Germany, and Sweden, battery recycling is a success- ful practice. For these regions it is useful to study the established recycling processes of Li-ion batteries [5]. The spent batteries can be recycled by pyrometallurgical or hydrometallurgical processes. The pyrometallurgical process is not desirable due to the emission of toxic gases into the environment. The hydrometallurgical process is thus more favorable from an environment conservation viewpoint. In the hydrometallurgical process, after battery dismantling occurs, the electrodes are dissolved in concentrated acids. After this stage, the resultant solution, which contains metal ions, can be recovered in one of three forms: precipitation, extraction, or electrodeposi- tion. Electrochemical recycling is a viable process to produce cobalt metallic films, alloys, and multilayer deposits with controlled struc- ture and morphology. For this reason, part of cobalt electrochemical recycling is the study of its electrodeposition mechanism. In order to study electrochemical recycling, it is necessary to analyze the mechanism of cobalt electrodeposition at different solution pH. The production of metallic cobalt is accomplished predomi- nantly via electrodeposition in an aqueous solution [6]. It has been suggested that cobalt electrodeposition at pH < 4.00 occurs together with a hydrogen detachment reaction [6–12]. During this electrodeposition, a rich hydrogen phase can be adsorbed in the deposits, as represented by Eqs. (1)–(4): Co (aq) 2+ + 2e - → Co (s) ; (1) H (aq) + + Co (s) + e - → CoH (ads) ; (2) 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.07.011