Preparation of LiCoO2 films from spent lithium-ion batteries by a combined recycling process

Hydrometallurgy 108 (2011) 220–225

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Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t

Preparation of LiCoO2 films from spent lithium-ion batteries by a combined recycling process Li Li a, b, Renjie Chen a, b,⁎, Feng Sun a, Feng Wu a, b,⁎, Jianrui Liu a a b

School of Chemical Engineering and the Environment, Beijing Key Laboratory of Environmental Science and Engineering, Beijing Institute of Technology, Beijing 100081, China National Development Center for High Technology Green Materials, Beijing 100081, China

a r t i c l e

i n f o

Article history: Received 16 February 2011 Received in revised form 22 April 2011 Accepted 26 April 2011 Available online 5 May 2011 Keywords: Spent lithium ion batteries Regeneration Electrochemical-deposition Lithium cobalt oxide

a b s t r a c t A new process is described for recovering and regenerating lithium cobalt oxide from spent lithium-ion batteries (LIBs) by a combination of dismantling, detachment with N-methylpyrrolidone (NMP), acid leaching and re-synthesis of LiCoO2 from the leach liquor as a cathode active material. The leach liquor, obtained from spent LIBs by using a nitric acid leaching solution, is used as electrolyte to regenerate LiCoO2 crystals on nickel plate at constant current in a single synthetic step using electrochemical deposition technology. The crystal structure and surface morphology of regenerated LiCoO2 were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. LiCoO2 phase with preferred (104) orientation was electro-deposited on nickel substrate at current density 1 mA cm − 2 for 20 h, and found to have good characteristics as a cathode active material in terms of charge and discharge capacity, and cycling performance. The particle size and layer thickness of the regenerated LiCoO2 crystalline powder were 0.5 μm and 0.2 mm, respectively. The initial charge and discharge capacity were 130.8 and 127.2 mAh g− 1, respectively. After 30 cycles, the capacity had decreased by less than 4% compared with the first cycle. This process involves simple equipment and could be feasible for recycling LIBs in large scale. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.

1. Introduction Since LIBs were first marketed by Sony in 1991, they have replaced Ni–Cd and Ni–MH batteries in many applications due to their high energy density, high voltage, very low self-discharge rate, safe handling and good cyclability (Freitas and Garcia, 2007). LIBs are extensively used in laptops, mobile phones, video cameras and other portable electronic devices, and the lithium battery market is increasing significantly. The worldwide consumption of LIBs in 2000 and 2004 was about 500 and 700 million cells, respectively, and their production is estimated to be 7.0 billion in 2015. The annual amount of spent LIBs, containing 5–15 wt.% Co and 2–7 wt.% Li, has been estimated at 200–500 MT (Lee and Rhee, 2003; Li et al., 2010; Paulino et al., 2008). The more LIB waste that is produced, the more attention should be focused on dealing with the waste in the coming years. Although LIBs have been progressively introduced into the consumer market, and are taking the place of the more polluting and less well-performing Ni–Cd batteries, LIBs have a limited life. When they reach the end of their practical life, they produce environmental pollutants; and therefore proper post-treatment of spent LIB materials is required ⁎ Corresponding authors at: School of Chemical Engineering and the Environment, Beijing Key Laboratory of Environmental Science and Engineering, Beijing Institute of Technology, Beijing 100081, China. Tel.: + 86 10 68912508; fax: + 86 10 68451429. E-mail address: [email protected] (R. Chen).

(Castillo et al., 2002; Contestabile et al., 1999; Lain, 2001). LIBs contain heavy metals, organic chemicals and some plastics. The metal residues are normally found at very high concentration levels, sometimes even higher than in natural ores. By analysis of the metal content of LIBs, it's found that valuable metals such as aluminum, cobalt, lead and lithium were the main species needed to be separated. (Dorella and Mansur, 2007). LiCoO2 is a favored material for LIB cathodes due to its good performance, and needs large amounts of Co to meet the market demand. Moreover, Co and Li are not only rare and precious metals, but are also toxic to the environment. From the viewpoint of environmental protection, the recycling of spent LIBs is highly desirable at present or in the future; in addition, it can bring economic benefits (Bernardes et al., 2004; Espinosa et al., 2004; Mantuano et al., 2006). The current status of the recycling process has been reviewed in several studies, and it is important that good recoveries are obtained during recycling of spent battery materials. Most of the proposed processes are based on hydrometallurgical chemistry and have been developed on a laboratory scale, mainly with the aim of recovering valuable metals from the cathode. Recycling plants and protocols are appearing in several developed countries, and we considered it to be important to devise an efficient collection system to receive and recycle spent LIBs worldwide (Contestabile et al., 2001; Li et al., 2009; Zhang et al., 1998). Unlike other batteries, LIBs often explode during the recycling process due to the vigorous oxidation of metallic lithium, which is formed on the graphite anode by overcharging and abnormal

0304-386X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2011.04.013

L. Li et al. / Hydrometallurgy 108 (2011) 220–225

deposition. There are two problems to be solved during recycling LIB waste: disposal of harmful waste and the prevention of explosions (Lee and Rhee, 2002). At the present time, two basic classes of recycling processes, physical and chemical, are used for the separation or recovery of cobalt, lithium and other components from spent LIBs (Xu et al., 2008). Recovery and separation of valuable metals were mainly achieved by the recycling process. Re-synthesis of electrode materials or synthesis of other reactive materials from the spent LIBs has also been studied in many investigations. A new hydrometallurgical process was proposed to obtain crystalline cobalt oxide from spent LIBs, through precipitation of cobalt as cobalt oxalate (Kang et al., 2009). A new combined recovery process comprising reductive leaching, chemical precipitation and solvent extraction has been proposed for obtaining valuable metals from spent LIBs (Kang et al., 2010). Electrochemical technology is used in the recycling process due to the low energy consumption, and safe and less recycling steps. A new process for recycling LIBs was developed, in which layered LiCoO2 phase was recovered and renovated in a single synthetic step using Etoile–Rebatt technology (Ra and Han, 2006). The recovered LiCoO2 exhibited significant electrochemical activity. It was reported that cobalt ions, extracted from waste LiCoO2 using a nitric acid leaching solution, were potentiostatically transformed into hydroxide on a titanium electrode, and cobalt oxide was then recovered via a dehydration procedure (Myoung et al., 2002). The aim of the present work was regeneration of LiCoO2 films on nickel plate, as cathode active materials, from leach liquor via electrochemical technology. The process has the advantages of low energy consumption and less recycling steps, and be feasible for recycling LIBs in large scale. 2. Experimental We recently successfully fabricated LiCoO2 films by an aqueous solution reaction combined with electrochemical–hydrothermal reactions. The following reaction pathway to LiCoO2 phase has been proposed (Tao et al., 2006, 2007):

221

−

HCoO2 →CoOOH þ e:

ð3Þ

The re-synthesis mechanisms of LiCoO2 are shown in Fig. 1. If we control the reaction conditions for electrochemical deposition, regeneration of LiCoO2 can be accomplished without any additional chemical impurities. After nitric acid leaching of waste LiCoO2 electrode, the pH = 11 was adjusted by adding fresh 4 M LiOH solution. Then electrolysis was performed under galvanostatic conditions with current density 1.0 mA cm− 2 at 100 °C for 20 h. In the 4 M LiOH solution the suspended Co(OH)2 was dissolved as HCoO2− ions, which migrated to the anode (nickel plate) in the electric field. As the consequence, while the concentration of HCoO2− ions reached saturation in the vicinity of the anode, the HCoO2− ions precipitated on the nickel plate as Co(OH)2. At the same time, one electron transfer from Co(OH)2 to the electrode, with the oxidation state of Co changing to +3, generated a thin film of CoOOH. In the highly concentrated LiOH solution Li+/H+ exchange occurred to give LiCoO2 due to its Gibbs energy being less than zero (Larcher et al., 1997): the reaction can be represented as: þ

þ

Li þ CoOOH→LiCoO2 þ H :

ð4Þ

2.1. Dismantling and preparation of the electrodeposition solutions Spent LIBs were dismantled to eliminate package, protection circuit module, etc. The recycling procedure, as schematized in the flow chart of Fig. 2, consists of six steps: dismantling, discharging, separation, detachment, leaching and recycling treatment. The unit cells were completely discharged for safety reasons, then anode, separator, electrolyte and cathode were separated. The discharge capacity for the positive electrode of the cell dismantled for recycling is about 91 mAh g − 1. Black pastes were separated from the cathode by applying ultrasonic energy together with NMP. The cathode active material was then obtained by combustion of carbon and residual binder at 800 °C for 2 h. The resulting LiCoO2 powder was leached at 80 °C for 1 h with 1 M HNO3 containing 1.0 vol.% H2O2 in a reactor, in which the initial S:L (Solid: Liquid) ratio was 20 g L − 1. 2.2. Preparation of LiCoO2 by electrochemical method

OH−

−

Liþ

CoðOHÞ2 ðsuspendingÞ → HCoO2 →CoOOH → LiCoO2 −

−

CoðOHÞ2 þ OH ⇔HCoO2 þ H2 O

ð1Þ ð2Þ

Preparation of LiCoO2 films was performed in a hermetically sealed 80 ml polytetrafluoroethylene vessel. The electrochemical deposition experiments were carried out with a nickel plate as the anode and

Fig. 1. Illustration of the re-synthesis mechanisms of LiCoO2.

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Fig. 2. Schematic of waste Li ion battery recycling steps using a combined recycling process.

platinum as cathode. The electrolyte was an alkaline solution composed of 20 ml leaching liquor, whose pH was adjusted to 11 with 30 ml LiOH solution. Fig. 3 shows schematically the apparatus used for the electrochemical deposition of LiCoO2 material from the leaching liquor. During the electrolysis process, the current was maintained at 1.0 mA/cm 2, the temperature was 100 °C and electrochemical reaction duration was 20 h. After preparation, the LiCoO2 samples were washed with doubly distilled water, then dried at 80 °C for 24 h.

Electrochemical properties of the samples were examined in CR2025 coin type cells. The cathode was regenerated LiCoO2 film and lithium foil was used as anode. The electrolyte was 1 M LiPF6/EC + DMC (1:1 by volume). The cells were assembled in an argon-filled glove box, then aged for 12 h before electrochemical cycling between 2.8 and 4.5 V (versus Li/Li+) using a CT2001A Land instrument. Cyclic voltammograms (CV) were obtained at 5 mV s − 1 with a CHI660a instrument. 3. Results and discussion

2.3. Material characterization 3.1. SEM micrographs and EDX analysis XRD analysis was carried out using a D Max-RD12Kw diffractometer with Cu Kα radiation. The scan data were collected in the 2θ range 10–90° at scan rate 1° min − 1. Scanning electron microscopy (SEM) was performed using a Quanta 600 instrument.

SEM micrographs of regenerated LiCoO2 crystals are shown in Fig. 4, which shows fine particles. The size of the regenerated, homogenously distributed LiCoO2 crystals is about 5 μm (from Fig. 4(b)). The grains

Galvanostatic current

Ni

Pt

Leaching liquor

Temperature sensor

PTFE vessel

Rotator

Oil bath

Fig. 3. Schematic of the recycling instrument using electrochemical deposition.

L. Li et al. / Hydrometallurgy 108 (2011) 220–225

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Fig. 5. EDX spectroscopy of regenerated LiCoO2 material.

3.2. Material structure analysis During the recycling of waste LiCoO2, the formation of a dark-gray layer was visually observed on the nickel plate. Fig. 6 shows the XRD pattern of the regenerated LiCoO2 material. By comparison with the Committee on Powder Diffraction Standards (JCPDS), the cathode material from spent LIBs consisted of LiCoO2, Co3O4 and carbon. The presence of Co3O4 is due to the LiCoO2 solid-state reaction that occurs during the charge–discharge cycles. The molar ratio of Li:Co becomes unbalanced and the characteristics are changed during the charge– discharge processes. The reaction that occurs can be represented by (Yamaki et al., 2003): Li0:5 CoO2 →0:5LiCoO2 +

1 1 Co O + O2 : 6 3 4 6

ð5Þ

(108)

(110)

(104) (101) (006)

20

(108) (110)

(104)

(101)

are closely integrated, with a large number of micropores between them. Spherical LiCoO2 particles grew in a laminar fashion and formed a compact film. The cross-sectional SEM image of LiCoO2 grown on a nickel substrate (Fig. 4(c)) shows that that the material was composed of small, well-defined grains growing in layers with thickness 0.2 mm. The regenerated LiCoO2 film electrode had the characteristics of a porous electrode. Fig. 5 shows EDX data for the recycled LiCoO2 crystals. It is apparent that the regenerated material was composed of Co, O and a small amount of carbon which is derived from the testing process. No other chemical elements were detected.

(003)

Fig. 4. SEM images of (a) surface (500×), (b) surface (10,000×), and (c) cross-section (400×) of the LiCoO2 electrode prepared at 1 mA cm− 2 and 100 °C, for 20 h.

Intensity

(003)

In the XRD pattern of recovered LiCoO2 (Fig. 6(b)) some peaks correspond to metallic Ni and others to LiCoO2. No other chemical component was detected. Apart from the Ni diffraction peaks (from the nickel plate), the (003), (101), (006), (104), (108) and (101) reflections from LiCoO2 were observed. The (104) peak had the highest intensity, indicating that the preferred orientation of LiCoO2 crystals is the (104) plane, which can be explained as follows. (1) The calculated a and c lattice parameters are 2.72 and 13.32 Å, respectively based on the (003) and (104) peak positions. The c/a ratio is 4.897, which is in good agreement with a reported value (4.991) for bulk

40

60

(b) --LiCoO2 --Co3O4 --C --Ni

(a) 80

2θ/ θ/° Fig. 6. X-ray diffraction patterns for (a) cathodic material after dismantling and calcination at 800 °C for 2 h; (b) LiCoO2 material regenerated using electrochemical technology.

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4.5

5.0

st

Spent LiCoO charge

1 cycle th 10 cycle th 20 cycle th 30 cycle

Spent LiCoO discharge

Regenerated LiCoO discharge

4.0

3.5

3.0

4.0

3.5 Capacity(mAhg-1)

Potential VS.Li/Li+(V)

Potential VS.Li/Li + (V)

Regenerated LiCoO charge

4.5

3.0

Charge Discharge

2.5

Cycle number

0

2.5 0

20

40

60

80

100

120

140

20

40

60

80

100

120

140

Capacity(mAhg-1)

160

Capacity(mAhg-1) Fig. 9. Cycling performance of regenerated LiCoO2 at 0.1 C rate. Fig. 7. Charge–discharge characteristics of the waste and regenerated LiCoO2 at 0.1 C rate.

material (Reimers and Dahn, 1992), proving a well-defined layered structure. (2) The atom arrangement of the Ni(111) plane is close to that of the LiCoO2 (104) plane and different from that of the (003) plane. Thus the preferred LiCoO2 (104) texture is presumably induced by the Ni(111) orientation (Xia and Lu, 2007).

3.3. Electrochemical properties Fig. 7 shows voltage versus capacity profiles for the used and regenerated LiCoO2 at 0.1 C rate. The charge potential plateau is reduced, and the discharge potential plateau is elevated by comparison with the used materials. The initial charge and discharge capacities were 130.8 and 127.1 mAh g − 1, respectively. The cyclic voltammograms (5 mV s − 1) of the LiCoO2 electrode, shown in Fig. 8, were used to investigate the redox behavior of the material. The anodic peak at 4.2 V corresponds to de-intercalation, and the cathodic peak at 3.7 V is associated with intercalation of Li ions into LiCoO2 on discharging. The cycle curves are in good coincidence, and the loss of capacity is small with increasing number of cycles. Fig. 9 shows after 30 cycles, the discharge capacity of the LiCoO2 electrode was 122.9 mAh g − 1 and the charge efficiency was 99.1%. Thus the regenerated LiCoO2 has good characteristics as a cathode active material in terms of cycling performance. 0.0008 st

1 cycle

0.0006

nd

2

cycle

Current(A)

0.0004 rd

3 cycle

0.0002 0.0000 -0.0002 -0.0004 3.2

3.4

3.6

3.8

4.0

4.2

4.4

Potential(V) Fig. 8. Cyclic voltammogram of LiCoO2 material at scan rate 5 mV s− 1.

4.6

4. Conclusions Spent LIBs potentially could be important raw materials such as lithium, cobalt, aluminum and copper, and also the environmental benefits are obvious in recycling spent LIBs. In this paper, using electrochemical technology the re-synthesized LiCoO2 film on nickel plate from leach liquor exhibited preferred (104) orientation. The regenerated LiCoO2 material had good electrochemical characteristics, with initial discharge capacity of 127.2 mAh g − 1 and charge efficiency of 97.2%. The regenerated material had good cycling performance. After 30 cycles, the discharge capacity decreased by less than 4% compared with the first cycle, and charge efficiency was 99.1%. The proposed recovery/regeneration process is simple, environmentally benign and adequate for the recovery of valuable metals from spent LIBs. Acknowledgment This work was financially supported by the National 973 Program (2009CB220106), Excellent Young Scholars Research Fund of BIT (2011CX04052), the National Natural Science Foundation of China (20803003) and New Century Educational Talents Plan of Chinese Education Ministry (NCET-10-0038). References Bernardes, A.M., Espinosa, D.C.R., Tenorio, J.A.S., 2004. Recycling of batteries: a review of current processes and technologies. J. Power Sources 130, 291–298. Castillo, S., Ansart, F., Laberty-Robert, C., et al., 2002. Advances in the recovering of spent lithium battery compounds. J. Power Sources 112, 247–254. Contestabile, M., Panero, S., Scrosati, B., 1999. A laboratory-scale lithium battery recycling process. J. Power Sources 83, 75–78. Contestabile, M., Panero, S., Scrosati, B., 2001. A laboratory-scale lithium-ion battery recycling process. J. Power Sources 92, 65–69. Dorella, G., Mansur, M.B., 2007. A study of the separation of cobalt from Li-ion battery residues. J. Power Sources 170, 210–215. Espinosa, D.C.R., Bernardes, A.M., Tenorio, J.A.S., 2004. An overview on the current processes for the recycling of batteries. J. Power Sources 135, 311–319. Freitas, M.B.J.G., Garcia, E.M., 2007. Electrochemical recycling of cobalt from cathodes of spent lithium-ion batteries. J. Power Sources 171, 953–959. Kang, J., Sohn, J., Chang, H., et al., 2009. Preparation of cobalt oxide from concentrated cathode material of spent lithium ion batteries by hydrometallurgical method. Adv. Powder Technol. doi:10.1016/j.apt.2009.10.015 Kang, J., Senanayake, G., Sohn, J., et al., 2010. Recovery of cobalt sulfate from spent lithium ion batteries by reductive leaching and solvent extraction with Cyanex 272. Hydrometallurgy 100, 168–171. Lain, M.J., 2001. Recycling of lithium cells and batteries. J. Power Sources 97–8, 736–738. Larcher, D., Polacin, M.R., Amatucci, G.G., et al., 1997. Electrochemically active LiCoO2 and LiNiO2 made by cationic exchange under hydrothermal conditions. J. Electrochem. Soc. 144, 408–417.

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