Recycle and synthesis of LiCoO₂ from incisors bound of Li-ion batteries

LIU Yun-jian(刘云建), HU Qi-yang(胡启阳), LI Xin-hai(李新海),

WANG Zhi-xing(王志兴), GUO Hua-jun(郭华军)

School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China

Received 19 October 2005; accepted 23 February 2006

Abstract：A new LiCoO₂ recovery technology of Li-ion battery was studied. LiCoO₂ was initially separated from the Al foil with dimethyl acetamide(DMAC), and then the polyvinylidene fluoride(PVDF) and carbon powders in the active material were eliminated by high temperature calcining. The content of the elements in the recovered powder was analyzed. The structure and morphology of the resulted samples were observed by XRD and SEM. Then the Li₂CO₃ was added in the recycled powder to adjust the Li/Co molar ratio to 1. The new LiCoO₂ was synthesized by calcining at 850 ℃ for 12 h in air. The well-crystallized single phase LiCoO₂ without Co₃O₄ phase was obtained. The recycle-synthesized LiCoO₂ powders have good characteristics as a cathode active material in terms of charge-discharge capacity and cycling performance.

Key words：Li-ion battery; direct recovery; LiCoO₂; synthesis; electrochemical performance

Since the Sony Energytec unveiled the first commercial Li-ion cell[1], the Li-ion battery has become the most attractive energy source for portable electronic products, such as mobile phone, notebook computers. The market for Li-ion battery has expanded rapidly because of the increase in demand for mobile electronics. It is reported that the total sales of the cell in 2002 have reached 6.5 billion dollars, and are expected to be more than 10 billion dollars in 2005[2]. The layered LiCoO₂ is used most for commercial products at present. It demands large amount of Co to meet the market. It is very important to recycle the Co in the Li-ion battery, because Co is a rare element, and is not friendly to environment. The spent Li-ion batteries and its incisors bound come out from the made process can give rise to the environmental poisoning. In other hand recycling the Co can also bring economical interests.

At present, many researchers have studied how to recycle the spent Li-ion batteries. It has been reported[3] that cobalt ions extracted from waste LiCoO₂ by using a nitric acid solution leaching, were potentostatically transformed into cobalt hydroxide on a titanium electrode and cobalt oxide was then obtained via a dehydration procedure. ZHANG et al[4] reported the recycle of the metal values such as cobalt and lithium from the spent Li-ion secondary batteries. LAIN[5] recycled metal values from the cell using AEA technology. They just recycled metal values from the waste batteries. But LEE et al[6] and CONTESTAILE et al[7] not only recycled the metal values but also prepared new LiCoO₂ just using the recycled metal values, and showed good results.

Many incisors bound of LiCoO₂ is produced in the process of Li-ion battery manufacturing. It is waste to discard the incisors bound. In this paper, a new LiCoO₂ recovery technology from the incisors bound of Li-ion battery is studied. After recycle process, there is little Co₃O₄ in the cycled LiCoO₂. The final LiCoO₂ powder is synthesized at high temperature with Li₂CO₃. The electrochemical performances of the synthesized LiCoO₂ has also been studied.

At first, a certain incisors bound of Li-ion battery was dipped in DMAC. Several hours later the aluminum foil was picked out. And then the solution was filtrated after several hours deposit. The cathode material without aluminum was gained after filtrating. Then the cathode material was heated at 120 ℃ in air for 12 h. The solvent DMAC was vaporized during the heating process. The powder was gained after milling. The dried powder was firstly heated at 450 ℃ in air for 2 h, then heated at 600 ℃ for 5 h. To prevent the agglomeration, the powder should be filled loosely. Then the recovered powder was gained after washing the heated powder several times with distilled water and drying at 80 ℃ for several hours. The structure of the recycled powders was identified with XRD technique. The content of the Co was analysed by titrating, and the element Li by atomic absorption spectrometry.

The recycled powders containing LiCoO₂, Co₃O₄ and Li₂CO₃ were used as starting materials. The ratio of Li/Co was adjusted to 1 by adding a certain amount of Li₂CO₃. The final LiCoO₂ was synthesized by calcaning at 850 ℃for 12 h in air, and cooled to the room temperature in a tube-furnace. The heat-treated products were ground in an agate mortar. The structure and morphology of the obtained samples were measured with XRD and SEM, respectively.

The powder X-ray diffraction (XRD, Rint-2000, Rigaku) using Cu K_α radiation was employed to identify the crystalline phase of the synthesized materials. The particle size and morphology of the LiCoO₂ powders were measured by scanning electron microscope (JEOL, JSM-5600LV) with an accelerating voltage of 20 kV.

The electrochemical characterization was performed using CR2025 coin-type cell. For cathode fabrication, the prepared powders were mixed with 10%(mass fraction) carbon black and 10% polyvinylidene fluoride in N-methyl pyrrolidinone to obtain slurry. And then, the blended slurries were pasted onto an aluminum current collector, and the electrode was dried at 100 ℃ for 12 h in vacuum. The test cell consisted of the cathode and lithium foil anode separated by a porous polypropylene film, cellgard 2 300 as the separator and 1 mol/L LiPF₆ in EC:EMC:DMC (1:1:1 in volume) as the electrolyte. The assembly of the cells was carried out in a dry Ar-filled glove box. The capacity measurements and cycling tests of the coin-type cells were carried out between 3.0 V and 4.2 V at 0.2C rate at 25 ℃.

The PVDF used in the cathode as the binder can be dissolved in organic solvent such as N-methyl pyrrolidinone(NMP), DMAC. The solubility of PVDF in the NMP or DMAC is about 10%. In this study DMAC was chosen as solvent in the experiment for the economic consideration. The solution will become more viscid when the PVDF is dissolved in the solvent DMAC. So the ratio of solid and solution should be controlled. The ratio was controlled between 1:4 and 1:5 in our experiment. The result shows that the incisors bound was easily dissolved in the solvent. The cathode material can be easily separated from the aluminum foil, and can be easily filtrated from the solvent. The boiling point of DMAC is 165 ℃, so DMAC can be evaporated by heating at 120 ℃ for 12 h. There are cathode material LiCoO₂, PVDF and carbon powders in the recycled powders.

The cathode of Li-ion battery is made up of the LiCoO₂, PVDF and carbon powders. So LiCoO₂ can be gained after eliminating PVDF and carbon powers.

The sample was heated at 450 ℃ for 2 h in our experiment. The heated and unheated samples were characterized by IR spectrum (Fig.1). In Fig.1(a) the organic compound can be found at the wavenumber of  2 910, 1 400 and 1 183  cm^-1 obviously in the unheated powders. But no organic compound exits in the heated powders as shown in Fig.1(b). So it can be concluded that PVDF is decomposed after heating at 450 ℃ for  2 h.

The XRD pattern of the recycled powders after heating is shown in Fig.2. The peaks of Co₃O₄ at 31.3?, 36.8? and CoO at 42.4? were observed. The pure LiCoO₂ added 5% PVDF and 5% carbon powder respectively were heated to identify the presence of Co₃O₄ and CoO. The two samples were tested with XRD (Fig.3). In Fig.3 the peaks of Co₃O₄ and CoO do not exit in the carbon added LiCoO₂ powders. But the peak of Co₃O₄ is observed in the sample added PVDF. So it can be concluded that the appearance of Co₃O₄ is due to PVDF addition.

Fig.1 IR spectra of samples

Fig.2 XRD pattern of heated sample

Fig.3 XRD patterns of LiCoO₂ reacting with carbon and PVDF

Because PVDF can give out HF when heating, HF reacts with LiCoO₂ to produce HCoO₂, and HCoO₂ is not steady at high temperature, it will decompose to Co₃O₄.

The carbon powder is easy to eliminate because it is very easy to oxidize by O₂ at high temperature such as 600℃ in air. So when the powder was heated at 600 ℃ for 5 h, the carbon powder should be eliminated.

The content of the elements in the recycled powders was analysed. The result is shown in Table 1. From Table 1, the contents of C and F are very low, and the Li/Co molar ratio is 0.914.

Table 1 Content of elements in recycled LiCoO₂                  (mass fraction, %)

Fig.4 shows the XRD pattern of the recovered sample after heating. In Fig.4 the peak of CoO appearing in Fig.2 disappears. This is because the CoO has been oxidized to Co₃O₄ by O₂ at high temperature. So there is only little Co₃O₄ in the recycled LiCoO₂ powders.

The final LiCoO₂ was obtained by adding a certain amount of Li₂CO₃ in the recycled LiCoO₂ and calcining

Fig.4 XRD pattern of recycled sample

at 850 ℃ for 12 h. The structure of HT-LiCoO₂ belongs to the trigonal system (space group R3m, O3 phase) with an ideal NaFeO₂ layered structure, in which Co and Li planes alternate in the ABCABC oxygen stacking[8]. Fig.5 shows the XRD pattern of the recycle-synthesized LiCoO₂. From Fig.5, we can see that the spinel phase of cobalt oxide, Co₃O₄, belonging to the space group Fd3m, disappears, because Co₃O₄ reacts with Li₂CO₃ at high temperature. After calcined at 850 ℃ for 12 h, the well-crystallized single phase LiCoO₂ can be obtained. The high intensity of the (003) peak and the clear splitting between the (006)/(012) and (018)/(110) peaks can be observed in Fig.5. The lattice parameters of the sample calcined at 850 ℃ for 12 h are a=2.817?, c=14.063 ? (c/a=4.992), which agrees with literature data for LiCoO₂[9].

Fig.5 XRD pattern of final LiCoO₂

Fig.6 shows the SEM photograph of LiCoO₂ obtained. The fine particles can be observed. The size of the recovered LiCoO₂ with homogenous distribution is 1-5 μm. The well-defined shape is observed for LiCoO₂ calcined at 850 ℃ for 12 h.

The coin-type cells were charge/discharged between 3.0 V and 4.2 V at 0.2C rate. The first charge-discharge curves for the recycle-synthesized LiCoO₂ are shown in Fig.7. The major potential plateau around 3.9 V is shown in both charge and discharge profiles. It is one of the typical properties for the layered LiCoO₂ phase, which corresponds to the reversible two-phase reactions in Li_1-xCoO₂ (0＜x＜1/4) in a topotactic manner[9-11]. Two smaller plateaus are also present at higher potentials, which correspond to the order/disorder phase transition arising at around x=0.5 in the HT-Li_1-xCoO₂ [12].

Fig.6 SEM of final LiCoO₂

Fig.7 First charge-discharge curves for recycle-synthesized LiCoO₂

The charge capacity in the first cycle is 161 mA?h/g, and the discharge capacity is 151mA?h/g. The discharge efficiency is 93.5%.

The cycle performance of the recycle-synthesized LiCoO₂ is shown in Fig.8. A capacity loss is observed in

Fig.8 Cycling performance of recycle-synthesized LiCoO₂

the first tenth cycles, and with the cycle number increasing, the capacity loss becomes smaller. After 30 cycles, the discharge capacity is still 141 mA?h/g, 6.3% fading compared with the values on the first discharge.

The technology of recycle and synthesis of LiCoO₂ from the incisors bound of Li-ion batteries was studied. The active material containing PVDF and carbon powder can be separated from the Al foil by using DMAC as impregnant. PVDF and carbon can be eliminated by heating at 450 ℃ and 600 ℃, respectively. At last, there is only little Co₃O₄ in the recycled LiCoO₂ powders.

The final LiCoO₂ is obtained by adding a certain amount of Li₂CO₃ in the recycled powders and calcining at 850 ℃ for 12 h in air. The first discharge capacity of the recycle-synthesized LiCoO₂ is 151 mA?h/g. After 30 cycles, the discharge capacity is still 141 mA?h/g, 6.3% fading compared with the first discharge capacity.

[1] BOK J S, LEE J H, LEE B K, KIM D P, RHO J S, YANG H S, HAN K S. Effects of synthetic conditions on electrochemical activity of LiCoO₂ prepared from recycled cobalt compounds [J]. Solid State Ionics, 2004, 169(1-4): 139-144.

[2] KIM J, KIM B, LEE J G, CHO J, PARK B. Differential voltage analyses of high-power, lithium-ion cells(1): Technique and application [J]. J Power Sources, 2005, 139(-2): 289-294.

[3] MYONG J, JUNG Y W, LEE J Y, YONGSUG T. Cobalt oxide preparation from waste LiCoO₂ by electrochemical–hydrothermal method [J]. J Power Sources, 2002, 112(2): 639-642.

[4] ZHANG P W, TOSHIRO Y, OSAMU I, SUZUKI T M, KATSUTOSHI I. Hydrometallurgical process for recovery of metal values from spent lithium-ion secondary batteries [J]. Hydro- metallurgy, 1998, 47 (2-3): 259-271.

[5] LAIN M J. Recycling of lithium ion cells and batteries [J]. J Power Sources, 2001, 97-98(1): 736-738.

[6] LEE C K, RHEE K I. Preparation of LiCoO₂ from spent lithium-ion batteries [J]. J Power Sources, 2002, 109(1): 17-21.

[7] CONTESTAILE M, PANERO S, SCROSATI B. A laboratory-scale lithium-ion battery recycling process [J]. J Power Sources, 2001, 92(1-2): 65-69.

[8] ERMETE A. LiCoO₂: formation, structure, lithium and oxygen nonstoichiometry, electrochemical behaviour and transport properties [J]. Solid State Ionics, 2004, 170(3-4): 159-171.

[9] AMATUCCI G G, TARASCON J M, KLEIN L C. CoO₂, the end member of the Li_xCoO₂ solid solution [J]. J Electrochem Soc, 1996, 143(4): 1114-1118.

[10] PAULSEN J M, MUELLER-NEUHAUS J R, DAHN J R. Layered LiCoO₂ with a different oxygen stacking (O₂ structure) as a cathode material for rechargeable lithium batteries [J]. J Electrochem Soc, 2000, 147(3): 508-516.

[11] OHZUKU T, UEDA A. Solid-state redox reactions of the LiCoO₂(R3m) for 4 volt secondary lithiun cell [J]. J Electrochem Soc, 1994, 141(10): 2972-2975.

[12] REIMIERS J N, DAHN J R. Electrochemical and in situ X-ray diffraction studies of lithium intercation in Li_xCoO₂ [J]. J Electrochem Soc, 1992, 139(7): 2091-2196.

(Edited by YUAN Sai-qian)

Corresponding author: LIU Yun-jian; Tel/Fax: +86-731-8836633; E-mail: lyjian122331@163.com