Effect of Phase Transition in Roasting on the Concentration Behavior of Cathode Materialsof Spent Lithium Ion Battery

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1 Paper ID 115 Effect of Phase Transition in Roasting on the Concentration Behavior of Cathode Materialsof Spent Lithium Ion Battery Toru ISHII 1, Naoya SANTO 1, Shuji OWADA 2*, Chiharu TOKORO 2* and Yoshitsugu MIYABAYASHI 3 1 Department of Earth, Resources and Environmental Engineering, Graduate School of Creative Science and Engineering, Waseda University, Japan 2 Faculty of Science and Engineering, Waseda University, Japan 3 JX Nippon Mining & Metals, Japan * Corresponding author, owadas@waseda.jp ABSTRACT Recently large amount of lithium-ion battery (LIB), which is used for hybrid and electric vehicles, has become discharged and the cathod materials, such as Co, Ni, Mn, and Li, should be recovered from them, in order to secure the stable supply. In this study, we applied roasting and physical separation technologies for concentrating the cathode materials and could concentrate them with high recovery. It was found that the concentration behavior was much influenced by the phase transition in the first stage roasting, and the paper describes the mechanism of phase transition and the concentration behavior. KEY WORDS: Lithium ion battery / Cathode material / Roasting / Physical concentration / Phase transition 1. INTRODUCTION Lithium-ion batteries (LIBs) are used in electric vehicles, because of their high power and energy density, low self-discharge rate and wide operating temperature range. In Japan, unit sales of LIBs increased from 450 million in 2001 to 1.31 billion in 2010 [1], which will increase as the demand of hybrid and electric vehicles become enlarged. In LIBs recycling, the technology which extracts the rare metals such as Co, Ni, Mn and Li from the leachate of cathode materials was already established, but the technology which concentrates such metals from spent LIBs for feeding the above extraction process has not been created in commercial plant level. In this research work, we tried to creat a new process of concentrating cathode materials from spent LIBs by combining roasting and physical separation methods utlizing phase transition of cathode materials in the roasting process. For concentrating cathode materials from spent automobile LIBs, the technologies applied were reported such as selective grinding [2], flotation [3], roasting [4] and leaching [5]. However, in order to extract valuable Co and Ni selectively, the removal of Al components is necessary, then, the possibility of using wet high magnetic separation was discussed. 2. SAMPLE AND EXPERIMENTAL 2.1 Sample The LIBs used in electric vehicles consisted of a cathode, an anode, a separater, an electrolyte and SUS case, and so on. The cathode was composed of an aluminam foil, pasted active materials (LiCo x Ni y Mn z O 2 (x+y+z=1))and the binder (PVDF) bonding them. The anode was composed of a copper foil, pasted active materials (graphite) and the same binder as mentioned above. The SUS case was SUS430F which showed ferromagnetism. The LIB cells (1.6 kg) used in this study were composed of a cathode (40 wt%), an anode(24 wt%), the amount of SUS case and some connecters (30 wt%) and a separater (6 wt%). 2.2 Experimental Proposed recycling flow to treat spent LIBs is shown in Fig Roasting and analysis of cathode and anode Spent LIBs were roasted by a furnace from room temperature to 900 in an air atmosphere with no temperature control. Before and after roasting LIBs were dismantled and separated manually into different parts, the cathode and anode were comminuted to fine particles (under 106 μm) by vibration rod mill (CMT, T1-100) for chemical analysis. Mineral composition of cathode, anode and magnetic products in mm particle fraction were identified by X-ray diffraction (XRD, Rigaku, RINT-ULTIMAⅢ). In order to estimate the ratio of Co bearing compounds in the sample (-32 m particle fraction) after roasting, X-ray absorption fine structure (XAFS), especially, X-ray absorption near edge structure (XANES) measurement was performed at Co K absorption edge. This measurement was performed at the beam line BL15 of SAGA-LS. Analysis software REX2000 Ver2.5 was used for pattern fitting to the spectrum of each Co bearing compounds (Co, LiCoO 2, CoO, Co 3 O 4 ). Resources Recycling 11

2 Fig. 1 Proposed recycling flow to treat spent LIBs In order to create the inside of LIBs in roasting in lab scale, the cathode was heated from 20 to 400, 600, 900 with a heating rate of 30 min -1 by tube furnace (YAMADA DENKI, T-740) in Ar atmosphere and XRD was carried out for each sample Crushing and sieving After roasting the LIBs were crushed by single shaft crusher (MTB-Recycling, BDR2000BN), which had 155 kw of motor power and 125 rpm of rotation speed. Crushed LIBs were classified by using ro-tap sieve vibrator (Yoshida seisakusho, 1038-A) into various particle fractions, and in order to determine the best cut size for concentrating cathode active materials in a fine size fractions, the sample in each particle fraction was analyzed by induced coupled plasma atomic emission spectroscopy (ICP-AES, SII, SPS7800). The SUS over 4 mm particle were analyzed by X-ray fluorescence (XRF, Rigaku, ZSX PrimusII)) Wet high gradient magnetic separation After roasting, crushing and sieving, LIB powders (-0.5 mm particle fraction) were separated into magnetic and non-magnetic products by wet high gradient magnetic separation (ERIZ MAGNETICS, HIW-L4). In the tests, pulp density was set at 5 wt%, magnetic flux density was changed at 500, 1000, 2000, 2500, 5000 and 7500 G in no matrix base. Magnetic products, which must be rich in Co, Ni, Mn and Fe, and non-magnetic products, probably rich in Cu, C and Al, were analyzed by ICP-AES. Scanning electron microscopy (SEM, JEOL, JSM-6360) combined with energy dispersive X-ray spectroscopy (EDX, OXFORD INSTRUMENTS, INCA X-Sight Model 7582) was used to observe Al element at cathode active materials surface in the magnetic products. 3. RESULTS AND DISCUSSION 3.1 Phase transition of cathode materials in roasting process Illustration of before and after roasting the LIBs is shown in Fig. 2. LIBs have four-layered structure, cathode, separator, anode and separator. Compared with the original LIBs, the anode composition was not changed, but the cathode got brittle and separator was burned off. XRD patterns of the cathode in spent LIBs before and after roasting are shown in Fig. 3. While Al and cathode active material LiMO 2 (M=Co, Ni, Mn) were detected in original cathode, LiAlO 2 and MnO were generated from LiMO 2 (M=Co, Ni, Mn) because of phase transition in the roasting. Metal phases of Co and Ni could be detected in magnetic products in mm particle fraction. XRD patterns of the cathode after roasting in tube furnace at 400, 600, 900 are shown in Fig. 4. LiAlO 2, MnO, Co and Ni were detected at each temperature, then, metal phases of Co and Ni, which existed as originally LiMO 2 (M=Co, Ni, Mn), were found to be transformed into the metal phases of Co and Ni. In order to clarify the mechanism of this phase transition, the phase of Co was identified by XANES spectrum pattern fitting. The ratio of Co bearing compounds in after roasting sample (-32 μm particle fraction) is shown in Table. 1. In this sample, Co element formed three phases, which were Co (38 mol%), CoO (46 mol%) and LiCoO 2 (16 mol%). Cathode active material LiCoO 2 was resolved into CoO at over 900 [6], transforming into Co reaction can be represented as follows: CoO + C = Co + CO (1) CoO + CO = Co + CO 2 (2) ΔG of these two reactions are slightly negative, then, CoO could become reduced to Co in a step-by-step manner due to the presence of anode active material C and the conductive agent, or CO gas generated by Resources Recycling 12

3 Table. 1 The ratio of Co bearing compounds after roasting Co CoO LiCoO 2 R mol% Fig. 3 XRD patterns: (a) cathode before roasting, (b) cathode after roasting, (c) magnetic product in mm particle fraction heating them. The similar reaction could be occurred also for Ni component. Fig. 2 Illustration of LIB: (a) before roasting, (b) after roasting 3.2 Effect of crushing and determining the best cut size Recovery of each element into fine size fractions by cut size is shown in Fig. 5 assuming that the screening can be applied, and separation efficiency of each compound to other elements by the cut size is shown in Fig. 6. The best cut size is discussed by these results in order for Ni component to be separated from SUS. Fig. 5 shows that Cu used in the anode and SUS of LIB case are concentrated in coarse particle fractions, while Mn, Ni, Co and Li as cathode active materials are concentrated in fine particle fractions. Al and Cu are concentrated in different particle fractions because Al foil got brittle but Cu foil did not as shown in Fig. 1. Cathode active materials, which should be recovered, were concentrated into fine particle fractions, then, these materials can be separated from Cu and SUS which Fig. 4 XRD patterns of the cathodes after roasting in a tube furnace at 400, 600, 900 concentrated into coarse particle fractions, by screening. Separation efficiency of Ni and Co to other elements were maximized at 0.5 mm as the cut size, and Fig.5 shows that Li, Mn, Ni, Co, Al, C can be recovered with the recovery of 87.6, 91.6, 90.2, 92.7, 46.5, 89.2 % into -0.5 mm particle fractions. Then, the best cut size could be determined as 0.5 mm. 3.3 Wet high gradient magnetic separation Recovery of each element by magnetic flux density is shown in Fig. 7, separation efficiency of each compound to other elements by magnetic flux density is shown in Fig. 8, SEM-EDX elemental mapping of each element in magnetic product are shown in Fig. 9. Ni and Co which exit as metal phases after roasting have a ferromagnetism, then, high recovery can be got at low magnetic flux densities such as 500 and 1000 G. As shown in Fig. 7, 30 % of Al was recovered at low magnetic flux density. As shown in Fig. 9, the adhesion of melted Al to the surface of cathode active materials was observed because melting point of Al (660 ) is lower the heating temperature (900 ) in roasting process. Thus, this mapping indicates that it is difficult to separate Al from Mn, Ni and Co by physical separation in this roasting condition. Recovery of Mn increases as magnetic flux density becomes high because MnO has paramagnetism. As shown in Fig. 8, changes in separation efficiency of Co and Ni are different from that of MnO because of the difference in the magnetism. This result indicates that it is possible to concentrate Co and Ni by applying low magnetic field, for example, wet magnetic separation Resources Recycling 13

4 Fig. 5 Recovery of each element by cut size Fig. 6 Separation efficiency of each compound to other elements by cut size Fig. 7 Recovery of each element by magnetic flux density (not high gradient). Recovery of C, which has diamagnetism, increases as magnetic flux density becomes high, because inside of the matrix in magnetic separator was filled with strongly magnetic particles as the increase of magnetic flux density, and Fig. 8 Separation efficiency of each compound to other elements by magnetic flux density C particles were entrapped by other magnetic particles one after another. Most of the Li component LiAlO 2 after roasting would be dissolved into water, probably with the ratio of approx. 70 %. Fig. 9 Elemental mapping of magnetic products by SEM-EDX Resources Recycling 14

5 4. CONCLUSION In this study, roasting and subsequent physical separations, such as crushing, screening and wet high gradient magnetic separation were conducted in order to concentrate the cathode materials, Li, Mn, Ni and Co from spent LIBs used in electric vehicles. The main results are as follows, 1) Because of phase transition in roasting process, elements of Mn, Li and Al were transformed into MnO and LiAlO 2, in addition, elements of Ni and Co were transformed into metal phase, which have ferromagnetism, in a step-by-step manner. 2) Since Cu used in anode and SUS of LIB case were concentrated in coarse particle fractions, while Li, Mn, Ni, and Co as cathode active materials were concentrated in fine particle fractions by crushing. Cathode active materials could be separated from Cu and SUS by an adequate screening, then, Li, Mn, Ni, Co, Al, C could be concentrated into -0.5 mm particle fractions with the recovery of 87.6, 91.6, 90.2, 92.7, 46.5, 89.2 %, respectively. 3) Wet high gradient magnetic separation for concentrating cathode active materials was carried out. It was found possible to concentrate Ni and Co, which have ferromagnetism, in the magnetic field of low flux density, but it was difficult to separate cathode active materials from Al because melted Al in the roasting process would be adhered to the surface of cathode active material particles. 4) Cathode materials of Li, Co, Ni, Mn, Al and C could be concentrated with the recovery of 23.2, 74.6, 81.8, 27.3, 13.9, 12.7 % from spent LIBs, respectively, by our proposed recycling flow. ACKNOWLEDGEMENTS The authors appreciate Japan Oil, Gas and Metals National Corporation (JOGMEC) for the financial support to our research work. REFERENCE [1] BATTERY ASSOSIATION OF JAPAN, Web site: May, 2013 [2] Shigeki KOYANAKA, Effect of Selective Grinding and Physical Separation for After Roasting Lithium Ion Batteries, Resources Processing, No.1, 2011, [3] Younghun KIM, Recovery of LiCoO2 from Wasted Lithium Ion Batteries by using Mineral Processing Technology, Resources Processing, Vol.51 No.1, 2004, 3-7 [4] Li Li, Ascorbic-acid-assisted recovery of cobalt and lithium from spent Li-ion batteries, Journal of Power Sources, 218, 2012, [5] Valentina Innocenzi, Separation of manganese, zinc and nickel from leaching solution of nickel-metal hydride spent batteries by solvent extraction, Hydrometallurgy, 2012, [6] Antolini Ferretti, Synthesis and Thermal Stability of LiCoO 2, Journal of Solid State Chemistry 117 (1), 1995, 1-7 Resources Recycling 15