Sustainable Recovery of Cathode Materials from Spent Lithium-Ion

Research Article pubs.acs.org/journal/ascecg

Sustainable Recovery of Cathode Materials from Spent Lithium-Ion Batteries Using Lactic Acid Leaching System Li Li,†,‡ Ersha Fan,† Yibiao Guan,§ Xiaoxiao Zhang,† Qing Xue,† Lei Wei,† Feng Wu,†,‡ and Renjie Chen*,†,‡ †

Beijing Key Laboratory of Environmental Science and Engineering, School of Materials Science and Engineering, Beijing Institute of Technology, No. 5 South Zhongguancun Street, Beijing 100081, China ‡ Collaborative Innovation Center of Electric Vehicles in Beijing, No. 5 South Zhongguancun Street, Beijing 100081, China § State Key Laboratory of Operation and Control of Renewable Energy & Storage Systems, China Electric Power Research Institute, Haidian District, Beijing 100192, China ABSTRACT: An environmentally friendly leaching process for recycling valuable metals from spent lithium-ion batteries is developed. A sol−gel method is utilized to resynthesize LiNi1/3Co1/3Mn1/3O2 from the leachate. Lactic acid is chosen as a leaching and chelating agent. The leaching efficiency is investigated by determining the contents of metal elements such as Li, Ni, Co, and Mn in the leachate using inductively coupled plasma optical emission spectroscopy. The spent cathode materials for the pretreatment process and the regenerated and freshly synthesized materials are examined using X-ray diffraction and scanning electronic microscopy. The results show that the leaching efficiencies of Li, Ni, Co, and Mn reached 97.7, 98.2, 98.9, and 98.4%, respectively. The optimum conditions are lactic acid concentration of 1.5 mol L−1, solid/liquid ratio of 20 g L−1, leaching temperature of 70 °C, H2O2 content of 0.5 vol %, and reaction time of 20 min. The leaching kinetics of cathode scrap in lactic acid fit well to the Avrami equation. Electrochemical analysis indicate that the regenerated LiNi1/3Co1/3Mn1/3O2 cathode materials deliver a highly reversible discharge capacity, 138.2 mA h g−1, at 0.5 C after 100 cycles, with a capacity retention of 96%, comparable to those of freshly synthesized LiNi1/3Co1/3Mn1/3O2 cathodes. KEYWORDS: Spent lithium-ion batteries, Lactic acid, Recovery, Kinetic analysis

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INTRODUCTION Lithium-ion batteries (LIBs), which were first produced commercially by Sony in 1991, are widely used as electrochemical power sources in electronic equipment and electric vehicles due to their high energy density, long cycling life, and low self-discharge rate.1−4 Worldwide production of LIBs reached about 500 million cells in 2000, and annual production increased by 800% between 2000 and 2010.5 Recently, the development of the electric vehicle industry has stimulated growth in LIB use. It is estimated that the quantity and weight of discarded LIBs in 2020 will exceed 25 billion units and 500 thousand tons, respectively.5 Recycling of the valuable metals in spent LIBs is therefore imperative for at least two important reasons: (1) Governments will enforce recycling of spent LIBs for environmental protection. (2) Recovery of valuable materials, particularly those that have limited sources, is necessary.6−8 Recently, much research has focused on the use of alternatives to LiCoO2 as the cathode material because of its high cost and poor safety. New cathode materials such as LiFePO4, LiNi1/3Co1/3Mn1/3O2, LiNi0.8Co0.15Al0.05O2, and LiMn2O4 have been developed, which use cheap transition © 2017 American Chemical Society

metals such as Ni, Mn, and Fe as complete or partial substitutes for Co.9 A survey of the battery market in 2012 showed that cathode materials used commercially are accounted for as follows: LiCoO2, 37.20%, LiNi1/3Co1/3Mn1/3O2, 29.00%, LiMn2O4, 21.40%, LiNiO2, 7.20%, and LiFePO4, 5.20%.10 Because of the rapid development of ternary materials, the market share of LiNi1/3Co1/3Mn1/3O2 is increasing annually. Much research has been performed on recycling waste LIBs with LiCoO2 as the cathode material. We have developed a novel approach to reusing valuable metals from spent LiNi1/3Co1/3Mn1/3O2. LIBs are currently recycled using methods based on pyrometallurgy,11,12 hydro-metallurgy,13 and biometallurgy.14,15 Pyro-metallurgical processes are often associated with hazardous gas emissions.16 Because of the long treatment period and difficulty of growing bacteria, biohydrometallurgical processes have gradually been replaced by hydrometallurgical methods.14 Hydrometallurgical processes are widely used in industry to Received: February 24, 2017 Revised: April 13, 2017 Published: May 4, 2017 5224

DOI: 10.1021/acssuschemeng.7b00571 ACS Sustainable Chem. Eng. 2017, 5, 5224−5233

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. Flowsheet of recycling and regeneration process. distilled water to a specified concentration. A low-concentration NaOH solution was used to dissolve Al foil to enable its separation from the cathode material. HNO3 was used to leach the spent cathode material completely so that the total contents of Ni, Co, Mn, and Li could be determined to calculate the leaching efficiency. Experimental Procedures. The spent LIBs were completely discharged by electrolyzing with saturated saline solution to avoid the potential dangers of short circuiting or self-ignition.39 A flowsheet of the process used for separation and regeneration of the cathode material is shown in Figure 1. The main procedures were as follows. Dismantling and Anode/Cathode Separation. The spent LIBs were manually dismantled to remove and recycle the plastic and steel cases. The anodes and cathodes were then separated, and the cathode foils were cut into small pieces with dimensions 1 cm × 1 cm. The copper foil in anode can be recycled after removing the spent carbon materials. Alkaline Leaching and Thermal Treatment. The cathode foils were immersed in NaOH solution at room temperature with simple stirring. The process can be expressed as follows:

separate and recycle metal ions because of their benefits such as high efficiency and less toxic emissions to the atmosphere.17 Among the hydrometallurgical techniques for recycling spent LIBs, acid leaching is the most cost-effective, simple, and environmentally friendly.18 The leaching of cathode materials from spent LIBs is usually performed using inorganic acids such as HCl,19−21 HNO3,22,23 H2SO4,10,24−26 H3PO4,27 and organic acids such as citric,13,28,29 DL-malic,30 ascorbic,4,13 succinic,18 oxalic,31,32 L-tartaric,33 and formic acids34 as leaching agents. The use of the inorganic strong acids results in release of Cl2, SO3, and NOx during leaching, and these are a threat to the environment and human health. In contrast to inorganic acids, organic acids are almost natural and easily degradable, and some organic acids can be used as reductant,4,13 precipitant,31,32,35 or chelating agent36 during the recovery process of the cathode materials. As for the leachate, most research is focused on the separation of different metals,31,32,34,35 and a few reports investigated the regeneration of new materials. In this work, we developed a new hydrometallurgical process that uses a natural organic acid for recycling spent LIBs. Lactic acid, widely distributed in nature and miscible with water, is chosen to be the leaching acid. Meanwhile, the industrial production of lactic acid is also a green process, mainly through fermentation. As a green platform compound, lactic acid aroused widespread concern in research.37,38 For example, Tang and Valix38 studied the use of lactic acid as a reagent to recover nickel and cobalt from limonite and nontronite ores. Here we established an acid leaching system using lactic acid and determined the optimum reaction conditions for recycling of spent LiNi1/3Co1/3Mn1/3O2 cathode materials. In contrast to conventional leachate treatments, the cathode material is resynthesized using a sol−gel method, without separation of metal ions.

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2Al + 2NaOH + 2H 2O → 2NaAlO2 + 3H 2

(1)

After washing with distilled water and filtration, the cathode active material and Al foil were effectively separated. Al ions in the filtrate were recycled and reused in the next study, and the residue was dried at 60 °C for 24 h. Impurities such as carbon and poly(vinylidene fluoride) (PVdF) binder were burnt off by calcining the cathode material at 610 °C for 5 h in a muffle furnace and cooling to room temperature. The waste gas can be collected and purified in a system, which consists of a cooler, a condensation chamber, activated carbon filters, and bag filters.28 After roasting and cooling, the obtained powder was ground using a planetary ball mill for 30 min to obtain smaller particles with larger surface areas to increase the dissolution rate and leaching efficiency. Lactic Acid Leaching. All the metal-leaching tests were performed in a 100 mL three-necked, round-bottomed, thermostatic Pyrex reactor. The reactor was placed in a water bath to maintain a constant reaction temperature. The reactor was equipped with a stirrer to accelerate the reaction and a condenser pipe to reduce water loss. A measured amount of powder was added to the reactor. A solution of lactic acid and H2O2 of known concentration was poured into the reactor, and the mixture was stirred at 300 rpm. The following

EXPERIMENTAL SECTION

Materials and Reagents. Spent LIBs were collected from the Shenzhen BAK Battery Co., Ltd. (Shenzhen, China). All reagents used were analytical-grade, and all solutions were prepared or diluted with 5225


Research Article

ACS Sustainable Chemistry & Engineering variables in the leaching process were investigated: lactic acid concentration (0.25−2 mol L−1), solid/liquid (S/L) ratio (10−40 g L−1), temperature (40−90 °C), H2O2 volume percentage (0−3 vol %), and reaction time (10−60 min). Regeneration and Fresh Synthesis of LiNi1/3Co1/3Mn1/3O2. The stoichiometric amounts of Li+, Ni2+, Co2+, and Mn2+ in the leachate were obtained together after acid leaching, and their molar ratios were adjusted to 3.05:1:1:1 by adding CH3COOLi·2H2O, (CH3COO)2Ni· 4H2O, (CH3COO)2Co·4H2O, and (CH3COO)2Mn·4H2O. The solution was stirred at room temperature for 0.5 h, and the pH was adjusted to 7 with NH3·H2O solution. The solution was heated at 80 °C with magnetic stirring until a transparent sol formed. The obtained gel was dried at 100 °C for 24 h, followed by heating at 450 °C for 5 h in a muffle furnace to remove the organic contents. The decomposed precursor were ground for 0.5 h and then calcined in air at 900 °C for 12 h. The final product, denoted by R-NCM, was obtained by grinding. For comparison, LiNi1/3Co1/3Mn1/3O2 was synthesized by the same method using stoichiometric amounts of CH3COOLi·2H2O, (CH3COO)2Ni·4H2O, (CH3COO)2Co·4H2O, and (CH3COO)2Mn· 4H2O. Lactic acid was used as a chelating agent. This product was denoted by F-NCM. Characterization. After leaching with lactic acid, the amounts of Li, Ni, Co, and Mn metals in the pink filtrate were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). The leaching efficiency is defined as the ratio of the amount of a component in the leachate to the total amount of that species in the original cathode powder.4 Thermogravimetric analysis and differential scanning calorimetry (TG/DSC; Netzsch STA 449F3) were utilized to determine the optimum temperature for calcination of the spent cathode material after alkaline leaching. The measurements were performed in an air flow at a heating rate of 10 °C min−1. Crystal structures were identified using X-ray diffraction (XRD; Rigaku Ultima IV-185). The surface configuration and particle size were examined using field-emission scanning electron microscopy (FESEM; FEI, Quanta 200f). The LIB electrode consisted of 80 wt % active materials, 10 wt % acetylene black, and 10 wt % PVdF. A slurry was smoothly cast on Al foil. The electrode was dried at 80 °C in a vacuum oven. The electrolyte was a 1 mol L−1 solution of LiPF6 in a mixture of equal volumes of ethyl carbonate, dimethyl carbonate, and diethyl carbonate. A 2025 coin cell was assembled in an Ar-filled glovebox, with Li metal as the anode. The electrochemical performance was examined using a Land battery tester (LAND-CT2001A) with a voltage window of 2.8− 4.3 V at selected rates from 0.2 to 5 C (1 C = 150 mA g−1). Electrochemical impedance spectroscopy (EIS) tests were performed on a CHI660d workstation in the frequency range from 0.1 MHz to 0.01 Hz.

Table 1. Weight-Loss Rate of Cathode Materials no.

temperature range (°C)

weight loss rate (%)

1 2

27−320 °C 320−610 °C

2.77 5.62

3

610−1000 °C

6.10

thermal decomposition process loss of bound water burning of acetylene black and decomposition of PVDF phase change of LiNi1/3Co1/3Mn1/3O2 and the loss of lithium

Figure 3. XRD patterns and SEM micrographs of (a) the cathode materials after treatment with NaOH from spent LIBs and (b) materials after heat treatment.

6.79%, respectively. Figure 2 and the data in Table 1 show the thermal behavior of the cathode material after alkaline leaching. There are three main weight-loss regions at 27−320, 320−610, and 610−1000 °C, respectively. The first weight-loss region, i.e., between 27 and 320 °C, arises from the loss of bound water (ca. 2.77 wt %). In the second weight-loss region, i.e., between 320 and 610 °C (ca. 5.62 wt %), there are two exothermic DSC peaks at 456 and 609 °C, which likely correspond to the pyrolysis of PVdF and burning of acetylene black, respectively. The optimum calcination temperature is therefore 610 °C. A phase change of LiNi1/3Co1/3Mn1/3O2 and loss of Li occur in the temperature range of 610−1000 °C (ca. 6.10 wt %). Figure 3 shows the XRD patterns and SEM images of the spent cathode material (a) after alkaline leaching and (b) after heat treatment. The XRD patterns clearly show the characteristic peaks of a layered structure. The differences between Figure 3a,b arise from impurities. The peak from conductive carbon cannot be seen in Figure 3b, indicating that the carbon was burnt off during calcination.28 MnO, which can be identified in Figure 3a, mainly comes from decomposition of the active materials when batteries are charged/discharged. Co3O4 and MnO2 are present in the calcined dust. This indicates that during heat treatment the PVdF binder decomposes to HF which leads to the decomposition of LiNi1/3Co1/3Mn1/3O2 and generation of impurities.40 The morphology of the spent cathode material was examined using SEM (Figure 3). The images show that small particles agglomerate and form larger active material particles because of the PVdF binder; acetylene black is also present in the unheated scrap materials (Figure 3a). In Figure 3b, the agglomeration degree is clearly lower, and the particle surfaces are smooth. The difference between Figure 3a,b is caused by the presence in the former case of floccules and acetylene black;

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RESULTS AND DISCUSSION Composition of the Cathode Active Material and Its Characterization. The Ni, Co, Mn, and Li contents of the cathode material were determined as 17.58, 17.68, 16.46, and

Figure 2. TG/DSC curves of the spent cathode materials. 5226


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ACS Sustainable Chemistry & Engineering Table 2. Experimental Results of the Orthogonal Design influencing factor

leaching rate (%)

no.

temperature (°C)

reaction time (min)

concentration (mol L−1)

H2O2 (vol %)

solid/liquid ratio (g L−1)

Li

Ni

Co

Mn

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

60 60 60 60 70 70 70 70 80 80 80 80 90 90 90 90

30 40 50 60 30 40 50 60 30 40 50 60 30 40 50 60

0.5 1 1.5 2 1 0.5 2 1.5 1.5 2 0.5 1 2 1.5 1 0.5

0.5 1 1.5 2 1.5 2 0.5 1 2 1.5 1 0.5 1 0.5 2 1.5

10 20 30 40 40 30 20 10 20 10 40 30 30 40 10 20

70.62 82.37 87.77 75.21 47.12 24.89 73.54 76.15 77.98 100 26.94 78.25 86.92 82.32 82.14 50.23

71.42 72.45 75.97 72.19 42.88 28.66 75.09 75.37 73.99 92.8 23.72 62.65 76.78 69.66 84.57 48.17

70.19 70.77 76.06 72.89 43.91 29.49 73.71 76.07 72.75 93.37 23.91 63.01 77.43 70.53 85.17 47.09

71.25 78.64 80.21 75.54 43.93 29.95 78.24 75.81 77.18 94.38 24.39 66.25 81.43 73.59 81.81 48.88

Table 3. Analysis Results of Orthogonal Experiments temperature

time

acid

H2O2

S/L ratio

K1 K2 K3 K4 extreme deviation

78.992 55.425 70.793 75.403

70.660 72.395 67.597 69.960

43.170 72.470 81.055 83.918

76.183 68.095 71.280 65.055

82.228 71.030 69.457 57.897

23.567

4.798

40.748

11.128

24.331

priority order

lactic acid concentration > solid/liquid ratio amount of H2O2 > time 73.007 66.268 42.992 69.705 55.500 65.892 65.638 62.080 63.290 64.838 73.748 64.955 69.795 64.595 79.215 64.852

effect factor

Li

Ni

K1 K2 K3 K4 extreme deviation priority order

17.507

1.673

36.223

7.625

effect factor

Co


> temperature > priority order 81.040 67.425 61.015 52.112

Mn

28.928


lactic acid concentration > solid/liquid ratio > temperature > priority order amount of H2O2 > time

temperature

time

acid

H2O2

S/L ratio

72.477 55.795 63.260 70.055

66.070 66.040 64.712 64.765

42.670 65.715 73.852 79.350

69.360 62.045 65.108 65.075

81.200 66.080 61.498 52.810

16.682

1.358

36.680

7.315

28.390

lactic acid concentration > solid/liquid ratio temperature > amount of H2O2 > time 76.410 68.448 43.617 72.333 56.983 69.140 67.657 65.067 65.550 66.162 76.697 66.850 71.428 66.620 82.398 66.120 19.427

2.978

38.781

7.266

> 80.813 70.735 64.460 54.363 26.450

lactic acid concentration > solid/liquid ratio > temperature > amount of H2O2 > time

36.51, and 37.16%, respectively, at a low lactic acid concentration, i.e., 0.25 mol L−1. The leaching efficiencies of the four metals increase rapidly with increasing lactic acid concentration from 0.25 to 1.0 mol L−1. Almost 98% of Ni, Co, and Mn and 93% of Li are leached at a lactic acid concentration of 1.0 mol L−1. As the concentration increases from 1.0 to 1.5 mol L−1, the Li-leaching efficiency increases to 96.73%, but those of the other metals change little. When the concentration is greater than 1.5 mol L−1, there is a small improvement in the efficiency. The optimum initial lactic acid concentration is therefore 1.5 mol L−1. Effect of S/L Ratio on Acid Leaching. Figure 4b shows the effect of the S/L ratio on the leaching efficiency under the conditions lactic acid concentration of 1.5 mol L−1, 0.5 vol % H2O2, temperature 60 °C, and leaching time 30 min. The leaching efficiencies of the four metals decrease slightly as S/L increases from 10 to 20 g L−1. However, the leaching efficiencies of Ni, Co, Mn, and Li decrease to 88.52, 88.4, 88.69, and 91.81%, respectively, at an S/L ratio of 40 g L−1. In terms of a high leaching efficiency, the best S/L ratios is 20 g L−1. Meanwhile, when the S/L ratio increases to 40 g L−1, the leaching efficiencies of metals are still higher than 80%, which is acceptable in the scale-up industry applications.

this shows that most of the PVdF and acetylene black was burned off during calcination. Acid Leaching. Order of Parameter Effects on Leaching Process. Orthogonal experiments were performed to determine the order of parameter effects on the leaching process. The results and analysis are shown in Tables 2 and 3. The presence of Ni, Co, Mn, and Li in the solution indicates that LiNi1/3Co1/3Mn1/3O2 reacts with lactic acid (Table 2). The concentrations of these metals in solution frequently change depending on the conditions; this indicates that the five conditions jointly influence the leaching efficiency. The obtained results (Table 3) show that the conditions affect the leaching process in the order lactic acid concentration, S/L ratio, temperature, amount of H2O2, and leaching time. Use of Single Variable to Explore Optimum Conditions for Leaching Process. Effect of Lactic Acid Concentration on Acid Leaching. The orthogonal experimental results show that the concentration of lactic acid significantly affects the leaching process. The concentration of lactic acid was varied from 0.25 to 2.0 mol L−1 at 60 °C, with an S/L ratio of 15 g L−1, a reductant concentration of 0.5 vol % H2O2, and a leaching time of 30 min. Figure 4a shows that the leaching efficiencies of Ni, Co, Mn, and Li are 38.81, 39.13, 5227


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Figure 4. Effect on leaching efficiency of (a) initial acid concentration, (b) solid/liquid ratio, (c) temperature, (d) amount of H2O2, (e) reaction time, and (f) metal leaching efficiencies under optimized conditions.

Effect of Temperature on Acid Leaching. We also investigated the effect of temperature on the efficiency of waste LiNi1/3Co1/3Mn1/3O2 leaching. The temperature varied from 40 to 90 °C; the other conditions were lactic acid concentration of 1.5 mol L−1, 0.5 vol % H2O2, S/L ratio of 20 g L−1, and leaching time of 30 min. Figure 4c shows that almost 67% of Ni, Co, and Mn and 69.6% of Li can be leached at 40 °C. The leaching efficiencies increase rapidly to 90% at 50 °C. More than 96.7% of Li, Ni, Co, and Mn is leached at 70 °C. A plateau is observed above 70 °C. A temperature of 70 °C is therefore suitable for the leaching process. Effect of Amount of H2O2 on Acid Leaching. Figure 4d shows the effect of the volume concentration of H2O2 (vol %) on leaching for a leaching time of 30 min at 70 °C. Only about 33.22% of Ni, 33.63% of Co, 30.72% of Mn, and 59.34% of Li are leached without the addition of H2O2. The leaching efficiencies of Ni, Co, Mn, and Li increase to 96.27, 96.73, 96.32, and 96.84%, respectively, with increasing H 2 O 2 concentration from 0 to 0.5 vol %. However, the leaching

efficiencies of the metals are almost constant at H 2 O2 concentrations from 0.5 to 3 vol %. This confirms that a low volume concentration of H2O2 (0.5 vol %) is sufficient for the leaching process. Effect of Leaching Time on Acid Leaching. The effect of the reaction time on the leaching efficiency was investigated from 10 to 60 min under the following conditions: lactic acid concentration of 1.5 mol L−1, S/L ratio of 20 g L−1, 0.5 vol % H2O2, and temperature 70 °C. The leaching efficiencies of the different metals rapidly reach more than 95% at 10 min (Figure 4e). At 20 min, the total efficiencies are about 98%. Extending the time from 20 to 60 min does not improve the efficiencies, which indicates that acid leaching reaches its reaction equilibrium within 20 min. Kinetic Analysis of LiNi1/3Co1/3Mn1/3O2 Leaching with Lactic Acid. Multimetal leaching in acid solution was investigated by performing kinetic studies for different leaching times (0−30 min) and temperatures (40−80 °C) under the following conditions: lactic acid concentration of 1.5 mol L−1, 5228


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Figure 5. Effects of reaction temperature and time on the leaching rates of Li (a), Ni (b), Co (c), and Mn (d) (1.5 mol L−1, 0.5 vol % H2O2, S/L ratio of 20 g L−1).

Figure 6. Plots of ln(−ln(1 − x)) vs ln t at different reaction temperatures: Li (a), Ni (b), Co (c), and Mn (d).

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ACS Sustainable Chemistry & Engineering Table 4. Parameters of the Kinetics Model for Li, Ni, Co, and Mn at Different Leaching Temperatures Li

Ni

Co

Mn

T (°C)

n

ln k

R2

n

ln k

R2

n

ln k

R2

n

ln k

R2

40 50 60 70 80

0.8094 0.8486 0.6319 0.6251 0.7740

−2.6843 −2.1250 −0.8647 −0.4704 −0.1087

0.9746 0.9918 0.9876 0.9671 0.9606

0.8710 0.8785 0.6307 0.6683 0.7648

−2.9053 −2.2392 −0.9188 −0.5934 −0.2698

0.9903 0.9872 0.9649 0.9687 0.9893

0.8559 0.8742 0.6356 0.6362 0.7593

−2.8480 −2.2178 −0.9254 −0.5452 −0.2873

0.9887 0.9881 0.9701 0.9761 0.9702

0.9464 0.9138 0.6136 0.6666 0.7145

−3.1152 −2.3130 −0.8226 −0.5419 −0.1857

0.9955 0.9920 0.9873 0.9693 0.9609

Figure 9. XRD and SEM patterns of R-NCM (a) and F-NCM (b) samples.

core models. The Avrami equation is therefore used to explain the leaching kinetics:

Figure 7. Arrhenius plots for the leaching of Li, Ni, Co, and Mn in the temperature range 313.15−353.15K.

ln[− ln(1 − x)] = ln k + n ln t −1

S/L ratio of 20 g L , and 0.5 vol % H2O2. The results are shown in Figure 5. The optimum leaching conditions identified in the kinetic studies are in agreement with those already obtained (Figure 4). Metal leaching from the cathode materials is a solid−liquid heterogeneous reaction and is considered to occur on the outer surfaces of unreacted particles. Multimetal leaching kinetics has been successfully interpreted on the basis of shrinking-core models and the Avrami equation.41−43 However, the metal extraction data shown in Figure 5 do not fit various shrinking-

(2)

where x is the fraction reacted (i.e., leaching rate), k is the reaction rate constant (min−1), n is a suitable parameter, and t is the reaction time (min). Fitting plots of ln[−ln(1 − x)] versus ln t at different temperatures for different metals, based on the data in Figure 5, are shown in Figure 6. The plots show good linear relationships for Li, Ni, Co, and Mn with R2 values all greater than 0.96 (Table 4). This shows that the Avrami equation describes well the leaching process under the given leaching conditions. The values of n are calculated to be 0.5−1. This indicates that the initial reaction rate is high and

Figure 8. Possible products and mechanism in the lactic acid leaching process. 5230


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Figure 10. Electrochemical performances of R-NCM and F-NCM samples: (a−c) cycling performances at 0.2 C, 0.5 C, and 1 C, (d) rate performances at different currents, (e) charge/discharge profiles at 0.2 C, and (f) Nyquist plots in the frequency range of 100 kHz to 0.01 Hz.

Mechanism of Acid Leaching. Lactic acid (C3H6O3) is an αhydroxy acid and contains a carboxyl group adjacent to a hydroxyl group. The presence of an α-hydroxyl group increases the acidity compared with that of an average monobasic acid. The pKa of lactic acid is 3.86. The possible products and mechanism of the reaction of LiNi1/3Co1/3Mn1/3O2 with lactic acid are shown in Figure 8. This reaction occurs at the liquid− solid interfaces, and the reaction rate is influenced by the acid concentration, S/L ratio, amount of reductant, reaction temperature, and reaction time. This leaching reaction is mainly controlled by the chemical reaction, and the leaching reaction between LiNi1/3Co1/3Mn1/3O2 and lactic acid is a multiphase reaction, which can be explained in two steps: (1) conversion of high valence Ni, Co, and Mn to Ni2+, Co2+, and Mn2+ in the presence of H2O2 and subsequent dissolution of spent LiNi1/3Co1/3Mn1/3O2 in the acid solution and (2) the chelation of Ni2+, Co2+, Mn2+, and Li+ with lactate. The leaching reaction can be represented as

continually decreases with time until the reaction reaches equilibrium.42 The Arrhenius equation is used to describe the relationship between reaction rate constant and the reaction temperature:

k = A e−Ea / RT

(3)

where k is the reaction rate constant (min−1), A is the preexponential factor, Ea is the apparent activation energy (kJ/ mol), R is the universal gas constant (8.314 J/K/mol), and T is the absolute temperature (K). The activation energies of the leaching reactions are usually calculated by the linear form of the Arrhenius equation. ln k = ln A −

Ea RT

(4)

Plots of ln k (see in Table 4) versus 1/T are shown in Figure 7, and the activation energies for the leaching of Li, Ni, Co, and Mn are 62.81, 63.96, 62.83, and 70.62 kJ/mol, respectively, indicating that the rate-controlling step of this leaching process is the surface chemical reactions. 5231


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important effects on the leaching efficiencies of the four metals. More than 98% of Ni, Co, Mn, and Li can be leached from spent LiNi1/3Co1/3Mn1/3O2 under the optimum leaching conditions: 1.5 mol L−1 lactic acid, 0.5 vol % H2O2, a relatively low temperature of 70 °C, an S/L ratio of 20 g L−1, and a short time of 20 min. The leaching kinetics of Li, Ni, Co, and Mn can be explained by the Avrami equation. The leaching mechanism was investigated in terms of the material structure. The regenerated cathode material has a high specific capacity, good rate capability, and excellent cycling performance compared with those of freshly synthesized LiNi1/3Co1/3Mn1/3O2. More importantly, lactic acid has proved an effective chelating agent for the sol−gel method. This closed-loop recycling process for regenerating spent LIB cathode material for LIBs will enable conservation and recycling of resources.

3LiNi1/3Co1/3Mn1/3O2 (s) + 9C3H6O3(aq) + 1/2H 2O2 → 3C3H5O3Li(aq) + (C3H5O3)2 Ni(aq) + (C3H5O3)2 Co(aq) + (C3H5O3)2 Mn(aq) + 5H 2O(l) + O2 (g)

(5)

Characterization and Electrochemical Performance of Regenerated LiNi1/3Mn1/3Co1/3O2. Figure 9 shows XRD patterns and SEM images of the regenerated LiNi1/3Co1/3Mn1/3O2 (R-NCM) and freshly synthesized LiNi1/3Co1/3Mn1/3O2 (F-NCM) samples. All peaks can be indexed to the hexagonal α-NaFeO2 structure, with the space group R3̅m. The distinct splits of (006)/(012) and (008)/ (110) peaks indicate the formation of a well-layered structure. The ratio of the intensities of the (003) and (104) peaks is greater than 1.2, and c/a is high, indicating low cation mixing and good ordering of the transition metal ions in the metal layer. The SEM images clearly show that both samples have a uniform particle size (100−300 nm). Generally, small particles make Li insertion/extraction easy because of decreased Li+ diffusion. The surface area of LiNi1/3Co1/3Mn1/3O2 synthesized using a sol−gel method is large, which improves the electrochemical performance. The regenerated material disperses well without addition of a chelating agent. The cycling performances of R-NCM and F-NCM at 0.2 C, 0.5 C, and 1 C are shown in Figure 10a−c. The reversible discharge capacity of R-NCM is 142.6 mA h g−1 at 0.2 C after 70 cycles, 138.2 mA h g−1 at 0.5 C after 100 cycles, and 128.3 mA h g−1 at 1 C after 100 cycles. F-NCM achieves 136.8 mA h g−1 at 0.2 C after 70 cycles, 125.4 mA h g−1 at 0.5 C after 100 cycles, and 109.8 mA h g−1 at 1 C after 100 cycles. The regenerated LiNi1/3Mn1/3Co1/3O2 clearly gives a higher discharge capacity and has the highest capacity retention (95.2% at 0.2 C, 96.0% at 0.5 C, and 94.5% at 1 C) under the same conditions. The rate capacities of the samples were investigated by charging the cells at 0.2 C and discharging them at various current rates (0.2−5 C), as shown in Figure 10d. The discharge capacities of R-NCM are 151.6, 145.7, 138.3, 129.7, and 120.6 mA h g−1 at 0.2 C, 0.5 C, 1 C, 2 C, and 5 C, respectively. After cycling at 5 C, the discharge capacity recovers to 148 mA h g−1, indicating that the regenerated material has a superior rate capability. The electrochemical reactions of the samples were further investigated based on the charge/discharge profiles for different cycles and EIS tests (Figure 10e,f). The plateaus of the charge/discharge curves occur at around 3.8 V. Long charge/discharge curve plateaus improve the electrode stability and reversibility. Figure 10f shows that the charge-transfer resistance of R-NCM (Rct = 58.78 Ω) is lower than that of F-NCM (Rct = 70.02 Ω), which indicates better Li intercalation/deintercalation kinetic properties. This is because the ratio of the intensities of the (003) and (104) peaks of R-NCM (I003/I104 = 1.469) is greater than that of F-NCM (I003/I104 = 1.415), indicating low cation mixing and good ordering of the transition metal ions in the metal layer in R-NCM. Meanwhile, Al or Mg compounds are usually doped or coated in commercial NCM cathode.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Renjie Chen: 0000-0002-7001-2926 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The experimental work of this study was supported by the Chinese National 973 Program (2015CB251106), the Joint Funds of the National Natural Science Foundation of China (U1564206), and the Major achievements Transformation Project for Central University in Beijing and Beijing Science and Technology Project (D151100003015001).

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REFERENCES

(1) Armand, M.; Tarascon, J. M. Building better batteries. Nature 2008, 451, 652−657. (2) Evarts, E. C. Lithium Batteries: To the Limits of Lithium. Nature 2015, 526, S93−S95. (3) Xu, Y.; Dong, Y.; Han, X.; Wang, X.; Wang, Y.; Jiao, L.; Yuan, H. Application for Simply Recovered LiCoO2 Material as a HighPerformance Candidate for Supercapacitor in Aqueous System. ACS Sustainable Chem. Eng. 2015, 3 (10), 2435−2442. (4) Li, L.; Lu, J.; Ren, Y.; Zhang, X. X.; Chen, R. J.; Wu, F.; Amine, K. Ascorbic-acid-assisted recovery of cobalt and lithium from spent Li-ion batteries. J. Power Sources 2012, 218, 21−27. (5) Zeng, X.; Li, J.; Singh, N. Recycling of Spent Lithium-ion Battery: A Critical Review. Crit. Rev. Environ. Sci. Technol. 2014, 44 (10), 1129−1165. (6) Chagnes, A.; Pospiech, B. A brief review on hydrometallurgical technologies for recycling spent lithium-ion batteries. J. Chem. Technol. Biotechnol. 2013, 88 (7), 1191−1199. (7) Li, L.; Zhai, L.; Zhang, X.; Lu, J.; Chen, R.; Wu, F.; Amine, K. Recovery of valuable metals from spent lithium-ion batteries by ultrasonic-assisted leaching process. J. Power Sources 2014, 262, 380− 385. (8) Sun, L.; Qiu, K. Q. Vacuum pyrolysis and hydrometallurgical process for the recovery of valuable metals from spent lithium-ion batteries. J. Hazard. Mater. 2011, 194, 378−384. (9) Ellis, B. L.; Lee, K. T.; Nazar, L. F. Positive Electrode Materials for Li-Ion and Li-Batteries†. Chem. Mater. 2010, 22 (3), 691−714. (10) Zou, H.; Gratz, E.; Apelian, D.; Wang, Y. A novel method to recycle mixed cathode materials for lithium ion batteries. Green Chem. 2013, 15, 1183−1191.

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CONCLUSION A hydrometallurgical method was developed for recycling LiNi1/3Co1/3Mn1/3O2 cathode active materials in spent LIBs. The results show that the concentration of lactic acid, S/L ratio, temperature, amount of H2O2, and leaching time have 5232


Research Article

ACS Sustainable Chemistry & Engineering (11) Paulino, J. F.; Busnardo, N. G.; Afonso, J. C. Recovery of valuable elements from spent Li-batteries. J. Hazard. Mater. 2008, 150 (3), 843−849. (12) Yang, L.; Xi, G.; Xi, Y. Recovery of Co, Mn, Ni, and Li from spent lithium ion batteries for the preparation of LiNixCoyMnzO2 cathode materials. Ceram. Int. 2015, 41 (9), 11498−11503. (13) Nayaka, G. P.; Manjanna, J.; Pai, K. V.; Vadavi, R.; Keny, S. J.; Tripathi, V. S. Recovery of valuable metal ions from the spent lithiumion battery using aqueous mixture of mild organic acids as alternative to mineral acids. Hydrometallurgy 2015, 151, 73−77. (14) Mishra, D.; Kim, D. J.; Ralph, D. E.; Ahn, J. G.; Rhee, Y. H. Bioleaching of metals from spent lithium ion secondary batteries using Acidithiobacillus ferrooxidans. Waste Manage. 2008, 28 (2), 333−338. (15) Xin, B.; Zhang, D.; Zhang, X.; Xia, Y.; Wu, F.; Chen, S.; Li, L. Bioleaching mechanism of Co and Li from spent lithium-ion battery by the mixed culture of acidophilic sulfur-oxidizing and iron-oxidizing bacteria. Bioresour. Technol. 2009, 100 (24), 6163−6169. (16) Ordoñez, J.; Gago, E. J.; Girard, A. Processes and technologies for the recycling and recovery of spent lithium-ion batteries. Renewable Sustainable Energy Rev. 2016, 60, 195−205. (17) Huang, K.; Li, J.; Xu, Z. A Novel Process for Recovering Valuable Metals from Waste Nickel-Cadmium Batteries. Environ. Sci. Technol. 2009, 43, 8974−8978. (18) Li, L.; Qu, W.; Zhang, X.; Lu, J.; Chen, R.; Wu, F.; Amine, K. Succinic acid-based leaching system: A sustainable process for recovery of valuable metals from spent Li-ion batteries. J. Power Sources 2015, 282 (0), 544−551. (19) Li, J.; Shi, P.; Wang, Z.; Chen, Y.; Chang, C. C. A combined recovery process of metals in spent lithium-ion batteries. Chemosphere 2009, 77 (8), 1132−1136. (20) Wang, R.; Lin, Y.; Wu, S. A novel recovery process of metal values from the cathode active materials of the lithium-ion secondary batteries. Hydrometallurgy 2009, 99, 194−201. (21) Joulié, M.; Laucournet, R.; Billy, E. Hydrometallurgical process for the recovery of high value metals from spent lithium nickel cobalt aluminum oxide based lithium-ion batteries. J. Power Sources 2014, 247 (0), 551−555. (22) Li, L.; Chen, R.; Sun, F.; Wu, F.; Liu, J. Preparation of LiCoO2 films from spent lithium-ion batteries by a combined recycling process. Hydrometallurgy 2011, 108 (3−4), 220−225. (23) Lee, C. K.; Rhee, K. I. Preparation of LiCoO2 from spent lithium-ion batteries. J. Power Sources 2002, 109, 17−21. (24) Jha, M. K.; Kumari, A.; Jha, A. K.; Kumar, V.; Hait, J.; Pandey, B. D. Recovery of lithium and cobalt from waste lithium ion batteries of mobile phone. Waste Manage. 2013, 33 (9), 1890−1897. (25) Chen, X.; Chen, Y.; Zhou, T.; Liu, D.; Hu, H.; Fan, S. Hydrometallurgical recovery of metal values from sulfuric acid leaching liquor of spent lithium-ion batteries. Waste Manage. 2015, 38, 349− 356. (26) Chen, X.; Xu, B.; Zhou, T.; Liu, D.; Hu, H.; Fan, S. Separation and recovery of metal values from leaching liquor of mixed-type of spent lithium-ion batteries. Sep. Purif. Technol. 2015, 144, 197−205. (27) Chen, X.; Ma, H.; Luo, C.; Zhou, T. Recovery of valuable metals from waste cathode materials of spent lithium-ion batteries using mild phosphoric acid. J. Hazard. Mater. 2017, 326, 77−86. (28) Li, L.; Ge, J.; Wu, F.; Chen, R.; Chen, S.; Wu, B. Recovery of cobalt and lithium from spent lithium ion batteries using organic citric acid as leachant. J. Hazard. Mater. 2010, 176 (1−3), 288−293. (29) Chen, X.; Zhou, T. Hydrometallurgical process for the recovery of metal values from spent lithium-ion batteries in citric acid media. Waste Manage. Res. 2014, 32 (11), 1083−1093. (30) Li, L.; Ge, J.; Chen, R.; Wu, F.; Chen, S.; Zhang, X. Environmental friendly leaching reagent for cobalt and lithium recovery from spent lithium-ion batteries. Waste Manage. 2010, 30 (12), 2615−2621. (31) Nayaka, G. P.; Pai, K. V.; Santhosh, G.; Manjanna, J. Recovery of cobalt as cobalt oxalate from spent lithium ion batteries by using glycine as leaching agent. J. Environ. Chem. Eng. 2016, 4 (2), 2378− 2383.

(32) Zeng, X.; Li, J.; Shen, B. Novel approach to recover cobalt and lithium from spent lithium-ion battery using oxalic acid. J. Hazard. Mater. 2015, 295, 112−118. (33) He, L.; Sun, S.; Mu, Y.; Song, X.; Yu, J. Recovery of Lithium, Nickel, Cobalt, and Manganese from Spent Lithium-Ion Batteries Using l-Tartaric Acid as a Leachant. ACS Sustainable Chem. Eng. 2017, 5 (1), 714−721. (34) Gao, W.; Zhang, X.; Zheng, X.; Lin, X.; Cao, H.; Zhang, Y.; Sun, Z. Lithium Carbonate Recovery from Cathode Scrap of Spent Lithium-Ion Battery: A Closed-Loop Process. Environ. Sci. Technol. 2017, 51 (3), 1662−1669. (35) Nayaka, G. P.; Pai, K. V.; Manjanna, J.; Keny, S. J. Use of mild organic acid reagents to recover the Co and Li from spent Li-ion batteries. Waste Manage. 2016, 51, 234−238. (36) Yao, L.; Feng, Y.; Xi, G. X. A new method for the synthesis of LiNi1/3Co1/3Mn1/3O2 from waste lithium ion batteries. RSC Adv. 2015, 5 (55), 44107−44114. (37) Fedje, K. K.; Yillin, L.; Stromvall, A. M. Remediation of metal polluted hotspot areas through enhanced soil washing–evaluation of leaching methods. J. Environ. Manage. 2013, 128, 489−496. (38) Tang, J. A.; Valix, M. Leaching of low grade limonite and nontronite ores by fungi metabolic acids. Miner. Eng. 2006, 19 (12), 1274−1279. (39) Nie, H.; Xu, L.; Song, D.; Song, J.; Shi, X.; Wang, X.; Zhang, L.; Yuan, Z. LiCoO2: recycling from spent batteries and regeneration with solid state synthesis. Green Chem. 2015, 17 (2), 1276−1280. (40) Song, D.; Wang, X.; Zhou, E.; Hou, P.; Guo, F.; Zhang, L. Recovery and heat treatment of the Li(Ni1/3Co1/3Mn1/3)O2 cathode scrap material for lithium ion battery. J. Power Sources 2013, 232, 348− 352. (41) Zhang, X.; Cao, H.; Xie, Y.; Ning, P.; An, H.; You, H.; Nawaz, F. A closed-loop process for recycling LiNi1/3Co1/3Mn1/3O2 from the cathode scraps of lithium-ion batteries: Process optimization and kinetics analysis. Sep. Purif. Technol. 2015, 150, 186−195. (42) Li, G.; Rao, M.; Jiang, T.; Huang, Q.; Peng, Z. Leaching of limonitic laterite ore by acidic thiosulfate solution. Miner. Eng. 2011, 24 (8), 859−863. (43) Demirkıran, N.; Künkül, A. Dissolution kinetics of ulexite in perchloric acid solutions. Int. J. Miner. Process. 2007, 83 (1−2), 76−80.

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Sustainable Recovery of Cathode Materials from Spent Lithium-Ion

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