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C cathode powders from spent LiMn2O4 batteries
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Novel efficient and environmentally friendly recovering of high performance nano-LiMnPO4/C cathode powders from spent LiMn2O4 batteries Qi Meng, Jianguo Duan* , Yingjie Zhang, Peng Dong* National and Local Joint Engineering Laboratory for Lithium-ion Batteries and Materials Preparation Technology, Key Laboratory of Advanced Battery Materials of Yunnan Province, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 24 November 2018 Received in revised form 25 April 2019 Accepted 21 August 2019 Available online xxx
In this study, a novel efficient and environmentally friendly recycling process is developed to recover spent LiMn2O4 powder as raw materials for high-performance LiMnPO4/C nanocomposites. The process comprises a mechanochemical liquid-phase activation of the precursor mixture followed by a single-step solid-state heat treatment. The results indicate that the recovered LiMnPO4/C nano-composite has a promising electrochemical performance with discharge capacities of 148.5, 136.1, and 116.5 mA h g 1 at 0.05, 0.2, and 1C rate, respectively, in the voltage range of 2.5–4.5 V. A perfect cyclic performance is also displayed with a capacity retention of 98% after 100 cycles at 1C rate. © 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Keywords: Spent lithium-ion batteries Recycling Mechanochemical liquid-phase activation Spent LiMn2O4 LiMnPO4
Introduction LiMn2O4-based lithium-ion batteries (LIBs) have been widely used in hybrid electric vehicles (HEVs), scale energy storage, and electric power tools owing to their relatively high energy density, low cost, safety, and environment protection [1,2]. However, the LiMn2O4 particles in the spent LiMn2O4 batteries suffer from significant metal decomposition and irreversible phase transformation during the long-term repeated charge/discharge cycles, resulting in a low specific capacity and poor cyclic stability. Therefore, a numerous spent LiMn2O4 batteries must be disposed and recycled appropriately for improving the environmental and social–economic sustainability. To achieve the desired efficient recycling and reusing of the valuable elements from the spent LIBs, one needs to focus on the material chemical property. This is because, the particle size, crystal structure, and chemical action of each component during the recycling process and the energy consumption, environmental effect, and cost are difficult to regulate once the elements are separated and reused [3–6]. In this context, the conventional recovering processes for the spent LIBs have employed physical and chemical methods. Typically, the physical processes include
* Corresponding authors. E-mail addresses: [email protected] (J. Duan), [email protected] (P. Dong).
mechanical separation process, mechanochemical process, and thermal treatment, whereas the chemical methods include leaching, extraction separation, precursor precipitation, and calcination [5,7–10] These processes inevitably suffer from low atom utilization, long technics process, high energy consumption, and large scale of waste liquid treatment. Therefore, simple and economical recycling of spent LiMn2O4 batteries with high efficiency and high value-added still remains significantly challenging. One efficient strategy for recycling spent LIBs is the direct regeneration of the cathode materials from the spent cathodes. Successful results have been reported recently for the regeneration of cathode materials such as LiCoO2, LiCoxMnyNizO2, and LiFePO4. Sita et al. [11] regenerated LiCoO2 by thermal decomposition followed by a solid-state reaction. The obtained material displayed good initial charging and discharging capacities (130.0 mA h g 1 and 125.0 mA h g 1, respectively), which were very close to those presented by new LiCoO2 cathodes. Recently, Sen canski et al. [12] regenerated LiNi1/3Co1/3Mn1/3O2 (NCM) from spent NCM cathode materials by a solid-state reaction method. The regenerated material showed a charge capacity of 201 mA h g 1 and discharge capacity of 155 mA h g 1. However, the direct regeneration of the spent widely used LiMn2O4-based LIBs has rarely been reported. As the market share of LiMn2O4 material is annually increasing with the rapid development of global new energy vehicles, developing a simple process for the regeneration of LiMn2O4 materials is highly desirable.
https://doi.org/10.1016/j.jiec.2019.08.051 1226-086X/© 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Q. Meng, et al., Novel efficient and environmentally friendly recovering of high performance nano-LiMnPO4/C cathode powders from spent LiMn2O4 batteries, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.08.051
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LiMnPO4 (LMP) is one of the most promising cathode materials for electric vehicles (EVs) or HEVs because of its low price, high energy density (697 Wh Kg 1), and excellent chemical thermal stability [13–17]. However, the electrical and ionic insulation of LiMnPO4 seriously hampers its commercial promotion and application [18]. Various relevant studies have focused on compensating the above negative features via various methods, and successful syntheses of high-performance LiMnPO4 has been achieved by ion doping [19–21], nano-structure designing [13,22], and surface modification [23–26]. For simplicity and from the environmental perspective, polyvinylidene fluoride (PVDF) residue and well-dispersed conductive carbon and atomic-scale mixed Li and Mn without any detrimental impurity in the spent LiMn2O4 electrode are promising raw materials for LiMnPO4/C. Hence, in this study, a simple and eco-efficient process for recycling spent LiMn2O4 is developed by involving a mechanochemical activation-assisted solid-state technique for synthesizing a nano-LiMnPO4/C composite. In its typical process, the spent LiMn2O4 particles and self-contained, well-dispersed carbon source (PVDF and conductive carbon) were reused 100% without leaching, extraction, precipitation, filtration, or washing steps during the entire regeneration process. The highly efficient mechano-chemical activation-assisted solid-state technique ensured the uniform mixing and nanocrystallization of the raw materials, which is crucial for high-performance LiMnPO4 materials. Moreover, in the entire recycling process, only CO2, H2O, and recyclable NH3 were released. Therefore, this is a facile and ecoefficient method for reusing spent LiMn2O4 batteries. Experimental Raw materials preparation and material synthesis The flow chart for the regeneration of LiMnPO4/C from spent LiMn2O4 batteries is shown in Fig. 1. Here, the 18,650 spent LiMn2O4 batteries used were collected from Dongguan PLB Battery Co., Ltd. (Dongguan, China). The spent LiMn2O4 powders were collected from the spent batteries by discharging, dismantling, separating, and detaching according to our previous reports [27–29]. In a typical mechano-chemical activation-assisted solidstate process, stoichiometric amounts of spent LiMn2O4 powder, NH3H2PO4 (analytical grade), Li2CO3, and polyvinyl alcohol (PVA, 99.5 wt.%, GJ29-JX09, 1 g per 0.1 mol Mn) were milled with
Fig. 1. Schematic of the recycling procedure.
ethyl alcohol as the dispersion medium using a planetary ball mill (PULVERISETTE 5, Germany). In this process, the zirconia ballsto-powder weight ratio was 20:1 at room temperature, and milling was performed for 4 h at 800 rpm. The obtained precursor slurry was dried at 80 C for 12 h. The LiMnPO4/C active materials were obtained by calcining the precursor powder at 650 C for 6 h in Ar atmosphere and cooling to room temperature with a heating rate and furnace cooling rate of 3 C min 1. Characterization The elemental composition of the powder sample was analysed using an atomic adsorption spectrophotometer (AAS, Thermo iCE 3000, USA). The X-ray diffraction (XRD, Rigaku, Japan) was performed with Cu Ka radiation (1.5418 Å) at 40 kV, 150 mA at a scan rate of 2 min 1. The morphology and particle size estimation of the samples were examined via a scanning electron microscope (SEM, TESCAN VEGA3, CZE). A transition electron microscope (TEM, Tecnai G2 F20 S-Twin) was employed for the microstructure and morphology analysis. The chemical changes in the elements during the synthesis process were detected via X-ray photoelectron spectroscopy (XPS, with a PHI5000 Versa probe-II spectrometer). Thermogravimetric analysis (TGA/DSC, NETZSCH STA 449C) was employed to investigate the thermal behaviour of the synthesis process. TGA/DSC profiles were obtained in argon atmosphere by increasing the temperature from 35 C to 1000 C at a heating rate of 10 C min 1. For the electrochemical performance evaluation, charge–discharge tests were performed with a LAND-CT2001A test system, and the cyclic voltammetry (CV) results of the cathode materials were obtained by an electrochemical workstation (CHI660D, Shanghai, China). The coin cell preparation and detailed electrochemical analysis procedures followed our previous reports [27–29]. Results and discussion The morphology and microstructure of as-prepared spent LiMn2O4 powders are investigated by SEM and high-resolution TEM (HR-TEM). Fig. 2(a) displays an SEM image of the spent LiMn2O4 powder. Obviously, the spent LiMn2O4 powder exhibits an irregular morphology with 1–10 mm particle size. Furthermore, TEM and HR-TEM were performed to investigate the local structure of the spent LiMn2O4 powder, and the results are shown in Fig. 2(b–d). As shown in Fig. 2(b), severe structural corrosion holes and deformation evidence are clearly detected, indicating that the spent LiMn2O4 particles suffer from dissolution of the transition mental and lattice distortion during the repeated charging and discharging cycles. This is also an evidence of the Jahn–Teller effect and considerable manganese dissolution in commercially used LiMn2O4 materials, which are the key problems for spinel-structured LiMn2O4 cathode materials [30–32]. The lattice collapse and bulk corrosion are observed more clearly in the HR-TEM images (Fig. 2(c) and (d), respectively). The outer surface of the spent LiMn2O4 is covered with an amorphous phase, disordered regions, and widespread lattice corrosion areas. These undesirable phases are detected by high ionic/increased electronic resistance with the absence of electrochemical activity, which result in capacity decrease and impedance increase during the cycling of the LiMn2O4 cathode materials [30,33,34]. The changes in the crystal structure and elementary chemical evolution of the samples were investigated via TGA/DSC, XRD, and FTIR. Fig. 3(a) displays the TGA/DSC profiles of the precursor mixture. The endothermic peaks located between 30 C and 400 C, correspond to the volatilization of the surface water (108 C) and decomposition of PVA, NH4H2PO4, and PVDF (180 C). There is a
Please cite this article in press as: Q. Meng, et al., Novel efficient and environmentally friendly recovering of high performance nano-LiMnPO4/C cathode powders from spent LiMn2O4 batteries, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.08.051
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Fig. 2. SEM (a), TEM (b), and HRTEM (c and d) images of the spent LiMn2O4 particles.
Fig. 3. TGA–DSC curve of the precursor mixture (a), XRD profiles (b), and FTIR comparison (c), of the spent LiMn2O4, precursor powders, and recovered LiMnPO4. XRD diffraction pattern with rietveld refinement of the regenerated LiMnPO4 sample conducted with GSAS (d).
Please cite this article in press as: Q. Meng, et al., Novel efficient and environmentally friendly recovering of high performance nano-LiMnPO4/C cathode powders from spent LiMn2O4 batteries, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.08.051
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mass loss of 20% from room temperature to 400 C in the TG curve, corresponding to the release of H2O, NH3, and CO2 from the precursors. The formation temperature of the LiMnPO4/C composite is approximately 450 C, corresponding to an exothermic peak located at 445 C in the DSC curve. An extensive endothermic process followed by a slight weight decrease is detected after 450 C, which may be attributed to the continuous pyrogenation of the PVDF and PVA organic components and carbon thermal reduction reaction of Mn3+ in LiMn2O4. This illustrates that the formation of the LiMnPO4 crystal and conductive carbon film coating on the LiMnPO4 particles occurs simultaneously during the heating treatment. To further demonstrate the above reactions, Fig. 3(b) displays the XRD profiles of the spent LiMn2O4, middle precursor mixture, and final material formed by this method. The diffraction peaks of the spinel-structured LiMn2O4 matching well with those of PDF #88-0598, belonging to the Fd-3 m space group, can be observed in both the spent LiMn2O4 sample and middle precursor. However, the peaks of the middle precursor become low and wide. This confirms that the mechanical activation process destroys the original spinel structure of the spent LiMn2O4 to a large extent. The XRD pattern of the final sample calcinated at 750 C fits well with the standard XRD profiles of the olivinestructured LiMnPO4, assigned to PDF #74-0375, ICSD#25834, space group of Pmnb (62). This further demonstrates that a highly crystallized LiMnPO4/C composite can be synthesized successfully from spent LiMn2O4 electrodes by using the proposed mechanochemical activation-assisted solid-state technique. Fig. 3 (c) shows the FTIR spectra of the spent LiMn2O4, middle precursor mixture, and final LiMnPO4/C composite. The spent LiMn2O4 and middle precursor exhibit two obvious infrared bands at 511 and 617 cm 1, respectively, which can be classified as O Mn O vibrations in the spinel-structured LiMn2O4. The peaks replace by symmetric and antisymmetric bending modes between 500 and 650 cm 1 as well as stretching modes located between 950 and 1150 cm 1 in the FTIR spectrum of the regenerated LiMnPO4 can be assigned to the features of PO43- present in the olivine-structured LiMnPO4 composite [35]. The XRD patterns of the regenerated LiMnPO4 were further analysed by the Rietveld method by using GSAS with the EXPGUI program. It should be noted that all the refined data are obtained after the diffraction profiles could not be optimized further. The diffraction peak fitness results and corresponding refinement results are compared in Fig. 3(d) and Table 1. Obviously, the regenerated LiMnPO4 composite is composed of a single olivine-structured LiMnPO4 phase, and there is no evidence of crystallized carbon or other unwanted parasitic phases (such as Li3PO4, FeP or V2O5). Al3+ and Mg2+ ions in the spent LMO occupy the Mn2+ site in the olivine phase, and a part of the F ions substitute the PO43 site. The optimized atomic occupancy result of the regenerated composite is Li(Mn0.97Al0.01Mg0.02) (PO4)0.99F0.01. The cell lattice parameters of the regenerated LiMnPO4 is clearly decreased compared to that of the standard data of LiMnPO4 (PDF#74-0375, 25834-ICSD). This is due to the Al3+ and Mg2+ ions doping the Fe2+ site and F doping the PO43- site, and the ionic radii of the doping ions are smaller than those of the Mn2+ ions. It has been previously reported that a reduction in the lattice parameters of the original crystals via ionic doping will ease the volume shrinkage/ expansion during the insertion/de-insertion processes [36–38]. Thus,
in this study, the raw material itself introduced Al-Mg-F doping effect may have a positive effect on improving the electrochemical performance of the regenerated LiMnPO4/C composites. High-resolution XPS spectra analysis was employed for further discussing the chemical state changes of the samples during the recycling process. Fig. 4(a–d) displays the high-resolution XPS spectrums of Mn 2P, P 2P, O 1s, and C1s of the spent LiMn2O4, precursor powders, and recovered LiMnPO4, respectively. Some apparent differences in the features of oxidation states of Mn are identified in Fig. 4(a). The binding energy of Mn2 P3/2 shifts from 641.78 eV of the spent LiMn2O4 to 640.4 eV of the regenerated in LiMnPO4. The XPS result of LiMnPO4 here is consistent well with the data of LiMnPO4 reported in previous reports [39,40]. P2P peak locates at 132 eV, which can be assigned to P in PO43 ionic group appears after LiMnPO4 regeneration [39], demonstrating that phosphate radical is introduced by this strategy successfully. O 1S spectrums (Fig. 4(c)) of spent LMO can be separates into two peaks, the peak locates at 529 eV belong the lattice oxygen in Mn-O, and the peak appears at 531 eV can be classified to oxygen in nonmetal functional group. After regenerating process, the peak located at lower binding energy disappeared while the other at 531 becomes higher, this feature is in line with the O 1s spectrums in olivine structured samples. Fig. 4(d) shows the XPS spectrums of C1s, in which the peaks of spent LMO and middle precursor at 290 eV is belong to the oxygen-containing carbon-based functional group and the peaks between 283 and 284.5 eV can be attributed to carbon, demonstrating that oxygencontaining carbon-based functional group contained residues mixed with conductive carbon (C0) [41,42]. This situation however disappeared in the regenerated LiMnPO4/C. This indicates that the chemical state of carbon in LiMnPO4/C is almost conductive carbon (C0). Thus, both the FTIR and XPS results illustrate that a highly crystallized LiMnPO4/C composite can be prepared by this mechano-chemical activation-assisted solid-state technique. From the perspective of materials metallurgy, only CO2, H2O, and recyclable NH3 are released in the entire recycling process, which is considered to be economic and eco-efficient. Fig. 5(a) and (b) display the SEM images of the recycled LiMnPO4. Obviously, the LiMnPO4 samples exhibit a spherical morphology in the nano sized regime, which suggests that the recycling strategy can produce LiMnPO4/C composites with ultrafine particle size and uniform distribution. The micromorphology and nanostructure of the as-prepared LiMnPO4 were also studied by TEM and HRTEM. Fig. 5(c) and (d) show the TEM images of LiMnPO4, which exhibits the fine and uniformly distributed nano-sized morphology more distinctly. Fig. 5(e) and (f) present high-resolution TEM images of LiMnPO4, in which the lattice fringes of LiMnPO4 can be observed clearly, indicating that LiMnPO4 has a high crystallinity. Moreover, a thin amorphous film of thickness of approximately 3–5 nm is coated on the outer surface of the bulk phase, which corresponds to the in situ coated amorphous carbon film. This mainly originates from the selfcontained, well-dispersed carbon source (PVDF and conductive carbon) in the raw materials, a highly mixed mechano-chemical activation technique, and a synchronous process between the decomposition of the contained carbon source and crystallization of the olivine-structured LiMnPO4. These ensure that the
Table 1 Refined unit cell lattice parameters and atomic site occupantion of the regenerated LiMnPO4 and the standard data of LiMnPO4 (PDF#74-0375, 25834-ICSD). Sample
Regenerated LiMnPO4 LiMnPO4
Lattice parameters
TM ratio
3
a (Å)
b (Å)
c (Å)
β( )
V (Å )
6.08772 6.100
10.41531 10.460
4.74078 4.744
90.0 90.0
300.59 302.7
Li(Mn0.97Al0.005Mg0.025)(PO4)0.99F0.01 /
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Fig. 4. High-resolution XPS profiles for Mn 2P (a), P 2P (b), O 1s (c), and C1s (d) of samples the spent LiMn2O4, precursor powders, and recovered LiMnPO4.
Fig. 5. SEM (a, b) and TEM (c–f) images of the recovered LiMnPO4.
regenerated composite has a nano-sized uniform particle size distribution and homogeneous carbon coating. From the chemical synthesis technology perspective, a new synthesis method may provide promising lithium storage properties for LIBs. A homogeneous coating film with high conductivity is expected to improve the electrochemical performance of olivinestructured phosphates. The electrochemical performances of the spent LiMn2O4 and recycled LiMnPO4 are displayed in Fig. 6. Fig. 6(a) shows the initial charge–discharge curves of the spent LiMn2O4 at 0.2 and 1C. The spent cathode material displays a poor electrochemical performance with approximately 54 and 50 mA h
g 1 discharge capacities at 0.2 and 1C rate, respectively, attributed to the unwanted phase transformation and rapid side reactions during the long-term cycling [43–45]. The charge and discharge curves of the regenerated LiMnPO4 at different rates are shown in Fig. 6(b), in which an apparent plateau is detected at 4.1 V. This is homologous to the intercalation/de-intercalation of the Li+ ions from olivine-structured LiMnPO4. The capacity of the active sample is 148.5, 136.1, 125.2, 116.5, and 97.5 mA h g 1 at 0.05, 0.2, 0.5, 1, and 2 C rate, respectively. The results indicate that the formation of regenerated LiMnPO4/C composites with high discharge capacity and high discharge plateau ratio at various rates. This mainly
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Fig. 6. Electrochemical performance of the spent LiMn2O4 and recovered LiMnPO4/C. The charge/discharge profiles of the spent LiMn2O4 at 0.2C and 1C rate (a), the charge/ discharge curves of the recovered LiMnPO4/C at different rates (b), the cyclic stability comparison of the as-prepared materials (c), and the CV profiles of LiMnPO4/C (d).
attributed to the excellent raw material choice, nanocrystallization technique, and in situ carbon coating of the facile recycle strategy. The cycle performance of the spent LiMn2O4 and recycled LiMnPO4/C at 1 C rate is displayed in Fig. 6(c). Obviously, the cycling stability of LiMnPO4/C is very high with a capacity retention of 100% after 100 charge/discharge cycles. The result also illustrates that the olivine-structured LiMnPO4 samples have high structure stabilization and stable cycling performance. To illustrate the stabilization effect, further cyclic voltammogram (CV) test was performed to investigate the lithium storage property of LiMnPO4. Fig. 6(d) presents the CV profiles of the regenerated LiMnPO4 – Li half cells after 1, 50, and 100 cycles at 1C rate. The test was performed between 2.5 and 4.8 V at a scan rate of 0.1 mV s 1. Consistent with previous works [21,46–48], only one peak pair is detected on the CV curve, which corresponds to an anodic peak (4.32 V) and a cathodic peak (4.0 V) during the Mn2+/Mn3+ redox processes [49]. As expected, the sample displays a perfect reproducibility of the peaks from the 1st to 50th and 100th cycles, illustrating good reversibility of the asprepared LiMnPO4/C sample. Both the CV curves and cycling performance indicate distinctly a good Li+ ion storage property of the regenerated LiMnPO4/C. Conclusion In this study, we developed a facile and an eco-efficient strategy for the regeneration of LiMnPO4/C cathode materials directly from the spent LiMn2O4 cathodes. The spent LiMn2O4 particles and self-contained and well-dispersed carbon source were reused 100% without leaching, extraction, precipitation, filtration, or washing processes. The highly efficient mechanochemical activation-assisted solid-state technique ensured uniform mixing and nanocrystallization of the raw materials, which is crucial for the high performance of LiMnPO4 cathode
materials. The recovered LiMnPO4/C nano-composite displayed a promising electrochemical performance with a discharge capacity of 148.5 mA h g 1 at 0.05C rate and exhibited a perfect cyclic performance. Moreover, only CO2, H2O, and recyclable NH3 were released in the entire recycle process. Thus, this is a potential strategy for reusing LiFePO4, LiMn2O4, and the NCMbased spent LIBs materials for commercial purposes. Acknowledgements We gratefully acknowledge the National Natural Science Foundation of China (Grant Nos. 51764029 and 51904135), Provincial Natural Science Foundation of Yunnan (No. 2017FB085), Applied Basic Research Plan of Yunnan Province (No. 2018FB087). References [1] W. Li, B. Song, A. Manthiram, Chem. Soc. Rev. 46 (2017) 3006. [2] J. Jiang, K. Du, Y. Cao, Z. Peng, G. Hu, J. Duan, J. Alloys Compd. 577 (2013) 138. [3] C.S. dos Santos, J.C. Alves, S.P. da Silva, L. Evangelista Sita, P.R.C. da Silva, L.C. de Almeida, J. Scarminio, J.Hazard. Mater. 362 (2019) 458. [4] Q. Meng, Y. Zhang, P. Dong, Waste Manag. 64 (2017) 214. [5] J. Chen, Q. Li, J. Song, D. Song, L. Zhang, X. Shi, Green Chem. 18 (2016) 2500. [6] H. Ku, Y. Jung, M. Jo, S. Park, S. Kim, D. Yang, K. Rhee, E.-M. An, J. Sohn, K. Kwon, J. Hazard. Mater. 313 (2016) 138. [7] J.F. Paulino, N.G. Busnardo, J.C. Afonso, J. Hazard. Mater. 150 (2008) 843. [8] Y. Zhang, Q. Meng, P. Dong, J. Duan, Y. Lin, J. Ind. Eng. Chem. 66 (2018) 86. [9] P. Meshram, B.D. Pandey, T.R. Mankhand, Chem. Eng. J. 281 (2015) 418. [10] Y. Zhang, Y. Zhang, Y. Zhang, P. Dong, Q. Meng, M. Xu, J. Alloys Compd. 783 (2019) 357. [11] L.E. Sita, S.P. da Silva, P.R.C. da Silva, J. Scarminio, Mater. Chem. Phys.194 (2017) 97. [12] Y. Weng, S. Xu, G. Huang, C. Jiang, J. Hazard. Mater. (2013) 246 163–172. [13] N.H. Kwon, H. Yin, T. Vavrova, J.H.W. Lim, U. Steiner, B. Grobéty, K.M. Fromm, J Power Sources 342 (2017) 231. [14] J.-K. Kim, C.-R. Shin, J.-H. Ahn, A. Matic, P. Jacobsson, Electrochem. Commun. 13 (2011) 1105. [15] M. Pivko, M. Bele, E. Tchernychova, N.Z. Logar, R. Dominko, M. Gaberscek, Chem. Mater. 24 (2012) 1041.
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Journal of Industrial and Engineering Chemistry xxx (2019) xxx–xxx
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Novel efficient and environmentally friendly recovering of high performance nano-LiMnPO4/C cathode powders from spent LiMn2O4 batteries Qi Meng, Jianguo Duan* , Yingjie Zhang, Peng Dong* National and Local Joint Engineering Laboratory for Lithium-ion Batteries and Materials Preparation Technology, Key Laboratory of Advanced Battery Materials of Yunnan Province, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 24 November 2018 Received in revised form 25 April 2019 Accepted 21 August 2019 Available online xxx
In this study, a novel efficient and environmentally friendly recycling process is developed to recover spent LiMn2O4 powder as raw materials for high-performance LiMnPO4/C nanocomposites. The process comprises a mechanochemical liquid-phase activation of the precursor mixture followed by a single-step solid-state heat treatment. The results indicate that the recovered LiMnPO4/C nano-composite has a promising electrochemical performance with discharge capacities of 148.5, 136.1, and 116.5 mA h g 1 at 0.05, 0.2, and 1C rate, respectively, in the voltage range of 2.5–4.5 V. A perfect cyclic performance is also displayed with a capacity retention of 98% after 100 cycles at 1C rate. © 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Keywords: Spent lithium-ion batteries Recycling Mechanochemical liquid-phase activation Spent LiMn2O4 LiMnPO4
Introduction LiMn2O4-based lithium-ion batteries (LIBs) have been widely used in hybrid electric vehicles (HEVs), scale energy storage, and electric power tools owing to their relatively high energy density, low cost, safety, and environment protection [1,2]. However, the LiMn2O4 particles in the spent LiMn2O4 batteries suffer from significant metal decomposition and irreversible phase transformation during the long-term repeated charge/discharge cycles, resulting in a low specific capacity and poor cyclic stability. Therefore, a numerous spent LiMn2O4 batteries must be disposed and recycled appropriately for improving the environmental and social–economic sustainability. To achieve the desired efficient recycling and reusing of the valuable elements from the spent LIBs, one needs to focus on the material chemical property. This is because, the particle size, crystal structure, and chemical action of each component during the recycling process and the energy consumption, environmental effect, and cost are difficult to regulate once the elements are separated and reused [3–6]. In this context, the conventional recovering processes for the spent LIBs have employed physical and chemical methods. Typically, the physical processes include
* Corresponding authors. E-mail addresses: [email protected] (J. Duan), [email protected] (P. Dong).
mechanical separation process, mechanochemical process, and thermal treatment, whereas the chemical methods include leaching, extraction separation, precursor precipitation, and calcination [5,7–10] These processes inevitably suffer from low atom utilization, long technics process, high energy consumption, and large scale of waste liquid treatment. Therefore, simple and economical recycling of spent LiMn2O4 batteries with high efficiency and high value-added still remains significantly challenging. One efficient strategy for recycling spent LIBs is the direct regeneration of the cathode materials from the spent cathodes. Successful results have been reported recently for the regeneration of cathode materials such as LiCoO2, LiCoxMnyNizO2, and LiFePO4. Sita et al. [11] regenerated LiCoO2 by thermal decomposition followed by a solid-state reaction. The obtained material displayed good initial charging and discharging capacities (130.0 mA h g 1 and 125.0 mA h g 1, respectively), which were very close to those presented by new LiCoO2 cathodes. Recently, Sen canski et al. [12] regenerated LiNi1/3Co1/3Mn1/3O2 (NCM) from spent NCM cathode materials by a solid-state reaction method. The regenerated material showed a charge capacity of 201 mA h g 1 and discharge capacity of 155 mA h g 1. However, the direct regeneration of the spent widely used LiMn2O4-based LIBs has rarely been reported. As the market share of LiMn2O4 material is annually increasing with the rapid development of global new energy vehicles, developing a simple process for the regeneration of LiMn2O4 materials is highly desirable.
https://doi.org/10.1016/j.jiec.2019.08.051 1226-086X/© 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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LiMnPO4 (LMP) is one of the most promising cathode materials for electric vehicles (EVs) or HEVs because of its low price, high energy density (697 Wh Kg 1), and excellent chemical thermal stability [13–17]. However, the electrical and ionic insulation of LiMnPO4 seriously hampers its commercial promotion and application [18]. Various relevant studies have focused on compensating the above negative features via various methods, and successful syntheses of high-performance LiMnPO4 has been achieved by ion doping [19–21], nano-structure designing [13,22], and surface modification [23–26]. For simplicity and from the environmental perspective, polyvinylidene fluoride (PVDF) residue and well-dispersed conductive carbon and atomic-scale mixed Li and Mn without any detrimental impurity in the spent LiMn2O4 electrode are promising raw materials for LiMnPO4/C. Hence, in this study, a simple and eco-efficient process for recycling spent LiMn2O4 is developed by involving a mechanochemical activation-assisted solid-state technique for synthesizing a nano-LiMnPO4/C composite. In its typical process, the spent LiMn2O4 particles and self-contained, well-dispersed carbon source (PVDF and conductive carbon) were reused 100% without leaching, extraction, precipitation, filtration, or washing steps during the entire regeneration process. The highly efficient mechano-chemical activation-assisted solid-state technique ensured the uniform mixing and nanocrystallization of the raw materials, which is crucial for high-performance LiMnPO4 materials. Moreover, in the entire recycling process, only CO2, H2O, and recyclable NH3 were released. Therefore, this is a facile and ecoefficient method for reusing spent LiMn2O4 batteries. Experimental Raw materials preparation and material synthesis The flow chart for the regeneration of LiMnPO4/C from spent LiMn2O4 batteries is shown in Fig. 1. Here, the 18,650 spent LiMn2O4 batteries used were collected from Dongguan PLB Battery Co., Ltd. (Dongguan, China). The spent LiMn2O4 powders were collected from the spent batteries by discharging, dismantling, separating, and detaching according to our previous reports [27–29]. In a typical mechano-chemical activation-assisted solidstate process, stoichiometric amounts of spent LiMn2O4 powder, NH3H2PO4 (analytical grade), Li2CO3, and polyvinyl alcohol (PVA, 99.5 wt.%, GJ29-JX09, 1 g per 0.1 mol Mn) were milled with
Fig. 1. Schematic of the recycling procedure.
ethyl alcohol as the dispersion medium using a planetary ball mill (PULVERISETTE 5, Germany). In this process, the zirconia ballsto-powder weight ratio was 20:1 at room temperature, and milling was performed for 4 h at 800 rpm. The obtained precursor slurry was dried at 80 C for 12 h. The LiMnPO4/C active materials were obtained by calcining the precursor powder at 650 C for 6 h in Ar atmosphere and cooling to room temperature with a heating rate and furnace cooling rate of 3 C min 1. Characterization The elemental composition of the powder sample was analysed using an atomic adsorption spectrophotometer (AAS, Thermo iCE 3000, USA). The X-ray diffraction (XRD, Rigaku, Japan) was performed with Cu Ka radiation (1.5418 Å) at 40 kV, 150 mA at a scan rate of 2 min 1. The morphology and particle size estimation of the samples were examined via a scanning electron microscope (SEM, TESCAN VEGA3, CZE). A transition electron microscope (TEM, Tecnai G2 F20 S-Twin) was employed for the microstructure and morphology analysis. The chemical changes in the elements during the synthesis process were detected via X-ray photoelectron spectroscopy (XPS, with a PHI5000 Versa probe-II spectrometer). Thermogravimetric analysis (TGA/DSC, NETZSCH STA 449C) was employed to investigate the thermal behaviour of the synthesis process. TGA/DSC profiles were obtained in argon atmosphere by increasing the temperature from 35 C to 1000 C at a heating rate of 10 C min 1. For the electrochemical performance evaluation, charge–discharge tests were performed with a LAND-CT2001A test system, and the cyclic voltammetry (CV) results of the cathode materials were obtained by an electrochemical workstation (CHI660D, Shanghai, China). The coin cell preparation and detailed electrochemical analysis procedures followed our previous reports [27–29]. Results and discussion The morphology and microstructure of as-prepared spent LiMn2O4 powders are investigated by SEM and high-resolution TEM (HR-TEM). Fig. 2(a) displays an SEM image of the spent LiMn2O4 powder. Obviously, the spent LiMn2O4 powder exhibits an irregular morphology with 1–10 mm particle size. Furthermore, TEM and HR-TEM were performed to investigate the local structure of the spent LiMn2O4 powder, and the results are shown in Fig. 2(b–d). As shown in Fig. 2(b), severe structural corrosion holes and deformation evidence are clearly detected, indicating that the spent LiMn2O4 particles suffer from dissolution of the transition mental and lattice distortion during the repeated charging and discharging cycles. This is also an evidence of the Jahn–Teller effect and considerable manganese dissolution in commercially used LiMn2O4 materials, which are the key problems for spinel-structured LiMn2O4 cathode materials [30–32]. The lattice collapse and bulk corrosion are observed more clearly in the HR-TEM images (Fig. 2(c) and (d), respectively). The outer surface of the spent LiMn2O4 is covered with an amorphous phase, disordered regions, and widespread lattice corrosion areas. These undesirable phases are detected by high ionic/increased electronic resistance with the absence of electrochemical activity, which result in capacity decrease and impedance increase during the cycling of the LiMn2O4 cathode materials [30,33,34]. The changes in the crystal structure and elementary chemical evolution of the samples were investigated via TGA/DSC, XRD, and FTIR. Fig. 3(a) displays the TGA/DSC profiles of the precursor mixture. The endothermic peaks located between 30 C and 400 C, correspond to the volatilization of the surface water (108 C) and decomposition of PVA, NH4H2PO4, and PVDF (180 C). There is a
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Fig. 2. SEM (a), TEM (b), and HRTEM (c and d) images of the spent LiMn2O4 particles.
Fig. 3. TGA–DSC curve of the precursor mixture (a), XRD profiles (b), and FTIR comparison (c), of the spent LiMn2O4, precursor powders, and recovered LiMnPO4. XRD diffraction pattern with rietveld refinement of the regenerated LiMnPO4 sample conducted with GSAS (d).
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mass loss of 20% from room temperature to 400 C in the TG curve, corresponding to the release of H2O, NH3, and CO2 from the precursors. The formation temperature of the LiMnPO4/C composite is approximately 450 C, corresponding to an exothermic peak located at 445 C in the DSC curve. An extensive endothermic process followed by a slight weight decrease is detected after 450 C, which may be attributed to the continuous pyrogenation of the PVDF and PVA organic components and carbon thermal reduction reaction of Mn3+ in LiMn2O4. This illustrates that the formation of the LiMnPO4 crystal and conductive carbon film coating on the LiMnPO4 particles occurs simultaneously during the heating treatment. To further demonstrate the above reactions, Fig. 3(b) displays the XRD profiles of the spent LiMn2O4, middle precursor mixture, and final material formed by this method. The diffraction peaks of the spinel-structured LiMn2O4 matching well with those of PDF #88-0598, belonging to the Fd-3 m space group, can be observed in both the spent LiMn2O4 sample and middle precursor. However, the peaks of the middle precursor become low and wide. This confirms that the mechanical activation process destroys the original spinel structure of the spent LiMn2O4 to a large extent. The XRD pattern of the final sample calcinated at 750 C fits well with the standard XRD profiles of the olivinestructured LiMnPO4, assigned to PDF #74-0375, ICSD#25834, space group of Pmnb (62). This further demonstrates that a highly crystallized LiMnPO4/C composite can be synthesized successfully from spent LiMn2O4 electrodes by using the proposed mechanochemical activation-assisted solid-state technique. Fig. 3 (c) shows the FTIR spectra of the spent LiMn2O4, middle precursor mixture, and final LiMnPO4/C composite. The spent LiMn2O4 and middle precursor exhibit two obvious infrared bands at 511 and 617 cm 1, respectively, which can be classified as O Mn O vibrations in the spinel-structured LiMn2O4. The peaks replace by symmetric and antisymmetric bending modes between 500 and 650 cm 1 as well as stretching modes located between 950 and 1150 cm 1 in the FTIR spectrum of the regenerated LiMnPO4 can be assigned to the features of PO43- present in the olivine-structured LiMnPO4 composite [35]. The XRD patterns of the regenerated LiMnPO4 were further analysed by the Rietveld method by using GSAS with the EXPGUI program. It should be noted that all the refined data are obtained after the diffraction profiles could not be optimized further. The diffraction peak fitness results and corresponding refinement results are compared in Fig. 3(d) and Table 1. Obviously, the regenerated LiMnPO4 composite is composed of a single olivine-structured LiMnPO4 phase, and there is no evidence of crystallized carbon or other unwanted parasitic phases (such as Li3PO4, FeP or V2O5). Al3+ and Mg2+ ions in the spent LMO occupy the Mn2+ site in the olivine phase, and a part of the F ions substitute the PO43 site. The optimized atomic occupancy result of the regenerated composite is Li(Mn0.97Al0.01Mg0.02) (PO4)0.99F0.01. The cell lattice parameters of the regenerated LiMnPO4 is clearly decreased compared to that of the standard data of LiMnPO4 (PDF#74-0375, 25834-ICSD). This is due to the Al3+ and Mg2+ ions doping the Fe2+ site and F doping the PO43- site, and the ionic radii of the doping ions are smaller than those of the Mn2+ ions. It has been previously reported that a reduction in the lattice parameters of the original crystals via ionic doping will ease the volume shrinkage/ expansion during the insertion/de-insertion processes [36–38]. Thus,
in this study, the raw material itself introduced Al-Mg-F doping effect may have a positive effect on improving the electrochemical performance of the regenerated LiMnPO4/C composites. High-resolution XPS spectra analysis was employed for further discussing the chemical state changes of the samples during the recycling process. Fig. 4(a–d) displays the high-resolution XPS spectrums of Mn 2P, P 2P, O 1s, and C1s of the spent LiMn2O4, precursor powders, and recovered LiMnPO4, respectively. Some apparent differences in the features of oxidation states of Mn are identified in Fig. 4(a). The binding energy of Mn2 P3/2 shifts from 641.78 eV of the spent LiMn2O4 to 640.4 eV of the regenerated in LiMnPO4. The XPS result of LiMnPO4 here is consistent well with the data of LiMnPO4 reported in previous reports [39,40]. P2P peak locates at 132 eV, which can be assigned to P in PO43 ionic group appears after LiMnPO4 regeneration [39], demonstrating that phosphate radical is introduced by this strategy successfully. O 1S spectrums (Fig. 4(c)) of spent LMO can be separates into two peaks, the peak locates at 529 eV belong the lattice oxygen in Mn-O, and the peak appears at 531 eV can be classified to oxygen in nonmetal functional group. After regenerating process, the peak located at lower binding energy disappeared while the other at 531 becomes higher, this feature is in line with the O 1s spectrums in olivine structured samples. Fig. 4(d) shows the XPS spectrums of C1s, in which the peaks of spent LMO and middle precursor at 290 eV is belong to the oxygen-containing carbon-based functional group and the peaks between 283 and 284.5 eV can be attributed to carbon, demonstrating that oxygencontaining carbon-based functional group contained residues mixed with conductive carbon (C0) [41,42]. This situation however disappeared in the regenerated LiMnPO4/C. This indicates that the chemical state of carbon in LiMnPO4/C is almost conductive carbon (C0). Thus, both the FTIR and XPS results illustrate that a highly crystallized LiMnPO4/C composite can be prepared by this mechano-chemical activation-assisted solid-state technique. From the perspective of materials metallurgy, only CO2, H2O, and recyclable NH3 are released in the entire recycling process, which is considered to be economic and eco-efficient. Fig. 5(a) and (b) display the SEM images of the recycled LiMnPO4. Obviously, the LiMnPO4 samples exhibit a spherical morphology in the nano sized regime, which suggests that the recycling strategy can produce LiMnPO4/C composites with ultrafine particle size and uniform distribution. The micromorphology and nanostructure of the as-prepared LiMnPO4 were also studied by TEM and HRTEM. Fig. 5(c) and (d) show the TEM images of LiMnPO4, which exhibits the fine and uniformly distributed nano-sized morphology more distinctly. Fig. 5(e) and (f) present high-resolution TEM images of LiMnPO4, in which the lattice fringes of LiMnPO4 can be observed clearly, indicating that LiMnPO4 has a high crystallinity. Moreover, a thin amorphous film of thickness of approximately 3–5 nm is coated on the outer surface of the bulk phase, which corresponds to the in situ coated amorphous carbon film. This mainly originates from the selfcontained, well-dispersed carbon source (PVDF and conductive carbon) in the raw materials, a highly mixed mechano-chemical activation technique, and a synchronous process between the decomposition of the contained carbon source and crystallization of the olivine-structured LiMnPO4. These ensure that the
Table 1 Refined unit cell lattice parameters and atomic site occupantion of the regenerated LiMnPO4 and the standard data of LiMnPO4 (PDF#74-0375, 25834-ICSD). Sample
Regenerated LiMnPO4 LiMnPO4
Lattice parameters
TM ratio
3
a (Å)
b (Å)
c (Å)
β( )
V (Å )
6.08772 6.100
10.41531 10.460
4.74078 4.744
90.0 90.0
300.59 302.7
Li(Mn0.97Al0.005Mg0.025)(PO4)0.99F0.01 /
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Fig. 4. High-resolution XPS profiles for Mn 2P (a), P 2P (b), O 1s (c), and C1s (d) of samples the spent LiMn2O4, precursor powders, and recovered LiMnPO4.
Fig. 5. SEM (a, b) and TEM (c–f) images of the recovered LiMnPO4.
regenerated composite has a nano-sized uniform particle size distribution and homogeneous carbon coating. From the chemical synthesis technology perspective, a new synthesis method may provide promising lithium storage properties for LIBs. A homogeneous coating film with high conductivity is expected to improve the electrochemical performance of olivinestructured phosphates. The electrochemical performances of the spent LiMn2O4 and recycled LiMnPO4 are displayed in Fig. 6. Fig. 6(a) shows the initial charge–discharge curves of the spent LiMn2O4 at 0.2 and 1C. The spent cathode material displays a poor electrochemical performance with approximately 54 and 50 mA h
g 1 discharge capacities at 0.2 and 1C rate, respectively, attributed to the unwanted phase transformation and rapid side reactions during the long-term cycling [43–45]. The charge and discharge curves of the regenerated LiMnPO4 at different rates are shown in Fig. 6(b), in which an apparent plateau is detected at 4.1 V. This is homologous to the intercalation/de-intercalation of the Li+ ions from olivine-structured LiMnPO4. The capacity of the active sample is 148.5, 136.1, 125.2, 116.5, and 97.5 mA h g 1 at 0.05, 0.2, 0.5, 1, and 2 C rate, respectively. The results indicate that the formation of regenerated LiMnPO4/C composites with high discharge capacity and high discharge plateau ratio at various rates. This mainly
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Fig. 6. Electrochemical performance of the spent LiMn2O4 and recovered LiMnPO4/C. The charge/discharge profiles of the spent LiMn2O4 at 0.2C and 1C rate (a), the charge/ discharge curves of the recovered LiMnPO4/C at different rates (b), the cyclic stability comparison of the as-prepared materials (c), and the CV profiles of LiMnPO4/C (d).
attributed to the excellent raw material choice, nanocrystallization technique, and in situ carbon coating of the facile recycle strategy. The cycle performance of the spent LiMn2O4 and recycled LiMnPO4/C at 1 C rate is displayed in Fig. 6(c). Obviously, the cycling stability of LiMnPO4/C is very high with a capacity retention of 100% after 100 charge/discharge cycles. The result also illustrates that the olivine-structured LiMnPO4 samples have high structure stabilization and stable cycling performance. To illustrate the stabilization effect, further cyclic voltammogram (CV) test was performed to investigate the lithium storage property of LiMnPO4. Fig. 6(d) presents the CV profiles of the regenerated LiMnPO4 – Li half cells after 1, 50, and 100 cycles at 1C rate. The test was performed between 2.5 and 4.8 V at a scan rate of 0.1 mV s 1. Consistent with previous works [21,46–48], only one peak pair is detected on the CV curve, which corresponds to an anodic peak (4.32 V) and a cathodic peak (4.0 V) during the Mn2+/Mn3+ redox processes [49]. As expected, the sample displays a perfect reproducibility of the peaks from the 1st to 50th and 100th cycles, illustrating good reversibility of the asprepared LiMnPO4/C sample. Both the CV curves and cycling performance indicate distinctly a good Li+ ion storage property of the regenerated LiMnPO4/C. Conclusion In this study, we developed a facile and an eco-efficient strategy for the regeneration of LiMnPO4/C cathode materials directly from the spent LiMn2O4 cathodes. The spent LiMn2O4 particles and self-contained and well-dispersed carbon source were reused 100% without leaching, extraction, precipitation, filtration, or washing processes. The highly efficient mechanochemical activation-assisted solid-state technique ensured uniform mixing and nanocrystallization of the raw materials, which is crucial for the high performance of LiMnPO4 cathode
materials. The recovered LiMnPO4/C nano-composite displayed a promising electrochemical performance with a discharge capacity of 148.5 mA h g 1 at 0.05C rate and exhibited a perfect cyclic performance. Moreover, only CO2, H2O, and recyclable NH3 were released in the entire recycle process. Thus, this is a potential strategy for reusing LiFePO4, LiMn2O4, and the NCMbased spent LIBs materials for commercial purposes. Acknowledgements We gratefully acknowledge the National Natural Science Foundation of China (Grant Nos. 51764029 and 51904135), Provincial Natural Science Foundation of Yunnan (No. 2017FB085), Applied Basic Research Plan of Yunnan Province (No. 2018FB087). References [1] W. Li, B. Song, A. Manthiram, Chem. Soc. Rev. 46 (2017) 3006. [2] J. Jiang, K. Du, Y. Cao, Z. Peng, G. Hu, J. Duan, J. Alloys Compd. 577 (2013) 138. [3] C.S. dos Santos, J.C. Alves, S.P. da Silva, L. Evangelista Sita, P.R.C. da Silva, L.C. de Almeida, J. Scarminio, J.Hazard. Mater. 362 (2019) 458. [4] Q. Meng, Y. Zhang, P. Dong, Waste Manag. 64 (2017) 214. [5] J. Chen, Q. Li, J. Song, D. Song, L. Zhang, X. Shi, Green Chem. 18 (2016) 2500. [6] H. Ku, Y. Jung, M. Jo, S. Park, S. Kim, D. Yang, K. Rhee, E.-M. An, J. Sohn, K. Kwon, J. Hazard. Mater. 313 (2016) 138. [7] J.F. Paulino, N.G. Busnardo, J.C. Afonso, J. Hazard. Mater. 150 (2008) 843. [8] Y. Zhang, Q. Meng, P. Dong, J. Duan, Y. Lin, J. Ind. Eng. Chem. 66 (2018) 86. [9] P. Meshram, B.D. Pandey, T.R. Mankhand, Chem. Eng. J. 281 (2015) 418. [10] Y. Zhang, Y. Zhang, Y. Zhang, P. Dong, Q. Meng, M. Xu, J. Alloys Compd. 783 (2019) 357. [11] L.E. Sita, S.P. da Silva, P.R.C. da Silva, J. Scarminio, Mater. Chem. Phys.194 (2017) 97. [12] Y. Weng, S. Xu, G. Huang, C. Jiang, J. Hazard. Mater. (2013) 246 163–172. [13] N.H. Kwon, H. Yin, T. Vavrova, J.H.W. Lim, U. Steiner, B. Grobéty, K.M. Fromm, J Power Sources 342 (2017) 231. [14] J.-K. Kim, C.-R. Shin, J.-H. Ahn, A. Matic, P. Jacobsson, Electrochem. Commun. 13 (2011) 1105. [15] M. Pivko, M. Bele, E. Tchernychova, N.Z. Logar, R. Dominko, M. Gaberscek, Chem. Mater. 24 (2012) 1041.
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Please cite this article in press as: Q. Meng, et al., Novel efficient and environmentally friendly recovering of high performance nano-LiMnPO4/C cathode powders from spent LiMn2O4 batteries, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.08.051