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postgraduate thesis: Low-temperature thermal strategies for the relithiation and destructure of layered cathodes for spent lithium-ion batteries
Title | Low-temperature thermal strategies for the relithiation and destructure of layered cathodes for spent lithium-ion batteries |
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Authors | |
Issue Date | 2022 |
Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
Citation | Meng, Z. [孟喆]. (2022). Low-temperature thermal strategies for the relithiation and destructure of layered cathodes for spent lithium-ion batteries. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. |
Abstract | Currently, the rapidly generated spent lithium-ion batteries (LIBs) are causing serious environmental concern due to the exploding market of electric vehicles and portable electronics. Despite the toxicity, the layered cathodes, mostly LiCoO2 (LCO) and LiNixCoyMnzO2 (x+y+z = 1, NCM), possess high contents of valuable metals as potential urban mines. Thus, this study aims to find green and profitable recovery methods for the valuable metals from layered cathodes, and the top priority is on reducing the energy consumptions.
First of all, the study proposed plastic synergetic pyrolysis strategies for the decomposition of layered cathodes by applying two types of commonly used plastics – polyvinyl chloride (PVC) and polyethylene terephthalate (PET). PVC and PET successfully accelerated the lattice decay and decomposition of layered cathodes (LCO and NCM), and reduced reaction temperature to 450 °C and 550 °C, respectively. The valuable metals in cathodes includes Li, Ni, Co and Mn, of which Li were transformed mainly into lithium carbonate and transition metals formed oxides and metallic simple substances. Thereafter, a simple water leaching could separate lithium and transition metals with relatively high recovery rate (92-100 %) and ideal purities (approximating 100 %). Hence the synergetic pyrolysis strategies possessed significant privileges of chemical-free, energy-saving, highly efficient, and simultaneous utilization of plastic wastes. The insight mechanism study of synergetic pyrolysis was inferred according to both experimental data and theoretical calculation. DFT calculation verified that the Cl in PVC and O in PET were mostly preferable bonding to lithium atoms in cathodes, accelerating the capture of metal atoms from the crystals of LCO/NCM. In addition, the degradation of plastic generated char, free radicals and reductive gas, e.g., CH4, C6H6, CO2, and HCl. The reductants could spontaneously destructure LCO/NCM and reduce transition metals to a lower valence state under elevated temperatures. As a result, the atom capture caused by surface adsorption and free radical/gaseous reduction reaction explained the synergetic reaction and effect of plastics on promoting the lattice destructure of layered cathodes. In addition, NCM was regenerated using recovered Li and transition metal products of pyrolysis, and a one-step sintering at 800 °C could both crystallize NCM and decompose residual char. For the direct regeneration of LCO, a low-temperature hydrothermal treatment at only 180 °C successfully relithiated spent LCO to Li0.97CoO2 and meanwhile remove impurity elements Al, F, and P. Meanwhile, the treatment dosage was enhanced to 120 g/L with the assistance of magnetic stirring. The following short-term sintering at 800 °C with supplemented Li2CO3 fully lithiated LiCoO2 and formed well-defined layered structure. The regenerated LiCoO2 maintained high cycling stability, with a discharge capacity of 118.6 mAh g-1 after 300 cycles and attenuation rate of less than 6 %.
Overall, this study proposed ideal recovery strategies for layered cathodes adopting low-temperature pyrometallurgy through destructure and relithiation routes. Moreover, the intrinsic mechanism of synergetic pyrolysis was explored based on theoretical calculation and experimental study. The proposed metal recovery strategies and mechanism studies are believed to show outstanding performance in achieving green production and improving economic benefits.
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Degree | Doctor of Philosophy |
Subject | Cathodes Lithium ion batteries |
Dept/Program | Civil Engineering |
Persistent Identifier | http://hdl.handle.net/10722/322811 |
DC Field | Value | Language |
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dc.contributor.author | Meng, Zhe | - |
dc.contributor.author | 孟喆 | - |
dc.date.accessioned | 2022-11-18T10:40:43Z | - |
dc.date.available | 2022-11-18T10:40:43Z | - |
dc.date.issued | 2022 | - |
dc.identifier.citation | Meng, Z. [孟喆]. (2022). Low-temperature thermal strategies for the relithiation and destructure of layered cathodes for spent lithium-ion batteries. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. | - |
dc.identifier.uri | http://hdl.handle.net/10722/322811 | - |
dc.description.abstract | Currently, the rapidly generated spent lithium-ion batteries (LIBs) are causing serious environmental concern due to the exploding market of electric vehicles and portable electronics. Despite the toxicity, the layered cathodes, mostly LiCoO2 (LCO) and LiNixCoyMnzO2 (x+y+z = 1, NCM), possess high contents of valuable metals as potential urban mines. Thus, this study aims to find green and profitable recovery methods for the valuable metals from layered cathodes, and the top priority is on reducing the energy consumptions. First of all, the study proposed plastic synergetic pyrolysis strategies for the decomposition of layered cathodes by applying two types of commonly used plastics – polyvinyl chloride (PVC) and polyethylene terephthalate (PET). PVC and PET successfully accelerated the lattice decay and decomposition of layered cathodes (LCO and NCM), and reduced reaction temperature to 450 °C and 550 °C, respectively. The valuable metals in cathodes includes Li, Ni, Co and Mn, of which Li were transformed mainly into lithium carbonate and transition metals formed oxides and metallic simple substances. Thereafter, a simple water leaching could separate lithium and transition metals with relatively high recovery rate (92-100 %) and ideal purities (approximating 100 %). Hence the synergetic pyrolysis strategies possessed significant privileges of chemical-free, energy-saving, highly efficient, and simultaneous utilization of plastic wastes. The insight mechanism study of synergetic pyrolysis was inferred according to both experimental data and theoretical calculation. DFT calculation verified that the Cl in PVC and O in PET were mostly preferable bonding to lithium atoms in cathodes, accelerating the capture of metal atoms from the crystals of LCO/NCM. In addition, the degradation of plastic generated char, free radicals and reductive gas, e.g., CH4, C6H6, CO2, and HCl. The reductants could spontaneously destructure LCO/NCM and reduce transition metals to a lower valence state under elevated temperatures. As a result, the atom capture caused by surface adsorption and free radical/gaseous reduction reaction explained the synergetic reaction and effect of plastics on promoting the lattice destructure of layered cathodes. In addition, NCM was regenerated using recovered Li and transition metal products of pyrolysis, and a one-step sintering at 800 °C could both crystallize NCM and decompose residual char. For the direct regeneration of LCO, a low-temperature hydrothermal treatment at only 180 °C successfully relithiated spent LCO to Li0.97CoO2 and meanwhile remove impurity elements Al, F, and P. Meanwhile, the treatment dosage was enhanced to 120 g/L with the assistance of magnetic stirring. The following short-term sintering at 800 °C with supplemented Li2CO3 fully lithiated LiCoO2 and formed well-defined layered structure. The regenerated LiCoO2 maintained high cycling stability, with a discharge capacity of 118.6 mAh g-1 after 300 cycles and attenuation rate of less than 6 %. Overall, this study proposed ideal recovery strategies for layered cathodes adopting low-temperature pyrometallurgy through destructure and relithiation routes. Moreover, the intrinsic mechanism of synergetic pyrolysis was explored based on theoretical calculation and experimental study. The proposed metal recovery strategies and mechanism studies are believed to show outstanding performance in achieving green production and improving economic benefits. | - |
dc.language | eng | - |
dc.publisher | The University of Hong Kong (Pokfulam, Hong Kong) | - |
dc.relation.ispartof | HKU Theses Online (HKUTO) | - |
dc.rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works. | - |
dc.rights | This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. | - |
dc.subject.lcsh | Cathodes | - |
dc.subject.lcsh | Lithium ion batteries | - |
dc.title | Low-temperature thermal strategies for the relithiation and destructure of layered cathodes for spent lithium-ion batteries | - |
dc.type | PG_Thesis | - |
dc.description.thesisname | Doctor of Philosophy | - |
dc.description.thesislevel | Doctoral | - |
dc.description.thesisdiscipline | Civil Engineering | - |
dc.description.nature | published_or_final_version | - |
dc.date.hkucongregation | 2022 | - |
dc.identifier.mmsid | 991044609104503414 | - |