Date of Award
2021
Document Type
Open Access Dissertation
Degree Name
Doctor of Philosophy in Chemical Engineering (PhD)
Administrative Home Department
Department of Chemical Engineering
Advisor 1
Lei Pan
Committee Member 1
Timothy C. Eisele
Committee Member 2
Yixin Liu
Committee Member 3
Kathryn A. Perrine
Abstract
The surges in the volume of the retired Li-ion batteries (LIBs) in future motivate Li-ion battery recycling R&D activities worldwide. Within the Li-ion batteries, the most valuable component is cathode active materials that consist of critical minerals and materials such as lithium, cobalt, nickel, manganese. The LIB recycling has been investigated at both the lab scale and industrial scale. There are three existing recycling methods, namely physical separation, pyrometallurgy, and hydrometallurgy. Physical separation methods sort individual battery components without changing materials’ physical properties, while both pyrometallurgical and hydrometallurgical recycling routes aim to recover valuable metals using a high-temperature process and a leaching process, respectively. The conventional pyrometallurgical and hydrometallurgical processes are targeted to a few metal elements only. The goal of this work is to take the physical recycling methods to the next level by separating and concentrating individual battery components to the highest purity in the solid phase while preserving the electrochemical integrity of individual battery components.
In this work, two physical separation methods were investigated to separate two electrode active materials from LIBs. They are froth flotation and enhanced gravity separation technology. First, separation of the black mass from spent and new LIBs by froth flotation have been investigated. Graphite is commonly used as the anode active material and it is naturally hydrophobic, while lithium transitional metal oxides are commonly used as the cathode active materials, and they are hydrophilic. By taking the advantage in the surface property between the two electrode active materials, froth flotation method separates the two electrode active materials from spent LIBs. Our result showed that all anode active materials from new and lightly degraded EV batteries were reported in the froth product in the presence of kerosene as the collector, while the sink (tailing) product contained over 87% purity of lithium transitional metal oxides. The cathode recovery was approximately 60-80%, which was attributed to the presence of PVDF binders in the cathode composite materials. The separation performance deteriorated for spent LIBs due to the formation of solid electrolyte interphase (SEI) layers on the anode surfaces. To restore the original surface properties of the electrode active materials, a heating process was applied to the black mass. Over 99% purity of graphite and lithium metal oxide was obtained by multistage stages of the froth flotation process. In addition, a high-shear blending process was developed to de-agglomerate cathode active particles from PVDF binders in cathode composites. Individual cathode active particles got liberated from binders. Froth flotation concentrated PVDF binders and carbon additives in the froth product, leaving high purity (98% purity or above) of lithium metal oxides in the tailing product.
Centrifugal gravity separation method was introduced for the first time to separate both the pristine and spent electrode active materials by taking the advantage of the difference in specific densities between the two electrode active materials. Graphite was flushed with the overflow slurry, while lithium metal oxides were retained at the inner wall of the concentrator bowl to achieve a separation between the two materials. Over 99% purity of lithium metal oxides from spent Li-ion batteries in the concentrate product was xvii demonstrated for the first time. Circuit design and locked-cycle experiments were conducted to validate the separation results. Compared with froth flotation process, the centrifugal gravity separation has an advantage for spent Li-ion batteries since the specific gravity of the electrode active materials remained unchanged after numerous charge-discharge cycles.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Zhan, Ruiting, "Lithium-ion Battery Recycling Using Mineral Processing Methods", Open Access Dissertation, Michigan Technological University, 2021.