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Selective recovery of valuable cobalt-nickel alloys and inorganic compounds from spent lithium ion battery cathodes for open and closed loop recycling
Author(s)
Tawonezvi, Tendai
Date Issued
2024
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Lithium-ion batteries (Li-ionBs) have been extensively deployed as the primary electrochemical
power source for many applications, and their demand has increased significantly over the past
decade, with the market projected to reach 116 billion United States dollars (USD) by 2030.
Consequently, a considerable amount of end-of-life Li-ionBs are disposed of as waste annually.
The current processes utilized for recycling spent Li-ionBs involve high-cost, energy-intensive,
and eco-hazardous processes and materials. This has resulted in only a mere 5% of the spent
Li-ionBs currently being recycled. Therefore, the development of an effective, low-cost, lowenergy-
intensive, and eco-friendly recycling process route for recovering valuable metals (i.e.,
lithium [Li], cobalt [Co], nickel [Ni], and manganese [Mn]) is imperative and imminent.
The cathode, in this study composed of Lithium Nickel Manganese Cobalt Oxide
(LiNixMnyCozO2, or NMC) material, is a key determinant of a NMC Li-ionB’s cost and
performance. While NMC is one of the predominant cathode chemistries used in Li-ionBs due
to its favourable balance of performance, stability, and cost, other types of cathode materials
are also widely employed in various applications. NMC cathode combines the valuable metals
Ni, Co, and Mn in varying ratios (x, y, z in LiNixMnyCozO2) for optimal performance, stability,
and cost. For example, NMC 532, used in this study, has a Ni:Mn:Co ratio of 5:3:2,
corresponding to the formulation LiNi0.5Mn0.3Co0.2O2. Conventional pure metal recovery, from
Li-ionB waste, processes include solvent extraction, ion exchange, and selective precipitation,
followed by galvanostatic electrowinning to obtain solid metal deposits. In this work, valuable
Ni-Co alloys from spent Li-ionBs were selectively recovered from multi-ion (Ni2+, Co2+, Mn2+,
and Li+) NMC 532 leachate solutions through potentiostatic electrowinning. Since the postelectrowinning
spent liquor still contains traces of Ni and Co and significant amounts of Li and
Mn, an additional sodium (Na)-based chemical precipitation unit operation was added to
recover the nickel hydroxide (Ni(OH)2) , manganese hydroxide (Mn(OH)2) and cobalt hydroxide
(Co(OH)2) composite mixture (0.6[Ni(OH)2].0.3[Mn(OH)2].0.1[Co(OH)2]), Mn(OH)2, and lithium
carbonate (Li2CO3) materials.
The rationale of this research was based on the elimination of cost and energy-intensive
hydrometallurgical intermediate processes like solvent extraction, ion exchange, and selective
precipitation (to extract Ni and Co selectively), utilization of potentiostatic techniques (instead
of conventional galvanostatic techniques) to selectively extract specific metals and enhance purity, integration of rotating cathodes to increase the deposition rate, and utilization of Platinum (Pt)-coated Titanium (Ti) dimensionally stable anodes (DSA) to reduce deposit
contamination and consequently levelize the cost of operation. It is believed that by applying
a constant potential suitable for Co and Ni reduction reactions (potentiostatic electrowinning),
valuable Ni and Co can be selectively deposited and separated from less valuable Li and Mn.
Recovered Ni-Co alloys can be used as feedstock for Lithium Nickel Manganese Cobalt Oxide
(NMC) cathode production processes. Ni-Co alloys can also be used in the production of
magnetic films, electrocatalysis materials, and other various technological applications.
In the first experimental phase, this research demonstrated the applicability of inorganic acidreductant
leachant-based leaching of NMC 532 to effectively leach and recover all valuable
metals in the cathode material. This approach provides quantitative recovery data for each
element of the entire particle population at different operational parameters: reductant and
inorganic acid concentration, solid-to-liquid (S/L) ratio, reaction time, and temperature. The
quantification of elemental recovery data was done through Inductively Coupled Plasma
Optical Emission Spectroscopy (ICP-OES) and Energy Dispersive Spectroscopy (EDS). Phase
composition was assessed through X-ray Diffraction (XRD) analysis. Morphology and particle
size were analysed using High-Resolution Scanning Electron Microscopy (HR-SEM). By utilising
optimised leaching parameters, aluminium (Al) foil and carbon (C) flakes were freed from the
cathode matrix and peak leaching recovery efficiencies of 98.9% for Li, 97.1% for Co, 96.9% for
Ni, and 95.7% for Mn were attained.
In the second experimental phase, the effects of key electrowinning parameters were
quantified and studied, and alternative electrodes were tested to suppress the extent of scaling,
electrode resistivity, operational and capital costs, and life cycle duration limitations. This
optimisation study was conducted using synthetic Ni, Co, Mn, and Li sulphate solutions
mimicking the NMC 532 ratio of elements. The optimised electrowinning parameters such as
applied potential, temperature, pH, Co-Ni, Na₂SO₄ and buffer dosage, and electrode distance
and active area were then utilised to recover Ni0.65Co0.35 alloy from real NMC leachate at a
minimum rate of 0.06 g/cm².hr with 88% current efficiency. 90% of the Co and 77% of the Ni
in the leachate were recovered in a 3-hour electrowinning run.
In the last phase of the experiments, the metals remaining in the post-electrowinning
electrolyte from the electrowinning were recovered through multi-stage precipitation to
recover Mn(OH)₂ and Li₂CO₃, and a hydroxide composite formulation of Ni, Mn, and Co
(0.6[Ni(OH)2].0.3[Mn(OH)2].0.1[Co(OH)2]) at over 99% precipitation efficiency. Approximately
19% of Ni, 7.5% of Co, and 95% of Li were recovered during multi-stage precipitation. The
varied and optimized key parameters for pH-based precipitation were temperature, reactants
ratio, and pH. The semi-closed loop recycling cost (R/kg) of the cathode was calculated to be
R 153/kg, which is at least 50% lower than R 360/kg, R 308/kg, and R 258/kg recycling costs
for direct recycling, pyrometallurgical, and hydrometallurgical processes, respectively.
A significant fraction of the process resultant solution from the whole process can be recycled
for use in the leachate pH adjustment stage, while the minority portion will need further
treatment (to remove sulphate (SO2-4) and sodium (Na+) before being discarded per National
Environmental Protection Agency (NEPA) regulations since it contains negligible and
environmentally tolerant metal concentrations of Mn, Li, Ni and Co. The obtained results
demonstrate the feasibility of a semi-closed loop spent Li-ionB cathode recycling process
comprising battery pre-treatment, single-stage leaching, single-compartment electrowinning
cell, and Na-based precipitation. The main objective of this work, high purity Ni0.65Co0.35 alloy
recovery, was successfully achieved. The recovered Ni0.65Co0.35 alloy, Li2CO3, Mn(OH)₂, and
0.6[Ni(OH)2].0.3[Mn(OH)2].0.1[Co(OH)2] are versatile compounds with applications ranging
from the production of Li-ionBs to medicine and material production, among other
applications.
power source for many applications, and their demand has increased significantly over the past
decade, with the market projected to reach 116 billion United States dollars (USD) by 2030.
Consequently, a considerable amount of end-of-life Li-ionBs are disposed of as waste annually.
The current processes utilized for recycling spent Li-ionBs involve high-cost, energy-intensive,
and eco-hazardous processes and materials. This has resulted in only a mere 5% of the spent
Li-ionBs currently being recycled. Therefore, the development of an effective, low-cost, lowenergy-
intensive, and eco-friendly recycling process route for recovering valuable metals (i.e.,
lithium [Li], cobalt [Co], nickel [Ni], and manganese [Mn]) is imperative and imminent.
The cathode, in this study composed of Lithium Nickel Manganese Cobalt Oxide
(LiNixMnyCozO2, or NMC) material, is a key determinant of a NMC Li-ionB’s cost and
performance. While NMC is one of the predominant cathode chemistries used in Li-ionBs due
to its favourable balance of performance, stability, and cost, other types of cathode materials
are also widely employed in various applications. NMC cathode combines the valuable metals
Ni, Co, and Mn in varying ratios (x, y, z in LiNixMnyCozO2) for optimal performance, stability,
and cost. For example, NMC 532, used in this study, has a Ni:Mn:Co ratio of 5:3:2,
corresponding to the formulation LiNi0.5Mn0.3Co0.2O2. Conventional pure metal recovery, from
Li-ionB waste, processes include solvent extraction, ion exchange, and selective precipitation,
followed by galvanostatic electrowinning to obtain solid metal deposits. In this work, valuable
Ni-Co alloys from spent Li-ionBs were selectively recovered from multi-ion (Ni2+, Co2+, Mn2+,
and Li+) NMC 532 leachate solutions through potentiostatic electrowinning. Since the postelectrowinning
spent liquor still contains traces of Ni and Co and significant amounts of Li and
Mn, an additional sodium (Na)-based chemical precipitation unit operation was added to
recover the nickel hydroxide (Ni(OH)2) , manganese hydroxide (Mn(OH)2) and cobalt hydroxide
(Co(OH)2) composite mixture (0.6[Ni(OH)2].0.3[Mn(OH)2].0.1[Co(OH)2]), Mn(OH)2, and lithium
carbonate (Li2CO3) materials.
The rationale of this research was based on the elimination of cost and energy-intensive
hydrometallurgical intermediate processes like solvent extraction, ion exchange, and selective
precipitation (to extract Ni and Co selectively), utilization of potentiostatic techniques (instead
of conventional galvanostatic techniques) to selectively extract specific metals and enhance purity, integration of rotating cathodes to increase the deposition rate, and utilization of Platinum (Pt)-coated Titanium (Ti) dimensionally stable anodes (DSA) to reduce deposit
contamination and consequently levelize the cost of operation. It is believed that by applying
a constant potential suitable for Co and Ni reduction reactions (potentiostatic electrowinning),
valuable Ni and Co can be selectively deposited and separated from less valuable Li and Mn.
Recovered Ni-Co alloys can be used as feedstock for Lithium Nickel Manganese Cobalt Oxide
(NMC) cathode production processes. Ni-Co alloys can also be used in the production of
magnetic films, electrocatalysis materials, and other various technological applications.
In the first experimental phase, this research demonstrated the applicability of inorganic acidreductant
leachant-based leaching of NMC 532 to effectively leach and recover all valuable
metals in the cathode material. This approach provides quantitative recovery data for each
element of the entire particle population at different operational parameters: reductant and
inorganic acid concentration, solid-to-liquid (S/L) ratio, reaction time, and temperature. The
quantification of elemental recovery data was done through Inductively Coupled Plasma
Optical Emission Spectroscopy (ICP-OES) and Energy Dispersive Spectroscopy (EDS). Phase
composition was assessed through X-ray Diffraction (XRD) analysis. Morphology and particle
size were analysed using High-Resolution Scanning Electron Microscopy (HR-SEM). By utilising
optimised leaching parameters, aluminium (Al) foil and carbon (C) flakes were freed from the
cathode matrix and peak leaching recovery efficiencies of 98.9% for Li, 97.1% for Co, 96.9% for
Ni, and 95.7% for Mn were attained.
In the second experimental phase, the effects of key electrowinning parameters were
quantified and studied, and alternative electrodes were tested to suppress the extent of scaling,
electrode resistivity, operational and capital costs, and life cycle duration limitations. This
optimisation study was conducted using synthetic Ni, Co, Mn, and Li sulphate solutions
mimicking the NMC 532 ratio of elements. The optimised electrowinning parameters such as
applied potential, temperature, pH, Co-Ni, Na₂SO₄ and buffer dosage, and electrode distance
and active area were then utilised to recover Ni0.65Co0.35 alloy from real NMC leachate at a
minimum rate of 0.06 g/cm².hr with 88% current efficiency. 90% of the Co and 77% of the Ni
in the leachate were recovered in a 3-hour electrowinning run.
In the last phase of the experiments, the metals remaining in the post-electrowinning
electrolyte from the electrowinning were recovered through multi-stage precipitation to
recover Mn(OH)₂ and Li₂CO₃, and a hydroxide composite formulation of Ni, Mn, and Co
(0.6[Ni(OH)2].0.3[Mn(OH)2].0.1[Co(OH)2]) at over 99% precipitation efficiency. Approximately
19% of Ni, 7.5% of Co, and 95% of Li were recovered during multi-stage precipitation. The
varied and optimized key parameters for pH-based precipitation were temperature, reactants
ratio, and pH. The semi-closed loop recycling cost (R/kg) of the cathode was calculated to be
R 153/kg, which is at least 50% lower than R 360/kg, R 308/kg, and R 258/kg recycling costs
for direct recycling, pyrometallurgical, and hydrometallurgical processes, respectively.
A significant fraction of the process resultant solution from the whole process can be recycled
for use in the leachate pH adjustment stage, while the minority portion will need further
treatment (to remove sulphate (SO2-4) and sodium (Na+) before being discarded per National
Environmental Protection Agency (NEPA) regulations since it contains negligible and
environmentally tolerant metal concentrations of Mn, Li, Ni and Co. The obtained results
demonstrate the feasibility of a semi-closed loop spent Li-ionB cathode recycling process
comprising battery pre-treatment, single-stage leaching, single-compartment electrowinning
cell, and Na-based precipitation. The main objective of this work, high purity Ni0.65Co0.35 alloy
recovery, was successfully achieved. The recovered Ni0.65Co0.35 alloy, Li2CO3, Mn(OH)₂, and
0.6[Ni(OH)2].0.3[Mn(OH)2].0.1[Co(OH)2] are versatile compounds with applications ranging
from the production of Li-ionBs to medicine and material production, among other
applications.
Additional information
Thesis (DEng (Chemical Engineering))--Cape Peninsula University of Technology, 2024
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