Lithium-Ion Battery Recycling - Influence of Recycling Processes on Component Liberation and Flotation Separation Efficiency

Abstract

Recycling is a potential solution to narrow the gap between the supply and demand of raw materials for lithium-ion batteries (LIBs). However, the efficient separation of the active components and their recovery from battery waste remains a challenge. This paper evaluates the influence of three potential routes for the liberation of LIB components (namely mechanical, thermomechanical, and electrohydraulic fragmentation) on the recovery of lithium metal oxides (LMOs) and spheroidized graphite particles using froth flotation. The products of the three liberation routes were characterized using SEM-based automated image analysis. It was found that the mechanical process enabled the delamination of active materials from the foils, which remained intact at coarser sizes along with the casing and separator. However, binder preservation hinders active material liberation, as indicated by their aggregation. The electrohydraulic fragmentation route resulted in liberated active materials with a minor impact on morphology. The coarse fractions thus produced consist of the electrode foils, casing, and separator. Notwithstanding, it has the disadvantage of forming heterogeneous agglomerates containing liberated active particles. This was attributed to the dissolution of the anode binder and its rehardening after drying, capturing previously liberated particles. Finally, the thermomechanical process showed a preferential liberation of individual anode active particles and thus was considered the preferred upstream route for flotation. However, the thermal treatment oxidized Al foils, rendering them brittle and resulting in their distribution in all size fractions. Among the three, the thermomechanical black mass showed the highest flotation selectivity due to the removal of the binder, resulting in a product recovery of 94.4% graphite in the overflow and 89.4% LMOs in the underflow product.

Full text

Lithium-Ion Battery Recycling�Influence of Recycling Processes on
Component Liberation and Flotation Separation Eciency
Anna Vanderbruggen,*Neil Hayagan, Kai Bachmann, Alexandra Ferreira, Denis Werner, Daniel Horn,
Urs Peuker, Rodrigo Serna-Guerrero, and Martin Rudolph
Cite This: https://doi.org/10.1021/acsestengg.2c00177
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sı Supporting Information
ABSTRACT: Recycling is a potential solution to narrow the gap between the supply and demand of raw materials for lithium-ion
batteries (LIBs). However, the ecient separation of the active components and their recovery from battery waste remains a
challenge. This paper evaluates the influence of three potential routes for the liberation of LIB components (namely mechanical,
thermomechanical, and electrohydraulic fragmentation) on the recovery of lithium metal oxides (LMOs) and spheroidized graphite
particles using froth flotation. The products of the three liberation routes were characterized using SEM-based automated image
analysis. It was found that the mechanical process enabled the delamination of active materials from the foils, which remained intact
at coarser sizes along with the casing and separator. However, binder preservation hinders active material liberation, as indicated by
their aggregation. The electrohydraulic fragmentation route resulted in liberated active materials with a minor impact on
morphology. The coarse fractions thus produced consist of the electrode foils, casing, and separator. Notwithstanding, it has the
disadvantage of forming heterogeneous agglomerates containing liberated active particles. This was attributed to the dissolution of
the anode binder and its rehardening after drying, capturing previously liberated particles. Finally, the thermomechanical process
showed a preferential liberation of individual anode active particles and thus was considered the preferred upstream route for
flotation. However, the thermal treatment oxidized Al foils, rendering them brittle and resulting in their distribution in all size
fractions. Among the three, the thermomechanical black mass showed the highest flotation selectivity due to the removal of the
binder, resulting in a product recovery of 94.4% graphite in the overflow and 89.4% LMOs in the underflow product.
KEYWORDS: lithium-ion battery, automated mineralogy, liberation, froth flotation, recycling
1. INTRODUCTION
Lithium-ion batteries (LIBs) are widely used nowadays in
various devices, from portable electronics to electric vehicles.
Growing global demands for Co, Mn, Ni, Li, and graphite, which
are present in LIBs, have further stressed the already scarce
supply of such raw materials worldwide.
1
These surging
demands can lead to supply risks, price fluctuations, and market
monopoly. Eective recycling strategies are thus necessary to
reduce the need of virgin raw materials and to promote resource
preservation and environmental protection. Such eorts are
exemplified in the current stipulation by the European Union,
where a minimum recycling eciency of 50 wt % for LIB
(Directive 2006/66/EC) is required, with an ongoing proposal
to reach 70 wt % by 2030.
2
Furthermore, the European Union
categorized Li was as a critical raw material in 2020, while Co
and natural graphite have been considered as such since 2010,
highlighting their economic importance and supply risks.
3
The current and emerging recycling technologies for LIBs
typically focus on the recovery of components that have high
economic value, such as Co, Ni, and Cu. To reach a higher
recycling eciency, new products such as graphite should be
considered, as it represents 15−20% of LIB’s total mass.
4
Furthermore, to meet the revised Battery Directive with possible
specific material recovery targets, for example., 95% Co, Cu, and
Ni by 2030,
2
more robust recycling strategies are sorely needed.
It is also noteworthy that despite the aforementioned
Received: May 16, 2022
Revised: September 15, 2022
Accepted: September 15, 2022
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regulations, the supply risk of graphite has only recently gained
attention. Indeed, graphite will remain an essential component
of LIBs in the foreseeable future.
1,5
According to a survey carried
out by Benchmark Mineral Intelligence,
6
anode materials are
forecasted to experience the highest increase in demand among
all the raw materials used in LIBs, that is, +700% between 2018
and 2028. Currently, China has a dominant position regarding
this critical material, accounting for 64% of the flake graphite
global production and almost 90% of anodic spherical graphite.
As a result, Western countries are actively searching for
strategies to develop their own graphite supply chain for battery
production, including plans to integrate recycled graphite.
7
During typical LIB recycling processes, a comminution stage
is used as a first stage to separate electrode particles from their
current collectors, producing foils in the coarse size fraction and
active particles in the fine fraction. This is possible since
electrode foils present a ductile behavior and, as reported by
Schubert,
8
ductile materials can be liberated through shear,
cutting, and tearing stresses. The resulting fine fraction is
typically referred to as “black mass” and contains mixed cathode
and anode active materials.
9,10
Most of the state-of-the-art recycling technologies use black
mass resulting from the pretreatment (e.g., mechanical or
thermomechanical pretreatment) as a starting point for chemical
processes for metal recovery. Indeed, in industry, this black mass
is usually not further sorted and is directly fed to either
established or newly developed pyro- and/or hydrometallurgical
processes to extract metals from the lithium metal oxides
(LMOs), although at the expense of graphite losses.
11
In the case
of hydrometallurgical processes, the removal of graphite from
the black mass beforehand would lead to a feed with high metal
content, reducing significantly the volume of material to leach
and decreasing the leaching reagent consumption caused by the
porosity of graphite. Therefore, the feed composition to
metallurgical purification stages needs to be controlled to
minimize losses and operating costs and preconcentration with
froth flotation is an option that has recently gained attention.
Previous studies have demonstrated the use of froth flotation on
black mass to separate the graphite particles from the
LMOs,
12−16
either resulting in two valuable products for direct
remanufacturing or as feed streams for metallurgical stages with
an increased overall eciency of LIB recycling.
Nevertheless, one major challenge in the separation of black
mass components is the presence of a polymeric binder, which
adheres the active particles together and onto the current foils.
In LIBs, the anode is made of graphite particles calendered on
Cu, and the cathode of LMOs adhered to Al. Recently, eorts
have been carried out to develop removal strategies for the
polyvinylidene difluoride (PVDF) binder, one of the most
commonly used due to its good electrochemical stability.
17
Some studies propose PVDF decomposition by thermal
treatment over 450 °C
18−20
or with the aid of solvents such as
N-methyl-2-pyrrolidone (NMP)
21
or dimethyl isosorbide
(DMI).
22
On the other hand, water-soluble binders are more
common for anode electrodes, such as styrene−butadiene
Rubber (SBR),
23,24
resulting in higher liberation eciencies of
the anode components.
This paper provides insights into the influence of three
liberation processes prior to froth flotation: mechanical (M),
thermomechanical (TM), and electrohydraulic fragmentation
(EHF). The impact of each strategy on the characteristics of
black mass particles was studied using automated mineralogy.
This novel approach for black mass characterization was recently
proposed by Vanderbruggen et al.
10
and Dadeet al.
25
and
provides information on the chemical composition, morphol-
ogy, and degree of liberation of LIB components. While most
research on LIB recycling has focused on the operating
conditions and design of separation processes, there is a need
to gain a fundamental understanding of particle behavior and
liberation as a result of treatment stages that systematically aect
their overall recycling eciency. Such knowledge could also
support the LIB design and production practices.
2. MATERIALS AND METHODS
2.1. Material and Processing. The material for this study
consisted of 200 discharged identical LIBs (Samsung
INR18650-29E, batch n°BRGA29E82105). One battery was
manually opened and dismantled to estimate the mass of each
major component, as presented in Figure 1. In this particular
case, the active materials were scrapped o manually from the
foils. After dismantling, the recovered material was placed in an
oven at a maximum of 40 °C for safety reasons for 24 h and then
the weight of each fraction was measured with a scientific
balance (ENTRIS6202I−1S, Sartorius Lab Instruments GmbH
& Co, Germany), and the dierence in weight corresponds to
the estimated electrolyte, which was evaporated (Figure 1). The
electrolyte value is quite low compared to the literature,
26
which
can testify that the electrolyte is not entirely evaporated at that
temperature and some electrolyte compounds such as the
conducting salts might have remained.
Complementary experiments have been carried out to identify
the nature of the binder, which is important information in order
to understand the electrode behavior during recycling. The
electrodes of a dismantled INR18650-29E were immersed in tap
water for 10 min. As observed in the Supporting Information
(Figure S1), all the graphite particles were thus detached from
the Cu foils, confirming the hypothesis of a water-soluble binder
for the anodic electrode. For the cathodic electrode, the LMOs
remained laminated on the Al foil, testifying to the presence of a
binder insoluble in water, likely PVDF.
For this study, the batteries underwent three recycling routes
(Figure 2), hereby referred to as M, TM, and EHF, to determine
the influence of each process on the liberation of battery
components and their eventual recovery. The pretreatment
processes are described next.
1. The M process used a single-shaft rotary impact shear
crusher UG300MS (MeWa universal granulator, Andritz,
Schwabisch, Germany) operated at a peripheral speed of
Figure 1. Estimation of INR18650-29E battery composition (wt %)
after manual dismantling.
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6.4 m/s with a bottom grid of 10 mm. The feed consisted
of intact batteries producing shredded materials passing
through the discharge grate, while coarser particles
undertake further stress. The operating principle of this
crusher is the comminution of the feed material by
applying shearing stress between a block-shaped rotor and
stator tools, as detailed by Lyon et al.
27
2. In the TM route, vacuum pyrolysis was performed at
500−650 °C. Subsequently, comminution of thermally
treated products was carried out using a Retsch SM 2000
cutting mill (Retsch, Inc., Newtown, USA) with a bottom
sieve of 10 mm mesh size.
3. The EHF route employed an EHF unit (EHF-400
ImpulsTec GmbH, Germany. The EHF uses three
cathodes at 40 kV to produce shock waves, discharging
at a rate of 1 to 4 Hz. The process produced two fractions:
float and sink, which were dried in an oven at 80−100 °C.
Further information on this equipment is found in O
hl et
al.
28
The resulting black mass products (<1000 μm) from M, TM,
and the sink fraction from the EHF process were classified with a
vibratory column sieve (Fritsch Analysette 3, Idar-Oberstein,
Germany) using four nominal sizes: 1000, 500, 125, and 63 μm.
For each fraction of the black mass, a representative subsample
of 1.5 g was taken using a rotary splitter (PT100, Retsch GmbH,
Haan, Germany) for analytical investigations. Each black mass
type had five samples, one per size fraction and two epoxy blocks
for the fraction 500−1000 μm to minimize particle size eect on
samples representativeness.
In addition, the fine fraction (<63 μm) was further processed
by froth flotation to separate graphite particles from the LMOs.
The fraction below 63 μm was chosen in this study because it
was expected to contain the most liberated particles. The batch
flotation tests were conducted using a mechanically agitated
laboratory flotation machine (XFG, series Hang Slot). The black
mass sample was dispersed in water down to a solid
concentration of 50 g/L and with an impeller speed of 1200
rpm. The sample was dispersed for 2 min and then followed by
the conditioning stage, and the parameters were chosen based
on previous studies.
12,29
In all tests, 350 g/t EscaidTM 110
(ExxonMobil Hydrocarbon fluid, Product no. 20171206) was
used as a collector, conditioned for 3 min, followed by the
addition of 150 g/t methyl isobutyl carbinol (MIBC, 99% Alfa
Aesar Product no. A13435) as a frother, stirred for 1 min. During
flotation, the airflow rate was fixed to 20 mL/min, and the froth
was collected for 10 min. After each experiment, the flotation
products were dried in an oven under natural convection for 12 h
at 45 °C. Finally, a representative sample of the froth phase and
underflow products was collected with a rotary sample splitter
(Retsch PT100, Retsch GmbH, Haan, Germany) and was
submitted for automated mineralogy analysis.
2.2. Characterization. The chemical composition, degree
of liberation of LIB components, and their distribution were
evaluated using SEM-based automated image analysis, also
commonly called automated mineralogy. This analytical
technique combines high-resolution backscattered images
obtained by scanning electron microscopy (SEM) with energy
dispersive X-ray (EDX) measurements to determine the phase
composition (volume or mass fraction) and geometrical
parameters (e.g., size, shape, and association) of particles on a
polished surface.
The preparation of epoxy blocks followed the method as
originally suggested by Rahfeld and Gutzmer
30
to analyze
graphite particles and modified in Vanderbruggen et al.
10
The
particles were embedded in a homogeneous mixture of epoxy
resin and iodoform. To minimize errors and bias caused by
sedimentation and settling, vertical slices (B-sections) were
used, as suggested by Heinig et al..
31
These slices were rotated
90°and fixed in a new epoxy resin. The sample was then
polished and carbon-coated, thereby creating a conductive
surface and scanned by SEM.
The mineral liberation analysis (MLA) system hereby used
combines a SEM (FEI Quanta 650F) equipped with two EDX
spectrometers (Bruker Quantax X-Flash 5030). The image was
Figure 2. Studied recycling routes: M, TM, and (EHF). Followed by froth flotation of the fine black mass fraction.
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processed with MLA Suite 3.1.4 software for automated data
acquisition. The working principle is summarized in Figure 3. In
the first place, a BSE image is obtained (Figure 3A), which is
used to determine the grain boundaries. Next, the sample is
scanned using the grain X-ray mapping (GXMAP); on each red
point in Figure 3B an X-ray spectrum was acquired. The same
operating conditions and measurement mode were applied to all
the samples, that is, 0.5 μm pixel size at 15 kV.
The individual X-ray measurement (Figure 3B) was classified
using a generated reference phase list for this project (Figure
3C). For data processing, the spectra were grouped according to
battery components: anode active material, lithium metal oxides,
Cu foil, Al foil, and casing, as shown in Supporting Information
S2. The battery component can be estimated and highlighted on
the processed image (Figure 3D); the Al foil appears in green,
whereas the lithium metal oxides appear in blue. In addition, the
calculated assay obtained by MLA was cross-checked with bulk
analysis using X-ray fluorescence (XRF NitonTM XL3t 980
from Thermo Scientific), as explained in the paper Vander-
bruggen et al.
10
and can be found in Supporting Information S3.
In addition, SEM images with imposed colors were taken from
the polished grain mounts and also on loose powder. The loose
powder samples were fixed on a tab (PELCO Tabs TM, 6 mm
OD from TED PELLA, INC, Redding, CA, USA). For these
SEM images, the backscattered electron (BSE) image and
secondary electron (SE) image were superimposed, and false
colors were attributed for generating an image with composi-
tional, textural, and topographic information. The BSE signal
intensity is governed by the density [by means of the atomic
number (Z)] of the particles and shows a contrast in the
elemental composition between each particle. The blue color
was selected for high-density species, likely LMO particles made
of heavy metals, while the black color was used for low-density
material, highlighting the graphite and residual binder particles.
The SE signal is sensitive toward the topography of the substrate
surface and is highlighted through orange colors.
3. RESULTS AND DISCUSSION
3.1. LIB Component Distribution. Each process was
compared according to their individual performances starting
from the mass distribution and losses, as presented in Figure 4.
The results indicated that losses of material occur for all the
processes from 5.8 to 24 wt %. The M process is the least at 5.8
wt %, likely including fine dust and electrolyte. The electrolyte in
LIBs consists of a mixture of organic solvents and conducting
salts, such as LiPF6. A significant amount of solvent may
evaporate when exposed to the atmosphere; however, some
electrolyte compounds, such as the conducting salts, might have
remained in the M-BM. Although new methods have been
explored to recover the electrolyte, they require controlled
atmospheres or the use of supercritical fluids, such as CO2.
32,33
On the other hand, the EHF process reported 11.1 wt % mass
losses corresponding to electrolyte removal, dispersion, or
dilution of fine particles such as conductive carbon and graphite
and partial binder dissolution.
27,28
Finally, the TM process presented the highest losses at 24.2 wt
%, which can be due to the decomposition and consumption of
organic materials during the vacuum pyrolysis stage. As reported
in the literature, the separator decomposes first, then
polypropylene (155 °C) and polyethylene (135 °C),
34
followed
by binder decomposition, for example, PVDF (450 °C) and SBR
(248 °C).
35
In addition, possible graphite losses could occur
during pyrolysis, as shown by Lombardo.
20
In all processes, the particles associated with casing materials
are eciently recovered in the coarse fraction (<1000 μm). As
shown in Figure 5, almost no casing particles were identified in
the black mass (less than 0.4 wt %.) These heavy particles are
usually recovered by an established industrial process after
mechanical crushing using a densimetric table, such as those
practiced by Retriev Technologies, Recupyl Valibat, AkkuSer,
Accurec.
36
The main dierence between the processes results in the
distribution of the cell components. The comparatively low mass
of the black mass (36.2 wt %) obtained with mechanical
treatment shows that the majority of the components are not
comminuted and remained coarse, especially the Cu and Al foils.
Furthermore, due to its elasticity, the separator particles
remained in the coarse fraction, which can be easily recovered
using, for example, an air classifier.
37
Figure 3. Working principle of SEM-based automated image analysis. This example shows in blue LMOs (NCA spectra) and in green Al foils (Al
spectra). 3A: Backscattered image with SEM, 3B X-ray mapping with EDX, 3C phase composition, and 3D processed image by automated mineralogy.
Figure 4. Mass distribution and losses of LIB materials after three
dierent routes. (100% represents the initial battery feed, the standard
deviations for the weight fraction were obtained from the sieving
experiments, and the losses were calculated from the full process).
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In the case of the EHF process, the separator particles may
also be recovered in a relatively simple manner. Indeed, during
experiments, these particles were reported to the surface of the
aqueous medium due to their low density.
In addition, the distribution of cathode and anode active
particles during each processing is distinct. These dierences
reflect the variable impact that each processing strategy has on
the properties of the LIB components. To understand this
influence and further evaluate these processes, it is necessary to
carry out an in-depth characterization of the resulting material
particles.
3.2. Black Mass Characterization. One of the most
relevant parameters for the evaluation of the eectiveness of a
recycling pretreatment operation is liberation, as it aects the
eciency of downstream separation processes. Therefore, the
three black masses (<1000 μm) were further evaluated by
automated mineralogy, as shown in Figure 6. The objective of
this characterization is to understand the behavior of each
species after processing, as will be discussed in subsequent
sections.
3.2.1. Mechanical Preprocessing. In the black mass treated
via mechanical preprocessing, the active particles, graphite, and
LMOs comprise over 95% of the mass in all size fractions
(Figure 6). These results are similar to the ones obtained by
Widikatmoko et al.,
9
where only a few particles of Al and Cu foils
were found below 850 μm after milling.
The M-BM contains the least Cu and Al foil residues
compared to the other processes, as foils are deformed rather
than comminuted in the rotary crusher (Figure 6A). The foils
are known to be ductile, non brittle, and have a good tensile
strength, requiring more energy and stress for their comminu-
tion.
38,39
The electrode foils were well delaminated from the
active particles.
Despite this eective delamination of the active particles from
the electrode foils, only 5.1 wt % of black mass was reported to
<63 μm (Figure 6B). This is due to the preservation of the
polymeric binder, as observed in Figure 7. During the battery
production, the active particles are coated with the binder,
forming aggregates that are laminated onto the foils using a
calendering process. Thus, mechanical comminution can
delaminate but not liberate individual active particles. The
aggregates shape resulting from lamination can be observed on
the Figure 6A.
3.2.2. Thermomechanical Preprocessing. The volume of
fine black mass obtained with the TM route is higher compared
to mechanical processing (i.e., 51 wt % than 36 wt %,
respectively). In this case, the anode active particles were not
evenly distributed within all size fractions, being preferentially
concentrated in sizes below 63 μm. Figure 6D shows
spheroidized graphite particles that are mostly well liberated,
highlighting the full decomposition of the anode binder. Indeed,
a binder such as SBR degrades above 248 °C.
35
Based on several studies, the PVDF cathode binder
decomposes above 450 °C
40−42
and optimal pyrolysis temper-
atures of 550 °C, according to Zhang et al.
43
Thus, the use of
vacuum pyrolysis above 500 °C should eliminate the binders.
However, despite the treatment of black mass at 550−650 °C in
this work, the cathode electrodes preserved their lamination, as
observed in Figure 6C. This preservation could mean that only a
partial decomposition of PVDF was achieved. One of the
contributing factors for a partial decomposition of the cathode
binder might be that entire batteries were fed into the pyrolysis
chamber in this study. The compacted structure of the
electrodes in the battery may hinder the eciency of the
pyrolysis process because the electrode surfaces are not directly
exposed, reducing the decomposition of the binder.
Another explanation might be that Al melted, protecting the
laminated structure of the cathode. Also, despite the discharging
step for safety, a thermal runaway may have occurred, leading to
higher temperatures than expected in some areas of the
sample.
44
As seen in Figure 6C, there is a Cu particle containing
Al traces with patterns characteristic of melting, suggesting a
temperature above its melting point of Al at 660 °C was reached.
Al melting is an issue for LMO liberation, as mentioned by Li et
al.
40
The TM-BM contains Al foils in its dierent size fractions
(Figure 6 in the modal composition). Unlike the M-BM, the Al
foils after thermal treatment appeared uneven and punctured
(Figure 8), probably caused by corrosion promoted by HF in the
electrolyte during pyrolysis. The thermal process caused fissures
and a subsequent increase in brittleness of the Al fraction.
20,40
The change in mechanical properties of Al explains its presence
in all size fractions of the black mass after comminution. The
change in mechanical properties of Al explains its presence in all
size fractions of the black mass after comminution. Therefore, it
might be recommended to apply the mechanical-thermal (MT)
route: first a mechanical process to produce BM with a low
amount of fine Al impurity particles to avoid Al melting during
the subsequent pyrolysis. Another advantage of conducting the
pyrolysis on the BM and not on the input batteries is that it
would lead to more uniform binder decomposition due to
increase in exposed surfaces, which could facilitate liberation.
After pyrolysis, the produced MT-BM should then be milled to
liberate the active particles and concentrate them into the fine
fraction.
Another aspect of the TM-BM is the dierence in metal oxide
species present. As observed in Figure 9, only the TM-BM
presented a NiCo phase. This suggests that during the thermal
process, there was a partial reduction of metal oxides. Yang et
al.
45
concluded that Ni ions from NMC were reduced to metallic
Ni, while the Co3+ and Mn3+ ions appeared to maintain their
trivalent form. Various studies explained that thermal pretreat-
ment can promote the carbothermic reduction of the LMOs and
has the advantage of improving their leaching eciency and
decreasing the amount of reducing agents (e.g., H2O2) needed
during hydrometallurgical treatment.
45−47
3.2.3. Electrohydraulic Fragmentation Preprocessing.
Among the three routes, the EHF process leads to the highest
relative mass of LIB, reporting to the fraction below 1000 μm,
Figure 5. Composition of the black mass (<1000 μm) after the three
processes implemented derived from automated mineralogy data.
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56.3 wt %. The EHF method uses only high voltage pulsations
and liberates battery components without comminution tools.
After thousands of pulsations, the batteries were completely
opened. Most of the active particles were well liberated from the
foils and concentrated in the fine fractions of the black mass. The
active particles, graphite, and LMOs conserved their spherical
shape during this process (Figure 6F). Ohl et al.
28
showed that
the LMOs after the EHF process can be reused in new battery
Figure 6. On the right: black mass modal composition, showing component percentage in each size fraction. (100% represents the initial battery feed).
On the left: processed images obtained from automated mineralogy: Pictures A, C, and E show the fraction of 500−1000 μm (scale of 1000 μm), and
pictures B, D, and F show the fraction <63 μm (scale of 500 μm).
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cell production but at a lower grade than the new material.
Alternatively, the EHF-BM can be further refined to pure
chemical elements via hydrometallurgy.
The presence of a water-soluble anode binder, such as CMC,
SBR, or PAA, helps graphite delamination from the Cu foil and
its deaggregation (as shown in the Supporting Information
Figure S1). The pH of water after the operation remained
neutral (ca. 7). Interestingly, while graphite particles appeared to
be well liberated, and its presence in the fraction <63 μm was
comparatively lower than for the TM route. A reaggregation
mechanism has occurred, leading to heterogeneous aggregates
containing liberated active particles, as observed in Figure 6E.
This can be due to the anode binder dissolution and its
rehardening during the drying stage. Indeed, in LIB production,
the water used as a solvent for the anode binder is removed by
evaporation before calendering onto the Cu foil.
48
On the SEM
image in Figure 10, the cathode particle is surrounded by a
matrix, which is not iodine epoxy resin and could be the
rehardened anode binder. Therefore, a continuously wet
recycling process might be the solution to maintain this
liberation eciency and avoid unselective agglomeration of
LIB components. A wet screening should be applied right after
the EHF process to further separate the foils from the liberated
active particles.
It is also observed in Figure 10 that most nonliberated cathode
active materials remain bound to the Al foil, proving that only
the anode binder is dissolving and revealing a dierent behavior
for the anode and cathode binders. Recently, Lyon et al.
27
showed that the combination of mechanical comminution to
open the batteries, followed by EHF for decoating of electrodes,
presented a higher liberation eciency for the cathode electrode
than the EHF alone.
3.3. Froth Flotation. Froth flotation was used to separate
graphite particles from the LMOs based on their dierence of
wettability.
29
The results of the rougher flotation experiments
carried out in this study are summarized in Figure 11. Since the
feed of flotation have dierent grades of graphite and LMOs as a
result of the preparation process (Figure 6 modal composition),
the flotation eciencies cannot be directly compared.
The M-BM shows a moderate selectivity with a recovery of
63.2% graphite in the froth product and 66.6% LMOs in the
underflow product. This comparatively low selectivity is
attributed to the residual binder coating active particles,
resulting in a decrease in the wettability dierence between
the graphite and the LMO particles. Indeed, the commonly used
cathode binder, that is, PVDF, has a hydrophobic behavior
promoting the recovery of LMOs:
29
These results are
comparable to the study of Zhang et al.,
43
where they floated
crushed electrodes and 62.5% of the LMOs were recovered in
the underflow product. The low eciency of graphite recovery
may be the result of two conditions that require further study. In
the first place, it is dicult to disperse the oily kerosene used as a
collector, and thus, it may not be eciently adsorbed on the
graphite surface, even in cases where they are well liberated.
Furthermore, if both graphite particles and binder-coated LMOs
present similar hydrophobicity, this might result in a competitive
flotation eect.
The TM-BM presented the highest selectivity of the samples
hereby studied, with a graphite recovery of 94.4% in the froth
product and 89.4% LMOs particles in the underflow product.
With this treatment process, the active particles present a
stronger dierence in wettability due to a comparatively superior
binder removal. The anode binder is decomposed during the
pyrolysis stage, aiding kerosene adsorption on the graphite
surface. As mentioned above, the LMO phase has been modified
Figure 7. SEM image with imposed colors on loose powder of an LMO
aggregate from M-BM. The blue spheres are the LMOs, and in between,
there is the residual binder.
Figure 8. Left: SEM image with imposed colors on polished grain mount of a cathode particle. The dierence of grey colors shows the Al-oxidation on
the side of the foil. Some holes can be observed on the Al foils. The black particles, for instance, on the left of the foil, are the resin which went through
the porosity during sample preparation.
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G

during this TM process (Figure 9), which might also aect their
wettability, an unexpected phenomenon that should be further
studied. With this TM process, the true flotation of the LMOs is
diminished due to binder removal. Furthermore, in a recent
publication by our research group, it was shown that the
flotation eciency of the TM black mass can be improved by
applying an attrition pretreatment.
12
Such pretreatment
refreshes the particle surface, removing the anode binder and
pyrolysis residues, resulting in an improved graphite flotation.
Attrition also removes a part of the cathode residual binder,
reducing the true flotation of LMOs. In addition, with this high-
shearing pretreatment, there is a disaggregation of graphite and
LMOs, decreasing the entrainment of the metals in the graphite
overflow product.
12
The EHF-BM shows graphite recovery in the overflow
product of 83.9%. As earlier discussed, it is possible that the
anode binder is better dissolved during the EHF process,
allowing a better adsorption of kerosene and thus leading to a
higher recovery. However, some graphite particles might be
trapped in heavy agglomerates and hence not recovered.
Nevertheless, the flotation selectivity was harmed by a
significant recovery of LMOs in the overflow product (
42.2%). Similar to the M-BM, the residual PVDF promoted
the recovery of LMO particles, in addition to some possible
Figure 9. Modal mineralogy of Ni phases in wt % occurring in the black mass samples, and three examples of processed images of particles.
Figure 10. SEM image with imposed colors on the polish grain mount of a cathode particle surrounded by a “matrix” and entrapped particles.
Figure 11. Grade and recovery of the graphite particles in the overflow
product (O/F). Grade and recovery of the LMO particles in the
underflow product (U/F).
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H

Table 1. Summary Table of the Advantages and Drawbacks of the Three Studied Preprocessing Routes
Process type Advantages Drawbacks
Mechanical (M) (+) possibility of recovering the electrolyte and separator. (−) aggregates of active particles under the laminated shape due to the residual binder.
(+) low content of foils and casing particles in the BM. The BM contains mainly the active particles. (−) low volume of BM and especially in the fractions below 125 μm due to the
conservation of active particle lamination shape.
(+) good delamination of the foils present in the BM. (−) residual binder results in a lack of selectivity for flotation. True flotation of LMOs
due to coated organic binder.
(−) mix of active particles in the flotation; therefore, the products have to be sent to
hydrometallurgy to recover the metals. The graphite ends up in the leaching cake.
Thermomechanical
(TM)(+) anode binder well removed, resulting in a high liberation degree of the graphite and copper foils. (−) electrolyte and separator lost.
(+) low impurity content in the graphite flotation product, potential for graphite recycling. (−) Possibility of Al melting decreasing cathode liberation.
(+) ecient separation of LMOs and graphite with froth flotation due to binder removal. (−) after pyrolysis, Al foil has a brittle behavior. Al particles are spread in the whole BM.
These impurities are challenging for the following hydrometallurgy stage.
(+) LMO flotation product presents a high content of metals and a really low content of graphite particles compare
to the BM. The removal of the graphite particles, which are porous, reduces the acid reagent consumption during
hydrometallurgical treatment.
(−) partial reduction of metal oxides during pyrolysis so no possibility of direct
recycling of the LMOs. The LMO product needs to go through hydrometallurgical
treatment to recover the metals.
(+) partial reduction of the metal oxides has the advantage to improve their leaching eciency and decreasing the
amount of reducing agents needed during the hydrometallurgical treatment
Electrohydraulic
fragmentation
(EHF)
(+) recovery of separator foil (skimming). (−) electrolyte lost.
(+) high liberation of the active particles from the foils. A wet screening can further separate the foils from the active
particles. (−) Al and especially Cu impurities, which are not found in the other BM.
(+) high volume of BM. (−) if followed by a drying stage, there is rehardening of the soluble binder, leading to
heterogeneous agglomerates. Therefore, it is recommended to remain in the wet
process.
(+) liberation of active particles while conserving morphology, so there is possibility of direct recycling of LMOs
and graphite.
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I

entrapment mechanisms. In addition, the fact that the EHF-BM
was dried after the EHF stage might influence the surface, and it
should be further studied. Nevertheless, to avoid binder
rehardening and, therefore, unselective agglomerates, it is
recommended that the BM remains under slurry between the
EHF product and the flotation process.
These results, compiled together, point out the need to
rethink binder chemistry. Indeed, the PVDF binder is one of the
biggest challenges during LIB recycling due to its toxicity and
the diculties to remove it, diminishing the cathode component
liberation during comminution and also flotation selectivity due
to its hydrophobic behavior. Therefore, finding alternatives for
the cathode binder chemistry, such as water-soluble binders,
which are already commercialized for the anode electrode,
would increase the LIB recycling eciency.
Currently, many dierent pretreatment methods are estab-
lished and produce a black mass of dierent quality. Based on the
obtained results, the advantages and drawbacks of each route is
summarized in Table 1.
4. CONCLUSIONS
The aim of increasing the recycling eciency of LIBs requires an
understanding of how the LIB components are liberated during
the recycling process. This paper characterized black mass
samples obtained from dierent preprocessing routes: M, TM,
and EHF. For the characterization, automated mineralogy
enabled qualitative and quantitative observations of the
properties of LIB components and their dependence on
comminution processes. As it is hereby shown, LIB liberation
is component-specific, a function of material properties, and
influenced by the methods employed, resulting in dierent black
masses. The presence of the binder and its preservation is found
to have a strong impact on the separation of active materials
using froth flotation.
•With the M process, the active particles were well
delaminated from the electrode foils. The BM contained a
really low amount of foils and casing impurities. The
active particles remained under their lamination shape
due to the binder conservation, leading to only a fine
fraction of active particles being individually liberated. In
addition, the conservation of the cathode binder harmed
the flotation selectivity.
•With the EHF route, most of the active particles were
individually liberated. Nevertheless, the following drying
step leads to anode binder rehardening, forming
unselective agglomerates. If a wet screening is performed
right after the EHF process, the foils and active particles
can be further separated, decreasing the content of foil
impurities in the BM. Therefore, this method showed
potential, provided that the recycling process is designed
to remain under wet conditions.
•With the TM process, the Al foils were oxidized, corroded,
and sometimes melted, which increased their fragility.
These mechanisms scattered the Al foil and became a
contaminant in the separation process despite binder
decomposition. Therefore, it might be recommended to
first allow the mechanical process to produce a BM with a
low amount of Al foil, which is then pyrolyzed, reducing
the amount of fine Al impurities. In addition, the pyrolysis
stage decomposition of the binders leads to a dierence in
wettability between the active particles in the fine fraction
of the BM. Hence, this TM route is the preferred route for
a selective separation of the graphite and LMO particles.
By using automated mineralogy, this paper showed the unique
influences of three recycling operations, revealing their strengths
and weaknesses, which could be controlled, avoided, or
improved to increase the LIB recycling eciency. This work
also demonstrates that only by understanding the relationships
between the design of cell components and recycling it is
possible to identify the inherent challenges posed by the existing
battery designs, thus highlighting the design-for-recycling needs
for future battery technologies.
■ASSOCIATED CONTENT
*
sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acsestengg.2c00177.
Dissolution of the binder; and major phases grouped
according to the LIB components (PDF)
■AUTHOR INFORMATION
Corresponding Author
Anna Vanderbruggen −Helmholtz Zentrum Dresden
Rossendorf (HZDR), Helmholtz Institute Freiberg for
Resource Technology (HIF), Freiberg 09599, Germany;
Department of Chemical and Metallurgical Engineering,
School of Chemical Engineering, Aalto University, Aalto
00076, Finland; orcid.org/0000-0003-4092-4374;
Email: a.vanderbruggen@hzdr.de
Authors
Neil Hayagan −Helmholtz Zentrum Dresden Rossendorf
(HZDR), Helmholtz Institute Freiberg for Resource
Technology (HIF), Freiberg 09599, Germany; orcid.org/
0000-0003-4330-738X
Kai Bachmann −Helmholtz Zentrum Dresden Rossendorf
(HZDR), Helmholtz Institute Freiberg for Resource
Technology (HIF), Freiberg 09599, Germany
Alexandra Ferreira −Universitéde Lorraine, CNRS,
Laboratoire GeoRessources, Nancy F-54000, France;
orcid.org/0000-0001-5475-114X
Denis Werner −Institute of Mechanical Process Engineering
and Mineral Processing, TU Bergakademie Freiberg, Freiberg
09599, Germany
Daniel Horn −Fraunhofer Research Institution for Materials
Recycling and Resource Strategies IWKS, Hanau 63457,
Germany
Urs Peuker −Institute of Mechanical Process Engineering and
Mineral Processing, TU Bergakademie Freiberg, Freiberg
09599, Germany
Rodrigo Serna-Guerrero −Department of Chemical and
Metallurgical Engineering, School of Chemical Engineering,
Aalto University, Aalto 00076, Finland
Martin Rudolph −Helmholtz Zentrum Dresden Rossendorf
(HZDR), Helmholtz Institute Freiberg for Resource
Technology (HIF), Freiberg 09599, Germany
Complete contact information is available at:
https://pubs.acs.org/10.1021/acsestengg.2c00177
Author Contributions
Anna Vanderbruggen conceptualization, data curation, inves-
tigation, methodology, writing-original draft, writing-review &
editing; Neil Hayagan software, writing-review & editing; Kai
ACS ES&T Engineering pubs.acs.org/estengg Article
https://doi.org/10.1021/acsestengg.2c00177
ACS EST Engg. XXXX, XXX, XXX−XXX
J

Bachmann software, writing-review & editing; Alexandra
Ferreira investigation, writing-review & editing; Denis Werner
investigation, resources, writing-review & editing; Daniel Horn
investigation, resources, writing-review & editing; Urs Peuker
supervision, writing-review & editing; Rodrigo Serna-Guerrero
supervision, writing-review & editing; Martin Rudolph super-
vision, writing-review & editing.
Funding
The authors gratefully acknowledge the Helmholtz foundation
for base funding within the PoF III (project-oriented funding
part III) for the BooMeRanG project. A.V acknowledges her
recent funding through the BMBF Competence Cluster
Recycling and Green Battery (GreenBatt) within the project
“ecoLiga” (03XP0326B). R.S.G. acknowledges the BAT-
Circle2.0 project (Business Finland grant number 44886/31/
2020).
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
The authors would also like to thank Accurec GmbH for
pyrolyzing the batteries and UVR FIA GmbH for grinding the
pyrolyzed black mass and the XRF analysis. The authors thank
Roland Wuerkert, Michael Stoll, and Sebastian Thormeier from
Helmholtz Institute Freiberg for the epoxy block preparation,
Simon Obando Sierra and David Guzman Gallo for their help
with sample preparation, and Alejandro Abadías Llamas for his
help with the flowsheet design.
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