sustainability
Article
A Sustainable Process for the Recovery of Anode and
Cathode Materials Derived from Spent
Lithium-Ion Batteries
Guangwen Zhang 1 , Zhongxing Du 1 , Yaqun He 1,2, *, Haifeng Wang 1 , Weining Xie 2,3 and
Tao Zhang 4
1
2
3
4
*
School of Chemical Engineering and Technology, China University of Mining and Technology,
No.1 Daxue Road, Xuzhou 221116, China; gwzhang@cumt.edu.cn (G.Z.); 06152238@cumt.edu.cn (Z.D.);
whfcumt@cumt.edu.cn (H.W.)
Advanced Analysis and Computation Center, China University of Mining and Technology,
No.1 Daxue Road, Xuzhou 221116, China; aacc_xwn5718@cumt.edu.cn
Jiangsu Huahong Technology Stock Limited Company, Wuxi 214400, China
Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China; zhangt@tsinghua-sz.org
Correspondence: yqhe@cumt.edu.cn; Tel.: +86-516-8359-2928; Fax: +86-516-8399-5026
Received: 15 March 2019; Accepted: 15 April 2019; Published: 20 April 2019
Abstract: The recovery of cathode and anode materials plays an important role in the recycling
process of spent lithium-ion batteries (LIBs). Organic binders reduce the liberation efficiency and
flotation efficiency of electrode materials derived from spent LIBs. In this study, pyrolysis technology
is used to improve the recovery of cathode and anode materials from spent LIBs by removing
organic binders. Pyrolysis characteristics of organics in electrode materials are investigated, and on
this basis, the effects of pyrolysis parameters on the liberation efficiency of electrode materials are
studied. Afterwards, flotation technology is used to separate cathode material from anode material.
The results indicate that the optimum liberation efficiency of electrode materials is obtained at a
pyrolysis temperature of 500 ◦ C, a pyrolysis time of 15 min and a pyrolysis heating rate of 10 ◦ C/min.
At this time, the liberation efficiency of cathode materials is 98.23% and the liberation efficiency of
anode materials is 98.89%. Phase characteristics of electrode materials cannot be changed under these
pyrolysis conditions. Ultrasonic cleaning was used to remove pyrolytic residues to further improve
the flotation efficiency of electrode materials. The cathode material grade was up to 93.89% with a
recovery of 96.88% in the flotation process.
Keywords: electrode materials; spent lithium-ion battery; pyrolysis; liberation; flotation; recovery
1. Introduction
Lithium-ion batteries (LIBs) are widely used as an energy-storage component in various electrical
and electronic products, including mobile phones, cameras, laptop computers, and new-energy
vehicles, due to their excellent characteristics, such as high energy density, safe handling, and low
self-discharge [1,2]. The demand for LIBs is presenting a rapid growth trend [3]; meanwhile, the growth
rate is increasing gradually, which means that large amounts of spent LIBs need to be treated because
of their limited lifetime [4]. Spent LIBs mainly comprise a metallic shell, membrane separator, cathode
materials (LiCoO2 , LiMn2 O4 , LiFePO4 , as well as other lithium metal oxides), aluminum foil, anode
materials (graphite), copper foil, and organic electrolytes [5]. The abundant components of spent LIBs
indicate that the recycling of valuable metals from spent LIBs is a significant process.
From the viewpoint of environmental protection and resource recovery, the recycling of spent LIBs
has attracted more and more attention, and some sophisticated processes including hydrometallurgy,
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pyrometallurgy, and bio-metallurgy have been proposed [6–8]. It is worth noting that current
metallurgy technologies always focus on the recovery of high economic value metals derived from
cathode materials, especially Co, Li, Mn, and Ni [9]. Therefore, how to obtain pure cathode materials
is the core process that connects the pretreatment process with metallurgy. Manual dismantling is
extensively used to obtain cathode materials for the metallurgy process. Each component is obtained
using the dismantling process and then cathode is selected as a research target. N-methyl-2-pyrrolidone
or other chemical solutions are usually used to remove the organic binder, and then cathode materials
are liberated from the aluminum foils [10,11]. By sieving, pure cathode materials are used in subsequent
metallurgy processes. However, manual dismantling is harmful to people’s health and limits the
industrial recovery efficiency of spent LIBs. At the same time, using a chemical solution to remove the
organic binder has some problems, including low liberation efficiency and secondary pollution.
In recent years, with the production increase of spent LIBs, mechanical-physical methods have
been applied in the pretreatment process for spent LIBs. Multistage crushing can liberate electrode
particles from foils, while screening processes are utilized to achieve the separation of electrode
materials and foils [12–14]. Flotation technology is then utilized to realize the separation of cathode
and anode materials due to their obvious hydrophilic/hydrophobic differences [15–17]. This flowchart
is significant for large scale industrial application and the preparation of pure cathode materials for the
metallurgy process. Two main problems need to be solved in this process: (a) Electrode particles are
attached to foils by organic binder and they are difficult to liberate under only the action of mechanical
crushing force, which results in some electrode materials remaining on the foils and decreases the
recovery efficiency; (b) electrode materials from this flowchart are still enveloped by electrolyte and
organic binder, which will decrease their flotation efficiency because the hydrophilic/hydrophobic
differences between cathode materials and anode materials are decreased. Therefore, the removal
of organic binder and electrolyte is an essential process in order to obtain high purity cathode
materials [18,19]. Some chemical agents, including N-methyl-2-pyrrolidone, dimethylformamide,
dimethyl acetamide, and dimethyl sulfoxide, have been utilized to dissolve the organic binder [20,21].
However, chemical dissolution methods characterized by high cost, low efficiency, and potential
pollution limit its wide application. A Fenton high-order oxidation process has been used to remove
organic binder and residual electrolytes to improve the flotation efficiency of electrode materials.
However, Fe2+ was introduced into this reaction, and the Fe element remained on the surface of the
electrode material, complicating the subsequent metallurgical process [15,22]. Yu et al. adopted a
grinding process to improve the flotation efficiency of electrode materials. Although grinding can
improve the flotation efficiency, the organic binders and electrolytes still remain on the particles,
resulting in a low cathode material recovery [23]. A roasting method can remove the organic binder
and electrolytes adequately [24], but the serious secondary pollution limits its application. Pyrolysis is
an effective method that can not only remove organics from electrode materials but also reduce the
environmental pollution.
A sustainable process for the recovery of cathode and anode materials derived from spent
lithium-ion batteries is proposed in this study. The main purpose of this research work is to obtain high
purity cathode material to lay the foundation for metallurgy. This research focuses on the following
aspects: (a) The pyrolysis characteristics of cathode and anode materials; (b) the facilitation effect of
pyrolysis on the liberation of electrode materials; (c) the effects of pyrolysis on the phase properties of
electrode materials; and (d) the enhancement of electrode materials’ flotation behavior by pyrolysis.
2. Experimental Section
2.1. Experimental Methods
Spent LIBs derived from waste mobile phones were collected, comprising various types of batteries.
The main cathode material was LiCoO2 , but there was a small amount of Mn and Ni elements in the
cathode material [15]. The anode material was graphite. In this study, the spent LIBs were treated
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following the flowchart shown in Figure 1. They were firstly discharged with 5 wt% NaCl solution for
were treated following the flowchart shown in Figure 1. They were firstly discharged with 5 wt%
48 h and then naturally air-dried. The discharged spent LIBs were firstly cut up by a shredder. As a
NaCl solution for 48 h and then naturally air-dried. The discharged spent LIBs were firstly cut up by
result, the metallic shells were shredded while the membrane separator, electrode sheets, and other
a shredder. As a result, the metallic shells were shredded while the membrane separator, electrode
components were liberated from each other. After this shredding process, the metallic shell, membrane
sheets, and other components were liberated from each other. After this shredding process, the
separator, and electrode sheets presented flake shapes, and pneumatic separation was then used
metallic shell, membrane separator, and electrode sheets presented flake shapes, and pneumatic
to remove the membrane separator and other plastics. Magnetic (for steel shell) or eddy current
separation was then used to remove the membrane separator and other plastics. Magnetic (for steel
(for aluminum shell) separations were applied to remove metallic shells. The mixture of cathode
shell) or eddy current (for aluminum shell) separations were applied to remove metallic shells. The
and anode scraps were obtained after the pretreatment. Part of the cathode and anode scraps was
mixture of cathode and anode scraps were obtained after the pretreatment. Part of the cathode and
directly crushed and sieved. Other electrode mixtures were treated using pyrolysis combined with
anode scraps was directly crushed and sieved. Other electrode mixtures were treated using pyrolysis
a mechanical-physical process. Afterwards, a flotation process was used to achieve the separation
combined with a mechanical-physical process. Afterwards, a flotation process was used to achieve
of the cathode and anode materials. The effects of pyrolysis on the liberation efficiency and flotation
the separation of the cathode and anode materials. The effects of pyrolysis on the liberation efficiency
efficiency of electrode materials were then investigated.
and flotation efficiency of electrode materials were then investigated.
Figure 1.
1. Experimental
Experimental flowchart
flowchart of
of this
this study.
study.
Figure
2.2. Pyrolysis Experiment
2.2. Pyrolysis Experiment
A portion of the cathode and anode scraps were hand-sorted to analyze their pyrolysis
A portion of the cathode and anode scraps were hand-sorted to analyze their pyrolysis
characteristics. Pyrolysis experiments of cathode and anode mixtures were conducted in a
characteristics. Pyrolysis experiments of cathode and anode mixtures were conducted in a controlledcontrolled-atmosphere tube furnace (MXG1200-80, Shanghai Micro-X furnace Co., Ltd., Shanghai,
atmosphere tube furnace (MXG1200-80, Shanghai Micro-X furnace Co., Ltd., Shanghai, China), using
China), using the pyrolysis system shown in Figure 2. The mixed cathode and anode scraps were
the pyrolysis system shown in Figure 2. The mixed cathode and anode scraps were placed into the
placed into the tube furnace. Afterwards, the corun-dum tube was filled with nitrogen, with the
tube furnace. Afterwards, the corun-dum tube was filled with nitrogen, with the nitrogen flow
nitrogen flow remaining at 100 mL/min to carry pyrolysis products away. Pyrolysis parameters were
remaining at 100 mL/min to carry pyrolysis products away. Pyrolysis parameters were set using a
set using a temperature control system. Pyrolysis products from the organics in electrode materials
temperature control system. Pyrolysis products from the organics in electrode materials were taken
were taken out of the tube by nitrogen flow, and pyrolysis oils were then collected by condensation,
out of the tube by nitrogen flow, and pyrolysis oils were then collected by condensation, while
while organic gas was collected and treated by a gas collector system. Deionized water and an NaOH
organic gas was collected and treated by a gas collector system. Deionized water and an NaOH
solution were used to remove the acidic gas.
solution were used to remove the acidic gas.
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Figure 2. Schematic
Schematicdiagram
diagramofofthe
thelaboratory
laboratorypyrolysis
pyrolysis
device:
temperature
control
system,
device:
(A)(A)
temperature
control
system,
(B)
(B)
tubular
furnace,
condenser
pipe,
condensation
products
collector,
deionized
water
1,
tubular
furnace,
(C) (C)
condenser
pipe,
(D) (D)
condensation
products
collector,
(E) (E)
deionized
water
1, (F)
(F)
deionized
water
2,
(G)
NaOH
solution,
(H)
tailing
gas
drying
device.
deionized water 2, (G) NaOH solution, (H) tailing gas drying device.
2.3. Flotation Experiment
2.3. Flotation Experiment
Flotation technology was used to separate cathode material from anode material, because cathode
Flotation technology was used to separate cathode material from anode material, because
material is hydrophilic, while anode material is hydrophobic. After flotation, anode material will attach
cathode material is hydrophilic, while anode material is hydrophobic. After flotation, anode material
to bubbles and be collected in the froth product. Flotation experiments were conducted on electrode
will attach to bubbles and be collected in the froth product. Flotation experiments were conducted on
materials before and after pyrolysis. Before the flotation experiments, the pyrolytic electrode materials
electrode materials before and after pyrolysis. Before the flotation experiments, the pyrolytic
were ultrasonically-cleaned to remove the pyrolysis residues. Flotation experiments were conducted
electrode materials were ultrasonically-cleaned to remove the pyrolysis residues. Flotation
using an XFD-63 flotation machine (Jianfeng Mining Machinery Manufacturing co. LTD, Nanchang,
experiments were conducted using an XFD-63 flotation machine (Jianfeng Mining Machinery
China) at room temperature with an impeller speed of 1800 rpm, an aeration quantity of 2.0 L/min,
Manufacturing co. LTD, Nanchang, China) at room temperature with an impeller speed of 1800 rpm,
and a pulp density of 40 g/L. A dilute pulp concentration was used in this study because of the fine size
an aeration quantity of 2.0 L/min, and a pulp density of 40 g/L. A dilute pulp concentration was used
of the electrode materials. n-Dodecane was used as a collector with a dosage of 300 g/t, while methyl
in this study because of the fine size of the electrode materials. n-Dodecane was used as a collector
isobutyl carbinol (MIBC) was used as frother with a dosage of 150 g/t. Cathode material concentrate
with a dosage of 300 g/t, while methyl isobutyl carbinol (MIBC) was used as frother with a dosage of
and anode material concentrate were obtained by filtration and drying. Afterwards, cathode material
150 g/t. Cathode material concentrate and anode material concentrate were obtained by filtration and
grade in flotation products was tested by ICP.
drying. Afterwards, cathode material grade in flotation products was tested by ICP.
2.4. Analytical Methods
2.4. Analytical Methods
The pyrolysis characteristics of cathode and anode materials were analyzed by a
The pyrolysis characteristics of cathode and anode materials were analyzed by a
Thermogravimetric Analyzer (TGA) (NETZSCH, STA 449-F5, Selb, Germany, testing condition:
Thermogravimetric Analyzer (TGA) (NETZSCH, STA 449-F5, Selb, Germany, testing condition:
temperature rose from 20 to 700 ◦ C with a heating rate of 10 ◦ C/min; N2 was used as a shielding gas
temperature rose from 20 to 700 °C with a heating rate of 10 °C/min; N2 was used as a shielding gas
with an airflow velocity of 20 mL/min). An Electro-probe microanalyzer (EPMA) (EPMA-8050G, Kyoto,
with an airflow velocity of 20 mL/min). An Electro-probe microanalyzer (EPMA) (EPMA-8050G,
Japan) was used to investigate the pyrolysis-enhanced liberation mechanism of electrode materials.
Kyoto, Japan) was used to investigate the pyrolysis-enhanced liberation mechanism of electrode
Surface chemical states of electrode materials were analyzed using an X-ray photoelectron spectroscopy
materials. Surface chemical states of electrode materials were analyzed using an X-ray photoelectron
(XPS), (ESCALAB 250Xi, Thermo Fisher Scientific Inc., Waltham, MA, USA). A scanning electron
spectroscopy (XPS), (ESCALAB 250Xi, Thermo Fisher Scientific Inc., Waltham, MA, USA). A scanning
microscope (SEM), (FEI quanta 250, Hillsboro, Oregon, USA) was used to determine the morphology
electron microscope (SEM), (FEI quanta 250, Hillsboro, Oregon, USA) was used to determine the
of the electrode material particles before and after pyrolysis. The cathode material grades in flotation
morphology of the electrode material particles before and after pyrolysis. The cathode material
products were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) (NWR 213-7900
grades in flotation products were analyzed by inductively coupled plasma-mass spectrometry (ICPICP-MS, Palo Alto, California, USA). X-ray powder diffractometry (XRD) (Bruker D8 advance, Bremen,
MS) (NWR 213-7900 ICP-MS, Palo Alto, California, USA). X-ray powder diffractometry (XRD)
Germany, database: Inorganic Crystal Structural Database and Powder Diffraction File) was used to
(Bruker D8 advance, Bremen, Germany, database: Inorganic Crystal Structural Database and Powder
analyze the effects of pyrolysis on the mineral phases.
Diffraction File) was used to analyze the effects of pyrolysis on the mineral phases.
3. Results and Discussion
3. Results and Discussion
3.1. TG Analysis of Cathode and Anode Materials
3.1. TG Analysis of Cathode and Anode Materials
TG analysis played an important role in guiding the selection of the pyrolysis parameters. Cathode
TG analysis
played
important
role inprocessing.
guiding theAfterwards,
selection ofTG
the
pyrolysis
parameters.
and anode
materials
werean
obtained
by manual
analyses
of cathode
and
Cathode
and anode
were
obtained by
manual
processing.
of
anode
materials
werematerials
conducted
respectively,
with
the results
shown Afterwards,
in Figure 3. TG
Theanalyses
first main
cathode and anode materials were conducted respectively, with the results shown in Figure 3. The
first main weight-loss stage appeared at about 100 °C, while the second main weight-loss stage
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weight-loss stage appeared at about 100 ◦ C, while the second main weight-loss stage presented at
about
500 ◦at
C. about
The evaporation
of electrolyte
caused
the first weight-loss
second weight-loss
presented
500 °C. The
evaporation
of electrolyte
caused thestage.
first The
weight-loss
stage. The
was
from
the
decomposition
of
organic
binders
that
are
wrapped
on
the
surface
of
electrode
materials.
second weight-loss was from the decomposition of organic binders that are wrapped on the
surface
On
the
basis
of
the
TG
analysis,
cathode
and
anode
materials
have
similar
pyrolysis
characteristics,
of electrode materials. On the basis of the TG analysis, cathode and anode materials have similar
and
the mixed
pyrolysis of
cathode
and anode
materials
is feasible.
pyrolysis
characteristics,
and
the mixed
pyrolysis
of cathode
and anode materials is feasible.
Figure
3. TG
from spent
spent LIBs.
LIBs.
Figure 3.
TG curves
curves of
of cathode
cathode and
and anode
anode materials
materials derived
derived from
3.2.
Crushing Characteristics
Characteristics of
of Electrode
Electrode Scraps
3.2. Crushing
Scraps Derived
Derived from
from Spent
Spent LIBs
LIBs
Cathode
and anode
anode scraps
scrapswere
weremanually
manuallysorted
sortedand
andthen
then
crushed
using
impact
crusher.
Cathode and
crushed
using
anan
impact
crusher.
A
A
sieving
process
was
conducted
to obtain
different
sized
fractions,
and afterwards,
ICPused
was
sieving
process
was
conducted
to obtain
fivefive
different
sized
fractions,
and afterwards,
ICP was
used
to analyze
the element
distributions
in each
fraction
the results
being
given
in Table
1. Co,
to analyze
the element
distributions
in each
fraction
size, size,
the results
being
given
in Table
1. Co,
Ni,
Ni,
Mn,
and
Li,
derived
from
cathode
materials,
and
C,
derived
from
anode
materials,
were
mainly
Mn, and Li, derived from cathode materials, and C, derived from anode materials, were mainly
concentrated
in the
the−0.2
−0.2mm
mmsize
sizefraction,
fraction,
while
and
foils
were
mainly
concentrated
in+1.4
the
concentrated in
while
AlAl
and
CuCu
foils
were
mainly
concentrated
in the
+1.4
mm
size
fraction,
which
demonstrates
that
electrode
scraps
have
selective
crushing
properties.
mm size fraction, which demonstrates that electrode scraps have selective crushing properties.
However,
materials
were
distributed
in +1.4
mmmm
and and
−0.5−0.5
+ 0.2+mm
size
However, some
someelements
elementsfrom
fromelectrode
electrode
materials
were
distributed
in +1.4
0.2 mm
fractions,
which
indicates
that some
electrode
materials
still attach
foils to
under
action
organic
size fractions,
which
indicates
that some
electrode
materials
still to
attach
foilsthe
under
theofaction
of
binders.
It
is
also
worth
noting
that
some
electrode
materials
that
were
liberated
from
foils
were
hard
organic binders. It is also worth noting that some electrode materials that were liberated from foils
to
separate
from
foils using
the sieving
process,
because
they
still attached
each other
under
the
were
hard to
separate
from foils
using the
sieving
process,
because
they stilltoattached
to each
other
action
of
organic
binders.
Based
on
this
element
distribution
analysis,
the
removal
of
organic
binders
under the action of organic binders. Based on this element distribution analysis, the removal of
is
a necessary
process
to improve
the recycling
efficiency
of electrode
materials.
organic
binders
is a necessary
process
to improve
the recycling
efficiency
of electrode materials.
Table
inin
different
sized
fractions
of crushing
products
of the of
raw
electrode
scraps.
Table1.1.Element
Elementdistribution
distribution
different
sized
fractions
of crushing
products
the
raw electrode
scraps.
Cathode
Anode
Size Fraction (mm)
Cathode
Anode
Co
Ni
Mn
Li
Al
Cu
C
Size Fraction (mm)
Mn
+1.4
5.79 Co 5.80 Ni 5.72
5.72
−1.4 + 0.71+1.4
1.06 5.790.99 5.80 1.03
−0.71 +−1.4
0.5 + 0.71 0.29 1.060.31 0.99 0.26
1.03
−0.5 +−0.71
0.2 + 0.5 2.29 0.292.09 0.31 2.63
0.26
−0.2
90.57
90.81
90.36
Li
5.55
5.55
1.01
0.28
1.01
1.95
0.28
91.21
Al
80.45
80.45
16.17
0.60
16.17
2.09
0.60
0.69
−0.5 + 0.2
2.29
2.09
2.63
1.95
2.09
−0.2
90.57 90.81 90.36 91.21 0.69
3.3. Facilitation Effect of Pyrolysis on the Liberation of Electrode Materials
Cu84.01 C 2.62
84.01
13.20 2.62 0.26
0.61 0.26 0.16
13.20
0.611.53 0.16 6.70
0.65
90.26
1.53
6.70
0.65 90.26
3.3. Facilitation
Effect of Pyrolysis
on theto
Liberation
Electrode
Materials
Cathode materials
were adopted
analyze of
the
facilitation
effect of pyrolysis on the liberation of
electrode
materials.
Before
and
after pyrolysis,
electrode
materialseffect
wereof
first
embedded
in self-curing
Cathode
materials
were
adopted
to analyze
the facilitation
pyrolysis
on the
liberation
of electrode materials. Before and after pyrolysis, electrode materials were first embedded in selfcuring resin. After polishing, a smooth section of electrode materials was exposed. The EPMA images
are shown in Figure 4. As we can see from Figures 4a–c, the electrode particles were tightly adhered
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resin. After polishing, a smooth section of electrode materials was exposed. The EPMA images are
shown
Figure
Asorganic
we can binder.
see fromThe
Figure
the electrode
particles
were
tightly
adhered
to each
to eachinother
by4.the
gaps4a–c,
between
electrode
materials
were
filled
with organic
other
by Electrode
the organic
binder. The
gaps to
between
materials
were filled
withFigure
organic
binders.
materials
are hard
liberateelectrode
using only
mechanical
crushing.
4dbinders.
shows
Electrode
materials
are
hard
to
liberate
using
only
mechanical
crushing.
Figure
4d
shows
that
organic
that organic binders were decomposed after pyrolysis treatment. Pyrolysis residues are porous
and
binders
wereby
decomposed
pyrolysis
treatment.
Pyrolysisthe
residues
are porous
and easy
crush by
easy crush
mechanicalafter
crushing,
which
can improve
liberation
efficiency
of electrode
mechanical
materials. crushing, which can improve the liberation efficiency of electrode materials.
Figure 4. EPMA analysis of cathode materials: (a–c) before pyrolysis, (d) after pyrolysis.
A
pyrolysis treatment
liberation
A pyrolysis
treatment combined
combined with
with mechanical
mechanical crushing
crushing was
was applied
applied to
to achieve
achieve the
the liberation
between
After crushing,
crushing, aa sieving
sieving process
process was
was used
used to
to obtain
between electrode
electrode materials
materials and
and foils.
foils. After
obtain electrode
electrode
materials
with
a
size
of
−0.2
mm.
The
effects
of
the
pyrolysis
parameters
on
the
liberation
efficiency
of
materials with a size of −0.2 mm. The effects of the pyrolysis parameters on the liberation efficiency
the
cathode
and
anode
materials
were
investigated.
The
crushing
parameters
remained
unchanged
of the cathode and anode materials were investigated. The crushing parameters remained unchanged
in
The liberation
liberation efficiencies
efficiencies of
of the
the cathode
in every
every crushing
crushing experiment.
experiment. The
cathode and
and anode
anode materials
materials with
with
different
pyrolysis
parameters
are
given
in
Figure
5.
different pyrolysis parameters are given in Figure 5.
The
played
the the
mostmost
important
role inrole
the in
liberation
process of
the electrode
The pyrolysis
pyrolysistemperature
temperature
played
important
the liberation
process
of the
materials.
The effectThe
of the
pyrolysis
temperature
on the liberation
efficiency efficiency
of the electrode
materials
electrode materials.
effect
of the pyrolysis
temperature
on the liberation
of the electrode
◦ C/min. As the
was
evaluated
at a pyrolysis
time of 15
min
andmin
a pyrolysis
heatingheating
rate ofrate
10 of
materials
was evaluated
at a pyrolysis
time
of 15
and a pyrolysis
10 °C/min. As
pyrolysis
temperature
rose, the
liberation
efficiency
first increased
and thenand
decreased.
The optimum
the pyrolysis
temperature
rose,
the liberation
efficiency
first increased
then decreased.
The
◦ C for the anode material. However,
pyrolysis
of the cathode
material
was
500 ◦ Cwas
and500
550°C
optimum temperature
pyrolysis temperature
of the
cathode
material
and 550 °C for the anode material.
the
pyrolysis
had little had
effectlittle
on the
liberation
of the anode
at 450 ◦ C.
Under
However,
the temperature
pyrolysis temperature
effect
on the liberation
of thematerial
anode material
at 450
°C.
the
higher
pyrolysis
temperature,
the liberation
of cathode
material
declined
sharply
because
of the
Under
the higher
pyrolysis
temperature,
the liberation
of cathode
material
declined
sharply
because
sintering
of organic
binders. binders.
Differences
in organicinbinders
differinginliberation
of the sintering
of organic
Differences
organicresulted
bindersinresulted
differingefficiencies
liberation
between
the
cathode
material
and
the
anode
material.
The
optimum
pyrolysis
temperature
of the
efficiencies between the cathode material and the anode material. The optimum
pyrolysis
◦
mixed
electrode
materials
was intended
to be was
500 intended
C.
temperature
of the
mixed electrode
materials
to be 500 °C.
The effect
of
the
pyrolysis
time
on
the
liberation
efficiency
of electrode
investigated
effect of the pyrolysis time on the liberation efficiency
of materials
electrodewas
materials
was
◦
◦
at
a pyrolysis at
temperature
oftemperature
500 C with aof
pyrolysis
rate of 10 heating
C/min. The
efficiency
investigated
a pyrolysis
500 °C heating
with a pyrolysis
rateliberation
of 10 °C/min.
The
of
cathodeefficiency
materialsofchanged
significantly
as thesignificantly
pyrolysis heating
rate changed.
liberation
cathode materials
changed
as the pyrolysis
heatingThe
rateoptimum
changed.
pyrolysis
time of
cathodetime
materials
was 15materials
min. At the
time,At
thethe
pyrolysis
timethe
hadpyrolysis
little effect
on
The optimum
pyrolysis
of cathode
wassame
15 min.
same time,
time
the
of anode
longer materials.
pyrolysis time
the sintering
phenomenon
hadliberation
little effect
on thematerials.
liberation The
of anode
The aggravated
longer pyrolysis
time aggravated
the
sintering phenomenon of the organic binder, decreasing the liberation efficiency of the electrode
materials. The optimum pyrolysis time of the mixed electrode materials was 15 min.
Sustainability 2019, 11, 2363
7 of 11
of the organic binder, decreasing the liberation efficiency of the electrode materials. The optimum
pyrolysis time of the mixed electrode materials was 15 min.
Sustainability 2019, 11, x FOR PEER REVIEW
7 of 11
Figure5.5.Effects
Effectsofofpyrolysis
pyrolysisparameters
parameterson
onthe
theliberation
liberationefficiency
efficiencyof
ofelectrode
electrodematerials:
materials: (a)
(a) effect
effect of
Figure
of pyrolysis
temperature
liberation
cathodematerials;
materials; (b)
(b) effect
onon
pyrolysis
temperature
on on
thethe
liberation
ofofcathode
effect of
ofpyrolysis
pyrolysistemperature
temperature
the
liberation
of
anode
materials;
(c)
effect
of
pyrolysis
time
on
the
liberation
of
cathode
materials;
(d)
the liberation of anode materials; (c) effect of pyrolysis time on the liberation of cathode materials;
ofof
anode
materials;
(e)(e)
effect
ofof
pyrolysis
heating
rate
onon
thethe
(d)effect
effectofofpyrolysis
pyrolysistime
timeononthe
theliberation
liberation
anode
materials;
effect
pyrolysis
heating
rate
liberation
of
cathode
materials;
(f)
effect
of
pyrolysis
heating
rate
on
the
liberation
of
anode
materials.
liberation of cathode materials; (f) effect of pyrolysis heating rate on the liberation of anode materials.
Pyrolysis-crushingexperiments
experimentswere
wereconducted
conductedtotoevaluate
evaluatethe
the
effect
pyrolysis
heating
Pyrolysis-crushing
effect
ofof
thethe
pyrolysis
heating
rate
rate
on
the
liberation
efficiency
of
electrode
materials
at
a
pyrolysis
temperature
of
500
°C
and a
◦
on the liberation efficiency of electrode materials at a pyrolysis temperature of 500 C and a pyrolysis
pyrolysis
timeThe
of 15
min. Theefficiency
liberationofefficiency
electrodedecreased
materials as
decreased
as theheating
pyrolysis
time
of 15 min.
liberation
electrodeofmaterials
the pyrolysis
rate
heating rate rose. The fast heating rate resulted in the inadequate decomposition of the organic
rose. The fast heating rate resulted in the inadequate decomposition of the organic binder, and then
binder, and then decreased the liberation efficiency. The effect of the pyrolysis heating rate on the
decreased the liberation efficiency. The effect of the pyrolysis heating rate on the liberation efficiency
liberation efficiency of electrode materials was not obvious. There was no obvious change in the
of electrode materials was not obvious. There was no obvious change in the liberation efficiency of
liberation efficiency of electrode materials when the pyrolysis heating rate improved from 5 °C/min
electrode materials when the pyrolysis heating rate improved from 5 ◦ C/min to 10 ◦ C/min, but the time
to 10 °C/min, but the time was saved by half. From the viewpoint of energy saving, the optimum
was saved by half. From the viewpoint of energy saving, the optimum pyrolysis heating rate was set at
pyrolysis heating rate was set at 10 °C/min.
10 ◦ C/min.
The optimum pyrolysis parameters for the liberation of electrode materials were determined to
be a pyrolysis temperature of 500 °C, a pyrolysis time of 15 min, and a pyrolysis heating rate of 10
°C/min. Electrode scraps were pyrolysis-treated at the optimum parameters and were mechanically
crushed. At this time, the liberation efficiency of cathode materials was 98.23% and the liberation
Sustainability 2019, 11, 2363
8 of 11
The optimum pyrolysis parameters for the liberation of electrode materials were determined to be
a pyrolysis temperature of 500 ◦ C, a pyrolysis time of 15 min, and a pyrolysis heating rate of 10 ◦ C/min.
Electrode scraps were pyrolysis-treated at the optimum parameters and were mechanically crushed.
x FOR PEER
REVIEW of cathode materials was 98.23% and the liberation efficiency
8 of 11
AtSustainability
this time,2019,
the 11,
liberation
efficiency
of anode materials was 98.89%. Afterwards, the element distribution of different sized fractions of
efficiency of anode materials was 98.89%. Afterwards, the element distribution of different sized
crushing
products of the pyrolytic electrode scraps was analyzed, and the results are shown in Table 2.
fractions of crushing products of the pyrolytic electrode scraps was analyzed, and the results are
From the results, we can see that the contents of Co, Ni, Mn, Li, and C in coarse fractions decreased
shown in Table 2. From the results, we can see that the contents of Co, Ni, Mn, Li, and C in coarse
after pyrolysis treatment, which indicates that the electrode materials had been adequately liberated
fractions decreased after pyrolysis treatment, which indicates that the electrode materials had been
from the foils and that the liberation between electrode materials was more adequate.
adequately liberated from the foils and that the liberation between electrode materials was more
adequate.
Table 2. Element distribution in different sized fractions of crushing products from the pyrolytic
electrode scraps.
Table 2. Element distribution in different sized fractions of crushing products from the pyrolytic
electrode scraps.
Cathode
Anode
Size Fraction (mm)
Cathode
Anode
Co
Ni
Mn
Li
Al
Cu
C
Size Fraction (mm)
Co 0.73 Ni 0.59
Mn
Li
Al83.76 Cu 88.63C
0.55
0.67
0.630.37 0.73 0.31
0.59
0.55
0.39 83.76
11.2188.63 8.930.67 0.03
0.08 11.21
1.03 8.93 0.550.03 0.06
0.360.11 0.37 0.09
0.31
0.39
0.42
0.62
0.95
2.79
0.09
0.11
0.09
0.08
1.03
0.55 1.060.06 0.53
98.37
98.39
98.03
1.21
0.79
0.42
0.62
0.95
2.79
1.06 0.830.53 98.71
−0.2
98.13 98.37 98.39 98.03 1.21
0.83 98.71
3.4. Effects of Pyrolysis on the Phase Properties of Electrode Materials
3.4. Effects of Pyrolysis on the Phase Properties of Electrode Materials
XRD was used to evaluate the effects of pyrolysis on the phase properties of electrode materials.
to evaluate
the◦ C,
effects
of pyrolysis
on the
phase
properties
of electrode
Before XRD
and was
afterused
pyrolysis
at 500
electrode
materials
were
tested
by XRD,
and theirmaterials.
results are
Before
and
after
pyrolysis
at
500
°C,
electrode
materials
were
tested
by
XRD,
and
their
results
are 2 ,
shown in Figure 6. The raw electrode material phase indicated that the cathode material was LiCoO
◦
shown
in
Figure
6.
The
raw
electrode
material
phase
indicated
that
the
cathode
material
was
LiCoO
2,
and the anode material was graphite. After pyrolysis treatment at 500 C, no new material peaks were
and theby
anode
was graphite.
After
pyrolysis
treatment
at 500 °C,
no new material
peaks
were
detected
XRDmaterial
in electrode
materials,
which
indicated
that phase
properties
of electrode
materials
detected by XRD in electrode materials, which indicated◦ that phase properties of electrode materials ◦
were not changed at the pyrolysis temperature of 500 C. The XRD results demonstrate that 500 C
were not changed at the pyrolysis temperature of 500 °C. The XRD results demonstrate that 500 °C is
is an optimum pyrolysis temperature and it not only can achieve adequate liberation of electrode
an optimum pyrolysis temperature and it not only can achieve adequate liberation of electrode
materials, but also does not change their phase properties.
materials, but also does not change their phase properties.
+1.4
0.63
−1.4 + 0.71 +1.4
0.36
−0.71 + −1.4
0.5 + 0.71 0.09
−0.5 + 0.2
−0.71 + 0.5 0.79
−0.2 −0.5 + 0.2 98.13
Figure6.6.XRD
XRDresults
results of
of electrode
electrode materials
treatment.
Figure
materialsbefore
beforeand
andafter
afterpyrolysis
pyrolysis
treatment.
3.5. Enhancement Flotation Behavior of Electrode Materials by Pyrolysis
XPS was used to analyze the surface properties of the pyrolytic electrode materials, and the
results are given in Figure 7a and Table 3. C–CF and C–CF groups that were from the pyrolysis
products (fluorobenzene) were detected on the surface of the pyrolytic electrode materials, and the
Sustainability 2019, 11, 2363
9 of 11
3.5. Enhancement Flotation Behavior of Electrode Materials by Pyrolysis
XPS was used to analyze the surface properties of the pyrolytic electrode materials, and the results
are
given
Figure
7a and
3. C–CF and C–CF groups that were from the pyrolysis products
Sustainabilityin
2019,
11, x FOR
PEERTable
REVIEW
9 of 11
(fluorobenzene) were detected on the surface of the pyrolytic electrode materials, and the contents of
C–CF
andofC–CF
weregroups
10.89%.were
In addition,
carbon
was also
detected
surfaceon
of
contents
C–CFgroups
and C–CF
10.89%. pyrolytic
In addition,
pyrolytic
carbon
was on
alsothe
detected
the pyrolytic
materials,
the relative
content
of pyrolytic
carbon
was 7.98%.
Thewas
pyrolysis
surface ofelectrode
the pyrolytic
electrode
materials,
the relative
content
of pyrolytic
carbon
7.98%.
residues
were hydrophobic,
some cathode
easily attach
to bubbles
and collect
in the
The pyrolysis
residues weremaking
hydrophobic,
makingmaterials
some cathode
materials
easily attach
to bubbles
froth
product,
which
reduced
its which
flotation
efficiency.
and collect
in the
froth
product,
reduced
its flotation efficiency.
In order to improve the separation efficiency of cathode and anode material, ultrasonic cleaning
was used to remove the pyrolysis residues. Figure 7b and Table 3 show the XPS analysis of pyrolytic
electrode
cleaning.
The
contents
of C–CF
and C–CF
groups
decreased
to 2.18%,
electrodematerials
materialsafter
afterultrasonic
ultrasonic
cleaning.
The
contents
of C–CF
and C–CF
groups
decreased
to
while
content
pyrolytic
carbon decreased
4.59%. After
ultrasonic
some
hydrophobic
2.18%,the
while
the of
content
of pyrolytic
carbon to
decreased
to 4.59%.
Aftercleaning,
ultrasonic
cleaning,
some
pyrolysis
residues
were residues
removed.were
Theremoved.
hydrophily
of hydrophily
cathode material
improved,
enhancing
the
hydrophobic
pyrolysis
The
of cathode
material
improved,
flotation
behavior
of cathode
and of
anode
materials.
enhancing
the flotation
behavior
cathode
and anode materials.
Figure 7.
7. C
C 1s
1s XPS
XPS spectrums
spectrums of
of electrode
electrode materials
materials before
before and
and after
after pyrolysis:
pyrolysis: (a)
(a) before
before ultrasonic
ultrasonic
Figure
cleaning,
(b)
after
ultrasonic
cleaning.
cleaning, (b) after ultrasonic cleaning.
Table 3.
Chemical states
Table
3. Chemical
states of
of carbon
carbon in
in the
the surface
surface of
of electrode
electrode materials
materials before
before and
and after
after pyrolysis.
pyrolysis.
Pyrolytic Electrode Materials
Pyrolysis-Ultrasonic
Cleaning
ElectrodeElectrode
Materials
Pyrolysis-Ultrasonic
Cleaning
Pyrolytic Electrode
MaterialsAtomic (%)
Components BE (eV)
FWHM (eV)
Components
Pyrolytic
BE
283.97
Components
carbon
(eV)
Graphite
284.30
Pyrolytic
C–C
284.80
283.97
C–H
285.71
carbon
C–CF
286.00
Graphite
284.30
O–C–O
287.14
C–C
284.80
C–CF
288.10
CF
289.40
C–H
285.71
C–F
291.02
Pyrolytic
FWHM 2206.17
283.97 BE
0.95
Components
Area
carbon
(eV)
(eV)
Graphite
284.30
27,161.01
0.55
Pyrolytic
C–C
284.80
7791.765
0.75
283.97 3607.48
0.95
2206.17
C–H
1.12
carbon 285.71
C–CF
286.00
589.84
0.93
Graphite 287.14
284.30 1491.15
27,161.01 1.09
0.55
O–C–O
C–C
284.80 938.791
7791.765
0.75
C–CF
288.10
1.15
CF
289.40
1.23
C–H
285.71 1230.962
3607.48
1.12
C–F
291.02
3001.55
1.88
FWHM
0.87
(eV)
0.57
0.93
0.87
1.00
1.21
0.57
0.99
0.93
1.01
1.25
1.00
1.85
Atomic
2058.53
(%)
8442.1
5574.71
2058.53
350.76
1803.41
BE (eV)
FWHM (eV)
Materials
Area
8442.1
734.85
5574.71
489.02
619.15
350.76
975.02
C–CF
286.00
1.21
1803.41
C–CF
286.00
589.84
0.93
O–C–O
287.14
0.99
734.85
O–C–O
287.14
1491.15
1.09
Flotation
and the 1.15
results
C–CF technology
288.10 was used
1.01 to separate
489.02anode material
C–CF from cathode
288.10 material
938.791
were shown
4. The cathode
grade in the cathode
material
concentrate
was increased
CF in Table
289.40
1.25 material
619.15
CF
289.40
1230.962
1.23
to 93.89%,
while
it
was
only
2.09%
in
anode
material
concentrate.
The
cathode
material
recovery
C–F
291.02
1.85
975.02
C–F
291.02
3001.55
1.88
increased to 96.88%, which indicates a better flotation efficiency was obtained than in the previous
studyFlotation
[23]. Therefore,
highwas
separation
is beneficial
forfrom
the subsequent
purification.
technology
used to efficiency
separate anode
material
cathode material
and the results
In
this
recycling
process,
organics
in
electrode
materials
were
removed
using
pyrolysis
were shown in Table 4. The cathode material grade in the cathode material concentrate wastechnology.
increased
At
the samewhile
time, it
thewas
pyrolysis
products
were collected
reduce the The
environmental
pollution
of the
to 93.89%,
only 2.09%
in anode
material to
concentrate.
cathode material
recovery
process.
After
pyrolysis,
the
liberation
efficiency
and
flotation
efficiency
of
electrode
materials
were
increased to 96.88%, which indicates a better flotation efficiency was obtained than in the previous
study [23]. Therefore, high separation efficiency is beneficial for the subsequent purification.
In this recycling process, organics in electrode materials were removed using pyrolysis
technology. At the same time, the pyrolysis products were collected to reduce the environmental
pollution of the process. After pyrolysis, the liberation efficiency and flotation efficiency of electrode
materials were improved, which is advantageous to the subsequent treating process. This research
Sustainability 2019, 11, 2363
10 of 11
improved, which is advantageous to the subsequent treating process. This research may provide an
alternative flowchart for recycling spent LIBs.
Table 4. Flotation results of pyrolysis-ultrasonic cleaning electrode materials.
Flotation Products
Cathode Material Grade (%)
Yield (%)
Anode material concentrate
Cathode material concentrate
2.09
93.89
30.87
69.13
Cathode material recovery
96.88
4. Conclusions
Pyrolysis technology was used to improve the recovery of cathode and anode materials from spent
LIBs. Pyrolysis can remove organic binders that are wrapped on the surface of electrode materials,
improving their liberation efficiency and flotation efficiency. The optimum pyrolysis parameters for the
liberation of electrode materials were determined to be a pyrolysis temperature of 500 ◦ C, a pyrolysis
time of 15 min, and a pyrolysis heating rate of 10 ◦ C/min. At this time, the liberation efficiency of
cathode materials was 98.23% and the liberation efficiency of anode materials was 98.89%. Pyrolysis
residues were further removed using ultrasonic cleaning. After this treatment, the flotation efficiency
of electrode materials was clearly improved. The cathode material grade increased to 93.89% with
a recovery of 96.88%. This research work provides an alternative method for recycling cathode and
anode materials from spent LIBs.
Author Contributions: In this research, G.Z. is responsible for data processing and paper writing while Y.H. is in
charge of directing the whole research work. Z.D. and T.Z. are in charge of carrying out the experiments. H.W. and
W.X. are responsible for test analysis.
Funding: This research was funded by the National Natural Science Foundation of China (No. 51574234 and
No. 51674257), the National College Students’ innovative and entrepreneurial training program (No.201710290029)
and Jiangsu Planned Projects for Postdoctoral Research Funds (1701038C). Guangwen Zhang also appreciates the
support of Shanghai Tongji Gao Tingyao Environmental Science and Technology Development Foundation.
Conflicts of Interest: The authors declare no conflict of interest.
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