Recycling of graphite anode from spent lithium‐ion batteries: Advances and perspectives

Abstract

There is growing production for lithium‐ion batteries (LIBs) to satisfy the booming development renewable energy storage systems. Meanwhile, amounts of spent LIBs have been generated and will become more soon. Therefore, the proper disposal of these spent LIBs is of significant importance. Graphite is the dominant anode in most commercial LIBs. This review specifically focuses on the recent advances in the recycling of graphite anode (GA) from spent LIBs. It covers the significance of GA recycling from spent LIBs, the introduction of the GA aging mechanisms in LIBs, the summary of the developed GA recovery strategies, and the highlight of reclaimed GA for potential applications. In addition, the prospect related to the future challenges of GA recycling is given at the end. It is expected that this review will provide practical guidance for researchers engaged in the field of spent LIBs recycling.
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Full text

REVIEW
Recycling of graphite anode from spent lithium-ion
batteries: Advances and perspectives
Yu Qiao
1,2
| Huaping Zhao
2
| Yonglong Shen
3
| Liqiang Li
4
|
Zhonghao Rao
1
| Guosheng Shao
3
| Yong Lei
2
1
School of Energy and Environmental Engineering, Hebei Key Laboratory of Thermal Science and Energy Clean Utilization, Hebei University of
Technology, Tianjin, China
2
Fachgebiet Angewandte Nanophysik, Institut für Physik & IMN MacroNano, Technische Universität Ilmenau, Ilmenau, Germany
3
School of Materials Science and Engineering, Zhengzhou University, Zhengzhou, China
4
Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry, Institute of Molecular Aggregation Science, Tianjin
University, Tianjin, China
Correspondence
Zhonghao Rao, School of Energy and
Environmental Engineering, Hebei Key
Laboratory of Thermal Science and
Energy Clean Utilization, Hebei
University of Technology, Tianjin 300401,
China
Email: 2021101@hebut.edu.cn
Guosheng Shao, School of Materials
Science and Engineering, Zhengzhou
University, Zhengzhou 450001, China.
Email: gsshao@zzu.edu.cn
Yong Lei, Fachgebiet Angewandte
Nanophysik, Institut für Physik & IMN
MacroNano, Technische Universität
Ilmenau, 98693 Ilmenau, Germany.
Email: yong.lei@tu-ilmenau.de
Funding information
Chinesisch-Deutsche Zentrum für
Wissenschaftsförderung, Grant/Award
Number: GZ1579; Deutsche
Forschungsgemeinschaft, Grant/Award
Number: LE 2249/15-1; Research
Foundation; Sino-German Center for
Research Promotion; China Scholarship
Council, Grant/Award Number:
202006420028
Abstract
There is growing production for lithium-ion batteries (LIBs) to satisfy the
booming development renewable energy storage systems. Meanwhile, amounts
of spent LIBs have been generated and will become more soon. Therefore, the
proper disposal of these spent LIBs is of significant importance. Graphite is the
dominant anode in most commercial LIBs. This review specifically focuses on
the recent advances in the recycling of graphite anode (GA) from spent LIBs. It
covers the significance of GA recycling from spent LIBs, the introduction of
the GA aging mechanisms in LIBs, the summary of the developed GA recovery
strategies, and the highlight of reclaimed GA for potential applications. In
addition, the prospect related to the future challenges of GA recycling is given
at the end. It is expected that this review will provide practical guidance for
researchers engaged in the field of spent LIBs recycling.
KEYWORDS
graphite anode, recycling, regeneration, reutilization, spent lithium-ion batteries
Received: 8 November 2022 Revised: 18 December 2022 Accepted: 28 December 2022
DOI: 10.1002/eom2.12321
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided
the original work is properly cited.
© 2023 The Authors. EcoMat published by The Hong Kong Polytechnic University and John Wiley & Sons Australia, Ltd.
EcoMat. 2023;5:e12321. wileyonlinelibrary.com/journal/ecomat 1of27
https://doi.org/10.1002/eom2.12321

1|INTRODUCTION
Attributing to the advantages of high energy density, low
self-discharge, and memoryless effect, lithium-ion batte-
ries (LIBs) have become the most promising secondary
batteries,
1–5
and have been widely employed as energy
storage units in portable electronics, electric vehicles,
aerospace applications, and large-scale electric energy
storage systems (Figure 1A).
6–13
It is predicted that the
global LIBs demand will approach up to 3600 GWh by
2030 (Figure 1B).
14
However, limited by a certain service
life (3–10 years), amounts of spent LIBs have been gener-
ated.
15
Only in 2020, the global production of spent LIBs
has exceeded to 150 000 tons,
16
and will hit 3.7 million
tons by 2030 (Figure 1C).
17
It is well known that LIBs are
mainly composed of four parts, for example, cathode,
anode, electrolyte, and separator (Figure 1D).
18
Cathode
materials (such as LiCoO
2
, LiMn
2
O
4
, and LiFePO
4
) and
anode materials (lithium titanate, silicon based compos-
ites and graphite) are coated on aluminum foil and cop-
per foil, respectively.
19–21
The electrolyte is generally
made of lithium salts dissolved in high-purity organic sol-
vents, while the separator is polyolefin-based porous
membranes.
22
From both economic and environmental
points of view, there is of great significance to recycle
spent LIBs.
23–29
Particularly, recycling the valued compo-
nents (i.e., cathode, anode, and current collectors) in
spent LIBs is an efficient strategy to address the challenge
of resource scarcity.
30
Meanwhile, it can effectively
reduce environmental destruction due to the excessive
exploitation of resources.
At present, well-established hydrometallurgy,
31
pyrometallurgy,
32
and bioleaching
33
technologies have
been successfully employed in industrial production to
recover valuable metals from cathode materials in spent
LIBs. In contrast, the efficient recycling of graphite anode
(GA) from spent LIBs is also economically and environ-
mentally important,
34
but the progress lags behind cath-
ode recycling. At present, GA occupies a dominant
position in the anode market of LIBs,
35
other anode
materials such as silicon-based anode, amorphous carbon
and lithium titanate only account for about 9%.
36
More-
over, it is a little-known fact that 1 kg of graphite is
needed for achieving 1 kWh of battery capacity of com-
mercial LIBs, which means that the demand for GA in
commercial LIBs is about 10–20 times higher than that
for lithium.
37
Considering the 12–21 wt% content of GA
in LIBs and the ever-increasing amount of spent LIBs,
FIGURE 1 (A) Application fields of lithium-ion batteries (LIBs). (B) Estimated global battery demand by 2030. (C) Estimated global
spent LIBs market. (D) Schematic structure of LIBs
2of27 QIAO ET AL.

the disposal of GA from spent LIBs has attracted more
and more attention.
38
On the one hand, the discard of
the spent GA will cause serious environmental pollution
because of the presence of undesired metal impurities
(including Li, Al, Co, Cu, Ni, Fe, and Mn)
39
and toxic
organic electrolytes.
40
On the other hand, all grades of
natural and synthetic graphite cannot be directly applied
to LIBs, and the production of battery-grade graphite is a
complex process. Natural graphite is mainly found in
associated graphite deposits, and its production mainly
including four steps: mining, beneficiation, purification
and processing.
41
Natural graphite mining not only has a
huge impact on the environment (vegetation, air, water
pollution, etc.) but also poses a huge health risk (pneu-
moconiosis) to the workers involved. To meet the
requirements of battery grade graphite, it also needs to be
treated with acid leaching, alkali roasting or inert
atmosphere heating treatment, which is also contrary to
the requirements of clean production. Synthetic graphite
is made by calcining petroleum coke, needle coke and
bitumen at a certain temperature, then crushing, grading
and high-temperature graphitization treating (usually
2500C).
42
High-temperature treating is supported by fos-
sil fuels and electricity consumption, which result in
huge carbon emissions. It is proved that the energy
consumption and greenhouse gas emissions in the
graphitization stage are about 13.8 kg CO
2
-eq/kg and
45.9 MJ/kg, respectively.
43
Currently, the price of
battery-grade graphite has reached as high as $8000–
$13 000/ton, accounting for nearly 10% of the overall
cost of LIBs.
37
In comparison, GA recovery from spent LIBs and its
further reuse in new LIBs would be more cost-effective
and sustainable. Not only the reemployment as the anode
in LIBs, but recovered graphite also possesses great appli-
cation potentials in the fields of supercapacitors, cataly-
sis, and water treatment. Meanwhile, graphite recycling
from spent LIBs will also be beneficial to environmental
protection. Given that, graphite recycling from spend
LIBs has gained more attention in the last years.
In this study, we firstly start from the failure mecha-
nism of GA to provide a solid theoretical basis for under-
standing the structural changes of negative graphite.
Next, the morphological and structural changes of spent
GA generated in the actual process were summarized,
which provides important data support and directional
guidelines for the recycling and resource utilization of
spent GA. Then, the current status of spent GA recycling
was reviewed, including regeneration, secondary applica-
tions in other energy storage fields, as raw materials for
graphene-based materials, and catalysts and functional
composite materials. Finally, the current problems and
challenges facing the recycling of spent GA are presented,
and the commercial prospects of GA recycling are also
prospected by reviewing the existing studies.
2|FAILURE MECHANISMS AND
CHARACTERISTICS OF GA IN
SPENT LIBS
2.1 |Failure mechanisms
The failure of LIBs refers to the attenuation or abnormal
performance of the battery caused by some specific rea-
sons.
44
It mainly divided into two categories: perfor-
mance failure
45
and safety failure.
46
Performance failure
represents the performance of LIBs fails to meet the ser-
vice requirements and relevant indicators, mainly includ-
ing capacity diving, attenuation of cycle life, abnormal
voltage, excessive internal resistance, self-discharge,
high/low temperature failure, poor rate performance and
consistency. Safety failure refers to the failure of LIBs
with certain safety risks due to improper use or abuse,
mainly including thermal runaway, short circuit,
gas/liquid leakage, lithium plating, expansion deforma-
tion, extrusion puncture and so on.
47–50
In the view of
micro-level, it can be investigated by internal causes and
the research scale can be traced back to the atomic and
molecular scale. In addition, there are also some thermo-
dynamic and kinetic changes on the failure process.
51
The failure occurs on anode materials usually including
solid electrolyte interface (SEI) overgrowth and decompo-
sition, lithium dendritic growth, particle breakage as well
as current collector erosion.
52,53
In the cases of both per-
formance failure and safety failure, the GA in LIBs will
be simultaneously destroyed due to (1) SEI decomposi-
tion, (2) lithium dendrite and dead lithium, (3) graphite
cracking and exfoliation, and (4) copper corrosion and
cracking, as shown in Figure 2. Next, the main failure
mechanisms occurs on GA are detailed discussed sepa-
rately, providing a theoretical basis for the structural
changes in spent graphite.
2.1.1 | SEI failure
During the initial lithiation, an ionically conducting but
electronically insulating SEI layer is firstly formed on GA
surfaces from the decomposition products of electrolytes
at low potentials.
54
This SEI layer passivates the graphite
surface to allow Li
+
transport but to block electrons
tunneling, thus preventing the continuous electrolyte
decomposition and enabling the reversible lithiation/
delithiation of the GA. In general, a dense and intact SEI
layer is crucial for the service life and performance of
QIAO ET AL.3of27

LIBs.
55
However, the SEI layer on the GA surface is
chemically unstable and mechanically fragile, and it will
gradually fail during continuous charge–discharge cycles
due to mechanical, chemical, or thermal reasons
(Figure 3).
56
Upon charging-discharging of LIBs, continuous lithia-
tion/delithiation of the GA leads to the repeated tensile
and compressive strains of the SEI layers and thus will
generate cracks in the SEI layers. This phenomenon is
usually named the mechanical failure of SEI.
57
Electro-
lytes will diffuse through these cracks in the broken SEI
layers to reach the GA surfaces and further decompose.
The ongoing electrolyte decomposition will consume
more Li
+
ions to form new SEI layers, leading to an
increased thickness of the SEI layers. The thicker SEI
layers will increase the ionic resistance. At the same time,
organic compounds (such as lithium ethylene di-
carbonate and lithium ethylene mono-carbonate) in the
SEI layers will also decompose to change the composi-
tions of the SEI layers, which is the so-called chemical
failure of SEI. On the one hand, the decomposition of
organic compounds leads to the increasing concentration
of inorganic salts (such as LiF and Li
2
CO
3
) in the SEI
layers, making the SEI layers more fragile. On the other
hand, the decomposition of organic compounds will pro-
duce gaseous products (e.g., C
2
H
4
and CO
2
) and soluble
organolithium compounds (e.g., lithium methyl carbon-
ate and lithium propionate). The escape of gaseous
FIGURE 2 The failure mechanisms
of graphite anode in spent lithium-ion
batteries
FIGURE 3 Failure mechanisms of
solid electrolyte interface (SEI) layers
and the evolution of SEI layers
4of27 QIAO ET AL.

products from the SEI layers and the dissolution of orga-
nolithium compounds into the electrolytes will make the
SEI layers porous. Consequently, the porous SEI layers
are not electrochemically stable enough to protect the
GA. Moreover, the decomposition reactions of SEI layers
and electrolytes are exothermic, This is known as the
thermal failure of SEI. As a result, the thermal failure
will further aggravate the mechanical and chemical fail-
ure of the SEI layers.
In above, the failure of SEI layer is not unitary but
different failure mechanisms interact with each other
and aggravate the damage of SEI layer jointly. With the
failure of SEI, the electrolyte can diffuse through the
damaged SEI layer to the GA and have side reactions
with the electrons in GA. The deposition of side reaction
products on the surface of GA will not only cause the sur-
face defects of graphite, but also increase the interfacial
impedance and hinder the interfacial transport of Li
+
.
This can reduce the reversibility of charge transfer, make
the internal resistance of the battery continue to increase
and even lead to battery failure.
2.1.2 | Lithium dendrites
Lithium dendrites are formed at the anode and grow
toward the cathode during the charging/discharging pro-
cess of LIBs.
58
The constantly growth of lithium dendrites
can puncture the separator and make a connection of
electrodes, which causing an internal short circuit of
LIBs. The formation of lithium dendrites can be divided
into three stages (Figure 4A).
59
In the first stage, highly
reactive Li
+
reacts instantly when it comes into compo-
nents such as organic solvents in electrolytes, forming
SEI film, which is earlier than lithium dendrites. The
ideal SEI film is a great ionic conductor, which could pre-
vent further reaction between electrolyte and Li
+
. How-
ever, in the actual cycling process, Li
+
can still pass
through the SEI layer and deposits on the anode surface.
Furthermore, due to the unstable characteristics of elec-
trolyte, SEI layers and the influence of charge–discharge
circumstances, the distribution of lithium deposition is
not uniform. Then is the nucleation stage, the continuous
accumulation of heterogeneous precipitation causes
FIGURE 4 Schematic
illustrations of lithium dendrites
(A) The generation of lithium
dendrite. (B) Types of lithium
dendrites morphology.
Reproduced with permission.
65
Copyright 2015, IOP Science.
Reproduced with permission.
66
Copyright 1998, Elsevier.
Reproduced with permission.
67
Copyright 2014, Elsevier.
Reproduced with permission.
62
Copyright 1998, Elsevier.
(C) The subsequent
phenomenon of lithium
dendrite after continuous cycles.
Reproduced with permission.
63
Copyright 2017, Springer Nature
QIAO ET AL.5of27

bulging in some places until the SEI layer destroyed. The
last stage is the growth stage, the growth of lithium depo-
sition continuously exacerbates in the length direction
after piercing the SEI film, producing visible dendrites.
Besides, the number of dendrites is mainly dependent on
the nucleation stage, while the morphology of lithium
dendrites is mainly determined by the growth stage. The
morphology of lithium dendrites generally includes four
types, including whiskers, moss, trees and globules.
(Figure 4B). It is believed that current density has a direct
correlation with the morphology of lithium dendrites and
high current density enhances the growth of lithium den-
drites.
60
The rough globus lithium deposition occurs at
very low current density (less than 0.1 mA/cm
2
),
61
which
is a relatively ideal sedimentary morphology because of
no sharp cusp. The whiskers dendrites usually formed at
low current density (0.2 mA/cm
2
),
62
the whiskers
diameter broaden and stick to a mossy structure with the
current density increases. High current density
(0.7 mA/cm
2
) accelerates the growth of lithium den-
drites, which causes the dendrite tips to grow quickly and
split to generate longer, straighter trees dendrites.
62
With
repeated cycles, lithium dendrites will be stripped and
resulting in dead lithium, thick SEI as well as porous
electrode finally (Figure 4C).
63
Lithium dendrites can sig-
nificantly expand the interlayer distance of graphite
(10%) during the nucleation stage, and the continuous
growth of lithium dendrites can cause dislocation/cracks
of graphite sheets, and even lead to particle breakage.
64
When the lithium dendrites connect two electrodes, it
can cause short circuits and lead to catastrophic failures
and even fires.
2.1.3 | Particle fracture
Graphite has a layer structure and the original distance
between graphite layers is 0.335 nm.
68
In the charging
and discharging process, the interlayer spacing of graph-
ite expands to accommodate Li
+
.
69
Previous researches
indicated that the interlayer spacing of recovered GA is
about 0.3703 nm,
70
which is 10.5% higher than fresh
GA. It is revealed that the particle diameter and volume
expansion increased with the cycling times under at same
current density. For example, the average GA particle
diameter and volume increases 10% and 30% at
200 cycle times, whereas that is 20% and 70% at
800 cycle times.
71
The increase in the size of GA is also
due to the formation of SEI in the primary particles or
the increase in porosity in the secondary particles. The
enlarge of graphite particle volume causes the breakage
and regeneration of SEI film, thus leading to the con-
sumption of electrolyte and the increase of internal
resistance.
72
However, this expansion cannot only be
explained by the growth of the SEI layer on the surface of
GA. The stress generated during the lithiation and de-
lithiation process can also facilitate the generation and
propagation of cracks. In addition, the cracks spread
along the grain boundaries of the polycrystalline graphite
(Figure 5). The micro-cracks continuous growth and
makes the volume of GA further extend.
73
The propaga-
tion of micro-cracks also leads to the cracking and shed-
ding of graphite particles. In addition, solvated Li
+
and
organic solvent embed between the GA layers and the
organic solvent generates gas through the oxidation–
reduction reaction between the GA layers. The presence
of gas further expands the damage to GA particles, which
accelerates the cracking of GA particles or even the exfo-
liation from the current collector.
74
2.1.4 | Copper corrosion
Copper foil is the most common current collector for
anode due to its high conductivity, electrochemical stabil-
ity and good mechanical properties.
76
It plays an impor-
tant role in the electronic exchange between the
electrode materials and the external circuits. Cu current
collector faces some challenges during practical applica-
tions, especially the environmentally assisted cracking.
77
Therefore, before going to service in commercial LIBs,
Cu current collector needs some pretreatments such as
acid–base etching, corrosion-resistant coating conductive
coating in order to improve the adhesion properties and
reduce corrosion rates. These pretreatments have signifi-
cantly help for Cu current collector (Figure 6A). Even so,
copper current collector still suffer corrosion over the
charging/discharging cycles.
78
When the anode electrode
of the LIBs reaches its own high potential, the corrosion
of the Cu current collector by the over-discharging of the
LIBs is inevitable (Figure 6B). After over-discharging to
0.0 V, about 6% copper is detected on the cathode side by
Energy-dispersive X-ray spectroscopy (EDX) analysis
which demonstrated that dissolved copper (Cu
2+
) could
indeed migrate through the separator from the anode
side to the cathode side.
79
The dissolve of copper current
collector will cause a series of chemical, electrochemical
and electrical phenomena elsewhere in the battery. Cu
2+
can be redeposited on the GA surfaces as Cu metal to
form dendrites, which cause surface contamination and
damage to the GA.
80
The dendrites gradually grow and
eventually penetrate the separator to connect the anode
and cathode, causing short circuits and failure of
battery.
79,81
The failure of LIBs is a complex process involving
multiple factors, including physical, mechanical,
6of27 QIAO ET AL.

electrochemical and other aspects evolutions. The fail-
ure of the battery will have more or less impact on
GA. Understanding the changes and characteristics of
spent GA after failure is an important prerequisite for
its subsequent utilization. Next, the changes occur on
GA in spent LIBs will be discussed detailed, especially
in the morphology and structure.
2.2 |Characteristics of spent GA
The typical scanning electron microscope (SEM) images
of initial GA are shown in Figure 7A, which indicated
that GA has an obvious layered structure, smooth surface
without impurity and uniformly distribution. The weak
van der Waals forces between two-dimensional layered
graphitic structures make it easy for ions and molecules
to be introduced, which is beneficial for the intercalation
and extraction of Li
+
and could provide high-rate charge
and discharge performance.
Graphite materials have a relatively stable body struc-
ture and a small degree of change during short-term
charging and discharging, but their surface structure will
be attenuated to a certain extent. When the Li
+
deinter-
calated at a shallow degree, the surface structure of GA
appears the attenuation, and the degree of disorder
increases significantly.
82
In addition, the locations of
structure attenuation are non-uniformly distributed on
FIGURE 5 Schematic
diagram and scanning electron
microscope images of particles
fracture in graphite anode.
Reproduced with permission.
75
Copyright 2011, Elsevier
FIGURE 6 Schematic diagram and
scanning electron microscope images
(A) Raw copper current collector.
Reproduced with permission.
78
Copyright 2009, Springer Nature.
(B) Copper corrosion. Reproduced with
permission.
78
Copyright 2009, Springer
Nature
QIAO ET AL.7of27

the graphite surface. Previous studies have shown that in
rechargeable LIBs, GA usually suffers severe surface
structure damage after long-term cycling.
83,84
Li et al.
85
investigated the morphology variation of GA in prismatic
Sanyo UF653467 batteries with a nominal capacity of
930 mAh under charging/discharging cycles. The SEM
images (Figure 7B) showed GA consisting of large parti-
cles and some changes occurring on the surface of the
anode with cycle times increasing. After 286 cycles, many
deep cracks appeared on the GA surface, and a
passivation film with a detectable thickness could be
observed with the naked eye. Furthermore, the harm of
overcharge to GA should not be underestimated.
86
The
morphology and structure of GA during the overcharge
process were investigated by SEM and TEM.
87
It was
found that no obvious abnormal feature on the surface of
GA after normal cycling test while the overcharged
cycling graphite shows totally different facial characteris-
tics. It is attributed to the lithium dendrites formation
and the morphology images indicated that most of the
FIGURE 7 (A) Scanning electron microscope (SEM) images of natural graphite. Reproduced with permission.
94
Copyright 2001,
Elsevier. Reproduced with permission.
91
Copyright 2011, Spring Nature. (B) SEM images of GA under 0 and 286 cycles. Reproduced with
permission.
85
Copyright 2001, Elseiver. (C) SEM and TEM images of fresh and degraded GA. Reproduced with permission.
90
Copyright 2016,
Chen Lin et al. (D) SEM images of GA with cracks. Reproduced with permission.
91
Copyright 2011, Spring Nature. (E) SEM images and
Schematic diagram of degraded GA exfoliation. Reproduced with permission.
92
Copyright 2021, Spring Nature
8of27 QIAO ET AL.

structure of the GA is not strongly affected by abuse.
However, the surface of the GA particles has undergone
major changes. This change will cause irreversible capac-
ity loss, making it difficult for lithium ions to diffuse into
the graphite and accelerating the surface changes.
The structure of GA changes by the repeated Li
+
intercalation/delamination during the long-term
charging-discharging cycles. The van der Waals forces
between graphite layers are weakened and leading
mechanical fatigue. The continuous intercalation/
delamination of Li
+
further aggravates the mechanical
changes and results a larger layer spacing as well as the
volume expansion of GA particles.
88
It is believed that
the structural damage is extremely severe during high
current density.
62
The local space charge generated by
the excess of positive charges at the GA are easy to cause
an unstable internal structure and induce lithium den-
drites.
89
The growth of lithium dendrites could be initi-
ated in several different positions of the graphite
particles, and do not need to correspond to each other.
88
Internal structure changes and growth of lithium den-
drites induced a large volume expansion, resulting the
evolution of diffusion induced stresses and mechanical
failure.
90
As shown in Figure 7C, the average particle size
was about 100 nm, the edge structure of degraded GA
began to mellow, some circular particles (100–150 nm)
appeared on the surface, and the cracks and fracture can
be clearly observed in the TEM images. Besides, the
highly anisotropic nature of the grains should be noted
particularly, because the insertion of Li
+
is anisotropic,
which occurs at the edge of the prism rather than the
base planes.
91
As shown in Figure 7D, it can be seen that
the growth of the typical hairline cracks and the bifurca-
tion of the cracks in the particles, indicating that the
crack path has anisotropic properties. From surface
defects to trans crystalline cracks, there are pores of
different sizes in graphite particles. The presence of
grain boundaries, cracks and pores indicate that if the
electrolyte can enter into the interior of particles, then
Li
+
can also be carried out by grain boundary/pore dif-
fusion and volume diffusion. In situ synchrotron x-ray
techniques and in situ mass spectroscopy can examine
the changes occurring on the GA during the heating
process by tube furnace.
92
It is observed that the meso-
porous graphite with a particle size of 15 μm, PVDF
binder and conductive carbon black are located on the
graphite surface and gaps. During the heating process,
the lithium flowing out of the graphite lattice will
gather on the edge of the graphite sheet and move in
the in-plane direction. Then, as the temperature rises,
the gas is released, and the reaction product covers the
surface of the anode. At the same time, the violent
reaction will cause the graphite layer to peel off. The
peeling may increase the reaction area exponentially,
which will have an adverse effect during the charging/
discharging cycling (Figure 7E).
In conclusion, GA from spent LIBs exhibits the fol-
lowing characteristics. First, GA recovered from spent
LIBs usually appears severe surface damage. Besides,
spent GA maintain the layer structure, but the interlayer
spacing is larger than fresh GA and the interlaminar
stress is weakened. Furthermore, there are some residual
impurities in GA, including organic binders, metal spe-
cies such as Li, Cu, and trace amounts of amorphous car-
bon species.
93
And the types and contents of residual
impurities in GA of spent LIBs are also different, because
of the different process formulas and working conditions
of different manufacturers. Recycling of GA from spent
LIBs is an important approach for turning waste to
wealth by preventing raw material consumption and
avoiding environmental pollution, which is beneficial for
the sustainable development of the LIBs industry. A
detailed discussion of the spent GA recycling is listed in
the following section.
3|RECYCLING OF SPENT GA
Pretreatment processes are essential before downstream
recycling processes of spent LIBs. In order to recycle
spent LIBs more efficiently, many pretreatment methods
have been developed. After common pretreatment
methods such as complete discharge,
95,96
mechanical
disassembly,
97–100
seperation
101,102
and so on, each com-
ponent is ready to second recycle treatment. Here, we
concentrate on the recycling processes of spent GA.
3.1 |Regeneration of GA
Some studies have revealed that recovered GA could be
regenerated as anode materials for energy storage devices
after some retreatments.
103–106
Low-cost regeneration of
GA from spent LIBs is of great significance to solve the
problem of waste graphite utilization and pollution.
Comparing with the fresh graphite, the directly recycled
GA (with coating, SEI layer and other Impurities)
exhibits lower initial discharge capacity, which are 354.2
and 298.7 mAh/g respectively. Due to the presence of
residual impurities, the graphite content in the directly
recycled GA is low, leading a low specific capacity.
107
In
order to restore the initial properties of the spent GA, it is
crucial to remove the residual impurities in it. Pyrolysis
treatment is a common way to remove impurities before
regenerating the GA from spent LIBs. Cu current collec-
tors melt into spheres by high-temperature smelting, then
QIAO ET AL.9of27

GA and Cu can be completely separated by the sieving
process. The recovery rate of GA is related to the size of
mesh, 77.53% GA can be recovered under 300 mesh.
Under 300 mesh, the purity of recovered GA powders is
about 99% while that can reach to 99.5% at 600 mesh,
which meets the standard of anode electrode for LIBs.
108
Pyrolysis treatment can also remove electrolytes and
binder, which is beneficial to the following process. All
the styrene-butadiene rubber, carboxymethylcellulose
sodium and most acetylene black can be removed after
heat-treated. But at the same time, the coating layer on
the GA surface is also damaged, so that heat-treated GA
needs to be recoated by pyrolytic carbon from phenolic
resin. Although regenerated GA with coating layer still
containing residual acetylene black and a little carboxy-
methylcellulose sodium pyrolysis product, it has a little
negative effect on the electrochemical performances. The
regenerated GA could fully meet the requirements of
reuse, and the initial discharge capacity is 377.1 mAh/g
and capacity retention is 98.76% after 50 cycles
(Figure 8A), which is higher than the midrange graphite
in the same type.
107
By combining advanced microscopy
and spectroscopy techniques, it is noted that although
thermal annealing can restore most of the capacity of
FIGURE 8 (A) Cycle performance curves of regenerated graphite anode (GA). Reproduced with permission.
107
Copyright 2018, Elsevier.
(B) Scheme of GA after different treatment. Reproduced with permission.
110
Copyright 2021, Elsevier. (C) The initial charge–discharge
performance and cycling stability for the pilot graphite product and the commercial graphite. Reproduced with permission.
111
Copyright
2011, IOP Science
10 of 27 QIAO ET AL.

spent GA, the remaining lithium in GA particles cannot
completely removed.
109
In order to remove the residual
lithium completely, boric acid solution pretreatment and
short-time annealing at medium temperature were
proposed (Figure 8B). Boric acid treatment can not only
repair the composition/structural defects of degraded
GA, but also form functional boron doping on the surface
of GA particles, ensuring high electrochemical activity
FIGURE 9 (A) Flow chart of the recycling process, specific surface area, pore size distribution of spent graphite anode (GA) separated
from anode, current collectorrate, rate capacities and cycle performance of regenerated GA. Reproduced with permission.
112
Copyright 2019,
Elsevier. (B) Spherical aberration electron microscopy images of spent GA, the cycle performance and rate capacities of prepared samples.
Reproduced with permission.
113
Copyright 2020, American Chemical Society. (C) Dissemble of anode materials from spent LIBs, the process
of separation of GA from copper foil, current changes with electrolytic time and the rate capability of recovered GA. Reproduced with
permission.
115
Copyright 2021, Elsevier
QIAO ET AL.11 of 27

and excellent cycle stability (initial capacity is 330 mAh/g
and retained the capacity after 100 cycles). During the
process, it is also noted that heat temperature will influ-
ence the crystal lattice restoration of regenerated
GA. The increase of temperature can accelerate the
growth of graphite crystallites and the degree of graphiti-
zation, thereby promoting the close packing and arrange-
ment of the crystallites. Treating at 3000C for 6 h is
proved to be one of the optimal approaches for eliminat-
ing the internal stress and achieving the highest degree of
graphitization.
110
The regenerated GA exhibits great elec-
trochemical properties and the capacity retention rate is
97.3% after 1000 cycles while the initial capacity is
352.5 mAh/g (Figure 8C). Furthermore, after 1600 cycles,
the release capacity of the product is 351.9 mAh/g, and
the capacity retention rate is 87.88%.
Pyrolysis treatment not only needs high temperature
but also generates toxic gases, which leading to high
energy consumption and air pollution. Therefore, some
chemical solvents have also been employed to avoid high
energy consumption and obtain pure GA in the recovery.
Yang et al. proposed an acid leaching method to regener-
ate pure GA after a two-stage calcination.
112
After being
leached in 1.5 M HCl solution, almost 100% lithium,
98.5% copper and 99.2% aluminum were dispersed in the
leaching solution. In addition, lithium was recovered as
lithium carbonate with a purity of up to 99% by adding
sodium carbonate to the leaching solution. It is found
that regenerate GA has high initial specific capacity at
37.2 mAh/g (591 mAh/g), 74.4 mAh/g (510 mAh/g) and
186 mAh/g (335 mAh/g). The retention rate after
100 cycles is as high as 97.9%, and it also shows excellent
cycle performance at a high rate of 372 mA/g
(Figure 9A). To further improve the purity of regenerated
GA, a systematic approach combined sulfuric acid curing,
leaching and calcination were proposed.
113
Comparing
with direct acid leaching, sulfuric acid solidified acid
leaching has a higher impurity removal efficiency, which
the purity of recovered GA can reach to 99.6%. Besides,
the regenerated graphite is close to unused commercial
graphite in both morphology and structure. It also shows
an excellent electrochemical performance in terms of
charging capacity and cycling. The retention rate can
reach 98.8% when the initial charge capacity is 349 mAh/g,
which proves the feasibility of recycled GA used in LIBs
(Figure 9B).
113
Inorganic acids are demanding to handle,
harmful to the environment, and prone to produce second-
ary pollution. In order to meet the needs of environmentally
friendly development, green chemical solvents have been
used to replace inorganic acid. Wang et al.
114
found that
water can react with the residual lithium in GA to precipi-
tate hydrogen, which can separate the thick SEI from GA
and remove most of the impurities and restore the
electrochemical activity of graphite. The electrochemical
measurements demonstrate that after 100 cycles, the
capacity of recycled graphite is 345 mAh/g, which is
similar to industrial graphite (347 mAh/g) and also com-
parable to the products from acid leaching. Moreover,
the electrolysis method is also an effective and clean
process to separate copper and GA from spent LIBs
(Figure 9C).
115
In this process, Cu foil can be reused
directly and the residual lithium can dissolve in the elec-
trolyte and be recovered by precipitation method. The
recovered GA shows excellent cycling stability and rate
capability (427.81 and 350.47 mAh/g). Meanwhile, it also
shows excellent rate performance and the specific capac-
ity recovered to 347 mAh/g after a high rate.
3.2 |Reuse in other energy storage
devices
In addition to being repaired and regenerated and re-
used in LIBs, the recycled GA can also be used in other
energy storage systems after treatment, such as lithium-
sulfur batteries, sodium-ion batteries, potassium-ion bat-
teries
68
and super capacitors.
116
The GA from spent LIBs
has two special characterizations to enhance trapping
and catalytic performance toward polysulfides. On the
one hand, the porous structure and defects formed in the
repeated lithiation-intercalation process can provide
many adsorbent sites to limit the soluble polysul-
fide.
117,118
At the same time, due to the decomposition of
the electrolyte, several polar functional groups are pro-
duced on the graphite surface, which is beneficial to the
adsorption of polysulfide and the wetting of the electro-
lyte.
119
On the other hand, due to the dissolution of the
active cathode material, transition metal elements such
as Ni, Co, and Mn are introduced into the waste GA,
which can also fix polysulfides, improve conductivity,
and promote polysulfide conversion kinetics.
120
A spent-
graphite-based interlayer is developed to reduce the
“shuttle effect”in high-performance lithium-sulfur batte-
ries (Figure 10A).
121
The discharge capacity of lithium-
sulfur batteries using spent GA modified separators can
reach to 968 mAh/g, the attenuation rate at 1C is 0.08%,
and the discharge times can reach more than 500 times.
In addition, the spent GA and sulfur composite can be
considered as the cathode material for lithium-sulfur bat-
teries.
120
And compared with commercial graphite, the
cathode has an excellent cycling performance, with an
average capacity decay of only 0.006%/cycle after
500 cycles. Spent GA also shows great potential as anode
material in lithium-ion capacitors (LICs) due to its larger
d-spacing than commercial graphite.
122
Before the fabri-
cation of LICs, GA was pre-lithiated (LiC
6
) into a
12 of 27 QIAO ET AL.

graphite intercalation compound for supplying Li
+
. The
dual carbon LICs based on GA/LiC
6
anode material
shows an energy density of 185.5 Wh/kg at a power of
0.319 kW/kg under room temperature (Figure 10B).
Unlike lithium embedding, sodium embedding in
graphite is extremely limited due to the large size. Spent
GA is considered as a pre-sodiated anode for Na-ion
capacitor, therefore it can provide higher energy density
than commercial graphite.
123
The maximum energy
density and maximum power are 59.93 and 6.8 kW/kg,
respectively. Furthermore, it has a capacity retention rate
of approximately 98% after 5000 cycles. Some studies
have revealed that recovered GA can also be considered
as an anode for sodium ion batterires.
124
The results indi-
cated that recovered GA displayed excellent rate perfor-
mance in both half-cell and full-cell. Meanwhile, it also
has a stable capacity retention of 84% and 78% after
100 cycles, respectively.
FIGURE 10 (A) The schematic illustration of the adsorption properties and catalytic effects of a graphite anode (GA)-modified
separator in lithium-sulfur batteries; the electrochemical performances of lithium-sulfur batteries with different separators. Reproduced with
permission.
121
Copyright 2021, Royal Society of Chemistry. (B) The morphology features of GA, cyclic performance of the dual carbon LICs
at different temperatures, and Nyquist plots for the electrochemical impedance spectroscopy analysis for the assembled dual carbon lithium-
ion capacitors before and after cycling, in which the circles relate to the experimental data and the lines corresponds to the fitting values.
Reproduced with permission.
122
Copyright 2013, Royal Society of Chemistry. (C) Schematic diagram of the synthesis process for recycled
nagative graphite and scanning electron microscope images. Reproduced with permission.
125
Copyright 2022, Elsevier
QIAO ET AL.13 of 27

In addition, spent GA also has great potential in dual-
ion batteries. As shown in Figure 10C, a two-step method
of regenerating spent GA by anhydrous ethanol cleaning
and inert gas atmosphere heating treatment was pro-
posed.
125
The expanded layer spacing of spent GA was
restored through reconstructing the crystal structure and
FIGURE 11 (A) Scanning electron microscope (SEM), transmission electron microscope images of GA from spent lithium-ion batteries
(LIBs) and graphene prepared by graphite anode (GA). Reproduced with permission.
133
Copyright 2018, Elsevier. (B) FTIR spectra of
prepared samples. Reproduced with permission.
134
Copyright 2019, Springer Nature. (C) High resolution transmission electron microscopy
(HRTEM) and atomic force microscopy (AFM) of glucose thermal treated graphene. Reproduced with permission.
135
Copyright 2021,
Chemistry Europe. (D) The schematic diagram for different treatment of GA. Reproduced with permission.
136
Copyright 2018, American
Chemical Society. (E) Flow diagram for the synthesis of reduced graphene oxide (RGO) with recovered materials from spent LIBs.
Reproduced with permission.
116
Copyright 2018, Elsevier. (F) Schematic diagram for the formation of soluble graphene. SEM images of
graphene under different temperature and TEM images of graphene under 400C. Reproduced with permission.
138
Copyright 2018, Springer
Nature
14 of 27 QIAO ET AL.

morphology by heating process. The recycled negative
graphite not only has reduced disordering but also
exhibits a good layered structure, which facilitates Li
+
transport. Electrochemical results demonstrated that the
recycled negative graphite applied to dual-ion batteries
exhibited a comparable specific capacity to that of com-
mercial graphite (about 87 mAh/g). In addition to recy-
cling GA alone, Du et al.
126
proposed a novel method to
recover both lithium ferro phosphate (LFP) cathode and
GA from used batteries, considering the excellent stabil-
ity of LFP and the high electrical conductivity of graphite.
The recovered cathode and anode mixture was used as
the cathode in a new type of dual-ion battery to store
both anions and cations. The hybrid cathode combines
the advantages of both LFP and GA, and exhibits a good
electrochemical performance, which the reversible capac-
ity is about 130 mAh/g at 25 mA/g.
3.3 |Graphite based materials
Graphene is a single-atom-thick carbon sheet with sp
2
structure,
127
which has attracted massive attention due to
its fascinating electronic, thermal and chemical proper-
ties and has potential in the nanocomposite, sensors,
microelectronics, thin films, micro-electrical devices and
other applications.
128–130
Recently, GA from spent LIBs
have been employed to prepare graphene and graphene
oxide (GO) because of their special structure especially
large layer spacing.
131,132
The Hummers method is one of
the most common methods to prepare GO and reduced
graphene oxide (RGO). The acid solution was used to
remove the metal impurities on spent GA, and a mesh
sieve was employed to uniform the particles size.
133
Through the Hummers method, GO and RGO were pre-
pared by spent GA and commercial graphite, respec-
tively. After thermal explosion and exfoliation of solidly
stacked graphene layers, the specific surface area of RGO
increased from 36.2 to 362.4 m
2
/g (Figure 11A). Further-
more, the specific surface area of RGO prepared by GA is
8% higher than that prepared by commercial graphite.
This result indicates that spent GA from LIBs could pro-
vide a larger surface area than commercial graphite
under the same condition. To reduce environmental pol-
lution, Yang et al.
134
proposed an ultrasonic assistant
method to separate GA from copper foil with water as a
solvent. Then the collected GA was prepared into GO
through a modified Hummers method. And vitamin C
was used to replace the traditional agent to reduce the
GO into graphene. The fourier-transform infrared spec-
troscopy (FTIR) measurements indicates that vitamin C
has good reducibility, a number of oxygen-containing
groups have been removed, and the structure of graphene
has been restored (Figure 11B). And the characterizations
also demonstrate that the prepared RGO exhibits obvious
layered structures, smooth and ordered surface texture,
wide interlayer spacing as well as small resistivity. Glu-
cose was also considered as a reductant to prepare high-
quality graphene sheets.
135
As shown in Figure 11C, the
size of prepared RGO is about 5 μm and the thickness
ranges from 0.82 to 1.09 nm. Moreover, the yield of RGO
is about 84.3% and the number of layers ranging from
2 to 9 which was calculated by measuring thickness of
45 flakes.
135
Except for adding extra reducing agents, the
Al current collector and stainless steel shell from spent
LIBs can also be reducing agents to prepare RGO
(Figure 11D).
136
When preparing RGO by the Hummers method, the
consumption of acid solution and oxidizing agent is an
important factor from both environmental and economic
considerations. Due to the existence of structural defects
in GA, the consumption of H
2
SO
4
and KMnO
4
are about
40% and 28.6% less than that of natural graphite respec-
tively.
137
Besides, GA from spent LIBs has the character-
istic of irregular expansion after the Li
+
intercalation and
deintercalation during the charge–discharge cycles, and
this prefabrication process facilitated the exfoliations of
graphite both in chemical and physical. Shear mixing can
enhance the expansion which increase the productivity
of graphene by four times.
136
Furthermore, acid treat-
ment can further expand the GA lattice and increase the
yield of RGO to 83.7%, which is 10 times higher than that
of normal graphite (Figure 11E).In addition to traditional
GO, soluble RGO nanosheets can also be prepared by
spent GA from LIBs.
138
NaOH and KOH eutectic solvent
was used to reduce the GO prepared by spent GA
through the Hummers method. And the unsaturated
oxygen-containing part on GO sheets can be effectively
removed. As shown in Figure 11F, RGO prepared under
different temperatures are in different degree of disor-
dered and wrinkled. Furthermore, the higher the treated
temperature is, the worse the disorder of RGO is. The
prepared soluble RGO dispersed in water or ethanol
exhibit excellent stability, and no visible settlement after
gravity standing for 4 weeks. The excellent dispersibility
of soluble RGO has wide potential applications in many
areas such as energy, chemical industry and micro-
electronics.
In addition to Hummers method, other methods have
also been employed to prepare GO or RGO by spent GA
from LIBs. A one-pot redox reaction method is suggested
to prepare RGO using a ternary system containing
H
2
SO
4
, KMnO
4
, and C
2
H
4
O
3
.
139
This method can not
only avoid the subsequent reducing agents and other
high-temperature reduction processes but also has a high
yield of 61.2%. The electrochemical method has also been
QIAO ET AL.15 of 27

widely used in preparing graphene in recent researches.
Graphene produced by electrochemical exfoliation
method is easy to agglomerate, so that surfactants are
added to avoid this phenomenon. The type of aqueous
electrolytes containing different surfactants (cationic,
nonionic and anionic) can make influences on electro-
chemical exfoliation process.
140
It is also found that the
addition of NaCl in electrolytes could increase the yield
of graphene compared with that in pure surfactants elec-
trolyte systems during the graphite exfoliation. This is
because NaCl can enhance the hydrolysis process of
water due to its high electrical conductivity, resulting in
an enhancement of the edge exfoliation of graphite to
produce graphene. The Z-height profiles obtained from
AFM images demonstrates that the exfoliated samples
contained only a few-layer graphene sheets. Kang
et al.
141
creatively proposed a short-circuit discharge
method to prepare large-size GR sheets. This method
including two steps, the lithium intercalated graphene
compound was first obtained after the short-circuit of
FIGURE 12 (A) Schematic diagram of the recycling process for waste mixed cathode material with graphite anode (GA) as reductant.
Reproduced with permission.
143
Copyright 2020, Elsevier. (B) A typical microstructure of a quenched sample. Reproduced with
permission.
144
Copyright 2020, MDPI. (C) Preparation diagram for magnesium hydroxide-modified mesocarbon microbeads composite.
Reproduced with permission.
149
Copyright 2016, American Chemical Society. (D) Schematic diagram and scanning electron microscope
images of MnO
2
modified GA materials. Reproduced with permission.
150
Copyright 2019, American Chemical Society. (E) The degradation
rate of on methylene blue by CuO and GA-Cu composite. Reproduced with permission.
152
Copyright 2018, Springer Nature
16 of 27 QIAO ET AL.

LIBs, then the compound was exfoliated into graphene
by ultrasonic. The prepared graphene has the characteris-
tics of large size, few defects, single layer or less than
three layers. Compared with electrochemical methods
reported in the literature, the quality of graphene has
been significantly improved and the yield can reach to
8.76%. Furthermore, the battery-grade Li salt also can be
efficiently recovered as by-product.
142
The lithium graph-
ite intercalation compounds were obtained from re-
charge the spent LIBs, then they were into a hydrolysis
procedure which the expansion/micro-explosion mecha-
nism could make it to graphene. Meanwhile, lithium was
simultaneously recovered in the form of battery-grade
lithium carbonate in the above process. According to eco-
nomic analysis, the production cost of graphene prepared
by GA was extremely low ($540/ton) compared to that of
commercial graphene. It is indicated that preparing gra-
phene by spent GA in LIBs cannot only alleviate the
shortage of natural graphite but also has huge economic
benefits.
3.4 |Catalyst
GA also has attracted some attention on catalyst and
reduction areas due to its economic and abundant yield.
Pindar et al.
143
proposed a short duration, cost-effective
recycling process for waste mixed cathode material
(Figure 12A). It is worth mentioning that GA was crea-
tively used to improve the metal extraction rate in
cathode materials as a reductant during the microwave-
assisted method. Moreover, GA shows better-reduced
ability on lithium cobalt oxides and lithium nickel man-
ganese oxide than activated charcoal, which avoid addi-
tional external reductants in the recycling process. Based
on this phenomenon, experiments on GA to replace con-
ventional reducing agent coke during the nickel slag
cleaning process were carried on.
144
Rapidly reduction
results were obtained in the conditions of combination
with GA. Just in the 5 min reduction process, the
valuable metals Co, Ni and Cu were distributed in the
iron-rich alloy, and the remaining Mn and Al in the foam
part were discharged into the slag (Figure 12B). Previous
studies have shown that graphene-based materials have
excellent oxygen reduction reaction performance in alka-
line media, especially when they are doped with hetero-
atoms such as nitrogen, sulfur, boron or fluorine.
145–147
Therefore, high nitrogen doped graphene with uniform
distribution of carbon, nitrogen and oxygen was prepared
by GA from spent LIBs.
148
X-ray diffraction (XRD),
Raman and X-ray photoelectron spectroscopy (XPS) mea-
surements indicate that the electrocatalytic activity of
synthetic nitrogen-doped graphene for oxygen reduction
reaction is higher than that of commercially available
nitrogen graphene because of the presence of carbon
vacancies and higher content of active nitrogen on the
surface of graphene. From these results, it is clear that
GA from spent LIBs could be recycled and reutilized in
the catalyst.
In addition, GA also exhibits an effective catalytic
ability on the adsorption enhancement of water pollu-
tion. For example, the GA compound modified with
nanoscale Mg(OH)
2
on surface was employed to remove
excessive phosphate, which can lead to freshwater eutro-
phication and deterioration of aquatic ecosystems
(Figure 12C).
149
The adsorb quantity can reach to
588.4 mg/g, which is one order higher magnitude higher
than previously reported carbon-based adsorbents. Fur-
thermore, GA also exhibits adsorption ability on heavy
metal polluted water containing plumbum, cadmium,
and silver. To improve the sorption ability, MnO
2
nano-
particles can be loaded to the supporting GA by a facile
hydrothermal method. Compared with single GA pow-
der, the MnO
2
-modified GA exhibits a higher removal
rate on plumbum, cadmium and silver, which reach to
99.9%, 79.7% and 99.8%, respectively (Figure 12D).
150
In
order to further evaluate the adsorb ability of GA,
Nguyen et al.
151
conducted batch adsorption experi-
ments on cadmium, barium, 2,4-dinitrotoluene (DNT),
2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-
1,3,5-triazine (RDX), and 2,4-dichlorophenol (DCP). In
addition, the catalytic performance of GA in thiol (-SH)
reducing agent, dithiothreitol (DTT) and hydrogen sul-
fide (H
2
S) reduction of DNT and RDX and persulfate
oxidation were also investigated. The results demon-
strate that GA has better adsorption performance for
toxic metals compared with other types of carbonaceous
materials. And in the oxidation and reduction process, it
has shown a strong ability to promote redox reactions,
which indicates that it may be suitable for environmen-
tal remediation. To comprehensive reutilize spent LIBs,
GO-Cu composite material was prepared due to the defect
structure of GA and copper foil from spent LIBs. The com-
posite exhibits a better catalytic photodegradation perfor-
mance on methylene blue than CuO (Figure 12E).
152
These
studies provide the possibility to recycle GA for synthesizing
high-efficiency adsorbents from spent LIBs, which is an eco-
nomical and environmentally friendly method for heavy
metal polluted water treatment and waste recycling.
3.5 |Functional composite materials
Based on the special structure and performance of GA
from spent LIBs, researchers explored and investigated
some potential applications of spent GA experimentally,
QIAO ET AL.17 of 27

especially as functional composite materials. It is noted
that GA could indeed improve the mechanical properties
of the polymer film. The composite films are synthesized
by recycled GA through a solution intercalation
method.
153
The tensile strength of graphite composite
film combined with polyethylene and polypropylene is
10 times higher than original polyethylene and polypro-
pylene film, which was increased from 3.0 to 38.1 and 3.4
to 33.9 MPa respectively (Figure 13A). Meanwhile,
compared with pure polypropylene and polyethylene, the
specific conductance of prepared nanocomposite films is
increased by 5–6 orders of magnitude, which is a good
substitute for the commercial graphite and polymers for
the synthesis of the polymer-nanocomposite thin film.
Furthermore, GA has also been used as the carbon source
for the application in gas storage capabilities like N
2
,H
2
,
and CO
2
. For that, hollow carbon spheres were synthe-
sized by a one-step carbonization process, and RGO was
FIGURE 13 (A) The mechanical properties of the graphite anode (GA) with polypropylene and polyethylene nanocomposite thin films.
Reproduced with permission.
153
Copyright 2015, Elsiver. (B) H
2
adsorption and CO
2
adsorption of RGO prepared by GA. Reproduced with
permission.
154
Copyright 2013, Royal Society of Chemistry
18 of 27 QIAO ET AL.

prepared by GA with Al cases as a reductant
(Figure 13B).
154
The generated RGO exhibits good gas
storage performance for both H
2
and CO
2
. It also shows a
superior CO
2
uptake capacity of 61.17 cm
3
/g, while the
H
2
storage capacity can reach 200.46 cm
3
/g at 77 K,
which is greater and comparable to the other literature
reports.
155,156
Moreover, GA can be used as nanoparticles
in the heat transfer medium. We presented a facile
freeze–thaw ultrasonic assisted circulation method to
prepare two-dimensional low-layer graphite flakes using
GA from spent LIBs.
157
GA was easier to exfoliate to pre-
pare low-layer graphite flakes than commercial graphite
and the prepared also exhibited a better thermophysical
performance in nanofluids than base fluids.
Overall these studies, GA from spent LIBs has been a
potential candidate of carbon source in various applica-
tions. Furthermore, the potential on other application
areas should be explored considering the special structure
and performance of GA. And the recovery of GA should
obtain more attention from researchers for that the reuti-
lization of GA is a win-win opportunity for both resource
shortage and environmental pollution.
Among the methods mentioned above, they are cur-
rently focused on laboratory scale and are still have some
distance away from commercial production. The pyro-
lytic regeneration of spent GA has great potential in com-
mercial production, especially with s the normal end of
life LIBs. Because of its stable change and easy handling,
it can continue to be applied to energy storage systems
without excessive processing. Besides, the graphene mar-
ket is also gradually expanding and relatively mature for
industrialization due to the wide range of graphene appli-
cations.
158,159
Spent GA has been proved to have the
advantages of low cost consumption and high yield in the
process of graphene preparation. Therefore, it has a broad
market prospect as a graphene raw material and can be
applied on a large scale. In addition, the application
method of spent GA in other fields is relatively compli-
cated, and a mature industrial chain foundation has not
yet been formed so that it will take some time to develop
and grows.
4|CHALLENGES AND
PROSPECTS
Previous studies demonstrates that the extraction rate of
valuable metals and other useful materials could reach
almost 100% in spent LIBs. However, the recycling and
reutilization of waste GA in spent LIBs is of equivalent
importance to that of cathode materials. Because of the
great large demand for graphite in batteries, the
United States and the European Union countries have
proposed graphite as a key material for recycling.
34,160,161
From the above discussion, the continued growth of LIBs
used in consumer electronics, electric vehicles and grid
power storage will increase the demands for graphite
material. The increase in demand for electric vehicles
will be partially but not fully offset by changes in LIBs
such as new anode using silicon
162
or titanite.
163
There-
fore, recycling of GA from spent LIBs has been applied as
an effective approach to achieve the predicted demand of
battery-grade graphite. Although there has been some
progress on the recovery, regeneration and reuse of GA,
there is still a need for developing new and effective
methods to meet changing recycling needs. Besides,
future development in spent GA recycling till faces some
challenges based on the existing experience and predic-
tion. More efforts should be made from the following
aspects to improve the development of GA recycling:
1. The purity of recovered graphite should have a certain
evaluation standard. In the recycling process, metal
impurities including residual lithium, binder, and bro-
ken copper foil or the fragments of the cathode mate-
rial are possible appear in the recovered GA. The
impurities can affect the purity of GA seriously and
hander its next applications. Therefore, the purity of
recovered GA should be ensured before reuse in fur-
ther applications.
2. It also should be noted that the recovered GA surface
damage is influenced by the aging mechanism like
SEI formation and intercalation of solvent molecules
which lead to surface changes and graphite degrada-
tion. Thus, effective surface treatments are needed to
remodify the surface structure, reduce irreversible
capacity loss and improve the capacities.
3. The recovered GA is not only limited to the applica-
tions of LIBs and capacitors, but can also be extended
to sodium batteries and capacitors, and it is also possi-
ble to explore as electrode materials for emerging
energy storage systems, such as potassium ion batte-
ries, super capacitors, aluminum ion batteries, and
flow batteries, and so forth. In addition, graphite and
its derivatives not only have great application value in
clean energy but also can extend to other aspects such
as gas storage, catalytic reduction reaction as well as
membrane area. So that the recycling and retreating
techniques of GA need to be multivariate, in-depth
and targeted.
4. Besides, the price of graphite recovery should be cal-
culated in an appropriate way to maximize the econ-
omy. Therefore, environmentally friendly, less time
and cost consuming approaches are more receptive.
Based on the above points, we tentatively propose a
guideline for the recycling process of spent GA based on
the previous researches and our own insights. First of all,
QIAO ET AL.19 of 27

according to the failure of spent LIBs, they should be
roughly divided into two types, normal spent LIBs with
limited service life and severely damaged LIBs due to
obvious safety failures. The structure changes on GA in
natural scrap LIBs are relatively stable, and the main
change is the expansion of interlayer spacing. Simple and
effective methods (solvent leaching and heating treat-
ment) can restore its lattice and lamellar structure,
enabling its secondary application in energy storage sys-
tems. In severely damaged LIBs, the surface or structure
damage and impurity doping are complex due to the vari-
ous failure mechanism, and it is impossible to perform
simple and unified repairs. In short, recycling of spent
GA should be targeted and utilized step by step. Spent
GA without seriously affected should be given priority to
regeneration, and those are severely damaged are more
suitable for secondary processing as raw materials, and
can be used in related fields by taking advantage of their
advantages.
5|SUMMARY
In above, spent GA increasing with the continued growth
of LIBs. Despite graphite resource is not as short as other
metal resources, it should be noted that not all kinds of
graphite can be employed as anode. The recovery
approaches of GA with high performance and high yield
purity are necessary for resource shortage and environ-
mental pollution. Moreover, the recycling of GA can
reduce the dependence on overseas graphite source and
ensure the sustainable supply chain of graphite. Recy-
cling and resourceful utilization of GA should attract
continuous attention for economic and environmental
considerations. The recycling process needs to emphasize
the principles of 3R (Reduction, recovery and reutiliza-
tion)
164
and 3E (energy, environment and economy)
165
have been suggested. Here, we proposed a new principle
called 3 S, which presents systematic, security and sus-
tainability. For that, the recovery process of GA from
spent LIBs should be systematic, disassemble, remake
and reuse stages are coherent step by step. Especially in
commercial production, manufacturers should classify
spent LIBs into normal spent LIBs and severely damaged
LIBs after safety failures. Then it is sent to different recy-
cling systems, which can realize the step-by-step utiliza-
tion of spent GA in different degrees. A low-cost, simple
and effective recovery system should be designed for the
waste graphite with a lesser degree of failure to help
improve economic benefits. Security emphasizes the
safety during the whole recycling process of spent GA,
there are more safety hazards in the recycling of used bat-
teries, such as incomplete discharge, short circuit and
battery breakage, especially the high risk in the process
of disassembly which are potential to cause a fire and
explosion. Therefore, the environment and atmosphere
of the workshop should be strictly required to avoid the
risk of combustion and explosion caused by a large
amount of GA stacked or electrolyte volatilized in large
quantities together. In addition, in view of the pneumo-
coniosis hazards caused by graphite, the health and safety
of the staff in the recycling site should also be taken into
consideration. Sustainability means that the process
should be a beneficial development from the resource,
environmental and economic perspective. Considering
the increasing energy crisis and environmental pollution
problems, the recycling process of spent GA should pay
attention to the recycling of the instrumentation or
reagents used to avoid secondary pollution and waste of
resources. In addition, all components of spent LIBs
should be considered for recycling, instead of focusing
only on the much-noticed electrode materials, in order to
promote the overall sustainability of spent LIBs. In the
future, the recycling of GA is promising to achieve the
closed-loop development of in spent LIBs industries
(Figure 14).
AUTHOR CONTRIBUTIONS
Yu Qiao: conceived and designed the project, writing –
original draft, writing-review & editing. Huaping Zhao:
conceived and designed the project, writing –original
draft. Yonglong Shen: Conceptualization, writing-
review & editing, supervision. Liqiang Li:
FIGURE 14 Challenges and suggesting principles of spent
graphite anode (GA) recovery
20 of 27 QIAO ET AL.

Conceptualization, writing-review & editing, supervision.
Zhonghao Rao: Conceptualization, writing-review &
editing, supervision. Guosheng Shao: Conceptualiza-
tion, writing-review & editing, supervision. Yong Lei:
Conceptualization, writing-review & editing, supervision,
project administration and funding acquisition.
ACKNOWLEDGMENTS
The authors acknowledge support from the German
Research Foundation (DFG: LE 2249/15-1) and the Sino-
German Center for Research Promotion (GZ1579). Yu
Qiao appreciates the support from the China Scholarship
Council (No. 202006420028).
CONFLICT OF INTEREST
The authors declare no conflict of interest.
ORCID
Yong Lei https://orcid.org/0000-0001-5048-7433
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