batteries

Review
Recycling of Lithium-Ion Batteries via Electrochemical Recovery:
A Mini-Review
Lu Yu , Yaocai Bai * and Ilias Belharouak *

Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA;
yul1@ornl.gov
* Correspondence: baiy@ornl.gov (Y.B.); belharouaki@ornl.gov (I.B.)

Abstract: With the rising demand for lithium-ion batteries (LIBs), it is crucial to develop recycling
methods that minimize environmental impacts and ensure resource sustainability. The focus of this
short review is on the electrochemical techniques used in LIB recycling, particularly electrochemical
leaching and electrodeposition. Our summary covers the latest research, highlighting the principles,
progress, and challenges tied to these methods. By examining the current state of electrochemi-
cal recovery, this review intends to provide guidance for future advancements and enhance LIB
recycling efficiency.

Keywords: lithium-ion battery; battery recycling; electrochemical recovery; electrochemical leaching;

electrodeposition

1. Introduction
Lithium-ion batteries play a crucial role in advancing the development of electric
vehicles and consumer electronic devices. As these markets expand, there is a growing de-
mand for lithium-ion batteries, emphasizing their essential role in modern technology and
sustainable energy systems [1–3]. However, the increasing reliance on lithium-ion batteries
brings challenges related to natural resource limitations and sustainable development. The
limited availability of natural resources, such as lithium, cobalt, and nickel, necessitates
Citation: Yu, L.; Bai, Y.; Belharouak, I. the development of efficient and low-cost recycling processes [4–6]. These processes are
Recycling of Lithium-Ion Batteries via crucial for recovering valuable materials, with a particular emphasis on cathode materials,
Electrochemical Recovery: A Mini- which are essential components of lithium-ion batteries. Currently, lithium-ion battery
Review. Batteries 2024, 10, 337. recycling is still in its early stages at the industrial scale, with significant challenges related
https://doi.org/10.3390/batteries to the quality of regenerated materials and the cost of the process. Recycling methods for
10100337 lithium-ion batteries are typically classified into pyrometallurgical, hydrometallurgical,
Academic Editor: Elod Gyenge and direct recycling processes [4,7]. Within these categories, various techniques have been
applied for cathode recycling, including acid leaching [8–10], direct delamination [11–13],
Received: 26 August 2024 solvent extraction [14], hydrothermal treatment [15], membrane separation [16,17], and
Revised: 16 September 2024
electrochemical method [18–20]. Among these approaches, the electrochemical method is
Accepted: 20 September 2024
gaining attention because of its potential for energy efficiency, scalability, and selectivity
Published: 24 September 2024
and reduced environmental impact with less harmful emissions and waste products.
The electrochemical method for battery recycling uses electrochemical reactions to
recover critical metals from battery scraps and end-of-life batteries. Recent advancements in
Copyright: © 2024 by the authors.
the electrochemical recovery of lithium-ion batteries are divided into two main approaches:
Licensee MDPI, Basel, Switzerland. electrochemical leaching and electrodeposition [21–23]. For electrochemical leaching, the
This article is an open access article electric current is applied to the battery materials, thus achieving the dissolution of metal
distributed under the terms and ions in the solution. As for electrodeposition, the electric current is applied to the solution
conditions of the Creative Commons with dissolved metal ions and promotes the reduction of the dissolved metal ions, thus
Attribution (CC BY) license (https:// enabling the recovery of high-purity metals on the electrode. Electrodeposition was applied
creativecommons.org/licenses/by/ for pure metal recovery, the separation of metals, and cathode relithiation. In this work, we
4.0/). summarize the most recent advancements in electrochemical leaching and electrodeposition

Batteries 2024, 10, 337. https://doi.org/10.3390/batteries10100337 https://www.mdpi.com/journal/batteries

Batteries 2024, 10, 337 2 of 11

for cathode material recycling. Additionally, we provide insights into the challenges
of, potential improvements in, and future directions for enhancing the efficiency and
sustainability of these electrochemical recycling methods.

2. Electrochemical Leaching
Electrochemical leaching is the extraction of metal ions from the anode electrode
into the solution through an external current. Currently, inorganic acid combined with
hydrogen peroxide for cathode leaching is the most commonly used method for lithium-
ion battery recycling. However, the usage of inorganic acid with hydrogen peroxide
involves the usage of a large amount of water and leads to a complicated separation
and precipitation process. Electrochemical leaching provides an alternative method for
effectively extracting metal ions from the cathode electrode in a greener process [24–29].
Recently, Adhikari et al. conducted a lifecycle assessment to compare the electrochemical
leaching process with the traditional hydrometallurgical leaching method. The results
showed that the electrochemical leaching process greatly relieved the environmental impact.
by 80–87%, owing to its reduced usage of acid and hydrogen peroxide [30]. Table 1 provides
a summary of recent research studies on electrochemical leaching for cathode recycling.
In 2020, Diaz et al. proposed an electrochemical method for cathode leaching to recover
valuable metals from mixed cathodes. In this work, the three-electrode system was used
with nickel foam as the anode electrode, a stainless-steel mesh as the cathode electrode,
and Ag/AgCl as the reference electrode. KOH solution (1 M) was used as an anolyte
and a bipolar membrane was used for separating the anode and cathode. The researchers
applied this electrochemical leaching process to an industry LIB metal oxide filter cake
(MOFC), which is composed of mixed anode graphite and different cathode materials,
including LiCoO2 , LiMnx Coy O2 , LiNix Mny CoZ O2 , LiCux MnO2 , and LiNix Cox Alz O2 . The
MOFC was mixed in sulfuric acid (H2 SO4 ) solution (0.5–2 M) with a low concentration
of FeSO4 (10 mM) as a reducing agent. The electrochemical leaching was operated at a
controlled voltage of −0.3 V vs. Ag/AgCl. During the process, the water was oxidized
to produce protons and hydroxyl ions. The produced protons were transferred to the
cathode and facilitated the leaching process, while the hydroxyl ions were transferred to
the anode for oxygen evolution in alkaline media. With this electrochemical design, the
leaching efficiencies of active metals, including Li, Ni, Mn, and Co, reached over 96%.
The economic analysis showed that the energy and chemical costs of this process are
about 80% less than that of the conventional hydrometallurgical process [31]. In 2021,
Lei et al. applied an electrochemical method for co-leaching the Li, Ni, Mn, and Co from
a reduced LiNix Mny Coz O2 (NMC) cathode. Before the electrochemical leaching process,
the NMC cathode materials were first annealed at 1600 ◦ C for 120 mins to obtain the
reduced cathode mixture, which included Li2 CO3 , NiO, Co3 O4 , Mn2 O3 , and MnO2 . The
mixture was kept in a polypropylene bag and immersed in a sulfuric acid electrolyte. In
this work, a two-electrode system was used with titanium as an anode and graphite as the
cathode. An anion exchange membrane was set in the middle for separating the cathode
and anode electrodes. The H2 SO4 concentration, electric current, and reaction time were
adjusted and optimized. The leaching efficiencies of the metal ions showed a trend of
first increasing and then decreasing with the increase in the H2 SO4 concentration and the
electric current, as more H+ existed in the solution and the higher electric current promoted
the electrochemical leaching reaction, while the extra-high concentration of H+ and electric
current promoted the hydrogen evolution reaction, thus decreasing the electrochemical
leaching performance. Regarding the leaching time, the leaching efficiencies of the metals
reached equilibrium after the reaction for about 150 mins. Therefore, the optimal conditions
for electrochemical leaching were set as 1.5 M H2 SO4 solution, 0.8 A of electric current, and
150 min of leaching time. Under this condition, the leaching efficiencies of Li, Ni, Mn and
Co reach 100%, 90.59%, 66.40%, and 90.53%, respectively [26]. Besides the electrochemical
co-leaching of metals, including Li, Mn, Ni, and Co together, Yang et al. recently proposed
an electrochemical leaching approach for selectively extracting Li from spent cathode
Batteries 2024, 10, 337 3 of 11

materials. In this study, spent LiNi0.6 Mn0.2 Co0.2 O2 (NMC622) cathode materials were used
as research subjects and a K2 SO4 solution was used as the electrolyte solution. The impact
of the applied voltage (1.0–3.0 V) on the delithiation performance was detailed. The SEM
images of the delithiated samples are displayed in Figure 1a–d, and the leaching efficiency
of the Li and a comparison of the Li with Co, Ni, and Mn under different operation voltages
are presented in Figure 1e. The voltage of 2.5 V gave the best Li leaching performance
as the low voltage led to low efficiency, while the high voltage resulted in a strong side
reaction, which led to the leaching of the transition metals (Ni, Co, and Mn) instead of
the selective leaching of Li. The working mechanism is displayed in Figure 1f. Under
optimized voltage, the NiOx releases electrons synchronously, which further facilitates
Batteries 2024, 10, x FOR PEER REVIEW
the
3 of 11
Li leaching process [32].

Table 1. A summary of electrochemical leaching studies for cathode recycling.

metals, including Li, Mn, Ni, and Co together, Yang et al. recently proposed an electro-
Leaching Items
Operation chemical
Leachingleaching
Agents approach for selectively extracting
Applied Voltage/
pH Li fromEfficiency
Leaching spent cathode materials.
Reference In
System Current
this study, spent LiNi0.6Mn 0.2Co0.2O2 (NMC622) cathode materials were used as research
H2 SO4and
solution
a K2(0.5–2 Li, Co,solution.
Mn, and Ni:The
>96%,
LIB metal oxide Threeelectrodesubjects SO4 solution was used as the electrolyte impact of the ap-
M), FeSO4 (10 mM) as a −0.3 V >1 Fe: > 40%, Cu: >70%, [31]
filter cake system plied voltage
reducing (1.0 V–3.0 V) on the delithiation performance
agent was
Zn: >80%, Al:detailed.
>30% The SEM images
Reduced NMC Twoelectrode
of the delithiated samples are displayed in Figure 1a–d,
H2 SO4 solution (0.5, 1,
and the leaching efficiency of the
Li: 100%, Ni: 90.59%,
Li and a comparison 0.2–1.0
of the A Co, Ni, and
Li with \ Mn under different operation voltages [26] are
cathode system 1.5, and 2 M) Co: 90.53%, and Mn: 66.40%
Two-electrode presented in Figure 1e. The voltage of 2.5 V gave the best Li leaching performance as the
NMC622 cathode K2 SO4 solution 1.0–3.0 V 9–12 Li: 95.02% [32]
system low voltage led to low efficiency, while the high voltage resulted in a strong side reaction,
Twoelectrode which led to the leaching of the transition metals (Ni,Li: Co, andNi:
100%, Mn) instead of the selective
99.87%,
NMC cathode Malic acid solution 2.0–10.0 V <6.6 [28]
system leaching of Li. The working mechanism is displayedCo: in 99.58%,
FigureMn:1f. 99.82%
Under optimized volt-
LiCoO2 (LCO) Twoelectrode age, the NiOx releases electrons synchronously, which further facilitates the Li leaching
Malic acid solution 2.0–10.0 V <6.22 Li: 94.17%, Co: 90.45%, [24]
cathode system
process [32].

Figure1.1.(a–d)
Figure (a–d)SEM
SEMimages
imagesofofspent
spent NMC622
NMC622 cathodes
cathodes after
after lithium
lithium released
released under
under different
different volt-
voltages,
ages, (e) leaching efficiencies under various voltages, and (f) schematic diagram of the electrochem-
(e) leaching efficiencies under various voltages, and (f) schematic diagram of the electrochemical
ical leaching for delithiation of spent cathode electrode [32].
leaching for delithiation of spent cathode electrode [32].
Table
3. 1. A summary of electrochemical leaching studies for cathode recycling.
Electrodeposition
Electrodeposition is an electrochemical
Applied Volt-process wherein the metal ions withinRefer-the
Leaching Items Operation solution
System Leaching Agents
are reduced with an external electric
pH andLeaching
current
Efficiency
subsequently deposited
age/Current enceonto
the electrode surface. This technique is used for battery recycling for precipitation
Li, Co, Mn, and Ni: of the
critical H2SO4 solution
transition metals (0.5
from–2the
M),solution. The order and yield of electro-deposited metals
LIB metal oxide Threeelectrode >96%, Fe: > 40%, Cu:
FeSO4 (10influenced
are significantly mM) as a re- −0.3 Vsuch as the
by factors >1characteristics of the metal [31]
ions, the
filter cake system >70%, Zn: >80%, Al:
ducing
composition agent
and concentration of the electrolyte solution, the pH levels, the operating
>30%
temperature, and the applied electric current. Consequently, the electrodeposition process
Li: 100%, Ni: 90.59%,
Reduced NMC Twoelectrode cansys-
be precisely controlled
H2SO4 solution (0.5,by1,adjusting these parameters.
0.2–1.0 A \ Co: 90.53%, and Mn: [26]
cathode tem 1.5, and 2 M)
66.40%
Two-electrode sys-
NMC622 cathode K2SO4 solution 1.0–3.0 V 9–12 Li: 95.02% [32]
tem
Li: 100%, Ni: 99.87%,
Twoelectrode sys-
NMC cathode Malic acid solution 2.0–10.0 V <6.6 Co: 99.58%, Mn: [28]
tem
99.82%
LiCoO2 (LCO) Twoelectrode sys- Li: 94.17%, Co:
Malic acid solution 2.0–10.0 V <6.22 [24]
Batteries 2024, 10, 337 4 of 11

3.1. Lithium Electrodeposition

As an essential element for batteries, lithium recovery has received significant at-
tention [33]. Generally, lithium recovery via electrodeposition from various resources,
including ores, brine, and seawater, has been well explored [34,35]. With the emerging
market for electric vehicles, a substantial number of end-of-life batteries will accumulate in
the future. Consequently, lithium recovery from spent batteries is particularly appealing to
battery manufacturers. Commercially, the hydrometallurgical method is applied for spent
battery recycling and results in the leachate. Jang et al. conducted electrodeposition for
selective lithium recovery from an acidic LIB leachate. In this work, an electrode system was
employed with MnO2 as the working electrode and activated carbon (AC) as the counter
electrode. The LIB leachate was applied as an electrolyte with various cations dissolved,
including Li, Ni, Co, and Mn ions. The researchers conducted a detailed investigation
about the effect of current density and reaction time on the selective recovery of Li. With the
increased electric current, the recovery capacity of the lithium improved, while the recovery
capacities of Ni, Mn, and Co decreased. Therefore, the selective recovery of lithium from
coexisting ions was achieved at a higher current density. Additionally, the delithiated
MnO2 demonstrated high selectivity for Li over other coexisting cations, probably because
of the intercalation of the lithium into the MnO2 lattice during the electrodeposition process.
Regarding the reaction time, the longer the reaction proceeded, the more lithium was
recovered, while other ions were not. Thus, extending the reaction time enhanced both the
purity and the recovery capacity of lithium. Restricted by the electrochemical stability of
the leachate, the reaction time was optimized at 15 min and the maximum lithium recovery
capacity of 3.51 mmol g−1 was delivered under a current density of 0.2 A g−1 [36]. Further-
more, Jang et al. also used the MnO2 //AC system for lithium recovery from pre-treated
ammonium LIB leachate. The lithium recovery capacity was 1.39 mmol g−1 , with a purity
of 96.8%, under a current density of 0.2 mA cm−2 [37].
Besides lithium recovery, lithium electrodeposition has been proposed as an effective
method for cathode relithiation. Spent cathode materials often suffer from damage, par-
ticularly Li vacancy defects, after the cycling process. The traditional hydrometallurgy
process involves cathode breakdown and resynthesis processes, which add complexity
to the overall recycling process. Relithiation via lithium electrodeposition provides an
option for closed-loop recycling by simplified process. Recently, researchers have applied
electrochemical relithiation to various types of spent cathode chemistries for direct regener-
ation [38–42]. Liu et al. conducted electrochemical relithiation of a spent LiFePO4 (LFP)
cathode. The Li-containing solution was adopted as an electrolyte. A three-electrode sys-
tem was used with platinum as the counter electrode, spent LFP as the working electrode,
and Ag/AgCl as the reference electrode. As illustrated in Figure 2a, the Li ions would be
intercalated into a spent LFP cathode under applied voltage, and the effect of the current
densities on the relithiation performance is detailed in this work. As shown in Figure 2b,
the potential vs. time curves of the electrodeposition process for the Li ions were collected
under various current densities, ranging from 0.25 to 0.45 mA cm−2 . As the relithiation
proceeds, the potential of the relithiated electrode rapidly drops and gradually stabilizes
at a plateau, indicating the completion of the relithiation process. With increased current
densities, less time was required to reach the plateau, showing that the Li ions were easier
to insert into the spent LFP electrode under high current densities. The crystal structures of
the relithiated LFP cathodes under different current densities were characterized by XRD
(Figure 2c,d). The phase transformation of FePO4 into LFP confirmed that the Li ions were
successfully lithiated into the spent LFP cathodes. However, the high current density led
to excess lithium and introduced Li3 PO4 impurity phases. The Li/Fe ratio was further
examined through ICP measurement, revealing a rise in the Li/Fe ratio with increasing
current densities (as illustrated in Figure 2e). This observation confirmed the feasibility of
electrochemical relithiation for spent LFP cathodes. The electrochemical performance of the
obtained relithiated LFP cathodes was assessed by a half-cell configuration. These cathodes
delivered a discharge capacity of 154.2 mAh g−1 at C/2 and maintained 91% of the capacity
 examined through ICP measurement, revealing a rise in the Li/Fe ratio with increasing
current densities (as illustrated in Figure 2e). This observation confirmed the feasibility of
electrochemical relithiation for spent LFP cathodes. The electrochemical performance of
the obtained relithiated LFP cathodes was assessed by a half-cell configuration. These
Batteries 2024, 10, 337 5 of 11
cathodes delivered a discharge capacity of 154.2 mAh g−1 at C/2 and maintained 91% of
the capacity after 300 cycles at 1 C [42]. Zhang et al. performed electrochemcial relithiation
on a spent LCO cathode using a three-electrode system. In this setup, a platinum plate
after 300 cycles at 1 C [42]. Zhang et al. performed electrochemcial relithiation on a spent
served as the anode, the spent LCO electrode as the cathode, and Ag/AgCl as the reference
LCO cathode using a three-electrode system. In this setup, a platinum plate served as the
electrode. A Li2SO4 solution (0.1–1 M) was used as elelctrolyte and various current
anode, the spent LCO electrode as the cathode, and Ag/AgCl as the reference electrode.
densities (−0.12 to −0.42 mA/cm2) were applied and compared for relithiation performance.
A Li2 SO4 solution (0.1–1 M) was used as elelctrolyte and various current densities (−0.12
toThe results
−0.42 mA/cm indicated
2 ) were that the and
applied higher concentration
compared of elelctrolytes
for relithiation and The
performance. current density
results
lead to a more efficient relithiation process. The relithiated LCO cathode exhibited
indicated that the higher concentration of elelctrolytes and current density lead to a more ef- a
capacity
ficient of 136 mAh/g,
relithiation process.which is slightly
The relithiated lower
LCO than exhibited
cathode the commercial LCO
a capacity of cathode
136 mAh/g,capacity
of 140 mAh/g [39].
which is slightly lower than the commercial LCO cathode capacity of 140 mAh/g [39].

Figure2.2.(a)(a)Schematic
Figure Schematic diagram
diagram of the
of the electrochemical
electrochemical system
system for LFP
for LFP relithiation;
relithiation; (b) voltage—time
(b) voltage—time
curves of relithiation process at various current densities; (c,d) XRD spectra of relithiated
curves of relithiation process at various current densities; (c,d) XRD spectra of relithiated LFPs at LFPs at
various current densities; (e) Li/Fe ratios of electrode samples
various current densities; (e) Li/Fe ratios of electrode samples [42]. [42].
Batteries 2024, 10, 337 6 of 11

3.2. Cobalt Recovery

Cobalt is a strategic material that typically contributes to the cathode and enables
lithium-ion batteries to achieve high energy densities and stability over cycling. However,
it is relatively expensive and has limited natural resources [43]. Several research studies
have delved into the utilization of the electrodeposition method as a means of cobalt
recovery [44,45]. Tran et al. applied electrodeposition for Co recovery from an obtained
metal leachate. The deep eutectic solvent (DES), which is a combination of ethylene glycol
and choline chloride, was applied for LCO cathode leaching. With the obtained leachate,
the electrodeposition of Co was conducted with a three-electrode setup. A stainless-steel
mesh was used for both the working and the counter electrodes, and Ag/AgCl served as the
reference electrode. The cobalt was deposited and recovered as Co(OH)2 under a constant
current of −4.5 mA for 1 h [43]. Recently, Cheng et al. also applied electrodeposition for
co-precipitation from metal leachate. The DES, composed of choline chloride, tartaric acid,
and ethylene glycol, was first used for LiNi0.8 Mn0.1 Co0.1 O2 (NMC811) cathode leaching.
The separation of cobalt and nickel was achieved as the nickel preferred to complex with
the ethylene glycol and form precipitates while the cobalt ions were still dissolved in the
DES. The electrodeposition of cobalt was conducted with a three-electrode system, with
carbon cloth as the counter electrode, a stainless-steel mesh as the working electrode, and
Ag/AgCl as a reference electrode. H2 O was added to decrease the viscosity of the DES,
thus decreasing the resistance for charge transfer during the electrodeposition process. The
cobalt was recovered as Co(OH)2 with a purity of 97.3% and a recovery yield of 98.1%, with
an optimized potential of −1.3V and a reaction time of 4 h [46].

3.3. Electrodeposition of Ni-Co Alloy

In many scenarios, Ni2+ and Co2+ always coexist in the leachate of lithium-ion batteries,
while there still a lack of an effective method to separate nickel and cobalt due to their
similar reduction potentials [20,46,47]. In other words, the electrodeposition of Ni-Co alloy
is feasible [48]. In 2020, Landa-Castro et al. used a choline-chloride-based DES for Ni-MH
battery leaching. The collected leachate was used as an electrolyte for the electrodeposition
of a Ni-Co alloy. A three-electrode system was employed in that work, with glassy carbon
as the working electrode, platinum wire as the counter electrode, and silver wire as the
reference electrode. The deposited Ni-Co alloy contained 64.09% nickel and 35.90% cobalt
in the form of Ni and Co hydroxyl complexes [49]. Recently, Liu et al. conducted a one-
step electrodeposition of a Ni-Co alloy from LIB leachate and detailed the effect of the
potential (−0.7 to −1.5V) and pH (2–6) on the electrodeposition of the Ni-Co alloy. The
initial LIB leachate was obtained after sulfuric acid leaching, and it was directly obtained
from industry. The concentrations of the Li+ , Ni2+ , Co2+ , and Mn2+ in the LIB leachate
were 2430, 71,560, 15,840 and 24,160 mg/L, respectively. The workflow process is shown
in Figure 3a. A three-electrode system was used here, with Ag/AgCl as the reference
electrode, and both the counter electrode and the working electrode used carbon cloth.
As shown in Figure 3b–e, as the reduction potential increased, the concentrations of Ni2+
and Co2+ greatly decreased, indicating Ni-Co electrodeposition. The −1.3 V gave the
best performance for Ni-Co electrodeposition and the amount of electrodeposited Ni-Co
even decreased at a higher potential at −1.5 V, probably because of the severe hydrogen
precipitation on the cathode, which affects the deposition of Ni-Co alloys. Regarding
the pH values, the optimal removal rates of Ni2+ and Co2+ , resulting in the best Ni-Co
electrodeposition performance, were achieved at pH = 3. At pH = 2, the positive potential
(as shown in Figure 3f) due to the protonation on the cathode surface led to a repulsive effect
on the Ni2+ and Co2+ , which inhibited the deposition of the Ni-Co alloy. For electrolytes
with pH values of 4 to 6, the experimental results show that the pH of the leachate quickly
fell below 2 within 0.5 h of the reaction (as shown in Figure 3g). This severe drop in pH
led to increased protonation on the surface of the cathode, reducing electrostatic attraction,
thereby inhibiting the reduction of the Ni2+ and Co2+ . Additionally, the presence of Mn2+
acted as an electron donor, which was found to be a crucial factor contributing to the Ni-Co
Batteries 2024, 10, x FOR PEER REVIEW 7 of 11

Batteries 2024, 10, 337 7 of 11

acted as an electron donor, which was found to be a crucial factor contributing to the Ni-
Co alloy’s electrodeposition. By supplementing the2+Mn2+ ions in the solution, the Mn2+ was
alloy’s electrodeposition. By supplementing the Mn ions in the solution, the Mn2+ was
oxidized at the anode, which further promoted the cathodic electrodeposition. With this
oxidized at the anode, which further promoted the cathodic electrodeposition. With this
proposed
proposed method,
method,the
thepurity of the
purity of theelectrodeposited
electrodepositedMnOMnO 2 at the anode reached 99.52%,
2 at the anode reached 99.52%,
andand
that of of
that the Ni-Co
the Ni-Coalloy
alloy at the cathode
at the cathodereached
reached 99.80%
99.80% [47].[47].

Figure 3. (a)
Figure Schematic
3. (a) diagramofof
Schematic diagram electrodeposition
electrodeposition of Ni-Co
of Ni-Co alloys; alloys; the concentration
the concentration of Ni2+ (b)
of Ni2+ (b) and
andCo
Co 2+
2+ (c)(c)atat reduction
reduction potentials
potentials (−0.7(−0.7 to V)
to −1.5 −1.5 V) under
under pH = 3,pHand=the3, concentration
and the concentration of Ni2+ (d)
of Ni2+ (d) and
andCo
Co (e)atatpH
2+2+(e) pH2–6
2–6 under
under −1.3
−1.3 V;zeta
V; (f) (f) zeta potential
potential of carbon
of carbon cloth andcloth andcloth/Ni-Co
carbon carbon cloth/Ni-Co
under pH under
pH values
valuesofof1–6; 1–6; and
and (g)(g) changes
changes in electrolyte
in electrolyte pH aspH
the as the reaction
reaction proceeded proceeded
[47]. [47].

3.4.3.4.
Ni Ni
andand
CoCo Separationvia
Separation via Electrodeposition
Electrodeposition
As previously mentioned, it is challenging to separate Ni2+ and Co2+ via electrode-
As previously mentioned, it is challenging to separate Ni2+ and Co2+ via electrodepo-
position because of their similar reduction potentials. Over the past few years, many
sition becausehave
researchers of their similar reduction
been investigating methodspotentials.
to achieveOver
Ni/Cothe past fewInyears,
separation. 2021, Kimmany re-
searchers have been
et al. proposed investigating
a strategy to achievemethods to achieve
nickel and Ni/Co separation.
cobalt separation In 2021, Kim et
via electrodeposition
al. through
proposed the acombined
strategyfunction
to achieve nickel and
of interfacial cobalt and
engineering separation via
electrolyte electrodeposition
control. In this
work, the
through the researchers
combined employed
function 10 of M hydrochloric
interfacial acid as a leaching
engineering agent for control.
and electrolyte the NMCIn this
cathode
work, and manipulated
the researchers the pH10
employed value of the collectedacid
M hydrochloric metalasleachate solution
a leaching by for
agent adding
the NMC
LiOH. LiCl was added to obtain highly concentrated chloride as the electrolyte, which
cathode and manipulated the pH value of the collected metal leachate solution by adding
helped the formation of negatively charged CoCl4 2− and positively charged [Ni(H2 O)4 Cl]+ .
LiOH. LiCl was added to obtain highly concentrated chloride as the electrolyte, which
With the formed nickel and cobalt complex, the LSV curves of the cobalt and nickel showed
helped the formation
significant differences,of with
negatively
reductioncharged CoCl
potentials
2− and positively charged [Ni(H2O)4Cl]+.
of 4−0.68 V vs. Ag/AgCl and −0.59 V vs.
With the formed nickel and cobalt complex, the
Ag/AgCl, respectively (shown in Figure 4a–c). The researchers LSV curves of the
compared thecobalt and nickel
electrodepo-
showed
sition significant
with differentdifferences, with reduction
chloride concentrations (0.1 Mpotentials ofM−0.68
Li2 SO4 , 0.1 LiCl,Vand
vs.10Ag/AgCl
M LiCl) andand −0.59
theAg/AgCl,
V vs. results showed that the anomalous
respectively (shown in deposition of Co/Ni
Figure 4a–c). The was highest in the
researchers 10 M LiClthe
compared at elec-
− 0.75 V vs. Ag/AgCl (shown in Figure 4d–f). Subsequently, as shown
trodeposition with different chloride concentrations (0.1 M Li2SO4, 0.1 M LiCl, and 10 Min Figure 4g, with
the controlled PDAMA polymer loading on the Cu substrate, the electrode potential could
LiCl) and the results showed that the anomalous deposition of Co/Ni was highest in the
be fine-tuned, thereby directly separating the opposite charged nickel and cobalt complexes.
10 M LiCl at −0.75 V vs. Ag/AgCl (shown in Figure 4d–f). Subsequently, as shown in Fig-
The final purities of the cobalt and nickel were 96.4 ± 3.1% and 94.1 ± 2.3% [20].
ure 4g, with the controlled PDAMA polymer loading on the Cu substrate, the electrode
potential could be fine-tuned, thereby directly separating the opposite charged nickel and
cobalt complexes. The final purities of the cobalt and nickel were 96.4 ± 3.1% and 94.1 ±
2.3% [20].
 Batteries2024,
Batteries 2024,10,
10,337
x FOR PEER REVIEW 88 of
of 11
11

Figure4.4.(a)
Figure (a)Linear
Linearsweep
sweepvoltammograms
voltammogramsofofa10 a10mM
mMCoCo orNi
2+2+or Ni2+2+ in
in (a)
(a)0.1
0.1MMLiLi2 SO
2SO4,, (b)
4
(b)0.1
0.1M
M
LiCl,and
LiCl, and(c)(c)10
10MMLiCl;
LiCl;electrodeposition
electrodepositionofofCo/Ni
Co/Ni atomic
atomic ratios
ratios with
with the the electrolyte
electrolyte of
of(d)(d)0.1
0.1M
M
Li SO4,, (e)
Li2SO (e) 0.1
0.1 M
M LiCl
LiCl and
and (f)
(f) 10
10 M
M LiCl;
LiCl; and
and (g)
(g) schematic
schematicdiagram
diagramof ofselective
selectivedeposition
depositionof ofNi
Niand
and
2 4
Co by synergistic electrolyte and interfacial control [20].
Co by synergistic electrolyte and interfacial control [20].

4.4.Conclusions
Conclusionsand andPerspectives
Perspectives
Thismini-review
This mini-review outlined the recent recent progress
progressin inelectrochemical
electrochemicaltechniques
techniquesfor recy-
for re-
cling lithium-ion
cycling lithium-ion batteries. The
batteries. Thediscussion
discussion was
wasdivided
divided into two
into main
two maindirections:
directions:electro-
elec-
chemical leaching
trochemical leaching forfor
dissolving
dissolvingcathode
cathodematerials andand
materials electrodeposition
electrodeposition for metal pre-
for metal
cipitation. Effective
precipitation. processes
Effective havehave
processes beenbeen
developed for co-leaching
developed lithium,
for co-leaching nickel,nickel,
lithium, cobalt,
and manganese
cobalt, from cathode
and manganese materials,
from cathode as well as
materials, asfor theas
well selective
for the leaching
selectiveofleaching
lithium.of In
lithium.
terms ofInelectrodeposition,
terms of electrodeposition, efficient have
efficient methods methods
beenhave been established
established for recover-
for recovering cobalt
ing
andcobalt and cobalt–nickel
cobalt–nickel alloy, electrodepositing
alloy, electrodepositing lithium forlithium
cathode forrelithiation,
cathode relithiation,
and nickelandand
nickel
cobaltand cobalt separation.
separation. SignificantSignificant
progress has progress
been has
madebeeninmade in developing
developing electro-
electrochemical
chemical
methodsmethods
tailored tailored for lithium-ion
for lithium-ion battery battery recycling.
recycling. However, However, these processes
these processes are stillare
in
still
the in the early
early stages,stages,
with with
manymany challenges
challenges remaining.
remaining. Further
Further research
research andand exploration
exploration are
are necessary,
necessary, as as outlined
outlined below:
below:
(1)
(1) The
The reaction
reactionmechanisms
mechanisms behind
behindelectrochemical
electrochemical leaching and electrodeposition
leaching need
and electrodeposition
further clarification. Advanced characterization techniques, such as
need further clarification. Advanced characterization techniques, such as neutron neutron scattering
and in situand
scattering X-rayin analysis,
situ X-rayshould be used
analysis, should forbe
more
usedin-depth
for moreinvestigation.
in-depth investigation.
(2)
(2) There is still a lack of efficient methods for selectively leaching
There is still a lack of efficient methods for selectively leaching or
or depositing
depositing metals.
metals.
It remains challenging to separate nickel and cobalt via electrochemical
It remains challenging to separate nickel and cobalt via electrochemical methods methodsbe-
because
cause ofof their
their similar
similar chemical
chemical reactivities.
reactivities.
(3)
(3) The
Theprocess
processrequires
requiresfine-tuning
fine-tuningwithwithprecise control
precise over
control purities.
over Maintaining
purities. purity
Maintaining pu-
levels remains a significant hurdle in both the electrochemical leaching
rity levels remains a significant hurdle in both the electrochemical leaching process process and
electrodeposition.
and electrodeposition.
(4)
(4) Further
Furtheradvanced
advancedresearch
researchisisneeded
needed forfor
investigating
investigating and controlling
and thethe
controlling morphology
morphol-
of the obtained metals through electrodeposition.
ogy of the obtained metals through electrodeposition.
(5)
(5) There
There isis aacrucial
crucialneed
needfor
forefficient,
efficient,customized
customizedelectrochemical
electrochemicalmethods
methodstailored
tailoredto
to
various battery chemistries. A comprehensive investigation is required to elucidate
various battery chemistries. A comprehensive investigation is required to elucidate
Batteries 2024, 10, 337 9 of 11

the mechanism behind relithiation through lithium electrodeposition, and to develop

cathodes that exhibit the desired electrochemical performance.
(6) Electrochemical methods for recycling lithium-ion batteries primarily target cathode
materials. However, the pretreatment process involves complexities, such as battery
dismantling and electrode delamination. Additional research is required to develop
efficient pretreatment methods.
(7) The current electrochemical recycling process is limited to the laboratory scale. Ex-
tensive further research is necessary to upscale the process for commercialization.
Rigorous testing and validation procedures are essential to showcase the scalability,
reliability, cost-effectiveness, and sustainability of the technology.
In summary, electrochemical methods show promise for recycling lithium-ion batteries.
The ongoing research and development in this field offers great potential for advancing
battery technology while promoting sustainability.

Author Contributions: Conceptualization, L.Y. and Y.B.; methodology, L.Y.; validation, L.Y., Y.B. and
I.B.; formal analysis, L.Y.; investigation, L.Y. and Y.B.; data curation, L.Y.; writing—original draft
preparation, L.Y.; writing—review and editing, L.Y., Y.B. and I.B.; visualization, L.Y.; supervision,
Y.B., I.B.; project administration, I.B.; funding acquisition, I.B. All authors have read and agreed to the
published version of the manuscript.
Funding: This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the US
Department of Energy under contract DE-AC05-00OR22725, was sponsored by the Office of Energy
Efficiency and the Renewable Energy Vehicle Technologies Office.
Data Availability Statement: No new data were created or analyzed in this study. Data sharing is
not applicable to this article.
Acknowledgments: This research at Oak Ridge National Laboratory, managed by UT Battelle,
LLC, for the US Department of Energy under contract DE-AC05-00OR22725, was sponsored by
the Office of Energy Efficiency and the Renewable Energy Vehicle Technologies Office (Program
managers: Jake Herb and Tina Chen). This manuscript was authored by UT-Battelle, LLC, under
contract DE-AC05-00OR22725 from the US Department of Energy (DOE). The publisher, by accepting
the article for publication, acknowledges that the US government retains a nonexclusive, paid-
up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript,
or allow others to do so, for US government purposes. The DOE will provide public access to
these results of federally sponsored research in accordance with the DOE Public Access Plan (http:
//energy.gov/downloads/doe-public-access-plan (accessed on 25 August 2024)).
Conflicts of Interest: The authors declare no conflict of interest.

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