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TECHNICAL ARTICLE
Usage of Recycled Alkali Waste for Delamination of Cathode
Electrodes: Systematic Selection and Optimization
of Hydrometallurgical Approach
TUSHAR MASKE
1
and RAVI METHEKAR
1,2
1.—Department of Chemical Engineering, Visvesvaraya National Institute of Technology, South
Ambazari Road, Nagpur 440010, India. 2.–e-mail: ravimethekar@che.vnit.ac.in
Numerous studies on the delamination process of cathode electrodes from
spent lithium-ion batteries have been conducted. Unfortunately, the system-
atic selection of economically viable and environmentally friendly delamina-
tion process has hardly been investigated. In this study, most of the
hydrometallurgical processes were investigated based on the delamination
efficiency and cost of solvent, and four were chosen: solvent dissolution, alkali
dissolution, deep eutectic solvent, and ethylene glycol. Chosen processes were
performed in the laboratory and compared using four important parameters:
delamination efficiency, economic assessment, environmental assessment,
and overall process time. This comparison indicates that the alkali dissolution
process (ADP) is superior to the other processes. However, it is still unclear
how the process variables will affect the delamination efficiency in ADP. To
address this issue, we have investigated the impact of the reaction variables
using optimization. Furthermore, it was discovered that the delamination can
be carried out using alkali waste solution, and it has the same ability to
selectively react with aluminum foil, leaving behind the delaminated cathode
material for three cycles without changing the metal (Li, Co, Mn, Ni, etc.)
content. As a result, an economically viable and environmentally friendly
delamination process has been established.
INTRODUCTION
Nowadays, lithium-ion batteries (LIBs) have be-
come the major power source for portable and hea-
vy-duty energy applications. An increasing use of
LIBs in current and future energy applications will
generate a huge amount of spent LIBs.
1,2
These
batteries are a rich secondary source of metals such
as lithium (Li), nickel (Ni), manganese (Mn), cobalt
(Co), etc.
3–5
Apart from this, it also contains toxic
electrolytes such as lithium hexafluorophosphate
(LiPF
6
), lithium perchlorate (LiClO
4
), lithium tri-
fluoromethanesulfonate (LiCF
3
SO
3
), etc.
6
Since
LIBs contain valuable metals and toxic electrolytes,
proper recycling methods are required to recover
valuable metals and minimize environmental haz-
ards.
7,8
A lithium-ion battery consists of a cathode, an
anode, an organic electrolyte, and a separator. Re-
search on battery recycling has mostly been focused
on finding ways to recover the cathode electrode
materials, since this is the most valuable part of the
battery. In LIBs, various cathode materials such as
LiCoO
2
(LCO), LiMn
2
O
4
(LMO), LiNiO
2
(LNO), and
their mixed oxides are used.
9,10
Polyvinylidene flu-
oride binder (PVDF) is used to bind the cathode
material onto the current collector (aluminum
foil).
11
The rapid and effective delamination of un-
treated cathode material (UCM) from the cathode
electrode is a highly challenging operation due to
(Received February 14, 2023; accepted May 19, 2023)
JOM
https://doi.org/10.1007/s11837-023-05916-1
©2023 The Minerals, Metals & Materials Society
the strong adhesion bond between PVDF and alu-
minum foil.
12,13
Traditional metallurgical methods, such as
pyrometallurgy and hydrometallurgy, are often
used for the delamination of UCM from the cathode
electrode.
14
The pyrometallurgy process, which is
based on the chemical and physical properties of
materials for UCM recovery and is highly operable,
can be implemented at the pilot-plant scale.
15
However, it involves high temperature, which lib-
erates hazardous gases in the environment.
16–18
The hydrometallurgical method is another promis-
ing approach for delaminating UCM from cathode
electrodes, which involves the use of alkaline solu-
tions or inorganic/organic acids.
15
This method
outperforms the pyrometallurgical method in terms
of product purity and extraction efficiency while
requiring less energy, cost and time.
19–22
The list of
solvents studied in the literature for the delamina-
tion of UCM using the hydrometallurgical approach
is provided in Table S-i (Supplementary informa-
tion). Unfortunately, the excessive use of these sol-
vents has a negative impact on both the
environment and the economic aspects of the pro-
cess. Although several solvents have been reported
in the literature for delamination, to the authors’
knowledge, a comparative study of UCM delami-
nation has not been conducted, despite its impor-
tance from an environmental and economic
perspective.
In this article, an investigation of an economically
viable and environmentally friendly delamination
process is explored. The selection of four processes
from 15 different hydrometallurgical processes was
explored based on delamination efficiencies (given
in the literature) and economic assessment. Solvent
dissolution, alkali dissolution, deep eutectic solvent,
and ethylene glycol processes were then selected. A
comparison was made between the four selected
hydrometallurgical delamination processes based
on delamination efficiency, economic assessment,
environmental assessment, and overall process
time. These parameters were estimated based on
laboratory experiments and “GaBi” educational
software (ver. 9.2.1.68). After the systematic inves-
tigation of the four important parameters listed
above, it is found that the alkali dissolution process
(ADP) is the best among the other selected delami-
nation processes. The parametric optimization of
the ADP is carried out using Box-Behnken design
(BBD) and response surface methodology (RSM).
Additionally, the delamination of the UCM was
studied using waste alkali solution (generated after
the delamination of the UCM from pristine alkali
solution) to reduce the process economics. Material
characteristics like crystallinity (XRD), morphology
(SEM), and metal content (ICP-OES) were studied
for delaminated samples using both alkali and al-
kali waste solution. After careful investigation, it
was determined that the optimized ADP and reuse
alkali waste solution is an economically viable and
environmentally benign delamination process that
can be carried out at a large scale.
EXPERIMENTAL
Preliminary Selection of Delamination
Processes
An extensive literature survey reveals that
approximately fifteen hydrometallurgical processes
are available for the delamination of UCM from the
cathode electrode. The list of these processes, along
with solvents, is given in Table S-i. The cost of sol-
vents, delamination efficiency, and availability of
solvents served as selection factors for these pro-
cesses. Four of these 15 processes were finally cho-
sen for further investigation: solvent dissolution
process (SDP), alkali dissolution process (ADP),
deep eutectic solvent (DES), and ethylene glycol
(EG) process. The corresponding used solvents are
N,methyl-2-pyrrolidone (NMP), sodium hydroxide
(NaOH), choline chloride:glycerol (C
5
H
14
ClNO:
C
3
H
8
O
3
), and ethylene glycol (EG), respectively.
Materials and Reagents
Spent LG mobile phone LIBs were procured from
the street market in Nagpur, Maharashtra, India.
All the chemicals including sodium chloride (NaCl),
N-methyl-2-pyrrolidone (C
5
H
9
NO), sodium hydrox-
ide (NaOH), choline chloride (C
5
H
14
ClNO), glycerol
(C
3
H
8
O
3
), and ethylene glycol (C
2
H
6
O
2
) were pur-
chased from Sigma-Aldrich, Mumbai, India. All the
solutions were prepared in deionized water (Milli-
pore, Milli-Q).
Methods
The selected four different solvent processes were
studied, and data were collected for further analy-
sis.
Discharging and Dismantling of Spent
Batteries
In any LIB recycling process, to avoid short-cir-
cuiting and to minimize the possibility of a transient
spark during dismantling due to the presence of
unused electrolytes, batteries are discharged using
a 5% (wt/v) NaCl solution for 3 h. Afterwards, the
discharged batteries were manually dismantled
using pliers and cutters to remove the positive and
negative electrodes and separator with proper
safety precautions. The positive electrode scraps
were cut into small pieces using scissors and used
further for the selected hydrometallurgical
approaches.
Delamination Using Chosen Processes
The solid-to-liquid (S/L) ratio was set at C g/ml for
all of the chosen processes during the delamination
of the UCM. For every 10 g of the cathode electrode,
100 ml of solvent (B) was added to the beaker. Then,
Maske and Methekar
that beaker was placed in the respective equipment
(A), depending on the requirements of the process, at
D°C for E min. The resulting reaction mixture was
passed through a circular stainless-steel filter after a
predetermined period of time, and the separated
aluminum foil was washed with deionized water
(except in the alkali dissolution process). The alu-
minum-deprived slurry of cathode material was then
centrifuged [Remi Elektrotechnik Limited, Model
No. R-24] to separate the supernatant and wet UCM.
After centrifugation, UCM was dried at 200 °Cina
vacuum oven [Bio-Technics India, model no. BTI-52]
for 60 min. After drying, the delaminated UCM was
weighed to calculate the delamination efficiency (%).
The schematic of the delamination process and val-
ues of the operating conditions (A, B, C, D, and E) for
all the chosen processes are shown in Fig. 1and
Table I, respectively.
Delamination Efficiency Formula
The delamination process needs to be very effi-
cient to make the overall recycling process eco-
nomically feasible. The delamination efficiency of
UCM was calculated by Eq. 1:
DE;gr¼a2
a1a3
100%(1)
where a
1
is the initial weight of the positive elec-
trode, a
2
is the final weight of recovered cathode
material, and a
3
is the weight of aluminum foils
present in the cathode electrode. The value of a
3
for
SDP, DES, and EG was determined by measuring
the weight of cleaned aluminum foil since the alu-
minum foil neither dissolves nor reacts with the
solvents used in the aforementioned processes. For
ADP, the value of a
3
was taken as the weight of
cleaned aluminum foil using the SDP for two rea-
sons, the first of which was the same initial weights
of cathode electrode that were subjected to the
delamination process. The second and more impor-
tant reason was the dissolution of aluminum foils in
the alkali solution during the ADP.
Life Cycle Assessment (LCA)
LCA is extensively used for the estimation of envi-
ronmental impacts incurred by the material and
energy consumption in the system. Four chosen process
plans were modeled and simulated using GaBi educa-
tional software (ver. 9.2.1.68). According to the Inter-
national Organization for Standardization (ISO) 14040
framework, LCA includes the following major steps:
goal and scope of the study, life cycle in ventory analysis,
impact assessment methods, and interpretations.
25
Goal and Scope
The goal of this study was to quantify the envi-
ronmental impact associated with the chosen
delamination processes. The global warming
potential (GWP), along with other midpoint envi-
ronmental indicators such as acidification potential
(AP), human toxicity potential (HTP), eutrophica-
tion potential (EP), and ozone depletion potential
(ODP), is quantified. The estimation of all of these
environmental indicators would be beneficial in
determining whether the delamination of the UCM
process is environmentally sustainable or not. Here,
cradle-to-gate boundary condition was imple-
mented, which monitors emissions associated with
the production of raw materials as well as the
extraction of finished products. The following
assumptions are made for modelling purposes:
1. The boundary of the LCA was assumed for these
processes as follows:
(a) For SDP, it starts with ultrasonication and ends
with UCM drying.
(b) For DES, it starts with DES preparation and
ends with UCM drying.
(c) For ADP, it starts with the preparation of a
NaOH solution and ends with UCM drying.
(d) For EG, it starts with electrolyte washing and
ends with UCM drying.
2. The emissions associated with the transporta-
tion, discharge, and dismantling of spent LIBs
are not included in this research since this step is
similar in all the processes.
3. The geographical scope of this research is con-
strained to India, and as a result, the Indian
dataset is being used to replicate background
operations, including electricity generation.
4. Water discharge was supposed to end with
emissions to groundwater.
Table I. Operating conditions for all chosen solvents for the delamination process
Sample no. Process
Operating conditions
Types of
equipment (A) Solvents (B)
Solid-to-liquid
ratio (C) in g/ml
Temperature
(D) in °C
Time (E)
in min
1. Solvent dissolution
23
Ultrasonication NMP 1:10 60 60
2. Alkali dissolution
24
Not required NaOH 1:10 27 30
3. Deep eutectic solvent
13
Oil-bath device CH-Cl:GLY 1:10 190 15
4. Ethylene glycol
22
Oil-bath device EG 1:10 160 15
CH-Cl:GLY choline chloride and glycerol (2:1).
Usage of Recycled Alkali Waste for Delamination of Cathode Electrodes:
Systematic Selection and Optimization of Hydrometallurgical Approach
Life Cycle Inventory Analysis (LCIA)
LCIA is the study of energy and material flows
associated with a specific process as well as the
associated environmental impact for the selected
processes. LCIA was performed for all the chosen
delamination processes. In any LCA, the functional
unit plays a very important role. A functional unit
can be used as a reference point for comparing and
evaluating the environmental impact of a process.
In this study, the delamination of 10 g of cathode
electrode is used as a functional unit. The quantity
of electricity used (kWh) throughout the procedure
was computed based on the wattage rating and
duration of all the equipment involved in the
delamination processes. All the processes are mod-
eled using the database listed in Table S-ii. Energy
and mass flows are depicted in Table S-iii for chosen
processes, the input and output streams, which are
also referred to as the life cycle inventories.
Impact Assessment Method
The following are a few techniques used for
environmental impact assessment: CML 2001
(Center of Environmental Science),
8
TRACI (Tool
for the Reduction and Assessment of Chemical and
Other Environmental Impacts),
26
and ReCiPe (as it
provides a “recipe” to calculate LCIA).
27
These
methods represent the environmental footprint as
endpoint and mid-point indicators. Mid-point indi-
cators such as GWP, AP, HTP, EP, and ODP are
directly affected by the system emission. Endpoint
indicators, such as damage to human health, dam-
age to the natural environment, and damage to a
natural resource, are calculated based on the mid-
point indicator emission. To assess the environ-
mental impact of chosen processes, the traditional
LCIA method CML 2001 was used.
Interpretations
Based on the inventory datasheet and the acces-
sibility of the GaBi educational software database,
the five midpoint environmental indicators, viz.,
GWP in kg CO
2
equivalent, AP in kg SO
2
equiva-
lent, HTP in kg 1,4-dichlorobenzene (DCB) equiva-
lent, EP in kg phosphate equivalent, and ODP in kg
R11 equivalent, are computed for chosen processes.
Economic Assessment
The economic assessment for delaminating 10 g of
cathode electrode was estimated using laboratory-
based data (Table S-iii). The focus of our analysis is
the assessment of the overall cost required to re-
cover delaminated UCM from selected processes.
The economic assessment at the laboratory scale
was done by comparing the cost of consumables
(chemicals and electricity) required during the
delamination of UCM from selected processes. The
chemical cost was supplied by the Sigma-Aldrich.
Similarly, the cost of energy (electricity) was as-
sessed based on the power ratings of the specific
laboratory equipment utilized in the experiment.
The average electricity rate in India, as utilized in
this research, was 5.2 `per kWh (0.070 $/kWh),
which was provided by the Maharashtra state
electricity board (MSEB). The cost of chemicals and
electricity, which might differ from one region to the
other, is included in these estimates.
Process Time
The amount of time that elapses between the
point at which a raw material enters (cathode elec-
trode pieces) the process and the point at which a
product departs (UCM) from the process is referred
to as “process time.” The amount of overall process
time required for all the chosen processes for 10 g of
cathode electrode was calculated as seen in Table I
and “Delamination using chosen processes” section.
Fig. 1. Schematic diagram for all the chosen processes.
Maske and Methekar
Characterizations
The phase identification of the samples before and
after delamination was carried out using X-ray
diffractometry (XRD, X-Pert Pro, PANalytical) with
Cu Kαradiation (γ=1.5406 A
˚) from 10°to 80°(2θ).
To study the thermal stability of the recovered
samples, thermal gravimetric analysis (TGA-EX-
STAR 6300) was carried out using a scan rate of 10 °
C/min and a temperature range of 800 °C under air
atmosphere. The surface morphology and elemental
content of the samples before and after delamina-
tion were analyzed by scanning electron microscopy
with energy-dispersive analysis of X-rays (SEM-
EDAX, JEOL 6380A) at an accelerating voltage of
15 kV at various magnifications. To determine the
metal contents of spent and delaminated cathode
materials, inductively coupled plasma-optical emis-
sion spectroscopy was used (ICP-OES, Perkin
Elmer, The Netherlands, Optima 7000 DV).
RESULTS AND DISCUSSIONS
Delamination Efficiencies of Selected
Hydrometallurgical Processes
The experiments were conducted in triplicate for
all of the chosen delamination processes, and the
mean delamination efficiencies are tabulated in
Table II, which indicates that the delamination
efficiency of UCM using ADP is the highest
(100%), followed by SDP, DES, and EG processes.
The ADP exploits the high affinity of NaOH towards
aluminum and the inertness of NaOH towards UCM
to selectively dissolve the aluminum foil into the
alkali solution, which results in the highest recov-
ery of UCM.
Life Cycle Assessment (LCA)
Figure 2a depicts the GWP of chosen processes
(SDP, DES, ADP, and EG) for the delamination of
10 g of the cathode electrode; the values are 1.41,
0.872, 0.532, and 1.08 kg CO
2
equivalent, respec-
tively. Also, Fig. 2b-e shows that the effects of other
environmental indicators such as AP, HTP, EP, and
ODP were found to be significantly higher in the
SDP, DES, and EG processes compared to ADP.
Hence, it can be concluded that the ADP is more
environmentally friendly than the chosen processes.
In the ADP, preparation of a 5 M NaOH solution,
centrifugation, and drying steps produce approxi-
mately 4.51, 34.59, and 61% of GWP, respectively.
Economic Assessment
An economic impact assessment of the chosen
processes was conducted and tabulated in Table II.
Table II demonstrates that ADP is less expensive
than all of the other chosen processes. It is con-
cluded that the ADP has a lower overall process cost
because of its lower consumption of electricity and
NaOH.
Process Time
From Table II, it is concluded that the overall
process time for the SDP is the highest among the
other chosen processes because of the additional
time required in the centrifugation step. The cavi-
tation effect in the ultrasonication step is the main
cause as it makes the UCM highly dispersed in
NMP, making the separation of UCM from the sol-
vent more difficult. Comparatively, DES and EG
need less time than ADP because PVDF easily melts
at a higher temperature in an oil-bath device for
DES and EG processes.
Selection of an Environmentally Benign
and Economically Viable Process
The selection of an environmentally benign and
economically viable process is carried out based on
four important parameters such as delamination
efficiency, environmental assessment, economic
assessment, and overall process time, as tabulated
in Table III. Based on the data in Table III, it can be
seen that, except for processing time, the ADP has
Table II. Delamination efficiency, economic assessment, and overall process time assessment for selected
hydrometallurgical processes
Processes SDP DES ADP EG
Delamination efficiency (%) 93.40±1.54 91.90±1.20 99.72 ±0.33 85.23 ±6.86
Economic assessment in (`and $)
Solvent cost 885.6 (11.14 $) 1115.34 (14.03 $) 233.20 (2.92 $) 266.90 (3.36 $)
Electricity cost 4.94 (0.062 $) 5.20 (0.065 $) 2.44 (0.031 $) 4.55 (0.057 $)
Overall process cost 890.54 (11.20 $) 1120.54 (14.09 $) 235.64 (2.96 $) 271.45 (3.41 $)
Process time (minutes)
Reaction system 60 25 30 15
Centrifuge 30 10 10 10
Drying 60 60 60 60
Overall process time 150 95 100 85
*(1 INR= 0.013 USD) as of 9 October 2022.
Usage of Recycled Alkali Waste for Delamination of Cathode Electrodes:
Systematic Selection and Optimization of Hydrometallurgical Approach
1.41
0.532
0.872
1.08
SDP ADP DES EG
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
GWP (kg CO
2
equivalent)
Processes
(a)
0.016
0.006
0.01 0.01
SDP ADP DES EG
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
AP (kg SO
2
equivalent)
Processes
(b)
0.441
0.159
0.272
0.208
SDP ADP DES EG
0.0
0.1
0.2
0.3
0.4
0.5
HTP (kg DCB equivalent)
Processes
(c)
7.58E-4
2.81E-4
4.68E-4 4.9E-4
SDP ADP DES EG
0.0000
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.0007
0.0008
EP (kg Phosphate equivalent)
Processes
(d)
4.23E-15
2.23E-15
2.62E-15
3.42E-15
SDP ADP DES EG
0.00E+00
1.00E-15
2.00E-15
3.00E-15
4.00E-15
5.00E-15
ODP (kg R11 equivalent)
Processes
(e)
Fig. 2. Environmental indicators (GWP, AP, HTP, EP, and ODP) for selected hydrometallurgical processes; SDP, ADP, DES, and EG.
Maske and Methekar
good agreement with the aforementioned parame-
ters. As a result, we can say that the ADP is both
environmentally friendly and economically viable.
It has been reported in the literature that the
time needed for delamination of UCM decreased
dramatically as the concentration of NaOH was in-
creased (Table IV). Furthermore, it has been
demonstrated that stirring the contents can speed
up the delamination process.
28,29
Despite the find-
ings, it is still unclear how the process variables,
such as NaOH concentration, pulp density (S/L ra-
tio), stirring speed, and reaction time, affect the
outcomes. To address this issue, we have investi-
gated the effect of these factors through optimiza-
tion.
Optimization of ADP
The parametric optimization of the ADP is carried
out using BBD from RSM. Four independent vari-
ables and one dependent variable have been chosen
for the optimization study. A single-factor experi-
ment was used to determine the optimal level of
each parameter, and then response surface
methodology (RSM) experiments were prepared.
Table S-iv shows the three levels and four factors
that were chosen to optimize the process to get the
maximum delamination efficiency of UCM. Based
on the inputs (from Table S-iv), the Design Expert
software (version 13.0) creates a design of experi-
ments with 29 trials and 5 replicates (central
points). The outputs of each experiment for the
delamination efficiency of UCM were examined
using analysis of variance (ANOVA), and the sim-
plified regression equation was then developed. The
design expert software created the 3D surface plots,
allowing the study of these factor’s influence on the
output.
13
Table S-v shows that the maximum
delamination efficiency of UCM was achieved in the
20th experimental run with the NaOH concentra-
tion of 2 M, a solid-to-liquid ratio (S/L) of 1/10 g/ml,
a stirring speed of 700 rpm, and a reaction time of
10 min. A second-order regression equation was
fitted to the experimental data and is given as:
Y¼67:85 þ26:8A þ4:08B þ9:51C þ8:59D 0:645AB þ2:24AC þ1:75AD
0:67BC þ1:91BD þ0:81CD 9:67A23:72B21:79C2
5:32D2
(2)
Table III. Comparative study of processes based on delaminating 10 g of the cathode electrode
Process
Delamination
efficiency (%)
Environmental
assessment (GWP)
Economic
assessment (in `and $)
Overall process
time (min)
SDP 93.40±1.54 1.41 890.54 (11.20 $) 150
DES 91.90±1.20 0.87 1120.0 (14.09 $) 95
ADP 99.72±0.33 0.53 235.64 (2.96 $) 100
EG 85.23±6.86 1.08 271.45 (3.41 $) 85
Table IV. Literature review for ADP
Sample no.
Molar
ratio M (wt.%)
S/L
ratio (g/ml)
Stirring
speed (rpm)
Reaction
time (min) References
Delamination
efficiency (%)
1 2.5 M (10%) 1/10 – 300 30 –
2 2.5 M (10%) 1/10 – 300 31 –
3 1.25 M (5%) 1/10 – 240 32 –
4 3.75 M (15%) – 500 180 33 –
5 2 M (8%) – – 60 28 –
6 5 M (20%) 1/10 – 30 24 100
7 1.25 M (5%) – – – 34 –
8 2 M (8%) – – 120 29 –
9 3 M (12%) – – – 35 –
Usage of Recycled Alkali Waste for Delamination of Cathode Electrodes:
Systematic Selection and Optimization of Hydrometallurgical Approach
Fig. 3. Three-dimensional surface plots for the delamination efficiency of UCM by varying two factors at a time.
Maske and Methekar
where Yis the delamination efficiency of UCM (%),
Ais the molar concentration of NaOH, Bis the solid-
to-liquid ratio in g/ml, Cis the stirring speed in rpm,
and Dis the reaction time in minutes. The analysis
of variance (ANOVA) function was used to do a more
statistical assessment of the data. The coefficient of
determination (R
2
) values for the second-order
polynomial Eq. 2obtained from an ANOVA are
0.9895, which suggests that the model is able to
capture the variation in the data satisfactorily.
According to the pvalues (the model is significant
when pvalues are<0.05) and Fvalues (higher val-
ues represent the order of impacts on the dependent
variable) of linear variables, all of the independent
parameters have a significant impact on the
delamination efficiency of UCM in the following
order: concentration of NaOH (A), stirring speed
(C), reaction time (D), and solid-to-liquid ratio (B).
The two-way interaction term that has the most
significant impact on the delamination efficiency of
UCM is the concentration of NaOH and stirring
speed (A9C). (A
2
), (B
2
), (C
2
), and (D
2
) are the
square interaction parameters, as shown in Table S-
vi. The square interaction term has a significant
impact, and the order of impact is the concentration
of NaOH (A
2
), reaction time (D
2
), and solid-to-liquid
ratio (B
2
).
The impact of the operating parameters and their
interactions on the delamination efficiency of the
UCM is shown graphically in Fig. 3a-f. The follow-
ing conclusions can be made based on the response
surface plots:
●As NaOH concentration rises from 0.5 to 2 M
(Fig. 3a-c and Table S-v (runs 19 and 20)), UCM
delamination efficiency increases by 259.48%.
This can be attributed to the presence of higher
amounts of hydroxyl ions in the solution.
31
●The delamination efficiency of UCM increases by
37.44% [Fig. 3b, d, and f and Table S-v (runs 18
and 20)] when the stirring speed increases from
300 rpm to 700 rpm. This happens because of an
improved mass transfer rate in the solution.
36
●Additionally, the increase in the S/L ratio from
1/5 to 1/10 g/ml was observed to rapidly enhance
the delamination efficiency, as seen in Fig. 3(a, d,
and e). Also, when the S/L ratio was increased
further to 1/15 g/ml, the delamination efficiency
increased slightly. However, the economic cost
increased, suggesting that the optimal S/L ratio
was 1/10 g/ml.
●The delamination efficiency of UCM increased
when the reaction time was increased from 5 to
10 min. However, when the reaction time was
further increased to 15 min, the delamination
efficiency did not remarkably increase, as shown
in Fig. 3(c and e–f). As a result, the optimal
required time for delamination was determined to
be 10 min.
Reusability of Alkali Waste
To reduce the cost of the solvent used for the
delamination process, we tried to reuse the waste
alkali solution for further delamination of the
cathode electrode. During the delamination process,
the following reaction takes place:
31,37
2Al sðÞþ6H2Oþ2NaOH aqðÞ
þUCM sðÞ
!2NaAl OHðÞ
4aqðÞ
þ3H2gðÞ
þUCM sðÞ
(3)
In reaction 3, aluminum foil and NaOH are reacted,
and sodium meta-aluminate is formed, leaving be-
hind unreacted UCM. In our study, a single batch
of0.2010±0.0035 g of aluminum was present in
the cathode electrode. So, stoichiometrically, it
needs1.08 g of aluminum for its complete conver-
sion to sodium meta-aluminate as per reaction 3.
Since we are using a 2 M NaOH solution for the
delamination of cathode material, we can reuse it
for multiple cycles. From Table V, the delamination
efficiency after three cycles of recycling alkali waste
was around 99.61±0.24%. After using the same al-
kali solution for the fourth time, the mass of the
delaminated UCM sample collected was greater
than expected, indicating that sodium meta-alumi-
nate crystals might be formed along with the
delaminated UCM according to reaction 3. After
three uses in a row, the solution will become satu-
rated with sodium meta-aluminate and begins to
precipitate out. Therefore, it can be concluded that
the alkali solution obtained from the delamination
of UCM can be reused three more times (excluding
the use of pristine 2 M NaOH solution).
Characterization of Delaminated UCM
XRD analysis was performed to examine the
changes in the delaminated cathode materials after
treatment with pristine alkali solution and alkali
waste solution for multiple times (generated after
using pristine alkali), as shown in Fig. 4. The XRD
patterns of the extracted UCM samples (Fig. 4) from
pristine and alkali waste solutions (up to 3rd use)
revealed the hexagonal crystalline phase of the
material as pure LiCoO
2
(JCPDS card no: 96-450-
5483) with well-defined major diffraction peaks at 2
thetas along with plane values of 18.93°(003),
Table V. Delamination efficiencies of UCM using
alkali and alkali waste solution
No. of uses Delamination efficiency of UCM
Pristine 2 M NaOH 99.67±0.28
1st 99.52±0.21
2nd 99.68±0.28
3rd 99.62±0.23
Usage of Recycled Alkali Waste for Delamination of Cathode Electrodes:
Systematic Selection and Optimization of Hydrometallurgical Approach
37.41°(101), 39.08°(102), 45.24°(104), 49.45°(105),
59.61°(107), 65.44°(108), and 66.36°(110), respec-
tively.
38,39
This indicates that the delaminated
UCM samples from pristine and recycled alkali
solutions did not alter the crystal structure of Li-
CoO
2
. However, after the third consecutive recy-
cling of waste alkali solution, some minor peaks
were observed in the XRD spectra of the UCM
sample, specifically at 16.67°, 20.54°, 33.62°, 35.76°,
and 39.15°, which correspond to the presence of
NaAlO
2
. For comparison purposes, the XRD spectra
of pure NaAlO
2
and the UCM sample delaminated
using fourth alkali waste solution are shown in the
inset of Fig. 4. These minor peaks in the XRD
spectra of the UCM sample after the fourth con-
secutive use align with the reported XRD spectra of
NaAlO
2
in literature.
40,41
The appearance of minor
peaks of NaAlO
2
in the XRD spectra indicates the
precipitation of NaAlO
2
(as per reaction 3), which is
expected to contaminate the UCM sample obtained
by the recycled alkali solution (after its 4th consec-
utive use). Furthermore, the existence of NaAlO
2
in
the delaminated sample using alkali waste (after
the 4th use) was verified using TGA analysis as
follows:
A TGA analysis was performed to examine the
weight loss characteristics of cathode material be-
fore treatment, delaminated UCM samples from
pristine and alkali waste (4th use of alkali waste)
solutions, as shown in Fig. 5. Figure 5indicates that
the weight loss of cathode material before treatment
with alkali solution is slightly higher when com-
pared to the weight loss of cathode material after
treatment with pristine alkali solution. This addi-
tional weight loss of nearly 1% in the cathode
material before treatment may be attributed to the
loss of more physically bound water, leftover elec-
trolytes, PVDF binder, and other organic compo-
nents.
28,42
These weight losses observed for cathode
material before and after treatment with pristine
and waste alkali solution were in good agreement
with the literature.
28,42–44
Additionally, Fig. 5
shows the extensive weight loss of the delaminated
sample using an alkali waste solution compared to
the pristine alkali solution. This extra weight loss of
8.05% from the waste alkali delaminated sample
10 20 30 40 50 60 70 80
15 20 25 30 35 40
Intensity (a.u.)
2
θ
(degree)
3
rd
use
Pristine
2
nd
use
1
st
use
4
th
use
2
θ
(degree)
4
th
use
Pure NaAlO
2
Fig. 4. XRD patterns of delaminated UCM samples using pristine alkali and alkali waste solutions.
100 200 300 400 500 600 700 800
82
84
86
88
90
92
94
96
98
100
Weight loss (%)
Temperature (ºC)
Pristine alkali
Before treatment
Waste alkali
8.89 %
9.89 %
16.94 %
Fig. 5. TGA analysis of the cathode material before treatment,
delaminated UCM samples from pristine alkali and waste alkali
solutions (4th consecutive use).
Maske and Methekar
was attributed to the release of chemically bound
water (dehydration reaction) along with the amor-
phous to the crystalline transformation of
NaAlO
2
.
45,46
XRD and TGA measurements verified
the existence of NaAlO
2
in the fourth-use delami-
nated sample of alkali waste. Therefore, it is rec-
ommended to use the alkali waste solution not more
than three times.
Figure 6shows the SEM and EDAX surface
analysis of the cathode electrode before and after
treatment with pristine alkali and alkali waste
solutions. Figure 6shows that the surface mor-
phology and elemental content of cathode material
before and after treatment have changed signifi-
cantly. SEM analysis [Fig. 6(a(i))] shows that the
surface of the cathode electrode before treatment
consists of LiCoO
2
agglomerated particles with un-
Fig. 6. SEM-EDAX analysis of the separated samples: (a) cathode electrode before treatment; (b) delaminated UCM sample from pure alkali
solution; (c) delaminated UCM sample from waste (3rd use) alkali solution.
Table VI. ICP-OES analysis of the spent cathode electrode, delaminated UCM sample from pure alkali
solution, and waste (3rd use) alkali solution
Metals
Spent cathode
electrode
Delaminated UCM
using pure alkali
Delaminated UCM
using waste alkali
Li 5.42 6.07 5.94
Co 50.62 52.62 51.77
Mn 3.98 4.12 4.35
Ni 7.49 6.81 7.45
Al 9.07 0.52 0.67
Usage of Recycled Alkali Waste for Delamination of Cathode Electrodes:
Systematic Selection and Optimization of Hydrometallurgical Approach
even shapes and sizes.
47
The surface of the cathode
electrode was coated with a flocculent layer, i.e.,
PVDF organic binder, as can be seen in further
magnification [Fig. 6(a(ii))]. In LIBs, PVDF was
used as a binder; it contains a significant amount of
fluorine (F), which is a threat to the environment.
Hence, EDAX was carried out to track the presence
of the F element on the surface of the sample before
and after treatment. The amount of F element pre-
sent on the surface of the sample before treatment
was 10.15%, which represents the existence of a
PVDF binder. EDAX results [Fig. 6(a(iii)] demon-
strate that the primary elements detected were Co,
O, F, C, Ni, Mn, and Al; this is proven to be com-
patible with the primary components of the LiCoO
2
cathode material. Also, just a minute quantity of
aluminum was present on the surface of the cathode
material before treatment, which was an indication
that the photoelectron beam was unable to break
through the layer of cathode material that was
covering the aluminum foil.
Figure 6b(i) and c(i) shows the surface
microstructure morphology of the UCM samples
after treatment with alkali and alkali waste solu-
tions. After treatment, the surface morphology of
the sample altered significantly, i.e., LiCoO
2
parti-
cles became clear, as seen in Fig. 6(b(i) and c(i)). A
small amount of PVDF residue is present on the
surface of the sample after treatment with both
solutions, as seen in the further magnification
[Fig. 6b(ii) and c(ii)]. In addition, the EDAX results
[Fig. 6b(iii) and c(iii)] revealed that the samples
after treatment with alkali consist of a small
amount of F element present as compared to the
sample before treatment. This decrease in the
amount of F content (PVDF) from the surface of
delaminated UCM indicates that PVDF was de-
graded,
48,49
with half the amount of fluoride present
in the delaminated samples. As depicted in Fig. 6b
(iii) and c(iii), a very small amount of aluminum is
present in the recovered samples, which indicates
that the UCM was perfectly delaminated from the
aluminum foil. Furthermore, the metal content of
the spent and delaminated cathode materials was
analyzed using ICP-OES analysis. Table VI shows
that the percentage of Li, Co, Mn, Ni, and Al was
found to be more or less the same from the delami-
nated samples using pure and waste alkali solu-
tions. Hence, we conclude that the UCM sample
delaminated using pristine alkali and alkali waste
(up to 3rd use) obtained is also LiCoO
2
and can be
employed in the manufacturing of coin cells.
28
Based on the observations made, the literature
suggests that ADP needs more time (30 min), even
after the use of a higher concentration of alkali
(5 M), to achieve optimal delamination efficiency.
Here, we define and explore the ADP thoroughly to
reveal its parametrical effects on the delamination
process. Then, we demonstrate that the stirring can
speed up the delamination process (from 30 to
10 min), even at lower concentrations of alkali
(2 M), compared to the literature using a higher
concentration (5 M) because stirring the mixture
can accelerate both the mass and hydroxyl ion
transfer rates. Table S-vii indicates that the opti-
mized ADP required 20% less overall process time
compared to the literature ADP. Additionally, we
investigated the use of alkali waste solution for
delamination and discovered that it could be reused
up to three times without affecting the delamination
efficiency and material characteristics. After careful
investigation (from Table S-vii), we found that the
optimized ADP and reused alkali waste strategy
required 1.909and 3.629less cost compared to the
literature ADP. Therefore, we conclude that the
optimized ADP and reused alkali waste strategy is
more cost-effective than the literature ADP.
CONCLUSION
In this work, four hydrometallurgical processes
are investigated for an economically viable and
environmentally friendly delamination process:
SDP, DES, ADP, and EG. A comparison of these
processes was made using four important parame-
ters: the delamination efficiency of UCM, economic
assessment, environmental assessment, and overall
process time. After careful investigation, ADP was
found to be a more economically feasible, environ-
mentally sustainable process with the highest
delamination capability compared to the other three
processes. Furthermore, optimization of ADP was
carried out using BBD to study the delamination
behavior of UCM using four process variables. The
highest delamination efficiency of UCM was found
to be 99.67% using the molar ratio of 2 M NaOH, a
solid-to-liquid (S/L) ratio of 1/10 g/ml, a stirring
speed of 700 rpm, and a reaction time of 10 min. To
the authors’ best knowledge, this is the first time it
has been reported in the literature that delamina-
tion can be achieved in only 10 min using a 2 M
alkali solution. Furthermore, we report the usage of
the spent alkali solution up to three times and
achieved nearly the same delamination efficiency
and material characteristics. The overall process
cost of optimized ADP and reuse alkali waste
strategy was reduced by 47.31% and 72.38% com-
pared to the literature ADP. Hence, it is evident
that the optimized ADP, along with the reuse alkali
waste strategy, is a more economical and intensified
delamination process that requires less time to
achieve complete delamination and has the poten-
tial to be explored on a large scale.
SUPPLEMENTARY INFORMATION
The online version contains supplementary
material available at https://doi.org/10.1007/s11837-
023-05916-1.
Maske and Methekar
ACKNOWLEDGEMENTS
The author (Dr. Ravi Methekar, VNIT, Nagpur,
Life Member of Indian Institute of Chemical Engi-
neers: LM 64856) acknowledges the Indian Institute
of Chemical Engineers and the Department of Sci-
ence and Technology, Government of India, for
providing financial support for this study (Vide
Sanction Order No. ECR/2016/000422).
AUTHOR CONTRIBUTIONS
TM: Main Investigator, Methodology, Formal anal-
ysis, Writing-original draft; RM: Conceptualization,
Supervision, Validation, Writing-review & final editing.
DATA AVAILABILITY
Upon a reasonable request, the data will be
available from the corresponding author.
COMPETING INTEREST
The authors declare that they have no known compet-
ing financial interests or personal relationships that could
have appeared to influence the work reported in this
paper.
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Usage of Recycled Alkali Waste for Delamination of Cathode Electrodes:
Systematic Selection and Optimization of Hydrometallurgical Approach
