Journal of Electroanalytical Chemistry 977 (2025) 118808
Contents lists available at ScienceDirect
Journal of Electroanalytical Chemistry
journal homepage: www.elsevier.com/locate/jelechem
Synthesis and electrochemical performance Assessment of sunflower
oil-based organosulfur Co-Polymers as the cathode additive for Li-S battery
Angamuthu Gnanavel a , Derek Ovc-Okene a,b, Lakshmi Shiva Shankar a, László Trif c ,
Robert Kun a,b,*
a
Solid-State Energy Storage Research Group, Institute of Materials and Environmental Chemistry, HUN-REN Research Centre for Natural Sciences, H-1117 Budapest,
Magyar tudósok krt. 2., Budapest, Hungary
Department of Chemical and Environmental Process Engineering, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and
Economics, Műegyetem rkp. 3, H-1111 Budapest, Hungary
c
Functional Nanoparticles Research Group, Institute of Materials and Environmental Chemistry, HUN-REN Research Centre for Natural Sciences, H-1117 Budapest,
Magyar tudósok krt. 2., Budapest, Hungary
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Sunflower oil
Used cooking oil
Organosulfur copolymer
Sulfur
Cathode additive
Electroactive material
Li-Sulfur batteries
Sustainable material
Lithium-Sulfur battery (Li-S) is considered as a promising new generation battery chemistry. Nevertheless, the
sulfur based battery chemistry has downsides in terms of the low electronic conductivity, polysulfide shuttle
effect, and low active material utilization. Currently, there are several strategies available to suppress LiPS
shuttling and thereby enhance cycle life behavior of the Li-S battery. However, there is no existing literature on
the use of organosulfur-based copolymer as a cathode additive material in Li-S. Herein, we have investigated the
feasibility of organosulfur copolymer synthesized using sulfur, fresh and used cooking (sunflower) oil. The
developed polymers were used cathode additives. The results reveal that the copolymer developed by used
cooking oil-loaded cathode (poly-S-UCO@SC) delivers high specific discharge capacity of 936mAh/g at 0.05Crate and the copolymer developed by fresh sunflower oil loaded cathode (poly-S-SF@SC) exhibits 828mAh/g.
However, the poly-S-UCO@SC exhibited poor structural stability, continuous cathode degradation and poor
electrochemical performances than poly-S-SF@SC. The poly-S-SF@SC showed improved polysulfide conversion,
reduced shuttle effect, reversible redox process, 66.5 % capacity retention for 40 cycles with stable cycling
stability and shows much potential as a suitable cathode additive material compared to poly-S-UCO. The results
demonstrate that utilization of biomass-based components in Li-S batteries may trigger new research pathways in
Li-Sulfur battery science and technology.
1. Introduction
Developing advanced battery material will contribute to our high
standards of living especially in the developed economy possessing na­
tions. The synthesis methods which we use to make the materials and
their applications, directly or indirectly affects the environment, sub­
sequently can lead us to jeopardize the forthcoming generations and
place them in danger of economic peril, climate change, energy crisis,
scarcity of resources. To avert this, developing sustainable material
based on circular economy principles, carbon neutrality is a key solu­
tion. The sustainable technologies play a significant role in energy
economy. Notably, the battery technology could help in reducing the
carbon emission and improve the energy economy. The current elec­
trical and electronic market is dominated by Lithium-ion batteries (LIB)
technology. LIB utilizes graphite as the anode and transition metal ox­
ides- based cathodes [1]. Because there are very limited natural re­
sources in the European Union (EU), graphite and other chemical
elements, such as Cu, Ni, Mn, Co are a key resource, which will be crucial
material in future. They are listed as critical raw materials (CRM) of the
EU. Out of the already existing LIB cathodes, cobalt (Co) and its pre­
cursors are the endangered high-cost resource material with heavy
dependence on the Democratic Republic of the Congo (DRC). [2] While
replacing the expensive transition metal- based cathode with elemental
sulfur [Lithium- Sulfur Battery, LSB] it leads to more sustainable
* Corresponding author at: HUN-REN Research Centre for Natural Sciences, Institute of Materials and Environmental Chemistry, Solid-State Energy Storage
Research Group, Magyar tudósok körútja 2., 1117 Budapest, Hungary.
E-mail address: kun.robert@ttk.hu (R. Kun).
https://doi.org/10.1016/j.jelechem.2024.118808
Received 29 August 2024; Received in revised form 5 November 2024; Accepted 13 November 2024
Available online 22 November 2024
1572-6657/© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
A. Gnanavel et al.
Journal of Electroanalytical Chemistry 977 (2025) 118808
batteries with high theoretical energy density of 2600 Wh kg− 1 and the
practical energy density of 400–600 Wh kg− 1. However, the issues such
as low electronic conductivity of Sulfur (S), lithium polysulfide formed
during the cycling process, the concomitant shuttle effect, selfdischarge, volume expansion of the sulfur cathode, the gases produced
by the use of LiNO3 additives impede Li-S battery performance. [3]
Among the above-mentioned issues, almost fifty years of research has
been focused on aspects such as electronic conductivity and the shuttle
effect during the cell charge–discharge process. During the charge
discharge cycles, the active material undergoes conversion reaction
forming various lithium polysulfides (LiPSs) intermediates, which
further get soluble in the electrolyte. The formed Li2S deposits at the
anode surface and reduces the electrochemical performances. In the
cathode side, the continuous polysulfide diffusion affects the electrode’s
porosity, active surface area of the cathode and gets disconnected from
the current collector. Further, the LiPSs affect the electrolyte viscosity,
which decreases the ionic conductivity and results in increased resis­
tance. [4] Moreover, lower order LiPSs that are insoluble and gets
accumulated on the surface of cathode and reduces the further active
material utilization. To address these above-mentioned issues various
strategies have been implemented such as designing suitable cathode
host materials [5] interlayers [6] substituting binders [7] altering the
separator [8] anode modifications by electrolyte additives [9] and
developing solid electrolytes. [10] Furthermore, it has been shown from
literature, that most efforts focus heavily on sulfur cathode architecture,
which is divided into two major types. The first is the development of
micro, meso-porous carbon-based materials capable of accommodating
higher sulfur loading and enhancing electronic conductivity. [11–13]
However, the increase in the amount of inactive material in the cathode,
low active material utilization and unidentified reaction mechanism are
still major concerns. Hence, sulfur containing polymers-organosulfur
seems to be a viable solution owing to its precise redox process, novel
redox mechanism, functional tunability, strong covalent bonds between
sulfur and copolymer framework which will help suppressing the LiPSs
upon cycling, and stable battery performance. The organosulfur based
co-polymers were developed using inverse vulcanization strategy and
are used as the cathode materials as in poly(S-r-DIB) [14] poly (S-DVB)
[15] S-BT obtained by using elemental sulfur with sustainable algae oil
[16] Poly(S-r-DIB) [17] Sulfur-Based polymer composites from Vege­
table Oils [linseed oil (LSO), sunflower oil (SFO), and olive oil (OO)]
[18] 3D printing sulfur copolymer-graphene (3DP-pSG) [19] SDIB@CNT hybrid [20] sulfur-co-polymer-LCNT (Sco-poly-LCNT) com­
posite [21] p(S-DVB) [22] copolymer of thiourea aldehyde resin (cp (STAR)
[23]
organic
polysulfane
nanosheets
[24]
sulfurmediatedsynthesis of CTF-1(S-CTF-1) [25] organosulfur from
elemental and porous trithiocyanuric acid (TTCA). [26,27] The abovementioned cathode materials shows high initial discharge capacity,
notable improvements in electronic conductivity, and reversible ca­
pacity. But the shuttle effect and low active material utilization remains
as one of the major concerns. In this aspect, the scientific community
thought that using an additive to the cathode can effectively bind the
LiPSs within the structure. These strategies can either physically or
chemically anchor the LiPSs and prevents the out-diffusion and im­
proves the cell performance. [28,29] The additive loaded cathodes such
as nanostructured magnesium nickel oxide Mg0.6Ni0.4O by P. Chen et al.,
observed that the addition of Mg0.6Ni0.4O to the S cathode alters the
surface morphology from a smooth flat to the rough agglomeration of
nanoparticles, which enhances the reactivity at the electrolyte/electrode
interface. [30] Next, the metal oxides and metal compounds such as
MnO, MnO2, Ti4O7, TiO2, Fe2O3, ITO like MXene, TiC, MSx, M(OH)x
were used as an additive material. These materials improved cycling
stability and rate performance due to the strong bonding between ad­
ditive and LiPSs and prevented the dissolution of LiPSs. [31] Further, inhouse synthesized graphene-based porous carbon (ResFArGO) [32], 3D
WS2/carbon nanotube (CNT) [33] Chitosan as a functional additive
[34], Lithium Aluminate (LiAlO2) [35], ionic liquid (IL) as a functional
additive [36], These additives improved performances in terms of high
initial discharge capacity, stability. Despite the above notable perfor­
mances, Li-S still need to overcome the shuttle effect, low active material
utilization, conductivity, control at the electrolyte-cathode interface,
LiPSs diffusion and slow reaction kinetics. [37] In search of a suitable
additive material, it has been identified from literature that organosulfur
was used as the positive electrode, additive and binder in Li-ion, Li-O2,
and Na battery technologies. Particularly, organosulfur used as elec­
trolyte additive or artificial SEI layer creating material to protect the Li
metal anode in LIB technology. [38] Also, the organosulfur acts as an
electrolyte additive, assisting in the formation of stable Electrode/
electrolyte interphases [39] Overall, the following conclusions have
been drawn from the literatures (i) there is need for sustainable material
and facile, up-scalable synthesis strategy in cathode development (ii) in
Li-S battery, the organosulfur based materials are used as an electrolyte
additive and cathode active material, but not as a cathode additive ma­
terial (iii) low active material utilization, poor energy density, nonhomogeneous Li2S deposition at the electrode surface are notable is­
sues to be addressed while developing advanced Li-S battery.
Hence, herein we have developed an organosulfur based cathode
additive material using waste material streams such as by-product or
waste elemental sulfur from the petroleum industry (known as Claussulfur) as an alternative feedstock combined with fresh as well as used
cooking oil. The fresh sunflower oil (SF) and used cooking sunflower oil
(UCO) act as the cross linker which is possessing more diene-type
chemical bonds and assist in forming copolymers with elemental sul­
fur. we have assessed carefully whether the SF and/or UCO oil based
organosulfur polymer material can be applied as a cathode additive
material in
Li-S battery technology. We presumed that the developed additive
material would have enhanced physicochemical properties, enhanced
sulfur content, improved active material utilization, and uniform Li2S
deposition at the electrode surface. In addition to that, the developed
copolymers are expected to show high affinity towards LiPSs, superior
capacity and improved electrochemical performance.
2. Materials and methods
2.1. Preparation of organosulfur polymers poly-S-SF and poly-S-UCO
The organosulfur based copolymers were developed using elemental
sulfur and commercial sunflower oil (diene source) purchased from local
market. The fresh and used cooking oils were used to develop organo­
sulfur copolymers using inverse vulcanization strategy. The aspurchased sunflower oil was used to fry carbohydrate-rich compo­
nents and also protein-based sources in repeated multiple cycles frying
between 160–180 ◦ C, then, after frying the oil was filtered and used it for
the synthesis of copolymers. Initially the copolymer developed using
fresh sunflower oil and the procedure as follows, 70 wt% of sulfur (S8)
was added to a 250 mL round bottom flask and heated to 185 ◦ C in a
thermal stainless-steel mantle with continuous stirring, until a clear
orange coloured molten phase formation was observed. Around the
temperature range of 160–165 ◦ C, 30 wt% fresh sunflower oil was
gradually added (over the period of 30 min) to the molten sulfur using a
syringe. Two immiscible biphasic-phases viscous solution were
observed, which was further stirred at 185 ◦ C. As the reaction pro­
gressed, the reaction media became increasingly viscous and after a
period of 40 min the gel state was reached, forming a solid Benita mink
colour and then turned into a darker, rubbery-like polymer material. The
final product was washed well with 0.1 M sodium hydroxide (NaOH) to
remove H2S impurities, and further washed well with double distilled
water several times and dried at 60 ◦ C for 12 h. [17] The final asprepared product is denoted as Poly-S-SF (fresh sunflower oil). Similar
strategies were followed to develop Poly-S-UCO (used cooking oil). Also,
copolymers were prepared by varying the weight percentages of sulfur
and oil in the reaction media in order to test solubility and conduct
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Journal of Electroanalytical Chemistry 977 (2025) 118808
comparative studies.
3. Results and Discussion
3.1. Structural characterization
2.2. Material characterization
The synthetic scheme shown in Fig. 1, represents the copolymeri­
zation of elemental sulfur with diene consisting of fresh and used
cooking oils. Then various copolymers were developed by altering the
weight percentage of oil and sulfur. [Sulfur: oil (90:10, 80:20, 70:30,
50:50, 30:70; 20:80; 10:90, 5:95 wt%)] in the reaction medium. The
poly-S-SF formation is quicker and takes less time for completion of the
reaction in comparison with poly-S-UCO, which is attributed to the
complete consumption of SF and low complexity nature in the structure.
However, the UCO possess different number of carbon possessing free
fatty acids along with impurities thus requires much time to participa­
tion in the cross linking reactions. [40–42].
The chemical structure of the polymers was confirmed with NMR
spectroscopy using deuterated chloroform (CDCl3) at ambient temper­
ature. Since the polymers are not completely soluble in the solvents, the
sample preparation procedure for the analysis was adopted from the
literature. The sample of copolymers poly-S-SF and poly-S-UCO
(500 mg) was mixed with CDCl3 (10 mL) and stirred, to extract the
soluble part of the polymer then the resultant solution was filtered
before being subjected to 1H NMR analysis. The obtained NMR spectra
for the developed polymers are shown in Fig. 2a and b. the chemical shift
and peak values resembles the initial oils. However, the increasing peak
integration denotes the formation of organosulfur polymer, which was
further confirmed with FT-IR and Raman spectroscopy. The 1H NMR
spectra of the fresh sunflower and used cooking oils possess the
following peaks, the signals at 4.14 ppm indicates H–C–S bond and
4.29 ppm (CH-OCO, CH2-OCO-CH2-CH2), 5.26 ppm (OCH) also re­
sembles CH = CH, the signal at 2.31 ppm indicates CH2-CH = CH and
2.73 belongs to CH = CHCH2CH = CH, then terminal CH3 appears at
0.88 ppm. In addition to that, the peak at 1.27 ppm corresponds to the
HC-S and (CH2)n.[43] The developed polymers poly-S-SF and poly-SUCO which are obtained from fresh sunflower and used cooking oils
showed similar characteristics with fresh and used cooking oil. The main
difference between the initial oils and final polymer composites is the
enhancement in the integration of the peak chemical shift at 1.27 ppm.
This indicates the total reactions of all vinyl groups of the fresh and
The developed polymers were investigated using various character­
isation techniques such as Nuclear Magnetic Resonance Spectroscopy
(Varian Inova 500 NMR spectrometer), to confirm the structure of the
polymers. Next, to identify the functional group of the developed co­
polymers poly-S-SF, poly-S-UCO and confirm the polysulfide formation,
Fourier-Transform Infrared spectroscopy (FT-IR) measurements was
carried out (Model: Varian Scimitar 2000 FT-IR spectrometer [Varina
Inc., US] fitted with MCT detector, a “Golden Gate” single reflection
diamond ATR unit (SPECAC Ltd., UK]). The vibrational properties of the
polymers were evaluated using a Bio-Rad (Digilab) specialised FTRaman spectrometer fitted with a Spectra-Physics Nd-YAG laser
(1064 nm) and a high sensitivity liquid-N2 cooled Ge detector was used
to record the Raman spectra. About 100 mW of laser power was applied
to the samples. The Raman instrument has a resolution of about 4 cm− 1
and 256 scans. The crystal structure and phase purity of the developed
copolymers and sulfur were identified using powder X-ray diffraction
(PXRD) using a PW3040/60 (Philips, Netherlands) X-ray diffractometer
equipped with a Cu-Kα radiation source (λ = 1.5418 Å; 40 kV acceler­
ation voltage and 35 mA current).TGA (TA: Q100 instrument): to
analyse the thermal stability and weight percentage of existing sulphur:
to identify the surface morphology and elemental percentage scanning
electron microscopy (SEM: FEI Quanta 3D dual-beam equipment, EDAX
Apollo SSD detector coupled with Genesis software).
2.3. Electrode preparations and coin cell assembly
The synthesized polymers were used as the additive material to the
cathode of LiSB. By considering battery application viewpoint, complete
conversion of starting material, high yield nature, we have taken the
polymers developed by using 70 wt% S: 30 wt% of oil-based polymers
for our studies. To prepare carbon sulfur composite cathode, 70 wt% of
elemental sulfur and 30 wt% of super-P carbon was dry milled for 2 h
from the above mixture, 80 wt% was taken mixed with 10 wt% PVDF
and 10 wt% carbon black (80:10:10 wt%) milled for an hour in NMP
solvent. The slurry was coated onto an aluminium current collector and
dried for 12 h at 60 ◦ C in a vacuum chamber. The dried electrode was cut
into 12 mm diameter and weighed, the active material content was 1 mg
cm− 2 and denoted as SC. To prepare the additive loaded composite
cathode, the carbon sulfur composite, PVDF and co-polymer (poly-S-SF)
mixed in weight ratio of 80:10:10, milled for an hour in NMP solvent.
The slurry was coated onto an aluminium current collector and dried for
12 h at 60 ◦ C in a vacuum chamber. The dried electrode was denoted as
poly-S-SF@SC and the active material weight was 0.98 mg cm− 2. The
same strategy was applied to the polymer developed by using used
cooking oil (poly-S-UCO) and the electrode was denoted as poly-SUCO@SC the active material was 0.72 mg cm− 2. Then using the above
prepared electrodes, coin-type cells (CR2032) were assembled inside the
argon-filled glovebox (H2O, O2 level restricted to ≤ 0.1 ppm, MBraun)
with lithium-metal foil (99.9 %, Sigma Aldrich) as the counter electrode
(10 mm diameter) as well as the reference electrode, Whatman glass
fiber as the separator (diameter 18 mm) and the as-prepared organo­
sulfur copolymer additive loaded SC composites as the cathode. The
electrolyte used was 1 M lithium(tri-fluoromethanesulfonyl) imide
(LiTFSI) with (99.95 %, Sigma Aldrich) in 1:1 vol ratio of 1,3-dioxolane
(99 %, Sigma Aldrich) and 1,2-dimethoxy ethane (99.5 %, Sigma
Aldrich) as solvents. No additives were added to the electrolyte and the
quantity of the electrolyte was 100 µL per coin cell. The fabricated coin
cells were characterized using various electrochemical measurements
such as cyclic voltammetry, galvanostatic charge–discharge (GCD),
electrochemical impedance spectroscopy (EIS) and rate performance at
different current rates.
Fig. 1. Synthetic scheme showing the copolymerization of S8 with dienes
possessing fresh and used cooking oil.
3
A. Gnanavel et al.
7.5
7.0
6.5
0.07
0.90
0.88
1.61
1.56
1.29
1.26
9.13
1.5
1.0
0.5
0.0
0.07
2.0
58.47
6.13
2.5
1.29
1.26
0.90
0.88
0.87
3.0
67.51
3.5
f1 (ppm)
1.61
4.0
4.16
4.15
4.14
4.13
6.0
5.5
5.0
4.5
4.0
f1 (ppm)
3.5
3.0
2.5
2.0
1.5
12.28
7.48
4.10
1.12
4.15
2.00
2.35
4.25
4.20
f1 (ppm)
0.93
4.30
2.35
4.31
4.30
4.28
4.28
2.00
4.35
4.5
19.11
5.0
2.75
2.73
2.72
2.32
2.31
2.29
5.5
4.31
4.30
4.28
4.28
4.16
4.15
4.14
4.13
6.0
5.26
6.5
22.89
4.10
1.67
4.15
2.00
2.22
4.25
4.20
f1 (ppm)
7.26
7.0
2.75
2.73
2.72
2.32
2.31
2.29
4.31
4.30
4.28
4.28
4.16
4.15
4.14
4.13
2.22
4.16
4.15
4.14
4.13
5.26
4.30
0.93
4.35
2.00
4.31
4.30
4.28
4.28
7.26
Journal of Electroanalytical Chemistry 977 (2025) 118808
1.0
0.5
0.0
Fig. 2. H1 NMR Spectra of (a) poly-S-SF (b) poly-S-UCO.
used cooking oil. It can be concluded that the number of vinylic groups
in the monomer copolymerized with sulfur dictates the level of the
crosslinking in the structure of sulfur-based polymers and also their
solubility in most solvents is in turn a function of the degree of cross­
linking. Further, to know the solubility of the developed copolymers, the
copolymer developed using sulfur: oil (70: 30) solubility analysis was
carried out. However, the observation that some sample is only partially
soluble and not completely soluble in polar and non-polar solvents could
be explained with the fact that high(i) sulfur content and (ii) high degree
of crosslinking of the oil and sulfur affects the solubility of the formed
organosulfur polymers crucially. Furthermore, to check the solubility,
by taking polymers synthesized at 1:1 ratio, i.e., 50 wt% of oil and 50 wt
% of sulfur, which are shown in the Table S1 and Table S2 in supple­
mentary information. Figure S1 and S2 (supplementary information)
represents the photo image of solubility test with different solvents. Both
polymers poly-S-SF and poly-S-UCO are having less soluble nature in
polar and non-polar solvents and completely insoluble in water and
partially soluble in NMP, THF and CHCl3. Also, it was noted that, co­
polymers developed using sulfur: oil ratio (5:95, 10:90 wt%) are soluble
in THF, CHCl3 and NMP and remaining copolymers are rather insoluble.
As it was said, the lowered solubility at higher sulfur ratios is attributed
to the increasing crosslinking nature of organosulfur polymers. [44] The
obtained IR spectra are shown in Fig. 3a. The band at 2992, 2852 cm− 1
represents C–H, 1738 cm− 1 indicates the C–
–O bond, the peaks at 1456,
1376 cm− 1 denote bending vibration of alkane group, further 1160 cm− 1
corresponds to stretching of C–
–O ester group, the bands at 798,723 and
633 cm− 1 may be C–S bond, next the bands at 532, 438 cm− 1 may be
attributed to stretching vibrations of S–S. In general, the oil has a two
notable bands one is at 3000 cm− 1 and another 1650 cm− 1 corre­
sponding to the vinylic C–H and C–
–C double bond. [45] These two
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Journal of Electroanalytical Chemistry 977 (2025) 118808
Fig. 3. Structural characterization of poly-S-SF and poly-S-UCO (a) FT-IR spectra (b) Raman spectra (c) powder X-Ray diffraction pattern (d) TGA thermograms (e)
DSC thermograms (f) DTG curves.
bands indicated in the oil were absent in the polymers which confirms
the copolymer formation by the S and diene of oils. Also, few copolymers
IR bands are similar and possessing features of oil. In addition to that
enhanced the poly-S-UCO possess intense peaks indicating the deterio­
ration and quality of the oil samples. Further, in order to understand the
structural information, interaction between the carbon–sulfur compos­
ite and copolymers, for the developed cathode materials (SC, poly-SSF@SC, poly-S-UCO@SC), IR measurements were carried out and rep­
resented in Figure S3. (supplementary information). The SC composite
consisting of band resembling respective peaks of carbon black and
sulphur. The band at 485 cm− 1 represents sulfur in the composite,
1059 cm− 1 1738 cm− 1 indicates the carbonyl groups. The carbon black
C–
–C stretching vibration mode disappeared at 1740 cm− 1 may be due to
interaction with sulfur. 2800–2950 cm− 1 region indicates the stretching
vibration of C–H bond; OH stretching band appears in the range of
3500–3800 cm− 1. The polymers loaded cathodes consist, resembles
respective bands of CB, S, and copolymers. However, the absorbance
peak intensity is increased after adding the oil-based polymers to the SC
composite, which may be attributed to the change in the enhanced sulfur
concentration, increased dipole moment and modified surface in the SC
composite. This additionally supports the enhanced electrochemical
performances. Next, the vibrational properties obtained by the Raman
spectroscopy analysis shown in Fig. 3b, reveals that poly-S-UCO possess
four bands. The band at 472 cm− 1, 364 cm− 1 are may S–S vibrational
modes of polysulfide and 218 cm− 1, 154 cm− 1 which are representing
S–S stretching of elemental sulfur. The broad band between 1100 to
1900 cm− 1 indicates the sunflower oil domain of the polymer. [46] The
similar features are observed in the case of poly-S-SF, however, the
enhanced peak intensity of poly-S-UCO indicating the enriched sulfur
content. Further, the obtained diffraction patterns are shown in Fig. 3c.
The diffraction patterns for pure sulfur match with the orthorhombic
phase of sulfur’s (ICDD no. 08–0247). The pure sulfur shows three peaks
2θ = 23, 26 and 27.8 which represent the (222), (026), and (040) planes
of sulfur. The copolymer’s XRD patterns are well match with the
elemental Sulfur patterns. This suggests that the apparent crystallinity
depends on the amount of sulphur present in the copolymers, that are
responsible for the crystalline reflections seen in the PXRD patterns. [47]
In addition to that, we carried out the P-XRD for the developed cathode
materials (SC, poly-S-SF@SC, poly-S-UCO@SC) shown in Figure S4
(supplementary information). The 2θ peaks at 23.2◦ , 26◦ , 26.8◦ , 26.8◦ ,
29◦ and 31◦ representing the (222), (220), (026), (040), (313) and (044)
planes of sulfur there is no new phase, or peaks of carbon black, which
are not observed which may be due to the dominant sulfur content in SC
composite. In the case of polymers loaded SC, similar features are
observed as in SC, but addition of colpolymer to the SC decrease the peak
intensity which indicates the microstructural change and surface
modification.
The thermal stability organosulfur polymer was investigated by TGA,
TDG and DSC with nitrogen purge of 50 mL min− 1, temperature range
from 0 to 700 ◦ C and heating rate of 10 ◦ C.min− 1. Samples (3–8 mg)
were sealed in aluminium sample pans. The obtained results are shown
in Fig. 3(d–f). The TGA thermogram of the copolymer poly-S-SF show
four degradation mass loss steps could be identified shown in Fig. 3d,
degradation before 109–126 ◦C may be attributed to evaporation of the
moisture and volatile impurities. The second weight loss in the range of
222 ◦C to 290 ◦C, it is corresponding to the elemental sulfur which is
62 wt%. Then combined two different degradation process observed
between 291 ◦C to 370 ◦C which is belonging to the sublimation of
sulfur, free unbound sulfur sublimes out of the system from the copol­
ymer which is considered to be the additional S quantity and the second
one attributed to the pyrolytic degradation of the organic content carbon
and oxygen from the oils is most likely to occur in parallel. The fourth
and last phases above 371 ◦C include slow, post-pyrolytic or slow
oxidative reactions (owing to the carrier gas’s 10 ppm O2 concentra­
tion). The latter (oxidative) processes would be aided by the heat flow,
curves shifting towards the exothermic area (above 0 mW). It has been
observed that sulfur-oil copolymers did not fully volatile, residues are
leftover which may be the S chain and C with varying densities
remained. In the case of poly-S-UCO, similar features observed as in the
poly-S-SF. However, there was enhanced sulfur content 64.73 wt% and
the additional weight confirms the corresponds to existing higher im­
purities. Then the DSC measurements shown in Fig. 3e, reveals that
thermogram of the copolymers possessing four peaks 109, 126, 261 and
370–383 ◦C which may be attributed to the elemental sulfur existing in
different crystalline phases varying in melting temperature along with
sulfur chain from the copolymers. Further, the thermal degradation of
copolymers occurs at faster rates than elemental sulfur. The copolymer’s
sulfur breakdown temperature drops below that of elemental sulfur. As
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Journal of Electroanalytical Chemistry 977 (2025) 118808
the amount of sulfur in the reaction mixture increases, the thermal
breakdown temperatures of the polymerized sunflower oil in the co­
polymers drop, when sulfur increases from 4 to 5 wt%, the temperature
drops from 383 to 371 ◦ C. which is identified from the DTG curves
shown in Fig. 3f.The thermal breakdown behavior of sulfur-based co­
polymers derived from sulphur with canola and corn oils was also
observed to exhibit similar patterns. [48].
The SEM analysis shows that the presence of two different phases in
the form of smooth surface with embedded isolated sulfur particles
similar to original elemental sulfur. The micrographs of poly-S-SF
copolymer are shown in Fig. 4(a–f) and micrographs of poly-S-UCO
copolymer are illustrated in Fig. 5(a–f) The aggregated morphology
was observed for both samples, but it was more in the case of polymers
developed by using UCO. The surface was consisting different region
some regions are rich in sulfur which is attributed from the copolymer
S–S chain and some region are rich in carbon. Also, more grooves and
slits had appeared on both the copolymers. The EDS shown in Fig. 4(g)
and (g) analysis the atomic sulfur content in the poly-S-UCO polymer
higher than the poly-S-SF which further confirmed with TGA
measurements.
In addition to that we also investigated the surface morphologies of
developed cathode materials (SC, poly-S-SF@SC, poly-S-UCO@SC)
shown in Figure S5 (supplementary information). the SC reveals that
even distribution sulfur on the carbon surface and wrapped by the car­
bon black in the composite. Next, the micrographs of poly-S-SF@SC
(e–h) and poly-S-UCO@ indicates similar features as like SC but parti­
cle size seems to be smaller size due to the extended milling for an hour.
Also, noticed that the addition of polymer o the SC slightly creates no
homogeneous distribution of the copolymer on the surface.
sulfur to higher order polysulfides then appearance of a peak
between + 1.93 V to + 1.98 V corresponds to the reduction of higher
order lithium polysulfides (HLiPSs) to lower order small chain poly­
sulfide (LLiPSs) and finally to Li2S. In the anodic sweep of SC consists of
two oxidation peaks one in the range of + 2.36 V to + 2.4 V indicates the
oxidation of Li2S to HLiPSs and the peak at between + 2.45 V to + 2.5 V
is the conversion of HLiPSs to sulfur. Next, Fig. 6b showing the CV
curves of poly-S-SF@SC, during the first cathodic sweep there is two
reductive peaks and in the anodic sweep three oxidative peaks, the
reductive sweep at + 2.22 V indicates that sulfur is reduced to HLiPSs
and further converting to LLiPSs (Li2S2/Li2S) which is identified
from + 1.73 V. In the anodic sweep, a small shoulder appeared at + 2.34
indicates the formation of solid electrolyte interface by the oxidation of
organosulfur copolymers to LiPSs. The peak at + 2.39 V indicates
oxidation of HLiPSs to LLiPSs and + 2.45 V indicates LLiPSs to sulfur. In
the next cycle, there are seven reductive peaks show in Figure S6, in
supplementary information (+2.32 V, +2.009 V, +1.99 V, +1.98 V,
+1.97 V, +1.96 V, and + 1.8 V) were obtained, which indicates the
serious of reaction occurred by the reduction and conversion of sulfur to
HLiPSs to formation of serious of LLiPSs but it is difficult assign the exact
polysulfides and further investigations are in the laboratory progress.
However, in the anodic sweep, there is single peak observed which in­
dicates that the fast conversion of lower, higher order polysulfides to
elemental sulfur. [49] In fact, the overlapping nature of the cyclic vol­
tammetry curves, however, indicates the high reversible process during
the consecutive cycles. Also, decreasing anodic cathode peak current
were observed which is attributed to the active material consumption in
subsequent chemical process. [50,32] The CV of poly-S-UCO@SC shown
in Fig. 6c, in the initial cycle there is formation HLiPSs by the reduction
of elemental S observed. Also, it was noted that there is a partial con­
version of HLiPSs to LLiPSs in the first cycle, but in the subsequent cy­
cles, proper reduction and formation of LiPSs were obtained. Later, the
patterns of pure sulphur redox process features observed. In the anodic
sweep the conversion of HLiPSs to LLiPSs and then converted to sulfur
which are identified at + 2.6 V to 2.75 V with decreasing anodic
cathodic peak current, attributed to the better active material utiliza­
tion, reaction kinetics towards polysulfide conversions and enhanced
catalytic activity. [51] Additionally, there is only a slight shift in the
anodic and cathodic peak potential, demonstrating that the conversion
3.2. Electrochemical performance
To understand the redox process, cyclic voltammetry studies of
copolymer loaded cathodes poly-S-SF@SC and poly-S-UCO@SC and
sulfur-carbon composite cathode (SC) were carried out between the
potential range of + 1.4 V to + 2.8 V vs. Li/Li + at a scan rate of
0.001 mV s− 1 and the results are illustrated in Fig. 6a–c. The cyclic
voltammogram shown in Fig. 6a, corresponds to SC, the peak
between + 2.6 V to + 2.30 V assigned to the reduction process that is
Fig. 4. (a-i) SEM micrographs of poly-S-SF (g) EDS of poly-S-SF.
6
A. Gnanavel et al.
Journal of Electroanalytical Chemistry 977 (2025) 118808
Fig. 5. (a-i) SEM micrographs of poly-S-UCO (g) EDS of poly-S-UCO.
Fig. 6. Cyclic voltammogram of (a) Sulfur-Carbon (SC) composite cathode (b) poly-S-SF@SC (c) poly-S-UCO@SC. Discharge- charge profile of (d) SC (e) poly-SSF@SC (f) poly-S-UCO@SC.
reaction is largely reversible. There is low polarization in the cell indi­
cating the effective electrochemical process by the addition of copol­
ymer additives, which is observed by the lower oxidation potential and
larger reduction potentials. [51,52] This also suggests that LiPSs diffu­
sion occurs in a slow and controlled manner. Furthermore, notable
features were observed from the CV analysis. For the poly-S-SF@SC has
sharp and overlapping curves are obtained and which indicates the high
reversible process. The first cathodic sweep of poly-S-UCO@SC
mechanism is unclear and seems to be ambiguity in the system because
of existing free fatty acids and other impurities involving in electro­
chemical reactions later its optimized having proper cyclic voltammetry
curves. The poly-S-SF@SC possess good redox activities and high
reversibility seems to be suitable cathode additive material for the Li-S
batteries. According to the above assertions, the addition of the devel­
oped organosulfur copolymer to the sulfur cathode boosts active mate­
rial usage, improves overall cathode conductivity by presence of carbon
7
A. Gnanavel et al.
Journal of Electroanalytical Chemistry 977 (2025) 118808
backbone, forms suitable surface film at the anode surface, promotes
polysulfide conversion, reduces the shuttle effect, resulting in enhancing
the reversibility and electrochemical stability which are based on the
poly-S-SF@SC system.
To understand the storage properties, the galvanostatic char­
ge–discharge measurement were performed between the potential
range + 1.7 V to + 2.6 V at 0.05C for 40 cycles and the obtained results
are represented in Fig. 6d–f. The Fig. 6f reveals that poly-S-UCO@SC
showed specific discharge capacity of 936 mAh g− 1. The high specific
discharge capacity.
of poly-S-UCO@SC is attributed to the high sulfur content which was
obtained by high cross linking between the elemental sulfur with many
alkene monomers, unsaturated C–
–C bond resulted by the heating the oil
that increasing the free fatty acid and linoleic acid content. [53,54] Also,
it has been observed that it delivers 396 mAhg− 1 at 40th cycle. Further
cycling revealed that there is severe capacity fading, which is owing to
the numerous contaminants present in the organosulfur copolymer
formed by utilizing (burnt) cooking oil. The existing impurities may
participate in the electrochemical process which increases side products
by reacting with electrolyte which further increase resistance and con­
centration polarization. In the case of poly-S-UCO@SC the over poten­
tial is higher than the poly-S-SF@SC which is attributed to the mixing of
the LiPSs to the electrolyte enhances the viscosity of the electrolyte and
decrease in ion conductivity. However, the slight improvements in the
electronic conductivity is attributed to the carbon and other impurity
consisting by the used cooking oil. Next, poly-S-SF@SC shown in Fig. 6e
delivers specific initial discharge capacity of 828 mAh g− 1 and for 40th
cycle it delivers capacity of 551 mAh g− 1. This shows better retention
capacity and stable cycling in comparison with poly-S-UCO@SC (42.3 %
for 40 cycles) and SC cathodes, which can be attributed to the addition
of the copolymer poly-S-SF@SC, which generated a better surface
property for LiPSs anchoring, resulting in enhanced better capacity
retention and due to its sulfur content, this sulfur-rich domains could be
utilized more effectively in electrochemical sense. Furthermore, orga­
nosulfur polymer-based additives generate a passivation layer called
Solid Electrolyte Interface (SEI) on the anode surface, reducing shuttle
effect and increasing the solubility of low order LiPSs. [55] Apparently,
this strategy works better if we apply fresh sunflower oil-based poly-S-SF
organosulfur polymer, with more homogeneous chemical structure
(compared to poly-S-UCO). For the comparative purpose, the SC cathode
shown in Fig. 6d prepared which delivers initial discharge capacity of
710 mAh g− 1. This reveals that the addition of oil derived copolymer
additive has a significant role in the cathode development. The over
potential is lower for poly-S-SF@SC in comparison with SC and poly-SUCO@SC. The low over potential indicates low polarization, favourable
lithium diffusion coefficients. Further, SC and poly-S-UCO@SC, during
the extended cycling, higher overpotential with enhanced polarization
were noticed. Overall, among the three cathode SC, poly-S-UCO@SC
and poly-S-SF@SC, the fresh oil derived copolymer additives shows
better performances and acts as a suitable cathode additive. In addition
to the above electrochemical analyses, EIS analyses were performed
using a BioLogic (VMP-300) impedance analyzer with a frequency range
of 100 kHz to 100 mHz with sinusoidal potential of 5 mV and six points
per decade. Fig. 7a show Nyquist plots of SC, poly-S-SF@SC and poly-SUCO@SC cells. The poly-S-UCO@SC consist ohmic resistance at high
frequency region including the electrode and electrolyte resistance,
semicircle formation at middle frequency region representing charge
transfer resistance and Warburg impedance from the spike appearance
in the low-frequency region. The larger semicircle of poly-S-UCO@SC
indicates higher charge transfer resistance in comparison with SC and
poly-S-SF@SC attributed to the various side reactions occurred between
LiPSs with electrode, electrolyte and copolymer additives increasing the
side products that leads to high resistance. Also, existence of free fatty
acids, impurities may participate in the electrochemical process, thus
increases in the charge transfer resistance and complicates the kinetic
process. In the case of poly-S-SF@SC similar features are observed along
with appearance of slightly depressed semicircle which may corresponds
to the formation of Li2S and Li2S2 on the carbon matrix. The charge
transfer resistance is much lower than the poly-S-UCO@SC which in­
dicates the uniform distribution of sulfur and suitable electrochemical
active sites, interlayer formation. In addition to that the addition of
copolymer poly-S-SF@SC plays a significant role in the formation
Fig. 7. (a) Nyquist plot of SC, poly-S-SF@SC and poly-S-UCO@SC. (b) Rate performances analysis of poly-S-SF@SC and poly-S-UCO@SC at various C-rates (c) long
term cycling performances of poly-S-SF@SC for 100 cycles, poly-S-UCO@SC for 40 cycle at 0.05C rate.
8
A. Gnanavel et al.
Journal of Electroanalytical Chemistry 977 (2025) 118808
suitable surface films on the anode and cathodes rather than the addition
of poly-S-UCO@SC. The decrease in the charge transfers resistance also
associated with enhanced sulfur utilization, active sites by the organo­
sulfur additive material that exposes more access to the electrolyte,
mitigate polysulfide diffusion through chemical interactions, which
leads to reduced charge transfer resistance, and improved interfacial
properties between the electrode and electrolyte are observed.
Furthermore, it was discovered that the Poly-S-SF@SC loaded cathode
had better interfacial characteristics and kinetics than the Poly-SUCO@SC loaded cathode and bare SC.
Finally, it is believed that the inclusion of an organosulfur polymer
additive created by fresh sunflower oil (SF) improves electrochemical
performances significantly more than the polymer generated by used
sunflower oil (UCO). Poly-S-SF@SC cathode possess lower charge
transfer resistance, which increases redox and polysulfide conversion
kinetics. [56] Furthermore, poly-S-SF@SC having appropriate electro­
de–electrolyte interface, increases the surface area affords abundant
surface active sites to have better strong interaction with LiPSs attrib­
uted to the high adsorption and promoting the conversion reaction of
polysulfides, prevents the shuttle effect more effectively. Moreover,
accelerates the kinetics by Lewis acid base interaction, and the poly­
meric nature aids in controlling the volume expansion of sulfur durably.
[57].
To identify the rate capability and structural stability, the developed
poly-S-SF@SC and poly-S-UCO@SC are cycled at various C-rates and the
obtained results are illustrated in Fig. 7b. at 0.05C the poly-S-UCO@SC
delivers discharge capacity of 936 mAh g-1 for the 0.1C, 0.5C, 1C, 1.5 C
which delivers 404, 215, 139, 75 mAh g− 1and when switched it to its
original C-rate the original capacity was not retained, one third of the
original capacity only was obtained due to poor stability caused by
different undetermined/unknown electrochemical processes by other
components present in the cathode((see chemical complexity of the
burnt oil). In the given case of poly-S-SF@SC, the measured specific
discharge capacity at 0.05C is 828 mAhg− 1. As the current rate in­
creases, the capacity decreases, and when returned to its initial C-rate, it
maintains its original capacity that is 819 mAhg− 1. This signifies that the
material is structurally stable. Then flexibility of poly-S-SF@SC control
the volume expansion. To illustrate the material benefit, cycling per­
formance was performed at 0.05C-rate for 100 cycles, as shown in
Fig. 7c. The first discharge capacities of the poly-S-SF@SC electrode is
828 mAhg− 1 and after 100 cycles (58.4 % retention capacity) it delivers
capacity of 484 mAhg− 1 which is higher than poly-S-UCO@SC, which
shows retention capacity of 336 mAhg− 1 for 40 cycles shown in Fig. 7c.
The poly-S-SF@SC shows better retention capability than the SC elec­
trode developed in this work for the purpose of comparison. This also
may be attributed to the factice like polymer network that may physi­
cally adsorb or prevent the polysulfide dissolution, which improves the
capacity retention. Though the first discharge capacity is higher for
Poly-S-UCO@SC cell but subsequent cycles, it declined very fast due to
low active material utilization, unreacted sulfur, slow Li2S2 to S then
Li2S unfavorable surface film, increase volume expansion by unwanted
side products. The Poly-S-SF@SC system demonstrated high retention
capacity of 66.5 %, which may be attributed to the higher number of
electro-active sites and the high chemical adsorption nature of Poly-SSF, which improves the electrochemical reaction kinetics. Due to their
strong catalytic nature, non-conductive lithium sulfides produced on the
surface might also regulate with the poly-S-SF@SC. The good cycling
stability of poly-S-SF@SC is attributed to the presence of high S–S
content from the flexible chain is taking part in repetitive reduction and
oxidation process. The role of the non–S–S containing component of
the copolymers should be taken into account. Also, the cell with poly-SSF@SC has significant role in SEI formation at Li metal anode and per­
forms better without LiNO3, improved rate performance and excellent
capacity retention for the poly-S-SF@SC, are due to (i) the expanded
contact area between the electrode- electrolyte, enhanced charge
transfer and redox kinetics (ii) the distribution of polar poly-S-SF@SC on
the electrode surface, which offers sufficient space for lithium storage.
(iii) the poly-S-SF@SC restricts polysulfide outward diffusion in elec­
trolytes and decreases the shuttle effect by chemical anchoring (iv) The
poly-S-SF active sites and boundary defects minimize the overpotential
of Li2S nucleation and enhance the nucleation/conversion redox ki­
netics. finally, (v) the poly-S-SF@SC containing S–S bond could be
involved in reversible reduction and oxidation process, to higher extent
than the S–S bond in the poly-S-UCO@SC. As a consequence of the
synergistic impact of the poly-S-SF@SC and overall cathode design, the
poly-S-SF@SC offers greater retention and rate capabilities than the
poly-S-UCO@SC. Further, compared the acquired results with the earlier
literature reports and which are tabulated in Table 1.
4. Conclusion
In conclusion, we conducted preliminary tests on the synthesized
organosulfur-based polymer, which was employed as a cathode additive
material, and evaluated its electrochemical performances. Various
physicochemical and electrochemical characterization techniques were
applied to characterize the as-synthesized poly-S-SF and poly-S-UCO
organosulfur copolymers. The synthesis of organosulfur copolymer
required less time in fresh sunflower oil than in used cooking oil. Both
polymers are less soluble in polar and non-polar solvents and are only
partly soluble in THF, NMP, and CHCl3. The electrode slurry preparation
was carried out using THF, NMP, and CHCl3, and it was found that the
electrodes created with THF, and CHCl3 did not have strong adhesion to
the aluminum current collector, which was readily peeled off. The
electrode was then coated on aluminum foil using a homogenous slurry
created with NMP, which adhere well to the current collector. The PolyS-UCO@SC had a high initial discharge capacity but a reduced retention
capacity 42.3 % (for 40 cycles comparison shown in Figure S7 in Sup­
plementary information), poor structural stability because of the
different side reactions and higher charge transfer resistances, and poor
kinetics because of the impurities present in UCO. Better polysulfide
conversion, reduced polysulfide diffusion, and 66.5 % capacity retention
with sustained cycle stability are all features of Poly-S-SF@SC. In a
nutshell, the poly-S-SF acts as better cathode additive material than the
Poly-S-UCO. In addition to that copolymers developed by oils provide
much research possibility and remain challenging material. It can be
concluded that the fresh oil-based copolymers can be used as the cath­
ode additive rather than the copolymer developed by used cooking oil.
However, used/burnt oils may be utilized after proper physical
(filtering) and chemical cleaning, extraction, washing procedure to
decrease chemical complexity caused by the by-products of the Maillard
reaction, or thermal decomposition of the triglycerols found in the
sunflower oil. We find immense possibilities and perspectives in further
research to investigate deeper the cross linking reaction mechanism
between the oil and elemental sulfur, determining the precise quantity
of sulfur chain, and finding sulfur in copolymers that participate in the
electrochemical process. Furthermore, atomic and molecular-level
knowledge of the material might be sought. Combining used cooking
oil with Claus sulfur for electrochemical energy storage would be a great
strategy because of its inexpensive, open a new avenue in developing
novel electrochemically active materials, sulfur rich polymers material,
adding long-term stability to the valorization chain and harm free
environment. Also, besides the biodiesel production using oils, the
method of utilization described in this work considered to be effective
and valuable utilization method. Thus, UCO has to be double counted
mentioned based on public policies by Renewable Energy Directive from
EU, hence the price can be higher than first generation biodiesel.
5. Author’s contribution
Gnanavel Angamuthu and Robert Kun conceived the idea, planned
the experiments. Gnanavel Angamuthu performed the experiments,
interpreted the results and took the lead in writing the manuscript.
9
A. Gnanavel et al.
Journal of Electroanalytical Chemistry 977 (2025) 118808
Table 1
Comparison of electrochemical performance of poly-S-SF copolymer with earlier literature reports. using various electrode additives.
S.
No
Cathode additive used
in Li-S batteries
C-rate
Initial Capacity
(mAh g− 1)
Final Capacity
mAhg− 1. (cycle
number
Capacity
retention %
Electrolyte & additives
Reference
01
02
03
04
05
06
07
Mg0.6Ni0.4O
ResFArGO
WS2/CNTs
Chitosan
LiAlO2 Nanoflakes
TiS2 nano-sheets
Li2S@C with PAN
1185
1070
1046
1145
847
>1000
~900
300 (20)
632 (50)
528(1000)
680 (100)
703(100)
~600(200)
500 (20)
25
79
91.8
59
83
60
55
MnO2
Ti4O7
Poly-S-UCO@SC PolyS-SF@SC
1110
1044
936 828
644(1500)
1033(100)
396 (40) 551(40)
71. 7
99
42.3
66.5
1 M LiTFSI
0.5 M LiTFSI with 0.4 M LiNO3
1 MLiTFSI with 1 wt% LiNO3
0.6LiTFSI with 0.4 M LiNO3
Li-[TFSA]0.9[FSA]0.1/SL2/HFE2
1 M LiTFSI with 0.4 M LiNO3
1 M LiTFSI: n-methyl-(n-butyl) pyrrolidiniumbis
(trifluoromethanesulfonyl)imide (1:1 v/v)
1 MLiTFSI with 2 wt% LiNO3
1 M LiTFSI without LiNO3
1 M LiTFSI
[30]
[32]
[33]
[34]
[35]
[58]
[59]
08
09
10
0.1C
C/10
1C
C/2
0.1C
0.05C
10 mA
g− 1
0.5C
0.1C
0.05C
Derek Ovc-Okene, Lakshmi Shiva Sankar, László Trif took part in data
evaluation and manuscript finalization. All the above processes are
monitored, supervised and assisted by Robert Kun. All authors provided
critical feedback and helped shape the research, analysis, and
manuscript.
[60]
[61]
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CRediT authorship contribution statement
Angamuthu Gnanavel: Writing – original draft, Methodology,
Investigation. Derek Ovc-Okene: Writing – original draft, Investigation.
Lakshmi Shiva Shankar: Writing – original draft, Methodology. László
Trif: Investigation. Robert Kun: Writing – review & editing, Supervi­
sion, Funding acquisition, Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
The support provided by Recovery and Resilience Facility of the
European Union within the framework of Programme Széchenyi Plan
Plus (Project no. RRF-2.3.1-21-2022-00009, Titled National Laboratory
for Renewable Energy), by the National Research, Development and
Innovation Fund of Hungary, co-financed by the European Regional
Development Fund is gratefully acknowledged.
The authors thank Zoltán Dankházi, Dora Zalka, Dávid Ugi, Eötvös
Loránd University Budapest for SEM-EDX instrumentation support,
Mihály Judith for FT-IR, FT-Raman measurements and Kristóf Hegedüs
for NMR measurements.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.jelechem.2024.118808.
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