Low cost and green preparation process for -Fe …...Low cost and green preparation process for...
Transcript of Low cost and green preparation process for -Fe …...Low cost and green preparation process for...
Low cost and green preparation process for α-Fe2O3@gum
arabic electrode for high performance sodium ion
batteries
Li Xu,a,b
Hansinee Sitinamaluwa,c
Henan Li,a,c
Jingxia Qiu,a
Yazhou Wang,b
Cheng Yan,c
Huaming Li,*,a
Shouqi Yuana
and Shanqing Zhang*,b
aInstitute for Energy Research, School of Chemistry and Chemical Engineering, Jiangsu
University, Zhenjiang 212013, P. R. China. E-mail: [email protected]
bCentre for Clean Environment and Energy, Griffith School of Environment, Gold Coast
Campus, Griffith University, QLD 4222, Australia. E-mail: [email protected]
cSchool of Chemistry, Physics and Mechanical Engineering, Queensland University of
Technology, Brisbane, QLD 4001, Australia
Abstract
Conventional electrode manufacturing processes for lithium ion batteries involve the use of
toxic organic solvents (such as N-methyl-2-pyrrolidone, NMP). A low cost and green
preparation process for high performance electrodes for sodium ion batteries (SIBs) is
important to address simultaneously the environmental and health risks of production
processes and the shortage of lithium metal. Herein, gum arabic (GA), which is a non-toxic
biodegradable biopolymer, is used as a water soluble binder to design a water-based electrode
preparation process to fabricate α-Fe2O3 electrodes (i.e., α-Fe2O3@GA electrode). The α-
Fe2O3@GA electrode demonstrates better mechanical properties and binding capability than
that of the α-Fe2O3 electrode with poly(vinylidene fluoride) (PVDF) as the binder (α-
Fe2O3@PVDF electrode). Due to these merits, a higher rate and cycling performance of the
α-Fe2O3@GA electrode are achieved compared with the α-Fe2O3@PVDF electrode when
both electrodes are used for SIBs' application. The α-Fe2O3@GA electrode demonstrates high
initial discharge and charge capacities of 2437 and 1102 mA h g-1
at the current density of 0.2
A g-1
. The α-Fe2O3@GA electrode maintains a high reversible discharge capacity of 492 mA
h g-1
at the current density of 5 A g-1
after 500 cycles with a fading rate of 0.08% per cycle
after the first cycle, which indicates a superior cycling performance. The outstanding
performance of the resultant SIBs suggests that the green fabrication process of the α-
Fe2O3@GA electrode would play a critical role in the future battery industry.
1. Introduction
It has been reported that 80% of the annual global energy consumption (4.1 ×1020
J) is
derived from the combustion of non-renewable fossil fuels including natural gas, coal, and
oil.1 On account of the imminent shortage of non-renewable fossil fuels, the excessive
reliance on fossil fuels has caused severe environmental problems and become a heavy
burden to the current and future society. In response to this problem, the requirements for
sustainable energy are swiftly growing. To cope with the ever-increasing energy demand, it is
the holy-grail in the field of sustainable energy to develop high-efficiency energy storage
technologies with high safety, low cost, high energy density, and high power density.2
Among the energy storage technologies, lithium ion batteries (LIBs) have been widely
utilized as a good choice in hybrid electric vehicles and portable electronic devices by virtue
of their high energy density and long life span.3 However, the large-scale applications of
LIBs in energy storage will be curtailed due to the rarity, uneven distribution and high price
(approximately $5000 per ton) of lithium.4 Compared to lithium, sodium has a high natural
abundance (ranked 4th
among the most abundant elements) and is fairly inexpensive
(approximately $150 per ton).5 Situated below lithium in the periodic table, sodium exhibits
similar physical and chemical properties as lithium.6 Sodium is widely considered as a
promising alternative for lithium in large-scale energy storage systems,7 and great efforts
have been devoted to the exploration and development of sodium ion batteries (SIBs). Kim
and co-workers calculated that SIBs are ca. 10% less expensive in total cost than LIBs,
assuming the same energy density.8 The large ionic radius of Na
+ (Na
+ versus Li
+: 1.02
versus 0.76 Å) causes large volume expansion, large polarization and slow reaction kinetics,
which result in low rate capacities and a poor cycle life.10,11
Nevertheless, the superiority in
SIBs development is the similarities in the manufacturing process between NIBs and LIBs.9
Prior work on LIBs can provide a great guidance into the material selection for SIBs, which
can significantly accelerate the technological advancement of SIBs.12
A multitude of efforts
have been devoted to explore suitable electrodes with fast reversible sodiation/desodiation
reaction kinetics and high rate capacities.10,13,14
In general, electrodes are commonly composed of electrode materials, conducting agents,
binders and current collectors. These electrode materials occupy about 80% of the mass in the
entire battery and directly determine the performance of the battery.15
As one of the mature
anode materials, transition metal oxides have captured a multitude of attention owing to their
high theoretical specific capacities (around 1000 mAh g-1
), which are almost three times as
much as that of graphite (372mAh g-1
).16
α-Fe2O3, as the most stable phase of iron oxide, is
considered as a promising active anode material on the basis of its abundant distribution, low
cost, environmental benignity, corrosion resistance, and high theoretical specific capacity
(~1007 mA h g-1
).17
Despite its great promise, the practical application of α-Fe2O3 is still
plagued by intrinsically low conductivity, agglomeration, large volume expansion and
pulverization upon charge/discharge, which eventually result in a low-rate capability and
short-term cyclability.18
Two common methods have been employed to circumvent these
problems. The first approach involves the use of nanomaterials with different dimensions and
morphologies to mitigate the mechanical stress due to volume expansion.19
The other
approach is coating or combining conductive materials (such as carbon nanotubes and
graphene) with α-Fe2O3.20
Essentially, another effective approach is to apply a suitable binder
in the electrode fabrication process for enhancing the adhesion between the active material,
conductive additives and current collector.21
The primary goal of the binder is to glue the electrode materials and conducting
agents on the current collector. Although binders only account for 2–5% of the mass in an
electrode, the electrochemical performances of the electrode strongly depend on the binder,
which can enhance the electrical contact between the active materials and conducting
agents.15,22,23
The ideal binder for application in SIBs should have a low resistance, low cost,
high electrochemical stability, strong bonding strength, and be soluble in green solvents (such
as water).24
Due to the high electrochemical stability, bonding strength, and adhesion of
poly(vinylidene fluoride) (PVDF), PVDF is the most widely used binder for both cathodes
and anodes in the battery industry.25
However, the major drawback of PVDF is that it is
expensive (1.24 AUD per g from Sigma-Aldrich) and only soluble in highly toxic organic
solvents (such as N-methyl-2-pyrrolidone, NMP). NMP is volatile, flammable, explosive, and
expensive (around 1 AUD per mL from Sigma-Aldrich).23
As early as 2001, NMP has been
confirmed as a reproductive toxicant by the Californian Environmental Protection Agency.
Thus, it is compulsory by law to recycle it in the fabrication process of electrodes; however,
the recycling of NMP significantly increases production cost. In order to address this
problem, water-soluble binders have recently drawn much attention owing to their
nontoxicity, high stability, and low-cost.24
Gumarabic (GA) is a cheap, widely available (with
an annual production of over 1 million tons), non-toxic and biodegradable biopolymer from
the exudates of the Arabic Senegal and Acacia Seyal trees.26
GA is a complex mixture
consisting of polysaccharides and glycoproteins.27
Polysaccharides, which have a highly
branched structure, are composed of long carbohydrate monosaccharide units with a great
deal of hydroxyl groups and make up about 90 wt% of the total components of GA.28,29
That
is to say, GA is hydrophilic and enables the fabrication of electrodes in a green aqueous
process. Glycoproteins are high molecular weight proteins containing long oligosaccharide
chains covalently attached to polypeptide side-chains.26
The long spiral glycoprotein chain
behaves like fibers, which can enhance the strength, toughness and energy absorption of
composites.28
As an electrode binder, GA can enhance the tolerance of volume expansion of
electrode materials. Inspired by these properties, PVDF binders can be substituted for the cost
effective and green GA to fabricate high performance electrodes for SIBs.
Herein, a facile and green electrode fabrication process is designed to enhance the
performance of SIBs (Scheme 1). The α-Fe2O3 electrode is prepared via a green GA-water
based electrode fabrication process for SIBs for the first time. GA is soluble in water,
indicating that the electrode fabrication process with GA as binder can refrain from
application of toxic NMP solvent. Owing to the addition of GA, α-Fe2O3 and conductive
additives can be uniformly dispersed with good contact in the electrodes, which contributes to
the charge transfer and enhances the rate performance of SIBs. Furthermore, the
glycoproteins of GA can form a strong network, which can immobilize the α-Fe2O3
nanoparticles and conductive additives on the current collector, and finally contribute to
improving the toughness of the electrode. The mechanical properties of the α-Fe2O3 electrode
are systematically researched via nanoscratch and nanoindentation tests. The α-Fe2O3
electrode with GA as the binder (α-Fe2O3@GA electrode) demonstrates better mechanical
properties and binding capability than that of the α-Fe2O3 electrode with PVDF as the binder
(α-Fe2O3@PVDF electrode). Compared with PVDF as the conventional binder, the GA
binder can effectively enhance the electrochemical performance of α-Fe2O3 electrodes in
SIBs.
Scheme 1. Schematic of the green gum arabic-water based electrode fabrication
process.
2. Experimental
Material fabrication and characterization
All chemicals were of analytical grade and used as received without further purification.
Sodium hydroxide (NaOH), GA, PVDF, sodium carboxymethylcellulose (NaCMC) and poly
(acrylic acid) (PAA) were obtained from Sigma-Aldrich. The ionic liquid, 1-octyl-3-
methylimidazolium chloride ([Omim]Cl), was obtained from the Centre for Green Chemistry
and Catalysis, Lanzhou Institute of Chemical Physics, CAS. According to the literature,30,31
the iron ion-containing ionic liquid, 1-octyl-3-methylimidazolium tetrachlorideferrate(III)
([Omim]FeCl4), was synthesized with [Omim]Cl.
α-Fe2O3 hollow microspheres were synthesized via a simple ionic liquid assisted
solvothermal method according to the report on the previous study by our group.32
In a
typical reaction, the appropriate ionic liquid [Omim]FeCl4 (16 mmol) was dissolved in 80 ml
absolute ethanol to form a homogeneous solution. Then, the appropriate amount of NaOH (24
mmol) was added into the abovementioned solution with vigorous stirring and continued for
30 min. The solution was then placed in a 100 mL Teflon-sealed autoclave and maintained at
140 oC for 24 h and then cooled to room temperature. The final product was separated by
centrifugation, washed with distilled water and absolute ethanol four times, and dried under
vacuum at 60 oC for 12 h before further use.
Electrode preparation
To fabricate the α-Fe2O3@GA electrode, a conventional slurry coating process was
applied. Briefly, GA was firstly dissolved in deionized water to 40 mg ml-1
to produce a
binder solution. α-Fe2O3, carbon black conductive additive and polymer binder were mixed
with a weight ratio of 7 : 1.5 : 1.5. The sonicated homogeneous slurry was uniformly coated
onto copper foil with an area of ca. 1.0 cm2. All the pasted Cu foil electrodes were dried at
60o C in a high vacuum oven overnight to assume the complete removal of water. The areal
mass loading was typically ca. 0.3 mg cm-2
(dried weight of α-Fe2O3). For comparison, α-
Fe2O3@PVDF electrodes were also prepared under the same conditions, and GA binder and
water solvent were replaced with PVDF binder and NMP solvent, respectively.
Electrochemical evaluation
The electrochemical behavior of the resultant α-Fe2O3 electrodes was tested in coin
cells with galvanostatic discharge–charge cycling tests at room temperature (ca. 23 oC) on an
LANDCT 2001A battery tester (Wuhan, China) in the voltage range from 0.001 to 2.5 V vs.
Na/Na+. All current density and specific capacity calculations are based on the active mass of
α-Fe2O3. CR2032 coin-type cells were assembled in an argon-filled glove box (MBRAUN;
O2 and H2O content #0.1 ppm), using a glass fiber (GA-55) membrane as the separator,
sodium metal sheet as the counter electrode, and 1.0 M NaClO4 in ethylene carbonate
(EC)/propylene carbonate (PC) (1 : 1 by volume) as the electrolyte. A CHI 660D
electrochemical workstation (CHI Instrument, Shanghai, China) was used to perform CV
measurements at a scan rate of 0.1 mV s-1
and potential from 0.001 V to 2.5 V. EIS
measurements were conducted over the frequency range from 100 kHz to 10 mHz.
Materials characterisation
X-Ray powder diffraction (XRD) data in the 2q range of 20-80o were collected on a Bruker
D8 diffractometer with high-intensity Cu-Ka radiation (l ¼ 1.54 Å). Surface images of the
composite electrode were collected on a JEOL 7001F field emission scanning electron
microscope (SEM) coupled with energy-dispersive X-ray. Nanoindentation and nanoscratch
tests were conducted using a Hysitron TI 950 nanoindentation system with a Berkovich
indenter (three-sided pyramidal tip with a radius of approximately 150 nm, and 142.3o total
included angles).
3. Results and Discussion
The XRD patterns of the α-Fe2O3@GA electrode, α-Fe2O3@PVDF electrode and pristine
α-Fe2O3 are shown in Fig. 1. Clearly, the XRD patterns of all the samples match the α-Fe2O3
hexagonal structure (JCPDS no. 33-0664), and no other iron-containing compounds are
observed, such as Fe3O4, γ-Fe2O3, and β-FeOOH. This indicates that the crystalline structure
of α -Fe2O3 is not altered when the α-Fe2O3 electrodes are prepared with GA and PVDF as
binders.
Fig. 1. XRD patterns of the α-Fe2O3@GA electrode, α-Fe2O3@PVDF electrode and
pristine α-Fe2O3 powder.
The mechanical properties of the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes were
measured by nanoscratch and nanoindentation tests. The nanoscratch test was conducted
under a normal force of 500 mN and the scratch length was 6 mm. As shown in Fig. 2A, the
friction coefficient of the α-Fe2O3@GA electrode is higher than that of the α-Fe2O3@PVDF
electrode. This indicates that GA possesses stronger binding capability than PVDF.
Compared with the α-Fe2O3@PVDF electrode, the friction coefficient of the α-Fe2O3@GA
electrode is steadier over the entire scratch length due to the improved homogeneity of the α-
Fe2O3@GA electrode.33
The 3D in-situ nanoscratch images of the electrodes obtained via
scanning probe microscopy (SPM) are shown in Fig. 2, which further display the
homogeneity of electrode materials. As shown in Fig. 2(C and D), the 3D in situ nanoscratch
images of the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes are very different after the
nanoscratch test. The depth of the scratch track of the α-Fe2O3@GA electrode (870 nm) is
much smaller than that of the α-Fe2O3@PVDF electrode (1410 nm), which indicates that the
deformation of the α-Fe2O3@GA electrode is much less when subjected to the same normal
force. The increased mechanical strength in the α-Fe2O3 electrodes with GA binder can
provide greater tolerance to volume change than that of the α-Fe2O3 electrode with PVDF
binder. During the charge/discharge process of SIBs, the appropriate mechanical strength will
benefit the overall stability and binding capability. To this end, nanoindentation tests were
conducted on the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes with the loading forces of
500 mN and 1000 mN. The indentation depth of the α-Fe2O3@GA electrode (300 nm) is
smaller than that of the α-Fe2O3@PVDF electrode (700 nm) under 500 mN (Fig. 2B). The
indentation depths of the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes increase to 425 and
1000 nm under 1000 mN (Fig. S1), respectively. Therefore, the hardness of the α-Fe2O3@GA
electrode is approximately two times greater than that of the α-Fe2O3@PVDF electrode.
Fig. 2. (A) Friction coefficient of the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes; (B)
load–displacement curves for the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes under the
force of 500 mN; 3D in situ nanoscratch images of the α-Fe2O3@GA electrode (C) and α-
Fe2O3@PVDF electrode (D) after nanoscratch tests.
The mechanical properties of these two electrodes in electrolyte environment were also
investigated by nanoscratch and nanoindentation tests. The friction coefficient of the α-
Fe2O3@GA electrode is almost the same as the dry condition; however, a significant decrease
is observed in the α-Fe2O3@PVDF electrode (Fig. S2A). The 3D in situ nanoscratch indicates
that the scratch depth in the α-Fe2O3@GA electrode is smaller compared with that in the α-
Fe2O3@PVDF electrode after electrolyte uptake (Fig. S2C and D). The nanoindentation depth
under 500 mN in the α-Fe2O3@PVDF electrode is 60% deeper than that in the α-Fe2O3@GA
electrode after electrolyte uptake (Fig. S2B). All these results indicate that the α-Fe2O3@GA
electrode has better mechanical strength and stability than the α-Fe2O3@PVDF electrode.
In addition, the compatibility and dispersion of the GA binder were compared with those
of the PVDF binder. The surface morphologies of the α-Fe2O3@GA and α-Fe2O3@PVDF
electrodes were obtained via SEM imaging and the related elemental mappings (Fig. 3). The
SEM image and related elemental mappings of the α-Fe2O3@GA electrode indicate a better-
distributed contact between α-Fe2O3 and conductive carbon black on the surface of the α-
Fe2O3@GA electrode. In contrast, the α-Fe2O3 particles and conductive carbon black are
agglomerated on the surface of the α-Fe2O3@PVDF electrode. This demonstrates that GA has
better dispersion compared with that of PVDF. The α-Fe2O3 electrode prepared with the GA
binder is able to form a strong network between the α-Fe2O3 particles and conductive carbon
black, which can probably reduce the resistance between adjacent α-Fe2O3 particles and
promote charge transfer, and thus result in outstanding electrochemical performances.25,34
Fig. 3. SEM images and elemental mappings of the α-Fe2O3@GA (A) and α-
Fe2O3@PVDF electrodes (B).
The α-Fe2O3@GA and α-Fe2O3@PVDF electrodes were tested as anodes of SIBs. The
electrochemical properties of the α-Fe2O3@GA electrode were first evaluated via cyclic
voltammetry (CV) measurements for three cycles in the potential range of 0.001–2.5 V (vs.
Na/Na+) at a scan rate of 0.1 mV s
-1 (Fig. 4A). During the initial cathodic process of the first
cycle, the weak peak at about 1.0 V is associated with sodium ion insertion into the Fe2O3
crystal to form NaxFe2O3 and the reversible reduction reaction of Fe2O3 to form Fe0.19
The
broad peak at about 0.4 V is assigned to the irreversible formation of a solid electrolyte
interface (SEI) film and some side reactions between the electrode materials and electrolyte.35
During the anodic process of the first cycle, the weak anodic peaks at about 0.7 and 1.40 V
are associated with the two-step oxidation of Fe0 (Fe
0 / Fe
2+ and Fe
2+/Fe
3+, respectively).
36 On
account of the heavy mass, large size, and poor mobility of the sodium ion, it is difficult for
strong redox peaks to emerge.17
The diversity between the initial and subsequent scan cycles
is attributed to irreversible processes in the first cycle due to the formation of an SEI film.
The CV curves overlap well after the first cycle, which indicates the superior stability of the
α-Fe2O3@GA electrode for repeated electrochemical reactions. The CV curves of the α-
Fe2O3@PVDF electrode are also shown in Fig. S3(A). The stability of the α-Fe2O3@PVDF
electrode is weaker compared with the α-Fe2O3@GA electrode. Fig. 4B depicts the
representative charge–discharge voltage profiles of the α-Fe2O3@GA electrode at 0.2 A g-1
between 0.001 and 2.5 V. The α-Fe2O3@GA electrode demonstrates high initial discharge
and charge capacities of 2437 and 1102 mA h g-1
. In the first cycle, the irreversible capacity
is mainly due to the decomposition of the electrolyte to form an SEI film,18
which is
consistent with the CV result. The initial capacity of the α-Fe2O3@GA electrode far exceeds
the theoretical capacity of α-Fe2O3 (~1007 mA hg-1
), which can be attributed to the formation
of the SEI film and further Na+ storage via a pseudocapacitance process by virtue of the
charge separation at the metal/Na2O phase boundary.37
The α-Fe2O3@PVDF electrode shows
lower initial discharge and charge capacities (708 and 434 mA h g-1
, respectively) (Fig. S3B).
The rate capabilities of the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes are illustrated in
Fig. 4C. The α-Fe2O3@GA electrode delivers a high reversible capacity of 547 mA h g-1
at a
current density of 5 A g-1
. The reversible capacity of 372 mA h g-1
is also exhibited at a high
current density of 15 A g-1
. 99% of the original capacity (540 mA h g-1
) recovers when the
current density reverts to 5 A g-1
. Moreover, the excellent coulombic efficiency of the α-
Fe2O3@GA electrode is ca. 99% (Fig. 4D). The α-Fe2O3@PVDF electrode only delivers a
low reversible capacity of 12 mA h g-1
at 5 A g-1
(Fig. 4C). The reversible capacities of the α-
Fe2O3@PVDF electrode have no difference at high current densities (10 and 15 A g-1
).
Clearly, the α-Fe2O3@GA electrode exhibits excellent rate performances, which indicate fast
reaction kinetics.
The long-term cycling performance of the α-Fe2O3@GA and α-Fe2O3@PVDF electrodes
was also tested at a current density of 5 A g-1
, as shown in Fig. 5. The α-Fe2O3@GA
electrode delivers an initial discharge capacity of 792 mA h g-1
, which is ca. 80% of the
theoretical capacity (1007 mA h g-1
) and much higher than that of the α-Fe2O3@PVDF
electrode (554 mA h g-1
). It can be observed that the α-Fe2O3@GA electrode maintains the
high reversible discharge capacity of 492 mA h g-1
after 500 cycles with an outstanding
coulombic efficiency (~100%), which indicates a superior cycling performance with a fading
rate of 0.08% per cycle after the first cycle. The α-Fe2O3@GA electrode exhibits an
outstanding cycling performance. The question is whether the structure of the α-Fe2O3@GA
electrode can tolerate the strain associated with Na+ insertion. As revealed in Fig. S4, the
surface morphology of the α-Fe2O3@GA electrode is very well retained after 500 cycles,
which to a certain extent explains the stable cycling. It is interesting that the Na-ion storage
performance of the α-Fe2O3@GA electrode does not significantly change at different mass
loadings (Fig. S5). NaCMC and PAA, as aqueous binders, have been widely used in SIBs. α-
Fe2O3@NaCMC and a-Fe2O3@PAA electrodes have been also prepared, replacing GA
binder with NaCMC and PAA binder, respectively. The friction coefficients of the α-
Fe2O3@NaCMC and α-Fe2O3@PAA electrodes are lower compared with that of the a α-
Fe2O3@GA electrode (Fig. 2A and S6). This indicates that PAA and NaCMC possess weaker
binding capabilities than GA, which thus cause the poor cycling performance of the α-
Fe2O3@NaCMC and α-Fe2O3@PAA electrodes (Fig. 5). The reversible discharge capacity of
the α-Fe2O3@PVDF electrode also quickly fades with the following cycles (Fig. 5); it can
only deliver a reversible discharge capacity of ca. 31 mA h g-1
after 100 cycles. The GA
binder exhibits better capacity retention than the PVDF binder. Fig. S7 and S8 show the
electrochemical impedance spectra (EIS) for the α-Fe2O3@GA and the α-Fe2O3@PVDF
electrodes measured after different cycles at a current density of 5 A g-1
. The Nyquist plots of
the two electrodes show a semicircle at the high-medium-frequency region before cycling.
Note that the diameter of the semicircle for the α-Fe2O3@GA electrode is smaller than that of
the α-Fe2O3@PVDF electrode (355.6 Ω vs. 570.4 Ω). This demonstrates that the α-
Fe2O3@GA electrode possesses outstanding electrical conductivity and small charge-transfer
resistance. The well-distributed contact between α-Fe2O3 and conductive carbon black
benefits sodium-ion diffusion. The GA binder can enhance the interfacial properties of the
electrode and promote charge transfer at the electrode/electrolyte interface, which eventually
result in an outstanding electrochemical performance.25,38,39
After the first cycle, the charge
transfer resistance (Rct) of the α-Fe2O3@GA electrode decreases to 242 Ω and subsequently
reduces to 170.8 Ω after 10 cycles. In the following cycles, the Rct of the α-Fe2O3@GA
electrode is stabilized at about 160 Ω. The Rct of the α-Fe2O3@PVDF electrode during
cycling is unstable (Fig. S8). The stabilization of Rct of the α-Fe2O3@GA electrode confirms
that the sodium-ion diffusion and electron transfer are stabilized after extensive cycling,
which contributes to the enhanced cycling performance of the α-Fe2O3@GA electrode.
Several recent studies related to α-Fe2O3-based anodes for SIBs are summarized in Fig.
6.18,19,35,40–45
Compared with other Fe2O3-based electrodes, the α-Fe2O3@GA electrode
exhibits a high reversible capacity and excellent cycling performance after 500 cycles at the
high current density of 5 A g-1
. The outstanding electrochemical performance of the α-
Fe2O3@GA electrode can be attributed to the application of GA binder. The “fiber in
concrete” provides strong binding capability, reinforced mechanical strength and flexibility.28
GA can enhance the mechanical properties of the electrode, which results in improved
tolerance to volume expansion in the α-Fe2O3 anode during the charge/discharge process. GA
also contributes to the optimum contact between α-Fe2O3 and conductive carbon black, which
can promote charge transfer and result in outstanding electrochemical performances for the α-
Fe2O3@GA electrode for SIBs.
Fig. 4 (A) Cyclic voltammetry curves of the α-Fe2O3@GA electrode; (B) voltage capacity
profiles of the α-Fe2O3@GA electrode at a current density of 0.2 A g-1
; (C) rate cycling
capacities of the α-Fe2O3 @GA and α-Fe2O3 @PVDF electrodes at different current densities;
and (D) coulombic efficiency of the α-Fe2O3 @GA electrode.
Fig. 5 (A) Cyclic performance of the α-Fe2O3 @GA, α-Fe2O3 @PVDF, α-Fe2O3 @PAA
and α-Fe2O3 @NaCMC electrodes at a current density of 5A g-1
; and (B) charge–discharge
curves of the α-Fe2O3@GA electrode at a current density of 5 A g-1
.
Fig. 6. Specific capacity versus cycle number for Fe2O3-based electrodes.
4. Conclusions
In summary, a high performance α-Fe2O3 electrode as an anode for SIBs is fabricated with
GA as the binder via a green water-based electrode fabrication process. The α-Fe2O3@GA
electrode demonstrates better mechanical properties and binding capability than that of the α-
Fe2O3@PVDF electrode. GA can uniformly disperse and strongly contact the α-Fe2O3 and
conductive additives, which result in enhanced charge transfer in the α-Fe2O3 electrode. GA
can also enhance the tolerance of volume expansion in the α-Fe2O3 electrode. Thus, the α-
Fe2O3@GA electrode exhibits a high rate performance and excellent cycling performance.
The α-Fe2O3@GA electrode demonstrates high initial discharge and charge capacities of
2437 and 1102 mA h g-1
at a current density of 0.2 A g-1
. A reversible capacity of 372mA h g-
1 is also exhibited at a high current density of 15 A g
-1. The α-Fe2O3@GA electrode maintains
the high reversible discharge capacity of 492 mA h g-1
at a current density of 5 A g-1
after 500
cycles with a fading rate of 0.08% per cycle after the first cycle, which indicates a superior
cycling performance.
Acknowledgement
This study has been financially supported by the National Natural Science Foundation of
China (no. 21476098, 21506081 and 21506077), Jiangsu University Scientific Research
Funding (15JDG048), University Natural Science Research of Jiangsu (15KJB530004), the
Jiangsu Province Postdoctoral Science Foundation (1501026B), Chinese Postdoctoral
Foundation (2016M590420 and 2016M591787) and a Project Funded by the Priority
Academic Program Development of Jiangsu Higher Education Institutions.
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Supplemental Information
A low cost and green preparation process of -Fe2O3 @gum
arabic electrode for high performance sodium ion battery
Li Xua,b
, Hansinee Sitinamaluwa c, Henan Li
a,c, Jingxia Qiu
a, Yazhou Wang
b, Cheng Yan
c, Huaming
Lia,*
, Shouqi Yuana, Shanqing Zhang
b,*
a Institute for Energy Research, School of Chemistry and Chemical Engineering,
Jiangsu University, Zhenjiang 212013, P. R. China
b Centre for Clean Environment and Energy, Griffith School of Environment,
Gold Coast Campus, Griffith University, QLD 4222, Australia
c School of Chemistry, Physics and Mechanical Engineering, Queensland
University of Technology, Brisbane, QLD 4001, Australia.
*Corresponding authors:
Prof. Huaming Li, email: [email protected]
Prof. Shanqing Zhang, email: [email protected]
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2017
0 200 400 600 800 10000
300
600
900
1200L
oad
(
N)
Indent depth (nm)
-Fe2O
3@GA
-Fe2O
3@PVDF
Fig. S1 Nanoscratch and indentation tests for -Fe2O3@GA and -Fe2O3@PVDF electrodes with
the force of 1000 μN.
0 1 2 3 4 5
0.2
0.3
0.4
0.5
0.6
Fri
ctio
n C
oef
fici
ent
Lateral Displacement (m)
-Fe2O
3@GA
-Fe2O
3@PVDF
(A)
0 200 400 600 800 10000
150
300
450
600
Lo
ad (
N)
Indent depth (nm)
-Fe2O
3@GA
-Fe2O
3@PVDF
(B)
Fig. S2 Nanoscratch tests (A) and nanoindentation tests (B) for -Fe2O3@GA and
-Fe2O3@PVDF electrodes after electrolyte uptake; 3D in-situ nanoscratch image of
-Fe2O3@GA (C) and -Fe2O3@PVDF (D) electrodes after electrolyte uptake by nanoscratch
tests.
0.0 0.5 1.0 1.5 2.0 2.5-0.6
-0.4
-0.2
0.0
0.2
Cu
rren
t (m
A)
Voltage (V)
(A)
0 500 1000 1500 2000 25000.0
0.5
1.0
1.5
2.0
2.5
Vo
ltag
e (V
)
Capacity (mAh g-1
)
1st Cycle
2nd
Cycle
3rd
Cycle
(B)
Fig. S3 (A) Cyclic voltammetry curves of the -Fe2O3@PVDF electrodes; and (B) voltage
capacity profiles of the -Fe2O3@PVDF electrodes at a current density of 0.2 A g-1
.
Fig. S4 SEM images of the α-Fe2O3@GA electrode before (A,B) and after (C,D) 500 cycles.
0 20 40 60 80 1000
200
400
600
800
Mass loading of 1 mg/cm2
Sp
ecif
ic C
apac
ity
(m
Ah
g-1
)
Cycle number
Mass loading of 0.3 mg/cm2
Fig. S5 Cyclic performance of the -Fe2O3@GA electrode at different mass loading.
0 1 2 3 4 50.35
0.40
0.45
0.50
0.55
0.60
Fri
ctio
n C
oef
fici
ent
Lateral Displacement (m)
-Fe2O
3@PAA
-Fe2O
3@NaCMC
Fig. S6 Nanoscratch tests for -Fe2O3@PAA and -Fe2O3@NaCMC electrodes
0 500 1000 15000
300
600
900
1200
1500
Pristine
1st cycle
10th cycle
50th cycle
100th cycle
250th cycle
500th cycle
-Z''
(Ohm
)
Z' (Ohm)
(A)
0 100 200 300 400 5000
200
400
600
Rct (
Ohm
)
Cycle number
(B)
Fig. S7 EIS of the -Fe2O3@GA electrode after different cycles.
0 400 800 1200 16000
500
1000
1500
2000
2500
3000
Pristine
1st cycle
10th
cycle
50th
cycle
100th
cycle
-Z''
(Ohm
)
Z' (Ohm)
(A)
0 20 40 60 80 1000
150
300
450
600
(B)
Rct (
Ohm
)Cycle number
Fig. S8 EIS of the -Fe2O3@PVDF electrode after different cycles.