Photon Factory Activity Report 2022 #40 (2023)

BL-12C, BL-9A/2022G011

Enhancement of Electrical Conductivity and Thermal Stability of Iron- or Tinsubstituted Vanadate Glass and Glass-Ceramics nanocomposite to be used as aHigh-Performance Cathode Active Material in Sodium-Ion Batteries
Ahmed IBRAHIM1, Satoshi WATANABE1, Koki KUBO1, Yuki ARITA1 and Shiro KUBUKI1*1
Department of Chemistry, Graduate Course of Science, Tokyo Metropolitan University
1
1-1 Minami-Osawa, Hachi-Oji, Tokyo 192-0397, Japan
1 Introduction
Rechargeable Li-ion batteries (LIBs) are now
commonly applied as a portable energy source forpowering various electronic devices and household
appliances. Meanwhile, there is still more interest inachieving high-capacity rechargeable batteries for broader
applications like electric vehicles (EVs) while maintaining
their safety and economic feasibility [1]. Although having
high performance with a theoretical capacity of 274 mAh
g-1for LiCoO2 cathode [2], commercially available Li-ion
battery faces the crisis of Li and Co scarcities in the future
because of their abundance in Earth’s crust is only about
20 and 25 ppm respectively [3]. Due to this reason, newsecondary batteries composed of ubiquitous elements withhigh capacity and recyclability are intensively investigated.
Many scientists have recently started looking for new
elements abundant in nature and inexpensive to utilize inbatteries. Many batteries have recently been developed that
apply different chemical elements instead of lithium, suchas Al3+ [4], Ca2+ [5], K+ [6], Mg2+ [7] and Na+ [8]. The Naion battery with a theoretical capacity of 235 mAh g-1 for
NaCoO2 cathode [2] is one of the most promising
candidates for a post-Li-ion battery age because Na has anabundance in Earth’s crust of 23600 ppm, which is muchlarger than that of Li and Co [3]. As a result, the interest in
Na-ion batteries (SIBs) as a viable alternative to LIBs forlarge-scale energy storage has grown significantly since2010 [9].
To develop a Na-ion battery with high capacity,
vanadate glass and ceramics are suitable candidates for thecathode active material because the expected theoretical
capacity is about 400 mAh g-1 [10]. It was reported that
vanadate bronze (MxV2O5, M: Na+, Ag+) showed relatively
high cathode performance when applied in a Na-ion
battery [11]. For example, the capacity of 62 and 83 mAh
g-1 was recorded for Na2.46V6O16 and Na0.33V2O5 under thecurrent density of 1.5 and 0.02 mA g-1, respectively [11].
Also, vanadate glass upper is a promising cathode material
for Na-ion batteries because of the large pore size due tothe amorphous structure and the electrical conductivity ()of about 10-7~10-5 S cm-1. This latter is due to electron
hopping between the vanadium ions of different oxidation
states [12]. In our previous study, a large initial discharge
capacity of 382.3 mAh g-1 was recorded for a Li-ion battery
which contained 15LiO2•10Fe2O3•20SnO2• 5P2O5•70V2O5glass cathode with the electrical conductivity () of 7.4•10-7S cm-1 [13, 14]. The 57Fe- and 119Sn- Mössbauer spectraof this glass showed that FeIII was substituted at thenetwork forming site of vanadium ions with the isomer
shift () of 0.35 mm s-1 and quadrupole splitting () of 0.88mm s-1. In comparison, SnIV accommodated network
modifying sites of Li-ions showing of 0.08 mm s-1 and of 0.52 mm s-1 [15]. Recently, Kubuki et al. found that Naion battery with a cathode of xNa2O•(90-x)V2O5•10P2O5glass with ‘x’ of 5, 25 and 45 mol% showed a large initial
capacity of 307, 184 and 258 mAh g-1, respectively, and asmall irreversible capacity of 86, 6 and 21 mAh g-1 under
the current density of 5 mA g-1 [16]. These results imply
that vanadate glass can be a better cathode active materialfor Na-ion batteries if Fe2O3 or SnO2 is introduced.
In this work, a novel vanadium glass and glassceramics nanocomposite series have been prepared. Therelationships between local structure, physical properties
and cathode-active properties in the Na-ion battery ofFe2O3 or SnO2 substituted Na2O-V2O5-P2O5 glass wereinvestigated to develop a Na-ion battery with a highcapacity and recyclability.
2 Experiment2.1. Sample preparation
2.1.1. Vanadate glasses and glass-ceramicsxNa2O•(85-x) V2O5•10P2O5•5Fe2O3 and xNa2O•(85x) V2O5•10P2O5•5SnO2 (x=5, 25 and 45 mol%) glasses
respectively denoted as xFeV and xSnV were prepared bya conventional melt-quenching method. The mixture ofchemical reagents of Na2CO3(199-01585, Wako),
V2O5(226-00125, Wako), NH4H2PO4(012-03305, Wako),
Fe2O3(096-04825, Wako) and SnO (205-01612, Wako)
was placed into a platinum crucible and melted at 1200 ℃
for 1 h in an electric furnace (NHK-170, Nitto). Darkbrown glass samples were obtained by quenching thecrucible bottom with ice-cold water. For the 57FeMössbauer measurement, 10 mg of 57Fe2O3 (57Fe: 95.90%,ISOFLEX USA) was added to Fe2O3 for the preparation ofxFeV glasses. Additionally, each glass sample was heattreated at 500 ℃ for 100 min in an electrical furnace toprepare glass-ceramics samples.
2.1.2 Na-ion battery
Na-ion battery was assembled in the type of CR2032,
in which Ti- and Ni- mesh fixed the active materials at thecathode and the anode. A separator separated them, and theinside space of the coin cell was filled with electrolyte

Photon Factory Activity Report 2022 #40 (2023)(LIPASTE-P/S1, NaClO4 1mol/L Propylene Carbonatesolution, Tomypure). The cathode of the Na-ion battery
was prepared in the mass ratio of xFeV or xSnV glass andglass-ceramics: acetylene black (ab, 06-0025, StremChemicals) to polytetrafluoroethylene (PTFE) as 70:25:5.
For the preparation, first, the finely pulverized xFeV orxSnV glass/glass-ceramics powder and ab with therespective weight of 500 and 178 mg were mixed with azirconia planetary ball mill (Planet Min(-F), Nagano)under 900 r.p.m for 30 min. The cathode with a weight of30 mg in 1 cm diameter was formed by pressing 95 mg of
the mixture after adding 5 mg of PTFE. Next, an anode wasprepared with 30 mg metallic Na (750-70852, Wako) withthe same dimension.
2.2. Characterization
2.2.1. X-ray diffraction
RINT-TTR III diffractometer measured the X-ray
diffraction (XRD) patterns (Rigaku) using Cu-K X-ray(= 0.1581 nm) generated by setting the tube voltage andcurrent at 50 kV and 300 mA, respectively. The XRD
patterns were recorded between 2 of 10 and 80o at a scan
speed of 5o min-1 and sampling width of 0.02o. The analysisof the XRD patterns was carried out by PDXL2 ver.2.8.1
using the database ICDD PDF-4.
2.2.2. X-ray absorption fine structure (XAFS)
X-ray absorption spectra (XANES / EXAFS)
measurements around the vanadium K-edge were carriedout in transmission mode using a beamline BL-12C at theHigh Energy Accelerator Research Organization (KEK-PF,
1-1 Oh-ho, Tsukuba, Ibaraki, 3050801, Japan). The X-ray
beam from the synchrotron was monochromatized by Si(111) double-crystal and cut the higher harmonic waves by
Ni mirror. The X-ray intensity was recorded by setting
ionization chambers before and after the transmission. The
front chamber was filled with N2+He gas (N2: 30%, He:70 %), while the rear was with Ar+N2 gas (Ar:30 %, N2:70 %). A pellet with 0.8 cm in diameter was prepared bypressing the mixture composed of a 5 mg powdered sample
and 95 mg boron nitride at 5 kN. The software “Athenaversion:0.9.26” was used to analyze obtained spectra.
2.2.3. 57Fe- and 119Sn Mössbauer spectroscopies
57
Fe- and 119Sn- Mössbauer spectra of glasses and glassceramics samples were measured at room temperature by
the conventional constant acceleration method intransmission mode. 57Co in Rh matrix with the activity of925 MBq (MCo7. 123, produced on Oct. 1, 2018, Ritverc),
and 119mSn in CaSnO3 with 185 MBq (MSn9. 222,produced on Jul. 22, 2015, Ritverc) were used for thesources, while -Fe and BaSnO3 served for the referenceof isomer shifts, respectively. The movement of thesources was controlled by a Mössbauer velocity transducer(MVT-1000, Wissel) connected with a digital function
generator (DFG-1000, Wissel) and Mössbauer driving unit
(MDU-1200, Wissel). The -ray signals from the source
through the sample were detected by the proportionalcounter (454131, LND) and amplified by a preamplifier(142IH, ORTEC) and an amplifier (485, ORTEC), which
was applied by 2 kV by high voltage power supply (510,ORTEC). The amplified signals were monitored by apersonal computer attached to a single-channel analyzer(SCA-550, ORTEC) and multi-channel scaler (EASYMCS, ORTEC). Mösswinn 4.0 analyzed the obtained
spectra by Lorentzian fitting.
2.2.4. Differential thermal analysis (DTA)
Differential thermal analysis (DTA) measurements
were performed by Thermo plus TG8120, Rigaku, under
the heating rate of 10 K min-1 and the temperature range
between 100 and 600 ℃. The weight of the glass sample
and -Al2O3 reference was fixed to be 10 mg.
2.2.5. Electrical Conductivity
Both DC and AC conductivity measurements werecarried out to evaluate the electrical property of the glasssamples. The DC conductivity was measured by the fourprobe method using DC current-voltage monitor (6241A,ADC). The resistance (R) was evaluated by measuring
voltage (V) by changing current (I) from -0.3 to 0.3 mA.
The value (R) can be calculated from the slope of the V– I
plot, which obeys Ohm’s law:
R =V/I(1)
The conductivity (was calculated from the relation
 = l / (A R)(2)where l and A are the sample’s longitudinal length (in cm)
and cross-section (in cm2), respectively. AC conductivity
was measured by an impedance analyzer (Alpha-AN
Dielectric Spectrometer, Novocontrol Tech.) in thefrequency range from 10-2 to 106 Hz and at a temperaturefrom 30 to 150 ℃ with 20 ℃ steps. The impedance
spectrum at each temperature was measured twice. The
specimens were prepared as 5 mm in diameter and 1 mm
in thick disk by applying a pressure of 2×103 kg to thepowdered glass samples. Gold electrodes 3.8 mm indiameter were sputtered onto both sides of the disk using
Sputter coater SC7620, Quorum Technologies for theelectrical contact.
2.2.6. Na-ion battery performance
The charge-discharge capacity and recyclability of theNa-ion battery were measured by a constant current
providing device (TOSCAT-3100SK, Toyo-system) in thevoltage range between 0.8 and 3.6 V and a current densityof 0.2 mA cm-2 (= 0.15 mA g-1) and 2 mA cm-2 (=1.5 mAg-1) at 25 ℃. The charge-discharge process was repeated
up to 30 times, including 10 min breaks between the charge
and discharge processes.
3 Results and Discussion
From DTA curves, gradual decreases in glasstransition temperature (Tg) from 266 to 201 ℃ and incrystallization temperature (Tc) from 343 to 260 ℃ wereobserved for xFeV glasses as ‘x’ increased from 5 to 45mol%. The same behaviour, i.e. decrease of Tg from 244 to202 ℃, and decrease of Tc from 307 to 252℃ withincreasing ‘x’ from 5 to 45 mol% observed for xSnV glassceramics. This indicates that the introduction of Na2O
reduces thermal stability. Furthermore, the DC
conductivity at 303K for xFeV and xSnV glasses and glassceramics nanocomposite, before heat treatment, decreases
from 2.82 × 10-5 to 6.61 × 10-7 S cm-1 and from 1.26 × 10-5

Photon Factory Activity Report 2022 #40 (2023)

to 4.27× 10-7 S cm-1, respectively, with increasing Na2O
content from 5 to 45 mol%. The values of electricalconductivity of xFeV and xSnV glasses and glass-ceramics
nanocomposite are higher than in xNa2O•10P2O5•(90x)V2O5, abbreviated as xV glasses, where the electricalconductivity of xV decreased from 5.13× 10-6 to 9.55× 108
S cm-1 with increasing Na2O content from 5 to 45 mol%.
This indicates that the introduction of Fe2O3 and SnO2
produces an increase in electrical conductivity. 57FeMössbauer spectra of xFeV glass could be described by
one doublet and showed a constant isomer shift of 0.25 mms-1 and decreasing quadrupole splitting from 0.73 to 0.63mm s-1, indicating that FeIII ion forms less distorted
tetrahedra upon increasing ‘x’ from 5 to 45 mol%. 119SnMössbauer spectra of xSnV glass-ceramics nanocomposite,
containing also only one doublet, showed an isomer shift
increasing from 0.033 to 0.077 mm s-1 and decreasing
quadruple splitting value from 0.526 to 0.520 mm s-1, withincreasing ‘x’ from 5 to 45 mol%. Additionally, a highcapacity of about 200 mAh g-1 was achieved for the SIB
made of 5FeV glasses as a cathode. This capacity was larger
than the previously reported value of 158 mAh g-1 in
Na1.25V3O8. In particular, the high capacity was maintained
for up to 30 recharging cycles. The same changes wereobserved in the xSnV glass-ceramics nanocomposite.
Therefore, it can be concluded that the introduction of Fe
or Sn ions into the phospho-vanadate glass as a cathodecauses an increase in durability and conductivity, so theseglasses can be considered promising for a highperformance cathode active material with significant
improvement of cyclability in sodium-ion batteries.
4 Conclusion
Sodium Vanadate Phosphate glasses with the addition ofiron or tin oxides and their glass and glass-ceramics
nanocomposite of the composition of xNa2O•(85-x)
V2O5•10P2O5•5Fe2O3andxNa2O•(85-x)
V2O5•10P2O5•5SnO2 (x=5, 25 and 45 mol%) wereinvestigated in as prepared and heat-treated form bydifferent techniques as DTA, XRD, Mössbauer
spectroscopy, DC four-probe method and chargedischarge capacity. The DTA study of xFeV and xSnV
glasses with increasing Na2O content from 5 to 45 mol%showed a decrease in crystallization temperature (Tc) andglass transition temperature (Tg) with increasing Na2Ocontent. Meanwhile, the Tc and Tg increased for xFeV andxSnV as compared to xV. The Tc and Tg were increased
after adding Fe2O3 and SnO2 to the previous glasses system(xV). These results indicated that introducing iron and tin
increases the thermal stability of the glass network. This
indicates that the 3D V-O network basic construction wassplitting into VO5 and VO4 substructures by increasingNa2O content. XRD study of xFeV and xSnV showed anamorphous structure similar to previously investigated
xFeV samples. At the same time, some crystals phases
appeared increasingly in xSnV, forming glass-ceramics
nanocomposite with particle sizes ranging from 28 to 33
nm. The crystallinity increased with increasing Na2O
content. Also, we conclude that the results of XRD of xFeV

showed that after heat treatment, several crystalline phases
formed: Na0.282V2O5, V2O5, Na0.282V2O5, Na1.1V3O7.9,
NaVO3 and Na1.164V3O8. Also, the crystallite size of xFeV
glass-ceramics increased from 26 to 39 (nm) with ‘x’ of 5
to 45 mol%. The crystal size values of xSnV glassceramics nanocomposite decreased from 37 to 30 (nm),with ‘x’ of 5 to 25 mol% Na2O content. 57Fe Mössbauer
spectra of xFeV glasses where 5 mol% of Fe2O3 issubstituted for V2O5 showed a decrease in quadrupole
splitting (Δ) with the increase of Na2O content, indicatinga decrease in the distortion of the iron polyhedral. 119SnMössbauer spectra of xSnV glass-ceramics nanocomposite
where 5 mol% of SnO2 is substituted for V2O5 showed anincrease in Δ with the increase of Na2O content, referringto that the structure transforms from tetrahedral tooctahedral Sn4+. Electrical conductivity for xFeV and xSnV
before heat treatment decreased from 2.82 × 10-5 to 6.61 ×
10-7 S cm-1 and 1.26 × 10-5 to 4.27× 10-7 S cm-1 withincreasing Na2O content from 5 to 45 mol%, respectively.
While 5FeV had higher electrical conductivity than any
other prepared samples, the electrical conductivity of xFeV
samples showed decreasing values as the Na2O content
was increased. This result may be attributed to the decreasein V2O5 content. According to the data obtained fromcharge and discharge capacity, it is concluded that 25FeV(BHT), 5FeV (AHT), 5SnV (BHT), 5SnV (AHT) and25SnV(BHT)
glass
and/orglasses-ceramics
nanocomposite can be considered good candidates forusing as a cathode material for Na-ion batteries because of
the large capacity of 142, 110, 162, 103 and 114 mAh g-1
recorded at room temperature after 30 cycles.
Acknowledgement
The author (SK) expresses his gratitude for the financial
support from the TMU fund for international collaboration
and National Grant-in-aid for Scientific Research(23H02070, 15H03882, 23550238).
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* kubuki@tmu.ac.jp