Arabian Journal of Chemistry (2016) 9, 400–407

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ORIGINAL ARTICLE

Synthesis and ion conduction mechanism on

hot-pressed sodium ion conducting nano composite

polymer electrolytes

* Corresponding author. Tel.: +91 7712120555; fax: +91

7712120666.

E-mail address: chandrassi@gmail.com (A. Chandra).

Peer review under responsibility of King Saud University.

Production and hosting by Elsevier

1878-5352 ª 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

http://dx.doi.org/10.1016/j.arabjc.2013.07.014

Angesh Chandraa,*, Archana Chandra

a,b, K. Thakur

c

a Department of Applied Physics, Shri Shankaracharya Institute of Professional Management & Technology,Raipur 492 015, Chhattisgarh, Indiab Dr. C.V. Raman University, Kargi Road, Kota, Bilaspur, Chhattisgarh, Indiac Department of Chemistry, Govt. Pataleswar College, Masturi 495 551, Chhattisgarh, India

Received 8 October 2012; accepted 13 July 2013Available online 20 July 2013

KEYWORDS

Nano-composite polymer

electrolytes;

Ionic conductivity;

XRD;

FTIR;

SEM;

DSC

Abstract Synthesis and ion conduction studies on SiO2 dispersed hot-pressed sodium ion conduct-

ing nano-composite polymer electrolytes (100 � x)[70PEO:30NaHCO3] + xSiO2, where x is in

wt.%, are reported. The nano-composite polymer electrolytes (NCPEs) are cast by the dispersion

of nano-filler SiO2 using a hot-press method in place of the traditional solution-cast technique.

The effect of nano-filler SiO2 is characterized with the help of some basic ion transport parameters

viz. ionic conductivity, ionic mobility, mobile ion concentration and activation energy measure-

ments. The material characterization and polymer–salt/SiO2 complexation are reported with the

help of XRD, FTIR, SEM, DSC and TGA studies. Based on SPE host and NCPE OCC, a solid

state polymeric battery fabrication and cell-potential discharge characteristics are also reported

at different load conditions.ª 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

1. Introduction

Ion conducting materials comparable to liquid/aqueous

electrolytes, show great technological promises as potential

electrolyte systems for the development of all solid-state elec-trochemical devices viz. batteries, fuel cells, super-capacitors,

memories, electrochromic displays etc. (Van Gool, 1973; Ma-han and Roth, 1976; Chandra, 1981; Laskar and Chandra,1989; Maier, 2000; Maier et al., 2006). A large number of solidstate ionic materials in different phases such as crystalline/

polycrystalline, glassy/amorphous, composite, ceramic, poly-meric etc. and involving a variety of mobile ionic species viz.H+, Li+, Ag+, Cu+, Na+, F�, O2� etc. have been discovered

in the last 3–4 decades. Among the known superionic materi-als, polymeric electrolytes, the conventional as well as micro/nano composites, attracted widespread attention in recent

times. The polymer electrolyte membranes are the most

Synthesis and ion conduction mechanism on hot-pressed sodium ion conducting nano composite polymer electrolytes 401

appropriate candidates to fabricate/flexible/compact/lami-nated all-solid-state thin film batteries (Gray, 1991; Appetecchiet al., 2000, 2001; Bhide and Kariharan 2006; Mohapatra

et al., 2008; Agrawal and Chandra, 2007; Kumar et al.,2007; Chandra et al., 2009; Chandra and Chandra, 2010;Chandra, 2010). Majorities of solid polymer electrolytes

(SPEs) reported so far are mostly PEO-based electrolytes.Polymer electrolytes exhibiting room temperature conductivityP10�4 Scm�1 are considered as good candidates for practi-

cally useful devices. The high-ionic conduction in these systemsis supported by the presence of a high degree of the amorphousphase in the polymeric host materials. However, the conven-tional polymer–salt complex films are usually mechanically less

stable and have poor conductivity behavior. Very recently, ithas been reported that the electrical and mechanical propertyenhancements in polymer electrolytes have been achieved by

different techniques. The addition of nano-fillers such asSiO2, TiO2, Al2O3 etc. in the host polymer electrolytes is oneof the widely used techniques (Croce et al., 1998; Qian et al.,

2001; Dissanayak, 2004; Chandra et al., 2012; Hu et al.,2007; Shukla and Thakur, 2009; Dey et al., 2008, 2009; Laksh-mi and Chandra, 2001, 2002; Choudhary and Sengwa,

2011a,b; Appetecchi et al., 2003). In general, the polymer elec-trolytes prepared via conventional solution–cast/sol–gel tech-niques in a variety of ionic salts are complexed/dissolvedinto different kinds of polymeric hosts. Recently, a hot-press

(extrusion) method which is relatively a least-expensive as wellas much more-rapid procedure is widely being employed toprepare solution free/dry SPEs and NCPEs (Agrawal and

Chandra, 2007; Kumar et al., 2007; Chandra et al., 2009,2011, 2010; Choudhary and Sengwa, 2011a, 2011b; Appetecchiet al., 2003; Agrawal et al., 2008). Among the known polymers,

Poly (ethylene oxide) PEO is widely used as a host polymer be-cause of its ability to dissolve a wide variety of metal salts, itsgood electrochemical stability and good mechanical properties

(Baril et al., 1997; Mohan et al., 2006). Na+ ion salts have sev-eral advantageous merits over other alkali ion salts viz. K+,Li+ etc. They are relatively less expensive, abundantly avail-able and less moisture prone.

To understand the ion conduction mechanisms and deviceapplications of Na+ ion conducting hot-pressed nano-com-posite polymer electrolytes, the present paper reports, synthe-

sis and ion conduction studies on SiO2 dispersed hot-pressedsodium ion conducting nano-composite polymer electrolytes(100 � x)[70PEO:30NaHCO3] + xSiO2, where x is in wt.%.

The material characterization and ion transport parametersare studied using different experimental as well as theoreticalmodels. The solid-state polymeric battery fabrication is also re-ported by using SPE host and NCPE OCC for direct

comparison.

2. Experimental

The AR grade precursor chemicals: poly (ethylene oxide) PEO(105 MW, Aldrich, USA), NaHCO3 (purity >98%, Merck, In-dia), SiO2 (>99.8%, size �8 nm, Sigma, USA) were used for

the synthesis of NCPEs: (100 � x)[70PEO:30NaHCO3] +xSiO2, where x is in wt.%. Firstly the host polymer electrolyte:(PEO:NaHCO3), was synthesized using the hot-press tech-

nique. Details related to the hot-press casting of solid polymerelectrolytes/nano-composite polymer electrolytes were

explained in our earlier communications (Agrawal and Chan-dra, 2007; Kumar et al., 2007; Chandra et al., 2009, 2010;Chandra et al., 2011, 2012). On the basis of the salt-concentra-

tion dependent-conductivity measurements, the composition:(70PEO:30NaHCO3) was identified as the highest conductingpolymer electrolyte, to be used as the first phase host for the

dispersal of nano-sized SiO2 particles as second phase disper-soid. For the synthesis of nano-composite polymer electrolytes(NCPEs), we followed the same hot-press method. The dry

powders of host polymer: (70PEO:30NaHCO3), were homoge-neously mixed with different wt.% ratios of SiO2, heated at�70 �C to form slurry, then hot-pressed between SS blocksresulting finally in a mechanically stable membrane. The con-

ductivity (r) measurements were carried out at room tempera-ture as a function of SiO2 concentration and the optimumconducting composition (OCC) of the nano-composite poly-

mer electrolyte was identified. The ionic mobility (l) and ionictransference number (tion) of SPE host and NCPE OCC mem-branes at room temperature were carried out employing the

Transient Ionic Current (TIC) technique (Chandra et al.,1988; Hashmi and Chandra, 1995). The conductivity (r) –measurements were carried out on different samples using an

LCR-bridge (model: HIOKI 3520-01, Japan). Subsequently,mobile ion concentration (n) was evaluated from ‘r’ and ‘l’data. Material characterization and polymer–salt/SiO2 com-plexation were done with the help of XRD (model: Shimadzu),

FTIR (model: Shimadzu-8400), DSC (model: Perkin Elmer),TGA (model: SDT Universal) techniques. The activation en-ergy (Ea) values were also determined by temperature depen-

dent conductivity studies on different samples of NCPEs.A solid-state polymeric battery was fabricated using NCPE

OCC and SPE host as electrolytes in the following cell config-

uration:

Na-metal foil

(Anode)

95[70PEO:30NaHCO3] + 5SiO2 and

(70PEO:30NaHCO3)

(C+I2+Electrolyte)

(Hot-pressed cathode film)

The cathode in the film form has been prepared by hot-pressing the physical mixture of elemental iodine (I2), the con-

ducting graphite (C) and NCPE in 1:1:1 weight ratios at�50 oC. The cell performances of both the cells were studiedunder different load conditions at room temperature. The cellpotential discharge profiles were drawn as a function of time

and the important cell parameters were calculated from theplateau region of the profiles.

3. Results and discussion

Fig. 1 shows the ‘log conductivity (r) – y’ plot of hot-pressed solid polymeric electrolyte (SPE) films:

(100 � y)PEO: y NaHCO3, where y in wt.% at room tem-perature. Three orders of conductivity increased as the saltNaHCO3 concentration increased. A moderate-sized r –

maxima r (�6.92 · 10�7 Scm�1) was observed at 30 wt.%of NaHCO3 [i.e. for the composition: (70PEO:30NaHCO3)].The addition of salt in PEO resulted in an increase in the

degree of amorphicity and number of mobile ions whichin turn gave rise to an abrupt increase in the conductivityof SPEs. The ionic conductivity of SPE films decreases onfurther addition of salts (beyond 30 wt.%) and this is due

to the ion-ion association effect.

-9

-8.5

-8

-7.5

-7

-6.5

-6

0 10 20 30 40 50 60 70

Log

σσ(S

.cm

-1)

y (wt. %)

RT: 27 oC

Figure 1 ‘Log r – y’ plot of SPE films: (100 � y)PEO: y

NaHCO3, where y in wt.%.

-6.5

-6

-5.5

-5

-4.5

0 2 4 6 8 10 12 14 16 18 20

Log

σσ(S

.cm

-1)

x (wt. %)

RT: 27 oC

Figure 2 ‘Log r – x, plot of NCPE films:

(100 � x)[70PEO:30NaHCO3] + xSiO2, where x is in wt.%.

402 A. Chandra et al.

Fig. 2 shows the ‘log conductivity (r) – x’ plot of nano-

composite polymer electrolyte (NCPE) films:(100 � x)[70PEO:30NaHCO3] + xSiO2, where x is in wt.%.The ionic conductivity (r) of NCPE increases with increasing

the addition of nano-filler SiO2 and two orders of r – enhance-ment were observed from that of the pure SPE host:(70PEO:30NaHCO3). The two maximum conductivity values

of 2.04 · 10�5 and 1.1 · 10�5 Scm�1 were observed at 5 and12 wt.% of dispersal SiO2. However, the maximum conductiv-ity of 2.04 · 10�5 Scm�1 has been observed at 5 wt.% of SiO2

and this has been referred to as optimum conducting composi-

tion (OCC). The existence of two peaks for the NCPEs has al-ready been reported by Lakshmi and Chandra (2001, 2002).

Table 1 Some important ion transport parameters of the hot-press

System r (Scm�1)

SPE host: (70PEO:30NaHCO3) 6.92 · 10�7

NCPE OCC: 95(70PEO:30NaHCO3):5SiO2 2.04 · 10�5

The existence of two r-maxima in the present NCPEs can beattributed to two separate percolation thresholds involvingtwo different kinds of mobile species: cation (Na+) and anion

(HCO�3 ). The ionic conductivity enhancement in NCPE is alsodue to the Lewis acid–base reaction and it is also well acceptedby various workers (Croce et al., 1998; Qian et al., 2001; Dis-

sanayak, 2004; Chandra et al., 2012; Hu et al., 2007; Shuklaand Thakur, 2009). The room temperature values of some ofthe ionic parameters: r, l, n, tion are listed in Table 1. It is obvi-

ous from the table that the increase in room temperature con-ductivity of NCPE OCC is due to the increase in mobility andnumber of mobile Na+ ions in the system.

Fig. 3 shows the two types of possible cross linking: (a)

transient cross-linking of polymer segments via cation-cationinteraction and (b) transient cross-linking of polymer segmentsvia cation–anion interaction. The formation of inter/intra –

molecular transient cross linking of PEO chains with saltand filler SiO2 is responsible for the conductivity enhancementin present NCPEs. This type of behavior in PEO-based sys-

tems was also reported by various workers (Wieczorek et al.,1998; Albinson and Mellander, 1993; Thakur, 2011).

Fig. 4 shows the XRD patterns of pure PEO, pure NaH-

CO3, SPE host: (70PEO:30NaHCO3), pure SiO2, and NCPEOCC: 95[70PEO:30NaHCO3] + 5SiO2. The characteristicpeaks of pure PEO are observed at 2h = �17o, 23o and 39o.The intensity of the peaks of pure PEO drastically decreases

after the polymer–salt complexation, as shown in Fig. 4c.The decrease in the intensity of the peaks is indicative of an in-crease in amorphous nature of the polymer–salt complex. A

new peak at 2h = �20o has been observed in the diffractionpattern by the addition of nano-filler SiO2 (as shown inFig. 4e) and it is indicative of the formation of nano-composite

polymer electrolyte. Finally, it can be concluded from the fig-ure that some of the peaks of pure PEO became relativelybroader as well as less-prominent/ feeble after salt complexa-

tion and SiO2 dispersal. This is usually attributed to the in-crease in the degree of amorphicity and confirmation ofpolymer–salt complexation as well as to some extent, dispersalof filler SiO2 in the pure polymeric host (Dissanayak, 2004;

Agrawal et al., 2008; Chandra et al., 2013).Fig. 5 shows the FTIR spectra for the pure PEO, NaHCO3,

SPE host: (70PEO:30NaHCO3) and NCPE OCC: 95[70PEO:

30NaHCO3] + 5SiO2. The most important absorption fea-tures present in PEO are CH2 bending at 1466 cm�1, C–Cstretching at 1147 cm�1, C–O–C asymmetric stretching at

962 cm�1, CH2 asymmetric rocks at 843 cm�1. It is clearlyindicated from the spectra that the width of the C–O–C andC–H stretching modes decreases after addition of salts at�1100 and �2900 cm�1 respectively and broadening of peaks

at �820 cm�1. The small changes in the spectra at �980 and�1600 cm�1 were also observed after the addition of nano-fil-ler SiO2. Some additional bands appeared in the SPE host and

NCPE OCC other than the pure PEO and salt NaHCO3 suchas between 4000–3200, 2700, 2400 cm�1. The band in the

ed SPE host and NCPE OCC at room temperature.

l (cm2V�1s�1) n (cm�3) tion

(4.1 ± 1)·10�3 1.05 · 1015 �0.92(8.8 ± 1) · 10�3 1.44 · 1016 �0.92

Figure 3 Schematic presentation of two kinds of cross-linking in

NCPEs: (a) polymer segments via cation-cation interaction and (b)

polymer segments via cation–anion interaction.

Figure 4 XRD patterns: (a) NaHCO3, (b) pure PEO, (c) SPE

host: (70PEO:30NaHCO3), (d) pure nano-sized SiO2 and (e)

NCPE OCC: [95 (70PEO:30NaHCO3) + 5SiO2].

Synthesis and ion conduction mechanism on hot-pressed sodium ion conducting nano composite polymer electrolytes 403

spectral region 700–400 cm�1 has been affected with dispersionof nano filler SiO2 in the host polymer matrix. This may be due

to changes in the chemical environment and ion–ion interac-tions associated with HCO�3 . Some other changes have alsobeen observed in the ion spectral region of 1000–700 cm�1,

due to filler dispersion. The appearance of these extra bandsand all the above results indicated that the complexation ofPEO-salts/filler and such type of interesting behavior were also

suggested in the literature (Kumar et al., 2007; Albinson andMellander, 1993; Thakur, 2011).

Fig. 6 shows the Scanning Electron Micrograph (SEM)images of SPE host: (70PEO:30NaHCO3) and NCPE OCC:

95[70PEO:30NaHCO3] + 5SiO2. It can be clearly seen fromthe figures the smooth surface morphology observed in SPEhost and NCPE OCC while the pure PEO shows the rough

morphology structure (Mohapatra et al., 2008; Chu et al.,2003). The smooth surface morphology in SPE host andNCPE OCC is closely related to the reduction of PEO

crystallinity.Fig. 7 shows the DSC thermograms for the pure PEO, SPE

host: (70PEO:30NaHCO3) and NCPE OCC: 95[70PEO:30-NaHCO3] + 5SiO2. The broad endothermic peak was

observed in polymeric films at �54–70 oC and it is correspond-ing to the melting point temperature of pure PEO (�70 oC),

SPE host and NCPE OCC films. It is clearly shown from thefigure that the melting temperature (Tm) of pure host decreasedfrom 70 to 66 oC and this is usually observed in various PEO-

based systems (Qian et al., 2001; Bhide and Kariharan, 2006;Wen et al., 1996; Stephan et al., 2009). In case of NCPEOCC the Tm decreased up to 54 oC. It is due to the interaction

between the PEO backbone and the filler SiO2 that has affectedthe main chain dynamics of the SPE host. A possible mecha-nism for this behavior could be understood with the creation

of additional hopping sites and favorable conducting pathwaysfor ionic migration. DSC analysis clearly indicated that NCPEOCC shows a low degree of crystallinity and high amorphousnature, which is responsible for increase in ionic conductivity.

The degree of crystallinity (v) has been calculated by assumingpure PEO being 100% with the equation v ¼ ðDHf=DHfoÞ(where DHfo is the heat of fusion of pure PEO and DHf is

the heat enthalpy related to salt in PEO). Table 2 lists the ob-tained degree of crystallinity (v) and melting temperature (Tm)of polymeric films. The decrease in the degree of crystallinity

Figure 7 DSC thermograms: (a) pure PEO, (b) SPE host:

(70PEO:30NaHCO3) and (c) NCPE OCC: [95

(70PEO:30NaHCO3) + 5SiO2].

Table 2 Melting temperatures (Tm), degree of crystalline (v)and weight loss for pure PEO, SPE host and NCPE OCC films.

Systems Tm (oC) v (%) Weight loss (%)

Pure: PEO 70 100 95

SPE host:

(70PEO:30 NaHCO3)

66 83 76

NCPE OCC: 95(70PEO:

30NaHCO3):5 SiO2

54 48 60

Figure 5 FTIR spectra: (a) pure PEO, (b) pure NaHCO3, (c)

SPE host: (70PEO:30NaHCO3) and (d) NCPE OCC: 95

(70PEO:30NaHCO3) + 5SiO2.

404 A. Chandra et al.

and melting temperature in NCPE OCC is indicative of an in-

crease in amorphousness.Fig. 8 shows the Thermo Gravimetric Analysis (TGA)

curves for pure PEO, SPE host: (70PEO:30NaHCO3) and

NCPE OCC: 95[70PEO:30NaHCO3] + 5SiO2. It can beclearly observed from the figure that the total weight loss forpure PEO is larger as compared to both SPE host and NCPE

OCC. The total weight loss for NCPE OCC is �60% and SPEhost is �76% whereas for pure PEO is �95%. The thermalstability of polymer is improved when the nano-filler SiO2 is

doped and it is indicative of the formation of hot-pressedNCPEs, similar type of behavior was also reported by Deyet al. (2009).

The ionic transference number (tion) of SPE host and NCPE

OCC has been evaluated using the dc polarization technique.The variation of current with time is shown in Fig. 9. tionwas calculated using the following equation:

Figure 6 SEM images: (a) SPE host: (70PEO:30NaHCO3)

tion ¼ 1� IeIT

ð1Þ

where Ie is the electronic current and IT is the total current ofthe cell: [SS/NCPE OCC and SPE host/SS]. tion � 0.92 ob-

tained by using the above Eq. (1) and is indicative that the

and (b) NCPE OCC: [95 (70PEO:30NaHCO3) + 5SiO2].

0

20

40

60

80

100

120

140

-5 5 15 25 35 45Time (min.)

Cur

rent

( μA

)

RT: 27 oC

Figure 9 ‘Current vs. time’ plot for the cell: SS // NCPE OCC //

SS.

-6.5

-6

-5.5

-5

-4.5

-4

-3.5

2.6 2.8 3 3.2 3.41000/T (K-1)

Log

σ (S

/cm

)

Figure 10 ‘Log r � 1/T’ plots for hot-pressed NCPEs:

(100 � x)[70PEO:30NaHCO3] + xSiO2, where x = 0 ( ), 2 ( ),

5 ( ), 10 ( ), 14 ( ) is in wt.%.

Figure 8 TGA curves: (a) NCPE OCC: [95 (70PEO:30NaH-

CO3) + 5SiO2], (b) SPE host: (70PEO:30NaHCO3) and (c) pure

PEO.

3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35-3.5

-3.0

-2.5

-2.0

-1.5

(1000/T) K-1

16.0

16.5

17.0

17.5

18.0

Log

μ (c

m2 V-1

s-1)

Log

n (c

m-3 )

Figure 11 ‘Log l – 1/T’ and ‘Log n – 1/T’ plots for NCPE OCC:

[95 (70PEO:30NaHCO3) + 5SiO2].

Synthesis and ion conduction mechanism on hot-pressed sodium ion conducting nano composite polymer electrolytes 405

majority of charge carriers (�92%) are cations Na+ and onlya very small contribution (�8%) of anion HCO�3 .

Fig. 10 shows the ‘log r – 1/T’ plots for hot-pressedNCPEs: (100 � x)[70PEO:30NaHCO3] + xSiO2, where x var-

ies from 0 to 14. ‘Log r – 1/T’ plots exhibited straight linebehavior below at 60 oC and then upward changes have beenobserved in the slope after �60 oC, which is due to the well-

known semi-crystalline to amorphous phase change/meltingpoint temperature of PEO-based polymers, as reported inour earlier communications (Chandra et al., 2010, Chandra

et al., 2011, 2012). The straight line portions of SPE hostand NCPE OCC below the transition temperature (�60 oC)governed the following Arrhenius type equations:

SPE host : log rðTÞ¼ 8:19� 10�4 expð�0:185=kTÞ ½Scm�1� ð2Þ

NCPE OCC : log rðTÞ¼ 7:74� 10�1 expð�0:154=kTÞ ½Scm�1� ð3Þ

where Ea = 0.18 and 0.15 in eV are the activation energy val-ues for hot-pressed SPE host and NCPE OCC respectively.The slight decrease in the activation energy for NCPE OCC

from that of SPE host is indicative of increased mobility as aconsequence increase in the degree of amorphicity of PEOafter nano-filler SiO2 dispersal.

Fig. 11 shows ‘log l – 1/T’ and ‘log n – 1/T’ plots for the

hot-pressed NCPE OCC: 95[70PEO:30NaHCO3] + 5SiO2.The linear portion of this Fig. 11 can be expressed by the fol-lowing Arrhenius type equations:

lðTÞ ¼ 4:64� 10�10 expðþ0:43=kTÞ ½cm2V�1s�1� ð4Þ

406 A. Chandra et al.

nðTÞ ¼ 9:26� 1025 expð�0:59=kTÞ ½cm�3� ð5Þ

where the numerals 0.43 and 0.59 in eV are the energies in-volved in the two thermally activated processes and can be des-ignated as the energy of migration (Em) and energy of

formation (Ef) respectively. (�) ve or (+) ve signs appearingin the argument of the exponential terms indicate the increaseor decrease respectively of the factor on the left hand side of

the equation with increasing temperature. It can be obviouslynoted from the figure that ionic mobility (l) decreased andmobile ion concentration (n) increased as the temperature

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40

Tim

Volta

ge (V

)

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40Tim

Volta

ge (V

)

Cell: I

Cell: II

Figure 12 Cell potential discharge profiles for the solid state poly

(C + I2 + Electrolye), (b) cell II: Na // (70PEO:30NaHCO3) // (C + I2room temperature.

Table 3 Some important cell parameters of the cells (I and II) at r

Cells Load

(kX)

Working voltage

(V)

Current density

(lA cm�2)

I 100 2.3 1.84

50 1.0 0.80

II 100 1.9 1.52

50 1.0 0.80

increased. The decrease in ionic mobility with increasing tem-

perature is probably due to the decrease in the preferred con-ducting pathways and/ or blocking effect created by the nano-filler SiO2 at higher temperatures while the increase in mobile

ion concentration is most probably a consequence of dissocia-tion of more number of Na+ ions from the ionic salt NaHCO3

as temperature increases.Fig. 12 shows the cell potential discharge profiles for the

cells I and II under different loads viz. 100 and 50 kX at roomtemperature. The Open Circuit Voltage (OCV) �2.7 V was ob-tained for both the cells. It can be clearly noticed that except

50 60 70 80 90 100

e (h)

50 60 70 80 90 100e (h)

RT: 27 oC

RT: 27 oC

meric cells: (a) cell I: Na // [95(70PEO:30NaHCO3) + 5SiO2] //

+ Electrolye), under 100 kX (d) and 50 kX (m) load resistances at

oom temperature.

Discharge Capacity

(lA h)

Power density

(mW kg�1)

Energy

density (mWh kg�1)

161 33.7 2358

25 6.28 157.2

114 22.7 1362

25 6.28 157.2

Synthesis and ion conduction mechanism on hot-pressed sodium ion conducting nano composite polymer electrolytes 407

for the initial potential drop, OCV value remained practicallystable for �65 and �27 h. when discharged through 100 and50 kX respectively (i.e. during a low current drain state). How-

ever, the cell potential decreased relatively faster when dis-charged through 50 kX load (i.e. during higher current drainstates). Direct comparison of cell parameters, is listed in

Table 3. On the basis of these studies, it can be observed thatthe cell I, based on newly synthesized NCPE, performed fairlysatisfactorily especially during low current drains as compared

to cell II.

4. Conclusions

A new Na+ ion conducting nano-composite polymer electro-lyte (NCPE) membrane: 95 (70PEO:30NaHCO3) + 5SiO2

(wt.%) has been synthesized employing a hot-press/solvent

free dry technique. Dispersal of nano filler SiO2 particles intothe polymer electrolyte host: (70PEO:30NaHCO3) resulted inan enhancement in the electrical as well as mechanical proper-ties of the film. The ionic conductivity enhancements were ex-

plained with the help of ionic mobility (l), mobile ionconcentration (n) studies and different models. The polymer–salt/SiO2 complexation has been successfully explained with

the help of XRD, FTIR, DSC and TGA studies. The ionictransference number measurements indicated the fact thatapproximately 92% of the total Na+ ions take part in conduc-

tion process in the hot-press synthesized NCPE system. Solidstate polymeric batteries were fabricated using NCPE OCCand SPE host as electrolyte and the cell potential dischargecharacteristics have been studied under a different load condi-

tion at room temperature.

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