polymers Article
Enhancement of Plasticizing Effect on Bio-Based Polyurethane Acrylate Solid Polymer Electrolyte and Its Properties Tuan Syarifah Rossyidah Tuan. Naiwi 1 , Min Min Aung 1,2, * , Azizan Ahmad 3,4 , Marwah Rayung 2 , Mohd Sukor Su’ait 4 , Nor Azah Yusof 1 and Khine Zar Wynn Lae 5 1 2 3 4 5
*
Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, UPM Serdang 43400, Selangor, Malaysia;
[email protected] (T.S.R.T.N.);
[email protected] (N.A.Y.) Higher Education Centre of Excellence (HiCoE), Institute of Tropical Forestry and Forest Products, University Putra Malaysia, UPM Serdang 43400, Selangor, Malaysia;
[email protected] School of Chemical Science and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia;
[email protected] Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia, UKM Bangi 43600, Selangor, Malaysia;
[email protected] Department of Chemistry, Yangon University, Yangon11041, Myanmar;
[email protected] Correspondence:
[email protected] or
[email protected]
Received: 6 September 2018; Accepted: 9 October 2018; Published: 12 October 2018
Abstract: Polyurethane acrylate (PUA) from vegetable oil has been synthesized and prepared for solid polymer electrolyte. Polyol has been end-capped with Toluene 2,4-Diisocyanate (TDI) followed by hydroxylethylmethylacrylate (HEMA) in a urethanation process to produce PUA. The mixtures were cured to make thin polymeric films under UV radiation to produce excellent cured films which exhibit good thermal stability and obtain high ionic conductivity value. 3 to 15 wt. % of ethylene carbonate (EC) mixed with 25 wt. % LiClO4 was added to PUA to obtain PUA electrolyte systems. PUA modified with plasticizer EC 9 wt. % achieved the highest conductivity of 7.86 × 10−4 S/cm, and relatively improved the linear sweep voltammetry, transference number and dielectric properties. Fourier Transform Infrared Spectroscopy (FTIR) and dielectric analysis were presented. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), followed by X-ray Diffraction (XRD) and morphology have been studied. The addition of plasticizer to the polyurethane acrylate shows significant improvement in terms of the conductivity and performance of the polymer electrolyte. Keywords: biopolymer electrolyte; plasticizer; solid polymer; polyurethane acrylate; conductivity
1. Introduction Polyurethane acrylate (PUA) is a copolymer that consists of urethane linkage (-NHCOO-) and the acrylate group in its molecular structure. It was synthesized from polyol and isocyanate with the addition of acrylate compound [1–5]. Commonly, PUA has been synthesized from polyether or polyester polyol of synthetic polymers as they have reactive sites to react with the isocyanate group. The properties of vegetable oil that can be modified to polyol have been studied to produce bio-based polymer PUA [6–10]. Urethane acrylate is mostly applicable for coating purposes with in situ polymerization via UV and is curable in the presence of reactive diluent and free radical photoinitiator. Urethane acrylate oligomer has been studied specifically for the UV curable polymer. Most of the studies on acrylate polymers are related to the UV radiation preparation method that have very high speeds of curing that lead to high productivity, lower energy consumption, reduction of volatile organic compound Polymers 2018, 10, 1142; doi:10.3390/polym10101142
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emission, reducing risk of fires, improving aspects of occupational safety and health and so forth [11,12]. Moreover, monomers derived from vegetable oil are environmentally friendly and low-cost compared to the synthetic polymer from petroleum. The enhancement in ionic conductivity of polymer electrolyte can be achieved by the addition of either organic or inorganic filler into electrolyte systems such as TiO2 , SiO2 , Al2 O3 , ethylene carbonate (EC), and propylene carbonate. [13,14]. Inorganic filler promotes more free lithium ions and produces more amorphous regions in the electrolyte for the transfer of charge carriers. Meanwhile, organic filler acts as a plasticizer to reduce the glass transition temperature, Tg , of polymer, which helps to increase the segmental motion of the polymer backbone and generate free volume. Therefore, the ions can easily migrate through the void, resulting in a better ionic conductivity [15]. Plasticizers with high electric constant and low viscosity behavior enable them to be incorporated with a polymer host to facilitate the formation of dissociated ions [16]. Incorporation of a plasticizer into a polymer system is also a way to reduce crystallinity and increase the amorphous phase of a polymer electrolyte, thereby increasing the mobility of ions, and generating higher ionic conductivity [17]. The addition of EC increases the degree of salt dissociation and ionic mobility [18]. As the concentration of plasticizer increases, the amorphous nature of the electrolyte increases, thus improving the ionic conductivity of the polymer electrolyte. Plasticizers of poly(ethylene glycol) (PEG) with different molecular weight, PEG200 , PEG400 , and PEG600, showed that the conductivity of a polymer electrolyte decreases as molecular weight of plasticizer increases [19]. PEG200 has the largest concentration of free ions associated only with the anti-symmetric stretching mode in the matrix polymer. A longer chain length contributes to more oxygen, implying that lithium ions and few ions are available for ionic conduction, hence lower the ionic conductivity in the system. The smooth surface of the polymer electrolyte also observed for polymer with the highest conductivity in the present of EC. P(GMA-co-MMA) matrix has good flexibility of polymer chains with inclusion of EC and consequently improved the ionic conductivity [20]. In this research, biopolymer polyurethane acrylate electrolyte was synthesized from polyol of Jatropha oil in the presence of TDI and HEMA. The effect of plasticizing on conductivity and thermal stability of biopolymer electrolyte were studied. PUA modified with plasticizer EC 9% has the highest conductivity of 7.86 × 10−4 S/cm and the dielectric analysis was studied. The synthesized PUA was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The thermal behavior of the biopolymer electrolyte was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and followed by X-ray Diffraction (XRD) and morphology study. 2. Experimental 2.1. Material Jatropha oil was obtained from Biofuel Bionas, Kuala Lumpur, Malaysia and the oil was used as received. Hydrogen peroxide 30% (H2 O2 ) and N,N-dimethylformamide (DMF) (98%) were purchased form R&M chemicals, Petaling Jaya, Malaysia. Formic acid (98%) and tolulene 2,4-diisocyanate (TDI) (98%) were purchased from Acros Organic, New Jersey, US). EC, 2-Hydroxyethylmethyl acrylate (HEMA) (99%), 1,6-Hexanediol diacrylate (HDDA), 2-methylpropiopropanone (Darocure) and lithium perchlorate (LiClO4 ) was obtained from Sigma Aldrich, St.Louis, Missouri, USA. All chemicals were used as received without further purification. 2.2. Preparation of PUA Oligomer The PUA oligomer was prepared by reaction of the Jatropha oil-polyol with TDI in a four-necked round-bottom flask equipped with a mechanical stirrer, a thermometer, and a reflux condenser under nitrogen atmosphere. DMF was used as solvent. The TDI was added in a dropwise manner at 60 ◦ C and the reaction was continued for two hours to complete the NCO-terminated pre-polymer after confirmation by FTIR [21]. After that, the reaction was cooled down to 40 ◦ C and HEMA was added
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in a dropwise manner. After complete adding of HEMA, the temperature was raised to 60 ◦ C and thereaction reactionwas wascontinuously continuously stirred one hour. From time time, DMF was added control stirred forfor one hour. From time to to time, DMF was added to to control thethe viscosity mixture since DMF solvent boiling point was high, was control usage [21].InIn viscosity of of thethe mixture since DMF solvent boiling point was high, asas was control forfor usage [21]. this this the study, theratio molar oftopolyol to TDI andused HEMA usedThe is 1:1:1. The PUA resulting was study, molar of ratio polyol TDI and HEMA is 1:1:1. resulting was PUA transparent transparent yellowish in color. and yellowishand in color. Preparation PUAFilm FilmElectrolyte Electrolyte 2.3.2.3. Preparation of ofPUA The PUA solid polymer electrolyte prepared by UV-curing and solution-casting The PUA solid polymer electrolyte filmfilm was was prepared by UV-curing and solution-casting method. method. Initially, the PUA was mixed together with HDDA (monomer) and Darocure Initially, the PUA was mixed together with HDDA (monomer) and Darocure (photoinitiator) for (photoinitiator) for 3 25 h. In flask, 25perchlorate wt. % of lithium perchlorate and ECinwas dissolved 3 h. In separate flask, wt.separate % of lithium salt and EC was salt dissolved acetone for 12 in acetone for 12 h. The amount of EC used was varied from 0–15 wt. % to find the optimum h. The amount of EC used was varied from 0–15 wt. % to find the optimum conductivity of the conductivity of the[21]. polymer [21]. were The two mixtures thenand mixed together and stirredfor polymer electrolyte Theelectrolyte two mixtures then mixed were together stirred continuously continuously for another 12 h to obtain a homogenous mixture. After that, the mixture was casted on another 12 h to obtain a homogenous mixture. After that, the mixture was casted on a Teflon mold a Teflon mold (diameter 100 mm) and irradiated 3 times by a medium-pressure mercury vapor lamp (diameter 100 mm) and irradiated 3 times by a medium-pressure mercury vapor lamp from IST-UV from IST-UV Dryer (Switzerland) at 7.5 mA with the conveyor speed at 3 m/s. The solid film shows Dryer (Switzerland) at 7.5 mA with the conveyor speed at 3 m/s. The solid film shows a uniform and a uniform and transparent appearance as depicted in Scheme 1. The solid film was stored in a transparent appearance as depicted in Scheme 1. The solid film was stored in a desiccator for one day to desiccator for one day to remove the residual solvent and undergo further characterization study. remove the residual andas undergo further The were designated The samples were solvent designated PUA/25Li with characterization 0 wt. %, 3 wt. %, study. 9 wt. %, 12 samples wt. % and 15 wt. % EC as in PUA/25Li with 0 wt. %, 3 wt. %, 9 wt. %, 12 wt. % and 15 wt. % EC in all characterizations. all characterizations.
Scheme Theprocess processofofpreparing preparingsolid solid polymer polymer electrolyte 4 and EC. Scheme 1. 1.The electrolytefrom fromPUA PUAand andLiClO LiClO 4 and EC.
CharacterizationofofSolid SolidPolymer PolymerElectrolyte Electrolyte 2.4.2.4. Characterization Infrared spectrawere wererecorded recordedwith with an an ATR-FTIR, ATR-FTIR, Perkin US) in in Infrared spectra PerkinElmer Elmermodel model1650 1650(Waltham, (Waltham, US) −1 −1 − 1 − 1 wavenumberrange rangebetween between4000 4000toto280 280cm cm with scanning scanning resolution was thethe wavenumber resolutionof of44 cm cm . TGA . TGA was ◦ Cto performed using Mettler TA300(Polaris (PolarisPkwy, Pkwy,Columbus ColumbusOh, Oh, US) US) from with a heating performed using Mettler TA300 from 50 50°C to600 600°C◦ C with a heating ◦ C/min rate °C/minininaadynamic dynamicnitrogen nitrogen atmosphere atmosphere at DSC Mettler rate of of 1010 at 20 20 mL/min mL/minflow flowrate. rate.Meanwhile, Meanwhile, DSC Mettler TA300 was used to study the phase transition of the polymer electrolyte during the heating process. TA300 was used to study the phase transition of the polymer electrolyte during the heating process. The study was conductedbetween between−−50 atat1010 °C◦ C scanning ◦ C(with ◦ C, The study was conducted 50 ◦°C C (for (for 0% 0% EC), EC),00°C (withEC) EC)toto150 150°C, scanning rate under nitrogen atmosphere at 10 mL/min flow rate. The structural information was studied by rate under nitrogen atmosphere at 10 mL/min flow rate. The structural information was studied by using XRD model D-5000 Siemen (Tempe, AZ, USA). The diffraction angle, 2θ, is in the range of 3 to using XRD model D-5000 Siemen (Tempe, AZ, USA). The diffraction angle, 2θ, is in the range of 3 to 60 at 0.004 °/S. Scanning electron microscopy, SEM model JEOL JSM-7600F (Singapore) was used to 60 at 0.004 ◦ /S. Scanning electron microscopy, SEM model JEOL JSM-7600F (Singapore) was used to investigate the surface morphology of the PUA electrolyte. Prior to analysis, the sample was coated investigate the surface morphology of the PUA electrolyte. Prior to analysis, the sample was coated with gold to avoid electrostatic charging. with gold to avoid electrostatic charging.
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Electrochemical Study The room-temperature ionic conductivity of the PUA SPE was studied by using Electrochemical Impedance Spectroscopy (EIS) using Hioki 3532-50 LCR Hi-tester (Nagano, Japan) that was interfaced to a computer in the frequency range of 50 Hz to 500 kHz. The film was cut into disc shapes with 16 mm diameter and 5.13 cm2 contact surface area. The film thickness was 0.05 cm. The film was sandwiched between two stainless steel (SS) electrodes. The ionic conductivity, σ, was calculated based on the following equation: l σ S cm−1 = (1) A × Rb where l is the thickness of the film, A is the area and Rb is the bulk resistance obtained from the EIS measurement. The ratio which gave the highest conductivity will be subjected to temperature dependence study from room temperature, 303 to 383 K. The same ratio was used to study the electrochemical properties of the polymer electrolyte by using Linear Sweep Voltammetry (LSV) and Transference Number (TN) employing Princeton, Versa-STAT-4. For LSV, the sample was assembled in a symmetric SS/PE/Li configuration using 10 mV scan rate in the range of 0–7 V. Sample preparations were carried out in the glove box with less than 0.1 ppm H2 O and O2 . For TN measurement, the PUA electrolyte was assembled in a SS/PE/SS and polarized under a fixed direct current voltage with 0.1 V. The value of tion was calculated from the current versus time plot by applying Wagner’s polarization technique following the equation: tion =
Io − Iss Io
(2)
Iss Io
(3)
tele =
where tion is ionic TN, tele —electronic TN, I0 —initial current, Iss —the steady-state current. The equations for dielectric constant (εr ), dielectric loss (εi ), real electrical modulus (Mr ), imaginary electrical modulus (Mi ) and tan σ were written as below: εr =
Zi ωCo Zr2 + Zi2
(4)
εi =
Zr ωCo Zr2 + Zi2
(5)
Mr = Mi =
ε2r
εr + ε2i
(6)
ε2r
εi + ε2i
(7)
tan δ =
εr εi
(8)
where CO = εO A/t, εO = permittivity of free space and ω = 2πf. 3. Results and Discussion The FTIR spectra of PUA with 25 wt. % LiClO4 in different concentrations of EC are presented in Figure 1. The foremost interest in the PUA polymer electrolytes are region-free and hydrogen bonded –NH stretching mode (3800–3100 cm−1 ), oxygen atoms of the carbonyl (C=O) (1750–1710 cm−1 , 1650 cm−1 ), amine functional groups (C–N and N–H) (1550–1500 cm−1 ) and ether and ester group (C-O-C) (1300–1000 cm−1 ) stretch of acrylate group [22]. The carbonyl group of first band was electrostatically interacting within the polymer chain and with Li+ ions, and the latter is interacting
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through H-bonds. The absorption peak of free and H-bonded –NH stretching of PUA have shifted −1PEER −1 to2018, Polymers 10, cm x FOR 5 of 18 salt (3500 cm 3700 ) andREVIEW showed an increase in the wavenumber when doping with lithium + due to coordination of Li ions to nitrogen atoms of the –NH groups. The peak between 1072–1173 cm−1 (3500 cm−1 to 3700 cm−1) and showed an increase in the wavenumber when doping with lithium salt was assigned for the C-O-C for atoms acrylate urethane groups experienced a shift due to coordination ofstretching Li+ ions to band nitrogen of group. the –NHThe groups. The peak between 1072–1173 −1 to 1740 cm−1 ). When adding salt, H-bonded C-O-C groups become to a lower frequency (1750 cm cm−1 was assigned for the C-O-C stretching band for acrylate group. The urethane groups experienced −1). When free due to an of Li+ (1750 ions with the1740 ether and its ability to form C-O-C H-bonds [23,24]. a shift tointeraction a lower frequency cm−1 to cmoxygen adding salt, H-bonded groups The PUA region of lithiumofsalt withwith an addition of EC inand theitsregion atoms of become freeinteraction due to an interaction Li+ ions the ether oxygen abilityof to oxygen form H-bonds 1 ) stretch [23,24]. (C=O) The PUA region interaction of lithium salt with addition of EC (1300–1000 in the regioncm of −oxygen the carbonyl (1750–1710 cm−1 ) and ether and esterangroup (C-O-C) −1) and ether and ester group (C-O-C) (1300–1000 cm−1) atoms of the carbonyl (C=O) (1750–1710 cm of acrylate group. The peak of polymer electrolyte shows no significant changes of wavenumber in stretch of acrylate group. The electrolyte shows no addition significant of the region of both carbonyl group andpeak esterofofpolymer stretch acrylate group upon of changes EC. However, wavenumber in the region of both carbonyl group and ester of stretch acrylate group upon addition an incorporation of EC into polymer electrolyte showed high intensity peak of C=O carbonyl group of of EC. However, an incorporation of EC into polymer electrolyte showed high intensity peak of C=O PUA. Thus, the plasticizer is essentially a filler dispersed in polymeric composite [16]. With addition of carbonyl group of PUA. Thus, the plasticizer is essentially a filler dispersed in polymeric composite lithium[16]. saltWith the peaks shifted toward frequency and thehigher peak of C=O of PUA gave a high-intense, addition of lithium salthigher the peaks shifted toward frequency and the peak of C=O of − 1 strong,PUA and gave sharpa high-intense, peak at 1719–1712 . Thepeak addition of 25 wt.cm%−1.lithium shifted intensity about strong,cm and sharp at 1719–1712 The addition of the 25 wt. % lithium −1 7 cm−1shifted . This the showed an interaction occurred between carbonyl group with lithium salt. The oxygen intensity about 7 cm . This showed an interaction occurred between carbonyl group with atoms lithium act as electron form coordinate bondsand with thecoordinate lithium in the structure salt. The donor oxygenatoms atoms and act as electron donor atoms form bonds with the of lithium the structure of polymer host. Thus,to vibration shifted to a lower wavenumber. polymer host.inThus, vibration frequency shifted a lowerfrequency wavenumber.
Figure 1. FT-IR spectra of PUA electrolyte ofEC ECplasticizer. plasticizer. Figure 1. FT-IR spectra of PUA electrolyteatatdifferent different loading loading of
The effect that that plasticizing has polymer electrolyte is shown in 2. Figure The effect plasticizing hason onPUA/LiClO PUA/LiClO4 4polymer electrolyte is shown in Figure The 2. −4 −5 at 25 wt. % −4 ohm, ohm, The spectra resistancefor for2525wt. wt. at ~10 decreasing spectrashows showsthe thebulk bulk resistance %% ECEC at ~10 decreasing to ~10−5to at ~10 25 wt. % of EC. of EC. A A graph graph of of log log conductivity conductivityversus versusconcentration concentration added Figure 3 shows higher of of ECEC added in in Figure 3 shows thethe higher conductivity achieved 9 wt. ECand and the in Table 1. The of EC of conductivity achieved withwith 9 wt. %%ofofEC the value valueisisillustrated illustrated in Table 1. addition The addition showedfluctuating fluctuating value value of nono apparent trend can be However, the EC showed of conductivity conductivityand and apparent trend canobserved. be observed. However, −4 − optimum conductivity 7.86 × 10 S/cm had achieved with 9 wt. % of EC, which was one order higher 4 the optimum conductivity 7.86 × 10 S/cm had achieved with 9 wt. % of EC, which was one order than 0 wt. % EC. The conductivity decreased with addition of 3 to 6 wt. % of EC then the conductivity higher than 0 wt. % EC. The conductivity decreased with addition of 3 to 6 wt. % of EC then the increased and decreased again at 12 wt. % of EC. EC acts as an organic plasticizer in the polymer conductivity increased and decreased again at 12 wt. % of EC. EC acts as an organic plasticizer electrolyte, enhancing the conductivity of the polymer electrolyte [20]. With the addition of 9 wt. % in the EC, polymer electrolyte, enhancing might the conductivity thedielectric polymerconstant electrolyte With the the conductivity improvement be due to theof high of the[20]. plasticizer, addition of 9 wt. % EC, the conductivity improvement might be due to the high dielectric constant increasing the number of ions by weakening the columbic force between anion and cation salts. of the plasticizer, number ions by weakening the columbic force anion Therefore,increasing dissociationthe of salts in theofsystem increased and more free Li+ ions can between be produced [16].and + + ions and dissociation EC moleculesofcan transfuse into the increased polymer matrix and increase chain cation More salts. LiTherefore, salts in the system and more free Li the ions can be segmental mobility, leading enhancement conductivity. However, the conductivity starts to produced [16]. More Li+ ions andtoEC molecules of can transfuse into the polymer matrix and increase the chain segmental mobility, leading to enhancement of conductivity. However, the conductivity
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decrease, since its saturated level for EC results in less space for Li ions to move within the polymer starts to decrease, since its saturated level for EC results in less space for Li ions to move within the matrix [20]. The ionic conductivity could be explained by interaction between polymer LiClO4 and polymer matrix [20]. The ionic conductivity could be explained by interaction between polymer LiClO4 EC. The main three interactions among them are ion-ion interaction between Li+ cations and ClO4and EC. The main three interactions among them are ion-ion interaction between Li+ cations and + anions; ion-dipole interaction between Li cations and chlorine in polymer; and ion-molecule ClO4 - anions; ion-dipole interaction between Li+ cations and chlorine in polymer; and ion-molecule interaction between Li++ and EC. Polymer LiClO4-EC with different compounds of polymer –Li++, interaction between Li and EC. Polymer LiClO4 -EC with different compounds of polymer –Li , polymer –Li++/EC and Li+/EC exist by these interactions. The oxygen of C=O in EC is an electron donor polymer –Li /EC and Li+ /EC exist by these –interactions. The oxygen of C=O in EC is an electron which participates in competition with ClO4 and –polymer. The Li+/EC +interaction exists not only donor which participates in competition with ClO and polymer. The Li /EC interaction exists not 4 between Li+ and+ another two oxygen atoms of C=O group, but also between Li++and another two only between Li and another two oxygen atoms of C=O group, but also between Li and another two oxygen atoms in the ring structure of EC. Moreover, Li++/EC interaction plays an important role in the oxygen atoms in the ring structure of EC. Moreover, Li /EC interaction plays an important role in the conductivity of the polymer LiClO4-EC system. The addition of EC leads to the formation of a Li++/EC conductivity of the polymer LiClO4 -EC system. The addition of EC leads to the formation of a Li /EC complex and enhances the flexibility of polymer chains by decreasing the crystalline fraction of the complex and enhances the flexibility of polymer chains by decreasing the crystalline fraction of the polymer Li+ complex [25]. polymer Li+ complex [25]. Table 1. Ionic conductivity of PUA electrolyte with EC plasticizer. Table 1. Ionic conductivity of PUA electrolyte with EC plasticizer.
EC, wt. % EC, wt. % 0% 0% 3% 3% 6% 6% 9% 9% 12% 12% 15% 15%
−1) Conductivity, σ (S cm Conductivity, σ (S cm−1 ) 6.40 × 10−5 −5 6.40 3.51×× 10 10−−66 3.51 × 10 −6 7.05 × 10 7.05 × 10−6 7.86×× 10 10−−44 7.86 7.59×× 10 10−−66 7.59 5.95 5.95×× 10 10−−66
Figure 2. Nyquist plot of PUA electrolyte with EC plasticizer. Figure 2. Nyquist plot of PUA electrolyte with EC plasticizer.
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Figure 3. Log conductivity of PUA electrolyte at varied concentrations of EC plasticizer. Figure Figure 3. 3. Log Log conductivity conductivity of of PUA PUA electrolyte electrolyte at at varied varied concentrations concentrations of of EC EC plasticizer. plasticizer.
The conductivity of polymer electrolyte at ambient temperature to 100 ◦ C was fitted using The of electrolyte at temperature to °C fitted The conductivity conductivity of polymer polymerdependence electrolyte ionic at ambient ambient temperature to 100 100 °C was was fitted using using Arrhenius theory. The temperature conductivity was study to analyze mechanism of Arrhenius theory. The temperature dependence ionic conductivity was study to analyze mechanism Arrhenius theory. The temperature dependence ionic conductivity was study to analyze mechanism ion transportation in polymer electrolytes. The log σ versus 1000/T grafted in Figure 4 showed linear of transportation in electrolytes. The of ion ion transportation in polymer polymer electrolytes. The log log σ σ versus versus 1000/T 1000/T grafted grafted in in Figure Figure 44 showed showed plot well-fitted with Arrhenius theory as follows: linear plot well-fitted with Arrhenius theory as follows: linear plot well-fitted with Arrhenius theory as follows: exp[E [Eaaa/kT] /kT] σσ exp σ= ==AA A exp [E /kT]
(9) (9) (9)
where A is constant which is proportional to the amount of charge carriers, Eaa is activation energy, where A A is is aaa constant constant which which is is proportional proportional to to the the amount amount of of charge charge carriers, carriers, E where a is activation energy, kk is Boltzmann constant and T represents the absolute temperature in K. is Boltzmann Boltzmann constant constant and and TT represents representsthe theabsolute absolutetemperature temperaturein inK. K. k is
Figure Arrhenius plot ionic conductivity PUA/LiClO /EC Figure (9 wt. wt. %) %) electrolyte. electrolyte. Figure4.4. 4.Arrhenius Arrheniusplot plotofof ofionic ionicconductivity conductivityofof ofPUA/LiClO PUA/LiClO444/EC /EC (9 (9 wt. %) electrolyte.
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The pseudo-activation energy, Ea of the polymer electrolyte was determined from the Arrhenius graph. –Ea/k is denoted on the graph and the activation is 0.29 eV. The of activation The pseudo-activation energy, Ea ofslope the polymer electrolyteenergy was determined fromvalue the Arrhenius energy is denoted related toonthe conductivity. The higher ionic conductivity onlyvalue has lower activation graph. –Eafor /k is theionic graph slope and the activation energy is 0.29 eV. The of activation energy and vice versa. This indicated that the higher conducting electrolyte requires only a smaller energy for is related to the ionic conductivity. The higher ionic conductivity only has lower activation energy to start a migration process [22]. Based on reported study, the lower E a provides a smaller energy and vice versa. This indicated that the higher conducting electrolyte requires only a smaller bandtogap which allows process the conducting ion on to move more easily a freeEion-like state, hence increase energy start a migration [22]. Based reported study, theinlower a provides a smaller band ionic conductivity. This phenomenon also related to the conduction process, and lower Ea is required gap which allows the conducting ion to move more easily in a free ion-like state, hence increase ionic for the migration of ions in aalso highly conducting sample. Since migration of ions tremendously conductivity. This phenomenon related to the conduction process, and lower Ea isisrequired for affected by polymer segmental motion, an electrolyte with a lower E a facilitates ionic movement, the migration of ions in a highly conducting sample. Since migration of ions is tremendously affected then increases conductivity [23]. The current was observed as a function of time by which polymer segmental motion, an electrolyte withDC a lower Ea facilitates ionic movement, which then on application of a fixed[23]. voltage SS/polymer electrolyte/SS cells. The current versus increases conductivity The across DC current was observed as a function ofnormalized time on application of time plots was shown in Figure 5 for PUA electrolyte with EC. Based on the plotted graph, the initial a fixed voltage across SS/polymer electrolyte/SS cells. The normalized current versus time plots current decreased due to with depletion of ionic in thegraph, electrolyte and becomes wastotal shown in Figure 5 forwith PUAtime electrolyte EC. Based onspecies the plotted the initial total constant in thewith fullytime depleted cell was polarized and current when electrons current decreased due tosituation. depletionThe of ionic species in the electrolyte andflows becomes constant migrate thesituation. electrolyteThe andcell interface under a and steady-state condition. is because ionic in the fully across depleted was polarized current flows whenThis electrons migrate currents through anand ion-blocking electrode fall rapidly condition. with time ifThis the electrolyte primarily ionic across the electrolyte interface under a steady-state is because is ionic currents [24]. The value of TN for PUA electrolyte is 0.99, and a PUA electrolyte with plasticizer is 0.95, through an ion-blocking electrode fall rapidly with time if the electrolyte is primarily ionic [24]. respectively. This clearly reveals that Li salt complexes with PUA and PUA electrolyte with The value of TN for PUA electrolyte is 0.99, and a PUA electrolyte with plasticizer is 0.95, respectively.EC becomes an almost perfect ionic conductor. ionic TN This clearly reveals that Li salt complexes with PUAThe andreported PUA electrolyte withofECbiopolymer becomes anelectrolyte almost containing corn starch by Liew & Ramesh (2013) [26] is 0.98 with ionic conductivity of 3.21 × 10−4 S perfect ionic conductor. The reported ionic TN of biopolymer electrolyte containing corn starch −1 −1 accepted a biopolymer The electrochemical window of polymer by cm Liew accepted & Rameshfor(2013) [26] is 0.98electrolyte. with ionic conductivity of 3.21 ×stability 10−4 S cm for electrolyte was obtained by LSV technique. The sample was sandwiched between SS/PUA a biopolymer electrolyte. The electrochemical stability window of polymer electrolyte was obtained metal at sandwiched ambient temperature. The potential was scanned between 1.0 to by electrolyte/Li LSV technique. The electrodes sample was between SS/PUA electrolyte/Li metal electrodes at 5.0 −1 − V at a temperature. sweep rate of 5The mVpotential s . The stability windows are increased from to 4.1 Vrate for PUA electrolyte ambient was scanned between 1.0 to 5.0 V at1.6 a sweep of 5 mV s 1. addition of 9 wt. % EC as plasticizer, in Figure 6. Based the results, these PUA Thewith stability windows are increased from 1.6 to as 4.1shown V for PUA electrolyte withon addition of 9 wt. % EC electrolytes are similar to those of Monisha (2016), which could be used for energy storage devices as plasticizer, as shown in Figure 6. Based on the results, these PUA electrolytes are similar to those of [27]. (2016), which could be used for energy storage devices [27]. Monisha
Figure 5. Normalized polarization current versus timetime for PUA/LiClO (9 wt. %) electrolyte. 4 /EC Figure 5. Normalized polarization current versus for PUA/LiClO 4/EC (9 wt. %) electrolyte.
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Figure (9 wt. wt. %) %)electrolyte. electrolyte. Figure6.6.Linear LinearSweep SweepVoltammetry VoltammetryofofPUA/LiClO PUA/LiClO44/EC /EC (9
In In this this research, research, EC EC was was added added as as plasticizer plasticizer to to increase increase ionic ionic conductivity, conductivity, σ, σ, in in the the PUA PUA solid solid polymer electrolyte. This was because EC (small organic molecules) had high dielectric constant polymer electrolyte. This was because EC (small organic molecules) had high dielectric constant and and low To prove and log log dielectric dielectric loss loss (log (log εεii)) low vapor vapor pressure pressure [1]. [1]. To prove that, that, log log dielectric dielectric constant constant (log (log εεrr)) and versus versus log log frequency frequency for for different different percentages percentages of of EC EC plasticizer plasticizer with with fixed fixed Li Li content content (25% (25% Li) Li) were were plotted and shown in Figure 7. From the figure, it can be seen that log ε and log ε had higher values r i plotted and shown in Figure 7. From the figure, it can be seen that log εr and log εi had higher values at at low low frequency frequency of of about about 22 Hz. Hz. This This may may be be due due to to electrode electrode polarization polarization effect effect [28], [28], while while at at high high frequency, it was observed that log ε and log ε had lower values because of the periodic reversal frequency, it was observed that log εrrand log εi ihad lower values because of the periodic reversal of of electric field occurring at high speed, caused to have insufficient to diffuse electric field occurring at high speed, andand thisthis caused the the ionsions to have insufficient timetime to diffuse into into the electric field [28]. Furthermore, with the addition of EC plasticizer, it will cause a large the electric field [28]. Furthermore, with the addition of EC plasticizer, it will cause a large amount of amount of charge carriers to localize along with mobile ions. Thus, it will help to improve the value of charge carriers to localize along with mobile ions. Thus, it will help to improve the value of ionic ionic conductivity [1]. Figure 8 presented real electrical modulus r ) and imaginary conductivity [1]. Figure 8 presented the realthe electrical modulus (Mr) and(M imaginary electrical electrical modulus modulus (M ) with log frequency for different ratio percentages of EC plasticizer added intothe thefixed fixed Li i frequency for different ratio percentages of EC plasticizer added into (Mi) with log Li content. Both M and M had a value of almost zero with a long tail when approaching high frequency. r i content. Both Mr and Mi had a value of almost zero with a long tail when approaching high frequency. This This happened happened because because of of the the electrode electrode polarization polarization phenomena, phenomena, which which makes makes it it an an insignificant insignificant contribution [28]. The presence of the long tail at low frequency (1.5 Hz to 4.5 Hz) observed contribution [28]. The presence of the long tail at low frequency (1.5 Hz to 4.5 Hz) observed that that there there was a large capacitance associated with the electrodes [29]. Other than that, at high frequency, both Mr was a large capacitance associated with the electrodes [29]. Other than that, at high frequency, both and M observed increased linearity. From Figure 8, it can be seen that M peak was much higher than r Mr peak was much higher Mr andi Mi observed increased linearity. From Figure 8, it can be seen that M This This was due thetosamples of PUA solidsolid polymer electrolyte beingbeing an ionic conductor [29]. i peaks. than Mi peaks. was to due the samples of PUA polymer electrolyte an ionic conductor Figure 6 compared the variation of tan σ with log frequency for different additions of percentages [29]. Figure 6 compared the variation of tan σ with log frequency for different additions of of EC plasticizer the Li content. 9, From it can Figure be seen9,that thebe tanseen σ peaks were gradually percentages ofinto EC plasticizer into From the LiFigure content. it can that the tan σ peaks shifted to 3.5 Hzshifted to 5.0 Hz (higher Withfrequency). increase inWith EC plasticizer, canplasticizer, help to increase were gradually to 3.5 Hz tofrequency). 5.0 Hz (higher increase initEC it can the amorphous content in the PUA solid polymer electrolyte [27]. As the tan σ peaks shifted help to increase the amorphous content in the PUA solid polymer electrolyte [27]. As the tan σtoward peaks the right-hand it will reduce relaxation (τ), whichtime can(τ), be demonstrated from Table 2. shifted toward side, the right-hand side,the it will reduce time the relaxation which can be demonstrated − 4 From Figure2.9,From PUAFigure 25% Li9,+ PUA 9% EC hadLithe lowest τ which was 0.0955 × 10wass0.0955 with highest from Table 25% + 9% EC had the lowest τ which × 10−4 s ionic with −4 S cm−1 . conductivity up to 7.86 × 10 −4 −1 highest ionic conductivity up to 7.86 × 10 S cm .
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Figure 7. Variation of (a)oflog log frequency PUA/LiClO electrolytes. r and Figure 7. Variation (a)εlog εr (b) andlog (b)εlog εi versus log frequency PUA/LiClO 4/EC electrolytes. 4 /EC i versus
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Figure 8. Variation of (a) electrical modulus (Mr )(M and (b) imaginary electrical modulus (Mi )(M ofi) of Figure 8. Variation ofreal (a) real electrical modulus r) and (b) imaginary electrical modulus PUA/LiClO electrolytes. 4 /EC 4/EC electrolytes. PUA/LiClO
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Figure 9. Variation of tan σ with log log frequency at different percentage of EC Figure 9. Variation of tan σ with frequency at different percentage of plasticizer. EC plasticizer. Table 2. Relaxation parameter for different ratio percentage of EC plasticizer. Table 2. Relaxation parameter for different ratio percentage of EC plasticizer. EC Content (%) Maximum Peak (Hz) τ (×10−4 s)
EC Content (%) Maximum Peak (Hz) τ (×10−4 s) 3 4.04 0.912 3 4.04 0.912 6 3.56 2.75 9 6 5.02 3.56 0.09552.75 12 9 3.46 5.02 3.470.0955 15 12 3.61 3.46 2.45 3.47 18 3.78 1.66 15 3.61 2.45 18 3.78 1.66 TGA is the preferred technique for evaluation of the thermal stability of a polymer and indicates TGA is the preferred technique for evaluation of the thermal of a polymer indicates the decomposition of the polymer at various temperatures. From stability Figure 10a, the pureand PUA has ◦ C up to ◦ Chas the decomposition of the polymer various temperatures. From by Figure 10a, stage the pure PUA decomposed in three steps beginning at at 53.4 186.8 ◦ C, followed a second at 199.7 ◦ C with Tin three ◦ C. PUA decomposed steps beginning at 53.4 up to 186.8 °C,◦ Cfollowed by a second stage at 199.7 to 277.2 had started to°C decompose at 53 due to decomposition of solvent max 253.8 to 277.2about °C with Tmax °C. loss PUA[30]. hadThere started to still decompose at 53 °Cof due to decomposition and°C moisture 12.26 wt.253.8 % mass was a small quantity solvent degraded at of solvent and moisture about wt.7.43 % mass loss [30].supports There was a small quantity ofPUA solvent second stage since the mass loss 12.26 is about wt. %, which thestill decomposition of pure ◦ degraded second stage since mass loss about 7.43 wt.of%, which the decomposition at 278 C withatmajor loss 90 wt. % the whenever theispure polymer PUA hassupports decomposition at single pure PUA at 278 °C loss 90 wt. % et whenever polymer of [31–33]. PUA has stepofbeginning, as reported by with Digarmajor et al. (2002), Santhosh al. (2006)the and pure Salih et al. (2014) ◦ C was decomposition at single step beginning, as at reported by Digar et al. (2002), Santhosh et al. (2006) and From DTG, the major decomposition of PUA Tmax 415.8 attributed to the decomposition Salih et al. (2014) [31–33]. Fromthe DTG, thesegment major decomposition of PUAand at Tmax was attributed of organic polymer chains, both hard of urethane linkage the415.8 soft °C segment from to the decomposition of organic chains, the hard segment of urethane and the polyether or polyester. The analysispolymer of TG and DTG both thermograms was stated in Table 3.linkage From DTG soft segment polyetheroformaximum polyester.decomposition, The analysis of TTG thermograms was stated in in Figure 10b, thefrom temperature , forDTG ruptures of urethane linkage maxand Table 3.upon Fromincreased DTG in Figure 10b, the temperature of maximum decomposition, Tmaxsegment , for ruptures decreased concentration of the salt. The degradation of the PUA hard was of ◦ C but decreased linkage decreased increased of the The degradation of the PUA 415urethane to 300 ◦ Cupon for PUA 25 wt.concentration % lithium salt. Thissalt. phenomenon was suggested hard segment was 415Tg°Cvalue but decreased toelectrolyte. 300 °C for PUA 25 wt. % lithium salt. Thisofphenomenon to be related to the low of polymer The dipole-dipole interaction polymer wasweakened suggested when to be related thewas lowadded, Tg value of polymer electrolyte. The dipole-dipole interaction chains lithiumtosalt where it softens the backbone of the polymer chain of polymer chains weakened when lithium salt was added, where it softens the backbone of the and reduces the Tg of the polymer. The same pattern result was obtained by Ugur et al., 2013 [34]. ◦ polymer chain and reduces the Tg of the The same pattern result wasatobtained bytoUgur Based on Figure 10a,b, the decomposition of polymer. PUA electrolyte with EC was started 50 C due the et [34]. and Based on Figure 10a,b, the decomposition of PUA electrolyte with EC was started at 50 lossal., of 2013 moisture solvent at the first stage of decomposition with 6–20% weight loss. There were °C decomposition due to the loss of moisture and solvent at the firstinstage with loss 6–20% loss. three stages of polymer, as evaluated Tableof3.decomposition The major weight of weight polymer There three◦ C decomposition stages of evaluated in Tablepreviously. 3. The majorAs weight loss of with Tmaxwere 250–350 was decomposition of polymer, urethane as linkage, as mention reported polymer with Tmax 250–350 °C was decomposition of urethane linkage, as mention previously. As reported by Ramesh & Ling, 2010 [35], the increase of plasticizer reduces the thermal stability of the
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by Ramesh & Ling, 2010 [35], the increase of plasticizer reduces the thermal stability of the polymer polymer matrix. this case, thewith polymers withlower EC have lower decomposition temperature matrix. In this case,Inthe polymers EC have decomposition temperature comparedcompared to the to the without one. without one.
Figure 10. (a) andand (b) DTG thermograms of neat PUA andand PUA/LiClO electrolytes. Figure 10. TG (a) TG (b) DTG thermograms of neat PUA PUA/LiClO 4/EC electrolytes. 4 /EC
Table 3. Analysis of TG and DTG of PUA and PUA/LiClO4/EC electrolytes. Composition
PUA 0 wt. % Li 0 wt. % EC
Decomposition Stage d1 d2 d3 d1 d2
Onset Final Degradation Temp (°C) 53.38 186.75 199.67 277.18 278.02 646.83 55.98 208.62 209.87 371.83
Temp of Max Decomposition (°C)
Weight Loss (%)
79.43 253.75 415.77 107.07 304.55
12.26 7.43 90.45 19.62 44.59
Residue (%) 0 17.34
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Table 3. Analysis of TG and DTG of PUA and PUA/LiClO4 /EC electrolytes. Composition
PUA 0 wt. % Li
Decomposition Stage d1 d2
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d1
0 wt. % EC
3 wt. % EC
3 wt. % EC
wt.EC % EC 9 wt.9 %
15 wt. % EC
15 wt. % EC
dd32 dd13 dd21 d dd32 3 dd1 1 dd22 dd33 d d44 d dd11 2 dd23 dd34 d4
Onset
Final
Degradation Temp (◦ C) 53.38 199.67 278.02
Temp of Max Decomposition (◦ C)
Weight Loss (%)
Residue (%)
79.43 253.75 415.77
12.26 7.43 90.45
0
107.07 304.55 447.94
19.62 44.59 18.1
186.75 277.18 646.83
55.98 208.62 372.66371.83579.84 209.87 372.66 53.67 579.84108.96
447.94 82.88 53.67 82.88 112.41108.96146.72 129.37 112.41 146.72 129.37 215.72 544.02 345.07 215.72 544.02 345.07 52.12 132.48 97.77 52.12 132.48 97.77 134.24 233.3 233.3 185.55 134.24 185.55 234.36 294.33 234.36363.81363.81 294.33 368.36 585.98 424.8 368.36 585.98 424.8 54.7 141.67 97.51 54.7 141.67 97.51 146.95 230.59 187.2 146.95368.37230.59 187.2 234.49 305.06 353.33 433.31 234.49520.54368.37 305.06 * All ◦353.33 C values are ±0.05 ◦ C deviation. 520.54 433.31
6.58 1.99 67.93 16.92 9.94 39.45 9.57 11.03 8.12 42.57 11.09
18.117.34 6.58 1.99 21.14 67.93 16.92 9.94 23.76 39.45 9.57 11.03 8.1218.46 42.57 11.09
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21.14
23.76
18.46
* All °C values are ±0.05 °C deviation.
The thermal behavior of polymer electrolyte with difference concentration of EC was obtained by DSC Theatthermal of polymer electrolyte with11difference concentration of EC was thermogram Figure behavior 11 and illustrated in Table 4. Figure showed that the PUA sample onlyobtained exhibited by DSC thermogram at Figure 11 and illustrated◦ in Table 4. Figure 11 showed that the PUA sample the glass transition temperature measured at −18.1 C showed similar result with Feng et al. (2012) [36]. only exhibited the glass transition temperature measured at −18.1 °C showed similar result with Feng Each samples of polymer electrolyte showed one Tg with addition of Li salt. Digar et al. suggest three major et al. (2012) [36]. Each samples of polymer electrolyte showed one Tg with addition of Li salt. Digar types of interaction of polymer electrolyte. (1) interaction of the ether oxygen with the Li+ ions, leading et al. suggest three major types of interaction of polymer electrolyte. (1)+interaction of the ether to theoxygen formation of transient crosslinks between the polyether chains via the Li ions, which restricts the with the Li+ ions, leading to the formation of transient crosslinks between the polyether chains segmental (2)which interaction of urethane –NHmotion; and carbonyl groups with the Li+ ions to inter via themotion; Li+ ions, restricts the segmental (2) interaction of urethane –NHleading and carbonyl + ions leading to phase or intra molecular crosslinking; and (3) mixed ether-urethane interactions with the Li + groups with the Li ions leading to inter or intra molecular crosslinking; and (3) mixed ether-urethane + ions leading mixing of the hard andthe soft Oxygen present in the acrylate group also coordinate with Li+ interactions with Lisegments. to phase mixing of the hard and softmay segments. Oxygen present + ions [16]. interaction Li also happened within ether and possibility of of interaction with within oxygen in theThe acrylate groupof may coordinate with Li+ oxygen ions [16]. The interaction Li+ happened present in acrylate increased of theinteraction Tg of hardwith segment. Thispresent suggests addition of increased salt transforms ether oxygengroup and possibility oxygen in that acrylate group the TPUA g of hard segment. This suggests that addition of salt transforms PUA into amorphous. into amorphous.
Figure 11. DSC thermograms PUA/LiClO electrolytes. 4 /EC Figure 11. DSC thermograms PUA/LiClO 4/EC electrolytes.
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Table 4. Tm of PUA electrolyte with EC. Table 4. Tm of PUA electrolyte with EC. Tm1 ◦ ◦ Sample Sample Tm1 (°C)Tm2T( m2C)(°C) TgT( g C) (°C) (◦ C)
PUA 0 wt. % EC 108.9108.9 −15.7 PUA 0 wt. % EC −15.7 PUA 3 wt. % EC 88.9488.94 PUA 3 wt. % EC PUA 9 wt. % EC PUA 9 wt. % EC 94.7494.74 156.50 156.50 PUA 15 wt. % EC PUA 15 wt. % EC95.8995.89 —melting temperature; Tg —glass transition temperature. TTmm—melting temperature; Tg—glass transition temperature.
XRD analysiswas wascarried carried out to crystallinity behavior of the materials. Figure XRD analysis tostudy studythe the crystallinity behavior of polymer the polymer materials. 12 shows the XRD pattern of PUA and PUA with EC electrolyte. The addition of EC to the Figure 12 shows the XRD pattern of PUA and PUA with EC electrolyte. The addition of EC PUA to the semi-crystalline phase by reducing the hump a broad the region between thedecreases PUA decreases the semi-crystalline phase by reducing the to hump to a shape broad in shape in the region ◦ . By referring 15° to 25°. By25referring to the to XRD of LiClO 4 as reported by [37], the semi-crystalline peaks between 15◦ to the pattern XRD pattern of LiClO by [37], the semi-crystalline 4 as reported are peaks of lithium salt. The lithium salt may be associated from the polymer matrix as shown in the peaks are peaks of lithium salt. The lithium salt may be associated from the polymer matrix as shown discussion, andand agglomeration of polymer exists. PUA with ECEC hashas four broader humps in SEM the SEM discussion, agglomeration of polymer exists. PUA with four broader humpsofofthe polymergive givesignificant significantreason reasonfor forthe the increment theamorphous amorphousregion. region.The Theamorphous amorphous properties properties of polymer increment of ionic conductivity, which might be due to the free volume created by continuous segmental motion of ionic conductivity, which might be due to the free volume created by continuous segmental motion polymer chain. This helps migration and facilitates movement ions [38]. The amorphous of of polymer chain. This helps ionion migration and facilitates thethe movement of of ions [38]. The amorphous nature of the polymer electrolyte was responsible for reducing T g value. It was shown that more nature of the polymer electrolyte was responsible for reducing Tg value. It was shown that thethe more amorphous polymer had low . This explains that low g in amorphous phase had caused amorphous polymer had low TgT . gThis explains that thethe low TgTin thethe amorphous phase had caused polymer chains produce faster bond rotations and segmental motion, hence giving better ionic thethe polymer chains to to produce faster bond rotations and segmental motion, hence giving better ionic mobility to the polymer electrolyte. The more amorphous region of polymer leads to a more mobility to the polymer electrolyte. The more amorphous region of polymer leads to a more disordered disordered of arrangement of matrix. the polymer matrix. Hence, the disorder flexible polymer arrangement the polymer Hence, the disorder induces moreinduces flexiblemore polymer backbone backbone then thecharge mobility of charge carriers The PUA plasticizer then increases theincreases mobility of carriers [20]. The PUA[20]. electrolyte withelectrolyte plasticizerwith shows good shows good ionic conductivity. ionic conductivity.
Figure 12.12. XRD pattern of PUA/LiClO atat different ECEC concentrations. Figure XRD pattern of PUA/LiClO 4 electrolyte different concentrations. 4 electrolyte
The SEM micrograph forfor PUA electrolyte with ECEC 3 wt. %,%, 9 wt. %% and 1515 wt.wt. %% is is shown in in The SEM micrograph PUA electrolyte with 3 wt. 9 wt. and shown Figure 13a–d. The surface morphology of PUA electrolyte is rough and porous surface. The surface Figure 13a–d. The surface morphology of PUA electrolyte is rough and porous surface. The surface roughness increased with addition of of EC. Incorporation of of ECEC with 3 wt. %% and 1515 wt.wt. %% have dark roughness increased with addition EC. Incorporation with 3 wt. and have dark
spot (porous structure) assumed phase separation occurred between EC and polymer matrix. Based on Ulaganathan et al. [37], this porosity leads to the entrapment of large volumes of liquid in the pores enhancing higher ionic conductivity. Pores present when the solvent evaporates then increase
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spot (porous structure) assumed phase separation occurred between EC and polymer matrix. Based on Ulaganathan et al. [37], this porosity leads to the entrapment of large volumes of liquid in the Polymers 2018, 10, x FOR PEER REVIEW 16 of 18 pores enhancing higher ionic conductivity. Pores present when the solvent evaporates then increase the retention ability ability in in the the electrolyte electrolytesystem. system.The The99wt. wt.%%EC ECseems seems theamorphous amorphous region region and and solvent solvent retention to be optimum for this system as Figure 13c shows smoothest surface morphology and no phase to be optimum for this system as Figure 13c shows smoothest surface morphology and no phase separation conductivity because thethe conducting ions will separationoccurred. occurred.The Thesmoother smoothersurface surfaceenhances enhancesthe the conductivity because conducting ions move freely in the electrolyte. The 9 wt. % EC has higher conductivity due to increase of the ions will move freely in the electrolyte. The 9 wt. % EC has higher conductivity due to increase of the ionsin the polymer matrix [16]. Furthermore, presence leads leadsto tohigher higherionic ionic in the polymer matrix [16]. Furthermore,the thecrystallinity crystallinityof oflithium lithium salt salt presence conductivity. The spherical sizes relate to the lithium salt in the polymer matrix so that lithium does conductivity. The spherical sizes relate to the lithium salt in the polymer matrix so that lithium does not dissolve completely on the polymer matrix. However, with the addition of 15 wt. % EC, the dark not dissolve completely on the polymer matrix. However, with the addition of 15 wt. % EC, the dark spot in low low ionic ionic conductivity conductivity compared comparedto to99wt. wt.%%EC. EC. spotand and rough rough surface surface morphology morphology resulted resulted in
Figure13. 13.SEM SEM micrograph micrograph PUA/LiClO PUA/LiClO4425% Figure 25%electrolyte electrolytewith withEC EC(a) (a)0% 0%(b) (b)3% 3%(c)(c)9% 9%(d) (d)15%. 15%.
4.4. Conclusions Conclusions The Thesolid solidpolymer polymerelectrolytes electrolytesof ofPUA PUAfrom frompolyol polyolof ofJatropha Jatrophaoil oilwith withdifferent differentconcentrations concentrationsof EC have been successfully prepared by solution-casting method under UV irradiation technique. of EC have been successfully prepared by solution-casting method under UV irradiation technique. The conductivityofofPUA PUA electrolyte at room temperature was achieved approximately The highest conductivity electrolyte at room temperature was achieved approximately ~7.86 ~7.86 10−4atS/cm 9 wt. %25 EC with 25 wt. % LiClO which is increased by five magnitudes × 10−4×S/cm 9 wt. at % EC with wt. % LiClO 4 which is increased by five magnitudes of order from 4 of order the pure PUA.ofInteraction of with lithium ions with atoms at was ethershown groupin was shown the purefrom PUA. Interaction lithium ions oxygen atomsoxygen at ether group infrared in infrared spectra. Incorporation EC into electrolyte polymer electrolyte wasinshown in the high-intense spectra. Incorporation of EC intoofpolymer was shown the high-intense of peak of peak the of the carbonyl C=O carbonyl of PUA. Amorphous behavior the polymer electrolyte canobserved be observed C=O groupgroup of PUA. Amorphous behavior of theofpolymer electrolyte can be by morphology study and was then confirmed byby the thermal behavior ofofpolymer by morphology study and was then confirmed the thermal behavior polymerelectrolyte electrolyteofofTGA TGA andDSC. DSC.XRD XRDalso alsoshowed showedthe thepolymer polymerelectrolytes electrolytesare areamorphous amorphousininthe thepresence presenceofoflithium lithiumsalt saltby and by absence of crystallinity peak. Therefore, the ideal material for practical application a wide absence of crystallinity peak. Therefore, the ideal material for practical application with with a wide range, range, battery and solar cell application couldpotential show potential application. battery and solar cell application could show useful useful application. Author Contributions: A.A., M.S.S., N.A.Y., M.M.A. and K.Z.W.L. designed the overall research. T.S.R.T.N. conducted the experiments. M.M.A., T.S.R.T.N. and M.R. wrote the manuscript. All authors reviewed the manuscript.
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Author Contributions: A.A., M.S.S., N.A.Y., M.M.A. and K.Z.W.L. designed the overall research. T.S.R.T.N. conducted the experiments. M.M.A., T.S.R.T.N. and M.R. wrote the manuscript. All authors reviewed the manuscript. Acknowledgments: The authors acknowledge the Ministry of Science, Technology and Innovation for a grant of financial support (GP-IPB/9532000) University Putra Malaysia. Conflicts of Interest: The authors declare no conflict of interest.
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