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Solid polymer electrolytes prepared from poly(methacrylamide) derivative having tris(cyanoethoxymethyl) group as its side chain
Solid State Ionics 286 (2016) 1–6
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Solid polymer electrolytes prepared from poly(methacrylamide) derivative having tris(cyanoethoxymethyl) group as its side chain Yohei Nakano, Kohsuke Shinke, Kazuhide Ueno, Hiromori Tsutsumi ⁎ Graduate School of Medicine, Yamaguchi University, 2-16-1, Tokiwadai, Ube 755-8611, Japan
a r t i c l e
i n f o
Article history: Received 1 September 2015 Received in revised form 1 December 2015 Accepted 4 December 2015 Available online xxxx Keywords: Solid polymer electrolyte Lithium Poly(methacrylamide) Nitrile
a b s t r a c t A new methacrylamide monomer (MCA) was synthesized by coupling reaction between methacrylic acid and branched amine having tri(cyanoethoxymethyl) groups. PMCA was prepared by radical polymerization of MCA using AIBN as a radical initiator. The solid polymer electrolyte films were prepared from PMCA and lithium bis(trifluoromethanesulfonyl)amide, LiTFSA. The highest ionic conductivity for PMCA-based electrolyte films was 1.06 μS cm−1 at 293 K and 0.12 mS cm−1 at 343 K. Lithium salt (LiTFSA) dissolution in the PMCA-based electrolyte films was enhanced by the coordination of the lithium ions with the nitrile groups in the PMCA side chains. Ion conduction in the PMCA matrix was also affected by the motion of the tris(cyanoethoxymethyl) side chains in the PMCA matrix. The PMCA-based electrolyte film showed oxidation stability up to ca. 3.1 V against a lithium electrode. Reversible electrochemical plating and stripping processes of lithium was observed on a nickel plate in the PMCA-based electrolyte. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Solid polymer electrolytes (SPEs) including a polymer as a matrix and an inorganic salt have been developed by many scientists to expand their application area [1,2]. The main roles of SPEs for battery technology are enhancing safety and durability of the batteries, especially large batteries for electric vehicles and load leveling systems with solar or wind power plants, and simplifying the cell structure. Polyethylene oxide (PEO) have been used as a matrix of SPEs because of its low glass transition temperature (Tg, 213 K) [3] and its ability of dissolution of inorganic salts [1]. Conductivity of the typical PEO-based electrolyte is 10− 7 S cm− 1 at ambient temperature [1]. This value is about 4–5 orders of magnitude lower than ionic conductivity of liquid electrolytes (ca. 10−2–10−3 S cm−1) [4]. Many scientists have been investigating new-type systems for enhancing conductivity and/or performance of SPEs [1]. Four basic approaches for enhancing conductivity and/or performance of the SPEs are (1) decreasing in the Tg of the SPEs, (2) preventing crystallization of the SPE matrix, (3) enhancing the dissolution of the inorganic salt in the SPEs, and (4) introducing of anchor anion groups to the SPE matrix to increase the cation transference number [5–7]. Typical technique for reducing Tg of the SPEs is addition of plasticizer into the matrix. Propylene carbonate, ethylene carbonate, and other carbonates were used as a plasticizer for SPEs [8–11]. Phthalic esters
⁎ Corresponding author. E-mail address: [email protected] (H. Tsutsumi).
http://dx.doi.org/10.1016/j.ssi.2015.12.001 0167-2738/© 2015 Elsevier B.V. All rights reserved.
and some nitriles also show similar functionality as a plasticizer [12–17]. The plasticizers having polar groups also act as a dissolution enhancer of the inorganic salt in the SPEs. Additives and micro- or nano-meter-sized inorganic particles (Al2O3, TiO2, BaTiO3, etc.) are effective to prevent crystallization of SPEs' matrixes [18]. The inorganic particles also act as a dissolution enhancer of the inorganic salts in the SPE matrix. Many scientists have designed and synthesized new polymer skeletons to realize reducing Tg and/or preventing crystallization of the matrix polymers. Polymer matrixes with lower Tg have been investigated, such as poly(siloxane)-based [19] and poly(phosphazene)based [20,21] SPEs. Comb shaped polymers [22–24], star-shaped or dendritic polymers [24,25], and polymers with dendritic side chains [24,26] have been also investigated as matrix polymers for SPEs. Another approach of polymer design for high conductive SPE matrixes is polymers bearing polar groups (for example, carbonate, nitrile, ether, or ester) as their side chains [1,2]. Polymers that have dendritic (multi-armed) side chains with terminal polar groups have been very few cases as far as we know. We have reported characterization of the SPEs based on poly(oxetane) with tris(cyanoethoxymethyl) group (PCOA) [27,28]. The molecular weight of the PCOA was low and the resulted PCOA was sticky. We needed to form free-standing electrolyte films by addition of poly(vinylidene fluoride-co-hexafluoropropylene) to PCOA as an additive for reinforcement of the electrolyte films. Conductivity of the PCOA-based electrolyte film was ca. 0.1 mS cm−1 at ambient temperature. Poly(acrylamide) and poly(methacrylamide) are suitable candidates for SPEs' matrix because of their highly polar side groups in the
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structure for increasing the dielectric constant of the matrix and ease of radical polymerization. However, they show high Tg value. Wieczorek et al. have resolved the problem by blending the poly(acrylamide) or poly(methacrylamide) with PEO [29,30]. A new-type monomer was synthesized by coupling reaction between methacrylic acid and branched amine with tri(cyanoethoxymethyl) groups (Fig. 1). The monomer (MCA) was polymerized using a radical initiator, AIBN. Solid polymer electrolyte films were prepared from PMCA and lithium bis(trifluoromethanesulfonyl)amide, LiTFSA. The PMCA-based electrolyte films were characterized with FTIR, DSC, and conductivity measurements. Electrochemical stability of the PMCAbased electrolyte films and depositing and stripping of Li in the PMCAbased electrolytes were also investigated.
flask and stirred at 338 K for 20 h. After polymerization, the CHCl3 was removed with a rotary evaporator. The residue was dissolved into acetone. The acetone solution was poured into methanol to purity PMCA by precipitation method. The resulted polymer (PMCA) was collected and dried at 333 K under reduced pressure (266 Pa) for 24 h. The structure was confirmed by 1H NMR and FTIR measurements. Yield: 80 mg, 13%. 1 H NMR ((CD3)2CO, ppm) 1.29 (2 H, C-CH2-C), 2.05 (3 H, − CH3), 2.82 (6 H, − CH2CN), 3.82 (6 H, − CH2CH2CN), 3.96 (6 H, C-CH2-O), 6.24 (1 H, −CONH-). FTIR (cm−1) 2884, 2937 (−CH3, −CH2-), 2251 (−CN), 1552, 1664, 3435 (−CONH-), 1112 (−O-). 2.4. Preparation of solid polymer electrolyte films
2. Experimental 2.1. Materials All chemicals were purchased and used without further purification unless otherwise mentioned. 2,2′-Azoisobutyronitrile (AIBN) was purified by recrystallization from its methanol solution. 2.2. Preparation of monomer (MCA) Preparation route of the monomer, tris(2-cyanoethoxymethylene) carbomethacrylamide (MCA), is shown in Fig. 1. Tris(cyanoethoxymethyl)aminomethane (TCEMAM) was prepared from tris(hydroxymethyl)aminomethane and acrylonitrile following a similar procedure reported by Partha et al. [31]. CH2Cl2 (30 mL) contained TCEMAM (6.05 g, 21.6 mmol), methacrylic acid (2.0 mL, 23.5 mmol), and 1-ethyl-3-(3-diethylaminopropyl)carbodiimide hydrochloride salt (4.00 g, 21.6 mmol) and was stirred at room temperature for 48 h. The reaction mixture was washed with 1 mol dm− 3 hydrochloric acid (3 times) and then water (3 times). After the CH2Cl2 solution was dried with anhydrous magnesium sulfate, the CH2Cl2 was removed with a rotary evaporator. The residue was purified by silica gel column chromatography (eluent; ethyl acetate/n-hexane =4/1, volume ratio) to obtain MCA. The structure was checked by 1 H- and 13 C-NMR, FTIR, and TOF-MS measurements. Yield: 3.32 g, 44%. 1 H-NMR (CDCl3, ppm) 1.93 (3 H, s, −CH3), 2.58 (6 H, t, J = 6.1 Hz, −CH2CN), 3.68 (6 H, t, J = 6.1 Hz, −CH2CH2CN), 3.87 (6 H, s, C-CH2-O), 5.33 (1 H, s, CH2 =), 5.69 (1 H, s, CH2 =), 6.09 (1 H, s, −NH-). 13 C-NMR (CDCl3, ppm) 18.31 (− CH3), 18.55 (− CH2CN), 59.33 (−CONH-C), 65.66 (− CH2CH2CN), 68.61 (C-CH2-O-), 117.78 (− CN), 119.72 (CH2 = C), 140.62 (CH2 = C), 168.49 (−CONH-). FTIR (cm−1) 2883, 2931 (−CH3, −CH2-), 2251 (−CN), 1517, 1669, 3430 (−CONH-), 1120 (−O-), 919, 1419 (CH2 = C). HR-ESI-MS m/z 349.1885 [M + H]+ (calc. C17H25N4O4, 348.18). 2.3. Polymerization of MCA A tri-necked round flask was filled with argon, and MCA (0.61 g, 1.75 mmol), AIBN (2.87 mg, 0.17 mmol), CHCl3 (30 mL) were added to the
The typical procedure of PMCA-based electrolyte films was as follows. PMCA(30 mg, 0.086 mmol) and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) (9.8 mg, 0.034 mmol) were dissolved into acetone (1 mL). The acetone solution was stirred at room temperature for 1 h. The solution was cast on a Teflon plate. The acetone was removed under dynamic vacuum condition. The resulted electrolyte film is presented as (PMCA)1(LiTFSA)0.4. This means that the film contains in PMCA and LiTFSA(0.4 mol per molar of repeating unit of PMCA). Other electrolyte films were also prepared by similar procedure. 2.5. Measurements Infrared spectra of samples were recorded with an FTIR spectrophotometer (IR Prestige-21, Shimadzu). Peak fitting in the spectra was performed by using peak separation and analysis software (PeakFit™ ver. 4.12, Seasolve Co.). 1 H and 13 C NMR spectra were obtained on an NMR spectrophotometer (JNM-Lambda-500 or JNM-ECA500, JEOL). Mass spectra were obtained with TOF-MS (LCT Premier XE, Waters). Molecular weight of PMCA was determined with GPC (gel permeation chromatograph) technique with a liquid chromatographic system (Shimadzu, SCL-10Avp, CTO-10Avp, and RID-10A) equipped with a column (Shodex GPC LF-804, 8.0 mm diameter and 300 mm length, Showa Denko). Tetrahydrofuran was used as eluent at a flow rate of 1 ml min−1. The GPC charts were calibrated with poly(styrene) standards (Shodex polystyrene standard, SL105, Showa Denko). An electrolyte film was sandwiched with two stainless steel plates (13 mm in diameter). Conductivity of the electrolyte film was measured with an LCR meter (HIOKI 3532-80 chemical impedance meter, 50 mVp-p, 5 Hz-1 MHz) under various temperature conditions from 293 K to 343 K. DSC measurements of the samples were performed with a differential scanning calorimeter (DSC3100S, Bruker AXS), and heating rate was at 10 K min− 1. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) measurements were performed with a two-electrode cell. The cell for LSV had a platinum (12 mm in diameter) as a working electrode, a lithium foil (12 mm in diameter) as a counter electrode, and a reference electrode. The cell for CV had a nickel plate
Fig. 1. Structure and synthetic route of MCA.
Y. Nakano et al. / Solid State Ionics 286 (2016) 1–6
(12 mm in diameter) as a working electrode, a lithium foil (12 mm in diameter) as a counter electrode, and a reference electrode. The PMCAbased electrolyte film ((PMCA)1(LiTFSA)0.6) was sandwiched with these electrodes. Unless otherwise stated, potentials are referred to the lithium electrode. Electrochemical measurements were performed with a computer-controlled potentiogalvanostat (HZ-5000, Hokuto Denko) under Ar atmosphere (dew point was at 193 K) at 333 K.
3. Results and discussion 3.1. Characterization of PMCA and PMCA-based electrolyte films PMCA (Fig. 2(a)) was prepared by radical polymerization of MCA using AIBN as an initiator. The average molar mass of PMCA used in this investigation was 5550 (number-average molar mass) and 9620 (weight-average molar mass), which were determined by the GPC measurements (calibrated with polystyrene standards). The (PMCA)1(LiTFSA)x (x = 0.4, 0.6, and 0.8) films were transparence and flexible ((PMCA)1(LiTFSA)0.4, Fig. 2(b)). Glass transition temperature (Tg) of PMCA and the PMCA-based electrolyte films are listed in Table 1. The Tg of PMCA was 299 K. The Tg of poly(methacrylamide) derivative, poly(N-tert-butylmethacrylamide), is 433 K [32]. Lower Tg of PMCA is due to its bulky and flexible side chain, tris(cycanoethoxymethyl) moiety. The Tg of the PMCA electrolyte films was from 268 K to 278 K. This indicates that the large anion, TFSA anion from dissociated LiTFSA, acts as a plasticizer of PMCA [33].
3.2. Temperature dependence of conductivity for PMCA-based electrolyte films Fig. 3 shows the temperature dependence of conductivity for the PMCA-based electrolyte films. The conductivity for all of the PMCA-based electrolyte films increases with elevation of temperature. The highest conductivity for the (PMCA)1(LiTFSA)0.8 film was 1.06 μS cm−1 at 293 K and 0.12 mS cm−1 at 343 K. Conductivity of the poly(acrylate) or poly(methacrylate)-based solid polymers including LiTFSA is 10 μS cm−1 at room temperature and 0.254 mS cm−1 at 333 K in comb-like polymer (main chain is polystyrene and grafted side chain is poly(ethylene glycol) monomethyl ether methacrylate), PEGMEMA [34], 0.115 mS cm−1 at 298 K and 0.803 mS cm−1 at 333 K in polysiloxane-graftPEGMEMA [35], and 18.2 μS cm−1 at 293 K in UV-cured methacrylic-
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Table 1 Glass transition temperature of PMCA and PMCA-based electrolyte films. Sample
Tg/K
PMCA (PMCA)1(LiTFSA)0.4 (PMCA)1(LiTFSA)0.6 (PMCA)1(LiTFSA)0.8
299 268 276 278
based SPE [36]. The conductivity of the PMCA-based electrolyte film, (PMCA)1(LiTFSA)0.8, is slightly lower than those of SPEs. The temperature dependence curves of conductivity for the PMCAbased electrolyte films are slightly convex as shown in Fig. 3. The ionic conduction mechanism depends on the motions of the coupling of charge carriers with polymeric segments and the temperature dependence conductivity follows the Vogel–Tamman–Fulcher (VTF) empirical form [37,38]. The curves are best fitted to an expression of the Eq. (1): σ ¼ AT 1=2 exp½−B=RðT−T 0 Þ
ð1Þ
where σ is the conductivity; Α is the pre-exponential factor, which is proportional to the number of charge carriers; B is the estimated pseudo-activation energy for conduction; R is the gas constant; T is the absolute temperature; and T0 is the normally called the equilibrium glass transition temperature, which is usually 50 K lower than that of the glass transition temperature (Tg). Fig. 4 shows the VTF plots of PMCAbased electrolyte systems. The estimated parameters of A and B from Fig. 4 are listed in Table 2. The parameter A increases and the B decreases as the LiTFSA concentration increases. This indicates that the number of charge carriers, anion, and cation in the PMCA-based electrolytes increase and the values of pseudo-activation energy of conduction decrease as the LiTFSA concentration increases. The mechanism is discussed in the next section. 3.3. Conduction mechanism in the PMCA-based electrolytes Fig. 5 shows the expanded FTIR spectra of PMCA and the PMCAbased electrolyte films in the region from 2230 cm−1 to 2300 cm−1. The observed peaks are attributed to nitrile groups in the PMCA and PMCA-based electrolyte films, (PMCA)1(LiTFSA)x, x = 0.4, 0.6, and 0.8. The peak height is normalized to the maximum peak height in each spectrum. The peak at 2250 cm− 1 attributed to the free nitrile
Fig. 2. Structure of PMCA (a) and appearance of (PMCA)1(LiTFSA)0.4 electrolyte film (b).
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Y. Nakano et al. / Solid State Ionics 286 (2016) 1–6 Table 2 VTF parameters of the PMCA-based electrolyte films. (PMCA)1(LiTFSA)x 0.4 0.6 0.8
Fig. 3. Temperature dependence of conductivity for PMCA-based electrolyte films, (PMCA)1(LiTFSA)x; closed triangle x = 0.4, closed square x = 0.6, and closed circle x = 0.8.
A/Scm−1 K1/2
B/kJ mol−1
B/eV
0.39 0.52 1.14
8.91 6.00 5.99
0.092 0.062 0.062
decrease in the peak area at 2250 cm−1, which is attributed to free nitrile groups (Peak 1), and the increase in the peak area at 2277 cm−1, which is attributed to coordinated nitrile groups with lithium ions (Peak 3), are shown with increase in conductivity for the PMCA-based electrolytes. This indicates that the dissolution of LiTFSA by the PMCA matrix increases the number of charge carriers and conductivity for the electrolytes. This estimation is also supported from the results in the VTF plots of the PMCA-based electrolyte films as listed in Table 2. The value of pseudo-activation energy of conduction in the PMCAbased electrolytes (listed in Table 2) is also lower than those of other electrolyte systems. The values are ca. 10 kJ mol−1 in comb-like polymer [34], 3.85 kJ mol− 1 in polysiloxane-graft-PEGMEMA [35], and 44.39 kJ mol−1 in PMMA-graft-natural rubber [44]. As listed in Table 1 the increase in the glass transition temperature due to the addition of the salt is not observed. This indicates that TFSA anion acts as a
groups in the PMCA was shifted to higher wave number by addition of LiTFSA into the PMCA matrix. Similar peak shifts to higher wave number have been reported in the poly(acrylonitrile)-based electrolyte films [39–42] and poly(oxetane)-based electrolyte films with tris(cyanoethoxymethyl) groups [27,28]. The peak shift suggests that the lithium ions in the polymer electrolyte films coordinate to the nitrile groups of the polymer matrix. Fig. 6 shows the expanded FTIR spectrum of the (PMCA)1(LiTFSA)0.4 electrolyte film in the region from 2230 cm−1 to 2300 cm−1 and its peak fitting result. Peak 1 at 2250 cm−1 is attributed to the free nitrile group. Peak 2 at 2257 cm−1 and peak 3 at 2277 cm−1 are attributed to the nitrile groups, which coordinate to lithium ions. Xuan et al. [43] have been reported that coordination between one or two nitrile groups and one lithium ion induces the peak shift (ca. 10 cm−1) and between three or four nitrile groups and one lithium ion induces the peak shift (ca. 720 cm− 1). We estimated that peak 2 at 2257 cm−1 is attributed to coordination between one or two nitrile groups and one lithium ion and peak 3 at 2277 cm−1 is attributed to coordination between three or four nitrile groups and one lithium ion. Peak fitting results of PMCA-based electrolyte films are listed in Table 3. Fig. 7 shows the relationships between conductivity at 293 K of the PMCA-based electrolyte films and peak area ratio listed in Table 3. The
Fig. 5. Extended FTIR peaks (from 2230 cm−1 to 2300 cm−1) of PMCA and (PMCA)1(LiTFSA)x; x = 0.4, 0.6, and 0.8. The peak height is normalized to the maximum peak height in each spectrum.
Fig. 4. VTF plots for PMCA-based electrolyte films, (PMCA)1(LiTFSA)x; closed triangle x = 0.4, closed square x = 0.6, and closed circle x = 0.8.
Fig. 6. Peak fitting result (from 2230 cm−1 to 2300 cm−1) of (PMCA)1(LiTFSA)0.4 electrolyte film.
Y. Nakano et al. / Solid State Ionics 286 (2016) 1–6
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Table 3 Peak fitting results of the expanded FTIR spectra from 2230 cm−1 to 2300 cm−1. Sample (PMCA)1(LiTFSA)x
Peak 1/% (2250 cm−1)
Peak 2/% (2257 cm−1)
Peak 3/% (2270 cm−1)
100
0
0
30
53
17
5
50
45
2
46
52
0 0.4 0.6 0.8
plasticizer of PMCA [33] and the pseudo-cross-linking between the PMCA main chains is also suppressed. The PMCA-based electrolyte films show lower activation energy of conduction than those of other PMMA-based electrolytes. Conductivity approximated by VTF equation at Tg (at 278 K) was about 10−8 S cm−1 for (PMCA)1(LiTFSA)0.8. The value is higher than that of the linear and star-branched PEO-LiTFSA system (b 10−10 S cm−1 at their Tg) [45]. The results also indicate that ionic conduction in the PMCA-based electrolyte films depends on the motion of the side chain and decoupling of ionic transport from segmental motion of polymer main chains [46]. The PMCA provided the SPE films with low pseudo-activation energy for conduction and highconcentration dissolved LiTFSA in their matrix.
reduction current of some impurities in the electrolyte film and/or on the Ni plate. At the cathodic scan from 0 V to −0.5 V, an increase in current was observed. It is attributed to the lithium deposition on the Ni electrode. In the anodic scan from −0.5 V to 0.5 V, the anodic peak at 0.2 V, which is due to the dissolution of lithium from the Ni plate, was also observed. This indicates that plating and stripping of lithium in
3.4. Electrochemical stability and performance of plating and stripping of lithium in the PMCA-based electrolyte films Electrochemical stability of the PMCA-based electrolyte film was investigated by linear sweep voltammetry (LSV) technique. Fig. 8 shows the LSV curve for the (PMCA)1(LiTFSA)0.6 electrolyte film. A low background current was detected in a potential region between 2 and 3.1 V for the cell prepared with a Pt electrode. An increase in the oxidation current was observed at ca. 3.1 V. This result shows that the PMCAbased electrolyte is electrochemically stable up to ca. 3.1 V vs. Li/Li+. Electrochemical plating and stripping of lithium in an electrolyte system is a key reaction for application of the electrolyte to lithium metal secondary batteries. We demonstrated electrochemical plating and stripping of lithium on a nickel plate in the PMCA-based electrolyte film. Fig. 9 shows the cyclic voltammogram of a nickel electrode in the (PMCA)1(LiTFSA)0.6 electrolyte with slow scan rate (0.1 mV s−1). At first cathodic scan from the rest potential (1.6 V) of the cell to 0 V, the broad peaks at 0.7 V and 0.3 V were observed. It may be due to the
Fig. 7. Relationship between conductivity at 293 K for the PMCA-based electrolyte films and peak fitting results listed in Table 3.
Fig. 8. Linear sweep voltammogram of a Pt plate in the PMCA-based electrolyte, (PMCA)1(LiTFSA)0.6 electrolyte film at 333 K and scan rate at 1 mV s−1.
Fig. 9. Cyclic voltammograms of a Ni electrode in the PMCA-based electrolyte, (PMCA)1(LiTFSA)0.6 electrolyte film at 333 K and scan rate at 0.1 mV s−1.
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the PMCA-based electrolyte film is reversible and slow in our experiment condition. 4. Conclusions We prepared a new methacrylamide derivative bearing three cyanoethoxymethyl units as its side chain by coupling reaction between methacrylic acid and tris(cyanoethoxymethyl)aminomethane. PMCA was prepared by radial polymerization of MCA using a radical initiator. The flexible and free-standing polymer electrolyte films were prepared from PMCA and LiTFSA. The highest conductivity for PMCA-based electrolyte film ((PMCA)1(LiTFSA)0.8 film) was 1.06 μS cm−1 at 293 K and 0.12 m S cm−1 at 343 K. FTIR spectra of the PMCA-based electrolyte films suggest that the nitrile groups in the PMCA coordinate to the lithium ions in the matrix, support the dissolution of the lithium salt, and increase in the number of charge carriers in the matrix. Temperature dependence of conductivity for the PMCA-based electrolyte films obeys the VTF relation. The pseudo-activation energy for conduction in the PMCA matrix was from 5.99 kJ mol−1 to 8.91 kJ mol−1. Lower pseudo-activation energy for conduction and higher carrier concentration in the matrix provided the high conductive poly(methacrylamide)based SPEs. The PMCA-based electrolyte film showed oxidation stability up to ca. 3.1 V against a lithium electrode. Reversible electrochemical plating and stripping processes of lithium was observed on a nickel plate in the PMCA-based electrolyte. References [1] J.W. Fergus, J. Power Sources 195 (15) (2010) 4554. [2] E. Quartarone, P. Mustarelli, Chem. Soc. Rev. 40 (5) (2011) 2525. [3] P.W.M. Jacobs, J.W. Lorimer, A. Russer, M. Wasiucionek, J. Power Sources 26 (3–4) (1989) 503. [4] K.M. Abraham, J. Phys. Chem. Lett. 6 (5) (2015) 830. [5] Y.S. Zhu, X.J. Wang, Y.Y. Hou, X.W. Gao, L.L. Liu, Y.P. Wu, M. Shimizu, Electrochim. Acta 87 (2013) 113. [6] Y.S. Zhu, X.W. Gao, X.J. Wang, Y.Y. Hou, L.L. Liu, Y.P. Wu, Electrochem. Commun. 22 (2012) 29. [7] D. Benrabah, S. Sylla, F. Alloin, J.Y. Sanchez, M. Armand, Electrochim. Acta 40 (13–14) (1995) 2259. [8] S. Rajendran, T. Mahalingam, R. Kannan, Solid State Ionics 130 (1) (2000) 143. [9] M. Forsyth, M. Garcia, D.R. MacFarlane, S. Ng, M.E. Smith, J.H. Strange, Solid State Ionics 1365 (Pt 2) (1996) 86–88. [10] D. Peramunage, D.M. Pasquariello, K.M. Abraham, J. Electrochem. Soc. 142 (6) (1995) 1789. [11] M. Forsyth, P.M. Meakin, D.R. MacFarlane, Electrochim. Acta 40 (13–14) (1995) 2339. [12] A.M. Sukeshini, A.R. Kulkarni, A. Sharma, Solid State Ionics 113-115 (1998) 179.
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Solid State Ionics journal homepage: www.elsevier.com/locate/ssi
Solid polymer electrolytes prepared from poly(methacrylamide) derivative having tris(cyanoethoxymethyl) group as its side chain Yohei Nakano, Kohsuke Shinke, Kazuhide Ueno, Hiromori Tsutsumi ⁎ Graduate School of Medicine, Yamaguchi University, 2-16-1, Tokiwadai, Ube 755-8611, Japan
a r t i c l e
i n f o
Article history: Received 1 September 2015 Received in revised form 1 December 2015 Accepted 4 December 2015 Available online xxxx Keywords: Solid polymer electrolyte Lithium Poly(methacrylamide) Nitrile
a b s t r a c t A new methacrylamide monomer (MCA) was synthesized by coupling reaction between methacrylic acid and branched amine having tri(cyanoethoxymethyl) groups. PMCA was prepared by radical polymerization of MCA using AIBN as a radical initiator. The solid polymer electrolyte films were prepared from PMCA and lithium bis(trifluoromethanesulfonyl)amide, LiTFSA. The highest ionic conductivity for PMCA-based electrolyte films was 1.06 μS cm−1 at 293 K and 0.12 mS cm−1 at 343 K. Lithium salt (LiTFSA) dissolution in the PMCA-based electrolyte films was enhanced by the coordination of the lithium ions with the nitrile groups in the PMCA side chains. Ion conduction in the PMCA matrix was also affected by the motion of the tris(cyanoethoxymethyl) side chains in the PMCA matrix. The PMCA-based electrolyte film showed oxidation stability up to ca. 3.1 V against a lithium electrode. Reversible electrochemical plating and stripping processes of lithium was observed on a nickel plate in the PMCA-based electrolyte. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Solid polymer electrolytes (SPEs) including a polymer as a matrix and an inorganic salt have been developed by many scientists to expand their application area [1,2]. The main roles of SPEs for battery technology are enhancing safety and durability of the batteries, especially large batteries for electric vehicles and load leveling systems with solar or wind power plants, and simplifying the cell structure. Polyethylene oxide (PEO) have been used as a matrix of SPEs because of its low glass transition temperature (Tg, 213 K) [3] and its ability of dissolution of inorganic salts [1]. Conductivity of the typical PEO-based electrolyte is 10− 7 S cm− 1 at ambient temperature [1]. This value is about 4–5 orders of magnitude lower than ionic conductivity of liquid electrolytes (ca. 10−2–10−3 S cm−1) [4]. Many scientists have been investigating new-type systems for enhancing conductivity and/or performance of SPEs [1]. Four basic approaches for enhancing conductivity and/or performance of the SPEs are (1) decreasing in the Tg of the SPEs, (2) preventing crystallization of the SPE matrix, (3) enhancing the dissolution of the inorganic salt in the SPEs, and (4) introducing of anchor anion groups to the SPE matrix to increase the cation transference number [5–7]. Typical technique for reducing Tg of the SPEs is addition of plasticizer into the matrix. Propylene carbonate, ethylene carbonate, and other carbonates were used as a plasticizer for SPEs [8–11]. Phthalic esters
⁎ Corresponding author. E-mail address: [email protected] (H. Tsutsumi).
http://dx.doi.org/10.1016/j.ssi.2015.12.001 0167-2738/© 2015 Elsevier B.V. All rights reserved.
and some nitriles also show similar functionality as a plasticizer [12–17]. The plasticizers having polar groups also act as a dissolution enhancer of the inorganic salt in the SPEs. Additives and micro- or nano-meter-sized inorganic particles (Al2O3, TiO2, BaTiO3, etc.) are effective to prevent crystallization of SPEs' matrixes [18]. The inorganic particles also act as a dissolution enhancer of the inorganic salts in the SPE matrix. Many scientists have designed and synthesized new polymer skeletons to realize reducing Tg and/or preventing crystallization of the matrix polymers. Polymer matrixes with lower Tg have been investigated, such as poly(siloxane)-based [19] and poly(phosphazene)based [20,21] SPEs. Comb shaped polymers [22–24], star-shaped or dendritic polymers [24,25], and polymers with dendritic side chains [24,26] have been also investigated as matrix polymers for SPEs. Another approach of polymer design for high conductive SPE matrixes is polymers bearing polar groups (for example, carbonate, nitrile, ether, or ester) as their side chains [1,2]. Polymers that have dendritic (multi-armed) side chains with terminal polar groups have been very few cases as far as we know. We have reported characterization of the SPEs based on poly(oxetane) with tris(cyanoethoxymethyl) group (PCOA) [27,28]. The molecular weight of the PCOA was low and the resulted PCOA was sticky. We needed to form free-standing electrolyte films by addition of poly(vinylidene fluoride-co-hexafluoropropylene) to PCOA as an additive for reinforcement of the electrolyte films. Conductivity of the PCOA-based electrolyte film was ca. 0.1 mS cm−1 at ambient temperature. Poly(acrylamide) and poly(methacrylamide) are suitable candidates for SPEs' matrix because of their highly polar side groups in the
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structure for increasing the dielectric constant of the matrix and ease of radical polymerization. However, they show high Tg value. Wieczorek et al. have resolved the problem by blending the poly(acrylamide) or poly(methacrylamide) with PEO [29,30]. A new-type monomer was synthesized by coupling reaction between methacrylic acid and branched amine with tri(cyanoethoxymethyl) groups (Fig. 1). The monomer (MCA) was polymerized using a radical initiator, AIBN. Solid polymer electrolyte films were prepared from PMCA and lithium bis(trifluoromethanesulfonyl)amide, LiTFSA. The PMCA-based electrolyte films were characterized with FTIR, DSC, and conductivity measurements. Electrochemical stability of the PMCAbased electrolyte films and depositing and stripping of Li in the PMCAbased electrolytes were also investigated.
flask and stirred at 338 K for 20 h. After polymerization, the CHCl3 was removed with a rotary evaporator. The residue was dissolved into acetone. The acetone solution was poured into methanol to purity PMCA by precipitation method. The resulted polymer (PMCA) was collected and dried at 333 K under reduced pressure (266 Pa) for 24 h. The structure was confirmed by 1H NMR and FTIR measurements. Yield: 80 mg, 13%. 1 H NMR ((CD3)2CO, ppm) 1.29 (2 H, C-CH2-C), 2.05 (3 H, − CH3), 2.82 (6 H, − CH2CN), 3.82 (6 H, − CH2CH2CN), 3.96 (6 H, C-CH2-O), 6.24 (1 H, −CONH-). FTIR (cm−1) 2884, 2937 (−CH3, −CH2-), 2251 (−CN), 1552, 1664, 3435 (−CONH-), 1112 (−O-). 2.4. Preparation of solid polymer electrolyte films
2. Experimental 2.1. Materials All chemicals were purchased and used without further purification unless otherwise mentioned. 2,2′-Azoisobutyronitrile (AIBN) was purified by recrystallization from its methanol solution. 2.2. Preparation of monomer (MCA) Preparation route of the monomer, tris(2-cyanoethoxymethylene) carbomethacrylamide (MCA), is shown in Fig. 1. Tris(cyanoethoxymethyl)aminomethane (TCEMAM) was prepared from tris(hydroxymethyl)aminomethane and acrylonitrile following a similar procedure reported by Partha et al. [31]. CH2Cl2 (30 mL) contained TCEMAM (6.05 g, 21.6 mmol), methacrylic acid (2.0 mL, 23.5 mmol), and 1-ethyl-3-(3-diethylaminopropyl)carbodiimide hydrochloride salt (4.00 g, 21.6 mmol) and was stirred at room temperature for 48 h. The reaction mixture was washed with 1 mol dm− 3 hydrochloric acid (3 times) and then water (3 times). After the CH2Cl2 solution was dried with anhydrous magnesium sulfate, the CH2Cl2 was removed with a rotary evaporator. The residue was purified by silica gel column chromatography (eluent; ethyl acetate/n-hexane =4/1, volume ratio) to obtain MCA. The structure was checked by 1 H- and 13 C-NMR, FTIR, and TOF-MS measurements. Yield: 3.32 g, 44%. 1 H-NMR (CDCl3, ppm) 1.93 (3 H, s, −CH3), 2.58 (6 H, t, J = 6.1 Hz, −CH2CN), 3.68 (6 H, t, J = 6.1 Hz, −CH2CH2CN), 3.87 (6 H, s, C-CH2-O), 5.33 (1 H, s, CH2 =), 5.69 (1 H, s, CH2 =), 6.09 (1 H, s, −NH-). 13 C-NMR (CDCl3, ppm) 18.31 (− CH3), 18.55 (− CH2CN), 59.33 (−CONH-C), 65.66 (− CH2CH2CN), 68.61 (C-CH2-O-), 117.78 (− CN), 119.72 (CH2 = C), 140.62 (CH2 = C), 168.49 (−CONH-). FTIR (cm−1) 2883, 2931 (−CH3, −CH2-), 2251 (−CN), 1517, 1669, 3430 (−CONH-), 1120 (−O-), 919, 1419 (CH2 = C). HR-ESI-MS m/z 349.1885 [M + H]+ (calc. C17H25N4O4, 348.18). 2.3. Polymerization of MCA A tri-necked round flask was filled with argon, and MCA (0.61 g, 1.75 mmol), AIBN (2.87 mg, 0.17 mmol), CHCl3 (30 mL) were added to the
The typical procedure of PMCA-based electrolyte films was as follows. PMCA(30 mg, 0.086 mmol) and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) (9.8 mg, 0.034 mmol) were dissolved into acetone (1 mL). The acetone solution was stirred at room temperature for 1 h. The solution was cast on a Teflon plate. The acetone was removed under dynamic vacuum condition. The resulted electrolyte film is presented as (PMCA)1(LiTFSA)0.4. This means that the film contains in PMCA and LiTFSA(0.4 mol per molar of repeating unit of PMCA). Other electrolyte films were also prepared by similar procedure. 2.5. Measurements Infrared spectra of samples were recorded with an FTIR spectrophotometer (IR Prestige-21, Shimadzu). Peak fitting in the spectra was performed by using peak separation and analysis software (PeakFit™ ver. 4.12, Seasolve Co.). 1 H and 13 C NMR spectra were obtained on an NMR spectrophotometer (JNM-Lambda-500 or JNM-ECA500, JEOL). Mass spectra were obtained with TOF-MS (LCT Premier XE, Waters). Molecular weight of PMCA was determined with GPC (gel permeation chromatograph) technique with a liquid chromatographic system (Shimadzu, SCL-10Avp, CTO-10Avp, and RID-10A) equipped with a column (Shodex GPC LF-804, 8.0 mm diameter and 300 mm length, Showa Denko). Tetrahydrofuran was used as eluent at a flow rate of 1 ml min−1. The GPC charts were calibrated with poly(styrene) standards (Shodex polystyrene standard, SL105, Showa Denko). An electrolyte film was sandwiched with two stainless steel plates (13 mm in diameter). Conductivity of the electrolyte film was measured with an LCR meter (HIOKI 3532-80 chemical impedance meter, 50 mVp-p, 5 Hz-1 MHz) under various temperature conditions from 293 K to 343 K. DSC measurements of the samples were performed with a differential scanning calorimeter (DSC3100S, Bruker AXS), and heating rate was at 10 K min− 1. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) measurements were performed with a two-electrode cell. The cell for LSV had a platinum (12 mm in diameter) as a working electrode, a lithium foil (12 mm in diameter) as a counter electrode, and a reference electrode. The cell for CV had a nickel plate
Fig. 1. Structure and synthetic route of MCA.
Y. Nakano et al. / Solid State Ionics 286 (2016) 1–6
(12 mm in diameter) as a working electrode, a lithium foil (12 mm in diameter) as a counter electrode, and a reference electrode. The PMCAbased electrolyte film ((PMCA)1(LiTFSA)0.6) was sandwiched with these electrodes. Unless otherwise stated, potentials are referred to the lithium electrode. Electrochemical measurements were performed with a computer-controlled potentiogalvanostat (HZ-5000, Hokuto Denko) under Ar atmosphere (dew point was at 193 K) at 333 K.
3. Results and discussion 3.1. Characterization of PMCA and PMCA-based electrolyte films PMCA (Fig. 2(a)) was prepared by radical polymerization of MCA using AIBN as an initiator. The average molar mass of PMCA used in this investigation was 5550 (number-average molar mass) and 9620 (weight-average molar mass), which were determined by the GPC measurements (calibrated with polystyrene standards). The (PMCA)1(LiTFSA)x (x = 0.4, 0.6, and 0.8) films were transparence and flexible ((PMCA)1(LiTFSA)0.4, Fig. 2(b)). Glass transition temperature (Tg) of PMCA and the PMCA-based electrolyte films are listed in Table 1. The Tg of PMCA was 299 K. The Tg of poly(methacrylamide) derivative, poly(N-tert-butylmethacrylamide), is 433 K [32]. Lower Tg of PMCA is due to its bulky and flexible side chain, tris(cycanoethoxymethyl) moiety. The Tg of the PMCA electrolyte films was from 268 K to 278 K. This indicates that the large anion, TFSA anion from dissociated LiTFSA, acts as a plasticizer of PMCA [33].
3.2. Temperature dependence of conductivity for PMCA-based electrolyte films Fig. 3 shows the temperature dependence of conductivity for the PMCA-based electrolyte films. The conductivity for all of the PMCA-based electrolyte films increases with elevation of temperature. The highest conductivity for the (PMCA)1(LiTFSA)0.8 film was 1.06 μS cm−1 at 293 K and 0.12 mS cm−1 at 343 K. Conductivity of the poly(acrylate) or poly(methacrylate)-based solid polymers including LiTFSA is 10 μS cm−1 at room temperature and 0.254 mS cm−1 at 333 K in comb-like polymer (main chain is polystyrene and grafted side chain is poly(ethylene glycol) monomethyl ether methacrylate), PEGMEMA [34], 0.115 mS cm−1 at 298 K and 0.803 mS cm−1 at 333 K in polysiloxane-graftPEGMEMA [35], and 18.2 μS cm−1 at 293 K in UV-cured methacrylic-
3
Table 1 Glass transition temperature of PMCA and PMCA-based electrolyte films. Sample
Tg/K
PMCA (PMCA)1(LiTFSA)0.4 (PMCA)1(LiTFSA)0.6 (PMCA)1(LiTFSA)0.8
299 268 276 278
based SPE [36]. The conductivity of the PMCA-based electrolyte film, (PMCA)1(LiTFSA)0.8, is slightly lower than those of SPEs. The temperature dependence curves of conductivity for the PMCAbased electrolyte films are slightly convex as shown in Fig. 3. The ionic conduction mechanism depends on the motions of the coupling of charge carriers with polymeric segments and the temperature dependence conductivity follows the Vogel–Tamman–Fulcher (VTF) empirical form [37,38]. The curves are best fitted to an expression of the Eq. (1): σ ¼ AT 1=2 exp½−B=RðT−T 0 Þ
ð1Þ
where σ is the conductivity; Α is the pre-exponential factor, which is proportional to the number of charge carriers; B is the estimated pseudo-activation energy for conduction; R is the gas constant; T is the absolute temperature; and T0 is the normally called the equilibrium glass transition temperature, which is usually 50 K lower than that of the glass transition temperature (Tg). Fig. 4 shows the VTF plots of PMCAbased electrolyte systems. The estimated parameters of A and B from Fig. 4 are listed in Table 2. The parameter A increases and the B decreases as the LiTFSA concentration increases. This indicates that the number of charge carriers, anion, and cation in the PMCA-based electrolytes increase and the values of pseudo-activation energy of conduction decrease as the LiTFSA concentration increases. The mechanism is discussed in the next section. 3.3. Conduction mechanism in the PMCA-based electrolytes Fig. 5 shows the expanded FTIR spectra of PMCA and the PMCAbased electrolyte films in the region from 2230 cm−1 to 2300 cm−1. The observed peaks are attributed to nitrile groups in the PMCA and PMCA-based electrolyte films, (PMCA)1(LiTFSA)x, x = 0.4, 0.6, and 0.8. The peak height is normalized to the maximum peak height in each spectrum. The peak at 2250 cm− 1 attributed to the free nitrile
Fig. 2. Structure of PMCA (a) and appearance of (PMCA)1(LiTFSA)0.4 electrolyte film (b).
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Y. Nakano et al. / Solid State Ionics 286 (2016) 1–6 Table 2 VTF parameters of the PMCA-based electrolyte films. (PMCA)1(LiTFSA)x 0.4 0.6 0.8
Fig. 3. Temperature dependence of conductivity for PMCA-based electrolyte films, (PMCA)1(LiTFSA)x; closed triangle x = 0.4, closed square x = 0.6, and closed circle x = 0.8.
A/Scm−1 K1/2
B/kJ mol−1
B/eV
0.39 0.52 1.14
8.91 6.00 5.99
0.092 0.062 0.062
decrease in the peak area at 2250 cm−1, which is attributed to free nitrile groups (Peak 1), and the increase in the peak area at 2277 cm−1, which is attributed to coordinated nitrile groups with lithium ions (Peak 3), are shown with increase in conductivity for the PMCA-based electrolytes. This indicates that the dissolution of LiTFSA by the PMCA matrix increases the number of charge carriers and conductivity for the electrolytes. This estimation is also supported from the results in the VTF plots of the PMCA-based electrolyte films as listed in Table 2. The value of pseudo-activation energy of conduction in the PMCAbased electrolytes (listed in Table 2) is also lower than those of other electrolyte systems. The values are ca. 10 kJ mol−1 in comb-like polymer [34], 3.85 kJ mol− 1 in polysiloxane-graft-PEGMEMA [35], and 44.39 kJ mol−1 in PMMA-graft-natural rubber [44]. As listed in Table 1 the increase in the glass transition temperature due to the addition of the salt is not observed. This indicates that TFSA anion acts as a
groups in the PMCA was shifted to higher wave number by addition of LiTFSA into the PMCA matrix. Similar peak shifts to higher wave number have been reported in the poly(acrylonitrile)-based electrolyte films [39–42] and poly(oxetane)-based electrolyte films with tris(cyanoethoxymethyl) groups [27,28]. The peak shift suggests that the lithium ions in the polymer electrolyte films coordinate to the nitrile groups of the polymer matrix. Fig. 6 shows the expanded FTIR spectrum of the (PMCA)1(LiTFSA)0.4 electrolyte film in the region from 2230 cm−1 to 2300 cm−1 and its peak fitting result. Peak 1 at 2250 cm−1 is attributed to the free nitrile group. Peak 2 at 2257 cm−1 and peak 3 at 2277 cm−1 are attributed to the nitrile groups, which coordinate to lithium ions. Xuan et al. [43] have been reported that coordination between one or two nitrile groups and one lithium ion induces the peak shift (ca. 10 cm−1) and between three or four nitrile groups and one lithium ion induces the peak shift (ca. 720 cm− 1). We estimated that peak 2 at 2257 cm−1 is attributed to coordination between one or two nitrile groups and one lithium ion and peak 3 at 2277 cm−1 is attributed to coordination between three or four nitrile groups and one lithium ion. Peak fitting results of PMCA-based electrolyte films are listed in Table 3. Fig. 7 shows the relationships between conductivity at 293 K of the PMCA-based electrolyte films and peak area ratio listed in Table 3. The
Fig. 5. Extended FTIR peaks (from 2230 cm−1 to 2300 cm−1) of PMCA and (PMCA)1(LiTFSA)x; x = 0.4, 0.6, and 0.8. The peak height is normalized to the maximum peak height in each spectrum.
Fig. 4. VTF plots for PMCA-based electrolyte films, (PMCA)1(LiTFSA)x; closed triangle x = 0.4, closed square x = 0.6, and closed circle x = 0.8.
Fig. 6. Peak fitting result (from 2230 cm−1 to 2300 cm−1) of (PMCA)1(LiTFSA)0.4 electrolyte film.
Y. Nakano et al. / Solid State Ionics 286 (2016) 1–6
5
Table 3 Peak fitting results of the expanded FTIR spectra from 2230 cm−1 to 2300 cm−1. Sample (PMCA)1(LiTFSA)x
Peak 1/% (2250 cm−1)
Peak 2/% (2257 cm−1)
Peak 3/% (2270 cm−1)
100
0
0
30
53
17
5
50
45
2
46
52
0 0.4 0.6 0.8
plasticizer of PMCA [33] and the pseudo-cross-linking between the PMCA main chains is also suppressed. The PMCA-based electrolyte films show lower activation energy of conduction than those of other PMMA-based electrolytes. Conductivity approximated by VTF equation at Tg (at 278 K) was about 10−8 S cm−1 for (PMCA)1(LiTFSA)0.8. The value is higher than that of the linear and star-branched PEO-LiTFSA system (b 10−10 S cm−1 at their Tg) [45]. The results also indicate that ionic conduction in the PMCA-based electrolyte films depends on the motion of the side chain and decoupling of ionic transport from segmental motion of polymer main chains [46]. The PMCA provided the SPE films with low pseudo-activation energy for conduction and highconcentration dissolved LiTFSA in their matrix.
reduction current of some impurities in the electrolyte film and/or on the Ni plate. At the cathodic scan from 0 V to −0.5 V, an increase in current was observed. It is attributed to the lithium deposition on the Ni electrode. In the anodic scan from −0.5 V to 0.5 V, the anodic peak at 0.2 V, which is due to the dissolution of lithium from the Ni plate, was also observed. This indicates that plating and stripping of lithium in
3.4. Electrochemical stability and performance of plating and stripping of lithium in the PMCA-based electrolyte films Electrochemical stability of the PMCA-based electrolyte film was investigated by linear sweep voltammetry (LSV) technique. Fig. 8 shows the LSV curve for the (PMCA)1(LiTFSA)0.6 electrolyte film. A low background current was detected in a potential region between 2 and 3.1 V for the cell prepared with a Pt electrode. An increase in the oxidation current was observed at ca. 3.1 V. This result shows that the PMCAbased electrolyte is electrochemically stable up to ca. 3.1 V vs. Li/Li+. Electrochemical plating and stripping of lithium in an electrolyte system is a key reaction for application of the electrolyte to lithium metal secondary batteries. We demonstrated electrochemical plating and stripping of lithium on a nickel plate in the PMCA-based electrolyte film. Fig. 9 shows the cyclic voltammogram of a nickel electrode in the (PMCA)1(LiTFSA)0.6 electrolyte with slow scan rate (0.1 mV s−1). At first cathodic scan from the rest potential (1.6 V) of the cell to 0 V, the broad peaks at 0.7 V and 0.3 V were observed. It may be due to the
Fig. 7. Relationship between conductivity at 293 K for the PMCA-based electrolyte films and peak fitting results listed in Table 3.
Fig. 8. Linear sweep voltammogram of a Pt plate in the PMCA-based electrolyte, (PMCA)1(LiTFSA)0.6 electrolyte film at 333 K and scan rate at 1 mV s−1.
Fig. 9. Cyclic voltammograms of a Ni electrode in the PMCA-based electrolyte, (PMCA)1(LiTFSA)0.6 electrolyte film at 333 K and scan rate at 0.1 mV s−1.
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the PMCA-based electrolyte film is reversible and slow in our experiment condition. 4. Conclusions We prepared a new methacrylamide derivative bearing three cyanoethoxymethyl units as its side chain by coupling reaction between methacrylic acid and tris(cyanoethoxymethyl)aminomethane. PMCA was prepared by radial polymerization of MCA using a radical initiator. The flexible and free-standing polymer electrolyte films were prepared from PMCA and LiTFSA. The highest conductivity for PMCA-based electrolyte film ((PMCA)1(LiTFSA)0.8 film) was 1.06 μS cm−1 at 293 K and 0.12 m S cm−1 at 343 K. FTIR spectra of the PMCA-based electrolyte films suggest that the nitrile groups in the PMCA coordinate to the lithium ions in the matrix, support the dissolution of the lithium salt, and increase in the number of charge carriers in the matrix. Temperature dependence of conductivity for the PMCA-based electrolyte films obeys the VTF relation. The pseudo-activation energy for conduction in the PMCA matrix was from 5.99 kJ mol−1 to 8.91 kJ mol−1. Lower pseudo-activation energy for conduction and higher carrier concentration in the matrix provided the high conductive poly(methacrylamide)based SPEs. The PMCA-based electrolyte film showed oxidation stability up to ca. 3.1 V against a lithium electrode. Reversible electrochemical plating and stripping processes of lithium was observed on a nickel plate in the PMCA-based electrolyte. References [1] J.W. Fergus, J. Power Sources 195 (15) (2010) 4554. [2] E. Quartarone, P. Mustarelli, Chem. Soc. Rev. 40 (5) (2011) 2525. [3] P.W.M. Jacobs, J.W. Lorimer, A. Russer, M. Wasiucionek, J. Power Sources 26 (3–4) (1989) 503. [4] K.M. Abraham, J. Phys. Chem. Lett. 6 (5) (2015) 830. [5] Y.S. Zhu, X.J. Wang, Y.Y. Hou, X.W. Gao, L.L. Liu, Y.P. Wu, M. Shimizu, Electrochim. Acta 87 (2013) 113. [6] Y.S. Zhu, X.W. Gao, X.J. Wang, Y.Y. Hou, L.L. Liu, Y.P. Wu, Electrochem. Commun. 22 (2012) 29. [7] D. Benrabah, S. Sylla, F. Alloin, J.Y. Sanchez, M. Armand, Electrochim. Acta 40 (13–14) (1995) 2259. [8] S. Rajendran, T. Mahalingam, R. Kannan, Solid State Ionics 130 (1) (2000) 143. [9] M. Forsyth, M. Garcia, D.R. MacFarlane, S. Ng, M.E. Smith, J.H. Strange, Solid State Ionics 1365 (Pt 2) (1996) 86–88. [10] D. Peramunage, D.M. Pasquariello, K.M. Abraham, J. Electrochem. Soc. 142 (6) (1995) 1789. [11] M. Forsyth, P.M. Meakin, D.R. MacFarlane, Electrochim. Acta 40 (13–14) (1995) 2339. [12] A.M. Sukeshini, A.R. Kulkarni, A. Sharma, Solid State Ionics 113-115 (1998) 179.
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