Article
Density Functional Theory (DFT) Study on the Ternary Interaction System of the Fluorinated Ethylene Carbonate, Li+ and Graphene Model Mami Mutoh 1 , Shigeaki Abe 1, *, Teruo Kusaka 1 , Mariko Nakamura 2 , Yasuhiro Yoshida 1 , Junichiro Iida 1 and Hiroto Tachikawa 3 Received: 23 September 2015; Accepted: 21 December 2015; Published: 29 December 2015 Academic Editors: James Babb and Hyun-Kyung Chung 1
2 3
*
Graduate School of Dental Medicine, Hokkaido University, Sapporo 060-8586, Japan;
[email protected] (M.M.);
[email protected] (T.K.);
[email protected] (Y.Y.);
[email protected] (J.I.) School of Health Science, Kyushu University of Health and Welfare, 1714-1 Yoshino-cho, Nobeoka, Miyazaki 882-8508, Japan;
[email protected] Division of Materials Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan;
[email protected] Correspondence:
[email protected]
Abstract: The ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium ion (Li+ ) and a model of nano-structured graphene has been investigated by means of the density functional theory (DFT) method. For comparison, fluorinated vinylene carbonate, denoted by VC(F), was also used. The model of graphene consisting of 14 benzene rings was examined as a nano-structured graphene. The effects of fluorine substitution on the electronic state and binding energy were investigated from a theoretical point of view. It was found that both EC(F) and VC(F) bind to a hexagonal site corresponding to the central benzene ring of the model of the graphene surface. The binding energies of Li+ EC(F) and Li+ VC(F) to the model of graphene decreased with increasing number of fluorine atoms (n). Keywords: density functional theory; fluorinated ethylene carbonate; nano-structured graphene model; lithium ion secondary battery; surface interaction
1. Introduction There are several interactions in a lithium ion secondary battery. Desolvation, Li+ -EC Ñ Li+ + EC, is an important process in the movement of the Li+ ion from the solvent to graphene. The weaker solvation of the Li+ ion by ethylene carbonate (EC) is a positive factor as a solvent. Ethylene carbonate (EC) and its related compounds are widely used in the high dielectric solvent in the lithium secondary battery, because EC has many desirable properties as an electrolyte solvent for lithium batteries. For example, EC has a high dielectric constant and low viscosity [1–4]. The interaction of the electrode (graphite) with the solvent molecule (EC) plays an important role in the redox process in electrochemistry. Recently, Zhu et al. (2014) [5] have synthesized a new family of polyfluoroalkyl-substituted ethylene carbonates, and they have been tested as additives in lithium-ion cells. The four additives studied were 4-(trifluoromethyl)-1,3-dioxolan-2-one (TFM-EC), 4-(perfluorobutyl)-1,3-dioxolan-2-one (PFB-EC), 4-(perfluorohexyl)-1,3-dioxolan-2-one (PFH-EC) and 4-(perfluorooctyl)-1,3-dioxolan-2-one (PFO-EC). Differential capacity plots from graphite-Li cells suggest that PFO-EC is involved in solid electrolyte interphase (SEI) formation. Raman data from anodes after cycling suggest that structural disordering of graphite is reduced by the addition of
Atoms 2016, 4, 4; doi:10.3390/atoms4010004
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Atoms 2016, 4, 4 2 of 10 Atoms 2016, 4, 4 2 of 10 PFO-EC, which may explain the improved cell capacity retention. For comparison, fluorinated vinylene carbonate, denoted by VC(F), was also used. Figure 1 shows the typical interaction systems, carbonate,denoted by VC(F), was also used. Figure 1 shows the typical interaction systems, such as carbonate,denoted by VC(F), was also used. Figure 1 shows the typical interaction systems, such as such as solvent-graphene, solvent-lithium ion and lithium ion-graphene. solvent‐graphene, solvent‐lithium ion and lithium ion‐graphene. solvent‐graphene, solvent‐lithium ion and lithium ion‐graphene.
Scheme 1. Structures of ethylene carbonate (EC) and vinylene carbonate (VC). Scheme 1. Structures of ethylene carbonate (EC) and vinylene carbonate (VC). Scheme 1. Structures of ethylene carbonate (EC) and vinylene carbonate (VC).
Figure 1. Schematic illustration of the types of interactionsin the graphene-ethylene carbonate Figure 1. Schematic illustration of the types of interactionsin the graphene‐ethylene carbonate (EC)‐ Figure 1. Schematic illustration of the types of interactionsin the graphene‐ethylene carbonate (EC)‐ (EC)-lithium system. lithium system. lithium system.
Several theoretical works on the water in carbon nanotubes and on graphene have recently been Several theoretical works on the water in carbon nanotubes and on graphene have recently Several theoretical works on the water in carbon nanotubes and on graphene have recently been performed to feature of Werber et [6] out been performed to the gaindynamical the dynamical feature the interaction. Werber et al. (2003) [6] carried performed to gain gain the dynamical feature of the the ofinteraction. interaction. Werber et al. al. (2003) (2003) [6] carried carried out a a theoretical calculation of the carbon‐water interaction system and showed the importance of out a theoretical calculation the carbon-water interaction system showed the importance of theoretical calculation of the ofcarbon‐water interaction system and and showed the importance of the the relation between the contact angle of a water‐carbon the relation between contact angle a waterdroplet dropleton ongraphite graphitechanges changes and and the the water-carbon relation between the the contact angle of of a water water droplet on graphite changes and the water‐carbon interaction energy. Rana and Chandra (2007) [7] investigated the interaction of water containing a interaction energy. Rana and Chandra (2007) [7] investigated the interaction of water containing a interaction energy. Rana and Chandra (2007) [7] investigated the interaction of water containing a narrow carbon nanotube. The hydrogen bond distributions of water inside and also in the vicinity of narrow carbon nanotube. The hydrogen bond distributions of water inside and also in the vicinity narrow carbon nanotube. The hydrogen bond distributions of water inside and also in the vicinity of the outer surfaces of the simulation. The of the outer surfaces thenanotube nanotubewere wereobtained obtainedby bya molecular dynamics dynamics (MD) (MD) simulation. the outer surfaces of of the nanotube were obtained by a a molecular molecular dynamics (MD) simulation. The The solvation mechanism of lithium ions in pure ethylene carbonate (EC) solutions was studied in a wide solvation mechanism of lithium ions in pure ethylene carbonate (EC) solutions was studied in a wide solvation mechanism of lithium ions in pure ethylene carbonate (EC) solutions was studied in a wide concentration range by different techniques and temperatures Thus, the interaction of concentration techniques and temperatures [8]. [8]. Thus, the interaction of solvent with concentration range range by by different different techniques and temperatures [8]. Thus, the interaction of solvent solvent + with++ with carbon materials has been investigated by several groups. However, the interaction of EC‐Li carbon materials has been investigated by several groups. However, the interaction of EC-Li with carbon materials has been investigated by several groups. However, the interaction of EC‐Li with graphene is not clearly understood. graphene is not clearly understood. with graphene is not clearly understood. ++ the In our previous papers [9–11], we investigated the interaction systems of graphene‐Li In In our our previous previous papers papers [9–11], [9–11], we we investigated investigated the the interaction interaction systems systems of of graphene-Li graphene‐Li+, ,, the the graphene‐Li atom and graphene‐water and showed that the water molecule can bind an edge graphene-Li atom and graphene-water and showed that the water molecule can bind an edge graphene‐Li atom and graphene‐water and showed that the water molecule can bind an edge of of graphene. of graphene. graphene. In In the the present present study, study, the the density density functional functional theory theory (DFT) (DFT) method method [12–14] [12–14] was was applied applied to to a a ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium + ion (Li ion (Li+) and a nano‐structured graphene. For comparison, fluorinated vinylene carbonate,denoted ) and a nano‐structured graphene. For comparison, fluorinated vinylene carbonate,denoted by VC(F), was also used. by VC(F), was also used.
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In the present study, the density functional theory (DFT) method [12–14] was applied to a ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium ion (Li+ ) and a nano-structured graphene. For comparison, fluorinated vinylene carbonate, denoted by VC(F), was also used. 2. Method of Calculations 3 of 10 AsAtoms 2016, 4, 4 a graphene system, a carbon sheet composed of 14 benzene rings (C42 H16 ) was used as the nano-structured graphene in the present study. The edge carbon atom of graphene was terminated by 2. Method of Calculations a hydrogen atom. First, each structure of graphene, EC and VC was individually optimized using the As a graphene system, a carbon sheet composed of 14 benzene rings (C42H16) was used as the Handy and coworkers’ long-range corrected version of B3LYP using the Coulomb-attenuating method nano‐structured graphene in the present study. The edge carbon atom of graphene was terminated (CAM-B3LYP) with a 6-31G(d) basis set [15]. Next, the graphene-EC-Li+ ternary interaction system by a hydrogen atom. First, each structure of graphene, EC and VC was individually optimized using was fully optimized at the same level. All density functional theory (DFT) calculations were carried the Handy and coworkers’ long‐range corrected version of B3LYP using the Coulomb‐attenuating + ternary interaction method (CAM‐B3LYP) with a 6‐31G(d) basis set [15]. Next, the graphene‐EC‐Li out using the Gaussian 09 program package [16].
system was fully optimized at the same level. All density functional theory (DFT) calculations were
3. Results carried out using the Gaussian 09 program package [16]. 3. Results 3.1. Structures of EC(F) and VC(F)
Figure 2 shows the optimized structures of EC(F) and VC(F) used in the present study. The 3.1. Structures of EC(F) and VC(F) notation of n in EC(Fn) and VC(Fn) means the number of fluorine atoms in EC and VC, respectively. Figure 2 shows the optimized structures of EC(F) and VC(F) used in the present study. The The number n in EC(Fn) and VC(Fn) was varied as (n = 0 to 4) and (n = 0 to 2), respectively. notation of n in EC(Fn) and VC(Fn) means the number of fluorine atoms in EC and VC, respectively. The bond lengths of C=O carbonyl and the C–O single bond of EC(F0) were 1.190 and 1.355 Å, The number n in EC(Fn) and VC(Fn) was varied as (n = 0 to 4) and (n = 0 to 2), respectively. The bond lengths of C=O carbonyl and the C–O single bond of EC(F0) were 1.190 and 1.355 Å, respectively. These bond lengths were slightly changed by the F-substitution: 1.078 and 1.367 Å in EC(F4).respectively. These bond lengths were slightly changed by the F‐substitution: 1.078 and 1.367 Å in A large, different point appeared as a distance of r(C–C): 1.628 Å in EC and 1.552 Å in EC(F4). EC(F4). A large, different point appeared as a distance of r(C–C): 1.628 Å in EC and 1.552 Å in EC(F4). The F-substitution largely decreases the C–C single bond of EC. The F‐substitution largely decreases the C–C single bond of EC.
Figure Figure 2. Optimized structures of EC, fluorinated ethylene carbonate (EC(F)), vinylene carbonate (VC) 2. Optimized structures of EC, fluorinated ethylene carbonate (EC(F)), vinylene carbonate (VC) and fluorinated vinylene carbonate (VC(F)), calculated at the B3LYP/6‐31G(d) level. The notation of n and fluorinated vinylene carbonate (VC(F)), calculated at the B3LYP/6-31G(d) level. The notation of n in EC(Fn) and VC(Fn) means the number of fluorine atoms. Bond lengths are in Å. in EC(Fn) and VC(Fn) means the number of fluorine atoms. Bond lengths are in Å. The dipole moments of EC(F) and VC(F) are given in Table 1. The dipole moment of EC in n = 0 was 5.42 Debye, which in reasonable agreement with experimental value (4.9 Debye). The The dipole moments of is EC(F) and VC(F) are given in the Table 1. The dipole moment of EC in n = 0 dipole moment decreased significantly with increasing n. In the case of EC(F), the value (n = 4) was was 5.42 Debye, which is in reasonable agreement with the experimental value (4.9 Debye). The 1.39 D, which is lower than that of n = 0 (5.42 D). This is due to the fact that the dipole moment of the C=O carbonyl vanishes in the presence of the C‐F dipole. Thus, the effect of the halogen atom on the electronic state is very important in ethylene carbonate. In the case of the VC system, a similar diminishing was found after the F‐substitution.
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dipole moment decreased significantly with increasing n. In the case of EC(F), the value (n = 4) was 1.39 D, which is lower than that of n = 0 (5.42 D). This is due to the fact that the dipole moment of the C=O carbonyl vanishes in the presence of the C-F dipole. Thus, the effect of the halogen atom on the electronic state is very important in ethylene carbonate. In the case of the VC system, a similar diminishing was found after the F-substitution. Table 1. Dipole moments of EC, EC(F), VC and VC(F) (in Debye). The number of fluorine atoms in EC is denoted by n. The experimental value of the dipole moment is given in parenthesis [17]. CAM, Atoms 2016, 4, 4 4 of 10 Coulomb-attenuating method. Table 1. Dipole moments of EC, EC(F), VC and VC(F) (in Debye). The number of fluorine atoms in Dipole Moment EC is denoted by n. The experimental value of the dipole moment is given in parenthesis [17]. CAM, Coulomb‐attenuating method. n CAM-B3LYP/6-31G(d) CAM-B3LYP/6-311G(dp)
EC0 5.36 (4.9)Dipole Moment 5.42 EC(F1)1 4.76 4.80 CAM‐B3LYP/6‐31G(d) CAM‐B3LYP/6‐311G(dp) n EC(F2)2 3.61 3.50 EC0 5.36 (4.9) 5.42 EC(F3)3 2.87 2.75 EC(F1)1 4.76 4.80 EC(F4)4 1.67 1.39 EC(F2)2 3.61 3.50 VC0 4.71 4.69 EC(F3)3 2.87 2.75 VC(F1)1 3.70 3.59 EC(F4)4 1.67 1.39 VC(F2)2 2.61 2.40 VC0 4.71 4.69 VC(F1)1 3.70 3.59 VC(F2)2 In EC, the C–C bond is composed of 2.61 sp3 -sp3 carbons. On the2.40 other hand, the C–C bond in VC is
the sp2 -sp2 carbons. Hence, the C=C bond length of VC is significantly shorter than that of EC. The 3‐sp3 carbons. On the other hand, the C–C bond in VC is In EC, the C–C bond is composed of sp C=C bond lengths of VC, VC(F1) and VC(F2) were 1.326, 1.323 and 1.321 Å, respectively. the sp2‐sp2 carbons. Hence, the C=C bond length of VC is significantly shorter than that of EC. The C=C bond lengths of VC, VC(F1) and VC(F2) were 1.326, 1.323 and 1.321 Å, respectively. 3.2. Structures of Li+ -EC and Li+ -VC Complexes
+‐EC and Li+‐VC Complexes 3.2. Structures of Li The optimized structures of Li+ -EC and -VC complexes are given in Figure 3. The procedure of optimization was carried out without +symmetry restriction. The Li+ ion binds to the oxygen atom of The optimized structures of Li ‐EC and ‐VC complexes are given in Figure 3. The procedure of + ion binds to the oxygen atom of the C=O carbonyl of EC. The moiety of Li–O–C is almost linear in the Li+ EC complexes. The bond optimization was carried out without symmetry restriction. The Li + EC complexes. The bond the C=O carbonyl of EC. The moiety of Li–O–C is almost linear in the Li distances of Li–O and C=O carbonyl were calculated to be 1.740 and 1.225 Å, respectively. The C–O distances of Li–O and C=O carbonyl were calculated to be 1.740 and 1.225 Å, respectively. The C–O bond in the C=O carbonyl is elongated by the interaction with the Li+ ion. In the Li+ -VC system, + ion. In the Li+‐VC system, similar similar bond in the C=O carbonyl is elongated by the interaction with the Li binding structures were obtained.
binding structures were obtained.
Figure Figure 3. Optimized structures of lithium‐EC and ‐VC complexes calculated at the B3LYP/6‐31G(d) 3. Optimized structures of lithium-EC and -VC complexes calculated at the B3LYP/6-31G(d) level. Bond lengths are in Å. level. Bond lengths are in Å. The distances of Li+ from the oxygen atom of C=O carbonyl are plotted in Figure 4 as a function of the number of F atoms. The Li+‐EC complex has a distance of 1.740 Å. The distance increases with increasing n. In n = 4, the distance is as large as 1.779 Å.
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The distances of Li+ from the oxygen atom of C=O carbonyl are plotted in Figure 4 as a function of the number of F atoms. The Li+ -EC complex has a distance of 1.740 Å. The distance increases with increasing n. In n = 4, the distance is as large as 1.779 Å. Atoms 2016, 4, 4
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3.3. Binding Structures of Li+‐EC Complexes on Graphene Atoms 2016, 4, 4
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The optimized structures of the complexes of EC(F) and EC(F4) with graphene are illustrated The optimized structures of the complexes of EC(F) and EC(F4) with graphene are illustrated in 3.3. Binding Structures of Li+‐EC Complexes on Graphene in FigureFigure 5. In 5. both complexes, thethe C=O carbonyl towardthe thecenter center benzene In both complexes, C=O carbonyl orients orients toward of of the the benzene ring ring of of The optimized structures of the complexes of EC(F) and EC(F4) with graphene are illustrated in graphene. The bond lengths of the C=O carbonyl of EC and the height of the oxygen atom (h) of EC graphene. The bond lengths of the C=O carbonyl of EC and the height of the oxygen atom (h) of EC Figure 5. In both complexes, the C=O carbonyl orients toward the center of the benzene ring of are 1.783 and 1.915 Å, respectively. In the case of EC(F4), the height becomes lower (h = 1.882 Å). are 1.783 and 1.915 Å, respectively. In the case of EC(F4), the height becomes lower (h = 1.882 Å). graphene. The bond lengths of the C=O carbonyl of EC and the height of the oxygen atom (h) of EC are 1.783 and 1.915 Å, respectively. In the case of EC(F4), the height becomes lower (h = 1.882 Å).
Figure 4. Bond lengths of the Li ‐oxygen atom of Li‐EC complexes plotted as a function of the number + +
Figure 4. Bond lengths of the Li -oxygen atom of Li-EC complexes plotted as a function of the number +‐oxygen atom of Li‐EC complexes plotted as a function of the number of F‐atoms. The values were calculated at the B3LYP/6‐31G(d) level. Figure 4. Bond lengths of the Li of F-atoms. The values were calculated at the B3LYP/6-31G(d) level. of F‐atoms. The values were calculated at the B3LYP/6‐31G(d) level.
+‐graphene ternary systems. Bond lengths are in Å. (A); Li +‐ +‐graphene ternary systems. Bond lengths are in Å. (A); Li +‐ Figure 5. Optimized structures of EC‐Li Figure 5. Optimized structures of EC‐Li
+ -graphene ternary systems. Bond lengths are in Å. (A); Li` -EC Figure 5.EC Complexeson Graphene, (B); Li Optimized structures of EC-Li+‐EC(F4) Complexeson Graphene. EC Complexeson Graphene, (B); Li+‐EC(F4) Complexeson Graphene. ` Complexes on Graphene, (B); Li -EC(F4) Complexes on Graphene.
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Figure 6 shows the distance the oxygen of EC the graphene as a Figure 6 shows the distance of theof oxygen of EC from thefrom graphene surface (h)surface plotted(h) as aplotted function +‐VC are also function of n. The distance decreases slightly from 1.915 to 1.883 Å. The values of Li of n. The distance decreases slightly from 1.915 to 1.883 Å. The values of Li+ -VC are also plotted as a plotted as a dashed line in Figure 6: 1.907 Å (n = 0), 1.899 Å (n = 1) and 1.893 Å (n = 2). dashed line in Figure 6: 1.907 Å (n = 0), 1.899 Å (n = 1) and 1.893 Å (n = 2).
+‐EC (or Li+‐VC) from the graphene surface (h) plotted as Figure 6. Distances of the lithium atom of Li Figure 6. Distances of the lithium atom of Li+ -EC (or Li+ -VC) from the graphene surface (h) plotted a function of n, the number of F‐atoms. The values were calculated at the B3LYP/6‐31G(d) level. (a) as a function of n, the number of F-atoms. The values were calculated at the B3LYP/6-31G(d) level. + + + -VC. (a) Li Li+‐EC; (b) Li -EC; (b) Li‐VC.
3.4. Binding Energies of Li+‐EC Complexes on Graphene 3.4. Binding Energies of Li+ -EC Complexes on Graphene The binding energies of EC and VC in several binding systems are calculated;these systems are The binding energies of EC and VC in several binding systems are calculated;these systems are expressed by: expressed by: → EC(F)‐( Li EC(F) + Li ECpFq ` Li+ +Ñ ECpFq-pLi+ q+)(a) paq + + +)‐graphene (b) ECpFq-pLi q` graphene Ñ ECpFq-pLi+ q-graphene pbq ) + graphene → EC(F)‐( Li EC(F)‐( Li
VCpFq ` Li++Ñ VCpFq-pLi++q) (c) pcq VC(F) + Li → VC(F)‐( Li + VCpFq-pLi q +` graphene Ñ VCpFq-pLi+ q-graphene pdq +)‐graphene (d) VC(F)‐( Li ) +graphene → VC(F)‐( Li
Reaction (a) means the binding reaction of lithium ion to solvent EC(F). The solvated lithium ion Reaction (a) means the binding reaction of lithium ion to solvent EC(F). The solvated lithium ion is formed by Reaction (a). Reaction (b) is the binding reaction of the solvated lithium ion EC(F)-(Li+ ) to +) is formed by Reaction (a). Reaction (b) is the binding reaction of the solvated lithium ion EC(F)‐(Li theto the graphene surface. Reactions (c) and (d) in VC(F) are the same as EC(F). graphene surface. Reactions (c) and (d) in VC(F) are the same as EC(F). The reverse reaction of Reaction (a), i.e., desolvation of Li+ from+ from solvent EC(F), Li solvent EC(F), Li+ -EC Ñ+‐EC → Li Li+ + EC,+ + The reverse reaction of Reaction (a), i.e., desolvation of Li is the important process process in the movement of the Li+of ion from tosolvent graphene. The weaker EC, most is the most important in the movement the Li+ solvent ion from to graphene. The + + ion by EC is a positive factor as a solvent. Namely, the weak solvation of solvation of the Li ion by EC is a positive factor as a solvent. Namely, the weak solvation of Li+ is weaker solvation of the Li preferred as an effective solvent. Li+ is preferred as an effective solvent. The calculated binding energies generated by Reactions (a) to (d) are plotted in Figure 7. The The calculated binding energies generated by Reactions (a) to (d) are plotted in Figure 7. The binding energies of Li+ to+ to EC(F) (Reaction (a)) decreases with increasing n: 56.1 kcal/mol (n = 0) and EC(F) (Reaction (a)) decreases with increasing n: 56.1 kcal/mol (n = 0) and binding energies of Li 39.6 kcal/mol (n = 4). The results suggest that EC(F4) is more preferred as the solvent than EC(H), 39.6 kcal/mol (n = 4). The results suggest that EC(F4) is more preferred as the solvent than EC(H), + ion is the positive factor as the Li + solvent. because the weaker solvation of the Li+ ion is the positive factor as the Li+ solvent. because the weaker solvation of the Li Furthermore, the binding energies for Reactions (b), (c) and (d) show the same tendency as Reaction (a).
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Figure 7. Binding energies in several systems plotted as a function of n, the number of F‐atoms. (a) Figure 7. Binding energies in several systems plotted as a function of n, the number of F-atoms. +‐graphene; (c) VC‐Li+; and (d) VC‐Li+‐graphene. EC‐Li+; (b) EC‐Li (a) EC-Li+ ; (b) EC-Li+ -graphene; (c) VC-Li+ ; and (d) VC-Li+ -graphene.
Furthermore, the binding energies for Reactions (b), (c) and (d) show the same tendency as 4. Discussion Reaction (a). The weaker solvation of Li+ ion is a positive factor as the solvent. In the present study, the effects of4. Discussion F-substitution on the binding energies of EC to the Li+ ion and Li+ (EC) to the graphene surface have been investigated by means of the DFT method. The calculations showed that the binding energy The weaker solvation of Li+ ion is a positive factor as the solvent. In the present study, the effects decreases with increasing n. F-substitution makes the interaction of graphene with EC(F) significantly of F‐substitution on the binding energies of EC to the Li+ ion and Li+(EC) to the graphene surface have weaker due to the small dipole moment of EC(F) (1.4 D vs. 5.4 D). This result implies that desolvation been investigated by means of the DFT method. The calculations showed that the binding energy of the Li+ ion from the F-substituted system, EC(F)-Li+ , occurs more easily than that of EC(H). Hence, decreases with increasing n. F‐substitution makes the interaction of graphene with EC(F) significantly the ability of EC(F) is greater than that of EC(H). weaker due to the small dipole moment of EC(F) (1.4 D vs. 5.4 D). This result implies that desolvation In the present study, a carbon sheet composed of 14 benzene rings (C42 H16 ) was used as a model of of the Li+ ion from the F‐substituted system, EC(F)‐Li+, occurs more easily than that of EC(H). Hence, the graphene surface. This is a small number of rings for modeling a finite graphene surface. However, the ability of EC(F) is greater than that of EC(H). recent theoretical calculations indicated that this size of graphene sheet can reasonably represent the In the present study, a carbon sheet composed of 14 benzene rings (C42H16) was used as a model electronic states of the graphene system [18–21]. Therefore, the present calculations would provide of the graphene surface. This is a small number of rings for modeling a finite graphene surface. useful information on the ternary interaction system. However, recent theoretical calculations indicated that this size of graphene sheet can reasonably represent the electronic states of the graphene system [18–21]. Therefore, the present calculations would Acknowledgments: The author acknowledges partial support from JSPS KAKENHI Grant Number 15K05371 provide useful information on the ternary interaction system. and MEXT KAKENHI Grant Number 25108004. Author Contributions: Mami Mutoh, Teruo Kusaka and Mariko Nakamura carried out the DFT calculations of Acknowledgments: The author acknowledges partial support from JSPS KAKENHI Grant Number Li` -EC Complexes on Graphene. Yasuhiro Yoshida, Junichiro Iida, and Hiroto Tachikawa conceived of the study, 15K05371 and MEXT KAKENHI Grant Number 25108004. and participated in its design and coordination and helped to draft the manuscript.
Author Mami Mutoh, Teruo ofKusaka Conflicts ofContributions: Interest: The authors declare no conflict interest.and Mariko Nakamura carried out the DFT calculations of Li+‐EC Complexeson Graphene. Yasuhiro Yoshida, Junichiro Iida, and Hiroto References Tachikawa conceived of the study, and participated in its design and coordination and helped to 1. draft the manuscript. Bhatta, M.D.; Cho, M.; Cho, K. Interaction of Li+ ions with ethylene carbonate (EC): Density functional theory calculations. Appl. Surf. Sci. 2010, 257, 1463–1468. [CrossRef] Conflicts of Interest: The authors declare no conflict of interest. 2. Nakagawa, H.; Fujino, Y.; Kozono, S.; Katayama, Y.; Nukuda, T.; Sakaebe, H.; Matsumoto, H.; Tatsumi, K. Application of nonflammable electrolyte with room temperature ionic liquids (RTILs) for lithium-ion cells. References J. Power Sources 2007, 174, 1021–1026. [CrossRef] 1. Bhatta, M.D.; Cho, M.; Cho, K. Interaction of Li+ ions with ethylene carbonate (EC): Density functional Xing, L.; Li, W.; Wang, C.; Gu, F.; Xu, M.; Tan, C.; Yi, J. Theoretical Investigations on Oxidative Stability 3. theory calculations. Appl. Surf. Sci.2010, 257, 1463–1468. of Solvents and Oxidative Decomposition Mechanism of Ethylene Carbonate for Lithium Ion Battery Use. 2. Nakagawa, H.; Fujino, Y.; Kozono, S.; Katayama, Y.; Nukuda, T.; Sakaebe, H.; Matsumoto, H.; Tatsumi, K. J. Phys. Chem. B 2009, 113, 16596–16602. [CrossRef] [PubMed] Application of nonflammable electrolyte with room temperature ionic liquids (RTILs) for lithium‐ion cells. J. Power Sources 2007, 174, 1021–1026. 3. Xing, L.; Li, W.; Wang, C.; Gu, F.; Xu, M.; Tan, C.; Yi, J. Theoretical Investigations on Oxidative Stability of Solvents and Oxidative Decomposition Mechanism of Ethylene Carbonate for Lithium Ion Battery Use. J. Phys. Chem. B 2009, 113, 16596–16602.
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Zhang, H.L.; Sun, C.H.; Li, F.; Liu, C.; Tan, J.H.; Cheng, M. New insight into the interaction between propylene carbonate-based electrolytes and graphite anode material for lithium ion batteries. J. Phys. Chem. C 2007, 111, 4740–4748. [CrossRef] Zhu, Y.; Casselman, M.D.; Li, Y.; Wei, A.; Abrahama, D.P. Perfluoroalkyl-substituted ethylene carbonates: Novel electrolyte additives for high-voltage lithium-ion batteries. J. Power Sources 2014, 246, 184–191. [CrossRef] Werber, T.; Walther, J.H.; Jaffe, R.L.; Halicioglu, T.; Koumoutsakos, P. On the water-carbon interaction for use in molecular dynamics simulations of graphite and carbon nanotubes. J. Phys. Chem. B 2003, 107, 1345–1352. Rana, M.; Chandra, A. Filled and empty states of carbon nanotubes in water: Dependence on nanotube diameter, wall thickness and dispersion interactions. J. Chem. Sci. 2007, 119, 367–376. [CrossRef] Castriota, M.; Cazzanelli, E.; Nicotera, I.; Coppola, L.; Oliviero, C.; Ranieri, G.A. Temperature dependence of lithium ion solvation in ethylene carbonate-LiClO4 solutions. J. Chem. Phys. 2003, 118, 5537–5541. [CrossRef] Tachikawa, H. A direct molecular orbital-molecular dynamics study on the diffusion of the Li ion on a fluorinated graphene surface. J. Phys. Chem. C 2008, 112, 10193–10199. [CrossRef] Abe, S.; Nagoya, Y.; Watari, F.; Tachikawa, H. Interaction of Water Molecules with Graphene: A Density Functional Theory and Molecular Dynamics Study. Jpn. J. Apl. Phys. 2010, 49, AH071–AH074. [CrossRef] Abe, S.; Nagoya, Y.; Watari, F.; Tachikawa, H. Structures and Electronic States of Water Molecules on Graphene Surface: A Density Functional Theory Study. Jpn. J. Apl. Phys. 2010, 49, GJ131–GJ133. [CrossRef] Amft, M.; Sanyal, B.; Eriksson, O.; Skorodumova, N.V. Small gold clusters on graphene, their mobility and clustering: A DFT study. J. Phys. Condens. Matter 2011, 23, 205301. [CrossRef] [PubMed] Ding, N.; Lu, X.Q.; Wu, C.M.L. Nitrated tyrosine adsorption on metal-doped graphene: A DFT study. Comput. Mater. Sci. 2012, 51, 141–145. [CrossRef] Lim, D.H.; Wilcox, J. DFT-Based Study on Oxygen Adsorption on Defective Graphene-Supported Pt Nanoparticles. J. Phys. Chem. 2011, 115, 22742–22747. [CrossRef] Yanai, T.; Tew, D.; Handy, N. A new hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51–57. [CrossRef] Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Montgomery, J.A., Jr.; Vreven, T.; Kudin, K.N.; Burant, J.C.; et al. Gaussian 03, Revision B.04; Gaussian, Inc.: Pittsburgh, PA, USA, 2003. Payne, R.; Theodorou, I.E. Dielectric properties and relaxation in ethylene carbonate and propylene carbonate. J. Phys. Chem. 1972, 76, 2892–2900. [CrossRef] Mirzaei, M.; Ahangari, R.S. Formations of CNT modified 5-(halogen)uracil hybrids: DFT studies. Superlattice Microstruct. 2014, 65, 375–379. [CrossRef] Peyghan, A.A.; Noei, M.; Yourdkhani, S. Al-doped graphene-like BN nanosheet as a sensor for para-nitrophenol: DFT study. Superlattice Microstruct. 2013, 59, 115–122. [CrossRef] Jenness, G.R.; Karalti, O.; Jordan, K.D. Benchmark calculations of water-acene interaction energies: Extrapolation to the water-graphene limit and assessment of dispersion-corrected DFT methods. Phys. Chem. Chem. Phys. 2010, 12, 6375–6381. [CrossRef] [PubMed] Pisula, W.; Feng, X.; Mullen, K. Charge-Carrier Transporting Graphene-Type Molecules. Chem. Mater. 2011, 23, 554–567. [CrossRef] © 2015 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
