Hybrid Quantum-Classical Simulation of Li-Ion Dynamics and the

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Hybrid Quantum-Classical Simulation of Li-Ion Dynamics and the Decomposition Reaction of Electrolyte Liquid at a Negative-Electrode/Electrolyte Interface Nobuko Ohba, Shuji Ogata, and Ryoji Asahi J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b11737 • Publication Date (Web): 01 Apr 2019 Downloaded from http://pubs.acs.org on April 2, 2019

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The Journal of Physical Chemistry

Hybrid Quantum-Classical Simulation of Li-Ion Dynamics and the Decomposition Reaction of Electrolyte Liquid at a Negative-Electrode/Electrolyte Interface

Nobuko Ohba,a,* Shuji Ogata,b and Ryoji Asahia

a

Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan

b

Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Nagoya, Aichi

466-8555, Japan

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ABSTRACT: Solid electrolyte interphase (SEI) films play a key role in the operation of Li-ion batteries, however, the formation mechanism of SEI remains unclear. In this study, the dynamics of Li-ions inserted between a negative graphite electrode and an ethylene carbonate (EC) electrolyte solvent were investigated using a hybrid quantum-classical (QM-CL) molecular dynamics (MD) simulation. The activation energy of the Li-ion insertion process was estimated to be 0.73 eV, which is nearly equal to the experimental one of the Li-ion desolvation process. This was converted to 0.22 V/Å (the critical electric field strength required to overcome the activation energy of the 3.29 Å distance between the transition and equilibrium states). Upon applying an electric field of 0.3 V/Å in the hybrid QM-CL MD simulation, the desolvated Li-ion was rapidly inserted into the graphite. On the other hand, when an electric field strength of 0.2 V/Å was applied, the EC molecule received an electron from the graphite electrode at the interface coexisting with a Li-ion and decomposed then to C2H4 and Li-CO3. This indicated that the Li-ions catalyzed the decomposition of the EC, thereby clarifying the initial stage of the formation of a SEI by the reductive decomposition of the EC molecules.


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INTRODUCTION

In Li-ion secondary batteries, Li-ions move between the positive and negative electrodes via an electrolyte phase. Charging and discharging of the battery take place via various chemical reactions that occur on the electrode surface, which are accompanied by the movement of the Li-ions. For an organic electrolyte liquid based on ethylene carbonate (EC), the electrolyte undergoes a reductive decomposition reaction around 1 V during the initial charging stage.1,2 Consequently, a passive film is formed on the surface of the negative electrode, which suppresses the further decomposition of the electrolyte. A passive film that is permeable to Li-ions is known as a solid-electrolyte interphase (SEI). Although a SEI is known to affect the migration of Li-ions at the electrode interface, its detailed formation process and structural features remain unclear. Neutron reflectometry, used for the operando measurement of the formation of an SEI at an electrode, was conducted to determine the mechanism whereby an SEI is formed.3 Furthermore, the thicknesses of the interfacial layers and the chemical composition of the SEI during charging were estimated. Verma et al.4 reviewed the nature, formation, and features of an SEI on a carbon negative electrodes, and concluded that it was difficult to control its formation and growth to obtain an ideal SEI for use in a battery.



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Graphite is usually used as the active material in the negative electrodes of Li-ion batteries because with an EC-based electrolyte, a graphite surface is stabilized by the formation of an SEI.5,6 The formation of an SEI begins with a reduction reaction of the liquid electrolyte, which occurs during the first charging process of the Li-ions from the liquid to the graphite. The graphite electrode, Li-ions, and nonaqueous EC electrolyte solvent participate in this reaction. The following two possible reaction models7,8 were investigated for the initial stage of the SEI formation process: (a) Co-intercalation reaction model: The solvated Li-ions are intercalated into the graphite layers with solvent molecules, such as EC. The reductive reaction (or electron transfer reaction) of the solvated Li-ions occurs between the graphite layers, where this reaction are accelerated by interlayer compression forces. In other words, the starting point of the formation of the SEI films is the interlayer of the graphite. (b) Interface reaction model: The EC decomposition reaction occurs only at the interface of the graphite electrode and the liquid electrolyte, where the difference in the electric potential is large and the electronic state of the EC molecule changes. In the support of model (a), Inaba et al.9,10 observed the basal plane of highly oriented pyrolytic graphite in 1 M LiClO4/EC/DEC using in-situ electrochemical STM, and reported that the height of the observed peaks was 1nm, which was equivalent to the increment in the graphite 4 ACS Paragon Plus Environment

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interlayer spacing during the formation of ternary graphite intercalation compounds [Li(solv)yCn]. Besenhard et al.11 and Chung et al.12 suggested that the ternary graphite intercalation compounds formed as a result of the co-intercalation of the Li-ions with solvent molecules, which decomposed between the graphite layers. Chung et al.12 reported that the co-intercalation of the Li-ions with solvent caused the exfoliation of graphite. In the recent review by Xu 13 and references therein, model (a) is expressed as “3D SEI formation mechanism” and the experimental results about the voltage dependence 14 and the heat effects 15 for the decomposition process of electrolytes are referred. Moreover, “EC-PC Disparity” for the formation of SEI is discussed by Xing et al. 16 On the other hand, Aurbach et al.,17,18 in support of model (b), reported that the Li-ions were intercalated into graphite without solvent, with the reduction of a solvated molecule occurring on the surface of the graphite and with the formation of an intermediate radical anion. Therefore, unlike co-intercalation model (a), the radical anion can diffuse away from the edge of the graphite and the decomposition products can form and spread on the interface between the liquid electrolyte and the graphite.7 Simulations of the SEI formation process require the transportation of Li-ions and the chemical reactions at the negative-electrode/electrolyte interface to be considered simultaneously.1,19 Wang et al. 20 overview the computational modeling progress for better 5 ACS Paragon Plus Environment


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understanding of SEI. The eReaxFF molecular dynamics simulation was developed for large-scale simulations and to describe the charge transfer reaction and analyzed the EC decomposition mechanism. 21 Yun et al. predict the components of SEI generated from the chemical reaction between the anodes and liquid electrolyte using ReaxFF force field simulation. 22

These ReaxFF methods are useful for large-scale simulation, but the accuracy is depending

their parameters. Although the conventional ab initio molecular dynamics (AIMD) simulation is a valuable means of investigating SEI formation mechanisms,1 it incurs a high computational costs. Li and Qi 23 develop the self-consistent-charge density functional tight-binding (SCC-DFTB) approach and investigate the charge transfer reactions at a Li/SEI/electrolyte interface considering the balance of the computational cost and precision. Alternatively, the hybrid Monte Carlo (MC)-molecular dynamics (MD) reaction method reveals the atomistic differences between the EC- and propylene-carbonate-based SEI films on negative graphite electrodes.24 This method requires the assumption of a list of elementary reaction processes to be assumed in advance. Both the AIMD and hybrid MC-MD simulation methods were originally proposed for unbiased potential systems under periodic boundary conditions. To enable the reactions on the biased electrode to be taken into account, additional, specialized computation methods must incorporated, as follows. Using the AIMD simulation, Leung et al.25-27 estimated the electrode voltage dependence of the free energy and the surface charges, assuming the 6 ACS Paragon Plus Environment

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number of electrons to be constant. Recently, a sophisticated simulation method that combined the effective screening medium method and the reference interaction site model with density-functional theory (DFT) was reported.28 29 However, if the boundary conditions can be freely set, the electrode reaction can be simulated using a very simple model of the application of an electric field. We have been developing an O(N)-type real-space grid based DFT (RGDFT) code30 with a flexible boundary condition and a hybrid quantum-classical (QM-CL) simulation method that uses this code, as a large-scale calculation method.31-33 The hybrid QM-CL simulation method entails applying a high-precision quantum-mechanical calculation method, such as DFT, to the quantum (QM) region in which the change of in the electronic state becomes important. This QM cluster region is then embedded into the entire system, as represented by an empirical interaction model. Therefore, this method can account for both the transport properties and the chemical reactions of a large-scale system at a reasonable calculation cost. Basically, the free boundary condition can be set as the boundary of the QM region and the dependence of the electrode potential can be considered by applying the electric field to the QM region. It is not necessary to apply an electric field in the CL calculation, where the change in the electronic state is not considered. Moreover, the interlayer distance of the graphite extends by about 10% as a result of the intercalation of the Li-ions.34,35 Graphite exfoliation may occur when the Li-ions are 7 ACS Paragon Plus Environment


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co-intercalated with solvent molecules.5 Therefore, when evaluating the details of the process whereby Li-ions are inserted into graphite, it is necessary to consider the changes in the graphite structure as a stress field with long-distance effects. The hybrid QM-CL method is well suited to this situation. We previously applied the hybrid QM-CL simulation method to an analysis of the diffusivity of Li-ions in graphite.36-38 Assuming the use of EC as the electrolyte solution solvent and lithium dimethyl carbonate (Li2EDC) as the organic compound component of the SEI, we executed a first-principles MD calculation of several thousand atoms at the EC/Li2EDC interface.39 We analyzed the details of the Li-ion transfer process near the interface and clarified that the PF6- ions of LiPF6, which was added to the electrolyte as a salt, promoted the migration of the Li-ions at the interface. In the present study, using graphite as the anode and EC as the electrolyte solvent, we focused on the Li-ion insertion process at the graphite/EC interface. The initial process leading to the formation of the SEI was analyzed using the hybrid QM-CL simulation method to clarify the mechanism of the interface. As a result, we were able to find the essential reaction process for the initial stage of SEI formation using simplified modeling without explicitly considering the salt anion.

METHODOLOGY AND MODELING 8 ACS Paragon Plus Environment

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Hybrid QM-CL Simulation Method.

For the quantum mechanics calculation, O(N)-type RGDFT code using a norm-conserving pseudopotential was employed.30 This method is more suitable for large-scale calculations than the density-functional method based on a plane wave expansion approach, and it enabled the boundary conditions to be set flexibly. The mesh size of the space division was initially set to h = 0.219 Å; however, for the pseudopotential near the nucleus, a finer mesh (h/3) was used. The periodic boundary conditions were imposed on the classical MD calculations, and for the numerical integration of Newton’s equation of motion, the velocity Verlet method was used. Moreover, a Brenner-type potential40 was used as the interaction potential between the carbon atoms, with an original, potential model we developed for the interlayer interaction.38 (refer to our previous reports 30,39 and related reference41 for details on the calculation method.) The buffered cluster method31 was used to model the boundary between the quantum region and the classical region in the hybrid QM-CL simulation; this is a highly accurate method and a robust model because it is independent of the shape of the boundary condition.

Simulation Model for Static Calculation.



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As a preliminary examination, the change in the energy level as a result of inserting a Li-ion from the EC electrolyte into the negative graphite electrode was evaluated. Figure 1 shows the model used for the calculation. Assuming the initial stage of the Li-ion insertion process, the graphite had an AB stacking structure and hydrogen atoms terminated the edge of the graphite. This termination suppressed any chemical reactions except for Li-ion and/or solvent EC intercalation and de-intercalation at the interface. First, an EC cluster model including one Li and the graphite model were prepared separately and they were combined. After that, the initial structure were obtained by fixing the Li position and relaxing other atoms by 2000 steps of MD simulation. QM calculations were performed for the region in which the charge transfer takes place, given the changes in the electronic structure. Therefore, the QM calculation included part of the graphite, a Li-ion, and four EC molecules. This region is denoted as the “cluster region” in Figure 1.

Model for MD Simulation with Biased System.

The simulation model, shown in Figure 2, is an extension of the static study presented in the previous section. For the simulation, the graphite was composed of 10 layers in an AB stacking structure, while 16 EC molecules and one Li atom were arranged next to the graphite.


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The bright atoms in Fig. 2, indicated by the large sphere, are a group of 521 atoms that were included in the QM calculation. The entire system was set with a periodic boundary condition and a confinement-type potential was set to retain the liquid state of the EC molecules. Moreover, in consideration of the spread of the interlayer distance of the graphite accompanying the insertion of the Li-ions, a vacuum region of 12 Å was set on the upper and lower layers of the graphite. The outer edge of the graphite in contact with the EC was terminated by hydrogen atoms. As the driving force for the Li-ion insertion, an electric field of constant strength was applied to the QM region from the EC in the direction of the graphite. On the other hand, an electric field was not considered in the CL calculation. In the present hybrid QM-CL simulation, the range where the electronic structure change accompanying Li insertion is included in the QM region. In graphite, it is at most a six-membered ring containing Li-ion and a one next to it. There is no change in the electronic structure in the CL region, so it is not necessary to consider the effect of the electric field in the CL region.

RESULTS AND DISCUSSION Activation Barrier for Li Insertion Process.



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The total energy for the model shown in Fig. 1 was obtained by fixing the position of the Li-ion relative to the graphite and by relaxing the atoms surrounding each Li-ion. In this static simulation, the co-intercalation of the solvent EC accompanying the movement of the Li-ion was not confirmed. Figure 3 shows the energy change at each Li-ion position. The activation barrier energy for the desolvation of a Li-ion and its insertion into the graphite was estimated to be 0.73 eV. This value is similar to the Li-ion desolvation activation energy of 0.64 – 0.72 eV measured via electrochemical impedance spectroscopy by Xu et al.42 As can be seen from Figure 3, the structure of the EC molecule has not changed significantly. This suggests that the movement of EC molecules cannot follow the movement of Li ions and that the structural relaxation of the EC molecules may be insufficient. Therefore, the activation energy obtained in this simulation may be overestimated. The migration distance of the Li-ion from a stable location in the EC electrolyte to the maximum value of the activation barrier energy was found to be approximately 3.29 Å. Therefore, the electric field strength required to overcome this activation barrier was estimated to be 0.73/3.29 = 0.22 V/Å. Although it is difficult to directly compare the magnitude of the electric field strength estimated from the activation barrier energy with an experimental value, the SEI formation potential and the diffusion distance at the interface may be useful references. In the experiment, when the electrons initially charged the graphite, the reductive decomposition reaction of the EC 12 ACS Paragon Plus Environment

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began at a potential near 0.8 V vs. Li/Li+, as the SEI film formed.4,43,44 Then, as previously confirmed, the insertion of Li-ions into the graphite commenced at a potential of 0.25 V vs. Li/ Li+ or lower.4,17 Moreover, because the diffusion distance at the interface of a typical electrolyte liquid seems to be several angstroms, the electric field strength as observed from above was considered to be of approximately the same order as the experimentally estimated field strength generated in the vicinity of the electrolyte-negative electrode/graphite interface.

Insertion of Li-ion from EC into Graphite.

The hybrid QM-CL MD simulation was conducted at a temperature of T = 398 K, and the effect of the electric field strength on the dynamics of the insertion process of a Li-ion at the graphite/EC interface was investigated. The strength of the electric field (E) was set to 0, 0.2, and 0.3 V/Å. Figure 4(a-c) shows snapshots at each time step. In the case of E = 0 (Figure 4a) and 0.2 V/Å (Figure 4b), the Li-ion was not inserted into the graphite after a simulation time of 0.52 ps. However, the Li-ion was desolvated and immediately inserted into the graphite when E = 0.3 V/Å (Figure 4c). These results corresponded to the static simulation result mentioned in the previous section and revealed that the electric field strength necessary for Li-ion insertion was 0.22 V/Å. 13 ACS Paragon Plus Environment


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Reductive Decomposition of EC in Presence of Li.

The MD simulation was continued for approximately 1 ps with an electric field strength of 0.2 V/Å. Consequently, the decomposition of the EC molecule into ethylene (C2H4) and carbonic acid (CO3) in the presence of Li-ions was observed at around t =0.78 ps, as shown in the snapshot in Figure 5. This indicated that the Li-ions catalyzed the decomposition of the EC, which is considered to be the initial step leading to SEI formation. Verma et al. 4 reported that the electrode potential of the SEI formation (namely the reductive reaction of electrolytes) was higher than that of the Li-ion intercalation for an ordered carbon electrode. Our simulation results indicated that the reductive decomposition reaction of EC occurs before the intercalation of the Li-ions into graphite, which is in good agreement with the experimental results. The decomposition process of the EC was examined in detail by analyzing the Mulliken charge and the distance between the Li-ion and the center of mass of the EC molecule. Figure 6(a-c) shows the values of the Mulliken charge at different times during the simulation. Strictly, the magnitude of the Mulliken charge did not correspond to the general valence charge; for example, the Li did not give a valence value of +1. However, for analyses of the charge transfer between atoms, the Mulliken charges generally give reliable results. Figure 6a shows the changes


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in the Mulliken charges of the C atoms in the graphite, the Li, and the group of EC molecules, respectively. Although the graphite charge increased over time, the charge on the group of EC molecules tended to decrease. This indicated that the electrons were transferred from the graphite to the EC molecules. The value of the Mulliken charge of the Li remained almost constant. Figure 6b shows the values of the Mulliken charge for each EC molecule. The Mulliken charge of EC molecule number 8 (EC8) changed significantly from positive to negative, with an electron being transferred to EC8. This suggested that EC8 was a decomposed molecule, as reductive decomposition had occurred by electron transfer from the graphite electrode. The changes in the valence charges of the C2H4 and CO3 portion of the decomposed EC8 are shown in Figure 6c. After the decomposition, the C2H4 had a slight positive charge and the CO3 was slightly negatively charged. Consequently, the C2H4 was attracted to the graphite edge after the decomposition and the CO3 was repelled from the graphite while bonding with the Li-ion. The time evolution of the distance between the Li-ion and the EC is plotted in Figure 7. This figure shows that the Li-ion was first solvated by four EC molecules, within a distance of 4 Å, and that the number of solvated EC molecules then decreased to approximately two at a simulation time of t = 0.1 ps. In addition, EC molecule number 3 (EC3) and EC8 solvated to the Li-ion for a limited time until an electron was transferred from the graphite C atoms to EC8. The EC molecule then decomposed into C2H4 and CO3-Li in the presence of the Li-ion. 15 ACS Paragon Plus Environment


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This result was confirmed by analyzing the reaction route using the global reaction route mapping (GRRM) method.45 The electronic structure calculation was conducted using Gaussian 03 and 09, with a calculation condition of B3LYP/6-311 ++ G (d, p)-PCM//B3LYP/6-31G (d, p). The results are shown in Figure S1. In the absence of Li, the EC mainly decomposed to carbon dioxide (CO2) and acetaldehyde (C2H4O), whereas, in the presence of Li, a reaction pathway involving the decomposition of EC to C2H4 and CO3 was obtained. Therefore, Li can be considered to contribute catalytically to the EC decomposition reaction by changing the decomposition reaction pathway. In addition, it has also been reported that in the presence of vinylene carbonate (VC) additives in Li-ion batteries, the compounds generated from the reductive decomposition reaction of VC differ depending on whether a Li-ion exists close to a VC molecule.46

CONCLUSION

This study investigated the process of Li-ion insertion and the reductive decomposition reaction at the graphite/EC interface by performing an MD simulation using a hybrid QM-CL simulation method. In the static simulation study, the electric field strength required for the Li-ion insertion was estimated to be 0.22 V/Å by calculating the activation barrier of the


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Li-insertion process. When the graphite edge is terminated with oxygen or a hydroxyl group, which are stronger in electron donating ability than hydrogen, Li-ions tend to be attracted and there is a possibility that the activation energy is lowered. The Li-ions were desolvated and rapidly inserted into the graphite by the application of an electric field of 0.3 V/Å in the hybrid QM-CL MD simulation. However, an electric field strength of less than 0.22 V/Å was insufficient to achieve the insertion of the Li-ions into the graphite. However, at an electric field strength of 0.2 V/Å, an electron was transferred from the graphite to the EC electrolyte, and consequently, the EC decomposed into ethylene and Li-carbonic acid in the presence of Li-ions. This reaction can be thought of as the initial process of SEI formation. The EC decomposition products in the presence of Li-ions were consistent with the results obtained by reaction path analysis using the GRRM calculation, which was performed separately. This study confirmed the initial process of SEI formation and our simulation results advocate the use of an interface reaction model rather than a co-intercalation reaction model under a relatively strong electric field. Since the decomposition reaction is assumed to depend on the structure of the graphite edge, the completeness of the stacking order of graphite layers, the existence of some defects, and the strength of electrode voltage, the possibility of co-intercalation cannot be completely denied.



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The reductive decomposition reactions of EC actually occur in sequence, and the formation of an SEI film continues until the entire graphite surface is covered. Understanding the details of the formation process of an SEI film and the structure of the SEI has become important for the development of Li-ion batteries. In the future, we plan to clarify the details of the phenomenon at the interface of the negative electrode and the electrolyte liquid of a Li-ion secondary battery by extending the classical model region to include the electrolyte liquid, while increasing the number of samples for the chemical reactions. In addition, we are working on developing a chemical reaction acceleration algorithm to investigate the chemical reactions over an extended period, such as during the formation of thicker SEI films.


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Figure 1. Static simulation model of the graphite-EC electrolyte interface. The magenta, gray, white, and red spheres denote Li, C, H, and O atoms, respectively. The region included in the QM calculation (the cluster region) is surrounded by a dashed line. Two Li atoms equivalent to the initial and final positions are pictured in this figure, but only one Li atom is set in the simulation.



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Figure 2. Simulation model of the graphite-EC interface for the MD calculation. The blue, gray, pink, and red spheres represent Li, C, H, and O atoms, respectively. The group of atoms shown as a bright large sphere (the cluster region) was the object of the QM calculation. An electric field, E, was applied to the cluster region.


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Figure 3. Energy diagram for each Li-ion position upon insertion into the graphite anode after being transferred from the EC electrolyte.



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Figure 4. Snapshots of different stages of the simulation. (a) E =0 V/Å, (b) E =0.2 V/Å, (c) E = 0.3 V/Å.


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Figure 5. Snapshot of the simulation at t = 0.78 ps with an electric field strength E = 0.2 V/Å. Mulliken charge analysis suggests that the decomposed molecule is the EC molecule number 8 (EC8).



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Figure 6. Evolution of Mulliken charges with time. (a)Mulliken charges of C atom-group of the graphite, Li, and 16 EC molecules. (b)Mulliken charges of each EC molecule. (c)Mulliken charges of the C2H4 and CO3 portions of the decomposed EC8.


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Figure 7. Time evolution of distance between Li-ion and EC molecule.



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ASSOCIATED CONTENT

Supporting Information. The following files are available free of charge. The energy diagram of the EC and Li+EC decomposition reactions calculated using the GRRM method. (HybridQMCL-SI2.pdf)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Phone: +81-561-71-7354

ORCID Nobuko Ohba: 0000-0001-9779-6401 Shuji Ogata: 0000-0002-5396-5864 Ryoji Asahi: 0000-0002-2658-6260 Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT This research was supported by the MEXT Strategic Programs for Innovative Research (SPIRE), the Computational Materials Science Initiative, the High Performance Computing Infrastructure (HPCI) of RIST (hp120123, hp13022, hp140096, hp140214, hp150041), and the Grant-in-Aid for Scientific Research (Kakenhi: 23310074) of Japan. The computations were performed using K computer at AICS of RIKEN, a Fujitsu FX10 at the Information Technology Center of the University of Tokyo, a Fujitsu FX10 at the Institute for Solid State Physics of the University of Tokyo, a Hitachi SR16000 at the Institute of Material Research of the Tohoku University, a Fujitsu FX1, FX10, and FX100 at the Information Technology Center of the Nagoya University, and a Fujitsu PRIMERGY at the Research Center for Computational Science (Okazaki).

REFERENCES 1.

Leung, K., Electronic Structure Modeling of Electrochemical Reactions at

Electrode/Electrolyte Interfaces in Lithium Ion Batteries. J. Phys. Chem. C 2012, 117, 1539-1547. 2.

Xuan, W. Y., Lithium-Ion Batteries: Solid-Electrolyte Interphase; World Scientific, 2004.

3.

Kawaura, H.; Harada, M.; Kondo, Y.; Kondo, H.; Suganuma, Y.; Takahashi, N.; Sugiyama,

J.; Seno, Y.; Yamada, N. L., Operando Measurement of Solid Electrolyte Interphase Formation at



Page 28 of 32

Working Electrode of Li-Ion Battery by Time-Slicing Neutron Reflectometry. ACS applied materials

& interfaces 2016, 8, 9540-9544. 4.

Verma, P.; Maire, P.; Novák, P., A Review of the Features and Analyses of the Solid

Electrolyte Interphase in Li-Ion Batteries. Electrochim. Acta 2010, 55, 6332-6341. 5.

Fong, R.; Von Sacken, U.; Dahn, J. R., Studies of Lithium Intercalation into Carbons Using

Nonaqueous Electrochemical Cells. J. Electrochem. Soc. 1990, 137, 2009-2013. 6.

Xu, K., Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries. Chem.

Rev. 2004, 104, 4303-4418. 7.

Yan, J.; Zhang, J.; Su, Y.-C.; Zhang, X.-G.; Xia, B.-J., A Novel Perspective on the Formation

of the Solid Electrolyte Interphase on the Graphite Electrode for Lithium-Ion Batteries. Electrochim.

Acta 2010, 55, 1785-1794. 8.

An, S. J.; Li, J.; Daniel, C.; Mohanty, D.; Nagpure, S.; Wood III, D. L., The State of

Understanding of the Lithium-Ion-Battery Graphite Solid Electrolyte Interphase (Sei) and Its Relationship to Formation Cycling. Carbon 2016, 105, 52-76. 9.

Inaba, M.; Siroma, Z.; Ogumi, Z.; Abe, T.; Mizutani, Y.; Asano, M., Electrochemical Stm

Study on Surface Morphology Change of Hopg Basal Plane in an Organic Electrolyte Solution. Chem.

Lett. 1995, 24, 661-662. 10.

Inaba, M.; Siroma, Z.; Funabiki, A.; Ogumi, Z.; Abe, T.; Mizutani, Y.; Asano, M.,

Electrochemical Scanning Tunneling Microscopy Observation of Highly Oriented Pyrolytic Graphite Surface Reactions in an Ethylene Carbonate-Based Electrolyte Solution. Langmuir 1996, 12, 1535-1540. 11.

Besenhard, J.; Winter, M.; Yang, J.; Biberacher, W., Filming Mechanism of Lithium-Carbon

Anodes in Organic and Inorganic Electrolytes. J. Power Sources 1995, 54, 228-231. 12.

Chung, G. C.; Kim, H. J.; Yu, S. I.; Jun, S. H.; Choi, J. w.; Kim, M. H., Origin of Graphite

Exfoliation an Investigation of the Important Role of Solvent Cointercalation. J. Electrochem. Soc. 2000, 147, 4391-4398. 13.

Xu, K., Electrolytes and Interphases in Li-Ion Batteries and Beyond. Chem. Rev. 2014, 114,

11503-11618. 14.

Hahn, M.; Buqa, H.; Ruch, P.; Goers, D.; Spahr, M.; Ufheil, J.; Novák, P.; Kötz, R., A

Dilatometric Study of Lithium Intercalation into Powder-Type Graphite Electrodes. Electrochem.

Solid-State Lett. 2008, 11, A151-A154. 15.

Spahr, M. E.; Palladino, T.; Wilhelm, H.; Würsig, A.; Goers, D.; Buqa, H.; Holzapfel, M.;

Novák, P., Exfoliation of Graphite During Electrochemical Lithium Insertion in Ethylene Carbonate-Containing Electrolytes. J. Electrochem. Soc. 2004, 151, A1383-A1395.


Page 29 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


16.

Xing, L.; Zheng, X.; Schroeder, M.; Alvarado, J.; von Wald Cresce, A.; Xu, K.; Li, Q.; Li, W.,

Deciphering the Ethylene Carbonate–Propylene Carbonate Mystery in Li-Ion Batteries. Acc. Chem.

Res. 2018, 51, 282-289. 17.

Aurbach, D.; Levi, M. D.; Levi, E.; Schechter, A., Failure and Stabilization Mechanisms of

Graphite Electrodes. J. Phys. Chem. B 1997, 101, 2195-2206. 18.

Aurbach, D.; Markovsky, B.; Weissman, I.; Levi, E.; Ein-Eli, Y., On the Correlation between

Surface Chemistry and Performance of Graphite Negative Electrodes for Li Ion Batteries.

Electrochim. Acta 1999, 45, 67-86. 19.

Kim, S.-P.; Van Duin, A. C.; Shenoy, V. B., Effect of Electrolytes on the Structure and

Evolution of the Solid Electrolyte Interphase (Sei) in Li-Ion Batteries: A Molecular Dynamics Study. J.

Power Sources 2011, 196, 8590-8597. 20.

Wang, A.; Kadam, S.; Li, H.; Shi, S.; Qi, Y., Review on Modeling of the Anode Solid

Electrolyte Interphase (Sei) for Lithium-Ion Batteries. npj Computational Materials 2018, 4, 15. 21.

Islam, M. M.; Van Duin, A. C., Reductive Decomposition Reactions of Ethylene Carbonate by

Explicit Electron Transfer from Lithium: An Ereaxff Molecular Dynamics Study. J. Phys. Chem. C 2016, 120, 27128-27134. 22.

Yun, K.-S.; Pai, S. J.; Yeo, B. C.; Lee, K.-R.; Kim, S.-J.; Han, S. S., Simulation Protocol for

Prediction of a Solid-Electrolyte Interphase on the Silicon-Based Anodes of a Lithium-Ion Battery: Reaxff Reactive Force Field. J. Phys. Chem. Lett. 2017, 8, 2812-2818. 23.

Li, Y.; Qi, Y., Transferable Self-Consistent Charge Density Functional Tight-Binding

Parameters for Li–Metal and Li-Ions in Inorganic Compounds and Organic Solvents. J. Phys. Chem.

C 2018, 122, 10755-10764. 24.

Takenaka, N.; Suzuki, Y.; Sakai, H.; Nagaoka, M., On Electrolyte-Dependent Formation of

Solid Electrolyte Interphase Film in Lithium-Ion Batteries: Strong Sensitivity to Small Structural Difference of Electrolyte Molecules. J. Phys. Chem. C 2014, 118, 10874-10882. 25.

Leung, K.; Budzien, J. L., Ab Initio Molecular Dynamics Simulations of the Initial Stages of

Solid–Electrolyte Interphase Formation on Lithium Ion Battery Graphitic Anodes. Phys. Chem.

Chem. Phys. 2010, 12, 6583-6586. 26.

Leung, K.; Tenney, C. M., Toward First Principles Prediction of Voltage Dependences of

Electrolyte/Electrolyte Interfacial Processes in Lithium Ion Batteries. J. Phys. Chem. C 2013, 117, 24224-24235. 27.

Leung, K., Predicting the Voltage Dependence of Interfacial Electrochemical Processes at

Lithium-Intercalated Graphite Edge Planes. Phys. Chem. Chem. Phys. 2015, 17, 1637-1643. 28.

Haruyama, J.; Ikeshoji, T.; Otani, M., Analysis of Lithium Insertion/Desorption Reaction at

Interfaces between Graphite Electrodes and Electrolyte Solution Using Density Functional+ Implicit Solvation Theory. J. Phys. Chem. C 2018, 122, 9804-9810. 29 ACS Paragon Plus Environment


29.

Page 30 of 32

Haruyama, J.; Ikeshoji, T.; Otani, M., Electrode Potential from Density Functional Theory

Calculations Combined with Implicit Solvation Theory. Physical Review Materials 2018, 2, 095801. 30.

Ohba, N.; Ogata, S.; Kouno, T.; Tamura, T.; Kobayashi, R., Linear Scaling Algorithm of

Real-Space Density Functional Theory of Electrons with Correlated Overlapping Domains. Comput.

Phys. Commun. 2012, 183, 1664-1673. 31.

Ogata, S., Buffered-Cluster Method for Hybridization of Density-Functional Theory and

Classical Molecular Dynamics: Application to Stress-Dependent Reaction of H 2 O on Nanostructured Si. Phys. Rev. B 2005, 72, 045348. 32.

Ogata, S.; Abe, Y.; Ohba, N.; Kobayashi, R., Stress-Induced Nano-Oxidation of Silicon by

Diamond-Tip in Moisture Environment: A Hybrid Quantum-Classical Simulation Study. J. Appl.

Phys. 2010, 108, 064313. 33.

Kouno, T.; Ogata, S.; Shimada, T.; Tamura, T.; Kobayashi, R., Enhanced Si–O Bond

Breaking in Silica Glass by Water Dimer: A Hybrid Quantum–Classical Simulation Study. J. Phys.

Soc. Jpn. 2016, 85, 054601. 34.

Nicklow, R.; Wakabayashi, N.; Smith, H., Lattice Dynamics of Pyrolytic Graphite. Phys. Rev.

B 1972, 5, 4951. 35.

Holzwarth, N.; Rabii, S., Energy Band Structure of Lithium—Graphite Intercalation

Compound. Materials Science and Engineering 1977, 31, 195-200. 36.

Ohba, N.; Ogata, S.; Tamura, T.; Yamakawa, S.; Asahi, R., A Hybrid Quantum-Classical

Simulation Study on Stress-Dependence of Li Diffusivity in Graphite. Computer Modeling in

Engineering and Sciences 2011, 75, 247. 37.

Ohba, N.; Ogata, S.; Tamura, T.; Kobayashi, R.; Yamakawa, S.; Asahi, R., Enhanced

Thermal Diffusion of Li in Graphite by Alternating Vertical Electric Field: A Hybrid Quantum-Classical Simulation Study. J. Phys. Soc. Jpn. 2012, 81, 023601. 38.

Ohba, N.; Ogata, S.; Kouno, T.; Asahi, R., Thermal Diffusion of Correlated Li-Ions in

Graphite: A Hybrid Quantum–Classical Simulation Study. Computational Materials Science 2015,

108, 250-257. 39.

Ogata, S.; Ohba, N.; Kouno, T., Multi-Thousand-Atom Dft Simulation of Li-Ion Transfer

through the Boundary between the Solid–Electrolyte Interface and Liquid Electrolyte in a Li-Ion Battery. J. Phys. Chem. C 2013, 117, 17960-17968. 40.

Brenner, D. W., Empirical Potential for Hydrocarbons for Use in Simulating the Chemical

Vapor Deposition of Diamond Films. Phys. Rev. B 1990, 42, 9458. 41.

Shimojo, F.; Campbell, T. J.; Kalia, R. K.; Nakano, A.; Vashishta, P.; Ogata, S.; Tsuruta, K.,

A Scalable Molecular-Dynamics Algorithm Suite for Materials Simulations: Design-Space Diagram on 1024 Cray T3e Processors. Future Generation Computer Systems 2000, 17, 279-291. 30 ACS Paragon Plus Environment

Page 31 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


42.

Xu, K.; von Cresce, A.; Lee, U., Differentiating Contributions to “Ion Transfer” Barrier from

Interphasial Resistance and Li+ Desolvation at Electrolyte/Graphite Interface. Langmuir 2010, 26, 11538-11543. 43.

Bryngelsson, H.; Stjerndahl, M.; Gustafsson, T.; Edström, K., How Dynamic Is the Sei? J.

Power Sources 2007, 174, 970-975. 44.

Edström, K.; Herstedt, M.; Abraham, D. P., A New Look at the Solid Electrolyte Interphase

on Graphite Anodes in Li-Ion Batteries. J. Power Sources 2006, 153, 380-384. 45.

Ohno, K.; Maeda, S., A Scaled Hypersphere Search Method for the Topography of Reaction

Pathways on the Potential Energy Surface. Chem. Phys. Lett. 2004, 384, 277-282. 46.

Miyamoto, K.; Asahi, R.; Ohno, K. In Ab Initio Study on Reduction Mechanisms of Vinylene

Carbonate Using Global Reaction Route Mapping Method, Meeting Abstracts, The Electrochemical Society: 2012; pp 1258-1258.



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