Subscriber access provided by Kaohsiung Medical University
C: Energy Conversion and Storage; Energy and Charge Transport
Density Functional Theory Modeling Assisted Investigation of Thermodynamics and Redox Properties of BoronDoped Corannulenes for Cathodes in Lithium-Ion Batteries Jiwoong Kang, Ki Chul Kim, and Seung Soon Jang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b00827 • Publication Date (Web): 02 May 2018 Downloaded from http://pubs.acs.org on May 3, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 9 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
The Journal of Physical Chemistry
Density Functional Theory Modeling Assisted Investigation of Thermodynamics and Redox Properties of Boron-Doped Corannulenes for Cathodes in Lithium-Ion Batteries Jiwoong Kang,†,# Ki Chul Kim,*,‡ and Seung Soon Jang*,†,ǁ,§ †
Computational NanoBio Technology Laboratory, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA # School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0100, USA ‡ Department of Chemical Engineering, Konkuk University, Seoul 05029, Republic of Korea ǁ Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332, USA § Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA
Abstract: Understanding thermodynamics and reduction potentials of boron-doped corannulenes (BDCs) can provide meaningful insight to establish strategies for designing doping processes of organic materials applicable to cathodes in lithium-ion batteries (LIBs). In this study, a comprehensive set of BDC models is prepared to investigate the effect of the number and geometric position of doped boron atoms on the thermodynamic stability and redox properties of the corannulene. Our investigation enables us to evaluate their potential as organic cathode materials in LIBs. In this study, it is found that the first and second boron atoms can be exclusively doped in thermodynamically stable positions. Corannulene derivatives doped by the boron atom shows enhanced reduction potentials ranged from 2.41 up to 5.05 V vs. Li/Li+ as compared with the pristine corannulene (0.9 V vs. Li/Li+). A higher level of structural heterogeneity created by another boron atom does not guarantee a higher reduction potential (3.03 and 2.51 V vs. Li/Li+ for probabilityaveraged reduction potentials of one- and two-boron-doped corannulenes, respectively). Reduction potential is strongly correlated with the spin state as well as the structural and electronic properties. The doped boron atoms play a critical role in improving the stability of the Li binding thermodynamics, showing their positive impact on the enhancement of the charge capacity.
Introduction Recently, lithium-ion batteries (LIBs) have been utilized as main power sources for electric vehicles (EVs) due to their high charge and energy densities.1-3 However, a couple of shortcomings have to be overcome for wide applications of the LIBs. Specifically, the relatively low power density arising from the slow diffusion of Li ions through the entire battery system during the charge and discharge processes is a primary issue to be addressed.3-7 To improve ionic diffusion, significant efforts have been made by introducing organic molecules for fast surface redox reactions.8-16 For example, Gall et al. studied the specific charge capacity and cycling stability of poly(2,5-dihydroxy-1,4-benzoquinone-3,6methylene) as an organic cathode material in LIBs.8 They reported that the polymerized cathode material achieved moderately good performance. Likewise, Liu et al. employed density functional theory (DFT) method to investigate the potential of carbon nanotubes coated by self-polymerized dopamines as organic cathode materials in LIBs,15 reporting that the surface redox activity of the carbonyl group in the dopamines
could be consistently sustained at high cell voltages during the discharge process, suggesting that the organic materials could be ideal candidates for the next generation cathode materials in LIBs. All these studies have contributed to developing molecules that could enhance the ionic diffusion without losing charge and energy densities. However, despite such significant efforts, it should be noted that only a limited number of molecules has been explored, and thereby comprehensive understanding of the molecular structure-electrochemical properties relationship has not been accomplished. Corannulene is an organic molecule consisting of a five benzene rings around cyclopentane ring as shown in Figure 1. The molecule has a unique structural characteristics with curved carbon lattices in which the existence of the highly overlapped π orbitals is expected to provide a highly attractive Li binding environment.17-19 A couple of studies have been explored to unravel the structural and electronic properties of the molecule.18, 20-23 For example, Baldridge and Siegel reported that the convex face of the corannulene would have a considerably different environment in the electron density as compared with its concave face, provoking dipole moment to this polycyclic aromatic hydrocarbon.20 Various computational studies on binding strengths of transition-metal ions with the corannulene have been performed.18, 21 Dunbar employed the DFT method to investigate the binding properties of seven metal cations, namely three alkali metal cations (Li+, Na+, and K+) and four transitionmetal cations (Ti+, Cr+, Ni+, and Cu+), with the corannulene. They reported that lithium cation would stably bind to corannulene with the binding energy of 43.3 kcal/mol. 21 Nonetheless, to date, corannulene has not been considered to be utilized for the cathode in LIBs. It is therefore worthwhile to evaluate the potential of the molecule and its modified ones as cathode materials. On the other hand, doping materials with boron has been regarded as one of the promising approaches to improve their performance.24-29 For instance, Feng et al. investigated the potential of boron-doped lithium trivanadate (LiV3O8) as cathode materials and verified that the doping process enhanced the charge capacity and cyclic stability of the LiV3O8. They inferred that the doped boron atoms could improve the electrochemical performance of the LiV3O8 cathode by promoting the deintercalation and intercalation thermodynamics of lithium during the charge and discharge processes, respectively.24 Veluchamy et al. synthesized boron-substituted manganese spinels to investigate their physical and electrochemical
ACS Paragon Plus Environment
The Journal of Physical Chemistry 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
characteristics for cathode materials in lithium ion batteries. They reported that the synthesis through solution route enhanced the charge capacity and cyclability.29 All these imply that borondoping approach might be a good strategy to design promising cathodes based on organic molecules, such as corannulene. In this study, we aim at establishing an appropriate boron-doping strategy for better redox properties of the corannulene for positive electrodes in LIBs. To achieve this goal, we systematically generated a comprehensive set of boron-doped corannulene (BDC) models with various number of boron atoms and their geometric positions. It is assumed that lithium ions can reach the redox-active sites of individual corannulene molecules fixed by binders in positive electrode. It is worthwhile to note that electrons travel through the external circuit toward the molecules in the positive electrode during the discharge process as long as the positive electrode has higher reduction potential compared to negative electrode (Li). Also, note that the corannulene derivatives can be chemically bound onto conductive carbon materials, such as graphenes and carbon nanotubes, which would be a strategy to use the corannulene derivatives in cathodes by preventing the molecular dissolution. Polymerization is another strategy to resolve this issue. Liu et al. demonstrated the high cycling stability with self-polymerized dopamines which were spontaneously coated on the surfaces of few-walled carbon nanotubes, indicating the successful incorporation of organic molecules in cathodes.15, 30 Here, we focus on determining the reduction potential of corannulene derivatives as a function of the number of borons and their positions by employing the DFT method that has been used in our previous studies, in which all the technical details were reported.15, 31-34 The predicted redox properties were further correlated with their electronic properties including the electron affinity, the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO). Our investigation was finally extended to understand how corannulene binds with Li atoms during the discharge process.
Computational Method All the DFT calculations to predict the thermodynamics and redox properties of the BDC models were performed using the Jaguar software35 with the PBE036 functional and the 6-31+G (d,p) basis set.37 The restricted open shell calculations were performed in this study. Please note that our test calculations on a given set of molecules based on both the restricted and unrestricted open shell approaches validated the reliability of the restricted open shell approach. The reduction potential of a corannulene derivative with respect to Li/Li+ (E.. ) were computed by ∆ ,
E.. [ ] = −
+ E − E
∆! "# $, %&' = [−∆! ( $] + [∆! "# $, )*%] + [∆! ( $+ ] . (2)
Here, ∆! ( $ and ∆! ( $+ respectively account for the solvation free energies for the molecule in neutral and anion states, while ∆! "# $, )*% represents the Gibbs free energy change for the reduction of the molecule in gas phase. A dielectric constant, 16.14 was used to calculation of ∆! ( $ and ( $ + ∆! corresponding to the mixed solvent consisting of ethylene carbonate and dimethyl carbonatein 3:7 v/v ratio. Please note that our previous studies on various organic materials including quinones, dopamines, ketones, and graphenes have consistently presented the reliability of our computational approach with its conditions such as DFT functional, basis set, implicit model, and so on, demonstrating accurate prediction of reduction potential with the uncertainty of ~0.3 V with respect to Li/Li+.15, 31-34 For a set of M molecules with a given number of doped boron atoms, Boltzmann distributions of the molecules defined by the probability of molecule i, , = -0∑/ - , were calculated to assess their relative thermodynamic stabilities. The Boltzmann factor, 4 - = exp − 756,
was utilized to evaluate the Boltzmann distribution.
Here, E is the Gibbs free energy, k represents Boltzmann constant, and T is the room temperature (298.15K). The probability89:9;+:(":
