1
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Markiewitz DM, Goodwin ZAH, McEldrew M, Pedro de Souza J, Zhang X, Espinosa-Marzal RM, Bazant MZ. Electric field induced associations in the double layer of salt-in-ionic-liquid electrolytes. Faraday Discuss 2024. [PMID: 39176453 DOI: 10.1039/d4fd00021h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/24/2024]
Abstract
Ionic liquids (ILs) are an extremely exciting class of electrolytes for energy storage applications. Upon dissolving alkali metal salts, such as Li or Na based salts, with the same anion as the IL, an intrinsically asymmetric electrolyte can be created for use in batteries, known as a salt-in-ionic liquid (SiIL). These SiILs have been well studied in the bulk, where negative transference numbers of the alkali metal cation have been observed from the formation of small, negatively charged clusters. The properties of these SiILs at electrified interfaces, however, have received little to no attention. Here, we develop a theory for the electrical double layer (EDL) of SiILs where we consistently account for the thermoreversible association of ions into Cayley tree aggregates. The theory predicts that the IL cations first populate the EDL at negative voltages, as they are not strongly bound to the anions. However, at large negative voltages, which are strong enough to break the alkali metal cation-anion associations, these IL cations are exchanged for the alkali metal cation because of their higher charge density. At positive voltages, we find that the SiIL actually becomes more aggregated while screening the electrode charge from the formation of large, negatively charged aggregates. Therefore, in contrast to conventional intuition of associations in the EDL, SiILs appear to become more associated in certain electric fields. We present these theoretical predictions to be verified by molecular dynamics simulations and experimental measurements.
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Affiliation(s)
- Daniel M Markiewitz
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
| | - Zachary A H Goodwin
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
- Department of Materials, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Michael McEldrew
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
| | - J Pedro de Souza
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
- Omenn-Darling Bioengineering Institute, Princeton University, Princeton, New Jersey 08544, USA
| | - Xuhui Zhang
- Department of Civil and Environmental Engineering, University of Illinois at Urbana - Champaign, Urbana, IL, 61801, USA
| | - Rosa M Espinosa-Marzal
- Department of Civil and Environmental Engineering, University of Illinois at Urbana - Champaign, Urbana, IL, 61801, USA
- Department of Materials Science and Engineering, University of Illinois at Urbana - Champaign, Urbana, IL, 61801, USA
| | - Martin Z Bazant
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
- Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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2
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Goodwin ZAH, Wenny MB, Yang JH, Cepellotti A, Ding J, Bystrom K, Duschatko BR, Johansson A, Sun L, Batzner S, Musaelian A, Mason JA, Kozinsky B, Molinari N. Transferability and Accuracy of Ionic Liquid Simulations with Equivariant Machine Learning Interatomic Potentials. J Phys Chem Lett 2024; 15:7539-7547. [PMID: 39023916 DOI: 10.1021/acs.jpclett.4c01942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/20/2024]
Abstract
Ionic liquids (ILs) are an exciting class of electrolytes finding applications in many areas from energy storage to solvents, where they have been touted as "designer solvents" as they can be mixed to precisely tailor the physiochemical properties. As using machine learning interatomic potentials (MLIPs) to simulate ILs is still relatively unexplored, several questions need to be answered to see if MLIPs can be transformative for ILs. Since ILs are often not pure, but are either mixed together or contain additives, we first demonstrate that a MLIP can be trained to be compositionally transferable; i.e., the MLIP can be applied to mixtures of ions not directly trained on, while only being trained on a few mixtures of the same ions. We also investigated the accuracy of MLIPs for a novel IL, which we experimentally synthesize and characterize. Our MLIP trained on ∼200 DFT frames is in reasonable agreement with our experiments and DFT.
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Affiliation(s)
- Zachary A H Goodwin
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Malia B Wenny
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Julia H Yang
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- Harvard University Center for the Environment, 26 Oxford St., Cambridge, Massachusetts 02138, United States
| | - Andrea Cepellotti
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Jingxuan Ding
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Kyle Bystrom
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Blake R Duschatko
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Anders Johansson
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Lixin Sun
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Simon Batzner
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Albert Musaelian
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Jarad A Mason
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Boris Kozinsky
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- Research and Technology Center, Robert Bosch LLC, Cambridge, Massachusetts 02142, United States
| | - Nicola Molinari
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- Research and Technology Center, Robert Bosch LLC, Cambridge, Massachusetts 02142, United States
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3
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Liang X, Zhou Y, Zhu W, Xu WW, Francisco JS, Zeng XC, Zhao W. Formation of compounds with diverse polyelectrolyte morphologies and nonlinear ion conductance in a two-dimensional nanofluidic channel. Chem Sci 2024; 15:8170-8180. [PMID: 38817585 PMCID: PMC11134406 DOI: 10.1039/d4sc01071j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2024] [Accepted: 04/29/2024] [Indexed: 06/01/2024] Open
Abstract
Aqueous electrolytes subjected to angstrom-scale confinement have recently attracted increasing interest because of their distinctive structural and transport properties, as well as their promising applicability in bioinspired nanofluidic iontronics and ion batteries. Here, we performed microsecond-scale molecular dynamics simulations, which provided evidence of nonlinear ionic conductance under an external lateral electric field due to the self-assembly of cations and anions with diverse polyelectrolyte morphologies (e.g., extremely large ion clusters) in aqueous solutions within angstrom-scale slits. Specifically, we found that the cations and anions of Li2SO4 and CaSO4 formed chain-like polyelectrolyte structures, whereas those of Na2SO4 and MgSO4 predominantly formed a monolayer of hydrated salt. Additionally, the cations and anions of K2SO4 assembled into a hexagonal anhydrous ionic crystal. These ion-dependent diverse polyelectrolyte morphologies stemmed from the enhanced Coulomb interactions, weakened hydration and steric constraints within the angstrom-scale slits. More importantly, once the monolayer hydrated salt or ionic crystal structure was formed, the field-induced ion current exhibited an intriguing gating effect at a low field strength. This abnormal ion transport was attributed to the concerted movement of cations and anions within the solid polyelectrolytes, leading to the suppression of ion currents. When the electric field exceeded a critical strength, however, the ion current surged rapidly due to the dissolution of many cations and anions within a few nanoseconds in the aqueous solution.
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Affiliation(s)
- Xiaoying Liang
- Department of Physics, Ningbo University Ningbo Zhejiang 315211 China
| | - Yanan Zhou
- School of Material Science and Chemical Engineering, Institute of Mass Spectrometry, Ningbo University Ningbo 315211 China
| | - Weiduo Zhu
- Department of Physics, Hefei University of Technology Hefei Anhui 230009 China
| | - Wen Wu Xu
- Department of Physics, Ningbo University Ningbo Zhejiang 315211 China
| | - Joseph S Francisco
- Department of Chemistry, University of Pennsylvania Philadelphia Pennsylvania 19104 USA
| | - Xiao Cheng Zeng
- Department of Materials Science & Engineering, City University of Hong Kong Kowloon 999077 Hong Kong China
| | - Wenhui Zhao
- Department of Physics, Ningbo University Ningbo Zhejiang 315211 China
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4
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Lee Y, Cho J, Kim J, Lee WB, Jho Y. Anomalous diffusion of lithium-anion clusters in ionic liquids. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2023; 46:105. [PMID: 37917274 DOI: 10.1140/epje/s10189-023-00365-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Accepted: 10/12/2023] [Indexed: 11/04/2023]
Abstract
Lithium-ion transport is significantly retarded in ionic liquids (ILs). In this work, we performed extensive molecular dynamics simulations to mimic the kinetics of lithium ions in ILs using [N-methyl-N-propylpyrrolidium (pyr[Formula: see text])][bis(trifluoromethanesulfonyl)imide (Ntf[Formula: see text])] with added LiNtf[Formula: see text] salt. And we analyzed their transport, developing a two-state model and comparing it to the machine learning-identified states. The transport of lithium ions involves local shell exchanges of the Ntf[Formula: see text] in the medium. We calculated train size distributions over various time scales. The train size distribution decays as a power law, representing non-Poissonian bursty shell exchanges. We analyzed the non-Poissonian processes of lithium ions transport as a two-state (soft and hard) model. We analytically calculated the transition probability of the two-state model, which fits well to the lifetime autocorrelation functions of LiNtf[Formula: see text] shells. To identify two states, we introduced the graph neutral network incorporating local molecular structure. The results reveal that the shell-soft state mainly contributes to the transport of the lithium ions, and their contribution is more important in low temperatures. Hence, it is the key for enhanced lithium ion transport to increase the fraction of the shell-soft state.
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Affiliation(s)
- YeongKyu Lee
- Department of Physics, Gyeongsang National University, Jinjudae-ro 501, Jinju, Gyeongsangnam-do, 52828, Republic of Korea
| | - JunBeom Cho
- School of Chemical and Biological Engineering, Seoul National University, 1, Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Junseong Kim
- Department of Physics, Gyeongsang National University, Jinjudae-ro 501, Jinju, Gyeongsangnam-do, 52828, Republic of Korea
| | - Won Bo Lee
- School of Chemical and Biological Engineering, Seoul National University, 1, Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea.
| | - YongSeok Jho
- Department of Physics, Gyeongsang National University, Jinjudae-ro 501, Jinju, Gyeongsangnam-do, 52828, Republic of Korea.
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5
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Chen X, Kong X. Nanoscale Confinement Effects on Ionic Conductivity of Solid Polymer Electrolytes: The Interplay between Diffusion and Dissociation. NANO LETTERS 2023. [PMID: 37220138 DOI: 10.1021/acs.nanolett.3c01171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Solid polymer electrolytes (SPEs) are attractive for next-generation lithium metal batteries but still suffer from low ionic conductivity. Nanostructured materials offer design concepts for SPEs with better performance. Using molecular dynamics simulation, we examine SPEs under nanoscale confinement, which has been demonstrated to accelerate the transport of neutral molecules such as water. Our results show that while ion diffusion indeed accelerates by more than 2 orders of magnitude as the channel diameter decreases from 15 to 2 nm, the ionic conductivity does not increase significantly in parallel. Instead, the ionic conductivity shows a nonmonotonic variation, with an optimal value above, but on the same order as, its bulk counterparts. This trend is due to enhanced ion association with decreasing channel size, which reduces the number of effective charge carriers. This effect competes with accelerated ion diffusion, leading to the nonmonotonicity in ion conductivity.
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Affiliation(s)
- Xiupeng Chen
- South China Advanced Institute for Soft Matter Science and Technology, School of Emergent Soft Matter, South China University of Technology, Guangzhou 510640, China
| | - Xian Kong
- South China Advanced Institute for Soft Matter Science and Technology, School of Emergent Soft Matter, South China University of Technology, Guangzhou 510640, China
- Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, South China University of Technology, Guangzhou 510640, China
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6
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Zheng Q, Goodwin ZAH, Gopalakrishnan V, Hoane AG, Han M, Zhang R, Hawthorne N, Batteas JD, Gewirth AA, Espinosa-Marzal RM. Water in the Electrical Double Layer of Ionic Liquids on Graphene. ACS NANO 2023; 17:9347-9360. [PMID: 37163519 DOI: 10.1021/acsnano.3c01043] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The performance of electrochemical devices using ionic liquids (ILs) as electrolytes can be impaired by water uptake. This work investigates the influence of water on the behavior of hydrophilic and hydrophobic ILs─with ethylsulfate and tris(perfluoroalkyl)trifluorophosphate or bis(trifluoromethyl sulfonyl)imide (TFSI) anions, respectively─on electrified graphene, a promising electrode material. The results show that water uptake slightly reduces the IL electrochemical stability and significantly influences graphene's potential of zero charge, which is justified by the extent of anion depletion from the surface. Experiments confirm the dominant contribution of graphene's quantum capacitance (CQ) to the total interfacial capacitance (Cint) near the PZC, as expected from theory. Combining theory and experiments reveals that the hydrophilic IL efficiently screens surface charge and exhibits the largest double layer capacitance (CIL ∼ 80 μF cm-2), so that CQ governs the charge stored. The hydrophobic ILs are less efficient in charge screening and thus exhibit a smaller capacitance (CIL ∼ 6-9 μF cm-2), which governs Cint already at small potentials. An increase in the total interfacial capacitance is observed at positive voltages for humid TFSI-ILs relative to dry ones, consistent with the presence of a satellite peak. Short-range surface forces reveal the change of the interfacial layering with potential and water uptake owing to reorientation of counterions, counterion binding, co-ion repulsion, and water enrichment. These results are consistent with the charge being mainly stored in a ∼2 nm-thick double layer, which implies that ILs behave as highly concentrated electrolytes. This knowledge will advance the design of IL-graphene-based electrochemical devices.
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Affiliation(s)
- Qianlu Zheng
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Zachary A H Goodwin
- Department of Materials, Imperial College London, London SW7 2AZ, United Kingdom
- John A. Paulson School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Varun Gopalakrishnan
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Alexis G Hoane
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Mengwei Han
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Ruixian Zhang
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Nathaniel Hawthorne
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
| | - James D Batteas
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States
- Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77843, United States
| | - Andrew A Gewirth
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Rosa M Espinosa-Marzal
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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7
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Dziubinska-Kühn K, Maddah M, Pupier M, Matysik J, Viger-Gravel J, Kowalska M, Karg B. Influence of alkali metals on water dynamics inside imidazolium-based ionic liquid nano-domains. Front Chem 2022; 10:1028912. [DOI: 10.3389/fchem.2022.1028912] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Accepted: 10/31/2022] [Indexed: 11/17/2022] Open
Abstract
The global need to expand the design of energy-storage devices led to the investigation of alkali metal - Ionic Liquid (IL) mixtures as a possible class of electrolytes. In this study, 1D and 2D Nuclear Magnetic Resonance (NMR) and Electrochemical Impedance Spectroscopy (EIS) as well as Molecular Dynamics (MD) simulations were used to study the intermolecular interactions in imidazolium-based IL - water - alkali halide ternary mixtures. The 1H and 23Na 1D and 1H DOSY NMR spectra revealed that the presence of small quantities of NaCl does not influence the aggregation of water molecules in the IL nano-domains. The order of adding ionic compounds to water, as well as the certain water and NaCl molecular ratios, lead to the formation of isolated water clusters. Two ternary solutions representing different orders of compounds mixing (H2O+ IL + NaCl or H2O+ NaCl + IL) showed a strong dependence of the initial solvation shell of Na+ and the self-clustering of water. Furthermore, the behaviour of water was found to be independent from the conditions applied during the solution preparation, such as temperature and/or duration of stirring and aging. These findings could be confirmed by large differences in the amount of ionic species, observed in the ternary solutions and depending on the order of mixing/solute preparation.
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8
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Goodwin ZA, Kornyshev AA. Cracking Ion Pairs in the Electrical Double Layer of Ionic Liquids. Electrochim Acta 2022. [DOI: 10.1016/j.electacta.2022.141163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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9
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Goodwin ZAH, McEldrew MP, de Souza JP, Bazant MZ, Kornyshev AA. Gelation, Clustering and Crowding in the Electrical Double Layer of Ionic Liquids. J Chem Phys 2022; 157:094106. [DOI: 10.1063/5.0097055] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Understanding the bulk and interfacial properties of super-concentrated electrolytes, such as ionic liquids (ILs), has attracted significant attention lately for their promising applications in supercapacitors and batteries. Recently, McEldrew et al. developed a theory for reversible ion associations in bulk ILs, which accounted for the formation of all possible Cayley tree clusters and a percolating ionic network (gel). Here we adopt and develop this approach to understand the associations of ILs in the electrical double layer at electrified interfaces. With increasing charge of the electrode, the theory predicts a transition from a regime dominated by a gelled or clustered state to a crowding regime dominated by free ions. This transition from gelation to crowding is conceptually similar to the overscreening to crowding transition.
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Affiliation(s)
| | - Michael Patrick McEldrew
- Massachusetts Institute of Technology Department of Chemical Engineering, United States of America
| | - J. Pedro de Souza
- MIT, Massachusetts Institute of Technology Department of Chemical Engineering, United States of America
| | | | - Alexei A. Kornyshev
- Department of Chemistry, Imperial College London Faculty of Natural Sciences, United Kingdom
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10
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Lewis NHC, Dereka B, Zhang Y, Maginn EJ, Tokmakoff A. From Networked to Isolated: Observing Water Hydrogen Bonds in Concentrated Electrolytes with Two-Dimensional Infrared Spectroscopy. J Phys Chem B 2022; 126:5305-5319. [PMID: 35829623 DOI: 10.1021/acs.jpcb.2c03341] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Superconcentrated electrolytes have emerged as a promising class of materials for energy storage devices, with evidence that high voltage performance is possible even with water as the solvent. Here, we study the changes in the water hydrogen bonding network induced by the dissolution of lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in concentrations ranging from the dilute to the superconcentrated regimes. Using time-resolved two-dimensional infrared spectroscopy, we observe the progressive disruption of the water-water hydrogen bond network and the appearance of isolated water molecules interacting only with ions, which can be identified and spectroscopically isolated through the intermolecular cross-peaks between the water and the TFSI- ions. Analyzing the vibrational relaxation of excitations of the H2O stretching mode, we observe a transition in the dominant relaxation path as the bulk-like water vanishes and is replaced by ion-solvation water with the rapid single-step relaxation of delocalized stretching vibrations into the low frequency modes being replaced by multistep relaxation through the intramolecular H2O bend and into the TFSI- high frequency modes prior to relaxing to the low frequency structural degrees of freedom. These results definitively demonstrate the absence of vibrationally bulk-like water in the presence of high concentrations of LiTFSI and especially in the superconcentrated regime, while additionally revealing aspects of the water hydrogen bond network that have been difficult to discern from the vibrational spectroscopy of the neat liquid.
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Affiliation(s)
- Nicholas H C Lewis
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States.,Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Bogdan Dereka
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States.,Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Yong Zhang
- Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States.,Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Edward J Maginn
- Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States.,Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Andrei Tokmakoff
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States.,Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States
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11
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Cheng J, Tao H, Ma K, Yang J, Lian C, Liu H, Wu J. A Theoretical Model for the Charging Dynamics of Associating Ionic Liquids. FRONTIERS IN CHEMICAL ENGINEERING 2022. [DOI: 10.3389/fceng.2022.852070] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Association between cations and anions plays an important role in the interfacial structure of room-temperature ionic liquids (ILs) and their electrochemical performance. Whereas great efforts have been devoted to investigating the association effect on the equilibrium properties of ILs, a molecular-level understanding of the charging dynamics is yet to be established. Here, we propose a theoretical procedure combining reaction kinetics and the modified Poisson-Nernst-Planck (MPNP) equations to study the influences of ionic association on the dynamics of electrical double layer (EDL) in response to an applied voltage. The ionic association introduces a new decay length λS and relaxation time scale τRC=λSL/D, where L is the system size and D is ion diffusivity, that are distinctively different those corresponding to non-associative systems. Analytical expressions have been obtained to reveal the quantitative relations between the dynamic timescales and the association strength.
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12
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McEldrew M, Goodwin ZAH, Molinari N, Kozinsky B, Kornyshev AA, Bazant MZ. Salt-in-Ionic-Liquid Electrolytes: Ion Network Formation and Negative Effective Charges of Alkali Metal Cations. J Phys Chem B 2021; 125:13752-13766. [PMID: 34902256 DOI: 10.1021/acs.jpcb.1c05546] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Salt-in-ionic liquid electrolytes have attracted significant attention as potential electrolytes for next generation batteries largely due to their safety enhancements over typical organic electrolytes. However, recent experimental and computational studies have shown that under certain conditions alkali cations can migrate in electric fields as if they carried a net negative effective charge. In particular, alkali cations were observed to have negative transference numbers at small mole fractions of alkali-metal salt that revert to the expected net positive transference numbers at large mole fractions. Simulations have provided some insights into these observations, where the formation of asymmetric ionic clusters, as well as a percolating ion network, could largely explain the anomalous transport of alkali cations. However, a thermodynamic theory that captures such phenomena has not been developed, as ionic associations were typically treated via the formation of ion pairs. The theory presented herein, based on the classical polymer theories, describes thermoreversible associations between alkali cations and anions, where the formation of large, asymmetric ionic clusters and a percolating ionic network are a natural result of the theory. Furthermore, we present several general methods to calculate the effective charge of alkali cations in ionic liquids. We note that the negative effective charge is a robust prediction with respect to the parameters of the theory and that the formation of a percolating ionic network leads to the restoration of net positive charges of the cations at large mole fractions of alkali metal salt. Overall, we find excellent qualitative agreement between our theory and molecular simulations in terms of ionic cluster statistics and the effective charges of the alkali cations.
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Affiliation(s)
- Michael McEldrew
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Zachary A H Goodwin
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College of London, White City Campus, Wood Lane, London W12 0BZ, U.K.,Thomas Young Centre for Theory and Simulation of Materials, Imperial College of London, South Kensington Campus, London SW7 2AZ, U.K
| | - Nicola Molinari
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Boris Kozinsky
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Alexei A Kornyshev
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College of London, White City Campus, Wood Lane, London W12 0BZ, U.K.,Thomas Young Centre for Theory and Simulation of Materials, Imperial College of London, South Kensington Campus, London SW7 2AZ, U.K.,Institute of Molecular Science and Engineering, Imperial College of London, South Kensington Campus, London SW7 2AZ, U.K
| | - Martin Z Bazant
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.,Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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13
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Kubisiak P, Wróbel P, Eilmes A. How Temperature, Pressure, and Salt Concentration Affect Correlations in LiTFSI/EMIM-TFSI Electrolytes: A Molecular Dynamics Study. J Phys Chem B 2021; 125:12292-12302. [PMID: 34706539 PMCID: PMC8591607 DOI: 10.1021/acs.jpcb.1c07782] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 10/13/2021] [Indexed: 11/29/2022]
Abstract
Classical polarizable molecular dynamics simulations have been performed for LiTFSI solutions in the EMIM-TFSI ionic liquid. Different temperature or pressure values and salt concentrations have been examined. The structure and dynamics of the solvation shell of Li+ cations, diffusion coefficients of ions, conductivities of the electrolytes, and correlations between motions of ions have been analyzed. The results indicated that regardless of the conditions, significant correlations are present in all systems. The degree of correlations depends mainly on the salt fraction in the electrolyte and is much less affected by temperature and pressure changes. A positive correlation between motions of Li+ cations and TFSI anions, leading to the occurrence of negative Li+ transference numbers, exists for all conditions, although temperature and pressure changes affect the speed of anion exchange in Li+ solvation shells.
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Affiliation(s)
- Piotr Kubisiak
- Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland
| | - Piotr Wróbel
- Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland
| | - Andrzej Eilmes
- Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Kraków, Poland
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