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Lim C, Jeon J, Park K, Liang C, Chae Y, Kwak K, Cho M. Revisiting Ultrafast Dynamics in Carbonate-Based Electrolytes for Li-Ion Batteries: Clarifying 2D-IR Cross-Peak Interpretation. J Phys Chem B 2023; 127:9566-9574. [PMID: 37905968 DOI: 10.1021/acs.jpcb.3c05480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
Understanding chemical exchange in carbonate-based electrolytes employed in Li-ion batteries (LIBs) is crucial for elucidating ion transport mechanisms. Ultrafast two-dimensional (2D) IR spectroscopy has been widely used to investigate the solvation structure and dynamics of Li-ions in organic carbonate-based electrolytes. However, the interpretation of cross-peaks observed in picosecond carbonyl stretch 2D-IR spectra has remained contentious. These cross-peaks could arise from various phenomena, including vibrational couplings between neighboring carbonyl groups in the first solvation shell around Li-ions, vibrational excitation transfers between carbonyl groups in distinct solvation environments, and local heating effects. Therefore, it is imperative to resolve the interpretation of 2D-IR cross-peaks to avoid misinterpretations regarding ultrafast dynamics found in LIB carbonate-based electrolytes. In this study, we have taken a comprehensive investigation of carbonate-based electrolytes utilizing 2D-IR spectroscopy and molecular dynamics (MD) simulations. Through meticulous analyses and interpretations, we have identified that the cross-peaks observed in the picosecond 2D-IR spectra of LIB electrolytes predominantly arise from intermolecular vibrational excitation transfer processes between the carbonyl groups of Li-bound and free carbonate molecules. We further discuss the limitations of employing a picosecond 2D-IR spectroscopic technique to study chemical exchange and intermolecular vibrational excitation transfer processes, particularly when the effects of the molecular photothermal process cannot be ignored. Our findings shed light on the dynamics of LIB electrolytes and resolve the controversy related to 2D-IR cross-peaks. By discerning the origin of these features, we could provide valuable insights for the design and optimization of next-generation Li-ion batteries.
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Affiliation(s)
- Chaiho Lim
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Jonggu Jeon
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
| | - Kwanghee Park
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Chungwen Liang
- Creyon Bio Inc., San Diego, California 92121, United States
| | - Yeongseok Chae
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Kyungwon Kwak
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Minhaeng Cho
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
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Solvation structure and dynamics of a small ion in an organic electrolyte. J Photochem Photobiol A Chem 2023. [DOI: 10.1016/j.jphotochem.2023.114666] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/11/2023]
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Cho M. Molecular Photothermal Effects on Time-Resolved IR Spectroscopy: Solute-Solvent Intermolecular Energy Transfer. J Phys Chem B 2023; 127:300-307. [PMID: 36576754 DOI: 10.1021/acs.jpcb.2c07043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Time-resolved IR pump-probe (IR-PP) and two-dimensional IR (2D-IR) spectroscopy are valuable tools for studying ultrafast chemical and biological processes in solutions. However, the corresponding signals at long times are obscured by the molecular photothermal effects resulting from the heat dissipation of vibrationally photoexcited molecules to the surroundings. Recently, a phenomenology model was used to describe molecular photothermal effects on IR-PP signals and the diagonal and cross-peaks of 2D-IR spectra at long pump-probe delay times. Here, we consider the thermal diffusion equation with a time-dependent heat source term to describe the solute-solvent energy transfer process. An approximate solution to the nonhomogeneous differential equation shows that the molecular photothermal effect is determined by the mean intermolecular distance between IR-absorbing molecules. We show that the time profile of heat dissipation from a vibrationally excited molecule to the surroundings, which provides information about the mechanisms involved in the solute-solvent intermolecular energy transfer process in solutions, can be directly measured by analyzing the molecular photothermal IR-PP and 2D-IR signals. We anticipate that the present work can be used to interpret local heating-induced time-resolved IR spectroscopic signals and understand the rate of and the mechanisms involved in the conversion from high-frequency molecular vibrational energy to solvent kinetic energy in condensed phases.
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Affiliation(s)
- Minhaeng Cho
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea.,Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
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Deng R, Chu F, Kwofie F, Guan Z, Chen J, Wu F. A Low-Concentration Electrolyte for High-Voltage Lithium-Metal Batteries: Fluorinated Solvation Shell and Low Salt Concentration Effect. Angew Chem Int Ed Engl 2022; 61:e202215866. [PMID: 36333270 DOI: 10.1002/anie.202215866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Indexed: 11/08/2022]
Abstract
Concentration of electrolyte has significant effects on performances of rechargeable batteries. Previous studies mainly focused on concentrated electrolytes. So far, only several recipes on low-concentration electrolytes were studied, performing enhanced performance in advanced rechargeable batteries. Here, based on common electrolyte components, a low-concentration electrolyte composed of 0.2 M lithium hexafluorophosphate (LiPF6 ) solvated in fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) is employed for high-voltage Li metal battery. The synergistic working mechanisms of introducing fluorine-containing solvent in the solvated structure and low salt concentration effect are revealed, resulting in LiF-rich, uniform, and robust solid electrolyte interphase layer and fewer unfavorable decomposition products. As a result, this low-concentration electrolyte significantly enhances electrochemical performances of Li||Li symmetric cells and high-voltage LiCoO2 ||Li batteries.
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Affiliation(s)
- Rongyu Deng
- School of Metallurgy and Environment, Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Hunan Provincial Key Laboratory of Nonferrous Value-added Metallurgy, State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China
| | - Fulu Chu
- School of Metallurgy and Environment, Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Hunan Provincial Key Laboratory of Nonferrous Value-added Metallurgy, State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China
| | - Felix Kwofie
- School of Metallurgy and Environment, Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Hunan Provincial Key Laboratory of Nonferrous Value-added Metallurgy, State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China
| | - Zengqiang Guan
- School of Metallurgy and Environment, Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Hunan Provincial Key Laboratory of Nonferrous Value-added Metallurgy, State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China
| | - Jieshuangyang Chen
- School of Metallurgy and Environment, Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Hunan Provincial Key Laboratory of Nonferrous Value-added Metallurgy, State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China
| | - Feixiang Wu
- School of Metallurgy and Environment, Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Hunan Provincial Key Laboratory of Nonferrous Value-added Metallurgy, State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China
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Samajdar RN, Brown SA, Kairy SK, Robertson SD, Wain AJ. Methodologies for Operando ATR-IR Spectroscopy of Magnesium Battery Electrolytes. Anal Chem 2022; 94:14985-14993. [PMID: 36260706 DOI: 10.1021/acs.analchem.2c02843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We explore the suitability of operando attenuated total reflection infrared (ATR-IR) spectroscopy methodologies for the study of organoaluminate electrolytes for Mg battery applications. The "all-phenyl complex" in tetrahydrofuran (THF), with the molecular structure [Mg2Cl3·6THF]+[AlPh4]-, is used as an exemplar electrolyte to compare two different spectroelectrochemical cell configurations. In one case, a Pt gauze is used as a working electrode, while in the second case, a thin (∼10 nm) Pt film working electrode is deposited directly on the surface of the ATR crystal. Spectroscopic measurements indicate substantial differences in the ATR-IR response for the two configurations, reflecting the different spatial arrangements of the working electrode with respect to the ATR sampling volume. The relative merits and potential pitfalls associated with the two approaches are discussed.
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Affiliation(s)
- Rudra N Samajdar
- Department of Electromagnetic and Electrochemical Technologies, National Physical Laboratory, Teddington TW11 0LW, U.K.,WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Scott A Brown
- Department of Electromagnetic and Electrochemical Technologies, National Physical Laboratory, Teddington TW11 0LW, U.K.,WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Shravan K Kairy
- Department of Electromagnetic and Electrochemical Technologies, National Physical Laboratory, Teddington TW11 0LW, U.K
| | - Stuart D Robertson
- WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, U.K
| | - Andrew J Wain
- Department of Electromagnetic and Electrochemical Technologies, National Physical Laboratory, Teddington TW11 0LW, U.K
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Cho M. Molecular photothermal effects on time-resolved IR spectroscopy. J Chem Phys 2022; 157:124201. [DOI: 10.1063/5.0108826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Time-resolved IR pump-probe (IR-PP) and two-dimensional IR (2D-IR) spectroscopy are valuable techniques for studying various ultrafast chemical and biological processes in solutions. The time-dependent changes of nonlinear IR signals reflecting fast molecular processes such as vibrational energy transfer and chemical exchange provide invaluable information on the rates and mechanisms of solvation dynamics and structural transitions of multi-species vibrationally interacting molecular systems. However, due to the intrinsic difficulties in distinguishing the contributions of molecule-specific processes to the time-resolved IR signals from those resulting from local heating, it becomes challenging to interpret time-resolved IR-PP and 2D-IR spectra exhibiting transient growing-in spectral components and cross-peaks unambiguously. Here, theoretical considerations of various effects of vibrational coupling, energy transfer, chemical exchange, the generation of hot ground states, molecular photothermal process, and their combinations on the lineshapes and time-dependent intensities of IR-PP spectra and 2D-IR diagonal and cross-peaks are presented. We anticipate that the present work will help researchers using IR pump-probe and 2D-IR techniques to distinguish local heating-induced photothermal signals from genuine nonlinear IR signals.
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Affiliation(s)
- Minhaeng Cho
- Chemistry, Korea University, Korea, Republic of (South Korea)
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Chae Y, Lim C, Jeon J, Kim M, Lee KK, Kwak K, Cho M. Lithium-Ion Solvation Structure in Organic Carbonate Electrolytes at Low Temperatures. J Phys Chem Lett 2022; 13:7881-7888. [PMID: 35979999 DOI: 10.1021/acs.jpclett.2c02106] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Lithium-ion batteries face insufficient capacity at low temperatures. The lithium-ion desolvation process in the vicinity of a solid electrolyte interphase (SEI) layer is considered the major problem. Thus, an accurate determination of lithium-ion solvation structures is a prerequisite for understanding this process. Here, using a cryostat combined with an FTIR spectrometer, we found that as the temperature decreased, the number of coordinating carbonates in the first solvation shell of the lithium ion increased with a decreased population of the contact ion pair (CIP). More specifically, we found that two or more carbonate molecules replace a single PF6- anion upon CIP dissociation. This experimental finding shows that the prevailing notion that four carbonate molecules coordinate each lithium ion to form a tetrahedral structure is invalid for describing lithium-ion solvation structures. We anticipate that the present work will elucidate one of the molecular origins behind the low performance of lithium-ion batteries at low temperatures.
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Affiliation(s)
- Yeongseok Chae
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Chaiho Lim
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Jonggu Jeon
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
| | - Minju Kim
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Kyung-Koo Lee
- Department of Chemistry, Kunsan National University, Gunsan 54150, Republic of Korea
| | - Kyungwon Kwak
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Minhaeng Cho
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
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