Effect of Solvation Shell Structure and Composition on Ion Pair Formation: The Case Study of LiTDI in Organic Carbonates

Rushing, Jeramie C.; Leonik, Fedra M.; Kuroda, Daniel G.

doi:10.1021/acs.jpcc.9b07469

Cited by 16 publications

(13 citation statements)

References 91 publications

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“…This may be attributed to the preferential decomposition of LiTDI on Gr, acting as a sacrificial SEI former. [ 55,56 ] Another obvious difference can be found in the intensity of the Ni – fragment, which decreases in the order of baseline, 20F1.5M and 20F1.5M‐LiTDI. Apparently, due to the better‐stabilized NMA90 cathodes in the cells with EC‐free electrolytes, fewer Ni 2+ ions are dissolved into the electrolyte and deposited on the Gr anode.…”

Section: Resultsmentioning

confidence: 99%

Ethylene Carbonate‐Free Electrolytes for Stable, Safer High‐Nickel Lithium‐Ion Batteries

Pan

Cui

et al. 2022

Advanced Energy Materials

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highly oxidized transition-metal (TM) ions, particularly Ni. [6,10] This process not only leads to the generation of protons that can further induce a decomposition of lithium hexafluorophosphate (LiPF 6 ) to form hydrofluoric acid (HF), [11][12][13] but also causes the formation of spinel-like and rock salt-like phases at the cathode/electrolyte interphase (CEI). [14][15][16][17][18] Moreover, the generated TM ions and HF can crossover and exert side effects on the performance of Gr anodes. [19][20][21] In addition, EC molecules can also easily react with the oxygen released from high-Ni cathodes at elevated temperatures, leading to a catastrophic heat release and eventual safety hazards. [5,22] This problem is exacerbated when high-Ni cathodes are involved since they tend to release more oxygen at lower temperatures compared to low-Ni cathodes. [23] Consequently, much effort has been devoted to searching for new electrolytes that are compatible with high-Ni LIBs in the past years through an exploration of new electrolyte additives and the development of novel electrolyte systems, such as high concentration electrolytes (HCEs), localized HCEs (LHCEs), and EC-free electrolytes. [9,[24][25][26][27][28][29][30][31][32][33][34][35] Among these approaches, removing the EC from the state-ofthe-art EC-containing electrolytes to make EC-free electrolytes is of particular interest, since it solves the stability and safety issues from the root, and is also considerably more straightforward and cost-effective compared to other approaches. In early studies, Dahn and co-workers demonstrated that a significantly improved cycling stability and a mitigated cell impedance growth could be achieved by removing EC from a conventional electrolyte (i.e., 1 m LiPF 6 in EC:ethyl methyl carbonate (EMC), 3:7 by weight, with 2 wt% vinyl carbonate, VC) and adding a small amount of "enablers," such as VC and fluoroethylene carbonate (FEC). [9,36] However, these reports were focused on low-Ni cathodes (e.g., LiNi 0.4 Mn 0.4 Co 0.2 O 2 and LiNi 0.5 Mn 0.3 Co 0.2 O 2 ) with nonoptimized electrolyte compositions and limited mechanistic insights. [9,36] More recently, our group reported that with an optimized EC-free electrolyte (Gen 1, 1.0 m lithium bis(fluorosulfonyl) imide-0.5 m LiPF 6 in EMC with 3 wt% VC), the electrochemical performance and safety features of a high-Ni (LiNi 0.94 Co 0.6 O 2 ) cell were significantly enhanced owing to the stabilized electrode/electrolyte interphases (EEIs) and the reduced chemical reactivity of the electrolyte toward the cathode. [5] Advanced Ethylene carbonate (EC) is an important component in state-of-the-art electrolytes for lithium-ion batteries (LIBs). However, EC is highly susceptible to oxidation on the surface of high-nickel layered oxide cathodes, making it undesirable for next-generation high-energy-density LIBs. In this study, a simple, yet effective, EC-free electrolyte (20F1.5M-1TDI) is presented by adding 20 wt% fluoroethylene carbonate (FEC) and 1 wt% lithium 4,5-dicyano-2-(trifluoromethyl)im...

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Section: Resultsmentioning

confidence: 99%

Ethylene Carbonate‐Free Electrolytes for Stable, Safer High‐Nickel Lithium‐Ion Batteries

Pan

Cui

et al. 2022

Advanced Energy Materials

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“…Furthermore, a substantial difference is observed in T w dependence of 2DIR spectra due to the growth of off-diagonal features (i.e., cross peaks). In the MP electrolyte, the presence and growth of cross peaks at [ω τ , ω t = ∼1713, ∼1741] and [ω τ , ω t = ∼1741, ∼1713] are only evident at longer waiting times, while for the DMC electrolyte, a cross peak appears at T w = 0 ps at [ω τ , ω t = ∼1736, ∼1748] indicating the presence of vibrationally coupled transitions between the symmetric and asymmetric modes of Li(TFSI) 2 (DMC) 2 . − , In addition, the 2DIR spectra of the DMC electrolyte show the appearance and growth of additional cross peaks at [ω τ , ω t = ∼1724, ∼1756] and [ω τ , ω t = ∼1756, ∼1724] with waiting time, which is similar to the 2DIR spectral evolution observed for the MP electrolyte. In the case of the BC electrolytes, the 2DIR spectrum at T w = 0 ps shows a cross peak between the lower part of the main band and the isolated lower frequency band, but it does not appear to show changes in intensity with T w .…”

Section: Resultsmentioning

confidence: 99%

Molecular Structure, Chemical Exchange, and Conductivity Mechanism of High Concentration LiTFSI Electrolytes

Kankanamge

Kuroda

2020

J. Phys. Chem. B

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High concentration lithium electrolytes have been found to be good candidates for high energy density and high voltage lithium batteries. Recent studies have shown that limiting the free solvent molecules in the electrolytes prevents the degradation of the battery electrodes. However, the molecular level knowledge of the structure and dynamics of such an electrolyte system is limited, especially for electrolytes based on typical organic carbonates. In this article, the interactions and motions involved in lithium bis(trifluoromethanesulfonyl)imide in carbonyl-containing solvents are investigated using linear and timeresolved vibrational spectroscopies and computational methods. Our results suggest that the overall structure and the speciation of the three high concentration electrolytes are similar. However, the cyclic carbonate-based electrolyte presents an additional interaction as a result of dimer formation. Time-resolved studies reveal similar and fast dynamics for the structural motions of solvent molecules in electrolytes composed of linear molecules, while the electrolyte made of cyclic solvent molecules shows slower structural changes as a result of the dimer formation. Additionally, a picosecond time scale process is observed and assigned to the coordination and decoordination of solvent molecules from a lithium-ion solvation shell. This process of solvent exchange is found to be directly correlated to the making and breaking of structures between the lithium-ion and the anion and, consequently, to the conduction mechanism. Overall, our data show that the molecular structure of the solvent does not significantly affect the speciation and distribution of the lithium-ion solvation shells. However, the presence of dimerization between solvent molecules of two neighboring lithium-ions appears to produce a microscopic ordering that it is manifested macroscopically in properties of the electrolyte, such as its viscosity.

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“…VET can mask other dynamical events, such as a chemical exchange. Some of the recent time-resolved IR studies have interrogated the solvent modes of organic carbonates, − ureas, and acetonitrile in Li + electrolytes, but they could not discern the competing VET and chemical exchange pathways. One of the common ways to combat this issue is by introducing isotope-edited solvent molecules.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Acetonitrile Isotopologues as Vibrational Probes of Electrolytes

et al. 2021

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Acetonitrile has emerged as a solvent candidate for novel electrolyte formulations in metal-ion batteries and supercapacitors. It features a bright local C≡N stretch vibrational mode whose infrared (IR) signature is sensitive to battery-relevant cations (Li + , Mg 2+ , Zn 2+ , Ca 2+ ) both in pure form and in the presence of water admixture across a full possible range of concentrations from the dilute to the superconcentrated regime. Stationary and time-resolved IR spectroscopy thus emerges as a natural tool to study site-specific intermolecular interactions from the solvent perspective without introducing an extrinsic probe that perturbs solution morphology and may not represent the intrinsic dynamics in these electrolytes. The metal-coordinated acetonitrile, water-separated metal–acetonitrile pair, and free solvent each have a distinct vibrational signature that allows their unambiguous differentiation. The IR band frequency of the metal-coordinated acetonitrile depends on the ion charge density. To study the ion transport dynamics, it is necessary to differentiate energy-transfer processes from structural interconversions in these electrolytes. Isotope labeling the solvent is a necessary prerequisite to separate these processes. We discuss the design principles and choice of the CD 3 13 CN label and characterize its vibrational spectroscopy in these electrolytes. The Fermi resonance between 13 C≡N and C–D stretches complicates the spectral response but does not prevent its effective utilization. Time-resolved two-dimensional (2D) IR spectroscopy can be performed on a mixture of acetonitrile isotopologues and much can be learned about the structural dynamics of various species in these formulations.

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Effect of Solvation Shell Structure and Composition on Ion Pair Formation: The Case Study of LiTDI in Organic Carbonates

Cited by 16 publications

References 91 publications

Ethylene Carbonate‐Free Electrolytes for Stable, Safer High‐Nickel Lithium‐Ion Batteries

Ethylene Carbonate‐Free Electrolytes for Stable, Safer High‐Nickel Lithium‐Ion Batteries

Molecular Structure, Chemical Exchange, and Conductivity Mechanism of High Concentration LiTFSI Electrolytes

Characterization of Acetonitrile Isotopologues as Vibrational Probes of Electrolytes

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