A study of the Li/Li+ couple in DMC and PC solvents

Doucey, L; Revault, M.; Lautié, A.; Chaussé, A.; Messina, R.

doi:10.1016/s0013-4686(98)00365-x

Cited by 80 publications

(75 citation statements)

References 26 publications

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“…Figure 6 shows the conductivity of X_E electrolytes versus molarity and temperature. Figure 6 shows that the conductivity of X_E electrolyte drops dramatically when the concentration of LiPF 6 decreases below 0.4 M, completely unlike the results for LiPF 6 :PC:DEC electrolytes described by Ding et al 48 The conductivity versus molarity results for X_E electrolytes are very similar to the results described by Doucey et al 49 and Delsignore et al 50 for the conductivity of LiAsF 6 /DMC solutions at low salt concentrations measured at 25…”

Section: Resultssupporting

confidence: 67%

“…This suggests that changes in desolvation energy due to changes in salt concentration in the 0.5 to 2.0 M range in LiPF 6 :EMC electrolyte does not contribute significantly to the change in R ct of the cells. However, In dilute LiPF 6 solutions in EMC or DMC, by analogy to LiAsF 6 in DMC, as reported by Doucey et al 49 the salt is not well-dissociated at low concentration, which is why the conductivity is so small. Doucey The area-specific electrolyte resistance of the coin full cells described by Figure 11a and Figure 11b extracted from the four-wire EIS measurement plotted vs. the electrolyte resistivity obtained using the data in Figure 11c.…”

Section: Resultsmentioning

confidence: 86%

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Dramatic Effects of Low Salt Concentrations on Li-Ion Cells Containing EC-Free Electrolytes

Xiong¹,

Hynes²,

Dahn³

2017

J. Electrochem. Soc.

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Different concentrations of LiPF 6 (0.3 M-2 M) in ethyl methyl carbonate (EMC) electrolyte and ethylene carbonate (EC)-based electrolyte were studied in LiNi 0.4 Mn 0.4 Co 0.2 O 2 (NMC442)/graphite pouch cells. Fresh cells containing 0.3 M LiPF 6 in EMC electrolyte showed extremely large charge transfer resistance while those with 0.3 M LiPF 6 in EC/EMC electrolyte did not. Impedance spectra taken on symmetric cells and ionic conductivity measurements suggest this difference is due to difficulty in dissociating and desolvating Li + ions from the EMC-based electrolyte to intercalate into both the electrodes. After elevated temperature storage experiments at 4.5 V, cells with 0.3 M LiPF 6 in EC/EMC showed a large increase in positive electrode charge transfer impedance, presumably caused by electrolyte oxidation. With salt concentrations greater than 1 M, charge transfer resistance was much smaller in EMC-based electrolytes and was stable during storage for both electrolyte types. Conductivity and cycle testing measurements suggest that 1.5 M LiPF 6 should be used in EC-free EMC-based electrolytes to optimize cell performance. Using high potential positive electrodes can increase the energy density of Li-ion cells. [1][2][3][4] Layered LiNi x Mn y Co z O 2 (x + y + z = 1) (NMC) electrodes have been extensively studied because they are cheaper materials than LiCoO 2 (LCO) and can operate at high working potentials.5-15 LiNi 0.4 Mn 0.4 Co 0.2 O 2 (NMC442) is a possible choice for high voltage application due to its high working potential, high specific capacity, moderate cost and excellent safety. [16][17][18][19] NMC442 has been shown to be structurally stable up to 4.7 V 16,17 and its specific capacity increases almost linearly as the upper cutoff voltage increases from 4.1 V to 4.7 V. At 4.7 V, NMC442 can deliver a reversible specific capacity of ∼207 mAh/g. NMC442 shows attractive safety features compared to other NMC grade materials as well. 19It is difficult to create NMC442/graphite cells that show long lifetime when operated continually to an upper cutoff potential above 4.4 V. Electrolyte additives such as pyridine boron fluoride (PBF), 20,21 triallyl phosphate (TAP) 22 and additive blends such as prop-1-ene-1,3-sultone (PES) + 1,3,2-dioxathiolane-2,2-dioxide (DTD) + tris-(trimethyl-silyl) phosphite (TTSPi) [23][24][25][26][27] in EC-based electrolyte have been used to improve charge-discharge cycle life and calendar life of cells operated to 4.4 V. Sulfone-based and fluorinated electrolyte systems have also shown to be of value in getting NMC442/graphite cells to operate beyond 4.4 V. 28,29 In spite of these improvements, further improvement is required. Recently, it was found that EC-free electrolyte using only ethyl methyl carbonate as the solvent can enhance high voltage operation and lifetime of NMC442/graphite pouch cells compared to EC-based electrolyte.30-32 However, only a salt concentration of 1 M LiPF 6 in this novel electrolyte was investigated.The concentration of LiPF 6 in EC-based electrolyte...

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Section: Resultssupporting

confidence: 67%

Section: Resultsmentioning

confidence: 86%

Dramatic Effects of Low Salt Concentrations on Li-Ion Cells Containing EC-Free Electrolytes

Xiong¹,

Hynes²,

Dahn³

2017

J. Electrochem. Soc.

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“…FT-IR is a good tool that has been applied to investigate solvation behavior and ion pair formation for a wide variety of salts and solvents. 30,31,[39][40][41][42] Figure 2 and Figure 3 show FT-IR spectra (800-900 and 1600-1900 cm −1 ) of EMC and mixed FEC:EMC (10:90) electrolyte containing different concentrations of LiPF 6 . Figure S1 shows FT-IR spectra of mixed FEC:EMC (5:95) electrolyte containing different concentrations of LiPF 6 .…”

Section: Resultsmentioning

confidence: 99%

Some Physical Properties of Ethylene Carbonate-Free Electrolytes

Xiong

Bauer

Ellis

et al. 2018

J. Electrochem. Soc.

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Physical properties of LiPF 6 in ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) electrolytes were studied by conductivity measurements, Fourier transform infrared spectroscopy (FT-IR) and differential thermal analysis (DTA). Conductivity measurements show that the addition of additive levels of FEC to EMC electrolyte can dramatically increase the conductivity of EC-free EMC electrolytes at low salt concentrations below 0.4 M. FT-IR results show that the added FEC hinders ion pair formation by competing with EMC to dissociate LiPF 6 resulting in increased conductivity in EMC electrolytes. Conductivity measurements show that the conductivity of DMC electrolytes decreases significantly below 0 • C due to the high melting point of DMC. Differential thermal analysis was used to determine the LiPF 6 -DMC phase diagram which then can be used to explain the conductivity results. The results presented here identify avenues by which EC-free electrolytes can be improved for use in practical Li-ion cells. Li-ion battery packs for electrified vehicles and grid energy storage require high energy density and long lifetime cells.1-3 One approach to increase the energy density of Li-ion cells is to adopt high potential positive electrodes. Layered Li[Ni x Mn y Co 1-x-y ]O 2 materials have been extensively investigated since they are cheaper alternatives to LCO and since they can function at high potentials. 4-9However, it is a great challenge to cycle high voltage NMC cells (above 4.3V) well. The use of new solvent blends and the introduction of electrolyte additives are two common ways to improve the lifetime of high voltage NMC Li-ion cells. 24-32 Therefore, it is important to study the physical properties of EC-free electrolytes to optimize the performance of cells where EC-free electrolytes are used.Differential scanning calorimetry (DSC) 29,32,33 and differential thermal analysis (DTA) 34 can be used to examine the phase diagrams of solvent blends and of electrolytes. Ding et al. showed that supercooling and superheating during DSC measurements for phase diagram determination could be dramatically reduced if carbon black and/or electrode powders were present in the samples during measurement. 33Recently Day et al. demonstrated that the DTA technique can be applied to an entire Li-ion cell and is a non-invasive in-situ method to probe the state of the liquid electrolyte within intact Li-ion cells. 34The DTA measurements provide information about the amount of liquid electrolyte remaining in the cell and about the electrolyte composition. The interpretation of the DTA results requires information about the phase diagram of the electrolyte of interest. However, the phase diagrams of LiPF 6 :ethyl methyl carbonate and LiPF 6 :dimethyl carbonate electrolytes have not yet been reported.In this report, the conductivity of LiPF 6 :EMC electrolytes with various salt concentrations were measured over a wide range of temperatures. Fourier transform infrared spectroscopy (FT-IR) was used to study the interactions between t...

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“…With respect to the IR spectrum several carbonate vibration modes are known to be sensitive to Li + coordination [30][31][32]. Due to the Li + coordination by carbonyl-functional groups, a new band arises at lower frequencies.…”

Section: Salt-solvent Interactionsmentioning

confidence: 99%