• Journal of the Korean Electrochemical Society
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• v.14 no.2
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• pp.92-97
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• 2011

In this study we have investigated the Li-ion coordination, thermal behavior and electrochemical stability of N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ($Py_{14}TFSI$) with lithium bis(trifluoromethanesulfony)imide (LiTFSI) doping intended for use as electrolytes for lithium batteries. The ionic conductivity is reduced and glass transition temperature ($T_g$) increases with LiTFSI doping concentration. Also, the electrochemical stability increases with LiTFSI doping. A high LiTFSI doping could enhance the electrochemical stability of electrolytes for lithium batteries, whereas the decrease in the ionic conductivity limits the capacity of the battery.

• Journal of the Korean Electrochemical Society
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• v.19 no.3
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• pp.101-106
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• 2016

In this study, we prepared an ionic liquid composite solid polymer electrolyte (PEO-LiTFSI-$Pyr_{14}TFSI$) with poly(ethylen oxide), lithium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide by blending-cross linking process. Although the PEO-LiTFSI-$Pyr_{14}TFSI$ composite solid polymer electrolyte displayed a small peak at 4.4 V, it had high electrochemical oxidation stability up to 5.7 V. Ionic conductivity of the PEO-LiTFSI-$Pyr_{14}TFSI$ composite solid polymer electrolyte increased with increasing temperature from $10^{-6}S\;cm^{-1}$ at $30^{\circ}C$ to $10^{-4}S\;cm^{-1}$ at $70^{\circ}C$. To investigate the electrochemical properties, the PEO-LiTFSI-$Pyr_{14}TFSI$ composite solid polymer electrolyte assembled with $LiFePO_4$ cathode and Li-metal anode. At 0.1 C-rate, the cell delivered $40mAh\;g^{-1}$ for $30^{\circ}C$, $69.8mAh\;g^{-1}$ for $40^{\circ}C$ and $113mAh\;g^{-1}$ for $50^{\circ}C$, respectively. The PEO-LiTFSI-$Pyr_{14}TFSI$ solid polymer electrolyte exhibited good charge-discharge performance in Li/SPE/$LiFePO_4$ cells at $50^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.28 no.9
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• pp.1567-1572
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• 2007

New pyrrolidinium and piperidinium bis(trifluoromethanesulfonyl)imide (TFSI) ionic liquids (ILs) having allyl substituents were synthesized and characterized. All of them are liquid at room temperature and stable up to 300 oC. The pyrrolidinium-based ILs showed better conductivities and lower viscosities than the corresponding piperidinium-based ILs. Among them, 1-allyl-1-methylpyrrolidinium TFSI showed the lowest viscosity of 52 cP, the highest conductivity of 5.7 mS cm?1, and the most negative cathodic voltage window of ?3.2 V (vs. Fc/Fc+) on a platinum electrode, which are the improved results compared to the corresponding analogue having a saturated substituent, 1-methyl-1-propylpyrrolidinium TFSI.

• Journal of the Korean Electrochemical Society
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• v.17 no.2
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• pp.103-110
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• 2014

In the study, a room temperature ionic liquids as a co-solvent was used to evaluate the feasibility with various electrodes in Li-ion batteries. 1-Ethyl-1-methyl piperidinium bis(trifluoromethanesulfonyl) imide(PP12 TFSI) is an ionic liquid that melts at $85^{\circ}C$. Pure PP12 TFSI is not able to be used as an electrolyte because it is a solid salt at room temperature. PP12 TFSI is mixed with EC/DEC(1/1 vol.%) to prepare mixed solvents. The electrolyte 1.5M $LiPF_6$ in a mixed solvent having 44 wt.% PP12 TFSI is prepared to evaluated the various electrodes. The electrolytes provides good cycles life of cells with $LiNi_{0.5}Mn_{1.5}O_4(LNMO)$, $LiFePO_4(LFP)$, $Li_4Ti_5O_{12}(LTO)$ and artificial graphite. Further improvement of the cell performances can be accomplished by enhancing wettability of electrolytes to electrodes.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.152-156
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• 2011

A room temperature ionic liquid (RTIL) based on trihexyl (tetradecyl)phosphonium bis(trifluoromethanesulfonyl) imide ([$(C_6H_{13})_3P(C_{14}H_{29)}$] [TFSI];P66614TFSI) was synthesized and analyzed to determine their characteristics and properties. The bis(trifluoromethanesulfonyl)imide (TFSI) anion is widely studied as an ionic liquid (IL) forming anion which imparts many useful properties, notably electrochemical stability. Especially its electrochemical and physical characteristics for solvent of lithium ion battery were investigated in detail. $P_{66614}$ TFSI exhibits fairly low conductivity (0.89 mS $cm^{-1}$) and higher viscosity (298 K: 277 cP; 343 K: 39 cP) than other ionic liquids, but it exhibits a high thermal stability (over $400^{\circ}C$). Especially corrosion behavior on Al current collector was tested at room temperature and further it was confirmed that thermal resistivity for Al corrosion was highly increased in 1.0M LiTFSI/$P_{66614}$-TFSI electrolyte comparing with other RTILs by linear sweep thermometry.

• Journal of the Korean Electrochemical Society
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• v.18 no.2
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• pp.51-57
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• 2015

We report the effect of the impurities including water and bromide in the propylmethylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PMPyr-TFSI) on the electrochemical performance of lithium ion batteries. The several kinds of PMPyr-TFSI electrolytes with different amount of impurities are applied as the electrolyte to the cell with the high potential electrode, $LiNi_{0.5}Mn_{1.5}O_4$ spinel. It is found that the impurities in the electrolytes cause the detrimental effect on the cell performance by tracing the cycleability, voltage profile and Coulombic efficiency. Especially, the polarization and Coulombic efficiency go to worse by both impurities of water and bromide, but the cycleability was not highly influenced by bromide impurity unlike the water impurity.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1795-1799
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• 2013

The corrosion property of aluminum by lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is investigated in liquid and gel electrolytes consisting of ethylene carbonate/propylene carbonate/ethylmethyl carbonate/diethyl carbonate (20:5:55:20, vol %) with vinylene carbonate (2 wt %) and fluoroethylene carbonate (5 wt %) using conductivity measurement, cyclic voltammetry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. All corrosion behaviors are attenuated remarkably by using three gel electrolytes containing 3 wt % of hydrophilic and hydrophobic fumed silica. The addition of silica particles contributes to the increase in the ionic conductivity of the electrolyte, indicating temporarily formed physical crosslinking among the silica particles to produce a gel state. Cyclic voltammetry also gives lower anodic current responses at higher potentials for repeating cycles, confirming further corrosion attenuation or electrochemical stability. In addition, the degree of corrosion attenuation can be affected mainly by the electrolytic constituents, not by the hydrophilicity or hydrophobicity of silica particles.

• Resources Recycling
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• v.21 no.6
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• pp.45-50
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• 2012

The room-temperature electrodeposition of metallic lithium was investigated from ionic liquid, 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI) with lithium bis (trifluoromethanesulfonyl)imide (LiTFSI) as a lithium source. Cyclic voltammograms on gold working electrode showed the possibility of the electrodeposition of metallic lithium, and the reduction current on a gold electrode was higher than the value on platinum and copper. The metallic lithium could be electrodeposited on the gold electrode under potentiostatic condition at -2.4 V (vs. Pt-QRE) and was confirmed by analytical techniques including XRD and SEM-EDS. The dendrite-typed electrodeposits were composed of a metallic lithium and a alloy with gold substrate. And any impurity could be detected except for trace oxygen introduced during handling for the analyses.

• Journal of Electrochemical Science and Technology
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• v.2 no.1
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• pp.8-13
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• 2011

Interfacial compatibility between the Si-Cu electrode and diluted ionic liquid electrolyte containing 50 vol.% of 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide (MPP-TFSI) and 50 vol.% dimethyl carbonate (DMC) in a lithium cell and dilution effect on surface chemistry are examined. ex-situ ATR FTIR analysis results reveal that the surface of the Si-Cu electrode cycled in the diluted ionic liquid electrolyte is effectively passivated with the SEI layer mainly composed of carboxylate salts-containing polymeric compounds produced by the decomposition of DMC. Surface species by the decomposition of TFSI anion and MPP cation are found to be relatively in a very low concentration level. Passivation of electrode surface with the SEI species contributes to protect from further interfacial reactions and to preserve the electrode structure over 200 cycles, delivering discharge capacity of > 1670 $mAhg^{-1}$ and capacity retention of 88% of maximum discharge capacity.

• Bulletin of the Korean Chemical Society
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• v.31 no.11
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• pp.3190-3194
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• 2010

Mixed electrolytes formed by the combination of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP-TFSI) ionic liquid and standard liquid electrolyte are prepared and characterized. Linear sweep voltammetry measurements demonstrate that these mixed systems exhibit a wide electrochemical stability window, allowing them to be suitable electrolyte for carbonaceous anode-based lithium-ion batteries. Lithium-ion cells composed of graphite anode and $LiCoO_2$ cathode are assembled using the mixed electrolytes, and their cycling performances are evaluated. The cell containing proper content of BMP-TFSI shows good cycling performance comparable to that of a cell assembled with organic electrolyte. The presence of BMP-TFSI in the mixed electrolyte contributes to the reduction of the flammability of electrolyte solution and the improvement of the thermal stability of charged $Li_{1-x}CoO_2$ in the electrolyte solution.