Lithium bis(trifluoromethane)sulfonimide

December 06, 2021
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Lithium bis(trifluoromethane)sulfonimide (LiTFSI) is a hydrophilic organic salt that has many uses in electric and electronic systems. Its bis(trifluoromethane)sulfonimide anion, often referred to as bistriflimide, has the useful property of coordinating weakly with cations.

LiTFSI ‘s other important property is its extremely high solubility in water: 21 molal or ≈6 kg/L of solution. Because of its solubility, it has been explored as an electrolyte for lithium-ion batteries, solar cells, and similar applications since at least the late 1980s. LiTFSI is a safer material than the formerly used salt, lithium hexafluorophosphate (LiPF6).

In a 2021 Nature article, André D. Taylor at New York University (New York City) and Yale University (New Haven, CT) and 18 colleagues there and at other institutions in the United States and the Republic of Korea reported a refinement in the use of LiTFSI in solar cells.

Photovoltaic cells made of inexpensive light-absorbing perovskites that have high power-conversion efficiencies have been developed over the past several years. To improve the cells’ ability to transport electrical charges, they are doped with a combination of LiTFSI and a semiconductor called Spiro-OMeTAD1; but this process is extremely slow.

Taylor and his fellow researchers solved the problem by bubbling carbon dioxide into a solution of spiro-OMeTAD and LiTFSI while irradiating the mixture with ultraviolet light. They then cast a film made from the solution onto the perovskite light absorber. The process can be completed in ≈1 min, compared with the older, hours-long doping procedure.

The authors state, “The CO2-treated interlayer exhibits approximately 100 times higher conductivity than a pristine [untreated] film while realizing stable, high-efficiency solar cells without any post-treatments.” They also report that their method is useful for doping π-conjugated polymers.

1. 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene, CAS Reg. No. 207739-72-8.

Lithium bis(trifluoromethane)sulfonimide 
hazard information*

Hazard class** GHS code and hazard statement
Acute toxicity, oral, category 3 H301—Toxic if swallowed  Chemical Safety Warning
Acute toxicity, dermal , category 3 H311—Toxic in contact with skin Chemical Safety Warning
Skin corrosion/irritation, category 1B H314—Causes severe skin burns and eye damage Chemical Safety Warning
Serious eye damage/eye irritation, category 1 H318—Causes serious eye damage Chemical Safety Warning
Specific target organ toxicity (nervous system), repeated exposure, oral, category 2 H373—May cause damage to nervous system through prolonged or repeated exposure if swallowed Chemical Safety Warning
Short-term (acute) aquatic hazard, category 3 H402 —Harmful to aquatic life
Long-term (chronic) aquatic hazard, category 3 H412—Harmful to aquatic life with long-lasting effects

*Compilation of selected safety data sheets.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. 
Explanation of pictograms.

Lithium bis (trifluoromethane) sulfonimide fast facts

CAS Reg. No. 90076-65-6
Methanesulfonamide, 1,1,1-trifluoro-N-[(trifluoromethyl)
sulfonyl]-, lithium salt (1:1)
Empirical formula C2F6LiNO4S2
Molar mass 287.09 g/mol
Appearance Hygroscopic white powder
Melting point 234–238 °C
Water solubility ≈6 kg/L
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