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Screening of contaminants and forced degradation products in lithium ion battery electrolyte

Electrolytes in rechargeable batteries for cars, mobile phones, and other portable electric devices typically contain negatively charged counterions that together with lithium and a non-aqueous solvent form an ionic liquid. The bis(fluorosulfonyl)imide anion is a rather new ionic liquid constituent which thus need new quality control procedures.

This application uses a straightforward carbonate eluent to screen for contaminants and forced degradation products in a lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte. The screening procedure did not include any sample preparation at this point, but a formalized quality control procedure would require either gradient elution or a sample preparation procedure to avoid that the FSI¯ anion is extensively retained on the analytical separation column.

Anions in ionic liquid electrolyte

Ion chromatographic analysis of lithium bis(fluorosulfonyl)imide (LiFSI) ionic liquid on a Shodex IC SI-50 4E column (250×4 mm) equipped with Shodex IC SI-50G (4.6×10 mm) guard column, using an eluent containing 3.2 mM Na₂CO₃ and 1.0 mM NaHCO₃ in water pumped at 0.75 mL/min at 24 °C from an EQAX-B1 eluent bottle equipped with an EQAX-TC1 trap cartridge for carbon dioxide removal. Background reduced to ~14 µS/cm by XAMS suppressor with ASUREX-A200 automatic regenerator. Eluent pumping and conductivity detection by Metrohm 761 Compact IC. Injection of 20 µL of LiFSI solid raw material dissolved in ultra-pure water and diluted 1:1000, giving signals up to 2.8 µS/cm. Qualitative identification of anions by separate standard injections of F¯, Cl¯, NO₂¯, HPO₄²¯, SO₃²¯, SO₄²¯ in water. HCO₃¯ eluted due to eluent ion displacement by the strongly retained FSI¯ ion.

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