Lithium bis(Fluorosulfonyl)imide

Electrolyte Chemistry

Solvation of this salt in carbonate solvents reduces viscosity, which accelerates lithium-ion migration. The weaker binding energy between the fluorosulfonyl imide anion and the lithium cation leads to a higher dissociation fraction compared to lithium hexafluorophosphate. This leads to higher ionic flux across the separator under demanding charging loads.

This mechanism also decreases the likelihood of lithium plating on the anode surface.

Sourcing Benefit

Battery cell procurement specialists choose this salt for cells targeted at fast-charging applications. Although lithium bis(fluorosulfonyl)imide is more expensive than conventional salts, it reduces the total cost of ownership by extending the cycle life of high-power cells. Sourcing managers negotiate long-term supply agreements for this salt to secure the materials needed for next-generation electric vehicle batteries.

This helps to meet the growing demand for rapid-charging vehicles.

Material Limitation

Corrosion of the aluminum current collector is a major concern at voltages above four volts. Sourcing specifications should require the inclusion of protective additives, such as lithium difluorophosphate, to passivate the metal surface when lithium bis(fluorosulfonyl)imide is used. Without these protective additives, the aluminum will dissolve, leading to high leak currents and eventual cell failure.

Sourcing contracts should therefore specify the exact blend of additives required for high-voltage cells.