In secondary lithium batteries like lithium ion batteries organic carbonates, ethers, esters and ionic liquids are used as sufficiently polar solvents for solvating the conducting salt(s). Most state of the art lithium ion batteries in general comprise not a single solvent but a solvent mixture of different organic aprotic solvents.

Besides solvent(s) and conducting salt(s) an electrolyte composition usually contains further additives to improve certain properties of the electrolyte composition and of the electrochemical cell comprising said electrolyte composition. Common additives are for example flame retardants, overcharge protection additives and film forming additives which react during first charge/discharge cycle on the electrode surface thereby forming a film on the electrode. The film protects the electrode from direct contact with the electrolyte composition.

Due to their versatile applicability, electrochemical cells like lithium batteries are often used at elevated temperatures e.g. arising in a car exposed to sunlight. At elevated temperatures decomposition reactions in the electrochemical cell take place faster and the electrochemical properties of the cell degrade faster e.g. shown by accelerated capacity fading and increase of internal resistance of the cell.

WO 2013/149073 A1 describes lithium ion batteries including an alkali transition metal oxoanion material like lithium iron phosphate as cathode active material and an electrolyte containing sulfur trioxide amine complex additive. The electrolyte additive is added to delay the thermal decomposition of the electrolyte.