Abstract: The present invention relates to a method for preparing a carbonate solution of an alkali metal or an alkaline earth metal bis(fluorosulfonyl)imide, more specifically to a method for obtaining a carbonate solution of an alkali metal or an alkaline earth metal bis(fluorosulfonyl)imide by preparing an alkali metal or an alkaline earth metal bis(fluorosulfonyl)imide in a carbonate and a solvent other than a carbonate, and then removing the solvent other than the carbonate.

Abstract: The present invention relates to a method for preparing lithium difluorophosphate salt in high yield by using low-unit-cost raw materials. In particular, the present invention relates to a method for preparing lithium difluorophosphate salt with high purity and high yield by preparing same without using lithium hexafluorophosphate salt. Therefore, the lithium difluorophosphate salt prepared according to the present invention may be used in an electrolyte for a lithium secondary battery, and when used in an electrolyte for a lithium secondary battery, has electrochemical property, output, and gas reduction effects, and so on.

Abstract: The present invention relates to an electrolyte additive composition comprising lithium salt of bisfluorosulfonylimide and at least one selected from the group consisting of Cs+ ion and Rb ion+.