Lithium bis(fluorosulfonyl)imide and preparation method thereof, electrolytic solution and secondary battery

A method for preparing lithium bis(fluorosulfonyl)imide, comprising:

• a synthesis step, comprising subjecting sulfuryl fluoride, ammonia gas, and triethylamine to reaction in a reaction device in presence of a solvent to obtain a stream α1 containing (SO2F—NH—SO2F)·Et3N, a triethylamine hydrogen fluoride salt, and triethylamine;
• an evaporation step, comprising performing evaporation on the stream α1 to obtain a stream α2 containing (SO2F—NH—SO2F)·Et3N and the triethylamine hydrogen fluoride salt;
• an extraction step, comprising washing the stream α2 with water in an extraction tower or a static mixer to obtain an oil phase α3 containing (SO2F—NH—SO2F)·Et3N and an aqueous phase αwater containing the triethylamine hydrogen fluoride salt, and separating out the oil phase α3;
• an alkalinization step, comprising delivering the oil phase α3 to an evaporator to be mixed with a lithium hydroxide aqueous solution to obtain a mixture stream β1-1, and then performing reduced-pressure evaporation on the stream β1-1 to obtain a stream β1-2 containing lithium bis(fluorosulfonyl)imide;
• a dehydration step, comprising mixing the stream β1-2 containing the lithium bis(fluorosulfonyl)imide with an ester solvent, and then performing evaporation in an evaporator to obtain a stream β2 containing lithium bis(fluorosulfonyl)imide;
• and
• a desolventization step, comprising mixing the stream β2 with an ester solvent, and then performing evaporation in an evaporator to obtain lithium bis(fluorosulfonyl)imide β3.