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

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

• (a) a synthesis step:
• subjecting sulfuryl fluoride, ammonia gas and triethylamine to reaction in a reaction kettle in the presence of a solvent to obtain a stream α1 containing (SO2F—NH—SO2F)·Et3N, a triethylamine hydrogen fluoride salt and triethylamine;
• (b) an evaporation step:
• performing evaporation on the stream α1 to obtain a stream α2 containing (SO2F—NH—SO2F)·Et3N and the triethylamine hydrogen fluoride salt, performing post-treatment on the evaporated solvent and the triethylamine optionally, and then looping back to step (a);
• (c) an extraction step:
• washing the stream α2 obtained in step (b) 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;
• (d) an alkalinization step:
• delivering the oil phase α3 obtained in step (c) 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;
• (e) a dehydration step:
• adding the stream β1-2 containing the lithium bis(fluorosulfonyl)imide and an ester solvent to an evaporator for evaporation to obtain a stream β2 containing lithium bis(fluorosulfonyl)imide;
• (f) a desolventization step:
• adding the stream β2 obtained in step (e) and an ester solvent to an evaporator for evaporation to obtain crude lithium bis(fluorosulfonyl)imide β3;
• and
• (g) a crystallization step:
• pumping the crude lithium bis(fluorosulfonyl)imide β3 obtained in step (f) to a crystallization kettle, and adding dichloromethane to precipitate lithium bis(fluorosulfonyl)imide crystals.