Preparation method for bis-(fluoro-sulfonyl) imide lithium salt

Provided is a preparation method for lithium bis-(fluoro-sulfonyl) imide, comprising the following steps: (1) carrying out fluorination: synthesizing an intermediate bis-(fluoro-sulfonyl) imide by using bis-(chloro-sulfonyl) imide and hydrogen fluoride in presence of a catalyst; and (2) enabling the obtained bis-(fluoro-sulfonyl) imide and alkaline lithium to react, and carrying out solid-liquid separation after the reaction to obtain the lithium bis-(fluoro-sulfonyl) imide. The preparation method is low in cost, fewer in by-products and simple in aftertreatment, and is capable of guaranteeing the quality and purity of products, thereby being suitable for industrial production.