The method for synthesizing hexafluorophosphate successively includes the procedures of pretreating anhydrous hydrogen fluoride, synthesizing hexafluorophosphate, low-temp. recrystallization, crystallizing-filtering and washing-filtering, pneumatic drying and vacuum forced drying. Said synthesizing equipment includes electrolytic dewatering device of anhydrous hydrogen fluoride and synthesis reaction device of lithium hexafluorophosphate. Before synthesis reactino the water content of the solvent can be reduced to the allowable range so as to eliminate impurity produced by water content and reduce content of free acid, the low-temp. solid-liquid separation process is adopted so as to raise the purity of the product. Said invention product can be directly used as electrolyte of secondary lithium ion cell. |