Preparation method of sodium difluorophosphate

The invention belongs to the technical field of sodium ion battery electrolyte, and particularly relates to a preparation method of sodium difluorophosphate. The preparation method of the sodium difluorophosphate comprises the following steps that oxygen-containing sodium salt and PF5 react in supercritical carbon dioxide fluid, generated NaF is not dissolved in the supercritical carbon dioxide fluid, sodium difluorophosphate is dissolved in the supercritical carbon dioxide fluid, the supercritical carbon dioxide fluid containing the sodium difluorophosphate is obtained after the reaction, and the sodium difluorophosphate is obtained. And separating to obtain sodium difluorophosphate. The supercritical carbon dioxide (SCO2) is adopted as a solvent, the solubility of the oxygen-containing sodium salt in the SCO2 is greatly improved, the contact area of PF5 and the oxygen-containing sodium salt is increased, the reaction efficiency is improved, the whole steps are simple, the reaction is easy to control, and th