Ammonium oxalyldifluoro borate electrolyte and preparation method and purification method thereof

Embodiments of the invention disclose an ammonium oxalyldifluoro borate electrolyte and a preparation method and a purification method thereof; the preparation method comprises the following steps: mixing quaternary ammonium base with oxalic acid, reacting to obtain an ammonium oxalate salt; mixing the ammonium oxalate salt with boron trifluoride ether in a first organic solvent, reacting at 10-120 DEG C to obtain the ammonium oxalyldifluoro borate electrolyte. The preparation method has a mild reaction condition, simple operation, high product purity, and low cost, and facilitates industrialization. The ammonium oxalyldifluoro borate electrolyte prepared in the invention has excellent properties of both quaternary ammonium compounds and oxalyldifluoro borate compounds; ammonium oxalyldifluoro borate is easy to dissolve in water and organic solvents, has high conductivity in organic solutions, can be used as an electrolyte of energy storage devices such as lithium batteries and super capacitors which have high requirements for electrolyte salt purity, and can improve the electrochemical performance of energy storage devices.