Method for producing difluorophosphate, non-aqueous electrolyte for secondary cell and non-aqueous electrolyte secondary cell
View Patent ↗A difluorophosphate effective as an additive for a nonaqueous electrolyte for secondary battery is produced by a simple method from inexpensive common materials. The difluorophosphate is produced by reacting lithium hexafluorophosphate with a carbonate in a nonaqueous solvent. The liquid reaction mixture resulting from this reaction is supplied for providing the difluorophosphate in a nonaqueous electrolyte comprising a nonaqueous solvent which contains at least a hexafluorophosphate as an electrolyte lithium salt and further contains a difluorophosphate. Also provided is a nonaqueous-electrolyte secondary battery employing this nonaqueous electrolyte.
1. A process for producing a difluorophosphate of a structure PO 2 F 2 − , which comprises reacting a lithium hexafluorophosphate with a carbonate in a nonaqueous solvent, at a temperature of 30° C. to 70° C. at a molar ratio of said carbonate to said lithium hexafluorophosphate of 1×10 −3 to 1 or higher and a time of at least two hours and filtering a reaction product of said lithium hexafluorophosphate and said carbonate.
2. The process for producing a difluorophosphate as claimed in claim 1 , wherein the carbonate is selected from the group consisting of alkali metal salts, alkaline earth metal salts, and salts represented by NR 1 R 2 R 3 R 4 , wherein R 1 to R 4 may be the same or different and each represents either an organic group having 1 to 12 carbon atoms or a hydrogen atom).
3. The process for producing a difluorophosphate as claimed in claim 1 , wherein the nonaqueous solvent is one or more solvents selected from the group consisting of cyclic carbonates, linear carbonates, cyclic esters, linear esters, cyclic ethers, linear ethers, and sulfur-containing organic solvents.
4. The process for producing a difluorophosphate as claimed in claim 1 , wherein the nonaqueous solvent is a nonaqueous solvent having a relative permittivity of lower than 10.