METHOD FOR PRODUCING PHOSPHORYL IMIDE SALT, METHOD FOR PRODUCING NONAQUEOUS ELECTROLYTE SOLUTION CONTAINING SAID SALT, AND METHOD FOR PRODUCING NONAQUEOUS SECONDARY BATTERY

To provide a method for producing a phosphoryl imide salt represented by the following general formula (1) at a satisfactory yield by cation exchange. The method comprises the step of performing cation exchange by bringing a phosphoryl imide salt represented by the following general formula (2) into contact with a cation exchange resin having M or a metal salt represented by the general formula (4) in an organic solvent having a water content of 0.3% by mass or less.