ELECTROLYTE SOLUTION, ELECTROCHEMICAL DEVICE, AND LITHIUM ION SECONDARY BATTERY AND MODULE

An electrolyte solution containing lithium ethyl sulfate and ethyl sulfate. The lithium ethyl sulfate is present in an amount of 0.1 to 2.0% by mass relative to the electrolyte solution. The lithium ethyl sulfate and the ethyl sulfate give a mass ratio of the lithium ethyl sulfate to the ethyl sulfate of 80 to 1500. Also disclosed is an electrochemical device and lithium ion secondary battery containing the electrolyte solution, a module including the electrochemical device and a method for producing lithium ethyl sulfate.