Method of testing lithium-ion secondary battery, and method of producing lithium-ion secondary battery using the same

A method of testing a lithium-ion secondary battery, the battery comprising a cathode containing lithium iron phosphate as a cathode active material, an anode containing a carbon material as an anode active material, and an electrolyte layer arranged between the cathode and the anode, the method comprising:

• adjusting a charging rate of the lithium-ion secondary battery to be in a plateau region and to be in the range from 25 to 35% or 70 to 90%;
• setting voltage of a test power supply to a voltage equal to or higher than voltage of the lithium-ion secondary battery;
• building a circuit by connecting the lithium-ion secondary battery and the test power supply;
• measuring a leakage current that flows through the circuit until the leakage current converges;
• and
• determining whether the lithium-ion secondary battery is good or bad based on the leakage current after the leakage current has converged.