A production method is provided for producing a lithium ion secondary battery. The lithium ion secondary battery has an external casing that houses an electrolytic solution and a power generating element. The power generating element includes a positive electrode and a negative electrode layered with a separator. The production method includes first charging the lithium ion secondary battery at a voltage range of 4.0 V or lower and then opening the external casing of the lithium ion secondary battery that has been charged at a range of 4.0 V or lower to discharge gas inside the lithium ion secondary battery to the exterior. Next, the production method further includes re-sealing the external casing and charging the lithium ion secondary battery from which the gas has been discharged until the cell voltage is greater than 4.0 V.