A lithium ion secondary battery system includes a chamber to accommodate a lithium ion secondary battery, a charging/discharging device for electrically charging and discharging the lithium ion secondary battery, a pressure plate disposed in the chamber and configured to press the lithium ion secondary battery when the lithium ion secondary battery is electrically charged, a pointed portion disposed in the chamber and configured to bore a hole in a pouch of the lithium ion secondary battery to enable gas generated during the electrical charging of the lithium ion secondary battery to be removed from the pouch, and a sealer configured to seal the pouch after the gas is removed.