Formation method of lithium ion battery

A formation method of a lithium ion battery comprises the following steps of placing a battery cell of which aging is finished in a device for high-temperature pressurized formation, wherein the charging cutoff voltage is 3.5-3.8V; cooling the battery cell under a room temperature and a fixed pressure to make the temperature of the battery cell reduced to a room temperature; placing the cooled battery cell in a vacuum environment, puncturing an air bag of the battery cell, pumping air, and sealing; placing the battery cell of which air pumping is finished in a formation device for high-temperature pressurized formation, wherein the charging cutoff voltage is 3.9-4.5V; and cooling the battery cell under a room temperature and a fixed pressure to make the temperature of the battery cell reduced to the room temperature, and finishing formation. According to the formation method, the steps of puncturing the air bag and pumping air are added during hot-press formation, reaction gas can be timely eliminated, and th