Liquid filling method of lithium ion battery

The invention relates to a manufacturing technology of a lithium ion battery and in particular relates to a liquid filling method of the lithium ion battery. The method comprises the following steps: 1, filling a lithium ion secondary battery to be filled with liquid with an electrolytic solution A containing vinylene carbonate for the first time, wherein the liquid filling quantity is 30%-45% by mass of the total liquid filling quantity; 2, forming; 3, filling the lithium ion secondary battery with an electrolytic solution B containing vinylene carbonate for the second time, wherein the liquid filling quantity is 25%-35% by mass of the total liquid filling quantity; 4, forming; 5, filling the lithium ion secondary battery with an electrolytic solution C containing vinylene carbonate for the third time, wherein the liquid filling quantity is 15%-25% by mass of the total liquid filling quantity; 6, forming; 7, filling the lithium ion secondary battery with an electrolytic solution D for the fourth time, wherei