The invention provides a preparation method of a lithium ion battery with long storage performance, an active substance in a positive electrode in the lithium ion battery is LiCo0.97Al0.1Mg0.2O2, andthe positive electrode also comprises polyaniline accounting for 2-3% by mass of the active substance; the negative electrode of the lithium ion battery is a graphite negative electrode and can be selected from natural graphite or artificial graphite; the chain carbonate in the electrolyte of the lithium ion battery accounts for less than 20% of the total volume of the electrolyte, and the electrolyte comprises an additive composed of dimethyl sulfoxide (DMSO), trifluoroethyl phosphonic acid (TTFP) and hexylbenzene (CHB). The preparation method comprises the following steps: stacking a positive electrode, a diaphragm and a negative electrode to prepare a battery cell, placing the battery cell in a battery shell, injecting liquid, and performing formation, wherein the formation comprises aconstant-voltage charging process under a predetermined voltage, and the lithium ion battery obtained by the preparation method disclosed by the invention can be stored for a long time without capacity attenuation, and has good storage performance.