The invention provides a lithium ion battery and a preparation method. The lithium ion battery includes a positive electrode, a negative electrode, a diaphragm, and an electrolyte. The positive electrode and the negative electrode are separated by the diaphragm; the positive electrode, the negative electrode and the diaphragm are encapsulated in an enclosed space; the electrolyte is filled in theenclosed space; the positive electrode includes a positive active material, the positive active material includes a nickel-cobalt-manganese ternary material, and the percentage of the amount of a substance of nickel in the nickel-cobalt-manganese ternary material is 50-60%; the negative electrode includes a negative active material, the negative active material includes graphite, and the degree ofgraphitization of the graphite is 91-94%, and an OI value is 6-7; and the electrolyte includes a lithium salt, a solvent and an additive, wherein the lithium salt includes lithium hexafluorophosphateand lithium bis(fluorosulfonyl)imide, the solvent includes ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and propyl propionate, and the additive includes lithium difluorophosphate, lithium bis(oxalate)borate, tris(trimethylsiloxy)boron, vinylene carbonate, and succinonitrile. The lithium ion battery has the characteristics of high safety, low cost, long service life and excellentusage performance.