The invention discloses a high-capacity 18650 lithium battery and a preparation process thereof, and relates to the technical field of new energy manufacturing. The lithium battery comprises a positive electrode material, a negative electrode material, an electrolyte, a shell and a diaphragm. The preparation process comprises the following steps: S1, performing dosing; S2, preparing materials; S3,performing coating; S4, performing coiling; S5, injecting liquid. During actual use, environment-friendly electrolyte is employed for preparing the lithium battery, so the lithium battery is green and environment friendly and the use capacity of the lithium battery can reach more than 85% of the theoretical capacity of the lithium battery. Moreover, the safety, the charge-discharge rate and the comprehensive performance of the lithium battery completely exceed national standard requirements, and the high-voltage, high-safety and high-rate charging and discharging are achieved. In addition, the spontaneous combustion risk of the battery can be effectively reduced through the added bromine-containing compound, the use safety of the lithium battery is improved, and the lithium battery is lowin cost and good in quality and has a good development prospect.