This data-file tabulates the CO2 intensity of producing lithium ion batteries for automotive use, split across 10 different components, informed by the technical literature. Producing the average EV battery emits 9T of CO2.
Electric Vehicles should have c40% lower emissions than gasoline vehicles over their entire useful lives, assuming equivalent mileages.
But manufacturing EVs has an energy deficit, which means the ascent of EVs could increase net fossil fuel demand all the way out to 2037 (note here).
This data-file can be used to calculate the crossover point, which comes after around 3.5 years and c50,000 miles (chart above). The numbers will vary as a function of grid composition, technical improvements and vehicle specifications.