While having electric cars may reduce some of the various pollutants regular cars emit, to claim they are 'emission free' is a flat-out lie, and the making of their batteries? According to Driving, the production of them make far more pollution than making a normal car.
If the electricity they use is produced "greenly" then sure! Like in Canada or Albania. They reduce emissions... mostly. But since most nations (especially China and India) use lots of dirty coal (as opposed to 'clean coal' in the USA) they end up being no better than gasoline powered ones. Perhaps worse.
And to top it off, the making of the batteries for a Tesla produces as much CO2 as 8 years of driving a regular car. And the batteries do not last for 8 years...
More reading on the subject here and here.