I just saw a TED talk about the actual carbon output of electric vehicles when the battery production and energy for charging is factored in - and also taking into account the shortened range of EVs
So right now they are not really breaking even compared to regular gas vehicles, all things considered - and they did figure in the costs of both in the chain.
Batteries require materials that are harder to get.
I'm not ant-electric vehicle at all, but right now they really are not cutting carbon emissions. One thing though is that electric vehicles are way more efficient in their energy to power output.