The big issue is making enough batteries for millions of EVs, and that will take some planning for the necessary expansion.
Luckily all the big manufacturers have been building battery plants - the problem is that automobile manufacturers haven't been building good enough cars around those proposed battery packs to fully utilize those factories.
A few examples:
Nissan / AESC: Finished a large battery plant earlier this year in Tennessee thanks to DOE loan. Currently only supplies batteries for the Nissan LEAF (24 kWh battery pack), which sells about 1,600 / month or 20,000 / year in the USA. Maximum capacity of the plant when fully ramped up is claimed to be around 150,000 / year or over 12,000 / month.
LG Chem: Finished a large battery plant last year in Michigan thanks to DOE loan. Unfortunately, has been sitting idle for some time, though is finally starting to produce batteries for the Chevrolet Volt (16.5 kWh battery pack). Maximum capacity of the plant is claimed to be around 60,000 / year, currently the Volt is selling about 1,600 / month or 20,000 / year in the USA.
A123: Finished a large battery plant in 2010 in Michigan thanks to DOE loan. Capable of 30,000 battery packs/year. Unfortunately a very large bad bad of batteries delivered to Fisker and Fisker's demise also lead to A123's demise whose assets were bought out. Still operating, and delivering batteries for the Chevrolet Spark EV (20 kWh battery pack). Unfortunately the Spark EV is a low volume vehicle so far only available in a few markets. Launched late June, only sold 130 through July (August sales numbers should be out soon).
Anyway - my point is that there is plenty of supply out there for lithium batteries right now - there are more plants than just the ones mentioned here - both in the USA and abroad. The competition is tough (see A123's bankruptcy and others, too) so despite low interest loans manufacturers are going under. What's needed is a few more plug-ins with a bit more appear - either more utility or lower price.
Both Nissan / GM / Tesla have shown that the public will buy electric cars if they are good products and priced right.
Nissan says they are actually selling all the LEAFs they can make and are currently capacity constrained after a big price drop for the '13 model - they are apparently being conservative in ramping up production capability. Inventory levels support their claims. If Nissan could get at least 25% more range into the car (and perhaps a more neutral package) without increasing the price, I think they could easily sell quite a few more EVs.
GM needed to drop the price of the Volt - they finally did so for the '14 model and they are saying as a result August will be their best sales result yet. Inventory levels support their claims. If GM could get the Volt drivetrain into a slightly roomier vehicle without sacrificing much efficiency and keeping the price down, I think they could easily sell quite a few more PHEVs.
Tesla has finally worked through most of the backlog of their USA orders (there's only so many people who can afford $70k+ cars) and are starting to ship product to Europe. They are expecting to stay at maximum capacity for the foreseeable future (over 2,000 Model Ss / month).