Early sales of plug-in cars have been disappointing, but automakers are continuing to bet on electricity as the best available technology to curb pollution and reduce foreign oil dependence. LMB Automotive says Americans bought 19,874 plug-in cars in 2011 and predicts the number to rise to about 70,000 in 2012, 170,000 in 2013, and 250,000 by 2015.