Sales of electric cars accelerated last year but the availability of critical raw materials such as lithium risked slowing the sector’s growth, a report warned Monday. At 6.6 million last year, electric vehicles sales more than doubled and they now account for one in 10 new cars sold, according to the International Energy Agency’s annual report on the sector. China alone accounted for half of those sales. Electric vehicle sales continue to soar, rising by 75 percent in the first quarter of this year compared to the same period last year. Public subsidies to lower the cost to consumers have bee…