China's Tianqi Lithium Corp. has struck a deal to buy a 24% stake in Sociedad Quimica y Minera de Chile (NYSE: SQM), or SQM, for $4.07 billion, the companies involved said on Thursday. Chile's SQM is the world's second-largest producer of lithium, while Tianqi is third or fourth, behind U.S.-based Albemarle and SQM, and either a spot ahead of or behind China's Ganfeng.Demand for lithium has been growing at a rapid clip over the last few years, driven by the increasing popularity of electric vehicles.