German chemicals giant BASF has invested $50 million in Tucson-based Sion Power Corp. to acquire an equity ownership position in the local company, a developer of lithium-sulfur battery technology.

The size of BASF's stake in privately-held Sion was not disclosed in today's announcement, and company officials were not immediately available for comment.

"The progress of the technical collaboration between Sion Power and BASF for more than two years now has led BASF to take a significant financial stake in Sion," Sion CEO Dennis Mangino said in a news release.

The equity partnership expands upon an existing joint development agreement that BASF Future Business GmbH, established with Sion Power in 2009 to accelerate the commercialization of Sion's proprietary lithium-sulfur battery technology for electric vehicles and other high-energy applications.

Sion has more than 100 U.S. and international patents on its lithium-sulfur technology, which offers lighter weight and higher energy capacity than other technologies. The company was founded as Moltech Corp. in 1994.

The partnership will allow the companies to deliver leading-edge lithium-sulfur technologies to the battery market in the years ahead, said Andreas Kreimeyer, BASF board member and research executive director.