Panasonic has struck a deal with Tesla Motors to jointly build the Gigafactory making automotive-grade battery cells in the United States, reported Nikkei on July 29. The total investment is estimated to reach around US$5 billion, with Panasonic shouldering US$1 billion. The Gigafactory will begin mass production of lithium-ion cells in 2017, and will gradually ramp up its capacity to make enough batteries to power 500,000 electric vehicles a year in 2020.The first phase of construction will begin this fiscal year. Panasonic currently owns a stake in Tesla and manufactures batteries for Tesla cars.