It's Tesla Motors' biggest bet yet: a massive, $5 billion factory in the Nevada desert that could nearly double the world's production of lithium-ion batteries.

Tesla officially opened its Gigafactory on Tuesday, a little more than two years after construction began. The factory is about 14 percent complete, but when it's finished, it will be about 10 million square feet, or about the size of 262 NFL football fields. That will make it one of the largest buildings in the world.

The factory is key to the future of Palo Alto, California-based Tesla. The 13-year-old electric car company, which has never made a full-year profit, wants to transition from a niche maker of luxury vehicles to a full-line maker of affordable cars, pickups and even semi-trucks. It also runs Tesla Powerwall, a solar energy storage business for homes and businesses.