Tesla Inc said it would invest more than $3.6 billion to expand its Nevada Gigafactory complex with two new factories, one to mass produce its long-delayed Semi electric truck and the other to make its new 4680 battery cell. The cell plant could make enough batteries for 2 million light-duty vehicles annually, including batteries using the 4680-type cell. The 4680 is key to Tesla’s goal of halving battery costs and ramping up battery production nearly 100-fold by 2030.