The company is currently building its first factory in the US, in Georgia, with a planned investment of 1.2 trillion won (roughly R16.81bn).
The 9.8-GWh factory will serve Volkswagen's EV base in neighbouring Tennessee, with production on track to begin in 2022.
The proposed second plant will have an annual capacity of 11.7GWh of batteries.
SK Innovation, South Korea's biggest oil refiner, has rapidly expanded into EV batteries, with factories in South Korea, China and Hungary.
The company is also currently involved in a legal battle in the US with its South Korean rival LG Chem Ltd. A win for LG Chem could stop SK Innovation importing EV batteries and components.
Researcher Wood Mackenzie this month forecast that global EV sales would drop 43% this year to 1.3 million vehicles because of the coronavirus outbreak, lower oil prices and a wait-and-see approach to buying new models.