Adds more details, background from paragraph 2 onwards

July 7 (Reuters) - Electric-vehicle maker Rivian RIVN.O on Tuesday priced its previously announced offering of 75 million shares at $15.50 per share, aiming to raise around $1.2 billion.

Rivian said it plans to use the proceeds to fund equity contributions as part of a loan agreement with the U.S. Department of Energy.

Shares of Rivian closed around 18% lower at $16.49 on Tuesday.

The offering, announced on Monday, comes as Rivian, known for its high-end R1S SUVs and R1T pickups, ramps up the rollout of its smaller, more affordable R2 SUVs, seen as critical to the company's success.

The company reported strong second-quarter deliveries and raised its annual delivery forecast last week.