WASHINGTON (Reuters) - The U.S. Justice Department said on Friday a Chinese national had been arrested for stealing trade secrets from a U.S.-based petroleum company, his employer, related to a product worth more than $1 billion.

The department alleged Hongjin Tan downloaded hundreds of files related to the manufacture of a “research and development downstream energy market product,” which he planned to use to benefit a company in China that had offered him a job. He was arrested on Thursday in Oklahoma and will next appear in court on Wednesday, the department said.

Tan's LinkedIn page said he has worked as a staff scientist for Phillips 66 PSX.N in Bartlesville, Oklahoma, since May 2017.

Phillips 66 said in a statement it was cooperating with the Federal Bureau of Investigation in a probe involving a “former employee at our Bartlesville location,” but declined to comment further.

An FBI affidavit said Phillips 66 called the agency last week to report the theft of trade secrets and Tan told a former co-worker he was leaving to return to China.

The FBI found on Tan’s laptop an employment agreement from a Chinese company that has developed production lines for lithium ion battery materials.

Tan accessed files for marketing the trade secret “in cell phone and lithium-based battery systems,” the FBI said. Phillips 66 said it has one of two refineries in the world that manufacture the unspecified product.

Tan was responsible for research and development of the U.S. company’s battery program and developing battery technologies using its proprietary processes. Phillips 66 told the FBI it had earned an estimated $1.4 billion to $1.8 billion from the unspecified technology.