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Celgard sues Chinese firm over battery technology

Complaint alleges trade secret theft, patent infringement on separator films

by Craig Bettenhausen
March 11, 2020 | A version of this story appeared in Volume 98, Issue 10


A photo of rolls of whitish material.
Credit: Celgard
Celgard accuses a former employee with stealing technology for making membranes used to separate battery electrodes.

Celgard, a North Carolina-based maker of battery separator films, has filed a lawsuit accusing a former employee of stealing trade secrets related to separators and bringing it to a Chinese company. The suit alleges that the employee changed his name in the process to cover his tracks.

The move follows three successful lawsuits in 2018 and 2019 in which Celgard stopped companies in the US and Canada from selling battery separators that it says infringed its patents. They included products made by Shenzhen Senior Technology Material, the main defendant in the current suit.

The new allegations against Senior involve the same patents: Celgard’s US patent 6,692,867 covers polypropylene separators and US patent RE47,520 covers ceramic-coated battery separators.

Celgard says Xiaomin (Steven) Zhang worked at Celgard starting in 2005, earning the highest technical ranks at the firm and its parent company, Polypore, for his work on separators. Asahi Kasei purchased Polypore in 2015 for $2.2 billion. Zhang left in 2016, saying he was taking a job at General Electric, but, the suit alleges, actually going to work for Senior under the name Bin Wang.

The complaint goes on to describe how Senior has brought 20 battery separators to market since 2016, all of which have similar or identical properties to the separators it took Celgard 30 years to develop and on which Zhang worked.

The previous suits sought only to halt sales of the allegedly infringing technology, but this one is more aggressive. Celgard is seeking damages and demanding a jury trial, signs that it is confident in the strength of its case. The complaint, filed in the US District Court for the Western District of North Carolina, depicts a complex conspiracy to undercut Celgard by Senior involving Zhang, shell companies owned by Senior, and distributors.

Intellectual property disputes with Chinese companies have been a major issue in recent years, with both former president Barack Obama and the current administration pushing China’s leaders to protect US IP rights through better policy and enforcement.



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