Is it right to use 'X is a new research topic of interest to our lab' to indicate that the lab has not done research on 'X'?
I have angst about writing this answer. When you say our lab, it potentially sounds like you are speaking for the lab in an official context and taking an ownership stake in the lab. Depending on your role, I am not sure you can talk about the lab as being yours. I am also not sure you cannot, and hence the angst.

As a PI of a lab, I have research interests that the lab has never followed through on due to a variety of reasons including a lack of funding and expertise. I would be a little upset if a student/post doc implied the lab was not interested in a topic just because the lab didn't have the expertise or equipment to do any research on the topic. Similarly, I would be a little upset if a student post doc implied that their personal interest automatically becomes an interest of the lab.