The 'We Belong Together' singer took to Twitter on Thursday (September 27) to share a photo of the pair behind the mic in a recording studio.
"Me and Kells in the lab in Chi town working on a new song!" she posted. "OMG-his voice sounds A++"
She also praised the R&B singer's Trapped in the Closet series of narrative songs and music videos, referring to them as a "total classic".
Carey is currently working on her 14th studio album while filming the new series of American Idol. In August, she told members of the press that she was "collaborating with a lot of [her] favourite people" on forthcoming tracks.
"The main thing is [that] I'm not trying to follow any particular trend," she said. "I want it to be well received. I want to stay true to myself and the music that I love and make the fans happy."
Carey recently revealed that she expects the LP to be ready for release early next year.
"I want to go sooner, but I guess it wouldn't be ready until around January, somewhere around there," Carey told On Air with Ryan Seacrest.
"I wanted to put another single out, a ballad. I love it, but I'm still writing, I'm still working. So, you never know what it's going to end up being."
Watch the video for Mariah Carey's latest single 'Triumphant (Get 'Em)' below: