The singer admitted that she worked on a song with the producer during a recent visit to London.
"I come to London a lot - I actually made some of the first record out here," she said.
"I love it here - I love the weather, the men and the unpredictability. I even made a track with Calvin Harris that has never seen the light of day."
She added: "It's a great track - I'm sure we'll release it one day!"
The star, who wrote Britney Spears's 'Till The World Ends', also admitted that she hasn't had time to pen songs for other artists, adding: "I've been so focused on the record.
"I also have a picture book coming out which I'm really proud of, a five-song 'Deconstructed' EP of acoustic tracks, a fake fur line and a jewellery line, which includes a teeth range.
"Basically I'm doing a bunch of incredibly fun s**t."
Ke$ha's new album Warrior is out now. Watch the music video for her latest track 'Die Young' below: