The X Factor winner is due to release her third album Glassheart on October 15.
"On my new album I will be rapping. I've discovered my voice for rapping," she told fans in a live stream.
''I could probably go up against Nicki Minaj now. I'm actually that good, so I'm coming for you Nicki!" she joked. "London-style MCing.''
Her new record also includes dubstep and dance tracks, as well as a song called 'Trouble' written by Emeli Sandé.
She previewed 'Come Alive' at the Radio 1 Hackney Weekend in June, telling Digital Spy: "We wanted to do an uptempo song, but for it to remain true to what I do. We added a tiny bit of dubstep and drum and bass and just rocked it."
When asked whether the track is a good indication of the rest of the album, she responded: "It's definitely a piece of it, but there's much more quiet-sounding instrumentals. The album is a good mixture of programmed synths and live music."
Watch the video for Leona Lewis and Avicii's 'Collide' below: