Sunrise ~LOVE is ALL~ lyrics

[music_*]

A question about the lyrics!
Okay, here's the thing. I'm currently studying Japanese and there's this part in the lyrics I don't get.
The unofficial lyrics go:
大きな愛
大きな声
something like that.

So my question is: isn't 大きい an　い-adj?
Why is it paired with な？
It could be just to fit the song, but I wonder if it's something that the Japanese do in real-life; or is it just for Ayu's lyrics?
Something like that~
Could be my mistake since the lyrics aren't official.
And this might even be in the wrong place.