Hi, I wouldn’t use the ionic formula, it’s out of date. I have asked them to update it.
Take a look at this post Customizing the splashscreen / launch image
Also, the link posted by @kai23 is for Cordova 3.1. and there have been changes since then. Here’s a link to the latest docs:
http://cordova.apache.org/docs/en/4.0.0/config_ref_images.md.html#Icons%20and%20Splash%20Screens