There is some cross-over between EE and Materials Science (for example, nanotechnology). However, my advice is to pursue what interests you and not worry at this time about needing a graduate degree. Getting an engineering degree is difficult enough. It’s easier to stay motivated studying what interests you. The rest will fall into place.
Focus on getting your BS. You do not need the minor. You can take electives in another field if you have the time and space to do so. At this point, you don’t know what you don’t know. You might develop some other interest along the way.
Best of luck at Michigan!