What's your tv?
Adoptable storage wasn't introduced until Android 6, so you're kind of out of luck there.
Frankly, you shouldn't be using such an outdated version anyway. Disconnect your TV from your network, get yourself a cheap device like a MiBox S or a Tivo Stream 4k and enjoy a more up-to-date OS.
What antique device do you have that's still running 5.1.1?