Assault and Battery
targets an enemy champion and chases it down, knocking it up for 1.25 seconds, dealing physical damage.
While charging, Vi is immune to crowd control and will knock aside enemies in her way, dealing 75% damage to them.

I was ganking a lee sin while in my ult and he was able to kick me away while charging o.o
is that suppose to happen? or is the ult bugged?

if you were kicked while charging, as in the red line was still there. and you had no control, then yes that would be a bug, or were you kicked right before you started the charge, or as soon as you reached your target? in that case, it could have been lag that made it seem like you were charging but really you just hadnt started or had just finished thus ending your CC immunity

Yep your not suppose to have your ult interrupted.