Slip and Split rings are basically two different ways of making a connection between a stationary and a rotating object for the current to flow through them.A split-ring commutator makes the current change direction every half-rotation,whereas a slip-ring commutator merely maintains a connection between the moving rotor and the stationary stator.
So,slip rings are useful for DC motors where the current has to change direction every half revolution whereas split rings are used to make constant current connection to a commutator thus useful for AC motors.