Question

what is the potential difference of capacitor after disconnecting battery and increasing distance between plates?

Answer 1

potential difference between plates is zero

Answer 2

When  battery is disconnected, charge stored (Q) in the capacitor remains constant. 
Increasing distance between plates will decrease capacitance (C).
Potential difference(V)  across plates is given by the relation, V = $\frac{Q}{C}$.

As Q is constant and C is decreasing, potential difference will increase.