Imagine that you would like to design a parallel plate capacitor that could store 1 J of electrical energy in the electric field between its plates when connected to a 1.5 V battery. Imagine that you can arrange things so that the plates can be separated by a distance d as small as 0.5 mm. (Hint argue that the electric field strength between the plates is E approximately equal to V/d, where V is th potental difference between the plates).
You have not mentioned exactly what do you want. But I'm assuming that you want to design the capacitor i.e., want to calculate the size (i.e. area) of parallel plates used.
because, energy stored in a capacitor:
U = (1/2)*C*V^2
V = 1.5 ...
With good explanations and calculations, the problem is solved.