Why is lattice energy considered to be potential energy?
Lattice energy is the amount of energy required to break an ionic lattice.
When an ionic compound is formed, it releases energy as indicated by the Born - Haber cycle. Now, lattice energy is released when the gaseous cation and anion come closer and form a lattice. This energy was released to decrease the energy of the system and thus attain a stable state.
Before the ions attracted each other, they had a very high amount of potential energy. When the ions came closer, i.e they did work, the potential energy in them was converted to heat energy and released as lattice energy. So, lattice energy is a type of potential energy.