Why can Nautilus submarine breathe freely in the sea?

All electric propulsion, all electric system. The main battle weapon is the punching angle. Nautilus is a slender spindle-shaped submarine, 70 meters long and 8 meters wide. It has excellent navigation performance and the highest speed can reach 50 knots. This is an idealized submarine. The ship is completely driven by electricity, which is extracted from seawater and mixed with mercury to form an alloy to replace zinc in bunsen burner battery cells, and then converted into electricity and stored in the battery.

The food is full of fish, seaweed, etc. So the energy and necessities of the crew come from the sea. It doesn't need land supply at all, and it can sail indefinitely at sea. Nautilus has a huge compressed air storage cabinet inside, so it can sneak under the sea for several days without floating on the sea surface. The interior of the ship is spacious and comfortable, and there are even museums and libraries! The weapon of the ship is the steel horn of the bow. Coupled with the high speed and solid shell of the ship itself, the horn is very powerful. In the novel, Nautilus used it to fight back against enemy ships that attacked it. Nautilus crashed into the side of the warship at high speed and its horn penetrated the hull.