Energy storage device

1. An energy storage device, comprising: a supercapacitor first electrode, a supercapacitor second electrode, a first electrolyte, a metal electrode, and a separator; wherein:

the supercapacitor first electrode and the supercapacitor second electrode are parallel to and spaced apart from each other, the supercapacitor first electrode, the supercapacitor second electrode, and the first electrolyte together form a supercapacitor;

the metal electrode and the supercapacitor second electrode form an Ohmic contact, the metal electrode is spaced apart from and opposite to the supercapacitor first electrode to form a first gap, the metal electrode is configured as a negative electrode of a metal-air cell, and the supercapacitor first electrode is configured as a positive electrode of the metal-air cell; and

the separator is sandwiched between the metal electrode and the supercapacitor first electrode, the separator is configured to absorb moisture in a surrounding environment to electrically conduct the metal electrode and the supercapacitor first electrode.

2. The energy storage device of claim 1 , wherein the separator comprises a plurality of hygroscopic particles.

3. The energy storage device of claim 2 , wherein the plurality of hygroscopic particles is anhydrous calcium chloride particles, anhydrous calcium sulfate particles, anhydrous magnesium sulfate particles, anhydrous sodium sulfate particles, or anhydrous potassium carbonate particles.

4. The energy storage device of claim 1 , wherein the separator is prepared by soaking a metal-air battery separator in a solution with a hygroscopic solute; and removing the solution and drying the metal-air battery separator.

5. The energy storage device of claim 1 , wherein the separator is attached to the metal electrode.

6. The energy storage device of claim 1 , wherein the separator is attached to the supercapacitor first electrode.

7. The energy storage device of claim 1 , wherein a conductive adhesive is located between the metal electrode and the supercapacitor second electrode.

8. The energy storage device of claim 7 , wherein the conductive adhesive is silver paste.

9. The energy storage device of claim 1 , wherein a material of the metal electrode is selected from the group consisting of magnesium, aluminum, zinc, and iron.

10. The energy storage device of claim 1 , wherein a thickness of the metal electrode is in a range from about 25 μm to about 100 μm.

11. The energy storage device of claim 1 , wherein the supercapacitor first electrode is a carbon nanotube/polyaniline composite film.

12. The energy storage device of claim 11 , wherein the carbon nanotube/polyaniline composite film comprises a carbon nanotube network structure and a polyaniline layer.

13. The energy storage device of claim 12 , wherein the carbon nanotube network structure is a free-standing film network and comprises a plurality of carbon nanotubes combined by van der Waals attractive force therebetween.

14. The energy storage device of claim 13 , wherein the carbon nanotube network structure comprises a plurality of micropores defined by the plurality of carbon nanotubes.

15. An energy storage device, comprising: a supercapacitor first electrode, a supercapacitor second electrode, a first electrolyte, a metal electrode, and a separator; wherein:

the supercapacitor first electrode, the supercapacitor second electrode, and the first electrolyte together form a supercapacitor;

the metal electrode and the supercapacitor second electrode form an Ohmic contact, the metal electrode is configured as a negative electrode of a metal-air cell, and the supercapacitor first electrode is configured as a positive electrode of the metal-air cell; and

the separator is sandwiched between the metal electrode and the supercapacitor first electrode, the separator is configured to absorb moisture in a surrounding environment to electrically conduct the metal electrode and the supercapacitor first electrode.