A button battery, comprising: a metal housing; and a cell arranged in the metal housing; wherein the button battery is characterized in that: a cover plate is arranged on the metal housing; the cell comprises a cathode and an anode; the cover plate and the metal housing have a same polarity; a cap is arranged at and protruded from an outer surface of the cover plate; an insulating member is arranged between the cap and the cover plate, such that the cover plate and the cap are not short-circuited; one of the cathode and the anode is electrically connected to the metal housing, and the other one of the cathode and the anode is electrically connected to the cap; an injection hole is defined on the cover plate and communicated with an inner space of the metal housing; wherein a film is located on the outer surface of the cover plate for sealing the injection hole; a cover bowl is arranged on the outer surface of the cover plate so that the film is between the cover bowl and the cover plate, and an air layer is defined between the cover bowl and the film; when a volume of a gas inside the metal housing is excessively expanded, the gas breaks through the film and the metal housing is communicated with the air layer. a metal housing; and a cell arranged in the metal housing; wherein the button battery is characterized in that: a cover plate is arranged on the metal housing; the cell comprises a cathode and an anode; the cover plate and the metal housing have a same polarity; a cap is arranged at and protruded from an outer surface of the cover plate; an insulating member is arranged between the cap and the cover plate, such that the cover plate and the cap are not short-circuited; one of the cathode and the anode is electrically connected to the metal housing, and the other one of the cathode and the anode is electrically connected to the cap; an injection hole is defined on the cover plate and communicated with an inner space of the metal housing; wherein a film is located on the outer surface of the cover plate for sealing the injection hole; a cover bowl is arranged on the outer surface of the cover plate so that the film is between the cover bowl and the cover plate, and an air layer is defined between the cover bowl and the film; when a volume of a gas inside the metal housing is excessively expanded, the gas breaks through the film and the metal housing is communicated with the air layer. a cover plate is arranged on the metal housing; the cell comprises a cathode and an anode; the cover plate and the metal housing have a same polarity; a cap is arranged at and protruded from an outer surface of the cover plate; an insulating member is arranged between the cap and the cover plate, such that the cover plate and the cap are not short-circuited; one of the cathode and the anode is electrically connected to the metal housing, and the other one of the cathode and the anode is electrically connected to the cap; an injection hole is defined on the cover plate and communicated with an inner space of the metal housing; wherein a film is located on the outer surface of the cover plate for sealing the injection hole; a cover bowl is arranged on the outer surface of the cover plate so that the film is between the cover bowl and the cover plate, and an air layer is defined between the cover bowl and the film; when a volume of a gas inside the metal housing is excessively expanded, the gas breaks through the film and the metal housing is communicated with the air layer.