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 . <EOS>