Electrochemical cell with flat casing and vent

#The invention relates to an electrochemical cell having a vent aperture in the wall of the outer casing and rupturable membrane covering the vent aperture. The invention relates to a flat cell, which may be an alkaline cell having an anode comprising zinc, a cathode comprising manganese dioxide, and an electrolyte comprising aqueous potassium hydroxide.

#Conventional alkaline batteries (alkaline electrochemical cells) have an anode comprising zinc and a cathode comprising manganese dioxide. The cell is typically formed of an elongated cylindrical outer casing. The fresh cell has an open circuit voltage (EMF) of about 1.5 volt and typical average running voltage of between about 1.0 to 1.2 Volt in medium drain service (100 to 300 milliamp.) The cylindrical casing is initially formed with an enlarged open end and opposing closed end. After the cell contents are supplied, an end cap with insulating plug is inserted into the open end of the casing to form the negative terminal. The cell's open end is closed by crimping the casing edge over an edge of the insulating plug and radially compressing the casing around the insulating plug to provide a tight seal. A portion of the cell casing at the opposing closed end forms the positive terminal.

#Primary alkaline electrochemical cells typically include a zinc anode active material, an alkaline electrolyte, a manganese dioxide cathode active material, and an electrolyte permeable separator film, typically of cellulose or cellulosic and polyvinylalcohol fibers. The anode active material can include for example, zinc particles admixed with conventional gelling agents, such as sodium carboxymethyl cellulose or the sodium salt of an acrylic acid copolymer, and an electrolyte. The gelling agent serves to suspend the zinc particles and to maintain them in contact with one another. Typically, a conductive metal nail inserted into the anode active material serves as the anode current collector, which is electrically connected to the negative terminal end cap. The electrolyte can be an aqueous solution of an alkali metal hydroxide for example, potassium hydroxide, sodium hydroxide or lithium hydroxide. The cathode typically includes particulate manganese dioxide as the electrochemically active material admixed with an electrically conductive additive, typically graphite material, to enhance electrical conductivity. Optionally, small amount of polymeric binders, for example polyethylene binder and other additives, such as titanium-containing compounds can be added to the cathode.

#FIG. 1 is a longitudinal cross section of a first embodiment of the flat alkaline battery of the invention.

#FIG. 1A is an exploded view showing the vent assembly of the embodiment of the flat alkaline battery shown in FIG. 1.

#FIG. 1B is a perspective view of the battery comprising the components shown in FIG. 1.

#An embodiment of the flat alkaline primary battery (alkaline cell) 10 of the invention is shown in FIGS. 1-1B. The alkaline cell 10 (FIGS. 1-1B) has an outer metal casing 89 having an elongated metal body surface with a major portion thereof having a flat polygonal shape. The outer casing 89 may have the overall shape of a polyhedron having flat polygonal surfaces. In a preferred embodiment the finished battery 10 has the overall shape of a cuboid (rectangular parallelepiped). Battery 10, for example, can have an overall size and shape the same or similar to an 7/5F6 size (IEC standard) rechargeable battery. Such battery has the overall cuboid shape shown in FIG. 1B with a length of about 67 mm, width of 17 mm and thickness of 6 mm. In such size and shape the battery 10 of the invention can be used as a replacement for the 7/5F6 size nickel metal hydride rechargeable battery as power source for electronic devices such as the mini disk (MD) player model MZ-900 from Sony Corp. Such replacement service is offered by way of example and is not intended to be limiting. The embodiment of the battery shown in FIGS. 1-1B can be made in larger or smaller sizes.

#The alkaline cell 10 (FIGS. 1 and 1B) has an outer metal casing 89 having an elongated metal body surface with a major portion thereof having at least one flat polygonal shape. The outer casing 89 may have the overall shape of a polyhedron having flat polygonal surfaces. In a specific embodiment shown in FIGS. 1 and 1B, the alkaline cell 10 has the overall shape of a cuboid (rectangular parallelepiped). Cell 10 has an outer metal casing 89 comprising a housing 90 which is sealed with a top cover 15 after the cell contents are supplied. The housing 90 is preferably of nickel plated cold rolled steel or stainless steel. The top cover 15 is preferably tin plated cold rolled steel or stainless steel. The cell contents comprises an anode 40 comprising particulate zinc, a cathode 60 comprising manganese dioxide and a separator 50 therebetween. Any portion of the top cover can function as the cell's negative terminal (−) and any portion of the housing 90 can function as the cell's positive terminal (+).

#The metal housing 90 has a bottom flat surface 92 with a pair of opposing vertical end walls 94a and 94b forming opposing ends of the housing and a pair of vertical side wall 94c and 94d forming the long sides of the housing (FIG. 1B). Housing 90 thus has an elongated top opening 93 (FIG. 1) which is closed with top cover 15. The side walls 94a and 94b (FIG. 1B) are preferably all integral with the bottom surface 92, that is, the housing 90 is an integral piece. The top cover 15 has a flat top surface 16 which extends to downwardly sloping edge 17 terminating in outer peripheral edge 18 (FIG. 1). There is an outer insulating seal 85 circumventing the outer edge 18 of the top cover 15. Preferably outer insulating seal 85 is in the form of a molded plastic ring which is molded to and covers outer edge 18 of top cover 15, or is the form of a separate “stand-alone” molded plastic ring that is placed over outer edge 18 of top cover 15. After the cell contents are inserted into the interior of housing 90, cover 15 is inserted over the top opening 93 of housing 90 and the peripheral edge 96 of housing 90 is crimped over outer insulating seal 85.