The present invention relates to a button type alkaline battery for use in small-sized electronic equipments such as an electronic wristwatch, an electronic desktop calculator or the like.
Recently, a button type alkaline battery is increasingly demanded as small-sized electronic equipments such as an electronic wristwatch, an electronic desktop calculator or the like are developed. Under this condition, in terms of efficiency of the button type alkaline battery, it is demanded for the button type alkaline battery to have longer life-time since such small-sized electronic equipments have lower consumed power, and it is also demanded to supply large current since such small-sized electronic equipments have higher functions.
As shown in FIGS. 1, 2 and 3, the button type alkaline battery has a positive electrode can 1 serving as a positive electrode terminal and a negative electrode cup 3 serving as a negative electrode terminal. After the positive electrode can 1 is filled with a positive electrode mixture 2 and the negative electrode cup 3 is filled with a negative electrode mixture 4 and an alkaline electrolysis solution, the negative electrode cup 3 is held on the positive electrode can 1 through a separator 5 therebetween and a gasket 6 around the negative electrode cup 3. In this state, an opening edge portion of the positive electrode can 1 is bent in the direction toward the negative electrode cup 3 to form the button type alkaline battery.
In an arrangement shown in FIG. 1, the gasket 6 has a projecting portion 9 which is drawn or squeezed perpendicularly and only whose upper edge corner portion is in contact with an inner surface of the negative cup 3. In an arrangement shown in FIG. 2, the projecting portion 9 of the gasket 6 is bent perpendicularly and its upper side surface is in contact with the inner surface of the negative cup 3. In an arrangement shown in FIG. 3, the gasket 6 does not have the projecting portion 9 and is not in contact with the inner surface of the negative cup 3.
In the above process of squeezing the opening edge portion of the positive electrode can 1 of the battery inward, when compression of the gasket 6 is increased by bending the opening edge portion of the positive electrode can 1 further in the radius direction of the battery in order to keep satisfactory resistance to leakage of the electrolysis solution, a compressing force of the gasket 6 toward the negative electrode cup 3 is increased. It is frequently observed that a cuff bottom portion 7a of the negative electrode cup 3 is deformed toward the center of the battery. Since the cuff bottom portion 7a of the negative electrode cup 3 is deformed toward the center of the battery, it becomes impossible to obtain the compression of the gasket 6 required to keep the satisfactory resistance to leakage of the electrolysis solution and the battery's resistance to leakage of the electrolysis solution is lowered.
In the process of bending the opening edge portion of the positive electrode can 1 inward, unless a volume of the negative electrode mixture 4 is set lower than a capacity of the negative electrode cup 3 by an amount of 5 to 15% of the capacity, there is then the disadvantage that a negative-electrode-active material particle is brought between the negative electrode cup 3 and the gasket 6 and the electrolysis solution permeates a portion therebetween to lower the battery's resistance to leakage of the electrolysis solution. On the other hand, if the volume of the negative electrode mixture 4 is reduced relative to the capacity of the negative electrode cup 3, there is then the disadvantage that current characteristics of the battery is lowered.
In order to avoid such disadvantages, some countermeasures are taken, such as providing the projecting portion 9 such that the inner edge surface of the gasket 6 is in contact with the inside of a step portion of the negative electrode cup 3 as shown in FIGS. 1 and 2, forming the negative electrode cup 3 and the gasket 6 integrally, or the like.
In the arrangement shown in FIGS. 1 and 2, if the projecting portion 9 of the gasket 6 is in tight contact with the inner surface of the negative electrode cup 3, then the negative-electrode-active material particle and the electrolysis solution are prevented from permeating the portion between the negative electrode cup 3 and the gasket 6 and hence the battery's resistance to leakage of the electrolysis solution is improved. However, when the projecting portion 9 is in tight contact with the inner surface of the negative electrode cup 3, the projecting portion 9 pushes the negative electrode cup 3 outward to prevent the negative electrode and the positive electrode from being in satisfactory contact with each other. Therefore, the current characteristic of the button type alkaline battery is lowered.
If the projecting portion 9 of the gasket 6 is in loose contact with the inner surface of the negative electrode cup 3, although the current characteristic is not lowered, then efficiency to prevent the negative-electrode-active material particle and the electrolysis solution from permeating the portion between the negative electrode cup 3 and the gasket 6 becomes lowered and hence the battery's resistance to leakage of the electrolysis solution is lowered. Therefore, the contact between the projecting portions 9 of the gasket 6 and the inner surface of the negative electrode cup 3 must be not tight and also not loose. However, it is difficult to design such battery structure.
In the arrangement in which the negative cup 3 and the gasket 6 are formed integrally, when the opening edge portion of the positive electrode can 1 of the button type alkaline battery is bent inward, a force caused by the bend process is applied in the radius direction of tile battery to produce a clearance between the negative electrode cup 3 and the gasket 6 which are formed integrally. Therefore, there is then the disadvantage that the negative-electrode-active material particle and the electrolysis solution permeate the clearance to thereby lower the resistance to leakage of the electrolysis solution.