JPS628901B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sealing body for an explosion-proof battery that performs a sealing action under normal conditions, but when the internal pressure of the battery rises abnormally, the sealing body partially ruptures and releases gas generated inside the battery to the outside of the battery. be. Batteries that have a built-in power generating element and whose opening is hermetically sealed using a sealing body made of crystalline engineering plastic, such as alkaline-zinc primary or secondary batteries, constructed using an organic electrolyte. In the case of lithium batteries, etc., if the battery is short-circuited or under abnormal usage conditions such as over-discharging or over-charging, internal gas generation will occur rapidly.
There was a risk that the battery could swell or explode, damaging the equipment used or causing harm to humans. In order to prevent this, as is already known from Japanese Patent Publication No. 37-15358, a thin wall part is formed in a part of the sealing body to prevent gases generated during the storage period. The gas is released by the gas diffusion effect of the sealing body itself, and when excessive gas is generated during abnormal use, the thin wall part ruptures at a pressure lower than the pressure at which the sealing part ruptures, and the gas is scattered from there. It is. However, as a practical matter, the aforementioned sealing body is made of polyethylene,
Since it is made from crystalline engineering plastics such as polyamide and polysulfon using a molding machine, the thickness of the thin part is at least 0.2 ~
If the thickness is less than about 0.3 mm, preferably 0.3 to 0.5 mm, a homogeneous and stable thin film cannot be formed. Therefore, the durable pressure of the thin-walled part will be large, approximately 70 to 80 kg/cm ² or more, and in such cases,
If the sealing strength of the battery is not made greater than the durability pressure of the thin-walled part of the sealing body, the battery will explode during abnormal use, and it is necessary to increase the thickness of the battery constituent materials excluding the sealing body. This inevitably leads to an increase in material costs, and has many problems, including a decrease in battery capacity and the risk of spewing out high-pressure gas in the event of an abnormality, causing damage to equipment. Even if the thickness of the thin part is about 0.2 to 0.3 mm, the present invention can
The purpose of this invention is to improve and modify the sealing body so that the thin wall portion of the sealing body can be destroyed at a relatively low pressure, for example, a pressure of about 20 to 40 kg/cm ² . That is, the purpose is achieved by adding a nucleating agent to a crystalline engineering plastic to increase the degree of crystallinity after molding and make it brittle. Incidentally, the main purpose of such a sealing body is to increase the brittleness of the thin-walled portion, and does not affect the normal battery sealing function in any way. This is achieved by adding a nucleating agent consisting of an alkali metal salt powder of a monobasic carboxylic acid or a dibasic carboxylic acid to the plastic, and this nucleating agent produces extremely fine spherulites when the molten polymer is cooled and solidified. This is because when an impact such as pressure is applied between the crystals of these spherulites, cracks are easily generated and destroyed by the impact, especially in the thin walled portions. DESCRIPTION OF THE PREFERRED EMBODIMENTS A cylindrical alkaline manganese battery shown in the drawings will be described in detail below as an example of the present invention. In the figure,
1 is a cylindrical metal case with a bottom, which is made of stainless steel or iron with anti-corrosion plating such as nickel. Manganese dioxide, which is a positive electrode active material, is cylindrically arranged in contact with the inner bottom and inner wall of the case. , a mixed powder 2 of graphite is press-molded as a conductive aid. Reference numeral 3 denotes a bottomed cylindrical separator inserted into the positive electrode active material 2, and is made of a material such as vinylon or cotton that has the ability to absorb and retain an electrolyte. 4 is zinc chloride powder which is a negative electrode active material,
It is mixed with a mixture of caustic alkaline electrolyte and a thickener such as sodium salt of carboxymethyl cellulose and sodium polyacrylate to form a gel-like mixture. Reference numeral 5 denotes a sealing plate, the peripheral edge of which is fitted into a thick wall portion provided at the peripheral edge of the sealing body 6. The sealing body 6 has a thick part in the center having a hole through which the current collector of the negative electrode passes, and a ring-shaped thin part 7 is connected between the thick part in the center and the peripheral part. . After the battery case 1 is closed with the sealing body 6, the opening 1a of the case 1 is bent inward to tighten the sealing body 6. The sealing plate made of a conductive material such as a metal plate has a current collector 8 integrated into its inner central portion 9 by spot welding. Since the current collector 8 comes into contact with zinc, which is a negative electrode active material, it is made of a material, such as copper, brass, indium, etc., which is oxidized by mercury and increases the hydrogen overvoltage according to electrochemical findings. Note that 5a is a hole through which gas is discharged when the thin wall portion 7 of the sealing body 6 is damaged. Next, a specific method for manufacturing the sealing body of the present invention will be described. The sealing body 6 may be any moldable crystalline engineering plastic, and 1 to 3% by weight of a nucleating agent is added to the crystalline engineering plastic to increase the degree of crystallinity. is obtained by adding a predetermined amount of a nucleating agent to a polymer before or after melting the plastic, and molding the mixture into a predetermined shape using an injection molding machine. Note that if the amount of the nucleating agent is less than 1% by weight, crystallization cannot be sufficiently increased, the physical properties will be close to the initial physical properties of the material, and the thin-walled portion will not be damaged even under the desired pressure. On the other hand, if the amount is more than 3% by weight, the melt viscosity of the material itself increases, resulting in poor flowability and problems in mass production. As the nucleating agent used, alkali metal salts of monobasic carboxylic acids or dibasic carboxylic acids are effective. Benzoic acid and diphenyl acetic acid are effective as monobasic carboxylic acids, and succinic acid, adipic acid, phthalic acid, sebacic acid, etc. are effective as dibasic carboxylic acids. The table below compares the pressure resistance (pressure at breakage) of the sealing body of the present invention and that of a crystalline engineering plastic sealing body to which no nucleating agent is added.
In addition, the thickness of the thin part of the sealing body is 0.2 to 0.3 mm.
The range of This is also an example of experimental results using polyethylene and polypropylene as plastic materials, sodium benzoate as a monobasic carboxylic acid, and sodium phthalate as a dibasic carboxylic acid. There were five samples in each case, and the compressive strength shows the minimum-maximum values. In addition,
To determine the pressure resistance, make a hole in the bottom of the battery case, insert a metal pipe connected to a gas cylinder into the hole, fix the pipe and battery case by welding or soldering, then immerse the battery in water, and then insert the metal pipe connected to the gas cylinder into the hole. If high-pressure gas is sent into the battery from the inside, bubbles will be generated in the water when the thin wall of the sealing body breaks, so this was determined by reading the gas cylinder pressure at this point.

[Table] As is clear from the above table, crystalline engineering plastics containing a nucleating agent will break at relatively low pressures because the impact strength of the material decreases due to the increase in crystallinity. As described above, the safety of the battery using the sealing body according to the present invention can be ensured.

[Brief explanation of the drawing]

The figure is a side sectional view of a cylindrical alkaline manganese battery according to an embodiment of the present invention. 5... Sealing plate, 6... Sealing body, 7... Sealing body 6
Thin wall part provided in the.

Claims (1)

[Scope of Claims] 1. A thick wall portion having a peripheral edge fitted with a sealing plate inside and tightened with a case on the outside, and a hole in the center through which a current collector integrated with the sealing plate is passed. A battery using a crystalline plastic sealing body having thick-walled parts and a thin-walled part connecting the two thick-walled parts, wherein the plastic contains a monobasic carboxylic acid or a dibasic carboxylic acid. A battery characterized in that a small amount of nucleating agent powder made of an alkali metal salt of an acid is added. 2 The amount of nucleating agent added to the plastic is
2. A battery according to claim 1, wherein the amount is 1 to 3% by weight of the plastic. 3. The battery according to claim 1, wherein the thin portion has a wall thickness of 0.2 to 0.3 mm.