JPH01241750A - Lithium storage battery - Google Patents

Abstract

PURPOSE:To make it possible to improve the sealing property in the normal condition and to exhaust the gas in the battery securely to the outside in the abnormal condition by forming a thin part less than the area 20mm<2> at a part of a battery container. CONSTITUTION:At a part of a battery container 3, a thin part 4 is provided. As the method of forming the thin part 4, a thickness cutting process in a drilling or the like at the part of the battery container 3, and a thin part forming method with a heat source of laser beams or the like, for example, are available. In this case, the area and the thickness of the part 4 are set adequately depending on the material (the breakdown strength of the material) and the set pressure, but the area is made less than 20mm<2>. As a result, the sealing property in the normal condition is increased, and the gas in the battery can be exhausted out of the battery when the battery inner pressure reaches the preset value in the abnormal condition, that is, the battery inner pressure rises abnormally following the generation of gas in the battery. A trouble of exposing the electrode to the outside and the like can be prevented consequently.

Description

[Detailed Description of the Invention] Example of Fruits and Disasters The present invention reliably discharges gas to the outside to reduce the battery internal pressure when the battery internal pressure rises abnormally due to gas generation due to a chemical reaction within the battery. This invention relates to a highly safe lithium battery equipped with a lowering gas discharge mechanism.

Previously, various mechanisms have been proposed to relieve the abnormal rise in internal gas pressure caused by gas generated from inside sealed batteries.
For example, the resin sealing body of a battery is broken using a sharp gold blade.

Those that use a glass-metal or ceramic fully-flexible seal that cracks due to an increase in internal pressure, those that use a thin film of soft metal such as aluminum, and those that have circular, polygonal, or linear thin grooves. There are some that use rupture, some that use a rubber stopper with an exhaust valve structure, and some that use a gas permeable membrane.

However, these mechanisms are difficult to adopt as a gas discharge mechanism for lithium batteries. In other words, lithium batteries usually use water-prohibitive lithium synthetics, lithium alloys, etc. as the negative electrode, and combustible and flammable non-aqueous solvents are used as the electrolyte, so the battery container is free from oxygen, nitrogen, moisture, etc. It has a sealed structure that prevents impurities from entering inside, and therefore requires a V& structure to reliably exhaust the internal gas to the outside when the battery gas pressure rises abnormally. If a rubber stopper with an exhaust valve structure is used in a lithium battery, the rubber stopper may react with a non-aqueous solvent and swell, impairing the function of the rubber stopper itself.Furthermore, the poor sealing performance may cause impurities to form inside the battery. They are easy to penetrate, which may reduce battery performance. In addition, when considering the use of gas permeable membranes, the gas component generated within lithium batteries is carbon dioxide.

Because it contains low-boiling point organic compounds such as acetylene, ethane, and propylene, it is possible to discharge these gases to the outside through the pores of the permeable membrane. Moisture can enter the battery through the holes, degrading battery characteristics. Also,
In the method of providing a fracture structure using thin grooves, the fracture location is large, the electrode is easily exposed, and there is a risk of ignition and combustion due to contact between the electrode and external air. In addition, donations of aluminum etc.
The method using a thin film cannot be used because these soft metals alloy with lithium and become brittle.

The present invention has been developed in view of the above circumstances, and has a high airtightness under normal conditions, and in an abnormal situation, that is, when the internal pressure of the battery rises due to gas generation within the battery, it is ensured that the internal pressure of the battery reaches the set pressure. It operates to ensure that the gas inside the battery is exhausted to the outside of the battery.

An object of the present invention is to provide a lithium battery equipped with a highly reliable gas discharge mechanism that prevents electrodes from being exposed to the outside during and after operation.

In order to achieve the above object, the inventors of the present invention have conducted intensive studies and found that by forming a thin walled part with a surface area of 20 mm2 or less on a part of the battery container, the airtightness is maintained during normal operation. However, when the internal pressure of the battery rises and reaches a predetermined internal pressure, the thin wall portion is crushed and an exhaust hole is formed that communicates the inside and outside of the battery, and gas is discharged from the exhaust hole to the outside of the battery to reduce the internal pressure of the battery. Moreover, according to this method, the exhaust hole formed by the crushing can be made extremely small, so that the electrode will not be unnecessarily exposed to the outside after the thin wall part is crushed. This discovery led to the present invention.

Accordingly, the present invention provides a lithium battery characterized in that a part of the battery container is provided with a thin part having a breakable area of 20 mm2 or less when the battery internal pressure rises above a predetermined level.

The present invention will be explained in more detail below.

As described above, the lithium battery of the present invention has a thin wall portion provided in a part of the battery container.

In this case, there are no particular restrictions on the material and shape of the battery container;
Those normally used as battery containers for lithium batteries can be suitably used. Specifically, nickel-plated mild steel, stainless steel, etc. are preferably used because they are difficult to alloy with lithium and have excellent corrosion resistance against organic electrolytes, and the shapes are coin-shaped, cylindrical, box-shaped, etc. It can be of various shapes. In this case, the battery container is usually composed of a container body and a lid, but the thin wall portion may be formed on one or both of them.

There are no particular restrictions on the method for forming the thin walled portion, and various methods may be employed.For example, a method of cutting a portion of the battery container into a thinner wall using a drill or the like, or a method of forming the thin wall portion of the battery container using a heat source such as a laser beam. Method of thinning a part, method of forming a thin wall part in a battery container by press working, ff
Examples include a method in which a hole is made in a part of the i-ike container and a thin-walled portion is formed by welding or bonding a thin foil to the hole using an epoxy adhesive or the like. When adopting the method of making a hole in a part of the battery container and welding or gluing a thin foil to the hole, the material of the foil must be one that is difficult to alloy with lithium and has excellent corrosion resistance against organic electrolytes. The material may be the same as or different from the material of the battery container.

The area and thickness of this thin part are appropriately set depending on the material of the thin part (breaking strength of the material) and the set pressure, but one area is 20 mm2 or less, preferably an area of 10-1 to 1
The thickness is about 10-3 to 10-1.

The lithium battery of the present invention has battery components such as a positive electrode, a negative electrode, and an electrolyte housed in a battery container in which the thin wall portion is formed.

Here, 1. As the negative electrode of the lithium battery of the present invention, any material can be used as long as it releases lithium ions during discharge.1 For example, lithium metal, lithium alloy, lithium composite, or carbon material that occludes and releases lithium. etc. can be mentioned.

Here, there is no particular restriction on the type of lithium alloy; for example, lithium and aluminum, magnesium, indium,
An alloy of one or more of mercury, zinc, cadmium, lead, bismuth, tin, antimony, etc. can be suitably used. Among these, it is particularly preferable to use an alloy of aluminum and lithium in terms of negative electrode characteristics and formability.

Note that when a lithium alloy is used, lithium alloying of the metal to be alloyed with lithium can be performed within the battery container.

Next, as the positive electrode, various types can be used as long as they occlude lithium ions or release anions of the electrolyte during discharge. Specifically, organic conductive materials such as polyaniline.

Examples include polyacetylene, poly-p-phenylene, polybenzene, polypyridine, polythiophene, polyfuran, polypyrrole, anthracene, polynaphthalene, etc., and polymers of these derivatives.
n O□+ va o, lMoO3,Cr,○,,
Metal oxides such as CuO, MoS, TiS, FeS,
It is also possible to use metal sulfides such as.

Note that there is no particular restriction on the form of the positive electrode substrate, and it can be used in various forms such as fiber, cloth, nonwoven fabric, film, and plate.

Further, as the electrolyte, a liquid electrolyte or a solid electrolyte is used. The liquid electrolyte consists of a non-aqueous liquid solvent containing lithium ions, and the lithium ion source is:
Although not particularly limited, LiCllO4, LiB F4.
LiP F,, LiS O, CF,.

etc. are preferably used. On the other hand, as the non-aqueous solvent, relatively polar solvents are preferably used, specifically,
Examples include, but are not limited to, one or more mixed organic solvents selected from propylene carbonate, tetrahydrofuran, ethylene carbonate, dimethoxyethane, γ-butyrolactone, dioxolane, butylene carbonate, and dimethylformamide. do not have.

In addition, solid electrolytes that can be used in the battery of the present invention include:
An organic solid electrolyte in which the liquid electrolyte is impregnated with a polymer such as polyethylene oxide, polypropylene oxide, isocyanate crosslinked product of polyethylene oxide, phosphazene polymer having ethylene oxide oligomer in the side chain, Li, N, LiBCfi, Li4S
Examples include inorganic solid electrolytes such as lithium glass such as in, Li, BO3, etc.

Note that when interposing the electrolyte between the positive and negative electrodes, a separator can be interposed between the two electrodes. In this case, the separator is made of a porous material that can pass or contain the electrolyte, such as polytetrafluoroethylene,
Nonwoven fabrics, woven fabrics, porous bodies, nets, etc. made of synthetic resins such as polypropylene and polyethylene can be used.

In the lithium battery of the present invention, the positive and negative electrodes, electrolyte, and if necessary a separator are used as battery elements, and other battery elements used depending on the type of battery are housed in the battery container and sealed. The container can be wrapped with vA Lin film, such as shrink tubing. It is particularly preferable to cover the thin-walled portions, thereby preventing the electrolyte from leaking outside after the thin-walled portions are crushed.

As explained above, the lithium battery of the present invention has a high airtightness under normal conditions, and when there is an abnormality, that is, when the internal pressure of the battery rises due to gas generation within the battery, the internal pressure of the battery is reduced to the set level. The gas inside the battery is reliably discharged to the outside of the battery when the specified pressure is reached, and the electrodes are not exposed to the outside during and after the gas is discharged, making it highly reliable.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

〔Example〕

As shown in Figures 1 and 2, the diameter is 23 un and the height is 43 mm.
A battery container 3 consisting of a bottomed cylindrical container body 1 made of stainless steel with a diameter of 22 mm and a lid body 2 of stainless steel 11 with a wall thickness of 0.3 mm is prepared. Drill a through hole of (area 1.and),
A stainless steel plate with a wall thickness of 0.003 mm is bonded from the bottom surface of the lid body 2 to cover the through hole using an epoxy adhesive.
A thin wall portion 4 was formed.

Next, the length is 180nw11. Width 34m, thickness 200 tones aluminum plate with length 180nw++ and width 30I on both sides
, thickness 200p, length 140mm, medium 30mm, thickness 2
The negative electrode is made by laminating and alloying 00p lithium plates or lithium-aluminum alloy, and the positive electrode is made of polyaniline electrolytically polymerized on stainless steel, with a length of 200 mm.

A polyaniline sheet with a width of 34 mm and a length of 11 mm is packed in a porous polypropylene membrane as a separator, and the positive and negative electrodes are rolled up so that the exposed aluminum part is the outermost part, and this is inserted into the container body 1. did.

Next, a positive terminal part consisting of a positive terminal 6 having a through hole 5 and an insulator 7 is inserted into the through hole 8 of the lid 2, and then spot welded, and the lid 2 is attached to the upper opening of the container body 1. The container body 1 and the lid 2 were sealed by YAG laser welding 9.

Next, the pressure inside the battery container 3 is reduced to 1a+lIg through the through hole 5 provided in the positive electrode terminal 6, and 311101
/Q L x B F4/propylene carbonate/dimethoxyethane 1:1 (volume ratio) W1 solution 5.6mG
I injected the liquid. After leaving it for 2 days and confirming that no hydrogen gas is generated, a hole with a diameter of 0.7 mm and a length of 10 cm is inserted into the through hole 5.
After inserting stainless steel to fill the through hole,
Laser welding was performed to construct a cylindrical lithium secondary battery 10. Note that all of the above preparation operations were performed in an argon gas inert atmosphere. Further, the diameter of the through hole 5 was 0.7 am. When this secondary battery was vacuum dried in a 60°C oven for one week, there was no weight loss at all.

Next, this battery was subjected to an overcharge test in which abnormal gas was generated. The test method was to apply 5V to both electrodes of the battery and measure the total weight of the battery. Furthermore.

Instead of inserting a stainless steel rod into the through hole of the positive terminal, a different diameter joint is used in the positive terminal to
A pressure sensor capable of measuring up to 5 kg/aJ was connected, and changes in internal pressure were measured under the same conditions as the above test. Figure 3 shows changes in battery weight and internal pressure.

From the results shown in Figure 3, there was no weight loss due to gas leakage until the 6th day, the airtightness was maintained, and the internal pressure of the battery was 20%.
When the pressure reached kg/cd, it was confirmed that the thin wall part was definitely crushed and the internal gas was discharged.

(Comparative example) A battery container similar to that of the example was prepared, and the example except that instead of providing the thin wall portion 4, the positive electrode terminal portion 6 was covered with a rubber stopper, which is a Bunsen type exhaust valve commonly used in shielded lead-acid batteries. A cylindrical lithium secondary battery was constructed in the same manner.

Next, the weight change and the internal pressure change when 5V was applied to this battery were measured in the same manner as in the example.

The results are shown in Figure 4.

From the results shown in Figure 4, when using a rubber stopper, O~4
It can be seen that gas leakage occurs even at low internal pressures of kg/ad. Further, when the rubber stopper was observed after 10 days, swelling of the rubber stopper was observed.

From the above examples, the lithium battery of the present invention maintains high airtightness under normal conditions, and gas is generated within the battery.
In the event of an abnormal situation where the internal battery pressure rises, it has been confirmed that this is a highly safe system that reliably exhausts the gas inside the battery to the outside and lowers the battery internal pressure once the battery internal pressure reaches the set pressure. Ta.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the lithium battery of the present invention;
Figure 2 shows the lid constituting the ipsilateral battery, A is a cross-sectional view,
B is a plan view, FIG. 3 is a graph showing changes in battery weight and battery internal pressure in an overcharge test for the same-side battery, and FIG. 4 is a graph showing changes in battery weight and battery internal pressure in an overcharge test for a comparative example battery. It is a graph. DESCRIPTION OF SYMBOLS 1... Container main body, 2... Lid body, 3... Battery container, 4... Thin wall part, 6... Positive electrode terminal, 7...
Insulator, 1o...lithium battery.

Claims (1)

[Claims] 1. A lithium battery characterized in that a thin walled portion having an area of 20 mm^2 or less that can be destroyed when the battery internal pressure rises above a predetermined level is provided in a part of the battery container.