JP2000021366A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance safety by preventing an explosion by reducing working pressure at high temperature time when a safety valve is actuated by forming a metallic film such as aluminum, copper, nickel and chromium on one surface or a part of both surfaces of a plastic cover by vacuum evaporation or plating. SOLUTION: When internal pressure of a battery case 20 becomes about an operation value of a safety valve 22, the thin part 23 cleaves to blow off gas so as to prevent an explosion of a battery. Since a plastic cover 21 is covered with a metallic film 24, moisture of an external part can be prevented from infiltrating by passing through plastic. Since a permeation quantity of moisture from the thin part 23 of the safety valve 22 having a thin plate thickness of plastic is particularly large, when this part is covered with the metallic film 24, a moisture permeation preventive effect is remarkable. Since the metallic film is formed in the contact part with a seal member 17 of the plastic cover 21 by vacuum evaporation and plating, the plastic surface part can be smoothed and strengthened to enhance sealing performance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mobile devices such as electric vehicles and electric carts, portable devices such as video cameras and personal computers, backup devices in the event of a power outage, and power storage devices.
This is related to a safety valve that prevents the explosion of a battery can by releasing gas from the battery case when an abnormality occurs in a secondary battery used as a power supply for products such as security equipment, etc., and to prevent electrolyte from leaking from a sealed battery case. is there.

[0002]

2. Description of the Related Art A conventional safety valve of an electrolyte secondary battery is provided with a weak groove by partially cutting or pressing a part of a metal battery container, or a gas discharge hole provided in the battery container by a metal foil. When the internal pressure of the battery rises due to a temperature rise such as a short circuit or overcharge of the battery or the generation of gas, the gas in the battery is released by breaking the weak point groove or the metal thin film, thereby causing an explosion of the battery. Had been prevented. For example, Japanese Patent Application Laid-Open No. 6-140012 discloses a safety valve including a valve hole penetrating the inside of a battery and a valve body that closes the valve hole by an elastic body pressing means. As a comparative example, an aluminum foil having a diameter larger than the valve hole was placed on a valve hole formed in a sealing plate forming a part of a battery container, and the periphery of the aluminum foil was adhered with denatured polypropylene to close the valve hole. Safety valve is introduced.

In Japanese Patent Application Laid-Open No. Hei 6-36752, a pressure relief hole formed in a sealing plate forming a part of a battery container and a groove provided at a position corresponding to the pressure relief hole provide a valve membrane at the bottom. There has been known a safety valve in which a thin film on which is formed is sealed to the sealing plate by laser welding. In the case of a non-aqueous electrolyte secondary battery, when moisture enters the sealed case of the battery, the non-aqueous electrolyte and the moisture react with each other to generate an acid, thereby corroding and deteriorating the inside of the battery. For the case and the lid of the liquid secondary battery, a plastic having no moisture permeability was used and a metal having no moisture permeability was used.

[0004]

However, the above-mentioned Japanese Patent Application Laid-Open No. 6-140012 has a structure in which a valve element is pressed against the valve hole to close the valve hole. There is a problem with sealing. For this reason, measures to prevent electrolyte leakage, such as filling grease between the valve element and the valve hole, have been taken. However, contact by pressing cannot completely prevent electrolyte leakage. When the electrolyte leaks and the electrolyte in the battery runs short, the charging capacity is reduced and the battery life is shortened. In addition, the leaked electrolyte is corrosive and corrodes the battery container and peripheral devices. Occurs.

In a safety valve in which an aluminum foil is bonded to a valve hole with denatured polypropylene, the adhesive has a reduced adhesive strength due to a reaction with an electrolyte solution in a battery or various gases in the atmosphere or a weathering action, and the relationship with the battery life is reduced. There is a problem in maintaining long-term airtightness. Furthermore, plastic materials such as polypropylene are permeable to moisture, and when used for a long period of time, moisture permeates into the battery and deteriorates the electrolyte, and the acid generated by the chemical reaction with the electrolyte corrodes the electrodes inside the battery. And rapidly degrade the battery.

In the above-mentioned Japanese Patent Application Laid-Open No. 6-36752, 50
A groove is formed on a thin film of 〜60 μm by pressing or etching to form a valve film of 20 to 33 μm on the bottom of the groove.
Therefore, it is difficult to accurately form the thickness of the valve film due to variations in pressing and etching processes for forming a thinner valve film from a thin film, and there has been a problem that the operating pressure of the safety valve varies.

Further, since a thin metal thin film is directly laser-welded to a thick sealing plate, which is a part of a battery container requiring strength, the metal thin film having a small heat capacity is first heated to a high temperature. There is a problem that it melts and a hole is formed in a welded portion, and a thin metal film is thinned by welding to form a weld defect.

[0008] The object of the present invention has been made in view of the above-mentioned problems of the prior art.
It is an object of the present invention to provide a secondary battery which has high productivity, is provided with a safety valve which is easy to operate in the event of an abnormality, and has improved battery safety and quality by means of a highly sealed battery lid.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a power generation element composed of an electrode group in which a film-like positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween and an electrolytic solution in a metal battery case. In a secondary battery sealed in a plastic lid via a sealing material such as a gasket or packing, a thin safety valve and an electrode terminal are provided on the plastic lid, and aluminum or copper is provided on one or both sides of the plastic lid. , Nickel, chromium and the like are formed by vacuum evaporation or plating.

According to the present invention, the safety valve element which is ruptured by pressure can be formed by injection molding of a plastic to have a uniform thickness and high productivity and can be formed simultaneously with the lid and the electrode terminal by integral molding. In addition to being inexpensive without the need for such operations, the use of a thermoplastic resin lowers the operating pressure at high temperatures to provide a safer explosion-proof valve.

Further, by covering the plastic surface with a metal film, it is possible to suppress the moisture permeability peculiar to the plastic, to enable an explosion-proof safety valve by plastic molding, and to make the surface of the plastic smooth with the sealing member. By increasing the adhesion, it is possible to suppress the passage of the electrolytic solution and moisture, and to enhance the sealing property with the outside of the battery case.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a secondary battery according to the present invention will be described below with reference to the drawings, taking a lithium ion secondary battery as an example. FIG. 1 is a structural vertical sectional view showing an embodiment of the secondary battery of the present invention, FIG. 2 is a view A viewed from the inside of the lid of FIG. 1, and FIG. It is sectional drawing which shows another Example. In FIG. 1, reference numeral 1 denotes a positive electrode, and a positive electrode mixture 3 (for example, as an active material) using an inorganic lithium intercalation / deintercalation material as a positive electrode active material on both surfaces of a positive electrode current collector 2 made of a strip-shaped aluminum foil. LiMn ₂ O ₄ , LiCoO ₂ , LiNiO
_{2 and the} like, which are prepared by mixing and adjusting carbon as a conductive material and polyvinylidene fluoride as a binder).

Reference numeral 4 denotes a negative electrode, and a negative electrode mixture 6 (for example, as an active material) using a lithium intercalation / deintercalation carbon material as a negative electrode active material on both surfaces of a negative electrode current collector 5 made of a strip-shaped copper foil. A mixture of graphite, amorphous carbon, and polyvinylidene fluoride as a binder)
Is applied and pressed. Reference numeral 7 denotes a separator made of a microporous thin film or a nonwoven fabric of a thermoplastic resin such as polyethylene or polypropylene. When the temperature of the polyethylene film rises, the shutdown start temperature at which the micropores close due to melting of the film itself is about 130 ° C., and the shutdown start temperature of the polypropylene film is about 150 ° C.

That is, when the temperature of the battery rises due to an abnormal condition such as an internal short-circuit or an external short-circuit, the thermoplastic resin of the separator melts to cause microporous or non-woven fabric to be clogged, thereby preventing the movement of ions between the positive and negative electrodes. By shutting off, the current of the battery is shut off, and the battery is protected. The positive electrode 1 and the negative electrode 4 are spirally wound in a state where they face each other with the separator 7 interposed therebetween, thereby forming an electrode group 11. In this case, the separator 7 is wound slightly wider than the positive electrode 1 and the negative electrode 4, and is further wound several times alone at the core portion and at the end of the winding. Has insulation properties. The electrode group 11 is immersed in an electrolytic solution (not shown) to become a power generating element. The electrolyte is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAs
A solution in which a lithium salt such as F ₆ is dissolved as an electrolyte in an organic solvent (alone or a mixture of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and the like) is used.

Reference numeral 20 denotes a metal battery case made of stainless steel, nickel-plated iron, nickel-plated copper, aluminum, or the like. The power generation element including the electrode group 11 and the electrolytic solution is housed in the battery case 20, and is made of plastic. Lid 21
And the battery case opening end is sealed by caulking or curling via a sealing member 17 such as a polyolefin-based plastic gasket or rubber-based packing.

The lid 21 needs heat resistance and electrolytic solution resistance,
Thermosetting phenol or thermoplastic resin polyphenylene sulfide (PPS) is suitable. The plastic lid 21 is provided with a safety valve 22 having a circular hollow, and the bottom of the safety valve 22 is a thin portion 23. When forming the safety valve 22 on the lid, the plastic material is a thermoplastic resin P.
PS is suitable because it can lower the operating pressure at high temperatures.
The operating pressure of the safety valve 22 is 100 ° C.
The temperature is set to be about 10 kg / cm ² at a high temperature of 130 ° C. The positive electrode terminal 14 and the negative electrode terminal 15 pass through the lid 21 and are hermetically sealed by insert molding.

Further, a metal film 24 is coated on one or both sides of the surface of the plastic lid 21 by vacuum deposition or plating of aluminum, copper, nickel, chromium or the like, except for the electrical insulation around the electrode terminals 14 and 15. ing. Vacuum evaporation heats and melts a metal in a vacuum vessel and attaches the metal vapor to the surface of the plastic.In order to increase the adhesion strength of the deposited film, unevenness treatment on the plastic surface is performed before evaporation or coating treatment is performed after evaporation. In some cases.

The metal plating on the plastic surface is performed by an electrolytic plating method or an electroless plating method. As the material of the metal film 24, aluminum, copper, nickel, and chromium which are electrochemically stable to the electrolytic solution are suitable, aluminum having a low melting point is suitable for vacuum deposition, and copper, nickel, chromium or the like is suitable for plating. The composite plating is suitable.

The portion covered with the metal film 24 is intended to prevent at least the moisture / gas permeability of the plastic thin portion 23 of the safety valve 22 and the passage of the lid 21 and the seal member 17 from the contact surface. The contact portion between the surface of the thin portion 23 and the seal member 17 needs to be covered. In the case of vacuum deposition of aluminum, the thickness of the metal film 24 is desirably 200 ° or more in order to keep the moisture permeability of the plastic low, and more preferably 400 ° to 10 °.
A thickness of 00 ° is desirable. In other words, the permeability of water vapor is remarkably reduced from the aluminum deposition film of 200 ° or more.
When the temperature exceeds 00 °, the decrease in transmittance almost completely reaches the saturation state region.

Insulating plates 13a and 13b are provided on the can bottom portion 20a and the lid 21 side of the battery case 20 in order to maintain electrical insulation between the battery charging section and the battery case. The insulating plate is perforated where the safety valve is located so as not to hinder the operation of the safety valve. Reference numeral 8 denotes a positive electrode lead made of a strip-shaped aluminum material.
And a positive electrode terminal 14 of aluminum material by welding or the like. Reference numeral 9 denotes a strip-shaped nickel or copper negative electrode lead, which is connected to the negative electrode current collector 5 of the negative electrode 4 and the nickel or copper negative electrode terminal 15 by welding or the like. In addition, the positive electrode lead 8 and the negative electrode lead 9 become 1
In the book, since current capacity cannot be obtained, it is necessary to connect a plurality of lead wires.

Reference numeral 12 denotes a cylindrical insulating destant;
A separating plate 12a for insulating and separating the positive electrode lead 8 and the negative electrode lead 9 is provided in the cylinder between the electrode group 11 and the lid 21 to secure an independent space for accommodating each electrode lead wire, and the electrode group 11 is provided inside the battery case. And hold it so that it does not move.
Therefore, the plurality of positive electrode leads 8 and negative electrode leads 9 are separated from each other by the separation plate 12a, and the insulation is maintained without contact.

Next, a method of manufacturing the plastic lid 21 of the secondary battery according to the present invention will be described. The lid 21 is formed by injection molding of plastic. In the thin portion 23 of the safety valve 22, the diameter and thickness of the valve portion hole are determined by the diameter and the protrusion size of the circular pin incorporated in the molding die, and the operating pressure is determined. The positive and negative electrode terminals 14 and 15 are set in a molding die, are protruded on both surfaces of the lid 21 by insert molding, are sealed with plastic, and are fixed therethrough. That is, the safety valve 22 and the positive and negative electrode terminals 14 and 15 are manufactured by integral injection molding.

Thereafter, in the case of the vacuum evaporation method, a plastic portion around the positive and negative electrode terminals 14 and 15 of the lid 21 is covered with oil or a film or the like, and a metal such as aluminum is evaporated in a vacuum container. The thickness of the deposited film is controlled by controlling the amount of heat for melting and evaporating the metal and the deposition time. When the vacuum deposition step is completed, the lid 21 without the vacuum-deposited metal film is formed only on the portion of the deposited surface where the oil is applied or the film is peeled off, that is, only around the terminal, and electrical insulation of the terminal can be easily secured.

In the case of plating on plastic, copper,
After metal plating such as nickel and chromium, resist masking is performed by painting, and etching treatment is performed to dissolve and remove unnecessary plating by chemical treatment liquid.
There is a method of applying a conductive coating to a portion to be plated and then performing a plating process to secure an electrically insulating portion. Therefore, a plastic lid having the safety valve 22 and the terminals 14 and 15 can be produced accurately at low cost.

Next, the operation of the secondary battery according to the present invention will be described. If the battery is overcharged beyond the set voltage due to a failure in the charging circuit, it decomposes the electrolytic solution other than the battery reaction as lithium intercalation and generates gas, deteriorating the battery, and reducing the temperature and pressure of the battery. To raise.
Further, when overcharging proceeds or is rapidly charged, lithium metal called dendrite is deposited on the surface of the negative electrode, breaks through the separator 7 which is an insulating material between the electrodes, and causes an accident that a short circuit occurs between the positive electrode and the negative electrode.

The battery also generates heat and becomes abnormally high temperature and high pressure due to use at a high temperature exceeding the normal use temperature range of the battery, external short-circuit due to misuse, and internal short-circuit in the battery due to some cause. When the temperature of the secondary battery increases, the film of the separator 7 between the positive electrode 1 and the negative electrode 4
It melts at ~ 150 ° C and has the function of shutting off the current by the shutdown effect of stopping the movement of lithium ions between the positive and negative electrodes by closing the microporous film.

However, a polyethylene film or a polypropylene film, which is a material of the separator, may melt and shrink due to a further rise in temperature, and may not be able to secure insulation between the positive and negative electrodes, resulting in a short circuit between the electrodes. When the temperature inside the battery exceeds 150 ° C., the positive electrode active material used for the electrode causes a thermal runaway, resulting in a dangerous temperature range where smoke, ignition and explosion occur. In other words, LiM which is a positive electrode active material
Due to the oxygen elimination reaction from the crystal lattice of n ₂ O ₄ , LiCoO ₂ , LiNiO _2, etc., rapid heat generation occurs and a thermal runaway state occurs. The oxygen desorption starting temperature varies depending on the type of active material, the composition ratio of each element, and the state of charge, but is in the range of 150 ° C to 400 ° C. A condition that causes the battery to be in a dangerous state is that a high temperature and a high pressure are simultaneously generated inside the battery case. Under the low temperature condition, the battery does not suddenly become abnormally high pressure such as exploding.

Here, the battery abnormally rises in temperature for some reason, the electrolytic solution in the battery is decomposed to generate gas, or the electrolytic solution and the active material of the positive electrode and the negative electrode cause a chemical reaction to generate gas, and the battery case Consider the case where the pressure inside rises. The internal pressure of the battery case is the operating value of the safety valve 22 10kg / cm
^At around ² , the thin portion 23 of the safety valve is cleaved to release gas out of the battery case to prevent the battery from exploding. Since the safety valve is made of thermoplastic,
The strength at high temperature is softer and weaker than at room temperature (25 ° C.). For example, in the case of polyphenylene sulfide (PPS), the tensile strength at 25 ° C. is 133 MPa.
75MPa at 100 ℃, 67M at 130 ℃
Pa and about half. Therefore, when the operating value at a high temperature (100 ° C. to 130 ° C.) at which the safety valve operates is set to about 10 kg / cm ^2, the operating value of the safety valve at normal temperature is 20
It is around Kg / cm ² , and when the battery is normal, the safety factor against the operating pressure is high and the battery case is securely sealed. In other words, when the battery is used normally, the safety valve is difficult to work, and when the battery is abnormal, the temperature rises.
The safety valve is easy to work and protects the battery from explosion safely.

In addition, since the plastic is permeable to moisture, the lid of the battery case has conventionally been made of metal. moisture
When (H ₂ O) enters the battery case, the lithium salt (LiPF ₆ , LiBF ₄ , L) which is the electrolyte in the non-aqueous electrolyte is used.
iClO ₄ , LiAsF ₆ etc.) to react with hydrofluoric acid (HF)
And acid such as hydrogen chloride (HCl), and corrodes and degrades not only the electrodes but also the metal of the battery case and the plastic of the insulating material. In the present invention, since the surface of the plastic lid is covered with the metal film, it is possible to prevent water vapor in the outside air from permeating the plastic and entering the sealed case from outside the battery case. In particular, since the amount of permeation of moisture from the thin portion 23 of the safety valve 22 having a small thickness of plastic is large,
If this portion is covered with the metal film 24, the effect of preventing moisture permeation is remarkable.

According to the data obtained by measuring the moisture permeability according to the thickness of the aluminum vacuum-deposited film, in the case of a 12 μm polyethylene terephthalate (PET) film, the moisture permeability of the film alone is 40.4 g / m ² · 24 hrs · 40 ° C. 2.3 g / m ² · 24 when coating with a 200Å aluminum film
hrs ・ 40 ℃, 1.4g / m ²・ 400 ℃
The water vapor permeability can be reduced to 24 hrs / 40 ° C.
The formation of the metal film on the surface of the plastic lid has the effect of reducing the moisture permeability on one side inside or outside the lid, but the effect is more perfect when deposited on both sides. When the inside of the lid is covered with a metal film, the electrolytic solution is covered with metal so as not to come into direct contact with the plastic lid, so that there is also an effect of preventing the plastic from being attacked by the electrolytic solution.

That is, it is possible to prevent the electrolytic solution from penetrating into the plastic and swelling, and prevent the plastic from being damaged by the electrolytic solution due to the permeation into the weld line generated during the molding of the plastic. In addition, when the outside of the lid is covered with a metal film, it also has an effect of protecting the plastic from factors that degrade the plastic such as polluting gas in the atmosphere and ultraviolet rays. The data of the light transmittance of the aluminum vacuum deposited film on the plastic film is 4 to 7% when the deposited film thickness is 200 mm and 1% or less when the deposited film thickness is 400 mm, and the effect of blocking the light beam is large.

With respect to the sealing structure between the battery case and the lid, the plastic lid 2 is interposed via an elastic sealing material 17.
1 is sealed in a state where the sealing material is compressed by caulking or curling at the opening of the metal battery case 20. Therefore, it is necessary to have a close contact between the sealing member and the plastic lid and the contact portion between the sealing member and the battery case without any gap. By forming a metal film on the contact portion of the plastic lid with the sealing material by vacuum evaporation or plating, the plastic surface can be smoothed and the plastic surface can be strengthened, and the sealing performance can be improved.

[0033]

As described above, according to the present invention, a power generating element composed of an electrode group and an electrolytic solution in which a film-shaped positive electrode and a negative electrode are opposed via a separator is housed in a metal battery case, and a gasket is provided. In a secondary battery that is sealed with a plastic lid via a sealing material such as plastic or packing, a thin-walled safety valve and electrode terminals are provided on the plastic lid by integral molding, and aluminum is applied to one or both sides of the plastic lid except for the area around the electrode terminals. , Copper, nickel, chromium, etc., were formed by vacuum evaporation or plating. Therefore, despite being a plastic lid, the moisture permeability is kept low, a thin-walled safety valve can be formed by plastic integral molding, and the operating pressure at a high temperature at which the safety valve operates can be reduced, so that the safety of explosion prevention is enhanced. .

Further, since an electrical insulating portion can be formed by masking or etching the portion where the metal film is not desired to be formed, the insulating portion of the terminal insert-molded in plastic can be easily formed, and the production cost can be reduced. Covering the plastic surface with an aluminum vacuum-deposited film not only reduces the permeability of moisture and gas, but also improves the light-shielding properties, enhances the plastic surface, and improves the smoothness, and improves the electrolyte resistance and the tightness of the battery case. Degradation can be prevented, which greatly contributes to the reliability of the secondary battery.

[Brief description of the drawings]

FIG. 1 is a structural sectional view showing one embodiment of a secondary battery of the present invention.

FIG. 2 is a plan view of the lid of FIG.

FIG. 3 is a cross-sectional view showing another embodiment of a structure for sealing a battery case and a lid.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Positive electrode collector, 3 ... Positive electrode mixture, 4 ... Negative electrode,
5 ... negative electrode current collector, 6 ... negative electrode mixture, 7 ... separator, 8 ...
Positive electrode lead, 9 ... negative electrode lead, 11 ... electrode group, 12 ... insulating distant, 12a ... separating plate, 13a, 13b ... insulating plate, 14 ... positive electrode terminal, 15 ... negative electrode terminal, 17 ... sealing member, 20 ... battery case, 20a: bottom of can, 21: lid, 2
2: safety valve, 23: thin portion, 24: metal film.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H011 AA09 AA13 CC02 DD05 DD18 KK01 5H012 AA01 BB02 DD05 EE01 FF01 GG01 5H028 AA01 BB01 CC07 EE06

Claims (5)

[Claims] 1. A secondary battery in which a power generating element comprising an electrode group in which a film-like positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween and an electrolytic solution is housed in a battery case and sealed with a plastic lid. A secondary battery, wherein a metal film is coated on one or both surfaces of a lid by vacuum evaporation or plating. 2. The plastic lid according to claim 1, wherein a thin portion of the safety valve is provided on a part of the lid, and a portion covering the surface of the thin portion is covered with a metal film. Rechargeable battery. 3. The secondary battery according to claim 1, wherein an electrode terminal is provided through the plastic lid, and a portion excluding the periphery of the electrode terminal is covered with a metal film. 4. The secondary battery according to claim 1, wherein the battery case is sealed with a plastic lid via a sealing member such as a gasket or a packing, and a contact portion of the lid with the sealing member is covered with a metal film. battery. 5. The material of the vacuum-deposited metal film is aluminum,
The secondary battery according to any one of claims 1 to 4, wherein a thickness of the secondary battery is 200 ° or more.