JPH1125933A - Sealed nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To assemble a secondary battery having an electrolyte belonged to a hazardous material easily and safely, and lighten the battery. SOLUTION: An exterior can 9 loaded with a plate group and with its opening sealed by a sealing material 8 is formed out of a magnesium alloy. This magnesium alloy, in the case of composition containing 10 wt.% or less of aluminum and 2 wt.% or less of zinc, can be formed by injection molding, and can be sealed safely by ultrasonic welding even in the case of having an electrolyte that belongs to hazardous material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed nonaqueous electrolyte secondary battery, and more particularly to an outer can of a sealed nonaqueous electrolyte lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, a lithium secondary battery using light metal lithium as a negative electrode active material has a high energy density, so that a main power supply of electronic equipment such as a notebook personal computer or communication equipment such as a mobile phone and a PHS. Has been attracting attention. In particular, with the rapid progress of cordless, portable, and lightweight small communication devices such as mobile phones and PHSs, it is also important to reduce the size and weight of lithium secondary batteries used as the main power supply for such devices. It is demanded as an important point.

As an effective means for reducing the weight of a lithium secondary battery, changing the material of the outer can from iron or stainless steel to aluminum increases the effect. The reason is that the ratio of the weight of the outer can to the total weight of the lithium secondary battery is large. Also, when iron is used for the outer can, the outer can needs to be a negative electrode. However, when aluminum is used, the outer can can also be used as a positive electrode.

However, when the material of the outer can is changed from iron to aluminum, there is a problem that the strength is significantly reduced. For example, when changing the outer can made of iron or stainless steel to an aluminum outer can, the tensile strength and longitudinal elastic modulus of aluminum are about 1/3 of that of iron. The strength of the outer can is drastically reduced to 1/3 of the strength of the iron outer can. Incidentally, the tensile strength of iron is 42 kgf / mm ² , the tensile strength of aluminum is 13.5 kgf / mm ² , and the proof strength that determines the force that the deformed outer can restores to its original shape is that of an iron outer can. There 26.6kgf / mm ^2, when the aluminum outer can is 12.5kgf / mm ^2.

[0005] When the strength of the outer can decreases, in the case of a sealed lithium secondary battery, there is a problem that the outer can is deformed when the internal pressure increases. The sealed lithium secondary battery is short-circuited, overcurrent flows, or when a battery abnormality such as overdischarge occurs,
When gas is generated inside and the internal pressure of the battery is increased, and the internal pressure of the battery is increased, the outer can having insufficient strength may be deformed.

[0006] When the outer can is greatly deformed and damaged, it damages a communication device or the like containing a battery as a power supply, and further houses a spiral electrode group in the outer can, and the spiral can is stored in the spiral can. In the case of a sealed lithium secondary battery in which the outermost periphery of the electrode group is in contact with the outer can, when the outer can is deformed, the contact resistance between the electrode and the outer can increases, the internal resistance increases, and the battery capacity increases. However, there is a problem that the number is reduced.

[0007] In order to solve such a problem, a technique of making the outer can have a unique reinforcing structure is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-1987.
No. 93854. This disclosed technology provides a thick portion in a part of an outer can of a sealed battery,
The thick portion reinforces the outer can to reduce deformation. However, when a part of the outer can is made thicker, the outer diameter of the outer can becomes larger, which causes a new problem that the battery cannot be downsized.

[0008] In order to enhance the strength of aluminum, alloys in which magnesium is added to aluminum have been developed. For example, an aluminum alloy containing 2.3% by weight of magnesium and 0.25% by weight of chromium in aluminum has a tensile strength of 29.5 kgf / mm ² and a proof stress of 26.6 kgf / mm ² , which is considerably equivalent to aluminum. Become stronger. However, when an aluminum alloy containing magnesium is used for an outer can, there is a problem that mass production cannot be efficiently performed due to the impact processing, which is easy to perform deep drawing, and for sealing the outer can and the battery. There is also a problem that cracks are easily generated when welding the sealing member, and such an aluminum alloy is excellent in strength, but cannot be used as an outer can of a secondary battery.

The melting point of aluminum is about 600 ° C.
It is possible to mold the outer can by injection molding method like resin, so it is conceivable to increase the thickness of the weak part which is likely to occur in the conventional impact processing and to reinforce it. The rate is 3% at the maximum, and the process of resistance welding to attach the lead plate when manufacturing the secondary battery,
There is also a problem that a post-processing step such as a step of bending an opening for hermetic sealing becomes very complicated.

To solve these problems, 0.5
There has been disclosed a technique using an aluminum alloy containing manganese in an amount of not less than wt% and not more than 2.5 wt% as an outer can (for example, see Japanese Patent Application Laid-Open No. 8-329908).

[0011]

In a conventional lithium secondary battery having an outer can formed of an aluminum alloy containing manganese, when the outer can and the sealing member are welded to each other to seal the battery. Although it can be improved so as not to cause cracks, when the size of the battery is reduced, the mass of the battery and the method of injecting the electrolyte have been regarded as very problematic. In other words, in the case of a secondary battery using lithium as a negative electrode, in the case of a large-sized secondary battery, the equipment used is large and the mass is large, so the mass of the secondary battery in the secondary battery is large. Although this is not a problem, the demand from the main market for portable,
In the case of a small secondary battery used for a small communication device, for example, which is aimed at reducing the weight, its mass is a problem.

A secondary battery using lithium as a negative electrode is as follows:
As an electrolytic solution, a non-aqueous solvent such as ethylene carbonate, propylene carbonate, or 1,2-butylene carbonate in which a salt having an anion is dissolved to obtain electric conductivity, for example, LiPF _{6 having} a concentration of about 1 mol, LiClO ₄ , LiAsF ₆
Is used, but this electrolyte is
Because it is a flammable substance classified as a dangerous goods type 4 by the Fire Service Law,
After the electrolyte is injected in the battery assembling process, there is a problem in safety when the member for sealing the battery is welded by laser. In particular, with the miniaturization of batteries, accurate injection of an electrolytic solution into a battery increases the danger, which has been a major problem in battery manufacturing processes.

According to the present invention, an outer can is formed from an alloy mainly composed of magnesium, so that deep drawing can be performed by impact molding which is an inefficient production method.
It is an object of the present invention to provide a lightweight battery efficiently and to assemble a battery safely even when a flammable electrolyte is used.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an outer can which is loaded with an electrode group and whose opening is sealed with a sealing member, which is made of an alloy mainly composed of magnesium. I have to do that. When a magnesium alloy containing 10 wt% or less of aluminum and 2 wt% or less of zinc is used as an alloy mainly containing magnesium, injection molding becomes possible as in the case of a general synthetic resin.
By attaching a plurality of molds to the injection molding machine, a plurality of outer cans can be efficiently manufactured by one molding, and efficient mass production becomes possible.

Further, a conventional sealing gasket is interposed only between the sealing member for sealing the opening of the outer can and the outer can, with a sealing plate support formed of an alloy mainly composed of magnesium interposed therebetween. Unlike when you let
The dimensional accuracy can be significantly improved. That is, when sealing the battery, since the outer can can be injection molded, the dimensional accuracy of the opening of the outer can in which the sealing plate support is interposed can be within a tolerance range of ± 0.02 mm,
The dimensional accuracy of the sealing plate support is also ± 0.02m by injection molding.
This is because it can be in the range of m. By using the highly accurate outer can and the sealing plate support, it is possible to prevent liquid leakage from the sealing portion when the battery is sealed.

Further, since the outer can and the sealing plate support are formed of an alloy mainly composed of magnesium, ultrasonic sealing can be performed when the battery is sealed, and the fourth type of hazardous material electrolytic solution is used. The safety in assembling a sealed non-aqueous electrolyte secondary battery incorporating a battery is improved.

In addition, by forming the outer can from an alloy mainly composed of magnesium, it is possible to reduce the weight and weight of a small secondary battery, which is strongly demanded in the market.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, an outer can for loading an electrode plate group is formed of an alloy mainly composed of magnesium, and the opening of the outer can is sealed with a sealing member. And since it becomes possible to reduce the weight compared with the conventional sealed non-aqueous electrolyte secondary battery using an outer can made of aluminum or iron, the equipment used as a power source can be downsized.
Applicable for weight reduction.

As an alloy mainly composed of magnesium for forming the outer can, an alloy containing 10% by weight or less of aluminum and 2% by weight or less of zinc is effective.
By using a magnesium alloy having such a composition, injection molding becomes possible, and as a result, mass production with high precision is facilitated.

Further, an outer can having the electrode group loaded therein, and a sealing member for mounting a resin gasket on the periphery of the sealing plate and sealing the opening of the outer can are provided. Between them, a sealing plate support made of an alloy mainly composed of magnesium is interposed. And
Since the dimensional accuracy is improved as compared with the case where the outermost can is brought into contact with the resin gasket on the outermost periphery of the sealing member as in a conventional battery, the structure can be formed into a liquid-tight structure.

It is effective to form the sealing plate support with a magnesium alloy containing 10% by weight or less of aluminum and 2% by weight or less of zinc. And since injection molding becomes possible, mass production becomes easy with high precision. In addition, since magnesium alloy contains aluminum and zinc, it has high extensibility, bending work becomes easy, and opening of the outer can can be performed. By bending the end portion, it can be fastened to the peripheral edge of the sealing member, and the liquid leakage resistance is excellent.

The outer can and the sealing plate support interposed between the outer can and a sealing member for sealing the opening of the outer can are formed of an alloy mainly composed of magnesium. By using an alloy mainly composed of magnesium, a light-weight sealed non-aqueous electrolyte secondary battery can be obtained, and the dimensional accuracy of the sealing portion is increased, so that the leakage resistance is excellent.

When the outer can and the sealing plate support are made of a magnesium alloy containing 10% by weight or less of aluminum and 2% by weight or less of zinc, injection molding becomes possible, dimensional accuracy becomes higher, and liquid leakage resistance becomes higher. improves.

Further, when the outer can and the sealing plate support are formed of an alloy mainly composed of magnesium, the two can be ultrasonically welded to each other, and the sealed nonaqueous electrolyte secondary having excellent leakage resistance can be obtained. A battery is obtained, and safety in the battery assembly process is ensured.

[0025]

FIG. 1, FIG. 2 and FIG.
This will be described with reference to FIG.

A prismatic lithium secondary battery using an outer can molded from a magnesium alloy by the injection molding machine shown in FIG. 3 will be described with reference to FIG. Cap-shaped sealing plate 1 and ring-shaped PT
The C element 2 and the upper valve body 3 are stacked, and the peripheral edge thereof is fastened and integrated by a first gasket ring 4 made of resin. The filter 5 is brought into contact with the lower surface of the integrated member, and the peripheral portions thereof are further integrated by bending the peripheral edge of the lower valve body 6 and tightening the peripheral portion, and the peripheral edge portion is formed of a second gasket ring made of resin. 7 to form a sealing member 8. The positive electrode layer and the negative electrode layer laminated via the separator are spirally wound to form an electrode group, and are housed in the outer can 9. The open end of the outer can 9 is It is sealed by bending it to the part and tightening it. The positive electrode side of the electrode plate group is connected to the sealing plate 1 via the positive electrode lead 10, and the negative electrode side is connected to the outer can 9.

The basic structure of the prismatic lithium secondary battery shown in FIG. 2 is the same as that of FIG. 1, and therefore, the same components are denoted by the same reference numerals and description thereof will be omitted.

Then, a sealing plate support 11 made of a magnesium alloy is fitted to the periphery of the sealing member 8, and a contact portion 12 between the sealing plate support 11 and the outer can 9 is ultrasonically welded. The configuration of welding and sealing is different.

Next, the outer can 9 will be described. Outer can 9
M1 and M2 as magnesium alloys forming
Were prepared. The composition of the alloy M1 is 89% by weight or more of magnesium, 9% by weight of aluminum, and 1% by weight of zinc.
The composition of the alloy M2 is 93 wt% or more of magnesium, 6 wt% of aluminum, and 0.2 wt% of zinc.
The physical properties of the outer cans formed using these materials are as shown in Table 1. As the magnesium alloy, an alloy mainly composed of magnesium containing 10% by weight or less of aluminum and 2% by weight or less of zinc is preferable from the viewpoint of injection molding.

[0030]

[Table 1]

Table 1 also shows, for comparison, the physical properties of an aluminum outer can manufactured by injection molding and an impact-processed iron outer can.

In FIGS. 1 and 2, the positive electrode is
Lithium cobaltate is used as the positive electrode active material, polytetrafluoroethylene is used as the binder, and the thickness of the positive electrode current collector is 1
80-90 μm thick on both sides of 5 μm aluminum foil
And dried to form a long layer. The negative electrode is mainly composed of mesophase carbon in which lithium ions are intercalated, and neoprene rubber is used as a binder. The negative electrode current collector is coated on both sides of a 15 μm thick copper foil to a thickness of 100 to 110 μm. And dried to form a long layer. The separator has a thickness of 25 to 2
Made of polyethylene of 8 μm, pore size 800-1000Å
Microporous membrane was used.

In the lithium secondary battery, the positive electrode layer and the negative electrode layer formed into a long layer as described above are overlapped with a separator interposed therebetween, and the electrode plate group formed by winding several times is formed into an outer can 9. It is configured to be loaded inside. A lead plate is attached to each of the current collectors, and a metal terminal is formed by resistance welding to the outer can 9 and the sealing plate 1 which also serve as electrode terminals in the process of assembling the battery. Here, the negative electrode side is connected to the exterior can 9 made of a magnesium alloy, and the positive electrode side is connected to the sealing plate 1.

The electrolyte was made of ethylene carbonate and ethyl methyl carbonate as base electrolytes.
An electrolyte prepared by dissolving lithium hexafluorophosphate as an electrolyte in a concentration of 1 mol in a base electrolyte solution was used.

Next, a case where an outer can is molded by an injection molding machine shown in FIG. 3 using an alloy mainly composed of magnesium will be described. Chip shaped magnesium alloy M
1 and M2 are respectively charged into the raw material hopper 13 and supplied from the raw material supply device 16 to the cylinder 15 heated to 600 to 700 ° C. by the heater 14. The alloy is
In the cylinder 15, a thixotropic semi-molten state is formed, and the high-speed injection system 17 and the screw 18 inject the resin into the cavity of the mold 20 from the nozzle 19 to be molded. Reference numeral 21 denotes a backflow prevention ring. Such molding is generally called a thixomolding method.

While the density of aluminum is 2.7 g / cm ³ , the density of magnesium alloy is 1.7 to 1.
It is 9 g / cm ³ , about 35% lighter, and has the same tensile strength and resistance as aluminum alloy, making it an excellent outer can.

Example 1 Injection molding was performed using the alloy M1, and the height was 47.5 mm, the width was 29.5 mm, and the thickness was 5.8.
An outer can having a side thickness of 0.4 mm and a bottom thickness of 0.2 mm was produced. Using this outer can, a lithium secondary battery having the configuration shown in FIG. 1 was assembled.

Example 2 Example 1 using alloy M2
A lithium secondary battery having the configuration shown in FIG. 1 was assembled using an outer can that was injection-molded under the same conditions as in the case of (1).

(Example 3) A sealing plate support 11 injection-molded into an L-shaped section using an alloy M1 is positioned at the periphery of the sealing member 8, and the upper end of the sealing plate support 11 is sealed with a sealing member. 8 was bent inward and fitted to the peripheral portion of the sealing member 8, and an outer can which was injection-molded with the alloy M1 under the same conditions as in Example 1 was used. A lithium secondary battery was assembled. The sealing plate support 11 and the outer can 9
Is closed by ultrasonic welding and closed.

(Example 4) In the case of Example 3, except that the alloy M2 was used as the sealing plate support 11,
Assembled in the same configuration.

Comparative Examples 1 and 2 A lithium secondary battery having the structure shown in FIG. 1 was assembled using an aluminum outer can formed by a die casting method as Comparative Example 1, and an impact-processed iron secondary battery was used as Comparative Example 2. The lithium secondary battery having the configuration shown in FIG. 1 was assembled using the outer can.

Each of the lithium secondary batteries described in each of the examples and the comparative examples was assembled into 20 pieces, and the average value of the evaluation results of these batteries is as shown in Table 2.

[0043]

[Table 2]

The evaluation of liquid leakage from the sealed part in Table 2 is as follows.
After assembling the battery, store it at -10 ° C for 6 hours.
The temperature was raised linearly from 0 ° C to 60 ° C over 6 hours,
At 60 ° C. for 6 hours, then from 60 ° C. to −10 ° C. for 6 hours.
The cycle of linear cooling over time was defined as one cycle, and the leakage after 30 cycles was visually inspected. The denominator indicates the number of inspections, and the numerator indicates the number of leaked liquids. From this evaluation result, the lithium secondary battery in the example,
It can be seen that the battery has leakage resistance higher than that of the conventional battery.

From the results of the evaluation of the battery mass, the lithium secondary battery in the example is about 20% lighter than the battery using the conventional iron outer can, and is more lightweight than the battery using the aluminum outer can. It can be about 4% lighter.

Further, by closing the sealed portion between the outer can and the sealing member by ultrasonic welding, the battery can be assembled safely even if a flammable electrolyte is used, and the leakage resistance after storage is significantly reduced. Can be improved.

[0047]

The present invention is embodied in the form described above, and has the following effects.

Since the outer can made of an alloy mainly composed of magnesium is provided, the obtained sealed nonaqueous electrolyte secondary battery has a light weight suitable for miniaturization and weight reduction of the equipment used, and is 10 wt% or less. When a magnesium alloy containing 2% by weight or less of zinc is used, an outer can can be manufactured by injection molding, and mass production can be performed efficiently.

Further, a sealing member in which a resin gasket is attached to the periphery of a sealing plate for sealing the opening of the outer can is used.
By arranging a sealing plate support made of an alloy mainly composed of magnesium on the outer periphery, the dimensional accuracy is remarkably improved, unlike the case of a battery using only a conventional resin gasket, and the battery is sealed when the battery is sealed. The effect of preventing liquid leakage from the sealing portion becomes very large.

Further, the outer can and the sealing plate support formed of an alloy mainly composed of magnesium can be welded to each other by ultrasonic welding, so that the secondary battery containing the fourth type of hazardous substance electrolyte is sealed. The safety in the step of performing can be improved.

[0051] In addition, the strength of magnesium alloy is slightly deteriorated as the content of aluminum and zinc is reduced, but the elongation is increased. Can be reduced in weight as compared with a secondary battery using the same.

Further, it is expected that an era in which used products need to be recycled will surely come in the future. However, magnesium alloys can be regenerated at an energy cost of about 4% of new bullion, and secondary It is promising for battery cans in the future.

[Brief description of the drawings]

FIG. 1 is a cross-sectional side view showing a main part of a sealed nonaqueous electrolyte secondary battery in Examples 1 and 2 of the present invention.

FIG. 2 is a side view showing a cross section of a main part of a sealed nonaqueous electrolyte secondary battery in Examples 3 and 4 of the present invention.

FIG. 3 is a schematic view of an injection molding machine for molding an outer can used in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sealing plate 4, 7 Gasket ring 8 Sealing member 9 Outer can 11 Sealing plate support

Claims (10)

[Claims] 1. A sealed nonaqueous electrolyte secondary battery in which an outer can for loading an electrode plate group is formed of an alloy mainly composed of magnesium, and an opening of the outer can is sealed with a sealing member. 2. The sealed nonaqueous electrolyte secondary battery according to claim 1, wherein the outer can is formed of a magnesium alloy containing 10% by weight or less of aluminum and 2% by weight or less of zinc. 3. The sealed nonaqueous electrolyte secondary battery according to claim 1, wherein the outer can is formed by injection molding. 4. An exterior can loaded with an electrode plate group, and a sealing member for mounting a resin gasket on a peripheral portion of a sealing plate and sealing an opening of the exterior can, wherein the exterior can, the sealing member and A sealed non-aqueous electrolyte secondary battery having a sealing plate support made of an alloy mainly composed of magnesium interposed therebetween. 5. The sealed nonaqueous electrolyte secondary battery according to claim 4, wherein the sealing plate support is formed of a magnesium alloy containing 10% by weight or less of aluminum and 2% by weight or less of zinc. 6. The sealed nonaqueous electrolyte secondary battery according to claim 4, wherein the sealing plate support is formed by injection molding. 7. An exterior can loaded with an electrode plate group, a sealing member for mounting a resin gasket on a peripheral portion of a sealing plate, and sealing an opening of the exterior can, and between the sealing member and the exterior can. A sealed non-aqueous electrolyte secondary battery in which the outer can and the sealing plate support are formed of an alloy mainly composed of magnesium. 8. The sealed nonaqueous electrolyte secondary battery according to claim 7, wherein the outer can and the sealing plate support are formed of a magnesium alloy containing 10% by weight or less of aluminum and 2% by weight or less of zinc. 9. The sealed nonaqueous electrolyte secondary battery according to claim 7, wherein the outer can and the sealing plate support are formed by injection molding. 10. The sealed nonaqueous electrolyte secondary battery according to claim 7, wherein the outer can and the sealing plate support are ultrasonically welded.