JPH0982361A - Square nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a square nonaqueous electrolyte secondary battery by which an internal short circuit is hardly caused and whose battery capacity is comparatively large. SOLUTION: An electrode layered body by successively layering a rectangular positive electrode 7 where a positive electrode active material 7b is applied to a positive electrode current collecting body 7a and a rectangular negative electrode 5 where a negative electrode active material 5b is applied to a negative electrode current collecting body 5a through a separator 6, is housed in a square battery vessel 10. Corner parts 7c, 7d and 5c, 5d on the inserting side of these rectangular positive electrode 7 and negative electrode 5 to at least this square battery vessel 10, are formed in a circular arc shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectangular non-aqueous electrolyte solution suitable for use as a power source for portable electronic equipment such as a VTR with a built-in camera, a portable CD player, a laptop computer and a cellular telephone. Regarding the next battery.

[0002]

2. Description of the Related Art In recent years, advances in electronic technology have led to advances in performance, miniaturization, and portability of electronic equipment, and the demand for high energy density batteries used in such portable electronic equipment is increasing. Conventionally, secondary batteries used in this portable electronic device include nickel-cadmium batteries and lead batteries, but these batteries have a low discharge potential and sufficiently meet the demand for batteries with high energy density. The reality is that they are not.

[0003] Recently, lithium secondary batteries have attracted attention as a battery system that meets these requirements, and are being actively studied. However, lithium secondary batteries using lithium metal or lithium alloy as a negative electrode have come to recognize problems such as cycle life, safety, and quick charging performance, which are major obstacles to practical use.

It is considered that these problems are caused by dissolution of metallic lithium as a negative electrode, generation of dendrites at the time of precipitation, and miniaturization, and they are only partially used in a coin type.

In order to solve these problems, research and development of a lithium ion secondary battery (non-aqueous electrolyte secondary battery) using as a negative electrode active material a substance capable of doping and dedoping lithium ions such as a carbon material. Is being actively conducted. Since lithium is not present in a metallic state in this lithium-ion secondary battery, there is no problem regarding cycle deterioration or safety due to the metallic lithium negative electrode, and by using a lithium compound having a high redox potential as the positive electrode active material, Since the voltage is high, it has the feature of high energy density.

Furthermore, this lithium-ion secondary battery has less self-discharge than the nickel-cadmium battery,
It is a very good secondary battery.

Conventionally, as an example of this lithium ion secondary battery, a prismatic lithium ion secondary battery as shown in FIGS. 5 and 6 has been proposed. In this conventional example, a strip-shaped negative electrode 5, strip-shaped separator 6, strip-shaped positive electrode 7, strip-shaped separator 6 ... Strip-shaped negative electrode 5 and a predetermined number of electrode laminates are sequentially stacked. Made of, for example, a nickel-plated iron plate, for example, having a thickness of 8 mm and a width of 34 m
The prismatic battery container 10 has a height of m and a height of 48 mm.

The positive electrode 7 was prepared as follows. As the positive electrode active material of the positive electrode 7, lithium carbonate and cobalt oxide are mixed so that Li: Co = 1: 1,
Li obtained by firing at 900 ° C. for 5 hours in air
CoO ₂ is used. As a result of X-ray diffraction measurement of this material LiCoO ₂ , it was in good agreement with the JCPDS card.

After that, it is pulverized to have a desired particle size.
LiCoO₂And obtain this LiCoO ₂As the positive electrode active material
And this LiCoO₂91% by weight, as a conductive material
6% by weight of phyto and 3% by weight of polyvinylidene fluoride
A positive electrode mixture is prepared by mixing, and this is mixed with N-methyl-2-pi
Disperse it in loridone to make a slurry.
Of the positive electrode mixture 7b having a thickness of 20 μm, which is the positive electrode current collector 7a.
Apply to both sides of aluminum foil, dry, and then roll
It was compression-molded with a machine.

After that, as shown in FIG. 6, by cutting, the uncoated portion of the positive electrode mixture 7b of the positive electrode current collector 7a is used as a lead portion,
The strip-shaped positive electrode 7 extended to this lead portion was formed.

The negative electrode 5 was prepared as follows.
As the negative electrode active material of the negative electrode 5, petroleum pitch was used as a starting material, and a functional group containing oxygen was added in an amount of 10 to 20%.
A non-graphitizable carbon material having properties close to those of a glassy carbon material obtained by introducing (oxygen crosslinking) and firing at 1000 ° C. in an inert gas was used.

90% by weight of the carbon material thus obtained and 10% by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, and this negative electrode mixture was mixed with N--
Disperse in methyl-2-pyrrolidone to form a slurry,
This slurry-like negative electrode mixture 5b was applied to both surfaces of a negative electrode current collector 5a of a copper foil having a thickness of 10 μm, dried, and then compression molded with a roller press.

Then, as shown in FIG. 6, after cutting, the uncoated portion of the negative electrode mixture 5b of the negative electrode current collector 5a is used as a lead portion, and the strip-shaped negative electrode 5 extended to this lead portion is formed. did.

The strip-shaped negative electrode 5 and positive electrode 7 prepared as described above are laminated with a separator 6 made of a microporous polypropylene film having a thickness of 30 μm interposed therebetween to prepare an electrode laminated body, and this electrode laminated body is formed. Metal pressing plates 8 are arranged on both sides of the body, and an adhesive tape 9 is wound around the pressing plates 8 so as to be integrated.

The electrode laminated body integrated by the adhesive tape 9 is housed in the prismatic battery container 10 together with the electrode pressing member 12 made of a spring material. In this case, the insulating sheet 11 is arranged at the bottom of the battery container 10.

Further, the lead portions 4 of the positive electrode 7 are connected to each other, and the lead portions 4 are fixed to the center of the lid 1 of the battery container 10 via the aluminum sub lead 14 and the gasket 2 to fix the positive terminal 3. Connect to.

Further, the lead portions of the negative electrode 5 are connected to each other, and the connection point of the lead portions is connected to the battery container 10 via the copper lead 13, and this battery container 10 serves as a negative electrode terminal.

An electrolytic solution is injected into the battery container 10. As this electrolytic solution, LiPF ₆ was dissolved in an organic solvent in which propylene carbonate and diethyl carbonate were mixed at a ratio of 5: 5 at a ratio of 1 mol / l.

The average battery capacity of 30 of such prismatic lithium ion secondary batteries of the conventional example was 732 mAh.

[0020]

In the conventional prismatic lithium-ion secondary battery, an electrode laminate is formed by laminating strip-shaped electrodes like the nickel-cadmium battery and the nickel-hydrogen battery. . However, the conductivity of the electrolyte of this lithium-ion secondary battery (non-aqueous electrolyte secondary battery) is 1 compared with the conductivity of the electrolyte of an aqueous battery.
Since it is as small as about / 40, it is necessary to reduce the thickness of the positive and negative electrodes 7 and 5 and increase the number of electrodes.

As a result, the positive electrode 7 and the negative electrode 5
And the strip-shaped positive electrode 7 is inserted into the prismatic battery container 10 when the strip-shaped positive electrode 7 and the negative electrode 5 are stacked. Also, the corners of the negative electrode 5 come into contact with the prismatic battery container 10, and the positive electrode and the negative electrode active material may fall off, or the electrodes may be bent, which increases the defective rate of internal short circuit of the battery and improves productivity. There was an inconvenience that it was low.

By the way, the prismatic lithium ion secondary battery of the above-mentioned conventional example is used in a charging voltage of 4.20 V, a charging current of 800 mA,
Charging was performed under the condition of charging time of 2.5 hours, the occurrence rate of internal short circuit was investigated, and discharging was performed at a constant current of 400 mA and a cutoff of 2.75 V.
The number of internal short-circuits after left for 0 days was 11/30, about 37% of the batteries had internal short-circuits, and the average battery capacity of these 30 batteries was 732 mAh, due to the dropout of the positive and negative electrode active materials. It was low.

In view of the above problems, an object of the present invention is to obtain a prismatic non-aqueous electrolyte secondary battery which has few internal short circuits, is highly productive, and has a relatively large battery capacity.

[0024]

Means for Solving the Problems In a prismatic non-aqueous electrolyte secondary battery of the present invention, a positive electrode current collector is coated with a positive electrode active material, and a rectangular positive electrode and a negative electrode current collector are coated with a negative electrode active material. In a rectangular non-aqueous electrolyte secondary battery in which a rectangular negative electrode and an electrode laminate sequentially laminated via a separator are housed in a rectangular battery container, at least this rectangular positive electrode and negative electrode The corner portion on the insertion side into the prismatic battery container has an arc shape.

According to the present invention, since the corners of the rectangular positive and negative electrodes on the side of insertion into the prismatic battery container are arcuate, the positive and negative electrode active materials are formed by the contact between the positive and negative electrodes and the rectangular battery container. Is suppressed, and the bending of the positive electrode and the negative electrode is suppressed, whereby internal short circuit of the battery is eliminated, and the battery capacity is maintained relatively large.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the prismatic non-aqueous electrolyte secondary battery of the present invention will be described below with reference to the drawings.

As shown in FIG. 5, the prismatic lithium-ion secondary battery according to this example also has a strip-shaped negative electrode 5, strip-shaped separator 6, strip-shaped positive electrode 7, strip-shaped separator 6,
The strip-shaped negative electrode 5 and a predetermined number of stacked electrode laminates are housed in a rectangular battery container 10 made of, for example, a nickel-plated iron plate having a thickness of 8 mm, a width of 34 mm, and a height of 48 mm. I will do it.

The positive electrode 7 was prepared as follows. As the positive electrode active material of the positive electrode 7, LiCoO ₂ obtained by mixing a predetermined amount of lithium carbonate and cobalt oxide so that Li: Co = 1: 1 and calcining this in air at 900 ° C. for 5 hours. To use. As a result of X-ray diffraction measurement of this material LiCoO ₂ , it was in good agreement with the JCPDS card.

Then, it is pulverized to have a desired particle size.
LiCoO₂And obtain this LiCoO ₂As the positive electrode active material
And this LiCoO₂91% by weight, as a conductive material
6% by weight of phyto and 3% by weight of polyvinylidene fluoride
A positive electrode mixture is prepared by mixing, and this is mixed with N-methyl-2-pi
Disperse it in loridone to make a slurry.
Of the positive electrode mixture 7b having a thickness of 20 μm, which is the positive electrode current collector 7a.
Apply to both sides of aluminum foil, dry, and then roll
It was compression-molded with a machine.

After that, it is cut, and as shown in FIG. 1, the uncoated portion of the positive electrode mixture 7b of the positive electrode current collector 7a is used as a lead portion, and a strip-shaped positive electrode 7 extending to this lead portion is formed.

In this example, the strip-shaped positive electrode 7 is used.
The corners 7c and 7d on the side of the insertion into the prismatic battery container 10 (arrow a indicates this insertion direction) are arcuate.
In this case, as shown in FIG. 4, the corner portions 7c, 7d
The radius R of the circular arc is set to, for example, 0.5 mm.

Further, as the positive electrode active material of the positive electrode 7, LiNiO ₂ , LiNi _y C may be used in addition to LiCoO _2.
Lithium composite oxides such as o-yO ₂ and LiMn ₂ O ₄ are preferable. The lithium composite oxide is, for example, lithium,
It is possible to use cobalt, nickel, manganese carbonates, nitrates, oxides, hydroxides, etc. as starting materials. The lithium composite oxides are mixed according to the composition, and the mixture is heated at 600 ° C. in an oxygen atmosphere. It is obtained by firing in a temperature range of up to 1000 ° C.

The negative electrode 5 was prepared as follows.
As the negative electrode active material of the negative electrode 5, petroleum pitch was used as a starting material, and a functional group containing oxygen was added in an amount of 10 to 20%.
A non-graphitizable carbon material having properties close to those of a glassy carbon material obtained by introducing (oxidative crosslinking) and then firing at 1000 ° C. in an inert gas was used.

90% by weight of the carbon material thus obtained and 10% by weight of polyvinylidene fluoride as a binder
To prepare a negative electrode mixture, and mix this negative electrode mixture with N
-Methyl-2-pyrrolidone is dispersed to form a slurry, and the slurry-like negative electrode mixture 5b is applied to both surfaces of a negative electrode current collector 5a of a copper foil having a thickness of 10 μm, dried, and then compressed with a roller press. Molded.

Then, as shown in FIG. 1, after cutting, the uncoated part of the negative electrode mixture 5b of the negative electrode current collector 5a is used as a lead part, and the strip-shaped negative electrode 5 extended to this lead part is formed.

In this example, the strip-shaped negative electrode 5 is used.
The corners 5c and 5d on the insertion side of the prismatic battery container 10 (arrow a indicates this insertion direction) are arcuate.
In this case, as shown in FIG. 4, the corner portions 5c, 5d
The radius R of the circular arc is set to, for example, 0.5 mm.

As the negative electrode active material used for the negative electrode 5, a carbon material capable of doping and dedoping lithium with charge / discharge reaction can be used. The negative electrode active material is doped with lithium and dedoped. Any material that can be doped may be used, such as a low crystalline carbon material obtained by firing at a relatively low temperature of 2000 ° C. or lower, artificial graphite obtained by treating a raw material that is easily crystallized at a high temperature of around 3000 ° C., and natural graphite. Highly crystalline materials such as

For example, pyrolytic carbons, cokes (pitch cokes, needle cokes, petroleum cokes, etc.), graphites, glassy carbons, organic polymer compound calcined products (furan resin, etc. are calcined at an appropriate temperature to carbonize. Used), carbon fiber, activated carbon, etc. can be used.

In this case, the carbon material is (002)
The surface spacing is 0.370 nm or more, the true specific gravity is less than 1.70, and the value is 700 in the differential thermal analysis in the air flow.
The true specific gravity is 2.10 g / in order to obtain a low crystalline carbon material having no exothermic peak above ℃ and a high negative electrode mixture filling property.
It is preferable to use a highly crystalline graphite material having a cm ³ or more.

Further, not only the low crystalline carbon material and the high crystalline graphite material can be used alone, but also a coexisting body of the graphite material and the carbonaceous material having low crystallinity can be used. The proportion of low crystalline carbon in the coexisting body is limited to 10% to 90%, and 20% to 80% based on the total weight of the negative electrode carbon coexisting body.
Is more preferable.

The strip-shaped negative electrode 5 and positive electrode 7 produced as described above are laminated with the separator 6 made of a microporous polypropylene film having a thickness of 30 μm interposed therebetween to produce an electrode laminate. In this case, the lead portions of the negative electrode 5 and the positive electrode 7 are located on the upper side and the opposite sides.

As shown in FIG. 5, a holding plate 8 made of, for example, a stainless steel plate is arranged on both sides of the electrode laminated body, and an adhesive tape 9 is wound around the holding plate 8 so as to be integrated. As shown in FIG. 5, the electrode laminated body integrated with the adhesive tape 9 is housed in a prismatic battery container 10 together with an electrode pressing member 12 made of a spring material. in this case,
The insulating sheet 11 is arranged on the bottom of the battery container 10.

As shown in FIG. 5, the lead portions 4 of the positive electrode 7 are connected to each other, and the lead portions 4 are connected via the sub-leads 14 made of aluminum to the lid of the battery case 10 made of, for example, a nickel-plated iron plate. It is connected to the positive electrode terminal 3 fixed in the center of 1 through a gasket 2 for sealing and insulation.

Further, the lead parts of the negative electrode 5 are connected to each other, and the connection point of the lead parts is connected via the copper lead 13.
It is connected to the battery container 10, and this battery container 10 is used as a negative electrode terminal.

An electrolytic solution is injected into the battery container 10. In this example, as this electrolyte, LiPF ₆ was dissolved in an organic solvent in which propylene carbonate and diethyl carbonate were mixed at a ratio of 5: 5 at a ratio of 1 mol / l.

In this case, as the electrolytic solution, an electrolytic solution in which a lithium salt is used as a supporting electrolyte and this is dissolved in an organic solvent is used. Here, as the organic solvent, a mixed solvent of cyclic carbonic acid esters and chain carbonic acid esters is used.

As the cyclic carbonic acid esters, propylene carbonate, butylene carbonate and the like can be used. As the chain carbonic acid ester, symmetric carbonic acid ester such as dimethyl carbonate, diethyl carbonate and dipropyl carbonate, and asymmetrical carbonic acid ester such as methyl ethyl carbonate, methyl propyl carbonate and ethyl propyl carbonate can be used. Is.

As the supporting electrolyte, LiCl, LiBr and LiCF ₃ which are generally used for lithium batteries are used.
SO ₃ , LiAsF ₆ , LiPF ₆ , LiBF _4, etc. can be used alone or in combination of two or more kinds.

The non-aqueous electrolyte is not limited to a liquid state, and may be a solid, and a conventionally known fixed electrolyte can be used.

According to this example, since the corner portions 7c, 7d and 5c, 5d on the insertion side of the strip-shaped positive and negative electrodes 7 and 5 into the prismatic battery container 10 are arcuate, the positive and negative electrodes are formed. The positive electrode and the negative electrode active material are prevented from falling off due to the contact between 7 and 5 and the prismatic battery container 10, and the bending of the positive electrode and the negative electrode 7 and 5 is suppressed, thereby eliminating the internal short circuit of the battery and comparing the battery capacities. Is maintained as large as possible.

Incidentally, the above embodiment is referred to as Embodiment 1, and the prismatic battery container 10 of the positive and negative electrodes 7 and 5 of the above embodiment is used.
The radius R of the circular arcs of the corners 7c, 7d and 5c, 5d on the insertion side into is set to 0.01 mm, and the others are configured in the same manner as in the above-described embodiment to form a prismatic lithium-ion secondary battery as Embodiment 2, and Corner portions 7c, 7 on the side of insertion of the positive and negative electrodes 7 and 5 of the above embodiment into the prismatic battery container 10.
The radius R of each arc of d, 5c, and 5d is 1 mm,
A prismatic lithium-ion secondary battery having the other configurations similar to those of the above-described embodiment is referred to as Embodiment 3, and further, corner portions 7c, 7d on the insertion side of the positive and negative electrodes 7 and 5 of the above-described embodiment into the prismatic battery container 10 and Radius R of arcs of 5c and 5d
Is 1.5 mm, and the others are configured in the same manner as in the above-described embodiment, which is referred to as Embodiment 4, and the corner portions 7c and 7d on the insertion side of the positive and negative electrodes 7 and 5 of the above-described embodiment into the prismatic battery container 10. And the radius R of each arc of 5c and 5d is 2
mm, and a rectangular lithium ion secondary battery having the same configuration as in the above-described example was used as a comparative example.

The prismatic lithium ion secondary battery thus manufactured was charged with a charging voltage of 4.20 V and a charging current of 800 m.
A, charge under the condition of charging time 2.5 hours, then investigate the rate of occurrence of internal short circuit, discharge at 400mA constant current, cut-off 2.75V, and then perform normal temperature (23 ° C)
The number of internal short-circuits after standing for 30 days was as shown in Table 1.

In Table 1, the conventional example is the positive electrode 7 and the negative electrode 7.
The corners on the insertion side of the rectangular battery container 10 of Nos. 5 and 5 are not arcuate, and the radius R of the arc is 0, and the battery capacities in Table 1 are average battery capacities of 30 batteries, respectively. is there.

[0054]

[Table 1]

From Table 1, when the radius R of the conventional example is set to 0, as described above, when the positive and negative electrodes 7 and 5 are inserted into the prismatic battery container 10, the corner portions of the electrodes 7 and 5 are located in the battery container 10. When the positive electrode and the negative electrode active material fell off and the electrodes 7 and 5 were bent, an internal short circuit was likely to occur, and 11 out of 30 had an internal short circuit, and the battery capacity was low.

On the other hand, the corner portions 7c, 7d and 5
c and 5d have an arc shape, and the radius R is 0.5 mm,
In Examples 1, 2, 3, 4 and Comparative Examples with 0.01 mm, 1 mm, 1.5 mm and 2 mm, no internal short circuit occurred in 30 regardless of the size of the radius R, and an internal short circuit occurred. The rate was 0%.

However, in the comparative example in which the radius R was 2 mm, the average battery capacity was as low as 728 mAh. This is because the positive and negative electrodes 7 and 5 are formed by the arc shape.
It is considered that the capacity decreases due to the decrease in the amount of the positive electrode and negative electrode active materials that can be input due to the decrease in the area.

On the other hand, the radius R is 0.5 mm,
Example 1 with 0.01 mm, 1 mm and 1.5 mm
The batteries 2, 3, and 4 having a relatively large battery capacity of 800 mAh or more were obtained.

In Examples 1, 2, 3 and 4 described above,
When the positive and negative electrodes 7 and 5 are inserted into the prismatic battery container 10, since the corners 7c, 7d and 5c, 5d are arcuate, the positive and negative electrodes 7 and 7 are formed.
And 5 and the prismatic battery container 10 are less in contact with each other, the positive electrode and the negative electrode active material are prevented from falling off, the bending of the positive electrode and the negative electrode 7 and 5 is suppressed, and the internal short circuit of the battery is eliminated. Radius R = 0.01m
In the range of m to 1.5 mm, the decrease in the areas of the positive and negative electrodes 7 and 5 is small, and it is considered that the decrease in the battery capacity is not so affected.

In the above-mentioned embodiment, the corner portions 7c of the positive electrode 7 and the negative electrode 5 on the side of insertion into the prismatic battery container 10,
Although 7d, 5c, and 5d have an arc shape, the corner portion 7e (5e) other than the lead portion may have an arc shape as shown in FIG. 2, and as shown in FIG. When the lead portion of the negative electrode 5 is formed on the center side, the four corner portions 7c of each of the equal electrodes 7 and 5,
Each of 7d, 7e, 7f and 5c, 5d, 5e, 5f may have an arc shape.

It can be easily understood that the same effects as those of the above-mentioned embodiment can be obtained when the positive and negative electrodes 7 and 5 are arranged as shown in FIG. 2 or FIG.

Further, in the above-mentioned embodiments, the example in which the shape of the positive electrode and the negative electrode 7 and 5 is a strip shape has been described.
This shape is the same even if it is another rectangular shape.

Further, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[0064]

According to the present invention, since at least the corners of the rectangular positive and negative electrodes on the side of insertion into the prismatic battery container are arcuate, the positive and negative electrodes due to contact between the positive and negative electrodes and the prismatic battery container are The negative electrode active material is prevented from falling off,
Further, the bending of the positive electrode and the negative electrode is suppressed, which eliminates the internal short circuit of the battery and has the advantage that the battery capacity is maintained relatively large.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a positive electrode and a negative electrode of an embodiment of a prismatic non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a plan view showing another example of the positive electrode and the negative electrode according to the present invention.

FIG. 3 is a plan view showing another example of the positive electrode and the negative electrode according to the present invention.

FIG. 4 is a diagram for describing the present invention.

FIG. 5 is a cross-sectional view showing an example of a prismatic non-aqueous electrolyte secondary battery.

FIG. 6 is a plan view showing an example of a conventional positive electrode and negative electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lid 2 Gasket 3 Positive electrode terminal 5 Negative electrode 5a Negative electrode current collector 5b Negative electrode mixture 5c, 5d, 5e, 5f Corner part 6 Separator 7 Positive electrode electrode 7a Positive electrode current collector 7b Positive electrode mixture 7c, 7d, 7e, 7f Corner Part 10 prismatic battery container

Claims (2)

[Claims] 1. A rectangular positive electrode in which a positive electrode active material is applied to a positive electrode current collector and a rectangular negative electrode in which a negative electrode active material is applied to a negative electrode current collector are sequentially laminated via a separator. In a prismatic non-aqueous electrolyte secondary battery adapted to house the electrode laminate in a prismatic battery container, at least a corner portion of the rectangular positive electrode and the negative electrode on the side of insertion into the prismatic battery container has an arc shape. A prismatic non-aqueous electrolyte secondary battery characterized by the above. 2. The prismatic non-aqueous electrolyte secondary battery according to claim 1, wherein a radius of an arc of the arc shape of the corner portion is R.
When it is set to 0.01 mm <= R <= 1.5 mm, the prismatic nonaqueous electrolyte secondary battery characterized by the above-mentioned.