JPH11250873A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To house a power generating element having a positive electrode, a negative electrode, a separator or a polymer electrolyte in a container made of a laminated sheet of metal and resin without decreasing the safety of a battery by welding a resin sheet covering the separator or an electrode body together with sealing of the laminate sheet. SOLUTION: A nonaqueous electrolyte secondary battery 1 is formed by housing an electrode body 12 comprising a positive electrode, a negative electrode, and a separator in a battery container 6 made of an aluminum laminated sheet together with a nonaqueous electrolyte. When the length of resin layer welded part of only the resin layers of the laminated sheet in a laminated sheet welded sealing part is represented by (a), the length of a separator melt- bonding part or a resin sheet melt-bonding part where the end of the separator or the end of the resin sheet is melt-bonded to the welded part of the resin layer to the resin layer is represented by (b), satisfaction of the relation of 0.125<=b/(a+b)<=0.5 is preferable. Even if the battery is abnormally heated by overcharge or the like, or the battery becomes such a high temperature that the sealing part is opened, supply of oxygen to a power generating element is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery. A typical battery that satisfies such a requirement is an active material such as lithium metal or lithium alloy, or a host material containing lithium ions (here, a host material refers to a material that can occlude and release lithium ions). Lithium intercalation compound occluded in a certain carbon is used as a negative electrode material, and LiC
This is a non-aqueous electrolyte secondary battery using an aprotic organic solvent in which a lithium salt such as 10 ₄ or LiPF ₆ is dissolved as an electrolyte.

This non-aqueous electrolyte secondary battery has a negative electrode plate in which the above-mentioned negative electrode material is held on a negative electrode current collector as a support, and a reversible electrochemical reaction with lithium ions such as a lithium-cobalt composite oxide. The positive electrode plate, which holds the positive electrode active material that reacts on the positive electrode current collector that is the support, from the separator that holds the electrolytic solution and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between the two electrodes Has become.

In the case of a non-cylindrical battery, each of the positive electrode plate and the negative electrode plate is formed into a thin sheet or foil and wound spirally and non-circularly in section through a separator. The outermost circumference of the body is wrapped with tape. Then, the completed electrode body is housed in a battery container made of a metal such as stainless steel, nickel-plated iron, or aluminum. After the electrolyte is injected, the battery is assembled by hermetically sealing with a lid plate.

[0005]

However, as described above, some battery containers are made of stainless steel or nickel-plated iron, and have high airtightness and excellent mechanical strength, but have a light weight. There are significant restrictions on the design and design of materials and battery containers. In order to solve the problem, there has been proposed a method in which an electrode body is housed in a battery container formed of an aluminum laminate sheet.

However, when the conventional non-circular spiral electrode body is housed in a battery container made of an aluminum laminate sheet and the container is sealed, the battery may generate abnormal heat due to overcharging or the like, or the battery may not be placed. If the environment to be removed exceeds the heat fusion temperature at which the battery case is sealed, the sealed portion is broken by the heat fusion. In such a state, a large amount of oxygen is supplied into the battery power generating element at that moment, which promotes a thermochemical reaction of the active material, thereby causing a problem that battery safety is reduced.

Accordingly, the present invention provides a power generation element having a positive electrode, a negative electrode, a separator or a polymer electrolyte, which is a laminated sheet of a metal and a resin, without lowering battery safety and without complicating the manufacturing method. And a non-aqueous electrolyte secondary battery housed in a battery container.

[0008]

Therefore, a non-aqueous electrolyte secondary battery according to the first invention is characterized in that an electrode body having a positive electrode, a negative electrode, a separator and / or a polymer electrolyte is a laminated sheet of a metal and a resin. And a resin sheet coated with a separator and / or an electrode body is welded together with a welding seal of the laminate sheet. In this case,
The overcharge resistance can be significantly improved.

A non-aqueous electrolyte secondary battery according to a second aspect of the present invention has a structure in which the electrode body is wound in a non-circular cross section, and protrudes from a winding shaft end surface of the electrode body. The separator and / or the resin sheet thus formed are welded together with the welding seal of the laminate sheet. In this case, the overcharge resistance can be significantly improved.

The non-aqueous electrolyte secondary battery according to the first or second aspect of the present invention is the non-aqueous electrolyte secondary battery according to the third aspect of the present invention, wherein the length of the resin layer welded portion between only the resin layers of the laminate sheet at the welded sealing portion of the laminate sheet. Assuming that a is the length of the separator or resin sheet welded portion where the end of the separator or resin sheet is welded between the welded portions of the resin layers, b satisfies the relationship of 0.125 ≦ b / (a + b) ≦ 0.5. It is characterized by the following.

Here, the metal of the laminate sheet of the metal and the resin is, for example, aluminum or an alloy thereof, and other examples include titanium foil. Further, the resin layer and the metal foil layer of the metal laminate sheet are not limited to one layer each, and may be two or more layers. The resin sheet is made of a material such as low-density or high-density polyethylene, polyamide, polyimide, and polyamideimide.

In the present invention, a sheet and a film have the same meaning. Further, in the non-aqueous electrolyte secondary battery according to the present invention, as its configuration, a combination of a positive electrode, a negative electrode and a separator with a non-aqueous electrolyte,
Or, a positive electrode, a combination of only an organic or inorganic solid electrolyte as a negative electrode and a separator or a non-aqueous electrolyte, or a combination of a positive electrode, a negative electrode, a separator and only an organic or inorganic solid electrolyte or a non-aqueous electrolyte may be used. . Examples of the organic electrolyte include PAN and PEO, which are organic polymer electrolytes. Of course, the separator or organic or inorganic solid electrolyte, non-aqueous electrolyte,
In each case, known ones can be used.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 2 is an explanatory diagram of the nonaqueous electrolyte secondary battery according to the present invention.

The non-aqueous electrolyte secondary battery 1 in the present embodiment has an electrode assembly 1 comprising a positive electrode plate, a negative electrode plate, and a separator.
2 is stored in an aluminum laminated sheet battery container 6 together with a non-aqueous electrolyte (not shown).

The positive electrode plate is a current collector in which a lithium-cobalt composite oxide is held as an active material. The current collector was obtained by laminating an aluminum foil having a thickness of 4 μm on both sides of a PET film having a thickness of 6 μm and bonding the aluminum foil with an adhesive. The positive electrode plate was prepared by mixing 8 parts of polyvinylidene fluoride as a binder and 5 parts of acetylene black as a conductive agent together with 87 parts of an active material, appropriately adding N-methylpyrrolidone to prepare a paste, and then collecting the paste. It was manufactured by applying and drying both sides of an electric conductor material.

The current collector of the negative electrode plate is a PET having a thickness of 12 μm.
After sputtering copper on both surfaces of the film, the film was obtained by electroplating copper having a thickness of 1 μm.

The negative electrode plate is prepared by mixing 86 parts of graphite (graphite) as a host material and 14 parts of polyvinylidene fluoride as a binder to prepare a paste on both surfaces of the current collector, and applying and drying the mixture. It was made by doing.

The separator is a microporous polyethylene membrane. The electrolyte was ethylene carbonate: diethyl carbonate = 1: 1 containing 1 mol / l of LiPF _6.
(Volume ratio).

The respective dimensions are such that the positive electrode plate has a thickness of 180 μm.
m, width 55 mm, separator thickness 25 μm, width 6
2.4 mm, the negative electrode plate has a thickness of 170 μm and a width of 57 mm. The lead terminals are welded to the positive electrode plate and the negative electrode plate, respectively, and the positive electrode, the separator, the negative electrode, and the separator are superimposed in this order, and a rectangular winding of polyethylene is formed. The electrode body 12 having a non-circular cross section was formed so as to be spirally wound around the electrode body 12 such that the long side thereof was parallel to the winding axis of the electrode body 12 and the separator became the outer periphery. Then, the end portion of the separator is wound around a length corresponding to the electrode width (length of the electrode body parallel to the winding axis) with a tape for stopping winding made of polyethylene (here, an adhesive is applied on one side). The electrode body 12 was stuck and fixed to the side of the electrode body parallel to the axis. Then, the aluminum laminate sheet was accommodated in a battery container 6 formed into a cylindrical shape. Next, the lead terminals 10, 10 '
The unexposed separator protruding from the electrode end surface perpendicular to the winding axis was heat-sealed together with the laminate sheet.
At this time, the length (a) of the resin layer welded portion of only the resin layers of the laminate sheet was 4.8 mm, and the length of the separator welded portion where the separator end was welded between the welded portions of the resin layers ( b) was set to 1.2 mm. (See FIG. 1; electrodes are not shown.) However, b / (a + b) = 0.2. Next, each electrode and the separator were sufficiently wetted with the electrolytic solution, and vacuum injection was performed in such an amount that no free electrolytic solution was present outside the electrode group.
Next, heat-fusion was similarly performed on the winding shaft surface side on which the lead terminals were provided. Here, although a cylindrical laminated sheet was prepared, a pair of plate-like laminated sheet processed products may be used, an electrode may be interposed therebetween, and fusion sealing may be performed. However, the present invention is not limited to this.

As shown in FIG. 3, the battery container 6 for the hermetically sealed port has a surface protective layer 15 of 12 μm PET as the outermost layer.
A 9 μm aluminum foil is adhered as a barrier layer 16 with a urethane adhesive under the film. Further, it is made of a laminate sheet having a 100 μm acid-modified LDPE (low density polyethylene) as a heat sealing layer 17 thereunder. Also, the lead terminals 10, 10 '
Is a metal conductor of 50 to 100 μm such as copper, aluminum, nickel, etc.
And a 70 μm Eval resin (ethylene-vinyl alcohol copolymer resin manufactured by Kuraray Co., Ltd.) as an electrolyte barrier layer 19 on the outside thereof. Here, aluminum is used for the positive electrode and copper is used for the negative electrode.
However, it goes without saying that the configuration of the battery container 6 and the leads 10 and 10 ′ and the drawing out from the battery container 6 are not limited to these.

As described above, three batteries A to H according to the present embodiment having a design capacity of 800 mAh, three of each of eight types, totaling 24 batteries.
This was produced. However, by appropriately changing the width of the separator, b
The relationship of / (a + b) is 0.1, 0.12, 0.15,
0.2, 0.4, 0.5, and 0.6. (A> 0, b
> 0) Next, three conventional comparative batteries (I) were produced in the same manner as described above. However, the difference is that the separator end is not welded and sealed together with the laminate sheet.

[Tests and Results] These batteries A to H,
The I (comparative battery) was left for several hours, subjected to a constant current constant voltage charge to 4.1 V at a current of 0.5 C for 3 hours, made into a fully charged state, and subjected to a cycle characteristic test under the condition of discharging to 2.75 V. Was. FIG. 4 shows the result at this time. (Each value used the average value of each three.) As a result, b / (a + b)
When the ratio was 0.6 or more, it was found that the cycle characteristics were deteriorated.

Next, using each of these three batteries, a constant current of 1 A was continuously supplied from the discharged state to perform an overcharge test up to 10 V. Table 1 shows the results.

[0024]

[Table 1] In the conventional battery I and when the ratio of b / (a + b) is 0.12 or less, the case rapidly expands due to gas generation due to the oxidative decomposition of the electrolyte from the vicinity where the charging voltage exceeds 5 V, and at the same time, the battery temperature sharply increases. When the battery temperature rose and the battery temperature exceeded 100 ° C., the welded portion opened. A few seconds later, rapid heat generation and smoke generation due to the thermochemical reaction of the active material were observed, and the battery temperature reached 200 ° C. or higher. In addition, b / (a + b)
When the ratio is 0.12 or less, it is considered that the welding of the separator becomes insufficient, a large amount of oxygen is supplied into the battery power generating element, and the thermochemical reaction of the active material lowers the safety of the battery.

Therefore, 0.125 ≦ b / (a + b) ≦
By performing welding or fusing satisfying the condition of 0.5, a nonaqueous electrolyte secondary battery of a laminated battery container having excellent cycle characteristics and excellent overcharge resistance can be provided. The same effect can be obtained even when the electrode body is a wound electrode having a flat shape, an elliptical cross section, or the like, or a laminated electrode. However, in the case of a laminated electrode, it is preferable that the outermost portion is used as a separator and the four directions are fused together with a laminated sheet serving as a battery case. In this case, since the productivity in the manufacturing process is reduced, the laminated electrode body may be housed in a tubular resin sheet (such as polyethylene), and the sheet at the opening may be fused together with the laminated sheet serving as the battery case. That is, even when the sealed portion is broken by heat fusion, the supply of a large amount of oxygen into the battery power generating element is satisfactorily suppressed. If it has, it is not limited to these. Also, a +
If the length of b is too long, the energy density per volume will decrease, and if it is too short, poor welding will occur. Therefore, the length of b is preferably 3 mm to 10 mm. Further, when a = 0 or when the separator or the resin sheet protrudes from the aluminum laminate battery case, if the length of b has at least the above length, the overcharge resistance can be improved. . In the present embodiment, the welding method employs heat fusion, but is not limited to this, and it goes without saying that any method can be used as long as a hermetic seal can be obtained.

[0026]

According to the present invention, a power generation element having a positive electrode, a negative electrode, a separator or a polymer electrolyte without causing a reduction in battery safety and without complicating the manufacturing method is made of metal and resin. And a non-aqueous electrolyte secondary battery housed in a battery container constituted by a laminate sheet of the above. In addition, by specifying the length of the welded part, the battery may generate abnormal heat due to overcharging, etc., or the environment in which the battery is placed may exceed the heat fusion temperature that sealed the battery container. Even if the sealed portion is torn, the supply of a large amount of oxygen into the battery power generation element is favorably suppressed, and a reduction in battery safety due to the thermochemical reaction of the active material can be prevented. . In addition, a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

FIG. 3 is an enlarged sectional explanatory view of a lead terminal portion of the nonaqueous electrolyte secondary battery according to one embodiment of the present invention.

FIG. 4 is a diagram showing a cycle life test result according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte secondary battery 10 Positive electrode lead terminal 10 'Negative electrode lead terminal 6 Battery container 12 Electrode body 15 Surface protective layer 16 Barrier layer 17 Heat fusion layer 18 Adhesive layer 19 Electrolyte barrier layer 30 Separator welding part 31 Resin layer welding Department

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery in which an electrode body having a positive electrode, a negative electrode, a separator and / or an organic or inorganic electrolyte is housed in a battery container made of a laminated sheet of a metal and a resin. Alternatively, a non-aqueous electrolyte secondary battery characterized in that a resin sheet coated with an electrode body is welded together with a welding seal of the laminate sheet. 2. A structure in which the electrode body is wound in a non-circular cross section, wherein a separator or the resin sheet protruding from an end surface perpendicular to a winding axis of the electrode body is provided together with a sealing opening of the laminate sheet. A non-aqueous electrolyte secondary battery characterized by being welded. 3. The length of a resin layer welded portion of only the resin layers of the laminate sheet at the welded sealing portion of the laminate sheet is a, and a separator end or a resin sheet end is located between the welded portions of the resin layers. 3. The relationship of 0.125 ≦ b / (a + b) ≦ 0.5 is satisfied, where b is the length of the welded portion of the separator or the welded portion of the resin sheet where is welded. Non-aqueous electrolyte secondary battery.