JP2001243931A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of reliability caused by leakage of electrolytic solution from a lead take-out part or by vapor intrusion. SOLUTION: Between a positive and a negative electrode with a lead provided for taking out an electrochemical energy, an electrolyte is arranged to form a electricity-generating element, which is contained in a battery case made of a bag-like laminated sheet so that an end side of the lead is located outside of the laminated sheet. The taking-out part of the lead from the laminated sheet is clad with synthetic rubber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium battery, and more particularly to a lithium battery in which a power generation element provided with a lead for extracting electrochemical energy to the outside is accommodated in a battery case.

[0002]

2. Description of the Related Art In recent years, as portable devices have become smaller and lighter, there is a strong demand for lithium batteries used as power sources for such portable devices to be smaller and lighter, particularly thinner.

In order to respond to the demand for thinning, instead of stainless steel or aluminum, which has been conventionally used for a battery case of a sealed battery, a thin laminated sheet made of a metal foil and a resin film is adopted. Lithium batteries have been developed and some have already been put into practical use.

In a film battery or a card battery using a laminate sheet as a battery case, two dish-shaped metal current collectors and a battery case are bonded with a heat-fusible resin, or the opening of the laminate sheet is fused with a heat-sealing resin. It has been proposed to seal by heat-sealing with an adhesive resin (for example, JP-A-7-6743 and JP-A-8-83596).

When a pair of metal current collector and battery case is bonded with a heat-fusible resin (Japanese Patent Laid-Open No. 7-6743), the heat and pressure of the upper and lower heaters are evenly transmitted to the seal portion. However, when the lead is pulled out from the inside of the battery case through the seal portion (Japanese Patent Laid-Open No. 8-83596), the pressure is not evenly transmitted to the lead extraction portion during sealing because the lead has a thickness. In addition, there have been problems that the adhesive strength of the lead extraction portion varies, and that the end face of the lead does not sufficiently adhere to the heat-fusible resin.

[0006] In addition, poor adhesion between a metal generally used for a laminate sheet and a polyolefin resin having adhesiveness causes problems such as leakage of electrolyte and intrusion of moisture.

[0007] Therefore, it has been proposed to coat a lead sheet bonding portion of a lead with a heat-fusible resin having excellent adhesion to metal in advance (Japanese Patent Laid-Open No. 11-233133).
No.).

As a method of coating the lead with the heat-fusible resin, a method is used in which the lead is sandwiched between film-like heat-fusible resins and heated and pressed. It is said that this can completely cover the surface of the lead,
The heater is in direct contact with the heated and pressurized lead surface, but the heater is not in direct contact with the end face of the lead. It cannot be said that the power has been obtained, and there has been still a problem such as leakage of the electrolyte solution and intrusion of moisture in long-term use.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional lithium battery, and has been made in consideration of the above problem. An object is to provide a lithium battery using a sheet as a battery case.

[0010]

In order to achieve the above object, in the lithium battery of the present invention, an electrolyte is disposed between a positive electrode and a negative electrode provided with a lead for extracting electrochemical energy to the outside. And forming a power generating element, the lithium battery containing the power generating element in a battery container made of the bag-shaped laminated sheet so that the end side of the lead is located outside the bag-shaped laminated sheet. The portion where the lead was removed from the laminate sheet was covered with synthetic rubber.

In the above lithium battery, the synthetic rubber is S
Desirably, it is a BR synthetic rubber.

The above-mentioned synthetic rubber is soluble in an organic solvent or the like, and can be handled as a one-part adhesive ink. A strong synthetic rubber film is formed by applying it to a predetermined position of a lead and drying it. can do. In addition, this film is made of resin and has good adhesiveness not only to metal but also to polyolefin and modified polyolefin used in laminate sheets, and can prevent leakage of electrolyte and moisture from the lead-out portion. .

The SBR synthetic rubber is particularly excellent in adhesion to metals and polyolefins, and has high solvent resistance.
In the case of a lithium battery using an organic electrolyte, dissipation and leakage of the electrolyte can be effectively prevented.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the lithium battery of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a plan view showing a configuration example of a lithium battery according to the present invention, FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB of FIG. 1 to 3, 1 is a battery case, 2 is a power generation element,
Reference numeral 3 denotes a positive electrode lead, 4 denotes a negative electrode lead, 5 denotes a synthetic rubber, 6 denotes a positive electrode current collector, 7 denotes a positive electrode active material layer, 8 denotes an electrolyte layer, 9 denotes a negative electrode current collector, and 10 denotes a negative electrode active material layer. Here, the positive electrode current collector 6 and the positive electrode active material layer 7 may be collectively referred to as a positive electrode, or the negative electrode current collector 9 and the negative electrode active material layer 10 may be collectively referred to as a negative electrode.

The laminate sheet used for the battery case 1 is made of a metal foil such as aluminum or stainless steel on one or both sides, a polyolefin such as polyethylene, polypropylene, polyethylene terephthalate, a modified polyolefin such as modified polyethylene or modified polypropylene, a polyimide, a polymethacryl. Methyl acid or ethylene
What integrated and laminated | stacked the resin films, such as a propylene copolymer, can be used. Here, the resin film that forms inside when the battery case 1 is formed is not particularly required to have adhesiveness to metal, and may be any as long as the resin that forms inside can be thermally fused to each other.

FIG. 1 shows an example in which the battery case 1 is formed by folding one laminated sheet at the lower end portion of the battery element 2 and sealing the three sides. However, two laminated sheets are opposed to each other and four sides are sealed. Alternatively, the power generating element 2 may be housed in a tubular shape in which one side of a laminate sheet is sealed, and the remaining two sides may be sealed to form an H-shaped seal portion.

As shown in FIG. 3, the power generating element 2 includes a positive electrode active material layer 7 formed on a positive electrode current collector 6 and a negative electrode active material layer 10 formed on a negative electrode current collector 9. It has a structure of being laminated via a. In the present invention, the constituent members of the power generating element 2, that is, the constituent materials and compositions such as the current collector, the active material layer, and the electrolyte are not limited, and all materials usable in conventional lithium batteries and their combinations are used. Can be used. In addition, the method for manufacturing the power generation element 2 can be applied to all the methods used in conventional lithium batteries.

FIG. 3 shows, as an example, a power generating element in which a non-woven fabric is impregnated with a gel electrolyte and a cured electrolyte layer 8 is provided. First, the positive electrode including the positive electrode current collector 6 and the positive electrode active material layer 7 is coated with a positive electrode mixture including a positive electrode active material, a conductive material, and a binder on the positive electrode current collector 6 made of aluminum foil, and dried. It is made by sticking. Next, the negative electrode composed of the negative electrode current collector 9 and the negative electrode active material layer 10 is fixed by applying a negative electrode mixture composed of a negative electrode active material and a binder to both surfaces of the negative electrode current collector 9 made of copper foil and drying the mixture. To make. The electrolyte layer 8 is produced by impregnating a nonwoven fabric with a stock solution of a gel electrolyte composed of an electrolyte solution, a polymer, and a polymerization initiator and curing the solution. The power generating element 2 is manufactured by stacking the positive electrode, the negative electrode, and the electrolyte layer manufactured as described above as shown in FIG.

In the lithium battery according to the present invention, as shown in FIG. 1, a power generation element 2 is housed in a battery case 1 formed by sealing three sides of a laminate sheet. The structure is such that electrochemical energy is taken out through the negative electrode lead 4.

The portion of the positive electrode lead 3 and the negative electrode lead 4 passing through the laminate sheet, that is, the lead-out portion, is covered with a synthetic rubber 5 as shown in FIGS. As this synthetic rubber, SBR synthetic rubber can be used. This SBR synthetic rubber has excellent adhesion to metals, polyolefins such as polypropylene and polyethylene, and also has excellent solvent resistance to organic electrolytes and the like.

The coating of the leads 3 and 4 is performed by dissolving the SBR synthetic rubber in toluene to obtain an appropriate viscosity, and then brushing or printing a pattern on a predetermined portion of the solution, and adding the leads 3 and 4 in the solution. Dip coating is performed by dipping a predetermined portion of No. 4 and then drying and volatilizing toluene.

For the positive electrode lead 3 and the negative electrode lead 4, the same metals as those used for the current collector of the conventional lithium battery, such as aluminum, nickel, copper, and stainless steel, can be used. Further, in a lithium battery using an organic electrolyte, it is preferable to use the same metal as the positive electrode current collector and the negative electrode current collector from the viewpoint of preventing corrosion of the leads 3 and 4. On the other hand, if the electrolytic solution does not touch the leads 3 and 4, such as a lithium battery using a solid electrolyte, the current collectors 6 and 9 may be formed of a different material.

FIG. 1 shows an example in which the lead connecting tabs provided on the current collectors 6 and 9 and the leads 3 and 4 are joined by resistance welding or ultrasonic welding. In the case of a lithium battery composed of the electrolyte layer 8, for example, it is not necessary to join the tab and the lead, and the lead is integrated with the current collectors 6, 9 drawn from the current collectors 6, 9. Is also good.

[0024]

EXAMPLE A positive electrode active material layer 7 containing LiMn ₂ O ₄ as an active material was formed on a positive electrode current collector 6 made of aluminum foil provided with a tab for lead connection. A negative electrode active material layer 10 using Li ₄ Ti ₅ O ₁₂ as an active material was formed on both surfaces of a negative electrode current collector 9 made of copper foil provided with, and used as a positive electrode and a negative electrode, respectively. In the electrolyte layer 8, an organic electrolyte 1M Li
PF6-EC / DEC (volume ratio 1/1) and polyethylene glycol diacrylate (molecular weight: about 400) were mixed at a weight ratio of 4: 1, and the photopolymerization initiators 2,4,6
A non-woven fabric was impregnated with a stock gel electrolyte solution containing 1,000 ppm of trimethylbenzoyldiphenylphosphine oxide, and a UV-cured gel electrolyte was used. These positive electrode, negative electrode, and electrolyte layer were laminated in the order shown in FIG. 3 to produce a power generating element.

The positive electrode lead 3 and the negative electrode lead 4 were each used by cutting an aluminum thin plate and a copper thin plate having the same material as the current collector and having a thickness of 0.1 mm into predetermined dimensions. Next, the SBR-based synthetic rubber is dissolved in toluene so as to have a concentration of 20% by weight, and a portion of the lead passing through the sealing portion of the laminate sheet is immersed, pulled up, and dried to be coated with the synthetic rubber. A lead was prepared.

The produced positive electrode lead 3 and negative electrode lead 4 are joined to the tabs of the positive and negative electrode current collectors by ultrasonic welding, respectively, and the completed power generating element 2 is composed of polyethylene terephthalate / aluminum foil / modified polypropylene. The three sides of the opening were sequentially sealed by heating and pressurizing, and a lithium battery was produced.

Comparative Example 1 Positive Lead 3 and Negative Lead 4
A lithium battery was produced in the same manner as in Example 1, except that the portion to be adhered to the laminate sheet was previously coated with a modified polypropylene having adhesiveness to metal.

Comparative Example 2 A lithium battery was produced in the same manner as in Example 1 except that the portions of the positive electrode lead 3 and the negative electrode lead 4 that were bonded to the laminate sheet were bonded to the laminate sheet without previously coating. (Evaluation) In the lithium battery manufactured in the above example, the lead was coated in advance with synthetic rubber, so that the invasion of moisture from the lead draw-out portion was prevented, and the discharge capacity did not decrease even when the battery was left in a late charged state. It is presumed that. Therefore, the lithium batteries prepared in Examples and Comparative Examples 1 and 2 were charged and discharged at room temperature for 3 cycles, and then charged for 6 cycles before charging in the fourth cycle.
It was left in a constant temperature layer at 0 ° C. for 30 days, and a comparative experiment was performed on the discharge amount before and after leaving. The charge / discharge test was performed at a constant current charge / discharge of 0.2 C, and the upper limit voltage for charging and the lower limit voltage for discharging were set to 2.9 V and 1.5 V, respectively.

Table 1 shows the ratio of the discharge capacity at the fourth cycle after leaving at high temperature to the discharge capacity at the third cycle of each lithium battery in%.

[0030]

[Table 1]

As is evident from Table 1, no decrease in the discharge capacity was observed in Examples in comparison with Comparative Examples.

Further, when the bonding state of the lead lead-out portion of each lithium battery after the end of the experiment was disassembled, it was found that in the lithium battery of Comparative Example 2, the modified polypropylene of the laminated sheet and the lead hardly adhered. . Although the battery of Comparative Example 2 was relatively strongly adhered, the lead and the laminate sheet could be peeled off. On the other hand, in the lithium batteries of Examples, the laminate sheet could not be peeled off.

From these results, it is presumed that in the lithium batteries of the examples, the strong adhesion between the lead and the SBR-based synthetic rubber was maintained for a long period of time, and no water entered. On the other hand, in the lithium batteries of Comparative Examples 1 and 2, moisture penetrated into the batteries during high-temperature storage, causing an irreversible reaction with lithium in the active material, particularly lithium taken in the negative electrode active material, resulting in a decrease in discharge capacity. It is presumed to have been done.

[0034]

As described above, according to the lithium battery according to the present invention, since the portion from which the lead is taken out of the laminate sheet is covered with synthetic rubber, a gap may be formed between the battery case and the lead at the time of bonding. In addition, the laminated sheet does not peel off during use, leakage of the electrolyte solution and intrusion of moisture are prevented, and a highly reliable lithium battery can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration example of a lithium battery according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

[Explanation of symbols]

1: battery case, 2: power generation element, 3: positive electrode lead, 4: negative electrode lead, 5: synthetic rubber, 6: positive electrode current collector, 7: positive electrode active material layer, 8: electrolyte layer, 9: negative electrode current collector , 10: negative electrode active material layer

Claims (2)

[Claims] An electrolyte is disposed between a positive electrode and a negative electrode provided with a lead for extracting electrochemical energy to the outside to form a power generating element, and the end side of the lead is a bag-like laminated sheet. A lithium battery in which the power generating element is housed in a battery case made of the bag-shaped laminated sheet so as to be located outside, wherein a portion of the lead from the laminated sheet is covered with synthetic rubber. Lithium battery. 2. The lithium battery according to claim 1, wherein the synthetic rubber is an SBR synthetic rubber.