JPH0855637A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] [Object] To provide a non-aqueous electrolyte secondary battery having a low internal resistance and no swelling of the battery due to the progress of charge / discharge cycles. [Structure] A negative electrode made of a substance that absorbs and releases lithium.
A battery in which an electrode group formed by winding a positive electrode and a separator in an elliptic spiral shape is housed in a battery case. An electrolytic solution resistant elastic body is provided at the center of the elliptical spiral electrode group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having a high energy density and high safety as a power source for driving an electronic device or a memory holding power source or a battery for an electric vehicle. .

[0002]

2. Description of the Related Art With the rapid miniaturization and weight reduction of electronic equipment, the development of a secondary battery that is smaller, lighter in weight and high in energy density, and that can be repeatedly charged and discharged with respect to the power source battery The demand is increasing. Non-aqueous electrolyte secondary batteries are the most promising as secondary batteries that meet these requirements.

Various positive electrode active materials for non-aqueous electrolyte secondary batteries such as titanium disulfide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide have been studied. Has been done. Among them, lithium cobalt composite oxide (Li
Since xCoO ₂ ) charges and discharges at an extremely noble potential of 4 V (Li / Li ⁺ ) or more, a battery having a high discharge voltage can be realized by using it as a positive electrode.

Various negative electrode active materials for non-aqueous electrolyte secondary batteries, such as metallic lithium, Li-Al alloys and carbon materials capable of absorbing and desorbing lithium, have been investigated. Among them, carbon is particularly preferable. The material has the advantage that a battery with high safety and long cycle life can be obtained.

As the lithium salt, lithium perchlorate, lithium trimethanesulfonate, lithium hexafluorophosphate and the like are generally used. Among them, lithium hexafluorophosphate has been widely used in recent years because of its high safety and high ionic conductivity of the dissolved electrolyte.

There are two types of battery shapes, namely, a cylindrical shape and a prismatic shape. The rectangular shape has a feature that it is more space efficient than the cylindrical shape, and thus its demand is increasing in recent years. The structure of the electrode group was such that in rectangular batteries such as conventional lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries, strip-shaped negative electrode plates and positive electrode plates were alternately laminated. In the electrolyte secondary battery, the ion conductivity of the electrolyte is lower than that of an aqueous solution by about two orders of magnitude, so that a structure in which a negative electrode, a positive electrode, and a separator are wound in an elliptic spiral shape is generally used. is there. This is because the electrode is made thin and the electrode facing area is made large in order to obtain the same discharge performance as the aqueous battery.

The method of treating the core of the elliptical spiral electrode group is as follows:
Two types of methods are conceivable: a method of extracting the core and leaving a hollow portion, and a method of inserting the core. We have proposed a method in which a battery in which a lithium cobalt composite oxide (Li _x CoO ₂ ) positive electrode, a carbon material negative electrode, and a separator are wound in an elliptical spiral shape and housed in a battery case is one of the above two methods. I made a prototype.
As a result, the former method increased the internal resistance of the battery and the latter method decreased the internal resistance of the battery, but the battery swelled as the charge / discharge cycle proceeded. The swelling of the battery causes destruction of peripheral parts, destruction of the battery storage case, and the like in electronic devices which have been highly concentrated in recent years. Further, in the assembled battery, various problems such as disconnection of connection leads between the batteries and deformation of terminals connecting the leads are caused.

Therefore, there has been a demand for a non-aqueous electrolyte secondary battery which has a low internal resistance and does not swell as the charging / discharging cycle progresses.

[0009]

Means for Solving the Problems The present invention provides a battery in which a negative electrode made of a substance that absorbs and releases lithium, a positive electrode, and a separator, in which an electrode group formed by spirally winding an elliptical spiral shape is housed in a battery case, The above problem is solved by providing an electrolytic solution resistant elastic body at the center of the elliptical spiral electrode group.

[0010]

[Function] The lithium-cobalt composite oxide (Li _x CoO ₂ ) that is the positive electrode active material has a layered structure, but as the charging reaction accompanying desorption of lithium ions proceeds, cobalt-
It is known that the oxygen layer extends and the crystal expands.
It is known that the carbon material used for the negative electrode also has a layered structure and the crystal expands as the charging reaction proceeds with the insertion of lithium. That is, the power generation element including these positive and negative electrodes expands in volume during the charge reaction and contracts during the discharge reaction.

In a battery in which a winding core is inserted at the center of an elliptical spiral electrode group, the cause of the swelling of the battery with the progress of charge / discharge cycles is that the electrode swollen by the expansion and contraction of the active material causes the battery to swell from inside. It is possible that it was oppressed. On the other hand, the internal resistance increased in the battery in which the core was removed and the hollow portion was left, because the linear distance of the elliptical spiral electrode was bent into the hollow portion of the electrode group, which increased the inter-electrode distance. Conceivable.

As in the present invention, when the elliptical spiral electrode group is provided with the electrolytic solution resistant elastic body at the center thereof, the elastic body prevents the electrode group from being bent into the hollow portion, and the charging / discharging cycle is performed. Since the swelling of the electrode due to the progress of the above is absorbed, the conventional adverse effects are unlikely to occur.

[0013]

EXAMPLES The present invention will be described below with reference to preferred examples.

The positive electrode plate was prepared by mixing lithium cobalt composite oxide (Li _x CoO ₂ ), carbon powder as a conductive agent and polyvinylidene fluoride as a binder in a weight ratio of 91: 2: 7, and using an organic solvent. The paste prepared by using is uniformly applied to both sides of an aluminum foil having a thickness of 20 μm and then dried.

For the negative electrode plate, graphite and fluororesin powder as a binder were mixed in a weight ratio of 91: 9, and a paste prepared using an organic solvent was uniformly applied to both sides of a copper foil having a thickness of 18 μm. It has been dried.

FIG. 1 is a vertical sectional view of an embodiment of the present invention.
An electrode group is produced by winding the positive electrode plate 1 and the negative electrode plate 2 in an elliptical spiral shape with a winding shaft having a width of 33 mm and a thickness of 1.0 mm via a separator 3 made of a polypropylene microporous film having a width of 22 mm and a thickness of 25 μm. did. Width 20 in the hollow part where the core is pulled out.
mm, length 30 mm, thickness 2.0 mm open-cell polyethylene foam (Sanwa Kako Co., Ltd., Opcell LC-
External dimensions after inserting (300WE) 6.4mm × 22mm × 46
It was inserted into the mm battery case.

Ethylene carbonate (E
C), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed at a volume ratio of 2: 2: 1, and 1 mol / liter of lithium hexafluorophosphate was dissolved in the solvent.

The above-mentioned organic electrolyte secondary battery of the present invention is referred to as (A). For comparison, a comparative battery having the same structure as (A) except that the open-cell polyethylene foam is not inserted in the hollow portion from which the core is pulled out is called (A),
A comparative battery in which a polyethylene plate having a width of 20 mm, a length of 30 mm and a thickness of 1.0 mm is inserted in the hollow portion is referred to as (a). Ten batteries were prepared for each condition.

The results of measuring the internal resistance of these batteries with an AC impedance of 1 KHz are summarized in Table 1 (average value of 10 batteries). As is clear from the results in Table 1,
It can be seen that the comparative battery (A) having a hollow portion in the center of the electrode group has a large internal resistance of the battery.

[0020]

[Table 1] Next, a charge-discharge cycle test is performed in which these batteries are charged with a constant current of 0.2 C until the terminal voltage reaches 4.1 V, and then discharged with a constant current of 0.2 C until the terminal voltage reaches 3 V. 100 cycles were performed at room temperature. After stopping in the discharged state, the swelling of the battery was measured. Table 2 shows the thickness of the central portion of each battery before and after the cycle test (10 pieces average value). As is clear from the results of Table 2, in Comparative Battery (a), the battery thickness is increased, whereas
The battery (A) of the present invention shows no increase in thickness.

[0021]

[Table 2] In the above embodiment has been described with respect to the case of using a lithium-cobalt composite oxide as a cathode active material, manganese dioxide including the titanium disulfide, spinel-type lithium manganese oxide (LixMn ₂ O _4), vanadium pentoxide and three Various materials such as molybdenum oxide can be used. Although a carbon material was used as the negative electrode, the negative electrode active material is basically not limited when using the positive electrode of the present invention, and the negative electrode active material used in the conventional non-aqueous electrolyte secondary battery, for example, pure Lithium, a lithium alloy, or the like can be used.

Further, the electrolytic solution which is a lithium ion conductive material is not basically limited, and the one used in the conventional organic electrolytic solution secondary battery can be used. Examples of the organic solvent include cyclic esters such as ethylene carbonate which is an aprotic solvent and ethers such as tetrahydrofuran and dioxolane. These can be used alone or in a mixture of two or more kinds. Also, the supporting electrolyte dissolved in such a non-aqueous solvent or solid ionic conductor is not basically limited. For example, LiAsF ₆ , LiPF ₆ , LiCF ₃
One or more such as SO ₃ can be used.

In the above embodiment, the case where the open cell polyethylene foam is used as the electrolytic solution resistant elastic body has been described, but the material and the kind of elastic body are not particularly limited. As the material, in addition to polyethylene, plastics such as polypropylene and fluororesin, rubber such as butyl rubber and ethylene propylene rubber, and metal materials such as stainless steel and copper can be used. However, from the viewpoint of cost, polyolefin resin such as polyethylene is used. Is preferably used. As the structure of the elastic body, a closed cell porous body, a spring, a leaf spring, etc. may be considered in addition to the open cell porous body, but it is considered that the open cell porous body is preferable in view of the retention property of the excess electrolyte and the cost. .

[0024]

As described above, in the battery in which the electrode group formed by winding the negative electrode made of a substance that absorbs and desorbs lithium, the positive electrode, and the separator in the elliptical spiral shape is housed in the battery case, the elliptical spiral electrode. It is possible to provide a non-aqueous electrolyte secondary battery in which the internal resistance is small by providing an electrolytic solution-resistant elastic body in the central part of the group, and swelling of the battery does not occur with the progress of charge and discharge cycles, Its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a non-aqueous electrolyte secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Battery case 5 Positive electrode terminal 6 Gasket 7 Battery lid 8 Spacer 9 Continuous foam polyethylene foam

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery in which an electrode group formed by winding a negative electrode made of a substance that absorbs and releases lithium, a positive electrode, and a separator in an elliptic spiral shape is housed in a battery case. A non-aqueous electrolyte secondary battery comprising an electrolytic solution resistant elastic body at the center of an elliptical spiral electrode group.