JP2000243376A - Lithium secondary battery - Google Patents

Abstract

(57) Abstract: The present invention relates to a lithium secondary battery, and more particularly to a configuration of an electrode plate thereof, which has a high capacity, a good current collecting property, and excellent characteristics. A battery is provided. SOLUTION: An electrode plate formed by arranging a mixture layer containing the active material and a binder on a current collector has an area corresponding to an area where a current collecting lead is bonded to both sides or one side of one side edge of an electrode plate. A lithium secondary battery having a region where a mixture layer is not formed, and a current collecting lead bonded to the region, whereby the height of an electrode plate having a mixture uncoated portion is reduced. The mixture filling density within a predetermined thickness can be improved without causing problems such as wrinkles and cracks caused by compression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a structure of an electrode plate thereof.

[0002]

2. Description of the Related Art In recent years, electronic devices have been rapidly becoming smaller and lighter.
Demands for weight reduction and higher capacity are increasing. In response to the demand, great expectations have been placed on a high energy density lithium secondary battery using metallic lithium or a lithium alloy as the negative electrode active material. However, when lithium metal or a lithium alloy is used as the negative electrode active material, there are problems such as lithium being precipitated in a dendritic manner upon charging, poor cycle characteristics due to the miniaturization of the alloy, and the occurrence of an internal short circuit. Therefore, many problems remain for the practical use of this battery system.

On the other hand, lithium secondary batteries using a carbonaceous material as a negative electrode active material and LiCoO2 as a positive electrode active material have been put to practical use by various companies. This battery system has good cycle characteristics because lithium does not precipitate on the negative electrode due to charging, and small lithium secondary batteries are currently being actively developed. Also, lithium secondary batteries have been developed as means for solving global environmental problems or energy problems in recent years. Practical application of load leveling technology as one of the measures to ensure stable power while preserving the global environment is desired. By promoting the use of devices and electric vehicles that use electric power stored at night, a large load leveling effect can be expected.In response to such demands for home battery power storage and electric vehicles, the unit cell capacity is 100 Ah. A large-sized lithium secondary battery has been developed.

[0004]

In order to spread this large-sized lithium secondary battery, high capacity, long life, high reliability, and low price are required. However, in the case of a large lithium secondary battery, the volume and area of the mixture layer increase, so that the current collecting structure is one of the issues, and is one of the factors that greatly affect the characteristics of the battery. Conventionally, a mixture layer forming portion in which a mixture is coated on both surfaces of a current collector of a metal foil, and an uncoated portion in which a mixture layer is not disposed on a side edge portion have a continuous electrode in a length direction. After preparing a plate and compressing this electrode plate with a press roll or the like in order to increase the mixture density within a predetermined thickness, a current collecting lead is connected to the metal foil portion of the continuous current collector not coated with the mixture. It was a configuration method of joining a plurality. However, in this electrode plate structure, there is a difference in the thickness of the mixture layer between the mixture-coated part and the uncoated part. In addition, the mixture-coated electrode plate is elongated, and the uncoated portion where no pressure is applied does not extend. As a result, wrinkles or cracks occur near the boundary between the two. Therefore, it is conceivable to stop the pressure in the limit area where the electrode plate does not extend,
In this case, the mixture filling density cannot be increased, so that the amount of mixture filling per unit volume cannot be increased, resulting in a battery having a small capacity.

The present invention solves the above problems and provides a lithium secondary battery having a high capacity, a good current collecting property, and excellent characteristics.

[0006]

According to the present invention, there is provided an electrode plate having only a mixture-free portion near a junction of a current collecting lead and having no continuous mixture-free portion at a side edge. It is assumed that. Accordingly, the compression ratio can be increased without producing a problem that occurs at the boundary between the coated portion and the non-mixture portion, and a highly mixed electrode plate can be produced.

The method of forming the non-mixture portion is to form a mixture layer on the entire surface of the current collector plate and then apply the mixture-coated portion on either one or both sides of the side edge of the electrode plate to the current collecting lead. There is a method of peeling the mixture according to the bonding area, and a method of not applying the mixture by masking.

[0008] Then, by joining a plurality of leads, a good current collecting property can be obtained, and the filling amount of the mixture can be increased. A battery is obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a lithium secondary battery using a lithium-containing transition metal oxide as a positive electrode active material and a material capable of occluding and releasing lithium ions as a negative electrode active material. In the above, an electrode plate formed by arranging a mixture layer containing the active material and the binder on the current collector, on both sides or one side of one side edge of the electrode plate, the area corresponding to the area for joining the current collection lead, A lithium secondary battery having a region in which the agent layer is not formed, and a current collecting lead is bonded to the region. The mixture filling density within the specified thickness can be improved without causing wrinkles, cracks, etc., and then the mixture layer is partially peeled off and the current collecting leads are joined, resulting in high filling. Electrode plates can be created, and high-capacity lithium secondary batteries It is.

According to a second aspect of the present invention, there is provided the lithium secondary battery according to the first aspect, wherein a plurality of current collecting leads are joined to the positive electrode and the negative electrode. In this case, the current collecting property can be enhanced by joining a plurality of leads, and the current concentration on the mixture around the current collecting leads can be reduced, so that a lithium secondary battery having excellent characteristics can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
2 will be described.

(Embodiment 1) FIG. 1 is a sectional view of a cylindrical lithium secondary battery ((a) overall view, (b) partially enlarged view),
FIG. 2 is a development view of the electrode plate. In FIG. 1, reference numeral 1 denotes a positive electrode, and a mixture layer containing a positive electrode active material and a binder is disposed on both surfaces of a current collector. And a positive electrode current collecting lead. As the positive electrode active material, LiCoO2, LiMn2O4, LiNiO2, a material in which Co, Mn, and Ni are partially substituted with another transition metal, or another lithium-containing transition metal oxide is used. For large lithium secondary batteries, Mn-based lithium-containing transition metal oxides such as LiMn2O4, which are abundant on the earth and inexpensive, are particularly suitable.

Reference numeral 4 denotes a negative electrode, and a mixture layer containing a negative electrode active material and a binder is disposed on both surfaces of the current collector of 5, and a part of the side edge opposite to the positive electrode is peeled off from the mixture. And a negative electrode current collecting lead 6 joined thereto. For the negative electrode active material, use a carbonaceous material such as graphite, petroleum coke, carbon fiber, or fired organic polymer, or occlude lithium,
Releasable metals or oxides or composites of these are used.

In forming these electrode plates, when the current collecting lead is joined to the mixture, the contact resistance between the mixture and the lead is large, so that the effect as the current collecting lead is not exhibited. Therefore, it is necessary to peel off the mixture part from the joint surface. The mixture is peeled off as shown in FIG. A conventional ultrasonic peeling method, a scratch peeling method, or the like is used as a method of peeling the mixture after the electrode plate is compressed. As a method for joining the current collecting lead 14 to the current collecting portion, ultrasonic welding, jagged joining, or the like is used. In the case of ultrasonic welding, it is necessary to peel the mixture on both the lead joint surface and the back surface, and in the case of boring bonding, lead joining can be performed by peeling the mixture only on the joint surface. The method for joining the leads is not limited to these as long as the current collecting property is improved.

In the case where the current collector leads of the positive electrode and the negative electrode are long and have a large area, the current collecting property is improved by joining a plurality of current collector leads as shown in FIG. Since the current concentration on the agent can be reduced, the battery characteristics can be improved. If the number of the current collecting leads is small, the reactivity of the entire surface of the electrode plate becomes non-uniform, the deterioration of the active material due to the concentration of current near the junction is accelerated, and the battery characteristics are deteriorated.

The electrolyte is a solute such as lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium borofluoride (LiBF4) or the like, and the solvent is ethylene carbonate (EC) or propylene carbonate (Li). PC), diethylene carbonate (DEC), ethyl methyl carbonate
A solution obtained by dissolving the above solute in a nonaqueous solvent such as (EMC) alone or a mixed solvent thereof at a concentration of 0.5 mol / dm3 to 2 mol / dm3 is used.

[0017]

Next, specific examples of the present invention will be described.

Embodiment 1 FIG. 1 is a sectional view of a cylindrical battery used in an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a positive electrode. Electrolytic manganese dioxide (MnO2) and lithium carbonate (Li2
CO3) and Li / Mn = 1/2, and mixed at 800 ° C. for 20 hours.
A mixture of LiMn2O4 as a positive electrode active material, acetylene black as a conductive agent, and polytetrafluoroethylene as a binder at a weight ratio of 90: 3: 7, which was fired in the air, was used as a positive electrode mixture. In order to knead this positive electrode mixture into a paste, a water-soluble dispersion liquid was used as polytetrafluoroethylene as a binder. The above mixing ratio is a ratio as a solid content. This positive electrode mixture paste is 0.02 mm thick as the positive electrode current collector of 2.
Was coated on both sides of the aluminum foil and dried, and then cut into a state in which the entire mixture layer having a width of 300 mm was arranged. Both film thicknesses of the positive electrode mixture layer formed on both surfaces of the positive electrode current collector are the same,
The sum W of both film thicknesses after drying was 0.28 mm. Then W is 0.18mm
Then, after compression molding using a press roll, the positive electrode plate was cut into a length of 6000 mm. At this time, the filling amount of the positive electrode active material was 900 g in total on both sides, and the mixture density was 3.0 g / cm3. The filling capacity is 100 Ah as a reaction of 0.74 electrons.

On one side edge of the positive electrode, 150 mm 2 (width 10 mm,
Both sides of the mixture layer having a length of 15 mm) were subjected to ultrasonic peeling, and three aluminum leads having a width of 10 mm, a length of 50 mm, and a thickness of 0.2 mm were ultrasonically bonded to one surface thereof. A total of five leads were joined in the same manner.

Reference numeral 4 denotes a negative electrode composed of artificial graphite and a styrene-butadiene rubber (SBR) as a binder, each of which was mixed at a weight ratio of 97: 3 and kneaded into a paste to obtain a negative electrode of 5 After coating on both sides of a copper foil having a thickness of 14 μm, which is a current collector, the copper foil is dried, rolled, and cut into a predetermined size. A styrene-butadiene rubber as a binder for the negative electrode also uses a water-soluble dispersion liquid, and the above mixing ratio is a solid content. After coating and drying, the thickness of the negative electrode is 0.170mm
325mm negative electrode length, 6400mm negative electrode length
Cut into pieces. At this time, the filling amount of the negative electrode active material was 440 g. The density of the negative electrode mixture is 1.4 g / cm3, and the capacity density of the negative electrode is 260 mAh / g with respect to the above positive electrode.

A 150 mm2 (width 10 mm,
After applying ethanol on only one side of the mixture layer for 15 mm),
After scratching and peeling the surface, width 10 mm, length 50 mm, thickness
A 0.15 mm copper lead was welded. A total of five leads were joined in the same manner.

The positive electrode and the negative electrode are spirally wound through the polyethylene separator of FIG. 1 and inserted into a stainless steel case of 8. A positive electrode lead is inserted into an aluminum positive electrode column of 9 and a negative electrode lead is inserted after the insertion. Ultrasonic bonding was performed on each of the ten copper negative poles. After laser welding of the sealing plate of No. 11 and the case, the electrolyte was injected from the injection port of No. 12, then the injection port was covered with a stainless steel lid, and laser sealing was performed on the sealing plate.

The electrolytic solution is a mixed solvent of ethylene carbonate (EC) and diethylene carbonate (DEC) mixed at a mixing ratio of 1: 1 by volume. Lithium hexafluorophosphate (LiPF
6) dissolved at a concentration of 1 mol / dm3 was used. The battery having the above configuration is referred to as battery A.

The battery A was subjected to a charge / discharge cycle test under a 20 ° C. environment at a constant current of 1 mA / cm 2 within a voltage range of 4.3 V to 3.0 V.

(Example 2) A battery B having the same structure as the battery A except that four current collecting leads of the positive electrode are joined is referred to as a battery B.

The battery B was subjected to a charge / discharge cycle test at a constant current of 1 mA / cm 2 at a constant current of 1 mA / cm 2 in a voltage range of 4.3 V to 3.0 V, similarly to the battery A.

(Example 3) A battery having the same structure as the battery A except that three current collecting leads of the positive electrode are joined is referred to as a battery C.

The battery C was subjected to a charge / discharge cycle test at a constant current of 1 mA / cm 2 in a voltage range of 4.3 V to 3.0 V under the environment of 20 ° C. in the same manner as the battery A.

(Comparative Example 1) A positive electrode plate having an uncoated portion continuously on one side edge of the positive electrode in the length direction was prepared, and compression molding was performed with the uncoated portion. Battery was created. In this configuration, a mixture stripping step for lead bonding is unnecessary, and the lead can be directly bonded to the uncoated portion.
However, when the electrode plate is subjected to high compression to form a mixture density of about 2 g / cc or more, the electrode plate extends, so that wrinkles and cracks are formed at the boundary between the mixture-coated portion and the uncoated rear portion. Therefore, in order to obtain the same final mixture film thickness of 0.18 mm as that of the battery A, the mixture was applied so that the total active material loading on both surfaces of the positive electrode became 580 g, and the mixture density was 2 g / cc. Compression molding was performed using the same press roll as that for Battery A so that the agent film thickness W was 0.18 mm. After cutting to a state where the mixture-coated part width was 300 mm and the uncoated part width was continuously 15 mm on one side edge, five aluminum leads were ultrasonically bonded to the uncoated part in the same manner as the battery A. . The filling capacity of this positive electrode is 64 Ah by a 0.74 electron reaction.

The other configuration is the same as the battery A. This battery is referred to as a battery D. This battery D is the same as battery A at 20 ° C.
A charge / discharge cycle test was performed at a constant current of 1 mA / cm2 in a voltage range of 4.3 V to 3.0 V under the environment described above.

(Comparative Example 2) A battery E having the same structure as the battery A except that two current collecting leads of the positive electrode are joined is referred to as a battery E.

The battery E was subjected to a charge / discharge cycle test at a constant current of 1 mA / cm 2 at a constant current of 1 mA / cm 2 in a voltage range of 4.3 V to 3.0 V, similarly to the battery A.

(Comparative Example 3) A battery having the same structure as that of the battery A except that one current collecting lead of the positive electrode is joined is referred to as a battery F.

The battery F was subjected to a charge / discharge cycle test at a constant current of 1 mA / cm 2 at a constant current of 1 mA / cm 2 within a voltage range of 4.3 V to 3.0 V, similarly to the battery A.

FIG. 3 shows the relationship between the cycles of these batteries A to F and the discharge capacity. Battery D has a significantly smaller discharge capacity than A. This is because the active material filling amount cannot be increased due to the constitution. When the batteries A are compared with B, C, E, and F, the initial discharge capacity and the cycle characteristics are improved in the order of the batteries F <E <C <B <A. In the batteries E and F, the capacity is small and the cycle characteristics are deteriorated even though the amount of the positive electrode active material charged is the same as that of the battery A. These results show that the larger the number of leads, the better the current collecting property, the lower the current concentration near the leads, the more uniform the reaction over the entire surface of the electrode plate, and the higher the utilization rate and the lower the degradation rate of the active material. It is considered that this was achieved.

[0036]

As described above, as a method for manufacturing an electrode plate constituting a lithium secondary battery of the present invention, a mixture-coated electrode plate is formed on the entire surface, and after performing high filling by compression molding, a lead joint portion is formed. And a plurality of current collecting leads are joined to obtain a lithium secondary battery having high capacity and excellent characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical battery according to one embodiment of the present invention.

FIG. 2 is a development view of an electrode plate according to an embodiment of the present invention.

FIG. 3 is a diagram showing cycle characteristics of batteries A to F;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode current collector 3 Positive electrode current collecting lead 4 Negative electrode 5 Negative electrode current collector 6 Negative electrode current collecting lead 7 Separator 8 Case 9 Positive electrode column 10 Negative electrode column 11 Sealing plate 12 Filling port 13 Mixing agent peeling area 14 Current collecting lead

Continuing on the front page (72) Inventor Seiichi Uemoto 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Reference) 5H014 AA04 BB08 5H022 AA09 BB11 CC12 CC19 5H029 AJ01 AJ03 AK03 AL06 AL07 AM03 AM05 AM07 BJ02 CJ05 DJ07 HJ12

Claims (2)

[Claims] 1. A material capable of occluding and releasing lithium ions is used as a positive electrode active material and a lithium ion is used as a negative electrode active material. A mixture layer containing the active material and a binder serves as a current collector. A lithium secondary battery provided on a metal foil to be used, and a current collecting lead for leading a current to the outside is attached to the current collector, wherein the current collector is joined to the current collecting lead. A lithium secondary battery characterized in that a part is formed with a non-mixture part. 2. The lithium secondary battery according to claim 1, wherein a plurality of current collecting leads are attached.