JPH11121041A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the temperature change in a battery uniform and perform uniform charging/discharging for the whole battery by setting a battery case to an approximately ring shape constituted of an inner cylindrical wall and an outer cylindrical wall and by fitting the internal electrode body, which is formed by winding a positive electrode body and a negative electrode body into a spiral shape via a separator between both cylindrical walls. SOLUTION: A battery case 14 is set to a ring shape constituted of an inner cylindrical wall 15 and an outer cylindrical wall 16, a bottom plate 18 is integrally formed in one end between both cylindrical walls 15, 16, and a through hole 17 is formed in the central part, of the battery case 14. An internal electrode body 30 with approximately ring section which is formed by winding a positive electrode plate 11 and a negative electrode plate 12 into a spiral shape via a separator film 13 so as not to be in contact with each other is fittedly inserted between the both cylindrical walls 15, 16 of the battery case 14. Secondly, the electrolyte is fed in the inner electrode body 30, the other end of the open battery case 14 is tightly sealed so as to form the external output terminal, and the lithium secondary battery 10 is thus manufactured.

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 having excellent heat dissipation and a high output density, and more particularly to a high output lithium secondary battery suitably used for electric vehicles.

[0002]

2. Description of the Related Art In recent years, as the issue of global environmental protection has attracted worldwide attention, in order to halt the global warming phenomenon due to carbon dioxide, the use of fossil fuels has been urgently required. For vehicles that use fuel,
The development of hybrid vehicles that use both electric vehicles or gasoline or the like and electricity is being studied, and reduction of gasoline consumption by introducing them to the market is being studied.

Conventionally, lead-acid batteries have been used in automobiles as a power source for electrical equipment. However, lead-acid batteries have a low output despite the heavy weight of the batteries themselves, that is, because the output density is small. Since sufficient acceleration performance could not be obtained, the electromotive force voltage was low, and the discharge duration per unit weight was short, it was not suitable as a power supply for driving a motor of an electric vehicle. However, in the past, lead-acid batteries were used at the beginning of the development of electric vehicles because there were no other suitable secondary batteries.

[0004] In recent years, nickel-metal hydride batteries having a higher output density than lead storage batteries have been developed and put into practical use, and have been applied to electric vehicles, and have demonstrated excellent performance in practical use tests. . Furthermore, with the rapid improvement in performance of lithium secondary batteries, which have higher power density than nickel-metal hydride batteries, lithium secondary batteries have become the favorite power source for electric vehicle motor drives. Attention has been focused on its development and commercialization.

The basic characteristics of a lithium secondary battery, such as the battery voltage, largely depend on the positive electrode active material, and the electrode potential is high and the electric capacity is large. In particular, lithium stable oxides such as LiCoO ₂ and LiMn ₂ O ₄ are being studied.

On the other hand, the negative electrode active material has a large electric capacity (lithium ion capacity), a good charge / discharge cycle property, a high battery voltage, a flat charge / discharge characteristic, and a high packing density. It is required and mainly carbonaceous materials are used.

In addition, the electrolyte is an aprotic solvent that does not react with the electrode active material and particularly lithium, and is required to have a high dielectric constant and a low viscosity in order to be a high ionic conductive solution. As a substrate, a mixed solution to which various organic solvents are added is used.

Further, the electrolyte to be added to the selected electrolytic solution has a high solubility in the electrolytic solution in order to enhance ionic conductivity, exists as dissociated ions, and does not chemically react with the electrode active material and the like. A property for producing a stable electrolytic solution is required, and a Lewis acid salt such as LiPF ₆ , LiBF ₄ or LiAsF ₆ is preferably used.

As a structure of an internal electrode body of a lithium secondary battery using each of the above-mentioned members, a wound type shown in FIG. 2 is generally employed. This is because the ionic conductivity of a non-aqueous electrolyte used for a lithium secondary battery is about two orders of magnitude lower than the ionic conductivity of an aqueous electrolyte used for a conventional secondary battery. This is because, in order to obtain the same charge / discharge performance as a battery using an aqueous electrolyte, it is necessary to make the electrode thinner and increase the electrode facing area.

The internal electrode body 1 is configured such that a positive electrode plate 2 and a negative electrode plate 3 are wound via a separator 4 so that a large-area positive electrode plate 2 and the like can be stored in a metal cylindrical container.
In the case of such an internal electrode body 1, the number of lead wires 5 from each of the electrode plates 2 and 3 only needs to be at least one, and even if it is desired to reduce the current collecting resistance from each of the electrode plates 2 and 3, Since several leads are sufficient, the internal structure of the battery is not complicated, and there is an advantage that the battery can be easily assembled.

The internal electrode body 1 is housed in a metal cylindrical battery case so that each electrode plate and a lead wire do not come into contact with each other when a battery is manufactured. At this time, one of the electrode lead wires is connected to the battery case, and the battery case may be electrically connected to the external output terminal as a conductive path. Between body 1 and the inner surface of the battery case,
An insulating sheet is inserted.

[0012]

SUMMARY OF THE INVENTION A lithium secondary battery for an electric vehicle generally includes a large number of cells having a capacity of about 100 to 300 Wh connected in series and parallel, and a total of 10 to 30 cells.
Used as a unit of kWh size. here,
As described above, a lithium secondary battery for an electric vehicle is required to have a high output density in order to secure acceleration performance and the like.For example, a large capacity discharge during vehicle acceleration or a continuous discharge during operation is required. A rise in the internal temperature of the battery causes an increase in the resistance value of the electrode plate itself, the occurrence of poor contact between the electrode active material particles due to the expansion of the electrode plate, or the inhibition of lithium ion movement due to partial evaporation of the electrolytic solution. Because of this, the resistance value of the internal electrode body increases, and the output density decreases. Therefore, in order to increase the output density, when the material used is the same, the internal resistance is reduced, and further excellent heat dissipation is suppressed to suppress the rise in the battery temperature and the increase in the internal resistance. It becomes important.

However, in the above-described lithium secondary battery, since the internal electrode body 1 formed in a columnar shape is housed in a bottomed cylindrical battery case, heat dissipation during use of the battery is performed from the outer surface of the battery case. Will only be performed.
For this reason, the difference in charge / discharge performance occurs between the central portion and the outer peripheral portion in the same battery due to the accumulation of heat in the central portion of the battery, and when the output per unit area of the electrode plate is compared, the outer peripheral portion is closer to the central portion. Cannot be obtained.

[0014]

Means for Solving the Problems The present invention has been made to improve the output density of the above-described lithium secondary battery for electric vehicles. That is, according to the present invention, between the inner cylindrical wall and the outer cylindrical wall of the battery case having a substantially ring-shaped cross section having the inner cylindrical wall and the outer cylindrical wall, the positive electrode plate and the negative electrode plate have the separator film interposed therebetween. A lithium secondary battery having a structure in which a spirally wound internal electrode body is inserted so as not to contact with each other. Here, as the battery case used for the lithium secondary battery of the present invention, one made of aluminum and formed by impact molding is preferably used.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the lithium secondary battery according to the present invention, a sufficient heat radiation characteristic is secured over the entire battery, so that when the battery is used, a difference in temperature distribution in the battery is reduced, and the internal electrode plate is reduced. There is an advantage that good charge / discharge characteristics can be obtained as a whole and a large output can be obtained as a whole battery. Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

FIG. 1 is a sectional view showing an embodiment of the lithium secondary battery of the present invention. The battery case 14 used for the lithium secondary battery 10 has a double cylindrical structure having an inner cylindrical wall 15 and an outer cylindrical wall 16, that is, a substantially ring-shaped cross section, and has an inner cylindrical wall 15 and an outer cylindrical wall. A bottom plate 18 is integrally formed at one end between the walls 16, and the other end is open. Therefore, a through hole 17 is formed in the center of the battery case 14.

As will be described later, as the substrate of the positive electrode plate 11, an aluminum foil having excellent electrolytic solution resistance and electrochemical reaction resistance is used. Aluminum is also suitably used for the battery case 14. The aluminum battery case 14 is preferably manufactured by impact molding. This is because, if a double cylindrical structure shown in FIG. 1 is manufactured from two aluminum pipes having different diameters, the sealing at the end becomes complicated, resulting in a lack of reliability such as partial sealing failure. Also, if the cylinder bottom is formed at the same time as the cylinder wall by impact molding, the productivity is good and the production can be performed at low cost.

A positive electrode plate 11 and a negative electrode plate 12 are provided between an inner cylindrical wall 15 and an outer cylindrical wall 16 of the battery case 14.
Are wound in a spiral so that they do not contact each other via the separator film 13. Therefore, the positive electrode plate 1
In the case where only the internal electrode body 30 composed of the negative electrode 1, the negative electrode plate 12, and the separator film 13 is taken out of the battery case 14, the internal electrode body 30 is wound so that a cylindrical hollow portion is formed at the center. The turned internal electrode body 30 has a substantially ring-shaped cross section.

As the positive electrode plate 11, a material obtained by applying lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material and carbon powder to an aluminum foil having excellent electrochemical corrosion resistance with an electrolytic solution is preferably used. Since cobalt is generally expensive, it has lower battery characteristics such as electromotive force than LiCoO ₂ , but is inexpensive lithium manganate (LiM
n ₂ O ₄ ) can also be used. Ultimately, which cathode active material to use depends on the application of the battery, usage conditions,
It is determined by cost and the like.

Note that the carbon powder is added to impart conductivity to the positive electrode active material, and acetylene black, graphite powder, or the like can be used. In addition, it is preferable to use a high-purity material for the aluminum foil constituting the positive electrode plate 11 in order to prevent a decrease in battery performance due to corrosion due to an electrochemical reaction of the battery.

As the negative electrode plate 12, a material obtained by applying an amorphous carbonaceous material such as soft carbon or hard carbon or a carbonaceous powder such as natural graphite to a copper foil as an anode active material is preferably used. Here, as with the aluminum member used for the positive electrode, it is preferable to use a high-purity material for the copper foil used as the substrate of the negative electrode plate 12 in order to withstand corrosion caused by an electrochemical reaction.

As a material of the separator film 13, a material having a three-layer structure in which a lithium ion permeable polyethylene film having micropores is sandwiched between porous lithium ion permeable polypropylene films is preferably used. When the battery temperature rises, the polyethylene film softens at about 130 ° C. and the micropores are crushed to move lithium ions, which also serves as a safety mechanism that suppresses the battery reaction. Between the separator film 13 and the positive and negative electrode plates can be prevented by sandwiching the separator film 13 with polypropylene having a softening temperature higher than that of polyethylene.

In this way, the positive electrode plate 11 and the negative electrode plate 12 are
The inner electrode body 30 wound in a substantially ring-shaped cross section so that the inner electrode body 30 does not come into contact with each other, and further has a central portion forming a columnar cavity, is made of an aluminum battery case 1.
4 is inserted between the inner cylindrical wall 15 and the outer cylindrical wall 16.

At this time, in order to avoid direct contact between the internal electrode body 30 and the inner cylindrical wall 15 and the outer cylindrical wall 16 of the battery case 14, the separator film 13 wound together with the positive electrode plate 11 and the like is used. It is preferable to cover the surface of 30. Alternatively, the internal electrode body 3
An insulating sheet 19 may be inserted between the battery case 14 and the battery case 14. When the insulating sheet 19 is used, it is preferable that the insulating sheet 19 has the same heat resistance and electrolytic solution resistance as the separator film 13, so that a polymer mainly composed of polypropylene is generally suitably used.

When the internal electrode body 30 is inserted into the battery case 14, the internal electrode body 30 and the battery case 14
It is preferable that there is no gap between the internal electrode body 30 and the internal electrode body 30 in which a suitable compressive stress is applied from the battery case 14. By doing so, even when the battery temperature rises, it is possible to avoid the occurrence of poor contact due to expansion and contraction of the electrode active material particles, and to maintain the internal resistance of the battery at a low level.

In this manner, when the internal electrode body 30 is inserted into the battery case 14, the electrolytic solution is removed from the internal electrode body 3.
0, and then the other end of the open battery case 14 is hermetically sealed so as to form an external output terminal, thereby producing the battery of the present invention. Here, as the electrolytic solution, a suitable composition is selected in each case in consideration of the characteristics of the positive and negative electrode active materials, but generally, a mixed mixture obtained by adding diethyl carbonate, such as propylene carbonate to ethylene carbonate, is used. Add LiPF ₆ or LiBF ₄ to the solution
Is used.

Regarding the hermetic sealing of the battery case 14,
As shown in FIG. 1, in a part of the opening, a current collecting lead wire 21 connected to each of the positive electrode plate 11 or the negative electrode plate 12 is connected to output terminals 22 and 23 of the positive and negative electrodes,
Each of the output terminals 22 and 23 is connected to a ring-shaped bakelite plate 20.
Through the bakelite plate 20 and the battery case 14 via an insulator 24 such as polypropylene rubber. In addition,
The bakelite plate 20 used to seal the battery case 14 is provided with a pressure relief groove (pressure relief valve) 25 that releases the battery internal pressure when the pressure inside the battery rises abnormally.

With the above-described structure of the lithium secondary battery 10, the outside air passes through the through hole 17 of the battery case 14 so that heat is radiated, and the generation of a high-temperature temperature region in one battery is suppressed. Is done. Further, when air is blown into the through hole 17 by a fan or the like, the heat radiation from the through hole 17 can be more effectively performed.

As a result, uniform charging / discharging is performed over the entire internal electrode body 30, so that heat is conventionally trapped inside the battery to generate a large temperature distribution in the battery, and the output density decreases in a high temperature portion. However, the problem of not being able to obtain the originally required output density and the problem of the internal pressure being increased due to the evaporation of the electrolyte to release the pressure relief valve 25 and making the battery unusable are solved, and the output density is improved. Is done. Specifically, as shown in Examples described later, when the electrode plate area is 0.8 m ² (width 20 cm, length 4 m),
Although the output density of the conventional battery was about 300 W / kg, it was clarified that the output density of 600 W / kg was doubled by using the battery structure of the present invention.

By the way, since a lithium secondary battery has a higher voltage, a larger output density and a discharge capacity than a conventional lead storage battery or the like, overdischarge or overcharge occurs by mistake and the battery temperature rises rapidly. When the electrolyte in the battery evaporates and the battery explodes, there is a risk that not only the battery but also the surroundings may be seriously damaged. Therefore, in a lithium secondary battery, a current limiting device by mounting a current limiting element or forming a pressure contact, or, as described above, ruptures when the battery internal pressure reaches a predetermined pressure and releases the battery internal pressure to atmospheric pressure. A safety mechanism such as a pressure relief groove is provided.

In the lithium secondary battery of the present invention,
Needless to say, it is preferable to mount the above-mentioned safety mechanism. In addition, the inventors have previously reported Japanese Patent Application No. 9-317.
No. 75 and Japanese Patent Application No. 9-202963 propose various types of pressure relief mechanisms using low melting point metal members and metal foils, and these safety mechanisms are also mounted on the lithium secondary battery 10 of the present invention. It is possible. By mounting such a safety mechanism, the lithium secondary battery 10 of the present invention can be used.
Can improve the battery performance as well as improve the battery safety.

[0032]

Hereinafter, examples of the present invention will be described.
LiMn ₂ O ₄ as a positive electrode active material mixed with acetylene black for improving conductivity is applied to an aluminum foil to produce a positive electrode plate. On the other hand, as a negative electrode plate, soft carbon which is a negative electrode active material is used. Was applied to a copper foil. Here, the area of each electrode plate is 0.8 m
² (20 cm × 4 m). A non-woven fabric made of polypropylene is used as a separator, and the produced positive electrode plate and negative electrode plate are separated by the separator, so that the inner cylindrical wall 15 and the outer cylindrical wall 16 of the battery case 14 shown in FIG. A cylindrical wound body having a shape capable of being inserted therebetween was produced. Next, after inserting this cylindrical wound body into the battery case via a polypropylene sheet so as not to come into direct contact with the battery case 14, an electrolyte prepared by dissolving 1 mol% of LiPF ₆ in propylene carbonate (PC). And the battery case was sealed to produce a battery having the structure shown in FIG. In this battery, a pressure relief valve 15 as shown in FIG. 1 was formed, and its release pressure was 4 kg / cm ^2.
Set to.

The inner cylindrical wall 14 of the battery thus manufactured
A thermocouple for measuring the battery temperature was fixed to the through hole 17 side surface and the outer cylindrical wall 15 by an adhesive. These thermocouples were fixed at the center of the battery in the length direction. Hereinafter, the thermocouple provided on the inner cylindrical wall 14 is referred to as a thermocouple D, and the outer cylindrical wall 1
The thermocouple provided in 5 is referred to as a thermocouple C.

As a comparative example, a battery having a conventional structure was manufactured in comparison with the above-described battery according to the example of the present invention. The battery of this conventional structure is a thermocouple in which the cylindrical wound body of the conventional structure shown in FIG. 2 is coated with Teflon at the center of the core of the cylindrical wound body using the same material as that of the embodiment. (Hereinafter referred to as “thermocouple B”), and then a cylindrical wound body is inserted into a cylindrical battery case via a polypropylene sheet, and one end is sealed. It was fabricated by injecting and finally sealing the other end of the battery case. In addition, like the battery of the example, the battery of the comparative example also
A pressure relief valve that is released at a pressure of 4 kg / cm ² is provided at one end of the battery case, and a thermocouple B wire is taken out from the other end of the battery case that does not have a pressure relief valve. The outlet was sealed with resin to prevent the internal pressure from being released. Further, a thermocouple (hereinafter, referred to as “thermocouple A”) was fixed to the central portion in the length direction of the outer surface of the battery case with an adhesive.

The outer shapes of the batteries according to the example and the comparative example thus manufactured are both 50 mmφ × 250 mm, but in the battery of the example, the diameter of the battery is 8 m at the center of the battery.
It has a through hole of mφ. The charge / discharge test was performed by measuring the average voltage when the discharge rate was changed between 0.2 C and 7 C, and measuring the temperature rise change of each of the thermocouples A to D during the discharge. In the discharge test of the battery according to the example, the fan was cooled by blowing air through the through hole formed in the battery, and at this time, a windbreak wall was provided on the outer wall of the battery so that the fan did not blow air.

FIG. 3 is a graph showing measured temperature changes of the thermocouples A to D when the discharge rate is changed variously.
In the battery according to the embodiment of the present invention, the temperature change on the battery outer surface and the battery inner surface measured by the thermocouples C and D are almost the same, and the battery is discharged even when a large capacity discharge of 7 C is performed. The rise in temperature was kept below 40 ° C.

On the other hand, in the battery of the comparative example,
In particular, the temperature rise inside the battery measured by the thermocouple B increases as the discharge rate is increased, and shows a large temperature change at a discharge rate of 3C that was not measured in the example of 50 ° C. It can be seen that as the size increases, the temperature change outside the battery measured by the thermocouple A also increases. Further, in the battery of the comparative example, when the discharge rate was set to 3.2 C,
The pressure relief valve ruptured, making the battery unusable. This is considered to be mainly attributable to an increase in the internal pressure of the battery due to the vaporization of the electrolytic solution due to an increase in the internal temperature of the battery.

FIG. 4 is a graph showing the relationship between the discharge rate and the output density. Regarding the output density when the discharge rate is 3 C or less, almost the same characteristics are obtained in the batteries of the example and the comparative example, but in the battery of the comparative example,
When the discharge rate was 3.2 C, the pressure relief valve burst and the battery became unusable.
It stayed at 96 W / kg. On the other hand, in the battery of the example of the present invention, when the discharge rate was 7 C, the output density was 627 W / kg, which was about 2
Double power density could be obtained.

[0039]

As described above, according to the lithium secondary battery of the present invention, the temperature change in the battery is kept uniform,
Since the temperature does not become partially high, the partial evaporation of the electrolytic solution is suppressed, the rise in the internal pressure of the battery is suppressed, and uniform charging / discharging is performed over the entire battery. This makes it possible to discharge at a high discharge rate,
An excellent effect of obtaining a high output density, which could not be obtained conventionally, is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of an embodiment of a lithium secondary battery of the present invention.

FIG. 2 is a perspective view showing a structure of an internal electrode body of a conventional lithium secondary battery.

FIG. 3 is a graph showing the relationship between the battery discharge rate and battery temperature change according to the present invention and the prior art.

FIG. 4 is a graph showing the relationship between the discharge rate and the output density of batteries according to the present invention and the prior art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Lead wire, 10 ... Lithium secondary battery, 11 ...
Positive electrode plate, 12 negative electrode plate, 13 separator film, 1
4 ... battery case, 15 ... inner cylindrical wall, 16 ... outer cylindrical wall, 17 ... through hole, 18 ... bottom plate, 19 ... insulating sheet, 2
0: bakelite plate, 21: collecting lead wire, 22: positive output terminal, 23: negative output terminal, 24: insulator, 25:
Pressure relief groove (pressure relief valve), 30 ... internal electrode body.

Claims (2)

[Claims] 1. A positive electrode plate and a negative electrode plate contact each other via a separator film between the inner cylindrical wall and the outer cylindrical wall of a battery case having a substantially ring-shaped cross section having an inner cylindrical wall and an outer cylindrical wall. A lithium secondary battery having a structure in which a spirally wound internal electrode body is inserted so as not to be disturbed. 2. The lithium secondary battery according to claim 1, wherein said battery case is made of aluminum and is formed by impact formation.