JP2000277176A - Lithium secondary battery and method for using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery improved in safety in using, and a method for using the same by avoiding the occurrence of accidents such as explosion by quickly and precisely sensing heating of the battery. SOLUTION: This lithium secondary battery 50 uses an inner electrode body 1 comprising positive and negative electrode plates wound around the outer periphery of a core 13 via a separator and a nonaqueous electrolyte. A PTC element 21 is disposed inside the battery 50 as a temperature sensor while being insulated from the current path of the battery. Thus, heating of the battery is quickly and precisely sensed without causing an increase in internal resistance of the battery to avoid the occurrence of accidents such as explosion so as to enhance service safety remarkably.

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 in which the occurrence of an accident such as an explosion can be avoided by improving the safety of use by quickly and accurately sensing the heating of the battery, and a method of using the same. .

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as power batteries for portable electronic devices such as mobile phones, VTRs, and notebook computers. In addition, since lithium secondary batteries have a high energy density, not only the portable electronic devices but also electric vehicles (eg, electric vehicles, which are being actively spread as low-emission vehicles due to recent environmental problems). It is also attracting attention as a motor drive power supply for EVs or hybrid electric vehicles (HEVs).

In applications such as EV, 2
Although a high voltage such as 00 to 300 V is required, since the cell voltage of the lithium secondary battery is about 3.8 V on average, it is necessary to form a battery pack by connecting many cells in series. Here, even in a state where the assembled battery is configured, each cell is required to have a high output as one important characteristic in order to obtain a predetermined acceleration performance, a climbing performance, and the like. Often, it is necessary to discharge such a large current.

[0004] In addition, while electric components of general automobiles (gasoline-powered cars, etc.) such as power windows and car navigation systems tend to increase, there is a concern that conventional lead-acid battery batteries with a voltage of 12 V may have insufficient power. There is a demand for a higher voltage. If this attempt is made to increase the voltage by using a lead storage battery, the volume and weight of the lead storage battery will be increased by a factor of 3.5, which is a major problem in terms of space utility and fuel efficiency.

[0005] Therefore, studies have been made to use a lithium secondary battery as an automotive battery that replaces a lead storage battery. Here, a voltage 4 using a lithium secondary battery is used.
When a 2V battery (assembled battery) is mounted on a general automobile, it is estimated that, for example, a maximum current of 250 A flows when the engine is started.

[0006]

As described above, when a large current flows through a battery pack, the same amount of current flows through all the cells constituting the battery pack. At this time, it is conceivable that some cells are heated by Joule heat due to variations in capacity, output characteristics, and internal resistance of the cells. The maximum temperature at which a lithium secondary battery can be used stably is about 60 ° C at present,
The battery performance degrades at an accelerated rate due to heating, and in the worst case, an accident such as an explosion or fire of the battery is expected. Therefore, even one of the cells constituting the assembled battery,
For example, when the temperature reaches 60 ° C., some kind of alarm means for limiting charging and discharging of the battery pack is required.

[0007]

Means for Solving the Problems The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to monitor a battery temperature by mounting a temperature sensor inside a single battery, thereby enabling a battery to be monitored. An object of the present invention is to provide a lithium secondary battery that facilitates charge / discharge control of a battery and a battery pack.
That is, according to the present invention, there is provided a lithium secondary battery using a non-aqueous electrolyte and an internal electrode body obtained by winding a positive electrode plate and a negative electrode plate around a winding core via a separator.
A lithium secondary battery is provided, wherein the element is a temperature sensor and is disposed inside the battery while being insulated from a current path of the battery.

Here, as the PTC element, an element containing barium titanate as a main component is preferably used, but an element in which at least a part of barium is replaced with lead or strontium to adjust the Curie point is used. Is also preferred. Such a PTC element is preferably disposed in the through hole of the core and substantially in the center of the battery, and is bonded to the inner wall surface of the core using a resin having corrosion resistance to a non-aqueous electrolyte. It is preferable to dispose them. The present invention is preferably applied to a battery having a battery capacity of 2 Ah or more and a PTC element is provided.

According to the present invention, the following method is provided as a preferred method of using the above-described lithium secondary battery. That is, according to the present invention, the PTC element is insulated from the current path of the battery using the internal electrode body and the non-aqueous electrolyte obtained by winding the positive electrode plate and the negative electrode plate around the winding core via the separator. A method of using a lithium secondary battery disposed inside a battery, wherein a plurality of unit cells of the lithium secondary battery are connected in series to form an assembled battery, and at the same time, the PTC elements are connected to a current path. The use of a lithium secondary battery in which, in an insulated state, a rechargeable battery is formed by connecting in series to form a resistor circuit and monitoring a change in the resistance value of the resistor circuit to control charging and discharging of the battery pack. A method is provided.

[0010]

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In the lithium secondary battery of the present invention, as shown in FIG. 1, an internal electrode body 1 formed by winding a positive electrode plate 2 and a negative electrode plate 3 around the outer periphery of a core 13 via a separator 4 is preferably used. Positive electrode tabs 5 (hereinafter, referred to as “tabs 5”) as current collecting electrode leads are respectively provided at end portions in the width direction of the positive electrode plate 2 and the negative electrode plate 3, that is, near the end surfaces in the length direction of the internal electrode body 1. ) And a negative electrode tab 6 (hereinafter, referred to as “tab 6”).

The positive electrode plate 2 is formed by using a metal foil having good corrosion resistance to a positive electrode electrochemical reaction such as an aluminum foil or a titanium foil as a current collecting substrate, and forming a positive electrode active material layer on the surface of the current collecting substrate. It is made. In addition, a punching metal or a mesh (net) in which a plurality of holes are formed can be used as the current collecting substrate.

As the positive electrode active material, lithium manganate (LiMn ₂ O ₄ ) or lithium cobalt oxide (LiCoO ₂ )
₂ ) and lithium transition metal composite oxides such as lithium nickel oxide (LiNiO ₂ ) are suitably used, and preferably, fine carbon powder such as acetylene black is added as a conductive additive thereto. A slurry or paste prepared by adding a solvent, a binder, or the like to such a positive electrode active material powder is applied to the surface of the current collecting substrate using a roll coater method or the like,
The positive electrode plate can be manufactured by drying and pressing.

On the other hand, the negative electrode plate 3 can also be manufactured using the same method as the positive electrode plate 2. As the current collecting substrate of the negative electrode plate 3, a metal foil having good corrosion resistance to a negative electrode electrochemical reaction such as a copper foil or a nickel foil is preferably used. As the negative electrode active material, amorphous carbon such as soft carbon or hard carbon is used. A highly graphitized carbonaceous powder such as a synthetic material or artificial graphite or natural graphite is used.

As shown in FIG. 1, the positive electrode plate 2 and the negative electrode plate 3 thus manufactured are wound around the outer periphery of the core 13 via the separator 4 so that the positive electrode plate 2 and the negative electrode plate 3 do not come into contact with each other. By doing so, the internal electrode body 1 can be obtained. Here, the core 13 is preferably in the form of a pipe having a through hole in the length direction, and usually, the core 13 is preferably made of a material such as aluminum.

The separator 4 has a three-layer structure in which a lithium ion permeable polyethylene film (PE film) having micropores is sandwiched between porous lithium ion permeable polypropylene films (PP films). Is preferably used. This is because when the temperature of the internal electrode body rises, the PE film
It softens at 0 ° C., crushes the micropores, and also serves as a safety mechanism for suppressing the movement of lithium ions, that is, the battery reaction. By sandwiching the PE film between PP films having a higher softening temperature, even when the PE film is softened, the PP film retains its shape and prevents contact and short circuit between the positive electrode plate 2 and the negative electrode plate 3. In addition, it is possible to reliably suppress the battery reaction and ensure the safety.

At the time of this winding operation, tabs 5 and 6 are attached to the positive electrode plate 2 and the negative electrode plate 3, respectively. In order to attach the tabs 5 and 6, it is preferable that the positive electrode plate 2 and the negative electrode plate 3 have a portion where the current collecting substrate is exposed without forming the positive electrode active material layer and the negative electrode active material layer. As the tabs 5 and 6, foil-like tabs made of the same material as the current collecting substrates of the positive electrode plate 2 and the negative electrode plate 3 are preferably used. In this case, the tabs 5 and 6 and the current collecting board can be welded to each other face to face, and the contact resistance can be reduced.

The attachment of the tabs 5 and 6 to the current collecting board can be performed by using ultrasonic welding, spot welding, or the like. At this time, as shown in FIG. 1, when the tabs 5 and 6 are attached so that the tabs of one electrode are arranged on one end surface of the internal electrode body 1, contact between the tabs 5 and 6 can be prevented. Is preferred.

Now, in the lithium secondary battery using the above-described internal electrode body 1, in the present invention, the temperature sensor is disposed inside the battery while being insulated from the current path of the battery. The temperature sensor must have corrosion resistance to the electrolyte, and a temperature range in which the battery can operate normally.
It is preferable to use one whose electric characteristics and the like change near the boundary temperature between the temperature range where heating occurs and the charging and discharging of the battery must be stopped.

From such a viewpoint, it is preferable to use a PTC element as the temperature sensor. In particular, a sensor mainly containing barium titanate (BaTiO ₃ ) is preferably used. The PTC element containing BaTiO ₃ as a main component is based on the Curie temperature of BaTiO ₃ ceramic (about 120 ° C.).
The temperature switch is a kind of temperature switch in which the resistance rises by several orders of magnitude when the temperature exceeds (° C.). When the temperature falls, the resistance returns to the original small value, and can be used permanently. Also,
Since the PTC element is a contactless switch, it has excellent reliability and is inexpensive.

Therefore, the upper limit temperature of use of the cell is determined,
A PTC element having a Curie temperature that increases the resistance when the temperature of the cell rises above the set temperature may be used. During the production of BaTiO ₃ ceramic,
By substituting a part of Ba in BaTiO ₃ with lead (Pb) to raise the Curie point, or by substituting strontium (Sr) to lower the Curie point, PTC is reduced.
It is possible to adjust the switching temperature of the device.

It is preferable that the PTC element is disposed at the center of the battery where the temperature rises most easily when the temperature of the battery rises. Therefore, as shown in the sectional view of FIG.
The PTC element 21 is preferably disposed in the through hole of the core 13 and substantially at the center of the battery, that is, at the center of the core 13. Here, a resin 22 having corrosion resistance to a non-aqueous electrolyte, for example, in order to accurately detect the temperature by making the thermal coupling between the core 13 and the PTC element 21 dense and accurately fix the temperature in the battery, for example, Using polyimide varnish, P
It is preferable that the TC element 21 is adhered to the inner wall surface of the core 13 and disposed.

FIG. 2 shows that the PTC element 21 is
2 shows a form embedded in the core 13 and fixed inside the core 13, but a resin 2 is provided between the inner wall surface of the core 13 and the PTC element 21.
2 may be used for bonding and fixing.

As the lead wire 23 of the PTC element 21, a bare copper wire can be used, but it is preferable to use a Teflon-coated wire or the like in order to avoid electrical contact with the internal electrode body 1. The fixing of the PTC element 21 to the inside of the core 13 may be performed at any time before or after the operation of winding the positive electrode plate 2 or the like to manufacture the internal electrode body 1.
That is, when the internal electrode body 1 is inserted into the battery case,
It is sufficient that the PTC element 21 is attached.

The internal electrode body 1 thus manufactured is connected to the terminals for extracting current to the outside and the tabs 5 and 6, while the lead wire of the PTC element 21 is insulated from the current path. The battery can be manufactured by guiding the battery 23 to the outside of the battery, inserting and placing the battery in the battery case, impregnating the non-aqueous electrolyte, and sealing the battery case.

Here, it goes without saying that the shape of the battery case and the structure at the battery end are not particularly limited.
FIG. 3 is a cross-sectional view showing one embodiment of a battery 50 using the internal electrode body 1 provided with the PTC element 21. Battery 50
, The tabs 5 and 6 of the internal electrode body 1 are provided with a positive electrode internal terminal 74A (made of aluminum) and a negative electrode internal terminal
It is collectively connected to a rivet used as 4B (made of copper) by caulking. The positive electrode internal terminal 74A is joined to a positive electrode lid 71A made of aluminum, and a female screw-shaped positive external terminal 73A also made of aluminum is joined to the positive electrode lid 71A. In addition,
An electrolyte injection port 77 is provided below the positive electrode external terminal 73A so as to penetrate the positive electrode cover 71A.

The structure of the negative electrode is the same as that of the positive electrode,
A copper member is preferably used for all of the negative electrode internal terminal 74B, the negative electrode cover 71B, and the externally threaded negative electrode external terminal 73B. However, the electrolyte inlet 77 is not provided in the negative electrode lid 71B. Thus, the external terminals 73A and 73B of each pole
Are preferably designed to have complementary shapes so that they can be easily coupled to each other, because the series connection between the batteries 50 can be easily performed, which is preferable. In the battery 50, the battery 50 may be rotated to screw the negative external terminal 73B into the positive internal terminal 73A.

The lead wire 23 of the PTC element 21 is
Sensor terminals 75A and 75B formed on 1A and 71B
Connected to Here, since the lids 71A and 71B are made of metal and also serve as a current path as described above, the sensor terminals 75A and 75B are insulated from the lids 71A and 71B by the insulating members 76A and 76B. I have. There is no limitation on the shape of the sensor terminals 75A and 75B.
It is preferable that the structure be such that, when the two terminals are connected to each other, they do not come into contact with the current path of the battery of the other party, and the connection between the opposite sensor terminals is facilitated.

Projection 81 formed on battery case 72
After inserting the internal electrode body 1 connected to the internal terminals 74A and 74B of both positive and negative electrodes into the cylindrical battery case 72,
The battery case 72 is formed by drawing in the vicinity of both ends of the internal electrode body 1. And the battery case 7
The end face 2 is formed by caulking both ends of the battery case 72 by using a sealing material 82 made of an insulating material so as to prevent conduction between the battery case 72 and the lids 71A and 71B of the positive and negative electrodes. . Note that an insulating polymer film 79 is disposed between the internal electrode body 1 and the inner peripheral surface of the battery case 72.
As 9, it is preferable to use a porous film having air permeability.

To fill the non-aqueous electrolyte in the battery 50, the battery 50 is placed under a reduced pressure atmosphere with the electrolyte injection port 77 facing upward, and penetrates the electrolyte injection port 77 and the hollow portion of the core 13. Thus, the electrolyte injection nozzle is inserted into the bottom of the battery, a predetermined amount of the electrolyte is injected, and the internal electrode body 1 is sufficiently impregnated.
Unnecessary electrolytic solution can be easily discharged using a method of discharging the electrolytic solution with an electrolytic solution injection nozzle and sealing the electrolytic solution injection port 77 with a screw or the like. When performing such an electrolytic solution filling method, the PTC element 21 needs to be fixed to the inner wall of the core 13 so as not to close the through hole of the core 13.

Examples of the non-aqueous electrolyte include carbonate-based solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), and organic solvents such as propylene carbonate (PC), γ-butyrolactone, tetrahydrofuran, and acetonitrile. In a single solvent or a mixed solvent of solvents, L as an electrolyte
A non-aqueous electrolyte in which one or two or more lithium complex fluorine compounds such as iPF ₆ and LiBF ₄ or lithium halides such as LiClO ₄ are dissolved is preferably used.

Incidentally, when an abnormally large current flows due to an internal short circuit, an external short circuit, or the like, the battery temperature rises rapidly, the electrolyte evaporates, and the battery internal pressure suddenly rises in the lithium secondary battery. Various pressure relief valves are provided to prevent battery rupture accidents caused by rising. FIG. 3 does not show such a pressure relief valve,
The inventors have previously proposed various pressure relief valves (pressure release mechanisms) using V-shaped grooves and metal foils in Japanese Patent Application No. 10-165213. Such a pressure relief valve is suitably applied to the lithium secondary battery of the present invention.

Next, a method of controlling charging and discharging of a battery provided with the above-described PTC element will be described by taking a case where an assembled battery is formed as an example, but the method described below is, of course, applied to a single cell. Needless to say, it can be used for charge / discharge control, and it can also be used for abnormality monitoring of individual cells in a battery pack.

First, a plurality of cells are connected in series to form an assembled battery, and at the same time, a PTC
The elements are connected in series while being insulated from the current path to form a resistance circuit. In this way, the resistance value of the entire resistor circuit is constantly monitored in a manner independent of the charging and discharging of the battery pack. Then, when the resistance value of the entire resistance circuit becomes equal to or more than a predetermined reference value, it is determined that the battery is heated and an alarm is issued, or an operation stop signal is sent to the charge / discharge circuit of the battery pack. By doing so, the reliability of the battery pack can be improved.

At this time, by monitoring the resistance change of the PTC element in each unit cell at the same time as monitoring the entire resistance of the resistance circuit, it becomes easy to specify the unit cell that has caused the abnormal heating.

The above-described lithium secondary battery of the present invention
In consideration of its characteristics, it can be particularly preferably used as a unit cell constituting the assembled battery. For example, the above-described electric power source for driving a motor such as an EV or a battery of a general automobile can be used as an example of an application. However, the present invention is not limited to such a use. In addition, the PTC element may be provided for a battery having a large battery capacity, which may cause a serious accident if left unattended when a single cell is heated, specifically, a battery having a battery capacity of 2 Ah or more. preferable. However, it is needless to say that the present invention can be applied to a battery having a lower capacity.

Now, the present invention has been described with reference to the battery using the wound internal electrode body. However, the arrangement of the PTC element as such a temperature sensor is performed in a stacked type as shown in FIG. It is also possible to apply to a battery using the internal electrode body 7. The internal electrode body 7 is formed by alternately stacking a positive electrode plate 8 and a negative electrode plate 9 with a separator 10 interposed therebetween.

As shown in FIG. 5, a PTC element 21 is disposed at the center of a plate 24 made of resin or the like having a surface shape equivalent to that of the positive electrode plate 7 or the like, as shown in FIG. By inserting and leading the lead wire 23 of the PTC element 21 to the outside of the battery case, it becomes possible to use and use the same configuration as the battery 50 using the wound internal electrode body 1 described above.

Japanese Patent Application Laid-Open No. 7-220755 discloses a lithium secondary battery using a laminated internal electrode body, in which a PTC is provided on at least one electrode surface of a current collecting substrate.
A lithium secondary battery in which elements are superposed is disclosed. This structure is a structure in which the PTC element forms a part of the current path, and is completely different in form from the PTC element in which the PTC element is insulated from the current path as in the present invention.

That is, the PTC element provided in the lithium secondary battery disclosed in Japanese Patent Application Laid-Open No. 7-220755
The C element itself is used as a current limiting element for limiting the current flowing when the temperature becomes high. in this case,
Since the PTC element is a member constituting a part of the current path, an increase in the internal resistance of the battery cannot be avoided. The increase in the internal resistance of the battery causes a reduction in charge / discharge efficiency (an increase in heat generation) and a decrease in cycle characteristics.

On the other hand, the PTC element provided in the above-described lithium secondary battery of the present invention does not limit the current itself, but is used as a means for detecting an abnormal temperature of the battery. Therefore, since the PTC element is not a member constituting a current path, the internal resistance of the battery does not increase, and therefore, the charge / discharge efficiency and the like do not decrease. As is apparent from such a comparison, the invention disclosed in Japanese Patent Application Laid-Open No. 7-220755 and the present invention differ not only in form but also in the spirit and effect of the invention.

[0041]

As described above, according to the lithium secondary battery of the present invention, the PTC element as the temperature sensor is disposed at the center of the battery, which is insulated from the current path and has the highest temperature in the battery. Therefore, without increasing the internal resistance of the battery, it is possible to quickly and accurately sense the heating of the battery, to avoid occurrence of an accident such as an explosion, and to significantly improve the use safety. Further, by using the PTC element, it becomes possible to manufacture a battery at low cost and without lowering the productivity. Further, the present invention has excellent effects such as easy control of charging and discharging when a battery pack is formed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a general structure of a wound internal electrode body used for a lithium secondary battery.

FIG. 2 is a cross-sectional view illustrating an example of an arrangement of a PTC element on a core.

FIG. 3 is a cross-sectional view showing one embodiment of a battery structure suitably adopted for the lithium secondary battery of the present invention.

FIG. 4 is a perspective view showing a general structure of a laminated internal electrode body used in a lithium secondary battery.

FIG. 5 is a perspective view showing an embodiment of a plate on which a PTC element to be inserted and disposed in the laminated internal electrode body is disposed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Positive electrode tab, 6 ... Negative electrode tab, 7 ... Internal electrode body, 8 ... Positive electrode plate, 9 ... Negative electrode plate, 10 ... Separator, 11
... Positive electrode tab, 12 ... Negative electrode tab, 13 ... Core, 21 ...
PTC element, 22 resin, 23 lead wire, 24 plate, 50 battery, 71A positive cover, 71B negative cover,
72: battery case, 73A: positive external terminal, 73B: negative external terminal, 74A: positive internal terminal, 74B: negative internal terminal, 75A / 75B: sensor terminal, 76A / 76B ...
Insulating member, 77: electrolyte injection port, 79: insulating film,
81: Projection, 82: Sealing material.

Claims (7)

[Claims] 1. A lithium secondary battery using an internal electrode body and a non-aqueous electrolyte obtained by winding a positive electrode plate and a negative electrode plate around a core around a separator, wherein a PTC element is used as a temperature sensor. A lithium secondary battery, which is disposed inside a battery while being insulated from a current path of the battery. 2. The lithium secondary battery according to claim 1, wherein the PTC element contains barium titanate as a main component. 3. The lithium secondary battery according to claim 2, wherein at least a part of barium in the barium titanate is replaced with lead or strontium. 4. The lithium according to claim 1, wherein the PTC element is disposed in a through hole of the core and substantially in the center of the battery. Rechargeable battery. 5. The PTC element according to claim 1, wherein said PTC element is adhered to an inner wall surface of said core with a resin having corrosion resistance to said non-aqueous electrolyte.
The lithium secondary battery according to claim 1. 6. The lithium secondary battery according to claim 1, having a battery capacity of 2 Ah or more. 7. A PTC element is provided inside a battery in a state in which the PTC element is insulated from a current path of the battery by using an internal electrode body formed by winding a positive electrode plate and a negative electrode plate around a winding core via a separator and a non-aqueous electrolyte. A method of using a lithium secondary battery arranged, comprising: connecting a plurality of cells of the lithium secondary battery in series to form an assembled battery, and simultaneously insulating the PTC elements from a current path. A method for using a lithium secondary battery, comprising: connecting a series connection in a state to form a resistor circuit; and monitoring a change in the resistance value of the resistor circuit to control charging and discharging of the battery pack.