JPH09298054A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery in which workability in manufacturing the battery can be improved while improving shutdown characteristics and achieving high film breakage temperature. SOLUTION: A device is provided with a positive electrode 1 comprising lithium containing compound oxide, a negative electrode 2 comprising negative electrode material capable of storing and emitting metal lithium or lithium ion, a separator, and organic electrolyte. In this case, the separator 3 comprises a multi-layer structure comprising plural polyethylene fine porous films laminated with each other, and at least one polyethylene fine porous film has a different fusing point than that of the others.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous secondary battery provided with a positive electrode made of a lithium-containing composite oxide, a negative electrode using lithium as an active material, a separator, and an organic electrolytic solution.

[0002]

2. Description of the Related Art This type of battery has a high energy density, but on the other hand, when an external short circuit occurs, the following problems occur. That is, when an external short circuit occurs,
Since a large short-circuit current flows in the battery and Joule heat is generated, an abnormal temperature rise occurs in the battery. Therefore, there is a problem that the organic electrolytic solution and the electrode (particularly, the positive electrode) may react with each other to burn the organic electrolytic solution. Therefore, conventionally, when the temperature of the battery is abnormally increased, the separator made of the polyolefin microporous film is melted down and the pores are clogged, and the current is shut down to ensure safety. However,
When the temperature becomes higher than the meltdown temperature, there is a problem that the separator may rupture and an internal short circuit may occur, causing the organic electrolyte solution to burn.

Therefore, a microporous film made of polyethylene (hereinafter abbreviated as PE microporous film) and a microporous film made of polypropylene (hereinafter abbreviated as PP microporous film) are laminated (specifically, PP microporous film). A separator having a three-layer structure in which a PE microporous film is arranged between the porous films) has been proposed. With such a structure, it is possible to prevent the separator from rupturing due to the presence of the PP microporous film having a high melting point, and to shut down the current at a low temperature due to the presence of the PE microporous film having a low melting point.

[0004]

However, in the above-mentioned conventional structure, since the microporous membranes made of different materials are in close contact with each other, the interfacial strength between the microporous membranes becomes weak. Therefore, there are problems in the battery manufacturing process such that the microporous membranes are easily separated from each other and the workability is poor.

The present invention has been made in consideration of the above-mentioned conventional problems, and is a non-aqueous system capable of improving workability at the time of manufacturing a battery while improving shutdown characteristics and raising the film rupture temperature. The purpose is to provide secondary batteries.

[0006]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention is a positive electrode comprising a lithium-containing composite oxide, and stores and releases metallic lithium or lithium ions. In the non-aqueous secondary battery comprising a negative electrode using the substance to be obtained as a negative electrode material, a separator, and an organic electrolytic solution, the separator has a multilayer structure in which a plurality of polyethylene microporous membranes are laminated, and at least One polyethylene microporous membrane is characterized by having a different melting point from other polyethylene microporous membranes.

As described above, among the multi-layered polyethylene microporous membranes, if at least one polyethylene microporous membrane has a different melting point from other polyethylene microporous membranes, the presence of the polyethylene microporous membrane having a high melting point The separator can be prevented from rupturing and the current can be shut down at a low temperature due to the presence of the polyethylene microporous film having a low melting point.

In addition, since the microporous membranes made of the same material are in close contact with each other, the interfacial strength between the microporous membranes becomes strong. Therefore, the microporous membranes are unlikely to peel off from each other, and the battery can be easily manufactured.

According to a second aspect of the present invention, in the first aspect of the invention, the separator comprises a three-layer polyethylene microporous membrane, and the polyethylene microporous membrane in the central portion is formed of the polyethylene microporous membrane. It is characterized by having a lower melting point than the polyethylene microporous membrane on the outside.

With such a construction, the outer polyethylene microporous membrane is more excellent in heat resistance, so that the separator shape can be sufficiently maintained even when the central polyethylene microporous membrane is melted down. There is.

According to a third aspect of the present invention, in the invention of the second aspect, the melting point of the polyethylene microporous membrane in the central portion is 140 ° C. or higher and 200 ° C. or lower, and the melting point of the outer polyethylene microporous membrane is 100 ° C. or higher. It is characterized by being less than 140 ° C. With such a configuration, the action of claim 2 is further exerted.

The positive electrode material (active material) is LiC.
oO_Two, LiNiO_Two, LiMnO _Two, LiFeO_TwoBut
Is exemplified. Further, as the negative electrode material, metallic lithium or
Is an alloy and carbon material that can store and release lithium ions
Is exemplified.

Further, as the electrolytic solution, ethylene carbonate is used.
, Vinylene carbonate, propylene carbonate
Organic solvents such as these and dimethyl carbonate, di
Ethyl carbonate, 1,2-dimethoxyethane, 1,
2-diethoxyethane, ethoxymethoxyethane, etc.
As a mixed solvent with a low boiling point solvent, LiPF₆, LiCl
O _Four, LiCF_ThreeSO_ThreeAn example is a solution in which a solute such as
Is shown.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a cross-sectional view schematically showing the non-aqueous secondary battery of the present invention. The present invention battery of FIG. 1 is made of LiCoO ₂
A positive electrode 1 made of graphite, a negative electrode 2 made of graphite, a separator 3 separating these electrodes, a positive electrode lead 4, a negative electrode lead 5,
It comprises a positive electrode external terminal 6, a negative electrode can 7 and the like. The positive electrode 1 and the negative electrode 2 are housed in a negative electrode can 7 while being wound in a spiral shape via a separator 3, and then an electrolytic solution is injected into the negative electrode can 7. The negative electrode 2 is connected to the positive electrode external terminal 6 via the lead 4 and the negative electrode 2 is connected to the negative electrode can 7 via the negative electrode lead 5 so that chemical energy generated inside the battery can be taken out as electric energy to the outside. The electrolytic solution used was a solution of LiPF ₆ as a solute dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a rate of 1 mol / liter.

Here, as the separator 3, a laminate of three polyethylene microporous membranes was used. Of these polyethylene microporous membranes, the two polyethylene microporous membranes located on the outer side have a higher melting point than the polyethylene microporous membrane sandwiched between these polyethylene microporous membranes. Specifically, the outer polyethylene microporous film had a melting point of 180 ° C., and the central polyethylene microporous film had a melting point of 130 ° C.
Further, the thickness of each blend polymer microporous membrane is about 8 μm.

Such a separator 3 was prepared by placing a polyethylene microporous membrane having a low melting point between polyethylene microporous membranes having a high melting point, and then heating the polyethylene microporous membrane at a temperature not higher than the melting point of the polyethylene microporous membrane.

The number of polyethylene microporous membranes is 3
The number of sheets is not limited to two, and may be two or four or more. Further, the structure of the polyethylene microporous film is not limited to the structure in which the polyethylene microporous film having a low melting point is disposed between the two polyethylene microporous films having a high melting point. It may have a structure in which a polyethylene microporous film having a high melting point is arranged between the polyethylene microporous films. However, with the former structure, the outer polyethylene microporous membrane has better heat resistance,
Even if the polyethylene microporous film in the center is melted at the meltdown temperature, the separator shape can be sufficiently maintained.

In addition, as a method of changing the melting point temperature of the polyethylene microporous membrane, there is a method of changing the molecular weight of the polyethylene microporous membrane.

[0020]

EXAMPLE An example of the present invention will be described in more detail with reference to FIGS.

(Example 1) As the non-aqueous secondary battery of the example, the battery shown in the embodiment of the present invention was used. The battery having such a structure is hereinafter referred to as Battery A1 of the invention.

Example 2 The structure is the same as that of the battery of Example 1 except that the outer polyethylene microporous film having a melting point of 160 ° C. is used. The battery having such a structure is hereinafter referred to as Battery A2 of the invention.

(Comparative Example 1) As a separator, a microporous membrane made of polyethylene (single layer, melting point: 130 ° C.)
The structure is similar to that of the battery of Example 1 except that The battery having such a structure is hereinafter referred to as comparative battery X1.

(Comparative Example 2) As a separator, a microporous film made of polypropylene (a single layer, having a melting point of 160).
(° C.) is used, but the structure is similar to that of the battery of Example 1 above. The battery having such a structure is hereinafter referred to as comparative battery X2.

(Comparative Example 3) As a separator, one polypropylene microporous membrane (melting point 130 ° C) is arranged between two polypropylene microporous membranes (melting point 160 ° C) (that is, three layers). The structure is the same as that of the battery of Example 1 except that the structure) is used. The battery having such a structure is hereinafter referred to as comparative battery X3.

(Experiment 1) The above-mentioned batteries A1 and A2 of the present invention and comparative batteries X1 to X3 were used, and after the respective batteries were fully charged, the elapsed time and the change in battery temperature and current when externally shorted. The results are shown in FIGS. 2 to 6. The batteries A1 and A2 of the present invention are shown in FIGS. 2 and 3, and the comparative batteries X1 to X3 are shown in FIGS.

As is apparent from FIGS. 2 to 6, when the respective batteries are externally short-circuited, the present batteries A1 and A2 (see FIGS. 2 and 3) and the comparative batteries X1 and X3 (see FIGS. 4 and 6). ), After a few minutes, no current flows, and then the battery temperature gradually decreases. On the other hand, the comparative battery X2
(See FIG. 5) After several minutes (however, the battery A1
A2 and comparative batteries X1 and X3 require a little more time), but the battery temperature continues to rise after that. As a result, it was confirmed that smoking and ignition occurred in Comparative Battery X2.

This is because the central polyethylene microporous membrane completely melts down at about 130 ° C. in the present invention batteries A1, A2 and X3, and the entire separator completely melts down at about 130 ° C. in the comparative battery X1. As a result of no current flowing, the battery temperature does not rise above 130 ° C. On the other hand, it is considered that the comparative battery X2 does not completely melt down at 130 ° C., and further current flows, so that the battery temperature rises to 180 ° C. or higher and becomes the overreaction mode.

(Experiment 2) The battery A2 of the present invention was fully charged and then held in an atmosphere of 130 ° C., and the relationship between elapsed time and atmosphere temperature, battery temperature and battery voltage was investigated. The results are shown in Fig. 7. As is clear from FIG. 7, no rapid increase in the battery temperature was observed even after a long time, and it can be seen that no abnormality occurred in the battery. It is considered that this is because the separator does not rupture even after a long time, so that an internal short circuit of the battery does not occur. The fact that the separator did not break is apparent from the fact that there is no sudden drop in battery voltage.

Although not shown, the same experiment was carried out on the battery A1 of the present invention and the comparative batteries X1 to X3. As with the battery A2 of the present invention, the separator did not break even after a long time. Was confirmed.

(Experiment 3) The battery A2 of the present invention and the comparative battery X1 were fully charged and then held in an atmosphere of 150 ° C. to evaluate the relationship between the elapsed time and the ambient temperature, battery temperature and battery voltage. The results are shown in FIGS. 8 and 9, respectively. As is clear from FIG. 8, the present invention battery A2
Then, even after a lapse of a long time, no rapid rise in the battery temperature was observed, and it can be seen that no abnormality occurred in the battery. It is considered that this is due to the same reason as that shown in Experiment 2.

On the other hand, as is clear from FIG. 9, in the comparative battery X1, the battery voltage started to sharply decrease after about 45 minutes (when the ambient temperature reached 160 ° C.), and completely disappeared in about 57 minutes. It is recognized that it is 0V. From this, the rupture of the separator begins after about 45 minutes,
It can be seen that the separator completely ruptured in about 57 minutes, and as a result, the overreaction mode was entered and the battery temperature rapidly increased. In the comparative battery X1, it has been confirmed that the battery smokes and ignites due to a rapid increase in the battery temperature.

(Experiment 4) The above-mentioned batteries A1 and A2 of the present invention were fully charged and then held in an atmosphere of 170 ° C., and the relationship between elapsed time and atmosphere temperature, battery temperature and battery voltage was investigated. The results are shown in FIGS. 10 and 11, respectively. As is clear from FIG. 10, in the battery A1 of the present invention, no rapid increase in battery temperature was observed even after a long time, and no abnormality occurred in the battery. It is considered that this is due to the same reason as that shown in Experiment 2.

On the other hand, as is apparent from FIG. 11, in the battery A2 of the present invention, after about 30 minutes (at ambient temperature of 160 ° C.
Battery voltage started to drop suddenly from about 4
It is recognized that the voltage is completely 0 V in 8 minutes. From this, the rupture of the separator started after about 30 minutes, and the rupture of the separator was completely completed in about 48 minutes.
It can be seen that the battery temperature rises rapidly in the overreaction mode. In the battery A2 of the present invention, it was confirmed that the battery smokes and ignites when the battery temperature rapidly rises. From the above, it can be seen that it is preferable to use the outer polyethylene microporous film having a higher melting point in order to prevent the separator from rupturing and prevent the battery from smoking and igniting.

[0035]

As described above, according to the present invention,
The presence of the polyethylene microporous membrane with a high melting point can prevent the separator from rupturing, and the presence of the polyethylene microporous membrane with a low melting point can shut down the current at low temperature, and also enhances the interfacial strength between the microporous membranes. Therefore, the microporous films are less likely to be peeled from each other, and the battery is easily manufactured, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a non-aqueous secondary battery of the present invention.

FIG. 2 is a graph showing the relationship between the elapsed time at the time of an external short circuit, the change in battery temperature, and the current value in battery A1 of the present invention.

FIG. 3 is a graph showing the relationship between the elapsed time at the time of an external short circuit, the change in battery temperature, and the current value in battery A2 of the present invention.

FIG. 4 is a graph showing the relationship between the elapsed time at the time of an external short circuit, the change in battery temperature, and the current value in the comparative battery X1.

FIG. 5 is a graph showing the relationship between the elapsed time at the time of an external short circuit, the change in battery temperature, and the current value in the comparative battery X2.

FIG. 6 is a graph showing the relationship between the elapsed time at the time of an external short circuit, the change in battery temperature, and the current value in comparative battery X3.

FIG. 7 is a graph showing the relationship between the elapsed time and the ambient temperature, the battery temperature, and the battery voltage when the present invention battery A2 was held in an atmosphere of 130 ° C.

FIG. 8 is a graph showing the relationship between the elapsed time and the ambient temperature, the battery temperature, and the battery voltage when the present invention battery A2 was held in an atmosphere of 150 ° C.

FIG. 9 is a graph showing the relationship between the elapsed time and the ambient temperature, the battery temperature, and the battery voltage when the comparative battery X1 was held in the atmosphere at 150 ° C.

FIG. 10 is a graph showing the relationship between the elapsed time and the ambient temperature, the battery temperature, and the battery voltage when the battery A1 of the invention was held in an atmosphere at 170 ° C.

FIG. 11 is a graph showing the relationship between the elapsed time and the ambient temperature, the battery temperature, and the battery voltage when the present invention battery A2 was held in an atmosphere of 170 ° C.

[Explanation of symbols] 1: Positive electrode 2: Negative electrode 3: Separator

Claims (3)

[Claims] 1. A non-aqueous secondary battery comprising a positive electrode composed of a lithium-containing composite oxide, a negative electrode using a substance capable of occluding and releasing metallic lithium or lithium ions as a negative electrode material, a separator, and an organic electrolytic solution. In the above, the separator has a multilayer structure in which a plurality of polyethylene microporous membranes are laminated, and at least one polyethylene microporous membrane has a melting point different from that of other polyethylene microporous membranes. Secondary battery. 2. The separator is composed of a three-layer film of the polyethylene microporous film, and the polyethylene microporous film at the center has a lower melting point than the polyethylene microporous film on the outside sandwiching the polyethylene microporous film. The non-aqueous secondary battery according to claim 1. 3. The melting point of the polyethylene microporous membrane in the central portion is 140 ° C. or more and 200 ° C. or less, and the melting point of the outer polyethylene microporous membrane is 100 ° C. or more and less than 140 ° C. The non-aqueous secondary battery described.