JP3419393B2 - Non-aqueous electrolyte secondary battery, separator and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a separator for a highly safe non-aqueous electrolyte secondary battery and a practical method for manufacturing the separator.

[0002]

2. Description of the Related Art As a method of electrically isolating a positive electrode and a negative electrode of a non-aqueous electrolyte secondary battery, there are roughly classified a method using a separator and a method using a solid electrolyte.

Regarding the safety of the battery, the separator plays a role of preventing a short circuit between the positive electrode and the negative electrode at normal times, but as a function peculiar to the separator of the non-aqueous electrolyte secondary battery, the porous polyolefin separator or the like has a function. When the battery temperature rises remarkably due to an excess current due to an external short circuit, the porous separator is softened to become substantially non-porous so that no current can flow.

If the temperature of the battery rises even after shutdown, the separator melts and a large hole opens, resulting in a short circuit between the positive electrode and the negative electrode. (Hereinafter referred to as meltdown) At this time, the temperature is high, but it can be said that the safety is high. If the heat melting property is increased to enhance the shutdown function, the meltdown temperature becomes lower, and the safety is decreased. Solving this conflicting relationship has been a problem.

In order to solve this problem, many separators made of composite membranes having different functions have been proposed.
For example, there are a composite film composed of a heat resistant porous layer and a shutdown layer (JP-A 2000-100408), a composite film composed of a para-aramid resin layer and a thermoplastic polymer (JP-A-10-6453), and the like. In addition, a separator surface coated with a solid electrolyte (Japanese Patent Laid-Open No. 2000-195494) or a separator made of aramid fiber and polyvinylidene fluoride (Japanese Patent Laid-Open No. 11-3
39555).

[0006]

[Problems to be Solved by the Invention] Due to recent development competition, the capacity of non-aqueous electrolyte secondary batteries is increasing. This increase in capacity is partly due to improvements in the active material of the electrodes, but due to the structure of the battery, the volume of members other than the active material is reduced to reduce the substantial amount of active material in the battery. Has been done a lot. Therefore, the separator is becoming thinner and thinner. As the separator becomes thinner, the safety against short circuits and the like tends to worsen, but since the amount of the active material increases substantially, the requirement for safety increases conversely.

The above-mentioned conventional composite film has a problem in that it cannot be made thinner than a single-composition film, or if it is made thinner, the safety becomes lower than the required performance.

An object of the present invention is to solve the above problems and to provide a non-aqueous electrolyte secondary battery having a high capacity and excellent reliability by using a thin and highly safe separator.

[0009]

In order to solve the above problems, in the battery of the present invention, the separator used in the spirally wound electrode plate group is composed of a heat-resistant porous resin, a porous polyolefin and a gel polymer. The heat-resistant porous resin is arranged on the positive electrode side, and the gel polymer is arranged on the negative electrode side, with the porous polyolefin as the center.

With this multi-layered separator, it is possible to achieve high capacity and improved safety of the battery, even though the separator is thin in thickness. for that reason,
It is possible to provide a non-aqueous electrolyte secondary battery having high capacity and excellent reliability.

The separator of the present invention has a porous polyethylene layer (referred to as a PE layer) as a center, an aramid resin layer on one side, and a copolymer layer having a polyvinylidene fluoride structure in the repeating unit on the other side. (Hereinafter referred to as PVdF layer) is a separator for a non-aqueous electrolyte secondary battery. This aramid resin plays the role of a heat-resistant support at the time of abnormal temperature rise of the battery, and its preferable thickness is 2-3 μm.
Further, the PE layer plays a role of performing a shutdown function at the time of abnormal temperature rise of the battery, and its preferable thickness is 5 to 9 μm. The PVdF layer plays a role of protecting the negative electrode, and its preferable thickness is 2 to 3 μm. Therefore, the thickness of the entire separator is 9 to 15 μm.

Furthermore, the separator of the present invention is PE
A separator having a aramid resin layer on one side of the layer and a gel polymer (hereinafter referred to as PEO-based gel polymer) composed of a polymer having a polyethylene oxide structure in the repeating unit and an electrolytic solution on the other side. And These preferably have an aramid resin layer thickness of 2
The thickness of the PE layer is 5 to 9 μm, the thickness of the gel polymer that protects the negative electrode is 3 to 5 μm, and the thickness of the entire separator is 10 to 17 μm.

Next, the manufacturing method of the separator of the present invention is as follows.
A method for producing a separator, in which a PE film to be a support is manufactured, and then integrated with an aramid resin film, and then a copolymer (PVdF polymer) having a polyvinylidene fluoride structure in the repeating unit is coated on the PE side. is there. The completed separator is wound up and stored, and is unwound and used when forming the electrode plate group.

The method of manufacturing the separator of the present invention is
After producing a PE film as a support and further integrating it with an aramid resin film, a polymer having a polyethylene oxide structure in the repeating unit before three-dimensional crosslinking (PEO) on the PE side.
It is a method for producing a separator in which a precursor solution consisting of a (system macromer), a polymerization initiator and an electrolytic solution is coated and three-dimensionally crosslinked by heat or ultraviolet rays. The completed separator is protected by a PET film or the like and stored, and the PET film is peeled off and used when the electrode plate group is prepared.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and a separator. Consists of three layers of a heat resistant porous resin, a porous polyolefin and a gel polymer, with the porous polyolefin as the center, the heat resistant porous resin on the positive electrode side,
The non-aqueous electrolyte secondary battery is characterized in that the gel polymer is arranged on the negative electrode side. As the non-aqueous electrolyte prepared by dissolving the electrolyte salt in the positive electrode, the negative electrode and the non-aqueous solvent, conventionally known ones can be used. Among them, the porous polyolefin has a function of shutting off current and suppressing heat generation when the battery temperature abnormally rises due to an excess current due to an external short circuit. Heat resistant porous resin is
Even after the shutdown, even if the temperature of the battery rises for some reason and the porous polyolefin melts down, the insulating function of the separator is maintained. Furthermore, the gel polymer is integrated with the negative electrode,
It has the function of assisting the action of the heat-resistant porous resin to prevent thermal contraction of the separator even when the environmental temperature is abnormally high, and at the same time protecting the negative electrode and suppressing gas generation during high temperature storage.

If the gel polymer is used not on the negative electrode side but on the positive electrode side, the gel polymer is apt to be decomposed by oxidation when the positive electrode is at a high potential and is at a high temperature, which is not suitable. The heat resistant porous resin arranged on the positive electrode side is
Since it is strong against oxidative decomposition, the above-mentioned problems do not occur.

The invention according to claim 2 of the present invention is the non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-resistant porous resin is an aramid resin. Examples of the heat-resistant porous resin preferable for the non-aqueous electrolyte secondary battery according to claim 1 include resins having excellent heat resistance such as aramid resin, polyimide resin, polyamideimide, polyethersulfone, and polyetherimide. An aramid resin is particularly preferable from the viewpoint of producing a porous thin film.

The invention according to claim 3 of the present invention is the non-aqueous electrolyte secondary battery according to claim 1, wherein the porous polyolefin is porous polyethylene (PE) having a shutdown temperature of 120 to 140 ° C. It is a thing. Preferred porous polyolefins for the non-aqueous electrolyte secondary battery according to claim 1 include low density polyethylene, high density polypropylene, and a mixture of polyethylene and polypropylene. The lower the shutdown temperature, the higher the safety, but the lower the meltdown temperature. Therefore, as the central layer of the multilayer separator used in the battery of the present invention, it is particularly preferable that the shutdown temperature of the porous polyethylene is 120 to 140. Those at ° C.

The invention according to claim 4 of the present invention is the non-aqueous electrolyte secondary battery according to claim 1, wherein the gel polymer is a copolymer having a polyvinylidene fluoride structure in the repeating unit or in the repeating unit. It is intended to include a polymer having a polyethylene oxide structure. The main component of the gel polymer preferable for the non-aqueous electrolyte secondary battery according to claim 1 is a polymer having a polyethylene oxide structure in the repeating unit (PEO-based polymer), and a copolymer having a polyacrylonitrile structure in the repeating unit. (PAN-based polymer), copolymer having a polymethylmethacrylate structure in the repeating unit (PMMA-based polymer) and copolymer having a polyvinylidene fluoride structure (PVdF-based polymer)
However, PVdF-based polymers and PEO-based polymers are particularly preferable from the viewpoint of compatibility with the electrolytic solution and mechanical strength.

Particularly preferred PVdF polymers of the present invention include vinylidene fluoride and hexafluoropropylene (Vd
F-HFP) copolymer, vinylidene fluoride, trifluoromonochloroethylene (VdF-CTFE) copolymer, vinylidene fluoride, perfluoromethyl vinyl ether (VdF-
FMVE) copolymer.

Further, particularly preferable PEO-based polymers of the present invention include polyethers made of ethylene oxide (EO) polymers, polyethers made of ethylene oxide and propylene oxide (EO-PO) copolymers, diethylene glycol, Adipic acid (DEG-A
A) There is a polyester composed of a copolymer. It is preferable to introduce a functional group having a double bond into the terminal of these polymers, and it is more preferable that the functional group is modified with an acryloyl group or a methacrylate group.

The invention according to claim 5 of the present invention comprises a porous polyethylene layer (PE layer) as a center, an aramid resin layer on one side, and a copolymer having a polyvinylidene fluoride structure in the repeating unit on the other side. Which has a layer (PVdF layer) formed therein, wherein the thickness of the aramid resin is 2 to 3
The thickness of the PE layer is 5 to 9 μm, the thickness of the PVdF layer is 2 to 3 μm, and the thickness of the entire separator is 9 to 15 μm. It was used as a separator.

The aramid resin plays a role of a heat-resistant support at the time of abnormal temperature rise of the battery, but if the thickness of the aramid resin is less than 2 μm, it is difficult to form a uniform thin film, and when used in a lithium secondary battery, When the PE layer melts down, it is easily short-circuited. Further, if it is 4 μm or more, there is no problem in safety, and 10 μm or more may be used, but 3 μm or less is preferable from the viewpoint of high capacity of the battery and battery characteristics such as high rate discharge. The PE layer serves as a support for the entire separator. Further, when the temperature of the battery rises abnormally, it shuts down to prevent the reaction from proceeding. If the thickness of the PE layer is less than 5 μm, it is difficult to form a uniform thin film, the strength becomes extremely weak, and the shutdown function does not function sufficiently. Also 10μ
If it is at least m, there is no problem in terms of safety, and it may be at least 20 μm, but it is preferably at most 9 μm from the viewpoint of high capacity of the battery and battery characteristics such as high rate discharge. PVd
The F layer absorbs the electrolytic solution and swells, and the gel polymer (PV
It becomes a dF-based gel polymer) and has a role of protecting the negative electrode. The PVdF-based gel polymer serves as an endothermic substance at an abnormally high temperature of the negative electrode, and at the same time, delays the supply of an electrolytic solution or the like during an abnormal reaction to hinder the progress of the reaction. It also has the effect of reducing the amount of gas generated from the negative electrode during storage. PVdF
If the layer thickness is less than 2 μm, it is difficult to form a uniform thin film, the strength becomes very weak, and the protective function of the negative electrode fails to function sufficiently. If it is 4 μm or more, there is no problem in terms of safety, and 10 μm or more may be used.
From the viewpoint of increasing the capacity of the battery and the characteristics of the battery such as high rate discharge, it is preferably 3 μm or less.

The invention according to claim 6 of the present invention is a gel polymer (PEO) comprising a PE layer as a center, an aramid resin layer on one side, and a polymer having a polyethylene oxide structure in the repeating unit on the other side, and an electrolytic solution. System gel polymer), the aramid resin has a thickness of 2 to 3 μm, the PE layer has a thickness of 5 to 9 μm, and the gel polymer has a thickness of 3 to 5 μm.
A separator for a non-aqueous electrolyte secondary battery is characterized in that the thickness of the entire separator is 10 to 17 μm.

The action, effect and suitable thickness of the PE layer and the aramid resin are the same as in the invention described in claim 5. Like the PVdF gel polymer, the PEO gel polymer serves as an endothermic substance at an abnormally high temperature of the negative electrode, and at the same time, delays the supply of an electrolytic solution or the like during an abnormal reaction to hinder the progress of the reaction. Further, it also has an effect of reducing the amount of gas generated from the negative electrode during storage. If the thickness of the PEO-based gel polymer is less than 3 μm, it is difficult to form a uniform thin film, the strength becomes extremely weak, and the protective function of the negative electrode does not function sufficiently. If it is 6 μm or more, there is no problem in terms of safety, and 10 μm or more may be used.
From the viewpoint of increasing the capacity of the battery and the characteristics of the battery such as high rate discharge, the thickness is preferably 5 μm or less. The PVdF layer is slightly thicker than the PVdF layer because the electrolytic solution is already contained at the stage of the separator.

The invention according to claim 7 of the present invention is (1)
A porous polyethylene membrane (PE membrane) is produced, (2) one surface of the PE membrane is coated with an aramid resin, (3) the aramid resin is made porous, and further,
(4) A method for producing a separator in which the other surface of the PE film is coated with a copolymer (PVdF polymer) having a polyvinylidene fluoride structure in the repeating unit.

In the step (1), a polyethylene film having microporosity is produced by a conventionally known method such as a phase separation method or a stretch opening method.

In the step (2), the aramid resin is applied to the PE film in a solution state, and the PE film is subjected to solvent removal treatment for coating. The solvent is preferably a polar organic solvent. This polar organic solvent includes N-methyl-2-pyrrolidone (NM
P) etc.

The aramid solution is preliminarily mixed with several wt% of a chloride of an alkali metal or an alkaline earth metal for the later step (3).

In the step (3), the coated aramid resin layer is washed with water to remove chlorides of alkali metal or alkaline earth metal. At that time, the remaining polar organic solvent is also washed.

Regarding the step (4), the PE film is coated with the PVdF polymer in a solution state on the surface of the PE film on which the aramid resin is not coated,
Desolvation treatment is performed and coating is performed. The solvent is preferably a polar organic solvent. The polar organic solvent includes NMP and acetone.

The invention according to claim 8 of the present invention is (1)
A PE film is produced, and (2) one surface of the PE film is coated with an aramid resin, (3) the aramid resin is made porous, and (4) a third layer is formed on the other surface of the PE film. A separator was prepared by coating a precursor solution consisting of a polymer having a polyethylene oxide structure (PEO-based macromer), a polymerization initiator and an electrolytic solution in the repeating unit before the original crosslinking and three-dimensionally crosslinking by heat or ultraviolet rays. It is a thing.

The steps (1) to (3) are the same as those described in the embodiment of the present invention.

In the step (4), a precursor solution containing a PEO polymer, a polymerization initiator and an electrolytic solution is prepared. The polymerization initiator is preferably a photopolymerization initiator such as 2,2-dimethoxy-2-phenylacetophenone (DMPA) or a thermal polymerization initiator such as an organic peroxide or an azo compound. Then, the precursor solution is coated on the other surface of the PE film, and three-dimensionally crosslinked by heat or ultraviolet rays. This crosslinking reaction depends largely on the composition ratio of the precursor solution, but in the case of thermal crosslinking, the reaction rate and the reaction end time differ depending on the heating time and heating temperature conditions. Further, in the case of ultraviolet irradiation, the irradiation intensity also becomes a large factor. Further, in this manufacturing method, since the electrolytic solution is already contained as the gel polymer, in the case of thermal cross-linking, it is sandwiched between PET films to carry out thermal polymerization. In the case of UV irradiation, photopolymerization is carried out as it is, but immediately after crosslinking, immediately turn it into a battery assembly or P
Store in ET film.

[0035]

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

In order to evaluate the temperature change during overcharge of the battery of the present invention, a cylindrical battery described below was produced.

FIG. 1 shows a structural view (partially sectional view) of a cylindrical battery according to an embodiment of the present invention.

In FIG. 1, the non-aqueous electrolyte secondary battery 1 is
The positive electrode 2, the negative electrode 3, and the separator 4 are wound and incorporated in a case 5 together with a non-aqueous electrolyte (not shown) in which an electrolyte salt is dissolved in a non-aqueous solvent, and are sealed with a sealing plate 6. There is.

For the sealing plate, in a general commercial battery,
Although safety elements such as a safety valve and a PTC element are incorporated, in the battery of the embodiment, no safety mechanism is incorporated in the sealing plate 6 for the safety test.

The positive electrode 2 was prepared by mixing 10% by weight of carbon powder as a conductive agent and 5% by weight of polyvinylidene fluoride resin (PVdF resin) as a binder with 85% by weight of lithium cobalt oxide powder, and dehydrating NMP. To prepare a slurry, which is applied as a positive electrode current collector made of aluminum foil and dried,
It was made by rolling.

For the negative electrode 3, artificial graphite powder was used as the negative electrode active material, and the binder PVdF was added to 95% by weight of the artificial graphite powder.
5 wt% of a resin was mixed, and these were dispersed in dehydrated NMP to prepare a slurry, which was applied on a positive electrode current collector made of copper foil, dried, and then rolled.

The non-aqueous electrolyte used was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1 in which LiPF ₆ was dissolved at 1 mol / liter.

The cylindrical battery thus produced had a diameter of 18
mm and height 65 mm. This size, which is generally commercially available, has a design capacity of 1800 mAh, and the thickness of the separator 4 is generally 25 to 27 μm. The battery of this example has a higher capacity of 2200 m.
Ah was taken as the design capacity. For this reason, when the thickness of the separator 4 was 20 μm or more, the wound electrode plate group could not be reliably inserted into the case.

FIG. 2 shows an enlarged schematic diagram centering on the separator of the electrode plate group of the battery of the present invention.

The separator 4 is composed of three layers of a heat-resistant porous resin 4a, a porous polyolefin 4b and a gel polymer 4c, and the heat-resistant porous resin 4a is on the positive electrode 2 side with the porous polyolefin 4b as the center, and the gel polymer. 4c is arranged on the negative electrode 3 side.

Batteries of Examples and Comparative Examples described below were produced by changing the conditions only for the separator 4.

<Example 1> In this example, the heat-resistant porous resin 4a is an aramid resin or a porous polyolefin 4b.
A PE film was prepared as the above, and a PVdF gel polymer was prepared as the gel polymer 4c.

First, a PE film was manufactured by the method described below.

High density polyethylene (average molecular weight 150,000)
40 parts by weight and 60 parts by weight of liquid paraffin were melt-kneaded in a twin-screw extruder. A polymer gel sheet was produced by extrusion casting from a coat hanger die onto a cooling roll. The thickness was 0.9 mm at this point. This polymer gel sheet was stretched 8 × 8 times at 122 ° C. before extraction using a simultaneous biaxial stretching machine. Then, it was immersed in methylene chloride to extract and remove the liquid paraffin to form a PE film having a thickness of 8 μm, which was used as a support for the separator. When the shutdown temperature (SD temperature) of this separator was measured, it was 130 ° C.

Next, the surface of the PE film was coated with an aramid resin by the method described below.

In the reaction vessel, with respect to 100 parts by weight of NMP,
6.5 parts by weight of dried anhydrous calcium chloride was added and heated to completely dissolve. This calcium chloride added NMP
After returning the solution to room temperature, paraphenylenediamine (PP
3.2 parts by weight of D) were added and completely dissolved. The reaction tank was placed in a thermostat at 20 ° C., and 5.8 parts by weight of terephthalic acid dichloride (TPC) was added dropwise little by little over 1 hour to synthesize polyparaphenylene terephthalamide (PPTA) by polymerization reaction. After that, the mixture was left for 1 hour in a constant temperature bath, and after the reaction was completed, it was replaced with a vacuum bath, and degassed by stirring for 30 minutes under reduced pressure. The obtained polymerization liquid is further diluted with a calcium chloride-added NMP solution to obtain PP.
A PPTA solution having a TA concentration of 1.4% by weight was prepared.

A PPTA solution was thinly coated on a PE film with a bar coater and dried by heating at 60 ° C. to form an aramid resin layer made of PPTA to form a composite film. This composite membrane was washed sufficiently with pure water to remove calcium chloride, thereby making the aramid resin layer porous and dried. The film thickness of the aramid resin layer after drying was 2 μm.

Finally, the P of the composite film is prepared by the method described below.
The surface on the E side was coated with PVdF polymer.

In the reaction vessel, VdF-HFP (88: 1 having an average molecular weight of about 380,000) was added to 100 parts by weight of acetone.
2) Copolymer (Atofina Japan Kynar FL
10 parts by weight of EX 2801) was added and suspended, and 10 parts by weight of dibutyl phthalate (DBP) was added to this suspension and heated to completely dissolve. Then, it was aged at room temperature for several hours. This solution was thinly coated on the surface of the composite membrane on the PE side with a bar coater, and dried with dry air at room temperature. Dip the dried composite film in xylene to remove DB
After extracting P, it was dried under reduced pressure. The film thickness of the gel polymer layer after drying was 2 μm.

After temporarily storing the completed separator 4,
Assembled into batteries.

<Comparative Example 1> A PE film having a thickness of 8 μm and an SD temperature of 130 ° C. was prepared by the same method as the PE film preparation method of Example 1, and the separator 4 alone was prepared.

<Examples 2 to 7 and Comparative Examples 2 to 4>
Hereinafter, in the same manner as in Example 1, batteries of Examples 2 to 7 and Comparative Examples 1 to 4 made of a heat resistant porous resin, a porous polyolefin and a gel polymer as shown in Table 1 were produced.

[0058]

[Table 1]

Here, an aramid resin having a film thickness of 1 μm or less,
Porous polyethylene having a film thickness of 4 μm or less and PVdF-based polymer having a film thickness of 1 μm or less could not be produced.

<Embodiment 8> In this embodiment, an aramid resin and a porous polyolefin 4b are used as the heat resistant porous resin 4a.
A PE film was prepared as the above, and a PEO gel polymer was prepared as the gel polymer 4c.

First, in the same manner as in Example 1, the thickness is 8 μm.
m, an PE film having an SD temperature of 130 ° C. was prepared and used as a support for the separator.

Then, in the same manner as in Example 1, the surface of the PE film was coated with an aramid resin having a thickness of 2 μm.

Finally, the P of the composite film is prepared by the method described below.
The surface on the E side was coated with a PEO-based gel polymer.

EC and E in a reaction vessel under a dry air atmosphere.
1 mol / mL of LiPF _{6 in} a mixed solvent of MC with a volume ratio of 1: 1.
Polyethylene / polypropylene copolymer (Elexel TA-140 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), which is a trifunctional acrylate having an average molecular weight of about 8,000 and having an acryloyl group at the end, based on 90 parts by weight of the dissolved non-aqueous electrolyte.
Parts by weight were added and mixed. To this mixed solution, 0.1 part by weight of DMPA as a polymerization initiator was added and completely dissolved. This solution was thinly coated with a bar coater on the PE-side surface of the composite film in a dry air atmosphere. Further, in a dry air atmosphere, ultraviolet rays having an irradiation intensity of 7 mW / cm 2 were irradiated for 10 minutes to perform photocrosslinking. The thickness of the gel polymer layer at this time was 4 μm.

The resulting separator 4 was sandwiched between PET films and temporarily stored, and then assembled into a battery.

<Examples 9 to 14 and Comparative Examples 5 to 7
In the following, in the same manner as in Example 8, batteries of Examples 2 to 7 and Comparative Examples 1 to 4 made of a heat resistant porous resin, a porous polyolefin and a gel polymer as shown in Table 2 were prepared.

[0067]

[Table 2]

Here, an aramid resin having a film thickness of 1 μm or less,
Porous polyethylene having a film thickness of 4 μm or less and PVdF polymer having a film thickness of 2 μm or less could not be produced.

<Evaluation of Batteries> A total of 2 batteries were prepared.
One piece was evaluated by the method described below.

The designed capacity of the battery is 2200 mA.
First, a charging / discharging cycle in which the battery was charged at a constant current of 1100 mA to 4.2 V and then discharged at a constant current of 1100 mA to 3.0 V was repeated 10 times. The discharge capacity at the 10th cycle was used as the initial capacity of each battery. In addition, charge and discharge was performed in a constant temperature bath at 20 ° C. After that, each battery was charged to 4.2V with a constant current of 1100 mA, and further subjected to an overcharge test for 3 hours at a constant current of 1800 mA, and the surface temperature of the battery in this process was measured.
The maximum temperature reached by the battery was evaluated. These results are shown in Table 3.
Shown in.

[0071]

[Table 3]

As can be seen from Table 3, in the batteries of Examples, the abnormal temperature rise was suppressed even though the separator was thin. In the batteries of all the examples, current stopped flowing, and the shutdown function of the separator worked normally.

In the battery of Comparative Example 1, the shutdown function worked, but after that, meltdown occurred and a rapid temperature rise was exhibited. This is because the separator is thin because it is composed only of polyethylene, so meltdown has occurred.

In the batteries of Comparative Examples 2 and 5, the shutdown function worked, but the deformation of the batteries due to the generation of gas was large, so that a rapid temperature rise occurred. This was because the separator was too thick and the remaining space of the battery was small, so that a small amount of gas generation had a great influence.

In the batteries of Comparative Examples 3 and 6, the shutdown function did not work normally, and abnormal temperature rise of the batteries occurred. This was because the polyethylene shutdown temperature was too high.

In the batteries of Comparative Examples 4 and 7, abnormal temperature rise of the batteries occurred before the shutdown was completely completed.
This was because the polyethylene shutdown temperature was too low.

[0077]

As described above, according to the present invention, it is possible to enhance the safety of a non-aqueous electrolyte secondary battery under high temperature conditions even though a thin separator is used.

[Brief description of drawings]

FIG. 1 is a schematic view (partially sectional view) of a cylindrical battery used in an example of the present invention.

FIG. 2 is an enlarged schematic view of a main part of a cylindrical battery used in an example of the present invention.

[Explanation of symbols]

1 Non-aqueous electrolyte secondary battery 2 positive electrode 3 Negative electrode 4 separator 4a Heat resistant porous resin 4b Porous polyolefin 4c gel polymer 5 cases 6 sealing plate

Continuation of front page (56) Reference JP 2000-100408 (JP, A) JP 7-220761 (JP, A) JP 11-339555 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 2/16 H01M 10/40

Claims (8)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and a separator, wherein the separator is made of a heat-resistant porous resin, a porous polyolefin and a gel polymer. A non-aqueous electrolyte secondary battery comprising a layer, wherein the heat-resistant porous resin is arranged on the positive electrode side and the gel polymer is arranged on the negative electrode side, with the porous polyolefin as the center. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat resistant porous resin is an aramid resin. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the porous polyolefin is porous polyethylene having a shutdown temperature of 120 to 140 ° C. at which the porous polyolefin becomes substantially non-porous. 4. The non-aqueous solution according to claim 1, wherein the gel polymer contains a copolymer having a polyvinylidene fluoride structure in a repeating unit or a polymer having a polyethylene oxide structure in a repeating unit. Electrolyte secondary battery. 5. A separator comprising a porous polyethylene layer as a center, an aramid resin layer on one side and a layer made of a copolymer having a polyvinylidene fluoride structure in a repeating unit on the other side, which are integrated, The aramid resin has a thickness of 2 to 3 μm, and the polyethylene has a thickness of 5 to 9 μm.
m, the thickness of the layer made of a copolymer having a polyvinylidene fluoride structure in the repeating unit is 2 to 3 μm, and the thickness of the entire separator is 9 to 15 μm. Secondary battery separator. 6. A separator comprising a porous polyethylene layer as a center, an aramid resin layer on one side, and a thin film gel polymer consisting of a polymer having a polyethylene oxide structure in the repeating unit and an electrolyte solution on the other side, The thickness of the aramid resin is 2-3 μm, the thickness of the polyethylene is 5-9 μm, the thickness of the gel polymer is 3-5 μm, and the thickness of the entire separator is 10-1.
A separator for a non-aqueous electrolyte secondary battery, which has a thickness of 7 μm. 7. A porous polyethylene membrane is produced, and one surface of the porous polyethylene membrane is coated with an aramid resin, the aramid resin is made porous, and the other surface of the porous polyethylene membrane is further coated. , A method for producing a separator, which comprises coating a copolymer having a polyvinylidene fluoride structure in a repeating unit. 8. A porous polyethylene membrane is produced, one surface of the porous polyethylene membrane is coated with an aramid resin, the aramid resin is made porous, and the other surface of the porous polyethylene membrane is further coated. A method for producing a separator in which a repeating unit is coated with a precursor liquid comprising a polymer having a polyethylene oxide structure, a polymerization initiator, and an electrolytic solution, and three-dimensionally crosslinked by heat or ultraviolet rays.