JP2007149507A - Nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery in which a separator with a shut down function and a separator for maintaining electron insulating characteristics are provided, and which is superior in safety and has high reliability. <P>SOLUTION: This nonaqueous electrolyte secondary battery 10 includes a positive electrode plate 12, a negative electrode 11, the separator 13 for isolating the positive electrode plate 12 and the negative electrode plate 11, and the nonaqueous electrolyte. The separator consists of at least two layers of which the separator with the shut down function and the high heat resistant separator of the high heat resistance higher than that of the separator with the shut down function are overlapped without mutual adhesion. In this case, it is preferable that the width of the separator with the shut down function is larger than that of the high heat resistant separator, and furthermore, that as for the separator with the shut down function, the separator includes one of which the shut down temperature is ≤140°C, and that as for the high heat resistant separator, the separator includes one of which heat shrinkage factor at 150°C is ≤10%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery having excellent safety and high reliability including a separator having a shutdown function and a separator that maintains electronic insulation.

  With the rapid spread of portable electronic devices, the required specifications for the batteries used in them are becoming stricter year by year, and in particular, there is a demand for smaller, thinner and higher capacity. There are demands for excellent characteristics and stable performance. In the field of secondary batteries, lithium ion non-aqueous electrolyte secondary batteries, which have a higher energy density than other batteries, are attracting attention. The proportion of lithium ion non-aqueous electrolyte secondary batteries accounts for a significant increase in the secondary battery market. Is shown.

  By the way, in a device in which this type of non-aqueous electrolyte secondary battery is used, the space for accommodating the battery is often a square (flat box shape), so the power generation element is accommodated in a rectangular outer can. The formed rectangular non-aqueous electrolyte secondary battery is often used. An example of such a rectangular nonaqueous electrolyte secondary battery will be described with reference to the drawings.

  FIG. 1 is a perspective view showing a conventional rectangular nonaqueous electrolyte secondary battery cut in the longitudinal direction. The non-aqueous electrolyte secondary battery 10 accommodates a flat spiral electrode body 14 in which a positive electrode plate 12 and a negative electrode plate 11 are wound via a separator 13 inside a rectangular battery outer can 15. The battery outer can 15 is sealed with a sealing plate 16. The spiral electrode body 14 is wound so that the positive electrode plate 12 is exposed at the outermost periphery, and the exposed outermost positive electrode plate 12 is in direct contact with the inner surface of the battery outer can 15 that also serves as a positive electrode terminal. And are electrically connected. The negative electrode plate 11 is electrically connected to a negative electrode terminal 18 attached to the center of the sealing plate 16 via an insulator 17 via a current collector 19.

  Since the battery outer can 15 is electrically connected to the positive electrode plate 12, in order to prevent a short circuit between the negative electrode plate 11 and the battery outer can 15, the upper end of the spiral electrode body 14 and the sealing plate 16 The insulating spacer 20 is inserted between the negative electrode plate 11 and the battery outer can 15 so as to be electrically insulated. In this rectangular nonaqueous electrolyte secondary battery, after the spiral electrode body 14 is inserted into the battery outer can 15, the sealing plate 16 is laser welded to the opening of the battery outer can 15, and then from the electrolyte injection hole 21. It is produced by injecting a non-aqueous electrolyte and sealing the electrolyte injection hole 21. Such a rectangular non-aqueous electrolyte secondary battery has an excellent effect that there is little wasted space during use, and the battery performance and battery reliability are high.

As a positive electrode active material used for such a non-aqueous electrolyte secondary battery, high energy is obtained by combining a lithium composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ and a negative electrode made of a carbon material. It is known that a non-aqueous electrolyte secondary battery of density 4V class can be obtained. Of these, LiCoO ₂ is often used because various battery characteristics are superior to others. Further, as the negative electrode active material, carbonaceous materials such as graphite and amorphous carbon are generally used. In addition, the nonaqueous solvent (organic solvent) used in the nonaqueous electrolyte secondary battery must have a high dielectric constant in order to ionize the electrolyte, and must have high ionic conductivity over a wide temperature range. For this reason, lactones such as carbonates and γ-butyrolactone, and other organic solvents such as ethers, ketones and esters are used.

  It is known that the separator used for such a nonaqueous electrolyte secondary battery has a great influence on battery characteristics and safety. In other words, this separator needs to prevent the short circuit between the positive electrode and the negative electrode in a normal use state of the nonaqueous electrolyte secondary battery and maintain the battery voltage even in a high load state by suppressing the electrical resistance by the porous structure. However, when a large current flows through the nonaqueous electrolyte secondary battery due to an external short circuit or incorrect connection, etc., and the battery temperature rises, the non-porous state is maintained while maintaining the predetermined length and width dimensions. Therefore, there is a need for a shutdown function that suppresses an excessive temperature rise of the battery by increasing the electrical resistance and stopping the battery reaction. Therefore, as a separator for a non-aqueous electrolyte secondary battery, in addition to a microporous film mainly composed of polyethylene resin, a microporous film mainly composed of polyethylene resin and polypropylene resin are mainly composed to ensure further insulation. A multilayer film obtained by laminating and integrating microporous films is often used (see Patent Documents 1 to 3 below).

  As a manufacturing method of these separators, for example, in Patent Document 1 below, a laminated film having an inner layer containing polyethylene as an essential component and two outer layers composed of a polypropylene layer provided on both surfaces of the inner layer is obtained by a melt extrusion method. A method is disclosed in which a separator is produced by molding and making the laminated film porous by a stretch opening method.

  In Patent Document 3 below, high-density polyethylene and polypropylene are melt-kneaded together with liquid paraffin, and then extruded to form a film by an extruder equipped with a T-die. A microporous membrane containing polyethylene and polypropylene is produced by the phase separation method, and a polyethylene microporous membrane is produced by the phase separation method using high-density polyethylene and liquid paraffin, and polyethylene is formed on both sides of the polyethylene microporous membrane. And a method of producing a separator composed of a three-layer film by laminating a microporous film containing polypropylene and longitudinally stretching the film.

  In Patent Document 4 below, a separator breakage protective film made of polyphenylene sulfide (PPS) or a polyester film having a relatively high strength and having a through hole is provided for the purpose of preventing a short circuit inside the battery of the nonaqueous electrolyte secondary battery. An invention of a cylindrical organic electrolyte battery provided adjacent to a separator made of a polypropylene and polyethylene microporous membrane is disclosed, but the same separator as that of the prior art is used.

JP-A-8-244152 (claims, paragraphs [0006] to [0008], [0023] to [0034]) JP 2002-279956 A (Claims) JP 2002-321323 A (claims, paragraphs [0012], [0020] to [0021]) JP-A-5-335007 (Claims, FIG. 1)

  These conventional separators are separators formed by laminating and integrating at least a microporous membrane mainly composed of polyethylene resin and a microporous membrane mainly composed of polypropylene resin, and among these, a microporous membrane mainly composed of polyethylene resin. The film ensures shut-down at a low temperature and the microporous film mainly composed of polypropylene resin ensures high-temperature electronic insulation. However, with such a configuration, a high heat resistance microporous film is dragged due to shrinkage of the microporous film having a shutdown function for electronic insulation at high temperatures, and a high heat resistance microporous is also provided for shutdown performance. There is a problem that a sufficient shutdown function cannot be obtained at the contact surface between the membrane and the microporous membrane with a shutdown function, and the performance of the separator is still insufficient.

  Therefore, the inventors of the present application have conducted various studies to solve the problems of the above-described conventional separators, and as a result, the problems of the above-described conventional techniques are the microporous film having a shutdown function and the heat resistance. It was found that this was caused by laminating and integrating a highly microporous membrane, and the microporous membrane with a shutdown function and the highly heat-resistant microporous membrane were simply stacked without being laminated and integrated. The present inventors have found that the problem can be solved by combining them, and have completed the present invention.

  That is, an object of the present invention is to provide a highly reliable non-aqueous electrolyte secondary battery that is excellent in safety and includes a separator having a shutdown function and a separator that maintains electronic insulation.

  The above object of the present invention can be achieved by the following configurations. That is, the invention of the nonaqueous electrolyte secondary battery according to claim 1 is a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator separating the positive electrode and the negative electrode, and a nonaqueous electrolyte. The separator includes at least two layers in which a separator with a shutdown function and a high heat-resistant separator having higher heat resistance than the separator with a shutdown function are overlapped without being bonded to each other.

Examples of the positive electrode active material that can be used in the nonaqueous electrolyte secondary battery of the present invention include well-known Li _X MO ₂ and Li _x M ₂ O ₄ (where M is at least one transition metal such as Co, Ni, and Mn). ), That is, LiCoO ₂ , LiNiO ₂ , LiNiyCo _(1-y) O ₂ , LiMn ₂ O ₄ , LiMnO ₂ , or the like may be used singly or in appropriate combination. it can. Different elements such as Zr, Mg, Ti, and F may be added to the lithium transition metal composite oxide.

In particular, Li _a Co _(1-xyz) Zr _x Mg _y M _z O ₂ (where 0 ≦ a ≦ 1.1, x> 0, y> 0, z ≧ 0, 0 <x + y + z ≦ 0) .03, M = Al, Ti, an Sn. lithium-containing cobalt composite oxide represented _{by), Li b Mn s Ni t} Co u O 2 ( however, 0 ≦ b ≦ 1.2,0 <s ≦ 0.5, 0 <t ≦ 0.5, u ≧ 0, s + t + u = 1, 0.95 ≦ s / t ≦ 1.05)) When the positive electrode active material is used, a positive thermal active material with high thermal stability can be obtained. When used in combination with a carbon-based negative electrode active material, the charge voltage can be charged at a high voltage of 4.3 V to 4.5 V. This is preferable because a nonaqueous electrolyte secondary battery can be obtained.

  In addition, as a negative electrode active material that can be used in the nonaqueous electrolyte secondary battery of the present invention, carbonaceous materials such as natural graphite, artificial graphite, and amorphous carbon have a discharge potential comparable to lithium metal or lithium alloy. However, it is preferable because dendrite does not grow and has high safety, excellent initial efficiency, good potential flatness, and high density.

  Examples of organic solvents that can be used in the nonaqueous electrolyte secondary battery of the present invention include carbonates, lactones, ethers, and esters. Two or more of these solvents can be used in combination. Specific examples include carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, γ-valerolactone, γ-dimethoxyethane, tetrahydrofuran, 1,4-dioxane, diethyl carbonate, and the like. From the point of increasing charge and discharge efficiency, a mixed solvent of chain carbonates such as EC and DMC, DEC, EMC, etc. Are preferably used. Furthermore, since cyclic carbonates are generally oxidatively decomposed at a high potential, for example, when EC is contained in a non-aqueous electrolyte, the EC content is preferably 5% by volume or more and 35% by volume or less.

Further, as the electrolyte salt dissolved in the nonaqueous solvent, a lithium salt generally used in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof Illustrated. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. When charged with a high charging voltage, although aluminum is a current collector of the positive electrode is easily dissolved in the presence of LiPF _6, by LiPF ₆ decomposes, coating is formed on the aluminum surface, the aluminum by the coating Can be dissolved. Therefore, it is preferable to use LiPF ₆ as the lithium salt. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

  The invention according to claim 2 is the nonaqueous electrolyte secondary battery according to claim 1, wherein the width of the separator with a shutdown function is larger than the width of the high heat resistant separator.

  The invention according to claim 3 is the non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the separator with a shutdown function includes a separator having a shutdown temperature of 140 ° C. or less, and the high heat resistant separator is 150 The heat shrinkage rate at 10 ° C. is 10% or less.

  Furthermore, the invention according to claim 4 is the nonaqueous electrolyte secondary battery according to claim 3, wherein the separator with a shutdown function is a microporous membrane separator mainly composed of an olefin resin, and the high heat resistant separator is: A microporous membrane mainly composed of a resin selected from polypropylene resin, polytetrafluoroethylene resin and polyacrylamide resin or a non-woven fabric mainly composed of a resin selected from polyethylene resin, polyvinyl alcohol resin, polyacrylonitrile resin and aramid resin. It is characterized by that.

  By providing the above configuration, the present invention has the following excellent effects. That is, according to the invention according to claim 1, since the separator with the shutdown function and the high heat resistant separator are not bonded and integrated, the separator with the shutdown function has a large heat shrinkability, and conversely, the high heat resistant separator is Even though the heat shrinkability is small, even if the temperature of the nonaqueous electrolyte secondary battery rises, the high heat resistant separator is not dragged by the shrinkage of the separator with the shutdown function, and the shutdown function of the separator with the shutdown function is Since it is not affected by the high heat-resistant separator, it is possible to obtain a nonaqueous electrolyte secondary battery that maintains good electronic insulation at high temperatures and has very high safety.

  According to the invention of claim 2, the separator with the shutdown function has a large heat shrinkage, and conversely, the high heat resistance separator has a small heat shrinkage, but the width of the separator with the shutdown function is the width of the high heat resistance separator. Therefore, even if the temperature of the nonaqueous electrolyte secondary battery increases, the positive electrode and the negative electrode can be isolated by both the separator with a shutdown function and the high heat resistant separator. A non-aqueous electrolyte secondary battery that can be remarkably produced is obtained. In the invention according to claim 2, the difference between the width of the separator with a shutdown function and the width of the high heat-resistant separator is not critical because it varies depending on the size of the nonaqueous electrolyte secondary battery. In the case of a non-aqueous electrolyte secondary battery size generally used for equipment, a favorable effect is obtained if the thickness is 0.5 mm or more.

  According to the invention of claim 3, the upper limit of the shutdown temperature of the separator with the shutdown function is 140 ° C. in consideration of the heat resistance temperature of the surrounding parts used with the nonaqueous electrolyte secondary battery. Although the lower limit of the shutdown temperature is not critical, it is preferably 100 ° C. or higher because the shutdown function is too low and the overprotection state occurs. The more preferable shutdown temperature of the separator with a shutdown function is 130 ° C. or lower and 110 ° C. or higher.

  Further, according to the invention of claim 3, the heat shrinkage rate of the high heat resistant separator is preferably 10% or less at 150 ° C. in relation to the combination with the separator with a shutdown function, and the lower limit of the heat shrinkage rate is Although not a critical limit, 0% or more at 150 ° C. is preferable.

  According to the invention of claim 4, the microporous membrane separator mainly composed of olefin resin is used in many non-aqueous electrolyte secondary batteries as a separator with a shutdown function, and further, polypropylene resin, polytetrafluoro High heat-resistant separator made of non-woven fabric mainly composed of resin selected from ethylene resin, polyacrylamide resin mainly microporous membrane or polyethylene resin, polyvinyl alcohol resin, polyacrylonitrile resin, aramid resin Therefore, a non-aqueous electrolyte secondary battery that is safe and highly reliable can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using examples and comparative examples. The configuration of the nonaqueous electrolyte secondary battery used in this example and the comparative example is substantially the same as the conventional nonaqueous electrolyte secondary battery shown in FIG. The description will be given with reference. However, the examples shown below illustrate an example of a rectangular non-aqueous electrolyte secondary battery as a non-aqueous electrolyte secondary battery for embodying the technical idea of the present invention. The present invention is not intended to be specified as an example, and the present invention is equally applicable to a cylindrical nonaqueous electrolyte secondary battery and the like that have been variously modified without departing from the technical concept shown in the claims. It can be applied.

First, a specific method for manufacturing a non-aqueous electrolyte secondary battery common to Examples and Comparative Examples and a method for measuring various characteristics will be described.
[Production of positive electrode]
As a positive electrode mixture, 85 parts by mass of lithium cobaltate (LiCoO ₂ ), 5 parts by mass of graphite powder as a conductive agent, and 5 parts by mass of carbon black were sufficiently mixed. Thereafter, a vinylidene fluoride polymer as a binder dissolved in N-methyl-2-pyrrolidone (NMP) was mixed to a solid content of 5 parts by mass to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector (aluminum foil or aluminum alloy foil) having a thickness of 15 μm by a doctor blade method to form a positive electrode mixture layer on both surfaces of the positive electrode current collector. Subsequently, after drying, it was rolled with a roller press until a predetermined thickness was obtained, and then cut into a strip shape having a width of 44.5 mm to produce a positive electrode plate 12.

[Production of negative electrode]
A slurry was prepared by dispersing 95 parts by mass of graphite powder and 2 parts by mass of styrene-butadiene rubber (SBR) as a binder in water. This slurry was applied to both surfaces of a copper current collector having a thickness of 8 μm by a doctor blade method and dried to form active material layers on both surfaces of the negative electrode current collector. Then, it compressed using the compression roller and produced the negative electrode plate 11 whose length of a short side is 45.5 mm.

[Preparation of electrolyte]
A mixed solvent having 30% by volume of ethylene carbonate (EC) and 70% by volume of ethyl methyl carbonate (MEC) was prepared, and LiPF ₆ was dissolved therein to 1 mol / L to obtain an electrolyte.

[Production of battery]
As separators having a shutdown function, the thicknesses are all 16 μm, and as shown in Table 1 below, four kinds of A1 to A4 with different widths (short side lengths) and shad down temperatures are used. A polyethylene resin microporous membrane separator was prepared. In addition, as the high heat-resistant separator, all the thickness is 10 μm, the width (short side length) is all 46.5 mm, and the heat shrinkage rate at 150 ° C. is changed as shown in Table 2 below. A microporous membrane separator (B1 and B2) mainly composed of B and a microporous membrane (B3) mainly composed of polytetrafluoroethylene resin were prepared.

  Then, using the positive electrode plate 12 and the negative electrode plate 11 prepared as described above, the microporous membrane separators A1 to A4 and the high heat resistant microporous membrane separators B1 to B3 each having a shutdown function as the separator 13 are respectively shown in the following tables. 3 and Table 4 are used in combination, a separator 13 is disposed between the positive electrode plate 12 and the negative electrode plate 11, and the positive electrode plate 12 and the negative electrode plate 11 are insulated from each other by the separator 13 and are cylindrical. A cylindrical spiral electrode body was produced by spirally winding the core. Next, the cylindrical spiral electrode body was crushed with a press and formed into a shape that could be inserted into a rectangular battery outer can, and then the rectangular nonaqueous electrolytes of Examples 1 to 4 and Comparative Examples 1 to 5 were used. A secondary battery (thickness 5.5 mm × width 34 mm × height 50 mm) was produced. The design capacity of these nonaqueous electrolyte secondary batteries is all 900 mAh. These nonaqueous electrolyte secondary batteries were subjected to the heating test and overcharge test described below.

[Heating test]
First, each battery is charged at a constant current of 1 It (1C) = 900 mA at 25 ° C. After the battery voltage reaches 4.2 V, it is fully charged until it reaches 1/50 It at a constant voltage of 4.2 V, and then Each battery was left at 150 ° C. for 10 minutes or longer. A cell in which smoke or combustion did not occur during the first 10 minutes was marked with ◯, and a cell in which smoke or combustion occurred was marked with ×. In addition, smoke or combustion did not occur in the first 10 minutes, but the case where smoke or combustion occurred later was indicated by Δ. The results are summarized in Table 3 and Table 4.

[Overcharge test]
In the overcharge test, the battery was charged at a constant current of 1 It (1 C) = 900 mA until the battery voltage, which was far more severe than normal use conditions, reached 12V. During this period, the battery was not burned and ruptured, and the burned or ruptured battery was marked as x. The results are summarized in Table 3 and Table 4.

  Further, the results of Tables 3 and 4 are displayed in matrix so that the relationship between the combination of the microporous membrane separators A1 to A4 having the shutdown function and the high heat resistant microporous membrane separators B1 to B3 can be understood. Shown in

The results shown in Table 3 were as follows.
(1) The microporous membrane separator with shutdown function A1 alone (Comparative Example 1) burned after 20 minutes during the heating test, but it satisfies the conditions determined as good by the heating test result, and the overcharge test result is good It is.
(2) The high heat resistance microporous membrane separator B1 alone (Comparative Example 2) shows good heat test results but poor overcharge test results.
(3) When the microporous membrane separator A1 with shutdown function and the high heat resistant microporous membrane separator B1 are bonded together by pressure bonding (Comparative Example 3), both the heating test result and the overcharge test result are inferior.
(4) When the microporous membrane separator A1 with shutdown function and the high heat-resistant microporous membrane separator B1 are simply overlapped (Example 1), both the heating test result and the overcharge test result are good.

  Then, it can be seen from the results shown in Table 3 that good thermal test results and overcharge test results can be obtained by simply overlaying the microporous membrane separator with shutdown function and the high heat resistant microporous membrane separator. In this case, the width of the microporous membrane separator A1 with a shutdown function is larger than the width of the high heat resistant microporous membrane separator B1.

The results shown in Table 4 were as follows.
(5) When the microporous membrane separator A1 with shutdown function and the high heat-resistant microporous membrane separator B1 are simply overlapped (Example 1), both the heating test result and the overcharge test result are good.
(6) When the microporous membrane separator A2 with the same width shutdown function and the high heat-resistant microporous membrane separator B1 were simply overlapped (Example 2), smoke was emitted after 30 minutes during the heating test. In this case, the condition to be judged as non-defective is satisfied, and the overcharge test result is also good.
(7) Microporous membrane separator A3 (shutdown temperature: 127 ° C.) with a shutdown function slightly higher than the microporous membrane separators A1 and A2 (shutdown temperature: 121 ° C.) with a shutdown function and a highly heat-resistant microporous membrane When the separator B1 was simply superimposed (Example 3), liquid leakage was observed in the overcharge test, but the conditions for determining good products in the overcharge test result were satisfied, and the heating test result was also It is good.
(8) Microporous membrane separator A4 with shutdown function (shutdown temperature: 142 ° C.) and a highly heat-resistant microporous membrane having a shutdown temperature much higher than that of microporous membrane separators A1 and A2 with shutdown function (shutdown temperature: 121 ° C.) When the separator B1 was simply overlapped (Comparative Example 4), the heating test result was good, but the overcharge test result was inferior.
(9) High heat-resistant microporous membrane separator B1 (150 ° C. heat shrinkage rate: 10%) and higher heat-resistant microporous membrane separator B2 (150 ° C. heat shrinkage rate: 22%) and shutdown When the microporous membrane separator with function A1 was simply overlapped (Comparative Example 5), the overcharge test result was good, but the heating test result was inferior.
(10) High heat-resistant microporous membrane separator B1 (150 ° C. heat shrinkage rate: 10%) and high heat-resistant microporous membrane separator B3 (150 ° C. heat shrinkage rate: 2%) and shutdown When the microporous membrane separator A1 with function is simply overlapped (Example 4), both the heating test result and the overcharge test result are good.

Then, the results shown in Table 4 show the following.
(A) The shutdown temperature of the microporous membrane separator with a shutdown function is preferably 140 ° C. or lower, and more preferably 130 ° C. or lower.
(B) Even if the separator width is the same width for both the microporous membrane separator with shutdown function and the high heat resistant microporous membrane separator, good results can be obtained. However, the microporous membrane separator with shutdown function has higher heat resistance. A better result is obtained when the thickness is 0.5 mm or more than the porous microporous membrane separator.
(C) The heat shrinkage rate at 150 ° C. of the high heat resistant microporous membrane separator is preferably 10% or less.

  In the above Examples 1 to 4, a non-aqueous electrolyte secondary battery using a separator composed of two layers in which a separator with a shutdown function and a high heat-resistant separator are bonded to each other as a separator was shown. If the attached separator and the high heat-resistant separator are overlapped without being bonded, the same effect can be obtained even when the multilayer is composed of two or more layers. In addition, if the heat shrinkage rate of the high heat-resistant separator at 150 ° C. is 10% or less, a non-aqueous electrolyte secondary battery with good heat test results and overcharge test results can be obtained. In addition to the microporous membrane separator mainly composed of polytetrafluoroethylene resin, the microporous membrane separator mainly composed of polyacrylamide resin, polyethylene resin, polyvinyl alcohol resin, polyacrylonitrile resin, aramid resin, etc. Nonwoven fabric separators can also be used.

It is a perspective view which cuts the square nonaqueous electrolyte secondary battery produced conventionally from the lengthwise direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Nonaqueous electrolyte secondary battery 11 Negative electrode plate 12 Positive electrode plate 13 Separator 14 Flat spiral electrode body 15 Rectangular battery outer can 16 Sealing plate 17 Insulator 18 Negative electrode terminal 19 Current collector 20 Insulating spacer 21 Electrolyte injection hole

Claims (4)

In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator separating the positive electrode and the negative electrode, and a non-aqueous electrolyte,
The separator is composed of at least two layers in which a separator with a shutdown function and a high heat-resistant separator having higher heat resistance than the separator with a shutdown function are stacked without adhering to each other. battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a width of the separator with a shutdown function is larger than a width of the high heat resistant separator.   3. The separator according to claim 1, wherein the separator with a shutdown function includes a separator having a shutdown temperature of 140 ° C. or lower, and the high heat-resistant separator includes a separator having a thermal shrinkage at 150 ° C. of 10% or less. Non-aqueous electrolyte secondary battery.   The separator with a shutdown function is a microporous membrane separator mainly made of an olefin resin, and the high heat-resistant separator is a microporous membrane mainly made of a resin selected from polypropylene resin, polytetrafluoroethylene resin, and polyacrylamide resin. 4. The nonaqueous electrolyte secondary battery according to claim 3, wherein the nonaqueous electrolyte secondary battery is made of a nonwoven fabric mainly composed of a resin selected from polyethylene resin, polyvinyl alcohol resin, polyacrylonitrile resin, and aramid resin.

Images