JP2000048794A - Separator for cell, and non-aqueous electrolyte cell using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a cell low in SD(shut-down) temperature, rapid in closing a hole, and excellent in mechanical strength. SOLUTION: In a separator for cell formed of a thermoplastic resin porous membrane, the shrinkage ratio in at least one direction of the porous membrane is set to be 2 to 40%, the porous membrane has at least one endothermic peak in a range of 110 to 150 deg.C through the differential scanning thermal analysis, and the porous membrane is set to shut off the ion transmission by the thermal shrinkage at the temperature lower than the endothermic peak temperature by 3 deg.C or under. In a cylindrical non-aqueous electrolyte cell using the separator, a laminate wound body in which the separator 3 is interposed between a positive electrode 1 and a negative electrode 2 is arranged in a negative electrode can 7 in which a non-aqueous electrolyte is poured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator and a non-aqueous electrolyte battery using the same.

[0002]

2. Description of the Related Art In recent years, various types of batteries have been developed and put to practical use with the development of electric appliances and electronic devices. Among them, for example, non-aqueous electrolyte batteries such as lithium primary batteries and lithium ion secondary batteries have high energy density and high output, and have low self-discharge, so that they are widely used for communication devices such as mobile phones. Have been.

[0003] Usually, a battery is made of a nonwoven fabric between its positive and negative electrodes.
By interposing a battery separator using a porous film or paper, a short circuit between the two electrodes is prevented.
Above all, in the non-aqueous electrolyte battery using an organic solvent as an electrolyte, a single-layer or multilayer porous membrane formed of a thermoplastic resin is used as a battery separator. The battery separator formed from such a thermoplastic resin porous membrane, due to the characteristics of its porous structure, normally allows ions to permeate to allow a battery reaction, reduces the electrical resistance between the two electrodes, and improves the power supply efficiency. Is increasing. On the other hand,
When an abnormal current is generated due to an erroneous connection or the like and the internal temperature of the battery rises, the separator is melted and deformed at a predetermined temperature, so that the pores of the porous film are closed and the porous structure changes from a porous structure to a nonporous structure. I do. For this reason, ion transmission is cut off, the electric resistance between both electrodes increases, and the battery reaction stops. As a result, a further increase in the temperature inside the battery is prevented, and the safety of the battery is ensured. Such a function of increasing the electric resistance and stopping the battery reaction is called a shutdown (SD) function, which is an important function for securing safety in the battery separator of the non-aqueous electrolyte battery. Have been.

Further, recently, since the battery capacity has been required to be further increased in the non-aqueous electrolyte battery and the like, further improvement in the SD function of the battery separator has been required from the viewpoint of safety improvement. It has been demanded. That is, the amount of heat generated at the time of abnormality increases with an increase in the battery capacity, and thus it is necessary to stop the battery reaction at a lower temperature than in the past.

To meet this demand, a battery separator formed from a porous membrane containing a low-melting polymer such as low-density polyethylene or low-molecular-weight polyethylene has been disclosed (JP-A-5-25305). This is to melt the porous film at a lower temperature by using the low melting point polymer, and to lower the nonporous temperature of the porous film. However, it is difficult to make such a low-melting polymer porous, and the production process is complicated. In addition, since the low-melting polymer has lower mechanical strength than the high-melting polymer, there is a problem that the mechanical strength of a battery separator made of a porous film made of the low-melting polymer is not sufficient. Therefore, when the separator is used in a battery, a short circuit between both electrodes may not be sufficiently prevented, so that it is difficult to obtain a highly safe battery.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a battery separator made of a porous membrane having a low SD temperature, rapidly closing pores, and having excellent mechanical strength, and safety using the same. It is to provide a non-aqueous electrolyte battery having a high density.

[0007]

In order to achieve the above object, a battery separator of the present invention is a battery separator formed from a thermoplastic resin porous membrane, and is left at 90 ° C. for 1 hour. In this case, the contraction rate (C) in at least one direction of the porous membrane represented by the following formula (1) is 2 to 4
0%, wherein the porous film has at least one endothermic peak by differential scanning calorimetry in the range of 110 to 150 ° C., and the porous film has a temperature higher than the endothermic peak temperature by 3%.
Blocks ion transmission by heat shrinkage at temperatures below ° C.

[0008]

C (%) = [(Lb−La) / Lb] × 100 (1) Lb: length of porous film before shrinkage La: length of porous film after shrinkage

As described above, the battery separator of the present invention differs from the conventional battery separator in the principle of expressing the SD function in that the pores of the porous membrane are closed by heat shrinkage. Therefore, since the battery separator of the present invention does not require a low-melting polymer, it has excellent mechanical strength and can be manufactured at low cost. Further, the battery separator of the present invention can sufficiently lower the SD temperature, has high heat resistance, and can quickly close the pores of the porous membrane. Therefore, the non-aqueous electrolyte battery using the battery separator of the present invention has high safety.

When the porous film is formed of a plurality of thermoplastic resins, the number of the endothermic peaks is plural. Therefore, it is sufficient that at least one of the plurality of endothermic peaks is within the above range. The ion permeation blocking temperature refers to a temperature at which the permeation of ions is blocked and the battery reaction stops when the porous membrane is disposed in an electrolytic solution.

In the battery separator according to the present invention, the shrinkage (C) is preferably in the range of 5 to 35%, particularly preferably in the range of 7 to 20%. If the shrinkage is less than 2%, the SD temperature may increase. If the shrinkage is more than 40%, the heat shrinkage of the porous film may be too large to expose the electrodes and cause a short circuit between the two electrodes.

In the battery separator of the present invention, the opening ratio of the porous membrane before shrinkage is in the range of 35 to 60%, and
It is preferable that the average pore diameter of the porous membrane before shrinkage in the shrinkage direction when left at 0 ° C. for 1 hour is in the range of 0.02 to 1.0 μm. The opening ratio is particularly preferably in the range of 40 to 55%, and the average pore diameter is particularly preferably in the range of 0.05 to 0.2 μm. If the average pore diameter or the opening ratio is smaller than the preferred range, ion permeability may decrease. If the average pore diameter or the aperture ratio is greater than the preferred range, pores may not be sufficiently closed due to heat shrinkage. The opening ratio is a ratio of the total opening area of the holes to the entire surface area of the battery separator.

In the battery separator of the present invention, the thermoplastic resin is preferably a polyolefin.

The non-aqueous electrolyte battery of the present invention is a non-aqueous electrolyte battery in which a battery separator is interposed between the positive and negative electrodes, and these are disposed in a can into which the non-aqueous electrolyte has been injected. The battery separator of the present invention is used as the battery separator. Since this battery uses the battery separator of the present invention, the battery is excellent in performance and safety. From the characteristics of the separator, for example, a lithium primary battery, a lithium ion secondary battery, or the like is preferable.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The battery separator of the present invention is formed of a thermoplastic resin porous film having the above-mentioned specific physical properties.

As described above, the thermoplastic resin is preferably a polyolefin, for example, polyethylene, polypropylene, poly-4-methyl-1-pentene, poly-1-butene and the like, and among them, particularly preferred. Are polyethylene and polypropylene.

The polyethylene is preferably a high-density polyethylene because of its excellent mechanical strength.

As the polypropylene, an isotactic polypropylene having high crystallinity is preferable because a porous structure is easily formed.

The thermoplastic resin is not limited to one type, and two or more types may be used in combination.

The porous film contains, in addition to the thermoplastic resin, other resins or various additives such as an antioxidant, an ultraviolet absorber, an antistatic agent, a colorant, and a flame retardant. Is also good. The content ratio is not particularly limited as long as the characteristics of the separator of the present invention are not hindered.

The thickness of the battery separator of the present invention is not particularly limited, and is usually in the range of 10 to 100 μm, preferably 20 to 70 μm, and its porosity is
Usually, it is in the range of 35-60%, preferably 40-55%. In addition, the said thickness and porosity can be measured by the method mentioned later, for example.

The battery separator of the present invention may have a single layer, but in the case of a multilayer structure, it is preferable that at least one layer is formed of the porous film.
It is particularly preferable to have a P) porous membrane and a polyethylene (PE) porous membrane. Examples of the combination of the porous films include a two-layer structure in which a PP porous film and a PE porous film are laminated, a three-layer structure in which a PP porous film is laminated on both sides of a PE porous film, and a PP porous film. Three-layer structure in which a PE porous membrane is laminated on both sides of a porous membrane

The battery separator of the present invention may be laminated with a porous film formed of a different material, a support layer of a nonwoven fabric, or the like, in addition to the porous film of the present invention.

The battery separator of the present invention is optimally used as a battery separator for a non-aqueous electrolyte battery, particularly a lithium primary battery, a lithium ion secondary battery or the like, due to its characteristics, but is not limited thereto. .

Next, the battery separator of the present invention can be manufactured, for example, as follows.

That is, first, the thermoplastic resin is extruded to produce a non-porous sheet. During the extrusion,
If necessary, for example, the above-mentioned other resins or various additives may be blended in an appropriate amount in advance.

The thickness of the non-porous sheet is preferably in the range of 15 to 150 μm, more preferably in the range of 25 to 100 μm, in consideration of the ease of operation in the stretching step performed after the extrusion molding.

The non-porous sheet may be subjected to a heat treatment, if necessary, prior to a subsequent stretching step.

Examples of the heat treatment method include a method of contacting the non-porous sheet with a heated roll or metal plate, a method of heating the non-porous sheet in air or an inert gas, and a method of heating the non-porous sheet in an inert gas. A method in which the core is wound into a roll and heated in a gaseous phase may be used. In the case where the non-porous sheet is wound into a roll around a core and heated in a gaseous phase, it is preferable that a release sheet is superimposed on the non-porous sheet and wound to prevent blocking. Examples of the release sheet include a polyethylene terephthalate sheet, a fluororesin sheet, and a paper or plastic sheet coated with a release agent such as a silicone resin or a fluororesin.

The temperature and time of the heat treatment are appropriately determined according to the heat treatment method and the like.
170 ° C., time 2 seconds to 50 hours. By performing the heat treatment, the crystallinity of the non-porous sheet is improved, and the formation of holes in the subsequent stretching step is facilitated, so that a porous film having a higher porosity can be obtained.

In the case of producing a porous film having a multilayer structure, for example, various non-porous sheets are separately prepared in the same manner as described above, and a laminate obtained by laminating these non-porous sheets is subjected to heat treatment, and thereafter, stretching or the like is performed. May be made porous. The combination of the non-porous sheets to be laminated is, for example, a PP sheet and a P sheet.
A combination such as a two-layer structure with an E sheet, a three-layer structure in which a PP sheet is arranged on both sides of a PE sheet, or a PE sheet is arranged on both sides of a PP sheet, is preferred.

The stretching method for making the non-porous sheet porous is not particularly limited. As shown below, a multi-stage stretching method in which stretching is performed at a low temperature and then at a high temperature is employed. Is preferred. The multi-stage stretching method is suitable for producing a porous film having a high porosity and a low electric resistance.

First, the above-mentioned non-porous sheet is usually subjected to -20 to 20.
The film is uniaxially stretched in a low temperature range of 60 ° C., preferably 0 to 50 ° C. (hereinafter referred to as “low temperature stretching”). Stretching temperature is-
If the temperature is lower than 20 ° C., the non-porous sheet may be broken during the stretching process, while if the stretching temperature is higher than 60 ° C., it may be difficult to make the sheet porous. The low-temperature stretching method is not particularly limited, and includes a conventionally known roll stretching method, tenter stretching method and the like.

The range of the stretching ratio in the low temperature stretching is as follows:
Although not particularly limited, it is usually 20 to 200%, preferably 30 to 100%. This low-temperature stretching ratio (M ₁ ) can be calculated from the following equation (2). In the following equation (2), L
₀ is the length before cold drawing, L ₁ is the length after cold drawing.

[0035]

M ₁ (%) = [(L ₁ −L ₀ ) / L ₀ ] × 100 (2)

Following the low temperature stretching, usually 90 to 1
Stretching is performed in a high temperature range of 30 ° C., preferably 110 to 128 ° C. (hereinafter referred to as “high temperature stretching”). The reason for setting the temperature at the time of high-temperature stretching to the above-mentioned temperature range is the same as the reason for setting the temperature range of the above-mentioned low-temperature stretching. The high-temperature stretching is usually performed in the same direction as the low-temperature stretching, but may be performed in another direction. Further, as a stretching method in the high-temperature stretching, a stretching method similar to the low-temperature stretching described above can be used.

The range of the stretching ratio in the high-temperature stretching is as follows.
Although not particularly limited, it is usually 10 to 500%, preferably 100 to 250%. This hot stretch ratio (M ₂ )
It can be calculated from the following equation (3). In the following equation (3),
L ₁ is the length after cold drawing (front high-temperature stretching), L ₂ is the length after hot drawing.

[0038]

M ₂ (%) = [(L ₂ −L ₁ ) / L ₁ ] × 100 (3)

The non-porous sheet is made porous by such a multi-stage stretching method. In the porous membrane obtained in this way, since the stress acting during the stretching treatment remains,
Shrinks when heated. If the contraction rate of the porous membrane when left at 90 ° C. for 1 hour is in the range of 10 to 40%, the porous membrane can be used as it is for the battery separator of the present invention. If the shrinkage is not in the above range, a heat shrink process is performed to adjust the shrinkage.

The heat shrinking treatment is preferably performed, for example, at a temperature lower by 12 to 20 ° C. than the high temperature stretching temperature, particularly preferably at 98 to 108 ° C.

The porous membrane of the present invention may be formed by, for example, mixing and extruding the thermoplastic resin and the agent to be extracted, followed by stretching, etc., in addition to the so-called dry film forming method described above. The film can be manufactured by a so-called wet film forming method in which the film is made porous by extracting and extracting the agent to be extracted from the film obtained by the above process with a solvent or the like.

The porous film produced by the wet film forming method also has a shrinkage of 10 to 40 when left at 90 ° C. for 1 hour, similarly to the porous film produced by the dry film forming method.
%, The porous membrane can be used as it is for the battery separator of the present invention. If the shrinkage is not in the above range, a heat shrink treatment is performed to adjust the shrinkage. The heat shrinking treatment in this case is appropriately determined depending on the kind of the thermoplastic resin and the like, but is preferably performed in a range of 100 to 125 ° C.

According to such a manufacturing method, the battery separator of the present invention can be manufactured.

Next, in the non-aqueous electrolyte battery of the present invention, the battery separator of the present invention is interposed between the positive electrode and the negative electrode, and these are disposed in a battery can into which the non-aqueous electrolyte is injected.

The positive electrode and the negative electrode are usually each formed of a current collector and a thin layer of each active material laminated thereon. The thickness of each of the electrodes is not particularly limited, and is usually 500 μm or less, preferably 5 to 300 μm.
Range.

As the current collector, generally, a metal having excellent conductivity can be used. For example, copper, aluminum, silver, S
US and the like. Among them, as the current collector used for the positive electrode, for example, aluminum, SUS or the like is preferable, and as the current collector used for the negative electrode, for example, copper is preferable.

The form of the current collector is usually appropriately determined depending on the form of the battery, but may be a sheet, a tape, a mesh or the like, and is preferably a sheet. The thickness is not particularly limited, and is usually 100 μm or less, preferably in the range of 5 to 50 μm.

The positive electrode active material in the positive electrode is not particularly limited, but, for example, a ceramic material can be used. Among them, for example, titanium, molybdenum,
Copper, niobium, vanadium, manganese, chromium, nickel, iron, cobalt or a composite oxide of lithium and the like with lithium, sulfide or selenide and the like, for example,
LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiC
_{oO 2, LiCrO 2, LiFeO 2} , LiVO 2 , and the like, other vanadium pentoxide, or the like can be used.

The negative electrode active material in the negative electrode is not particularly limited. For example, a carbon-based material, a lithium-based material, a tin oxide-based material, and the like can be used, and a carbon-based material is preferable.

The carbon-based material is preferably, for example, a graphite-based material, an amorphous carbon-based material, or the like.

As the lithium-based material, for example, lithium metal, lithium alloy and the like can be used. Examples of the lithium alloy include aluminum, lead, tin, indium, bismuth, silver, barium, calcium, mercury,
Binary, ternary or higher alloys of lithium with palladium, platinum, strontium or tellurium or the like are preferred, and those obtained by adding silicon, cadmium, zinc or lanthanum to these may be used as necessary.

Each of the electrodes can be manufactured by, for example, applying the active material to the current collector. In addition, each of the electrodes may be coated with, for example, a conductive material, a binder, or the like, as necessary, on the current collector together with each of the active materials. As the conductive material, for example, acetylene black, Ketjen black, graphite, or the like can be used. As the binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, styrene-butadiene rubber, or the like can be used.

In addition to the above, for example, a method of vapor-depositing or hot-dip each of the above-mentioned active materials on the above-mentioned current collector can be adopted as a method of producing each of the above-mentioned electrodes. Further, each of the active materials, for example, may be used as an electrode as it is formed into a sheet by various means such as rolling, extrusion, compression or the like, or when the active material is a metal, the metal foil may be used. The electrode may be used as it is.

The non-aqueous electrolyte is usually prepared by dissolving an electrolyte in an organic solvent, and the type is appropriately determined according to the battery to be manufactured. As described above, the non-aqueous electrolyte battery of the present invention is preferably a lithium battery, and for this reason, a non-aqueous electrolyte which allows lithium ions to move is preferable. Examples of the non-aqueous electrolyte include a solution in which a lithium salt as an electrolyte is dissolved in an organic solvent such as an ester compound or an ether compound.

Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, 1,2-dimethoxyethane, dimethyl sulfoxide, sulfolane, γ-butyrolactone, diethyl ether, Examples thereof include 3-oxolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl propionate, N, N-dimethylformamide, and acetonitrile, and these can be used alone or as a mixture of two or more.

Examples of the lithium salt include lithium hexafluorophosphate, anhydrous lithium perchlorate, lithium borofluoride and the like.

Although the concentration of the lithium salt in the non-aqueous electrolyte is not particularly limited, it is usually 0.1.
It is in the range of 5 to 3 mol / liter.

Further, a solid electrolyte obtained by mixing the above lithium salt with an electrolytic polymer can also be used. As the electrolytic polymer, for example, polyethylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, or derivatives thereof can be used. The electrolytic polymer is not limited to one type, and two or more types may be used in combination.

Next, an example of a non-aqueous electrolyte battery using the battery separator of the present invention is shown in FIG. As shown in the figure, this battery is a cylindrical battery having a spiral structure.

As shown in the figure, a positive electrode 1, a first battery separator 3, a negative electrode 2, and a second battery separator 3 are laminated in this order and wound in a spiral shape. 7. It is preferable that an end of the battery separator 3 is fixed to the wound body.
This fixation can be performed by, for example, adhesion with an adhesive tape, heat sealing, or the like. A positive electrode lead body 4 is led out of the positive electrode 1, and its tip is connected to a positive electrode terminal 6. Similarly, a negative electrode lead body 5 is led out of the negative electrode 2, and its tip is at the bottom (negative electrode) of a negative electrode can 7. Terminal). A non-aqueous electrolytic solution is injected into the negative electrode can 7, the upper portion of the negative electrode can 7 is closed by a lid, and the inside of the negative electrode can 7 is in a sealed state.

The form of the battery of the present invention is not particularly limited, and is appropriately determined according to the purpose. In addition to the above-mentioned cylindrical type, for example, a coin type, a button type, and a square type having a spiral structure are used. Alternatively, a square shape having a laminated structure and the like can be given. In addition, the form of the electrode and the like are appropriately determined according to the form of the battery.

As described above, the non-aqueous electrolyte battery of the present invention
Since the battery separator of the present invention is used, the battery separator has excellent safety. In addition, for example, a safety means such as a current interrupting device, a safety valve, and a PTC thermistor may be employed. Thereby, a battery having even higher safety can be obtained.

[0063]

Next, examples of the present invention will be described together with comparative examples.

Example 1 (1) Preparation of Porous Film Isotactic PP having a melt index (MI) of 0.4 was extruded at a die temperature of 250 ° C. using a T-die single screw extruder, and a PP having a thickness of 11 μm was formed. A sheet was prepared.
On the other hand, a high-density PE having an MI of 0.25 was extruded at a die temperature of 220 ° C. using the extruder, and a P
An E sheet was prepared. The PP on both sides of the PE sheet
The sheets were stacked and heat-treated at 132 ° C. for 1 minute using an iron roll to obtain a sheet having a three-layer structure (PP / PE / PP). The sheet having the three-layer structure is stretched at 25 ° C. in the machine direction (MD direction) at a low temperature at a stretching rate of 60%, and then stretched at 120 ° C. at a stretching rate of 150% in the same direction at a stretching rate of 150%. Was done. Then, it is heated at a temperature of 105 ° C. to thermally shrink the length in the stretching direction (MD direction) by 25%,
A three-layer porous membrane was produced. The porous membrane had a thickness of 26 μm and a porosity of 43%. As a result of measurement using a scanning electron microscope (manufactured by Hitachi, Ltd.), the PP
The average pore diameter in the heat shrink direction of the layer and the PE layer is 0.04 μm and 0.11 μm, respectively, and the aperture ratio is
They were 41% and 44%, respectively. The thickness and the porosity are measured by the methods described below, and the same applies to the porous films of the following examples and comparative examples.

(2) Preparation of Battery Using the porous membrane as a battery separator, a non-aqueous electrolyte battery was prepared as follows. A paste containing lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material was prepared, and the paste was applied on an aluminum foil and dried to prepare a positive electrode. On the other hand, a paste containing graphite as a negative electrode active material was prepared, and the paste was applied on a copper foil and dried to prepare a negative electrode. Then, the battery separator, the positive electrode, the battery separator, and the negative electrode were stacked so as to overlap with each other in this order, and these were all spirally wound. The outermost end of the separator of the obtained wound body was fixed to the wound body with an adhesive tape, and then the wound body was disposed in a stainless steel negative electrode can. Then, similarly to the conventional battery, after appropriately arranging each electrode lead body, insulating plate and the like, a non-aqueous electrolyte was injected into the negative electrode can. The electrolyte solution,
Ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2, and lithium hexafluorophosphate (LiPF ₆ ) was dissolved therein to prepare a concentration of 1.2 mol / dm ³ . Then, the negative electrode can was sealed to produce a rocking chair type lithium ion secondary battery.

(Example 2) A porous membrane and a porous membrane were prepared in the same manner as in Example 1 except that after stretching at a high temperature, the length in the stretching direction (MD direction) was thermally contracted by 20% by heating at a temperature of 102 ° C. A non-aqueous electrolyte battery using was prepared. The obtained porous film had a thickness of 26 μm and a porosity of 45%.

(Example 3) After stretching at a high temperature after stretching at a temperature of 100 ° C, the length in the stretching direction was thermally shrunk by 15%.
A porous membrane and a non-aqueous electrolyte battery using the same were produced in the same manner as in Example 1. The obtained porous membrane has a thickness of 2
5 μm, porosity 47%.

(Comparative Example 1) After stretching at a high temperature after stretching at a high temperature of 125 ° C, the length in the stretching direction was thermally shrunk by 20%.
A porous membrane and a non-aqueous electrolyte battery using the same were produced in the same manner as in Example 1. The obtained porous membrane has a thickness of 2
5 μm and porosity was 44%.

Comparative Example 2 A porous membrane and a non-aqueous electrolyte battery using the same were produced in the same manner as in Example 1 except that heat shrinkage was not performed after high-temperature stretching. The obtained porous film had a thickness of 24 μm and a porosity of 49%.

Various characteristics of the porous membrane and the non-aqueous electrolyte battery prepared in the above Examples and Comparative Examples were evaluated by the following measuring methods. The results are shown in Tables 1 and 2 below.

(1) Thickness The thickness was measured using a dial gauge G-6 (manufactured by Ozaki Seisakusho) having a minimum scale of 1/1000 mm.

(2) Porosity The density (ρ0) of the unstretched sheet was determined, and then the apparent density (ρ1) was determined from the thickness, area and weight of the porous film obtained after stretching. Then, the porosity was calculated from the following equation (4). Note that the density (ρ0) is determined by using a hydrometer (DE
NSIMETER-ΙΙ, manufactured by Toyo Seiki Seisaku-sho, Ltd.).

[0073]

Porosity (%) = [1− (ρ1 / ρ0)] × 100 (4)

(3) Electric Resistance Electric resistance was measured according to JIS C2313. The porous membrane is fixed to a cell for measuring electric resistance, and the porous membrane is immersed in an electrolytic solution, and a resistance meter LCR meter KC-532 (manufactured by Kokuyo Electric Industries Co., Ltd.) is connected to the cell.
The AC resistance of 1 kHz was measured by the following. As the electrolytic solution, a solution obtained by mixing propylene carbonate and 1,2-dimethoxyethane in the same volume, and dissolving anhydrous lithium perchlorate as an electrolyte so as to have a concentration of 1 mol / liter was used. In addition, the electric resistance of only the electrolytic solution as a blank was measured. Then, the electric resistance value (R) of the porous film was calculated from the following equation (5).

[0075]

R = (R1−R0) × S (5) R: electric resistance (Ω · cm ² ) R1: electric resistance (Ω) measured with the porous membrane immersed in the electrolytic solution ) R0: Electric resistance value of electrolytic solution (Ω) S: Cross-sectional area of porous film (cm ² )

(4) Differential Scanning Calorimetry (DSC) The endothermic peak of the porous film was measured by DSC. This analysis was performed using a DSC 3100 (manufactured by Mac Science) in a nitrogen gas atmosphere under the condition of a heating rate of 10 ° C./min. FIG. 2 shows a chart of the measurement results of the porous film of Example 1. In the figure, PE indicates the endothermic peak of the PE layer, and PP indicates the endothermic peak of the PP layer. Also,
Table 2 shows the PE in the porous membranes of the examples and comparative examples.
5 shows the endothermic peak temperature of the layer.

(5) Shrinkage rate The porous membrane was molded into a 10 cm square to obtain a sample, which was
It was put into an oven adjusted to ° C. for 1 hour, the length (La) in the stretching direction (MD direction) after shrinkage was measured, and the shrinkage ratio was determined from the above equation (1).

(6) Nonporous Temperature A porous film having a width of 60 mm was prepared and fixed to a stainless steel frame so that the stretching direction (MD direction) did not shrink. Put this in an oven adjusted to various temperatures for 5 minutes,
The Gurley value of the porous film after the treatment was measured by the method described below. And the Gurley value is 20,000 seconds / 10
The processing temperature when 0 ml or more was indicated was defined as the non-porous temperature.
This nonporous temperature can be used as an index for evaluating the ion-blocking temperature when the porous membrane is disposed in the battery electrolyte.

(7) Gurley value According to JIS P 8117, the time required for 10 ml of air to pass through a porous membrane (area 6.45 cm ² ) was measured, and the value obtained by multiplying the time by 10 was defined as the Gurley value. Table 1 shows Gurley values after the porous membrane of Example 1 was treated at each temperature. In the same table, infinity (∞) means 10 m of air
This shows a case where it takes 2000 seconds or more for 1 to pass, that is, a case where the Gurley value is 20000 seconds / 100 ml or more.

(8) One-Line Short-Circuit Test of the Battery The battery was fully charged, and the ambient temperature of the battery was 20 ° C.
, And a thermocouple was fixed to the battery can wall, and the maximum temperature of the battery can wall at the time of temperature rise was measured.

[0081]

(Table 1) Non-porous temperature of porous membrane of Example 1 Processing temperature (° C) Untreated 129 130 131 132 133 Gurley value (sec / 100 ml) 560 630 790

[0082]

[Table 2] Shrinkage condition of 90 ° C PE layer after high-temperature stretching Electric resistance Non-porous after treatment Endothermic peak Battery can wall temperature Shrinkage rate Shrinkage rate Temperature Temperature (° C) (%) (Ω · cm ² ) (%) (° C) (° C) (° C) Example 1 105 25 2.8 2.2 131 134.9 92 Example 2 102 20 2.9 7.3 129 134.7 84 Example 3 100 10 3.0 34.6 127 134.5 83 Comparative Example 1 125 20 2.9 1.1 136 135.1 125 Compare Example 2 Untreated 2.8 45.8 120 134.7 127

As shown in Table 2, the porous film of Example 1 showed a low electric resistance in a normal state before the heat treatment. As a result of DSC analysis of the porous film, two endothermic peaks derived from the PE layer and the PP layer were obtained as shown in FIG. 2, and the endothermic peak temperatures of the PE layer were 134.
9 ° C., and the PP layer was 169.8 ° C. Then, as shown in Table 1 above, the porous membrane was nonporous immediately after the temperature exceeded 130 ° C., and the nonporous temperature was 3 ° C. or lower than the endothermic peak temperature of the PE layer. The can wall temperature in the one-line short-circuit test of a battery incorporating this porous membrane was:
The temperature was 92 ° C., which indicates that the rise in the battery temperature was kept low even if the battery was short-circuited. In addition, good results were similarly obtained for the porous membranes and batteries of Examples 2 and 3.

On the other hand, in the batteries incorporating the porous membranes of Comparative Examples 1 and 2 each having a shrinkage rate after leaving at 90 ° C. for one hour outside the predetermined range of the present invention, the results of the direct short-circuit test , The temperature of the battery can wall (125 ° C, 127
° C) was high. In particular, when the battery of Comparative Example 2 where this temperature was high was disassembled and examined, the porous membrane was significantly shrunk,
The electrodes were exposed.

[0085]

As described above, the battery separator of the present invention has a low SD temperature, has a fast SD function, and has excellent mechanical strength. If this battery separator is used for a non-aqueous electrolyte battery such as a lithium battery, a low-cost battery with high performance and excellent safety can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a chart showing the results of differential scanning calorimetry of a porous membrane according to another example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode 2 negative electrode 3 battery separator 4 positive electrode lead 5 negative electrode lead 6 positive electrode terminal 7 negative electrode can

Continued on the front page (72) Inventor Masayuki Kiuchi 1-12-32 Nishihonmachi, Ube-shi, Yamaguchi Ube Industries, Ltd. Polymer Research Laboratory F-term (reference) 4F074 AA17 AA18 AA24 AA26 CC04Z CC32Z DA02 DA03 DA22 DA24 DA49 5H021 CC00 EE04 HH00 HH01 HH02 HH03 HH06 5H024 AA01 AA02 CC02 DD01 DD09 DD14 DD17 EE09 HH01 HH10 HH11 HH13 5H029 AJ12 AK03 AL07 AM03 AM05 AM06 BJ02 BJ14 DJ04 EJ12 HJ00 HJ04 HJ06 HJ09 HJ14

Claims (5)

[Claims] 1. A battery separator formed from a thermoplastic resin porous membrane, which is left at 90 ° C. for 1 hour in at least one direction of the porous membrane represented by the following formula (1). Shrinkage (C) is in the range of 2 to 40%,
The porous membrane has at least one endothermic peak by differential scanning calorimetry in the range of 110 to 150 ° C, and the porous membrane blocks ion transmission by thermal contraction at a temperature of 3 ° C or less from the endothermic peak temperature. Battery separator. C (%) = [(Lb−La) / Lb] × 100 (1) Lb: length of porous film before contraction La: length of porous film after contraction 2. The battery separator according to claim 1, wherein the shrinkage (C) is in the range of 5 to 35%. 3. The porous membrane before shrinkage has an aperture ratio of 35 to 60.
%, And the average pore diameter of the porous membrane before shrinkage in the shrinkage direction when left at 90 ° C. for 1 hour is 0.0%.
The battery separator according to claim 1, wherein the thickness is in a range of 2 to 1.0 μm. 4. The battery separator according to claim 1, wherein the thermoplastic resin is a polyolefin. 5. A non-aqueous electrolyte battery in which a battery separator is interposed between the positive and negative electrodes, and these are disposed in a can into which the non-aqueous electrolyte has been poured, wherein the battery separator is provided. A non-aqueous electrolyte battery which is the battery separator according to any one of claims 1 to 4.