JP2000223106A - Separator for battery and battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous electrolyte battery excellent in ion permeability. SOLUTION: In this separator for a battery using an ultrahigh molecular weight polyethylene porous sheet, an air permeability measured with a fragile type tester based on JIS L 1096 is set to 10 cm/(cm2.s) or above. The separator for a battery is manufactured by sintering ultrahigh molecular weight polyethylene powder, then cutting it in a sheet shape. A viscosity-average molecular weight of the ultrahigh molecular weight polyethylene is preferably 500,000-16,000,000.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a battery separator used for a non-aqueous electrolyte battery and a non-aqueous electrolyte battery using the same.

[0002]

2. Description of the Related Art Non-aqueous electrolyte batteries such as lithium secondary batteries are light-weight, have high electromotive force and high energy, and have low self-discharge, so they are widely used as power sources for various electric and electronic devices. It is also expected as a power source for electric vehicles.

As a battery separator used in a non-aqueous electrolyte battery, a porous sheet made of polyolefin is used (for example, JP-A-5-25305, JP-A-8-64194, JP-A-6-64194). -212006, JP-A-8-138644).

However, the conventional non-aqueous electrolyte battery separator has a problem in ion permeability. In particular, since batteries used in electric vehicles are required to have a significantly higher output, battery separators used therefor are also required to have improved ion permeability.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a battery separator used in a non-aqueous electrolyte battery, which has excellent ion permeability.

[0006]

In order to achieve the above object, a battery separator of the present invention is a battery separator used for a non-aqueous electrolyte battery, which is made of ultra-high molecular weight polyethylene (hereinafter referred to as "UHPE"). Porosity sheet), and has a configuration in which the air permeability measured by a JIS L 1096 Frazier type prototype is 10 cm / (cm ² · s) or more.

[0007] As described above, in a battery separator using a UHPE porous sheet, if the air permeability is set within the above-mentioned predetermined range, the ion permeability becomes sufficient, and the battery can be sufficiently used for an electric vehicle battery. . The preferable range of the air permeability is 10 to 50 cm / (cm ² · s), and the optimum range is 10 to 30 cm / (cm ² · s). Also,
The viscosity average molecular weight of the UHPE is preferably in the range of 500,000 to 16,000,000.

[0008] The UHPE porous sheet comprises a plurality of U
The sheet is preferably a sheet in which HPE particles are connected and a porous structure is formed by voids between the particles. A battery separator using such a sheet has a larger pore diameter and is more excellent in heat shrink resistance than a conventional battery separator. By using this battery separator in a high-power battery such as a battery for an electric vehicle due to its excellent heat shrink resistance, a short circuit at a high temperature is prevented and safety is improved.

Next, a battery of the present invention is a non-aqueous electrolyte battery using the battery separator of the present invention as a battery separator interposed between positive and negative electrodes. As aforementioned,
Since the battery separator of the present invention has excellent ion permeability, the non-aqueous electrolyte battery of the present invention can achieve high output.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The battery separator used in the present invention can be manufactured, for example, as follows.

First, UHPE powder is filled into a shape retainer.
The average particle diameter of the UHPE powder is usually from 10 to 200.
It is in the range of μm, preferably in the range of 20 to 180 μm. Then, the UHPE powder is sintered in a steam atmosphere heated above its melting point. At this time, in a reduced pressure atmosphere, the water vapor can quickly penetrate into the UHPE powder and be uniformly sintered. Then, after cooling this sintered body, it is formed into a sheet shape by cutting or the like, whereby a porous sheet (battery separator) is obtained. In this sheet, a plurality of UHPE particles are interconnected, and a porous structure is formed by voids between the particles. And the pore size of this sheet is much larger than the separator for conventional non-aqueous electrolyte batteries, and as described above,
The air permeability measured by a JIS L 1096 Frazier tester is 10 cm / (cm ² · s) or more. The UHPE porous sheet usually has a porosity of 25.
７０70% by volume, thickness 25〜100 μm. Further, this sheet has a small shrinkage under high temperature, and the ratio (A2 / A1) of the sheet area (A2) after the treatment at 170 ° C. for 10 minutes to the sheet area (A1) before the heat treatment is usually A2 /
A1 ≧ 0.9, preferably A2 / A1 ≧ 0.95
It is. On the other hand, the ratio (A2 / A1) of the conventional battery separator is usually A2 / A1 ≦ 0.4.

The UHPE porous sheet according to the present invention has a UHP
Components other than E may be included.

Next, the non-aqueous electrolyte battery of the present invention is not particularly limited, except that the separator of the present invention is used as a battery separator. In the nonaqueous electrolyte battery of the present invention, as each component other than the battery separator,
For example, the following can be used.

As the positive electrode material, for example, Ti, Mo,
Oxides, sulfides, and selenides of metals such as Co, Nb, V, Mn, Cr, Ni, Fe, P, etc., which contain Li as necessary, LiMnO ₄ , LiNi
₂ O ₂ , LiCoO ₂ , LiCrO ₂ , LiFeO ₂ , Li
VO ₂ or the like can be used. Further, conductive polymers such as polypyrrole and polyaniline are also preferable. The positive electrode can be formed by casting or the like using these active materials, conductive materials such as acetylene black, ketjen black, and graphite, which are blended as necessary, and a binder such as polyvinylidene fluoride.

Examples of the negative electrode material include carbon, particularly graphite-based materials, Li-based materials, tin oxide, and the like.
Examples of the Li-based material include lithium metal and lithium alloy. As a lithium alloy, Li
And Al, Pb, Sn, IN, Bi, Ag, Ba, C
a, Hg, Pt, Sr, Te and other metals and binary or ternary alloys; and, if necessary, Si,
Those to which Cd, Zn, La or the like is added can also be used. The negative electrode may be formed using a binder, or the metal foil of the metal may be used as it is.

As the non-aqueous electrolyte, for example, a solution in which a lithium salt is dissolved in an organic solvent such as an ester or an ether can be used. Examples of the organic solvent include, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, dimethoxyethane, dimethyl sulfoxide, sulfolane, γ-butyl lactone,
Examples include 1,2-dimethoxyethane, diethyl ether, ethyl acetate, N, N-dimethylformamide, acetonitrile, or a mixture thereof. As the lithium salt, for example, LiPF ₆ , LiBF ₄ , LiI, Li
ClO ₄ , LiCF ₃ SO ₃ , LiAsF _{6 and the} like. The concentration of the lithium salt in the non-aqueous electrolyte is not particularly limited, and is usually 0.5 to 3 mol / L.

[0017]

Next, examples will be described together with comparative examples.

Example 1 2 kg of UHPE powder (viscosity average molecular weight: 4.4 million, melting point: 135 ° C., average particle diameter: 35 μm (mesh classified product)) was filled in a shape retainer. This shape retainer has a metal cylindrical outer mold having a large number of holes with a polytetrafluoroethylene porous film adhered to the inner peripheral surface thereof, and a fixing member arranged at the bottom of the outer mold to fix the outer mold. It consists of a type. The shape retainer was placed in a metal heat-resistant and pressure-resistant container (provided with a steam introduction pipe and a valve for opening and closing the same), and the atmospheric pressure was set to 1.3 kPa by a vacuum pump.
The time required at this time was 30 minutes. Then, after stopping the pump, the valve was opened, steam (temperature: 145 ° C., pressure: 0.4 MPa) was introduced, and the mixture was heated and sintered for 1 hour. Thereafter, the resultant was cooled to obtain a columnar porous body. The obtained porous body was cut into a sheet shape by a cutting lathe to produce a battery separator having a thickness of 54 μm and a porosity of 51% by volume. The air permeability of this battery separator measured by a Frazier type tester of JIS L 1096 is 14 cm ³
/ (Cm ² · s). The average pore size of this battery separator by a mercury porosimeter method (Autoscan mercury intrusion-type pore distribution measuring device manufactured by Yuasa Ionics Inc .: Autoscan-33) was 12 μm. Using this battery separator, a non-aqueous electrolyte battery was fabricated as follows, and its discharge characteristics were examined. The results are shown in Table 1 below. Further, the battery separator was examined for heat shrinkage resistance by the following method.
The results are shown in Table 2 below.

The positive electrode includes lithium cobalt oxide (active material),
Polyvinylidene fluoride (binder) and graphite (conduction aid) were mixed, and this mixture was applied on an aluminum foil (current collector) to prepare a battery. The negative electrode was prepared by mixing graphite (active material) and polyvinylidene fluoride (binder), and applying this mixture on a copper foil (current collector). The electrolyte was prepared by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1 and dissolving lithium hexafluorophosphate at a concentration of 1.0 mol / l in the mixture. Then, a sealed battery was manufactured using the battery separator, the positive electrode, the negative electrode, and the electrolytic solution. The battery was first charged and discharged at 0.544 mA / cm ² , followed by break-in charge and discharge at 1.36 mA / cm ^2.
After charging / discharging for 8 cycles at 13.6 mA / cm
² discharge tests were performed. The charge and discharge of the battery was 25
The test was performed in a thermostat at 0 ° C.

(Heat shrink resistance) A sheet made of polytetrafluoroethylene was placed on a glass plate, and the area (A1)
The battery separator for which the measurement was performed was placed. Then, after leaving this in a dryer at 170 ° C. for 10 minutes, it is taken out and cooled to room temperature, and the area of the battery separator (A2)
Was measured, and the area ratio (A2 / A1) was calculated.

Comparative Example 1 UHPE (viscosity average molecular weight 2)
5,000,000 by weight, 100,000, melting point 134 ° C), 10% by weight of high-density polyethylene powder (viscosity average molecular weight 200,000, melting point 131 ° C) and 85% by weight of solvent (liquid paraffin, kinematic viscosity at 40 ° C 59 cst) 85% by weight The mixture was uniformly mixed and kneaded at 160 ° C. with a twin-screw extruder. The kneaded product was sandwiched between rolls cooled to 0 ° C. or lower, and formed into a sheet while crystallizing. This molded product was simultaneously stretched 4 × 4 times vertically and horizontally (about 115 ° C.), and the solvent was removed using methylene chloride to obtain a porous sheet. This porous sheet was heat-set at 120 ° C. for 10 seconds to obtain a battery separator. This battery separator has a thickness of 44 μm, a porosity of 41% by volume, and a BET average pore size (specific surface area / pore distribution measuring device ASAP2010, manufactured by Shimadzu Corporation) of 0.04 μm. Further, the gas permeability of this battery separator was 0.1 cm ³ / (cm ² · s) or less. Using this battery separator, a battery was fabricated in the same manner as in Example 1, and its discharge characteristics were examined. This result
It is shown in Table 1 below. Further, the heat shrinkage resistance of the battery separator was examined in the same manner as in Example 1. The results are shown in Table 2 below.

[0022]

Table 1 Discharge capacity A Discharge capacity B Capacity ratio (mA.h) (mA.h) (B / A) Example 1 5.3 1.1 0.21 Comparative example 1 5.0 0.6 0.0 12 discharge capacity A: discharge capacity at 1.36 mA / cm ² discharge capacity B: discharge capacity at 13.6 mA / cm ²

[0023]

[Table 2]

As can be seen from Table 1 above, Example 1 had better discharge characteristics than Comparative Example 1. Also, as can be seen from Table 2, the battery separator of Example 1 showed significantly less shrinkage at high temperatures than the battery separator of Comparative Example 1.

[0025]

As described above, the battery separator of the present invention has high ion permeability. Therefore, a non-aqueous electrolyte battery using the same has excellent discharge characteristics and can be suitably used for batteries requiring high output such as batteries for electric vehicles.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Junichi Moriyama 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Takashi Yamamura 1-1-2 Shimohozumi, Ibaraki-shi, Osaka F-term in Nitto Denko Corporation (reference) 4F074 AA17 AB01 CA52 CC03X CC12Y CC47 CC62 DA10 DA49 5H021 CC00 EE04 HH00 HH07

Claims (4)

[Claims] 1. A battery separator using a porous sheet made of ultra-high molecular weight polyethylene, which is used for a non-aqueous electrolyte battery and has a gas permeability of 10 cm / measured by a Frazier type tester of JIS L 1096. (Cm ² · s) or more. 2. The battery separator according to claim 1, wherein the ultrahigh molecular weight polyethylene porous sheet is a sheet in which a plurality of ultrahigh molecular weight polyethylene particles are connected and a porous structure is formed by voids between the particles. . 3. The battery separator according to claim 1, wherein the ultrahigh molecular weight polyethylene has a viscosity average molecular weight in a range of 500,000 to 16,000,000. 4. A non-aqueous electrolyte battery using the battery separator according to claim 1 as a battery separator interposed between positive and negative electrodes.