JP3511946B2 - Polymer electrolyte support and battery using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a useful polymer electrolyte support which can be filled with a polymer electrolyte to form a polymer electrolyte film for lithium batteries having high ionic conductivity, and lithium using the same. It relates to a polymer battery.

[0002]

2. Description of the Related Art Conventionally, a negative electrode, a positive electrode, a non-aqueous electrolyte and a separator have been used as main constituent materials of a lithium secondary battery, and a polyolefin porous film has been used as the separator. Further, as the negative electrode, for example, metallic lithium, an alloy of lithium and another metal, a carbon material having the ability to adsorb lithium ions such as carbon or graphite, or the ability to occlude by intercalation, high conductivity doped with lithium ions Molecular materials and the like are known, and positive electrodes include, for example, fluorinated graphite represented by (CF _x ) _n , MnO ₂ , V ₂ O ₅ , CuO, and Ag ₂ Cr.
Known metal oxides, sulfides, and chlorides such as O ₄ , TiO ₂ , LiCoO ₄ , and LiMn ₂ O ₄ .

On the other hand, the non-aqueous electrolyte may be an organic solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane or tetrahydrofuran. LiPF ₆ , LiBF ₄ , LiCl
O ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN
It is known that an electrolyte such as (SO ₂ C ₂ F ₅ ) ₂ is dissolved, but in recent years, from the viewpoint of safety, the non-aqueous electrolytic solution contains polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile and copolymers thereof. Polymer electrolytes immobilized with such polymer materials have come into practical use.

By fixing a non-aqueous electrolyte with a polymer material, the polymer electrolyte has the effect of preventing the non-aqueous electrolyte from seeping out and making it flame-retardant. Alternatively, there is a problem that a short circuit occurs when the battery is used. For improving the mechanical strength, for example, Japanese Patent Laid-Open No.
A method of filling a polymer electrolyte into an electrolyte support such as 284125 has been proposed, and a nonwoven fabric or a porous film made of a material such as polyolefin is used as the polymer electrolyte support.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention In a lithium battery using an electrolyte film in which a polymer electrolyte is filled in an electrolyte support as a constituent material, the porosity is increased for the purpose of obtaining ionic conductivity necessary for ensuring capacity characteristics. It is necessary to use a polymer electrolyte support having a high pore size and a large pore size. on the other hand,
Since increasing the porosity and pore diameter of the polymer electrolyte support causes a decrease in the mechanical strength of the electrolyte film, the polymer electrolyte support is used to improve the mechanical strength of the electrolyte film. It is feared that the purpose of the period will be spoiled. Furthermore, it is feared that the polymer electrolyte support having a high porosity and a large pore diameter may have a reduced thickness and an increased air permeability due to the application of the surface pressure in the operating temperature range of the battery. In particular, in the case of a polymer electrolyte support manufactured by a wet method, it is easily inferred that the reduction in thickness and the increase in air permeability due to the application of surface pressure are easily caused due to the stretching at a large surface magnification in the manufacturing process. Therefore, the development of a more excellent polymer electrolyte support is desired.

Conventionally, in the process of assembling a lithium secondary battery, a battery element in which a positive electrode sheet, a negative electrode sheet and a separator are stacked is wound in a spiral shape using a metal winding pin, and the wound product is used as a battery. The battery was manufactured by injecting the non-aqueous electrolytic solution after storing it in the container. However, in a lithium polymer battery using a polymer electrolyte film as a constituent material, in order to provide a thin and bendable flexible battery shape, a battery element in which a positive electrode sheet, a negative electrode sheet and an electrolyte film are stacked is used. Instead of rolling to fit in a small volume, they are stacked in a thin plate shape.

In a lithium polymer battery having a structure in which a positive electrode sheet, a negative electrode sheet and an electrolyte film are laminated in a thin plate shape, it is preferable that a large area change does not occur in the electrolyte film due to heat generation when the battery is abnormal. When the area of the electrolyte film is reduced due to heat shrinkage, there is a concern that the positive electrode sheet and the negative electrode sheet may come into contact with each other to cause a short circuit. Since such a short circuit due to heat shrinkage of the electrolyte film is particularly likely to occur in a lithium polymer battery in which battery elements are stacked in a thin plate shape, it is necessary to make the heat shrinkage ratio of the polymer electrolyte support as small as possible.

Further, in the lithium polymer battery, how to smoothly carry out the step of filling the polymer support with the electrolyte support becomes a problem. It can be easily inferred that it is difficult to fill the polymer support with the electrolyte support, as compared with the case where the non-aqueous electrolyte is injected into the separator in the conventional manufacturing process of the non-aqueous electrolyte battery. In order to facilitate the filling of the polymer electrolyte, it is desirable that the surface tension of the electrolyte support is low and the porosity and pore structure of the surface of the electrolyte support are high.

An object of the present invention is to provide a polymer electrolyte support having high ionic conductivity and excellent mechanical strength when it is filled with a polymer electrolyte to form an electrolyte film. Another object of the present invention is to provide a polymer electrolyte support which is easy to fill with the polymer electrolyte and has a small thermal shrinkage and excellent safety in use, and a lithium polymer battery using the same.

[0010]

As a result of earnest research, the inventors of the present invention have a hole structure that linearly extends in the film thickness direction, in other words, transfer of lithium ions between electrodes when incorporated in a battery. By stacking a short-stroke porous film, it is possible to obtain a polymer electrolyte support having high ionic conductivity when filled with a polymer electrolyte and forming an electrolyte film, and having excellent mechanical strength. I found it. That is, the present invention is a polymer electrolyte support comprising a laminate of a polyolefin porous film porous by a stretching method, wherein the porous film is formed substantially parallel to the film thickness direction at substantially predetermined intervals. Formed by a group of unstretched plate-like planes and a group of stretch-oriented thin fibrils that run between the plate-like planes substantially in parallel with each other in the stretching direction of the film at substantially predetermined intervals and that connect between the plate-like planes. by the gap between the thin fibrils leading to inter-plane to form fine pores of substantially uniform shape extending substantially two-dimensionally, have a through hole extending linearly in the thickness direction of the film, the polymer electrolyte
Porosity of the support is 40-80%, air permeability is 30-500 seconds
/ 100 cc, tensile strength in machine direction 12 kg / mm ^{2 or} less
Upper, film width direction when heat treated at 150 ° C for 10 minutes
And a heat shrinkage ratio of 15% or less . The present invention also provides a lithium polymer battery including a positive electrode made of a lithium-containing metal oxide, a sulfide or a chloride, a negative electrode made of a carbon material, and a polymer electrolyte in which a non-aqueous electrolyte is fixed with a polymer material. A lithium polymer battery containing the polymer electrolyte support as a constituent material.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The polyethylene constituting the polyelectrolyte support of the present invention may be any of high density polyethylene, medium density polyethylene, linear low density polyethylene, etc., but high density polyethylene was used. In this case, it is preferable that the porosification is performed by the stretching method. The number average molecular weight of polyethylene is 10,000 or more, more preferably 2
It is over 10,000. When the molecular weight of polyethylene is small, the mechanical strength of the polymer electrolyte support is lowered, which is not preferable.

The polypropylene used for the polymer electrolyte support of the present invention has a pentad fraction of 94% or more and a number average molecular weight of 50,000 or more, more preferably 7
Tens of thousands or more are preferable because they have high mechanical strength. Further, the melting point of polypropylene is preferably 155 ° C. or higher, more preferably 160 ° C. or higher because the heat shrinkage can be suppressed to a small level.

The pentad fraction of polypropylene was calculated by the peak height method from the ¹³ C-NMR spectrum assigned based on the description in Polymer Analysis Handbook (edited by Japan Society for Analytical Chemistry). ^{The 13} C-NMR measurement was carried out by using an EX-400 FT-NMR manufactured by JEOL Ltd.
In dichlorobenzene, measurement temperature 130 ℃, total number of times 80
It was carried out under the condition of 00 times. The pentad fraction is an index of stereoregularity of polypropylene, and as this value approaches 100%, the rigidity and melting point of polypropylene increase.

In the present invention, the number average molecular weights of polyethylene and polypropylene were determined by standard polystyrene conversion using a 150C type gel permeation chromatograph manufactured by WATERS. Two Shodex HT-806M columns were used, and the measurement was carried out at 135 ° C. in ortho-dichlorobenzene adjusted to 0.3 wt / vol%. Further, the melting point of polypropylene was measured using DSC-7 manufactured by Perkin Elmer. The sample was held at 230 ° C for 10 minutes to remove the thermal history, completely melted, and then cooled to room temperature at 10 ° C / min. The maximum melting point was measured at a temperature rising rate of 10 ° C / min. And

Further, the polyelectrolyte support is filled with a polyelectrolyte to the extent that the performance of the electrolyte film is not impaired, a plasticizer, a lubricant, a flame retardant, a coloring agent,
Alternatively, a reinforcing material such as glass fiber or silicon fiber may be appropriately contained. The method of blending the additive with the polymer electrolyte support is not particularly limited, but it can be blended by kneading using an ordinary kneader. For example, pellets can be obtained by melt-kneading using a single-screw extruder, a twin-screw extruder, a mixing roll or the like. Alternatively, they may be blended by dry blending using a Henschel mixer, a tumbler or the like.

The layer structure of the polymer electrolyte support of the present invention is not particularly limited as long as it is a laminate, such as the number of layers and materials, and polypropylene multi-layer, polyethylene multi-layer, polypropylene surface layer and polyethylene intermediate layer. It may have any of a three-layer structure and a three-layer structure in which polyethylene is arranged in the surface layer and polypropylene is arranged in the intermediate layer, but a three-layer structure in which polyethylene is arranged in the surface layer and polypropylene is arranged in the intermediate layer is preferable. The polyethylene porous layer arranged on the surface layer has a large porosity and a pore diameter and an appropriate surface tension for the purpose of facilitating the filling of the polymer electrolyte. In addition, the polypropylene disposed in the intermediate layer plays a role of preventing the electrolyte film from being greatly heat-contracted due to heat generation when the battery is abnormal.

Specific methods for producing the polymer electrolyte support of the present invention include, for example, a method in which polyethylene and polypropylene are melt-coextruded and then stretched and porous to obtain a laminated porous film, and a polyethylene film and a polypropylene film are used, respectively. There is a method in which melt-extrusion layers are separately laminated and then stretched and porous to obtain a laminated porous film. Further, in the stretched porous step, when the performance of the porous film such as the air permeability, the porosity and the maximum pore size is impaired by greatly reducing the length of the film in the width direction, the present inventors The method described in Japanese Patent Application No. 10-99633 filed by K.K., the method of stretching while fixing both ends in the width direction of the film with chucks, pinch rolls, etc. The widthwise reduction in the film length can be improved by a method such as a method of restoring by transverse stretching. The polymer electrolyte support of the present invention can be produced by any method.

The melt extrusion method may be a melt extrusion molding method using a T die, an inflation method, or the like. For example, when a film is melt-molded by a T-die, it is generally performed at a temperature 20 to 60 ° C. higher than the melting temperature of the resin, and a draft ratio of 5 to 500, preferably 50 to 300, and the take-up speed is particularly limited. Not usually but 10
Molded at ~ 50 m / min. The melt extruded film is heat treated to enhance its crystallinity and its orientation. Heat treatment temperature is 1 for polyethylene film
The temperature is 00 to 130 ° C, preferably 110 to 125 ° C, and the polypropylene film is 110 to 160 ° C, preferably 120 to 150 ° C. If the heat treatment temperature is low, it will not be sufficiently porous, and if it is too high, the film will melt, which is not suitable. The heat treatment time is not particularly limited, but 3
It is performed in the range of seconds to 180 seconds.

The heat-treated polyethylene film has a birefringence of 25 × 10 ^{−3 to} 48 × 10 ⁻³ , preferably 3
It is 0x10 ^{-3 to} 45x10 ^-3 , and the elastic recovery rate at 50% elongation is 40 to 80%, preferably 50 to 75%. The heat-treated polypropylene film has a birefringence of 10 × 10 ^{−3 to} 25 × 10 ^3.
-3 , preferably 12 × 10 ^-3 to 23 × 10 ^-3 , 100
Elastic recovery rate at 70% elongation is 70 to 94%, preferably 7
It is preferably in the range of 5 to 93%. When the birefringence and the elastic recovery rate are out of these ranges, the degree of porosity becomes insufficient, and the porous film after stretching, that is, the pore size and pore size distribution of the polymer electrolyte support, the porosity, the delamination strength, The above range is appropriate because it affects mechanical strength and the like, and variations in quality are likely to occur.

In the present invention, birefringence is a value measured by using a polarizing microscope and a Berek compensator under crossed Nicols. The elastic recovery rate is calculated by the following equations (1) and (2). Formula (1) is for a polyethylene film, and formula (2) is for a polypropylene film. The polyethylene film is 25 ° C and 65%
The sample was set in a tensile tester with a sample width of 15 mm and a length of 2 inches at a relative humidity, expanded to 50% at a speed of 2 inches / min, held in an expanded state for 1 minute, and then relaxed at the same speed. , Polypropylene film is 2
Sample width 10 mm, length 5 at 5 ° C and 65% relative humidity
The test piece was set at 0 mm in a tensile tester, stretched to 100% at a speed of 50 mm / min, and then immediately relaxed at the same speed to measure.

Formula (1) Elastic recovery rate (%) = ((Length at 50% elongation-Length at 50% elongation after zero load) / (Length at elongation-
Length before extension)) x 100

Formula (2) Elastic recovery rate (%) = ((100% extension length-100
% Length when the load becomes 0 after extension) / Length before extension) ×
100

The heat-treated polyethylene film and polypropylene film are laminated by thermocompression bonding.
The layer structure of the polymer electrolyte support of the present invention is preferably a three-layer structure in which polyethylene is arranged in the surface layer and polypropylene is arranged in the intermediate layer. As for lamination, three films are unwound from three sets of original roll stands, nipped between heated rolls and pressure-bonded to be laminated. At this time, it is necessary to perform thermocompression bonding so that the birefringence and elastic recovery rate of each film are not substantially reduced.

The temperature of the heated roll, that is, the thermocompression bonding temperature is 110 to 130 ° C., preferably 115 to 125.
℃. If the temperature is too low, the adhesiveness between the films will be weak and peeling will occur in the subsequent stretching step, while if it is too high, the birefringence and elastic recovery of the film will decrease due to the melting of polyethylene, making it difficult to make the film porous. The above range is suitable. The nip pressure for thermocompression bonding is 1 to 3 kg / cm ² , and the unwinding speed is 0.5 to 8 m / min. The peel strength between the thermocompression bonded films is 3 to 60 g / 15.
A range of mm is preferred.

The heat-treated and laminated film is made porous by stretching. Stretching is carried out in the order of low temperature stretching and then high temperature stretching, and is usually performed at the peripheral speed difference of the stretching roll. The temperature of the low temperature stretching is -20 to 50 ° C, particularly preferably 20 to 35 ° C. If the stretching temperature is low, the film is likely to be broken during the work. On the contrary, if the stretching temperature is too high, the porosity is insufficient, which is not suitable. Draw ratio for low temperature stretching is 5 to 200
%, Preferably 10 to 100%. If the draw ratio is too low, only those having a low porosity can be obtained, and if it is too high, those having a predetermined porosity and pore diameter cannot be obtained, so the above range is suitable. In the present invention, the low temperature draw ratio (E ₁ ) is according to the following formula (3). In the formula (3), L ₁ means the film size after the low temperature stretching, and L ₀ means the film size before the low temperature stretching.

Formula (3) E ₁ = [(L ₁ −L ₀ ) / L ₀ ] × 100

The cold-stretched film is then hot-stretched. Hot stretching is 70-1 in a heated air circulation oven.
It is carried out in a temperature range of 30 ° C., particularly preferably 100 to 125 ° C. If the stretching temperature is out of the above range, the porosity becomes insufficient, which is not suitable. Further, the high temperature drawing is preferably performed at a temperature 40 to 100 ° C. higher than the temperature of the low temperature drawing. The draw ratio of the high temperature stretching is in the range of 100 to 400%.
If the stretching ratio is too low, the porosity will be insufficient, and if it is too high, the desired air permeability, porosity and pore diameter will not be obtained, so the above range is suitable. In the present invention, the high temperature draw ratio (E ₂ ) is in accordance with the following formula (4). L _{2 in the} formula (4) means the film size after the high temperature drawing, and L ₁ means the film size after the low temperature drawing.

Formula (4) E ₂ = [(L ₂ −L ₁ ) / L ₁ ] × 100

In the process of stretching and porousizing the laminated porous film of the present invention, the length in the width direction of the film is greatly reduced and the performance of the porous film such as air permeability, porosity and maximum pore size is impaired. The method includes stretching both ends in the width direction of the film with a chuck, a pinch roll or the like while stretching, and a method of restoring the width direction film length reduction caused during stretching after stretching the film by transverse stretching. Improvements can be made by the method. For example, in order to restore the reduction in the length of the film in the width direction, transverse stretching is performed at high temperature after stretching at low temperature and high temperature.

For high-temperature transverse stretching, a method of stretching the film in the width direction in a tenter system by fixing it with chucks at both ends in the width direction in a heating air circulation oven, and a method of stretching according to the lead angle using a spiral roll are used. Etc. The temperature of the high-temperature transverse stretching is 70 to 130 ° C., particularly preferably 100 to 130 ° C.
It is 125 ° C. Outside this range, the air permeability, porosity, and maximum pore size are not improved even at high temperature transverse stretching, which is not suitable.

Usually, by low-temperature stretching and high-temperature stretching, the width of the film is 80 to 9 with respect to that before stretching.
It decreases to about 0%. It is preferable that the stretching ratio of the high-temperature transverse stretching is within a range in which the reduction of the length in the width direction is appropriately restored. The stretching ratio of the high temperature transverse stretching is 5 to 40%, more preferably 10 to 30%. If the stretching ratio is too low, the reduction in film length in the width direction that occurs during low temperature and high temperature stretching cannot be restored, and if it is too high, the variation in the film thickness becomes large, and in some cases, the porous film is broken. The above range is preferable because a film is formed. In the present invention, the high temperature transverse stretching ratio (E ₃ ) is according to the following formula (5). L ₄ of the formula (5) means the width-direction length of the film after high-temperature transverse stretching, and L ₃ means the width-direction length of the film after low-temperature stretching and high-temperature stretching.

Formula (5) E ₃ = [(L ₄ −L ₃ ) / L ₃ ] × 100

In the present invention, the porous film is heat set after the low temperature stretching, the high temperature stretching and the high temperature transverse stretching.
The heat setting is performed by a method of preliminarily reducing the length of the film after stretching by 10 to 50% in order to prevent the film from shrinking in the stretching direction due to the residual stress applied during stretching, and the dimension in the stretching direction does not change. It is carried out by a method such as regulation and heating. By this heat setting, a polymer electrolyte support having good dimensional stability and satisfying the intended problem can be obtained.

When the pressure of 35 kg / cm ² is applied at a temperature of 60 ° C. in the thickness direction of the polymer electrolyte support thus produced, the reduction rate of the film thickness is 5% or less, and the air permeability is increased. The rate is 10% or less. If the thickness of the polymer electrolyte support is easily reduced by applying a surface pressure at 60 ° C., which is the operating temperature range of the battery, the polymer electrolyte is discharged. Further, similarly, an increase in air permeability is not preferable because it causes a decrease in the capacity characteristics of the battery. The tensile strength of the polymer electrolyte support in the machine direction is 12k.
It is preferably g / mm ² or more. Further, the heat shrinkage in the film width direction when heat-treated at 150 ° C. for 10 minutes is preferably 15% or less, particularly preferably 10% or less. If the tensile strength in the machine direction is too low, the polymer electrolyte support may be deformed during battery production. Further, when the polyelectrolyte support is thermally contracted in the width direction of the film by heat treatment to a degree larger than the above range, the dimension of the polyelectrolyte support in the width direction becomes small when the battery is abnormal, and the electrodes in the width direction end portions It is not appropriate because there is concern that it may be exposed and cause a short circuit.

The porosity of the polymer electrolyte support is 40-80.
%, Especially 35 to 70% is preferable. The air permeability is 30.
~ 500 sec / 100 cc, especially 70 sec / 100 cc-4
00 seconds / 100 cc is preferable. If the porosity is too small, the capacity characteristics of the battery will deteriorate, and if it is too large, the mechanical strength will decrease. Further, if the air permeability is too high, the function when filled with a polymer electrolyte to form an electrolyte film is insufficient, and if it is too low, the mechanical strength is lowered, so the above range is appropriate.

The maximum pore diameter of the polyethylene porous layer disposed on the surface of the polymer electrolyte support is 0.2 to 5 μm.
m, and the porosity is 50 to 90%. If the maximum pore size and the porosity are not within the above ranges, it is not appropriate because not only it takes a long time to fill the polymer electrolyte, but also the filling cannot be performed uniformly.

The polymer electrolyte support of the present invention has a contact angle of 55 degrees or less, more preferably 50 degrees or less, evaluated by the following measuring device. The evaluation of the contact angle was conducted by using 1: 1 (vol / v of dimethoxyethane / propylene carbonate).
ol) Lithium perchlorate was dissolved in the mixed solution to prepare 1 M / L of the non-aqueous electrolytic solution, and the non-aqueous electrolytic solution was dropped on the polymer electrolyte support, and the contact angle immediately after the droplet formation was measured. The smaller the contact angle, the better the wettability and penetrability of the polymer electrolyte support with respect to the non-aqueous electrolyte, and the easier the filling of the polymer electrolyte. Measurement conditions: Temperature 23 ° C., humidity 50% Measuring device Image processing type contact angle meter CA-X type Kyowa Interface Science Co., Ltd.

In the polymer electrolyte support of the present invention, a porous film having a pore structure that linearly extends in the film thickness direction, in other words, a porous film having a short movement path of lithium ions between electrodes when incorporated in a battery is provided. By stacking, a polymer electrolyte support having high ionic conductivity and excellent mechanical strength when an electrolyte film is formed by filling the polymer electrolyte can be obtained. The thickness of the polymer electrolyte support is adjusted to 5 to 100 μm, particularly preferably 10 to 40 μm from the viewpoints of mechanical strength, performance, thinning and the like.

Further, the polymer electrolyte support of the present invention has a surface structure capable of being easily filled with the polymer electrolyte and a small heat shrinkage ratio, so that a lithium polymer battery having a simple manufacturing process and excellent safety can be obtained. It can be manufactured. The lithium polymer battery of the present invention is manufactured into a cylindrical shape, a rectangular shape, a coin shape, a thin plate shape or the like by a usual method using the polymer electrolyte support. The components other than the polymer electrolyte support constituting the lithium polymer battery are not particularly limited, but the following components are used.

For example, as the positive electrode material (positive electrode active material), a lithium-containing metal compound such as a lithium-containing metal oxide, sulfide or chloride is used. As the lithium-containing metal oxide, for example, a lithium composite oxide of lithium and at least one metal selected from the group consisting of cobalt, manganese, nickel, chromium, iron and vanadium is used. Examples of such a lithium composite oxide include LiCoO ₂ , LiMn ₂ O ₄ ,
Examples thereof include LiNiO ₂ .

The positive electrode is prepared by kneading the above positive electrode material with a conductive agent such as acetylene black or carbon black and a binder such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) to prepare a positive electrode mixture. After applying the positive electrode material to an aluminum foil or a stainless steel lath plate as a current collector, drying and press molding, 5
It is produced by heat treatment under vacuum at a temperature of about 0 ° C. to 250 ° C. for about 2 hours.

As the negative electrode (negative electrode active material), a lithium metal, a lithium alloy, and a carbon material containing carbon or graphite capable of occluding / releasing lithium, for example, carbon materials such as coke, natural graphite and artificial graphite, and composite tin. Oxides are used. In particular, it is preferable to use a carbon material having a graphite type crystal structure in which the lattice spacing (d ₀₀₂ ) of the lattice plane (002) is 0.335 to 0.340 nm.
The powdery carbon material is kneaded with a binder such as ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF) to be used as a negative electrode mixture.

As the polymer electrolyte, a non-aqueous electrolyte fixed with a polymer material such as polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, or a copolymer thereof is used. As non-aqueous electrolyte,
Ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane,
A solution in which an electrolyte is dissolved in an organic solvent such as tetrahydrofuran is used. As the electrolyte, for example, LiP
F ₆ , LiBF ₄ , LiClO ₄ , CF ₃ SO ₃ Li, (C
F ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, LiC
(SO ₂ CF ₃ ) _{3 and the} like. These electrolytes may be used alone or in combination of two or more. These electrolytes are used after being dissolved in the above-mentioned non-aqueous solvent at a concentration of usually 0.1 to 3M, preferably 0.5 to 1.5M.

The production of a lithium polymer battery using the above constituent members is not particularly limited, but for example, a coin battery can be produced by the following method. LiC
80% by weight of oO ₂ (positive electrode active material), 10% by weight of acetylene black (conductive agent), and 10% by weight of polyvinylidene fluoride (binder) were mixed, and 1-methyl-2-pyrrolidone was mixed therein. A mixture obtained by adding a solvent is applied on an aluminum foil, dried, pressure-molded, and heat-treated to prepare a positive electrode. 90% by weight of natural graphite (negative electrode active material) and 10% by weight of polyvinylidene fluoride (binder) were mixed, and 1-methyl-2-pyrrolidone solvent was added thereto,
The mixed material is applied onto a copper foil, dried, pressure-molded, and heat-treated to prepare a negative electrode. Then, the polymer electrolyte support of the present invention was filled with the polymer electrolyte in which the non-aqueous electrolyte was fixed with 10% by weight of polyethylene oxide, and the coin-type lithium secondary battery (diameter 20 mm, thickness 3.2 m) was filled.
m) can be produced.

[0045]

EXAMPLES Next, the polymer electrolyte support of the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

Example 1 As polyethylene, high-density polyethylene having a number average molecular weight of 20,000, a density of 0.964 and a melting point of 134 ° C. was melt extruded using a T die having a discharge width of 1000 mm and a discharge lip opening of 2 mm. The discharge film was guided to a cooling roll of 117 ° C., cooled by blowing cold air of 25 ° C., and then taken off at 20 m / min. The thickness of the obtained polyethylene film was 9.5 μm. This unstretched polyethylene film was heat-treated at 120 ° C. for 60 seconds in a state where the take-up direction was fixed, and then cooled to room temperature. The birefringence of the heat-treated unstretched polyethylene film was 35.5 × 10 ⁻³ , and the elastic recovery rate was 52%.

As polypropylene, a number average molecular weight of 70
000, pentad fraction 94.3%, crystallization temperature 112
Polypropylene at 0 ° C. was melt extruded using a T die having a discharge width of 1000 mm and a discharge lip opening of 2 mm. The discharge film was guided to a cooling roll at 80 ° C., cooled by blowing cold air at 25 ° C., and then taken off at 50 m / min. The thickness of the obtained polypropylene composition film was 13.1 μm. This unstretched polypropylene film is fixed at 135 ° C with the take-up direction fixed.
After heat-treating for 60 seconds, it was cooled to room temperature. The birefringence of the heat-treated unstretched polypropylene film is 22.
Elastic recovery rate at 6 × 10 ⁻³ , 100% stretching was 93%

The heat-treated polyethylene film and polypropylene film were laminated in a three-layer structure in which polyethylene was placed in the surface layer and polypropylene was placed in the inner layer (intermediate layer). Lamination was carried out by unwinding the polyethylene film and polypropylene film from three sets of roll stands at a unwinding speed of 6.5 m / min, and guiding them to a heating roll.
Thermocompression bonding was performed at a temperature of 120 ° C. and a linear pressure of 1.8 kg / cm, and then the film was guided to a cooling roll at 50 ° C. at the same speed and wound. Winding speed is 6.5m / min, unwinding tension is 0.9kg
Met. The thickness of the obtained unstretched laminated film was 31.
It was 8 μm.

The unstretched laminated film was stretched at a low temperature of 30% between nip rolls held at 30 ° C. At this time, the distance between the rolls is 350 mm, and the roll speed on the supply side is 2 m / mi.
It was n. The low temperature stretched laminated film continues to be 12
The film was introduced into a hot air circulation oven heated to 3 ° C, drawn at a high temperature to a total drawing amount of 250% between the rolls by using the difference in roll peripheral speed, and then 2 rolls were heated to 123 ° C.
It was relaxed by 5% and heat-set for 72 seconds to continuously obtain a laminated porous film, that is, a polymer electrolyte support.

The film thickness, porosity, air permeability, tensile strength and thermal shrinkage of the obtained polymer electrolyte support are shown in Table 1, and the maximum pore diameter and porosity of the surface layer of the polymer electrolyte support are shown. Table 2 shows.
The surface tension of the polymer electrolyte support was 47 degrees. The cross-sectional structure of the polymer electrolyte support is shown in FIG. Further, the polyelectrolyte support is placed in the thickness direction at a temperature of 60 ° C.
Table 3 shows the rate of decrease in film thickness and the rate of increase in air permeability when a pressure of 5 kg / cm ² was applied. The evaluation method was performed as follows. 1) Porosity and maximum pore size Measured using a mercury porosimeter manufactured by Yuasa Ionics. After 0.03 to 0.07 g of the sample is weighed and evacuated in a glass cell, mercury is pressed in and filled. The maximum pore size and porosity were determined from the mercury pressure during filling and the amount of mercury injected. 2) Air permeability Measured according to JIS P8117. A B-type Gurley Densometer (manufactured by Toyo Seiki Co., Ltd.) was used as a measuring device. The sample piece is clamped in a circular hole having a diameter of 28.6 mm and an area of 645 mm ² . With the inner cylinder weight of 567 g, the air in the cylinder is passed outside the cylinder from the test circular hole. The time taken for 100 cc of air to pass was measured and was taken as the air permeability (Gurley value). 3) Tensile strength Measured according to ASTM D-822. Using a UTM-III-100 type tensile tester manufactured by Orientec, the maximum stress was measured under the conditions of a sample width of 10 mm, an initial sample length (between chucks) of 50 mm, and a pulling speed of 50 mm / min. 4) Thermal shrinkage 200 mm initial length in the width direction of the polymer electrolyte support
The scale was marked, and the dimensions were measured after the product was left standing for 10 minutes in an oven set to 150 ° C. with the machine direction being restrained. The heat shrinkage is according to the following equation (6). L _{6 in} equation (6) means the film size after removal from the oven and L ₅ means the initial film size. Formula (6) Heat shrinkage rate = (L ₅ −L ₆ ) / L ₅ × 100 5) A reduction rate of film thickness and an increase rate of air permeability by applying surface pressure Using a polyelectrolyte support in the thickness direction at 60 ° C. and 35 kg / cm ²
Was applied. As the sample, four pieces cut into 50 × 50 mm were stacked, preheated for 60 seconds, applied with a surface pressure for 5 seconds, and immediately cooled. The film thickness and air permeability of the polymer electrolyte support that had been left to stand for 10 minutes after cooling were measured, and the film thickness decrease rate and air permeability increase rate were calculated according to the following equations (7) and (8). In Formula (7), D ₁ and D ₂ represent the film thickness before and after applying the surface pressure, and S ₁ and S ₂ in Formula (8) represent the air permeability before and after applying the surface pressure. . Equation (7) thickness reduction rate _{= (D 1 -D 2) /} D 1 × 100 Equation (8) air permeability increase rate _{= (S 2 -S 1) /} S 1 × 100

Example 2 As polyethylene, high density polyethylene having a number average molecular weight of 20,000, a density of 0.964 and a melting point of 134 ° C. was melt extruded using a T die having a discharge width of 1000 mm and a discharge lip opening of 2 mm. The discharge film was guided to a cooling roll of 114 ° C., cooled by blowing cold air of 25 ° C., and then taken off at 20 m / min. The thickness of the obtained polyethylene film was 8 μm. This unstretched polyethylene film was heat-treated at 120 ° C. for 60 seconds in a state where the take-up direction was fixed, and then cooled to room temperature. The birefringence of the heat-treated unstretched polyethylene film was 35.1 × 10 ⁻³ , and the elastic recovery rate was 42%.

As polypropylene, a number average molecular weight of 70
000, pentad fraction 94.3%, crystallization temperature 112
Polypropylene at 0 ° C. was melt extruded using a T die having a discharge width of 1000 mm and a discharge lip opening of 2 mm. The discharge film was guided to a cooling roll at 90 ° C., cooled by blowing cold air at 25 ° C., and then taken off at 50 m / min. The thickness of the obtained polypropylene composition film was 10.8 μm. This unstretched polypropylene film was heat-treated at 135 degrees for 60 seconds in a state where the take-up direction was fixed, and then cooled to room temperature. The birefringence of the heat-treated unstretched polypropylene film is 22.
Elastic recovery rate at 3 × 10 ⁻³ , 100% stretching was 92%

The heat-treated polyethylene film and polypropylene film were laminated in a three-layer structure in which polypropylene was placed in the surface layer and polyethylene was placed in the inner layer (intermediate layer). Lamination was carried out by unwinding the polypropylene film and the polyethylene film from three sets of roll stands at a unwinding speed of 6.5 m / min, and guiding them to a heating roll.
Thermocompression bonding was performed at a temperature of 120 ° C. and a linear pressure of 1.8 kg / cm, and then the film was guided to a cooling roll at 50 ° C. at the same speed and wound. Winding speed is 6.5m / min, unwinding tension is 0.9kg
Met. The thickness of the obtained unstretched laminated film was 28.
It was 8 μm.

The unstretched laminated film was stretched at a low temperature of 25% between nip rolls held at 30 ° C. At this time, the distance between the rolls is 350 mm, and the roll speed on the supply side is 2 m / mi.
It was n. The low temperature stretched laminated film continues to be 12
The film was introduced into a hot air circulation oven heated to 4 ° C, was drawn at a high temperature to a total drawing amount of 180% between the rolls by using the difference in peripheral speed of the rolls, and then was rolled with a roll heated to 124 ° C to 3
It was relaxed by 0% and heat-set for 72 seconds to continuously obtain a laminated porous film, that is, a polymer electrolyte support. The film thickness, porosity, air permeability, tensile strength and thermal shrinkage of the obtained polymer electrolyte support are shown in Table 1, and the maximum pore diameter and porosity of the surface layer of the polymer electrolyte support are shown in Table 2. . The surface tension of the polyelectrolyte support was 62 degrees. Further, Table 3 shows the rate of decrease in film thickness and the rate of increase in air permeability when a pressure of 35 kg / cm ² was applied to the polymer electrolyte support at a temperature of 60 ° C. in the thickness direction.

[0055]

According to the present invention, a porous film having a pore structure extending linearly in the film thickness direction, in other words, having a short movement path of lithium ions between electrodes when incorporated in a battery is laminated. Thus, a polymer electrolyte support having high ionic conductivity and excellent mechanical strength was obtained when an electrolyte film was formed by filling the polymer electrolyte.
By using the polymer electrolyte support of the present invention, it is possible to provide a polymer electrolyte film having high mechanical strength and a small heat shrinkage ratio at the time of battery abnormality and excellent in safety, and a lithium polymer battery using the same. .

[0056]

[Table 1]

[0057]

[Table 2]

[0058]

[Table 3]

[Brief description of drawings]

FIG. 1 is a photograph replacing a drawing showing a cross-sectional structure of a polymer electrolyte support of the present invention.

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-4-36959 (JP, A) JP-A-7-220761 (JP, A) JP-A-10-284125 (JP, A) JP-A-8- 244152 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 6/18 H01B 1/06-1/12

Claims (6)

(57) [Claims] 1. A polymer electrolyte support comprising a laminate of a polyolefin porous film which has been made porous by a stretching method, wherein the porous film is formed substantially parallel to the film thickness direction at substantially predetermined intervals. Formed by a group of stretched plate-like planes and a group of stretch-oriented thin fibrils running between the plate-like planes substantially in parallel with each other in the stretching direction of the film at substantially predetermined intervals and connecting between the plate-like planes. by the gap between the thin fibrils leading to between to form a substantially uniform shape of the micropores extending substantially two-dimensionally, have a through hole extending linearly in the thickness direction of the film, the polymer electrolyte supported
Porosity of holding body is 40-80%, air permeability is 30-500 seconds /
100 cc, tensile strength in machine direction 12 kg / mm ^{2 or} less
Upper, film width direction when heat treated at 150 ° C for 10 minutes
The polymer electrolyte support is characterized by having a thermal shrinkage of 15% or less . 2. The polymer electrolyte support according to claim 1, wherein the polymer electrolyte support comprises a laminated porous film in which polyethylene and polypropylene are alternately laminated. 3. A or claim 1, characterized in that polyethylene polymer electrolyte support surface layer, inner layer composed of a laminated porous film laminated to a polypropylene
2. The polymer electrolyte support according to item 2 . 4. The polymer electrolyte support according to claim 3, wherein the polyethylene disposed on the surface layer has a maximum pore size of 0.2 to 5 μm and a porosity of 50 to 90%. 5. A decrease rate of the film thickness is 5% or less and an increase rate of air permeability is 10% when a pressure of 35 kg / cm ² is applied at a temperature of 60 ° C. in the thickness direction of the polymer electrolyte support. polyelectrolyte support according to claim 1-4, wherein the or less. 6. A lithium polymer battery comprising a positive electrode made of a lithium-containing metal oxide, a sulfide or a chloride, a negative electrode made of a carbon material, and a polymer electrolyte in which a non-aqueous electrolyte is fixed with a polymer material. there are, lithium polymer battery comprising as a constituent material a polymer electrolyte support according to claim 1-5.