JP2003059480A - Separator for battery and battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery using a separator quickly effectively deactivating the battery when battery temperature is abnormally raised and hardly causing deformation of the separator. SOLUTION: This porous separator is used for the battery comprising a positive electrode 1, a negative electrode 2, an electrolyte, and a separator 3. The separator is composed of a porous substrate sheet and a organic polymer layer having microporous structure, the porous substrate sheet is not dissolved in an electrolyte at a temperature less than at least 135 deg.C, the organic polymer layer is formed in at least a part of the substrate surface comprising the face surface, back surface, and hole inner wall surface of the porous substrate sheet, and a polymer forming the organic polymer layer has a dissolution starting point starting dissolution in the electrolyte in a temperature range of 100-120 deg.C.

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 battery using the same, and more particularly to improvement of materials used for the battery separator.

[0002]

2. Description of the Related Art In recent years, portable devices such as mobile phones, PHSs, and small personal computers have been remarkably miniaturized and lightened with the progress of electronics technology, and even in batteries used as a power source for these devices. There is an increasing demand for smaller size and lighter weight.

A lithium battery is one of the batteries that can be expected for such applications. In addition to the lithium primary battery which has already been put into practical use, a lithium secondary battery has been put into practical use.
Higher capacity and longer life are required. In particular, conventional lithium-ion secondary batteries are mainly cylindrical or prismatic, whereas various research and development efforts have been made toward the practical application of thin lithium-ion secondary batteries and lithium polymer secondary batteries. Has been done.

In the case of a cylindrical or prismatic lithium secondary battery, a step of inserting a pole group consisting of a positive electrode, a negative electrode and a separator into a cylindrical or prismatic metal battery case and then injecting a liquid non-aqueous electrolyte. It is produced through. On the other hand, in the thin-shaped lithium polymer secondary battery, the positive electrode and the negative electrode are made to face each other through the gel electrolyte, and then packed by the metal resin composite material.
There are manufacturing advantages. However, such a lithium polymer secondary battery has a drawback that it has poor high-rate charge / discharge performance and low-temperature performance as compared with a cylindrical or prismatic lithium secondary battery.

The causes are as follows.
To be That is, in the case of cylindrical or prismatic batteries, the liquid
To inject the body-shaped non-aqueous electrolyte, the electrode and separator
The lithium ion conductivity in the battery is generally necessary for battery operation.
1 × 10 that is said to be a level ^-3Secure S / cm order
Easy to do. In contrast, lithium polymer
In the case of secondary batteries, the electrolyte is solid, so
Generally does not require an injection process, but lithium ion
The conductivity is inevitably lower than that of liquid systems, and is generally 1
× 10^-3It is difficult to secure the S / cm order.
It was Therefore, there is a drawback that the charge and discharge performance is inferior.

Therefore, a thin lithium ion secondary battery packed with a metal resin composite material using a liquid non-aqueous electrolyte, which has the advantages of a cylindrical or prismatic lithium secondary battery and the advantages of a lithium polymer secondary battery. Various researches and developments have been made on batteries, and in recent years, they have almost been put into practical use.

Further, a lithium polymer secondary battery and a lithium polymer secondary battery using a gel-like polymer electrolyte use an organic solvent as an electrolyte, but these organic solvents are generally volatile and highly flammable. Therefore, it is classified as a flammable substance. Therefore, there is a problem in safety during use such as overcharging, overdischarging, short-circuiting, or the like, or in a high temperature environment.

Therefore, in order to ensure safety in a high temperature environment, it has been proposed that the separator made of a microporous film also has a thermal fuse function. That is, in a normal use state, it exists between the positive electrode and the negative electrode to prevent a short circuit between both electrodes, and the microporous structure keeps the resistance between both electrodes low to maintain the battery performance. If the internal temperature of the battery rises,
By melting the material that composes the separator, it closes the micropores of the membrane at a predetermined temperature to make it non-porous (heat blocking), increases the resistance and shuts off the battery reaction, and prevents further temperature rise and is safe. It aims to secure the sex. The function of shutting off the battery reaction due to this thermal blockage is called the shutdown characteristic of the separator, and is one of the important functions required for the separator for lithium ion batteries.

Further, from the viewpoint of ensuring safety, it is necessary to maintain the increased resistance up to an appropriate temperature for an appropriate time. When the thermal blockage occurs completely, the separator will become an insulator, so ideally the current will instantly drop to 0, but in reality, even after the shutdown start temperature is reached, the inside of the battery The temperature often rises further. Therefore, even when the temperature exceeds the shutdown start temperature and further rises, the property of maintaining a constant membrane area (shape retention) without shrinkage or damage is also important. In addition, important parameters that affect the temperature (heat resistant temperature) at which the shape retention of the microporous film is lost include the melting point, thickness, and porosity of the material forming the separator. On the other hand, if a microporous membrane with poor shape retention is used as a separator, the microporous membrane contracts or is damaged when the internal temperature of the battery rises above the shutdown start temperature, and the positive and negative electrodes come into direct contact to cause an internal short circuit. It may cause a very dangerous state such as a thermal runaway, resulting in a serious result.

Therefore, in the lithium secondary battery, in order to combine the shutdown characteristic and the shape retention power, in recent years, resins having different melting points have been used instead of the conventional microporous membrane made of a single resin such as polyethylene or polypropylene. It has been proposed to use them in combination. In addition, in the lithium polymer secondary battery, it has been proposed that the gel electrolyte itself has a shutdown characteristic.

For example, Japanese Examined Patent Publication No. 4-38101 discloses at least one type 1 microporous sheet which is substantially non-porous at a temperature of about 80 ° C. to 150 ° C., and at least one first type sheet. A battery separator having at least two layers of a second seed sheet having a shape-retaining force at a temperature that is at least about 10 ° C. higher than the temperature at which the seed sheet becomes non-porous has been proposed.

However, a battery separator using such a microporous membrane is, for example, a combination of polyethylene and polypropylene, and it is said that the shutdown characteristic and the shape-retaining power can be combined only between the melting points of polyethylene and polypropylene. There was a problem. That is, since the temperature at which the shutdown characteristic appears is relatively high at 135 ° C., when the battery temperature continues to rise to around 135 ° C., the battery temperature easily exceeds the shutdown temperature and further accelerates, There is a possibility that the shape retention force may exceed the temperature at which it is destroyed, resulting in serious consequences. To avoid this, set the shutdown temperature to 13
It is desired that the temperature is lower than 5 ° C, preferably around 100 to 120 ° C, but it is difficult to obtain a microporous membrane having a melting point substantially in the temperature range of 100 to 120 ° C, and the above-mentioned critical This has been an obstacle to a highly safe battery that can avoid the possibility of causing a result.

Further, Japanese Patent Laid-Open No. 11-86910 uses a porous polymer electrolyte whose pores are clogged within a temperature range of 100 ° C. or higher and 190 ° C. or lower and which is swollen and / or wetted by a non-aqueous electrolyte. Non-aqueous electrolyte batteries have been proposed.

However, in a non-aqueous electrolyte battery using such a polymer electrolyte, the polymer reacts with the organic solvent or lithium salt in the electrolyte solution to close the pores of the polymer membrane, and then the electrode group. It is said that it solidifies as a whole and prevents a short circuit between the positive and negative electrodes, but since the polymer film is in a molten state until it solidifies after the pores of the polymer film are closed, the above-mentioned important parameter However, there is a problem that the shape retention power is poor.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and when the battery temperature rises abnormally, the battery is quickly and effectively deactivated, and the temperature rise continues. Even in such a case, it is an object to provide a battery using a separator that is less likely to cause shape breakage of the separator.

[0016]

In order to solve the above-mentioned problems, the present invention provides a porous battery separator for use in a battery comprising a positive electrode, a negative electrode, an electrolytic solution and a separator as described in claim 1. The separator is composed of a porous base material sheet and an organic polymer layer having a fine pore structure, and the organic polymer layer is a surface of the porous base material sheet, a back surface and a surface of the base material including inner wall surfaces of the pores. The polymer forming the organic polymer layer has a dissolution starting point for starting the dissolution in the electrolytic solution in a temperature range of 100 ° C. or higher and 120 ° C. or lower. It is a battery separator for.

According to this structure, the porous base material forming the battery separator makes it possible to obtain a battery separator which is excellent in mechanical strength and durability against repeated high temperature and temperature changes and is easy to handle. Becomes possible,
The organic polymer layer has a fine pore structure and is formed on at least a part of the surface of the porous base material sheet, which is composed of the surface, the back surface and the inner wall surface of the pores. If the separator is applied to a battery, the affinity with the electrolytic solution is kept high, ensuring high ionic conductivity and realizing smooth movement of lithium ions.
It functions as a separator with excellent electrolyte retention. Here, the organic polymer layer having the fine pore structure may be filled in the pores of the porous substrate, but on the surface of the porous substrate sheet, the back surface and the substrate surface consisting of the inner wall surface of the holes. It is preferable that the separator is formed to be very thin and the distribution state of the pores of the porous substrate is maintained as it is, so that the separator having a sufficiently low resistance can be obtained. At this time, by setting the pore size of the porous substrate to an appropriate value, it is possible to impart sufficient electrolytic solution holding ability.

Further, since the polymer forming the organic polymer layer has a melting start point for starting the melting in the electrolytic solution in a temperature range of 100 ° C. or higher and 120 ° C. or lower, the battery temperature becomes the melting start point. When the temperature reaches, the organic polymer layer is dissolved in the electrolytic solution and the resistance of the electrolytic solution is rapidly increased, so that the shutdown characteristic can be expressed at an appropriate temperature which is relatively lower than in the conventional case. For this reason,
It is possible to very efficiently avoid the above-described accelerated increase in battery temperature that has been found in conventional batteries. That is,
Rather than using a microporous membrane that becomes non-porous by melting as in the prior art, by dissolving the organic polymer layer in the electrolytic solution, the resistance value of the electrolyte impregnated in the separator is increased, and the shutdown function is substantially achieved. It is characterized by being expressed.

The present invention also provides a porous battery separator for use in a battery comprising a positive electrode, a negative electrode, an electrolytic solution and a separator, as described in claim 2, wherein the separator is a porous substrate sheet. And an organic polymer layer having a fine pore structure, wherein the organic polymer layer is formed on at least a part of the surface of the porous substrate sheet, the back surface and the substrate surface consisting of the inner wall surface of the pores, The polymer forming the organic polymer layer is a polymer in which, in the temperature range of 100 ° C. or higher and 120 ° C. or lower, at least the electrolytic solution present in the pores of the porous substrate sheet forms the organic polymer layer in the electrolytic solution. It is a battery separator characterized by including and gelling.

When the battery separator having such a structure is applied to a battery, the operation and effect are the same as those of the invention according to claim 1, and the shutdown characteristics can be more effectively exhibited. it can.

Further, according to the present invention, as described in claim 3, the porous substrate sheet has no melting point at a temperature of at least less than 135 ° C.

Here, "having no melting point at least at a temperature lower than 135 ° C." means having no melting point at any temperature, or having a melting point at a temperature of 135 ° C. or higher.

When the battery separator having such a structure is applied to a battery, in addition to exhibiting shutdown characteristics at an appropriate temperature which is relatively lower than in the past, the shape of the separator is maintained up to at least 135 ° C. Since the difference between the shutdown characteristic expression temperature and the shape destruction temperature is widened, it is possible to greatly reduce the possibility that the battery temperature may exceed the shape destruction temperature of the separator and cause a serious problem due to thermal runaway as described above. .

Further, according to the present invention, as described in claim 4, the porous substrate sheet is a microporous film having a thickness of 25 μm or less and a porosity of 40% or more. I am trying.

When the battery separator having such a structure is applied to a battery, higher ion conductivity is ensured and smooth movement of ions is achieved by using a porous base material having a large opening ratio and a large pore diameter. Since the above can be realized, the above-mentioned action can be obtained more effectively.

Further, according to the present invention, as described in claim 5, the organic polymer layer contains polyvinylidene fluoride or polyacrylonitrile as a raw material.

According to this structure, the separator having the above-mentioned excellent function can be realized with an inexpensive material.

Further, the present invention is a battery using the battery separator as described in claim 6.

As an application of the present invention, a porous base material which does not melt or melt below 135 ° C. and 100 to 12
In addition to the organic polymer layer that dissolves in the electrolyte solution or gels the electrolyte solution at 0 ° C., a separator may be formed by combining a microporous film that melts at around 120 to 140 ° C. to close the pores. With such a configuration of the separator, the resistance increasing stage can be set to two stages, so that a battery with higher safety can be provided.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail by way of examples applied to a lithium battery, but the present invention is not limited to these descriptions.

Examples of the porous base material that can be used in the battery separator of the present invention include microporous membranes, non-woven fabrics and woven fabrics which are generally used as liquid type battery separators. As the material of the porous base material, a material that is chemically stable to a solvent or an electrolytic solution and electrochemically stable can be used. For example, those containing polyolefin such as polyethylene or polypropylene as a main raw material, those containing polyester such as polyethylene terephthalate or polybutylene terephthalate as a main raw material, those containing cellulose as a main raw material and the like can be mentioned.

Of these, the melting point of the resin forming the porous base material must be 135 ° C. or higher, and particularly 135 to 180 ° C., in order to maintain the shape up to an appropriate temperature after the start of shutdown. Is desirable. Specifically, polyolefins, particularly those containing polyethylene or polypropylene as a main raw material are suitable. Here, as the polyethylene, any of high-density, medium-density, low-density linear polyethylene, branched polyethylene, and the like can be used.

At this time, the porous substrate is preferably a microporous film having a thickness of 25 μm or less and a porosity of 40% or more, and more specifically, a thickness of 5 to 15 μm and a porosity. It is preferably 45 to 80%. When the thickness of the porous substrate is 25 μm or more, or the porosity is less than 40%,
The electric resistance of the porous base material, which is originally electrically insulating, is large,
Batteries using such battery separators are not preferable because it is difficult to keep various battery performances good.
From this, the thickness is 25 μm or less, and the open area ratio is 40%.
Or more, more preferably, by using a porous substrate having a thickness of 15 μm or less, or a porosity of 45% or more, particularly a microporous membrane, the electric resistance of the porous substrate is sufficiently low, The effect of the battery separator of the present invention can be effectively obtained. However, when a porous substrate having a thickness of 5 μm or less or a porosity of 80% or more is used, the mechanical strength is poor and handling becomes difficult. Furthermore, in a battery using such a battery separator, not only is it easy for a micro short circuit to occur between the electrodes, but also when the internal temperature of the battery rises above the melting point, the microporous membrane contracts or breaks. The positive and negative electrodes are in direct contact with each other to cause an internal short circuit, which increases the possibility of thermal runaway, which is not preferable.

The organic polymer layer that can be used in the battery separator of the present invention does not dissolve in the electrolytic solution at the normal operating temperature of the battery, and has a solubility in the electrolytic solution when heated to 100 to 120 ° C. It has to appear.
Furthermore, it is preferable that the organic polymer layer has a high affinity for the electrolytic solution. In order for the organic polymer layer and the electrolytic solution to have a high affinity, it is more preferable that at least the surface of the organic polymer has a property of swelling in the electrolytic solution.

In order to further increase the affinity, the organic polymer preferably has a micropore structure.

As the material of the organic polymer, the polymer forming the organic polymer layer is dissolved in the electrolytic solution as the temperature inside the battery rises, and the resistance of the electrolytic solution is rapidly increased. The shut-down property is expressed as, and the melting start point is 100 to
A temperature of 120 ° C, preferably 110 to 120 ° C, is suitably selected. Further, it is more preferable that the dissolved polymer gels the electrolytic solution. Specifically, various physically cross-linked polymers, particularly those containing polyvinylidene fluoride or polyacrylonitrile as a main raw material are preferable.

When forming the organic polymer layer, an inorganic filler may be added in order to prevent the organic polymer skeleton from being densified or crystallized and more effectively form a fine pore structure. As the inorganic filler, similar to the porous substrate, chemical,
Particulate metal compounds that are electrochemically stable and that form a matrix with the organic polymer backbone can be used. Examples include, but are not limited to, silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide, metal oxides such as iron oxide, and metal carbonates such as calcium carbonate and magnesium carbonate. is not. These may be used alone or in combination of two or more.

As the electrolytic solution used in the battery of the present invention, for example,
For example, if it is a non-aqueous electrolyte battery, the solvent that constitutes the electrolytic solution.
Chemically stable as commonly used in lithium batteries
Anything that is can be used. For example, ethylene carbon
G, propylene carbonate, dimethyl carbonate,
Diethyl carbonate, methyl ethyl carbonate, γ
-Butyrolactone, propiolactone, valerolacto
Amine, tetrahydrofuran, dimethoxyethane, dietoki
Ciethane, methoxyethoxyethane, etc.
However, it is not limited thereto. These alone
They may be used, or two or more kinds may be mixed and used. This and
As the electrolyte salt that constitutes the electrolytic solution, a lithium battery
Lithium that is stable in a wide potential range commonly used in
Um salts can be used. For example, LiBF_Four, LiPF₆,
LiClO_Four, LiSO₃CF₃, LiN (SO₂C
F₃)₂, LiN (SO₂C₂F_Five)₂, LiN (SO₂C
F₃) (SO₂C _FourF₉), Etc., but not limited to these
It is not fixed. These may be used alone,
You may use it in mixture of 2 or more types.

[0039]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these descriptions.

Example 1 Separator a for battery of the present invention 3 g of polyvinylidene fluoride powder and 22 g of N-methyl-2-pyrrolidone were mixed and completely dissolved. This solution was added to a polyethylene microporous membrane (thickness 16 μm, porosity 45
%) Applied to the surface and immersed in water. In the process, N
The replacement of methyl-2-pyrrolidone with water forms a microporous structure composed of polyvinylidene fluoride. Next, the water content was dried to obtain a battery separator a of the present invention having a film thickness of 20 μm. When the surface and the cross section of the battery a of the present invention were observed with a scanning electron microscope, a layer consisting only of polyvinylidene fluoride polymer having a fine pore structure with an average pore diameter of about 0.5 μm was formed on the surface of the microporous membrane. The average thickness is 2.5 μm each, and
It was confirmed that in the pores of the microporous membrane, a very thin layer made of polyvinylidene fluoride polymer having a micropore structure having an average pore diameter of about 0.8 μm was formed.

(Example 2) Battery separator b of the present invention 3 g of polyvinylidene fluoride powder, 1 g of silicon oxide and N
22 g of -methyl-2-pyrrolidone were mixed and completely dissolved. This solution was added to a polyethylene microporous membrane (thickness 16
μm, porosity of 45%), and was immersed in water and dried to obtain a battery separator b of the present invention having a film thickness of 20 μm. Observation of the surface and cross section of the battery a of the present invention with a scanning electron microscope revealed that a layer consisting only of polyvinylidene fluoride polymer having a fine pore structure with an average pore diameter of about 0.7 μm was formed on the surface of the microporous membrane. An average thickness of 2.5 μm each is formed, and in the pores of the microporous membrane, a layer made only of polyvinylidene fluoride polymer having a micropore structure with an average pore diameter of about 0.8 μm is formed very thinly. Was confirmed.

(Example 3) Battery separator c of the present invention 3 g of polyacrylonitrile and 2 g of N-methyl-2-pyrrolidone were mixed and completely dissolved. This solution was applied to the surface of a polyethylene microporous membrane (thickness 16 μm, porosity 45%), immersed in water, and then dried to a film thickness of 20.
A μm-thick battery separator c of the present invention was obtained. Observation of the surface and cross section of the battery separator b of the present invention with a scanning electron microscope revealed that a layer consisting only of polyacrylonitrile polymer having a micropore structure with an average pore diameter of about 0.2 μm was formed on one side of the microporous membrane. It has a thickness of 4 μm and the average pore diameter is about 0.5 μm in the pores of the microporous membrane.
It was confirmed that the layer composed of only the polyacrylonitrile polymer in which the micropore structure was formed was extremely thin.

Comparative Example 1 Comparative Battery Separator d 3 g of a bifunctional acrylate monomer having the structure shown in Chemical formula 1 and 12 g of ethanol were mixed and completely dissolved to obtain a monomer liquid. A polypropylene microporous film (thickness: 16 μm, open area ratio: 45%) was impregnated with the monomer solution, and the monomer was polymerized by electron beam irradiation to form an organic polymer skeleton. Then, ethanol was dried to obtain a film thickness of 2
A 0 μm comparative battery separator d was obtained. Observation of the surface and cross-section of this comparative battery separator d with a scanning electron microscope revealed that a layer consisting of only an organic polymer having a fine pore structure with an average pore diameter of about 0.5 μm was formed on the surface of the microporous membrane. It was confirmed that 2.5 μm each was formed, and that a layer consisting only of an organic polymer having a micropore structure with an average pore diameter of about 0.8 μm was formed very thin in the pores of the microporous membrane. Was done.

[0044]

[Chemical 1] Comparative Example 2 Comparative Battery Separator e Polyvinylidene fluoride powder (3 g) and N-methyl-2-pyrrolidone (22 g) were mixed and completely dissolved. This solution was cast on a polyethylene terephthalate film, immersed in water, and then dried to remove the polyethylene terephthalate film to give a film thickness of 2
A 0 μm comparative battery separator e was obtained. The porosity of this comparative battery separator e was 45%, and its surface and cross section were observed by a scanning electron microscope, and it was confirmed that a fine pore structure having an average pore diameter of about 0.5 μm was formed. It was

Comparative Example 3 Separator f for Comparative Battery A polypropylene / polyethylene / polypropylene 3-layer laminated microporous membrane (thickness 25 μm, porosity 38%) was used as a separator f for comparative battery.

Table 1 shows these battery separators a of the present invention.
˜c and comparative battery separators df are collectively shown at 20 ° C. for ionic conductivity.

[0047]

[Table 1] From Table 1, it can be seen that each of the battery separators of the present invention has the same or higher ionic conductivity as compared with the comparative battery separator.

Example 4 Battery A of the present invention A cross-sectional view of a lithium battery according to the present invention is shown in FIG.

The lithium battery according to the present invention comprises the positive electrode 1,
The negative electrode 2 and the electrode group 4 including the separator 3, the non-aqueous electrolyte, and the metal-resin composite film 5 are included.
The positive electrode 1 is formed by coating the positive electrode mixture 11 on the positive electrode current collector 12. In the negative electrode 2, the negative electrode mixture 21 is the negative electrode current collector 2
2 is applied on top. The non-aqueous electrolyte is impregnated in the pole group 4. The metal-resin composite film 5 covers the pole group 4 and the periphery thereof is sealed by heat welding.

Next, a method of manufacturing the battery having the above structure will be described.

The positive electrode 1 was obtained as follows. First, Li
CoO ₂ and acetylene black, which is a conductive agent, are mixed, and then a polyvinylidene fluoride N-methyl-2-pyrrolidone solution is mixed as a binder, and this mixture is applied to one surface of the positive electrode current collector 12 made of aluminum foil. After coating, it was dried and pressed so that the thickness of the positive electrode mixture 11 was 0.1 mm. The positive electrode 1 was obtained through the above steps.

The negative electrode 2 was obtained as follows. First, graphite, which is a negative electrode active material, and an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride, which is a binder, are mixed, and this mixture is applied to one surface of a negative electrode current collector 22 made of a copper foil. It is dried and the negative electrode mixture 21 has a thickness of 0.1.
It was pressed to have a size of mm. Through the above steps, the negative electrode 2
Got

On the other hand, as the separator 5, the battery separator a of the present invention was used.

The electrode group 4 was constructed by placing the positive electrode mixture 11 and the negative electrode mixture 21 facing each other, disposing the separator 3 therebetween, and laminating the positive electrode 1, the separator 3 and the negative electrode 2 in this order. The non-aqueous electrolyte was obtained by dissolving 1 mol of LiBF ₄ in 1 liter of a mixed solvent in which γ-butyrolactone and ethylene carbonate were mixed at a volume ratio of 3: 2. Next, the electrode group 4 was immersed in the non-aqueous electrolyte to impregnate the electrode group 4 with the non-aqueous electrolyte. Further, the electrode group 4 was covered with the metal-resin composite film 5, and its four sides were sealed by heat welding.

The battery obtained by the above production method is referred to as Battery A of the present invention. The designed capacity of the battery A of the present invention is 10 m.
It is Ah.

(Example 5) Battery B of the present invention A battery having a capacity of 10 mAh was produced by the same raw material and manufacturing method as the battery A of the present invention except that the separator b for the battery of the present invention was used as the separator 5. Battery B was used.

(Example 6) Battery C of the present invention A battery having a capacity of 10 mAh was produced by the same raw material and manufacturing method as the battery A of the present invention except that the separator c for the battery of the present invention was used as the separator 5. Battery C was used.

(Comparative Example 4) Comparative Battery D A battery having a capacity of 10 mAh was prepared by using the same raw material and manufacturing method as the battery A of the present invention except that the separator d for the comparative battery was used as the separator 5. did.

(Comparative Example 5) Comparative Battery E A battery having a capacity of 10 mAh was prepared by the same raw material and manufacturing method as the battery A of the present invention except that the separator e for the comparative battery was used as the separator 5. did.

Comparative Example 6 Comparative Battery F A battery having a capacity of 10 mAh was prepared by the same raw material and manufacturing method as the battery A of the present invention except that the separator f for the comparative battery was used as the separator 5. did.

(Battery Performance Test) Next, the discharge rate characteristics of these batteries A, B and C of the present invention and comparative batteries D, E and F were obtained. The test temperature was 20 ° C. The charging was a constant-current constant-voltage charge with a current of 2 mA and a final voltage of 4.2 V, and the discharging was a constant-current discharge with various current values, and the final voltage was 2.7 V. The ratio of the obtained discharge capacity to the battery design capacity was defined as the discharge capacity (%). The results are shown in Figure 2.

In FIG. 2, comparing the discharge capacities at a discharge current of 30 mA, the comparative battery D has a design capacity of 45.
%, About 50% of the designed capacity of the comparative battery E and about 60% of the designed capacity of the comparative battery F, whereas the discharge capacity of the battery A of the present invention is about 80% of the designed capacity.
In the battery B of the present invention, about 85% of the designed capacity, the battery C of the present invention
It was found that a discharge capacity of about 70% of the designed capacity can be obtained. (Shutdown Characteristic Evaluation) Further, the shutdown characteristic evaluation was carried out on the batteries A, B and C of the present invention and the comparative batteries D, E and F. In the oven, current 2
Install a battery charged with constant current and constant voltage of mA and final voltage of 4.2V, and measure the battery voltage and internal resistance at 1 ℃ /
The temperature was raised to 140 ° C. at a rate of minutes, and the temperature at which the internal resistance sharply increased was measured and used as the shutdown start temperature. After that, the battery was taken out from the oven and disassembled, and the contraction of the taken-out separator, the presence or absence of film rupture, and the degree of blockage were observed. The results are shown in Table 2.

[0063]

[Table 2] From Table 2, it was found that the comparative batteries D and F have excellent shape retention, but the shutdown start temperature is around 135 ° C. which is the melting point of polyethylene, and is relatively high.
Further, it was found that the comparative battery E had a relatively low shutdown start temperature, but lacked shape retention. On the other hand, it was found that the batteries A, B, and C of the present invention had a relatively low shutdown start temperature and exhibited good shape retention.

Summarizing the above results, the present invention battery separators a, b and c and the present invention battery A using the same are
It can be said that B and C have good performance and safety in comparison with the comparative battery separators d, e and f and the comparative batteries D, E and F using the separators.

Although the lithium battery has been described above as an example, the battery separator of the present invention is not limited to the lithium battery, and may be used in various battery systems including an aqueous electrolyte such as a nickel hydrogen battery. be able to.

[0066]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, if the battery separator having such a configuration is applied to a battery, a high ionic conductivity is ensured and smooth movement of lithium ions is realized. , Excellent in electrolyte retention, when the battery temperature reaches the melting start point, the organic polymer layer is dissolved in the electrolyte, to rapidly increase the resistance of the electrolyte, or because the electrolyte gels, The shutdown characteristic can be expressed at an appropriate temperature that is relatively low compared to the conventional one. Further, it is possible to greatly reduce the risk that the battery temperature will exceed the shape destruction temperature due to thermal runaway and cause a serious problem.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a lithium battery of the present invention.

FIG. 2 is a diagram showing discharge rate characteristics of a battery of the present invention and a comparative battery.

[Explanation of symbols]

1 positive electrode 11 Positive electrode mixture 12 Positive electrode current collector 2 Negative electrode 21 Negative electrode mixture 22 Negative electrode current collector 3 separator 4 pole group 5 Metal resin composite film

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Claims (6)

[Claims] 1. A porous battery separator for use in a battery, comprising a positive electrode, a negative electrode, an electrolytic solution and a separator,
The separator comprises a porous substrate sheet and an organic polymer layer having a fine pore structure, the organic polymer layer is at least the surface of the porous substrate sheet, the back surface and at least the substrate surface consisting of the inner wall surface of the pores. A battery which is partially formed and has a dissolution starting point at which the polymer for forming the organic polymer layer starts to dissolve in the electrolyte solution in a temperature range of 100 ° C. or higher and 120 ° C. or lower. Separator. 2. A porous battery separator for use in a battery, comprising a positive electrode, a negative electrode, an electrolytic solution and a separator,
The separator comprises a porous substrate sheet and an organic polymer layer having a fine pore structure, the organic polymer layer is at least the surface of the porous substrate sheet, the back surface and at least the substrate surface consisting of the inner wall surface of the pores. The polymer which is formed in a part and forms the organic polymer layer has a temperature range of 100 ° C. or higher and 120 ° C. or lower.
A battery separator, wherein at least the electrolytic solution present in the pores of the porous substrate sheet contains the polymer forming the organic polymer layer and gels. 3. The porous substrate sheet is at least 1
The battery separator according to claim 1 or 2, which has no melting point at a temperature lower than 35 ° C. 4. The porous substrate sheet has a thickness of 25 μm.
The separator for a battery according to any one of claims 1 to 3, which is a microporous membrane having a porosity of 40% or more, which is the following. 5. The battery separator according to claim 1, wherein the organic polymer layer contains polyvinylidene fluoride or polyacrylonitrile as a raw material. 6. A battery using the battery separator according to claim 1.